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An international team of physicists, materials scientists and string theoreticians have observed a phenomenon on Earth that was previously thought to only occur hundreds of light years away or at the time when the universe was born. This result could lead to a more evidence-based model for the understanding the universe and for improving the energy-conversion process in electronic devices.

Using a recently discovered material called a Weyl semimetal, similar to 3D graphene, scientists at IBM Research (NYSE: IBM) have mimicked a gravitational field in their test sample by imposing a temperature gradient. The study was supervised by Prof. Kornelius Nielsch, Director at the Leibniz Institute for Materials and Solid State Research Dresden (IFW) and Prof. Claudia Felser, Director at the Max Planck Institute for Chemical Physics of Solids in Dresden.

After conducting the experiment in a cryolab at the University of Hamburg with high magnetic fields, a team of theoreticians from TU Dresden, UC Berkeley and the Instituto de Fisica Teorica UAM/CSIC confirmed with detailed calculations that they observed a quantum effect known as an axial-gravitational anomaly, which breaks one of the classical conservation laws, such as charge, energy and momentum.

This law-breaking anomaly had previously been derived in purely theoretical reasoning with methods based on string theory. It was believed to exist only at extremely high temperatures of trillions of degrees, as an exotic form of matter, called a quark-gluon plasma, at the early stages of the universe deep within the cosmos or created using particle colliders. But to their surprise, the researchers discovered that it also exists on Earth in the properties of solid-state physics, on which much of the computing industry is based on, spanning from tiny transistors to cloud data centers. This discovery is appearing today in the peer-reviewed journal Nature.

“For the first time, we have experimentally observed this fundamental quantum anomaly on Earth which is extremely important towards our understanding of the universe,” said Dr. Johannes Gooth, an IBM Research scientist and lead author of the paper. “We can now build novel solid-state devices based on this anomaly that have never been considered before to potentially circumvent some of the problems inherent in classical electronic devices, such as transistors.”

“This is an incredibly exciting discovery. We can clearly conclude that the same breaking of symmetry can be observed in any physical system, whether it occurred at the beginning of the universe or is happening today, right here on Earth,” said Prof. Dr. Karl Landsteiner, a string theorist at the Instituto de Fisica Teorica UAM/CSIC and co-author of the paper.

IBM scientists predict this discovery will open up a rush of new developments around sensors, switches and thermoelectric coolers or energy-harvesting devices, for improved power consumption.

An international team of researchers has found a way to determine whether a crystal is a topological insulator — and to predict crystal structures and chemical compositions in which new ones can arise. The results, published July 20 in the journal Nature, show that topological insulators are much more common in nature than currently believed.

Topological materials, which hold promise for a wide range of technological applications due to their exotic electronic properties, have attracted a great deal of theoretical and experimental interest over the past decade, culminating in the 2016 Nobel Prize in physics. The materials’ electronic properties include the ability of current to flow without resistance and to respond in unconventional ways to electric and magnetic fields.

Until now, however, the discovery of new topological materials occurred mainly by trial and error. The new approach described this week allows researchers to identify a large series of potential new topological insulators. The research represents a fundamental advance in the physics of topological materials and changes the way topological properties are understood.

The team included: at Princeton University, Barry Bradlyn and Jennifer Cano, both associate research scholars at the Princeton Center for Theoretical Science, Zhijun Wang, a postdoctoral research associate, and B. Andrei Bernevig, professor of physics; professors Luis Elcoro and Mois Aroyo at the University of the Basque Country in Bilbao; assistant professor Maia Garcia Vergniory of University of the Basque Country and Donostia International Physics Center (DIPC) in Spain; and Claudia Felser, professor at the Max Planck Institute for Chemical Physics of Solids in Germany.

“Our approach allows for a much easier way to find topological materials, avoiding the need for detailed calculations,” Felser said. “For some special lattices, we can say that, regardless of whether a material is an insulator or a metal, something topological will be going on,” Bradlyn added.

Until now, of the roughly 200,000 materials catalogued in materials databases, only around a few hundred are known to host topological behavior, according to the researchers. “This raised the question for the team: Are topological materials really that scarce, or does this merely reflect an incomplete understanding of solids?” Cano said.

