The First Junction Transistor

Evolution of the Transistor



In the beginning, there was the point-contact transistor.  This was the very first transistor ever made, built by Walter Brattain with the help of John Bardeen.  It was made of two gold foil contacts sitting on a germanium crystal.  Current coming in one contact would cause the germanium crystal to boost the strength of the current flowing through the other contact. 

Next, there was the Type-A transistor -- the first transistor that Bell actually sold.  This was still a point contact transistor, but modified so that it worked consistently and could be easily mass produced. 

The first big change in transistors occurred when William Shockley developed a junction transistor. The first junction transistors were sandwiches of  N- and P-type germanium (germanium with an excess and scarcity of electrons, respectively).  A weak voltage coming into the middle layer would affect another current traveling across the entire sandwich. 

The methods for building transistors improved substantially as the decade went on.  By laying patterns over the crystal, scientists could etch away specific parts of the crystal, or add impurities to other parts as necessary. The first of these transistors, developed at Bell, left a little protrusion sticking out of the middle, and so they were named "mesa" transistors after the Spanish word for table.  Later, Fairchild Semiconductor developed a version which was entirely flat -- these were called "planar" transistors.

Germanium transistors broke down at high temperatures, so they were eventually replaced by silicon transistors.  Gordon Teal built the first silicon transistor, which worked just like a germanium junction transistor.

The next big jump in transistor evolution came with the field-effect transistor.   Most modern transistors are  field-effect transistors -- specifically metal-oxide semiconductor field-effect transistors, or "MOSFETs."  Instead of being a sandwich, MOSFETs have a channel of either N- or P- type semiconductor running through a ridge on top of the other type.  As a voltage is applied to this channel, it creates an electric field which acts like a faucet to turn on or off current through the rest of the transistor.  MOSFETs were not originally better than the junction transistor, but they are much easier to make on an integrated circuit or microprocessor, and so they soon became the preferred type of transistor.  

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