Minni Singla*1, Sudeep Chatterji2, V.Kleipa2, W.F.J.Mueller2 and J.M.Heuser2

1Goethe University, Frankfurt2GSI, Darmstadt

IEEE Nuclear Science Symposium 201231st Oct. 2012 1

DipoleMagnet

The Compressed Baryonic Matter Experiment

Ring ImagingCherenkovDetector

Transition Radiation Detectors

ResistivePlate Chambers(TOF)

Electro-magneticCalorimeter

SiliconTrackingStations

Tracking Detector

Muondetection System

Projectile SpectatorDetector(Calorimeter)

VertexDetector

M.Singla IEEE-NSS 2012 2

• Central 25A GeV Au+Au collision overlaid with GEANT simulation• 10MHz interaction rate• Up to 700 charged particles/evt• Track densities up to 30 cm-2/ evt

10MHz interaction rate Fast electronicsMinimize multiple scattering Low material budgetExpected Fluence 1014 neqcm-2 Radiation hard sensors

Technological Challenges

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To develop low-mass, low noise system of rad-hard DSSDs and signal transmission line

Double Sided silicon Strip Detectors Radiation hard DSSDs tolerant up to 1014 neq cm-2

Loss of Charge Collection efficiency with fluence Any increase in Capacitive/Resistive Noise? Continuous need of increased operating voltage limited by breakdown Comparison of various Isolation techniques to optimize DSSDs

performance Readout cables

Low material budget Minimize ENC Comparison of various designs in this direction Expected transmission losses

Motivation

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Layout of sensor module

MODULE

AC coupled Double Sided Senors by CiS, Erfurt Germany p+ strips on n-type bulk n+ strips with p-stop, p-spray, schottky metal Orthogonal strips Sensor thickness: 300 m

With Hamamatsu, Japan (in preparation)

CABLECABLE

FEE

SENSORS

SE

CT

OR

Series Capacitive Noise (ENCc) C tot => Total capacitance (sensor+cable) a + b×C tot e- R s => Series resistance (sensor+cable) τ => Shaping time Series Resistive Noise (ENCRs) I => Leakage Current 24×Ctot (pF) ×√{Rs (Ω) / τ (ns)} e- R s => Parallel resistance

Shot Noise (ENCI) 108×√{I(μA).τ(ns)} e-

Parallel Resistive Noise (ENCRp) 24×√{τ (ns)/ Rp(MΩ)} e-

(ENCtot)2 = (ENCc)2+(ENCRs)2+(ENCI)2+(ENCRp)2

Ref.: C. Bozzi, ”Signal-to-Noise evaluations for the CMS Silicon Microstrip Detectors,” CMS note

1997/026

n-XYTER parameters (for CBM-STS)fast channel slow channel 200e- +27 e-/pF 233e- + 13 e-/pF

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Cables Manufactured: SE SRTIIE, Kharkov, Ukraine

Simulated grids for various Isolation Techniques (SYNOPSYS)

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Metal workfunction = 4.29eVBarrier height (n-type) = 0.7eVBarrier height (p-type) = 0.58eV

p-spray

Measured / Simulated Cint

Good match after depletion Schottky worse than P-Stop/P-Spray when under-depleted => probably betterif schottky contact is reverse-biased

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CCE/Rint, Conventional Vs. Schottky

Schottky discarded (for UNBIASED schottky contact)8M.Singla IEEE-NSS 2012

Various combinations for modulated p-spray(@1x1014neqcm-2) p-stop => region with higher p-dose in modulated p-spray

p-spray dose (cm-3)

1×1015

(Very low dose)4×1016

(Low Dose)8×1016

(Medium Dose)12×1016

(High Dose)

p-stop width (μm)

Vbd (V)

Cint (pF cm-1)

