Tag Archives: letter-wafer-tech

Since the 2003 discovery of the single-atom-thick carbon material known as graphene, there has been significant interest in other types of 2-D materials as well.

These materials could be stacked together like Lego bricks to form a range of devices with different functions, including operating as semiconductors. In this way, they could be used to create ultra-thin, flexible, transparent and wearable electronic devices.

However, separating a bulk crystal material into 2-D flakes for use in electronics has proven difficult to do on a commercial scale.

The existing process, in which individual flakes are split off from the bulk crystals by repeatedly stamping the crystals onto an adhesive tape, is unreliable and time-consuming, requiring many hours to harvest enough material and form a device.

Now researchers in the Department of Mechanical Engineering at MIT have developed a technique to harvest 2-inch diameter wafers of 2-D material within just a few minutes. They can then be stacked together to form an electronic device within an hour.

The technique, which they describe in a paper published in the journal Science, could open up the possibility of commercializing electronic devices based on a variety of 2-D materials, according to Jeehwan Kim, an associate professor in the Department of Mechanical Engineering, who led the research.

The paper’s co-first authors were Sanghoon Bae, who was involved in flexible device fabrication, and Jaewoo Shim, who worked on the stacking of the 2-D material monolayers. Both are postdocs in Kim’s group.

The paper’s co-authors also included students and postdocs from within Kim’s group, as well as collaborators at Georgia Tech, the University of Texas, Yonsei University in South Korea, and the University of Virginia. Sang-Hoon Bae, Jaewoo Shim, Wei Kong, and Doyoon Lee in Kim’s research group equally contributed to this work.

“We have shown that we can do monolayer-by-monolayer isolation of 2-D materials at the wafer scale,” Kim says. “Secondly, we have demonstrated a way to easily stack up these wafer-scale monolayers of 2-D material.”

The researchers first grew a thick stack of 2-D material on top of a sapphire wafer. They then applied a 600-nanometer-thick nickel film to the top of the stack.

Since 2-D materials adhere much more strongly to nickel than to sapphire, lifting off this film allowed the researchers to separate the entire stack from the wafer.

What’s more, the adhesion between the nickel and the individual layers of 2-D material is also greater than that between each of the layers themselves.

As a result, when a second nickel film was then added to the bottom of the stack, the researchers were able to peel off individual, single-atom thick monolayers of 2-D material.

That is because peeling off the first nickel film generates cracks in the material that propagate right through to the bottom of the stack, Kim says.

Once the first monolayer collected by the nickel film has been transferred to a substrate, the process can be repeated for each layer.

“We use very simple mechanics, and by using this controlled crack propagation concept we are able to isolate monolayer 2-D material at the wafer scale,” he says.

The universal technique can be used with a range of different 2-D materials, including hexagonal boron nitride, tungsten disulfide, and molybdenum disulfide.

In this way it can be used to produce different types of monolayer 2-D materials, such as semiconductors, metals, and insulators, which can then be stacked together to form the 2-D heterostructures needed for an electronic device.

“If you fabricate electronic and photonic devices using 2-D materials, the devices will be just a few monolayers thick,” Kim says. “They will be extremely flexible, and can be stamped on to anything,” he says.

The process is fast and low-cost, making it suitable for commercial operations, he adds.

The researchers have also demonstrated the technique by successfully fabricating arrays of field-effect transistors at the wafer scale, with a thickness of just a few atoms.

“The work has a lot of potential to bring 2-D materials and their heterostructures towards real-world applications,” says Philip Kim, a professor of physics at Harvard University, who was not involved in the research.

The researchers are now planning to apply the technique to develop a range of electronic devices, including a nonvolatile memory array and flexible devices that can be worn on the skin.

They are also interested in applying the technique to develop devices for use in the “internet of things,” Kim says.

“All you need to do is grow these thick 2-D materials, then isolate them in monolayers and stack them up. So it is extremely cheap — much cheaper than the existing semiconductor process. This means it will bring laboratory-level 2-D materials into manufacturing for commercialization,” Kim says.

