Tag Archives: letter-pulse-tech

The pattern of arrangement of atoms in a crystal, called the crystal lattice, can have a huge effect on the properties of solid materials. Controlling and harnessing these properties is a challenge that promises rewards in applications such as novel sensors and new solid-state devices. An international research collaboration, including researchers from Osaka University, has reported the induction of an interesting type of magnetic order, called helimagnetism, in a cobalt oxide material by expanding its lattice structure. Their findings were published in Physical Review Materials.

This is a schematic illustration of the helimagnetic-ferromagnetic transition driven by the lattice expansion/compression in the cubic perovskite Sr1-xBaxCoO3. Credit: S. Ishiwata and H. Sakai

Magnetic behavior results from the order of the magnetic moments of the many individual atoms in a material. In helimagnetism, instead of the magnetic moments being aligned–as they are in permanent magnets, producing ferromagnetism–the moments arrange themselves in a helical pattern. This behavior is generally only observed in complicated lattice structures where different types of magnetic interactions compete with each other, therefore the report of induced helimagnetism in a simple cubic cobalt oxide structure, is highly significant.

“We have shown emergent helical spin order in a cubic perovskite-type material, which we achieved simply by expanding the lattice size,” study first author Hideaki Sakai says. “We were able to control the size of the lattice expansion by using a high-pressure technique to grow a series of single crystals with particular chemical compositions. Changing the amount of different ions in our materials provided us with sufficient control to investigate the magnetic properties.”

Systematically replacing strontium ions in the structure with larger barium ions caused the lattice to continually expand until the regular ferromagnetic magnetic order present at room temperature was disrupted, resulting in helimagnetism. These experimental findings were successfully supported by calculations.

“The fact that we were able to largely reproduce our findings by first principles calculations verifies that the magnetic interactions in the materials are highly sensitive to the lattice constant,” Sakai says. “The more we can understand about the magnetic behavior of crystalline materials, the closer we move towards translating their properties into useful functions. We hope that our findings will pave the way for novel sensor applications.

The control of magnetic order simply by changing the lattice chemistry, as demonstrated by this research, provides a foundation for investigating the properties of many other crystalline materials.

The ideal optoelectronic semiconductor material should be a strong light emitter i.e. should emit light very efficiently upon optical excitation as well as be an efficient charge conductor to allow for electrical injection in devices. These two conditions when met can lead to highly efficient light emitting diodes as well as to solar cells with the possibility to approach the Shockley-Queisser limit. Until now the materials that have come close to meeting these conditions have been based on epitaxially-grown costly III-V semiconductors that cannot be monolithically integrated to CMOS electronics.

The ICFO team has reported a solution processed nanocomposite system comprising infrared colloidal quantum dots that also meets these criteria and at the same time offers low cost and facile CMOS integration. Colloidal Quantum Dots (CQDs) are extremely small semiconductor particles or crystals, as small as a few nanometers in size, and because of their size they are capable of having unique optical and electronic properties. They are excellent absorbers and emitters of light, having their properties change as a function of their size and shape: smaller quantum dots emit in the blue range while larger quantum dots emit in the red.

The use of colloidal quantum dot (CQD) light-emitting diodes (LEDs) has become one of the key ingredients in leading technologies such as, for example, 3rd generation, solution processed, and inorganic solar cells. The implementation of these nanocrystals in devices for optical sensing in the short-wave and mid- infrared have triggered a vast number of applications including surveillance, night vision, product, process and environmental monitoring and spectroscopy.

In this recent study published in Nature Nanotechnology, ICFO researchers Santanu Padhan, Francesco Di Stasio, Yu Bi, Shuchi Gupta, Sotirios Christodoulou, and Alexandros Stavrinadis, led by ICREA Prof. at ICFO Gerasimos Konstantatos, have developed CQD infrared emitting LEDs, which have achieved unprecedented values in the infrared range, with an external quantum efficiency of 7.9% and a power conversion efficiency of 9.3%, a value never attained before with these type of devices.

The key feature of this work has been the development of a CQD composite structure engineered at the suprananocrystalline level to reach unprecedently low electronic defect density. Prior efforts in suppressing electronic defects in CQD solids have been primarily been based on chemical passivation of the CQD surface, something that could not solve the problem in PbS QDs. The researchers at ICFO took an alternative path of creating the appropriate matrix in which they embedded the emitting QDs, to serve as a remote electronic passivant for the emitter CQDs. Moreover, the energetic landscape of the matrix was engineered in order to facilitate efficient charge funnelling into the QD emitters in order to achieve efficient electrical injection.

