Papers

ICMCTF2009 Session HP: Symposium H Poster Session

Thursday, April 30, 2009 5:00 PM in Room Town & Country

Thursday Afternoon

Time Period ThP Sessions | Topic H Sessions | Time Periods | Topics | ICMCTF2009 Schedule

HP-1 Impact of Strain Engineering on Nanoscale Strained Si NMOSFETs with a Silicon-Carbon Alloy Stressor W.-C. Wang (National Chung Hsing University, Taiwan); C.-C. Lee (Taiwan Semiconductor Manufacturing Company, Taiwan); J. Huang, S.-T. Chang (National Chung Hsing University, Taiwan) The stress distribution in the Si channel regions of a Silicon-Carbon source/drain NMOSFETs with various widths were studied using 3D ANSYS simulations. The mobility enhancement was found to be dominated by the tensile stress along the transport direction and compressive stress along the growth direction in wide width devices. Stress along the width direction was found to have the least effect on the drain current in wide width cases. Stress along the width direction slightly degraded the mobility gain in the narrow width regime, contributing a slight degradation of the total drive current gain in the smaller width region. The compressive stress along the vertical direction perpendicular to the gate oxide contributes significantly to the mobility enhancement and cannot be neglected in nanoscale NMOSFETs. The impact of width on performance improvements such as the drive current gain was also analyzed using 3D TCAD simulations.
HP-2 Growth and Characterization of ZnO Nanoflowers J.H. Park, S. Prikhodko, M. Pozuelo (University of California - Los Angeles); S.D. Sitzman (Oxford Instruments America); S. Kodambaka (University of California - Los Angeles) ZnO is a direct wide band gap (3.37 eV) semiconducting piezoelectric material with potential applications in a wide variety of areas including radiation-hardened electronics, optoelectronics, spintronics, piezotronics, and catalysis. Here, we report the formation of nanoscale hexagonal dendrites ("flowers") during chemical vapor deposition of ZnO on Au-coated Si(100) and SiO₂/Si(100) substrates. All our growth experiments are carried out in a three-zone 2" tube furnace using high-purity (99.9 %) metallic Zn powder (average particle size of ~ 15 µm) and purified air as Zn and O sources, respectively. We observe highly regular ~1-µm-sized flower structures on 100-nm-thick Au-coated substrates maintained at 340°C while flowing 200 Torr of argon/air gas mixture at 200/2 sccm. We characterized the as-grown structures in situ using scanning electron microscopy coupled with electron backscattered diffraction (SEM-EBSD) and energy dispersive X-ray spe ctroscopy (EDS), and ex situ using transmission electron microscopy (TEM). From SEM imaging, we estimate the thickness of these flowers to be ~ 52 ± 5 nm. EDS data suggests that the flowers are primarily composed of Zn and O. Selected area electron diffraction and EBSD patterns acquired from individual ZnO flowers indicate that they are single crystals with a wurtzite (hexagonal) structure. We find that ZnO flower growth depends sensitively on the growth temperature, gas environment, and Au film thickness. Based upon these results, we suggest a tentative mechanism for the growth of these flower structures.
HP-4 Reliability Study of Through-Silicon via (TSV) Copper Filled Interconnects A. Kamto (The University of Alabama); Y. Liu, L. Schaper (University of Arkansas); S.L. Burkett (The University of Alabama) Through-silicon vias (TSVs) have been extensively studied because of their ability to achieve chip stacking for enhanced system performance. The fabrication process is becoming somewhat mature, however, reliability issues need to be addressed in order for an eventual transition from laboratory to production. In our laboratory, vias with tapered sidewalls are formed through a modified Bosch process using deep reactive ion etching (DRIE). Vias are; lined with silicon dioxide using plasma enhanced chemical vapor deposition (PECVD); followed by sputter deposited titanium barrier and copper seed layers before filling with a reverse pulse copper electroplating process. Following attachment of the process wafer to a carrier wafer, the process wafer is thinned from the backside by a combination of mechanical methods and reactive ion etching (RIE). Fabricated vias are subjected to thermal cycling, using a Physical Property Measurement System (PPMS), with temperature ranging from -25°C to 125°C; and the resistance is measured as a function of temperature. For long via chains, resistance changes somewhat linearly upon cycling for temperatures above room temperature; and values change erratically at lower temperatures. This test method forms the basis of reliability studies, to be presented in this paper, in which via chain size, temperature ramp rates, temperature regions, and number of cycles are varied.
