bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition Behaviour between Erosion and Deposition on a Tungsten Surface Exposed to Deuterium Plasmas Containing Carbon Impurities
Authors: Hamada Yoshitaka , Ebisu Shinji , Ohya Kaoru
Published: February 2005

The erosion and deposition processes of tungsten (W) exposed to deuterium (D) plasmas containing a small amount (<10%) of carbon (C) ions are investigated by using a dynamic Monte Carlo simulation. The emphasis is placed on an abrupt transition from C deposition to W erosion as the plasma temperature is increased from 10 eV to 100 eV. The transition occurs as a result of little reflection (much deposition) of incident C ions from a C-rich layer and enhanced sputtering of deposited C atoms from a W–C mixed layer. When the deposited C thickness is increased just below the transition temperature, the C emission yield (i.e., the sum of the C reflection coefficient and the C sputtering yield) decreases so that a thick C-rich layer (2–8 µm or more), growing in proportion to the plasma fluence, is formed on W. When the deposited C thickness is decreased above the transition temperature, the C emission yield increases so that there is only a thin W–C mixed layer (100–300 nm), where the depth profile of deposited C is independent of the temperature, fluence and C-concentration of the plasma. The transition is strongly related to the depth profile of the deposited C in the W bulk, therefore, the transition temperature fluctuates according to the erosion and deposition histories and is strongly influenced by the chemical sputtering yield of the deposited C.
Modeling and Initial Growth Mode of Ultrathin Film on the basis of Electrical Conductivity of Substrate
Authors: Song Seok-Kyun , Koh Seok-Keun , Lee Deuk Yeon , Song Kie Moon , Baik Hong-Koo
Published: February 2005

A model for the electrical conductance of a semiconductive substrate with an average thickness is proposed for a region of initial growth before the appearance of a tunneling effect. Based on this model, we propose 6 different growth modes according to the film thickness, measuring in situ electrical conductivity. As the film thickness increased, the island size was constant and then increased, while the number of islands first increased and then decreased. The proposed model may be useful for in situ study of the growth of ultrathin films prior to the onset of tunneling conductance.
Design and Power Tests of 500 MHz RF Cavity of CW Microtron for Industrial Applications
Authors: Makita Yo , Nakanishi Tetsuya , Pu Yuehu , Tanaka Hirofumi , Maruyama Akihiko , Kim Tae Hyun , Tsukishima Chihiro , Yamamoto Shunji , Nakamura Shiro
Published: February 2005

The 500 MHz RF cavity of a high intensity CW microtron for industrial applications was designed, and power tests of this cavity have been carried out. The cavity is composed of two cells with nose cones and coupling slots, having a total gap voltage of about 1 MV. The calculated Q-value was 37400 and the measured value was about 93% of the calculated one. An input power of 40 kW was successfully obtained in 65 h conditioning.
Dynamics of Single Sonoluminecsing Bubble in Concentrated Aqueous Alkaline Halide Solutions
Authors: Nozaki Kenji , Hatanaka Shin-ichi , Hayashi Shigeo
Published: February 2005

The dynamics of a single sonoluminescing bubble in dense aqueous NaCl and KCl solutions is studied using a high-speed framing camera. Although the bubble became unstable, the luminescence intensity increased for larger driving pressures and higher concentrations. In this state, the bubble was found to split into a main sonoluminescing one and a number of daughter ones. Such unstable behavior is usually regarded as characteristic of the bubble dynamics near the lower sonoluminescience threshold of acoustic pressure, but the present finding suggests that, for dense aqueous solutions, there exists still another regime where the bubble is unstable and yet has more luminosity.
Sonolysis of Sodium Hydrogencarbonate Solution
Authors: Harada Hisashi , Sogawa Ryo
Published: February 2005

Sonolysis of a sodium hydrogencarbonate solution was carried out. As products, CO2, CO, H2, O2, and H2O2 were obtained. CO2 evolved from NaHCO3 solution by a thermal reaction. The yield of CO2 increased with increasing the concentration of the NaHCO3 solution. The yield of H2, on the other hand, decreased with increasing the concentration of the reactant solution. CO and O2 were produced from CO2 by sonolysis. The highest yield of CO was observed for a 0.35 mol/l NaHCO3 solution. H2O2 was obtained from H2O together with H2 by sonolysis.
Mechanical Polishing Technique for Carbon Nanotube Interconnects in ULSIs
Authors: Horibe Masahiro , Nihei Mizuhisa , Kondo Daiyu , Kawabata Akio , Awano Yuji
Published: February 2005

We examined a mechanical polishing technique for multiwalled carbon nanotube (MWNT) vias. This polishing technique involved the use of diamond particles fixing MWNT protrusions of the samples. The 1-µm-high outthrust MWNTs were polished, and then flat sample surfaces were obtained by controlling polishing pressure and polishing time. A cross-sectional image of a cut MWNT was obtained by high-resolution scanning electron microscopy. Mechanically polished MWNT interconnects with a high current density and a low resistance were developed.
Light Intensity Enhancement and Optical Nonlinear Response due to Localized Surface Plasmons in Nanosize Ag Sphere
Authors: Okamoto Toshihiro , Haraguchi Masanobu , Fukui Masuo
Published: February 2005

Field enhancement due to localized surface plasmons excited in nanosize Ag and coated Ag spheres has been numerically studied using the Mie theory. It has been found that light intensity enhancement becomes maximum at an appropriate diameter of spheres. This maximum has been expected to be determined from mediation of a size-dependent light-confinement effect and a size-dependent dielectric constant of Ag spheres. Such field enhancement should play a crucial role in observing strong nonlinear optical effects. For a nanosize metal sphere coated with a Kerr-nonlinear film, we have succeeded in finding optical switching and optical bistability phenomena using the modified Mie theory.
A Bidirectional Iteration Algorithm for Determining Lidar Ratios and its Use to Evaluate Boundary Values in the Lidar Inversion
Authors: Iokibe Kengo , Itoh Yoshinori , Toyota Yoshitaka , Wada Osami , Koga Ryuji
Published: February 2005

