Tuesday, November 22, 2011

Silicon : chemical element with the symbol Si and atomic number 14

. Atetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discovery: Sony VPCM12M1E/W Battery

silicon was first prepared and characterized in pure form in 1824, and given the name silicium (fromLatin: silicis, flints), with an -ium word-ending to suggest a metal. However, its final name, suggested in 1831, reflects the more physically similar elements carbon and boron.Sony VPCM13M1E/L Battery

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) orsilicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the earth's crust (about 28% by mass) after oxygen. Sony VPCM13M1E/P Battery

Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building-use of clays, silica sand and stone. Silica is used in ceramic brick. Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concrete. Sony VPCM13M1E/W Battery

Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass. More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called silicones.Sony VAIO VGN-Z11MN/B Battery

Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Sony VAIO VGN-Z11VN/X Battery

Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on it.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals, however various sea sponges need silicon in order to have structure. Sony VAIO VGN-Z11WN/B Battery

It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatoms.

Silicon is a solid at room temperature, with relatively high melting and boiling points of approximately 1,400 and 2,800 degrees Celsius respectively.Sony VAIO VGN-Z11XN/B Battery

Interestingly, silicon has a greaterdensity in a liquid state than a solid state. Therefore, it does not contract when it freezes like most substances, but expands, similar to how ice is less dense than water and has less mass per unit of volume than liquid water. With a relatively high thermal conductivity of 149 W·m?1·K?1, silicon conducts heat well and as a result is not often used to insulate hot objects.Sony VAIO VGN-Z15 Battery

In its crystalline form, pure silicon has a gray color and a metallic luster. Like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of approximately 0.5430710 nm (5.430710 Å).Sony VAIO VGN-Z15N Battery

The outer electron orbital of silicon, like that of carbon, has four valence electrons. The 1s,2s,2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six.

Pure silicon has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. Sony VAIO VGN-Z17 Battery

The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.

Chemical

Silicon is a semiconductor, readily either donating or sharing its four outer electrons, allowing for many different forms of chemical bonding. Sony VAIO VGN-Z17N Battery

Even though it is, similar to carbon, a relatively inert element, silicon still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) have no known effect on it. However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.Sony VAIO VGN-Z19 Battery

Isotopes

Naturally occurring silicon is composed of three stable isotopes, silicon-28, silicon-29, and silicon-30, with silicon-28 being the most abundant (92% natural abundance). Out of these, only silicon-29 is of use in NMR and EPR spectroscopy.Sony VAIO VGN-Z19N Battery

Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-life of 170 years, and silicon-31 with a half-life of 157.3 minutes. All of the remainingradioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half lives that are less than one tenth of a second. Silicon does not have any known nuclear isomers.Sony VAIO VGN-Z21MN/B Battery

The isotopes of silicon range in mass number from 22 to 44. The most common decay mode of six isotopes with mass numbers lower than the most abundant stable isotope, silicon-28, is ?+, primarily forming aluminium isotopes (13 protons) as decay products. The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is ??, primarily forming phosphorus isotopes (15 protons) as decay products.Sony VAIO VGN-Z21VN/X Battery

Occurrence

Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance. Silicon is usually found in the form of silicon dioxide (silica', a major component of common sand), and other more complexsilicate minerals; pure silicon crystals are very rarely found in nature.Sony VAIO VGN-Z21WN/B Battery

Silica occurs in minerals consisting of very pure silicon dioxide in different crystalline forms, including amethyst, agate, quartz, rock crystal, chalcedony, flint, jasper, and opal. The crystals have the empirical formula of silicon dioxide, but do not consist of separate silicon dioxide molecules in the manner of solid carbon dioxide. Sony VAIO VGN-Z21XN Battery

Rather, silica is structurally a network solid consisting of silicon and oxygen in three-dimensional crystals, like diamond. Less pure silica forms the natural glass obsidian. Biogenic silica occurs in the structure of diatoms, radiolariaand siliceous sponges.

The silicate minerals—various minerals containing silicon, oxygen and one or another metal—account for 90% of the mass of the Earth's crust. Sony VAIO VGN-Z21ZN/X Battery

Examples of such minerals include those in thepyroxene, amphibole, mica, and feldspar groups. These minerals occur in clay and various types of rock such as granite andsandstone. Silicon is also a principal component of many meteorites, and also is a component of tektites, a silicate mineral of possibly lunar origin, or (if Earth-derived) which has been subjected to unusual temperatures and pressures, possibly from meteorite strike.Sony VAIO VGN-Z25 Battery

Alloys

Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with China, the leading supplier of elemental silicon, providing 4.6 million tonnes (or 2/3 or the world output) of silicon, most of which is in the form of ferrosilicon. Sony VAIO VGN-Z25/B Battery

It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t) and the United States (170,000 t). Ferrosilicon is primarily used by the steel industry (see below).

Aluminum-silicon alloys are heavily used in the aluminum alloy casting industry, where silicon is the single most important additive to aluminum to improve its casting properties. Sony VAIO VGN-Z25TN/B Battery

Since cast aluminum is widely used in the automobile industry, this use of silicon is thus the single largest industrial use of "metallurgical grade" pure silicon (as this purified silicon is added to pure aluminum, whereas ferrosilicon is never purified before being added to steel).Sony VAIO VGN-Z26TN/B Battery

Metallurgical grade

Elemental silicon not alloyed with significant quantities of other elements, and usually > 95% is often referred to loosely as silicon metal. It makes up about 20% of the world total elemental silicon production, with less than 1 to 2% of total elemental silicon (5–10% of metallurgical grade silicon) ever purified to higher grades for use in electronics.Sony VAIO VGN-Z27 Battery

Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in anelectric arc furnace using carbon electrodes. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo thechemical reaction SiO2 + 2 C ? Si + 2 CO. Sony VAIO VGN-Z27/B Battery

Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide (SiC) may also form from an excess of carbon in one or both of the following ways: SiO2 + C ? SiO + CO or SiO + 2 C ? SiC + CO.Sony VAIO VGN-Z27TN/X Battery

However, provided the concentration of SiO2 is kept high, the silicon carbide can be eliminated by the chemical reaction 2 SiC + SiO2? 3 Si + 2 CO.

As noted above, metallurgical grade silicon "metal" has its primary use in the aluminum casting industry to make aluminum-silicon alloy parts. Sony VAIO VGN-Z29N Battery

The remainder (about 45%) is used by the chemical industry, where it is primarily employed to make fumed silica.

As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg),[15] up from $0.77 per pound ($1.70/kg) in 2005.Sony VAIO VGN-Z29N/X Battery

Electronic grade

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Very pure silicon (>99.9%) can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis.Sony VAIO VGN-Z31MN/B Battery

This method, known as early as 1854 (see also FFC Cambridge Process), has the potential to directly produce solar-grade silicon without any carbon dioxideemission at much lower energy consumption.

Solar grade silicon cannot be used for semiconductors, where purity must be extreme in order to properly control the process.Sony VAIO VGN-Z31VN/X Battery

Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which requires repeated applications of refining technology.

The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. Sony VAIO VGN-Z31WN/B Battery

However, single crystals grown by the Czochralski process contain impurities because the crucible containing the melt often dissolves. Historically, a number of methods have been used to produce ultra-high-purity silicon.

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities.Sony VAIO VGN-Z31ZN/X Battery

The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. Sony VAIO VGN-Z35 Battery

As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end.Sony VAIO VGN-Z35/B Battery

Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and re-solidifies behind it. Since most impurities tend to remain in the molten region rather than re-solidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted.Sony VAIO VGN-Z35TN/B Battery

This end is then cut off and discarded, and the process repeated if a still higher purity is desired.

