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The improvements in random access memory that have driven many advances of the digital age owe much to the innovative application of physics and chemistry at the atomic scale.

Accordingly, a team led by UNL researchers has employed a Nobel Prize-winning material and common household chemical to enhance the properties of a component primed for the next generation of high-speed, high-capacity RAM.

The team, which published its findings in the Nov. 24 edition of the journal Nature Communications, engineered and tested improvements in the performance of a memory structure known as a ferroelectric tunnel junction.

The junction features a ferroelectric layer 100,000 times thinner than a sheet of paper, so thin that electrons can “tunnel” through it. This layer resides between two electrodes that can reverse the direction of its polarization — the alignment of positive and negative charges used to represent “0” and “1” in binary computing — by applying electric voltage to it.

The researchers became the first to design a ferroelectric junction with electrodes made of graphene, a carbon material only one atom thick. While its extreme conductivity makes graphene especially suited for small-scale electronics, the authors’ primary interest lay in how it accommodated nearly any type of molecule — specifically, ammonia — they placed between it and the ferroelectric layer.

A junction’s polarity determines its resistance to tunneling current, with one direction allowing current to flow and the other strongly reducing it. The researchers found that their graphene-ammonia combination increased the disparity between these “on” and “off” conditions, a prized outcome that improves the reliability of RAM devices and allows them to read data without having to rewrite it.

“This is one of the most important differences between previous technology that has already been commercialized and this emergent ferroelectric technology,” said Alexei Gruverman, a Charles Bessey Professor of physics who co-authored the study.

Ferroelectric materials naturally boast the quality of “non-volatility,” meaning they maintain their polarization — and can hence retain stored information — even in the absence of an external power source. However, the infinitesimal space between the positive and negative charges in a tunnel junction makes maintaining this polarization especially difficult, Gruverman said.

“In all memory devices, there is a gradual relaxation, or decrease, of this polarization,” he said. “The thinner the ferroelectric layer is, the more difficult it is to keep these polarization charges separate, as there is a stronger driving force in the material that tries to get rid of it.”

Gruverman said the team’s graphene-ammonia combination also shows promise for addressing this prevalent issue, significantly improving the stability of the junction’s polarization during the study.

Gruverman’s UNL co-authors included Haidong Lu and Dong Jik Kim, postdoctoral researchers in physics and astronomy; Alexey Lipatov, a postdoctoral researcher in chemistry; Evgeny Tsymbal, George Holmes University Professor of physics and astronomy; and Alexander Sinitskii, assistant professor of chemistry. The study was also authored by researchers from the University of Wisconsin-Madison and the Moscow-based Kurnakov Institute for General and Inorganic Chemistry.

The team’s research was conducted with the assistance of UNL’s Materials Research Science and Engineering Center — part of a nationwide network of MRSECs sponsored by the National Science Foundation — and also received support from the U.S. Department of Energy.

Nature Communications is the Nature Publishing Group’s multidisciplinary online journal of research in all areas of the biological, physical and chemical sciences.

A potential path to identify imperfections and improve the quality of nanomaterials for use in next-generation solar cells has emerged from a collaboration of University of Oregon and industry researchers.

To increase light-harvesting efficiency of solar cells beyond silicon’s limit of about 29 percent, manufacturers have used layers of chemically synthesized semiconductor nanocrystals. Properties of quantum dots that are produced are manipulated by controlling the synthetic process and surface chemical structure.

This process, however, creates imperfections at the surface-forming trap states that limit device performance. Until recently, improvements in production quality have relied on feedback provided by traditional characterization techniques that probe average properties of large numbers of quantum dots.

“We want to use these materials in real devices, but they are not yet optimized,” said co-author Christian F. Gervasi, a UO doctoral student.

In their study, detailed in the Journal of Physical Chemistry Letters, researchers investigated electronic states of lead sulfide nanocrystals. By using a specially designed scanning tunneling microscope, researchers created atomic-scale maps of the density of states in individual nanocrystals. This allowed them to pinpoint the energies and localization of charge traps associated with defects in the nanocrystal surface structure that are detrimental to electron propagation.

