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Energy loss due to scattering from material defects is known to set limits on the performance of nearly all technologies that we employ for communications, timing, and navigation. In micro-mechanical gyroscopes and accelerometers, such as those commonly found in cellphones today, microstructural disorder impacts measurement drift and overall accuracy of the sensor, analogous to how a dirty violin string might impact one’s enjoyment of beautiful music. In optical fiber communication systems, scattering from material defects can reduce data fidelity over long distances thereby reducing achievable bandwidth. Since defect-free materials cannot be obtained, how can we possibly improve on the fundamental technological limits imposed by disorder?

A research collaboration between the University of Illinois at Urbana-Champaign, the National Institute of Standards and Technology, and the University of Maryland has revealed a new technique by which scattering of sound waves from disorder in a material can be suppressed on demand. All of this, can be simply achieved by illuminating with the appropriate color of laser light. The result, which is published in Nature Communications, could have a wide-ranging impact on sensors and communication systems.

This is a microscope image of a silica glass resonator and optical fiber waveguide. Light and sound circulating in this type of resonator are shown to exhibit chiral effects in this study. (Credit: Gaurav Bahl, University of Illinois Department of Mechanical Science and Engineering)

This is a microscope image of a silica glass resonator and optical fiber waveguide. Light and sound circulating in this type of resonator are shown to exhibit chiral effects in this study. (Credit: Gaurav Bahl, University of Illinois Department of Mechanical Science and Engineering)

Gaurav Bahl, an assistant professor of mechanical science and engineering, and his research team have been studying the interaction of light with sound in solid state micro-resonators. This new result is the culmination of a series of experiments pursued by his team over the past several years, and a new scientific question posed in the right place.

“Resonators can be thought of as echo chambers for sound and light, and can be as simple as micro-spherical balls of glass like those we used in our study,” Bahl explained. “Our research community has long understood that light can be used to create and amplify sound waves in resonators through a variety of optical forces. The resonant echoes help to increase the interaction time between sound, light, and material disorder, making these subtle effects much easier to observe and control. Since interactions within resonators are fundamentally no different from those taking place in any other system, these can be a really compact platform for exploring the underlying physics.”

The key to suppressing scattering from disorder is to induce a mismatch in the propagation between the original and scattered directions. This idea is similar to how an electric current prefers to flow along the path of least resistance, or how water prefers to flow through a wider pipe rather than a constricted one. To suppress back-scattering of forward-moving sound waves, one must create a large acoustic impedance in the backward direction. This asymmetry for forward and backward propagating waves is termed as chirality of the medium. Most solid-state systems do not have chiral properties, but these properties can be induced through magnetic fields or through space-time variation of the medium.

“A few years ago, we discovered that chirality can be induced for light using an opto-mechanical phenomenon, in which light couples with propagating sound waves and renders the medium transparent. Our experiments at that time showed that the induced optical transparency only allows light to move unidirectionally, that is, it creates a preferentially low optical impedance in one direction,” Bahl said. “It is then that we met our collaborator Jacob Taylor, a physicist at NIST, who asked us a simple question. What happens to the sound waves in such a system?”

“Our theoretical modeling predicted that having a chiral system for sound propagation could suppress any back-scattering that may have been induced by disorder,” explained Taylor. “This concept arose from work we’ve been doing in the past few years investigating topological protection for light, where chiral propagation is a key feature for improving the performance of devices. Initially the plan with Bahl’s team was just to show a difference between the forward and backward propagating sound waves, using a cooling effect created by light. But the system surprised us with an even stronger practical effect than expected.”

That simple question launched a new multi-year research effort in a direction that has not been explored previously. Working in close collaboration, the team discovered that Brillouin light scattering, a specific kind of opto-mechanical interaction, could also induce chirality for sound waves. Between the experimental tools in Bahl’s lab, and the theoretical advancements in Taylor’s lab, the pieces of the puzzle were already in place.

“We experimentally prepared a chiral optomechanical system by circulating a laser field in the clockwise direction in a silica glass resonator. The laser wavelength, or color, was specially arranged to induce optical damping of only clockwise sound waves. This created a large acoustic impedance mismatch between clockwise and counter-clockwise directions of propagation,” explained Seunghwi Kim, first author of the study. “Sound waves that were propagating the clockwise direction experienced very high losses due to the opto-mechanical cooling effect. Sound waves moving in the counter-clockwise direction could move freely. Surprisingly, we saw a huge reduction of scattering loss for counter-clockwise sound waves, since those waves could no longer scatter into the clockwise direction! In other words, even though disorder was present in the resonator, its action was suppressed.”

Just as sound is the primary method of voice communication between humans, electromagnetic waves like radio and light are the primary technology used for global communications. What could this discovery mean for the communications industry? Disorder and material defects are unavoidable optical fiber systems, resulting in lower data fidelity, bit errors, and bandwidth limitations. The team believes that technologies based on this discovery could be leveraged to circumvent the impact of unavoidable material defects in such systems.

“We’ve seen already that many sensors, such as those found in your phone or in your car, can be limited by intrinsic defects in the materials,” added Taylor. “The approach introduced here provides a simple means of circumventing those challenges, and may even help us approach the limits set by quantum mechanics, rather than our own engineering challenges.”

