Krause, S., Mityashkin, V., Antipov, S., Gol'tsman, G., Meledin, D., Desmaris, V., et al. (2016). Study of IF bandwidth of NbN hot electron bolometers on GaN buffer layer using a direct measurement method. In Proc. 27th Int. Symp. Space Terahertz Technol. (pp. 30–32).
Abstract: In this paper, we present a reliable measurement method to study the influence of the GaN buffer layer on phonon-escape time in comparison with commonly used Si substrates and, in consequence, on the IF bandwidth of HEBs. One of the key aspects is to operate the HEB mixer at elevated bath temperatures close to the critical temperature of the NbN ultra-thin film, where contributions from electron-phonon processes and self-heating effects are relatively small, therefore IF roll-off will be governed by the phonon-escape.Two independent experiments were performed at GARD and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. The entire IF chain was characterized by S-parameter measurements. We compared the measurement results of epitaxial NbN grown onto GaN buffer-layer with Tc of 12.5 K (4.5nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5K (5nm) and observed a strong indication of an enhancement of phonon escape to the substrate by a factor of two for the NbN/GaN material combination.
|
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.
|
Svechnikov, S., Gol'tsman, G., Voronov, B., Yagoubov, P., Cherednichenko, S., Gershenzon, E., et al. (1997). Spiral antenna NbN hot-electron bolometer mixer at submm frequencies. IEEE Trans. Appl. Supercond., 7(2), 3395–3398.
Abstract: We have studied the phonon-cooled hot-electron bolometer (HEB) as a quasioptical mixer based on a spiral antenna designed for the 0.3-1 THz frequency band and fabricated on sapphire and high resistivity silicon substrates. HEB devices were produced from superconducting 3.5-5 nm thick NbN films with a critical temperature 10-12 K and a critical current density of approximately 10/sup 7/ A/cm/sup 2/ at 4.2 K. For these devices we reached a DSB receiver noise temperature below 1500 K, a total conversion loss of L/sub t/=16 dB in the 500-700 GHz frequency range, an IF bandwidth of 3-4 GHz and an optimal LO absorbed power of /spl sime/4 /spl mu/W. We experimentally analyzed various contributions to the conversion loss and obtained an RF coupling factor of about 5 dB, internal mixer loss of 10 dB and IF mismatch of 1 dB.
|
Ekström, H., Kroug, M., Belitsky, V., Kollberg, E., Olsson, H., Goltsman, G., et al. (1996). Hot electron mixers for THz applications. In E. J. Rolfe, & G. Pilbratt (Eds.), Proc. 30th ESLAB (pp. 207–210).
Abstract: We have measured the noise performance of 35 A thin NbN HEB devices integrated with spiral antennas on antireflection coated silicon substrate lenses at 620 GHz. From the noise measurements we have determined a total conversion gain of the receiver of—16 dB, and an intrinsic conversion of about-10 dB. The IF bandwidth of the 35 A thick NbN devices is at least 3 GHz. The DSB receiver noise temperature is less than 1450 K. Without mismatch losses, which is possible to obtain with a shorter device, and with reduced loss from the beamsplitter, we expect to achieve a DSB receiver noise temperature of less ‘than 700 K.
|
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).
|
