People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Popular
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Hmmmm... I never really thought about the transistor as a crystal
amplifier (a la the 'crystal detector'),
but in fact it was fabricated from a crystal of germanium with
two 'cat whisker' wires pressing on its surface. Before the
transistor was the simple rectifier made of a crystal of selenium
or even carborundum with a point contact. Those were used for
turning AC into DC and for detecting radio wave modulation envelopes.
For a really good synopsis of the early development path of
semiconductors, read this story from a 1968 edition of Popular
Electronics that commemorated the 20th anniversary of Bardeen,
Shockley, and Brattain announcing their transistor. Having been
written much closer to the days of discovery, the story has
not been filtered through as many writers' points of view, and
contains some information I'll bet you have never read before.
E.g., did you know that semiconductor dopants were originally
referred to as adulterants? Did you know that Shockley's early
research was on field effect devices and, if successful, would
had made FETs the first forms of transistors rather than bipolar
junction types? Did you know that the name 'transistor' (trans-resistor)
was coined after the vacuum tube's amplification action called
'transconductance?' Read on for more.
The Quest for the Crystal That Amplifies
We call it a transistor - but 20 years ago it was and ugly duckling.
by Daniel M. Costigan
The birth of the transistor was not something that happened
overnight. It marked the culmination of many years of dreaming
and searching, not only by scientists, but by a couple of generations
of quixotic tinkerers as well, seeking to extract from a tiny
chunk of the mineral galena some magical energy that might eliminate
the need for power-consuming vacuum tubes in radio receivers.
Some of these experimenters actually produced crystal sets that
could operate loudspeakers-at low volumes - perpetually and
without need for external power.
Sir Oliver Lodge (1851-1940) made many important
contributions to wireless transmission and reception, which
led to UHF transmission techniques.
These devotees of the galena mystique thrived for some thirty
years on trial-and-error and wishful thinking. During this time,
they were joined by a handful of scientists who worked unnoticed
behind the scenes, taking a more methodical approach to essentially
the same goal. The scientists were mostly engineers, metallurgists,
and physicists who had been recruited by industry - some of
them from university faculties - to help seek new ways to improve
the efficiency of electric power and communications devices.
Finally, in the late 1940's, the quest for the crystal that
amplifies ended in triumph for a trio of distinguished industrial
scientists. The year 1968 marks the 20th anniversary of what
has since become recognized as one of the most momentous events
in the annals of electrical science.
How The Quest Began.
The primordial spark to which this quest can be traced occurred
around the turn of the century when the need for a practical
rectifying device arose almost simultaneously in two budding
young industries: electric power, and radio.
In electric power, the advocates of alternating current had
won their battle against the d.c. interests and had begun to
distribute a.c. power on a wide scale. This meant that some
kind of practical converter, other than a motor-generator, would
be needed to permit the operation of d.c. apparatus - battery
chargers, electroplating equipment, telephonic devices, etc.
- on commercial a.c. power.
The rectifying properties of selenium had been known for
nearly a century, but it wasn't until 1924 that semiconductor
rectifiers became commercially available. By the early thirties,
copper-oxide rectifiers had come into wide use as converters.
Selenium, which had at first proved unsatisfactory for use in
power conversion, was gradually improved and eventually surpassed
copper-oxide in popularity.
The names Mott and Schottky are two that stand out in connection
with the early evolution of rectifier theory. Working independently
of one another - Sir Nevill Mott in England and W. Schottky
in Germany - both men concluded that rectification took place
in a thin electrical barrier that formed at the junction of
a metal contact and a semiconductor. Schottky called this surface
barrier an "inversion region" within the thickness of which
a change of conductivity took place. The theory was to play
a prominent role in the reasoning that later led to the invention
of the transistor.
Radio's need was for a practical rectifying detector of received
signals, and it arose with the advent of voice transmission.
In its embryonic stage (1894 to about 1906), a radio receiver
had at its heart a "coherer," in which metal filings clung together
on exposure to electromagnetic disturbances, thereby varying
the current in a local battery circuit. The disturbances were
set up by a spark transmitter being turned on and off with a
First used by England's Sir Oliver Lodge in 1894, the coherer*
had been steadily improved in design and had reached a fairly
high level of refinement by 1900 when Professor Reginald Fessenden
of the University of Pittsburgh succeeded in transmitting voice
on a continuous wave.
Professor Reginald Aubrey Fessenden (1866-1932).
a pioneer in wireless communication, was the first man to voice-modulate
a continuous-wave carrier.
Radio suddenly found itself faced with much the same situation
that had created the need for rectifiers in the electrical industry.
The transmitted radio wave became a "carrier," its cargo a modulation
envelope that was electrically self-cancelling until the alternating
current could be made to flow in one direction only. Radio detection
thus became a matter of rectification.
Fessenden's first detector was an electrolytic device of
his own design. It was highly sensitive, but also critical and
The first practical crystal detectors appeared in 1906. The
one invented by G. W. Pickard used silicon and featured a "catwhisker"
(fine wire) contacting arrangement similar to that suggested
by a German experimenter named Braun some 30 years earlier.
