Difference between JFET and MOSFET:

The Difference between JFET and MOSFET are quite similar in their operating principles and in their electrical characteristics. However, they differ in some aspects, as detailed here :

1. In MOSFETs (DE-MOSFETs as well as E-MOSFETs), the transverse electric field induced across an insulating layer deposited on the semiconductor material controls the conductivity of the channel whereas in the JFETs the transverse electric field across the reverse-biased PN junction controls the conductivity of the channel.

2. JFETs can only be operated in the depletion mode whereas MOSFETs can be operated in either depletion or in enhancement mode. In a JFET, if the gate is forward biased, excess carrier injunction occurs and the gate current is substantial. Thus channel conductance is enhanced to some degree due to excess carriers but the device is never operated with gate forward biased because gate current is undesirable.

3. MOSFETs have input impedance much higher than that of JFETs because of small leakage currents. The input impedance of the MOSFET is of the order of 10¹⁰ to 10¹⁵ Ω whereas the input impedance of JFET is of the order of 10⁸ Ω.

4. JFETs have characteristic curves more flatter than those of MOSFETs indicating a higher drain resistance. The drain resistance of a JFET is of the order of 10⁵ to 10⁶ Ω whereas the drain resistance of a MOSFET is of the order of 1 to 50 kΩ.

5. MOSFET is very susceptible to overload voltage and needs special handling during installation. It may get damaged easily if not properly handled.

6. Capacitive effects may be considerably lower in dual gate MOSFETs.

7. Special digital CMOS circuits are available which involve near zero power dissipation and very low voltage and current requirements. This makes them most suitable for portable systems.

8. When JFET is operated with a reverse bias on the junction, the gate current I_G is larger than it would be in a comparable MOSFET. The current caused by minority carrier extraction across a reverse biased junction is greater, per unit area, than the leakage current that is supported by the oxide layer in a MOSFET. Thus MOSFET devices are more useful in electrometer applications than are the JFETs.

For the above reasons, and also because MOSFETs are somewhat easier to manufacture, they are more widely used than are the JFETs.