Ultra-sensitive Transition-Edge Sensors for the Background Limited Infrared/Sub-mm Spectrograph (BLISS)

We report progress in fabricating ultra-sensitive superconducting transition-edge sensors (TESs) for BLISS. BLISS is a suite of grating spectrometers covering 35–433?μm with R～700 cooled to 50?mK that is proposed to fly on the Japanese space telescope SPICA. The detector arrays for BLISS are TES bolometers readout with a time domain SQUID multiplexer. The required noise equivalent power (NEP) for BLISS is NEP=10^?19?W/Hz^1/2 with an ultimate goal of NEP=5×10^?20?W/Hz^1/2 to achieve background limited noise performance. The required and goal response times are τ=150?ms and τ=50?ms respectively to achieve the NEP at the required and goal optical chop frequency 1–5?Hz. We measured prototype BLISS arrays and have achieved NEP=6×10^?18?W/Hz^1/2 and τ=1.4?ms with a Ti TES (T _C=565?mK) and NEP～2.5×10^?19?W/Hz^1/2 and τ～4.5?ms with an Ir TES (T _C=130?mK). Dark power for these tests is estimated at 1–5?fW.