Effect of Gate-Oxide Degradation on Electrical Parameters of Power MOSFETs

Gate oxide in power metal-oxide-semiconductor field effect transistors (MOSFETs) degrades over time. The degradation leads to an accumulation of oxide-trapped charges within the gate oxide and an accumulation of interface-trapped charges at the oxide-semiconductor surface of power MOSFETs. Overtime, such charges significantly alter the electrical parameters of power MOSFETs; to observe this, the electrical parameters are utilized as precursors of gate-oxide degradation. The purpose of this paper is threefold: 1) to propose a new online precursor of gate-oxide degradation-the gate plateau time; 2) to demonstrate a simultaneous dip-and-rebound variation pattern of four precursors of gate-oxide degradation: threshold voltage, gate plateau voltage, gate plateau time, and on-resistance; and 3) to compare the shift tendencies of each precursor over the course of gate-oxide degradation. The existing studies of gate-oxide degradation mechanisms and their effects on threshold voltage and mobility reduction were extended to correlate a variation of all four precursors using analytical expressions. The variation patterns were experimentally verified using high-electric field stressing in two different commercial power MOSFETs. The new precursor, the gate plateau time, was found to be a competitive gate-oxide degradation precursor, as it had a higher positive shift than threshold voltage and gate plateau voltage. In addition, the threshold voltage was found to be the most sensitive indicator of the negative shift (dip), while the on-resistance and gate plateau time were found to be the most sensitive indicators of the positive shift (rebound).