Simulation results from double-sided and
standard 3D detectors
David Pennicard, University of Glasgow
Celeste Fleta, Chris Parkes, Richard Bates – University of Glasgow
G. Pellegrini, M. Lozano - CNM, Barcelona
10th RD50 Workshop, June 2007, Vilnius, Lithuania
Overview
• Simulations of different 3D detectors in ISETCAD
– Comparison of double-sided 3D and full-3D
detectors before irradiation
– Radiation damage models
– Preliminary results of radiation damage
modelling
Overview
• Simulations of different 3D detectors in ISETCAD
– Comparison of double-sided 3D and full-3D
detectors before irradiation
– Radiation damage models
– Preliminary results of radiation damage
modelling
Double-sided 3D detectors
•
Proposed by CNM, also
being produced by IRST
•
Columns etched from
opposite sides of the
substrate
•
•
Metal layer on back
surface connects bias
columns
– Backside biasing
Separate contact to
each n+ column
p-stop
Inner radius 10µm
Outer radius 15µm
Dose 10 13cm-2
Oxide layer
n+ column
250µm length
10µm diameter
p- substrate
300µm thick,
doping 7*10 11cm-3
p+ column
250µm length
10µm diameter
Medipix configuration
(55µm pitch) and 300µm
thickness
55µm pitch
p+ column
On back side:
Oxide layer covered with metal
All p+ columns connected together
Double-sided 3D: Depletion behaviour
•
•
~2V lateral depletion (same as standard 3D)
~8V to deplete to back surface of device
0V
0V
Doping
Doping
1V
1V
10V
10V
Mostly
depleted
Fully
depleted
Space
charge
3
(e/cm )
+00
0.0x10
+11
-1.0x10
+11
-2.0x10
+11
-3.0x10
+11
-4.0x10
+11
-5.0x10
+11
-6.0x10
+11
-7.0x10
n+
p+
n+
p+
n+
Undepleted
around p+
column and
base
Depletion
around
n+
column
p+
n+
p+
Double-sided 3D: Electric field
Double sided 3D
Standard
3D
Electric field (V/cm) in cross-section
of double-sided detector at 100V bias
p+
25
20
Y (um)
Similar
behaviour
in overlap
region
15
Electric
field (V/cm)
10
5
n+
0
0
10
20
X (um)
80000
70000
60000
50000
40000
30000
20000
10000
0
Double-sided 3D: Electric field at front
Detail of electric field (V/cm) around top of
double-sided 3D device (100V bias)
0
Detail of electric field (V/cm) around top of
double-sided 3D device (100V bias)
25
p-stop
10
10
50
0
20
00
130000
90000
60000
40000
30000
20000
10000
0
0
20
n+
Z (um)
Z (um)
Electric
field (V/cm)
20000
0
30
40
50
p+
30
10
n+
10
20
D (um)
30
00
0
High field at
column tip
40
2000
60
0
0
40
Electric field matches
full 3D where columns
overlap
Low fields
around front
50
p+
130000
60
0
10
20
D (um)
30
40
Double-sided 3D detectors: Collection time
Simulated particle track passing midway between n+ and p+ columns
Variation
in charge
collection
time
with250depth
50
100
150
200
0
Double-sided detector
Standard 3D detector
5
50%
90%
Full
Time (ns)
for given
collection:
3.00
Collection time (ns)
Electrode current (µΑ)
MIP signals in double-sided and standard 3D at 100V
24
22
20
18
16
14
12
10
8
6
4
2
0
0.0
300
4.00
4
3
2.00
2
1.00
1
0.5
1.0
1.5
2.0
