Complementary metal–oxide–semiconductor (CMOS), is a major class of integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data converters, and highly integrated transceivers for many types of communication.
CMOS is also sometimes referred to as complementary-symmetry metal–oxide–semiconductor. The words “complementary-symmetry” refer to the fact that the typical digital design style with CMOS uses complementary and symmetrical pairs of p-type and n-type metal oxide semiconductor field effect transistors (MOSFETs) for logic functions.
Two important characteristics of CMOS devices are high noise immunity and low static power consumption. Significant power is only drawn when the transistors in the CMOS device are switching between on and off states. Consequently, CMOS devices do not produce as much waste heat as other forms of logic, for example transistor-transistor logic (TTL). CMOS also allows a high density of logic functions on a chip.
The phrase “metal–oxide–semiconductor” is a reference to the physical structure of certain field-effect transistors, having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Instead of metal, current gate electrodes (including those up to the 65 nanometer technology node) are almost always made from a different material, polysilicon, but the terms MOS and CMOS nevertheless continue to be used for the modern descendants of the original process. Metal gates have made a comeback with the advent of high-kbased electrostatic capacitors (EC), with energy density greater than 200 Jcm 3, which rival the best reported energy density of electric double layer capacitors (EDLC), also known as
s in the CMOS process, as announced by IBM and Intel for the 45 nanometer node and beyond