12.15 :  MOSFET

The Metal-Oxide-Semiconductor Field-Effect Transistor, or MOSFET is a semiconductor device with three terminals: the Source, the Drain, and the Gate and is also known as IGFET, MISFET, and MOST.

It can be either n-channel or p-channel, depending on the doping of the substrate and the source or drain regions.

In an n-channel MOSFET, the substrate has two heavily doped n-type source and drain regions. A thin layer of silicon dioxide is grown on the surface, and metal is deposited on top to form the gate electrode.

With zero gate voltage, no current flows from the source to the drain except for a small leakage current.

When a positive bias is applied at the gate, the electrons from the substrate move towards the gate, forming an inversion layer and enabling a large flow of electrons from the source to the drain. The conductance of this channel can be modulated by varying the gate voltage.

The conventional current flows from the drain to the source and is called the Drain Current.

MOSFETs are integral in various applications, including smartphones, laptops, and electric cars.