research
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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 10149 -
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 11436 -
KAIST Develops Transparent Oxide Thin-Film Transistors
With the advent of the Internet of Things (IoT) era, strong demand has grown for wearable and transparent displays that can be applied to various fields such as augmented reality (AR) and skin-like thin flexible devices. However, previous flexible transparent displays have posed real challenges to overcome, which are, among others, poor transparency and low electrical performance. To improve the transparency and performance, past research efforts have tried to use inorganic-based electronics, but the fundamental thermal instabilities of plastic substrates have hampered the high temperature process, an essential step necessary for the fabrication of high performance electronic devices.
As a solution to this problem, a research team led by Professors Keon Jae Lee and Sang-Hee Ko Park of the Department of Materials Science and Engineering at the KAIST has developed ultrathin and transparent oxide thin-film transistors (TFT) for an active-matrix backplane of a flexible display by using the inorganic-based laser lift-off (ILLO) method. Professor Lee’s team previously demonstrated the ILLO technology for energy-harvesting (Advanced Materials, February 12, 2014) and flexible memory (Advanced Materials, September 8, 2014) devices.
The research team fabricated a high-performance oxide TFT array on top of a sacrificial laser-reactive substrate. After laser irradiation from the backside of the substrate, only the oxide TFT arrays were separated from the sacrificial substrate as a result of reaction between laser and laser-reactive layer, and then subsequently transferred onto ultrathin plastics ( thickness). Finally, the transferred ultrathin-oxide driving circuit for the flexible display was attached conformally to the surface of human skin to demonstrate the possibility of the wearable application. The attached oxide TFTs showed high optical transparency of 83% and mobility of even under several cycles of severe bending tests.
Professor Lee said, “By using our ILLO process, the technological barriers for high performance transparent flexible displays have been overcome at a relatively low cost by removing expensive polyimide substrates. Moreover, the high-quality oxide semiconductor can be easily transferred onto skin-like or any flexible substrate for wearable application.”
These research results, entitled “Skin-Like Oxide Thin-Film Transistors for Transparent Displays,”
(http://onlinelibrary.wiley.com/doi/10.1002/adfm.201601296/abstract) were the lead article published in the July 2016 online issue of Wiley’s Advanced Functional Materials.
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References
[1] Advanced Materials, February 12, 2014, Highly-efficient, Flexible Piezoelectric PZT Thin Film Nanogenerator on Plastic Substrates
(http://onlinelibrary.wiley.com/doi/10.1002/adma.201305659/abstract)
[2] Advanced Materials, September 8, 2014, Flexible Crossbar-structured Resistive Memory Arrays on Plastic Substartes via Inorganic-based Laser Lift-off
(http://onlinelibrary.wiley.com/doi/10.1002/adma.201402472/abstract)
Picture 1: A Schamatic Image of Ultrathin, Flexible, and Transparent Oxide Thin-film Transistors
This image shows ultrathin, flexible, and transparent oxide thin-film transistors produced via the ILLO process.
Picture 2: Application of Uultrathin, Flexible, and Transparent Oxide Thin-film Transistors
This picture shows ultrathin, flexible, and transparent oxide thin-film transistors attached to a jumper sleeve and human skin.
2016.08.01 View 11599 -
Professor Seyun Kim Identifies a Neuron Signal Controlling Molecule
A research team led by Professor Seyun Kim of the Department of Biological Sciences at KAIST has identified inositol pyrophosphates as the molecule that strongly controls neuron signaling via synaptotagmin.
Professors Tae-Young Yoon of Yonsei University’s Y-IBS and Sung-Hyun Kim of Kyung Hee University’s Department of Biomedical Science also joined the team.
The results were published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on June 30, 2016.
This interdisciplinary research project was conducted by six research teams from four different countries and covered a wide scope of academic fields, from neurobiology to super resolution optic imaging.
Inositol pyrophosphates such as 5-diphosphoinositol pentakisphos-phate (5-IP7), which naturally occur in corns and beans, are essential metabolites in the body. In particular, inositol hexakisphosphate (IP6) has anti-cancer properties and is thought to have an important role in cell signaling.
Inositol pentakisphosphate (IP7) differs from IP6 by having an additional phosphate group, which was first discovered 20 years ago. IP7 has recently been identified as playing a key role in diabetes and obesity.
Psychopathy and neurodegenerative diseases are known to result from the disrupted balance of inositol pyrophosphates. However, the role and the mechanism of action of IP7 in brain neurons and nerve transmission remained unknown.