A new algorithm to estimate lidar ratios of aerosol layers with a monochromatic Mie-scattering lidar profile is proposed. The algorithm employs both the forward and the backward solutions of the monochromatic single-scattering lidar equation. The lidar ratios are estimated through an iterative procedure to match the two solutions by correcting a lidar ratio assigned at the beginning of the procedure. The algorithm has been applied to simulated lidar profiles and a measured one from the literature. In testing of the simulated profiles, the estimation errors of the lidar ratios were investigated for four boundary conditions–clear to turbid conditions–by scanning boundary values and extinction coefficients of an aerosol layer. This investigation indicated that the algorithm estimates the lidar ratio with sufficient accuracy under clear boundary conditions even with inaccurate boundary values, but requires correct boundary values under turbid boundary conditions. The algorithm was successfully applied to the measured lidar profile of a thin aerosol layer. The obtained lidar ratio was reasonably plausible. This suggests that an enhanced form of this algorithm using the forward and the backward solutions would be able to determine the lidar ratios and boundary values from only a lidar profile measured under arbitrary atmospheric conditions.
Preparation and Dielectric Properties of SrZrO3/SrTiO3 Superlattices
Authors: Harigai Takakiyo , Tanaka Daisuke , Nam Song-Min , Kakemoto Hirofumi , Wada Satoshi , Saito Keisuke , Tsurumi Takaaki
Published: February 2005

SrZrO3/SrTiO3 (SZO/STO) artificial superlattices were fabricated on STO substrates by the molecular beam epitaxy. The structures of the superlattices were analyzed by reflection high-energy electron diffraction, normal θ-2θ scan mode X-ray diffraction analyses and reciprocal space mapping measurement. Their lattice parameters showed that the lattice distortion is dependent on stacking periodicity and is maximum in the [(SZO)10/(STO)10]4 superlattice. The dielectric properties were measured using interdigital electrodes at frequencies up to 110 MHz, and dielectric relaxation was observed in the [(SZO)1/(STO)1]40 and [(SZO)10/(STO)10]4 superlattices in the low-frequency domain. The dielectric permittivities of all superlattices with interdigital electrodes were more than 10,000 at 110 MHz. The charge vs voltage (Q-V) measurement revealed that the SZO/STO superlattices show distinct hysteresis curves, which indicated that ferroelectricity is induced by the superlattices. The origin of the ferroelectricity seems to be related to the anisotropic lattice distortion incorporated into the superlattice structure.
Investigation into Electrical Conduction Mechanisms of Pb(Zr,Ti)O3 Thin-Film Capacitors with Pt, IrO2 and SrRuO3 Top Electrodes
Authors: Masuda Yoichiro , Nozaka Takashi
Published: February 2005

The conduction mechanisms of Pb(Zr,Ti)O3 (PZT) thin-film capacitors with Pt bottom electrodes and Pt, IrO2 and SrRuO3 (SRO) top electrodes were investigated. In the case of SRO top electrode prepared by pulsed laser deposition, the Schottky barrier was not formed at the interface due to the interdiffusion and the space-charge-limited current with a trap energy of 2.1 eV was dominant. On the other hand, for the Pt and IrO2 top electrodes prepared by sputtering, the capacitors showed the Schottky emission current at low electric field and the Fowler-Nordheim current at a high electric field. The Schottky barrier heights for Pt/PZT and IrO2/PZT interfaces were estimated to be 0.93 and 0.67 eV, respectively. An ultra thin alteration layer between the Pt top electrodes and PZT films seems to degrade the barrier height of the Pt/PZT interface. Furthermore, the Pt/PZT/Pt capacitor showed negative resistance at room temperature. We concluded that the potential well formed near the top interface by band bending is the origin of this negative resistance.
Ferroelectric Properties of Bi4Ti3O12 Thin Films Prepared on TiO2 Anatase Layer
Authors: Higuchi Tohru , Nakamura Makoto , Hachisu Yuji , Saitoh Masanori , Hattori Takeshi , Tsukamoto Takeyo
Published: February 2005

Undoped Bi4Ti3O12 (BIT) thin films with a TiO2 anatase buffer layer were prepared on the Pt/Ti/SiO2/Si substrates by metalorganic chemical vapor deposition. The BIT thin film with the TiO2 anatase buffer layer prepared at 500°C exhibited highly a- and b-axis-oriented BIT single phases, although the BIT thin film with no buffer layer exhibited a c-axis orientation. The interface between the BIT thin film and the substrate was very smooth. The BIT thin film consisted of small grains and exhibited a good P-E hysteresis loop. The ferroelectricity of the BIT thin film with the TiO2 anatase buffer layer strongly depends on the thickness ratio of the BIT thin film to the TiO2 anatase layer, indicating that the TiO2 anatase buffer layer acts not as barrier layer but as an initial nucleation layer of the BIT thin film. When the thickness ratio is fixed at [(BIT)/(TiO2)]=15, the remanent polarization (P
r) and the coercive field (E
c) were 2P
r=81.6 µC/cm2 and 2E
c=250 kV/cm, respectively. The dielectric constant (ε
r) was 160.
Ferroelectric Properties of Mn-Doped Bi3.6La0.4Ti3O12 Thin Films Prepared under Different Annealing Conditions
Authors: Kim Jong-Pil , Hwang Jae-Yeol , Cho Chae-Ryong , Ryu Min-Ki , Jang Min-Su , Jeong Se-Young
Published: February 2005

