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Encyclopedia > TFT LCD
A 15" TFT-LCD

TFT-LCD (thin film transistor liquid crystal display) is a variant of liquid crystal display (LCD) which uses thin film transistor (TFT) technology to improve image quality. TFT LCD is one type of active matrix LCD, though it is usually synonymous with LCD. It is used in televisions, flat panel displays and projectors. Image File history File links Download high resolution version (1280x960, 240 KB) Summary This is a picture taken in 2005 from the LCD display model Samsung SyncMaster 510N that was in my home in São Paulo, Brazil. ... Image File history File links Download high resolution version (1280x960, 240 KB) Summary This is a picture taken in 2005 from the LCD display model Samsung SyncMaster 510N that was in my home in São Paulo, Brazil. ... Reflective twisted nematic liquid crystal display. ... A thin film transistor (TFT) is special kind of field effect transistor made by depositing thin films for the metallic contacts, semiconductor active layer, and dielectric layer. ... An active matrix liquid crystal display (AMLCD) is a type of flat panel display, currently the overwhelming choice of notebook computer manufacturers, due to light weight, very good image quality, wide color gamut, and response time. ... Flat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays using cathode ray tubes, usually less than 10 cm (4 inches) thick. ... Projectors are used for displaying an image on a projection screen or similar surface for the view of an audience. ...

Contents

Construction

A diagram of the pixel layout
A diagram of the pixel layout

Normal liquid crystal displays like those found in calculators have direct driven image elements – a voltage can be applied across one segment without interfering with other segments of the display. This is impractical for a large display with a large number of picture elements (pixels), since it would require millions of connections - top and bottom connections for each one of the three colors (red, green and blue) of every pixel. To avoid this issue, the pixels are addressed in rows and columns which reduce the connection count from millions to thousands. If all the pixels in one row are driven with a positive voltage and all the pixels in one column are driven with a negative voltage, then the pixel at the intersection has the largest applied voltage and is switched. The problem with this solution is that all the pixels in the same column see a fraction of the applied voltage as do all the pixels in the same row, so although they are not switched completely, they do tend to darken. The solution to the problem is to supply each pixel with its own transistor switch which allows each pixel to be individually controlled. The low leakage current of the transistor also means that the voltage applied to the pixel does not leak away between refreshes to the display image. Each pixel is a small capacitor with a transparent ITO layer at the front, a transparent layer at the back, and a layer of insulating liquid crystal between. Image File history File links TFT_Matrix. ... Image File history File links TFT_Matrix. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Only meanings of encyclopedic scope are listed here for disambiguation purposes. ... This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–750 nm. ... Leafy green fountain in Wattens, Austria. ... The term blue may refer to any of a number of similar colours. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ... Indium tin oxide (ITO) is a mixture of indium(III) oxide (In2O3) and tin(IV) oxide (SnO2), typically 90% In2O3, 10% SnO2 by weight. ... This article or section is in need of attention from an expert on the subject. ...


The circuit layout of a TFT-LCD is very similar to the one used in a DRAM memory. However, rather than building the transistors out of silicon which has been formed into a crystalline wafer, they are fabricated from a thin film of silicon deposited on a glass panel. Transistors take up only a small fraction of the area of each pixel, and the silicon film is etched away in the remaining areas, allowing light to pass through. Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ... Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms... Thin films are material layers of about 1 µm thickness. ... Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ...


The silicon layer for TFT-LCDs is typically deposited using the PECVD process from a silane gas precursor to produce an amorphous silicon film. Polycrystalline silicon is also used in some displays where higher performance is needed from the TFTs, typically in very high resolution displays or ones where performing some data processing on the display itself is desirable. Both amorphous and polycrystalline silicon TFTs have very poor performance compared with transistors fabricated from single-crystal silicon. Plasma Enhanced Chemical Vapor Deposition (PECVD) is a process mainly to deposit thin films from a gas state (vapor) to a solid state on some substrate. ... Silane is a chemical compound with chemical formula SiH4. ... An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... Polycrystalline silicon or polysilicon or poly-Si or simply poly (in context) is a material consisting of multiple small silicon crystals, and has long been used as the conducting gate material in MOSFET and CMOS processing technologies. ...


Types

TN + film

The 'TN (twisted nematic) + film' display is the most common consumer display type, due to its low production cost and wide development. The pixel response time on modern TN panels is sufficiently fast to most users to avoid the shadow-trail and ghosting artifacts that were a cause for complaint in the past. This fast response time has been a heavily marketed aspect of TN displays, although in most cases this number does not reflect performance across the entire range of possible color transitions. Traditional response times were quoted as an ISO standard black > white transition and did not reflect the speed of transitions across grey tones (a much more common transition for liquid crystals to make in practice). Modern use of RTC (Response Time Compensation – Overdrive) technologies has allowed manufacturers to significantly reduce grey to grey (G2G) transitions, while the ISO response time remains practically unchanged. Response times are now quoted in G2G figures, with 4ms and 2ms now being commonplace for TN Film based models. This marketing strategy, combined with the relatively lower cost of production for TN panels, has led to the dominance of TN in the consumer market. // The twisted nematic effect (TN-effect) in liquid crystals is claimed to be first discovered by James Fergason in 1970 at the International Liquid Xtal Company in Kent Ohio. ...


