How TFT LCD Works - explained

Liquid Crystal Displays (LCDs) have become ubiquitous in our daily lives, from smartphones to large televisions. At the heart of many modern displays lies a technology called Thin-Film Transistor Liquid Crystal Display (TFT LCD). This article demystifies the complex workings of TFT LCDs, explaining how they create the vibrant images we see on our screens.

Structure of TFT LCD

TFT is an abbreviation for "Thin Film Transistor". The color TFT LCD display has transistors made up of thin films of Amorphous silicon deposited on a glass. It serves as a control valve to provide an appropriate voltage onto liquid crystals for individual sub-pixels. That is why TFT LCD display is also called Active Matrix display.

1. Liquid Crystal Layer

The liquid crystal layer is the core of the TFT LCD, sandwiched between two sturdy glass plates. This layer contains liquid crystals—rod-shaped molecules capable of aligning in various directions when an electric field is applied. This alignment is crucial for the modulation of light that produces images on the screen.

2. TFTs (Thin-Film Transistors)

Behind each pixel lies a tiny thin-film transistor (TFT). These transistors function as switches, controlling the voltage applied to the liquid crystals. When a voltage signal is sent, the corresponding TFT turns on, allowing electric current to flow to the pixel, thus influencing the liquid crystal layer.

3. Pixel Electrodes

Transparent pixel electrodes are positioned to apply an electric field directly to the liquid crystals. The voltage applied to these electrodes is what determines how the liquid crystals orient themselves, directly impacting light modulation.

4. Color Filter

The color filter, situated above the liquid crystal layer, consists of red, green, and blue filters. These filters are essential for controlling the color of each pixel, enabling the display to produce a full spectrum of colors.

5. Backlight

An essential element behind the display is the backlight, a light source that illuminates the liquid crystals. This light provides the necessary brightness that allows us to see images and colors on the display.

The Working Mechanism of TFT LCDs

A TFT LCD has a liquid crystal layer between a glass substrate formed with TFTs and transparent pixel electrodes and another glass substrate with a color filter (RGB) and transparent counter electrodes. Each pixel in an active matrix is paired with a transistor that includes capacitor which gives each sub-pixel the ability to retain its charge, instead of requiring an electrical charge sent each time it needed to be changed. This means that TFT LCD displays are more responsive.

TFT LCD Driving Principal

To understand how TFT LCD works, we first need to grasp the concept of field-effect transistor (FET). FET  is a type of transistor which uses electric field to control the flow of electrical current. It is a component with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.

Using FET, we can build a circuit as below. Data Bus sends signal to FET Source, when SEL SIGNAL applies voltage to the Gate, driving voltage is then created on TFT LCD panel. A sub-pixel will be lit up. A TFT LCD display contains thousand or million of such driving circuits.

Voltage Application

When the display receives a signal, the TFTs switch on and apply a voltage to the pixel electrodes. This voltage causes the liquid crystals to align in a specific direction, preparing them for light modulation.

Light Modulation

As light passes through the aligned liquid crystals, their orientation twists the light's polarization. The degree to which the light passes through depends on how the liquid crystals are positioned, effectively controlling the brightness and clarity of the image produced.

Color Filtering

Once the light has been modulated by the liquid crystals, it encounters the color filter. This filter allows only light of specific colors—red, green, or blue—to pass through, determining the final color of each pixel.

Image Formation

Finally, the combined effect of aligned liquid crystals, colored filters, and backlight culminates in the creation of vibrant images on the display. This intricate process allows TFT LCDs to produce high-quality visuals with rich colors and sharp details.

Key Advantages of TFT LCDs

• High Resolution: TFT LCDs are capable of displaying high-resolution images, making them ideal for everything from detailed graphics to intricate designs.
• Fast Response Times: These monitors refresh quickly, which is especially advantageous for displaying fast-moving content like videos and games.
• Wide Viewing Angles: TFT LCDs allow viewers to see images clearly from various angles without significant color distortion.
• Low Power Consumption: This technology is designed to be energy-efficient, extending the longevity and sustainability of devices.

Conclusion

TFT LCD technology is a fascinating synthesis of liquid crystals, thin-film transistors, and color filters that work together to deliver high-quality imagery. Its ability to produce sharp, vibrant images has transformed how we consume digital content, making it a crucial technology in almost all modern displays. Understanding the components and working of TFT LCDs not only enhances our appreciation of this technology but also highlights the complexity behind the screens we often take for granted.

Topway started TFT LCD manufacturing more than15 years ago. We produce color TFT LCD display from 1.8 to 21+ inches with different resolutions and interfaces. Here is some more readings about how to choose the right TFT LCD.