To find out, the researchers turned to the nearly century-old band theory of solids, considered one of the early landmark achievements of quantum mechanics. Pioneered by Swiss-born physicist Felix Bloch and others, the theory describes the electrons in crystals as residing in specific energy levels known as bands. If all the states in a group of bands are filled with electrons, then the electrons cannot move and the material is an insulator. If some of the states are unoccupied, then electrons can move from atom to atom and the material is capable of conducting an electrical current.

Because of the symmetry properties of crystals, however, the quantum states of electrons in solids have special properties. These states can be described as a set of interconnected bands characterized by their momentum, energy and shape. The connections between these bands, which on a graph resemble tangled spaghetti strands, give rise to topological behaviors such as those of electrons that can travel on surfaces or edges without resistance.

The team used a systematic search to identify many previously undiscovered families of candidate topological materials. The approach combined tools from such disparate fields as chemistry, mathematics, physics and materials science.

First, the team characterized all the possible electronic band structures arising from electronic orbitals at all the possible atomic positions for all possible crystal patterns, or symmetry groups, that exist in nature, with the exception of magnetic crystals. To search for topological bands, the team first found a way to enumerate all allowed non-topological bands, with the understanding that anything left out of the list must be topological. Using tools from group theory, the team organized into classes all the possible non-topological band structures that can arise in nature.

Next, by employing a branch of mathematics known as graph theory — the same approach used by search engines to determine links between websites — the team determined the allowed connectivity patterns for all of the band structures. The bands can either separate or connect together. The mathematical tools determine all the possible band structures in nature — both topological and non-topological. But having already enumerated the non-topological ones, the team was able to show which band structures are topological.

By looking at the symmetry and connectivity properties of different crystals, the team identified several crystal structures that, by virtue of their band connectivity, must host topological bands. The team has made all of the data about non-topological bands and band connectivity available to the public through the Bilbao Crystallographic Server. “Using these tools, along with our results, researchers from around the world can quickly determine if a material of interest can potentially be topological,” Elcoro said.

The research shows that symmetry, topology, chemistry and physics all have a fundamental role to play in our understanding of materials, Bernevig said. “The new theory embeds two previously missing ingredients, band topology and orbital hybridization, into Bloch’s theory and provides a prescriptive path for the discovery and characterization of metals and insulators with topological properties.”

David Vanderbilt, a professor of physics and astronomy at Rutgers University who was not involved in the study, called the work remarkable. “Most of us thought it would be many years before the topological possibilities could be catalogued exhaustively in this enormous space of crystal classes,” Vanderbilt said. “This is why the work of Bradlyn and co-workers comes as such a surprise. They have developed a remarkable set of principles and algorithms that allow them to construct this catalogue at a single stroke. Moreover, they have combined their theoretical approach with materials database search methods to make concrete predictions of a wealth of new topological insulator materials.”

The theoretical underpinnings for these materials, called “topological” because they are described by properties that remain intact when an object is stretched, twisted or deformed, led to the awarding of the Nobel Prize in physics in 2016 to F. Duncan M. Haldane, Princeton University’s Sherman Fairchild University Professor of Physics, J. Michael Kosterlitz of Brown University, and David J. Thouless of the University of Washington.

Chemistry and physics take different approaches to describing crystalline materials, in which atoms occur in regularly ordered patterns or symmetries. Chemists tend to focus on the atoms and their surrounding clouds of electrons, known as orbitals. Physicists tend to focus on the electrons themselves, which can carry electric current when they hop from atom to atom and are described by their momentum.

“This simple fact — that the physics of electrons is usually described in terms of momentum, while the chemistry of electrons is usually described in terms of electronic orbitals — has left material discovery in this field at the mercy of chance,” Wang said.

“We initially set out to better understand the chemistry of topological materials — to understand why some materials have to be topological,” Vergniory said.

Aroyo added, “What came out was, however, much more interesting: a way to marry chemistry, physics and mathematics that adds the last missing ingredient in a century-old theory of electronics, and in the present-day search for topological materials.”

A little fluorine turns an insulating ceramic known as white graphene into a wide-bandgap semiconductor with magnetic properties. Rice University scientists said that could make the unique material suitable for electronics in extreme environments.

A proof-of-concept paper from Rice researchers demonstrates a way to turn two-dimensional hexagonal boron nitride (h-BN) – aka white graphene – from an insulator to a semiconductor. The magnetism, they said, is an unexpected bonus.

