Browsing by Author "Chen, Yi-Chun"

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A gate-free monolayer WSe2 pn diode
(2018-08-07)
Chen, Jhih-Wei
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Lo, Shun-Tsung
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Ho, Sheng-Chin
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Wong, Sheng-Shong
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Vu, Thi-Hai-Yen
Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron microspectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics.
A hierarchical approach for online temporal lobe seizure detection in long-term intracranial EEG recordings
(2013-08-01)
Liang, Sheng-Fu
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Chen, Yi-Chun
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Wang, Yu-Lin
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Chen, Pin-Tzu
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Yang, Chia-Hsiang
Objective. Around 1% of the world's population is affected by epilepsy, and nearly 25% of patients cannot be treated effectively by available therapies. The presence of closed-loop seizure-triggered stimulation provides a promising solution for these patients. Realization of fast, accurate, and energy-efficient seizure detection is the key to such implants. In this study, we propose a two-stage on-line seizure detection algorithm with low-energy consumption for temporal lobe epilepsy (TLE). Approach. Multi-channel signals are processed through independent component analysis and the most representative independent component (IC) is automatically selected to eliminate artifacts. Seizure-like intracranial electroencephalogram (iEEG) segments are fast detected in the first stage of the proposed method and these seizures are confirmed in the second stage. The conditional activation of the second-stage signal processing reduces the computational effort, and hence energy, since most of the non-seizure events are filtered out in the first stage. Main results. Long-term iEEG recordings of 11 patients who suffered from TLE were analyzed via leave-one-out cross validation. The proposed method has a detection accuracy of 95.24%, a false alarm rate of 0.09/h, and an average detection delay time of 9.2 s. For the six patients with mesial TLE, a detection accuracy of 100.0%, a false alarm rate of 0.06/h, and an average detection delay time of 4.8 s can be achieved. The hierarchical approach provides a 90% energy reduction, yielding effective and energy-efficient implementation for real-time epileptic seizure detection. Significance. An on-line seizure detection method that can be applied to monitor continuous iEEG signals of patients who suffered from TLE was developed. An IC selection strategy to automatically determine the most seizure-related IC for seizure detection was also proposed. The system has advantages of (1) high detection accuracy, (2) low false alarm, (3) short detection latency, and (4) energy-efficient design for hardware implementation.
Algorithm and Architecture of Disparity Estimation With Mini-Census Adaptive Support Weight
(2010-06-01)
Chang, Nelson Yen-Chung
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Tsai, Tsung-Hsien
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Hsu, Bo-Hsiung
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Chen, Yi-Chun
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Chang, Tian-Sheuan
High-performance real-time stereo vision system is crucial to various stereo vision applications, such as robotics, autonomous vehicles, multiview video coding, freeview TV, and 3-D video conferencing. In this paper, we proposed a high-performance hardware-friendly disparity estimation algorithm called mini-census adaptive support weight (MCADSW) and also proposed its corresponding real-time very large scale integration (VLSI) architecture. To make the proposed MCADSW algorithm hardware-friendly, we proposed simplification techniques such as using mini-census, removing proximity weight, using YUV color representation, using Manhattan color distance, and using scaled-and-truncate weight approximation. After applied these simplifications, the MCADSW algorithm was not only hardware-friendly, but was also 1.63 times faster. In the corresponding realtime VLSI architecture, we proposed partial column reuse and access reduction with expanded window to significantly reduce the bandwidth requirement. The proposed architecture was implemented using United Microelectronics Corporation (UMC) 90 nm complementary metal-oxide-semiconductor technology and can achieve a disparity estimation frame rate of 42 frames/s for common intermediate format size images when clocked at 95 MHz. The synthesized gate-count and memory size is 563k and 21.3 kB, respectively.
Atomic-Scale Evolution of Local Electronic Structure Across Multiferroic Domain Walls
(2011-04-05)
Chiu, Ya-Ping
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Chen, Yu-Ting
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Huang, Bo-Chao
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Shih, Min-Chuan
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Yang, Jan-Chi
Direct evidence of the electronic configurations across domain walls in BiFeO(3) is quantitatively characterized by cross-sectional scanning tunneling microscopy. Atomic-scale band evolution and the asymmetrically built-in potential barrier at domain boundaries are demonstrated. The 109 degrees domain walls register a remarkable decrease in the bandgap, suggesting a new route to control the local conducting channels within 2 nm.
