czt room-temp semiconductor detector - cells · czt room-temp semiconductor detector ... £3million...

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28.9.07 Barcelona Hexitec Paul Seller, RAL

CZT room-temp semiconductor detectorCZT has been proposed as good stopping power material and gives radiation-hard detectors in proton environments (HEP and space)There is good reason believe it is good in low energy X-ray systems

– do not have oxide interfaces– heavier atom than Si so low bulk damage

Transmission of

1E-15 at 12keV

0

0.2

0.4

0.6

0.8

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1.2

0 20 40 60 80 100 120 140 160

Energy (keV)

Ab

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SiGaAsCTCZT

Usual reason to choose High-Z Another possible reason

- stop most of the X-rays so shield ASICs and bonding interface


High Energy X-ray Imaging Technology

Focussed on large area pixellated CZT detectors

£3Million EPSRC funded project

4 year program involving 5 institutes

– also involves networks of application institutes and organisations

Started 2006

The HEXITEC Project

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HEXITEC Project objectives

fabricate large area CZT detector material for X-ray imaging

characterise to improvement material performance

develop cutting/polishing/contact-deposition and passivation techniques

develop bump-bonding techniques for CZT

develop pixellated spectroscopy ASIC for CZT

insert this technology into a diverse network of scientific users

create a sustainable base for continued CZT detector production


Dr Andrew Brinkman, Durham University– growth of 3 inch CZT by fast PVD (commercialised for CdTe PVD)

Dr Paul Sellin, Surrey University– CZT characterisation (PL mapping, PICTS, IBIC, Alpha TOF, NCR mapping)– development of contacts and passivation

Paul Seller, CCLRC– detector fabrication from raw material– detector characterisation (Spectroscopy, noise/temperature, small-pixel effect)– large area ASIC development

Prof Bob Cernik, The University of Manchester Principle Investigator– lead of Application Networks

• Imaging + tomography for engineering• Space Science• Synchrotrons• Security• Medical and biological

Prof Paul Barnes, Birkbeck College London Materials Imaging Network • TEDDI

HEXITEC Investigators (In order of functions)

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Fabrication of pixellated detectors from CZT material

(HEXITEC infrastructure at RAL)

Gold-Stud bond Bump bond

Shear/pull test

FC 150 for Gold-Stud /Indium bonding

Die Attach + wire bond to modules

Epoxy dispense

Lap and hydroplane polish

Sputter contacts


HEXITEC ASIC OVERVIEW

•Bump bonded readout chip for CZT

•80*80 pixels each 250um* 250um

•1keV to 150keV dynamic range (x10 option)

•200eV FWHM noise

•Sequential Rolling shutter readout (not data driven)

•Intended for 2mm thick CZT material

•1000 frames a second (variable) readout rate

Clocks and control signals

3 analogue outputs @ 6.4Meg samples/sec

Output multiplexer

20mm

1mm

20mm

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HEXITEC ASIC: Simulations and measurements

•With 250um pixels and 2mm thick detectors the small-pixel effect is quite strong

•See <<1us rise-time signals due to the electrons moving when close to the anode contact. Do not see the several microsecond electron and hole transit times through bulk

•Can chose a faster shaping time without significant ballistic deficit

Weighting Field in CdZnTe

electrons

holes


OutPre-amp

Shaper

Pixel electronics

Peak -Hold

Value sent to Output Multiplexer

Start of frame n End of frame n

Start of frame n+1

Peak-Hold

Events

Data timing from a single pixel

time

In Pixel control circuitry

Output buffer

Output Multiplexer

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7

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5

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2

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8 7 6 5 4 3 2 1

Columns

Rows

Rolling shutter output scheme

ASIC (8*8 of 80*80 pixels shown)

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Software

Data write

GUI

Data read and display

Zoom

Energy range

Signal correction/processing•Pedestal and gain adjust

•Nearest neighbour correction

•Summing

•Rejection

•Bipolar induced signals

•End of frame correction

Data from Hardware

Hardware Control

D

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A

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I

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DISK

Energy range

Pixel area

Hardware control

Data write and read

Signal correctionSpectra

Image

Detector + ASIC Simulation

czt room-temp semiconductor detector - cells · czt room-temp semiconductor detector ... £3million...

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