Browsing by Author "Chang, Chia-Tsung"

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Annealing effect on the photoluminescence characteristics of ZnO-nanowires and the improved optoelectronic characteristics of p-NiO/n-ZnO nanowire UV detectors
(2015-06-01)
Li, Yu-Ren
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Wan, Chung-Yun
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Chang, Chia-Tsung
;
Huang, Yu-Chin
;
Tsai, Wan-Lin
Transparent ultraviolet (UV) detectors with nanoheterojunctions (NHJs) of p-type NiO and n-type ZnO nanowires (ZnO-NWs) were successfully fabricated using a DC sputtering system and a hydrothermal process, respectively. After annealing in nitrogen ambient, the near-band-edge emission to deep level emission ratio (NBE/DLE) of ZnO-NWs gradually increased as the temperature increased and reached a maximum of 28.9 at a temperature setting of 500 degrees C. In contrast, after annealing in oxygen atmosphere, the NBE/DLE of ZnO-NWs initially increased from 1.2 to 5.9 and then decreased to 3.2. At a reverse bias of 2V, the devices with the 500-degrees C-N-2-annealed ZnO-NWs exhibited better sensitivity (J(UV)/J(Dark) = 5.65; J(Visible)/J(Dark) = 1.35) to UV light (365 nm, 0.3 mW/cm(2)) than those with the as-grown ZnO-NWs (J(UV)/J(Dark) = 4.98; J(Visible)/J(Dark) = 3.82) because the structural defects in ZnO-NWs were effectively eliminated after annealing in nitrogen ambient at 500 degrees C. (C) 2015 The Japan Society of Applied Physics
Effect of arrangement of carbon nanotube pillars on its gas ionization characteristics
(2013-06-01)
Chang, Chia-Tsung
;
Huang, Chun-Yu
;
Li, Yu-Ren
;
Cheng, Huang-Chung
;
電子工程學系及電子研究所
The gas ionization sensors (GISs) using the carbon nanotube (CNT) pillars which has the pillar height (H) of 15 mu m with interpillar spacing (R) of 30 mu m as the cathode had been proposed for the first time to exhibit the 20 times higher field enhancement factor (beta) and the lower breakdown voltage of 350V with respect to the CNT film ones for nitrogen gas at the pressure of 0.035 Torr. As the H increased from 5 mu m to 15 mu m, the beta increased with increasing the H since the electrical field could be enhanced via the aspect ratio increment. However, as the H increased from 15 mu m to 60 mu m, the beta decreased with increasing the H owing to the increased field-screening effect. Such an optimum GIS with the CNT pillars also exhibited high sensitivity and selectivity for different kinds of gases detection as well as the good linearity for detecting the gas mixture. (C) 2013 Elsevier B.V. All rights reserved.
Effect of Oxygen Annealing on the Ultraviolet Photoresponse of p-NiO-Nanoflower/n-ZnO-Nanowire Heterostructures
(2011-07-01)
Yang, Po-Yu
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Wang, Jyh-Liang
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Tsai, Wei-Chih
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Wang, Shui-Jinn
;
Lin, Jia-Chuan
A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O(2)) ambient exhibited better rectification behavior (l(forward)/l(reverse) = 427), a lower forward threshold voltage (V(th) = 0.98 V), a lower leakage current (1.68 x 10(-5) A/cm(2)), and superior sensitivity (l(UV)/l(dark) = 57.8; l(visible)/l(dark) = 1.25) to UV light (lambda = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity. A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O(2) ambient indicate that they can be applied to nano-integrated optoelectronic devices.
