Category Archives: Materials

Virginia Commonwealth University researchers have discovered a novel strategy for creating superatoms — combinations of atoms that can mimic the properties of more than one group of elements of the periodic table. These superatoms could be used to create new materials, including more efficient batteries and better semiconductors; a core component of microchips, transistors and most computerized devices.

Batteries and semiconductors rely on the movement of charges from one group of atoms to another. During this process, electrons are transferred from donor atoms to acceptor atoms. Forming superatoms that can supply or accept multiple electrons while maintaining structural stability is a key requirement for creating better batteries or semiconductors, said Shiv Khanna, Ph.D., Commonwealth Professor and chair of the Department of Physics in the College of Humanities and Sciences. The ability of superatoms to effectively move charges while staying intact is attributed to how they mimic the properties of multiple groups of elements.

“We have devised a new approach in which one can synthesize such metal-based superatoms,” Khanna said.

In a paper published in Nature Communications last week, Khanna theoretically proved a method of building superatoms that could result in the creation of more effective energetic materials. The work was funded by the Air Force Office of Scientific Research.

“Semiconductors are used in every sphere of life,” Khanna said. “Superatoms that could substantially enhance electron donation would be a significant societal benefit.”

Currently, alkali atoms, which form the first column of the periodic table, are optimal for donating electrons. These naturally occurring atoms require a low amount of energy to donate an electron. However, donating more than one electron requires a prohibitively high amount of energy.

Khanna and colleagues Arthur Reber, associate professor of physics, and Vikas Chauhan, a postdoctoral fellow in the Department of Physics, have created a process by which clusters of atoms can donate or receive multiple electrons using low levels of energy.

“The possibility of having these building blocks that can accept multiple charges or donate multiple charges would eventually have wide-ranging applications in electronics,” Khanna said.

While such superatoms already have been made, there has never been a guiding theory for doing so effectively. Khanna and his colleagues theorize that organic ligands — molecules that bind metal atoms to protect and stabilize them — can improve the exchange of electrons without compromising energy levels.

They considered this theory using groups of aluminum clusters mixed with boron, carbon, silicon and phosphorous, paired with organic ligands. Using computational analysis, they demonstrated the cluster would use even less energy to donate an electron than francium, the strongest naturally occurring alkali electron donor.

“We could use ligands to take any cluster of atoms and turn it into either a donor or acceptor of electrons,” Khanna said. “We could form electron donors that are stronger than any element found on the periodic table.”

Researchers at Chalmers University of Technology, Sweden, have developed a graphene assembled film that has over 60 percent higher thermal conductivity than graphite film – despite the fact that graphite simply consists of many layers of graphene. The graphene film shows great potential as a novel heat spreading material for form-factor driven electronics and other high power-driven systems.

Until now, scientists in the graphene research community have assumed that graphene assembled film cannot have higher thermal conductivity than graphite film. Single layer graphene has a thermal conductivity between 3500 and 5000 W/mK. If you put two graphene layers together, then it theoretically becomes graphite, as graphene is only one layer of graphite.

Today, graphite films, which are practically useful for heat dissipation and spreading in mobile phones and other power devices, have a thermal conductivity of up to 1950 W/mK. Therefore, the graphene-assembled film should not have higher thermal conductivity than this.

Research scientists at Chalmers University of Technology have recently changed this situation. They discovered that the thermal conductivity of graphene assembled film can reach up to 3200 W/mK, which is over 60 percent higher than the best graphite films.

In the graphene film, phonons — quantum particles that describe thermal conductivity — can move faster in the graphene layers rather than interact between the layers, thereby leading to higher thermal conductivity. Credit: Chalmers University of Technology/Krantz Nanoart

Professor Johan Liu and his research team have done this through careful control of both grain size and the stacking orders of graphene layers. The high thermal conductivity is a result of large grain size, high flatness, and weak interlayer binding energy of the graphene layers. With these important features, phonons, whose movement and vibration determine the thermal performance, can move faster in the graphene layers rather than interact between the layers, thereby leading to higher thermal conductivity.

“This is indeed a great scientific break-through, and it can have a large impact on the transformation of the existing graphite film manufacturing industry”, says Johan Liu.

Furthermore, the researchers discovered that the graphene film has almost three times higher mechanical tensile strength than graphite film, reaching 70 MPa.