Practical applications of this result may not be too many years off. Reduction of mechanical losses could also directly improve mechanics-based inertial navigation sensors that we use today. Examples that we encounter in daily life are accelerometers and gyroscopes, without which our mobile phones would be a lot less capable, and our cars and airplanes a lot less safe.

Cadence Design Systems, Inc. (NASDAQ: CDNS) today announced that its full-flow digital and signoff tools and the Cadence® Verification Suite have been optimized to support Arm® Cortex®-A75 and Cortex-A55 CPUs, based on Arm DynamIQ™ technology, and the Arm Mali™-G72 GPU, the latest offerings from Arm for premium mobile, machine learning, and consumer devices. To accelerate the adoption of Arm’s latest processors, Cadence delivered new 7nm-ready Rapid Adoption Kits (RAKs) for the Cortex-A75 and the Cortex-A55 CPUs, which include the DynamIQ Shared Unit (DSU) that provides a shared level 3 cache between the CPUs, and a 7nm-ready RAK for the Mali-G72 GPU.

Customers are already using the complete digital and signoff flow and the Cadence Verification Suite to tape out complex systems-on-chip (SoCs) containing the latest Arm Cortex and Mali processors. To learn more about the Cadence full-flow digital and signoff solutions that support the Cortex-A75, Cortex-A55, and Mali-G72 processors, please visit www.cadence.com/go/dandsarmraks7nm. For more information on the Cadence Verification Suite that enables Arm-based designs using the Cortex-A75, Cortex-A55 and Mali-G72 processors, please visit www.cadence.com/go/vsuitearm7nm.

The Cadence RAKs accelerate physical implementation, signoff, and verification of 7nm designs, allowing designers to deliver mobile and consumer devices to market faster. With the delivery of the new RAKs, Cadence is also providing specialized technical support for Arm IP implementation based on the deep collaboration between Arm and Cadence over many years.

The Cadence digital and signoff tools have been configured to provide optimal power, performance and area (PPA) results using the RAKs, which include scripts, an example floorplan, and documentation for Arm’s 7nm IP libraries. The comprehensive Cadence RTL-to-GDS flow incorporates the following digital and signoff tools in the RAKs:

  • Innovus™ Implementation System: Statistical on-chip variation (SOCV) propagation and optimization results in improved timing, power, and area closure for 7nm designs
  • Genus™ Synthesis Solution: Register-transfer level (RTL) synthesis supports all the latest 7nm advanced-node requirements and provides convergent design closure using the Innovus Implementation System
  • Conformal® Logic Equivalence Checking (LEC): Ensures the accuracy of logic changes and engineering change orders (ECOs) during the implementation flow
  • Conformal Low Power: Enables the creation and validation of power intent in context of the design, combining low-power equivalence checking with structural and functional checks to allow full-chip verification of power-efficient designs
  • Tempus™ Timing Signoff Solution: Offers path-based, signoff-accurate and physically aware design optimization, providing the quickest path to tapeout
  • Voltus™ IC Power Integrity Solution: Static and dynamic analysis used during implementation and signoff ensures optimal power distribution
  • Quantus™ QRC Extraction Solution: Fulfills all 7nm advanced-node requirements to ensure accurate correlation to final silicon

“The Cortex-A75 and Cortex-A55 CPUs deliver distributed intelligence from edge-to-cloud, and pairing them with the Mali-G72 GPU enables consumers to experience stunning graphics efficiently across multiple devices,” said Nandan Nayampally, vice president and general manager, Compute Products Group, Arm. “By continuing to collaborate with Cadence on the delivery of new digital implementation and signoff RAKs along with optimization of the Cadence Verification Suite, our mutual customers can quickly integrate and augment their differentiated solutions for next-generation devices.”

The Cadence Verification Suite that has also been optimized for Arm-based designs includes:

  • JasperGold® Formal Verification Platform: Enables IP and subsystem verification including formal proofs for Arm AMBA® protocols
  • Xcelium® Parallel Logic Simulation: Provides production-proven multi-core simulation accelerating SoC development and validation of Arm-based designs
  • Palladium® Z1 Enterprise Emulation Platform: Includes hybrid technology that is integrated with Arm Fast Models for up to 50X faster OS and software bring-up and up to 10X faster software-based testing in addition to Dynamic Power Analysis technology for low power
  • Protium™ S1 FPGA-Based Prototyping Platform: Integration with the Palladium Z1 enterprise emulation platform combined with Arm DS-5 provides pre-silicon embedded software debug
  • vManager™ Planning and Metrics: Metric-driven verification across the JasperGold platform, Xcelium simulation, Palladium Z1 platform and Cadence VIP solutions for Arm-based SoC verification convergence
  • Perspec™ System Verifier: Provides software-driven use-case verification with the PSLib for Armv8 architectures, delivering up to 10X productivity improvement versus typical manual test development
  • Indago™ Debug Platform: RTL design, testbench and embedded software debug capabilities synchronized with Arm CPUs for accurate combined views of hardware and software
  • Cadence Verification Workbench: Integrates with Arm Socrates™ packaged Armv8 IP and VIP for fast SoC integration and UVM testbench assembly
  • Cadence Interconnect Workbench: Provides fast performance analysis and verification of Arm CoreLink™interconnect intellectual property (IP)-based systems in combination with Xcelium simulation, the Palladium Z1 platform, and Cadence Verification IP
  • Verification IP Portfolio: Enables IP and SoC verification including Arm AMBA interconnect, supporting Xcelium simulation, the JasperGold platform, and the Palladium Z1 platform

