17 June 2020
ROHM unveils fourth-generation SiC MOSFETs
Power semiconductor maker ROHM Semiconductor of Kyoto, Japan has announced its 4th Generation 1200V silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) optimized for automotive powertrain systems, including the main drive inverter, as well as power supplies for industrial equipment.
In recent years, the proliferation of next-generation electric vehicles (xEVs) has been accelerating the development of smaller, lighter and more efficient electrical systems. In particular, improving efficiency while decreasing the size of the main inverter that plays a central role in the drive system remains among the most important challenges, requiring further advances in power devices.
To improve the cruising range of EVs, the capacity of the onboard battery is increasing. In conjunction with this, the use of higher-voltage batteries (800V) is progressing to meet the demand for shorter charging times.
To solve these various challenges, designers urgently need SiC power devices capable of providing high breakdown voltage with low losses. ROHM says that it began mass producing SiC MOSFETs ahead of the industry in 2010. ROHM has since strengthened its lineup to include AEC-Q101-qualified products, allowing it to hold a large market share for automotive onboard chargers (OBC).
For power semiconductors there is often a trade-off relationship between lower ON-resistance and short-circuit withstand time (the time it takes for a MOSFET to fail due to a short-circuit). Normally, when a short-circuit occurs, a large current exceeding the maximum rating flows, which can lead to abnormal heat generation, thermal runaway and ultimately destruction. Longer short-circuit withstand time is in a trade-off relationship with higher-performance characteristics, such as ON-resistance. So, there is a need to strike a balance to achieve lower power losses in SiC MOSFETs.
Although the adoption of a trench structure to SiC MOSFETs was shown to be effective in reducing ON-resistance, it was necessary to mitigate the electric field generated in the trench gate section to ensure long-term reliability of the device. In response, ROHM adopted a unique double-trench structure that minimizes electric field concentration, allowing it in 2015 to be first to mass produce trench-type SiC MOSFETs. By further improving its original double-trench structure, the firm has now been able to improve the trade-off relationship and reduce ON-resistance per unit area by 40% compared with the firm’s previous generation of SiC MOSFETs without sacrificing short-circuit withstand time (see Figure 1).
Also, in general, lower ON-resistances and larger currents tend to increase the various parasitic capacitances in MOSFETs, which can inhibit the inherent high-speed switching characteristics of SiC. However, by significantly reducing the gate-drain capacitance (Cgd), ROHM was able to achieve 50% lower switching loss over the firm’s previous generation of SiC MOSFETs (see Figure 2).
As a result, ROHM’s new 4th Generation SiC MOSFETs are capable of delivering low ON-resistance with high-speed switching performance, contributing to greater miniaturization and lower power consumption in a variety of applications, including automotive traction inverters and switching power supplies. Bare chip samples have been made available from June, with discrete packages to be offered in the future.
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