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Professor Young Jae Jang Receives the Grant Award from Mathworks
Professor Young Jae Jang of KAIST’s Industrial and Systems Engineering Department won the Grant Award from Mathworks, Inc., an American developer of mathematical computing software. Headquartered in Massachusetts in the United States, Mathworks has been known for its MATLAB software that is used by many engineers and scientists around the world for algorithm development, data analysis, visualization, and numeric computation.
Winners of the Grant Award are selected from proposals submitted by educational institutions in 18 different countries based on their innovative lab curricula and future potential for innovation and creativity.
Award winners receive a cash grant of up to USD 40,000 as well as various other forms of support including software and technical guidance for creating a course.
Professor Jang has researched combining the concept of industrial engineering education with Lego principles since 2014. He developed Lego-based experimental equipment and utilized it to teach students about difficult ideas, for example, big data and manufacturing technologies needed for Industry 4.0, such as automation, cyber-physical systems, the Internet of Things, and cloud computing. He created an innovative teaching environment where students learn engineering concepts and then conduct experiments on their own to understand the new paradigm of industrial systems.
Lego-based education allows students to personalize their learning process, shifting lecture-centered approaches toward learner-oriented approaches. Students apply theories to operate tools and equipment made with Lego, identify problems, and find solutions. In such processes, they can understand the content of their study more easily and efficiently and become more motivated.
Professor Jang’s research has attracted a great deal of interest overseas, and he is frequently invited to international conferences as a keynote speaker.
Picture: Lego-based Learning Model of Experiment Equipment Developed by Professor Young Jae Jang
2016.12.08 View 6143 -
Professor Kwon to Represent the Asia-Pacific Region of the IEEE RAS
Professor Dong-Soon Kwon of the Mechanical Engineering Department at KAIST has been reappointed to the Administrative Committee of the Institute of Electrical and Electronics Engineers (IEEE) Robotics and Automation Society (IEEE RAS). Beginning January 1, 2017, he will serve his second three-year term, which will end in 2019. In 2014, he was the first Korean appointed to the committee, representing the Asia-Pacific community of the IEEE Society.
Professor Kwon said, “I feel thankful but, at the same time, it is a great responsibility to serve the Asian research community within the Society. I hope I can contribute to the development of robotics engineering in the region and in Korea as well.”
Consisted of 18 elected members, the administrative committee manages the major activities of IEEE RAS including hosting its annual flagship meeting, the International Conference on Robotics and Automation.
The IEEE RAS fosters the advancement in the theory and practice of robotics and automation engineering and facilitates the exchange of scientific and technological knowledge that supports the maintenance of high professional standards among its members.
2016.12.06 View 8068 -
Mystery of Biological Plastic Synthesis Machinery Unveiled
Plastics and other polymers are used every day. These polymers are mostly made from fossil resources by refining petrochemicals. On the other hand, many microorganisms naturally synthesize polyesters known as polyhydroxyalkanoates (PHAs) as distinct granules inside cells.
PHAs are a family of microbial polyesters that have attracted much attention as biodegradable and biocompatible plastics and elastomers that can substitute petrochemical counterparts. There have been numerous papers and patents on gene cloning and metabolic engineering of PHA biosynthetic machineries, biochemical studies, and production of PHAs; simple Google search with “polyhydroxyalkanoates” yielded returns of 223,000 document pages. PHAs have always been considered amazing examples of biological polymer synthesis. It is astounding to see PHAs of 500 kDa to sometimes as high as 10,000 kDa can be synthesized in vivo by PHA synthase, the key polymerizing enzyme in PHA biosynthesis. They have attracted great interest in determining the crystal structure of PHA synthase over the last 30 years, but unfortunately without success. Thus, the characteristics and molecular mechanisms of PHA synthase were under a dark veil.
In two papers published back-to-back in Biotechnology Journal online on November 30, 2016, a Korean research team led by Professor Kyung-Jin Kim at Kyungpook National University and Distinguished Professor Sang Yup Lee at the Korea Advanced Institute of Science and Technology (KAIST) described the crystal structure of PHA synthase from Ralstonia eutropha, the best studied bacterium for PHA production, and reported the structural basis for the detailed molecular mechanisms of PHA biosynthesis. The crystal structure has been deposited to Protein Data Bank in February 2016. After deciphering the crystal structure of the catalytic domain of PHA synthase, in addition to other structural studies on whole enzyme and related proteins, the research team also performed experiments to elucidate the mechanisms of the enzyme reaction, validating detailed structures, enzyme engineering, and also N-terminal domain studies among others.
