Browsing by Author "Yeh, Ping-Hung"

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Applications of p-n homojunction ZnO nanowires to one-diode one-memristor RRAM arrays
(2020-10-01)
Chen, Jui-Yuan
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Wu, Min-Ci
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Ting, Yi-Hsin
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Lee, Wei-Che
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Yeh, Ping-Hung
Nanowire (NW) structure is superior at defining the direction of device due to its one-dimension feature. In this work, the p-n ZnO NWs were successfully synthesized, and were able to vertically grow on Ta2O5 substrate. Thus, the well-performed Au/p-n ZnO NWs/Ta2O5/Au one-diode one-memoristor device was fabricated. The p-n ZnO NWs not only exhibited excellent rectifying behavior, but also played the role of oxygen storing during filaments formation. Therefore, the low-leakage device aimed to build high-density crossbar arrays which was required for accelerating the combination of 5 G with AI in near future applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Cobalt Silicide Nanostructures: Synthesis, Electron Transport, and Field Emission Properties
(2009-10-01)
Tsai, Chun-I
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Yeh, Ping-Hung
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Wang, Chiu-Yen
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Wu, Han-Wei
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Chen, Uei-Shin
Cobalt silicide nanostructures have been synthesized by a spontaneous chemical vapor transport and reaction method. The temperature and the vapor flow rate were shown to critically influence the growth of nanostructures. The effects of two main parameters on the growth of nanostructures were discussed. The phases formed were determined by the Gibbs free energy changes in the reactions. Various phases (CoSi, Co(2)Si) and morphologies, such as single-stern nanowires, three-dimensional (3D) nanowire networks, and aloelike nanostructures, have been synthesized. Very low turn-on field (1.42 V/mu m) and good conductance obtained from field-emission and electrical property measurements, respectively, indicate that CoSi nanowires are potentially useful for electronic devices.
Correlation among photoluminescence and the electronic and atomic structures of Sr2SiO4:xEu(3+) phosphors: X-ray absorption and emission studies
(2020-07-29)
Zheng, Shi-Yan
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Chiou, Jau-Wern
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Li, Yueh-Han
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Yang, Cheng-Fu
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Ray, Sekhar Chandra
A series of Eu3+-activated strontium silicate phosphors, Sr2SiO4:xEu(3+) (SSO:xEu(3+), x=1.0, 2.0 and 5.0%), were synthesized by a sol-gel method, and their crystalline structures, photoluminescence (PL) behaviors, electronic/atomic structures and bandgap properties were studied. The correlation among these characteristics was further established. X-ray powder diffraction analysis revealed the formation of mixed orthorhombic alpha'-SSO and monoclinic beta-SSO phases of the SSO:xEu(3+) phosphors. When SSO:xEu(3+) phosphors are excited under ultraviolet (UV) light (lambda=250 nm,similar to 4.96 eV), they emit yellow (similar to 590 nm), orange (similar to 613 nm) and red (similar to 652 and 703 nm) PL bands. These PL emissions typically correspond to 4f-4f electronic transitions that involve the multiple excited D-5(0)-> F-7(J) levels (J=1, 2, 3 and 4) of Eu3+ activators in the host matrix. This mechanism of PL in the SSO:xEu(3+) phosphors is strongly related to the local electronic/atomic structures of the Eu3+-O2- associations and the bandgap of the host lattice, as verified by Sr K-edge and Eu L-3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure, O K-edge XANES and K-alpha X-ray emission spectroscopy. In the synthesis of SSO:xEu(3+) phosphors, interstitial Eu2O3-like structures are observed in the host matrix that act as donors, providing electrons that are nonradiatively transferred from the Eu 5d and/or O 2p-Eu 4f/5d states (mostly the O 2p-Eu 5d states) to the D-5(0) levels, facilitating the recombination of electrons that have transitioned from the D-5(0) level to the F-7(J) level in the bandgap. This mechanism is primarily responsible for the enhancement of PL emissions in the SSO:xEu(3+) phosphors. This PL-related behavior indicates that SSO:xEu(3+) phosphors are good light-conversion phosphor candidates for use in near-UV chips and can be very effective in UV-based light-emitting diodes.
