Bias dependence of buried oxide hardness during total dose irradiation

Abstract

Direct correlation is reported between single-transistor back channel leakage and the anomalous increase in 16 K-SRAM standby current after total dose irradiation. 16 K-SRAMs fabricated on SIMOX (separation by implantation of oxygen) substrates were total-dose tested up to 10 Mrad (SiO/sub 2/) using an ARACOR X-ray source with zero substrate bias. Different bias conditions were examined to determine the worst case condition for the buried oxide. The worst bias condition for back channel buried oxide threshold voltage shift is when irradiated with zero substrate bias. The standby current hump of the 16 K-SRAM after total dose irradiation can be directly correlated with the NMOS transistor back channel leakage current. Reduction of standby current with increased total dose can be explained by the buildup of interface charge which reduces the back channel leakage.<>