Low-noise and wideband hot-electron superconductive mixers for THz frequencies

Superconductive hot-electron bolometer (HEB) mixers have been built and tested in the frequency range 1.1-2.5 THz. The mixer device is a 0.15-03 μm microbridge made from a 10 nm thick Nb film. This device employs diffusion as a cooling mechanism for hot electrons. The double sideband noise temperature was measured to be ⩽3000 K at 2.5 THz and the mixer IF bandwidth is ≈9-10 GHz for a 0.1 μm long device. The local oscillator (LO) power dissipated in the HEB microbridge was 20-100 nW. Further improvement of the mixer characteristics can be potentially achieved by using Al microbridges. The advantages and parameters of such devices are evaluated The HEB mixer Is a primary candidate for ground based, airborne and spaceborne heterodyne instruments at THz frequencies. HEB receivers are planned for use on the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA) and the ESA Far Infrared and Submillimeter Space Telescope (FIRST). The prospects of a submicron-size YBa₂Cu₃O_7-δ (YBCO) HEB are also discussed. The expected LO power of 1-10 μW and SSB noise temperature of ≈2000 K may make this mixer attractive for various remote sensing applications