Tag Archives: letter-mems-tech

Faster production of advanced, flexible electronics is among the potential benefits of a discovery by researchers at Oregon State University’s College of Engineering.

Taking a deeper look at photonic sintering of silver nanoparticle films — the use of intense pulsed light, or IPL, to rapidly fuse functional conductive nanoparticles — scientists uncovered a relationship between film temperature and densification. Densification in IPL increases the density of a nanoparticle thin-film or pattern, with greater density leading to functional improvements such as greater electrical conductivity.

The engineers found a temperature turning point in IPL despite no change in pulsing energy, and discovered that this turning point appears because densification during IPL reduces the nanoparticles’ ability to absorb further energy from the light.

This previously unknown interaction between optical absorption and densification creates a new understanding of why densification levels off after the temperature turning point in IPL, and further enables large-area, high-speed IPL to realize its full potential as a scalable and efficient manufacturing process.

Rajiv Malhotra, assistant professor of mechanical engineering at OSU, and graduate student Shalu Bansal conducted the research. The results were recently published in Nanotechnology.

“For some applications we want to have maximum density possible,” Malhotra said. “For some we don’t. Thus, it becomes important to control the densification of the material. Since densification in IPL depends significantly on the temperature, it is important to understand and control temperature evolution during the process. This research can lead to much better process control and equipment design in IPL.”

Intense pulsed light sintering allows for faster densification — in a matter of seconds – over larger areas compared to conventional sintering processes such as oven-based and laser-based. IPL can potentially be used to sinter nanoparticles for applications in printed electronics, solar cells, gas sensing and photocatalysis.

Earlier research showed that nanoparticle densification begins above a critical optical fluence per pulse but that it does not change significantly beyond a certain number of pulses.

This OSU study explains why, for a constant fluence, there is a critical number of pulses beyond which the densification levels off.

“The leveling off in density occurs even though there’s been no change in the optical energy and even though densification is not complete,” Malhotra said. “It occurs because of the temperature history of the nanoparticle film, i.e. the temperature turning point. The combination of fluence and pulses needs to be carefully considered to make sure you get the film density you want.”

A smaller number of high-fluence pulses quickly produces high density. For greater density control, a larger number of low-fluence pulses is required.

“We were sintering in around 20 seconds with a maximum temperature of around 250 degrees Celsius in this work,” Malhotra. “More recent work we have done can sinter within less than two seconds and at much lower temperatures, down to around 120 degrees Celsius. Lower temperature is critical to flexible electronics manufacturing. To lower costs, we want to print these flexible electronics on substrates like paper and plastic, which would burn or melt at higher temperatures. By using IPL, we should be able to create production processes that are both faster and cheaper, without a loss in product quality.”

Products that could evolve from the research, Malhotra said, are radiofrequency identification tags, a wide range of flexible electronics, wearable biomedical sensors, and sensing devices for environmental applications.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences have made the world’s smallest radio receiver – built out of an assembly of atomic-scale defects in pink diamonds.

This tiny radio — whose building blocks are the size of two atoms — can withstand extremely harsh environments and is biocompatible, meaning it could work anywhere from a probe on Venus to a pacemaker in a human heart.

The research was led by Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at SEAS, and his graduate student Linbo Shao and published in Physical Review Applied.

The radio uses tiny imperfections in diamonds called nitrogen-vacancy (NV) centers. To make NV centers, researchers replace one carbon atom in a diamond crystal with a nitrogen atom and remove a neighboring atom — creating a system that is essentially a nitrogen atom with a hole next to it. NV centers can be used to emit single photons or detect very weak magnetic fields. They have photoluminescent properties, meaning they can convert information into light, making them powerful and promising systems for quantum computing, phontonics and sensing.

Radios have five basic components — a power source, a receiver, a transducer to convert the high-frequency electromagnetic signal in the air to a low-frequency current, speaker or headphones to convert the current to sound and a tuner.

