Thin films seek a solar future

Energy from the sun—available everywhere, for everybody—has motivated research on solar-energy technologies for about three decades. The U.S. Photovoltaic Industry Roadmap, intended to guide companies in developing solar-energy systems, takes a more prosaic but realistic view of the next three decades. It aims for solar energy to provide 10% of U.S. peak generation capacity and supply a considerable share of foreign markets by 2030.

Most photovoltaic (PV) solar technologies rely on semiconductor-grade crystalline-silicon wafers, which are expensive to produce compared with energy from fossil fuel sources. However, potentially less costly thin-film alternatives may make major inroads in the world market in five years, suggests Franz Karg, research manager at the Shell Solar facility in Munich, Germany. Or maybe not. Thin-film solar panels are hard to mass-produce cost-effectively because of the difficulty of coating large areas of glass. “It is my opinion that crystalline- silicon technologies will dominate for at least the next 10 years,” says Jeffrey Mazer of the U.S. Department of Energy (DOE) Office of Solar Energy Technologies (Washington, DC).

Figure 1. The main entrance facade of Technology Place, a research incubator facility for emerging high-tech companies on the Burnaby campus of British Columbia Institute of Technology, incorporates sufficient thin-film solar panels to power all lighting in the building. (British Columbia Institute of Technology)

Solar-energy systems pose many challenges for developers, particularly in the current world economy. Last October, Shell Solar (Amsterdam, The Netherlands) announced the closing of two production operations—in Helmond, The Netherlands, and in Munich—in a restructuring meant to make the c o m p a n y more competitive. The next month, BP Solar (Linthicum, MD) decided to close down production of its thin-film amorphous silicon and cadmium telluride (CdTe) solar panels to focus on crystalline- silicon technologies. “While the thin-film technology continues to show promise, lack of present economics does not allow for continued investment,” said Harry Shimp, BP Solar’s president and chief executive officer.

Figure 2. Copper and indium are deposited by magnetron sputtering, followed by selenization to form the high-absorbing ptype semiconductor CuInSe2, which is combined with an n-type electrode of ZnO to create thin-film solar modules.
(Ian Worpole/Shell Solar, Munich, Germany)

A=Barrier/Mo deposition; B= Laser patterning; C=Cu/In/Se deposition; D=Heat treatment 500°C; E=Chemical deposition 60°C; F=Patterning; G=2nd deposition 200°C; H=Patterning; I=Contacts/lamination

BP’s decision is a setback to the marketing of new thin-film solar technologies. However, First Solar, LLC (Perrysburg, OH), a major maker of CdTe solar cells, remains strongly committed to the technology. Shell Solar continues development of its thin-film technologies. And DOE’s National Renewable Energy Laboratory (NREL) in Golden, Colorado, continues to provide funds for thin-film PV research to its 40 industrial and university partners.

Why solar power?
In 2001, the global market for PV panels and equipment was valued at $2 billion. Worldwide in 2000, solar, geothermal, wind, combustible renewables, and burning garbage and other wastes collectively provided 1.6% of electricity production, according to the International Energy Agency (IEA) in Paris. In its World Energy Outlook 2002, IEA described two scenarios for world energy demand and supply until 2030. One scenario assumes only the continuation of current government measures to stimulate sustainable-energy supply and demand. In it, fossil fuels continue to meet more than 90% of energy demand. All renewables except hydropower grow by 3.3% annually, but they will not meet a large share of the total energy demand because of their low-percentage base. Carbon dioxide (CO²) emissions will grow 70% by 2030 to 38 billion metric tons annually.

In the alternative scenario, governments will implement policies such as promoting energy efficiency, the use of cleaner energy sources, and reducing the environmental impact of producing and burning fossil fuels. Compared with1990, those changes would result in an estimated 16% fewer CO² emissions in 2030—a year when the United Nations estimates the world population will be about 8.3 billion—in part because renewable energy sources will grow rapidly.

Current applications of PV solar panels include providing power to spacecraft and isolated villages in developing countries, solar-energy systems in homes and buildings in Western countries (Figure 1), and even powering the lamps of remote lighthouses. “Especially where there is no connection to the grid, solar energy is easily cheaper than small-scale electricity production with a diesel generator, to give an example,” Karg says. “For electricity production in rural areas in developing countries, solar is the cheaper alternative. To achieve more, we need breakthroughs in large-scale storage of electricity, and solar must be developed in combination with wind, biomass, energy-storage systems, and fossil fuels.”

Most people in solar energy consider government subsidies for R&D and sales as necessary for its successful development and increased usage. Indeed, the PV energy business is still largely dependent on government intervention, and most U.S., European, and Japanese projects are subsidized. The Bush administration seeks $79.7 million from Congress for fiscal year (FY) 2004 to support solar-energy research, up 0.1% from its amended FY 2003 request but down from the $87.1 million that Congress appropriated in FY 2002.

Crafting photovoltaics
PV solar panels convert sunlight directly into electricity. A panel consists of several connected 0.6-V dc PV cells, which are made out of a semiconducting material sandwiched between two metallic electrodes. “The photovoltaic effect refers to the separation of minority carriers [electrons and holes] by a built-in electric field,” such as a pn-junction or Schottky barrier, says DOE’s Mazer. The cells are usually encapsulated behind glass to weatherproof them. In a PV array, several panels are connected to provide sufficient power for common electrical applications such as household electricity. The arrays can be connected to an electricity grid or work as standalone systems.

Researchers at what is now Lucent Technologies’ Bell Laboratories first demonstrated silicon solar cells in 1954, and most PV systems today use mono- or multicrystalline silicon as the semiconducting material. “We obtain monocrystalline wafers by sawing them from silicon rods, which we grow by the Czochralski growth process,” explains Ronald van Zolingen, professor of sustainable energy at the Technical University in Eindhoven, The Netherlands, and a senior business advisor to Shell Solar. “In this process, we pull a monocrystalline rod from a liquid, starting with a small crystal. The growth speed is relatively low. but we obtain excellent material. Monocrystalline silicon solar cells have the advantage of a high efficiency, about 15%, which is an advantage for specific applications.”

