How Do I Choose the Best Flat Panel Monitor?

^[1] TFT (Thin Film Transistor) is a thin film field effect transistor. The so-called thin film transistor means that each liquid crystal pixel point on a liquid crystal display is driven by a thin film transistor integrated behind it. Thus, high-speed, high-brightness, and high-contrast display screen information can be achieved. TFT belongs to active matrix liquid crystal display.

TFT LCD display

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TFT-LCD liquid crystal display ^[2]

(1) How does TFT work? TFT is the abbreviation of "Thin Film Transistor", which generally refers to a thin film liquid crystal display, but actually refers to a thin film transistor (matrix)-it can "actively" control each independent on the screen. The pixels are controlled, which is the origin of the so-called active matrix TFT. So how exactly is the image produced? The basic principle is simple: the display screen consists of many pixels that can emit light of any color, as long as each pixel is controlled to display the corresponding color to achieve the purpose. Backlight technology is generally used in TFT LCDs. In order to accurately control the color and brightness of each pixel, a shutter-like switch is required behind each pixel. When the "louver" is opened, light can pass through, and When the blinds are closed, light cannot pass through. Of course, it's actually not technically as easy to implement as just said. LCD (Liquid Crystal Display) uses the characteristics of liquid crystal (liquid when heated and crystallizes to solid when cooled). Generally, liquid crystal has three forms:

Clay-like Smectic LCD

Nematic liquid crystal resembling a thin matchstick

Cholesteric liquid crystal

The liquid crystal display uses a filament shape. When the external environment changes, its molecular structure will also change, so it has different physical characteristics-it can achieve the purpose of letting light pass or block it-that is, just like the shutters.

Everyone knows the three primary colors, so each pixel on the display screen needs to be composed of three similar basic components described above, which control the three colors of red, green, and blue, respectively.

The most commonly used currently is Twisted Nematic TFT LCD. The following figure explains the working principle of this type of TFT display. Existing technologies vary widely, and we will cover them in detail in the second part of this article.

There are grooves on the upper and lower layers. The grooves on the upper layer are arranged vertically and the lower layers are arranged horizontally. When the non-voltage applied liquid crystal is in a natural state, the light emitted from the light-emitting layer 2a twisted nematic TFT display working schematic diagram passes through the interlayer, and then it will be twisted at 90 degrees, so that it can pass through the lower layer smoothly.

When a voltage is applied between the two layers, an electric field is generated, and the liquid crystals are aligned vertically, so the light does not twist-the result is that the light cannot pass through the lower layer.

(2) TFT pixel architecture: color filters are divided into three types: red, green, and blue according to color, which are arranged on a glass substrate in order to form a group (dot pitch) corresponding to each pixel. Each monochrome filter is called Is a sub-pixel. That is, if a TFT display supports a maximum resolution of 1280 × 1024, then at least 1280 × 3 × 1024 sub-pixels and transistors are required. For a 15-inch TFT display (1024 x 768), a pixel is approximately 0.0188 inches (equivalent to 0.30 mm), and for a 18.1-inch TFT display (1280 x 1024), it is 0.011 inches (equivalent to 0.28 mm). .

Everyone knows that the pixels are decisive for the display. The smaller the size of each pixel, the larger the maximum resolution that the display can achieve. However, due to the limitation of the physical characteristics of the transistor, the size of each pixel of the TFT at this stage is basically 0.0117 inches (0.297mm), so for a 15-inch display, the maximum resolution is only 1280 × 1024. ^[1]

TFT liquid crystal displays are characterized by good brightness, high contrast, strong layering, and bright colors, but they also have disadvantages of relatively high power consumption and high cost. TFT LCD technology has accelerated the development of mobile phone color screens. Many of the new-generation color screen mobile phones support 65536 color displays, and some even support 160,000 color displays. At this time, the high contrast of TFT and the advantages of rich colors are very important.

Technical characteristics

TFT technology was developed in the 1990s. It is a large-scale semiconductor all-integrated circuit manufacturing technology using new materials and processes. It is used in liquid crystal (LC), inorganic and organic thin-film electroluminescence (EL and OEL) flat panel displays. basis. TFT is a non-single wafer (such as glass or plastic substrate) (of course, it can also be on the wafer) through sputtering, chemical deposition process to form various films necessary for circuit manufacturing, processing of the film to produce large-scale semiconductor integrated circuits (LSIC) . The use of non-single crystal substrates can greatly reduce costs, which is an extension of traditional large-scale integrated circuits to large-area, multi-functional, and low-cost directions. Fabrication of control pixels (LC or

International technology level and status

TFT-LCD technology has matured, and three major problems that have long plagued LCD flat panel displays: viewing angle, color saturation, and brightness have been resolved. Multi-area vertical alignment mode (MVA mode) and in-plane switching mode (

The main components of a TFT-type liquid crystal display include: a fluorescent tube, a light guide plate, a polarizing plate, a filter plate, a glass substrate, an alignment film, a liquid crystal material, a thin-mode transistor, and the like.