“That makes it perfect for IoT networks, because if you were to use conventional semiconductors for the sensing systems it would be expensive.”

A paper published in Nature Communications by Sufei Shi, assistant professor of chemical and biological engineering at Rensselaer, increases our understanding of how light interacts with atomically thin semiconductors and creates unique excitonic complex particles, multiple electrons, and holes strongly bound together. These particles possess a new quantum degree of freedom, called “valley spin.” The “valley spin” is similar to the spin of electrons, which has been extensively used in information storage such as hard drives and is also a promising candidate for quantum computing.

Research on Light-Matter Interaction Could Lead to Improved Electronic and Optoelectronic Devices. Credit: Rensselaer Polytechnic Institute

The paper, titled “Revealing the biexciton and trion-exciton complexes in BN encapsulated WSe2,” was published in the Sept. 13, 2018, edition of Nature Communications. Results of this research could lead to novel applications in electronic and optoelectronic devices, such as solar energy harvesting, new types of lasers, and quantum sensing.

Shi’s research focuses on low dimensional quantum materials and their quantum effects, with a particular interest in materials with strong light-matter interactions. These materials include graphene, transitional metal dichacogenides (TMDs), such as tungsten diselenide (WSe2), and topological insulators.

TMDs represent a new class of atomically thin semiconductors with superior optical and optoelectronic properties. Optical excitation on the two-dimensional single-layer TMDs will generate a strongly bound electron-hole pair called an exciton, instead of freely moving electrons and holes as in traditional bulk semiconductors. This is due to the giant binding energy in monolayer TMDs, which is orders of magnitude larger than that of conventional semiconductors. As a result, the exciton can survive at room temperature and can thus be used for application of excitonic devices.

As the density of the exciton increases, more electrons and holes pair together, forming four-particle and even five-particle excitonic complexes. An understanding of the many-particle excitonic complexes not only gives rise to a fundamental understanding of the light-matter interaction in two dimensions, it also leads to novel applications, since the many-particle excitonic complexes maintain the “valley spin” properties better than the exciton. However, despite recent developments in the understanding of excitons and trions in TMDs, said Shi, an unambiguous measure of the biexciton-binding energy has remained elusive.

“Now, for the first time, we have revealed the true biexciton state, a unique four-particle complex responding to light,” said Shi. “We also revealed the nature of the charged biexciton, a five-particle complex.”

At Rensselaer, Shi’s team has developed a way to build an extremely clean sample to reveal this unique light-matter interaction. The device was built by stacking multiple atomically thin materials together, including graphene, boron nitride (BN), and WSe2, through van der Waals (vdW) interaction, representing the state-of-the-art fabrication technique of two-dimensional materials.

This work was performed in collaboration with the National High Magnetic Field Laboratory in Tallahasee, Florida, and researchers at the National Institute for Materials Science in Japan, as well as with Shengbai Zhang, the Kodosky Constellation Professor in the Department of Physics, Applied Physics, and Astronomy at Rensselaer, whose work played a critical role in developing a theoretical understanding of the biexciton.

The results of this research could potentially lead to robust many-particle optical physics, and illustrate possible novel applications based on 2D semiconductors, Shi said. Shi has received funding from the Air Force Office of Scientific Research. Zhang was supported by the Department of Energy, Office of Science.

The vast majority of computing devices today are made from silicon, the second most abundant element on Earth, after oxygen. Silicon can be found in various forms in rocks, clay, sand, and soil. And while it is not the best semiconducting material that exists on the planet, it is by far the most readily available. As such, silicon is the dominant material used in most electronic devices, including sensors, solar cells, and the integrated circuits within our computers and smartphones.

Now MIT engineers have developed a technique to fabricate ultrathin semiconducting films made from a host of exotic materials other than silicon. To demonstrate their technique, the researchers fabricated flexible films made from gallium arsenide, gallium nitride, and lithium fluoride — materials that exhibit better performance than silicon but until now have been prohibitively expensive to produce in functional devices.

