Tag Archives: letter-dd-tech

Engineers at Oregon State University have invented a way to fabricate silver, a highly conductive metal, for printed electronics that are produced at room temperature.

There may be broad applications in microelectronics, sensors, energy devices, low emissivity coatings and even transparent displays.

A patent has been applied for on the technology, which is now available for further commercial development. The findings were reported in Journal of Materials Chemistry C.

Silver has long been considered for the advantages it offers in electronic devices. Because of its conductive properties, it is efficient and also stays cool. But manufacturers have often needed high temperatures in the processes they use to make the devices, adding to their cost and complexity, and making them unsuitable for use on some substrates, such as plastics that might melt or papers that might burn.

This advance may open the door to much wider use of silver and other conductors in electronics applications, researchers said.

“There’s a great deal of interest in printed electronics, because they’re fast, cheap, can be done in small volumes and changed easily,” said Chih-hung Chang, a professor in the OSU College of Engineering. “But the heat needed for most applications of silver nanoparticles has limited their use.”

OSU scientists have solved that problem by using a microreactor to create silver nanoparticles at room temperatures without any protective coating, and then immediately printing them onto almost any substrate with a continuous flow process.

“Because we could now use different substrates such as plastics, glass or even paper, these electronics could be flexible, very inexpensive and stable,” Chang said. “This could be quite important and allow us to use silver in many more types of electronic applications.”

Among those, he said, could be solar cells, printed circuit boards, low-emissivity coatings, or transparent electronics. A microchannel applicator used in the system will allow the creation of smaller, more complex electronics features.

The latest manufacturing, materials and production developments in semiconductor and related technologies will be featured at SEMICON West 2015 on July 14-16 at Moscone Center in San Francisco, Calif.  Semiconductor processing is at a crossroads and is changing how companies operate to be competitive. Learning about breakthrough technology and networking is essential to remain ahead of the curve.  

More than 25,000 professionals are expected, and over 600 companies will exhibit the latest in semiconductor manufacturing.  Major semiconductor manufacturers, foundry, fabless companies, equipment and materials suppliers — plus leading companies in MEMS, displays, printed/flexible electronics, PV, and other emerging technologies — attend SEMICON West.

SEMICON West will feature valuable on-exhibition floor technical sessions and programs that are included in the  $100 registration “expo pass” (registration fee increases on July 11).  Keynote events include: 

·         “Scaling the Walls of Sub-14nm Manufacturing” with panelists from Qualcomm, Stanford University, ASE and IBM, moderated by imec’s Jo de Boeck, senior VP of Corporate Technology (July 14, 9:00-10:00am)

·         “The Internet of Things and the Next Fifty Years of Moore’s Law“ by Intel’s Doug Davis, senior VP and GM of loT (July 15, 9:00am-9:45am)

TechXPOTs will provide updates in areas including test, advanced materials and processes, advanced packaging, productivity and emerging markets and technologies. TechXPOTs include:

·      What’s Next for MEMS? With speakers from ASE, CEA-Leti, EV Group, MEMS Industry Group, Silicon Valley Band of Angels, Teledyne DALSA, and Yole Developpement (July 14, 10:30am-12:30pm)

·      Automating Semiconductor Test Productivity with speakers from ASE, Optimal+, Texas Instruments, and Xcerra (July 14, 10:30am-12:30pm)

·      Materials Session: Contamination Control in the Sub-20nm Era with speakers from Entegris, Intel, JSR Micro, Matheson, and Nanometrics; moderated by Mike Corbett, Linx (July 14, 1:30pm-3:30pm)

·      Emerging Generation Memory Technology: Update on 3DNAND, MRAM, and RRAM (July 14, 1:30pm-3:40pm).