“With the advantages of ultra-high thermal conductivity, and thin, flexible, and robust structures, the developed graphene film shows great potential as a novel heat spreading material for thermal management of form-factor driven electronics and other high power-driven systems”, says Johan Liu.

As a consequence of never-ending miniaturisation and integration, the performance and reliability of modern electronic devices and many other high-power systems are greatly threatened by severe thermal dissipation issues.

“To address the problem, heat spreading materials must get better properties when it comes to thermal conductivity, thickness, flexibility and robustness, to match the complex and highly integrated nature of power systems”, says Johan Liu. “Commercially available thermal conductivity materials, like copper, aluminum, and artificial graphite film, will no longer meet and satisfy these demands.”

The IP of the high-quality manufacturing process for the graphene film belongs to SHT Smart High Tech AB, a spin-off company from Chalmers, which is going to focus on the commercialisation of the technology.

Scientists of the Far Eastern Federal University (FEFU) in cooperation with colleagues from the Russian Academy of Sciences (RAS), Australian and Lithuanian Universities have improved the technique of ultrasensitive nonperturbing spectroscopic identification of molecular fingerprints.

A group of physicists experimentally confirmed that molecular fingerprints of toxic, explosive, polluting and other dangerous substances could be reliably detected and identified by surface-enhanced Raman spectroscopy (SERS) using black silicon (b-Si) substrate. The results of the work are published in the authoritative scientific journal Nanoscale.

The needle-shaped surface structure of black silicon where needles are made of single-crystal silicon. The nanomaterial is absolutely chemically inert, non-invasive, and could support a strong and non-distorted signal Credit: FEFU press office

“When detecting the smallest molecules using SERS spectroscopy their interaction with the nanostructured substrate – the platform allowing ultrasensitive identification – is crucial”, the head of research team Alexander Kuchmizhak, Ph.D., reported. Alexander is a researcher of the Department of Theoretical and Nuclear Physics of the School of Natural Sciences of the FEFU. He also added: “Currently noble metals-based substrates are chemically active and as a result, they distort the characteristic molecules signals.”

“Due to its’ special morphology black silicon significantly enhances the signal from the molecules wanted. This nanomaterial doesn’t support catalytic conversion of the analyte as it could be in the case of the metal-based substrates applying. The ‘black silicon’- based substrate is unique: being absolutely chemically inert and non-invasive it could support a strong and non-distorted signal,” told Alexander Kuchmizhak.

The substrate can be fabricated by using the easy-to-implement scalable technology of plasma etching, thus has good prospects for commercial implementation. Such inexpensive non-metallic substrates with high accuracy of detection can be promising for routine SERS applications, where the non-invasiveness is of high importance.

Valuable properties of black silicon were discovered thanks to extensive scientific cooperation. Samples of the material were developed and provided by Australian colleagues, experimental work was carried out in the laboratories of the Institute of Chemistry and the Institute of Automation and Control Processes of the Far Eastern Branch of the RAS, as well as in the Scientific and Educational Center “Nanotechnologies” of the Engineering School of the FEFU.

The way that electrons paired as composite particles or arranged in lines interact with each other within a semiconductor provides new design opportunities for electronics, according to recent findings in Nature Communications.

What this means for semiconductor components, such as those that send information throughout electronic devices, is not yet clear, but hydrostatic pressure can be used to tune the interaction so that electrons paired as composite particles switch between paired, or “superconductor-like,” and lined-up, or “nematic,” phases. Forcing these phases to interact also suggests that they can influence each other’s properties, like stability – opening up possibilities for manipulation in electronic devices and quantum computing.

Two different kinds of electron arrangements in a semiconductor, paired as composite particles or lined-up, can interact with and tweak each other in the presence of hydrostatic pressure. Credit: Purdue University image/Gábor Csáthy

“You can literally have hundreds of different phases of electrons organizing themselves in different ways in a semiconductor,” said Gábor Csáthy, Purdue professor of physics and astronomy. “We found that two in particular can actually talk to each other in the presence of hydrostatic pressure.”