With these new blend devices, the team of researchers took a step further and constructed solar cells to test their performance in the infrared range. In doing so they discovered that the effective passivation achieved in these nanocomposites along with the modulation of the electronic density of states has resulted in solar cells that deliver open circuit voltage very close to the theoretical limit. The open circuit voltage (VOC), which is the maximum voltage available from a solar cell, increased from 0.4 V for a single QD configuration, up to ~0.7 V for the ternary blend configuration, an impressive value considering the lower bandgap of the cell at ~0.9 eV.

As ICREA Prof at ICFO Gerasimos Konstantatos comments, “The most surprising finding of this study is the extremely low electronic trap density that can be achieved in a conductive QD material system that is full of chemical defects arising on the surface of the dots, the very high quantum efficiency of those LEDs has been the consequence of this passivation strategy we demonstrate. The other exciting outcome has been the potential to reach so high Voc values for QD solar cells that was synergistically achieved thanks to the very low trap density as well as to a novel engineering approach of the density of states in a semiconductor film”. Santanu Pradhan, the first author of this study adds: “Next we will focus on how to further exploit this reduction of electronic density of states synergistically with other means to allow for simultaneous achievement of high Voc and current production, thereby targeting record power conversion efficiencies in solar cell devices”.

The results obtained in this study prove that the engineering of QCD infrared-emitting LEDs at the nanoscale integrated in solar cells can significantly improve the performance efficiency of these devices in the infrared range. Such results open the pathway into a range of the spectra that is still to be fully exploited and offers amazing new applications, such as on-chip spectrometers for food inspection, environmental monitoring, manufacturing process monitoring as well as active imaging systems for biomedical or night vision applications.

Scientists from Jülich together with colleagues from Aachen and Turin have produced a memristive element made from nanowires that functions in much the same way as a biological nerve cell. The component is able to both save and process information, as well as receive numerous signals in parallel. The resistive switching cell made from oxide crystal nanowires is thus proving to be the ideal candidate for use in building bioinspired “neuromorphic” processors, able to take over the diverse functions of biological synapses and neurons.

Computers have learned a lot in recent years. Thanks to rapid progress in artificial intelligence they are now able to drive cars, translate texts, defeat world champions at chess, and much more besides. In doing so, one of the greatest challenges lies in the attempt to artificially reproduce the signal processing in the human brain. In neural networks, data are stored and processed to a high degree in parallel. Traditional computers on the other hand rapidly work through tasks in succession and clearly distinguish between the storing and processing of information. As a rule, neural networks can only be simulated in a very cumbersome and inefficient way using conventional hardware.

Systems with neuromorphic chips that imitate the way the human brain works offer significant advantages. Experts in the field describe this type of bioinspired computer as being able to work in a decentralised way, having at its disposal a multitude of processors, which, like neurons in the brain, are connected to each other by networks. If a processor breaks down, another can take over its function. What is more, just like in the brain, where practice leads to improved signal transfer, a bioinspired processor should have the capacity to learn.

“With today’s semiconductor technology, these functions are to some extent already achievable. These systems are however suitable for particular applications and require a lot of space and energy,” says Dr. Ilia Valov from Forschungszentrum Jülich. “Our nanowire devices made from zinc oxide crystals can inherently process and even store information, as well as being extremely small and energy efficient,” explains the researcher from Jülich’s Peter Grünberg Institute.

For years memristive cells have been ascribed the best chances of being capable of taking over the function of neurons and synapses in bioinspired computers. They alter their electrical resistance depending on the intensity and direction of the electric current flowing through them. In contrast to conventional transistors, their last resistance value remains intact even when the electric current is switched off. Memristors are thus fundamentally capable of learning.

In order to create these properties, scientists at Forschungszentrum Jülich and RWTH Aachen University used a single zinc oxide nanowire, produced by their colleagues from the polytechnic university in Turin. Measuring approximately one ten-thousandth of a millimeter in size, this type of nanowire is over a thousand times thinner than a human hair. The resulting memristive component not only takes up a tiny amount of space, but also is able to switch much faster than flash memory.

