https://scholar.dgist.ac.kr/handle/20.500.11750/11859 2026-04-04T14:15:15Z https://scholar.dgist.ac.kr/handle/20.500.11750/59971 Title: Heterojunction Wide-Bandgap Amorphous Metal Oxide High-Voltage Thin-Film Transistors with High Driving Current and Low Process Temperature Author(s): Lee, Jungha; Lee, Junhee; Kim, Duhee; Kwon, Hyuk-Jun; Jang, Jae Eun; Kang, Hongki Abstract: The implementation of high-voltage (HV) applications in monolithic integration has led to increased demand for wide-bandgap high-voltage thin-film transistors (HVTFTs) to solve voltage mismatch problems between HV devices and complementary metal oxide semiconductor (CMOS) integrated circuits. However, typical HVTFTs possess several limitations, including low driving current due to the drain offset structure and high process temperature (>300 degrees C), limiting high-frequency switching operation and flexible substrate compatibility, thus impeding their application in flexible and wearable HV electronics. This study presents heterojunction wide-bandgap channel-based HVTFTs fabricated using amorphous indium tin zinc oxide (a-ITZO) and indium gallium zinc oxide (a-IGZO) to overcome the limitations of the current HVTFTs. Owing to the heterojunction channel layer, we achieved a much higher driving current of >0.37 mA/mm (I-D/W) at V-GS = 210 V and V-DS = 5 V with a flexible-electronics-compatible channel layer annealing temperature (150 degrees C), indicating that the TFTs can be even applied in HV flexible/wearable electronics. Therefore, ITZO/IGZO TFTs can withstand considerably higher power than single-layer IGZO HVTFTs, while exhibiting similar HV breakdown characteristics. Additionally, the ITZO/IGZO HVTFTs demonstrate superior electrical stability under high-voltage-bias conditions compared to conventional IGZO HVTFTs. Thus, heterojunction amorphous metal oxide TFTs are suitable for fast switching flexible HV electronic systems while gate-controlled by CMOS technologies. 2025-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59969 Title: Study of active-matrix high-power transistor design for electrical stimulation Author(s): Kim, Joonghyun; Lee, Jeonghun; Chae, Ji Won; Kim, Dongsu; Pyo, Goeun; Heo, Su Jin; Jang, Jeonggyun; Park, Heechang; Kang, Hongki; Kwon, Hyuk-Jun; Jang, Jae Eun Abstract: Among various methods for generating artificial tactile sensations, a haptic device that employs electrical stimulation has attracted significant attention due to its high potential for realizing hyper-realistic touch. Considering the high skin impedance and the dense population of tactile receptors in the fingers, achieving a high-resolution electrode design with high-power operation and a flexible form-factor is required. In this study, an electrical stimulation haptic device employing a high-power transistor with an active matrix (AM) design on a flexible substrate was demonstrated. We optimized parameters for the thin-film transistor (TFT) employing Indium-Gallium-Zinc-Oxide (IGZO) to sustain biphasic signal conditions as well as high power driving for electrical stimulation and its compatibility with low-process temperature for flexible form-factor. In order to secure the operating range of the driving TFT, the skin resistance value was measured based on the actual electrical stimulation waveform and confirmed to be 20-30 k Omega on average. The resulting device achieved a spatial resolution of 64 channels within a 1 cm(2) area. To achieve high drain current of TFT, a comb-shaped design of source and drain was suggested. The TFT can transfer high biphasic voltage (similar to +/- 50 V) with high simulation current (>10 mA). Therefore, the electrical stimulation device with high electrode density can supply sufficient power with wide bipolar stimulus signal swings stably for finger skin stimulation and various human interface devices. 2026-02-28T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58886 Title: High-frequency (> 65 MHz) broadband transparent transducer with ultrathin gold electrode for dual-mode photoacoustic and laser-induced ultrasound microscopy Author(s): Park, Sunghun; Hong, Woongki; Park, Hyeongyu; Lee, Eunji; Nam, Sangwoo; Jung, Jin Hwan; Hyun, Jung Ho; Yu, Jaesok; Kang, Hongki; Chang, Jin Ho Abstract: For high-performance combined photoacoustic (PA) and Ultrasound (US) microscopy, precise coaxial alignment of the US and laser beams is essential. This can be realized using broadband transparent ultrasound transducers (TUTs). However, the current dual-mode imaging systems encounter significant challenges in simultaneous PA and US data acquisition due to sequential transmission of light and ultrasound and mechanical movement of dual-mode probes, leading to longer acquisition times and potential registration inaccuracies. To overcome these limitations, we propose a recently developed high-frequency broadband TUT with an ultrathin (< 10 nm) gold electrode, achieving a center frequency of 65.6 MHz and a –6 dB bandwidth of 71.6 %. The ultrathin gold electrode facilitates laser-induced ultrasound (LUS), enabling simultaneous acquisition of PA and US images. In vivo experiments demonstrate that LUS imaging can effectively replace conventional US imaging, offering highly efficient dual-mode PA/US imaging with minimized registration errors. 2025-09-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58249 Title: Simultaneous Detection of Neural Activity and Temperature in Photothermal Neural Stimulation Author(s): Kim, Duhee; Lee, Jee Woong; Kang, Seoyoung; Hong, Woongki; Lee, Jungha; Kwon, Hyuk-Jun; Jang, Jae Eun; Lee, Luke P.; Kang, Hongki Abstract: Photothermal neuromodulation is a promising non-electrical neural stimulation technology for treating brain diseases through optically induced cell membrane temperature changes. However, the technology faces limitations in understanding its mechanism and impact on cellular behavior due to the restriction of directly measuring temperature changes at the cell interface from a very close distance during optical stimulation of neural cells, necessitating advancements in high-precision temperature sensing and electrical recording without light interference. This challenge is addressed by developing ultrasensitive cell membrane interface temperature sensors integrated with low-noise electrical recording capabilities. Transparent resistive temperature detectors, composed of a 10 nm thickness of ultrathin Au film fabricated by polyelectrolyte seed layer-induced thermal evaporation, achieved precise measurement and control of temperature changes without significant light interference and self-heating. A transparent electrode composed of the same ultrathin Au layer shows low-noise electrical recordings of neural signals upon photothermal stimulation. Using this multifunctional system, it is demonstrated that an average increase of 2.34 degrees C at neuronal cell surfaces results in over 95% suppression of hippocampal neural spike activities. The approach provides unprecedented insights into the mechanisms of photothermal neuromodulation and its effects on cellular behavior, paving the way for advanced treatments of neurological disorders 2025-04-30T15:00:00Z