The Innovators: How a Group of Inventors, Hackers, Geniuses, and Geeks Created the Digital Revolutio - Isaacson Walter - Страница 39

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Progress was slow over the next year, but in November 1947 a series of breakthroughs led to what became known as the Miracle Month. Bardeen built on the theory of the “photovoltaic effect,” which says that shining light on two dissimilar materials that are in contact with one another will produce an electric voltage. That process, he surmised, might dislodge some of the electrons that created the shield. Brattain, working side by side with Bardeen, devised ingenious experiments to test out ways to do this.

After a while, serendipity proved to be their friend. Brattain conducted some of the experiments in a thermos so he could vary the temperature. But condensation on the silicon kept gunking up the measurements. The best way to solve that would be to put the entire apparatus in a vacuum, but that would have required a lot of work. “I’m essentially a lazy physicist,” Brattain admitted. “So I got the idea to immerse the system in a dielectric liquid.”²⁰ He filled the thermos with water, which proved a simple way to avoid the condensation problem. He and Bardeen tried it out on November 17, and it worked beautifully.

That was a Monday. Throughout that week, they bounced through a series of theoretical and experimental ideas. By Friday, Bardeen had come up with a way to eliminate the need to immerse the apparatus in water. Instead, he suggested, they could just use a drop of water, or a little gel, right where a sharp metal point jabbed down into the piece of silicon. “Come on, John,” Brattain responded enthusiastically. “Let’s go make it.” One challenge was that the metal point couldn’t be allowed contact with the water drop, but Brattain was an improvisational wizard and solved that with a bit of sealing wax. He found a nice slab of silicon, put a tiny drop of water on it, coated a piece of wire with wax to insulate it, and jabbed the wire through the water drop and into the silicon. It worked. It was able to amplify a current, at least slightly. From this “point-contact” contraption the transistor was born.

Bardeen went into the office the next morning to record the results in his notebook. “These tests show definitely that it is possible to introduce an electrode or grid to control the flow of current in a semiconductor,” he concluded.²¹ He even went in on Sunday, which he normally reserved for golf. They also decided it was time to call Shockley, who had been immersed for months in other matters. Over the next two weeks he would come down and offer suggestions, but he mainly let his dynamic duo proceed apace.

Sitting side by side at Brattain’s lab bench, Bardeen would quietly offer ideas and Brattain would excitedly try them out. Sometimes Bardeen wrote in Brattain’s notebook as the experiments were being conducted. Thanksgiving passed with little notice as they tried different designs: germanium instead of silicon, lacquer rather than wax, gold for the contact points.

Usually Bardeen’s theories led to Brattain’s experiments, but sometimes the process worked in reverse: unexpected results drove new theories. In one of the germanium experiments, the current seemed to flow in the opposite direction from what they expected. But it was amplified by a factor of more than three hundred, far more than they had previously achieved. So they ended up acting out the old physicist joke: they knew that the approach worked in practice, but could they make it work in theory? Bardeen soon found a way to do so. He realized that the negative voltage was driving away electrons, causing an increase in “electron holes,” which occur when there is no electron in a position where one could exist. The existence of such holes attracts a flow of electrons.

There was one problem: this new method did not amplify higher frequencies, including audible sounds. That would make it useless for telephones. Bardeen theorized that the water or electrolyte drop was making things sluggish. So he improvised a few other designs. One involved a wire point stuck into the germanium just a tiny distance from a gold plate that was creating a field. It succeeded in amplifying the voltage, at least slightly, and it worked at higher frequencies. Once again Bardeen supplied a theory for the serendipitous results: “The experiment suggested that holes were flowing into the germanium surface from the gold spot.”²²

Like a call-and-response duet sitting together at a piano, Bardeen and Brattain continued their iterative creativity. They realized that the best way to increase the amplification would be to have two point-contacts jabbed into the germanium really close together. Bardeen calculated that they should be less than two-thousandths of an inch apart. That was a challenge, even for Brattain. But he came up with a clever method: he glued a piece of gold foil onto a small plastic wedge that looked like an arrowhead, then he used a razor blade to cut a thin slit in the foil at the tip of the wedge, thus forming two gold contact points close together. “That’s all I did,” Brattain recounted. “I slit carefully with the razor until the circuit opened, and put it on a spring and put it down on the same piece of germanium.”²³

When Brattain and Bardeen tried it on the afternoon of Tuesday, December 16, 1947, something amazing happened: the contraption worked. “I found if I wiggled it just right,” Brattain recalled, “that I had an amplifier with the order of magnitude of one hundred amplification, clear up to the audio range.”²⁴ On his way home that evening, the voluble and talkative Brattain told the others in his carpool he had just done “the most important experiment that I’d ever do in my life.” He then made them pledge not to say anything.²⁵ Bardeen, as was his wont, was less talkative. When he got home that night, however, he did something unusual: he told his wife about something that happened at the office. It was only a sentence. As she was peeling carrots at the kitchen sink, he mumbled quietly, “We discovered something important today.”²⁶

Indeed, the transistor was one of the most important discoveries of the twentieth century. It came from the partnership of a theorist and an experimentalist working side by side, in a symbiotic relationship, bouncing theories and results back and forth in real time. It also came from embedding them in an environment where they could walk down a long corridor and bump into experts who could manipulate the impurities in germanium, or be in a study group populated by people who understood the quantum-mechanical explanations of surface states, or sit in a cafeteria with engineers who knew all the tricks for transmitting phone signals over long distances.

Shockley convened a demonstration for the rest of the semiconductor group and a few Bell Labs supervisors on the following Tuesday, December 23. The executives put on earphones and took turns speaking into a microphone so that they could hear for themselves the actual amplification of a human voice using a simple, solid-state device. It was a moment that should have resonated like Alexander Graham Bell’s first words barked on a telephone, but no one later could recall the words spoken into the device on that momentous afternoon. Instead the event was memorialized for history by understated entries made into lab notebooks. “By switching the device in and out, a distinct gain in speech level could be heard,” Brattain wrote.²⁷ Bardeen’s entry was even more matter-of-fact: “Voltage amplification was obtained with use of two gold electrodes on a specifically prepared germanium surface.”²⁸

SHOCKLEY’S ONE-UPMANSHIP

Shockley signed Bardeen’s historic notebook entry as a witness, but he did not make any entries of his own that day. He was clearly rattled. The pride he should have felt in the success of his team was overshadowed by his intense and dark competitive drive. “My emotions were somewhat conflicted,” he later admitted. “My elation with the group’s success was tempered by not being one of the inventors. I experienced some frustration that my personal efforts, started more than eight years before, had not resulted in a significant inventive contribution of my own.”²⁹ There were demons that increasingly gnawed away deep in his psyche. He would never again be friends with Bardeen and Brattain. Instead he started working feverishly to claim equal credit for the invention and to create, on his own, an even better version.

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