What Does a Transistor Do?

A transistor is a solid state device used to amplify a signal or serve as a switch. Transistors are referred to as solid state because they do not contain electro-mechanical components and, thus, are solid and do not move. Transistors were developed as the natural progression from vacuum tube electronics, and were a response to cost, manufacturing complexity, and reliability issues with vacuum tubes. The development of the transistor was one of the primary drivers behind the development of modern micro and digital electronics.

History

The first recognized patent on a field effect solid state transistor was issued in 1947 to Bell Laboratories. The transistor was patented after two scientists at Bell, John Bardeen and Walter Brattain, noticed that germanium acted as a natural amplifier. They made a simple audio amplifier, and demonstrated it to the director of Bell, who immediately recognized the discovery's potential: low power consumption and no warm-up time. This first transistor was a bipolar junction transistor (BJT). BJT transistors contain two poles, or diodes, with a shared anode.

Transistors as Amplifiers

The first transistors, developed by Bell Labs, were amplifiers. When power is applied to the transistor, a signal's input voltage was increased, creating a more powerful output. The input signal is applied to one pole of the transistor, when power is applied to the anode, the anode pulls electrons to the other pole at a higher rate than the input. The net effect is an amplification of the voltage output by the second pole.

Transistors as Switches

Transistorized switches have evolved as the basis of digital electronics. In a transistor, a current is applied to a pole of the transistor. In many switching transistors, the current will not flow across the anode to the opposite pole, unless power is applied to the anode. This effectively turns the transistor in to an electronic on-off switch. When power is applied to the anode, power or signal flows out of the transistor. When power is not applied, the transistor is effectively in the "Off" position.

How a Transistor is Made

Transistors have now been miniaturized to the point that millions can be etched onto the surface of a single silicon based microchip. Early transistors were made by sandwiching semiconductor materials. When current is applied to the material in between the two diodes, it allows current to flow between the diodes, thus acting as a switch. If the transistor is a current amplifier, the material between the two diodes increases the power output by the transistor, creating amplification. Early transistors were made by growing semiconductor crystals with the diode junctions in place. There are numerous modern methods of manufacturing transistors, with the most common being etching transistor components on silicon.

Modern Transistor Miniaturization

Modern transistors have been miniaturized to incredibly small levels. Intel's proposed Itanium processor will contain over 2 billion transistors on a single integrated circuit. British scientists have made the smallest practical transistor measuring one atom thick by 10 atoms across. This experimental transistor is 1/3 of the size of the current smallest transistor possible on silicon integrated circuits.