MIT researchers have devised a way to grow single crystal GaN thin film on a GaN substrate through two-dimensional materials. The GaN thin film is then exfoliated by a flexible substrate, showing the rainbow color that comes from thin film interference. This technology will pave the way to flexible electronics and the reuse of the wafers. Credit: Wei Kong and Kuan Qiao

The new technique, researchers say, provides a cost-effective method to fabricate flexible electronics made from any combination of semiconducting elements, that could perform better than current silicon-based devices.

“We’ve opened up a way to make flexible electronics with so many different material systems, other than silicon,” says Jeehwan Kim, the Class of 1947 Career Development Associate Professor in the departments of Mechanical Engineering and Materials Science and Engineering. Kim envisions the technique can be used to manufacture low-cost, high-performance devices such as flexible solar cells, and wearable computers and sensors.

Details of the new technique are reported today in Nature Materials. In addition to Kim, the paper’s MIT co-authors include Wei Kong, Huashan Li, Kuan Qiao, Yunjo Kim, Kyusang Lee, Doyoon Lee, Tom Osadchy, Richard Molnar, Yang Yu, Sang-hoon Bae, Yang Shao-Horn, and Jeffrey Grossman, along with researchers from Sun Yat-Sen University, the University of Virginia, the University of Texas at Dallas, the U.S. Naval Research Laboratory, Ohio State University, and Georgia Tech.

Now you see it, now you don’t

In 2017, Kim and his colleagues devised a method to produce “copies” of expensive semiconducting materials using graphene — an atomically thin sheet of carbon atoms arranged in a hexagonal, chicken-wire pattern. They found that when they stacked graphene on top of a pure, expensive wafer of semiconducting material such as gallium arsenide, then flowed atoms of gallium and arsenide over the stack, the atoms appeared to interact in some way with the underlying atomic layer, as if the intermediate graphene were invisible or transparent. As a result, the atoms assembled into the precise, single-crystalline pattern of the underlying semiconducting wafer, forming an exact copy that could then easily be peeled away from the graphene layer.

The technique, which they call “remote epitaxy,” provided an affordable way to fabricate multiple films of gallium arsenide, using just one expensive underlying wafer.

Soon after they reported their first results, the team wondered whether their technique could be used to copy other semiconducting materials. They tried applying remote epitaxy to silicon, and also germanium — two inexpensive semiconductors — but found that when they flowed these atoms over graphene they failed to interact with their respective underlying layers. It was as if graphene, previously transparent, became suddenly opaque, preventing atoms of silicon and germanium from “seeing” the atoms on the other side.

As it happens, silicon and germanium are two elements that exist within the same group of the periodic table of elements. Specifically, the two elements belong in group four, a class of materials that are ionically neutral, meaning they have no polarity.

“This gave us a hint,” says Kim.

Perhaps, the team reasoned, atoms can only interact with each other through graphene if they have some ionic charge. For instance, in the case of gallium arsenide, gallium has a negative charge at the interface, compared with arsenic’s positive charge. This charge difference, or polarity, may have helped the atoms to interact through graphene as if it were transparent, and to copy the underlying atomic pattern.

“We found that the interaction through graphene is determined by the polarity of the atoms. For the strongest ionically bonded materials, they interact even through three layers of graphene,” Kim says. “It’s similar to the way two magnets can attract, even through a thin sheet of paper.”

Opposites attract

The researchers tested their hypothesis by using remote epitaxy to copy semiconducting materials with various degrees of polarity, from neutral silicon and germanium, to slightly polarized gallium arsenide, and finally, highly polarized lithium fluoride — a better, more expensive semiconductor than silicon.

They found that the greater the degree of polarity, the stronger the atomic interaction, even, in some cases, through multiple sheets of graphene. Each film they were able to produce was flexible and merely tens to hundreds of nanometers thick.

The material through which the atoms interact also matters, the team found. In addition to graphene, they experimented with an intermediate layer of hexagonal boron nitride (hBN), a material that resembles graphene’s atomic pattern and has a similar Teflon-like quality, enabling overlying materials to easily peel off once they are copied.

