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Material scientists at Lawrence Livermore National Laboratory have found certain metal oxides increase capacity and improve cycling performance in lithium-ion batteries.

The team synthesized and compared the electrochemical performance of three graphene metal oxide nanocomposites and found that two of them greatly improved reversible lithium storage capacity.

The research appears on the cover of the March 21 edition of the Journal of Materials Chemistry A.

Graphene-metal oxide (GMO) nanocomposites have become renowned for their potential in energy storage and conversion, including capacitors, lithium-ion batteries, catalysis (for fuel cells, water splitting and air cleaning) and sensors.

For applications in lithium-ion batteries, nanosized metal oxide (MO) particles and highly conductive graphene are considered beneficial for shortening lithium diffusion pathways and reducing polarization in the electrode, leading to enhanced performance.

In the experiments, the team dipped prefabricated graphene aerogel electrodes in metal ion solutions where all metal oxide nanoparticles appear to be anchored on the surface of graphene and are fully accessible to the electrolyte (i.e., open pore space).

“In essence, our approach helps to optimize the system-level performance by ensuring that most metal oxides are active,” said LLNL material scientist Morris Wang and corresponding author of the paper.

The method can deposit most types of MOs onto the same prefabricated 3D graphene structure, allowing for direct comparison of electrochemical performance of a wide range of GMOs.

“We found that the experiments showed large reversible lithium storage capacities of graphene sheets, enabled by the unheralded roles of metal oxides,” Wang said. “Surprisingly we saw the magnitude of capacity contributions from graphene is mainly determined by active materials and the type of MO bound onto the graphene surface.”

Specifically, the lithium storage mechanisms of MOs and their loading ratio versus graphene play key roles in determining graphene capacity contributions.

Scientists have created the world’s thinnest lens, one two-thousandth the thickness of a human hair, opening the door to flexible computer displays and a revolution in miniature cameras.

Lead researcher Dr Yuerui (Larry) Lu from The Australian National University (ANU) said the discovery hinged on the remarkable potential of the molybdenum disulphide crystal.

Larry Lu (left), and Jiong Yang with the lens shown on screen. Credit: Stuart Hay, ANU

Larry Lu (left), and Jiong Yang with the lens shown on screen. Credit: Stuart Hay, ANU

“This type of material is the perfect candidate for future flexible displays,” said Dr Lu, leader of Nano-Electro-Mechanical System (NEMS) Laboratory in the ANU Research School of Engineering.

“We will also be able to use arrays of micro lenses to mimic the compound eyes of insects.”

The 6.3-nanometre lens outshines previous ultra-thin flat lenses, made from 50-nanometre thick gold nano-bar arrays, known as a metamaterial.

“Molybdenum disulphide is an amazing crystal,” said Dr Lu. “It survives at high temperatures, is a lubricant, a good semiconductor and can emit photons too.

“The capability of manipulating the flow of light in atomic scale opens an exciting avenue towards unprecedented miniaturisation of optical components and the integration of advanced optical functionalities.”

Molybdenum disulphide is in a class of materials known as chalcogenide glasses that have flexible electronic characteristics that have made them popular for high-technology components.

Dr Lu’s team created their lens from a crystal 6.3-nanometres thick – 9 atomic layers – which they had peeled off a larger piece of molybdenum disulphide with sticky tape.

They then created a 10-micron radius lens, using a focussed ion beam to shave off the layers atom by atom, until they had the dome shape of the lens.

The team discovered that single layers of molybdenum disulphide, 0.7 nanometres thick, had remarkable optical properties, appearing to a light beam to be 50 times thicker, at 38 nanometres. This property, known as optical path length, determines the phase of the light and governs interference and diffraction of light as it propagates.

“At the beginning we couldn’t imagine why molybdenum disulphide had such surprising properties,” said Dr Lu.

Collaborator Assistant Professor Zongfu Yu at the University of Wisconsin, Madison, developed a simulation and showed that light was bouncing back and forth many times inside the high refractive index crystal layers before passing through.

