When was LCD display introduced?

Display that uses the light-modulating properties of liquid crystals

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"LCD" redirects here. For other uses, see LCD (disambiguation)

Not to be confused with LED

The layers of a reflective twisted nematic liquid crystal display:

1. Polarizing filter film with a vertical axis to polarize light as it enters.
2. Glass substrate with ITO electrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is switched ON. Vertical ridges etched on the surface are smooth.
3. Twisted nematic liquid crystal.
4. Glass substrate with common electrode film (ITO) with horizontal ridges to line up with the horizontal filter.
5. Polarizing filter film with a horizontal axis to block/pass light.
6. Reflective surface to send light back to viewer. (In a backlit LCD, this layer is replaced or complemented with a light source.)

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in color or monochrome.

LCDs can display arbitrary images (as in a general-purpose computer display) or fixed images with low information content, such as preset words, digits, and seven-segment displays (as in a digital clock). They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements.

LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with letters that are the same color as the backlight.

LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, calculators, and mobile phones, including smartphones. LCD screens have replaced heavy, bulky, and less energy-efficient cathode-ray tube (CRT) displays in almost all applications. The phosphors used in CRTs make them vulnerable to image burn-in when a static image is displayed on a screen for a long time. LCDs do not have this weakness, although they are still susceptible to image persistence.

General characteristics

An LCD screen used as a notification panel for travellers

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, often made of indium tin oxide (ITO), and two polarizing filters (parallel and perpendicular polarizers), the axes of which are (in most cases) perpendicular to each other. Without the liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. Before an electric field is applied, the alignment at the surfaces of electrodes determines the orientation of the liquid-crystal molecules. In a twisted nematic (TN) device, the surface alignment directions at the two electrodes are perpendicular to each other, so the molecules arrange themselves in a helical structure, or twist. This induces the rotation of the polarization of the incident light, making the device appear gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted, and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, thus being blocked, and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, varying amounts of light can be allowed to pass through, resulting in different levels of gray.

The chemical formulas of the liquid crystals used in LCDs may vary. Some formulas are patented. An example is a mixture of 2-(4-alkoxyphenyl)-5-alkylpyrimidine with cyanobiphenyl, patented by Merck and Sharp Corporation. The patent for that specific mixture has expired.

Most color LCD systems use the same technique, with color filters used to generate red, green, and blue subpixels. The LCD color filters are made through a photolithography process on large glass sheets that are later glued with other glass sheets containing a thin-film transistor (TFT) array, spacers, and liquid crystal. This creates several color LCDs that are then cut from one another and laminated with polarizer sheets. Red, green, blue, and black photoresists (resists) are used. All resists contain a finely ground powdered pigment, with particles being just 40 nanometers across. The black resist is the first to be applied; this creates a black grid (known as a black matrix) to separate red, green, and blue subpixels from one another, increasing contrast ratios and preventing light from leaking from one subpixel to surrounding subpixels. After the black resist has been dried in an oven and exposed to UV light through a photomask, the unexposed areas are washed away, creating a black grid. The remaining resists are applied using the same process. This fills the holes in the black grid with their corresponding colored resists.

Another color-generation method used in early color PDAs and some calculators was varying the voltage in a Super-twisted nematic LCD, where the variable twist between tighter-spaced plates causes varying double refraction birefringence, thus changing the hue. These were typically restricted to 3 colors per pixel: orange, green, and blue.

TN displays with low information content and no backlighting are often operated between crossed polarizers, such that they appear bright with no voltage (since the eye is much more sensitive to variations in the dark state than in the bright state). Most 2010-era LCDs used in television sets, monitors, and smartphones have high-resolution matrix arrays of pixels to display arbitrary images using backlighting with a dark background. Different arrangements are used when no image is displayed. TN LCDs are operated between parallel polarizers, whereas IPS LCDs feature crossed polarizers. IPS LCDs have replaced TN LCDs in many applications, particularly in smartphones. Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period, these ionic materials are attracted to the surfaces, degrading device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).

Displays for a small number of individual digits or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment. In contrast, full alphanumeric or variable graphics displays are usually implemented with pixels arranged as a matrix, consisting of electrically connected rows on one side of the LC layer and columns on the other side, making it possible to address each pixel at the intersections. The general method of matrix addressing consists of sequential addressing on one side of the matrix, for example by selecting the rows one-by-one and applying the picture information on the other side at the columns row-by-row. For details on the various matrix addressing schemes, see passive-matrix and active-matrix addressed LCDs.