·      The Evolution of the New 200mm Fab for the Internet of Everything with speakers from Entrepix, Genmark Automation, Lam Research, Qorvo, and Surplus Global (July 15, 2:00pm-4:00pm)

·      Monetizing the IoT: Opportunities and Challenges for the Semiconductor Sector with Amkor, Cadence Design Systems, Ernst & Young, Freescale Semiconductor, and Gartner; moderated by Edward Sperling, Semiconductor Engineering (July 16, 10:30am-12:30pm)

·      The Factory of the (Near) Future: Using Industrial IoT and 3D Printing  with speakers from AirLiquide, Applied Materials, Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, and Proto Cafe (July 16, 1:00pm-3:00pm) 

The Silicon Innovation Forum will be held on July 14-15.  A special exposition segment, this area will include exhibits and two days of presentations.  The first day will be a forum where start-up companies seeking investment capital will present to a panel of investors.  Open to all attendees, this session will feature exciting new technologies.  The second day will be a forum on new research. Attendees can hear presentations on advanced research from SLAC National Accelerator Laboratory, International Consortium for Advanced Manufacturing Research, SUNY Network of Excellence – Materials & Advanced Manufacturing, Novati Technologies, MIST Center, Micro/Nano Electronics Metrology at NIST, Texas State University and Georgia Tech Heat Lab. 

On July 16, University Day welcomes students and faculty to learn about the microelectronics industry, connect with industry representatives, and explore career opportunities. University Day is on the Keynote Stage (North Hall E). The agenda includes career networking, exploration forum, expo and SEMICON West tours.

For the eighth year, SEMICON West will be co-located with Intersolar North America, the leading solar technology conference and exhibition in the U.S.  Premier sponsors of SEMICON West 2015 include Applied Materials, KLA-Tencor, and Lam Research.  Register now at www.semiconwest.org.

Researchers from North Carolina State University have created stretchable, transparent conductors that work because of the structures’ “nano-accordion” design. The conductors could be used in a wide variety of applications, such as flexible electronics, stretchable displays or wearable sensors.

“There are no conductive, transparent and stretchable materials in nature, so we had to create one,” says Abhijeet Bagal, a Ph.D. student in mechanical and aerospace engineering at NC State and lead author of a paper describing the work.

“Our technique uses geometry to stretch brittle materials, which is inspired by springs that we see in everyday life,” Bagal says. “The only thing different is that we made it much smaller.”

The researchers begin by creating a three-dimensional polymer template on a silicon substrate. The template is shaped like a series of identical, evenly spaced rectangles. The template is coated with a layer of aluminum-doped zinc oxide, which is the conducting material, and an elastic polymer is applied to the zinc oxide. The researchers then flip the whole thing over and remove the silicon and the template.

What’s left behind is a series of symmetrical, zinc oxide ridges on an elastic substrate. Because both zinc oxide and the polymer are clear, the structure is transparent. And it is stretchable because the ridges of zinc oxide allow the structure to expand and contract, like the bellows of an accordion.

“We can also control the thickness of the zinc oxide layer, and have done extensive testing with layers ranging from 30 to 70 nanometers thick,” says Erinn Dandley, a Ph.D. student in chemical and biomolecular engineering at NC State and co-author of the paper. “This is important because the thickness of the zinc oxide affects the structure’s optical, electrical and mechanical properties.”

The 3-D templates used in the process are precisely engineered, using nanolithography, because the dimensions of each ridge directly affect the structure’s stretchability. The taller each ridge is, the more stretchable the structure. This is because the structure stretches by having the two sides of a ridge bend away from each other at the base – like a person doing a split.

The structure can be stretched repeatedly without breaking. And while there is some loss of conductivity the first time the nano-accordion is stretched, additional stretching does not affect conductivity.

“The most interesting thing for us is that this approach combines engineering with a touch of surface chemistry to precisely control the nano-accordion’s geometry, composition and, ultimately, its overall material properties,” says Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and corresponding author of the paper. “We’re now working on ways to improve the conductivity of the nano-accordion structures. And at some point we want to find a way to scale up the process.”

The researchers are also experimenting with the technique using other conductive materials to determine their usefulness in creating non-transparent, elastic conductors.

They are thin, light-weight, flexible and can be produced cost- and energy-efficiently: printed microelectronic components made of synthetics. Flexible displays and touch screens, glowing films, RFID tags and solar cells represent a future market. In the context of an international cooperation project, physicists at the Technische Universität München (TUM) have now observed the creation of razor thin polymer electrodes during the printing process and successfully improved the electrical properties of the printed films.

