[ECSCRM] Honda Claims Highest Current Gain of SiC BJT

Sept 16, 2008 15:57 Tadashi Nezu, Nikkei Electronics

Honda R&D Co Ltd and Shindengen Electric Manufacturing Co Ltd announced a new SiC BJT (bipolar junction transistor) that they claim has the highest current gain.

The two companies, which are engaged in research and development of next-generation power semiconductor devices for use in DC-DC converters and inverters for hybrid and electric vehicles, made the announcement at the 7th European Conference on Silicon Carbide and Related Materials (ECSCRM). Honda R&D's first appearance at a SiC-related academic conference attracted a good deal of attention.

The new BJT was named "Suppressed Surface Recombination Structure (SSR)-BJT" after its unique structure. Its current gain is 134 with a withstand voltage of 950V.

So far, the highest current gain has been about 70 when a withstand voltage is 600 to 1,000V. The higher the current gain, the smaller the current needed to switch a BJT, enabling to downsize its control circuit. BJTs, though they have an advantage of low on resistance, tend to have large control circuits due to their current control systems, Honda R&D said.

This time, current gain was improved by developing a structure in which the area for carriers is separated from the trap of carriers. Specifically, an n-type layer called "Lightly Doped N-type layer (LDN-layer)" was formed between the emitter and base, and a high-resistance p-type area dubbed "a High Resistive P-type region (HRP-region)" was formed in the contact area of the emitter's mesa edge and base.

Current gain is expected to improve with only the HRP-region, but the LDN-layer was formed to make the HRP-region by injecting Al with a high degree of accuracy.

The prototype of the BJT also has a high heat resistance; its current gain is 134 at room temperature and 60 at 250°C. Its on resistance is 3.2mΩcm². Those properties were realized by a small-size chip whose active area measures 1.5 × 10^-4cm², but equivalent qualities can be achieved with larger chips, Honda R&D said.

The company has already made a 5.4 × 5.4mm chip whose active area is as large as 0.25cm².

"We made this chip on the same substrate as used for the small-size chip that we tested this time, so we expect equivalent properties," Honda R&D said.

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