Prof. Sachin Sapatnekar to lead $5.3 million federal grant to improve electronic circuit design

The University of Minnesota recently received a four-year, $5.3 million grant from the Defense Advanced Research Projects Agency (DARPA), an agency of the U.S. Department of Defense, to lead an effort that could spark the next wave of U.S. semiconductor innovation and broaden the competitive field for circuit design. Integrated circuits power almost every electronic device we use today.

The University of Minnesota is one of only 11 lead universities or companies to receive funding from the DARPA Intelligent Design of Electronic Assets (IDEA)  program, a new program under the DARPA Electronics Resurgence Initiative. Other partners on the University of Minnesota-led grant are Texas A&M University and Intel, a leader in the semiconductor industry.

The complex circuitry in today’s semiconductor chips is built using software that automates the design of analog and digital circuits, but consumers continue to demand even more complex chip designs.

Today’s system-on-chip platforms incorporate billions of transistors with miles of electrical wiring that are integrated within a tiny chip. This technological feat requires large teams and complex software. As a result, the cost of circuit design continues to skyrocket, narrowing the competitive field to large, multinational companies capable of keeping up with the demand for capital and skilled talent. It’s becoming increasingly difficult for small entities, as well as the Department of Defense, to leverage the high-performance technology it needs to design complex circuits for defense applications.

“The high cost of this software creates a barrier to entry for smaller entities to compete in design efforts,” said Sachin Sapatnekar, a University of Minnesota professor of electrical and computer engineering who will lead the grant. “The goal of our research is to replace the proprietary model with an open-source software environment for analog and mixed-signal designs. In short, we seek to ‘democratize’ chip design by facilitating open access to chip design tools and seeding a
community of users. The result will be lower costs to consumers for electronics.”

Through the creation of a software-based, completely automated physical layout generator and an open-source intellectual property (IP) ecosystem, the IDEA program aims to create a “no human in the loop” layout generator that would enable users with limited electronic design expertise to complete the physical design of electronic hardware within 24 hours. The software created under IDEA would be capable of automatically creating circuit design files ready for manufacturing, reducing design time from months or years to a single day.

By applying machine learning methodologies, IDEA hopes to continuously evolve and improve the performance of the layout generator for digital circuits, mixed-signal integrated circuits, systems-in-package, and printed circuit boards.

“Through the IDEA program, DARPA aims to eliminate the Department of Defense’s resource and expertise gap associated with custom electronic hardware design for the most advanced technologies by enabling full automation and applying machine intelligence,” said Andreas Olofsson, the Microsystems Technology Office program manager leading IDEA. To read more about DARPA’s IDEA program and the newest round of funding, visit the DARPA website.

Congratulations to Eric Konitzer on the DEPS Scholarship

ECE graduate student Eric Konitzer is a recipient of the 2018-2019 Directed Energy Professional Society (DEPS) scholarship. Eric works with Prof. Joey Talghader in his optical MEMS group, investigating the next generation of infrared detectors for long wavelength infrared light. These sensors could eventually be used for very high precision thermal imaging. Specifically, Eric is examining how micro scale devices are prone to vibrations due to thermal energy. Although this effect is typically considered undesirable noise in MEMS systems, the optical MEMs group uses it to to their advantage as part of the design. Eric has been fabricating MEMS structures, and evaluating fabrication and measurement capabilities to learn what to expect for thermomechanical noise in some typical systems. Going forward, Eric will work on creating more complex structures that exploit materials’ properties in ways that can maximize an infrared detection signal. After graduation, he plans on working in related industry in research and development.

DEPS is the leading organization that facilitates and promotes communication on the development and application of directed energy (DE) (high energy lasers, and high power microwave systems and technologies). The Society supports research and development of directed energy technology for both defense and civil applications. Academic disciplines engaged in DE research include physics, electrical engineering, chemistry, chemical engineering, materials sciences, optical sciences, optical engineering, and aerospace engineering.

The deadline for the next round of scholarships (2019-2020) is April 12, 2019.

Congratulations to Our 2018-2019 Doctoral Dissertation Fellowship Winners

The recipients are Yanning Shen (advisor: Prof. Georgios Giannakis), Hari Cherupalli (advisor: Prof. John Sartori), Ahmed Zamzam (advisor: Prof. Nikos Sidiropoulos), and Zhengyang Zhao (advisor: Prof. Jian-Ping Wang).

