Researchers Develop Method for Finding SiC Transistor Defects

January 15, 2019 by Scott McMahan

Researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have devised a simple yet accurate process for locating defects in the in silicon carbide transistors. The method is expected to speed up the process of developing more energy-efficient transistors in the future. They published their findings in the journal Communications Physics.

Power electronic components should ideally use as little electricity as possible. If not, heat is produced unnecessarily, and additional complex cooling systems are required, resulting in energy being wasted.

Unfortunately, silicon, the standard semiconductor material, is not robust enough to take the high power and high temperatures for many power electronics devices. However, silicon carbide (SiC) both withstands high voltages and high temperatures. It can also work at high switching frequencies. These three capabilities translate into better energy efficiency. For this reason, SiC components have been used very successfully for several years now. In the above image, physicist Martin Hauck fits a silicon carbide transistor into the measuring apparatus at FAU. (photo: FAU/Michael Krieger, Martin Hauck).

Charge trapping reduces efficiency

MOSFET power electronic switches made of SiC work because of the interface between the SiC and a very thin layer of silicon oxide that is either deposited or grown on it.

This interface layer poses a significant challenge for researchers because during fabrication, undesired defects inherently created at the interface. These defects trap charge carriers thereby reducing the electrical current from the device. So, research into these defects is important to ensure that SiC MOSFETs achieve their full potential.

Pattern found

The researchers pointed out that conventional measurements techniques of MOSFET devices simply ignore the existence of such defects. And while other measurement techniques are available, they are more time-consuming and complex and are either unsuitable for large scale or are simply not suitable for finished components.

This is why researchers at the Chair of Applied Physics at FAU focused on finding new, improved techniques for examining interface defects. They were successful. They observed that the interface defects invariably follow the same pattern.

"We translated this pattern into a mathematical formula," explained doctoral candidate Martin Hauck. "Using the formula gives us a clever way of taking interface defects into account in our calculations. This doesn't only give us very precise values for typical device parameters like electron mobility or threshold voltage, it also lets us determine the distribution and density of interface defects almost on the side."

The researchers employed specially designed transistors from industrial partners Infineon Technologies Austria AG and its subsidiary Kompetenzzentrum für Automobil- & Industrie-Elektronik GmbH to conduct experiments with the new defect detection method. According to the researchers, the straightforward method also proved to be highly accurate.

Now the researchers claim that taking a close look at the inner core of the field-effect transistors enhances innovations and shortens innovation cycles. Also, they contend that by using this technique, processes targeting reduced defects can be evaluated quickly, accurately, and simply. So, work at developing new, more energy-saving power electronics can be accelerated.