The energy efficiency of electronic components is playing an increasingly important role in numerous fields of application. And that's not all: ever faster active components, higher power densities of miniaturized systems and absolute reliability are in demand. Added to this is the demand for environmentally conscious resource procurement and the requirement that module performance should increase in parallel with lower energy consumption.

The electronics industry has therefore been relying on silicon (Si) for over 50 years; in recent years, silicon-based microelectronics has repeatedly reached new performance peaks. The number of transistors on a chip has doubled almost every two years and so has the computing power of processors. However, the limits have almost been reached. For this reason, the Institute of Electrical Engineering and Information Technology (ET&IT) and the Institute of Materials Science at the Faculty of Engineering at Kiel University (CAU Kiel) are working on new semiconductor materials. Research topics at this faculty include renewable energies, sensor technology and electromobility.

Future semiconductor materials

More powerful semiconductor materials are a prerequisite for the electronics market of the future in general and for power electronics in particular. Specifically, more powerful semiconductor materials are required for significantly smaller components. For this reason, power semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) are outstripping the silicon (Si) used to date. GaN transistors in particular enable a smaller size and potentially lower costs. They have a significantly lower conductive resistance for the same size of electronic components and achieve faster commutation, which in turn results in lower switching losses. The lack of reverse recovery charging also enables a higher frequency and power density. All of these factors offer significantly higher energy efficiency than silicon-based technologies.

However, this increase in performance coupled with advancing miniaturization is also changing the requirements in the research and development of power electronics. Temperature in particular is becoming an even more critical parameter for all power systems. GaN-based power modules, for example, operate at temperatures of up to +600 °C - higher than other silicon-based electronics. Thermal management is extremely important to ensure that the individual elements can withstand the high thermal stress and do not fail prematurely. The GaN transistors operate at very high switching frequencies, which means that the temperatures also cycle quickly. This places high demands on the technology used for monitoring and/or process optimization.

Thermography in use for power electronics

Based on the knowledge gained through thermography, high-frequency components and materials are to be developed that can withstand such high thermal loads. As both the electronic components and the transistors are very small, the thermal imaging camera used must meet a number of requirements.

Measuring set-up for investigating various semiconductor materials in the laboratory at Kiel University.

© CAU Kiel

A measurement setup suitable for this purpose was designed for the CAU, which uses a cooled thermographic system from Infratec 's 'ImageIR' thermal imaging camera series. With its high thermal resolution of up to 20 mK, it detects even the smallest temperature changes and, thanks to its 50 mm optics together with special close-up optics, resolves structures of less than 50 μm in size in this application. The thermal imaging camera has a cooled photon detector and therefore enables the imaging of particularly fast processes. Switching peaks can therefore be analyzed without any problems. The non-contact measurement is non-destructive and enables the detection of several critical points, as the entire object is displayed as an image. The camera can be connected to the existing 'Matlab' controller using the Infratec Software Development Kit (SDK) supplied.

Research at the CAU in Kiel

The Faculty of Engineering at Kiel University is researching the changes and developments in temperatures and their distribution in various semiconductor materials in the field of power electronics in order to optimize processes and technologies. In particular, this involves 'U-Heart' - a concept of isolated DC-DC converters with several connections. It is equipped with a fault detection circuit that excludes a detected faulty cell from power transmission.

Thermographic system of the 'ImageIR' thermal imaging camera series from Infratec

© CAU Kiel

For areas where maintaining the operation of all cells is required, self-healing approaches are being developed to maintain the operation of all cells and continue working at full power. U-Heart is an ERC proof of concept grant for a maintenance-friendly power converter and can be used as a multi-port converter for connecting multiple voltage grids, for example for energy storage (batteries, supercapacitors), renewable energy sources (solar PV modules, fuel cells) and DC loads. The development of this energy superstar also benefited from knowledge gained through thermography from the previous Heart project (ERC grant).

The author
Jens Vogt is Head of International Sales at Infratec in Dresden.