Science
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Professor Ji-Hyun Lee Awarded the Sasada Prize
Professor Ji-Hyun Lee from the Graduate School of Culture Technology was awarded the Sasada Prize during the 24th annual Conference of Computer-Aided Architectural Design Research in Asia (CAADRIA) held in Wellington, New Zealand on April 15.
The Sasada Award honors the late Professor Tsuyoshi Sasada (1941-2005), the former Professor of Osaka University and co-founder and fellow of CAADRIA. It is given to an individual who has contributed to the next generation of researchers and academics, to the wider profession and practice in computer-aided design and research, and has earned recognition in the academic community.
Professor Lee was recognized for her development of CAAD (Computer-Aided Architectural Design) through her research work on the land price precision system using case-based reasoning. Her research team proposed a model for estimating the average apartment price in an administrative district after collecting 40 variables from the six major Korean cities, excluding Seoul and Ulsan. Their follow-up studies showed the possibility of replacing existing experts’ predictions.
Professor Lee has been steadily researching for 20 years on case-based reasoning (CBR), a field of artificial intelligence, and has published more than 40 papers in the field of CBR. Meanwhile, the CAAD Future 2019 event will be held at KAIST in June.
2019.04.23 View 6659 -
Next-Generation Small Satellite Starts Operations
Korea’s next generation small satellite developed by KAIST started its space observation missions after completing its performance checkup, the Ministry of Science and ICT announced on April 16.
The Ministry said that the Next Sat-1, launched on Dec. 4, has successfully deployed its solar panels, adjusted its posture and carried out internal checks to see if all system were functioning normally. The Next Sat-1, expected to be operation for some two years, is the first locally made satellite to have instruments for the Study of Space Storms (ISSS) that can check the impact of solar storms on the magnetic field of the pole areas. It can be further used to detect changes to the Earth's ionosphere in low longitude regions.
The ministry said the satellite's near-infrared imaging spectrometer (NISS) camera will be used to peer into space with one of tasks to determine the brightness of the M95 barred spiral galaxy in the constellation Leo.
KAIST built the large capacity memory and communication equipment with others, like Asia Pacific Satellite Inc., building star tracking sensors, computers and high speed data processors specifically designed for space.
The satellite weighs 100 kg and is in orbit 575 km from the surface of the Earth. “Everything has been checked to be in working order with initial tests utilizing its sensors and camera revealing positive results,” the Ministry said in a statement. (Yonhap News)
(The photos shows details of the Next Sat-1 satellite.)
2019.04.16 View 2803 -
Unravelling Inherent Electrocatalysis to Improve the Performance of Hydrogen Fuel Cells
(Figure 1. Electrode structure for the precise evaluation of the metal nanoparticles’ electrochemical catalytic characteristics at a high temperature.)
A KAIST team presented an ideal electrode design to enhance the performance of high-temperature fuel cells. The new analytical platform with advanced nanoscale patterning method quantitatively revealed the electrochemical value of metal nanoparticles dispersed on the oxide electrode, thus leading to electrode design directions that can be used in a variety of eco-friendly energy technologies.
The team, working under Professor WooChul Jung and Professor Sang Ouk Kim at the Department of Materials Science and Engineering, described an accurate analysis of the reactivity of oxide electrodes boosted by metal nanoparticles, where all particles participate in the reaction. They identified how the metal catalysts activate hydrogen electro-oxidation on the ceria-based electrode surface and quantify how rapidly the reaction rate increases with the proper choice of metals.
Metal nanoparticles with diameters of 10 nanometers or less have become a key component in high-performance heterogeneous catalysts, primarily serving as a catalytic activator. Recent experimental and theoretical findings suggest that the optimization of the chemical nature at the metal and support interfaces is essential for performance improvement.
However, the high cost associated with cell fabrication and operation as well as poorer stability of metal nanoparticles at high temperatures have been a long-standing challenge. To solve this problem, the team utilized a globally recognized metal nano patterning technology that uses block copolymer self-assembled nano templates and succeeded in uniformly synthesizing metal particles 10 nanometers in size on the surface of oxide fuel cell electrodes. They also developed a technology to accurately analyze the catalyst characteristics of single particles at high temperatures and maximize the performance of a fuel cell with minimal catalyst use.
