Technology developments toward large format long wavelength bolometer arrays

Abstract

We are developing a kilopixel, filled bolometer array for infrared astronomy. The array consists of three individual components, to be merged into a single, working unit; 1) a transition edge sensor (TES) bolometer array, operating in the milliKelvin regime, 2) quarter-wave resonance backshorts, and 3) superconducting quantum interference device (SQUID) multiplexer readout. The detector array is a filled, square-grid of suspended, silicon membrane bolometers with superconducting thermistors. The spacing of the backshort beneath the detector grid can be set from ~30-300 microns by adjusting two process parameters during fabrication. We have produced prototype, monolithic arrays having 1 mm and 2 mm pitch detectors. The key technologies required for kilopixel arrays of detectors to be hybridized to SQUID multiplexer readout circuits have been demonstrated. Mechanical models of large-format detector grids have been indium bump-bonded to dummy multiplexer readouts to study electrical continuity. A monolithic array of 1 mm pitch detectors has been mated to a backshort grid optimized for a 350 micron resonant wavelength. Through-wafer microvias, for electroplated, low-resistance electrical connection of detector elements, have been prototyped using deep reactive ion etching. The ultimate goal of this work is to develop large-format (thousands of pixels) bolometer array architecture with background-limited sensitivity, suitable for a wide range of long wavelengths and a wide range of astronomical applications such as imaging, spectroscopy, and polarimetry and applicable for ground-based, suborbital, and space-based instruments.

Instrument performance of GISMO, a 2 millimeter TES bolometer camera used at the IRAM 30 m Telescope

“…In order to permit background-limited observations in the 2 mm atmospheric window at Pico Veleta, the required sensitivity expressed in Noise Equivalent Power (NEP) for the detectors is~4·10 -17 W/sqrt(Hz) [3]. The array architecture we use is based on the Backshort Under Grid (BUG) design [4], which consists of three components: 1) a TES-based bolometer array with background-limited sensitivity and high filling factor, 2) a quarter-wave reflective backshort grid providing high optical efficiency, and 3) a superconducting bump-bonded large format Superconducting Quantum Interference Device (SQUID) multiplexer readout. This design is scalable to kilopixel size arrays for future ground-based, suborbital and space-based X-ray and far-infrared through millimeter cameras.…”