Figure 3. A scanning electron micrograph shows a cross section of the p-type semiconductor CuInSe2 film, about 1.5 µm thick, and the n-type layer of ZnO.
(Shell Solar, Munich, Germany)

“We obtain multicrystalline wafers from ingots grown by casting liquid silicon in a large container followed by controlled cooling,” van Zolingen adds. “This technique is less complicated than the pulling of single-crystalline rods. Multicrystalline-silicon solar cells have a slightly lower efficiency than monocrystalline, about 13.5%.” Worldwide, the production of multicrystalline-silicon solar cells outpaces that of monocrystalline-silicon solar cells.

Figure 4. Optical-beam-induced current imaging (in false color) of these four CdS/CuInSe² thin-film solar cells connected in parallel gives a high-resolution photocurrent map, in which defects appear dark.
(University of Waterloo, Ontario, Canada)

Among the major bottlenecks to the output of crystalline-silicon PVs is the high loss of materials during production of the wafers. “In addition, we need to saw the silicon. We typically lose 0.2 mm at the kerf,” says van Zolingen. Despite these problems, crystalline silicon remains the dominant solarcell material. One reason for this is the support provided by the federal government’s PV program since the 1970s for R&D projects focused on crystalline-silicon technologies.

Thin-film alternatives to standard PV solar cells are already available or in development. Amorphous silicon, the most advanced of the thin-film technologies, has been on the market for about 15 years. It is widely used in pocket calculators, but it also powers some private homes, buildings, and remote facilities. An amorphoussilicon solar cell contains only about 1/300th the amount of active material in a crystalline-silicon cell. Amorphous silicon is deposited on an inexpensive substrate such as glass, metal, or plastic, and the challenge is to raise the stable efficiency. The best-stabilized efficiencies achieved for amorphous-silicon solar panels in the U.S. PV program are about 8%. The goal is to produce a stable device with 10% efficiency. United Solar Systems Corp. (Troy, MI) pioneered amorphous-silicon solar cells and remains a major maker today.

Thin-film crystalline-silicon solar cells consist of layers about 10 µm thick compared with 200- to 300-µm layers for crystalline-silicon cells. Researchers at NREL use porous polycrystalline silicon on low-cost substrates and trap light in the silicon to enable total absorption. They have fabricated working solar cells with this material.

New thin films

Copper indium diselenide (CIS) is a more recent thin-film PV material. Siemens Solar developed a process for depositing layers of the three elements on a substrate in a vacuum, and Shell Solar later acquired the technology when it bought Siemens Solar (Figures 2 and 3). CIS modules currently on the market reach stable efficiencies of more than 11%. In the laboratory, NREL scientists have achieved cell efficiencies of 19.2% with the semiconductor. Research now focuses on increasing efficiency (Figure 4), reducing costs, and raising the production yield of CIS panels. Karg predicts that thin-film technology will eventually halve the present production cost per unit kilowatt peak (kWp), which is the peak power that a solar panel can produce at optimum intensity and sun angle (90°). This implies a cost reduction for a complete system of 35% or more.

In 2000, CdTe solar panels were field-tested on a large scale in the United States. NREL researchers consider CdTe a promising material because of its lower cost of production, which uses techniques that include electrodeposition and high-rate evaporation. Prototype CdTe panels have reached 11% efficiency, and research now focuses on improving efficiency and reducing panel degradation at the electrode contacts. “Studies at Brookhaven National Laboratory strongly suggest that CdTe modules can be safely made in a large-scale manufacturing environment, and that CdTe can be safely disposed of when the modules are eventually retired,” Mazer says.

Figure 5. Examples of local photovoltaic installations include, left to right: Tibetan home with 20-W panel and 500-W wind machine (Simon Tsuo); water-pumping station in West Bengal, India (Harin Ullal); and the world's largest residential project, in Amersfoort, The Netherlands (BP Solarex).

Progress in solar PV research and the development of new applications are guided by national and international collaborations between industry and government, such as those described in the U.S. PV roadmap and carried out by national research teams organized by NREL. Japan and Germany have similar ongoing programs, and leading manufacturers are collaborating with other companies to install solar panels on commercial buildings. For example, a recent agreement between Volkswagen and BP Solar calls for installing solar-energy systems on the roofs of the automaker's dealerships throughout Germany. Each company is investing in several different technologies.

Solar's big four

Which PV technologies will dominate future solarenergy markets may depend on the companies developing, manufacturing, and selling them. The four industry leaders are Sharp (Osaka, Japan), BP Solar, Kyocera (Kyoto, Japan), and Shell Solar.

Sharp produces mono- and multicrystalline and amorphous silicon solar cells. The monocrystalline modules have an efficiency of 17.5%, and the multicrystalline cells have 16% efficiency. In 2001, the company shipped 19.2% (75 MWp) of the world's total solar cells. Last July, Sharp opened a new multicrystalline-silicon solar-cell production plant in Nara Prefecture, Japan, and the company's total production capacity now totals 200 MWp.

BP Solar also manufactures nearly 20% of the world's solar-electric panels and systems, using technologies that include polycrystalline solar cells. "We also have our own Saturn technology, which is a highly efficient monocrystalline technology," said a spokesman at BP Solar's U.K. office in Sunbury on Thames, England. The company also sells amorphous silicon thin-film modules. BP developed its proprietary PowerView thin-film silicon laminate partly with funds from NREL. The PV coating converts part of the incoming light into electricity while remaining transparent to the rest of the light. The coating can be used to integrate a solar-energy-generating capacity into building skylights and windowpanes to produce electricity and reduce reliance on utility companies.

Kyocera focuses on off-grid solar systems for private homes in developing countries, communication systems, water pumping, and industry (Figure 5). It sells its own multicrystalline-silicon systems, and amorphous silicon systems produced by United Solar Systems.