The microscope was designed in the lab of co-author George V. Nazin, a professor in the UO Department of Chemistry and Biochemistry. Its use was described in a previous paper in the same journal, in which Nazin’s lab members were able to visualize the internal structures of electronic waves trapped by external electrostatic charges in carbon nanotubes.

“This technology is really cool,” said Peter Palomaki, senior scientist for Voxtel Nanophotonics and co-author on the new paper. “When you really dig down into the science at a very fundamental level, this problem has always been an open-ended question. This paper is just the tip of the iceberg in terms of being able to understand what’s going on.”

The insight, he said, should help manufacturers tweak their synthesis of nanocrystals used in a variety of electronic devices. Co-author Thomas Allen, also a senior scientist at Voxtel, agreed. The project began after Allen heard Gervasi and Nazin discussing the microscope’s capabilities.

“We wanted to see what the microscope could accomplish, and it turns out that it gives us a lot of information about the trap states and the depths of trap states in our quantum dots,” said Allen, who joined Voxtel after completing the Industrial Internship Program in the UO’s Materials Science Institute. “The information will help us fine-tune the ligand chemistry to make better devices for photovoltaics, detectors and sensors.”

The trap states seen by the microscope in this project may explain why nanoparticle-based solar cells have not yet been commercialized, Nazin said.

“Nanoparticles are not always stable. It is a fundamental problem. When you synthesize something at this scale you don’t necessarily get the same structure for all of the quantum dots. Working at the atomic scale can produce large variations in the electronic states. Our tool allows us to see these states directly and allow us to provide feedback on the materials.”

The international technology group SCHOTT is expanding its HermeS wafers with hermetically sealed, solid through glass vias (TGV) into MEMS applications. HermeS glass substrates are fully gastight, and therefore enable long-term, robust enclosures for MEMS devices. The fine-pitched vias reliably conduct electrical signals and guide power into and out of the MEMS device. Since HermeS glass can be placed directly under the silicon MEMS, it makes miniaturized, fully hermetic 3-D wafer-level chip-size packaging (WLCSP) possible. Thanks to its extremely high reliability, HermeS wafers provide advantages for MEMS devices used in industrial, medical, and radio-frequency (RF) applications.

MEMS-powered devices and sensors must function perfectly over long periods of time, even when they are exposed to extremely harsh environments, such as pressure sensors in corrosive industrial production lines. The reliability and performance of the MEMS device depends on the long-term robustness of the MEMS packaging technology. SCHOTT’s HermeS solution with TGV offers several customer advantages over other technologies, such as through silicon vias or hermetic ceramic packaging, due to glass’ superior material characteristics compared to silicon or ceramics.

First, due to the higher mechanical, thermal, and chemical resistance of glass, the packaging is especially reliable, leading to long-term performance of the MEMS device. Second, thanks to the low dielectric constant of glass and the ability to use highly conductive via materials, HermeS wafer packaging also offers excellent RF performance. Finally, the optical transparency of the glass wafer enables better processing and quality control during the production process of a MEMS device.

“Based on the key features of our material, SCHOTT identified three major applications in which the HermeS TGV substrates offer significant advantages over competitive solutions,” said Yutaka Onezawa, Sales Manager for HermeS at SCHOTT Electronic Packaging. When used in industrial hermetic MEMS sensors, HermeS glass wafers enable long-term, reliable, and extremely rugged packaging of industrial sensors. Equipped with SCHOTT’s product, medical electronics can be packaged robustly to withstand body fluids and sterilization cycles over long periods of time. For RF MEMS, HermeS wafers provide superior RF properties through absolute hermeticity in an extremely miniaturized design.

SCHOTT’s HermeS TGV substrates also allow for the miniaturization of MEMS-powered devices, a reduction in package die size, and a more compact design. The footprint can be reduced by up to 80 percent compared to conventional ceramic packaging.

“We are also able to apply state-of-the-art, wafer-scale bonding, such as anodic bonding with silicon, glass frit, and solder. Thanks to our vast competencies, our customers can rely on a complete packaged solution with a total cost-of-ownership advantage regarding yield and process reduction,” added Onezawa.

