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Kroug, M., Yagoubov, P., Gol'tsman, G., & Kollberg, E. (1997). NbN quasioptical phonon cooled hot electron bolometric mixers at THz frequencies. In Inst. Phys. Conf. Ser. (Vol. 1, pp. 405–408). Bristol.
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Gerecht, E., Musante, C. F., Jian, H., Yngvesson, K. S., Dickinson, J., Waldman, J., et al. (1998). Measured results for NbN phonon-cooled hot electron bolometric mixers at 0.6-0.75 THz, 1.56 THz, and 2.5 THz. In Proc. 9th Int. Symp. Space Terahertz Technol. (pp. 105–114).
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Hübers, H. - W., Semenov, A. D., Richter, H., Schubert, J., Hadjiloucas, S., Bowen, J. W., et al. (2001). Antenna pattern of the quasi-optical hot-electron bolometric mixer at terahertz frequencies. In Proc. 12th Int. Symp. Space Terahertz Technol. (pp. 286–296). San Diego, CA, USA.
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Goltsman, G. N., Vachtomin, Y. B., Antipov, S. V., Finkel, M. I., Maslennikov, S. N., Polyakov, S. L., et al. (2005). Low-noise NbN phonon-cooled hot-electron bolometer mixers for terahertz heterodyne receivers. In Proc. 9-th WMSCI (Vol. 9, pp. 154–159). International Institute of Informatics and Systemics.
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Gao, J. R., Hajenius, M., Baselmans, J. J. A., Yang, Z. Q., Baryshev, A. M., Barends, R., et al. (2005). Twin-slot antenna coupled NbN hot electron bolometer mixers for space applications. In Proc. 9-th WMSCI (Vol. 9, pp. 148–153). International Institute of Informatics and Systemics.
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Gao, J. R., Hajenius, M., Baselmans, J. J. A., Klapwijk, T. M., de Korte, P. A. J., Voronov, B., et al. (2004). NbN hot electron bolometer mixers with superior performance for space applications. In E. Armandillo, & B. Leone (Eds.), Proc. Int. workshop on low temp. electronics (pp. 11–17). Noordwijk.
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Antipov, S. V., Svechnikov, S. I., Smirnov, K. V., Vakhtomin, Y. B., Finkel, M. I., Goltsman, G. N., et al. (2001). Noise temperature of quasioptical NbN hot electron bolometer mixers at 900 GHz. Physics of Vibrations, 9(4), 242–245.
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Svechnikov, S. I., Antipov, S. V., Vakhtomin, Y. B., Goltsman, G. N., Gershenzon, E. M., Cherednichenko, S. I., et al. (2001). Conversion and noise bandwidths of terahertz NbN hot-electron bolometer mixers. Physics of Vibrations, 9(3), 205–210.
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Gerecht, E., Musante, C. F., Jian, H., Zhuang, Y., Yngvesson, K. S., Dickinson, J., et al. (1999). Improved characteristics of NbN HEB mixers integrated with log-periodic antennas. In Proc. 10th Int. Symp. Space Terahertz Technol. (pp. 200–207).
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Schubert, J., Semenov, A., Hübers, H. - W., Gol'tsman, G., Schwaab, G., Voronov, B., et al. (1999). Broad-band terahertz NbN hot-electron bolometric mixer. In Inst. Phys. Conf. (Vol. 167, pp. 663–666).
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Gerecht, E., Musante, C. F., Yngvesson, K. S., Waldman, J., Gol'tsman, G. N., Yagoubov, P. A., et al. (1997). Optical coupling and conversion gain for NbN HEB mixer at THz frequencies. In Proc. 4-th Int. Semicond. Device Research Symp. (pp. 47–50).
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Cherednichenko, S., Drakinskiy, V., Baubert, J., Lecomte, B., Dauplay, F., Krieg, J. - M., et al. (2007). 2.5 THz multipixel heterodyne receiver based on NbN HEB mixers. In Proc. 18th Int. Symp. Space Terahertz Technol. (112).
Abstract: A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4 / SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. Measurements of the mixers sensitivity and the input RF band are presented, and compared against calculations.
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Cherednichenko, S., Drakinskiy, V., Lecomte, B., Dauplay, F., Krieg, J. - M., Delorme, Y., et al. (2008). Terahertz heterodyne array based on NbN HEB mixers. In Proc. 19th Int. Symp. Space Terahertz Technol. (43).
Abstract: A 16 pixel heterodyne receiver for 2.5 THz is been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4 / SiO2 membranes. Miniature mirrors (one per pixel) and back short for the antenna were used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si3N4 / SiO 2 membranes was found to be about 3 GHz, when an MgO buffer layers is applied on the membrane. We will also present the progress in the camera heterodyne tests.
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Svechnikov, S. I., Okunev, O. V., Yagoubov, P. A., Gol'tsman, G. N., Voronov, B. M., Cherednichenko, S. I., et al. (1997). 2.5 THz NbN hot electron mixer with integrated tapered slot antenna. IEEE Trans. Appl. Supercond., 7(2), 3548–3551.
Abstract: A Hot Electron Bolometer (HEB) mixer for 2.5 THz utilizing a NbN thin film device, integrated with a Broken Linearly Tapered Slot Antenna (BLTSA), has been fabricated and is presently being tested. The NbN HEB device and the antenna were fabricated on a SiO2membrane. A 0.5 micrometer thick SiO2layer was grown by rf magnetron reactive sputtering on a GaAs wafer. The HEB device (phonon-cooled type) was produced as several parallel strips, 1 micrometer wide, from an ultrathin NbN film 4-7 nm thick, that was deposited onto the SiO2layer by dc magnetron reactive sputtering. The BLTSA was photoetched in a multilayer Ti-Au metallization. In order to strengthen the membrane, the front-side of the wafer was coated with a 5 micrometer thick polyimide layer just before the membrane formation. The last operation was anisotropic etching of the GaAs in a mixture of HNO3and H2O2.
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Cherednichenko, S., Kroug, M., Merkel, H., Khosropanah, P., Adam, A., Kollberg, E., et al. (2002). 1.6 THz heterodyne receiver for the far infrared space telescope. Phys. C: Supercond., 372-376, 427–431.
Abstract: A low noise heterodyne receiver is being developed for the terahertz range using a phonon-cooled hot-electron bolometric mixer based on 3.5 nm thick superconducting NbN film. In the 1–2 GHz intermediate frequency band the double-sideband receiver noise temperature was 450 K at 0.6 THz, 700 K at 1.6 THz and 1100 K at 2.5 THz. In the 3–8 GHz IF band the lowest receiver noise temperature was 700 K at 0.6 THz, 1500 K at 1.6 THz and 3000 K at 2.5 THz while it increased by a factor of 3 towards 8 GHz.
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Cherednichenko, S., Khosropanah, P., Berg, T., Merkel, H., Kollberg, E., Drakinskiy, V., et al. (2004). Optimization of HEB mixer for the Herschel Space Observatory. In Proc. 15th Int. Symp. Space Terahertz Technol. (16).
Abstract: A mixer development for the HIFI instrument of the Herschel Space Observatory has come to the final stage. In our paper and conference presentation we will describe the most important details of the Band 6 Low and High Mixer Unit design. Special attention will be given to the optimization of the hot- electron bolometer mixer chip, which is based on 3.5nm NbN superconducting film on silicon. As the HEB’s local oscillator power requirements depend on the bolometer size, we have compared mixer noise temperature for different bolometer width- to- length ratio. A trade- off between mixer performance and local oscillator power requirements results in the mixer units equipped with optimized mixer chips, providing the largest coverage of the Band6 RF band with the lowest possible receiver noise. A short account of the beam pattern measurements of Band6 mixers will be given as well.
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Tong, C. - Y. E., Trifonov, A., Shurakov, A., Blundell, R., & Gol’tsman, G. (2015). A microwave-operated hot-electron-bolometric power detector for terahertz radiation. IEEE Trans. Appl. Supercond., 25(3), 2300604 (1 to 4).
Abstract: A new class of microwave-operated THz power detectors based on the NbN hot-electron-bolometer (HEB) mixer is proposed. The injected microwave signal ( 1 GHz) serves the dual purpose of pumping the HEB element and enabling the read-out of the internal state of the device. A cryogenic amplifier amplifies the reflected microwave signal from the device and a homodyne scheme recovers the effects of the incident THz radiation. Two modes of operation have been identified, depending on the level of incident radiation. For weak signals, we use a chopper to chop the incident radiation against a black body reference and a lock-in amplifier to perform synchronous detection of the homodyne readout. The voltage measured is proportional to the incident power, and we estimate an optical noise equivalent power of 5pW/ √Hz at 0.83 THz. At higher signal levels, the homodyne circuit recovers the stream of steady relaxation oscillation pulses from the HEB device. The frequency of these pulses is in the MHz frequency range and bears a linear relationship with the incident THz radiation over an input power range of 15 dB. A digital frequency counter is used to measure THz power. The applicable power range is between 1 nW and 1 μW.
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Semenov, A. D., Hübers, H. - W., Richter, H., Smirnov, K., Gol'tsman, G. N., & Voronov, B. M. (2004). Superconducting hot-electron bolometer mixer for terahertz heterodyne receivers. In Proc. 15th Int. Symp. Space Terahertz Technol. (164).
Abstract: A number of on-going astronomical and atmospheric research programs are aimed to the Terahertz (THz) spectral region. At frequencies above about 1.4 THz heterodyne receivers planned for these missions will use superconducting hot-electron bolometers as a mixers. We present current results on the development of superconducting NbN hot- electron bolometer mixer and quasioptical radiation coupling scheme for GREAT (German Receiver for Astronomy at Terahertz Frequencies, to be used aboard of SOFIA) and TELIS (Terahertz Limb Sounder). The mixer is incorporated into hybrid antenna consisting of a planar feed antenna, which has either logarithmic spiral or double-slot configuration, and hyperhemispherical silicon lens. For the log-spiral feed antenna, the double side-band receiver noise temperature of 5500 K was achieved at 4.3 THz. The noise temperature shows less than 3 dB increase in the intermediate frequency band from 4 GHz to 7 GHz. The hybrid antenna had almost frequency independent and symmetric radiation pattern with the beam-width slightly broader than expected for a diffraction limited pattern. Results of FTS measurements in the direct detection regime agreed with the spectral dependence of the noise temperature for spiral antennas with different spacing of inner terminals.
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Semenov, A. D., Hiibers, H. - W., Richter, H., Smirnov, K., Gol'tsman, G. N., Kaurova, N., et al. (2003). Superconducting hot-electron bolometer mixer for terahertz heterodyne receivers. In Proc. 14th Int. Symp. Space Terahertz Technol. (pp. 33–40).
Abstract: A number of on-going astronomical and atmospheric research programs are aimed to the Terahertz (THz) spectral region. At frequencies above about 1.4 THz heterodyne receivers planned for these missions will use superconducting hot-electron bolometers as a mixers. We present recent results of the terahertz antenna development of superconducting NbN hot-electron bolometer mixer for GREAT (German Receiver for Astronomy at Terahertz Frequencies, to be used aboard of SOFIA) and TELIS (Terahertz Limb Sounder). The mixer is incorporated into hybrid antenna consisting of a planar feed antenna, which has either logarithmic spiral or double-slot configuration, and hyper hemispherical silicon lens. The hybrid antenna showed almost frequency independent and symmetric radiation pattern with the beam-width slightly broader than expected for diffraction limited antenna. The noise temperature as well as its spectral dependence changes with the bolometer sizes that provides additional tool for mixer optimization. FTS spectra measured in the direct detection regime agreed with the noise temperature spectra.
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Tong, C. - Y. E., Kawamura, J., Todd, R. H., Papa, D. C., Blundell, R., Smith, M., et al. (2000). Successful operation of a 1 THz NbN hot-electron bolometer receiver. In Proc. 11th Int. Symp. Space Terahertz Technol. (pp. 49–59).
