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. Liquid crystals do not emit light
directly, instead using a backlight or reflector to produce images in
colour or monochrome. LCDs are available to display arbitrary
images (as in a general-purpose computer display) or fixed images with
low information content, which can be displayed or hidden, such as
preset words, digits, and
7-segment displays, as in a digital clock.
They use the same basic technology, except that arbitrary images are
made up of a large number of small pixels, while other displays have
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 portable consumer devices such as digital cameras, watches,
calculators, and mobile telephones, including smartphones. LCD screens
are also used on consumer electronics products such as DVD players,
video game devices and clocks. LCD screens have replaced heavy, bulky
cathode ray tube (CRT) displays in nearly all applications. LCD
screens are available in a wider range of screen sizes than CRT and
plasma displays, with LCD screens available in sizes ranging from tiny
digital watches to huge, big-screen television sets.
Since LCD screens do not use phosphors, they do not suffer image
burn-in when a static image is displayed on a screen for a long time
(e.g., the table frame for an aircraft schedule on an indoor sign).
LCDs are, however, susceptible to image persistence. The LCD screen
is more energy-efficient and can be disposed of more safely than a CRT
can. Its low electrical power consumption enables it to be used in
battery-powered electronic equipment more efficiently than CRTs can
be. By 2008, annual sales of televisions with LCD screens exceeded
sales of CRT units worldwide, and the CRT became obsolete for most
1 General characteristics
4 Connection to other circuits
5 Passive and active-matrix
6 Active-matrix technologies
6.1 Twisted nematic (TN)
6.2 In-plane switching (IPS)
6.2.1 Comparison to AMOLED
6.3 Super In-plane switching (S-IPS)
6.4 Advanced fringe field switching (AFFS)
6.5 Vertical alignment (VA)
6.6 Blue phase mode
7 Quality control
8 "Zero-power" (bistable) displays
10 Advantages and disadvantages
11 Chemicals used
12 See also
14 External links
14.1 General information
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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, and two polarizing filters
(parallel and perpendicular), the axes of transmission of which are
(in most of the 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 orientation of the
liquid-crystal molecules is determined by the alignment at the
surfaces of electrodes. In a twisted nematic (TN) device, the surface
alignment directions at the two electrodes are perpendicular to each
other, and so the molecules arrange themselves in a helical structure,
or twist. This induces the rotation of the polarization of the
incident light, and the device appears 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, and thus be blocked and the pixel will appear black. By
controlling the voltage applied across the liquid crystal layer in
each pixel, light can be allowed to pass through in varying amounts
thus constituting different levels of gray. Color LCD systems use the
same technique, with color filters used to generate red, green, and
LCD in a Texas Instruments calculator with top polarizer removed from
device and placed on top, such that the top and bottom polarizers are
The optical effect of a TN device in the voltage-on state is far less
dependent on variations in the device thickness than that in the
voltage-off state. Because of this, TN displays with low information
content and no backlighting are usually operated between crossed
polarizers such that they appear bright with no voltage (the eye is
much more sensitive to variations in the dark state than the bright
state). As most of 2010-era LCDs are used in television sets, monitors
and smartphones, they have high-resolution matrix arrays of pixels to
display arbitrary images using backlighting with a dark background.
When no image is displayed, different arrangements are used. For this
purpose, TN LCDs are operated between parallel polarizers, whereas IPS
LCDs feature crossed polarizers. In many applications IPS LCDs have
replaced TN LCDs, in particular in smartphones such as iPhones. 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 of time, this ionic material is attracted to
the surfaces and degrades the 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
Casio Alarm Chrono digital watch with LCD.
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, which
makes it possible to address each pixel at the intersections. The
general method of matrix addressing consists of sequentially
addressing 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.
The origins 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
Center. A description of Swiss contributions to LCD developments,
written by Peter J. Wild, can be found at the Engineering and
Technology History Wiki.
Friedrich Reinitzer (1858–1927) discovered the liquid
crystalline nature of cholesterol extracted from carrots (that is, two
melting points and generation of colors) and published his findings at
a meeting of the Vienna Chemical Society on May 3, 1888 (F. Reinitzer:
Beiträge zur Kenntniss des Cholesterins, Monatshefte für Chemie
(Wien) 9, 421–441 (1888)). In 1904, Otto Lehmann published his
work "Flüssige Kristalle" (Liquid Crystals). In 1911, Charles Mauguin
first experimented with liquid crystals confined between plates in
Georges Friedel described the structure and properties of
liquid crystals and classified them in 3 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 on the subject "Molecular Structure and
Properties of Liquid Crystals", 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.
In 1964, George H. Heilmeier, then working at the
RCA laboratories on
the effect discovered by 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 the achievement of 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 they required a considerable current to flow
for their operation.