LCDs are manufactured in cleanrooms, borrowing techniques from semiconductor manufacturing, and using large sheets of glass whose size has increased over time. Several displays are manufactured at the same time and then cut from the sheet of glass, also known as the mother glass or LCD glass substrate. The increase in size allows more displays or larger displays to be made, similar to increasing wafer sizes in semiconductor manufacturing.

History

The origin and the complex history of liquid-crystal displays from the perspective of an insider during the early days were described by Joseph A. Castellano in Liquid Gold: The Story of Liquid Crystal Displays and the Creation of an Industry. Another report on the origins and history of LCD from a different perspective until 1991 has been published by Hiroshi Kawamoto, available at the IEEE History Center. A description of Swiss contributions to LCD developments, written by Peter J. Wild, can be found at the Engineering and Technology History Wiki.

Background

In 1888, Friedrich Reinitzer (1858–1927) discovered the liquid crystalline nature of cholesterol extracted from carrots (that is, two melting points and the generation of colors) and published his findings. In 1904, Otto Lehmann published his work "Flüssige Kristalle" (Liquid Crystals). In 1911, Charles Mauguin first experimented with liquid crystals confined between plates in thin layers.

In 1922, Georges Friedel described the structure and properties of liquid crystals and classified them in three types (nematics, smectics, and cholesterics). In 1927, Vsevolod Frederiks devised the electrically switched light valve, called the Fréedericksz transition, the essential effect of all LCD technology. In 1936, the Marconi Wireless Telegraph company patented the first practical application of the technology, "The Liquid Crystal Light Valve". In 1962, the first major English language publication Molecular Structure and Properties of Liquid Crystals was published by Dr. George W. Gray. In 1962, Richard Williams of RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what are now called "Williams domains" inside the liquid crystal.

Building on early MOSFETs, Paul K. Weimer at RCA developed the thin-film transistor (TFT) in 1962. It was a type of MOSFET distinct from the standard bulk MOSFET.

1960s

In 1964, George H. Heilmeier, who was working at the RCA laboratories on the effect discovered by Richard Williams, achieved the switching of colors by field-induced realignment of dichroic dyes in a homeotropically oriented liquid crystal. Practical problems with this new electro-optical effect made Heilmeier continue to work on scattering effects in liquid crystals and finally achieve the first operational liquid-crystal display based on what he called the dynamic scattering mode (DSM). Application of a voltage to a DSM display switches the initially clear transparent liquid crystal layer into a milky turbid state. DSM displays could be operated in transmissive and in reflective mode but required a considerable current flow for their operation. George H. Heilmeier was inducted into the National Inventors Hall of Fame and credited with the invention of LCDs. Heilmeier's work is an IEEE Milestone.

In the late 1960s, pioneering work on liquid crystals was undertaken by the UK's Royal Radar Establishment at Malvern, England. The team at RRE supported ongoing work by George William Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals, which had the correct stability and temperature properties for application in LCDs.

The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968. Lechner, F.J. Marlowe, E.O. Nester, and J. Tults demonstrated the concept in 1968 with an 18x2 matrix dynamic scattering mode (DSM) LCD using standard discrete MOSFETs.

1970s

On December 4, 1970, the twisted nematic field effect (TN) in liquid crystals was filed for a patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261) with Wolfgang Helfrich and Martin Schadt (then working for the Central Research Laboratories) listed as inventors. Hoffmann-La Roche licensed the invention to Swiss manufacturer Brown, Boveri & Cie, its joint venture partner at that time, which produced TN displays for wristwatches and other applications during the 1970s for the international markets including the Japanese electronics industry, which soon produced the first digital quartz wristwatches with TN-LCDs and numerous other products. James Fergason, while working with Sardari Arora and Alfred Saupe at Kent State University Liquid Crystal Institute, filed an identical patent in the United States on April 22, 1971. In 1971, the company of Fergason, ILIXCO (now LXD Incorporated), produced LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption. Tetsuro Hama and Izuhiko Nishimura of Seiko received a US patent dated February 1971 for an electronic wristwatch incorporating a TN-LCD. In 1972, the first wristwatch with TN-LCD was launched on the market: The Gruen Teletime which was a four digit display watch.

