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Engineering and physics researchers at North Carolina State University have developed a new technology for steering light that allows for more light input and greater efficiency – a development that holds promise for creating more immersive augmented-reality display systems.

At issue are diffraction gratings, which are used to manipulate light in everything from electronic displays to fiber-optic communication technologies.

“Until now, state-of-the-art diffraction gratings configured to steer visible light to large angles have had an angular acceptance range, or bandwidth, of about 20 degrees, meaning that the light source has to be directed into the grating within an arc of 20 degrees,” says Michael Escuti, a professor of electrical and computer engineering at NC State and corresponding author of a paper on the work. “We’ve developed a new grating that expands that window to 40 degrees, allowing light to enter the grating from a wider range of input angles.

“The practical effect of this – in augmented-reality displays, for example – would be that users would have a greater field of view; the experience would be more immersive,” says Escuti, who is also the chief science officer of ImagineOptix Corp., which funded the work and has licensed the technology.

The new grating is also significantly more efficient.

“In previous gratings in a comparable configuration, an average of 30 percent of the light input is being diffracted in the desired direction,” says Xiao Xiang, a Ph.D. student at NC State and lead author of the paper. “Our new grating diffracts about 75 percent of the light in the desired direction.”

This advance could also make fiber-optic networks more energy efficient, the researchers say.

The new grating achieves the advance in angular bandwidth by integrating two layers, which are superimposed in a way that allows their optical responses to work together. One layer contains molecules that are arranged at a “slant” that allows it to capture 20 degrees of angular bandwidth. The second layer is arranged at a different slant, which captures an adjacent 20 degrees of angular bandwidth.

The higher efficiency stems from a smoothly varying pattern in the orientation of the liquid crystal molecules in the grating. The pattern affects the phase of the light, which is the mechanism responsible for redirecting the light.

“The next step for this work is to take the advantages of these gratings and make a new generation of augmented-reality hardware,” Escuti says.

The paper, “Bragg polarization gratings for wide angular bandwidth and high efficiency at steep deflection angles,” is published in the journal Scientific Reports. The paper was co-authored by Jihwan Kim, a research assistant professor of electrical and computer engineering at NC State.

In the wake of its recent discovery of a flat form of gallium, an international team led by scientists from Rice University has created another two-dimensional material that the researchers said could be a game changer for solar fuel generation. Rice materials scientist Pulickel Ajayan and colleagues extracted 3-atom-thick hematene from common iron ore. The research was introduced in a paper today in Nature Nanotechnology.

Hematene may be an efficient photocatalyst, especially for splitting water into hydrogen and oxygen, and could also serve as an ultrathin magnetic material for spintronic-based devices, the researchers said.

“2D magnetism is becoming a very exciting field with recent advances in synthesizing such materials, but the synthesis techniques are complex and the materials’ stability is limited,” Ajayan said. “Here, we have a simple, scalable method, and the hematene structure should be environmentally stable.”

Ajayan’s lab worked with researchers at the University of Houston and in India, Brazil, Germany and elsewhere to exfoliate the material from naturally occurring hematite using a combination of sonication, centrifugation and vacuum-assisted filtration.

Hematite was already known to have photocatalytic properties, but they are not good enough to be useful, the researchers said.

“For a material to be an efficient photocatalyst, it should absorb the visible part of sunlight, generate electrical charges and transport them to the surface of the material to carry out the desired reaction,” said Oomman Varghese, a co-author and associate professor of physics at the University of Houston.

“Hematite absorbs sunlight from ultraviolet to the yellow-orange region, but the charges produced are very short-lived. As a result, they become extinct before they reach the surface,” he said.

Hematene photocatalysis is more efficient because photons generate negative and positive charges within a few atoms of the surface, the researchers said. By pairing the new material with titanium dioxide nanotube arrays, which provide an easy pathway for electrons to leave the hematene, the scientists found they could allow more visible light to be absorbed.

The researchers also discovered that hematene’s magnetic properties differ from those of hematite. While native hematite is antiferromagnetic, tests showed that hematene is ferromagnetic, like a common magnet. In ferromagnets, atoms’ magnetic moments point in the same direction. In antiferromagnets, the moments in adjacent atoms alternate.