Ferroelectric Bi3.6La0.4Ti3O12 (BLT) and Mn-doped (0.1 wt%, 0.2 wt%, and 0.3 wt%) BLT thin films were prepared by sol-gel processing. In the X-ray diffraction (XRD) results, all films exhibited a randomly oriented perovskite phase. Concerning surface morphology, the grain boundaries of the Mn-doped (0.2 wt%) BLT thin film are more closely packed than those of the nondoped BLT film without the presence of many crevices and cracks around the grain boundaries due to the volatilization of the Bi components at high temperature. The remanent polarization of the stoichiometric, 0.1 wt%, 0.2 wt% and 0.3 wt% Mn-doped BLT films annealed at a heating rate of 50°C/h, were 14 µC/cm2, 18 µC/cm2, 31 µC/cm2 and 13 µC/cm2, respectively. The 0.2 wt% Mn-doped BLT thin film is a good candidate for ferroelectric memory cells and nonvolatile random access memory (NvRAM) applications.
Structural and Ferroelectric Properties of Ba2NaNb5O15 Thin Films on La-Doped SrTiO3 Substrates
Authors: Kamei Takayuki , Higuchi Tohru , Sogawa Minoru , Ebina Yoshiki , Hattori Takeshi , Masuda Yoichiro , Tsukamoto Takeyo
Published: February 2005

The c-axis-oriented Ba2NaNb5O15 (BNN) thin films were prepared on La0.05Sr0.95TiO3 substrates by pulsed laser deposition. The c-axis orientation and surface roughness of the BNN thin films depend on oxygen gas pressure (Po2) and substrate temperature (T
sub) during the deposition. When Po2 and T
sub were fixed at 5.0 mTorr and 700°C, respectively, the BNN thin film exhibited a strong c-axis orientation and a smooth surface. Its remanent polarization (P
r) and coercive field (E
c) were 2P
r=48.5 µC/cm2 and 2E
c=290 kV/cm, respectively. The band gap of this strongly c-axis-oriented BNN thin film was about 3.1 eV, which accords with that of the BNN single crystal.
Structure and Electrical Properties of Lead-Free (Na0.5K0.5)NbO3-BaTiO3 Ceramics
Authors: Guo Yiping , Kakimoto Ken-ichi , Ohsato Hitoshi
Published: February 2005

(Na0.5K0.5)NbO3 with 0–20 mol% BaTiO3 has been prepared following the conventional mixed oxide process. High-density samples were obtained through the addition of BaTiO3 into (Na0.5K0.5)NbO3 because of an increase in grain size. X-ray diffraction analysis revealed that, during sintering, all of the BaTiO3 diffuses into the lattice of (Na0.5K0.5)NbO3 to form a solid solution, in which orthorhombic symmetry changes to tetragonal symmetry at x≈0.06, and tetragonal symmetry changes to cubic symmetry at x=0.20 or higher. It was found that the samples with a low content of BaTiO3 exhibit relatively good ferroelectric and piezoelectric properties. For 0.98(Na0.5K0.5)NbO3-0.02 BaTiO3 ceramics, the remanent polarization (P
r) is 7.5 µC/cm2 with a coercive field (E
c) of 12 kV/cm. The piezoelectric constant d
33 reaches 104 pC/N. The electromechanical coupling coefficients of the planar mode k
p and the thickness mode k
t reach ∼29% and ∼38%, respectively. Our results show that (Na0.5K0.5)NbO3-BaTiO3 is a good lead-free piezoelectric ceramic.
Solid-Solution Structure and Piezoelectric Property of KNbO3 Ceramics Doped with Small Amounts of Elements
Authors: Kakimoto Ken-ichi , Masuda Izumi , Ohsato Hitoshi
Published: February 2005

The origin of the improvement of the ferroelectric and piezoelectric properties of KNbO3 ceramics by the addition of small amounts of La and Fe has been investigated. The La/Fe-codoped KNbO3 ceramics formed a single (K1-x
La
x
)(Nb1-x
Fe
x
)O3 solid solution, and their unit-cell volume decreased significantly with an x of 0.002 mol, while they recovered at x=0.004. In this region, the lattice parameters of the a-b basal plane decreased and the elongation in the c direction toward apical oxygen in NbO6 octahedra occurred. These results were correlated with the enhanced polarization and piezoelectric properties measured for the x=0.002 specimen. The x=0.002 specimen demonstrated a k
t of 0.48 which corresponds to approximately 70% of the k
t value predicted for a KNbO3 single crystal as its maximized property. Furthermore, La/Fe-codoped KNbO3 ceramics with MnO2 addition were prepared to observe the effect of multivalent ion (Fe and Mn) doping into the KNbO3 structure on the properties. Synchrotron near-edge X-ray absorption spectroscopy (XANES) study revealed a mixture of k-edge spectra consisting of Mn4+/Mn3+/Mn2+, while Fe3+ maintained its valence state. The influence of valence fluctuation on the ferroelectric and piezoelectric properties of KNbO3 ceramics was discussed.
Characterization of Thin-Film Decoupling and High-Frequency (Ba,Sr)TiO3 Capacitors on Al2O3 Ceramic Substrates
Authors: Koutsaroff Ivoyl P. , Bernacki Thomas A. , Zelner Marina , Cervin-Lawry Andrew , Jimbo Takehito , Suu Koukou
Published: February 2005

In this paper we present the results of the characterization of parallel-plate thin-film (Ba1-x
,Sr
x
)TiO3 (BST) capacitors, to demonstrate their suitability for use as decoupling capacitors (a capacitance as high as 0.34 µF and a capacitance density of up to 70 fF/µm2) and as tunable RF components (a small capacitance from 0.5 pF to 16 pF, a high tunability of 4.22:1 at 10 V and a capacitance density of up to 34 fF/µm2). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering on Pt/TiO
x
/SiO2/Al2O3 ceramic substrates. For large capacitors (2.25 mm2), capacitance and tan
δ were measured at low frequencies (1 kHz) using an LCR meter. Smaller capacitors (16 µm2 to 961 µm2) were characterized in the frequency range of 0.01–20 GHz. Capacitance, tan
δ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationships between dielectric loss, tunability and commutation quality factor (CQF) vs BST composition and deposition conditions were outlined.
Novel Evaluation Method of the Complex Dielectric Constant of High-Permittivity Material at Microwave Frequency
Authors: Wakino Kikuo , Kumagai Sousuke , Shiraishi Takeshi , Kitazawa Toshihide , Fujii Takashi , Ando Akira
Published: February 2005

