Study of Radiation Damage of Silicon Mecrostrip Detectors

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The most serious effect of the surface radiation damage on silicon microstrip detectors is accumulation of positive charge on the interface of a silicon bulk and silicon oxide which covers the detectors. The positive charge causes the microdischarge. We developed a silicon microstrip detector which is against to the microdischarge. Important points to realize this detector are 1) to make readout strips narrower than implant strips and 2) to implant impurities for strips deeper than before. For the bulk damage, the bulk-type inversion followed by an increase of the full depletion voltage, reduction of interstrip isolation and charge collection efficiency were measured. The relation between these effects was discussed for the first time. This study finishes the fundamental study of radiation damage of the silicon microstrip detector.For fabrication of radiation-hard silicon microstrip detectors, 1) reduction of the micro-discharge, 2) prevention of increasing the full depletion voltage and 3) allowance for the high bias voltage are essential. Such radiation-hard silicon microstrip detectors were produced and tested by irradiation, a pulsed laser and beam tests. We confirm that irradiated detectors up to 1MRad were still alive. These results are applied for production of the silicon microstrip detectors of the vertex detector SVXII which our collaboration are building at Fermi National Accelerator Laboratory. The tracking detector SCT of the ATLAS detector at CERN will also be developed by taking our results into account.