LOW-NOISE HIGH-T-C SUPERCONDUCTING BOLOMETERS ON SILICON-NITRIDE MEMBRANES FOR FAR-INFRARED DETECTION

High-T-c GdBa2Cu3O7-delta superconductor bolometers with operation tem peratures near 89 K, large receiving areas of 0.95 mm(2) and very high detectivity have been made. The bolometers are supported by 0.62 mu m thick silicon nitride membranes. A specially developed silicon-on-nit ride layer was used to enable the epitaxial growth of the high-T-c sup erconductor. Using a old black absorption layer an absorption efficien cy for wavelengths between 70 and 200 mu m of about 83% has been estab lished. The noise of the best devices is fully dominated by the intrin sic phonon noise of the thermal conductance G, and not by the 1/f nois e of the superconducting film. The temperature dependence of the noise and the resulting optimum bias temperature have been investigated. In the analysis the often neglected effect of electrothermal feedback ha s been taken into account. The minimum electrical noise equivalent pow er (NEP) of a bolometer with a time constant tau of 95 ms is 2.9 pW/Hz (1/2) which corresponds with an electrical detectivity D of 3.4 X 10( 10) cm Hz(1/2)/W. Similar bolometers with tau=27 ms and NEP=3.8 pW/Hz( 1/2) were also made. No degradation of the bolometers could be observe d after vibration tests, thermal cycling and half a year storage, Meas urements of the noise of a Pr doped YBa2Cu3O7-delta film with T-c=40 K show that with such films the performance of air bridge type high-T-c bolometers could be improved. (C) 1997 American Institute of Physics.