Professor Kim’s team has worked on inositol pyrophosphates for several years and discovered that very small quantities of IP7 control cell-signaling transduction. Professor Yoon of Yonsei University identified IP7 as a much stronger inhibitor of neuron signaling compared to IP6. In particular, IP7 directly suppresses synaptotagmin, one of the key proteins in neuron signaling. Moreover, Professor Kim of Kyung Hee University observed IP7 inhibition in sea horse neurons.
Together, the joint research team identified inositol pyrophosphates as the key switch metabolite of brain-signaling transduction.
The researchers hope that future research on synaptotagmin and IP7 will reveal the mechanism of neuron-signal transduction and thus enable the treatment of neurological disorders.
These research findings were the result of cooperation of various science and technology institutes: KAIST, Yonsei-IBS (Institute for Basic Science), Kyung Hee University, Sungkyunkwan University, KIST, University of Zurich in Switzerland, and Albert-Ludwigs-University Freiburg in Germany.
Schematic Image of Controlling the Synaptic Exocytotic Pathway by 5-IP7 , Helping the Understanding of the Signaling Mechanisms of Inositol Pyrophosphates
2016.07.21 View 10495 -
Synthesized Microporous 3D Graphene-like Carbons
Distinguished Professor Ryong Ryoo of the Chemistry Department at KAIST, who is also the Director of the Center for Nanomaterials and Carbon Materials at the Institute for Basic Science (IBS), and his research team have recently published their research results entitled "Lanthanum-catalysed Synthesis of Microporous 3D Graphene-like Carbons in a Zeolite Template" on June 29, 2016 in Nature on a new method to synthesize carbons having graphene structures with 3D periodic micropores, a trait resulted from using a zeolite as a template for the synthesis. The research team expects this technology to find a range of useful applications such as in batteries and catalysts.
Graphene, an allotrope of carbon, which was discovered more than a decade ago, has led to myriad research that seeks to unlock its vast potential. Zeolites, commonly used microporous solid catalysts in the petrochemical industry, have recently attracted attention in the field of material science as a template for carbon synthesis. Zeolites’ individual crystal is distinguished by its unique 1 nanometer (nm)-size pore structures. These structures facilitate the accommodation of carbon nanotubes inside zeolites. In their paper, the research team showed that these nanoporous systems are an ideal template for the carbon synthesis of three-dimensional (3D) graphene architecture, but zeolite pores are too small to accommodate bulky molecular compounds like polyaromatic and furfuryl alcohol that are often used in carbon synthesis. Small molecules like ethylene and acetylene can be used as a carbon source to achieve successful carbonization within zeolite pores, but it comes at a great cost. The high temperatures required for the synthesis cause reactions of carbons being deposited randomly on the external surfaces of zeolites as well as their internal pore walls, resulting in coke deposition and consequently, causing serious diffusion limitations in the zeolite pores.
The team from the IBS Center for Nanomaterials and Carbon Materials solved this conundrum with a novel approach. First author Dr. KIM Kyoungsoo explains: “The zeolite-template carbon synthesis has existed for a long time, but the problem with temperatures has foiled many scientists from extracting their full potential. Here, our team sought to find the answer by embedding lanthanum ions (La3+), a silvery-white metal element, in zeolite pores. This lowers the temperature required for the carbonization of ethylene or acetylene. Graphene-like sp2 carbon structures can be selectively formed inside the zeolite template, without carbon deposition at the external surfaces. After the zeolite template is removed, the carbon framework exhibits the electrical conductivity two orders of magnitude higher than amorphous mesoporous carbon, which is a pretty astonishing result. This highly efficient synthesis strategy based on the lanthanum ions renders the carbon framework to be formed in pores with a less than 1 nm diameter, just like as easily reproducible as in mesoporous templates. This provides a general method to synthesize carbon nanostructures with various topologies corresponding to the template zeolite pore topologies, such as FAU, EMT, beta, LTL, MFI, and LTA. Also, all the synthesis can be readily scaled up, which is important for practical applications in areas of batteries, fuel storage, and other zeolite-like catalyst supports.”
The research team began their experiment by utilizing La3+ ions. Dr. KIM elucidates why this silvery-white element proved so beneficial to the team, “La3+ ions are unreducible under carbonization process condition, so they can stay inside the zeolite pores instead of moving to the outer zeolite surface in the form of reduced metal particles. Within the pores, they can stabilize ethylene and the pyrocondensation intermediately to form a carbon framework in zeolites.”
