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Posts Tagged ‘flexible electronics’

Roll-to-Roll Coating Technology: It’s a Different Ball of Wax

Monday, April 18th, 2016

Compiled and edited by Jeff Dorsch, Contributing Editor

Manufacturing flexible electronics and coatings for a variety of products has some similarities to semiconductor manufacturing and some substantial differences, principally roll-to-roll fabrication, as opposed to making chips on silicon wafers and other rigid substrates. This interview is with Neil Morrison, senior manager, Roll-to-Roll Coating Products Division, Applied Materials.

1. What are the leading market trends in roll-to-roll coating systems?

Neil Morrison: Several market trends are driving innovations in roll-to-roll technology and barrier films.  One is the flexible electronics market where we see the increasing use of film-based components within displays for portable electronic devices such as smartwatches, smartphones, tablets and laptops.

The majority of these passive applications are for anti-reflection films, optical polarizers and hard coat protected cover glass films.

Examples of active device applications include touch sensors. Roll-to-roll vacuum processing dominates this segment through the use of low-temperature deposited, optically matched layer stacks based on indium tin oxide (ITO). Roll-to-roll deposition of barrier film is also increasing with the emergence of quantum dot-enhanced LCD displays and the utilization of barrier films in organic light-emitting diode (OLED) lighting.

In addition to the electronics industry, roll-to-roll technology is used for food packaging and industrial coatings. What’s new today for food packaging is consumers want to be able to view the freshness of the food inside the packaging. Given this, the use of both aluminum foil and traditional roll-to-roll evaporated aluminum layers is slowly being phased into vacuum-deposited aluminum oxide (AlOx) coated packaging.

Within the industrial coatings market segment, significant growth is being driven by the use of Fabry-Perot color shift systems for “holographic” security applications, such as those used to protect printed currency from counterfeiting. This requires the use of electron-beam evaporation tooling to deposit highly uniform, optical quality dielectric materials sandwiched between two metallic reflector layers.

2. What are the leading technology trends in roll-to-roll coating systems?

Neil Morrison: Roll-to-roll coating is being extended to the display industry through the use of higher optical performance substrates with enhanced transmission, optical clarity and color neutrality. These materials are typically more difficult to handle than traditional polyethylene terephthalate (PET) substrates due to inherent properties and the properties of the primer and/or hard coat layers used to treat or protect their surface.

The majority of displays used in mobile applications are moving to thinner substrates, to reduce the “real estate” within the display and enable thinner form factor products and more space for larger batteries.

At the technology level, roll-to-roll sputter tooling dominates the touch panel industry with continual improvements in substrate handling, pre-treatment and inline process monitoring and control. Roll-to-roll chemical vapor deposition (CVD) equipment has also entered the marketplace to address high barrier requirements and to reduce cost compared with traditional sputter-based solutions. Roll-to-roll CVD technology is still in its infancy but is expected to become more prevalent in the near future within the barrier and hard coat market segments.

In the display industry, defect requirements are becoming more and more stringent and are moving towards metrics previously unseen in the roll-to-roll industry.

3. How would you best and briefly describe the Applied SmartWeb, Applied TopBeam, and Applied TopMet systems?

Neil Morrison: The Applied SmartWeb roll-to-roll modular sputtering or physical vapor deposition tool is used to deposit metals, dielectrics and transparent conductive oxides on polymeric substrates for the touch panel and optical coating industry. Its high-precision substrate conveyance system permits winding of polymeric substrates down to thickness levels of ~23 microns at speeds of up to 20 meters/minute depending upon the application. Up to six process compartments with separate gas flow control and pumping allow the deposition of complex layer stacks within a single pass.

Our Applied TopBeam system is a roll-to-roll e-beam evaporation tool used to deposit dielectrics on substrate thicknesses as low as 12 micron and at speeds up to approximately 10 meters/second.  Key to the tool is Applied’s unique electron-beam steering and control system, which provides excellent layer deposition and uniformity at exceptionally high processing speeds by permitting uniform and stable heating of the evaporant material  over the entire width of the substrate.

The Applied TopMet is a high-productivity roll-to-roll thermal evaporation platform available for depositing Al and AlOx layers on substrates down to 12 microns in thickness and is used primarily for food and industrial packaging.

Applied SmartWeb (Source: Applied Materials)

4. Who are Applied’s leading competitors in this market?

Neil Morrison: Other companies in the roll-to-roll market include Von Ardenne, Leybold Optics (Buehler), Schmid, Ulvac and Kobelco.

5. How big is the worldwide market on annual basis?

Neil Morrison: It is difficult to accurately size the entire roll-to-roll market because of the wide variety of applications across multiple industries from flexible electronics to food packaging. Just estimating the size of the market within the flexible electronics category alone is tough because there are three areas that combine to make up the current flexible electronics market – OLEDs for flexible displays, flexible printed circuit boards, and flexible touch panels for phones and tablets. And with applications continuing to grow, it is difficult to provide a specific market size.