A novel accurate measurement method for high-permittivity materials in the microwave region, by adopting a discontinuity structure in the coaxial transmission line, is proposed. Electromagnetic field analysis is carried out using the extended spectral domain approach in combination with the mode-matching method (ESDMM). Numerical results obtained by ESDMM are compared with the values obtained by the finite element method (FEM) and excellent agreement is observed. However, ESDMM is more efficient in numerical computations and can be utilized for the iterative fitting of the measured values to identify the material. A simple but practically effective characterization method for high-permittivity materials at microwave frequency was developed.
Piezoelectric Characteristics of Polymer Film Oriented under a Strong Magnetic Field
Authors: Nakiri Takuo , Imoto Kenji , Ishizuka Masayuki , Okamoto Satoshi , Date Munehiro , Uematsu Yoshiko , Fukada Eiichi , Tajitsu Yoshiro
Published: February 2005

The possibility has been indicated that polymers with helical chirality, such as poly-γ-benzyl-L-glutamate (PBLG) and poly-L-lactic acid (PLLA), exhibit a large shear piezoelectric constant. To attempt the realization of a PBLG membrane with a large piezoelectric constant, we fabricated the PBLG membrane oriented by magnetic field force. Concretely, the PBLG membranes were casted from 1,2-dichloroethane solution with various PBLG concentrations under the magnetic field generation equipment incorporating a superconducting magnet. First, the orientation of the chain molecules of the PBLG membranes obtained was observed macroscopically by means of a polarizing microscope (POM). The orientation of the chain molecules of the PBLG membranes was recognized for the case of casting from the PBLG 1,2-dichloroethane solution in the liquid crystal state. Also, from X-ray photograph measurements, it was found that the orientation direction of the chain molecules of PBLG was perpendicular to the magnetic field direction. We then measured the shear piezoelectric constant d
14 of the oriented PBLG membranes. With increasing the strength of the applied magnetic field in the casting process for the film preparation, d
14
* of the PBLG membranes obtained increases. Finally, a large piezoelectric constant of 26 pC/N was found in the PBLG membrane. It is assumed that d
14
* is not saturated even at the magnetic field of 10 T.
Ab initio Determination of Total-Energy Surfaces for Distortions of Ferroelectric Perovskite Oxides
Authors: Hashimoto Takatoshi , Nishimatsu Takeshi , Mizuseki Hiroshi , Kawazoe Yoshiyuki , Sasaki Atsushi , Ikeda Yoshiaki
Published: February 2005

We established a new ab initio structure optimization technique of determining the valley line on a total-energy surface accurately for the zone-center distortions of ferroelectric perovskite oxides, and applied this technique to the analysis of barium titanate (BaTiO3), lead titanate (PbTiO3), and lead zirconate (PbZrO3). The proposed technique is an improvement over King-Smith and Vanderbilt's scheme [Phys. Rev. B 49 (1994) 5828] of evaluating total energy as a function of the amplitude of atomic displacements. The results of numerical calculations show that total energy can be expressed as a fourth-order function of the amplitude of atomic displacements in BaTiO3 but not in PbTiO3 and PbZrO3. These results will provide some hints about the reason Pb(Zr
x
Ti1-x
)O3(PZT) has a large piezoelectric response. These results are due to the fact that our structure optimization technique automatically takes account of the higher-order coupling between atomic displacements and strains, and not only the atomic displacements of the Γ15 soft mode but also that of the hard modes.
X-Ray Topography on Domain-Controlled BaTiO3 Crystals
Authors: Yoneda Yasuhiro , Mizuki Jun'ichiro , Kohmura Yoshiki , Suzuki Yoshio , Hamazaki Shin'ichi , Takashige Masaaki
Published: February 2005

The effect of the domain configuration on the microscopic and macroscopic crystal structures of BaTiO3 is reported using polarizing microscopy observations and high-spatial-resolution synchrotron X-ray measurements. The size of the ferroelectric domain was controlled by defects produced by substituting strontium for barium. The domain configuration of Sr-substituted BaTiO3 consisted of small and uniform domains. The tetragonality of the Sr-substituted BaTiO3 was smaller than that of undoped tetragonal BaTiO3 due to the lattice strain from the domain boundaries. We investigated the domain-controlled BaTiO3 crystal and discussed the relationship between the domain configuration and microscopic crystal structure.
Observation of Relaxation Mode in Ferroelectric Barium Dititanate by Micro-Brillouin Scattering
Authors: Hushur Anwar , Shigematsu Hirotake , Akishige Yukikuni , Kojima Seiji
Published: February 2005

New ferroelectric single crystals of BaTi2O5 have been studied in detail by high-resolution micro-Brillouin scattering with focus on the central component of the relaxation mode over a wide temperature range (20–600°C). A relaxation mode has been clearly observed in these single crystals for the first time. In addition, the usual phonon features are also observed in the Brillouin shifts determined by selection rules for a monoclinic phase. The ferroelectric phase transition at T
c∼470°C, sharp anomaly has been observed from both the frequency shift and hypersonic damping. The relaxation time slows down and intensity of central peak increases markedly when temperature approaches T
c from above and below. Furthermore, the relaxation mode has an A(y) symmetry which implies that the relaxation mode involves interwell motion of Ti ions parallel to the polar axis. The temperature dependence of the relaxation time and integrated intensity of the relaxation mode are well reproduced by the extended semiclassical tunneling model in which the off-center ion in the octahedra tunnels between two sites of a double-well potential.
Evaluation of InGaP/InGaAs/Ge Triple-Junction Solar Cell under Concentrated Light by Simulation Program with Integrated Circuit Emphasis
Authors: Nishioka Kensuke , Takamoto Tatsuya , Agui Takaaki , Kaneiwa Minoru , Uraoka Yukiharu , Fuyuki Takashi
Published: February 2005

