CMOS stands for "Complementary Metal Oxide Semiconductor." It is one of the more popular technologies in the computer chip design industry and is now widely used to form integrated circuits in many different applications. Today's computer memory, CPUs, and mobile phones all utilize this technology because it has several key advantages. The technology utilizes both P-channel and N-channel semiconductor devices. One of the more popular MOSFET technologies today is Complementary MOS or CMOS technology. This is the primary semiconductor technology for microprocessors, microcontroller chips, memory such as RAM, ROM, EEPROM, and Application-Specific Integrated Circuits (ASICs).

　　 Introduction to MOS Technology

　　In IC design, the most basic and important component is the transistor. Therefore, MOSFET is a type of transistor used in many applications. The formation of this transistor can be done like a sandwich, including a semiconductor layer, a single crystal silicon wafer, a silicon dioxide layer, and a metal layer. These layers allow the transistor to be formed within the semiconductor material. A good insulator like Sio2 has a thin layer with a thickness of one hundred molecules.

　　We use polysilicon (poly) instead of metal as the gate part of the transistor. The polysilicon gate of the FET can be almost replaced by the metal gate in large-scale ICs. Sometimes, both polysilicon and metal FETs are called IGFETs, which is Insulated Gate FET, because the Sio2 under the gate is an insulator.

　　 CMOS (Complementary Metal Oxide Semiconductor)

　　The main advantage of CMOS over NMOS and BIPOLAR technologies is its much lower power consumption. Unlike NMOS or BIPOLAR circuits, complementary MOS circuits have virtually no static power consumption. Power is only dissipated when the circuit actually switches. This allows for the integration of more CMOS gates on an IC than NMOS or bipolar technologies, resulting in better performance. Complementary Metal Oxide Semiconductor transistors consist of P-channel MOS (PMOS) and N-channel MOS (NMOS).

　　 NMOS

　　NMOS is built on a p-type substrate, with n-type source and drain diffused on it. In NMOS, the majority carriers are electrons. When a high voltage is applied to the gate, the NMOS will conduct. Similarly, when a low voltage is applied to the gate, the NMOS will not conduct. NMOS is considered faster than PMOS because the carriers (electrons) in NMOS move twice as fast as holes.

　 　PMOS

　　A P-channel MOSFET consists of P-type source and drain diffused into an N-type substrate. The majority carriers are holes. When a high voltage is applied to the gate, the PMOS will not conduct. When a low voltage is applied to the gate, the PMOS will conduct. PMOS devices are more resistant to noise than NMOS devices.

　 　CMOS Working Principle

　　In CMOS technology, both N-type and P-type transistors are used to design logic functions. The signal that turns on one transistor is the same as the signal that turns off the other. This characteristic allows logic devices to be designed using only simple switches without the need for pull-up resistors.

　　In CMOS logic gates, a set of n-type MOSFETs is arranged in a pull-down network between the output and the low-voltage power rail (Vss or typically ground). CMOS logic gates do not have the load resistor of NMOS logic gates, but instead have a set of p-type MOSFETs arranged in a pull-up network between the output and the high-voltage rail (typically called Vdd).

　　Therefore, if the gates of both p-type and n-type transistors are connected to the same input, when the n-type MOSFET is off, the p-type MOSFET will be on, and vice versa. As shown in the figure below, the network is arranged so that for any input pattern, one is on and the other is off.

　　CMOS has relatively high speed, low power consumption, high noise margin in both states, and can operate over a wide range of source and input voltages (provided the source voltage is fixed). Furthermore, to better understand the working principle of Complementary Metal Oxide Semiconductor, we need to briefly discuss CMOS logic gates.

　 　Which Devices Use CMOS?

　　Technologies like CMOS are used in a variety of chips such as microcontrollers, microprocessors, SRAM (Static RAM), and other digital logic circuits. The technology is widely used in various analog circuits, including data converters, image sensors, and highly integrated transceivers used in various communications.

　 　CMOS Battery Lifespan

　　The typical lifespan of a CMOS battery is around 10 years. However, this can change depending on PC usage and environment.

　 　CMOS Characteristics

　　The most important characteristics of CMOS are low static power consumption and strong noise immunity. When a single transistor in a pair of MOSFET transistors is off, the series combination consumes significant power when switching between the on and off states.

　　Therefore, unlike other types of logic circuits such as TTL or NMOS logic, these devices do not generate waste heat, even if they do not change state, they use some static current.

　　These characteristics of CMOS allow for high-density integration of logic functions on integrated circuits. Because of this, CMOS has become the most commonly used technology in VLSI chips.

　　The term MOS refers to the physical structure of a MOSFET, which includes an electrode with a metal gate on top of an oxide insulator of semiconductor material.

　　Materials like aluminum were used only once, but now the material has changed to polysilicon. Other metal gate designs can be achieved by the emergence of high-k materials in CMOS processes.

　　 Advantages

　　The advantages of CMOS include the following.

　　The main advantages of CMOS over TTL are good noise immunity and low power consumption. This is because there is no direct conductive path from VDD to GND, and the fall time depends on the input conditions, so transmitting digital signals through CMOS chips will become easy and inexpensive.

　　It uses a single power supply, such as +VDD;

　　These gates are very simple;

　　High input impedance;

　　CMOS logic consumes less power when holding a set state;

　　Power consumption is negligible;

　　High fan-out;

　　TTL compatibility;

　　Temperature stability;

　　Good noise immunity;

　　Good design;

　　Mechanically robust;

　　Large logic swing (VDD);

　　CMOS applications

　　Complementary MOS technology is widely used and has fundamentally replaced NMOS and bipolar processes in almost all digital logic applications. CMOS technology has been used in the following digital IC designs.

　　Computer memory, CPU

　　Microprocessor design

　　Flash memory chip design

　　Used to design application-specific integrated circuits (ASICs)

　　Therefore, CMOS transistors are very famous because they use electrical energy efficiently. They do not consume power when they transition from one state to another. In addition, complementary semiconductors interact to prevent o/p voltage. The result is a low-power design that generates less heat. For this reason, these transistors have replaced other earlier designs, such as CCDs in camera sensors, and are used in most current processors. The memory in CMOS in computers is a non-volatile RAM used to store BIOS settings as well as time and date information.