Where are the High-Voltage GaN Products?

Jun 1, 2010 12:00 PM
BY ARNOLD N. ALDERMAN President, Anagenesis, Inc., El Segundo, CA

I was discussing the compound semiconductor landscape with fellow attendees at APEC 2010. Our discussion was probably one of many prompted by IRís further introduction of devices and the presence of Cree, TranSiC, and others at APEC. I posed the question, “Where are the high voltage gallium nitride (GaN) power switching devices? After all, GaN is reputed to be a high voltage technology by leading technologists in that field.”

In the past few years, compound semiconductors have become the focus of development as semiconductor engineers have strived to get to the next better device. The bulk of the development has been for applications such as radio frequency (RF) power transistors and light emitting diodes (LEDs). Now, as of this writing, two suppliers have introduced low voltage GaN power switching devices.

However, we saw that GaN might well be the technology to provide 600 volt and 1200 volt semiconductor devices for every type of high voltage power conversion, including variable-speed motion control, solid-state lighting, electric vehicle drives, wind and solar converters, uninterruptible power supplies, and, yes, eventually the higher power distribution, transmission, and traction markets.

WHY GALLIUM NITRIDE?

GaN is the most practical, lowest loss, power semiconductor material available today. SiC can achieve reasonable performance as a low-loss device, but experts have assured me the performance of fully developed GaN will be two times (2X) better than SiC.

GaN provides the fastest path to market. As one expert told me, “GaN has always had a high natural speed of device development and market accessibility.” Technologists will develop GaN materials and products faster than either gallium arsenide or silicon carbide devices. The reason: material problems plague GaN far less than other compound semiconductors. For instance, if a non-GaN LED had as many imperfections as a GaN LED, it would not emit any light. It would be absolutely dead! Yet the GaN LED operates extremely well, even with imperfections.

Let's use previous compound semiconductor LED development history as a guide. The figure illustrates GaAs development taking 26 years to obtain 15 lumens per watt (lm/W) which is the equivalent of the incandescent lamp. SiC never got onto the roadmap before GaN development took off. In only six years, GaN LEDs reached 15 lumens per watt. GaN material development was considerably shorter than either GaAs or SiC so therefore product development could commence sooner. In the development of both GaAs and SiC devices, it was first necessary to create a near-perfect material. For instance, perfect SiC material has taken over a decade to develop! According to Yole's market analysis, it is still plagued with micro-pipe and basal plane dislocations. GaN material development was much faster! Thus, GaN engineers could start on product creation a lot sooner in the development process than their SiC or GaAs counterparts could. Experts tell me that we can expect the same fast GaN development time line for high voltage power switching devices. A leading GaN technologist recently shared with me, “If we needed to develop GaN power device material to the extent that they had to develop GaAs material, we would not have seen the devices that are already introduced. We would have to spend a billion dollars before the material became clean. That would make the whole industry not only late in device development but also make the devices expensive. Fortunately, that will not be the case!”

SCALABILITY

GaN has much better device size scalability. We can also conclude from the figure that technologists were able to scale GaN four times (4X) beyond either SiC or GaAs materials, reaching a benchmark of 168 lm/W. We can expect this to be the case for GaN power switching device scalability. GaN will happen sooner, and then will scale to a much higher device size. Presently, the low voltage GaN designers are proving that very point.

GaN is low cost. It is higher cost than silicon, but GaN will always cost less than SiC because GaN is compatible with silicon substrates affording a large-area foundation substrate - and SiC is not compatible. At APEC 2010, low voltage GaN speakers very accurately emphasized this point. However, if there ever is a fundamental breakthrough to make SiC compatible with silicon, then that will seriously reduce its cost. If we look ahead, diamond is the only material better than GaN, but that is most probably more than 20 years away from becoming a reality. Even if developed, experts cannot even get a glimpse of a roadmap to cost-competitive devices yet.

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