branch of electronic technology devoted to the design and development of extremely small electronic devices that consume very little electric power. Although the term is sometimes used to describe discrete electronic components assembled in an extremely small and compact form, it is often taken as a synonym for integrated circuit technology. Discrete components that can be made using microelectronic techniques include resistors, capacitors, and transistors; inductors are excluded for practical purposes. Microelectronic tuned circuits can be built using piezoelectric electromechanical components. Hybrid microcircuits contain a mixture of discrete and integrated circuits on a single substrate. Thick-film techniques use specially formulated inks or pastes that are applied to ceramic substrates by screen-printing techniques. Thin-film devices are fabricated using electron-beam evaporation or sputtering. Although other materials can be used, integrated circuits are usually fabricated on wafers of single-crystal silicon; that is, silicon in which the orientation of all of the crystal is the same. The major fabricating steps include film formation, impurity doping, photolithography, and packaging. Silicon oxide, also called silica, is grown on the surface of the silicon during the film-formation stage. Photolithographic methods are used to selectively remove the oxide from areas of the silicon: A layer of photoresist is added to the oxide layer and then exposed to ultraviolet light through a mask. After exposure, the silicon wafer is developed, and the unwanted areas of the oxide are removed by an etching process. Impurity doping adds charge carriers to the silicon; the unique electronic properties of semiconductors are produced by this process. Additional layers of silicon are deposited to create bipolar transistors. Metal, usually aluminum, is deposited where contacts are desired. Other transistor types—MOS or metal-oxide-semiconductor devices, for example—are fabricated using similar techniques. Integrated circuits that contain over one billion transistors have been developed.
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