CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. Two important characteristics of CMOS devices are high noise immunity and low bicmos fabrication process steps pdf 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. CMOS also allows a high density of logic functions on a chip.
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 beyond. 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.
As of 2010, CPUs with the best performance per watt each year have been CMOS static logic since 1976. 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. Similarly, all NMOS transistors must have either an input from ground or from another NMOS transistor. The composition of a PMOS transistor creates low resistance between its source and drain contacts when a low gate voltage is applied and high resistance when a high gate voltage is applied.
On the other hand, the composition of an NMOS transistor creates high resistance between source and drain when a low gate voltage is applied and low resistance when a high gate voltage is applied. CMOS accomplishes current reduction by complementing every nMOSFET with a pMOSFET and connecting both gates and both drains together. A high voltage on the gates will cause the nMOSFET to conduct and the pMOSFET not to conduct, while a low voltage on the gates causes the reverse. This arrangement greatly reduces power consumption and heat generation.
However, during the switching time, both MOSFETs conduct briefly as the gate voltage goes from one state to another. This induces a brief spike in power consumption and becomes a serious issue at high frequencies. When the voltage of input A is low, the NMOS transistor’s channel is in a high resistance state.
This limits the current that can flow from Q to ground. The PMOS transistor’s channel is in a low resistance state and much more current can flow from the supply to the output.
Because the resistance between the supply voltage and Q is low, the voltage drop between the supply voltage and Q due to a current drawn from Q is small. The output, therefore, registers a high voltage. Because the resistance between Q and ground is low, the voltage drop due to a current drawn into Q placing Q above ground is small.