CCD based Vertex Detector for GLC
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Transcript of CCD based Vertex Detector for GLC
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CCD based Vertex Detector for GLC 1
CCD based Vertex Detector for GLC
Yasuhiro SugimotoKEK
KEK/Niigata/Tohoku/Toyama Collaboration
@VERTEX2003, Sep. 16, 2003
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Outline
Project Overview of GLC Accelerator Detector
CCD Vertex Detector Merit/Demerit of CCD at GLC/TESLA
R&D Status Radiation Damage : Energy Dependence of Electron Damage
Dark Current, Flat-band Voltage Shift, Hot Pixels Charge Transfer Inefficiency
Summary
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GLC Project
JLC has changed its name as GLC (Global Linear Collider) 500GeV – 1TeV LC based on X-band linac Future global organization is anticipated Start experiment at 2013
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GLC Accelerator
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GLC Acc. Parameters
500 GeV 1000 GeV
Luminosity 2.5x1034cm-2s-1 2.5x1034cm-2s-1
Rep. rate 150 Hz 100 Hz
Bunch population 0.75 x 1010 0.75 x 1010
# of bunch/train 192 192
Bunch separation 1.4 ns 1.4 ns
x/y at IP 243/3 nm 219/2.1 nm
z at IP 110 m 110 m
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GLC Beam Structure
GLC/NLC: Readout between trains ( 1 frame/6.7ms )
TESLA: Readout during trains ( 1 frame/50s ) GLC/NLC is more favorable for vertex detectors
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GLC Detector
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GLC Detector
Baseline Design Possible Option
Vertex Detector CCD MT-CCD or CP-CCD
Intermediate Tracker Silicon Strip Det.
Central Tracker Jet Chamber TPC
Solenoid Field 3T 4T
Calorimeter Pb/Sci (Tile-Fiber) Digital Cal.
Beam X’ing Angle 7 mrad 20 mrad
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CCD Vertex Detector
Structure of CCD
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CCD Vertex Detector
Structure of CCD (Cont.)
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CCD Vertex Detector Merits of CCD for Vertex Detectors
Very thin (~20m) sensitive region (=Epitaxial (p-type) layer) Small multiple scattering Diffusion of electrons in epitaxial layer
Key of excellent spatial resolution for CCD ( and CMOS ) Takes time to diffuse : d = sqrt(Dt) ~ 6m @ t=10ns OK for GLC/NLC (Fully depleted CCD at TESLA)
CCD has simple structure Large area sensor High yield
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CCD Vertex Detector
Demerits of CCD for Vertex Detectors Long charge transfer path
Charge transfer inefficiency (CTI) by traps created by radiation damage
Long readout time Multi-port readout
CP-CCD
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CCD Vertex Detector
Baseline Design of GLC Vertex Detector R=24, 36, 48, 60 mm |cos| < 0.9 = 4 m Wafer thickness = 300 m B = 3T
b = 7 20/(psin3/2m
This design is just a working assumption and the starting point of further R&D
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R&D Issues
Design Criteria : “The Highest Vertex Resolution with Technical Feasibility”
High spatial resolution of the sensors Minimize multiple scattering Thin wafer Close to the IP Radiation Hardness Room temperature operation, if possible
Next milestone: b = 5 10/(psin3/2m
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R&D Status
Spatial Resolution: < 3m has been demonstrated by beam tests
Thin Wafer: Partially thinned (honeycomb type) wafer is being
designed ( average thickness ~100 m ) Radiation Damage Study:
Neutron damage study by Cf-252 Electron damage study by Sr-90/150MeV beam
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Electron Damage Study
Damage in CCDs Surface Damage
dE/dx in SiO2 Surface dark current Flat-band voltage shift
Bulk Damage Lattice dislocation in Si bulk
Bulk dark current Charge transfer inefficiency (CTI) Trap Levels
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Electron Damage Study
Expected Beam Background at GLC At LC, e+/e- pair background is created at IP through beam-
beam interaction Simulation using generator ‘CAIN’ and GEANT4-based sim
ulator ‘JUPITER’
B=3T, R=24mm
B=3T, R=15mm
B=4T, R=15mm
Hits/train
( /mm2)0.3 2 1
Hits/y (107sec)
( /cm2)0.5x1011 3x1011 1.5x1011
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Electron Damage Study
Test Sample CCDs 256x256 pixels Made by Hamamatsu Readout Freq : 250kHz Readout Cycle : 2 sec Irradiation:
At room temperature Without bias/clock Sr-90: 0.6, 1.0, 2.0 x 1011/cm2
150 MeV beam: 0.5, 1.0 x 1011/cm2 (5x1011/cm2 in Oct.)
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Electron Damage Study NIEL Hypothesis
Bulk damage is thought to be proportional to non-ionizing energy loss (NIEL)
NIEL of electrons has strong energy dependence
e+/e- pair background hitting the inner-most layer of VTX at LC peaks at ~20MeV
High energy electron beam irradiation test
Sr-90 GLC b.g.
