VerGaN: Research into integration technologies for vertical power transistors based on gallium nitride

With the "VerGaN" research project, part of the "Research for New Microelectronics" initiative (ForMikro 2.0), the Fraunhofer ISIT, together with strong partners, is driving the development of a new generation of power semiconductors. The goal is the research and integration of vertical power transistors based on gallium nitride (GaN), which can be used in particular in power electronic converters—the heart of modern energy and drive systems. The technology promises increases in efficiency, making it an important building block for the energy transition as well as future electric drive concepts, such as in the automotive industry.

Until now, power electronic systems have been predominantly based on silicon semiconductors. In recent years, however, materials such as silicon carbide (SiC) and particularly gallium nitride have increasingly gained importance. GaN is characterized by excellent electrical properties that enable higher switching speeds and lower losses. To date, however, mainly so-called lateral components are available, which are limited in their performance.

This is where the VerGaN project comes in: By developing vertical power transistors based on the innovative GaN-on-QST technology (Qromis Substrate Technology), the project aims to achieve a breakthrough in efficiency and sustainability. These novel components significantly reduce both on-state and switching losses, while simultaneously providing access to higher voltage classes in the range of 650 to 1200 volts and beyond. Of particular note is the ability to significantly minimize switching losses through extremely fast switching operations, which represents a decisive advantage over existing technologies.

To fully exploit this potential, the project examines not only the semiconductors themselves but also their embedding into modules and systems. The high switching speeds of GaN require an exceptionally close integration between the driver and the power semiconductor, which is why new integration concepts are being developed within the project. Effects such as stray inductance and stray capacitance also play a central role, as they significantly influence performance.

The project pursues a holistic approach: From chip development and module design to the layout of the power stage, all essential aspects are taken into account. The goal is to develop a system that is both high-performing and industrially scalable. Specifically, the aim is to create a power module concept that significantly exceeds the currently standard 150 amperes in the 650-volt class while simultaneously being suitable for future vehicle architectures in the 800-volt range.

A central milestone has already been achieved: In a comprehensive design and simulation phase, the fundamental physical and electrical parameters were defined and optimized. Building on this, a detailed process development involving around 290 individual steps was established, covering both front-end processing—meaning the fabrication of the MOS structure—and back-end processing. The goal is a fully functional chip that meets the demanding requirements of future applications.

The results to date show that all relevant process steps have been successfully implemented. This is due not least to Fraunhofer ISIT’s long-standing expertise in the field of GaN power semiconductors, as well as its know-how in MEMS technology. The project is being carried out in close cooperation with the Kiel University of Applied Sciences (HAW Kiel) and industrial partners Volkswagen and Semikron Danfoss. Both companies were involved in defining the requirements at an early stage, ensuring that the developed technologies are practical and application-oriented.

With a view to the second phase of the project, VerGaN is excellently positioned: The first vertical GaN power semiconductors are close to becoming available, while the necessary test environments are already being prepared. This will allow the new chips to be tested in realistic applications in the near future.