Solar cells out of a printer? This seemed unthinkable only a few years ago. There were hardly any alternatives to classical silicon technology available. In the mean time touch screens, sensors and solar cells can be made of conducting polymers. Flexible monitors and glowing wall paper made of organic light emitting diodes, so-called OLEDs, are in rapid development. The “organic electronics” are hailed as a promising future market.

However, the technology also has its pitfalls: To manufacture the components on an industrial scale, semiconducting or insulating layers – each a thousand times thinner than a human hair – must be printed onto a carrier film in a predefined order. “This is a highly complex process, whose details need to be fully understood to allow custom-tailored applications,” explains Professor Peter Müller-Buschbaum of the Chair of Functional Materials at TU München.

A further challenge is the contacting between flexible, conducting layers. Hitherto electronic contacts made of crystalline indium tin oxide were frequently used. However, this construction has numerous drawbacks: The oxide is more brittle than the polymer layers over them, which limits the flexibility of the cells. Furthermore, the manufacturing process also consumes much energy. Finally, indium is a rare element that exists only in very limited quantities.

Polymers in X-ray light 

A few months ago, researchers from the Lawrence Berkeley National Laboratory in California for the first time succeeded in observing the cross-linking of polymer molecules in the active layer of an organic solar cell during the printing process. In collaboration with their colleagues in California, Müller-Buschbaum’s team took advantage of this technology to improve the characteristics of the polymer electronic elements.

The researchers used X-ray radiation generated in the Berkley synchrotron for their investigations. The X-rays are directed to the freshly printed synthetic layer and scattered. The arrangement and orientation of the molecules during the curing process of the printed films can be determined from changes in the scattering pattern.

“Thanks to the very intensive X-ray radiation we can achieve a very high time resolution,” says Claudia M. Palumbiny. In Berkeley the physicist from the TUM investigated the “blocking layer” that sorts and selectively transports the charge carriers in the organic electronic components. The TUM research team is now, together with its US colleagues, publishing the results in the trade journal Advanced Materials.

Custom properties

“In our work, we showed for the first time ever that even small changes in the physico-chemical process conditions have a significant influence on the build-up and properties of the layer,” says Claudia M. Palumbiny. “Adding solvents with a high boiling point, for example, improves segregation in synthetics components. This improves the crystallization in conducting molecules. The distance between the molecules shrinks and the conductivity increases.

In this manner stability and conductivity can be improved to such an extent that the material can be deployed not only as a blocking layer, but even as a transparent, electrical contact. This can be used to replace the brittle indium tin oxide layers. “At the end of the day, this means that all layers could be produced using the same process,” explains Palumbiny. “That would be a great advantage for manufacturers.”

To make all of this possible one day, TUM researchers want to continue investigating and optimizing the electrode material further and make their know-how available to industry. “We have now formed the basis for pushing ahead materials development with future investigations so that these can be taken over by industrial enterprises,” explains Prof. Müller-Buschbaum.

The research was supported by the GreenTech Initiative “Interface Science for Photovoltaics” (ISPV) of the EuroTech Universities together with the International Graduate School of Science and Engineering (IGSSE) at TUM and by the Cluster of Excellence “Nanosystems Initiative Munich” (NIM). Further support came from the Elite Network of Bavaria’s International Doctorate Program “NanoBioTechnology” (IDK-NBT) and the Center for NanoScience (CeNS) and from “Polymer-Based Materials for Harvesting Solar Energy” (PHaSE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences. Portions of the research were carried out at the Advanced Light Source which receives support by the Office of Basic Energy Sciences of the U.S. Department of Energy.

Led by Young Duck Kim, a postdoctoral research scientist in James Hone’s group at Columbia Engineering, a team of scientists from Columbia, Seoul National University (SNU), and Korea Research Institute of Standards and Science (KRISS) reported today that they have demonstrated — for the first time — an on-chip visible light source using graphene, an atomically thin and perfectly crystalline form of carbon, as a filament. They attached small strips of graphene to metal electrodes, suspended the strips above the substrate, and passed a current through the filaments to cause them to heat up. The study, “Bright visible light emission from graphene,” is published in the Advance Online Publication (AOP) on Nature Nanotechnology‘s website on June 15.

