Metal Nitride Oxide Semiconductor (MNOS) Dosimeter.
DEPARTMENT OF THE AIR FORCE WASHINGTON DC
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This patent discloses a high radiation level dosimeter capable of measuring total ionizing radiation doses from gamma ray, X-ray, or E-beam sources by detecting charge variations in the gate structure of a metal nitride oxide semiconductor MNOS type transistor. The MNOS device displays a unique combination of characteristics allowing the storage, removal and measurement of the electrical charge trapped within its gate structure. The magnitude of the charge remaining is ascertained by measuring the threshold voltage necessary to produce a prescribed output current response, while the rate at which this charge decays is dependent on both the elapsed time and total ionizing radiation dose. Since the time and radiation dose effects on the charge are independent and cumulative, the device is capable of being subjected to high radiation doses without permanent effects, and the electrical performance of the device is repeatable to a high degree of accuracy, isolation and measurement of the total radiation dose is readily discernible from the MNOS response. After calibration the device is restored to its unradiated state and subjected to the ionizing radiation source of unknown level, while both the MNOS device response and the elapsed time are recorded. The total ionizing radiation dose administered by the source being measured is obtained by referring to the calibration results containing responses independently attributable to time and total ionizing radiation dose.