11
Development of Radiation Hard Si Detectors
Dr. Ajay K. SrivastavaOn behalf of Detector Laboratory of the
Institute for Experimental PhysicsUniversity of Hamburg, D-22761, Germany.
Ajay K. Srivastava Uni.- Hamburg 107/09/2008
22
• Activities of our group
• Motivation to develop radiation harder Si detectors
• CMS Silicon Tracker
• An overview of Si detectors (why?, types, relevant parameters,working principle)
• Radiation damage in silicon detectors* Macroscopic Radiation damage in Si detectros* Microscopic Radiation damage in Si
• Effects of microscopic defect on device performance * Strategies to develop radiation hard Si detectors* Experimental studies of radiation damage.
* Macroscopic measurements* Microscopic measurements* Kinetics of defects.
• Summary of my work done for pixel detector (HPAD) development for European Free-electron-laser XFEL at Hamburg, Germany
Ajay K. Srivastava Uni.- Hamburg07/09/2008
OutlineOutline
33
• ZEUS experiment at HERA collider, DESY, Hamburg, Germany: silicon vertex detector, physics
•CMS experiment at CERN, Geneva, Switzerland: silicon tracking detector, detector calibration, GRID computing, physics
• Radiation hard detector research & development
Since the early 1960s our group has been investigating silicon detectors for nuclear spectroscopy and high-energy physics experiments. Our research covers device physics, detector systems, radiation damage and sensor optimization
• Development of pixel detector (HPAD) for European Free-electron-laser XFEL at Hamburg, Germany
07/09/2008 Ajay K. Srivastava Uni.- Hamburg
Activity of Our GroupActivity of Our Group
44
LHC (2008), L = 1034cm-2s-1
(14 TeV pp collider, 25 ns bunch spacing)
Φ(r=4cm) ~ 3·1015cm-2
LHC upgrade:Super-LHC (?), L = 1035cm-2s-1
Φ(r=4cm) ~ 1.6·1016cm-2
• Detector for the European Free-Electron-Laser XFEL at Hamburg (start in 2013): photon fluxes up to: 1016 /cm2 ≙ 109 Gy [109 J/kg]
5 years
2500 fb-1
10 years
500 fb-1
× 5
0 10 20 30 40 50 60r [cm]
1013
51014
51015
51016
Φeq
[cm
-2] total fluence Φeqtotal fluence Φeq
neutrons Φeq
pions Φeq
other charged
SUPER - LHC (5 years, 2500 fb-1)
hadrons ΦeqATLAS SCT - barrelATLAS Pixel
Pixel (?) Ministrip (?)Macropixel (?)
(microstrip detectors)
[M.Moll, simplified, scaled from ATLAS TDR]
Ajay K. Srivastava Uni.- Hamburg 407/09/2008
Main Motivations for R & D on Radiation TolerantMain Motivations for R & D on Radiation TolerantDetectorsDetectors
(2oo ns distance between pulses)
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CMS Silicon Tracker
Ajay K. Srivastava Uni.- Hamburg 507/09/2008
• Finely segmented silicon sensors (strips and pixels) enable charged particles to be tracked and their momenta to be measured. They also reveal the positions at which long-lived unstable particles decay.This part of the detector is the world's largest silicon detector. It has 205 m2
of silicon sensors (approximately the area of a tennis court) comprising 9.3 million microstrips and 66 million pixels.
CMS Silicon TrackerCMS Silicon Tracker
66
•Why Si detectors for particle tracking in High-Energy-Physics Experiments?
1. Fast response 2. High position resolution (~10μm) 3. Reliable operation
•Types: I. Si strip detector (single sided/double sided)II. Si pixel detectorIII.Si pad detector
Ajay K. Srivastava Uni.- Hamburg 607/09/2008
Si DetectorSi Detector
Strip detector Pixel detector Pad detector
77
• Depletion depth and Voltage
• Reverse current = generation current
• Capacitance
• Noise
• Charge collection
Relevant parameters
Ajay K. Srivastava Uni.- Hamburg 707/09/2008
Working principle of Si strip detector (AC coupled)Working principle of Si strip detector (AC coupled)
8Ajay K. Srivastava Uni.- Hamburg 8
• Bulk (crystal) damage due to Non Ionizing Energy Loss (NIEL)- displacement damage, crystal defects/microscopic defect
I. Change of effective doping concentration Neff (higher depletion voltage Vdep) II. Increase of leakage current (increase of shot noise, thermal runaway)
III.Increase of charge carrier trapping (reduced charge collection efficiency (CCE))
• Surface damage due to Ionizing Energy Loss (IEL)
I. Charge build-up in SiO2 (shift of flatband voltage Vfb, II. Traps of Si-SiO2 interface breakdown of critical corners)
III Surface generation current (increase shot noise)
07/09/2008
Macroscopic Radiation Damage in Silicon DetectorsMacroscopic Radiation Damage in Silicon Detectors
99
[TRIM-simulation, G. Davies, RD50 workshop Ljubljana 2008, modified]
Examples for defect reactions:
Ajay K. Srivastava Uni.- Hamburg07/09/2008
Microscopic Radiation Damage in SiliconMicroscopic Radiation Damage in Silicon
(Ek>25 eV)
(Ek>5 keV) I- Interstitials Cs- substitutional C
V- Vacancy Ci – Interstitials C
• Interstitials and vacancies are mobile at room temperature
• 50 keV Si ion with fluence 3 x 1016 cm-2
1010
trapping (e and h)⇒ CCE