Molybdenum disulphide crystal’s refractive index, the property that quantifies the strength of a material’s effect on light, has a high value of 5.5. For comparison, diamond, whose high refractive index causes its sparkle, is only 2.4, and water’s refractive index is 1.3.

This study is published in the Nature serial journal Light: Science and Applications.

Think small


March 9, 2016

A single human hair, barely visible to the naked eye, is about 100 microns in diameter.

That’s huge compared to the device components students build in the Microfabrication Laboratory course at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).Under the instruction of Evelyn Hu, Tarr-Coyne Professor of Applied Physics and of Electrical Engineering, and Peter Stark, Visiting Associate Professor in Engineering Sciences, students are learning the “tricks of the trade” that could enable them to eventually form structures 1,000 times smaller than a strand of hair.

Using a specially designed “teaching clean room” that opened in the SEAS Active Learning Labs last spring, students fabricate electronic and photonic devices, such as light-emitting diodes, by developing components that are so small they must be crafted and analyzed with the help of a microscope.

Nabiha Saklayen, a graduate student pursuing a Ph.D. in physics, completes a photolithography workshop in the SEAS teaching clean room. (Photo by Adam Zewe/SEAS Communications.)

Nabiha Saklayen, a graduate student pursuing a Ph.D. in physics, completes a photolithography workshop in the SEAS teaching clean room. (Photo by Adam Zewe/SEAS Communications.)

Microfabrication involves crafting electronic devices in an unusual way: by printing them onto a material, like silicon. The concept of printed integrated circuits led to a Nobel Prize in physics for electrical engineer Jack Kilby in 2000, and also gave rise to the sophistication and complexity of today’s microprocessors, which can contain more than a billion transistors.

“In order to get a billion transistors into an area that is only an inch or so on a side, obviously you can’t just put the pieces together with your hands,” Hu said. “That set of really intricate techniques is what this course is all about.”

As in printing, shrinking the “font size” allows a tremendously greater amount of information to be represented on the same size page. The economic consequences are enormous, although balanced by the challenges of creating ever-smaller components, Hu explained.

The SEAS teaching clean room provides a first introduction to these techniques, and experience working at larger dimensions with building-block processes and devices. During one afternoon session, students completed a workshop on photolithography, which is a method for transferring a pattern to a substrate. Working at the micron level, they utilized chemicals and UV light to create a metal structure in a grid pattern. They will use this structure in a subsequent lab to measure the flow of electrons.

The course also enables students to work in Harvard’s Center for Nanoscale Systems (CNS), a shared-used core facility that holds a world-class nanofabrication laboratory. Students benefit from the expertise of CNS staff and the guidance of teaching fellows Sarah Schlotter and Laura Adams.

“The students concentrate not only on the fabrication of small devices, which is the main goal of the course, but also how to extract fundamental physical properties from the devices that they fabricate,” said Adams. “Since the course attracts a wide range of concentrators, we like to engage the students at all levels and disciplines to have a really collaborative experimental class.”

For electrical engineering concentrator Samwell Emmanuel, S.B. ’17, it was fascinating to see the tiny pattern take shape.

“We’re used to working with things that we can manipulate with our hands,” he said. “How do you work with something that you can’t even see with the naked eye? That’s what makes this course so interesting to me.”

Nabiha Saklayen, a graduate student pursuing a Ph.D. in physics, enjoyed the opportunity to learn about the fundamental techniques involved in fabricating the kinds of devices she uses regularly for research.

“We usually buy the devices that we need, so these are techniques that we often don’t think about,” she said. “It is incredible how much goes into actually preparing all these different compounds.”

While Hu doesn’t expect students to leave the course with perfect microfabrication skills, she hopes they develop a deeper appreciation for the inevitable challenges of working at the micron-scale.

“That frustration, and the ability to gain insight and intuition from their failures, is a critical thing for the students in this course. I want them to use the imperfections in their devices as a source of feedback to better understand the process,” she said. “My goal is to open their eyes to a world whose features they can’t see. I hope they learn that these techniques are powerful and that they could give them the capability to solve a problem in a different way.”