However, hBN is made of oppositely charged boron and nitrogen atoms, which generate a polarity within the material itself. In their experiments, the researchers found that any atoms flowing over hBN, even if they were highly polarized themselves, were unable to interact with their underlying wafers completely, suggesting that the polarity of both the atoms of interest and the intermediate material determines whether the atoms will interact and form a copy of the original semiconducting wafer.

“Now we really understand there are rules of atomic interaction through graphene,” Kim says.

With this new understanding, he says, researchers can now simply look at the periodic table and pick two elements of opposite charge. Once they acquire or fabricate a main wafer made from the same elements, they can then apply the team’s remote epitaxy techniques to fabricate multiple, exact copies of the original wafer.

“People have mostly used silicon wafers because they’re cheap,” Kim says. “Now our method opens up a way to use higher-performing, nonsilicon materials. You can just purchase one expensive wafer and copy it over and over again, and keep reusing the wafer. And now the material library for this technique is totally expanded.”

Kim envisions that remote epitaxy can now be used to fabricate ultrathin, flexible films from a wide variety of previously exotic, semiconducting materials — as long as the materials are made from atoms with a degree of polarity. Such ultrathin films could potentially be stacked, one on top of the other, to produce tiny, flexible, multifunctional devices, such as wearable sensors, flexible solar cells, and even, in the distant future, “cellphones that attach to your skin.”

“In smart cities, where we might want to put small computers everywhere, we would need low power, highly sensitive computing and sensing devices, made from better materials,” Kim says. “This [study] unlocks the pathway to those devices.”

Engineers at The Australian National University (ANU) have invented a semiconductor with organic and inorganic materials that can convert electricity into light very efficiently, and it is thin and flexible enough to help make devices such as mobile phones bendable.

The invention also opens the door to a new generation of high-performance electronic devices made with organic materials that will be biodegradable or that can be easily recycled, promising to help substantially reduce e-waste.

The huge volumes of e-waste generated by discarded electronic devices around the world is causing irreversible damage to the environment. Australia produces 200,000 tonnes of e-waste every year – only four per cent of this waste is recycled.

The organic component has the thickness of just one atom – made from just carbon and hydrogen – and forms part of the semiconductor that the ANU team developed. The inorganic component has the thickness of around two atoms. The hybrid structure can convert electricity into light efficiently for displays on mobile phones, televisions and other electronic devices.

Lead senior researcher Associate Professor Larry Lu said the invention was a major breakthrough in the field.

“For the first time, we have developed an ultra-thin electronics component with excellent semiconducting properties that is an organic-inorganic hybrid structure and thin and flexible enough for future technologies, such as bendable mobile phones and display screens,” said Associate Professor Lu from the ANU Research School of Engineering.

PhD researcher Ankur Sharma, who recently won the ANU 3-Minute Thesis competition, said experiments demonstrated the performance of their semiconductor would be much more efficient than conventional semiconductors made with inorganic materials such as silicon.

“We have the potential with this semiconductor to make mobile phones as powerful as today’s supercomputers,” said Mr Sharma from the ANU Research School of Engineering.

“The light emission from our semiconducting structure is very sharp, so it can be used for high-resolution displays and, since the materials are ultra-thin, they have the flexibility to be made into bendable screens and mobile phones in the near future.”

The team grew the organic semiconductor component molecule by molecule, in a similar way to 3D printing. The process is called chemical vapour deposition.

“We characterised the opto-electronic and electrical properties of our invention to confirm the tremendous potential of it to be used as a future semiconductor component,” Associate Professor Lu said.

“We are working on growing our semiconductor component on a large scale, so it can be commercialised in collaboration with prospective industry partners.”

The American Institute for Manufacturing Integrated Photonics (AIM Photonics) and Analog Photonics (AP) today announced the release of the AP SUNY Process Design Kit v2.5a (APSUNY_PDKv2.5a). In this latest release, Analog Photonics (AP) expanded the comprehensive set of Silicon Photonics Integrated Circuit (PIC) component libraries within SUNY Poly’s process capabilities to address the needs for O+C+L band applications. Combined with Multi-Project Wafer (MPW) runs, this updated PDK will give AIM Photonics’ members access to world-class silicon photonics components for the development of optical transceivers or systems used in all levels within data centers and high-performance computers.

