Multi-dimensional power devices
Advancing power electronics is not all about new materials.
Architectures really matter, with the likes of superjunctions, multiple
channels and multiple gates offering the opportunity to revolutionise
power devices.
BY YUHAO ZHANG FROM VIRGINIA TECH
Power Electronics is key to realising high-efficiency energy conversion in various applications, including data centres, electric vehicles, electric grids and renewable energy processing. The global market for power semiconductor devices and ICs is already worth $40 billion per annum, and it is rapidly increasing.
Many working in this sector hold the belief that to advance power devices there’s a need to introduce new materials. Transistors made from silicon should be replaced by those made from wide-bandgap semiconductors, such as SiC and GaN, and there will come a time when it’s right to move on to ultra-wide-bandgap variants, such as Ga2O3, AlN and diamond.
But my view, shared by colleagues including Florin Udrea of the University of Cambridge and Han Wang of the University of Southern California, is that innovation in device concept and architecture is equally important – and such innovation is material agnostic. This has led us to publish a roadmap late last year for device architecture innovation (for the details of that paper, see Further Reading).
History supports our position. Just track the evolution of silicon power devices before the advent of wide bandgap materials. During that era, innovation in device architecture drove the development of power electronics, from the commercialisation of thyristors in the 1950s to the power MOSFETs of the 1970s and the insulated gate bipolar transistors (IGBTs) of the 1980s. We believe that a new wave of power devices hinges on the introduction of multi-dimensional architectures.
The role of the power device is to conduct a high current in its on-state, block a high voltage in its off-state, and be capable of continuously switching between these two states at a high frequency. For conventional power devices, such as MOSFETs and IGBTs, the main current flow and the blocking electric field are aligned in same direction, rendering them as effective uni-dimensional devices.
Recently, several innovative architectures have been developed that introduce electrostatic engineering in at least one additional geometrical dimension. Such architectures include super-junctions, multiple channels and multiple gates. Depicted in Figure 1, these multi-dimensional devices overcome the capacity-frequency trade-off that holds back the performance of their conventional cousins, enabling them to realise a lower power loss and a higher frequency. Armed with these attributes, designers can enhance the efficiency of their power electronics systems, while reducing the form factor.