Chemical vapor deposition of diamond on an adamantane-coated sapphire substrate
(2014)
Chen, Yi-Chun
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
Continuous diamond thin films can be grown on sapphire substrates by microwave plasma chemical vapor deposition utilizing a pretreatment of adamantane dip coating on the substrate for enhanced nucleation. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy show that < 111 > oriented diamond films of good crystallinity can be deposited on adamantane-coated sapphire substrates. Cross-sectional transmission electron microscopy at the diamond/sapphire interface shows that diamond can be directly synthesized on sapphire without any interlayer.
Chemical vapor deposition of diamond on silicon substrates coated with adamantane in glycol chemical solutions
(2013)
Chen, Yi-Chun
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
Diamonds were synthesized on adamantane-coated mirror-polished Si (100) substrates by microwave plasma chemical vapor deposition (MPCVD) using a gas mixture of H-2 and CH4. Before MPCVD deposition, Si substrates were dip-coated in chemical solutions of ethylene glycol and diethylene glycol with adamantane. With the coating of adamantane, the diamond nucleation can be enhanced with a density over 1 x 10(8) cm(-2) and the deposited diamond films are shown to be of good crystallinity by scanning electron microscopy and Raman spectrometry. The study demonstrates a simple and efficient way of diamond deposition on a smooth Si substrate.
Controllable electrical conduction at complex oxide interfaces
(2014-06-01)
Vu Thanh Tra
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Yang, Jan-Chi
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Hsieh, Ying-Hui
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Lin, Jiunn-Yuan
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Chen, Yi-Chun
Oxide interfaces have sparked considerable interest due to their fascinating physical properties and promising possibilities for next-generation nanoelectronics. Three intriguing oxide interfaces, hetero-, homo-, and tubular interfaces, will be discussed in detail in this review. First, the development and fundamental properties of classical heterointerfaces will be elaborated. Using LaAlO3/SrTiO3 as a case study, we present the most generic approach to control the two-dimensional electron conduction at the heterointerface. Secondly, several key issues based on interesting observations on ferroic homointerfaces will be addressed. Multiple controls of fascinating functionalities based on multiferroic BiFeO3 domain walls will be presented as a model system. Finally, as the most challenging task, we review a new type of complex oxide interfaces, the tubular interface. Further insights of recently emerged tubular interfaces in BiFeO3/CoFe2O4 system will be explored, which serve as one of the focal roles in developing new functional interfaces and potentially new type of nanostructures. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Crossover between superconductivity and magnetism in SrRuO3 mesocrystal embedded YBa2Cu3O7-x heterostructures
(2016)
Suresh, Vandrangi
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Lin, Jheng-Cyuan
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Liu, Heng-Jui
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Zhang, Zaoli
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Chiang, Ping-Chih
The competition between superconductivity and ferromagnetism poses great challenges and has attracted renewed interest for applications in novel spintronic devices. In order to emphasize their interactions, we fabricated a heterostructure composed of superconducting YBa2Cu3O7-delta (YBCO) film embedded with itinerant ferromagnetic SrRuO3 (SRO) mesocrystals. Starting from a doping concentration of 10 vol% of SRO mesocrystal in a YBCO matrix, corresponding to the density of SRO nanocrystals similar to 5 x 10(9) cm(-2), which exhibits the typical characteristic of a metal-superconductor transition, and then increasing the magnetic interactions as a function of SRO embedment, the electronic correlation and the interplay between superconductivity and magnetism throughout the temperature regime were investigated. A metal-insulator transition in the normal state of YBCO and a crossover between superconductivity and magnetism at low temperatures were found upon increasing the density of nano-size SRO crystallites in the YBCO matrix as a consequence of competing interactions between these two ordered phases.
Current-Mode Synthetic Control (CSC) Technique for High Efficiency DC-DC Boost Converters Over a Wide Load Range
(2011)
Su, Yi-Ping
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Chen, Yi-Chun
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Huang, Han-Hsiang
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Lee, Yu-Huei
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Yang, Yao-Yi
The proposed current-mode synthetic control (CSC) technique in the design of boost converters can improve the transient response time and maintain high conversion efficiency over a wide load range. The CSC technique has high accuracy similar to the current-mode control and doesn't need the slope compensation for simplicity. Besides, the transient response is also improved due to the current-mode hysteresis control. The load-dependent switching frequency at light loads results in high power conversion efficiency. Experimental results show that the output voltage ripple can be kept smaller than 50mV over a wide load current range from 0mA to 400mA with power conversion efficiency higher than 90% at load current of 10mA.
