Radiation damage to electronic devices
for LHC and Super-LHC experiments
Presented by Julien Mekki
IES, University Montpellier II, France
CERN, Geneva, Switzerland
Seminar
IPNL – Lyon – France
14th January 2011
1
Outline
I.
Introduction
II.
Packaging effect on RadFET sensors for the radiation monitoring
project
III.
Forward biased p-i-n diodes used as dosimeters
IV.
Perspectives and outlook on future studies
V.
Conclusion
2
Who am I ?
Actual position
Assistant professor at University of Montpellier 2 – CERN USER.
Study of silicon detector performances for LHC and Super-LHC experiments.
PhD in Electronics (Nov. 2009) – (CERN, Université Montpellier 2)
Characterization and performance optimization of radiation monitoring sensors for high
energy physics experiments at the CERN LHC and Super-LHC
Master thesis in Science and Technology (2006) (CNES, EADS Astrium)
Radiation hardness of electronic components used for space applications.
February 2011:
Senior fellow at CERN – Emerging Energy Technologies department
Project: Radiation to electronics (R2E)
3
CERN Technologies
Accelerating
particle beams
Three keys technologies at CERN
Detecting particles
Balloon (30 Km)
GRID
CD stack with 1 year LHC data!
(~ 20 Km)
Large-scale computing (Grid)
Concorde
(15 Km)
Mt. Blanc
(4.8 Km)
4
The Large Hadron Collider (LHC)
CMS
5
The Large Hadron Collider (LHC)
Mixed radiation field
Hadrons (n, p, k+,k-, π+, π-)
Leptons (e-, e+, μ-, μ+)
Photons
Intense close to the interaction point
ATLAS
7 TeV
General design principle
Sub-detectors:
1) Inner detectors → Trackers
7 TeV
2) Calorimeters → Energy deposited
3) Muon gas chamber
6
Radiation monitoring project – Why ?
The effect of radiation on electronic and detector components → Major
All equipments → Affected
issue
by radiation damage
LHC experiments are designed to operate for 10 years.
→ Radiation level survey needed for damage and failure analysis.
Different radiation field parameters have to be monitored… Different
sensitivity and range are required… Different small active devices have been
investigated !
7
Radiation monitoring project – What ?
Ionization effect
ATLAS
TID (Total Ionizing Dose)
e.g. accumulation of charge in SiO2 : damage to microelectronic components
Unit Gray: 1 Gy = 1 Joule released in 1 kg of matter = 1 J/kg
Non-Ionizating effect
NIEL (Non Ionizing Energy Loss)
causing e.g. crystal defects in semiconductor crystals: silicon detector damage
Unit: 1 MeV neutrons/ cm2 “equivalent fluence” (Фeq)
Luminosity: 1034 cm-2.s-1
Ideal:
Measure the full radiation spectrum
(particle type, energy and intensity at all locations)
→ Impossible (there is no such device)
Dose
Annual Фeq
(Gy/y)
(×1013(neq/cm2))
80-90
17382
2.9
40-50
340-350
5625
2
80-90
340-350
1249
1
r (cm)
Z (cm)
A
20-30
B
C
In space (Geostationary orbit) 10-30 Gy/y
8
Radiation monitoring project – How ?
Many radiation sensors tested, only few of them was selected and installed in
the LHC experiments
2 major issues:
Measure of the 1-MeV Фeq
BPW34 Commercial Silicon
p-i-n diodes
Measure of the TID
2 types of RadFET:
250 nm oxyde thickness → REM,UK
1600 nm oxyde thickness → LAAS, France
9
Radiation monitoring project – How ?
Many radiation sensors tested, only few of them was selected and installed in
the LHC experiments
2 major issues:
Measure of the 1-MeV Фeq
BPW34 Commercial Silicon
p-i-n diodes
Measure of the TID
2 types of RadFET:
250 nm oxyde thickness → REM,UK
1600 nm oxyde thickness → LAAS, France
Packaging can induce possible dose enhancement in the measurements.
