Nonlinearity and electrothermal feedback of high T-c transition edge bolometers

The effects of electrothermal feedback on the performance of a micromachine d superconducting high T-c transition edge bolometer, over a temperature ra nge 85-95 K, have been investigated. The system behaves nonlinearly, due to the variation of the resistance-temperature coefficient beta with temperat ure. Optimum operating points of constant current mode (CCM) and constant v oltage mode (CVM) modes vary with temperature and biasing conditions. In CC M, effective response time tau(eff) varies little with temperature. The opt imum output signal of CVM occurs at approximately 3-5 K lower temperature w ithin the tail region, where beta is maximum. The biasing voltage also disp lays a maximum, above which the bolometric performance degrades. The CCM ex hibits a comparatively limited linear dynamic range. Negative thermal feedb ack causes a decrease of tau(eff) of up to 2 orders of magnitude in CVM. CC M requires precise thermal stabilization at midtransition. Noise in both mo des is limited by the 1/f contribution. Maximum D* values are slightly high er for CVM at higher frequencies. Bolometer operation in the CVM mode requi res cooling the heatsink below 77 K, but does not need accurate temperature control. (C) 2000 American Institute of Physics. [S0003-6951(00)03705-0].