The Transistor Revolution (Part 1)
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Feature by Dr Bruce Taylor HB9ANY l E-mail: [email protected] t Christmas 1938, working in their small rented garage in Palo Alto, California, two The Transistor enterprising young men Acalled Bill Hewlett and Dave Packard finished designing a novel wide-range Wien bridge VFO. They took pictures of the instrument sitting on the mantelpiece Revolution (Part 1) in their house, made 25 sales brochures and sent them to potential customers. Thus began the electronics company Dr Bruce Taylor HB9ANY describes the invention of the that by 1995 employed over 100,000 people worldwide and generated annual tiny device that changed the course of radio history. sales of $31 billion. The oscillator used fve thermionic valves, the active devices that had been the mainstay of wireless communications for over 25 years. But less than a decade after HP’s frst product went on sale, two engineers working on the other side of the continent at Murray Hill, New Jersey, made an invention that was destined to eclipse the valve and change wireless and electronics forever. On Decem- ber 23rd 1947, John Bardeen and Walter Brattain at Bell Telephone Laboratories (the research arm of AT&T) succeeded in making the device that set in motion a technological revolution beyond their wildest dreams. It consisted of two gold contacts pressed on a pinhead of semi-conductive material on a metallic base. The regular News of Radio item in the 1948 New York Times was far from being a blockbuster column. Relegated to page 46, a short article in the edition of July 1st reported that CBS would be starting two new shows for the summer season, “Mr Tutt” and “Our Miss Brooks”, and that “Waltz Time” would be broadcast for a full hour on three successive Fridays. But right at the end, after another unexciting story about the broadcasting of road traffc reports, the article mentioned that Bell Labs had dem- onstrated a small metal cylinder that could “create and send radio waves” but contained “no vacuum, grid, plate, or glass envelope to keep the air away”. It could amplify and The point contacts of the frst transistor were created by a razorblade slit in gold foil wrapped around the oscillate and had been named a “Transistor”. edge of a triangular plastic wedge. (Bell Labs) The name had been chosen by internal ballot among Bell Labs executives and germanium transistor, which he called a Origins research staff. Semiconductor Triode and Transitron, while working for CFS Westing- The roots of the invention were much Surface States Triode were considered fairly house near Paris. By mid-1949 many of older. The rectifying properties of crystals good but unwieldy, and Transistor came out them were in use as amplifers in the French had been discovered by Karl Braun in well ahead of Crystal Triode, Solid Triode and telephone system. At this time European 1874, before wireless existed, and the Iotatron. Little did the apathetic NYT reporter industry was still recovering from the devas- cat’s whisker detectors that became popu- realise that he had witnessed the frst public tation of war but research at UK companies lar in the early 1900s were semiconductor demonstration of an invention that would such as BTH, GEC and STC was not far diodes in all but the name. Nor was the spawn a world-changing technology. behind the US and their frst products were concept of a three-electrode solid-state Quite independently, Herbert Mataré in named Crystal Valve and Germanium Triode amplifer a new one. As far back as 1926, June 1948 also invented the point-contact as well as Crystal Triode. the German-American engineer Julius 24 Practical Wireless October 2018 physicist who had been engaged on anti- submarine warfare research during WW2. When he learned of Ohl’s discovery, Shock- ley immediately postulated that it might be possible to make a solid-state amplif er by applying an electric f eld across a p-n junc- tion but, initially, all attempts to vary the con- ductivity with the control f eld failed. Without any tools to see what was happening inside the crystals at the subatomic level, progress was dependent on intuition and trial-and- error. By January 1946 the group admitted that they were “groping in the dark”. However, the failures led Bardeen to postulate a theory of surface states in semi- To the chagrin of Walter Brattain (right) and John conductors and to continue experimenta- Bardeen (glasses), Bill Shockley insisted on sitting tion. By late 1947, Bardeen and Brattain had at their workplace for this posed Bell Labs publicity switched from silicon to n-type germanium Research Director Ralph Bown introduces the f rst photo. (Bell Labs) and felt that they were getting close to suc- point-contact transistor to the press. (Bell Labs) cess. Then Brattain tried a conf guration in old pipe-cleaner