The transistor manufacturing technology is briefly explained.

The imperceptible and insignificant electromagnetic waves that reach the antennae of your radio are about a million times weaker than the current that comes from a flashlight battery. Obviously, these waves are totally useless unless they are magnified millions of times.

With the help of batteries and the house current, the vacuum tube can magnify these vibrations to such an extent that they will affect the loudspeaker or cathode beam in your radio or TV and give you the sound and pictures that you are so familiar with.

Amplification using vacuum tubes has been common practice for years, and up to 1948 the idea of carrying a radio set in your pocket, or, perhaps, a TV set in place of a wristwatch, was undreamed.

To function, radio and TV had to have two or three vacuum tubes, many batteries, and another mechanism, as well as a wire to be attached to the house current. This prevented them from being carried around because of the weight and the bulk necessary for all these parts.

While the vacuum tube fulfils its function very well, it has many disadvantages. It takes time to warm up. It frequently blows itself out and becomes useless. It exhibits considerable static at times.

On June 30, 1948, three scientists of the Bell Telephone Laboratories, William Shockley, Walter H. Brattain, and John Bardeen, announced one of the most remarkable inventions of the present age and were duly rewarded by receiving the Nobel Prize for their efforts.

This device, known as the transistor, is extremely small, about the size of the tip on a shoelace, and is slowly but surely making the vacuum tube obsolete.

The transistor is capable of doing everything that a vacuum tube can do and a great deal that it cannot do, yet it is not a vacuum tube. It is no larger than a small pea, it has no grid, no cathode, no plate, and it is not a tube.

It never gets out of order, nor does it need changing unless considerable damage is done to it. It produces its own current instantly from sunlight artificial light, or an increase in temperature.

It actually changes heat energy and light energy into electricity, and by the nature of the elements of which this tiny speck of an instrument is composed, it can amplify the feeble current and bring it to a point where it can produce sound.

In other words, just as the style radio and TV need the assistance of the house current and batteries to affect the vacuum tube and amplify the weak incoming radio wave, tiny transistor uses sunlight and artificial light, or an increase in temperature to affect the elements of which it is composed and magnify these same radio waves to a point of audibility.

At present millions of transistors are being manufactured for pocket radio and hearing aids in which the amplifying source is no bigger than a dime, all kinds of signal devices, electronic computers, long-distance telephone circuits, and the replacement of bulky equipment in missiles and space capsules that hold great promise for future astronauts and scientific research in outer space.

Briefly, the transistor is based on the fact that certain elements, notably silicon and germanium, exhibit unusual properties in the structure of their atoms. They are neither conductor nor are they insulators, but are known as semiconductors.

Related post:

LASER fundamental to applications

Bipolar junction transistor explained 

The purer these two elements are the more they can perform the function of a semiconductor, and hence, in the manufacture of the transistor, the greatest precaution must be taken to see that, tiny as the thin flake of germanium is, it must be at least 99% pure. The regular transistor, when examined through a magnifying glass, consists of two very fine wires a couple of thousandths of an inch apart attached to a “wafer” of almost pure germanium.

 In the atoms of the element germanium, there are very few current-carrying electrons, perhaps one for every million atoms. But, small as this number is, it can be varied many thousand times through the influence of light or an electric field from outside.

In the metals that conduct electricity, the valence band overlaps the conduction band, and the electrons flow very readily along the metal. In nonconductors, the valence and conduction bands are widely separated.

In semiconductors the valence and conduction band, but the slightest outside stimulation kicks the electrons up to it and in doing so leaves what the physicist calls “holes” in the element holes which not only accommodate incoming electrons but, in doing so, move themselves toward the conduction band. The action of the germanium or silicon is best described in a bulletin given out by Bell Laboratories, which states:

Transistor action depends upon the fact that electrons in a semiconductor can carry current in two distinctly different ways. This is because most of the electrons in a semiconductor do not contribute to carrying the current at all. Instead, they are held in fixed positions and act as a rigid cement to bind together the atoms in a solid.

Only if one of these electrons gets out of place, or if another electron is introduced in one of several ways, can current be carried. If, on the other hand, one of the electrons normally present in the cement is removed, then the ‘hole’ left behind can move like a bubble in a liquid and thus carry current.

“In a transistor made of a semiconductor, which normally conducts only by the extra electron process, current flows easily into the input point, which is at a higher negative voltage. The area of interaction is produced by ‘hole’ introduced by the input current and collected by the output point.”

Related post :

Overview of capacitor - what is a capacitor? - what is the use of capacitors?