George H. Heilmeier
George H. Heilmeier was inducted
in 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
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
University of Hull who ultimately discovered the cyanobiphenyl liquid
crystals, which had correct stability and temperature properties for
application in LCDs.
On December 4, 1970, the twisted nematic field effect (TN) in liquid
crystals was filed for 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 then licensed the invention to the
Swiss manufacturer Brown, Boveri & Cie 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
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 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.
Sharp Corporation introduced the use of LCD displays for
calculators, and then mass-produced TN LCD displays for watches in
1975. A particular type of color LCD was invented 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.
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
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,
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, another
Seiko Hattori subsidiary (along with
Epson), introduced the Citizen Pocket TV, a 2.7-inch color LCD
TV, with the first commercial
TFT LCD display. 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
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.
In 1990, under different titles, inventors conceived electro optical
effects as alternatives to twisted nematic field effect LCDs (TN- and
STN- LCDs). One approach was to use interdigital electrodes on one
glass substrate only to produce an electric field essentially parallel
to the glass substrates. To take full advantage of the
properties of this
In Plane Switching
In Plane Switching (IPS) technology further work
was needed. After thorough analysis, details of advantageous
embodiments are filed in
Germany by Guenter Baur et al. and patented
in various countries. The Fraunhofer Institute in Freiburg,
where the inventors worked, assigns these patents to Merck KGaA,
Darmstadt, a supplier of LC substances. In 1992, shortly thereafter,
Hitachi work out various practical details of the IPS
technology to interconnect the thin-film transistor array as a matrix
and to avoid undesirable stray fields in between pixels.
Hitachi also improved the viewing angle dependence further by
optimizing the shape of the electrodes (Super IPS).
NEC and Hitachi
become early manufacturers of active-matrix addressed LCDs based on
the IPS technology. This is a milestone for implementing large-screen
LCDs having acceptable visual performance for flat-panel computer
monitors and television screens. In 1996,
Samsung developed the
optical patterning technique that enables multi-domain LCD.
In Plane Switching
In Plane Switching subsequently remain the dominant
LCD designs through 2006. In the late 1990s, the LCD industry
began shifting away from Japan, towards
South Korea and Taiwan.
In 2007 the image quality of
LCD televisions surpassed the image
quality of cathode-ray-tube-based (CRT) TVs. In the fourth quarter
LCD televisions surpassed CRT TVs in worldwide sales for the
first time. LCD TVs were projected to account 50% of the
200 million TVs to be shipped globally in 2006, according to
Displaybank. In October 2011,
2560 × 1600 pixels on a 6.1-inch (155 mm) LCD panel,
suitable for use in a tablet computer, especially for Chinese
Since LCD panels produce no light of their own, they require external
light to produce a visible image. In a transmissive type of LCD, this
light is provided at the back of the glass stack and is called the
backlight. While passive-matrix displays are usually not backlit (e.g.
calculators, wristwatches), active-matrix displays almost always
are. Over the last years (1990 - 2017), the LCD backlight
technologies have strongly been emerged by lighting companies such as
Philips, Lumileds (a Philips subsidiary) and more.
The common implementations of LCD backlight technology are:
18 parallel CCFLs as backlight for a 42-inch (106 cm) LCD TV
CCFL: The LCD panel is lit either by two cold cathode fluorescent
lamps placed at opposite edges of the display or an array of parallel
CCFLs behind larger displays. A diffuser then spreads the light out
evenly across the whole display. For many years, this technology had
been used almost exclusively. Unlike white LEDs, most CCFLs have an
even-white spectral output resulting in better color gamut for the
display. However, CCFLs are less energy efficient than LEDs and
require a somewhat costly inverter to convert whatever DC voltage the
device uses (usually 5 or 12 V) to ~1000 V needed to light a
CCFL. The thickness of the inverter transformers also limits how
thin the display can be made.
EL-WLED: The LCD panel is lit by a row of white LEDs placed at one or
more edges of the screen. A light diffuser is then used to spread the
light evenly across the whole display. As of 2012, this design is the
most popular one in desktop computer monitors. It allows for the
thinnest displays. Some LCD monitors using this technology have a
feature called dynamic contrast, invented by Philips researchers
Douglas Stanton, Martinus Stroomer and Adrianus de Vaan  Using PWM
(pulse-width modulation, a technology where the intensity of the LEDs
are kept constant, but the brightness adjustment is achieved by
varying a time interval of flashing these constant light intensity
light sources), the backlight is dimmed to the brightest color
that appears on the screen while simultaneously boosting the LCD
contrast to the maximum achievable levels, allowing the 1000:1
contrast ratio of the LCD panel to be scaled to different light
intensities, resulting in the "30000:1" contrast ratios seen in the
advertising on some of these monitors. Since computer screen images
usually have full white somewhere in the image, the backlight will
usually be at full intensity, making this "feature" mostly a marketing
gimmick for computer monitors, however for TV screens it drastically
increases the perceived contrast ratio and dynamic range, improves the
viewing angle dependency and drastically reducing the power
consumption of conventional LCD televisions.