“We worked closely with Arm to optimize our advanced digital implementation and signoff solutions and our verification solutions for the new Arm CPUs and GPU so our customers can efficiently create 7nm mobile and consumer designs,” said Dr. Anirudh Devgan, executive vice president and general manager of the Digital & Signoff Group and the System & Verification Group at Cadence. “Designers using the RAKs and the Cadence Verification Suite can benefit from improved PPA and reduced project times, while creating the most advanced Arm-based products.”

Topological insulators, a class of materials which has been investigated for just over a decade, have been heralded as a new ‘wonder material’, as has graphene. But so far, topological insulators have not quite lived up to the expectations fueled by theoretical studies. University of Groningen physicists now have an idea about why. Their analysis was published on 27 July in the journal Physical Review B.

Topological insulators are materials that are insulating in the bulk but allow charge to flow across the surface. These conducting states at the surface originate from ordering patterns in the states where electrons reside that are different from ordinary materials. This ordering is linked to the physical concept of ‘topology’, analogous to that used in mathematics. This property gives rise to very robust states with some special properties.

Heavy atoms

For one, their spin — a magnetic property of electrons which can have the values ‘up’ or ‘down’ — is locked to their movement. ‘This means that electrons moving to the right have spin down, and those moving to the left have spin up’, explains first author of the study Eric de Vries, PhD student in the ‘Spintronics of Functional Materials’ research group led by his supervisor prof. dr. Tamalika Banerjee. This is group is part of the Zernike Institute for Advanced Materials. ‘But it also means that when you inject electrons with spin up into such a topological insulator, they will travel to the left!’ Topological insulators might therefore be very useful in the realization of spintronics: electronics based on the quantized spin value rather than the charge of electrons.

The special properties of topological insulators are predicted by the theoretical analysis of the surface structures of these materials, made from crystals of heavy atoms. But experiments show mixed results, which don’t quite live up to the theoretical predictions. ‘We wondered why, so we devised experiments to investigate the behaviour of the surface state electrons. Specifically, we wanted to see if transport is really limited to the surface, or if it is also present in the bulk of the material.’

Surprising

Earlier experiments by the group, in which they used ferromagnets to detect the spins of electrons generated in the topological insulator, were surprising, says De Vries. ‘We demonstrated that a voltage presumably originating from spin detection can originate in factors other than the locking of electron spin to its movement. Using different geometries, we showed that artefacts related to stray magnetic fields generated by the ferromagnets can mimic similar spin voltages.’ This observation may lead to a re-evaluation of some published results.

This time, they used a different approach. ‘We analyzed the topological insulators using strong magnet fields. This causes electrons to oscillate in transport channels.’ De Vries went to the national High Field Magnet Laboratory at the Radboud University Nijmegen, where a 33-Tesla magnet is available, one of the stronger magnets in the world. ‘Others have done similar tests with weaker magnets, but these are not sensitive enough to reveal the additional transport channels that coexist with the surface states.’ De Vries’s experiments showed that a considerable part of the charge transport occurred in the bulk phase of the material, and not only at the surface.

Transport channels

The reason for this, explains De Vries, is the imperfect crystal structure of the topological insulator. ‘Sometimes there are atoms missing in the crystal structure. This results in freely moving electrons. These start to conduct as new transport channels, generating electric current in the bulk of the material.’

So why has no one noted this before? De Vries stresses that interpreting transport measurements made on topological insulators can be difficult. ‘We experienced this in our previous experiments. Our message is that extreme care is needed in the interpretation of experimental observations for devices based on these materials.’ Also, experiments which might lead to clearer conclusions require very high magnetic fields in specialized labs.

Glitches

The results point to a way to improve topological insulators. ‘The key is to grow the crystals without any missing atoms. Another solution is to fill the holes, for example with calcium ions that bind the free electrons. But that might cause other disturbances to the electrons’ mobility.’ For ten years, topological insulators were all the rage. They were compared to the wonder material graphene. The discovery that, in practice, topological insulators have glitches serves as a reality check. De Vries: ‘We need to study and understand the interaction between the surface states and the bulk material in much more detail.’

Advances in modern electronics has demanded the requisite hardware, transistors, to be smaller in each new iteration. Recent progress in nanotechnology has reduced the size of silicon transistors down to the order of 10 nanometers. However, for such small transistors, other physical effects set in, which limit their functionality. For example, the power consumption and heat production in these devices is creating significant problems for device design. Therefore, novel quantum materials and device concepts are required to develop a new generation of energy-saving information technology. The recent discoveries of topological materials — a new class of relativistic quantum materials — hold great promise for use in energy saving electronics.