“We’ve created what is essentially the world’s thinnest light bulb,” says Hone, Wang Fon-Jen Professor of Mechanical Engineering at Columbia Engineering and co-author of the study. “This new type of ‘broadband’ light emitter can be integrated into chips and will pave the way towards the realization of atomically thin, flexible, and transparent displays, and graphene-based on-chip optical communications.”

Creating light in small structures on the surface of a chip is crucial for developing fully integrated “photonic” circuits that do with light what is now done with electric currents in semiconductor integrated circuits. Researchers have developed many approaches to do this, but have not yet been able to put the oldest and simplest artificial light source — the incandescent light bulb — onto a chip. This is primarily because light bulb filaments must be extremely hot — thousands of degrees Celsius — in order to glow in the visible range and micro-scale metal wires cannot withstand such temperatures. In addition, heat transfer from the hot filament to its surroundings is extremely efficient at the microscale, making such structures impractical and leading to damage of the surrounding chip.

By measuring the spectrum of the light emitted from the graphene, the team was able to show that the graphene was reaching temperatures of above 2500 degrees Celsius, hot enough to glow brightly.

“The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification,” explains Young Duck Kim, first and co-lead author on the paper and postdoctoral research scientist who works in Hone’s group at Columbia Engineering.

Interestingly, the spectrum of the emitted light showed peaks at specific wavelengths, which the team discovered was due to interference between the light emitted directly from the graphene and light reflecting off the silicon substrate and passing back through the graphene. Kim notes, “This is only possible because graphene is transparent, unlike any conventional filament, and allows us to tune the emission spectrum by changing the distance to the substrate.”

The ability of graphene to achieve such high temperatures without melting the substrate or the metal electrodes is due to another interesting property: as it heats up, graphene becomes a much poorer conductor of heat. This means that the high temperatures stay confined to a small ‘hot spot’ in the center.

“At the highest temperatures, the electron temperature is much higher than that of acoustic vibrational modes of the graphene lattice, so that less energy is needed to attain temperatures needed for visible light emission,” Myung-Ho Bae, a senior researcher at KRISS and co-lead author, observes. “These unique thermal properties allow us to heat the suspended graphene up to half of temperature of the sun, and improve efficiency 1000 times, as compared to graphene on a solid substrate.”

The team also demonstrated the scalability of their technique by realizing large-scale of arrays of chemical-vapor-deposited (CVD) graphene light emitters.

Yun Daniel Park, professor in the department of physics and astronomy at Seoul National University and co-lead author, notes that they are working with the same material that Thomas Edison used when he invented the incandescent light bulb: “Edison originally used carbon as a filament for his light bulb and here we are going back to the same element, but using it in its pure form — graphene — and at its ultimate size limit — one atom thick.”

The group is currently working to further characterize the performance of these devices — for example, how fast they can be turned on and off to create “bits” for optical communications — and to develop techniques for integrating them into flexible substrates.

Hone adds, “We are just starting to dream about other uses for these structures — for example, as micro-hotplates that can be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.”

CEA-Leti today announced that it has demonstrated a path to fabricating high-density micro-LED arrays for the next generation of wearable and nomadic systems in a process that is scalable to the IC manufacturing process.

The high-brightness, enhanced-vision systems such as head-up and head-mounted displays can improve safety and performance in fields such as aeronautics and automotive, where the displays allow pilots and drivers to receive key navigation data and information in their line of sight. For consumers, smart glasses or nomadic projection devices with augmented reality provide directions, safety updates, advertisements and other information across the viewing field. LED microdisplays are ideally suited for such wearable systems because of their low footprint, low power consumption, high-contrast ratio and ultra-high brightness.

Leti researchers have developed gallium-nitride (GaN) and indium gallium-nitride (InGaN) LED technology for producing high-brightness, emissive microdisplays for these uses, which are expected to grow dramatically in the next three to five years. For example, the global research firm MarketsandMarkets forecasts the market for head-up displays alone to grow from $1.37 billion in 2012 to $8.36 billion in 2020.

