Category Archives: Process Materials

Graphene’s unusual electronic structure enables this extraordinary material to break many records of strength, electricity and heat conduction. Physicists at the Center for Theoretical Physics of Complex Systems (PCS), in collaboration with the Research Institute for Standards and Science (KRISS), used a model to explain the electronic structure of graphene measured by a new spectroscopic platform. These techniques, published in the journal Nano Letters, could promote future research on stable and accurate quantum measurements for new 2D electronics.

(Left) Nanodevice structure to measure graphene's electronic properties. Graphene is sandwiched between two hBTN layers and the two electrodes (graphite and silicon). (Right) Conductance of single layer graphene at different voltages, showing the dip at around 350 mV. Credit: IBS

(Left) Nanodevice structure to measure graphene’s electronic properties. Graphene is sandwiched between two hBTN layers and the two electrodes (graphite and silicon). (Right) Conductance of single layer graphene at different voltages, showing the dip at around 350 mV. Credit: IBS

Recently, interest in 2D materials has risen exponentially in both academia and industry. These materials are made by extremely thin sheets, which have different physical properties compared to conventional 3D materials. Moreover, when different 2D sheets are stacked on the top of each other, new electrical, optical, and thermal properties emerge. One of the most promising and much studied 2D materials is graphene: a single sheet of carbon atoms. In order to study the electronic properties of both single and double layer graphene, the team constructed a nanodevice with graphene sandwiched between two layers of an insulating material known as hexagonal boron nitride (hBN). On top of this device they placed graphite as electrode. Graphite is essentially made up of hundreds of thousands of layers of graphene. The bottom layer consisted of one layer of silicon and one of silica.

By tuning the voltages applied via the graphite and the silicon, the scientists measured the changes in the conductance of graphene, which reflects its electronic properties. The electrons of graphene have a particular energy structure, represented by the so-called Dirac cone, which is actually made by two cones that look like a sandglass, with only an infinitesimally small point in between (Dirac Point). You can think of it as an unusual cocktail glass shaped liked a sandglass, where the drink plays the function of the graphene’s electrons. At temperature close to zero Kelvin (-273 degrees Celsius), the electrons pack into the lowest available energy states and fill up the double-cone glass from the bottom up, until a certain energy level, called Fermi level, is reached. Applying a negative voltage via the silicon and graphite layers is equivalent to drinking from the glass, while a positive voltage has the same effect as adding liquid to the glass. Through modulating the applied voltages, the scientists could deduce the electronic structure of graphene by following the Fermi level. In particular, they noticed that when the voltage applied to graphite is around 350 milliVolts, there is a dip in the conductance measurement, by which the Fermi level matches with the Dirac point. This is a well-known property of single layer graphene.

Finally, the electrical properties change again when a magnetic field is applied to the single layer graphene. In this case, instead of a sandglass cocktail glass, the energy of the electrons is more similar to a ladder where electrons of increasing energies can be found on the higher rungs. Gaps between the ladder rungs are devoid of electrons, while the steps fill with electrons from the bottom upwards. Interestingly, the data obtained by the scientists of KRISS was successfully reproduced by the theoretical physicists at IBS showed more than 40 rungs, technically known as Landau levels. Each level clearly distinguished because of the low background noise.

Indeed, the scientists could also match the theoretical and experimental data relative to the electronic properties of bilayer graphene. Double layer graphene, has a different conductance behavior with a broader dip, better known as an energy gap. In the presence of an electric field perpendicular to it, this energy gap makes double layer graphene more similar to the current tunable semiconductors. “We used an intuitive model to reproduce the experimental measurement and we gave a theoretical explanation to why these energy configurations form with single and double layer graphene,” explains MYOUNG Nojoon, first co-author of this study. “This model provides a gauge between voltages and energy in spectroscopic measurements, and we believe that this is a fundamental step to study graphene’s electronic properties further.”

Researchers in Singapore and China have collaborated to develop a self-powered photodetector that can be used in a wide range of applications such as chemical analysis, communications, astronomical investigations and much more.

