Littler Than Lilliput: Microminiature Electronics
March 1963 Popular Electronics

March 1963 Popular Electronics Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

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 a shipwreck.

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Littler Than Lilliput: Microminiature Electronics

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 a dime.

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 pin.

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!

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 with-in 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 truly fantastic.

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.

The 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).

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 bombard-ing the raw material with gas ions ac-celerated 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.

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 micro-miniaturization will be applied to such units as hearing aids, walkie-talkies, personal receivers, amplifiers, and similar products in the not-too-distant future.

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