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SiC: Going Through The Gears


There's a positive outlook for the SiC device market. Sales of Schottky barrier diodes are well-established, and shipments of the MOSFET are tipped to take off over the next three years RICHARD STEVENSON REPORTS

The 16th February, 2017, could well go down in history as the most important day in the SiC industry. At that point in time, the US Committee on Foreign Investment barred Infineon from buying Wolfspeed.

If the acquisition had proceeded, an $850 million cash deal would have equipped the German power electronics manufacturer with an incredibly strong position within the SiC power device market. Not only would it have had more than half of all global sales, which approached $300 million in 2017, according to market analyst Yole Développement "“ it would have given the company the leading source of substrate production. Armed with this, it could influence the supply of material for all its rivals, and adopt a vertically integrated approach to its own chip production, using the cream of the substrates that it manufactured.

Unsurprisingly, many of Infineon's peers breathed a sigh of relief when the deal fell through.

"The key competitors are happy," says Hong Lin, a technology and market analyst at Yole Développement. She believes that the failure of the acquisition has given competitors the space to develop. "That will give the end user a choice of different suppliers. When there is only one dominant supplier, that's not necessarily good for the market."

Dominating diodes

Even with the failure of the Infineon-Wolfspeed deal, there's not much space for the little guy. Sales are dominated by SiC Schottky barrier diodes, which currently account for more than 80 percent of the SiC power device market, according to Lin "“ and over half of those sales are going to Infineon and Wolfspeed.

The other two big players, Rohm Semiconductor and STMicrolectronics, are also big names in the power industry. "On-Semi have their products that they are launching, so they could be an important supplier in the future."

Infineon is the longest-serving manufacturer in this market, having introduced its first SiC Schottky barrier diode back in 2001. It is now offering a si generation product. Gains between one generation and the next are more evolutionary, than revolutionary, according to Lin. She argues that this form of diode is now mature, although it is still improving in areas such as current handling and reliability "“ and the chip is getting smaller.

Yole Développement is predicting tremendous growth in the SiC market, led by a hike in MOSFET sales.

Lin says that the price of the diode has dropped significantly since its launch at the turn of the millennium. "In the past five years the price has dropped by 50 percent, but we think the pace will slow down a little bit, and be less than ten percent year by year."

Manufacturers of these Schottky diodes are keen to migrate production from a 4-inch to a 6-inch line. "However, there is still a short supply of 6-inch [substrates], so both of them are used," explains Lin.

The majority of diode sales are for products providing blocking voltages of 600 V, 1.2 kV and 1.7 kV. However, there are also products with a 3.3 kV rating. According to Lin, the primary application for 600 V SiC Schottky barrier diodes is in power factor correction circuits for power supplies. The diodes with the higher blocking voltages are used in photovoltaic inverters, and in powers supplies with higher ratings.

To reach even higher blocking voltages, needed for the engines of electric trains, some companies are developing SiC p-n diodes. The leader of this device is Wolfspeed. Note, however, that it's not easy to compare its technology with that of the leading companies in Japan. "Japanese companies mostly use SiC products for internal use, so even though they have this kind of product, they are not necessarily on the market," says Lin.

Mushrooming MOSFETs

Part of the motivation behind Infineon's attempt to purchase Wolfspeed is that it would have equipped the German outfit with a leading MOSFET technology. "Infineon have long-term experience in SiC, in general, but they are late for SiC MOSFET products," says Lin. "Their first product was released in 2016." Part of the reason for this is that Infineon spent many years pursuing the SiC JFET, only to discover that this product did not find favour with end users.

Wolfspeed and Rohm are currently the leaders for the SiC MOSFET. "But based on their client portfolio, and their understanding of power electronics, Infineon could quickly catch up," says Lin.

There are also some start-ups that are trying to enter this market. "They have some prototyping, but to go to mass production will be another issue," says Lin.

If start-ups are to enjoy any success, they will need to differentiate themselves from the established players. "I think they will try to use the foundry model," says Lin, who believes that this approach could lower production costs. "In terms of mass production "“ personally, I would like to say that the big companies have more advantages."

Many SiC MOSFETs manufacturers also make SiC diodes. "I think that customers try to buy products from the same manufacturers," says Lin, who adds that it is much more challenging to make a MOSFET.

She says that there are still concerns over the reliability of the SiC MOSFET. "For example, there are standards for silicon devices. For all wide bandgap devices "“ for SiC and for GaN "“ they don't have established standards. They still need some international co-working to develop standards."

There is also a need for more field testing of the SiC MOSFET. There are many prototypes, some of which are already in use, but very little data on the performance of these devices.

During the next few years Lin is tipping the sales of the SiC MOSFET to take off. "In the next two or three years, we will see SiC MOSFETs massively deployed. At the moment we are still on small-volume sales."

Due to the small volumes, SiC MOSFETs are currently manufactured on 4-inch SiC substrates. As these devices are more challenging to make than Schottky barrier diodes, there is more concern over substrate quality, which applied the brakes to the transition to 6-inch substrates, which are in short supply.

Prices for MOSFETs are falling fast, with this device is seeing traction in the market. Opportunities exist in the photovoltaic industry, and in on-board chargers for electric vehicles. For example, leading Chinese electric vehicle manufacturer BYD recently confirmed that it is using SiC in its on-board chargers. SiC is also hitting the headlines for its deployment in Formula Electric, with Rohm's SiC power devices slashing losses in the inverter, while offering the capability to operate at higher temperatures.

The rise of the module

In addition to discrete diodes and MOSFETs, the SiC power industry has a third source of revenue: SiC modules. It is a really small proportion of the market right now, but it is set to grow.

"There are lots of kinds of modules," explains Lin. "You have the old generation, using old IGBT packaging. And then you have a lot of innovative packaging designs, for example, Fuji Electric."

Customers are often seeking bespoke designs. They may involve new materials "“ producers are trying to maximise the performance of the SiC devices with the likes of new diode attach materials, different types of heat sink, and the placing of different materials around the diodes and transistors.

Lin expects that in the high-voltage market, sales of modules will be very strong. "For 1.2 kV and above, the module will be dominant. That's not the case at the moment, because the module is very expensive."

She believes that the leading suppliers of modules may differ from those that dominate diode and transistor sales. Wolfspeed acquired APEI in 2015 to enhance its module design capability, but the company does not have that much experience in module design and manufacture compared to leading modules players. Due to this, Lin expects this sector to be led by those that do, such as Mitsubishi, Fuji Electric and Infineon.

One threat to the success of SiC sales is the rival wide bandgap semiconductor, GaN, which can form devices on silicon substrates. This combination has the potential to lower the cost of wide bandgap power electronics, and stymie sales of SiC devices. However, Lin doesn't expect this to happen anytime soon.

SiC modules, which currently account for a very small proportion of the SiC market, come in wide variety of formats.

"For the diode side, SiC is quite well established," says Lin. "The SiC MOSFET, for 1.2 kV and above, GaN is not challenging at all." She believes that GaN could provide some competition to the SiC MOSFET in the 650 V range, but argues that SiC is more mature. "I don't think in the next five years GaN will take over SiC devices."

Instead, she expects SiC to take market share from silicon in the power device market. SiC sales are predicted to grow fast, with an estimated compound annual growth rate of 28 percent.