【World Express】The Eleventh Annual IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA 2024)——Opportunities with Ga₂O₃

      Industry-facing academics championed the capabilities of devices based on SiC, GaN and Ga₂O₃ at the recent European workshop on wide bandgap power devices and applications.

      Once dominated by just silicon, this is now complemented by a growing portfolio of wider bandgap semiconductor, each with a particular set of attributes that come together to offer the designer a tremendous palette for constructing circuits. There’s GaN, delivering great efficiency and incredibly fast switching without a significant increase in cost while operating at several hundred volts; SiC, a more mature technology that’s well-suited to handling higher voltages; and Ga₂O₃, with the potential to outperform this duo, thanks to an even higher bandgap, along with the promise of lower costs that stem from melt-growth of crystal boules.

      Promotion of this symphony of semiconductors came from many of the speakers at the IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA) in Europe, held on 16-18 September, at the Royal Welsh College of Music & Drama, part of Cardiff University. At this venue, as well as outlining the pros and cons of the many diodes and transistors within the wide bandgap portfolio.

Johan Kolar from ETH Zurich suggested that the power electronics industry is in its fourth era, and championed a move to a circular economy that involves recycling of materials when moving to the fifth era.

      A keynote presentation from Martin Kuball from the University of Bristol detailed the promise of Ga₂O₃, alongside approaches to accommodate its weaknesses, by pairing this oxide with other materials.

      In terms of substrate size, it’s already possible to buy 4-inch material, and there are research demonstrations up to 6-inch, according to Kuball: “You could think about commercialisation at that moment in time, because the substrate size of gallium oxide is already at the level where you could do manufacturing.”

      Kuball pointed out that devices made from Ga₂O₃ have the potential to withstand very high electric fields while exhibiting an incredibly low on-resistance. However, there’s a need for thermal management, to compensate for the low thermal conductivity of this oxide, and to introduce new materials to provide p-doping within the device, if it’s required.

      Among a number of devices that Kuball and his colleagues are developing, arguably the most exciting is that incorporating a superjunction, based on the pairing of n-type Ga₂O₃ and p-type diamond, which is used to fill trenches. Back in 2021 the team simulated such structures, using realistic properties for diamond that account for a lower thermal conductivity due to the grain structure, and found that this still led to a dramatic improvement in thermal management. This work also showed that by optimising charge balancing and adjusting the field distribution, it’s possible to boost the breakdown voltage quite significantly.

Martin Kuball, Director of the UKRI Innovation and Research Centre REWIRE at the University of Bristol, is driving development of Ga₂O₃ devices featuring hetero-integration.

      Working with Stanford, Kuball and coworkers have started working towards the fabrication of superjunction devices, looking at sidewall properties. Initial structures have a breakdown voltage of 900 V, limited by the peak electric field not sitting at the interface between the two materials. Addressing this could increase the breakdown to 5 kV or more.

      “Just to point out, it’s not good diamond. It’s nanocrystalline diamond, so there’s still need for optimisation,” revealed Kuball, who views these early results as quite promising.

      He clearly has many plans for the future, as do all of those working on the development of wide bandgap devices and the design of the circuits that incorporate them. There is much to look forward to, due to these harmonious efforts.

Around 130 delegates attended the IEEE Workshop on Wide Bandgap Power Devices and Applications in Europe, held in mid-September at Cardiff University.