bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation Method for Buried Oxide Formation of Separation by Implanted Oxygen Structure during Post-Implantation Thermal Annealing
Authors: Nakao Motoi , Sudoh Koichi , Iikawa Hirofumi , Iwasaki Hiroshi , Izumi Katsutoshi
Published: July 2005

We have developed a simulation method for buried oxide layer formation of separation by implanted oxygen (SIMOX) structures during thermal annealing after oxygen implantation into Si. The SiO2 precipitation in oxygen-implanted Si substrates is numerically simulated, introducing the Cahn-Hilliard equation for the evolution of oxygen concentration distribution in a Si matrix. We have found that different initial depth profiles of oxygen cause different types of profiles of domain structures distinguished as a continuous oxide layer, an array of discontinuous oxide islands, and an oxide layer including Si islands. Our simulation well reproduces the SIMOX structures observed experimentally for different oxygen doses. Also, the dynamic simulation results agree well with experimental ones. These results indicate that our simulation method enables to extract the dose window for continuous oxide layer formation as well as to study the formation mechanism of the buried oxide layer of the SIMOX substrate by post-implantation thermal annealing.
Characteristics of Ultra Thin Hf-Silicate Gate Dielectrics on Si0.9954C0.0046/Si Heterolayers
Authors: Liu Kou-Chen , Maikap Sidhu , Chen Pang-Shiu
Published: July 2005

For the first time, the characteristics of ultrathin (capacitance equivalent thickness = ∼1.4 nm) Hf-silicate gate dielectrics deposited by RF sputtering on tensile-strained Si0.9954C0.0046 layers are investigated. The formation of Hf-silicate film is confirmed by X-ray photoelectron spectroscopy. The physical thickness of ∼5.5 nm is measured by high-resolution transmission electron microscopy and the effective dielectric constant of κ ∼15.5 is calculated from the accumulation capacitance. The leakage current density of ∼1×10-4 A/cm2 at -2 V is significantly decreased as compared with SiO2 for the same capacitance equivalent thickness.
Enhancement of 1.54 µm Photoluminescence in β-FeSi2 by Surface Oxidation
Authors: Terai Yoshikazu , Maeda Yoshihito
Published: July 2005

We present the photoluminescence (PL) properties of surface oxidized β-FeSi2/Si(100) samples. X-ray photoelectron spectroscopy measurements showed the formation of a thick SiO2 layer at the surface when samples were annealed in air. In PL measurements, the samples annealed in air showed much larger PL intensity and activation energy for a nonradiative recombination than those annealed in vacuum. Surface oxidation is a new technique to enhance the PL at 1.54 µm of β-FeSi2.
Epitaxial Growth of (100)-Oriented β-FeSi2 Thin Films on Insulating Substrates
Authors: Akiyama Kensuke , Kaneko Satoru , Kimura Takeshi , Funakubo Hiroshi
Published: July 2005

Epitaxial β-FeSi2 thin films were grown on insulating substrates by rf magnetron sputtering. (100)-Oriented β-FeSi2 films were epitaxially grown on (100) yttria-stabilized zirconia (YSZ) and (001) Al2O3 substrates. The epitaxial relationship of the β-FeSi2 film with the (100) YSZ substrate was the same as that with the (100) Si substrate. On the (001) Al2O3 substrate, the epitxial film had a threefold symmetry domain structure, which has not been reported on a film grown on a Si substrate. Epitaxial growth of (100)-oriented β-FeSi2 film was affected by not only lattice mismatch but also atomic or ionic matching between β-FeSi2 and substrate and requires substrates consisting of either a single element or only cations.
High Brightness InGaN/GaN Blue Light Emitting Diode Realized by a 6×2'' MOCVD System
Authors: Ju Jin-Woo , Lee Cheul-Ro , Baek Jong-Hyeob , Lee Young Hee , Lee In-Hwan
Published: July 2005