Nanowires offer promising novel physical properties compared to other solids and are used among other things in the development of new types of solar cells, sensors, batteries and computer chips. Their manufacture is comparatively simple. Nanowires result from the evaporation deposition of specified materials onto a suitable substrate, where they practically grow of their own accord.

In order to create a functioning cell, both ends of the nanowire must be attached to suitable metals, in this case platinum and silver. The metals function as electrodes, and in addition, release ions triggered by an appropriate electric current. The metal ions are able to spread over the surface of the wire and build a bridge to alter its conductivity.

Components made from single nanowires are, however, still too isolated to be of practical use in chips. Consequently, the next step being planned by the Jülich and Turin researchers is to produce and study a memristive element, composed of a larger, relatively easy to generate group of several hundred nanowires offering more exciting functionalities.

Leti, a research institute at CEA Tech, has proven that RRAM-based ternary-content addressable memory (TCAM) circuits, featuring the most compact structure developed to date, can meet the performance and reliability requirements of multicore neuromorphic processors.

TCAM circuits provide a way to search large data sets using masks that indicate ranges. These circuits are, therefore, ideal for complex routing and big data applications, where an exact match is rarely necessary.  TCAM circuits allow searching for stored information by its content, as opposed to classic memory systems in which a memory cell’s stored information is retrieved by its physical address. They shorten the search time compared to classic memory-based search algorithms, as all the stored information is compared with the searched data in parallel, within a single clock cycle.

But conventional SRAM-based TCAM circuits are usually implemented with 16 CMOS transistors, which limits storage capacity of TCAMs to tens of Mbs in standard memory structures, and takes up valuable silicon real estate in neuromorphic computing spiking neural-network chips.

The breakthrough of the CEA-Leti project replaced SRAM cells with resistive-RAM (RRAM) in TCAM circuits to reduce the number of required transistors to two (2T), and to two RRAMs (2R), which is the most compact structure for these circuits produced to date. In addition, the RRAMs were fabricated on top of the transistors, which also consumed less area. This suggests such a 2T2R structure can decrease the required TCAM area by a factor of eight compared to the conventional 16-transistor TCAM structure.

But while using RRAMs in TCAM circuits significantly reduces both silicon chip area needed and power consumption, and guarantees similar search speed compared to CMOS-based TCAM circuits, this approach brings new challenges:

  • Circuit reliability is strongly dependent on the ratio between the ON and OFF states of the memory cells. RRAM-based TCAM reliability could be affected by the relatively low ON/OFF ratio (~10-100) with respect to the 16-transistor structure (~), and
  • RRAMs have a limited endurance with respect to CMOS transistors, which can affect the lifespan of the system.

Overcoming these challenges requires trade-offs:

  • The voltage applied during a search operation can be decreased, which improves system reliability. However, this also degrades system performance, e.g. slower searches, and
  • The limited endurance can be overcome by either decreasing the voltage applied during each search, or increasing the power used to program the TCAM cells beforehand. Both increase system endurance, while slowing searches.

The work, presented Dec. 4 at IEDM 2018 in a paper entitled, “In-depth Characterization of Resistive Memory-based Ternary Content Addressable Memories”, clarifies the link between RRAM electrical properties and TCAM performance with extensive characterizations of a fabricated RRAM-based circuit.

The research showed a trade-off exists between TCAM performance (search speed) and TCAM reliability (match/mismatch detection and search/read endurance). This provides insights into programming RRAM-based TCAM circuits for other applications, such as network packets routing.

“Assuming many future neuromorphic computing architectures will have thousands of cores, the non-volatility feature of the proposed TCAM circuits will provide an additional crucial benefit, since users will have to upload all the configuration bits only the first time the network is configured,” said Denys R.B. Ly, a Ph.D. student at Leti and lead author of the paper. “Users will also be able to skip this potentially time-consuming process every time the chip is reset or power-cycled.”

Leti, a research institute at CEA Tech, has reported breakthroughs in six 3D-sequential-integration process steps that previously were considered showstoppers in terms of manufacturability, reliability, performance or cost.

CoolCubeTM, CEA-Leti’s 3D monolithic or 3D sequential CMOS technology allows vertically stacking several layers of devices with a unique connecting-via density above tens of million/mm2. This MoreMoore technology decreases dice area by a factor of two, while providing a 26 percent gain in power. The wire-length reduction enabled by CoolCubeTM also improves yield and lowers costs. In addition to power savings, this true 3D integration opens diversification perspectives thanks to more integration of functions. From a performance optimization and manufacturing-enablement perspective, processing the top layer in a front end of line (FEOL) environment with a restricted thermal budget requires process modules optimization.

