V - RD50

Università degli Studi
di Perugia
Radiation hardness simulation of
silicon thin detectors
F.Moscatelli1,2 , M. Petasecca1 , G.U. Pignatel1
1 DIEI - Università di Perugia, via G.Duranti,93 - Italy
2IMM-CNR sez.di Bologna, via Gobetti 101 - Italy
Outline
Università degli Studi
di Perugia
• Radiation damage modelling (F. Moscatelli)
• Thin structures (M. Petasecca)
Simulation Tool
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di Perugia
• Simulation tool:
–ISE-TCAD – discrete time and spatial solutions to equations
• Damage modelling:
- Deep levels: Nt , Et, σn and σp
- SRH statistics.
- Donor removal mechanism
- Other effects: high density defect concentration (clusters) produces an
increase of the leakage current.
Radiation Damage Model
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• Four levels*:
- V2-/0 located at E=EC-0.42
- CiOi located at E=EV+0.36
- V2O located at E= EC-0.50
- E(70) located at E=EC-0.45
• Direct charge exchange between V2-/0 and E(70) to reproduce cluster effects.
• Donor removal mechanism.
• Reproduce variation of the Vdep and Ileakage as a function of the fluence
• Over Φ=2×1014 n/cm2 computational problems
*F. Moscatelli, et al.Nuclear Instruments and Methods in Physics Research B 186 (2002)
ISE-TCAD Damage Model
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• Three levels*:
- V2-/0 located at E=EC-0.42
- CiOi located at E=EV+0.36
- V2O located at E= EC-0.50
• To reproduce cluster effects, we use increased V2-/0 occupancy
• Donor removal mechanism.
*D. Passeri, P. Ciampolini, G. Bilei and F. Moscatelli, IEEE Trans. Nucl. Sci., vol. 48, pp. 1688, 2001.
Three-level model
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• Level characteristics:
V2-/0
V2O
CiOi
E
Ec -0.42eV
Ec -0.50eV
Ev+0.36eV
σp
8 ⋅10-15cm2
10-15 cm2
10-16 cm2
σn
10-16 cm2
10-16 cm2
10-15 cm2
η
26 cm-1
0.1 cm-1
1 cm-1
Effective Doping Concentration Università
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and Leakage Current
∆I/Volume = αΦ, with
α =(2.9÷10) 10-17A/cm.
Simulations results as a
function of T
15
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di Perugia
1E-13
Vdep [V]
2
σp V2 [cm ]
12
9
6
3
0
100
measurements
simulations
150
200
250
300
Φ=2.2×1013
protons/cm2
1E-14
1E-15
180
200
220
240
260
280
Temperature [K]
Temperature [K]
140
1E-14
Vdep [V]
2
100
80
60
measurements
simulations
40
20
100
σpV2O [cm ]
120
150
200
250
Temperature [K]
300
Φ=4.7×1014
protons/cm2
1E-15
180
200
220
240
260
Temperature [K]
280
Thin detectors
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• Thin detectors have been proposed to investigate the
possibility to get a low depletion voltage and to limit
the leakage current of heavily irradiated silicon devices
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Simulation setup
Simulated structures:
58µm Æ thin device
D=
300 µm Æ thick device
Guard Ring
•
Simulated device structure and
parameters
•
Doping profiles:
9µm
15µm
Diode
40µm
D
– n-doped substrate (7×1011 cm-3)Æ
6kΩcm.
– Charge concentration at the siliconoxide interface of :
• 4 ×1011 cm-3 pre-irradiation
• 1 ×1012 cm-3 post-irradiation
Back
Guard Ring
6µm
Simulation setup
Diode
- Variable mesh definition:
¾ the mesh is better refined in
correspondence of the critical
points of the device to improve
simulator performance.
- The typical electric field distribution
at the full depletion voltage of the
diodes: red areas correspond to the
maximum
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Guard Ring
Simulation results
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400
16
300
12
V dep [V]
V dep [V]
Simulated Depletion Voltage as function of the fluence
200
100
300 µ m
1.0x10
14
2.0x10
2
Fluence [(1M eV) n/cm ]
4
58 µ m
0
0
0.0
8
14
0.0
1.0x10
14
2.0x10
14
2
Fluence [(1M eV) n/cm ]
- Vdep in thin structures is one order of magnitude lower than in thick one
- Vdep of thin diode at a fluence of 1×1015 n/cm2 is about 120 V while in
thick diode is more than 3000 V !
CCE Simulation results
Q = ∫ I (t )dt
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MIP: 80 e-h pairs/ µm
Cylinder diameter= 2µm
CCE Simulation results
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CCE Simulation results
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CCE Simulation results
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CCE Simulation results
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CCE Simulation results
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CCE Simulation results
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CCE Simulation results
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Simulated CCE as function of the fluence
Thick
Φ=2e14 n/cm2 Q@300V= 1.6 fC
CCE = 45%
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Thin
Q@14V= 0.58 fC
CCE = 98%
Exp. [1, 2] CCE = 42%
Φ=1e15 n/cm2 Q@VBD=300V= 1 fC
CCE = 27%
Q@120V= 0.57 fC
CCE = 95%
Exp.CCE = 20-30%
For Φ=1e15 n/cm2
Qthin=57% Qthick
Thin @ 120V NO Breakdown risk and full depleted
[1] L.Beattie et al./
NIM 412A (98)
[2] M.Bruzzi et al./
NIM 61B(98)
Conclusions
Università degli Studi
di Perugia
• Irradiated thin and thick diodes have been analyzed considering a
three levels simulation model until Φ=1e15 n/cm2
• Thin features:
– Vdep in thin structures is one order of magnitude lower
– CCE at very high fluence (1015 n/cm2) is 95% for thin
structures.
– Qthin=57% Qthick
• Next step is to simulate thin structures at higher fluences (1e16
n/cm2) and measure irradiated ones.