Time (ns)
2.5
0.00
0
0
50
100
150
200
Depth (um)
Variation in charge collection time with choice of device structure
Detector
Column length
90% collection
99% collection
Double-sided 3D
250µm
0.75ns
2.5ns
Double-sided 3D
270µm
0.40ns
1.0ns
Double-sided 3D
290µm
0.35ns
0.5ns
Standard 3D
300µm
0.35ns
0.5ns
250
300
Overview
• Simulations of different 3D detectors in ISETCAD
– Comparison of double-sided 3D and full-3D
detectors before irradiation
– Radiation damage models
– Preliminary results of radiation damage
modelling
University of Perugia trap models
IEEE Trans. Nucl. Sci., vol. 53, pp. 2971–2976, 2006
“Numerical Simulation of Radiation Damage Effects in p-Type and n-Type FZ
Silicon Detectors”, M. Petasecca, F. Moscatelli, D. Passeri, and G. U. Pignatel
Ec
Perugia P-type model (FZ)
Energy
(eV)
Type
Trap
σe
(cm2)
σh
(cm2)
η
(cm-1)
Acceptor
Ec-0.42
VV
2.0*10-15
2.0*10-14
1.613
Acceptor
Ec-0.46
VVV
5.0*10-15
5.0*10-14
0.9
Donor
Ec+0.36
CiOi
2.5*10-14
2.5*10-15
0.9
--
0
•
•
2 Acceptor levels: Close to midgap
– Leakage current, negative charge (Neff), trapping of free electrons
Donor level: Further from midgap
– Trapping of free holes
Ev
University of Perugia trap models
•
Aspects of model:
I
= αΦ
Vol
– Leakage current – reasonably close to α=4.0*10-17A/cm
– Depletion voltage – matched to experimental results (M. Lozano et al.,
IEEE Trans. Nucl. Sci., vol. 52, pp. 1468–1473, 2005)
– Carrier trapping –
• Model reproduces CCE tests of 300µm pad detectors
• But trapping times don’t match experimental results
∂n − n
=
τe
∂t
•
•
1
τe
1
= β e Φ eq
τe
e
= vth σ e N
e
= vth σ e Φ eqη
Link between model
and experiment
β e = vth eσ eη
Experimental trapping times for p-type silicon (V. Cindro et al., IEEE NSS,
Nov 2006) up to 1015neq/cm2
– βe= 4.0*10-7cm2s-1
βh= 4.4*10-7cm2s-1
Calculated values from p-type trap model
– βe= 1.6*10-7cm2s-1
βh= 3.5*10-8cm2s-1
Altering the trap models
•
•
Priorities: Trapping time and depletion behaviour
– Leakage current should just be “sensible”: α = 2-10 *10-17A/cm
Chose to alter cross-sections, while keeping σh/σe constant
Carrier
trapping:
Space
charge:
β e,h = vth e,hσ e,hη
ne ,Trap
h
− Et  n σ h vth

− Et  
= N trap f n ≈ N trap exp
+
exp
kT  n σ v e
kT  


e th
 i

Modified P-type model
Type
Energy
(eV)
Trap
σe
(cm2)
σh
(cm2)
η
(cm-1)
Acceptor
Ec-0.42
VV
9.5*10-15
9.5*10-14
1.613
Acceptor
Ec-0.46
VVV
5.0*10-15
5.0*10-14
0.9
Donor
Ec+0.36
CiOi
3.23*10-13
3.23*10-14
0.9
Modified P-type model and experimental data
Type
Energy
(eV)
Trap
σe
(cm2)
σh
η
(cm-1)
Acceptor
Ec-0.42
VV
9.5*10-15
9.5*10-14
1.613
Acceptor
Ec-0.46
VVV
5.0*10-15
5.0*10-14
0.9
Donor
Ec+0.36
CiOi
3.23*10-13
3.23*10-14
0.9
P-type trap models: Depletion voltages
P-type trap model: Leakage Current
600
550
(cm2)
0.20
“Comparison of Radiation Hardness of P-in-N, N-in-N, and N-in-P Silicon
Pad Detectors”, M. Lozano et al., IEEE Trans. Nucl. Sci., vol. 52, pp. 1468–
1473, 2005
α=3.75*10-17A/cm