LED array: The LCD panel is lit by a full array of white LEDs placed
behind a diffuser behind the panel. LCDs that use this implementation
will usually have the ability to dim the LEDs in the dark areas of the
image being displayed, effectively increasing the contrast ratio of
the display. As of 2012, this design gets most of its use from
upscale, larger-screen LCD televisions.
LED array: Similar to the W
LED array, except the panel is lit by a
full array of RGB LEDs. While displays lit with white LEDs usually
have a poorer color gamut than CCFL lit displays, panels lit with RGB
LEDs have very wide color gamuts. This implementation is most popular
on professional graphics editing LCDs. As of 2012, LCDs in this
category usually cost more than $1000. As of 2016 the cost of this
category has drastically reduced and such
LCD televisions obtained
same price levels as the former 28" (71 cm) CRT based categories.
Today, most LCD screens are being designed with an
instead of the traditional CCFL backlight, while that backlight is
dynamically controlled with the video information (dynamic backlight
control). The combination with the dynamic backlight control, invented
by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus
de Vaan, simultaneously increases the dynamic range of the display
system (also marketed as HDR, high dynamic range
The LCD backlight systems are made highly efficient by applying
optical films such as prismatic structure to gain the light into the
desired viewer directions and reflective polarizing films that recycle
the polarized light that was formerly absorbed by the first polarizer
of the LCD (invented by Philips researchers Adrianus de Vaan and
Paulus Schaareman), generally achieved using so called DBEF films
manufactured and supplied by 3M. These polarizers consist of a
large stack of uniaxial oriented birefringent films that reflect the
former absorbed polarization mode of the light. Such reflective
polarizers using uniaxial oriented polymerized liquid crystals
(birefringent polymers or birefringent glue) are invented in 1989 by
Philips researchers Dirk Broer, Adrianus de Vaan and Joerg
Brambring. The combination of such reflective polarizers, and LED
dynamic backlight control make today's
LCD televisions far more
efficient than the CRT-based sets, leading to a worldwide energy
saving of 600 TWh (2017), equal to 10% of the electricity consumption
of all households worldwide or equal to 2 times the energy production
of all solar cells in the world.
Due to the LCD layer that generates the desired high resolution images
at flashing video speeds using very low power electronics in
combination with these excellent
LED based backlight technologies, LCD
technology has become the dominant display technology for products
such as televisions, desktop monitors, notebooks, tablets, smartphones
and mobile phones. Although competing O
LED technology is pushed to the
market, such O
LED displays does not feature the HDR capabilities like
LCDs in combination with 2D
LED backlight technologies have, reason
why the annual market of such LCD-based products is still growing
faster (in volume) than OLED-based products while the efficiency of
LCDs (and products like portable computers, mobile phones and
televisions) may even be further improved by preventing the light to
be absorbed in the colour filters of the LCD. Although
until today such reflective colour filter solutions are not yet
implemented by the LCD industry and did not made it further than
laboratory prototypes, such reflective colour filter solutions still
likely will be implemented by the LCD industry to increase the
performance gap with O
Connection to other circuits
A pink elastomeric connector mating an LCD panel to circuit board
traces, shown next to a centimeter-scale ruler. (The conductive and
insulating layers in the black stripe are very small, click on the
image for more detail.)
A standard television receiver screen, an LCD panel today in 2017, has
over six million pixels, and they are all individually powered by a
wire network embedded in the screen. The fine wires, or pathways, form
a grid with vertical wires across the whole screen on one side of the
screen and horizontal wires across the whole screen on the other side
of the screen. To this grid each pixel has a positive connection on
one side and a negative connection on the other side. So the total
amount of wires needed is 3 x 1920 going vertically and 1080 going
horizontally for a total of 6840 wires horizontally and vertically.
