Tag Archives: letter-pulse-tech

Conventional electronics rely on controlling electric charge. Recently, researchers have been exploring the potential for a new technology, called spintronics, that relies on detecting and controlling a particle’s spin. This technology could lead to new types of more efficient and powerful devices.

In a paper published in Applied Physics Letters, from AIP Publishing, researchers measured how strongly a charge carrier’s spin interacts with a magnetic field in diamond. This crucial property shows diamond as a promising material for spintronic devices.

Diamond is attractive because it would be easier to process and fabricate into spintronic devices than typical semiconductor materials, said Golrokh Akhgar, a physicist at La Trobe University in Australia. Conventional quantum devices are based on multiple thin layers of semiconductors, which require an elaborate fabrication process in an ultrahigh vacuum.

“Diamond is normally an extremely good insulator,” Akhgar said. But, when exposed to hydrogen plasma, the diamond incorporates hydrogen atoms into its surface. When a hydrogenated diamond is introduced to moist air, it becomes electrically conductive because a thin layer of water forms on its surface, pulling electrons from the diamond. The missing electrons at the diamond surface behave like positively charged particles, called holes, making the surface conductive.

Researchers found that these holes have many of the right properties for spintronics. The most important property is a relativistic effect called spin-orbit coupling, where the spin of a charge carrier interacts with its orbital motion. A strong coupling enables researchers to control the particle’s spin with an electric field.

In previous work, the researchers measured how strongly a hole’s spin-orbit coupling could be engineered with an electric field. They also showed that an external electric field could tune the strength of the coupling.

In recent experiments, the researchers measured how strongly a hole’s spin interacts with a magnetic field. For this measurement, the researchers applied constant magnetic fields of different strengths parallel to the diamond surface at temperatures below 4 Kelvin. They also simultaneously applied a steadily varying perpendicular field. By monitoring how the electrical resistance of the diamond changed, they determined the g-factor. This quantity could help researchers control spin in future devices using a magnetic field.

“The coupling strength of carrier spins to electric and magnetic fields lies at the heart of spintronics,” Akhgar said. “We now have the two crucial parameters for the manipulation of spins in the conductive surface layer of diamond by either electric or magnetic fields.”

Additionally, diamond is transparent, so it can be incorporated into optical devices that operate with visible or ultraviolet light. Nitrogen-vacancy diamonds — which contain nitrogen atoms paired with missing carbon atoms in its crystal structure — show promise as a quantum bit, or qubit, the basis for quantum information technology. Being able to manipulate spin and use it as a qubit could lead to yet more devices with untapped potential, Akhgar said.

GLOBALFOUNDRIES today announced that its 45nm RF SOI (45RFSOI) technology platform has been qualified and is ready for volume production. Several customers are currently engaged for this advanced RF SOI process, which is targeted for 5G millimeter-wave (mmWave) front-end module (FEM) applications, including smartphones and next-generation mmWave beamforming systems in future base stations.

As next-generation systems move to frequencies above 24GHz, higher performance RF silicon solutions are required to exploit the large available bandwidth in the mmWave spectrum. GF’s 45RFSOI platform is optimized for beam forming FEMs, with features that improve RF performance through combining high-frequency transistors, high-resistivity silicon-on-insulator (SOI) substrates and ultra-thick copper wiring. Moreover, the SOI technology enables easy integration of power amplifiers, switches, LNAs, phase shifters, up/down converters and VCO/PLLs that lowers cost, size and power compared to competing technologies targeting tomorrow’s multi-gigabit-per-second communication systems, including internet broadband satellite, smartphones and 5G infrastructure.

“GF’s leadership in RF SOI solutions makes the company a perfect strategic partner for Peregrine’s next generation of RF SOI technologies,” said Jim Cable, Chairman and CTO of Peregrine Semiconductor. “It enables us to create RF solutions that provide our customers with new levels of product performance, reliability and scalability, and it allows us to push the envelope of integrated RF front-end innovation for evolving mmWave applications and emerging 5G markets.”

