Saturday, October 26, 2013

Black silicon is a needle-shaped surface

Aerosol Jet Printing (also known as Maskless Mesoscale Materials Deposition or M3D)[24] is another material deposition technology for printed electronics. The Aerosol Jet process begins with atomization of an ink, which can be heated up to 80 °C, producing droplets on the order of one to two micrometres in diameter. HP 480481-001 CPU Fan The atomized droplets are entrained in a gas stream and delivered to the print head. Here, an annular flow of clean gas is introduced around the aerosol stream to focus the droplets into a tightly collimated beam of material. The combined gas streams exit the print head through a converging nozzle that compresses the aerosol stream to a diameter as small as 10 µm. HP 622029-001 CPU Fan The jet of droplets exits the print head at high velocity (~50 meters/second) and impinges upon the substrate. Electrical interconnects, passive and active components[25] are formed by moving the print head, equipped with a mechanical stop/start shutter, relative to the substrate. The resulting patterns can have features ranging from 10 µm wide, with layer thicknesses from tens of nanometers to >10 µm.[26] Toshiba Satellite L555-12P CPU Fan A wide nozzle print head enables efficient patterning of millimeter size electronic features and surface coating applications. All printing occurs without the use of vacuum or pressure chambers and at room temperature. The high exit velocity of the jet enables a relatively large separation between the print head and the substrate, typically 2–5 mm. HP GB0507PGV1-A CPU Fan The droplets remain tightly focused over this distance, resulting in the ability to print conformal patterns over three dimensional substrates. Despite the high velocity, the printing process is gentle; substrate damage does not occur and there is generally no splatter or overspray from the droplets.[27] Once patterning is complete, the printed ink typically requires post treatment to attain final electrical and mechanical properties. HP Pavilion dv7-1135nr CPU Fan Post-treatment is driven more by the specific ink and substrate combination than by the printing process. A wide range of materials has been successfully deposited with the Aerosol Jet process, including diluted thick film pastes, thermosetting polymers such as UV-curable epoxies, and solvent-based polymers like polyurethane and polyimide, and biologic materials.[28] Dell Latitude E6510 CPU Fan Other methods with similarities to printing, among them microcontact printing and nano-imprint lithography are of interest.[29] 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.[30][31] DELL DC280005FF0 CPU Fan Sporadically pad printing is used in a similar manner.[32] Occasionally so-called transfer methods, where solid layers are transferred from a carrier to the substrate, are considered printed electronics.[33]Electrophotography is currently not used in printed electronics. Both organic and inorganic materials are used for printed electronics. HP KSB0605HB CPU Fan Ink materials must be available in liquid form, for solution, dispersion or suspension.[34] They must function as conductors, semiconductors, dielectrics, or insulators. Material costs must be fit for the application. Electronic functionality and printability can interfere with each other, mandating careful optimization.[5] For example, a higher molecular weight in polymers enhances conductivity, but diminishes solubility. HP 580696-001 CPU Fan 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. 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. HP Pavilion dv7-4014eo CPU Fan Printable materials provide decisive advantages beside printability, such as mechanical flexibility and functional adjustment by chemical modification (e.g. light color in OLEDs).[35] Printed conductors offer lower conductivity and charge carrier mobility.[36] With a few exceptions, inorganic ink materials are dispersions of metallic or semiconducting micro- and nano-particles. DELL Studio 1555 CPU Fan Semiconducting nanoparticles used include silicon [37] and oxide semiconductors.[38] Silicon is also printed as an organic precursor [39] which is then converted by pyrolisis and annealing into crystalline silicon. Organic printed electronics integrates knowledge and developments from printing, electronics, chemistry, and materials science, especially from organic and polymer chemistry. HP G62-339WM CPU Fan Organic materials in part differ from conventional electronics in terms of structure, operation and functionality,[41] which influences device and circuit design and optimization as well as fabrication method.[42] The discovery of conjugated polymers[36] and their development into soluble materials provided the first organic ink materials. HP Pavilion dv5-1145ev CPU Fan Materials from this class of polymers variously possess conducting, semiconducting, electroluminescent, photovoltaic and other properties. Other polymers are used mostly as insulators and dielectrics. In most organic materials, hole transport is favored over electron transport.[43] HP F787 CPU Fan Recent studies indicate that this is a specific feature of organic semiconductor/dielectric-interfaces, which play a major role in OFETs.[44] Therefore p-type devices should dominate over n-type devices. Durability (resistance to dispersion) and lifetime is less than conventional materials.