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon by SiCl4 + 2 Zn ? Si + 2 ZnCl2. Sony VAIO VGN-Z36GD Battery

However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process. In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C.Sony VAIO VGN-Z36GD/B Battery

The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them because 2 HSiCl3 ? Si + 2 HCl + SiCl4. Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than one part per billion.Sony VAIO VGN-Z36GD/J Battery

In 2006 REC announced construction of a plant based on fluidized bed (FB) technology using silane: 3 SiCl4 + Si + 2 H2 ? 4 HSiCl3, 4 HSiCl3 ? 3 SiCl4 + SiH4, SiH4 ? Si + 2 H2. The advantage of fluid bed technology is that processes can be run continuously, yielding higher yields than Siemens Process, which is a batch process.Sony VAIO VGN-Z36TD/B Battery

Today, silicon is purified by converting it to a silicon compound that can be more easily purified by distillation than in its original state, and then converting that silicon compound back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, althoughsilicon tetrachloride and silane are also used. Sony VAIO VGN-Z36TD/J Battery

When these gases are blown over silicon at high temperature, they decompose to high-purity silicon.

In addition, there exists the Schumacher process, which utilizes tribromosilane in place of trichlorosilane and fluid bed technology.Sony VAIO VGN-Z37D Battery

It requires lower deposition temperatures, lower capital costs to build facilities and operate, no hazardous polymers nor explosive material, and no amorphous silicon dust waste, all of which are drawbacks of the Siemens Process. However, there are yet to be any major factories built on this process.Sony VAIO VGN-Z37D/B Battery

Compounds

  • Silicon forms binary compounds called silicides with many metallic elements whose properties range from reactive compounds, e.g.magnesium silicide, Mg2Si through high melting refractory compounds such as molybdenum disilicide, MoSi2.Sony VAIO VGN-Z37GD Battery
  • Silicon carbide, SiC (carborundum) is a hard, high melting solid and a well known abrasive. It may also be sintered into a type of high-strength ceramic used in armor.
  • Silane, SiH4, is a pyrophoric gas with a similar tetrahedral structure to methane, CH4. When pure, it does not react with pure water or dilute acids;Sony VAIO VGN-Z37GD/X Battery
  • however, even small amounts of alkali impurities from the laboratory glass can result in a rapid hydrolysis. There is a range of catenated silicon hydrides that form a homologous series of compounds, SinH2n+2 where n = 2–8 (analogous to the alkanes). These are all readily hydrolyzed and are thermally unstable, particularly the heavier members.Sony VAIO VGN-Z39D Battery
  • Disilenes contain a silicon-silicon double bond (analogous to the alkenes) and are generally highly reactive requiring large substituent groups to stabilize them. A disilyne with a silicon-silicon triple bond was first isolated in 2004; although as the compound is non-linear, the bonding is dissimilar to that in alkynes.Sony VAIO VGN-Z39D/X Battery
  • Tetrahalides, SiX4, are formed with all of the halogens. Silicon tetrachloride, for example, reacts with water, unlike its carbon analogue, carbon tetrachloride. Silicon dihalides are formed by the high temperature reaction of tetrahalides and silicon; with a structure analogous to a carbene they are reactive compounds. Silicon difluoride condenses to form a polymeric compound, (SiF2)n. Sony VAIO VGN-Z41MD/B Battery
  • Silicon dioxide is a high melting solid with a number of different crystal forms; the most familiar of which is the mineral quartz. In quartz each silicon atom is surrounded by four oxygen atoms that bridge to other silicon atoms to form a three dimensional lattice.Sony VAIO VGN-Z41WD/B Battery
  • Silica is soluble in water at high temperatures forming a range of compounds called monosilicic acid, Si(OH)4.
  • Under the right conditions monosilicic acid readily polymerizes to form more complex silicic acids, ranging from the simplest condensate, disilicic acid (H6Si2O7) to linear, ribbon, layer and lattice structures which form the basis of the many different silicate minerals and are called polysilicic acids {Six(OH)4–2x}n.Sony VAIO VGN-Z45GD/B Battery
  • With oxides of other elements the high temperature reaction of silicon dioxide can give a wide range of glasses with various properties.[35] Examples include soda lime glass, borosilicate glass and lead crystal glass.
  • Silicon sulfide, SiS2 is a polymeric solid (unlike its carbon analogue the liquid CS2).Sony VAIO VGN-Z45TD/B Battery
  • Silicon forms a nitride, Si3N4 which is a ceramic. Silatranes, a group of tricyclic compounds containing five-coordinate silicon, may have physiological properties.
  • Many transition metal complexes containing a metal-silicon bond are now known, which include complexes containing SiHnX3?n ligands, SiX3 ligands, and Si(OR)3ligands.Sony VAIO VGN-Z46GD/B Battery
  • Silicones are large group of polymeric compounds with an (Si-O-Si) backbone. An example is the silicone oil PDMS (polydimethylsiloxane). These polymers can be crosslinked to produce resins and elastomers.
  • Many organosilicon compounds are known which contain a silicon-carbon single bond. Sony VAIO VGN-Z46GD/U Battery
  • Many of these are based on a central tetrahedral silicon atom, and some are optically active when central chirality exists. Long chain polymers containing a silicon backbone are known, such as polydimethysilylene (SiMe2)n.Polycarbosilane, [(SiMe2)2CH2]n with a backbone containing a repeating -Si-Si-C unit, is a precursor in the production of silicon carbide fibers.Sony VAIO VGN-Z46MD/B Battery

History

Attention was first drawn to quartz as the possible oxide of a fundamental chemical element by Antoine Lavoisier, in 1787. Sony VAIO VGN-Z46SD/B Battery

In 1811, Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon, through the heating of recently isolated potassium metal with silicon tetrafluoride, but they did not purify and characterize the product, nor identify it as a new element. Sony VAIO VGN-Z46TD/B Battery

In 1824, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac (potassium metal and potassium fluorosilicate), but purifying the product to a brown powder by repeatedly washing it. He named the product silicium from the Latinsilex, silicis for flint, flints, and adding the "-ium" ending because he believed it was a metal. Sony VAIO VGN-Z46TD/R Battery

As a result he is usually given credit for element's discovery. Silicon was given its present name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius's name but added "-on" because he believed silicon a nonmetal more similar to boron and carbon.Sony VAIO VGN-Z47GD/X Battery

Silicon in its more common crystalline form was not prepared until 31 years later, by Deville. By electrolyzing impure sodium-aluminum chloride containing approximately 10% silicon, he was able to obtain a slightly impure allotrope of silicon in 1854.Later, more cost-effective methods have been developed to isolate silicon in several allotrope forms.Sony VAIO VGN-Z48GD/X Battery

Because silicon is an important element in semiconductors and high-technology devices, many places in the world bear its name. For example, Silicon Valley inCalifornia, since it is the base for a number of technology related industries, bears the name silicon. Other geographic locations with connections to the industry have since been named after silicon as well.Sony VAIO VGN-Z48TD/X Battery

Examples include Silicon Forest in Oregon, Silicon Hills in Austin, Texas, Silicon Saxony in Germany, Silicon Valley inIndia, Silicon Border in Mexicali, Mexico, Silicon Fen in Cambridge, England, and Silicon Gorge in Bristol, England.

Compounds

Most silicon is used industrially without being separated into the element, and indeed often with comparatively little processing from natural occurrence. Sony VAIO VGN-Z51WG/B Battery

Over 90% of the Earth's crust is composed of silicate minerals. Many of these have direct commercial uses, such as clays, silica sand and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). Sony VAIO VGN-Z51XG/B Battery

For example, silica is an important part of ceramic brick. Silicates are used in making Portland cement which is used in building mortar and stucco, but more importantly combined with silica sand, and gravel (usually containing silicate minerals like granite), to make the concrete that is the basis of most of the very largest industrial building projects of the modern world.Sony VAIO VGN-Z530N/B Battery

Silicate minerals are also in whiteware ceramics, an important class of products usually containing various types of fired clay (natural aluminum silicate). An example is porcelain which is based on silicate mineral kaolinite. Ceramics include art objects, and also domestic, industrial and building products. Sony VAIO VGN-Z540EBB Battery

Traditionalquartz-based soda-lime glass also functions in many of the same roles.

