BASIC KNOWLEDGE: INVERTERS CMOS: The most basic inverter

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CMOS is the most basic type of inverter. In addition, most legacy chips are manufactured using the CMOS process. CMOS is both a device and a fabrication process. The article talks about CMOS devices and the CMOS fabrication process.

Initially developed as a device, CMOS offered better results compared to p-type and n-type MOSFETs. In the late 1960s, CMOS was commercialized as a manufacturing process to build integrated circuits!

CMOS symbol

The CMOS, NOT gate, or any type of inverter has the same circuit symbol. The CMOS symbol is a combination of a triangle and a small circle.

CMOS circuit diagram

In a CMOS circuit, pMOS and nMOS are connected in a complementary fashion. PMOS is connected at the top and NMOS is at the bottom.

The source terminal of pMOS is connected to the supply voltage and the source terminal of nMOS is grounded. The input signal is given at the gate terminal of both pMOS and nMOS transistors. The drain terminals of both PMOS and NMOS transistors are connected to the output.

CMOS working

CMOS working is explained through the truth table.

CMOS truth table
In digital electronics, the truth table represents the functionality of the circuit. The CMOS truth table represents the action of CMOS. Any input given to the CMOS gets inverted at the output.

For a low (0) input, CMOS generates a high (1) output. Similarly, for a high (1) input, CMOS generates a low (0) output. In simple words, CMOS completely reverses the input signal or complements it!

CMOS operation
A low voltage signal (0) is given at the input terminal of CMOS. The pMOS turns on and the nMOS turns off. The current flows through the gate channel to produce a high-voltage signal (1) at the output.

A high voltage signal (1) is given at the input terminal of CMOS. The pMOS turns off and the nMOS turns on. No current or extremely small number of electrons flow through the gate channel to produce a low voltage signal (0) at the output.

CMOS fabrication process

CMOS meaning is an inverter as well as a semiconductor manufacturing process. The CMOS fabrication process, called CMOS technology, is used extensively to manufacture chips. The CMOS technology creates the physical structure of the CMOS inverter. In simple words, CMOS technology is a fabrication process to manufacture ICs.

In our semiconductor manufacturing series, the fabrication process is detailed. CMOS n-well process is a common CMOS manufacturing process. The CMOS n-well process starts with the creation of the n-well region over a moderately doped p-type substrate. N-well region defines the creation of pMOS and nMOS transistors.

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CMOS advantages

The benefits of CMOS devices are numerous and far-reaching including:

• CMOS devices offer high speed.

• CMOS devices consume less static power.

• CMOS devices consume reasonable dynamic power for battery applications.

• CMOS devices offer low-power dissipation. Simply put, CMOS devices generate little heat for temperature stability.

• CMOS devices have a high noise immunity.

• CMOS devices are smaller in size.

• CMOS fabrication process is scalable, flexible, and compatible with standard processes.

• CMOS fabrication process offers large-scale and very large-scale integration.

CMOS disadvantages

Despite their widespread use, CMOS devices do have certain drawbacks that need to be considered.

• CMOS devices have high switching speed.

• CMOS devices have a high propagation delay.

• CMOS circuits can be slow.

• CMOS devices have poor analog performance.

• CMOS devices may have a significant amount of leakage currents.

• The CMOS fabrication process is complex.

• The CMOS process is replaced by FinFET, GAAFET, ribbonFET, etc in modern nanometer processes.

CMOS applications

CMOS devices
CMOS means a logic "NOT gate" in digital electronics. A CMOS NOT gate performs the binary functions operations in a variety of applications like computers, cameras, converters, and transceivers. In analog applications, CMOS devices are used in op-amps, sensors, and radio frequency devices.

CMOS fabrication process
The CMOS process is still used in modern LSI and VLSI designs to manufacture ICs like logic circuits, microprocessors, microcontrollers, and semiconductor memories. The CMOS process has been the main process that enables large-scale integration of transistors in VLSI design.

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