“To bring 5G into the future, mmWave innovations are needed for allocating more bandwidth to deliver faster, higher-quality video, and multimedia content and services,” Bob Donahue, CEO of Anokiwave. “GF’s RF SOI technology leadership and 45RFSOI platform enables Anokiwave to develop differentiated solutions designed to operate between the mmWave and sub-6GHz frequency band for high-speed wireless communications and networks.”

“GF continues to expand its RF capabilities and portfolio to provide competitive RF SOI advantages and manufacturing excellence that will enable our customers to play a critical role in bringing 5G devices and networks to real-world environments,” said Bami Bastani, senior vice president of the RF Business Unit at GF.  “Our 45RFSOI is an ideal technology for customers that are looking to deliver the highest- performing mmWave solutions that will handle demanding performance requirements in next-generation mobile and 5G communications.”

GF’s RF SOI solutions are part of the company’s vision to develop and deliver the next wave of 5G technology aimed at enabling connected intelligence for next-generation devices, networks and wired/wireless systems. GF has a successful track record in manufacturing RF SOI solutions at its 300mm production line in East Fishkill, N.Y.  Customers can now start optimizing their chip designs to develop differentiated solutions for high performance in the RF front end for 5G and mmWave applications.

Researchers have identified a mechanism that triggers shape-memory phenomena in organic crystals used in plastic electronics. Shape-shifting structural materials are made with metal alloys, but the new generation of economical printable plastic electronics is poised to benefit from this phenomenon, too. Shape-memory materials science and plastic electronics technology, when merged, could open the door to advancements in low-power electronics, medical electronics devices and multifunctional shape-memory materials.

The findings are published in the journal Nature Communications and confirm the shape-memory phenomenon in two organic semiconductors materials.

Illinois chemistry and biomolecular engineering professor Ying Diao, right, and graduate student Hyunjoong Chung are part of a team that has identified a mechanism that triggers shape-memory in organic crystals used in plastic electronics. Credit: L. Brian Stauffer

Illinois chemistry and biomolecular engineering professor Ying Diao, right, and graduate student Hyunjoong Chung are part of a team that has identified a mechanism that triggers shape-memory in organic crystals used in plastic electronics. Credit: L. Brian Stauffer

Devices like the expandable stents that open and unblock clogged human blood vessels use shape-memory technology. Heat, light and electrical signals, or mechanic forces pass information through the devices telling them to expand, contract, bend and morph back into their original form – and can do so repeatedly, like a snake constricting to swallow its dinner. This effect works well with metals, but remains elusive in synthetic organic materials because of the complexity of the molecules used to create them.

“The shape-memory phenomenon is common in nature, but we are not really sure about nature’s design rules at the molecular level,” said professor of chemical and biomolecular engineering and co-author of the study, Ying Diao. “Nature uses organic compounds that are very different from the metal alloys used in shape-memory materials on the market today,” Diao said. “In naturally occurring shape-memory materials, the molecules transform cooperatively, meaning that they all move together during shape change. Otherwise, these materials would shatter and the shape change would not be reversible and ultrafast.”

The discovery of the shape-memory mechanism in synthetic organic material was quite serendipitous, Diao said. The team accidentally created large organic crystals and was curious to find out how they would transform given heat.

“We looked at the single crystals under a microscope and found that the transformation process is dramatically different than we expected,” said graduate student and co-author Hyunjoong Chung. “We saw concerted movement of a whole layer of molecules sweeping through the crystal that seem to drive the shape-memory effect – something that is rarely observed in organic crystals and is therefore largely unexplored.”

This unexpected observation led the team to want to explore the merger between shape-memory materials science and the field of organic electronics, the researchers said. “Today’s electronics are dependent on transistors to switch on and off, which is a very energy-intensive process,” Diao said. “If we can use the shape-memory effect in plastic semiconductors to modulate electronic properties in a cooperative manner, it would require very low energy input, potentially contributing to advancements in low-power and more efficient electronics.”