Shell Solar makes mono- and multicrystalline silicon as well as thin-film CIS solar systems. It produced solar panels with a total capacity of about 50 MWp in 2002, and it expects to double its crystalline production capacity by 2004. The company now employs about 900 people in the United States, Canada, Portugal, and Germany after cutting 170 jobs last October.

Although the market growth rate for PV solar panels has declined sharply after four years of annual growth of more than 30%, the growth rate is predicted to be 15 to 20% this year and next. Worldwide production capacity almost doubled last year to 760 MWp, up from 400 MWp in 2001. The main producers of these panels have different business strategies. Shell Solar strongly believes in thin-film alternatives, including its CIS technology. Other companies see crystalline silicon as the dominant technology during the next decade.

Few people doubt solar energy's potential, but many wonder when it will be reached. "In the long term, solar may well play an important role," Karg says. "I personally expect a contribution of 10 to 20% of the global electricity production, mainly in the form of grid-connected systems." However, he does not foresee that happening within the next 20 years.

Fuente: http://www.aip.org/tip/INPHFA/vol-9/iss-2/p16.html
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer:[Jn6:55]

GranFilm : Optical Properties of Granular Thin Films-Introduction:

Since the pioneering work of Maxwell Garnett [1] and Mie [2] at the turn of the century, there has been large scientific interest in the optical properties of metallic clusters [3]. Their optical behavior are driven to a large extent by the Mie excitations [3] which can be viewed as surface plasmon-polaritons [4]. Nearly hundred years ago Mie [3] derived an exact theory for the scattering of light from a free standing spherical particle. If, for isolated clusters with simple shapes, such as spheres or spheroids in vacuum, the exact solution of the Maxwell equations is well known, the difficulty of a reliable description of the optical properties of particles dramatically increases for interacting particles of complex shapes, either in a matrix or on a surface. Even though the Maxwell Garnett effective medium theory and other such theories [5] have been quite successful in tackling these questions, an accurate description of the macroscopic optical properties of a collection of particles supported on a substrate, such as the Fresnel coefficients (absorption, reflection and transmission), requires a more sophisticated approach that accounts correctly for the break of symmetry brought by the substrate and for realistic cluster shape. Indeed for clusters deposited on a surface, a quantitative description of the optical properties of thin films is not only hampered by the interactions between aggregates but also by the image interactions between the latter and the substrate [6-9].

In order to handle this latter situation in an adequate way, Bedeaux and Vlieger [10-14] in the first half of the 1970's introduced a model valid for layers whose thickness are in the sub-wavelength regime. In this case, they introduced modified boundary conditions on the surface for the electromagnetic fields which depend on what they called integrated excess quantities. In the closure relation between these quantities, they introduced surface susceptibilities which govern completely the far field behavior of the electromagnetic fields and thus the Fresnel quantities. In this way, they get rid of the complex behavior of the field on the surface. This approach is really analogous to the model of Feibelmann [15] and Barrera [16] who applied these notions in the case of the electromagnetic jump at metallic surfaces. However, Bedeaux and Vlieger were mainly interested in the description of the optical properties of island layers. For such layer, the main quantity which is directly related to the surface susceptibilities is the island polarizability. For simple shape like truncated spheres or spheroids with an axis of revolution normal to the surface of the substrate, a model based on a multipole expansion of the electrical potential in the non retarded limit was developed [17-20]. A nice recent, detailed and pedagogical introduction to this fascinating field of optics can be found in the recent book: Optical properties of Surfaces (Imperial College Press, 2001) by D. Bedeaux and J. Vlieger [21]. The aim of the present web page is to give access to the softwares which englobes most of the models developped in [21]. This software package we have named -- GranFilm.

Fuente: http://web.phys.ntnu.no/~ingves/Software/GranFilm/Current/ we have named -- GranFilm.
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer:[Jn6:35]

Prof. Lars Hultman - Materials Science of Thin Film Nanostructures at Linköping

Abstract
The research program of the Thin Film Group at Linköping concerns the materials science and nanotechnology of thin films. It is aimed at increasing the understanding of vapor phase deposition, ion-surface interactions, and reactions in advanced functional materials. Specifically, we focus on the nature of epilayers, textured films, and nanoscale materials. Model systems include transition metal nitrides, wide-band gap nitrides, multifunctional ceramics (MAX phases; e.g., Ti3SiC2, Ti2AlN), nanocomposites, superlattices, fullerene-like compounds, and nm-sized metallic multilayers. Several deposition techniques are covered including magnetron sputter epitaxy (MSE) and cathodic arc. Our laboratory specializes in applying and developing methods for plasma characterization, analytical and high-resolution electron microscopy, X-ray diffraction, nanoindentation, ab initio calculations, and multi-billion time-step molecular dynamics simulations.

This seminar provides results from studies of nanostructuring in transition metal nitrides, which are used for advanced surface engineering and electronics. Analysis of the TiAlN, TiSiN, ScAlN, and InAlN systems by nanoindentation, XRD, HREM, and Atom Probe Tomography is coupled with ab initio calculations of phase stability and decomposition behavior by lattice mismatch and electronic band structure effects.

Fuente: http://www.campuskista.se/adimo4/%28S%284qaj2hmtm5uipguxu5dk4w45%29%29/Site/kista/web/default.aspx?p=1350&artid=567&artview=full&artcat=calendar&AspxAutoDetectCookieSupport=1
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer:[Jn10:14]

Journal of Vacuum Science and Technology

The name Journal of Vacuum Science and Technology (JVST) combines two scientific journals, JVST A and JVST B, published by the American Vacuum Society since 1964.

1964-1982 Journal of Vacuum Science and Technology [0022-5355]

1983-present Journal of Vacuum Science & Technology. A. Vacuum, surfaces, and films

1983-1990 Journal of Vacuum Science & Technology. B, Microelectronics processing and phenomena

1991-present Journal of Vacuum Science & Technology. B, Microelectronics and nanometer structures

JVST A

Journal of Vacuum Science and Technology A specializes in applied surface science, electronic materials and processing, fusion technology, plasma technology, surface science, thin films, vacuum metallurgy, and vacuum technology.

