What is FinFET? What are the pros and cons of FinFETs?

FinFET is a transistor design process that attempts to overcome the worst type of short-channel effects that transistors encounter, while enabling chips to achieve higher performance metrics at lower cost.

Throughout the history of integrated circuit design since the breakthrough in semiconductors, Moore's Law—that the number of transistors on a piece of silicon doubles every two years—has remained constant.

The number of transistors on today's advanced processors runs into the tens of billions, as foundries develop increasingly advanced process nodes to meet consumer demand. That's a far cry from the processors of the mid-1970s, which had only a few thousand transistors, which were state-of-the-art at the time.

One of the key technology trends driving the semiconductor industry and making today's chips possible is the adoption of FinFET processes. Another promising technology, is the gate-all-around (GAA) transistor. This provides the most significant capacitive coupling between gate and channel. The problem with the GAAfinFET is that it's only a temporary solution. It may only last a few decades. However, it's likely to be the future replacement for FinFETs, at least until someone comes up with an entirely new transistor architecture.

1. What is FinFET?

FinFET, known as Fin Field Effect Transistor, is a new type of Complementary Metal Oxide Semiconductor Transistor. The inventor of this technology is Professor Hu Zhengming of the University of California, Berkeley.

The main difference between FinFeT and planar MOSFET structure is that its channel is composed of tall and thin fins protruding from the insulating substrate. Auxiliary current control, this fin-shaped structure increases the surface of the gate around the channel and strengthens the control of the gate on the channel, which can effectively alleviate the short channel effect in planar devices, greatly improve circuit control and reduce leakage current , can also greatly shorten the gate length of the transistor, and because of this characteristic, FinFET does not need a highly doped channel, so it can effectively reduce the scattering effect of impurity ions and improve the carrier mobility of the channel.

The main feature of FinFET is that the channel region is a fin-shaped semiconductor surrounded by the gate.

The length of the fin along the source-drain direction is the channel length.

The gate-wrapped structure enhances the control ability of the gate and provides better electrical control over the channel, thereby reducing leakage current and suppressing short-channel effects.

3. Different Types of FinFETs

There are many kinds of FinFETs, and different FinFETs have different electrical characteristics.

The following will give an introduction according to the substrate type, the direction of the channel, the number of gates, and the structure of the gates. SOI FinFET and Bulk FinFET.

According to the FinFET substrate, FinFET can be divided into two types. One is SOI FinFET and the other is bulk FinFET.

FinFETs are formed on bulk silicon substrates. Due to the different manufacturing processes, bulk silicon substrates have the advantages of low defect density and low cost compared to SOI substrates.

In addition, due to the low thermal conductivity of the buried oxide layer in the SOI substrate, the heat dissipation performance of the bulk silicon substrate is also better than that of the SOI substrate.

Bulk FinFET, SOI FinFET has similar parasitic resistance and parasitic capacitance, so it can provide similar power performance at the circuit level. However, light fin-doped FinFETs on SOI substrates exhibit lower junction capacitance, higher mobility and electrical performance of voltage gain than Buk FinFETs.

3. FinFET and planar transistors (for example, MOSFET)

Designers choose to use FinFET devices instead of traditional planar transistors such as MOSFETs for a number of reasons.

Increasing computing power means increasing computing density. Of course more transistors are needed to achieve this, which results in a larger chip. However, for practical reasons, it's important to keep the area roughly the same.

One way to get more computing power is to shrink the size of the transistor, but as the size of the transistor shrinks, the distance between the drain and source shrinks the gate's ability to control the current flow in the channel region. Therefore, planar MOSFETs suffer from short-channel effects.

In short, FinFET devices exhibit superior short-channel behavior, shorter switching times, and higher current densities compared to conventional planar MOSFET technologies.

4. The advantages and disadvantages of FinFET

FinFETs have several key advantages over other transistor technologies that make them ideal for applications requiring higher power and performance:

(1) Better channel control;

(2) Inhibit the short channel effect;

(3) Faster switching speed;

(4) Higher drain current;

(5) Lower switching voltage;

(6) Lower power consumption.

Of course, there are also disadvantages. Some of their disadvantages include:

(1) The voltage threshold is difficult to control;

(2) The three-dimensional profile leads to higher parasitic effects;

(3) Very high capacitance;

(4) High cost.