knife and these detectors which a pair of very closely spaced point Lilienfeld, who patented a forerunner to famously outperformed those that were not contacts were created by using a razor blade the modern electrolytic capacitor, f led optimised in this way. He refused to allow to cut a minute gap in the gold foil wrapped a patent for an FET-like device that was anyone to clean the dirty knife, which had around the edges of a small triangle of plas- granted in 1930. Since materials of the pu- acquired “exactly the right momentum for tic. The contacts were pressed into the sur- rity required weren’t available at the time, the job”! face of the germanium by a spring fashioned it is unlikely that Lilienfeld succeeded in This war effort also gave rise to the next from a paper clip. By December 16th the making a working transistor but his claim important breakthrough. While working on team had achieved signif cant power gain was strong enough to prevent Bell Labs radar detectors in 1940, Bell Labs chemist and on December 23rd they demonstrated from patenting the f eld-effect approach Russell Ohl made the fortuitous discovery speech amplif cation to Bell Labs manage- 18 years later. of a rectifying junction at a defect in a bar of ment. An “entirely new thing in the world” The theoretical foundations for tran- silicon and noted its photovoltaic behaviour. had been created. sistor operation were laid in 1931, when Ohl had been bitten by the radio bug when Cambridge University mathematician Alan using spark transmitters on 150m during Patenting Wilson formulated the quantum mechanical WW1 and had built a superhet as early as Everyone at Bell Labs was familiar with the theory of conduction in semiconductors. He 1921. He coined the terms n-type, for mate- legend that their company originated be- correctly attributed their properties to the rial containing some atoms of phosphorus, cause Alexander Bell had beaten Elisha presence of impurity atoms in the crystals, antimony or arsenic (in which conduction Gray in a race to the patent off ce. So, the opening the way for less empirical work on is by electrons), and p-type, for material transistor invention was classif ed as Bell solid-state devices. During WW2, Wilson containing some atoms of boron, aluminium Labs Conf dential until it was better un- worked on radio communications for the or gallium (in which conduction is by holes), derstood and patent protection had been secret Special Operations Executive (the and the p-n junction was born. Initially this applied for. But in whose name? Shockley ‘Ministry of Ungentlemanly Warfare’) and discovery wasn’t disclosed outside Bell was Bardeen and Brattain’s supervisor, later on the UK project to develop the atomic Labs, and Ohl was instructed to cut any and was disgruntled that his subordinates bomb. He was knighted in 1961. chance p-n junctions out of silicon that was had made the breakthrough without his With the development of the high-power sent to his British counterparts. active participation. Bell Labs’ lawyers 10cm cavity magnetron by John Randall advised that Shockley’s own work was and Harry Boot at Birmingham University, Bell Labs overshadowed by that of Lilienfeld, and high resolution microwave radar became Work on semiconductors at Bell Labs had that Bardeen and Brattain were the actual feasible if a reliable detector could be found. begun before the war, and energetic boss inventors. Consequently, they refused to After Bell Labs were unsuccessful in devel- Mervin Kelly initiated a new unif ed solid- put his name on the patent for the point- oping thermionic valves for this very short state programme in June 1945, as soon contact transistor. wavelength, attention was turned once again as the men who had been assigned to Professional jealousy and bruised ego to cat’s whisker crystal diodes. In Britain, the military work began to return to the lab’s spurred Shockley into a frenzy of independ- Telecommunications Research Establish- new ‘Idea Factory’ at Murray Hill. The aim ent work, which he initially kept secret from ment (TRE) developed an aluminium-doped was specif cally to devise an alternative to the rest of the group, thus starting to alienate silicon cartridge that was manufactured by thermionic valve telephone amplif ers and them. By the end of January 1948 he had BTH and GEC. While at TRE, the eccentric the initial funding of $417,000 was billed come up with a theoretical transistor design Bristol physicist Herbert Skinner improvised to AT&T. that worked quite differently from that of a technique for f nding a sweet spot for As manager of the programme, Kelly ap- Bardeen and Brattain, being composed of a the contact by tapping the crystals with an pointed William Shockley, a London-born sandwich of p-type germanium between two October 2018 Practical Wireless 25 The Transistor Revolution n-type regions.