 

Yanning Shen

Yanning Shen’s research interests are network science, big data analytics, and nonlinear modeling. Fittingly, her dissertation has to do with the introduction of nonlinear models and scalable online algorithms for inference and learning over large-scale dynamic networks. Her work aims to develop a unified framework to capture the dynamics and non-linearities in real-world networks. The title of her dissertation is “Topology identification and learning over graphs: Accounting for nonlinearities and dynamics” and she is working under the guidance of Prof. Georgios Giannakis. The outcomes of her research will benefit several domains such as social networks, epidemiological studies, transportation, financial networks and brain networks. For instance, with respect to brain networks, Yanning’s research can significantly enrich the information provided by an MRI and highlight key features that distinguish abnormalities from what is normal, improving medical diagnosis and treatment. Yanning comes to ECE from the University of Electronic Science and Technology in China. Post graduation, she hopes to continue her research at a university or other institution.

 

Hari Cherupalli

Hari Cherupalli’s research interests are computer architecture, computer aided design, security, low power, embedded processors. His dissertation is titled, “Application-specific design and optimization for ultra low-power embedded systems,” and he is working under the guidance of Prof. John Sartori. His work opens up a new direction in application analysis of microprocessors, crossing multiple layers of design abstraction, from binary to processor layout. Such an analysis can lead to significant benefits in power, cost, and security of ultra low-power microprocessors that drive the Internet of Things revolution. One of the immediate benefits is that battery operated devices could last longer on the same battery. Yet another benefit is improved form factor of systems where area and cost are critical. Currently, Hari is working on commercializing his research, and has filed patents for his work. Hari comes to ECE from the Indian Institute of Technology, Kharagpur, where he earned his bachelor’s and master’s degrees in electrical engineering.

 

Ahmed Zamzam

Ahmed Zamzam’s research interests lie in monitoring, learning, and management for smart power grids. His dissertation is titled “Intelligent monitoring and control for next generation smart grids,” and he is working under the guidance of Prof. Nikos Sidiropoulos. His research contributes to the development of efficient monitoring and resource management tools in power systems. The overarching goal is to support more reliable and secure energy systems, and a greener environment. Ahmed enjoys the research process and environment and working with students. After graduation, he hopes to pursue his interests at a research university, or work as a scientist at a national laboratory. Prior to arriving at the University, Ahmed earned his bachelor’s degree from Cairo University, Egypt, and his master’s degree from Nile University, Egypt, both in electrical engineering.

 

Zhengyang Zhao

Zhengyang Zhao’s research interests lie in the development of novel spintronic devices and using them in advanced memory and computing applications. His work includes resolving fundamental challenges and improving the performance of spintronic devices, and expanding the range of applications enabled by novel devices. His dissertation is titled, “Development of spintronic devices for ultra-energy efficient non-volatile memory and logic applications,” and he is working under the guidance of Prof. Jian-Ping Wang. Zhengyang’s dissertation focuses on one of the most significant application of spintronics: magnetic random access memory (MRAM). MRAM uses the spin of electrons to store data and bears certain critical advantages: non-volatility, read/write speed comparable to that of DRAM, and an unlimited lifetime. Spin Hall effect (SHE), a recently discovered phenomenon, provides a new means of spin generation that allows MRAM to be faster and more energy efficient. However, there are gaps between basic SHE devices and SHE-based MRAM. Zhengyang’s research addresses these gaps, proposing different strategies along with experimental prototyping. He is also developing solutions to mitigate limitations that arise from the speed of the computer being constrained by the data transfer between memory and CPU. Zhengyang hopes to apply his expertise in industry after he graduates. Zhengyang comes to us from Xi’an Jiaotong University, China, where he earned his bachelor’s degree in electrical engineering.

To read about other graduate awards and honors, and their recipients, please check this link

 

Tin-Based Semiconductors Show Experimental Promise

University Scientists Report Breakthroughs in Stannate Semiconductors

In the world of semiconductors, silicon has reigned supreme for over half a century. It is the foundation of microprocessors and memory devices which are now ubiquitous entities deeply involved in most aspects of our lives, from running our smartphones to reminding us when our cars need an oil change. However, silicon does have some shortcomings: it is opaque to visible light, and does not handle high levels of power well. So, in recent years, scientists have been working to discover new semiconductors, such as gallium nitride (GaN), that can provide these additional capabilities. Currently, scientists at the University of Minnesota are developing a new class of semiconductors that could greatly expand the application range of semiconductor technology, and the essential component of this new material might come as a surprise: it is tin. The charge is being led by Prof. Steven Koester from the Department of Electrical and Computer Engineering, and Prof. Bharat Jalan from the Department of Chemical Engineering and Materials Science.

