Browsing by Author "Chen, Po-Wen"

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A magnetic-piezoelectric smart material-structure sensing three axis DC and AC magnetic-fields
(2017-12-01)
Hung, Chiao-Fang
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Chen, Chin-Chung
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Yeh, Po-Chen
;
Chen, Po-Wen
;
Chung, Tien-Kan
In this paper, we demonstrate a smart material-structure can sense not only three-axis AC magnetic-fields but also three-axis DC magnetic-fields. Under x-axis and z-axis AC magnetic field ranging from 0.2 to 3.2 gauss, sensing sensitivity of the smart material-structure stimulated at resonant frequency is approximate 8.79 and 2.80 mV/gauss, respectively. In addition, under x-axis and z-axis DC magnetic fields ranging from 2 to 12 gauss, the sensitivity of the smart material-structure is 1.24-1.54 and 1.25-1.41 mV/gauss, respectively. In addition, under x-axis and z-axis DC magnetic fields ranging from 12 to 20 gauss, the sensitivity of the smart material-structure is 5.17-6.2 and 3.97-4.57 mV/gauss, respectively. These experimental results show that the smart material-structure successfully achieves three-axis DC and AC magnetic sensing as we designed. Furthermore, we also compare the results of the AC and DC magnetic-field sensing to investigate discrepancies. Finally, when applying composite magnetic-fields to the smart material-structure, the smart material-structure shows decent outputs as expected (consistent to the sensing principle). In the future, we believe the smart material-structure capable of sensing AC and DC magnetic fields will have more applications than conventional structures capable of sensing only DC or AC magnetic field. Thus, the smart material-structure will be an important design reference for future magnetic-field sensing technologies.
Coordination-induced emission enhancement in gold-nanoclusters with solid-state quantum yields up to 40% for eco-friendly, low-reabsorption nano-phosphors
(2019-03-11)
Huang, Hsiu-Ying
;
Cai, Kun-Bin
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Talite, Maria Jessabel
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Chou, Wu-Ching
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Chen, Po-Wen
Colloidal quantum dots (CQDs) have gained much attention as light-emitting materials for light-conversion nano-phosphors and luminescent solar concentrators. Unfortunately, those CQDs involve toxic heavy metals and frequently need to be synthesized in the hazardous organic solvent. In addition, they suffer from severe solid-state aggregation-induced self-quenching and reabsorption losses. To address these issues, here we prepare Zn-coordinated glutathione-stabilized gold-nanocluster (Zn-GSH-AuNCs) assemblies without involving heavy metals and organic solvent. Unlike GSH-AuNCs dispersed in an aqueous solution with poor photoluminescence quantum yields (PL-QYs, typically similar to 1%), those Zn-GSH-AuNCs powders hold high solid-state PL-QYs up to 40 +/- 5% in the aggregated state. Such Zn-induced coordination-enhanced emission (CEE) is attributed to the combined effects of suppressed non-radiative relaxation and enhanced charge-transfer interaction. In addition, they also exhibit a large Stokes shift, thus mitigating both aggregation-induced self-quenching and reabsorption losses. Motivated by these photophysical properties, we demonstrated white-light emission from all non-toxic, aqueous-synthesis nano-materials.
Effects of Backchannel Passivation on Electrical Behavior of Hetero-Stacked a-IWO/IGZO Thin Film Transistors
(2018-01-01)
Liu, Po-Tsun
;
Chang, Chih-Hsiang
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Kuo, Po-Yi
;
Chen, Po-Wen
;
光電工程學系
This study investigates the effects of positive gate-bias stress (PGBS) on the electrical instability of amorphous InWO/InGaZnO (a-IWO/IGZO) stacked thin-film transistors (TFTs) with a backchannel passivation layer of SiO2 or Al2O3 film. After the application of PGBS to a-IWO/IGZO TFTs with an SiO2 passivation layer, abnormal negative threshold voltage (Vth) shifts were observed, while positive Vth shifts were observed in the TFTs with an Al2O3 passivation layer. This unusual positive bias instability is explained using a two-step electrical degradation behavior model, including both electron trapping and moisture absorption at the damaged back channel interface between a-IWO/IGZO TFTs and the SiO2 passivation layer. (C) 2018 The Electrochemical Society.
