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Mar 3rd, 2011
 
Demand pressurises super junction MOSFET producers
 
Super junction MOS FET manufacturers are evolving their strategies after rapid growth in interest in 2010 and with further applications set to take off, Andy Extance finds.
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What technologies define the 21st century so far? Flat screen displays? Smartphones? Cloud computing? Solid-state lighting? Any of these look like good candidates, and they all rely on world-changing innovation – but few would single out power electronics as playing a pivotal role in their development. However either in their physical form or in the infrastructure supporting them, managing power requirements relating to each application can be far from straightforward.

One particular challenge is dealing with the growing hunger for power at the same time as products become more compact. Consequently super junction MOSFETs, which can reduce on-resistance per unit area and therefore offer competitive losses from miniaturized devices, are attracting great interest. So much so, that at demand was stronger than supply last year – although this is as much due to how hard it is to expand manufacturing as their popularity. But with this sector promising more rapid growth than the rest of the power semiconductor sector, the past year has seen further manufacturers arriving that could help open up the market.

Super junction MOSFETs just have such an advantage purely in terms of RDSon compared to traditional planar devices,” David Grey, senior director of market development at Vishay Siliconix, told Power Dev'. “It allows you to reduce component count at the high end of the power supply performance area, where before you may have needed multiple parallel planar devices you can now use fewer super junction parts. It wouldn't necessarily reduce your bill of material costs, but it would allow you to provide a higher density, more efficient solution in a smaller space than was previously possible.”

This can be useful for standards like the 80-plus initiative for computing power supplies, which demands that the power supplies have more than 80 percent energy efficiency at 20 percent, 50 percent and 100 percent of rated load. “In some cases maybe this is only addressable if you've got a super junction device as opposed to a traditional planar,” Grey explained. “They really fit into the high end of the market.

Server and telecom power supplies that also have prescriptive space and efficiency requirements are another key market for Vishay Siliconix's super junction MOSFETS. After launching its technology in January 2010, the Santa Clara, California division is also finding that there is strong demand for new 600V super junction MOSFET products in lighting applications. “The DPAK package is becoming more popular in some of the small lighting ballasts,” Grey explained. “This is a situation where you can put a high performance super junction device into a DPAK, whereas before it was impossible, it was the domain of the TO-220 with the traditional planar device.

Another space limited manufacturing setting where there are increasingly strict efficiency standards that super junction MOSFETs can help with is in LCD TVs. “The latest fashion is to have a very thin screen, so you need something which is very compact,” explained Marc Laudani, manager for high voltage MOSFETs at STMicroelectronics. “They can afford a very good performance. They want a smaller, thinner, super-efficient, device and only super junction MOSFETs can give you these features.”

However, super junction MOSFETs are also primed for deployment in other settings. STMicroelectronics offers in the region of 50 different 650V super junction MOSFETs for existing applications and is also closely watching developing markets that they could be exploited in. “Photovoltaic converters have been under pressure,” Laudani said. “The systems have to give money back to the end user as soon as possible, so they need to have a very high efficiency, and the super-junction MOSFETs fit this requirement very well.”

Outdistancing other MOSFETs

The Switzerland-headquartered semiconductor giant is also has its sights set on another potentially world-changing “green” technology – electric vehicles. “The automotive market has not needed super-junction MOSFETS until now,” Laudani explained. “But there are new applications coming out, like hybrid electric vehicles. Now, automotive manufacturers understand that they need efficient transistors for their system. They are looking into super-junction MOSFETs and understanding that this is the best that they can get for their application.”

Any super junction MOSFET market expansion that these new applications may bring will come on top of 30-40 percent growth from 2009 to 2010 according to Alfred Hesener, senior director for applications and marketing at Fairchild Semiconductor. While this was down to what he calls a “huge recovery of demand” he predicts growth of up to 10 percent in 2011. “2010 was an existing market that was coming back,Hesener said. “Now, we're going back to the old pattern that is really being driven by megatrends such as energy efficiency, green electronics, and new applications finding their way to the customers, to the end market. The move to higher efficiencies will make these products grow faster than the rest of the market. These are not commodities but do require design-in support, so the business side will depend on the individual projects our customers realise with them. That should make for more stable growth.”

