MOS-capacitor-based ionizing radiation sensors for occupational dosimetry applications

Presented is the first accumulating capacitive radiation sensor for low-dose, long-term exposures observed in occupational dosimetry. The sensor's capacitance-voltage curve undergoes a semi-permanent negative shift due to ionizing radiation. By measuring the change in capacitance at a given voltage in the depletion region, the ionizing radiation that has been present on the sensor can be extracted. In order to achieve the low dose resolution required (less than 100 μGy) for occupational dosimetry, parameters such as the oxide thickness and annealing conditions are optimized. The result for a 2 mm × 2 mm sensor is 1.6 fF per 100 μGy, a capacitance shift detectable with commercial electronics.