The characteristics of a multi-junction solar cell under concentrated light were evaluated by Simulation Program with Integrated Circuit Emphasis (SPICE). We developed the multi-unit model and analyzed the affects of the chromatic aberration and intensity distribution for the multi-junction cells. In the multi-unit model, the same numbers of units as grid numbers are installed for every electrode, and the units were connected to each other via lateral resistances. In order to obtain the generation current from each diode, we measured the intensity of concentrated light through the pinhole using single-junction solar cells consisting of InGaP, GaAs and Ge as detectors. By using the multi-unit model, we could successfully calculate the electrical cell performances taking the chromatic aberration and intensity distribution into account, and the calculated value agreed well with the experimental value. The multi-unit model will be very useful for cell designs and performance analysis of the concentrator cells.
Phonon-Assisted Auger Recombination Processes in InGaAs/GaAs Single-Quantum-Well Lasers
Authors: Nee Tzer-En , Cheng Chao-Ching , Lin Ray-Ming
Published: February 2005

The Auger recombination processes for InGaAs/GaAs single-quantum-well semiconductor ridge lasers with various stripe widths have been systematically investigated. It was found that the Auger recombination temperature dependence is a function of laser stripe width. An Auger coefficient activation energy of 31.3±5.1 meV characterized the phonon-assisted Auger processes. Above the crossover temperature, the nonradiative component was the major contributor to the operating current, while the radiative current was dominant below this temperature. Increases, not only in the crossover temperature but also in the differential quantum efficiency, were obtained with increasing stripe width. These findings should greatly aid in the better design and optimization of stripe-geometry lasers.
Influence of Field-Induced Drain on the Characteristics of Poly-Si Thin-Film Transistor using a Self-Aligned Double Spacer Process
Authors: Ahn Jeong-Ah , Kim Ohyun
Published: February 2005

The electric characteristics of field-induced drain (FID) poly-Si thin-film transistors (poly-Si TFT) with an independently biased self-aligned sub-gate using a double space process are investigated. The on/off current ratio of this FID TFT is approximately 9.3×107 and the off-state leakage current is 200 times lower than that of the conventional TFT and 60 times lower than that of the LDD TFT at V
SG=V
DS=5 V. The self-aligned double spacer process can remove the sub-gate misalignment error and the length of the sub-gate can be easily controlled by the poly-Si thickness and a hard mask. In particular, the use of the dual hard mask can realize a long sub-gate without thick sub-gate poly-Si (>500 nm). The optimum sub-gate voltage is about 5 V and the optimum effective sub-gate length is between 200 nm and 300 nm in these FID TFTs.
Characteristics of Irregular Forward Current Conduction in 4H-SiC pn Junction Diodes
Authors: Ohyanagi Takasumi , Ohno Toshiyuki , Watanabe Atsuo
Published: February 2005

SiC diodes show an irregular forward current conduction deviating from the standard diode theory, J
F∝exp
(V
F), where J
F is the forward current conduction density and V
F is the forward voltage. However, it is not known whether this irregular conduction is due to defects formed by ion implantation or to native defects in the epitaxial layer. This paper reports how we analyzed an irregular forward current conduction in 4H-SiC pn junction diodes by a combination of gate-controlled diodes and X-ray topography. We found that one of the two irregular forward current conductions is due to defects formed by ion implantation, and the other conduction was due to the defects penetrating the pn junction. An x-ray topography image showed that the quantity of isolated native defects in the epitaxial layer does not affect the forward current conduction and that “linear defect” could be observed when the forward current conduction is particularly irregular.
Effective Channel Length Shortening and Mobility Increase of p-Channel Metal Oxide Semiconductor Transistors Resulting in Higher Drive Current Using Short Source–Drain Diffusion Length
Authors: See Kwang-Seng , Lau Wai-Shing , Liao Hong , Eng Chee-Wee , Tee Kian-Meng , Quek Elgin Kiok-Boone , Tee Kheng-Chok , Chan Lap-Hung
Published: February 2005

Local lattice strain around the channel in metal oxide semiconductor (MOS) transistors of 0.13 µm gate length using shallow trench isolation can be altered using different source–drain diffusion lengths (L
ov). It is known that as L
ov is reduced, the drive current of p-channel metal oxide semiconductor (PMOS) transistors can be increased due to stress-enhanced hole mobility. However, in this study, we found that as L
ov is reduced below 0.62 µm, the effective channel length (L
eff) of the PMOS transistors is also reduced. This unexpected L
eff shortening effect for very small L
ov has instead led to a reduction of µeff, as shown through our calculations. We thus propose that the drive current increase for L
ov reduction is due to stress-enhanced hole mobility for larger L
ov and that the L
eff shortening due to stress-enhanced diffusion is the secondary and the more dominating mechanism for L
ov values below 0.62 µm.
Relationship between C=C Bonds and Mechanical Properties of Carbon Rich Low-k Films deposited by Plasma Enhanced Chemical Vapor Deposition
Authors: Shim Cheonman , Jung Donggeun
Published: February 2005

