A Sensitive Floating Gate MOSFET Gamma Ray Dosimeter

A new MOSFET dosimeter consisting of a floating gate sensor transistor and a reference transistor of identical geometry fabricated in close proximity on the same silicon chip is described. Sensitivity is maximized by not overlapping the floating gate with a control gate. The floating gate is precharged prior to irradiation by tunneling. No bias is applied during irradiation. The dosimeter output is the reference transistor gate bias required to give the same drain current in the sensor and reference MOSFETs at the same drain-source bias. Sensitivities up to 3 mV/rad have been achieved. The dosimeter provides excellent first-order temperature compensation. With second-order temperature compensation using an external temperature sensor, doses less than 500 mrad should be resolvable