Another type, invented by H. H. Dunwoody, an executive of the
De Forest Wireless Company, used a small chunk of carborundum
clamped between two electrodes.
Vacuum Tubes and Diodes.
The crystal detector reigned supreme until the early twenties
when the vacuum tube began to make inroads. Silicon had proved
to be the most stable crystal, but galena (lead sulphide) was
the most sensitive and therefore the most popular.
As in everything, however, it takes power to beget power;
thus, there were the inevitable "A" and "B" supplies wherever
vacuum tubes were used. What's more, some of the power had to
be wasted in heating the tube filament - an unfortunate requisite
that was to impose serious restrictions on the tube's useful
life and on the design of the tube-using equipment.
Crystal detectors needed no external power supply; they were
simple and compact, and there was no heat problem. But they
couldn't amplify - at least not until a group of scientists
at a major industrial research laboratory had undertaken an
intensive investigation into the mysteries of solid-state semiconductors.
In 1934, the Bell Telephone Laboratories began to develop
fixed semiconductor diodes for use in microwave experiments.
The earlier ones were silicon and germanium point-contact devices
resembling the "fixed" detectors that had been used in some
crystal broadcast receivers. ("Point-contact" is a sophisticated
term for the old familiar catwhisker.) The more advanced junction
diodes were developed during and immediately following World
A New Turn.
Walter H. Brattain had come to Bell Labs shortly after having
received his Ph.D from the University of Minnesota. His involvement
during the thirties in the study of electrical conductivity
in semiconducting materials eventually brought him in contact
with William Shockley, a brilliant young Ph.D who joined the
staff in 1936 and soon began to form some ideas of his own on
the potentials of semiconductors.
In that same year (1936), Dr. Mervyn Kelly was appointed
Director of Research at Bell Labs, and one of his first acts
was to assemble a team of physicists to formally explore the
behavior of electrons in solids. Brattain and Shockley were
among those selected.
Since the late thirties, Shockley had been entertaining the
notion that a semiconductor ought somehow to be able to amplify
an electric current. His attempts to achieve "valve action"
in a copper-oxide device were interrupted by World War II. Immediately
following the war, he constructed a special device based on
a scheme he had worked out on paper. But, as is so often the
case, what appeared workable on paper did not work in actuality.
Ironically, the device that had failed was the forerunner
of the field-effect transistor (FET), which was to re-emerge
many years later to be heralded as one of the more important
advances in solid-state technology. Had Shockley's experiment
been successful - if more had been known about the characteristics
of semiconductor materials - the development of solid-state
devices might have taken a completely different course.
It was about the time of Shockley's "field-effect" experiment
that the Bell Labs team was enhanced by the addition of a new
member. He was John Bardeen, a 37-year-old theoretical physicist
and former university professor whom Shockley had personally
recruited. During the preceding decade, Bardeen had done extensive
work in the field of electroconductivity in solids. The fact
that Shockley's experiment had not yielded the expected result
interested Bardeen and set him working on a theory to explain
Taking his cue from Mott and Schottky, Bardeen theorized
that surplus electrons gathered at the surface of a semiconductor
and became immobilized so that, in effect, they acted as a sort
of barrier to externally applied currents. To test his "surface
states" theory, he and Brattain performed a series of interesting
At first they used a liquid electrolytic as a current-carrying
medium between one side of a power source and the surface of
a piece of semiconducting silicon. They found that by passing
a current through the electrolyte, the surface charge on the
silicon could be altered.
William Shockley, John Bardeen, and Walter
H. Brattain, co-discoverers of the transistor, received the
1956 Nobel Physics Award for their invention.
This led Brattain to suggest a slightly modified approach.
Germanium was substituted for silicon, and a thin layer of gold
for the electrolyte as the special contacting interface. Two
currents were made to flow in opposite directions through the
germanium, one between the gold contact and a solid connection
at the base of the material, and the other between the base
connection and a cat-whisker contacting the surface - near the
gold contact. As had by now been anticipated, varying the one
current produced corresponding variations, but of greater magnitude,
in the other. Amplification had been achieved!
The technical explanation for the phenomenon was highly complex
and dealt with such things as atomic valences, "holes," "donors,"
and "defect conductivity." Stated simply, what had happened
was that the tiniest plus charge at one of the two contact points
on the semiconductor surface had drawn off enough of the material's
surplus electrons to create "holes," which, in turn, were attracted
to the adjacent negative point and therefore functioned as vehicles
by which the lesser current could influence the greater one.
In essence, then, the semiconductor had become a variable resistance,
enabling control of current flow in one circuit by varying the
current in another.
By the close of 1947, experiments had proved the new device
capable of amplifying audio frequency signals. Bardeen and Brattain
quietly announced their discovery via a letter to the editor
of "The Physical Review," published in the July 15, 1948, issue.
The First Transistors.
The name transistor, by which the device was to become known,
was suggested by another Bell Labs physicist, John R. Pierce.
