Transcript PCC-800Mm

Image quality and spectroscopic
characteristics of different silicon
pixel imaging systems
M. G. Bisogni, D.Bulajic, M. Boscardin, G. F. Dalla Betta, P.
Delogu, M. E. Fantacci, M. Novelli, C. Piemonte, M.
Quattrocchi, V. Rosso*, A. Stefanini and N. Zorzi
* Universita’ degli Studi e
Sezione I.N.F.N., Pisa, Italy

[email protected]
14TH INTERNATIONAL WORKSHOP ON ROOM-TEMPERATURE
SEMICONDUCTOR X-RAY AND GAMMA-RAY DETECTORS
ROME 18-21 OCTOBER 2004
Outline
3 imaging systems based on different thickness Si
pixel detectors were compared:
Spectroscopic characteristics
109Cd source
Imaging quality
contrast
signal to noise ratio (SNR)
Spatial resolution
modulation transfer function (MTF)
Imaging system
Si detector
ITC-Irst Detector
Si <111>
300-800 mm thick
pixel 170 x 170 mm2
p+ side 150x150 mm2
64 x 64 chs
1.2 cm2 area
SACMOS 1 mm technology
pixel: 170 x 170 mm2
64 x 64 channels
area 1.7 cm2
threshold adjust 3-bit
15-bit counter
with multiguardrings
without multiguardrings
electric potential (Volt)
100
80
60
40
20
0
0
200
400
600
800
width (mm)
1000
1200
1400
VTT Bump-bonding:
http://medipix.web.cern.ch/MEDIPIX/
p+
side
Photon Counting Chip
Medipix collaboration
Spectroscopic capability
30000
300 mm @ 60 V
525 mm @ 120 V
800 mm @ 100 V
300 mm @ 60 V
525 mm @ 120 V
800 mm @ 100 V
normalized counts
1,0
Counts
20000
10000
0,8
0,6
0,4
0,2
0
10
15
20
25
0,0
30
5
Energy(keV)
10
15
20
25
30
Energy (keV)
30000
300 mm @ 60 V
525 mm @ 120 V
800 mm @ 200 V
1,0
normalized counts
300 mm @ 60 V
525 mm @ 120 V
800 mm @ 200 V
Counts
20000
10000
0,8
0,6
0,4
0,2
0
10
15
20
25
30
0,0
5
Energy(keV)
109Cd
Integral spectra
10
15
20
25
30
Energy (keV)
109Cd
Differential spectra
109Cd
Integral spectra
30000
Detection efficiencies ratio
Vth=11keV
300 mm @ 60 V
525 mm @ 120 V
800 mm @ 200 V
Counts
20000
10000
Thickness
ratio
Calculated
ratio
Experimental
ratio
525/300
1.62
1.61
800/525
1.39
1.38
800/300
2.25
2.23
0
10
15
20
25
30
Energy(keV)
Wafers characteristics
J (nA/cm2) VDEP (V)
V OVER-DEP (V)
Thickness (mm)
resistivity
300+15
>= 6 KW cm
0.5
30
60
525+20
>= 5 KW cm
1.2
90
120
800+25
12 ÷ 30 KW cm
26
80
200
Contrast measurements
X-ray (W-anode) settings : 40 kV, 25 mA, 500 ms
X-ray focus
Al thickness 75 mm
Collimator
1.5 cm
140 cm
Air
800mm detector
3,8
3,6
Al
Si detector
N air  N Al
C
N air
Contrast (%)
3,4
3,2
3,0
2,8
2,6
2,4
8
10
12
14
16
18
Energy threshold (keV)
20
22
24
4 ,2
Contrast
4 ,0
( m Al ( E )  m air ( E )) ( E ) S ( E ) dE