HP-5 Properties of Pure and Silver Doped Ti₃SiC₂ Films Deposited by HiPIMS R. Bandorf, M. Schmidt, H. Gerdes (Fraunhofer Institute for Surface Engineering and Thin Films IST, Germany); G. Mark (MELEC GmbH, Germany) M_n+1AX_n-phase materials are used as electrical conductive ceramic. Especially Ti₃SiC₂ is synthesized as wear resistant contact material. High Power Impulse Magnetron Sputtering (HiPIMS) opens new horizons tailoring the resulting film properties. In contrast to the usually applied DC sputtering for HiPIMS films an improved wear resistance, a reduced resistivity, and a modified structure were observed. For further improvement of the conductivity the films were doped with silver. Since the HiPIMS process realizes a glassy structure besides the reduction of resistivity also an improved corrosion resistance is expected.
HP-6 Effects of Alloying Elements(Zr,Hf) on the Nanopore and Nanotube Formation of Ti-30(Nb,Ta) Alloys H.-C. Choe, Y.-M. Ko (Chosun University, Korea); W.A. Brantley (Ohio State University) The two-step anodization techniques have been used to improve the bone tissue integration. The electrochemical formation of ordered nanopore and nanotube has been reported for Ti anodization in fluoride-containing acid electrolytes at moderate voltage. Nanopore and nanotube formation on the Ti oxide is important to improve the cell adhesion and proliferation in clinical use. In this study, nanopore and nanotube formation of Ti-30Nb-xZr(Hf) and Ti-30Ta-xZr(Hf) alloy have been investigated using various condition of , nanopore and nanotube formation methods. Ternary Ti-30Nb-xZr(Hf)(x=3, 10, 15wt%) and Ti-30Ta-xZr(Hf) (x=3, 10, 15wt%) alloys were prepared by using high purity sponge Ti (G&S TITANIUM, Grade. 4, USA), Ta, Zr, Hf and Nb sphere (Kurt J. Lesker Company, 99.95% wt.% in purity). Two kinds of Ti alloys prepared using the vacuum arc melting furnace. In order to homogenize, solution treatment was carried out for 1hr at 1050°C in an argon atmosphere, followed by wat er quenching to stabilize the β phase. Microstructures of the alloys were examined by optical microscopy (OM, OLYMPUS BM60M, JAPAN) and scanning electron microscopy (SEM, HITACHI-3000, JAPAN). Two-step anodizing was used for surface modification; nanopore formation was performed by potentiostatic experiment using a conventional two electrode configuration at 180V in 1 M H3PO4 electrolyte at room temperature. Nanotube formation were carried out with a conventional three-electrode configuration with a platinum counter electrode and a saturated calomel(SCE) reference electrode. Experiments were performed in 1M H3PO4 with small additions of NaF(0.1-0.8wt%). All experiments were conducted at room temperature. Electrochemical treatments were performed by using potentiostat (EG&G Co, 362, U.S.A). The electrochemical treatment consisted of a potential ramp from the open-circuit potential to an end potential at 10 V with a scan rate of 500mV/s followed by holding the sample at 5-10V for 30min-120min. The nanopores and nanotubes could be controlled by two-step anodizing. It was depended on the composition and surface oxide films.
HP-10 Effect of Seed-Layer Films on the Growth of ZnO Nanowires via Hydrothermal Technique S.-N. Bai (Chienkuo Technology University, Taiwan) ZnO nanowires have been prepared on the ZnO film-coated silicon substrates (100) by a hydrothermal method. The ZnO films were deposited by spin-coating polymeric precursors. Then, the ZnO thin films were annealed in air at various temperatures ranging from 350 to 850°C for 1h. On the ZnO thin films, the well-oriented nanowires were synthesized by a solution growth process using zinc nitrate and hexamethylenetetramine in aqueous solution. The ZnO nanowires were characterized by different structural and optical techniques, including the X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL). The XRD analysis with grazing incidence and SEM results indicate that the ZnO nanowires are single crystalline structure with preferential orientation along the c-axis direction with a full-width at half-maximum (FWHM) less than 0.5°. The TEM analysis further verifies that the ZnO nanowires are highly preferr ed grown along the (002) crystal plane. The spacing between adjacent (002) lattice planes is estimated as 0.52 nm. The optical properties of the nanowires were measured using CL for the ZnO seed-layer films annealed in air from 350 to 850°C for 1h. The CL spectra in the visible spectrum exhibit one strong broad deep-level emission band that may be due to the intrinsic or extrinsic defects. It can be observed that the ZnO nanowires synthesized on the seed-layer films, which annealed at different temperatures, show different optical behaviors. The dependence of the optical characteristics on the ZnO nanowires with various substrate properties is also discussed.