In order to test this hypothesis, the team compared the amount of carbon deposited in La3+-containing form of Y zeolite (LaY) sample against a host of other samples such as NaY and HY. The experimental results indicate that all the LaY, NaY, and HY zeolite samples show rapid carbon deposition at 800°C. However, as the temperature decreases, there appears to be a dramatic difference between the different ionic forms of zeolites. At 600°C, the LaY zeolite is still active as a carbon deposition template. In contrast, both NaY and HY lose their carbon deposition functions almost completely.
The results, according to their paper published in Nature, highlight a catalytic effect of lanthanum for carbonization. By making graphene with 3D periodic nanoporous architectures, it promises a wide range of useful applications such as in batteries and catalysts but due to the lack of efficient synthetic strategies, such applications have not yet been successful. By taking advantage of the pore-selective carbon filling at decreased temperatures, the synthesis can readily be scaled up for studies requiring bulk quantities of carbon, in particular high electrical conductivity, which is a highly sought aspect for the production of batteries.
YouTube Link: https://youtu.be/lkNiHiB8lBk
Image 1: (Top to Bottom) Zeolite Template: Microporous Aluminosilicate; Zeolite ion exchanged with La3+ ions in aqueous solution; and Zeolite Template with La3+ ions
Image 2: (Top to Bottom) Catalytic carbonization progressed at La3+ ions-exchanged sites using ethylene as a carbon precursor. Carbon is highlighted in grey; Zeolite template removed in an acid solution (HF/ HCl); Microporous 3D graphene-like carbon
2016.07.01 View 8637 -
Unveiling the Distinctive Features of Industrial Microorganism
KAIST researchers have sequenced the whole genome of Clostridium tyrobutyricum, which has a higher tolerance to toxic chemicals, such as 1-butanol, compared to other clostridial bacterial strains.
Clostridium tyrobutyricum, a Gram-positive, anaerobic spore-forming bacterium, is considered a promising industrial host strain for the production of various chemicals including butyric acid which has many applications in different industries such as a precursor to biofuels. Despite such potential, C. tyrobutyricum has received little attention, mainly due to a limited understanding of its genotypic and metabolic characteristics at the genome level.
A Korean research team headed by Distinguished Professor Sang Yup Lee of the Chemical and Biomolecular Engineering Department at the Korea Advanced Institute of Science and Technology (KAIST) deciphered the genome sequence of C. tyrobutyricum and its proteome profiles during the course of batch fermentation. As a result, the research team learned that the bacterium is not only capable of producing a large amount of butyric acid but also can tolerate toxic compounds such as 1-butanol. The research results were published in mBio on June 14, 2016.
The team adopted a genoproteomic approach, combining genomics and proteomics, to investigate the metabolic features of C. tyrobutyricum. Unlike Clostridium acetobutylicum, the most widely used organism for 1-butanol production, C. tyrobutyricum has a novel butyrate-producing pathway and various mechanisms for energy conservation under anaerobic conditions. The expression of various metabolic genes, including those involved in butyrate formation, was analyzed using the “shotgun” proteome approach.
To date, the bio-based production of 1-butanol, a next-generation biofuel, has relied on several clostridial hosts including C. acetobutylicum and C. beijerinckii. However, these organisms have a low tolerance against 1-butanol even though they are naturally capable of producing it. C. tyrobutyricum cannot produce 1-butanol itself, but has a higher 1-butanol-tolerance and rapid uptake of monosaccharides, compared to those two species.
The team identified most of the genes involved in the central metabolism of C. tyrobutyricum from the whole-genome and shotgun proteome data, and this study will accelerate the bacterium’s engineering to produce useful chemicals including butyric acid and 1-butanol, replacing traditional bacterial hosts.
Professor Lee said,
“The unique metabolic features and energy conservation mechanisms of C. tyrobutyricum can be employed in the various microbial hosts we have previously developed to further improve their productivity and yield. Moreover, findings on C. tyrobutyricum revealed by this study will be the first step to directly engineer this bacterium.”
Director Jin-Woo Kim at the Platform Technology Division of the Ministry of Science, ICT and Future Planning of Korea, who oversees the Technology Development Program to Solve Climate Change, said,
“Over the years, Professor Lee’s team has researched the development of a bio-refinery system to produce natural and non-natural chemicals with the systems metabolic engineering of microorganisms. They were able to design strategies for the development of diverse industrial microbial strains to produce useful chemicals from inedible biomass-based carbon dioxide fixation. We believe the efficient production of butyric acid using a metabolic engineering approach will play an important role in the establishment of a bioprocess for chemical production.”