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have developed a chip that allows new radar cameras to be made a hundred times smaller than current ones.

With this NTU technology, radar cameras that usually weigh between 50 kg and 200 kg and are commonly used in large satellites can be made to become as small as palm-sized.

Despite being small, they can produce images that are of the same high quality if not better compared to conventional radar cameras. They are also 20 times cheaper to produce and consume at least 75 per cent less power.

Developed over the past three years at NTU, the promising technology has already secured S$2.5 million in research funding from Singapore government agencies.

The radar chip has attracted the attention of several multinational corporations, and is now being researched for use in Unmanned Aerial Vehicles (UAVs) and satellite applications.

Assistant Professor Zheng Yuanjin from NTU’s School of Electrical and Electronic Engineering who led the research, said that the size and effectiveness of the chip will open up new applications not possible previously.

“We have significantly shrunk the conventional radar camera into a system that is extremely compact and affordable, yet provides better accuracy. This will enable high resolution imaging radar technology to be used in objects and applications never before possible, like small drones, driverless cars and small satellite systems,” said Asst Prof Zheng.

NTU's tiny microchip for radar imaging embedded on a PCB board (small square chip on the upper right). Credit: NTU Singapore

NTU’s tiny microchip for radar imaging embedded on a PCB board (small square chip on the upper right). Credit: NTU Singapore

Advantages over current technology

Current radar camera systems are usually between half and two metres in length and weigh up to 200 kg. They cost more than US$1 million on the market and can consume over 1000 watts in electricity per hour, the energy equivalent of a household air-conditioning unit running for an hour.

Known as Synthetic Aperture Radar (SAR), these large radar cameras are often carried by large satellites and aircrafts that produce detailed images of the Earth’s surface. Objects longer than a metre, such as cars and boats, can be easily seen by the radar camera mounted on an aircraft flying at a height of 11 kilometres.

Unlike optical cameras which cannot work well at night due to insufficient light or in cloudy conditions, a radar camera uses microwaves (X-band or Ku-band) for its imaging, so it can operate well in all weather conditions and can even penetrate through foliage.

These detailed images from radar cameras can be used for environmental monitoring of disasters like forest fires, volcano eruptions and earthquakes as well as to monitor cities for traffic congestions and urban density.

But the huge size, prohibitive cost and energy consumption are deterrents for use in smaller unmanned aerial vehicles and autonomous vehicles. In comparison, NTU’s new radar chip (2mm x 3mm) when packaged into a module measures only 3cm x 4cm x 5cm, weighing less than 100 grams.

Production costs can go as low as US$10,000 per unit, while power consumption ranges from 1 to 200 watts depending on its application, similar to power-efficient LED TVs or a ceiling fan.

It can also capture objects as small as half a metre which is twice as detailed as the conventional radar camera used in large aircrafts or satellites.

Potential applications of the new radar chip

Asst Prof Zheng said that when mounted on UAVs, it can take high quality images on demand to monitor traffic conditions or even the coastlines for trespassers.

“Driverless cars will also be able to better scan the environment around them to avoid collisions and navigate more accurately in all weather conditions compared to current laser and optical technologies,” he added.

“Finally, with the space industry moving towards small satellite systems, such as the six satellites launched by NTU, smaller satellites can now also have the same advanced imaging capabilities previously seen only in the large satellites.”

Large satellites can weigh up to 1,000 kg, but microsatellites weigh only 100 to 200 kg.

Recognized internationally with strong market interest

NTU’s new radar chip was presented and published at the prestigious International Solid-State Circuits Conference (ISSCC) 2016. Commonly referred to as the “Olympics of Integrated Circuits Design,” ISSCC is the world’s top forum for presenting advances in solid-state circuits and systems and is attended by major industry players.

The chip was developed by Asst Prof Zheng’s team of five at NTU’s VIRTUS IC Design Centre of Excellence. The group was the first from Singapore to publish in ISSCC and is also the most published local group, with seven papers to date.