Field Emission Properties of Carbon Nanotube Arrays on the Thickness-Controlled Flexible Substrate by the Pattern Transfer Process
(2012-07-01)
Chang, Chia-Tsung
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Juan, Chuan-Ping
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Lin, Yi-Chan
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Li, Yu-Ren
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Tsai, Wan-Lin
A technigal with the polydimethylsiloxane (PDMS) solution infiltrated into the SiOx-coated CNTAs has been utilized to directly transfer the CNTAs away from the silicon substrate. The oxide coating layer was utilized to protect the morpholgy of as-grown patterned vertical aligmed carbon nanotube (CNTs) arrays. The high density plasma reactive ions etching (HDP-RIE) system was used to make the CNTs emerge from the surface of the flexible substrate and modify the crystallines of CNTs. After the protecting oxide was HDP-RIE-processed for 8 min, the emission current properties were enhanced to be 1.03 V/mu m and 1.43 V/mu m, respectively, for the turn-on field and the threshold field, as compared with 1.25 V/mu m and 1.59 V/mu m for the as-grown CNTs, accordingly. The Field Emission (FE) enhancement after dry etching could be attributed to the open-ended structures and better crystalline.
Field-Emission Characteristics of Al-Doped ZnO Nanostructures Hydrothermally Synthesized at Low Temperature
(2011-07-01)
Yang, Po-Yu
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Wang, Jyh-Liang
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Tsai, Wei-Chih
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Wang, Shui-Jinn
;
Lin, Jia-Chuan
The aluminum-doped ZnO (AZO) nanostructures with different Al concentrations were synthesized on AZO/glass substrate via a simple hydrothermal growth method at a temperature as low as 85 degrees C. The morphologies, crystallinity, optical emission properties, and chemical bonding states of AZO nanostructures show evident dependence on the aluminum dosage. The morphologies of AZO nanostructures were changed from vertically aligned nanowires (NWs), and NWs coexisted with nanosheets (NSs), to complete NSs in respect of the Al-dosages of 0 similar to 3 at.%, 5 at.%, and 7 at.%, correspondingly. The undoped ZnO and lightly Al-doped AZO (<= 3 at.%) NWs are single-crystalline wurtzite structure. In contrast, heavily Al-doped AZO sample is polycrystalline. The AZO nanostructure with 3 at.% Al-dosages reveals the optimal crystallinity and less structural defects, reflecting the longest carrier lifetime and highest conductivity. Consequently, the field-emission characteristics of such an AZO emitter can exhibit the higher current density, larger field-enhancement factor (beta) of 3131, lower turn-on field of 2.17 V/mu m, and lower threshold field of 3.43 V/mu m.
High Field-Emission Stability of Offset-Thin-Film Transistor-Controlled Al-Doped Zinc Oxide Nanowires
(2011-04-01)
Yang, Po-Yu
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Wang, Jyh-Liang
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Tsai, Wei-Chih
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Wang, Shui-Jinn
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Lin, Jia-Chuan
Aluminum-doped zinc oxide (AZO) nanowire (NW) arrays incorporating an offset thin-film transistor (offset-TFT) have been proposed to achieve high field-emission (FE) stability. The AZO NW field emission arrays (FEAs) were hydrothermally grown at a low temperature of 85 degrees C. The uncontrolled AZO NW FEAs demonstrated superior FE characteristics (i.e., turn-on field of similar to 2.17 V/mu m and threshold field of similar to 3.43 V/mu m) compared with those of the conventional CNT FEAs grown at a temperature below 600 degrees C. However, uncontrolled AZO NW FEAs show a larger current fluctuation of 15.6%. Therefore, the offset-TFTs were used to control the AZO NW FEAs. Consequently, the fluctuation of AZO NW FEAs could be significantly reduced to less than 2%. This novel field emission device exhibits good emission stability, low-voltage controllability, low-temperature processing, and structural simplicity, making it promising for applications in flat panel displays. (C) 2011 The Japan Society of Applied Physics
High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads
(2016-04)
Li, Yu-Ren
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Chang, Shih-hsueh
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Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Chiu, Yu-Kai
A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1-13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9mV/pH compared with 45.0mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance. (C) 2016 The Japan Society of Applied Physics
High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads
(2016-04-01)
Li, Yu-Ren
;
Chang, Shih-hsueh
;
Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Chiu, Yu-Kai
A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1-13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9mV/pH compared with 45.0mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance. (C) 2016 The Japan Society of Applied Physics
Highly Sensitive pH Sensors of Extended-Gate Field-Effect Transistor With the OxygenFunctionalized Reduced Graphene Oxide Films on Reverse Pyramid Substrates
(2015-11-01)
Li, Yu-Ren
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Chang, Shih-Hsueh
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Tsai, Wan-Lin
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Chang, Chia-Tsung
;
Wang, Kuang-Yu
The oxygen-plasma-treated reduced graphene oxide films (OPT-RGOFs) as the pH sensing membranes for the extended-gate field-effect transistors were demonstrated to achieve the higher pH sensitivity of 52 mV/pH and better linearity of 0.996 in a wide sensing range of pH 1-13 than those without plasma treatment. It was attributed to the oxygen-containing functional groups on the RGOF induced from the plasma treatment. In addition, the OPT-RGOFs sprayed on the reverse pyramid substrates were also proposed to further enhance the sensing sites, leading to a superior pH sensitivity of 57 mV/pH with an excellent linearity of 0.996.
