Design and Performance of Hybrid Arrays of Mo/Au Bilayer Transition-Edge Sensors

Abstract

For future X-ray astrophysics missions, X-ray microcalorimeters can be optimized with different properties in different regions of the focal plane. This approach has the potential to improve microcalorimeter instrument capabilities with efficient use of instrument resources. For example a point-source array optimized for high angular resolution, high count-rate observations could be accompanied by a main array to expand the field of view for diffuse observations. In this approach, it is desirable to be able to simultaneously optimize different transition-edge sensor (TES) geometries on a single wafer design. The key properties of TESs such as transition temperature and shape are a strong function of size and geometry due to the complex interplay between the proximity effect from the superconducting bias electrodes and the normal metal features used for noise suppression and absorber contact. As a result, devices fabricated with the same deposited layer but with different sizes will have different transition temperatures and different response to X-ray events. In this paper, we present measurements of the transition temperature and properties of devices with different sizes and normal metal features, and discuss how by tuning the geometry we can achieve the desired pixel parameters for a given application. We also describe measurements of transition properties from large-format hybrid arrays containing three different pixel types.