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Rare Combinations

The saga of the invention of the transistor at Bell Labs is a fairly well-known tale that is often retold when questions arise about the importance of basic research in the innovation process. Much less familiar is the story of technology development that ensued. It was this rare combination of basic research and fundamental technology development that made modern transistors and microchips possible. Few, if any, episodes in the history of innovation can compare.

The Labs combined a pragmatic, goal-oriented research philosophy with what Shockley called “respect for the scientific aspects of practical problems.” Research was guided by the long-range goal of improving the components and services of the Bell System-better switches, clearer signals, etc. But within that context, scientists had ample freedom to do basic research on the properties of materials. Leading theoretical physicists worked shoulder to shoulder with first-rate experimenters and some of the best device-development engineers in the country. The invention and development of the transistor illustrates this interplay between the practical and the scientific that characterized Bell Labs in its heyday.

When Shockley’s original ideas for making a solid-state amplifier failed, for example, Bardeen proposed an entirely different theory of semiconductor behavior that he eventually published in the Physical Review. Shockley’s “field effect” approach involved the use of external electric fields to induce an excess of electrons near the surface of crystalline materials such as silicon; with more electrons congregating there, more current should flow. Or so he thought. To account for the apparent lack of any such effect, Bardeen proposed his theory of “surface states,” in which electrons become trapped on the surface and block electric fields from penetrating. This was a brand new starting point that reoriented the group’s research efforts toward understanding these troublesome states. “We abandoned the attempt to make an amplifying device,” recalled Shockley, “and concentrated on new experiments related to Bardeen’s surface states.”

When Brattain stumbled upon a crude way to overcome this blockage in November 1947, however, the group’s attention returned almost immediately to the practical goal of making a solid-state amplifier. A month later they invented the first transistor, the point-contact transistor, which had two strips of gold foil glued to the sides of a plastic wedge that pressed the foil edges into a germanium slab. Although this weird gizmo stretched nearly an inch, the novel physical process responsible for power gain occurred in a mere 2 mils-or 50 microns, about the thickness of a sheet of paper-of germanium between the metal points touching its surface. Positively charged quantum-mechanical entities known as “holes” generated beneath one point trickled along a surface layer to the other point, reducing the resistance of the material beneath it and thereby en-hancing the current flowing through it.

Under the enlightened man-agement of Mervin Kelly and Jack Morton, Bell Labs soon began to pour resources into developing technologies to make transistors commercially viable. It perfected methods of purifying germanium and silicon, and growing large crystals of these elements. Within a few years, these technologies permitted Shockley and colleagues to realize his idea of a junction transistor, which proved far more reliable than Bardeen and Brattain’s odd device and lent itself much more readily to mass production. In this kind of transistor, so-called p-n junctions replace the metal-to-semiconductor point contacts; these junctions are formed between two dissimilar layers of semiconductor material impregnated with different impurities to induce a slight excess of electrons or holes. This approach proved to be crucial in manufacturing the cheap, reliable transistors that began appearing in electrical devices such as radios and hearing aids during the 1950s.

What’s more, the Labs made these and other technologies readily available to firms that were eager to get into the semiconductor business. Combining them with a few additional innovations of their own, Noyce and Jack Kilby invented the integrated circuit at Fairchild Semiconductor and Texas Instruments toward the end of the decade. Better known today as microchips, which now incorporate millions of transistors on a single sliver of silicon, these circuits form the basis of today’s $150 billion semiconductor industry. As Morton observed, “Sometimes when you spread your bread on water, it comes back as angel’s food cake.”

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Tagged: Computing

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