CCD-style imagingCCD-style imagingfor the JCMTfor the JCMT

SCUBA-2 technology

the ability to construct large format detector arrays

signal readouts that can be multiplexed

To fill an 88 arcmin field-of-view of the JCMT requires many thousands of pixels! Conventional bolometer technology is impractical!

We need:

Indium bump bondsQuarter-wave

Si Brick

Not to scale

Pixel geometry

Deep-etched trench (10 μm)

TES Nitride membrane(0.5 μm)

1.135 mm

SQUID MUX Wafer

Detector Wafer

Bump bond

TES on SiN membraneSi 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

Two components: A sensitive thermometer and high cross-section absorber

temperature

time

• Thermometer and absorberare connected by a weak thermallink to a heat sink

• Incoming photon is converted to heat in the absorber:

T = T T0 = 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

RN

Temperature

RC

Tc

Bias point

ISQUID

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 flexisHot bar reflowed

Magnetically sensitiveSSA module pcb

High density connectionsto woven cables to room temp

Subassembly and readout

Detector subassembly and readoutThe TES wafer bump bonded to the SQUID multiplexer Glue writer depositing

epoxy on individual tines

Detector wirebonded to ceramicbatwing PCB

Batwing PCB connectedto the SSA amplifier board viasuperconducting niobium flexiblecircuits using hot bar reflow technique

SQUID amplifiers

completed subassembly

Detector array on the epoxy bonding machineDuring attachment of the Be/Cu hairbrush

Woven ribbon cablestakes signals from 1K to 300K

MultichannelReadout Electronics

COST

SCUBA-2 is the first large-format CCD-style imager for submillimetre astronomy

Interesting Facts:

Instrument No. of pixels Map speed Cost per pixel

SCUBA 128 7000 $ 70,000 SCUBA-2 12800 1,000,000+ $ 875

UKT14 1 1 $700,000