Browsing by Author "Chen, Po-Chun"

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A CMOS 256-pixel Photovoltaics-powered Implantable Chip with Active Pixel Sensors and Iridium-oxide Electrodes for Subretinal Prostheses
(2018-01-01)
Wu, Chung-Yu
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Kuo, Po-Han
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Lin, Po-Kang
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Chen, Po-Chun
;
Sung, Wei-Jie
A CMOS implantable chip with 256 active pixel sensors (APSs), on-chip photovoltaic cells, and iridium-oxide (IrOx) electrodes is proposed and designed for subretinal prostheses. In the proposed chip, the on-chip electrode surface is deposited with IrOx by RF sputtering and photolithography patterning. The divisional power supply scheme (DPSS) is adopted to generate sufficient stimulation current whereas the APS is used to enhance the image sensitivity. The proposed chip consists of a 16 x 16 photodiode array with 8 DPSS divisions, control signal generator circuits, and photovoltaic cells. It is designed and fabricated into 180 nm CMOS image sensor (CIS) technology and postprocessed with an IrOx coating. From the electrical measurement results, the fabricated chip has a peak output stimulation current of 16.7 mu A under the equivalent electrode impedance load. The stimulation frequency is 30.2 Hz and the amount of injected charges at each pixel is 3.5 nC. Both image light sensitivity and injection charges are significantly improved. The surface morphology, crystallinity, charge storage capacity, and biocompatibility of sputtering iridium oxide film (SIROF) were investigated. As a result, the SIROF has desirable physical and electrochemical properties that make it suitable for the neurostimulation electrodes on the 256-pixel implantable chip. The 7-month biocompatibility and charge delivery capability of the fabricated chip have been confirmed by electroretinography (ERG) measurement on a Lanyu minipig in in vivo animal tests.
A cost-effective fabrication of iridium oxide films as biocompatible electrostimulation electrodes for neural interface applications
(2017-01-25)
Chen, Yong-Min
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Chung, Tsai-Wei
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Wu, Pu-Wei
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Chen, Po-Chun
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材料科學與工程學系
Electrostimulation medical devices for neural diseases require electroactive and biocompatible interface materials to transmit signals from electrodes to targeting tissues. Iridium oxide is an attractive ceramic material for neurostimulation electrodes due to its desirable stability and biocompatibility. In this study, we developed a cost effective and thickness controllable process to fabricate iridium oxide film by chemical bath deposition (CIROF). Surface morphology, crystallinity, roughness, hydrophilicity, and charge storage capacity as well as biocompatibility of the CIROFs with different thicknesses were analyzed. Accordingly, the CIROFs present rough and hydrophilic surfaces for cell attachment and good biocompatibility for cell viability. In addition, the charge storage capacity (CSC) of the as-deposited and the annealed CIROFs were 78.29 mC/cm(2) and 71.76 mC/cm(2), respectively. Consequently, these results show advantages that make the CIROF a promising neurostimulation electrode material for implantable medical devices in neural systems. (C) 2016 Elsevier B.V. All rights reserved.
Bipolar Conduction in Tin-Oxide Semiconductor Channel Treated by Oxygen Plasma for Low-Power Thin-Film Transistor Application
(2016-03)
Chen, Po-Chun
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Wu, Yung-Hsien
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Zheng, Zhi-Wei
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Chiu, Yu-Chien
;
Cheng, Chun-Hu
In this paper, we investigated the bipolar conduction mechanism in thin-film transistors (TFTs) with oxygen plasma treatment on tin-oxide channel. The optimized p-type thin-oxide TFTs showed an on/off ratio of >10(4), a threshold voltage of -1.05 V, and a field-effect mobility of 2.14 cm(2).V-1.s(-1). By increasing the exposure time of oxygen plasma, excess oxygen was incorporated to thin-oxide channel and converted thin monoxide to oxygen-rich n-type thin dioxide, which in turn led to n-type operation. It indicated that oxygen plasma was the critical factor to determine oxygen concentration, oxygen vacancies, metal ions and channel polarity. This proposed oxygen-content tuning through plasma treatment approach shows great promise in simplification of TFT process that can achieve n-type and p-type TFTs under the same device process.
