Category Archives: Process Materials

A research team from Tokyo Institute of Technology (Tokyo Tech) and Waseda University have successfully produced high-quality thin film monocrystalline silicon with a reduced crystal defect density down to the silicon wafer level at a growth rate that is more than 10 times higher than before. In principle, this method can improve the raw material yield to nearly 100%. Therefore, it can be expected that this technology will make it possible to drastically reduce manufacturing costs while maintaining the power generation efficiency of monocrystalline silicon solar cells, which are used in most high efficient solar cells.

This is the monocrystalline Si thin film peeled off using adhesive tape. Credit: CrystEngComm

This is the monocrystalline Si thin film peeled off using adhesive tape. Credit: CrystEngComm

Background

Solar power generation is a method of generating power where solar light energy is converted directly into electricity using a device called a “solar cell.” Efficiently converting the solar energy that is constantly striking the earth to generate electricity is an effective solution to the problem of global warming related to CO2emissions. By making the monocrystalline Si solar cells that are at the core of solar power generation systems thinner, it is possible to greatly reduce raw material costs, which account for about 40% of the current module, and by making them flexible and lighter, usage can be expected to expand and installation costs can be expected to decrease.

In addition, as a method of reducing manufacturing cost, thin-film monocrystalline Si solar cells that use porous silicon (Double Porous Silicon Layer: DPSL) via lift-off are attracting attention as having a competitive edge in the future.

Among the technical challenges related to monocrystalline Si solar cells using lift-off are 1) the formation of a high-quality thin film Si at the Si wafer level, 2) achieving a porous structure that can easily be lifted off (peeled off), 3) improving the growth rate and Si raw material yield (necessary equipment costs are determined by the growth rate), and 4) being able to use the substrate after lift-off without any waste.

In order to overcome challenge 1), it was necessary to clarify the main factors that determine the quality of thin film crystals grown on porous silicon, and to develop a technique for controlling these.

Overview of research achievement

A joint research team consisting of Professor Manabu Ihara and Assistant Professor Kei Hasegawa of the Tokyo Tech, and Professor Suguru Noda of Waseda University has developed a high-quality thin film monocrystalline silicon with a thickness of about 10 μm and a reduced crystal defect density down to the silicon wafer level at a growth rate that is more than 10 times higher than before. First, double-layer nano-order porous silicon is generated on the surface of a monocrystalline wafer using an electrochemical technique. Next, the surface was smoothed to a roughness of 0.2 to 0.3 nm via a unique zone heating recrystallization method (ZHR method), and this substrate was used for high-speed growth to obtain a moonocrystalline thin film with high crystal quality. The grown film can easily be peeled off using the double-layer porous Si layer, and the substrate can be reused or used as an evaporation source for thin film growth, which greatly reduces material loss. When the surface roughness of the underlying substrate is reduced by changing the ZHR method conditions, the defect density of the thin film crystal that was grown decreased, and the team eventually succeeded in reducing it to the Si wafer level of about 1/10th. This quantitatively shows that a surface roughness in the range of only 0.1-0.2 nm (level of atoms to several tens of layers) has an important impact on the formation of crystal defects, which is also of interest as a crystal growth mechanism.

The film formation rate and the conversion rate of the Si source to the thin film Si are bottlenecks in the production of thin-film monocrystalline Si. With chemical vapor deposition (CVD), which is mainly used for epitaxy, the maximum film forming rate is a few μm/h and the yield is about 10%. At the Noda Laboratory of Waseda University, instead of the regular physical vapor deposition (PVD) where raw Si is vaporized at around its melting point of 1414 ?C, by vaporizing the raw Si at much higher temperature of >2000 ?C, a rapid evaporation method (RVD) was developed with a high Si vapor pressure capable of depositing Si at 10 μm/min.

It was found that the ZHR technology developed this time can resolves technical problems and drastically reduce the manufacturing cost of the lift-off process.

Future development

Based on the results of this study, not only did the team discover the main factors for improving the quality of crystals during rapid growth on porous silicon used for the lift-off process, they succeeded in controlling these. In the future, measurement of the carrier lifetime of the thin film, which is directly connected to the performances of solar cells, and fabrication of solar cells will be carried out with the goal of putting the technology into practical use. The use of this Si thin films as low cost bottom cells in tandem type solar cells with an efficiency of over 30% will also be considered.

