1. Characterization of double sided silicon micro-strip sensors with a pulsed infra- red laser system for the CBM experiment Pradeep Ghosh 1,2 & Jürgen Eschke 2,3 1 Goethe-Universität, Frankfurt am Main 2 GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt 3 Facility for Antiproton and Ion Research GmbH, Darmstadt

2. Contents Motivation Introduction Measurement setup Calibration of focuser Silicon sensor under test Measurements and results Planned activities and future work 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke2

3. 1. Motivation Band gap in silicon ~ 1.1 eV and Infrared light (1060nm) is equivalent to 1.17 eV Absorption depth of infrared light in silicon is around 500 µm. Silicon sensor is 300 µm thick. 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke3 Infrared light (1060nm ~ 1.17 eV) induces charge of about 24 kilo electrons and is equivalent to 1 Minimum Ionizing Particle. Idea is to mimic in-beam scenario and investigate sensor performance Arnaud Darmont, Aphesa, white paper, 04/2009

4. 2. Introduction Pulsed infrared Laser with ◦ Wavelength : 1060 nm ; Pulse duration : 10ns ◦ Laser current : 41mA ; Laser Power < 5mW ◦ Multi lens focuser: spot-size ~ 13 µm (1 strip/side) ◦ Fully depleted CBM02 double sided strip sensor Initial Goals ◦ To create 24 kilo electrons in the sensor with the help of LASER to mimic the MIP(~176 ADC) and observe sensor response. ◦ Focus the laser spot to fire only1 strip/side and able to scan the whole sensor with step motor. ◦ Understand the charge sharing function in the interstrip region 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke4

5. 3. Set up: Laser test stand 3. Set up: Laser test stand 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke5 Laser Step Motor Focuser Optical Fiber Sensor ReadOut Station Box Interlock

6. 3. Set up : Laser Test Stand 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke6 Focuser CBM02 sensor Optical fiber Coupling: Laser and Optical fiber Laser Nside-nx2Nside-nx0 Pside-nx2 Laser spot

7. 4. Calibration of Focuser Calibration of the Laser focuser was done at various heights(z-position above sensor surface) at different laser currents 43mA ; 45 mA and 48 mA Minimum number of fired strips/side was achieved at point 7 above the reference level. Furthermore, laser can be tuned to focus to 1 strip/side firing position by reducing the laser current. 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke7

8. 5. Sensor under test CBM02 SPID 0-b 006 sensor non irradiated Double sided, 256 strips with 50µm strip pitch. Size : 1.5 cm x 1.5 cm x 300 µm 1 dc pad and 4 ac pads per strip Full depletion Voltage: 70V Operating Voltage: 100 V Leakage current at V(op): 0.5µA Readout via self triggering nXYTER based FEE 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke8

9. 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke9 6. Measurements with Pulsed Laser

10. Strip number Number of hits Strip number Number of hits p-side ADC values Number of hits Channel hits(fired strips) per side 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke10 Digital amplitude with position per side  Equal number of hits on both p and n side of the microstrip sensor  Strip nr.132 on p-side and Strip nr. 122 on n-side is fired.  One strip cluster on both sides of sensor proves that charge collected only by one strip and not been shared by neighboring strips.  ADC counts suggest we are able to induce charge eqv. of 1 MIP. n-side ADC values Number of hits

11. Hit position in the detector 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke11 Sensor Size : 1.5 x 1.5 cm 2 Strip width is 18 µm; Strip pitch is 50 µm. Laser spot size ~ 13 µm Step motor attached to the Laser system has a pitch of few µm. Enabling to investigate the interstrip region.

12. 05-Mar-13 Laser Test Stand: P.Ghosh & J.Eschke12 18 µm 50 µm Charge collected in ADC Distance from the Strip, µm 050 1 MIP Charge Collected at Strip 1 Charge Collected at Strip 2 Charge sharing function- measurement The curve above is just a cartoon

13. Charge sharing function-results Red and Green curves shows the charge collected by individual strip when laser moves in the interstrip region. Blue curve shows the charge sharing function. Results shows a plateau region (10-12 µm) where charge is always shared equally with neighboring strip. 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke13 Preliminary result

14. Planned activities & future work Strip-by-strip characterization of silicon sensors by scanning over it. Preparing and pre-testing prototype sensors for the in-beam measurement. Charge sharing function will be investigated for more prototype sensors. Coupling capacitances will be determined to understand the charge loss to neighboring strips. To run data acquisition (DAQ) for laser scanning of sensors over EPICS. 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke14

15. Thank you for your attention! 05-Mar-13Laser Test Stand: P.Ghosh & J.Eschke15 H35.6 ; A. Lymanets Detector module development for the CBM-STS H35.7 ; M. Singla Study of low mass readout cables for the CBM-STS H35.8 ; T. Balog Performance of prototype module for the CBM-STS H63.1 ; C. Pauly The CBM experiment : Status and outlook H68.7 ; A. Senger FLUKA calculations for the CBM experiment Tue Thu Other interesting talks