Through several biochemical studies based on crystal structure, the authors show that PHA synthase exists as a dimer and is divided into two distinct domains, the N-terminal domain (RePhaC1ND) and the C-terminal domain (RePhaC1CD). The RePhaC1CD catalyzes the polymerization reaction via a non-processive ping-pong mechanism using a Cys-His-Asp catalytic triad. The two catalytic sites of the RePhaC1CD dimer are positioned 33.4 Å apart, suggesting that the polymerization reaction occurs independently at each site. This study also presents the structure-based mechanisms for substrate specificities of various PHA synthases from different classes.
Professor Sang Yup Lee, who has worked on this topic for more than 20 years, said,
“The results and information presented in these two papers have long been awaited not only in the PHA community, but also metabolic engineering, bacteriology/microbiology, and in general biological sciences communities. The structural information on PHA synthase together with the recently deciphered reaction mechanisms will be valuable for understanding the detailed mechanisms of biosynthesizing this important energy/redox storage material, and also for the rational engineering of PHA synthases to produce designer bioplastics from various monomers more efficiently.”
Indeed, these two papers published in Biotechnology Journal finally reveal the 30-year mystery of machinery of biological polyester synthesis, and will serve as the essential compass in creating designer and more efficient bioplastic machineries.
References:
Jieun Kim, Yeo-Jin Kim, So Young Choi, Sang Yup Lee and Kyung-Jin Kim. “Crystal structure of Ralstonia eutropha polyhydroxyalkanoate synthase C-terminal domain and reaction mechanisms” Biotechnology Journal DOI: 10.1002/biot.201600648
http://onlinelibrary.wiley.com/doi/10.1002/biot.201600648/abstract
Yeo-Jin Kim, So Young Choi, Jieun Kim, Kyeong Sik Jin, Sang Yup Lee and Kyung-Jin Kim. “Structure and function of the N-terminal domain of Ralstonia eutropha polyhydroxyalkanoate synthase, and the proposed structure and mechanisms of the whole enzyme” Biotechnology Journal DOI: 10.1002/biot.201600649
http://onlinelibrary.wiley.com/doi/10.1002/biot.201600649/abstract
2016.12.02 View 9053 -
Making Graphene Using Laser-induced Phase Separation
IBS & KAIST researchers clarify how laser annealing technology can lead to the production of ultrathin nanomaterials
All our smart phones have shiny flat AMOLED (active-matrix organic light-emitting diode) displays. Behind each single pixel of these displays hides at least two silicon transistors which are mass-manufactured using laser annealing technology. While the traditional methods to make the transistors use temperature above 1,000°C, the laser technique reaches the same results at low temperatures even on plastic substrates (melting temperature below 300°C). Interestingly, a similar procedure can be used to generate crystals of graphene. Graphene is a strong and thin nano-material made of carbon, its electric and heat-conductive properties have attracted the attention of scientists worldwide.
Professor Keon Jae Lee of the Materials Science and Engineering Department at KAIST and his research group at the Center for Multidimensional Carbon Materials within the Institute for Basic Science (IBS), as well as Professor Sung-Yool Choi of the Electrical Engineering School at KAIST and his research team discovered graphene synthesis mechanism using laser-induced solid-state phase separation of single-crystal silicon carbide (SiC). This study, available in Nature Communications, clarifies how this laser technology can separate a complex compound (SiC) into its ultrathin elements of carbon and silicon.
Although several fundamental studies presented the effect of excimer lasers in transforming elemental materials like silicon, the laser interaction with more complex compounds like SiC has rarely been studied due to the complexity of compound phase transition and ultra-short processing time.
With high resolution microscope images and molecular dynamic simulations, scientists found that a single-pulse irradiation of xenon chloride excimer laser of 30 nanoseconds melts SiC, leading to the separation of a liquid SiC layer, a disordered carbon layer with graphitic domains (about 2.5 nm thick) on top surface and a polycrystalline silicon layer (about 5 nm) below carbon layer. Giving additional pulses causes the sublimation of the separated silicon, while the disordered carbon layer is transformed into a multilayer graphene.