The results are published in the Royal Society of Chemistry (RSC) journal CrystEngComm and will be featured on the inside front cover of the issue.

One of the problems for Javier Vela and the chemists in his Iowa State University research group was that a toxic material worked so well in solar cells.

And so any substitute for the lead-containing perovskites used in some solar cells would have to really perform. But what could they find to replace the perovskite semiconductors that have been so promising and so efficient at converting sunlight into electricity?

What materials could produce semiconductors that worked just as well, but were safe and abundant and inexpensive to manufacture?

“Semiconductors are everywhere, right?” Vela said. “They’re in our computers and our cell phones. They’re usually in high-end, high-value products. While semiconductors may not contain rare materials, many are toxic or very expensive.”

Vela, an Iowa State associate professor of chemistry and an associate of the U.S. Department of Energy’s Ames Laboratory, directs a lab that specializes in developing new, nanostructured materials. While thinking about the problem of lead in solar cells, he found a conference presentation by Massachusetts Institute of Technology researchers that suggested possible substitutes for perovskites in semiconductors.

Vela and Iowa State graduate students Bryan Rosales and Miles White decided to focus on sodium-based alternatives and started an 18-month search for a new kind of semiconductor. The work was supported by Vela’s five-year, $786,017 CAREER grant from the National Science Foundation. CAREER grants are the foundation’s most prestigious awards for early career faculty.

They came up with a compound that features sodium, which is cheap and abundant; bismuth, which is relatively scarce but is overproduced during the mining of other metals and is cheap; and sulfur, the fifth most common element on Earth. The researchers report their discovery in a paper recently published online by the Journal of the American Chemical Society.

The paper’s subtitle is a good summary of their work: “Toward Earth-Abundant, Biocompatible Semiconductors.”

“Our synthesis unlocks a new class of low-cost and environmentally friendly ternary (three-part) semiconductors that show properties of interest for applications in energy conversion,” the chemists wrote in their paper.

In fact, Rosales is working to create solar cells that use the new semiconducting material.

Vela said variations in synthesis – changing reaction temperature and time, choice of metal ion precursors, adding certain ligands – allows the chemists to control the material’s structure and the size of its nanocrystals. And that allows researchers to change and fine tune the material’s properties.

Several of the material’s properties are already ideal for solar cells: The material’s band gap – the amount of energy required for a light particle to knock an electron loose – is ideal for solar cells. The material, unlike other materials used in solar cells, is also stable when exposed to air and water.

So, the chemists think they have a material that will work well in solar cells, but without the toxicity, scarcity or costs.

“We believe the experimental and computational results reported here,” they wrote in their paper, “will help advance the fundamental study and exploration of these and similar materials for energy conversion devices.”

The Silicon Integration Initiative’s (Si2) Compact Model Coalition (CMC) has approved two integrated circuit design simulation standards that target the fast-growing global market for gallium nitride semiconductors.

The approved standards are the 12th and 13th models currently funded and supported by the CMC, a collaborative group that develops and maintains cost-saving SPICE (Simulation Program with Integrated Circuit Emphasis) models for IC design.

John Ellis, president and CEO, said gallium nitride devices are used in many high-power and high-frequency applications, including satellite communications, radar, cellular, broadband wireless systems, and automotive. “Although it’s currently a small market, gallium nitride devices are expected to show remarkable growth over the coming years.”

To reduce research and developments costs and increase simulation accuracy, the semiconductor industry relies on the CMC to share resources for funding standard SPICE models. Si2 is a research and development joint venture focused on IC design and tool operability standards. “Once the standard models are proven and accepted by CMC, they are incorporated into design tools widely used by the semiconductor industry. The equations at work in the standard model-setting process are developed, refined and maintained by leading universities and national laboratories. The CMC directs and funds the universities to standardize and improve the models,” Ellis explained.

Dr. Ana Villamor, technology and market analyst at Yole Développement (Yole), Lyon, France, said that “2015 and 2016 were exciting years for the gallium nitride power business. We project an explosion of this market with 79% CAGR between 2017 and 2022. Market value will reach US $460 million at the end of the period1. It’s still a small market compared to the impressive US $30 billion silicon power semiconductor market,” Villamor said. “However, its expected growth in the short term is showing the enormous potential of the power gallium nitride technology based on its suitability for high performance and high frequency solutions.”

