Editing Liquid-crystal display (section)

==General characteristics==
[[File:Amersfoort LCD Display Valleilijn.jpg|thumb|An LCD screen used as a notification panel for travellers]]

Each [[pixel]] of an LCD typically consists of a layer of [[molecule]]s aligned between two transparent [[electrode]]s, often made of [[indium tin oxide]] (ITO), and two [[Polarizer|polarizing]] [[Filter (optics)|filters]] (parallel and perpendicular polarizers), 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 [[Alignment layer|surface alignment directions]] at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a [[Helix|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.{{Citation needed|date=February 2025}}

The chemical formula of the liquid crystals used in LCDs may vary. Formulas may be patented.<ref>{{Cite web|url=https://patents.google.com/patent/US20130062560A1/en|title=Liquid crystal composition and liquid crystal display device|access-date=October 3, 2020|archive-date=September 1, 2022|archive-url=https://web.archive.org/web/20220901192643/https://patents.google.com/patent/US20130062560A1/en|url-status=live}}</ref> An example is a mixture of 2-(4-alkoxyphenyl)-5-alkylpyrimidine with cyanobiphenyl, patented by [[Merck Group|Merck]] and [[Sharp Corporation]]. The patent that covered that specific mixture has expired.<ref>{{Cite web|url=https://patents.google.com/patent/US4722804|title=Liquid crystal composition|access-date=October 3, 2020|archive-date=March 19, 2022|archive-url=https://web.archive.org/web/20220319080645/https://patents.google.com/patent/US4722804|url-status=live}}</ref>

