Eschke, J.

Ghosh, P.

Heuser, J.

Niebur, W.

Zumbruch, P.

GSI Repository

Development of a laser test system for the characterization of prototype siliconmicro-strip sensors∗P. Ghosh1, J. Eschke3, W. Niebur2, P. Zumbruch2, and J. Heuser21Goethe University, Frankfurt, Germany; 2GSI, Darmstadt, Germany; 3FAIR, Darmstadt, GermanyFor the characterization and quality assurance of pro-totype micro-strip sensors produced for the CBM SiliconTracking System (STS), a semi-automated infra-red pulsedlaser test system has been developed [1]. The amount ofenergy deposited by the laser light is chosen such, that it isequivalent to charge created by a minimum ionizing parti-cle. The purpose of this investigation is to understand thecharge sharing and uniformity of sensor performance in theinter-strip regions. Two prototype sensor, namely CBM02(double-sided, 256 strips/side, pitch = 50 µm, full read-out)and CBM05 (double-sided, 1024 strips/side, pitch = 58 µm,one-eighth read-out) have been investigated [2]. The stripson the sensors are read-out via self-triggering n-XYTERbased front-end electronics.Figure 1: Schematic representation of the laser set-upFigure 2: Components of Laser Test Stand.The automated tests are performed at several positionsacross the sensor. The laser beam is focused to a spot-sizeof (σspot) ≈ 12 µm. The duration (∼ 5 ns) and power (fewmW) of the laser pulses are selected such that the absorp-tion of the laser light in the 300 µm thick silicon sensorsproduces about 24 000 electrons, which is similar to thecharge created by minimum ionizing particles (MIP). The∗Work supported by HIC-for-FAIR, H-QM and HGS-HIRe.wavelength of the laser is chosen to be 1060 nm because ofthe absorption depth being of the order of the thickness ofthe silicon sensors [3]. Figure 1 shows the measurement setup in a schematic view. Figure 2 shows various componentsinstalled in the laser test stand. The laser beam is transmit-ted through a 6 µm thick optical fibre to a single focusingsystem, which focuses the light to a spot of about 12 µmdiameter. The working distance is about 10 mm [1]. TheFigure 3: Charge sharing function (η) as a function of theposition of the laser spot on one side of the sensor.laser focuser is calibrated to a focused position on the sen-sor surface as a function of the number of strips fired with asignal just above threshold. At this reading the proper focaldistance has been achieved. Figure 3 shows a measurementof the charge sharing function (η) in the inter-strip region.The η function is defined as the ratio of charge collected byeither strip divided by the sum of both. The EPICS devicecontrol is used to control the step motor. A special pro-gram with a user interface has been developed to operateand move with the laser over the active area of the sensorto perform several measurements automatically. The dataacquisition software DABC accesses the motor position in-formation from EPICS. The on-line and off-line analysis isperformed using the Go4 analysis tool.References[1] P. Ghosh, PoS (Bormio 2013) 018, 2013[2] P. Ghosh, J.Phys.: Conf. Ser. 503 012028, 2014[3] P. O’Connor et al., Proc. of SPIE Vol. 6276 62761W-1, p. 2MU-NQM-CBM-36 GSI SCIENTIFIC REPORT 201472 DOI:10.15120/GR-2015-1-MU-NQM-CBM-36

Development of laser test system for the characterization of prototype silicon micro-strip sensors

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Development of laser test system for the characterization of prototype silicon micro-strip sensors

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