Unlike carbon and its 2D form, graphene, hematite is a non-van der Waals material, meaning it’s held together by 3D bonding networks rather than non-chemical and comparatively weaker atomic van der Waals interactions.

“Most 2D materials to date have been derived from bulk counterparts that are layered in nature and generally known as van der Waals solids,” said co-author Professor Anantharaman Malie Madom Ramaswamy Iyer of the Cochin University of Science and Technology, India. “2D materials from bulk precursors having (non-van der Waals) 3D bonding networks are rare, and in this context hematene assumes great significance.”

According to co-author Chandra Sekhar Tiwary, a former postdoctoral researcher at Rice and now an assistant professor at the Indian Institute of Technology, Gandhinagar, the collaborators are exploring other non-van der Waals materials for their 2D potential.

For years, manufacturers have offered computers with increasing amounts of memory packed into smaller devices. But semiconductor companies can’t reduce the size of memory components as quickly as they used to, and current designs are not energy-efficient. Conventional memory devices use transistors and rely on electric fields to store and read out information. An alternative approach being heavily investigated uses magnetic fields to store information. One promising version of magnetic device relies on the magnetoelectric effect which allows an electric field to switch the magnetic properties of the devices. Existing devices, however, tend to require large magnetic and electric fields that are difficult to produce and contain.

One potential solution for this problem is a new switching element made from chromia (Cr2O3), which, one day, may be used in computer memory and flash drives. “The device has better potential for scaling, so it could be made smaller, and would use less energy once it’s suitably refined,” said Randall Victora, a researcher at the University of Minnesota and an author on the paper. The researchers report their findings in Applied Physics Letters, from AIP Publishing.

Computer memory is composed of switching elements, tiny devices that can switch on and off to store bits of information as ones and zeros. Previous researchers discovered that chromia’s magnetoelectric properties means it can be “switched” with only an electric field, but switching requires the presence of a static magnetic field. Building on these elements, Victora and Rizvi Ahmed have created a design for a memory device with a heart of chromia that does not require any externally applied magnetic field to operate.

Their design surrounds the chromia with magnetic material. This provides an effective magnetic field through quantum mechanical coupling to Cr magnetic moments, while allowing devices to be arranged in a way that blocks stray magnetic fields from affecting nearby devices. An element to read out the state of the device, to determine if it’s in one or zero state, is placed on top of the device. This could potentially pack more memory into a smaller space because the interface between the chromia and the magnet is the key to the coupling that makes the device function. As the device shrinks, the greater surface area of the interface relative to its volume improves the operation. This property is an advantage over conventional semiconductors, where increases in surface area as size shrinks lead to greater charge leakage and heat loss.

Next, Victora and Ahmed aim to collaborate with colleagues who work with chromia to build and test the device. If successfully fabricated, then the new device could potentially replace dynamic random access memory in computers.

“DRAM is a huge market. It provides the fast memory inside the computer, but the problem is that it leaks a lot of charge, which makes it very energy-inefficient,” Victora said. DRAM is also volatile, so information disappears once the power source is interrupted, like when a computer crash erases an unsaved document. This device, as described in the paper, would be nonvolatile.

However, such a memory device will likely take years to perfect. One significant barrier is the device’s heat tolerance. Computers generate a lot of heat, and modeling predicts that the device would stop functioning around 30 degrees Celsius, the equivalent of a hot summer day. Optimizing the chromia, perhaps by doping it with other elements, may improve its functioning and make it more suitable to replace existing memory devices.

 

In a Nature Communications paper published this week (https://rdcu.be/MYO6), imec, the world-leading research and innovation hub in nano-electronics and digital technology, describes a new concept for direct identification of single DNA bases. The technique has the potential to detect, with an unprecedented spatial resolution and without any labeling, the genetic code, as well as epigenetic variations in DNA. The combination of nanopore fluidics and surface enhanced Raman spectroscopy makes it a unique concept and a very promising tool for evolutionary biologists and for research on disease development.