SCHOTT offers HermeS TGV substrates made from three proprietary glass types: BOROFLOAT 33 floated borosilicate glass, AF32 eco alkali-free flat glass, and D263 T eco borosilicate glass. HermeS TGV substrates are one example of how SCHOTT’s 130 years of expertise in special-purpose glass and 70 years of experience in electronic packaging help guide the development and production of the company’s new products.

Sand 9, Inc., a developer of piezoelectric micro-electromechanical systems (MEMS) timing products for wireless and wired applications, today announced that the United States Patent and Trademark Office has granted the company a core patent based on the use of piezoelectric MEMS for a wafer-level, chip-scale packaged (WLCSP) microphone (US20140084395 A1).

Today, most microphones are condenser microphones, which typically feature a fixed electrode (back plate) in close proximity to a moveable electrode (diaphragm). The back plate is usually rigid and is necessary because condenser microphones use electrostatic (i.e., capacitive) transduction between the diaphragm and the back plate to convert acoustic pressure into an electrical signal.

Condenser microphones typically use a small gap between the respective electrodes to achieve high signal-to-noise ratio (SNR), frequently resulting in reliability challenges such as stiction. Such a small gap can also degrade the thermal-mechanical noise performance by damping the overall mechanical structure. Moreover, a DC bias between the electrodes is normally required to enable capacitive detection of motion, which can be a significant source of power consumption.

In contrast, piezoelectric MEMS microphones offer high electromechanical coupling compared with electrostatic transduction, enabling improved SNR with lower power consumption. Piezoelectric MEMS structures are not susceptible to stiction from particles or other contaminants, resulting in a significantly higher quality product for OEMs. Finally, piezoelectric MEMS can be implemented in WLCSP with through-silicon-vias (TSVs) to support both top and bottom port configurations with matched performance in the smallest package size.

“We are delighted to receive this latest patent,” said Sand 9’s CEO, Vince Graziani. “This brings our total number of issued patents to 52, covering an array of piezoelectric MEMS products including timing devices, microphones, and gyroscopes. It validates our belief that piezoelectric MEMS technology offers significant advantages over traditional electrostatic technology to enable higher levels of performance and quality in an ultra-small form factor.”

Graphene Frontiers LLC, a developer of graphene materials and device technology, announces the issuance of a key industry patent. U.S. Patent 8,822,308, titled “Methods and Apparatus for Transfer of Films among Substrates,” covers the transfer of graphene films between surfaces using roll-to-roll manufacturing processes.

“We were aggressively pursuing this patent and securing it is a testament to the hard work and resiliency of the entire team,” Graphene Frontiers’ CEO Mike Patterson said.

This was the final hurdle in creating a cost-effective production process for graphene. With Graphene Frontiers’ etch-free transfer solution, manufacturers now have the option of not dissolving or consuming the substrate metal.

The approach is also compatible with other materials, and is particularly useful for nanomaterials, which are often difficult to develop.

“Graphene is a remarkable material, but it is only a building block,” Chief Science Officer Bruce Willner said. “The ability to handle graphene and place it among other materials – where and how we want – is critical to taking advantage of this technology.”

Recently, the company entered into an agreement to ramp-up production with The Colleges of Nanoscale Science and Engineering (CNSE) at SUNY Polytechnic Institute in Albany NY. It’s an alliance that will increase the amount of employees working at the company, as well as form relationships with potential buyers.

Graphene Frontiers is a nanotechnology materials and device company based in Philadelphia. Graphene Frontiers has developed innovative and exclusive manufacturing processes that makes it economically viable for companies to begin using graphene, the revolutionary nanomaterial with potential for disrupting numerous industries with its unique sensitivity and mechanical properties.

University of Utah engineers have developed a new type of carbon nanotube material for handheld sensors that will be quicker and better at sniffing out explosives, deadly gases and illegal drugs.

