The Constructional and Dimensional Details of FinFETs

Key Takeaways

• The special construction of FinFETs makes the leakage power lower than other semiconductor technologies. 

• In FinFETs, fin projections are the source and drain terminals.

• The gate that wraps the source-drain channel makes FinFET technology suitable for multi-gate transistor architecture.

Semiconductor electronic devices face functionality problems caused by leakage voltage and leakage current. However, in regards to leakage power, fin field-effect transistors (FinFETs) are different from other transistors; the special construction of FinFETs makes the leakage power lower than other semiconductor devices without FinFETs. 

What Are FinFETs? 

FinFETs are a type of field-effect transistor (FET), which controls the current flow using the electric field. FinFETs are just like any other FETs, but with fins in their structure. FinFETs are non-planar transistors and are most often used in IC design given their high device density. 

The Construction of FinFETs

Drain and Source

FinFETs have fins that project outside of the substrate, which is usually a lightly doped p-type semiconductor. These fin projections are the source and drain terminals. The three-dimensional source and drain fin (non-planar) structures in FinFETs permit more volume for a given area compared to conventional planar semiconductor devices. The fins are separated from each other using oxide deposition. 

Gate

The gate in a FinFET is wrapped around the fins. The orientation of the gate is such that it is perpendicular to the vertical fins. The gate covers the entire channel between the source and drain. This gate makes FinFET technology suitable for multi-gate transistor architecture.

Multiple gates surrounding the thin channel can deplete the charge carriers in the channel. This provides better electrostatic control of the channel. Planar FETs have less electrostatic control over the channel of carriers between source and drain, as the gate is away from it. The complete electrostatic control by the gate allows no leakage current between the source and drain when the gate is in an off state.

The wrap-around gate in a FinFET offers the advantage of low threshold voltage, which helps reduce power dissipation and increases the performance of the FinFET. 

The Dimension of Fins 

The three-dimensional fabrication of FinFETs on substrate makes them scalable. The vertical structure of FinFETs allows chips to be downsized while still holding many components.

The height, width, and channel length are the geometric dimensions that characterize a FinFET’s behavior. The thickness of a fin influences the short-channel behavior; it has control over the subthreshold swing, and hence on the efficiency of the FinFET.

The sum of height and width multiplied by a factor of two gives the electrical width of the FinFET. FinFETs follow width quantization, where the width is designed as the multiples of height. The height of a FinFET is one factor that controls the current flow through the channel between source and drain. The higher the height of a FinFET, the more current flows through the channel. 

Compared to planar transistors with the same footprint area, the high drive current of FinFETs makes them high speed, low-leakage, low power loss transistors. If you are designing an IC using FinFET technology, Cadence software can help.

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