"This research shows that the laser material interaction technology can be a powerful tool for the next generation of two dimensional nanomaterials," said Professor Lee.
Professor Choi added: "Using laser-induced phase separation of complex compounds, new types of two dimensional materials can be synthesized in the future."
High-resolution transmission electron microscopy shows that after just one laser pulse of 30 nanoseconds, the silicon carbide (SiC) substrate is melted and separates into a carbon and a silicon layer. More pulses cause the carbon layer to organize into graphene and the silicon to leave as gas.
Molecular dynamics simulates the graphene formation mechanism. The carbon layer on the top forms because the laser-induced liquid SiC (SiC (l)) is unstable.
(Press Release by Courtesy of the Institute for Basic Science (IBS))
2016.12.01 View 9995 -
KAIST's Doctoral Student Receives a Hoffman Scholarship Award
Hyo-Sun Lee, a doctoral student at the Graduate School of EEWS (Environment, Energy, Water and Sustainability), KAIST, is a recipient of the 2016 Dorothy M. and Earl S. Hoffman Scholarships presented by the American Vacuum Society (AVS). The award ceremony took place during the Society’s 63rd International Symposium and Exhibition on November 6-11, 2016 in Nashville, Tennessee.
Lee is the first Korean and foreign student to receive this scholarship.
The Hoffman Scholarships were established in 2002 to recognize and encourage excellence in graduate studies in the sciences and technologies of interest to AVS. The scholarships are funded by a bequest from Dorothy M. Hoffman, who was a pioneering member of the Society of Women Engineers and served as the president of AVS in 1974.
Lee received the scholarship for her research that detects hot electrons from chemical reactions on catalytic surface using nanodevices. Nano Letters, an academic journal published by the American Chemical Society, described her work in its February 2016 issue as a technology that allows quantitative analysis of hot electrons by employing a new nanodevice and therefore helps researchers understand better the mechanism of chemical reactions on nanocatalytic surface. She also published her work to detect the flow of hot electrons that occur on metal nanocatalytic surface during hydrogen oxidation reactions in Angewandte Chemie.
Lee said, “I am pleased to receive this honor from such a world-renowned academic society. Certainly, this will be a great support for my future study and research.”
Founded in 1953, AVS is an interdisciplinary, professional society composed of approximately 4,500 members worldwide. It supports networking among academic, industrial, government, and consulting professionals involved in a range of established and emerging science and technology areas such as chemistry, physics, engineering, business, and technology development.
2016.11.17 View 8171 -
Key Interaction between the Circadian Clock and Cancer Identified
Professor Jae Kyoung Kim and his research team from the Department of Mathematical Sciences at KAIST found that the circadian clock drives changes in circadian rhythms of p53 which functions as a tumor suppressor. Using a differential equation, he applied a model-driven mathematical approach to learn the mechanism and role of p53.
Kim’s mathematical modeling has been validated by experimental studies conducted by a research team at Virginia Polytechnic Institute and State University (Virginia Tech) in the United State, which is led by Professor Carla Finkielstein. As a result, the researchers revealed that there is an important link existed between the circadian clock and cancer.
The findings of this research were published online in Proceedings of the National Academy of Sciences of the United States of the America (PNAS) on November 9, 2016.
The circadian clock in our brain controls behavioral and physiological processes within a period of 24 hours, including making us fall asleep at a certain time by triggering the release of the sleep hormone melatonin in our brain, for example, around 9 pm. The clock is also involved in various physiological processes such as cell division, movement, and development.
Disruptions caused by the mismatch of the circadian clock and real time due to chronic late night work, shiftwork, and other similar issues may lead to various diseases such as diabetes, cancer, and heart disease.
In 2014, when Kim met with Finkielstein, her research team succeeded in observing the changes of p53 over a period of 24 hours, but could not understand how the circadian clock controls the 24-hour rhythm of p53. It was difficult to determine p53’s mechanism since its cell regulation system is far more complex than other cells
To solve the problem, Kim set up a computer simulation using mathematical modeling and ran millions of simulations. Instead of the traditional method based on trial and error experiments, mathematical modeling allowed to save a great deal of time, cost, and manpower.
