MOSFETs

A metal-oxide-semiconductor field-effect transistor (MOSFET) is a three-terminal electronic device used for switching and amplifying signals. It operates by using an electric field applied to a gate electrode to modulate the conductivity between the source and drain. MOSFETs offer very high input impedance and are the most widely used transistor type in integrated circuits.

A MOSFET consists of a channel of semiconductor material (usually silicon) between source and drain, with a gate separated from the channel by a thin insulating oxide layer. The gate voltage controls carrier density in the channel, effectively turning the device on or off. MOSFETs are classified by channel type (N-channel or P-channel) and by mode: enhancement-mode devices are normally off and require a gate voltage to create a channel, while depletion-mode devices are normally on and can conduct with zero gate voltage.

Common configurations include NMOS and PMOS, with CMOS technology combining both for low power digital logic. A built-in body diode exists between source and drain in most planar MOSFETs due to the body connection. Power MOSFETs handle larger currents and voltages and are widely used in switching power supplies and motor drives.

Fabrication uses silicon with a silicon dioxide gate dielectric. Key performance metrics include threshold voltage, transconductance, and on-resistance (Rds(on)) for power devices. Reliability concerns include oxide breakdown and hot-carrier effects, particularly in smaller geometries.

MOSFETs underpin modern electronics, from microprocessors and memory to analog circuits and power electronics. They were invented in the 1960s by Mohamed Atalla and Dawon Kahng at Bell Labs, and rapidly evolved into the dominant transistor technology due to simplicity of structure and scalability.