Hot-electron reliability improvement using perhydropolysilazane spin-on-dielectric passivation buffer layers for AlGaN/GaN HEMTs

We investigate the effects of perhydropolysilazane spin-on-dielectric (SOD) buffer layer adopted prior to Si3N4 passivation on the dc drain current level and degradation after the electrical stress in the AlGaNGaN high electron mobility transistors (HEMTs). The SOD-buffered HEMTs show ~1.6 times greater drain current densities (~257 mA/mm) than those of the devices with conventional-Si3N4 passivations (~155 mA/mm). After the hot electron stresses (step-wise and constant) applied to the devices, it is also found that the SOD-buffered structure produces greatly improved device reliability in terms of the dc current collapse (15% for step-stress and constant stress) compared to the conventional structure (25% for each case). We propose that the enhancement of SOD-buffered structure in dc current collapse is due to the reduction in surface state density at the passivation interface and the suppressed electron trapping.