The Magazine from Forschungszentrum J端lich
RESEARCH in J端lich
NANOELECTRONICS :: TURBO STORAGE FOR THE COMPUTERS OF TOMORROW :: GETTING STARTED WITH SPINTRONICS :: INSPIRED BY BIOLOGY
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RESEARCH in Jülich The Magazine from Forschungszentrum Jülich
Nanoelectronics: The Engine of Innovation
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nformation and communications technologies are the driving force behind growth and innovation” are the opening words of the Stuttgart Declaration (Stuttgarter Erklärung) published by the national IT summit at the end of 2009. In the declaration, senior representatives from politics, science and industry emphasize the central importance of these technologies for Germany. In its High-Tech Strategy for Germany, the Federal Government stresses that “information and communication technologies contribute significantly to the solution of societal challenges”. We are only too aware of this here at Forschungs zentrum Jülich. Information technology is one of our main research areas and we want to play an active role in shaping the modern information society. More than 20 years ago, Nobel Laureate in Physics Prof. Peter Grünberg laid the basis for spintronics here in Jülich when he discovered giant magnetoresistance. This effect opened the way for the technology that has since been implemented in almost all read heads in hard drives. Today, our scientists continue to work on challenges facing society and they are laying the foundation for the information society of tomorrow. In doing so, they do not just work with industry; they also cooperate closely with scientists at RWTH Aachen University in the Fundamentals of Future Information Technology (FIT) section of the Jülich-Aachen Research Alliance (JARA). Many of the articles in this edition of “Research in Jülich” make clear how this alliance overcomes the insularity of university and non-university research and teaching and unites the strengths of both systems. What can you expect from this magazine? The term “information technology” is often heard in one and the same breath as “microelectronics”, and a
In this part of the Nano-Spintronics Cluster Tool (see “The Universal Tool”, p. 26), nanocomponents can be fabricated, imaged and investigated in an ultrahigh vacuum. The chessboard pattern in the centre is much bigger than the structures on standard specimens and is used for calibrating purposes. Cover illustration: Using this measurement set-up, Jülich scientists characterize the electronic properties of carbon nanotubes and other sensitive components for the information technology of the future.
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“computer chip” is often considered a “microchip”. However, electronic components, which are predominantly based on the material of silicon, have since reached nanodimensions. Nanoelectronics has become a key concept and will help us to deal with future challenges in information technology. Read how Jülich researchers push the boundaries of established technology in an effort to allow computing power to continue to grow in the future. Learn about how scientists pursue alternative concepts for the hardware of tomorrow, how they develop new mate rials and blueprints for non-volatile storage and spintronics, which should help to make computers even faster and more energy efficient. Discover how biomolecules can be used for information processing and what components are needed to build quantum computers. Whoever wishes to take the lead in the global competition must pursue the right research strategies, invest in the right equipment and cooperation partners, and attract the right minds. Research is nothing without dedicated, knowledgeable and creative individuals. You will get to know some of the best young minds from Forschungszentrum Jülich and learn about their ideas for the IT of the 21st century in this magazine. We hope that it makes for interesting reading!
Prof. Dr. Achim Bachem Chairman of the Board of Directors
Prof. Dr. Sebastian M. Schmidt Member of the Board of Directors
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IN This ISSUE
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Editorial
:: SnapshOTs FROM Jülich
:: Highlights
6 Research at a Glance
20 Fit for the Future
A kaleidoscope of pictures illustrating some of the highlights of Jülich research – from the analysis of harmful proteins and a fuel cell record to findings on the climatic effects of forests.
:: GETTING STARTED WITH SPINTRONICS “Peapods” made of carbon atoms are ideal for investigating spin effects. In the future, they could become the building blocks of an energy-saving and fast information technology.
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Interview with Professors Markus Morgenstern and Detlev Grützmacher on the Jülich-Aachen Research Alliance (JARA). 22 Turbo Storage for the Computers of Tomorrow Jülich researchers are working on making the process of booting computers faster so that it doesn’t take what feels like an eternity.
9 Fresh Ideas 10 Inspired by Biology Bernhard Wolfrum’s basic research could pave the way towards prostheses that can be connected directly to the nervous system. 12 Getting Started with Spintronics Carola Meyer develops components based on the switching of the electron spin. 14 Creating Order in Oxides Manuel Angst is looking for materials that are both magnetic and ferroelectric. 16 Dynamic Adventures in the Nanoworld Janine Splettstößer calculates what happens when quantum dots are no longer in equilibrium. 18 Best Prospects
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INSPIRED BY BIOLOGY Jülich scientists want to improve the communication between living cells and electronic components. In order to do so, they are developing chips with nanostructured surfaces and methods that will amplify cell signals.
TURBO STORAGE FOR THE COMPUTERS OF TOMORROW In today’s computer memories, the data are either written and read slowly or the information is lost once the device is switched off. Jülich researchers are developing storage elements that will provide a way out of this dilemma.
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26 The Universal Tool The Jülich Nano-Spintronics Cluster Tool is the “Swiss Army knife” among research tools. 28 Nanosonar The flow of electrons in a scanning tunnelling microscope can be used to investigate the well-hidden properties of metals. 30 Tricks for Faster Transistors Jülich scientists expand the crystal lattice of silicon to allow charge carriers to flow through it faster. 32 Unique Insight into the World of Atoms The new supermicroscope PICO measures atom displacements with an accuracy of a billionth of a millimetre. 34 News from Information Technology From the creation of a state-of-the-art clean room centre and a model system made of ultracold atoms to the decoding of the structure of a material used in DVDs.
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SNAPSHOTS FROM JÜLICH
ESCAPE ROUTES Widening exits, even just a little, allows more people to flee from stadiums or halls in cases of emergency. Researchers from Jülich and Wuppertal discovered this in tests with volunteers. In the past, it was assumed that the flow of people would only increase if the bottlenecks were increased by the full width of an average person. Findings such as these help to create better computer models of escape movements. The Jülich Supercomputing Centre is coordinating the “Hermes” project funded by the German Federal Ministry of Research. The project aims to develop a computer-aided evacuation system.
FORESTS AND GLOBAL WARMING Trees release a mixture of volatile organic compounds into the atmosphere. As Jülich scientists reported in the journal Nature, this mixture changes as the temperature increases, leading to the formation of fewer suspended particles in the atmosphere. It therefore follows that global warming will reduce the cooling effect of forests. The reason for this? Suspended particles function like condensation nuclei for cloud droplets. Fewer suspended particles would therefore mean less cloud cover and increased solar radiation on the Earth’s surface.
Research at a Glance This magazine focuses on nanoelectronics research at Jülich. However, this is not the only area in which Jülich scientists have scored great successes.
ATMOSPHERIC TURBO WASH An international team that included Jülich researchers detected an accelerated degradation of pollutants during air measurements above South China. A previously unknown amplification mechanism increases the self-cleaning ability of the atmosphere three to five times over. As scientists reported in the journal Science, the mechanism – unlike previously known mechanisms – produces very little harmful ozone. For this reason, attention must now be turned to reviewing the computer models used to predict ground-level ozone concentrations.
THRIFTY SUPERCOMPUTER The German research computer QPACE is more than powerful. It was developed by an academic consortium in which the University of Regensburg, Forschungs zentrum Jülich and IBM Research & Development in Böblingen played a key role. In November 2009, QPACE topped the global ranking of the most energy-efficient supercomputers, the Green500 List. It is used to simulate fundamental natural forces in elementary particle physics.
BETTER ANALYSIS OF HARMFUL PROTEINS On the Jülich campus, scientists from the University of Düsseldorf and Forschungszentrum Jülich are conducting joint research on the structure and effect of proteins. Some proteins play a role in the proliferation of viruses or have a directly harmful effect, as is the case in Alzheimer’s amyloids, which are thought to cause the typical symptoms of Alzheimer’s. Thanks to a new 900-MHz NMR spectrometer, researchers can now analyse the appearance of harmful proteins atom for atom and precisely study their action in the body. The measuring instrument is among the most sensitive of its type worldwide.