More modern silicon compounds also function as high-technology abrasives and new high-strength ceramics based upon (silicon carbide), and also in superalloys.Sony VAIO VGN-Z540NLB Battery

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon bonds form the ubiquitous silicon-based polymeric materials known as silicones. These compounds containing silicon-oxygen and occasionally silicon-carbon bonds have the capability to act as bonding intermediates between glass and organic compounds,Sony VAIO VGN-Z540NMB Battery

and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are often used inwaterproofing treatments, molding compounds, mold-release agents, mechanical seals, high temperature greases and waxes, and caulking compounds. Sony VAIO VGN-Z550N/B Battery

Silicone is also sometimes used in breast implants, contact lenses, explosives and pyrotechnics. Silly Putty was originally made by adding boric acid to silicone oil.

Alloys

Elemental silicon is added to molten cast iron as ferrosilicon or silicocalcium alloys in order to improve performance in casting thin sections, and to prevent the formation of cementite where exposed to outside air.Sony VAIO VGN-Z55F Battery

The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steel, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is impure, it accounts for 80% of the world's use of free silicon.Sony VAIO VGN-Z55TG/B Battery

The properties of silicon itself can be used to modify alloys. Silicon's importance in aluminum casting is that a significantly high amount (12%) of silicon in aluminum forms a eutectic mixture which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidity.Sony VAIO VGN-Z56GG/B Battery

Silicon also significantly improves the hardness and thus wear-resistance of aluminum. Silicon is an important constituent of electrical steel, modifying its resistivity and ferromagnetic properties.

Metallurgical grade silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminum-silicon alloys for aluminum part casts, mainly for use in the automotive industry. Sony VAIO VGN-Z56GG/E Battery

The reason for the high silicon use in these alloys is noted above.Much of the rest of metallurgical-grade silicon is used by the chemical industry for production of the important industrial product fumed silica. The remainder is used in production of other fine chemicals such as silanes and some types of silicones.Sony VAIO VGN-Z56GGX Battery

Electronics

Since most elemental silicon produced remains as ferrosilicon alloy, only a relatively small amount (20%) of the elemental silicon produced is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year).Sony VAIO VGN-Z56TG/B Battery

The fraction of silicon metal which is further refined to semiconductor purity is estimated at only 15% of the world production of metallurgical grade silicon. However, the economic importance of this small very high-purity fraction (especially the ~ 5% which is processed to monocrystalline silicon for use in integrated circuits) is disproportionately large.Sony VAIO VGN-Z56TG/E Battery

Pure monocrystalline silicon is used to produce silicon wafers used in the semiconductor industry, in electronics and in some high-cost and high-efficiency photovoltaic applications. In terms of charge conduction, pure silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heat,Sony VAIO VGN-Z56TG/R Battery

and thus increase silicon's electrical conductance with higher temperatures. Pure silicon has too low a conductance to be used as a circuit element in electronics without being doped with small concentrations of certain other elements. This process greatly increases its conductivity and adjusts its electrical response by controlling the number and charge Sony VAIO VGN-Z570N/B Battery

(positive or negative) of activated carriers. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices, which are used in the computer industry and other technical applications. For example, in silicon photonics, silicon can be used as a continuous wave Raman laser medium to produce coherent light,Sony VAIO VGN-Z57G Battery

though it is ineffective as an everyday light source.

In common integrated circuits, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping, and insulated from each other by thin layers of silicon oxide, an insulator which is easily produced by exposing the element to oxygen under the proper conditions.Sony VAIO VGN-Z57GG/X Battery

Silicon has become the most popular material to build both high power semiconductors and integrated circuits, because of all the elements, silicon is the semiconductor which can withstand the highest powers and temperatures without becoming dysfunctional due to avalanche breakdown,Sony VAIO VGN-Z57GGX Battery

a process an electron avalanche is created by a chain reaction process where heat produces free electrons and holes, which in turn produce more current which produces more heat. In addition, the insulating oxide of silicon is not soluble in water, which gives it an advantage over germanium Sony VAIO VGN-Z57TG/X Battery

(an element with similar properties which can also be used in semiconductor devices) in certain type of fabrication techniques.

Monocrystalline silicon is expensive to produce, and is usually only justified in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. Sony VAIO VGN-Z58GG/X Battery

For other uses, other types of pure silicon which do not exist as single crystals may be employed. These include hydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) which are used in the production of low-cost, large-area electronics in applications such as Liquid crystal displays, and of large-area, low-cost, thin-film solar cells.Sony VAIO VGN-Z58GGX Battery

Such semiconductor grades of silicon which are either slightly less pure than those used in integrated circuits, or which are produced in polycrystalline rather than monocrystalline form, make up roughly similar amount of silicon as are produced for the monocrystalline silicon semiconductor industry, or 75,000 to 150,000 metric tons per year. Sony VAIO VGN-Z590NJB Battery

However, production of such materials is growing more quickly than silicon for the integrated circuit market. By 2013 polycrystalline silicon production, used mostly in solar cells, is projected to reach 200,000 metric tons per year, while monocrystalline semiconductor silicon production (used in computer microchips) remains below 50,000 tons/year.Sony VAIO VGN-Z590UAB Battery

Biological role

Although silicon is readily available in the form of silicates, very few organisms have a use for it. Diatoms, radiolaria andsiliceous sponges use biogenic silica as a structural material to construct skeletons. Sony VAIO VGN-Z591U/B Battery

In more advanced plants, the silicaphytoliths (opal phytoliths) are rigid microscopic bodies occurring in the cell; some plants, for example rice, need silicon for their growth. Although silicon was proposed to be an ultra trace nutrition its exact function in the biology of animals is still under discussion. Sony VAIO VGN-Z59G Battery

Higher organisms are only known to use it in very limited occasions in the form of silicic acid and soluble silicates.

Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO)."Sony VAIO VGN-Z620D Battery

Silicon has been shown in university and field studies to improve plant cell wall strength and structural integrity, improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems. Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yields.Sony VAIO VGN-Z620N/B Battery

Hypothetical silicon-based lifeforms are the subject of silicon biochemistry, in analogy with carbon-based lifeforms. Silicon, being below carbon in the periodic table, is thought to have similar enough properties that would make silicon-based life possible, but much different from life as we know it.Sony VAIO VGN-Z650N/B Battery

Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical andelectronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Sony VAIO VGN-Z670N/B Battery

Silicon is almost always used, but various compound semiconductors are used for specialized applications.

The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs.Sony VAIO VGN-Z690CTO Battery

When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing. As devices became more integrated,cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, which could come to rest on the wafers and contribute to defects.Sony VAIO VGN-Z690NAX Battery

The workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination.

