Degradation of silicon AC-coupled microstrip detectors induced by radiation damage

Results are presented showing the radiation response of FOXFET (field-oxide field effect transistor) biased AC-coupled microstrip detectors and related test patterns to be used in the CDF microvertex detector. The radiation tolerance of detectors to gamma and proton irradiation has been tested, and the radiation induced variations of the DC electrical parameters have been analyzed. The long-term post-irradiation behavior of detector characteristics has been studied, and the relevant room-temperature annealing phenomena have been considered. The main radiation damage effects after gamma or proton irradiation of FOXFET biased microstrip detectors consist of an increase of the total leakage current, while both the detector dynamic resistance and FOXFET switching voltage decrease. No radiation-induced variation of the strip self bias Vso is measured up to 1 Mrad. The above variations are due to the generation of Si/SiO₂ interface traps and positive charge accumulation in the oxide film, as confirmed by C-V measurements on MOS capacitors