Browsing by Author "Hu, Chih-Wei"

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A counter electrode based on hollow spherical particles of polyaniline for a dye-sensitized solar cell
(2012)
Huang, Kuan-Chieh
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Hu, Chih-Wei
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Tseng, Chen-Ya
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Liu, Chen-Yu
;
Yeh, Min-Hsin
Hollow spherical polyaniline (hsPANI) particles are synthesized and deposited on an ITO/glass substrate to prepare a counter electrode (designated as hsPANI-CE) for a dye-sensitized solar cell (DSSC). The structure and crystallization of the hsPANI particles are characterized by using high resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectra. A power-conversion efficiency (h) of 6.84% is obtained for the DSSC with the hsPANI-CE, while it is 6.02% in the case of the DSSC with a CE based on pristine PANI (designated as PANI-CE). Such enhancement is attributed to the hsPANI film having a larger active surface area (A) of 0.191 cm(2), compared to that of the PANI film (A = 0.126 cm(2)), both values being estimated by a rotating disk electrode (RDE). Cyclic voltammetric (CV) curves have evidenced that the electro-catalytic ability of the hsPANI-CE for the reduction of tri-iodide (I-3(-)) ions is higher than that of the PANI-CE. As a reference, the DSSC with a Pt-sputtered CE gives an h of 7.17%. Electrochemical impedance spectroscopic (EIS) spectra are used to substantiate the photovoltaic behaviors. The results suggest that the film consisting of hsPANI particles can be a potential catalytic layer for the replacement of Pt in the CE of a DSSC.
Bipolar Resistive Switching Characteristics of Transparent Indium Gallium Zinc Oxide Resistive Random Access Memory
(2010)
Chen, Min-Chen
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Chang, Ting-Chang
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Huang, Sheng-Yao
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Chen, Shih-Ching
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Hu, Chih-Wei
This study investigates a sputtered InGaZnO (IGZO) thin film to apply into a resistive random access memory device. After the formation of an indium tin oxide (ITO)/IGZO/ITO structure at room temperature, the device exhibits a repeatable bipolar resistance switching behavior without an electroforming process and an excellent transmittance in the visible region. The conduction mechanisms for low and high resistance states are dominated by Ohm's law and space-charge-limited current behavior, respectively. In retention and endurance tests, a resistance ratio of more than 1 order remains after 10(4) s at 90 degrees C and after 100 dc voltage sweeping cycles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3360181] All rights reserved.
Charge storage characteristics of high density Mo nanocrystal embedded in silicon oxide and silicon nitride
(2010-02-24)
Lin, Chao-Cheng
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Chang, Ting-Chang
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Tu, Chun-Hao
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Chen, Shih-Ching
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Hu, Chih-Wei
We investigated the formation and charge storage characteristics of Mo nanocrystals in silicon oxide and in silicon nitride by rapid thermal annealing of oxygen- and nitrogen-incorporated Mo and Si mixed layers. A high density of Mo nanocrystal (6 x 10(12) cm(-2)) was formed in the nitrogen-incorporated layer. Electrical analyses indicated that the memory window of the Mo nanocrystal embedded in the nitride is larger than that in the oxide. A reliability test showed that the Mo nanocrystal in the nitride has better reliability than the Mo nanocrystal in the oxide, which was explained by an electrical field simulation.
Charge storage characteristics of Mo nanocrystal dependence on Mo oxide reduction
(2008-12-01)
Lin, Chao-Cheng
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Chang, Ting-
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Tu, Chun-Hao
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Chen, Wei-Ren
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Hu, Chih-Wei
An oxygen incorporated Mo silicide was explored to form the Mo nanocrystals after rapid thermal annealing. Transmission electron microscopy showed the nanocrystals embedded in SiO(x). Charge storage characteristics of Mo nanocrystals influenced by the Mo oxide and the surrounding oxide were investigated through x-ray photoelectron spectroscopy and the electrical measurement. X-ray photoelectron spectra analyses revealed the redox reaction in the oxygen incorporated Mo silicide layer after rapid thermal annealing. The memory window and retention were improved due to reduction in Mo oxide.
