CCD-style imaging for the JCMT

SCUBA-2 technology  the ability to construct large format detector arrays  signal readouts that can be multiplexed To fill an 8  8 arcmin field-of-view of the JCMT requires many thousands of pixels!  Conventional bolometer technology is impractical! We need:

Indium bump bonds Quarter-wave Si Brick Not to scale Pixel geometry Deep-etched trench (10 μm) TESNitride membrane (0.5 μm) mm SQUID MUX Wafer Detector Wafer Bump bond TES on SiN membrane Si brick /4 thick SQUID mux backplane 1.135mm Time division multiplexing based on SQUID amplifier Mux is formed by columns of SQUIDS connected in series Address line turns on each row of SQUIDS Detector cooled to 100mK

Bolometers: Basic principles l Two components: A sensitive thermometer and high cross-section absorber temperature time Thermometer and absorber are connected by a weak thermal link to a heat sink Incoming photon is converted to heat in the absorber:  T = T  T 0 = E/C Temperature rise decays as power in absorber flows out to the heat sink Bolometer temperature is proportional to the incoming power

Transition edge sensors Voltage-biased on normal- superconducting transition Resistance is a very steep dependence on temperature in transition region Film held at constant voltage bias - change in resistance results in a change in current through the film Low noise, low power (~ 1nW) SQUID ammeter readout Resistance RNRN Temperature RCRC TcTc Bias point I SQUID Amplifier V bias R(T) TES Disadvantage: There is a fixed amount of power a device can handle

SCUBA-2 focal planes Key features include: Superconducting transition edge sensors SQUID multiplexer readouts 4 × 1280 pixel sub-arrays in each focal plane 100mK operation using liquid cryogen- free dilution refrigerator

Cold electronics module Ceramic ‘batwing’ pcb Niobium flexis Hot bar reflowed Magnetically sensitive SSA module pcb High density connections to woven cables to room temp

Subassembly and readout Detector subassembly and readout The TES wafer bump bonded to the SQUID multiplexer Glue writer depositing epoxy on individual tines Detector wire bonded to ceramic batwing PCB Batwing PCB connected to the SSA amplifier board via superconducting niobium flexible circuits using hot bar reflow technique SQUID amplifiers completed subassembly Detector array on the epoxy bonding machine During attachment of the Be/Cu hairbrush Woven ribbon cables takes signals from 1K to 300K Multichannel Readout Electronics

COST SCUBA-2 is the first large-format CCD-style imager for submillimetre astronomy Interesting Facts: InstrumentNo. of pixelsMap speedCost per pixel SCUBA $ 70,000 SCUBA ,000,000+$ 875 UKT14 1 1$700,000