In the Harvard device, electrons in diamond NV centers are powered, or pumped, by green light emitted from a laser. These electrons are sensitive to electromagnetic fields, including the waves used in FM radio, for example. When NV center receives radio waves it converts them and emits the audio signal as red light. A common photodiode converts that light into a current, which is then converted to sound through a simple speaker or headphone.

An electromagnet creates a strong magnetic field around the diamond, which can be used to change the radio station, tuning the receiving frequency of the NV centers.

Shao and Loncar used billions of NV centers in order to boost the signal, but the radio works with a single NV center, emitting one photon at a time, rather than a stream of light.

The radio is extremely resilient, thanks to the inherent strength of diamond. The team successfully played music at 350 degrees Celsius — about 660 Fahrenheit.

“Diamonds have these unique properties,” said Loncar. “This radio would be able to operate in space, in harsh environments and even the human body, as diamonds are biocompatible.”

Scientists at the National Institute of Standards and Technology (NIST) have developed a new device that measures the motion of super-tiny particles traversing distances almost unimaginably small–shorter than the diameter of a hydrogen atom, or less than one-millionth the width of a human hair. Not only can the handheld device sense the atomic-scale motion of its tiny parts with unprecedented precision, but the researchers have devised a method to mass produce the highly sensitive measuring tool.

Schematic shows laser light interacting with a plasmonic gap resonator, a miniature device designed at NIST to measure with unprecedented precision the nanoscale motions of nanoparticles. An incident laser beam (pink beam at left) strikes the resonator, which consists of two layers of gold separated by an air gap. The top gold layer is embedded in an array of tiny cantilevers (violet)--vibrating devices resembling a miniature diving board. When a cantilever moves, it changes the width of the air gap, which, in turn, changes the intensity of the laser light reflected from the resonator. The modulation of the light reveals the displacement of the tiny cantilever. Credit: Brian Roxworthy/NIST

Schematic shows laser light interacting with a plasmonic gap resonator, a miniature device designed at NIST to measure with unprecedented precision the nanoscale motions of nanoparticles. An incident laser beam (pink beam at left) strikes the resonator, which consists of two layers of gold separated by an air gap. The top gold layer is embedded in an array of tiny cantilevers (violet)–vibrating devices resembling a miniature diving board. When a cantilever moves, it changes the width of the air gap, which, in turn, changes the intensity of the laser light reflected from the resonator. The modulation of the light reveals the displacement of the tiny cantilever. Credit: Brian Roxworthy/NIST

It’s relatively easy to measure small movements of large objects but much more difficult when the moving parts are on the scale of nanometers, or billionths of a meter. The ability to accurately measure tiny displacements of microscopic bodies has applications in sensing trace amounts of hazardous biological or chemical agents, perfecting the movement of miniature robots, accurately deploying airbags and detecting extremely weak sound waves traveling through thin films.

NIST physicists Brian Roxworthy and Vladimir Aksyuk describe their work (link is external) in the Dec. 6, 2016, Nature Communications.

The researchers measured subatomic-scale motion in a gold nanoparticle. They did this by engineering a small air gap, about 15 nanometers in width, between the gold nanoparticle and a gold sheet. This gap is so small that laser light cannot penetrate it.

However, the light energized surface plasmons–the collective, wave-like motion of groups of electrons confined to travel along the boundary between the gold surface and the air.

The researchers exploited the light’s wavelength, the distance between successive peaks of the light wave. With the right choice of wavelength, or equivalently, its frequency, the laser light causes plasmons of a particular frequency to oscillate back and forth, or resonate, along the gap, like the reverberations of a plucked guitar string.

Meanwhile, as the nanoparticle moves, it changes the width of the gap and, like tuning a guitar string, changes the frequency at which the plasmons resonate.

The interaction between the laser light and the plasmons is critical for sensing tiny displacements from nanoscale particles, notes Aksyuk. Light can’t easily detect the location or motion of an object smaller than the wavelength of the laser, but converting the light to plasmons overcomes this limitation. Because the plasmons are confined to the tiny gap, they are more sensitive than light is for sensing the motion of small objects like the gold nanoparticle.

