Insulated Gate Bipolar Transistors -IGBT
Insulated gate bipolar transistors (IGBTs) are semiconductors that combine a high voltage and high current bipolar junction transistor (BJT) with a low power and fast switching metal-oxide semiconductor field-effect transistor (MOSFET). Consequently, IGBTs provide faster speeds and better drive and output characteristics than power BJTs and offer higher current densities than equivalent high-powered MOSFETs. Structurally, IGBTs feature a double diffusion of p-type and n-type regions. Applying a voltage to the gate contact forms an inversion layer under the gate. The p+ substrate layer serves as the drain, allowing the p-type region to fill the “holes” in the n-type drift region. The n+ buffer layer prevents the depletion region from extending to the bipolar collector, reducing on-state losses but drastically reducing the reverse blocking capability of the device.
Performance specifications for insulated gate bipolar transistors (IGBTs) include collector-emitter breakdown voltage, collector-emitter “on” or saturation voltage, maximum collector current, gate-emitter leakage current, rise time, fall time, switching speed, power dissipation and temperature. Optional features for insulated gate bipolar transistors include output diodes, gate resistors, and electrostatic discharge (ESD) protection. IGBT polarity can be n-channel or p-channel. Punch-through and non-punch-through structures are available. Some IGBTs support a specific temperature range and feature mechanical and electrical specifications that are suitable for commercial, industrial, or automotive applications. Other IGBTs meet screening levels for military specifications (MIL-SPEC).