bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Reflow on the Output Characteristics of Piezoelectric Microelectromechanical System Devices
Authors: Nogami Hirofumi , Kobayashi Takeshi , Okada Hironao , Masuda Takashi , Maeda Ryutaro , Itoh Toshihiro
Published: September 2012

An animal health monitoring system and a wireless sensor node aimed at preventing the spread of animal-transmitted diseases and improving pastoral efficiency which are especially suitable for chickens, were developed. The sensor node uses a piezoelectric microelectromechanical system (MEMS) device and an event-driven system that is activated by the movements of a chicken. The piezoelectric MEMS device has two functions: a) it measures the activity of a chicken and b) switches the micro-control unit (MCU) of the wireless sensor node from the sleep mode. The piezoelectric MEMS device is required to produce high output voltages when the chicken moves. However, after the piezoelectric MEMS device was reflowed to the wireless sensor node, the output voltages of the piezoelectric MEMS device decreased. The main reason for this might be the loss of residual polarization, which is affected by the thermal load during the reflow process. After the reflow process, we were not able to apply a voltage to the piezoelectric MEMS device; thus, the piezoelectric output voltage was not increased by repoling the piezoelectric MEMS device. To address the thermal load of the reflow process, we established a thermal poling treatment, which achieves a higher temperature than the reflow process. We found that on increasing the thermal poling temperature, the piezoelectric output voltages did not decreased low significantly. Thus, we considered that a thermal poling temperature higher than that of the reflow process prevents the piezoelectric output voltage reduction caused by the thermal load.
Fabrication and Characterization of Double-Layer Pb(Zr,Ti)O3Thin Films for Micro-Electromechanical Systems
Authors: Kanda Kensuke , Inoue Junichi , Saito Takashi , Fujita Takayuki , Higuchi Kohei , Maenaka Kazusuke
Published: September 2012

In this paper, we address the fabrication and characterization of bimorph structures with relatively thick double-layered Pb(Zr,Ti)O3(PZT) thin films. The PZT/PZT layers are deposited by RF magnetron sputtering. Hysteresis loops of polarization and electrical field for the top and bottom PZT thin films revealed good ferroelectric characteristics with remanent polarization at approximately 20 µC/cm2and a coersive electric field of about 100 kV/cm. The vibration tests of fabricated bimorph cantilevers during electrical voltage application revealed a twofold displacement compared with single layer driving, and the piezoelectric coefficient valued31is estimated to be 13 pm/V. The residual stress difference between the top and bottom layers after the annealing process is calculated to be -0.32 MPa. For a further thickening of the bimorph structure, 6-µm-thick PZT/PZT is also sputtered. The thicker bimorph has a smaller residual stress difference, -30 MPa, between the two layers prepared without the annealing process. The evaluated results demonstrate that the PZT/PZT bimorph structures are applicable to micro-electromechanical systems (MEMS) devices.
Shear-Mode Industrial Inkjet Head Using Lead-Free Piezoelectric Ceramics
Authors: Tanuma Chiaki , Shimosato Masashi , Nitta Noboru , Yamamoto Keizaburou , Takahashi Hirofumi
Published: September 2012

A shear-mode inkjet head utilizing alkaline niobate-based lead-free piezoelectric ceramics has been developed. A prototype inkjet head with a nozzle density 150 dots per inch (dpi) was achieved on a grayscale of eight levels with a minimum ink droplet ejection of 6 pl. Furthermore, the inkjet head with a nozzle density of 300 dpi was achieved on a grayscale of four levels with a minimum ink droplet ejection of 3 pl. Although the prototype inkjet head required a high voltage of approximately twice the driving voltage of the inkjet head using lead zirconate titanate (PZT) piezoelectric ceramics, the grayscale can be realized by a multidrop method. Thus, the alkaline niobate-based lead-free piezoelectric ceramics can be used to replace PZT ceramics as shear-mode actuators for inkjet heads.
Film Sensor Device Fabricated by a Piezoelectric Poly(L-lactic acid) Film
Authors: Ando Masamichi , Kawamura Hideki , Kageyama Keisuke , Tajitsu Yoshiro
Published: September 2012

Synthetic piezoelectric polymer films produced from petroleum feedstock have long been used as thin-film sensors and actuators. However, the fossil fuel requirements for synthetic polymer production and carbon dioxide emission from its combustion have raised concern about the environmental impact of its continued use. Eco-friendly biomass polymers, such as poly(L-lactic acid) (PLLA), are made from plant-based (vegetable starch) plastics and, thus, have a much smaller carbon footprint. Additionally, PLLA does not exhibit pyroelectricity or unnecessary poling. This suggests the usefulness of PLLA films for the human–machine interface (HMI). As an example of a new HMI, we have produced a TV remote control using a PLLA film. The intuitive operation provided by this PLLA device suggests that it is useful for the elderly or handicapped.
Fundamental Study of Application of Piezoelectric Chiral Polymer to Actuator
Authors: Inuzuka Yusuke , Onishi Katsuki , Kinoshita Shunsuke , Nakashima Yasuto , Nagata Takahiro , Yamane Hirotsugu , Nakai Takaaki , Kataoka Takuya , Ito Shuhei , Tajitsu Yoshiro
Published: September 2012