The amount of laser light reflected back from the plasmon device reveals the width of the gap and the motion of the nanoparticle. Suppose, for example, that the gap changes–due to the motion of the nanoparticle–in such a way that the natural frequency, or resonance, of the plasmons more closely matches the frequency of the laser light. In that case, the plasmons are able to absorb more energy from the laser light, and less light is reflected.

To use this motion-sensing technique in a practical device, Aksyuk and Roxworthy embedded the gold nanoparticle in a microscopic-scale mechanical structure–a vibrating cantilever, sort of a miniature diving board–that was a few micrometers long, made of silicon nitride. Even when they’re not set in motion, such devices never sit perfectly still, but vibrate at high frequency, jostled by the random motion of their molecules at room temperature. Even though the amplitude of the vibration was tiny–moving subatomic distances–it was easy to detect with the new plasmonic technique. Similar, though typically larger, mechanical structures are commonly used for both scientific measurements and practical sensors; for example, detecting motion and orientation in cars and smartphones. The NIST scientists hope their new way of measuring motion at the nanoscale will help to further miniaturize and improve performance of many such micromechanical systems.

“This architecture paves the way for advances in nanomechanical sensing,” the researchers write. “We can detect tiny motion more locally and precisely with these plasmonic resonators than any other way of doing it,” said Aksyuk.

The team’s fabrication approach allows production of some 25,000 of the devices on a computer chip, with each device tailored to detect motion according to the needs of the manufacturer.

Outfitting the future


December 12, 2016

Wearable technology is about more than smartwatches or counting steps. Across North Carolina State University, researchers are using it to solve problems — monitoring heart rate and environmental dangers, powering electronic devices, delivering medications, building better prosthetics and improving safety.

wearable-tech-top-1500x650

They’re developing technologies that are functional, efficient, innovative and practical, and that could have an impact on countless lives.

Here are a few of the NC State projects at the forefront of this evolving field.

What’s NEXT in wearables

What if the clothes you already wear not only covered your body but also kept track of how it’s functioning — and all you had to do was put them on?

Finding innovative, useful and economical ways to integrate electronics into clothing is the mission of the College of Textiles’ Nano-Extended Textiles (NEXT) Research Group.

Headed by Jesse Jur, assistant professor in the Department of Textile Engineering, Chemistry and Science, the NEXT group seeks to create cost-effective, energy-efficient wearable technology that’s powered by the user’s own body.

Jur’s team has gained attention for projects like customizable, iron-on sensors that monitor the heart’s performance and transmit the readings to a smartphone, or that monitor environmental levels of potentially dangerous gases like carbon monoxide and ozone.

The NEXT group has also explored bioluminescence in fashion through a collaboration with recent College of Textiles graduate Jazsalyn McNeil, who joined the group as a “fusion designer” to meld her design sensibility with the group’s research. McNeil’s Pulse Dress incorporates screen-printed sensors that make LED lights blink with the wearer’s heartbeat. NEXT and McNeil hope that the eye-catching dress will both influence fashion and draw attention to the possibilities of wearable electronics.

Heating up wearable tech

In recent years, smartwatches have turned up on the arms of millions of people who want convenient ways to keep track of their fitness, but these still depend on conventional batteries. At NC State’s Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) — a National Science Foundation Nanosystems Engineering Research Center — researchers are developing innovative health-monitoring devices that are battery-free and body-powered.

“The goal of ASSIST is to make wearable technologies that can be used for long-term health monitoring, such as devices that track heart health or monitor physical and environmental variables to predict and prevent asthma attacks,” said Daryoosh Vashaee, an associate professor of electrical and computer engineering in the NC State College of Engineering.

Vashaee and a team of undergraduates and faculty members have developed a new approach for harvesting body heat and converting it into electricity to power wearable electronics. The prototype armbands and embedded sensors in T-shirts are lightweight, conform to the shape of the body and can generate far more electricity than previous lightweight heat-harvesting technologies.

“We want to make devices that don’t rely on batteries,” Vashaee said. “And we think this design and prototype moves us much closer to making that a reality.”

Taking the sting out of diabetes

For some people with serious health issues, wearable technology has the potential to offer more than bells and whistles — it could make their treatments easier and even save lives.

