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Title: The Development of FPD Industry Rely on New Technologies

 

In the early days of computing, the monitors used to display data used cathode-ray tube (CRT) technology. In essence, CRT displays are TV sets modified to work with computer video outputs. Starting in the mid-1990s, the flat-screen monitors that are now so common began to replace CRT technology. These newer displays use thin-film transistor (TFT) technology. They offer substantial advantages in terms of power consumption, size and weight. TFT technology is most commonly found in computer monitors, laptop displays and LCD television sets. Increasingly, it is being used in portable DVD players, cash register displays and even automatic teller machines (ATMs).

Organic Light Emitting Diodes(OLED)

One of the most promising display technologies to come along in the past 25 years are Organic Light Emitting Diodes (OLEDs). Light emission from thin films of small molecule organo-metallic compounds was first discovered by Kodak in 1987. Three years later, a research group at Cambridge University, UK, observed similar properties in conjugated polymers, consisting of long carbon chains with alternating single and double or triple bonds. Meanwhile, oligomers and dendrimers are also utilized as OLED materials.
An OLED is made from a stack of organic layers, forming a p-n junction, similar to an inorganic LED. When a voltage is applied in forward direction, light is emitted from the region where injected holes and electrons recombine. As the organic material is very susceptible to water vapor and oxygen, thorough encapsulation is indispensable.
OLEDs are self-emissive, highly efficient, and show excellent optical properties. They have high potential to be mass-produced on flexible substrates which would enable processing in a roll-to-roll manner. Moreover, the possibility to simply print the organic material makes fabrication very inexpensive.
A wide range of applications from simple monochrome large-area lighting to full color, videocapable graphic displays can be covered by OLED technology. Commercialization started in 1999 with the introduction of a multicolor OLED display in a car stereo.

 Vacuum Fluorescence Displays (VFD)

VFDs are an established technology still widely used as low information content displays in audio-/video devices or household appliances. The VFD technology uses the fluorescence of phosphors under electron bombardment similar as in cathode ray tubes (CRT). However, the device structure is quite different from CRTs and resembles the classical triode: Electrons evaporate from the metal cathode, a filament with around 10 µm thickness. They are accelerated by a grid voltage around 50 V. VFDs can be easily identified by the honeycomb structure of that grid which is fabricated by etching a very thin steel foil. As soon as the electrons penetrate the anode at around 100 V, light is being emitted. VFDs are robust, reliable, with a high contrast ratio and long life span. One disadvantage is their large spatial dimensions compared to the active display area.

Electroluminescence Displays (ELD)

ELDs have a very simple device structure and can entirely be built employing solid state thin film technologies. Between two electrically conducting slabs (e. g. glass with structured ITO stripes in matrix configuration) with applied insulating layers a thin electroluminescent layer is deposited. Doped zinc sulfate ZnS, or strontium sulfate SrS with a rather broad emission spectrum (“white”) are used as EL compounds. Conventional color filters generate RGB colors. With the EL layer being only about 100 µm thick, fully transparent displays, like for OLEDs, can be achieved. Typical driving voltages are chosen around 200 V AC at up to 10 kHz which necessitates rather expensive driver ICs. With an AM driving scheme (AMEL) employing a transistor matrix on a silicon substrate, high-resolution microdisplays have been demonstrated.

Light Emitting Diodes (LED)

(Inorganic) Light Emitting Diodes (LED) are widely used as large-area video walls or displays for tickers. These LED displays are commonly monochrome or multicolor and are composed of commercially obtainable LEDs. Meanwhile high-efficiency blue LEDs are available, making full-color large-area LED displays possible. LEDs exhibit high luminescence, high efficiency and long life time, which makes them particularly attractive for outdoor use. However, LEDs are rather spacious. Therefore, medium-sized displays for monitors or PDAs are not feasible with this technique. Monolithic integration of LEDs on a single chip, however, can be used for virtual (monochrome) displays.

MEMS (DMD)

Another microdisplay-oriented technology is based on Micro-Electro-Mechanical Systems (MEMS). In these types of displays, silicon and other materials are machined using standard semiconductor processes to make miniature mechanical structures. In the case of a Digital Micromirror Device (DMD), the structure is a mirror supported by a hinge, which can be actuated by placing a charge on plates connected to an underlying memory cell. The size of each mirror is about the width of a human hair. This device has gained acceptance widely in portable business projectors and home theater projectors.

 Liquid Crystal Displays (LCD)

Liquid crystals were discovered already in 1888, but it took about 80 years before the materials and electronics were advanced enough to practically use them. Back in 1971, the twisted nematic cell (TN-cell) was invented by Martin Schadt and Wolfgang Helfrich, two researchers from Switzerland. The TN-cell is currently the most widely used type for active matrix LCDs.
A TN-cell consists of two parallel glass substrates, typically only 0.7 to 0.35 mm thick, which are coated with optically transparent, electrically conductive films of Indium-Tin-Oxide (ITO) on their inner surfaces. These ITO films form electrodes which are coated with a transparent orientation layer made from an organic material (e. g. polyimide, only several nanometers thin). Between these films sits a mixture of liquid crystals. On their outer sides the glass substrates are coated with polarizer films, perpendicularly aligned.
LCDs are non-emissive and the liquid crystal cell acts as a “light valve”. In the transmissive mode light sources are backlights (e. g. cold cathode fluorescent lamps [CCFL] or LEDs), while the reflective mode uses ambient light reflected by a mirror foil behind the display. So-called transflective LCDs (often used in cell phones or car stereos) use both light sources.
In a TN-cell, the optically birefringent liquid crystals cause a rotation of polarization in the incident light by about 90 degrees when the cell is activated by an electric field applied through the ITO-electrodes. When the cell is inactive, the light passes through without modification (a so-called normally-white cell). Vice versa, by using parallel polarizing films on either side of the display, one obtains a normally black cell, which allows the light to pass only when an electrical field is applied.
Early displays for calculators or wrist watches mostly used the TN mode. In 1984 the supertwisted nematic (STN) mode was invented, which vastly improved the contrast ratio. In this mode the LC molecule twists the polarization plane of the light by 270 degrees. The response characteristic of the material is steeper resulting in a better black and white appearance of the display, compared to TN materials.
Different developments (cf. e. g. MLA, DSTN, FSTN, CSTN) significantly improved the display performance and even made the other LC phases, smectic (“soap-like”) and cholesteric (“cholesterol-like”) LC, usable for display applications. Common disadvantages of LCDs like narrow viewing angles, slow response times, temperature and shock sensitivity are steadily being improved.
The LCD technology is an established, mature technology for a broad range of applications. The new Generation 5, 6, and 7 production fabs enable the production of large screen sizes (up to 52 inches) in diagonal. For desktop PC monitor applications LCDs are already the dominant technology. The large LCDs have the potential to replace the cathode ray tubes (CRT) in the TV sector as well, if lower manufacturing costs can be achieved.

2012 Highlights

FPD China covers the whole industrial chain of China FPD industry, providing one-stop purchase and sales platform.The anchor panel manufacturers and leading Chinese end product brand participate together.The Touch Screen Pavilion, covering equipments, materials, software, manufactures, applications and services, will bring you the hottest field today.

TheNext Display Pavilion will showcase the prospective display technologies and applications including naked-eye 3D, human-machine interaction, desk station display, new laser display and etc..

2012 China FPD Conference, co-organized by SEMI and SID, will bring you the world-class speakers and hot technical information of this year.

The varieties of social activities and events for docking of supply and demand will make your visit abundant.

 

 


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