MOSFET

A MOSFET, or metal-oxide-semiconductor field-effect transistor, is a voltage-controlled semiconductor switch or amplifier with three terminals: drain, source, and gate. The conducting channel between drain and source is formed in a silicon body and is controlled by the voltage applied to a gate electrode separated from the channel by a thin insulating layer of silicon dioxide. The gate draws negligible current, giving the device very high input impedance.

There are two main polarities: n-channel (NMOS) and p-channel (PMOS). Most modern devices use enhancement-mode transistors, which are normally off and require a gate voltage above a threshold to create a conducting channel for NMOS (or below for PMOS). Depletion-mode MOSFETs are normally on and can be turned off with gate bias.

MOSFETs are used as switches in power electronics and as active devices in amplifiers and digital logic. They are valued for high input impedance, fast switching, compact form, and easy integration in large arrays. Critical parameters include drain-source voltage rating (Vds), drain current (Id), on-resistance (Rds(on)), and threshold voltage (Vth).

In integrated circuits, complementary pairs of NMOS and PMOS transistors form CMOS logic, which dominates modern microprocessors and memory. Gate leakage, channel length modulation, body effect, and gate-oxide reliability are design considerations. Protection against electrostatic discharge is important for device reliability.

Manufacturing uses silicon with a thin insulating oxide; gate material is often polysilicon, with metal gates used in some processes. MOSFET technology has driven advances in computing, power management, and communications.