Development of PM2.5 management strategy in the industrial city of Ulsan : A comprehensive approach to understanding the risk and sources of PM2.5

Sang-Jin Lee Ulsan National Institute of Science and Technology 2024 국내박사

Particulate matter (PM) with an aerodynamic diameter of less than 2.5 μm (PM2.5) is major air pollutants in northeast Asia, with their primary sources being fuel combustion from industrial activity, heating, transportation, and power generation facilities. In addition, gaseous precursors such as sulfur oxides (SOX), nitrogen oxides (NOX), and volatile organic compounds (VOCs) generate secondary aerosols through chemical reactions. The major sources for high PM2.5 events in metropolitan cities are generally local vehicle emissions and secondary formation. Long-range atmospheric transport (LRAT) is also a major reason for high PM events in East Asian megacities such as the Seoul Metropolitan Area, which are frequently influenced by Asian continental outflow. On the other hand, industrial cities are often more strongly influenced by emissions from local industrial activity. The metropolitan city of Ulsan, with a population of 1.13 million, is located in the southeast of the Korean Peninsula. The east coast of Ulsan has a number of petrochemical, nonferrous, automobile, and shipbuilding facilities. Thus, the air quality in Ulsan is greatly influenced by the emissions of various air pollutants from these industrial complexes. However, studies on investigations of PM2.5 pollution in Ulsan have been limited, and there is a need to address the health of residents in an industrial city facing air pollution issues. In this study, we aim to develop comprehensive PM2.5 management strategies by considering source identification, human health assessment, and emission reduction. Currently, episodes of high levels of PM2.5 frequently occur in South Korea as a result of both local emissions and the LRAT of yellow dust and haze events from the Asian continent. Therefore, we investigated the characteristics of PM2.5 pollution episodes semi-continuous measurements obtained from the Yeongnam intensive air quality monitoring station (YN station) in Ulsan. The major source of PM2.5 for the pollution period during winter was LRAT from eastern China and North Korea. The industrial facilities in Ulsan were also responsible for the elevated PM2.5 concentration in winter. The major source of PM2.5 for the pollution period during summer was the local industrial facilities and ship emissions. In addition, secondary formation was enhanced by the air stagnation, high relative humidity, and low PBL height. The influence of thermal power stations and national industrial areas in southern coastal cities was also identified. Moreover, to comprehensively understand the pollution of primary and secondary PM2.5, we developed a technique by combining monitoring and modeling methods to map the spatial distribution of PM2.5. The monitoring data for PM2.5 components and precursors, as well as the air dispersion and receptor modeling data for Ulsan, South Korea were used. It was revealed that the petrochemical and non-ferrous industrial complexes are primary sources of PM2.5 in Ulsan. Similar levels between primary and secondary sulfate were observed, while nitrate concentrations were more influenced by secondary formation rather than primary emissions. Ammonium sulfate concentrations were significantly influenced by industrial activities, while ammonium nitrate concentrations were influenced by both industrial and urban emissions. Significant contributions to SOA formation were observed from the automobile, shipbuilding, and petrochemical industrial complexes, with aromatic compounds such as BTEX playing a significant role. Based on these findings, optimized strategies