High Temperature RF Characterisation of SiN Passivated and Unpassivated AlGaN/GaN HFETs

AlGaN/GaN heterojunction field effect transistors were tested at elevated temperatures, up to +180 °C, to determine the effect on the device performance. Ageing of the device during these measurements was also studied. A comparison between devices fabricated with and without silicon nitride surface passivation was made. For devices with surface passivation, both fT and fmax reduce with increasing temperature. This is different from the behaviour of the devices without surface passivation. In these devices, there is an initial increase in both fT and fmax. Above 70 °C, any further increase in temperature causes a reduction in both fT and fmax. When devices are allowed to cool to room temperature and are subsequently re-measured, they show an increase in fT and fmax from the values initially recorded; thus indicating some form of device anneal.