May 1958 Radio-Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published 1929 - 1948. All copyrights hereby acknowledged.
Did I ever tell the story about a manager I had at a major defense
electronics firm who thought he could make an NPN transistor by
wiring two diodes in series with the anodes tied together? He reasoned
that since a bipolar junction transistor consisted of three alternating
layers of n-type and p-type silicon, the device could be affected
per his scheme. That was in the mid 1980s when I was still a technician
(working diligently on my BSEE degree at
night). Needless to say the engineers who worked under him
were not too impressed with the guy's technical prowess
(nor his managerial prowess, as I remember
it). I didn't consider myself qualified at the time to judge
him one way or the other, so the fact that he was a good guy made
him OK in my book. This article from the year I was born (some doubt
the 'born' claim) reports on the advancements druing the first decade
of the transistor era. It was just before Christmas of 1948 that
Mssrs. Brattain, Bardeen, and Shockley announced to the world their
Ten Years of Transistors
Transistors have been with us for a decade and much has happened
in that brief period, Here is a condensed history of the transistor
from its inception in 1948.
By R. M. Ryder*
10 years ago - on June 30, 1948 - Bell Telephone Laboratories announced
the invention of a semiconductor amplifier and coined for it the
name transistor. This invention has been termed one of the most
significant milestones in the history of electronics. The transistor
in various forms, some of them barely as large as a shoelace tip,
is capable of doing most of the things electron tubes can do, and
many other things as well, most of them on amazingly small amounts
The first form of this device consisted of a tiny wafer of germanium
on which were placed two closely spaced point contacts, one controlling
the flow of current in the other. It was called a point-contact
transistor. Its invention, by John Bardeen and Walter H. Brattain,
stimulated a tremendous upsurge in semiconductor research, which
has continued without letup to the present. The upsurge has been
continually stimulated over the years by new developments and constantly
improving techniques, and there is no evidence that this interest
will wane in the foreseeable future.
The transistor has a long history of semiconductor research behind
it. As far back as 1833, Michael Faraday observed that silver sulfide
had a negative temperature coefficient of resistance. This characteristic
set it apart from other conductors (metals) whose resistance increased
with increasing temperature. By 1855, four of the fundamental properties
of semiconductors- negative temperature coefficient of resistance,
rectification, photoconductivity and photoelectromotive force -
had been observed.
A great body of knowledge on semiconductor materials was built up
and contributed greatly to the final success of the transistor.
Research workers were concerned with both surface and body phenomena.
With respect to surfaces, it was postulated that a space-charge
layer should exist at the surface of a semiconductor. Experiments
were set up to verify the existence of this layer, and these experiments
led to the birth of the point-contact transistor.
Internal structure of a single-diffused germanium transistor.
Bent wires from posts lead to emitter layer and base contact
on surface of crystal.
Heart of intrinsic-barrier transistor as seen through
a microscope. Tiny electrical sandwich in center of photo
contains positive, negative, neutral and positive layers
and holds two tiny dots of indium, to which input and output
electrodes are connected.
The junction transistor
Following rapidly on the heels of this development was the announcement
of the junction transistor in 1951 by William Shockley of Bell Laboratories.
This radically new form of the device was in many ways more effective
than the original point-contact type, being freer from noise and
more efficient. Most striking is that it was predicted theoretically
by Shockley more than 3 years before it was demonstrated.
Because of space limitations, it is not possible to review all
of the advantages of transistors. However, the basic abilities such
as low power consumption, small size, and reliability have been
widely publicized and are well known.
The junction transistor consists essentially of a sandwich of
semiconductor materials into which controlled amounts of impurities
have been introduced to provide specific characteristics. Germanium
has four valence electrons in its outer shell and, when formed into
a single crystal, there are no excess electrons or holes to conduct
electricity. However, if a small amount of an element having five
valence electrons is added to the germanium, excess electrons will
be present, and n-type germanium results. Two such elements are
antimony and arsenic. If the added element has only three valence
electrons, excess holes will exist, forming p-type germanium. Elements
in this class are typified by gallium and indium. The transistor
sandwich then consists of a layer of n-type germanium, for example,
with p-type on each side. The center layer of this sandwich is very
Several techniques have been developed for creating this alternate
n-p-n or p-n-p type of construction in a single crystal. For example,
if a single crystal is being grown of n-type material and the melt
is doped to make it p-type, a thin layer will grow. If the melt
is immediately doped to again make it n-type, a sandwich will be
formed with a very thin center layer. This is called a grown-junction
transistor. Steps involved in the fabrication of a germanium grown
junction transistor1 are shown in Fig. 1.