That’s three for red, green and blue and 1920 columns of pixels for
each color for a total of 5760 wires going vertically and 1080 rows of
wires going horizontally. For a panel that is 28.8 inches (73
centimeters) wide, that means a wire density of 200 wires per inch
along the horizontal edge. The LCD panel is powered by LCD drivers
that are carefully matched up with the edge of the LCD panel at the
factory level. These same principles apply also for smart phone
screens that are so much smaller than TV screens.LCD
panels typically use thinly-coated metallic conductive pathways on a
glass substrate to form the cell circuitry to operate the panel. It is
usually not possible to use soldering techniques to directly connect
the panel to a separate copper-etched circuit board. Instead,
interfacing is accomplished using either adhesive plastic ribbon with
conductive traces glued to the edges of the LCD panel, or with an
elastomeric connector, which is a strip of rubber or silicone with
alternating layers of conductive and insulating pathways, pressed
between contact pads on the LCD and mating contact pads on a circuit
Passive and active-matrix
Prototype of a passive-matrix STN-LCD with 540×270 pixels, Brown
Boveri Research, Switzerland, 1984
Monochrome and later color passive-matrix LCDs were standard in most
early laptops (although a few used plasma displays) and the
original Nintendo Game Boy until the mid-1990s, when color
active-matrix became standard on all laptops. The commercially
Macintosh Portable (released in 1989) was one of the
first to use an active-matrix display (though still monochrome).
Passive-matrix LCDs are still used in the 2010s for applications less
demanding than laptop computers and TVs, such as inexpensive
calculators. In particular, these are used on portable devices where
less information content needs to be displayed, lowest power
consumption (no backlight) and low cost are desired or readability in
direct sunlight is needed.
A comparison between a blank passive-matrix display (top) and a blank
active-matrix display (bottom). A passive-matrix display can be
identified when the blank background is more grey in appearance than
the crisper active-matrix display, fog appears on all edges of the
screen, and while pictures appear to be fading on the screen.
Displays having a passive-matrix structure are employing super-twisted
nematic STN (invented by Brown Boveri Research Center, Baden,
Switzerland, in 1983; scientific details were published) or
double-layer STN (DSTN) technology (the latter of which addresses a
color-shifting problem with the former), and color-STN (CSTN) in which
color is added by using an internal filter. STN LCDs have been
optimized for passive-matrix addressing. They exhibit a sharper
threshold of the contrast-vs-voltage characteristic than the original
TN LCDs. This is important, because pixels are subjected to partial
voltages even while not selected. Crosstalk between activated and
non-activated pixels has to be handled properly by keeping the RMS
voltage of non-activated pixels below the threshold voltage, while
activated pixels are subjected to voltages above threshold (the
voltages according to the "Alt & Pleshko" drive scheme)
Driving such STN displays according to the Alt & Pleshko drive
scheme require very high line addressing voltages. Welzen and de Vaan
invented an alternative drive scheme (a non "Alt & Pleshko" drive
scheme) requiring much lower voltages, such that the STN display could
be driven using low voltage CMOS technologies. STN LCDs have to be
continuously refreshed by alternating pulsed voltages of one polarity
during one frame and pulses of opposite polarity during the next
frame. Individual pixels are addressed by the corresponding row and
column circuits. This type of display is called passive-matrix
addressed, because the pixel must retain its state between refreshes
without the benefit of a steady electrical charge. As the number of
pixels (and, correspondingly, columns and rows) increases, this type
of display becomes less feasible. Slow response times and poor
contrast are typical of passive-matrix addressed LCDs with too many
pixels and driven according to the "Alt & Pleshko" drive scheme.
Welzen and de Vaan also invented a non RMS drive scheme enabling to
drive STN displays with video rates and enabling to show smooth moving
video images on an STN display. Citizen, amongst others, licensed
these patents and successfully introduced several STN based LCD pocket
televisions on the market
How an LCD works using an active-matrix structure
Bistable LCDs do not require continuous refreshing. Rewriting is only
required for picture information changes. In 1984 HA van Sprang and
AJSM de Vaan invented an STN type display that could be operated in a
bistable mode, enabling extreme high resolution images up to 4000
lines or more using only low voltages. Since a pixel however may
be either in an on-state or in an off state at the moment new
information needs to be written to that particular pixel, the
addressing method of these bistable displays is rather complex, reason
why these displays did not made it to the market. That changed when in
the 2010 "zero-power" (bistable) LCDs became available. Potentially,
passive-matrix addressing can be used with devices if their
write/erase characteristics are suitable, which was the case for
ebooks showing still pictures only. After a page is written to the
display, the display may be cut from the power while that information
remains readable. This has the advantage that such ebooks may be
operated long time on just a small battery only. High-resolution color
displays, such as modern LCD computer monitors and televisions, use an
active-matrix structure. A matrix of thin-film transistors (TFTs) is
added to the electrodes in contact with the LC layer. Each pixel has
its own dedicated transistor, allowing each column line to access one
pixel. When a row line is selected, all of the column lines are
connected to a row of pixels and voltages corresponding to the picture
information are driven onto all of the column lines. The row line is
then deactivated and the next row line is selected. All of the row
lines are selected in sequence during a refresh operation.