Yole_GaN_power_device_market_size_split_by_application_M_

Peter Lee, manager at Micron Memory Japan and CMC chair, said that “Gallium nitride devices are playing an increasingly important part in the field of RF and power electronics. With these two advanced models established as the first, worldwide gallium nitride model standards, efficiencies in design will greatly increase by making it possible to take into account accurate device physical behavior in design, and enabling the use of the various simulation tools in the industry with consistent results.”

Click here to download standard models.

 

Scientists at Rice University and the Indian Institute of Science, Bangalore, have discovered a method to make atomically flat gallium that shows promise for nanoscale electronics.

The Rice lab of materials scientist Pulickel Ajayan and colleagues in India created two-dimensional gallenene, a thin film of conductive material that is to gallium what graphene is to carbon.

Extracted into a two-dimensional form, the novel material appears to have an affinity for binding with semiconductors like silicon and could make an efficient metal contact in two-dimensional electronic devices, the researchers said.

The new material was introduced in Science Advances.

Gallium is a metal with a low melting point; unlike graphene and many other 2-D structures, it cannot yet be grown with vapor phase deposition methods. Moreover, gallium also has a tendency to oxidize quickly. And while early samples of graphene were removed from graphite with adhesive tape, the bonds between gallium layers are too strong for such a simple approach.

So the Rice team led by co-authors Vidya Kochat, a former postdoctoral researcher at Rice, and Atanu Samanta, a student at the Indian Institute of Science, used heat instead of force.

Rather than a bottom-up approach, the researchers worked their way down from bulk gallium by heating it to 29.7 degrees Celsius (about 85 degrees Fahrenheit), just below the element’s melting point. That was enough to drip gallium onto a glass slide. As a drop cooled just a bit, the researchers pressed a flat piece of silicon dioxide on top to lift just a few flat layers of gallenene.

They successfully exfoliated gallenene onto other substrates, including gallium nitride, gallium arsenide, silicone and nickel. That allowed them to confirm that particular gallenene-substrate combinations have different electronic properties and to suggest that these properties can be tuned for applications.

“The current work utilizes the weak interfaces of solids and liquids to separate thin 2-D sheets of gallium,” said Chandra Sekhar Tiwary, principal investigator on the project he completed at Rice before becoming an assistant professor at the Indian Institute of Technology in Gandhinagar, India. “The same method can be explored for other metals and compounds with low melting points.”

Gallenene’s plasmonic and other properties are being investigated, according to Ajayan. “Near 2-D metals are difficult to extract, since these are mostly high-strength, nonlayered structures, so gallenene is an exception that could bridge the need for metals in the 2-D world,” he said.

A research team led by UCLA scientists and engineers has developed a method to make new kinds of artificial “superlattices” — materials comprised of alternating layers of ultra-thin “two-dimensional” sheets, which are only one or a few atoms thick. Unlike current state-of-the art superlattices, in which alternating layers have similar atomic structures, and thus similar electronic properties, these alternating layers can have radically different structures, properties and functions, something not previously available.

This is an artist's concept of two kinds of monolayer atomic crystal molecular superlattices. On the left, molybdenum disulfide with layers of ammonium molecules, on the right, black phosphorus with layers of ammonium molecules. Credit: UCLA Samueli Engineering

This is an artist’s concept of two kinds of monolayer atomic crystal molecular superlattices. On the left, molybdenum disulfide with layers of ammonium molecules, on the right, black phosphorus with layers of ammonium molecules. Credit: UCLA Samueli Engineering

For example, while one layer of this new kind of superlattice can allow a fast flow of electrons through it, the other type of layer can act as an insulator. This design confines the electronic and optical properties to single active layers, and prevents them from interfering with other insulating layers.

Such superlattices can form the basis for improved and new classes of electronic and optoelectronic devices. Applications include superfast and ultra-efficient semiconductors for transistors in computers and smart devices, and advanced LEDs and lasers.

Compared with the conventional layer-by-layer assembly or growth approach currently used to create 2D superlattices, the new UCLA-led process to manufacture superlattices from 2D materials is much faster and more efficient. Most importantly, the new method easily yields superlattices with tens, hundreds or even thousands of alternating layers, which is not yet possible with other approaches.

