Power devices based on GaN-based wide-bandgap semiconductor devices using AlGaN/GaN heterostructures offer the potential to replace existing Si-based devices because of their advantageous material properties, such as high electron saturation velocity, high critical electric field, high electron mobility, and high carrier densities. Conversely, the manufacturing cost of GaN-based power devices is higher than that of Si-based devices. For the lower-cost manufacturing of devices, the critical areas of development include an efficient high throughput fabrication process with low-cost large-area substrates, and a high wafer utilization efficiency by increasing the number of active devices per area.

We develop 3D structured AlGaN/GaN power transistors by employing a multilevel metallization structure, which demonstrates the potential of the multilevel metallization structure as a key processing technology to improve the output power as well as wafer utilization efficiency.

Wide-bandgap III-nitride (III-N) materials are a promising candidate for high-power and high-temperature operation in flexible electronics, attributing to their superior properties such as high saturation velocity, sheet charge concentration, breakdown field, and thermal conductivity. A III-N thin-film structure on a wafer substrate can be transferred onto a flexible substrate to realize flexible devices by separating the thin film from the original wafer. Flexible AlGaN/GaN transistors have been developed for potential high-power applications. Whereas thermal management is the most probable cause of the negative differential conductance, as it is for high-power flexible light-emitting diodes and high-power switching and conversion HFETs.

We perform systematic studies on the thermo-electronic behaviors in flexible AlGaN/GaN HFETs as well as the dominant origin of the negative differential conductance in flexible AlGaN/GaN HFETs. We develop high-power transistors by suppressing the negative differential conductance using chemical lift-off (CLO) and modified metal bonding processes.

For improving the power of AlGaN/GaN HFETs, the various fabrication technologies such as surface-state passivation, source field-plate structure, and bonding pad-above-active structure have been reported. These technologies successfully improved the output power of AlGaN/GaN HFETs because of increased 2DEG concentration and enlarged active area. On the other hand, the improved output power of AlGaN/GaN HFETs can be drastically reduced after the TO-220 plastic package because of the filler-induced mechanical stress and the passivation layer cracking/metal deformation.

We develop inorganic/organic dual layers as a passivation layer for the AlGaN/GaN HFETs on Si substrates, in order to prevent the output power drop of the HFETs after TO-220 plastic package. The organic layer can endure the filler-induced mechanical stress, and the inorganic layer can prevent the diffusion of organic material during the curing process.