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TFT LCD (Thin Film Transistor Liquid Crystal Display) is a display technology based on the properties of liquid crystal materials and thin film transistor technology. Its basic definitions and working principles are as follows:
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Basic Definition and Structure
TFT LCD is an active matrix liquid crystal display that controls the arrangement of liquid crystal molecules by integrating thin film transistors (TFT) at each pixel point, thereby modulating light and displaying images. This display consists of multiple layers, including a glass substrate, liquid crystal layer, color filter layer, and backlight source.
The basic structure of a typical TFT-LCD display is shown in Figure 1, where a layer of liquid crystal material is sandwiched between two glass substrates, forming a parallel plate capacitor. The upper glass substrate is attached with a color filter, while the lower glass substrate has thin film transistors embedded in it. The optical polarization directions of the two polarizing plates are perpendicular to each other, with a phase difference of 90°. The liquid crystal layer is sandwiched between the two glass plates; under the influence of an electric field, the liquid crystal molecules change their arrangement direction, thereby controlling the light transmission.
Figure 1: Schematic Diagram of TFT-LCD Display Structure
Working Principle
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Since liquid crystal displays are not self-emitting devices, a backlight illumination module is required beneath the panel to provide a basic light source. The light emitted by the backlight passes through the lower polarizer into the liquid crystal layer, enabling image display. The liquid crystal molecules change their arrangement direction according to the applied voltage, controlling the polarization state of the light, allowing it to possess or not possess optical activity. The POL in the basic structure of TFT-LCD is used to adjust light coming from a certain direction and filter out light from other directions. The light adjusted by POL, after being deflected by the liquid crystal molecules, can control the brightness of the emitted light, thus achieving brightness adjustment of the TFT-LCD display. Figure 2 shows the working principle diagram of TFT-LCD. The driving core of the liquid crystal display mainly lies in the correlation between voltage and transmittance. Due to the dielectric anisotropy of the liquid crystal molecules, they will align in the same direction in an electric field. The arrangement of the liquid crystal molecules is also controlled by the liquid crystal capacitor, which is formed by preparing a conductive ITO layer on the TFT array substrate and the CF color film substrate. The TFT switching array is located on the TFT array substrate and acts as a switching element, controlling the current flow through gate voltage, adjusting the arrangement of liquid crystal molecules, and achieving grayscale display and color control. On the CF color film substrate, the pixels are divided into three sub-pixels (RGB), corresponding to red, green, and blue. The liquid crystal molecules, acting as light valves, adjust the brightness of the three sub-pixels to achieve color display.
Figure 2: Working Principle Diagram of TFT-LCD
TFT LCD adopts a matrix driving method, sending signals to each pixel through scanning lines and data lines, achieving precise point-to-point control.TFT LCD features high resolution, fast response time, vibrant colors, and high contrast, making it suitable for various devices such as televisions, computer monitors, and smartphones.
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Main Components and Their Functions
The main components of TFT LCD include:
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Liquid Crystal Layer: The layer of liquid crystal molecules is the core part of image display, achieving image display by controlling its arrangement state.
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Polarizers: Used to control the polarization direction of light, typically divided into upper and lower layers.
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Color Filter (CF): Provides the three primary colors of red, green, and blue, giving color to the image.
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TFT Substrate: Contains thin film transistors (TFT) used to control the voltage signals of pixel electrodes.
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Glass Substrate: Serves as a supporting structure, typically divided into upper and lower layers.
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Backlight Source: Provides the light source, commonly LED backlight and CCFL backlight.
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Diffuser and Light Guide Plate: Used to evenly distribute light, improving brightness and uniformity.
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Driver Circuit Unit: Includes row driver ICs, column driver ICs, etc., used to control the switching of the TFT array.
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Protective Layer and Sealing Frame: Protects the liquid crystal layer and prevents dust from entering.
These components work together to enable TFT LCD to achieve clear, high-contrast image display.
TFT LCD converts electrical signals into optical modulation through a multi-layer precision structure (backlight, polarization, TFT, liquid crystal, filter) and electronic drive. Its core technology encompasses materials science, microelectronics, and optical engineering. With breakthroughs in technologies such as Mini LED and oxide semiconductors, TFT LCD continues to evolve in resolution, energy efficiency, and form factor, remaining a mainstream solution in the medium to large display market.
Some data sources:
1. ESP-IoT-Solution User Guide. Espressif Technology. [2025-02-10]2. Driving and Design of TFT LCD Panels [2023-01-01]3. Breakthroughs in Mini LED Mass Production Technology, Supporting LCD Display Upgrades. Sun Can. [2020-04-19]4. Experiences with TFT LCD. Wang Guoqiang. [2006-08-06]5. Introduction to Flat Panel Displays (2) Liquid Crystal Displays: LCD. Engineering Doctor, et al. [2010-04-15]6. THE CHEMICAL TIMES. Tsurukai, et al. [2010-04-30]7. Working Principle of Thin Film Transistor Liquid Crystal Display [2024-08-12]
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