What is TFT LCD?

April 24, 2023
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A thin-film-transistor liquid-crystal display (TFT LCD) is a variant of a liquid-crystal display that uses thin-film-transistor technology to improve image qualities such as addressability and contrast.

 

TFT LCD is an active matrix LCD, in contrast to passive-matrix LCDs or simple, direct-driven (with segments directly connected to electronics outside the LCD) LCDs with a few segments.

 

It has the advantages of small size, lightweight, low power, full color, etc.

 

Structure of TFT LCD

 

TFT LCD is a type of flat panel display that uses thin-film transistor technology to control the alignment of liquid crystal molecules to produce images.

 

The structure of TFT LCD can be divided into several layers.

  • Upper polarize
  • Glass substrate
  • Color filter (CF)
  • Liquid crystal layer (LCD)
  • Thin-film transistor (TFT) substrate layer
  • Lower polarizer
  • Backlight

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The structure of TFT LCD is complex, and each layer plays an important role in producing high-quality images.

 

The backlight provides the light source, while the polarizers help to control the polarization of the light.

 

The color filter and liquid crystal layer work together to produce color images, and the TFT layer controls the voltage applied to each pixel.

How does TFT LCD Display work?

 

The working principle of TFT LCD is to use liquid crystal molecules to change their orientation under the action of an electric field to control the transmission and blocking of light.

 

The liquid crystal layer is sandwiched between two parallel glass substrates that are coated with transparent electrodes.

 

When no electric field is applied, the liquid crystal molecules are randomly oriented, and light passing through the display is not affected.

 

However, when an electric field is applied to the liquid crystal layer, the molecules align themselves along the direction of the electric field.

This alignment causes the polarization of light passing through the display to be rotated or blocked, depending on the orientation of the liquid crystal molecules.

 

The color filter is placed on top of the glass substrate and consists of red, green, and blue filters. For example, a 4.3-inch 480x272 TFT LCD (HG043HV008) has 480x3x272 dots (sub-pixel),

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Each pixel on the display has three sub-pixels, one for each primary color.

 

By controlling the electric field applied to each subpixel, the intensity of each color can be adjusted independently, allowing full-color images to be displayed.

 

Classification of TFT LCD

 

According to the material technology of TFT, it can be divided into the following five categories:

a-Si TFT LCD

a-Si (amorphous silicon) TFT LCD is the first commercialized TFT technology.

 

Due to the advantages of a simple manufacturing process, good stability, and low cost.

 

They are widely used in electronic displays, such as computer monitors, TVs, mobile phones, PDAs, etc.

 

LTPS TFT LCD

LTPS (Low-Temperature Polysilicon) TFT LCD is a new type of thin-film transistor technology.

 

It is manufactured using low-temperature polysilicon technology and has the advantages of high resolution, high response speed, and low power consumption.

 

They are widely used in high-end mobile devices, such as smartphones, tablets, etc.

IGZO TFT LCD

 

IGZO (Indium Gallium Zinc Oxide) TFT LCD is a new type of thin-film transistor technology.

 

It is manufactured using oxide semiconductor materials and has the advantages of high transparency, low power consumption, high response speed, etc.

 

They are widely used in laptop displays, flat-panel TVs, etc.

 

Oxide TFT LCD

 

Oxide TFT is a new type of thin-film transistor technology.

 

It is manufactured using oxide semiconductor materials and has the advantages of high transparency, high resolution, high response speed, etc.

 

They are widely used in display screens and electronic paper.

 

Microcrystalline TFT LCD

 

Microcrystalline TFT is a new type of thin-film transistor technology.

 

It is manufactured using microcrystalline silicon materials and has the advantages of high resolution, high brightness, low power consumption, etc. It is widely used in flat-panel TVs, projectors, etc.

 

Type of LCDs

 

Based on their physical structure, TFT LCDs can be divided into four types

 

Twisted Nematic (TN) LCDs

 

TN LCDs are the most common type of LCDs.

 

They consist of a layer of liquid crystal material sandwiched between two polarizing filters.

 

The liquid crystal material is twisted at a certain angle between the two polarizers, and the orientation of the liquid crystal molecules can be controlled by applying an electric field to the material.

 

This causes the polarization of light passing through the display to be rotated, allowing the display of images.

 

In-Plane Switching (IPS) LCDs

 

IPS LCDs use a different structure than TN LCDs.

 

They have two glass substrates with transparent electrodes and a layer of liquid crystal material between them.

 

The liquid crystal molecules in IPS LCDs are aligned parallel to the substrate, and the orientation of the molecules can be controlled by applying an electric field.

 

IPS LCDs have wider viewing angles and better color reproduction than TN LCDs.

 

Vertical Alignment (VA) LCDs:

 

VA LCDs also use a layer of liquid crystal material between two glass substrates with transparent electrodes.

 

In VA LCDs, the liquid crystal molecules are oriented perpendicular to the substrate when no electric field is applied.

 

When an electric field is applied, the molecules rotate and align themselves parallel to the substrate.

 

VA LCDs have higher contrast ratios than TN and IPS LCDs.

 

Related: TN vs. IPS vs. VA: What's the Best LCD Display Technology?

 

The most common interface types of TFT LCD

 

TFT LCDs typically use one of several interface types to communicate with the host system. The most common interface types are:

 

  • LVDS (Low-Voltage Differential Signaling)

  • MIPI (Mobile Industry Processor Interface)

  • RGB (Red, Green, Blue)

  • DVI (Digital Visual Interface)

  • HDMI (High-Definition Multimedia Interface)

  • SPI (Serial Peripheral Interface)

 

Related: What type of interface is TFT LCD?

 

 

The choice of interface type depends on factors such as the required data transfer rate, the complexity of the host system, and the power consumption of the interface.

 

Each interface type has its own advantages and disadvantages, and the appropriate interface type should be selected based on the specific application requirements.

 

Conclusion

 

At this stage, with the development of the display panel technology and product iterations, the LCD industry has matured and become the mainstream of the market.

 

Nowadays, TFT LCD can be found everywhere, from industrial control panels to ATMs, medical devices, and consumer electronics.

 

They have revolutionized the way we interact with technology and have become an essential part of our everyday lives.

 

Therefore, when choosing an LCD monitor, the most suitable technology should be selected according to the specific application requirements and budget.


If you want to know more about the TFT LCDs, feel free to contact our engineer term.