In an effort to increase profits, semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, such as Europe, Middle East, and Asia. It is a global business today.Sony VAIO VGN-Z690PAB Battery

The leading semiconductor manufacturers typically have facilities all over the world. Intel, the world's largest manufacturer, has facilities in Europe and Asia as well as the U.S. Other top manufacturers include Taiwan Semiconductor Manufacturing Company(Taiwan), Sony VAIO VGN-Z690PCB Battery

STMicroelectronics (Europe), Analog Devices (US), Integrated Device Technology (US), Atmel (US/Europe), Freescale Semiconductor (US), Samsung (Korea), Texas Instruments (US), IBM (US), GlobalFoundries (Germany, Singapore, future New York fab in construction), Toshiba (Japan), NEC Electronics (Japan), Infineon (Europe), Renesas (Japan), Fujitsu (Japan/US), NXP Semiconductors (Europe and US), Micron Technology (US), Hynix (Korea) and SMIC (China).Sony VAIO VGN-Z690PDB Battery

Wafers

A typical wafer is made out of extremely pure silicon that is grown into mono-crystalline cylindrical ingots (boules) up to 300 mm (slightly less than 12 inches) in diameter using the Czochralski process. These ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very regular and flat surface.Sony VAIO VGN-Z690PEB Battery

Once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. In general, the steps can be grouped into two major parts:

Processing

In semiconductor device fabrication, the various processing steps fall into four general categories: deposition, removal, patterning, and modification of electrical properties.Sony VAIO VGN-Z690YAD Battery

  • Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. Available technologies consist of physical vapor deposition (PVD),chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and more recently, atomic layer deposition (ALD) among others.Sony VAIO VGN-Z691Y/B Battery
  • Removal processes are any that remove material from the wafer either in bulk or selectively and consist primarily of etch processes, either wet etching or dry etching. Chemical-mechanical planarization (CMP) is also a removal process used between levels.Sony VAIO VGN-Z691Y/X Battery
  • Patterning covers the series of processes that shape or alter the existing shape of the deposited materials and is generally referred to as lithography. For example, in conventional lithography, the wafer is coated with a chemical called a photoresist.Sony VAIO VGN-Z698Y/X Battery
  • The photoresist is exposed by a stepper, a machine that focuses, aligns, and moves the mask, exposing select portions of the wafer to short wavelength light. The unexposed regions are washed away by a developer solution. After etching or other processing, the remaining photoresist is removed by plasma ashing.Sony VAIO VGN-Z699JAB Battery
  • Modification of electrical properties has historically consisted of doping transistor sources and drains originally by diffusion furnaces and later by ion implantation. These doping processes are followed by furnace anneal or in advanced devices, by rapid thermal anneal (RTA) which serve to activate the implanted dopants. Sony VAIO VGN-Z70B Battery
  • Modification of electrical properties now also extends to reduction of dielectric constant in low-k insulating materials via exposure to ultraviolet light in UV processing (UVP).

Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps.Sony VAIO VGN-Z71JB Battery

Front-end-of-line (FEOL) processing

FEOL processing refers to the formation of the transistors directly in the silicon. The raw wafer is engineered by the growth of an ultrapure, virtually defect-free silicon layer through epitaxy. In the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built.Sony VAIO VGN-Z73FB Battery

One method involves introducing a straining step wherein a silicon variant such as silicon-germanium (SiGe) is deposited. Once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility.Sony VAIO VGN-Z790DKX Battery

Another method, called silicon on insulatortechnology involves the insertion of an insulating layer between the raw silicon wafer and the thin layer of subsequent silicon epitaxy. This method results in the creation of transistors with reduced parasitic effects.Sony VAIO VGN-Z790DMR Battery

Gate oxide and implants

Front-end surface engineering is followed by: growth of the gate dielectric, traditionally silicon dioxide (SiO2), patterning of the gate, patterning of the source and drain regions, and subsequent implantation or diffusion of dopants to obtain the desired complementary electrical properties. Sony VAIO VGN-Z790DND Battery

In dynamic random access memory(DRAM) devices, storage capacitors are also fabricated at this time, typically stacked above the access transistor (implementing them as trenches etched deep into the silicon surface was a technique developed by the now defunct DRAM manufacturer Qimonda).Sony VAIO VGN-Z820DB Battery

Metal layers

Once the various semiconductor devices have been created, they must be interconnected to form the desired electrical circuits. This occurs in a series of wafer processing steps collectively referred to as BEOL (not to be confused with back end of chip fabrication which refers to the packaging and testing stages). Sony VAIO VGN-Z820G/B Battery

BEOL processing involves creating metal interconnecting wires that are isolated by dielectric layers. The insulating material was traditionally a form of SiO2 or asilicate glass, but recently new low dielectric constant materials are being used. These dielectrics presently take the form of SiOC and have dielectric constants around 2.7 (compared to 3.9 for SiO2), although materials with constants as low as 2.2 are being offered to chipmakers.Sony VAIO VGN-Z890GLX Battery

Interconnect

Historically, the metal wires consisted of aluminium. In this approach to wiring often called subtractive aluminium, blanket films of aluminium are deposited first, patterned, and then etched, leaving isolated wires. Dielectric material is then deposited over the exposed wires. Sony VAIO VGN-Z890GMR Battery

The various metal layers are interconnected by etching holes, called vias, in the insulating material and depositing tungsten in them with a CVD technique. This approach is still used in the fabrication of many memory chips such as dynamic random access memory (DRAM) as the number of interconnect levels is small, currently no more than four.Sony VAIO VGN-Z898H/X Battery

More recently, as the number of interconnect levels for logic has substantially increased due to the large number of transistors that are now interconnected in a modern microprocessor, the timing delay in the wiring has become significant prompting a change in wiring material from aluminium to copper and from the silicon dioxides to newer low-K material. Sony VAIO VGN-Z90FS Battery

This performance enhancement also comes at a reduced cost via damascene processing that eliminates processing steps. As the number of interconnect levels increases, planarization of the previous layers is required to ensure a flat surface prior to subsequent lithography. Sony VAIO VGN-Z90NS Battery

Without it, the levels would become increasingly crooked and extend outside the depth of focus of available lithography, interfering with the ability to pattern. CMP (chemical mechanical planarization) is the primary processing method to achieve such planarization although dry etch back is still sometimes employed if the number of interconnect levels is no more than three.Sony VAIO VGN-Z90PS Battery

Wafer test

The highly serialized nature of wafer processing has increased the demand for metrology in between the various processing steps. Wafer test metrology equipment is used to verify that the wafers haven't been damaged by previous processing steps up until testing.Sony VAIO VGN-Z90S Battery

If the number of dies—the integrated circuits that will eventually become chips— etched on a wafer exceeds a failure threshold (i.e. too many failed dies on one wafer), the wafer is scrapped rather than investing in further processing.Sony VAIO VGN-Z90US Battery

Device test

Once the front-end process has been completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. The proportion of devices on the wafer found to perform properly is referred to as the yield.Sony VAIO VGN-Z91DS Battery

The fab tests the chips on the wafer with an electronic tester that presses tiny probes against the chip. The machine marks each bad chip with a drop of dye. Currently, electronic dye marking is possible if wafer test data is logged into a central computer database and chips are "binned" (i.e. sorted into virtual bins) according to predetermined test limits. Sony VAIO VGN-Z91JS Battery

The resulting binning data can be graphed, or logged, on a wafer map to trace manufacturing defects and mark bad chips. This map can be also used during wafer assembly and packaging.

Chips are also tested again after packaging, as the bond wires may be missing, or analog performance may be altered by the package. This is referred to as "final test".Sony VAIO VGN-Z91PS Battery

Usually, the fab charges for test time, with prices in the order of cents per second. Test times vary from a few milliseconds to a couple of seconds, and the test software is optimized for reduced test time. Multiple chip (multi-site) testing is also possible, since many testers have the resources to perform most or all of the tests in parallel.Sony VAIO VGN-Z91YS Battery

Chips are often designed with "testability features" such as scan chains and "built-in self-test" to speed testing, and reduce test costs. In certain designs that use specialized analog fab processes, wafers are also laser-trimmed during test, to achieve tightly-distributed resistance values as specified by the design.Sony VAIO VGN-Z92DS Battery

Good designs try to test and statistically manage corners: extremes of silicon behavior caused by operating temperature combined with the extremes of fab processing steps. Most designs cope with more than 64 corners.