for managing PM2.5 were proposed for urban areas in individual districts and industrial complexes in Ulsan. However, it should be noted that the estimated concentration of SOA may be underestimated due to the limited number of analyzed VOC species. Particulate matter (PM) contains hazardous air pollutants (HAPs) that may adversely affect human health. In particular, residents living in an industrial city are seriously concerned about the health risks associated with major drivers of cancer risk, such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Therefore, in this study, a novel index called the comprehensive air-risk index (CARI) was developed, which represents the human health risks associated with HAPs. Furthermore, to enhance the spatiotemporal resolution of CARI, a machine-learning approach was implemented using measurement data for PAHs and heavy metals. Over the course of eight years, the risk of PAHs decreased, whereas the risk of heavy metals exhibited a different trend in Ulsan. In addition, the trends of PM2.5 concentration and risk can differ in Ulsan. Earlier studies have also documented elevated concentrations of highly toxic heavy metals in PM2.5 in Ulsan. CARI, CAI and AQHI displayed different seasonal patterns. Hence, in large industrial cities, the proportion of HAPs within PM2.5 and meteorological conditions bears greater significance in health risk assessment than the mass concentration of PM2.5. The effectiveness of CARI in reflecting the health risks associated with HAPs in an industrial city can be conclusively affirmed. Utilizing machine learning and the novel risk index, CARI allows for the identification of priority risk areas in an industrial city at high spatio-temporal resolution. While the average CARI was higher in petrochemical and nonferrous industrial areas, it did not surpass the ‘Unhealthy’ threshold of 150, and there were areas that only exceeded the ‘Unhealthy for sensitive groups’ level of 100. In addition, the Onsan and Yaeum districts were identified as high-risk areas, despite having low population density, as they are primarily industrial areas. Finally, to propose the most effective PM2.5 emission reduction policies in Ulsan, machine learning approach was considered based on reduction scenarios. Emission reduction scenarios were simulated for the major components of PM2.5, including SO4 2-, NO3 -, NH4 +, OC, and EC, which contribute significantly to the PM2.5 mass concentration. When the concentrations of five components were uniformly reduced, PM2.5 mass concentration exhibited the most significant decrease in the scenario where OC concentration was reduced. Moreover, 'Bad' days determined by PM2.5 concentration (exceed 35 µg/m3) also showed the greatest decreased in the scenario with decreased OC concentration. SO2 and meteorological conditions were found to be the main factors for CARI related to human health risks caused by HAPs. In addition to SO2, NH4 +, OC, and EC showed high importance. When simulating the concentration reduction scenarios for these four components, the CARI decreased the most when the SO2 concentration was reduced. Moreover, 'Unhealthy' days determined by CARI (exceed 150) also showed the greatest decreased in the scenario with decreased SO2 concentration. This means that SO2 emission should be prioritized for control to reduce the risk of PM2.5. In conclusion, OC-related (i.e. VOCs) emissions should be controlled to efficiently reduce PM2.5 mass concentration, and SO2-related emissions (i.e. industrial activity) should be controlled to reduce human health risk. These studies provide basic information for improving air quality and will benefit the residents of Ulsan. It can also be applied to other major cities around the world to help improve global air quality.

