MOSFET vs JFET Comparison

Comparison of MOSFET with JFET

In this post we will discuss about the comparison between MOSFET and JFET. Before proceeding further let us refresh the fundamentals about these semiconductor devices.

Field Effect Transistor (FET):

  • The Field Effect transistor(FET)  is a three terminal semiconductor device which has many similarities and dissimilarities with Bidirectional Junction Transistor (BJT).
  • The prime difference between BJT and FET is that the BJT is a current controlled device whereas the FET is a voltage controlled device.
  • The Field Effect Transistor is a device in which the flow of current through the conducting region is controlled by an electric field. Thus it is called as Field Effect Transistor (FET).
  • The current conduction in the device is only by majority carriers, so is known as Unipolar device.
  • The FET can be classified into two types based on the construction. They are namely
    Junction Field Effect Transistor(JFET)
    Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
  • The JFET has been classified into two types namely
    N – Channel JFET ( Electrons are the majority carriers) 
    P – Channel JFET (Holes are the majority carriers)

Metal Oxide Semiconductor Field Effect Transistor (MOSFET)

MOSFET_SYMBOLMetal-oxide semiconductor field-effect transistors (MOSFETs) are the unipolar transistor family. A distinguishing feature of MOSFET is its gate construction. The gate is completely insulated from the channel. Voltage applied to the gate will cause it to develop an electrostatic charge. No current is permitted to flow in the gate area of the device. The gate is simply an area of the device coated with metal. We will discuss about structure of MOSFET in another post.

The other names for MOSFET are Insulated Gate Field Effect Transistor (IGFET), Metal Oxide Silicon Transistor (MOST) The MOSFETs are classified into two types namely
Depletion Mode MOSFET
Enhancement Mode MOSFET

MOSFET vs JFET:

  1. Comparing to the JFET, MOSFETs are easier to fabricate.
  2. JFETs are operated only in the depletion mode. The depletion type MOSFET may be operated in both depletion and enhancement mode.
  3. The output characteristics of JFET is flatter than the MOSFET. because the drain resistance in the JFET (1 MΩ) is higher than the MOSFET (50kΩ)
  4. The gate leakage current of JFET is of the order of 10-9A. For MOSFET, the gate leakage current will be of the order of 10-12A. 
  5. The input resistance of JFET is in the range of 108Ω. For MOSFET, the input resistance will be in the range of 1010 to 1015Ω.
  6. Because of their advantages, MOSFETs are widely used in VLSI circuits than JFET. As the MOSFET is susceptible to overload voltages, special care should be taken during installation. 
  7. MOSFET has zero offset voltage. The source and drain terminals can be interchanged (so it is called as symmetrical device). Because of these two characteristics the MOSFET is widely used in analog signal switching.
  8. In JFET, the transverse electric field across the reverse biased PN junction controls the conductivity of the channel. In MOSFET, the transverse electric field induced across an insulating layer deposited on the semiconductor material controls the conductivity of the channel. 

Thanks for reading.. Please leave your valuable comments below….

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1 Response

  1. anonymous user says:

    For what reason might one ever choose a JFET instead of a MOSFET?

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