During this process, Kim proved that the biorhythm of p53 and Period2, an important protein in the circadian clock, are closely related. Cells usually consist of a cell nucleus and cytoplasm. While p53 exists in both nucleus and cytoplasm, it becomes more stable and its degradation slows down when it is in the nucleus.
Kim predicted that the Period2 protein, which plays a key role in the functioning of the circadian clock, could influence the nucleus entry of the p53 protein.
Kim’s predictions based on mathematical modeling have been validated by the Virginia team, thereby revealing a strong connection between the circadian clock and cancer.
Researchers said that this research will help explain the cause of different results from numerous anticancer drugs, which are used to normalize the level of p53, when they are administrated at different times and find the most effective dosing times for the drugs.
They also believe that this study will play an important role in identifying the cause of increasing cancer rates in shift-workers whose circadian clocks are unstable and will contribute to the development of more effective treatments for cancer.
Professor Kim said, “This is an exciting thing that my research can contribute to improving the healthy lives of nurses, police officers, firefighters, and the like, who work in shifts against their circadian rhythms. Taking these findings as an opportunity, I hope to see more active interchanges of ideas between biological sciences and mathematical science in Korea.”
This research has been jointly conducted between KAIST and Virginia Tech and supported by the T. J. Park Science Fellowship of POSCO, the National Science Foundation of the United States, and the Young Researcher Program of the National Research Foundation of Korea.
Picture 1. The complex interaction between tumor antigen p53 and Period2 (Per2) which plays a major role in the circadian clock as revealed by mathematical simulations and experiments
Picture 2. A portion of the mathematical model used in the research
Picture 3. Professor Jae Kyoung Kim (third from left) and the Virginia Tech Research Team
2016.11.17 View 7012 -
Technology to Allow Non-Magnetic Materials to Have Magnetic Properties by Professor Chan-Ho Yang
Professor Chan-Ho Yang and his research team from the Department of Physics at KAIST have developed a technology that allows non-magnetic materials to have magnetic properties or, in reverse, to remove magnetic properties from a magnet using an electric field.
Based on this research, it is expected that if magnetic-material-based data storage is developed, applications for high-speed massive data transfer will be possible.
The results of this research, with Ph.D. candidate Byung-Kwon Jang as the first author, were published online in Nature Physics on October 3.
Very small magnets exist inside of any materials. If the direction of the minuscule magnets is dis-aligned, pointing multiple directions, it is non-magnetic. If the direction is aligned in a certain direction, the material holds magnetic property just like any magnet we normally see.
Data storage capacity technology has rapidly advanced to the point where we can easily get a portable hard disk drive (HDD) with terabyte-level storage; however, the increase in storage is inevitably followed by slower data access speed for a storage device. Although HDDs are currently the most widely used data storage devices, their technical applications are limited due to their slow data access speed.
Other methods such as solid-state drives (SSDs), floating gates, and resistive switching have been developed as alternatives. Yet, they leave tracks every time data is written, and this can cause fatigue cumulative damage.
There have been many attempts to compose cells—the smallest data storage space on a storage device—with magnetic materials as that would enable faster data access speeds and remove fatigue cumulative damage. Generally, the techniques tried by researchers were to use induced magnetic fields through current flow. However, magnetic fields are very difficult to shield and can affect a large area. As a result, they alternate the magnetic property of adjacent cells. Because each cell cannot be adjusted one by one, it cannot also be arranged in a certain direction, and therefore, it is hard to change the magnetic state.
Professor Yang and his team adjusted the magnetic state by using magnetoelectric interaction to deal with this issue. Instead of using magnetic fields, magnetoelectric interaction is a method that uses an electric field to adjust the magnetic state. It has the advantage of smaller energy consumption as well.
Professor Yang's team demonstrated that cells facing random directions can be arranged in a certain direction by only inducing an electric field. In addition, the reverse was also proved to be feasible.
Until this research, most cases of previous findings were only feasible at extremely low temperatures or high temperatures, but the technology developed by the research team is practicable at room temperature by manipulating chemical pressure. It allows for a reversible magnetic state, and moreover, is non-volatile. Therefore, the results of this research are expected to provide the basis for developing next-generation information storage device.
Professor Yang said, “The changes in the electric magnetic state will be accompanied by entropy changes” and added, “Our research is expected to open new potential for future applications not only for magnetoelectric devices, but also for thermoelectric effect.”
