An integrated circuit (IC) is a single semiconducting chip that contains transistors and sometimes, capacitors, resistors, and diodes. These components are connected to create an electrical circuit. Integrated circuits can be found in almost all electronic devices today, including those in automobiles, microwave ovens, traffic lights, and watches.
Just a few years ago, the circuits required to operate a hand-held calculator would have taken up an entire room. But today, millions of microscopic parts can fit onto a small piece of silicon capable of fitting into the palm of your hand.
With the invention of the transistor in 1948, the need for bulky vacuum tubes in computers and other electronic devices was eliminated. As other components were also reduced in size, engineers were able to design smaller and increasingly complex electronic circuits. However, the transistors and other parts of the circuit were made separately and then had to be wired together—a difficult task that became even more difficult as circuit components became smaller and more numerous. Circuit failures often occurred when the wire connections broke. The idea of manufacturing an electronic circuit with multiple transistors as a single, solid unit arose as a way to solve this problem.
The integrated circuit concept was first suggested by British radar engineer G. W. A. Dummer in 1952. He imagined implanting electronic components in a solid layered block of semiconducting material, with connections made by cutting out areas of the layers instead of by wires. In the United States, where the Department of Defense was distributing millions of dollars attempting to miniaturize electronic components, Dummer's idea was made a reality in the late 1950s by two inventors.
In Dallas, Texas, Jack Kilby of Texas Instruments began wrestling with the circuit problem in 1958 and came up with an idea similar to Dummer's. By September 1958, Kilby had succeeded in making the first working integrated circuit—tiny transistors, resistors, and capacitors connected by gold wires on a single chip. Kilby's 1959 patent application added an important feature: the connections were made directly on the insulating layer of the semiconductor chip, eliminating the need for wires.
Meanwhile, Robert Noyce of Fairchild Semiconductor in Mountain View, California, was also pursuing a solution to the miniaturization problem. Working independently of Kilby, Noyce, too, had considered housing an electronic circuit and its connections on a single piece of silicon. Noyce's integrated circuit used a planar technique of laying down alternating layers of semiconductor and insulating material, with photoetching to establish the circuit. Noyce applied for a patent for this technology in 1959.
Despite an ensuing patent dispute, Noyce and Kilby became recognized as co-inventors of the integrated circuit, which completely revolutionized the electronics industry. The individual transistor, like the vacuum tube before it, became obsolete. The integrated circuit was much smaller, more reliable, less expensive, and far more powerful. It made possible the development of the microprocessor and therefore, the personal computer, along with an array of devices such as the pocket calculator, microwave ovens, and computer-guided aircraft.
The early integrated circuits contained only a few transistors. In the era of Small Scale Integration (SSI), IC's typically contained tens of transistors. With the advent of Medium Scale Integration (MSI), the circuits contained hundreds of transistors. With Large Scale Integration (LSI), the number of transistors increased to thousands. By 1970, LSI circuits were in mass production, being used for computer memories and hand-held calculators. With the advent of Very Large Scale Integration (VLSI), hundreds of thousands or more transistors could be accommodated in an IC. The year 1986 saw the introduction of the first one megabyte random access memory (RAM), containing more than one million transistors.
To construct an integrated circuit, a small rectangle is first cut from a silicon (or for special applications, sapphire) wafer. This wafer is known as the substrate. Separate areas of the substrate are deposited (doped) with other elements to make them generators of either positive ("p-type") or negative ("n-type") carriers. Tracks of polycrystalline silicon or aluminum are next etched into layers above the substrate surface. The wafer is then cut up into pieces called dies, and each die is then connected to input and output ports, usually located at the edge of the die using gold wires, to form the "chip."
There are three classes of integrated circuits: digital, analog and hybrid (both digital and analog on the same chip). Digital integrated circuits, which are characterized by the presence of logic gates, process information discretely (i.e., in Boolean 1's and 0's). Their small size permits digital IC's to operate at high speed, and with low power dissipation. Digital IC's have the distinct marketing advantage that they are relatively inexpensive to manufacture. In contrast to digital IC's, analog integrated circuits process information continuously, as would be required in a thermostat or light dimmer switch.
Logic gates are used in devises whose electronic output signals depend only on their input. The input and output values for logic gates are either 0 (False) or 1 (True). Logic gates are used to implement a variety of Boolean functions including AND (e.g., output is 1 when every input signal is 1), OR (e.g., output is 1 when one or more input signals is 1), NAND (e.g., output is 1 when any input is 0, and 0 when all inputs are 1), and NOR (e.g., output is 1 when all input signals are 0, and 0 when at least one input signal is 1). Other examples of logic gates are inverters, flip-flops, and multiplexors.
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