NTU’s new technology has attracted the attention of many multinational corporations, such as US aerospace company Space X; Netherlands semiconductor company NXP; Japanese electronics giant Panasonic, and French satellite maker Thales.

The next phase will be research in space applications to be carried out at the Smart Small Satellite Systems – Thales in NTU (S4TIN), a joint laboratory between NTU and Europe’s largest satellite manufacturer Thales Alenia Space.

Game changer for Singapore

Associate Professor Low Kay Soon, Director of NTU’s Satellite Research Centre, said the new radar chip will be a game changer in the space industry, which will bolster Singapore’s growing reputation as a satellite building nation.

“Monitoring the environment with a clear image using a traditional optical camera is always very challenging due to clouds and changing light conditions,” said Assoc Prof Low.

“This is especially the case for the tropics where the sky is always cloudy. With a miniature radar-on-chip system, it cuts down the required weight and size of the payload that a satellite needs to carry.

“More significantly, the lower power consumption makes it very suitable for microsatellites such as the X-SAT or VELOX-CI which NTU has launched. For small satellites, there is a limited area to mount the solar panels, which limits its power generation. Consequently the conventional SAR systems cannot be used due to its high power requirements.”

Asst Prof Zheng says it will take another three to six years before NTU’s new radar chip is ready for commercial use. He is now working with NTU’s innovation and enterprise company, NTUitive to find industry partners to license the technology or to spin off a company.

Director of VIRTUS, NTU Professor Joseph Chang added: “Singapore is one the very few select countries in the world with advanced technical capabilities to design complex microchips for space applications.”

“NTU professors associated with VIRTUS have received research funding of over S$5 million from Singapore and various countries like the United States, to design microchips for space applications. Recently, two patents have been filed for the novel design of these microchips.”

VIRTUS filed ten patents in the last year alone, for various innovative microchips with applications ranging from image processing to computing.

According to Markets and Markets global forecasts and analysis, the global market for radar systems is estimated to grow to US$24 billion by 2020.

Imagine a hand-held environmental sensor that can instantly test water for lead, E. coli, and pesticides all at the same time, or a biosensor that can perform a complete blood workup from just a single drop. That’s the promise of nanoscale plasmonic interferometry, a technique that combines nanotechnology with plasmonics–the interaction between electrons in a metal and light.

Now researchers from Brown University’s School of Engineering have made an important fundamental advance that could make such devices more practical. The research team has developed a technique that eliminates the need for highly specialized external light sources that deliver coherent light, which the technique normally requires. The advance could enable more versatile and more compact devices.

Plasmonic interferometers that have light emitters within them could make for better, more compact biosensors. Credit: Pacifici Lab / Brown University

Plasmonic interferometers that have light emitters within them could make for better, more compact biosensors. Credit: Pacifici Lab / Brown University

“It has always been assumed that coherent light was necessary for plasmonic interferometry,” said Domenico Pacifici, a professor of engineering who oversaw the work with his postdoctoral researcher Dongfang Li, and graduate student Jing Feng. “But we were able to disprove that assumption.”

Plasmonic interferometers make use of the interaction between light and surface plasmon polaritons, density waves created when light energy rattles free electrons in a metal. One type of interferometer looks like a bull’s-eye structure etched into a thin layer of metal. In the center is a hole poked through the metal layer with a diameter of about 300 nanometers–about 1,000 times smaller than the diameter of a human hair. The hole is encircled by a series of etched grooves, with diameters of a few micrometers. Thousands of these bulls-eyes can be placed on a chip the size of a fingernail.

When light from an external source is shown onto the surface of an interferometer, some of the photons go through the central hole, while others are scattered by the grooves. Those scattered photons generate surface plasmons that propagate through the metal inward toward the hole, where they interact with photons passing through the hole. That creates an interference pattern in the light emitted from the hole, which can be recorded by a detector beneath the metal surface.