This research has been worked on jointly with Dr. Si-Yong Choi from the Korea Institute of Materials Science, Prof. Yoon-Hee Jeong from the Pohang University of Science and Technology, Dr. Tae-Yeong Koo from the Pohang Accelerator Laboratory, Dr. Kyung-Tae Ko from the Max Planck Institute for Chemical Physics of Solids, Dr. Jun-Sik Lee and Dr. Hendrik Ohldag from the SLAC National Accelerator Laboratory of the United States, and Prof. Jan Seidel from the University of New South Wales of Australia.
The research was supported by the Mid-Career Researcher Program of the National Research Foundation of Korea, Global Research Network Support Project, Leading Research Center Support Project (Condensed Quantum Coherence Research Center), Global Frontier Project (Hybrid Interface Materials Research Group), and others.
Picture: The concept graphic for the electric-field-induced magnetic phase switching the magnetic direction
2016.11.04 View 7298 -
Professor Shin's Team Receives the Best Software Defined Network Solution Showcase Award
Professor Seungwon Shin of the Electrical Engineering School at KAIST and his research team won the Best Software Defined Networking (SDN) Solution Showcase Award hosted by the SDN World Congress, one of the biggest network summits held in Europe with over 2,000 participants. This year the conference took place in The Hague, the Netherlands, October 10-14, 2016.
SDN is an approach to computer networking that allows network administrators to respond quickly to changing business requirements via a centralized control console and to support the dynamic, scalable computing and storage needs of more modern computing environments such as data centers.
Collaborating with researchers from Queen’s University in the United Kingdom and Huawei, a global information and communications technology solutions provider in China, Professor Shin’s team, which is led by doctoral students Seungsoo Lee, Changhoon Yoon, and Jaehyun Nam, implemented a SDN security project called “DELTA.” ATTORESEARCH, a Korean SDN architecture and applications provider, conducted testing and verification for the project.
DELTA is a new SDN security evaluation framework with two main functions. It can automatically recognize attack cases against SDN elements across diverse environments and can assist in identifying unknown security problems within a SDN deployment.
The DELTA project consists of a control plane, the part of a network that carries signaling traffic and is responsible for routing; a data plane, the part of a network that carries user traffic; and a control channel that connects the two aforementioned planes. These three components have their own agents installed, which are all controlled by an agent manger. The agent manger can automatically detect any spots where the network security is weak.
Specifically, the project aimes to defense attacks against OpenFlow protocol, one of the first SDN standards; SDN controllers, a network operating system that is based on protocols; and network switch devices that use OpenFlow protocol.
The DELTA project was registered with the Open Networking Foundation, a user-driven organization dedicated to the promotion and adoption of SDN through open standards development, as an open source SDN security evaluation tool. This project is the only open source SDN which has been led by Korean researchers.
The SDN World Congress 2016 recognized the need for and importance of the DELTA project by conferring upon it the Best Solution Showcase Award. The Open Networking Foundation also widely publicized this award news.
Professor Shin said:
“In recent years, SDN has been attracting a large amount of interest as an emerging technology, but there still have not many SDN projects in Korea. This award acknowledges the advancement of Korean SDN technology, showing the potential for Korea to become a leader in SDN research.”
Picture: Major Components of the DELTA Project: Agents and Agent Manger
2016.10.25 View 7720 -
2016 KAIST EEWS Workshop
The Energy, Environment, Water and Sustainability (EEWS) Graduate School of KAIST hosted a workshop entitled “Progress and Perspectives of Energy Science and Technology” on October 20, 2016. The workshop took place at the Fusion Hall of the KAIST Institute on campus.
About 400 experts in energy science and engineering participated in the event. Eight globally recognized scientists introduced the latest research trends in nanomaterials, energy theory, catalysts, and photocatalysts and led discussions on the current status and prospects of EEWS.
Professors Yi Cui of Stanford University, an expert in nanomaterials, and William A. Goddard of California Institute of Technology presented their research experiments on materials design and recent results on the direction of theory under the topics of energy and environment.
Dr. Miquel Salmeron, a former head of the Material Science Division of Lawrence Berkeley National Laboratory, and Professor Yuichi Ikuhara of Tokyo University introduced their analysis of catalysts and energy matters at an atomic scale.
