Construction & Working of Enhancement-Type MOSFET (Part 1)

Neso Academy
13 Dec 201616:02

Summary

TLDRThis script introduces Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), emphasizing their classification into depletion and enhancement types. It focuses on the n-channel enhancement type MOSFET, detailing its construction and the process of channel formation through inversion, where a positive gate voltage induces a conductive n-type channel between the source and drain in a p-type substrate.

Takeaways

  • 😀 An active device is a circuit component capable of controlling the flow of electrons, such as BJT, JFET, and MOSFET.
  • 🔋 MOSFETs are classified into two types: depletion type and enhancement type, each with n-channel and p-channel variations.
  • 🌐 The construction of depletion and enhancement type MOSFETs is similar, but a key difference is the initial presence of a channel in depletion type MOSFETs.
  • 🌐 In an n-channel enhancement type MOSFET, the substrate is p-type, and the source and drain are n-type, while in a p-channel enhancement type MOSFET, the substrate is n-type, and the source and drain are p-type.
  • 🔌 The gate terminal of a MOSFET is not in direct contact with the body; it is separated by a thin layer of silicon dioxide, known as the gate oxide.
  • 🔬 The gate oxide layer is made very thin (approximately 1,000 angstroms) to allow the gate electrode to control the surface of the semiconductor.
  • 🔋 The formation of a channel in an enhancement type MOSFET occurs when the gate terminal is made more positive with respect to the substrate, causing an inversion from p-type to n-type material near the surface.
  • 🔄 The process of channel formation is called inversion, where the region near the surface changes from p-type to n-type due to the accumulation of negative charges.
  • 🌐 When the gate voltage (Vgs) is increased, the channel width or depth increases, allowing more current to flow between the source and drain.
  • 🔬 The lecture will continue to explore the complete working of the n-channel enhancement type MOSFET in the next session.

Q & A

  • What is an active device in electronics?

    -An active device is any type of circuit component with the ability to control the flow of electrons and eventually the current flow.

  • How does a MOSFET differ from a passive device?

    -A MOSFET is an active device because it can control the flow of electrons, unlike passive devices which cannot control the flow of electrons.

  • What are the two types of MOSFETs?

    -The two types of MOSFETs are depletion type MOSFET and enhancement type MOSFET.

  • What is the main difference between depletion type and enhancement type MOSFETs?

    -The main difference is that in a depletion type MOSFET, a channel exists between the drain and source from the beginning, while in an enhancement type MOSFET, there is no channel initially.

  • What is the purpose of doping the parent material with trivalent impurities in an n-channel enhancement type MOSFET?

    -Doping the parent material with trivalent impurities converts it into a P-type material, which is necessary for the construction of an n-channel enhancement type MOSFET.

  • What are the two end type wells created in the process of constructing an n-channel enhancement type MOSFET?

    -The two end type wells created are n-type wells, which act as the source and drain of the MOSFET.

  • What is the function of the gate terminal in an n-channel enhancement type MOSFET?

    -The gate terminal in an n-channel enhancement type MOSFET is not in direct contact with the body. It is located over a thin layer of silicon dioxide and is used to control the channel formation between the source and drain.

  • Why is the silicon dioxide layer in a MOSFET made very thin?

    -The silicon dioxide layer is made very thin to allow for better control over the surface by the gate electrode.

  • What is the process called when the region near the surface of a P-type material becomes N-type due to the application of a positive voltage to the gate?

    -The process is called inversion, where the P-type material is inverted to N-type, creating a conductive channel between the source and drain.

  • How does increasing the voltage (Vgs) between the gate and substrate terminals affect the channel in an n-channel enhancement type MOSFET?

    -Increasing Vgs causes more negative charge to accumulate near the surface, leading to the formation of an n-type channel between the source and drain, thus increasing the channel width or depth.

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Étiquettes Connexes
MOSFETElectronicsSemiconductorsTransistorsCircuitryActive DevicesDepletion TypeEnhancement TypeN-ChannelP-Channel
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