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 with 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, creating several color LCDs that are then cut from one another and laminated with polarizer sheets. Red, green, blue and black colored photoresists (resists) are used to create color filters. 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 will create a black grid (known in the industry as a black matrix) that will separate red, green and blue subpixels from one another, increasing contrast ratios and preventing light from leaking from one subpixel onto other surrounding subpixels.<ref>{{Cite journal|title=Light Leakage of Multidomain Vertical Alignment LCDs Using a Colorimetric Model in the Dark State|first1=Chuen-Lin|last1=Tien|first2=Rong-Ji|last2=Lin|first3=Shang-Min|last3=Yeh|date=June 3, 2018|journal=Advances in Condensed Matter Physics|volume=2018|pages=1–6|doi=10.1155/2018/6386428|doi-access=free}}</ref> 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. Then the same process is repeated with the remaining resists. This fills the holes in the black grid with their corresponding colored resists.<ref name=Castellano>{{cite book |last=Castellano |first=Joseph A. |date=2005 |title=Liquid Gold: The Story of Liquid Crystal Displays and the Creation of an Industry|publisher=World Scientific Publishing|isbn=978-981-238-956-5}}</ref><ref>{{Cite journal|url=https://www.researchgate.net/publication/223733321|title=LCD-based color filter films fabricated by a pigment-based colorant photo resist inks and printing technology|first1=Horng-Show|last1=Koo|first2=Mi|last2=Chen|first3=Po-Chuan|last3=Pan|date=November 1, 2006|journal=Thin Solid Films|volume=515|issue=3|pages=896–901|via=ResearchGate|doi=10.1016/j.tsf.2006.07.159|bibcode=2006TSF...515..896K}}</ref><ref>{{Cite book|chapter=Pigment-dispersed color resist with high resolution for advanced color filter application|date=March 10, 1999|pages=359–363|via=IEEE Xplore|doi=10.1109/ASID.1999.762781|isbn=957-97347-9-8|title=Proceedings of 5th Asian Symposium on Information Display. ASID '99 (IEEE Cat. No.99EX291)|last1=Rong-Jer Lee|last2=Jr-Cheng Fan|last3=Tzong-Shing Cheng|last4=Jung-Lung Wu|s2cid=137460486}}</ref> Black matrices made in the 1980s and 1990s when most color LCD production was for laptop computers, are made of Chromium due to its high opacity, but due to environmental concerns, manufacturers shifted to black colored photoresist with carbon pigment as the black matrix material.<ref>{{cite book | url=https://books.google.com/books?id=jjRjDwAAQBAJ&dq=lcd+black+matrix&pg=PA45 | title=Flat Panel Display Manufacturing | isbn=978-1-119-16134-9 | last1=Souk | first1=Jun | last2=Morozumi | first2=Shinji | last3=Luo | first3=Fang-Chen | last4=Bita | first4=Ion | date=September 24, 2018 | publisher=John Wiley & Sons }}</ref><ref>{{cite book | url=https://books.google.com/books?id=tkdf8FqQ5w4C&dq=lcd+black+matrix&pg=PA3 | title=Coatings on Glass 1998 | isbn=978-0-444-50247-6 | last1=Pulker | first1=H. | last2=Schmidt | first2=H. | last3=Aegerter | first3=M. A. | date=November 26, 1999 | publisher=Elsevier }}</ref><ref>{{cite book | url=https://books.google.com/books?id=EdEzJYJFyU0C&q=lcd+black+matrix | title=Active Matrix Liquid Crystal Displays: Fundamentals and Applications | isbn=978-0-08-045576-1 | last1=Boer | first1=Willem den | date=March 15, 2011 | publisher=Elsevier }}</ref> Another color-generation method used in early color PDAs and some calculators was done by varying the voltage in a [[Super-twisted nematic]] LCD, where the variable twist between tighter-spaced plates causes a varying double refraction [[birefringence]], thus changing the hue.<ref>{{Cite web|url=https://patents.google.com/patent/US5191454A/en|title=Multi-colored liquid crystal display device|access-date=September 3, 2020|archive-date=May 22, 2020|archive-url=https://web.archive.org/web/20200522103816/https://patents.google.com/patent/US5191454A/en|url-status=live}}</ref> They were typically restricted to 3 colors per pixel: orange, green, and blue.<ref>{{Cite book|url=https://support.casio.com/storage/en/manual/pdf/EN/004/fx_plus_ch_intro_EN.pdf|title=fx9750G PLUS, CFX-9850G PLUS, CFX-9850GB PLUS, CFX-9850GC PLUS, CFX-9950GC PLUS User's Guide|publisher=Casio|location=London, UK|pages=Page 4 |access-date=November 17, 2021|archive-date=January 21, 2022|archive-url=https://web.archive.org/web/20220121043445/https://support.casio.com/storage/en/manual/pdf/EN/004/fx_plus_ch_intro_EN.pdf|url-status=live}}</ref>

[[File:LCDneg.jpg|thumb|left|LCD in a [[Texas Instruments]] [[calculator]] with top [[polarizer]] removed from device and placed on top, such that the top and bottom polarizers are [[perpendicular]]. As a result, the [[color]]s are inverted.]]

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 panel|IPS LCDs]] feature crossed polarizers. In many applications IPS LCDs have replaced TN LCDs, particularly in [[smartphone]]s. Both the liquid crystal material and the [[Alignment layers|alignment layer]] material contain [[ionic compound]]s. 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 applied field).

[[File:Casio W-59 digital watch.jpg|thumb|A [[Casio]] Alarm Chrono [[digital watch]] with LCD]]

Displays for a small number of individual digits or fixed symbols (as in [[digital watch]]es and [[pocket calculator]]s) can be implemented with independent electrodes for each segment.<ref>{{Cite book |url=https://books.google.com/books?id=BRkNDgAAQBAJ&q=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.&pg=PA208 |title=Information Photonics: Fundamentals, Technologies, and Applications |last1=Datta |first1=Asit Kumar |last2=Munshi |first2=Soumika |date=November 25, 2016 |publisher=CRC Press |isbn=9781482236422 }}</ref> 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 liquid crystal (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 and active-matrix|passive-matrix and active-matrix addressed LCDs]].