Gulliver-Size Need

For Lilliputian Products

Medieval theologians who argued for years about the number of angels that could stand on the head of a pin never found a satisfactory answer. Contemporary scientists who are just as doggedly determined to see how much gadgetry they can cram into about the same amount of space have made remarkable progress. On a barely visible chip of silicon as small as one-twentieth of an inch square, they can now produce complex and virtually trouble-free electronic circuits containing more than 80 built-in transistors, diodes, resistors and capacitors.

These tiny devices--called integrated circuits because their components are built as inseparable parts of one solid chip--are already displacing the transistor as the glamour product of the electronics industry (see following color pages). First developed in 1958 by Texas Instruments Engineer Jack Kilby while he was tinkering in the laboratory during a hot summer vacation, integrated circuits (or ICs) did not become generally available until 1962, when design improvements and refinement of production techniques allowed electronics companies to turn out some 60,000 a year. In 1966, the industry will produce 35 million ICs worth $150 million, and even then it will be hard pressed to meet the explosive demands of its customers.

Integrated circuits are becoming one of the basic building blocks of the space age. They are vital to the electronic systems of the Minuteman II and Polaris missiles, the Navy A-7A attack bomber and the supersonic, swing-wing F-111A. They are at work in the radiation measurement system aboard Lunar Orbiter I and will be used in the Apollo Project's lunar excursion module. ICs are used in the new ground-surveillance radar system at the Atlanta airport and are being designed into most new military and commercial computers. Within the last year, the tiny chips have also begun to find their way into consumer products. Some Zenith hearing aids and RCA television sets now use integrated circuits, and General Electric will soon market an integrated-circuit clock radio.

Speed & Reliability. Though creation of the microscopic circuits marks a triumph of miniaturization for an industry that is obsessed with Lilliputian dimensions, the negligible weight and small size of the ICs (more than 9,000 will fit in a thimble) are even less important than their reliability, low cost and speed of operation.

The introduction of integrated circuits, for example, came just in time to rescue electronics engineers from the "tyranny of numbers." As electronic devices grew more complex, requiring hundreds of thousands, and even millions of separate components and interconnections, it became increasingly probable that at any given time they could be disabled by a single faulty part or connection. By the use of pretested ICs, each with scores of virtually indestructible components permanently connected within a solid chip, the probability of failure has been reduced.

ICs have also solved another dilemma for electronics engineers: because electric current travels at the speed of light (about a foot in a billionth of a second), the length of wires or other conductors connecting circuit components and the size of the components themselves are an increasingly important limitation on the speed of circuit operation. For circuits to operate billions of times per second--a requirement in many of the new computers and microwave communications systems--circuit components must be located within a tiny fraction of an inch of each other. The microscopic dimensions of integrated circuits not only make such high-speed operations possible but also leave room for the design of even higher-frequency devices.

The sophisticated techniques used to mass-produce integrated circuits have also substantially reduced costs just when the increasing complexity of electronic devices was threatening to price some of them right out of the market. One of today's larger computers may contain 25,000 ICs, and though some of the more complex circuits for military equipment cost as much as $8, simpler ICs are down in price to as little as 35-c- apiece, about the cost of a single transistor used in the same type of circuit.

Three-Layer Circuits. Like the transistor, the integrated circuit depends largely on the unique electrical properties that pure silicon crystals acquire when precise amounts of impurities, such as boron or phosphorus, are added to them. One type of impurity, or "dopant," leaves the silicon with a deficiency of electrons producing what scientists call a p-type region in the crystal. Another will provide the crystal with an excess of electrons creating an n-type region.

In a transistor, a negative, or n, layer of doped silicon is sandwiched between two positive, or p, layers--or a p layer is put between two n layers. Either way, the middle layer acts like the grid in a three-element vacuum tube, which regulates the flow of electrons between incandescent cathode and plate. When a small signal current is fed into the transistor's middle layer, it can control a much larger current flowing through the transistor from one outer layer to the other. When there is no signal, the transistor effectively blocks the passage of current from layer to layer. Thus the transistor can perform the basic function of the vacuum tube: the control and amplification of electric current.

Adjacent dopant-treated layers of silicon, one n-type, the other p-type, will allow current to pass through in only one direction. Such an arrangement duplicates the properties of a diode, which can change (rectify) alternating current into direct current. Used in another manner, the junction between p and n layers can be used to store electric current and serve as a capacitor. Silicon itself retards the flow of electrical current and can provide the necessary resistance for a circuit. Thus by the use of the proper combination of dopant-treated layers diffused onto a tiny chip of pure silicon, and by insulating here and connecting there, a complex integrated circuit containing transistors, diodes, capacitors and resistors can be constructed.

Photosensitive Pattern. To begin the ingenious process required to produce ICs, a p-type cylindrical crystal of silicon, 2 ft. long and 1 1/2 in. in diameter, is gradually drawn from a vat of molten silicon. After it cools, it is sliced into thin, half-dollar-size wafers, which are polished to a mirrorlike finish, then reheated and exposed to a precisely measured amount of dopant gas. This exposure causes an n-type region, known as the epitaxial layer, to grow on one side of the wafer. The wafer is then placed in an oven and exposed to steam, which oxidizes its surface and forms a protective coating.

As soon as the wafer has cooled once more, it is covered with a layer of photosensitive material and exposed to ultraviolet light projected through a photographic negative. On the negative are hundreds of identical 1C patterns, each reproduced from a master pattern 500 times larger. They are projected onto the photosensitive surface of the wafer, which is then dipped in acid that etches the oxide layer away wherever the shadow of the 1C pattern has fallen.

Back in an oven, the wafer is exposed to a p-type dopant, which diffuses into the silicon only where the protective oxide coating has been etched away. The entire process is then repeated, using a different pattern and an n-type dopant. A third pattern serves to produce metallic interconnections between the circuit components formed in the three dopant layers.

After each of the hundreds of ICs has been tested by a machine that automatically subjects it to 36 different electrical tests, the wafer is cut into its hundreds of individual circuits by workers armed with microscopes, diamond-tipped scribers and vacuum-tipped pencils. Each 1C is placed in a tiny container to which workers attach gold wires that are used to connect the 1C with other circuits or components, and sealed. Before they are shipped to the customer, the ICs are given high-and low-temperature tests, vibration and high-G tests often while automatic instruments check their performance.

Because the resistors and capacitors created in silicon integrated circuits are still not of high enough quality, the ICs are often combined in hybrid devices with tiny resistors and capacitors consisting of alternate thin films of metal and insulator. Though these thin film microcircuits can provide resistors and capacitors of higher performance, they cannot duplicate the functions of transistors or diodes.

Many electronics companies are beginning to use miniaturization techniques that allow them to produce as many as three different circuits on one tiny silicon chip the size of one present 1C. Texas Instruments has built an experimental device covering the entire surface of a silicon wafer. It contains more than 200 integrated and interconnected circuits, each made up of a dozen components, all packed into an area the size of half a dollar.

TV & Tax Returns. The sophisticated, practical and low-cost circuitry that will soon be available promises to outrace the fondest dreams of science fictioneers. Integrated circuits will surely be moving farther and farther into space; they will also work their way into more and more of man's life on earth. Worldwide TV networks and auto ignition systems that never wear out are likely to seem mundane indeed next to miniature home computers capable of controlling everything from garage doors and automatic sprinkling systems, to air conditioning and cook stoves--while working out the family tax returns in their spare time.

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