https://scholar.dgist.ac.kr/handle/20.500.11750/806 2026-04-04T14:43:22Z 2026-04-04T14:43:22Z 전창엽 김진우 김미진 양승희 김철기 https://scholar.dgist.ac.kr/handle/20.500.11750/58499 2025-07-25T03:23:07Z 2025-03-31T15:00:00Z

Title: 교환 이방성 유도 방법에 따른 PHMR 센서의 열 노출 특성 및 성능 분석 Author(s): 전창엽; 김진우; 김미진; 양승희; 김철기 Abstract: Planar Hall Magnetoresistance(PHMR) 센서는 낮은 오프셋 전압, 선형적인 자기장 응답, 높은 감도로 인해 다양한 산업 분야에서 활용되고 있다. 그러나 고온 환경에서는 자기적 특성이 변하면서 성능 저하 및 신뢰성 감소가 발생할 수 있으며, 특히 교환 바이어스의 변화가 중요한 영향을 미친다. 본 연구에서는 열적 노출 및 어닐링 공정이 P HM R 센서의 교환 바이어스에 미치는 영향을 두 가지 유도 방식(스퍼터링 중 자기장 인가 vs. 후열처리)을 통해 비교 분석하였다. 실험 결과, 교환 바이어스는 온도 상승에 따라 점차 감소하고, 블로킹 온도 이상에서는 급격히 약화되는 것으로 나타났다. 그러나 어닐링 조건을 최적화하면 교환 바이어스를 안정적으로 유지할 수 있었으며, 이를 통해 고온 환경에서도 센서의 성능과 신뢰성을 확보할 수 있음을 확인하였다. 이 결과는 PHMR 센서의 제조 및 공정 최적화에 중요한 지침이 될 수 있으며, 고온 환경에서 장기적 신뢰성이 요구되는 응용에 기여할 수 있다. Planar Hall Magnetoresistance (PHMR) sensors are widely used in industrial applications due to their low offset voltage and linear magnetic field response. However, their magnetic properties and reliability can degrade under high-temperature conditions. This study investigates the variation of exchange bias in PHMR sensors under thermal exposure and annealing. Two exchange bias induction methods were compared: magnetic field application during sputtering and annealing above the blocking temperature. Results show that exchange bias decreases with rising temperature, especially above the blocking point, while optimized annealing conditions can maintain its stability. These findings offer guidance for enhancing the thermal reliability of PHMR sensors in harsh environments.

2025-03-31T15:00:00Z Bae, Jihoon Song, Chong-Myeong Ponnaiah, Sathish Kumar Jang, Gain Choi, Hyeokjoo Hwang, Sieun Shin, Juhee Kim, Seokhwan Do, Juha Kim, Mijin Kim, Yeon Woo Kim, CheolGi You, Chun-Yeol Min, Yuho Roh, Jong Wook Kwon, Hyuk-Jun Lee, Sungwon https://scholar.dgist.ac.kr/handle/20.500.11750/58387 2025-12-18T02:41:57Z 2025-03-31T15:00:00Z

Title: High-Resolution Patterning of Breathable Polymer Nanomesh via Double-Side UV Exposure for Fabricating Micropatterned Wearable Devices Author(s): Bae, Jihoon; Song, Chong-Myeong; Ponnaiah, Sathish Kumar; Jang, Gain; Choi, Hyeokjoo; Hwang, Sieun; Shin, Juhee; Kim, Seokhwan; Do, Juha; Kim, Mijin; Kim, Yeon Woo; Kim, CheolGi; You, Chun-Yeol; Min, Yuho; Roh, Jong Wook; Kwon, Hyuk-Jun; Lee, Sungwon Abstract: Nanomesh electronics, renowned for their breathability and compatibility with long-term skin attachment, face significant challenges in achieving high-resolution micropatterning, which limits their applications in advanced devices. To address this, a method to fabricate durable, breathable, and highly conductive micropatterned nanomesh electrodes (MPNEs) with line widths as narrow as 10 mu m was developed. Using a double-side exposure technique, precise patterning was achieved on a polyimide nanomesh substrate. Silver nanowires (AgNWs) were selectively deposited via vacuum filtration, ensuring optimal alignment for enhanced conductivity. The MPNEs exhibit excellent electrical performance, achieving a sheet resistance of 3.9 Omega sq-1 at an AgNW loading of 1.6 mu g mm-2. They maintain consistent conductivity across various line widths and lengths, demonstrating high reproducibility. Mechanical testing confirmed exceptional durability under significant deformations, including bending, folding, and twisting. Furthermore, the porous structure remained breathable after AgNW deposition, preserving gas and moisture permeability. The versatility of MPNEs was demonstrated by fabricating intricate patterns such as interdigitated electrodes, multielectrode arrays, and coil antennas. These findings underscore the potential of MPNEs for advanced wearable electronics and multifunctional devices.