Abstract: A phonon-cooled NbN superconductive hot-electron bolometer receiver covering the frequency range 0.8-1.04 THz has successfully been used for astronomical observation at the Sub-Millimeter Telescope Observatory on Mount Graham, Arizona. This waveguide heterodyne receiver is a modified version of our fixed-tuned 800 GHz HEB receiver to allow for operation beyond 1 THz. The measured noise temperature of this receiver is about 1250 K at 0.81 THz, 560 K at 0.84 THz, and 1600 K at 1.035 THz. It has a 1 GHz wide IF bandwidth, centered at 1.8 GHz. This receiver has recently been used to detect the CO (9-8) molecular line emission at 1.037 THz in the Orion nebula. This is the first time a ground-based heterodyne receiver has been used to detect a celestial source above 1 THz.
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Zhang, W., Li, N., Jiang, L., Miao, W., Lin, Z. - H., Yao, Q. - J., et al. (2007). Noise behaviour of a THz superconducting hot-electron bolometer mixer. Chinese Phys. Lett., 24(6), 1778–1781.
Abstract: A quasi-optical superconducting NbN hot-electron bolometer (HEB) mixer is measured in the frequency range of 0.5–2.5 THz for understanding of the frequency dependence of noise temperature of THz coherent detectors. It has been found that noise temperature increasing with frequency is mainly due to the coupling loss between the quasi-optical planar antenna and the superconducting HEB bridge when taking account of non-uniform distribution of high-frequency current. With the coupling loss corrected, the superconducting HEB mixer demonstrates a noise temperature nearly independent of frequency.
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Chen, J., Kang, L., Jin, B. B., Xu, W. W., Wu, P. H., Zhang, W., et al. (2008). Properties of terahertz superconducting hot electron bolometer mixers. Int. J. Terahertz Sci. Technol., 1(1), 37–41.
Abstract: A quasi-optical superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixer has been fabricated and measured in the terahertz (THz) frequency range of 0.5~2.52 THz. A receiver noise temperature of 2000 K at 2.52 THz has been obtained for the mixer without corrections. Also, the effect of a Parylene C anti-reflection (AR) coating on the silicon (Si) lens has been studied.
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Tong, C. E., Blundell, R., Papa, D. C., Smith, M., Kawamura, J., Gol'tsman, G., et al. (1999). An all solid-state superconducting heterodyne receiver at terahertz frequencies. IEEE Microw. Guid. Wave Lett., 9(9), 366–368.
Abstract: A superconducting hot-electron bolometer mixer-receiver operating from 1 to 1.26 THz has been developed. This heterodyne receiver employs two solid-state local oscillators each consisting of a Gunn oscillator followed by two stages of varactor frequency multiplication. The measured receiver noise temperature is 1350 K at 1.035 THz and 2700 K at 1.26 THz. This receiver demonstrates that tunable solid-state local oscillators, supplying only a few micro-watts of output power, can be used in terahertz receiver applications.
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Tret’yakov, I. V., Ryabchun, S. A., Kaurova, N. S., Larionov, P. A., Lobastova, A. A., Voronov, B. M., et al. (2010). Optimum absorbed heterodyne power for superconducting NbN hot-electron bolometer mixer. Tech. Phys. Lett., 36(12), 1103–1105.
Abstract: Absorbed heterodyne power has been measured in a low-noise broadband hot-electron bolometer (HEB) mixer for the terahertz range, operating on the effect of electron heating in the resistive state of an ultrathin superconducting NbN film. It is established that the optimum absorbed heterodyne power for the HEB mixer operating at 2.5 THz is about 100 nW.
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Cherednichenko, S., Kroug, M., Yagoubov, P., Merkel, H., Kollberg, E., Yngvesson, K. S., et al. (2000). IF bandwidth of phonon cooled HEB mixers made from NbN films on MgO substrates. In Proc. 11th Int. Symp. Space Terahertz Technol. (pp. 219–227).
Abstract: An investigation of gain and noise bandwidth of phonon-cooled hot-electron bolometric (HEB) mixers is presented. The radiation coupling to the mixers is quasioptical through either a spiral or twin-slot antenna. A maximum gain bandwidth of 4.8 GHz is obtained for mixers based on a 3.5 nm thin NbN film with Tc= 10 K. The noise bandwidth is 5.6 GHz, at the moment limited by parasitic elements in the, device mount fixture. At 0.65 THz the DSB receiver noise temperature is 700-800 К in the IF band 1-2 GHz, and 1150-2700 К in the band 3.5-7 GHz.
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Kinev, N. V., Filippenko, L. V., Ozhegov, R. V., Gorshkov, K. N., Gol’tsman, G. N., & Koshelets, V. P. (2014). Superconducting integrated receiver with HEB-mixer. In Proc. 25th Int. Symp. Space Terahertz Technol. (78).
Abstract: Detectors in THz range with high sensitivity are very essential nowadays in different fields: space technology, atmospheric research, medicine and security. The most sensitive heterodyne detectors below 1 THz are the SIS- mixers due to its extremely high non-linearity and low noise level. Nevertheless, their effective range is strongly limited by superconducting gap Δ (about 1 THz for NbN circuits). Above 1 THz the detectors based on HEB (hot electron bolometers) are more effective [1]; their operation frequency is not limited from above and can be up to 70 THz [2]. HEBs can perform as both direct and heterodyne detectors (mixers). All HEB-mixers are used with external heterodyne, most useful are synthesizer with multipliers, quantum cascade lasers or far infrared lasers and backward-wave oscillators. Superconducting integrated receiver (SIR) is based on implementation of both SIS-miser and flux flow oscillator (FFO) acting as heterodyne at single chip [3]. Such receiver has been successfully applied at TELIS balloon-borne instrument for study of atmospheric constituents [4] and looks as very promising device for other THz missions including space research. Thus, there is a task to expand its operating range to higher frequencies. The frequency range of the SIR the operation is limited by both the SIS-mixer and the FFO maximum frequencies. The idea of present work is implementation of the HEB as a mixer in the SIR instead of the SIS traditionally used. We introduce the first results of integrating the HEB-mixer coupled to planar slot antenna with the FFO on one chip. For properly FFO operation the SIS harmonic mixer is used to phase lock the oscillator. The scheme of the SIR based on the HEB- mixer is presented in fig. 1. We have demonstrated the principal possibility of integration of both the HEB-mixer and the flux-flow oscillator on a single chip and succeed with sufficient power coupling for properly receiver operation. We measured the direct response of the HEB coupled to the antenna at THz frequencies by the FTS setup and noise temperature of the receiver with standard Y- factor measuring technique. The SIR operating range 450-620 GHz was achieved with the best uncorrected noise temperature of about 1000 К. One should note that it is still quite low frequencies for effective operation of the HEB-mixer; therefore we expect to obtain the better results for frequencies above 700 GHz (up to 1.2 THz). Another additional task is to increase the FFO frequencies by using NbTiN electrodes instead of NbN; currently we are working on this issue. This work was supported by the RFBR grant, the Ministry of Education and Science of Russia and Russian Academy of Sciences. References 1. D. Semenov, H.-W. Hubers, J. Schubert, G. N. Gol’tsman, A. I. Elantiev, B. M. Voronov, E. M. Gershenzon, Design and performance of the lattice-cooled hot-electron terahertz mixer, J. Appl. Phys. 88, 6758, 2000. 2. Maslennikov S. N., Finkel M. I., Antipov S. V. et al. Spiral antenna coupled and directly coupled NbN HEB mixers in the frequency range from 1 to 70THz. Proc. 17 th international symposium on space terahertz technology. Paris, France: 2006.—may. Pp. 177 – 179. 3. V.P. Koshelets, S.V. Shitov. Integrated Superconducting Receivers. Supercond. Sci. Technol. Vol. 13. P. R53-R59. 2000. 4. Gert de Lange, Dick Boersma, Johannes Dercksen et.al. Development and Characterization of the Superconducting Integrated Receiver Channel of the TELIS Atmospheric Sounder. Supercond. Sci. Technol. vol. 23, No 4, 045016 (8pp). 2010.
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Hübers, H. - W., Semenov, A., Richter, H., Birk, M., Krocka, M., Mair, U., et al. (2002). Terahertz Heterodyn Receiver with a hot-electron bolometer mixer. In U. Wolf, J. Farhoomand, & C. R. McCreight (Eds.), Far-IR, Sub-mm & MM Detector Technology Workshop (pp. 3–24). NASA CP. NASA.
Abstract: During the past decade major advances have been made regarding low noise mixers for terahertz (THz) heterodyne receivers. State of the art hot-electron-bolometer (HEB) mixers have noise temperatures close to the quantum limit and require less than a µW power from the local oscillator (LO). The technology is now at a point where the performance of a practical receiver employing such mixer, rather than the figures of merit of the mixer itself, are of major concern. We have incorporated a phonon-cooled NbN HEB mixer in a 2.5 THz heterodyne receiver and investigated the performance of the receiver. This yields important information for the development of heterodyne receivers such as GREAT (German receiver for astronomy at THz frequencies aboard SOFIA) [1] and TELIS (Terahertz limb sounder), a balloon borne heterodyne receiver for atmospheric research [2]. Both are currently under development at DLR.
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Hübers, H. - W., Semenov, A., Richter, H., Birk, M., Krocka, M., Mair, U., et al. (2002). Terahertz heterodyne receiver with a hot-electron bolometer mixer. In J. Wold, & J. Davidson (Eds.), Proc. Far-IR, Sub-mm, and mm Detector Technology Workshop.
Abstract: During the past decade major advances have been made regarding low noise mixers for terahertz (THz) heterodyne receivers. State of the art hot-electron-bolometer (HEB) mixers have noise temperatures close to the quantum limit and require less than a µW power from the local oscillator (LO). The technology is now at a point where the performance of a practical receiver employing such mixer, rather than the figures of merit of the mixer itself, are of major concern. We have incorporated a phonon-cooled NbN HEB mixer in a 2.5 THz heterodyne receiver and investigated the performance of the receiver. This yields important information for the development of heterodyne receivers such as GREAT (German receiver for astronomy at THz frequencies aboard SOFIA)[1] and TELIS (Terahertz limb sounder), a balloon borne heterodyne receiver for atmospheric research [2]. Both are currently under development at DLR.
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Hubers, H. - W., Semenov, A., Richter, H., Schwarz, M., Gunther, B., Smirnov, K., et al. (2004). Heterodyne receiver for 3-5 THz with hot-electron bolometer mixer. In J. Zmuidzinas, W. S. Holland, & S. Withington (Eds.), Proc. SPIE (Vol. 5498, pp. 579–586). SPIE.
Abstract: Heterodyne receivers for applications in astronomy and planetary research need quantum limited sensitivity. In instruments which are currently build for SOFIA and Herschel superconducting hot electron bolometers (HEB) will be used to achieve this goal at frequencies above 1.4 THz. The local oscillator and the mixer are the most critical components for a heterodyne receiver operating at 3-5 THz. The design and performance of an optically pumped THz gas laser optimized for this frequency band will be presented. In order to optimize the performance for this frequency hot electron bolometer mixers with different in-plane dimensions and logarithmic-spiral feed antennas have been investigated. Their noise temperatures and beam patterns were measured. Above 3 THz the best performance was achieved with a superconducting bridge of 2.0 x 0.2 μm2 incorporated in a logarithmic spiral antenna. The DSB noise temperatures were 2700 K, 4700 K and 6400 K at 3.1 THz, 4.3 THz and 5.2 THz, respectively. The results demonstrate that the NbN HEB is very well suited as a mixer for THz heterodyne receivers up to at least 5 THz.
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Richter, H., Semenov, A., Hubers, H. - W., Smirnov, K., Gol’tsman, G., & Voronov, B. (2004). Phonon cooled hot-electron bolometric mixer for 1-5 THz. In Proc. 29th IRMMW / 12th THz (pp. 241–242).
Abstract: Heterodyne receivers for applications in astronomy and planetary research need quantum limited sensitivity. In instruments which are currently built for SOFIA and Herschel, superconducting hot electron bolometers (HEB) are used to achieve this goal at frequencies above 1.4 THz. In order to optimize the performance for this frequency of hot electron bolometer mixers with different in-plane dimensions and logarithmic-spiral feed antennas have been investigated. Their noise temperatures and beam patterns were measured. Above 3 THz the best performance was achieved with a superconducting bridge of 2.0/spl times/0.2 /spl mu/m/sup 2/ incorporated in a logarithmic spiral antenna. The DSB noise temperatures were 2700 K, 4700 and 6400 K at 3.1 THz, 4.3 THz and 5.2 THz, respectively. The results demonstrate that the NbN HEB is very well suited as a mixer for THz heterodyne receivers up to at least 5 THz.
