The transistor: a device that changed the history of electronics forever

Awareness that transistors have changed the world is common knowledge, but what may not be known enough is the story of the people who have fostered this change . After all, the transistor didn't appear overnight , but it took years of trial and error to slowly transition from vacuum tubes to germanium transistors and later to silicon transistors. The story of the discovery of transistors is a story of battles between two tech giants like Texas Instruments and Bell Labs .

It all began with the invention of the telephone

The telephone patents to Alexander Graham Bell in 1906 represent a significant change in the telecommunications industry and allowed the construction of the first transcontinental telephone line. This telephone network was made possible thanks to the American inventor De Forest, who created the Audion device, a vacuum tube capable of amplifying the signals of a telephone line . This allowed communications to be sent across an entire continent at unexpected speeds, as long as there were switch boxes along the way. De Forest's invention is also known by the name of triode (1906), an electron tube which instead of having two electrodes like the diode, has a third one, the so-called control grid.

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Lee De Forest's triode. Credits: historyofinformation.com

The De Forest triode made it possible to have a telephone conversation from one coast of America to the other . But this solution was not without its problems. Vacuum tubes used too much energy, generated a large amount of heat, and were unreliable. An alternative was needed, and scientists at Bell Labs already had an idea thanks to studies on semiconductor materials.

The transistor as a replacement for the vacuum tube

Research into semiconductor materials was intensified after World War II, and at that time a team of scientists was assembled at Bell Labs to make a solid-state switch to replace the vacuum tube. This team was made up of some brilliant minds of the time, including the infamous trio Bill Shockley, Walter Brattain and John Bardeen.

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Bardeen, Shockley and Brattain. Credits: Wikipedia

The way of relating of the three was definitely not rosy. Shockley possessed a somewhat rough personality and, isolating himself from the group, spent most of his hours working alone around the house. During his isolation Shockley managed to develop his first design for a semiconductor amplifier . The device did not work as expected and Shockley asked Bardeen and Brattain to find out why. The two began an experiment with germanium and on December 16, 1947 were able to build their first contact tip transistor .

The first contact tip transistor. Credits: nutsvolts.com

The device consisted of a plastic triangle coated with a thin layer of gold, a configuration that essentially constitutes a contact diode. At the end of the triangle the gold foil had been carefully cut to form two very close but electrically insulated gold contacts. The two contacts resting on a germanium plate form a device with three terminals: the emitter, the collector and the base . A positive electric charge on the emitter affected the conductivity between the collector and the base on which the germanium plate was mounted. In particular, an amplification of current between the collector and the base was noted. This discovery was a huge win for the team of scientists, however there was one small problem: Bardeen and Brattain had initially left Shockley in the dark.

Only later did the two call Shockley to tell him what they had discovered. When the news was revealed, Shockley was shocked as he had been cut off from all progress. Then, Shockley channeled all his anger into a personal project in order to surprise Bardeen and Brattain with an invention of his own.

For the next four weeks, Shockley locked himself in a hotel room in Chicago and just during this time he developed what is now known as a junction transistor . Shockley's invention was sensational, providing a stronger and easier to manufacture design than the two colleagues' transistor.

The first junction transistor. Credits: www.autodesk.com

And so the three made history by enacting a patent , but the trio soon broke up as a group of touchy children, arguing over the name the patented device should have and who would appear in the propaganda photographs.

On June 30, 1948, the invention was presented to the whole world, but to Shockley's dismay the new invention did not arouse the interest of experts. Therefore, like any other inventor would have done when his invention doesn't get the interest it deserves, Shockley leaves Bell Labs and forms his own company bringing with him a group of talented scientists.

The new company, Shockley Semiconductor, was short-lived due to Shockley's strong personality. Some of his employees left the company and formed what are now Fairchild Semiconductor and Intel. Thus was born the semiconductor industry .

The limits of the Germanium transistor

Germanium was the semiconductor material of reference at the time of the invention of transistors, this had both positive and negative aspects. Compared to silicon it had a lower melting temperature, a lower threshold voltage and provided a higher frequency response.

However, the need to find a suitable replacement for germanium was quite clear due to poor thermal stability . As the temperature increased, the delicate balance between the transistor junctions was lost, making it difficult to control free electrons. In practice, the current increased as the temperature increased and, after 75 ° C, the transistor became practically useless . Thus, scientists and technicians began to look with renewed interest at silicon which had an unsurpassed value: it was widespread in nature, it was even found in dust, so production costs would have been significantly lower.

The race for Silicon

Silicon research had been ongoing since the early 1950s at Bell Labs, where Gordon Teal and Ernie Buehler grew crystals to make the first solid-state diodes. But Gordon's stay at Bell Labs was short-lived as his desire was to return home to Texas and so he did, finding a job at Texas Instruments Inc.

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Gordon Teal (right) in his laboratory where silicon crystals grew. Credits: www.computerhistory.org

Gordon had some problems with growing silicon , in fact this material had higher impurity levels than germanium, and creating a successful NPN or PNP junction transistor had become quite a challenge. So Gordon and his team struggled with this problem for over a year. In April 1954 their hard work finally paid off, managing to obtain the desired degree of purity for silicon. Thus, Gordon's team was able to build the first silicon NPN transistor structure .

The Silicon transistor: the presentation to the general public

It is May 10, 1954, when a group of engineers gathered at the Institute of Radio Engineers (IRE) for a National Conference on Electronics. It was quite clear the challenge at that time that all scientists were facing to make silicon an alternative material to germanium, so at that conference Gordon enters the scene and takes the stage to announce that Texas Instruments had three different types of silicon transistors. in production .

To prove it was real, Gordon turned on a turntable amplified by germanium transistors and poured a glass of hot oil on the device , obviously the music stopped. Then Gordon played the demonstration with the turntable amplified by the silicon transistors. As he poured hot oil onto the turntable, the music continued to play smoothly . And so the new silicon transistor was shown to the present public and to the whole world. Today, the proof of this discovery is all around us , in our smartphones, laptops and the many devices we use.

Curated by Antonino Pagano

The article The transistor: a device that changed the history of electronics forever comes from Tech CuE | Close-up Engineering .