[40] Organic semiconductors include the conductive polymers poly(3,4-ethylene dioxitiophene), dHP Pavilion dv7-3155eb CPU Fan oped with poly(styrene sulfonate), (PEDOT:PSS) and poly(aniline) (PANI). Both polymers are commercially available in different formulations and have been printed using inkjet,[45] screen[21] and offset printing[9] or screen,[21] flexo[10] and gravure[13] printing, respectively. Polymer semiconductors are processed using inkjet printing, such as poly(thiopene)s like poly(3-hexylthiophene) (P3HT)[46] and poly(9,9-dioctylfluorene co-bithiophen) (F8T2).[47DELL Studio 1458 CPU Fan ] The latter material has also been gravure printed.[11] Different electroluminescent polymers are used with inkjet printing,[15] as well as active materials for photovoltaics (e.g. blends of P3HT with fullerene derivatives),[48] which in part also can be deposited using screen printing (e.g. blends of poly(phenylene vinylene) with fullerene derivatives).[23] Toshiba Satellite A505-S6970 CPU Fan Printable organic and inorganic insulators and dielectrics exist, which can be processed with different printing methods.Inorganic electronics provides highly ordered layers and interfaces that organic and polymer materials cannot provide.Silver nanoparticles are used with flexo,[8] offset [50] and inkjet.[51] Gold particles are used with inkjet.[52] HP Pavilion dv6-3090si CPU Fan 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.[53] Silicon inks are used commercially in transistor circuits for RFID labels,[54] selective emitters and dopant layers for photovoltaics,[55] and temperature sensors.[5HP G60-215EM CPU Fan 6] Fully printed field effect transistors produced at room temperature using silicon nanoparticles have been demonstrated,[57] but the field effect mobility is low compared to crystalline silicon (being similar to that obtained in amorphous silicon transistors). In printed nanoparticle silicon, the low mobility arises from an activated charge transport between nanoparticles, Toshiba Satellite A100-011 CPU Fan which in turn enables its use as a negative temperature coefficient (NTC) thermistor material.[58] The corresponding varistor characteristics have recently been used to develop a current switching transistor,[59] which works as a two-way switch by changing the conductivity between the different pairs of terminals. CIGS cells can be printed directly onto molybdenum coated glass sheets. DELL XPS M1210 CPU Fan  HP G62-120SL CPU Fan 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 crystalline silicon. Printed electronics allows the use of flexible substrates, which lowers production costs and allows fabrication of mechanically flexible circuits. HP Pavilion dv6-2117eo CPU Fan While inkjet and screen printing typically imprint rigid substrates like glass and silicon, mass-printing methods nearly exclusively use flexible foil and paper.Poly(ethylene terephthalate)-foil (PET) is a common choice, due to its low cost and higher temperature stability. Poly(ethylene naphthalate)- (PEN) andpoly(imide)-foil (PI) are alternatives. Toshiba Satellite L305D-S5950 CPU Fan Paper's low costs and manifold applications make it an attractive substrate, however, its high roughness and large absorbency make it problematic for electronics.[50] 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. SONY Vaio VGN-BZ11MN CPU Fan 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. It can be preparedintrinsic, 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. SONY Vaio VGN-TX91S CPU Fan Most silicon monocrystals are grown by the Czochralski process, in the shape of cylinders up to 2 m long and 45 cm in diameter (figure on the right), which, cut in thin slices, give the wafers onto which the microcircuits will be fabricated. Single-crystal silicon is perhaps the most important technological material of the last decades (the "silicon era"),[1] Toshiba Satellite A100-849 CPU Fan 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. VLSI devices (Intel) fabricated on a single-crystal silicon wafer) Monocrystalline is opposed to amorphous silicon, in which the atomic order is limited to short range order only. Gateway MT6400 CPU Fan In between the two extremes there is polycrystalline silicon, which is made up of small crystals, known as crystallites. 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. Toshiba Satellite A100-849 CPU Fan 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[2]) of transistor-based circuits, all of which must reliably be working, are combined into a single chip to get e.g. a microprocessor. Dell Vostro 3350 CPU Fan Therefore, electronic industry has invested heavily in facilities to produce large single crystals of silicon. Monocrystalline silicon is also used in the manufacturing of high performance solar cells. 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.[3ACER Aspire 4733 CPU Fan ] Monocrystalline solar cells can achieve 21% efficiency[4] whereas other types of less expensive cells including thin film and polycrystallineare only capable of achieving around 10% efficiency.[5] 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. ACER Aspire 3003LCi CPU Fan The 2010 Consumer Electronics Show showcased one of these high-efficiency monocrystalline chargers known as the JOOS Orange and awarded it the 2010 Best of Innovations Award. 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