Editor: G. Lucovsky, Department of Physics, North Carolina State University.

Contnent of the Journal: http://scitation.aip.org/dbt/dbt.jsp?KEY=JVTAD6

JVST B

Journal of Vacuum Science and Technology B specializes in vacuum processing and plasma processing of various materials, the structural characterization, microlithography, and the physics and chemistry of submicrometer and nanometer structures and devices.

Editor: Gary E. McGuire, International Technology Center link required.

Content of the Journal: http://scitation.aip.org/dbt/dbt.jsp?KEY=JVTBD9

External links

Homepage of JVSTA: http://scitation.aip.org/jvsta
Homepage of JVSTB: http://www.avs.org/literature.jvst.b.aspx

Fuente: http://en.wikipedia.org/wiki/Journal_of_Vacuum_Science_and_Technology
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer:[Jn10:14]

Eray Aydil Becomes the New JVST Editor-in-Chief in September

The AVS Board of Directors is pleased to announce the appointment of Professor Eray Aydil as the Editor-in-Chief of the Journal of Vacuum Science and Technology (JVST), the flagship publication of the AVS, effective September 1, 2010. As Editor-in-Chief, he will oversee the editorial operations of both JVST A & B. Professor Aydil will succeed Professor Gerald Lucovsky, who has served as the JVST Editor-in- Chief since 1980.

Eray is a Professor and the Executive Officer of the Chemical Engineering and Materials Science Department at the University of Minnesota and he holds the Ronald L. and Janet A. Christenson Chair in Renewable Energy. He received his B.S. degrees in chemical engineering and in materials science from the University of California, Berkeley, both in 1986. He completed his graduate research at the University of Houston under the supervision of Demetre Economou and received his Ph.D. degree in chemical engineering in 1991.

He then joined the AT&T Bell Laboratories as a Postdoctoral Member of the Technical Staff working with Richard Gottscho. At Bell Labs, he focused on developing and applying surface sensitive diagnostic techniques that can be used in the harsh conditions encountered in plasma etching and deposition reactors.

He joined the faculty of the Chemical Engineering Department at the University of California, Santa Barbara (UCSB) in 1993 as an Assistant Professor and was promoted to Associate Professor with tenure in 1998 and then to full Professor and Vice Chair of the Department in 2001.

At UCSB, he and his students pioneered the development of in situ techniques to monitor composition, dielectric properties, and surface coverage of films during plasma etching and plasma enhanced chemical vapor deposition of materials such as SiO2, fluorinated SiO₂, Si₃N₄, hydrogenated amorphous Si and hydrogenated nanocrystalline Si.

In 2005, Eray joined the faculty of the University of Minnesota Chemical Engineering and Materials Science Department. His research is focused on solving technologically important and fundamental problems encountered in materials processing for applications in electronic and photovoltaic device manufacturing with emphasis on plasma etching and deposition, plasma modification of surfaces, and dye-sensitized and quantum dot solar cells.

He is interested in understanding thin film deposition and etching processes used in the synthesis of nanostructured materials and in manufacturing of integrated circuits and solar cells. He has authored and coauthored over 135 papers and holds 4 patents.

Eray has been an actively-involved member of AVS since he was a graduate student. He served on the editorial board of the JVST between 2004 and 2007. He was a member of the Plasma Science and Technology Division (PSTD) programming committee between 1999 and 2003 and again between 2006 and 2008.

He has served on the PSTD Executive Committee, first as a Member-at-Large between 1999 and 2003 and then as its Chair-Elect, Chair and Past-Chair in 2006, 2007 and 2008, respectively. He was the programming vice-chair of the AVS 56th International symposium in 2009 and he is currently the Chair of the AVS 57th International Symposium and Exhibition that will be held in Albuquerque during October 2010.

Eray received the Norman Hackerman Young Author Award of the Electrochemical Society, the National Young Investigator Award of the National Science Foundation, and the Camille and Henry Dreyfus Teacher- Scholar Award in 1993, 1994 and 1997, respectively. In

1999, he received the AVS Peter Mark Memorial Award “for pioneering work in the development and application of optical diagnostic techniques to understand chemistry and physics associated with plasma deposition of dielectric thin films.” He became a Fellow of the AVS in 2005.

He was awarded the 2009 Plasma Prize at the AVS 56th International Symposium in San Jose. The highest honor of the PSTD, the Plasma Prize is given each year to a researcher who has conducted outstanding research in science and technology of gas plasmas. He received the award for “pioneering work on the characterization of plasma species and their energy distributions in plasma assisted deposition and etching of materials.” He is a dedicated teacher; he has numerous teaching awards both at UCSB and at the University of Minnesota.

In naming Prof. Aydil as Editor-in-Chief, the AVS Board of Directors noted that he brings a breadth of knowledge and experience in research topics that crosscut the various facets of AVS. The Board of Directors is very confident JVST will flourish under his dynamic leadership.

Fuente: http://www.avs.org/
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer:[Jn10:41]

Kinetics of the initial stages of film formation during low pressure chemical vapour deposition of polysilicon by pyrolysis of silane

Abstract

A kinetic model for description of the process of silicon film formation on silica by thermal decomposition of silane at reduced pressure has been proposed. The model is based on the concept of kinetic interdependence between heterogeneous catalytic chemical reaction and fundamental structure forming phenomena - nucleation and nuclei growth. A number of experimental data for deposition rates and polysilicon grains sizes have been mathematically processed in order to derive kinetic equations for the rates of nucleation and nuclei growth as functions of reactor operating conditions (pressure and temperature) as well as process duration. Furthermore, based on both the good correspondence achieved between the experimental results and the model, and the deductions of thermodynamic theory of nucleation, the kinetic equations derived were analysed in regard to the general description of silicon film structure evolution. The analysis of the model, by confïrming the general trends established between the arrival and the surface diffusion rates of silicon adspecies, contributes to clarify the mechanism of the initial stages of film microstructure formation. The results obtained show that kinetics of structure evolution can be successfully described by developing the existing CVD phenomenological kinetic models further to an atomistic level.