We have fabricated high brightness blue light emitting diode (LED) with InGaN/GaN multi-quantum well (MQW) which is sandwiched simply between n-GaN and p-GaN. The LED epitaxial structure was grown by a newly designed metal organic chemical vapor deposition (MOCVD) system with RF heater and vertical gas injection type showerhead. The reactor exhibited a good uniformity of temperature and gas velocity. The uniformity of layer thickness and PL wavelength was less 2% and 1.2 nm, respectively. The epoxy molded LED lamp showed radiant power of 4 mW at a forward current of 20 mA. We note that the power is very high considering such a simple LED structure.
Monolithic Integration of InP-Based HEMT and MSM Photodiode Using InGaAsP (λ=1.3 µm) Buffer
Authors: Cha Jung-Ho , Kim Jaeho , Kim Choul-Young , Shin Seong-Ho , Kwon Young-Se
Published: July 2005

A new epitaxial layer structure for the integration of a high-electron-mobility transistor (HEMT) and a metal-semiconductor-metal photodiode (MSM PD) is proposed. With the aid of an InGaAsP (λ=1.3 µm) buffer, this epitaxial layer structure has an additional function of light absorption without performance degradation of the HEMT. With this light absorption ability, the epitaxial layer structure can support a MSM PD structure and makes the fabrication process of the MSM PD identical to that of a HEMT. The characteristics of a monolithically integrated HEMT and MSM PD are presented and discussed. Measured f
t and f
max are 18.7 GHz and 47 GHz, respectively, for the 1.5×100 µm2 gate HEMT, and a responsivity of 0.7 A/W at a wavelength of λ=1.3 µm has been acquired for the MSM PD.
Characteristics of Back-illumination UV Photodetector Fabricated with AlxGa1-xN Heterostructure
Authors: Chae Kyong-Seok , Lee In-Hwan , Baek Byung-Joon , Seol Kyeong-Won , Ahn Haeng-Keun , Lee Cheul-Ro
Published: July 2005

We report the growth, fabrication and characterization of an AlxGa1-xN heteroepitaxial back-illuminated UV photodetector used for flip-chip mounting. This device is grown on a one-side-polished sapphire substrate with a low-temperature AlN buffer layer by 6-pocket multi-wafer metalorganic chemical vapor deposition (MOCVD) using a vertical reactor. In order to attain the UV region, we increased the Al mole fraction in the AlxGa1-xN epilayer and acquired an AlxGa1-xN epilayer that shows a crack-free surface morphology when the Al mole fraction was 30%. This device consists of a 1.2-µm-thick Al0.3Ga0.7N “window layer”, 0.16-µm-thick Al0.08Ga0.92N i-layer, 0.46-µm-thick Al0.08Ga0.92N p-layer, 0.1-µm-thick GaN p-layer and a 30-nm-thick GaN:Mg p+-contact layer. All device processes were completed by standard semiconductor processing techniques that include photolithography, metallization and etching. In this device, the zero-bias peak responsivity is measured to be about 0.1 A/W at 350 nm, which corresponds to an external quantum efficiency of 36%. The rise-and-fall time of the photoresponse is 4.1 ns. This device exhibits a low dark current density of 31.9 pA/cm2 at zero bias. Therefore, we can successfully obtain the back-illuminated UV photodetector with good responsivity, fast photoresponse time and low dark current.
Dual-Wavelength High-Power Laser Diodes Fabricated by Selective Fluidic Self-Assembly
Authors: Tojo Tomoaki , Yamanaka Kazuhiko , Singh Brahm Pal , Onozawa Kazutoshi , Ueda Daisuke , Soga Ikuo , Maezawa Koichi , Mizutani Takashi
Published: July 2005

We have developed dual-wavelength high-power laser diodes (LDs) with a hybrid integrated solution, in which a 660 nm (red) LD chip and a 780 nm (infrared) LD chip are mounted side-by-side on the same substrate. To achieve the required mounting position accuracy, i.e., the distance between two emitting points is limited to 110±3 µm, we have developed a novel mounting technique called selective fluidic self-assembly (S-FSA). In this technique, we used new self-locking structures of guest-host pairs. Bumps formed on the bonding surfaces of the LD chips are used as guests. A substrate with recesses whose shapes correspond to those of the bumps is used as the host. By forming bumps aligned along the waveguide and assigning a rotationally asymmetric shape for the bumps, an accurate and selective mounting is realized. Dual-wavelength LDs fabricated by this technique demonstrated the required positioning accuracy and high-power operation.
InAs Quantum Cascade Lasers Based on Coupled Quantum Well Structures
Authors: Ohtani Keita , Fujita Kazuue , Ohno Hideo
Published: July 2005

