Symmetrical VTH/RON Drifts Due to Negative/Positive Gate Stress in p-GaN Power HEMTs

We investigate the drift of threshold voltage (V
TH
) and on-resistance (R
ON
) in p-GaN power HEMTs after being submitted to negative/positive gate stress. Negative (Positive) Gate Stress (NGS/PGS) was applied at a gate-to-source bias of |V
NGS
| = V
PGS
= 6 V up to a cumulative stress time of 8×10
³
s at room temperature. We found that during NGS both V
TH
and R
ON
increased over stress time, whereas during PGS both parameters decreased and stabilized to the values prior to stress application. This symmetric behavior was maintained after 5 full NGS/PGS stress cycles, indicating the absence of permanent degradation. To further characterize the V
TH
and R
ON
transients, the NGS/PGS stress cycles were repeated at different temperatures (T=30-105 °C). While V
TH
exhibited a strong Τ-dependence (E
A
≈ 0.6 eV) during NGS, a negligible variation of the V
TH
transients with T was found during PGS (E
A
≈ 0 eV). Instead, R
ON
transients exhibited approximately the same T-dependence during both NGS and PGS (E
A
≈ 0.3-0.4 eV).