Researchers in the Louisiana Consortium for Neutron Scattering, or LaCNS, led by LSU Department of Physics & Astronomy Chair and Professor John F. DiTusa and Tulane University Professor Zhiqiang Mao, with collaborators at Oak Ridge National Lab, the National High Magnetic Field Laboratory, Florida State University, and the University of New Orleans, recently reported the first observation of this topological behavior in a magnet, Sr1-yMn1-zSb2 (y, z < 0.1). These results were published this week in Nature Materials(doi:10.1038/nmat4953).

“This first observation is a significant milestone in the advancement of novel quantum materials and this discovery opens the opportunity to explore its consequences. The nearly massless behavior of the charge carriers offers possibilities for novel device concepts taking advantage of the extremely low power dissipation,” DiTusa said.

The phrase “topological materials” refers to materials where the current carrying electrons act as if they have no mass similar to the properties of photons, the particles that make up light. Amazingly, these electronic states are robust and immune to defects and disorder because they are protected from scattering by symmetry. This symmetry protection results in exceedingly high charge carrier mobility, creating little to no resistance to current flow. The result is expected to be a substantial reduction in heat production and energy saving efficiencies in electronic devices.

This new magnet displays electronic charge carriers that have almost no mass. The magnetism brings with it an important symmetry breaking property – time reversal symmetry, or TRS, breaking where the ability to run time backward would no longer return the system back to its starting conditions. The combination of relativistic electron behavior, which is the cause of much reduced charge carrier mass, and TRS breaking has been predicted to cause even more unusual behavior, the much sought after magnetic Weyl semimetal phase. The material discovered by this collaboration is thought to be an excellent one to investigate for evidence of the Weyl phase and to uncover its consequences.

GLOBALFOUNDRIES and Silicon Mobility today announced they have successfully produced the industry’s first automotive Field Programmable Controller Unit (FPCU) solution, called OLEA T222. The FPCU solution uses GF’s 55nm Low Power Extended (55LPx) automotive qualified technology platform, which includes Silicon Storage Technology’s (SST) SuperFlash memory technology, to integrate multiple functions onto a single chip, boosting performance for hybrid and electric vehicles.

Silicon Mobility’s OLEA T222 allows automotive processing to be fully deterministic through embedding a Flexible Logic Unit (FLU), with up-to 40 times acceleration, into the control processor architecture to accelerate the processing and control of real-time events. With FLU acceleration, OLEA T222 increases the quality of energy conversion controls to increase safety and achieve ASIL-D for ultra-fast safety applications. Moreover, automotive manufacturers can enhance energy efficiency of DC/DC and AC/DC controls as well as increase battery range, durability, and charging speed for electric motors.

“Efficiency of electric motors, power converters, and battery chargers are key factors for hybrid and electric vehicle control systems,” said Vincent Cruvellier, vice president of operation at Silicon Mobility.“GF’s 55LPx platform, with its fast, low-power logic and Automotive Grade 1 qualification, combined with SST’s highly-reliable SuperFlash memory technology, allowed us to integrate multiple functions into a single chip, creating the OLEA T222 product. Our collaboration with GF, a global foundry committed to the automotive market, helps ensure our customers have the highest quality, reliability and support for the manufacturing of our automotive products.”

GF’s 55nm LPx RF-enabled, automotive-qualified platform provides a fast path-to-product solution that includes silicon qualified RF IP, SST’s highly-reliable SuperFlash memory technology that features:

  • Very fast read speed (<10ns)
  • Small bitcell size
  • Superior data retention (> 20 years)
  •  Superior endurance (> 200K cycles)
  • Fully qualification for Auto Grade 1 operation (AEC-Q100)

“Our platform combined with Silicon Mobility’s design has delivered a highly integrated automotive solution at 55nm, achieving the first FPCU in the industry,” said David Eggleston, vice president of embedded memory at GF. “This is yet another example that GF’s 55LPx platform is becoming the preferred choice for a broad spectrum of markets, including automotive applications that require superior reliability in extreme environments.”

GF’s 55LPx eFlash platform is in volume production at the foundry’s 300mm line in Singapore. The 55LPx eFlash platform is a cost effective solution for a broad range of products, ranging from wearable devices to automotive MCU’s.

Process design kits are available now. Customers can start optimizing their chip designs to develop differentiated SuperFlash-enabled solutions that require cost effective performance, low power consumption, and superior reliability in extreme environments.

For more information on GF’s mainstream CMOS solutions, contact your GF sales representative or go to www.globalfoundries.com.

Producers sometimes face challenges that go deep into the soil. They need answers to help the soil, on site. A portable field sensor can accurately measure minerals in soils more easily and efficiently than existing methods. And a research team, including a middle school student and her scientist father, can confirm it.

Calcium, like other minerals, is necessary for healthy plant growth. However, an excess of calcium — particularly in the form of calcium carbonate — can cause issues as it builds up in the soil.

“Calcium carbonate is basically a type of salt. It dissolves in water after a rainfall event and moves down through the soil,” explains David Weindorf. Weindorf is at the Department of Plant and Soil Science at Texas Tech University.