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Huebers, H. - W., Semenov, A., Richter, H., Birk, M., Krocka, M., Mair, U., et al. (2003). Superconducting hot electron bolometer as mixer for far-infrared heterodyne receivers. In T. G. Phillips, & J. Zmuidzinas (Eds.), Proc. SPIE (Vol. 4855, pp. 395–401). Presented at the Society of Photo-Optical Instrumentation Engineers (SPIE) Conference, 4855. Tucson, USA: SPIE.
Abstract: Heterodyne receivers for applications in astronomy need quantum limited sensitivity. In instruments which are currently under development for SOFIA or Herschel superconducting hot electron bolometers (HEB) will be used to achieve this goal at frequencies above 1.4 THz. We present results of the development of a phonon-cooled NbN HEB mixer for GREAT, the German Receiver for Astronomy at Terahertz Frequencies, which will be flown aboard SOFIA. The mixer is a small superconducting bridge incorporated in a planar feed antenna and a hyperhemispherical lens. Mixers with logarithmic-spiral and double-slot feed antennas have been investigated with respect to their noise temperature, conversion loss, linearity and beam pattern. At 2.5 THz a double sideband noise temperature of 2200 K was achieved. The conversion loss was 17 dB. The response of the mixer was linear up to 400 K load temperature. The performance was verified by measuring an emission line of methanol at 2.5 THz. The measured linewidth is in good agreement with the linewidth deduced from pressure broadening measurements at millimeter wavelength. The results demonstrate that the NbN HEB is very well suited as a mixer for far-infrared heterodyne receivers.
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Huebers, H. - W., Semenov, A., Schubert, J., Gol’tsman, G. N., Voronov, B. M., Gershenzon, E. M., et al. (2000). NbN hot-electron bolometer as THz mixer for SOFIA. In R. K. Melugin, & H. - P. Roeser (Eds.), Proc. SPIE (Vol. 4014, pp. 195–202). SPIE.
Abstract: Heterodyne receivers for applications in astronomy need quantum limited sensitivity. We have investigated phonon- cooled NbN hot electron bolometric mixers in the frequency range from 0.7 THz to 5.2 THz. The devices were 3.5 nm thin films with an in-plane dimension of 1.7 X 0.2 micrometers 2 integrated in a complementary logarithmic spiral antenna. The best measured DSB receiver noise temperatures are 1300 K (0.7 THz), 2000 K (1.4 THz), 2100 K (1.6 THz), 2600 K (2.5 THz), 4000 K (3.1 THz), 5600 K (4.3 THz), and 8800 K (5.2 THz). The sensitivity fluctuation, the long term stability, and the antenna pattern were measured. The results demonstrate that this mixer is very well suited for GREAT, the German heterodyne receiver for SOFIA.
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Hübers, H. - W., Semenov, A., Richter, H., Smirnov, K., Gol'tsman, G., & Voronov, B. (2002). Phonon cooled far-infrared hot electron bolometer mixer. In NASA/ADS.
Abstract: Heterodyne receivers for applications in astronomy need quantum-limited sensitivity. At frequencies above 1.4 THz superconducting hot electron bolometers (HEB) can be used to achieve this goal. We present results of the development of a quasi-optical phonon-cooled NbN HEB mixer for GREAT, the German heterodyne receiver for SOFIA. Different mixers with logarithmic spiral and double slot feed antennas have been investigated with respect to their noise temperature, conversion loss, linearity and beam pattern at several frequencies between 0.7 THz and 5.2 THz. At 2.5 THz a double sideband noise temperature of 2200 K was achieved. The conversion loss was 16 dB. The response of the mixer was linear up to 400 K load temperature. This performance was verified by measuring an emission line of methanol at 2.5 THz. The results demonstrate that the NbN HEB is very well suited as a mixer for FIR heterodyne receivers.
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Karasik, B. S., Gol'tsman, G. N., Voronov, B. M., Svechnikov, S. I., Gershenzon, E. M., Ekstrom, H., et al. (1995). Hot electron quasioptical NbN superconducting mixer. IEEE Trans. Appl. Supercond., 5(2), 2232–2235.
Abstract: Hot electron superconductor mixer devices made of thin NbN films on SiO/sub 2/-Si/sub 3/N/sub 4/-Si membrane have been fabricated for 300-350 GHz operation. The device consists of 5-10 parallel strips each 5 /spl mu/m long by 1 /spl mu/m wide which are coupled to a tapered slot-line antenna. The I-V characteristics and position of optimum bias point were studied in the temperature range 4.5-8 K. The performance of the mixer at higher temperatures is closer to that predicted by theory for uniform electron heating. The intermediate frequency bandwidth versus bias has also been investigated. At the operating temperature 4.2 K a bandwidth as wide as 0.8 GHz has been measured for a mixer made of 6 nm thick film. The bandwidth tends to increase with operating temperature. The performance of the NbN mixer is expected to be better for higher frequencies where the absorption of radiation should be more uniform.
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Tretyakov, I., Maslennikov, S., Semenov, A., Safir, O., Finkel, M., Ryabchun, S., et al. (2015). Impact of operating conditions on noise and gain bandwidth of NbN HEB mixers. In Proc. 26th Int. Symp. Space Terahertz Technol. (39).
Abstract: Hot-electron bolometer mixers (HEB’s) are the most promising devices as mixing element for terahertz spectroscopy and astronomy at frequencies beyond 1.4 THz. They have a low noise temperature and low demands on local oscillator (LO) power. 1,2 An important limitation is the IF bandwidth, of the order of a few GHz, and which in principle depends on energy relaxation due to electron- phonon processes and on diffusion-cooling. It has been proposed by Prober that a reduction in length of the HEB would lead to an increased bandwidth. 3 This appeared to be achieved by Tretyakov et al by measuring the gain bandwidth close to the critical temperature of the NbN. 2 Unfortunately, the noise bandwidth of similar devices operated at temperatures around 4.2 K appear not depend on the length. The fundamental problem to be addressed is the position-dependent superconducting state of the HEB- devices under operating conditions, which determines the conditions for the cooling of the hot quasiparticles. Some progress has been made by Barends et al in a semi-empirical model to describe the I,V curves under operating conditions at a bath temperature around 4.2 K. 4 In more recent work Vercruyssen et al have analyzed the I,V curve, without any LO-equivalent bias, of a model NSN system. 5 This work suggests that the most appropriate model for an HEB under operating conditions is that of a potential-well in the superconducting gap in the center of the NbN, analogous the bimodal superconducting state described by Vercruyssen et al. Hot quasiparticles in the well can not diffuse out and can only cool by electron-phonon processes, those with higher energies than the heights of the walls of the well can diffuse out. Using this working hypothesis we have carried out experiments on a sub-micrometer NbN bridge connected to a gold (Au) planar spiral antenna. An in situ process is used to deposit Au on NbN. The Au is removed in the center to define the uncovered NbN, which will act as the superconducting mixer itself. The antenna is deposited on the remaining Au layer on the NbN. The Au contacts suppress the energy gap of the NbN film located underneath the gold layer 7,8 . The measured resistive transition is shown in Fig.1. It clearly shows a T c of the bilayer at 6.2 K and the resistive transition of the NbN itself around 9 K. In addition we show the measured noise bandwidth (red squares) for different bath temperatures. Clearly the noise bandwidth increases strongly by increasing the bath temperature from 5 K to 8 K, up to 13 GHz. We interpret this pattern as evidence for improved out-diffusion of hot electrons due to normal banks and a shallow superconducting potential well compared to k B T. As expected the noise temperature in this regime is much bigger than when biased at 4.2 K. R EFERENCES 1 W. Zhang, P. Khosropanah, J. R. Gao, E. L. Kollberg, K. S. Yngvesson, T. Bansal, R. Barends, and T. M. Klapwijk Appl. Phys. Lett. 96, 111113, (2010). 2 Ivan Tretyakov, Sergey Ryabchun, Matvey Finkel, Anna Maslennikova, Natalia Kaurova, Anastasia Lobastova, Boris Voronov, and Gregory Gol’tsman Appl. Phys. Lett. 98, 033507 (2011). 3 D. E. Prober, Appl. Phys. Lett. 62, 2119 (1992). 4 R. Barends, M. Hajenius, J. R. Gao, and T. M. Klapwijk, Appl. Phys. Lett. 87, 263506 (2005). 5 N. Vercruyssen, T. G. A. Verhagen, M. G. Flokstra, J. P. Pekola, and T. M. Klapwijk Physical Review B 85, 224503 (2012).
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Yagoubov, P., Gol'tsman, G., Voronov, B., Svechnikov, S., Cherednichenko, S., Gershenzon, E., et al. (1996). Quasioptical phonon-cooled NbN hot-electron bolometer mixer at THz frequencies. In Proc. 7th Int. Symp. Space Terahertz Technol. (pp. 303–317).
Abstract: In our experiments we tested phonon-cooled hot-electron bolometer (HEB) quasioptical mixer based on spiral antenna designed for 0.5-1.2 THz frequency band and fabricated on sapphire, Si-coated sapphire and high resistivity silicon substrates. HEB devices were produced from thin superconducting NbN film 3.5-6 nm thick with the critical temperature of about 11-12 K. For these devices we achieved the receiver noise temperature T R (DSB) = 3000 K in the 500-700 GHz frequency range and an IF bandwidth of 3-4 GHz. Prelimanary measurements at frequencies 1-1.2 THz resulted the receiver noise temperature about 9000 K (DSB).
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Gol'tsman, G., Svechnikov, S., et al. (1998). Noise temperature and local oscillator power requirement of NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies. Appl. Phys. Lett., 73(19), 2814–2816.
Abstract: In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband <cd><2018>DSB<cd><2019> noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2Ï«2 um. The amount of local oscillator power absorbed in the bolometer is less than 100 nW.
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Merkel, H. F., Yagoubov, P. A., Kroug, M., Khosropanah, P., Kollberg, E. L., Gol’tsman, G. N., et al. (1998). Noise temperature and absorbed LO power measurement methods for NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies. In Proc. 28th European Microwave Conf. (Vol. 1, pp. 294–299).
Abstract: In this paper the absorbed LO power requirements and the noise performance of NbN based phonon-cooled hot electron bolometric (HEB) quasioptical mixers are investigated for RF frequencies in the 0.55-1.1 range The minimal measured DSB noise temperatures are about 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz and 1250 K at 1.1 THz. The increase in noise temperature at 1.1THz is attributed to water absorption. The absorbed LO power is measured using a calorimetric approach. The results are subsequently corrected for lattice heating. These values are compared to results of a novel one dimensional hot spot mixer models and to a more traditional isotherm method which tends to underestimate the absorbed LO power for small bias powers. Typically a LO power between 50nW and 100nW is needed to pump the device to the optimal operating point.
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Kooi, J. W., Baselmans, J. J. A., Baryshev, A., Schieder, R., Hajenius, M., Gao, J. R., et al. (2006). Stability of heterodyne terahertz receivers. J. Appl. Phys., 100(6), 064904 (1 to 9).
Abstract: In this paper we discuss the stability of heterodyne terahertz receivers based on small volume NbN phonon cooled hot electron bolometers (HEBs). The stability of these receivers can be broken down in two parts: the intrinsic stability of the HEB mixer and the stability of the local oscillator (LO) signal injection scheme. Measurements show that the HEB mixer stability is limited by gain fluctuations with a 1∕f spectral distribution. In a 60MHz noise bandwidth this results in an Allan variance stability time of ∼0.3s. Measurement of the spectroscopic Allan variance between two intermediate frequency (IF) channels results in a much longer Allan variance stability time, i.e., 3s between a 2.5 and a 4.7GHz channel, and even longer for more closely spaced channels. This implies that the HEB mixer 1∕f noise is strongly correlated across the IF band and that the correlation gets stronger the closer the IF channels are spaced. In the second part of the paper we discuss atmospheric and mechanical system stability requirements on the LO-mixer cavity path length. We calculate the mixer output noise fluctuations as a result of small perturbations of the LO-mixer standing wave, and find very stringent mechanical and atmospheric tolerance requirements for receivers operating at terahertz frequencies.
