Dual Gate MOSFET: Advantages and Disadvantages

This page covers the basics of Dual Gate MOSFETs, along with their benefits and drawbacks. It explores the advantages and disadvantages of using Dual Gate MOSFETs.

What is a Dual Gate MOSFET?

A Dual Gate MOSFET is a type of MOSFET particularly useful in various RF (Radio Frequency) applications. As the name suggests, it features two control gates arranged in series, as depicted in the figure below.

These gates are constructed along the length of the channel, one after the other. They influence the level of current flowing between the Source (S) and Drain (D) terminals.

It essentially functions similarly to two MOSFET devices connected in series. These gates affect the normal operation of the MOSFET and, consequently, the output.

Dual Gate MOSFETs find applications in various circuits, including:

• RF mixers
• RF multipliers
• RF amplifiers
• Amplifiers with gain control

Dual Gate devices are popular in circuit designs using sub-50 nm technology. The figure illustrates the construction of a Dual Gate MOSFET, along with the symbols for n-channel and p-channel versions.

The second gate is often operated at a fixed voltage to minimize feedback capacitance between the drain and gate. The voltage applied to the gate terminals controls the electric fields, which in turn determines the amount of current flow through the channel.

Key Features of Dual Gate MOSFETs:

• Both upper and lower gates control the channel region.
• An ultra-thin body acts as a rectangular quantum well at device limits.
• Directly scalable down to 20nm channel length.

Applications:

• Construction of low-power logic gates
• Single transistor mixers
• SRAMs (Static Random-Access Memory)
• Demodulators, cascade amplifiers, RF amplifiers, AGC (Automatic Gain Control) amplifiers.

Different layouts are employed in Dual Gate designs, including planar double gate, vertical double gate, and horizontal double gate configurations.

Benefits or Advantages of Dual Gate MOSFET

Here are some of the key benefits and advantages of using Dual Gate MOSFETs:

• The two gates help control unwanted capacitive effects at higher frequencies.
• They offer better control of the channel from the gates, resulting in improved electrostatic control.
• They reduce short-channel effects, leading to better scalability and lower sub-threshold current.
• They provide improved I_ON/I_OFF ratio.
• They offer an improved sub-threshold slope (around 60mV/decade).
• They eliminate discrete dopant fluctuations.
• They exhibit lower gate leakage.

Challenges or Disadvantages of Dual Gate MOSFET

Despite their advantages, Dual Gate MOSFET technology also presents some challenges:

• Identically sized gates are necessary.
• Self-alignment of the source and drain to both gates is required.
• The alignment of both gates to each other is critical.
• Connecting the two gates with a low resistance path is essential.