“Currently available microdisplays for both head-mounted and compact head-up applications suffer from fundamental technology limitations that prevent the design of very low-weight, compact and low-energy-use products,” said Ludovic Poupinet, head of Leti’s Optics and Photonics Department. “Leti’s technology breakthrough is the first demonstration of a high-brightness, high-density micro-LED array that overcomes these limitations and is scalable to a standard microelectronic large-scale process. This technology provides a low-cost, leading-edge solution to companies that want to target the fast-growth markets for wearable vision systems.”

Announced during Display Week 2015 in San Jose, Calif., Leti’s technology innovation is based on micro-LED arrays that are hybridized on a silicon backplane. Key innovations include epitaxial growth of LED layers on sapphire or other substrates, micro-structuration of LED arrays (10μm pitches or smaller), and 3D heterogeneous integration of such LED arrays on CMOS active-matrices.

These innovations make it possible to produce a brightness of 1 million cd/m² for monochrome devices and 100 kcd/m² for full-color devices with a device size below one inch and 2.5 million pixels. This is a 100- to 1,000-times improvement compared to existing self-emissive microdisplays, with very good power efficiency. The technology also will allow fabrication of very compact products that significantly reduce system-integration constraints.

The high-density micro-LED array process was developed in collaboration with III-V Lab.

Applied Materials, Inc. today announced its Applied Endura Cirrus  HTX PVD system with breakthrough technology for patterning copper interconnects at 10nm and beyond. As chip features continue to shrink, innovations in hardmask are required to preserve the pattern integrity of tightly packed, tiny interconnect structures.With the introduction of this technology, Applied enables scaling of the TiN metal hardmask – the industry’s material of choice – to meet the patterning needs of copper interconnects in advanced microchips.

“Precision engineering of metal hardmask films is key to addressing the patterning challenges for advanced interconnects,” said Dr. Sundar Ramamurthy, vice president and general manager of Applied’s Metal Deposition Products business unit. “The Cirrus HTX TiN product represents Applied’s decades of expertise in applying PVD technology for engineering TiN film properties. Incorporating our unique VHF-based technology offers customers the flexibility of tuning stress in TiN films from compressive to tensile to overcome their specific integration challenges.”

Today’s advanced microchips can pack 20 kilometers of copper wiring in a 100 square millimeter area, stacked in 10 layers with up to 10 billion vias or vertical connections between layers. The role of the metal hardmask is to preserve the integrity of these patterned lines and vias in soft ULK dielectrics. However, with scaling, the compressive stress from conventional TiN hardmask layers can cause the narrow lines patterned in ULK films to deform or collapse. The tunable Cirrus HTX TiN hardmask with high etch selectivity delivers superior CD line width control and via overlay alignment resulting in yield improvement.

This breakthrough in TiN hardmask is made possible by precision materials engineering at the wafer level to produce a high density, low-stress film. Combining exceptional film thickness uniformity with low defectivity on a proven Endura platform, the Cirrus HTX system addresses the stringent high volume manufacturing needs of patterning multiple interconnect layers.

Applied Materials, Inc. is a developer precision materials engineering solutions for the semiconductor, flat panel display and solar photovoltaic industries.

Researchers at Lehigh University have identified for the first time that a performance gain in the electrical conductivity of random metal nanowire networks can be achieved by slightly restricting nanowire orientation. The most surprising result of the study is that heavily ordered configurations do not outperform configurations with some degree of randomness; randomness in the case of metal nanowire orientations acts to increase conductivity.

The study, Conductivity of Nanowire Arrays under Random and Ordered Orientation Configurations, is published in the current issue of Nature‘s journal Scientific Reports. The research was carried out by Nelson Tansu, Daniel E. ’39 and Patricia M. Smith Endowed Chair Professor in Lehigh’s Center for Photonics and Nanoelectronics and Department of Electrical and Computer Engineering, and lead author Milind Jagota, a Bethlehem-area high school student.

Transparent conductors are needed widely for flat screen displays, touch screens, solar cells, and light-emitting diodes, among many other technologies. Currently, Indium Tin Oxide (ITO) is the most widely used material for transparent conductors due to its high conductivity and high transparency. However, ITO-based technology has several issues. The material is scarce, expensive to manufacture and brittle, a particularly undesirable characteristic for anything being used in this modern age of flexible electronics.

