利用場效電板改善氮化鋁鎵/氮化鎵高電子遷移率電晶體高功率元件特性與可靠性之研究

Abstract

氮化鎵具有高電子遷移率、高崩潰電壓與低導通電阻等優點，而氮化鋁鎵/氮化鎵高電子遷移率電晶體相較於其它電子元件更適合在高功率的應用上。然而氮化鎵是一種壓電材料，其元件操作在長時間與高電壓下會產生反向的壓電效應，進而造成電流特性的退化現象。 本研究利用場效電板來提升元件的電性與可靠性。從電性量測結果來和傳統元件作比較，結果顯示場效電板的元件具有更高的崩潰電壓，更好閾值電壓，而在高壓測試下也可以成功減緩電性的退化現象並且表現很穩定的動態導通電阻。另外本研究透過小訊號等效電路模型來萃取本質電容的變化，進而驗證氮化鎵在長時間與高電壓下產生特性與可靠度退化的機制。這些研究成果將有助於解決氮化鎵高功率元件中電流特性退化等問題。

GaN has high mobility, high breakdown and low on-resistance, comparing with other electron device. It is more suitable for high power application. However, GaN is a piezoelectric material. It would create an inverse piezoelectric effect, which lead to current degradation further. This study applies a field plate structure to enhance the electric characteristics and reliability of device. DC measurement results are used to compare with conventional device. The results indicated that the field-plate HEMT has higher breakdown voltage, better threshold voltage Vth). It successfully reduced the current degradation and exhibited stable dynamic on-resistance (Ron). Besides, the small signal equivalent circuits are used to extract variation of the intrinsic capacitance. It can prove the mechanism of current degradation and reliability. These results would help solve the problem of current degradation in GaN high power devices.