Charge Storage Characteristics of Mo Nanocrystal Memory Influenced by Ammonia Plasma Treatment
(2009)
Lin, Chao-Cheng
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Chang, Ting-Chang
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Tu, Chun-Hao
;
Chen, Wei-Ren
;
Hu, Chih-Wei
Mo nanocrystal memory was fabricated through annealing the oxygen-incorporated Mo and Si layers. We then investigated the influence an of ammonia plasma treatment on the nonvolatile memory characteristics of a charge storage layer composed of Mo nanocrystal memory embedded in SiO(x). Transmission electron microscopy revealed the nanostructure of the charge storage layer, and X-ray photoelectron spectra analyses revealed that nitrogen was incorporated into the charge storage layer. Electric analyses indicated that the memory window reduced, and both retention and endurance improved after the treatment. The reduction in the memory window was attributed to the decrease in charge trapping centers in the surrounding oxide after the treatment. The improvement of retention was interpreted in terms of the nitrogen passivation of traps in the oxide around the Mo nanocrystals. The robust endurance characteristic was attributed to the improvement of the quality of the surrounding oxide by nitrogen passivation.
Cobalt nanodots formed by annealing the CoSiO layer for the application of the nonvolatile memory
(2009-03-09)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
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Shueh, Pei-Kun
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Lin, Chao-Cheng
Co nanodot memory devices formed by oxidation processes were studied. Transmission electron microscopy and x-ray photoelectron spectroscopy analyses showed that overoxidation of the cobalt and silicon degraded the charge-storage ability seriously. However, a precapped oxide can mildly oxidize the CoSi(2) film to protect the overoxidation to occur. In addition, an oxygen-incorporated CoSi(2) film is proposed to improve the oxidation process further. Through incorporating the limited oxygen during sputtering process, the Co nanodot memory device obtains a larger memory window. Also, the reliability characteristic of the Co nanodot memory device formed by annealing the oxygen-incorporated CoSi(2) film has been demonstrated.
Effects of mesoscopic poly (3,4-ethylenedioxythiophene) films as counter electrodes for dye-sensitized solar cells
(2010-01-01)
Lee, Kun-Mu
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Chiu, Wei-Hao
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Wei, Hung-Yu
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Hu, Chih-Wei
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Suryanarayanan, Vembu
Counter electrode coated with chemically polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) in a dye-sensitized solar cell (DSSC) was studied. The surface morphology and the nature of I(-)/I(3)(-) redox reaction based on PEDOT film were investigated using Atomic Force Microscopy and Cyclic Voltammetry, respectively. The performance of the DSSCs containing the PEDOT coated electrode was compared with sputtered-Pt electrode. We found that the root mean square roughness decreases and conductivity increases as the molar ratio of imidazole (Im)/EDOT in the PEDOT film increases. The DSSC containing the PEDOT coated on fluorine doped tin oxide glass with Im/EDOT molar ratio of 2.0, showed a conversion efficiency of 7.44% compared to that with sputtered-Pt electrode (7.77%). The high photocurrents were attributed to the large effective Surface area of the electrode material resulting in good catalytic properties for T(3) reduction. Therefore, the incorporation of a multi-walled carbon nanotube (MWCNT) in the PEDOT film, coated on various substrates was also investigated. The DSSC containing the PEDOT films with 0.6 wt.% of MWCNT on stainless steel as counter electrode had the best cell performance of 8.08% with short-circuit current density, open-circuit voltage and fill factor of 17.00 mA cm(-2), 720 mV and 0.66, respectively. (C) 2009 Elsevier B.V. All rights reserved.
