Sensitivity of MOS transistors to gamma radiation

Based on experimental results obtained by irradiating Czechoslovak-made MOS transistors of the MH 2009 type using a 137Cs source, a theoretical expression was derived for sensitivity of the MOS system with the P type channel to a low dose of radiation. The sensitivity change was explained dependent on the size and polarity of applied voltage to the MOS system during irradiation. The derived expression shows that the sensitivity limit for high values of voltage Usub(G) is proportional to the squared thickness of the oxide layer while for low voltage sensitivity linearly depends on Usub(G) rather than on the oxide thickness. The results may be used as a criterium for the design of sensitive gamma dosemeters. The use of an MOS dosemeter having an oxide layer thickness about 0.3 μm appears to be optimal offering the possibility of applying positive gate during irradiation because positive voltage gives higher sensitivity at low voltage values. (Ha)