Solid State Watch: January 23-29, 2015

Friday, January 30th, 2015

Research Alert: January 26, 2015

Monday, January 26th, 2015

Solving an organic semiconductor mystery

Organic semiconductors are prized for light emitting diodes (LEDs), field effect transistors (FETs) and photovoltaic cells. As they can be printed from solution, they provide a highly scalable, cost-effective alternative to silicon-based devices. Uneven performances, however, have been a persistent problem. Scientists have known that the performance issues originate in the domain interfaces within organic semiconductor thin films, but have not known the cause. This mystery now appears to have been solved.

Naomi Ginsberg, a faculty chemist with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory and the University of California (UC) Berkeley, led a team that used a unique form of microscopy to study the domain interfaces within an especially high-performing solution-processed organic semiconductor called TIPS-pentacene. She and her team discovered a cluttered jumble of randomly oriented nanocrystallites that become kinetically trapped in the interfaces during solution casting. Like debris on a highway, these nanocrystallites impede the flow of charge-carriers.

“If the interfaces were neat and clean, they wouldn’t have such a large impact on performance, but the presence of the nanocrystallites reduces charge-carrier mobility,” Ginsberg says. “Our nanocrystallite model for the interface, which is consistent with observations, provides critical information that can be used to correlate solution-processing methods to optimal device performances.”

Ginsberg, who holds appointments with Berkeley Lab’s Physical Biosciences Division and its Materials Sciences Division, as well as UC Berkeley’s departments of chemistry and physics, is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Exciton dynamics reveals aggregates with intermolecular order at hidden interfaces in solution-cast organic semiconducting films.” Co-authors are Cathy Wong, Benjamin Cotts and Hao Wu.

Ginsberg and her group overcame the challenges by using transient absorption (TA) microscopy, a technique in which femtosecond laser pulses excite transient energy states and detectors measure the changes in the absorption spectra. The Berkeley researchers carried out TA microscopy on an optical microscope they constructed themselves that enabled them to generate focal volumes that are a thousand times smaller than is typical for conventional TA microscopes. They also deployed multiple different light polarizations that allowed them to isolate interface signals not seen in either of the adjacent domains.

“Instrumentation, including very good detectors, the painstaking collection of data to ensure good signal-to-noise ratios, and the way we crafted the experiment and analysis were all critical to our success,” Ginsberg says. “Our spatial resolution and light polarization sensitivity were also essential to be able to unequivocally see a signature of the interface that was not swamped by the bulk, which contributes much more to the raw signal by volume.”

The methology developed by Ginsberg and her team to uncover structural motifs at hidden interfaces in organic semiconductor thin films should add a predictive factor to scalable and affordable solution-processing of these materials. This predictive capability should help minimize discontinuities and maximize charge-carrier mobility. Currently, researchers use what is essentially a trial-and-error approach, in which different solution casting conditions are tested to see how well the resulting devices perform.

“Our methodology provides an important intermediary in the feedback loop of device optimization by characterizing the microscopic details of the films that go into the devices, and by inferring how the solution casting could have created the structures at the interfaces,” Ginsberg says. “As a result, we can suggest how to alter the delicate balance of solution casting parameters to make more functional films.”

Rice-sized laser, powered one electron at a time, bodes well for quantum computing

Princeton University researchers have built a rice grain-sized laser powered by single electrons tunneling through artificial atoms known as quantum dots. The tiny microwave laser, or “maser,” is a demonstration of the fundamental interactions between light and moving electrons.

The researchers built the device — which uses about one-billionth the electric current needed to power a hair dryer — while exploring how to use quantum dots, which are bits of semiconductor material that act like single atoms, as components for quantum computers.

“It is basically as small as you can go with these single-electron devices,” said Jason Petta, an associate professor of physics at Princeton who led the study, which was published in the journal Science.

The device demonstrates a major step forward for efforts to build quantum-computing systems out of semiconductor materials, according to co-author and collaborator Jacob Taylor, an adjunct assistant professor at the Joint Quantum Institute, University of Maryland-National Institute of Standards and Technology.

“I consider this to be a really important result for our long-term goal, which is entanglement between quantum bits in semiconductor-based devices,” Taylor said.

The original aim of the project was not to build a maser, but to explore how to use double quantum dots — which are two quantum dots joined together — as quantum bits, or qubits, the basic units of information in quantum computers.

“The goal was to get the double quantum dots to communicate with each other,” said Yinyu Liu, a physics graduate student in Petta’s lab. The team also included graduate student Jiri Stehlik and associate research scholar Christopher Eichler in Princeton’s Department of Physics, as well as postdoctoral researcher Michael Gullans of the Joint Quantum Institute.

Because quantum dots can communicate through the entanglement of light particles, or photons, the researchers designed dots that emit photons when single electrons leap from a higher energy level to a lower energy level to cross the double dot.