The research team confirmed that platinum, which is a commonly used metal catalyst, could boost fuel cell performance by as much as 21 times even at an amount of 300 nanograms, which only costs about 0.015 KRW.
The team quantitatively identified and compared the characteristics of widely used metal catalysts other than platinum, such as palladium, gold, and cobalt, and also elucidated the precise principle of catalyst performance through theoretical analysis.
(Figure 2. Comparison of the electrochemical catalytic characteristics for various 10nm metal nanoparticles (platinum, palladium, cobalt, gold) at a high temperature.)
Professor Jung said, "We have broken the conventional methods of increasing the amount of catalyst which have deemed inefficient and expensive. Our results suggest a clear idea for high performance fuel cells using very small amounts of nanoparticles. This technology can be applied to many different industrial fields, advancing the commercialization of eco-friendly energy technologies such as fuel cells that generate electricity and electrolytic cells that produce hydrogen from water.”
The research has been published as the cover article of Nature Nanotechnology in the March issue. This research was carried out with support from the Nano-Material Technology Development Program through the National Research Foundation of Korea.
2019.03.28 View 30183 -
Stretchable Multi-functional Fiber for Energy Harvesting and Strain Sensing
(from left: Professor Steve Park, Jeongjae Ryu and Professor Seungbum Hong)
Fiber-based electronics are expected to play a vital role in next-generation wearable electronics. Woven into textiles, they can provide higher durability, comfort, and integrated multi-functionality. A KAIST team has developed a stretchable multi-functional fiber (SMF) that can harvest energy and detect strain, which can be applied to future wearable electronics.
With wearable electronics, health and physical conditions can be assessed by analyzing biological signals from the human body, such as pulse and muscle movements. Fibers are highly suitable for future wearable electronics because they can be easily integrated into textiles, which are designed to be conformable to curvilinear surfaces and comfortable to wear. Moreover, their weave structures offer support that makes them resistant to fatigue. Many research groups have developed fiber-based strain sensors to sense external biological signals. However, their sensitivities were relatively low.
The applicability of wearable devices is currently limited by their power source, as the size, weight, and lifetime of the battery lessens their versatility. Harvesting mechanical energy from the human body is a promising solution to overcome such limitations by utilizing various types of motions like bending, stretching, and pressing. However, previously reported, fiber-based energy harvesters were not stretchable and could not fully harvest the available mechanical energy.
Professor Seungbum Hong and Professor Steve Park from the Department of Materials Science and Engineering and their team fabricated a stretchable fiber by using a ferroelectric layer composed of P(VDF-TrFE)/PDMS sandwiched between stretchable electrodes composed of a composite of multi-walled carbon nanotubes (MWCNT) and poly 3,4-ethylenedioxythiophene polystyrenesulfonate (PEDOT:PSS).
Cracks formed in MWCNT/PEDOT:PSS layer help the fiber show high sensitivity compared to the previously reported fiber strain sensors. Furthermore, the new fiber can harvest mechanical energy under various mechanical stimuli such as stretching, tapping, and injecting water into the fiber using the piezoelectric effect of the P(VDF-TrFE)/PDMS layer.
Professor Hong said, “This new fiber has various functionalities and makes the device simple and compact. It is a core technology for developing wearable devices with energy harvesting and strain sensing capabilities.”
This article, led by PhD candidate Jeongjae Ryu, was published in the January 2019 issue of Nano Energy.
Figure 1.Schematic illustration of an SMF fiber and its piezoelectric voltage output and response to strain.
Figure 2. Photographs of a stretchable multi-functional fiber being stretched by 100%, bent, and twisted.
2019.01.31 View 8546 -
New Members of KAST and Y-KAST 2019
(Professor Eui-Cheol Shin from the Graduate School of Medical Science and Engineering)
Professor Eui-Cheol Shin from the Graduate School of Medical Science and Engineering became a new fellow of the Korean Academy of Science and Technology (KAST) along with 25 other scientists in Korea. He is one of the top virus immunologists in Korea and has published a review article in Nature Reviews Immunology.