Direct Observation of Dual-Filament Switching Behaviors in Ta2O5-Based Memristors
(2017-04-18)
Chang, Chia-Fu
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Chen, Jui-Yuan
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Lin, Ting-Yi
Electrochemical and in situ X-ray spectroscopic studies of MnO2/reduced graphene oxide nanocomposites as a supercapacitor
(2016-07-28)
Chang, Han-Wei
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Lu, Ying-Rui
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Chen, Jeng-Lung
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Chen, Chi-Liang
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Lee, Jyh-Fu
Electrochemical and in situ X-ray absorption spectroscopy (XAS) measurements of various MnO2-coated carbon materials (MnO2/acid-functionalized carbon nanotubes (C-CNT), MnO2/reduced graphene oxide (RGO), and MnO2/RGO-Au electrodes) were conducted to evaluate the supercapacitive performances and electronic structures. MnO2 was deposited on the surface of C-CNT, RGO, and RGO-Au via a spontaneous redox reaction to facilitate the growth of the bulk form of MnO2/C-CNT and the surface forms of MnO2/RGO-based materials. Various forms of MnO2 on the carbon materials exhibited different charge/discharge behaviors. The specific capacitances of the MnO2/RGO and MnO2/RGO-Au electrodes at a current density of 1 A g(-1) were about 433 and 469 F g(-1), respectively; these values are about 1.5 times that of the MnO2/C-CNT (259 F g(-1)) electrode. Specific capacitances of 220 and 281 F g(-1) with retention rates of about 50-60% were obtained from MnO2/RGO and MnO2/RGO-Au, respectively, even at a high current density of 80 A g(-1). Experimental results revealed that the long-term electrochemical stability of the MnO2/RGO-based electrodes (with similar to 90% retention) exceeded that of the MnO2/C-CNT electrode (with similar to 60% retention) after 1000 cycles at a high scan rate of 80 A g(-1). This finding indicates that MnO2/RGO-based electrodes feature excellent cycling stability and rate capacity retention performance. To elucidate the atomic/electronic structures of the MnO2/C-CNT, MnO2/RGO, and MnO2/RGO-Au electrodes during the charge/discharge process, in situ XAS of the Mn K-edge was performed. The MnO2/RGO-based electrodes exhibited the least variations in the pre-peak intensity of the Mn K-edge during the charge/discharge process because a nano-network of MnO2 is homogeneously decorated on the outer surfaces of RGO-based electrodes to facilitate the growth of surface forms of MnO2/RGO and MnO2/RGO-Au. Analytical results further revealed suppression of changes in tunnel size and promotion of insertion/extraction behavior. This work, particularly the combination of cyclic voltammetry with in situ XAS measurements, will be of general value in the fields of nanomaterials and nanotechnology, and in their use in energy storage.
Excellent piezoelectric and electrical properties of lithium-doped ZnO nanowires for nanogenerator applications
(2014-09-01)
Chang, Yu-Tsui
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Chen, Jul-Yuan
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Yang, Tzu-Ping
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Huang, Chun-Wei
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Chiu, Chung-Hua
The well-aligned Li-doped zinc oxide nanowires (ZnO NWs) were successfully grown on Si substrates with seed layer by the hydrothermal method. The presence of Li in ZnO NWs is confirmed through EELS spectrum analysis. The acceptor energy level of the Li dopant is estimated to be 93.6 meV from the temperature-dependent PL spectra. From the SQUID measurements, the coercivity and saturation magnetization of the Li-doped ZnO NWs at room temperature are found to be 166 Oe and 9.64 memu/g, respectively. Additionally, the Li-doped ZnO NWFET confirms that the NWs were p-type with a high carrier mobility of 14.59 cm(2/)V s and an effective hole carrier concentration of 1.13 x 10(17) CM-3. The piezoelectric response of the Li-doped ZnO NWs produces much higher piezoelectric output current, voltage, and power than pure ZnO NWs. These results indicated that p-type ZnO NWs are a promising candidate for nanogenerator devices. (C) 2014 Elsevier Ltd. All rights reserved.