Because the atomically thin material is an exceptional conductor of heat, the researchers suggested it may be useful for electronics in high-temperature applications, perhaps even as magnetic memory devices.

The discovery appears this week in Science Advances.

“Boron nitride is a stable insulator and commercially very useful as a protective coating, even in cosmetics, because it absorbs ultraviolet light,” said Rice materials scientist Pulickel Ajayan, whose lab led the study. “There has been a lot of effort to try to modify its electronic structure, but we didn’t think it could become both a semiconductor and a magnetic material.

“So this is something quite different; nobody has seen this kind of behavior in boron nitride before,” he said.

The researchers found that adding fluorine to h-BN introduced defects into its atomic matrix that reduced the bandgap enough to make it a semiconductor. The bandgap determines the electrical conductivity of a material.

“We saw that the gap decreases at about 5 percent fluorination,” said Rice postdoctoral researcher and co-author Chandra Sekhar Tiwary. The gap gets smaller with additional fluorination, but only to a point. “Controlling the precise fluorination is something we need to work on. We can get ranges but we don’t have perfect control yet. Because the material is atomically thin, one atom less or more changes quite a bit.

“In the next set of experiments, we want to learn to tune it precisely, atom by atom,” he said.

They determined that tension applied by invading fluorine atoms altered the “spin” of electrons in the nitrogen atoms and affected their magnetic moments, the ghostly quality that determines how an atom will respond to a magnetic field like an invisible, nanoscale compass.

“We see angle-oriented spins, which are very unconventional for 2-D materials,” said Rice graduate student and lead author Sruthi Radhakrishnan. Rather than aligning to form ferromagnets or canceling each other out, the spins are randomly angled, giving the flat material random pockets of net magnetism. These ferromagnet or anti-ferromagnet pockets can exist in the same swatch of h-BN, which makes them “frustrated magnets” with competing domains.

The researchers said their simple, scalable method can potentially be applied to other 2-D materials. “Making new materials through nanoengineering is exactly what our group is about,” Ajayan said.

Co-authors of the paper are graduate students Carlos de los Reyes and Zehua Jin, chemistry lecturer Lawrence Alemany, postdoctoral researcher Vidya Kochat and Angel Martí, an associate professor of chemistry, of bioengineering and of materials science and nanoengineering, all of Rice; Valery Khabashesku of Rice and the Baker Hughes Center for Technology Innovation, Houston; Parambath Sudeep of Rice and the University of Toronto; Deya Das, Atanu Samanta and Rice alumnus Abhishek Singh of the Indian Institute of Science, Bangalore; Liangzi Deng and Ching-Wu Chu of the University of Houston; Thomas Weldeghiorghis of Louisiana State University and Ajit Roy of the Air Force Research Laboratories at Wright-Patterson Air Force Base.

Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry.

A hypoallergenic electronic sensor can be worn on the skin continuously for a week without discomfort, and is so light and thin that users forget they even have it on, says a Japanese group of scientists. The elastic electrode constructed of breathable nanoscale meshes holds promise for the development of noninvasive e-skin devices that can monitor a person’s health continuously over a long period.

Wearable electronics that monitor heart rate and other vital health signals have made headway in recent years, with next-generation gadgets employing lightweight, highly elastic materials attached directly onto the skin for more sensitive, precise measurements. However, although the ultrathin films and rubber sheets used in these devices adhere and conform well to the skin, their lack of breathability is deemed unsafe for long-term use: dermatological tests show the fine, stretchable materials prevent sweating and block airflow around the skin, causing irritation and inflammation, which ultimately could lead to lasting physiological and psychological effects.

“We learned that devices that can be worn for a week or longer for continuous monitoring were needed for practical use in medical and sports applications,” says Professor Takao Someya at the University of Tokyo’s Graduate School of Engineering whose research group had previously developed an on-skin patch that measured oxygen in blood.

In the current research, the group developed an electrode constructed from nanoscale meshes containing a water-soluble polymer, polyvinyl alcohol (PVA), and a gold layer–materials considered safe and biologically compatible with the body. The device can be applied by spraying a tiny amount of water, which dissolves the PVA nanofibers and allows it to stick easily to the skin–it conformed seamlessly to curvilinear surfaces of human skin, such as sweat pores and the ridges of an index finger’s fingerprint pattern.

