CMOS

Complementary metal–oxide–semiconductor (CMOS) is a type of MOSFET (metal–oxide–semiconductor field-effect transistor) semiconductor device fabrication process used for constructing integrated circuits (ICs). CMOS technology is used in microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for several analog circuits such as image sensors (CMOS sensor), data converters, and highly integrated transceivers for many types of communication. CMOS was invented by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963, and was an adaptation of the PMOS and NMOS processes originally developed by MOSFET inventors Mohamed Atalla and Dawon Kahng in 1960. CMOS became the dominant MOSFET fabrication process for VLSI devices since it overtook NMOS in the 1980s. Complementary metal–oxide–semiconductor (CMOS) is a type of MOSFET (metal–oxide–semiconductor field-effect transistor) semiconductor device fabrication process used for constructing integrated circuits (ICs). CMOS technology is used in microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for several analog circuits such as image sensors (CMOS sensor), data converters, and highly integrated transceivers for many types of communication. CMOS was invented by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963, and was an adaptation of the PMOS and NMOS processes originally developed by MOSFET inventors Mohamed Atalla and Dawon Kahng in 1960. CMOS became the dominant MOSFET fabrication process for VLSI devices since it overtook NMOS in the 1980s. CMOS is sometimes referred to as complementary-symmetry metal–oxide–semiconductor (COS-MOS), but 'COS-MOS' was an RCA trademark, which forced other manufacturers to find another name. The words 'complementary symmetry' refer to the typical design style with CMOS using 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.Since one transistor of the pair is always off, the series combination draws significant power only momentarily during switching between on and off states. Consequently, CMOS devices do not produce as much waste heat as other forms of logic, like transistor–transistor logic (TTL) or N-type metal–oxide–semiconductor logic (NMOS) logic, which normally have some standing current even when not changing state. CMOS also allows a high density of logic functions on a chip. It was primarily for this reason that CMOS became the most used technology to be implemented in very-large-scale integration (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. Aluminium was once used but now the material is polysilicon. Other metal gates have made a comeback with the advent of high-κ dielectric materials in the CMOS process, as announced by IBM and Intel for the 45 nanometer node and smaller sizes. 'CMOS' refers to both a particular style of digital circuitry design and the family of processes used to implement that circuitry on integrated circuits (chips). CMOS circuitry dissipates less power than logic families with resistive loads. Since this advantage has increased and grown more important, CMOS processes and variants have come to dominate, thus the vast majority of modern integrated circuit manufacturing is on CMOS processes. CMOS circuits use a combination of p-type and n-type metal–oxide–semiconductor field-effect transistor (MOSFETs) to implement logic gates and other digital circuits. Although CMOS logic can be implemented with discrete devices for demonstrations, commercial CMOS products are integrated circuits composed of up to billions of transistors of both types, on a rectangular piece of silicon of between 10 and 400 mm2. CMOS always uses all enhancement-mode MOSFETs (in other words, a zero gate-to-source voltage turns the transistor off). Since the invention of the MOSFET by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959, there were originally two types of MOSFET technology, PMOS (p-type MOS) and NMOS (n-type MOS). Both types were developed by Atalla and Kahng when they originally invented the MOSFET, fabricating both PMOS and NMOS devices with a 20 µm process. A new type of MOSFET logic, CMOS, was invented by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor, and in February 1963 they published the invention in a research paper. Wanlass later filed US patent 3,356,858 for CMOS circuitry in June 1963, and it was granted in 1967. In both the research paper and the patent, the fabrication of CMOS devices was outlined, on the basis of thermal oxidation of a silicon substrate to yield a layer of silicon dioxide located between the drain contact and the source contact.