Radiation effects in double-sided silicon sensors for CDF

The inner layers of the vertex detector for CDF utilize double-sided silicon strip sensors. Radiation effects that limit the useful life of these sensors have been studied. From a series of irradiations with 8 GeV/c protons and measurements of bulk capacitance of the sensors during annealing, the removable portion of the initial dopant concentration in the silicon is determined to be Nc0=(5.0±0.2)×1011 cm−3. Measurement of this parameter allows a reliable prediction of depletion voltages after irradiation. A second factor suspected to limit the useful life of the sensors was found to be the degradation of interstrip resistance. For the p implanted side of the sensor, interstrip resistances (which begin in the 100 GΩ range) dropped sharply with fluence, reaching 10 MΩ after only about 7×1013 n/cm2. Both factors lead to about the same predicted maximum fluence and thus the same expected sensor lifetime. This lifetime will be long enough to meet the needs of CDF, but perhaps not future experiments.