March 1963 Popular Electronics
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Mr. Einstein believed everything is relative, and this 1963 article
on the revolution of "microminiature electronics" certainly attests
to the truth of it. Unlike with his Theory of Special Relativity
though, travel near the speed of light is not needed to witness
length contraction in the electronics realm; the passage of time
and its attendant evolution of technology does that for us. Today's
definition of 'microelectronics' will to our progeny seem laughingly
absurd when they read about (or more likely have wirelessly implanted
in their brain's memory cells) our current transistor gate widths
of tens of atoms.
BTW, Lilliput, in case you don't know, is the island nation of
Gulliver's Travels where the wee Lilliputians famously lashed
Lemuel Gulliver to the beach in his sleep after washing ashore following
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Littler Than Lilliput: Microminiature Electronics
Louis E. Garner
The story of the microminiature in today's electronics
The scene is a radio-TV service shop of the future. The technician
wears white coveralls, a tight-fitting headpiece, thin gloves, and
special covers for his shoes. He works in an atmosphere that is
dust- and lint-free, temperature-controlled, and air-conditioned.
His "workbench" is a vacuum-box equipped with tweezer-type micro-manipulators,
a binocular microscope, and an electron-beam welder/etcher. Missing
are such present-day tools as long-nose pliers, diagonal cutters,
and a soldering iron. Missing, too, are stocks of individual components
- such as resistors, capacitors, coils, diodes, and transistors.
Instead, the technician tests and replaces complete multi-stage
elements so small that an entire receiver circuit scarcely covers
Impossible? Not at all. In fact, prototypes of this future "service
shop" are already in use in the research and development laboratories
of several manufacturers - staffed by engineer/technicians who inspect,
test, and modify circuits which are no larger than the head of a
For decades, science-fiction writers and comic-strip artists
have envisioned all sorts of ultra-miniature electronic equipment.
Among these items have been rocket navigational systems and computers
no bigger than cigar boxes, tiny "spy" television cameras concealed
in cigarette cases, and vest-pocket-sized two-way radios.
As is often the case, however, science has a way of overtaking
and surpassing its prophets. If current progress in miniaturization
is any criteria, even Dick Tracy's two-way wrist radio will turn
out to be "oversized." The reason: it may one day be possible to
assemble a two-way radio in an ordinary finger ring!
Microminiature electronic module (in circle) performs
same functions as circuit board below it, also employs 35
components, yet is 1/47th the size!
Evolution. Before examining the current situation,
let's turn back the pages of history. The trend towards circuit
miniaturization began long before World War II. It was evidenced,
in part, by the introduction of "miniature" vacuum tubes for conventional
applications and "subminiature" tubes for compact equipment, such
as hearing aids. Quite understandably, this trend was given tremendous
impetus during the war. The result was development of a hand-held
transceiver (the handie-talkie) and the now-famous proximity fuse
- a transceiver so small that it could nestle within the nose of
a bomb or an artillery shell.
For nearly two decades, progress towards equipment miniaturization
followed a gradual, or evolutionary, rather than revolutionary,
path. Component parts were made smaller and circuits more or less
"squeezed" together into tinier packages. But the components still
resembled their full-sized counterparts, and conventional wiring
techniques were employed.
A giant step forward came with the invention of the transistor.
This device and its related semiconductor "cousins" - coupled with
etched wiring and tiny low-voltage, low-power components - permitted
the production of subminiature circuits. And the results have been
A little over a decade ago, for example, the common hearing aid
was about the size of a pack of cigarettes and weighed several ounces.
But today's transistorized hearing aid weighs only a small fraction
of an ounce and occupies about one-fifth of a cubic inch!
Today, two factors have made further miniaturization a prime
goal One is the increasing complexity of electronic equipment -
a typical computer uses tens of thousands of components and may
well fill a small room, even when transistorized and assembled with
conventional subminiature components.
second factor is the increasing need for a very short signal response
time, particularly in computers and high-frequency radio circuits.
Regardless of the speed at which individual circuits are made to
function, a certain amount of time is required for a signal to travel
from one part of the equipment to another. As a general rule, if
the equipment is made smaller, physically, the signal path is reduced
and the operation made speedier.
