Radiation Effects in Metal-Oxide-Semiconductor Transistors

The behavior of MOS transistors has been studied in both the ionizing radiation and neutron environments. Included in the study are both depletion and enhancement devices. Behavior in the radiation environment is considered in terms of the circuit application of the devices. Transient response in the flash x-ray enviroment is characterized in the common source configuration as a function of the device operation point and generator inpedance. Analysis of experimental data shows that the radiation induced transient drain current consists of two components, the drain-substrate diode photocurrent and the secondary drain photocurrent. A radiation inclusive small signal equivalent circuit has been established to predict the device response. Predicted responses agree with the experimental data quite well. For permanent damage study, MOS transistor specimens have been irradiated at the Northrop TRIGA reactor at steps of integrated fast neutron flux up to 5 × 1014nvt. Both the degradation of the device small signal parameters and a substantial shift in the dc operating characteristics were observed. The change in the small signal parameter is less when the device is biased at a constant quiescent drain current than when it is biased at a constant gate voltage. Comparison of the behavior of the MOS transistor to the bipolar junction transistor and the unipolar FET is difficult because of the lack of a good circuit criteria. It is felt that, considering the radiation environments, the MOS transistor shows promise as an effective circuit element.