This new class of superlattices alternates 2D atomic crystal sheets that are interspaced with molecules of varying shapes and sizes. In effect, this molecular layer becomes the second “sheet” because it is held in place by “van der Waals” forces, weak electrostatic forces to keep otherwise neutral molecules “attached” to each other. These new superlattices are called “monolayer atomic crystal molecular superlattices.”

The study, published in Nature, was led by Xiangfeng Duan, UCLA professor of chemistry and biochemistry, and Yu Huang, UCLA professor of materials science and engineering at the UCLA Samueli School of Engineering.

“Traditional semiconductor superlattices can usually only be made from materials with highly similar lattice symmetry, normally with rather similar electronic structures,” Huang said. “For the first time, we have created stable superlattice structures with radically different layers, yet nearly perfect atomic-molecular arrangements within each layer. This new class of superlattice structures has tailorable electronic properties for potential technological applications and further scientific studies.”

One current method to build a superlattice is to manually stack the ultrathin layers one on top of the other. But this is labor-intensive. In addition, since the flake-like sheets are fragile, it takes a long time to build because many sheets will break during the placement process. The other method is to grow one new layer on top of the other, using a process called “chemical vapor deposition.” But since that means different conditions, such as heat, pressure or chemical environments, are needed to grow each layer, the process could result in altering or breaking the layer underneath. This method is also labor-intensive with low yield rates.

The new method to create monolayer atomic crystal molecular superlattices uses a process called “electrochemical intercalation,” in which a negative voltage is applied. This injects negatively charged electrons into the 2D material. Then, this attracts positively charged ammonium molecules into the spaces between the atomic layers. Those ammonium molecules automatically assemble into new layers in the ordered crystal structure, creating a superlattice.

“Think of a two-dimensional material as a stack of playing cards,” Duan said. “Then imagine that we can cause a large pile of nearby plastic beads to insert themselves, in perfect order, sandwiching between each card. That’s the analogous idea, but with a crystal of 2D material and ammonium molecules.”

The researchers first demonstrated the new technique using black phosphorus as a base 2D atomic crystal material. Using the negative voltage, positively charged ammonium ions were attracted into the base material, and inserted themselves between the layered atomic phosphorous sheets.”

Following that success, the team inserted different types of ammonium molecules with various sizes and symmetries into a series of 2D materials to create a broad class of superlattices. They found that they could tailor the structures of the resulting monolayer atomic crystal molecular superlattices, which had a diverse range of desirable electronic and optical properties.”The resulting materials could be useful for making faster transistors that consume less power, or for creating efficient light-emitting devices,” Duan said.

Semiconductors–a class of materials that can function as both electrical conductor and insulator, depending on the circumstances–are an essential technology for all modern electronic innovations.

Silicon has long been the most famous semiconductor, but in recent years researchers have studied a wider range of materials, including molecules that can be tailored to serve specific electronic needs.

Perhaps appropriately, one of the most cutting-edge electronics–supercomputers–are indispensable research tools for studying complex semiconducting materials at a fundamental level.

Recently, a team of scientists at TU Dresden used the SuperMUC supercomputer at the Leibniz Supercomputing Centre to refine its method for studying organic semiconductors.

Illustration of a doped organic semiconductor based on fullerene C60 molecules (green). The benzimidazoline dopant (purple) donates an electron to the C60 molecules in its surrounding (dark green). These electrons can then propagate through the semiconductor material (light green). Credit: S. Hutsch/F. Ortmann, TU Dresden

Illustration of a doped organic semiconductor based on fullerene C60 molecules (green). The benzimidazoline dopant (purple) donates an electron to the C60 molecules in its surrounding (dark green). These electrons can then propagate through the semiconductor material (light green). Credit: S. Hutsch/F. Ortmann, TU Dresden

Specifically, the team uses an approach called semiconductor doping, a process in which impurities are intentionally introduced into a material to give it specific semiconducting properties. It recently published its results in Nature Materials.

“New kinds of semiconductors, organic semiconductors, are starting to get used in new device concepts,” said team leader Dr. Frank Ortmann. “Some of these are already on the market, but some are still limited by their inefficiency. We are researching doping mechanisms–a key technology for tuning semiconductors’ properties–to understand these semiconductors’ limitations and respective efficiencies.”

