TRIAC Structure & Fabrication

- an overview and notes on the structure and fabrication of the TRIAC widely used for switching in many electronics and electrical circuits.

The TRIAC structure is very different to that of the ordinary thyristor.

Having the ability to switch signals on both halves of a cycle requires the TRIAC structure to be considerably more complicated than other similar devices.

Nevertheless the TRIAC fabrication is well established and TRIACs are widely and cheaply available.

TRIAC structure

The structure of a TRIAC may be considered to be a DIAC with an additional gate contact provided to enable control of the device.

Like other power devices, the TRIAC is normally made of silicon. Using a silicon fabrication process further enables the devices to be produced very cheaply. The market would not tolerate the devices if they were made using more expensive technologies.

As can be seen, the TRIAC structure consists of a number of different areas - typically four n-type areas as shown and two p-type areas.

Structure of a TRIAC
The structure of a TRIAC

The gate contact is made to the p-base region, although there is an additional n-type diffusion layer placed under much of the gate.

Additionally connections for both anodes or main terminals, i.e. MT1 and MT2 cross p and n regions as shown. . . . . . . . . .

By Ian Poole

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