Today, direct, real-time identification of nucleobases in DNA strands in nanopores is limited by the sensitivity and the spatial resolution of established ionic sensing strategies. In addition, established DNA sequencing techniques often use fluorescent labeling which is costly and time-consuming. In its Nature Communications paper, imec demonstrated a promising alternative based on optical spectroscopy, with no need for labeling and with the unique ability to identify nucleobases, individually, and incorporated in a DNA strand. The technique is based on nanofluidics to drive the DNA strand through an engineered plasmonic nanoslit, and surface enhanced Raman spectroscopy to make a ‘fingerprint’ of the adsorbed nucleobases up to the level of molecular bonds. The spectroscopic signal is enhanced both by a gold coating on top of the nanoslit, and the engineered shape of the nanoslit.  “The result reported here is an important step towards a solution for fast and direct sequencing up to the epigenetic level,” stated and Chang Chen, senior researcher at imec.

The signal generated by Raman spectroscopy holds a lot of information about the molecules and the molecular bonds. Not only can the DNA code be ‘read’, but also base modifications such as methylation, histone acetylation, and microRNA modification, which carry more detailed information about epigenetic variations. Such variations are important for evolutionary studies as they influence gene expression in cells. Moreover, they have been shown to impact the origin and development of diseases such as cancer.

“We leverage our world-class expertise in chip design and 300 mm Si wafer manufacturing technology and bio-lab facilities to develop tailored solutions for the life sciences industry,” stated Pol Van Dorpe, principal member of technical staff. “The solution we describe here is only one example of the technologies we are working on. Our toolbox includes knowledge on nanopores, spectroscopy, photonics, single-molecule detection and nanofluidics which we use in developing next-generation solutions for our industry partners in genomics and diagnostics.

Researchers at Duke University and North Carolina State University have demonstrated the first custom semiconductor microparticles that can be steered into various configurations repeatedly while suspended in water.

With an initial six custom particles that predictably interact with one another in the presence of alternating current (AC) electric fields of varying frequencies, the study presents the first steps toward realizing advanced applications such as artificial muscles and reconfigurable computer systems.

The study appears online on May 3 in the journal Nature Communications.

“We’ve engineered and encoded multiple dynamic responses in different microparticles to create a reconfigurable silicon toolbox,” said Ugonna Ohiri, a recently graduated electrical engineering doctoral student from Duke and first author of the paper. “By providing a means of controllably assembling and disassembling these particles, we’re bringing a new tool to the field of active matter.”

While previous researchers have worked to define self-assembling systems, few have worked with semiconductor particles, and none have explored the wide range of custom shapes, sizes and coatings that are available to the micro- and nanofabrication industry. Engineering particles from silicon presents the opportunity to physically realize electronic devices that can self-assemble and disassemble on demand. Customizing their shapes and sizes presents opportunities to explore a wide-ranging design space of new motile behaviors.

“Most previous work performed using self-assembling particles has been done with shapes such as spheres and other off-the-shelf materials,” said Nan Jokerst, the J. A. Jones Professor of Electrical and Computer Engineering at Duke. “Now that we can customize whatever arbitrary shapes, electrical characteristics and patterned coatings we want with silicon, a whole new world is opening up.”

In the study, Jokerst and Ohiri fabricated silicon particles of various shapes, sizes and electrical properties. In collaboration with Orlin Velev, the INVISTA Professor of Chemical and Biomolecular Engineering at NC State, they characterized how these particles responded to different magnitudes and frequencies of electric fields while submerged in water.

Based on these observations, the researchers then fabricated new batches of customized particles that were likely to exhibit the behaviors they were looking for, resulting in six different engineered silicon microparticle compositions that could move through water, synchronize their motions, and reversibly assemble and disassemble on demand.

The thin film particles are 10-micron by 20-micron rectangles that are 3.5 microns thick. They’re fabricated using Silicon-on-Insulator (SOI) technology. Since they can be made using the same fabrication technology that produces integrated circuits, millions of identical particles could be produced at a time.

“The idea is that eventually we’re going to be able to make silicon computational systems that assemble, disassemble and then reassemble in a different format,” said Jokerst. “That’s a long way off in the future, but this work provides a sense of the capabilities that are out there and is the first demonstration of how we might achieve those sorts of devices.”