High-yield synthesis of ZnO nanowire arrays and their opto-electrical properties
(2012)
Kao, Chen-Yen
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Yu, Shih-Ying
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Wang, Chun-Wen
In this article, ZnO nanostructures were synthesized via the hydrothermal method which used ZnCl2 and HMTA mixed solution as the precursor. A multistep growth was adopted to improve the growth restriction of a closed system, not only the length but also the aspect ratio were increased with steps of growth, and the shape of nanorods maintained integrity. Furthermore, photoluminescence spectra which have the near-band-edge-emission (similar to 3.37 eV) and defect-related emission show the optical properties of ZnO nanostructures. The defect-related emission intensity was greatly enhanced with the increasing surface area of ZnO nanowires. The level of the OH group was attributed to the yellow-light emission (similar to 580 nm) and the red-shift phenomenon. In addition, we fabricated two types of ultraviolet photodetectors: a single nanowire device and a nanowire-array device, operating at a low bias (less than 5 mV). With the lower energy consumption and the weaker persistent photoconductive effect, our ultraviolet photodetectors have better performance, exhibiting a short response time and higher sensitivity.
Intensify the application of ZnO-based nanodevices in humid environment: O-2/H-2 plasma suppressed the spontaneous reaction of amorphous ZnO nanowires
(2014-06-02)
Lai, Chun-Yen
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Chien, Tzu-Chiao
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Lin, Ting-Yi
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Ke, Teng
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Hsu, Shih-Han
In this work, we have demonstrated that amorphous ZnO nanobranches (a-ZnO NBs) could spontaneously react from the crystalline ZnO NWs (c-ZnO NWs) at specific humid environment. The spontaneous reaction mechanism and result can be analyzed by humidity controlling and optical microscope (OM)/scanning electron microscope (SEM)/Kelvin probe force microscopy (KPFM)/transmission electron microscopy (TEM) system. We can make the c-ZnO NWs spontaneous reaction happen at different humid environments and suppress the a-ZnO NBs spontaneous reaction by oxygen/hydrogen plasma surface passivation. The hydrogen plasma surface treatment also can improve the UV sensing sensitivity more than twofold. This work provides the mechanism and methods of the a-ZnO NBs spontaneous growth and offers the passivation treatment for strengthening and enhancing ZnO-based nanodevice application in humid environment and UV light detection, respectively.
Investigation of the effect of different oxygen partial pressure to LaAlO3 thin film properties and resistive switching characteristics
(2011-12-01)
Liu, Kou-Chen
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Tzeng, Wen-Hsien
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Chang, Kow-Ming
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Huang, Jiun-Jie
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Lee, Yun-Ju
The pulsed laser deposition and growth of a high-k dielectric lanthanum aluminate LaAlO3 (LAO) thin film on indium tin oxide/glass substrate at different oxygen partial pressure was studied. Based on the pulsed laser deposition growth mechanism, we explain how a difference in the oxygen partial pressure influences the surface roughness, formation of an interfacial layer, and the transparent resistive switching characteristics of LAO thin films. The micro-structure and oxygen concentration difference inside LAO thin films may be the main reason for the difference in electrical and resistive switching properties. Films grown at higher oxygen partial pressure displayed more reliable resistive switching performance, due to the formation of the interfacial layer and a lower concentration of oxygen vacancies. The interfacial layer serves as a good oxygen reservoir and the involvement of more oxygen ions ensures the switching reliability. The migration of oxygen ions between the interfacial layer and the LAO film under applied bias may be the switching mechanism. (C) 2011 Elsevier B. V. All rights reserved.
Low Resistivity Metal Silicide Nanowires with Extraordinarily High Aspect Ratio for Future Nanoelectronic Devices
(2011-11-01)
Chen, Sheng-Yu
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Yeh, Ping-Hung
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Wu, Wen-Wei
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Chen, Uei-Shin
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Chueh, Yu-Lun
One crucial challenge for the integrated circuit devices to go beyond the current technology has been to find the appropriate contact and interconnect materials. NISI has been commonly used in the 45 nm devices mainly because it possesses the lowest resistivity among all metal silicides. However, for devices of even smaller dimension, its stability at processing temperature is in doubt. In this paper, we show the growth of high-quality nanowires of NiSi(2), which is a thermodynamically stable phase and possesses low resistivity suitable for future generation electronics devices. The origin of low resistivity for the nanowires has been clarified to be due to its defect-free single-crystalline structure instead of surface and size effects.
