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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, along with resistors, capacitors and diodes, are wired in patterns that make up logic gates. Logic gates wired in patterns make up circuits, and circuits wired in patterns make up electronic systems. See Boolean logic.

Conceptual View of a Transistor
In a digital circuit, a transistor is an on/off switch becoming conductive for a moment when it is pulsed with electricity. However, it can also function like a relay to amplify analog signals such as from an audio source, transferring a low voltage at the gate to a larger voltage at the drain.

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
All the transistors in every chip on the wafer are created at the same time. A 300 mm wafer can hold hundreds and even thousands of dies (chips), which means billions and even trillions of transistors are fabricated simultaneously. See wafer.

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.)