Meanwhile KAST selected and announced 26 young scientists under the age 43 who have shown great potential and the creativity to carry out next-generation research. The list of Y-KAST (Young Korean Academy of Science and Technology) includes six KAIST professors: Professor Ji Oon Lee from the Department of Mathematical Sciences, Professor Mi Hee Lim from the Department of Chemistry, Professor Shin-Hyun Kim from the Department of Chemical and Biomolecular Engineering, Professor Jung-Ryul Lee from the Department of Aerospace Engineering, Professor Hyunjoo Jenny Lee from the School of Electrical Engineering, and Professor Yeon Sik Jung from the Department of Materials Science and Engineering.
KAST conferred their fellowships and Y-KAST membership during the New Year Reception.
2019.01.22 View 8916 -
Noninvasive Light-Sensitive Recombinase for Deep Brain Genetic Manipulation
A KAIST team presented a noninvasive light-sensitive photoactivatable recombinase suitable for genetic manipulation in vivo. The highly light-sensitive property of photoactivatable Flp recombinase will be ideal for controlling genetic manipulation in deep mouse brain regions by illumination with a noninvasive light-emitting diode. This easy-to-use optogenetic module made by Professor Won Do Heo and his team will provide a side-effect free and expandable genetic manipulation tool for neuroscience research.
Spatiotemporal control of gene expression has been acclaimed as a valuable strategy for identifying functions of genes with complex neural circuits. Studies of complex brain functions require highly sophisticated and robust technologies that enable specific labeling and rapid genetic modification in live animals. A number of approaches for controlling the activity of proteins or expression of genes in a spatiotemporal manner using light, small molecules, hormones, and peptides have been developed for manipulating intact circuits or functions.
Among them, recombination-employing, chemically inducible systems are the most commonly used in vivo gene-modification systems. Other approaches include selective or conditional Cre-activation systems within subsets of green fluorescent protein-expressing cells or dual-promoter-driven intersectional populations of cells.
However, these methods are limited by the considerable time and effort required to establish knock-in mouse lines and by constraints on spatiotemporal control, which relies on a limited set of available genetic promoters and transgenic mouse resources.
Beyond these constraints, optogenetic approaches allow the activity of genetically defined neurons in the mouse brain to be controlled with high spatiotemporal resolution. However, an optogenetic module for gene-manipulation capable of revealing the spatiotemporal functions of specific target genes in the mouse brain has remained a challenge.
In the study published at Nature Communication on Jan. 18, the team featured photoactivatable Flp recombinase by searching out split sites of Flp recombinase that were not previously identified, being capable of reconstitution to be active. The team validated the highly light-sensitive, efficient performance of photoactivatable Flp recombinase through precise light targeting by showing transgene expression within anatomically confined mouse brain regions.
The concept of local genetic labeling presented here suggests a new approach for genetically identifying subpopulations of cells defined by the spatial and temporal characteristics of light delivery. To date, an optogenetic module for gene-manipulation capable of revealing spatiotemporal functions of specific target genes in the mouse brain has remained out of reach and no such light-inducible Flp system has been developed. Accordingly, the team sought to develop a photoactivatable Flp recombinase that takes full advantage of the high spatiotemporal control offered by light stimulation.
This activation through noninvasive light illumination deep inside the brain is advantageous in that it avoids chemical or optic fiber implantation-mediated side effects, such as off-target cytotoxicity or physical lesions that might influence animal physiology or behaviors. The technique provides expandable utilities for transgene expression systems upon Flp recombinase activity in vivo, by designing a viral vector for minimal leaky expression influenced by viral nascent promoters.
The team demonstrated the utility of PA-Flp as a noninvasive in vivo optogenetic manipulation tool for use in the mouse brain, even applicable for deep brain structures as it can reach the hippocampus or medial septum using external LED light illumination.
The study is the result of five years of research by Professor Heo, who has led the bio-imaging and optogenetics fields by developing his own bio-imaging and optogenetics technologies. “It will be a great advantage to control specific gene expression desired by LEDs with little physical and chemical stimulation that can affect the physiological phenomenon in living animals,” he explained.