FINITE ELEMENT MODELING OF ELECTROMAGNETIC-COILS TARGETING SYSTEM FOR LOCATING DISTAL SCREW-HOLE IN INTRAMEDULLARY INTERLOCKING-NAIL SURGERY
(2018-01-01)
Cheng, Ya-Wen
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Chen, Po-Wen
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Wong, Tze-Hong
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Chen, Chin-Chung
;
Hsu, Wensyang
In this paper, we report a finite element modeling of an electromagnetic-coils targeting system to locate a distal screw hole in intramedullary interlocking-nail surgery. The system consists of an internal coil, external coil, and control/measurement electronics. The internal coil is embedded in a distal screw-hole of the nail inserted into the bone. A current is applied to the internal coil to produce a directional magnetic flux penetrating the nail/bone. Thus, the external coil scans different regions of the nail/bone will receive different amount of magnetic flux, and thereby produces different voltage outputs due to the electromagnetic induction. By analyzing the voltage outputs, the distal screw-hole is targeted. However, to precisely apply this system to many different nails for people in different regions, modification and optimization of the system are needed. For rapid modification and optimization, we implement finite element method to model the targeting system. Because the modeling results are qualitatively consistent to experimental results, the modeling is successfully validated to be able to qualitatively predict experimental trends and thereby can be used for rapid system modification and optimization.
Heterostructured ferromagnet-topological insulator with dual-phase magnetic properties
(2018-01-01)
Chang, Shu-Jui
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Chuang, Pei-Yu
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Chong, Cheong-Wei
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Chen, Yu-Jung
;
Huang, Jung-Chun Andrew
The introduction of ferromagnetism at the surface of a topological insulator (TI) produces fascinating spin-charge phenomena. It has been assumed that these fascinating effects are associated with a homogeneous ferromagnetic (FM) layer possessing a single type of magnetic phase. However, we obtained phase separation within the FM layer of a Ni80Fe20/Bi2Se3 heterostructure. This phase separation was caused by the diffusion of Ni into Bi2Se3, forming a ternary magnetic phase of Ni:Bi2Se3. The inward diffusion of Ni led to the formation of an FeSe phase outward, transforming the original Ni80Fe20/Bi2Se3 into a sandwich structure comprising FeSe/Ni:Bi2Se3/Bi2Se3 with dual-phase magnetic characteristics similar to that driven by the proximity effect. Such a phenomenon might have been overlooked in previous studies with a strong focus on the proximity effect. X-ray magnetic spectroscopy revealed that FeSe and Ni:Bi2Se3 possess horizontal and perpendicular magnetic anisotropy, respectively. The overall magnetic order of the heterostructure can be easily tuned by adjusting the thickness of the Bi2Se3 as it compromises the magnetic orders of the two magnetic phases. This discovery is essential to the quantification of spin-charge phenomena in similar material combinations where the FM layer is composed of multiple elements.
Pulse-Driven Nonvolatile Perovskite Memory with Photovoltaic Read-Out Characteristics
(2019-09-18)
Chang, Shu-Jui
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Chen, Syuan-Ye
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Chen, Po-Wen
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Huang, Szu-Jung
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Tseng, Yuan-Chieh
This paper presents a unique GdFe08Ni0.2O3 perovskite thin film for use in pulse-controlled nonvolatile memory devices (combined with a SrTiO3 (STO) substrate) without the need for an electrical-stressing read-out process. The use of pulse voltage imposes permanent downward/upward polarization states on GFNO, which enables greater energy density and higher energy efficiency than the unpoled state for memory. The two polarization states produce carrier migrations in opposing directions across the GFNO/STO interface, which alter the depletion region of the device, as reflected in photovoltaic short-circuit current density (J(sc)) values. Modulating the duration (varying the number of sequential pulses but fixing the pulse width and delay time) and direction of continuous pulse voltage is an effective method for controlling J(sc), thereby allowing the fabrication of nondestructive, light-tunable, nonvolatile memory devices. In experiments, J(sc) in the downward polarized state was approximately 6 times greater than that in the upward polarized state. It is promising that more memory states can be enabled by the proposed heterostructure by selecting appropriate pulse trains. Real-time interfacial changes (relative to the nonvolatile characteristics of the device) were obtained by applying synchrotron X-ray techniques simultaneously with pulse characterization. This made it possible to separately probe the electronic and chemical states of the GFNO (a p-type-like semiconductor) and STO (an n-type-like semiconductor) while varying the pulse direction, thereby making it possible to identify the mechanisms underlying the observed phenomena.
