Mosfet

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Metal-oxide semiconductor field-effect transistor (mosfet) is the second type of field-effect transistor.

The mosfet gate is a channel isolated by a layer of silicon dioxide (Si02). The drain and the source are made from substrate materials.

they are connected to the gate by a narrow channel. Transistor has type of metals. The first is called the mosfet at depletion and the second is called the  enhancement mosfet (E).

The MOSFET transistor is different from the JFET in that the gate is isolated from the channel. Like diodes, these elements are most often made of silicon. They are used to make amplifiers.

The enhancement MOSFET


In the absence of a control signal at the Gate (Vgs = 0V), the Mosfet is blocked regardless of the type of channel (N or P).Conduction only begins to manifest from a threshold:+ Vth for Drain an N-channel MOS and –Vth for a P-channel MOS.


N-channel  enhancement mosfet is a positive voltage applied to the input. The positive charge sticks to the negative charge of the N channel. The voltage between the gate and the source(Vgs) increases. There is a greater attraction of electrons in the N channel. Thus the current circulates On the other hand, if the voltage of the gate is below the threshold, then there is more the conductivity of the channel.




characteristic of enhancement N-channel MOSFET


Depletion MOSFET:


In the absence of a control signal to the Gate(Vgs = 0V), the MOS is on regardless of the type of channel (N or P). The blockage only begins to manifest itself from a threshold: + Vth for Drain an N-channel MOS and –Vth for a P-channel MOS.

The N-channel depleted Mosfet is like a plate of a capacitor and on the other side is the P-channel. With a negative voltage at the gate, the negative charges repel the conduction electrons. leaving positive ions stable.

 The N channel still remains impoverished. Therefore, the more the voltage remains negative in the grid, the greater the depletion is in the region. The result shows that a sufficient negative voltage between the gate and the source (VGs (off)) causes a null current.. As long as the input voltage is negative it will have a null current. However, you must have a positive input voltage to drive.

characteristic of depletion N-channel MOSFET


VGS blocking <VGS <0: Depletion regime.

VGS> 0: enhancement regime.

Application of depleted Mosfet

Once the depletion Mosfet is polarized at a point Q, it amplifies small signals like a JFET. This MOS is also an ideal buffer amplifier, because its isolated grid makes its input resistance stretch to infinity.



sources:

http://emilie.baud.free.fr/EVAspip/IMG/pdf/22_fet_site.pdf

https://sites.google.com/site/electrocomposant/home/diagnostic-electronique/mosfet

https://mongosukulu.com/index.php/contenu/genie-electrique4/electronique/710-le-transistor-mosfet




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