Each double quantum dot can only transfer one electron at a time, Petta explained. “It is like a line of people crossing a wide stream by leaping onto a rock so small that it can only hold one person,” he said. “They are forced to cross the stream one at a time. These double quantum dots are zero-dimensional as far as the electrons are concerned — they are trapped in all three spatial dimensions.”

The researchers fabricated the double quantum dots from extremely thin nanowires (about 50 nanometers, or a billionth of a meter, in diameter) made of a semiconductor material called indium arsenide. They patterned the indium arsenide wires over other even smaller metal wires that act as gate electrodes, which control the energy levels in the dots.

To construct the maser, they placed the two double dots about 6 millimeters apart in a cavity made of a superconducting material, niobium, which requires a temperature near absolute zero, around minus 459 degrees Fahrenheit. “This is the first time that the team at Princeton has demonstrated that there is a connection between two double quantum dots separated by nearly a centimeter, a substantial distance,” Taylor said.

When the device was switched on, electrons flowed single-file through each double quantum dot, causing them to emit photons in the microwave region of the spectrum. These photons then bounced off mirrors at each end of the cavity to build into a coherent beam of microwave light.

One advantage of the new maser is that the energy levels inside the dots can be fine-tuned to produce light at other frequencies, which cannot be done with other semiconductor lasers in which the frequency is fixed during manufacturing, Petta said. The larger the energy difference between the two levels, the higher the frequency of light emitted.

Claire Gmachl, who was not involved in the research and is Princeton’s Eugene Higgins Professor of Electrical Engineering and a pioneer in the field of semiconductor lasers, said that because lasers, masers and other forms of coherent light sources are used in communications, sensing, medicine and many other aspects of modern life, the study is an important one.

“In this paper the researchers dig down deep into the fundamental interaction between light and the moving electron,” Gmachl said. “The double quantum dot allows them full control over the motion of even a single electron, and in return they show how the coherent microwave field is created and amplified. Learning to control these fundamental light-matter interaction processes will help in the future development of light sources.”

Carbon nanotube finding could lead to flexible electronics with longer battery life

University of Wisconsin-Madison materials engineers have made a significant leap toward creating higher-performance electronics with improved battery life — and the ability to flex and stretch.

Led by materials science Associate Professor Michael Arnold and Professor Padma Gopalan, the team has reported the highest-performing carbon nanotube transistors ever demonstrated. In addition to paving the way for improved consumer electronics, this technology could also have specific uses in industrial and military applications.

In a paper published recently in the journal ACS Nano, Arnold, Gopalan and their students reported transistors with an on-off ratio that’s 1,000 times better and a conductance that’s 100 times better than previous state-of-the-art carbon nanotube transistors.

“Carbon nanotubes are very strong and very flexible, so they could also be used to make flexible displays and electronics that can stretch and bend, allowing you to integrate electronics into new places like clothing,” says Arnold. “The advance enables new types of electronics that aren’t possible with the more brittle materials manufacturers are currently using.”

Carbon nanotubes are single atomic sheets of carbon rolled up into a tube. As some of the best electrical conductors ever discovered, carbon nanotubes have long been recognized as a promising material for next-generation transistors, which are semiconductor devices that can act like an on-off switch for current or amplify current. This forms the foundation of an electronic device.

However, researchers have struggled to isolate purely semiconducting carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and “short” the device. Researchers have also struggled to control the placement and alignment of nanotubes. Until now, these two challenges have limited the development of high-performance carbon nanotube transistors.

Building on more than two decades of carbon nanotube research in the field, the UW-Madison team drew on cutting-edge technologies that use polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

Previous techniques to align the nanotubes resulted in less-than-desirable packing density, or how close the nanotubes are to one another when they are assembled in a film. However, the UW-Madison researchers pioneered a new technique, called floating evaporative self-assembly, or FESA, which they described earlier in 2014 in the ACS journal Langmuir. In that technique, researchers exploited a self-assembly phenomenon triggered by rapidly evaporating a carbon nanotube solution.

The team’s most recent advance also brings the field closer to realizing carbon nanotube transistors as a feasible replacement for silicon transistors in computer chips and in high-frequency communication devices, which are rapidly approaching their physical scaling and performance limits.

“This is not an incremental improvement in performance,” Arnold says. “With these results, we’ve really made a leap in carbon nanotube transistors. Our carbon nanotube transistors are an order of magnitude better in conductance than the best thin film transistor technologies currently being used commercially while still switching on and off like a transistor is supposed to function.”

The researchers have patented their technology through the Wisconsin Alumni Research Foundation and have begun working with companies to accelerate the technology transfer to industry.