The researchers next conducted a skin patch test on 20 subjects and detected no inflammation on the participants’ skin after they had worn the device for a week. The group also evaluated the permeability, with water vapor, of the nanomesh conductor–along with those of other substrates like ultrathin plastic foil and a thin rubber sheet–and found that its porous mesh structure exhibited superior gas permeability compared to that of the other materials.

Furthermore, the scientists proved the device’s mechanical durability through repeated bending and stretching, exceeding 10,000 times, of a conductor attached on the forefinger; they also established its reliability as an electrode for electromyogram recordings when its readings of the electrical activity of muscles were comparable to those obtained through conventional gel electrodes.

“It will become possible to monitor patients’ vital signs without causing any stress or discomfort,” says Someya about the future implications of the team’s research. In addition to nursing care and medical applications, the new device promises to enable continuous, precise monitoring of athletes’ physiological signals and bodily motion without impeding their training or performance.

The electric current from a flexible battery placed near the knuckle flows through the conductor and powers the LED just below the fingernail. Credit: 2017 Someya Laboratory.

The electric current from a flexible battery placed near the knuckle flows through the conductor and powers the LED just below the fingernail. Credit: 2017 Someya Laboratory.

Transistors, as used in billions on every computer chip, are nowadays based on semiconductor-type materials, usually silicon. As the demands for computer chips in laptops, tablets and smartphones continue to rise, new possibilities are being sought out to fabricate them inexpensively, energy-saving and flexibly. The group led by Dr. Christian Klinke has now succeeded in producing transistors based on a completely different principle. They use metal nanoparticles which are so small that they no longer show their metallic character under current flow but exhibit an energy gap caused by the Coulomb repulsion of the electrons among one another. Via a controlling voltage, this gap can be shifted energetically and the current can thus be switched on and off as desired. In contrast to previous similar approaches, the nanoparticles are not deposited as individual structures, rendering the production very complex and the properties of the corresponding components unreliable, but, instead, they are deposited as thin films with a height of only one layer of nanoparticles. Employing this method, the electrical characteristics of the devices become adjustable and almost identical.

These Coulomb transistors have three main advantages that make them interesting for commercial applications: The synthesis of metal nanoparticles by colloidal chemistry is very well controllable and scalable. It provides very small nanocrystals that can be stored in solvents and are easy to process. The Langmuir-Blodgett deposition method provides high-quality monolayered films and can also be implemented on an industrial scale. Therefore, this approach enables the use of standard lithography methods for the design of the components and the integration into electrical circuits, which renders the devices inexpensive, flexible, and industry-compatible. The resulting transistors show a switching behavior of more than 90% and function up to room temperature. As a result, inexpensive transistors and computer chips with lower power consumption are possible in the future. The research results have now been published in the scientific journal “Science Advances“.

“Scientifically interesting is that the metal particles inherit semiconductor-like properties due to their small size. Of course, there is still a lot of research to be done, but our work shows that there are alternatives to traditional transistor concepts that can be used in the future in various fields of application”, says Christian Klinke. “The devices developed in our group can not only be used as transistors, but they are also very interesting as chemical sensors because the interstices between the nanoparticles, which act as so-called tunnel barriers, react highly sensitive to chemical deposits.”

Scientists from the Moscow Institute of Physics and Technology (MIPT) and the Kotelnikov Institute of Radio Engineering and Electronics (IRE) of the Russian Academy of Sciences (RAS), in collaboration with their colleagues from Finland, have developed a new type of optical fiber that has an extremely large core diameter and preserves the coherent properties of light. The paper was published in the journal Optics Express. The results of the study are promising for constructing high-power pulsed fiber lasers and amplifiers, as well as polarization-sensitive sensors.

When it comes to optical fiber applications, preserving the properties of light is crucial. There are two principal parameters that often need to be preserved: the distribution of light intensity in cross section and the polarization of light (a property that specifies the oscillation directions of the electric or magnetic field in a plane perpendicular to the wave propagation direction). In their study, the researchers managed to fulfill both conditions.

