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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. The p-channel is created by applying a negative voltage (-25V was common [ 18 ] ) to the third terminal, called the gate.
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 ...
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.
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.
A double-gate FinFET device. A fin field-effect transistor (FinFET) is a multigate device, a MOSFET (metal–oxide–semiconductor field-effect transistor) built on a substrate where the gate is placed on two, three, or four sides of the channel or wrapped around the channel (gate all around), forming a double or even multi gate structure.
The active FET layer is usually deposited onto this substrate using either (i) thermal evaporation, (ii) coating from organic solution, or (iii) electrostatic lamination. The first two techniques result in polycrystalline active layers; they are much easier to produce, but result in relatively poor transistor performance.
There is no inversion electron in the channel, the device is OFF. As gate voltage increase, the inversion electron density in the channel increase, the current increases, and the device turns on. The metal-oxide-semiconductor FET (MOSFET, or MOS transistor), a solid-state device, is by far the most used widely semiconductor device today.
CMOS inverter (a NOT logic gate). Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", / s iː m ɑː s /, /-ɒ s /) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. [1]