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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
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Characterization of double sided silicon micro-strip sensors with a pulsed infra-red laser system for the CBM experiment Pradeep Ghosh1,2 & Jürgen Eschke2,3 1Goethe-Universität, Frankfurt am Main 2GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt 3Facility for Antiproton and Ion Research GmbH, Darmstadt
Contents • Motivation • Introduction • Measurement setup • Calibration of focuser • Silicon sensor under test • Measurements and results • Planned activities and future work Laser Test Stand: P.Ghosh & J.Eschke
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. • 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 Laser Test Stand: P.Ghosh & J.Eschke
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 Laser Test Stand: P.Ghosh & J.Eschke
3. Set up: Laser test stand Box Interlock Optical Fiber Step Motor Focuser Laser Sensor Station ReadOut Laser Test Stand: P.Ghosh & J.Eschke
3. Set up : Laser Test Stand Laser Pside-nx2 Coupling: Laser and Optical fiber Optical fiber Focuser Laser spot Nside-nx0 Nside-nx2 CBM02 sensor Pside-nx2 Laser Test Stand: P.Ghosh & J.Eschke
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. Laser Test Stand: P.Ghosh & J.Eschke
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 Laser Test Stand: P.Ghosh & J.Eschke
6. Measurements with Pulsed Laser Laser Test Stand: P.Ghosh & J.Eschke
Digital amplitude with position per side Channel hits(fired strips) 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. Number of hits Number of hits Number of hits Number of hits p-side n-side Strip number Strip number ADC values ADC values Laser Test Stand: P.Ghosh & J.Eschke
Hit position in the detector Sensor Size : 1.5 x 1.5 cm2 • 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. Laser Test Stand: P.Ghosh & J.Eschke
Charge sharing function- measurement 18 µm 1 MIP Charge collected in ADC 0 50 Distance from the Strip, µm Charge Collected at Strip 1 Charge Collected at Strip 2 The curve above is just a cartoon 50 µm Laser Test Stand: P.Ghosh & J.Eschke
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. Preliminary result Laser Test Stand: P.Ghosh & J.Eschke
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. Laser Test Stand: P.Ghosh & J.Eschke
Thank you for your attention! Other interesting talks H35.6 ; A. Lymanets Detector module development for the CBM-STS Tue 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 Thu H68.7 ; A . Senger FLUKA calculations for the CBM experiment Laser Test Stand: P.Ghosh & J.Eschke