Typically, photodetectors require an external voltage to provide the driving force for separating and measuring photo-generated electrons that comprise the detection. To eliminate this need, the research team led by Junling Wang and Le Wang at Nanyang Technological University in Singapore developed a novel, sensitive and stable photodetector based on a semiconducting junction called a GdNiO3/Nb-doped SrTiO3 (GNO/NSTO) p-n heterojunction. An inherent electric field at the GNO/NSTO interface provides the driving force for efficient separation of photo-generated carriers, eliminating the need for an external power source.

In addition to its self-powered feature, Wang and his team report tuning the material properties to achieve broad sensitivity. For these compounds, most research work thus far has focused on studying the origin of metal-insulator transition, but this team took a different approach.

The properties of perovskite nickelates, the category of solar cell materials in which this structure falls, are very sensitive to oxygen content. This sensitivity enables fine tuning of the final electronic structures by varying the oxygen environment during film deposition (constructing the heterojunction).

“Our work is novel and confirms that nickelates films have tunable band gaps with changing of the oxygen vacancy concentration, which makes them ideal as light absorbing materials in optoelectronic devices,” said Wang. “Using the self-powered photodetector we designed, we study its photo responsivity using light sources with different wavelengths, with significant photo-response appearing when the light wavelength decreases to 650 nanometers.” Wang said.

A significant challenge in developing this photodetector was determining the correct band structure, or energy structure available to electrons, of the 10 nanometer thick GNO films.

“To obtain the band structures, we used both spectroscopic ellipsometry measurements and ultraviolet photoelectron spectroscopy (UPS) measurements,” said Wang. Using the deduced values for the optical bandgap from these measurements, along with known limits and values for GNO films, they could plot the energy levels and work functions of the various components in the devices.

The team hopes to explore more materials with similar features. “One of the remarkable features of nickelates […] is the dependence of their physical properties on the chosen rare earth element,” said Wang. “Thus far, we have only studied GdNiO3 film, but besides that we can also investigate other “R”-NiO3 films where “R” can be Nd (neodymium), Sm (animony), Er (erbium) and Lu (lutetium) and study their potential applications in the photodetector.”

The team also plans to improve the performance of the photodetector by adding an insulating SrTiO3 (STO) layer sandwiched between the GdNiO3 film and NSTO substrate.

This novel work has great potential for applications using optoelectronic devices. “We believe that this paper will stimulate further studies and enlarge the potential applications of systems based on nickelates,” said Wang.

University of Pennsylvania researchers are now among the first to produce a single, three-atom-thick layer of a unique two-dimensional material called tungsten ditelluride. Their findings have been published in 2-D Materials.

Unlike other two-dimensional materials, scientists believe tungsten ditelluride has what are called topological electronic states. This means that it can have many different properties not just one.

When one thinks about two-dimensional materials, graphene is probably the first that comes to mind.

The tightly packed, atomically thin sheet of carbon first produced in 2004 has inspired countless avenues in research that could revolutionize everything from technology to drinking water.

One of the most important properties of graphene is that it’s what’s called a zero bandgap semiconductor in that it can behave as both a metal and a semiconductor.

But there are tons of other properties that 2-D materials can have. Some can insulate, others can emit light and still others can be spintronic, meaning they have magnetic properties.

“Graphene is just graphene,” said A.T. Charlie Johnson, a physics professor in Penn’s School of Arts & Sciences. “It just does what graphene does. If you want to have functioning systems that are based on 2-D materials, then you want 2-D materials that have all of the different physical properties that we know about.”

The ability of 2-D materials to have topological electronic states is a phenomenon that was pioneered by Charles Kane, the Christopher H. Browne Distinguished Professor of Physics at Penn.

In this new research, Johnson, physics professor James Kikkawa and graduate students Carl Naylor and William Parkin were able to produce and measure the properties of a single layer of tungsten ditelluride.

“Because tungsten ditelluride is three atoms thick, the atoms can be arranged in different ways,” Johnson said. “These three atoms can take on slightly different configurations with respect to each other. One configuration is predicted to give these topological properties.”

Marija Drndi?, the Fay R. and Eugene L. Langberg Professor of Physics; Andrew Rappe, the Blanchard Professor of Chemistry and a professor of materials science and engineering in the School of Engineering and Applied Science, and Robert Carpick, the John Henry Towne Professor and chair of the Department of Mechanical Engineering and Applied Mechanics, also contributed to the research.

“It’s very much a Penn product,” Johnson said. “We’re collaborating with multiple other faculty members who investigate the material in their own ways, and we brought it all together to put a paper out there. Everybody comes along for the ride.”