To realize a new piezoelectric chiral polymer actuator, we studied the motion induced by the shear piezoelectricity of a poly(L-lactic acid) (PLLA) film under the application of an ac voltage. First, PLLA was subjected to a supercritical CO2 treatment to change its high-order structure, resulting in an improvement in its piezoelectricity. Then, we designed a PLLA film roll transducer, which consisted of a piece of the treated PLLA film rolled into a long thin roll. To demonstrate the transducer, we placed it vertically on a fixed stand. A plastic hemispherical container was placed on the upper end face of the transducer. It was found that the container rotated smoothly in the counterclockwise direction when an ac voltage was applied. We emphasize that no special complex mechanical parts were used in this study.
Sensing Using Piezoelectric Chiral Polymer Fiber
Authors: Ito Syuhei , Imoto Kenji , Takai Kyohei , Kuroda Shintaro , Kamimura Yuki , Kataoka Takuya , Kawai Naoki , Date Munehiro , Fukada Eiichi , Tajitsu Yoshiro
Published: September 2012

To realize a new polymer sensor fabricated from a piezoelectric chiral polymer fiber, we attempted to detect the response signal induced by the shear piezoelectricity of the chiral polymer poly(L-lactic acid) (PLLA) under the application of stress and strain, and we confirmed that the piezoelectric response signal was sufficiently large for use as a sensor signal. We then prepared a left-hand helical torsion coil (PLLA fiber left-hand coil), which was formed by drawing a PLLA fiber ten times. It was observed that, when twisted and released suddenly, the coil exhibited a torsion vibration, and we confirmed that the piezoelectric response signal followed the torsion vibration. Next, we prepared a system in which a PLLA fiber coil was linked to a personal computer used for simple image processing. The PLLA fiber left- and right-hand coils were placed on the arm of a subject, and the inward rotation and outward rotation of the forearm and upper arm were measured. Finally, using this system, we were able to visualize the rotation of the forearm and upper arm.
Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3
Authors: Umeda Yuji , Takano Kosuke , Kojima Takashi , Kuwabara Akihide , Moriwake Hiroki
Published: September 2012

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [E
f(VO)] in Zr-doped and undoped BaTiO3 was performed. The E
f(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K p
O2
= 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.
A First-Principles Study of the Ferroelectric Phase of AgNbO3
Authors: Moriwake Hiroki , Fisher Craig A. J. , Kuwabara Akihide , Fu Desheng
Published: September 2012

AgNbO3 has been reported to undergo an antiferroelectric–ferroelectric phase transition between two orthorhombic phases (labeled M2 and M1) on cooling below ∼340 K. However, the phase transition mechanism is still not well understood, with different space groups proposed for the structure on the basis of different experimental techniques. Here, we report the first-principles calculations of low-temperature phases of AgNbO3 using the projector augmented wave method based on the density functional theory. The calculated phonon dispersion curve for the antiferroelectric P
b
c
m structure shows that no soft mode is evident over all wave vectors, indicating that the structure is dynamically stable. The M2–M1 transition of AgNbO3 thus cannot be explained on the basis of these results. Further calculations are needed to uncover the precise phase transition mechanism for this compound.
Coexistence States near the Morphotropic Phase Boundary
Authors: Iwata Makoto , Ishibashi Yoshihiro
Published: September 2012

A model of coexistence states near the morphotropic phase boundary (MPB) in perovskite-type ferroelectric crystals was studied using a simplified simulation based on the Landau–Ginzburg-type free energy functional. It was found that, even when no imperfection causing the random field exists, a stable phase and a metastable phase coexist near MPB. The coexistence state in the engineered domain configuration near MPB was also found.
Crystal Structure of BaTiO3–KNbO3 Nanocomposite Ceramics: Relationship between Dielectric Property and Structure of Heteroepitaxial Interface
Authors: Magome Eisuke , Kuroiwa Yoshihiro , Yoshimura Hironori , Moriyoshi Chikako , Yamashita Kenta , Fujii Ichiro , Nakashima Kouichi , Kumada Nobuhiro , Wada Satoshi
Published: September 2012

High-energy synchrotron radiation powder diffraction experiments have been carried out to investigate the crystal structure of solvothermally synthesized KNbO3 (KN)/BaTiO3 (BT) nanocomposite ceramics in which a ceramic grain consists of a BT nanoparticle thinly coated with KN crystals through the heteroepitaxial interface. Rietveld analysis reveals that the ceramic grain has the core/multishell structure consisting of a BT core and distorted BT and KN multishells. BT is gradually distorted in the large region to form the interface with KN from the tetragonal structure at the core toward the cubic structure at the boundary between BT and KN. The variations of the volume of the distorted interface region of BT and the dielectric property of the ceramics show similar trends to the variation of KN/BT molar ratio, which suggests that the electrically soft interface of BT nanoparticles governs the dielectric properties of the ceramics.
Local Structure Analysis of Bi2WO6
Authors: Yoneda Yasuhiro , Kohara Shinji , Takeda Hiroaki , Tsurumi Takaaki
Published: September 2012

A local structure analysis of Bi2WO6 was performed by high-energy X-ray atomic pair-distribution function (PDF) analysis. We found a deviation between the local and average structures owing to the different coherence lengths between the Bi2O2 and WO6 layers. Bi atoms were displaced toward the b-axis of the orthorhombic P
c
a21 structure. The local off-center shift of Bi atoms coupled with the thermal factor but not with the average structure and thus was neglected. The coherence length of the Bi2O2 layer increased with increasing temperature and spread in the whole crystal when the average structure changed from the P
c
a21 structure to the A
b
a2 structure.
Observation of Nanoscale Ferroelectric Domains Using Super-Higher-Order Nonlinear Dielectric Microscopy
Authors: Chinone Norimichi , Yamasue Kohei , Hiranaga Yoshiomi , Cho Yasuo
Published: September 2012