That is, however, only the tip of the proverbial iceberg. Some of the particles were fabricated with both p-type and n-type regions to create p-n junctions — common electrical components that allow electricity to pass in only one direction. Tiny metal patterns were also placed on the particles’ surfaces to create p-n junction diodes with contacts. In the future, researchers could even engineer particles with patterns using other electrically conductive or insulating materials, complex integrated circuits, or microprocessors on or within the silicon.

“This work is just a small snapshot of the tools we have to control particle dynamics,” said Ohiri. “We haven’t even scratched the surface of all of the behaviors that we can engineer, but we hope that this multidisciplinary study can pioneer future studies to design artificial active materials.”

A simple method that uses hydrogen chloride can better control the crystal structure of a common semiconductor and shows promise for novel high-powered electronic applications.

The electronic components used in computers and mobile devices operate at relatively lower power. But high-power applications, such as controlling electrical power grids, require alternative materials that can cope with much higher voltages. For example, an insulating material begins to conduct electricity when the field is high enough, an effect known as electrical breakdown. For this reason, power electronics often use nitride-based semiconductors, such as gallium nitride, which have a very high breakdown field and can be epitaxially grown to create multilayered semiconductors.

However, ever-increasing energy demands and the desire to make electricity distribution more efficient requires even more electrically robust materials. Gallium oxide (Ga2O3) has a theoretical breakdown field more than twice that of gallium-nitride alloys and so has emerged as an exciting candidate for this function. The latest challenge however is a simple way to deposit high-quality gallium oxide on the substrates commonly used for power electronics, such as sapphire.

Haiding Sun, Xiaohang Li, and co-workers from KAUST worked with industry partners Structured Materials Industries, Inc. in the U.S. to demonstrate a relatively simple method to control the crystal structure of gallium oxides on a sapphire substrate using a technology known as metalorganic chemical vapor deposition (MOCVD). “We were able to control the growth by changing just one parameter: the flow rate of hydrogen chloride in the chamber,” explains Sun. “This is the first time that hydrogen chloride has been used during oxide growth in an MOCVD reactor.”

Working in a clean suit in the lab, Dr. Sun holds up a gallium-oxide template. Credit: © 2018 KAUST

Working in a clean suit in the lab, Dr. Sun holds up a gallium-oxide template. Credit: © 2018 KAUST

The atoms in gallium oxide can be arranged in a number of different forms known as polymorphs. β­­­?Ga2O3 is the most stable polymorph but is difficult to grow on substrates of other materials. ε?Ga2O3 has been grown on sapphire but its growth rate has been difficult to control.

Different polymorphs of gallium oxide can be grown in a MOCVD chamber by controlling the flow of hydrogen chloride.

Different polymorphs of gallium oxide can be grown in a MOCVD chamber by controlling the flow of hydrogen chloride.

Engineers at the University of California, Riverside, have demonstrated prototype devices made of an exotic material that can conduct a current density 50 times greater than conventional copper interconnect technology.

Current density is the amount of electrical current per cross-sectional area at a given point. As transistors in integrated circuits become smaller and smaller, they need higher and higher current densities to perform at the desired level. Most conventional electrical conductors, such as copper, tend to break due to overheating or other factors at high current densities, presenting a barrier to creating increasingly small components.

Microscopy image of an electronic device made with 1D ZrTe3 nanoribbons. The nanoribbon channel is indicated in green color. The metal contacts are shown in yellow color. Note than owing to the nanometer scale thickness the yellow metal contacts appear to be under the green channel while in reality they are on top. Credit: Balandin lab, UC Riverside

Microscopy image of an electronic device made with 1D ZrTe3 nanoribbons. The nanoribbon channel is indicated in green color. The metal contacts are shown in yellow color. Note than owing to the nanometer scale thickness the yellow metal contacts appear to be under the green channel while in reality they are on top. Credit: Balandin lab, UC Riverside

The electronics industry needs alternatives to silicon and copper that can sustain extremely high current densities at sizes of just a few nanometers.