Another technique is to alloy opposite faces of a thin wafer
of p-type germanium with some such material as arsenic to make the
faces n-type2. This is called an alloy junction transistor
is indicated in Fig. 2. Regardless of the method of fabrication,
these junction transistors operate on essentially the same basic
A closely related device is the phototransistor3.
This was an entirely new type of electric eye - much smaller and
sturdier than existing photoelectric devices. It is essentially
a transistor controlled by light rather than by electric current.
This transistor is employed extensively in the "card translator,"
a system used in telephone exchanges for automatic routing in toll
The materials needed for semiconductor device research are among
the purest and most perfect known to science. Large single crystals
having impurities of about 1 part in 10,000,000 are routinely required.
These small impurities must also be controlled to within a few percent.
The major breakthrough which made such material easily achievable
was the "zone-refining" technique, announced by W. G. Pfann of Bell
Laboratories in 1954.
Fig. 1 - Steps in the fabrication of a germanium grown-junction
Fig. 2 - Left: section through a grown-junction n-p-n
transistor element. Right: section through an alloyed-junction
n-p-n transistor element, showing alloyed layers.
In zone refining, a molten zone is swept through an ingot of
the semiconductor material, such as silicon or germanium, sweeping
impurities to one end of the bar. By repeated sweeps, undesirable
impurities can be reduced to less than 1 part in 1,000,000,000.
The technique takes advantage of the fact that the solubility of
impurities in liquid semiconductor material is different from the
solubility in the solid.
The importance of the purification process is apparent when you
realize that active impurities of as little as 1 part in 1,000,000,000
can affect transistor operation. It is essential that the material
be as pure as possible to begin with, so that the desirable properties
can be obtained by introducing controlled amounts of the desired
Throughout the semiconductor development process, efforts were
made to improve the frequency range of transistors, both as oscillators
and as amplifiers. One approach was to reduce the thickness of the
center layer of the sandwich, but certain limitations were encountered.
A major step in overcoming these limitations was achieved with the
invention of the tetrode transistor4. By 1955, this transistor
had been developed to the point where it could be made to oscillate
at more than 1,000 mc, thus breaking into the microwave region for
the first time with solid-state amplifiers.
Operation at such high frequencies was achieved by adding a fourth
electrode to the basic junction transistor, plus other refinements.
This fourth electrode permitted the center layer of the transistor
to be biased in a way that reduced its effective thickness. This,
combined with an actual reduction in thickeness to less than
0.2 mil, provided operation at ultra high frequencies.
metals can be produced by this zone-melting apparatus.
played by minute quantities of impurities in controlling the properties
of metals can then be determined.
The field-effect transistor
The foregoing discussion has revolved around a particular type of
transistor action, namely the injection of charge carriers by a
p-n type junction into a thin slice of semiconductor and their collection
by another junction. It is also possible to get amplification by
other means, as in the field-effect transistor, where a transverse
electric field controls the flow of current. A number of such "unipolar"
transistors were described by Shockley in 19525. This
type of operation may have important advantages; in particular,
high input impedance of the order of 10 megohms and the possibility
of very high frequency response. Very similar in concept are the
"analog" transistor and the spacistor.
A field-effect transistor using an external "gate" is shown schematically
in Fig. 3, while Fig. 4 shows a field-effect transistor using a
p-n junction to produce a capacitor "gate" within the body of the
Another significant step in high-power and high-frequency operation
was the introduction of the p-n-i-p, or "intrinsic-barrier" transistor.6
This transistor is in essence a club sandwich, in which a layer
of comparatively pure material is interposed between two of the
layers of a conventional transistor. This layer permits closer control
of the stream of charge carriers, isolates input and output areas
and reduces the stored energy to make functioning at higher frequencies
possible. The increased separation of input and output areas also
permits operation at higher voltages than possible with earlier
transistors. The intrinsic layer might be compared very roughly
with the screen grid in a vacuum tube.
Intrinsic barrier type transistors can provide uniform amplification
over bands of hundreds of megacycles, and theoretically units can
be made which will oscillate at 3,000 mc. They can also be designed
to produce some 3 to 10 times more power than earlier junction transistors
at high frequencies.
The surface-barrier transistor7 represented another step
toward high-frequency operation. In this unit, both sides of a thin
wafer of germanium are electrolytically etched away until only an
extremely thin layer remains. Electrodes are then deposited electrolytically.
Because of the very thin base layer, high-frequency operation is
possible. This transistor has since been further improved by incorporating
a diffused base and by closely controlled alloying of the junctions.