Scanning nonlinear dielectric microscopy is a powerful technique for measuring the domain structure of ferroelectrics. We observed congruent LiTaO3 and found the marked enhancement of nonlinear dielectric “constants” when the applied tip–sample voltage exceeded a particular threshold value. This is due to domain nucleation activated by a huge electric field under the tip. Moreover, low frequencies (less than a few hundred Hz) did not enhance the nonlinearity. An effectively lower electric field caused by ion conduction in the sample under the tip is a possible reason for the frequency-dependent characteristics of the enhanced nonlinearity for the applied voltage.
Preisach Modeling of Electric-Field-Induced Strain of Ferroelectric Material Considering 90° Domain Switching
Authors: Kadota Yoichi , Morita Takeshi
Published: September 2012

Preisach modeling of a field-induced nonlinear strain of a ferroelectric material was carried out. A hysteron having a tristable property was proposed. The three stable states correspond to the three stable polarization states of a ferroelectric material. The domain evolution under an electric field was calculated. Finally, the electric-field-induced strain of ferroelectric ceramics was calculated and compared with experimental values. The proposed model enables the description of major and minor strain butterfly loops of ferroelectric materials.
Doping Effect on Interlocked Ferroelectric and Structural Antiphase Domains in YMnO3
Authors: Kobayashi Keisuke , Koyama Tsukasa , Kamo Hideki , Togawa Yoshihiko , Horibe Yoichi , Cheong Sang Wook , Mori Shigeo
Published: September 2012

Changes in ferroelectric and structural antiphase domain structure by the partial substitution of nonmagnetic Ti4+ ions at the Mn site were investigated carefully by electron diffraction, dark-field imaging, and high-resolution lattice imaging experiments. The ferroelectric and structural antiphase domains are revealed to be mutually interlocked in YMnO3 and, on the other hand, when x was increased up to x∼0.30 in YMn1-x
Ti
x
O3, the ferroelectric domains disappeared and the size of the structural antiphase domains decreased to approximately 10 nm at x∼0.30. High-resolution lattice images clearly demonstrate the coexisting state of nanodomains characterized by the modulated structure due to the structural trimerization and the nonmodulated structures. Our experimental results suggest that a partial substitution of Ti4+ ions suppressed the ferroelectric displacement along the [001] direction and the correlation length of the Mn3+ trimerization decreased.
Fabrication Conditions of Diopside for Millimeterwave Dielectrics
Authors: Ohsato Hitoshi , Terada Mio , Kawamura Keizou
Published: September 2012

Recent developments in wireless communications have been expanded to millimeter waves for the high speed and the high rate transmission. Dielectrics with an ultrahigh quality factor Q and low dielectric constant εr are desired. Silicates are good candidates for millimeter wave dielectrics because of their low εr. Diopside (CaMgSi2O6) is one of the silicates with a chain SiO4 structure and a low εr. In this study, we focused on the fabrication conditions of diopside by the means of solid state reactions. The best ceramic of diopside with dielectric properties of εr = 7.6, Q ·f = 121,381 GHz and TCf= -66 ppm/°C was obtained by means of sintering a fine powder fabricated under the following conditions. Fine calcined grain powders were fabricated using fine raw materials with more than 99.9% purity, milling well for 24 h using ZrO2 balls with ca. 5 mmφ, and calcining at 1200 °C for 3 h. The powder was a fine isolated powder without necking with ca. 0.3 µm size, as observed by scanning electron microscopy (SEM), and the specific surface area was ca. 3 m2/g, corresponding to ca. 0.66 µm grain sizes, as determined by the Brunauer–Emmett–Teller (BET) method. The relative density of sintered ceramics with mainly diopside composition formed by sintering the high-density green pellet applied cold isostatic pressing (CIP) at 1300 °C for 3 h was ca. 97%. The necking at 1250 °C was formed by a eutectic liquid on the SiO2–MgO binary system, which is formed by residual SiO2 in the core of low SiO2 materials.
A Method of Evaluating High-Permittivity and Lossy Materials Using a Cylindrical Cavity Based on Hybrid Electromagnetic Theory
Authors: Kinoshita Motohiro , Kinouchi Hiroki , Karim Mohamad Shaiful Bin Abdul , Wakino Kikuo , Kitazawa Toshihide
Published: September 2012

A novel measurement method is proposed to evaluate the complex permittivity of material by using a cylindrical cavity resonator. The conventional cavity resonator methods have been based on the simple electromagnetic field analysis, and a rodlike sample should be loaded all the way from the top to the bottom of the resonator. However, the method proposed in this paper employs an accurate and efficient hybrid electromagnetic analysis method for the evaluation of materials and removes the restriction on the size of the sample materials. The radius and length of the sample are chosen considering the electrical characteristics of the sample, and the fact allows the expansion of the application range of the evaluation method to the materials with higher permittivity and/or higher loss. Also, the sample is not loaded in the insertion opening of the resonator in the proposed method. Therefore, it prevents the leakage of electromagnetic fields through opening and improves the accuracy of the evaluation of material with higher permittivity and/or higher loss. Complex permittivities of a few samples of ceramics with high permittivity and lossy electromagnetic absorber are measured in a microwave range to show the validity of this method.
Interaction Effect of Protons on Their Migration in Bulk Undoped Barium Zirconate Using Density Functional Theory
Authors: Kim Dae-Hee , Kim Byung-Kook , Kim Yeong-Cheol
Published: September 2012