We have studied the relationship between C=C bonds and the mechanical properties of different low-k films deposited by plasma enhanced chemical vapor deposition (PECVD) using a p-xylene and/or hexamethyldisilane (HMDS) precursor. The three types of films were called plasma polymerized p-xylene (PPpX) using p-xylene only, plasma polymerized p-xylene:hexamethyldisilane (PPpX:HMDS) using a mixture of p-xylene and HMDS, and plasma polymerized hexamethyldisilane (PPHMDS) using HMDS only as precursors. The mechanical strengths such as Young's modulus and hardness decreased as a function of annealing temperature, while C=C bonds increased in number. We suggest that the mechanical properties of low-k films containing a large amount of C and small amounts of Si and/or O are closely related to the generation of C=C bonds in the films after annealing, and not to the decrease in the film density. This was investigated by Fourier transform Raman (FT-Raman) spectroscopy.
High-Resolution Scanning Electron Microscopy Observation of GaN/AlGaN Strained-Layer Superstructures in GaN-Based Violet Laser Diodes
Authors: Saijo Hiroshi , Nakagawa Mine , Yamada Mitsuhiko , Hsu Jung-Tsung , Tu Ru-Chin , Yang Jer-Ren , Shiojiri Makoto
Published: February 2005

Two hundred coupled layers of n-Al0.14Ga0.86N (3 nm)/n-GaN (3 nm) strained-layer superstructures (SLSs) with a n-GaN:Si layer were grown directly on a (0001) sapphire substrate by metalorganic vapor-phase epitaxy. With the aid of image processing, each SLS was definitely resolved as a bright or dark fringe 3 nm wide in the mapping of secondary electrons in a high-resolution scanning electron microscope.
Vertically Aligned Nematic Liquid Crystal on Anodic Porous Alumina
Authors: Maeda Tsuyoshi , Hiroshima Kohki
Published: February 2005

A nematic liquid crystal that vertically aligns against the substrate was obtained on an anodic porous alumina (Al2O3) film fabricated by anodizing Al. As with a SiO rotation oblique evaporation film, the orientation mechanism is thought to be based on a nanostructure ranging in size from 5 to 30 nm that extends perpendicularly with respect to the substrate. This film is transparent and colorless, making it a suitable alignment layer for a liquid crystal display. Because it is inorganic and known as a stable material, an anodic porous alumina film would be particularly promising for use as an alignment layer in a projection display and other applications where a highly reliable, high-contrast, vertically aligned (VA) liquid crystal mode is used.
Physical Origin of Magnetically Induced Periodic Structure Observed in Terahertz Radiation Spectrum Emitted from InAs
Authors: Takahashi Hiroshi , Quema Alex , Goto Masahiro , Ono Shingo , Sarukura Nobuhiko , Nishijima Gen , Watanabe Kazuo
Published: February 2005

Terahertz (THz) radiation from femtosecond-laser-irradiated InAs (100) surface is investigated. It is found that THz-radiation spectrum exhibits two inter-related phenomena in a strong magnetic field under the Voigt configuration. The peak shift of THz-radiation spectrum toward lower frequency is observed with increasing magnetic field. Additionally, THz-radiation spectrum is found to posses a periodic structure owing to the interference of THz-radiation pulses from the front and back surfaces of the InAs substrate. The physical origin of the latter phenomenon is discussed by considering the magneto-plasma effect, which affects both real and imaginary parts of refractive index for THz-radiation propagating in a direction perpendicular to the magnetic field.
Controlled Carrier Generation at a Polarity-Discontinued Perovskite Heterointerface
Authors: Nishimura Jun , Ohtomo Akira , Ohkubo Atsushi , Murakami Youichi , Kawasaki Masashi
Published: February 2005

Electronic properties of polarity-discontinued heterointerfaces between two perovskite band insulators, LaAlO3 and SrTiO3, have been investigated. Various heterointerfaces with AlO2-LaO/TiO2-SrO and LaO-AlO2/SrO-TiO2 termination including the mixtures of these two domains are fabricated in a single experimental run. This is accomplished by pulsed laser depositions of prescribed coverage (θSrO) of SrO atomic layer on TiO2-terminated SrTiO3 (001) surface and successive LaAlO3 layer, where the processes are regulated in an atomic scale by in situ reflection high-energy electron diffraction. Increasing θSrO from 0 to 1, extra electrons density at the heterointerfaces decreases from a value, close to 0.5 electrons at one Ti site, to zero, while low temperature mobility remains above 100 cm2/V·s. Our result implies a way to control carrier density in polarity-discontinued heterointerfaces.
Simultaneous-Sweep Method for Evaluation of Single-Electron Transistors with Barriers Induced by Gate Electric Field
Authors: Inokawa Hiroshi , Takahashi Yasuo
Published: February 2005

In single-electron devices (SEDs) with gate-induced barriers, the barrier height may often be affected by the separate input gate used for controlling the potential of the Coulomb island. To compensate for this adverse effect, we introduce a simultaneous-sweep method, in which the gate voltage for the barrier is changed in inverse relation to the input gate voltage. By using this method, a two-gate narrow-channel metal-oxide-semiconductor (MOS) field-effect transistor was successfully operated as a single-electron transistor (SET). This is the first clear demonstration of a SET with gate-induced barriers in a silicon MOS system, where the presence of a disordered quantum wire or impurity quantum dots is excluded by the independent characterization of the channel using one gate at a time.
Study on Stable Operation Condition and Multi-level Recognition of Optical Digital-to-Analog Conversion-Type Header Processor for Optical Packet Switch
Authors: Seki Takeshi , Uenohara Hiroyuki
Published: February 2005

The method for the stable operation and possible multi-level recognition of an optical digital-to-analog converter are investigated for application to the optical header processor of an optical packet switch. The method of combining split header pulses in orthogonal polarization was utilized for suppressing power fluctuation due to phase noise. We measured the bit error rate (BER) dependence on the relative polarization angle between split header signals, and a BER of less than 10-9 was realized with a relative polarization angle range within 6°. We also performed BER measurements at various threshold voltages, and we verified that four-level recognition is possible with error-free performance.
Tunable and Low Noise Gain-Clamped Double-Pass L-Band Erbium-Doped Fiber Amplifier
Authors: Harun Sulaiman Wadi , Samsuri Norhakimah Md , Ahmad Harith
Published: February 2005

