ROHM’s New 4th Generation SiC MOSFETs Features Industry’s Lowest ON Resistance


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ROHM announces the cutting-edge 4th Generation 1200V SiC 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 advancements in power devices.

The capacity of the onboard battery is increasing to improve the cruising range of EVs. And 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 withstand voltage with low losses. ROHM, a pioneer in SiC, began mass producing SiC MOSFETs ahead of the industry in 2010. From early on, ROHM has strengthened its considerable lineup to include AEC-Q101 qualified products allowing the company 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, which is required to strike a balance for achieving lower power losses in SiC MOSFETs. ROHM was able to successfully improve this trade-off relationship and reduce ON resistance per unit area by 40% over conventional products without sacrificing short-circuit withstand time by further improving an original double trench structure. In addition, significantly reducing the parasitic capacitance (which is a problem during switching) makes it possible to achieve 50% lower switching loss over our previous generation of SiC MOSFETs.

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 2020, with discrete packages to be offered in the future.

ROHM is committed to continue to expand its SiC power device lineup while combining modularization technologies with peripheral devices such as control ICs designed to maximize performance in order contribute to technical innovation in next-generation vehicles. At the same time, ROHM will provide solutions that resolve customer issues – including web-based simulation tools that reduce application development man-hours and help prevent evaluation problems.

Key Features

1) Improved trench structure delivers the industry’s lowest ON resistance

In 2015, ROHM began mass production of the industry-first trench-type SiC MOSFETs utilizing an original structure. Now, ROHM has successfully reduced ON resistance by 40% compared to conventional products without sacrificing short-circuit withstand time by further improving its original double trench structure. 

2) Achieves lower switching loss by significantly reducing parasitic capacitance

Generally, 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, ROHM was able to achieve 50% lower switching loss over conventional products by significantly reducing the gate-drain capacitance (Cgd).

Terminology

MOSFETs (Metal Oxide Semiconductor Field Effect Transistors)

The most commonly used structure in FETs. Often adopted as switching elements. 

Short-Circuit Withstand Time

Indicates 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 will flow, 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.

Double Trench Structure

ROHM’s original trench structure. 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 device. In response, ROHM adopted a unique double-trench structure that minimizes electric field concentration, allowing it to become the first supplier to mass produce trench-type SiC MOSFETs in 2015.

Parasitic Capacitance

Inherent capacitance that occurs due to the physical structure within electronic components. In the case of a MOSFET, there is a gate-source capacitance (Cgs), gate-drain capacitance (Cgd), and drain-source capacitance (Cds). Cgs and Cgd are determined by the capacitance of the gate oxide film, while Cds is the junction capacitance of the parasitic diode.

Trench Structure

The word ‘trench’ means a narrow excavation or groove. This design involves forming a groove on the chip surface and the gate on the MOSFET side wall. JFET resistances don’t exist compared to a planar-type MOSFET configuration, making it possible to achieve a finer structure over planar topologies – resulting in an ON resistance close to the original performance of the SiC material.

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