The interaction effect of two protons on their migration in bulk barium zirconate was investigated to understand the difference between experimental and calculated energy barriers for proton migration using density functional theory. There were four different proton structure configurations in terms of proton interaction distance; symmetrically distorted, undistorted, symmetrically/asymmetrically distorted, and asymmetrically distorted. The asymmetrically distorted structure was obtained with the shortest distance between the two protons and was energetically the most stable. A high energy barrier of 0.41 eV was required for proton migration when a proton migrated near another proton owing to their repulsive interaction with each other and attractive interaction with neighboring oxygen ions. Therefore, the interaction between protons can contribute to reducing the difference between experimental and calculated energy barriers for proton migration in bulk barium zirconate.
Epitaxial Growth of Silicon Films on SiO2 Patterned Si(100) Substrates by Atmospheric Pressure Chemical Vapor Deposition
Authors: Duan Chunyan , Deng Youjun , Ai Bin , Liu Chao , Zhuang Lin , Shen Hui
Published: September 2012

In order to investigate the effect of selective area nucleation on epitaxial growth of silicon (Si) films, 35 µm thick Si films were deposited by atmospheric pressure chemical vapor deposition (APCVD) under the standard condition on two kinds of SiO2 patterned Si(100) wafers. One was circular patterns, and the other was striated patterns. Then, the structural properties of the as-deposited silicon thin films were investigated by metallurgical microscope, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). The results show that normal epitaxial growth occurs on the exposed Si(100) regions, while just polycrystalline Si deposition happens on the SiO2 regions. Moreover, for the substrates with circular patterns, the as-deposited Si thin films possess pyramid surface morphology thus excellent light trapping performance being spontaneously formed, and the sizes of the pyramid grains approximately equal to the sum of the diameter and spacing of the round exposed Si regions.
Organic Photovoltaic Cells Employing an Ultrathin Electron Donor of Arylamino-Substituted Fumaronitrile Material
Authors: Lee Chih-Chien , Su Wei-Cheng , Liu Shun-Wei , Yuan
Published: September 2012

In this paper, a novel electron donor, bis4-[N-(1-naphthyl)phenylamino]phenylfumaronitrile (NPAFN), was demonstrated as a potential for application in high open-circuit voltage (VOC) organic photovoltaic (OPV) cells. Devices based on NPAFN/C60heterojunction were firstly manipulated to their optimum optical property by tuning the thickness of C60without compromising the transport property. With the appropriate thickness of C60, the electrical configuration of the devices was improved when the thickness of NPAFN was less than 6.3 nm. The optimum efficiency was 2.1% with aVOCof 0.87 V when the thickness of NPAFN was 5 nm. In addition, the increase inVOCby increasing the thickness of NPAFN was observed and discussed.
Effect of Acetic Acid in TiCl4Post-Treatment on Nanoporous TiO2Electrode in Dye-Sensitized Solar Cell
Authors: Kim Soo-Kyoung , Son Min-Kyu , Kim Jin-Kyoung , Kim Byung-Man , Hong Na-Yeong , Prabakar Kandasamy , Kim Hee-Je
Published: September 2012

Titanium tetrachloride (TiCl4) is adopted as a post-treatment on the nanoporous titanium oxide (TiO2) layers to enhance the performance of dye-sensitized solar cells (DSCs). A TiCl4post-treatment is capable of improving electron transport and dye-loading on the surface of TiO2layers. In this study, the TiCl4solution mixed with acetic acid was employed to enhance the condition of the TiCl4post-treatment. Since acetic acid in the TiCl4solution prevents the formation of impurities and facilitates the crystallization, it improves dye adsorption and electron transport properties. To analyze the performance of the cell, we measured X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface measurements, UV–vis spectroscopy and electrochemical impedance spectroscopy (EIS) and photocurrent–voltage (I–V) measurements.
The Application of Graphene as a Support for Cathode Materials of Metal–Air Batteries
Authors: Moon Eunji , Kim Jeehoon , Nam Sangyong , Eom Seungwook
Published: September 2012

Graphene was compared with carbon black as a conducting and catalyst-supporting material of cathodes. A single-support electrode using carbon black and binary-support electrode using carbon black and graphene were prepared. The conductivity of the electrode using graphene was measured by the standard four-probe DC measurement. As the content of graphene in the electrode was increased, the conductivity of the electrode improved. The adoption of graphene helps in the formation of a mesopore structured electrode, and it makes the catalyst widely dispersed and increases the number of reaction sites of the catalyst. As a result of leaner sweep voltammetry (LSV), the binary-support electrode using carbon black and graphene showed improved oxygen reduction reaction (ORR) compared with the single-support electrode. We concluded that graphene affected the conductivity of the electrode and the ORR characteristics as a support material.
Analysis of Thermal Aging and Structural Stability of Li[Lix(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.11) Cathode Active Material for Rechargeable Li-Ion Batteries
Authors: Vediappan Kumaran , Jo Yong Nam , Park Suk-Jun , Kim Hyun-Soo , Lee Chang Woo
Published: September 2012

The high rate capability of Mn-rich Li[Li
x
(Ni0.3Co0.1Mn0.6)1-x
]O2 (x = 0.11) cathode active materials is investigated by cycling the cell at a given rate for five cycles and keeping the cell idle under thermal control chamber for 10 h and the same process repeating up to 30 cycles. The before and after thermal aging of Mn-rich cathode materials deliver the initial discharge capacity of 153 and 157.32 mA h g-1 up to 30 cycles and also it is maintained the average specific discharge capacity of 140 mA h g-1 for before thermal aging and more than 90% capacity retention. After thermal aging of cathode materials have maintain the average specific discharge capacity of 155 mA h g-1 and more than 97% capacity retentions. During charging, they are not oxidized further; Ni2+ and at least part of Co3+ ions are oxidized to higher valence states. During the discharge reactions, the small amount of Mn3+ reduced to the Mn4+ and some part of Ni3+ ions are reduced to Ni4+. Also the Co3+ ions are fully reduced to the Co4+ state, which due to thermal aging studies does not have major affects in the Mn-rich layered structure under thermal control chamber. These thermal aging analyses are essential to achieve a deeper understanding of the structural defects and safety views for Li-ion batteries to use in electric vehicle technologies.
Interfacial Dead Layers on Lead Free Ferroelectric (K0.5Na0.5)(Mn0.005Nb0.995)O3 Thin Films
Authors: Lee Sun Young , Seog Hae Jin , Ahn Chang Won , Ullah Aman , Kim Ill Won
Published: September 2012