TIN POISED TO TAKE ON A NEW ROLE

Tin is the key element in a class of complex oxide semiconductors known as “stannate perovskites.” Perovskites are materials with the chemical formula ABO3, where, in the case of stannates, the “B” element is tin. Although perovskites are interesting from the point of view of physics and have a wide range of uses in other fields, they do not have many room temperature electronics applications. However, stannates are set to change this; their high electron mobility and wide band gap give them several remarkable properties: they are transparent to visible light, they can sustain extremely high voltages over tiny distances in the material, and most importantly, they are great electrical conductors.

As Prof. Jalan notes, “In most complex oxides, electron ‘mobility’, or how easily electrons can move, is very low at practical temperature.  However, stannates have much higher electrical mobility among all perovskite materials.”

Papers recently published by University research teams led by professors Koester and Jalan have generated considerable excitement and interest in the use of tin-based semiconductors as transistors, a vital component in electronic devices. In “Depletion Mode MOSFET Using La-Doped BaSnO as a Channel,” the team demonstrated the use of barium stannate (BaSnO3) as a channel material in a field-effect transistor (FET). Critically, this work also details the role of dislocations (which, very crudely explained, occur when a crystal with a particular spacing between the atoms is grown on top of another crystal with a different atomic spacing) in BaSnO3-based FETs. The results point to ways by which the performance of BaSnO3 channel devices can be enhanced.

SHIFTING FOCUS

Among the stannate-based perovskites, BaSnO3 has garnered most of the recent attention due to its high mobility and its ability to be doped, or made electrically conductive by adding additional elements. However, lately Koester’s and Jalan’s teams have turned the spotlight on strontium stannate (SrSnO3), and for good reasons.

Pointing to the difference between barium stannate and strontium stannate, Prof. Koester says, “Strontium stannate is a particularly interesting material because it has an even wider band gap than barium stannate and thus can support even higher voltages.”

Pushing ahead their research into perovskites, the scientists have  demonstrated a SrSnO3 FET, the first demonstration of a transistor using this material. The results are presented in the paper, “Demonstration of a Depletion-Mode SrSnO n-Channel MESFET,” published in IEEE Electron Device Letters. The demonstration was made possible after the Jalan team recently learned how to dope SrSnO3, also a first for this material.

THE STRONTIUM STANNATE ADVANTAGE

The larger band gap present in SrSnO allows for visible light transparency, and greater breakdown voltage. Strontium stannate is also easier to grow on commercially available substrates because of its better lattice matching, compared to BaSnO. According to Jalan, this affords lower dislocation density, which entails the possibility of greater reliability of, and improved power handling capability by, the device.

Strontium stannate is also easier to grow on commercially available substrates, because of its better lattice matching, compared to barium stannate.

Other characteristics of this compound also suggest that it displays electron mobilities close to BaSnO3 and existing wide-gap semiconductors. For Prof. Koester’s team, the results of the recent demonstration of a SrSnO3 FETs are promising. The device displayed gain values that are a record for a stannate-based perovskite FET, and five times better than existing strontium titanate (SrTiO3)-based devices. SrTiO3, a more well-known perovskite, and regarded as the silicon among perovskites, has very low mobility, making it a weak candidate for transistors. While it is a worthwhile contender for many other applications and fundamental studies, its low mobility has hindered its widespread deployment in microelectronics.

LOOKING AHEAD

Even though the current performance of the SrSnO3 FETs still lags behind that of prevailing state-of-the-art GaN FETs, the research team believes the true potential lies in new capabilities that cannot be achieved in GaN. Perhaps the most important capability is the ability to integrate epitaxial ferroelectrics. SrSnO3 is closely lattice matched to one of the best known ferroelectric materials, barium titanate, and this could lead to applications with critical potential such as reconfigurable high power electronic devices.  

Based on the outcomes of their latest work, the University’s research teams are hopeful that SrSnO3 can open the door to incorporating a wide range of new properties, including ferroelectrics, piezoelectrics, and many others.  These ‘smart materials’ could lead to new kinds of reconfigurable electronics with a vast range of applications from military radars, to cell phone towers, to autonomous vehicles.

This research is primarily supported by the Young Investigator Program of the Air Force Office of Scientific Research (AFOSR), and the National Science Foundation through  its Ceramics program (CER) and the University’s MRSEC.