When a liquid is deposited on top of an interferometer, the light and the surface plasmons propagate through that liquid before they interfere with each other. That alters the interference patterns picked up by the detector depending on the chemical makeup of the liquid or compounds present in it. By using different sizes of groove rings around the hole, the interferometers can be tuned to detect the signature of specific compounds or molecules. With the ability to put many differently tuned interferometers on one chip, engineers can hypothetically make a versatile detector.

Up to now, all plasmonic interferometers have required the use of highly specialized external light sources that can deliver coherent light–beams in which light waves are parallel, have the same wavelength, and travel in-phase (meaning the peaks and valleys of the waves are aligned). Without coherent light sources, the interferometers cannot produce usable interference patterns. Those kinds of light sources, however, tend to be bulky, expensive, and require careful alignment and periodic recalibration to obtain a reliable optical response.

But Pacifici and his group have come up with a way to eliminate the need for external coherent light. In the new method, fluorescent light-emitting atoms are integrated directly within the tiny hole in the center of the interferometer. An external light source is still necessary to excite the internal emitters, but it need not be a specialized coherent source.

“This is a whole new concept for optical interferometry,” Pacifici said, “an entirely new device.”

In this new device, incoherent light shown on the interferometer causes the fluorescent atoms inside the center hole to generate surface plasmons. Those plasmons propagate outward from the hole, bounce off the groove rings, and propagate back toward the hole after. Once a plasmon propagates back, it interacts with the atom that released it, causing an interference with the directly transmitted photon. Because the emission of a photon and the generation of a plasmon are indistinguishable, alternative paths originating from the same emitter, the process is naturally coherent and interference can therefore occur even though the emitters are excited incoherently.

“The important thing here is that this is a self-interference process,” Pacifici said. “It doesn’t matter that you’re using incoherent light to excite the emitters, you still get a coherent process.”

In addition to eliminating the need for specialized external light sources, the approach has several advantages, Pacifici said. Because the surface plasmons travel out from the hole and back again, they probe the sample on top of the interferometer surface twice. That makes the device more sensitive.

But that’s not the only advantage. In the new device, external light can be projected from underneath the metal surface containing the interferometers instead of from above. That eliminates the need for complex illumination architectures on top of the sensing surface, which could make for easier integration into compact devices.

The embedded light emitters also eliminate the need to control the amount of sample liquid deposited on the interferometer’s surface. Large droplets of liquid can cause lensing effects, a bending of light that can scramble the results from the interferometer. Most plasmonic sensors make use of tiny microfluidic channels to deliver a thin film of liquid to avoid lensing problems. But with internal light emitters excited from the bottom surface, the external light never comes in contact with the sample, so lensing effects are negated, as is the need for microfluidics.

Finally, the internal emitters produce a low intensity light. That’s good for probing delicate samples, such as proteins, than can be damaged by high-intensity light.

More work is required to get the system out of the lab and into devices, and Pacifici and his team plan to continue to refine the idea. The next step will be to try eliminating the external light source altogether. It might be possible, the researchers say, to eventually excite the internal emitters using tiny fiber optic lines, or perhaps electric current.

Still, this initial proof-of-concept is promising, Pacifici said.

“From a fundamental standpoint, we think this new device represents a significant step forward,” he said, “a first demonstration of plasmonic interferometry with incoherent light.”

University of Colorado Boulder researchers have demonstrated the use of the world’s first ultrafast optical microscope, allowing them to probe and visualize matter at the atomic level with mind-bending speed.

The ultrafast optical microscope assembled by the research team is 1,000 times more powerful than a conventional optical microscope, said CU-Boulder physics Professor Markus Raschke, lead study author. The “image frame” rate, or speed captured by the team, is 1 trillion times faster than the blink of an eye, allowing the researchers to make real-time, slow-motion movies of light interacting with electrons in nanomaterials – in this case a thin gold film.

“This is the first time anyone has been able to probe matter on its natural time and length scale,” said Raschke. “We imaged and measured the motions of electrons in real space and time, and we were able to make it into a movie to help us better understand the fundamental physical processes.”

A paper on the subject appears in the Feb. 8 issue of Nature Nanotechnology.

