MODELIZATION AND EXPERIMENTS ON HIGH-TC SUPERCONDUCTING BOLOMETERS INTHE 10-90-K RANGE OF TEMPERATURE

As previously reported, the critical current I(c) dependence versus op tical power P in the mW range at 780 nm, with P focused on microbridge s of YBCO thin films, can be calculated using simple assumptions on he at production in the superconducting film and heat conduction to the s ubstrate. For the model was only valid on a limited range of temperatu re T where the thermal boundary resistance R(bd) lying at the film-sub strate interface- could be taken as a constant R0 = 10(-3) K cm2/W, we present a full model obtained by integration of the coupled Fourier e quations of the temperature in the superconducting anisotropic YBCO fi lm and in its substrate. We show that the thermal boundary resistance modelized as R(bd)(T) = B/T3+ R0, with B/T3 given by the acoustic mism ath model, is still limiting the heat transfer from the film to the su bstrate at least down to 10 K. As a consequence, the simple model that uses only R(bd)(T) and dl(c)/dT is still useful and allows realistic evaluations of the current sensitivity S(l) (P, T) to the applied powe r P on the temperature range 10-90 K. Calculated S(l)(p, T) in the 0.1 -1 A/W range agree well with those measured on YBCO/MgO or YBCO/SrTiO3 devices.