Active-matrix addressed displays look brighter and sharper than
passive-matrix addressed displays of the same size, and generally have
quicker response times, producing much better images.
Casio 1.8 in color TFT LCD, used in the
DSC-P93A digital compact cameras
Thin-film-transistor liquid-crystal display
Thin-film-transistor liquid-crystal display and
Active-matrix liquid-crystal display
See also: List of LCD matrices
Twisted nematic (TN)
See also: Twisted nematic field effect
Twisted nematic displays contain liquid crystals that twist and
untwist at varying degrees to allow light to pass through. When no
voltage is applied to a TN liquid crystal cell, polarized light passes
through the 90-degrees twisted LC layer. In proportion to the voltage
applied, the liquid crystals untwist changing the polarization and
blocking the light's path. By properly adjusting the level of the
voltage almost any gray level or transmission can be achieved.
In-plane switching (IPS)
In-plane switching is an LCD technology that aligns the liquid
crystals in a plane parallel to the glass substrates. In this method,
the electrical field is applied through opposite electrodes on the
same glass substrate, so that the liquid crystals can be reoriented
(switched) essentially in the same plane, although fringe fields
inhibit a homogeneous reorientation. This requires two transistors for
each pixel instead of the single transistor needed for a standard
thin-film transistor (TFT) display. Before LG Enhanced IPS was
introduced in 2009, the additional transistors resulted in blocking
more transmission area, thus requiring a brighter backlight and
consuming more power, making this type of display less desirable for
notebook computers. Currently Panasonic is using an enhanced version
eIPS for their large size LCD-TV products as well as Hewlett-Packard
in its WebOS based TouchPad tablet and their Chromebook 11.
Comparison to AMOLED
In 2011, LG claimed the smartphone LG Optimus Black (IPS LCD (LCD
NOVA)) has the brightness up to 700 nits, while the competitor has
only IPS LCD with 518 nits and double an active-matrix O
display with 305 nits. LG also claimed the NOVA display to be 50
percent more efficient than regular LCDs and to consume only 50
percent of the power of AMO
LED displays when producing white on
screen. When it comes to contrast ratio, AMO
LED display still
performs best due to its underlying technology, where the black levels
are displayed as pitch black and not as dark gray. On August 24, 2011,
Nokia announced the Nokia 701 and also made the claim of the world's
brightest display at 1000 nits. The screen also had Nokia's Clearblack
layer, improving the contrast ratio and bringing it closer to that of
Super In-plane switching (S-IPS)
Super-IPS was later introduced after in-plane switching with even
better response times and color reproduction.
This pixel-layout is found in S-IPS LCDs. A chevron-shape is used to
widen the viewing-cone (range of viewing directions with good contrast
and low color shift)
Advanced fringe field switching (AFFS)
Known as fringe field switching (FFS) until 2003, advanced fringe
field switching is similar to IPS or S-IPS offering superior
performance and color gamut with high luminosity. AFFS was developed
by Hydis Technologies Co., Ltd, Korea (formally Hyundai Electronics,
LCD Task Force). AFFS-applied notebook applications minimize color
distortion while maintaining a wider viewing angle for a professional
display. Color shift and deviation caused by light leakage is
corrected by optimizing the white gamut which also enhances white/gray
reproduction. In 2004, Hydis Technologies Co., Ltd licensed AFFS to
Hitachi is using AFFS to manufacture
high-end panels. In 2006, HYDIS licensed AFFS to Sanyo
Devices Corporation. Shortly thereafter, Hydis introduced a
high-transmittance evolution of the AFFS display, called HFFS (FFS+).
Hydis introduced AFFS+ with improved outdoor readability in 2007. AFFS
panels are mostly utilized in the cockpits of latest commercial
aircraft displays. However, it is no longer produced as of February
Vertical alignment (VA)
Vertical-alignment displays are a form of LCDs in which the liquid
crystals naturally align vertically to the glass substrates. When no
voltage is applied, the liquid crystals remain perpendicular to the
substrate, creating a black display between crossed polarizers. When
voltage is applied, the liquid crystals shift to a tilted position,
allowing light to pass through and create a gray-scale display
depending on the amount of tilt generated by the electric field. It
has a deeper-black background, a higher contrast ratio, a wider
viewing angle, and better image quality at extreme temperatures than
traditional twisted-nematic displays.
Blue phase mode
Main article: Blue phase mode LCD
Blue phase mode LCDs have been shown as engineering samples early in
2008, but they are not in mass-production. The physics of blue phase
mode LCDs suggest that very short switching times (~1 ms) can be
achieved, so time sequential color control can possibly be realized
and expensive color filters would be obsolete.
