1. GaN HEMT Power Switch 의 특성 향상 방안 2004- 21648 최영환

2. Contents Introduction GaN HEMT 의 구조 및 특성 Power Switch Design Breakdown voltage On-resistance Switching speed Substrate Conclusion

3. Introduction GaN 특성 Wide band gap (3.4 eV) Very low intrinsic carrier concentration High breakdown voltage (V B  E G 5 ) High electron mobility 2D e - Gas (1300 cm 2 /Vs ~ 2000 cm 2 /Vs) Bulk GaN (900 cm 2 /Vs) High saturation velocity 약 1.5x10 7 cm/s

4. Introduction MaterialBandgap (eV) Electron mobility (cm 2 /Vs) Critical electric field (V/m) Thermal conductivity (W/mK) T max ( ℃ ) Si1.11300300,000130300 GaAs1.45000400,00055300 SiC2.92602,300,000110600 GaN3.49003,000,000700 Properties of Competing Material on Power Electronics

5. Introduction Breakdown voltage 와 specific on-resistance 비교 타 물질보다 우수한 특성

6. GaN HEMT 의 구조 Substrate : sapphire or SiC Nucleation layer GaN AlGaN SourceDrainGate 2DEG AlGaN/GaN interface Large conduction band offset Spontaneous polarization Piezoelectric polarization 2D e- Gas (2DEG) 형성 The lack of GaN substrate Heteroepitaxy 필요 Lattice mismatch Nucleation layer 생성

7. Power Switch Design (1) High breakdown voltage Field crowding 방지 Circular design Electric field 완화 Field plate Impact ionization 억제 Low gate leakage current

8. Circular design Field crowding 소자의 blocking 특성 저하 Circular device design Electric field 의 고른 분산 Blocking 능력 저하 방지

9. Field plate Gate edge 의 electric field 완화 Electric field 를 보다 균일하게 분산 Breakdown voltage 증가

10. Double field plate Drain 에 field plate 추가 Drain edge 의 electric field 감소 향상된 breakdown voltage

11. Low gate leakage current Gate 절연막 Gate leakage current 감소 Impact ionization 억제 Breakdown voltage 증가

12. Power Switch Design (2) Low on-resistance 2DEG carrier density AlGaN layer 의 doping AlGaN layer 에 Al 함량 증가 Contact resistance Source/drain ohmic contact area Contact resistivity

13. R ON -V B trade-off AlGaN layer doping 농도 증가 Ohmic contact 면적 감소 낮은 contact resistivity Breakdown voltage 감소 On-resistance 향상

14. Power Switch Design (3) Switching speed Surface trap Dielectric material Parasitic capacitance Substrate

15. Surface trap Turn-off 상황 Gate 에서 electron 이 surface trap 으로 inject Channel 이 vertical depletion Electric field peak 감소 Breakdown voltage 증가

16. Dispersion I-V 특성 차이 Deep trap 에 의해서 발생 Slow emission process Dielectric material SiN (shallow trap 형성 ) SiO2 (deep trap 형성 ) Switching speed 감소

17. Dielectric material 선택 이중 gate 절연막 SiO 2 와 Si 3 N 4 의 장점을 결합 Dispersion 감소 Shallow trap 형성 Switching speed 향상

18. Power Switch Design (4) Substrate Conductive High breakdown voltage Large switching loss Insulating Small switching loss Low breakdown voltage SiC vs Sapphire Cost Thermal conductivity

19. SiC vs Sapphire (1) Sapphire substrate Breakdown voltage 감소 Undoped AlGaN layer Gate leakage 감소

20. SiC vs Sapphire (2) Drain-source capacitance Switching speed 결정 Parasitic 성분이 dominant Insulating Substrate Parasitic capacitance 감소 Switching speed 향상 Power efficiency 향상 Switching speed 감소

21. Conclusion GaN HEMT High power, high efficiency device GaN HEMT Design Insulating substrate High breakdown voltage R ON A 와 V B 의 trade-off 관계 개선 Shallow trap 형성 Future Work Epi 기술 개발 Cost 절감

22. Reference [1] UMESH K. MISHRA, FELLOW, IEEE, PRIMIT PARIKH, AND YI-FENG WU, “AlGaN/GaN HEMTs—An Overview of Device Operation and Applications”, Proceedings of The IEEE, VOL. 90, NO.6, June 2002 [2] S.J. Pearton, F. Ren, A.P. Zhang, K.P. Lee, “Fabrication and performance of GaN electronic devices”, Materials Science and Engineering, R30 pp. 55-212, 2000 [3] N.-Q. Zhang, B.Moran, S.P. DenBaars, U.K. Mishra, X.W.Wang and T.P.Ma, “Effects of surface traps on breakdown voltage and switching speed of GaN power switching HEMTs”, Electron Devices Meetings, IEDM Tech.Digest. pp.25.5.1-25.5.4, 2001 [4] Naiqian Zhang, Vivek Mehrotra, Sriram Chandrasekaran, Brendan Moran, Likun Shen, Umesh, Mishra, Edward Etzkorn and David Clarke, “Large Area GaN HEMT Power Devices for Power Electronic Applications: Switching and Temperature Characteristics”, IEEE Trans. Electron Device, pp 233-237. 2003

23. Reference [5] Wataru Saito, Yoshiharu Takada, Masahiko Kuraguchi, Kunio Tsuda, Ichiro Omura, Tsuneo Ogura, and Hiromichi Ohashi, “High Breakdown Voltage AlGaN–GaN Power-HEMT Design and High Current Density Switching Behavior”, IEEE Trans. Electron Device, VOL. 50, NO 12, 2003 [6] Wataru Saito, Masahiko Kuraguchi, Yoshiharu Takada, Kunio Tsuda, Ichiro Omura, and Tsuneo Ogura, “High Breakdown Voltage Undoped AlGaN–GaN Power HEMT on Sapphire Substrate and Its Demonstration for DC–DC Converter Application”, IEEE Trans. Electron Device, VOL. 51, NO. 11, 2004 [7] Wataru Saito, Masahiko Kuraguchi, Yoshiharu Takada, Kunio Tsuda and Ichiro Omura, “Design Optimization of High Breakdown Voltage AlGaN–GaN Power HEMT on an Insulating Substrate for R ON A–V B Tradeoff Characteristics”, IEEE Trans. Electron Device, VOL. 52, NO. 1, 2005