HP-13 Resistive Switching Characteristics and Mechanism of SrZrO₃ Thin Films M.-H. Lin, M.-C. Wu, S.-W. Jan, Y.-H. Huang (National Chiao Tung University, Taiwan); C.-H. Lin (Winbond Electronics Corporation, Taiwan); T.-Y. Tseng (National Chiao Tung University, Taiwan) The resistive switching behaviors of rf-sputtered SrZrO₃ (SZO) thin films were investigated in this paper. The memory states of Al/SrZrO₃/LaNiO₃/Pt structure can be switched between high resistance state (HRS) and low resistance state (LRS) by applying voltage signal, showing reversible and bistabe resistive switching characteristics. The SZO resistive thin film memory device exhibits lower switching voltages than doped SZO thin film device, reducing the power consumption during device operation. The retention characteristics of both HRS and LRS are stable up to 10⁶ s at room temperature (RT) and 85°C. After applying the successive read voltage stress (-0.3 V), the resistive ratio of HRS and LRS remains nearly 10³ over 12000 s at RT and 85°C. The conduction mechanisms of HRS and LRS are dominated by Frenkel-Poole emission and Ohmic conduction, respectively. As a result, the resistive switching from HRS to LRS might be ex plained due to the formation of conducting filaments constituted by the arrangement of the defects in the bulk SZO thin film. On the contrary, conducting filaments are ruptured by Joule heating effect, leading to the memory state switching back to HRS. The undoped SZO memory device with its superior memory characteristics is a promising candidate for next generation nonvolatile memory application.
HP-14 Surface Morphology Changes of Anodized Ti-x(Nb,Ta) Binary Alloys for Dental Implant K. Lee, H.-C. Choe, Y.-M. Ko (Chosun University, Korea); W.A. Brantley (Ohio State University) Commercial pure titanium(Cp-Ti) and Ti-6Al-4V alloy have been widely used for orthopedic implant materials and dental implant materials because of its excellent combination of biocompatibility, corrosion resistance and mechanical properties. However, the Ti-6Al-4V alloy is currently utilized and should be replaced, since the release of Al and V ions causes long-term health problems. And it can also lead to resorption of adjacent bone tissue due to the great elastic modulus difference between the implant and bone. Thus, there are efforts for developing new titanium alloys with non-toxic elements. Nb and Ta are found to reduce the elastic modulus when alloyed with titanium in certain preferred quantities. Recently, titanium oxide layer has been used for improving the biocompatibility of implants. The advantage of using titanium oxide layer is that it can be grown directly on the Ti and Ti alloys surfaces, by cost-effective techniques such as anodic oxidation. In this stud y, electrochemical characteristics of anodic oxide layer formed on titanium binary alloy surface have been investigated. Titanium oxide layers were grown on Ti-XTa and Ti-XNb(X=10, 20, 30 and 40 wt%) alloy substrates using phosphoric acid electrolytes. For this study, the Ti-Ta and Ti-Nb alloys were manufactured by arc melting on a water-sealed copper hearth under an argon gas atmosphere with a non-consumable tungsten electrode. These specimens were melted six times by inverting the metal for homogeneous structure. Ti-Ta and Ti-Nb alloys were homogenized in argon atmosphere at 1000℃ for 24h followed by a rapid quenching in ice water. The samples were incrementally polished by utilizing 120 grit emery paper down to 2000 grit emery paper. The polished and cleaned binary alloy disks were anodized in solution containing typically 1 M H₃PO₄ at room temperature. A direct current(D.C) power source was used for the process of anodization. For electrochemical measurement s, the cell consisted of conventional three-electrode configuration with Pt rod and a saturated calomel electrode (SCE) as the counter and reference electrode, respectively. All experiments were carried out in 0.9 % NaCl solution at 36.5±1℃. The corrosion resistance of anodized binary Ti-Ta and Ti-Nb alloys were higher than those of the non-anodized Ti alloys in 0.9% NaCl solution. Surface morphology changes of anodized Ti-x(Nb,Ta) binary alloys depend on content of Nb and Ta.
