1833:
In addition to his pioneering work in electricity and magnetism,
English "natural philosopher" (the contemporary term for a physicist)
Michael Faraday made the first documented experimental observations of
a material that we now call a semiconductor. The familiar unit of
measurement of electrical capacitance - the farad (F) - is named after
him.
While investigating the effect of temperature on the electrical
conductivity of sulphurette of silver (silver sulfide) in 1833 Faraday
found that conductivity increased with increasing temperature. (1)
This is the opposite of that measured on metals such as copper where
electrical conductivity decreases as temperature is increased.
Today this effect is used to make Negative Temperature Coefficient
(NTC) thermistors, devices that exhibit a predictable decrease in
electrical resistance when subjected to an increase in temperature.
1874:
A 24-year old Ph. D. graduate of the University of Berlin, German
physicist Karl Ferdinand Braun studied the characteristics of
electrolytes and crystals that conduct electricity at Würzburg
University in 1874. When he probed a galena crystal (lead sulfide)
with a sharp metal point, Braun found that current flowed freely in
one direction only. (1) He had discovered the point-contact rectifier
effect at a metal-semiconductor interface.
Braun demonstrated this first semiconductor device to an audience at
Leipzig on November 14, 1876, but it found no useful application until
the advent of radio early in the 1900's when it was used as the basis
for the "cat's whisker" crystal radio detector. This descriptive name
is derived from the fine metallic probe used to make electrical
contact with the crystal surface.
1926:
(1) Lilienfeld J E 1926 "Method and apparatus for controlling electric
currents" US Patent 1745175, application filed October 1926
Best known for his contributions to the technology of the electrolytic
capacitor, Austro-Hungarian physicist and inventor Julius E.
Lilienfeld filed a patent, "Method and Apparatus for Controlling
Electric Currents," in June 1926. This shows that he recognized the
concept of modulating the conductivity of a layer of semiconductor
material by varying an electric field applied perpendicular to the
flow of current. (1) The device he described would today be called a
Field Effect Transistor (FET) - although the name transistor was not
coined until 1948.
1931:
Although the materials had been used in radios for many years and the
term semiconductor from the German "halbleiter" first appeared in the
literature in 1911, as late as 1931 Austrian-Swiss Nobel prize winning
physicist Wolfgang Pauli exclaimed "One shouldn't work on
semiconductors, that is a filthy mess; who knows whether any
semiconductors exist."
1935:
(2) Heil O E "Improvements in or relating to electrical amplifiers and
other control arrangements and devices", British Patent 439457,
granted 6th December 1935
Working with Lord Rutherford at the Cavendish Laboratory in Cambridge,
England, in 1934 German electrical engineer and inventor Oskar Heil
obtained a patent on the control of current flow in a semiconductor
via capacitive coupling at an electrode - essentially a field effect
transistor.
1938:
(First successful effort to hack quantum mechanics
to explain the operation of a simple diode.)
Since its discovery in 1874, researchers had proposed numerous
theories to explain the phenomenon of point contact rectification. As
a follow-up to his 1931 semiconductor theory papers (see: "The Theory
of Electronic Semi-Conductors" - 1931) , in 1932 English scientist
Alan H. Wilson offered a quantum mechanical tunneling explanation for
rectification. Papers published in the same year in Germany (L.
Nordheim) and the USSR (J. Frenkel and A. Joffé) proposed similar
theories. While these interpretations were later all shown to be
incorrect - they predicted the wrong direction of flow of current -
they were important in their stimulation of semiconductor research.
A satisfactory explanation of semiconductor diode operation also came
from three independent sources in the same year. Such simultaneous
waves of insight occur frequently between scientists working
independently but from a common base of knowledge.
In 1938 Alexander Davydov in the Soviet Union (1), Nevill F. Mott of
Bristol University, England (2), and Walter Schottky of Siemens in
Germany (3) all attributed the phenomenon to the presence of an
electronic barrier that forms at the point of contact between a metal
and a semiconductor. Application of a voltage source raises the
barrier to current flow in one direction and reduces it in the other.
Being published in English, Mott's version was the most immediately
accessible to William Shockley and other scientists at Bell Labs.