Testing the alignment of phototransistors used to "read"
information stored by electronic computers, are Dr. J. N.
Shive (left), who developed the phototransistor and Dr.
R. M. Ryder, both of Bell telephone Laboratories.
Fig. 3 - Schematic representation of a field-effect transistor
in a circuit designed to illustrate how current through
the slab can be controlled by applying a voltage to the
Fig. 4 - A field-effect transistor using a p-n junction
to produce a "capacitor" within the body of the semiconductor.
A voltage that is applied between the p- and n-type material
causes a penetration of space charge, creating a region
within the body of the n-type material that will not contribute
to current flow through the semiconductor.
The diffusion technique
In 1954, Bell Laboratories announced a development which has
proved to be a major breakthrough in transistor technology - the
diffusion technique. Diffusion is a process by which minute amounts
of impurities are introduced into a material in a controlled manner.
As mentioned previously, one of the limitations in extending the
operation of conventional junction transistors to ever higher and
higher frequencies is the difficulty of reducing the thickness of
the center layer of the transistor sandwich. By introducing impurities
in a controlled manner by the diffusion process, this layer can
be made as thin as 30/1,000,000 inch.
The diffusion technique8,9 can be used for other semiconductor
devices as well. Among these devices is the Bell solar battery.10
This battery consists of a thin wafer cut from a single crystal
of n-type silicon into which a small amount of boron has been diffused
to produce a thin layer of p-type silicon. When illuminated, this
cell produces electricity. In direct sunlight, its conversion efficiency
may run as high as 11 %.
At present, it appears that the diffusion technique will achieve
widespread recognition as a reliable, controllable process for making
transistors and many other semiconductor devices. Enough information
has been obtained on this process to make it adaptable to mass-production
operations. Units have been fabricated which will oscillate and
amplify at well over 1,000 mc, and the frequency barriers are continually
being forced higher and higher.
The "drift transistor" emphasizes another feature which has importance
for high-frequency transistors.11 By control of the distribution
of impurities in the thin central layer, one can obtain a "built-in"
electrical field which speeds up the electron stream and thereby
makes the transistor somewhat faster. Experimentally, the easiest
way to achieve an appropriate structure is by diffusing the base
as just mentioned above. Typically, the frequency response improves
10 or 100 times by making the base layer thinner while the built-in
field gives a further improvement of the order of 1.5-4 times.
Last year a new device was announced which combines high-frequency
operation with high-power output to an extent not previously attained.
This new transistor can provide an output of better than 5 watts
at 10 mc, either as an oscillator or an amplifier. It has alpha-cutoff
frequency of about 100 mc and has produced an output of better than
1 watt at this frequency.
To achieve the combination of high power and high frequency required
extensive research and the utilization of many different techniques.
The unit employs the basic p-n-i-p type of construction and so takes
advantage of the intrinsic-layer idea. Silicon is employed to permit
operation at higher temperatures and thus allow greater heat dissipation.
Diffusion techniques are used to form the emitter and collector
regions. And the electrode areas themselves are kept as small as
possible consistent with the desired power-handling capacity. Thus,
by combining a number of techniques, both frequency and power barriers
have been lifted.
Electronic computing machines are one of the newest fields that
transistors are expected to dominate because of their size, power,
speed and reliability. Closely related is the field of automatic
telephone switching, which now uses electromechanical switches such
as relays but which is expected to go increasingly electronic in
coming years. A prominent new device for use here is expected to
be the p-n-p-n diode, a four-region transistor switch, invented
by Shockley. As now realized in diffusion techniques in silicon,
the device in the off condition has a resistance of 100 megohms.
When switched on either by a pulse or by a high voltage, its on
resistance is only about 2 ohms, with a less than 1-volt sustaining
voltage. The device can be switched between these conditions at
megacycle rates if necessary.
New fabricating processes
A major problem in fabricating transistors, particularly those
intended for high-frequency operation, is attaching leads to the
semiconductor material. A significant advance in this field is the
development of the thermocompression bonding technique at Bell Laboratories.
In this technique, the leads are attached by a combination of temperature,
pressure and time. One method that works very satisfactorily in
he laboratory is to force the lead against the semiconductor surface
with a heated wedge-shaped tool. Neither the temperature nor the
pressure is great enough to damage the semiconductor surface nor
to introduce any impurities, and the time can be kept short enough
to permit rapid assembly.
Advantages of this method over soldering or welding are many.
There is less danger of contamination; leads can be attached to
very small areas - particularly useful in high-frequency transistors
- and the bond between the lead and the semiconductor is stronger
than the lead itself.
