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Working Principles of MOSFET

Transistors are the fundamental building blocks of modern electronics, with billions of them being field effect transistors. One such transistor is the metal oxide semiconductor field effect transistor (MOSFET). A MOSFET is made from a semiconductor material like silicon and has two types of impurities: pentavalent (n-type) and trivalent (p-type). When connected, electrons from n-type fill holes in p-type, depleting charges near the junction. This depletion region is called forward bias, and reverse bias increases when the battery's polarity is reversed. MOSFETs are divided into enhancement and depletion types, with the N-channel type being the only focus in this video. To flow conventional current from drain to source, a battery is connected between the drain and source, creating a channel between them. This channel is created by connecting a small voltage source between the gate and substrate, creating an electric field inside the substrate. The substrate is a p-type semiconductor, with charge carriers being holes and free electrons as minority charge carriers. The MOSFET is a device that creates a channel between the source and drain, allowing electrons to move from the source to the drain. The thickness of the channel can be controlled by changing the gate voltage, and the threshold voltage is the voltage at which the channel is formed. The conventional current flows from drain to source, while the electron flow is from source to drain. The MOSFET is in the ohmic or linear region, following ohm's law. As the voltage increases, the depletion region between the drain and substrate increases, as they are reverse biased. The channel begins to deplete towards the drain end, as negative charges from the channel closest to the drain are pulled into the drain, reducing the width of the channel and reducing the flow of current. As the voltage increases, the channel is pinched off, but in real cases, a constant saturated current remains.