Csáthy’s group discovered that hydrostatic pressure, which is 10,000 times stronger than ambient pressure, compresses the lattice of atoms in a semiconductor and, therefore, influences the electron arrangement within a two-dimensional electron gas hosted by the semiconductor. The strength of the pressure determines which arrangement is favored and tunes the transition between the paired and lined-up phases, making them more tailorable for an application. Of the two phases, the paired phase may support a certain type of quantum computing.

“We can also tune the interaction by engineering the semiconductor,” Csáthy said. “Say, for example, we grew a semiconductor with a particular width and electron density that we estimated could stabilize the nematic phase. Then we’ve tuned the electron-electron interaction as a result.”

Michael Manfra, Purdue professor of physics and astronomy, electrical and computer engineering and materials engineering, and researchers Loren Pfeiffer and Kenneth West at Princeton University grew the semiconductor samples for this study. Yuli Lyanda-Geller, Purdue associate professor of physics and astronomy, provided theoretical support for the understanding on how these electron-electron interactions took place.

One of the leading challenges for autonomous vehicles is to ensure that they can detect and sense objects–even through dense fog. Compared to the current visible light-based cameras, infrared cameras can offer much better visibility through the fog, smoke or tiny particles that can scatter the visible light.

Artist’s rendering of light interacting with BaTiS3 crystals. Credit: Talia Spencer

Within the air, infrared light –within a specific range called mid-wave infrared– scatter much less compared to other visible or other infrared light waves. Infrared cameras can also see more effectively in the dark, when there is no visible light. However, currently the deployment of infrared cameras is limited by their heavy cost and scarcity of effective materials. This is where materials, which possess unique optical properties in the infrared and can be scalable, might make a difference in providing better object identification in several technologies including autonomous vehicles.

A new material developed by scientists at the USC Viterbi School of Engineering and the University of Wisconsin along with researchers from Air Force Research Laboratories, University of Missouri, and J.A. Woollam Co. Inc, might show promise for such infrared detection applications as autonomous vehicles, emergency services and even manufacturing.

The research group of Jayakanth Ravichandran, an assistant professor of materials sciences at the USC Viterbi School of Engineering has been studying a new class of materials called chalcogenide perovskites. Among these materials is Barium titanium sulfide (BTS), a material rediscovered and prepared in large crystal form by Shanyuan Niu, a doctoral candidate in the Materials Science program at the USC Mork Family Department of Chemical Engineering and Materials Science. Ravichandran’s research group collaborated with the research groups of Mikhail Kats, an assistant professor of electrical and computer engineering at University of Wisconsin-Madison and Han Wang, an assistant professor of electrical engineering and electrophysics in USC’s Ming Hsieh Department of Electrical Engineering to study how infrared light interacts with this material. These researchers discovered that this material interacted differently with light in two different directions.

“This is a significant breakthrough, which can affect many infrared applications,” says Ravichandran.

This direction dependent interaction with light is characterized by an optical property called birefringence. In simple terms, birefringence can be viewed as light moving at different speeds in two directions in a material. Much like sunglasses with polarized lenses block glare, BTS has the ability to block or slow down light depending on the direction in which it travels in the material. The researchers maintain that their material, barium titanium sulfide, has the highest birefringence among known crystals.

“The birefringence is larger than that of any known solid material, and it has low losses across the important long-wave infrared spectrum,” says Kats.

How BTS could improve infrared vision:

The BTS material can be used to construct a sensor to filter out certain polarizations of light to achieve better contrast of the image. It could also help filter light coming from different directions to enable sensing of a remote object’s features. This could be particularly important for improving infrared vision used in autonomous vehicles, which need to see the entire landscape around them even in low visibility conditions.

“The hope is that in the future, a BTS-enhanced sensor in a car would function as retinas do to the human body,” says Niu.

The authors believe these infrared-responsive materials can extend human perception. Beyond autonomous vehicles, there are other possible heat sensing or temperature measurement applications. One application could be in the creation of imaging tools used by firefighters to generate an instant temperature map outside a burning building to assess where a fire is spreading and where emergency responders need to rescue trapped individuals.

At present, the cost of infrared equipment makes it too expensive for all fire stations to have such equipment. BTS, which is made of elements readily abundant in earth crust–could make infrared equipment more affordable and effective. In addition, such materials are safer for the user and the environment, as well as easier to dispose of than the materials that are used now, which contain hazardous elements such as mercury and cadmium.