Some LCD panels have defective transistors, causing permanently lit or
unlit pixels which are commonly referred to as stuck pixels or dead
pixels respectively. Unlike integrated circuits (ICs), LCD panels with
a few defective transistors are usually still usable. Manufacturers'
policies for the acceptable number of defective pixels vary greatly.
At one point,
Samsung held a zero-tolerance policy for LCD monitors
sold in Korea. As of 2005, though,
Samsung adheres to the less
ISO 13406-2 standard. Other companies have been known
to tolerate as many as 11 dead pixels in their policies.
Dead pixel policies are often hotly debated between manufacturers and
customers. To regulate the acceptability of defects and to protect the
end user, ISO released the
ISO 13406-2 standard. However, not
every LCD manufacturer conforms to the ISO standard and the ISO
standard is quite often interpreted in different ways. LCD panels are
more likely to have defects than most ICs due to their larger size.
For example, a 300 mm SVGA LCD has 8 defects and a 150 mm
wafer has only 3 defects. However, 134 of the 137 dies on the wafer
will be acceptable, whereas rejection of the whole LCD panel would be
a 0% yield. In recent years, quality control has been improved. An
SVGA LCD panel with 4 defective pixels is usually considered defective
and customers can request an exchange for a new one.[according to
whom?] Some manufacturers, notably in
South Korea where some of the
largest LCD panel manufacturers, such as LG, are located, now have a
zero-defective-pixel guarantee, which is an extra screening process
which can then determine "A"- and "B"-grade panels.[original
research?] Many manufacturers would replace a product even with one
defective pixel. Even where such guarantees do not exist, the location
of defective pixels is important. A display with only a few defective
pixels may be unacceptable if the defective pixels are near each
other. LCD panels also have defects known as clouding (or less
commonly mura), which describes the uneven patches of changes in
luminance. It is most visible in dark or black areas of displayed
"Zero-power" (bistable) displays
See also: Ferro Liquid Display
The zenithal bistable device (ZBD), developed by
DERA), can retain an image without power. The crystals may exist in
one of two stable orientations ("black" and "white") and power is only
required to change the image. ZBD Displays is a spin-off company from
QinetiQ who manufactured both grayscale and color ZBD devices. Kent
Displays has also developed a "no-power" display that uses polymer
stabilized cholesteric liquid crystal (ChLCD). In 2009 Kent
demonstrated the use of a ChLCD to cover the entire surface of a
mobile phone, allowing it to change colors, and keep that color even
when power is cut off. In 2004 researchers at the University of
Oxford demonstrated two new types of zero-power bistable LCDs based on
Zenithal bistable techniques. Several bistable technologies, like
the 360° BTN and the bistable cholesteric, depend mainly on the bulk
properties of the liquid crystal (LC) and use standard strong
anchoring, with alignment films and LC mixtures similar to the
traditional monostable materials. Other bistable technologies, e.g.
BiNem technology, are based mainly on the surface properties and need
specific weak anchoring materials.
Resolution The resolution of an LCD is expressed by the number of
columns and rows of pixels (e.g., 1024×768). Each pixel is usually
composed 3 sub-pixels, a red, a green, and a blue one. This had been
one of the few features of LCD performance that remained uniform among
different designs. However, there are newer designs that share
sub-pixels among pixels and add Quattron which attempt to efficiently
increase the perceived resolution of a display without increasing the
actual resolution, to mixed results.
Spatial performance: For a computer monitor or some other display that
is being viewed from a very close distance, resolution is often
expressed in terms of dot pitch or pixels per inch, which is
consistent with the printing industry. Display density varies per
application, with televisions generally having a low density for
long-distance viewing and portable devices having a high density for
close-range detail. The Viewing Angle of an LCD may be important
depending on the display and its usage, the limitations of certain
display technologies mean the display only displays accurately at
Temporal performance: the temporal resolution of an LCD is how well it
can display changing images, or the accuracy and the number of times
per second the display draws the data it is being given. LCD pixels do
not flash on/off between frames, so LCD monitors exhibit no
refresh-induced flicker no matter how low the refresh rate. But a
lower refresh rate can mean visual artefacts like ghosting or
smearing, especially with fast moving images. Individual pixel
response time is also important, as all displays have some inherent
latency in displaying an image which can be large enough to create
visual artifacts if the displayed image changes rapidly.
Color performance: There are multiple terms to describe different
aspects of color performance of a display.
Color gamut is the range of
colors that can be displayed, and color depth, which is the fineness
with which the color range is divided.
Color gamut is a relatively
straight forward feature, but it is rarely discussed in marketing
materials except at the professional level. Having a color range that
exceeds the content being shown on the screen has no benefits, so
displays are only made to perform within or below the range of a
certain specification. There are additional aspects to LCD color
and color management, such as white point and gamma correction, which
describe what color white is and how the other colors are displayed
relative to white.
