Complementary metal–oxide–semiconductor (CMOS)
is a technology for making 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. Frank Wanlass successfully patented CMOS in 1967 (US Patent 3,356,858).
CMOS is also sometimes referred to as complementary-symmetry
metal–oxide–semiconductor (or COS-MOS). 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) or NMOS logic, which uses all n-channel
devices without p-channel devices. CMOS also allows a
high density of logic functions on a chip. It was primarily this reason why CMOS
won the race in eighties and become the most used technology to be implemented
in VLSI chips.
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. Aluminum was once used but now the material is polysilicon. Other
metal gates have made a comeback with the advent of high-k dielectric materials
in the CMOS process, as announced by IBM and Intel for the 45 nanometer node and beyond .
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