The team is currently using heat to demonstrate the shape-memory effect, but are experimenting with light waves, electrical fields and mechanical force for future demonstrations. They are also exploring the molecular origin of the shape-memory mechanism by tweaking the molecular structure of their materials. “We have already found that changing just one atom in a molecule can significantly alter the phenomenon,” Chung said.

The researchers are very excited about the molecular cooperativity aspect discovered with this research and its potential application to the recent Nobel Prize-winning concept of molecular machines, Diao said. “These molecules can change conformation cooperatively at the molecular level, and the small molecular structure change is amplified over millions of molecules to actuate large motion at the macroscopic scale.”

Accurately measuring electric fields is important in a variety of applications, such as weather forecasting, process control on industrial machinery, or ensuring the safety of people working on high-voltage power lines. Yet from a technological perspective, this is no easy task.

In a break from the design principle that has been followed by all other measuring devices to date, a research team at TU Wien has now developed a silicon-based sensor as a microelectromechanical system (MEMS). Devised in conjunction with the Department for Integrated Sensor Systems at Danube University Krems, this sensor has the major advantage that it does not distort the very electric field it is currently measuring. An introduction to the new sensor has also been published in the electronics journal “Nature Electronics”.

Tiny new sensor -- compared to a one-cent-coin. Credit: TU Wien

Tiny new sensor — compared to a one-cent-coin. Credit: TU Wien

Distorting measuring devices

“The equipment currently used to measure electric field strength has some significant downsides,” explains Andreas Kainz from the Institute of Sensor and Actuator Systems (Faculty of Electrical Engineering, TU Wien). “These devices contain parts that become electrically charged. Conductive metallic components can significantly alter the field being measured; an effect that becomes even more pronounced if the device also has to be grounded to provide a reference point for the measurement.” Such equipment also tends to be relatively impractical and difficult to transport.

The sensor developed by the team at TU Wien is made from silicon and is based on a very simple concept: small, grid-shaped silicon structures measuring just a few micrometres in size are fixed onto a small spring. When the silicon is exposed to an electric field, a force is exerted on the silicon crystals, causing the spring to slightly compress or extend.

These tiny movements now need to be made visible, for which an optical solution has been designed: an additional grid located above the movable silicon grid is lined up so precisely that the grid openings on one grid are concealed by the other. When an electric field is present, the movable structure moves slightly out of perfect alignment with the fixed grid, allowing light to pass through the openings. This light is measured, from which the strength of the electric field can be calculated by an appropriately calibrated device.

Prototype achieves impressive levels of precision

The new silicon sensor does not measure the direction of the electric field, but its strength. It can be used for fields of a relatively low frequency of up to one kilohertz. “Using our prototype, we have been able to reliably measure weak fields of less than 200 volts per metre,” says Andreas Kainz. “This means our system is already performing at roughly the same level as existing products, even though it is significantly smaller and much simpler.” And there is still a great deal of potential for improvement, too: “Other methods of measurement are already mature approaches – we are just starting out. In future it will certainly be possible to achieve even significantly better results with our microelectromechanical sensor,” adds Andreas Kainz confidently.

Imec today announced that it will demonstrate its very first shortwave infrared (SWIR) range hyperspectral imaging camera at next week’s SPIE Photonics West in San Francisco. The SWIR range provides discriminatory information on all kinds of materials, paving the way to hyperspectral imaging applications in food sorting, waste management, machine vision, precision agriculture and medical diagnostics. Imec’s SWIR camera integrates CMOS-based spectral filters together with InGaAs-based imagers, thus combining the compact and low-cost capabilities of CMOS technology with the spectral range of InGaAs.

Semiconductor CMOS-based hyperspectral imaging filters, as designed and manufactured by imec for the past five years, have been utilized in a manner where they are integrated monolithically onto silicon-based CMOS image sensors, which has a sensitivity range from 400 – 1000 nm visible and near-IR (VNIR) range. However, it is expected that more than half of commercial multi and hyperspectral imaging applications need discriminative spectral data in the 1000 – 1700 nm SWIR range.