Improving the stability and reproducibility of the carbon nanotube gas ionization sensor by Co-Ti/Ti co-deposited catalyst layer
(2013-12-01)
Chang, Chia-Tsung
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Huang, Chun-Yu
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Li, Yu-Ren
;
Cheng, Huang-Chung
;
電子工程學系及電子研究所
A novel gas ionization sensor (GIS) of the carbon nanotube (CNT) film using the Co-Ti/Ti co-deposited catalyst layer had been proposed for the first time to exhibit higher stability and better reproducibility with respect to the CNT film ones with the single catalyst layer. For the proposed CNT GIS, the variation of the breakdown voltage (V-br) was less than 25% for the ten devices with the same structure measurement since the lengths of the CNT synthesized were uniform and aligned. Besides, the fluctuation of the V-br was about 14% during 1000 operation times in nitrogen at the pressure of 0.035 Torr. It was attributed to the adhesion between CNTs and the substrate could be improved since the co-deposited catalyst layer and Ti adhesion layer would be coalesced so that the Co nanoparticles would be partially immersed into Ti layer after hydrogen pretreatment. Such a CNT GIS with the co-deposited catalyst layer also exhibited high sensitivity and selectivity for different kinds of gases detection as well as the good linearity for detecting the gas mixture. (C) 2013 Elsevier B.V. All rights reserved.
Photoresponse of hydrothermally grown lateral ZnO nanowires
(2010-10-01)
Yang, Po-Yu
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Wang, Jyh-Liang
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Tsai, Wei-Chih
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Wang, Shui-Jinn
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Lin, Jia-Chuan
In this paper, a simple self-assembled lateral growth of ZnO nanowires (NWs) photodetector has been synthesized by a hydrothermal method at a temperature as low as 85 degrees C. The ZnO NWs exhibit single-crystalline wurtzite with elongated c-axis and can be selectively lateral self-assembled around the edges of ZnO seeding layer. The current of ZnO NWs is sensitive to the variation of ambient pressures, i.e. 4.47 mu A was decreased to 1.48 mu A with 5 V-bias as 1.1 x 10(-6) Torr changed to 760 Torr. accordingly. Moreover, the current voltage characteristics of ZnO NWs photodetectors can be evidently distinguished by UV illumination (i.e. lambda = 325 nm). The photocurrent of ZnO NWs with UV illumination is twice larger than dark current while the voltage biased at 5 V. Consequently, this faster photoresponse convinces that the hydrothermally grown lateral ZnO NWs devices have a fairly good for the fabrication of UV photodetectors. (C) 2010 Elsevier B.V. All rights reserved.
