What Is a TFT LCD?
A Thin-Film Transistor Liquid Crystal Display (TFT LCD) is a liquid crystal display that utilizes thin-film transistors.
Widely employed in various electronic devices such as laptops and smartphones, it stands as a major choice in display technology. By utilizing thin-film transistors (TFT), it can control a large number of pixels, making it suitable for color displays that require higher pixel counts compared to monochrome displays.
Moreover, when combined with a touch panel, TFT LCDs can incorporate intuitive controls such as touch input and gesture input.
Uses of TFT LCD
TFT LCDs have been adopted in numerous applications due to their high resolution and color capabilities. Broadly categorized into consumer applications, sold as finished products, and industrial applications, sold as business-to-business (BtoB) products or embedded components, here are some key uses of TFT LCDs:
1. Consumer Applications (Products)
Used in products available for purchase by general consumers, such as smartphones, televisions, PCs, and car navigation systems. Particularly in high-end smartphone models, TFT LCDs with high resolution and brightness, incorporating the latest technology, are commonly used, making them the most cutting-edge display devices accessible to the general public.
2. Industrial Applications (Products)
In everyday products, they are used in devices like convenience store coffee machines, ATMs, and in-flight entertainment systems on aircraft. In less visible products, TFT LCDs are used in BtoB product displays for medical equipment, measuring instruments, production facilities, and more.
3. Industrial Applications (Components)
TFT LCDs are used in the production of consumer and industrial products as embedded components. Referred to as TFT LCD modules or TFT modules, these come in various types, ranging from ultra-small ones of less than 1 inch used in smart glasses to products exceeding 60 inches used in large TVs and digital signage. The most common application is for smartphones, accounting for approximately half of the worldwide shipment volume.
Principle of TFT LCD
The principle of TFT LCD is based on two main elements: liquid crystal and thin-film transistors (TFT).
1. Liquid Crystal
Liquid crystal is one of the states of matter that appears as an intermediate phase between liquid and solid (crystal). In some liquid crystals, applying voltage causes a change in the orientation of liquid crystal molecules, altering their optical properties. In a liquid crystal display, this change in optical properties, induced by applying voltage, is combined with a polarizing plate to control the transmission or blocking of light for each pixel.
2. Thin-Film Transistor (TFT)
The control methods for dot matrix-type liquid crystal displays, where pixels are arranged in a grid pattern, include passive matrix and active matrix methods. However, for liquid crystal displays with a high pixel count, the active matrix method is generally adopted.
In the active matrix method, at the intersections of scan lines (gate lines) and data lines (source lines), there are active elements, capacitors, and pixel electrodes arranged for each pixel. Typically, thin-film transistors (TFT) are used as active elements in the active matrix method, leading to displays being referred to as TFT LCDs.
Control of the applied voltage to pixels is achieved by sequentially scanning the gate lines to control the gate voltage and by controlling the ON/OFF between the source and drain of the pixel using the data lines. Even after the TFT is turned OFF, the state of the pixel is maintained until the next scan due to the charge stored in the capacitor.
How to Choose TFT LCD
When selecting TFT LCDs, several important factors need to be considered. Here are some examples of selection criteria:
1. Screen Size
Screen size is expressed in inches as the diagonal length of the display area, such as 2.4 inches or 10.1 inches. Even with similar inch sizes, the length of the sides may differ depending on the aspect ratio of the display. Therefore, confirmation of module dimensions and display area dimensions is necessary.
2. Resolution
Resolution refers to the number of pixels on the screen, expressed in terms of VESA standards like “QVGA,” common names like “4K,” or specific pixel counts like “800×600” or “1920×1080.” The combinations of available screen sizes and resolutions are somewhat limited, and generally, larger screen sizes have higher resolutions.
3. Type of LCD Panel
Usually, relatively small LCD panels up to around 15 inches use TN or IPS-type LCD panels. IPS-type LCD panels have a wider viewing angle compared to TN types.
4. Touch Panel
Touch panels are broadly divided into capacitive and resistive types. Capacitive touch panels are used in smartphones, while resistive touch panels are used in ATMs. The choice of whether to have a touch panel and the type depends on the application.
5. Interface
Commonly used video signal input interfaces include RGB, SPI, MIPI, LVDS, etc. When using a touch panel, consideration must also be given to its interface.
Even with identical specifications, the appearance of display devices may differ. Therefore, it is essential to physically confirm the display during the selection process.