Vbd

(V)Cint

(pF cm-1)Vbd

(V)Cint

(pF cm-1)Vbd

(V)Cint

(pF cm-1)

n-side p-side n-side p-side

n-side p-side n-side p-side

5 1125 1.56 1.75 490 2.40 1.75 210 2.46 1.76 161 2.47 1.77

10 1125 1.5 1.75 480 2.40 1.75 205 2.46 1.76 160 2.47 1.77

15 1150 1.6 1.75 488 2.37 1.75 205 2.43 1.76 160 2.47 1.77

20 650 2.09 1.75 450 2.51 1.75 205 2.42 1.76 160 2.47 1.77

Isolation

Technique

Fluence

(neqcm-2)

Vbd

(V)

Cint

(pFcm-1)

CCE

(%)

P-stop 2x1013

1x1014

800

610

2.08

2.09

93.15

88.87

P-spray 2x1013

1x1014

513

495

2.56

2.44

93.17

89

Optimized Modulated

P-spray

2x1013

1x1014

1600

1150

1.58

1.60

93.22

89

Optimized isolation technique

In optimized sensor design V bd twice

C int ~ 25 %

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εrANSYS (pF/cm)

RAPHAEL simulation

(pF/cm)

Relative diff .

1 0.328 0.337 2.2%

2 0.449 0.440 2.2%

3 0.566 0.531 6.1%

Package used : RAPHAEL (sub-package of SYNOPSYS)Validation of Package Used : a cable in the D0 silicon tracker simulated with the ANSYS simulations code, have been reproduced

and simulated results compared with measurements for CBM prototype readout cables.

Layers C tot (pF/cm)

Measured Simulated

Layer1 1.06 0.93

Layer 2 1.07 0.95

C tot => Capacitance of one trace w.r.t. all other traces

(Ref: Kazu Hanagaki, NIMA vol.511 2003, 121-123)

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Trace width* trace height

(μm*μm)Trace material

Capacitance (pF/cm)

Resistance (Ohm/cm)

Radiation length (%X0 )

Noise (ENCtot)e -

Slow shaper

Fast shaper

28*14 Aluminum 0.76 0.72 0.10 951 1922

Copper 0.76 0.43 0.15 932 1850

16*8 Aluminum 0.60 2.20 0.095 899 1892

Copper 0.60 1.31 0.11 856 1734

46*14 Aluminum 0.95 0.44 0.11 1077 2195

Copper 0.95 0.26 0.18 1062 2139

Same radiation length

Using Copper Same Radiation length300 e- less noise

Dependence of noise on trace geometry and material

However, when basing the electrical interconnection on tab bonding, the copper variant can not be applied, as opposed to the aluminum that is approved for wedge bonding the cable directly onto the silicon microstrip detectors or the front-end chip.

For now still working with the CBM prototype cables with Aluminum traces.

11M.Singla IEEE-NSS 2012ENCtot for 2.2 cm sensor + 50 cm long cable

Simulated/Experimental dB loss

Cable as a first orderlow-pass filter

V in

Vout

Readout Cable (10cm)

Vector Network Analyzer

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Transmission Losses for CBM readout cable prototype

For 30 cm. long cable

Transmission Coefficient (%)= (Vout / Vin ) *100

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Amplitude loss & Broadening of pulse=> ballistic deficit

Simulated I/O pulse 50 cm cable

Summary

TCAD tool SYNOPSYS used to design rad-hard DSSDs & low-noise system

New isolation technique “Schottky Barrier” compared with conventional isolation techniques

Optimized design of DSSD tolerant upto 1014 neq cm-2 and having low ENC proposed

Design optimization done for readout cables to reduce material budget and ENC

Expected dB loss for readout cables simulated and validated with measurements

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TCAD Validation (SYNOPSYS)

Measured I-V of DSSD having P-Stop Isolation Simulated I-V CharacteristicM.Singla IEEE-NSS 2012 17

TCAD Validation

Measured/Simulated I-V characteristics of DSSD having Schottky IsolationM.Singla IEEE-NSS 2012 18

Strip Isolation/Interstrip Resistance

Measured at MSU, M.Merkin et.al. Simulated Interstrip Resistance

Operating Voltage

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CCE Validation

G.Casse et. al., IEEE Trans. Nucl. Sci.,vol..55 (3), 2008, pp.1695 M.Singla IEEE-NSS 2012 20