The Silicon Photonics PDK includes design guide, design rule check deck, technology files, active and passive component documentation, abstracts, schematics, and compact models for the development of PICs.

The key features of the APSUNY_PDKv2.5a are:

  • O Band modulation, detection and coupling support.
  • C+L Band modulation, detection, filtering, switching, monitoring and coupling support.
  • Single-level and Multi-level modulation format support at 50Gbps, namely NRZ and PAM-4.
  •    Continued multi-vendor Electronics-Photonics-Design-Automation (EPDA) support with integrated EPDA PDK flow for hierarchical design and system-level simulation.

“We are thrilled to continue to expand the offerings of our state-of-the-art PDK to meet the needs of our more than 100 signed partners and other interested collaborators who can gain access to our unique capabilities. This also dovetails perfectly with our effort to efficiently process our Multi-Project Wafers (MPW’s) in the fab, with processing time decreasing from 130 days in 2016 to fewer than 90 days as we simultaneously add additional mask levels and functionality and continue to achieve world-class quality,” said Dr. Michael Liehr, AIM Photonics CEO and SUNY Poly Executive Vice President for Innovation and Technology.

The combined APSUNY_PDKv2.5a and MPW offering provides unmatched access to PIC systems for companies who desire a reduction in the time to market, product development risk, and investment.  By incorporating the design, verification, and process development within the PDK, interested organizations can rapidly modify their designs while reducing cost.

“The IEEE standards and multi-source-agreements (MSAs) for communications compatibility are key for our PDK component library. These standards require optical components to operate at O band (1260nm-to-1360nm), C band (1530nm-to-1565nm) and L band (1565nm-to-1625nm). With the PDKv2.5a component library, we are enabling components that cover all these bands in a single fabrication flow, and we look forward to the advancement of this library while innovating to meet industry needs,” said Director of PDK Development at Analog Photonics, Dr. Erman Timurdogan.

In the near future, the PDK will be empowered by laser and CMOS integration with an interposer, a capability that will be made possible at AIM Photonics’ Test, Assembly, and Packaging (TAP) facility, located in Rochester, NY. Additional releases of the AP SUNY Process Design Kit are planned over the next several years each quarter, with improved statistical models, optical components, and PIC systems.

“We are seeing customers take advantage of our repeatedly characterized and proven devices in the APSUNY PDK. With this valuable resource, which is validated on our 300mm advanced  semiconductor toolset, customers are able to rapidly address global standards, shrink their design sizes, and most importantly, reduce their time to market,” said AIM Photonics Design Center Offering Director Barton Bergman.

AIM Photonics is leveraging SUNY Poly’s state-of-the-art facilities for three total full-build/passive MPW runs that incorporate the PDK updates, with an interposer MPW run anticipated later in 2018. To ensure space for all interested parties, AIM Photonics is accepting reservations for these MPW runs. Those interested in participating in any of the AIM Photonics 2018 MPW silicon photonics runs should contact Chandra Cotter at [email protected] in order to guarantee a spot on these exciting new silicon photonics offerings. Interested parties can also sign up for the 2018 runs by visiting the initiative’s website at the following link: http://www.aimphotonics.com/mpw-schedule/

PDK and MPW fab access is solely available through the AIM Photonics MPW aggregator, MOSIS. Please contact MOSIS for access to the most current PDK version release at the following link: www.mosis.com/vendors/view/AIM.

A team of semiconductor researchers based in France has used a boron nitride separation layer to grow indium gallium nitride (InGaN) solar cells that were then lifted off their original sapphire substrate and placed onto a glass substrate.

Ph.D. Student Taha Ayari measures the photovoltaic performance of the InGaN solar cells with a solar simulator. (Credit: Ougazzaden laboratory)

By combining the InGaN cells with photovoltaic (PV) cells made from materials such as silicon or gallium arsenide, the new lift-off technique could facilitate fabrication of higher efficiency hybrid PV devices able to capture a broader spectrum of light. Such hybrid structures could theoretically boost solar cell efficiency as high as 30 percent for an InGaN/Si tandem device.

