METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR

INTRODUCTIONMOSFET is a three terminal device.

MOSFET is a voltage-controlled device.

MOSFET is one of the type of FET.

CharacteristicsThe most important characteristic of the

MOSFET is its high input impedance.

MOSFET are more temperature stable than BJT’s .

MOSFET are usually smaller than BJT’s

Types of MOSFETThere are two type of MOSFET1.Depletion type P-channel depletion typeN-channel depletion type2.Enhancement typeP-channel enhancement typeN-channel enhancement type

N-channel depletion type MOSFETIn this, the substrate is formed by a slab of p-

type material. It is the foundation of device.The source and drain terminals are

connected through metallic contacts to n-doped region linked by an n-channel.

The gate is also connected to a metal contact surface but remain insulated from the n-channel by a very thin

(SiO2) layer. SiO2 is a dielectric.

Working Diagram of MOSFET

Working A voltage VDS is applied across a drain to source

terminal. Firstly gate to source voltage is set to zero volt. When Vgs is set at negative voltage such as -1 volt the negative potential at the gate will tend to pressure electrons towards the p-type substrate and attract hole from the p-type substrate. The more negative the bias the higher is the rate of recombination. The resulting levels of drain current is therefore reduced so at pinch-off level of -6 volt, it will stop. For positive value of Vgs

,positive gate will draw additional electron from the p-type substrate due to which the reverse leakage current establish.

P-channel depletion type MOSFET

Enhancement type MOSFETThe construction of enhancement type

MOSFET is similar to the depletion type mosfet , but there is no physical channel between source and drain.

In enhancement type mosfet voltage source Vgs is connected between gate and source terminal which is not present in the depletion type mosfet

N-channel enhancement type MOSFET

P-channel enhancement type MOSFET

ApplicationsThe MOSFET transistor has become one of

the most important device used in the design and construction of integrated circuits for digital computers.

Its thermal stability and other general characteristics make it extremely popular in computer circuit design.

Its also use in fast switching device and for making flash memories.

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Presented by: Shakti Rajput

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