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Posts Tagged ‘Georgia Tech’

Solid State Technology: August 7-14, 2015

Monday, August 24th, 2015
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Solid State Watch: April 24-30, 2015

Monday, May 4th, 2015
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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: April 29, 2014

Tuesday, April 29th, 2014

Graphene not all good

In a first-of-its-kind study of how a material some think could transform the electronics industry moves in water, researchers at the University of California, Riverside Bourns College of Engineering found graphene oxide nanoparticles are very mobile in lakes or streams and therefore likely to cause negative environmental impacts if released.

Graphene oxide nanoparticles are an oxidized form of graphene, a single layer of carbon atoms prized for its strength, conductivity and flexibility. Applications for graphene include everything from cell phones and tablet computers to biomedical devices and solar panels.

The use of graphene and other carbon-based nanomaterials, such as carbon nanotubes, are growing rapidly. At the same time, recent studies have suggested graphene oxide may be toxic to humans.

As production of these nanomaterials increase, it is important for regulators, such as the Environmental Protection Agency, to understand their potential environmental impacts, said Jacob D. Lanphere, a UC Riverside graduate student who co-authored a just-published paper about graphene oxide nanoparticles transport in ground and surface water environments.

“The situation today is similar to where we were with chemicals and pharmaceuticals 30 years ago,” Lanphere said. “We just don’t know much about what happens when these engineered nanomaterials get into the ground or water. So we have to be proactive so we have the data available to promote sustainable applications of this technology in the future.”

The paper co-authored by Lanphere, “Stability and Transport of Graphene Oxide Nanoparticles in Groundwater and Surface Water,” was published in a special issue of the journal Environmental Engineering Science.

Other authors were: Sharon L. Walker, an associate professor and the John Babbage Chair in Environmental Engineering at UC Riverside; Brandon Rogers and Corey Luth, both undergraduate students working in Walker’s lab; and Carl H. Bolster, a research hydrologist with the U.S. Department of Agriculture in Bowling Green, Ky.

Walker’s lab is one of only a few in the country studying the environmental impact of graphene oxide. The research that led to the Environmental Engineering Science paper focused on understanding graphene oxide nanoparticles’ stability, or how well they hold together, and movement in groundwater versus surface water.

The researchers found significant differences.

In groundwater, which typically has a higher degree of hardness and a lower concentration of natural organic matter, the graphene oxide nanoparticles tended to become less stable and eventually settle out or be removed in subsurface environments.

In surface waters, where there is more organic material and less hardness, the nanoparticles remained stable and moved farther, especially in the subsurface layers of the water bodies.

The researchers also found that graphene oxide nanoparticles, despite being nearly flat, as opposed to spherical, like many other engineered nanoparticles, follow the same theories of stability and transport.

How to create nanowires only 3 atoms wide with an electron beam

Junhao Lin, a Vanderbilt University Ph.D. student and visiting scientist at Oak Ridge National Laboratory (ORNL), has found a way to use a finely focused beam of electrons to create some of the smallest wires ever made. The flexible metallic wires are only three atoms wide: One thousandth the width of the microscopic wires used to connect the transistors in today’s integrated circuits.

According to his advisor Sokrates Pantelides, University Distinguished Professor of Physics and Engineering at Vanderbilt University, and his collaborators at ORNL, the technique represents an exciting new way to manipulate matter at the nanoscale and should give a boost to efforts to create electronic circuits out of atomic monolayers, the thinnest possible form factor for solid objects.

“Junhao took this project and really ran with it,” said Pantelides.

Lin made the tiny wires from a special family of semiconducting materials that naturally form monolayers. These materials, called transition-metal dichalcogenides (TMDCs), are made by combining the metals molybdenum or tungsten with either sulfur or selenium. The best-known member of the family is molybdenum disulfide, a common mineral that is used as a solid lubricant.

Atomic monolayers are the object of considerable scientific interest these days because they tend to have a number of remarkable qualities, such as exceptional strength and flexibility, transparency and high electron mobility. This interest was sparked in 2004 by the discovery of an easy way to create graphene, an atomic-scale honeycomb lattice of carbon atoms that has exhibited a number of record-breaking properties, including strength, electricity and heat conduction. Despite graphene’s superlative properties, experts have had trouble converting them into useful devices, a process materials scientists call functionalization. So researchers have turned to other monolayer materials like the TMDCs.

Other research groups have already created functioning transistors and flash memory gates out of TMDC materials. So the discovery of how to make wires provides the means for interconnecting these basic elements. Next to the transistors, wiring is one of the most important parts of an integrated circuit. Although today’s integrated circuits (chips) are the size of a thumbnail, they contain more than 20 miles of copper wiring.

“This will likely stimulate a huge research interest in monolayer circuit design,” Lin said. “Because this technique uses electron irradiation, it can in principle be applicable to any kind of electron-based instrument, such as electron-beam lithography.”

One of the intriguing properties of monolayer circuitry is its toughness and flexibility. It is too early to predict what kinds of applications it will produce, but “If you let your imagination go, you can envision tablets and television displays that are as thin as a sheet of paper that you can roll up and stuff in your pocket or purse,” Pantelides commented.

In addition, Lin envisions that the new technique could make it possible to create three-dimensional circuits by stacking monolayers “like Lego blocks” and using electron beams to fabricate the wires that connect the stacked layers.

The nanowire fabrication was carried out at ORNL in the microscopy group that was headed until recently by Stephen J. Pennycook, as part of an ongoing Vanderbilt-ORNL collaboration that combines microscopy and theory to study complex materials systems. Junhao is a graduate student who pursues both theory and electron microscopy in his doctoral research. His primary microscopy mentor has been ORNL Wigner Fellow Wu Zhou.

