An integrated circuit is an organized assembly or interconnected electrode components contained within the upper layer of a small, flat semiconductor chip, usually made of silicon. Silicon is one of the few elements, germanium is another that can be made to act as a semiconductor. In a pure form it will not conduct electricity, but if impurities are introduced. It be chip of silicon can produce a circuit of electronic components. Because the components are of microscopic size, millions can be placed on a single chip measuring less than a centimeter on a side and a few millimeters thick.
In fabrication, after the circuit to be integrated has been designed and tested, the entire circuit is drawn on a master transparancy. The various components that require identical processing steps are then drawn on separate transparancies. The various overlays are then photographically reduces to the actual size of the integrated circuit chip, and arrays of up to a hundred or more pattern are formed on individual transparancies. The transparancies are then used to photographically reproduce a sequence of productive patterns on the surface of a circular water of silicon. Visible light is commonly used. In addition, advanced optical techniques employing diferent phase of light are making much greater miniaturization possible.
A series of production steps such as etching, heating and diffusion of impurities into the silicon is carried out simultaneously on the unprotected silicon surface. Finally, a network of aluminum interconnections is applied to interconnect the various components. The water is then separated into individual integrated circuits, which are tested and installed in protective plastic, ceramic or metal packages.
Numerous kinds of integrated circuits have been developed by solid state research laboratories. Most can be categorized as analog, digital, or analog digital, according to their function.
Analog integrated circuits generally respond to a variable incoming voltage by producing a correspondingly variable output voltage. Many analog integrated circuits particularly audio-frequency Amplifier and operational amplifliers, are designed to produce an output voltage that is an amplified but faitful copy of the input voltage. These are called linear.