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| Physical properties |
| State of matter States of matter are the distinct forms that different phases of matter take on. Solid, liquid and gas are the most common states of matter on Earth. However, much of the baryonic matter of the universe is in the form of hot plasma, both as rarefied interstellar medium and as dense...
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Solid |
Melting pointThe melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
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1800–2200 K The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
(2800–3500 °F) |
| Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
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7120–7160 kg/m3 at 293 K |
ColorColor or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
(in powder form) |
Pale yellow to greenish yellow, depending on SnO2 concentration |
| Values vary with composition. |
| SI Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
units and STP are used except where noted. |
Indium tin oxide (
ITO, or
tin-doped indium oxide) is a
solid solutionA solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
of
indium(III) oxideIndium oxide is a chemical compound, an amphoteric oxide of indium.-Crystal structure:Amorphous indium oxide is insoluble in water but soluble in acids, whereas crystalline indium oxide is insoluble in both water and acids. The crystalline form exist in two phases, cubic and rhombohedral . Both...
(In
2O
3) and tin(IV) oxide (SnO
2), typically 90% In
2O
3, 10% SnO
2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey. In the infrared region of the spectrum it is a metal-like mirror.
Indium tin oxide is one of the most widely used transparent conducting oxides because of its two chief properties, its electrical conductivity and optical transparency, as well as the ease with which it can be deposited as a thin film. As with all transparent conducting films, a compromise must be made between conductivity and transparency, since increasing the thickness and increasing the concentration of
charge carrierIn physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
s will increase the material's conductivity, but decrease its transparency.
Thin filmA thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s of indium tin oxide are most commonly deposited on surfaces by electron beam evaporation,
physical vapor depositionPhysical 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 desired film material onto various workpiece surfaces...
, or a range of
sputter depositionSputter deposition is a physical vapor deposition method of depositing thin films by sputtering, that is ejecting, material from a "target," that is source, which then deposits onto a "substrate," such as a silicon wafer...
techniques.
Common uses
ITO is mainly used to make transparent conductive coatings for
liquid crystal displayA liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
s,
flat panel displayFlat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
s,
plasma displayA plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
s,
touch panelA touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus...
s,
electronic inkElectronic paper, e-paper and electronic ink are a range of display technology which are designed to mimic the appearance of ordinary ink on paper. Unlike conventional backlit flat panel displays, electronic paper displays reflect light like ordinary paper...
applications,
organic light-emitting diodeAn OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
s,
solar cellA solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s, antistatic coatings and
EMIElectromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
shieldings. In
organic light-emitting diodeAn OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
s, ITO is used as the
anodeAn anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
(hole injection layer).
ITO has been used as a conductive material in the plastic
electroluminescentElectroluminescence is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field...
lamp of toy
Star WarsStar Wars is an American epic space opera film series created by George Lucas. The first film in the series was originally released on May 25, 1977, under the title Star Wars, by 20th Century Fox, and became a worldwide pop culture phenomenon, followed by two sequels, released at three-year...
type
lightsaberA lightsaber is a fictional weapon in the Star Wars universe, a "laser sword." It consists of a polished metal hilt which projects a blade of light about 1.33 metres long. The lightsaber is the signature weapon of the Jedi order and their Sith counterparts, both of whom can use them for close...
s.
ITO is also used for various
optical coatingAn optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and...
s, most notably
infraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
-reflecting coatings (
hot mirrorA hot mirror is a specialized dielectric mirror, a dichroic filter, often employed to protect optical systems by reflecting infrared light back into a light source, while allowing visible light to pass...
s) for architectural, automotive, and
sodium vapor lampA sodium vapor lamp is a gas discharge lamp that uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure...
glasses. Other uses include gas sensors, antireflection coatings,
electrowettingElectrowetting is the modification of the wetting properties of a surface with an applied electric field.-History:...
on dielectrics, and Bragg reflectors for
VCSELThe vertical-cavity surface-emitting laser, or VCSEL , is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers which emit from surfaces formed by cleaving the individual chip out of a...
lasers.