A highly efficient, low-noise and tunable gain-clamped L-band erbium-doped fiber amplifier is demonstrated using a Fabry-Perot laser in a double-pass system. The broad-band fiber Bragg grating (FBG) operating in the L-band region is used to retro pass the test signal to the system for enhanced gain. Gain clamping is achieved by incorporating a narrow-band FBG operating at the C-band wavelength in conjunction with an optical circulator to generate a Fabry-Perot laser, which can be tuned by a variable optical attenuator (VOA). The gain is clamped at 19.0 dB for all input signal powers from -40 to -12 dBm with a gain variation of less than 0.2 dB at a VOA setting of 0 dB. The clamped gain can be controlled between 19.0 and 21.4 dB by varying cavity loss setting. The corresponding noise figures obtained are below 4.8 dB within the dynamic input power range. The low noise figure is achieved due to the incorporation of a short forward-pumped erbium-doped fiber in front of a double-pass amplifier.
Field Emission Properties of Short Crystalline Carbon Nanotubes Cut by Sonication on Substrate
Authors: Jeong Soo-Hwan , Lee Kun-Hong
Published: February 2005

Anodic aluminum oxide (AAO) templates were fabricated by anodizing Al sheets. After the Co catalyst had been electrochemically deposited into the bottom of the AAO template, carbon nanotubes (CNTs) were grown by the catalytic pyrolysis of C2H2 at 650°C. Short and crystalline CNT field emitters were prepared by cutting the overgrown CNTs on the AAO template via sonication method. The electron field emission measurements on the samples showed a turn-on field of 2.84 V/µm and a field enhancement factor of 2580. We expect these CNT emitters could be applied to an integrated triode structure for cold cathodes.
Generation of Extremely Weak Sub-Poissonian Light Using High-Efficiency Light-Emitting Diodes
Authors: Nakano Masanobu , Tanaka Kenichi , Higashi Amane , Masuyama Ryuji , Kadoya Yutaka , Yamanishi Masamichi
Published: February 2005

The squeezing of the intensity noise in the extremely weak light emanating from a light-emitting diode (LED) was investigated. By the use of a tailor-made high-efficiency LED, in which the active region is heavily doped (∼3.5×1019 cm-3), we successfully observed sub-Poissonian light at an injection current and photocurrent as low as 1 µA and 160 nA, respectively, at room temperature. The experimental results also implied that the theoretical model describing the noise behavior needs to be refined, particularly in the case of extremely low injection levels where the nonradiative recombination process has a serious effect.
A Single Gap Transflective Display using In-Plane Switching Mode
Authors: Song Je Hoon , Lee Seung Hee
Published: February 2005

A single gap transflective liquid crystal display (LCD) using an in-plane switching (IPS) mode is being studied. In the IPS mode, the degree of the rotation of the LC director, between and above electrodes is different. When it is 45° between the electrodes, it is only 22.5° above the electrodes for an optimized cell design. Utilizing this mechanism and an in-cell retarder with a quarter-wave plate that is used below the LC layer, the transflective IPS mode is realized as such that the area between the electrodes is used as a transmissive part and the area above the electrodes is used as a reflective part.
A Novel Silicon-Dioxide Etching Process Employing Pulse-Modulated Electron-Beam-Excited Plasma
Authors: Takeda Keigo , Tomekawa Yutaka , Iwasaki Masahiro , Ito Masafumi , Ohta Takayuki , Yamakawa Koji , Hori Masaru
Published: February 2005

We developed a novel silicon-dioxide (SiO2) etching process employing a pulse-modulated electron-beam-excited plasma (EBEP) and investigated its etching characteristics. The pulse-modulated EBEP was found to have an excellent potential for resolving problems such as the plasma-induced thermal damage on a photoresist film on a substrate and the nonuniformity of etching in a conventional EBEP. Furthermore, the anisotropic SiO2 etching at a high rate of 375 nm/min was successfully performed without any thermal damage to the photoresist film. The etching rate of the pulse-modulated EBEP was a few tens times higher than those of conventional etching processes without any additional bias power supply. As a result, the microfabrication on the end surface of the optical fiber was demonstrated.
Effects of HfOxNy Gate-Dielectric Nitrogen Concentration on the Charge Trapping Properties of Metal–Oxide–Semiconductor Devices
Authors: Cheng Chin-Lung , Chang-Liao Kuei-Shu , Huang Ching-Hung , Wang Tien-Ko
Published: February 2005

Effects of nitrogen concentration near the HfO
x
N
y
/Si interface on the charge trapping properties of metal–oxide–semiconductor (MOS) capacitors were investigated. The nitrogen concentration in HfO
x
N
y
gate dielectric was adjusted by sputtering the Hf target in a nitrogen-flow-modulated ambient. The trapped charges in the HfO
x
N
y
dielectric are positive. The mechanism related to the relatively large stress-induced leakage current (SILC) at low electrical fields can be explained using trap-assisted tunneling. On the other hand, the relatively small leakage current found at high electric fields can be attributed to the electron trapping in bulk defects. A small flat-band voltage shift and SILC are observed for devices with a HfO
x
N
y
dielectric containing a higher nitrogen at the dielectric/Si interface, which possesses less strain near the interface.
Investigation of Shape Transformation of Silicon Trenches during Hydrogen Annealing
Authors: Kuribayashi Hitoshi , Hiruta Reiko , Shimizu Ryosuke , Sudoh Koichi , Iwasaki Hiroshi
Published: February 2005