SIGNALS IN THE BRAIN Researchers from Jülich and Freiburg have discovered that the chemical neurotransmitter acetylcholine in the brain does not always – as previously believed – intensify the signal transduction between neurons. The opposite is true in the fourth layer of the cerebral cortex, where its only function is to repress the signal transduction of neurons. As brain diseases such as Alzheimer’s or schizophrenia are accompanied by a malfunction in the excretion of acetylcholine, understanding how the substance works is important.
WORLD RECORD WITH FUEL CELLS Jülich scientists successfully operated two stacks of high-temperature fuel cells for 15,000 hours each. The stacks provided a power of 0.4 watts per square centimetre, which is almost double that of today’s commercial systems. This has brought researchers one step closer to their objective of developing solid oxide fuel cells (SOFCs) to maturity for application in buildings and power plants. Fuel cells directly convert chemical energy into electric current in an efficient and environmentally friendly manner.
LINK TIP www.fz-juelich.de/portal/home
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:: FRESH IDEAS Many excellent young scientists are involved in research on the information technology of the future. We focus on four of them in this issue – together with the fresh new ideas that they are pursuing in a knowledgeable and dedicated manner. The young researchers not only benefit from financial support, which provides them with scientific independence early on, but also from collaborations with recognized leading researchers at Forschungszentrum Jülich and those involved in the Jülich-Aachen Research Alliance (JARA).
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Far left: A myocardial cell grows on a “field” of tiny gold bars. The bars enlarge the surface of an electrode. Left: Dr. Bernhard Wolfrum works on combining electronics with biology.
Inspired by Biology Bernhard Wolfrum develops instruments that improve communication between living cells and electronic components. His basic research could pave the way towards sensors for environmental chemicals – or towards prostheses that can be directly connected to the nervous system.
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hey populate science-fiction novels, comics and sci-fi films: hybrid beings part-human and part-machine known as cyborgs. In Dr. Bernhard Wolfrum’s laboratory at the Institute of Bio- and Nanosystems, you would look for them in vain, although his team does work on combining electronics with biology. “But we’re far away from some sort of biotechno monster,” says the young physicist reassuringly with a laugh.
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“Cells on chips” Wolfrum and his team are particularly interested in the communication between neurons, which are bilingual, so to speak. On the one hand, they pass on information electrically; their projections function like tiny “cables”. On the other hand, they speak to each other chemically at the relay stations from one cell to the next, the synapses. This is where they excrete certain messenger substances – neurotransmitters – which transport a message from one cell to the next. Wolfrum wants to eavesdrop on this chemical dialogue and exploit what he learns for the exchange of information between neurons and electronics. In order to do this, the scientists grow networks of cells on electronic chips with special contact points. They develop nanostructured surfaces, filled with tiny gold bars, for example, to which the cells
Two electrodes on a nanochannel amplify the signal of a neurotransmitter molecule through multiple oxidation and reduction.
can securely attach themselves. The scientists also design chips with nanochannels in which electrochemical processes occur. “The most important thing is to amplify the cell signals so that they can be registered at all,” explains Wolfrum. In order to “eavesdrop” on the cells, a single electrode is generally used. When it meets a molecule of the excreted dopamine or
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a nother neurotransmitter, this molecule is oxidized. The current signal that is created as a result is relayed. “But for the few neurotransmitter molecules on a single synapsis, such a system is not sensitive enough,” says Wolfrum. His trick: he brings a second electrode into play that reduces the dopamine again. If both electrodes lie close enough together in a nanochannel through which the messenger molecules travel, one and the same dopamine molecule can be oxidized and reduced time and again. “The signal in these cycles is amplified significantly. This provides us with a very sensitive sensor for neurotransmitters,” explains Wolfrum. “Even a single molecule can thus generate a measurable current.” In this way, he hopes to understand the conversation of the neurons better and to improve the coupling to electronic components. Horror scenarios and reality Could such research lead to a chip that could be planted in a human brain in order to improve an individual’s memory or intelligence, or even to control them at the touch of a button? Although Wolfrum is of the opinion that we should bear such ethically controversial developments in mind, he also believes that “such horror scenarios are very far away
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from reality.” He is convinced that the useful applications of bioelectronic chips will be of great benefit in the future. In an artificial retina, for example, they could help blind people to see again, or they could be used in prostheses controlled by the nervous systems as if they were natural limbs. Areas of application that are conceivable in the near future include sensors for environmental chemicals or test systems for drug development. This would allow a bioelectronic chip to be used to measure how a network of neurons reacts to an environmental toxin or to a pharmaceutical agent. Even though Wolfrum considers his work more as basic research, industry is already interested in his results. Multiple networks do not just exist between cells and electronics on Wolfrum’s chips, but also with the Jülich groups working on bio- and nanoelectronics. Cooperation within Forschungszentrum Jülich and with RWTH Aachen University in the Jülich-Aachen Research Alliance (JARA) is outstanding according to Wolfrum. Having studied physics in Göttingen and Santa Barbara, California, he worked in places such as the renowned
Kavli Institute of Nanoscience at TU Delft in the Netherlands before coming to Jülich in the summer of 2008. He values his current position as head of a Helmholtz Young Investigators Group. “For an academic career, this is an ideal starting position,” says Wolfrum. “On the one hand, I can work independently and set my own goals, while on the other, interdisciplinary cooperation in JARA-FIT creates the best preconditions for me to achieve these goals.” This naturally means a lot of work admits the young father. “But I’m very flexible when it comes to time management – which also benefits my family.” This allows him and his wife who has a fixed schedule as a doctor in a hospital to plan day-care for their two children, who are of playschool and primary-school age. “I certainly spend a lot more time with my son and daughter than many other fathers,” says Wolfrum. Wiebke Rögener
Scanning electron micrographs of gold bars on different surfaces.
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Getting Started with Spintronics Carola Meyer traps spins in cages made of carbon molecules, is not impressed by the male majority in quantum physics, and favours cooperation more than competition when it comes to her research projects.
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f a good fairy flew into Dr. Carola Meyer’s laboratory and offered her the answers to unsolved research questions, the fairy would fly away without having got very far. “I don’t want any ready-made answers,” says the physicist. “What drives me is the question of “what would happen if” – it’s a process of thinking and experimenting – and this is what I find so exciting about my work.” Her field of research – that of spintronics – certainly provides enough opportunities for that.
Dr. Carola Meyer conducts her quantum transport measurements in a cryostat that is colder than the temperatures in space.
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Spins instead of charges Up to now, information processing in computers has been based on the trans-
port of electric charges. This movement also inevitably creates heat, unnecessarily consuming energy, which in turn makes noisy fans essential in computers. “Such losses could be avoided by a technology that exploits other properties of electrons, making use of their spin instead of their charge,” explains Carola Meyer. This quantum mechanical property can be imagined as a sort of angular momentum of the electron. The spin can assume two states: spin up or spin down. It is measured by its interaction with magnetic fields. Read heads in computer hard drives already work with spin effects today. They exploit giant magnetoresistance, which is based on the quantum mechanical coupling of electron spins in thin magnetic layers. This effect was discovered in 1988 by Jülich researcher Prof. Peter Grünberg and the French scientist Albert Fert, who were jointly awarded the Nobel Prize for Physics in 2007 in recognition of their work. Still in its infancy, on the other hand, is the attempt to manipulate individual spin-polarized electrons for quantum information processing. “If we succeed in developing components based on the switching of spins, we will not only be able to process information with very little energy but also at very high speed,” says Meyer. In order to gain control of the spin, the researcher traps it. Cages made of carbon are particularly good for this, she
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“Peapods” as the predecessor of future nanoelectronic components: a carbon nanotube filled with fullerenes – spheres made of carbon atoms. Each sphere (green) encloses an atom (red). This allows the researcher to experiment with a countable number of spins.
explains. “When the electron spin interacts with the spin of the atomic nuclei, the information is lost. The good thing about carbon atoms is that they don’t have a nuclear spin.” Carola Meyer and her team fill carbon tubes with a dia meter of a few nanometres (millionths of a millimetre) with spherical molecules composed of 60 carbon atoms. In some experiments each of these spheres, known as fullerenes, also contain one metal atom as this allows stronger spin effects to be generated. The fullerenes line up in the tube one behind the other
In the three-dimensional image produced by a scanning electron microscope, a nanotube looks like a thread (the bright horizontal line) running between two gold contacts. The gate electrode stretches out behind. It controls the number of electrons that flow through the tube. This type of structure is referred to as a fieldeffect transistor.