A Gene-Centric Perspective of Scientific and Technological Innovations

Woochul Jung Ulsan National Institute of Science and Technology 2023 국내석사

유전자와 유전자 산물에 대한 연구는 현대 생명공학의 기초가 되며, 의학, 농업, 식량산업, 에너지 공급, 환경 정화 등 여러 분야로 응용이 가능한 것으로 알려져 있다. 이러한 과학적 발견들과 기술 혁신을 유전자 중심의 관점에서 거시적으로 조사하고자, 본 논문에서는 연구 논문과 특허에 대한 대규모 선별이 진행되었다. 각 유전자가 갖는 과학적 파급력을 보기 위해서 PubMed에서 접근 가능한 연구 논문 중 제목과 초록에 유전자 또는 유전자 산물이 언급된 자료들을 수집하였다. 기술 혁신 부분에 대응하는 자료로는 미국특허청(USPTO)에서 공개된 특허 출판물이 수집되었다. 문헌 자료 선별과 함께, 유럽 생물정보학 연구소에서 관리하는 UniProt 협의체 데이터베이스 중 선별·제공되는 일부 항목들의 유전자-단백질 명칭을 수집하였고, 이는 이후 유전자 간에 지나치게 중복된 명칭이나 두문자어로 인한 혼동을 방지하기 위해 원소가 공유되지 않는 집합들로 일관되게 군집되었다. 결과적으로 제목/초록에 이러한 유전자 항목을 언급한 논문과 특허들의 연도별 수치를 바탕으로 인간 유전체 프로젝트가 시작된 이후의 추세를 보고하였다. 각 유전자 인용 추세는 연구 논문에서와 비교할 때 발명 문헌에서 변동이 더 큰 것으로 보였고, 두 부문 모두 의료 분야에서 유전자 인용에 대한 기여가 두드러졌다. 지금까지 유전자를 인용한 문헌들은 증가 추세였으나 제목이나 초록에 새롭게 언급되는 유전자의 수는 최근들어 감소하였다. 반면, 이미 연구된 유전자들의 새로운 조합들이 활발히 탐구되는 것으로 보이며, 이러한 조합에 자주 포함된 유전자일수록 단순 인용 횟수의 상위권 유전자보다 생명공학의 발전을 잘 설명히는 것으로 보인다. Research on genes and gene products is a foundation of modern biotechnology, and recognized for its applicability in medicine, agriculture, food industry, energy supply, environmental remediation, and many others. To investigate a macroscopic and gene-centric perspective of scientific discoveries and technological innovations, we employed a large-scale curation of research papers and patents. As a raw data to represent the scientific impact of each gene, we collected the entire set of research articles available on PubMed, that have the names of genes or gene products in their title or abstract. The more dedicated literature source, the United States Patent and Trademark Office (USPTO) patent publication, was retrieved as a source data to represent the counterpart in technological innovations. In parallel with this literature curation, the gene symbols were collected from curated subset of UniProt consortium database maintained by European Bioinformatics Institute, and then clustered into the non-overlapping standardized sets to eliminate the overwhelming duplicates and possible contamination by common acronyms. Based on the annual counts of papers or patents whose titles/abstracts include a given gene, we show the overall trends of genetic research since the launch of the Human Genome Project. The gene citation fluctuated more in inventive activity compared to those in the research, while both sides were largely contributed by medicinal discipline. The volume of publications mentioning genes has been increased while the debut of new genes on titles and abstracts has been deflated. In contrast, new combinations of previously-studied genes kept actively explored, and their frequently adopted genes informed biotechnology innovations rather than sheerly top-studied genes.

