Effect of Radiation on Interface Traps of SOI NMOSFETs by the Direct-Current Current-Voltage Technique

Abstract

This paper investigates the effect of total ionizing dose radiation on back-gate interface traps in SOI NMOSFETs. The concentration and energy distribution of interface traps at Si/SiO2 back-gate interface of SOI NMOSFETs during irradiation are studied by the direct-current current-voltage technique. When transistors are subjected to radiation, DCIV bulk current increases. The calculated results suggest that the interface trap density increases and its equivalent energy level is far away from the midgap with irradiation dose increasing, which can be explained by the energy distribution of interface traps. The interface trap energy density DIT(EIT) as a function of the energy level EIT has been obtained by the least square optimization and shows the typical “U-shape”distribution. In detail, the rising humps at equivalent energy level in DIT(EIT) curves are due to Si-H bonds that are broken down after irradiation, which corresponds to the increasing trap density. Moreover, it is found that the energy level of interface traps is redistributed after irradiation. The peak of humps in DIT(EIT) curves occurs at the farther energy level with the increase of dose, which is similar to the equivalent energy level. It might arise from the shallow energy level of interface traps induced by radiation.

Keywords

• SOI
• interface traps
• radiation
• energy distribution