Nanoflaky MnO2/functionalized carbon nanotubes for supercapacitors: an in situ X-ray absorption spectroscopic investigation
(2015-01-01)
Chang, Han-Wei
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Lu, Ying-Rui
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Chen, Jeng-Lung
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Chen, Chi-Liang
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Lee, Jyh-Fu
The surfaces of acid- and amine-functionalized carbon nanotubes (C-CNT and N-CNT) were decorated with MnO2 nanoflakes as supercapacitors by a spontaneous redox reaction. C-CNT was found to have a lower edge plane structure and fewer defect sites than N-CNT. MnO2/C-CNT with a highly developed surface area exhibited favorable electrochemical performance. To determine the atomic/electronic structures of the MnO2/functionalized CNTs (MnO2/C-CNT and MnO/N-CNT) during the charge/discharge process, in situ X-ray absorption spectroscopy (XAS) measurements were made at the Mn K-edge. Both C-CNT and N-CNT are highly conductive. The effect of the scan rate on the capacitance behavior was also examined, revealing that the pi* state of CNT and the size of the tunnels in pseudo-capacitor materials (which facilitate conduction and the transport of electrolyte ions) are critical for the capacitive performance, and their role depends on the scan rate. In the slow charge/discharge process, MnO2/N-CNT has a more symmetrical rectangular cyclic voltammetry (CV) curve. In the fast charge/discharge process, MnO2/C-CNT with a highly developed surface provides fast electronic and ionic channels that support a reversible faradaic redox reaction between MnO2 nanoflakes and the electrolyte, significantly enhancing its capacitive performance over that of MnO2/N-CNT. The MnO2/C-CNT architecture has great potential for supercapacitor applications. The information that was obtained herein helps to elucidate CNT surface modification and the design of the MnO2/functionalized CNT interface with a view for the further development of supercapacitors. This work, and especially the combination of CV with in situ XAS measurements, will be of value to readers with an interest in nanomaterial, nanotechnology and their applications in energy storage.
Near-Infrared Laser-Annealed IZO Flexible Device as a Sensitive H2S Sensor at Room Temperature
(2020-06-03)
Chang, Po-Yi
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Lin, Ching-Fu
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Rouphael, Samer El Khoury
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Huang, Ting-Hsuan
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Wu, Chang-Mao
A metal-oxide material (indium zinc oxide [IZO]) device with near-infrared (NIR) laser annealing was demonstrated on both glass and bendable plastic substrates (polycarbonate, polyethylene, and polyethylene terephthalate). After only 60 s, the sheet resistance of IZO films annealed with a laser was comparable to that of thermal-annealed devices at temperatures in the range of 200-300 degrees C (1 h). XPS, ATR, and AFM were used to investigate the changes in the sheet resistance and correlate them to the composition and morphology of the thin film. Finally, the NIR-laser-annealed IZO films were demonstrated to be capable of detecting changes in humidity and serving as a highly sensitive gas sensor of hydrogen sulfide (in ppb concentration), with room-temperature operation on a bendable substrate.