Fuente: http://jp4.journaldephysique.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/jp4/pdf/2001/03/jp4200111PR324.pdf
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer: [Jn10:27]

Premium OLED materials for displays

In recent years, Organic Light Emitting Diode (OLED) technology has gained increasing importance for display applications. As one of the leading manufacturers of OLED materials, Merck offers a complete product portfolio of materials for OLED displays, comprising small molecule as well as polymer materials (evaporable and soluble systems), under the brand name livilux®.

Your advantages - High-purity and high-stability materials

Based on more than 10 years of experience in manufacturing OLED materials, a strong worldwide intellectual property position, and the background of more than 100 years of expertise in high-tech product development, we can supply high-purity and high-stability materials that exactly meet customer requirements.

On request, Merck will provide effective application support to optimize the material stack in close cooperation with the customer.

Applications - The world of OLED displays

Merck's OLED materials are used in OLED displays that offer an unparalleled viewing experience with a number of benefits, among them an extremely wide viewing angle, superb video capabilities, very high intrinsic contrast at any viewing angle, a low power consumption for mobile applications, and a remarkable lifetime.

With its extraordinary properties, OLEDs are a promising display technology of the future. Possible applications range from simple passive-matrix monochrome and area-color to active-matrix full-color displays. Today, the technology is used in MP3 players and high-end cell phones and it is likely to soon be used in notebook computers, PC and even TV screens.

The technology - How do OLEDs work?

Based on either small molecule (SM) or polymer (PLED) materials and technologies, OLEDs work by the passage of an electrical current from two conducting electrodes through layers of organic semiconductor materials on a substrate, usually indium tin oxide (ITO) coated glass, silicon, or a special plastic substrate. Light emission is caused by electrically generated electron-hole pairs forming neutral excited states that relax to a ground state with the emission of light. Importantly, each individual OLED material has its own characteristic emission color.

OLED's high precision emissive thin-film structure and excellent optical properties at low power consumption offer considerable advantages to display manufacturers and end users alike. Additionally, as OLEDs are fabricated into extremely thin layer structures and usually need only a single substrate, they are thin, light and potentially offer lower costs.

Fuente:http://www.merck-chemicals.com.ve/lcd-emerging-technologies/oled-materials/c__QOb.s1OuggAAAEh_cUsgkMs?PortalCatalogID=merck4lcds&CountryName=Venezuela
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer:[Jn10:17]

Magnetic Tag Designs: Planar and Pillar Structures

The crux of the technology lies in a sequence of magnetic elements that store information based on their magnetic alignment. Using rectangular or elliptical elements naturally defines two stable states, parallel (and anti-parallel) to the long axis. By assigning each magnetisation direction to be either state 1 or 0, a magnetic barcode is created, and the number of possible combinations doubles with every additional bit, e.g. 10-bit tags can code for up to 1024 different biological compounds .

The group is working on two different tag designs that will be capable of offering a medium number of codes (32 - 8192) in the short-term, and a very large number for gene (re)sequencing applications in the long-term.
Planar Tags:

This tag design features magnetic elements encapsulated in a bio-compatible polymer backbone of size 100μm x 30μm and less than 2μm in thickness. The elliptical magnetic elements are spaced along the length of the backbone and typically only 20nm high, which makes these tags free-floating in aqueous solutions. The tags will be flown through microfluidic channels with integrated sensors where they will be read and sorted in a high-throughput system (see section 3).

Figure 1 a) schematic of a 7-bit equi-element magnetic tag, b) schematic of a 5-bit `multi-coercivity' tag and an F-MOKE image of a real tag.

Fabrication: These structures were grown in a sandwich process, where the SU8 backbones are spin-coated to a thickness of 1μm and shaped using standard photolithographic techniques. A second photolithography step is used to grow and align a PDMS mask on these backbones before vacuum deposition (e.g. evaporation, MBE, sputtering) of the magnetic elements. Finally another 1μm of SU8 is patterned on top, which now protects the magnetic bits from oxditation and the environment.

Figure 2 the main steps in the fabrication of free floating planar tags, (the detailed photolithography has been omitted).

A simplified fabrication procedure uses ion etching and reduces the number of complicated alignment steps, however the pay-off is reduced chemical functionality (see section 4). For details on these tags and their new fabrication procedure, please read the following paper: "Design and Fabrication of SU8 Encapsulated Digital Magnetic Carriers for High Throughput Biological Assays." B. Hong et al., J. App. Phys. 105 034701
Pillar Tags:These tags are aimed at creating an extremely large number of codes (106 to 109), so must be easily scalable for mass production and must be highly cost-effective to manufacture. The coding density is dramatically increased in this design by using a pure metal stack, featuring magnetic elements interleaved with non-magnetic spacers (figure 2). The top is capped with gold to allow a route for chemical modification (see section 4).

Figure 3 (left) schematic of a 10-bit pillar tag, (right) SEM image of a 15μm diameter pillar tag with 8 magnetic layers (some Cu layers are highlighted to aid the eye) and a gold cap, (inset) SEM demonstrating the homogenity of the electrodeposition process.

Fabrication: A single photolithography process is used to define elliptical holes in a non-conducting photo-resist, which is spin-coated onto a conductive substrate. This is usually a 4" silicon wafer with an evaporated novel aluminium/copper bi-layer, which is important for releasing the tags at the end of the process. The substrate is used as the cathode of an electrochemical cell, and when a voltage is applied the metallic ions in the electrolyte are deposited onto the substrate.

Figure 4 The two-step fabrication process: (left) a template is photolithographically defined on a conducting substrate, (right) the substrate is used as the cathode in a basic 3-electrode electrochemical cell.

