Minni Singla* 1 , Sudeep Chatterji 2 , V.Kleipa 2 , W.F.J.Mueller 2 and J.M.Heuser 2

1. Optimization of rad-hard DSSDs & low-mass readout cables for the CBM-STS Minni Singla*1, Sudeep Chatterji2, V.Kleipa2, W.F.J.Mueller2and J.M.Heuser2 1Goethe University, Frankfurt 2GSI, Darmstadt IEEE Nuclear Science Symposium 2012 31st Oct. 2012

2. The Compressed Baryonic Matter Experiment Transition Radiation Detectors Tracking Detector Electro- magnetic Calorimeter Muon detection System Ring Imaging Cherenkov Detector Silicon Tracking Stations Projectile Spectator Detector (Calorimeter) Vertex Detector Dipole Magnet Resistive Plate Chambers (TOF) M.Singla IEEE-NSS 2012

3. Technological Challenges 10MHz interaction rate  Fast electronics Minimize multiple scattering  Low material budget Expected Fluence 1014 neqcm-2  Radiation hard sensors • Central 25A GeVAu+Au collision • overlaid with GEANT simulation • 10MHz interaction rate • Up to 700 charged particles/evt • Track densities up to 30 cm-2/ evt M.Singla IEEE-NSS 2012

4. Motivation • 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 M.Singla IEEE-NSS 2012

5. Layout of sensor module FEE 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 CABLE n-XYTER parameters (for CBM-STS) fast channel slow channel 200e- +27 e-/pF233e- + 13 e-/pF • 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) SENSORS SECTOR • Cables Manufactured: SE SRTIIE, • Kharkov, Ukraine MODULE M.Singla IEEE-NSS 2012

6. Simulated grids for various Isolation Techniques (SYNOPSYS) Metal workfunction = 4.29eV Barrier height (n-type) = 0.7eV Barrier height (p-type) = 0.58eV M.Singla IEEE-NSS 2012

7. Measured / Simulated Cint p-spray • Good match after depletion • Schottky worse than P-Stop/P-Spray when under-depleted => probably better • if schottky contact is reverse-biased M.Singla IEEE-NSS 2012

8. CCE/Rint, Conventional Vs. Schottky • Schottky discarded (for UNBIASED schottky contact) M.Singla IEEE-NSS 2012

9. Optimized isolation technique • Various combinations for modulated p-spray(@1x1014neqcm-2) • p-stop => region with higher p-dose in modulated p-spray In optimized sensor design V bdtwice C int ~ 25 % M.Singla IEEE-NSS 2012

10. RAPHAEL Validation 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 (Ref: Kazu Hanagaki, NIMA vol.511 2003, 121-123) and simulated results compared with measurements for CBM prototype readout cables. C tot => Capacitance of one trace w.r.t. all other traces M.Singla IEEE-NSS 2012

11. 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. Same radiation length • Using Copper • Same Radiation length • 300 e- less noise ENCtot for 2.2 cm sensor + 50 cm long cable M.Singla IEEE-NSS 2012

12. Simulated/Experimental dB loss Vector Network Analyzer Vout V in Readout Cable (10cm) Cable as a first order low-pass filter M.Singla IEEE-NSS 2012

13. Transmission Losses for CBM readout cable prototype For 30 cm. long cable Simulated I/O pulse 50 cm cable Transmission Coefficient (%) = (Vout / Vin ) *100 Amplitude loss & Broadening of pulse => ballistic deficit M.Singla IEEE-NSS 2012

14. 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 M.Singla IEEE-NSS 2012

15. Thank you M.Singla IEEE-NSS 2012

16. Backup Slide M.Singla IEEE-NSS 2012

17. TCAD Validation (SYNOPSYS) Measured I-V of DSSD having P-Stop Isolation Simulated I-V Characteristic M.Singla IEEE-NSS 2012

18. TCAD Validation Measured/Simulated I-V characteristics of DSSD having Schottky Isolation M.Singla IEEE-NSS 2012

19. Strip Isolation/Interstrip Resistance Operating Voltage Simulated Interstrip Resistance Measured at MSU, M.Merkin et.al. M.Singla IEEE-NSS 2012

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