Microchip




Microchip

█ LARRY GILMAN

Microchips, also termed "integrated circuits" or "chips," are small, thin rectangles of a crystalline semiconductor, usually silicon, that have been inlaid and overlaid with microscopically patterned substances so as to produce transistors and other electronic components on its surface. It is the components on the chip, not the chip itself, that are micro or too small see with the naked eye. The microchip has made it possible to miniaturize digital computers, communications circuits, controllers, and many other devices. Since 1971, whole computer CPUs (central processing units) have been placed on some microchips; these devices are termed microprocessors.

Manufacture of a microchip begins with the growing of a pure, single crystal of silicon or other semiconducting element. A semiconductor is a substance whose resistance to electrical current is between that of a conductive metal and that of an insulating material such as glass (silicon dioxide, SiO 2 ). This large, single crystal is then sawed into thin, disc-shaped wafers 4–12 inches (10–30 cm) across and only .01–.024 inches (.025–.06 cm) thick. One side of each wafer is polished to high precision, then processed to produce on it a number of identical microchips. These are cut apart later, placed in tiny protective boxes or packages, and connected electrically to the outside world by metal pins protruding from the packages.

Producing a microchip requires industrial facilities that cost billions of dollars and must be retooled every few years as technology advances. The basics of the microchip fabrication process, however, remain the same: by bombarding the surface of the wafer with atoms of various elements, impurities or "dopants" can be introduced into its crystalline structure. These atoms have different electron-binding properties from the silicon atoms around them and so populate the crystal either with extra electrons or with holes, gaps that behave much like positively charged electrons. Holes and extra electrons confer specific electrical properties on the regions of the crystal where they reside. By arranging the doped regions containing holes or extra electrons and covering them with multiple, interleaved layers of SiO 2 , polycrystalline silicon (silicon comprised of small, jumbled crystals), and metal strips to conduct current from one place to another, each microchip can be endowed with thousands or millions of microscopic devices. Such chips are termed integrated because the electronic components in them are integral parts of a single, solid object; this both decreases their size and increases their reliability.

The microchip was conceived simultaneously in 1958 by U.S. engineers Jack Kilby and Robert Noyce (1927–1990). In 1962, microchips were used in the guidance computer of the U.S. Minuteman missile (a nuclear-tipped intercontinental ballistic missile based in holes or silos in the American Midwest); the U.S. government also funded early microchip mass-production facilities as part of its Apollo program, for which it requires lightweight digital computers. The Apollo command and lunar modules each had microchip-based computers with 32-kilobyte memories.

For some 40 years, the number of electronic components on an individual microchip has doubled every few years; this trend has been described as Moore's Law ever since 1965, when U.S. engineer Gordon Moore described the beginning of the trend. Engineers continually strive to fit more electronic components on each microchip; however, this is becoming steadily more difficult as device dimensions decrease toward the atomic scale, where quantum uncertainty renders traditional electronics unreliable. Microchip engineers predict that by about 2020, the exponential increases of the last few decades will cease.

Since their advent, microchips have transformed much of human society. They permit the manufacture of small electronic devices containing many millions of components; they are essential to computers, missiles, "smart" bombs, satellites, communications devices, televisions, aircraft, spacecraft, and motor vehicles. Without microchips the personal computer, cell phone, calculator, Global Positioning System, and many other familiar technologies, both military and civil, would be impossible. As chip complexity increases and cost decreases thanks to improvements in manufacturing technique, new applications are continually being found.

█ FURTHER READING:

ELECTRONIC:

Moore, Gordon. "No Exponential is Forever…but We Can Delay 'Forever'." International Solid State Circuits Conference, February 10, 2003. <ftp://download.intel.com/research/silicon/Gordon_Moore_ISSCC_02100 .pdf> (April 3, 2003).

SEE ALSO

Nanotechnology




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