The researchers were able to grow this material using a process called chemical vapor deposition. Using a hot-tube furnace, they heated a chip containing tungsten to the right temperature and then introduced a vapor containing tellurium.

“Through good fortune and finding exactly the right conditions, these elements will chemically react and combine to form a monolayer, or three-atom-thick regions of this material,” Johnson said.

Although this material degrades extremely rapidly in air, Naylor, the paper’s first author, figured out ways to protect the material so that it could be studied before it was destroyed.

One thing the researchers found is that the material grows in little rectangular crystallites, rather than the triangles that other materials grow in.

“This reflects the rectangular symmetry in the material,” Johnson said. “They have a different structure so they tend to grow in different shapes.”

Although the research is still in its beginning stages and the researchers haven’t yet been able to produce a continuous film, they hope to conduct experiments to show that it has the topological electronic properties that are predicted.

One property of these topological systems is that any current traveling through the material would only be carried on the edges, and no current would travel through the center of the material. If researchers were able to produce single-layer-thick materials with this property, they may be able to route an electrical signal to go off into different locations.

The ability of this material to have multiple properties could also have implications in quantum computing, which taps into the power of atoms and subatomic phenomena to perform calculations significantly faster than current computers. These 2-D materials might allow for an intrinsically error-tolerant form of quantum computing called topologically protected quantum computing, which requires both semiconducting and superconducting materials.

“With these 2-D materials, you want to realize as many physical properties as possible,” Johnson said. “Topological electronic states are interesting and they’re new and so a lot of people have been trying to realize them in a 2-D material. We created the material where these are predicted to occur, so in that sense we’ve moved towards this very big goal in the field.”

Intel Corporation yesterday announced plans to invest more than $7 billion to complete Fab 42, a project Intel had previously started and then left vacant. The high-volume factory is in Chandler, Ariz., and is targeted to use the 7 nanometer (nm) manufacturing process. The announcement was made by U.S. President Donald Trump and Intel CEO Brian Krzanich at the White House.

Intel Corporation on Tuesday, Feb. 8, 2017, announced plans to invest more than $7 billion to complete Fab 42. On completion, Fab 42 in Chandler, Ariz., is expected to be the most advanced semiconductor factory in the world. (Credit: Intel Corporation)

Intel Corporation on Tuesday, Feb. 8, 2017, announced plans to invest more than $7 billion to complete Fab 42. On completion, Fab 42 in Chandler, Ariz., is expected to be the most advanced semiconductor factory in the world. (Credit: Intel Corporation)

According to Intel’s official press release, the completion of Fab 42 in 3 to 4 years will directly create approximately 3,000 high-tech, high-wage Intel jobs for process engineers, equipment technicians, and facilities-support engineers and technicians who will work at the site. Combined with the indirect impact on businesses that will help support the factory’s operations, Fab 42 is expected to create more than 10,000 total long-term jobs in Arizona.

Mr. Trump said of the announcement: “The people of Arizona will be very happy. It’s a lot of jobs.”

There will be no incentives from the federal government for the Intel project, the White House said.

Context for the investment was outlined in an e-mail from Intel’s CEO to employees.

“Intel’s business continues to grow and investment in manufacturing capacity and R&D ensures that the pace of Moore’s law continues to march on, fueling technology innovations the world loves and depends on,” said Krzanich. “This factory will help the U.S. maintain its position as the global leader in the semiconductor industry.”

“Intel is a global manufacturing and technology company, yet we think of ourselves as a leading American innovation enterprise,” Krzanich added. “America has a unique combination of talent, a vibrant business environment and access to global markets, which has enabled U.S. companies like Intel to foster economic growth and innovation. Our factories support jobs — high-wage, high-tech manufacturing jobs that are the economic engines of the states where they are located.”

Intel is America’s largest high-technology capital expenditure investor ($5.1 billion in the U.S. 2015) and its third largest investor in global R&D ($12.1 billion in 20151). The majority of Intel’s manufacturing and R&D is in the United States. As a result, Intel employs more than 50,000 people in the United States, while directly supporting almost half a million other U.S. jobs across a range of industries, including semiconductor tooling, software, logistics, channels, OEMs and other manufacturers that incorporate our products into theirs.