“Optical fiber research is one of the most rapidly developing fields of optics. Over the last decade, numerous technological solutions have been proposed and implemented. For instance, researchers and engineers at IRE RAS can now produce optical fiber of almost any diameter with arbitrary transverse structure,” says Vasily Ustimchik, who is a co-author of the study, a senior research scientist at IRE RAS and the Russian Quantum Center, and a professor at MIPT. “In the course of this study, a specific structure was formed in the optical fiber. It varies along two orthogonal axes, and its diameters change proportionally along the fiber. Individually, such solutions are already widely used, so it is critical to continue to work in this direction.”

An optical fiber is generally a very thin flexible strand drawn from glass or transparent plastic. At first glance, it seems to be a rather simple system, but in practice, we are confronted with a number of major issues limiting its applications, the first being signal attenuation in fiber-optic lines. The solution to this problem has long been found, paving the way for fiber-optic communications. However, communications are not the only area where optical fibers can be applied. Today, one of the most common types of lasers are based on fiber-optic technology. A fiber laser, just like any other, incorporates an optical resonator, which causes light to travel back and forth repeatedly. The geometrical parameters of the fiber resonator allow for only a limited set of transverse patterns of light intensity distribution in the output beam — the so-called transverse modes of the resonator (see Fig. 1). Naturally, one would want to control the mode structure of the light, and in fact, when it comes to practice, researchers and engineers are mostly seeking to excite nothing but one pure fundamental mode (see the upper left corner of Fig. 1) that does not change with time.

In order to maintain single-mode operation, the fiber must consist of a core and a cladding — materials with different refractive indexes. Ordinarily, the thickness of the inner part (fiber core), through which radiation propagates, normally has to be less than 10 micrometers.

An increase in the optical power of the light propagating in the fiber results in a greater amount of energy being absorbed. This translates into a change in the properties of the fiber. Specifically, it causes uncontrolled variation of the refractive index of the fiber material. This gives rise to parasitic nonlinear effects, resulting in additional spectral lines of emission etc., which limits the strength of the optical signals that are transmitted. An existing solution to the problem — which the authors also used — lies in the variation of the core and outer diameters along the length of the fiber (see Fig. 2).

If the expansion of the fiber occurs adiabatically — that is, relatively slowly — it is possible to reduce the amount of energy transferred to other modes to less than 1 percent, even with a core diameter of up to 100 micrometers (which is exceptionally large for single-mode fibers). Moreover, the fact that the core diameter is large and varies along the fiber increases the threshold for nonlinear effects occurrence.

To achieve the second goal — which was to preserve the polarization state of the light — the authors of the study made the cladding of the fiber anisotropic: The width and the height of the inner cladding are different (the cladding is elliptical), which means the propagation speed of light with different field oscillation directions is not the same. In a structure like this, the process of transferring energy from one polarized mode to another is almost entirely disrupted. In their study, the researchers have shown that the geometric length of the path traveled by light through the fiber at which the oscillations of the two different polarizations are in antiphase depends on the fiber core diameter: It decreases as the diameter is increased. This length, known as the polarization beat length, corresponds to one complete rotation of the linear polarization state in the fiber. In other words, if you launch linearly polarized light into a fiber, it will be linearly polarized again after traveling precisely this distance. The ability to measure this parameter is in itself evidence of the fact that the polarization state in the fiber is preserved.

In order to investigate the properties related to light polarization in the fiber, the method of optical frequency-domain reflectometry was used. It involves launching an optical signal into the fiber and detecting the backscattered signal. The reflected signal contains a lot of information. This method is normally used to determine the location of defects and impurities in optical fibers, but it can also determine both the coherence length and the spatial distribution of polarization beat length. Coherence reflectometry techniques are widely used to monitor the state of optical fibers. However, the method used in this study is notable for enabling data collection at a high resolution of up to 20 micrometers along the fiber length.

Professor Sergey Nikitov, who is deputy head of MIPT’s Section of Solid State Physics, Radiophysics and Applied Information Technologies, corresponding member of RAS, the director of IRE RAS, and the leader of the research group, commented: “The fiber samples we obtained have demonstrated great results, indicating good prospects for further development of such technological solutions. They will find use not only in laser systems but also in optical fiber sensors, where the change of polarization characteristics is known in advance, since they are determined by external environmental factors, such as temperature, pressure, biological and other impurities. Besides, they have a number of advantages over semiconductor sensors. For example, they need no electrical power and are capable of carrying out distributed sensing, and that is not a complete list.”