2019.01.22 View 7007 -
Professor Jeong-Ho Lee Named the KAISTian of 2018
(Professor Jeong-Ho Lee (right) poses with President Sung-Chul Shin)
Professor Jeong-Ho Lee from the Graduate School of Medical Science and Engineering was selected as the KAISTian of the Year of 2018. The award was established in 2001 and recognizes the most outstanding scholars who have made significant research and scholastic achievements during the year. Professor Lee was awarded during the New Year ceremony held in the auditorium on January 2.
Professor Lee has investigated mutations arising in the brain for decades and has published in renowned journals such as Nature, Nature Medicine, and Cell. Last August, Professor Lee reported breakthrough research on glioblastoma in Nature, giving insight into understanding how the mutation causing glioblastoma starts and suggested novel ways to treat glioblastoma, which was thought to be incurable. (Click for more)
Professor Lee’s Translational Neurogenetics Laboratory lab is investigating innovative diagnostics and therapeutics for untreatable brain disorders including intractable epilepsy and glioblastoma. To commercialize his technology, he established the tech-startup SoVarGen and now works as its CTO.
Professor Lee credited all his lab colleagues and staff. “I know all of this research would not have possible without their sweat and effort. I am happy to receive this honorable award on behalf of them.”
Remembering the beginning of his career at KAIST in 2012, Professor Lee said “KAIST seemed to be a very high and formidable barrier for me, after completing my medical education in Korea. I thank my department professors and colleagues who led me to focus on the research path that I really wanted. They provided everything for my research environment to help make good results.”
“I will continue to strive for promoting the well-being of humanity by addressing various incurable diseases as well as developing novel therapeutics. That will be the way to promote the stature of KAIST at home and abroad,” he added.
2019.01.02 View 5766 -
Fabrication of Shape-conformable Batteries with 3D-Printing
(from left: Dr. Bok Yeop Ahn, Dr. Chanhoon Kim, Professor Il-Doo Kim and Professor Jennifer A. Lewis)
Flexible, wireless electronic devices are rapidly emerging and have reached the level of commercialization; nevertheless, most of battery shapes are limited to either spherical and/or rectangular structures, which results in inefficient space use. Professor Il-Doo Kim’s team from the Department of Materials Science at KAIST has successfully developed technology to significantly enhance the variability of battery design through collaboration research with Professor Jennifer A. Lewis and her team from the School of Engineering and Applied Sciences at Harvard University.
Most of the battery shapes today are optimized for coin cell and/or pouch cells. Since the battery as an energy storage device occupies most of the space in microelectronic devices with different designs, new technology to freely change the shape of the battery is required.
The KAIST-Harvard research collaboration team has successfully manufactured various kinds of battery shapes, such as ring-type, H, and U shape, using 3D printing technology. And through the research collaboration with Dr. Youngmin Choi at the Korea Research Institute of Chemical Technology (KRICT), 3D-printed batteries were applied to small-scale wearable electronic devices (wearable light sensor rings).
The research group has adopted environmentally friendly aqueous Zn-ion batteries to make customized battery packs. This system, which uses Zn2+ instead of Li+ as charge carriers, is much safer compared with the conventional lithium rechargeable batteries that use highly inflammable organic electrolytes. Moreover, the processing conditions of lithium-ion batteries are very complicated because organic solvents can ignite upon exposure to moisture and oxygen.
As the aqueous Zn-ion batteries adopted by the research team are stable upon contact with atmospheric moisture and oxygen, they can be fabricated in the ambient air condition, and have advantages in packaging since packaged plastic does not dissolve in water even when plastic packaging is applied using a 3D printer.
To fabricate a stable cathode that can be modulated in various forms and allows high charge-discharge, the research team fabricated a carbon fiber current collector using electrospinning process and uniformly coated electrochemically active polyaniline conductive polymer on the surface of carbon fiber for a current collector-active layer integrated cathode. The cathode, based on conductive polyaniline consisting of a 3D structure, exhibits very fast charging speeds (50% of the charge in two minutes) and can be fabricated without the detachment of active cathode materials, so various battery forms with high mechanical stability can be manufactured.
Prof. Kim said, “Zn-ion batteries employing aqueous electrolytes have the advantage of fabrication under ambient conditions, so it is easy to fabricate the customized battery packs using 3D printing.”
