This paper describes the design, fabrication and assembly of the SCUBA-2 (Submillimetre Common User Bolometer Array) which has involved contributions from the UK Astronomy Technology Centre, the Universities of Edinburgh and Cardiff, NIST (Boulder) and a consortium of Canadian Universities. It has recently replaced the SCUBA-1 detector, which during its lifetime was the most cited astronomical instrument after the Hubble telescope. SCUBA-2 provides a step change in performance and consists of two detector arrays, each with 5,120 pixels that use Transition Edge Sensor (TES) technology biased at a temperature of ~100mK. This provides a 100 fold increase in scan speed compared with the detectors they replace in SCUBA-1 as well as delivering a significantly improved sensitivity of 10-17 W/√Hz. Each pixel consists of a silicon brick approximately 1000 μm square, which is supported on a 0.5 μm thick silicon nitride membrane, with the brick thickness being ~100 and 62μm for the 450 and 850μm detectors respectively. The TES films are located on a silicon nitride membrane and these, and the pixel heaters, are electrically connect to the SQUID wafer using indium cold welded bump bonds. The balance of the 218,000 indium bumps are used to increase the thermal conductivity of the pathway to cool the bonded wafer stack both during processing and device operation. The completed detector chip is bonded to a copper beryllium hairbrush heat sink used to cool the detector and the four detector quadrants are assembled into a single array and then installed into the telescope’s cryo-system. The paper discusses the design issues and describes the novel fabrication associated with the wafer bonding and deep etching procedures that enable the thermally isolated bricks on the membrane to be fabricated. Finally, the assembly procedures are detailed which enables the new detectors to deliver stunning new images.
|Publication status||Published - 22 Mar 2011|
|Event||Smart Systems Integration - Dresden, Germany|
Duration: 22 Mar 2012 → 23 Mar 2012
|Conference||Smart Systems Integration|
|Period||22/03/12 → 23/03/12|