FinFET

Semiconductor Industry is a very dynamic industry as it changes from time to time. As per Moore’s Law, the number of transistors present in a chip doubles every 18 months or 2 years. So the size of chips and electronic device get smaller and smaller. The introduction of FinFET technology in the semiconductor industry played a crucial role.

FinFET is a non-planar transistor that has replaced common planar MOSFET. The Introduction of FinFET not only overcame the challenges of common MOSFET but also helped to make the size of the electronic device compact due to its 3D and fin-shaped vertical structure. FinFET has been widely used in mobile, laptops, and IoT devices due to energy efficiency, fast switching speed, and various such advantages.

What is FinFET?

FINFET stands for Fin Field Effect Transistor it belongs to the FET family and it is a type of Multi gate MOSFET that is used in place of a common MOSFET. Unlike regular FETs which are planar in shape, FINFET is non-planar having a 3D structure. FINFET is built on the silicon substrate and the gate is surrounded by the channel forming drain and source. The name FINFET is derived from the fin of fish as the top view of FINFET drain and source appears like fin. Fin can also be defined as the channel between the drain and the source.
Like MOSFET, FINFET is also built on silicon on an insulator (SOI) It is also a three-terminal device forming gate, drain, and source, and the fabrication of FINFET is similar to MOSFET. FINFET and MOSFET work on the same principle.

Why use a FinFET device in place of MOSFET?

As to increase the number of transistors in a chip the size of transistor is to be reduced, the size of the transistor is reduced by decreasing the channel length between the drain and source, but as channel length decreases drain and source come close to each other and the problem of short channel effect arises in common MOSFETs and the leakage current increases between source and drain.

Short channel effect is when the width of depletion region between source and drain become approximately equals to channel length between drain and source.

Some of The problem that arise due to short channel effect are :

• Drain Induced barrier lowering (DIBL)
• Surface Scattering
• Velocity saturation
• Impact Ionization
• Hot Electron Effect

FinFET overcomes this problem of short channel effect because of its fins and gate surrounded by channel from three sides the fins increase the area covered by gate and increase the control of gate over the channel which reduces the leakage current and helps to reduce the channel length and size of transistor .

Basic Structure of FinFET

The basic structure of FinFET consist of 3D shaped Fin , gate , drain and source and substrate

• Fin : Name of FinFET is derived from this 3 D vertical shaped fin like structure that act as channel in FinFET . Fin is made of semiconductor material or silicon.
• Gate : Role of gate in FinFET is similar to common MOSFET.Fin of the FinFET surrounds the gate of FinFET and gate form 3 D structure , their can be more than one gate in FinFET . Gate is made up of metal . Gate is used to control the flow of electric current in channel .
• Drain and Source : Drain and source of FinFET plays similar role as in MOSFET . Current enter from source and drain and gate is used to control the current . Carriers in channel enter through source and exist from drain . As in MOSFET , In FinFET also drain is in high potential and source is in low potential.
• Substrate : Substrate of FinFET act a base for whole structure and it helps to isolate device in chips.

Basic Structure of FinFET

Computing FinFET Transistor Width

Width of transistor is denoted by w , w plays a crucial role in determining the current flowing through transistor , short – channel effect . width is also used to determine aspect ratio(w/l) which decide the design rule of transistor . For a double gate finFET w is equals to twice of FinFET effective height.

FinFET Dimensions

Here,

L= length of gate

T= thickness of Fin

H=height of fin

w= 2(H) for digate FinFET

w=(2(H)+T ) for trigate FinFET

Difference Between FinFET and MOSFET

FinFET and MOSFET belongs to the family of FET and following are the difference between and FinFET and MOSFET

MOSFET	FinFET
It is single gate device.	It is multi gate device.
MOSFET is planar in shape.	FinFET is non planar in shape having 3d structure fins.
It consume more power as compared to FinFET.	It consume less power as compared to MOSFET.
Switching speed is comparatively slower than FinFET.	Switching Speed faster than MOSFET.
More Leakage current.	Less leakage current than MOFSET.
Less parasitic capacitance and resistance.	More parasitic capacitance and resistance due to non-planar shape.
Less voltage gain.	More voltage gain.
Easy to fabricate and less costly.	Complex to fabricate and costly.

