Thin film transistor
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{{otheruses4|TFT technology|TFT LCD|TFT LCD}}
A '''thin film transistor''' ('''TFT''') is a special kind of [[field effect transistor]] made by depositing [[thin film]]s of a [[semiconductor]] active layer as well as the [[dielectric]] layer and metallic contacts over a supporting substrate. A common substrate is [[glass]], since the primary application of TFTs is in [[liquid crystal display]]s. This differs from the conventional [[transistor]] where the semiconductor material typically is the substrate, such as a [[silicon wafer]].
TFTs can be made using a wide variety of semiconductor materials. A common material is [[silicon]]. The characteristics of a silicon based TFT depend on the crystalline state. That is, the semiconductor layer can be either [[amorphous silicon]],<ref name=Kanicki1>{{cite book |last=Kanicki |first=Jerzy |title=Amorphous & Microcystalline Semiconductor Devices Volume II: Materials and Device Physics |publisher=Artech House, Inc. |date=1992 |isbn=0-89006-379-6}}</ref> [[microcrystalline silicon]],<ref name=Kanicki1/> or it can be annealed into [[polysilicon]]. Other materials which have been used as semiconductors in TFTs include compound semiconductors such as cadmium selenium (CdSe)<ref name="Brody1">{{cite journal |last = Brody |first = T. Peter |title=The Thin Film Transistor - A Late Flowering Bloom |journal=IEEE Transactions on Electron Devices |volume=31 |issue =11 |pages =1614–1628 |date=November 1984 |doi=10.1109/T-ED.1984.21762}}</ref><ref name="Brody2">{{cite journal |last = Brody |first = T. Peter |title=The birth and early childhood of active matrix - a personal memoir |journal=Jounal of the SID|volume=4/3|pages =113–127|date=1996}}</ref> and metal oxides such as Zinc Oxide.<ref name="WagerZnO"/> TFT's have also been made using organic materials (referred to as an Organic TFT or [[OTFT]]).
By using transparent semiconductors and transparent electrodes, such as [[indium tin oxide]] (ITO), some TFT devices can be made completely transparent.
Because the substrate cannot withstand the high annealing temperature, the deposition process has to be completed under relatively low temperature. [[Chemical vapor deposition]], [[physical vapor deposition]] (usually [[sputtering]]) are applied. Also the first solution processed transparent TFTs (TTFTs), based on [[zinc oxide]] were reported in [[2003]] by researchers at [[Oregon State University]].<ref name="WagerZnO">Wager, John. [http://oregonstate.edu/dept/ncs/newsarch/2003/Mar03/transparent.htm OSU Engineers Create World's First Transparent Transistor]. College of Engineering, Oregon State University, Corvallis, OR: OSU News & Communication, 2003. 29 July 2007.</ref>
==Applications==
The best known application of thin-film transistors is in [[TFT LCD]]s, a variant of [[Liquid crystal display|LCD]] technology. Transistors are embedded within the panel itself, reducing crosstalk between [[pixel]]s and improving image stability. [[As of 2004]], all but the cheapest color LCD screens use this technology.{{Citation broken|date=February 2008}} TFT panels are heavily used in digital radiography applications in General Radiography. It is used in both Direct and Indirect capture as a base for the Image Receptor in Radiography.
The new AMOLED ([[Active Matrix Liquid Crystal Display|Active Matrix]] [[OLED]]) screens also contain a TFT layer.
==See also==
*[[Liquid crystal display television]]
*[[OFET|Organic Thin Film Transistors]]
==References==
<references/>
[[Category:Transistor types]]
[[Category:Thin films]]
[[Category:Semiconductors]]
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