The Effects of Gamma Radiation on Glass Coated Silicon Transistors

It has previously been found that semiconductor devices employing various gas encapsulation techniques exhibited significant alterations of their electrical responses under gamma and neutron exposure. Since the neutron bombardment produces bulk or volume damage, the device surface environment has little effect on the neutron induced changes. It has been observed that gamma exposures at doses well below the threshold for permanent damage have caused changes in several electrical characteristics of transistors and diodes which may be described as of surface origin. The parameters exhibiting significant change are the transistor ICBO and the reverse biased diode leakage current. This paper will describe the results of experiments performed to study the effects of exposure to gamma radiation on selected silicon transistors when coated with a low temperature melting glass. The surface sensitive parameters of the coated transistors degraded to a much lesser extent than observed for the gas encapsulated units, indicating a more favorable surface environment to minimize the effect of gamma radiation. Comparison of the glass coated transistors with devices employing a planar structure incorporating a silicon-oxide coating on the device material surface yielded comparable results. The results of these experiments are consistent with the model proposed to explain this effect and its various ramifications.