The only freedom remaining in the design is the chip carrier cover.
10
But, like the chip carrier, it has an effect on the TID measurement.
Packaging effect on
RadFET sensors for the
radiation monitoring project
11
RadFETs General
(1) e-/h+ pair generation;
(2) e-/h+ pair recombination;
(3) e- / h+ transport;
(4) hole trapping;
(5) Interface state.
Build-up of charge in SiO2
increase of the p-MOS Threshold Voltage  integrated
Dose Measurement
Exposure: “zero bias”
Readout: iDS
VGS ∝ TID
12
γ-neutron Irradiation
Chip carrier was placed into the reactor core
Various materials and thicknesses
Measurement: dose
Slight increase of TID
was
measured
for
thicknesses exceeding
1 mm.
13
Ref : F. Ravotti. Phd thesis, University Montpellier II, France.
Packaging Effect on RadFET sensors
How the RadFETs response is influenced by the cover ?
and also ….
How much dose is deposited by different particles with different
energies in the RadFETs ?
RadFET response studied using the simulation toolkit:
14
What is
GEometry ANd Tracking
C++ based / Object Oriented Toolkit for the
simulation of particle interactions with matter.
Geant4 provides the possibility to describe
accurately an experimental setup.
(Geometry and Materials)
The program provides the possibility of generating physics events and
efficiently track particles through the simulated detector.
The interactions between particles and matter must be simulated by
taking into account all possible physics processes, for the whole energy
range.
15
Geant4 Model
Without cover
With ceramic cover
Packaging
REM-TOT-500
LAAS-1600
Chip carrier has been hit perpendicularly in the front side.
Result of the simulation is the total energy deposited by primary and secondary
particles.
First set of simulation:
→ Full dies size are taken as sensitive volume
Second set of simulation:
→ sensitive volume: thin oxide Layer (SiO2)
16
Packaging comparison
Results for Pions:
Charged
hadrons
are
dominated by pions close to
the interaction point.
Most important contribution
on the total energy deposited in
a mixed field.
Low energy pions are absorbed in the cover.
Simulation have been carried out for all particles and energies present in the
LHC radiation field.
17
RadFET sensors in the ATLAS detector
Provide information about the TID in the LHC experiments
2
2 locations are taken as
example:
Inner detector (1)
Liquid Argon Calorimeter (2)
260 µm cover has been
investigated and compared
to uncovered RadFETs
1
Estimation of the total energy deposited in the RadFETs as well as the
cover effect for each particle type.
18
Results
Detailed results for the Inner Detector :
% of the total number
Annual dose without cover in
Annual dose with cover in units
Dose enhancement (%)
of particles
units of kGy/year and
of kGy/year and
(260µm /no-cover)
(contribution %)
(contribution %)
Protons
1.2
1.73×100 (26.7)
1.65×100 (22.9)
-4.3
Photons
54.9
2.46×10-2 (0.4)
8.29×10-2 (1.1)
237.1
Electrons
5.9
1.13×100 (17.4)
1.34×100 (18.4)
19.4
Pions
10.8
2.89×100 (44.7)
3.39×100 (46.4)
17.2
Neutrons
25.2
3.17×10-2 (0.5)
3.72×10-2 (0.5)
17.2
Muons
1.9
6.66×10-1 (10.3)
7.42×10-1 (10.5)
11.5
Total dose enhancement: 12.1±1 %
About 45 % of the energy is deposited by pions.
Significant dose enhancement for photons due to secondary particles.
Photons deposit less than 2 % of the overall energy.
19
Results
Pions:
Energy deposited in the medium
(MeV.cm-2.g-1)
Pions are charged hadrons: heavy particles
Mass 270 times higher than e-.
Energy deposited → Bragg peak
Photons:
Bragg peak
Compton e-
Alpha
Depth (cm)
(e-; e+)
Secondary particles (e-, e+)
→ Compton, pair production effects
→ Photonuclear absorption (α)
20
Results
Results for the Liquid Argon Calorimeter:
Total Dose enhancement = 23.6 ± 2.4%
Pions represent 0.1 % of particles → contribution to dose ≈ 7 %
Protons deposit about 35% of the overall energy
(represent only 0.08 % of particles, but mass 1800 times higher than e-.)