Quantum impurities

When someone changes a material’s physical properties, he or she also changes its electronic properties and, therefore, the role it can play in electronic devices. Small changes in material makeup can lead to big changes in a material’s characteristics–in certain cases one slight atomic alteration can lead to a 1000-fold change in electrical conductivity.

While changes in material properties may be big, the underlying forces–exerting themselves on atoms and molecules and governing their interactions–are generally weak and short-range (meaning the molecules and the atoms of which they are composed must be close together). To understand changes in properties, therefore, researchers have to accurately compute atomic and molecular interactions as well as the densities of electrons and how they are transferred among molecules.

Introducing specific atoms or molecules to a material can change its conducting properties on a hyperlocal level. This allows a transistor made from doped material to serve a variety of roles in electronics, including routing currents to perform operations based on complex circuits or amplifying current to help produce sound in a guitar amplifier or radio.

Quantum laws govern interatomic and intermolecular interactions, in essence holding material together, and, in turn, structuring the world as we know it. In the team’s work, these complex interactions need to be calculated for individual atomic interactions, including interactions among semiconductor “host” molecules and dopant molecules on a larger scale.

The team uses density functional theory (DFT)–a computational method that can model electronic densities and properties during a chemical interaction–to efficiently predict the variety of complex interactions. It then collaborates with experimentalists from TU Dresden and the Institute for Molecular Science in Okazaki, Japan to compare its simulations to spectroscopy experiments.

“Electrical conductivity can come from many dopants and is a property that emerges on a much larger length scale than just interatomic forces,” Ortmann said. “Simulating this process needs more sophisticated transport models, which can only be implemented on high-performance computing (HPC) architectures.”

Goal!

To test its computational approach, the team simulated materials that already had good experimental datasets as well as industrial applications. The researchers first focused on C60, also known as Buckminsterfullerene.

Buckminsterfullerene is used in several applications, including solar cells. The molecule’s structure is very similar to that of a soccer ball–a spherical arrangement of carbon atoms arranged in pentagonal and hexagonal patterns the size of less than one nanometer. In addition, the researches simulated zinc phthalocyanine (ZnPc), another molecule that is used in photovoltaics, but unlike C60, has a flat shape and contains a metallic atom (zinc).

As its dopant the team first used a well-studied molecule called 2-Cyc-DMBI (2-cyclohexyl-dimethylbenzimidazoline). 2-Cyc-DMBI is considered an n-dopant, meaning that it can provide its surplus electrons to the semiconductor to increase its conductivity. N-dopants are relatively rare, as few molecules are “willing” to give away an electron. In most cases, molecules that do so become unstable and degrade during chemical reactions, which in this context can lead to an electronic device failure. 2-Cyc-DMBI dopants are the exception, because they can be sufficiently weakly attractive for electrons–allowing them to move over long distances–while also remaining stable after donating them.

The team got good agreement between its simulations and experimental observations of the same molecule-dopant interactions. This indicates that they can rely on simulation to guide predictions as they relate to the doping process of semiconductors. They are now working on more complex molecules and dopants using the same methods.

Despite these advances, the team recognizes that next-generation supercomputers such as SuperMUC-NG–announced in December 2017 and set to be installed in 2018–will help the researchers expand the scope of their simulations, leading to ever bigger efficiency gains in a variety of electronic applications.

“We need to push the accuracy of our simulations to the maximum,” Ortmann said. “This would help us extend the range of applicability and allow us to more precisely simulate a broader set of materials or larger systems of more atoms.”

Ortmann also noted that while current-generation systems allowed the team to gain insights in specific situations and prove its concept, there is still room to get better. “We are often limited by system memory or CPU power,” he said. “The system size and simulation’s accuracy are essentially competing for computing power, which is why it is important to have access to better supercomputers. Supercomputers are perfectly suited to deliver answers to these problems in a realistic amount of time.”

Linde LienHwa, a key supplier of gases and chemicals to the electronics industry, continues to invest with its customers in Mainland China and Taiwan. On-site nitrogen generator plants are an early, tangible and significant demonstration of commitment to individual customers as they plan and execute new semiconductor and display panel plants.

