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Rohm Braves High Voltage SiC Markets


With its 1700 V SiC power module delivered, Rohm is eyeing even higher voltage markets and industry domination, reports Rebecca Pool.

Be it for photovoltaics, electric vehicles, 5G infrastructure or industrial high power supplies, silicon carbide is steadily infiltrating markets around the globe. As analysts forecast a compound annual growth rate of at least 25%, and a $1.5 billion SiC market come 2023, industry players up and down the supply chain are readying for action.

US-based GT Advanced Technologies recently opened a SiC crystal growth facility to meet the imminent silicon carbide market boom while Infineon has bought SiC wafer-splitting process developer, Silectra, to secure substrate supply.

Wolfspeed, Infineon, GeneSiC and more are diligently pioneering packaging structures to take on the extreme switching speeds and temperatures that SiC can handle. And in a bold move, Cree has sold its Lighting business to focus on power semiconductors, having spent the last year-and-a-half year bolstering its SiC supply and honing devices.

Amongst these front-runners is Japan-based Rohm, having had its eyes firmly fixed on SiC for some two decades. Preliminary SiC MOSFET development began in 2002, with initial samples shipped in 2005. Trial manufacture of 300A MOSFETs followed in 2007 with trench-type devices released in 2008.

Then, in 2009, the company acquired SiC crystal manufacturer, SiCrystal, with the now vertically integrated business delivering its first mass-produced SiC Schottky diodes and MOSFETs in 2010. Mass-produced full SiC modules followed in 2012 with six inch Schottky barrier diodes delivered in 2017.

Today, the company claims to have the industry's largest line-up of automotive-grade 650V and 1200V SiC MOSFETs, but is also intent on delivering devices at ever-higher voltages for more and more gruelling applications.

As Aly Mashaly, Power Systems Manager at Rohm highlights, the industry trend towards higher power density has led to higher systems voltages. And, given this, the company recently developed a 1700V, 250A rated SiC power module that is currently being used in customer projects.

According to Mashaly, the module's high voltage surpasses the requirements of electric hybrid vehicles, for now, but is instrumental in inverted and converter applications for outdoor power generation systems and industrial high power supplies.

Aly Mashaly, Power Systems Manager at Rohm.

Crucially, the latest system promises to provide the same energy-saving performance as 1200V devices with a high reliability, meaning the 1700V SiC module is ready to take on the 1700V silicon IGBT module.

“The big challenge in silicon carbide is to provide high reliability especially at higher voltages,” says Mashaly. “But we have tested our devices at high voltages, temperatures up to 85ºC and high humidities, and for more than 1000 hours, and we haven't seen any degradation in performance.”

The module comprises SiC MOSFETs and Schottky barrier diodes, vastly diminishing chip area and reducing ON resistance by 10% relative to similar SiC products, says Mashaly. But while this cuts energy use and heat dissipation, it doesn't cut upfront costs, a fact that the Power Systems Manager knows only too well.

“We are working to reduce the level of the price compared to the IGBT [module], and while I cannot provide exact numbers, I do know that we will always be getting closer,” he says. “I don't ever expect the cost of the SiC module to come down to that of the IGBT module but if we look at system cost , the benefits of using SiC has already been proven to many tier one companies and automotive OEMs.”

So with the demand for SiC power devices rising, how exactly is Rohm meeting market needs? While the company is in the process of ongoing capacity expansion at its Nuremberg site, in June 2018, it revealed plans to massively expand silicon carbide production capacity at its Apollo plant in Chikugo, Japan. Construction has now started and will continue until at least the end of 2020.

At the same time, the transfer of manufacturing from four inch to six inch wafers is also well underway, boosting production efficiencies. “We have already started this for our planar MOSFETs and this year we will try to make this transition with our trench MOSFETs,” says Mashaly.

What's more, Mashaly reckons that the wafer quality of Rohm's six inch wafers is better than that of its four inch wafers. “We have nineteen years of experience in SiC and we saw a huge improvement in the quality of [our] four inch wafers compared to two inch wafers, and we now see that quality is even better with the six inch wafers,” he says. “Year by year we have this improvement in our production process and we are confident that the quality in the next level of substrate will be high.”

So with manufacturing in hand, where next for Rohm on the road to silicon carbide success in an increasingly crowded market-place? Mashaly is keen to highlight that aside from Wolfspeed, Rohm is the only vertically integrated business in this market, and as such, intends to capture 30% market-share by 2025, making it the number one player.

And as well as an ever-larger market share, the company will also be looking towards ever-higher voltages. “Right now we are focusing on the 1200 V and 1700 V areas due to the big potential for mass production of SiC here,” he says. “But we already have research and development activities in place for 3.3 and 6.5 kV [devices]... we don't have a defined time of when we will launch these products but we also see the potential for SiC here.”

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