Eschke, J.

Ghosh, P.

Heuser, J.

GSI Repository

Quality assurance of CBM-STS silicon micro-strip sensors using pulsedinfra-read laser∗P. Ghosh1, J. Eschke2, and J. Heuser31Goethe University, Frankfurt, Germany; 2FAIR, Darmstadt, Germany; 3GSI, Darmstadt, GermanyThe Silicon tracking system (STS) of the CBM ex-periment is aimed to reconstruct the trajectories of thehundreds of charged particles created in heavy-ion colli-sion, and to determine their momenta with a resolutionof around ∆p/p ≈1%. This precision is prerequisite forhigh-resolution mass measurements of e.g. rare probesand implies a thin detection system, with high-resolutionspace-point measurement and capable of interaction ratesup to 10 MHz. The STS will comprise 1220 silicon micro-strip sensors from which 896 detector modules will be con-structed [1]. Quality assurance of the sensors is an impor-tant pre-requisite for the detector module production as theassembly steps are non-reworkable to a good extend. Thesetests can be either invasive or non-invasive as explained be-low. From the results entered into a database, one can iden-tify sensors or detector modules with certain characteristicsand grade them according to their performance.Figure 1: Amplitude response of a few strips from a detec-tor module scanned with a laser spot.Invasive methods are the characterization with methodsthat require physical contact of probes to the objects. Theimportant features are: (i) this allows detailed analyses ofthe device under test (DUT), (ii) this leaves scratches ormarks on the surface, (iii) this is limited to sensors, not todetector modules, (iv) this method involves passive electri-cal measurements using a wafer prober and micro-probingneedles [2].Non-invasive methods are the characterization withmethods that do not require physical contact of probes. Theimportant features are: (i) a few significant parameters ofthe DUT can be investigated, (ii) this leaves no scratches ormarks on the surface, (iii) this is not limited to bare sensorsbut can be applied to detector modules, (iv) this method in-∗Work supported by HIC-for-FAIR, H-QM and HGS-HIRe.volves injection of localized charge using a pulsed infra-redlaser [3].The laser test stand (LTS) is developed with the ideato perform key quality assurance tests on silicon detec-tor modules. The significant parameters that can be anal-ysed or investigated using the LTS are: (i) Uniformityof charge collection (or strip integrity) from scanning thestrips. An example of such laser scan is shown in Fig. 1.(ii) Operation voltage from the bias scan. An example ofcharge collection as function of the bias voltage is shownin Fig. 2 (a). (iii) Charge coupling to neighbour and next-neighbour strips from bias scan. An example is shown inFig. 2 (a). (iv) Ratio of AC-coupling to inter-strip capac-itance from amplitude response at specific positions. Anexample is shown in Fig. 2 (b). (v) Charge sharing func-tion (η) in the inter-strip region can be determined. Fig-ure 3 shows η-function dependence with the position of thelaser spot.(a) (b)Figure 2: a) Operating voltage determination and chargesharing between neighbouring and next to neighbouringstrips and b) Ratio of coupling to inter-capacitance.(a) (b)Figure 3: Charge sharing measurements in the inter-stripregion of a silicon detector module: a) p-side and b) n-side.References[1] P. Ghosh, J.Phys.: Conf. Ser. 503 012028, 2014[2] P. Ghosh, PoS (Bormio 2013) 018, 2013[3] P. Ghosh, CBM Progress Report 2013, Darmstadt 2014, p. 48GSI SCIENTIFIC REPORT 2014 MU-NQM-CBM-35DOI:10.15120/GR-2015-1-MU-NQM-CBM-35 71

Quality assurance of CBM-STS silicon micro-strip sensors using pulsed infra-read laser

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Quality assurance of CBM-STS silicon micro-strip sensors using pulsed infra-read laser

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