The company is also expanding its production of electronic special gases (ESGs). This enhances its portfolio to meet the growing demand of local customers in the semiconductor and display industries. Linde LienHwa is leveraging access to global expertise to build first-in-kind capabilities in Taiwan to innovate locally for customers.

In March, Linde LienHwa will highlight its position in the electronics material sector with presentations by its executives at two industry forums held in Shanghai. The company invites customers and others in the electronics industry to visit its booth at the SEMICON China trade show for one-on-one discussions about their requirements and how Linde LienHwa is their local partner with global expertise.

Investing and growing with customers in Mainland China with on-site nitrogen production

Mainland China has made a large commitment to the electronics industry through the Sino IC Industry Investment Fund, more commonly known as The Big Fund. This has spurred an unprecedented number of new semiconductor and display projects launch in 2017, on top of very active preceding years in 2015 and 2016.

Nitrogen gas is used in high volumes at these facilities in almost all manufacturing steps to purge and inert chemically sensitive processes. For most facilities, it is much more economical to produce the required volume of nitrogen on-site, rather than to supply the gas by truck delivery. On-site nitrogen generators are built at an early phase of each project because nitrogen is required to be ready before the facility equipment arrives.

SPECTRA-N® nitrogen generators from the Linde Engineering division of the Linde Group support customers with their high quality products, flexible capacity and production and energy efficiency. These plants are designed, fabricated and executed by teams located in Hangzhou and Dalian, China.

Linde LienHwa has been successful in addressing the market needs with a number of new project signings. “These wins were punctuated in 2017 by a Linde LienHwa commitment of over RMB 1.5 billion investment in on-site gas production and bulk gas installations for electronics customers in Mainland China, which will fuel electronics revenue growth for us over the next five years,” said Stan Tang, President of LLH China. “This is only possible with a strong network of bulk gas production plants and fleet delivery throughout Mainland China, which back-up the on-site nitrogen plants as well as offer competitive supplies of oxygen, argon, hydrogen and other products.”

GeH4 precision blending and filling at Taichung Harbor

Linde LienHwa’s capability for blending and filling of germane in Taichung Harbor is the first and only of its kind in Taiwan. The facility produces mixtures between 1 to 20% germane in ultra-high purity hydrogen with extreme precision and state-of-the-art analysis. Germane-hydrogen mixtures are used by leading-edge semiconductor companies to make the most critical elements of computer chips, and precision of the blend is essential to making a working device.

Fluorine production at Guanyin

Another first in Taiwan is Linde LienHwa’s production of electronics-grade fluorine in Guanyin, a district of Taoyuan City. This special high-purity grade of fluorine is produced using generators from Linde developed for the electronics industry. The fluorine is typically blended with nitrogen or other inert gases, packaged in cylinders and used by electronics customers to remove particles and unwanted deposits from the interior surfaces of manufacturing tools.

Local partner. Global expertise.

“By investing locally in material processing, we are significantly reducing the supply chain risk and increasing material availability for our customers,” notes Alex Tong, President of Linde LienHwa. “These new facilities represent the latest phases in our commitment to expand ESG production in both Taiwan and China.”

Linde LienHwa maintains an extensive network of on-site gas production, bulk gases for electronics customers, ESGs, ultra-pure wet chemicals, chemical production and stocking facilities. Linde LienHwa offers a widest number of electronics materials. Its products enable leading-edge manufacturing in the semiconductor, solar, display and solid state lighting/LED industries.

Linde Electronics, its global partner, is the electronics materials and service business of The Linde Group, an industry leader in the industrial gas sector. Linde Gas operates in more than 100 countries, with world-class R&D centers, including its newest Electronics R&D Center in Taichung Harbor, Taiwan.

SEMICON China and the Global Semiconductor Forum

Linde LienHwa will be exhibiting at the SEMICON China tradeshow in Shanghai 14-16 March 2018. Its focus will be on the quality, expertise, service and technical leadership that Linde LienHwa and its global partner Linde Electronics bring to the semiconductor industry through such offerings as electronic specialty gases, bulk gases for electronics customers and on-site solutions like SPECTRA-N nitrogen plants.

Anshul Sarda, Vice President of Electronics Special Gases for the Linde Group, will be speaking at the SEMICON China Win-Win: Build China’s IC Ecosystem forum, for which LLH is a sponsor, on 15 March in the Pudong Ballroom of the Kerry Hotel. His talk entitled “Integrating domestic and international electronic material solutions” given at 16:00 will explain the challenges of materials supply in a dynamic landscape of established and newly-launched customers and material producers.

