Thermal effects on near-critically biased superconducting thin film particle detectors

Measurements of dc critical current as a function of temperature, and spontaneous voltage transients, are reported for superconducting thin films of Nb, Mo, and Ti near their critical temperatures and currents. The form of the temperature dependence is found to reflect the presence of stable and/or metastable normal regions in the films, as well as the different temperature scaling laws for the intrinsic and thermal-runaway critical currents. Voltage transients (pulses) occur in the nominally superconducting samples when the current is below both the intrinsic and thermal-runaway values. Thermal coupling between film and substrate is reported for a wide variety of samples fabricated by different methods. The coupling in all cases follows a thermal boundary resistance law with power flux proportional to the difference of fourth powers of film and substrate temperatures. Applications to minimum-ionizing particle detection above liquid helium temperatures are discussed. (C) 1996 American Institute of Physics.