Effect of oxide-trapped charge on the anomalous drain avalanche hot carrier degradation of a SiO2 dielectric nMOSFET

Abstract

This paper presents an investigation of the effect of oxide-trapped charge on the anomalous drain avalanche hot carrier degradation of SiO2 dielectric nMOSFET. In contrast to the conventional degradation behavior, saturation threshold voltage degradation Delta V-th,V-sat sar decreased during the first 2000 s of stress, then increased because the polarity of the charge, which is trapped 60 nm away from the drain, changed from positive to negative over time. During the first 2000 s, the holes generated by impact ionization were transported to similar to 60 nm away from the drain by the lateral field, and were trapped there. Thereafter, the vertical oxide field varied with the change in the energy band diagram and this caused an increase in electron trapping over time. Then interface traps and electron trapping became dominant after 2000 s. To accurately predict the anomalous degradation, a model is proposed that includes an oxide-trapped charge, in addition to the interface traps that is considered in the conventional models.