GLOBALFOUNDRIES and VeriSilicon today announced a collaboration to deliver the industry’s first single-chip IoT solution for next-generation Low Power Wide Area (LPWA) networks. Leveraging GF’s 22FDX® FD-SOI technology, the companies plan to develop intellectual property that could enable a complete cellular modem module on a single chip, including integrated baseband, power management, RF radio and front-end module combining both Narrowband IoT (NB-IoT) and LTE-M capabilities. The new approach is expected to deliver significant improvements in power, area, and cost compared to current offerings.

With the proliferation of connected devices for smart cities, homes, and industrial applications, network providers are developing new communications protocols that better meet the needs of emerging IoT standards. LPWA technology takes advantage of the existing LTE spectrum and mobile infrastructure, but focuses on delivering ultra-low power, extended range, and much lower data rates for devices that transmit small amounts of infrequent data, such as connected water and gas meters.

The two leading LPWA connectivity standards are LTE-M, which is expected to get traction in the U.S. market, and NB-IoT, which is gaining ground in Europe and Asia. For example, the Chinese government has targeted NB-IoT for nationwide deployment over the coming year. The combination of these two technologies is expected to push cellular M2M module shipments to nearly half a billion by 2021, according to ABI Research.

GF and VeriSilicon are developing a suite of IP to enable customers to create single chip cost- and power-optimized solutions for worldwide deployment, based on a dual-mode carrier-grade baseband modem with integrated RF front-end module. The design will be fabricated using GF’s 22FDX process, which leverages a 22nm FD-SOI technology platform to provide cost-effective scaling and power reduction for IoT applications. 22FDX is the only technology that allows efficient single-chip integration of RF, transceiver, baseband, processor, and power management components. This integration is expected to deliver more than an 80 percent improvement in both power and die size compared to today’s 40nm technologies.

“Our 22FDX technology is perfectly positioned to support the explosive growth of low-power, battery-operated IoT devices,” said Alain Mutricy, senior vice president of product management at GF. “We are especially excited about the opportunities presented by the China market, which is leading the way with a nationwide commitment to IoT and smart cities. This new initiative expands on our long standing relationship with VeriSilicon—an important partner helping us build an FD-SOI ecosystem around our new 300mm fab in Chengdu.”

“Started from more than five years ago, as a Silicon Platform as a Service (SiPaaS) company, VeriSilicon has developed FD-SOI IPs and achieved first silicon success of many chips based on FD-SOI technologies. For IoT applications, besides cost advantages, integrated RF, body bias, and embedded memory, such as MRAM, are the key benefits of FD-SOI technologies beyond 28 nm bulk CMOS.” said Wayne Dai, VeriSilicon Chairman, President and CEO. “Integrated with RF and PA on GF 22FDX, the baseband and protocol stack are being implemented on our energy efficient and programmable ZSPnano that is optimized for control and data flow with powerful low latency, single cycle instructions for signal processing. GF’s new 300 mm fab for FDX in Chengdu and IP platforms such as this single chip solution for integrated NB-IoT and LTE-M, will have significant impact on China IoT and AIoT (AI of Things) industries.”

GF and VeriSilicon expect to tape out a test chip based on the integrated solution, with silicon validation in Q4 2017. The companies plan to pursue carrier certification in mid-2018.

ASM International introduced the Intrepid® ESTM 300mm epitaxy (epi) tool for advanced-node CMOS logic and memory high-volume production applications. Intrepid ES introduces innovative closed loop reactor control technology that enables optimal within wafer and wafer-to-wafer process performance, critical for today’s advanced transistors and memories. Furthermore, Intrepid ES reduces the cost per wafer significantly for a 7nm epi process compared with prior node processes. The new tool has been qualified for production at a leading-edge foundry customer, and is targeting production applications in other industry segments as well. To date, over 40 reactors have been delivered.

“Over the past several years, multiple customers have been very clear that there is a need to address several technical and cost challenges in the epi market,” said Chuck del Prado, President and Chief Executive Officer of ASM International. “Intrepid ES is the result of a focused development program to address major challenges in this market, including film non-uniformity, process repeatability, tool uptime and high cost per wafer. This early success of the Intrepid ES clearly demonstrates that we are on track in addressing our customers’ emerging epi requirements.”

