New generations of semiconductor switch technology appear faster and faster and SiC is no exception. In its infancy still, next generations of this wide band-gap technology promise further improvements in efficiency, size and cost in many application areas.
‘Generation’ has meant different things in history. In 1965, the rock band ‘The Who‘ were ”talking ‘bout my generation”, startling the establishment with radical music and outrageous behavior. Technology wasn’t changing at the same rate though; although transistors had been invented a generation before in 1945, it would be another five years, in 1970, before a pocket calculator appeared and yet another 15 years before Motorola sold the first ‘mobile telephone’, straining the pockets, in both senses, of early adopters.
Today, generations of technology come and go rapidly. 5G is here and work already started on 6G more than two years ago. The same has been true of semiconductor power switch technology, particularly with wide band-gap devices fabricated in SiC and GaN. SiC has leapt ahead from its commercial beginnings five years ago to its third generation today, with price parity with Si switches now in sight, especially when knock-on benefits are taken into account. The latest cascode ultrafast, normally-off SiC-FETs for example, are as easy to drive and use as IGBTs or Si-MOSFETs but show dramatic advantages in speed and much lower static and dynamic losses. Class-leading on-resistance for devices from UnitedSiC is now below 9 milliohms for their 1200V devices and below 7 milliohms for 650V versions with new packages introduced such as the DFN8x8, leveraging SiC performance with low internal inductance and thermal resistance.
The advantages of SiC were obvious from the beginning with its wide bandgap improving critical breakdown voltage and temperature rating. Better still, the ‘Rds.A’ figure of merit is 2.5x better than Si-MOSFETs and 13x better than IGBTs in the same voltage class, switching energy loss is low because of low device capacitances and thermal conductivity is 10x that of silicon.
This has opened up wide-ranging applications for SiC devices where low loss is the driver in space-constrained and energy-conscious areas such as 5G/data centers and in EVs where higher traction inverter efficiency means smaller heatsinking size and cost, and better vehicle range. SiC-FETs have characteristics though that also make them ideal in other applications such as home and commercial solid-state circuit breakers, circuit protection and even in linear operation. Sectors addressed are just as wide, from aerospace through IT, industry, domestic and renewables where better efficiency helps if there is no cooling available and where there is a need to reduce cost, size and the burden on the environment.
But with SiC still at the start of its evolutionary curve, how much further can it go? System engineers are eagerly waiting to find out but we can make some predictions, based on how the evolution of SiC has mimicked that of Si devices so far:
Cell design will be refined with a further-improved Rds. A figure of merit, meaning smaller die with faster switching and smaller on-resistance; reduced die size will lead directly to lower device capacitances which implies lower energy lost during switching and lower gate drive losses; voltage rating will increase to 1700V and beyond, with increasing use of ‘stacked cascodes’ which can be rated at several kV and current ratings will increase and reach the limit of traditional bond-lead packaging so leadless devices will become common, which will also enable in turn, higher switching frequencies. TO-247 three- and four-leaded packages will still have a place though, as drop-in alternatives to IGBTs and Si-MOSFETs in legacy designs. As the technology matures, reliability will be increasingly demonstrated and as yield improves and as die size shrinks, costs can be expected to reduce.
There will be challenges ahead as SiC technology progresses; wafers, for example need to be thicker for the high processing temperature involved with consequent higher cost and some parameters currently only improve at the expense of others. UnitedSiC has its roadmap in place though and we’ll soon be “talking ‘bout the next generation” of SiC-FETs again.
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