CEA-Leti’s recent 3D sequential integration results were presented Dec. 3 at IEDM 2018 in the paper, “Breakthroughs in 3D Sequential Integration”. The breakthroughs are:

  • Low-resistance poly-Si gate for the top field-effect transistors (FETs)
  • Full LT RSD (low temperature raised source and drain) epitaxy, including surface preparation
  • Stable bonding above ultra low-k (ULK)
  • Stability of intermediate back end of line (iBEOL) between tiers with standard ULK/Cu technology
  • Efficient contamination containment for wafers with Cu/ULK iBEOL, enabling their re-introduction in front end of line (FEOL) for top FET processing, and
  • Smart CutTM process above a CMOS wafer.

 

To obtain high-performance top FETs, low gate access resistance was achieved using UV nano-second laser recrystallization of in-situ doped amorphous silicon. Full 500°C selective silicon-epitaxy process was demonstrated with an advanced LT surface preparation and a combination of dry-and-wet etch preparation.  Epitaxial growth was demonstrated with the cyclic use of a new silicon precursor and dichlorine Cl2 etching. At the same time, the project paved the way to manufacturability of 3D sequential integration including iBEOL with standard ULK and Cu-metal lines.

A bevel-edge contamination containment strategy comprised of three steps (bevel etch, decontamination, encapsulation) enabled reintroducing wafers in an FEOL environment following the BEOL process. In addition, the project also demonstrated for the first time the stability of line-to-line breakdown voltage for interconnections submitted to 500°C. The work also demonstrated a Smart CutTM transfer of a crystalline silicon layer on a processed bottom level of FD-SOI CMOS devices, as an alternative to the SOI bonding-and-etch back process scheme for top channel fabrication.

A team of scientists from Arizona State University’s School of Molecular Sciences and Germany have published in Science Advances online today an explanation of how a particular phase-change memory (PCM) material can work one thousand times faster than current flash computer memory, while being significantly more durable with respect to the number of daily read-writes.

PCMs are a form of computer random-access memory (RAM) that store data by altering the state of the matter of the “bits”, (millions of which make up the device) between liquid, glass and crystal states. PCM technology has the potential to provide inexpensive, high-speed, high-density, high-volume, nonvolatile storage on an unprecedented scale.

The basic idea and material were invented by Stanford Ovshinsky, long ago, in1975, but applications have lingered due to lack of clarity about how the material can execute the phase changes on such short time scales and technical problems related to controlling the changes with necessary precision. Now high tech companies like Samsung, IBM and Intel are racing to perfect it.

The semi-metallic material under current study is an alloy of germanium, antimony and tellurium in the ratio of 1:2:4. In this work the team probes the microscopic dynamics in the liquid state of this PCM using quasi-elastic neutron scattering (QENS) for clues as to what might make the phase changes so sharp and reproducible.

On command, the structure of each microscopic bit of this PCM material can be made to change from glass to crystal or from crystal back to glass (through the liquid intermediate) on the time scale of a thousandth of a millionth of a second just by a controlled heat or light pulse, the former now being preferred. In the amorphous or disordered phase, the material has high electrical resistance, the “off” state; in the crystalline or ordered phase, its resistance is reduced 1000 fold or more to give the “on” state.

These elements are arranged in two dimensional layers between activating electrodes, which can be stacked to give a three dimension array with particularly high active site density making it possible for the PCM device to function many times faster than conventional flash memory, while using less power.

“The amorphous phases of this kind of material can be regarded as “semi-metallic glasses”,” explains Shuai Wei, who at the time was conducting postdoctoral research in SMS Regents’ Professor Austen Angell’s lab, as a Humboldt Foundation Fellowship recipient.

“Contrary to the strategy in the research field of “metallic glasses”, where people have made efforts for decades to slow down the crystallization in order to obtain the bulk glass, here we want those semi-metallic glasses to crystallize as fast as possible in the liquid, but to stay as stable as possible when in the glass state. I think now we have a promising new understanding of how this is achieved in the PCMs under study.”

