From Si to GaN, What Power Electronics Engineers Need to Know about GaN

Abstract: Power semiconductor devices are the key components in today’s power electronics systems. Since 1950s, power semiconductor technology has gone through many iterations: from BJT to DMOS, from IGBT to Super Junction MOS. Wide band-gap semiconductor materials, such as SiC and GaN can offer much better performance with higher frequency, higher efficiency and lower system profile and are positioned to replace silicon in many applications.
To give a better understanding of power semiconductor devices, this tutorial start from a brief introduction of Silicon MOS and GaN HEMT device structures, including an illustration of the conduction channels to conduct current and the drift regions to sustain high voltage. This will help solve the mystery of why GaN HEMT is superior than silicon MOS in terms of Rdson*Qg and how come there is no avalanche breakdown in GaN. We will also use these structures to give the audience some idea such as why CoolMOS suffers a Coss linearity problem (thus EMI issue) and why there is a dynamic Rdson issue in GaN and how to deal with it. For GaN, a special session will be given to present the different structures of D-mode and E-mode HEMT, their merits and drawbacks.
The second part will be dedicated to how power semiconductor devices are processed / packaged and tested. Both silicon MOS and GaN HEMT will be included so that the audience can have a clearer picture of how the devices are made and how to choose different packaging formats based on applications. We will show that how GaN can be more cost effective and why GaN HEMTs are only for lower to middle power range and why high voltage (>1700V) GaN devices are rare in the market. Also, device testing and characterization will be briefly explained to help audience comprehend the parameters listed on the data-sheet. In this session, we will give the audience an idea of why GaN is more expensive than silicon and why we believe the cost of GaN fabrication will be dramatically reduced in the near future.
In the third part, GaN applications will be highlighted, with a special focus on LLC topology. First we will explain some common issues for using GaN devices, such as temperature coefficients for Rdson and Vth, power and gate drive loop common source inductance, miller capacitance under high dV/dt, etc. Then, we will explain how we implement GaN HEMTs to our digitally controlled LLC resonant converters with practical solutions. We will show to the audience why we believe LLC resonant topology is an ideal choice for high frequency GaN based converters. In this part, we will present our innovative ultra-small and high frequency (>1MHz) 65W USB-PD adapter solution with efficiency as high as 94%. For higher power applications, such as Electric Vehicle on board charger (OBC) and DC/DC converters, we will introduce our novel SCC (switch controlled capacitor) topology with mutli-phase LLC solution so that we can achieve a much better performance compared to traditional design with higher frequency, lower transformer / inductor profile, smaller output capacitors and potentially lower overall cost.

Fred Yue Fu is the co-founder and COO of GaNPower International Inc., a Vancouver, Canada based GaN power devices and related system solutions provider. Before co-founding GaNPower in 2015, Dr. Fred was a vice president, member of the technical staff and R&D engineer of Crosslight Software, Freescale Semiconductor and Delta Electronics, respectively. Dr. Fu received his Ph.D. and M.S. from University of Central Florida and B.S. from Zhejiang University. He has co-authored two technical books (published by CRC press and Springer) in power semiconductor devices; authored and co-authored 30 peer reviewed papers and hold multiple US patents in both semiconductor devices and power electronics circuitry. He is a senior member of IEEE with over 15 years experience in power semiconductor device industry.