Researchers searching for a replacement for ITO are increasingly employing random networks of metal nanowires to match ITO in both transparency and conductivity. Metal nanowire-based technologies display better flexibility and are more compatible with manufacturing processes than ITO films. The technology, however, is still in an early phase of development and performance must be improved. Current research is focused on the effect of rod orientation on conductivity of networks to improve performance.

In this work, Lehigh researchers developed a computational model for simulation of metal nanowire networks, which should speed the process towards idealizing the configuration of nanowires. The model predicts existing experimental results and previously published computational results.

The researchers then used this model to extract results for the first time on how conductivity of random metal nanowire networks is affected by different orientation restrictions of varying randomness. Two different orientation configurations are reported.

In the first, a uniform distribution of orientations over the range (?θ, θ) with respect to a horizontal line is used. In the second, a distribution of orientations over the range [?θ] _ [θ] is used, also with respect to a horizontal line. In each case θ is gradually decreased from 90° to 0°. Conductivity is measured both in directions parallel and perpendicular to alignment.

Researchers found that a significant improvement in conductivity parallel to direction of alignment can be obtained by slightly restricting orientation of the uniform distribution. This improvement, however, comes at the expense of a larger drop in perpendicular conductivity. The general form of these results matches that demonstrated by researchers experimenting with carbon nanotube films. Surprisingly, it was found that the highly ordered second case is unable to outperform isotropic networks for any value of θ; thus demonstrating that continuous orientation configurations with some degree of randomness are preferable to highly ordered configurations.

Prior research in this field has studied the effects of orientation on conductivity of 3D carbon nanotube composites, finding that a slight degree of alignment improves conductivity. Computational models have been used to study how percolation probability of 2D random rod dispersions is affected by rod orientation. Others have developed a more sophisticated computational model capable of calculating conductivity of 3D rod dispersions, again finding that a slight degree of axial alignment improves conductivity.

“Metal nanowire networks show great potential for application in various forms of technology,” said Jagota. “This computational model, which has proven itself accurate through its good fit with previously published data, has demonstrated quantitatively how different orientation configurations can impact conductivity of metal nanowire networks.”

“Restriction of orientation can improve conductivity in a single direction by significant amounts, which can be relevant in a variety of technologies where current flow is only required in one direction,” said Tansu. “Surprisingly, heavily controlled orientation configurations do not exhibit superior conductivity; some degree of randomness in orientation in fact acts to improve conductivity of the networks. This approach may have tremendous impacts on improving current spreading in optoelectronics devices, specifically on deep ultraviolet emitter with poor p-type contact layer.”

A revolution is coming in flexible electronic technologies as cheaper, more flexible, organic transistors come on the scene to replace expensive, rigid, silicone-based semiconductors, but not enough is known about how bending in these new thin-film electronic devices will affect their performance, say materials scientists at the University of Massachusetts Amherst.

Writing in the current issue of Nature Communications, polymer scientists Alejandro Briseño and Alfred Crosby at UMass Amherst, with their doctoral student Marcos Reyes-Martinez, now a postdoctoral researcher at Princeton, report results of their recent investigation of how micro-scale wrinkling affects electrical performance in carbon-based, single-crystal semiconductors.

They are the first to apply inhomogeneous deformations, that is strain, to the conducting channel of an organic transistor and to understand the observed effects, says Reyes-Martinez, who conducted the series of experiments as part of his doctoral work.

As he explains, “This is relevant to today’s tech industry because transistors drive the logic of all the consumer electronics we use. In the screen on your smart phone, for example, every little pixel that makes up the image is turned on and off by hundreds of thousands or even millions of miniaturized transistors.”

“Traditionally, the transistors are rigid, made of an inorganic material such as silicon,” he adds. “We’re working with a crystalline semiconductor called rubrene, which is an organic, carbon-based material that has performance factors, such as charge-carrier mobility, surpassing those measured in amorphous silicon. Organic semiconductors are an interesting alternative to silicon because their properties can be tuned to make them easily processed, allowing them to coat a variety of surfaces, including soft substrates at relatively low temperatures. As a result, devices based on organic semiconductors are projected to be cheaper since they do not require high temperatures, clean rooms and expensive processing steps like silicon does.”

