From wafers to modules
According to ROHM representatives at the show, one of the company’s strengths is its ability to provide a full range of SiC power devices, from wafers to modules. Christian André, ROHM president and chairman of ROHM subsidiary SiCrystal, says the message that ROHM most wanted to get across at PCIM Europe was that they have “lined up a broad portfolio of power products, including not only SiC devices, which are the driving force in the power sector, but also peripheral devices including SiC drive ICs and digital power control”.
Regarding the SiC power device market in Europe, André expressed the view that “If you look in terms of sales, the SiC market is still small.
But particularly over the last three years, I think interest in SiC technology has increased. At this year’s PCIM Europe, you could see SiC power devices being displayed everywhere. This is completely different from five years ago. Five years ago, I think we were the only company exhibiting SiC.”
SiC is expected to be adopted in a wide range of applications, including solar power systems, railways, electric/hybrid vehicles, and industrial equipment. “At the beginning the market driving SiC was solar energy systems. ROHM has been supplying SiC power devices to the solar market for more than three years. This is because the product cycle in inverters and the like for solar generating systems is about three years, which is relatively short compared to other markets like railways, automotive, and industrial equipment.”
Costs need to be considered for the entire system
One big issue with SiC is cost. While admitting that “If you think about discrete device units, certainly the cost is high. For example, the cost of an SiC MOSFET is three to four times that of an Si IGBT,” André notes that it is important to think about the cost benefits of adopting SiC for the entire system. “Using SiC power devices makes it possible to use smaller passive components like capacitors, and cooling mechanisms such as heat sinks. There are even instances where a cooling mechanism becomes unnecessary. If you look at the system as a whole, right now with SiC we can expect a cost savings of around 10% on average.”
Going to 6-inch wafers by the end of 2017
“At ROHM we are targeting the mass market”, says André. And as strategies for achieving this, he says they are considering two directions. One is incorporating new structures such as trenches. In April 2015, ROHM announced an SiC MOSFET using a trench structure. The other is making larger-diameter SiC wafers. At present, ROHM is transitioning from 4-inch to 6-inch SiC wafers.
The company has already started developing 8-inch wafers as well. However, André indicated that these will take time. “SiC power devices involve extremely complex technology using SiC, which is a very hard substance. In fact the only material harder than SiC is diamond. If diamond is a 10, SiC is about a 9. Because of this, the difficulty in manufacturing tends to be more mechanical than technological.”
The history of research and development of SiC is a long one, and research into its use as a semiconductor dates back to the 1950s. ROHM has been actively engaged in the research and development of SiC for over 10 years. In April 2010 ROHM was the “first in Japan to mass-produce an SiC SBD (Schottky Barrier Diode).” And in December of that year ROHM was the “first in the world” to succeed in mass-producing an SiC DMOSFET (Double-diffusion MOSFET). Even so, the size of the market is small compared to silicon, but according to André, “Growth in the SiC power device market is accelerating, and six to seven years from now we expect sales to surpass a billion dollars.”
Targeting the automotive and industrial fields
For SiC power devices, going forward ROHM plans to focus more on automotive and industrial equipment. “For example, inverters for electric cars and onboard chargers are a target. We already have an 80% share of the world market for SiC power devices for onboard chargers. But even though it’s 80%, sales are still very small. The key to increasing sales is promoting the spread of SiC technology to other applications, along with providing full SiC modules. At the moment, in ROHM’s SiC power device business, almost all of our sales is comprised of SiC SBDs. So the next step is to grow sales of full SiC modules consisting of SiC MOSFETs and/or SiC SBD + SiC MOSFETs”. André believes that modularization is essential in order to fully exploit the benefits of SiC power devices. In Europe there are many makers of such modules, and ROHM has formed partnerships with several module manufacturers.
Until a few years ago, there were said to have been several serious issues remaining regarding SiC power devices in general, such as defects in SiC crystals and the life of the oxide film. However, according to André, “Now, technologically, SiC is reaching maturity. We are at a level where we can apply SiC power devices even in the (demanding) automotive field. The critical problems with SiC power devices were cleared when we went into mass production in 2010, and I think they are gradually becoming more widespread as the they continue to see increased adoption”. André went on to say that the number of applications of SiC power devices is growing, and that what remains is to improve the cost structure by transitioning to larger-diameter wafers as he mentioned previously.
“The SiC power device business is often seen as more of a development project than a business. But the maturity of the technology is already almost there, and SiC power devices are starting to be used in more visible applications, which is helping to increase interest in SiC”, André said.
It should be noted that, according to ROHM, SiC power devices account for 50% of their power device business, which includes high-voltage IGBTs, MOSFETs, and diodes.
About the author:
Mayuko Murao is associate editor of EE Times Japan.