ITO was used as a sensor coating in the later
Kodak DCSThe Kodak Digital Camera System is a series of digital single-lens reflex cameras and digital camera backs that were released by Kodak in the 1990s and 2000s, and discontinued in 2005. They were all based on existing 35mm film SLRs from Nikon and Canon...
cameras, starting with the Kodak DCS 520, as a means of increasing blue channel response. It is reportedly used as a sensor coating in the Canon 400D/XTi and Sony Alpha DSLR-A100.
ITO thin film
strain gaugeA strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...
s can operate at temperatures up to 1400 °C and can be used in harsh environments, e.g.
gas turbineA gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
s,
jet engineA jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s, and
rocket engineA rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
s.
Material and spectral properties
ITO is a heavily-doped n-type semiconductor with a large bandgap. Because of the bandgap, it is mostly transparent in the visible part of the spectrum. In the
ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
, it is opaque because of band-to-band absorption (a UV photon can excite an electron from the valence band to the conduction band). In the near
infraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
, it also opaque, because of
free carrier absorptionFree carrier absorption occurs when a material absorbs a photon and a carrier is excited from a filled region below the Fermi level to an unoccupied region above the Fermi level . This is different from interband absorption in semiconductors because the electron being excited is a conduction electron...
(an infrared photon can excite an electron from near the bottom of the conduction band to higher within the conduction band).
Alternatives
Because of high cost and limited supply of indium, the fragility and lack of flexibility of ITO layers, and the costly layer deposition requiring vacuum, alternatives are being sought.
Carbon nanotubeCarbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
conductive coatings are a prospective replacement. As another carbon-based alternative, films of
grapheneGraphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...
are flexible and have been shown to allow 90% transparency with a lower electrical resistance than standard ITO. Thin metal films are also seen as a potential replacement material. Inherently conductive polymers (ICPs) are also being developed for some ITO applications. Typically the conductivity is lower for conducting polymers, such as
polyanilinePolyaniline is a conducting polymer of the semi-flexible rod polymer family. Although the compound itself was discovered over 150 years ago, only since the early 1980s has polyaniline captured the intense attention of the scientific community. This is due to the rediscovery of its high electrical...
and
PEDOTPedot is the eleventh album of the Finnish rock band CMX. "Pedot" means "Beasts" in Finnish.The opening track "Eteläisen tähtitaivaan kartoitus" breaks a CMX tradition of starting their albums with powerful rock songs. It is a minimalistic piano-based ballad with no drums...
:PSS, than inorganic materials, but they are more flexible, less expensive and more environmentally friendly in processing and manufacture. Other, inorganic alternatives include
aluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
,
galliumGallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
or
indiumIndium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...
—doped
zinc oxideZinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is 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,...
(AZO, GZO or IZO).
Constraints and trade-offs
The main concern about ITO is the cost. ITO can be priced at several times that of aluminium zinc oxide (AZO). AZO is a common choice of
transparent conducting oxideTransparent conducting films are optically transparent and electrically conductive in thin layers.TCFs for photovoltaic applications have been fabricated from both inorganic and organic materials...
(TCO) because of cost and relatively good optical transmission performance in the solar spectrum. However, ITO does consistently defeat AZO in almost every performance category including chemical resistance to moisture. ITO is not affected by moisture and it can survive in a CIGS cell for 25–30 years on a rooftop.
While the sputtering target or evaporative material that is used to deposit the ITO is significantly more costly than AZO, consider that the amount of material placed on each cell is quite small. Therefore the cost penalty per cell is quite small too.
Benefits
The primary advantage of ITO compared to AZO as a transparent conductor for
LCDsA liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
is that ITO can be precisely etched into fine patterns. AZO cannot be etched as precisely: It is so sensitive to acid that it tends to get over-etched by an acid treatment.
Another benefit of ITO compared to AZO is that if moisture does penetrate, ITO will degrade less than AZO.
Research examples
ITO can be used in nanotechnology to provide a path to a new generation of solar cells. Solar cells made with these devices have the potential to provide low-cost, ultra-lightweight, and flexible cells with a wide range of applications. Because of the nanoscale dimensions of the nanorods, quantum-size effects influence their optical properties. By tailoring the size of the rods, they can be made to absorb light within a specific narrow band of colors. By stacking several cells with different sized rods, a broad range of wavelengths across the solar spectrum can be collected and converted to energy. Moreover, the nanoscale volume of the rods leads to a significant reduction in the amount of semiconductor material needed compared to a conventional cell.
External links