A Deviation from the expected

Over a century ago, Einstein wrote in his Ph.D. thesis that the diffusion of particles undergoing Brownian motion could be understood if the frictional force retarding the motion of a particle was that derived by Stokes for a round ball falling through a jar of honey. The simple equation: D (diffusivity) = kBT/6??r where T is the temperature, ? is the viscosity and r is the particle radius, implies that the product D?/T should be constant as T changes, and the surprising thing is that this seems to be true not only for Brownian motion, but also for simple molecular liquids whose molecular motion is known to be anything but that of a ball falling through honey!

“We don’t have any good explanation of why it works so well, even in the highly viscous supercooled state of molecular liquids until approaching the glass transition temperature, but we do know that there are a few interesting liquids in which it fails badly even above the melting point,” observes Angell.

“One of them is liquid tellurium, a key element of the PCM materials. Another is water which is famous for its anomalies, and a third is germanium, a second of the three elements of the GST type of PCM. Now we are adding a fourth, the GST liquid itself..!!! thanks to the neutron scattering studies proposed and executed by Shuai Wei and his German colleagues, Zach Evenson (Technical University of Munich, Germany) and Moritz Stolpe (Saarland University, Germany) on samples prepared by Shuai with the help of Pierre Lucas (University of Arizona).”

Another feature in common for this small group of liquids is the existence of a maximum in liquid density which is famous for the case of water. A density maximum closely followed, during cooling, by a metal-to semiconductor transition is also seen in the stable liquid state of arsenic telluride, (As2Te3), which is first cousin to the antimony telluride (Sb2Te3 ) component of the PCMs all of which lie on the “Ovshinsky” line connecting antimony telluride (Sb2Te3 ) to germanium telluride (GeTe) in the three component phase diagram. Can it be that the underlying physics of these liquids has a common basis?

It is the suggestion of Wei and coauthors that when germanium, antimony and tellurium are mixed together in the ratio of 1:2:4, (or others along Ovshinsky’s “magic” line) both the density maxima and the associated metal to non-metal transitions are pushed below the melting point and, concomitantly, the transition becomes much sharper than in other chalcogenide mixtures.

Then, as in the much-studied case of supercooled water, the fluctuations associated with the response function extrema should give rise to extremely rapid crystallization kinetics. In all cases, the high temperature state (now the metallic state), is the denser.

“This would explain a lot,” enthuses Angell “Above the transition the liquid is very fluid and crystallization is extremely rapid, while below the transition the liquid stiffens up quickly and retains the amorphous, low-conductivity state down to room temperature. In nanoscopic “bits”, it then remains indefinitely stable until instructed by a computer-programmed heat pulse to rise instantly to a temperature where, on a nano-second time scale, it flash crystallizes to the conducting state, the “on” state.

Lindsay Greer at Cambridge University has made the same argument couched in terms of a “fragile-to-strong” liquid transition”.

A second slightly larger heat pulse can take the “bit” instantaneously above its melting point and then, with no further heat input and close contact with a cold substrate, it quenches at a rate sufficient to avoid crystallization and is trapped in the semi-conducting state, the “off” state.

“The high resolution of the neutron time of flight-spectrometer from the Technical University of Munich was necessary to see the details of the atomic movements. Neutron scattering at the Heinz Maier-Leibnitz Zentrum in Garching is the ideal method to make these movements visible,” states Zach Evenson.

Researchers from Intel Corp. and the University of California, Berkeley, are looking beyond current transistor technology and preparing the way for a new type of memory and logic circuit that could someday be in every computer on the planet.

In a paper appearing online Dec. 3 in advance of publication in the journal Nature, the researchers propose a way to turn relatively new types of materials, multiferroics and topological materials, into logic and memory devices that will be 10 to 100 times more energy-efficient than foreseeable improvements to current microprocessors, which are based on CMOS (complementary metal-oxide-semiconductor).

Single crystals of the multiferroic material bismuth-iron-oxide. The bismuth atoms (blue) form a cubic lattice with oxygen atoms (yellow) at each face of the cube and an iron atom (gray) near the center. The somewhat off-center iron interacts with the oxygen to form an electric dipole (P), which is coupled to the magnetic spins of the atoms (M) so that flipping the dipole with an electric field (E) also flips the magnetic moment. The collective magnetic spins of the atoms in the material encode the binary bits 0 and 1, and allow for information storage and logic operations. Credit: Ramamoorthy Ramesh lab, UC Berkeley

The magneto-electric spin-orbit or MESO devices will also pack five times more logic operations into the same space than CMOS, continuing the trend toward more computations per unit area, a central tenet of Moore’s Law.

