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Progress in R&D on silicon edgeless strip
detectors with Current Terminating
Structure
E. Verbitskaya1, A. Cavallini2, V. Eremin1, S. Golubkov3
G. Pellegrini4, G. Ruggiero5, T. Tuuva6
1Ioffe
Physico-Technical Institute RAS, St. Petersburg, Russia
2University of Bologna, Bologna, Italy
3Research Institute of Material Science and Technology
4Centro Nacional de MicroelectrГіnica, CNM-IMB, Barcelona, Spain
5CERN, Switzerland
6Lappeenranta University of Technology, Finland
13 RD50 Woskshop
CERN, Geneva, Nov 10-12, 2008
1
Outline
п‚Ё Overview of the approaches for rad-hard edgeless detectors
п‚Ё Edgeless detector with CTS: design
п‚Ё Models for potential and electric field distribution in p-on-n
edgeless detector and experimental results
п‚Ё Simulation of irradiated detectors
п‚Ё Experimental results on CCE (test beam)
п‚Ё Development of n-on-p edgeless detectors
Conclusions
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
2
Requirements
Requirement: diminished dead area adjacent
to detector sensitive area пѓЁ
Close-to-beam applications (CERN, TOTEM, Roman pot)
- maximal dead area width less than 50 Вµm
Other applications: imaging tileable arrays for diagnostics
(medicine, biology etc.)
Solution: edgeless detectors (diced or cut)
Problem: elimination of the influence of high current
from damaged cut on the properties of detector sensitive bulk
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
3
Prehistory
Z. Li et al., IEEE Trans. Nucl. Sci. NS-49 (2002) 1040-1046
Pad detectors diced across p-n junction
I-V improvement:
• Dicing from the back side
• Aging at RT
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
4
Overview of the approaches
for edgeless detectors
V o lt a g e t e r m i n a t i n g s t r u c t u r e ( V T S )
( f l o a t in g r i n g s )
V=Vb
V=0
Regular planar strip detector
with Voltage Terminating
Structure (VTS)
Strip S e n s i ti v e a r e a ( p + )
d
(n + )
> 2 d (> 6 0 0 Вµ )
Vb
C u r r e n t t e r m in a t i n g s t r u c t u r e ( C T S )
(g r o u n d e d rin g s )
I = I b u lk
I= I e d g e
S e n s it i v e a r e a ( p + )
d
<50 Вµ
(n + )
V b et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
E. Verbitskaya
5
Approach: Edgeless strip detector
with Current Terminating Structure (CTS)
Voltage terminating structure (VTS)
(floating rings)
V=Vb
V=0
Sensitive area (p+)
d
Regular p+-n-n+ strip
detector with Voltage
Terminating Structure
(VTS)
(n+)
> 2d (>600 Вµ)
Vb
Current terminating structure (CTS)
(grounded rings)
I=Ibulk
I=Iedge
Cut through
p+ outer
ring
Sensitive area (p+)
d
(n+)
<50 Вµ
TOTEM:
Edgeless p+-n-n+
strip detector with
CTS
Vb
1. G. Ruggiero et al. IEEE Trans. Nucl. Sci. 52 (2005) 1899.
2. E. Noschis et al. Nucl. Instr. and Meth. A 563 (2006) 41.
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
6
Alternative approach:
full 3D active edge detectors
C. Da Via et al., NIM A587 (2008) 243-249
Main features of design:
• p+ and n+ through entire
bulk
• p+ active edge
collection distance ≤ 50 mm
пЃђ fast response
пЃђ higher electric field due to
cylindrical geometry
пЃђradiation hardness
but
пЃђComplicated technology
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
7
Further development of edgeless detectors with CTS:
INTAS-CERN project TOSTER:
TOtem STrip Edgeless Radiation hard detectors
# 05-103-7533 Started: July 2006
CONSORTIUM
CERN - Switzerland
Ioffe Physico-Technical Institute RAS - Russia
Research Institute of Material Science and Technology - Russia
Centro Nacional de Microelectronica - CSIC – Barcelona, Spain
University of Bologna - Italy
Lappeenranta University of Technology – Finland
Head of the project: Gennaro Ruggiero (CERN)
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
8
Conceptual design
of edgeless detector with CTS
Current Terminating
Structure (grounded)
Clean-Up Ring (CUR)
Current Terminating
Ring (CTR)
Sensitive area
Voltage Terminating Rings
(floating)
Non-sensitive corner
The current of CTR: ohmic current along the damaged cut
The current of CUR: diffusion current from the cut to the bulk
The current of sensitive area: bulk generated current
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
9
Performance
of edgeless detector with CTS
Dead area 47 mm
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
10
Electrical characteristics
of p-on-n edgeless detectors
Statistics of reverse current
Processed by Ioffe&RIMST
n-Si, r ~ 20 kпЃ—В·cm Vfd: ~20 V; S = 8 cm2
I-V characteristics
512 strips with a pitch of 66 Вµm
I(U ), w 3 -1 5 (4 )
1.E -03
CTR
1.E -04
V = 100 V
80
b ulk
1.E -05
statistics on 204 detectors
60
1.E -06
number
I (A )
C UR
1.E -07
Bulk current:
Imean = 120 nA
Jmean ~ 12 nA/cm2
I
strip = 20 pA
40
1.E -08
1
10
100
U (V)
1000
20
0
0
100
200
300
400
500
600
700
800
900
1000 1100
current (nA)
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
11
Potential distribution on VTS rings
in p-on-n detector before and after scribing
Before cut
After cut
Test detectors
200
b)
ring 2
ring 3
ring 1
250
ring 2
potential (V)
150
potential (V)
300
a)
ring 1
100
50
200
ring 3
150
100
50
0
0
50
100
150
200
bias v oltag e (V)
250
300
0
0
50
100
150
200
250
300
bias v oltag e (V)
Before the cut: potential distribution occurs via punch-though effect,
and potentials between the rings are distributed linearly.
After cut: potential distribution is controlled by the increased
current across the damage surface (~mA).
VTS operates and distributes potential outside the detector active area
and eventually prevents the electric field focusing at the border of the detector
12
active area.
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
Models of potential and electric field
distribution at the sensitive cut
Components of potential and electric field
z
0
p+
Ez
Surface
current Is
Exs
In x direction:
Exb
x
n+
2
Potential in the bulk Vxb ~ x
Vxs, Exs
Vxb, Exb
at the cut (s)
and inside the bulk (b)
In z direction:
Ez – normal to the cut
Ez ≈ (Vsurf –Vbulk)/Wz
Exb ~ x
X
Wz – distance at which Vxs
dissipates to Vxb
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
13
1. Model of resistive edge layer
Damaged edge with high concentration of defect levels
z
Nd
Nd
1: Resistive layer:
controls potential
distribution Vxs(x)
2: Generation layer:
electrons and holes are
generated
x
z
z
Free carriers in the generation layer do not disturb Is and Vxs
E. Verbitskaya
E. Verbitskaya,
et al., 13
RESMDD’08,
RD50 Workshop,
Florence,
CERN,
OctNov
15-17,
10-12,
2008
2008
14
Potential in the bulk Vxb
Exb – const
Exb - linear
X
X
Vxb
p+
E(z)
n+
Ez
Vxs
X
Potential at the cut Vxs
Surface ohmic current
Model of resistive edge layer
Generated carriers:
holes move to CTS;
electrons may partially flow
inside the bulk
X
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
15
2. Model of amorphous edge layer
z
0
p+
Ie I
h
Ez
Exs
Exb
x
I=
Ie + Ih
jh = gh(d - x)
je = (ge – ηe )x
g – generation rate
n+
Ez
Vx
ηe ↑
Inversion of Ez sign!