The advent of graphene resulted in a massive, worldwide effort directed at investigation of other two-dimensional, or 2D, layered materials that would meet the need for nanoscale electronic components that can sustain a high current density. While 2D materials consist of a single layer of atoms, 1D materials consist of individual chains of atoms weakly bound to one another, but their potential for electronics has not been as widely studied.

One can think of 2D materials as thin slices of bread while 1D materials are like spaghetti. Compared to 1D materials, 2D materials seem huge.

A group of researchers led by Alexander A. Balandin, a distinguished professor of electrical and computer engineering in the Marlan and Rosemary Bourns College of Engineering at UC Riverside, discovered that zirconium tritelluride, or ZrTe3, nanoribbons have an exceptionally high current density that far exceeds that of any conventional metals like copper.

The new strategy undertaken by the UC Riverside team pushes research from two-dimensional to one-dimensional materials­­– an important advance for the future generation of electronics.

“Conventional metals are polycrystalline. They have grain boundaries and surface roughness, which scatter electrons,” Balandin said. “Quasi-one-dimensional materials such as ZrTe3consist of single-crystal atomic chains in one direction. They do not have grain boundaries and often have atomically smooth surfaces after exfoliation. We attributed the exceptionally high current density in ZrTe3 to the single-crystal nature of quasi-1D materials.”

In principle, such quasi-1D materials could be grown directly into nanowires with a cross-section that corresponds to an individual atomic thread, or chain. In the present study the level of the current sustained by the ZrTe3 quantum wires was higher than reported for any metals or other 1D materials. It almost reaches the current density in carbon nanotubes and graphene.

Electronic devices depend on special wiring to carry information between different parts of a circuit or system. As developers miniaturize devices, their internal parts also must become smaller, and the interconnects that carry information between parts must become smallest of all. Depending on how they are configured, the ZrTe3 nanoribbons could be made into either nanometer-scale local interconnects or device channels for components of the tiniest devices.

The UC Riverside group’s experiments were conducted with nanoribbons that had been sliced from a pre-made sheet of material. Industrial applications need to grow nanoribbon directly on the wafer. This manufacturing process is already under development, and Balandin believes 1D nanomaterials hold possibilities for applications in future electronics.

“The most exciting thing about the quasi-1D materials is that they can be truly synthesized into the channels or interconnects with the ultimately small cross-section of one atomic thread– approximately one nanometer by one nanometer,” Balandin said.

TowerJazz today announced the release of its 300mm 65nm BCD (Bipolar-CMOS-DMOS) process, the most advanced power management platform for up to 16V operation and 24V maximum voltage.  This technology is manufactured in TowerJazz’s Uozu, Japan facility, with best-in-class quality and cycle time, and is based on the Company’s 300mm 65nm automotive qualified flows.

This platform provides significant material competitive advantages for any type of power management chip up to 16V regardless of application, including a wide variety of products such as: PMICs, load switches, DC-DC converters, LED drivers, motor drivers, battery management, analog and digital controllers, and more. IHS Markit Power IC Analyst, Kevin Anderson forecasts a $9.4 billion available market, which this technology addresses, in 2018 with continual growth.

TowerJazz’s 65nm BCD process is leading this low voltage market segment with the highest power efficiency, very small die size, best digital integration capability; and superior cost effectiveness through both the smallest aerial footprint and the lowest mask count.

The process includes four leading edge power LDMOS transistors: 5V, 7V, 12V and 16V operation, each with the best available Rdson and Qgd parameters. In addition to the new aforementioned cost and figure of merit benchmarks, multiple chips can be integrated to a single monolithic IC solution replacing a multiple chip module for an improved system cost structure and system performance.

TowerJazz’s power transistors are fully isolated to withstand high currents, all with an ultra-low Rdson, e.g. less than 1mΩ*mm² for the 5V LDMOS. For products which operate at the megahertz (MHz) switching frequencies, the 65nm BCD power transistors benefit from a very low Qgd down to 2.6mΩ*nC. In addition, very low metal resistance is achieved using a single or dual 3.3um top thick copper. The 65nm BCD also offers aggressive 113Kgate/mm² 5V digital density and an 800Kgate/mm² 1.2V digital library.