The 7nm semiconductor manufacturing process targeted for Fab 42 will be the most advanced semiconductor process technology used in the world and represents the future of Moore’s Law. In 1968, Intel co-founder Gordon Moore predicted that computing power will become significantly more capable and yet cost less year after year.

The chips made on the 7nm process will power the most sophisticated computers, data centers, sensors and other high-tech devices, and enable things like artificial intelligence, more advanced cars and transportation services, breakthroughs in medical research and treatment, and more. These are areas that depend upon having the highest amount of computing power, access to the fastest networks, the most data storage, the smallest chip sizes, and other benefits that come from advancing Moore’s Law.

After the announcement, President Trump tweeted his thanks to Krzanich, calling the factory a great investment in jobs and innovation. In his email to employees, Krzanich said that he had chosen to announce the expansion at the White House to “level the global playing field and make U.S. manufacturing competitive worldwide through new regulatory standards and investment policies.”

“When we disagree, we don’t walk away,” he wrote. “We believe that we must be part of the conversation to voice our views on key issues such as immigration, H1B visas and other policies that are essential to innovation.”

During Mr. Trump’s presidential campaign, Krzanich had reportedly planned a Trump fundraiser event and then cancelled following numerous controversial statements from Trump regarding his proposed immigration policies. Intel has continued to be critical of the Trump administration’s immigration policies, joining over 100 other companies to file a legal brief challenging President Trump’s January 27 executive order which blocked entry of all refugees and immigrants from seven predominantly Muslim countries. Recently, Krzanich took to Twitter to criticize the order, voicing the company’s support of lawful immigration.

In 2012, Paul Otellini, then Intel’s CEO, made a similar promise about Fab 42 in the company of Obama, during a visit to Hillsboro, Oregon.

A team of researchers, affiliated with UNIST has created a new technique that greatly enhances the performance of Schottky Diodes (metal-semiconductor junction) used in electronic devices. Their research findings have attracted considerable attention within the scientific community by solving the contact resistance problem of metal-semiconductor, which had remained unsolved for almost 50 years.

Shown above is the Internal Photoemission (IPE) Measurement System, developed by Hoon Hahn Yoon, combined M.S./Ph.D. student of Natural Science at UNIST. Credit: UNIST

Shown above is the Internal Photoemission (IPE) Measurement System, developed by Hoon Hahn Yoon, combined M.S./Ph.D. student of Natural Science at UNIST. Credit: UNIST

As described in the January issue of Nano Letters, the researchers have created a new type of diode with a graphene insertion layer sandwiched between metal and semiconductor. This new technique blows all previous attemps out the water, as it is expected to significantly contribute to the semiconductor industry’s growth.

The Schottky diode is one of the oldest and most representative semiconductor devices, formed by the junction of a semiconductor with a metal. However, due to the atomic intermixing along the interface between two materials, it has been impossible to produce an ideal diode. (An ideal diode acts like a perfect conductor when voltage is applied forward biased and like a perfect insulator when voltage is applied reverse biased.)

Professor Kibog Park of Natural Science solved this problem by inserting a graphene layer at the metal-semiconductor interface. In the study, the research team demonstrated that this graphene layer, consisting of a single layer of carbon atoms can not only suppress the material intermixing substantially, but also matches well with the theoretical prediction.

“The sheets of graphene in graphite have a space between each sheet that shows a high electron density of quantum mechanics in that no atoms can pass through,” says Professor Park. “Therefore, with this single-layer graphene sandwiched between metal and semiconductor, it is possible to overcome the inevitable atomic diffusion problem.”

The study also has the physiological meaning of confirming the theoretical prediction that “In the case of silicon semiconductors, the electrical properties of the junction surfaces hardly change regardless of the type of metal they use,” according to Hoon Hahn Yoon (Combined M.S./Ph.D. student of Natural Science), the first author of the study.

The internal photoemission method was used to measure the electronic energy barrier of the newly-fabricated metal/graphene/n-Si(001) junction diodes. The Internal Photoemission (IPE) Measurement System in the image shown above has contributed greatly to these experiments. This system has been developed by four UNIST graduate students (Hoon Han Yoon, Sungchul Jung, Gahyun Choi, and Junhyung Kim), which was carried out as part of an undergraduate research project in 2012 and was supported by the Korea Foundation for the Advancement of Science and Creativity (KOFAC).