These materials could also be useful in devices that sense harmful molecules, gases, even biological systems. The applications range from heat sensing, pollution monitoring to medicine.

“To date, the constraint of existing mid-IR materials is a big bottleneck to translate many of these technologies,” says USC’s Wang.

The researchers hope that intense research in this area will make several of these technologies a reality in the near future.

The research on BTS is documented in “Giant optical anisotropy in a quasi-1D crystal” featured in Nature Photonics.

An international team of scientists, including NUST MISIS’s Professor Gotthard Seifert, have made an important step towards the control of excitonic effects in two-dimensional van der Waals heterostructures. In the future, this research will help to create electronics with more controlled properties. The research has been published in Nature Physics.

The creation of two-dimensional semiconductor materials is one of the most important areas of modern materials science. These materials can be the basis for elements needed to create the next generation of electronics.

One two-dimensional material with suitable electronic characteristics is two-dimensional molybdenum disulfide (MoS2), which has a single-layer structure (one atom layer) of molybdenum located between two sulfur layers: this material has a high charge mobility and high on/off in the transistor element.

In 2017, Professor Gotthard Seifert described the mechanism of defect germination in the structure of two-dimensional molybdenum disulfide as a process that will make it possible for scientists to capitalize on two-dimensional MoS2’s full potential use in microelectronics. This work was published in the leading journal, ACS Nano.

The study of other two-dimensional materials’ properties for their application in electronics has become the next step in this field. Monolayers of molybdenum disulfide (and, for example, wolframite diselenides–WSe2) have shown exceptional optical properties due to excitons: tightly bound pairs of electron-hole (quasiparticles acting as a carrier of a positive charge).

At the same time, the creation of the MoS2/WSe2 heterostructure by laying separate monolayers on each other leads to the appearance of a new type of exciton in it, where the electron and the hole are spatially divided into different layers.

Scientists have shown that interlayer excitons give a very specific optical signal display when layered. This allow scientists to study quantum phenomena, making it ideal for experiments in volitronics (a field of quantum electronics, «valley», or the local minimum of an element’s conduction zone) to control electrons in the «valleys» of semiconductors. In the future, these breakthroughs could lead to the most effective way to code information (by placing an electron in one of these valleys).

“Thanks to the use of spectroscopic methods and quantum-chemical calculations from the first principles, we have revealed a partially charged electron-hole in MoS2/WSe2 heterostructures, as well as [the electron-hole’s] location. We have managed to control the radiation energy of this new exciton by changing the relative orientation of the layers”, commented Professor Gotthard Seifert, one of NUST MISIS`s leading scientists.

According to Seifert, this result is an important step towards understanding and controlling exciton effects in Van der Waals heterostructures (where these distance-dependent atomic interactions occur). The research team is continuing to study the effect of layer rotations on the material’s electronic properties. In the future, this will allow for the creation of unique new materials for solar panels or electronics.

At this week’s 2018 Symposia on VLSI Technology and Circuits, imec, the world-leading research and innovation hub in nanoelectronics and digital technology, demonstrates for the first time the possibility to fabricate spin-orbit torque MRAM (SOT-MRAM) devices on 300mm wafers using CMOS compatible processes. With an unlimited endurance (>5×1010), fast switching speed (210ps), and power consumption as low as 300pJ, the SOT-MRAM devices manufactured in a 300mm line achieve the same or better performance as lab devices. This next-generation MRAM technology targets replacement of L1/L2 SRAM cache memories in high-performance computing applications.

SOT-MRAM has recently emerged as a non-volatile memory technology that promises a high endurance and low-power, sub-ns switching speed. With these properties, it can potentially overcome the limitations of spin-transfer torque MRAM (STT-MRAM) for L1/L2 SRAM cache memory replacement. But so far, SOT-MRAM devices have only been demonstrated in the lab. Imec has now for the first time proven full-scale integration of SOT-MRAM device modules on 300mm wafers using CMOS-compatible processes.

At the core of the SOT-MRAM device is a magnetic tunnel junction in which a thin dielectric layer is sandwiched between a magnetic fixed layer and a magnetic free layer. Similar as for STT-MRAM operation, writing of the memory is performed by switching the magnetization of this free magnetic layer, by means of a current. In STT-MRAM, this current is injected perpendicularly into the magnetic tunnel junction, and the read and write operation is performed through the same path – challenging the reliability of the device. In an SOT-MRAM device, on the contrary, switching of the free magnetic layer is done by injecting an in-plane current in an adjacent SOT layer – typically made of a heavy metal. Because of the current injection geometry, the read and write path are de-coupled, significantly improving the device endurance and read stability.

