JFET or Field effect transistors are electrical devices that are either used as amplifiers or switches and have become an integral part of memory chips. JFET and MOSFET are two kinds of FET that work on the principle of junction transistors but are quite different from each other.
JFET vs MOSFET
The difference between JFET and MOSTFET is that the current through JFET is channeled by the electric field across the reverse-biased PN junction whereas in MOSFET the conductivity is due to the transverse electric field in the metal-oxide insulator embedded on the semiconductor.
The next key difference between the two is that JFET allows less input Impedance than MOSFET and since the latter which has an insulator embedded allows less leakage of current.
JFET which is normally termed as “ON device” is a depletion type tool that has low drain resistance while its successor MOSFET is termed as normally “OFF device” that can work on both depletion mode and enhanced mode and has high drain resistance.
Comparison Table Between JFET and MOSFET (in Tabular Form)
| Parameter of Comparison | JFET | MOSFET |
|---|---|---|
| Input impedance | Low input impedance of about 108 Ω | High input impedance of about 1010 to 1015 Ω |
| Drain resistance | Low drain resistance | High drain resistance |
| Easy of manufacture | It is more difficult to fabricate than MOSFET | It is comparatively easier to assemble than JFET |
| Price | Lower cost than MOSFET | Costlier than JFET |
| Functioning Mode | Depletion type | Both depletion and enhancement type |
What is JFET?
JFET, which is an abbreviation for Junction Gate Field Effect Transistor is a unipolar device that basically has three parts, a source, a drain, and a gate. It is mostly used in amplifiers, resistors, and switches.
It is a basic type of FET that works when a small voltage is applied to the gate terminal. This small voltage allows for the current to flow from source to drain and beyond.
The voltage applied on the gate (VGS) controls the width of the depletion zone and thus the amount of current flowing through the semiconductor. Hence, the drain current flowing through the channel is proportional to the applied voltage.
As the negative voltage on the gate terminal increases the depletion zone widens and lesser current flows through the channel and finally, a stage reaches where the depletion zone stops the current flow completely.
JFET is further classified into N-Channel JFET where the channel that connects drain and source is heavily doped with electrons and P-Channel JFET where the channel is rich in holes
What is MOSFET?
MOSFET or Metal oxide semiconductor FET is an advanced configuration of FET which has four parts to carry out its functions. They are widely used in computer memory chips such as in metal oxide semiconductor memory cells for storing bits.
Although MOSFET follows the basic principle of FET, it has a more complicated design which also makes it more efficient. MOSFET is also a unipolar device that works both in depletion and enhancement modes to amplify signals.
All types of MOSFET have a metal-oxide insulator that separates the substrate from the gate. When a voltage is applied on the gate terminal a channel is formed, due to the electrostatic force, between the drain and source that allows the current.
The D-MOSFET works on depletion-mode where there exists a pre-constructed channel and this channel is closed on applying a voltage whereas E-MOSFET that works on the enhancement mode requires a potential to create a channel for current flow. MOSFET is a more advanced FET made to increase the drain resistance and apply infinite input impedance while lowering the leakage current. However, MOSFET requires well maintenance because of the risk of corrosion associated due to the metal oxide insulator.
Main Differences between JFET and MOSFET
- The key difference between JFET and MOSFET is that current in JFET flows due to the electric field in the PN junction and that in MOSFET is due to the transverse electric field in the metal oxide layer.
- The next crucial difference is that JFET has lower input impedance while MOSFET practically has infinite impedance since there is no direct contact between the gate and the substrate.
- Another notable difference is that JFET has lower drain resistance while MOSFET has a high drain resistance.
- JFET also has a higher leakage current but MOSFET was curetted to be more efficient with lower leakage current.
- Although JFET is more difficult to assemble than MOSFET, it is less costly than the latter.
Conclusion
JFET and its successor MOSFET both are widely used as amplifiers and switches in various fields of application. However, MOSFET has emerged as more competent transistors to be used in computer memory chips.
The main difference between the two is that JFET uses an electric field in the PN junction whereas MOSFET utilizes a transverse electric field in the embedded metal oxide layer for electrical conductivity through the substrate.
Another key difference is that JFET has no metal oxide layer for insulation which MOSFET possesses in its design and hence the name Metal Oxide Semiconductor Field Effect Transistor or MOSFET was given.
JFET is the most basic form of FET whereas MOSFET was engineered to be more efficient and has less Leakage current. This was achieved by incorporating the metal oxide barrier between the gate terminal and the substrate.
Although JFET and MOSFET belong to the same family of transistors, JFET is very much different from its cousin MOSFET which has a much higher drain resistance and impedance than JFET.
The difference between JFET and MOSFET has led them to a different field of use such as JFET is used more in amplifiers, rectifiers, and switches whereas MOSFET is incorporated in computer memory chips for their high level of efficiency.
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