ROHM and Honda R&D Develop the World's First High-power Module
with Semiconductor Devices Based on the New Material SiC
for Use in Next-generation Electric Vehicles

Semiconductor manufacturer ROHM CO., LTD. and Honda R&D Co., Ltd. (Head Office: Saitama Prefecture) have developed a 1,200 V/230 A (280 kVA equivalent) class high-power inverter module featuring SiC-SBD and SiC-MOSFET devices and designed for use in next-generation electric vehicles. The module combines ROHM’s SiC device technology with Honda R&D’s high-power module technology, making it the world’s first high-power inverter module to be fully driven by SiC devices. Functionally, it incorporates a converter circuit (1-phase) and an inverter circuit (3-phase) in a single package to deliver a more compact design.

Designers of components for applications requiring power electronics—for example, the rapidly growing hybrid vehicle (HEV) and electric vehicle (EV) segments of the automobile market—have been awaiting the commercialization of SiC devices, which offer exceptional material properties and lower loss during power conversion than the Si devices that are currently used in those applications.

In terms of standalone element properties, the SiC devices developed by ROHM have been shown to dramatically reduce switching losses by a factor of approximately 1/7 compared to Si-IGBT devices. They also offer superior performance for power modules, where a switching loss reduction of approximately 1/4 has been observed compared to conventional Si devices. These improvements pave the way for component designers to slash total losses during power conversion, including on-losses. Moreover, every reduction in switching loss enables a corresponding increase in drive frequency: for example, a conventional Si-IGBT-based module limited to a PWM frequency of 20 kHz could realize a fourfold increase to 80 kHz by adopting the new SiC devices.

Use of the newly developed SiC-based high-power modules in HEVs and EVs is expected to drive a series of significant improvements, including by reducing losses and allowing smaller, more lightweight systems. Looking to the future, ROHM believes improvements in the structure of power modules will enable them to take full advantage of the standalone performance of SiC-MOSFET devices and expects to see significant performance gains deriving from SiC-MOSFET miniaturization and structural

Employed to reduce total loss in inverter applications, the new modules can be expected to shrink cooling equipment and expand the scope of design for thermal management thanks to their reduced heat value. Alternately, used in step-up converter applications, they will enable a fourfold increase in drive frequency over previous technologies, promising significant improvements in output density thanks to the use of smaller, more lightweight peripheral components.

Furthermore, the high-temperature stability of SiC devices’ thermal properties will simplify failsafe designs for onboard use. ROHM and Honda R&D are poised to bring the new modules to an increasingly broad range of products, focusing on the technology’s ability to deliver the power conversion characteristics required by high-current power electronics applications.

•Terminology

• Inverter
  A circuit or device for converting DC voltages and currents to AC voltages and currents.
• Converter
  A circuit or device for performing AC-to-DC conversion or for converting the voltage or frequency of a signal.
• SiC (silicon carbide)
  A compound semiconductor with properties that are superior to those of silicon, specifically approximately 3 times the band gap, approximately 10 times the dielectric breakdown field, and approximately 3 times the thermal conductivity. Those properties are well suited for use in power device applications.
• MOSFET (metal oxide semiconductor field effect transistor)
  Metal oxide semiconductor field effect transistors are the most commonly used FET structure. MOSFETs are also used as switching elements.
• SBD (Schottky barrier diode)
  Schottky barrier diodes have rectifying properties (diode characteristics) by virtue of their use of a Schottky junction formed by the contact between a metal and a semiconductor. The absence of the minority carrier storage effect gives SBDs excellent high-speed performance.
• Power electronics
  Power electronics refers to technology for using semiconductor devices (electronics) to freely control power by converting it into the desired form. This technology plays an essential role in modern life and is used in applications ranging from household appliances to industrial, railroad, and power systems. (from Power Electronics by Eisuke Masada and Kazuyuki Kusumoto [published by Ohmsha]).
• HEV (hybrid electric vehicle)
  Hybrid vehicles combine multiple power sources in the form of an internal combustion engine and an electric motor, which they can use separately or in combination as driving conditions dictate. Hybrid vehicles achieve total efficiency comparable to an electric vehicle or fuel cell vehicle and are widely viewed as practical vehicles with a low environmental impact.
• EV (electric vehicle)
  Electric vehicles are driven by electricity. They use a secondary (or primary) battery as a power source and obtain power for driving either by being recharged from an outside source or having their battery replaced.
• IGBT (insulated gate bipolar transistor)
  Insulated gate bipolar transistors deliver low ON resistance by enabling currents to flow as a result not only of electrons but also of holes. The high switching loss of this design is a problem, with the accumulation time for injected holes preventing high-speed operation.

■Figure 1, SiC High-power Inverter Module Developed by ROHM and Honda R&D

■Figure 2, Comparison of Loss