“SWIR range is key for hyperspectral imaging as it provides extremely valuable quantitative information about water, fatness, lipid and protein content of organic and inorganic matters like food, plants, human tissues, pharmaceutical powders, as well as key discriminatory characteristics about plastics, paper, wood and many other material properties,” commented Andy Lambrechts, program manager for integrated imaging activities at imec. “It was a natural evolution for imec to extend its offering into the SWIR range while leveraging its core capabilities in optical filter design and manufacturing, as well as its growing expertise in designing compact, low-cost and robust hyperspectral imaging system solutions to ensure this complex technology delivers on its promises.”

Imec’s initial SWIR range hyperspectral imaging cameras feature both linescan ‘stepped filter’ designs with 32 to 100 or more spectral bands, as well as snapshot mosaic solutions enabling the capture of 4 to 16 bands in real-time at video-rate speeds. Cameras with both USB3.0 and GIGE interface are currently in the field undergoing qualification with strategic partners.

“The InGaAs imager industry is at a turning point,” explained Jerome Baron, business development manager of integrated imaging and vision systems at imec. “As the market recognizes the numerous applications of SWIR range hyperspectral imaging cameras beyond its traditional military, remote sensing and scientific niche fields, the time is right for organizations such as imec to enable compact, robust and low-cost hyperspectral imaging cameras in the SWIR range too. Imec’s objectives will be to advance this offering among the most price sensitive volume markets for this technology which include food sorting, waste management and recycling, industrial machine vision, precision agriculture and medical diagnostics.”

The first SWIR range hyperspectral imaging cameras will be demonstrated through Feb. 1 at SPIE Photonics West, booth #4321 in the North Hall of Moscone center in San Francisco.

For the first time an international research group has revealed the core mechanism that limits the indium (In) content in indium gallium nitride ((In, Ga)N) thin films – the key material for blue light emitting diodes (LED). Increasing the In content in InGaN quantum wells is the common approach to shift the emission of III-Nitride based LEDs towards the green and, in particular, red part of the optical spectrum, necessary for the modern RGB devices. The new findings answer the long-standing research question: why does this classical approach fail, when we try to obtain efficient InGaN-based green and red LEDs?

This is a scanning transmission electron microscopy image of the atomic ordering in (In, Ga)N monolayer: single atomic column, containing only indium (In) atoms (shown by higher intensity on the image), followed by two, containing only gallium (Ga) atoms. Credit: IKZ Berlin

This is a scanning transmission electron microscopy image of the atomic ordering in (In, Ga)N monolayer: single atomic column, containing only indium (In) atoms (shown by higher intensity on the image), followed by two, containing only gallium (Ga) atoms. Credit: IKZ Berlin

Despite the progress in the field of green LEDs and lasers, the researchers could not overcome the limit of 30% of indium content in the films. The reason for that was unclear up to now: is it a problem of finding the right growth conditions or rather a fundamental effect that cannot be overcome? Now, an international team from Germany, Poland and China has shed new light on this question and revealed the mechanism responsible for that limitation.

In their work the scientists tried to push the indium content to the limit by growing single atomic layers of InN on GaN. However, independent on growth conditions, indium concentrations have never exceeded 25% – 30% – a clear sign of a fundamentally limiting mechanism. The researchers used advanced characterization methods, such as atomic resolution transmission electron microscope (TEM) and in-situ reflection high-energy electron diffraction (RHEED), and discovered that, as soon as the indium content reaches around 25 %, the atoms within the (In, Ga)N monolayer arrange in a regular pattern – single atomic column of In alternates with two atomic columns of Ga atoms. Comprehensive theoretical calculations revealed that the atomic ordering is induced by a particular surface reconstruction: indium atoms are bonded with four neighboring atoms, instead of expected three. This creates stronger bonds between indium and nitrogen atoms, which, on one hand, allows to use higher temperatures during the growth and provides material with better quality. On the other hand, the ordering sets the limit of the In content of 25%, which cannot be overcome under realistic growth conditions.