Realization of an H-2/CO dual-gas sensor using CoPd magnetic structures
(2018-10-29)
Liang, Jaw-Yeu
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Chou, Yu-Jun
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Yin, Chiao-Wen
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Lin, Wen-Chin
;
Lin, Hong-Ji
We demonstrated the application of CoPd magnetic devices in single (H-2) and dual (H-2 and CO) gas detection by varying the thin-film structure. The anomalous Hall effect provided the read-out signal of the devices. The dual-gas sensor was particularly useful for examining whether methane reformation by steam was completed during H-2 production where CO is a byproduct. Through in situ Fourier transform infrared and X-ray absorption spectroscopy, we discovered that H-2 detection involved a charge-transfer effect between Co and Pd in addition to a surface-adsorption process, for both multilayer and alloy structures; however, CO detection was solely associated with a surface-adsorption process, which only occurred in the alloy structure. The proposed devices demonstrated performances exceeding those of current commercial models (solid-state based) regarding power consumption (<5 mW) because they were not required to undergo a heating process. An Arduino prototype platform was employed to test the modularization of the device, and adequate feasibility was demonstrated. Published by AIP Publishing.
Superparamagnetic ground state of CoFeB/MgO magnetic tunnel junction with dual-barrier
(2018-11-01)
Thanh-Nga Tran
;
Tu-Ngoc Lam
;
Yang, Chao-Yao
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Lin, Wen-Chin
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Chen, Po-Wen
CoFeB/MgO-based magnetic tunnel junctions (MTJs) have considerable potential in magnetic random access memory (MRAM), thanks to their tunable perpendicular magnetic anisotropy (PMA). We found significant reduction of dead-layer by inserting additional MgO into the MTJ structure. Interface, electronic and transport characterizations were utilized to approach the modified magnetic properties driven by the dual-MgO structure in this work. The dual-MgO structure appeared to hinder boron (B) diffusion into the metallic layer and prevent capping-layer (Ta) penetration across the interface. This suppressed the dead-layer effect and promoted overall magnetization despite PMA degradation. A robust BOx phase that formed within the dual-MgO structure presented a superparamagnetic ground state. In the single-MgO structure, any reduction in the thickness of the CoFeB promoted PMA, albeit at the cost of spin-polarization. The dual-MgO structure could restore spin-polarization by preferentially populating spin electrons into Fe/Co minority states. X-ray magnetic spectroscopy and anomalous Hall effect suggest that, the dual-MgO differs from the single-MgO with a favorable longitudinal polarized spin-channel. This makes the dual-MgO structure applicable to applications requiring in-plane rather than out-of-plane sensing.
Tailor magnetic order and spin-polarized gap states of opto-spintronic compounds by carrier mediation
(2018-08-15)
Yang, Chao-Yao
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Chiu, Yi-Hsuan
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Tsai, Kai-An
;
Hsu, Hua-Shu
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Lin, Jun-Xiao
We investigate the role of carriers in the presence of oxygen vacancies (Vo) in mediating the ferromagnetic order and spin-polarized gap states of Cu-doped ZnO nanoparticles. We demonstrate the tuning of magnetic order via post-annealing under Ar/O-2. Carrier (Vo)-rich condition (Ar-treatment) is found to favor higher magnetic order of the nanoparticles with enhanced thermal stability and wide spin-polarized gap states from ultra-violet (UV) to visible energy range. Conversely, carrier (Vo)-poor condition (O-2-treatment) reduces resistance to thermal fluctuations and quenched spin-polarization due to lack of carrier mediation. The proposed method is effective to tailor the magnetic order as well as the wide polarized band-gap states, of oxide opto-spintronic compounds by finding the physical equivalency between charge carriers and spin electrons. (C) 2018 Elsevier B.V. All rights reserved.