– forces holes
to move towards the
bulk
Vxb
Vxs
X
X
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
16
Tools for study
of potential and electric field distribution
пѓљ Simulation of potential, electric field and hole trajectories
(Ioffe Institute)
пѓљ Conductive MicroProbe Technique (Bologna University)
пѓљ Scanning Transient Current Technique (Ioffe Institute)
пѓљ E(x) simulation using ISE-TCAD with implemented
Poisson and continuity equations (CNM Barcelona)
Additionally:
пЃђ Optical Beam Induced Current (Bologna Univ.)
пЃђ Scanning Electron Microscope (LUT)
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
17
Simulations: potential and electric field
distribution, resistive edge
Neff = 3пѓ—1011 cm-3; Vfd = 15 V
20
300
0
250
-40
Ez (V/cm)
Vb, Vs (Volt)
-20
Vb, 20 V
Vs, 20 V
Vb, 50 V
Vs, 50 V
Vb, 100 V
Vs, 100 V
Vb, 150 V
Vs, 150 V
-60
-80
-100
-120
200
20 V
50 V
100 V
150 V
150
100
50
-140
0
-160
0
0.005
0.01
0.015
0.02
0.025
0.03
0
0.005
0.01
0.015
0.02
0.025
0.03
x (cm)
x (cm)
Ez ≈ (Vsurf –Vbulk)/Wz
Wz = 300 mm
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
18
Experimental results on MicroProbe Technique:
surface potential SP(x), and E(x) at the cut edge
-10 to -150 V
Main
features:
пЃђ Potential is nonlinear
пЃђ E(x) is not constant
пЃђ Slope of E(x) grows with voltage
disagreement with
resistive edge model
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
19
Potential and Ez distributions
based on CMPT data
-10
2.0E+02
-30
0.0E+00
Electric field Ez, V/cm
Potential, V
Ez sign inversion
-50
-70
-90
red: Vs (CMPT)
blue: Vb
-110
-2.0E+02
-4.0E+02
-6.0E+02
20V
50V
100V
-8.0E+02
-130
150V
-1.0E+03
-150
0
0.005
0.01
0.015
0.02
Coordinate, cm
0.025
0.03
0
0.005
0.01
0.015
0.02
0.025
Coordinate, cm
Experimental results on surface potential are in agreement
to the amorphous edge model
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
20
0.03
Exs derived from STCT
V = 100 V, Vfd = 20 V, d = 300 mm
1.0E-01
5000
n+
Electric field (V/cm)
9.0E-02
Current, mkA
8.0E-02
7.0E-02
6.0E-02
5.0E-02
4.0E-02
3.0E-02
4000
3000
2000
STCT data
Ebulk
1000
Trend of CMPT
data
2.0E-02
1.0E-02
0
p+
0.0E+00
0
0
10
20
30
40
0.005
0.01
0.02
0.025
0.03
Coordinate (cm)
50
Time, ns
At V > Vfd
0.015
E ( x) пЂЅ
2V fd пѓ¦
x пѓ¶ V пЂ­ V fd
1
пЂ­
пѓ§
пѓ·пЂ«
d пѓЁ
d пѓё
d
Results on Ex(x) derived from CMPT and STCT show the
same tendency of Es reduction
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
21
Ez simulation in irradiated
p-on-n edgeless detectors
0
0
0.005
0.01
0.015
0.02
0.025
0
0.03
0
-20
0.005
0.01
0.015
0.02
0.025
0.03
-40
-60
Vbulk
Vsurface
-80
Vbulk after
irradiation
-100
-120
Ez (V/cm)
potential (Volt)
-200
-400
non-irradiated
Fn = 5E13 cm-2
-600
-800
-1000
x (cm)
x (cm)
E. Verbitskaya, RESMDD’08, Florence, Oct 15-17, 2008
22
Ez simulation in irradiated
p-on-n detectors
V = 400 V
0
Electric field Ex (V/cm)
0
-50
Potential (V)
-100
-150
-200
F↑
-250
red: Vs
blue: Vb
-300
-350
-500
-1000
-1500
E(z); 2e14
E(z); 1e14
E(z); 2e13
-2000
-2500
-3000
-3500
-400
0
0.01
0.02
0.03
0
Coordinate (cm)
0.01
0.02
0.03
Coordinate (cm)
Ez is ~kV/cm and increases with fluence пѓЁ
predicts the increase of the hole current flow into the bulk
and corresponding increase of the bulk current.
