Minni Singla & Sudeep Chatterji Goethe University, Frankfurt Development of radiation hard silicon microstrip detectors for the CBM experiment Special Thanks to Neha Sharma, Namarta Joshi, Nidhi Tiwari &Yashika Bansal MITS, India 1

 To develop radiation hard DSSDs tolerant up to 1.2x10 14 n eq cm -2.  Various isolation techniques being explored  p-stop  p-spray  schottky barrier  SYNOPSYS TCAD simulation being used to understand radiation damage and propose an optimized detector design.  To propose a detector design which is best for strip isolation and charge collection efficiency. Motivation 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 electronics Avoid multiple scattering Low material budget Expected Fluence 1.2× n eq cm -2 Radiation hard detectors The Challenge 3

PrototypeIsolation Technique Stereo Angle Double Metallization CBM01Full size Prototypepspray15 0 P-side CBM02-SPIDTechnology waferpstop/pspray CBM03Full size Prototypepspray±7.5 0 Both p & n- side CBM04-FSD01Technology waferSchottky Barrier CBM05 (Upcoming) Resubmission of CBM03 with stacked dielectric (to avoid pin holes), decreased trace resistance for better noise performance CBM prototype detectors CBM strips 5.5 cm CBM02CBM cm Double metal interconnections for short corner strips CiS, Erfurt, Germany 4

Static Characteristics : Significance  Noise  Shot noise (leakage current)  Series capacitive noise ( dominant factor C int for small pitch sensors )  Many components of C int ( C mm, C ii, C mi )  Capacitive load seen by FEE is C mm component of C int  Series resistive noise ( Metal Trace Resistance : 21 Ωcm -1 ) C mm between metal strips C ii between implants C mi between implant and neighbouring metal strip C coupl – coupling capacitance C b – strip backplane capacitance 5

 Charge Collection  better the strip isolation more is the charge collection  Static parameter : Interstrip Resistance (R int )  R int ≥ 100 MΩ for proper isolation  Various Isolation techniques possible : Static Characteristics : Significance Cont.. S1S2S1S2 p-spray p-stop high-field regions Schottky Barrier (CBM04/FSD) S1S2 Modulated p-spray 6

Grids for various Isolation techniques Metal workfunction = 4.28eV Barrier Height = 0.70eV for n-type Barrier Height = 0.58eV for p-type 7

Measured / Simulated Interstrip Capacitance (p-spray Vs. p-stop) Good match after depletion. p-stop is better in terms of series capacitive noise. p-spray 8

Interstrip Resistance for CBM01 (p-spray) Low Leakage currentLow shot NoiseHigh Isolation unirradiated 9

Measured Vs. Simulated FSD (Schottky Barrier) V FD = 35V  V BD ↓ with ↑ in Q F  Q F = 1×10 12 cm -2 (used in simulation), better match possible with higher Q F  Observed breakdown voltage ~ 230 V; Simulated breakdown voltage ~ 250 V 10

Measured / Simulated C-V for FSD (Schottky Barrier) C int for schottky higher than p-spray before full depeletion No isolation observed in measured schottky detectors 11

CCE variation with fluence in Schottky Charge collection efficiency (CCE) degrades with fluence 12

Conclusion / Future Plans  R&D status of current detector development for CBM-STS reported.  Various isolation techniques compared in terms of breakdown performance, charge collection and noise.  Interstrip resistance used to understand strip isolation and hence charge Collection efficiency.  In terms of interstrip capacitance, p-stop seems to be the most efficient isolation technique.  Charge collection efficiency degrades with fluence. 13

Back up 14

CBM02 (p-stop) Measurement Vs. Simulation Irradiated sensors Measured at MSU, M.Merkin et.al. Simulated I-V with Fluence 15

R int Measurement technique & Results for FSD01 16

Low Leakage currentLow shot NoiseHigh Isolation CBM01_Wafer17 CBM01_Wafer20B1 17

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