Planar MOSFET

FINFET

FINFET

Classification Of FinFET

FinFET Can be classified as following on the basic of –

1. Number of gates
2. Type of substrate

Classification Of FinFET on the basis of Number of Gates

On the basis of number of gates FinFET is of two types :

• Shorted gate FinFET (SG FinFET)
• Independent Gate FinFET (IG FinFET)

In shorted gate FinFET their is channel between front and back gate as it is sorted and in Independent gate FinFET their is no channel present between front and back gate both gate work independently ,they are not sorted.

Shorted Gate FinFET	Independent Gate FinFET
Front and back gate is shorted and connected to each other.	Front and back gate are not shorted and independent of each other.
It is 3 terminal device.	It is 4 terminal device.
It need less area.	It need more area.
We cannot externally control threshold voltage.	We can externally control threshold voltage.

Independent Gate FinFET

Shorted Gate FinFET

Shorted Gate FinFET

Classification Of FinFET on the basis of Type of Substrate

On the basic of type of substrate FINFET is of following two types

1. Bulk FinFET
2. SOI FinFET

The type of substrate means the type of base in FinFET .

Bulk FinFET : In Bulk FinFET the base of the FinFET is regular silicon wafer.

SOI FinFET : In SOI FinFET the base is made of Silicon on Insulator wafer.

Bulk FinFET	SOI FinFET
Easy to fabricate.	Complex to fabricate.
Due to impurities in channel it is tough to control performance parameter.	Easy to control performance parameter.
Isolation is done separately.	Between adjacent devices isolation is present.
High power consumption and high leakage current.	Less power consumption and less leakage current.
Less costly.	More costly.
Threshold and sub-threshold voltage Is not good.	Good threshold and sub-threshold voltage as compared to bulk FINFET.
High power consumption.	Low power consumption.

Bulk FinFET

SOI FinFET

SOI FinFET

Advantages of FinFET

• Less power consumption
• Less leakage current
• Short channel effect is less
• Less channel doping
• Higher scalability
• High voltage gain and good subthreshold voltage

Disadvantages of FinFET

• It is difficult to control dynamic threshold voltage.
• Due to 3d structure it have higher internal resistances and capacitances.
• Complex in fabrication and costly.
• Complex to design its structure.
• More Temperature sensitivity.
• More heat dissipation.
• Very high capacitances.

Application Of Fin FET

Fin FET is widely used in various applications due to its various advantages some of the applications of FinFET are listed below :

• IOT Devices such as smart wearables and smart gadgets.
• In Artificial and Machine learning devices.
• In Mobile phones , Laptops and smartphones.
• In medical Field.
• In defense and aerospace devices.
• In routers and switching devices.

Future Of FinFET

Introduction of FinFET have changed semiconductor industry a lot . As every coin have two face same with the future of FinFET it have lots of opportunities as well as lots of challenges in industry . In future FinFET will be scaled down to 5nm to 3 nm with more energy efficient but this will be costly .so researchers are exploring new ways and have developed Gate All Around Transistor (GAAFET) It have multiple gate around fins. It can be scaled down below 3 nm and have faster switching speed then FinFET .

Conclusion

FinFET is a great innovation in field of microelectronics which have helped in the solving the challenges of microelectronic and helped to reach semiconductor industry to a good extent . It not only helped to scale down size of transistor but also helped to improve electric current and use less energy consumption . It have increased the performance of transistor and due to its structure also reduced the leakage current . Despite of its complex fabrication and typical complexity in designing process it have been widely used in devices and have bring new turn in semiconductor industry innovations.

FAQs on FinFET

1. FINFET is voltage controlled or current controlled?

FINFET is voltage controlled device as like MOSFET.

2. What are the area where FINFETs are used widely ?

FINFETs are widely used in devices like Mobile phones , laptops , smart devices like smart watches etc.

3. Why is future of FINFET is not for long time ?

The future of FINFET is not for long time as its size cannot be reduced to less than 7 – 5 nm

4. What is the direction of flow of current in FINFET ?

Current can flow in both the direction , direction depend on the types of FINFET in n-type it flow from drain to source and source to drain in P-type.

5. Can FINFET have more than one fin in same structure?

Yes , FINFET can have 2 to 4 Fins in same structure.