Study of the Transient Radiation Response of Thin Film Field Effect Transistors

The effects of transient gamma radiation on thin film insulated gate field effect transistors have been studied. N-and p-channel thin film epitaxial silicon nonjunction devices on insulating sapphire substrates manufactured by Autonetics have been irradiated in the study. The experimental work was performed using a 600 kev flash X-ray. The devices were irradiated in a common source test circuit configuration. A vacuum chamber operated at a pressure of 10-5 Torr was used to eliminate air ionization effects. All data were obtained at a dose of 1.0 rad (LiF)/pulse. The reproducibility of the radiation pulse was monitored by a PIN diode photodetector. The effect on the drain current of transient voltages generated in the gate circuit was observed by varying the external gate resistance. In n-type devices, the drain current transient increased with increasing gate resistance, indicating a positive gate voltage transient. In the p-type devices, there was a transient decrease in the drain current. The magnitude of these signals increased with increasing gate resistance. These data indicate the generation of a positive transient gate voltage in both the n- and p-channel devices. The same data are shown in a nitrogen atmosphere to show the effects of gas ionization leakage currents. Using standard techniques to measure the effect of radiation on the gate dielectric, no conductivity through the dielectric could be detected. Electron emission currents were the predominant effect in the gate circuit.