Chemical bath deposition of IrO2 films on ITO substrate
(2014-11-01)
Chen, Jing-Yu
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Chen, Yong-Min
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Sun, Yu
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Lee, Jyh-Fu
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Chen, San-Yuan
A chemical bath is shown to deposit an IrO2 film on an ITO substrate. The chemical bath is prepared by mixing an Ir precursor (Na3IrCl6 center dot xH(2)O), an oxidizer (NaClO), a complexing agent (NaNO2), and a complex agent/stabilizer (NaOH) in an aqueous solution at a molar ratio of 1:1.5:10:30. From the UV-vis absorption spectra, complexes such as [Ir(OH)(6)]m(3-), [Ir(NO2)(4)Cl-2](3-), and [Ir(NO2)(3)Cl-3](3-) are identified. These complexes are relatively stable, minimizing the undesirable homogeneous precipitation of IrO2 nanoparticles in favor of the heterogeneous growth of the IrO2 film on the ITO substrate. Diffraction patterns from the as-deposited IrO2 film reveal an amorphous structure. In addition, profiles from X-ray absorption spectroscopy and X-ray photoelectron spectroscopy indicate that the oxidation state of the Ir in the as-deposited IrO2 film is +4. Thermogravimetric analysis confirms the inclusion of 10 wt% hydrated water in the as-deposited IrO2 film. Scanning electron microscope images reveal a continuous solid film with a smooth surface. The amorphous IrO2 film becomes rutile IrO2 phase after a mild heat treatment in air. (c) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Chemical stability and electrical conductivity of BaCe0.4Zr0.4Gd0.1Dy0.1O3-delta perovskite
(2015-11-01)
Tsai, Yen-Chang
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Chen, San-Yuan
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Wang, Jeng-Han
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Wu, Pu-Wei
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Chen, Po-Chun
A proton-conducting BaCe0.4Zr0.4Gd0.1Dy0.1O3-delta (BCZGD) perovskite is fabricated via a wet chemical route using precursors including Ba(NO3)(2), Ce(NO3)(3)center dot 6H(2)O, ZrO(NO3)(4)center dot 6H(2)O, Gd(NO3)(3)center dot 6H(2)O, and Dy(NO3)(3)center dot 5H(2)O. The synthesis process involves the dissolution of relevant precursors and glycine in deionized water at proper molar ratios. Subsequently, the mixture undergoes a heat treatment at 1300 degrees C for 10 h in air to form the perovskite powders. The as-synthesized BCZGD powders are filtered and pressed at 440 MPa, following by a sintering at 1450 degrees C for 24 h in air to render a free-standing proton-conductive disk with a thickness of 850 mu m. Material characterization including scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), and electrical conductivity measurements are performed. The electrical conductivity of the BCZGD sample is recorded at 1.93 x 10(-3) S cm(-1) at 700 degrees C in a humid hydrogen atmosphere with an activation energy of 0.41 eV. TGA results confirm chemical stability of the BCZGD against carbon dioxide without any decomposition. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Conformal deposition of Pt on titania nanotubes to produce a bio-electrode for neuro-stimulating applications
(2018-03-01)
Wu, Yi-Jia
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Chung, Tsai-Wei
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Huang, Jun-Qian
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Wu, Pu-Wei
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Chen, Po-Chun
We develop an alkaline electroless bath for deposition of a conformal Pt layer 40 nm thick on titania nanotubes 800 nm long. The charge storage capacity (CSC) and electrochemically active surface area (ECSA) of this Pt-coated titania nanotube array have been studied to evaluate its potential as a bio-electrode for implantable bioelectronic devices. Images from electron microscopes confirm the formation of a uniform Pt film on both the internal and external surfaces of the nanotubes. The X-ray diffraction pattern indicates a preferred (111) orientation. Analysis from X-ray absorption spectroscopy on the plating bath suggests a reduction sequence of Pt4+ -> Pt2+ -> Pt. The Pt-coated titania nanotube array has large CSC and ECSA values, attributed to the hollow tubular nanostructure with a conformal Pt coating.