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like peas in a pod, which also explains why the system is known as a “peapod” system. “This provides us with a one- dimensional spin chain, a model system with a countable number of spins,” says Meyer. Using spectroscopic methods and an electron microscope, her team studies the structure and properties of these entities. From the “peapods”, for example, transistors and other components could be developed on a nanoscale. Their spin properties could then be studied in detail at very low temperatures. That she will be able to replace her laptop in the near future with a practical computer based on quantum effects is not something that Carola Meyer expects. “Some people have jumped too hastily to conclusions,” she says. Scientists are still in the process of studying the basic properties of quantum objects. Highly qualified and dedicated In 2005, Meyer came to the Jülich Institute of Solid State Research within the framework of the Tenure Track Programme. This programme was originally aimed at highly qualified young women scientists, offering them the opportunity to set up their own working group at an early stage of their career, and after an evaluation, to be employed on a permanent contract. The programme has since been opened to young male scientists. “When I moved from TU Delft in the Netherlands to Jülich, doors were always
open here. The potential for cooperation was huge,” says Meyer. She names the Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons as an example. She is convinced that “the expansion of such collaborations within the JülichAachen Research Alliance (JARA) would be extremely positive.” She is of the opinion that the role of competition in science is often overestimated: “Science lives more from the exchange of ideas and from cooperation than from compe tition.” Does she also come up against difficulties in her collaborative work in a research field that is still dominated by men? “It is true that there are very few women working in the area of quantum computing compared to other areas of physics,” says Meyer, “but here in the institute, this is not an issue. The climate is extremely pleasant.” In her working group, women are actually in the majority. “I chose my team myself. Applications that began with ‘Dear Sir’ landed directly in the rubbish bin,” she grins. She dedicates part of her limited free time to the Equal Opportunities Working Group in the German Physics Society (DPG) for which she is deputy spokesperson. “I believe that it is important to give something back to society – technology is not the only thing that needs to be improved.” Wiebke Rögener
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The crystal structure of lutetium iron oxide – a material in which interesting ordering phenomena appear.
circle” seems possible. Angst’s experiments suggest that lutetium iron oxide does not just possess a magnetic order but also an antiferroelectric order. “In order to change the magnetism using an external voltage, antiferroelectricity is not enough,” says the young physicist with disappointment. He is hoping for a material that combines magnetism and ferroelectricity. This is where his second motive comes into play – the desire for change. “You can basically push different buttons,” he explains. He wants to replace the lutetium with another element from the rare earths group. As the anti ferroelectric order in lutetium iron oxide is only slightly more stable than the ferro electric order, we could end up with a material in which a ferroelectric order and magnetism are both simultaneously stable. Angst wants to fabricate candi-
Creating Order in Oxides Swiss-born Manuel Angst conducts research in Jülich on unusual materials that also have excellent magnetic and electrical properties. He sums up his motivation in a nutshell: understanding and changing.
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nyone who has ever pinned their shopping list to the fridge door knows what magnetism is. But what is ferroelectricity? “Crystals that possess a permanent electric polarization, even without an external electrical field, are ferroelectric,” explains Dr. Manuel Angst from the Jülich Institute of Solid State Research. In a ferroelectric crystal lattice, ions with different charges
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are arranged in such a way that the centres of the charges do not overlap and electric dipoles appear instead. The principle is similar to a magnet that has been assembled from a number of tiny bar magnets. These magnetic dipoles are arranged in a certain order. The same holds for electric dipoles. If they all have the same direction, the material is ferroelectric. If on the other hand, dipoles with opposing electric polarization lie side by side, the overall polarization is zero and a physicist would talk about an antiferro electric order. Huge potential Of particular interest are materials in which both magnetism and ferroelectricity – or antiferroelectricity – occur, and in which both phenomena influence the order in the crystal lattice. These materials are known as multiferroitics, and include lutetium iron oxide. “It becomes interesting when a coupling exists between dif-
ferent orders, in other words when ferroelectricity can be influenced by a magnetic field or the magnetism can be changed with an electric field,” explains Angst with visible enthusiasm for his field of research. He wants to know how the orders are created and how they can be changed. “On the one hand, this is a hot topic for basic research,” he explains. “On the other hand, it has huge potential for applications in information technology.” Highly sensitive sensors made of multiferroic materials could be ready for the market in just a few years. In the long term, non-volatile computer storage is viable, whereby information will be written simply by applying a voltage without current actually flowing. The energy demand would therefore be much lower than that of today’s storage systems. According to conventional theories, however, magnetism and ferroelectricity are mutually exclusive. In the case of lutetium iron oxide, this “squaring of the
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Scattering images of lutetium iron oxide measured with synchrotron X-ray radiation. At around minus 70 degrees Celsius (top), strong superstructure reflections are clearly visible They indicate a specific charge ordering with polar structural units that have an antiferroelectric order. At temperatures above around 80 degrees Celsius (bottom), on the other hand, strong superstructure reflections are no longer present.
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A insightful device – Dr. Manuel Angst working on the single-crystal X-ray diffractometer.
dates whose structure he considers interesting in the laboratory and then analyse them using synchrotron and neutron radiation. He emphasizes: “In Jülich, I have all the possible experimental facilities I could ever want.” From the USA to Jülich Angst came to Jülich to work as a scientist in 2008. Having completed his PhD at ETH Zurich with a thesis on superconducting materials, he went to the internationally respected Oak Ridge National Laboratory in Tennessee, USA, to conduct research. “From collaborations back then, I knew that I would find an excellent research climate here in the institute at Jülich,” says Angst. He believes one of the biggest advantages is the involvement in the Jülich-Aachen Research Alliance (JARA): “Here, many different research approaches are combined and focussed on information technology – this creates enormous opportunities.”
Angst has set up his own working group within the framework of the Helmholtz Young Investigators Groups. Having successfully gone through many rounds of competition, the materials researcher was granted funding by external experts. For the next five years, he can finance his own job plus up to three other positions, as well as laboratory equipment. Every year, he receives € 250,000 – 50 % of which comes from the Helmholtz Association’s Initiative and Networking Fund, with the other 50 % from Forschungszentrum Jülich’s budget. Angst has also applied for a position as junior professor at RWTH Aachen University. He is already involved in teaching activities there. “I really enjoy the lectures for advanced students,” says the physicist in his charming Swiss accent. “It’s not unusual for the students’ questions to provide me with inspiration for my own research.” Wiebke Rögener
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Dynamic Adventures in the Nanoworld Whether she’s out hiking or on intellectual flights of fancy – Janine Splettstößer likes to be on the go. Professionally, the young professor of theoretical physics is also interested in dynamic processes. Her métier is switching processes in nanometre dimensions or electrons that are pumped through quantum dots.
She likes working with chalk or a pencil: Prof. Janine Splettstößer
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ravelling is what she likes to do most in her free time, says Prof. Janine Splettstößer. On her last holiday, she explored Nigeria together with a friend. Her scientific career to date also reflects her interest in foreign countries: she spent a year studying in France, wrote her PhD thesis under the shadow of the Leaning Tower of Pisa, and a postdoc position took her to Geneva. The physicist speaks four languages fluently and her partner comes from Italy.