Annual dose values in the covered and uncovered RadFET sensors for both
locations.
Inner Detector
Simulated TID (SiO2)
Liquid Argon Calorimeter
Without cover
With cover
Without cover
With cover
6.5 kGy/year
7.3 kGy/year
5 Gy/year
6.1 Gy/year
21
Conclusion of this study
Dose enhancement as TID was simulated using Geant4 for all particles and energies
present within the LHC radiation field.
Understanding of each particle and energy influence.
260 µm thick Alumina cover can alter the measured dose up to 25 %.
The choice of RadFET packages is thus important for measuring the TID in High
Energy Physics Experiments.
Study published in J. Mekki et al, IEEE TNS, vol. 56, no. 4, pp. 2061-2069, 2009.
22
Forward biased p-i-n diodes
used as dosimeters
23
Radiation Monitoring at the LHC Experiments
2 major issues:
Measure of the 1-MeV Фeq
Measure of the TID
→ 108 ≤ Фeq ≤ 1014 -1015 neq/cm2 for LHC
BPW34 Commercial silicon
p-i-n diodes
2 types of RadFET:
250 nm oxide thickness → REM,UK
1600 nm oxide thickness → LAAS, France
24
p-i-n diodes (NIEL)
Displacement damage in high r Si-base
 Resistivity increases vs Фeq
VF
FORWARD BIAS
Fixed IF  VF  Фeq
iF
VF =  (material parameters, geometry [W], readout current [J], pulse length)
BPW34 p-i-n diode:
Thickness ≈ 300 µm,
Area = 2.65×2.65 mm2,
ρ ≈ 2.7 kΩ.cm
25
Readout protocol for LHC
BPW34 diode
FORWARD BIAS
Fixed Readout Current IF  VF  Фeq
IF = 1 mA with a short duration pulse
F. Ravotti et al., IEEE TNS, vol. 55, no. 4,pp. 2133-2140, 2008
Hadron sensitivity range from 2×1012 to 4×1014 neq/cm2.
Perspectives for the future Super-LHC:
Luminosity and radiation level (×10).
Detectors will be exposed to fluences up to 1016 1-MeV equivalent neutrons.
26
A solution to measure very high fluences has to be found
First study
New readout protocol
Different current steps of 50ms pulse duration
Current used: 10µA – 100µA – 1mA – 5mA – 10mA – 15mA – 25mA
Increase of bulk resistivity with Фeq
Thyristor - like behavior (F. Ravotti et al, IEEE TNS, vol. 55, no. 4, pp. 2016-2022, 2008.)
Self-heating of the diode
27
Second Study
Detailed study of the detectors behavior
Development of 2 tests benches
for the detector characterization
Modifications of the electrical
properties of the material
28
Second study(1/2)
I-V curves from very low voltages (=1mV), to high voltages.
Up to 6.26×1015 neq/cm2 (60% of the expected Super-LHC fluences)
2 differents regimes can be distinguished:
At low fluences:
1) At low voltages a linear
region can be observed.
Forward current (A)
First regime:
2) As VF increases: linear
region → sharp increase of
IF.
29
Rise of IF vs Фeq increases
up to ≈ 1 × 1013 neq/cm2
Second regime:
Forward current (A)
Second study (2/2)
1) For Фeq > 1 × 10 13 neq/cm2, I-V
characteristics are linear at low voltages.
2) With further increase of the radiation
level, this linear behaviour extend to
higher VF.
30
New formulation (1/3)
This new formulation is based on the relaxation material theory
Relaxation materials have a large density of g-r centers near Eg/2.
