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SiC device with record efficiency will boost power electronics

22 September, 2017

Mitsubishi Electric has developed a silicon carbide (SiC) power device which, it claims, has the world's highest power efficiency for a device of its type (a 1.2kV power device with a short-circuit time longer than 8μs). The new device, designed to be used in power modules, does not need a high-speed protection circuit to interrupt the supply when an excess current is detected. Mitsubishi says it will improve the reliability and efficiency of power electronics equipment in applications ranging from industrial machinery and railways to domestic appliances.

The superior reliability and efficiency of the new device is the result of a new source structure. In conventional Mosfets (metal-oxide-semiconductor field-effect transistors), the source area is formed as a single region. The new device has an extra region to control its source series resistance.

This structure reduces the incidence of excessive current flows caused by short circuits. As a result, based on the general short-circuit time used for Si power semiconductor devices, the new SiC-Mosfet has an on-resistance that is 60% lower than that of Si devices and is 40% lower than that of a conventional SiC-Mosfets. Power losses are at least 20% lower than those of other SiC-Mosfets.

A simplified circuit design allows the technology to be applied to SiC-Mosfets with various voltage ratings. Circuit technology already proven to protect silicon components from damage in the event of short-circuits, can be applied to the new devices without needing any modifications. This will make it easy to implement protective functions in power electronics equipment using the SiC-Mosfets.

Short circuits in power electronics can cause large overcurrent flows into their semiconductor devices, which can damage them or cause them to fail. To prevent this, excess currents must be interrupted as quickly as possible. The “short-circuit time” is the length of time a device can withstand an overcurrent. Because the resistance of SiC-Mosfet devices is lower than that of Si devices, any overcurrent tends to be large, reducing the short-circuit time. To protect SiC-Mosfets, overcurrents in these devices have to be terminated faster than with Si devices. This is usually achieved by including special protection circuits in these devices.

Mitsubishi claims that its new SiC device cuts power losses by more than 20%

In addition, there is 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. Improvements in this trade-off have been sought for a long time.

The structure of the new SiC power device reduces the short-circuit current and can improve the trade-off between short-circuit time and on-resistance. As a result, it can simultaneously offer high reliability, high energy efficiency and reduced size.

Mitsubishi Electric plans to refine the new device further and is aiming to make it available commercially from 2020.

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