MOSFET transistor

MOSFET transistor

MOSFET transistor as its name suggests is a p type (n type) semiconductor bar (with two heavily doped n type regions diffused into it) with a metal oxide layer deposited on its surface and holes taken out of the layer to form source and drain terminals. A metal layer is deposited on the oxide layer to form the gate terminal. One of the basic applications of field effect transistor is using a MOSFET as a switch.

This type of FET transistor has three terminals, which are source, drain, and gate. The voltage applied to the gate terminal controls the flow of current from source to drain. The presence of an insulating layer of metal oxide results in the device having high input impedance.

Types of MOSFET Transistor Based on Operation Modes

A MOSFET transistor is the most commonly used type of field effect transistor. MOSFET operation is achieved in two modes, based upon which MOSFET transistors are classified. MOSFET operation in enhancement mode consists of a gradual formation of a channel whereas in depletion mode MOSFET, it consists of an already diffused channel. An advanced application of MOSFET is CMOS.

Enhancement MOSFET Transistor

When a negative voltage is applied to the gate terminal of MOSFET, the positive charge carrying carriers or holes get accumulated more near the oxide layer. A channel is formed from the source to drain terminal.

As the voltage is made more negative, the channel width increases and current flows from source to drain terminal. Thus as the flow of current ‘enhances’ with applied gate voltage, this device is called Enhancement type MOSFET.