We have investigated the corner rounding of a micron-sized silicon trench by annealing under hydrogen pressure of 40–760 Torr in the temperature range of 1000 to 1100°C, and have obtained plots showing the relationship between the curvature of the trench corner and annealing time for various annealing conditions. It was found that the evolution of the curvature of the trench corner follows a time scaling law, expressed by t
-1/4. This finding strongly suggests that the shape transformation is attributable to the self-diffusion of the silicon surface under the experimental conditions studied. The surface self-diffusion coefficient in the case of hydrogen pressure of 40 Torr and a temperature of 1000°C was estimated to be approximately 2 ×106 nm2/s.
Epitaxial Growth of Semiconducting BaSi2 Films on Si(111) Substrates by Molecular Beam Epitaxy
Authors: Inomata Yuya , Nakamura Tomoyuki , Suemasu Takashi , Hasegawa Fumio
Published: February 2005

We have grown [100]-oriented BaSi2 multidomain epilayers on Si(111) substrates by molecular beam epitaxy (MBE) using a BaSi2 epitaxial template formed by reactive deposition epitaxy (RDE). The [100]-oriented BaSi2 films were obtained over a wide temperature range from 450 to 700°C: The optimum growth temperature was about 600°C at which the integrated intensity of X-ray diffraction peak was maximum and the full width at half maximum (FWHM) was minimum. X-ray pole figure measurements revealed that there were three epitaxial variants of [100]-oriented BaSi2 due to the three-fold symmetry of the Si(111) surface.
Effect of Partial Pressure of TiCl4 and NH3 on Chemical Vapor Deposition Titanium Nitride (CVD-TiN) Film Cl Content and Electrical Resistivity
Authors: Jun Keeyoung , Shimogaki Yukihiro
Published: February 2005

Chemical vapor deposition titanium nitride (CVD-TiN) films were deposited from TiCl4 and NH3 at 410°C, that was sufficiently low for making ULSI multi-level interconnections. We investigated the Cl content and resistivity of CVD-TiN films as a function of TiCl4 and NH3 partial pressure (P
TiCl4
, P
NH3
). We found that Ti/(Ti+N) ratio was almost constant against different P
TiCl4
and P
NH3
conditions, while the resistivity and residual chlorine concentration were sensitive to these conditions. The lowest resistivity of 480 µΩ·cm and the lowest Cl concentration of 2% were achieved in the condition of the step coverage of 96% and the throughput of 16 nm/min when P
TiCl4
= 0.01 Torr, and P
NH3
= 0.25 Torr, respectively. These values may be further improved by using flow modulation method.
Magnetic Property of Stable Icosahedral Quasicrystal in Zn-Fe-Sc Alloy
Authors: Kashimoto Shiro , Motomura Senni , Maezawa Ryo , Matsuo Susumu , Ishimasa Tsutomu
Published: February 2005

We report the observation on the magnetic property of the stable Zn77Fe7Sc16icosahedral quasicrystal discovered recently. As a result of measurements of magnetization, it became clear that the new Zn-based icosahedral quasicrystal has large local magnetic moments and exhibits spin glass behavior. The magnetization curves show Curie-like paramagnetism, where the magnetizationMis 4.45 cgsemu/g at 5 K under 70 kOe. The temperature dependence of the magnetic susceptibility obeys the Curie-Weiss law between 76 and 300 K. On the assumption that all of the Fe atoms have the same magnitude of local magnetic moment, the effective number of Bohr magnetonpof each Fe atom was estimated at 5.30 on average. Moreover, in the low-temperature region, the spin glasslike cusp of the magnetic susceptibility was observed with a freezing temperatureTf= 7.2 K.
Orientation-Controlled Growth of Pentacene Single Crystal Films on an Alignment Layer Using Liquid Crystal as Solvent
Authors: Fujikake Hideo , Suzuki Takaaki , Isaka Fumito , Sato Fumio
Published: February 2005

We found that organic semiconductor pentacene is soluble in some liquid crystal materials with large π-electron conjugated groups. The solubility of pentacene in the heated cyanoterphenyl liquid crystal reached 20 wt%. We considered that both elongated molecular structures of pentacene and liquid crystal produce temporary molecular aggregates in the solution. We also clarified that a large molecular-alignment-controlled thin plate of single crystal pentacene up to 200 µm in length can be grown on a rubbed alignment layer of polyimide when the heated solution film was slowly cooled between glass substrates.
Analysis of the Structure of Vertical Combdrives of Fast Scanning Micromirrors
Authors: Wada Hiroyuki
Published: February 2005

The advantages of the fast scanning micromirror above vertical combdrives (bottom type) fabricated by the self-alignment process are reported. The fill factor of the bottom type was larger than that of a fast scanning micromirror beside vertical combdrives (side type) fabricated previously. The maximum tilt angle of the bottom type was larger than that of the side type. The probability of the failure mode at applied high voltage and the narrow gap between the upper and lower comb teeth (snap down) of the bottom type was lower than that of the side type. A bottom-type fast scanning micromirror the resonant frequency of which was 50.8 kHz was fabricated.
High Tunnel Magnetoresistance at Room Temperature in Fully Epitaxial Fe/MgO/Fe Tunnel Junctions due to Coherent Spin-Polarized Tunneling
Authors: Yuasa Shinji , Fukushima Akio , Nagahama Taro , Ando Koji , Suzuki Yoshishige
Published: February 2005

We fabricated fully epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs) and observed a magneto-resistance (MR) ratio of 88% at T = 293 K (146% at T = 20 K), the highest value yet reported. The origin of the high MR ratio is not the diffusive tunneling of Julliere's model but the coherent spin-polarized tunneling in epitaxial MTJs, in which only the electrons with totally symmetric wave functions with respect to the barrier-normal axis can tunnel. The bias-voltage dependence of the MR was very small, resulting in a high output voltage of 380 mV. This high voltage will help overcome problems in the development of high-density magnetoresistive random-access-memory (MRAM).