Progress on background-limited membrane-isolated TES bolometers for far-IR/submillimeter spectroscopy

Abstract

To determine the lowest attainable phonon noise equivalent power (NEP) for membrane-isolation bolometers, we fabricated and measured the thermal conductance of suspended Si 3 N 4 beams with different geometries via a noise thermometry technique. We measured beam cross-sectional areas ranging from 0.35 × 0.5 µm 2 to 135 × 1.0 µm 2 and beam lengths ranging from 700 µm to 8300 µm. The measurements directly imply that membrane-isolation bolometers are capable of reaching a phonon noise equivalent power (NEP) of 4 × 10 −20 W/Hz 1/2 . This NEP is adequate for the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) proposed for the Japanese SPICA observatory, and adequate for NASA's SAFIR observatory, a 10-meter, 4 K telescope to be deployed at L2. Further, we measured the heat capacity of a suspended Si 3 N 4 membrane and show how this result implies that one can make membrane-isolation bolometers with a response time which is fast enough for BLISS.

THz radiation sensors

“…At present, TES bolom− eters can be applied for THz photons counting because of high sensitivity (NEP~3×10 -19 W/Hz 1/2 at T = 300 mK) and low thermal time constant (t = 25 μs at T = 190 mK) [49,153]. Membrane isolated TES bolometers are capable of reaching a phonon NEP~4×10 -20 W/Hz 1/2 [47]. The cur− rent generation of sub−orbital experiments, largely rely on TES bolometers [62,154].…”

“…Among the direct detectors, low−temperature bolometers currently offer the highest sen− sitivity from the far−infrared to millimetre−wave region of the electromagnetic spectrum providing background limited performance with NEP~(0.4-3)×10 -19 W/Hz 1/2 at operation temperature~100-300 mK [5,47,49]. Direct detection bo− lometers have been used for decades in measurements of CMB spectrum and anisotropy, including space−flight COBE−FIRAS instrument [61].…”

Development of the nano-HEB array for low-background far-IR applications

“…The electron-phonon thermal conductance, G e-ph , has stronger temperature dependence than that of phonon transport in narrow Si 3 N 4 beams commonly used in geometrically isolated bolometers [2]. In fact, G e-ph is about two orders of magnitude smaller at 40-50 mK than the lowest thermal conductance found in suspended bolometers [3]. The very low G e-ph ≈ 0.1 fW/K at 40 mK found in [1] suggests the very low Thermal Energy Fluctuation (TEF) (aka phonon) noise NEP TEF ≈ 3×10 -21 W/Hz 1/2 which matches to the photon shot noise expected for the cosmic background in the most sensitive instruments for moderate resolution submillimeter spectroscopy in space [4][5][6].…”

“…In our recent work [2], we studied the electrical noise of small nano-HEBs (volume 10 -20 -10 -19 m 3 ) and found it being mostly dominated by the TEF noise. Electrical NEP TEF derived from those measurements was as low as ~ 10 -18 W/Hz 1/2 for smallest devices at 350 mK.…”

Antenna-coupled TES bolometers for the SPIDER experiment

“…State-of-the-art photolithography can now reliably produce silicon nitride legs with extremely high aspect ratio. 18 The NEP required by a space-borne CMB mission is now routinely achieved in the laboratory with appropriate time constant.…”