IGCT: Advancing Power Semiconductor Technology

The Integrated Gate Commutated Thyristor (IGCT) is a power semiconductor electronic device used for switching currents in industrial equipment. It is jointly developed by Mitsubishi and ABB. The IGCT is similar to the Gate Turn-Off Thyristor (GTO) but with multiple gate terminals in parallel.

The IGCT can be controlled for conduction and cutoff by gate signals, offering lower conduction losses and the ability to withstand higher voltage rise rates compared to GTO thyristors. This eliminates the need for buffers in most applications.

In the IGCT, due to the parallelism of multiple gate terminals, the cutoff current is greater than the anode current. This results in a shorter time to completely eliminate minority carriers, providing faster cutoff speed. The parallel gate terminals also reduce the inductance and resistance in the gate drive circuit. Compared to GTO thyristors, IGCT has a faster cutoff time, allowing it to operate at frequencies as high as several kHz within a short time. IGCT devices can be manufactured with or without reverse blocking capability. However, to enhance reverse blocking capability, a long and lightly doped drift region is required, leading to increased forward voltage drop. IGCTs capable of blocking reverse voltage are known as Symmetrical IGCT (S-IGCT), with a structure similar to GTO thyristors. Typically, the reverse blocking voltage rating of S-IGCT is the same as the forward blocking voltage rating. S-IGCT is commonly used in current source inverters.

IGCTs unable to block reverse voltage are termed Asymmetrical IGCT (A-IGCT) and usually have a reverse breakdown voltage of several tens of volts. However, the addition of an n-type buffer layer shortens the drift region, resulting in a lower forward voltage drop compared to S-IGCT. A-IGCTs are used in parallel with reverse-conducting diodes (for example, in voltage source inverters) or in situations without reverse voltage (for example, in switch-mode power supplies or DC choppers).

If a portion of the p⁺ collector electrode is changed to an n⁺ region, that portion becomes a reverse-conducting diode in parallel with the IGCT. An Asymmetrical IGCT manufactured with a reverse-conducting diode in the same package is known as an RC-IGCT, designed for reverse conduction.

IGCTs find primary applications in variable frequency inverters, used in driving electric motors for propulsion and traction systems.