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Jiang, L., Antipov, S. V., Voronov, B. M., Gol'tsman, G. N., Zhang, W., Li, N., et al. (2007). Characterization of the performance of a quasi-optical NbN superconducting HEB mixer. IEEE Trans. Appl. Supercond., 17(2), 395–398.
Abstract: In this paper we focus mainly on the investigation of the performance of a quasi-optical (planar log-spiral antenna) phonon-cooled NbN superconducting hot electron bolometer (HEB) mixer, which is cryogenically cooled by a close-cycled 4-K cryocooler, at 500 and 850 GHz frequency bands. The mixer's noise performance, stability of IF output power, and local oscillator (LO) power requirement are characterized for three NbN superconducting HEB devices of different sizes. The transmission characteristics of Mylar and Zitex films with incidence waves of an elliptical polarization are also examined by measuring the mixer's noise temperature. The lowest receiver noise temperatures (with no corrections) of 750 and 1100 K are measured at 500 and 850 GHz, respectively. Experimental results also demonstrate that the bigger the HEB device is, the higher the stability of IF output power becomes.
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Zhang, W., Miao, W., Zhong, J. Q., Shi, S. C., Hayton, D. J., Vercruyssen, N., et al. (2014). Temperature dependence of the receiver noise temperature and IF bandwidth of superconducting hot electron bolometer mixers. Supercond. Sci. Technol., 27(8), 085013 (1 to 5).
Abstract: In this paper we study the temperature dependence of the receiver noise temperature and IF noise bandwidth of superconducting hot electron bolometer (HEB) mixers. Three superconducting NbN HEB devices of different transition temperatures (Tc) are measured at 0.85 THz and 1.4 THz at different bath temperatures (Tbath) between 4 K and 9 K. Measurement results demonstrate that the receiver noise temperature of superconducting NbN HEB devices is nearly constant for Tbath/Tc, less than 0.8, which is consistent with the simulation based on a distributed hot-spot model. In addition, the IF noise bandwidth appears independent of Tbath/Tc, indicating the dominance of phonon cooling in the investigated HEB devices.
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Yazoubov, P., Kroug, M., Merkel, H., Kollberg, E., Gol'tsman, G., Lipatov, A., et al. (1998). Quasioptical NbN phonon-cooled hot electron bolometric mixers with low optimal local oscillator power. In Proc. 9th Int. Symp. Space Terahertz Technol. (pp. 131–140).
Abstract: In this paper, the noise perform.ance of NIN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixers is investigated in the 0.55-1.1 THz frequency range. The best results of the DSB noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz and 1250 K at 1.1 THz. The water vapor in the signal path causes a significant contribution to the measured noise temperature around 1.1 THz. The required LO power is typically about 60 nW. The frequency response of the spiral antenna+lens system is measured using a Fourier Transform Spectrometer with the HEB operating in a detector mode.
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Jiang, L., Miao, W., Zhang, W., Li, N., Lin, Z. H., Yao, Q. J., et al. (2006). Characterization of a quasi-optical NbN superconducting HEB mixer. IEEE Trans. Microwave Theory Techn., 54(7), 2944–2948.
Abstract: In this paper, the performance of a quasi-optical NbN superconducting hot-electron bolometer (HEB) mixer, cryogenically cooled by a close-cycled 4-K refrigerator, is thoroughly investigated at 300, 500, and 850 GHz. The lowest receiver noise temperatures measured at the respective three frequencies are 1400, 900, and 1350 K, which can go down to 659, 413, and 529 K, respectively, after correcting the loss and associated noise contribution of the quasi-optical system before the measured superconducting HEB mixer. The stability of the quasi-optical superconducting HEB mixer is also investigated here. The Allan variance time measured with a local oscillator pumping at 500 GHz and an IF bandwidth of 110 MHz is 1.5 s at the dc-bias voltage exhibiting the lowest noise temperature and increases to 2.5 s at a dc bias twice that voltage.
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Meledin, D. V., Marrone, D. P., Tong, C. - Y. E., Gibson, H., Blundell, R., Paine, S. N., et al. (2004). A 1-THz superconducting hot-electron-bolometer receiver for astronomical observations. IEEE Trans. Microwave Theory Techn., 52(10), 2338–2343.
Abstract: In this paper, we describe a superconducting hot-electron-bolometer mixer receiver developed to operate in atmospheric windows between 800-1300 GHz. The receiver uses a waveguide mixer element made of 3-4-nm-thick NbN film deposited over crystalline quartz. This mixer yields double-sideband receiver noise temperatures of 1000 K at around 1.0 THz, and 1600 K at 1.26 THz, at an IF of 3.0 GHz. The receiver was successfully tested in the laboratory using a gas cell as a spectral line test source. It is now in use on the Smithsonian Astrophysical Observatory terahertz test telescope in northern Chile.
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Kawamura, J., Blundell, R., Tong, C. - Y. E., Papa, D. C., Hunter, T. R., Paine, S. N., et al. (2000). Superconductive hot-electron-bolometer mixer receiver for 800-GHz operation. IEEE Trans. Microw. Theory Techn., 48(4), 683–689.
Abstract: In this paper, we describe a superconductive hot-electron-bolometer mixer receiver designed to operate in the partially transmissive 350-μm atmospheric window. The receiver employs an NbN thin-film microbridge as the mixer element, in which the main cooling mechanism of the hot electrons is through electron-phonon interaction. At a local-oscillator frequency of 808 GHz, the measured double-sideband receiver noise temperature is TRX=970 K, across a 1-GHz intermediate-frequency bandwidth centered at 1.8 GHz. We have measured the linearity of the receiver and the amount of local-oscillator power incident on the mixer for optimal operation, which is PLO≈1 μW. This receiver was used in making observations as a facility instrument at the Heinrich Hertz Telescope, Mt. Graham, AZ, during the 1998-1999 winter observing season.
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Krause, S., Mityashkin, V., Antipov, S., Gol’tsman, G., Meledin, D., Desmaris, V., et al. (2017). Reduction of phonon escape time for nbn hot electron bolometers by using gan buffer layers. IEEE Trans. Terahertz Sci. Technol., 7(1), 53–59.
Abstract: In this paper, we investigated the influence of the GaN buffer layer on the phonon escape time of phonon-cooled hot electron bolometers (HEBs) based on NbN material and compared our findings to conventionally employed Si substrate. The presented experimental setup and operation of the HEB close to the critical temperature of the NbN film allowed for the extraction of phonon escape time in a simplified manner. Two independent experiments were performed at GARD/Chalmers and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. By fitting the normalized IF measurement data to the heat balance equations, the escape time as a fitting parameter has been deduced and amounts to 45 ps for the HEB based on Si substrate as in contrast to a significantly reduced escape time of 18 ps for the HEB utilizing the GaN buffer layer under the assumption that no additional electron diffusion has taken place. This study indicates a high phonon transmissivity of the NbN-to-GaN interface and a prospective increase of IF bandwidth for HEB made of NbN on GaN buffer layers, which is desirable for future THz HEB heterodyne receivers.
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Antipov, S., Trifonov, A., Krause, S., Meledin, D., Desmaris, V., Belitsky, V., et al. (2017). Gain bandwidth of NbN HEB mixers on GaN buffer layer operating at 2 THz local oscillator frequency. In Proc. 28th Int. Symp. Space Terahertz Technol. (pp. 147–148).
Abstract: In this paper, we present IF bandwidth measurement results of NbN HEB mixers, which are employing NbN thin films grown on a GaN buffer-layer. The HEB mixers were operated in the heterodyne regime at a bath temperature of approximately 4.5 K and with a local oscillator operating at a frequency of 2 THz. A quantum cascade laser served as the local oscillator and a reference synthesizer based on a BWO generator (130-160 GHz) and a semiconductor superlattice (SSL) frequency multiplier was used as a signal source. By changing the LO frequency it was possible to record the IF response or gain bandwidth of the HEB with a spectrum analyzer at the operation point, which yielded lowest noise temperature. The gain bandwidth that was recorded in the heterodyne regime at 2 THz amounts to approximately 5 GHz and coincides well with a measurement that has been performed at elevated bath temperatures and lower LO frequency of 140 GHz. These findings strongly support that by using a GaN buffer-layer the phonon escape time of NbN HEBs can be significantly lower as compared to e.g. Si substrate, thus, providing higher gain bandwidth.
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Meledin, D., Tong, C. Y. - E., Blundell, R., Kaurova, N., Smirnov, K., Voronov, B., et al. (2003). Study of the IF bandwidth of NbN HEB mixers based on crystalline quartz substrate with an MgO buffer layer. IEEE Trans. Appl. Supercond., 13(2), 164–167.
Abstract: In this paper, we present the results of IF bandwidth measurements on 3-4 nm thick NbN hot electron bolometer waveguide mixers, which have been fabricated on a 200-nm thick MgO buffer layer deposited on a crystalline quartz substrate. The 3-dB IF bandwidth, measured at an LO frequency of 0.81 THz, is 3.7 GHz at the optimal bias point for low noise receiver operation. We have also made measurements of the IF dynamic impedance, which allow us to evaluate the intrinsic electron temperature relaxation time and self-heating parameters at different bias conditions.
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Jiang, L., Zhang, W., Yao, Q. J., Lin, Z. H., Li, J., Shi, S. C., et al. (2005). Characterization of a quasi-optical NbN superconducting hot-electron bolometer mixer. In Proc. PIERS (Vol. 1, pp. 587–590).
Abstract: In this paper, we report the performance of a quasi-optical NbN superconducting HEB (hot electron bolome-ter) mixer measured at 500 GHz. The quasi-optical NbN superconducting HEB mixer is cryogenically cooled bya 4-K close-cycled refrigerator. Its receiver noise temperature and conversion gain are thoroughly investigatedfor different LO pumping levels and dc biases. The lowest receiver noise temperature is found to be approxi-mately 1200 K, and reduced to about 445 K after correcting theloss of the measurement system. The stabilityof the mixer’s IF output power is also demonstrated.
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Zhang, W., Jiang, L., Lin, Z. H., Yao, Q. J., Li, J., Shi, S. C., et al. (2005). Development of a quasi-optical NbN superconducting HEB mixer. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 209–213).
Abstract: In this paper, we report the performance of a quasi-optical NbN superconducting HEB (hot electron bolometer) mixer measured at 500 and 850GHz. The quasi-optical NbN superconducting HEB mixer is cryogenically cooled by a 4-K close-cycled refrigerator. Measured receiver noise temperature at 850 and 500GHz are 3000K and 2500K respectively with wire grid as beamsplitter, while the lowest receiver noise temperature is found to be approximately 1200K with Mylar film. The theoretical receiver noise temperature (taking into account the elliptical polarization of log-spiral antenna) is consistent with measured one. The receiver noise temperature and conversion gain with 15-μm Mylar film as the beamsplitter at 500GHz are thoroughly investigated for different LO pumping levels and dc biases. The stability of the mixer’s IF output power is also demonstrated.
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Jiang, L., Miao, W., Zhang, W., Li, N., Lin, Z. H., Yao, Q. J., et al. (2006). Characterization of quasi-optical NbN phonon-cooled superconducting HEB mixers. In Proc. 17th Int. Symp. Space Terahertz Technol. (pp. 55–58).
Abstract: In this paper, we thoroughly investigate the performance of quasi-optical NbN phonon-cooled superconducting hot-electron bolometer (HEB) mixers, cryogenically cooled by a close-cycled 4-K refrigerator at 500 GI-1z and 850 GHz. The uncorrected lowest receiver noise Abstract---In temperatures measured are 800 K at 500 CHz without anti-reflection coating, and 1000 K @ 850 GHz with a 50 11M thick Mylar anti-reflection coating. The dependence of receiver noise temperature on the critical current and bath temperature of HEB mixer is also investigated here. Lifetime of quasi-optical superconducting NbN HEB mixers of different volumes, room temperature resistances, and critical temperatures are thoroughly studied. Increased room temperature resistance with time over the initial resistance changes between 1 and 1.2, and the reduced critical current with time over the initial value fluctuates slightly around 0.7 for most HEB mixers even of different volumes, room temperature resistances, and critical temperatures. The critical current degrades sharply vvhile room temperature resistance varies over 1.25.