“3D-printed batteries can be easily applied for niche applications such as wearable, personalized, miniaturized micro-robots, and implantable medical devices or microelectronic storage devices with unique designs,” added Professor Lewis.
With Dr. Chanhoon Kim in the Department of Materials Science and Engineering at KAIST and Dr. Bok Yeop Ahn School of Engineering and Applied Sciences at Harvard University participating as equally contributing first authors, this work was published in the December issue of ACS Nano.
This work was financially supported by the Global Research Laboratory (NRF-2015K1A1A2029679) and Wearable Platform Materials Technology Center (2016R1A5A1009926).
Figure 1.Fabrication of shape-conformable batteries based on 3D-printing technology and the application of polyaniline carbon nanofiber cathodes and wearable electronic devices
Figure 2.Fabricated shape-conformable batteries based on a 3D-printing method
Meanwhile, Professor Il-Doo Kim was recently appointed as an Associate Editor of ACS Nano, a highly renowned journal in the field of nanoscience.
Professor Kim said, “It is my great honor to be an Associate Editor of the highly renowned journal ACS Nano, which has an impact factor reaching 13.709 with 134,596 citations as of 2017. Through the editorial activities in the fields of energy, I will dedicate myself to improving the prominence of KAIST and expanding the scope of Korea’s science and technology. I will also contribute to carrying out more international collaborations with world-leading research groups.”
(Associate Editor of ACS Nano Professor Il-Doo Kim)
2018.12.20 View 10451 -
Optimal Immuno-Therapeutic Strategies for Liver Cancer
KAIST medical scientists have presented a heterogeneity of immune cell exhaustion in the cancer environment, providing evidence and rationale for designing optimal strategies for immune checkpoint inhibitors in liver cancer patients.
They succeeded in distinguishing the hepatocellular carcinoma group from the exhausted tumor infiltrating immune cell composition of liver cancer patients. The study, conducted in collaboration with Asan Medical Center, confirmed the applicability for liver cancer patients, providing a new path for personalized precision medicine as well as a new model for translational research.
Our immune system is able to destroy cancerous cells in our body, however sometimes cancer cells can adapt and mutate, effectively hiding from our immune system. One of the mechanisms that has evolved to prevent eradication by the immune system is to functionally silence effector T cells, termed T-cell exhaustion, that is mainly mediated by immune checkpoint molecules such as PD-1, TIM-3, and LAG-3.
Recent breakthroughs and encouraging clinical results with various immune checkpoint inhibitors (ICIs), such as anti-PD-1 monoclonal antibodies (mAbs) and anti-CTLA-4 mAbs, have demonstrated tremendous potential to cure cancers through the immune activation of exhausted T cells. Immune checkpoint inhibitors showed significant clinical benefits for several types of cancers, leading to their wide application in clinical practice.
Anti-PD1 blocking antibodies are one of the most representative agents in this class of drug. However, it has been challenging to precisely understand the biological and clinical significance of T-cell exhaustion in cancer. A KAIST research team led by Professor Su-Hyung Park reported the heterogeneity of T-cell exhaustion in hepatocellular carcinoma (HCC) and its potential clinical implications in Gastroenterology on December 4.
The team revealed that heterogeneous T-cell exhaustion status is determined by the differential PD-1 expression levels in CD8+ T cells in liver cancer patients. The authors found that tumor-infiltrating CD8+ T cells with high PD-1 expression from liver cancer patients are functionally impaired and co-express other immune checkpoint receptors such as TIM-3 and/or LAG3, compared to those with low PD-1 expression.
Moreover, based on these results, the authors suggested that liver cancer patients can be classified into two distinct subgroups. Patients having high PD-1 expression levels in the tumor microenvironment showed more aggressive tumor features and biomarkers predicting a favorable response to anti-PD1 therapy. The research team also demonstrated that only liver cancer patients having high PD-1 expression are susceptible to combined immune checkpoint blockade-based therapies.
Prof. Park said, “The new classification of liver cancer patients identified by this study can be utilized as a biomarker to predict the response of current cancer immunotherapy targeting the PD-1 pathway.” He also said they will continue to conduct research on T-cell exhaustion and activation in various types of cancer, which could lead to a better understanding of T-cell response against cancer, thereby providing evidence for future cancer immunotherapy to achieve the ultimate goal to prolong the survival of cancer patients.