It is possible to deposit multilayers from a single bath containing a mixture of nickel, cobalt, iron and copper ions, by varying the applied potential, different ions deposit preferentially. This makes this process highly automatable, and material waste is minimised making this procedure ideal for mass production. Further details of this design and fabrication procedure can be found in the following paper: "Digital Biomagnetism: Electrodeposited Multilayer Magnetic Barcodes." J.J. Palfreyman et al., JMMM 321 (10) 1662-1666

Fuente: http://www.tfm.phy.cam.ac.uk/bio/tags.html
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01
Leer: [Jn10:14]

Fundamentos Tecnológicos:

Sin ninguna duda, en un futuro próximo la tecnología LCD sustituirá a la tecnología CRT (tubo de rayos catódicos). Ahorro de espacio, ahorro de energía, motivos de salud,…Lo cierto es que las ventajas de las pantallas LCD son muchas y la calidad de la imagen que ofrecen no tiene nada que envidiar a las pantallas CRT, o de tubo de rayos catódicos.

TECNOLOGIA BASICA LCD

LCD o Liquid Cristal Display (pantalla de cristal líquido), es el acrónimo de una tecnología aparecida ya en el año 1.971 en el mundo de las calculadoras, que pasó a campos tan diversos como los relojes digitales o los ordenadores portátiles. Hoy, no es raro verlas como monitores de ordenadores de sobremesa, en tamaños que van desde las 15” hasta las 22” o incluso 24”.

Básicamente ésta tecnología se basa en las propiedades físicas de los cristales líquidos, con cualidades propias de las sustancias sólidas y de las sustancias líquidas. Por ello, al igual que ocurre con las sustancias sólidas, la luz sigue el alineamiento de las moléculas que forman el cristal líquido. A la vez, y del mismo modo que ocurre en las sustancias líquidas, es posible alterar la alineación de dichas moléculas mediante la aplicación de un campo eléctrico, alterando así la forma en que la luz las atraviesa.

Una explicación sencilla del funcionamiento de éstas pantallas es la siguiente: en una pantalla LCD, hay colocados dos filtros polarizantes, con filas de cristales líquidos que forman 90° entre ellas. Cuando aplicamos o no una corriente eléctrica, la luz pasará o no a través de ellos (siendo el segundo filtro el que permitirá el paso de la luz que haya atravesado al primero: dos filtros de éste tipo en perpendicular no permiten el paso de la luz, así que el segundo “gira” de determinada forma permitirá que pase determinada dirección de luz), permitiendo así que se forme o no imagen en la pantalla.

Para conseguir el color se emplean además tres filtros adicionales (rojo, verde y azul). Las variaciones de color se obtienen con diferentes voltajes aplicados a los filtros.

CLASES DE TECNOLOGIAS LCD

-DSTN (o matriz pasiva)
Son las pantallas LCD básicas que emplean la tecnología LCD ya explicada.

-TFT (o matriz activa)
Las pantallas LCD con tecnología TFT cuentan con una matriz de transistores (un transistor por cada color de cada píxel de la pantalla) que mejoran el color, el contraste y la velocidad de respuesta de la pantalla a las variaciones de la imagen a representar. Es importante observar que la mayoría de los monitores del mercado de ordenadores de sobremesa utilizan ésta tecnología, aunque no ocurre lo mismo en el mundo de los portátiles, donde se pueden encontrar pantallas de todo tipo.

-HDP (o matriz pasiva híbrida)
Es un puente entre las dos tecnologías anteriores (DSTN y TFT): los cristales tienen una viscosidad menor de modo que también aumenta la velocidad de respuesta a las variaciones de la imagen.

-HPA (o de direccionamiento de alto rendimiento)
En el que la tecnología de matriz pasiva se aproxima, aún más, a la tecnología de matriz activa.

-PLASMA
Son pantallas que hacen pasar voltajes altos por un gas a baja presión, generando así luz: el gas (Xenón) pasa de estado gaseoso a estado de plasma como consecuencia del alto voltaje produciendo una luz ultravioleta. Este haz incide sobre el fósforo rojo, verde y azul de la pantalla, de forma parecida a lo que sucede en los monitores CRT. El problema de éstas pantallas es el enorme tamaño del píxel, por lo que su aplicación se reduce a las pantallas grandes, de hasta 70”. Sin embargo su coste de fabricación es comparativamente bajo, frente a los monitores TFT.

VENTAJAS DE LOS MONITORES LCD

-Costes de propiedad
Los estudios sobre costes totales de propiedad llevados a cabo sobre pantallas LCD frente a monitores CRT, revelan que es más económico, a corto-medio plazo, adquirir una pantalla LCD. Esto, unido a las constantes bajadas de precios de éste tipo de pantallas, marcará, poco a poco el liderato de éstos productos frente a los monitores tradicionales.

La Asociación de Industrias de la Electrónica de Japón ha llevado a cabo diversos estudios sobre costes de la propiedad. Entre ellos, el de las pantallas LCD frente a los monitores CRT. A éste dato hay que sumarle que la vida media de un monitor CRT no suele superar los 5 años.

En cuanto al ahorro que supone tener una pantalla LCD frente a un monitor CRT durante 5 años, los resultados son asombrosos: los costes de electricidad se reducen en un 80%, debido a que las emisiones de calor de una pantalla LCD son prácticamente nulas, se ahorra hasta un 75% en aire acondicionado, un ahorro del 58% de costes corresponden al menor espacio empleado. Estudios hechos en base a jornadas de trabajo de 5 horas de uso de monitor y 4 horas de reposo de éste al día, con una media de 20 días al mes de trabajo. Así, si en 5 años, las pantallas LCD sustituyeran al 50% de los monitores CRT, la reducción en el consumo de energía eléctrica haría innecesaria la existencia de cuatro plantas petroquímicas, con reducciones más que considerables por tanto en las emisiones de CO2. Y si en un solo edificio se instalaran pantallas LCD en 1000 PCs, sustituyendo a los monitores CRT, los costes de tan solo la instalación eléctrica (debido a los menores requerimientos de potencia de éstas pantallas) bajarían más de 20 millones de pesetas.

