臺灣博碩士論文加值系統

氮化鋁鎵/氮化鎵高電子遷移率電晶體擁有高能帶及高電子遷移率的材料特性，使其大量應用於高電壓電子元件及高效率電源轉換系統。其異質接面所產生的大量二維電子氣提供元件大電流、低阻抗之元件特性，因而近年來越來越被重視。然而當元件在高速切換下，材料缺陷所造成的漏電流以及電流坍塌現象使得電晶體無法達到所預期之高效率電能轉換。本研究致力於增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體之研發及其動態電特性之分析。
根據先前研究氮化鋁鎵/氮化鎵高電子遷移率電晶體的實驗經驗，我們發展金氧半結構並探討其電性，發現藉由原子層沉積系統所沉積出的氧化鋁能夠成功鈍化p型氮化鎵表面受到電漿轟擊所留下的缺陷，抑制長脈衝下的電流坍塌現象，進一步分析單、雙異質結構對於電性的影響及抑制電流坍塌效應之能力，發展出有效利用於p型氮化鎵金氧半高電子遷移率電晶體轉換效率提升之方法。
另外我們在氮化鋁鎵/氮化鎵高電子遷移率電晶體上發展電場板結構並且探討其電流特性，經由實驗結果發現在增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體加上電場板結構，能夠大幅提高增強型元件之閾值電壓。我們由電場板增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體之電流行為提出模型，並且解釋其閾值電壓大幅上升之原因。

The applications of gallium nitride high electron mobility transistors (GaN HEMTs) have become more and more important in recent years. Due to the outstanding material properties including wide-band-gap and high electron mobility, GaN HEMTs are widely applied to high voltage electronics and high efficiency power conversion systems. The two dimensional electron gas (2DEG) formed in heterojunction ensures the large operating output current and low on-resistance of the device. However, the leakage current and current collapse phenomenon concerning to the material defects reduce the power conversion efficiency of the device in high speed switching. In this research, enhancement-mode (E-mode) AlGaN/GaN HEMTs are demonstrated; the electrical characteristics and dynamic characteristics are also investigated.
Based on our previous experience of developing AlGaN/GaN HEMTs, we construct MIS structures with atomic layer deposition (ALD) Al2O3. The Al2O3 can passivate the surface defects formed by plasma bombardment and suppress current collapse in long pulse mode. Also, we investigate the impact of epi structures on electrical characteristics and the phenomenon of current collapse. The power conversion efficiency in p-GaN MIS-HEMTs can be effectively improved by double heterostructure.
In this research, p-GaN gate double heterostructure HEMTs with various gate field plate lengths are fabricated and we investigate the influence of field plates on the current behavior of p-GaN gate HEMTs. Transfer curves of the devices indicate field plates extended toward the source play some role in suppressing channel current, and the threshold voltage tilt toward even higher voltage in double heterostructure. P-GaN gate HEMTs with field plates show three stages current raises, and exhibit much higher threshold voltage than the one without field plate (i.e. Vth=5.90V ). We propose a Threshold Enhancement model to explain the mechanism of three stage current behavior.

口試委員審定書 i
誌謝 ii
摘要 iii
Abstract iv
List of Figure viii
Chapter 1 Introduction 1
1.1 Limitation of silicon power devices 1
1.2 GaN Applications Overview 1
1.3 AlGaN/GaN HEMTs 4
1.4 Enhancement-mode AlGaN/GaN HEMTs 6
1.5 Phenomenon of Current Collapse 8
1.6 Field Plate Design of GaN HEMT 10
1.7 Thesis Outline 10
Chapter 2 MIS E-mode AlGaN/GaN HEMTs 12
2.1 Introduction 12
2.2 Development of MIS E-mode AlGaN/GaN HEMTs 13
2.2.1 Device Structure Design and Fabrication 13
2.2.2 I-V Characteristics and Discussion 15
2.3 Investigations of Current Collapse Phenomenon 19
2.3.1 Measurement Setup 19
2.3.2 Dynamic characteristics 22
2.3.3 Effect of insulator on current collapse 25
2.3.4 Mechanism of current collapse suppression 28
2.4 Summary 30
Chapter 3 Field Plate E-mode AlGaN/GaN HEMTs 31
3.1 Introduction 31
3.2 Development of Field Plate E-mode AlGaN/GaN HEMTs 31
3.2.1 Device Structure Design and Fabrication 31
3.2.2 I-V Characteristics 33
3.2.3 Mechanism of Current Behavior 39
3.3 Summary 47
Chapter 4 Conclusion 48
Reference 50

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