Conformal Deposition of RuO2 on Cu via a Galvanic Cementation Reaction
(2019-06-28)
Lin, Chun
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Chou, Shih-Cheng
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Tso, Kuang-Chih
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Hsieh, Yi-Chieh
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Chan, Ting-Shan
We develop a seedless wet chemical process to deposit uniform RuO2 on a Cu substrate. Our approach entails the synthesis of volatile RuO4 colloids in a pH 9 aqueous solution from the oxidation of RuCl52- by ClO-, followed by a galvanic cementation reaction in which the Cu undergoes a mild oxidation in conjunction with the reduction of RuO4 to produce a dense and conformal RuO2 thin film on the Cu surface. The nature for the chemical reactions and constituents involved are investigated by UV-Vis, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both as-deposited and annealed RuO2 films are characterized by scanning electron microscope and X-ray diffractometer. The as-deposited RuO2 film, with a thickness of 199 nm, reveals an amorphous structure and after an Ar annealing, becomes crystalline in rutile phase. In between the RuO2 and Cu, there are presence of CuO from the displacement cementation reaction, and Cu2O from the parasitic Cu corrosion as expected from the Pourbaix diagram. These Cu oxides, with a thickness of 330 nm, provide sufficient adhesive bonding between RuO2 and Cu. (c) The Author(s) 2019. Published by ECS.
Effective N-methyl-2-pyrrolidone wet cleaning for fabricating high-performance monolayer MoS2 transistors
(2019-02-01)
Chen, Po-Chun
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Lin, Chih-Pin
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Hong, Chuan-Jie
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Yang, Chih-Hao
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Lin, Yun-Yan
Two-dimensional semiconductors, such as MoS2 are known to be highly susceptible to diverse molecular adsorbates on the surface during fabrication, which could adversely affect device performance. To ensure high device yield, uniformity and performance, the semiconductor industry has long employed wet chemical cleaning strategies to remove undesirable surface contaminations, adsorbates, and native oxides from the surface of Si wafers. A similarly effective surface cleaning technique for two-dimensional materials has not yet been fully developed. In this study, we propose a wet chemical cleaning strategy for MoS2 by using N-methyl-2-pyrrolidone. The cleaning process not only preserves the intrinsic properties of monolayer MoS2, but also significantly improves the performance of monolayer MoS2 field-effect-transistors. Superior device on current of 12 Am-1 for a channel length of 400 nm, contact resistance of 15 km, field-effect mobility of 15.5 cm(2)V(-1)s(-1), and the average on-off current ratio of 10(8) were successfully demonstrated
Electrochemical Evaluation of Geometrical Effect and Three-dimensionalized Effect of Iridium Oxide Electrodes Used for Retinal Stimulation
(2018-01-01)
Noda, Toshihiko
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Noda, Yoshiko
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Chen, Po-Chun
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Haruta, Makito
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Sasagawa, Kiyotaka
The geometry dependence and three-dimensionalized effect of the electrochemical properties of iridium oxide electrodes used in retinal prosthesis are discussed herein. Planar electrodes with various geometries were fabricated. Three-dimensionalized electrodes with microfabricated resin cores were also fabricated. The charge storage capacity (CSC) and charge injection capacity (CIC), both of which are important properties for neural stimulation, were quantitatively evaluated. This evaluation showed the important electrode property that the surface area dominantly affects the CSC. On the other hand, the CIC was not proportionally related to the electrode area, confirming that the edge region of the electrodes is significant in the mechanism of action. Moreover, performance enhancement with a three-dimensionalized electrode was clearly confirmed. The fundamental properties of highly effective stimulus electrodes were successfully evaluated and a detailed discussion is presented.