“Junhao used a scanning transmission electron microscope (STEM) that is capable of focusing a beam of electrons down to a width of half an angstrom (about half the size of an atom) and aims this beam with exquisite precision,” Zhou said.

Graphene only as strong as weakest link

There is no disputing graphene is strong. But new research by Rice University and the Georgia Institute of Technology should prompt manufacturers to look a little deeper as they consider the miracle material for applications.

The atom-thick sheet of carbon discovered this century is touted not just for its electrical properties but also for its physical strength and flexibility. The bonds between carbon atoms are well known as the strongest in nature, so a perfect sheet of graphene should withstand just about anything. Reinforcing composite materials is among the material’s potential applications.

But materials scientists know perfection is hard to achieve. Researchers Jun Lou at Rice and Ting Zhu at Georgia Tech have measured the fracture toughness of imperfect graphene for the first time and found it to be somewhat brittle. While it’s still very useful, graphene is really only as strong as its weakest link, which they determined to be “substantially lower” than the intrinsic strength of graphene.

“Graphene has exceptional physical properties, but to use it in real applications, we have to understand the useful strength of large-area graphene, which is controlled by the fracture toughness,” Zhu said.

The researchers reported in the journal Nature Communications the results of tests in which they physically pulled graphene apart to see how much force it would take. Specifically, they wanted to see if graphene follows the century-old Griffith theory that quantifies the useful strength of brittle materials.

It does, Lou said. “Remarkably, in this case, thermodynamic energy still rules,” he said.

Imperfections in graphene drastically lessen its strength – with an upper limit of about 100 gigapascals (GPa) for perfect graphene previously measured by nanoindentation – according to physical testing at Rice and molecular dynamics simulations at Georgia Tech. That’s important for engineers to understand as they think about using graphene for flexible electronics, composite material and other applications in which stresses on microscopic flaws could lead to failure.

The Griffith criterion developed by a British engineer during World War I describes the relationship between the size of a crack in a material and the force required to make that crack grow. Ultimately, A.A. Griffith hoped to understand why brittle materials fail.

Graphene, it turns out, is no different from the glass fibers Griffith tested.

“Everybody thinks the carbon-carbon bond is the strongest bond in nature, so the material must be very good,” Lou said. “But that’s not true anymore, once you have those defects. The larger the sheet, the higher the probability of defects. That’s well known in the ceramic community.”

A defect can be as small as an atom missing from the hexagonal lattice of graphene. But for a real-world test, the researchers had to make a defect of their own – a pre-crack – they could actually see. “We know there will be pinholes and other defects in graphene,” he said. “The pre-crack overshadows those defects to become the weakest spot, so I know exactly where the fracture will happen when we pull it.

“The material resistance to the crack growth – the fracture toughness – is what we’re measuring here, and that’s a very important engineering property,” he said.

Just setting up the experiment required several years of work to overcome technical difficulties, Lou said. To suspend it on a tiny cantilever spring stage similar to an atomic force microscopy (AFM) probe, a graphene sheet had to be clean and dry so it would adhere (via van der Waals force) to the stage without compromising the stage movement necessary for the testing. Once mounted, the researchers used a focused ion beam to cut a pre-crack less than 10 percent of the width into the microns-wide section of suspended graphene. Then they pulled the graphene in half, measuring the force required.

While the Rice team was working on the experiment, Zhu and his team performed computer simulations to understand the entire fracture process.

“We can directly simulate the whole deformation process by tracking the motion and displacement with atomic-scale resolution in fairly large samples so our results can be directly correlated with the experiment,” said Zhu. “The modeling is tightly coupled with the experiments.”

The combination of modeling and experiment provides a level of detail that allowed the researchers to better understand the fracture process – and the tradeoff between toughness and strength in the graphene. What the scientists have learned in the research points out the importance of fabricating high-quality graphene sheets without defects, which could set the stage for fracture.

“Understanding the tradeoff between strength and toughness provides important insights for the future utilization of graphene in structural and functional applications,” Zhu added. “This research provides a foundational framework for further study of the mechanical properties of graphene.”

Lou said the techniques they used should work for any two-dimensional material. “It’s important to understand how defects will affect the handling, processing and manufacture of these materials,” he said. “Our work should open up new directions for testing the mechanical properties of 2-D materials.”

The Week in Review: April 4, 2014

Friday, April 4th, 2014

Park Systems this week introduced the Automatic Defect Review AFM for 300mm bare wafers, a fully automated AFM solution that improves throughput of AFM defect review by up to 1,000 percent.

ON Semiconductor announced this week that it will acquire Trusense Imaging, Inc. ON Semiconductor will pay approximately $92 million in cash to acquire Truesense Imaging.

SureCore announced that early testing of its innovative low power SRAM design confirms its simulations that deliver in excess of 50 percent power savings over other SRAM technologies.

Researchers from Georgia Tech, University of Texas at Austin, and the Raytheon Company have developed a thermal interface material able to conduct heat 20 times better than the original polymer. The modified material can reliably operate at temperatures of up to 200 degrees Celsius.

UVOTECH announced the release of the UV Ozone Cleaning solution. The UV Ozone Cleaning process is a photo-sensitized oxidation process in which the contaminant molecules of photo resists, resins, human skin oil, cleaning solvent residues, silicone oils, and flux are excited and/or dissociated by the absorption of short wavelength UV radiation.

Solid State Watch: March 29-April 3, 2014

Friday, April 4th, 2014
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