CARACTERISTICAS DE UNA PANTALLA LCD

-Tamaño de la pantalla

Actualmente suelen encontrarse monitores desde las 15” hasta las 22” (incluso también de 24”). Además, teniendo en cuenta que las pantallas LCD no disponen de esa banda negra que rodea a la imagen, tan característica de los monitores CRT, el tamaño de la imagen visualizable hace que prácticamente una pantalla LCD de 15” tenga un área tan útil visible como la de un monitor de 17” CRT.

-Resolución

Es el número de puntos que el monitor puede representar en pantalla, y se representa en “número de puntos en horizontal” x “número de puntos en vertical”. Por ejemplo, una resolución de 1024x768 implica que la pantalla nos muestra 768 líneas en horizontal, de 1024 puntos ( o columnas) cada una. Cuanto mayor es la resolución, la calidad de la imagen será también mayor. En cualquier caso, la resolución de un monitor ha de ser consecuente con el tamaño de éste: es tan incómodo trabajar a 1024x768 en un monitor de 15”, como trabajar a 800x600 en un monitor de 21”. Por ello, los fabricantes de pantallas nos hablan tanto de resoluciones máximas como de resoluciones recomendadas, para obtener los mejores resultados en cuanto a la comodidad del usuario. Además, la resolución puede limitar el número de colores que podamos ver: combinación de valores que dependerá sobre todo de la tarjeta gráfica que tenga el ordenador.

-Refresco de Pantalla

Es una frecuencia de refresco sólo en vertical. Es comparable al número de fotogramas por segundo de una película de cine: cuanto más alta es ésta velocidad , mejor es la calidad de visionado, pues no se observan saltos de imagen. Sin embargo, hay un límite visual que el ojo humano es capaz de apreciar. Pasado este límite no hay percepción de una mayor calidad de imagen por mucho que aumente esta velocidad, aunque si puede afectar enormemente a la fatiga visual durante el uso del monitor. Esta frecuencia se mide en Herzios y no debería ser en ningún caso inferior a 60Hz, aunque lo más recomendado es trabajar a partir de 80Hz. Sin embargo, en las pantallas LCD este parpadeo prácticamente desaparece: cada celda en la que se alojan los cristales líquidos está o encendida o apagada, con lo que desaparece la renovación de la pantalla (o refresco) y con ella el parpadeo y la fatiga visual que ésta produce.

-Tiempo de respuesta

A pesar de la inexistencia del parpadeo, sí que hay un valor que puede ser similar, y que se refiere al tiempo que tarda cada celda en responder a los cambios del campo eléctrico aplicado, renovando así, la imagen en la pantalla. Un tiempo de respuesta no debería bajar, en ningún caso, de los 70 ms.

-Angulo de Visión

En los principios de las pantallas LCD este valor era el gran inconveniente, pues resultaba casi imposible ver la imagen de la pantalla si no se colocaba uno justo enfrente de ella. Como mínimo, los valores ideales de éste ángulo de visión para ver la imagen desde posiciones más o menos normales, son de 45° hacia arriba y hacia abajo, y de 60° a la izquierda y a derecha.

-Fase y Reloj

La calidad de visualización en pantallas LCD puede verse afectada al ser utilizada en conjunción una tarjeta gráfica y una pantalla que trabajen con señal analógica. Debe de realizarse una sincronización perfecta entre las frecuencias de la tarjeta de vídeo y de la pantalla. Si ésta sincronización no se hace correctamente, pueden aparecer unas bandas verticales en la pantalla. Casi todos los monitores LCD hacen una calibración automática que reduce y casi hace desaparecer este problema. Pero son realmente los monitores y tarjetas DVI, con señal digital, los que eliminan este problema, al no tener que realizar ninguna conversión de señal analógica a digital, pues la información es interpretada de forma absolutamente precisa.

-Brillo y Contraste

El brillo hace referencia a la intensidad luminosa de una fuente de luz en un área concreta. Se mide en cd/m cuadrados, es decir, en candela por metro cuadrado. Una pantalla TFT tiene un valor mínimo, siempre, de 150 cd/ m cuadrados, y el contraste es la relación que existe entre la intensidad del punto más claro y la intensidad del punto más oscuro. Cuanto mayor es este valor más nítida será la imagen de la pantalla, y más viva la gama de colores y nítido el texto. Como mínimo debería de tener un valor de 100:1.

LCD frente a CRT

Con todo lo explicado, es fácil determinar cuáles son las ventajas e inconvenientes de una tecnología frente a la otra:
Las pantallas LCD no funcionan con un tubo de rayos catódicos, con lo que su tamaño de fondo es mucho menor que los monitores CRT tradicionales. Hoy en día, en la mayoría de las empresas el ahorro de espacio es tan importante como el ahorro de energía.
Además, su consumo también es bastante inferior al de un monitor CRT.
El parpadeo queda prácticamente anulado, puesto que las celdas no tienen un refresco en sí, sino que se encienden o se apagan según han de mostrar o no luz. El tiempo de respuesta apenas incide, en la tecnología TFT de las pantallas de sobremesa, en la percepción de la imagen ni en la fatiga visual.

Su geometría es perfecta: son las celdas las que se encienden o apagan, desapareciendo los incómodos problemas de convergencia de la imagen de los monitores CRT.

Una pantalla LCD de tan solo 15” nos permite trabajar con la misma resolución y tamaño “práctico” de pantalla que un monitor de 17” tradicional: el área visible abarca la casi totalidad de la pantalla al desaparecer los márgenes negros tradicionales de los monitores CRT.

El coste de las pantallas LCD TFT disminuye constantemente gracias a su éxito: ya no resulta prohibitivo trabajar con éstas pantallas.

El campo electromagnético que genera un monitor de tubo LCD es considerablemente inferior al que genera un monitor CRT: esto, unido además a la inexistencia del modesto parpadeo de la imagen, hace que las pantallas LCD proporcionen un entorno de trabajo y/o de ocio ergonómicamente saludable, reduciendo considerablemente la fatiga visual, dolores de cabeza, y otros síntomas propios de un entorno de trabajo con monitores tradicionales, como el insomnio o la irritabilidad.