NFC IGZO TFT for Game Cards

Thursday, November 20th, 2014

By Ed Korczynski, Senior Technical Editor, SemiMD

Thin-film transistors (TFT) made with indium-gallium-zinc-oxide (IGZO) can perform significantly better than TFTs made with low-temperature-poly-silicon (LTPS), and can be made ultra-thin and flexible for integration into a wide variety of devices. Researchers at the Holst Centre—an R&D incubator launched by the Belgian imec and the Dutch TNO in 2005—have been working on flexible TFTs for many years for many applications include flexible displays, intelligent food packaging, and paper identification (ID) documents. Now Holst Center is collaborating with Cartamundi NV, a world leader in production and sales of card and board games, to develop ultra-thin flexible near field communication (NFC) tags for game cards. The goal is an enhanced gaming experience that is interactive and intuitive.

Cartamundi creates specialized game cards such as these, and has been working on cards with embedded silicon NFC chips for many years. (Source: Cartamundi)

Cartamundi has been working on “iCards” that provide a connection between the physical products and the digital world for many years, and has recently claimed traction with games for the “connected generation”. By working with the Holst Centre to create IGZO TFTs on plastic, Cartamundi aims to lower overall costs while also creating both a thinner and a more robust NFC chip. Currently, Cartamundi NV embeds silicon-based NFC chips in their game cards, connecting traditional game play with electronic devices such as smartphones and tablets. The advanced IGZO TFT technology should improve and broaden the applicability of interactive technology for game cards, compared to the currently-used silicon based NFC chips.

Chris Van Doorslaer, chief executive officer of Cartamundi, said, “Cartamundi is committed to creating products that connect families and friends of every generation to enhance the valuable quality time they share during the day. With Holst Centre’s and imec’s thin-film and nano-electronics expertise, we’re connecting the physical with the digital which will enable lightweight smart devices with additional value and content for consumers.”

“Not only will Cartamundi be working on the NFC chip of the future, but it will also reinvent the industry’s standards in assembly process and the conversion into game cards,” says Steven Nietvelt, chief innovation and marketing officer at Cartamundi. “All of this is part of an ongoing process of technological innovation inside Cartamundi. I am glad our innovation engineers will collaborate with the strongest technological researchers and developers in the field at imec and Holst Centre. We are going to need all expertise on board. Because basically what we are creating is game-changing technology.”

The major challenges are two-fold:  low-temperature formation of the IGZO layer, and integration of the IGZO into a complex NFC circuit on plastic. Control of surface states and defect densities is always essential for the production of any working semiconductor device, and defects act as traps for electrons flowing through circuitry. Consequently, for TFT instead of bulk crystal devices the precise control of the many deposited thin-films is essential.

Holst Centre, imec and Cartamundi engineers will look into NFC circuit design and TFT processing options, and will investigate routes for up-scaling of Holst processes to run on large production presses. By keeping the IGZO TFT manufacturing costs low, the flexible chips are intended to be a critical part of Cartamundi’s larger strategy of developing game cards for the connected generation.

“Imec and Holst Centre aim to shape the future and our collaboration with Cartamundi will do so for the future of gaming technology and connected devices,” says Paul Heremans, Department Director Thin Film Electronics at imec and Technology Director at the Holst Centre. “Chip technology has penetrated society’s daily life right down to game cards. We are excited to work with Cartamundi to improve the personal experience that gaming delivers.”

While game cards may not seem as important as healthcare and communications, flexible NFC integration into cards could generate IGZO TFT production volumes that are game changing.

—E.K.

Research Alert: July 16, 2014

Wednesday, July 16th, 2014

A nanosensor to identify vapors based on a graphene/silicon heterojunction Schottky diode

Among other carbon-based nanomaterials, graphene represents a great promise for gas sensing applications. In 2009 the detection of individual gas molecules of NO2 adsorbed onto graphene surface was reported for the first time. This initial observation has been successfully explored during the recent years. The Nanobioelectronics & Biosensors Group at Institut Català de Nanociència i Nanotecnologia (ICN2), led by ICREA Research Professor Arben Merkoçi, published in Small a work showing how to use a Graphene/Silicon Heterojunction Schottky Diode as a sensitive, selective and simple tool for vapors sensing. The work was developed in collaboration with researchers from the Amirkabir University of Technology (Tehran, Iran).

The Graphene/Silicon heterojunction Schottky diode is fabricated using a silicon wafer onto which Cr and Au were deposited to form the junction between graphene and silicon (see the attached figure). The adsorbed vapor molecules change the local carrier concentration in graphene, which yields to the changes in impedance response. The vapors of the various chemical compounds studied change the impedance response of Graphene/Silicon heterojunction Schottky diode. The relative impedance change versus frequency dependence shows a selective response in gas sensing which makes this characteristic frequency a distinctive parameter of a given vapor.

The device is well reproducible for different concentrations of phenol vapor using three different devices. This graphene based device and the developed detection methodology could be extended to several other gases and applications with interest for environmental monitoring as well as other industries.

