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Fundamentals of Silicon Carbide Technology: Growth, Characterization, Devices and Applications by James A. Cooper, Tsunenobu Kimoto

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9.2 Insulated-Gate Bipolar Transistors (IGBTs)

We now turn our attention to the IGBT. The silicon IGBT was developed to reduce the drift region resistance c09-math-0376 of power MOSFETs through the use of conductivity modulation. Indeed, an early term for the IGBT was “COMFET”, short for conductivity-modulated field effect transistor. Structurally, an n-channel IGBT can be viewed as a vertical n-channel power MOSFET, such as shown in Figure 8.17, where the c09-math-0377 substrate has been replaced by a c09-math-0378 substrate. In the conducting state, current flows through the channel of the MOSFET, vertically through the c09-math-0379 drift region, then through the forward-biased c09-math-0380 diode into the substrate. However, the physics of the IGBT is much richer than this. A more insightful interpretation would view the IGBT as an n-channel MOSFET merged with a pnp BJT. In the conducting state, the thick n-base of the pnp BJT is in high-level injection, resulting in conductivity modulation that reduces the voltage drop across this region. The penalty ...

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