A Review of GaN HEMT Dynamic ON-Resistance and Dynamic Stress Effects on Field Distribution

Gallium nitride (GaN) is an emerging wide-bandgap material with superior physical characteristics, including critical electric field, electron mobility, and specific on-resistance compared to silicon counterparts. GaN's inherent material properties allow for the development of power electronics with improved performance, such as efficiency, power density, and weight. However, GaN high-electron-mobility transistors (HEMTs) exhibit a parasitic phenomenon of time-varying on-resistance, known as dynamic on-resistance or “current collapse,” largely due to charge trapping and hot-electron injection in undesirable locations of the device structure. Evaluating and characterizing this phenomenon based on GaN's intended operating conditions is crucial to perform design tradeoff studies for target applications. Therefore, this article provides an extensive review of prior research related to GaN dynamic on-resistance, while identifying limitations, challenges, and opportunities based on a survey of the state-of-the-art approaches in literature. Converter-based dynamic operations can create electric fields and leakage paths that are not seen in dc operation, which can lead to serious reliability concerns that should be factored into a device design optimal for power electronic applications. In light of understanding time-dependent stress effects linked to dynamic on-resistance, this article provides several simulation studies analyzing field distribution on the field plates when varying voltage stress slew rates are applied. Such simulation studies seek to identify key elements and analysis missing in prior literature and foreshadow the importance of the research topic to realize the true dynamic behavior of on-resistance in GaN HEMTs.