One main source of this calcium is limestone. At low levels, it makes thin threads or small white masses in the soil. However, in extreme cases it can actually take over the entire subsoil. Its hard surface can limit the ability of plant roots to grow. Getting this information on-the-fly is important for growers and soil scientists solving problems in the field.

Traditionally, soil scientists use their expertise to look at the soil and determine the stage of the calcium visually. There are also laboratory-based techniques that are very accurate, but they are not portable. The researchers wanted to see if a portable x-ray device — called PXRF, portable x-ray fluorescence spectrometry — would be better.

Based on their comparisons, the researchers found that, indeed, the device is a good method for measuring the calcium in the soil. The device can provide data on about 20 different elements, all in 60 seconds.

This can be a big advantage for soil scientists working in the field. It can also help scientists and farmers in developing countries who can’t afford expensive laboratory tests, or don’t have the expertise to visually appraise the soil.

“We are not advocating doing away with traditional assessment. We are simply providing a new data stream to help field soil scientists when evaluating carbonates in the field,” Weindorf explains. “Essentially, PXRF is another tool in the tool belt of the modern soil scientist, but it is by no means the only tool.”

Weindorf’s daughter was also part of the research. For Camille, this study was a way to branch out for her school’s science fair and do some original research. She scanned the soil samples and then helped her father perform the laboratory tests. She also helped calculate the summary statistics and write the paper.

“As a father, I just can’t overemphasize how proud I am of my daughter for taking on this science challenge with me,” he says. “I hope a project like this can inspire other students around her age to engage in original scientific inquiry. Truly, they are the future which will keep our country at the forefront of scientific innovation.”

The new SRP 5000 angular positioning system from HEIDENHAIN incorporates its high accuracy MRP 5000 angle encoder with accomplished bearing technology along with a unique ETEL torque motor with ultra-low detent torque. This combination allows for very high stiffness with low cost of ownership and can easily replace rotary air bearing systems used for metrology. Industries that could take advantage of the SRP 5000 system are semiconductor manufacturing, metrology, and micromachining.

HEIDENHAIN's New SRP Angular Positioning System (PRNewsfoto/HEIDENHAIN CORPORATION)

HEIDENHAIN’s New SRP Angular Positioning System (PRNewsfoto/HEIDENHAIN CORPORATION)

The SRP 5000 is compact in size and is only 46.3mm in height and 124mm in diameter.

The system can be ordered in incremental or absolute models, where the incremental versions have encoders with 30,000 signal periods per revolution and system accuracies down to +/- 2.5 arc seconds. The absolute version has the same accuracy level and resolutions to 28 bits via the EnDat 2.2 interface.

The slotless iron-core ETEL torque motor has a peak torque of 2.7 Nm, a rated torque of 0.387Nm and the detent torque is just a mere 0.2% of the rated value. The motor is rated for 300 RPM and permits an extraordinarily smooth motion.

The SRP 5000 is best used with the AccurET position controllers from ETEL as absolute peak performance can be achieved with regard to dynamics, thermal management, and position stability. Other controllers can be used, however thermal overload protection must be maintained in the controller.

HEIDENHAIN CORPORATION is the North American subsidiary of DR. JOHANNES HEIDENHAIN GmbH, an international manufacturer of precision measurement and control equipment.  Our product line includes linear scales, rotary and angular encoders, digital readouts, length gauges, CNC controls, and machine inspection equipment.

ETEL S.A. is based in Switzerland with exclusive North American distribution through HEIDENHAIN CORPORATION in Schaumburg, IL.  As an international supplier of direct drive and motion control components and integrated systems, ETEL supports high tech industry with linear motors, torque motors, positioning stages, and motion controllers/systems.

Flux-closure domain (FCD) structures are microscopic topological phenomena found in ferroelectric thin films that feature distinct electric polarization properties. These closed-loop domains have garnered attention among researchers studying new ferroelectric devices, ranging from data storage components and spintronic tunnel junctions to ultra-thin capacitors.

In the development of thin films for such devices, researchers have thought that contact with commonly used oxide electrodes limits FCD formation. However, a group of researchers in China has shown otherwise. The findings are reported this week as the cover article in Applied Physics Letters, from AIP Publishing.

Ferroelectric materials are typically developed and studied as thin films, sometimes as thin as only a few nanometers. As a result, researchers have begun discovering the abundant domain structures and unique physical properties that these ferroelectrics possess, such as skyrmion and FCD formation that could benefit next-generation electronic devices. Because the films are so thin, however, their interaction with electrodes is inevitable.

“The general thinking has been that oxide electrodes would destabilize flux-closure domains. However, our work has shown that this is no longer true when the top and bottom electrodes are symmetric, which physically makes sense,” said Yinlian Zhu, professor at the Institute of Metal Research at the Chinese Academy of Sciences and a co-author of the paper.

Zhu and colleagues used two types of oxide electrodes: one based on strontium ruthenate, the other based on lanthanum strontium manganite, chosen as oxide electrodes because of their similar perovskite structures, which work well in layer-by-layer film growth. They studied how these electrodes influenced FCD formation in PbTiO3 (PTO) perovskite-oxide-based thin films deposited on gadolinium scandium oxide (GSO) substrates.