2018.12.18 View 5104 -
KAIST Seals the Deal for Kenya KAIST Project
KAIST will participate in Kenya’s strategic economic development plan under the provision of a turnkey-based science and technology education consultancy for the establishment of the Kenya Advanced Institute of Science and Technology (Kenya KAIST).KAIST signed the contract on November 30 with the Konza Technopolis Development Authority to establish Kenya KAIST. Korea Eximbank will offer a 95 million USD loan to the Kenyan government for this project. The project will include the educational and architectural design and construction of Kenya KAIST. The campus will be constructed in the Konza Techno City nearby Nairobi by 2021, with the first batch of 200 graduate students starting classes in 2022. KAIST, in consortium with Samwoo and Sunjin architecture and engineering companies, will take the lead of the three-year project, with the kick-off ceremony planned at the end of next January in Nairobi. The Kenyan government plans to transform Kenya into a middle-income country under Vision 2030 through promoting science, technology, and innovation for national economic growth. Nicknamed Africa’s Silicon Savannah, Konza Techno City is a strategic science and technology hub to realize this vision. To this end, the medium-term plan set a goal to provide specialized research and training in various leading-edge engineering and advanced science fields.In the two-phase evaluation of the consultancy bidding, KAIST won preferred bidder status in the technical proposal evaluation, outbidding three other Korean consortia. Invited to the financial proposal bidding, the KAIST consortium successfully completed month-long contract negotiations with Kenya last week.KAIST will develop academic curricula for six initial departments (Mechanical Engineering, Electrical/Electronic Engineering, ICT Engineering, Chemical Engineering, Civil Engineering, and Agricultural Biotechnology), which will lay the ground work for engineering research and education in Kenya to meet emerging socioeconomic demands. In addition, KAIST will provide the education of basic sciences of math, physics, chemistry, and biology for students.It is also notable that the Kenyan government asked to develop an industry-academy cooperation program in Konza Techno City. It reflects the growing industrial needs of Kenya KAIST, which will be located in the center of the Konza Technopolis. It is anticipated that the technopolis will create 16,675 jobs in the medium term and over 200,000 after completion, positioning Kenya as an ICT hub within the region.KAIST also shares a similar history of establishment with Kenya KAIST, as it will be built with a foreign loan. KAIST, created by the Korean government in 1971 to drive the economic engine through advancement of science and technology with a six-million USD loan from USAID, has now become a donor institution that hands down science and technology education systems including the construction of campuses to underdeveloped countries.The successful case of KAIST has been benchmarked by many countries for years. For instance, KAIST set up the curriculum of the nuclear engineering program at the Khalifa University of Science and Technology in UAE in 2010. In China, Chongqing University of Technology is running its electrical engineering and computer science programs based on the educational systems and curricula offered by KAIST from 2015. In October, KAIST also signed an MOU with the Prince Mohammad Bin Salman College of Cyber Security, AI, and Advanced Technologies in Saudi Arabia to provide the undergraduate program for robotics.Among all these programs benchmarking KAIST, Kenya KAIST clearly stands out, for it is carrying out a turnkey-based project that encompasses every aspect of institution building ranging from educational curriculum development to campus construction and supervision.President Sung-Chul Shin is extremely excited about finalizing the deal, remarking, “It is of great significance that KAIST’s successful development model has carved out a unique path to becoming a global leading university that will benefit other countries. In only a half century, we have transitioned from a receiver to a donor institution, as the country itself has done.”“KAIST will spare no effort for Kenya KAIST to become a successful science and technology university that will play a crucial role in Kenya’s national development. I believe Kenya KAIST will be an exemplary case of an ODA (Official Development Assistance) project based on the development of science and technology to benefit underdeveloped countries,” he added.
2018.12.03 View 9731 -
New Anisotropic Conductive Film for Ultra-Fine Pitch Assembly Applications
(Professor Paik(right) and PhD Candidate Yoon)
Higher resolution display electronic devices increasingly needs ultra-fine pitch assemblies. On that account, display driver interconnection technology has become a major challenge for upscaling display electronics.