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In order to attract such a globetrotter back to Germany, you have to offer her something special. The returning resear chers’ programme of the state of North Rhine-Westphalia (Rückkehrprogramm des Landes NRW) was obviously attractive enough! In May 2009, not yet 32 years of age, Janine Splettstößer returned to Germany and is now involved in research at the Institute of Physics at RWTH Aachen University. Here, she has a five-year contract as professor. “For me, this is a super opportunity,” she says with enthusiasm. She also expects a lot from the cooperation with Forschungszentrum Jülich as part of “Fundamentals of Future Information Technology (FIT)” within the Jülich-Aachen Research Alliance (JARA). It’s undoubtedly no coincidence that all four young researchers participating in the NRW programme for returning researchers in 2008 wanted to go to one of the JARA-FIT institutes. The programme supporting the return of top young scientists from abroad is aimed at scientists who have been successfully working outside of Germany for at least two years. It helps them to set up their own groups at one of the universities in North RhineWestphalia. The state awards these returning researchers funding of up to € 1.25 million over a period of five years.
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In 2008, the programme was aimed specifically at top young researchers in the field of nanotechnology. “I came across the call for applications by chance in a journal and decided to give it a try,” Splettstößer recalls. And she was successful. She was selected as one of four applicants by an international panel in a cut-throat competition. She was the only woman. “Most importantly, I was the only theoretical physicist,” she emphasizes. Researching with pen and paper Her journey into the quantum world is a purely theoretical one. In order to explore the electronic properties of nanosystems, Janine Splettstößer requires no more than a laptop. “Often, I work with just pen and paper,” she says. Above all, she wants to know what happens when elements from the nanoworld – for example electrons – move, interact with other objects or hit each other under different conditions. “What I am mainly concerned with is relatively large objects that just about exhibit quantum properties,” explains Splettstößer. These “objects” are spatially enclosed arrays of a limited number of atoms, usually semiconductor structures, in which the electrons are prevented from moving freely in all directions. Compared to single elementary
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particles, these objects truly are “relatively large”. Experts refer to these as quantum dots because their energy cannot take on any form but has very definite discrete values – in other words it is quantized. “Here, we are moving along the border between the quantum world and macroscopic objects,” says the physicist, who obviously does not just limit her love of border crossing to her free time. Most of all, she is interested in the dynamics of this nanocosmos. In her PhD thesis, for example, she studied what happens when single electrons are pumped through such quantum dots. “We already know quite a bit about stationary quantum dots,” says Splettstößer. “I want to know what happens when they are no longer in equilibrium.” She formulates mathematical equations to describe such quantum-dot states. At the moment, she is concentrating on electron emitters – components that direct electrons with a certain energy into a system. It becomes particularly exciting when two such electrons influenced by magnetic fields meet at a quantum dot contact and – as the experts would say – become entangled. “When
this happens, you can’t tell the difference between the two electrons in principle, and you can no longer say which electron has come from where,” explains the physicist. Such phenomena are not intuitively conceivable. Is it sometimes difficult to explain her work to friends and family? “Not really,” says Splettstößer. “There are enough analogies with the everyday world: pumps, switches – everyone can imagine what is meant by these. I conduct research on similar processes, albeit in much smaller dimensions, although of course matter does behave differently there.” In reality, the eccentric behaviour of quantum-mechanical systems is already being exploited – for example in the encryption of information using quantum cryptography. “It is a fascinating field of work,” says Splettstößer. “I can work something out theoretically and then ask my colleagues to actually implement it in experiments.” JARA-FIT also offers excellent conditions for this journey from theory to practice. Wiebke Rögener
Janine Splettstößer calculates what happens when electrons begin to interact with each other. The system’s dependence on the magnetic field – shown here in a computer graphic – alludes to interesting quantummechanical effects.
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Nanoelectronics is a key technology of today, tomorrow and the day after tomorrow. As a result, industrial research is just as sought after as completely new concepts beyond established technology – a promising variety as reflected in these pictures.
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Magnetic vortices form in wafers that are only a few nano metres thick. A short pulse of electric current can quickly switch the magnetization inside this vortex – a process shown by this computer simulation. An electron micrograph showing the atomic structure of the high-temperature superconductor YBaCuO. An electronic effect appears here that can be used in what is known as
Hilbert spectroscopy. This method developed at Jülich uses microwaves to quickly and reliably differentiate between different liquids – at security checkpoints for example.
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Graphic representation of an electrochemical sensor (green with yellow conductors) that detects neurotransmitter molecules. These molecules are secreted by neurons (dark red).
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Microscopic partial view of a sensor for communication between cells and electronics. The bright blue structures are the same as the yellow structures in Fig. 3.
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Islets of the semiconductor material germanium have formed in the well-ordered hollows in a silicon wafer, which are between four and eight nanometres deep.
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Nanocolumns made of gallium nitride as the basic elements for future circuits.
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Four electrodes (orange) and a nanowire made of indium nitride (bright purple) form a structure that Jülich scientists have investigated as a potential component for future quantum computers.
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Quantum computers can achieve tremendous speeds thanks to the quantum-mechanical superpositioning and processing of the states in which information is stored.
8 Optical micrograph of a crossbar structure. Jülich scientists have reduced this component to a tenth of its original size for use in future computer storage (see article on page 23). This means that an optical microscope is no longer powerful enough to make the fine structure visible.
9 Neurons (beige) on a field effect transistor. 10 Computer simulation of the electronic structure of a semiconductor after the injection of charge carriers with a pre-set spin.
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HIGHLIGHTS
An interview with Prof. Markus Morgenstern and Prof. Detlev Grützmacher
FIT for the Future
Question: Prof. Morgenstern, as JARAFIT came into being more than two years ago, what did you and your colleagues in Aachen hope to achieve from the alliance with Forschungs zentrum Jülich? Morgenstern: To even think about working on certain research projects and acquiring funding for the necessary research, you need a certain number of qualified scientists who work in the same area. We hoped to achieve this critical mass, to use a term from physics, through the alliance with Jülich. Another factor was that Forschungszentrum Jülich not only has particularly powerful science instruments at its disposal, but also the know-how required to use and further develop them. We therefore expected to profit from this unique strength at Jülich. And finally, we also wanted to create new opportunities for our students at Aachen, for example, by offering them work placements at Jülich. Question: And what were the motives behind Jülich’s decision to join forces with RWTH Aachen University in an alliance? Grützmacher: In information technology, you have poor prospects as a single institution on the global science market. The issues are very complex and interdisciplinary. You need enormous resources to get to the top internationally. This idea of a scientific environment and promising young scientists is exactly what benefits Jülich in this alliance.
In the Jülich-Aachen Research Alliance (JARA), RWTH Aachen University and Forschungszentrum Jülich combine their expertise and capacities to work on complex scientific issues. In the four sections, JARA-BRAIN, JARA-ENERGY, JARA-SIM and JARA-FIT, they decide together what research objectives to pursue, what scientific instruments to purchase and what scientists to appoint. The section known as FIT (Fundamentals of Future Information Technology) has set itself the goal of laying the foundation for the information technology of the future. The directors of JARA-FIT are Prof. Markus Morgenstern, head of II Institute of Physics B at RTWH Aachen University, and Prof. Detlev Grützmacher, director of the Institute of Bio- and Nanosystems at Forschungszentrum Jülich. Together, they take a look back at the strategic partnership to date. 20
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Question: With JARA, RWTH Aachen University and Forschungszentrum Jülich have embarked on a unique journey to overcome the insularity of university and non-university research. What do you see as JARA’s strength? Grützmacher: JARA is like a marriage. When two people get married, they promise to help and support each other and this involves a certain commitment. Partnerships without a marriage certificate, in contrast – like cooperations between universities and non-university institutions – will not necessarily last for ever. Of course, forced marriages also exist: here pressure is applied from outside on research institutions to amalgamate. I believe the first marriage model to be the best.