Current-Mode Synthetic Control Technique for High-Efficiency DC-DC Boost Converters Over a Wide Load Range
(2014-08-01)
Su, Yi-Ping
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Luo, Yean-Kuo
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Chen, Yi-Chun
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Chen, Ke-Horng
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交大名義發表
This paper proposes a current-mode synthetic control (CSC) technique for the design of boost converters to overcome the difficulty in designing a current-ripple hysteresis boost converter and to maintain high conversion efficiency over a wide load range. The CSC technique has a high accuracy because of the additional voltage path through the error amplifier. A smooth load transient response is maintained when the operation transits from continuous conduction mode with a nearly constant switching frequency to discontinuous conduction mode with a load-dependent switching frequency. Generally, ripple performance, light-load efficiency, and switching frequency are traded off in the design of hysteresis control regulator. In this paper, a balance among the load-dependent switching frequencies at light loads results in high power conversion efficiency compared with conventional pulsewidth modulation converter and attains compact ripple performance. The experimental results show that the output voltage ripple can be kept <50 mV over a wide load current range from 10 to 400 mA, where as power conversion efficiency is maintained at 78% at a load current of 10 mA when the switching frequency is decreased from 5 to 2 MHz.
Deterministic optical control of room temperature multiferroicity in BiFeO3 thin films
(2019-06-01)
Liou, Yi-De
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Chiu, Yu-You
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Hart, Ryan Thomas
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Kuo, Chang-Yang
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Huang, Yen-Lin
Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.
Development and verification of the coaxial heterogeneous hyperspectral system for the Wax Apple tree
(2019-01-01)
Li, Yi-Sheng
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Yan, Yung-Jhe
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Shih, Ruei-Siang
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Chang, Chao-Hsin
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Chen, Tzung-Cheng
This paper presents the design of the coaxial heterogeneous hyperspectral system, concurrently sensing for the visible (YES) light and short-wave infrared (SWIR) light wavelengths under the same space axis. By the designed mechanism, this hyperspectral system can provide more hands and broader wavelengths in every scan. The adequate spectral information of the target makes the analysis more comprehensive. For this hyperspectral system, the spatial correction and spectral correction are required. The spatial correction deals with the spatial match between the VIS and SWIR data. Moreover, the spectral correction is to eliminate the different response of the YES and SWIR sensor. The purpose of these corrections was to verify the design and provide the accurate reflection spectrum.
Direct spectroscopic evidence of charge reversal at the Pb(Zr(0.2)Ti(0.8))O(3)/La(0.7)Sr(0.3)MnO(3) heterointerface
(2011-01-21)
Wu, Chung-Lin
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Lee, Pei-Wei
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Chen, Yi-Chun
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Chang, Lo-Yueh
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Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ultrathin film and a bottom La(0.7)Sr(0.3)MnO(3) (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Direct spectroscopic evidence of charge reversal at the Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterointerface
(2011-01-21)
Wu, Chung-Lin
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Lee, Pei-Wei
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Chen, Yi-Chun
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Chang, Lo-Yueh
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Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr0.2Ti0.8)O-3 (PZT) ultrathin film and a bottom La0.7Sr0.3MnO3 (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
DLWV2: a Deep Learning-based Wearable Vision-system with Vibrotactile-feedback for Visually Impaired People to Reach Objects
(2018-01-01)
Shih, Meng-Li
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Chen, Yi-Chun
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Tung, Chia-Yu
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Sun, Cheng
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Cheng, Ching-Ju
We develop a Deep Learning-based Wearable Vision-system with Vibrotactile-feedback (DLWV2) to guide Blind and Visually Impaired (BVI) people to reach objects. The system achieves high accuracy in object detection and tracking in 3-D using an extended deep learning-based 2.5D detector and a 3-D object tracker with the ability to track 3-D object locations even outside the camera field-of-view. We train our detector with a large number of images with 2.5D object ground-truth (i.e., 2-D object bounding boxes and distance from the camera to objects). A novel combination of HTC Vive Tracker with our system enables us to automatically obtain the ground-truth labels for training while requiring very little human effort to set up the system. Moreover, our system processes frames in real-time through a client-server computing platform such that BVI people can receive realtime vibrotactile guidance. We conduct a thorough user study on 12 BVI people in new environments with object instances which are unseen during training. Our system outperforms the non-assistive guiding strategy with statistic significance in both time and the number of contacting irrelevant objects. Finally, the interview with BVI users confirms that our system with distance-based vibrotactile feedback is mostly preferred, especially for objects requiring gentle manipulation such as a bottle with water inside.