Matter is sometimes described as the “stuff of the universe” – the molecules, atoms and charged particles, or ions, that make up everything around us. Matter has several states, most prominently solid, liquid and gas.

According to the CU-Boulder researchers, a number of important processes like photosynthesis, energy conversion and use, and biological functions are based on the transfer of electrons and ions from molecule to molecule. The team used a technique called “plasmonic nanofocusing” to focus extraordinarily short laser pulses into tiny bits of gold film matter using a nanometer-sized metal tip.

“Our study brings nanoscale microscopy to the next level, with the ability to capture detailed images evolving on extremely fast time scales,” said Vasily Kravtsov, a CU-Boulder graduate student in physics and first author of the paper.

Other co-authors on the Nature Nanotechnology paper include CU-Boulder postdoctoral researcher Ronald Ulbricht and former CU-Boulder postdoctoral researcher Joanna Atkin, now a faculty member at the University of North Carolina-Chapel Hill.

“This work expands the reach of optical microscopes,” said Raschke. “Using this technique, researchers can image the elementary processes in materials ranging from battery electrodes to solar cells, helping to improve their efficiency and lifetime.”

Unlike electron microscope approaches, the new technique does not require ultra-high vacuum techniques and is particularly promising for studying ultrafast processes like charge and energy transport in soft matter, including biological materials, said Kravtsov.

Renesas Electronics Corp. reported the development of 90-nanometer (nm) one-transistor MONOS (1T-MONOS) flash memory technology that can be used in combination with a variety of processes, such as CMOS and bipolar CMOS DMOS (BiCDMOS), and provides high program/erase (P/E) endurance and low rewrite energy consumption.

Renesas said that it anticipates that the new flash memory circuit technology will enable it to add flash memory to automotive analog devices with improved performance and reliability.
In a release, the Company noted that this circuit technology makes possible the industry’s first P/E endurance of over 100 million cycles under a high junction temperature (Tj) (Note 2) 175 degrees C, while also delivering low rewrite energy of 0.07 mJ/8 KB (millijoule: one thousandth of a joule) for low energy consumption.

Renesas reported that the newly developed flash memory technology restrains additional process costs while providing an easy way to add flash memory to automotive analog and power devices. This means that analog circuits for connecting sensors and motors can employ devices that mix microcontroller (MCU) logic and flash memory based on the new technology. It has the potential to substantially reduce the number of chips used in motor control systems, while helping to make them more compact, lightweight, and power efficient.

Additionally, the new flash memory technology achieves over 100 million P/E cycles, making it suitable for applications such as automatic calibration or status recording using high-frequency sampling under actual usage conditions in the field.

Renesas Electronics Corp. is a supplier of microcontrollers.

The road to more versatile wearable technology is dotted with iron. Specifically, quantum dots of iron arranged on boron nitride nanotubes (BNNTs). The new material is the subject of a study to be published in Scientific Reports later this week, led by Yoke Khin Yap, a professor of physics at Michigan Technological University.

Yap says the iron-studded BNNTs are pushing the boundaries of electronics hardware. The transistors modulating electron flow need an upgrade.

“Look beyond semiconductors,” he says, explaining that materials like silicon semiconductors tend to overheat, can only get so small and leak electric current.

The key to revamping the fundamental base of transistors is creating a series of stepping-stones that use quantum tunneling.

The nanotubes are the mainframe of this new material. BNNTs are great insulators and terrible at conducting electricity. While at first that seems like an odd choice for electronics, the insulating effect of BNNTs is crucial to prevent current leakage and overheating. Additionally, electron flow will only occur across the metal dots on the BNNTs.

In past research, Yap and his team used gold for quantum dots, placed along a BNNT in a tidy line. With enough energy potential, the electrons are repelled by the insulating BNNT and hopscotch from gold dot to gold dot. This electron movement is called quantum tunneling.

“Imagine this as a river, and there’s no bridge; it’s too big to hop over,” Yap says. “Now, picture having stepping stones across the river–you can cross over, but only when you have enough energy to do so.”