A cool approach to flexible electronics

A nanoparticle ink that can be used for printing electronics without high-temperature annealing presents a possible profitable approach for manufacturing flexible electronics.

Printing semiconductor devices are considered to provide low-cost high performance flexible electronics that outperform amorphous silicon thin film transistors currently limiting developments in display technology. However the nanoparticle inks developed so far have required annealing, which limits them to substrates that can withstand high temperatures, ruling out a lot of the flexible plastics that could otherwise be used. Researchers at the National Institute of Materials Science and Okayama University in Japan have now developed a nanoparticle ink that can be used with room-temperature printing procedures.

Developments in thin film transistors made from amorphous silicon have provided wider, thinner displays with higher resolution and lower energy consumption. However further progress in this field is now limited by the low response to applied electric fields, that is, the low field-effect mobility. Oxide semiconductors such as InGaZnO (IGZO) offer better performance characteristics but require complicated fabrication procedures.

Nanoparticle inks should allow simple low-cost manufacture but the nanoparticles usually used are surrounded in non-conductive ligands – molecules that are introduced during synthesis for stabilizing the particles. These ligands must be removed by annealing to make the ink conducting. Takeo Minari, Masayuki Kanehara and colleagues found a way around this difficulty by developing nanoparticles surrounded by planar aromatic molecules that allow charge transfer.

The gold nanoparticles had a resistivity of around 9 x 10-6 Ω cm – similar to pure gold. The researchers used the nanoparticle ink to print organic thin film transistors on a flexible polymer and a paper substrate at room temperature, producing devices with mobilities of 7.9 and 2.5 cm2 V-1 s-1 for polymer and paper respectively – figures comparable to IGZO devices.

As the researchers conclude in their report of the work, “This room temperature printing process is a promising method as a core technology for future semiconductor devices.”

Graphene grain boundaries reviewed

Graphene has attracted overwhelming attention both for exploring fundamental science and for a wide range of technological applications. Chemical vapor deposition (CVD) is currently the only working approach to grow high-quality graphene at very large scale, which is required for industrial applications such as high-frequency devices, sensors, transparent electrodes, etc. Unfortunately, the produced graphene is typically polycrystalline, consisting of a patchwork of grains with various orientations and sizes, joined by grain boundaries of irregular shapes. The understanding of the relation between polycrystalline morphology and charge transport is crucial for the development of applications, as recently reported by SAMSUNG.

Researchers from the ICN2 Theoretical and Computational Nanoscience Group curated a review article in Advanced Materials to determine whether graphene grain boundaries are a blessing or a curse. ICREA Research Professor Stephan Roche, Group Leader at ICN2, together with Dr Aron CummingsJose Eduardo Barrios Vargas and Van Tuan Dinh, from the same Group, share the authorship of the review with researchers from Sungkyunkwan University. The review article not only provides guidelines for the improvement of graphene devices, but also opens a new research area of engineering graphene grain boundaries for highly sensitive electro-biochemical devices.

The review analyses the challenges and opportunities of charge transport in polycrystalline graphene, which means summarizing the state-of-the-art knowledge about graphene grain boundaries (GGBs). The review is divided in the following sections: Structure and Morphology of GGBs; Methods of Observing GGBs; Measurement of Electrical Transport across GGBs; Manipulation of GGBs with Functional Groups.

The work describes how TEM and STM, combined with theory and simulation, can provide information for the observation and characterization of GGBs at the atomic scale. These boundaries have interesting properties, such as the fact that they can be a good template for the synthesis of 1D materials, might be useful to design sensors for detecting gases and molecules or allow selective diffusion of limited gases and molecules. Controlling the atomic structure of GGBs by CVD is a big challenge from a scientific point of view, but would be a huge step forward in the realization of next-generation technologies based on this material.

The work has been partly funded by SAMSUNG within the Global Innovation program.

Research Alert: June 3, 2014

Tuesday, June 3rd, 2014

Georgia Tech research develops physics-based spintronic interconnect modeling for beyond-CMOS computing

Georgia Institute of Technology researchers collaborating with and sponsored by Intel Corporation through the Semiconductor Research Corporation (SRC) have developed a physics-based modeling platform that advances spintronics interconnect research for beyond-CMOS computing.

Spin-logic aims at reducing power consumption of electronic devices, thereby improving battery life and reducing energy consumption in computing for a whole range of electronic product applications from portable devices to data centers.

“After more than four decades of exponential growth in the performance of electronic integrated circuits, it is now apparent that improving the energy efficiency of computing is a primary challenge,” said Ian A. Young, a collaborator and co-author of the research and a Senior Fellow at Intel Corporation. “There is a global search for information processing elements that use computational state variables other than electronic charge, and these devices are being sought to bring in new functionalities and further lower the power dissipation in computers.”

