Thermal stability of Mo/Au bilayers for TES applications

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 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.This work has been carried out with financial support from the Spanish MICINN (projects ESP2006-13608-C02, AYA2008-00591/ESP, MAT2008-01077/NAN and MAT2009-13977-C03). The authors acknowledge financial support from the European Union 6th Framework program (Integrated Infrastructure Initiative-026019 ESTEEM). MPB and OG would like to thank the Spanish Education Ministry and MICINN for an FPU grant and an FPI grant and for the Juan de la Cierva financial support.Peer Reviewe