Ionizing Radiation Effect on the Electrical Properties of Metal/ultra-thin Oxide/Semiconductor Structures

Abstract

This paper deals with the effects of X-ray radiation (7 Mrad (Si) dose) on the electrical properties of Metal/Oxide/Semiconductor (MOS) structures with ultra thin oxide layer (45 Å to 80 Å), P-type semiconductor (Si), and a chromium gate.

These effects are investigated on the Fowler-Nordheim (FN) conduction and the excess current when the MOS structure is biased with a positive gate voltage (V_g>0) (inversion regime); and on the breakdown field when electrons are injected from the metal (accumulation regime, V_g<0).

By using the theoretical conduction model developed in a previous paper [1], we have found that the FN conduction parameters improve after radiation. We have interpreted this result, by modelling the excess current before and after radiation, by improving the conduction parameters of defects localized in the oxide layer. Thus the defect barrier was increased by 6.5% while the effective area decreased by 68%.

The analysis of the radiation effect on breakdown distribution shows the degradation of the breakdown field after radiation. These results suggest that the ionising radiation can be involved in the formation of another type of defects in the oxide layer that can lead to the breakdown phenomenon but cannot impact the FN conduction mechanism.