EU HiPoSwitch project delivers GaN power switches
HiPoSwitch, an EU group project, has successfully developed lightning-fast, high-efficiency enhancement mode GaN power switches. Eight European institutional and industrial project partners led by the Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik (FBH) were involved.
"The single transistor measures only 4.5 x 2.5 mm and is optimised for switching 600V. It has an on-resistance of 75mΩ and handles a maximum of 120A. We are the only ones in Europe who can manufacture these kinds of normally-off transistors at present," says Joachim Wuerfl, head of both the HiPoSwitch project and the GaN Electronics Business Area at FBH.
GaN has already been used in microwave transistors for a long while, while applied in thin layers mostly on SiC substrates. This technology has been further developed by FBH over the last few years for 600V-rated power transistor switches. "This works well, but it is too expensive for mass markets. As an alternative, the processes developed for SiC can be transferred to considerably more cost-effective, but technologically more challenging silicon substrates," Wuerfl explains.
FBH was so successful in optimising the processing of GaN switching transistors on SiC and silicon that nearly ideal components became feasible. Among others, comprehensive investigations of drift and degradation effects carried out by University of Padua and University of Vienna provided the foundation for this. The finished transistor chips were finally assembled into low-induction ThinPAK housings by Infineon in Malaysia.
The Belgian company EpiGaN together with Aixtron moved the epitaxy to silicon - so that the manufacturing costs for the substrates drop by more than a factor of ten. At the same time, the wafer diameter increased to 6in or even 8in, a necessary step towards cost-effective industrial production.
Chip-manufacturer Infineon matched up the newly developed GaN technology with a Si process line for industrial production of power semiconductors at their Austrian location in Villach.
Part of the project possessed a decidedly "exploratory character", as Wuerfl puts it, due to the completely new techniques and processes for implementing GaN power transistors that had never before been tried. Promising ideas for producing semiconductors were successfully tested together with colleagues at the University of Vienna and the Academy of Sciences in Bratislava, Slovakia.
The Austrian company Artesyn is positioned at the end of the value-added chain as a systems-level partner.
They developed a 3kW rectifier for telecommunications applications including cellular base stations. This unit converts line voltage to DC with an efficiency of 98 percent. A specialised switching topology was developed and implemented that is matched to the properties of the GaN switching transistors.Their smaller size and weight also makes them highly attractive for aerospace applications.