2025-03-31T15:00:00Z Kim, Jinwoo Nayak, Bibhutibhusan Soldatov, I.V. Schäfer, R. Lim, Byeonghwa Kim, CheolGi https://scholar.dgist.ac.kr/handle/20.500.11750/58381 2025-12-18T18:01:09Z 2025-05-31T15:00:00Z

Title: Shape anisotropy-induced local incoherent magnetization: Implications for magnetic sensor tuning Author(s): Kim, Jinwoo; Nayak, Bibhutibhusan; Soldatov, I.V.; Schäfer, R.; Lim, Byeonghwa; Kim, CheolGi Abstract: The geometry of magnetoresistive sensors based on thin magnetic films plays a crucial role in shaping their magnetization behavior and overall performance. This study investigates Wheatstone bridge sensors made with NiFe single-layer films (thickness: 10–40 nm; width: 20–60 μm; length: 500 μm) to analyze the impact of shape anisotropy on magnetization distribution. We observed domain images and sensor signals by applying a magnetic field with a constant direction and strength while varying the strength of a second magnetic field applied perpendicularly to the first. Wide-field Kerr microscopy revealed that magnetization reversal occurs locally and incoherently, with the degree of incoherence increasing in geometries with stronger demagnetizing fields. The demagnetizing field in rectangular-shaped thin films was calculated, revealing a sharp increase in field strength 3–4 μm from the bridge element edge when magnetized in the short-length direction, which results in localized magnetization behavior. The sensor signals were calculated and measured for various width-to-length ratios of the bridge elements and external magnetic field strengths. Results show that variations in sensor geometry and external magnetic fields can influence peak-to-peak voltage by up to 41 % and make significant hysteresis in the sensor signal. These findings provide valuable insights into optimizing the design and performance of magnetoresistive sensors for advanced applications. © 2025 Vietnam National University, Hanoi

2025-05-31T15:00:00Z Kim, Hyeonseol Ali, Abbas Kang, Yumin Lim, Byeonghwa Kim, CheolGi https://scholar.dgist.ac.kr/handle/20.500.11750/58243 2025-07-25T02:43:12Z 2025-01-31T15:00:00Z

Title: Surface-Driven Particle Dynamics: Sequential Synchronization of Colloidal Flow Attempted in a Static Fluidic Environment Author(s): Kim, Hyeonseol; Ali, Abbas; Kang, Yumin; Lim, Byeonghwa; Kim, CheolGi Abstract: The collective behavior of colloids in microsystems is characterized by precise micro-object control, broadening the applications of cargo manipulation in drug delivery, microfluidics, and nanotechnology. To further investigate this potential, we introduce a cargo-manipulating platform that utilizes micromagnetic patterns and fluid flow rather than conventional fluidic components. This platform, called the flowless micropump, comprises an encapsulating fluid system within a chip, containing both actuation particles (2.8 mu m in diameter) and control targets, thereby eliminating external interactions. This platform enables two distinct modes of cargo manipulation: direct control of nonmagnetic cargo (e.g., MCF-7 and THP-1 cells) and indirect manipulation of particles (e.g., polymer particles) through secondary localized fluid flow. Direct manipulation is achieved via coordinated particle collisions, facilitated by an optimized guiding wall with a height of 25 mu m. Conversely, indirect manipulation allows for high-speed control and mode change of individual targets. These manipulation events are achieved using two patterned structures: railway-track and connected half-disk (conductor) patterns. By employing a conductor pattern in conjunction with a railway-track pattern, precise and agile control of microcargo (MCF-7 and THP-1 cells and polymer bead clusters) was achieved at frequencies of 1-3 Hz and a magnetic field strength of 10 mT. This study establishes a programmable platform for designing flowless micropumps with diverse functionalities for various experimental purposes. By using colloidal flow and localized fluid flow generated by the shape of magnetic patterns and semi-three-dimensional (3D) structures, this platform holds significant promise for applications in drug screening, cell-cell interaction studies, and organoid-on-chip research.

2025-01-31T15:00:00Z