The new Intrepid ES tool is based on a combination of reactor and platform design improvements. It demonstrates improved film performance and enhanced reactor stability. Fundamental to its technology is an isothermal reactor environment in which the wafer is processed. This provides consistent and repeatable temperature control across the wafer and wafer-to-wafer.

By Ed Korczynski

Veeco Instruments (Veeco) recently announced that Veeco CNT—formerly known as Ultratech/Cambridge Nanotech—shipped its 500th Atomic Layer Deposition (ALD) system to the North Carolina State University. The Veeco CNT Fiji G2 ALD system will enable the University to perform research for next-generation electronic devices including wearables and sensors. Veeco announced the overall acquisition of Ultratech on May 26 of this year. Executive technologists from Veeco discussed the evolution of ALD technology with Solid State Technology in an exclusive interview just prior to SEMICON West 2017.

Professor Roy Gordon from Harvard University been famous for decades as an innovator in the science of thin-film depositions, and people from his group were part of the founding of Cambridge Nanotech in 2003. Continuity from the original team has been maintained throughout the acquisitions, such that Veeco inherited a lot of process know-how along with the hardware technologies. “Cambridge Nanotech has had a broad history of working with ALD technology,” said Ganesh Sandaren, VP of Veeco CNT Applied Technology, “and that’s been a big advantage for us in working with some major researchers who really appreciate what we’re providing.”

The Figure shows that the company’s ALD chambers have evolved over time from simple single-wafer thermal ALD, to single-wafer plasma-enhance ALD (PEALD), to a large chamber targeting batch processing of up to ten 370 mm x 470 mm (Gen2.5) flat-panels for display applications, and a “large area” chamber capable of 1m x 1.2m substrates for photovoltaic and FPD applications. The large area chamber allows customers to do things like put down an encapsulating layer or an active layer such as buffer materials on CIGS-based solar cells.

Evolution of Atomic-Layer Deposition (ALD) technology starts with single-wafer thermal chambers, adds plasma energy, and then goes to batch processing for manufacturing. (Source: Veeco CNT).

Evolution of Atomic-Layer Deposition (ALD) technology starts with single-wafer thermal chambers, adds plasma energy, and then goes to batch processing for manufacturing. (Source: Veeco CNT).

“There a tendency to think that ALD only belongs in the high-k dielectric application for semiconductor devices, but there are many ongoing applications outside of IC fabs,” reminded Gerry Blumenstock, VP and GM of MBE business unit and Veeco CNT. “Customers who want to do heterogeneous materials develop can now have MBE and ALD in a single tool connected by a vacuum cluster configuration. We have customers today that do not want to break vacuum between processes.” Veeco’s MBE tools are mostly used for R&D, but are also reportedly used for HVM of laser chips.

To date, Cambridge Nanotech tools are generally used by R&D labs, but Veeco is open to the possibility of creating tools for High-Volume Manufacturing (HVM) if customers call for them. “Now that this is part of Veeco, we have the service infrastructure to be able to support end-users in high-volume manufacturing like any of the major OEMs,” said Blumenstock. “It’s an interesting future possibility, but in the next six months to a year we’re focusing on improving our offering to the R&D community. Still, we’re staying close to HVM because if a real opportunity arose there’s no reason we couldn’t get into it.”

In IC fab R&D today, some of the most challenging depositions are of Self-Assembled Monolayers (SAM) that are needed as part of the process-flow to enable Direct Self-Assembly (DSA) of patterns to extend optical lithography to the finest possible device features. SAM are typically created using ALD-type processes, and can also be used to enable selective ALD of more than a monolayer. Veeco-CNT is actively working on SAM in R&D with multiple customers now, and claim that major IC device manufacturers have purchased tools.

At the leading edge of materials R&D, researchers are always experimenting with new chemical precursors. “Having a precursor that has good vapor-pressure, and is reactive yet somewhat stable is what is needed,” reminded Sundaram. “People will generally chose a liquid over a solid precursor because of higher vapor pressure. There are many classes of precursors, and many are halogens but they have disadvantages in some reactions. So we see continue to move to metal-organic precursors, which tend to provide good vapor-pressures and not form undesirable byproducts.”

