Denso Develops Silicon Carbide Process
Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 5/27/2008 7:10:00 AM
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Intended for cars with electric motors and hybrid drive trains, Denso demonstrated a power module integrating the power MOSFETs and SBDs at the Automotive Engineering Exposition in Yokohama, Japan, organized by the Society of Automotive Engineers of Japan.
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| Denso demonstrates SiC devices, including (from right) a 3 in. wafer, power MOSFET, SBD, a power module before capping, and a module after capping. The products are aimed at hybrid cars with both electric motors and gasoline engines. |
Denso, a tier-one supplier of Toyota Motor Corp. (Toyota City, Japan), produced the 3 in. SiC wafer ingot using vapor phase deposition from a small seed crystal in an atmosphere over 2000°C. Rohm Co. Ltd. (Kyoto, Japan) announced a SiC power MOSFET a week ago based on wafers it purchased from Cree Inc. (Durham, N.C.).
The Denso SiC process features a non-liquid (gas phase) state above the melting temperature point but at a normal pressure, precluding the use of the familiar Czochralski method used in silicon crystal growth. Higher pressure enables liquid crystal growth but requires a more complicated equipment set, leading Denso to use the gas phase growth method. The ingot is sliced into 300-µm-thick wafers.
The prototype MOSFET delivers a 1200 V breakdown voltage and 30-40 A current, and the SBD is rated at a 1200 V breakdown voltage and 200 A of current.
Why SiC? Why not silicon?
SiC features a higher temperature operation than silicon (200°C) as well as a higher breakdown voltage, higher current density and higher switching speed, suitable for automotive applications. The SiC is a wide bandgap semiconductor, stable at temperatures as high as 300°C.
The SBD is connected to a MOSFET in a reverse parallel arrangement. An electric automobile uses three-phase drive motors to rotate wheels, and each motor has three combinations of MOSFETs and SBDs. The prototype devices handle 200 A, but an automotive motor requires 600 V and 400 A as a switching device. The demonstration module includes six 200 A devices (six MOSFETs and six SBDs). Denso plans to develop a 400 A device as the next step.
At the show, Rohm also demonstrated an SiC MOSFET and SBD showing their DC characteristics using a 4 in. SiC wafer.
Toyota announced on May 15 that worldwide cumulative sales of the Toyota Prius — the world's first mass-produced gasoline/electric hybrid vehicle — have passed the 1 million mark. The Prius was introduced in 1997.
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