Leakage current (A/cm^3)
Depletion voltage (V)
0.16
500
450
400
Default p-type sim
0.08
0.04
Modified p-type sim
350
0.12
Experimentally,
α=3.99*10-17A/cm3 after 80 mins
anneal at 60˚C (M. Moll thesis)
Experimental
0.00
300
0
1E+14
2E+14
3E+14
4E+14
Fluence (Neq/cm2)
5E+14
6E+14
7E+14
0
1E+15
2E+15
3E+15
4E+15
Fluence (neq/cm^2)
5E+15
6E+15
Perugia N-type model
Perugia N-type model (FZ)
Type
Energy
(eV)
Trap
σe
(cm2)
Donor removal
σh
(cm2)
η
(cm-1)
Acceptor
Ec-0.42
VV
2.0*10-15
1.2*10-14
13
Acceptor
Ec-0.50
VVO
5.0*10-15
3.5*10-14
0.08
CiOi
2.0*10-18
2.5*10-15
1.1
Donor
Ec+0.36
N D = N D 0 exp(−cD Φ )
N D 0 * c D = K C = const
KC=(2.2±0.2)*10-2cm-1
•
•
Works similarly to the p-type model
Donor removal is modelled by altering the substrate doping directly
•
Experimental trapping times for n-type silicon (G. Kramberger et al., NIMA,
vol. 481, pp297-305, 2002)
βh= 5.3*10-7cm2s-1
– βe= 4.0*10-7cm2s-1
Calculated values from n-type trap model
– βe= 5.3*10-7cm2s-1
βh= 4.5*10-8cm2s-1
•
Modified N-type model
Energy
(eV)
Type
σe
σh
η
(cm-1)
(cm2)
VV
1.5*10-15
0.9*10-14
13
Ec-0.5
VVO
5.0*10-15
3.5*10-14
0.08
Ec+0.36
CiOi
2.5*10-17
3.1*10-15
1.1
Acceptor
Ec-0.42
Acceptor
Donor
Trap
(cm2)
N-type trap models: Depletion voltages
N-type trap model: Leakage Current
500
0.16
α=2.35*10-17A/cm
Leakage current (A/cm^3)
Depletion voltage (V)
“Characterization of n and p-type diodes processed on Fz
and MCz silicon after irradiation with 24 GeV/c and 26
MeV protons and with reactor neutrons”, Donato Creanza
400 et al., 6th RD50 Helsinki June 2-4 2005
300
200
Default n-type sim
100
0.12
0.08
0.04
Experimentally,
α=3.99*10-17A/cm after 80 mins
anneal at 60˚C (M. Moll thesis)
Modified n-type sim
Experimental
0.00
0
0
2E+14
4E+14
6E+14
8E+14
Fluence (Neq/cm2)
1E+15
1.2E+15
0
1E+15
2E+15
3E+15
4E+15
Fluence (neq/cm^2)
5E+15
6E+15
Bug in ISE-TCAD version 7
•
•
•
Currently using Dessis, in ISE-TCAD v7 (2001)
Non time-dependent simulations with trapping
are OK
Error occurs in transient simulations with traps
– Carrier behaviour in depletion region is OK
– Displacement current is miscalculated
– This affects currents at the electrodes
Correct behaviour:
Error:
•
∇.J tot = ∇.J disp + ∇.J n + ∇.J p = 0
∇.J disp ,error = ∇.J tot = q ( Re,Trap − Rh ,Trap ) * (~)1.73
This bug is not present in the latest release of Synopsis TCAD (2007)
– Synopsis bought ISE TCAD, and renamed Dessis as “Sentaurus
Device”
– Don’t know which specific release fixed the problem
Test of charge trapping in Synopsis TCAD
•
Simulated a simple diode with carriers generated at its midpoint
No traps
“Double step”
seen because
electrons are
collected
before holes
Test of charge trapping in Synopsis TCAD
•
•
Simulated a simple diode with carriers generated at its midpoint
Acceptor and donor traps further from the midgap
– Produces charge trapping but little change in Neff
– Trap levels should give τe≈ τh ≈ 1ns
ISE TCAD traps
?!