Professor Sukbok Chang of the Chemistry Department at KAIST, a deputy editor of ACS Catalysis and the head of the Center for Catalytic Hydrocarbon Functionalizations at the Institute of Basic Science, and Professor Yang-Kook Sun of Energy Engineering at Hanyang University, who is also a deputy editor of ACS Energy Letters, presented their latest research results on new catalytic reaction development and energy storage.
The workshop consisted of three sections which addressed the design of energy and environment materials; analysis of energy and catalytic materials; and energy conversion and catalysts.
The EEWS Graduate School was established in 2008 with the sponsorship of the Korean government’s World Class University (WCU) project to support science education in Korea. Professor J. Fraser Stoddart, the winner of the 2016 Nobel Prize in Chemistry, was previously worked at the KAIST EEWS Graduate School as a WCU visiting professor for two years, from 2011 to 2013. Professor Ali Coskun, who was a postdoctoral researcher in the laboratory of Professor Stoddart, now teaches and conducts research as a full-time professor at the graduate school.
Dean Yousung Jung of the EEWS Graduate School said:
“This workshop has provided us with a meaningful opportunity to engage in discussions on energy science and technology with world-class scholars from all around the world. It is also a good venue for our graduate school to share with them what we have been doing in research and education.”
2016.10.20 View 10886 -
Extremely Thin and Highly Flexible Graphene-Based Thermoacoustic Speakers
A joint research team led by Professors Jung-Woo Choi and Byung Jin Cho of the School of Electrical Engineering and Professor Sang Ouk Kim of the Material Science and Engineering Department, all on the faculty of the Korea Advanced Institute of Science and Technology (KAIST), has developed a simpler way to mass-produce ultra-thin graphene thermosacoustic speakers.
Their research results were published online on August 17, 2016 in a journal called Applied Materials & Interfaces. The IEEE Spectrum, a monthly magazine published by the Institute of Electrical and Electronics Engineers, reported on the research on September 9, 2016, in an article titled, “Graphene Enables Flat Speakers for Mobile Audio Systems.” The American Chemical Society also drew attention to the team’s work in its article dated September 7, 2016, “Bringing Graphene Speakers to the Mobile Market.”
Thermoacoustic speakers generate sound waves from temperature fluctuations by rapidly heating and cooling conducting materials. Unlike conventional voice-coil speakers, thermoacoustic speakers do not rely on vibrations to produce sound, and thus do not need bulky acoustic boxes to keep complicated mechanical parts for sound production. They also generate good quality sound in all directions, enabling them to be placed on any surface including curved ones without canceling out sounds generated from opposite sides.
Based on a two-step, template-free fabrication method that involved freeze-drying a solution of graphene oxide flakes and the reduction/doping of oxidized graphene to improve electrical properties, the research team produced a N-doped, three-dimensional (3D), reduced graphene oxide aerogel (N-rGOA) with a porous macroscopic structure that permitted easy modulation for many potential applications.
Using 3D graphene aerogels, the team succeeded in fabricating an array of loudspeakers that were able to withstand over 40 W input power and that showed excellent sound pressure level (SPL), comparable to those of previously reported 2D and 3D graphene loudspeakers.
Choong Sun Kim, the lead author of the research paper and a doctoral student in the School of Electrical Engineering at KAIST, said:
“Thermoacoustic speakers have a higher efficiency when conducting materials have a smaller heat capacity. Nanomaterials such as graphene are an ideal candidate for conductors, but they require a substrate to support their extremely thinness. The substrate’s tendency to lose heat lowers the speakers’ efficiency. Here, we developed 3D graphene aerogels without a substrate by using a simple two-step process. With graphene aerogels, we have fabricated an array of loudspeakers that demonstrated stable performance. This is a practical technology that will enable mass-production of thermosacoustic speakers including on mobile platforms.”
The research paper is entitled “Application of N-Doped Three-Dimensional Reduced Graphene Oxide Aerogel to Thin Film Loudspeaker.” (DOI: 10.1021/acsami.6b03618)
Figure 1: A Thermoacoustic Loudspeaker Consisted of an Array of 16 3D Graphene Aerogels
Figure 2: Two-step Fabrication Process of 3D Reduced Graphene Oxide Aerogel Using Freeze-Drying and Reduction/Doping
Figure 3: X-ray Photoelectron Spectroscopy Graph of the 3D Reduced Graphene Oxide Aerogel and Its Scanning Electron Microscope Image
2016.10.05 View 11905 -
Continuous Roll-Process Technology for Transferring and Packaging Flexible Large-Scale Integrated Circuits
A research team led by Professor Keon Jae Lee from KAIST and by Dr. Jae-Hyun Kim from the Korea Institute of Machinery and Materials (KIMM) has jointly developed a continuous roll-processing technology that transfers and packages flexible large-scale integrated circuits (LSI), the key element in constructing the computer’s brain such as CPU, on plastics to realize flexible electronics.
