Analysis of slow-current transients or current collapse in AlGaN/GaN HEMTs with field plate and high-k passivation layer

We study how the dielectric constant of passivation layer epsilon r and field-plate related parameters (its length LFP, passivation-layer thickness Ti) affect the reduction rates of drain current arising from drain lag, gate lag and current collapse in AlGaN/GaN HEMTs. We plot the current-reduction rates versus Ti for different epsilon r. It is indicated that depending on epsilon r, the drain-lag and current-collapse rates take minimum at certain Ti. When epsilon r is 7, 20, 30 and 50, the current-reduction rates become minimum at Ti = 0.03, 0.1, 0.1, and 0.2 mu m, respectively. Hence, at the minimum point, epsilon r/Ti which is proportional to capacitance of the passivation layer takes a nearly constant value at 250 +/- 50/mu m. At this value of Ti, the lags and current collapse are reduced when LFP becomes long for every epsilon r considered here.