EQCM Study on Pulse Current Pt Electrodeposition
(2015-12-01)
Lu, I-Te
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Hsieh, Yu-Chi
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Chen, Po-Chun
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Wu, Pu-Wei
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材料科學與工程學系
Electrochemical Quartz Crystal Microbalance (EQCM) was used to investigate the events occurring during current-on (T-on) and current-off (T-off) for pulse current electrodeposition of Pt in both air and Ar atmospheres. The EQCM profiles indicated a transient mass loss when the current was turned on, followed by a linear mass gain associated with the Pt electrodeposition from the H2PtCl6 plating bath. During the T-off, the mass revealed a steady increase until it leveled off after 10 sec. The minute transient mass loss during the initial stage of T-on was attributed to the reduction of the adsorbed PtCl62- whereas the mass gain during the T-off was due to the absorption of PtCl62- onto the freshly-deposited Pt surface. In air atmosphere, the parasitic oxygen reduction reaction consumed part of the reduction current and thus, reduced the Pt plating efficiency by 6%. In addition, smaller mass gains during T-off and T-on were observed for the Pt plating in air atmosphere.
Fabrication of Ni nanowires for hydrogen evolution reaction in a neutral electrolyte
(2009-08-01)
Chen, Po-Chun
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Chang, Yun-Min
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Wu, Pu-Wei
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Chiu, Yu-Fan
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材料科學與工程學系
Hydrogen evolution reaction in 1 M Na(2)SO(4) was investigated using Ni nanowires in diameter of 250 nm with exposed lengths of 20, 35, and 45 mu m, respectively. The Ni nanowires were fabricated by a direct-current pulse electrodeposition technique using an anodic aluminum oxide template, followed by selective removal of the supporting pore walls. Scanning Electron Microscope images revealed structural stabilities and X-ray diffraction pattern indicated a polycrystalline fcc phase. In current-potential (i-V) polarizations, the Ni nanowires with longer exposed lengths demonstrated larger current responses. Analysis from impedance spectroscopy confirmed increasing double-layer capacitances with longer Ni nanowires. in galvanostatic lifetime experiments, the freestanding Ni nanowires exhibited a reduced overpotential over that of supported ones. Similar procedures were performed for the oxygen evolution reaction in both i-V and lifetime measurements. For the Ni nanowires of 45 pm length, we estimated the energy cost for hydrogen production was 5.24 x 10(5) J/mole. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Fast Low-Temperature Plasma Process for the Application of Flexible Tin-Oxide-Channel Thin Film Transistors
(2017-09-01)
Chen, Po-Chun
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Chiu, Yu-Chien
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Zheng, Zhi-Wei
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Lin, Ming-Huei
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Cheng, Chun-Hu
In this study, we demonstrated a p-type and n-type SnO TFTs on flexible polyimide substrate. The fabricated p-type SnO TFT showed a high I-on/I-off of 5.7 x 10(5) and a high mu(FE) of 10.7 cm(2) V-1 s(-1). Through optimizing the oxygen plasma condition, the n-type channel TFT transfered from prime p-type channel exhibits excellent characteristics, including a high on/off current ratio of 6.6 x 10(3), a low threshold voltage of -0.13 V, and a very high field-effect mobility of 28 cm(2) V-1 s(-1). This proposed low-temperature oxygen plasma treatment shows the potential in simplification of TFT process that can achieve n-type and p-type TFTs under the same device process.
Formation of Cu/MnOx composite film by concurrent electroplating and electrophoresis in an organic solvent
(2018-08-30)
Chiang, Wei-Shen
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Huang, Jun-Qian
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Tso, Kuang-Chih
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Hung, Pei-Sung
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Chen, Po-Chun
A composite Cu/MnOx thin film was fabricated by conducting electroplating of Cu and electrophoresis of MnOx colloids simultaneously in an organic electrolyte. The organic electrolyte was prepared by dissolving copper (II) acetylacetonate and manganese (II) acetylacetonate in ethylene glycol, with addition of 10 vol% acetic acid to improve ionic conductivity. Since both Cu ions and MnOx colloids carry positive charges, the formation of a composite film was achieved by a pulse current mode in which a low current pulse was used for Cu2+ reduction, followed by a high current pulse for the electrophoresis of the MnOx colloids. The Cu/MnOx composite film was dense and its X-ray diffraction pattern revealed a mixture of Cu, Mn2O3, and Mn3O4. Both X-ray photoelectron spectroscopy and X-ray absorption spectroscopy show consistent results confirming the metallic nature of Cu and oxidized state of Mn.
