Fundamentals of Silicon Carbide Technology: Growth, Characterization, Devices and Applications

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 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IGBT can be viewed as a vertical n-channel power MOSFET, such as shown in Figure 8.17, where the substrate has been replaced by a substrate. In the conducting state, current flows through the channel of the MOSFET, vertically through the drift region, then through the forward-biased 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 ...