Effective and Efficient Patch Validation via Differential Fuzzing

Eui Bin Bae Ulsan National Institute of Science and Technology 2022 국내석사

Developments in APR(automatic program repair) technology have made it possible to automate the creation of patches. However, due to the loose precision(the current technology only recognizes a patch if it passed a test), it is still left up to the developer to determine whether the generated patch is correct. Accordingly, techniques for determining whether a generated patch is correct are being studied these days. Existing methods mainly score how likely a patch is correct. The calculated score is compared with a predetermined threshold to determine whether the patch is correct. However, it is difficult to improve both recall and precision no matter how the threshold is set. For example, in the case of ODS, it shows a problem that filters out many bad patches, but also filters out many correct patches. In this study, we try to solve this problem through an evidence-based method. We take different results before and after the patch as the minimum condition for determining that the patch is wrong. In this condition, if the input that derives different results represents the passing test, the different test results can be the evidence for showing that the patch is incorrect. We use Differential Fuzzing technology to find program inputs that have different results before and after patching. Also, in order to figure out whether the found input represents a passing test, we use the TEST-SIM+ heuristic, which is an improved version of the existing TEST-SIM heuristic. Finally, we develop a purging technology specialized for TEST-SIM+ technology.

Bioinspired composite cilia for active and passive droplet control

Sang-Hyeon Lee Ulsan National Institute of Science and Technology 2022 국내박사

Water droplets and wetting phenomena on various surfaces are ubiquitous in nature and pose significant challenges in various fields. Water droplets in contact with surfaces for a long period lead to the formation of biofilms and cause hygiene problems. They also cause surface icing and metal corrosion, which affect social infrastructure. In addition, water droplets on transparent surfaces degrade optical performance, such as light transmission. Various techniques have been used to address these problems, such as mechanical removal, chemical fluid release (de-icing, anti-corrosion, biocidal, etc.), and Joule heating. However, these techniques are ineffective, expensive, and environmentally harmful. Bioinspired droplet control technology has emerged as a fundamental solution to various problems caused by water droplets and the wetting phenomena. Inspired by living organisms, surfaces with nano/micro-scale cilia structures have been proposed as excellent candidates for droplet control. Multiscale cilia structure-based surfaces can solve the existing problems by maximizing the surface wettability to control the wetting / de-wetting behavior of droplets. A superhydrophobic surface, consisting of cilia array and hydrophobic material, removes the droplets from the surfaces and minimizes the contact between them, preventing freezing and corrosion. In contrast, a superhydrophilic surface, made of cilia array and hydrophilic material, spreads the droplets and forms a thin and continuous aqueous film on the surface, preventing settling of impurities and fogging caused by droplet condensation. However, single-strategy droplet control technologies based on such a simple structure still have several limitations. For example, if a typical superhydrophobic surface based on a cilia array is horizontally arranged, the droplets cannot be removed without additional external force. Moreover, superhydrophilic surfaces with cilia arrays are susceptible to fouling by airborne contaminants, such as dust, due to high surface energy of the hydrophilic materials. Recently, research has been conducted on active and passive droplet control technologies using functional materials to solve the problems caused by wetting phenomena and to address the limitations of the existing technology. First, active droplet control techniques based on stimuli-responsive materials can modulate the droplet manipulation and drop bouncing dynamics using various external stimuli. Among the stimuli-responsive materials, a magneto-responsive composite material was chosen as the primary functional material for active droplet control because it has a fast response speed and doesn’t require additional external power source for precise deformation control. The surface morphology of the magneto-responsive composite elastomer can be actively controlled using a magnet, which enables droplet manipulation and easy removal of droplets from the surface. Second, passive droplet control techniques based on anti-fouling materials can prevent a wide range of contamination such as airborne and waterborne pollution by the hydration barrier and weak adhesion. Second, owing to hydration barrier and weak adhesion, passive droplet control techniques based on anti-fouling materials can prevent a wide range of contamination such as airborne and waterborne pollution. An amphiphilic copolymer with both hydrophilic and hydrophobic segments is also being considered as a suitable material for passive droplet spreading. It was found that an amphiphilic copolymer has droplet spreading ability and exhibits “fouling-resistant” property in the hydrophilic segment and the “fouling-release” property in the hydrophobic segment. Therefore, based on their unique properties, amphiphilic material-based surfaces exhibit excellent anti-fogging and anti-biofouling properties. In addition, these surfaces can prevent external contaminants from firmly adhering to the surface and reduce surface contamination. However, single-strategy active and passive droplet control technologies based only on functional materials also have some limitations. Owing to the lack of de-wetting or wetting properties, planar surfaces composed of only functional materials without multiscale cilia structures do not exhibit a sufficiently high capability to remove or spread droplets on the surface. For example, droplets may adhere to a magneto-responsive composite planar surface because of insufficient hydrophobicity. In addition, it is not easy to spread droplets over a wide area on an amphiphilic planar surface because of its insufficient wetting performance. Many previous studies on droplet control focused on single-strategy techniques, such as typical superwetting surfaces based on multiscale structures or planar surfaces based on functional materials. However, such single-strategy approaches to droplet control have many limitations. Therefore, new strategies in multi-approaches, that integrate both strategies in approaches of multiscale architectures and functional composite materials, are needed to overcome the problems of existing technologies. We proposed a bioinspired magneto-responsive cilia array for active droplet control based on a superhydrophobic and hierarchical cilia array composed of a magneto-responsive composite elastomer. In this study, the dynamic cilia array showed robust droplet shedding performance by actively controllable multimodal drop bouncing dynamics and precise droplet manipulation. Furthermore, it exhibited remarkable anti-icing properties compared to conventional technologies. We also presented a bioinspired amphiphilic copolymer nanocilia array for passive droplet spreading. The hybrid of hydrophilic hydrogel, hydrophobic lubricant, and nanostructures showed significantly enhanced spreading ability due to the synergetic integration of the amphiphilic copolymer and nanoscale cilia array. The amphiphilic nanocilia hybrid exhibited a pronounced anti-fogging performance due to its water-spreading properties and retardation of droplet nucleation. It also exhibited notable anti-biofouling performance by integrating fouling-resistant, fouling-release, and foulant-killing mechanisms.