HP-15 Nonvolatile Memory Effect of W Nanocrystals Thin Film Under Various Nitride-Base Plasma Treatments S.-C. Chen, T.-C. Chang (National Sun Yat-Sen University, Taiwan); W.-R. Chen (National Chiao Tung University, Taiwan); Y.-C. Lo, K.-T. Wu (National Tsing Hua University, Taiwan); S.M. Sze (National Chiao Tung University, Taiwan); J. Chen, I.H. Liao (ProMOS Technologies); F.-S. Huang (National Chiao Tung University, Taiwan) In this study, a Tungsten nanocrystal thin film as charge storage center of nonvolatile memory was prepared and we focused on the electrical influence of nonvolatile memory effect for using the nitride-base various plasma treatments on our prepared sample. Transmission electron microscopy analyses revealed the microstructure in the thin film and X-ray photon-emission spectra indicated the variation of chemical composition after the nitride-base various plasma treatments. Electrical measurement analyses show the improvement of charge storage effect because the nitride-base various plasma treatments can enhance the surrounding silicon oxide quality of W nanocrystals. Moreover, the data retention and endurance characteristics of the W nanocrystals thin film nonvolatile memory were compared their performances under the different plasma treatment with passivated effect. In the previous research, this plasma treatment technique is first proposed to use on the metal nanocrysta ls nonvolatile memory application and to study the electrical characteristics. In addition, the process is compatible with the current flash memory fabrication technology.
HP-16 Influence of Annealing Temperature on Formation of Mo Nanocrystal Memory in Oxygen Incorporated Mo and Si Thin Film C.-C. Lin (National Chiao Tung University, Hsin-Chu, 300, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); C.-H. Tu (National Chiao Tung University, Taiwan); S.-C. Chen, J.-Y. Lin (National Yunlin University of Science and Technology, Taiwan); S.M. Sze, C.-W. Hu, T.-Y. Tseng (National Chiao Tung University, Taiwan) In this study, we investigated the influence of rapid thermal annealing temperature on formation of Mo nanocrystal memory in oxygen incorporated Mo and Si thin film. X-ray photon-emission spectra and transmission electron microscopy analyses reveal a change of chemical bonds and microstructure in the thin film at the various annealing temperatures. Electric measurement analyses indicate the charge storage effect of the thin film at the higher annealing temperatures due to formation of Mo nanocrystals embedded in nonstoichiometry silicon oxide. The difference in electric characteristics for the thin film at the various annealing temperatures was correlated to the change of the chemical bonds and the microstructure after the annealing.
HP-17 Charge Stored Effects of Ni-O-Si and Ni-Si-N Nanocrystals Thin Film Using a Low Temperature Fabrication W.-R. Chen (National Chiao Tung University, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); C.-Y. Chang (National Chiao Tung University, Taiwan) In recent years, most methods of nanocrystals thin film fabrication generally need the thermal treatment with high temperature and long duration. This procedure will influence thermal budget and throughput for the current manufacture technology of semiconductor industries. Hence, an ease and low temperature fabrication technique of Ni-O-Si and Ni-Si-N nanocrystals was demonstrated for nonvolatile memory application in this study. The memory structure of Ni-O-Si nanocrystals embedded in the SiO_x layer was fabricated by sputtering a commixed target (Ni_0.3Si_0.7) in an Ar/O₂ environment at room temperature. It can be considered that the oxygen plays a critical role during sputter process for the nanocrystal formation. In addition, a high density (~10¹² cm^-2) nanocrystal also can be simple and uniform to be fabricated in our study. We also proposed a formation of Ni-Si-N nanocrystals by replacing O₂ by N₂ environment during the sputtering process. It was also found that a high density Ni-Si-N nanocrystal was embedded in the silicon nitride (SiN_x) which presented larger memory effect. Therefore, by using this internal competition mechanism of charge trapping layer for these elements (Ni, Si, and O/N), we can obtain a metallic nanocrystals nonvolatile memory with a low temperature process.