The TN display suffers from limited viewing angles, especially in the vertical direction, and most are unable to display the full 16.7 million colors (24-bit truecolor) available from modern graphics cards. These particular panels, with 6 bits per color channel as opposed to 8, can approach 24-bit color using a dithering method which combines adjacent pixels to simulate the desired shade. They can also use FRC (Frame Rate Control), the less conspicuous of the two. FRC quickly cycles pixels over time to simulate a given shade. These color simulation methods are noticeable to most people and discomforting for some. FRC tends to be most noticeable in darker tones. Dithering has the tendency to appear as if the individual pixels of the LCD were actually visible. Overall, color reproduction and linearity on TN panels is poor. Shortcomings in display color gamut (often referred to as a percentage of the NTSC 1953 color gamut) can also be attributed to backlighting technology. It is not uncommon for displays with CCFL (Cold Cathode Fluorescent Lamps) based lighting to range from 40% to 76% of the NTSC color gamut, whereas displays utilizing white LED backlights may extend past 100% of the NTSC color gamut – a difference quite perceivable by the human eye. This article is about the unit of information. ... Truecolor (also spelled Truecolour; called Millions on a Macintosh) graphics is a method of storing image information in a computers memory such that each pixel is represented by three or more bytes. ... A graphics/video/display card/board/adapter is a computer component designed to convert the logical representation of visual information into a signal that can be used as input for a display medium. ... This article or section should be merged with Dither An illustration of dithering. ... In color reproduction, including computer graphics and photography, the gamut, or color gamut (pronounced ), is a certain complete subset of colors. ... An RGB color space is any additive color space based on the RGB color model. ...


With LCD displays, the transmittance of a pixel is typically not linear with the applied voltage,[1] and the sRGB standard for computer monitors requires a specific nonlinear dependence of the amount of emitted light as a function of the RGB value. In the fields of optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. ... The title given to this article is incorrect due to technical limitations. ... REDIRECT RGB color model ...


IPS

IPS (in-plane switching) was developed by Hitachi in 1996 to improve on the poor viewing angles and color reproduction of TN panels. Most also support true 8-bit color. These improvements came at a loss of response time, which was initially on the order of 50ms. IPS panels were also extremely expensive. It has been suggested that Hitachi Works be merged into this article or section. ...


IPS has since been superseded by S-IPS (Super-IPS, Hitachi in 1998), which has all the benefits of IPS technology with the addition of improved pixel refresh timing. Though color reproduction approaches that of CRTs, the contrast ratio remains relatively weak. S-IPS technology is widely used in panel sizes of 20" and above. LG and Philips remain one of the main manufacturers of S-IPS based panels. It has been suggested that Hitachi Works be merged into this article or section. ... The contrast ratio is a measure of a display system, defined as the ratio of the luminosity of the brightest color(White) to that of the darkest color(black) that the system is capable of producing. ...

AS-IPS – Advanced Super IPS, also developed by Hitachi in 2002, improves substantially on the contrast ratio of traditional S-IPS panels to the point where they are second only to some S-PVAs. AS-IPS is also a term used for NEC displays (e.g., NEC LCD20WGX2) based on S-IPS technology, in this case, developed by LG.Philips.
A-TW-IPS – Advanced True White IPS, developed by LG.Philips LCD for NEC, is a custom S-IPS panel with a TW (True White) color filter to make white look more natural and to increase color gamut. This is used in professional/photography LCDs.
H-IPS – Released sometime late 2006, was the H-IPS panel which is an evolution of the IPS panel which improves upon it’s predecessor, the S-IPS panel. The H-IPS panel can be seen in the NEC LCD2690WUXi and the Mitsubishi RDT261W 26″ LCD monitors.

So to sum up, the pros/cons of the H-IPS over the S-IPS: It has been suggested that Hitachi Works be merged into this article or section. ...


Pros:

  • Much less backlight bleed.
  • No purple hue visible at an angle
  • Backlight bleed improves looking at an angle
  • Less noise or glitter seen on the panel surface (smoother surface)

Cons:

  • Still some backlight bleed in areas that are green.
  • Viewing angles may have sacrificed in order to improve pros.
Image of a (switched on) transreflective color TFT LCD taken under a microscope with reflected light illumination lamp off (top, self-illumination only) and on (bottom).
Image of a (switched on) transreflective color TFT LCD taken under a microscope with reflected light illumination lamp off (top, self-illumination only) and on (bottom).