By Ed Korczynski 

Global industry R&D hub IMEC defines the “IMEC 7nm-Node” (I7N) for finFETs to have 56nm Contacted Gate Pitch (CGP) with 40nm Metal Pitch (MP), and such critical mask layers can be patterned with a single exposure of 0.33 N.A. EUVL as provided by the ASML NXE:3400B tool. To reach IMEC 3nm-Node (I3N) patterning targets of ~40 CGP and ~24 MP, either double exposure of 0.33 N.A. EUVL would be needed or else single-exposure of 0.55 N.A. EUVL as promised by the next-generation ASML tool. All variations of EUVL require novel photoresists and anti-reflective coatings (ARC) to be able to achieve the desired patterning.

The Figure shows that IMEC has led tremendous progress on the photoresists, with best resolution in a single 0.33 N.A. EUVL exposure of 13nm half-pitch (HP) line arrays. The most important parameter for the photoresist is the sensitivity target of 20 mJ/cm2, but at that dosage the best materials seen today have unacceptably high line-width roughness of >5nm three-sigma.

“If you’re talking about lines of 16nm width, for 3-sigma you want to be less than 3nm line-width-roughness,” explained Steegen during the 2017 IMEC Technology Forum. “Smoothing techniques are post-develop technologies that basically reduce line-width-roughness. We are working with many partners, and all are making progress in reducing line-width roughness though post-develop techniques.”

Top-down SEM images of the best achieved EUVL resolutions using 0.33 N.A. stepper and Chemically-Amplified Resist (CAR) or metal-oxide Non-Chemically-Amplified Resist (NCAR) formulations, along with post-development “smoothing” technologies to improve the Line-Width Roughness (LWR) to meet target specifications. (Source: IMEC)

Top-down SEM images of the best achieved EUVL resolutions using 0.33 N.A. stepper and Chemically-Amplified Resist (CAR) or metal-oxide Non-Chemically-Amplified Resist (NCAR) formulations, along with post-development “smoothing” technologies to improve the Line-Width Roughness (LWR) to meet target specifications. (Source: IMEC)

The Figure also shows that IMEC has been working with vacuum deposition companies on atomic-layer deposition (ALD) or chemical-vapor deposition (CVD) processes to ideally take off 2 nm of sidewall roughness. Plasma energy may be capacitively- or inductively-coupled to a vacuum chamber to allow for either PEALD or PECVD processing. Such precise atomic-scale processing may be composed of “dep/etch” sequences of one/few atomic layer depositions followed by light plasma etching such that the nominal line-width would not necessarily change. However, this approach necessitates that the wafer leave the lithography track and move to a separate vacuum-tool.

To save on cost and time, LWR smoothing may be accomplished to some extent today in the litho track by specialized spin-on materials. Companies that supply lithography resolution extension (EXT) materials such as spin-on hard masks (SOHM) and anti-reflective coatings (ARC) have looked at ways spin-on materials can improve the LWR of post-developed resist lines. This can be combined with “shrink” materials that add controlled thicknesses to sidewalls of holes, or with “trim” materials that subtract controlled thicknesses from the sidewalls of lines. Generally, some manner of complex chemical engineering is used to create a film that either forms or breaks bonds when thermally driven by a bake step, and after image transfer to underlying SOHM layers the shrink/trim material is typically stripped in a solvent such as propylene glycol methyl ether acetate (PGMEA).

EUVL photoresists may be based on metal-oxide nano-particles, instead of on extensions to the Chemically-Amplified Resist (CAR) formulations that have been mainstays of ArF/ArFi lithography for decades. Inpria Corp.—the 10-year-old-start-up supported by industry—has ultimately developed a tin-oxide family of blends that are shown as the Non-Chemically-Amplified Resist (NCAR) in the Figure. NCAR metal-oxide resists show similar LWR at similar exposure doses to CARs. However, the metal-oxides in the NCAR can often replace SOHM materials, saving cost and complexity in the resist stack.

IMEC’s work on EUVL with ASML steppers leads to the belief that the source power will increase to allow throughput to rise from today’s ~100 wph to ~120 wph by the end of this year. However, those throughputs assume 20mJ/cm2 resist-speed, and masks may require 30 mJ/cm2 target exposures even with post-develop smoothing steps.

[DISCLOSURE: Ed Korczynski is also Sr. Technology Analyst with TECHCET Group, and author of the “Critical Materials Report: Photoresists and Extensions and Ancillaries 2017”.]