Brightness and contrast ratio:
Contrast ratio is the ratio of the
brightness of a full-on pixel to a full-off pixel. The LCD itself is
only a light valve and does not generate light; the light comes from a
backlight that is either fluorescent or a set of LEDs.
usually stated as the maximum light output of the LCD, which can vary
greatly based on the transparency of the LCD and the brightness of the
backlight. In general, brighter is better, but there is always a
trade-off between brightness and power consumption.
Advantages and disadvantages
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Some of these issues relate to full-screen displays, others to small
displays as on watches, etc. Many of the comparisons are with CRT
Further information: Comparison of CRT, LCD, Plasma, and OLED
Very compact, thin and light, especially in comparison with bulky,
heavy CRT displays.
Low power consumption. Depending on the set display brightness and
content being displayed, the older CCFT backlit models typically use
less than half of the power a CRT monitor of the same size viewing
area would use, and the modern
LED backlit models typically use
10–25% of the power a CRT monitor would use.
Little heat emitted during operation, due to low power consumption.
No geometric distortion.
The possible ability to have little or no flicker depending on
Usually no refresh-rate flicker, because the LCD pixels hold their
state between refreshes (which are usually done at 200 Hz or
faster, regardless of the input refresh rate).
Sharp image with no bleeding or smearing when operated at native
Emits almost no undesirable electromagnetic radiation (in the
extremely low frequency range), unlike a CRT
monitor.[better source needed]
Can be made in almost any size or shape.
No theoretical resolution limit. When multiple LCD panels are used
together to create a single canvas, each additional panel increases
the total resolution of the display, which is commonly called stacked
Can be made in large sizes of over 60-inch (150 cm) diagonal.
Masking effect: the LCD grid can mask the effects of spatial and
grayscale quantization, creating the illusion of higher image
Unaffected by magnetic fields, including the Earth's.
As an inherently digital device, the LCD can natively display digital
data from a DVI or
HDMI connection without requiring conversion to
analog. Some LCD panels have native fiber optic inputs in addition to
DVI and HDMI.
Many LCD monitors are powered by a 12 V power supply, and if
built into a computer can be powered by its 12 V power supply.
Can be made with very narrow frame borders, allowing multiple LCD
screens to be arrayed side-by-side to make up what looks like one big
Limited viewing angle in some older or cheaper monitors, causing
color, saturation, contrast and brightness to vary with user position,
even within the intended viewing angle.
Uneven backlighting in some monitors (more common in IPS-types and
older TNs), causing brightness distortion, especially toward the edges
Black levels may not be as dark as required because individual liquid
crystals cannot completely block all of the backlight from passing
Display motion blur on moving objects caused by slow response times
(>8 ms) and eye-tracking on a sample-and-hold display, unless a
strobing backlight is used. However, this strobing can cause eye
strain, as is noted next:
As of 2012, most implementations of LCD backlighting use pulse-width
modulation (PWM) to dim the display, which makes the screen
flicker more acutely (this does not mean visibly) than a CRT monitor
at 85 Hz refresh rate would (this is because the entire screen is
strobing on and off rather than a CRT's phosphor sustained dot which
continually scans across the display, leaving some part of the display
always lit), causing severe eye-strain for some people.
Unfortunately, many of these people don't know that their eye-strain
is being caused by the invisible strobe effect of PWM. This
problem is worse on many LED-backlit monitors, because the LEDs switch
on and off faster than a CCFL lamp.
Only one native resolution. Displaying any other resolution either
requires a video scaler, causing blurriness and jagged edges, or
running the display at native resolution using 1:1 pixel mapping,
causing the image either not to fill the screen (letterboxed display),
or to run off the lower or right edges of the screen.
Fixed bit depth (also called color depth). Many cheaper LCDs are only
able to display 262,000 colors. 8-bit S-IPS panels can display
16 million colors and have significantly better black level, but
are expensive and have slower response time.
Low refresh rate. All but a few high-end monitors support no higher
than 60 or 75 Hz; while this does not cause visible flicker due
to the LCD panel's high internal refresh rate, the low input refresh
rate limits the maximum frame-rate that can be displayed, affecting
gaming and 3D graphics.
Input lag, because the LCD's
A/D converter waits for each frame to be
completely been output before drawing it to the LCD panel. Many LCD
monitors do post-processing before displaying the image in an attempt
to compensate for poor color fidelity, which adds an additional lag.
