|
Over the past decade, the performance of GaN power devices has rapidly improved. There are two types of devices currently being developed, with either a lateral or a vertical structure. Though mainstream GaN power devices have still a lateral structure, vertical structure devices that is on GaN power devices have recently attracted additional research attention. The vertical structure has the advantages of a small chip size, easy wiring, a high breakdown voltage, and current-collapse-free operation. These characteristics are highly suited for high-power applications, for example, to control high-power motors used in electric automobiles.
Though recent reports showed high performance of the vertical structure, the development issues of the fabrication process still remain. The main issue is the quality of GaN substrates. Recent substrates have sufficient quality for high-voltage experiments like fabricating high-voltage devices, which make possible to obtain high-voltage devices over 1kV. However, the entire GaN substrate area does not yet have a uniform quality. It is the large issue. Other important issue is a normally-off gate structure and the gate insulator. Gate structure of the threshold voltage of > 3V like inverted type gate must be developed. The gate insulator which has low interface state density and high reliability is also required. Progress of the gate insulator is very rapid and low interface state density was established using SiO2 and resulted in the inverted MOSFET operation. The recent progress of the on GaN power devices will inspire the researches more.
|
