37 research outputs found
Improvement of Breakdown Characteristics in AlGaN/GaN Power HEMTs
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ผ๋ฌธ (๋ฐ์ฌ)-- ์์ธ๋ํ๊ต ๋ํ์ : ์ ๊ธฐยท์ปดํจํฐ๊ณตํ๋ถ, 2013. 8. ํ๋ฏผ๊ตฌ.Gallium Nitride (GaN) based high electron mobility transistor (HEMT) or heterostructure field effect transistor (HFET) are promising device for high-power switches which has to operate in electrically and environmentally harsh condition. The devices benefits from the material properties GaN offers: high critical field, high carrier mobility and a high saturation velocity of carriers.
The breakdown voltage in AlGaN/GaN HEMTs is known to be triggered by gate leakage caused by the concentration of the electrical field at the drain-side edge of the gate electrode. The influence of gate leakage on blocking characteristics is alleviated by reducing the peak intensity of the electric field at the drainโside of the gate. There are two methods to reduce the peak intensity of the electric field: one is to decease the probability of tunneling of electrons into device active area the other is to relieve the crowding of electric field at the drain-side edge of gate.
Nickel has been used as a gate electrode of the AlGaN/GaN HEMTs to form the Schottky contact due to its relatively high work function (5.15 eV). In this work, nickel oxide (NiOx) was inserted as the interfacial layer between main gate (Ni) and AlGaN barrier layer for improve the reliability of the AlGaN/GaN HEMTs. NiOx film was formed through the thermal oxidation in furnace. Material property of NiOx film depended on the two main factors: oxidation temperature, density of the film controlled by deposition rate. Only the NiOx film oxidized proper temperature range from 400โ to 500โ gave a favorable effect on the device performance. The NiOx film with high atomic density exhibited resistive switching characteristics, which can be used for GaN based memory device. Experiments to verify the effect of NiOx on reverse blocking operation were carried out. At the high temperature reverse bias (HTRB) test, it was found that work function of the NiOx was maintained. Moreover, it played an important role to improve the stable blocking operation. The result of electroluminescence (EL) analysis was consistent with the results obtained from HTRB test. Leakage current of the AlGaN/GaN HEMTs with NiOX interfacial layer measured at 200โ was lower than that of the conventional device by 3 orders of magnitude. The breakdown voltage of the proposed device was up to 1.5 kV (1480 V).
In recent years, improvements of the overall device performance were achieved by adopting metal-insulator-semiconductor (MIS) or metal-oxide-semiconductor (MOS) structure. At the gate region, by insulating gate electrode by means of a dielectric layer, electron injection is suppressed effectively. In this work, improvement of the blocking capability and reliability of AlGaN/GaN MIS-HEMTs employing atomic-layer-deposited (ALD) Al2O3 material was confirmed by experimental results. Mechanism responsible for the leakage current of the proposed device was investigated. Measured Leakage current of the fabricated MIS-HEMT was reduced to the range from sub pA (fA) to few pA. At the HTRB test, MIS-HEMT exhibited proved its thermal stability. Although drain leakage current (IDSS) was increased in proportion to the operational temperature, the leakage current of the proposed device was still lower than that of conventional device by 2 orders of magnitude. Breakdown voltage of the proposed device was up to 2 kV.Contents