You can learn more about Prof. Steven J. Koester’s pioneering work here, and check his research lab here

More information about Professor Jalan’s research can be found here. 

 

Spinning toward Advancements in Science and Technology

In a cross-departmental collaborative undertaking, scientists at the University of Minnesota have successfully grown a quantum material, bismuth selenide, by magnetron sputtering, a process compatible with large scale production, and currently in use commercially. The development bears significance for the semiconductor industry, holding the possibility of improved energy efficiency for computing and memory devices.

The details of the team’s research are reported in “Room-temperature high spin-orbit torque due to quantum confinement in sputtered BixSe(1-x) films,” published in Nature Materials.

TOPOLOGICAL MATERIALS AND SPIN-ORBIT TORQUES

The class of materials known as topological insulators (TI) has been of interest to scientists in the fields of physics and material science.  The unique property they possess–insulating interior and conducting surface–can improve the energy efficiency of post-CMOS computing devices, and magnetoresistive random access memory (MRAM), a non-volatile memory. TIs can convert charge into non-equilibrium spin density efficiently because of the perpendicular locking of an electron’s spin with its momentum. Such efficient conversion is critical to magnetoresistive random access memory (MRAM) and post-CMOS computing devices for faster writing of data, reduced power consumption, and greater device reliability.

Typically spin-polarized current is generated using a ferromagnetic polarizer which transfers its spin angular momentum to another ferromagnetic layer. This is the mechanism for the creation of spin-transfer torque (STT). However, the inefficiency of the ferromagnetic polarizer entails higher power consumption, and lower reliability. On the other hand, spin-orbit torque (SOT), an outcome of spin-orbit interaction, essential to the atomic structure of specific materials such as heavy metals (for instance, tungsten, W)  has advantages over STT. The absence of a separate polarizer gives SOT-based memory and logic devices an edge over STT-based devices in terms of energy efficiency and device reliability. Recently, topological materials have been reported to generate large spin-orbit torques. 

GROWING BISMUTH SELENIDE

However these developments can be worthwhile only if they can be nudged into the mainstream, and commercially viable processes for growing TI are developed. Typically, topological insulators are created either using a single crystal growth process, or a process called molecular beam epitaxy. Both of these techniques cannot be easily scaled up for use in the semiconductor industry. In the present study, researchers started with bismuth selenide (Bi₂Se₃), a compound of bismuth and selenium. They then used a thin film deposition technique called “sputtering,” which is driven by momentum exchange between the ions and atoms in the target materials due to collisions. While the sputtering technique is common in the semiconductor industry, this is the first time it has been used to create a topological insulator material. Significantly, this could be scaled up for semiconductor and magnetic industry applications. It is also worth noting that on testing the new material, researchers found it to be 18 times more efficient in computing processing and memory compared to current materials.

According to lead scientist, and Distinguished McKnight University Professor and Robert F. Hartmann Chair in Electrical Engineering Jian-Ping Wang, “The unique feature of the sputtered bismuth selenide is the presence of nano-sized grains, which were missing in molecular beam epitaxy grown single crystalline topological insulator films.” 

Prof. Tony Low, co-author of the paper and faculty in the Department of Electrical and Computer Engineering points out, “The nano-sized grains present in the sputtered bismuth selenide films yield higher spin-accumulation due to the spin momentum locking in the deeply located bands. As grains shrink, quantum confinement of the wave function further enhances spin-accumulation.”

Prof. Wang’s excitement is palpable, “Using the sputtering process to fabricate a quantum material like a bismuth-selenide-based topological insulator is against the intuitive instincts of all researchers in the field and actually is not supported by any existing theory. Four years ago, we started with a big idea to search for a practical pathway to grow and apply the topological insulator material for future computing and memory devices. Our surprising experimental discovery led to a new theory for topological insulator materials. Research is all about being patient and collaborating with team members. This time there was a big pay off,” Wang said.

THE ROAD AHEAD

With support from the Semiconductor Research Corporation, the researchers have filed for a materials-related patent, and experts in the semiconductor industry have requested samples of the material. The current paper represents the latest development in the research led by Prof. Wang, and collaborating scientists at the University of Minnesota and other institutions in the field of spintronics. His team has been at the forefront of the search for novel materials, and fabrication techniques that can enhance computation in semiconductor-based devices by improving storage and processing speeds, and the development of magnetic biomedical technologies and devices that can improve patient comfort and outcomes.

