Gate Control Scheme of Monolithically Integrated Normally OFF Bidirectional 600-V GaN HFETs

The design and gate-control management of monolithically integrated bidirectional normally OFF GaN-HFET-based switches are presented. Unidirectional 600-V p-GaN-gate HFETs are converted into bidirectional devices by adding a second gate to the transistor drift zone. As demonstrated in direct comparison, the double-gate structure exhibits a similar specific on-state resistance and voltage capabilities as its related unidirectional counterparts. The gate-control scheme of bidirectional devices is studied for the first time, and it is demonstrated that the second (drain side) gate needs to be forward biased by 3-4 V with respect to the drain to ensure stable ON-state operation. Referencing the second gate to source potential can result in uncontrolled operating conditions of the bidirectional switch. Straightforward advantages regarding their implementation into power converters are identified, such as significantly smaller commutation loops, decrease of parasitic inductances, and an ON-state resistance being approximately 50% smaller for the monolithically integrated bidirectional HFET against the conventional silicon-based implementation.