Real-Time and Low-Noise Terahertz Imager Based on CMOS Technology

Sang Hyo Ahn Ulsan National Institute of Science and Technology 2024 국내박사

Terahertz (THz) technology has immense applications in imaging, communication, and spectroscopy because electromagnetic waves in the THz band (0.1 - 10 THz) exhibit unique straightness and permeability characteristics. In particular, “THz see-through” imaging using the transmittance properties into non-metallic materials at THz frequency is an impactful application. Nevertheless, few THz imaging systems have been developed considering that THz frequency is higher than the cutoff frequency of Si-based FET, the most widely used device in RF applications. Moreover, it has too low photon energy to be detected by a photo-diode used in CMOS image sensor (CIS). However, FET- based plasmonic THz detectors have received considerable attention considering the multi-pixel integration potentials for real-time imaging. In the plasmonic mode, THz detection mechanism involves detecting the density oscillation of local electrons with DC offset voltage instead of detecting the electron transfer. While plasmonic THz detectors utilizing high-electron-mobility transistor (HEMT) technologies offer exceptional sensitivity, integrating such detectors with signal processing circuits on a single chip presents challenges. To address this issue, CMOS technology has garnered attention due to its advantages in terms of cost-effectiveness and high integration capabilities. In recent developments, THz detectors employing CMOS technology have utilized Schottky diodes, which function as current-driven transit-mode devices, and field-effect transistors (FETs), known for their plasmonic power detection capabilities. Within CMOS FET-based detectors, the advantages of the plasmonic power detection mechanism are evident. Unlike transit-mode devices limited by cutoff frequency, plasmonic detection isn't restricted in the same manner. This feature enables enhanced performance with increasing THz frequencies and imparts robustness against high-input THz power. CMOS technology-based plasmonic THz detectors have attracted much attention for real-time/large- scale multi-pixel THz imagers. Recently, we reported a remarkable THz detector performance enhancement by reconfiguring the boundary conditions in nano-ring FETs. To accelerate the commercialization of THz imagers, pixel-level high-performance and low-noise characteristics should be guaranteed in large-scale array operation with peripheral analog circuitry. Therefore, optimizing the analog buffer design considering the pixel’s ac boundary conditions is essential based on compact simulation model simulation. In addition, high-speed modulation must be performed to reduce flicker noise that increase due to additional circuitry. In this work, we report a record-high performance THz imager based on trantenna (transistor-antenna) integrated with an analog system using a 65-nm CMOS foundry. We investigate the high-speed and low-noise operation of ground (gnd)-out trantenna pixel-based single-chip THz imager array with low- impedance analog buffers and the reset modulation switch.

Arrangement Free Wireless Power Transfer for Mid-range Applications via Electrically Strong Resonance

Bonyoung Lee Ulsan National Institute of Science and Technology 2024 국내박사

Wireless Power Transfer (WPT) is a cutting-edge technology that enables energy transfer without the need for physical connectors, offering significant potential for various applications. This thesis provides an in-depth examination of the challenges, benefits, and trade-offs associated with different WPT technologies, with a particular focus on enhancing the degree of freedom between power transmitters and receivers. Achieving greater freedom in positioning and mounting of these components is critical for mitigating issues related to wear, damage, and maintenance costs, thereby improving the overall reliability and usability of WPT systems. The realm of WPT can be divided into near-field and far-field methodologies, each characterized by distinct degrees of freedom and efficiency considerations. Near-field WPT includes technologies such as Inductive Power Transfer (IPT) and Magnetic Resonant Wireless Power Transfer (MRWPT). IPT is limited by its requirement for close proximity between the transmitter and receiver, typically in the millimeter to centimeter range, resulting in minimal spatial freedom. MRWPT, developed by MIT researchers in 2007, offers greater flexibility but its efficiency is highly dependent on the relative orientations of the transmitter and receiver. Despite advancements in these technologies, the quest for an optimal balance between system complexity and freedom remains ongoing. Far-field WPT, particularly microwave WPT, provides another approach, achieving high efficiency through focused energy transmission. However, this method restricts freedom to a quasi-one- dimensional domain, and while three-dimensional freedom can be attained through omni-directional energy dispersion, it comes at the cost of significant efficiency loss. This thesis underscores the necessity of balancing efficiency with the degree of freedom to drive broader adoption of WPT technologies. Central to this research is the introduction of a novel two-dimensional WPT paradigm utilizing Spoof Surface Plasmon Polaritons (SSPP) and surface waves. This approach offers a middle ground, providing greater flexibility than one-dimensional systems while maintaining reasonable efficiency. The use of plasmonic metamaterial structures, such as lattice-type SSPP unit-cells, allows for fine-tuning of propagation characteristics, optimizing the system for microwave applications. Additionally, the implementation of surface wave receivers and the incorporation of non-reciprocal ferrite components enhance the specificity and effectiveness of power transfer. Beyond two-dimensional WPT, this thesis proposes Electrical Resonant Wireless Power Transfer (ERWPT) as a significant advancement over traditional MRWPT. ERWPT leverages the monopole capabilities of electric fields to overcome the spatial limitations imposed by magnetic dipole configurations. This new approach facilitates consistent PTE despite variations in receiver arrangement, demonstrating non-radiative power transfer of up to 50 watts with a PTE of 46% over a distance of 2 meters. The theoretical foundation of ERWPT is rooted in Maxwell's equations and the fundamental equivalence of electric and magnetic forces, providing a robust framework for exploring electric field- based WPT. The findings of this research highlight the potential of ERWPT to address longstanding challenges in WPT, offering a more versatile and efficient solution compared to magnetic field-based approaches. By revisiting the principles of electromagnetism and examining the intrinsic properties of electric and magnetic fields, this thesis lays the groundwork for future advancements in WPT technologies. The practical implementation of ERWPT at midrange distances represents a significant step forward, with implications for a wide range of applications, from consumer electronics to industrial automation. In conclusion, this thesis contributes to the WPT field by presenting innovative solutions that enhance the flexibility and efficiency of power transmission systems. The introduction of the development of ERWPT demonstrate the potential for overcoming current limitations and driving the next generation of wireless power technologies. This research not only advances our understanding of WPT mechanisms but also paves the way for practical and versatile wireless power solutions capable of meeting the diverse needs of modern technology.