Polycrystalline silicon, also called polysilicon, is a material consisting of small silicon crystals. Sony VAIO VGN-Z92JS Battery

It differs from single-crystal silicon, used for electronics and solar cells, and from amorphous silicon, used for thin film devices and solar cells.

Single crystalline vs polycrystalline silicon

In single crystal silicon, the crystalline framework is homogenous, which can be recognized by an even external colouring.Sony VAIO VGN-Z92PS Battery

In single crystal silicon, also called monocrystal, the crystal lattice of the entire sample is continuous and unbroken with no grain boundaries. Large single crystals are exceedingly rare in nature and can also be difficult to produce in the laboratory (see alsorecrystallisation). Sony VAIO VGN-Z92YS Battery

In contrast, in an amorphous structure the order in atomic positions is limited to short range.

Polycrystalline and paracrystalline phases (see Polycrystal) are composed of a number of smaller crystals or crystallites.Polycrystalline silicon (or semicrystalline silicon, polysilicon, poly-Si, or simply "poly") is a material consisting of multiple small silicon crystals.Sony VAIO VGN-Z93FS Battery

Polycrystalline cells can be recognized by a visible grain, a “metal flake effect”. Semiconductor grade (also solar grade) polycrystalline silicon is converted to "single crystal" silicon – meaning that the randomly associated crystallites of silicon in "polycrystalline silicon" are converted to a large "single" crystal.Sony VAIO VGN-Z93GS Battery

Single crystal silicon is used to manufacture most Si-based microelectronic devices. Polycrystalline silicon can be as much as 99.9999% pure. Ultra-pure poly is used in the semiconductor industry, starting from poly rods that are five to eight feet in length.Sony VAIO VGN-Z93HS Battery

In microelectronic industry (semiconductor industry), poly is used both at the macro-scale and micro-scale (component) level. Single crystals are grown using the Czochralski process, float-zone and Bridgman techniques.

Polycrystalline silicon components

Polysilicon is a key component for integrated circuit and central processing unit manufacturers such as AMD and Intel. Sony VAIO VGN-Z93VS Battery

At the component level, polysilicon has long been used as the conducting gate material in MOSFET and CMOS processing technologies. For these technologies it is deposited using low-pressure chemical-vapour deposition (LPCVD) reactors at high temperatures and is usually heavily doped n-type or p-type.Sony A1258274A Battery

More recently, intrinsic and doped polysilicon is being used in large-area electronics as the active and/or doped layers in thin-film transistors. Although it can be deposited by LPCVD, plasma-enhanced chemical vapour deposition (PECVD), or solid-phase crystallization (SPC) of amorphous silicon in certain processing regimes, Sony VGP-BPL10 Battery

these processes still require relatively high temperatures of at least 300 °C. These temperatures make deposition of polysilicon possible for glass substrates but not forplastic substrates. The deposition of polycrystalline silicon on plastic substrates is motivated by the desire to be able to manufacture digital displays on flexible screens. Sony VGP-BPS10 Battery

Therefore, a relatively new technique called laser crystallization has been devised to crystallize a precursor amorphous silicon (a-Si) material on a plastic substrate without melting or damaging the plastic. Short, high-intensity ultraviolet laser pulses are used to heat the deposited a-Si material to above the melting point of silicon, without melting the entire substrate.Sony VGP-BPS10/S Battery

The molten silicon will then crystallize as it cools. By precisely controlling the temperature gradients, researchers have been able to grow very large grains, of up to hundreds of micrometers in size in the extreme case, although grain sizes of 10 nanometers to 1 micrometer are also common. Sony VGP-BPS10A/B Battery

In order to create devices on polysilicon over large-areas however, a crystal grain size smaller than the device feature size is needed for homogeneity of the devices. Another method to produce poly-Si at low temperatures is metal-induced crystallization where an amorphous-Si thin film can be crystallized at temperatures as low as 150C if annealed while in contact of another metal film such as aluminium, gold, or silver.Sony VGP-BPS10B Battery

Polysilicon has many applications in VLSI manufacturing. One of its primary uses is as gate electrode material for MOS devices. A polysilicon gate's electrical conductivity may be increased by depositing a metal (such as tungsten) or a metal silicide (such as tungsten silicide) over the gate. Sony VGP-BPS10A Battery

Polysilicon may also be employed as a resistor, a conductor, or as an ohmic contact for shallow junctions, with the desired electrical conductivity attained by doping the polysilicon material.

One major difference between polysilicon and a-Si is that the mobility of the charge carriers of the polysilicon can be orders of magnitude larger and the material also shows greater stability under electric field and light-induced stress. Sony VGP-BPS11 Battery

This allows more complex, high-speed circuity to be created on the glass substrate along with the a-Si devices, which are still needed for their low-leakage characteristics. When polysilicon and a-Si devices are used in the same process this is called hybrid processing.Sony VGP-BPL11 Battery

A complete polysilicon active layer process is also used in some cases where a small pixel size is required, such as in projection displays.

Solar panel and applications

Polycrystalline silicon is also a key component of solar panel construction. Growth of the photovoltaic solar industry was limited by the supply of the polysilicon material.Sony VGP-BPL12 Battery

For the first time, in 2006, over half of the world's supply of polysilicon was being used for production of renewable electricity solar power panels. Only twelve factories were known to produce solar-grade polysilicon in 2008. Monocrystalline silicon was higher priced and more efficient than multicrystalline. Sony VGP-BPS12 Battery

This however changed and, in 2011, there was a large excess of production capacity of polysilicon.

Deposition methods

Polysilicon deposition, or the process of depositing a layer of polycrystalline silicon on a semiconductor wafer, is achieved by pyrolyzing silane (SiH4) at 580 to 650 °C. This pyrolysis process releases hydrogen.Sony VGP-BPL13 Battery

Polysilicon layers can be deposited using 100% silane at a pressure of 25–130 Pa (0.2 to 1.0 Torr) or with 20–30% silane (diluted in nitrogen) at the same total pressure. Both of these processes can deposit polysilicon on 10–200 wafers per run, at a rate of 10–20 nm/min and with thickness uniformities of ±5%. Sony VGP-BPS13 Battery

Critical process variables for polysilicon deposition include temperature, pressure, silane concentration, and dopant concentration. Wafer spacing and load size have been shown to have only minor effects on the deposition process. The rate of polysilicon deposition increases rapidly with temperature, since it follows Arrheniusbehavior, Sony VGP-BPS13/B Battery

that is deposition rate = A·exp(–qEa/kT) where q is electron charge and k is the Boltzmann constant. The activation energy (Ea) for polysilicon deposition is about 1.7 eV. Based on this equation, the rate of polysilicon deposition increases as the deposition temperature increases. Sony VGP-BPS13/S Battery

There will be a minimum temperature, however, wherein the rate of deposition becomes faster than the rate at which unreacted silane arrives at the surface. Beyond this temperature, the deposition rate can no longer increase with temperature, since it is now being hampered by lack of silane from which the polysilicon will be generated. Sony VGP-BPS13/S Battery

Such a reaction is then said to be 'mass-transport-limited.' When a polysilicon deposition process becomes mass-transport-limited, the reaction rate becomes dependent primarily on reactant concentration, reactor geometry, and gas flow.

When the rate at which polysilicon deposition occurs is slower than the rate at which unreacted silane arrives, then it is said to be surface-reaction-limited. Sony VGP-BPS13A/B Battery

A deposition process that is surface-reaction-limited is primarily dependent on reactant concentration and reaction temperature. Deposition processes must be surface-reaction-limited because they result in excellent thickness uniformity and step coverage.Sony VGP-BPS13A/S Battery

A plot of the logarithm of the deposition rate against the reciprocal of the absolute temperature in the surface-reaction-limited region results in a straight line whose slope is equal to –qEa/k.