In 1972, the concept of the active-matrix thin-film transistor (TFT) liquid-crystal display panel was prototyped in the United States by T. Peter Brody's team at Westinghouse, in Pittsburgh, Pennsylvania. In 1973, Brody, J. A. Asars and G. D. Dixon at Westinghouse Research Laboratories demonstrated the first thin-film-transistor liquid-crystal display (TFT LCD). As of 2013, all modern high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays. Brody and Fang-Chen Luo demonstrated the first flat active-matrix liquid-crystal display (AM LCD) in 1974, and then Brody coined the term "active matrix" in 1975.

In 1972 North American Rockwell Microelectronics Corp introduced the use of DSM LCDs for calculators for marketing by Lloyds Electronics Inc, though these required an internal light source for illumination. Sharp Corporation followed with DSM LCDs for pocket-sized calculators in 1973 and then mass-produced TN LCDs for watches in 1975. Other Japanese companies soon took a leading position in the wristwatch market, like Seiko and its first 6-digit TN-LCD quartz wristwatch, and Casio's 'Casiotron'. Color LCDs based on Guest-Host interaction were invented by a team at RCA in 1968. A particular type of such a color LCD was developed by Japan's Sharp Corporation in the 1970s, receiving patents for their inventions, such as a patent by Shinji Kato and Takaaki Miyazaki in May 1975, and then improved by Fumiaki Funada and Masataka Matsuura in December 1975. TFT LCDs similar to the prototypes developed by a Westinghouse team in 1972 were patented in 1976 by a team at Sharp consisting of Fumiaki Funada, Masataka Matsuura, and Tomio Wada, then improved in 1977 by a Sharp team consisting of Kohei Kishi, Hirosaku Nonomura, Keiichiro Shimizu, and Tomio Wada. However, these TFT-LCDs were not yet ready for use in products, as problems with the materials for the TFTs were not yet solved.

1980s

In 1983, researchers at Brown, Boveri & Cie (BBC) Research Center, Switzerland, invented the super-twisted nematic (STN) structure for passive matrix-addressed LCDs. H. Amstutz et al. were listed as inventors in the corresponding patent applications filed in Switzerland on July 7, 1983, and October 28, 1983. Patents were granted in Switzerland CH 665491, Europe EP 0131216, U.S. patent 4,634,229, and many more countries. In 1980, Brown Boveri started a 50/50 joint venture with the Dutch Philips company, called Videlec. Philips had the required know-how to design and build integrated circuits for the control of large LCD panels. In addition, Philips had better access to markets for electronic components and intended to use LCDs in new product generations of hi-fi, video equipment, and telephones. In 1984, Philips researchers Theodorus Welzen and Adrianus de Vaan invented a video speed-drive scheme that solved the slow response time of STN-LCDs, enabling high-resolution, high-quality, and smooth-moving video images on STN-LCDs. In 1985, Philips inventors Theodorus Welzen and Adrianus de Vaan solved the problem of driving high-resolution STN-LCDs using low-voltage (CMOS-based) drive electronics, allowing the application of high-quality (high resolution and video speed) LCD panels in battery-operated portable products like notebook computers and mobile phones. In 1985, Philips acquired 100% of the Videlec AG company based in Switzerland. Afterwards, Philips moved the Videlec production lines to the Netherlands. Years later, Philips successfully produced and marketed complete modules (consisting of the LCD screen, microphone, speakers, etc.) in high-volume production for the booming mobile phone industry.

The first color LCD televisions were developed as handheld televisions in Japan. In 1980, Hattori Seiko's R&D group began development on color LCD pocket televisions. In 1982, Seiko Epson released the first LCD television, the Epson TV Watch, a wristwatch equipped with a small active-matrix LCD television. Sharp Corporation introduced dot matrix TN-LCD in 1983. In 1984, Epson released the ET-10, the first full-color, pocket LCD television. The same year, Citizen Watch, introduced the Citizen Pocket TV, a 2.7-inch color LCD TV, with the first commercial TFT LCD. In 1988, Sharp demonstrated a 14-inch, active-matrix, full-color, full-motion TFT-LCD. This led to Japan launching an LCD industry, which developed large-size LCDs, including TFT computer monitors and LCD televisions. Epson developed the 3LCD projection technology in the 1980s, and licensed it for use in projectors in 1988. Epson's VPJ-700, released in January 1989, was the world's first compact, full-color LCD projector