The title of the research paper is “Deciphering Clostridium tyrobutyricum Metabolism Based on the Who-Genome Sequence and Proteome Analyses.” (DOI: 10.1128/mBio.00743-16)
The lead authors are Joungmin Lee, a post-doctoral fellow in the BioProcess Research Center at KAIST, currently working in CJ CheilJedang Research Institute; Yu-Sin Jang, a research fellow in the BioProcess Research Center at KAIST, currently working at Gyeongsang National University as an assistant professor; and Mee-Jung Han, an assistant professor in the Environmental Engineering and Energy Department at Dongyang University. Jin Young Kim, a senior researcher at the Korea Basic Science Institute, also participated in the research.
This research was supported by the Technology Development Program to Solve Climate Change’s research project entitled “Systems Metabolic Engineering for Biorefineries” from the Ministry of Science, ICT and Future Planning through the National Research Foundation of Korea (NRF-2012M1A2A2026556).
Schematic Diagram of C. tyrobutyricum’s Genome Sequence and Its Proteome Profiles
The picture below shows the complete genome sequence, global protein expression profiles, and the genome-based metabolic characteristics during batch fermentation of C. tyrobutyricum.
2016.06.20 View 9488 -
Graphene-Based Transparent Electrodes for Highly Efficient Flexible OLEDs
A Korean research team developed an ideal electrode structure composed of graphene and layers of titanium dioxide and conducting polymers, resulting in highly flexible and efficient OLEDs.
The arrival of a thin and lightweight computer that even rolls up like a piece of paper will not be in the far distant future. Flexible organic light-emitting diodes (OLEDs), built upon a plastic substrate, have received greater attention lately for their use in next-generation displays that can be bent or rolled while still operating.
A Korean research team led by Professor Seunghyup Yoo from the School of Electrical Engineering, KAIST and Professor Tae-Woo Lee from the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) has developed highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE) which is placed in between titanium dioxide (TiO2) and conducting polymer layers. The research results were published online on June 2, 2016 in Nature Communications.
OLEDs are stacked in several ultra-thin layers on glass, foil, or plastic substrates, in which multi-layers of organic compounds are sandwiched between two electrodes (cathode and anode). When voltage is applied across the electrodes, electrons from the cathode and holes (positive charges) from the anode draw toward each other and meet in the emissive layer. OLEDs emit light as an electron recombines with a positive hole, releasing energy in the form of a photon. One of the electrodes in OLEDs is usually transparent, and depending on which electrode is transparent, OLEDs can either emit from the top or bottom.
In conventional bottom-emission OLEDs, an anode is transparent in order for the emitted photons to exit the device through its substrate. Indium-tin-oxide (ITO) is commonly used as a transparent anode because of its high transparency, low sheet resistance, and well-established manufacturing process. However, ITO can potentially be expensive, and moreover, is brittle, being susceptible to bending-induced formation of cracks.
Graphene, a two-dimensional thin layer of carbon atoms tightly bonded together in a hexagonal honeycomb lattice, has recently emerged as an alternative to ITO. With outstanding electrical, physical, and chemical properties, its atomic thinness leading to a high degree of flexibility and transparency makes it an ideal candidate for TEs. Nonetheless, the efficiency of graphene-based OLEDs reported to date has been, at best, about the same level of ITO-based OLEDs.
As a solution, the Korean research team, which further includes Professors Sung-Yool Choi (Electrical Engineering) and Taek-Soo Kim (Mechanical Engineering) of KAIST and their students, proposed a new device architecture that can maximize the efficiency of graphene-based OLEDs. They fabricated a transparent anode in a composite structure in which a TiO2 layer with a high refractive index (high-n) and a hole-injection layer (HIL) of conducting polymers with a low refractive index (low-n) sandwich graphene electrodes. This is an optical design that induces a synergistic collaboration between the high-n and low-n layers to increase the effective reflectance of TEs. As a result, the enhancement of the optical cavity resonance is maximized. The optical cavity resonance is related to the improvement of efficiency and color gamut in OLEDs. At the same time, the loss from surface plasmon polariton (SPP), a major cause for weak photon emissions in OLEDs, is also reduced due to the presence of the low-n conducting polymers.