shallow defects do not contribute at room
temperature due to fast detrapping
charged defects ⇒ Neff , Vdepe.g. donors in
upper half of band gap and acceptors
close to midgap
generation⇒ leakage current
levels close to midgap
most effective
• Influence of defects on the material and device properties
Ajay K. Srivastava Uni.- Hamburg07/09/2008
Radiation Induced Defects and Impact on Device Radiation Induced Defects and Impact on Device PerformancePerformance
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Strategies to Develop Radiation Hard Si detector Strategies to Develop Radiation Hard Si detector
I. Material/Defect engineering
- Understanding of radiation damage
• Irradiation with different particles and energies• Thermal treatment to understand kinetics• Macroscopic effects to understand detector performance• Microscopic defects and simulation
Improved sensor performance with oxygen rich material.Study different materials : DOFZ, Cz, MCz, EPI-Si
07/09/2008 Ajay K. Srivastava Uni.- Hamburg
II. Device Engineering
- Simulation and study of prototype detectors• n+- in- p• 3D detectors• Thin detectors
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1011 1012 1013 1014 1015
Φeq [cm-2]10-6
10-5
10-4
10-3
10-2
10-1
ΔI /
V
[A/c
m3 ]
n-type FZ - 7 to 25 KΩcmn-type FZ - 7 KΩcmn-type FZ - 4 KΩcmn-type FZ - 3 KΩcm
n-type FZ - 780 Ωcmn-type FZ - 410 Ωcmn-type FZ - 130 Ωcmn-type FZ - 110 Ωcmn-type CZ - 140 Ωcm
p-type EPI - 2 and 4 KΩcm
p-type EPI - 380 Ωcm
[M.Moll PhD Thesis][M.Moll PhD Thesis]
I-V
C-V Effective doping concentration, Neff / Vdep
Dark Current & stability of device
Ajay K. Srivastava Uni.- Hamburg07/09/2008
I. Macroscopic MeasurementsI. Macroscopic Measurements
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TCT Analysis
• Electric field in sensor• Full depletion voltage• Effective trapping time• Charge collection efficiency
M Cz, Φeq = 1x1014 cm-2
-0.05
0.00
0.05
0.10
0.15
0.20
0 5 10 15 20 25 30 35
Time [ns]
curr
ent [
arb.
uni
ts]
100 V80 V60 V50 V40 V
Ajay K. Srivastava Uni.- Hamburg07/09/2008
I. Macroscopic MeasurementsI. Macroscopic Measurements
Electric field in a damaged silicon sensor (Φeq.= 1 x1014 cm-2)
14Ajay K. Srivastava Uni.- Hamburg 14
[K. Koch, diploma thesis 2007, modified]
CCE (Charge collection efficiency) – signal to noise ratio & detector efficiency
0 2.1015 4.1015 6.1015 8.1015 1016
Φeq [cm-2]
0.50
0.60
0.70
0.80
0.90
1.00
CCE
EPI-ST, 72 μmEPI-ST, 72 μmEPI-DO, 72 μmEPI-DO, 72 μmFZ, 100 μmFZ, 100 μmFZ, 50 μmFZ, 50 μm
244Cm source244Cm source5.8 MeV α-particles5.8 MeV α-particles
07/09/2008
I. Macroscopic MeasurementsI. Macroscopic Measurements
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DLTS TSC
07/09/2008
• Concentrations
• Activation energies
• Capture cross sections
Obtained electrical properties of defects:
Ajay K. Srivastava Uni.- Hamburg
II. Microscopic MeasurementsII. Microscopic Measurements
Φeq.≤ 1012cm-2 Φeq. ≤ 1014 cm-2
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Time developments of defects depends on
• Temperature• Impurities
Ajay K. Srivastava Uni.- Hamburg07/09/2008
Kinetics of DefectsKinetics of Defects
• I= I0 + VΦeq. α
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• Test structure: gated diode with 5 gate rings• Only damage in SiO2 and Si-SiO2 interface important
Circuit for I-V and C-V/G-V measurement of gated diode
07/09/2008 Ajay K. Srivastava Uni.- Hamburg
Radiation Damage of Si Detectors by XRadiation Damage of Si Detectors by X--RaysRays
1818Ajay K. Srivastava Uni.- Hamburg07/09/2008
• Nox reaches a maximum at 5MGy and then decreases – why?
Experimental Results on Oxide Charge DensityExperimental Results on Oxide Charge Density
7/10/2008 Ajay K. Srivastava Uni.- Hamburg 19
CC--V Characteristics of MOS CapacitorV Characteristics of MOS Capacitor
C HF, inv
Accumulation
Depletion
Inversion
Cox- Oxide related capacitance (F)
C HF, inv- High frequency inversion capacitance (F)
C fb- Flat band capacitance (F)
Vfb= Øms – Q’ss/Cox
2007/09/2008 Ajay K. Srivastava Uni.- Hamburg
ISEISE--TCAD Simulation of CMOS CapacitorTCAD Simulation of CMOS Capacitor
2107/09/2008 Ajay K. Srivastava Uni.- Hamburg
ISEISE--TCAD Simulation of CMOS CapacitorTCAD Simulation of CMOS Capacitor
2207/09/2008
S./E.= 1.1
Ajay K. Srivastava Uni.- Hamburg
Simulation Result and DiscussionSimulation Result and Discussion
2323Ajay K. Srivastava Uni.- Hamburg07/09/2008
Comparison: Simulation with DataComparison: Simulation with Data
Conclusion: I. Encouraging first result.II. Improve modelling.III. Extend to irradiated sensors.
242407/09/2008 Ajay K. Srivastava Uni.- Hamburg
SummarySummary
1.
High resolution silicon sensors are presently used in all collider experiments
Group has unique expertise and equipment for macroscopic and microscopic radiation damage studies
Detailed simulation for next generation of sensors started
2.
3.