IF Bandwidth and Optimum LO Power in Al Diffusion Cooled HEB Mixers
Abstract
We present first measurements on aluminum based superconducting diffusion-cooled hot-electron bolometer (HEB) mixers. HEBs are proposed for use as ultra-low noise heterodyne receivers for THz applications. The mixer consists of a thin (d ~130Åρ ~30-80 μΩ-cm) aluminum microbridge (L ~0.1-1.0μm, W ~0.1μm) biased to the resistive state, T_c ~1.6K. Local oscillator power (f_LO=26.5-40 GHz) and a weaker RF input signal are applied to the HEB. The electron temperature is modulated at the intermediate frequency (IF=f_LO-f_RF ~ 0.1-7.5GHz). If the device length is less than the electron-phonon interaction length L_e-ph≡√Dτ_e-ph, then cooling by diffusion of the hot-electrons into the contact pads is dominant. The contacts are a trilayer of thick aluminum/titanium/gold, with a transition temperature T_c,pads ~0.6K. Measurements of the IF bandwidth are performed at bath temperatures of 0.25-1.6K. We observe that the local oscillator power required for optimum mixer gain is less than ~ 1nW. We have measured a bandwidth of ~6GHz for a 0.3μm long Al HEB at 255mK. Results are given here for bandwidth and conversion efficiency as a function of device length and bath temperature, and are discussed within the framework of the diffusion-cooled bolometer model.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2000
- Bibcode:
- 2000APS..MAR.P9012S