Imec has compared SOT and STT switching behavior on one and the same device, fabricated on 300mm wafers. While switching speed during STT-MRAM operation was limited to 5ns, reliable switching down to 210ps was demonstrated during SOT-MRAM operation. The SOT-MRAM devices show unlimited endurance (>5×1010) and operation power as low as 300pJ. In these devices, the magnetic tunnel junction consists of a SOT/CoFeB/MgO/CoFeB/SAF perpendicularly magnetized stack, using beta-phase tungsten (W) for the SOT layer.

“STT-MRAM technology has a high potential to replace L3 cache memory in high-performance computing applications”, says Gouri Sankar Kar, Distinguished Member of Technical Staff at imec. “However, due to the challenging reliability and increased nergy at sub-ns switching speeds, they are unsuitable to replace the faster L1/L2 SRAM cache memories. SOT-MRAM technology will help us to expand MRAM operation into the SRAM application domain. By moving this next-generation MRAM technology out of the lab, we have now demonstrated the maturity of the technology.” Future work will focus on further reducing the energy  consumption, by bringing down current density and by demonstrating field-free switching operation.

These results will be presented at the VLSI Circuits Symposium on June 20 in the session C8 Emerging Memory. Imec’s research into advanced memory is performed in cooperation with imec’s key partners in its core CMOS programs including GlobalFoundries, Huawei, Micron, Qualcomm, Sony Semiconductor Solutions, TSMC and Western Digital.

pSemi™ Corporation (formerly known as Peregrine Semiconductor), a Murata company focused on semiconductor integration, announces the availability of the PE29101 gallium nitride (GaN) field-effect transistor (FET) driver for solid-state light detection and ranging (LiDAR) systems. The PE29101 boasts the industry’s fastest rise times and a low minimum pulse width. This high-speed driver enables design engineers to extract the full performance and switching speed advantages from GaN transistors. In solid-state LiDAR systems, faster switching translates into improved resolution and accuracy in the LiDAR image.

“As GaN is proving its relevance in applications like solid-state LiDAR, design engineers are using pSemi high-speed drivers to maximize the fast switching benefits of GaN,” says Jim Cable, chief technology officer of pSemi. “Because of its rise and fall speed, the PE29101 enables the highest possible resolution imagery—something the industry needs for LiDAR to reach its fullest potential.”

LiDAR operates on the same principles as radar but instead uses pulsed lasers to precisely map surrounding areas. Traditionally used in high-resolution mapping, LiDAR is now used in advanced-driver assistance programs (ADAS) and is widely seen as an enabling technology to fully autonomous vehicles. Furthermore, solid-state LiDAR has emerged as the future leader in the commercialization of LiDAR systems, largely due to its affordability, reliability and compact size compared to mechanical sensors.

In LiDAR systems, the pulse laser’s switching speed and rise time directly impacts the measurement’s accuracy. To improve resolution, the current must switch as quickly as possible through the laser diode. GaN technology offers LiDAR systems superior resolution and a faster response time because of its very low input capacitance and its ability to switch significantly faster than metal-oxide semiconductor field-effect transistors (MOSFETs).

GaN FETs must be controlled by a very fast driver to maximize their fast-switching potential. Increasing the switching speed requires a driver with fast rise times and a low minimum output pulse width. The PE29101 offers these key performance specifications, enabling GaN technology to improve LiDAR resolution.

WIN Semiconductors Corp (TPEx:3105), the world’s largest pure-play compound semiconductor foundry, has expanded its portfolio of highly integrated GaAs technologies with the release of a new pHEMT technology. The PIH0-03 platform incorporates monolithic PIN and vertical Schottky diodes with WIN’s high performance 0.1um pseudomorphic HEMT process, PP10. This integrated technology, PIH0-03, adds a highly linear vertical Schottky diode with cut-off frequency over 600GHz, as well as multi-function PIN diodes while preserving the state-of-the-art mmWave performance of the PP10 technology. The availability of monolithic PIN and Schottky diodes with a high performance mmWave transistor enables on-chip integration of a wide range of functions, including mixers, temperature/power detecting, limiters, and high frequency switching, and supports power, low noise and optical applications through100 GHz.

