Nb–Au bilayer hot-electron bolometers for low-noise THz heterodyne detection

Siddiqi, I.; Prober, D.E.
February 2004
Applied Physics Letters;2/23/2004, Vol. 84 Issue 8, p1404
Academic Journal
The sensitivity of present Nb diffusion-cooled hot-electron bolometer (HEB) mixers is not quantum limited, and can be improved by reducing the superconducting transition temperature T[sub C]. Lowering T[sub C] reduces thermal fluctuations, resulting in a decrease of the mixer noise temperature T[sub M]. However, lower T[sub C] mixers have reduced dynamic range and saturate more easily due to background noise. We present 30 GHz microwave measurements on a bilayer HEB system, Nb–Au, in which T[sub C] can be tuned with Au layer thickness to obtain the maximum sensitivity for a given noise background. These measurements are intended as a guide for the optimization of THz mixers. Using a Nb–Au mixer with T[sub C]=1.6 K, we obtain T[sub M]=50 K with 2 nW of local oscillator (LO) power. Good mixer performance is observed over a wide range of LO power and bias voltage and such a device should not exhibit saturation in a THz receiver. © 2004 American Institute of Physics.


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