Radiation tests with foxfet biased microstrip detectors

The silicon detectors at the future Large Hadron Collider (LHC) at CERN have to survive large particle fluxes up to a few 1014 particles per cm2. These high fluxes cause dramatic changes in the behaviour of the silicon detectors, like inversion of n-type silicon to p-type silicon. Here, we report on the high-voltage behaviour of silicon mictrostrip detectors up to doses of about 1014 particles/cm2, and the changes in the depletion voltage and inter-strip capacitance. The CMS baseline choice for the biasing element of the AC-coupled microstrip detectors is a polysilicon resistor. The silicon detectors, tested here, are Foxfet biased. We measured the changes in the Foxfet characteristics. Such detectors have been reported to show, after irradiation, a noise which is higher than expected. Using a fast amplifier (PREMUX chip), we also measure a higher noise.