Under this approach, graphene-based OLEDs exhibit 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency, which is unprecedented in those using graphene as a TE. Furthermore, these devices remain intact and operate well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm. This is a remarkable result for OLEDs containing oxide layers such as TiO2 because oxides are typically brittle and prone to bending-induced fractures even at a relatively low strain. The research team discovered that TiO2 has a crack-deflection toughening mechanism that tends to prevent bending-induced cracks from being formed easily.
Professor Yoo said, “What’s unique and advanced about this technology, compared with previous graphene-based OLEDs, is the synergistic collaboration of high- and low-index layers that enables optical management of both resonance effect and SPP loss, leading to significant enhancement in efficiency, all with little compromise in flexibility.” He added, “Our work was the achievement of collaborative research, transcending the boundaries of different fields, through which we have often found meaningful breakthroughs.”
Professor Lee said, “We expect that our technology will pave the way to develop an OLED light source for highly flexible and wearable displays, or flexible sensors that can be attached to the human body for health monitoring, for instance.”
The research paper is entitled “Synergistic Electrode Architecture for Efficient Graphene-based Flexible Organic Light-emitting Diodes” (DOI. 10.1038/NCOMMS11791). The lead authors are Jae-Ho Lee, a Ph.D. candidate at KAIST; Tae-Hee Han, a Ph.D. researcher at POSTECH; and Min-Ho Park, a Ph.D. candidate at POSTECH.
This study was supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) through the Center for Advanced Flexible Display (CAFDC) funded by the Ministry of Science, ICT and Future Planning (MSIP); by the Center for Advanced Soft-Electronics funded by the MSIP as a Global Frontier Project; by the Graphene Research Center Program of KAIST; and by grants from the IT R&D Program of the Ministry of Trade, Industry and Energy of Korea (MOTIE).
Figure 1: Application of Graphene-based OLEDs
This picture shows an OLED with the composite structure of TiO2/graphene/conducting polymer electrode in operation. The OLED exhibits 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency. The device prepared on a plastic substrate shown in the right remains intact and operates well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm.
Figure 2: Schematic Device Structure of Graphene-based OLEDs
This picture shows the new architecture to develop highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE).
2016.06.07 View 12478 -
Next-Generation Holographic Microscope for 3D Live Cell Imaging
KAIST researchers have developed a revolutionary bio-medical imaging tool, the HT-1, to view and analyze cells, which is commercially available.
Professor YongKeun Park of the Physics Department at KAIST and his research team have developed a powerful method for 3D imaging of live cells without staining. The researchers announced the launch of their new microscopic tool, the holotomography (HT)-1, to the global marketplace through a Korean start-up that Professor Park co-founded, TomoCube (www.tomocube.com).
Professor Park is a leading researcher in the field of biophotonics and has dedicated much of his research career to working on digital holographic microscopy technology. He collaborated with TomoCube’s R&D team to develop a state-of-the-art, 2D/3D/4D holographic microscope that would allow a real-time label-free visualization of biological cells and tissues.
The HT is an optical analogy of X-ray computed tomography (CT). Both X-ray CT and HT share the same physical principle—the inverse of wave scattering. The difference is that HT uses laser illumination whereas X-ray CT uses X-ray beams. From the measurement of multiple 2D holograms of a cell, coupled with various angles of laser illuminations, the 3D refractive index (RI) distribution of the cell can be reconstructed. The reconstructed 3D RI map provides structural and chemical information of the cell including mass, morphology, protein concentration, and dynamics of the cellular membrane.
The HT enables users to quantitatively and non-invasively investigate the intrinsic properties of biological cells, for example, dry mass and protein concentration. Some of the research team’s breakthroughs that have leveraged HT’s unique and special capabilities can be found in several recent publications, including a lead article on the simultaneous 3D visualization and position tracking of optically trapped particles which was published in Optica on April 20, 2015.
Current fluorescence confocal microscopy techniques require the use of exogenous labeling agents to render high-contrast molecular information. Therefore, drawbacks include possible photo-bleaching, photo-toxicity, and interference with normal molecular activities. Immune or stem cells that need to be reinjected into the body are considered particularly difficult to employ with fluorescence microscopy.
“As one of the two currently available, high-resolution tomographic microscopes in the world, I believe that the HT-1 is the best in class regarding specifications and functionality. Users can see 3D/4D live images of cells, without fixing, coating or staining cells. Sample preparation times are reduced from a few days or hours to just a few minutes,” said Professor Park.