(K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) thin films of thickness ranging from 200 to 500 nm were deposited on Pt/TiO
x
/SiO2/Si substrates using a chemical solution deposition. The films exhibit well-established ferroelectric hysteresis loops with a remanent polarization (P
r) of 13–16 µC/cm2. Their coercive voltages exhibit an increase with increasing film thickness, which is accounted for by the existence of an interfacial dead layer. Their dielectric constant demonstrates frequency and thickness dependent behavior, supporting the existence of the interfacial dead layer. We confirmed that interfacial dead layers with thickness d
i and dielectric constant εi existed in KNMN films using the “in-series capacitor” model. The ratios of dielectric constant and thickness of interfacial dead layers (εi/d
i) of KNMN thin films were obtained by calculations of 3.84 nm-1 and measurements of 3.75 nm-1, which are in good agreement with the “in-series capacitor” model and experimental results.
Ferroelectric and Piezoelectric Properties of Polycrystalline BiFeO3 Thin Films Prepared by Pulsed Laser Deposition under Magnetic Field
Authors: Park Jung Min , Nakashima Seiji , Sohgawa Masayuki , Kanashima Takeshi , Okuyama Masanori
Published: September 2012

Polycrystalline BiFeO3 (BFO) thin films have been prepared on Pt/TiO2/SiO2/Si substrates by using a pulsed laser deposition (PLD) method under a magnetic field. The X-ray diffraction (XRD) pattern shows a single-phase perovskite structure with no secondary phases, and (010) and (020) peaks slightly shift to lower angles in comparison with those of a BFO thin film prepared without a magnetic field. A columnar structure and small grain size were observed and the leakage current is slightly high in comparison with that of a BFO thin film prepared without a magnetic field. A polarization versus electric field (P–E) hysteresis loop was obtained at RT and the polarization at zero electric field is 50 µC/cm2. Ferroelectric domain switching corresponding to up and down polarization states was confirmed. An enhanced piezoelectric coefficient (d
33) of about 100 pm/V has been obtained at a certain point. Ferroelectric and piezoelectric properties were affected by a columnar microstructure formed by magnetic field application.
Dielectric, Piezoelectric Properties and Field-Induced Large Strain of Bi(Zn0.5Ti0.5)O3-Modified Morphotropic Phase Boundary Bi0.5(Na0.82K0.18)0.5TiO3Piezoelectric Ceramics
Authors: Ullah Aman , Ahn Chang Won , Kim Ill Won
Published: September 2012

In this study, the effects of Bi(Zn0.5Ti0.5)O3(BZT) on the structure, dielectric, ferroelectric, and piezoelectric properties of morphotropic phase boundary Bi0.5(Na0.82K0.18)0.5TiO3(BNKT18) piezoelectric ceramics were investigated. In the composition range studied, X-ray diffraction results revealed the coexistence of rhombohedral and tetragonal phases. It was found that BZT content decreased the depolarization temperature (Td) of BNKT18–BZT ceramics, and the degree of diffuseness of the phase transition became more obvious with increasing BZT content. The addition of a small amount of BZT improved the piezoelectric properties, with the maximum piezoelectric constant (d33=166 pC/N) and electromechanical coupling factor (kp=31.7%) obtained atx=0.03. However, at a high concentration of BZT, the remanent polarization and piezoelectric constantd33were drastically decreased, and a pronounced enhancement in electric field-induced strain was observed, with a peak of ∼0.27% atx=0.07, which corresponds to a normalized strain,Smax/Emax, of ∼385 pm/V.
Non-Stoichiometric Effect in (K,Na)NbO3-Based Perovskite Ceramics
Authors: Cho Jeong-Ho , Yeom Na-Ri , Kwon So-Jung , Jeong Young-Hun , Lee Young-Jin , Chun Myoung-Pyo , Nam Joong-Hee , Paik Jong-Hoo , Kim Byung-Ik
Published: September 2012

We prepared Li0.04(K0.5Na0.5)
x
(Nb
y
Sb0.06)O3 ceramics using the conventional solid-state sintering method and investigated the non-stoichiometric effect on sintering behavior and electrical properties in these material systems. The deficiency of B-site ions gave rise to poor densities, while the densification was improved by adding excess Nb2O5. As the vacancy concentration in the A-site of the perovskite structure increased, the diffuse phase transition was enhanced and the transition temperature (T
o–t) was lowered. Furthermore, high deficiency in the A-site with x=0.90 and y=0.98 promoted a second phase formation. An increase of alkali cation vacancies led to large remnant polarization and enhanced a pinched hysteresis loop, while the remnant polarization decreased due to a second phase formation. The electro-mechanical coupling factors were significantly influenced by density and second phase formation, not non-stoichiometry, while dielectric constants were influenced by non-stoichiometry, not second phase formation.
Dielectric and Piezoelectric Characteristics in Lead-Free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 Piezoelectric Ceramics Prepared by Two-Step Calcination Method
Authors: Chen Kai-Huang , Cheng Chien-Min , Tsai Jen-Hwan , Liao Chin-Hsiung , Liang Shu-Hua
Published: September 2012