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Zhang, W., Li, N., Jiang, L., Ren, Y., Yao, Q. - J., Lin, Z. - H., et al. (2008). Dependence of noise temperature of quasi-optical superconducting hot-electron bolometer mixers on bath temperature and optical-axis displacement. In C. Zhang, & X. - C. Zhang (Eds.), Proc. SPIE (Vol. 6840, 684007 (1 to 8)). Spie.
Abstract: It is known that the increase of bath temperature results in the decrease of critical current of superconducting hot-electron bolometer (HEB) mixers owing to the depression of superconductivity, thus leading to the degradation of the mixer’s sensitivity. Here we report our study on the effect of bath temperature on the heterodyne mixing performance of quasi-optical superconducting NbN HEB mixers incorporated with a two-arm log-spiral antenna. The correlation between the bath temperature, critical current, LO power requirement and noise temperature is investigated at 0.5 THz. Furthermore, the heterodyne mixing performance of quasi-optical superconducting NbN HEB mixers is examined while there is an optical-axis displacement between the center of the extended hemispherical silicon lens and the superconducting NbN HEB device, which is placed on the back of the lens. Detailed experimental results and analysis are presented.
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Jiang, L., Li, J., Zhang, W., Yao, Q. J., Lin, Z. L., Shi, S. C., et al. (2005). Characterization of NbN HEB mixers cooled by a close-cycled 4 Kelvin refrigerator. IEEE Trans. Appl. Supercond., 15(2), 511–513.
Abstract: It is quite beneficial to operate superconducting hot-electron-bolometer (HEB) mixers with a close-cycled 4 Kelvin refrigerator for real applications such as astronomy and atmospheric research. In this paper, a phononcooled NbN HEB mixer (quasioptical type) is thoroughly characterized under such a cooling circumstance. The effects of mechanical vibration, electrical interference, and temperature fluctuation of a two-stage Gifford-McMahon 4 Kelvin refrigerator upon the characteristics of the phononcooled NbN HEB mixer are investigated in particular. Detailed measurement results are presented.
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Kawamura, J., Blundell, R., Tong, C. -yu E., Gol’tsman, G., Gershenzon, E., Voronov, B., et al. (1997). Low noise NbN lattice-cooled superconducting hot-electron bolometric mixers at submillimeter wavelengths. Appl. Phys. Lett., 70(12), 1619–1621.
Abstract: Lattice-cooled superconducting hot-electron bolometric mixers are used in a submillimeter-wave waveguide heterodyne receiver. The mixer elements are niobium nitride film with 3.5 nm thickness and ∼10 μm2 area. The local oscillator power for optimal performance is estimated to be 0.5 μW, and the instantaneous bandwidth is 2.2 GHz. At an intermediate frequency centered at 1.4 GHz with 200 MHz bandwidth, the double sideband receiver noise temperature is 410 K at 430 GHz. The receiver has been used to detect molecular line emission in a laboratory gas cell.
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Vakhtomin, Y. B., Finkel, M. I., Antipov, S. V., Smirnov, K. V., Kaurova, N. S., Drakinskii, V. N., et al. (2003). The gain bandwidth of mixers based on the electron heating effect in an ultrathin NbN film on a Si substrate with a buffer MgO layer. J. of communications technol. & electronics, 48(6), 671–675.
Abstract: Measurements of the intermediate frequency band 900 GHz of mixers based on the electron heating effect (EHE) in 2-nm- and 3.5-nm-thick superconducting NbN films sputtered on MgO and Si substrates with buffer MgO layers are presented. A 2-nm-thick superconducting NbN film with a critical temperature of 9.2 K has been obtained for the first time using a buffer MgO layer.
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Baselmans, J. J. A., Hajenius, M., Gao, J. R., Klapwijk, T. M., de Korte, P. A. J., Voronov, B., et al. (2003). Noise performance of NbN hot electron bolometer mixers at 2.5 THz and its dependence on the contact resistance. In Proc. 14th Int. Symp. Space Terahertz Technol. (pp. 11–19).
Abstract: NbN hot electron bolometer mixers (HEBM) are at this moment the best heterodyne receivers for frequencies above 1 Thz. However, the fabrication procedure of these devices is such that the quality of the interface between the NbN superconducting film and the contact structure is not under good control. The result is a low transparency interface between the bolometer itself and the contact/antenna structure. In this paper we report a detailed experimental study on a novel idea to increase the transparency of this interface. This leads to a record sensitivity and more reproducible performance. We compare identical bolometers, coupled with a spiral antenna, with different NbN bolometer-contact pad interfaces. We find that cleaning the NbN interface alone results in an increase in the noise temperature. However, cleaning the NbN interface and adding a thin additional superconductor prior to the gold contact deposition improves the noise temperature of the HEBm with more than a factor of 2. A device with a contact pad on top of an in-situ cleaned NbN film consisting of 10 nm of NbTiN and 40 nm of gold has a DSB noise temperature of 1050 K at 2.5 THz.
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Gerecht, E., Musante, C. F., Jian, H., Yngvesson, K. S., Dickinson, J., Waldman, J., et al. (1999). New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz. IEEE Trans. Appl. Supercond., 9(2), 4217–4220.
Abstract: NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.
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Cherednichenko, S., Khosropanah, P., Adam, A., Merkel, H. F., Kollberg, E. L., Loudkov, D., et al. (2003). 1.4- to 1.7-THz NbN hot-electron bolometer mixer for the Herschel space observatory. In T. G. Phillips, & J. Zmuidzinas (Eds.), Proc. SPIE (Vol. 4855, pp. 361–370). SPIE.
Abstract: NbN hot- electron bolometer mixers have reached the level of 10hv/k in terms of the input noise temperature with the noise bandwidth of 4-6 GHz from subMM band up to 2.5 THz. In this paper we discuss the major characteristics of this kind of receiver, i.e. the gain and the noise bandwidth, the noise temperature in a wide RF band, bias regimes and optimisation of RF coupling to the quasioptical mixer. We present the status of the development of the mixer for Band 6 Low for Herschel Telescope.
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Gol'tsman, G., Jacobsson, S., Ekstrom, H., Karasik, B., Kollberg, E., & Gershenzon, E. (1994). Slot-line tapered antenna with NbN hot electron mixer for 300-360 GHz operation. In Proc. 5th Int. Symp. Space Terahertz Technol. (pp. 209–213a).
Abstract: NbN hot-electron mixers combined with slot-line tapered antennas on Si wdnitride membranes had been fabricated. Several strips of 1 gm wide and 5 tan long made from 100 A NbN film are inserted into the slot antenna. IV-curves under local oscillator power in 300-350 GHz frequency range and conversion gain dependencies on intermediate fre- quency in the 0.1-1 GHz range are measured and compared with that for 100 GHz frequency band. Our results show that pumped IV-curves and intermediate frequency bands are different for 100 GHz and 300 GHz frequency ranges. The interpretation exploits the fact that for the lowest radiation frequency the superconducting energy gap is larger than the radiation quantum energy while they are comparable at the higher frequency. Tha results show that such mixers have good perspectives for terahertz receiving technology.
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Gol'tsman, G. N., Karasik, B. S., Okunev, O. V., Dzardanov, A. L., Gershenzon, E. M., Ekstrom, H., et al. (1995). NbN hot electron superconducting mixers for 100 GHz operation. IEEE Trans. Appl. Supercond., 5(2), 3065–3068.
Abstract: NbN is a promising superconducting material for hot-electron superconducting mixers with an IF bandwidth larger than 1 GHz. In the 1OO GHz frequency range, the following parameters were obtained for 50 /spl Aring/ thick NbN films at 4.2 K: receiver noise temperature (DSB) /spl sim/1000 K; conversion loss /spl sim/10 dB; IF bandwidth /spl sim/1 GHz; and local oscillator power /spl sim/1 /spl mu/W. An increase of the critical current of the NbN film, increased working temperature, and a better mixer matching may allow a broader IF bandwidth up to 2 GHz, reduced conversion losses down to 3-5 dB and a receiver noise temperature (DSB) down to 200-300 K.
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0kunev, 0., Dzardanov, A., Ekstrom, H., Jacobsson, S., Kollberg, E., Gol'tsman, G., et al. (1994). NbN hot electron waveguide mixer for 100 GHz operation. In Proc. 5th Int. Symp. Space Terahertz Technol. (pp. 214–224).
Abstract: NbN is a promising superconducting material used to develope hot- electron superconducting mixers with an IF bandwidth over 1 GHz. In the 100 GHz frequency range, the following parameters were obtained for NbN films 50 A thick: the noise temperature of the receiver (DSB) 1000 K; the conversion losses 10 d13, the IF bandwidth 1 GHz; the local oscillator power 1 /LW. An increase of NbN film thickness up to 80-100 A and increase of working temperature up to 7-8 K, and a better mixer matching may allow to broader the IF band up to 3 Gllz, to reduce the conversion losses down to 3-5 dB and the noise tempera- ture down to 200-300 K.
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Baselmans, J., Kooi, J., Baryshev, A., Yang, Z. Q., Hajenius, M., Gao, J. R., et al. (2005). Full characterization of small volume NbN HEB mixers for space applications. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 457–462). Göteborg, Sweden.
Abstract: NbN phonon cooled HEB’s are one of the most promising bolometer mixer technologies for (near) future (space) applications. Their performance is usually quantified by mea- suring the receiver noise temperature at a given IF frequency, usually around 1 – 2 GHz. However, for any real applications it is vital that one fully knows all the relevant properties of the mixer, including LO power, stability, direct detection, gain bandwidth and noise bandwidth, not only the noise temperature at low IF frequencies. To this aim we have measured all these parameters at the optimal operating point of one single, small volume quasioptical NbN HEB mixer. We find a minimum noise temperature of 900 K at 1.46 THz. We observe a direct detection effect indicated by a change in bias current when changing from a 300 K hot load to a 77 K cold load. Due to this effect we overestimate the noise temperature by about 22% using a 300 K hot load and a 77 K cold load. The LO power needed to reach the optimal operating point is 80 nW at the receiver lens front, 59 nW inside the NbN bridge. However, using the isothermal technique we find a power absorbed in the NbN bridge of 25 nW, a difference of about a factor 2. We obtain a gain bandwidth of 2.3 GHz and a noise bandwidth of 4 GHz. The system Allan time is about 1 sec. in a 50 MHz spectral bandwidth and a deviation from white noise integration (governed by the radiometer equation) occurs at 0.2 sec., which implies a maximum integration time of a few seconds in a 1 MHz bandwidth spectrometer.
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Baryshev, A., Baselmans, J. J. A., Reker, S. F., Hajenius, M., Gao, J. R., Klapwijk, T. M., et al. (2005). Direct detection effect in hot electron bolometer mixers. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 463–464).
Abstract: NbN phonon cooled hot electron bolometer (HEB) mixers are currently the most sensitive heterodyne detectors at frequencies above 1.2 THz. They combine a good sensitivity (8-15 times the quantum limit), an IF bandwidth of the order of 4-6 GHz and a wide RF bandwidth from 0.7-5.2 THz. However, for use in a space based observatory, such as Herschel, it is of vital importance that the Local Oscillator (LO) power requirement of the mixer is compatible with the low output power of present day THz LO sources. This can be achieved by reducing the mixer volume and critical current. However, the large RF bandwidth and low LO power requirement of such a mixer result in a direct detection effect, characterized by a change in the bias current of the HEB when changing the RF signal from a black body load at 300 K to one at 77 K. As a result the measured sensitivity using a 300 K and 77 K calibration load differs significantly from the small signal sensitivity relevant for astronomical observations. In this article we describe a set of dedicated experiments to characterize the direct detection effect for a small volume quasi-optical NbN phonon cooled HEB mixer. We measure the direct detection effect in a small volume (0.15 μm · 1 μm · 3.5 nm) quasi- optical NbN phonon cooled HEB mixer at 1.6 THz. We found that the small signal sensitivity of the receiver is underestimated by approximately 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300 K and 77 K. Using a 200 GHz wide band-pass filter at the 4.2 K the direct detection effect virtually disappears. Heterodyne response measurements using water vapor absorption line in a gas cell confirms the existence and a magnitude of a direct detection effect. We also propose a theoretical explanation using uniform electron heating model. This direct detection effect has important implications for the calibration procedure of these receivers in real telescope systems. We are developing Nb HEBs for a large-format, diffusion-cooled hot electron bolometer (HEB) array submillimeter camera. The goal is to produce a 64 pixel array together with the University of Arizona to be used on the HHT on Mt Graham. It is designed to detect in the 850 GHz atmospheric window. We have fabricated Nb HEBs using a new angle- deposition process, which had previously produced high quality Nb-Au bilayer HEB devices at Yale. [1] We have characterized these devices using heterodyne mixing at ~30 GHz to compare to 345 GHz tests at the University of Arizona. We can also directly compare our Nb HEB mixers to SIS mixers in this same 345 GHz system. This allows us to rigorously calibrate the system’s losses and extract the mixer noise temperature in a well characterized mixer block, before undertaking the 850 GHz system. Here we give a report on the initial devices we have fabricated and characterized. * Department of Applied Physics, Yale University ** Department of Astronomy, University of Arizona [1] Applied Physics Letters 84, Number 8; p.1404-7, Feb 23 (2004)
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Hajenius, M., Baselmans, J. J. A., Gao, J. R., Klapwijk, T. M., de Korte, P. A. J., Voronov, B., et al. (2004). Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz. Supercond. Sci. Technol., 17(5), S224–S228.