Zhen Gu, an associate professor in the UNC/NC State Joint Department of Biomedical Engineering, has developed a glucose-responsive insulin patch for people living with Type 1 Diabetes. At around the size of a penny, the thin, square patch contains more than a hundred tiny, painless needles that supply the wearer with insulin as needed. This potential treatment could help to ensure consistent blood-sugar levels — and spare patients regular injections.

Gu, who has been honored as one of MIT Technology Review’s “Innovators Under 35” for his work with innovative drug-delivery systems, received $4.6 million in funding from JDRF (formerly the Juvenile Diabetes Research Foundation) and multinational pharmaceutical company Sanofi for the project. The patch is currently in animal trials. Gu is also working on patches to deliver melanoma drugs directly to tumor sites and to deliver blood thinners as needed to prevent blood clots.

Walking wearables

Amputees have always been among the earliest adopters of wearable technology, as even minor advances in prosthetics can markedly improve their mobility. Helen Huang, associate professor of biomedical engineering and director of the Rehabilitation Engineering Core in the UNC/NC State Joint Department of Biomedical Engineering, has made it her mission to develop the next generation of powered prosthetic limbs.

Huang’s projects include software that allows powered prosthetics to tune themselves automatically, making the devices more responsive and lowering the costs associated with powered prosthetic use.

“People are dynamic — a patient’s physical condition may change as he or she becomes accustomed to a prosthetic leg, for example, or they may gain weight,” said Huang. “These changes mean the prosthetic needs to be re-tuned, and working with a prosthetist takes time and money.”

Huang’s team has also worked on technology that translates electrical signals in human muscles into signals that control powered prosthetic limbs — enabling sensors in the prosthetics to follow simple cues from the user’s brain such as “open hand” or “close hand.”

A bright idea for safety

For College of Textiles alumnus Jeremy Wall, a near miss with a car while he was riding his bike one night became an unexpected source of inspiration: He now heads a company, Lumenus, that’s developing clothing and accessories with embedded smart LED lighting.

Wall, a 2014 graduate in fashion and textile management, began working on his tech with the help of an undergraduate research scholarship while he was still a student. His goal was to help cyclists, motorcyclists and runners be more visible to motorists at night while staying stylish and functional during the day.

The company will soon hit the market with apparel and accessories including jackets, vests, leggings, backpacks and armbands. It’s also licensing its technology to companies such as backpack manufacturer Timbuk2 and working with the Department of Defense to develop sensors for military gear.

Lumenus has also created an app that adds extra features to the apparel. For example, the wearer can enter a destination on the app, and the LED lights on the garment will flash strategically at intersections or other potentially hazardous points along the route.

Wall recently returned to NC State for help getting his company off the ground, enlisting three College of Textiles undergraduates to work with Lumenus as part of their senior design project.

The next time you place your coffee order, imagine slapping onto your to-go cup a sticker that acts as an electronic decal, letting you know the precise temperature of your triple-venti no-foam latte. Someday, the high-tech stamping that produces such a sticker might also bring us food packaging that displays a digital countdown to warn of spoiling produce, or even a window pane that shows the day’s forecast, based on measurements of the weather conditions outside.

Engineers at MIT have invented a fast, precise printing process that may make such electronic surfaces an inexpensive reality. In a paper published today in Science Advances, the researchers report that they have fabricated a stamp made from forests of carbon nanotubes that is able to print electronic inks onto rigid and flexible surfaces.

A. John Hart, the Mitsui Career Development Associate Professor in Contemporary Technology and Mechanical Engineering at MIT, says the team’s stamping process should be able to print transistors small enough to control individual pixels in high-resolution displays and touchscreens. The new printing technique may also offer a relatively cheap, fast way to manufacture electronic surfaces for as-yet-unknown applications.

“There is a huge need for printing of electronic devices that are extremely inexpensive but provide simple computations and interactive functions,” Hart says. “Our new printing process is an enabling technology for high-performance, fully printed electronics, including transistors, optically functional surfaces, and ubiquitous sensors.”