Recently, Prof. Wang as principal investigator received a $3.1 million grant from DARPA (Defence Advanced Research Projects Agency) under the Electronics Resurgence Initiative (ERI) for exploring novel materials and circuit structures that can take us beyond the limitations imposed by Moore’s Law, and meet looming engineering, economic, and defense challenges.

Another notable example of the pioneering work conducted by Prof. Wang’s research team is the development of Z-Lab, a portable diagnostic platform designed to perform on site testing of biological samples for various ailments. This is the first version of the prototype developed for point-of-care diagnostics. The details of the device and results of the test are reported in the paper “Portable GMR Handheld Platform for the Detection of Influenza A Virus” published recently in ACS Sensors.

Earlier in the year, a collaborative effort led by researchers at the University resulting in the experimental discovery of ferromagnetic properties in Ruthenium was published in Nature Communications under the title, “Demonstration of Ru as the 4th ferromagnetic element at room temperature. The discovery makes it the fourth single element with such properties in the periodic table. It opens an exciting new chapter in the fundamental studies of this element, and its application potential in the creation and scaling of magnetic memories, and breaking new ground in computing performance.

Late last year, Prof. Wang and his team in collaboration with researchers from Pennsylvania State University discovered the existence of magnetoresistance in topological insulator-ferromagnetic bilayers. This discovery has significant implications for the semiconductor industry, and opens up the door to enabling low power computing, brain-like computing, and chips for robots in the near future. The details of their research are published in Nature Communications under the title “Unidirectional spin-Hall and Rashba−Edelstein magnetoresistance in topological insulator-ferromagnet layer heterostructures.” The study confirms the existence of such unidirectional magnetoresistance and reveals that the adoption of TI, compared to heavy metals, improves the magnetoresistance performance by about twice at a temperature of 150 Kelvin (-123.15 Celsius).

Prof. Wang and his team of scientists are on an exciting path, unpacking and harnessing the potential of spinning electrons, translating it into applications disparate but critical to diverse aspects of our lives: low power computing, memory devices, biomedical devices. Translating these research outcomes into technologies that are adopted by industry, and impact our lives is only a matter of time. Our lives will certainly look different as these research outcomes make their way to industry and become commercially available.

 

The research for the paper, “Room-temperature high spin-orbit torque due to quantum confinement in sputtered BixSe(1-x) films,” was funded by the Center for Spintronic Materials, Interfaces and Novel Architectures (C-SPIN) at the University of Minnesota. C-SPIN is a Semiconductor Research Corporation program sponsored by the Microelectronics Advanced Research Corp. (MARCO) and the Defense Advanced Research Projects Agency (DARPA). C-SPIN is led by Prof. Wang.

Check the University’s coverage of Prof. Wang’s latest research here

Check the AAAS EurekAlert here

Prof. Jian-Ping Wang to Lead DARPA Funded Exploration into Novel Materials For Electronics

Researchers at the University of Minnesota will receive $3.1 million from the Department of Defense (DoD) to explore new materials, architectures, and systems that can overcome Moore’s Law, and push electronics technology forward, capable of meeting engineering, economic, and defense challenges.

Distinguished McKnight Professor and Robert F. Hartmann Chair in Electrical Engineering Jian-Ping Wang is the principal investigator of the University team and the funding is an outcome of the Electronics Resurgence Initiative (ERI) rolled out by Defense Advanced Research Projects Agency (DARPA), a DoD agency. The focus of the team will be the development of advanced magnetic tunnel junctions (MTJ) for novel computing. While the University will lead the effort, it will also be collaborating with National Institute of Standards and Technology, GlobalFoundries, and University of Arizona. Other participating University of Minnesota scientists are Prof. Tony Low and Prof. Bin Ma, both from the Department of Electrical and Computer Engineering.

DARPA’s ERI seeks to bring together research and technical expertise from academia and industry to explore new materials and architectures to bridge the gap between memory and logic functions and create new ways of computing information more quickly and efficiently. The Initiative is a $1.5 billion five-year investment designed to energize innovation in the electronics industry, and respond to anticipated challenges in the microelectronics technology industry.

One of the thrust areas under ERI is Materials & Integration which is organized into two programs: Three Dimensional Monolithic System-on-a-Chip (3DSoC), and Foundations Required for Novel Compute (FRANC). Current electronic system performance is governed by the constraints of time and power required to access memory, often referred to as the memory bottleneck. Researchers working under the FRANC program will address the bottleneck by exploring new circuit designs using novel materials and integration schemes that can minimize the movement of data between memory components and processors.

