Effect of OFF-State Stress and Drain Relaxation Voltage on Degradation of a Nanoscale nMOSFET at High Temperature

This paper investigates the degradation mechanism of a nanoscale n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) that is subjected to OFF-state stress at high temperature and the impact of stress-induced defects on threshold voltage V(th) during drain relaxation. Experimental results indicate that acceptor-like interface traps N(it), positive oxide charges Q(ox), and neutral electron traps were generated by the OFF-state stress. Although the N(it) generated by the OFF-state stress caused an increase in V(th), it did not influence V(th) during drain relaxation at a positive gate voltage. Drain relaxation filled the neutral electron traps and neutralized positive Q(ox)'s, which increased V(th) and decreased the OFF-current significantly. This new observation suggests that the OFF-state stress-induced defects in a nanoscaled nMOSFET should be seriously taken in evaluating the reliability of inverter circuits.