Entering the new millennium, as an important part of the information industry-display devices are accelerating the process of flattening. The world has entered the "information revolution" era. Display technology and display devices have occupied a very important position in the development of information technology. Televisions, computers, mobile phones, BP machines, PDAs and other portable devices and various instruments and meters The display provides a lot of information for people's daily life and work. Without the display, there would not be the rapid development of information technology today. The display integrates electronics, communication and information processing technology, which is considered to be another major development opportunity for the electronics industry after microelectronics and computers in the 20th century.

The development of science and technology is changing with each passing day, and display technology is undergoing a revolution, especially since the 1990s, with the breakthrough of technology and the sharp increase in market demand, the flat panel display (FPD) technology represented by liquid crystal display (LCD) rise rapidly. According to Stanford's forecast, the FPD market size is growing at an annual growth rate of 16.2%. By 2000, the FPD and CRT industries have reached 30 billion U.S. dollars, and the average annual growth rate of CRT is less than 6.3%, which is much lower than the average growth rate of FED. Rate, and the FPD growth rate continues to increase, CRT continues to decline, the replacement trend is very clear, it can be said that flat panel display will become the mainstream of display technology in the 21st century, and its industry and market are constantly expanding.

After more than 20 years of research, competition, and development, flat panel displays have entered the role and become the mainstream products of the new century display. At present, the most competitive flat panel displays have four varieties:

1. Field emission flat panel display (FED);

2. Plasma flat panel display (PDP);

3. Organic thin film electroluminescence device (OLED);

4. Thin film transistor liquid crystal display (TFT-LCD).

The principle of field emission flat panel display is similar to CRT. CRT only has one to three electron guns, up to six, while field emission display adopts electron gun array (electron emission micro-tip array, such as diamond film tip cone) with a resolution of VGA (640 × 480 × 3) display requires 921,600 electron emission microtips with uniform performance, and the material technology needs to be broken through. It is understood that the United States and France have a small batch of small-size display production for defense military industry, which is far from industrialization and commercialization.

Plasma light-emitting display is formed by exciting the light-emitting material in the cavity with a plasma discharge in a tiny vacuum discharge cavity. Its low luminous effect and large power consumption are its disadvantages (only 1.2lm / W, and the luminous efficiency of the lamp is 80lm / Above W, 6 watts per square inch display area), but has a strong competitive advantage in the large screen display field with a diagonal of 102-152 cm. Analysis by industry experts believes that CRT, LCD and digital micro mirror (DMD) three types of projection displays can compete with PDP. From the current large-screen TV market, CRT projection TVs are cheaper than PDPs and are the most powerful competitors of PDPs. However, the brightness and sharpness are not as good as those of PDP, LCD and DMD projection pixels and prices are still lacking competitive advantages at this stage. Although the color PDP has improved significantly in terms of image quality, display area, and capacity, its luminous efficiency, luminous brightness, and contrast have not reached the requirements of intuitive color televisions. The most important thing is that its price cannot be used by the majority of households. Accepted by consumers, this restricts the color PDP market expansion to a certain extent. At this stage, it is mainly used in public media.

Due to the successful development of GaN blue light-emitting diodes, the display scheme of semiconductor light-emitting diodes (LEDs) has gained absolute control of the ultra-large-screen video display market in one fell swoop. There is no market for it.

Experts in the display industry have long expected that organic thin-film electroluminescent materials will provide a display that is truly as thin as paper. Organic thin film electroluminescence is a solid, flat panel display that is light and thin, low power consumption, wide viewing angle, and high response speed (subtle subtle). The cost of large-scale industrial production is very low, and the service life at this stage is only a few thousand hours. OLED will first be used as the main competitor of TFT-LCD in the foreseeable future, but it is still in the research and trial stage at this stage.

Liquid crystal flat-panel displays, especially TFT-LCDs, are the only display devices that currently fully surpass and surpass CRTs in comprehensive performance such as brightness, contrast, power consumption, life, volume, and weight. With a high degree of automation, low raw material costs, and broad development space, it will quickly become the mainstream product in the new century and a bright spot in global economic growth in the 21st century.