The research team’s previous studies indicated that flux-closure domains can be stabilized in strained ferroelectric films in which the strain plays a critical role in the formation of flux-closure domains, such as multilayer PTO/strontium titanate systems grown on GSO-based (specifically GdScO3) substrates.

Based on their previous studies, the researchers consequently anticipated that similar phenomenon might also occur in PTO/electrode systems. They then grew PTO films sandwiched between symmetric oxide electrodes on GSO substrates using pulsed laser deposition.

They found that periodic FCD arrays can be stabilized in PTO films when the top and bottom electrodes are symmetric, while alternating current domains appear when they apply asymmetric electrodes.

“We successfully grew ferroelectric thin films with symmetric oxide electrodes in which flux-closure domains and their periodic arrays clearly do exist,” Zhu said. “Our work sheds light on understanding the nature of flux-closure domains in ferroelectrics. We expect that it will open research possibilities in the evolution of these structures under external electric fields.”

A newly discovered collective rattling effect in a type of crystalline semiconductor blocks most heat transfer while preserving high electrical conductivity – a rare pairing that scientists say could reduce heat buildup in electronic devices and turbine engines, among other possible applications.

A team led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) discovered these exotic traits in a class of materials known as halide perovskites, which are also considered promising candidates for next-generation solar panels, nanoscale lasers, electronic cooling, and electronic displays.

Rattling structures of halide perovskites: cesium tin iodide (left) and cesium lead iodide (right). Credit: UC Berkeley

Rattling structures of halide perovskites: cesium tin iodide (left) and cesium lead iodide (right). Credit: UC Berkeley

These interrelated thermal and electrical (or “thermoelectric”) properties were found in nanoscale wires of cesium tin iodide (CsSnI3). The material was observed to have one of the lowest levels of heat conductivity among materials with a continuous crystalline structure.

This so-called single-crystal material can also be more easily produced in large quantities than typical thermoelectric materials, such as silicon-germanium, researchers said.

“Its properties originate from the crystal structure itself. It’s an atomic sort of phenomenon,” said Woochul Lee, a postdoctoral researcher at Berkeley Lab who was the lead author of the study, published the week of July 31 in the Proceedings of the National Academy of Sciencesjournal. These are the first published results relating to the thermoelectric performance of this single crystal material.

Researchers earlier thought that the material’s thermal properties were the product of “caged” atoms rattling around within the material’s crystalline structure, as had been observed in some other materials. Such rattling can serve to disrupt heat transfer in a material.

“We initially thought it was atoms of cesium, a heavy element, moving around in the material,” said Peidong Yang, a senior faculty scientist at Berkeley Lab’s Materials Sciences Division who led the study.

Jeffrey Grossman, a researcher at the Massachusetts Institute of Technology, then performed some theory work and computerized simulations that helped to explain what the team had observed. Researchers also used Berkeley Lab’s Molecular Foundry, which specializes in nanoscale research, in the study.

“We believe there is essentially a rattling mechanism, not just with the cesium. It’s the overall structure that’s rattling; it’s a collective rattling,” Yang said. “The rattling mechanism is associated with the crystal structure itself,” and is not the product of a collection of tiny crystal cages. “It is group atomic motion,” he added.

Within the material’s crystal structure, the distance between atoms is shrinking and growing in a collective way that prevents heat from easily flowing through.

But because the material is composed of an orderly, single-crystal structure, electrical current can still flow through it despite this collective rattling. Picture its electrical conductivity is like a submarine traveling smoothly in calm underwater currents, while its thermal conductivity is like a sailboat tossed about in heavy seas at the surface.

Yang said two major applications for thermoelectric materials are in cooling, and in converting heat into electrical current. For this particular cesium tin iodide material, cooling applications such as a coating to help cool electronic camera sensors may be easier to achieve than heat-to-electrical conversion, he said.

A challenge is that the material is highly reactive to air and water, so it requires a protective coating or encapsulation to function in a device.

Cesium tin iodide was first discovered as a semiconductor material decades ago, and only in recent years has it been rediscovered for its other unique traits, Yang said. “It turns out to be an amazing gold mine of physical properties,” he noted.

To measure the thermal conductivity of the material, researchers bridged two islands of an anchoring material with a cesium tin iodide nanowire. The nanowire was connected at either end to micro-islands that functioned as both a heater and a thermometer. Researchers heated one of the islands and precisely measured how the nanowire transported heat to the other island.

They also performed scanning electron microscopy to precisely measure the dimensions of the nanowire. They used these dimensions to provide an exacting measure of the material’s thermal conductivity. The team repeated the experiment with several different nanowire materials and multiple nanowire samples to compare thermoelectric properties and verify the thermal conductivity measurements.

“A next step is to alloy this (cesium tin iodide) material,” Lee said. “This may improve the thermoelectric properties.”

