MOSFET

Two power MOSFETs in D2PAK surface-mount packages. Operating as switches, each of these components can sustain a blocking voltage of 120 V in the off state, and can conduct a con­ti­nuous current of 30 A in the on state, dissipating up to about 100 W and controlling a load of over 2000 W. A matchstick is pictured for scale.

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The term metal–insulator–semiconductor field-effect transistor (MISFET) is almost synonymous with MOSFET. Another near-synonym is insulated-gate field-effect transistor (IGFET).

The basic principle of the field-effect transistor was first patented by Julius Edgar Lilienfeld in 1925.[1]

The main advantage of a MOSFET is that it requires almost no input current to control the load current, when compared to bipolar junction transistors (BJTs). In an enhancement mode MOSFET, voltage applied to the gate terminal increases the conductivity of the device. In depletion mode transistors, voltage applied at the gate reduces the conductivity.[2]

The "metal" in the name MOSFET is sometimes a misnomer, because the gate material can be a layer of polysilicon (polycrystalline silicon). Similarly, "oxide" in the name can also be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages.

The MOSFET is by far the most common transistor in digital circuits, as billions may be included in a memory chip or microprocessor. Since MOSFETs can be made with either p-type or n-type semiconductors, complementary pairs of MOS transistors can be used to make switching circuits with very low power consumption, in the form of CMOS logic.

A cross-section through an nMOSFET when the gate voltage VGS is below the threshold for making a conductive channel; there is little or no conduction between the terminals drain and source; the switch is off. When the gate is more positive, it attracts electrons, inducing an n-type conductive channel in the substrate below the oxide (yellow), which allows electrons to flow between the n-doped terminals; the switch is on.
Simulation of formation of inversion channel (electron density) and attainment of threshold vol­tage (IV) in a nanowire MOSFET. Note: Threshold voltage for this device lies around 0.45 V.
  1. ^ Lilienfeld, Julius Edgar (1926-10-08) "Method and apparatus for controlling electric currents" U.S. patent 1745175A
  2. ^ "D‐MOSFET OPERATION AND BIASING" (PDF). Archived (PDF) from the original on 2022-10-22.

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