Progress with gaas pixel detectors
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Progress with GaAs Pixel Detectors. K.M.Smith University of Glasgow Acknowledgements: RD8 & RD19 (CERN Detector R.&D. collaboration) XIMAGE (Aixtron, I.M.C., Metorex, Freiburg, Glasgow, K.T.H.) MEDIPIX (CERN, Freiburg, Glasgow, Pisa)

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Progress with GaAs Pixel Detectors

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Progress with gaas pixel detectors

Progress with GaAs Pixel Detectors

K.M.Smith

University of Glasgow

Acknowledgements:

RD8 & RD19 (CERN Detector R.&D. collaboration)

XIMAGE (Aixtron, I.M.C., Metorex, Freiburg, Glasgow, K.T.H.) MEDIPIX (CERN, Freiburg, Glasgow, Pisa)

IMPACT (B.N.F.L., E.E.V., Oxford Instr., R.A.L., Glasgow, Imperial College, Leicester, UMIST)

NSS Toronto 11/11/’98

K.M.Smith


Imaging

Imaging

  • Requirements

  • Good 2-dimensional resolution(< 100 µm)

  • Linear dynamic range for low contrast (< 3%)

  • Lower dose to Patient/Sample in medical applications

  • Image processing capability (digital image)

    Readout ElectronicsDetector

    - Large dynamic range - 2-dimensional geometry (Pixel)

    - Single photon counting - High conversion efficiency for g

    - Low noise energies in the range 5 - 100 keV

    - Digital output - Good charge collection

K.M.Smith


Why single photon counting

Why Single Photon Counting?

  • Linear and extendable dynamic range

  • Energy threshold

    1) Compton suppression

    2) Large signal-to-noise ratio

    3) Insensitive to leakage current

  • Local threshold tuning ( for each pixel):

    - can also be used for gain equalisation

  • Asynchronous counting Minimum dead time

K.M.Smith


Photon counting devices monolithic pixel detectors

Photon Counting DevicesMonolithic Pixel Detectors

  • Material budget (H.E.P.)

  • fabrication

  • cost

  • material choices

  • efficiency

  • application specific

K.M.Smith


Photon counting devices hybrid pixel sensors

Photon counting devicesHybrid Pixel Sensors

  • separation of detector - r/o

  • material choice

  • efficiency

  • dynamic range

  • smart pixels

  • cost

  • spatial resolution

  • bump bonding

K.M.Smith


Hybrid pixel detectors

Hybrid Pixel Detectors

K.M.Smith


Detection modes

Detection Modes

Integration

spatial resolution

cheap

experience

dynamic range

detection efficiency

r/o speed

cost (if custom made)

charge integration

Photon Counting

individual particle counting

choice of active media

detection-r/o separated

efficiency

dynamic range

“smart” pixels

spatial resolution

bump bonding

cost

K.M.Smith


Pixel detectors

Pixel detectors

Ω3 ROIC (CERN)

  • Matrix of 128 rows and 16 columns

    • Row pitch (depth) = 50 mm

    • Column pitch (width) = 500 mm

    • total area = 8 x 6.35 mm2

  • ENC ~ 100 e- rms

  • Individual pixel addressing (mask + test)

  • Globally adjustable threshold

K.M.Smith


Progress with gaas pixel detectors

Ω3

500 m

28m

50m

K.M.Smith


Image washer al

Image - Washer (Al)

full matrix

single column 500m step

GaAs - 3

single column 50 m step

K.M.Smith


Image quality ii

Image Quality (II)

Flood image

K.M.Smith


Mtf comparison

MTF comparison

K.M.Smith


X ray diffraction

X-Ray Diffraction

2d sin = n 

Powder Method

2

X-ray beam

d

d sin

detector

Powder sample

detector

Bragg’s law

K.M.Smith


Silicon powder xrd

Silicon Powder (XRD)

K.M.Smith


Si xrd resolution

Si-XRD (Resolution)

K.M.Smith


Potassium niobate xrd

Potassium Niobate (XRD)

K.M.Smith


Potassium niobate xrd1

Potassium Niobate (XRD)

K.M.Smith


Potassium niobate

Potassium Niobate

K.M.Smith


Medipix

MEDIPIX

  • A true single photon counting readout chip

  • 64 x 64 pixel matrix

  • pixel dim. 170 x 170 m2

  • Sensitive area 1 cm2

  • Individually adjust threshold

  • 15-bit counter

  • Frame r/o 384 s at 10MHz

K.M.Smith


Image objects pb

Image - Objects (Pb)