Professor Lee previously demonstrated the silicon-based flexible LSIs using 0.18 CMOS (complementary metal-oxide semiconductor) process in 2013 (ACS Nano, “In Vivo Silicon-based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Biocompatible Liquid Crystal Polymers”) and presented the work in an invited talk of 2015 International Electron Device Meeting (IEDM), the world’s premier semiconductor forum.
Highly productive roll-processing is considered a core technology for accelerating the commercialization of wearable computers using flexible LSI. However, realizing it has been a difficult challenge not only from the roll-based manufacturing perspective but also for creating roll-based packaging for the interconnection of flexible LSI with flexible displays, batteries, and other peripheral devices.
To overcome these challenges, the research team started fabricating NAND flash memories on a silicon wafer using conventional semiconductor processes, and then removed a sacrificial wafer leaving a top hundreds-nanometer-thick circuit layer. Next, they simultaneously transferred and interconnected the ultrathin device on a flexible substrate through the continuous roll-packaging technology using anisotropic conductive film (ACF). The final silicon-based flexible NAND memory successfully demonstrated stable memory operations and interconnections even under severe bending conditions. This roll-based flexible LSI technology can be potentially utilized to produce flexible application processors (AP), high-density memories, and high-speed communication devices for mass manufacture.
Professor Lee said, “Highly productive roll-process was successfully applied to flexible LSIs to continuously transfer and interconnect them onto plastics. For example, we have confirmed the reliable operation of our flexible NAND memory at the circuit level by programming and reading letters in ASCII codes. Out results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing.”
Dr. Kim added, “We employed the roll-to-plate ACF packaging, which showed outstanding bonding capability for continuous roll-based transfer and excellent flexibility of interconnecting core and peripheral devices. This can be a key process to the new era of flexible computers combining the already developed flexible displays and batteries.”
The team’s results will be published on the front cover of Advanced Materials (August 31, 2016) in an article entitled “Simultaneous Roll Transfer and Interconnection of Silicon NAND Flash Memory.” (DOI: 10.1002/adma.201602339)
YouTube Link: https://www.youtube.com/watch?v=8OJjAEm27sw
Picture 1: This schematic image shows the flexible silicon NAND flash memory produced by the simultaneous roll-transfer and interconnection process.
Picture 2: The flexible silicon NAND flash memory is attached to a 7 mm diameter glass rod.
2016.09.01 View 10192 -
KAIST Team Develops Semi-Transparent Solar Cells with Thermal Mirror Capability
A research team led by KAIST and Sungkyunkwan University professors has created semi-transparent perovskite solar cells that demonstrate high-power conversion efficiency and transmit visible light while blocking infrared light, making them great candidates for solar windows.
Modern architects prefer to build exteriors designed with glass mainly from artistic or cost perspectives. Scientists, however, go one step further and see opportunities from its potential ability to harness solar energy. Researchers have thus explored ways to make solar cells transparent or semi-transparent as a substitute material for glass, but this has proven to be a challenging task because solar cells need to absorb sunlight to generate electricity, and when they are transparent, it reduces their energy efficiency.
Typical solar cells today are made of crystalline silicon, but it is difficult to make them translucent. Semi-transparent solar cells under development use, for example, organic or dye-sensitized materials, but compared to crystalline silicon-based cells, their power-conversion efficiencies are relatively low. Perovskites are hybrid organic-inorganic halide-based photovoltaic materials, which are cheap to produce and easy to manufacture. They have recently received much attention as the efficiency of perovskite solar cells has rapidly increased to the level of silicon technologies in the past few years.
Using perovskites, a Korean research team led by Professor Seunghyup Yoo of the Electrical Engineering School at KAIST and Professor Nam-Gyu Park of the Chemical Engineering School at Sungkyunkwan University developed a semi-transparent solar cell that is highly efficient and, additionally, functions very effectively as a thermal-mirror.
