Browsing by Author "Yao, I-Chuan"

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Bottom Electrode Modification of ZrO2 Resistive Switching Memory Device with Au Nanodots
(2012-02-01)
Lee, Dai-Ying
;
Yao, I-Chuan
;
Tseng, Tseung-Yuen
;
材料科學與工程學系
;
電子工程學系及電子研究所
The resistive switching properties of the ZrO2 memory devices with bottom electrode modification by using Au nanodots are investigated in this study. The regular arrays of Au nanodots are fabricated on Pt bottom electrode by nanosphere lithography. Due to the tip of the Au nanodots on the Pt bottom electrode, it causes the higher electric field within the ZrO2 film above the nanodots due to reduced effective film thickness and induces the localized conducting filaments easily. The operation parameters' variation for switching devices is, therefore, suppressed with lower operation voltage and resistance ratio. Long retention time (> 10(6) s) and stubborn nondestructive readout test (> 10(4) s) at room temperature and 150 degrees C are also demonstrated in this device. (C) 2012 The Japan Society of Applied Physics
Electrical Properties and Reliability of ZnO-Based Nanorod Current Emitters
(2012-07-01)
Yao, I-Chuan
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Lin, Pang
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Huang, Sheng-He
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Tseng, Tseung-Yuen
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材料科學與工程學系
"The fabrication, optical, and field emission properties of ZnO-based nanorod emitters were studied. Ga-doped ZnO nanorods combined with the formation of tip structure on top of a ZnO nanorod by oxygen plasma treatment are employed to improve the field emission properties of the nanorod emitters. By either of these two methods, the nanorod emitters exhibit significantly reduced turn-on field and enhanced field-emission factor. The morphology, crystal structure, and composition of all the nanorods used for making emitters are characterized by a scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectrometer. The nanorods exhibit the highly preferred c-axis orientation single crystal structure. The photoluminescence spectra indicate the nanorods have better crystalline structure after doping and oxygen plasma treatment. Combining gallium doping process (Ga/Zn molar ratio of 1% in solution) and oxygen plasma treatment (etching time of 60 s), the tip-structured GZO nanorod emitters with tip angle of 100 degrees have a turn-on field of 1.99 V/mu m under a current density of 1 mu A/cm(2), field enhancement factor of 2465, and stable operation over 2 x 10(4) s. Such improved field emission properties are attributed to decreased work function and sharp nanotips morphology. In addition, the GZO nanorod emitters with tip structure are successively and stably operated between 25 degrees C and 100 degrees C over 3000 s based on the high-temperature field emission measurement results. They have high potential for practical applications in flat panel display and light emitting device in the future."
Fabrication and resistive switching characteristics of high compact Ga-doped ZnO nanorod thin film devices
(2012-04-13)
Yao, I-Chuan
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Lee, Dai-Ying
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Tseng, Tseung-Yuen
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Lin, Pang
;
材料科學與工程學系
This study investigates the resistive switching behavior of Ga-doped ZnO (GZO) nanorod thin films with various Ga/Zn molar ratios. Vertically well-aligned and uniform GZO nanorod thin films were successfully grown on Au/Ti/SiO2/p-Si substrates using an aqueous solution method. X-ray diffraction (XRD) results indicate that GZO nanorods have [0001] highly preferred orientation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show the formation of highly ordered and dense nanorod thin films. These compact GZO nanorod thin films can be used to make resistive switching memory devices. Such memory devices can be reversibly switched between ON and OFF states, with a stable resistance ratio of ten times, narrow dispersion of ON and OFF voltages, and good endurance performance of over 100 cycles. The resistive switching mechanism in these devices is related to the formation and rupture of conducting filaments consisting of oxygen vacancies, occurring at interfaces between GZO nanorods (grain boundaries). Results show that the resulting compact GZO nanorod thin films have a high potential for resistive memory applications.
Hydrogen Gas Sensors Using ZnO-SnO(2) Core-Shell Nanostructure
(2010-12-01)
Yao, I-Chuan
;
Lin, Pang
;
Tseng, Tseung-Yuen
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材料科學與工程學系
;
電子工程學系及電子研究所
The fabrication and electrical properties of H(2) gas sensor with ZnO-SnO(2) core shell nanostructure were studied. The ZnO-SnO(2) core shell nanowires were synthesized through a novel two-step chemical growth. The structure, morphology and composition of the nanowires were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray photoelectron spectrometer (XPS), respectively. The experimental results showed that the amorphous SnO(2) was uniformly coated onto the entire ZnO single crystal nanowire to form ZnO-SnO(2) core shell nanostructure. The electrical properties of the core shell nanowires in 25-200 ppm of hydrogen (H2) were measured at temperature of 250 C. It was found that the ZnO-SnO(2) core shell nanowires exhibited excellent hydrogen sensor performance, such as the sensitivity is up to 89% against 200 ppm hydrogen. Such high sensitivity was believed to be controlled by the nanoscale SnO(2) layer, which was determined from pinch-off and fully conductive state. The ZnO SnO(2) core shell nanostructures made by two-step chemical growth have high potential for gas sensor application.
