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Fraunhofer Team Integrates Charging Solution Onto Single GaN Chip

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German researchers pave the way for more compact and efficient on-board chargers in electric vehicles

Researchers from Fraunhofer Institute for Applied Solid State Physics IAF have integrated current and temperature sensors onto a GaN-based semiconductor chip, along with 600 V-class power transistors, freewheeling diodes and gate drivers. The team believes that the development paves the way for more compact and efficient on-board chargers in electric vehicles.

Fraunhofer IAF has been conducting research on monolithic integration in the field of power electronics for several years. Back in 2014, the researchers at succeeded in integrating intrinsic freewheeling diodes and gate drivers on a 600 V-class power transistor. In 2017, a monolithic GaN half bridge was then operated at 400 V for the first time.

This latest breakthrough is part of the GaNIAL(Integrated and efficient power electronics based on GaN) project, funded by the German Federal Ministry of Education and Research. Since 2016, this collaboration between Fraunhofer IAF and the BMW Group, Robert Bosch GmbH, Finepower GmbH and the University of Stuttgart has been working to develop powerful, compact GaN-based components for electromobility.

"By additionally integrating sensors on the GaN chip, we have succeeded in significantly enhancing the functionality of our GaN technology for power electronics," explains Patrick Waltereit, project manager of GaNIAL and deputy head of the Power Electronics business unit at Fraunhofer IAF.

Integrated sensors for direct control

Compared to conventional voltage converters, the newly developed circuit simultaneously not only enables higher switching frequencies and a higher power density; it also provides for fast and accurate condition monitoring within the chip itself. "Although the increased switching frequency of GaN-based power electronics allows for increasingly compact designs, this results in a greater requirement for their monitoring and control. This means that having sensors integrated within the same chip is a considerable advantage," says Stefan Mönch, a researcher in the Power Electronics business unit at Fraunhofer IAF.

Previously, current and temperature sensors were implemented externally to the GaN chip. The integrated current sensor now enables feedback-free measurement of the transistor current for closed-loop control and short-circuit protection, and saves space compared to the customary external current sensors. The integrated temperature sensor enables direct measurement of the temperature of the power transistor, thereby mapping this thermally critical point considerably faster and more accurately than previous external sensors, as the distance and resulting temperature difference between the sensor and the point of measurement is eliminated by the monolithic integration.

"The monolithic integration of the GaN power electronics with sensors and control circuit saves space on the chip surface, reduces the outlay on assembly and improves reliability. For applications that require lots of very small, efficient systems to be installed in limited space, such as in electromobility, this is crucial," says Mönch, who designed the integrated circuit for the GaN chip. Measuring just 4 x 3 mm², the GaN chip is the basis for the further development of more compact on-board chargers.

Exploiting the unique characteristic of GaN

For the monolithic integration, the research team used the semiconductor material GaN deposited on a silicon substrate (GaN-on-Si). The unique characteristic of GaN-on-Si power electronics is the lateral nature of the material: the current flows parallel to the surface of the chip, meaning that all connections are located on the top of the chip and connected via conductor paths. This lateral structure of the GaN components allows for the monolithic integration of several components, such as transistors, drivers, diodes and sensors, on a single chip. "GaN has a further crucial market advantage compared to other wide-bandgap semiconductors, such as silicon carbide: GaN can be deposited on cost-efficient, large-area silicon substrates, making it suitable for industrial applications," explains Mönch.

Presentation at PCIM Europe

Project partner Finepower will be displaying the newly developed GaN power module at this year's PCIM Europe. Researchers from Fraunhofer IAF will unveil their latest research results and developments at the accompanying conference. PCIM Europe will be hosted from 7 to 9 May 2019 in Nuremberg.


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