Gettering Effect Induced by Oxygen-Deficient Titanium Oxide in InZnO and InGaZnO Channel Systems for Low-Power Display Applications
(2016-03)
Yen, Shiang-Shiou
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Chiu, Yu-Chien
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Cheng, Chun-Hu
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Chen, Po-Chun
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Yeh, Yu-Chen
This paper reported the IGZO and IZO thin-film transistor (TFT) with titanium-oxide semiconductor as channel capping layer. After the TiOx Gettering process, the oxygen vacancies in IGZO channel were successfully modified to maximize the carrier concentration and device mobility. The superior transfer characteristics included a low sub-threshold swing of 79 mV/decade, a very high mobility of 68 cm(2)/V.s, and good on/off-current ratio of 5.61 x 10(6). However, the IZO channel with nano-crystallized grains and without Ga atom doping showed unfavorable transistor characteristics. In addition to apparently degraded transfer properties, the spontaneously oxidized TiOx capping layer also lead to an increase of channel parasitic resistance that limits the output driving current. Therefore, we believe that the existence of Ga-O bonds among IGZO channel would be helpful to stabilize oxygen diffusion behavior and electric structure during Gettering process.
High Mobility Field-Effect Thin Film Transistor Using Room-Temperature High-kappa Gate Dielectrics
(2014-10-01)
Hsu, Hsiao-Hsuan
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Chang, Chun-Yen
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Cheng, Chun-Hu
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Chen, Po-Chun
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Chiu, Yu-Chien
This paper reports an InGaZnO thin-film transistor (TFT) that involves using fully room-temperature gate dielectrics on a flexible substrate. The wide bandgap dielectrics of HfO2 and Y2O3 exhibited favorable adhesion properties on a flexible substrate compared with conventional low-kappa SiO2 film. Based on the experimental results, the room-temperature IGZO/HfO TFTs demonstrated effective device integrity, and achieve a low drive voltage of < 2 V, a low threshold voltage of 0.46 +/- 006 V, a low sub-threshold swing of 110 +/- 6 mV/decade and an extremely high mobility of 60.2 +/- 32 cm(2)/V s. The excellent performance of this TFT indicated that it demonstrates considerable potential for active-matrix liquid crystal display applications requiring low power consumption and a high driving current.
Highly Sensitive Arrayed Indium-Antimony Nanowires for Infrared Detection
(2015-01-01)
Chen, Po-Chun
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Chen, Chien-Chon
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Chen, Shih-Hsun
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Chou, Chung-Yi
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Hsieh, Sheng-Jen
The objective of this study is to achieve a high sensitive infrared detector by fabricating highly ordered array of indium-antimony (In-Sb) nanowires which is a semiconductor material. The approach is to investigate an infrared detector with arrayed nanowires which can transport signals in one dimension to obtain high efficiency and sensitivity compared with In-Sb by using traditional thin film fabrications. This research expects to provide an infrared detector by fabricating III-V alloy nanowires to highly improve the resolution of infrared signal. To develop scaled-up functional devices, highly ordered nanowire arrays are essential building blocks. Many candidate materials (metals, alloys, oxides and semiconductors) have been studied for various potential applications in nanotechnology and have shown some promising results. The solid metallic nanowires have been exploited for a wide range of applications to take the advantages of their large length/diameter aspect ratio. Further development to synthesize nanowires efficiently at lower cost is the direction for manufacturing next generation nanodevices. In this study, various diameters of ordering nanowires, from 10 nm to 500 nm, were fabricated and evaluated the performance of the sensitivity of infrared detection. Moreover, a 1 inch plate, which can be regarded as a device, with nanowires array was fabricated by designing a new type of processing chamber.
