study of fpccd vertex detector 12 jul. 2005 @8 th acfa ws y. sugimoto kek
TRANSCRIPT
Study of FPCCD Vertex Detector
12 Jul. 2005
@8th ACFA WS
Y. Sugimoto
KEK
FPCCD Vertex Detector Accumulate hit signals for one train and read out between trains
(Other options read out 20 times per train) Fine pixel of ~5m (x20 more pixels than “standard” pixels) to ke
ep low pixel occupancy Fully depleted epitaxial layer to minimize the number of hit pixels
due to charge spread by diffusion Two layers in proximity make a doublet (super layer) to minimize
the wrong-tracking probability due to multiple scattering Tracking capability with single layer using cluster shape can help
background rejection Three doublets (6 CCD layers) make the detector Operation at low temperature to keep dark current negligible (r.o.
cycle=200ms)
Tracking efficiency
Large number of background hits may cause tracking inefficiency: mis-identification of signal hit with background hit
002
0 ,2 dRRpmis : Background hit density0 : Multiple scattering angle
For a normal incident track, the probabilityof mis-identification of hit is given by;
Angular and momentum dependence; 42 sin ppmis
Tracking efficiency
cos
p mis d=10mm, =40/mm2
d=2mm, =40/mm2
d=10mm, =2/mm2
Mis-identification Probability (p=1 GeV/c,tSi=50m)
Expected hit density 40/mm2/train (TESLA) 20/mm2/train (Nominal) 15/mm2/train (LowQ)
at R=20 mm, B=3 T
Cluster shape
Effective background rejection will be possible by requiring angles of hit clusters in two layers of a doublet and the angle of the line connecting the two hits to be consistent with the extrapolated track.
(tracking capability with single layer!)
Standard pixel FPCCD
Baseline design
Advantages of FPCCD Free from beam-induced RF noise x~1.4m even with digital readout Simple structure : advantageous for large size Active circuit on one edge : easy to control
temperature Readout speed: 15MHz is enough
(128(V)x20000(H)/200ms=12.8MHz) (CPCCD:>50MHz)
CCD
MAPS/FAPS/ISIS
Impact parameter resolution Full simulation study by Jupiter Parameters:
Old standard option: R=24, 36, 48, 60 mm t = 330 m/layer = 4 m
FPCCD option: R=20, 22, 39, 41, 58, 60 mm t = 80 m/layer = 2 m
Be beam pipe (common): R=18 mm t = 500 m
Impact parameter resolution
p=1, 3, 5, 10, 20, 50, 100 GeV/c
T. Nagamine
Lorentz angle
Lorentz angle in depleted-layer tan=nB
n: electron mobility Carrier velocity saturates at hig
h E field: n =0.07 m2/Vs @T=300
K, E=1x104V/cm n =0.045 m2/Vs @T=300
K, E=2x104V/cm Small angle can be cancelled b
y tilting the wafer May not be a serious problem
Number of hit pixels does not increase so much
B=3T B=5T
E=1x104V/cm =12deg =19deg
E=2x104V/cm =7.7deg =13deg
Lorentz angle
Calculation of E-field in epi-layer Tools
FEMLAB (COMSOL in Japan) 3.1 Solve Poisson equation by finite element analysis (FEA)
Parameters Material is assumed fully depleted (No free charge) n-layer: ND=1x1016/cm3=1.6x103 C/m3
Epi-layer: NA=1x1013/cm3=-1.6 C/m3
VG=4 V tSiO2=100 nm tn=1 m tepi=15 m
Lorentz angle
Result of E-field calculation
Lorentz angle Result of E-field calculation – Potential
Lorentz angle
Result of E-field calculation – Summary Almost constant E-field of ~104V/cm in epi-layer can be ac
hieved E-field in epi-layer depends on gate voltage
Higher (positive) gate voltage gives higher E-field Positive gate voltage should be applied during train crossin
g in order to get saturated carrier velocity and less Lorentz angle (Inverted (MPP) mode can be maintained for ~1ms)
The Lorentz angle of 12 degrees is expected at B=3T
Summary and outlook We propose FPCCD option for the ILC Vertex Detector
Fully depleted CCD with 5m-square fine pixel size Accumulate 2820 BX and readout between trains Two layers make a doublet (super layer) to pick up signal h
its out of background hits If the thickness of the wafers is less than 80 m, the impact para
meter resolution better than b = 5 10/(psin3/2) m can be achieved with Rin=20 mm and B=3T
Electric field in the epitaxial layer has been calculated. From the results, the Lorentz angle of ~12 degrees at B=3T is expected
Tracking efficiency under beam background is the most critical issue for FPCCD. Simulation study is urgent.