“Apparently, a technological bottleneck hampers all the attempts to shift the emission from the green towards the yellow and the red regions of the spectra. Therefore, new original pathways are urgently required to overcome these fundamental limitations,” states Dr. Tobias Schulz, scientist at the Leibniz-Institut fuer Kristallzuechtung; “for example, growth of InGaN films on high quality InGaN pseudo-substrates that would reduce the strain in the growing layer.”

However, the discovery of ordering may help to overcome well known limitations of the InGaN material system: localization of charge carriers due to fluctuations in the chemical composition of the alloy. Growing stable ordered (In, Ga)N alloys with the fixed composition at high temperatures could thus improve the optical properties of devices.

Illinois researchers have demonstrated that sound waves can be used to produce ultraminiature optical diodes that are tiny enough to fit onto a computer chip. These devices, called optical isolators, may help solve major data capacity and system size challenges for photonic integrated circuits, the light-based equivalent of electronic circuits, which are used for computing and communications.

Isolators are nonreciprocal or “one-way” devices similar to electronic diodes. They protect laser sources from back reflections and are necessary for routing light signals around optical networks. Today, the dominant technology for producing such nonreciprocal devices requires materials that change their optical properties in response to magnetic fields, the researchers said.

“There are several problems with using magnetically responsive materials to achieve the one-way flow of light in a photonic chip,” said mechanical science and engineering professor and co-author of the study Gaurav Bahl. “First, industry simply does not have good capability to place compact magnets on a chip. But more importantly, the necessary materials are not yet available in photonics foundries. That is why industry desperately needs a better approach that uses only conventional materials and avoids magnetic fields altogether.”

In a study published in the journal Nature Photonics, the researchers explain how they use the minuscule coupling between light and sound to provide a unique solution that enables nonreciprocal devices with nearly any photonic material.

However, the physical size of the device and the availability of materials are not the only problems with the current state of the art, the researchers said.

“Laboratory attempts at producing compact magnetic optical isolators have always been plagued by large optical loss,” said graduate student and lead author Benjamin Sohn. “The photonics industry cannot afford this material-related loss and also needs a solution that provides enough bandwidth to be comparable to the traditional magnetic technique. Until now, there has been no magnetless approach that is competitive.”

The new device is only 200 by 100 microns in size – about 10,000 times smaller than a centimeter squared – and made of aluminum nitride, a transparent material that transmits light and is compatible with photonics foundries. “Sound waves are produced in a way similar to a piezoelectric speaker, using tiny electrodes written directly onto the aluminum nitride with an electron beam. It is these sound waves that compel light within the device to travel only in one direction. This is the first time that a magnetless isolator has surpassed gigahertz bandwidth,” Sohn said.

The researchers are looking for ways to increase bandwidth or data capacity of these isolators and are confident that they can overcome this hurdle. Once perfected, they envision transformative applications in photonic communication systems, gyroscopes, GPS systems, atomic timekeeping and data centers.

“Data centers handle enormous amounts of internet data traffic and consume large amounts of power for networking and for keeping the servers cool,” Bahl said. “Light-based communication is desirable because it produces much less heat, meaning that much less energy can be spent on server cooling while transmitting a lot more data per second.”

Aside from the technological potential, the researchers can’t help but be mesmerized by the fundamental science behind this advancement.

“In everyday life, we don’t see the interactions of light with sound,” Bahl said. “Light can pass through a transparent pane of glass without doing anything strange. Our field of research has found that light and sound do, in fact, interact in a very subtle way. If you apply the right engineering principles, you can shake a transparent material in just the right way to enhance these effects and solve this major scientific challenge. It seems almost magical.”

Micron Technology, Inc. (Nasdaq:MU) today launched the Micron 5200 series of SATA solid state drives (SSDs), maintaining performance, consistency, capacity, reliability, and overall infrastructure value. Built on Micron’s new 64-layer 3D NAND technology, the Micron 5200 series of SSDs offers a cost-optimized SATA platform for business-critical virtualized workloads that cripple on a hard drive, such as OLTP, BI/DSS, VDI, block/object and media streaming.

