(Invited) Advances in High Power, High Voltage, Reliable GaN Products for Multi Kilo-Watt Power Conversion Applications.

Abstract

Gallium Nitride has been proven to be a superior material system for high performance, reliable, high power transistors enabling high efficiency in power conversion applications [1,2]. In this paper we highlight some recent advances in GaN technology which expand the capabilities and applications of GaN power switches.Transphorm, Inc, is a pioneer and leader in GaN power electronics with a wide product portfolio of products spanning <100W to >10kW applications with JEDEC and AEC-Q101 qualified products including qualified 650V and 900V products (Fig. 1), as well as demonstrated 1200V devices in development. Transphorm’s vertical integration allows for control over device design, GaN epitaxial growth, and device fabrication resulting in industry leading performance and reliability.Transphorm’s breadth of volume production applications from 45 W through 10 kW is in part due to its impressive Failure in Time (FIT) rate of < 0.3 failures per billion hours is based on Field Reliability Data collected over 40 billion hours.[3]Transphorm’s normally-off devices are built by combining a state-of-the-art high voltage (HV) GaN HEMT with a low voltage (LV) Silicon MOSFET into a cascode GaN FET configuration to offer superior reliability, performance, and ease of use. The LV Si MOSFET features low gate charge and high threshold voltage which makes for a very easy to drive switch with a large gate voltage drive margin and the HV GaN HEMT offers high performance due to the superior material and transport properties of GaN combining the best of both materials.The latest GenV 15 mΩ 650V SuperGaN® FET (TP65H015G5WS) is the lowest Ron packaged GaN FET in the market enabling >10kW output powers with a single switch [4]. Inductive switching waveforms in a half-bridge at 400 V/65 A for the SuperGaN FET and SiC MOSFET were compared (Fig. 2) and the GaN device delivered current and voltage switching speeds of 4 kA/μs and 60 kV/μs which is about 2x faster than that of the SiC MOSFET, resulting in a 50% reduction in switching loss.To assess the performance of the SuperGaN FET vs similarly rated SiC MOSFETs and SiC JFETs, the devices were configured into a 240V:400V boost converter operating at 70kHz (Fig. 3). The GaN FET based boost converter was able to operate up to 12kW of output power with a maximum junction temperature of just 139 oC while the SIC MOSFET and JFET boost converters were limited 11kW and 9.2kW respectively due to junction temperature reaching 165oC. At 9.2Wk output power, the SuperGaN FET power loss was 38% and 21% lower than the loss in the SiC JFET and SiC MOSFET respectively. This combination of lower temperature and higher output power demonstrates the importance of the high efficiency of the SuperGaN FET.The unparalleled efficiency of Transphorm’s SuperGaN FETs has enabled to the development of unique products such as a 3KVA datacenter UPS released by and industry leading supplier, which is the smallest, lightest, and most powerful 3KA datacenter UPS on the market with 93.3% peak efficiency and 2.5x higher power density which enabled the form factor to shrink form a 2U to 1U enclosure.Until recently, commercial GaN power electronic devices have only available up to 650V with Transphorm’s qualified 900V GaN FET (TP90H050WS) device being the exception. We have recently announced a breakthrough in GaN technology with the demonstration of a 1200V, 70mΩ lateral GaN FET in a TO-247 packageThe 1200V GaN FET achieved > 99% peak efficiency in a 450V:900V synchronous boost converter operating at 50kHz which is similar to the peak efficiency of our 650V Gen IV and Gen V products. Additionally, the 1200V GaN FET achieved higher efficiency than a similarly rated state-of-the-art 1200V SIC MOSFET in a 900V:450V buck converter at 100kHz and 5.5kW (Fig 4) demonstrating GaN can excel in 1200V applications [5].[1] Y.F. Wu, J. Gritters, L. Shen, R.P. Smith, J. McKay, R. Barr, R. Birkhahn, “Performance and robustness of first generation 600-V GaN-on-Si power transistors”, The 1st IEEE Workshop on Wide Bandgap Power Devices and Applications, 6-10, Oct, 2013.[2] Parikh, Y.F. Wu, L.K. Shen, "Commercialization of High 600V GaN-on-Silicon Power Devices", Materials Science Forum, Vols. 778-780, pp. 1174-1179, October 2014. [3] https://www.transphormusa.com/en/gan-technology/#quality-reliability [4] C. J. Neufeld, Y.-F. Wu, S. Wienecke, R.P. Smith, Y. Huang, M. Kamiyama, J. Ikeda, T. Hosoda,B. Swenson and R. Birkhahn, “650V/780A GaN Power HEMT Enabling 10kW-Class High-efficiency Power Conversion”, IEEE 8th Workshop on Wide Bandgap Power Devices and Applications, 7-11 Nov. 2021.[5] Gupta, et al. IEEE International Symposium on Power Semiconductor Devices 2022 (accepted for publication) Figure 1