Test of charge trapping in Synopsis TCAD
•
•
Simulated a simple diode with carriers generated at its midpoint
Acceptor and donor traps further from the midgap
– Produces charge trapping but little change in Neff
– Trap levels should give τe≈ τh ≈ 1ns
Synopsis traps
With traps,
signal decays
as exp (-t/1ns)
as expected
Overview
• Simulations of different 3D detectors in ISETCAD
– Comparison of double-sided 3D and full-3D
detectors before irradiation
– Radiation damage models
– Preliminary results of radiation damage
modelling
Full 3D – Depletion voltage (p-type)
•
•
Depletion voltage is low, but strongly dependent on pitch
Double sided 3D shows the same lateral depletion voltage as full 3D
Depletion voltages and radiation damage
133µm
160
Full 3D, ptype, Medipix (55um)
Full 3D, ptype, 3-column ATLAS
140
100
80
50µm
60
0
40
10
20
20
Y
Depletion voltage (V)
120
30
40
0
0
2E+15
4E+15
6E+15
8E+15
1E+16
1.2E+16
50
0
Fluence (Neq/cm^2)
20
40
X
55µm
60
Full 3D – electric field at 100V
Full depletion is achieved well under 100V, but electric field is altered
1016 neq/cm2
No damage
2
Full 3D, p-type
Full 3D, p-type, 1e+16neq/cm
40
35
30
30
p+
p+
00
20
30
20
0
00
30
Y (µm)
25
15
15
Electric
Field (V/cm)
35
1 00
00
30000
20
15
30
0
20
X (µm)
20
X (µm)
0
0
00
10
10
0
00
10
0
0
80
0
n+
n+
0
0
5
100
0
0
00
5
30
5
00
10
00
10
55
10
100000
80000
60000
40000
20000
0
p+
25
0
55
25
Electric
Field (V/cm)
Y (µm)
35
40
100000
80000
60000
40000
20000
0
10
00
0
40
Y (µm)
2
Full 3D, p-type, 0neq/cm
n+
0
0
10
20
X (µm)
Double-sided 3D – front surface
Once again, double-sided devices show different behaviour at front and back surfaces
1016 neq/cm2
No damage
Double-sided 3D, p-type,
front surface
Double-sided 3D, p-type,
2
0neq/cm , front surface
0
10
10
0
2500
2500
10
100
20
20
Electric
Field (V/cm)
30
40
0
2000
50
50
p+
0
25
D (µm)
50
0
n+
40
50
p+
60
30000
70
30
30000
70
30000
60
30000
60
p+
190000
170000
150000
130000
110000
90000
70000
50000
30000
20000
10000
5000
0
00
40
n+
Electric
Field (V/cm)
20 0
Z (µm)
n+
Z (µm)
30
Z (µm)
0
1000
20
00
5000
0
5 00
0
Double-sided 3D, p-type,
2
1e+16neq/cm , front surface
190000
170000
150000
130000
110000
90000
70000
50000
30000
20000
10000
5000
0
70
25
D (µm)
50
0
25
D (µm)
50
Double-sided 3D – back surface
Region at back surface depletes more slowly – not fully depleted at 100V bias
1016 neq/cm2
No damage
Double-sided 3D, p-type,
back surface
Double-sided
3D, p-type,
0neq/cm2, back surface
240
n+
p+
260
p+
260
270
00
150
270
7500
280
280
290
290
300
0
25
D (µm)
50
300
0
250 0
25
D (µm)
190000
170000
150000
130000
110000
90000
70000
50000
30000
20000
10000
5000
0
50
00
250
Electric
Field (V/cm)
25 0
00
Electric
Field (V/cm)
Z (µm)
Z (µm)
250
Z (µm)
250
n+
300
n+
25000
240
70000
240
230
40000
230
50000
230
Double-sided 3D, p-type,
1e+16neq/cm2, back surface
p+
260
0
00
10
270
2500
280
290
300
0
Undepleted
25
D (µm)
190000
170000
150000
130000
110000
90000
70000
50000
30000
20000
10000
5000
0
50
Further work
Simulate charge collection!
Consider effects of different available pixel layouts
– CCE, depletion voltage, insensitive area, capacitance
0
0
10
10
20
20
Y
Y
•
•
30
30
40
40
50
50
0
20
40
X
60
0
20
40
60
X
3
133µm
50µm
8
50µm
Conclusions
•
Double-sided 3D detectors:
– Behaviour mostly similar to standard 3D
– Depletion to back surface requires a higher bias
– Front and back surfaces show slower charge collection
•
Radiation damage model
– Trap behaviour is directly simulated in ISE-TCAD
– Trap models based on Perugia models, altered to match experimental
trapping times
•
Preliminary tests of damage model with 3D
– Relatively low depletion voltages, but electric field pattern is altered
– Double-sided 3D shows undepleted region at back surface at high
fluences
Thank you for listening
Additional slides
+ve
3D detectors
