Impedance analysis for Transition-Edge Sensor up to the MHz range

Impedance measurement of superconducting Transition-Edge sensors (TESs) is a powerful tool to extract information about the TES thermal and electrical properties. This technique has been already applied to X-ray and γ-ray TES up to tens of kHz and to UV-VIS TES up to hundreds of kHz. By comparing experimental data with the predicted values of a microcalorimeter model, some discrepancies at high frequency have been evidenced. For this reason impedance analysis up to MHz for TESs with effective response time constant τeff of hundreds of ns is needed. We apply this technique to a 10 μm × 10 μm Ti/Au TES made by INRIM and a 5 μm × 5 μm Ti TE S made by AIST. In this analysis, high frequency contributes of stray elements (present both in the TES bias circuit and in our set-up) and the high frequency response of SQUID amplifier in FLL mode, have been taken into account. These contributes have been evaluated and subtracted from the experimental data to fit as best as possible the predicted micorcalorimeter model. From these measurements and from noise analysis, important thermal and electrical device parameters have been deduced.