MTJs, created by sandwiching a thin insulator between two ferromagnets, have been critical to the field of spintronics; the MTJ is the basis of MRAM (magnetoresistive random-access memory), a type of non-volatile memory. The University has led research into spintronics, pursuing MTJ-based computation for more than 15 years. “In fact,” Prof. Wang notes, “our team proposed the very early idea to use magnetic tunnel junctions for the computation in random access memory (CRAM).”

With DARPA’s ERI funding, Prof. Wang and his team will work on demonstrating the value of MTJs in bridging the separation between the memory and logic functions that exist in conventional circuit designs. Their goal, under the FRANC program, is to leverage and integrate novel materials, architectures, and chip components to enhance computational speed, and performance, while lowering power consumption.

Learn more about the ERI

More information about Prof. Jian-Ping Wang’s work

Mehran Elyasi Receives ISIT Best Paper Award

The International Symposium on Information Theory, organized by the IEEE Information Theory Society has awarded Mehran Elyasi with the Jack Keil Wolf ISIT Best Student Paper Award for 2018. Mehran’s paper is titled, “A Cascade Code Construction for (n,k,d) Distributed Storage Systems,” published in Proceedings of the 2018 IEEE International Symposium on Information Theory.

Exact-repair regenerating codes are codes used for Distributed Storage Systems for the purpose of data recovery and repair when a storage unit fails. In his paper, Mehran introduces a novel class of these codes that hit an optimum trade-off between storage bandwidth and repair bandwidth.

Mehran’s Research

The award winning paper stems from Mehran’s doctoral research which focuses on, among other issues, the problem of reliability in Distributed Storage Systems (DSS). (As the volume of digital data generated on the Internet, and the users seeking access to such data  increases rapidly, DSS are used to maintain data availability.) But the unreliability of such systems remains a key concern. While the problem can be overcome by building in redundancy in the data, it leads to storage overheads. Additionally, with failures being common in large scale storage systems, a significant volume of network traffic is diverted to repair failed storage nodes. While the ideal goal is to minimize the repair bandwidth while also maximizing the storage efficiency of the system, currently one can be optimized only at the cost of the other.     

To counter these challenges, Mehran has worked on the design of a novel coding scheme, called Determinant Coding, for Distributed Storage Systems. The construction of the scheme provides encoding/decoding algorithms for storage as well as an efficient mechanism for the repair of failed storage units. These universally structured codes can operate in all the optimum points of the storage-bandwidth trade-off.

Mehran earned his Bachelor of Science in Electrical Engineering and Mathematics from Isfahan University of Technology, Iran, in 2014. His areas of interest include information theory and its applications in communication, distributed storage systems, and statistical machine learning. He is pursuing his doctoral degree under the guidance of Prof. Soheil Mohajer. He is the recipient of the Doctoral Dissertation Fellowship awarded by the University’s Graduate School, and is also a 2018 Facebook Fellow.

The Jack Keil Wolf ISIT Best Student Paper Award is given annually to three outstanding papers that are primarily authored and presented by the student. The content of the paper and the quality of its presentation are criteria for the award, which includes a plaque for each student author and a $500 honorarium to be shared by each of them.

 

Scientists Discover Ferromagnetic Properties in Ruthenium

University Scientists Lead the Discovery of Ferromagnetism in Ruthenium

A collaborative effort led by researchers at the University of Minnesota has resulted in the experimental discovery of ferromagnetic properties in Ruthenium, making it the fourth single element with such properties in the periodic table. The discovery opens an exciting new chapter in the fundamental studies of this element, and its application potential in the creation and scaling of magnetic memories, and breaking new ground in computing performance.

The importance and use of ferromagnetism reaches far back into ancient times, when lodestone was used for navigation. Since then only three elements on the periodic table have been found to be ferromagnetic at room temperature–iron (Fe), cobalt (Co), and nickel (Ni). Rare earth element gadolinium (Gd) misses this status by a mere 8 degrees celsius. These magnetic materials have been used for fundamental studies and in several everyday applications such as sensors, permanent magnets, memory devices, and most recently, spintronic memories.