The new devices will boost technologies that require intense computing power with low energy use, specifically highly automated, self-driving cars and drones, both of which require ever increasing numbers of computer operations per second.

“As CMOS develops into its maturity, we will basically have very powerful technology options that see us through. In some ways, this could continue computing improvements for another whole generation of people,” said lead author Sasikanth Manipatruni, who leads hardware development for the MESO project at Intel’s Components Research group in Hillsboro, Oregon. MESO was invented by Intel scientists, and Manipatruni designed the first MESO device.

Transistor technology, invented 70 years ago, is used today in everything from cellphones and appliances to cars and supercomputers. Transistors shuffle electrons around inside a semiconductor and store them as binary bits 0 and 1.

In the new MESO devices, the binary bits are the up-and-down magnetic spin states in a multiferroic, a material first created in 2001 by Ramamoorthy Ramesh, a UC Berkeley professor of materials science and engineering and of physics and a senior author of the paper.

“The discovery was that there are materials where you can apply a voltage and change the magnetic order of the multiferroic,” said Ramesh, who is also a faculty scientist at Lawrence Berkeley National Laboratory. “But to me, ‘What would we do with these multiferroics?’ was always a big question. MESO bridges that gap and provides one pathway for computing to evolve”

In the Nature paper, the researchers report that they have reduced the voltage needed for multiferroic magneto-electric switching from 3 volts to 500 millivolts, and predict that it should be possible to reduce this to 100 millivolts: one-fifth to one-tenth that required by CMOS transistors in use today. Lower voltage means lower energy use: the total energy to switch a bit from 1 to 0 would be one-tenth to one-thirtieth of the energy required by CMOS.

“A number of critical techniques need to be developed to allow these new types of computing devices and architectures,” said Manipatruni, who combined the functions of magneto-electrics and spin-orbit materials to propose MESO. “We are trying to trigger a wave of innovation in industry and academia on what the next transistor-like option should look like.”

Internet of things and AI

The need for more energy-efficient computers is urgent. The Department of Energy projects that, with the computer chip industry expected to expand to several trillion dollars in the next few decades, energy use by computers could skyrocket from 3 percent of all U.S. energy consumption today to 20 percent, nearly as much as today’s transportation sector. Without more energy-efficient transistors, the incorporation of computers into everything – the so-called internet of things – would be hampered. And without new science and technology, Ramesh said, America’s lead in making computer chips could be upstaged by semiconductor manufacturers in other countries.

“Because of machine learning, artificial intelligence and IOT, the future home, the future car, the future manufacturing capability is going to look very different,” said Ramesh, who until recently was the associate director for Energy Technologies at Berkeley Lab. “If we use existing technologies and make no more discoveries, the energy consumption is going to be large. We need new science-based breakthroughs.”

Paper co-author Ian Young, a UC Berkeley Ph.D., started a group at Intel eight years ago, along with Manipatruni and Dmitri Nikonov, to investigate alternatives to transistors, and five years ago they began focusing on multiferroics and spin-orbit materials, so-called “topological” materials with unique quantum properties.

“Our analysis brought us to this type of material, magneto-electrics, and all roads led to Ramesh,” said Manipatruni.

Multiferroics and spin-orbit materials

Multiferroics are materials whose atoms exhibit more than one “collective state.” In ferromagnets, for example, the magnetic moments of all the iron atoms in the material are aligned to generate a permanent magnet. In ferroelectric materials, on the other hand, the positive and negative charges of atoms are offset, creating electric dipoles that align throughout the material and create a permanent electric moment.

MESO is based on a multiferroic material consisting of bismuth, iron and oxygen (BiFeO3) that is both magnetic and ferroelectric. Its key advantage, Ramesh said, is that these two states – magnetic and ferroelectric – are linked or coupled, so that changing one affects the other. By manipulating the electric field, you can change the magnetic state, which is critical to MESO.

The key breakthrough came with the rapid development of topological materials with spin-orbit effect, which allow for the state of the multiferroic to be read out efficiently. In MESO devices, an electric field alters or flips the dipole electric field throughout the material, which alters or flips the electron spins that generate the magnetic field. This capability comes from spin-orbit coupling, a quantum effect in materials, which produces a current determined by electron spin direction.

