Examination Committee

Prof Ping GAO, CBME/HKUST (Chairperson)
Prof Kevin J CHEN, ECE/HKUST (Thesis Supervisor)
Prof Henry S H CHUNG, Department of Electronic Engineering, City University of Hong Kong (External Examiner)
Prof Johnny K O SIN, ECE/HKUST
Prof Wing Hung KI, ECE/HKUST
Prof Lilong CAI, MAE/HKUST 

Abstract

GaN power devices are promising candidates for next-generation power switches in numerous power electronics applications owning to their capabilities to deliver low ON-resistance (RON), fast switching speed, and high-temperature operation. Over recent years, significant efforts have been devoted to commercializing GaN power devices, as witnessed by the emergence of several first-generation products. Nevertheless, it still requires intensive efforts to resolve the remaining challenges (such as dynamic-RON degradation, threshold voltage instability (VTH), and reliability) for widespread acceptance of GaN power devices. 
 
This thesis is devoted to application-relevant characterization, implementation, and integration of normally-off GaN power transistors for their adoption in high-performance power converters. Firstly, the dynamic-RON of an AlN-passivated enhancement-mode device is evaluated under practical hard switching operations. It is found that unlike conventional SiNx-passivated devices with the dynamic-RON deteriorated by additional hot electron trapping, AlN-passivated devices exhibit small dynamic-RON degradation with weak temperature dependence even under hard switching operations, suggesting that the robust AlN passivation can effectively suppress hot-electron-induced surface trapping. Secondly, a commercial 650-V p-GaN device is characterized under both static and switching operations. The dynamic-RON degradation is found to be strongly dependent on the applied ON-state gate voltage VGS, as a result of a positive shift in VTH under switching operations. Switching characteristics of the device is evaluated up to 400 V, 10 A using a double-pulse test circuit. Fast switching characteristics and reliability/stability issues of the GaN power devices are addressed in the circuit design for maximized performance. Thirdly, to further demonstrate the integration capability of lateral GaN devices, a pulse width modulation (PWM) integrated circuit is demonstrated on the GaN smart power technology platform for the first time. The circuit is able to generate 1-MHz PWM signal, and can be monolithically integrated with high-voltage GaN power switches, thus realizing an all-GaN solution that can deliver improved system performance with suppressed parasitics, reduced footprint, and high-temperature operation capability.