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
23
E(x) simulation using ISE-TCAD
J.P. Balbuena et al., CNM, Barcelona, presented at NSS-2008 and are in progress
CTR
p-on-n detector, saw cut edge
Electric field at the
front contact
is maximal at CTR
(10 to 50 mm from the
edge) and becomes
lower under the strips
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
24
Ez simulation in irradiated
p-on-n detectors (preliminary)
Non-irradiated
Fn = 4В·1014 cm-2
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
25
Recent experimental results on CCE
in p-on-n edgeless detectors with CTS
Efficiency of CTS detector at the sensitive edge
The left-most vertical line
indicates the reconstructed
position of the physical edge, the
other two vertical lines indicate
the 10%-90% efficiency rise
interval.
Diminished non-sensitive
width of 47 Ојm is achieved!
G. Ruggiero et al. Planar Edgeless Silicon Detectors for the TOTEM Experiment.
Pres. 8th Intern.Conf. on Position Sensitive Detectors (PSD8), Glasgow, Sept 1-5, 2008,
Nucl. Instr. and Meth. A (in press).
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
26
CCE in irradiated
p-on-n edgeless detectors with CTS
24 GeV/c protons
T = -18C
1.0
13
1*10 pcm
-2
Efficiency
0.8
13
5*10 pcm
-2
0.6
14
1.4*10 pcm
0.4
-2
The efficiency has been
calculated by comparing the
hits in the irradiated detector
with the hits in a non-irradiated
detector placed in front, along
the beam axis.
0.2
100
200
300
400
500
Bias Voltage, V
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
27
Development of n-on-p
edgeless detectors with CTS
Clean-up ring
Current terminating ring
Sensitive area
Voltage terminating rings
(floating)
N+
P+
b)
1
2
3
4
5
6
7
8
9
10
Layout: 10 different designs
d1
c2
f2
MCZ p-type Si
e3
g4
c4
d5
h6
Processed by Ioffe&RIMST
f7
b7
d8
e9
f1 0
a b c d e f g h
28
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
I-V characteristics of n-on-p edgeless detectors
I-V characteristics
Statistics of reverse current
14 randomly selected detectors
with different design
V = 200 V; S = 8x8 mm2
35
5.E-08
Series1
b)
5.E-08
Series2
10-30 nA
4.E-08
Series4
4.E-08
Jmean
= 30 nA/cm2
25
Series5
Series6
3.E-08
Series7
3.E-08
Series8
2.E-08
Series9
Series10
2.E-08
Series11
1.E-08
Series12
5.E-09
Series13
Series14
0.E+00
0
50
100
150
Bias, V
200
250
Quantity
Current, A
84 samples
a)
30
Series3
20
15
10
5
0
0
5
10
15
20
25
30
35
40
45
50
Current, nA
MPT and TCT measurements are in progress!
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
29
55
Conclusions
пѓљ Performance of edgeless detectors with CTS allows realization of
edgeless detectors which characteristics are controlled by the bulk
properties
пѓљ The model of amorphous edge is adequate to the experimental
results on n-on-p edgeless detectors
пѓљ In detectors with CTS diminished non-sensitive width of 47 Ојm is
achieved
пѓљ N-on-P edgeless strip detector seems to be radiation hard that
needs experimental testing
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
30
Acknowledgements
This work was done in the frame of INTAS-CERN project # 03-52-5744
and supported in part by:
• RF President Grant # 2951.2008.2,
• contract of Russian Agency on Science and Innovation # 2.516.11.6098
Thank you for your attention!
E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008
31
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