Transistor -Only Science

Transistor

A transistor is a semiconductor device used to transmit or switch electrical signals and electrical energy. The word transistor came from two English words "Transfer" and "Resistor". It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. Those three terminals are 1. Collector(C) 2. Base(B) 3. Emitter(E). A current or voltage applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in ICs.


The first working device to be built was a point-contact transistor invented in 1947 by American physicists John Bardeen and Walter Brattain while working under William Shockley at Bell Labs. In 1959, Mohamed Atalla with Dawon Kahng invented the most widely used transistor is the MOSFET (metal-oxide-semiconductor field-effect transistor), also known as the MOS transistor at Bell Labs. The MOSFET was the first truly compact transistor that could be miniaturized and mass-produced for a wide range of uses. Most of the transistors are made from very pure silicon, and some are made from germanium, but certain other semiconductor materials are sometimes used. A transistor may have only one kind of charge carrier, in a field-effect transistor. Or it may have two kinds of charge carriers in bipolar junction transistor devices. Transistors are generally smaller and require less power than the vacuum tube. Certain vacuum tubes have advantages over transistors at very high operating frequencies or high operating voltages. Many types of transistors are made to standardized specifications by multiple manufacturers.

Structure of Transistor

In short, a transistor consists of an area of either p-type or n-type semiconductor sandwiched between regions of oppositely doped silicon. As such devices can be either a PNP or an NPN configuration. There are three connections, the emitter, base, and collector. The base is in the center, bounded by the emitter and collector. The collector is often made larger than the Emitter, as this is where most of the heat is dissipated.

Alloyed junction structure

The alloy junction is another transistor structure that was widely employed in the early days of transistors.

The alloy junction transistor structure used a germanium crystal as the base for the whole structure, as well as being the base connection then the emitter and collector alloy beads were then fused on opposite sides. There were several types of improved alloy-junction transistors developed over the years.

The alloy-junction transistors became obsolete in the early 1960s, with the introduction of the planar transistor. It could be mass-produced easily while alloy-junction transistors had to be made individually.

Diffusion transistors

Unlike the previous transistor structures where the contacts were added to the semiconductor crystal externally, the diffusion transistor enabled the various regions of the transistor to be created by diffusing dopants into the semiconductor crystal to give regions of the required characteristics, p-type, n-type, p+, n+, etc.

The earliest diffusion transistors used a form of the diffused-base transistor structure. These transistors still had alloy emitters and they even sometimes possessed alloy collectors like the earlier alloy-junction transistors. Only the base was diffused into the substrate, although sometimes the substrate formed the collector.

Planar transistor structure

The planar transistor structure was developed at Fairchild Semiconductor in 1959. It represented a major breakthrough in technology. It enabled bipolar transistors to be manufactured more easily, and it also set in place the basis of future integrated circuit technology as well.

The planar transistor structure also includes a passivation layer on the external areas of the crystal. This protects the junction edges from contamination and allows much less expensive plastic packaging to be used without risking degradation transistor performance as a result of contamination entering the crystal lattice, especially in the regions around the junctions.

The lateral planar transistor structure

the current flows in the horizontal plane rather than the vertical plane. This format has advantages in some applications. But it requires more diffusion processes and is, therefore, more complex and hence more expensive. It is only used when performance and characteristics demand it.

Transistor revolutionized the field of electronics and paved the way for smaller and cheaper radios, calculators, and computers, among other things.

(Collected from deferent sources)