“Students have teamed up and carried out all the necessary steps for the research since they were undergraduates,” Professor Park says. “Therefore, this research is a perfect example of time, persistence, and patience paying off.”

A new study, affiliated with Ulsan National Institute of Science and Technology (UNIST), South Korea, has introduced a novel method for fabrication of world’s thinnest oxide semiconductor that is just one atom thick. This may open up new possibilities for thin, transparent, and flexible electronic devices, such as ultra-small sensors.

This new ultra-thin oxide semiconductors was created by a team of scientists, led by Professor Zonghoon Lee of Materials Science and Engineering at UNIST. In the study, Professor Lee has succeeded in demonstrating the formation of two-dimensional zinc oxide (ZnO) semiconductor with one atom thickness.

The above graphic displays the growth of ZnO on graphene layer, consists of interconnected hexagons of carbon atoms. Zinc atom shown as red spheres, oxygen atom as green spheres. Credit: UNIST

The above graphic displays the growth of ZnO on graphene layer, consists of interconnected hexagons of carbon atoms. Zinc atom shown as red spheres, oxygen atom as green spheres. Credit: UNIST

This material is formed by directly growing a single-atom-thick ZnO layer on graphene, using atomic layer deposition. It is also the thinnest heteroepitaxial layer of semiconducting oxide on monolayer graphene.

“Flexible, high-performance devices are indispensable for conventional wearable electronics, which have been attracting attention recently,” says Professor Lee. “With this new material, we can achieve truly high-performance flexible devices.”

Semiconductor technology continually moves toward smaller feature sizes and greater operational efficiency and the existing silicon semiconductors seem to also follow this trend. However, as the fabrication process becomes finer, the performance becomes much critical issue and there has been much research on next-generation semiconductors, which can replace silicon.

Graphene has superior conductivity properties, but it cannot be directly used as an alternative to silicon in semiconductor electronics because it has no band gap. A bandgap gives a material the ability to start and stop the flow of electrons that carry electricity. In graphene, however, electrons move randomly at a constant speed no matter their energy and they cannot be stopped.

To solve this, the research team decided to demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation. Then, they experimentally determine that the thinnest ZnO monolayer has a wide band gap (up to 4.0 eV), due to quantum confinement and graphene-like ‘hyper-honeycomb’ structure, and high optical transparency.

The currently-existing oxide semiconductors have a relatively large bandgap in the range of 2.9-3.5 eV. The greater the band gap energy, the lower the leakage current and excess noise.

“This is the first time to actually observe the in situ formation of hexagonal structure of ZnO,” says Hyo-Ki Hong of Materials Science and Engineering, first author of the paper. “Through this process, we could understand the process and principle of 2D ZnO semiconductor productiom.”

“The heteroepitaxial stack of the thinnest 2D oxide semiconductors on graphene has potential for future optoelectronic device applications associated with high optical transparency and flexibility,” says Professor Lee. “This study can lead to a new class of 2D heterostructures including semiconducting oxides formed by highly controlled epitaxial growth through a deposition route.”

A team of scientists from the Energy Department’s National Renewable Energy Laboratory (NREL) determined that surface recombination limits the performance of polycrystalline perovskite solar cells.

Considerable research into perovskites at NREL and elsewhere has proved the material’s effectiveness at converting sunlight into electricity, routinely topping 20 percent efficiency. The sunlight creates mobile electrons whose movement generates the power but upon encountering defects can slip into a non-productive process. Known as a recombination, this process reduces the efficiency of a solar cell. For the cell to be the most efficient, the recombination must occur slowly.

With prior studies into perovskites focusing on bulk recombination, one area left unexamined until now concerned the surface recombination in lead iodide perovskites. NREL’s scientists determined recombination in other parts of a methylammonium perovskite film isn’t as important as what’s happening on the surface, both the top and bottom.

Matthew Beard and his colleagues within NREL’s Chemistry and Nanoscience Center studied surface recombination in single-crystal and polycrystalline films using transient reflection spectroscopy. Their findings, Top and bottom surfaces limit carrier lifetime in lead iodide perovskite films, appear in Nature Energy.

