Thin-film transistor

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Thin-film transistor

A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin film

Thin film

Thin films are thin material Layer s ranging from fractions of a nanometre to several micrometres in thickness. Electronics semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s of a semiconductor

Semiconductor

A semiconductor is a material that has electrical conductivity between those of a Electrical conductor and an electrical insulation; it can vary over that wide range either permanently or dynamically....
active layer as well as the dielectric

Dielectric

A dielectric is a nonconducting substance, i.e. an Insulator . The term was coined by William Whewell in response to a request from Michael Faraday....
layer and metal

Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
lic contacts over a supporting substrate

Substrate (materials science)

Substrate is a term used in materials science to describe the base material on which processing is conducted to produce new film or layers of material such as deposited coatings....
. A common substrate is glass

Glass

Glass generally refers to a Hardness, brittle, transparency amorphous solid, such as that used for windows, many Glass Bottles, or eyewear, including, but not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovite , or aluminium oxynitride....
, since the primary application of TFTs is in liquid crystal display

Liquid crystal display

A liquid crystal display is an Electro-optic modulator shaped into a thin, flat panel made up of any number of color or monochrome pixels filled with liquid crystals and arrayed in front of a Light#Light sources or reflector....
s. This differs from the conventional transistor

Transistor

In electronics, a transistor is a semiconductor device commonly used to Electronic amplifier or switch Electronics signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit....
where the semiconductor material typically is the substrate, such as a silicon wafer.

Manufacture
TFTs can be made using a wide variety of semiconductor materials.

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Manufacture

TFTs can be made using a wide variety of semiconductor materials. A common material is silicon

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
. The characteristics of a silicon based TFT depend on the crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions....
line state. That is, the semiconductor layer can be either amorphous silicon

Amorphous silicon

Amorphous silicon is the non-crystalline allotropic form of silicon. Silicon is a four-fold coordinated atom that is normally tetrahedron bonded to four neighboring silicon atoms....
, microcrystalline silicon, or it can be annealed into polysilicon.

Other materials which have been used as semiconductors in TFTs include compound semiconductors such as cadmium

Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. A relatively abundant , soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores....
selenium

Selenium

Selenium is a chemical element with the atomic number 34, represented by the chemical symbol Se, an atomic mass of 78.96. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurs in its elemental state in nature....
(CdSe) and metal oxides such as Zinc Oxide. TFT's have also been made using organic materials (referred to as an Organic TFT or OTFT).

By using transparent semiconductors and transparent electrode

Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a Electronic circuit . The word was coined by the scientist Michael Faraday from the Greek language words elektron and hodos, a way....
s, such as indium tin oxide

Indium tin oxide

Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight....
(ITO), some TFT devices can be made completely transparent.

Because the substrate cannot withstand the high annealing

Annealing

Annealing may refer to:*Annealing , a heat treatment that alters the microstructure of a material causing changes in properties such as strength and hardness...
temperature, the deposition process has to be completed under relatively low temperature. Chemical vapor deposition

Chemical vapor deposition

Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films....
, physical vapor deposition

Physical vapor deposition

Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the material onto various surfaces ....
(usually sputtering

Sputtering

Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic ions. It is commonly used for thin-film deposition, etching and analytical techniques ....
) are applied. Also, the first solution processed transparent TFTs (TTFTs), based on zinc oxide

Zinc oxide

Zinc oxide is an inorganic compound with the Chemical formula ZnO. It usually appears as a white powder, nearly insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants, pigments, foods , batteries,...
were reported in 2003 by researchers at Oregon State University

Oregon State University

Oregon State University is a coeducational, public university research university located in Corvallis, Oregon, Oregon, United States. The university offers undergraduate, graduate and doctoral degrees and a multitude of research opportunities....
.

Meanwhile, Portuguese laboratory CENIMAT, Universidade Nova de Lisboa, discovered a way of producing TFT at room temperature, having produced the world’s first completely transparent TFT at room temperature. CENIMAT also developed the first paper transistor, which may lead to applications such as magazines and journal pages with moving images.

Applications

The best known application of thin-film transistors is in TFT LCD

TFT LCD

File:Flat monitor.svgA thin film transistor liquid crystal display is a variant of liquid crystal display which uses thin film transistor technology to improve image quality ....
s, an implementation of LCD

Liquid crystal display

Pixel

In digital imaging, a pixel is the smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots, squares, or rectangles....
s and improving image stability.

, all color LCD TVs and monitors use this technology. TFT panels are heavily used in digital

Digital

A digital system uses discrete values, usually but not always symbolized numerically to represent information for input, processing, transmission, storage, etc....
radiography

Radiography

Radiography is the use of X-rays to view unseen or hard-to-image objects. The main diagnostic purposes of X-rays are to see inside one's body, most commonly the bones which can be viewed at an optimum resolution ....
applications in general radiography. It is used in both direct and indirect capture as a base for the image receptor in medical radiography

Medical radiography

Radiography is the use of ionizing electromagnetic radiation such as X-rays to view objects. Although not technically radiographic techniques, imaging modalities such as Positron emission tomography and Magnetic resonance imaging are sometimes grouped in radiography due to the fact that the radiology department of hospitals handle all forms o...
.

The new AMOLED (Active Matrix OLED) screens also contain a TFT layer.

The most beneficial aspect of TFT technology is a separate transistor for each pixel on the display. As each transistor is small, the amount of charges essential for controlling it also small. This allows for very fast re-drawing of the display.

Prior to TFT, passive matrix LCD displays could not keep up with fast moving images. A mouse dragged across the screen, for example, from point A to point B, would disappear between the two points. A TFT monitor can track the mouse, resulting in a display that can be used for video, gaming and all forms of multimedia.

Thin-film transistor

Manufacture

Applications

See also