Recombination pins the fermi level at minimum conductivity
Фeq
Maximum resistivity:
2q(n  p )1/ 2 ni
Forward current (A)
rmax 
1
(see references in my PhD thesis)
31
http://jmekki.web.cern.ch/jmekki/2009-11-27-Thesis-Mekki.pdf
New formulation (2/3)
V
Relaxation materials were experimentally fitted as : I  G0V exp
V0
Фeq = 6.3×1014 neq/cm2
Forward current (A)
Forward current (A)
IF ≤ 1mA
Фeq = 6.3×1015 neq/cm2
IF ≥ 1mA
FIT
G0rmax  cte
IF ≤ 1mA
IF ≥ 1mA
FIT
V0    eq

For IF > 1mA, possibility to have thyristor-like behavior1 and/or self-heating effect.
1F.
32
Ravotti et al., IEEE TNS, vol. 55, no. 4,pp. 2133-2140, 2008
New formulation (3/3)
At the LHC experiments, BPW34FS diodes are operated in forward bias.
A new formulation to predict and monitor values of VF versus Фeq:
For Фeq ≥ 1×1013 neq/cm2
For IF ≤ 1mA
Based
on: I F  G0VF exp
LambertW(x) function is
the inverse function of:
VF
V0
 IF 

VF  V0  Lam bertW
 G0  V0 
IF = 1 mA
f ( x)  x  e( x)
IF = 100 μA
G0rmax  cte
IF = 10 μA
V0  eq

33
Qualitative evaluation of the
temperature dependence
rmax 
1
2q(n  p )1/ 2 ni
Temperature Coefficient < 0
ni increases with T°, so ρmax
decreases when T° increases.
34
Conclusion of this study
Effects on radiation damage up to 6.3×1015 neq/cm2 on the OSRAM BPW34FS silicon
p-i-n diode have been studied.
Comparison with relaxation materials.
New formulation to predict VF versus Фeq for:
Фeq ≥ 1×1013 neq/cm2
IF ≤ 1mA
Sensitivity is increased, and Фeq measurement range can be expanded when diode is
measured at lower temperature.
Summary:
Allow to extend the existing readout protocol. (IF = 1 mA)
Permit to predict radiation response for expected SLHC fluences.
Study published in J. Mekki et al, IEEE TNS, vol. 57, no. 4, pp. 2066-2073, 2010.
35
Perspectives and outlook on
future studies
36
Perspectives and outlook
BPW34 p-i-n diode can be used for monitoring LHC and Super-LHC
fluences from 2×1012 neq/cm2.
2 possibility already exists:
→ Pre-irradiation allows to measure Фeq > 8×109 neq/cm2.
→ CMRP diode (Thickness = 1 mm; Area = 1.2 mm2, ρ ≈ 10 kΩ.cm):
1×108 < Фeq (neq/cm2 ) < 2×1012
With the intention to develop our specific dosimeter
→ An investigation on custom made devices (high resistivity silicon detector)
37
Silicon Detectors
Tested devices were made from n-type FZ and MCz silicon wafers.
Geometry dependence on the detector’s radiation response has been evaluated.
→ 2 different active area: 2.5×2.5 cm2 and 5×5 cm2
→ 2 different thicknesses: 300 µm and 1000 µm
Outcome:
The device thickness is the main parameter which influence
their radiation response.
38
Silicon Detectors
Detector A
Detector B
(300 µm)
(1000 µm)
100 µA
9.1×109 cm-2/mV
3.2×108 cm-2/mV
1 mA
4.2×109 cm-2/mV
1.9×109 cm-2/mV
Readout Current
Sensitivity is increased
by a factor ≈ 25
Thin detector
Thick detector
Study published in J. Mekki et al, IEEE TNS, vol. 57, no. 6, pp. 3483-3488, 2010.
39
Silicon Detectors
Detector A
Detector B
(300 µm)
(1000 µm)
100 µA
9.1×109 cm-2/mV
3.2×108 cm-2/mV
1 mA
4.2×109 cm-2/mV
1.9×109 cm-2/mV
Readout Current
Sensitivity is increased
by a factor ≈ 25
Фeq ≈ 8×1012 neq/cm2
Thick detector
Фeq = 2×1012 neq/cm2
Thin detector
Фeq = 2×1010 neq/cm2
Thick detector
Study published in J. Mekki et al, IEEE TNS, vol. 57, no. 6, pp. 3483-3488, 2010.
