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In the fall of 1947, a breakthrough seemed within reach: At Bell Labs in New Jersey, semiconductor researchers John Bardeen and Walter Brattain finally figured out why the first attempts at transistors were so disappointing. Because, despite the promising methods, the transistor models created in their working group simply did not want to work: they only slightly interacted with the applied control field.

As physicists discovered, the regulating electric field of the control electrode did not sufficiently penetrate the semiconductors of the first field-effect transistor models. As a result, the “flood gate” that this field controls for the current flow does not work properly. Instead, the electrons of the material were drawn to the surface and trapped in a kind of barrier layer. This prevented the regulatory effect and rendered the candidate transistors largely unusable.

Germanium, gold foil and a plastic wedge

In search of a solution, Brattain and Bardeen began experimenting with a different building principle than before. For this they used a metal base on which a germanium plate is placed. Because of the doping with foreign atoms such as phosphorus or arsenic, this contained an excess of mobile electrons – it was a dope. This was followed by a thin surface layer of p-doped germanium. In this layer, exotic atoms such as boron have created an excess of positively charged “holes”.

Now came the crucial flash of inspiration: Brattain and Bardeen built a triangular plastic wedge attached to a spring, and covered it with gold foil. They scored conductive gold foil at the tip of the wedge, creating two close contact points. These two electrodes may now be used as two electrodes, each forming a circuit with a conductive metal base and its electrode.

“The most important experience of my life”

On December 16, 1947, Brattain and Bardeen performed the first test of their transistor model in their laboratory. It worked: if they applied a current to one side of the gold terminal – the emitter – not only would a small current flow from it to the base, but also the current flow in the second circuit would change – depending on how much current was fed by applying the first gold electrode.

As hoped, the device acted as a controllable switch and also as an amplifier, amplifying the input signal by a factor of a thousand. On the way home that evening, Brattain told the members of his entourage, “I’ve done the most important experiment of my life today.” However, he did not reveal what it is about.

The first functional transistor

It wasn’t until December 23, 1947, that the two physicists formally presented their invention to Bell Labs management for the first time. In this internal demonstration, they demonstrated the amplifier effect of their transistor using a microphone and speaker: they connected the microphone to the “mini” circuit of the emitter electrode, and the amplifier to the second circuit. If the transistor succeeded in amplifying the microphone’s weak input signal, the speaker should be able to audibly reproduce what was said – which it did.

Brattain and Bardeen did it: They built the first efficient, efficient transistor. It was finally possible to build a small-scale semiconductor-based component that could replace the old, unwieldy vacuum tubes. On June 30, 1948, the two physicists presented their invention to the public for the first time at a Ball Labs press conference.

“double” transistor

The construction principle developed by Brattain and Bardeen is now referred to as the point-contact transistor. Unlike today’s prevalent field-effect transistors, positive and negative charge carriers together contribute to the amplification effect in these bipolar transistors. In other words: both electrons and “holes” are packed into a semiconductor.

First-party transistors were mass-produced as early as 1951 and were incorporated into telephone switchers, hearing aids, oscillators, and even the first experimental television receivers. Until 1953, these devices remained the fastest switching transistors. Brattain and Bardeen were awarded the Nobel Prize in Physics in 1956.

However, the two American physicists weren’t the only ones to come up with the transistor tip principle: on the other side of the Atlantic, German physicists Herbert Matari and Heinrich Welker were also working on a very similar model – without suspecting anything. Developments at Bell Labs. In 1948 they also succeeded in building a working terminal transistor – but they came too late to be the first.

December 16, 2022

– Nadia Podbrigar