Vertical GaN Fin Transistors for Power and RF Applications

While lateral HEMTs have traditionally dominated the GaN device market, they are still limited by issues such as current collapse and thermal management. These stem from device structures where current conduction takes place near the surface and is therefore highly dependent on surface conditions. To counteract these limitations, it is necessary to shift from lateral devices to those utilizing vertical current flow. These allow for bulk heat dissipation, area independent breakdown, and reduced dependence on surface states. Here we present our work on creating fin based vertical GaN transistors for 200 V Ka band operation and medium-voltage 600-2000 V power applications. By employing a variable-fin-width based structure, we are able to use device level threshold voltage engineering to study its effects on improving radio frequency RF device linearity. We also demonstrate vertical power transistors with extremely high current density by using a bulk GaN substrate, increasing the drift region to accommodate the larger voltages, and increasing the gate length.