Two Korean hospitals, Seoul National University Hospital in Bundang and Boramae Hospital in Seoul, are using this microscope currently. The research team has also introduced the HT-1 at the Photonics West Exhibition 2016 that took place on February 16-18 in San Francisco, USA.
Professor Park added, “Our technology has set a new paradigm for cell observation under a microscope. I expect that this tomographic microscopy will be more widely used in future in various areas of pharmaceuticals, neuroscience, immunology, hematology, and cell biology.”
Figure 1: HT-1 and Its Specifications
Figure 2: 3D Images of Representative Biological Cells Taken with the HT-1
2016.03.29 View 11943 -
Efficient Methane C-H Bond Activated by KAIST and UPenn Teams
Professor Mu-Hyun Baik of the Chemistry Department at KAIST and his team collaborated with an international team to discover a novel chemical reaction, carbon-hydrogen borylation using methane, and their research results were published in the March 25th issue of Science.
For details, please refer to the following press release from the Institute for Basic Sciences (IBS) in Korea and the University of Pennsylvania in the United States.
Efficient Methane C-H Bond Activation Achieved for the First Time
The Institute for Basic Science, March 24, 2016
Penn Chemists Lay Groundwork for Countless New, Cleaner Uses of Methane
University of Pennsylvania, March 24, 2016
2016.03.25 View 8786 -
KAIST Team Develops Technology to Enable Unzipping of the Graphene Plane
Professor Sang-Wook Kim’s research team of the Material Science and Engineering Department has developed a technique, which enables unzipping of the graphene plane without uncontrollable damage. The research findings were published online on the January 22 issue of Nature Communications.
Graphene is a form of carbon in which its atoms form a honey-comb structure through chemical bonding. If this structure can be cut to a desired form, other carbon materials with nanostructure can be created. Many researchers have tried to obtain the accurate unzipping of graphene structures, but faced challenges doing so.
To break a very strong bond between carbon atoms, an equivalently strong chemical reaction must be induced. But the chemical reaction not only cuts out the desirable borders, but also damages the surrounding ones. Conventional techniques, which cut out graphene at once, damaged the chemical properties of the graphene structure after unzipping. This is similar to wearing out paper while manipulating it.
To solve this problem, the research team adopted “heteroatom doping.” The idea is similar to a sheet of paper being split following a groove drawn on the sheet. After making some regions of the structure unstable by doping other atoms such as nitrogen on a carbon plane, the regions are electrochemically stimulated to split the parts. Nitrogen or other atoms act as the groove on the grapheme plane.
The researchers finely controlled the amount of unzipping graphene by adjusting the amount of heteroatom dopants, from which they were able to create a quality nano graphene without any damage in its 2-dimensional crystalline structure. Using this technique, the researchers were able to obtain a capacitor with state-of-the-art energy transfer speed. The nano graphene can be combined with polymer, metal, and semiconductor nano molecules to form carbon composites.
Professor Kim said, “In order to commercialize this technique, heteroatom doping should be researched further. We plan to develop fabric-like carbon materials with excellent mechanical and electrical properties using this technique.”
Picture 1: Unzipped Carbon Nano Tube
Picture 2: Development of Nano Graphene from Carbon Nano Tube Using Heteroatom Dopants
Korean descriptions translated into English:
Unzipping Process of Graphene
Carbon Nano Tube → Nano Graphen
Heteroatom
This process is similar to a paper being split in two from a tiny hole punched therein.
2016.03.22 View 8190 -
Non-Natural Biomedical Polymers Produced from Microorganisms
KAIST researchers have developed metabolically engineered Escherichia coli strains to synthesize non-natural, biomedically important polymers including poly(lactate-co-glycolate) (PLGA), previously considered impossible to obtain from biobased materials.
Renewable non-food biomass could potentially replace petrochemical raw materials to produce energy sources, useful chemicals, or a vast array of petroleum-based end products such as plastics, lubricants, paints, fertilizers, and vitamin capsules. In recent years, biorefineries which transform non-edible biomass into fuel, heat, power, chemicals, and materials have received a great deal of attention as a sustainable alternative to decreasing the reliance on fossil fuels.
A research team headed by Distinguished Professor Sang Yup Lee of the Chemical and Biomolecular Engineering Department at KAIST has established a biorefinery system to create non-natural polymers from natural sources, allowing various plastics to be made in an environmentally-friendly and sustainable manner. The research results were published online in Nature Biotechnology on March 7, 2016. The print version will be issued in April 2016.