Until now, Reyes-Martinez notes, most researchers have focused on controlling the detrimental effects of mechanical deformation to a transistor’s electrical properties. But in their series of systematic experiments, the UMass Amherst team discovered that mechanical deformations only decrease performance under certain conditions, and actually can enhance or have no effect in other instances.

“Our goal was not only to show these effects, but to explain and understand them. What we’ve done is take advantage of the ordered structure of ultra-thin organic single crystals of rubrene to fabricate high-perfomance, thin-film transistors,” he says. “This is the first time that anyone has carried out detailed fundamental work at these length scales with a single crystal.”

Though single crystals were once thought to be too fragile for flexible applications, the UMass Amherst team found that crystals ranging in thickness from about 150 nanometers to 1 micrometer were thin enough to be wrinkled and applied to any elastomer substrate. Reyes-Martinez also notes, “Our experiments are especially important because they help scientists working on flexible electronic devices to determine performance limitations of new materials under extreme mechanical deformations, such as when electronic devices conform to skin.”

They developed an analytical model based on plate bending theory to quantify the different local strains imposed on the transistor structure by the wrinkle deformations. Using their model they are able to predict how different deformations modulate charge mobility, which no one had quantified before, Reyes-Martinez notes.

Schematic of wrinkled rubrene single-crystal field-effect transistor. Wrinkles are obtained when in-plane compressive strain is applied on the elastomeric substrate. Electric current between gold (Au) electrodes is modulated by the deformation imposed by the wrinkles. Credit: UMass Amherst

These contributions “represent a significant step forward in structure-function relationships in organic semiconductors, critical for the development of the next generation of flexible electronic devices,” the authors point out.

From mobile phones and computers to television, cinema and wearable devices, the display of full color, wide-angle, 3D holographic images is moving ever closer to fruition, thanks to international research featuring Griffith University.

Led by Melbourne’s Swinburne University of Technology and including Dr Qin Li, from the Queensland Micro- and Nanotechnology Center within Griffith’s School of Engineering, scientists have capitalised on the exceptional properties of graphene and are confident of applications in fields such as optical data storage, information processing and imaging.

“While there is still work to be done, the prospect is of 3D images seemingly leaping out of the screens, thus promising a total immersion of real and virtual worlds without the need for cumbersome accessories such as 3D glasses,” says Dr Li.

First isolated in the laboratory about a decade ago, graphene is pure carbon and one of the thinnest, lightest and strongest materials known to humankind. A supreme conductor of electricity and heat, much has been written about its mechanical, electronic, thermal and optical properties.

“Graphene offers unprecedented prospects for developing flat displaying systems based on the intensity imitation within screens,” says Dr Li, who conducted carbon structure analysis for the research.

“Our consortium, which also includes China’s Beijing Institute of Technology and Tsinghua University, has shown that patterns of photo-reduced graphene oxide (rGO) that are directly written by laser beam can produce wide-angle and full-colour 3D images.

“This was achieved through the discovery that a single femtosecond (fs) laser pulse can reduce graphene oxide to rGO with a sub-wavelength-scale feature size and significantly differed refractive index.

“Furthermore, the spectrally flat optical index modulation in rGOs enables wavelength-multiplexed holograms for full colour images.”

Researchers say the sub-wavelength feature is particularly important because it allows for static holographic 3D images with a wide viewing angle up to 52 degrees.

Such laser-direct writing of sub-wavelength rGO featured in dots and lines could revolutionise capabilities across a range of optical and electronic devices, formats and industry sectors.

“The generation of multi-level modulations in the refractive index of GOs, and which do not require any solvents or post-processing, holds the potential for in-situ fabrication of rGO-based electro-optic devices,” says Dr Li.

“The use of graphene also relieves pressure on the world’s dwindling supplies of indium, the metallic element that has been commonly used for electronic devices.

“Other technologies are being developed in this area, but rGO looks by far the most promising and most practical, particularly for wearable devices. The prospects are quite thrilling.”