Ionizing Radiation Effects on Silicon-on-Sapphire Devices and Silicon Dioxide Films

This report describes results of several related studies of ionizing radiation effects on silicon-on-sapphire devices and on silicon dioxide films. In the SOS investigation, emphasis was placed on the study of radiation-induced back-channel leakage current and on a comparison of devices with wet and dry gate oxides. Differing behavior for wet and dry devices is accounted for in terms of a larger density of hole traps in the sapphire for dry transistors as compared to wet units. SEM studies reveal that energy must be deposited in the sapphire before significant increases in leakage current will occur. In addition, such studies indicate that energy deposition deep in the sapphire bulk is relatively unimportant in producing leakage current. A process of radiation-induced reduction of leakage current was observed in which this current can be dramatically reduced to near its pre-irradiation value by simply reducing the applied drain bias to zero and continuing the irradiation. Models for radiations effects on SOS devices are presented. Measurements of the temporal, temperature, and electric-field dependences of radiation-induced charge transport have been performed for radiation-hardened SiO2 films.