40
General Conclusion
Monitor the LHC radiation field: 2 devices
→ RadFET (TID)
→ p-i-n diodes (Фeq)
RadFETs:
Evaluation of packaging configurations
Evaluation of the TID and package impact on a real LHC experiment.
→ Dose enhancement up to 25 %
p-i-n diodes:
New formulation for monitoring very high fluences (Super-LHC).
At low temperature → expand to higher fluences
Custom made devices :
Sensitivity for low Фeq can be improve using thicker p-i-n diodes or detectors.
41
Thank you for your attention
The Atlas Detector
42
43
Self heating effect
Normal readout protocol:
Self heating
VF at IF = 1mA
VF at IF = 25mA
VF at IF = 100µA
50ms 50ms
VF at IF = 10µA
50ms
VF at IF = 10µA
50ms
50ms
VF at IF = 10µA
Wait for temperature stabilization inside
the diode after each measurement:
Measurement
• After measurement
Self heating
VF2 < VF1 (self-heating)
50 ms
VF1 at IF = 10µA
• Wait intil VF2=VF1
VF2 at IF = 10µA
Outcome:
Problem for measuring at high
44
injection level due to self-heating.
Summary of the relaxation materials theory (1/3)
Relaxation theory occurs when the material has high resistivity, and
contains defects due to impurities or damage which enhance the G-R rate.
Definition of the dielectric relaxation time:
Time to restore charge neutrality to a region when excess carrier are suddently
introduced.
When excess carriers are injected across the PN junction, at the instant of
injection (t=0), there will be an excess charge (Δn,p) , so that charge neutrality is
disturbed.
It is assumed to be the bulk equivalent of a RC time constant :
τD = ρεε0
45
Summary of the relaxation materials theory (2/3)
Example: Injection of minority carriers in the n side (Δp):
p(x)
n(x)
At t = 0 → there are excess holes but no excess e-
n0
Δp
p0
x
x
Diffusion of holes (gradient of holes)
e- (Δn) are attracted in this region by drift because of the field induce by Δp.
p(x)
n(x)
Δp
Δn flow in from the contact to neutralize Δp
Δn
p0
This neutralization occurs in a dielectric relaxation
time (τD).
n0
x
x
While neutrality is quickly established, Δp diffuse slowly and recombine with e- so that there is still excess
charges in the material : The conventionnal carrier lifetime τ0
Resistivity is decreased by the enhancement of carrier in the material.
In conventionnal lifetime material, neutrality is restored before excess carrier recombine. τ0 >> τD
The np product is equal to: np = ni2×exp[(Фn-Фp)/kT]; Фn and Фp are the quasi-fermi levels for e- and h+ , and is
dependent on the applied voltage.(V = Фn-Фp)
46
Summary of the relaxation materials theory (3/3)
For irradiated diodes, the material becomes highly recombinative do to high density of recombination centers.
Minority carrier injection increases the resistivity since the concentration of minority and majority carriers is
reduced by recombination. τD = ρεε0 increases. τD >> τ0
Injected minority carrier lead to a depletion of majority carriers through the g-r centers activity. Therefore the
carrier equilibrium is rapidly reached → no possible to influence it by externally applied voltage.
Recombination pins the fermi level at minimum conductivity (defect near Eg/2)
 q( p  n ) 
 qV 
2
2
np  ni exp

n
exp
 i
 kT 
 
 kT

n   
kT  p 
kT  n 
ln 
ln   p   
q
q  ni 
 ni 
 
Ei
q
→ np = ni2 as for the steady-state condition in lifetime diode.
Maxiumum resistivity of Silicon :
rmax 
1
2q(n  p )1/ 2 ni
47