“Unlocking the Future: How a Simple Discovery Revolutionized Technology and Changed Our Lives Forever”
The effort which resulted in the development of the first practical transistor was spearheaded by Mervin Kelly, director of research at Bell Telephone Laboratories in Murray Hill, New Jersey. Dissatisfied with the poor efficiency and reliability of vacuum tubes, in the late 1930s Kelly assembled a solid-state physics research team to come up with a semiconductor-based alternative. This work was interrupted by the Second World War, but resumed soon after. Strangely, this project was of relatively low priority for Bell, for while the triode or Audion had originally been developed for long-distance telephony, by the late 1940s the Bell Telephone System was based not on vacuum tubes, but complex yet reliable electromechanical devices known as Strowger Switches. A solid-state switch, if practical, was only anticipated to have limited, specialized applications, such as military radio and radar equipment.
Kelly assembled a diverse team of theoreticians, experimentalists, and engineers, including John Bardeen, Walter Brattain, Robert Gibney, Bert Moore, John Pearson, and the aptly-named William Shockley. Of these, it was the trio of Bardeen, Brattain, under the supervision of Shockley, who would ultimately make the vital breakthrough. While the often difficult Shockley preferred to work alone at home, Brattain and Bardeen formed a productive partnership, embracing the free-wheeling, anything-goes research culture of Bell Labs by working unsupervised late into the night.
The first design the team investigated was proposed by Shockley, and worked similarly to Julius Lilienfeld’s 1925 concept. Built around a block of silicon, like a vacuum tube the device had an anode and cathode – now named the source and drain – at either end, but instead of a grid used a third electrode called a gate to control the flow of electricity through the device. In theory, when current was applied to the gate, the electric field generated would impede electrons from flowing between the source and drain. In practice, however, the design failed to work. Nevertheless, Shockley was convinced his design was workable, and pushed Bell Labs to file a patent with himself named as sole inventor. To Shockley’s dismay, however, Bell had recently unearthed Lilienfeld’s original patents and informed Shockley that his idea was not original.
After much experimentation, Walter Brattain determined that the failure of Shockley’s design was due to a buildup of electrons on the surface of the silicon blocking the gate’s electric field. At the suggestion of Robert Gibnet, he and Bardeen tried getting around this problem by dunking the prototype in distilled water, filling in the air gap between the gate and the silicon and enhancing the strength of the electric field. Incredibly, this actually worked – though nowhere near as efficiently as the team had hoped. As Shockley later noted:
“This new finding was electrifying…at long last, Brattain and Gibney had overcome the blocking effect.”
Replacing the water with a chemical called glycol borate produced better results, but the device still had a slow response time and could not handle high frequencies – a key requirement for use in radio and radar equipment. Eventually, the team abandoned silicon as the substrate and focused instead on germanium, whose manufacture had already been perfected for use in diodes. But this material exhibited the same barrier effect as silicon, and though the team tried countless remedies like freezing the germanium with liquid nitrogen, full-scale amplification still continued to elude them.
It was at this point that a pair of serendipitous accidents nudged the team in the right direction. For their newest prototype, Brattain grew a thin layer of oxide on the surface of the germanium crystal and deposited an even thinner layer of gold onto this, hoping that the oxide would insulate the gold from the germanium. At first this seemed to work, but Brattain soon realized that the oxide layer had actually been washed away, meaning the gold was in direct contact with the germanium. This indicated that the device was not operating according to the field effect as Shockley had predicted, but some other, still unknown phenomenon.
On another occasion, while measuring the amplification or gain in a prototype, Brattain accidentally shorted out and ruined one of the gate electrodes by touching it with the emitter electrode. But when he placed the emitter close to the gate electrode, he suddenly observed the gain the team had been searching for.
Based on this, Bardeen suggested placing the emitter and gate electrodes extremely close to each other – within 50 micrometers – to enhance the effect. To accomplish this, Brattain wrapped a piece of thin gold foil around the point of a plastic triangle, cut a thin slit in the foil with a razor blade, and forced this pair of closely-spaced contacts into a crystal of germanium with a spring. Two electrodes known as the emitter and collector were connected to both halves of the gold foil, while a third base lead was connected to the germanium crystal, which had been specially prepared so that it consisted of two layers: an upper P-type layer full of electron holes and a lower N-type layer with excess electrons. In this configuration, the current flowing from the collector to the base was modulated by applying a current to the emitter.