Unlike with semiconductors, there is no classical resistance with quantum tunneling. No resistance means no heat. Plus, these materials are very small; the nanomaterials enable the transistors to shrink as well. An added bonus is that BNNTs are also quite flexible, a boon for wearable electronics.

Researchers at MIT and Texas Instruments have developed a new type of radio frequency identification (RFID) chip that is virtually impossible to hack.

If such chips were widely adopted, it could mean that an identity thief couldn’t steal your credit card number or key card information by sitting next to you at a café, and high-tech burglars couldn’t swipe expensive goods from a warehouse and replace them with dummy tags.

Texas Instruments has built several prototypes of the new chip, to the researchers’ specifications, and in experiments the chips have behaved as expected. The researchers presented their research this week at the International Solid-State Circuits Conference, in San Francisco.

According to Chiraag Juvekar, a graduate student in electrical engineering at MIT and first author on the new paper, the chip is designed to prevent so-called side-channel attacks. Side-channel attacks analyze patterns of memory access or fluctuations in power usage when a device is performing a cryptographic operation, in order to extract its cryptographic key.

“The idea in a side-channel attack is that a given execution of the cryptographic algorithm only leaks a slight amount of information,” Juvekar says. “So you need to execute the cryptographic algorithm with the same secret many, many times to get enough leakage to extract a complete secret.”

One way to thwart side-channel attacks is to regularly change secret keys. In that case, the RFID chip would run a random-number generator that would spit out a new secret key after each transaction. A central server would run the same generator, and every time an RFID scanner queried the tag, it would relay the results to the server, to see if the current key was valid.

Blackout

Such a system would still, however, be vulnerable to a “power glitch” attack, in which the RFID chip’s power would be repeatedly cut right before it changed its secret key. An attacker could then run the same side-channel attack thousands of times, with the same key. Power-glitch attacks have been used to circumvent limits on the number of incorrect password entries in password-protected devices, but RFID tags are particularly vulnerable to them, since they’re charged by tag readers and have no onboard power supplies.

Two design innovations allow the MIT researchers’ chip to thwart power-glitch attacks: One is an on-chip power supply whose connection to the chip circuitry would be virtually impossible to cut, and the other is a set of “nonvolatile” memory cells that can store whatever data the chip is working on when it begins to lose power.

For both of these features, the researchers — Juvekar; Anantha Chandrakasan, who is Juvekar’s advisor and the Vannevar Bush Professor of Electrical Engineering and Computer Science; Hyung-Min Lee, who was a postdoc in Chandrakasan’s group when the work was done and is now at IBM; and TI’s Joyce Kwong, who did her master’s degree and PhD with Chandrakasan — use a special type of material known as a ferroelectric crystals.

As a crystal, a ferroelectric material consists of molecules arranged into a regular three-dimensional lattice. In every cell of the lattice, positive and negative charges naturally separate, producing electrical polarization. The application of an electric field, however, can align the cells’ polarization in either of two directions, which can represent the two possible values of a bit of information.

When the electric field is removed, the cells maintain their polarization. Texas Instruments and other chip manufacturers have been using ferroelectric materials to produce nonvolatile memory, or computer memory that retains data when it’s powered off.

Complementary capacitors

A ferroelectric crystal can also be thought of as a capacitor, an electrical component that separates charges and is characterized by the voltage between its negative and positive poles. Texas Instruments’ manufacturing process can produce ferroelectric cells with either of two voltages: 1.5 volts or 3.3 volts.

The researchers’ new chip uses a bank of 3.3-volt capacitors as an on-chip energy source. But it also features 571 1.5-volt cells that are discretely integrated into the chip’s circuitry. When the chip’s power source — the external scanner — is removed, the chip taps the 3.3-volt capacitors and completes as many operations as it can, then stores the data it’s working on in the 1.5-volt cells.

When power returns, before doing anything else the chip recharges the 3.3-volt capacitors, so that if it’s interrupted again, it will have enough power to store data. Then it resumes its previous computation. If that computation was an update of the secret key, it will complete the update before responding to a query from the scanner. Power-glitch attacks won’t work.

