Ultimate Switches

Umesh K Mishra, Srabanti Chowdhury and Rakesh LalUC Santa Barbara, UC Davis and Transphorm

March 28, 2017

Project Objectives

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Month 41: Scaled OGFET (Vertical GaN MOSFET) device demonstration: 1200V, 5A, <3 mohm-cm2.

Leakage current threshold for breakdown is 10µA per mm of gate width.

M4.5.1 Month 42: Demonstration of a 200V to 400V, 500W boost converter operating at >50 kHz using 1200V, 5A OGFET devices. Evaluate efficiency at 50% duty cycle.

• The overall goals are to provide a 1200V trench OG-FET with a path towards 20c/A

• The reason for our optimism is that the team has deep experience in MOCVD growth and GaN device design and processing including novel dielectrics

• The challenge has been in • understanding the correct device structure that can be fabricated

with minimum process damage and complexity ?\• The state of the maturity of GaN substrates

• Demonstration of a 200V to 400V, 500W boost converter operating at >50 kHz using 1200V, 5A OGFET devices. Evaluate efficiency at 50% duty cycle

• The key outcomes we expect are• A well trained set of graduate students and post-docs• Success in meeting the program metrics• Continuous engagement with industrial stake holders for

successful T2M• The project team has re-focussed on scaling one device structure:

• the trench Oxide GaN Interlayer FET (OG-FET)

Team

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• The team at the outset consisted of UC Santa Barbara, ASU, NRL and Transphorm

• The team was well integrated as• UC Santa Barbara and ASU brought deep knowledge on vertical GaN

devices having invented one of the structures proposed ; the CAVET• NRL had invented the SMRTA Mg activation process to generate p-type

material by ion implantation in GaN• Transphorm is the leader in GaN power conversion and hence brought

device characterization expertise and a clear understanding of the value of vertical GaN technology relative to lateral GaN devices

• The PI has successfully launched two companies based on GaN and the team engaged with several companies active in vertical GaN devices. This enables rational transition to the market via licensing and/or a potential spin-off

• The effort was re-focused to concentrate on the OG-FET and hence the team was redefined to be UCSB, UC Davis and Transphorm

Team Achievements and Challenges

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3rd Year Accomplishments

• The team succeeded• in making CAVETs with a breakdown voltage of 550V and OG-FETs

with a breakdown of ~1kV with an Ron of 2.6 mohmcm2

• developed an MOCVD based oxide for GaN (in partnership with ONR and Power America)

• The key challenge the team faced early was the variability of GaN substrate quality and supply. The team also spent vast resources developing regrowth and processing technology for the CAVET and the OG-FET

• The quality of the substrate remains an issue to get large current devices with any reasonable yield, though it has improved significantly

• The team focused on the OG-FET to maximize synergy across the team• The most surprising and inspiring result thus far has been that after

enhancing our understanding of the growth and process technology the speed and predictability of progress has been amazing AND not surprisingly, students and post-docs rock!

Single Cell OG-FET

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3rd Year Accomplishments

RON = 2.6 mΩ.cm2 VBR ~ 1000 VVTH = 3 V

C. Gupta et al. IEEE EDL

Scaled OG-FET

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3rd Year Accomplishments

Scaled device schematic Scaled device comparison with144 unit cell devices

Achievements and Targets

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• The team will focus on • enhancing the breakdown voltage of the OG-FET to greater than

1200V with a Vth of 3V• Scaling the device to 5A • Team member Transphorm will make and test boost 200V/400V boost

converters at 50KHz.• We anticipate the project to evolve to be a seamless integration of

process and device enhancements at scale• The team has published 19 papers and had 18 conference publication

based on the work in the SWITCHES program. We aim to keep up the pace and quality of our publications and other means of dissemination of information to help make vertical GaN devices mainstream

• The team has over the 3 years of the program helped evaluate various devices and the Trench CAVET and OG-FET have emerged as important devices

Technology-to-Market

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• The team is focused on either licensing the technology or starting a spin-off

• The team will target the >50kW segment of the market and at a rating 1200V or higher as the technology favors higher power segments

• The incumbent is Si IGBT and a challenger is SiC• Advantage versus Silicon is much reduced loss with 1milliohmcm2

ultimately possible for 1200V devices• Advantage over SiC is the same but the disadvantage is the lack of a

competitive substrate• Teaming with Transphorm allows the team to be aware of acceptance

of GaN by the market (via lateral GaN-on-Si)• The key is the availability of a high quality large area substrate;

continuous progress is being made

Technology-to-Market

Technology-to-market progress

Summary:19 papers have been published in journals18 conference presentations2 Patents under consideration for licensing

JOURNAL PUBLICATIONS 1. C. Gupta et al., "In Situ Oxide, GaN Interlayer-Based Vertical Trench MOSFET (OG-FET) on Bulk GaN substrates,"

in IEEE Electron Device Letters, vol. 38, no. 3, pp. 353-355, March 2017. doi: 10.1109/LED.2017.2649599 2. S. H. Chan et al., “Exploring metalorganic chemical vapor deposition of Si-alloyed Al2O3 dielectrics using disilane”,

Journal of Crystal Growth, Volume 464, 15 April 2017, Pages 54-58, ISSN 0022-0248, http://dx.doi.org/10.1016/j.jcrysgro.2016.11.096.

