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What Is A TFT-LCD (thin Film Transistor Liquid Crystal Display)?

Views: 335     Author: Reshine Display     Publish Time: 2023-11-30      Origin: Site

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What Is A TFT-LCD (thin Film Transistor Liquid Crystal Display)?

TFT-LCDs (thin-film transistor liquid crystal displays) are one of the most common types of liquid crystal displays that use thin-film transistor technology to improve image quality. Although TFT-LCD is commonly referred to as LCD, it is an active matrix LCD found in televisions, flat panel displays, and projectors.


Simply put, a TFT-LCD screen is two pieces of glass substrate sandwiched between a layer of liquid crystals, with the upper layer of glass substrate containing color filters (ColorFilter) and the lower layer containing a transistor embedded in the upper. When the current flowing through the transistor causes changes in the electric field, causing the liquid crystal molecules to deflect, the polarization of the light changes and the brightness of the pixel (Pixel) state is determined. Furthermore, the upper layer of glass and color filters are formed by the paste, resulting in the formation of each pixel (Pixel) containing red, blue, and green colors, and these pixels emit red, blue, and green colors, which comprise the image of the skin screen.


The abbreviation for Thin Film Transistor-Liquid Crystal Display (TFT-LCD) is Thin Film Transistor-Liquid Crystal Display (TFT-LCD). TFT-LCD (Thin Film Transistor-Liquid Crystal Display) technology is a deft combination of microelectronics and liquid crystal display technology. Single crystal on the microelectronic fine processing technology, transplanted to a large area of glass on the thin film transistor (TFT) array processing, and then the array substrate and another piece of substrate with a color filter film, the use of mature liquid crystal display (LCD) technology, the formation of a liquid crystal box, and finally formed a liquid crystal display d


1. Operation principle

TFT-LCD (thin film transistor liquid crystal display, film transistor liquid crystal display) is a type of liquid crystal display that improves image quality by utilizing thin film transistor technology. Although TFT-LCD is collectively referred to as LCD, it is an active matrix LCD, which is used in TVs, flat panel displays, and projectors.


Simply put, TFT-LCD skin can be regarded as two pieces of glass substrate sandwiched in the middle of a layer of liquid crystal, the upper layer of glass substrate has color filters (Color Filter), and the lower layer of glass has a transistor embedded in the upper. When the electric current passes through the transistor, the electric field changes, causing the liquid crystal molecules to deflect, change the polarization of the light, and then use the polarizer to determine the brightness of the pixel (Pixel). In addition, the upper glass layer is laminated with color filters, resulting in each pixel containing red, blue, and green colors, and these pixels emit red, blue, and green colors to form the image on the skin.


A typical LCD monitor is similar to a calculator's display panel in that the image elements are directly driven by voltage; controlling one unit does not affect the others. When the number of pixels increases to enormous numbers, such as millions, this approach becomes impractical, because each pixel must have individual connecting wires for each color of red, green, and blue. To avoid this quandary, arrange the pixels in rows and columns, which reduces the number of connections to thousands. If all pixels in a column are driven by a positive potential and all pixels in a row are driven by a negative potential, the pixels at the intersection of the rows and columns will have the maximum voltage and will be switched state. However, there is still a problem with this method in that other pixels in the same row or column are only partially energized, but this partial switching can still cause the pixels to be dimmed (in the case of an LCD that doesn't switch to bright). The solution is to add a transistor switch to each pixel that belongs to it so that each pixel can be controlled independently. The low leakage current characteristic of the transistor means that the voltage applied to the pixel is not arbitrarily lost before the picture is updated. Each pixel is a small capacitor with a transparent Indium Tin Oxide (ITO) layer on the front, a transparent layer on the back, and an insulating liquid crystal.


This circuit arrangement is very similar to dynamic access memory, except that instead of being built on a silicon wafer, the entire architecture is built on glass. Many silicon wafer process technologies require temperatures that exceed the melting point of glass. The silicon substrate for unusual semiconductors utilizes liquid silicon to grow very large single crystals with the good qualities of transistors. The silicon layer used in thin film transistor liquid crystal displays is an amorphous silicon layer or a polycrystalline silicon layer created using silicide gas, and this manufacturing method is less suitable for making high-grade transistors.