The technique is the third major application for the hexagonal boron nitride lift-off technique, which was developed by a team of researchers from the Georgia Institute of Technology, the French National Center for Scientific Research (CNRS), and Institut Lafayette in Metz, France. Earlier applications targeted sensors and light-emitting diodes (LEDs).

“By putting these structures together with photovoltaic cells made of silicon or a III-V material, we can cover the visible spectrum with the silicon and utilize the blue and UV light with indium gallium nitride to gather light more efficiently,” said Abdallah Ougazzaden, director of Georgia Tech Lorraine in Metz, France and a professor in Georgia Tech’s School of Electrical and Computer Engineering (ECE). “The boron nitride layer doesn’t impact the quality of the indium gallium nitride grown on it, and we were able to lift off the InGaN solar cells without cracking them.”

The research was published August 15 in the journal ACS Photonics. It was supported by the French National Research Agency under the GANEX Laboratory of Excellence project and the French PIA project “Lorraine Université d’Excellence.”

The technique could lead to production of solar cells with improved efficiency and lower cost for a broad range of terrestrial and space applications. “This demonstration of transferred InGaN-based solar cells on foreign substrates while increasing performance represents a major advance toward lightweight, low cost, and high efficiency photovoltaic applications,” the researchers wrote in their paper.

“Using this technique, we can process InGaN solar cells and put a dielectric layer on the bottom that will collect only the short wavelengths,” Ougazzaden explained. “The longer wavelengths can pass through it into the bottom cell. By using this approach we can optimize each surface separately.”

The researchers began the process by growing monolayers of boron nitride on two-inch sapphire wafers using an MOVPE process at approximately 1,300 degrees Celsius. The boron nitride surface coating is only a few nanometers thick, and produces crystalline structures that have strong planar surface connections, but weak vertical connections.

The InGaN attaches to the boron nitride with weak van der Waals forces, allowing the solar cells to be grown across the wafer and removed without damage. So far, the cells have been removed from the sapphire manually, but Ougazzaden believes the transfer process could be automated to drive down the cost of the hybrid cells. “We can certainly do this on a large scale,” he said.

The InGaN structures are then placed onto the glass substrate with a backside reflector and enhanced performance is obtained. Beyond demonstrating placement atop an existing PV structure, the researchers hope to increase the amount of indium in their lift-off devices to boost light absorption and increase the number of quantum wells from five to 40 or 50.

“We have now demonstrated all the building blocks, but now we need to grow a real structure with more quantum wells,” Ougazzaden said. “We are just at the beginning of this new technology application, but it is very exciting.”

In addition to Ougazzaden, the research team includes Georgia Tech Ph.D. students Taha Ayari, Matthew Jordan, Xin Li and Saiful Alam; Chris Bishop and Simon Gautier from Institut Lafayette; Suresh Sundaram, a researcher at Georgia Tech Lorraine; Walid El Huni and Yacine Halfaya from CNRS; Paul Voss, an associate professor in the Georgia Tech School of ECE; and Jean Paul Salvestrini, a professor at Georgia Tech Lorraine and adjunct professor in the Georgia Tech School of ECE.

CITATION: Taha Ayari, et al., “Heterogeneous Integration of Thin-Film InGaN-Based Solar Cells on Foreign Substrates with Enhanced Performance,” (ACS Photonics 2018) https://pubs.acs.org/doi/abs/10.1021/acsphotonics.8b00663

ANSYS (NASDAQ: ANSS) announced TSMC certified ANSYS solutions for the 7 nanometer FinFET Plus (N7+) process node with extreme ultraviolet lithography (EUV) technology and validated the reference flow for the latest Integrated Fan-Out with Memory on Substrate (InFO_MS) advanced packaging technology. The certifications and validations are vital for fabless semiconductor companies that require their simulation tools to pass rigorous testing and validation for new process nodes and packaging technologies.

