Eric F. Schulte

Electrical and optical measurements on the first SCUBA-2 prototype 1280 pixel submillimeter superconducting bolometer array

SCUBA-2 is a submillimeter camera being built for the James Clerk Maxwell Telescope in Hawaii. Bringing CCD style imaging to the submillimeter for the first time, with over 10000 pixels, it will provide a revolutionary improvement in sensitivity and mapping speed. We present results of the first tests on a prototype 1280 pixel SCUBA-2 subarray; the full instrument will be made up of eight such subarrays. The array is made up of transition edge sensor (TES) detectors, with Mo/Cu bilayers as the sensing element. To keep the number of wires reasonable, a multiplexed readout is used. Unlike previous TES arrays, an in-focal plane multiplexer configuration is used, in which the multiplexing elements are located beneath each pixel. To achieve the required performance, the detectors are operated at a temperature of approximately 120 mK. We describe the results of a basic electrical and optical characterization of the array, demonstrating that it is fully operational. Noise measurements were made on several pixels and gave a noise equivalent power below 2.5 x 10(-17) W HZ(-0.5), within the requirements for SCUBA-2. The construction of the testbed used to carry out these measurements is also described.

Realization of a large-area microbolometer sensor array for submillimeter astronomy applications: SCUBA-2

The realization of a large (40x32) pixel sub-array on a 3-inch silicon wafer brings unique challenges involving the integration of a variety of microfabrication techniques. Design, development and fabrication procedures are described, with conventional MEMS techniques in silicon being used where possible. High resolution imaging in the sub-millimetre range requires a pixel size of the order of one millimetre with a high signal/noise ratio detector, which must be addressed at cryogenic temperatures via a very low noise amplifying system. This has been realized using a combination of Transition Edge Sensors (TES) with amplification and multiplexing (MUX) by Superconducting Quantum Interference Devices (SQUID), which imposes particular requirements in the method of construction. This paper describes the details of the technologies used to overcome the conflicting demands of the different elements. The need to operate at millikelvin temperatures limits the materials that can be selected. Particular attention has been paid to the stresses induced in the structure by overlying films, bump bonding and any thermal processing.

Prototype detector technology for the SCUBA-2 submillimetre bolometer array

This paper reports the latest design and the associated fabrication technology of the Mk II prototype infrared (IR) detector for the two 5120 pixel SCUBA-2 (submillimetre common user bolometer arry) instruments, which are to be mounted on the James Clerk Maxwell telescope (JCMT) in Hawaii. Progress is described on the design and the technology modules being developed for the new detector, which is based upon silicon micromachining. The two arrays of transition edge sensors (TES) are used to detect incoming radiation with wavelengths of 450 and 850 μ respectively and as the SCUBA-2 detector operates at about 100 mK, it consequently involves integration with low-temperature electronics and careful design of the associated interconnect. A key aspect of the connection between the TES detector and readout electronics is the use of indium flip-chip bumps, which become superconducting at cryogenic temperatures. The integration of nanoscale membranes and transition edge sensors together with microsystem technology enables SCUBA-2 to have of the order of 10 -17W (1 Hz bandwidth) sensitivity to incoming radiation.