Studies on Carrier Dynamics Using Nanoscale Cathodoluminescence in TEM and Optical Spectroscopy/Microscopy

Won-Woo Park Ulsan National Institute of Science and Technology 2025 국내박사

Highly Sensitive Plasmonic Terahertz Detector Based on Asymmetric FET Integrated with Sub-Wavelength Aperture

Min Jae Kim Ulsan National Institute of Science and Technology 2024 국내석사

Because of the peculiar characteristics of THz waves, which include penetrability and distinctiveness in feature recognition, Terahertz (THz) technology has great potential. THz imaging technology is unique among THz-frequency range technologies because of its extremely low energy levels, which make it safe for human health. In particular, field-effect transistor (FET)-based THz imaging detectors for real-time THz imaging are presently undergoing extensive research in a multi-pixel array configuration. This is due to the technology's ability to leverage silicon (Si) benefits, which include low cost and high integration density. The plasmonic wave detection technique based on FETs, which is not constrained by the cut-off frequency as in transit mode, has two attractive features: robustness against high THz input power and enhanced responsivity (RV) with rising frequency in the THz range. An analytical device model based on device physics has been built in order to fully comprehend the principles underlying the operation of THz plasmonic detectors. Not constrained by the cut-off frequency as in transit mode, the FET-based plasmonic wave detection mechanism has two attractive features: robustness against high THz input power and enhanced responsivity RV with rising frequency in the THz range. However, because of the diffraction limit, achieving sub-wavelength (λSub) resolution in the THz frequency range—which is characterized by long wavelengths (λ) is intrinsically difficult. A lot of emphasis has recently been paid to near-field approaches, which include both aperture-type and aperture-less (probe-tip) types. These methods remain independent of the THz wavelength; instead, the spatial resolution is dictated by the aperture or tip apex size. In order to improve resolution, a great deal of research has been done on various materials and architectures in aperture-based approaches as well as increasing the field that is transmitted in tip-based techniques. While the overdamped plasma wave drives the FET-based plasmonic detector to function as a power detection mechanism in NR mode, a significant amount of the signal is reflected at the aperture plane as it passes via the aperture. Specifically, for real-time imaging, the transmitted field (E) amplitude diminishes further with increasing pixel count. Addressing the low transmission issue at the aperture-based device level is therefore imperative. In this dissertation, we used 65-nm CMOS technology to examine the effects of aperture location and structural asymmetry on a FET-based plasmonic THz detector with aperture integration. Adding structural asymmetry between the FET's source and drain resulted in a photoresponse (Δu) of 9.3 mV (7-fold) when the aperture was placed close to the gate, compared to a symmetric FET. Furthermore, by creating an asymmetry in feeding the incoming THz wave with the aperture located at the drain, we were able to experimentally demonstrate significantly better detection performance—achieving an 18.5 mV (2-fold) Δu in contrast to the aperture located at the gate.

Analyzing the Fire Safety and Thermal Performances of the Liquid-Immersion Battery (LImB) Energy Storage System (ESS)

