NMOSTransistor

An NMOS transistor, or n-channel MOSFET, is a type of field-effect transistor that uses an n-type channel to conduct electrons from drain to source when a positive gate voltage above threshold is applied. It is built on a p-type silicon substrate with an insulating oxide layer forming the gate dielectric and heavily doped n+ regions for the source and drain. The gate electrode, separated from the channel by the oxide, modulates the conductivity of the channel: applying voltage induces an n-type inversion layer that creates a conduction path between source and drain.

Operation: Enhancement-mode NMOS devices are normally off at zero gate voltage; turning the device on requires Vgs above the threshold. Depletion-mode NMOS devices contain a channel at zero gate voltage and can be turned off with a suitable negative gate voltage. The current flowing from drain to source depends on the gate voltage, the drain-to-source voltage, and device geometry, with higher electron mobility giving typically faster switching than corresponding PMOS devices.

Characteristics: Key parameters include threshold voltage, transconductance, and the on-resistance when conducting. Because electrons have higher mobility than holes, NMOS devices generally provide higher drive current than PMOS devices of similar size. Short-channel effects and leakage become important as devices scale to nanometer dimensions.

Applications and integration: NMOS transistors are a core element of many analog and digital circuits. In modern CMOS technologies, NMOS and PMOS transistors are used together in complementary logic; NMOS devices often form pull-down networks that connect signals to ground. Scaling and advanced architectures such as FinFETs and high-k/metal gate stacks continue to refine NMOS performance in integrated circuits.