Nickel/Platinum Dual Silicide Axial Nanowire Heterostructures with Excellent Photosensor Applications
(2016-02)
Wu, Yen-Ting
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Chang, Chia-Fu
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Chen, Jui-Yuan
Transition metal silicide nanowires (NWs) have attracted increasing attention as they possess advantages of both silicon NWs and transition metals. Over the past years, there have been reported with efforts on one silicide in a single silicon NW. However, the research on multicomponent silicides in a single silicon NW is still rare, leading to limited functionalities. In this work, we successfully fabricated beta-Pt2Si/Si/theta-Ni2Si, beta-Pt2Si/theta-Ni2Si, and Pt, Ni, and Si ternary phase axial NW heterostructures through solid state reactions at 650 degrees C. Using in situ transmission electron microscope (in situ TEM), the growth mechanism of silicide NW heterostructures and the diffusion behaviors of transition metals were systematically studied. Spherical aberration corrected scanning transmission electron microscope (Cs-corrected STEM) equipped with energy dispersive spectroscopy (EDS) was used to analyze the phase structure and composition of silicide NW heterostructures. Moreover, electrical and photon properties for the silicide nanowire heterostructures demonstrated promising applications in nano-optoeletronic devices. We found that Ni, Pt, and Si ternary phase nanowire heterostructures have an excellent infrared light sensing property which is absent in bulk Ni2Si or Pt2Si. The above results would benefit the further understanding of heterostructured nano materials. sensing
Nonvolatile polycrystalline silicon thin-film-transistor memory with oxide/nitride/oxide stack gate dielectrics and nanowire channels
(2007-03-19)
Chen, Shih-Ching
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Chang, Ting-Chang
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Liu, Po-Tsun
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Wu, Yung-Chun
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Yeh, Ping-Hung
In this work, the authors study a polycrystalline silicon thin-film transistor (poly-Si TFT) with oxide/nitride/oxide (ONO) stack gate dielectrics and multiple nanowire channels for the applications of both nonvolatile silicon-oxide-nitride-oxide-silicon (SONOS) memory and switch transistor. The proposed device named as nanowire SONOS-TFT has superior electrical characteristics of a transistor such as on/off current ratio, threshold voltage (V-th), and subthreshold slope due to the good gate control ability originated from fringing electrical field effects. Moreover, the proposed device under adequate operation scheme can exhibit high program/erase efficiency and good retention time characteristics at high temperature. (c) 2007 American Institute of Physics.
Nonvolatile Si/SiO2/SiN/SiO2/Si type polycrystalline silicon thin-film-transistor memory with nanowire channels for improvement of erasing characteristics
(2007-11-05)
Chen, Shih-Ching
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Chang, Ting-Chang
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Liu, Po-Tsun
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Wu, Yung-Chun
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Chin, Jing-Yi
A silicon-oxide-nitride-oxide-silicon type polycrystalline silicon thin-film transistor (poly-Si TFT) with nanowire channels was investigated for both transistor and memory applications. The poly-Si TFT memory device has superior electrical characteristics, such as higher drain current, smaller threshold voltage, and steeper subthreshold slope. Also, the simulation result on electrical field reveals that the electrical field across the tunnel oxide is enhanced and that across the blocking oxide is reduced at the corner regions. This will lead to the parasitic gate injection activity and the erasing speed can be apparently improved in the memory device due to the pronounced corner effect and narrow channel width.
One-Minute Fish Freshness Evaluation by Testing the Volatile Amine Gas with an Ultrasensitive Porous-Electrode-Capped Organic Gas Sensor System
(2017-04-01)
Chang, Liang-Yu
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Chuang, Ming-Yen
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Zan, Hsiao-Wen
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Meng, Hsin-Fei
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Lu, Chia-Jung
In this work, we successfully demonstrate a fast method to determine the fish freshness by using a sensing system containing an ultrasensitive amine gas sensor to detect the volatile amine gas from the raw fish meat. When traditional titration method takes 4 h and complicated steps to test the total volatile basic nitrogen (TVB-N) as a worldwide standard for fish freshness, our sensor takes 1 min to deliver an electrical sensing response that is highly correlated with the TVB-N value. When detecting a fresh fish with a TVB-N as 18 mg/100 g, the sensor delivers an effective ammonia concentration as 100 ppb. For TVB-N as 28-35 mg/100 g, a well-accepted freshness limit, the effective ammonia concentration is as 200-300 ppb. The ppb-regime sensitivity of the sensor and the humidity control in the sensing system are the keys to realizing fast and accurate detection. It is expected that the results in this report enable the development of on-site freshness detection and real-time monitoring in a fish factory.
