In this study, the thermal characteristics of AlGaN/GaN HEMTs with different channel widths were investigated. The thermal characteristics including threshold voltage, maximum transconductance (g
m,max), on-state current, and on-resistance were investigated from 30 to 150 °C with the increment of 10°C. All devices have the same source, gate and drain widths, but difference in the channel widths. The channel width (W
channel) is determined by a current blocking region between the source and drain. Device A is a conventional device with gate width (W
G) of 50 mm without the current blocking region. Therefore, the channel width is the same as the gate width. Device B, C, and D have the gate width of 50 mm but different channel widths of 27.5, 25, and 12.5 mm, respectively. The dimension of the channel width was implemented by ion-implantation at the process step of device isolation. All epitaxial layers were grown on Si substrate. All devices were passivated by a 200-nm PECVD SiN without field plates. The devices under test are with a gate-source distance (L
GS) of 4-µm, a gate length (L
G) of 2-µm, gate width (W
G) of 50-µm, and a gate-drain distance (L
GD) of 10-µm.
At room temperature, device B, C, and D with smaller channel widths show the improved on-state current density, subthreshold swing, and gm. Device D shows a gm,max of 239 mS/mm compared to the 127 mS/mm of the device A. A significant improvement was observed in gm,max of device D due to the large ratio of WG/Wchannel. A better capability of the gate control is achieved. However, the thermal characteristics show the opposite trend. The measured thermal coefficients of the threshold voltage, gm,max, on-state current, and on-resistance of the device D are 2.1´10-4, -6.7´10-3, -3.4´10-3, and 1.1´10-2 1/°C compared with 1.5´10-5, -1.4´10-3, -2.1´10-3, and 7.2´10-3 1/°C of the device A. The possible reason is due to the current crowding at the corners of the blocking region. A suitable heatsink design or back side via are required to reduce the thermal impact.
