Normally Off Type SiC Power MOSFET (IEMOS) with World Record On-Resistance

The Power Electronics Research Center (PERC) of the National Institute of Advanced Industrial Science and Technology (AIST), has succeeded in the on-resistance of 4.3 mΩcm2 and blocking voltage 1100 V in a transistor structure developed by the PERC-AIST, named “implantation and epitaxial MOSFET (IEMOS) with high channel mobility of normally-off type SiC power MOSFET.This resistance value is smallest in the world, as small as 1/5 that of the insulated gate bipolar transistor (Si-IGBT), a power device used widely at present. The power loss at the time of operation is also 1/5 as small. The newly developed device will be applicable to switching power supply, air conditioner, uninterruptible power source (UPS), inverter for electric or hybrid vehicle, and so on. In these applications, switching loss inherent to conventional Si-based devices will be extensively reduced, saving energy in home electric appliances to break through the technological limitations, and opening the way to new generation switching devices for energy saving and eco-friendliness.

In SiC power MOFET, called double-implanted MOSFET (DIMOS), SiC reigionnamed P well in contact with gate oxide film (Figs. 3 and 5) is formed by aluminum implantation followed by heat treatment at 1600 °C or higher, which induces Si to evaporate from the flat SiC surface to make it rough (Fig. 4). Electrons flowing through this region are disturbed by scattering at the roughness to increase on-resistance. On the other hand, in the IEMOS developed by PERC-AIST, the surface of P well prepared by epitaxial growth is flat without heat treatment at 1600 °C or higher (Fig. 6), letting electrons flow smoothly to reduce On-resistance to 4.3 mΩcm2, the smallest value in the world. The bottom of P well is formed by high concentration implantation, with N- type region designed to high blocking voltage, the device is successfully made the blocking voltage 1100 V or higher. Moreover, the device is of normally-off type admitting no current when no gate voltage is applied , allowing gate control readily when used with general inverter.

While on-resistance of Si-IGBT with blocking voltage of 1000V widely used at present is around 20 mΩcm2 , that of IEMOS is 4.3 mΩcm2, 1/5 as small as that of Si-IGBT, which is of bipolar type with certain demerits such as slow switching speed and large power loss at the time of switching. The newly developed SiC-IEMOS is of unipolar type, and is characterized not only by small on-resistance, but also by high switching speed.

Details of the present study will be reported at the 52nd Spring Meeting,2005, The Japan Society of Applied Physics and Related Societies to be held at the Saitama University from March 29 to April 1.

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