Leveraging the proven architecture, performance and capacity of the well-regarded 5100 SATA SSDs, the Micron 5200 series is engineered to deliver a fast, easy and cost-effective enterprise storage solution to replace existing hard drives and legacy SSDs. Micron 5200 SSDs immediately deliver better total cost of ownership and improve data center efficiency through server and storage platform consolidation, reducing IT costs and simplifying infrastructure and maintenance. Now it is easier than ever before for enterprises to add more flash into the data center and get more out of server deployments.

As the first SATA enterprise SSD available with 64-layer 3D NAND technology, the Micron 5200 SSDs deliver improved densities, throughput, consistency, and power efficiency — all at a better value. The quality of an SSD depends on the NAND it’s built on, and the Micron 5200 series of SSDs is engineered to deliver improved reliability with the industry’s lowest annualized drive failure rate for SATA enterprise SSDs according to data sheet specifications, offering better value with Micron’s known silicon-to-system quality advantage.

“Micron 5200 SSDs unleash market-leading performance, capacity and reliability, paired with a rich feature set and unprecedented flexibility, adding up to the ideal storage solution for business-critical workloads,” said Micron Storage Business Unite Vice President and General Derek Dicker. “We simplified the server qualification process by leveraging the same foundational architecture that’s currently available on Micron SATA SSDs. Customers can trust the same proven controller and firmware design while taking advantage of advanced flash media for better performance, quality of service, and value.”

“Today’s business-critical, virtualized workloads simply cannot run at peak, consistent performance on yesterday’s technology,” said Dedicated Computing Senior Vice President Sales and Marketing Dave Guzzi. “Customers need advanced storage technology to achieve better performance and reliability — and a lower total cost of ownership. Fortunately, Micron offers all this along with the ease of a common platform that leverages the same proven controller and firmware design as previous SSD generations.”

“It says a lot that Micron chose to release its next-generation SSD based on the architecture of its prior generation while only changing the NAND from 32-layer to 64-layer technology,” said Jim Handy of Objective Analysis. “This shows that the company and its customers are pleased with the performance and reliability of the earlier 5100 series and are open to migrating to a new flash technology in a way that minimizes requalification costs.”

Join the SOLID Storage Revolution

Built on Micron’s industry-leading 64-layer 3D NAND technology for enterprise SATA SSDs, the Micron 5200 series of SSDs accelerates applications that need faster, more consistent performance, while offering overall infrastructure value and quality of service (QoS) at an improved total cost of ownership. Optimized for latency-sensitive, read-intensive workloads, these new SATA SSDs minimize storage bottlenecks with faster, predictable performance, making the move from hard drives to SSDs easier than ever before. Key features include:

  • Quality of Service — The Micron 5200 SSDs deliver extremely efficient QoS, offering up to 99.7 percent better QoS when compared to a mission-critical hard disk drive.1
  • Unmatched Capacity — Micron 5200 SSDs offer the industry’s broadest SATA portfolio with capacities up to 7.68TB, twice the capacity of other SSDs on the market.
  • Leading Performance — Engineered for fast random IO performance that fuels virtualized applications, Micron 5200 SSDs deliver up to 95k IOPS random reads and best-in-class 33,000 random writes, delivering strong performance in both areas. The drive is also highly flexible, as data center managers can use the innovative Flex Capacity feature to adjust the drive’s endurance, performance, and capacity to meet ever-changing workload demands.
  • Leader in MTTF Offering — Micron 5200 SSD data sheet specifications offer a mean time to failure (MTTF) of 3 million device hours, compared to the industry average for SATA enterprise SSD specifications of 2 million hours MTTF.
  • Easy to Manage — A fast, easy, affordable way to extend the life of existing server deployments, Micron 5200 SSDs are hot-swappable, easy to install, and only take minutes to configure, saving both time and money on setup and maintenance.

The Micron 5200 series of SSDs offers varying levels of performance and endurance to meet the diverse needs of low-latency, read-intensive workloads. Visit the Micron 5200 series SSD product flyer for additional information on the feature and function advantages. Micron 5200 SSDs are designed to replace 10K RPM hard drives and help IT managers deliver better performance and capacity – all while using less power. As an example, in an OLTP workload environment, a single Micron SSD allows you to get 3X more IOPS performance than an entire rack of 24 10K RPM hard drives.

