Design and fabrication of the SCUBA-2 detector for the JCM telescope

This paper reports on the design and fabrication of the prototype IR detector technology for the 5,120 pixel SCUBA-2 array (Submillimetre Common User Bolometer Array), which is to be mounted on the James Clerk Maxwell Telescope (JCMT) in Hawaii. The existing detector (SCUBA-1) consists of a 128 element feedhorn array but this technology is impractical for large arrays, as each feedhorn needs to be individually grown on a mandrel and then assembled. The design being developed for the replacement detector is based upon silicon micromachining, with Transition Edge Sensors (TES) being used to detect incoming radiation with wavelengths of 450 and 850m. Each TES (60nm Cu, 200nm Mo is located on a silicon brick suspended on a 500nm silicon nitride membrane and is supported by a silicon micromachined waffle. The purpose of the membrane with its essentially 2D phonon transport behavior is to thermally isolate each pixel. As with all array based technologies communication with each element is obviously essential and in this system it is achieved with low temperature indium bump bonding which connects each TES to a SQUID multiplexer chip. The SQUID chip contains Josephson junctions which very much depend upon nanoscale layer thicknesses. The SCUBA-2 detector operates at 100mK and consequently involves integration with low temperature electronics and the associated interconnect. The integration of nanoscale membranes and transition edge sensors together with microsystem technology enables the system to have 10^-17W (1 Hz bandwidth) sensitivity to incoming radiation.