One of the main motivations behind the search for a next-generation computing switch beyond CMOS (complementary metal oxide semiconductor) devices is to sustain the advancement of Moore’s Law. Nanomagnetic/spintronic devices provide a complementary option to electronics. The added functionality of this option includes the non-volatility of information on-chip, which is in essence a combination of logic and memory functions. However, to benefit from the increase in density of the on-chip devices, there has to be adequate connectivity among the switches—which is the focus of the Georgia Tech research.

Among the potential alternatives, devices based on nanoscale magnets in the field of spintronics have received special attention thanks to their advantages in terms of robustness and enhanced functionality. Magnets are non-volatile: their state remains even if the power to the circuit is switched off. Thus, the circuits do not consume power when not used—a very desirable property for modern tablets and smart phones.

One of the most important aspects of any new information processing element is how fast and power efficient they can communicate over an interconnect system with one another. In today’s CMOS chips, more energy is consumed communicating between transistor logic functions than actually processing of information. The Georgia Tech research has therefore focused on this important aspect of communicating between spin-logic devices and demonstrates that interconnects are an even more important challenge for beyond-CMOS switches.

To analyze spintronic interconnects, the Georgia Tech team and their Intel collaborators have developed compact models for spin transport in copper and aluminum—taking into account the scattering at wire surfaces and grain boundaries that become quite dominant at nanoscale dimensions. The research team has also developed compact models for the nanomagnet dynamic, electronic and spintronic transport through magnet to non-magnet interfaces, electric currents and spin diffusion. These models are all based on familiar electrical elements such as resistors and capacitors and can therefore be analyzed using standard circuit simulation tools such as SPICE.

New cost-effective nanoimprint lithography methodology improves ordering in periodic arrays from block copolymers

Block copolymers (BCPs) are the most attractive alternative to date for the fabrication of well-defined complex periodic structures with length scales below 100nm. Such small structures might be used in a wide range of technological applications but current available methods are very expensive, especially when those structures present length scales under 20nm.

A work led by the Institut Català de Nanociència i Nanotecnologia (ICN2) Phononic and Photonic Nanostructures Group suggests a new method to produce hexagonal periodic arrays with high fidelity while reducing time and costs. ICREA Research Professor Dr Clivia M. Sotomayor Torres and Dr Claudia Simão conducted, together with the authors listed below, a work published in a recent issue of Nanotechnology and featured cover article.

The methodology consists on in situ solvent-assisted nanoimprint lithography of block copolymers, a technique which combines a top-down approach – nanoimprint lithography – with a bottom-up one – self-assembled block copolymers (bottom-up). The process is assisted with solvent vapors to facilitate the imprint and simultaneous self-assembly of high Flory-Huggins parameter BCPs, the ones that yield sub-15nm size features, in what has been called solvent vapors assisted nanoimprint lithography (SAIL).

SAIL is a scalable technique which has shown its efficiency over a large area of up to four square inches wafers. The resulting sample was analysed using different methods, including field emission scanning electron microscopy (FE-SEM) and grazing-incidence small-angle x-ray scattering (GISAXS). The latter was performed at the Diamond synchrotron light source (UK) and allowed characterisation of structural features of the nanostructured polymer surfaces. It is the first time that GISAXS has been used to analyse a direct-nanoimprint BCP sample.

The results obtained with SAIL demonstrated an improvement in ordering of the nanodot lattice of up to 50%. It is a low cost, scalable and fast technique which brings self-assembled BCPs closer to their industrial application. These versatile materials are very interesting for applications such as storage devices, nano-electronics, low-k dielectrics or biochemical applications.

UT Dallas team creates flexible electronics that change shape inside body

Researchers from The University of Texas at Dallas and the University of Tokyo have created electronic devices that become soft when implanted inside the body and can deploy to grip 3-D objects, such as large tissues, nerves and blood vessels.

These biologically adaptive, flexible transistors might one day help doctors learn more about what is happening inside the body, and stimulate the body for treatments.

The research is one of the first demonstrations of transistors that can change shape and maintain their electronic properties after they are implanted in the body, said Jonathan Reeder BS ’12, a graduate student in materials science and engineering and lead author of the work.

“Scientists and physicians have been trying to put electronics in the body for a while now, but one of the problems is that the stiffness of common electronics is not compatible with biological tissue,” he said. “You need the device to be stiff at room temperature so the surgeon can implant the device, but soft and flexible enough to wrap around 3-D objects so the body can behave exactly as it would without the device. By putting electronics on shape-changing and softening polymers, we can do just that.”

Shape memory polymers developed by Dr. Walter Voit, assistant professor of materials science and engineering and mechanical engineering and an author of the paper, are key to enabling the technology.

The polymers respond to the body’s environment and become less rigid when they’re implanted. In addition to the polymers, the electronic devices are built with layers that include thin, flexible electronic foils first characterized by a group including Reeder in work published last year in Nature.

