MOSFET: Features, Advantages and Disadvantages of FET

A FET is a three-terminal unipolar semiconductor device. It is a voltage controlled device, not like a bipolar junction transistor. The main advantage of mosfet transistor is that it has a very high input impedance, which is in the order of Mega Ohms. It has many advantages like low power consumption, low heat dissipation and FETs are highly efficient devices. The following image shows however a sensible FET seems like.

The FET is a unipolar device, which means that it is made using either p-type or n-type material as the main substrate. Hence the current conduction of a FET is done by either electrons or holes.

Features of FET

The following are the various options of a Field effect transistor.

Unipolar − it's unipolar as either holes or electrons are liable for conductivity.

High input impedance − The input current in FET flows due to the reverse bias. Hence it has high input impedance.

Voltage controlled device − As the output voltage of a FET is controlled by the gate input voltage, FET is called as the voltage controlled device.

Noise is low − There aren't any junctions present within the physical phenomenon path. Hence noise is lower than in BJTs.

Gain is characterized as Transconductance. Transconductance is that the magnitude relation of amendment in output current to the amendment in input voltage.

The output impedance of a FET is low.

Advantages

An advantage of the FET is its high gate to main current resistance of the order of 100 MΩ or more, thus ensuring a high degree of isolation between control and flow. Since base current noise will increase with training time, a FET typically produces less noise than a bipolar transistor (BJT) and is thus found in noise-sensitive electronics such as tuners and low noise amplifiers for receivers VHF and satellite.

It is relatively immune to radiation. It doesn't show any compensation voltage to zero drain current and so makes a wonderful signal helicopter. It usually has higher thermal stability than a BJT. Since they are controlled by the gate, once the gate is closed or open, there is no extra power draw, as with a bipolar junction transistor or non-latching relays in some states. This allows extremely low power switching, which in turn allows for larger miniaturization of circuits because the heat dissipation needs are reduced compared to other types of switches.

Disadvantages 

It has a comparatively low information measure product compared to a BJT. The MOSFET has the disadvantage of being extremely liable to overloading voltages, so requiring special handling throughout installation.

The frail insulating layer of the mosfet transistor between gate and channel makes it at risk of electricity discharge or to vary the edge voltage throughout handling. This is typically not a drag when the device has been put in in an exceedingly properly designed circuit.

FETs often have very low resistance and high strength. However, intermediate resistances are significant, and so FETs can dissipate large amounts of energy during switching. Thus, the potency will place a premium on a fast switch, but this can cause transients that can excite street inductances and can generate significant voltages that can couple to the gate and cause unintentional switching.

FET circuits might, therefore, need an awfully careful look and will involve switch between switch speed and power dissipation. There is also a compromise between nominal voltages and “on” resistance so that high voltage FETs have relatively high resistance and hence conduction losses.