What are the functional differences between MOSFETs and JFETs?

In summary, a JFET is different from a BJT because the BJT requires current to control it, while the JFET is voltage-controlled. The JFET also has a much less input current requirement than the BJT.
  • #1
therash09
12
0
I am a beginner with respect to MOSFETs and have just begun studying them at college 2 weeks back.

What I am actually struggling with is the basic functional differences between MOSFETs and JFETs. Two of them are- dielectric and substrate, both of which are there in MOSFETs.

However, I don't understand much, the significance of having a dielectric, when I thought the direct application of a gate bias could have helped, though with opposite polarity.

Moreover, I don't understand why the term "junction" is used to describe the interface between Gate and Drain/Source?
And why do books talk about reverse/forward biasing these "junctions" when we know they are nothing but tiny overlaps of Gate over Drain/Source?
Do these tiny overlaps play such important role in MOSFET functioning or does it have something to do with the Substrate-Drain/Source junctions?
And, can't a substrate bias alone work without gate bias, as in the case of JFETs, where we have only one single voltage(gate) controlling the channel as input terminal?
Does a gate bias also control the substrate polarity, as the substrate bias does, but on the opposite face of the substrate?


These are a few initial doubts that I wanted to share. They might appear really stupid, but for me I know they're vital. If not cleared, they could snowball into a big trouble for me in the future.

So kindly reply...
Thankyou!

PS.:
This is not a homework question. Please don't mistake it for one!
 
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  • #2
The https://secure.wikimedia.org/wikipedia/en/wiki/JFET" does not, so there is no "j" in the name (acronym). The mosfet operates on an electric field that propagates across a very thin oxide layer and thus enhances or depletes the charge carrier concentration on the other side.

The JFET also enhances or depletes the charge carrier concentration in the same way that a https://secure.wikimedia.org/wikipedia/en/wiki/Diode" operates. It does not have an insulating oxide layer.

Otto
 
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  • #3
As I understand it, a JFET is distinguished still from a BJT (bipolar junction transistor). While both have pn junctions, the JFET is voltage-controlled, and requires much less input current, than the current-controlled BJT.
 

Related to What are the functional differences between MOSFETs and JFETs?

1. What is the difference between a JFET and MOSFET?

A JFET (Junction Field-Effect Transistor) is a type of transistor that uses a voltage-controlled electric field to control the current flow, while a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) uses a voltage-controlled electric field created by a metal-oxide-semiconductor structure.

2. Which one is better for high frequency applications?

MOSFETs are generally better for high frequency applications due to their lower input capacitance and higher switching speed. However, JFETs may be a better choice for certain specialized applications.

3. What are the main advantages of using a JFET over a MOSFET?

JFETs have a simpler structure, are easier to fabricate, and have a higher input impedance compared to MOSFETs. They also have a lower noise level and do not require a gate driver circuit.

4. When would you choose to use a MOSFET instead of a JFET?

MOSFETs are a better choice for applications that require high power handling, low on-resistance, and high switching speeds. They also have a wider range of operating voltages and can be easily integrated into digital circuits.

5. Can a JFET and MOSFET be used together in a circuit?

Yes, a JFET and MOSFET can be used together in a circuit. For example, a JFET can be used in the input stage of an amplifier to provide high input impedance, while a MOSFET can be used in the output stage for its high power handling capabilities.

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