Photo-assisted recovery in ammonia sensor based on organic vertical diode
(2019-04-01)
Lin, Yu-Ting
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Yu, Shang-Yu
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Zan, Hsiao-Wen
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Yeh, Ping-Hung
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Lu, Chia-Jung
In this article, a photo-assisted gas sensor was provided to solve the slow recovering issue of the organic gas sensor. The proposed organic gas sensor can detect ammonia in parts-per-billion regime in 30 s and can be multiple uses, but the long recovery time about 5 min places difficulty to realize rapidly multiple-time sensing. Therefore, we used the photo-absorption ability in the organic semiconductor layer to generate the photocurrent and hence to compensate the current drop due to the ammonia absorption. The recovery time was significantly reduced to be only 1 min. The specific wavelength was also found to match the absorption spectrum in different organic sensing materials. As a comparison, the quartz crystal microbalance (QCM) was used to clarify the gas absorption and desorption mechanism. It is believed that this photo-assisted gas detection could be a general method to solve the slow recovery in organic-based gas sensors.
Revealing conducting filament evolution in low power and high reliability Fe3O4/Ta2O5 bilayer RRAM
(2018-11-01)
Chang, Chia-Fu
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Chen, Jui-Yuan
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Huang, Guan-Min
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Lin, Ting-Yi
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Tai, Kuo-Lun
In this work, we used the polycrystalline-Fe3O4 to improve the reliability of the Ag/Ta2O5/Pt resistive random access memory (RRAM). In both the Ag/Ta2O5/Fe3O4/Pt and Ag/Fe3O4/Ta2O5/Pt structures, the switching properties for these bilayer RRAMs were measured in atmosphere and vacuum environments. The results demonstrated that the humidity would affect the Ag filament formation in different environments, and the Ta2O5 and Fe3O4 interface in a different sequence would change the performance of the device, particularly the Forming voltage. Furthermore, the switching voltage and reliability of these bilayer RRAMs was better than single-layer RRAM device, which significantly increased endurance, especially in the Ag/Fe3O4/Ta2O5/Pt device. We also observed the conducting filament shape and evolution during Forming via in/ex-situ transmission electron microscopy (TEM) in the Ag/Fe3O4/Ta2O5/Pt system. In low humidity, the conducting filament was composed of many weak filaments in a low-resistance state (LRS), where the grain boundaries in the Fe3O4 layer limited filament size. The results of energy dispersive spectrometry (EDS) analysis demonstrated that the filament was composed of Ag metal. This study provided detailed switching knowledge of the bilayer RRAM for improving the reliability and power consumption of the device and new design viewpoints of the RRAM structure in future applications.
Single-crystalline delta-Ni2Si nanowires with excellent physical properties
(2013-06-19)
Chiu, Wen-Li
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Chiu, Chung-Hua
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Chen, Jui-Yuan
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Huang, Chun-Wei
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Huang, Yu-Ting
In this article, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) via chemical vapor deposition method using NiCl2 center dot 6H(2)O as a single-source precursor. Various morphologies of delta-Ni2Si NWs were successfully acquired by controlling the growth conditions. The growth mechanism of the delta-Ni2Si NWs was thoroughly discussed and identified with microscopy studies. Field emission measurements show a low turn-on field (4.12 V/mu m), and magnetic property measurements show a classic ferromagnetic characteristic, which demonstrates promising potential applications for field emitters, magnetic storage, and biological cell separation.
Solution-processed finger-type organic proximity sensor with high displacement resolution
(2016)
Liao, Jung-Sung
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Wang, Kuan-Hsun
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Zan, Hsiao-Wen
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Meng, Hsin-Fei
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Yeh, Ping-Hung
Proximity sensors are interesting devices for applications like smart homes or human-machine interfaces. This work investigates a cheap and compact short-range proximity sensor based on an organic photo detector combined with a commercial LED. Low-cost solution-processed organic materials are used, and low process temperatures at 140 degrees C also facilitate future integration on, e.g., plastic substrates. In particular, to avoid damage of the organic layer during the patterning process, a new organic photo detector with a semi-transparent organic active layer and a transparent silver nanowire top electrode was designed. The proposed sensor can be realized by using only one shadow mask to pattern the opaque bottom electrode layer. The opaque finger-type bottom electrode not only partly shields the light emitted from below the device, but also defines the active regions with vertical electric field to generate and collect photo current. In the experiments conducted in this paper, the maximum detection distance was found to be 2 cm, whereas the lower end of the measurement range was 0.2 cm.