With its proven ability to reduce size (form factor) and save energy (high efficiency) Gallium Nitride (GaN) is now no longer a nice to have, it is a must-have for power conversion. In applications ranging from sub 100 watt to multi kilowatt highly efficient power converters and inverters, GaN HEMTs high switching speed and low efficiency make it a natural choice of Silicon based devices reaching their physical limits of performance. Transphorm has already commercialized JEDEC qualified GaN HEMT power switches manufactured in an automotive grade 6 inch Si CMOS fab [1]. With this strong base and its ability to reduce size, weight and improve miles per gallon, GaN HEMTs are now increasingly being investigated for EV & HEV applications such as on board chargers and other auxiliary power conversion within the automobile under 10 kW. We will review the first ever Automotive (AEC Q101) Qualification for GaN and also discuss results for highly stressed robustness tests, FIT rates & lifetime testing.
2. GaN Products and Qualification
Normally off GaN devices (Fig. 1) are achieve through integration of a low voltage Si-MOSFET input device with a high voltage depletion mode GaN device offering the best combination of input gate interface and the most robust high voltage GaN platform [2]. Electrical characteristics of the normally-off GaN power switch are summarized in Table 1 with a Low Rds(on), low gate charge (Qg) and low capacitance (Coss) that enable high efficiency, small form factor power systems. The Ron *Qg or Ron * Coss figure of merit is already better than mature Silicon Superjunction MOSFETs and achieved simultaneously with superior reliability performance. We have successfully passed (on multiple products and generations) the full suite of JEDEC qualification tests [3], as shown in Table 2.
3. Robustness, Long Term Reliability and Lifetime of High Voltage GaN
To further establish confidence in long term reliability and operation in the field with low FIT rates, we have extended JEDEC qualification to 3-5x the stresses, for e.g. 5,000 hours of HTRB (5x JEDEC stress) with no degradation in resistance, threshold or leakage (Fig 3). Systematic high voltage off-stage (HVOS) acceleration at over 1100 volts was done to determine intrinsic lifetime (MTTF) of over 100 Million hours and 1% failure of more than 1M hours (Fig 5). Similarly through accelerated high temperature on-state testing of GaN, a high temperature MTTF of over 100 Million hours at 175C was determined. Recently, in March 2017, we completed the first ever successful AEC-Q101 standard qualification of GaN products [4]. These will be discussed in detail at the conference.
4. GaN Products and Qualification
The comprehensive suite of data and results with a 3 year manufacturing history on over 3,000 wafers in a high volume commercial 6-inch Wafer fabrication facility unequivocally demonstrate that GaN power switches are now reliable and ready for a wide array of consumer & communication, industrial & renewable energy as well as automotive applications. The next milestones which are now happening include announcement of a variety of end system products (Titanium rated data server power supplies, PV Inverters, Telecom power supplies and Servo motor drives), paving the way for an exciting era in highest efficiency, highest reliability power conversion with GaN.
5. References
P. Parikh, et. al., “Commercialization of 600V GaN HEMTs,” 2014 SSDM, Tsukuba, Sep., 2014.
Power GaN Devices- Materials, Applications and Reliability, Edited by M. Meneghini et. al., Springer International Publishing, 2017.
T. Kikkawa, et al. 600 V JEDEC-Qualified Highly Reliable GaN HEMTs on Si Substrates,” IEEE IEDM, San Francisco, Dec. 2014.
APEC 2017, http://www.transphormusa.com/news/transphorm-announces-first-automotive-qualified-gan-fets/
