Explain construction and working of MOSFET
Answers
Working Principle of MOSFET: The aim of the MOSFET is to be able to control the voltage and current flow between the source and drain. It works almost as a switch. ... When we apply the positive gate voltage the holes present under the oxide layer with a repulsive force and holes are pushed downward with the substrate.
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Answer:
The detailed answer on the construction and working of MOSFET is given in the explanation section.
Explanation:
The most widely used transistor is the MOSFET, which is a voltage controlled transistor, basically used for switching and amplifying electronic signals in both analog and digital circuits.
A MOSFET consist of three terminals
(1) Gate
(2) Source
(3) Drain
It also has a body called substrate which is connected to the source internally.
Types of MOSFETs:
- Enhancement type
- Enhancement mode P channel
- Enhancement mode N channel
2.Depletion type
- Depletion mode P channel
- Depletion mode N channel
Construction:
A MOSFET is classified P-type or N-type depending upon the substrate used.
Voltage is controlled at the gate terminal. With negative gate bias voltage it acts as Depletion type and with positive gate bias voltage it acts as Enhancement type
Please refer the table below for construction differences in Enhancement Type and Depletion Type MOSFETs.
Working:
Working of Enhancement MOSFET:
In the enhancement mode the applied Gate voltage is always positive. When it crosses the threshold voltage it turns ON. The current is generated due to the movement of majority carriers. In N channel majority carriers are electrons and in P channel majority carriers are holes. The source is connected to the negative terminal. When the electrons move from source to drain the positive charges formed below the dielectric because of the repulsive force from gate combine with each other.
When the applied gate voltage is increased the number of majority carriers becomes more than the minority carriers below the dielectric medium. So the majority carriers overcomes the recombination of holes and electrons and the majority carrier move from source to drain in the channel, which forms the current. Thus the gate voltage controls the concentration of the majority carriers which is responsible for the formation of the channel.
Please refer the attached image of Working of Enhancement MOSFET
Working of Depletion MOSFET:
The depletion MOSFET is ON by default. The source and drain terminals are physically connected. When the gate terminal is connected to the negative terminal and source to the positive terminal, the electrons gets repelled below the dielectric layer. The positive charged carrier from the source gets combined with the majority carrier the electrons in the N type and thus depletion layer is formed and the channel resistance increases and the current flow decreases. Thus the increase in gate voltage decreases the drain current. They are inversely proportional. When the negative voltage is further increased it reaches the pinch off mode.
Please refer the attached image of Working of Depletion MOSFET
