12.15: MOSFET
The Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) plays a pivotal role in modern electronics thanks to its versatility and efficiency in controlling electrical currents. This device, also known as IGFET, MISFET, and MOSFET, has three main terminals: the Source, Drain, and Gate. MOSFETs are classified into n-channel or p-channel types based on the doping characteristics of their substrate and the source or drain regions.
In an n-MOSFET, the structure includes n-type source and drain regions isolated from a p-type substrate by reverse-biased p-n diodes. The gate, composed of a metal plate placed over an oxide layer and the ohmic contact on the substrate, makes up the four terminals of the MOSFET. Under normal conditions with no voltage applied to the gate, the n-MOSFET remains off, with no significant current flowing from the source to the drain except for a negligible leakage current.
However, applying a positive bias to the gate of an n-MOSFET creates an n-channel, facilitating the flow of a large current. The conductance of this channel can be adjusted by varying the gate voltage, allowing precise control over the current between the fixed source and drain regions.
MOSFETs are integral components in various applications, from the microprocessors in smartphones and laptops to the power management systems in electric vehicles. Their ability to efficiently control current with minimal power loss makes them indispensable in advancing technology across various sectors.