Sanha Kim, a postdoc in MIT’s departments of Mechanical Engineering and Chemical Engineering, is the lead author, and Hart is the senior author. Their co-authors are mechanical engineering graduate students Hossein Sojoudi, Hangbo Zhao, and Dhanushkodi Mariappan; Gareth McKinley, the School of Engineering Professor of Teaching Innovation; and Karen Gleason, professor of chemical engineering and MIT’s associate provost.

A stamp from tiny pen quills

There have been other attempts in recent years to print electronic surfaces using inkjet printing and rubber stamping techniques, but with fuzzy results. Because such techniques are difficult to control at very small scales, they tend to produce “coffee ring” patterns where ink spills over the borders, or uneven prints that can lead to incomplete circuits.

“There are critical limitations to existing printing processes in the control they have over the feature size and thickness of the layer that’s printed,” Hart says. “For something like a transistor or thin film with particular electrical or optical properties, those characteristics are very important.”

Hart and his team sought to print electronics much more precisely, by designing “nanoporous” stamps. (Imagine a stamp that’s more spongy than rubber and shrunk to the size of a pinky fingernail, with patterned features that are much smaller than the width of a human hair.) They reasoned that the stamp should be porous, to allow a solution of nanoparticles, or “ink,” to flow uniformly through the stamp and onto whatever surface is to be printed. Designed in this way, the stamp should achieve much higher resolution than conventional rubber stamp printing, referred to as flexography.

Kim and Hart hit upon the perfect material to create their highly detailed stamp: carbon nanotubes — strong, microscopic sheets of carbon atoms, arranged in cylinders. Hart’s group has specialized in growing forests of vertically aligned nanotubes in carefully controlled patterns that can be engineered into highly detailed stamps.

“It’s somewhat serendipitous that the solution to high-resolution printing of electronics leverages our background in making carbon nanotubes for many years,” Hart says. “The forests of carbon nanotubes can transfer ink onto a surface like massive numbers of tiny pen quills.”

Printing circuits, roll by roll

To make their stamps, the researchers used the group’s previously developed techniques to grow the carbon nanotubes on a surface of silicon in various patterns, including honeycomb-like hexagons and flower-shaped designs. They coated the nanotubes with a thin polymer layer (developed by Gleason’s group) to ensure the ink would penetrate throughout the nanotube forest and the nanotubes would not shrink after the ink was stamped. Then they infused the stamp with a small volume of electronic ink containing nanoparticles such as silver, zinc oxide, or semiconductor quantum dots.

The key to printing tiny, precise, high-resolution patterns is in the amount of pressure applied to stamp the ink. The team developed a model to predict the amount of force necessary to stamp an even layer of ink onto a substrate, given the roughness of both the stamp and the substrate, and the concentration of nanoparticles in the ink.

To scale up the process, Mariappan built a printing machine, including a motorized roller, and attached to it various flexible substrates. The researchers fixed each stamp onto a platform attached to a spring, which they used to control the force used to press the stamp against the substrate.

“This would be a continuous industrial process, where you would have a stamp, and a roller on which you’d have a substrate you want to print on, like a spool of plastic film or specialized paper for electronics,” Hart says. “We found, limited by the motor we used in the printing system, we could print at 200 millimeters per second, continuously, which is already competitive with the rates of industrial printing technologies. This, combined with a tenfold improvement in the printing resolution that we demonstrated, is encouraging.”

After stamping ink patterns of various designs, the team tested the printed patterns’ electrical conductivity. After annealing, or heating, the designs after stamping — a common step in activating electronic features — the printed patterns were indeed highly conductive, and could serve, for example, as high-performance transparent electrodes.

Going forward, Hart and his team plan to pursue the possibility of fully printed electronics.

“Another exciting next step is the integration of our printing technologies with 2-D materials, such as graphene, which together could enable new, ultrathin electronic and energy conversion devices,” Hart says.