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Question: Have your expectations been met so far? Morgenstern: Yes. Within JARA-FIT, we have already set up a new research group. Furthermore, JARA-FIT made it possible for us to make a joint application to the German Research Foundation (DFG) for a collaborative research centre. JARA has been up and running now for two years – a relatively short time but it has already become clear that we will reach the critical mass together and that we will be able to strategically position ourselves better than before. Grützmacher: The vacancies for professors we have recently filled testify to this. Our alliance allowed us to successfully attract prominent scientists with offers that neither Aachen nor Jülich would have been able to make on their own. It also became clear how attractive JARA-FIT is for young researchers. For example, all four nanoscientists selected by the North Rhine-Westphalian programme aiming to attract top young scientists back home from abroad wanted to work with us. Question: Why should the tax-payers’ money be invested in information technology? Can we not just leave research to industry? Morgenstern: No. Industry is not interested in investigating long-term alternatives to established silicon technology for the hardware of the future. For industrial companies, options such as quantum computing or the use of single molecules to transmit information are still too far away from actually meeting the technical specifications of a product. One of the unique things about JARA-FIT is that we pursue this basic research, while also participating in projects aiming to meet the current needs of industry.
Question: Where do you want to see JARA-FIT in 2015? Morgenstern: There will be a collaborative research centre, a joint master’s course, a collaborative graduate school … Grützmacher: ... and a joint infrastructure that will be used for high-performance science. An important step towards this was taken in spring 2009 with the foundation of the Peter Grünberg Centre as a central platform for basic research in the field of nanoelectronics in the region. JARA-FIT will be among the best research institutions worldwide in the field of information technology. Interview Frank Frick
Prof. Markus Morgenstern (left) and Prof. Detlev Grützmacher, directors of the “FIT” section of the Jülich-Aachen Research Alliance (JARA).
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HIGHLIGHTS
Turbo Storage for the Computers of Tomorrow Up to now, computer memories have involved a choice between two evils: either the data are written and read slowly or the information is lost once the device is switched off. Researchers at Jülich want to change this.
Dr. Carsten Kügeler holds a disc with turbo storage.
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A look through the microscope at a disc on which two conductors (yellow) are selectively contacted with two measuring needles (black). The tiny area in the middle of the merging radial conductors is where a novel storage element with 256 resistance channels is located.
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ven the most placid of people have been known to lose their patience: all you want to do is have a quick look at your emails from home or order a cinema ticket online, and booting your computer alone takes what feels like an eternity. The reason for this is DRAM (dynamic random access memory), a main memory module in computers. As the information stored here as electric charges volatilized the last time the PC was turned off, the operating system and all other programmes that are in constant use have to be reloaded before the computer can be used. Even when the computer is up and running, DRAM must be reloaded every 60 milliseconds. Data stored on the PC hard drive, in contrast, are permanently available. Here, they are stored in tiny oriented magnetic domains. However, hard drives also have a disadvantage: they are comparatively slow. Their read and write times amount to thousandths of a second, while DRAMs are ready for use within billionths of a second.
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Resistance wanted “My notebook takes a couple of minutes to boot at the moment,” says Dr. Carsten Kügeler. What causes despair among others is additional motivation for him. The reason? He is one of the scientists from the Institute of Solid State Research at Jülich who are working on a completely new type of storage technique under Prof. Rainer Waser. “The basic principle of our resistive storage is switching the electrical resistance of a material back and forth between a low and a high value,” he explains. Both of these resistance values are then assigned to the two basic elements in all computer languages – namely “zero” and “one”. Resistive storage will combine the advantages of hard drives with those of DRAM. The scientists are convinced that it will allow information to be stored without any connected mains voltage just like on a hard drive and simultaneously enable information to be written and read just as quickly as with DRAM. As if that
weren’t enough, the new storage elements also require very little space on the computer chip. “This space requirement is what counts. This causes costs to skyrocket – or indeed to nose dive,” says Kügeler. A number of groups of scientists from the Institute of Solid State Research are working hand in hand in an effort to realize this ambitious goal. The teams headed by Prof. Kristof Szot and Dr. Regina Dittmann are pursuing research on the basic physicochemical principles of resistive storage. Kügeler’s group is working on adapting the storage concept for integration into existing computer technology. And among other things, chemist Dr. Rainer Bruchhaus keeps the needs of industry firmly in sight having recently come to Forschungszentrum Jülich from industry. The first results of this pooling of expertise are excellent. The researchers have proven, for example, that conductive channels are formed in strontium titanate and titanium dioxide – materials
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HIGHLIGHTS
Dr. Regina Dittmann conducts research on the basic physicochemical principles of resistance channels, which may be used as tiny basic elements in memories.
that are being studied intensively for use as resistive storage elements – and that their electrical resistance increases rapidly when a certain threshold voltage is applied. The new higher resistance values remain intact when the voltage is turned off. Only when a corresponding high countervoltage is applied do the channels return to their original low resistance values. This behaviour makes the channels perfect for use as tiny basic elements in memories. No fundamental obstacles “The channels have a diameter of just a few nanometres, in other words a few millionths of a millimetre. We can therefore go right down to this order of magnitude when designing the smallest structural storage unit,” says Regina Dittmann. However, the size of Kügeler’s basic units, which are used to integrate the resistance channels into the computer periphery, are still much larger than this – namely between 50 and 100 nanometres. But the researchers are optimistic that
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there are no fundamental obstacles preventing further miniaturization. If they reach a magnitude of 10 nanometres, they will have achieved the objective they set themselves from the start: reducing the space requirements of resistive storage elements by a factor of 1000 compared to today’s conventional storage elements. While a base unit in DRAM comprises a condenser, the actual storage element, and a transistor, Kügeler’s base units require nothing other than a resistance channel and electrodes in order to create a link to the “outer world”. Even in the case of the space-hungry electrodes, the scientists have managed to make significant cuts. Their laboratory prototype comprises 4096 resistance channels, which are arranged in a square with an edge length of 64 channels. Instead of connecting each resistance channel separately to an incoming and an outgoing electrode, the scientists have covered the top outlets of a row of 64 channels with a bar-like vertical electrode. They
This crossbar structure (large image) contains 4096 storage channels but only measures around a hundredth of a milli metre. Each channel is connected at the top to a horizontal electrode (white in the small image) and at the bottom to a vertical electrode (grey); (see also the graphic on the next page).
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have done something similar with the bottom ends of the resistance channels – with a slight difference: the bottom bar electrodes run perpendicular to the top ones. In this way, a crossbar structure is created (see figure) for which only 128 electrodes (64 plus 64) are required. In contrast, 8192 electrodes (2 x 64 x 64) would be needed if each resistance channel was to be coupled separately with an incoming and an outgoing electrode. In spite of this, the crossbar structure also allows a certain number of specific resistance channels to be controlled by applying a voltage to a particular combination of vertical and horizontal electrodes. The system is similar to that used to identify a certain field on a chess board by its row and column number. However, every electronics enthusiast knows that it’s not always that easy in practice. On each electrode, there are also other resistance channels, which are therefore then also live. This gives rise to unwanted parasitic currents. “The strength and appearance of these currents depends on which of the individual resistance channels is switched to zero or one, respectively, at that time,” explains Kügeler. The scientists try to get around this problem by carefully choosing the voltage level so as to minimize the parasitic currents. This is not the only problem area that Kügeler’s team are still working on. In the past, the information that was stored in the resistance channels remained saved for around a day. This is actually 20,000 times longer than the storage period in DRAM. “But we still have to improve this by a few orders of magnitude,” admits Kügeler. At the same
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Each storage channel (red) is connected to the crossbars both at the top and the bottom via an electrode bar. By applying voltage to one of the top and one of the bottom bars, each individual channel can be selectively controlled.