In another paper that appeared earlier this month in Science Advances, UC Berkeley and Intel experimentally demonstrated voltage-controlled magnetic switching using the magneto-electric material bismuth-iron-oxide (BiFeO3), a key requirement for MESO.

“We are looking for revolutionary and not evolutionary approaches for computing in the beyond-CMOS era,” Young said. “MESO is built around low-voltage interconnects and low-voltage magneto-electrics, and brings innovation in quantum materials to computing.”

Leti, a research institute of CEA-Tech, and Silvaco Inc., a global provider of software, IP and services for designing chips and electronic systems for semiconductor companies, today announced during the IEDM 2018 conference a project to create innovative and unified SPICE compact models for the design of advanced circuits using nanowire and nanosheet technologies.

The new predictive and physical compact model under development, Leti-NSP, builds on Leti’s 15 years of model development, including the popular Leti-UTSOI model for FD-SOI technology. The Leti-NSP compact model uses a novel methodology for the calculation of the surface potential, including quantum confinement. The model is able to handle arbitrary cross-section shapes of stacked planar and vertical GAA MOSFETs (circular, square, rectangular). It provides an excellent tool for design exploration of nanowire and nanosheet device architectures.

This three-year collaboration will make the new device models available to designers through SmartSpiceTM, Silvaco’s high-performance parallel SPICE simulator for use by circuit designers. The corresponding model-parameters extraction flow will be implemented in Utmost IVTM, Silvaco’s database-driven environment for characterizing semiconductor devices, to ensure an accurate fit between simulated and measured device characteristics.

Accuracy of analysis at the nanometer scale is essential for co-optimization of silicon process technology and circuit performance. Besides accurate device characterization and simulation, a complete solution includes TCAD simulation, and 3D parasitic extraction. Silvaco’s partnership with leading research institutions for atomistic TCAD, and its proven in-house extraction solver technology, will provide the most accurate Design Technology Co-Optimization (DTCO) solution for nanometer technologies.

“Over two decades, CEA-Leti and Silvaco have collaborated on design-technology co-optimization, ranging from innovative TCAD simulation to the design of advanced nanoelectronics, and thus expanded and strengthened Silvaco’s suite of tools for designers,” said Emmanuel Sabonnadière, CEA-Leti CEO. “This project continues that partnership, andwhen these physics-based compact models are made available to designers worldwide, they will be able to evaluate the potential of advanced nanowire-based CMOS technologies under development at CEA-Leti.”

“DTCO, including circuit simulation, is fundamental to the development of electronic devices, and shrinking silicon geometries are placing an even greater premium on accuracy to capture and evaluate all the new physical effects in nanometer design,” said Eric Guichard, vice president of Silvaco’s TCAD Division. “Building on past successes of Leti and Silvaco’s collaboration, this project will provide circuit designers and technologists with powerful, advanced design flows that combine CEA-Leti’s physical, predictive, and easy-to-use models with Silvaco’s high-accuracy EDA tools.”

EV Group (EVG), a supplier of wafer bonding and lithography equipment for the MEMS, nanotechnology and semiconductor markets, today introduced the all new BONDSCALE™ automated production fusion bonding system. BONDSCALE is designed to fulfill a wide range of fusion/molecular wafer bonding applications, including engineered substrate manufacturing and 3D integration approaches that use layer-transfer processing, such as monolithic 3D (M3D). With BONDSCALE, EVG is bringing wafer bonding to front-end semiconductor processing and helping to address long-term challenges for “More Moore” logic device scaling identified in the International Roadmap for Devices and Systems (IRDS). Incorporating an enhanced edge alignment technology, BONDSCALE provides a significant boost in wafer bond productivity and lower cost of ownership (CoO) compared to existing fusion bonding platforms. It is already being shipped to customers.

BONDSCALE is being sold alongside EVG’s industry benchmark GEMINI® FB XT automated fusion bonding system, with each platform targeting different applications. While BONDSCALE will primarily focus on engineered substrate bonding and layer-transfer processing, the GEMINI FB XT will support applications requiring higher alignment accuracies, such as memory stacking, 3D systems on chip (SoC), backside illuminated CMOS image sensor stacking, and die partitioning.