Researchers in AMBER, the Science Foundation Ireland-funded materials science research centre, hosted in Trinity College Dublin, have used the wonder material graphene to make the novelty children’s material silly putty (polysilicone) conduct electricity, creating extremely sensitive sensors. This world first research, led by Professor Jonathan Coleman from TCD and in collaboration with Prof Robert Young of the University of Manchester, potentially offers exciting possibilities for applications in new, inexpensive devices and diagnostics in medicine and other sectors. The AMBER team’s findings have been published this week in the leading journal Science*.

Prof Coleman, Investigator in AMBER and Trinity’s School of Physics along with postdoctoral researcher Conor Boland, discovered that the electrical resistance of putty infused with graphene (“G-putty”) was extremely sensitive to the slightest deformation or impact. They mounted the G-putty onto the chest and neck of human subjects and used it to measure breathing, pulse and even blood pressure. It showed unprecedented sensitivity as a sensor for strain and pressure, hundreds of times more sensitive than normal sensors. The G-putty also works as a very sensitive impact sensor, able to detect the footsteps of small spiders. It is believed that this material will find applications in a range of medical devices.

Prof Coleman said, “What we are excited about is the unexpected behaviour we found when we added graphene to the polymer, a cross-linked polysilicone. This material as well known as the children’s toy silly putty. It is different from familiar materials in that it flows like a viscous liquid when deformed slowly but bounces like an elastic solid when thrown against a surface. When we added the graphene to the silly putty, it caused it to conduct electricity, but in a very unusual way. The electrical resistance of the G-putty was very sensitive to deformation with the resistance increasing sharply on even the slightest strain or impact. Unusually, the resistance slowly returned close to its original value as the putty self-healed over time.”

He continued, “While a common application has been to add graphene to plastics in order to improve the electrical, mechanical, thermal or barrier properties, the resultant composites have generally performed as expected without any great surprises. The behaviour we found with G-putty has not been found in any other composite material. This unique discovery will open up major possibilities in sensor manufacturing worldwide.”

Professor Mick Morris, Director of AMBER, said: “This exciting discovery shows that Irish research is at the leading edge of materials science worldwide. Jonathan Coleman and his team in AMBER continue to carry out world class research and this scientific breakthrough could potentially revolutionise certain aspects of healthcare.”

Leti researchers have demonstrated that memristive devices are excellent candidates to emulate synaptic plasticity, the capability of synapses to enhance or diminish their connectivity between neurons, which is widely believed to be the cellular basis for learning and memory.

The breakthrough was presented today at IEDM 2016 in San Francisco in the paper, “Experimental Demonstration of Short and Long Term Synaptic Plasticity Using OxRAM Multi k-bit Arrays for Reliable Detection in Highly Noisy Input Data”.

Neural systems such as the human brain exhibit various types and time periods of plasticity, e.g. synaptic modifications can last anywhere from seconds to days or months. However, prior research in utilizing synaptic plasticity using memristive devices relied primarily on simplified rules for plasticity and learning.

The project team, which includes researchers from Leti’s sister institute at CEA Tech, List, along with INSERM and Clinatec, proposed an architecture that implements both short- and long-term plasticity (STP and LTP) using RRAM devices.

“While implementing a learning rule for permanent modifications – LTP, based on spike-timing-dependent plasticity – we also incorporated the possibility of short-term modifications with STP, based on the Tsodyks/Markram model,” said Elisa Vianello, Leti non-volatile memories and cognitive computing specialist/research engineer.  “We showed the benefits of utilizing both kinds of plasticity with visual pattern extraction and decoding of neural signals. LTP allows our artificial neural networks to learn patterns, and STP makes the learning process very robust against environmental noise.”

Resistive random-access memory (RRAM) devices coupled with a spike-coding scheme are key to implementing unsupervised learning with minimal hardware footprint and low power consumption. Embedding neuromorphic learning into low-power devices could enable design of autonomous systems, such as a brain-machine interface that makes decisions based on real-time, on-line processing of in-vivo recorded biological signals. Biological data are intrinsically highly noisy and the proposed combined LTP and STP learning rule is a powerful technique to improve the detection/recognition rate. This approach may enable the design of autonomous implantable devices for rehabilitation purposes.