Lead-free Li
x
(K0.5Na0.5)1-x
(Nb0.8Ta0.2)O3 piezoelectric ceramics samples prepared by the conventional solid-state reaction and two-step calcination method were achieved and compared. The effects of the amount of Li2O3 on the phase structure, microstructure, dielectric, and piezoelectric properties of Li
x
(K0.5Na0.5)1-x
(Nb0.8Ta0.2)O3 ceramics samples were systematically discussed and investigated. It was found that the Li2O3 content in Li
x
(K0.5Na0.5)1-x
(Nb0.8Ta0.2)O3 ceramics samples strongly affects the structure and electrical properties. For the two-step calcination method, the lead-free ceramics samples exhibited excellent dielectric and piezoelectric properties. The relative dielectric constant (εr) and loss tangent (tan
δ) of the lead-free Li
x
(K0.5Na0.5)1-x
(Nb0.8Ta0.2)O3 piezoelectric ceramics samples for x = 0.03 compositions prepared by the two-step calcination method were 1223 and 0.021, respectively. In addition, the electromechanical coupling factor (k
p) and Curie temperature (T
C) were 48.5% and 315 °C, respectively. These results show that Li
x
(K0.5Na0.5)1-x
(Nb0.8Ta0.2)O3 ceramics samples are promising candidates for lead-free piezoelectric materials.
Effects of Zn Substitution on Dielectric and Piezoelectric Properties of (Na0.54K0.46)0.96Li0.04(Nb0.90Ta0.10)O3Ceramics
Authors: Byeon Sunmin , Yoo Juhyun
Published: September 2012

In this study, in order to develop lead-free composition ceramics for piezoelectric actuator and sensor applications, (Na0.54K0.46)0.96Li0.04(Nb0.90Ta0.10)1-2x/5ZnxO3(x= 0–1.5 mol %) composition ceramics were fabricated by a conventional sintering technique at 1110 °C for 5 h. The piezoelectric properties of resultant ceramics were studied with a special emphasis on the influence of Zn-substitution amount. The crystal structure of the specimen exhibited a pure perovskite phase with the coexistence of two phases (orthorhombic and tetragonal phases). However, the phases included tetragonal-rich phases to some extent. The scanning electron microscopy (SEM) images indicated that grain size increased with increasing the content of Zn substitution. High physical properties, namely, piezoelectric constantd33= 265 pC/N, electromechanical coupling factorkp= 47.5%, dielectric constant εr= 1223, and measured density ρ= 4.84 g/cm3were obtained from the composition ceramic withx= 0.5 mol %. The mechanical quality factor (Qm) was improved from 54 of pure (Na0.54K0.46)0.96Li0.04(Nb0.90Ta0.10)O3(abbreviated as NKLNT) to 106 by 1.5 mol % Zn substitution. The results reflect that the material is a promising candidate for lead-free high-performance piezoelectric device applications, such as piezoelectric actuators and sensors.
Design of a Piezoelectric-Driven Tilt Mirror for a Fast Laser Scanner
Authors: Park Jung-Ho , Lee Hu-Seung , Lee Jae-Hoon , Yun So-Nam , Ham Young-Bog , Yun Dong-Won
Published: September 2012

Recently, laser scanners have been used for laser processing such as cutting, welding, and grooving, especially in the automotive industry. The laser scanners need a high-speed driving to minimize cracks caused by thermal shock of brittle materials. Therefore, a novel laser processing system that is composed of a laser source and a piezoelectric-driven tilt mirror to control the reflection angle of the laser beam, and a stage equipped with the tilt mirror has been investigated. In this study, a piezoelectric-driven tilt mirror is designed and analyzed for scanning performance to achieve a beam spot of 30 µm, a pattern width of 1 mm, an overlap ratio of 70% of the circle area, and a scanning speed of 1 m/s. Then, structural analysis of the tilt mirror with three piezoelectric actuators is performed to determine the maximum reflection angle and resonance frequency. Finally, a prototype tilt mirror is fabricated and its basic characteristics are experimentally investigated and discussed.
Microwave Dielectric Properties of Ceramic/Semicrystalline Polymer Composites
Authors: Im Dong Hyeok , Ju Han Sae , Kim Eung Soo
Published: September 2012

The effects of various ceramics and semicrystalline polymers on the dielectric properties of MgMoO4/polypropylene (PP), MgWO4/PP, NiNb2O6/poly(tetrafluoroethylene) (PTFE), and MgNb2O6/PTFE composites were investigated at microwave frequencies. In the frequency range from 1 to 9.4 GHz, the dielectric constant (K) of the composites showed good frequency stability, while their dielectric loss (tan δ) increased with increasing frequency, due to the dipolar relaxation process associated with the matrices. With increasing ceramic content, theKand tan δ values of the composites increased, due to theKvalues of the individual components and interfacial polarization between the ceramics and polymers. For the composites with the same amounts of ceramics, theKvalue and temperature coefficient of the resonant frequency (TCF) of the composites were dependent on the type of ceramics. Also, the measuredKvalues of the composites were compared with the effective dielectric properties calculated by different theoretical models.
Near-Infrared Photodetection of n-Type β-FeSi2/Intrinsic Si/p-Type Si Heterojunctions at Low Temperatures
Authors: Promros Nathaporn , Yamashita Kyohei , Izumi Shota , Iwasaki Ryūhei , Shaban Mahmoud , Yoshitake Tsuyoshi
Published: September 2012

n-Type β-FeSi2/intrinsic Si/p-type Si heterojunction photodiodes were fabricated by facing-targets direct-current sputtering, and their infrared photodetection properties were studied at low temperatures. The rectification current ratio at bias voltages of ±1 V and the ratio of the photocurrent to the dark leakage current were dramatically enhanced with a decrease in temperature. The specific detectivities at 300 and 50 K were estimated to be 3.8×109 and 8.9×1011 cm Hz1/2 W-1, respectively. The enhanced detectivity upon cooling is attributed to the marked reduction in the dark leakage current. The insertion of the thin intrinsic Si layer slightly contributed to the suppression of the leakage current and the detectivity improvement. It was demonstrated that β-FeSi2 is a potential material for Si-compatible near-infrared photodetectors.
SiGe Synthesis by Ge Ion Implantation
Authors: Yuk Hyung-Sang , Oh Jin-Heon , Lim Kee-Joe
Published: September 2012

