Development of MOS-FET dosimeters for use in high radiation fields

Several sets of MOS-FET dosimeters dedicated for use in high dose environments at particle physics experiments and nuclear reactors were produced by NURDAM. Various oxide thicknesses ranging from 40 nm to 800 nm were employed to study sensitivity and dynamic range of the dosimeters. The sensors were exposed to ionization doses up to almost 700 kGy of reactor gamma-rays in two different ways; several sets of sensors were exposed in steps to fixed doses and read out in-between, while one set was continuously measured during the irradiations. A calibrated ionization cell in combination with precise simulation of the radiation environment in the reactor was used to accurately determine the dose received by the sensors. The agreement between sets of samples irradiated in different irradiation channels, hence dose rates, and different readout schemes was found to be very good. The dependence of the threshold voltage on the received dose was characterized over the entire range of doses. Sensitivity, dynamic range, saturation and breakdown voltages of sensors were investigated. After the irradiations, isothermal annealing at various temperatures took place to determine the sensor response over the extended periods of time in low dose rate fields.