1. CCD based Vertex Detector for GLC
Yasuhiro Sugimoto
KEK
KEK/Niigata/Tohoku/Toyama Collaboration
@VERTEX2003, Sep. 16, 2003
CCD based Vertex Detector for GLC

2. CCD based Vertex Detector for GLC
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
CCD based Vertex Detector for GLC

3. CCD based Vertex Detector for GLC
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
CCD based Vertex Detector for GLC

4. CCD based Vertex Detector for GLC
GLC Accelerator
CCD based Vertex Detector for GLC

5. CCD based Vertex Detector for GLC
GLC Acc. Parameters
500 GeV
1000 GeV
Luminosity
2.5x1034cm-2s-1
Rep. rate
150 Hz
100 Hz
Bunch population
0.75 x 1010
# of bunch/train
192
Bunch separation
1.4 ns
sx/sy at IP
243/3 nm
219/2.1 nm
sz at IP
110 mm
CCD based Vertex Detector for GLC

6. CCD based Vertex Detector for GLC
GLC Beam Structure
GLC/NLC: Readout between trains ( 1 frame/6.7ms )
TESLA: Readout during trains ( 1 frame/50ms )
 GLC/NLC is more favorable for vertex detectors
CCD based Vertex Detector for GLC

7. CCD based Vertex Detector for GLC
GLC Detector
CCD based Vertex Detector for GLC

8. CCD based Vertex Detector for GLC
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 based Vertex Detector for GLC

9. CCD based Vertex Detector for GLC
CCD Vertex Detector
Structure of CCD
CCD based Vertex Detector for GLC

10. CCD based Vertex Detector for GLC
CCD Vertex Detector
Structure of CCD (Cont.)
CCD based Vertex Detector for GLC

11. CCD based Vertex Detector for GLC
CCD Vertex Detector
Merits of CCD for Vertex Detectors
Very thin (~20mm) 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) ~ t=10ns
 OK for GLC/NLC
(Fully depleted CCD at TESLA)
CCD has simple structure
Large area sensor
High yield
CCD based Vertex Detector for GLC

12. CCD based Vertex Detector for GLC
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 based Vertex Detector for GLC

13. CCD based Vertex Detector for GLC
CCD Vertex Detector
Baseline Design of GLC Vertex Detector
R=24, 36, 48, 60 mm
|cosq| < 0.9
s = 4 mm
Wafer thickness = 300 mm
B = 3T
 sb = 7  20/(pbsin3/2q) mm
This design is just a working assumption and the starting point of further R&D
CCD based Vertex Detector for GLC

14. CCD based Vertex Detector for GLC
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: sb = 5  10/(pbsin3/2q) mm
CCD based Vertex Detector for GLC

15. CCD based Vertex Detector for GLC
R&D Status
Spatial Resolution:
< 3mm has been demonstrated by beam tests
Thin Wafer:
Partially thinned (honeycomb type) wafer is being designed ( average thickness ~100 mm )
Radiation Damage Study:
Neutron damage study by Cf-252
Electron damage study by Sr-90/150MeV beam
CCD based Vertex Detector for GLC

16. CCD based Vertex Detector for GLC
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
CCD based Vertex Detector for GLC

17. CCD based Vertex Detector for GLC
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 simulator ‘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
CCD based Vertex Detector for GLC

18. CCD based Vertex Detector for GLC
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.)
CCD based Vertex Detector for GLC

19. CCD based Vertex Detector for GLC
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.
CCD based Vertex Detector for GLC

20. CCD based Vertex Detector for GLC
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
CCD based Vertex Detector for GLC

21. CCD based Vertex Detector for GLC
Electron Damage Study
Dark Current (Cont.)
CCD based Vertex Detector for GLC

22. CCD based Vertex Detector for GLC
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)
CCD based Vertex Detector for GLC

23. CCD based Vertex Detector for GLC
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
Beam
Sr-90
CCD based Vertex Detector for GLC

24. CCD based Vertex Detector for GLC
Electron Damage Study
Hot Pixels
Measured at +10 C
Cycle Time: 2 sec
150MeV Beam
Before Irradiation
0.5x1011/cm2
150MeV Beam
Before Irradiation
1x1011/cm2
Sr-90
1x1011/cm2
2x1011/cm2
CCD based Vertex Detector for GLC

25. CCD based Vertex Detector for GLC
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
CCD based Vertex Detector for GLC

26. CCD based Vertex Detector for GLC
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
CCD based Vertex Detector for GLC

27. CCD based Vertex Detector for GLC
Electron Damage Study
CTI Improvements
Notch Channel:
Narrower channel with additional implant
Charge packets encounter less traps
CCD based Vertex Detector for GLC

28. CCD based Vertex Detector for GLC
Electron Damage Study
CTI Improvements (Cont.)
Fat-zero Charge Injection:
Fill-up traps with artificially injected charge
~1200e Fat-zero Injection
with LED
CCD based Vertex Detector for GLC

29. CCD based Vertex Detector for GLC
Electron Damage Study
CTI Improvements (Cont.)
Wider Vertical Gate Clock & Faster Horizontal Clock
CCD based Vertex Detector for GLC

30. CCD based Vertex Detector for GLC
Electron Damage Study
CTI Improvements (Cont.)
Reduction of number of transfer ( Increase number of output port) Multi Thread CCD (MT-CCD)
Expected CTI
Notch channel, f=20MHz, tw=40ms, fat-zero=500e
VCTI=2x10-5, HCTI=4x10-6 / 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
CCD based Vertex Detector for GLC

31. CCD based Vertex Detector for GLC
Summary
We are studying CCD-based vertex detector for GLC(/NLC) which 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 b 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
CCD based Vertex Detector for GLC

32. CCD based Vertex Detector for GLC
Summary (cont.)
Using a model calculation, CTI suppression by wider vertical clock and faster horizontal clock has been shown.
Combining all the CTI improve methods, and comparing with background 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=4T
even at room temperature. 　If CCD is cooled ( < -70 C), CTI
becomes still better. 　Dark current pedestal or hot pixels could put
possible limitation for room temperature operation, rather than CTI
If the design with R=15mm is possible, and thinner (~100mm) wafer is used, impact parameter resolution is improved from sb = 7 20/(pbsin3/2q) mm (baseline design) to sb = 5 10/(pbsin3/2q) mm, which is the milestone of our R&D.
CCD based Vertex Detector for GLC