  • 5200 ECO SATA SSD — Scale storage with fast, vast, built-to-last SSDs. Scale data center capabilities easily and efficiently. With capacities up to 7.68TB in a 2.5″ form factor, the Micron 5200 ECO SSD meets and surpasses the capacity per unit of rack space and cost advantages that had been previously owned by HDDs. Specially designed for read-intensive workloads, the Micron 5200 ECO SSD provides cloud services and content sharing companies a reliable, easy-to-deploy SATA storage solution that works within existing infrastructure deployment models to deliver radically faster performance than an HDD − and a significantly better value.
  • 5200 PRO SATA SSD — An all-purpose drive to power read-intensive workload demands. Micron 5200 PRO SSDs are an all-purpose drive to power read-intensive workloads that require higher random write performance and endurance. The Micron 5200 PRO is quick to respond and deliver on the unforecasted demand of today’s application workloads, including burst-driven transaction waves or sudden high volume web traffic. For IT administrators needing to ensure fast data throughput to keep their business running smoothly at all times, the Micron 5200 PRO SSD is a known storage workhorse and is engineered to deliver consistently fast, leading performance.

Micron 5200 SSDs are available now for OEM qualification and for purchase through distributors, such as ASI, Avnet, CDW, Ingram, Microland, WPG-Americas, Synnex and others.

One of the big challenges in computer architecture is integrating storage, memory and processing in one unit. This would make computers faster and more energy efficient. University of Groningen physicists have taken a big step towards this goal by combining a niobium doped strontium titanate (SrTiO3) semiconductor with ferromagnetic cobalt. At the interface, this creates a spin-memristor with storage abilities, paving the way for neuromorphic computing architectures. The results were published on 22 January in Scientific Reports.

The device developed by the physicists combines the memristor effect of semiconductors with a spin-based phenomenon called tunnelling anisotropic magnetoresistance (TAMR) and works at room temperature. The SrTiO3 semiconductor has a non-volatile variable resistance when interfaced with cobalt: an electric field can be used to change it from low to high resistance and back. This is known as the electroresistance effect.

Tunability

Furthermore, when a magnetic field was applied across the same interface, in and out of the plane of the cobalt, this showed a tunablity of the TAMR spin voltage by 1.2 mV. This coexistence of both a large change in the value of TAMR and electroresistance across the same device at room temperature has not previously been demonstrated in other material systems.

‘This means we can store additional information in a non-volatile way in the memristor, thus creating a very simple and elegant integrated spin-memristor device that operates at room temperature’, explains Professor of Spintronics of Functional Materials Tamalika Banerjee. She works at the Zernike Institute for Advanced Materials at the University of Groningen. So far, attempts to combine spin-based storage, memory and computing have been hampered by a complex architecture in addition to other factors.

Brain

The key to the success of the Banerjee group device is the interface between cobalt and the semiconductor. ‘We have shown that a one-nanometre thick insulating layer of aluminium oxide makes the TAMR effect disappear’, says Banerjee. It took quite some work to engineer the interface. They did so by adjusting the niobium doping of the semiconductor and thus the potential landscape at the interface. The same coexistence can’t be realized with silicon as a semiconductor: ‘You need the heavy atoms in SrTiO3 for the spin orbit coupling at the interface that is responsible for the large TAMR effect at room temperature.’

These devices could be used in a brain-like computer architecture. They would act like the synapses that connect the neurons. The synapse responds to an external stimulus, but this response also depends on the synapse’s memory of previous stimuli. ‘We are now considering how to create a bio-inspired computer architecture based on our discovery.’ Such a system would move away from the classical Von Neumann architecture. The big advantage is that it is expected to use less energy and thus produce less heat. ‘This will be useful for the “Internet of Things”, where connecting different devices and networks generates unsustainable amounts of heat.’

