IV. THE INSULATED GATE BIPOLAR TRANSISTOR (IGBT)
A. Physical Characteristics
The IGBT is the most popular power semiconductor currently used today. It combines the MOS gate structure with the bipolar current conduction to create a device that is the best of both the MOSFET and the BJT. For terminals, it is a hybrid between the BJT and the MOSFET.
It has three terminals: the collector, the gate, and the emitter. Schematically, the IGBT is basically a p-n-p BJT powered by an n-channel MOSFET.
B. Operational Advantages and Disadvantages
The IGBT brings together the advantages of a BJT and MOSFET. It has high input impedance, a low power consumption, and a large safe operating area. It also has a remarkably high power handling capability for a given chip size. And, because it is a minority carrier device on a p+ substrate, it has superior conduction to a standard MOSFET. When used in combination with power integrated circuits, one can expect a cost reduction by a factor of ten [2].
The only disadvantage comes in switching speed. While the IGBT can compete with the speed of the BJT, it cannot beat the MOSFET. The faster the switching, the greater the forward voltage drop, and it has a relatively high turn-off time due to the long lifetime of minority carriers. However, these problems recently have been overcome [4], allowing the IGBT to dominate in industrial applications.
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