With improvements in thin film growth over the past few decades, the ability to control the structure of crystal lattices has also improved, to the extent that scientists can even force structures that are impossible in nature. The discovery of Ru’s ferromagnetic properties was facilitated by the use of ultra-thin films to force the ferromagnetic phase of the element. The details of the work are published in Nature Communications in a paper titled “Demonstration of Ru as the 4th ferromagnetic element at room temperature.” The University of Minnesota team comprised Dr. Patrick Quarterman, the lead author, Prof. Jian-Ping Wang, the corresponding author, and doctoral candidate Yang Lv.

Prof. Jian-Ping Wang says, “This work will trigger the magnetic research community to look into fundamental aspects of magnetism for many well-known elements.”

For Prof. Wang, the potential that lies beyond this development is obvious. “Magnetism is always amazing. It proves itself again. We are excited and grateful to be the first group to experimentally demonstrate and add the fourth ferromagnetic element at room temperature to the periodic table. It took us about two years to find a right way to grow this material and validate it. This work will trigger the magnetic research community to look into fundamental aspects of magnetism for many well-known elements.”

Co-author Paul Voyles, who is Beckwith-Bascom Professor and Chair of the Department of Materials Science and Engineering at the University of Wisconsin-Madison echoes Prof. Wang’s enthusiasm. “The ability to manipulate and characterize matter at the atomic scale is the cornerstone of modern information technology. Our collaboration with University of Minnesota Professor Wang’s group shows that these tools can find new things even in the simplest systems, consisting of a just a single element.”

Industry experts agree about the critical nature of the discovery. “Spintronic devices are of rapidly increasing importance to the semiconductor industry,” according to Todd Younkin, the director of Defense Advanced Research Projects Agency (DARPA)-sponsored consortia at Semiconductor Research Corporation (SRC). “Fundamental advances in our understanding of magnetic materials, such as those demonstrated in this study by Prof. Wang and his team, is critical to realizing continued breakthroughs in computing performance and efficiency.”

Collaborating scientists from Intel point to the possibilities that lie ahead. “Intel is pleased with the long-term research collaboration it has with the University of Minnesota and the C-SPIN Center. We are excited to share these developments enabled by exploring the behavior of quantum effects in materials, which may provide insights for innovative, energy efficient logic and memory devices.”

Novel technologies require novel materials

Magnetic recording is still the dominant player in data storage technology, but magnetic based random-access memory and computing is beginning to take its place. These magnetic memories place additional constraints on the magnetic materials where data is stored, compared to traditional hard disk media magnetic materials. This push for novel materials has led to renewed interest in attempts to realize predictions which show that under the right conditions, non-ferromagnetic materials such as Ru, palladium (Pd), and osmium (Os) can become ferromagnetic. 

The discovery of ferromagnetism in Ruthenium has implications for the semiconductor industry

Building upon the established theoretical predictions, researchers at the University of Minnesota used seed layer engineering to force the tetragonal phase of Ru, which prefers to have a hexagonal configuration, and observed the first instance of ferromagnetism in a single element at room temperature. The crystal structure and magnetic properties were extensively characterized by collaborating with the University of Minnesota’s Characterization Facility and colleagues at the University of Wisconsin. The figure on the top left is a high resolution electron microscopy image confirming the tetragonal phase of Ru as predicted by the authors. (Image credit: University of Minnesota, Quarterman et al, Nature Communications)

From an application perspective, Ru is interesting because it is resistant to oxidation, and additional theoretical predictions claim it has a high thermal stability—a vital requirement for scaling magnetic memories. Examination of its high thermal stability is the focus of ongoing research at the University of Minnesota.

The lead author of the paper, Dr. Patrick Quarterman earned his doctoral degree under the guidance of Prof. Jian-Ping Wang. He is currently a National Research Council (NRC) postdoctoral fellow at the National Institute of Standards and Technology (NIST). In addition to Quarterman, Wang, and Voyles, researchers involved in this study include Javier Garcia-Barriocanal from the University of Minnesota Characterization Facility, Yang Lv from the University of Minnesota Department of Electrical and Computer Engineering, Mahendra DC from the University of Minnesota School of Physics and Astronomy, Sasikanth Manipatruni, Demitri Nikonov, and Ian Yang from Intel Components Research, and Congi Sun from the University of Wisconsin Department of Materials Science and Engineering. 

Research was funded by the Center for Spintronic Materials, Interfaces and Novel Architectures (C-SPIN) at the University of Minnesota, the University of Minnesota Distinguished Doctoral Fellowship, and the National Science Foundation (NSF) through the NSF-funded Materials Research Science and Engineering Center at the University of Minnesota.

