Nchannel

An N-channel MOSFET, or N-channel metal-oxide-semiconductor field-effect transistor, is a semiconductor device in which current between the drain and source is controlled by voltage applied to the gate, with electrons as the majority carriers. The device contains an n-type source and drain on a p-type substrate, separated from the gate by a thin insulating oxide. When a voltage is applied to the gate, an electrical field modulates a conductive channel linking the source and drain.

Operation and variants: In enhancement-mode devices, the channel forms only when the gate-to-source voltage exceeds a threshold. In depletion-mode devices, a channel exists at zero gate voltage and can be weakened or strengthened by Vgs. A positive Vgs induces electron conduction from source to drain when a voltage is present between those terminals. An intrinsic body diode lies between drain and source and is oriented to conduct when the drain is at a lower potential than the source.

Applications: N-channel MOSFETs are widely used as low-side switches in power supplies, motor controllers, DC-DC converters, and digital logic circuits. They are favored for high-speed switching and low on-resistance, due to the high mobility of electrons and the insulating gate that draws negligible DC current. High-side switching often uses a complementary P-channel MOSFET or a gate driver to offset drive requirements.

Electrical characteristics and design considerations: Typical enhancement devices have threshold voltages from about 1 to 4 volts, with logic-level parts designed for 3.3 or 5 volts. The drain–source on-resistance (Rds(on)) and breakdown voltage determine efficiency and safety margins. Because the gate is insulated, current into the gate is minimal; however, adequate heat sinking and safe operating area considerations are essential.

History: The MOSFET was invented in 1959 by Mohamed Atalla and Dawon Kahng at Bell Labs, and N-channel devices quickly became central to both discrete and integrated circuits.