Transcript GaN HEMT Power Switch의 특성 향상 방안

GaN HEMT Power Switch의
특성 향상 방안
2004- 21648
최영환
Contents



Introduction
GaN HEMT의 구조 및 특성
Power Switch Design





Breakdown voltage
On-resistance
Switching speed
Substrate
Conclusion
Introduction

GaN 특성

Wide band gap (3.4 eV)



High electron mobility



Very low intrinsic carrier concentration
High breakdown voltage (VB  EG5)
2D e- Gas (1300 cm2/Vs ~ 2000 cm2/Vs)
Bulk GaN (900 cm2/Vs)
High saturation velocity

약 1.5x107 cm/s
Introduction
Properties of Competing Material on Power Electronics
Material
Bandgap (eV)
Electron
mobility
(cm2/Vs)
Critical
electric field
(V/m)
Thermal
conductivity
(W/mK)
Tmax
(℃)
Si
1.1
1300
300,000
130
300
GaAs
1.4
5000
400,000
55
300
SiC
2.9
260
2,300,000
110
600
GaN
3.4
900
3,000,000
700
700
Introduction
• Breakdown voltage와 specific on-resistance 비교
• 타 물질보다 우수한 특성
GaN HEMT의 구조
Source
Gate
Drain
AlGaN
GaN
2DEG
Nucleation layer
Substrate : sapphire or SiC
• The lack of GaN substrate
• Heteroepitaxy 필요
• Lattice mismatch
• AlGaN/GaN interface
• Large conduction band offset
• Spontaneous polarization
• Piezoelectric polarization
• Nucleation layer 생성
2D e- Gas (2DEG) 형성
Power Switch Design (1)

High breakdown voltage

Field crowding 방지


Electric field 완화


Circular design
Field plate
Impact ionization 억제

Low gate leakage current
Circular design
• Field crowding
• 소자의 blocking 특성 저하
• Circular device design
• Electric field의 고른 분산
Blocking 능력 저하 방지
Field plate
• Gate edge의 electric field 완화
• Electric field를 보다 균일하게 분산
Breakdown voltage 증가
Double field plate
• Drain에 field plate 추가
• Drain edge의 electric field 감소
향상된 breakdown voltage
Low gate leakage current
• Gate 절연막
• Gate leakage current 감소
• Impact ionization 억제
Breakdown voltage 증가
Power Switch Design (2)

Low on-resistance

2DEG carrier density



AlGaN layer의 doping
AlGaN layer에 Al 함량 증가
Contact resistance


Source/drain ohmic contact area
Contact resistivity
RON-VB trade-off
• AlGaN layer doping 농도 증가
On-resistance 향상
Breakdown voltage 감소
• Ohmic contact 면적 감소
• 낮은 contact resistivity
On-resistance 향상
Power Switch Design (3)

Switching speed

Surface trap


Dielectric material
Parasitic capacitance

Substrate
Surface trap
• Turn-off 상황
• Gate에서 electron이 surface
trap으로 inject
• Channel이 vertical depletion
• Electric field peak 감소
Breakdown voltage 증가
Dispersion
• I-V 특성 차이
• Deep trap에 의해서 발생
• Slow emission process
Switching speed 감소
• Dielectric material
• SiN (shallow trap 형성)
• SiO2 (deep trap 형성)
Dielectric material 선택
• 이중 gate 절연막
• SiO2와 Si3N4의 장점을 결합
• Dispersion 감소
• Shallow trap 형성
Switching speed 향상
Power Switch Design (4)

Substrate

Conductive



Insulating



High breakdown voltage
Large switching loss
Small switching loss
Low breakdown voltage
SiC vs Sapphire


Cost
Thermal conductivity
SiC vs Sapphire (1)
• Sapphire substrate
• Breakdown voltage 감소
• Undoped AlGaN layer
• Gate leakage 감소
SiC vs Sapphire (2)
• Drain-source capacitance
• Switching speed 결정
• Parasitic 성분이 dominant
Switching speed 감소
• Insulating Substrate
• Parasitic capacitance 감소
Switching speed 향상
Power efficiency 향상
Conclusion

GaN HEMT


GaN HEMT Design





High power, high efficiency device
Insulating substrate
High breakdown voltage
RONA와 VB의 trade-off 관계 개선
Shallow trap 형성
Future Work


Epi 기술 개발
Cost 절감
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
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 RONA–VB Tradeoff
Characteristics”, IEEE Trans. Electron Device, VOL. 52, NO. 1, 2005