Thermal stability of Mo/Au bilayers for TES applications

Abstract

Mo/Au bilayers are among the most suitable materials to be used as transition-edge sensors (TES) in cryogenic microcalorimeters and bolometers, developed, among other fields, for space missions. For this purpose the thermal stability of TES at temperatures below 150°C is a critical issue. We report on the dependence of functional properties (superconducting critical temperature, residual resistance and α) as well as on microstructure, chemical composition and interface quality for optimized high quality Mo/Au bilayers on annealing temperature and time. Data show that the functional properties of the bilayers remain stable at T<150°C, but changes in microstructure, interface quality and functional properties were observed for layers heated at T > 200°C. Microstructural and chemical composition data suggest that the measured changes in residual resistance ratio (RRR) and T C at T > 200°C are mainly due to an increase in the average Au grain size and to Au migration along the Mo grain boundaries at the Au/Mo interface. A way to stabilize the functional properties of the Mo/Au bilayers against temperature enhancements is proposed. © 2012 IOP Publishing Ltd.