At reduced pressure levels for VLSI manufacturing, polysilicon deposition rate below 575 °C is too slow to be practical. Sony VGP-BPS13AS Battery

Above 650 °C, poor deposition uniformity and excessive roughness will be encountered due to unwanted gas-phase reactions and silane depletion. Pressure can be varied inside a low-pressure reactor either by changing the pumping speed or changing the inlet gas flow into the reactor. Sony VGP-BPS13B/B Battery

If the inlet gas is composed of both silane and nitrogen, the inlet gas flow, and hence the reactor pressure, may be varied either by changing the nitrogen flow at constant silane flow, or changing both the nitrogen and silane flow to change the total gas flow while keeping the gas ratio constant.Sony VGP-BPS13B/Q Battery

Polysilicon doping, if needed, is also done during the deposition process, usually by adding phosphine, arsine, or diborane. Adding phosphine or arsine results in slower deposition, while adding diborane increases the deposition rate. The deposition thickness uniformity usually degrades when dopants are added during deposition.Sony VGP-BPS13B/S Battery

Upgraded metallurgical-grade silicon

Upgraded metallurgical-grade (UMG) silicon (also known as UMG-Si) solar cell is being produced as a low cost alternative to polysilicon created by the Siemens process. UMG greatly reduces impurities in a variety of ways that require less equipment and energy than the Siemens process.Sony VGP-BPS13Q Battery

UMG is about 99% pure which is three or more orders of magnitude less pure and about 10 times less expensive than polysilicon ($1.70 to $3.20 per kg from 2005 to 2008 compared to $40 to $400 per kg for polysilicon). It has the potential to provide nearly-as-good solar cell efficiency at 1/5 the capital expenditure, half the energy requirements, and less than $15/kg.Sony VGP-BPS13S Battery

In 2008 several companies were touting the potential of UMG in 2010, but the credit crisis greatly lowered the cost of polysilicon and several UMG producers put plans on hold. The Siemens process will remain the dominant form of production for years to come due to more efficiently implementing the Siemens process.Sony VGP-BPL7 Battery

GT Solar claims a new Siemens process can produce at $27/kg and may reach $20/kg in 5 years. GCL-Poly expects production costs to be $20/kg by end of 2011. Elkem Solar estimates their UMG costs to be $25/kg, with a capacity of 6,000 tonnes by the end of 2010. Sony VGP-BPS7 Battery

Calisolar expects UMG technology to produce at $12/kg in 5 years with boron at 0.3 ppm and phosphorus at 0.6 ppm. At $50/kg and 7.5 g/W, module manufacturers spend $0.37/W for the polysilicon. For comparison, if a CdTe manufacturer pays spot price for tellurium ($420/kg in April 2010) and has a 3 micron thickness, their cost would be 10 times less, $0.037/Watt. At 0.1 g/W and $31/ozt for silver, polysilicon solar producers spend $0.10/W on silver. Sony VGP-BPL8 Battery

Q-Cells, Canadian Solar, and Calisolar have used Timminco UMG. Timminco is able to produce UMG-Si with 0.5 ppm boron for $21/kg but were sued by shareholders because they had expected $10/kg.[13] RSI and Dow Corning have also been in litigation over UMG-Si technology.Sony VGP-BPL8A Battery

Capacity

Polysilicon manufacturing market is in a very fast growth mode. According to Digitimes in July 2011, the total polysilicon production in 2010 was 209,000 tons and first-tier suppliers account for 64% of the market while China-based polysilicon firms have 30% of market share. Sony VGP-BPL8B Battery

The total production is likely to increase 37.4% to 281,000 tons by end of 2011. With high spot prices in 2008/2009 and lack of available material, many companies announced additional capacities for the coming years. Established producers (mentioned below) expand their capacities, additionally newcomers – especially from Asia – are moving into this market. Sony VGP-BPS8 Battery

Even long-time players in the field had difficulties recently to ramp-up new plants. It is yet unclear which companies will be able to produce at costs low enough to be profitable after the steep drop in spot-prices of the last months. Leading producer capacities:Sony VGP-BPS8A Battery

Price

Prices of polysilicon are often divided into two categories, contract and spot prices. While in booming installation times, price rally occurs in polysilicon. Not only spot prices surpass contract prices in the market; but it is also hard to acquire enough polysilicon.Sony VGP-BPS8B Battery

Buyers will accept down payment and long term agreements to acquire a large enough volume of polysilicon. On the contrary, spot prices will be below contract prices once the solar PV installation is in a down trend. In late 2010, booming installation brought up the spot prices of polysilicon.Sony VGP-BPL9 Battery

In the first half of 2011, prices of polysilicon kept strong owing to the FIT policies of Italy. The solar PV price survey and market research firm, PVinsights, reported that the prices of polysilicon might be dragged down by lack of installation in the second half of 2011.Sony VGP-BPS9 Battery

Covalent semiconductors are such solids as diamond, silicon, germanium, silicon carbide and silicon-germanium where atoms are linked by covalent bonds. Most of those materials, at least in their bulk form, are well studied and rarely hit the front pages of the top scientific journals in the last decade. Sony VGP-BPS9/B Battery

However, issue 23 of volume 93 (2004) of a major physics journal Physical Review Letters contained as many as 4 papers on diamond. Those papers were a reaction to a breakthrough discovery of superconductivity in synthetic diamond grown by high-pressure high-temperature (HPHT) method.Sony VGP-BPS9/S Battery

The discovery had no practical importance but surprised most scientists as superconductivity has not been considered seriously in covalent semiconductors.

Diamond

Superconductivity in diamond was achieved through heavy p-type doping by boron such that the individual doping atoms started interacting and formed an "impurity band".Sony VGP-BPS9A Battery

The superconductivity was of type-II with the critical temperature Tc = 4 K and critical magnetic field Hc = 4 T. Later, Tc ~ 11K has been achieved in homoepitaxial CVD films.

Regarding the origin of superconductivity in diamond, three alternative theories exist at the moment: Sony VGP-BPS9A/B Battery

conventional BCS theory based on phonon-mediated pairing, correlated impurity band theory and spin-flip-driven pairing of holes weakly localized in the vicinity of the Fermi level. Whereas there is no solid experimental support for either model, recent accurate measurements of isotopic shift of the transition temperature Tc upon boron and carbon isotopic substitutions favor the BCS theory.Sony VGP-BPS9A/S Battery

Silicon

It was suggested that "Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions", and indeed, discoveries of superconductivity in heavily boron doped Si (Si:B)[8] and SiC:B[9] have quickly followed. Sony VGP-BPS9B Battery

Similar to diamond, Si:B is type-II superconductor, but it has much smaller values of Tc = 0.4 K and Hc = 0.4 T. Superconductivity in Si:B was achieved by heavy doping (above 8 at.%), realized through a special non-equilibrium technique of gas immersion laser doping.Sony VGP-BPX11 Battery

Silicon carbide

Superconductivity in SiC was achieved by heavy doping with boron or aluminum. Both the cubic (3C-SiC) and hexagonal (6H-SiC) phases are superconducting and show a very similar Tc of 1.5 K. Sony VGP-BPL18 Battery

A crucial difference is however observed for the magnetic field behavior between aluminum and boron doping: SiC:Al is type-II, same as Si:B. On the contrary, SiC:B is type-I. In attempt to explain this difference, it was noted that Si sites are more important than carbon sites for superconductivity in SiC.Sony VGP-BPS18 Battery

Whereas boron substitutes carbon in SiC, Al substitutes Si sites. Therefore, Al and B "see" different environment that might explain different properties of SiC:Al and SiC:B.

