PROGRESS TOWARD A LOW-NOISE TEMPERATURE REGULATION USING A SUPERCONDUCTIVE HIGH-T-C MICROBRIDGE

Our results measuring I-V characteristics of YBCO/MgO microbridges sho w that large current sensitivities (10 mA/K) as a function of temperat ure can be obtained, roughly independently of the applied voltage V up to a few hundred mV. This offers the possibility of working with high values of the dynamic resistance so that the phonon noise associated to the thermal boundary resistance, located at the YBCO/MgO interface, becomes dominant. A noise equivalent temperature of 10(-8)K/root Hz ( T=85 K, f>1 kHz) has already been obtained in a 0.2x12x60 mu m(3) micr obridge. We describe a process involving the periodical sampling of th e I-V characteristics that eliminates 1/f amplifier noise and returns the current value (temperature dependent) at fixed voltage bias (+/-1 mV). This output, locked to a reference voltage through a commercial t emperature regulator, leads to temperature fluctuations less than 100 mu K-pp in a 10 Hz bandwidth. These results are promising to enhance p erformances of high-T-c microbolometers as infrared detectors.