SURFACE-MORPHOLOGY EFFECT ON THE PHOTORESPONSE OF HIGH-TEMPERATURE SUPERCONDUCTING MICROBRIDGES

Three Y1Ba2Cu3O7-delta superconducting thin films with 20%, 60%, and 1 00% coverage of precipitates were fabricated into microbridges of 25 x 650 mu m(2) by a conventional photolithography method. These microbri dges exhibit a T-co(R=0) from 83.6 to 87.2 K and a transition width of about 1.8 K. These also have (dR/dt)(max) values of about 71-78 Omega /K. We find that the fewer the precipitates on the film, the better th e thermal conduction, and a larger responsivity (S) can be achieved. T he best responsivity of 783 V/W measured at I-b = 8 mA, T-op = 86.8 K, and f = 2 Hz for various wavelengths of light sources is obtained fro m the film with 20% precipitation. The photoresponse signals decay exp onentially with the precipitation coverages, which indicates that thes e precipitates behave as thermal resistance layers that smooth out the ac incident signal, suppress the rise in microbridge temperature, and result in a smaller photoresponse signal for the bolometer. (C) 1996 American Institute of Physics.