Leti, which has worked on RRAM to develop hardware neuromorphic architectures since 2010, is the coordinator of the H2020 European project NeuRAM3. That project is working on fabricating a chip with architecture that supports state-of-the-art machine-learning algorithms and spike-based learning mechanisms.

Leti will present 13 papers at the conference, three of which are invited.

At the 2016 IEEE International Electron Devices Meeting, in a special poster session on MRAM, world-leading research and innovation hub for nano-electronics and digital technology imec presented a 8nm p-MTJ device with 100 percent tunnel magnetoresistance (TMR) and coercive field as high 1500Oe. This world’s smallest device enables the establishment of a manufacturing process for high-density spin-transfer-torque magnetic random access memory (STT-MRAM) arrays that meet the requirements of the 10nm and beyond logic node for embedded non-volatile memory applications. It also paves the way for high density stand-alone applications.

STT-MRAM has the potential to become the first embedded non-volatile memory technology on advanced logic nodes for advanced applications and is also considered an alternative to conventional dynamic random access memory (DRAM). The core element of an STT-MRAM is a magnetic tunnel junction (MTJ) in which a thin dielectric layer is sandwiched between a magnetic reference layer and a magnetic free layer, where writing of the memory cell is performed by switching the magnetization of the free layer. STT-MRAMs exhibit non-volatility, high-speed, low-voltage switching and nearly unlimited read/write endurance. However, significant challenges towards commercialization remain, primarily in scaling the processes for higher densities and in increasing the device switching current.

In addressing these challenges, imec scientists have demonstrated for the first time an electrical functional p-MTJ device as small as 8nm. Despite the small dimensions, the device exhibits a high TMR of 100 percent, a coercivity (Hc) of 1500Oe and a spin torque efficiency -the ratio of the thermal stability and switching current- as high as three. The p-MTJ stack, featuring a free layer and reference layer of CoFeB-based multilayer stacks, was developed on 300mm silicon wafers and the fabrication process is compatible with the thermal budget of standard CMOS back-end-of-line (BEOL) technology.

Moreover, imec integrated arrays of p-MTJ devices into a 1T1MTJ structure to build STT-MRAM Megabit arrays with pitches down to 100nm, proving that the technology meets the dimensional requirements for the 10nm logic node and beyond.

Imec’s research into advanced memory is performed in cooperation with imec’s key partners in its core CMOS programs including GlobalFoundries, Micron, Qualcomm, Sony and TSMC.

Delivering a power punch


December 5, 2016

Energy storage units that can be integrated into wearable and flexible electronic systems are becoming increasingly important in today’s world. A research team from KAUST has now developed a microsupercapacitor that exploits three-dimensional porous electrodes. These micropower units are expected to enable a new generation of “smart”products, such as self-powered sensors for wearables, security, structural health monitoring and “internet of things” applications.

Three-dimensional porous electrodes could lead to smaller and efficient integrated power sources.

Three-dimensional porous electrodes could lead to smaller and efficient integrated power sources.

However, for these units to be tiny yet still efficient, the highest energy density must go into the smallest area.

One approach to carrying this out is to construct microbatteries using films with a thickness of just a few micrometers or less and to replace traditional electrolytes with solid-state ones. Thin film batteries have demonstrated relatively high energy density, which is the amount of energy they can store in a given area. However, they are afflicted by limited cycle life and poor power density, meaning they are slow to charge and discharge.

Microsupercapacitors are a faster alternative, and these may prove suitable for applications requiring power pulsing and very long cycle life.

“Also, while batteries must be charged at a constant voltage, a supercapacitor charges most efficiently by drawing the maximum current that the source can supply, irrespective of voltage,” said KAUST Professor of Material Science and Engineering Husam Alshareef from the University’s Functional Nanomaterials & Devices group.

This makes supercapacitors more appealing for self-powered system applications where the power source may be intermittent.

Alshareef’s team has now developed integrated microsupercapacitors with vertically-scaled three-dimensional porous current collectors made from nickel foams to improve microsupercapacitor performance. The pores in the foam work to increase the surface area.

