What is the difference between JFET and MOSFET

    Voltage-controlled field effect transistors (FETs) are mainly used to amplify weak signals, mainly wireless signals, and to amplify analog and digital signals. A field effect transistor (FET) is a transistor that uses electric field effects to change the electrical properties of the device. They are used in electronic circuits ranging from RF technology to switching, from power control to amplification. They use electric fields to control the conductivity of the channel. FETs are divided into JFETs (junction field effect transistors) and MOSFETs (metal oxide semiconductor field effect transistors). Both are mainly used in integrated circuits and are very similar in their working principles, but their composition is slightly different. Let's take a closer look at both.

    What is a JFET?

    JFET is the simplest field effect transistor in which current can flow from source to drain or from drain to source. Unlike the bipolar junction transistor (BJT), the JFET uses a voltage applied to the gate terminal to control the current flowing through the channel between the drain terminal and the source terminal, resulting in an output current proportional to the input voltage. The gate terminal is reverse biased. It is a three-terminal unipolar semiconductor device used in electronic switches, resistors, and amplifiers. It requires a high degree of isolation between the input and output, which makes it more stable than the bipolar junction transistor. Unlike the BJT, the amount of current allowed is determined by the voltage signal in the JFET.

    JFETs are generally classified into two basic structures:

    N-Channel JFET – The current flowing through the channel between the drain and source is negative in the form of electrons. It has a lower resistance than the P-channel type. P-Channel JFET – The current flowing through this channel is positive in the form of holes. It has a higher resistance value than its N-channel counterpart.

    What is a MOSFET?

    MOSFET is a four-terminal semiconductor field effect transistor made of controlled silicon oxide, and the applied voltage determines the conductivity of the device. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. The gate located between the source and drain channels is electrically insulated from the channel by a thin layer of metal oxide. This is to control the voltage and current flow between the source and drain channels. MOSFET plays a vital role in integrated circuits due to its high input impedance. They are mainly used in power amplifiers and switches, in addition, they also play a vital role in embedded system design as a functional element.

    They are generally divided into two configurations:

    Depletion Mode MOSFET – When the gate to source voltage is zero, the device is normally “ON”. Applied voltage is lower than the drain to source voltage Enhancement Mode MOSFET – When the gate to source voltage is zero, the device is normally “OFF”.

    Difference between JFET and MOSFET?

    Basics of FET and MOSFET

    Both JFET and MOSFET are voltage-controlled transistors used to amplify analog and digital weak signals. Both are unipolar devices but have different compositions. JFET stands for Junction Field Effect Transistor while MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. The former is a three-terminal semiconductor device while the latter is a four-terminal semiconductor device.

    Operating modes of FET and MOSFET

    Both have less transconductance values ​​compared to the bipolar junction transistor (BJT). JFET can only operate in depletion mode, whereas MOSFET can operate in both depletion mode and enhancement mode.

    Input Impedance in FETs and MOSFETs

    The high input impedance of the JFET is about 1010 ohms, which makes it sensitive to input voltage signals. MOSFETs offer higher input impedance than JFETs, thanks to the metal oxide insulator, which makes them more resistive at the gate end.

    Gate leakage current

    It refers to the gradual loss of electrical energy due to electronic devices even when they are turned off. While a JFET allows for gate leakage currents of the order of 10^-9 A, a MOSFET will have gate leakage currents of the order of 10^-12 A.

    Damage Resistors in FETs and MOSFETs

    MOSFETs are more susceptible to damage from electrostatic discharge because the additional metal oxide insulator reduces the capacitance of the gate, making the transistor susceptible to damage from high voltages. On the other hand, JFETs have higher input capacitance than MOSFETs and are therefore less susceptible to ESD damage.

    Cost of FETs and MOSFETs

    JFET follows a simple, less complex manufacturing process which makes it cheaper than MOSFET which is expensive due to a more complex manufacturing process. The additional metal oxide layer increases the overall cost.

    Applications of FET and MOSFET

    JFETs are used in low noise applications like electronic switches, buffer amplifiers, etc. On the other hand, MOSFETs are mainly used in high noise applications like switching and amplifying analog or digital signals, furthermore, they are also used in motor control applications and embedded systems.