Regensburg 2000 – scientific programme
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TT: Tiefe Temperaturen
TT 25: HF-Anwendungen
TT 25.5: Talk
Friday, March 31, 2000, 12:00–12:15, H19
Phonon Relaxation and Noise in HTS Hot-Electron Bolometer Mixers — •Oliver Harnack1,2, Kostya Il’in1, Boris S. Karasik2, and William R. McGrath2 — 1Institut für Schicht- und Ionentechnik, Forschungszentrum Jülich, 52425 Jülich — 2Center for Space Microelectronics Technology, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
The hot-electron bolometer (HEB) mixer made from a high-TC superconductor (HTS) thin film was introduced recently as an alternative to a Schottky mixer at THz frequencies. The mixer performance depends on the total thermal conductance for heat removal from the phonon sub-system due to either phonon diffusion to the normal metal electrodes or phonon escape to the substrate.
We present a systematic study of the length, thickness, and temperature dependencies of the thermal relaxation times, as inferred from the -3dB intermediate frequency (IF) bandwidth of HTS HEB mixers on MgO and CeO2/sapphire substrates. For 50 nm to 1µm long devices on MgO, the bandwidth was about 100 MHz at 65 K and increased to unexpected high values of about 2 GHz at temperatures close to TC. We also discovered a remarkable strong dependence of the IF bandwidth on the bias voltage. Noise measurements at 65 K and around 2.7 GHz gave DSB mixer noise temperatures of 4000 K and 4850 K at IF’s of 120 MHz and 1 GHz, respectively. The impact of vortex effects on the measured device performance and the importance of the device geometry for an efficient contribution of phonon diffusion to the total thermal conductance will be discussed.