CMOS

CMOS technology and high-density integrated circuits (VLSI)

Modern electronic circuits use a variant of the bipolar transistor described above. This type of transistor is in fact too cumbersome, too energy-consuming and more difficult to produce on a very large scale. In the race towards miniaturization, this transistor was rapidly superseded by a new device known as the Field Effect Transistor (FET) and in particular the Metal Oxide Semi-conductor Field Effect Transistor (MOSFET).

In 1930, Julius Edgar Lilienfeld (1881-1963), from the University of Leipzig applied for a patent in which he described an element bearing resemblance to the MOS transistor and which could have been the first transistor in history. We had to wait until the 1960s in order to see the arrival of such devices, whose development was made possible with the noted progress in the field of bipolar transistors and in particular in the resolution of problems with the oxide semi-conductor interface. Today, the MOS transistor is the key element of digital integrated circuits on a large scale due to both the simplicity in its production and its small size.

The MOS transistor is a FET made up of a semi-conductor substrate (B or Bulk) and covered with a layer of oxide on which there is the gate electrode (G or Gate). By applying a potential difference between the gate (G) and the substrate (B), an electric field in the semi-conductor is created causing the dominant carriers to be pushed back far from the oxide semi-conductor interface, leaving the non-dominant carriers coming from two complementary sectors in the substrate known as the source (S) and the drain (D). These sectors form a thin layer of mobile charges known as a canal. These charges are able to transit between the drain and the source, both of which are found at the extreme ends of the canal.

Complementary Metal Oxide Silicon (CMOS) technology evolved from MOSFET technology and is destined for the development of Very Large Scale Integration (VLSI) systems. Thanks to the properties of complementary MOS transistors, this planar technology has enabled the creation of low-cost and low energy circuits. This advantage has meant that this technology is recognized as the central technology behind the microelectronics industry.

The underlying idea behind CMOS technology is to create pairs of complementary transistors (i.e. a P-type coupled transistor and an N-type coupled transistor). Each pair is able to create logic gates based on Boolean principles used in digital electronics.