A carbon nanotube is a cylindrical material that is a hexagonal or six-sided array of carbon atoms rolled up into a tube. Carbon nanotubes are known for their strength and high electrical conductivity and are used in products from baseball bats and other sports equipment to lithium-ion batteries and touchscreen computer displays.

Ling Zang, a University of Utah professor of materials science and engineering, holds a prototype detector that uses a new type of carbon nanotube material for use in handheld scanners to detect explosives, toxic chemicals and illegal drugs. Zang and colleagues developed the new material, which will make such scanners quicker and more sensitive than today's standard detection devices. Ling's spinoff company, Vaporsens, plans to produce commercial versions of the new kind of scanner early next year. Credit: Dan Hixon, University of Utah College of Engineering.

Ling Zang, a University of Utah professor of materials science and engineering, holds a prototype detector that uses a new type of carbon nanotube material for use in handheld scanners to detect explosives, toxic chemicals and illegal drugs. Zang and colleagues developed the new material, which will make such scanners quicker and more sensitive than today’s standard detection devices. Ling’s spinoff company, Vaporsens, plans to produce commercial versions of the new kind of scanner early next year.
Credit: Dan Hixon, University of Utah College of Engineering.

Vaporsens, a university spin-off company, plans to build a prototype handheld sensor by year’s end and produce the first commercial scanners early next year, says co-founder Ling Zang, a professor of materials science and engineering and senior author of a study of the technology published online Nov. 4 in the journal Advanced Materials.

The new kind of nanotubes also could lead to flexible solar panels that can be rolled up and stored or even “painted” on clothing such as a jacket, he adds.

Zang and his team found a way to break up bundles of the carbon nanotubes with a polymer and then deposit a microscopic amount on electrodes in a prototype handheld scanner that can detect toxic gases such as sarin or chlorine, or explosives such as TNT.

When the sensor detects molecules from an explosive, deadly gas or drugs such as methamphetamine, they alter the electrical current through the nanotube materials, signaling the presence of any of those substances, Zang says.

“You can apply voltage between the electrodes and monitor the current through the nanotube,” says Zang, a professor with USTAR, the Utah Science Technology and Research economic development initiative. “If you have explosives or toxic chemicals caught by the nanotube, you will see an increase or decrease in the current.”

By modifying the surface of the nanotubes with a polymer, the material can be tuned to detect any of more than a dozen explosives, including homemade bombs, and about two-dozen different toxic gases, says Zang. The technology also can be applied to existing detectors or airport scanners used to sense explosives or chemical threats.

Zang says scanners with the new technology “could be used by the military, police, first responders and private industry focused on public safety.”

Unlike the today’s detectors, which analyze the spectra of ionized molecules of explosives and chemicals, the Utah carbon-nanotube technology has four advantages:

  • It is more sensitive because all the carbon atoms in the nanotube are exposed to air, “so every part is susceptible to whatever it is detecting,” says study co-author Ben Bunes, a doctoral student in materials science and engineering.
  • It is more accurate and generates fewer false positives, according to lab tests.
  • It has a faster response time. While current detectors might find an explosive or gas in minutes, this type of device could do it in seconds, the tests showed.
  • It is cost-effective because the total amount of the material used is microscopic.

Rice University scientists who want to gain an edge in energy production and storage report they have found it in molybdenum disulfide.

The Rice lab of chemist James Tour has turned molybdenum disulfide’s two-dimensional form into a nanoporous film that can catalyze the production of hydrogen or be used for energy storage.

The versatile chemical compound classified as a dichalcogenide is inert along its flat sides, but previous studies determined the material’s edges are highly efficient catalysts for hydrogen evolution reaction (HER), a process used in fuel cells to pull hydrogen from water.

Tour and his colleagues have found a cost-effective way to create flexible films of the material that maximize the amount of exposed edge and have potential for a variety of energy-oriented applications.

Molybdenum disulfide isn’t quite as flat as graphene, the atom-thick form of pure carbon, because it contains both molybdenum and sulfur atoms. When viewed from above, it looks like graphene, with rows of ordered hexagons. But seen from the side, three distinct layers are revealed, with sulfur atoms in their own planes above and below the molybdenum.

