CCD based Vertex Detector for GLC

CCD based Vertex Detector for GLC 1

CCD based Vertex Detector for GLC

Yasuhiro SugimotoKEK

KEK/Niigata/Tohoku/Toyama Collaboration

@VERTEX2003, Sep. 16, 2003


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


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


GLC Accelerator


GLC Acc. Parameters

500 GeV 1000 GeV

Luminosity 2.5x1033cm-2s-1 2.5x1033cm-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


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


GLC Detector


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


CCD Vertex Detector

Structure of CCD


CCD Vertex Detector

Structure of CCD (Cont.)


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


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


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


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


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


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



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



Test Sample CCDs 256x256 pixcels 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



NIEL Hypothesis Bulk damage is thought to b

e 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.



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



Dark Current (Cont.)



Flatband Voltage Shift Surface damage in SiO

2 (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)



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



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



Hot pixels Average dark current of

150MeV beam irradiated CCD is x2~5 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



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


Electron Damage Study CTI Improvements

Notch Channel: Narrower channel with additional implant Charge packets encounter less traps



CTI Improvements (Cont.) Fat-zero Charge Injection:

Fill-up traps with artificially injected charge

~1200e Fat-zero Injectionwith LED



CTI Improvements (Cont.) Wider Vertical Gate Clock & Faster Horizontal Clock



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 @27C 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


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

x2 ~ x5 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


Summary (cont.) Using a model calculation, CTI suppression by wider vertical cloc

k and faster horizontal clock has been shown. Combining all the CTI improve methods, and comparing with bac

kground 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.

Documents

CCD based Vertex Detector for GLC