This integrated technology provides users with multiple pathways to add on-chip functionality and reduce the overall die count of complex multi-chip modules used in a variety of end-markets. In addition to high frequency switching, the monolithic PIN diodes can be used for low parasitic capacitance ESD protection circuits, and as an on-chip power limiter to protect sensitive LNAs in phased array radars. The vertical Schottky diodes enable numerous detecting and mixing functions and can be combined with the PIN diodes in unique limiter applications.

“Today’s complex systems and highly competitive markets require increased mmWave performance and more functionality per chip. The PIH0-03 platform is the latest example of how WIN Semiconductors is addressing these critical market needs by offering high performance GaAs technologies with new levels of multifunction integration. To meet the ever-increasing demands of next generation mobile user equipment, wireless infrastructure, fiber optics and military applications, WIN Semiconductors continues to commercialize advanced, highly integrated GaAs solutions and provide our customers a clear technology advantage,” said David Danzilio, Senior Vice President of WIN Semiconductors Corp.

Semiconductors N.V. (NASDAQ:NXPI) has expanded its cellular infrastructure portfolio of GaN and silicon laterally diffused metal oxide semiconductor (Si-LDMOS) products that deliver industry leading performance in a compact footprint to enable next-generation 5G cellular networks.

Spectrum expansion, higher order modulation, carrier aggregation, full dimension beam forming, and other enablers of 5G connectivity will require an expanded base of technologies to support enhanced mobile broadband connectivity. With spectrum usage and network footprints, multiple-input, multiple output (MIMO) technologies from four transmit (4TX) antennas to 64 TX and higher will be employed. The future of 5G networks will depend on GaN and Si-LDMOS technologies and NXP is at the forefront in its RF power amplifier development.

“Building on the success of 25 years of LDMOS leadership — NXP released the world’s first LDMOS product in 1992 — today, we are extending our RF leadership with industry leading GaN technology, developed with the highest linear efficiency for cellular applications,” said Paul Hart, senior vice president and general manager of NXP’s RF Power business. “Backed with the best supply chain, global applications support and unparalleled design expertise in the industry, NXP is positioned to be the leading RF partner for 5G solutions.”

At IMS 2018, NXP is introducing new RF GaN wideband power transistors and expanding its Airfast third-generation Si-LDMOS portfolio of macro and outdoor small cell solutions. The new offerings include:

  • A3G22H400-04S: Ideally suited for 40 W base stations, this GaN product yields up to 56.5 percent efficiency and 15.4 dB of gain and covers cellular bands from 1800 MHz to 2200 MHz.
  • A3G35H100-04S: Providing 43.8 percent efficiency and 14 dB of gain, this GaN product enables 16 TX MIMO solutions at 3.5 GHz.
  • A3T18H400W23S: This Si-LDMOS product is leading the way to 5G at 1.8 GHz with Doherty efficiency up to 53.4 percent and gain of 17.1 dB.
  • A3T21H456W23S: Covering the full 90 MHz band from 2.11 GHz to 2.2 GHz, this solution exemplifies NXP’s best-in-class Si-LDMOS performance for efficiency, RF power and signal bandwidth.
  • A3I20D040WN: Within NXP’s family of integrated ultra-wideband LDMOS products, this solution offers peak power of 46.5 dBm with 365 MHz wideband class AB performance of 32 dB of gain, 18 percent efficiency at 10 dB OBO.
  • A2I09VD030N: This offering boasts peak power of 46 dBm with class AB performance of 34.5 dB gain, 20 percent efficiency at 10 dB OBO. The RF bandwidth for this product is 575 MHz to 960 MHz.

The breadth of the company’s RF Power technologies—which include GaN, silicon-LDMOS, SiGe, and GaAs—allows product options for 5G that span frequency and power spectrums with varying levels of integration. This wide array of options, combined with the products that NXP builds for digital computing, and baseband processing, makes NXP a unique supplier of end-to-end 5G solutions.

To learn more, visit NXP at the International Microwave Symposium (IMS 2018) June 10-15 at booth #739 or at www.nxp.com/RF.