Dr. Anish Tolia, Vice President of Global Marketing for Linde Electronics, will be speaking at the Global Semiconductor Forum on 9 March at the Grand Kempinski Hotel in Shanghai. His workshop entitled “Supplying China: Combining local partnerships with global expertise by electronic material providers” will instruct on how material providers can adapt global experience in supply chains to the burgeoning opportunities and requirements of the China electronics market.

Phonons, which are packets of vibrational waves that propagate in solids, play a key role in condensed matter and are involved in various physical properties of materials. In nanotechnology, for example, they affect light emission and charge transport of nanodevices. As the main source of energy dissipation in solid-state systems, phonons are the ultimate bottleneck that limits the operation of functional nanomaterials.In an article recently published in Nature Communications, an INRS team of researchers led by Professor Luca Razzari and their European collaborators show that it is possible to modify the phonon response of a nanomaterial by exploiting the zero-point energy (i.e., the lowest possible – “vacuum” – energy in a quantum system) of a terahertz nano-cavity. The researchers were able to reshape the nanomaterial phonon response by generating new light-matter hybrid states. They did this by inserting some tens of semiconducting (specifically, cadmium sulfide) nanocrystals inside plasmonic nanocavities specifically designed to resonate at terahertz frequencies, i.e., in correspondence of the phonon modes of the nanocrystals.

“We have thus provided clear evidence of the creation of a new hybrid nanosystem with phonon properties that no longer belong to the original nanomaterial,” the authors said.

This discovery holds promise for applications in nanophotonics and nanoelectronics, opening up new possibilities for engineering the optical phonon response of functional nanomaterials. It also offers an innovative platform for the realization of a new generation of quantum transducers and terahertz light sources.

Solar cells have great potential as a source of clean electrical energy, but so far they have not been cheap, light, and flexible enough for widespread use. Now a team of researchers led by Tandon Associate Professor André D. Taylor of the Chemical and Biomolecular Engineering Department has found an innovative and promising way to improve solar cells and make their use in many applications more likely.

Most organic solar cells use fullerenes, spherical molecules of carbon. The problem, explains Taylor, is that fullerenes are expensive and don’t absorb enough light. Over the last 10 years he has made significant progress in improving organic solar cells, and he has recently focused on using non-fullerenes, which until now have been inefficient. However, he says, “the non-fullerenes are improving enough to give fullerenes a run for their money.”

Think of a solar cell as a sandwich, Taylor says. The “meat” or active layer – made of electron donors and acceptors – is in the middle, absorbing sunlight and transforming it into electricity (electrons and holes), while the “bread,” or outside layers, consist of electrodes that transport that electricity. His team’s goal was to have the cell absorb light across as large a spectrum as possible using a variety of materials, yet at the same time allow these materials to work together well. “My group works on key parts of the ‘sandwich,’ such as the electron and hole transporting layers of the ‘bread,’ while other groups may work only on the ‘meat’ or interlayer materials. The question is: How do you get them to play together? The right blend of these disparate materials is extremely difficult to achieve.”

Using a squaraine molecule in a new way – as a crystallizing agent – did the trick. “We added a small molecule that functions as an electron donor by itself and enhances the absorption of the active layer,” Taylor explains. “By adding this small molecule, it facilitates the orientation of the donor-acceptor polymer (called PBDB-T) with the non-fullerene acceptor, ITIC, in a favorable arrangement.”

This solar architecture also uses another design mechanism that the Taylor group pioneered known as a FRET-based solar cell. FRET, or Förster resonance energy transfer, is an energy transfer mechanism first observed in photosynthesis, by which plants use sunlight. Using a new polymer and non-fullerene blend with squaraine, the team converted more than 10 percent of solar energy into power. Just a few years ago this was considered too lofty a goal for single-junction polymer solar cells. “There are now newer polymer non-fullerene systems that can perform above 13 percent, so we view our contribution as a viable strategy for improving these systems,” Taylor says.