Image File history File links Download high resolution version (1993x3010, 969 KB) Summary Image of a Dell Axim x30 handleld computer thin film transistor LCD displaying a white background. ... Image File history File links Download high resolution version (1993x3010, 969 KB) Summary Image of a Dell Axim x30 handleld computer thin film transistor LCD displaying a white background. ... A transreflective liquid crystal display is a liquid crystal display (LCD) that reflects most of the sunlight the monitor is exposed to, and automatically increases or decreases the light emanating from the screen depending on how much light shines on it. ...

MVA

MVA (multi-domain vertical alignment) was originally developed in 1998 by Fujitsu as a compromise between TN and IPS. It achieved fast pixel response (at the time), wide viewing angles, and high contrast at the cost of brightness and color reproduction. Modern MVA panels can offer wide viewing angles (second only to S-IPS technology), good black depth, good color reproduction and depth, and fast response times thanks to the use of RTC technologies. There are several "next generation" technologies based on MVA, including AU Optronics' P-MVA and A-MVA, as well as Chi Mei Optoelectronics' S-MVA. For the district in Saga, Japan, see Fujitsu, Saga. ...


Analysts predicted that MVA would corner the mainstream market, but instead, TN has risen to dominance. A contributing factor was the higher cost of MVA, along with its slower pixel response (which rises dramatically with small changes in brightness). Cheaper MVA panels can also use dithering/FRC.


PVA

PVA (patterned vertical alignment) and S-PVA (super patterned vertical alignment) are alternative versions of MVA technology offered by Samsung. Developed independently, it offers similar features to MVA, but boasts very high contrast ratios such as 3000:1. Value-oriented PVA panels also use dithering/FRC. S-PVA panels all use true 8-bit color electronics and do not use any color simulation methods. PVA and S-PVA can offer good black depth, wide viewing angles and S-PVA can offer additionally fast response times thanks to modern RTC technologies. Samsung Group is one of the largest South Korean business groupings. ...


Display industry

Due to the very high cost of building TFT factories, there are few major OEM panel vendors for large display panels. The top six glass panel suppliers are as follows: Original equipment manufacturer, or OEM, is a term that refers to a situation in which one company purchases a manufactured product from another company and resells the product as its own, usually as a part of a larger product it sells. ...

  1. LG.Philips
  2. AU Optronics
  3. S-LCD Corporation (a Samsung/Sony joint venture)
  4. Chi Mei Optoelectronics
  5. Sharp Corporation
  6. Samsung

Raw LCD TFT panels are usually factory-sorted into three categories, with regard to the number of dead pixels, backlight evenness and general product quality. Additionally, there may be up to +/- 2ms maximum response time differences between individual panels that came off the same assembly line on the same day. The poorest-performing screens are then sold to no-name vendors or used in "value" TFT monitors (often marked with letter V behind the type number), the medium performers are incorporated in gamer-oriented or home office bound TFT displays (sometimes marked with the capital letter S), and the best screens are usually reserved for use in "professional" grade TFT monitors (often marked with letter P or S after their type number). LG.Philips LCD (hangul:엘지필립스엘씨디, LG필립스LCD) was formed as a joint venture by the Korean electronics company LG Electronics and the Dutch company Koninklijke Philips Electronics in 1999 to manufacture active matrix liquid crystal displays (LCDs). ... AU Optronics Corp. ... S-LCD Corporation (Hangul: 에스 엘씨디, Japanese: エス・エルシーディー) is a joint venture between Samsung Electronics Co. ... Samsung Group is one of the largest South Korean business groupings. ... Sony Corporation ) is a Japanese multinational corporation and one of the worlds largest media conglomerates with revenue of $66. ... Chi Mei Corporation (Chinese: 奇美實業廠) is a plastics producer in Taiwan. ... Sharp Corporation ) (TYO: 6753 ) is a Japanese electronics manufacturer, founded in 1912. ... Samsung Group is one of the largest South Korean business groupings. ... Close-up of an LCD display, showing a dead green subpixel A dead pixel is a defective pixel that remains unlit on an LCD screen or a CCD or CMOS sensor in a digital camera. ... A generic brand product is one made by a manufacturer the customer doesnt know much about who may or may not put thier name on the product. ...


Value TFT screens and most 15 inch sized LCDs usually lack a digital DVI interface, so their future proofing may be limited. Most 17 inch or 19 inch TFT screens have dual analog-VGA and DVI sockets. Almost all professional screens have DVI and some also include a pivot mode for portrait-mode display. An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... The Digital Visual Interface (DVI) is a video interface standard designed to maximize the visual quality of digital display devices such as flat panel LCD computer displays and digital projectors. ... The phrase Future proofing describes the elusive process of trying to anticipate future developments, so that action can be taken to minimise possible negative consequences, and to seize opportunities. ...


References

  1. ^ Marek Matuszczyk, Liquid crystals in displays. Chalmers University Sweden, ca. 2000.

See also

The tone or style of this article or section may not be appropriate for Wikipedia. ... A transreflective liquid crystal display is a liquid crystal display (LCD) that reflects most of the sunlight the monitor is exposed to, and automatically increases or decreases the light emanating from the screen depending on how much light shines on it. ...

External links


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