The research team adopted a systems metabolic engineering approach to develop a microorganism that can produce diverse non-natural, biomedically important polymers and succeeded in synthesizing poly(lactate-co-glycolate) (PLGA), a copolymer of two different polymer monomers, lactic and glycolic acid. PLGA is biodegradable, biocompatible, and non-toxic, and has been widely used in biomedical and therapeutic applications such as surgical sutures, prosthetic devices, drug delivery, and tissue engineering.
Inspired by the biosynthesis process for polyhydroxyalkanoates (PHAs), biologically-derived polyesters produced in nature by the bacterial fermentation of sugar or lipids, the research team designed a metabolic pathway for the biosynthesis of PLGA through microbial fermentation directly from carbohydrates in Escherichia coli (E. coli) strains.
The team had previously reported a recombinant E. coli producing PLGA by using the glyoxylate shunt pathway for the generation of glycolate from glucose, which was disclosed in their patents KR10-1575585-0000 (filing date of March 11, 2011), US08883463 and JP5820363. However, they discovered that the polymer content and glycolate fraction of PLGA could not be significantly enhanced via further engineering techniques. Thus, in this research, the team introduced a heterologous pathway to produce glycolate from xylose and succeeded in developing the recombinant E. coli producing PLGA and various novel copolymers much more efficiently.
In order to produce PLGA by microbial fermentation directly from carbohydrates, the team incorporated external and engineered enzymes as catalysts to co-polymerize PLGA while establishing a few additional metabolic pathways for the biosynthesis to produce a range of different non-natural polymers, some for the first time. This bio-based synthetic process for PLGA and other polymers could substitute for the existing complicated chemical production that involves the preparation and purification of precursors, chemical polymerization processes, and the elimination of metal catalysts.
Professor Lee and his team performed in silico genome-scale metabolic simulations of the E. coli cell to predict and analyze changes in the metabolic fluxes of cells which were caused by the introduction of external metabolic pathways. Based on these results, genes are manipulated to optimize metabolic fluxes by eliminating the genes responsible for byproducts formation and enhancing the expression levels of certain genes, thereby achieving the effective production of target polymers as well as stimulating cell growth.
The team utilized the structural basis of broad substrate specificity of the key synthesizing enzyme, PHA synthase, to incorporate various co-monomers with main and side chains of different lengths. These monomers were produced inside the cell by metabolic engineering, and then copolymerized to improve the material properties of PLGA. As a result, a variety of PLGA copolymers with different monomer compositions such as the US Food and Drug Administration (FDA)-approved monomers, 3-hydroxyburate, 4-hydroxyburate, and 6-hydroxyhexanoate, were produced. Newly applied bioplastics such as 5-hydroxyvalerate and 2-hydroxyisovalerate were also made.
The team employed a systems metabolic engineering application which, according to the researchers, is the first successful example of biological production of PGLA and several novel copolymers from renewable biomass by one-step direct fermentation of metabolically engineered E.coli.
Professor Lee said, “We presented important findings that non-natural polymers, such as PLGA which is commonly used for drug delivery or biomedical devices, were produced by a metabolically engineered gut bacterium. Our research is meaningful in that it proposes a platform strategy in metabolic engineering, which can be further utilized in the development of numerous non-natural, useful polymers.”
Director Ilsub Baek at the Platform Technology Division of the Ministry of Science, ICT and Future Planning of Korea, who oversees the Technology Development Program to Solve Climate Change, said, “Professor Lee has led one of our research projects, the Systems Metabolic Engineering for Biorefineries, which began as part of the Ministry’s Technology Development Program to Solve Climate Change. He and his team have continuously achieved promising results and been attracting greater interest from the global scientific community. As climate change technology grows more important, this research on the biological production of non-natural, high value polymers will have a great impact on science and industry.”
The title of the research paper is “One-step Fermentative Production of Poly(lactate-co-glycolate) from Carbohydrates in Escherichia coli (DOI: 10.1038/nbt.3485).” The lead authors are So Young Choi, a Ph.D. candidate in the Department of Chemical and Biomolecular Engineering at KAIST, and Si Jae Park, Assistant Professor of the Environmental Engineering and Energy Department at Myongji University. Won Jun Kim and Jung Eun Yang, both doctoral students in the Department of Chemical and Biomolecular Engineering at KAIST, also participated in the research.