“This three-dimensional porous architecture allows excellent electrolyte permeability, good conductivity and faster ion transportation with maximum mass-loading of active material, which increase energy and power density in a given area,” Alshareef said.

The microsupercapacitors were also asymmetric, using two different electrode materials for the cathode (nickel cobalt sulfide) and anode (carbon nanofiber), which nearly doubled the operating voltage. As a result, while delivering high power density (four milliwatts per square centimeter), the microsupercapacitors had an energy density of 200 microwatt-hours per square centimeter.

This is superior to state-of-the-art microsupercapacitors, which achieve between one and forty microwatt-hours per square centimeter, and is comparable to various types of thin film batteries. These high capacities were maintained even after 10,000 operating cycles.

“The high energy and power density achieve in these devices may meet the demand of on-chip storage for various types of integrated microsystems,” noted KAUST Ph.D. student Qiu Jiang, the lead author of the study.

DGIST announced that Professor Kyung-in Jang’s research team from the Department of Robotics Engineering succeeded in developing bio-signal measuring electrodes that can be mounted on Internet of Things (IoT) devices through joint research with a research team led by professor John Rogers of the University of Illinois, USA.

Optical image of bio-signal measurement electrode design developed by Professor Jang's research team. The electrode generates such a large force that it holds the circular magnet located under the glass only by attraction (gravitation) of the magnetic field. Credit: DGIST

Optical image of bio-signal measurement electrode design developed by Professor Jang’s research team. The electrode generates such a large force that it holds the circular magnet located under the glass only by attraction (gravitation) of the magnetic field. Credit: DGIST

The bio-signal measuring electrodes developed by the research team can be easily mounted on IoT devices for health diagnosis, thus they can measure bio-signals such as brain waves and electrocardiograms without additional analysis and measurement equipment while not interfering or restricting human activities.

Conventional hydro-gel based electrodes required external analysis and measurement devices to measure bio-signals due to their pulpy gel forms, which made their attachment to and detachment from IoT devices instable. In addition, since these electrodes were wet-bonded to the skin, there have been disadvantages that the characteristics of the electrodes deteriorated or their performance decreased when the electrodes were dried in the air over a long period.

In contrast, the electrodes developed by Professor Kyung-in Jang can be easily interlocked as if they are a part of IoT devices for health diagnosis. Also, since they are composed only of polymer and metal materials, they have the advantage of there being no possibility of drying in the air.

The bio-signal measurement electrodes developed by the research team consist of a composite material in which a magnetic material is folded with a soft and adhesive polymer, with a conductive electrode material wrapped around the composite material. The conductive electrode material electrically connects the bottom surface touching the skin and the top surface touching the electrode of the IoT device.

Electrodes with this structure reacting to the magnetic field can be easily attached and detached by using the attraction that occurs between the magnet and the electrode mounted on the IoT devices. Then, through the conductive electrode materials that connect the skin and the electrode part of the IoT device, the electric signals generated on the skin can be directly transmitted to the IoT device for health diagnosis.

The research team succeeded in storing and analyzing brain waves (electroencephalogram, EEG), electrocardiograms (ECG), eye movements (electrooculogram, EOG), and limb movements and muscle contractions (electromyogram, EMG) of the wearer for a long period through an experiment in which IoT devices with the electrodes are attached to various parts of the human body.

The bio-signal measurement electrodes can measure the bioelectric signal generated from the skin without loss or noise by using the IoT platform, thus they are expected to be applicable to the medical and healthcare fields since they cannot only measure the electrical signals of the body, but also analyze various forms of bio-signals such as body temperature change, skin change, and in-body ion concentration change.

Professor Kyung-in Jang said, “We have secured the source technology that can diagnose the state of human health anytime and anywhere by combining bio-electrode technology with IoT platforms utilizing advanced high-tech composite materials. We will carry out subsequent research to make it applicable for diseases that require ongoing medical diagnosis such as diabetes, insomnia, and epilepsy, and to make it available to people in medically vulnerable areas such as remote mountainous and rural areas.”