On the Origin of the $C_{\text{oss}}$ -Losses in Soft-Switching GaN-on-Si Power HEMTs

The unprecedented performance potential of gallium nitride-on-silicon (GaN-on-Si) high electron mobility transistors (HEMTs) is seen as the key enabler for the design of power converters featuring extreme power density figures, as demanded in next-generation power electronics applications. However, unexpected loss mechanisms, i.e. dynamic Rds,on phenomena and Coss-losses, are appearing in currently available GaN transistors and are compromising their operation. In this paper, measurements of Coss-losses are performed in a dedicated calorimetric measurement setup and, through a systematic approach, the root cause of the loss mechanism is potentially identified. Afterward, with the essential support of a manufacturer of power semiconductors, a novel transistor, featuring an enhanced multilayer III-N buffer, is developed according to the acquired knowledge. A significant reduction in terms of Coss-losses, i.e. of soft-switching losses, and the absence of dynamic Rds,on phenomena are verified experimentally on the new device. These achievements enable a significant performance improvement for future soft-switching power converters featuring GaN-on-Si HEMTs.