GaN Gate Injection Transistors moving toward Commercialization

The development status of GaN-based Gate Injection Transistors (GITs) with p-type gate over AlGaN/GaN hetero-junction that operate as normally-off devices with very low on-resistances was reported by Dr. Tetsuzo Ueda during the recent IEEE International Electron Devices Meeting in a paper titled "GaN-based Gate injection Transistors for Power Switching Applications" and prepared by a team of researchers from the Green Innovation Development Center, Automotive and Industrial Systems Company, Panasonic Corp. The team expects that further improvement in the performance of these devices will lead to their widespread use. The paper described recent developments and future expectations.

The three main areas of focus included; developments in epitaxial technology, progress in device and processing technologies, and assembly/packaging considerations. Recent progress in epitaxial technology has enabled wafer diameters up to 8 inches. This is a critical threshold to support the fabrication of cost-effective GaN GITs.

Turning to developments in devices, the authors pointed out the use of an InAlGEaN/GaN hetro structure enables reductions in on-resistance as well as supporting an increased maximum drain current while maintaining a threshold voltage of 1.1V. The reduction in on-resistance is expected to greatly help to reduce conduction losses in switching power converter circuits.

In addition, improved lateral device structures reduce the gate capacitances and the channel resistances enabling faster switching. The authors described an integrated point of load dc-dc converters that included two 30V GITs and two gate drivers. Operation between 1MHz to 3MHz was described with peak efficiencies of 88.2% at 2MHz for a 12Vdc to 1.8Vdc conversion.

The authors also noted that “how the GITs are packaged is a critical issue to enable faster switching.” For example, parasitic inductance for 600V GITs is reduced from 25nH for TO-220 packaged devices to only 2nH for flip-chip devices. The flip-chip devices were used in a simulation for the dc-dc boost converter section of a bridgeless power factor correction circuit. The 3kW design achieved a maximum efficiency of 99.3% when operated at 1kW. “GITs with these technologies (improved epi, more-refined device structures and advanced packaging) are very promising for future energy-efficient power electronics,” the paper concluded.