What is a MESFET : Advantages and Disadvantages

MESFET (Metal Semiconductor Field Effect Transistor) is a high frequency transistor commonly fabricated using GaAs and used in microwave communication systems. It offers fast switching and low noise performance. Advantages include excellent RF characteristics and high speed operation, while disadvantages include higher manufacturing costs and lower integration capability than CMOS technologies.

MESFET Structure and its working

MESFET is a type of FET derived from a metal-semiconductor Schottky barrier diode.

GaAs MESFETs are often preferred over silicon devices because GaAs provides higher electron mobility, a higher electric field, and a higher electron saturation drift velocity.

Figure 1: MESFET Structure

GaAs MESFETs are commonly used as microwave integrated circuits in broadband amplifiers. The structure of a typical MESFET is shown in Figure 1.

The working principle of a MESFET is similar to that of a JFET, but the MESFET only has one depletion region, whereas a JFET uses two. The source-gate junction is kept in reverse bias, while the source-drain is kept in forward bias.

Benefits or Advantages of MESFET

1. They offer much better noise figures at microwave frequencies.
2. They deliver high power output.
3. GaAs MESFETs offer high electron mobility, a higher electric field, and a higher electron saturation drift velocity compared to silicon MESFETs.
4. They offer a high transit frequency.

Drawbacks or Disadvantages of MESFET

1. The MESFET structure includes a Schottky metal gate. This limits the forward bias voltage on the gate to the turn-on voltage of the Schottky diode, which is typically 0.7V.
2. Due to the above reason, the threshold voltage must be less than the turn-on voltage. Therefore, it’s difficult to fabricate circuits that use a large number of enhancement-mode MESFETs.

Summary

MESFETs are widely used in microwave and RF applications due to their speed and low noise. Advantages include superior high-frequency performance, while disadvantages include cost and integration challenges.