Carbon nanotubes

Superconductivity in carbon nanotubes has been observed experimentally in 2001.Sony VGP-BPL20 Battery

Note however a crucial difference between nanotubes and diamond: Although nanotubes contain covalently bonded carbon atoms, they are closer in properties to graphite than diamond, and can be metallic without doping. Meanwhile, undoped diamond is an insulator.Sony VGP-BPS20/B Battery

The priority of many discoveries in science is vigorously disputed (see, e.g., Nobel Prize controversies). Another example, afterSumio Iijima has "discovered" carbon nanotubes in 1991, many scientists have pointed out that carbon nanofibers were actually observed decades earlier. Sony VGP-BPS20/S Battery

The same could be said about superconductivity in covalent semiconductors. Superconductivity ingermanium and silicon-germanium was predicted theoretically as early as in the 1960s. Shortly after, superconductivity was experimentally detected ingermanium telluride.Sony VGP-BPL21 Battery

In 1976, superconductivity with Tc = 3.5 K was observed experimentally in germanium implanted with copper ions; it was experimentally demonstrated that amorphization was essential for the superconductivity (in Ge), and the superconductivity was assigned to Ge itself, not copper.Sony VGP-BPS21 Battery

Monocrystalline silicon or single-crystal Si, or mono-Si is the base material of the electronic industry. It consists of silicon in which the crystal lattice of the entire solid is continuous, unbroken (with no grain boundaries) to its edges. Sony VGP-BPS21/S Battery

It can be prepared intrinsic, i.e. made of exceedingly pure silicon alone, or doped, containing very small quantities of other elements added to change in a controlled manner its semiconducting properties. Most silicon monocrystals are grown by the Czochralski process, in the shape of cylinders up to 2 m long and 30 cm in diameter (figure on the left), which, cut in thin slices, give thewafers onto which the microcircuits will be fabricated.Sony VGP-BPS21A Battery

Single-crystal silicon is perhaps the most important technological material of the last decades (the "silicon era"),[1] because its availability at an affordable cost has been essential for the development of the electronic devices on which the present day electronic and informatic revolution is based.Sony VGP-BPS21A/B Battery

Monocrystalline is opposed to amorphous silicon, in which the atomic order is limited to short range order only. In between the two extremes there is polycrystalline silicon, which is made up of small crystals, known as crystallites.Sony VGP-BPS21B Battery

Mono-Si in electronics

The monocrystalline form is used in the semiconductor device fabrication since grain boundaries would bring discontinuities and favor imperfections in the microstructure of silicon, such as impurities and crystallographic defects, which can have significant effects on the local electronic properties of the material.Sony VGP-BPL22 Battery

On the scale that devices operate on, these imperfections would have a significant impact on the functionality and reliability of the devices. Without the crystalline perfection, it would be virtually impossible to build Very Large-Scale Integration (VLSI) devices (figure at right), in which millions (up to billions, circa 2005) of transistor-based circuits, Sony VGP-BPS22 Battery

all of which must reliably be working, are combined into a single chip to get e.g. a microprocessor. Therefore, electronic industry has invested heavily in facilities to produce large single crystals of silicon.

Mono-Si in solar cells

Monocrystalline silicon is also used in the manufacturing of high performance solar cells. Sony VGP-BPS22/A Battery

Since, however, solar cells are less demanding than microelectronics for as concerns structural imperfections, monocrystaline solar grade (Sog-Si) is often used, single crystal is also often replaced by the cheaper polycrystalline or multicrystalline silicon.Sony VGP-BPS22A Battery

Monocrystalline solar cells can achieve 17% efficiency whereas other types of less expensive cells including thin film and polycrystalline are only capable of achieving around 10% efficiency.

Few solar charger companies use monocrystalline solar panels because of the higher cost to produce the solar cells, although these higher efficiency products are starting to pop up as consumers demand more efficient products. Sony VGP-BPL23 Battery

The 2010 Consumer Electronics Showshowcased one of these high-efficiency monocrystalline chargers known as the JOOS Orange and awarded it the 2010 Best of Innovations Award. The charger is manufactured by SolarJOOS, a Silicon Valley based solar company.Sony VGP-BPS23 Battery

Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment or other low-cost equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography and inkjet.Sony VGP-BPS23/B Battery

Electrically functional electronic or optical inks are deposited on the substrate, creating active or passive devices, such as thin film transistors or resistors. Printed electronics is expected to facilitate widespread, very low-cost, low-performance electronics for applications such as flexible displays, smart labels, decorative and animated posters, and active clothing that do not require high performance.Sony VGP-BPS23/D Battery

The term printed electronics is related to organic electronics or plastic electronics, in which one or more inks are composed of carbon-based compounds. These other terms refer to the ink material, which can be deposited by solution-based, vacuum-based or some other method.Sony VGP-BPS23/G Battery

Printed electronics, in contrast, specifies the process, and can utilize any solution-based material, including organic semiconductors, inorganic semiconductors, metallic conductors, nanoparticles, nanotubes, etc.

For the preparation of printed electronics nearly all industrial printing methods are employed. Sony VGP-BPS23/P Battery

Similar to conventional printing, printed electronics applies ink layers one atop another. so that the coherent development of printing methods and ink materials are the field's essential tasks.

The most important benefit of printing is low-cost volume fabrication. The lower cost enables use in more applications.Sony VGP-BPS23/W Battery

An example is RFID-systems, which enable contactless identification in trade and transport. In some domains, such as light-emitting diodes printing does not impact performance. Printing on flexible substrates allows electronics to be placed on curved surfaces, for example, putting solar cells on vehicle roofs.Sony Limited Edition 007 Battery

More typically, conventional semiconductors justify their much higher costs by providing much higher performance.

Resolution, registration, thickness, holes, materials

The maximum required resolution of structures in conventional printing is determined by the human eye. Sony VAIO VGC-LB15 Battery

Feature sizes smaller than approximately 20 µm cannot be distinguished by the human eye and consequently exceed the capabilities of conventional printing processes. In contrast, higher resolution and smaller structures are necessary in electronics printing, because they directly affect circuit density and functionality (especially transistors). Sony VGN-AR Series Battery

A similar requirement holds for the precision with which layers are printed on top of each other (layer to layer registration).

Control of thickness, holes, and material compatibility (wetting, adhesion, solvation) are essential, but matter in conventional printing only if the eye can detect them. Conversely, the visual impression is irrelevant.Sony VGN-CR Series Battery

Printing technologies

The attraction of printing technology for the fabrication of electronics mainly results from the possibility to prepare stacks of micro-structured layers (and thereby thin-film devices) in a much more simple and cost-effective way compared to conventional electronics.Sony VIAO VGN-G Series Battery

Beside this, also the possibility to implement new or improved functionalities (e.g. mechanical flexibility) plays a role. The selection of used printing methods is determined by requirements concerning printed layers, by properties of printed materials as well as economic and technical considerations in terms of printed products.Sony VIAO VGN-G118 Battery

Printing technologies divide between sheet-based and roll-to-roll-based approaches. Sheet-based techniques, such as inkjet and screen printing are best for low-volume, high-precision work. Gravure, offset and flexographic printing are more common for high-volume production, such as solar cells, reaching 10.000 square meters per hour (m²/h).Sony VIAO VGN-G118CN/B Battery

While offset and flexographic printing are mainly used for inorganic and organic conductors (the latter also for dielectrics), gravure printing is especially suitable for quality-sensitive layers like organic semiconductors and semiconductor/dielectric-interfaces in transistors, due to high layer quality.Sony VIAO VGN-G118CN/T Battery