time, the researchers are trying to increase the difference between the two resistance values represented by zero and one, respectively, in order to improve the reliability of the resistive storage process. Understanding what happens Parallel to Kügeler’s research, Regina Dittmann’s team is working on understanding what happens in the resistance channels when they suddenly change their resistance value. “We assume that oxygen ions are moved back and forth when threshold voltages are applied,” says Dittmann. “This allows the material to be switched back and forth from a conducting to an insulating state.” The researcher’s latest findings imply that this theory is indeed correct. While in earlier experiments, the resistance channels lost their switching ability after a certain number of storage cycles, this ability remained unaffected when the scientists attached an oxidizable electrode to the surface of the material. Dittmann: “This indicates that the material loses its oxygen ions when this electrode is not
there. The oxide layer on the electrode interface temporarily absorbs the oxygen and then releases it back into the material during the next switching process.” In this way, explains the physicist, the storage ability of the channels remains intact. The Jülich researchers, who are working closely together with other groups from RWTH Aachen University as part of the Jülich-Aachen Research Alliance (JARA), agree that it will still take some time before resistive storage is ready for the market. “When we successfully demonstrate the basic functionality of the crossbar, then our work here in Jülich is done,” says Rainer Bruchhaus. Dittmann’s and Kügeler’s colleague continues: “Turning the storage concept into a market able product is no longer basic research; this is a task for industry.” Companies such as Intel are already collaborating with the Jülich researchers today. This is a good sign for these new storage concepts. Industry obviously believes them to have good prospects for the future. Axel Tillemans
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HIGHLIGHTS
The Universal Tool On the search for future energy-efficient information technology, scientists at Jülich create and explore nanoscale components for spintronics. In their quest, they turn to the “Swiss Army knife” among the tools of research: the globally unique “Nano-Spintronics Cluster Tool”.
of electrons be produced with just one type of spin? How can the orientation of the spin be manipulated, and how can the orientation of the spin be read out? In order to effectively find answers to these questions, Jülich scientists have designed an instrument that combines multiple functions in one machine: the “NanoSpintronics Cluster Tool”.
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n 2007, information and communi cations technologies accounted for around 10 % of the total electricity consumption in Germany. Dr. Daniel Bürgler from the Jülich Institute of Solid State Research explains the global implications of this. “The economic growth of the threshold countries will also cause the global energy requirements for computers to rise rapidly if computers are not made more energy efficient.” However, the conservation of resources and climate protection are not the only reasons for developing less demanding processors: high energy consumption creates so much heat that it simply gets too hot for the sensitive electronics housed in computer cases. One solution could be spintronics – electronic components that exploit the spin of electrons for information processing. However, a number of key questions have yet to be answered. How can a flow
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From one station to the next In an ultrahigh vacuum that protects samples from dust and the highly reactive oxygen in the air, the scientists first fabricate very thin layers using molecular beam epitaxy. An electron beam evaporates the respective starting material. This allows a sample to be constructed atomic layer by atomic layer. In this part of the Nano-Spintronics Cluster Tool, the journey also begins towards creating a component referred to by Jülich physicist Julius Mennig as a “spin valve” because it spatially separates electrons with different spins. The Jülich PhD student first produces a basic structure out of non-magnetic conducting copper. Later, layers of magnetic cobalt are applied to specific strategic areas. Without taking the sample out of the protective vacuum, Mennig can push it into the next station of the universal tool. Here, he uses a photoemission
spectrometer and electron diffraction to verify whether the layers are clean and free of defects. Every dust particle, any contact with oxygen or any other contaminating substance would mean the end of the process at this stage. Once again, without having to take the sample out of the machine – thus saving time and keeping the sample shielded – the journey continues to an extremely precise cutting tool. Mennig’s valve now Recognizable only under an electron microscope: the “spin valve” of a few micrometres in size. The non-magnetic conducting copper structures gleam brightly. The two vertical magnetic cobalt pins appear somewhat darker in the image.
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Viewing windows allow a glimpse into the inside of the Nano-Spintronics Cluster Tool (left) – and also, for example, into the silver sample carousel with space for up to six samples (below).
takes on a concrete shape. Using an ion beam with a cutting width of only eight nanometres, the physicist shapes two bars of magnetic cobalt of his minute component. The physicist visually examines the result under the scanning electron microscope, which is also part of the universal tool. “The tool also has a scanning tunnelling microscope in another station, which is required just as often for analyses,” explains Daniel Bürgler. The final test reveals whether the spin valve functions as desired. Still in the universal tool, Mennig sends an electric current through one of the cobalt bars with the aid of tiny spring contacts. In the magnetized bars, left-handed electrons with a spin that is parallel to the magnetism of the bar should advance faster than electrons with an opposing spin. The reason for this assumption is that the cobalt atoms already contain the maximum number of left-handed electrons. There is no room for any more in the atoms. A left-handed electron should therefore pass through the cobalt bar almost undisturbed. On the other hand, the cobalt atoms offer right-handed electrons, whose spin is oriented in the opposite
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Tradition and the Future: Spintronics in Jülich The scientists Daniel Bürgler and Julius Mennig work in the same institute as the Nobel Laureate Prof. Peter Grünberg who revolutionized data storage on hard drives around 20 years ago with the discovery of giant magnetoresistance. Grünberg’s research laid the foundation for spintronics as a technology of the future. Today, scientists working under Prof. Claus Michael Schneider in the area of “electronic properties” are seeking to gain better control of spin currents and use them for data processing in energy-efficient computer components.
irection to the magnetization, numerous d free energy states, which hypothetically function like small traps. What percentage of electrons with the same spin actually ends up in the copper at the end of the bar can be detected by Mennig with the second magnetic bar. Although no electric current flows through this bar, it is possible to measure the electric voltage caused by the electrochemical potential of the electrons separated according to spin. Spin valve works “We succeeded in conclusively showing that the valve works,” says Mennig
with enthusiasm. However, he doesn’t want to mention any numbers yet. “The whole thing is much more complex than it sounds,” he admits. “The bars, which are only 200 nanometres away from each other, sometimes influence each other’s magnetic orientation – and this makes it more difficult to control the direction of the spin.” Despite this, the spintronics researchers are confident that they will be able to quickly overcome this problem with the aid of their universal tool and thus provide the impetus for information technology in the future. Brigitte Stahl-Busse
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HIGHLIGHTS
The Fermi surface of copper, where the colours make the curvature clearer. Where the Fermi surface is particularly flat (red), the electrons travel particularly fast through the solid. The Fermi surfaces provide, so to speak, the profile of a metal or a semiconductor.
Nanosonar Sonar sends out sound waves which are used to explore the depths of the ocean. As Jülich scientists discovered, a similar principle allows the flow of electrons in a scanning tunnelling microscope to be used to investigate the hidden properties of the atomic lattice of metals.
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mportant discoveries are often the work of researchers who dedicate themselves to studying phenomena that others have left by the wayside. “When using scanning tunnelling microscopes to investigate the surfaces of solids, a whole range of scientists have noticed spherical patterns,” says Dr. Samir Lounis. The theoretical physicist
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at the Jülich Institute of Solid State Research continues: “It is a well-known fact that foreign atoms inside the mate rial being studied can cause these rings.” However, in contrast to other scientists, Lounis and his colleagues Prof. Stefan Blügel and Prof. Peter Dederichs did not just see an annoying interference caused by impurities but a source of information on the internal structure of crystals. Decisive information was provided by scientists from Göttingen, who conducted new experiments.
