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PMOS uses p-channel (+) metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. PMOS transistors operate by creating an inversion layer in an n-type transistor body. This inversion layer, called the p-channel, can conduct holes between p-type "source" and "drain" terminals.
In PMOS, the polarities are reversed. The mode can be determined by the sign of the threshold voltage (gate voltage relative to source voltage at the point where an inversion layer just forms in the channel): for an N-type FET, enhancement-mode devices have positive thresholds, and depletion-mode devices have negative thresholds; for a P-type ...
The inversion layer confines the flow of minority carriers, increasing modulation and conductivity, although its electron transport depends on the gate's insulator or quality of oxide if used as an insulator, deposited above the inversion layer. Bardeen's patent as well as the concept of an inversion layer forms the basis of CMOS technology today.
In NMOS-type devices, the zone beneath the gate oxide is a thin n-type inversion layer on the surface of the p-type semiconductor substrate. It is induced by the oxide electric field from the applied gate voltage V G. This is known as the inversion channel. It is the conduction channel that allows the electrons to flow from the source to the ...
In 1948, Bardeen and Brattain patented an insulated-gate transistor (IGFET) with an inversion layer. Their concept forms the basis of CMOS technology today. [16] In 1957 Frosch and Derick were able to manufacture PMOS and NMOS planar gates. [17] Later a team at Bell Labs demonstrated a working MOS with PMOS and NMOS gates. [18]
In the figure, a two-layer structure is shown, consisting of an insulator as left-hand layer and a semiconductor as right-hand layer. An example of such a structure is the MOS capacitor , a two-terminal structure made up of a metal gate contact, a semiconductor body (such as silicon) with a body contact, and an intervening insulating layer ...
This is known as inversion. The threshold voltage at which this conversion happens is one of the most important parameters in a MOSFET. In the case of a p-type MOSFET, bulk inversion happens when the intrinsic energy level at the surface becomes smaller than the Fermi level at the surface. This can be seen on a band diagram.
Also at the interface with gate dielectric, Polysilicon forms an SiO x layer. Moreover, there remains a high probability for Fermi level pinning to occur. [9] So the effect with doped poly is an undesired reduction of threshold voltage that wasn't taken into account during circuit simulation.