Because the chip has to charge capacitors and complete computations every time it powers on, it’s somewhat slower than conventional RFID chips. But in tests, the researchers found that they could get readouts from their chips at a rate of 30 per second, which should be more than fast enough for most RFID applications.

Researchers from MIPT have found a solution to the problem of overheating of active plasmonic components. These components will be essential for high-speed data transfer within the optoelectronic microprocessors of the future, which will be able to function tens of thousands of times faster than the microprocessors currently in use today. In the paper published in ACS Photonics the researchers have demonstrated how to efficiently cool optoelectronic chips using industry-standard heatsinks in spite of high heat generation in active plasmonic components.

The speed of multicore and manycore microprocessors, which are already used in high-performance computer systems, depends not so much on the speed of an individual core, but rather on the time it takes for data to be transferred between the cores. The electrical copper interconnects used in microprocessors today are fundamentally limited in bandwidth, and they cannot be used to maintain the continuing growth of the processor performance. In other words, doubling the number of cores will not double the processing power.

Leading companies in the semiconductor industry, such as IBM, Oracle, Intel, and HP, see the only solution to this problem in switching from electronics to photonics, and they are currently investing billions of dollars into this. Replacing electrons with photons will mean that large amounts of data will be able to be transferred between processor cores almost instantly, which in turn will mean that the processor performance will be nearly proportional to the number of cores. However, due to diffraction, photonic components are not as easy to scale down as electronic components. Their dimensions cannot be smaller than the size approximately equal to the light wavelength (~ 1 micrometer or 1000 nanometers), but transistors will soon be as small as 10 nanometers. This fundamental problem can be solved by switching from bulk waves to surface waves, which are known as surface plasmon polaritons (SPPs). This will enable to confine light on the nanoscale. Along with the leading research centers of industrial companies and the laboratories of leading universities, Russian scientists from the Laboratory of Nanooptics and Plasmonics of MIPT’s Center of Nanoscale Optoelectronics are also making good progress in this field.

The main difficulty that scientists face is the fact that SPPs are absorbed by metal, which is a key material in plasmonics. This effect is similar to resistance in electronics, where the energy of electrons is lost and converted into heat when current passes through a resistor. The SPP loss can be compensated by pumping additional energy into the SPPs. However, this pumping will produce additional heat, which in turn will cause an increase in temperature not only in the plasmonic components, but also in the processor as a whole. The higher absorption in the metal, the greater the loss, and the stronger pumping will be required. This raises the temperature, which again causes a loss increase and makes it more difficult to create optical gain, which is required to compensate for the loss, and this means that more powerful pumping is required. A cycle is formed in which the temperature can rise to such an extent that a processor chip simply burns out. This is no surprise, since the heating power per surface unit of the active plasmonic waveguide with loss compensation exceeds 10 kW/cm2, which is twice as high as the intensity of solar radiation at the surface of the Sun!

Dmitry Fedyanin and Andrey Vyshnevyy, researchers at MIPT’s Laboratory of Nanooptics and Plasmonics, have found a solution to this problem. They have demonstrated that using high-performance thermal interfaces, i.e. layers of thermally conductive materials placed between the chip and the cooling system to ensure efficient heat removal from the chip, (thermal grease is a popular type of thermal interface, although it is not very efficient) high-performance optoelectronic chips can be cooled using conventional cooling systems.

Based on the results of numerical simulations, Fedyanin and Vyshnevyy concluded that if an optoelectronic chip with active plasmonic waveguides is placed in air, its temperature will increase by several hundred degrees Celsius, which will cause the device to malfunction. Multi-layered thermal interfaces of nano- and micrometer thickness combined with simple cooling systems can reduce the temperature of the chip from several hundred degrees to approximately ten degrees with respect to the ambient temperature. This opens the prospects for the implementation of high-performance optoelectronic microprocessors in a wide range of applications, ranging from supercomputers to compact electronic devices.