Statistical mechanics based model for negative bias temperature instability induced degradation

A physics based model for negative bias temperature instability (NBTI) induced degradation is proposed. Like previous models, this model attributes NBTI to depassivation of Si–H bonds at the SiO2∕Si interface. The two distinguishing features of the proposed model are: (i) statistical mechanics is applied to calculate the decrease in interfacial Si–H density as a function of stressing conditions, and (ii) hydrogen diffusion in the oxide is assumed to be dispersive and the diffusing species is identified with the positively charged hydrogen ion (Hi+). The model assumes that as Hi+ diffuses away from the interface into the oxide, interfacial and bulk traps are created. Based on these model assumptions, an equation for the threshold voltage shift (ΔVt) is derived as a function of stressing time, oxide field, temperature, oxide thickness, and initial Si–H density at the interface. The model predicts that ΔVt would increase with a power law dependence at earlier stressing times and would saturate at longer time...

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