HP-18 Correlations Between Microstructure and Properties of High Purity Electrodeposited Nickel Coatings A. Godon, J. Creus, X. Feaugas, E. Conforto, P. Girault (Université de la Rochelle, France); L. Pichon (Université de Poitiers, France); C. Savall (Université de la Rochelle, France) Protection of metallic surfaces against aqueous aggressive environments is a matter of great concern because of economical reasons and environmental issues. Protective coatings are commonly used to improve corrosion resistance. However, mechanical and/or tribological resistance may also be required to ensure the durability of structures, depending on the field of application. Recent studies have shown that polycrystalline metals with a grain size in the nanometer range seem to exhibit improved mechanical properties^1,2. Moreover corrosion resistance is also strongly influenced by grain size^3,4. The mechanisms by which these properties are linked to grain size have not been explained yet. In the case of nickel, some limitations of these studies arise from difficulties in controlling the microstructure and the purity of the coatings. The aim of this research is to acquire a better knowledge of the interplay between structure, composition, corrosion resistance and m echanical properties. In order to carry through these objectives, nanocrystalline nickel has been chosen as a model material. The coatings are obtained by electrodeposition in different baths (Sulfamate bath and Watts Bath) without additives, in order to avoid the incorporation of impurities⁵. The composition of the coatings is analyzed by Glow Discharge Optical Emission Spectrometry (GDOES). The microstructure is characterized using different techniques (XRD, SEM, TEM and AFM) in order to study the influence of deposition parameters on microstructure at different scales. Polarization curves (in H2SO4 1M) and micro-hardness measurements are used to characterize the properties of the coatings comparatively to several forms of nickel: microcrystalline bulk nickel with different grain sizes, single crystals of different crystallographic orientations and commercial nanocrystalline nickel. Our experimental approach includes a careful preparation of the surface in order to separ ate the effects due to several factors which can modify the surface reactivity: roughness, contamination, deformation, crystallographic orientation. ¹T.H. Yim, S.C. Yoon and H.S. Kim, Mater. Sci.Eng. A 449-451 (2007) 836-840. paragraph2²y.j. Li et al., Acta Mater. 55 (2007) 5708-5717.paragraph2³R. Mishra, R. Balasubramaniam, Corros. Sci. 46 (2004) 3019-3029. paragraph2⁴l.wang et al., Scripta Mater. 55 (2006) 657-660. super 5A. Godon et al., First International Conference on Functional Nanocoatings, Budapest (2008).
HP-19 Biocompatibility and Anti-Microbial Properties of TiO_x Thin Films S.E. Rodil, H. Arzate (Universidad Nacional Autónoma de México); A Almaguer-Flores (Universidad Nacional Autónoma de México, Mexico) Titanium oxide thin films were deposited by rf-magnetron sputtering using a pure titanium target and reactive plasma conditions (oxygen + argon). Neither substrate bias nor temperature were used, therefore the films were amorphous and substoichiometric. Nevertheless, the biological response of the oxide films in comparison to medical grade stainless steel (SS) and to Ti6Al4V samples was particularly good. As biocompatibility tests, we studied the attachment and proliferation/viability of human osteoblast cells on the TiO_x films. The number of attached cells on the TiO_x surfaces after 24 hours was twice the number on the SS substrate. While the proliferation after three days of incubation was one order of magnitude higher on TiO_x than on SS. Similarly results were obtained for the expression of Alkaline Phosphatase after 5 and 15 days of incubation, which is considered a marker of osteoblast differentation and new bone formation. These results suggest that these easily deposited TiO_x films could be used as a surface modification for orthopaedical implants and since microbial infection is still one of the main causes of implant failure, we decided to study the adhesion of bacteria in comparison to the standard Ti6Al4V material. The bacterial adhesion studies were done using nine different strains from the oral microbiota. The results showed that the number of colony forming units counted after 24 hours, 3 and 7 days was extremely low on the TiO_x films in comparison to SS and Ti6Al4V surfaces.
HP-20 Field Emission Properties of Zinc Oxide Nanorods Grown on ZnO/Si Substrates by Using Plasma Treatment I.-C. Yao, T.-Y. Tseng, P. Lin (National Chiao Tung University, Taiwan) The ZnO nanorods on ZnO/Si substrates were synthesized by using the low temperature growth aqueous solution method. The different Argon/Oxygen ratio plasma treatments were carried on the as-grown ZnO nanorods to provide the nanorods with various tip angles. The morphology and crystal structure of the ZnO nanorods were examined by scanning electron microscopy, transmission electron microscopy and X-ray diffraction, respectively. The field emission properties of the ZnO nanorods with different tip angle (95°and 110°) are: the turn-on electric fields (at the current density of 10μAcm^-2) are about 2.3 and 3.0 Vµm^-1, respectively, while the threshold electric fields (at the current density of 1mAcm^-2) are 6.0 and 6.6 Vµm^-1, respectively. The improved field emission properties are believed to benefit from decreased emitter tip angle.
