marianne Germain, Program manager gaN IIAP
ExTREmE mATERIALS FOR POwER ELECTRONICS AND LIgHTINg At imec, we explore the use of III-nitride materials – of which GaN (gallium-nitride) is best known – for use in two technologies: power electronics and solid-state lighting. Both are of key importance for a more sustainable use of energy. Consequently, we see a growing interest in GaN and in our R&D in this domain. Power electronics convert electric power through solid-state components. Such converters can be found wherever there is a need to modify the form of electricity, i.e. its voltage, current, or frequency. Take for example solar cell panels, which generate a DC current that must be converted to AC before it can be used in the grid or in home appliances. The market for such power-converting components is destined to grow considerably, because of the drive to use more hybrid electrical vehicles in transport, more solar installations, more wind farms, and the smart grids to connect it all. The key driver for power conversion is efficiency: ideally, there should be no loss when converting energy. Furthermore, you want components that are cheap, reliable and small, and that can work under high-voltage and high-temperature. These are the main challenges for improving power electronics. The current components for power electronics are based on Si. But R&D is reaching the limits of what can be done with Si. New materials are needed, typically wide-bandgap semiconductors. Intrinsically, these are more robust at high voltages. GaN is a good candidate: it has an electrical breakdown voltage that is 10 times higher than that of Si, and it has excellent transport properties. For our first generation of GaN components, we have already gained an order of magnitude in loss reduction for 600V-class breakdown voltage, just by switching to GaN. We expect that we can improve this further: the theoretical limit shows we could gain another 2 orders of magnitude. This will enable the high-voltage, high-power, and high-temperature circuits needed by tomorrow’s applications. Moreover, GaN has other advantages, notable a very high speed, and the possibility for further miniaturization by switching to a higher frequency, thus reducing the sizes of passive components. This of course requires a parallel development of passive components for high power applications. But before the use of GaN becomes widespread, and cheap GaN components can be fabricated, a few issues have to be tackled. First, to reduce the cost, you need processing on largearea wafers. To make such wafers, imec is proposing an approach where GaN is deposited on a Si wafer. Currently, we’re using 4inch and 6inch wafers, and INTERVIEW WITh MaRIaNNE GERMaIN IMEC ENERGY we‘ve succeeded in making a first demo 200mm GaNon-Si wafer, together with our equipment supplier. <strong>Imec</strong> is one of the few labs in the world that has the expertise to control the stresses that originate when GaN is deposited on Si. A second issue we’re working on is to make the GaN processing compatible with CMOS processing (Au-free). If we succeed, the uptake of GaN technology by the industry will be easier. There are many existing 6inch and 200mm fabs that are looking for new business. Solid-state lighting, with light-emitting diodes (LEDs), is our second area of interest. Currently, light bulbs are phased out, being replaced mainly by fluorescent lamps. The next generation of lighting, still more efficient, will be LED lighting. But today, LED technology is still at least a factor 10 too expensive. Also here we are looking to introduce GaN, with cheaper, large-area processing. Next to that, we also look at improving the light efficiency, getting more light for the same amount of energy. There is still a lot of room for im provement, from what is reached today in the labs and in production to what is theoretically possible. 45
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