The Voit and Reeder team from the Advanced Polymer Research Lab in the Erik Jonsson School of Engineering and Computer Science fabricated the devices with an organic semiconductor but used adapted techniques normally applied to create silicon electronics that could reduce the cost of the devices.

“We used a new technique in our field to essentially laminate and cure the shape memory polymers on top of the transistors,” said Voit, who is also a member of the Texas Biomedical Device Center. “In our device design, we are getting closer to the size and stiffness of precision biologic structures, but have a long way to go to match nature’s amazing complexity, function and organization.”

The rigid devices become soft when heated. Outside the body, the device is primed for the position it will take inside the body.

During testing, researchers used heat to deploy the device around a cylinder as small as 2.25 millimeters in diameter, and implanted the device in rats. They found that after implantation, the device had morphed with the living tissue while maintaining excellent electronic properties.

“Flexible electronics today are deposited on plastic that stays the same shape and stiffness the whole time,” Reeder said. “Our research comes from a different angle and demonstrates that we can engineer a device to change shape in a more biologically compatible way.”

The next step of the research is to shrink the devices so they can wrap around smaller objects and add more sensory components, Reeder said.

Research Alert: March 11, 2014

Tuesday, March 11th, 2014

New research could help make “roll up” screens a reality

A study, published today in Nature’s Scientific Reports identifies a new technology which could see flexible electronics such as roll-up tablet computers, widely available in the near future. So far, this area of electronic design has been hampered by unreliability and complexity of production.

Researchers from the University of Surrey worked together with scientists from Philips to further develop the ‘Source-Gated-Transistor’ (SGT) – a simple circuit component invented jointly by the teams.

Previously, they found that the component could be applied to many electronic designs of an analog nature, such as display screens. Through this current study, researchers have now shown that SGTs can also be applied to next-generation digital circuits.

SGTs control the electric current as it enters a semiconductor, which decreases the odds of circuit malfunction, improves energy efficiency and keeps fabrication costs to a minimum. These properties make SGTs ideal for next-generation electronic devices, and could enable digital technologies to be incorporated into those built using flexible plastics or clothing textiles.

Such technologies may include ultra-lightweight and flexible gadgets which can be rolled up to save space when not in use, smart plasters, thinner than a human hair, that can wirelessly monitor the health of the wearer, low-cost electronic shopping tags for instant checkout, and disaster prediction sensors, used on buildings in regions that are at high risk of natural disasters.

“These technologies involve thin plastic sheets of , similar to sheets of paper, but embedded with smart technologies. Until now, such technologies could only be produced reliably in small quantities, and that confined them to the research lab. However, with SGTs we have shown we can achieve characteristics needed to make these technologies viable, without increasing the complexity or cost of the design,” said lead researcher Dr. Radu Sporea, Advanced Technology Institute (ATI), University of Surrey.

Professor Ravi Silva, Director of the ATI and a co-author of the work, said, “This work is a classic example of academia working closely with industry for over two decades to perfect a concept which has wide-reaching applications across a variety of technologies. Whilst SGTs can be applied to mainstream materials such as silicon, used widely in the production of current consumer devices, it is the potential to apply them to new materials such graphene that makes this research so crucial.”

“By making these incredible devices less complex and implicitly very affordable, we could see the next generation of gadgets become mainstream much quicker than we thought,” Dr Sporea concluded.

Squeezing light into metals

Using an inexpensive inkjet printer, University of Utah electrical engineers produced microscopic structures that use light in metals to carry information. This new technique, which controls electrical conductivity within such microstructures, could be used to rapidly fabricate superfast components in electronic devices, make wireless technology faster or print magnetic materials.

A recently discovered technology called plasmonics marries the best aspects of optical and electronic data transfer. By crowding light into metal structures with dimensions far smaller than its wavelength, data can be transmitted at much higher frequencies such as terahertz frequencies, which lie between microwaves and infrared light on the spectrum of electromagnetic radiation that also includes everything from X-rays to visible light to gamma rays. Metals such as silver and gold are particularly promising plasmonic materials because they enhance this crowding effect.

“Very little well-developed technology exists to create terahertz plasmonic devices, which have the potential to make wireless devices such as Bluetooth – which operates at 2.4 gigahertz frequency – 1,000 times faster than they are today,” says Ajay Nahata, a University of Utah professor of electrical and computer engineering and senior author of the new study.

Using a commercially available inkjet printer and two different color cartridges filled with silver and carbon ink, Nahata and his colleagues printed 10 different plasmonic structures with a periodic array of 2,500 holes with different sizes and spacing on a 2.5-inch-by-2.5 inch plastic sheet.

The four arrays tested had holes 450 microns in diameter – about four times the width of a human hair – and spaced one-25th of an inch apart. Depending on the relative amounts of silver and carbon ink used, the researchers could control the plasmonic array’s electrical conductivity, or how efficient it was in carrying an electrical current.