3. A. Agarwal et al., “Suppression of Mg propagation into subsequent layers grown by MOCVD”. Journal of Applied Physics, 121(2), 025106. (2017)

4. C. Gupta et al., "OG-FET: An In-Situ $O$ xide, $G$ aN Interlayer-Based Vertical Trench MOSFET," in IEEE Electron Device Letters, vol. 37, no. 12, pp. 1601-1604, Dec. 2016. doi: 10.1109/LED.2016.2616508

5. C. Gupta et al., “Comparison between GaN trench-gate MOSFETs with a-plane and m-plane sidewall channel”, Applied Physics Express 9 121001 (2016)

6. A. Agarwal et al., “Controlled low Si doping and high breakdown voltages in GaN on sapphire grown by MOCVD” Semiconductor Science and Technology, 31 125018 (2016)

7. M. Tahhan et al., “Optimization of a chlorine-based deep vertical etch of GaN demonstrating low damage and low roughness,” J. Vac. Sci. Technol. A, May 2016

8. S. H. Chan et al., "High electron mobility recovery in AlGaN/GaN 2DEG channels regrown on etched surfaces" Semicond. Sci. Technol., vol. 31 pp. 065008, Apr. 2016.

9. S. H. Chan et al., “Metalorganic chemical vapor deposition and characterization of (Al,Si)O dielectrics for GaN-based devices”, Japanese Journal of Applied Physics 55 (2), 021501. Feb. 2016

10. C. Gupta et al., “High breakdown voltage p-n diodes on GaN on sapphire by MOCVD”, Phys. Status Solidi A, 213: 878–882. DOI: 10.1002/pssa.201532554 Jan. 2016

11. Dong Ji, Matthew A. Laurent, Anchal Agarwal, Wenwen Li, Saptarshi Mandal, Stacia Keller and Srabanti Chowdhury, “Regrown Aperture AlGaN/GaN Current Aperture Vertical Electron Transistor With Active Current Blocking Layer,” IEEE Transactions on Electron Devices, Dec. 2016.

12. Dong Ji, Jianyi Gao, Yuanzheng Yue, Srabanti Chowdhury, “Dynamic Modeling and Power Loss Analysis of High Frequency Power Switches Based on GaN CAVET,” IEEE Transactions on Electron Devices, vol. 63, no. 10, pp. 4011-4017, 2016.

13. Dong Ji and Srabanti Chowdhury, “Design of 1.2kV Power Switches With Low Ron Using GaN-based Vertical JFET,” IEEE Transactions on Electron Devices, vol. 62, no. 8, 2015.

14. Dong Ji and Srabanti Chowdhury, “A Discussion on the DC and Switching Performance of a Gallium Nitride CAVET for 1.2kV Application,” in Proceedings of The 3rd IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA), pp. 174-179, 2015.

15. Dong Ji, Wenwen Li, and Srabanti Chowdhury, “Potential of GaN vertical transistors presented through a comparative discussion on the dynamic performance of 1.2kV GaN and SiC VJFETs,” in Proceedings of The 4th IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA), pp. 114-117, 2016.

16. Wenwen Li, and Srabanti Chowdhury, "Design and fabrication of a 1.2kV GaN-based MOS vertical transistor for single chip normally off operation," Phys. Status Solidi A, vol. 213, no. 10, pp. 2714-2720, 2016.

17. Dong Ji, Jianyi Gao, Yuanzheng Yue, Srabanti Chowdhury, “Dynamic Modeling and Power Loss Analysis of High Frequency Power Switches Based on GaN CAVET,” IEEE Transactions on Electron Devices, vol. 63, no. 10, pp. 4011-4017, 2016.

18. “Low-Loss Power Conversion Enabled By Gallium Nitride Based Devices”, Srabanti Chowdhury, Wide Bandgap Semiconductor Materials and Devices 16, ECS Transactions Volume 66, May 2015

19. “Gallium Nitride based power switches for next generation of power conversion", Srabanti Chowdhury, Topical Review paper– special edition celebrating Nobel Prize in Physics for physica status solidi authors Isamu Akasaki, Hiroshi Amano and Shuji Nakamura, Phys. Status Solidi A. Volume 212, Issue 5, May 2015. Pages 1066-1074

CONFERENCE PRESENTATIONS

1. S. H. Chan et al., "Towards normally-off GaN power devices: Impact of GaN polarity and (Al,Si)O gate dielectrics on the MOS Flat-band voltage," CSW, Berlin, Germany, 2017.

