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Using FinFETs vs. MOSFETs for IC Design

Author Cadence System Analysis

Key Takeaways

  • FinFETs are three-dimensional structures with vertical fins forming a drain and source. 

  • MOSFETs are planar devices with metal, oxide, and semiconductors involved in their basic structure.

  • FinFETs have an excellent subthreshold slope and a higher voltage gain than planar MOSFETs.

IC design

FinFET technology offers high scalability for IC designs

Field-effect transistors (FETs) are a family of transistors that include junction-gate field-effect transistors (JFETs), fin field-effect transistors (FinFETs), and metal-oxide-semiconductor field-effect transistors (MOSFETs). All these devices are three-terminal devices with pins, namely the drain, source, and gate. The current flows from the drain to the source and the flow of carriers in this channel can be controlled by the voltage applied to the gate terminal.

Even though they belong to the same family of transistors, FinFETs and MOSFETs are constructed differently and have a different level of scalability. Let’s look more closely at these two transistors to better understand FinFETs vs. MOSFETs, their characteristics, and the advantages and disadvantages of using them for IC design. 

FinFETs vs. MOSFETs 

When considering FinFETs vs. MOSFETS, it is important to note that they are constructed differently, which makes their characteristics and properties fairly different as well. FinFETs are three-dimensional transistors, whereas MOSFETs are planar transistors. 

FinFETs: Three-Dimensional Transistors

A FinFET is a three-dimensional structure with vertical fins forming a drain and source. A gate is wrapped around the drain and source. This construction leaves the gate at a sufficient length and provides better electrostatic control over the channel of carriers between the drain and source.

MOSFETs: Planar Transistors

MOSFETs are planar devices with metal, oxide, and semiconductors involved in their basic structure. A planar n-channel MOSFET is formed by diffusing heavily doped n regions onto a p-substrate body. Over this planar structure, a layer of silicon dioxide is grown. Metallic terminals are etched on the insulating layer of silicon dioxide. The metallic terminals that are in contact with the n regions beneath form the drain and source. The gate terminal is the metallic layer on the silicon dioxide with no contact with n regions. 

The Desirable Characteristics of FinFETs 

The three-dimensional structure of FinFETs provides many advantages over MOSFETS.  Some of these merits include:

  1. A large number of transistors can be incorporated into a single chip. FinFET technology is suitable for IC fabrication, as it has higher scalability for the given footprint area than MOSFETs.
  2. As chips are downsized, transistors also shrink. This compactness brings the drain and source closer and reduces the gate control over the channel carriers. This type of short-channel effect can cause serious issues in MOSFETs. The presence of fins gives FinFETs better short-channel behavior. 
  3. To improve short-channel behavior, channel doping is common in planar MOSFETs. The wrap-around gate over the thin body makes channel doping optional in FinFETs. Therefore, no dopant-induced fluctuations are present in FinFETs.
  4. The length of the gate is significant in reducing leakage current, and thereby leakage power. As the gate is wrapped around the drain-source channel, there is sufficient gate length in FinFETs and there is no leakage current when the gate is not energized. However, in MOSFETs, as the gate is scaled down, leakage current exists. 
  5. Leakage current and leakage voltage are responsible for leakage power in switching devices. Since FinFETs are devices with low leakage current, their power consumption is less than that of MOSFETs.
  6. In planar MOSFETs, the device drive strength is dependent on the channel width, whereas a FinFET transistor’s drive strength can be increased by incorporating multiple or longer fins. 
  7. A higher drive current can be reflected as fast switching times in FinFETs. Otherwise, it can be said that three-dimensional FinFETs are high-speed devices compared to planar MOSFETs. 
  8. It is easy to fabricate multi-gate devices using FinFET technology. Planar construction makes multi-gate construction tedious in MOSFETs. 
  9. FinFETs offer an excellent subthreshold slope and higher voltage gain than planar MOSFETs. 

When considering FinFETs vs. MOSFETs, it is critical to understand the advantages and disadvantages of both to make an informed choice. If you decide to use FinFETs, Cadence software can assist you in your IC design using FinFET technology.

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