Enhancement of NiSi-Based Nanocrystal Formation by Incorporating Ge Elements for Nonvolatile Memory Devices
(2009)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
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Chiang, Cheng-Neng
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Lin, Chao-Cheng
In this work, a NiSiGe mixed film was deposited by the cosputtering approach. The rapidly thermal treatment condition was executed at 600 degrees C for 30 s in nitrogen ambient to form the nanocrystal structure. From the results of the transmission electron microscopy, the annealed NiSiGe film reveals a larger nanocrystal size and density distribution than pure NiSi. X-ray photoelectron spectroscopy analyses were used to confirm that the Ge elements provide the additional nucleation centers and enhance the nanocrystal formation during the thermal process. Raman spectroscopy and an energy-dispersive spectrometer also exhibit the compositions of nanocrystals including Ni, Si, and Ge elements. With the better formation process, a remarkable improvement of memory effect is observed by comparing with the NiSi and NiSiGe nanocrystal memory devices. Also, the NiSiGe nanocrystal device shows a better retention characteristic due to the lower quantum confinement effect.
Enhancing threshold voltage of AlGaN/GaN high electron mobility transistors by nano rod structure: From depletion mode to enhancement mode
(2012-09-10)
Xuan, Rong
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Kuo, Wei-Hong
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Hu, Chih-Wei
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Lin, Suh-Fang
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Chen, Jenn-Fang
This paper presents an approach in fabricating normally off AlGaN/GaN high electron mobility transistors (HEMTs). The fabrication technique was based on the carbon-doped GaN epitaxy layers on silicon substrate and the nano rod structure of the gate region in AlGaN/GaN HEMTs. Using this method, the threshold voltage of AlGaN/GaN HEMTs can be shifted from -2 V in a conventional depletion-mode (D-mode) AlGaN/GaN HEMT to 2 V in an enhancement-mode (E-mode) AlGaN/GaN HEMT. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752113]
Formation of cobalt-silicide nanocrystals in Ge-doped dielectric layer for the application on nonvolatile memory
(2008-04-14)
Hu, Chih-Wei
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Chang, Ting-Chang
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Liu, Po-Tsun
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Tu, Chun-Hao
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Lee, Sheng-Kai
In this work, Ge-doped cobalt-silicon thin film was synthesized using a cosputter system (Co and Si(0.5)Ge(0.5)). The deposited film was annealed in oxygen ambient at 650 degrees C to form cobalt-silicide nanocrystals. The formation of isolated silicide nanocrystals was confirmed by transmission electron microscopy and x-ray photoelectron spectroscopy analysis. In metal-oxide-insulator-oxide-silicon structure, a significant electrical hysteresis is observed and attributed by the presence of the cobalt-silicide nanocrystals and the oxidized Ge elements. (C) 2008 American Institute of Physics.
Formation of Mo silicide nanodot memory by rapid thermal annealing dual electron-gun evaporated Mo-Si layer
(2008)
Lin, Chao-Cheng
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Chang, Ting-Chang
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Tu, Chun-Hao
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Chen, Wei-Ren
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Hu, Chih-Wei
In this study, distributed charge trapping centers molybdenum silicide nanodots, are demonstrated. The Mo silicide nanodots were formed in the rapid thermal annealed mixed Mo-Si layer deposited by a dual electron gun system. A significant memory effect is observed through the electrical measurements, which is attributed to the formation of Mo silicide nanodots. In addition, the memory window is large enough to be identified as logic level "0" and "1" for the application on nonvolatile memory. The manufacture processes are simple and compatible with the conventional semiconductor manufacturing processes. (C) 2008 The Electrochemical Society.
Formation of the distributed NiSiGe nanocrystals nonvolatile memory formed by rapidly annealing in N(2) and O(2) ambient
(2010-10-01)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
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Chiang, Cheng-Neng
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Lin, Chao-Cheng
In this work, electrical characteristics of the Ge-incorporated Nickel silicide (NiSiGe) nanocrystals memory device formed by the rapidly thermal annealing in N(2) and O(2) ambient have been studied. The trapping layer was deposited by co-sputtering the NiSi(2) and Ge, simultaneously. Transmission electron microscope results indicate that the NiSiGe nanocrystals were formed obviously in both the samples. The memory devices show obvious charge-storage ability under capacitance-voltage measurement. However, it is found that the NiSiGe nanocrystals device formed by annealing in N(2) ambient has smaller memory window and better retention characteristics than in O(2) ambient. Then, related material analyses were used to confirm that the oxidized Ge elements affect the charge-storage sites and the electrical performance of the NCs memory. (C) 2010 Elsevier B.V. All rights reserved.