Revolution. An unprecedented effort at further
circuit miniaturization is now being made by a number of manufacturers.
The problem is being attacked on three broad fronts: (a) the use
of thin films; (b) the production of microcircuits; and (c) the
development of solid-state circuits. The final aim is the large-scale
commercial production of low-cost, extremely reliable circuits are
microscopic in size (hence, microminiaturization).
To this end, the concept of circuit integration has been adopted
by most firms. In essence, an integrated circuit is simply one in
which the various elements are manufactured and interconnected as
a unit - there are no separate resistors, capacitors, coils, and
wiring as such. This in itself is a revolutionary concept, since
past efforts at miniaturization generally have been based on the
use of individual components.
Space and military applications claim the bulk of current
"microminiature" production. New general-purpose digital
computer (shown undergoing visual inspection) was designed
for inertial guidance systems.
"Micropac" contains nearly 2000 micromodules, will be
used by U.S. Army Signal Corps.
A PRSG (pseudo-random sequence generator) which makes
300 million "logic decisions" each second.
The key phrase in these efforts is component density, i.e., the
number of individual circuit elements which can be packaged within
a cubic foot (or a cubic inch). Not too long ago, in the days of
the subminiature tube, a density of 6000 components per cubic foot
was considered pretty good. With the invention of the transistor,
maximum component density rose to about 100,000 elements per cubic
foot. But even newer techniques promise densities on the order of
10,000,000 parts per cubic foot!
Thin-Film Circuits. Many scientists and engineers
consider the use of thin films as the first true approach to genuine
integrated circuitry, since this technique permits almost all circuit
components and wiring to be formed as a direct part of the manufacturing
process. As the name implies, a thin-film circuit is one made up
of ultra-thin metallic films deposited on an insulating base called
the substrate. These films, which can be comprised of such metals
as gold, aluminum, and tantalum, are unbelievably thin - actually
one-hundredth as thick as the finest rolled or beaten foil.
Any of several techniques can be used in forming the thin film,
but the three most popular are electroplating, evaporation, and
sputtering. Of these three, electroplating is quite similar to the
methods used in more conventional work except for scale. Currently,
the most popular technique is evaporation. Here, the raw material
is heated to the boiling point in a crucible placed within a high
vacuum chamber. The heated material boils off and condenses on the
substrate suspended above the crucible in the same chamber. Unfortunately,
some metals are difficult to evaporate, and it is with these materials
that the sputtering process is employed. In sputtering, atoms of
the metal are splashed onto the substrate by bombarding the raw
material with gas ions accelerated by a strong electric field.
Regardless of the basic film forming process used, the circuit
elements and interconnections are produced by arranging the film(s)
in a precise pattern. Often, several film layers are employed, each
in a different pattern, to produce resistors, capacitors, and circuit
wiring. The circuit patterns can be developed by a photoengraving
and etching process, applied to a continuous film. Or they can be
formed during the original film deposition by interposing a "mask"
between the substrate and source of metallic atoms. The latter process
is roughly analogous to the use of a stencil for printing.
Testing microelectronic circuit materials is a highly exacting
science in itself. Above, scientist wearing special glasses monitors
preparation of silicon base material for a microcircuit. At right,
researcher subjects thin-film semiconductors to air pressure only
one-millionth that at sea level.
Production of a typical thin-film circuit begins with thin tantalum
and gold films applied to the insulating substrate (glass in this
case). Next, the basic circuit pattern is formed by photoengraving
and etching techniques, using suitable masks. With the basic circuit
pattern established, passive components (such as resistors and capacitors)
are formed by selective oxidation and anodization of parts of the
metallic film. In the last steps, active elements (such as diodes
and transistors) are inserted and final connections made through
the evaporation of aluminum electrodes. As a rule, scores (or even
hundreds) of circuits will be processed at the same time.
Generally speaking, thin-film techniques have been suitable only
for the deposition of circuit wiring and the production of passive
components ... resistors, capacitors, and coils. This means that
it's been necessary to produce the active elements (diodes, tunnel
diodes, transistors, etc.) separately and then insert these units
in the basic assembly during the last production steps. This process
is a costly one, of course, and - several firms are striving to
develop practical methods which will permit the formation of active
as well as passive components with thin-film methods.