•
N+ and p+ columns pass through
substrate
•
Fast charge collection
•
Low depletion voltage
•
Low charge sharing
•
Additional processing (DRIE for
hole etching)
n-electrode
Planar
e-
h+
p-electrode
-ve
Particle
~30um
+ve
-ve
3D
e-
h+
n-column Particle
p-column
~300um
Breakdown in double-sided 3D
Breakdown occurs at column tips
around 230V
– Dependent on shape, e.g. 185V
for square columns
40
60
00
0
42
44
000
10
00
00
46
48
200
Z (um)
•
Electric field (V/cm) around
tip of p+ column at 215V
50
343000
52
p+
54
56
25
30
D (um)
35
Breakdown in double-sided 3D
With 1012cm-2 charge, breakdown at 210V
Front
Electric field (V/cm) in double-sided 3D
12
-2
at 175V with 10 cm oxide charge
0
P-stop
10
Z (um)
20
Back
Column
tips
n+
30
40
50
p+
60
0
10
20
D (um)
30
40
Electric field (V/cm) in double-sided 3D
12
-2
at 175V with 10 cm oxide charge
60
Electric field
(V/cm)
300000
250000
200000
150000
100000
50000
0
n+
50
40
Z (um)
•
p+
30
Electric field
(V/cm)
20
300000
250000
200000
150000
10
100000
50000
0
0
30
P+
base
20
D (um)
10
0
Example of ISE TCAD bug
Current distribution after 0.06ns
4.00
3.50
Total Current
Current density (A/cm2)
3.00
2.50
2.00
1.50
1.00
0.50
0.00
0
50
100
150
200
250
300
-0.50
-1.00
N+
In simulation, charge
deposited at the front
Position (um)
300µm
P+
Example of ISE TCAD bug
Current distribution after 1ns
4.00
3.50
Total Current
Current density (A/cm2)
3.00
2.50
2.00
1.50
1.00
0.50
0.00
0
50
100
150
200
250
300
-0.50
-1.00
Position (um)
N+
Holes drift
300µm
P+
Example of ISE TCAD bug
Full 3D – Depletion voltage (p-type)
•
•
Depletion voltage is low, but strongly dependent on pitch
Double sided 3D shows the same lateral depletion voltage as full 3D
Depletion voltages and radiation damage
133µm
160
Full 3D, ptype, Medipix (55um)
140
Full 3D, ptype, 3-column ATLAS
3-column ATLAS test, point
where CCE maximised
100
80
50µm
60
0
40
10
20
20
Y
Depletion voltage (V)
120
30
40
0
0
2E+15
4E+15
6E+15
8E+15
1E+16
1.2E+16
50
0
Fluence (Neq/cm^2)
20
40
X
55µm
60
Weighting fields and electrode layouts
0
10
20
Y
Symmetrical layout of n+ and p+
30
Weighting potential is the same for
electrons and holes
40
50
0
20
40
60
X
Square layout, symmetrical layout of n+ and p+
Square layout, symmetrical layout of p+ and n+
0
Weighting
potential
0.
1
0
10
Abs(ElectricField)
30000
25000
20000
15000
10000
5000
0
20
4
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
5
0. 6
0. 7
0.
9
0.
Y
Y
20
0.
0.
8
10
2
0.
0.
3
Max field: 26500 V/cm
30
30
40
40
Electric field, 100V bias
50
0
5
10
15
20
25
30
35
40
X
45
50
55
60
65
70
Weighting potential
50
0
10
20
30
40
X
50
60
70
Weighting fields and electrode layouts
0
10
3 bias columns per readout column
Y
20
30
Weighing potential favours electron
collection
40
50
0
20
40
60
X
Square layout, 3 n+ bias columns per p+ readout column
Square layout, 3 p+ bias columns per n+ readout column
0
0
Abs(ElectricField)
30000
25000
20000
15000
10000
5000
0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
3
0.
5
0.
20
Y
Y
20
10
0
0. .7
9
10
Weighting
Potential
1
0.
0.
2
Max field: 44700 V/cm
30
30
40
40
Electric field, 100V bias
50
0
5
10
15
20
25
30
35
40
X
45
50
55
60
65
70
Weighting potential
50
75
0
10
20
30
40
X
50
60
70
Future work – Design choices with 3D
Choice of electrode layout:
– In general, two main layouts possible
0
0
10
10
20
20
Y
Y
•
30
30
40
40
50
50
0
20
40
X
60
0
20
40
60
X
– Second option doubles number of columns
– However, increasing no. of p+ columns means larger electron
signal
Future work – Design choices with 3D
•
ATLAS pixel (400µ
µm * 50µ
µm) allows a variety of layouts
– No of n+ electrodes per pixel could vary from ~3-8
– Have to consider Vdep, speed, total column area, capacitance
– FP420 / ATLAS run at Stanford already has different layouts
CMS (100 µm * 150µ
µm)
•
50µm
3
133µm
8
50µm