Abstract: NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized with negligible contact resistance between the bolometer itself and the contact structure. Using a combination of in situ cleaning of the NbN film and the use of an additional superconducting interlayer of a 10 nm NbTiN layer between the Au of the contact structure and the NbN film superior noise temperatures have been obtained as low as 950 K at 2.5 THz and 750 K at 1.9 THz. Here we address in detail the DC characterization of these devices, the interface transparencies between the bolometers and the contacts and the consequences of these factors on the mixer performance.
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Hajenius, M., Baselmans, J. J. A., Gao, J. R., Klapwijk, T. M., de Korte, P. A. J., Voronov, B., et al. (2003). Improved NbN phonon cooled hot electron bolometer mixers. In Proc. 14th Int. Symp. Space Terahertz Technol. (pp. 413–423). Tucson, USA.
Abstract: NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized with negligible contact resistance to Au pads. By adding either a 5 nm Nb or a 10 nm NbTiN layer between the Au and NbN, to preserve superconductivity in the NbN under the Au contact pad, superior noise temperatures have been obtained. Using DC I,V curves and resistive transitions in combination with process parameters we analyze the nature of these improved devices and determine interface transparencies.
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Gerecht, E., Musante, C. F., Zhuang, Y., Yngvesson, K. S., Gol’tsman, G. N., Voronov, B. M., et al. (1999). NbN hot electron bolometric mixerss—a new technology for low-noise THz receivers. IEEE Trans. Appl. Supercond., 47(12), 2519–2527.
Abstract: New advances in hot electron bolometer (HEB) mixers have recently resulted in record-low receiver noise temperatures at terahertz frequencies. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 2.24 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and local-oscillator power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers that will further increase the detection speed of terahertz systems.
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Smirnov, K. V., Vachtomin, Y. B., Antipov, S. V., Maslennikov, S. N., Kaurova, N. S., Drakinsky, V. N., et al. (2003). Noise and gain performance of spiral antenna coupled HEB mixers at 0.7 THz and 2.5 THz. In Proc. 14th Int. Symp. Space Terahertz Technol. (pp. 405–412).
Abstract: Noise and gain performance of hot electron bolometer (HEB) mixers based on ultrathin superconducting NbN films integrated with a spiral antenna was studied. The noise temperature measurements for two samples with different active area of 3 p.m x 0.24 .tni and 1.3 1..tm x 0.12 1.tm were performed at frequencies 0.7 THz and 2.5 THz. The best receiver noise temperatures 370 K and 1600 K, respectively, have been found at these frequencies. The influence of contact resistance between the superconductor and the antenna terminals on the noise temperature of HEB is discussed. The noise and gain bandwidth of 5GHz and 4.2 GHz, respectively, are demonstrated for similar HEB mixer at 0.75 THz.
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Hübers, H. - W., Schubert, J., Krabbe, A., Birk, M., Wagner, G., Semenov, A., et al. (2001). Parylene anti-reflection coating of a quasi-optical hot-electron-bolometric mixer at terahertz frequencies. Infrared Physics & Technology, 42(1), 41–47.
Abstract: Parylene C was investigated as anti-reflection coating for silicon at terahertz frequencies. Measurements with a Fourier-transform spectrometer show that the transmittance of pure silicon can be improved by about 30% when applying a layer of Parylene C with a quarter wavelength optical thickness. The 10% bandwidth of this coating extends from 1.5 to 3 THz for a center frequency of 2.3–2.5 THz, where the transmittance is constant. Heterodyne measurements demonstrate that the noise temperature of a hot-electron-bolometric mixer can be reduced significantly by coating the silicon lens of the hybrid antenna with a quarter wavelength Parylene C layer. Compared to the same mixer with an uncoated lens the improvement is about 30% at a frequency of 2.5 THz.
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Gol'tsman, G., Maslennikov, S., Finkel, M., Antipov, S., Kaurova, N., Grishina, E., et al. (2006). Nanostructured ultrathin NbN film as a terahertz hot-electron bolometer mixer. In Proc. MRS (Vol. 935, 210 (1 to 6)).
Abstract: Planar spiral antenna coupled and directly lens coupled NbN HEB mixer structures are studied. An additional MgO buffer layer between the superconducting film and Si substrate is introduced. The buffer layer enables us to increase the gain bandwidth of a HEB mixer due to better acoustic transparency. The gain bandwidth is widened as NbN film thickness decreases and amounts to 5.2 GHz. The noise temperature of antenna coupled mixer is 1300 and 3100 K at 2.5 and 3.8 THz respectively. The structure and composition of NbN films is investigated by X-ray diffraction spectroscopy methods. Noise performance degradation at LO frequencies more than 3 THz is due to the use of a planar antenna and signal loss in contacts between the antenna and the sensitive NbN bridge. The mixer is reconfigured for operation at higher frequencies in a manner that receiver’s noise temperature is only 2300 K (3 times of quantum limit) at LO frequency of 30 THz.
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Vachtomin, Y. B., Antipov, S. V., Maslennikov, S. N., Smirnov, K. V., Polyakov, S. L., Zhang, W., et al. (2006). Quasioptical hot electron bolometer mixers based on thin NBN films for terahertz region. In Proc. 16th Int. Crimean Microwave and Telecommunication Technology (Vol. 2, pp. 688–689).
Abstract: Presented in this paper are the performances of HEB mixers based on 2-3.5 nm thick NbN films integrated with log-periodic spiral antenna. Double side-band receiver noise temperature values are 1300 K and 3100 K at 2.5 THz and at 3.8 THz, respectively. Mixer gain bandwidth is 5.2 GHz. Local oscillator power is 1-3 muW for mixers with different active area
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Tretyakov, I., Kaurova, N., Voronov, B. M., & Goltsman, G. N. (2018). About effect of the temperature operating conditions on the noise temperature and noise bandwidth of the terahertz range NbN hot-electron bolometers. In Proc. 29th Int. Symp. Space Terahertz Technol. (113).
Abstract: Results of an experimental study of the noise temperature (Tn) and noise bandwidth (NBW) of the superconductor NbN hot-electron bolometer (HEB) mixer as a function of its temperature (Tb) and NbN bridge length are presented. It was determined that the NBW of the mixer is significantly wider at temperatures close to the critical ones (Tc) than are values measured at 4.2 K. The NBW of the mixer measured at the heterodyne frequency of 2.5 THz at temperature Tb close to Tc was ~13 GHz, as compared with 6 GHz at Tb = 4.2 K. This experiment clearly demonstrates the limitation of the thermal flow from the NbN bridge at Tb ≪ Tc for mixers manufactured by the in situ technique. This limitation is close in its nature to the Andreev reflection on the superconductor/metal boundary. In this case, the noise temperature of the studied mixer increased from 1100 to 3800 K.
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Kroug, M., Cherednichenko, S., Merkel, H., Kollberg, E., Voronov, B., Gol'tsman, G., et al. (2001). NbN hot electron bolometric mixers for terahertz receivers. IEEE Trans. Appl. Supercond., 11(1), 962–965.
Abstract: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.
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Baubert, J., Salez, M., Merkel, H., Pons, P., Cherednichenko, S., Lecomte, B., et al. (2005). IF gain bandwidth of membrane-based NbN hot electron bolometers for SHAHIRA. IEEE Trans. Appl. Supercond., 15(2), 507–510.
Abstract: SHAHIRA (Submm Heterodyne Array for HIgh-speed Radio Astronomy) is a project supported by the European Space Agency (ESA) and is designed to fly on the SOFIA observatory. A quasi-optic design has been chosen for 2.5/2.7 THz and 4.7 THz, for hydroxyde radical OH, deuterated hydrogen HD and neutral atomic oxygen OI lines observations. Hot electron bolometers (HEBs) have been processed on 1 /spl mu/m thick SiO/sub 2//Si/sub 3/N/sub 4/ stress-less membranes. In this paper we analyse the intermediate frequency (IF) gain bandwidth from the theoretical point of view, and compare it to measurements.
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Ekström, H., Karasik, B., Kollberg, E., Gol'tsman, G., & Gershenzon, E. (1995). 350 GHz NbN hot electron bolometer mixer. In Proc. 6th Int. Symp. Space Terahertz Technol. (pp. 269–283).
Abstract: Superconducting NbN hot-electron bolometer (HEB) mixer devices have been fabricated and measured at 350 GHz. The HEB is integrated with a double dipole antenna on an extended crystalline quartz hyper hemispherical substrate lens. Heterodyne measurement gave a -3 dB bandwidth, mainly determined by the electron- phonon interaction time, of about 680 and 1000 MHz for two different films with Tc = 8.5 and 11 K respectively. The measured DSB receiver noise temperature is around 3000 K at 800 MHz IF frequency. The main contribution to the output noise from the device is due to electron temperature fluctuations with the equivalent output noise temperature TFL-100 K. TH, has the same frequency dependence as the IF response. The contribution from Johnson noise is of the order of T. The RF coupling loss is estimated to be = 6 dB. The film with lower Tc, had an estimated intrinsic low-frequency conversion loss = 7 dB, while the other film had a conversion loss as high as 14 dB. The difference in intrinsic conversion loss is explained by less uniform absorption of radiation. Measurements of the small signal impedance shows a transition of the output impedance from the DC differential resistance Rd=dV/dI in the low frequency limit to the DC resistance R 0 =Uoff 0 in the bias point for frequencies above 3 GHz. We judge that the optimum shape of the IV-characteristic is more easily obtained at THz frequencies where the main restriction in performance should come from problems with the RF coupling.
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Cherednichenko, S., Yagoubov, P., Il'In, K., Gol'tsman, G., & Gershenzon, E. (1997). Large bandwidth of NbN phonon-cooled hot-electron bolometer mixers on sapphire substrates. In Proc. 8th Int. Symp. Space Terahertz Technol. (pp. 245–257).
Abstract: The bandwidth of NbN phonon-cooled hot electron bolometer mixers has been systematically investigated with respect to the film thickness and film quality variation. The films, 2.5 to 10 mm thick, were fabricated on sapphire substrates using DC reactive magnetron sputtering. All devices consisted of several parallel strips, each 1 1.1 wide and 211 long, placed between Ti-Au contact pads. To measure the gain bandwidth we used two identical BWOs operating in the 120-140 GHz frequency range, one functioning as a local oscillator and the other as a signal source. The majority of the measurements were made at an ambient temperature of 4.5 K with optimal LO and DC bias. The maximum 3 dB bandwidth (about 4 GHz) was achieved for the devices made of films which were 2.5-3.5 nm thick, had a high critical temperature, and high critical current density. A theoretical analysis of bandwidth for these mixers based on the two-temperature model gives a good description of the experimental results if one assumes that the electron temperature is equal to the critical temperature.
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Svechnikov, S. I., Finkel, M. I., Maslennikov, S. N., Vachtomin, Y. B., Smirnov, K. V., Seleznev, V. A., et al. (2006). Superconducting hot electron bolometer mixer for middle IR range. In Proc. 16th Int. Crimean Microwave and Telecommunication Technology (Vol. 2, pp. 686–687).