Domain relaxation dynamics in epitaxial BiFeO3 films: Role of surface charges
(2012-09-01)
Chen, Yi-Chun
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Ko, Cheng-Hung
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Huang, Yen-Chin
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Yang, Jan-Chi
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Chu, Ying-Hao
The thermodynamic parameters of domain relaxation process in the absence of external electric fields are related to the intrinsic electrostatic and stress/strain conditions inside the materials, such as the states at surface, states at interface with the electrode, and the atomic defects in the bulk. In order to perform systematical studies of these intrinsic effects, we investigated domain relaxation in a monodomain environment, which was obtained in strained epitaxial BiFeO3 (BFO)(111) films. Without as-grown domain walls and grain boundaries, the epitaxial BFO (111) film provided an ideal system for the dynamic observation of 180-degree domain wall motion. Nano-domains were initially created by writing voltage pulses under the tip of a scanning force microscope and then relaxed through time. The downward polarized domains exhibited much better retention behaviors than the upward domains. A two-step backswitching process was observed, and the behaviors varied with the initial domain sizes. Surface potential measurement showed the dissipation of surface screen charges with time, which was strongly coupled with the 1st step relaxation. The asymmetry behaviors for upward and downward backswitchings, and the two-stage relaxation processes can be explained by the mobile vacancies and the redistribution of surface charges. This study provides the basic understanding of the role of surface charges during the ferroelectric domain relaxation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746077]
Effect of crosslinking agents on the dispersive behaviour of polymer particles in seed swelling polymerisation
(2017-07-25)
Kao, Yu-Chen
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Whang, Wha-Tzong
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Chen, Yi-Chun
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Chen, Kai-Chi
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材料科學與工程學系
This study focused on the effect of crosslinker structure between PMMA on the dispersity of crosslinked particles in seed swelling polymerisation. We used five different crosslinking agents in an assessment of the dispersity of crosslinking monodisperse particles using PMMA seed particles in seed swelling polymerisation. These results show that the structure of the crosslinking agent affects the dispersity during the swelling stage. According to the solubility parameter theory of computation, the departure of similar solubility parameter causes the swollen particles to segregate into more dispersity. (C) 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Electrical Control of Multiferroic Orderings in Mixed-Phase BiFeO3 Films
(2012-06-12)
Chen, Yi-Chun
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He, Qing
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Chu, Feng-Nan
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Huang, Yen-Chin
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Chen, Jhih-Wei
Electrical Modulation of the Local Conduction at Oxide Tubular Interfaces
(2013-10-01)
Hsieh, Ying-Hui
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Strelcov, Evgheni
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Liou, Jia-Ming
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Shen, Chia-Ying
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Chen, Yi-Chun
Heterointerfaces between complex oxides have sparked considerable interest due to their fascinating physical properties and their offering of new possibilities for next-generation electronic devices. The key to realize practical applications is the control through external stimuli. In this study, we take the self-assembled BiFeO3-CoFe2O4 tubular interface as a model system to demonstrate the nonvolatile electric control of the local conduction at the complex oxide tubular interface. The fundamental mechanism behind this modulation was explored based on static and dynamic conductive atomic force microscopies. We found the movement of oxygen vacancies in the BiFeO3-CoFe2O4 heterostructure is the key to drive this intriguing behavior. This study delivers a possibility in developing next-generation electronic devices.
Electrical polarization induced by atomically engineered compositional gradient in complex oxide solid solution
(2019-04-12)
Wu, Ping-Chun
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Huang, Rong
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Hsieh, Ying-Hui
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Wang, Bo
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Yen, Min
Control of inhomogeneity in materials in order to avoid unexpected effects to the system remains a challenge. In this study, we seek to engineer inhomogeneity in materials and anticipate new properties. Through precise control of composition at the atomic scale, an electrical polarization is induced in the composition-graded LaAIO(3)-SrTiO3 solid solution epitaxially deposited on NdGaO3 substrates. By tailoring the direction of compositional gradient, the relationship between structure and electrical polarization is simulated via phase-field modeling and revealed by a combination of scanning transmission electron microscopy and scanning probe microscopy. The analysis of the results indicates that the induced polarization is due to the flexoelectric effect in the compositional gradient system. The results of this study provide a new pathway for obtaining a new material genome. Moreover, by a suitable design of the new genome, that is, by using different combinations of compositional gradient geometries, local conduction can be obtained and manipulated, providing a new approach to obtain the desired properties.