LOW-FREQUENCY 1/F NOISE MEASUREMENTS IN YBA2CU3O7 THIN-FILMS AND THE IMPLICATIONS FOR HTS IR DETECTORS

The low frequency noise voltage fluctuations were measured on c-axis textured thin films of YBa2Cu3O7 on (100) SrTiO3 and on mixed a- and c- axis textured thin films of YBa2Cu3O7 on (100) LaAlO3. In all cases, the power spectral density S(v)(f) approximately V2/f-alpha, where V is the average dc voltage across the film. Measurements on structures of different surface areas indicates S(v)(f) is inversely proportional to the film surface area. From room temperature to above the superconducting transition temperature, S(v)(f)/V2 approximately T2, while near the transition S(v)(f)/V2 levels off before increasing sharply as the resistance goes to zero. The linear dependence of S(v)1/2(f) on the bias current suggests that the noise arises from resistance fluctuations. The resistance fluctuations are interpreted as arising from two different mechanisms; a "weakly" temperature dependent contribution which is dominant above the superconducting transition and a "strongly" temperature dependent contribution which dominates at the transition. The implications of these measurements on the potential utility of HTS IR detectors will be discussed.