TES microcalorimeter development for future Japanese X-ray astronomy missions

We are developing a Ti/Au TES microcalorimeter array for future Japanese X-ray astronomy missions. The goal is an energy resolution of 2–5 eV at 6 keV, and an array of 100–1000 pixels to achieve a geometrical area of >1 cm2 and a moderate spatial resolution simultaneously. The energy resolution was improved to ∼6 eV at 6 keV with a very fast time constant (<100 μs). To achieve a high coverage fraction, it is necessary to fabricate mushroom-shaped X-ray microabsorbers. We are developing an electrodeposition fabrication technique that is suitable for our process. Sn was used as absorber material, but the energy resolution was not good due to the existence of long-lived quasiparticles. Bi is also used, and the process is under optimization now. The readout strategy is to multiplex signals in the frequency domain, using a bridge circuit. So far, we succeeded in multiplexing two pixels modulated with 50 and 20 kHz at 440 mK. The energy resolution obtained at 110 mK was 33 eV (25 kHz).