2. Anchal Agarwal et al., “Trench regrowth studies by MOCVD for GaN based power devices”, CSW, Berlin, Germany, 2017.

3. C. Gupta et al.,” Impact of dislocations on device performance and potential yield of large area devices”, CSW, Berlin, Germany, 2017.

4. C. Gupta et al., “Regrown Mg doped GaN interlayer to enhance the breakdown voltage in GaN trench MOSFETs”, accepted at International Workshop of Nitride Semiconductors, Oct. 2016, Orlando, FL, USA.

5. A. Agarwal et al., "Mg Blocking in GaN Using Low Temperature Flow Modulation Epitaxy", International Workshop on Nitrides, Orlando FL, Oct. 2016.

6. S. H. Chan et al., "Mapping the Growth Design Space of (Al,Si)O Dielectrics via MOCVD," ICMOVPE-18, San Diego, CA, 2016.

7. C. Gupta et al., “Comparsion between GaN trench MOSFETs with a-plane and m-plane sidewalls”, Lester Eastman Conference, Aug 2016, Allentown, PA, USA.

8. C. Gupta et al., “A novel device design to lower the on-resistance in GaN trench MOSFETs”, 74th Device Research Conference, June 2016, Newark, DE, USA.

9. A. Agarwal et al., “Controlled low Si doping and high breakdown voltages in GaN on sapphire grown by MOCVD”, 58th Electronic Materials Conference, June 2016, Newark, DE, USA.

10. S. H. Chan et al., “MOCVD Based Amorphous (Al,Si)O Dielectrics for GaN MOS Capacitors: A Route to Improved Interface and Bulk Properties”, 58th Electronic Materials Conference, June 2016, Newark, DE, USA.

11. S. H. Chan et al., "High mobility AlGaN/GaN HEMT channels regrown on etched GaN surfaces for device applications," ICNS-11, Beijing, China, 2015.

12. C. Gupta et al., “High breakdown voltage p-n diodes on GaN on sapphire”, 42nd International Symposium on Compound Semiconductors, June 2015, Santa Barbara, CA, USA. 2015

13. “High Breakdown, Low Interface State PEALD Al2O3/SiO2 Gate Stack for AlGaN/GaN MOS-HEMT,”Jianyi Gao, Yuanzheng Yue, Mei Hao, Wenwen Li, Dong Ji, Robert Nemanich and Srabanti Chowdhury, International Workshop on Nitride Semiconductors, Orlando, Florida, October 2016,

14. “Demonstration of Normally off GaN Trench-CAVET for High Power Application,” Dong Ji, Matthew A. Laurent, Anchal Agarwal, Stacia Keller, Umesh K. Mishra and Srabanti Chowdhury, International Workshop on Nitride Semiconductors, Orlando, Florida, October 2016

15. “pGaN Gate CAVET with Mg Ion-Implanted Current Blocking Layer Demonstrating a Blocking Voltage over 500V,” Saptarshi Mandal, Anchal Agarwal, Elaheh Ahmadi, Matthew Laurent, Stacia Keller, Mahadeva Bhat K, Wenwen Li, Dong Ji, Umesh K. Mishra and Srabanti Chowdhury, International Workshop on Nitride Semiconductors, Orlando, Florida, October 2016

16. “Design and Fabrication of Self-Aligned GaN Static Induction Transistors,”, Wenwen Li, Ryo Tanaka, Saptarshi Mandal1, Matthew Laurent and Srabanti Chowdhury, International Workshop on Nitride Semiconductors, Orlando, Florida, October 2016

17. “On the Compact Modeling of CAVETs for Circuit Simulation,” Fetene M. Yigletu, Dong Ji and Srabanti Chowdhury, International Workshop on Nitride Semiconductors, Orlando, Florida, October 2016

18. “Potential of GaN vertical JFETs presented through a comprehensive discussion of dynamic performance compared to SiC JFETs”, Dong Ji, Wenwen Li and Srabanti Chowdhury, Workshop on Wide Bandgap Power Devices and Applications (WiPDA) Nov. 7–9, 2016, Fayetteville, Arkansas.

Conclusions

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‣ Vertical GaN technology has received a tremendous push by the SWITCHES program

‣ The supply chain has been exercised and weaknesses such as regrowth technologies, low damage processing and large area substrates identified

‣ The OG-FET has emerged as an attractive candidate for 1200V applications

‣ Much needed advancement of dielectrics has occurred with more to come

‣ Development of large area, high quality, potentially low cost GaN substrates is necessary for deployment at scale