Solid State New Magic Word

Communications News, Sept, 1984

Solid-state, one of the buzzwords of CN's first decade and one of the key concepts behind all communications developments of these two dynamic decades, became a reality with the invention of the transistor in 1947. Since then it has been the basic building block leading to integrated circuits (see story, page 106) and miniaturization (see story, page 114).

Bell Labs gets credit for the transistor, Texas Instruments for the integrated circuit (1958), and Signetics for the linear integrated circuit (1964) . . . all of which added up to the magic of "solid state" during these two dynamic decades.

Solid-state, simply stated, describes a device, circuit or system whose operation in dependent upon any combination of optical, electrical or magnetics phenomena within a solid.

Inventions are sometimes thought to result from unexpected discoveries on the part of isolated researchers. Not so with the transistor. The transistor was the culmination of a directed interdisciplinary research effort at Bell Laboratories to find a solid-state amplifier and switch.

Prior to World War II, Dr. Mervin Kelly, director of research at Bell Labs, became aware of the constraints vacuum-tube technology would impose on the telephone industry's requirements 10 to 15 years hence.

The industry, Kelly felt, would be in trouble because of the inherent physical limitations of tubes and mechanical relays. Tubes were inefficient consumers of huge amounts of power. They were delicate, expensive to manufacturer, and had limited life. Relays, though inexpensive and reliable, operated slowly. And tubes and relays occupied a lot of space.

Clearly, new techniques and components had to be developed to satisfy the communications needs of the future. The most promising field to explore was research on semiconductors--materials whose electrical conductivity is between that of a conductor and an insulator. Bell Labs decided to explore the behavior of electrons in such solid materials.

World War II interrupted most of this work. But the war stimulated research at Bell Labs, Purdue University, and in England to satisfy the need for good silicon and germanium detectors for radar. Understanding these two semiconductors contributed greatly to the invention of the transistor.

In 1945, Dr. Mervin J. Kelly authorized a major them effort in solid-state physics, covering the fundamental investigation of conductors, semiconductors, dielectrics, insulators, piezoelectric, and magnetic materials. John Bardeen, Walter Brattain, and William Shockley, and many other Bell Labs scientists resumed full-time semiconductor research. Under the direction of William Shockley, the team's goal was to produce a device the would perform better in a solid what the electron tube does in a vacuum . . . conduct, modulate, and amplify electrical signals.

Research was centered on germanium and silicon with enphasis on understanding both chemical and physical properties. Experiments led to new theories. Shockley, for example, proposed a field-effect structure for a semiconductor amplifier. Performance was less than that anticipated in the theory. Bardeen then suggested extending the theory to include surface effects to explain why the device didn't work as expected.

Further advances required a better understanding of the basic physics--particularly of the regions near the surfaces of the materials. In this investigation of surface properties, the phenomenon later called the "transistor effect" was observed. (In naming the transistor, John Pierce took into consideration that the resistance of one point contact was found to depend on the current flowing through the other point contact. In other words, the resistance effect was transferable from one point to the other. The device was a "transfer resistor"--telescoped into "transistor".)

On December 23, 1947, John Bardeen, who had worked on theory, and Walter Brattain, who had worked on surface properties, demonstrated a device that amplified a speech signal 40 times. The device was called a point-contact transistor because it consisted of two pointed gold contacts, less than two thousandths of an inch apart, on one side of a piece germanium wafer.

In 1956, Bardeen, Brattain, and Shockley were awarded the Nobel prize for discovering the transistor effect.

Specificfally excluded from the marvelous world of "solid states" are devices, circuits or systems dependent on even macroscopic physical movement, rotation, contact or non-contact of any combination of solids, liquids, gases or plasmas.

Other solid-state developments followed the invention of the point-contact transistor in 1947.

The junction transistor was proposed by W. Shockley in a broad patent application in mid 1948. The junction transistor eventually became the dominant form of bipolar transistor. It employs a single crystal of a semiconductor, such as germanium or silicon, in which two closely spaced pn junctions are formed. These junctions are provided with an emitter, base, and collection electrode. The earliest practical form was the grown junction transistor in 1950, which was followed in 1952 by the alloy junction transistor, the diffused-base transistor (1955), and the epitaxial transistor (1960).