Feileffekt

Feileffekt refers to the field effect, the modulation of electrical conductivity in a material or device by an external electric field, typically applied via a gate electrode. The effect enables control of current flow with little or no current through the control terminal, a principle central to many electronic components.

Principle: In a semiconductor, applying a gate voltage changes the carrier density in a conducting channel. Depending on the device, this can induce accumulation, depletion, or inversion of charge carriers, altering conductance. In a metal-oxide-semiconductor field-effect transistor (MOSFET), the gate voltage creates an inversion layer at the semiconductor–oxide interface, effectively forming or removing a conductive channel. In a junction field-effect transistor (JFET), a reverse-biased junction modulates the width of a depletion region to control current.

Types: The main families are MOSFETs (including NMOS and PMOS), JFETs, and insulated-gate FETs (IGFETs). The CMOS technology combines complementary MOSFETs to implement logic circuits. Field-effect devices are also used in specialized sensors, such as ion-sensitive FETs (ISFETs) for chemical and biological detection.

Applications: Field-effect devices are fundamental to amplification and switching in digital and analog electronics. They are widely used in microprocessors, memory, RF circuits, and power electronics. In sensing, FET-based devices enable label-free detection of ions, biomolecules, and chemical species.

History: The concept of the field effect emerged in the early 20th century, with practical field-effect devices developed in the mid-20th century. The MOSFET, demonstrated in the 1960s, became the dominant technology for modern electronics and remains central to communications and computation.

See also: transistor, MOSFET, JFET, ISFET.