High-efficiency SiC power device developed

Mitsubishi Electric has developed a silicon carbide (SiC) power device with what is claimed to be the world’s highest power efficiency in a device of its type, thanks to the use of a proprietary source structure.

Designed to be installed in power modules, the newly developed unit is expected to help improve the energy efficiency of power electronics equipment used in applications such as home electronics, industrial machinery and railway operation. It does not require a high-speed protection circuit to interrupt supply when excess current is detected.

Because the resistance of a SiC-MOSFET is lower than that of a Si device, any overcurrent tends to be large, resulting in a reduction of the short-circuit time. In order to protect SiC-MOSFETs from damage, overcurrent in these devices has to be terminated more quickly than with a Si device. This is usually achieved by the inclusion of special protection circuits for SiC-MOSFETs. There is additionally a trade-off between the short-circuit time and on-resistance — a long short-circuit time requires high on-resistance and a large chip size.

While conventional MOSFETs form the source area as a single region, Mitsubishi Electric has introduced an additional region in the source area to control the source series resistance of its new SiC-MOSFET. Adopting this structure reduces the short-circuit current by the increased resistance resulting from temperature rise induced by the short circuit, at the same time keeping the on-resistance at low levels at normal operating temperatures. This technology can improve the trade-off between short-circuit time and on-resistance. As a result, on the general short-circuit time used for Si power semiconductor devices, the on-resistance of the SiC-MOSFET is reduced by 40% at room temperature, and power loss by more than 20%, compared to the company’s conventional 1200 V SiC-MOSFET.

A simplified circuit design allows the technology to be applied across SiC-MOSFETs with various voltage ratings. Circuit technology is used to protect silicon components from damage in the event of short-circuits, and can be applied to existing SiC-MOSFETs without any need for modification. This ensures easy implementation of protective functionality in power electronics equipment using SiC-MOSFETs.

At the time of its announcement, at the 2017 International Conference on Silicon Carbide and Related Materials (ICSCRM 2017), the SiC device had the world’s highest power efficiency rating of any 1200 V-class power device with a short-circuit time exceeding 8 μs, according to Mitsubishi Electric’s research. The company’s development teams will further refine the new device, aiming to make it available commercially from the year 2020.