1947:
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.
1948:
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.
1951:
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.
1956-1958:
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.
1958:
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.
1960s:
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.