Junho Bae Ulsan National Institute of Science and Technology 2025 국내박사

Lithium-ion batteries (LIBs) are a leading energy storage technology, recognized for their high energy density and outstanding electrochemical performance. They are widely used in electric vehicles (EVs), energy storage systems (ESS), and consumer electronics. However, a significant challenge for LIBs is their susceptibility to thermal runaway, which can lead to fire and explosion. This issue is particularly important in ESS applications where a large number of high-energy cells are concentrated. In these systems, the risk of thermal runaway is affected by heat generation, the presence of combustible materials, and oxygen exposure, so safety is a top priority in all applications. A variety of safety measures have been developed to reduce the risk of fire, such as battery thermal management systems (BTMS), fire extinguishers, and other suppression methods. Existing extinguishment technologies typically rely on oxygen separation or cooling mechanisms to control combustion. Chemicals such as Novec 1230, ABC powders, and phosphoric acid-based compounds are typically used to suppress flames, while cooling systems use liquid nitrogen or refrigerants to reduce battery temperature. However, these solutions only work after a fire has started and are reactive rather than preventive. These systems also struggle to manage the challenges of high-energy systems such as ESS, where slow heat release, excessive suppression, and anaerobic propagation limit their effectiveness. Among the various LIB applications, ESS poses the greatest safety risk due to its high concentration of high-density cells. ESS plays a critical role in grid stabilization and renewable energy integration, but safety concerns have hindered its widespread adoption. For example, South Korea, a leader in ESS deployment, has reported more than 50 fire-related ESS failures, destroying approximately 1 GWh of storage capacity, equivalent to 10% of its total installed capacity. These incidents are concerning because the root cause of the fires remains uncertain, complicating the development of effective countermeasures. Given the limitations of existing fire suppression systems, recent research has explored immersion- based cooling methods that continuously submerge batteries in a coolant. This approach provides immediate heat release and continuous thermal management in the event of thermal runaway. However, practical implementation is hampered by the lack of an appropriate immersion agent that meets safety and performance criteria. Ideally, the immersion agent should be non-corrosive, electrically non-conductive, and have high thermal conductivity and capacity. Unfortunately, most existing solutions are ineffective and incomplete in suppressing fires due to poor heat dissipation. Therefore, immersion-based solutions are primarily used for fire prevention rather than active suppression. Despite these challenges, fire suppression systems play a critical role in large-scale ESS with capacities exceeding 1,000 kWh, while smaller ESS (~10 kWh) commonly used in residential environments often lack adequate fire prevention measures. This gap in safety protocols exacerbates the risks in the rapidly expanding ESS market. To ensure the safe deployment of ESS, next-generation fire prevention and suppression technologies need to go beyond conventional response strategies. Future developments should focus on integrated thermal management solutions that provide both continuous fire prevention and effective suppression to enhance safety in large-scale ESS applications. 1. Battery-in-Fire-Proof Material (BIF) Module To expand the applicability of fire extinguishers, we have developed a system that immerses batteries in a fire-resistant material (BIF) with a hermetic seal to prevent direct exposure to fire extinguishers. In this system, all battery cells are fully immersed in a liquid fire-retardant material (FPM) with high thermal conductivity and heat capacity. This setup allows for immediate fire suppression under extreme conditions while improving electrochemical performance through effective thermal management during normal operation. This study investigates the key components and practical applications of BIF technology. First, the key materials, including fire-retardant and sealing materials, are described in detail and how they are integrated into the BIF cell and module. Second, a method to prevent fire propagation by intentionally overheating a single cell within the BIF module is evaluated and the results are compared to a conventional LIB module. Third, the electrochemical performance of the BIF system is analyzed, including cycle, capacity, EIS, maximum charge rate, and operating temperature under severe conditions. The BIF system overcomes the limitations of conventional post-ignition fire suppression methods and achieves breakthroughs in fire safety and thermal management. By providing both fire prevention and thermal control, BIF technology shows significant potential in the fields of electric mobility (e.g., electric scooters, kickboards), energy storage systems (ESS), and electric vehicles (EVs). 2. LImB (Liquid Immersion Battery) ESS This study evaluates the fire prevention and suppression performance of a liquid-immersed 10kWh ESS battery system compared to a conventional LIB-ESS equipped with a standard fire extinguisher such as ABC powder. In the fire stability test, the conventional LIB-ESS system experienced thermal runaway, which resulted in rapid fire spread and system destruction, with a maximum temperature exceeding 1300°C. In contrast, the liquid-immersed system effectively mitigated the fire risk. The maximum temperature of the abused battery was only 498°C, and the adjacent cells were kept below 50°C, preventing fire spread. The initial fire was extinguished within 2 seconds, significantly reducing the size and speed of the spread. In addition to the fire suppression function, the liquid-immersed system provides improved thermal management during normal operation. Compared with conventional LIBs, it reduces the temperature rise by 6.3 times and reduces the temperature fluctuation between cells from 3.4°C to 1.5°C, ensuring stable and uniform operation. To further evaluate the practical applicability, the liquid-immersed ESS was deployed in an independent power plant and underwent actual operation tests. Despite the increasing demand for small-scale ESS, empirical studies on fire suppression and thermal management are lacking. There are few studies that systematically compare empirical data according to various fire suppression methods in ESS, leaving a gap in the development of standardized operating requirements for ESS safety. This study aims to fill this gap, establish key performance indicators for ESS safety, and contribute to the development of science-based safety guidelines for the popularization of safe and reliable ESS technology.