Micro·Circuits. Another popular technique for manufacturing
microminiature circuits is based on the use of conventional transistor
assembly methods. The active "heart" of a modern small-signal diode
or transistor is a tiny chip of semiconductor material about the
size of a pinhead - and thus extremely small compared with the header
and case in which it's mounted. This fact first led a number of
semiconductor manufacturers to assemble several transistors and/or
diodes in a single standard-sized case, providing additional contact
leads for the extra units.
Later, several firms started interconnecting the various elements
to form such basic circuits as direct-coupled amplifiers, diode
matrices, complementary amplifiers, flip-flop's, Darlington stages,
and choppers. Externally, the completed circuit assembly is the
size and shape of a conventional transistor package, except for
the additional leads involved.
Circuit wafer for diode commutator contains 16 diodes
and four resistors, easily rests on finger tip.
Tunnel diode transistor modules for new computer employ
subminiature versions of standard parts.
While integrated and ultraminiature by definition, micro-circuits
assembled on standard headers from individual diodes and transistors
are not as representative of a new manufacturing process as they
are of a refinement in assembly techniques. The circuit designs
employed generally depend on direct coupling between semiconductor
devices, with a minimum of external components (such as resistors
and capacitors). The use of micro-circuit assemblies has made possible
a considerable increase in component density, however, with a corresponding
decrease in overall equipment size.
Price-wise, micro-circuits provide an excellent example of what
we can expect as production techniques are refined and as the economies
of mass production come into full play. When first introduced, these
units sold for over one hundred dollars each, even in modest quantities.
Today, some firms offer complete circuit assemblies in several standard
configurations at prices approximating those of some transistors!
Solid-State Circuits. Thin-film techniques and
micro-circuit assembly methods have accomplished miracles in miniaturization
and offer tremendous promise for the future. But perhaps the ultimate
approach to micromiaturization is the production of a complete circuit
as a single semiconductor device - in essence, a solid crystal which
performs the same function as a conventional circuit through a rearrangement
of its internal molecular structure, and without the need for individual
active and passive electrical elements.
When perfected, this technique may permit the manufacture of
a pinhead-sized crystal capable of performing all the functions
of an amplifier or oscillator stage. Interconnected, a few such
"pin-heads" could serve as a complete receiver or amplifier. One
manufacturer, for example, is now developing a computer using solid-state
circuits. The completed instrument will weigh less than 15 pounds
and occupy less than one-third of a cubic foot, compared with the
175-pound weight and three-cubic-foot space requirements of an equivalent
"miniature" transistorized computer.
The basic steps in the fabrication of at least one type of solid-state
circuit are essentially similar to the methods used for the production
of individual diodes and transistors (see "Transistors - Types and
Techniques," Popular Electronics, November, 1962, p. 64). The base
material on which the circuit is formed is a wafer of semiconductor
material (such as silicon) rather than an insulating substrate.
Area masking, photoengraving, etching, and impurity diffusion
techniques are used to form appropriate p- and n-type semiconductor
regions in the wafer to produce various circuit elements. Evaporation
methods are then employed to apply metallic conductors. And, finally,
the wafer is mounted in a suitable case (such as a ceramic wafer),
the crystal is diced to isolate individual elements, and circuit
interconnections are made.
Summing Up. At present, the majority of commercially
available thin-film, "micro-circuit," and solid-state microminiature
circuits are used in computer designs ... flip-flop's, gates, buffer
amplifiers, shift registers, adders, and memory arrays. There is
a good reason for this - of all electronic systems, computers require
the greatest number of repetitive circuits, and it is here that
the advantages of the multiple production of identical circuits
can be utilized to the fullest extent.
As far as consumer products are concerned, microminiaturization
of circuitry will offer few advantages until "accessory" components
(microphones, speakers, etc.) can be subjected to a similar "shrinking"
process. Research is being conducted along these lines, however,
and there is a definite possibility that microminiaturization will
be applied to such units as hearing aids, walkie-talkies, personal
receivers, amplifiers, and similar products in the not-too-distant
As for industrial applications, one firm has confidently estimated
that the market for microminiature circuits will approach twenty
billion dollars a year by 1980!
Posted May 30, 2014