ANSYS® RedHawk™ and ANSYS® Totem™ are certified for TSMC N7+ process technology that provides EUV-enabled features. Certification for N7+ includes extraction, power integrity and reliability, signal electromigration (EM) and thermal reliability analysis.

Industry-leading TSMC InFO advanced packaging technology is extended to integrate memory subsystem with logic die. TSMC and ANSYS enhanced the existing InFO design flow to support the new InFO_MS packaging technology, and validated the reference flow using ANSYS SIwave-CPA, ANSYS® RedHawk-CPA™, ANSYS® RedHawk-CTA™, ANSYS® CMA™ and ANSYS® CSM™ with the corresponding chip models. The InFO_MS reference flow includes die and package co-simulation and co-analysis for extraction, power and signal integrity analysis, power and signal electromigration analysis and thermal analysis.

“TSMC and ANSYS’ latest N7+ certification and InFO_MS enablement empowers customers to address growing performance, reliability and power demands for their next generation of chips and packages,” said Suk Lee, Senior Director of Design Infrastructure Marketing Division at TSMC.

“The number of smart, connected electronic devices continues to grow and manufacturers must keep pace to design power efficient, high-performing and reliable products at a lower cost and with a smaller footprint,” said John Lee, General Manager at ANSYS. “ANSYS semiconductor solutions address complex multi-physics challenges such as power, thermal, reliability and impact of process variation on product performance. ANSYS’ comprehensive Chip Package System solutions for chip aware system and system aware chip signoff help mutual customers accelerate design convergence with greater confidence.”

Transition metal dichalcogenides (TMDCs) possess optical properties that could be used to make computers run a million times faster and store information a million times more energy-efficiently, according to a study led by Georgia State University.

This is Dr. Mark Stockman, director of the Center for Nano-Optics and a Regents’ Professor in the Department of Physics and Astronomy at Georgia State University. Credit: Georgia State University

Computers operate on the time scale of a fraction of a nanosecond, but the researchers suggest constructing computers on the basis of TMDCs, atomically thin semiconductors, could make them run on the femtosecond time scale, a million times faster. This would also increase computer memory speed by a millionfold.

“There is nothing faster, except light,” said Dr. Mark Stockman, lead author of the study and director of the Center for Nano-Optics and a Regents’ Professor in the Department of Physics and Astronomy at Georgia State. “The only way to build much faster computers is to use optics, not electronics. Electronics, which is used by current computers, can’t go any faster, which is why engineers have been increasing the number of processors. We propose the TMDCs to make computers a million times more efficient. This is a fundamentally different approach to information technology.”

The researchers propose a theory that TMDCs have the potential to process information within a couple of femtoseconds. A femtosecond is one millionth of one billionth of a second. A TMDC has a hexagonal lattice structure that consists of a layer of transition metal atoms sandwiched between two layers of chalcogen atoms. This hexagonal structure aids in the computer processor speed and also enables more efficient information storage. The findings are published in the journal Physical Review B in the prestigious Rapid Communications section.

The TMDCs have a number of positive qualities, including being stable, non-toxic, thin, light and mechanically strong. Examples include molybdenum disulfide (MOS2) and tungsten diselenide (WSe2). TMDCs are part of a large family called 2D materials, which is named after their extraordinary thinness of one or a few atoms. In this study, the researchers also established the optical properties of the TMDCs, which allow them to be ultrafast.

In the hexagonal lattice structure of TMDCs, electrons rotate in circles in different states, with some electrons spinning to the left and others turning to the right depending on their position on the hexagon. This motion causes a new effect that is called topological resonance. Such an effect allows one to read, write or process a bit of information in only a few femtoseconds.

There are numerous examples of TMDCs, so in the future, the researchers would like to determine the best one to use for computer technology.

WIN Semiconductors Corp. (TPEx:3105), the world’’s largest pure-play compound semiconductor foundry, is driving the development and deployment of 5G user equipment and network infrastructure in the sub-6GHz and mmWave frequency bands. Front-end semiconductor technology has a significant influence on battery life and total power consumption of mobile devices and active antenna arrays employed in mmWave network infrastructure. GaAs is the technology of choice for front-ends used in LTE mobile devices and satisfies stringent linearity and efficiency requirements providing high quality of service while maximizing battery life. 5G user equipment and MIMO access points will impose more difficult linearity/power consumption specifications than LTE, and WIN’s portfolio of high performance GaAs technologies is well positioned to meet these new requirements and provide best value front-end solutions.