Also, just as computer chip manufacturers implant a succession of elements into silicon wafers to improve their electronic properties – a process known as “doping” – scientists hope to use similar techniques to more fully exploit the thermoelectric traits of this semiconductor material. This is relatively unexplored territory for this class of materials, Yang said.

Sub-Fab Fault Detection and Classification (FDC) software platforms collect, integrate and analyze operational data.

BY ERIK COLLART, Edwards, Sanborn, NY

The ability to provide the reliable high-quality vacuum environment that most semiconductor manufacturing requires is an often and easily overlooked aspect of the whole fab process. The unexpected failure of a vacuum pump can bring significant disruption to the manufacturing process, potentially imposing a heavy penalty in lost productivity and scrapped product. The sub-fab, where vacuum and abatement systems are typically located and so named because it is located literally below the fab floor, has evolved dramatically over the years, from simply a location outside the fab in which to house supporting equipment, to an environment that is in many ways as sophisticated as the fab itself. Just as manufacturers have adopted advanced monitoring and data analytics to optimize fab operations, they are finding significant benefit in applying the same techniques to sub-fab operations. Sub-Fab Fault Detection and Classification (FDC) software platforms such as Edcentra, Edwards’ newest equipment monitoring, data acquisition and analytics platform collect, integrate and analyze operational data from the sub-fab, providing a comprehensive solution to vacuum security.

The challenge of cost-effective innovation

The semiconductor industry faces many challenges, including the high pace of innovation and the need to constantly improve operational efficiencies, decrease costs, reduce adverse environmental impact and ensure the safety of personnel in the fab and residents of the surrounding community. Some of the ways these challenges have been met in the past no longer apply. For instance, although there is still device scaling in new technology nodes, the type of simple geometric device scaling driven by Constant-Field Scaling rules [1] – to drive innovation, improve efficiency and reduce costs per die – effectively ran out a decade ago.

Innovation has continued, though along very different lines, introducing ever more complex device architectures and increasing the use of exotic materials and manufacturing methods, such as epitaxial and atomic layer deposition. These innovations have all extended development time and time-to-market, driven up cost, reduced efficiency (lower yields, more frequent equipment preventive maintenance cycles) and brought new and higher environmental restrictions (stringent local, national and international regulations, as on CO2 emissions) and safety challenges (toxic precursor materials and waste products). Delivering timely and cost-effective innovation is now a major issue for the semiconductor industry. In response to this challenge, manufacturers have recognized the strategic necessity of integrating and analyzing all the information available from their processes. These manufacturers are therefore starting to adopt an integrated fab data and information management approach that accounts for all the factors affecting time-to-market at the lowest possible costs. The sub-fab and associated support systems cannot be omitted from this approach.

The importance of vacuum

Most of the critical steps in a chip manufacturing process are conducted under high vacuum conditions and vacuum quality is one of the most important parameters in these process step. Vacuum quality is a combination of vacuum level and vacuum content. No vacuum is absolute, and there are always trace amounts of non-process gases present in process chambers that can have a major impact on the process, if not controlled.

As any fab equipment or process engineer will tell you, maintaining vacuum quality is so important that pumps are almost never shut off and process chambers are almost never brought to atmospheric pressure, even when idle for long periods of time. Maintenance activities on process chambers are performed, whenever possible, with minimal or no exposure to atmosphere. This is for a very good reason: once a chamber has been vented to atmosphere it may take a very long time to return it to the previous known-good-vacuum state, affecting equipment uptime and process yield.

The vacuum state can therefore affect wafer quality and overall fab costs through its effect on yield or through losses incurred as a result of unplanned vacuum failures during wafer processing. For example, insufficient vacuum levels or trace amounts (ppm level) of unintended gases, such as O2 or H2O, in an ion implant process can greatly reduce the stability of high voltage power supplies, leading, in turn, to fluctuations in ion beam current, non-uniform implant conditions on the wafer, and ultimately to poor and non-reproducible wafer yields. A pump “crash” during a batch process that causes the scrap of an entire production batch–normally 125 wafers–is very costly in both direct product loss and process downtime. Even in single wafer process, unplanned pump failure can cause significant losses as some process tools require days or weeks to requalify.

Fab managers face a difficult choice between the costs of vacuum failure and the costs of too frequent maintenance. Optimizing this choice is one area where sub-fab equipment monitoring and advanced analytics can make an important contribution. Most effective optimization occurs in an adaptive maintenance regime, where pump maintenance is performed in parallel to tool mainte- nance, thereby virtually eliminating vacuum pumps as a cause of lost tool time. Long prediction horizons are required for successful adaptive maintenance, enabling the longer PM intervals (months) typical of sub-fab equipment to be synchronised to the shorter PM intervals (weeks) of the fab process equipment. For this to happen, and thereby assuring sustained vacuum quality, additional types of sensors and improved predictive capabilities and time horizons will be needed. The remainder of this paper highlights Edwards’ exploratory work on using mechanical vibration sensor data to obtain a reliable and long prediction horizon for mechanical failure modes [2].

