CMOS stands for Complementary Metal-Oxide-Semiconductor.

It is a structure that combines N-channel MOSFETs (NMOS) and P-channel MOSFETs (PMOS) in a complementary configuration, achieving low power consumption, high integration density, and high reliability.

 

Nearly every digital circuit found in modern microprocessors, memory, smartphones, and similar devices is built on CMOS technology.

CMOS operates using a pair of two different MOSFET types:

・NMOS: Uses electrons as carriers and turns ON with a positive gate voltage.

・PMOS: Uses holes as carriers and turns ON with a negative gate voltage.

By connecting these two devices in series and arranging the circuit so that the input signal turns one ON while the other is OFF, CMOS achieves a structure in which no wasted current flows.

The basic building block of CMOS is the inverter. Its structure is as follows:

・A PMOS positioned between the power supply (VDD) and the output

・An NMOS positioned between the output and ground (GND)

・Both gate terminals connected to a shared input signal

Its operation is remarkably simple:

When the input is “L” (0V): → PMOS turns ON, NMOS turns OFF. → The output becomes VDD (“H”).

When the input is “H” (VDD): → PMOS turns OFF, NMOS turns ON. → The output becomes GND (“L”).

As a result, the output is the inverse of the input signal.

CMOS’s greatest strength is its extremely low static power consumption.

・When the input is either H or L, only one of the two transistors is ever ON.

・As a result, almost no direct current flows from the power supply to ground.

・Power is consumed only during switching — that is, when the state changes.

This ability to retain information without a continuous current flow is what made CMOS the foundation of today’s ultra-low-power technology.

Building on the basic CMOS inverter, more complex logic circuits can be constructed, such as:

・NAND gates (the inverse of AND)

・NOR gates (the inverse of OR)

・XOR gates (exclusive OR)

By combining large numbers of these gates, sophisticated computational functions can be built — including adders (ALUs), control circuits, memory cells, and entire CPU cores.

CMOS technology became the industry standard because of its excellent overall balance:

・Extremely low static power consumption

・High noise immunity and stable operation

・Easy to integrate, with a relatively simple manufacturing process

・High operating speed and good temperature characteristics

Together, these qualities make it possible to design circuits that are simultaneously high-performance, compact, and low-power.

As devices continue to shrink, several challenges have become increasingly apparent:

・Increased leakage current between transistors, resulting in power loss

・Dielectric breakdown as the gate oxide layer becomes thinner

・Variation in threshold voltage (Vth)

・Increased delay caused by wiring resistance and parasitic capacitance

To address these challenges, next-generation CMOS architectures — such as FinFET and GAA structures — have been introduced.

・Logic circuits in CPUs and GPUs

・Memory (SRAM, DRAM)

・Microcontrollers and sensor ICs

・Power management ICs (PMICs)

・Display drivers and image sensors

In short, nearly everything that could be described as an “electronic brain” is built using CMOS technology.

・CMOS is a structure that combines NMOS and PMOS in a complementary configuration.

・Depending on the input voltage, one transistor turns ON while the other turns OFF.

・Static power consumption is nearly zero, with power drawn only during switching.

・As devices shrink further, CMOS continues to evolve toward new structures such as FinFET.

・CMOS remains the standard structure underlying modern integrated circuit technology.

1.What does “CMOS” stand for?

2.Why does CMOS consume so little power?

3.What are the basic building-block components of CMOS?

 

 

Column Supervisor: Koji Kakumoto (Otis Group Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined Otis Group Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as Representative Director, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.