“This new 65nm BCD platform establishes TowerJazz as a technology leader in the related growing markets for up to 16V power applications,” said Shimon Greenberg, Vice President and General Manager of Power Management & Mixed-Signal/CMOS Business Unit, TowerJazz. “Best addressing the vast low voltage power management market segment, we are experiencing very high interest from early adopter customers and plan a mass production ramp by the fourth quarter of 2018.”

TowerJazz will be exhibiting at ISPSD, the 30th IEEE International Symposium on Power Semiconductor Devices and ICs on May 13-17, 2018 in Chicago, USA.

Research appearing today in Nature Communications finds useful new information-handling potential in samples of tin(II) sulfide (SnS), a candidate “valleytronics” transistor material that might one day enable chipmakers to pack more computing power onto microchips.

Valleytronics utilizes different local energy extrema (valleys) with selection rules to store 0s and 1s. In SnS, these extrema have different shapes and responses to different polarizations of light, allowing the 0s and 1s to be directly recognized. This schematic illustrates the variation of electron energy in different states, represented by curved surfaces in space. The two valleys of the curved surface are shown. Credit: Berkeley Lab

Valleytronics utilizes different local energy extrema (valleys) with selection rules to store 0s and 1s. In SnS, these extrema have different shapes and responses to different polarizations of light, allowing the 0s and 1s to be directly recognized. This schematic illustrates the variation of electron energy in different states, represented by curved surfaces in space. The two valleys of the curved surface are shown. Credit: Berkeley Lab

The research was led by Jie Yao of the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Shuren Lin of UC Berkeley’s Department of Materials Science and Engineering and included scientists from Singapore and China. Berkeley Lab’s Molecular Foundry, a DOE Office of Science user facility, contributed to the work.

For several decades, improvements in conventional transistor materials have been sufficient to sustain Moore’s Law – the historical pattern of microchip manufacturers packing more transistors (and thus more information storage and handling capacity) into a given volume of silicon. Today, however, chipmakers are concerned that they might soon reach the fundamental limits of conventional materials. If they can’t continue to pack more transistors into smaller spaces, they worry that Moore’s Law would break down, preventing future circuits from becoming smaller and more powerful than their predecessors.

That’s why researchers worldwide are on the hunt for new materials that can compute in smaller spaces, primarily by taking advantage of the additional degrees of freedom that the materials offer – in other words, using a material’s unique properties to compute more 0s and 1s in the same space. Spintronics, for example, is a concept for transistors that harnesses the up and down spins of electrons in materials as the on/off transistor states.

Valleytronics, another emerging approach, utilizes the highly selective response of candidate crystalline materials under specific illumination conditions to denote their on/off states – that is, using the materials’ band structures so that the information of 0s and 1s is stored in separate energy valleys of electrons, which are dependent on the crystal structures of the materials.

In this new study, the research team has shown that tin(II) sulfide (SnS) is able to absorb different polarizations of light and then selectively reemit light of different colors at different polarizations. This is useful for concurrently accessing both the usual electronic – and the material’s valleytronic – degrees of freedom, which would substantially increase the computing power and data storage density of circuits made with the material.

“We show a new material with distinctive energy valleys that can be directly identified and separately controlled,” said Yao. “This is important because it provides us a platform to understand how valley signatures are carried by electrons and how information can be easily stored and processed between the valleys, which are of both scientific and engineering significance.”

Lin, the first author of the paper, said the material is different from previously investigated candidate valleytronics materials because it possesses such selectivity at room temperature without additional biases apart from the excitation light source, which alleviates the previously stringent requirements in controlling the valleys. Compared to its predecessor materials, SnS is also much easier to process.

With this finding, researchers will be able to develop operational valleytronic devices, which may one day be integrated into electronic circuits. The unique coupling between light and valleys in this new material may also pave the way toward future hybrid electronic/photonic chips.

Berkeley Lab’s “Beyond Moore’s Law” initiative leverages the basic science capabilities and unique user facilities of Berkeley Lab and UC Berkeley to evaluate promising candidates for next-generation electronics and computing technologies. Its objective is to build close partnerships with industry to accelerate the time it typically takes to move from the discovery of a technology to its scale-up and commercialization.