Energy efficiency

The physics of what exactly happens at the interface of cobalt and the strontium semiconductor is complicated, and more work needs to be done to understand this. Banerjee: ‘Once we understand it better, we will be able to improve the performance of the system. We are currently working on that. But it works well as it is, so we are also thinking of building a more complex system with such spin-memristors to test actual algorithms for specific cognition capabilities of the human brain.’ Banerjee’s device is relatively simple. Scaling it up to a full computing architecture is the next big step.

How to integrate these devices in a parallel computing architecture that mimics the working of the brain is a question that fascinates Banerjee. ‘Our brain is a fantastic computer, in the sense that it can process vast amounts of information in parallel with an energy efficiency that is far superior to that of a supercomputer.’ Banerjee’s team’s findings could lead to new architectures for brain-inspired computing.

Sometimes it pays to be two-dimensional. The merits of graphene, a 2D sheet of carbon atoms, are well established. In its wake have followed a host of “post-graphene materials” – structural analogues of graphene made of other elements like silicon or germanium.

Now, an international research team led by Nagoya University (Japan) involving Aix-Marseille University (France), the Max Planck Institute in Hamburg (Germany) and the University of the Basque country (Spain) has unveiled the first truly planar sample of stanene: single sheets of tin (Sn) atoms. Planar stanene is hotly tipped as an extraordinary electrical conductor for high technology.

High-resolution STM image of stanene prepared on a Ag2Sn surface alloy. The honeycomb stanene structure model is superimposed. Credit: Junji Yuhara

High-resolution STM image of stanene prepared on a Ag2Sn surface alloy. The honeycomb stanene structure model is superimposed. Credit: Junji Yuhara

Just as graphene differs from ordinary graphite, so does stanene behave very differently to humble tin in bulk form. Because of relatively strong spin-orbit interactions for electrons in heavy elements, single-layer tin is predicted to be a “topological insulator,” also known as a quantum spin Hall (QSH) insulator. Materials in this remarkable class are electrically insulating in their interiors, but have highly conductive surfaces/edges. This, in theory, makes a single-layered topological insulator an ideal wiring material for nanoelectronics. Moreover, the highly conductive channels at the edge of these materials can carry special chiral currents with spins locked with transport directions, which makes them also very appealing for spintronics applications.

In previous studies, where stanene was grown on substrates of bismuth telluride or antimony, the tin layers turned out to be highly buckled and relatively inhomogeneous. The Nagoya team instead chose silver (Ag) as their host – specifically, the Ag(111) crystal facet, whose lattice constant is slightly larger than that of the freestanding stanene, leading to the formation of flattened tin monolayer in a large area, one step closer to the scalable industrial applications.

Individual tin atoms were slowly deposited onto silver, known as epitaxial growth. Crucially, the stanene layer did not form directly on top of the silver surface. Instead, as shown by core-level spectroscopy, the first step was the formation of a surface alloy (Ag2Sn) between the two species. Then, another round of tin deposition produced a layer of pure, highly crystalline stanene atop the alloy. Tunneling microscopy shows striking images of a honeycomb lattice of tin atoms, illustrating the hexagonal structure of stanene.

The alloy guaranteed the flatness of the tin layer, as confirmed by density-functional theory calculations. Junji Yuhara, lead author of an article by the team published in 2D Materials, explains: “Stanene follows the crystalline periodicity of the Ag2Sn surface alloy. Therefore, instead of buckling as it would in isolation, the stanene layer flattens out – at the cost of a slight strain – to maximize contact with the alloy beneath.” This mutual stabilization between stanene and host not only keeps the stanene layers impeccably flat, but lets them grow to impressive sizes of around 5,000 square nanometers.

Planar stanene has exciting prospects in electronics and computing. “The QSH effect is rather delicate, and most topological insulators only show it at low temperatures”, according to project team leader Guy Le Lay at Aix-Marseille University. “However, stanene is predicted to adopt a QSH state even at room temperature and above, especially when functionalized with other elements. In the future, we hope to see stanene partnered up with silicene in computer circuitry. That combination could drastically speed up computational efficiency, even compared with the current cutting-edge technology.”