HP-21 Comparison of the Ti-Si-O Composites Nanocrystals Synthesized via Different Methods for Nonvolatile Memory Applications L.-W. Feng (National Chiao Tung University, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); P.-S. Wang (National Chiao Tung University, Taiwan); C.-F. Weng, M.-C. Chen, D.-S. Gan, N.-J. Ho, H.-J. Huang (National Sun Yat-Sen University, Taiwan); C.-Y. Chang (National Chiao Tung University, Taiwan) The purpose of this study was to compare the Ti-Si-O nanocrystals properties and electrical behavior prepared from two methods between co-sputtering TiSi₂-Si with post-annealing in oxygen ambient and co-sputtering Ti-SiO₂. The characteristics of Ti-Si-O composition were analyzed by X-ray photon-emission spectra and the formations of nanocrystals were observed by high resolution transmission electron microscopy under the various annealing temperatures. The charge storage properties of Ti-Si-O nanocrystals fabricated by different methods on the metal oxide semiconductor (MOS) structure has been investigated. capacitance–voltage (C–V) measurements for memory window and the endurance and retention characteristics are exhibited for nonvolatile memory application.
HP-24 Fabrication of Dye-Sensitized Solar Cells Based on ZnO Nanowires M.F. Hossain, S. Biswas, M. Shahjahan, T. Arakawa, T. Takahashi (University of Toyama, Japan) Recently, great attention has been paid to dye-sensitized solar cells (DSCs) due to their low fabrication cost. The high light-to-energy conversion efficiencies achieved with DSCs may be attributed to the nanoporous TiO₂ electrode. Zinc oxide (ZnO) is a wide band gap semiconducting material with a similar band gap and electron affinity to those of TiO₂ and has been considered as an alternative material in DSCs applications. One-dimensional (1D) nanowires have been extensively studied in recent years. ZnO nanowires have attracted great interest for promising applications in optoelectronics devices. Several methods have been demonstrated to fabricate 1D nanostructures, such as vapor liquid-solid epitaxy, chemical vapor deposition, and pulse laser deposition, but these gas phase techniques still have some limitations for substrate size and the need for high temperature operation (above 800°C). Among the various techniques for the preparation of ZnO nanowires, the relatively simple sol-gel method is the most widely used because of its ability to obtain films with tailored properties on large, curved substrates. In our present study, we systematically study the feature-controlled ZnO nanowires arrays via the hydrothermal method and ZnO sol-gel thin films were used as the seed layers on SnO₂ :F coated glass with different pretreatment conditions. The ZnO nanowires have been characterized by the TG-DTA, XRD, SEM AFM, FTIR and UV-VIS system. The surface morphology of the nanoporous ZnO nanowires strongly depends on the annealing temperature of the seeding ZnO layers. It was revealed from optical study that the dye absorption increases with the increase of annealing temperature. Incident photon-to-current efficiency is calculated for all the solar cells with different ZnO thin films. The variation of photoelectric conversion efficiency of the DSCs, deposited with various annealing temperature is discussed with the analysis of diffe rent structure of ZnO nanowires and the corresponding dye-incorporations.
HP-25 Comparative Study of Dye and CdS Sensitized Grätzel Solar Cells M.F. Hossain, S. Biswas, M. Shahjahan, T. Takahashi (University of Toyama, Japan) Dye-sensitized solar cells (DSCs) have been widely investigated as a next generation solar cells because of their simple structure and low manufacturing cost. One of the key factors for enhancing the efficiency of DSCs is the light harvesting properties of dye, attached on the surface of titanium oxide (TiO₂ ). Ruthenium has been mostly used as sensitizer in DSCs, which is very expensive. An alternative method is to couple the TiO₂ electrode with narrow band gap semiconductor which enhances the light absorbing property as well as the overall efficiency of DSCs. In this study, cadmium sulfide (CdS) and ruthenium based dye were used as sensitizers. The photovoltaic performances of the solar cells, consisting of these two sensitizers, were compared. TiO₂ photoelectrodes were prepared on SnO₂:F coated glass by facing target reactive sputtering technique. CdS was deposited on TiO₂ by inexpensive chemical bath deposition technique and was annealed at 400°C in high vacuum of 5x10^-5 Pa for improving crystallinity. The dye and CdS sensitized Grätzel solar cells consist of iodide and polysulfide-based electrolytes respectively. Mildly coated platinum counter electrode was used in both solar cells. The structural, optical and surface morphological properties of TiO₂ photoelectrodes were characterized by x-ray diffraction analysis, energy dispersive x-ray analysis, ultraviolet-visible spectroscopy, atomic force microscopy and field emission scanning electron microscopy. Interestingly, all the photovoltaics parameters of CdS sensitized Grätzel solar cells are higher for back side illumination than the front side illumination. The CdS sensitized solar cells shows higher photoelectric-conversion efficiency with back side illumination than the ruthenium based DSCs in both side illuminations. It is may be due to the fact that nanoporous TiO₂ electrode incorporates both the dye and CdS in a same manner, how ever thin polycrystalline layer of CdS remains as a separate layer on the TiO₂-surface, which enhances the photoelectric-conversion efficiency.
