Development of Superconducting Multilayer Wiring for Large Arrays of TES X-Ray Microcalorimeters

Abstract

We are developing TES (Transition Edge Sensor) X-ray Microcalorimeters for future X-ray astronomy missions such as DIOS (Diffuse Intergalactic Oxygen Surveyor). Standard wiring for a large-format array requires narrow and closely-packed configuration. This can cause deleterious crosstalk especially in the Frequency Domain Multiplexing readout. Hence we have employed multilayer wiring technique. In this paper, we tested a deposition of a TES film on the multilayer wiring by sputtering. Our first trial showed that the TES pixels have large residual resistances >50 mΩ and small critical currents of <1 µA. To improve the coverage of the TES film on the wiring, we increased the thickness of TES film (Ti/Au thickness of 100/200 nm). Also to remove an oxidation layer on the Al wiring, we strengthened a reverse-sputtering (150 W, 3 min) before the sputtering of TES. After these treatments, the TES film showed a sharp transition with small residual resistance (∼1 mΩ) and large critical current (>30 µA).