Abstract: The developed directly lens coupled hot electron bolometer (HEB) mixer was based on 5 nm superconducting NbN deposited on GaAs substrate. The layout of the structure, including 30x20 mcm^2 active area coupled with a 50 Ohm coplanar line, was patterned by photolithography. The responsivity of the mixer was measured in a direct detection mode in the 25-64 THz frequency range. The noise performance of the mixer and the directivity of the receiver were investigated in a heterodyne mode. A 10.6 mum wavelength CW CO2 laser was utilized as a local oscillator.
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Finkel, M. I., Maslennikov, S. N., Vachtomin, Y. B., Svechnikov, S. I., Smirnov, K. V., Seleznev, V. A., et al. (2005). Hot electron bolometer mixer for 20 – 40 THz frequency range. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 393–397). Göteborg, Sweden.
Abstract: The developed HEB mixer was based on a 5 nm thick NbN film deposited on a GaAs substrate. The active area of the film was patterned as a 30×20 μm 2 strip and coupled with a 50 Ohm coplanar line deposited in situ. An extended hemispherical germanium lens was used to focus the LO radiation on the mixer. The responsivity of the mixer was measured in a direct detection mode in the 25÷64 THz frequency range. The noise performance of the mixer and the directivity of the receiver were investigated in a heterodyne mode. A 10.6 μm wavelength CW CO 2 laser was utilized as a local oscillator.
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Schwaab, G. W., Sirmain, G., Schubert, J., Hubers, H. - W., Gol'tsman, G., Cherednichenko, S., et al. (1999). Investigation of NbN phonon-cooled HEB mixers at 2.5 THz. IEEE Trans. Appl. Supercond., 9(2), 4233–4236.
Abstract: The development of superconducting hot electron bolometric (HEB) mixers has been a big step forward in the direction of quantum noise limited mixer performance at THz frequencies. Such mixers are crucial for the upcoming generation of airborne and spaceborne THz heterodyne receivers. In this paper we report on new results on a phonon-cooled NbN HEB mixer using e-beam lithography. The superconducting film is 3 nm thick. The mixer is 0.2 μm long and 1.5 μm wide and it is integrated in a spiral antenna on a Si substrate. The device is quasi-optically coupled through a Si lens and a dielectric beam combiner to the radiation of an optically pumped FIR ring gas laser cavity. The performance of the mixer at different THz frequencies from 0.69 to 2.55 THz with an emphasis on 2.52 THz is demonstrated. At 2.52 THz minimum DSB noise temperatures of 4200 K have been achieved at an IF of 1.5 GHz and a bandwidth of 40 MHz with the mixer mounted in a cryostat and a 0.8 m long signal path in air.
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Loudkov, D., Khosropanah, P., Cherednichenko, S., Adam, A., MerkeI, H., Kollberg, E., et al. (2002). Broadband fourier transform spectrometer (FTS) measurements of spiral and double-slot planar antennas at THz frequencies. In Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 373–369).
Abstract: The direct responses of NbN phonon-cooled hot electron bolometer (HEB) mixers, integrated with different planar antennas, are measured, using Fourier Transform Spectrometer (F1S). One spiral antenna and several double slot antennas, designed for 0.6, 1.4, 1.6, 1.8 and 2.5 THz central frequencies, are investigated. The Optimization of the measurement set-up is discussed in terms of the beam splitter and the F11S-to-HEB coupling. The result shows that the spiral antenna is circular polarized and has a bandwidth of about 2 THz. The frequency bands of double slot antennas show some shift from the design values and their relative bandwidth increases by increasing the design frequency. The antenna responses do not depend on the HEB bias point and temperature, as long as the device is in the resistive state.
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Gol'tsman, G. N., Karasik, B. S., Svechnikov, S. I., Gershenzon, E. M., Ekström, H., & Kollberg E. (1995). Noise temperature of NbN hot—electron quasioptical superconducting mixer in 200-700 GHz range. In Proc. 6th Int. Symp. Space Terahertz Technol. (268).
Abstract: The electron heating effect in superconducting films is becoming very attractive for the development of THz range mixers because of the absence of frequency limitations inherent in the bolometric mechanism. However, the evidence for the spectral dependence of the position of optimal operating point has been found recently for NbN thin film devices 1.2 • The effect is presumably attributed to the variation in the absorption of radiation depending on the frequency. Since the resistive state is not spatially uniform the coupling efficiency of the mixer device with radiation can be different for frequencies larger than Zeilh and those smaller than 2Alh (d is the effective superconducting gap in the resistive state). To study the effect more thoroughly we have investigated the noise temperature of quasioptical NbN mixer device with broken hue tapered slot antenna in the frequency range 200-700 GHz. The device consists of several (5-10) parallel strips 1 jim wide and 6-7 tun thick made from NbN film on Si0 2 -Si 3 N 4 -Si membrane. The strips are connected with the gold contacts of the slot-line antenna which serves both as bias and IF leads. We used backward wave oscillators as LO sources and a standard hot/cold load technique for noise temperature measurements. The frequency dependence of noise temperature is mainly determined by two factors: frequency properties of the antenna and frequency dependence of the NbN film impedance. To separate both factors we monitored the frequency dependence of the device responsivity in the detector mode at a higher temperature within the superconducting transition where the impedance of NbN film is close to its normal resistance. In this case the impedance of the device itself is frequency independent. The experimental results will be reported at the Symposium. 1. G. Gollsman, S. Jacobsson, H. EkstrOm, B. Karasik, E. Kollberg, and E. Gershenzon, “Slot-line tapered antenna with NbN hot electron mixer for 300-360 GHz operation,” Proc of the 5th Int. Symp. on Space Terahertz Technology, pp. 209-213a, May 10-12,1994. 2. B.S. Karasik, G.N. Gol i tsman, B.M. Voronov, S.I. Svechnikov, E.M. Gershenzon, H. Ekstrom, S. Jacobsson, E. Kollberg, and K.S. Yngvesson, “Hot electron quasioptical NbN superconducting mixer,” presented at the ASC94, submitted to IEEE Trans. on Appl. Superconductivity.
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Kawamura, J., Blundell, R., Tong, C. ‐yu E., Gol’tsman, G., Gershenzon, E., & Voronov, B. (1996). Performance of NbN lattice‐cooled hot‐electron bolometric mixers. J. Appl. Phys., 80(7), 4232–4234.
Abstract: The heterodyne performance of lattice‐cooled hot‐electron bolometric mixers is measured at 200 GHz. Superconducting thin‐film niobium nitride strips with ∼5 nm thickness are used as waveguide mixer elements. A double‐sideband receiver noise temperature of 750 K at 244 GHz is measured at an intermediate frequency centered at 1.5 GHz with 500 MHz bandwidth and with 4.2 K device temperature. The instantaneous bandwidth for this mixer is 1.6 GHz. The local oscillator power required by the mixer is about 0.5 μW. The mixer is linear to within 1 dB up to an input power level 6 dB below the local oscillator power. A receiver incorporating a hot‐electron bolometric mixer was used to detect molecular line emission in a laboratory gascell. This experiment unambiguously confirms that the receiver noise temperature determined from Y‐factor measurements reflects the true heterodyne sensitivity.
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Anfertev, V., Vaks, V., Revin, L., Pentin, I., Tretyakov, I., Goltsman, G., et al. (2017). High resolution THz gas spectrometer based on semiconductor and superconductor devices. In EPJ Web Conf. (Vol. 132, 02001 (1 to 2)).
Abstract: The high resolution THz gas spectrometer consists of a synthesizer based on Gunn generator with a semiconductor superlattice frequency multiplier as a radiation source, and an NbN hot electron bolometer in a direct detection mode as a THz radiation receiver was presented. The possibility of application of a quantum cascade laser as a local oscillator for a heterodyne receiver which is based on an NbN hot electron bolometer mixer is shown. The ways for further developing of the THz spectroscopy were outlined.
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Schwaab, G. W., Auen, K., Bruendermann, E., Feinaeugle, R., Gol’tsman, G. N., Huebers, H. - W., et al. (1998). 2- to 6-THz heterodyne receiver array for the Stratospheric Observatory for Infrared Astronomy (SOFIA). In T. G. Phillips (Ed.), Proc. SPIE (Vol. 3357, pp. 85–96). SPIE.
Abstract: The Institute of Space Sensor Technology of the German Aerospace Center (DLR) is developing a heterodyne array receiver for the frequency range 2 to 6 THz for the Stratospheric Observatory for Infrared Astronomy (SOFIA). Key science issues in that frequency range are the observation of lines of atoms [e.g. (OI)], ions [e.g. (CII), (NII)], and molecules (e.g. OH, HD, CO) with high spectral resolution to study the dynamics and evolution of galactic and extragalactic objects. Long term goal is the development of an integrated array heterodyne receiver with superconducting hot electron bolometric (HEB) mixers and p-type Ge or Si lasers as local oscillators. The first generation receiver will be composed of HEB mixers in a 2 pixel 2 polarization array which will be pumped by a gas laser local oscillator. Improved Schottky diode mixers are the backup solution for the HEBs. The state of the art of HEB mixer and p-type Ge laser technology are described as well as possible improvements in the ’conventional’ optically pumped far-infrared laser and Schottky diode mixer technology. Finally, the frequency coverage of the first generation heterodyne receiver for some important astronomical transitions is discussed. The expected sensitivity is compared to line fluxes measured by the ISO satellite.
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Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., Voronov, B. M., & Gol'tsman, G. N. (2011). Direct measurement of the gain and noise bandwidths of HEB mixers. IEEE Trans. Appl. Supercond., 21(3), 645–648.
Abstract: The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement.
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Cherednichenko, S., Kroug, M., Merkel, H., Kollberg, E., Loudkov, D., Smirnov, K., et al. (2001). Local oscillator power requirement and saturation effects in NbN HEB mixers. In C. Iit.u.t.e of T. Jet Propulsion Laboratory (Ed.), Proc. 12th Int. Symp. Space Terahertz Technol. (pp. 273–285). San Diego, CA, USA.
Abstract: The local oscillator power required for NbN hot-electron bolometric mixers (P LO ) was investigated with respect to mixer size, critical temperature and ambient temperature. P LO can be decreased by a factor of 10 as the mixer size decreases from 4×0.4 µm 2 to 0.6×0.13 µm 2 . For the smallest volume mixer the optimal local oscillator power was found to be 15 nW. We found that for such mixer no signal compression was observed up to an input signal of 2 nW which corresponds to an equivalent input load of 20,000 K. For a constant mixer volume, reduction of T c can decrease optimal local oscillator power at least by a factor of 2 without a deterioration of the receiver noise temperature. Bath temperature was found to have minor effect on the receiver characteristics.
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Svechnikov, S., Verevkin, A., Voronov, B., Menschikov, E., Gershenzon, E., & Gol'tsman, G. (1998). Quasioptical phonon-cooled NbN hot electron bolometer mixers at 0.5-1.1 THz. In Proc. 9th Int. Symp. Space Terahertz Technol. (pp. 45–51).
Abstract: The noise performance of a receiver incorporating spiral antenna coupled NbN phonon-cooled superconducting hot electron bolometric mixer is measured from 450 GHz to 1200 GHz. The mixer element is thin (thickness nm) NbN 1.5 pm wide and 0.2 i.um long film fabricated by lift-off e-beam lithography on high-resistive silicon substrate. The noise of the receiver temperature is 1000 K at 800-900 GHz, 1200 K at 950 GHz, and 1600 K at 1.08 THz. The required (absorbed) local-oscillator power is —20 nW.
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Kawamura, J., Blundell, R., Tong, C. - Y. E., Gol'tsman, G., Gershenzon, E., Voronov, B., et al. (1997). Phonon-cooled NbN HEB mixers for submillimeter wavelengths. In Proc. 8th Int. Symp. Space Terahertz Technol. (pp. 23–28).