1939:
(Bell Labs begins effort to put a control grid
into Karl Ferdinand Braun's solid state diode,
much as De Forest put a control grid in Edison's diode.)
When William Shockley joined the Physical Research Department of Bell
Telephone Laboratories in New York in 1939, director Mervin Kelly
assigned him to investigate replacing electromechanical relays then
used for telephone switching with electronic devices. With vacuum
tubes considered unsuitable because of reliability and power
consumption issues and with his Ph.D. background in quantum theory,
Shockley felt that solid state devices could offer a better solution.
Under a notebook heading "A semiconductor triode or amplifier," dated
December 29, 1939 he wrote "It has today occurred to me that an
amplifier using semi conductors rather than vacuum is in principle is
possible." (Note that this thought was common to many people, and
note that it was inspired by the triode,
and not be some Quantum Mechanics computation.)
Walter Brattain performed the experiment as specified by Shockley but
failed to achieve amplification. Additional efforts by Shockley and
others also yielded disappointing results. While perceived as a
failure at that time, this work is now recognized as an important
milestone in the series of events leading to the discovery of the
transistor.
1940:
Russell Ohl, a metallurgist at Bell Labs, Holmdel began investigating
rectification in high purity silicon in the late 1930's. On February
23, 1940 he tested an ingot that yielded strange results. He noticed
that when it was exposed to bright light current flowing through the
silicon increased significantly.
Ohl and his colleagues found a crack at the center of the ingot that
marked a separation of the silicon into regions containing two
distinct kinds of impurities. One impurity, the element phosphorus,
had yielded an excess of electrons; the other, boron, caused a
deficiency (excess holes). They labeled the regions N-type (negative)
and P-type (positive). The area where they merged acted as a
rectifying diode and was called a P-N junction. (1) Light energy
striking the silicon stimulated a flow of electrons in one direction
resulting in a voltage difference across the junction. Ohl had
discovered the P-N junction photovoltaic effect that powers today's
solar cells.
1947:
(Bell Labs sticks a third electrode into a hunk of germanium,
and gets it to control the current flow through a diode.)
Using germanium ingots supplied by Purdue researchers they achieved
voltage amplification on December 16, 1947. By contacting the
germanium crystal with two gold tipped electrodes held in place by a
plastic wedge and a bent paperclip they were able to control current
flow through the material in a repeatable manner.
After extensive patent filing activity during which Shockley's
theoretical contributions to the invention were excluded due to
conflicts with Lilienthal's work, Bardeen and Brattain's point-contact
device was introduced to the public on July 1, 1948.
1948:
Herbert Mataré worked to produce crystal microwave detectors at a
Telefunken laboratory in Poland. While investigating germanium
material he noticed interference between two closely spaced point
contacts. By varying the voltage at one contact he influenced current
flowing in the other.
After the war, the Allies teamed Mataré up with another German
researcher Heinrich Welker to work on improved germanium rectifiers at
a Westinghouse subsidiary, Compagnie des Freins et Signaux
Westinghouse, in France. In researching the "interference" effect he
had noted during the war Mataré achieved amplification on a sporadic
basis. Using higher purity crystals fabricated by Welker in June 1948
he achieved consistent results. By 1949 the French company had the
"Transistron," as they called it, in limited production for use as
amplifiers in the government owned telephone system.
1955:
In 1955 Jules Andrus and Walter L. Bond at Bell Labs adapted
photolithographic (also called photoengraving) printing techniques to
masking and etching oxide layers laid down by Frosch and Derrick. By
coating a wafer with photosensitive material and exposing a desired
pattern through an optical mask, precise window areas could be opened
in the oxide with chemical etching. Impurities could then be diffused
through the openings into the underlying wafer. (1)
In 1957 at the Diamond Ordnance Fuze Laboraties of the U, S. Army in
Maryland Jay W. Lathrop and James R. Nall announced the use of
photolithography to deposit thin-film metal layers connecting discrete
transistors to patterns on a ceramic substrate in an early attempt to
build miniaturized electronic circuits. In 1959 Lathrop moved to Texas
Instruments and Nall to Fairchild Semiconductor where they applied
their expertise to developing the first monolithic integrated
circuits.
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