The full paper entitled “Demonstration of Ru as the 4th ferromagnetic element at room temperature,” by Quarterman et al, is available at the Nature Communications website.

Learn more about C-SPIN

Learn more about Prof. Jian-Ping Wang’s research

 

Alumnus and trailblazer Prof. Alejandro Ribeiro on the cover of Penn Engineering magazine

ECE alumnus and Associate Professor in the Department of Electrical and Systems Engineering at the University of Pennsylvania, Alejandro Ribeiro is featured in Penn Engineering Magazine, a biennial magazine put out by the School of Engineering and Applied Science (SEAS). In a feature titled “Expanding Applications of Network Science,” he points out that the real power of networks lies in the connections they establish. Prof. Ribeiro uses “complex mathematical frameworks to understand how networks behave” and spends his time examining not the individual parts of the network, but how these parts interact with each other.

His research has taken him in some interesting and perhaps slightly unlikely directions. One area is the examination of Shakespeare’s plays, especially the ones that have had particularly problematic authorship. Another area Prof. Ribeiro is investigating is the creation of ad-hoc communication networks that could help swarms of robots communicate with each other in a way where these drones can independently analyze and decide on what might constitute a good connection. A third area of research is an examination of why some individuals display greater cognitive flexibility (the ability to switch easily from one task to another) as compared to others. In all these explorations, Prof. Ribeiro uses a technique he has developed over the last several years called Graph Signal Processing (GSP). The technique allows him to scrutinize the network as a whole and how the parts connect to each other.

Prof. Ribeiro, clearly a pioneering researcher, is also an earnest teacher and mentor. He is the recipient of the S. Reid Warren, Jr. Award (2012) for outstanding mentorship presented by Penn Engineering undergraduate students, and the Lindback Award for Distinguished Teaching (2017) awarded by the University of Pennsylvania. Read more about this trailblazing ECE alumnus in the Penn Engineering Magazine’s spring 2018 issue.

Prof. Alejandro Ribeiro earned his doctoral degree in 2007 under the guidance of Prof. Georgios Giannakis

Prof. Randall Victora in the News: Interview in AIP

Prof. Randall Victora and doctoral student Rizvi Ahmed, recently presented a technique for the simulation of a magnetic field in chromia (Cr₂O₃), a material that in the not too distant future, could form the key component of computer memory. The findings appear in the paper “A fully electric field driven scalable magnetoelectric switching element,” published in the journal Applied Physics Letters. Prof. Victora was interviewed by the American Institute of Physics about the new development. 

A switching element made from chromia could be the answer to the problem of reducing the size of memory components while also increasing energy efficiency. While consumers have come to expect greater memory sizes in small devices as a matter of routine, semiconductor companies have had to slow down; the size of memory components is not going down as rapidly as they once did, and current designs display a marked reduction in energy efficiency.

To overcome these challenges, researchers are investigating the use of magnetic fields to store information, a move away from transistors and electric fields that are typically used in memory devices, to store and retrieve information. A promising version of such a magnetic device depends on the magnetoelectric effect to switch the magnetic properties of a devices. However, the challenge here is that currently such a device requires large electric and magnetic fields.

According to Prof. Victora, the use of chromia as a possible answer to this lies in the fact that it has shown better potential for scaling and with refinements, could possibly be sized down, and be more energy efficient. The authors have designed a device where the chromia is surrounded with magnetic material, thereby doing away with the need for an externally applied magnetic field for it to operate. The details of the technique are explained in the paper.

NEXT STEPS

The authors intend to collaborate with other researchers familiar with chromia to fabricate and test the device. If all ends well, then the new chromia-based device stands to replace dynamic random access memory (DRAM), and this could be a revolutionary change in computer memory components. DRAM is what provides the fast memory that we are all used to in our devices, but it is energy inefficient and volatile. (You can blame its volatility when you lose an unsaved document when your computer crashes.) A chromia-based device however would be non-volatile. There are challenges yet to be overcome; the study’s authors point to chromia’s low heat tolerance. Currently, their modeling predicts that the device will stop functioning around 30 degrees celsius, and computers tend to run hotter than that. A possible solution the authors suggest is the introduction of other elements to optimize its functioning. So rein in your excitement just a dash. It might be a few years before such a memory device hits the market.

This research was supported by C-SPIN, one of six STARnet centers, a Semiconductor Research Corporation Program sponsored by MARCO and DARPA.

Read the complete paper

Prof. Randall Victora’s research