The fundamental performance advantages of GaAs make it the dominant semiconductor technology for cellular and Wi-Fi RF front-ends used in mobile devices. The technical and manufacturing demands of these large and highly competitive markets have driven significant advances in GaAs technology, and now offers best-in-class front-end performance in all 5G bands and multifunction integration necessary for complex mmWave active antenna systems. WIN’s advanced GaAs platforms integrate best-in-class transmit and receive amplifier technologies with high performance switch, logic and ESD protection functions to realize compact high performance, single chip, front-ends for mobile devices and MIMO access points operating in the sub-6GHz and mmWave 5G bands.

WIN Semiconductors’ innovative GaAs technologies, such as PIH1-10, can now monolithically integrate a high efficiency Tx power amplifier (PA), ultra-low Fmin Rx low-noise amplifier (LNA) and low loss PIN switch in a single chip mmWave front-end. In addition, this highly integrated GaAs technology provides optional linear Schottky diodes for power detectors and mixers, low capacitance PIN diodes for ESD protection and optimized E/D transistors for logic interfaces. This suite of capabilities comes in a humidity-rugged back-end, available with a copper redistribution layer and copper pillar bumps to reduce die size and allow flip chip assembly, enabling GaAs front-ends to fit within 28 and 39 GHz antenna lattice spacing.

Researchers at the University of Illinois at Chicago have discovered a route to alter boron nitride, a layered 2D material, so that it can bind to other materials, like those found in electronics, biosensors and airplanes, for example. Being able to better-incorporate boron nitride into these components could help dramatically improve their performance.

Treatment with a superacid causes boron nitride layers to separate and become positively charged, allowing for it to interface with other nanoparticles, like gold. Credit: Berry, et al

The scientific community has long been interested in boron nitride because of its unique properties –it is strong, ultrathin, transparent, insulating, lightweight and thermally conductive — which, in theory, makes it a perfect material for use by engineers in a wide variety of applications. However, boron nitride’s natural resistance to chemicals and lack of surface-level molecular binding sites have made it difficult for the material to interface with other materials used in these applications.

UIC’s Vikas Berry and his colleagues are the first to report that treatment with a superacid causes boron nitride layers to separate into atomically thick sheets, while creating binding sites on the surface of these sheets that provide opportunities to interface with nanoparticles, molecules and other 2D nanomaterials, like graphene. This includes nanotechnologies that use boron nitride to insulate nano-circuits.

Their findings are published in ACS Nano, a journal of the American Chemical Society.

“Boron nitride is like a stack of highly sticky papers in a ream, and by treating this ream with chlorosulfonic acid, we introduced positive charges on the boron nitride layers that caused the sheets to repel each other and separate,” said Berry, associate professor and head of chemical engineering at the UIC College of Engineering and corresponding author on the paper.

Berry said that “like magnets of the same polarity,” these positively charged boron nitride sheets repel one another.

“We showed that the positive charges on the surfaces of the separated boron nitride sheets make it more chemically active,” Berry said. “The protonation — the addition of positive charges to atoms — of internal and edge nitrogen atoms creates a scaffold to which other materials can bind.”

Berry said that the opportunities for boron nitride to improve composite materials in next-generation applications are vast.

“Boron and nitrogen are on the left and the right of carbon on the periodic table and therefore, boron-nitride is isostructural and isoelectronic to carbon-based graphene, which is considered a ‘wonder material,'” Berry said. This means these two materials are similar in their atomic crystal structure (isostructural) and their overall electron density (isoelectric), he said.

“We can potentially use this material in all kinds of electronics, like optoelectronic and piezoelectric devices, and in many other applications, from solar-cell passivation layers, which function as filters to absorb only certain types of light, to medical diagnostic devices,” Berry said.