Abstract i
List of Tables vii
List of Figures ix
1. Introduction 1
1.1 Status quo of GaN power device 1
1.2 Research Background 26
1.3 Organization 42
2. Review of AlGaN/GaN HEMTs 45
2.1 Principle of AlGaN/GaN HEMTs 45
2.2 Structure and Polarization 55
2.3 Device fabrication 61
2.3.1 Pre-treatment 61
2.3.2 Isolation 63
2.3.3 Ohmic and Schottky contacts 67
2.4 Substrate used to AlGaN/GaN HEMTs 75
2.5 Factors limiting the HEMT performance 81
2.5.1 Current collapse 81
2.5.2 Leakage current 84
2.5.3 Breakdown mechanism and Failure 93
2.5.4 Technologies for high breakdown 102
3. AlGaN/GaN HEMT Employing NiOX Interfacial Layer 115
3.1 Overview 115
3.2 AlGaN/GaN HEMTs on SiC Substrate 117
3.2.1 Advantage of SiC substrate 117
3.2.2 Properties of HEMTs on SiC substrate 119
3.3 Device fabrication 122
3.4 Properties of the nickel oxide film 125
3.4.1 Resistive switching property of the NiOX 127
3.5 Device performance 138
3.5.1 Forward characteristics 138
3.5.2 Reverse blocking characteristics 151
3.6 Summary 173
4. AlGaN/GaN MOS-HEMT with ALD Al2O3 gate dielectric 174
4.1 AlGaN/GaN HEMT on Si Substrate 174
4.2 Atomic-Layer-Deposited Al2O3 dielectric 178
4.3 Device fabrication 186
4.4 Device performance 192
4.4.1 Forward characteristics 192
4.4.2 Reverse blocking characteristics 229
4.5 Summary 264
5. Conclusion. 265
Bibliography 268
์ด ๋ก 286
๊ฐ์ฌ์ ๊ธ 290Docto
Psuedo field plate effect of the fluoride ion complex implanted in AlGaNGan HEMT
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ผ๋ฌธ(์์ฌ) --์์ธ๋ํ๊ต ๋ํ์ :์ ๊ธฐ. ์ปดํจํฐ๊ณตํ๋ถ,2009.8.Maste
<ๆ็ซ >ํ ๋ฌธํ์ ๊ณ ์ ์์ฉ ์์ ์ฐ๊ตฌ
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ผ๋ฌธ(์์ฌ)--์์ธ๋ํ๊ต ๋ํ์ :๊ตญ์ด๊ตญ๋ฌธํ๊ณผ ํ๋๋ฌธํ์ ๊ณต,1999.Maste
The Effects of an Educational Computing Course on Preservice Teacher's Attitudes and Anxiety Toward Computers
๋ณธ ์ฐ๊ตฌ๋ ์ ์ ์ปดํจํฐ ๊ต์ฌ๊ต์ก๊ณผ์ ์ด ์๋น์ ์๊ต์ฌ๋ค์ ์ปดํจํฐ์ ๋ํ ํ๋ ๋ฐ ๋ถ์๊ฐ์ ๋ฏธ์น๋ ์ํฅ์ ๊ดํ ์ฐ๊ตฌ์ด๋ค. ์ฐ๊ตฌ๋์์ธ ์ ๋ถ I์ W ๋ํ์ ์ ์์ ์ปดํจํฐ ๊ต๊ณผ๋ชฉ ์๊ฐ์ ์ ์๊ต์ก๊ณผ 1ํ๋
40๋ช
์๊ฒ Ainsa(1992), Espinosa์ Chen(1996), Epstein(1993) ๋ฑ์ ์ฐ๊ตฌ์ ๊ธฐ์ดํ์ฌ ๊ตฌ์ฑํ ์ ์์ปดํจํฐ ๊ต์ฌ๊ต์ก ๊ณผ์ ์ 14์ฃผ๊ฐ ์ค์ํ์๋ค. Landerholm(1995)์ ์ปดํจํฐ์ ๊ดํ ํ๋ ๊ฒ์ฌ์ Spodek(1987)์ ์ปดํจํฐ์ ๊ดํ ๋ถ์๊ฐ ๊ฒ์ฌ๋ฅผ ์ฌ์ฉํ์๊ณ ์๋ฃ ๋ถ์์ ์ํด ๋ ์ข
์ํ๋ณธ t ๊ฒ์ฆ์ ์ค์ํ์๋ค. ์ฐ๊ตฌ ๊ฒฐ๊ณผ ์ ์์ปดํจํฐ ๊ต์ฌ๊ต์ก๊ณผ์ ์ ์๋น ๊ต์ฌ๋ค์ ์ปดํจํฐ์ ๋ํ ๊ฐ์ธ์ ํ๋๋ฟ๋ง ์๋๋ผ, ์ ๋ฌธ์ ํ๋๋ฅผ ํฅ์์ํค๋ฉฐ, ์ปดํจํฐ์ ๋ํ์ฌ ๊ฐ์ง๊ณ ์๋ ๋ถ์๊ฐ์ ๊ฐ์์ํค๋๋ฐ ๊ธ์ ์ ์ธ ์ํฅ์ ๋ฏธ์น๋ ๊ฒ์ผ๋ก ๋ํ๋ฌ๋ค.
This study investigates the effects of an educational computing course on preservice teacher's attitudes and anxiety toward computers. Research questions were as follows: 1) What is the effects of an educational computing course on preservice teacher's individual and professional attitudes toward computers? 2)What is the effects of an educational computing course on preservice teacher's anxiety toward computers. Subjects of this study were 40 students of freshman at W Univerity in I city. The educational computing course in this study was constructed by researchers based on Ainsa(1992), Espinosa & Chen(1996) and Epstein(1993)'s study. It was used over a 14-week period. The preservice teacher's attitudes and anxiety toward computers instruments were administered and analyzed by M, SD, two paired t-tests, with spss/pc program. The study results foundthat 1) The educational computing course increased positively preservice teacher's individual and professional attitudes toward computers and 2) it decreased preservice teacher's anxiety toward computers