Active matrix: Difference between revisions

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'''Active matrix''' is a type of [[addressing scheme]] used in [[flat panel display]]s. In this method of switching individual elements ([[pixel]]s) of a flat panel display, each pixel is attached to a [[transistor]] and [[capacitor]] which ''actively'' maintainmaintaining the pixel state while other pixels are being addressed. This is to bein contrastedcontrast with the older [[passive matrix]] technology in which each pixel must maintain its state passively, without being driven by circuitry.

The active matrix technology was invented by [[Bernard J. Lechner]] at [[RCA]] and first demonstrated as a feasible device using [[thin-film transistor]]s (TFTs) by [[T. Peter Brody]] and his Thin-Film Devices department at [[Westinghouse Electric Corporation]] in 1974,<ref>[http://www.ieee.org/about/news/2011/honors_ceremony/releases_nishizawa.html IEEE Jun-ichi Nishizawa Medal]</ref> and the term was introduced into the literature in 1975.<ref name=OEDActiveMatrix>{{cite web|url=http://www.oed.com/viewdictionaryentry/Entry/1953#eid19485882 |title=Active Matrix|year=2011|work=[[OED]]|publisher=[[Oxford University Press]]}}{{subscription required}}</ref><ref name=Castellano>{{cite book|last=Castellano|first=Joseph A.|title=Liquid gold : the story of liquid crystal displays and the creation of an industry|year=2005|publisher=World Scientific|___location=New Jersey [u.a.]|isbn=978-981-238-956-5|pages=176|url=http://www.amazon.com/Liquid-Gold-Displays-Creation-Industry/dp/9812389563|edition=[Online-Ausg.]}}</ref><ref>{{cite doi|10.1109/T-ED.1975.18214}}</ref>

Given an ''m''&nbsp;&times;&nbsp;''n'' matrix, the number of connectors needed to address the display is ''m''&nbsp;+&nbsp;''n'' (just like in passive matrix technology). Each pixel is attached to a switch-device, which ''actively'' maintains the pixel state while other pixels are being addressed, which also preventspreventing [[crosstalk]] from inadvertently changing the state of an unaddressed pixel. The most common switching devices use TFTs, i.e. a [[field effect transistor|FET]] based on either the cheaper [[amorphous|non-crystalline]] [[thin-film]] [[silicon]] ([[amorphous silicon|a-Si]]), [[polycrystalline]] silicon ([[polycrystalline silicon|poly-Si]]), or [[Cadmium selenide|CdSe]] [[semiconductor]] material.

Another variant is to use diodes or resistors, but neither [[diode]]s (e.g. [[Metal insulator metal diode]]s), nor non-linear voltage dependent [[resistor]]s (i.e. [[varistor]]s) are currently used. with The latter of these is not yet economical when, compared to TFT.

The [[Macintosh Portable]] (1989) was perhaps the first consumer laptop to employ an active matrix panel. Today, virtually all TVs, computer monitors and smartphone screens that use [[LCD]] or [[OLED]] technology employ active matrix technology.<ref>{{cite web|title=What is OLED TV?|author=|date=1 March 2012|work=Cnet.com|url=http://reviews.cnet.com/8301-33199_7-57386898-221/what-is-oled-tv/}}</ref>

== See also ==