This research was supported by the Technology Development Program to Solve Climate Change’s research project titled “Systems Metabolic Engineering for Biorefineries” from the Ministry of Science, ICT and Future Planning through the National Research Foundation of Korea (NRF-2012M1A2A2026556).
Figure: Production of PLGA and Other Non-Natural Copolymers
This schematic diagram shows the overall conceptualization of how metabolically engineered E. coli produced a variety of PLGAs with different monomer compositions, proposing the chemosynthetic process of non-natural polymers from biomass. The non-natural polymer PLGA and its other copolymers, which were produced by engineered bacteria developed by taking a systems metabolic engineering approach, accumulate in granule forms within a cell.
2016.03.08 View 10874 -
K-Glass 3 Offers Users a Keyboard to Type Text
KAIST researchers upgraded their smart glasses with a low-power multicore processor to employ stereo vision and deep-learning algorithms, making the user interface and experience more intuitive and convenient.
K-Glass, smart glasses reinforced with augmented reality (AR) that were first developed by KAIST in 2014, with the second version released in 2015, is back with an even stronger model. The latest version, which KAIST researchers are calling K-Glass 3, allows users to text a message or type in key words for Internet surfing by offering a virtual keyboard for text and even one for a piano.
Currently, most wearable head-mounted displays (HMDs) suffer from a lack of rich user interfaces, short battery lives, and heavy weight. Some HMDs, such as Google Glass, use a touch panel and voice commands as an interface, but they are considered merely an extension of smartphones and are not optimized for wearable smart glasses. Recently, gaze recognition was proposed for HMDs including K-Glass 2, but gaze cannot be realized as a natural user interface (UI) and experience (UX) due to its limited interactivity and lengthy gaze-calibration time, which can be up to several minutes.
As a solution, Professor Hoi-Jun Yoo and his team from the Electrical Engineering Department recently developed K-Glass 3 with a low-power natural UI and UX processor. This processor is composed of a pre-processing core to implement stereo vision, seven deep-learning cores to accelerate real-time scene recognition within 33 milliseconds, and one rendering engine for the display.
The stereo-vision camera, located on the front of K-Glass 3, works in a manner similar to three dimension (3D) sensing in human vision. The camera’s two lenses, displayed horizontally from one another just like depth perception produced by left and right eyes, take pictures of the same objects or scenes and combine these two different images to extract spatial depth information, which is necessary to reconstruct 3D environments. The camera’s vision algorithm has an energy efficiency of 20 milliwatts on average, allowing it to operate in the Glass more than 24 hours without interruption.
The research team adopted deep-learning-multi core technology dedicated for mobile devices. This technology has greatly improved the Glass’s recognition accuracy with images and speech, while shortening the time needed to process and analyze data. In addition, the Glass’s multi-core processor is advanced enough to become idle when it detects no motion from users. Instead, it executes complex deep-learning algorithms with a minimal power to achieve high performance.
Professor Yoo said, “We have succeeded in fabricating a low-power multi-core processer that consumes only 126 milliwatts of power with a high efficiency rate. It is essential to develop a smaller, lighter, and low-power processor if we want to incorporate the widespread use of smart glasses and wearable devices into everyday life. K-Glass 3’s more intuitive UI and convenient UX permit users to enjoy enhanced AR experiences such as a keyboard or a better, more responsive mouse.”
Along with the research team, UX Factory, a Korean UI and UX developer, participated in the K-Glass 3 project.
These research results entitled “A 126.1mW Real-Time Natural UI/UX Processor with Embedded Deep-Learning Core for Low-Power Smart Glasses” (lead author: Seong-Wook Park, a doctoral student in the Electrical Engineering Department, KAIST) were presented at the 2016 IEEE (Institute of Electrical and Electronics Engineers) International Solid-State Circuits Conference (ISSCC) that took place January 31-February 4, 2016 in San Francisco, California.
YouTube Link: https://youtu.be/If_anx5NerQ
Figure 1: K-Glass 3
K-Glass 3 is equipped with a stereo camera, dual microphones, a WiFi module, and eight batteries to offer higher recognition accuracy and enhanced augmented reality experiences than previous models.
Figure 2: Architecture of the Low-Power Multi-Core Processor
K-Glass 3’s processor is designed to include several cores for pre-processing, deep-learning, and graphic rendering.
Figure 3: Virtual Text and Piano Keyboard
K-Glass 3 can detect hands and recognize their movements to provide users with such augmented reality applications as a virtual text or piano keyboard.
2016.02.26 View 11921