Pillar Height Dependence of Field-Emission Properties in an Array of Carbon Nanotube Pillars
(2013-08-01)
Chang, Chia-Tsung
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Juan, Chuan-Ping
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Cheng, Huang-Chung
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Carbon nanotube pillars with optimal field-emission properties, including a high field enhancement factor beta of 5384 and a low turn-on field E-to of 0.84 V/mu m, have been achieved when the ratio of interpillar spacing to pillar height is 2. However, when this ratio exceeds 2, the field enhancement factor increases with increasing pillar height since the field can be enhanced by increasing the aspect ratio. When the ratio is smaller than 2, the field enhancement factor decreases with increasing pillar height owing to the increased field-screening effect. A simulation has been performed to verify the experimental results. (C) 2013 The Japan Society of Applied Physics
Sensitivity Enhancement of Ultraviolet Photodetectors With the Structure of p-NiO/Insulator-SiO2/n-ZnO Nanowires
(2015-08-01)
Li, Yu-Ren
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Wan, Chung-Yun
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Chang, Chia-Tsung
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Huang, Yu-Chih
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Tsai, Wan-Lin
A high-performance photodetector with the structure of NiO/SiO2/ZnO nanowires has been proposed. The devices with 6-nm-thick SiO2 exhibited a better rectification ratio (J(forward)/J(reverse)) of 246 at +/- 2 V, lower dark current density (J(dark)) of 3.5 x 10(-7) A/cm(2) at a reverse bias of 2 V, and superior ultraviolet (UV) sensitivity (I-UV/I-dark) of 16.23 than those without the SiO2 layer (J(forward)/J(reverse) = 44, Jdark = 4.7x10(-6) A/cm(2), and I-UV/I-dark = 5.5). The improved performance was mainly due to the ultrathin inserted SiO2 layer that builds a barrier height to minimize the transmission probability of low-energy carriers, leading to the enhancement of the UV sensing characteristics.
The Effects of Nanometal-Induced Crystallization on the Electrical Characteristics of Bottom-Gate Poly-Si Thin-Film Transistors
(2011-07-01)
Lee, I-Che
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Yang, Po-Yu
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Hu, Ming-Jhe
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Wang, Jyh-Liang
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Tsai, Chun-Chien
The effects of active layer thickness and device dimensions on nanometal-induced crystallization (nano-MIC) were studied to determine the electrical characteristics of the polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with bottom-gate structures. The nano-MIC poly-Si film was obtained via deposition of a 0.4-nm-thick Ni film on the amorphous silicon layer and subsequent annealing at 550 degrees C for 0.5 to 8 h. The EDS revealed a similar to 0.1% Ni concentration in the poly-Si film. The cross-sectional TEM image shows the vertical-grain growth mechanism, where the bottom side of the grain exhibits a larger crytalline area than the top side. Therefore, the field effect mobility of the bottom-gate poly-Si TFTs increases with increased active-amorphous-silicon (a-Si) thickness. Furthermore, the mobility increases when the device dimensions are scaled down. A mechanism for explaining such phenomenon in relation to the nano-MIC bottom-gate poly-Si TFTs was also proposed.
Thickness effect of NiO on the performance of ultraviolet sensors with p-NiO/n-ZnO nanowire heterojunction structure
(2015-08-01)
Li, Yu-Ren
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Wan, Chung-Yun
;
Chang, Chia-Tsung
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Tsai, Wan-Lin
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Huang, Yu-Chih
Based on the p-NiO/n-ZnO nanowire (NW) heterojunction structure, a high-performance ultraviolet (UV) sensor has been achieved in this work. The sputtered p-type NiO exhibited good coverage on the hydrothermally-grown n-type ZnO Nano-Wires (NW\'s). The devices with 250-nm-thick NiO obtained the highest UV light sensitivity (I-UV/I-Dark = 4.98; I-Visible/I-Dark = 3.82 biased at -2 V) under UV (lambda = 365 nm) intensity as low as 300 mu W/cm(2). Such p-n junction with thinner or thicker NiO layer led to worse UV detecting characteristics due to the fully-depleted NiO layer and larger series resistance, respectively. Furthermore, the N-2 annealing process can increase the UV light response and suppress the visible light response because of the reduced structural defects in ZnO NWs and the fewer interfacial defects (I-UV/I-Dark = 5.65; I-Visible/I-Dark = 1.35 biased at -2 V). (c) 2015 Elsevier Ltd. All rights reserved.