But before trying to satisfy any extra markets, manufacturers must first put in place the necessary production capacity. Around 90 percent of super junction MOSFETs sold today are made using multiple epitaxy processes, and this has important consequences for planning any expansion. “These technologies, especially super-junctions that are epi-based, take a lot of time to manufacture,” Hesener explained. “So you want to make sure you have the right mix in place in order to not waste capacity on something that nobody needs at the end of the day.”

San Jose, California, headquartered Fairchild also exploits a parallel “deep trench” process to produce its super junction MOSFETs, however. These products in fact offer significant improvements over rivals made using multiple epitaxy approaches, Hesener claimed. “It's an advanced technology, the lowest RDSon technology in the market today.” While introducing new products can trigger requalification tests to confirm their suitability in many applications, the Fairchild executive asserted that deep trench super junction MOSFETs are just as reliable as multiple epitaxy fabricated versions. “We do of course follow the same qualification procedures, and have seen no reliability issues,” Hesener said. “With some OEM customers we reveal some more details about the manufacturing process, but that is not a big concern for them anyway.”

Grey agrees with Hesener that because of the capital intensive nature of the multiple epitaxy approach, super junction MOSFET manufacturers are cautious about increasing capacity. “The rollout of super junction technology needs to be carefully managed,” he said. “The cycle times are longer than conventional high voltage MOSFETs and expensive tools may need to be dedicated to the super junction process.”

And despite Fairchild's alternative manufacturing approach and Vishay's entry into the market, limited capacity meant that demand for super junction MOSFETs was still very robust in 2010, according to Grey. That's good news for suppliers in terms of the future outlook, he added. “It's healthy, it's saying that super junction MOSFETs obviously are here to stay and are being adopted more and more. It's a definite viable alternative for high end applications.”

Satisfying demand

The strength of demand presented Vishay with a useful opportunity to launch their products, Grey added. “We targeted a few parts that we knew were popular that some customers would have been able to adopt relatively quickly, more in line with some industry standard products that are already being used,” he said. “With the recent strong demand for these MOSFETs we were quickly able to secure some opportunities.”

To try and satisfy the growing interest in super junction MOSFETs, Fairchild is adding to its production capacity, Hesener indicated. “We have been upgrading our manufacturing capabilities and putting quite a bit of equipment in place, for example converting production lines from 6-inch to 8-inch,” he said. “The other very important thing to do is to align our manufacturing planning closely with what our large customers want. That's an ongoing dialogue that needs to happen there.”

 

As well as Vishay's entrance to the super junction MOSFET market last year Japanese semiconductor manufacturer Renesas also announced its own offerings in January 2011. Could the increased competition further raise the risk associated with investing in capacity? Hesener indicated that he would wait and see what consequences the extra producers bring. “Making these devices is not for the faint of heart,” he said. “It was clear that at some point more competition would come, but we feel we have a strong technology base with manufacturing experience, IP portfolio, application support material, and are well-prepared.”

Further potential threats to the market share of super junction MOSFET producers come from gallium nitride (GaN) and silicon carbide (SiC) devices. Both materials promise lower on-resistance and faster switching that their silicon rival, but nonetheless Hesener currently remains calm on this threat too. He noted that in January 2011 International Rectifier, a leading developer of GaN products, downplayed the immediate potential of the technology when reporting its financial results. “They were commenting that gallium nitride won't make a big revenue contribution in 2011,” Hesener said. “So that's a year at least.”

But Laudani notes that GaN and SiC technologies are well positioned to capitalise on the trend to smaller, higher efficiency, transistors in power electronics. “We have really to understand what will be the future of super junction MOSFETs because they have to compete with these very high-performance new materials,” the STMicroelectronics executive said. “We have to reduce the costs of our MOSFETs, and not downgrade the performance by doing this. We're trying to completely change the way we make super junction MOSFETs to come up with less expensive and higher  performance products.

STMicroelectronics is also pushing the super junction MOSFET market boundaries still further by developing the industry's first 1200V product. “1200V is a niche market, but it's also a rich market because the MOSFETs are more expensive and there are fewer players,” Laudani explained. “We are very confident that the performance of the 1200V super-junction MOSFET in the area will be something that the market will accept from surveys that we have been conducting with our customers.”

But even though such advances are in the pipeline, Laudani emphasises that the strength of current demand for super junction markets already shows how highly they are valued by those employing them. “The people using our super junction MOSFETs, or even the ones from competition, are very well aware of their potential,” he said. “They know that what is achievable with those MOSFETs was not achievable 10 years ago. They have been learning what the features are for their applications - and they are ready to pay for them.”


 
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