New structure boosts SiC MOSFET efficiency
The devices uses a new proprietary source structure. In conventional metal-oxide-semiconductor field-effect transistors, known as MOSFETs, the source area is formed as a single region. However, Mitsubishi has added an extra region in the source area to control the source series resistance of the SiC-MOSFET (as shown above). This structure reduces the excessive current flows caused by short circuits and so allows the on resistance to be reduced by 40 percent at room temperature, and power loss by more than 20 percent compared to conventional SiC-MOSFET devices.
The device is designed to be installed in power modules, and does not require a high-speed protection circuit to interrupt supply when excess current is detected. This will will help improve the reliability and energy efficiency of power electronics equipment used in a wide range of applications such as home electronics, industrial machinery and railway operation, says the company.
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 also a trade-off between the short-circuit time and on-resistance. A long short-circuit time (around 8 μs) traditionally requires high on-resistance and a large chip size.
The structure of the newly-developed SiC MOSFET device 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 improves the trade-off between short-circuit time and on-resistance to provide higher reliability, higher energy efficiency and reduced size.
The simplified circuit design allows the technology to be applied across SiC-MOSFETs with various voltage ratings and can be applied to existing SiC-MOSFETs without any need for modification. This provides short circuit protection for existing designs, eliminating the need for extra protection components.
Mitsubishi Electric’s development team is refining the design of the device, aiming to make it available commercially from 2020.
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