Formation of the distributed NiSiGe nanocrystals nonvolatile memory formed by rapidly annealing in N-2 and O-2 ambient
(2010-10-01)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
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Chiang, Cheng-Neng
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Lin, Chao-Cheng
In this work, electrical characteristics of the Ge-incorporated Nickel silicide (NiSiGe) nanocrystals memory device formed by the rapidly thermal annealing in N-2 and O-2 ambient have been studied. The trapping layer was deposited by co-sputtering the NiSi2 and Ge, simultaneously. Transmission electron microscope results indicate that the NiSiGe nanocrystals were formed obviously in both the samples. The memory devices show obvious charge-storage ability under capacitance-voltage measurement. However, it is found that the NiSiGe nanocrystals device formed by annealing in N-2 ambient has smaller memory window and better retention characteristics than in O-2 ambient. Then, related material analyses were used to confirm that the oxidized Ge elements affect the charge-storage sites and the electrical performance of the NCs memory. (C) 2010 Elsevier B.V. All rights reserved.
High Density Ni Nanocrystals Formed by Coevaporating Ni and SiO(2) Pellets for the Nonvolatile Memory Device Application
(2010-01-01)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
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Huang, Yu-Hao
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Lin, Chao-Cheng
We propose a method to fabricate a Ni nanocrystal structure by simultaneously coevaporating Ni and SiO(2) pellets. An 800 degrees C rapid thermal annealing was used to enhance the Ni nanocrystals to aggregate. Transmission electron microscopy indicates that the formed Ni nanocrystals show a high density distribution of about 4.5x10(12) cm(-2). Then, the memory device using the Ni nanocrystals as charge-trapping centers was fabricated. The Ni nanocrystal memory device has an obvious memory window under capacitance-voltage measurement. X-ray photoelectron spectroscopy confirms the memory effect results from the Ni nanocrystals embedded in the SiO(2) dielectric layer. Moreover, related reliability characteristics have been extracted.
High Density Ni Nanocrystals Formed by Coevaporating Ni and SiO2 Pellets for the Nonvolatile Memory Device Application
(2010-01-01)
Hu, Chih-Wei
;
Chang, Ting-Chang
;
Tu, Chun-Hao
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Huang, Yu-Hao
;
Lin, Chao-Cheng
We propose a method to fabricate a Ni nanocrystal structure by simultaneously coevaporating Ni and SiO2 pellets. An 800 degrees C rapid thermal annealing was used to enhance the Ni nanocrystals to aggregate. Transmission electron microscopy indicates that the formed Ni nanocrystals show a high density distribution of about 4.5x10(12) cm(-2). Then, the memory device using the Ni nanocrystals as charge-trapping centers was fabricated. The Ni nanocrystal memory device has an obvious memory window under capacitance-voltage measurement. X-ray photoelectron spectroscopy confirms the memory effect results from the Ni nanocrystals embedded in the SiO2 dielectric layer. Moreover, related reliability characteristics have been extracted.
Improved reliability of Mo nanocrystal memory with ammonia plasma treatment
(2009-02-09)
Lin, Chao-Cheng
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Chang, Ting-Chang
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Tu, Chun-Hao
;
Chen, Wei-Ren
;
Hu, Chih-Wei
We investigated ammonia plasma treatment influence on the nonvolatile memory characteristics of the charge storage layer composed of Mo nanocrystals embedded in nonstoichiometry oxide (SiO(x)). X-ray photoelectron spectra analyses revealed that nitrogen was incorporated into the charge storage layer. Electric analyses indicated that the memory window was reduced and the retention and the endurance improved after the treatment. The reduction in the memory window and the improvement in retention were interpreted in terms of the nitrogen passivation of traps in the oxide around Mo nanocrystals. The robust endurance characteristic was attributed the improvement of the quality of the surrounding oxide by nitrogen passivation.