Further, a video scaler must be used when displaying non-native
resolutions, which adds yet more time lag. Scaling and post processing
are usually done in a single chip on modern monitors, but each
function that chip performs adds some delay. Some displays have a
video gaming mode which disables all or most processing to reduce
perceivable input lag.
Dead or stuck pixels may occur during manufacturing or after a period
of use. A stuck pixel will glow with color even on an all-black
screen, while a dead one will always remain black.
Subject to burn-in effect, although the cause differs from CRT and the
effect may not be permanent, a static image can cause burn-in in a
matter of hours in badly designed displays.
In a constant-on situation, thermalization may occur in case of bad
thermal management, in which part of the screen has overheated and
looks discolored compared to the rest of the screen.
Loss of brightness and much slower response times in low temperature
environments. In sub-zero environments, LCD screens may cease to
function without the use of supplemental heating.
Loss of contrast in high temperature environments.
Several different families of liquid crystals are used in liquid
crystals. The molecules used have to be anisotropic, and to exhibit
mutual attraction. Polarizable rod-shaped molecules (biphenyls,
terphenyls, etc.) are common. A common form is a pair of aromatic
benzene rings, with a nonpolar moiety (pentyl, heptyl, octyl, or alkyl
oxy group) on one end and polar (nitrile, halogen) on the other.
Sometimes the benzene rings are separated with an acetylene group,
ethylene, CH=N, CH=NO, N=N, N=NO, or ester group. In practice,
eutectic mixtures of several chemicals are used, to achieve wider
temperature operating range (-10..+60 °C for low-end and
-20..+100 °C for high-performance displays). For example, the E7
mixture is composed of three biphenyls and one terphenyl: 39 wt.% of
4'-pentyl[1,1'-biphenyl]-4-carbonitrile (nematic range
24..35 °C), 36 wt.% of 4'-heptyl[1,1'-biphenyl]-4-carbonitrile
(nematic range 30..43 °C), 16 wt.% of
4'-octoxy[1,1'-biphenyl]-4-carbonitrile (nematic range
54..80 °C), and 9 wt.% of
4-pentyl[1,1':4',1-terphenyl]-4-carbonitrile (nematic range
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Wikimedia Commons has media related to
Liquid crystal displays.
LCD Monitor Teardown – engineerguyvideo on YouTube
History and Physical Properties of Liquid Crystals by Nobelprize.org
Definitions of basic terms relating to low-molar-mass and polymer
liquid crystals (IUPAC Recommendations 2001)
An intelligible introduction to liquid crystals from Case Western
Liquid Crystal Physics tutorial from the Liquid Crystals Group,
University of Colorado
Molecular Crystals and Liquid Crystals a journal by Taylor and Francis
Development of Liquid Crystal Displays: Interview with George Gray,
Hull University, 2004 – Video by the Vega Science Trust.
Timothy J. Sluckin History of Liquid Crystals, a presentation and
extracts from the book Crystals that Flow: Classic papers from the
history of liquid crystals.
David Dunmur & Tim Sluckin (2011) Soap, Science, and Flat-screen
TVs: a history of liquid crystals, Oxford University Press
Oleg Artamonov (January 23, 2007). "Contemporary LCD Monitor
Parameters: Objective and Subjective Analysis". X-bit labs. Archived
from the original on May 16, 2008. Retrieved May 17, 2008.
3LCD technology, Presentation Technology
LCD Phase and
Clock Adjustment, Techmind offers a free test screen to
get a better LCD picture quality than the LCD's auto-tune function.
Alphanumeric LCD to Microcontroller
Animations explaining operation of LCD panels
Liquid crystals are distributed by
Merck Group (DE), and Yancheng
Electroluminescent display (ELD)
Light emitting diode display (LED)
Cathode ray tube
Cathode ray tube (CRT) (Monoscope)
Liquid-crystal display (LCD)
Plasma display panel (PDP)
Digital Light Processing
Digital Light Processing (DLP)
Liquid crystal on silicon (LCoS)
Organic light-emitting diode (OLED)
Organic light-emitting transistor (OLET)
Surface-conduction electron-emitter display
Surface-conduction electron-emitter display (SED)
Field emission display (FED)
Quantum dot display
Quantum dot display (QD-LED)
Ferro liquid crystal display (FLCD)
Thick-film dielectric electroluminescent technology (TDEL)
Telescopic pixel display (TPD)
Laser-powered phosphor display (LPD)
Vacuum fluorescent display
Vacuum fluorescent display (VFD)
Light-emitting electrochemical cell (LEC)
Seven-segment display (SSD)
Fourteen-segment display (FSD)
Sixteen-segment display (SISD)
History of display technology
Large-screen television technology
Optimum HDTV viewing distance
High-dynamic-range imaging (HDRI)
Color Light Output
Comparison of display technology
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