以氧化鑭/二氧化矽堆疊式氧化層作為高功率氮化鎵高電子遷移率電晶體之閘極氧化層之研究

Abstract

氮化鋁鎵/氮化鎵高電子遷移率電晶體具有高電子遷移率、高崩潰電壓、低導通電阻等優點，因此近年來氮化鋁鎵/氮化鎵高電子遷移率電晶體在高功率應用上備受注目。然而傳統氮化鋁鎵/氮化鎵高電子遷移率電晶體仍存在高閘極漏電流與高電壓下造成的電流崩潰這兩種現象影響著元件的穩定度，已有文獻證明使用金屬-絕緣體-半導體結構可以有效的降低閘極漏電流以及電流崩潰現象。 本研究主要分為兩個部分，第一部分使用二氧化矽、氧化鉿與氧化鑭作為氮化鋁鎵/氮化鎵高電子遷移率電晶體的閘極絕緣層，並與傳統氮化鋁鎵/氮化鎵高電子遷移率電晶體做比較；實驗結果顯示，在這三種不同絕緣層中使用二氧化矽做為絕緣層有最佳的電性表現:在閘極漏電流部分可以減少四個數量級以上，另外在最大汲極電流、轉導、電流崩潰現象、元件開啟/關閉狀態之電流比值與崩潰電壓都有很好的表現，藉由遲滯現象、電容-電壓特性與X光光電子能譜儀的分析也確認了二氧化矽本身與氮化鎵接面都具有不錯的品質。 第二部分使用二氧化矽、堆疊式氧化鉿/二氧化矽與堆疊式氧化鑭/二氧化矽作為氮化鋁鎵/氮化鎵高電子遷移率電晶體的閘極絕緣層，在氧化鉿與氧化鑭加入二氧化矽形成堆疊式氧化層後，可以降低閘極漏電流至與二氧化矽同一個數量級。使用堆疊式氧化鑭/二氧化矽絕緣層的元件在最大汲極電流、轉導、閘極漏電流、動態導通電阻與高壓測試方面皆擁有最佳的特性；另外，藉由脈衝模式電流-電壓特性、電容-電壓特性與X光光電子能譜儀的分析亦印證了堆疊式氧化鑭/二氧化矽本身與氮化鎵接面皆具有良好的品質，非常適合作為為氮化鋁鎵/氮化鎵高電子遷移率電晶體的閘極絕緣層。

GaN has high mobility, high breakdown and low on-resistance, comparing with other electron device. It is more suitable for high power application. However their performance and reliability are limited by the gate leakage current and drain current degradation. The utilization of insulator to form metal-insulator-semiconductor (M-I-S) gate structures has shown remarkable improvements in reducing gate leakage current and suppressing current degradation. There two topics in this study. In the first part, SiO2, HfO2 and La2O3 were used as gate insulator of AlGaN/GaN MIS-HEMTs, and then compared with conventional schottky AlGaN/GaN HEMT. The experimental results of SiO2 AlGaN/GaN MIS-HEMT showed best electrical property among these devices. Gate leakage current was reduced more than 4 orders compared with conventional HEMT. Beside, DC characteristics such as maximum drain current, transconductance ION/IOFF ratio and breakdown voltage also exhibited good performance. The good quality of SiO2 itself and interface between GaN were verified by hysteresis effect, C-V characteristics and X-ray Photoelectron Spectroscopy (XPS) analysis. In second part, SiO2, HfO2/SiO2 and La2O3/SiO2 were used as gate insulator of AlGaN/GaN MIS-HEMTs. After incorporating SiO2 into HfO2 and La2O3, forming composite HfO2/SiO2 and La2O3/SiO2 insulators, the gate leakage current of these two kinds of devices was reduced to the same level of SiO2 AlGaN/GaN MIS-HEMT. The La2O3/SiO2 AlGaN/GaN MIS-HEMT showed great DC characteristics such as maximum drain current, transconductance, gate leakage current and dynamic on-resistance. The current degradation of La2O3/SiO2 AlGaN/GaN MIS-HEMT was smallest after high voltage stress. Furthermore, the great quality of composite La2O3/SiO2 gate insulator was demonstrated by pulse-mode ID-VGS measurement, C-V characteristic and XPS analysis. It is suitable to apply composite La2O3/SiO2 as gate insulator of AlGaN/GaN MIS-HEMT for high power applications.