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Electron Damage Study
Dark Current Surface dark current is
very well suppressed by using MPP (multi pinned phase) mode (inverted mode)
In MPP mode, dark current is dominated by bulk current
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Electron Damage Study
Dark Current (Cont.)
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Electron Damage Study
Flat-band Voltage Shift Surface damage in SiO2
(positive charge build-up) causes shift of operation voltage
FVS is observed as shift of MPP threshold
No significant FVS is observed up to 2x1011e/cm2 irradiation
Amplitude of Negative Clock Voltage (V)
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Electron Damage Study Dark Current Pedestal
In MPP mode, however, spurious dark current (dark current pedestal: DCP) which is generated during clocking is observed
This DCP is thought to be due to impact ionization by holes trapped in Si-SiO2 interface levels
Beam-irradiated CCDs show larger DCP than Sr-90 irradiated one
Sr-90
Beam
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Electron Damage Study
Hot Pixels Measured at +10 C Cycle Time: 2 sec
Sr-90•1x1011/cm2
•2x1011/cm2
150MeV Beam•Before Irradiation•0.5x1011/cm2
150MeV Beam•Before Irradiation•1x1011/cm2
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Electron Damage Study
Hot Pixels (Cont.) Average dark current of
150MeV beam irradiated CCD is x1.5~x7 larger than Sr-90 irradiated CCD
But hot pixel generation rate is completely different
This could be due to cluster-defect generation by high-energy electrons
Recoil Energy
Electron Threshold Energy
Point Defect
~20 eV ~200 keV
Cluster Defect
~2 keV ~5 MeV
Tree-like defect
~20 keV ~16 MeV
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Electron Damage Study
Charge Transfer Inefficiency (CTI) Derived from position
dependence of Fe-55 X-ray(5.9keV) peak
CTI induced by 150MeV beam is x2~3 larger than Sr-90 induced CTI
Beam
Sr-90
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Electron Damage Study CTI Improvements
Notch Channel: Narrower channel with additional implant Charge packets encounter less traps
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Electron Damage Study
CTI Improvements (Cont.) Fat-zero Charge Injection:
Fill-up traps with artificially injected charge
~1200e Fat-zero Injectionwith LED
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Electron Damage Study
CTI Improvements (Cont.) Wider Vertical Gate Clock & Faster Horizontal Clock
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Electron Damage Study
CTI Improvements (Cont.) Reduction of number of transfer ( Increase number of outp
ut port) Multi Thread CCD (MT-CCD)
Expected CTI Notch channel, f=20MHz, tw=40s, fat-zero=500e VCTI=2x10-5, HCTI=4x10-6 / 1x1011e/cm2 @27 C 32(V)x2000(H) pixels 0.06%(V), 0.8%(H) signal loss
R=24mm, B=3T ~20% signal loss after 50 years R=15mm, B=4T ~25% signal loss after 20 years
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Summary We are studying CCD-based vertex detector for GLC(/NLC) whic
h has beam structure favorable for CCD (or any other) vertex detector
In order to estimate radiation damage effect by e+/e- pair background at LC, electron damage effects on CCDs are studied for both Sr-90 and 150MeV beam irradiated CCDs. We found : 150MeV electrons cause
X1.5 ~ x7 larger bulk dark current than Sr-90 x2 ~ x3 larger CTI larger dark current pedestal at higher temperature hot pixels, which cannot be found in Sr-90 irradiated CCD
no significant flat-band voltage shift up to 2x1011e/cm2 irradiation CTI suppression by notch channel and fat-zero injection
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Summary (cont.) Using a model calculation, CTI suppression by wider vertical clock a
nd faster horizontal clock has been shown. Combining all the CTI improve methods, and comparing with backgr
ound simulation, we expect life of CCD-based vertex detector is ~50 years with R=24mm, B=3T (baseline design) ~20 years with R=15mm, B=4Teven at room temperature. If CCD is cooled ( < -70 C), CTIbecomes still better. Dark current pedestal or hot pixels could putpossible limitation for room temperature operation, rather than CTI
If the design with R=15mm is possible, and thinner (~100m) wafer is used, impact parameter resolution is improved from
b = 7 20/(psin3/2m (baseline design) to
b = 5 10/(psin3/2m, which is the milestone of our R&D.