Background-limited membrane-isolated TES bolometers for far-IR/submillimeter direct-detection spectroscopy

We fabricated and measured the thermal conductance of suspended Si 3 N 4 beams via noise thermometry to determine whether membrane-isolation bolometers are capable of reaching a phonon noise equivalent power (NEP) of 4 × 10 - 20 W / Hz 1 / 2 . This sensitivity is necessary for the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) proposed for the Japanese SPICA observatory, and adequate for NASAʹs SAFIR observatory, a 10-m, 4 K telescope to be deployed at L2. The dimensions of the longest thermal isolation beams we measured are 3 × 0.5 × 8300 μ m 3 . We also fabricated and measured the electrical properties of superconducting molybdenum/gold transition-edge sensor (TES) bolometers with isolation beams of an identical geometry. The thermal conductance (G) values obtained from the noise thermometry and the TES bolometer data when the transition temperature ( T c ) of the thermistor is 60 mK correspond to an NEP of 5 × 10 - 20 W / Hz 1 / 2 , making membrane-isolated TES bolometers a strong candidate for use on BLISS-SPICA and SAFIR.