This crystal structure creates a more robust edge, and the more edge, the better for catalytic reactions or storage, Tour said.

“So much of chemistry occurs at the edges of materials,” he said. “A two-dimensional material is like a sheet of paper: a large plain with very little edge. But our material is highly porous. What we see in the images are short, 5- to 6-nanometer planes and a lot of edge, as though the material had bore holes drilled all the way through.”

The new film was created by Tour and lead authors Yang Yang, a postdoctoral researcher; Huilong Fei, a graduate student; and their colleagues. It catalyzes the separation of hydrogen from water when exposed to a current. “Its performance as a HER generator is as good as any molybdenum disulfide structure that has ever been seen, and it’s really easy to make,” Tour said.

While other researchers have proposed arrays of molybdenum disulfide sheets standing on edge, the Rice group took a different approach. First, they grew a porous molybdenum oxide film onto a molybdenum substrate through room-temperature anodization, an electrochemical process with many uses but traditionally employed to thicken natural oxide layers on metals.

The film was then exposed to sulfur vapor at 300 degrees Celsius (572 degrees Fahrenheit) for one hour. This converted the material to molybdenum disulfide without damage to its nano-porous sponge-like structure, they reported.

The films can also serve as supercapacitors, which store energy quickly as static charge and release it in a burst. Though they don’t store as much energy as an electrochemical battery, they have long lifespans and are in wide use because they can deliver far more power than a battery. The Rice lab built supercapacitors with the films; in tests, they retained 90 percent of their capacity after 10,000 charge-discharge cycles and 83 percent after 20,000 cycles.

“We see anodization as a route to materials for multiple platforms in the next generation of alternative energy devices,” Tour said. “These could be fuel cells, supercapacitors and batteries. And we’ve demonstrated two of those three are possible with this new material.”

Co-authors of the paper are Rice graduate students Gedeng Ruan and Changsheng Xiang. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of materials science and nanoengineering and of computer science.

The Peter M. and Ruth L. Nicholas Postdoctoral Fellowship of Rice’s Smalley Institute for Nanoscale Science and Technology and the Air Force Office of Scientific Research Multidisciplinary University Research program supported the research.

At this week’s VISION 2014 exhibition, imec presents a backside-illuminated (BSI) CMOS image sensor chip featuring a new anti-reflective coating (ARC) optimized for UV light. Targeting imaging solutions in new markets such as life sciences, the achievement is an important addition to imec’s customized 200mm CMOS fab. This 200mm process line enables imec to offer design, prototyping and low volume manufacturing of custom specialty chip solutions such as highly specialized CMOS image sensors.

Known for its superior enhanced light sensitivity compared with image sensors using front side illumination (FSI), BSI sensors are top candidates to further improve the performance of CMOS image sensors. Widely spread today in consumer applications such as smart phones, BSI imagers are expected to enter the higher-end application space of e.g. industrial inspection.

BSI imagers have a clear advantage when it comes to fill factor for the pixel area, angular response, and the complete avoidance of absorption or scattering losses in the metal interconnect layers.  The cost for these light gathering improvement are the extra process complexity for the backside fabrication and possible electrical and optical losses at the new backside silicon interface. Therefore the engineering of the backside layers and interfaces is key to develop high performance BSI devices.

Imec is tackling these challenges to exploit the benefits of BSI imagers for highly specialized customized imagers for space applications, high speed cameras, semiconductor inspection and medical applications. To minimize reflection losses and maximize transmission of light to the sensor, specific anti-reflective coatings (ARC) are developed for various applications targeting different regions of the light spectrum. The coatings are applied at wafer level as part of the BSI process flow.

Imec has already developed an ARC for visible light range (400nm-800nm) with >70% QE over the entire spectral range. Imec’s new ARC, targeting the UV range, shows excellent performance at near UV wavelengths, with Quantum Efficiency (Q.E.) values above 50 percent over the entire spectral range from 260nm to 400nm wavelength.