HP-27 The Role of Metal Plasma Ion Implantation in Anatase-Titanium Dioxide: Correlation Between Photoreactivity and Implantation Mechanism M.-H. Shih (Mingdao University, Taiwan); C.-C. Yen (National Chung Hsing University, Taiwan); D.-Y. Wang (Mingdao University, Taiwan); L.S. Chang, H.-C. Shih (National Chung Hsing University, Taiwan) The pure titanium dioxide thin films were prepared on glass substrates by the sol-gel spin coating method. The as-deposited TiO₂ thin films were subjected to metal plasma ion implantation at 30 KeV to incorporate transition metals to investigate the effect of impurity species and ion dosage. We theoretically investigated the photoreactivity of the metal ions as implants modify the band gap properties of anatase TiO₂. According to the results of X-ray photoelectron spectroscopy (XPS) analysis, the Me-implanted (Me= Cu, Fe, Ni, ...) TiO₂ leads to the formation of implanted metal oxide. The implanted metal oxides extended the photosensitivity range of the anatase TiO₂ to cover the visible light spectra. Compared to the pure TiO₂, a photo-catalysis was observed in the visible light regime. The implantation mechanism will be conducted by using UV-Vis spectrophotometer, photo-luminance spectroscopy and cathode-luminescence.
HP-29 The Properties of Transparent Semiconductor Zn_1-xTi_xO Thin Films Prepared by Sol-Gel Process C.-Y. Tsay (Feng Chia University, Taiwan); H.-C. Cheng (Industrial Technology Research Institute, Taiwan); C.-Y. Chen, K.-J. Yang, C.-K. Lin (Feng Chia University, Taiwan) Zinc oxide based transparent semiconductor films have attracted considerable interest for AMLCD, AMOLED display and E-paper applications. This work investigated the effect of various Ti addition (0, 1, 3, 5, and 10 at.%) on the microstructure, surface morphology, transparency, and resistivity of ZnO thin films prepared by sol-gel process. The as-prepared films were annealed in air at 500 °C for 1 hr. Experimental results showed that additions of Ti into ZnO thin films (Zn_1-xTi_xO) not only refined the grain size but also increased the transmittance and resistivity of thin films. In the present study, the Zn_0.9Ti_0.1O thin films exhibited the best performance with an average transmittance of 91.0% (an increase of ~12% over a pure ZnO thin film), a resistivity of 1.1×10⁵ ω-cm, and a RMS roughness value of 3.0 nm.
HP-30 Silver Phthalocyanine Films for Photovoltaic Applications A. Mahajan (DAV College, India); H. Gupta, R.K. Bedi (Guru Nanak Dev University, India) Silver phthalocyanine (AgPc) has attracted considerable interest in organic photovoltaic devices because of its outstanding optical and electrical properties. To improve performance of devices based on AgPc, a series of silver phthalocyanine (AgPc) films has been prepared under different experimental conditions. These samples have been studied for their structural, optical and electrical properties. The X-ray diffraction and SEM pattern of these films show crystalline behaviour of films. The electrical conductivity and optical band gap of the films increases with increase in substrate temperature, whereas activation energy decreases. The activation energy of the films found to lie in 0.41-0.83 eV. Analysis of optical absorption measurements on the films indicates that the interband transitions energies lie in 3.9-4.1 eV. Keeping in view, the electrical and optical properties of AgPc films single layer (Fluorine doped tin oxide / AgPc /Aluminium) and double layer (Fluori ne doped tin oxide / Crystal violet / AgPc /Aluminium) junctions have been fabricated under different experimental conditions. The J-V relationship for the single and double layer devices are found to be in good agreement with standard diode equation.
