What is a TFT LCD display ?

A TFT LCD (Thin-Film Transistor Liquid Crystal Display) is a type of liquid crystal display that uses thin-film transistor technology to enhance image quality and enable individual pixel control. Here's a detailed introduction:

Structure

• Glass Substrates2

  • TFT Glass Substrate Layer: The back-most layer of the circuit board, made of amorphous silicon deposited on glass. The TFTs in this layer are connected to each sub-pixel and control the voltage applied to them. There are also pixel electrodes between the substrate and the liquid crystal layer.

  • Surface Glass Substrate: On the surface, beneath this glass substrate is where the actual pixels and sub-pixels reside, forming the RGB color filter. This layer has counter (or common) electrodes on the side closer to the liquid crystals to close off the circuit between the two layers.

• Liquid Crystal Layer2: Sandwiched between the two glass substrates, the liquid crystal molecules can twist and align in response to electric fields, controlling the passage of light.

• Polarizers2: Filter layers on the outer sides of the glass substrates that allow only certain polarized light to pass through. If the light is not polarized correctly, it will not pass through the polarizer, resulting in an opaque screen.

• Color Filters4: Red, green, and blue color filters are placed over the sub-pixels to produce the full spectrum of colors, enabling the display to show a wide range of hues.

Working Principle

• Each pixel in a TFT LCD has its own transistor, which acts as a control valve to provide the appropriate voltage to the liquid crystal for each sub-pixel3. When a voltage is applied to the transistor, it controls the alignment of the liquid crystal molecules3.

• In the absence of an electric field, the liquid crystal molecules are in a 90-degree twisted pattern, allowing properly polarized light to pass through the surface polarizer in the display's "normal white" mode2.

• When an electric field is applied, the twist is broken as the crystals straighten out, and the passing light can no longer be polarized to pass through the surface polarizer, resulting in an opaque display. By adjusting the voltage, different degrees of crystal re-alignment can be achieved, allowing for different amounts of light to pass through and creating different shades of grey, known as the twisted nematic effect2.

Advantages

• High Resolution4: TFT LCDs can achieve high resolutions, enabling sharp and detailed images, which is crucial for applications such as high-definition televisions and computer monitors.

• Fast Response Time4: The individual control of pixels allows for quicker switching between different colors and states, reducing motion blur and making it suitable for displaying fast-moving images, such as in video games and action movies.

• Good Color Accuracy4: They provide excellent color accuracy, capable of reproducing a wide range of colors with high fidelity, making the visuals more vibrant and lifelike.

• Wide Viewing Angles4: Technologies like in-plane switching (IPS) have been developed to improve the viewing angles of TFT LCDs, allowing users to view the screen from various positions without significant loss of image quality.

Applications

• Televisions: TFT LCDs are widely used in modern televisions, offering high-definition and even 4K or 8K resolutions for a great viewing experience.

• Computer Monitors: They are the most common type of display for desktop computers and laptops, providing clear images and accurate colors for work and entertainment.

• Mobile Phones: TFT LCD screens are used in many smartphones, offering vibrant displays and support for touch screen technology.

• Tablets: Similar to mobile phones, tablets also utilize TFT LCDs to provide users with a good visual experience for reading, watching videos, and playing games.

• Video Game Systems: TFT LCDs are used in handheld game consoles and as monitors for home game consoles to display high-quality graphics.

Disadvantages

• Power Consumption: The backlight used in TFT LCDs consumes a significant amount of power, especially in larger displays. Although energy-saving technologies have been developed, it remains a concern compared to some other display technologies.

• Limited Contrast Ratio: Especially in displaying deep black colors, the contrast ratio of TFT LCDs may be limited compared to some other display technologies like OLED.

• Susceptibility to Image Burn-In: If a static image is displayed on the screen for a long time, there is a possibility of image burn-in, where the pixels may be damaged and leave a permanent imprint of the image.