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Definition: transistor

In the analog world of continuously varying signals, a transistor is a device used to amplify its electrical input. In the digital world, a transistor is a binary switch and the fundamental building block of computer circuitry. Like a light switch on the wall, the transistor either prevents or allows current to flow through. A single modern CPU can have hundreds of millions or even billions of transistors.

Made of Semiconductor Material
The active part of the transistor is made of silicon or some other semiconductor material that can change its electrical state when pulsed. In its normal state, the material may be nonconductive or conductive, either impeding or letting current flow. When voltage is applied to the gate, the transistor changes its state. To learn more about the transistor, see transistor concept and chip. See active area, phototransistor and High-K/Metal Gate.

From Transistors to Systems
Transistors are wired in patterns that make up logic gates. Gates make up circuits, and circuits make up electronic systems (for details, see Boolean logic and Boolean gates).

Conceptual View of a Transistor
In a digital circuit, a transistor is an on/off switch that is conductive when pulsed with electricity. Transistors are also used as amplifiers, transferring a low voltage at the base to a high voltage at the collector. Audio amplifiers use transistors in this manner.

Building the Transistor
Through multiple stages of masking, etching, and diffusion, the sublayers on the chip are created. The final stage lays the top metal layer (usually aluminum), which interconnects the transistors to each other and to the outside world.

At the Same Time
Most of the transistors in every chip on the wafer are created at the same time. A 300 mm wafer like this can hold hundreds and thousands of dies (chips), which means billions and trillions of transistors are fabricated simultaneously. See wafer. (Image courtesy of Intel Corporation.)

The First Silicon Transistor
In 1954, Texas Instruments pioneered production of discrete transistors on a commercial scale. About a quarter inch square, this amount of space can hold trillions of transistors today. See transistor concept. (Image courtesy of Texas Instruments, Inc.)

IBM "Solid Logic"
Instead of only one transistor per package, IBM's advanced engineering placed three transistors on a single module for its System/360 family in 1964. With the cover removed, the three are plainly visible. See active area. (Image courtesy of IBM.)