Accelerating the spread of SiC inverters for EVs and railcars

6th August 2019
Posted By : Lanna Cooper
Accelerating the spread of SiC inverters for EVs and railcars

Showa Denko has developed a second generation high-grade silicon carbide (SiC) epitaxial wafer (HGE-2G) suitable for power semiconductors. SDK has been mass-producing the first generation of high grade SiC epitaxial wafer with very low defect density under the trade name of 'High-Grade Epi' (HGE). HGE-2G achieves further improvements in quality with six inches (150mm) diameter.

When compared with the current mainstream silicon-based semiconductors, SiC-based power semiconductors can operate under greater high temperature, high voltage, and high current conditions, while substantially reducing energy loss. These features enable device manufacturers to produce smaller, lighter, and more energy-efficient power control modules, and this market is rapidly expanding.

SiC power semiconductors are already used in power modules for servers in data centres, power modules for dispersion type power sources to utilise new energy sources including solar power, on-board battery chargers and rapid charging stands for EVs, and inverter modules for railcars.

In addition, SiC power semiconductors are expected to start use in Power Control Units (PCU) for EVs in the first half of 2020s. Thus the demand for SiC-based power semiconductors is expected to grow further.

Inverter modules for high voltage, high current applications mainly contain Schottky Barrier Diode (SBD) devices and MOSFET transistors. SiC is widely used in SBD devices, and hybrid inverter containing SBD and Si-IGBT (Insulated Gate Bipolar Transistor) is already put in practical use. In recent years, however, improvement in quality of SiC epitaxial wafers and advances in device manufacturing process enabled manufacturers to put SiC-MOSFET into practical use, and full-SiC-based inverters with high energy efficiency have come into use.

For applications to inverter modules to drive motors for EVs and railcars, meanwhile, large chips measuring around 10mm square are made out of epitaxial wafers. This is because one device needs to handle a current as high as 100A. To prevent deterioration in the production yield of such large chips, the defect density on the surface of epitaxial wafers should be controlled to be less than 0.1/cm2.

In the new product 'HGE-2G,' SDK has succeeded in controlling the density of Surface Defect (SD), which affects production yield of power semiconductors, to be half of the current HGE by improving epitaxial SiC growth process.

In addition, SDK has succeeded in enhancing reliability of power semiconductors through improving the Basal Plane Dislocation (BPD) conversion rate by more than ten times compared with that of HGE. By making full use of these improvements, SDK will soon market 'HGE-2G' epitaxial wafer with better quality grade than current HGE.

The Showa Denko Group has a vision of becoming a corporate group of Koseiha businesses (individualised businesses), which can maintain profitability and stability at high levels in each business sector. The global demand for SiC epitaxial wafers is expected to increase to be about 150 billion yen by 2025.

As the largest independent manufacturer of SiC epitaxial wafers, and under a motto of 'Best in Class', SDK will continue coping with rapid expansion of the market for epitaxial wafers, developing reliable products, and investing positively to expand its production capacity, thereby making its SiC epitaxial wafer business a Koseiha business.

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