Spin Transfer Technologies, Inc., the developer of advanced STT-MRAM for embedded SRAM and stand-alone DRAM applications, today announced results of its unique Precessional Spin Current (PSC™) structure. The results from advanced testing of the PSC structure confirm that it will increase the spin-torque efficiency of any MRAM device by 40-70 percent — enabling dramatically higher data retention while consuming less power. This gain translates to retention times lengthening by a factor of over 10,000 (e.g., 1 hour retention becomes more than 1 year retention) while reducing write current. Improved efficiency is critical for enabling MRAM to replace SRAM and DRAM in mobile, datacenter and AI applications, as well as for improving retention and performance in high-temperature automotive applications. The company reported these results at the prestigious Intermag 2018 Conference.

Spin-torque efficiency is one of the core performance metrics of the pMTJ (perpendicular magnetic tunnel junction — the “bit” that stores the memory state in an MRAM memory) and is defined by the ratio between the thermal retention barrier, measuring how long data can be reliably stored in the memory, and the switching current necessary to change the value of the bit. In previous MRAM implementations, increasing the energy barrier to increase retention would require a proportional increase in write current — leading to higher power consumption and much faster wear-out of the pMTJ devices (lower endurance). The PSC structure is a breakthrough because it effectively decouples the static energy barrier that determines retention from the dynamic switching processes that govern the switching current. As a result, when the PSC structure is added to any pMTJ, benefits include:

  • A higher energy barrier when the pMTJ does not have current flowing through it, which is ideal for retaining data for long periods
  • An increased spin polarization when current is flowing and the device is writing a new state, which is ideal for minimizing switching current and extending the life of the device by many orders of magnitude

The PSC structure was designed from the outset to be modular and fabricated with any pMTJ — either the company’s own pMTJs, or a pMTJ from other sources. The PSC structure is fabricated during the pMTJ deposition process and adds approximately 4nm to the height of the pMTJ stack. The structure is compatible with a wide range of standard MRAM manufacturing processes, materials and tool sets — enabling any foundry to readily incorporate the PSC structure into existing pMTJ stacks without adding significant complexity or manufacturing costs.

“MRAM is attracting a lot of attention as an embedded memory for ASICs and MCUs, but issues of write current and data retention have caused concern,” said Jim Handy, general director of Objective Analysis. “Spin Transfer Technologies’ new PSC structure shows a lot of promise to solve a number of those issues and pave the path for MRAM to take a significant share of the embedded memory market.”

Spin Transfer Technologies’ testing of the PSC structure involved comparing the performance of the same pMTJ devices with and without PSC for a large number of devices within CMOS test chip arrays at various temperatures and device diameters. The tests exhibited a robust performance advantage due to the PSC structure, both during writing of the low-resistance (“0”) and the high-resistance (“1”) memory states. Some specific examples of the advantages that the data have shown are as follows:

  • Increase of the spin-torque efficiency by up to 70 percent
  • Demonstration of the efficiency gain across a range of sizes (40-60nm) and temperatures (30°C to 125°C)
  • Increase of the thermal energy barriers by 50 percent corresponding to an increase in data retention time of greater than four orders of magnitude while reducing the switching current
  • Reduction of read disturb error rate up to five orders of magnitude

These advantages have come without degradation to other performance parameters. The data for the PSC structure indicate significant potential for enabling high-speed applications as well as high-temperature automotive and other applications. Furthermore, since the data shows that the PSC structure’s efficiency gains actually increase as the pMTJ get smaller, the PSC structure opens new pathways to achieving embedded SRAMs in the latest 7nm and 5nm generations.

“There is a huge demand for a memory with the endurance of SRAM, but with higher density, lower operating power and with non-volatility. We believe the improvements the PSC structure brings to STT-MRAM technology will make it a highly attractive alternative to SRAM for these reasons,” said Mustafa Pinarbasi, CTO and SVP of Magnetics Technology at Spin Transfer Technologies. “We are excited to enable the next generation of STT-MRAM and to shake up the status quo of the memory industry through our innovation.”