Dobishuk, V.

Heuser, J.

Kyva, V.

Militsiya, V.

Momot, I.

Panasenko, I.

Pugatch, V.

Teklishyn, M.

GSI Repository

Charge collection in STS silicon microstrip sensors at their surface layer∗I. Panasenko1, V. Dobishuk1, J. Heuser2, V. Kyva1, V. Militsiya1, Ie. Momot1,3, V. Pugatch1, andM. Teklishyn11KINR, Kiev, Ukraine; 2GSI, Darmstadt, Germany; 3Goethe University, Frankfurt, GermanyTo provide radiation tolerant devices for the CBM exper-iment (Silicon Tracker Station) prototypes of silicon mi-crostrip sensors have been produced in two technologies.For the short-long stereo-strips connection, either double-metallization lines (“double metal” sensor) or a single-metallization design with an external microcable (“singlemetal” sensor) have been manufactured. We report here theresults of studies performed for those sensors with the Pu(triplet) alpha-source and laser (640 nm wavelength). Bothmethods provide test of the charge collection at the sensorsurface layer where double metallization is laid out. Mea-surements were carried out exploring discrete electronicsand the fast-slow coincidences setup at KINR. This allowsstudying a charge sharing between adjacent strips of the sil-icon sensor hit by alphas or laser pulses. The degradation ofthe cluster finding efficiency in the vicinity to the double-metal connecting lines in heavily irradiated microstrip sili-con sensors has been observed [1].The CBM05H4 ‘double metal’ and ‘single metal’(HAMAMATSU) sensors were full depleted at 80 V. In atwo-dimensional (Ei x Ei+1) energy distribution of eventsin adjacent strips ‘i’ and ‘(i+1)’ three loci for a 239Pu,238Pu and 233U alpha-particles source are shifted by ∼ 20% to lower energies for the double metallization sensor incomparison with the single metal one. Also the widthsof loci are larger. The evaluation shows that this couldbe explained by the alpha-particles energy loss and strag-gling in the SiO2 isolation layer present only in the sensorwith a second metallization layer. Biasing voltage scan hasdemonstrated expected performance for these sensor types,while CBM06C6 (CiS production) have shown appearanceof the dead layer (∼ 25 µm) in the interstrip gap at fulldepletion voltage.Also measurements with a 640 nm laser beam (7 µmspot) scanned over the sensor area were performed for sen-sors irradiated at the KINR isochronous cyclotron up to the2*1014 1 MeV neq/cm2. Figure 1 shows two dimensionaldistribution of amplitude of charges originated in the inter-strip gap of the CBM05 non-irradiated sensor illuminatedby the scanning laser beam. It demonstrates excellent po-sition resolution achieved: beam spot position is indicatedby figures of 15 µm, 18 µm, 21 µm etc. Figure 2 illustratesdegradation of the charge collection by 30% in the irra-diated sensor (the locus of laser events is shifted to loweramplitudes region). Analysis of data for other sensors is inprogress. Tests with the 90Sr β-source will be made soonexploring the ‘ALIBAVA’ microelectronics readout system.∗Work supported by HIC-for-FAIR.Figure 1: CBM05 – non-irradiated sensor: Laser scan inthe interstrip gap.ADC units (strip i)0 20 40 60 80 100 120ADC units (strip i+1)02040608010012005101520253035404550U = 147 VexpTime = 20 secnEvents = 2682Figure 2: CBM05 – irradiated sensor: Laser scan in theinterstrip gap.References[1] A. Affolder et al., Radiation damage in the LHCb vertex lo-cator, JINST 8 (2013) P08002, arXiv:1302.5259.GSI SCIENTIFIC REPORT 2014 MU-NQM-CBM-31DOI:10.15120/GR-2015-1-MU-NQM-CBM-31 67

Charge collection in STS silicon microstrip sensors at their surface layer

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Charge collection in STS silicon microstrip sensors at their surface layer

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