Combination of Vertical and Horizontal GaN Transistors for Efficient Power Conversion Electronics – C-PI-GaN

In a world where electrical energy plays a more and more important role in the energy mix in reason of the worldwide increasing use of renewable energies, the market of Power Electronic Conversion Systems (PECS) is constantly growing in size and in complexity to address the need and challenges of electric power conversion at all levels. Today’s PECS market is largely dominated by silicon-based technology, as it is low-cost and mature. However, this technology limits the trade-off between size, energetic efficiency and maximum operating voltage due to the intrinsic limitation of the Si semiconductor. While emerging technologies such as electric vehicles and further applications keep demanding higher performance for operating voltage up to the kV range, it appears crucial to overcome these limitations to follow these major technological changes.
One promising solution to this problem is the use of wide-bandgap semiconductor technologies Gallium Nitride (GaN) which is far superior in terms of electron mobility and breakdown voltage. GaN technology is presently being used in applications up to 650V by means of horizontally-configured high electron mobility transistors (HEMTs) on foreign substrates (Si or SiC). Although GaN HEMT technology is exhibiting impressive performance, we are still not using all the capabilities of this material owing to several limitations caused by the growing of GaN epi-layer in on foreign substrate.
On the other hand, recent progress in material science have enabled the fabrication of GaN substrates at reasonable costs. Therefore, in this project, we target to overcome these limitations by using a GaN substrate and a homo-epitaxial growth approach to fabricate Vertical GaN transistors (MOSVFETs). Indeed, previous works in literature have demonstrated the tremendous gain of power density with the vertical approach on GaN bulk substrate.
The cutting-edge idea driving this proposal is the monolithic combination of horizontal HEMT and vertical MOSVFET transistors within the same chip. What makes this proposal stand out from previous works is the fact that, for the first time, we will demonstrate the monolithic integration of a high-speed HEMT-based driver with a high-voltage MOSVFET-based power switch.
This approach enables to benefit from the superiority of normally-off GaN MOSVFETs in terms of specific ON-resistance while enabling the integration of a driver circuit featuring GaN HEMTs for very high speed switching. The result will be a state-of-the-art PECS capable of handling voltage up to 1200V with exceptional characteristics in terms of robustness, reactivity, power density and efficiency, all thanks to the combination of both configuration: high-voltage handling and current density of vertical devices and high cut-off frequency of horizontal devices. This technological challenge represents thus a significant breakthrough while being achievable by current expertise and technological capabilities of the partners of this project.