We report here the successful synthesis of SiGe by Ge ion implantation into Si-on-insulator (SOI) substrates. The fundamental principle for our SiGe synthesis is a chemical reaction preference by nature; oxygen molecules preferentially combine with Si atoms rather than Ge atoms since the formation energy of SiO2is lower than GeO/GeO2, and the chemical bond strength of SiO2is higher. This phenomenon consequently retards the diffusion of implanted Ge ions from the desired area, offering them sufficient time and chances to homogeneously unite with Si atoms and curing implantation damage during O2gas annealing. Thus, the result is practical synthesis of SiGe that can flexibly create various Ge concentrations along with high crystalline quality. Ge ions with a dose of 1017cm-2are implanted at 100 keV into 193-nm-thick top Si layers of SOIs at room temperature. The Ge-implanted samples are subsequently annealed at 1100 or 1200 °C in an O2gas ambient for 5 to 180 min. It is found that the implanted Ge ions mostly remain in the desired area during O2gas annealing. An apparent increase in Ge concentration and a significant decrease in defect density by increasing annealing time are also observed. A theoretical basis and useful simulation for this material synthesis method are presented in this study, being supported by evidential experimental data and comparison of theoretical calculation and measured values.
Electrical Characteristics of Ge25Se75 Thin Films by Ag Ion Doping Methods for Resistance Random Access Memory Applications
Authors: Nam Ki-Hyun , Kim Jang-Han , Chung Hong-Bay
Published: September 2012

Chalcogenide thin films have characteristics of both electric switching and individual optical reactivity. The resistance random access memory (ReRAM) using amorphous chalcogenide materials is based on the electrochemical control of photodiffused metal ions in chalcogenide thin films. In this study we focus on the formation of a straight filament pattern in Ge25Se75 thin films by changing the doping method for Ag ions. Ag photodissolution was performed by the general method (UV exposure) and a holographic lithography method [using He–Ne laser (632.8 nm)]. We measured the electrical characteristics of each device. Improved results were obtained with the induced straight filament pattern device. In the device patterned straightly, operation voltage and reliability were improved.
Schottky Diodes Prepared with Ag, Au, or Pd Contacts on a MgZnO/ZnO Heterostructure
Authors: Lee Jong Hoon , Kim Chang Hoi , Kim Ah Ra , Kim Hong Seung , Jang Nak Won , Yun Young , Kim Jin-Gyu , Pin Min Wook , Lee Won Jae
Published: September 2012

We successfully fabricated lateral Schottky diodes with a thin MgZnO layer inserted between the ZnO and Schottky contact metal layers. The MgZnO/ZnO heterostructure was deposited onto a c-sapphire substrate by pulsed laser deposition using Mg0.3Zn0.7O and ZnO targets. Ti/Au was used to achieve ohmic contact with the Mg0.3Zn0.7O thin film layer, whereas Schottky contacts were prepared using silver (Ag), gold (Au), and palladium (Pd). The Ag Schottky diode devices exhibited rectification ratios as high as ∼103 at a bias voltage of ±1 V, with an ideality factor of 2.37 and a work function of 0.73 eV. The possibility of preparing Schottky contacts with a high carrier concentration on the ZnO layer is discussed as a function of the presence or absence of a MgZnO thin layer and in terms of the measured current–voltage properties.
Fabrication and Characterization of All-Transparent Li0.15Ni0.85O/In–Mg0.5Zn0.5O Thin-Film p–n Heterojunction Diodes with Cube-on-Cube Epitaxial Structures
Authors: Zhuang Lin , Lau Chunhei , Wong Kinhung , Ai Bin , Li Baojun , Tang Xingui
Published: September 2012

All-oxide-based transparent p–n heterojunctions with the cubic epitaxial structure of Pt-electrode/p-Li0.15Ni0.85O (LNO)/n-In–Mg0.5Zn0.5O (In–MZO)/Pt-electrode on LaAlO3(LAO) (100) substrate were fabricated. The rectification ratioRcof forward current to reverse current of this heterojunction diode is larger than 60 in the range of applied voltages from -4.0 to +4.0 V. The reverse breakdown voltage is larger than 6 V at temperatures of 30 to 380 K, which confirms the possibility of high-temperature applications. The epitaxial relationships were confirmed to be cube-on-cube epitaxy of (100)LNO ∥ (100)In–MZO ∥ (100)LAO (out-of-plane) and (011)LNO ∥ (011)In–MZO ∥ (010)LAO (in-plane). The measured optical transmission of the heterojunction is 70–80% in the infrared and visible regions. Absorption occurs in the UV region, which corresponds to the band gaps of LNO and In–MZO, suggesting that these heterojunctions formed by transparent LNO and In–MZO films could be used as UV detectors and transparent electronic devices.
Electrical Characteristic Analysis of Postannealed ZnO Thin-Film Transistors under O2 Ambient
Authors: Jeong Kwang-Seok , Kim Yu-Mi , Yun Ho-Jin , Yang Seung-Dong , Lee Sang-Youl , Kim Young-Su , Lee Hi-Deok , Lee Ga-Won
Published: September 2012

