Conversion gain and noise of YBa/sub 2/Cu/sub 3/O/sub 7/ weak-link mixers

Microwave mixing and parametric conversion in YBa/sub 2/Cu/sub 3/O/sub 7/ microbridges were investigated. The devices have been operated as down-converters, converting a 20-GHz radio frequency to a 1.5-GHz intermediate frequency under the action of an 18.5-GHz local oscillator. The microbridges were fabricated both as granular films on MgO substrates possessing grain boundary weak links and as epitaxial films deposited over substrate steps in LaAlO/sub 3/ substrates. The authors have measured conversion gains as high as -8+or-4 dB when mixing on the nonlinear resistive (superconducting-normal) transition and as high as -30 to -40 dB when parametrically converting via the nonlinear inductance of the bridge at bias currents less than the critical current. Output referred noise powers as low as -206 dB/Hz (3*10/sup -21/ W/Hz) have been measured. In some samples, noise switching events were observed.<>