“This is an important milestone for imec’s customized 200mm CMOS process line, demonstrating our expertise and capability to design, prototype and manufacture high-end CMOS image sensors,” said Rudi Cartuyvels, senior vice president, Smart Systems & Energy Technologies at imec. “The development widens our portfolio towards new markets, offering solutions for both visible and UV imaging in semiconductor equipment applications, such as advance lithography and wafer and mask inspection.”

Kilopass Technology Inc., a provider of semiconductor logic embedded non-volatile memory (eNVM) intellectual property (IP), announced today that it has successfully ported its one-time programmable (OTP) NVM technology to TSMC’s 16 nanometer (nm) FinFET process.

“Embedded non-volatile memories are becoming an increasingly important part of SoC designs created by our key customers,” notes Suk Lee, TSMC senior director, Design Infrastructure Marketing Division. “Kilopass’ support for this technology at the 16FinFET node enables us to offer our mutual customers a complete solution that saves design time, chip area and power consumption.”

The Kilopass OTP 2T bit cell continues to be easily manufactured and demonstrates the high level of reliability and performance similar to results produced at other process geometries built with planar transistor structures. Kilopass’ OTP 2T bit cell technology can scale easily from 180nm to 28nm and beyond across a wide variety of process technologies including low power, high-voltage, and high-K metal gate.

As TSMC process migrates to FinFET transistor structures, Kilopass’ antifuse OTP NVM was successfully ported to the FinFET process. The solution provided will also cover the methodology that meets the challenges of OTP NVM memory IP design for FinFET technology to enable faster time to market with high quality and reliability for TSMC and Kilopass’ joint customers.

Christophe Chevallier, Kilopass’ vice president of engineering, presented the performance and reliability data of Kilopass OTP 16nm FinFET memory cell at the recent TSMC Open Innovation Platform Forum.

University of Oregon chemists have devised a way to see the internal structures of electronic waves trapped in carbon nanotubes by external electrostatic charges.

Carbon nanotubes have been touted as exceptional materials with unique properties that allow for extremely efficient charge and energy transport, with the potential to open the way for new, more efficient types of electronic and photovoltaic devices. However, these traps, or defects, in ultra-thin nanotubes can compromise their effectiveness.

Using a specially built microscope capable of imaging matter at the atomic scale, the researchers were able to visualize traps, which can adversely affect the flow of electrons and elementary energy packets called excitons.

The study, said George V. Nazin, a professor of physical chemistry, modeled the behavior often observed in carbon nanotube-based electronic devices, where electronic traps are induced by stochastic external charges in the immediate vicinity of the nanotubes. The external charges attract and trap electrons propagating through nanotubes.

“Our visualization should be useful for the development of a more accurate picture of electron propagation through nanotubes in real-world applications, where nanotubes are always subjected to external perturbations that potentially may lead to the creation of these traps,” he said.

The research, detailed in a paper in the Journal of Physical Chemistry Letters, was done with an ultra-high vacuum scanning tunneling microscope coupled to a closed-cycle cryostat — a novel device built for use in Nazin’s lab. The cryostat allowed Nazin and his co-authors Dmitry A. Kislitsyn and Jason D. Hackley, both doctoral students, to lower the temperature to 20 Kelvin to freeze all nanoscale motion, and visualize the internal structures of nanoscale objects.

The device captured the internal structure of electronic waves trapped in short sections, just several nanometers long, of nanotubes partially suspended above an atomically flat gold surface. The properties of the waves, to a large extent, Nazin said, determine electron transmission through such electronic traps. The propagating electrons have to be in resonance with the localized waves for efficient electronic transmission to occur.

“Amazingly, by finely tuning the energies of propagating electrons, we found that, in addition to these resonance transmission channels, other resonances also are possible, with energies matching those of specific vibrations in carbon nanotubes,” he said. “These new transmission channels correspond to ‘vibronic’ resonances, where trapped electronic waves excite vibrations of carbon atoms forming the electronic trap.”

The microscope the team used is detailed separately in a freely available paper (High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat) placed online Oct. 7 by the journal Review of Scientific Instruments.