An electrical characteristic analysis of postannealed ZnO thin-film transistors (TFTs) under O2 ambient from 200 to 300 °C for 1 h was carried out. The 250-°C-annealed device showed the best electrical characteristics, which can be explained by crystallinity improvement on the basis of X-ray diffraction (XRD) analysis. However, although having an active layer of the best crystal quality, the electrical properties of the 300-°C-annealed device were degraded, which can be due to the higher ΦB0 resulting from the oxidation of Ti used as the S/D electrodes. Next, the stability of ZnO TFTs was investigated. Under a positive bias stress of 20 V, it was found that the annealed devices showed smaller threshold voltage shifts (ΔV
TH) than the as-grown device. In addition, with the stress bias removed, all devices recover their original characteristics, which can be explained by temporary charge trapping into preexisting traps. Therefore, the post-thermal annealing under O2 ambient can improve the electrical and reliability characteristics of ZnO TFTs, which can be explained by a fewer grain boundary traps and a lower grain boundary potential barrier, as determined by 1/f noise analysis, closely related to the crystallinity improvement of the active layer and fewer zinc interstitials and/or oxygen vacancies near the grain boundary in the active layer.
Influences of Gate Bias and Light Stresses on Device Characteristics of High-Energy Electron-Beam-Irradiated Indium Gallium Zinc Oxide Based Thin Film Transistors
Authors: Yu Kyeong Min , Moon Hye Ji , Ryu Min Ki , Cho Kyoung Ik , Yun Eui-Jung , Bae Byung Seong
Published: September 2012

Under white light illumination, amorphous indium–gallium–zinc oxide (a-IGZO)-based thin-film transistors (TFTs) showed a large negative shift of threshold voltage of more than -15 V depending on the process conditions. We investigated the influences of both gate bias and white light illumination on device properties of IGZO-based TFTs untreated and treated with high-energy electron beam irradiation (HEEBI). The TFTs were treated with HEEBI in air at room temperature (RT), electron beam energy of 0.8 MeV, and a dose of 1×1014electrons/cm2. The HEEBI-treated TFTs showed an improved stability under negative bias illumination stress (NBIS) and positive bias illumination stress (PBIS) compared with non-HEEBI-treated TFTs, suggesting that the acceptor-like defects might be generated by HEEBI treatment near the valence band edge.
Effects of Oxygen Working Pressure on Structural and Optical Properties of TiO2 Films Grown on Glass Substrate
Authors: Pin Min-Wook , Lee Geun-Hyoung , Lee Won-Jae , Choi Eun-Ho , Yoo Young-Zo
Published: September 2012

TiO2 thin films were grown on glasses using a pulsed laser deposition (PLD) system. In order to fully clarify the correlation between their properties and the working pressure of oxygen at which they are grown, a wide range of pressures from 10 to 75 mTorr was investigated. The optical gap of TiO2 films gradually increased from 3.3 to 3.41 eV with increasing working pressure up to 25 mTorr but became notably large at 50 mTorr and continued to increase significantly with further pressure increase. X-ray diffraction (XRD) results showed that the films grew preferentially along the (101) orientation. (101) peak intensity increased as working pressure increased up to 25 mTorr. However, the peak intensity began to decrease and eventually disappeared with further increase in working pressure, indicating structural changes from crystalline to disorderlike phases. The TiO2 films showed high crytallinity with large grains at 25 mTorr but showed a columnar structure with small grains at 75 mTorr. The growth mode of TiO2 thin films was observed to change from lateral to islandlike growth in response to the increase in working pressure. The correlation between oxygen pressure and film properties is discussed in terms of structural and compositional changes.
Effects of Heating Time and Intermediate Heating on Sol–Gel-Processed ZrO2 Thin Films
Authors: Lee Seung Muk , Hwang Soo Min , Choi Jun Hyuk , Park Kyung , Kim Hyoungsub , Lim Jun Hyung , Joo Jinho
Published: September 2012

Nanoscale-thick high-k ZrO2 films were fabricated via sol–gel method and the effects of heating time and an intermediate heat treatment on the microstructure and dielectric properties were studied. One set of films was spin-coated with a thickness of ∼13 nm on Si substrates by two consecutive coating and drying sequences, followed by heating at 500 °C for 1, 5, or 10 h, while another sample was prepared by heating at 500 °C for 1 h after each drying step (intermediate heated sample). As the heating time was extended, the permittivity increased, but the leakage current property degraded. In contrast, both the permittivity and leakage current property were enhanced in the case of the intermediate heated sample. These improvements were likely due to the effective elimination of remnant organics and the development of a two-layer morphology consisting of lower amorphous and upper crystalline layers, the formation of which occurred via the minimization of surface and strain energies.
Effects of Surface and Plate-Gap Discharges on Panel-Aging Characteristics in Alternating-Current Plasma Display Panel
Authors: Park Choon-Sang , Tae Heung-Sik
Published: September 2012

In this study, we investigate the changes in surface morphology of the MgO layer on both the bus and indium tin oxide (ITO) electrodes in an alternating-current (AC) plasma display panel (PDP) under the surface and plate-gap discharges during the panel-aging process. It is found that the use of the surface discharge mixed with the plate-gap discharge during the panel-aging process contributes to obtaining uniform MgO surface morphologies for both bus and ITO electrodes within a fast panel-aging process time.