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MOSFET is also known as IGFET that is an insulated-gate field-effect transistor. Here, the word MOSFET is used because most devices are made using Si for semiconductors and gate electrodes of metal oxide. MOSFET is a three terminal device that has a source, a drain, and a gate terminal. These are voltage-controlled devices, in which the current flowing between source and drain is proportional to the provided input voltage.
Due to the small size of MOSFET, it is mostly used in digital circuits. There are two types of MOSFET that are as follows:
- Depletion Type MOSFET: The transistor requires the Gate-Source voltage (VGS) to switch the device “OFF”. The depletion-mode MOSFET is equivalent to a “Normally Closed” switch.
- Enhancement Type MOSFET: The transistor requires a Gate-Source voltage(VGS) to switch the device “ON”. The enhancement-mode MOSFET is equivalent to a “Normally Open” switch.
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MOSFET Operation
The working of a MOSFET depends upon the capacitors. The capacitor is an important part in the MOSFET.
1. P-Channel MOSFET
In the above diagram the drain and source are heavily doped p+ region and the substrate is in n-type. The current flows due to the flow of positively charged holes also known as p-channel MOSFET. When we apply negative gate voltage, the electrons present at the oxide layer experience repulsive force and they are pushed downward in to the substrate, the depletion region is populated by the bound positive charges which are associated with the donor atoms.
2. N-Channel MOSFET
In the above diagram the drain and source are heavily doped n+ region and the substrate is p-type. The current flows due to the flow of negatively charged electrons, also known as n-channel MOSFET. When we apply the positive gate voltage the holes present beneath the oxide layer experience repulsive force and the holes are pushed downwards in to the bound negative charges which are associated with the acceptor atoms. The positive gate voltage also attracts electrons from n+ source and drain region in to the channel thus an electron reach channel is formed.
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