TCAD-Based Variability Analysis and Optimization in 28-nm Ternary-CMOS Technology

Kwan Yong LEE Ulsan National Institute of Science and Technology 2025 국내석사

To overcome the limitations in power efficiency and information density of complementary metal- oxide-semiconductor (CMOS) technology, shifting from a binary to a ternary logic system has been proposed as a promising solution. Recently, we demonstrated a power-scalable and mass-producible Ternary-CMOS (T-CMOS) technology using a commercial 28nm foundry. This technology employs a highly doped retrograde channel doping profile to leverage band-to-band tunneling (BTBT) mechanism at the body-to-drain junction, enabling a constant off-state BTBT current (IBTBT). This mechanism creates a third voltage state, which is essential for obtaining ternary operation. A key advantage of the tunneling-based ternary device platform is its ability to scale both static and dynamic power consumption by scaling IOFF and supply voltage (VDD) due to the exponential dependence of tunneling current on VDS. Moreover, this platform can be implemented through simple doping process tuning, supporting CMOS-compatible designs and allowing commercialization within ultra-large-scale integrated circuits at the level of conventional CMOS. Despite these advantages, T-CMOS faces several critical challenges for successful commercialization. A key challenge is ensuring robust operation. The division into three states (0, 1, and 2) inherently lowers the noise margin compared to binary logic. This makes it more difficult to achieve reliable functionality. T-CMOS is well-suited for low-power operation due to its scalable VDD. However, these VDD scaling aggravates noise margin issues in ternary logic. The ternary system becomes increasingly vulnerable to process variations. This variability issues significantly weaken the stability of ternary inverters, leading to reliability problems with stored data. Previous studies have demonstrated that the output mid-state voltage variation (ΔVOM) is logarithmically reduced despite significant ΔIBTBT. However, the transition voltage variation (ΔVTR), which reduces the noise margin of all states (0, 1, and 2) in ternary logic, remains unresolved. This issue can be addressed by reducing threshold voltage (VT) variation. Overcoming these challenges requires innovative design solutions and advanced variability control techniques. This paper proposes an advanced T-CMOS technology development framework to mitigate variability. This approach utilizes TCAD simulations to calibrate extensive measurement data and analyze the electrical and variability characteristics of ternary devices. Additionally, it optimizes variability through process engineering based on the analysis results. C-V calibration was performed to analyze interface trap density (Dit) and channel doping concentration (Nch), while I-V calibration was used to evaluate off-state leakage (IOFF), subthreshold swing (SSW), Threshold voltage (VT) roll-off, and drain- induced barrier lowering (DIBL). These analyses enabled the characterization of scalable T-CMOS devices immune to short-channel effects under various ion implantation (I/I) conditions. Subsequently, statistical impedance field method (sIFM) tool is utilized to analyze key variability sources, including Random Dopant Fluctuation (RDF), Interface Trap Fluctuation (ITF), and Line Edge Roughness (LER). Based on the comprehensive characterization and analysis, we propose a novel design methodology called Gate-Underlap T-CMOS to optimize variability in the ternary device platform. The key idea is to reduce RDF, the dominant variability source, by extending the effective channel length through LDD engineering. This technique can also be applied to CMOS to mitigate variability and short-channel effects (SCE), but it involves a trade-off of ION degradation. However, since our ternary device operates in the off-state, it takes full advantage of this approach without performance degradation caused by ION reduction. By applying this approach, the effective channel length (Leff) increased by 1.26x/1.33x, and VT variability decreased by 0.84x/0.81x. Consequently, the reduction in ΔVTR, which significantly impacts the noise margin (NM) of the ternary inverter, resulted in a 29% improvement in NM, increasing it from 82 mV to 106 mV. These advancements address key challenges for the commercialization of T-CMOS, providing a platform for energy-efficient and mass-producible ternary devices.