Cuadro Comparativo de resoluciones

Las medidas de un monitor, por norma de aceptación, suelen darse en diagonal y en pulgadas. La pulgada equivale a 2,54 cm. Así tenemos las siguientes medidas:

15”: diagonal de 38.1 cm.
17”: diagonal de 43.18 cm.
18”: diagonal de 45.72 cm.
19”: diagonal de 48.26 cm.
21”: diagonal de 53.34 cm.

-Area visible

Respecto a éste valor, decir, que por ejemplo, en un monitor de 15” CRT, la diagonal visible suele ser de 13.8” como máximo: un monitor de 14” TFT tendría entonces una diagonal igual o incluso mayor que la de un monitor 15” CRT.

Podemos establecer la siguiente asignación, en cuanto a diagonales visibles, entre monitores TFT y CRT

Monitor 14” TFT……………15” CRt
Monitor 15” TFT……………16” CRT (en desuso)
Monitor 17” TFT……………18-19” CRT
Monitor 19” TFT……………20-21” CRT

Y hablando de resoluciones, el modo de trabajo óptimo en un monitor TFT de 15” sería de 1024x768, modo de trabajo soportado (para un trabajo ergonómicamente óptimo) en monitores de 17” de gama media-alta ( con frecuencias de refresco aceptables)

Resolución 1024x768…………15” TFT…………17” CRT
Resolución 1152x864…………17” TFT…………19” CRT
Resolución 1280x1024………..19” TFT…………21” CRT

Fuente: http://oriolrius.cat/article_fitxers/1206/FundamentsLCD.htm
Nombre: Juan J. Núñez C.
Materia: CRF
Sección: 01

Amoled

AMOLED es el acrónimo de "Active Matrix OLED" u OLED de matriz activa y es una tecnología de representación con una importancia al alza debido a su utilización en dispositivos móviles, como los teléfonos móviles. Con OLED nos referimos a un tipo específico de tecnología, unos dispositivos ultra-delgados y ultra-brillantes que no requieren ningún tipo de luz de fondo, sin embargo, AMOLED se refiere a la tecnología que permite dirigirnos a un pixel concreto.

El progreso que permite esta tecnología, se refleja en modelos superiores, más baratos y que consumen menos potencia de energía, por ejemplo, televisores.

Explicación técnica:

Un dispositivo OLED de matriz activa, consiste en un conjunto de píxeles OLED que se depositan o integran en una serie de transistores de película fina (TFT) para formar una matriz de píxeles, que se iluminan cuando han sido activados eléctricamente, controlados por los interruptores que regulan el flujo de corriente que se dirige a cada uno de los píxeles. El TFT continuamente regula la [corriente] que fluye por cada uno de los píxeles, para así caracterizar el píxel con el nivel de brillo que mostrará.

Generalmente esa corriente se controla mediante dos TFT por píxel, uno para empezar y parar de cargar el condensador, y el otro para proveer el nivel necesario de tensión al píxel para así crear una corriente de valor constante y poder evitar los picos de alta corriente que requiere un OLED pasivo para las operaciones en la matriz de píxeles.

Las pantallas de AMOLED se caracterizan en cuatro capas para el control de la imagen que muestra:

* Capa del ánodo.
* Capa intermedia orgánica.
* Capa del cátodo.
* Capa que contiene toda la circuitería.

Características:

Los OLED de matriz activa y los de matriz pasiva tienen las mismas posibilidades para mostrar una frecuencia de cuadro concreta, sin embargo el AMOLED consume menos potencia de forma significativa.

Esta propiedad hace que los OLED de matriz activa sean especialmente útiles para dispositivos electrónicos donde el consumo de energía de la batería puede ser crítico y para pantallas con una diagonal que van desde 2” a 3” pulgadas.

Cuando forzamos la pantalla doblándola con un ángulo mayor que el ángulo crítico que permite el dispositivo, provocaremos una rotura en el sustrato de plástico, rotura que se propagará a través de todo el bus de la línea correspondiente. Esta rotura provoca en la pantalla que la línea o líneas afectadas muestren un parpadeo, falle toda la línea, falle una región entera o incluso el dispositivo entero.

Beneficios:

Las pantallas AMOLED, fabricadas en sustratos plásticos flexibles, consiguen los siguientes beneficios:

* Son muy delgadas y muy ligeras
* Reforzados sistemas de protección de las roturas en el dispositivo
* Consumo muy bajo de potencia, alta rugosidad con una calidad de imagen superior y un bajo coste en comparación con las actuales pantallas LCD.
* Su rugosidad característica confiere a este dispositivo una enorme flexibilidad y posibilidad de incluso “enrollarlo”, aún estando activo, que se traduce en facilidad para su transporte o almacenamiento.

El elemento de matriz activa: Tecnología TFT Backplane

La tecnología del backplane del TFT es un elemento crucial para la fabricación de dispositivos AMOLED flexibles.

El proceso que se utiliza en los sustratos convencionales en los que se basan los TFT no se pueden utilizar con los sustratos de plástico flexibles que necesitamos, principalmente porque este proceso implicaría el no trabajar a temperaturas bajas, siendo este un límite necesario.

Para solucionar este problema, hoy en día existen principalmente dos tecnologías de fabricación del backplane del TFT utilizadas en los AMOLED: poly-Silicon (poly-Si) o amorphous-Silicon (a-Si).

Estas tecnologías ofrecen la posibilidad de fabricación de los backplanes de matriz activa a una baja temperatura (<150 °C), insertándolos directamente en el sustrato de plástico flexible posibilitando la producción de pantallas AMOLED flexibles.

Fuente: http://es.wikipedia.org/wiki/AMOLED
Materia: CRF
Sección: 01
Alumno: Juan J. Núñez C.
Leer: [Ecle12:1]