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.