Informative waves In order to understand the deliberations of the Jülich scientists, it is important to know the following: a scanning tunnelling microscope images a surface by tracing this surface with a tip. During this process, electrons tunnel from the tip to the surface. These electrons spread out like waves in the solid, following the laws of quantum mechanics. Like waves in water, they are scattered when they hit an obstacle or they are reflected and partially thrown back up to the surface. The
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reflected electron waves therefore contain information on the inside of a solid – similar to the reflected sound waves emitted by sonar, which provide information on the nature of the seabed. But what do these patterns actually look like? For example, what patterns are generated on the surface of copper by a cobalt atom embedded within the copper? The Jülich scientists quickly realized where they should look for the answer: in what are known as Fermi surfaces. “These constructions, which are not located in normal space but rather in a mathematically derived space, determine the electronic, magnetic, optical and thermal properties of metals and semiconductors. They therefore provide a sort of profile for a material,” says Stefan Blügel. The Fermi surfaces of a copper atom also determine how electrons – or to be more exact the electron waves – spread out in copper. “The electrons travel along certain roads, the direction and size of which are determined by the Fermi surfaces,” explains Lounis. “On some of these roads, the electrons travel at top speed, like cars on a motorway, while on others, they crawl along as if they were travelling on a dirt track.” The researchers therefore faced the task of using the known Fermi surfaces for copper in order to work out the “road map” for copper containing a deep impurity in the form of a cobalt atom. Although the physicists limited themselves to a piece of copper measuring only a few millionths of a millimetre, they still required the concentrated power of the Jülich supercomputer JUMP for the complex quantum physics calculations.
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The result: for the most part, “dirt tracks” run from the foreign atom. However, the electrons travelled at speed in some directions – as if they were on a motorway. In areas where the “motorways” penetrated the copper surface, patterns were visible. However, the calculations made by the Jülich physicists did not yield circles; they yielded rounded triangles that closely resembled rings. The very same triangles were also found by scientists in Göttingen who conducted high-precision experiments with copper samples doped with cobalt atoms.
mation. “This would make all other storage techniques look antiquated in comparison,” says Lounis with conviction. Axel Tillemans
Top: Rings recorded by the scanning tunnelling microscope that appear due to foreign atoms under the surface. Only when the image is very precisely analysed does it become clear that these structures are actually round triangles. Bottom: Computer simulation of the structures.
Pioneering results The Fermi surfaces are very well known for pure materials, such as copper. This is different in the case of alloys, which can be composed of all sorts of combinations of single chemical elements. “Our results point the way towards a technique that can be used to determine at least parts of these previously unknown Fermi surfaces,” Lounis is happy to report. The scanning tunnelling microscope studies of a surface can also be used to determine the exact position of a foreign atom in the depths of a metal. Lounis is certainly not short of ideas for further possible applications of the new theoretical information: “In the future, we could perhaps save information in atoms that are located deep below the surface.” To do so, electrons could be sent along “motorways” with a scanning tunnelling microscope leading directly to the corresponding atom in order to reverse the spin of one of its electrons. As the spin can assume two states (“up” and “down”), it is suitable for storing infor
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HIGHLIGHTS
Tricks for Faster Transistors Jülich researchers have developed methods that allow the crystal lattice of silicon to be expanded. This strained silicon can then be used to fabricate transistors for computer chips that work much faster than the conventional technology.
trick can speed up this flow of charge. If the crystal lattice of the silicon is strained, the charge carriers will move faster.
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n a square centimetre of today’s computer processors, up to two billion tiny on and off switches – transistors – fight for space. Making them even smaller is one way of making computers even faster in the future. However, there is one other option. In the silicon structure of a transistor, the charge carriers flow from A to B. A simple
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Germanium as a stretching aid The team headed by Prof. Siegfried Mantl at the Jülich Institute of Bio- and Nanosystems stretches the crystal lattice using a trick. The scientists exploit the natural difference in the crystal structure of silicon and germanium. The atoms in both materials are ordered in the same way but the interval at which they occur is 4.2% greater in germanium than in silicon. If a thin layer of silicon measuring around ten nanometres is grown on a pure germanium layer with a thickness of some hundred nanometres, the crystal lattice of the thinner layer adapts in line with the thicker layer. The result: the crystal lattice of silicon is stretched in planes parallel to the surface by a few percent. By using different germaniumsilicon alloys in the thick layer instead of pure germanium, the researchers can even set different strains in the thin layer. “Our objective is to achieve as even and defect-free a strained silicon layer as possible over a very large area,” says Dr. Bernhard Holländer who works with
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Mantl. The German Federal Ministry of Education and Research is funding the project with a total of € 8.1 million. A further € 6.4 is being provided by the collaborative partners Globalfoundries Dresden, Siltronic AG, Aixtron AG, Forschungszentrum Jülich and the Max Planck Institute of Microstructure Physics. The silicon wafers used in industry as substrates for circuits and transistors typically have a diameter of 300 milli metres. The Jülich researchers have ascertained that a 1% expansion of the crystal structure would be optimal at such magnitudes. The wafers do not bend and the transistors are 20 to 30% faster on average than conventional components. Getting to the point A somewhat different approach is followed by the team headed by Prof. Detlev Grützmacher, director of the Jülich Institute of Bio- and Nanosystems. He works
closely with Europe’s largest semiconductor manufacturer STMicroelectronics and concentrates on wafers on which islets of strained silicon are distributed like a host of tiny dots. To fabricate such wafers, the scientists first etch millions of holes in the wafers at regular intervals, each of which is between four and eight nanometres deep. They then deposit pure germanium on the wafer. Capillary action causes the germanium to collect in these holes and little domed islets are formed. The researchers then deposit a layer of silicon over the surface of the wafer as though covering it with a thin cloth. Wherever a germanium islet is covered by the “cloth”, there is a local bulge in the silicon layer. When the Jülich scientists remove the germanium again in another step, they are left with both highly conductive as well as highly insulating silicon bridges. “We have already used these wafers to fabricate transistors that are 15 to 30% faster than components that are not strained,” reports Grützmacher enthusiastically. Whether sheet-like or dotted strained silicon will come out on top in the end is hard to say today. “We have made sure that both methods create a transistor
Capillary action ensures that the germanium islets appear homogeneous and well ordered. The strong magnification shown in the top right-hand corner clearly shows how homogeneous the islets actually are.
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On the far right of the above image, a present-day 300-millimetre wafer is shown. On the far left, a silicon wafer with a diameter of 100 millimetres is pictured, representing the industrial standard around 30 years ago.
that is compatible with today’s production techniques,” emphasizes Grützmacher. Production conditions are indeed very demanding in the semiconductor industry. Huge importance is laid on perfect structures and layers, dust-free systems and products, and automation. After all, a company must be able to guarantee that all two billion transistors in a processor will run without any problems. In order to work at industry level, Jülich scientists have access to a clean room, four coating units and a new wafer cleaning system for 300-mm wafers. The equipment and know-how of scientists who have worked in industry guarantee the fabrication of structures and interfaces with an extremely high degree of purity and perfection. Detlev Grützmacher and Siegfried Mantl are convinced that the silicon era in information technology is only just beginning: “Before new technologies can be realized, the future will first belong to new material combinations that will all have one thing in common: silicon,” says Mantl. Brigitte Stahl-Busse
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Unique Insight into the World of Atoms With the electron microscopes at the Ernst Ruska Centre (ER-C), nanoelectronic materials can be studied – atom position by atom position. The supermicroscope known as PICO will move to ER-C in 2010. It measures atomic displacements with an accuracy of one picometre or a billionth of a millimetre. And that’s a world record!
Ernst Ruska Centre (ER-C) ER-C was founded in 2004 as a joint platform of excellence by Forschungszentrum Jülich and RWTH Aachen University. It functions as a national user centre for atomicresolution electron microscopy and spectroscopy. Today, ER-C is the top institution internationally in this field. It is operated under the auspices of the Jülich-Aachen Research Alliance (JARA) and its premises are on the Jülich campus. ER-C receives grants from the German Research Foundation (DFG) as well as the federal government and the federal state. Half of the centre’s measuring time is allocated to researchers from universities and industry both in Germany and abroad.
car keys, this question can meanwhile be answered very precisely. And not just with abstract words. Thanks to scientists at the Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons (see info box), this can be done in such a way that changes in the atomic lattice of the storage material are made visible in an image, thus making them easy to see for everyone.
