dc responsivity of proximity effect bridges to high frequency radiation

2014 The effect of microwave radiation on the dc current-voltage characteristic of proximity effect bridges has been studied at frequencies of 10, 35 and 90 GHz. We report the properties of bridges fabricated in layered films of Nb and Ta. The fraction 03B5 of the incident radiant power absorbed by the bridge is measured calorimetrically, permitting determination of the intrinsic responsivity (volts per watt of power absorbed when operated in a current-biased mode). In our test geometry 03B5 is typically ~ 10-4 for a 0.1 03A9 Nb-Ta bridge, and increases roughly linearly with dc junction resistance R. Broad-band responsivitv is generally independent of incident power. increases with increasing critical current Ic (decreasing temperature), and decreases with increasing frequency, varying approximately as 03A9-3 where 03A9 is the normalized frequency 012703C9/2 eRIc. Peak responsivities achieved to date are ~ 105 V/W (absorbed) at 10 GHz and ~ 102 V/W (absorbed) at 90 GHz. By mounting junctions in vacuum and exposing them to near-infrared radiation, we have found that their purely bolometric (thermal) response is much weaker than the microwave response at 90 GHz. REVUE DE PHYSIQUE APPLIQUÉE TOME 9, JANVIER 1974, PAGE