Q. Compare MOSFET with JFET?
a. In enhancement and depletion types of MOSFET,the transverse electric field induced across an insulating layer deposited on the semiconductor material controls the conductivity of the channel.In the JFET the transverse electric field across the reverse biased PN junction controls the conductivity of the channel.
b. The gate leakage current in a MOSFET is of the order of 10-12 A. Hence the input resistance of a MOSFET is very high in the order of 1010 to 1015 W.The gate leakage current of a JFET is of the order of 10-9 A and its input resistance is of the order of 108 W.
c. The output characteristics of the JFET are flatter than those of the MOSFET and hence , the drain resistance of a JFET (0.1 to 1MW)is much higher than that of MOSFET(1 to 50 kW).
d. JFETs are operated only in the depletion mode.The depletion type MOSFET may be operated in both depletion and enhancement mode.
e. Comparing to JFET , MOSFETs are eaiser to fabricate.
f. MOSFET is very susceptible to overload voltage and needs special handling during installation.It gets damaged easily if it is not properly handled.
g. MOSFET has zeo offset voltage. As it is a symmetrical device, the source and drain can be interchanged.These two properties are very useful in analog signal switching.