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he numerical sequence 1000001 1000010 1000011 represents the letters “ABC” – at least according to the widely used American Standard Code for Information Interchange, also known as ASCII code. In actual fact, all types of information can be expressed as a sequence of zeros and ones. But how are the two states “zero” and “one” written to electronic storage material and permanently stored? In the case of electronic storage, which we come across everyday for example in smart cards and electronic
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20 picometres make the difference Ferroelectric materials are permanently electrically polarized: in contrast to most chemical compounds, the centre of the positive and negative charge does not coincide on an atomic level – even when there is no external electric field. The reason for this polarization in oxidic ferroelectrics is that the negatively charged oxygen ions in the crystal lattice are not located exactly in the middle of two positively charged metal ions. Such materials are suitable for use as storage media because the direction of their polarization can be reversed with an applied external electric field. This switching always occurs in very small zones known as domains in technical jargon. Domains with a polarization in one direction therefore correspond to the state “zero”, while domains polarized in the opposite direction have the state “one”.
Every bit of information can be expressed as a sequence of the states “zero” and “one”. This electron micrograph shows how the position of oxygen ions in a material changes when information is written to the material.
“In our electron micrographs, we can see for the first time how the oxygen ions change their position in the crystal lattice when information is written to the material with the aid of an external electric
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field,” says Prof. Knut Urban, one of the two directors of ER-C. The oxygen ions are very slightly displaced by around 20 picometres (1 picometre is equal to a billionth of a millimetre, which corresponds to less than a hundredth of an atomic diameter). “Even just a few years ago, nobody would have believed that such displacements could be measured with the precision of a few picometres,” says Urban. Working together with researchers from Darmstadt and Heidelberg, the Jülich physicists successfully developed an electromagnetic correction element in
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the 1990s, which is used to correct strong aberrations in the objective lenses of electron microscopes in much the same way as glasses. Up to this point in time, these optical aberrations had greatly restricted the attainable sharpness and resolution of electron microscopes. The next step Equipped with such correctors, commercial electron microscopes are now capable of resolving atomic structures. In the complex task of adjusting the correctors, measuring techniques and compu-
ter programmes from Jülich, which have been licensed by the electron-optical industry, are used. “Despite this, the technical effort and the know-how required to generate such images are immense, and the requirements to be observed in fabricating preparations with a thickness of only a few atomic layers are stringent,” says Prof. Joachim Mayer, the second director of ER-C. The physicist from RWTH Aachen University continues: “The necessary performance of instruments and personnel can only be achieved if universities and non-university research institutions combine their efforts in a joint facility like ER-C.” The next step towards maintaining their position among the world leaders in electron microscopy has already been made: at the end of 2009, the first cut of the spade was made for an extension to ER-C. The extension will house the new supermicroscope PICO with a resolution that is almost double that of currently available instruments. At the same time, PICO will increase the precision with which scientists can measure atomic distances and atomic displacements from five picometres to a single picometre. “This will bring us to the physical limits of optics,” says Urban. However, this is not an end in itself, emphasizes Urban. “In order to be able to control and optimize the components in nanoelectronics and nanotechnology, we must be able to analyse them in the picometre range.” Frank Frick
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News
all about information technology
Ultracold Model
In the journal Science, researchers from Mainz, Cologne and Jülich reported on a new model system composed of ultracold atoms that can be used to study the behaviour of electrons in a solid. In this system, the atoms are trapped in an optical lattice created by superimposing a number of laser beams. Supported by simulations at the Jülich Supercomputing Centre, the scientists were able to use this experimental procedure to explain a spectacular phenomenon whereby a metal abruptly loses its conductivity when the interaction between electrons becomes too strong.
Decoded Structures
In 2010, work will begin in Jülich on the construction of the Helmholtz Nanoelectronic Facility (HNF), a state-of-the-art research and development facility in the field of nanoelectronics. The plans include clean rooms that are up to 10,000 times cleaner than operating theatres in hospitals. They will be equipped with instruments – including an epitaxy and nanofabrication cluster – that will make HNF a unique facility in Europe. The cluster comprises a continuous production facility measuring six metres by fifteen, which will be used initially to fabricate artificial crystal structures and subsequently to produce circuits on a nanoscale.
A German-Japanese research team with the major involvement of Jülich scientists succeeded in conclusively clarifying the long contested structure of a material that is used in DVDs and other optical data storage media. This material can be switched between two different states: a regular crystalline state and a more irregular “amorphous” state. We now know why this switching occurs on an atomic level, and can begin looking for better storage materials. The structure was decoded thanks to techniques such as simulations on the Jülich supercomputer known as JUGENE.
New Platform
At the beginning of 2009, the central platform for basic research in the field of nanoelectronics in the Jülich-Aachen region came into being: the Peter Grünberg Centre. Forschungs zentrum Jülich named the centre in honour of its Nobel Laureate, physicist Prof. Peter Grünberg. The research centre is rooted in the cooperation with RWTH Aachen University, namely the Jülich-Aachen Research Alliance (JARA). It is the first institution in the field of nanoelectronics throughout Germany that is also open to external users.
Cold Storage Scientists from Jülich and Slovenia have demonstrated that digital data can also be recorded without an electric or magnetic field. They saved one byte of information in structurally complex solids in which the atomic magnetic moments were unable to assume a ground state. To achieve this, they continuously cooled the samples right down to very low temperatures, taking defined breaks in between, during which they kept the temperature constant. This created a characteristic readable arrangement of magnetic moments in the solid. A patent application has been filed for the new storage principle, which could prove extremely useful in very different fields: in secure data transfer for example or the analysis of dust from space.
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State-of-the-Art Clean Room Centre
Research in Jülich 1 | 2010
Ultrafast Measurements Researchers from Jülich, Kaiserslautern and the USA have developed a new method to track ultrafast magnetic processes that are decisive for the write speed of future magnetic data storage media. The basis for the method is a femtosecond laser whose flashes of light are directed into the noble gas neon. This creates weak X-ray pulses, which are only around ten femtoseconds (ten quadrillionths of a second) long. If they hit a sample, the resulting diffraction patterns can be used to derive conclu-
sions on their properties. The advantages of the method, which does not require a large-scale facility, include extremely fine temporal resolution and a spatial resolution in the nanometre range.
PUBLICATION DETAILS Research in Jülich Magazine of Forschungszentrum Jülich, ISSN 1433-8514 Published by: Forschungszentrum Jülich GmbH | 52425 Jülich | Germany Conception and editorial work: Dr. Frank Frick, Dr. Anne Rother (responsible according to German press law), Kosta Schinarakis Authors: Dr. Wiebke Rögener, Dr. Frank Frick, Dr. Axel Tillemans, Brigitte Stahl-Busse Design and Layout: Graphical Media, Forschungszentrum Jülich Translation: Language Services, Forschungszentrum Jülich Photos: Forschungszentrum Jülich (cover illustration, pp. 2 – 4, pp. 7 – 15, p. 16 bottom left, pp. 18/19, pp. 22 – 27, p. 28 top, p. 29, p. 30 bottom, p. 31 bottom, p. 33, p. 34 top right, p. 35 top left), Hermes Verbund (p. 6 top left), Fotolia (p. 6 top right, p. 16 top, p. 28 middle, p. 34 bottom), Mauritius (p. 20, p. 35 bottom), AMD (p. 30 top), Siltronic (p. 31 top), FEI Company (p. 32), RWTH Aachen (p. 17 bottom), Martin Lux (p. 21), Max-Planck Institute for Quantum Optics (p. 34 top left) Contact: Corporate Communications | Telephone +49 2461 61 - 4661 | Fax +49 2461 61 -4666 | info@fz-juelich.de Printed by: Schloemer und Partner GmbH Print run: 2,500
1 | 2010 Research in Jülich
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