Low and midrange modulation frequency response for YBCO infrared detectors: interface effects on the amplitude and phase

Bolometers were designed and fabricated from YBa/sub 2/Cu/sub 3/O/sub 7-x/ films on MgO, SrTiO/sub 3/, and LaAlO/sub 3/ substrates. Both the magnitude and phase of the IR-response of the detectors were investigated from 0.5 Hz to 100 kHz modulation frequencies, and from 0.8 to 20 micron wavelengths. Effects of the film-substrate thermal boundary resistance, R/sub bd/, and the substrate-cold head thermal boundary resistance, R/sub s-c/, were investigated. The effect of R/sub bd/ is shown to be significant in the response only at high frequencies, above 100 kHz. The response at low frequencies is found to be determined by R/sub s-c/ up to "knee" frequencies of 15, 60, and 600 Hz, for 0.05-cm thick SrTiO/sub 3/, LaAlO/sub 3/, and MgO substrates, respectively. A model for the bolometric response is developed, that correctly predicts the "knee" frequencies and the measured phase and amplitude of the response versus frequency up to about 10 kHz, including the predicted change from a f/sup -1/ to a f/sup -1/2/ dependence at the "knee" frequency. At the low bias currents used to operate the bolometers, Joule heating effects are negligible. From the model and experimental data, a specific heat of 0.59 J/K/spl middot/cm/sup 3/ has been deduced for LaAlO/sub 3/ at T/spl ap/90 K.<>