x
 ( E ) S ( E ) dE

C  1 e
C
(% )
3 ,8
mAl(E) and mair(E) are the absorption
coefficients at the energy E
(E) is the detector efficiency at the
energy E
S(E) is the incident spectrum
3 ,4
3 ,2
3 ,0
2 ,8
8
13000
12000
11000
1 2
1 4
1 6
1 8
2 0
th r e s h o ld
2 2
(k e V )
4 ,2
40kV W
seen by 800 mm
seen by 525 mm
seen by 300 mm
14000
1 0
E n e rg y
4 ,0
3 ,8
3 ,6
(% )
10000
2
Photons per (mA s mm ) at 750 mm
15000
3 ,6
9000
8000
C
7000
6000
3 ,4
3 ,2
3 0 0
5 2 5
8 0 0
3 ,0
5000
2 ,8
4000
3000
m m
m m
m m
2 ,6
2000
2 ,4
1000
8
0
0
5
10
15
20
25
Energy (keV)
30
35
40
45
1 0
1 2
E n e rg y
1 4
1 6
1 8
th r e s h o ld
2 0
2 2
(k e V )
2 4
2 4
Signal to Noise Ratio
2 ,4
3 0 0
5 2 5
8 0 0
2 ,2
2 ,0
75 mm Al
m m
m m
m m
S N R
1 ,8
1 ,6
air
1 ,4
1 ,2
1 ,0
SNR 
0 ,8
0 ,6
1 0
8
1 2
E n e rg y
1 4
1 6
1 8
t h r e s h o ld
2 0
2 4
2 2
(k e V )
Thickness ratio
Calculated ratio
Experimental SNR ratio
525/300
1.24
1.25
800/300
1.41
1.42
800/525
1.14
1.14
N air  N Al
2
2
 air
  Al
Spatial resolution
W Slit :
c o u n ts
1 ,0
N o r m a liz e d
width: 10±1mm
length: 5.5±0.1mm
thikness: 1.5mm
800 mm Vth=11keV
Settings : 40 kV, 20 mA, 4000 ms
0 ,8
0 ,6
0 ,4
0 ,2
0 ,0
5
1 0
1 5
2 0
2 5
3 0
P ix e l n u m b e r
3 5
4 0
4 5
N o r m a liz e d
c o u n ts
1 ,0
0 ,8
Counts/row pixel number
0 ,6
0 ,4
0 ,2
0 ,0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
P ix e l n u m b e r
experimental finely sampled LSF
7 0 0 0
6 0 0 0
5 0 0 0
2 Boltzman functions
3 0 0 0
2 0 0 0
1 0 0 0
0
4 ,5
5 ,0
5 ,5
6 ,0
6 ,5
1
1


y  A2  ( A1  A2 )


( x  x ) / dx
1  e( x x0 ) / dx 
1 e 0
p o s itio n
1 ,0
LSFfitted fft MTF
0 ,8
M T F
L SF
4 0 0 0
0 ,6
0 ,4
0 ,2
0 ,0
1
2
3
4
5
6
S p a t ia l F r e q u e n c y
7
8
9
( lp / m m )
1 0
MTF
Energy threshold: 11 keV
300mm
525mm
800mm
1,0
0,8
Nyquist Freq. (2.94 lp/mm)
MTF: 64 %
Evaluated aperture 168 mm
Detector pitch 170 mm
MTF
0,6
0,4
0,2
0,0
1
2
3
4
5
6
7
Spatial Frequency (lp/mm)
1,0
800 mm detector
11 keV
15 keV
19 keV
23 keV
0,8
MTF
0,6
0,4
0,2
0,0
0
1
2
3
4
5
6
7
Spatial Frequency (lp/mm)
8
9
11
800 mm
aperture
(mm)
168
15
161
19
155
23
146
Vth
(keV)
10
Image of different Al thickness
100 micron
C=4,8%
75 micron
C=3,7%
50 micron
C=2,4%
25 micron
C=1,2%
300 mm
525 mm
Exposure condition: W anode, 40 kV, 40 mA, 630 ms
800 mm
Conclusions
Increasing the detector thickness:
 increases the detection efficiency
 SNR increases
 contrast decrease as expected
spatial resolution unchanges
More information on a PCC based digital mammographic
system: poster session R11-51 Thursday 11:00-12:30
Electric Field and Potential
with multiguardrings
without multiguardrings
with multiguardrings
without multiguardrings
30000
100
electric field (Volt/cm)
electric potential (Volt)
25000
80
60
40
20
20000
15000
10000
5000
0
0
0
200
400
600
800
width (mm)
width
1000
1200
1400
0
200
400
600
800
width (mm)
1000
1200
1400
Photos of some details
multiguardrings
Pixel 150 mm x 150 mm
Medipix 1
guardring
multiguardrings
Pixel 45 mm x 45 mm
guardring
Snake pads
multiguardrings
Medipix 2
Diffusione di carica
Con la diffusione, una carica che impiega un
tempo t per raggiungere l’elettrodo avrà una
fluttuazione sulla posizione cor rms diff
2diff = D*t D alla mobilita’ dei portatori di carica.
1 4
1 3
d iffu s io n

E
diff
(m m )
1 2
1 1
1 0
9
8
7
6
5
4
3
2
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
d e t e c t o r t h ic k n e s s ( m m )
4 0 k e V s im u la te d
5 2 5 m m
N o r m a liz e d c o u n ts
1 ,0
0 ,8
0 ,6
0 ,4
0 ,2
0 ,0
0
5
1 0
1 5
2 0
2 5
3 0
E n e rg y [k e V ]
3 5
4 0
4 5