Failure prediction using vibrational sensor data

Monitoring vibrations to assess the health of rotating machines has a long and successful history. Intrinsic bearings frequencies can be calculated from rotation speeds, and wear-generated perturbations to these frequencies can be detected to predict bearing failures and other mechanical failure modes. However, these existing methods do not translate well to a semicon- ductor environment where process-induced failure modes are more frequent. The sub-fab working environment also tends to be extremely noisy from a vibration spectrum perspective and the effects of process induced failure modes on standard vibration spectra are largely unknown.

We have developed a new method of unlocking key predictive information (Fault Detection or FD) from vibration data, based on a “fingerprinting” technique, which translates complex, noisy data into a single dynamic coefficient that can be compared easily with existing predictive maintenance parameters. Further vibrational sub-band analysis provides specific failure mode identifi- cation and root-cause analysis, thus providing a key fault classification (FC) capability. This method will be referred to as Vibration Indicator or VI from here on.

Results

FIGURE 1 shows an example of the power of VI to extend visibility of a catastrophic bearing failure in a fab working environment. A departure of VI from zero indicates the emerging signature of mechanical bearings wear. The time horizon in this example is at least 60 days, providing extended visibility and increased process security.

A second fab-based production environment example, taken from an LP-CVD Si3N4 batch deposition process and shown in FIGURE 2, illustrates the sensitivity and predictive power of VI compared to traditional pump parameters: power and temperature. The ultimate cause of failure in this case was deposition-related. As can be seen, from day 60 onward changing process conditions caused a step-change in the temperature. The power curve develops patterns of spike behavior around day 120. Previously existing best-known-methods (BKM) for predictive maintenance, based on analysis of power and temperature data, can detect this emerging behavior using spike- area and frequency-based techniques, in this case with a time horizon of 40 days. The key obser- vation in this example is that VI (blue curve) reacted immediately to an increased deposition of condensable materials, which led directly to an equipment failure 90 days later. The VI provided a time-to- failure horizon of 90 days (55% of observed pump life), more than double that of traditional parameters.

Accelerated lab testing provides further evidence of the extended time horizon VI affords. FIGURE 3 shows the results of a lab-based accelerated fluorine (F2) corrosion induced mechanical failure mode, with large F2 gas flows injected into the vacuum system and pump. The traditional power parameter is completely insensitive to the F2 flow and resulting corrosion. The VI, by contrast, shows a linear correlation with total accumulated flow, providing both early detection and a measure of the severity of the developing problem.

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A second lab-based test (not shown) investigated the effects of oil contaminants and again confirmed the ability of VI to detect and quantify failure modes inaccessible to established methods. As in the corrosion example, a linear correlation was found between accumulated contamination and VI, while power measurements proved to be completely insen- sitive to oil contamination levels.

These show that VI can significantly extend the time horizon of equipment failure modes, well beyond current predictive capabilities and into the regime where effective maintenance pooling and the resultant cost savings can be realized. Moreover, these results can be translated into precise RUL predictions using various parameter estimator techniques, complementing standard Weibull techniques. FIGURE 4 shows the results of an accelerated bearings failure lab test for a dry pump, comparing VI and estimated RUL.

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Performance comparison

Tables 1 and 2 compare and contrast VI performance with mainstream SPC-like control methods, such a single parameter threshold monitoring and multi-variate analysis (BKMS-F), in terms of detection capability, sensitivity, prediction time horizon and hit rate vs. false positives. Table 1 shows that VI considerably extends prediction time horizon and, based on data gathered to date for detectable results, has demon- strated a 100 percent hit rate with no false positives. From table 2 we see that VI extends predictability to mechanical failures, has high sensitivity, and detects problems as soon as they begin.

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Summary and conclusions

The need for increased operational efficiency in semiconductor manufacturing is driving the development of smarter interconnected vacuum sub-systems and the adoption of integrated data and information management technologies. A case study described the combined use of the EdCentra sub-fab information management system and an innovative approach to vibrational analysis. Compared to current mainstream methods, VI provided an extended, and in some cases unique, predictive maintenance capability for mechanical pump failures and a very high level of sensitivity. For the data gathered so far on detectable faults, the hit rate has been 100 percent, with no false positives. Finally, advanced analytics and VI consid- erably extended the prediction time horizon from weeks to months. Together with existing predictive algorithms and methodologies for pumps, abatement and ancillary equipment, the capabilities provided by advanced information management and innovative monitoring technologies like VI have the potential to significantly reduce costs and increase productivity.

Acknowledgements

The author would like to acknowledge and thank Antonio Serapligia and Angelo Maiorana for their ground-breaking work on vibrational analysis, and David Hacker and Alan Ifould for their inputs on the challenges and opportunities of sub-fab equipment maintenance and many fruitful discussions.

References

1. Dennard, Robert H.; Gaensslen, Fritz; Yu, Hwa-Nien; Rideout, Leo; Bassous, Ernest; LeBlanc, Andre (October 1974). “Design of ion-implanted MOSFET’s with very small physical dimensions” (PDF). IEEE Journal of Solid State Circuits. SC–9 (5).
2. Antonio Serapiglia, David Hacker, Erik J Collart, Alan Ifould, and Angelo Maiorana 28th Advanced Process Control Conference Proceedings, Mesa, Arizona, 2016