The team has developed a top transparent electrode (TTE) that works well with perovskite solar cells. In most cases, a key to success in realizing semi-transparent solar cells is to find a TTE that is compatible with a given photoactive material system, which is also the case for perovskite solar cells. The proposed TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive-index (high-index) layer and an interfacial buffer layer. This TTE, placed as a top-most layer, can be prepared without damaging ingredients used in perovskite solar cells. Unlike conventional transparent electrodes focusing only on transmitting visible light, the proposed TTE plays the dual role of passing through visible light while reflecting infrared rays. The semi-transparent solar cells made with the proposed TTEs exhibited average power conversion efficiency as high as 13.3% with 85.5% infrared rejection.
The team believes that if the semi-transparent perovskite solar cells are scaled up for practical applications, they can be used in solar windows for buildings and automobiles, which not only generate electrical energy but also enable the smart heat management for indoor environments, thereby utilizing solar energy more efficiently and effectively.
This result was published as a cover article in the July 20, 2016 issue of Advanced Energy Materials. The research paper is entitled “Empowering Semi-transparent Solar Cells with Thermal-mirror Functionality.” (DOI: 10.1002/aenm.201502466)
The team designed the transparent electrode (TE) stack in three layers: A thin-film of silver (Ag) is placed in between the bottom interfacial layer of molybdenum trioxide (MoO3) and the top high-index dielectric layer of zinc sulfide (ZnS). Such a tri-layer approach has been known as a means to increase the overall visible-light transmittance of metallic thin films via index matching technique, which is essentially the same technique used for anti-reflection coating of glasses except that the present case involves a metallic layer.
Traditionally, when a TE is based on a metal film, such as Ag, the film should be extremely thin, e.g., 7-12 nanometers (nm), to obtain transparency and, accordingly, to transmit visible light. However, the team took a different approach in this research. They made the Ag TE two or three times thicker (12-24 nm) than conventional metal films and, as a result, it reflected more infrared light. The high refractive index of the ZnS layer plays an essential role in keeping the visible light transmittance of the proposed TTE high even with the relatively thick Ag film when its thickness is carefully optimized for maximal destructive interference, leading to low reflectance (and thus high transmittance) within its visible light range.
The team confirmed the semi-transparent perovskite solar cell’s thermal-mirror function through an experiment in which a halogen lamp illuminated an object for five minutes through three mediums: a window of bare glass, automotive tinting film, and the proposed semi-transparent perovskite solar cell. An infrared (IR) camera took thermal images of the object as well as that of each window’s surface. The object’s temperature, when exposed through the glass window, rose to 36.8 Celsius degrees whereas both the tinting film and the cell allowed the object to remain below 27 Celsius degrees. The tinting film absorbs light to block solar energy, so the film’s surface became hot as it was continuously exposed to the lamp light, but the proposed semi-transparent solar cell stayed cool since it rejects solar heat energy by reflection, rather than by absorption. The total solar energy rejection (TSER) of the proposed cell was as high as 89.6%.
Professor Yoo of KAIST said, “The major contributions of this work are to find transparent electrode technology suitable for translucent perovskite cells and to provide a design approach to fully harness the potential it can further deliver as a heat mirror in addition to its main role as an electrode. The present work can be further fine-tuned to include colored solar cells and to incorporate flexible or rollable form factors, as they will allow for greater design freedom and thus offer more opportunities for them to be integrated into real-world objects and structures such as cars, buildings, and houses.”
The lead authors are Hoyeon Kim and Jaewon Ha, both Ph.D. candidates in the School of Electrical Engineering at KAIST, and Hui-Seon Kim, a student in the School of Chemical Engineering at Sungkyunkwan University. This research was supported mainly by the Climate Change Research Hub Program of KAIST.
Picture 1: Semi-transparent Perovskite Solar Cell
This picture shows a prototype of a semi-transparent perovskite solar cell with thermal-mirror functionality.
Picture 2: A Heat Rejection Performance Comparison Experiment
This picture presents thermal images taken by an infrared camera for comparing the heat rejection performance of bare glass, automotive tinting film, and a semi-transparent perovskite solar cell after being illuminated by a halogen lamp for five minutes.
2016.08.02 View 11482