“What’s important is to know where the recombination is coming from,” said Beard, lead author of the research paper. “There are multiple sources of possible recombination. In order to improve your device, you’re asked to get rid of all non-radiative recombination. Typically people forget about surfaces. They think about grain boundaries. They think about bulk defects and so forth.”

Beard’s co-authors are all from NREL: Ye Yang, Mengjin Yang, David T. Moore, Yong Yan, Elisa M. Miller, and Kai Zhu.

Beard said the research determined surface recombination emerged as an obstacle to overcome. Surface recombination directly affects the performance of a photovoltaic device. The ability to engineer surfaces stands poised to benefit perovskite-based optoelectronic applications. A fast surface recombination can be used to design photodetectors, while lasers and light-emitting diodes require a slower speed.

A second study that concurrently appeared in the journal Physical Chemistry Chemical Physics was authored by Mengjin Yang, Yining Zeng, Zhen Li, DongHoe Kim, Chun-Sheng Jiang, Jao van de Lagemaat, and Kai Zhu further strengthened the conclusions of the paper. This study, using high-resolution fluorescence-lifetime imaging, also showed that surface recombination is the determining factor instead of grain boundary recombination.

The researchers compared two types of samples: single crystals and polycrystalline films. Surprisingly surface recombination is worse for single crystalline samples compared to the polycrystalline samples found in solar cell devices. Chemically, excess methylammonium iodide was present on the surface of the polycrystalline film but absent on the single-crystal sample.

“That seems to help,” Beard said. “The single crystal has a lead-rich surface and a faster surface recombination.”

The research suggested a light coating of a protective material on the surface of the polycrystalline thin films could further improve the performance of perovskite solar cells.

Worldwide silicon wafer area shipments increased 3 percent in 2016 when compared to 2015 area shipments according to the SEMI Silicon Manufacturers Group (SMG) in its year-end analysis of the silicon wafer industry, while worldwide silicon revenues increased by 1 percent in 2016 compared to 2015.

Silicon wafer area shipments in 2016 totaled 10,738 million square inches (MSI), up from the previous market high of 10,434 million square inches shipped during 2015. Revenues totaled $7.21 billion, one percent higher from the $7.15 billion posted in 2015. “Annual semiconductor silicon volume shipments reached record levels for the third year in a row,” said Chungwei (C.W.) Lee, chairman SEMI SMG and Corporate Development VP of GlobalWafers. “However, despite historical shipment highs, the same cannot be said about silicon revenue. The market remains well below pre-downturn levels.”

Annual Silicon* Industry Trends

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016
Area Shipments (MSI)

8,661

8,137

6,707

9,370

9,043

9,031

9,067

10,098

10,434

10,738
Revenues ($B)

12.1

11.4

6.7

9.7

9.9

8.7

7.5

7.6

7.2

7.2

*Shipments are for semiconductor applications only and do not include solar applications

Silicon wafers are the fundamental building material for semiconductors, which in turn, are vital components of virtually all electronics goods, including computers, telecommunications products, and consumer electronics. The highly engineered thin round disks are produced in various diameters (from one inch to 12 inches) and serve as the substrate material on which most semiconductor devices or “chips” are fabricated.

All data cited in this release is inclusive of polished silicon wafers, including virgin test wafers and epitaxial silicon wafers, as well as non-polished silicon wafers shipped by the wafer manufacturers to the end-users.

Unavoidably, each digital information we send around the globe is prone to be lost. Travelling long ways in wires, the initial signal decays and scatters by colliding with impurities and neighboring electromagnetic fields. Therefore, beyond each bit of your desired message, it is necessary to send other hidden bits of information that check for mistakes and take action in case of losses; while devices become smaller and smaller, this issue becomes more significant. Scientists at the Center for Artificial Low Dimensional Electronic (CALDES), within the Institute for Basic Science (IBS) are aiming to find innovative ways at achieving a more stable transmission of information. One of their research interests focuses on self-reinforcing solitary wave packets called solitons, which are stable no matter the surroundings. In their most recent paper they demonstrated that solitons can be manipulated and outlined how to use them for logical operations. Their experiments and models are published in Nature Physics and pave the way to a new field of electronics: Solitonics.

