以氧化鑭/氧化鉿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研究

Abstract

近幾年,氮化鋁鎵/氮化鎵高電子遷移率電晶體在高功率應用上廣受注目。然而在應用中，仍存在閘極漏電流以及高電壓下造成的電流崩潰這兩個現象影響著元件的表現及穩定度。部分的文獻已經證明使用金屬-絕緣體-半導體的閘極結構能夠有效地降低閘極漏電流以及高電壓下造成的電流崩潰。 因此，本研究使用氧化鉿與氧化鑭/氧化鉿堆疊式氧化層結構來製作金屬絕緣層氮化鎵高電子遷移率電晶體，並與傳統的氮化鎵高電子遷移率電晶體做比較。在閘極漏電流的表現上，使用氧化鉿作為金屬絕緣層可以降低接近2~3個數量級的漏電流，而使用氧化鑭/氧化鉿堆疊式氧化層的金屬絕緣層結構則能夠降低近4個數量級的漏電流。在抑制高電壓下電流崩潰方面，傳統氮化鎵高電子遷移率電晶體的最大汲極電流降低了21%，而使用氧化鉿與氧化鑭/氧化鉿堆疊式氧化層作為金屬絕緣層的氮化鎵高電子遷移率電晶體則分別降低了7%與0.8%。另外，使用氧化鑭/氧化鉿堆疊式氧化層作為金屬絕緣層的氮化鎵高電子遷移率電晶體在其他的電性如最大汲極電流、臨界電壓、轉導等亦都有不錯的表現。除此之外，藉由電容的頻散現象與遲滯效應的量測以及X光光電子能譜儀(XPS)分析也都得到不錯的絕緣層沉積品質。

In recent years, AlGaN/GaN high electron mobility transistors (HEMTs) have been widely studied for high power applications. However their performance and reliability are limited by the gate leakage current and drain current degradation. The utilization of insulator to form metal-oxide-semiconductor (M-O-S) gate structures has shown remarkable improvements in reducing gate leakage current and suppressing current degradation. In this study, we developed two kinds of MOS-HEMTs by using HfO2 and La2O3/HfO2 stacks to compare the electric properties with conventional HEMT. The gate leakage current of HfO2 MOS-HEMT and La2O3/HfO2 MOS-HEMT are individually suppressed almost two and four orders of magnitude compared with conventional HEMTs in positive bias region. Moreover, the current degradation of MOS-HEMT with HfO2 (PDA at 500°C) and La2O3/HfO2 (PDA at 600°C) as gate insulator was only decreased 7% and 0.8% (conventional HEMT decreased 21%). Besides, other DC characteristics such as maximum drain current, threshold voltage and transconductance also exhibited good performance in La2O3/HfO2 MOS-HEMT after PDA at 600°C. Furthermore, we obtained good quality of insulator deposition as revealed by the frequency dispersion, hysteresis effect and X-ray Photoelectron Spectroscopy (XPS) analysis in this study.