Pierce observed that, where a vacuum tube amplified by transconductance
- the effect of the grid voltage on plate current - the new
device did its amplifying by what might more aptly be termed
"trans-resistance." The name may also be thought of as suggesting
the transfer of signals through a varistor, a varistor being
a semiconductor diode whose electrical resistance decreases
substantially with a moderate increase in applied voltage. (Varistors
are often used as buffers to protect delicate components from
The first transistors produced in quantity in the laboratory
contained a tiny chunk of slightly impure germanium on which
two "catwhiskers" converged, contacting the surface at points
less than a hair's breadth apart.
William Shockley, meanwhile, continued to pursue his own
ideas on how best to make a semiconductor amplify. His quest
led to the invention, later in 1948, of the junction transistor
in which transistor action was achieved by the sandwiching together
of p-type (electron deficiency) and n-type (electron surplus)
semiconductors. Shockley's design, although at first more difficult
to fabricate, proved more predictable in its properties and
less fragile than its "point contact" predecessor, and was therefore
soon to supersede it. The junction transistor was introduced
early in 1951.
A major obstacle to mass production was the requirement that
semiconductor materials contain carefully controlled degrees
of impurities to insure the proper electrical imbalance. This
meant starting with a nearly pure substance and then adding
adulterants (such as arsenic or gallium) by a carefully controlled
doping process. The introduction of zone refining in 1955 was
the first big breakthrough in high volume production of the
In recognition of the magnitude of the revolution they had
kindled, the transistor's trio of inventors - Shockley, Brattain,
and Bardeen - were awarded the 1956 Nobel Prize in Physics.
But, during the middle fifties, the widely acclaimed little
device still suffered a number of serious shortcomings. For
one thing, it was critically temperature-sensitive and therefore
unable to handle power beyond a fraction of a watt. What's more,
it was noisy and unstable, had ridiculously low input impedance,
and was a sluggish device whose switching speed and frequency
response left much to be desired.
These shortcomings, however, were gradually overcome as new
manufacturing processes were introduced and semiconductor materials
with improved electrical characteristics were developed. By
the late fifties, the reliability of the device had already
begun to exceed that of vacuum tubes.
The year 1957 was the best ever for the sale of vacuum tubes.
Unit for unit, they were still outselling transistors by thirteen
to one. But the gap was rapidly narrowing, with the turning
point due in the early sixties. (In 1959, 77.5 million germanium
transistors were sold for a total of 151.8 million dollars,
at an average price of $1.96 per unit. By 1966, the picture
was considerably changed: 368.7 million units were sold for
a total of 164.5 million dollars, an average price of 45 cents
Further Improvements. New developments followed in rapid
succession, and with them came a whole new electronics vocabulary:
p-type, n-type, bipolar, diffused junction, epitaxial growth.
The grown junction gave way to the alloy junction, which, along
with the introduction of the diffusion process, resulted in
improved frequency response and switching speeds. It was now
feasible to use transistors in computers - a marriage which,
in turn, was to enhance the evolution of still faster and more
reliable semiconductor devices.
The diffusion process also broke the transistor's power-handling
and temperature barriers by facilitating the use of silicon
in place of germanium. Mesa, planar, and epitaxial devices emerged
as some of the more prominent offshoots of the diffusion technique.
The field-effect transistor, which had continued to lie dormant
in the laboratories, seemed to hold the key to some of the improvements
still needed - higher input impedance, for example, and lower
levels of noise and distortion. Of all semiconductor devices,
it came closest to a vacuum tube in characteristics. But the
electrical surface properties of the semiconductor material
used in its fabrication were critical, and it was not until
recently that FET's finally became competitive with other semiconductors.
Similarly, the unijunction transistor, with its single p-n
junction, was originally developed in the early fifties, but
is just now beginning to emerge as one of the less expensive,
more stable, and temperature-resistant devices.
The late fifties saw the introduction of miniature circuit
modules, silicon-controlled rectifiers (SCR's), and Esaki's
remarkable tunnel diode, with which amplification was possible
without the traditional "third element." SCR's shrunk the gap
between tube and semiconductor capabilities by providing a highly
efficient solid-state replacement for thryatrons and mercury-arc
rectifier tubes in power control equipment.
What Does The Future Hold?
The pace of development of new transistor types has been
absolutely staggering. The list now numbers in the thousands,
and it continues to grow as the mighty midget celebrates its
Apart from its having reshaped an entire industry and opened
many new doors, perhaps the most fascinating offshoot of the
whole solid-state technology to date has been the subordinate
art of micro-electronics. Already in the making are integrated
circuits so minute that an entire amplifier could hide behind
a single transistor.
Solid-state technology has been growing and changing at such
a dizzying pace that it is difficult to predict what lies ahead
even in the next year or so. Perhaps at this very moment, somewhere
in the world, a small but persistent group of experimenters
is exploring a radically new concept that may someday render
the present technology obsolete.
*For more details,
see article entitled "The 'Coherer' " which appeared in the
May, 1961, issue of Popular Electronics.
Newsreel from 1956, showing William Shockley,
Walter Brattain and John Bardeen receiving the Nobel Prize for