Direct wafer bonding key to driving semiconductor performance scaling

According to the IRDS Roadmap, parasitic scaling will become a dominant driver of logic device performance in the coming years, requiring new transistor architectures and materials. The IRDS Roadmap also notes that new 3D integration approaches such as M3D will be necessary to support the long-term transition from 2D to 3D VLSI, including backside power distribution, N&P stacking, logic-on-memory, clustered functional stacks and beyond-CMOS adoption. Layer-transfer processes and engineered substrates are enabling technologies for logic scaling by helping to deliver significant improvements in device performance, functionality and power consumption. Direct wafer bonding with plasma activation is a proven solution for enabling heterogeneous integration of different materials, high-quality engineered substrates as well as thin-silicon-layer-transfer applications.

“As a pioneer and market leader in wafer bonding, EVG has been at the forefront in helping customers bring new semiconductor technologies from early R&D to full-scale manufacturing,” stated Paul Lindner, executive technology director at EV Group. “Nearly 25 years ago, EVG introduced the industry’s first silicon-on-insulator (SOI) wafer bonder to support the production of high-frequency and radiation-hard devices for niche applications. Since then, we have continuously enhanced the performance and CoO of our direct bonding platforms to help our customers bring the benefits of engineered substrates to a wider range of applications. Our new BONDSCALE solution takes this to the next level, boosting productivity to fulfill the growing need for engineered substrates and layer-transfer processing to enable continued performance, power and area scaling of next-generation logic and memory devices in the ‘More Moore’ era.”

BONDSCALE is a high-volume production system for fusion/direct wafer bonding needed for front-end-of-line applications. Featuring EVG’s LowTemp™ plasma activation technology, the BONDSCALE system combines all essential steps for fusion bonding — including cleaning, plasma activation, alignment, pre-bonding and IR inspection — in a single platform that is suitable for a wide range of fusion/molecular wafer bonding applications. Capable of processing both 200-mm and 300-mm wafers, the system ensures a void-free, high-throughput, and high-yield production process.

BONDSCALE incorporates next-generation fusion/direct bonding modules, a new wafer handling system and optical edge alignment to provide significantly higher throughput and productivity to support the needs of its customers to ramp up engineered substrate wafer production and M3D integration.

How long can tiny gears and other microscopic moving parts last before they wear out? What are the warning signs that these components are about to fail, which can happen in just a few tenths of a second? Striving to provide clear answers to these questions, researchers at the National Institute of Standards and Technology (NIST) have developed a method for more quickly tracking microelectromechanical systems (MEMS) as they work and, just as importantly, as they stop working.

By using this method for microscopic failure analysis, researchers and manufacturers could improve the reliability of the MEMS components that they are developing, ranging from miniature robots and drones to tiny forceps for eye surgery and sensors to detect trace amounts of toxic chemicals.

Over the past decade, researchers at the National Institute of Standards and Technology (NIST) have measured the motion and interactions between MEMS components. In their newest work, the scientists succeeded in making these measurements a hundred times faster, on the scale of thousandths, rather than tenths, of a second.

The faster time scale enabled the researchers to resolve fine details of the transient and erratic motions that may occur before and during the failure of MEMS. The faster measurements also allowed repetitive testing–necessary for assessing the durability of the miniature mechanical systems–to be conducted more quickly. The NIST researchers, including Samuel Stavis and Craig Copeland, described their work in the Journal of Microelectromechanical Systems.

As in their previous work, the team labeled the MEMS components with fluorescent particles to track their motion. Using optical microscopes and sensitive cameras to view and image the light-emitting particles, the researchers tracked displacements as small as a few billionths of a meter and rotations as tiny as several millionths of a radian. One microradian is the angle corresponding to an arc of about 10 meters along the circumference of the earth.

A faster imaging system and larger fluorescent particles, which emit more light, provided the scientists with the tools to perform their particle-tracking measurements a hundred times more rapidly than before.

“If you cannot measure how the components of a MEMS move at the relevant length and time scales, then it is difficult to understand how they work and how to improve them,” Copeland said.

In their test system, Stavis, Copeland and their colleagues tested part of a microelectromechanical motor. The test part snapped back and forth, rotating a gear through a ratchet mechanism. Although this system is one of the more reliable MEMS that transfer motion through parts in sliding contact, it nonetheless can exhibit such problems as erratic performance and untimely failure.

The team found that the jostling of contacting parts in the system, whether contact between the parts occurred at only one point or shifted between several points, and wear of the contacting surfaces, could all play a key role in the durability of MEMS.

“Our tracking method is broadly applicable to study the motion of microsystems, and we continue to advance it,” said Stavis.