2. TN liquid crystal

TN+film (Twisted Nematic + film) is the most common type, mainly due to the low price and variety of products. In modern TN-type panels, the pixel response time has been fast enough to significantly reduce the problem of ghosting, and even in the specifications of the response time has been very fast, but this traditional response time is a standard set by the ISO, which only defines the conversion time from all black to all white, but does not mean that it is the conversion time between gray levels. The transition time between gray levels (which is the more frequent transition of usual LCDs) is longer than that defined by ISO. The RTC-OD (Response Time Compensation-Overdrive) technology now in use allows manufacturers to effectively reduce the transition time between different grays (G2G), however, the ISO-defined response time has not changed. Response times are now expressed in G2G (Gray To Gray) numbers, such as 4ms and 2ms, and have become commonplace in TN+Film products. This market strategy, with the lower cost of TN panels compared to the VA type, has been dominating the direction of TN in the consumer market.


TN-type displays suffer from viewing angle limitations, especially in the vertical direction, and most of them are unable to display the 16.7 million colors (24-bit true colors) output by current graphics cards. In particular, the RGB tri-color uses 6 bits as 8 bits, and it uses downscaling by combining neighboring pixels to approximate 24-bit color to simulate the desired grayscale. FRC (Frame Rate Control) is also used. For LCDs, the actual penetration rate of a pixel generally does not vary linearly with the applied voltage. In addition, B-TN (Best TN) was developed by Samsung Electronics. It improves TN color and response time.


3. Super-twisted nematic display

Super-twisted nematic display (STN) is the abbreviation of super-twisted nematic display. after the invention of TN liquid crystal, people naturally thought of matrixing the TN liquid crystal to display complex graphics. In contrast to the 90-degree twist of TN liquid crystals, STN liquid crystals can be twisted 180 degrees to 270 degrees, and in the early 1990s, color STN liquid crystals were introduced, which consist of three liquid crystal units in a pixel, coated with a layer of color filters, and the color can be produced by controlling the brightness of the liquid crystal units with a voltage respectively.


4. VA Liquid Crystal

CPA (Continuous Pinwheel Alignment) was developed by Sharp. High color reproduction, low production, and expensive.

MVA (Multi-domain Vertical Alignment) was developed by Fujitsu in 1998 as a compromise between TN and IPS. At the time, it offered fast pixel response, wide viewing angles, and high contrast, but at the expense of brightness and color reproduction. Analysts predicted that MVA technology would dominate the mainstream market, but TN had the advantage. This is mainly due to the higher cost of MVA and the slower pixel response (which increases dramatically when brightness changes).


P-MVA (Premium MVA) was developed by AUO to improve the viewing angle and response time of MVA.

A-MVA (Advanced MVA) developed by AUO.

S-MVA (Super MVA) was developed by Chi Mei Optoelectronics.

PVA (Patterned Vertical Alignment) was developed by Samsung Electronics, and although the company claims that it is the best contrast technology available, it suffers from the same problems as MVA.

S-PVA (Super PVA) was developed by Samsung Electronics to improve the viewing angle and response time of PVA.

C-PVA was developed by Samsung Electronics.


5. Horizontal Field Effect Display Technology

IPS (In-Plane Switching) was developed by Hitachi in 1996 to improve the poor viewing angle and color reproduction of TN-type panels. This improvement has increased the response time, which is initially 50ms, and the cost of IPS-type panels is also extremely expensive.

S-IPS (Super IPS) has the advantages of IPS technology but also improves the pixel update time. The color reproduction is closer to CRTs and the price is lower, however, the contrast is still very poor and S-IPS is currently only used in larger displays for professional purposes.


6. Super PLS

Samsung Electronics developed PLS (Plane to Line Switching), which, in addition to having an amazing viewing angle, can improve the display's brightness by up to 10%. Its manufacturing costs are also 15% lower than those of IPS, and it currently offers a resolution of up to WXGA (1280 x 800). The MacBook Pro with Retina display, which has a resolution of up to 2880 x 1800, is also partially used in Samsung's production of this display; the remaining portion uses IPS. The primary application for this object is in smartphones and tablet PCs; it went into mass production in 2011.

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