Researchers have moved to one step closer to realizing ultra-fine resolution for displays with a novel thermoplastic anchoring polymer layer structure. This new structure can significantly improve the ultra-fine pitch interconnection by effectively suppressing the movement of conductive particles. This film is expected to be applied to various mobile devices, large-sized OLED panels, and VR, among others.
A research team under Professor Kyung-Wook Paik in the Department of Materials developed an anchoring polymer layer structure that can effectively suppress the movement of conductive particles during the bonding process of the anisotropic conductive films (ACFs). The new structure will significantly improve the conductive particle capture rate, addressing electrical short problems in the ultra-fine pitch assembly process.
During the ultra-fine pitch bonding process, the conductive particles of conventional ACFs agglomerate between bumps and cause electrical short circuits. To overcome the electrical shortage problem caused by the free movement of conductive particles, higher tensile strength anchoring polymer layers incorporated with conductive particles were introduced into the ACFs to effectively prevent conductive particle movement.
The team used nylon to produce a single layer film with well-distributed and incorporated conductive particles. The higher tensile strength of nylon completely suppressed the movement of conductive particles, raising the capture rate of conductive particles from 33% of the conventional ACFs to 90%. The nylon films showed no short circuit problem during the Chip on Glass assembly. Even more, they obtained excellent electrical conductivity, high reliability, and low cost ACFs during the ultra-fine pitch applications.
Professor Paik believes this new type of ACFs can further be applied not only to VR, 4K and 8K UHD display products, but also to large-size OLED panels and mobile devices.
His team completed a prototype of the film supported by the ‘H&S High-Tech,’ a domestic company and the ‘Innopolis Foundation.’ The study, whose first author is PhD candidate Dal-Jin Yoon, is described in the October issue of IEEE TCPMT.
Figure 1: Schematic process of APL structure fabrication.
Figure 2: Proto-type production of APL ACFs.
2018.11.13 View 6304 -
Controlling Crystal Size of Organic Semiconductors
A KAIST research team led by Professor Steve Park from the Department of Materials Science and Engineering
Recently, solution-processable organic semiconductors are being highlighted for their potential application in printed electronics, becoming a feasible technique to fabricate large-area flexible thin film at a low cost. The field-effect mobility of small-molecule organic semiconductors is dependent on the crystallinity, crystal orientation, and crystal size. A variety of solution-based coating techniques, such as ink-jet printing, dip-coating, and solution shearing have been developed to control the crystallinity and crystal orientation, but a method for developing techniques to increase the crystal size of organic semiconductors is still needed.
To overcome this issue, the research team developed an inorganic polymer micropillar-based solution shearing system to increase the crystal size of an organic semiconductor with pillar size. Using this technique, the crystallization process of organic semiconductors can be controlled precisely, and therefore large-area organic semiconductor thin film with controlled crystallinity can be fabricated.
A variety of solution-based coating techniques cannot control the fluid-flow of solutions appropriately, so the solvent evaporates randomly onto the substrate, which has difficulty in the fabrication of organic semiconductor thin film with a large crystal size.
The research team integrated inorganic polymer microstructures into the solution shearing blade to solve this issue. The inorganic polymer can easily be microstructured via conventional molding techniques, has high mechanical durability, and organic solvent resistance. Using the inorganic polymer-based microstructure blade, the research team controlled the size of small molecule organic semiconductors by tuning the shape and dimensions of the microstructure. The microstructures in the blade induce the sharp curvature regions in the meniscus line that formed between the shearing blade and the substrate, and therefore nucleation and crystal growth can be regulated. Hence, the research team fabricated organic semiconductor thin-film with large crystals, which increases the field-effect mobility.
The research team also demonstrated a solution shearing process on a curved surface by using a flexible inorganic polymer-based shearing blade, which expands the applicability of solution shearing.
Professor Park said, “Our new solution shearing system can control the crystallization process precisely during solvent evaporation.” He added, “This technique adds another key parameter that can be utilized to tune the property of thin films and opens up a wide variety of new applications.
The results of this work entitled “Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size” was published in the July 2018 issue of Advanced Materials as a cover article.
2018.10.30 View 5991