Electrical and electronics engineering

1. MOSFET
 Metal Oxide Semiconductor Field Effect Transistor or
 Metal Oxide Silicon Field Effect Transistor
 Also known as IGFET – insulated gate field effect transistor
 Operated in both depletion mode & enhancement mode
 used for switching purposes and amplification of electronic
signals
 3 terminals : source(S), gate (G), drain (D)
Construction
 Similar to FET
 An oxide layer is deposited on the substrate to which the gate
terminal is connected
 Oxide layer act as an insulator, known as IGFET
 Lightly dropped substrate is diffused with heavily dopped
region
 Depending upon the substrate used there are two types
1. P type MOSFET
2. N type MOSFET

2. Classification of MOSFETs

3. Working :
1. Depletion mode
 When no voltage is applied between gate and source
 some current flows due to the voltage between drain and source
 Let some negative voltage is applied at VGG.
 Then the minority carriers, holes get attracted and settle
near SiO2 layer.
 But the majority carriers, electrons get repelled.
 With some amount of negative potential at VGG a certain amount
of drain current ID flows through source to drain.
 When this negative potential is further increased, the electrons get
depleted and the current ID decreases

4. 2 Enhancement Mode
 Let some positive voltage is applied at VGG.
 then the minority carriers. holes, get repelled and the majority
carriers electrons gets attracted towards the SiO2 layer
 drain current ID flows through source to drain.
 When this positive potential is further increased, the
current ID increases due to the flow of electrons from source to
drain
MOSFET applications
 Radiofrequency applications use MOSFET amplifiers extensively.
 MOSFET behaves as a passive circuit element.
 Power MOSFETs can be used to regulate DC motors.
 MOSFETs are used in the design of the chopper circuit.