Influence of electrode material on the resistive memory switching property of indium gallium zinc oxide thin films
(2010-06-28)
Chen, Min-Chen
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Chang, Ting-Chang
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Tsai, Chih-Tsung
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Huang, Sheng-Yao
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Chen, Shih-Ching
The InGaZnO taken as switching layer in resistive nonvolatile memory is proposed in this paper. The memory cells composed of Ti/InGaZnO/TiN reveal the bipolar switching behavior that keeps stable resistance ratio of 10(2) with switching responses over 100 cycles. The resistance switching is ascribed to the formation/disruption of conducting filaments upon electrochemical reaction near/at the bias-applied electrode. The influence of electrode material on resistance switching is investigated through Pt/InGaZnO/TiN devices, which perform the unipolar and bipolar behavior as applying bias on Pt and TiN electrode, respectively. Experimental results demonstrate that the switching behavior is selective by the electrode. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456379]
Influence of Oxygen Partial Pressure on Resistance Random Access Memory Characteristics of Indium Gallium Zinc Oxide
(2011)
Chen, Min-Chen
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Chang, Ting-Chang
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Huang, Sheng-Yao
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Chang, Guan-Chang
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Chen, Shih-Cheng
This paper investigates the effect of oxygen concentrations of InGaZnO films on the resistive switching characteristics of a Pt/InGaZnO (IGZO)/TiN structure. The IGZO films were prepared by an RF magnetron sputtering system at various oxygen partial pressures at room temperature. The memory devices reveal a reversible unipolar switching behavior. In addition, the high-resistance state current was found to be strongly dependent on oxygen concentration. X-ray photoelectron spectroscopy analyses attributed this phenomenon to the non-lattice oxygen concentration in the IGZO thin films, rather than the change in crystalline constituent. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.007112esl] All rights reserved.
NiSiGe nanocrystals for nonvolatile memory devices
(2009-02-09)
Hu, Chih-Wei
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Chang, Ting-
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Tu, Chun-Hao
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Chiang, Cheng-Neng
;
Lin, Chao-Cheng
In this work, charge-storage characteristics of NiSiGe nanocrystal memory device have been studied. Transmission electron microscope shows that the annealed NiSiGe film has higher nanocrystal size and density distribution. Related material analyses such as x-ray photoelectron spectroscopy, Raman spectroscopy, and energy dispersive spectrometer were used to confirm that the Ge elements provide the additional nucleation centers and enhance the nanocrystals aggregation during thermal process. With the improved nanocrystal formation process, a remarkable improvement of the memory effect is observed by comparing the NiSi and NiSiGe nanocrystals. In addition, the retention characteristics of the nanocrystals memory devices have been discussed.
Nitric Acid Oxidation of Si for the Tunneling Oxide Application on CoSi(2) Nanocrystals Nonvolatile Memory
(2010-01-01)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
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Chen, Yang-Dong
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Lin, Chao-Cheng
In this work, nitric acid oxidation was studied to fabricate the tunneling oxide of nanocrystal memory devices. SiO(2) about 4 nm thick was formed through oxidizing the sputtered Si film by immersing in nitric acid solution (HNO(3):H(2)O=1:10) for 60 s. After oxide formation, a rapid thermal annealing process set at 700 degrees C for 30 s was used to improve oxide quality. In addition, the formed SiO(2) film was analyzed by X-ray photoelectron, capacitance-voltage, and current density-voltage measurements to study the process of the nitric acid oxidation. After the investigation of the nitric acid oxidized SiO(2), a 6 nm thick cobalt silicide thin film was deposited and aggregated on the formed SiO(2) layer as the charge-trapping layer. The cobalt silicide nanocrystal memory device showed an obvious memory effect and good reliability, which confirms that the nitric acid oxidation method has potential for memory application.