GaAs detector

Thickness

600m

K.M.Smith


Read out electronics

Read-out Electronics

Photon Counting Chip (PCC):

based on ideas developed by the

RD19 collaboration (CERN)

  • SACMOS 1mm FASELEC Technology

  • Matrix of 64 x 64 Pixels

  • Pixel size 170 mm x 170 mm

  • 1.2 cm2 sensitive area

  • 1.7 cm2 total area

  • 1.6 M transistors

K.M.Smith


Pixel design

Pixel Design

  • Charge sensitive amplifier with leakage current compensation

  • Discriminator with globally settable threshold

  • 3-bit local threshold adjustment

  • Individual pixel test and mask modes

  • Counting controlled by shutter signal

  • 15-bit pseudo-random counter

  • 16-bit I/O Bus

  • Readout frequency: max. 10 MHz

  • Readout time: 384ms

K.M.Smith


Performance of readout

Performance of readout

K.M.Smith


Detector performance

Detector performance

Interesting energy range for medicine

10 - 100 keV

[NIST Physical Reference Data]

K.M.Smith


Detector design

Detector design

  • Material: GaAs, S.I., 200 mm thick

  • 64 x 64 pixel matrix

  • square pixels of 170 x 170 mm2

  • 1.2 cm2 sensitive area

K.M.Smith


Electrical performance of system

Electrical performance of system

System = detector flip-chip

bonded to readout chip

Bonded detector settings:

  • min. mean threshold: ~2000 e-

  • trimmed threshold rms: ~125 e-

  • noise: ~200 e-

    (Note: a photon of 20 keV produces about 4700 e- in GaAs)

K.M.Smith


Measurement of contrast ratio

Measurement of contrast ratio

Object

| n - n’|

n

Detector

n’

n

| n - n’|

n

Incident photons

Signal Contrast Ratio:

SCR =

Signal to Noise:

SNR=

Distinguishing low contrast objects means:

  • Earlier recognition of tumours

  • Reduction of dose to patient

K.M.Smith


Results of contrast ratio measurements

Results of Contrast Ratio Measurements

Comparison of Experimental and Measured Contrast Ratios:

Objects with Contrast Ratio of 1.9% can be Identified

K.M.Smith


Summary and conclusions

Summary and Conclusions

  • Successful bump-bonding of 64 x 64 pixel array to ROIC

  • Measured threshold of ~2000 e- with ~125 e- rms

  • Images of a variety of objects illuminated with 241Am- and 109Cd-sources

  • Correctly identified objects of low contrast (1.9 %)

  • The system enables the evaluation of the potential and limitations of the photon counting method

K.M.Smith


Progress with gaas pixel detectors

Image correction method

Gain map: detector X2:3

K.M.Smith


Progress with gaas pixel detectors

Image correction

before

after

K.M.Smith


Progress with gaas pixel detectors

Hybridized

GaAs

pixel detector

Sens-A-Ray

Si-CCD

K.M.Smith


Source measurements 241 am g photons of 60 kev

Source Measurements: 241Am (g-photons of 60 keV)

Steel locking nut; Steel screw

300 - 500 mm thick 6 mm long; 1mm slot

K.M.Smith


Pixelcell

Pixelcell

Layout Photo

170 mm

K.M.Smith


First measurement of an organic sample with 109 cd source

First Measurement of an Organic Sample with 109Cd source

g

Fish Tail irradiation

K.M.Smith


Measurements with sources 109 cd photons of 22 and 25 kev

Measurements with sources: 109Cd (photons of 22 and 25 keV)

Tungsten wire,  500 mm 300 mm thick copper mask, 300 mm

K.M.Smith


Contrast measurements

Contrast Measurements

K.M.Smith


Electrical performance

Electrical performance

K.M.Smith


Source measurements 241 am g photons of 60 kev1

Source Measurements: 241Am (g-photons of 60 keV)

Steel screw Steel locking nut;

6 mm long; 1mm slot 300 - 500 mm thick

K.M.Smith


Pixel cell

Pixel cell

K.M.Smith


Hybrid pixel detector

Hybrid Pixel Detector

K.M.Smith


Simulated response of erd1 si pixel detector

Simulated response of ERD1 Si pixel detector

K.M.Smith


Simulated response of si pixel detector to 137 cs

Simulated response of Si pixel detector to 137 Cs

K.M.Smith


Preliminary evaluation of medipix read out chip on glasgow lec gaas pixel detector

Preliminary evaluation of MEDIPIX read-out chip on Glasgow LEC GaAs pixel detector

K.M.Smith


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