Tactical army dosimeter based on P-MOS single and dual gate insulators

This paper describes the properties of P-MOS transistors which will be used as ionization dose detectors in an Army RADIAC (radiation detection instrument and calculation) instrument. The application requires that this device correctly measure accumulated ionization-dose in a tactical radiation environment. This means that the detector must be independent of dose rates for a wide range of rates extending from typical Co-60 sources of 1 rad/min up to approximately 1×10⁹ rads (tissue)/s. In addition, it must be insensitive to neutrons, and independent of photon energy over a range from 80 keV to 1 MeV. Dose linearity must be maintained within ±20% out to a dose of 1000 rads (tissue), and for doses ⩽50 rads, the measurements must be accurate within ±15 rads. Two types of MOS technology were studied, one is the standard MOS transistor with a single gate-insulator of silicon dioxide, and the second type is the dual-insulator, consisting of a silicon nitride layer on silicon dioxide. Samples of both device types were tested for dose rate and energy dependence, linearity, and post irradiation effects at room and 55°C temperatures. A flash X-ray machine, pulse burst reactor, a low energy X-ray generator, and radioactive sources of cobalt and cesium were used to determine the properties of these devices relative to the requirements of a tactical environment