Hydrogen Gas Sensors Using ZnO-SnO2 Core-Shell Nanostructure
(2010-12-01)
Yao, I-Chuan
;
Lin, Pang
;
Tseng, Tseung-Yuen
;
材料科學與工程學系
;
電子工程學系及電子研究所
The fabrication and electrical properties of H-2 gas sensor with ZnO-SnO2 core shell nanostructure were studied. The ZnO-SnO2 core shell nanowires were synthesized through a novel two-step chemical growth. The structure, morphology and composition of the nanowires were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray photoelectron spectrometer (XPS), respectively. The experimental results showed that the amorphous SnO2 was uniformly coated onto the entire ZnO single crystal nanowire to form ZnO-SnO2 core shell nanostructure. The electrical properties of the core shell nanowires in 25-200 ppm of hydrogen (H2) were measured at temperature of 250 C. It was found that the ZnO-SnO2 core shell nanowires exhibited excellent hydrogen sensor performance, such as the sensitivity is up to 89% against 200 ppm hydrogen. Such high sensitivity was believed to be controlled by the nanoscale SnO2 layer, which was determined from pinch-off and fully conductive state. The ZnO SnO2 core shell nanostructures made by two-step chemical growth have high potential for gas sensor application.
Nanotip fabrication of zinc oxide nanorods and their enhanced field emission properties
(2009-03-25)
Yao, I-Chuan
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Lin, Pang
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Tseng, Tseung-Yuen
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材料科學與工程學系
;
電子工程學系及電子研究所
The ZnO nanorods on ZnO/Si substrates were synthesized by using the low temperature growth aqueous solution method. The chemical and plasma etching treatments were carried out on the as-grown ZnO nanorods to provide the nanorods with various tip angles. The crystal structure and morphology of the ZnO nanorods were examined by x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The nanorods grew along the [ 0001] direction and had various tip angles formed after the above etching processes. The field emission properties of the ZnO nanorods with tip angles of 110 degrees and 85 degrees are: the turn-on electric fields (at the current density of 10 mu A cm(-2)) are about 3.03 and 1.70 V mu m(-1), respectively, while field enhancement factors are 1972 and 3513, respectively. The lifetime measurement result indicates the turn-on field of the ZnO nanostructures reaches a stable value during 1000 cycle times. The enhanced field emission properties are believed to benefit from decreased tip angle of the nanorod emitter.
Unipolar Resistive Switching in ZrO2 Thin Films
(2013-04-01)
Zhang, Guo-Yong
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Lee, Dai-Ying
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Yao, I-Chuan
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Hung, Chung-Jung
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Wang, Sheng-Yu
Unipolar resistive switching behaviors including bistable memory switching and monostable threshold switching were found in ZrO2 thin films fabricated by a simple sol-gel method with the Ti/ZrO2/Pt structure. The multilevel resistive switching behaviors were also revealed by varying the compliance current from 9 to 38 mA. Physical mechanisms based on a conductive filament model were proposed to explain the resistive switching phenomena and the device breakdown. A figure of merit Z = rho(a)/rho(f) was defined as a criterion for evaluating OFF/ON resistance ratio, where rho(f) and rho(a) represent the resistivities of the conductive filament and the fracture region of the filament, respectively. The advantages such as unipolar resistive switching, multilevel resistive switching, good scalability, low operation voltage (<5 V), high OFF/ON resistance ratio (>10(3)), nondestructive readout, long retention (>10(4) s), and simple fabrication method make the ZrO2-based resistive switching device a promising candidate for next-generation nonvolatile memory applications. (C) 2013 The Japan Society of Applied Physics
ZnO nanorods grown on polymer substrates as UV photodetectors
(2012-05-01)
Yao, I-Chuan
;
Tseng, Tseung-Yuen
;
Lin, Pang
;
材料科學與工程學系
;
電子工程學系及電子研究所
Vertical well-aligned and uniform ZnO nanorods were successfully prepared on low cost and flexible PET polymer substrate by aqueous solution method under various growth conditions. Current-voltage (I-V) and current-time (I-t) relationships measurements demonstrate that the photocurrent can be increased by more than 25 times upon UV illumination (lambda = 365 nm) with a power density of 70 mu W/cm(2). The photocurrents can be repeatedly and reproducibly switched by modulating UV exposure with power densities of 25-70 mu W/cm(2). The fast response time (100s) and rapid recovery time (120s) are achieved in UV turn-on/off switching measurements. Owing to the good performance including mechanical flexibility, nondestructive properties, high reliability and multilevel photoresponse, the well-aligned ZnO nanorods grown on transparent and flexible PET polymer substrates have high potential for UV photodetector applications. (C) 2012 Elsevier B.V. All rights reserved.