Physicists know that one possible solution to the issue of signal attenuation or noise because of external interferences can come from a mathematical concept called topology. It is related to properties that are not affected by a change in shape. For example, believe it or not, a ball and a pencil are topologically the same, but different from a donut. This is because, with some imagination, you can mold the ball into the shape of the pencil. However, when you make a hole in the ball, it becomes a totally different topological object. Holes define the topological state, they can move within the material, but their number does not change even under the presence of pushing and pulling forces. A similar concept could be used in IT to protect the flow of information from external interferences and impurities and guarantee its stability over longer distances and time. It sounds like an amazing property but, paradoxically, it is also its own biggest enemy: The transmitted information is too stable, in a way that it is actually too difficult to modify and use. That seemed to be the sad end of the story, until IBS scientists demonstrated a way to manipulate the transmitted signal and possibly apply it to modern electronics.

One of the key components of the physics of topological system is the soliton, an extremely stable solitary wave packet of energy, which travels though some 1D materials without losing its shape and energy, a bit like a tsunami wave. Scientists began to study topological solitons in the 80’s, but were deterred by the seemingly impossibility of manipulating them.

Last year, IBS scientists explored the properties of solitons on a double chain of indium atoms placed on the top of a silicon surface and they found that solitons could exist in three forms. “In a topological sense, it is like having a donut with a lot of holes, where each hole can be of three different shapes corresponding to the three types of solitons,” explains YEOM Han Woong, the leading author of this study. “Physicists used to work with solitons (holes) of the same type and the operations you could do with them were limited, but now we have a bigger chance to play with them.”

In this new study, Yeom and his team proved, experimentally, that switching between these solitons is possible. They observed that when two solitons meet, they result in a different soliton, in other words they found that solitons can be transformed, and yet remain immune to the defects of the medium. “So far solitons could only be created or destroyed in pairs, no other manipulations were possible, but we showed that these solitons can be switched from one to another, and even used for logical operations”, continues Yeom.

These three types of solitons can also be represented by digits (1, -1 and 2) and the condition without solitons as zero (0), creating a quaternary mathematical system. The four digits can then be used for mathematical computations.

Quaternary digit systems, and multidigit systems in general, have several advantages over the binary (0, 1) system that we are currently using. They allow more operations and information storage in less space and they could bring us a step closer to brain-like devices, which mimic the way information is computed and stored by our neuronal circuits.

Opening a new field of electronics, dubbed solitonics, IBS scientists imagine new generation IT devices that combine silicon and solitons. “We are using solitons travelling in indium atoms on a silicon surface, and we imagine that this structure that could be implemented in current silicon devices, creating hybrid systems,” explains KIM Tae-Hwan, first author of this study.

A team of scientists from the Nanoelectronic Materials Laboratory (NaMLab gGmbH) and the Cluster of Excellence Center for Advancing Electronics Dresden (cfaed) at the Dresden University of Technology have demonstrated the world-wide first transistor based on germanium that can be programmed between electron- (n) and hole- (p) conduction. Transistors based on germanium can be operated at low supply voltages and reduced power consumption, due to the low band gap compared to silicon. Additionally, the realized germanium based transistors can be reconfigured between electron and hole conduction based on the voltage applied to one of the gate electrodes. This enables to realize circuits with lower transistor count compared to state-of-the-art CMOS technologies.

Energy-efficient germanium nanowire transistor with programmable p- and n- conduction is shown. Transmission electron microscope image of cross section. Credit: NaMLab gGmbH

Energy-efficient germanium nanowire transistor with programmable p- and n- conduction is shown. Transmission electron microscope image of cross section. Credit: NaMLab gGmbH

Today´s digital electronics are dominated by integrated circuits built by transistors. For more than four decades transistors have been miniaturized to enhance computational power and speed. Recent developments aim to maintain this trend by employing materials having higher mobility than silicon in the transistor channel, like germanium and indium-arsenide. One of the limitations in using those materials is the higher static power loss in the transistor´s off-state, also originating from their small band gaps. The scientist team around Jens Trommer and Dr. Walter Weber from NaMLab in cooperation with cfaed succeeded in solving this issue by conceiving the germanium-nanowire transistor with independent gating regions. Dr. Weber who leads cfaed’s Nanowire Research Group points out: “For the first time the results demonstrate the combination of low operation voltages with reduced off-state leakage. The results are a key enabler for novel energy efficient circuits.”

The work has been published in the journal ACS Nano.