The organic solar cells developed by his team are flexible and could one day be used in applications supporting electric vehicles, wearable electronics, or backpacks to charge cell phones. Eventually, they could contribute significantly to the supply of electric power. “We expect that this crystallizing-agent method will attract attention from chemists and materials scientists affiliated with organic electronics,” says Yifan Zheng, Taylor’s former research student and lead author of the article about the work in the journal Materials Today.

Next for the research team? They are working on a type of solar cell called a perovskite as well as continuing to improve non-fullerene organic solar cells.

Each year, Solid State Technology turns to industry leaders to hear viewpoints on the technological and economic outlook for the upcoming year. Read through these expert opinions on what to expect in 2018.

Enabling the AI Era with Materials Engineering

Screen Shot 2018-03-05 at 12.24.49 PMPrabu Raja, Senior Vice President, Semiconductor Products Group, Applied Materials

A broad set of emerging market trends such as IoT, Big Data, Industry 4.0, VR/AR/MR, and autonomous vehicles is accelerating the transformative era of Artificial Intelligence (AI). AI, when employed in the cloud and in the edge, will usher in the age of “Smart Everything” from automobiles, to planes, factories, buildings, and our homes, bringing fundamental changes to the way we live

Semiconductors and semiconductor processing technol- ogies will play a key enabling role in the AI revolution. The increasing need for greater computing perfor- mance to handle Deep Learning/Machine Learning workloads requires new processor architectures beyond traditional CPUs, such as GPUs, FPGAs and TPUs, along with new packaging solutions that employ high-density DRAM for higher memory bandwidth and reduced latency. Edge AI computing will require processors that balance the performance and power equation given their dependency on battery life. The exploding demand for data storage is driving adoption of 3D NAND SSDs in cloud servers with the roadmap for continued storage density increase every year.

In 2018, we will see the volume ramp of 10nm/7nm devices in Logic/Foundry to address the higher performance needs. Interconnect and patterning areas present a myriad of challenges best addressed by new materials and materials engineering technologies. In Inter- connect, cobalt is being used as a copper replacement metal in the lower level wiring layers to address the ever growing resistance problem. The introduction of Cobalt constitutes the biggest material change in the back-end-of-line in the past 15 years. In addition to its role as the conductor metal, cobalt serves two other critical functions – as a metal capping film for electro- migration control and as a seed layer for enhancing gapfill inside the narrow vias and trenches.

In patterning, spacer-based double patterning and quad patterning approaches are enabling the continued shrink of device features. These schemes require advanced precision deposition and etch technologies for reduced variability and greater pattern fidelity. Besides conventional Etch, new selective materials removal technologies are being increasingly adopted for their unique capabilities to deliver damage- and residue-free extreme selective processing. New e-beam inspection and metrology capabilities are also needed to analyze the fine pitch patterned structures. Looking ahead to the 5nm and 3nm nodes, placement or layer-to-layer vertical alignment of features will become a major industry challenge that can be primarily solved through materials engineering and self-aligned structures. EUV lithography is on the horizon for industry adoption in 2019 and beyond, and we expect 20 percent of layers to make the migration to EUV while the remaining 80 percent will use spacer multi- patterning approaches. EUV patterning also requires new materials in hardmasks/underlayer films and new etch solutions for line-edge-roughness problems.

Packaging is a key enabler for AI performance and is poised for strong growth in the coming years. Stacking DRAM chips together in a 3D TSV scheme helps bring High Bandwidth Memory (HBM) to market; these chips are further packaged with the GPU in a 2.5D interposer design to bring compute and memory together for a big increase in performance.

In 2018, we expect DRAM chipmakers to continue their device scaling to the 1Xnm node for volume production. We also see adoption of higher perfor- mance logic technologies on the horizon for the periphery transistors to enable advanced perfor- mance at lower power.

3D NAND manufacturers continue to pursue multiple approaches for vertical scaling, including more pairs, multi-tiers or new schemes such as CMOS under array for increased storage density. The industry migration from 64 pairs to 96 pairs is expected in 2018. Etch (high aspect ratio), dielectric films (for gate stacks and hardmasks) along with integrated etch and CVD solutions (for high aspect ratio processing) will be critical enabling technologies.

In summary, we see incredible inflections in new processor architectures, next-generation devices, and packaging schemes to enable the AI era. New materials and materials engineering solutions are at the very heart of it and will play a critical role across all device segments.

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