Power MOSFETs in 4H -SiC: Device Design and Technology A. Agarwal, S.-H. Ryu, and J. Palmour 1 Introduction Silicon (Si) power metal-oxide-semiconductor field-effect transistors (MOS- FETs) are widely used in audio and radio frequency (rf) amplifiers, switch mode power supplies (SMPS), power factor correction (PFC) circuits, lamp ballasts and many types of control circuits. Power MOSFETs have several desirable characteristics such as (a) high switching speed due to the absence of minority carrier storage, (b) voltage controlled input, and (c) ease of par- alleling due to the negative temperature coefficient of the on-state current. Power MOSFETs have largely replaced bipolar junction transistors (BJTs) in medium power (<20 kW) applications requiring high switching speeds (>10 kHz). In contrast to a power MOSFET, a power BJT requires a large continuous base current to turn it on and keep it on. The base current re- quirement can be as high as 25% of the collector current. It is difficult to parallel power BJTs due to the fact that the on-state current increases with temperature making the current sharing between different transistors un- equal. Furthermore, the switching speed of BJTs is much slower than power MOSFETs due to the storage of minority carriers in the base and collector regions. Thus, the switching losses become prohibitively high at switching frequencies higher than 10–20 kHz. Si power MOSFETs are available up to about 1200 V. However, for rat- ings above 200–300 V, the specific on-resistance becomes very high and a very large chip area is required to obtain an adequate current rating. For example, 200 V Si MOSFETs can be purchased as a single unit up to about 100 A whereas a 1200 V device is generally available for <10 A current rating. Therefore, above 600 V, it is customary to use Si insulated gate bipo- lar transistors (IGBTs), which are available in large current ratings but are extremely slow due to the minority carrier storage. In contrast, SiC power MOSFETs can be developed with voltage ratings up to 3000 V with a specific on-resistance similar to that of a 300 V Si MOSFET. Therefore, it will be advantageous to replace a Si IGBT with a SiC power MOSFET up to about 3 kV in applications requiring faster switching speed and lower switching losses. W.J. Choyke et al. (eds.), Silicon Carbide © Springer-Verlag Berlin Heidelberg 2004