Although today's practical transistors all use germanium or silicon,
at least passing mention must be made of a new family of materials
called intermetallic semiconductors. Silicon and germanium are in
Group IV of the periodic chart; that is, they each contain four
valence electrons in the outer ring. Compounds formed by taking
elements from Group III (three valence electrons) and Group V (five
valence electrons) will have an "average" of four valence electrons,
and thus may exhibit characteristics similar to the materials now
A great deal of exploratory work is being carried out in laboratories
both in this country and abroad to determine the characteristics
of these intermetallic compounds. Particularly active in his field
is H. Welker, in Germany. Results have been very encouraging - it
appears that these materials may be useful for producing more versatile
transistors and other devices. In fact, intermetallic diodes are
now on the market. Notable among the compounds under investigation
are indium antimonide, gallium arsenide and indium phosphide.
More complex compounds having an average of four valence electrons
in the outer ring are also being investigated, and it is reasonable
to expect that within a few years materials will be available which
are superior in specific areas to either germanium or silicon.
Important areas of exploration, at present, are in the areas
of surface phenomena and external contamination. To produce reliable
transistors having the desired characteristics without excessive
rejects requires careful control of all the steps in the manufacturing
process, with particular emphasis on avoiding contamination of any
kind. Past efforts in this direction have paid off handsomely. Work
is also under way to increase power and frequency capabilities of
transistors to approach more closely the performance now available
from electron tubes.
An attempt has been made here to touch on the highlights of the
last 10 years of transistor development. Many important contributions
and contributors have of necessity been omitted for lack of space.
It is important to emphasize that in this field, as well as any
other scientific endeavor, notable advances are the result of the
combined efforts of a number of scientists striving to unlock the
secrets of nature.
*Bell Telephone Laboratories.
1 W. Shockley, M. Sparks and G. K. Teal, "P-n
Junction Transistors"; Physical Review, Vol. 83, pp. 151-62, July
2 John S. Saby, "Fused Impurity P-n-p Junction
Transistors"; Proceedings of the IRE, Vol. 40, P. 1358, November,
33 J. H. Shive, "The Phototransistor"; The Transistor:
Selected Reference Material on Characteristics and Applications,
Bell Telephone Laboratories, Inc., New York, 1951 (prepared for
Western Electric Co.), p. 115.
4 R. L. Wallace, Jr., L. G. Schimpf and
El Dickten, "A Junction Transistor Tetrode for High-Frequency Use";
Proceedings of the IRE, Vol. 40, p. 1395, November 1952.
5 W. Shockley, "A Unipolar 'Field-Effect' Transistor";
Proceedings of the IRE, Vol. 40, p. 1377, November, 1952.
6 J. M. Early, "P-n-i-p and N-p-i-n Junction
Transistor Triodes" ; Bell System Technical Journal, Vol. 33, p.
517, May, 1954.
7 W. E. Bradley, et al, Proceedings of the IRE,
8 M. Tanenbaum, D. E. Thomas and C. A. Lee,
"Diffused Emitters and Bases for Silicon and Germanium Transistors";
Bell System Technical Journal, January, 1956.
9 C. S. Fuller and J. A. Ditzenberger, "Diffusion
of Donor and Acceptor Elements in Silicon"; Journal of Applied Physics,
Vol. 27, May, 1956.
10 D. M. Chapin, C. S. Fuller and G. L. Pearson,
"The Bell Solar Battery"; Bell Laboratories Record, July, 1955.
11 H. Kromer, "Theory of the Germanium Rectifier
and the Transistor"; Zeitschrift Physik, Vol. 134, pp. 435-50, March
Robert M. Ryder was born March 8, 1915, in Yonkers, N. Y. He
graduated from Yale in 1937, receiving a Bachelor of Science degree
in physics. He obtained a PhD degree, also from Yale, in 1940.
In July, 1940, he become a member of the technical staff of Bell
Labs, working on microwave amplifier circuits. During World War
II, he contributed to Bell Labs' research on the signal-to-noise
performance of radars. In 1945, he joined the Electronic Development
Department to work on microwave oscillators and amplifier tubes
for radar and radio relay applications. He is currently a transistor
development engineer, particularly interested in transistor development
for high-frequency and other transmission applications.
In 1957, Dr. Ryder received an award from the Institute of Radio
Engineers "for contributions to the development of microwave tubes
and applications of transistors."
He is a member of the American Association for the Development
of Science, Sigma Xi and the Yale Engineering Society.
Posted October 16, 2014