“Using a $60 inkjet printer, we have developed a low-cost, widely applicable way to make plasmonic materials,” Nahata says. “Because we can draw and print these structures exactly as we want them, our technique lets you make rapid changes to the plasmonic properties of the metal, without the million-dollar instrumentation typically used to fabricate these structures.”

Plasmonic arrays are currently made using microfabrication techniques that require expensive equipment and manufacture only one array at a time. Until now, controlling conductivity in these arrays has proven extremely difficult for researchers.

Nahata and his co-workers at the University of Utah’s College of Engineering used terahertz imaging to measure the effect of printed plasmonic arrays on a beam of light. When light with terahertz frequency is directed at a periodic array of holes in a metal layer, it can result in resonance, a fundamental property best illustrated by a champagne flute shattering when it encounters a musical tone of the right pitch.

Terahertz imaging is useful for nondestructive testing, such as detection of anthrax bacterial weapons in packaging or examination of insulation in spacecraft. By studying how terahertz light transmits through their printed array, the Utah team showed that simply changing the amount of carbon and silver ink used to print the array could be used to vary transmission through this structure.

With this new printing technique, Nahata says, “we have an extra level of control over both the transmission of light and electrical conductivity in these devices – you can now design structures with as many different variations as the printer can produce.” Nahata says these faster plasmonic arrays eventually could prove useful for:

  • Wireless devices, because the arrays allow data to be transmitted much more quickly. Many research groups are actively working on this application now.
  • Printing magnetic materials for greater functionality (lower conductivity, more compact) in different devices. This technology is more than five years away, Nahata says.

Although the Utah team used two different kinds of ink, up to four different inks in a four-color inkjet printer could be used, depending on the application.

Promising news for solar fuels from Berkley Lab researchers at JCAP

There’s promising news from the front on efforts to produce fuels through artificial photosynthesis. A new study by Berkeley Lab researchers at the Joint Center for Artificial Photosynthesis (JCAP) shows that nearly 90-percent of the electrons generated by a hybrid material designed to store solar energy in hydrogen are being stored in the target hydrogen molecules.

Gary Moore, a chemist and principal investigator with Berkeley Lab’s Physical Biosciences Division, led an efficiency analysis study of a unique photocathode material he and his research group have developed for catalyzing the production of hydrogen fuel from sunlight. This material, a hybrid formed from interfacing the semiconductor gallium phosphide with a molecular hydrogen-producing cobaloxime catalyst, has the potential to address one of the major challenges in the use of artificial photosynthesis to make renewable solar fuels.

“Ultimately the renewable energy problem is really a storage problem,” Moore says. “Given the intermittent availability of sunlight, we need a way of using the sun all night long. Storing solar energy in the chemical bonds of a fuel also provides the large power densities that are essential to modern transport systems. We’ve shown that our approach of coupling the absorption of visible light with the production of hydrogen in a single material puts photoexcited electrons where we need them to be, stored in chemical bonds.”

Moore is the corresponding author of a paper describing this research in the journal Physical Chemistry Chemical Physics titled “Energetics and efficiency analysis of a cobaloxime-modified semiconductor under simulated air mass 1.5 illumination.” Co-authors are Alexandra Krawicz and Diana Cedeno.

Bionic leaves that produce energy-dense fuels from nothing more than sunlight, water and atmosphere-warming carbon dioxide, with no byproducts other than oxygen, represent an ideal sustainable energy alternative to fossil fuels. However, realizing this artificial photosynthesis ideal will require a number of technological breakthroughs including high performance photocathodes that can catalyze fuel production from sunlight alone.

Last year, Moore and his research group at JCAP took an important step towards the photocathode goal with their gallium phosphide/cobaloxime hybrid. Gallium phosphide is an absorber of visible light, which enables it to produce significantly higher photocurrents than semiconductors that only absorb ultraviolet light. The cobaloxime catalyst is also Earth-abundant, meaning it is a relatively inexpensive replacement for the highly expensive precious metal catalysts, such as platinum, currently used in many solar-fuel generator prototypes.

“The novelty of our approach is the use of molecular catalytic components interfaced with visible-light absorbing semiconductors,” Moore says. “This creates opportunities to use discrete three-dimensional environments for directly photoactivating the multi-electron and multi-proton chemistry associated with the production of hydrogen and other fuels.”

The efficiency analysis performed by Moore and his colleagues also confirmed that the light-absorber component of their photocathode is a major bottleneck to obtaining higher current densities. Their results showed that of the total number of solar photons striking the hybrid-semiconductor surface, measured over the entire wavelength range of the solar spectrum (from 200 to 4,000 nanometers) only 1.5-percent gave rise to a photocurrent.

“This tells us that the use of light absorbers with improved spectral coverage of the sun is a good start to achieving further performance gains, but it is likely we will also have to develop faster and more efficient catalysts as well as new attachment chemistries. Our modular assembly method provides a viable strategy to testing promising combinations of new materials,” Moore says.


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