In connection with high resolution, is also suitable for inorganic[12] and organic [13] conductors. Organic field-effect transistors and integrated circuits can be prepared completely by means of mass-printing methods.[11]

Inkjets are flexible and versatile, and can be set up with relatively low effort. Sony VIAO VGN-G218 Battery

Inkjets are probably the most commonly used method.[14] However, inkjets offer lower througput of around 100 m2/h and lower resolution (ca. 50 µm).[4] It is well suited for low-viscosity, soluble materials like organic semiconductors. With high-viscosity materials, Sony VGN-TZ121 Battery

like organic dielectrics, and dispersed particles, like inorganic metal inks, difficulties due to nozzle clogging occur. Because ink is deposited via droplets, thickness and dispersion homogeneity is reduced. Simultaneously using many nozzles and pre-structuring the substrate allows improvements in productivity and resolution, respectively.Sony VGN-TZ13 Battery

However, in the latter case non-printing methods must be employed for the actual patterning step.[15] Inkjet printing is preferable for organic semiconductors in organic field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs), but also OFETs completely prepared by this method have been demonstrated.Sony VGN-TZ131 Battery

Frontplanes[17] and backplanes[18] of OLED-displays, integrated circuits,[19] organic photovoltaic cells (OPVCs) [20] and other devices can be prepared with inkjets.

Screen printing is appropriate for fabricating electrics and electronics on industrial scales due to its ability to produce thick layers from paste-like materials. Sony VGN-TZ132N Battery

This method can produce conducting lines from inorganic materials (e.g. for circuit boards and antennas), but also insulating and passivating layers, whereby layer thickness is more important than high resolution. Its 50 m²/h throughput and 100 µm resolution are similar to inkjets.Sony VGN-TZ132/N Battery

This versatile and comparatively simple method is used mainly for conductive and dielectric layers, but also organic semiconductors, e.g. for OPVCs, and even complete OFETs can be printed.

Other methods with similarities to printing, among them micro-contact printing and nano-imprint lithography are of interest.Sony VGN-TZ17N Battery

Here, µm- and nm-sized layers, respectively, are prepared by methods similar to stamping with soft and hard forms, respectively. Often the actual structures are prepared subtractively, e.g. by deposition of etch masks or by lift-off processes. For example electrodes for OFETs can be prepared Sporadically pad printing is used in a similar manner.Sony VGN-TZ16N Battery

Occasionally so-called transfer methods, where solid layers are transferred from a carrier to the substrate, are considered printed electronics. Electrophotography is currently not used in printed electronics.

Materials

Both organic and inorganic materials are used for printed electronics. Sony VGN-TZ18N Battery

Ink materials must be available in liquid form, for solution, dispersion or suspension. They must function as conductors, semiconductors, dielectrics, or insulators. Material costs must be fit the application.

Electronic functionality and printability can interfere with each other, mandating careful optimization.Sony VAIO VGN-AR47G/E1 Battery

For example, a higher molecular weight in polymers enhances conductivity, but diminishes solubility. For printing, viscosity, surface tension and solid content must be tightly controlled. Cross-layer interactions such as wetting, adhesion, and solubility as well as post-deposition drying procedures affect the outcome. Sony VAIO VGN-AR520E Battery

Additives often used in conventional printing inks are unavailable, because they often defeat electronic functionality.

Material properties largely determine the differences between printed and conventional electronics. Printable materials provide decisive advantages beside printability, such as mechanical flexibility and functional adjustment by chemical modification (e.g. light color in OLEDs). Sony VAIO VGN-AR53DB Battery

Printed conductors offer lower conductivity and charge carrier mobility.

With a few exceptions, inorganic ink materials are dispersions of metallic micro- and nano-particles.

PMOS but not CMOS is possible in printed electronics.Sony VAIO VGN-AR54DB Battery

Organic materials

Organic printed electronics integrates knowledge and developments from printing, electronics, chemistry, and materials science, especially from organic and polymer chemistry. Organic materials in part differ from conventional electronics in terms of structure, operation and functionality, which influences device and circuit design and optimization as well as fabrication method.Sony VAIO VGN-AR550E Battery

The discovery of conjugated polymers and their development into soluble materials provided the first organic ink materials. Materials from this class of polymers variously possess conducting, semiconducting, electroluminescent, photovoltaic and other properties. Other polymers are used mostly as insulators and dielectrics.Sony VAIO VGN-AR55DB Battery

In most organic materials, hole transport is favored over electron transport. Recent studies indicate that this is a specific feature of organic semiconductor/dielectric-interfaces, which play a major role in OFETs. Therefore p-type devices should dominate over n-type devices. Durability (resistance to dispersion) and lifetime is less than conventional materials.Sony VAIO VGN-AR630E Battery

Organic semiconductors include the conductive polymers poly(3,4-ethylene dioxitiophene), doped with poly(styrene sulfonate), (PEDOT:PSS) and poly(aniline) (PANI). Both polymers are commercially available in different formulations and have been printed using inkjet,screen and offset printing or screen, flexo and gravure printing, respectively.Sony VAIO VGN-AR64DB Battery

Polymer semiconductors are processed using inkjet printing, such as poly(thiopene)s like poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene co-bithiophen) (F8T2). The latter material has also been gravure printed. Different electroluminescent polymers are used with inkjet printing,Sony VAIO VGN-AR65DB Battery

as well as active materials for photovoltaics (e.g. blends of P3HT with fullerene derivatives), which in part also can be deposited using screen printing (e.g. blends ofpoly(phenylene vinylene) with fullerene derivatives).

Printable organic and inorganic insulators and dielectrics exist, which can be processed with different printing methods.Sony VAIO VGN-AR660U Battery

Inorganic materials

Inorganic electronics provides highly ordered layers and interfaces that organic and polymer materials cannot provide.

Silver nanoparticles are used with flexo,[8] offset [42] and inkjet.[43] Gold particles are used with inkjet.Sony VAIO VGN-AR690U Battery

A.C. electroluminescent (EL) multi-color displays can cover many tens of square meters, or be incorporated in watch faces and instrument displays. They involve six to eight printed inorganic layers, including a copper doped phosphor, on a plastic film substrate. Sony VAIO VGN-AR71ZU Battery

CIGS cells can be printed directly onto molybdenum coated glass sheets.

A printed gallium arsenide germanium solar cell demonstrated 40.7% conversion efficiency, eight times that of the best organic cells, approaching the best performance of heavy silicon.Sony VAIO VGN-AR730E/B Battery

Substrates

Printed electronics allows the use of flexible substrates, which lowers production costs and allows fabrication of mechanically flexible circuits. While inkjet and screen printing typically imprint rigid substrates like glass and silicon, mass-printing methods nearly exclusively use flexible foil and paper.Sony VAIO VGN-AR73DB Battery

Poly(ethylene terephthalate)-foil (PET) is a common choice, due to its low cost and higher temperature stability. Poly(ethylene naphthalate)- (PEN) and poly(imide)-foil (PI) are alternatives. Paper's low costs and manifold applications make it an attractive substrate, however, its high roughness and large absorbency make it problematic for electronics.Sony VAIO VGN-AR74DB Battery

Other important substrate criteria are low roughness and suitable wettability, which can be tuned pre-treatment (coating, corona). In contrast to conventional printing, high absorbency is usually disadvantageous.

Applications

Printed electronics are in use or under consideration for: Sony VAIO VGN-AR75UDB Battery

Standards development and activities

Technical standards and roadmapping initiatives are intended to facilitate value chain development (for sharing of product specifications, characterizationstandards, etc.) This strategy of standards development mirrors the approach used by silicon-based electronics over the past 50 years.Sony VAIO VGN-AR820E Battery

Initiatives include:

Posted by at
Labels:

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)