SiC High Blocking Voltage Transistor

Recently, energy saving is strongly required to prevent global warming. Electricity is the most common energy form and is necessary in our daily life and various activities, because it is comparatively easy to utilize in transmission and conversion after generation. Therefore, it is very important to reduce energy loss in electric power systems and improve their efficiency. The present power systems basically consist of semiconductor power devices made of silicon (Si). Though the devices have been developed by structural modification with advanced microfabrication, it is impossible to overcome the material limits of Si. Therefore, it is strongly expected to develop alternative power devices that exceed the material limits of Si. Silicon Carbide (SiC) has become a candidate material for next generation power devices to replace traditional Si power devices. Among the various crystalline polytypes of SiC, 4H-SiC is the most promising as a semiconductor material for power devices. In comparison to Si, 4H-SiC has several advantages, such as wide bandgap, high breakdown field, high thermal conductivity, and high saturation velocity. As the critical breakdown field of 4H-SiC is about three times higher than that of Si, SiC devices can be superior power devices in the category of higher voltage applications. Under conditions for keeping a certain blocking voltage, thickness of the drift region for SiC is one tenth of that for Si. Also, doping concentration is a hundred times higher than that of Si. As these give an advantage in decreasing resistance in the drift layer, a specific on-resistance of SiC is estimated to be two or three orders of magnitude less than that of Si. On the other hand, as the saturation drift velocity of 4H-SiC is twice higher than that of Si, 4H-SiC is also expected to be a better material for high speed switching applications. As thermal conductivity of 4H-SiC is three times higher than that of Si, 4H-SiC devices can be utilized under a simple cooling system. In the present application of high voltage inverters and converters for industrial motors, the Si Insulated Gate Bipolar Transistors (IGBTs) with a blocking voltage of 1,200-3,300 V are generally adopted. However, due to the advantages of 4H-SiC devices described above, SiC MOSFET are expected to replace Si IGBT. In this paper, the authors report on the SiC MOSFET with a blocking voltage of 2,200 V and 3,300 V and its characteristics. The device design and the fabrication processes are also discussed.