Improved Charge Pump Design and Ex Vivo Experimental Validation of CMOS 256-Pixel Photovoltaic-Powered Subretinal Prosthetic Chip
(2020-05-01)
Kuo, Po-Han
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Wong, Oi-Ying
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Tzeng, Chi-Kuan
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Wu, Pu-Wei
;
Chiao, Chuan-Chin
An improved design of CMOS 256-pixel photovoltaic-powered implantable chip for subretinal prostheses is presented. In the proposed subretinal chip, a high-efficiency fully-integrated 4x charge pump is designed and integrated with on-chip photovoltaic (PV) cells and a 256-pixel array with active pixel sensors (APS) for image light sensing, biphasic constant current stimulators, and electrodes. Thus the PV voltage generated by infrared (IR) light can be boosted to above 1V so that the charge injection is increased. The proposed chip adopts the 32-phase divisional power supply scheme (DPSS) to reduce the required supply current and thus the required area of the PV cells. The proposed chip is designed and fabricated in 180-nm CMOS image sensor (CIS) technology and post-processed with biocompatible IrOx electrodes and silicone packaging. From the electrical measurement results, the measured stimulation frequency is 28.3 Hz under the equivalent electrode impedance load. The measured maximum output stimulation current is 7.1 mu A and the amount of injected charges per pixel is 7.36 nC under image light intensity of 3200 lux and IR light intensity of 100 mW/cm(2). The function of the proposed chip has been further validated successfully with the ex vivo experimental results by recording the electrophysiological responses of retinal ganglion cells (RGCs) of retinas from retinal degeneration (rd1) mice with a multi-electrode array (MEA). The measured average threshold injected charge is about 3.97 nC which is consistent with that obtained from the patch clamp recording on retinas from wild type (C57BL/6) mice with a single electrode pair.
Improved high-temperature switching characteristics of Y2O3/TiOx resistive memory through carrier depletion effect
(2014-05-01)
Zheng, Zhi-Wei
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Hsu, Hsiao-Hsuan
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Cheng, Chun-Hu
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Chen, Po-Chun
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電子工程學系及電子研究所
We report a stacked Y2O3/TiOx resistive random access memory (RRAM) device, showing good high-temperature switching characteristics of extremely low reset current of 1 A at 150 degrees C, large off/on resistance window (>200) at 150 degrees C, large rectification ratio of approximate to 300 at 150 degrees C and good current distribution at 85 degrees C. The good rectifying property, lower high-temperature sneak current and tighter high-temperature current distribution can be attributed to the combined results of the oxygen vacancies in TiOx and the related carrier depletion effect. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of plasma fluorination on p-type channel tin-oxide thin film transistors
(2017-06-15)
Chen, Po-Chun
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Chiu, Yu-Chien
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Zheng, Zhi-Wei
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Cheng, Chun-Hu
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Wu, Yung-Hsien
This paper describes a high-performance p-type tin-oxide (SnO) thin film transistor (TFT) using fluorine plasma treatment on the SnO active channel layer. The influence of fluorine plasma treatment for this p-type SnO TFT device was also investigated. Through tuning the fluorine plasma power treated on the SnO active channel layer at low temperature, the optimal p-type SnO TFT device exhibits a very high on/off current ratio of 9.6 x 10(6), a field-effect mobility of 2.13 cm(2) V-1 s(-1), a very low subthreshold swing of 106 mV/dec and an extremely low off-state current of 1 pA at a low driven voltage of <3 V. These good characteristics can be attributed to fluorine plasma treatment on p-type SnO channel that reduced crystallized channel roughness and passivated oxygen vacancies and interface traps. This high-performance p-type SnO TFT device using fluorine plasma treatment on the active channel shows great promise for future high-resolution and high-speed display applications. (C) 2016 Elsevier B.V. All rights reserved.
Interface Polarization Fluctuation Effect of Ferroelectric Hafnium-Zirconium-Oxide Ferroelectric Memory with Nearly Ideal Subthreshold Slope
(2015)
Chiu, Yu-Chien
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Cheng, Chun-Hu
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Fan, Chia-Chi
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Chen, Po-Chun
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Chang, Chun-Yen