We give an overview of the baseline detector system for SAFARI, the prime focal-plane instrument on board the proposed space infrared observatory, SPICA. SAFARI's detectors are based on superconducting Transition Edge Sensors (TES) to provide the extreme sensitivity (dark NEP≤2×10^-19W/√Hz) needed to take advantage of SPICA's cold (<8 K) telescope. In order to read out the total of ∼3500 detectors we use frequency domain multiplexing (FDM) with baseband feedback. In each multiplexing channel, a two-stage SQUID preamplifier reads out 160 detectors. We describe the detector system and discuss some of the considerations that informed its design.

SRON is developing ultra-low-noise transition edge sensors (TESs) based on a superconducting Ti/Au bilayer on a suspended SiN island with SiN legs for SAFARI aboard SPICA. We have two major concerns about realizing TESs with an ultra-low NEP of 2×10-19W/Hz: achieving lower thermal conductance and no excess noise with respect to the phonon noise. To realize TESs with phonon-noise-limited NEPs, we need to make thinner (c of ∼93mK and R_n of ∼158mΩ. These TESs were characterized under AC bias using our frequency-division multiplexing readout (1–3 MHz) system. TESs without the absorber show NEPs as low as 1.1×10-19W/Hz with a reasonable response speed (