HP-34 Effects of the Anodizing Processon the Corrosion Behaviors of Ti-xHf Alloys Y.-H. Jeong, H.-C. Choe, Y.-M. Ko, H. Ahn (Chosun University, Korea) Titanium and its alloys, such as Cp-Ti and Ti-6Al-4V alloy have been extensively studied for the applications of orthopedic and dental implant materials because of their excellent mechanical properties, corrosion resistance, and outstanding biocompatibility. However, a native TiO2 has not enough bioactivity to osseointegrate with bone and the Ti-6Al-4V alloy in an acceptable prosthetic biomaterial, recent studies indicated that the release and accumulation of Al and V ions could have harmful effects on the human body. Hafnium belongs to the value metal group and hafnium oxide has numerous properties. These properties make hafnium oxide a valuable material to be used for various applications such as optical coatings, gas sensors of capacitor and as protective coatings for biomedical applications. Anodizing method of Ti-based alloys has attracted great attentions due to interfacial properties. In this study, Ti-xHf binary alloys containing 10, 20, 30 and 40 wt% Hf contents were manufactured by the vacuum furnace system. These Ti-xHf alloys were anodized in solution containing typically 1M H3PO4. A direct current power source was used for the process of anodization. Firstly, anodization power was controlled with 120, 170, and 220V, respectively, at room temperature. Secondly, the anodized surfaces of Ti-xHf alloys were crystallized by heat treatment at 300℃, 500℃, and 600℃ for 6 hours in Ar atmosphere. The microstructure was characterized by XRD and SEM. The corrosion behaviors of the anodized samples at different experimental conditions were studied using potentiodynamic test and A. C. impedance test in 0.9% NaCl solution at 36±1℃. The result shows that anodized Ti-xHf alloys showed that pore size increased as applied voltage increased, whereas, pore size decreased as Hf content increased. The anodized Ti-xHf alloys were exhibited more good corrosion resistance than non treated Ti-xHf alloys.
HP-35 The Studies of Flexible a-Si:H Y.-T. Chou, C.-Y. Su, P.-T. Liu, S.-Y. Tsai (National Chiao Tung University, Taiwan); I.-H. Peng (National Tsing-Hua University, Taiwan) We investigated the effects of the uneasily mechanical strain stress on flexible hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) in this work. The proposed a-Si TFTs were fabricated on thin steel foil and all process temperature was well-controlled below 200℃. The reliability of TFTs was discussed by applying DC bias stress on gate electrode up to 104 seconds and the strain was imposed on the device parallel to the source-drain current path. Our results indicated both outward and inward strain stress can lead to an un-recoverable destruction on a-Si:H TFTs at the first time bending behavior and derived the device in different performance from initial case permanently. We provided a model and used activation energy to explain the bending behavior. The passivation effect was also discussed in these studies. The device with passivation layer not only increased the performance, but also enhanced the reliability of devices. By adding one more thermal t reatment on the device with passivation layer, the threshold voltage was 1.3V closed to 0V, and electrical performance was obvious enhanced.
HP-36 Characterization of Electrically Conducting Polyaniline Nanofiber/polyimide Nanocomposites A. Hopkins (The Aerospace Corporation) Nanocomposites of polyaniline nanofibers and polyimide were fabricated and studied using small angle neutron scattering (SANS). The immiscible nature of the conformationally dissimilar polyaniline nanofiber and polyimide host is established by a series of experiments involving neutron scattering. Based on these techniques, we conclude that the crystal structure of the polyimides is not disrupted, and that there is no mixing between the two components on a molecular level. The morphology of the conducting salt component was analyzed by SANS data and was treated by two common models: Debye-Bueche (D-B) and inverse power law (IPL). Due to deviations in the linear curve fitting over a large scattering range, neither the D-B nor the IPL model could be used to characterize the size and shape of all PANI-0.5-CSA/polyimide blend systems. At 1 and 2% concentration, the D-B model suggested salt domains between 20 and 70 Å with fractal geometries implied by the IPL model. As salt concentrations are increased to 5%, the structures are observed to change, but there is no simple structural model that provides a suitable basis for comparison.

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