Silicon nitride micromesh bolometer array for submillimeter astrophysics

We present the design and performance of a feedhorn-coupled bolometer array intended for a sensitive 350-mum photometer camera. Silicon nitride microm esh absorbers minimize the suspended mass and heat capacity of the bolomete rs. The temperature transducers, neutron-transmutation-doped Ge thermistors , are attached to the absorber with In bump bonds. Vapor-deposited electric al leads address the thermistors and determine the thermal conductance of t he bolometers. The bolometer array demonstrates a dark noise-equivalent pow er of 2.9 x 10(-17) W/root Hz and a mean heat capacity of 1.3 pJ/K at 390 m K. We measure the optical efficiency of the bolometer and feedhorn to be 0. 45-0.65 by comparing the response to blackbody calibration sources. The bol ometer array demonstrates theoretical noise performance arising from the ph oton and the phonon and Johnson noise, with photon noise dominant under the design background conditions. We measure the ratio of total noise to photo n noise to be 1.21 under an absorbed optical power of 2.4 pW. Excess noise is negligible for audio frequencies as low as 30 mHz. We summarize the trad e-offs between bare and feedhorn-coupled detectors and discuss the estimate d performance limits of micromesh bolometers. The bolometer array demonstra tes the sensitivity required for photon noise-limited performance from a sp aceborne, passively cooled telescope. (C) 2001 Optical Society of America.