nMOS

An NMOS transistor, or n-channel MOSFET, is a type of metal-oxide-semiconductor field-effect transistor in which the conduction channel is formed by electrons. The device is controlled by the voltage between the gate and source, Vgs: when Vgs exceeds a threshold voltage, Vth, an n-type channel forms between source and drain and allows current to flow from drain to source under an applied drain–source voltage.

In a typical NMOS, the substrate is p-type and the source and drain regions are heavily doped n+. A thin insulating oxide separates the gate electrode from the channel. The threshold voltage depends on body bias (the body effect): applying a potential to the substrate alters the channel formation, shifting Vth.

There are two common modes of NMOS operation: enhancement-mode, which is normally off at Vgs = 0 and turns on when Vgs exceeds Vth; and depletion-mode, which is normally on at Vgs = 0 and can be turned off with a sufficiently negative gate bias. The gate oxide with high-k dielectrics is used in modern processes to reduce oxide thickness and increase gate capacitance.

NMOS devices are core components in many integrated circuits. In CMOS technology, NMOS transistors form the pull-down network, complementing PMOS pull-up devices to implement logic gates with low static power consumption. Electron mobility is higher than hole mobility, giving NMOS devices generally faster switching than analogous PMOS devices.

Historically, NMOS logic and NMOS memory cells preceded CMOS, but today NMOS and PMOS transistors are fabricated together on the same chip as CMOS, benefiting from the reduced power consumption, noise margins, and scalability of complementary architectures.