Abstract: The noise performance of receivers incorporating NbN phonon-cooled superconducting hot electron bolometric mixers is measured from 200 GHz to 900 GHz. The mixer elements are thin-film (thickness — 4 nm) NbN with —5 to 40 pm area fabricated on crystalline quartz sub- strates. The receiver noise temperature from 200 GHz to 900 GHz demonstrates no unexpected degradation with increasing frequency, being roughly TRx ,; 1-2 K The best receiver noise temperatures are 410 K (DSB) at 430 GHz, 483 K at 636 GHz, and 1150 K at 800 GHz.
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Semenov, A. D., Gousev, Y. P., Renk, K. F., Voronov, B. M., Gol'tsman, G. N., Gershenzon, E. M., et al. (1997). Noise characteristics of a NbN hot-electron mixer at 2.5 THz. IEEE Trans. Appl. Supercond., 7(2), 3572–3575.
Abstract: The noise temperature of a NbN phonon cooled hot-electron mixer has been measured at a frequency of 2.5 THz for various operating conditions. We obtained for optimal operation a double sideband mixer noise temperature of /spl ap/14000 K and a system conversion loss of /spl ap/23 dB at intermediate frequencies up to 1 GHz. The dependences of the mixer noise temperature on the bias voltage, local oscillator power, and intermediate frequency were consistent with the phenomenological description based on the effective temperature approximation.
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Gol’tsman, G. N., & Gershenzon, E. M. (1999). Phonon-cooled hot-electron bolometric mixer: overview of recent results. Appl. Supercond., 6(10-12), 649–655.
Abstract: The paper presents an overview of recent results for NbN phonon-cooled hot electron bolometric (HEB) mixers. The noise temperature of the receivers based on both quasioptical and waveguide versions of HEB mixer has crossed the level of 1 K·GHz−1 at 430 GHz (410 K) and 600–650 GHz (480 K) and is close to this level at 820 GHz (1100 K) and 900 GHz (980 K). The gain bandwidth measured for quasioptical HEB mixer at 620 GHz reached 4 GHz and the noise temperature bandwidth was almost 8 GHz. Local oscillator power requirements are about 1 μW for mixers made by photolithography and are about 100 nW for mixers made by e-beam lithography. The studies in terahertz receivers based on HEB superconducting mixers now present a dynamic, rapidly developing field.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Schubert, J., Hubers, H. - W., et al. (1999). Heterodyne measurements of a NbN superconducting hot electron mixer at terahertz frequencies. IEEE Trans. Appl. Supercond., 9(2), 3757–3760.
Abstract: The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The best results of the DSB noise temperature at 1.5 GHz IF frequency obtained with one device are: 1300 K at 650 GHz, 4700 K at 2.5 THz and 10000 K at 3.12 THz. The measurements were performed at 4.5 K ambient temperature. The amount of local oscillator (LO) power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain measured at 650 GHz is -9 dB, the total conversion gain is -14 dB.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Schubert, J., Hubers, H. - W., et al. (1998). Performance of NbN phonon-cooled hot-electron bolometric mixer at Terahertz frequencies. In Proc. 6-th Int. Conf. Terahertz Electron. (pp. 149–152).
Abstract: The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The results of the DSB noire temperature are: 1300 K at 650 GHz, 4700 K at 2.5 TBz and 10000 K at 3.12 THz. The RF bandwidth of the receiver is at least 2.5 THz. The amount of LO power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain is measured to be -9 dB, the total conversion gain -14 dB.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Hübers, H. - W., Schubert, J., et al. (1999). NbN hot electron bolometric mixers at frequencies between 0.7 and 3.1 THz. In Proc. 10th Int. Symp. Space Terahertz Technol. (pp. 238–246).
Abstract: The performance of NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixers is investigated in the 0.7-3.1 THz frequency range. The devices are made from a 3.5-4 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The length of the bolometer microbridge is 0.1- 0.2 gm, the width is 1-2 gm. The best results of the DSB receiver noise temperature measured at 1.5 GHz intermediate frequency are: 800 K at 0.7 THz, 1100 K at 1.6 THz, 2000 K at 2.5 THz and 4200 K at 3.1 THz. The measurements were performed with a far infrared laser as the local oscillator (LO) source. The estimated LO power required is less than 500 nW at the receiver input. First results on the spiral antenna polarization measurements are reported.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Schubert, J., & Hübers, H. - W. (1999). NbN hot electron bolometric mixers at frequencies between 0.7 and 3.1 THz. Supercond. Sci. Technol., 12(11), 989–991.
Abstract: The performance of NbN-based phonon-cooled hot electron bolometric (HEB) quasioptical mixers is investigated in the 0.7-3.1 THz frequency range. The devices are made from a 3.5-4 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The length of the bolometer microbridge is 0.1-0.2 µm; the width is 1-2 µm. The best results of the DSB receiver noise temperature measured at 1.5 GHz intermediate frequency are: 800 K at 0.7 THz, 1100 K at 1.6 THz, 2000 K at 2.5 THz and 4200 K at 3.1 THz. The measurements were performed with a far infrared laser as the local oscillator (LO) source. The estimated LO power requirement is less than 500 nW at the receiver input. First results on spiral antenna polarization measurements are reported.
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Okunev, 0., Dzardranov, A., Gol'tsman, G., & Gershenzon, E. (1995). Performances of hot—electron superconducting mixer for frequencies less than the gap energy: NbN mixer for 100 GHz operation. In Proc. 6th Int. Symp. Space Terahertz Technol. (pp. 247–253).
Abstract: The possibilities to improve the parameters of the 100 GHz NbN HEB superconducting waveguide mixers have been studied. The device consists of a signal strip 1 gm wide by 2 Am long made of 40 A thick NbN film. The best operation point was found at 5 K, where the mixer bandwidth made up 1.5-2 GHz and the total loss diminished down to 8 dB. The critical current density has been increased up to " 40 6 A/cm 2 , the noise temperature of the receiver (DSB) has reduced down to 450 K and the local oscillator power has decreased down to -.4).1 mcV.
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Trifonov, A., Tong, C. - Y. E., Lobanov, Y., Kaurova, N., Blundell, R., & Goltsman, G. (2017). Photon absorption near the gap frequency in a hot electron bolometer. IEEE Trans. Appl. Supercond., 27(4), 1–4.
Abstract: The superconducting energy gap is a fundamental characteristic of a superconducting film, which, together with the applied pump power and the biasing setup, defines the instantaneous resistive state of the Hot Electron Bolometer (HEB) mixer at any given bias point on the I-V curve. In this paper we report on a series of experiments, in which we subjected the HEB to radiation over a wide frequency range along with parallel microwave injection. We have observed three distinct regimes of operation of the HEB, depending on whether the radiation is above the gap frequency, far below it or close to it. These regimes are driven by the different patterns of photon absorption. The experiments have allowed us to derive the approximate gap frequency of the device under test as about 585 GHz. Microwave injection was used to probe the HEB impedance. Spontaneous switching between the superconducting (low resistive) state and a quasi-normal (high resistive) state was observed. The switching pattern depends on the particular regime of HEB operation and can assume a random pattern at pump frequencies below the gap to a regular relaxation oscillation running at a few MHz when pumped above the gap.
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Hübers, H. - W., Semenov, A., Holldack, K., Schade, U., Wüstefeld, G., & Gol’tsman, G. (2005). Time domain analysis of coherent terahertz synchrotron radiation. Appl. Phys. Lett., 87(18), 184103 (1 to 3).
Abstract: The time structure of coherent terahertz synchrotron radiation at the electron storage ring of the Berliner Elektronensynchrotron und Speicherring Gesellschaft has been analyzed with a fast superconducting hot-electron bolometer. The emission from a single bunch of electrons was found to last ∼1500ps at frequencies around 0.4THz, which is much longer than the length of an electron bunch in the time domain (∼5ps). It is suggested that this is caused by multiple reflections at the walls of the beam line. The quadratic increase of the power with the number of electrons in the bunch as predicted for coherent synchrotron radiation and the transition from stable to bursting radiation were determined from a single storage ring fill pattern of bunches with different populations.
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Pentin, I., Finkel, M., Maslennikov, S., Vakhtomin, Y., Smirnov, K., Kaurova, N., et al. (2017). Superconducting hot-electron-bolometer mixers for the mid-IR. Rus. J. Radio Electron., (10), http://jre.cplire.ru/jre/oct17/9/text.pdf. Retrieved August 18, 2024, from http://jre.cplire.ru/jre/oct17/9/abstract_e.html
Abstract: The work presents the result of development of the NbN superconducting hot-electron-bolometer (HEB) mixer. The sensitive element of the mixer is directly coupled to mid-IR radiation, and doesn’t have planar metallic antenna. Investigations of noise characteristics of NbN HEB mixer were performed at the frequency 28.4 THz (λ = 10.6 µm) by using gas-discharge CW CO2-laser without consideration of optical and electrical losses in the heterodyne receiver. The noise temperature of NbN HEB mixer with the size of the sensitive element 10 µm × 10 µm was 2320 K (~ 1.5hν/kB) at the heterodyne frequency of 28.4 THz. The noise temperature was determined by measuring the Y-factor taking into account the term which describes fluctuations of zero-point oscillations in accordance with the fluctuation-dissipation theorem of Calle-Welton. Isothermal method was used to estimate the absorbed heterodyne radiation power which was 9 µW at the optimal operating point for the minimum noise temperature of NbN HEB mixer.
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Kawamura, J., Blundell, R., Tong, C. - Y. E., Golts'man, G., Gershenzon, E., & Voronov B. (1996). Superconductive NbN hot-electron bolometric mixer performance at 250 GHz. In Proc. 7th Int. Symp. Space Terahertz Technol. (pp. 331–336).
Abstract: Thin film NbN (<40 A) strips are used as waveguide mixer elements. The electron cooling mechanism for the geometry is the electron-phonon interaction. We report a receiver noise temperature of 750 K at 244 GHz, with / IF = 1.5 GHz, Af= 500 MHz, and Tphysical = 4 K. The instantaneous bandwidth for this mixer is 1.6 GHz. The local oscillator (LO) power is 0.5 1.tW with 3 dB-uncertainty. The mixer is linear to 1 dB up to an input power level 6 dB below the LO power. We report the first detection of a molecular line emission using this class of mixer, and that the receiver noise temperature determined from Y-factor measurements reflects the true heterodyne sensitivity.
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Gol'tsman, G. N. (1999). Hot electron bolometric mixers: new terahertz technology. Infrared Physics & Technology, 40(3), 199–206.
Abstract: This paper presents an overview of recent results for NbN phonon-cooled hot electron bolometric (HEB) mixers. The noise temperature of the receivers based on both quasioptical and waveguide versions of HEB mixers has crossed the level of 1 K GHz−1 at 430 GHz (410 K), 600–650 GHz (480 K), 750 GHz (600 K), 810 GHz (780 K) and is close to that level at 1.1 THz (1250 K) and 2.5 THz (4500 K). The gain bandwidth measured for quasioptical HEB mixer at 620 GHz reached 4 GHz and the noise temperature bandwidth was almost 8 GHz. Local oscillator power requirements are about 1 μW for mixers made by photolithography and about 100 nW for mixers made by e-beam lithography. A waveguide version of 800 GHz receiver was installed at the Submillimeter Telescope Observatory on Mt. Graham, AZ, to conduct astronomical observations of known submillimeter lines (CO, J=7→6, CI, J=2→1). It was proved that the receiver works as a practical instrument.
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Gao, J. R., Hiajenius, M., Yang, Z. Q., Klapwijk, T. M., Miao, W., Shi, S. C., et al. (2006). Direct comparison of the sensitivity of a spiral and a twin-slot antenna coupled HEB mixer at 1.6 THz. In Proc. 17th Int. Symp. Space Terahertz Technol. (pp. 59–62).
Abstract: To make a direct comparison of the sensitivity between a spiral and a twin slot antenna coupled HEB mixer, we designed both types of mixers and fabricated them in a single processing run and on the same wafer. Both mixers have similar dimensions of NbN bridges (1.5-2 pm x0.2 pm). At 1.6 THz we obtained a nearly identical receiver noise temperature from both mixers (only 5% difference), which is in a good agreement with the simulation based on semi analytical models for both antennas. In addition, by using a bandpass filter to reduce the direct detection effect and lowering the bath temperature to 2.4 K, we measured the lowest receiver noise temperature of 700 K at 1.63 THz using the twin-slot antenna mixer.
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