development of radiation hard microstrip detectors for the cbm experiment
DESCRIPTION
Development of radiation hard microstrip detectors for the CBM Experiment. Sudeep Chatterji GSI Helmholtz Centre for Heavy Ion Research CBM Collaboration Meeting 12 April, 2010. CBM Silicon Tracking System Layout. Fluka Simulation. 1m. - PowerPoint PPT PresentationTRANSCRIPT
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Development of radiation hard microstrip detectors for the CBM Experiment
Sudeep Chatterji
GSI Helmholtz Centre for Heavy Ion Research
CBM Collaboration Meeting
12 April, 2010
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CBM Silicon Tracking System Layout
Fluka Simulation
STS has 8 stations of DSSDs, Strip Pitch ~ 58 m, Strip Width ~ 20 m, stereo angle ~ 7.5 0 Expected Radiation Damage ~ 1 x 1014 neq cm-2 year-1
Need detailed simulations to optimize device parameters to maximize VBD and minimize Noise. Also simulation needed to understand the impact of radiation damage.
1m
3
x set by strip pitchy set by stereo angle
3-Dimensional Grid
3-D TCAD simulation tools “SYNOPSYS” Sub packages
SentaurusInspectTecplotSPICE (Mixed Mode)
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Stereo Angle in Strips
X-Y plane of the 3D grid. One can see there is a stereo angle on either side of 7.50.
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Backside View
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Implementing Bias Ring & Resistor
System { Strip sample (nplus1=c1 nplus2=c2 nplus3=c3 nplus4=c4 pplus1=cp1 pplus2=cp2 pplus3=cp3 pplus4=cp4) Vsource_pset vn (dd 0) {dc=0} Vsource_pset vp (dd1 0) {dc=0} Resistor_pset rn1 (c1 dd) {resistance=2000000} Resistor_pset rn2 (c3 dd) {resistance=2000000} Resistor_pset rp1 (cp1 dd1) {resistance=2000000} Resistor_pset rp2 (cp3 dd) {resistance=2000000} } Solve {
Circuit Coupled (Iterations=100) {Poisson} Coupled {Poisson Electron Hole Contact Circuit} Quasistationary ( InitialStep=1e-3 MaxStep=0.025 Minstep=3e-5 Increment=1.2 Goal { Parameter = vp.dc Voltage = -100} Goal {Parameter = vn.dc Voltage=0} ) }
Implementing Pulse Generator (Future Plan) Vsource_pset vin (node1 node2) {pulse=(DCStart Vamp td tr tf tperiod)} Can simulate the entire readout chain
Mixed Mode Simulation (PSpice in TCAD)
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Understanding the Geometry
Using SYNOPSYS TCAD 3-D simulation package Silicon volume ~ Cuboid (Six Rectangular faces). Dopant Implants, P-Stop and Contacts ~ Parallelogram Oxide ~ Cuboid, Enough space needed at the corners for junction curvature (0.8*Junction Depth)
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Determination of full depletion voltage
c
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Determination of full depletion voltage
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Potential & Electric Field Distribution
0 V
50V
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Some Static Characteristics
CTotal = Cback+2*Cint
ENC α CTotal
Optimization needed to maximize breakdown voltage & minimize ENC
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Optimization of W/P & P-Spray Width
When W/P is too small, there is inappreciable impact of ↑ the strip width on VBD
A narrower strip width and a wide P-Spray width can reduce the ENC.
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Optimization of P-Spray Dose
With ↑ in P-Spray dose, the VBD ↓
Using P-Spray rather than P-Stop seems better for detector performance
What happens at high radiation damage?
Mixed Mode Simulation (TCAD + SPICE)
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Radiation Damage in Silicon
The major effect expected from bulk damage is the change in the effective carrier concentration (Neff) leading to Type Inversion.
The change in Neff is parameterized using Hamburg model:
eqK
TtNNTtNTtNNN aeqYeqcaeqAaeqeffeffeff
0/1/1
))(,()())(,())(,(0,
The change in Minority carrier lifetime is parameterized using Kraners model:
For high quality oxide, the value of surface oxide charge (Q f) is expected to be 3e11cm-2 (for non-irradiated detector) while after irradiation Q f increases and saturates at about 1e12 cm-2. Flatband Voltage gives an approx. of Qf.
Year Fluence (assumed each year) x 1014 (neq/cm2)
Integrated Fluencex 1014 (neq/cm2)
Neff x 1012
(cm-3)
1 1 1 - 1.73
2 1 2 - 5.47
3 1 3 - 9.87
4 1 4 - 14.8
5 1 5 - 19.25
6 1 6 - 23.78
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Impact of Radiation Damage
Trap Model, University of Perugia
0.92.5*10-152.5*10-14CiOi Ev+0.36Donor
0.95.0*10-145.0*10-15VVVEc-0.46Acceptor
1.6132.0*10-142.0*10-15VVEc-0.42Acceptor
η (cm-1)σh (cm2)σe (cm2)Trap
Energy (eV)Type VBD ↑ with fluence
Current ↑ by 3 orders Rint ↓ with fluence Detailed study needed
eqcmConc )( 3
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Transient Simulations
Can simulate the passage of Heavy Ion, α-particle and Laser. Can include angle in the passage of MIPs. Plan to do complete scan of interstrip region and compare with test beam data.
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Simulation of Readout Cables
Two connecting layers with constant pitch of 100 m are laminated together with a lateral shift of 50 m. A spacer layer is inserted between the two layers to reduce the capacitance. An external shielding layer is applied to reduce the noise.
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Simulation of Readout Cables
3-D grid of the kapton cable 3-D grid without insulator
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Summary
We need radiation hard Double Sided Silicon Strip detectors. TCAD simulation package, SYNOPSYS has been installed on
CBM batch farm and running. We are doing Mixed Mode simulation using SPICE models
available in Sentaurus. Have procured the Probe Station. Plan to carry out measurements before and after irradiation both
with proton and with neutrons. Carry out systematic annealing studies. Work closely with CiS, Erfurt on microstrip detector R&D.