We report the operation of mid-infrared InAs quantum cascade lasers based on coupled quantum well structures. The laser structures are grown on n-type InAs(100) substrate by solid-source molecular beam epitaxy. The resonant longitudinal optical phonon scattering is used for carrier extraction from ground state in active layers. The laser emitting around 9.1 µm in the pulse mode operates up to 160 K. The observed minimum threshold current density is 3.6 kA/cm2 at 80 K. We also measure the waveguide loss and compare with the design.
Effects of Channel Thinning on Threshold Voltage Shift in Ultrathin-Body Silicon Nanocrystal Memories
Authors: Yanagidaira Kosuke , Saitoh Masumi , Hiramoto Toshiro
Published: July 2005

We propose an ultrathin body silicon nanocrystal memory with a large threshold voltage shift (ΔV
th) and a small write/erase threshold voltage (V
th) distribution. Experimental results show that ΔV
th increases when body thickness decreases to 6 nm. Although ΔV
th also increases in an ultranarrow channel, the ultrathin-body memory has a much smaller write/erase V
th distribution than the ultranarrow-channel memory. It is confirmed by simulation that a large ΔV
th in an ultranarrow channel originates from a larger increase in the potential of a thin body than in that of a thick body.
Resistance Oscillations by Electron-Nuclear Spin Coupling in Microscopic Quantum Hall Devices
Authors: Yusa Go , Hashimoto Katsushi , Muraki Koji , Saku Tadashi , Hirayama Yoshiro
Published: July 2005

We study electron-nuclear spin coupled systems implemented in microscopic fractional quantum Hall (FQH) devices. We find that the longtitudinal resistance in such systems oscillates with a period of about ∼200 s and is driven by a constant voltage instead of a constant current. This anomalous behavior suggests that an average nuclear spin polarization self-sustainingly oscillates between randomized and polarized states which reveal the nonlinear nature of the mesoscopic electron-nuclear spin coupled systems.
Novel Si Codoped Pb(Zr,Ti,Nb)O3 Thin Film for High-Density Ferroelectric Random Access Memory
Authors: Kijima Takeshi , Aoyama Taku , Miyazawa Hiromu , Hamada Yasuaki , Ohashi Koji , Nakayama Masao , Natori Eiji , Shimoda Tatsuya
Published: July 2005

We have succeeded in fabricating Pb(Zr,Ti,Nb)O3 (PZTN) thin films with more than 10 at.% Nb at the B site in the A
B
O
3 structure, which are suitable for application to high-density and reliable ferroelectric random access memory (FeRAM). To prepare the PZTN thin films, we used a sol-gel spin-coating method in which we codoped 1–3 mol% Si to promote the solvation of Nb atoms into the original Pb(Zr,Ti)O3 (PZT) films as a solid solution. X-ray diffraction (XRD) reciprocal space mapping and Raman scattering revealed that our PZTN film was a single ferroelectric phase of the A
B
O
3 proposed perovskite-type structure with Nb substituted for B-site atoms. Additionally, we suggested that, through this Nb substitution, the formation of oxygen vacancies in PZTN was effectively suppressed; the number of vacancies was much lower than in conventional PZT. The resultant 150-nm-thick PbZr0.2Ti0.6Nb0.2O3 film had a very low leakage current and demonstrated excellent imprint and data retention properties. We have also succeeded in obtaining excellent electric properties in 0.8×0.8 µm2 capacitors fabricated with PZTN. In addition, we confirmed the high reliability and absence of data degradation of our PZTN material during operation as a 1 kbit FeRAM chip. The results of a first-principles calculation indicated that the reduction of the number of oxygen vacancies led to a sufficiently wide band gap to lower the leakage current in our PZTN films.
Advanced HSPICE Macromodel for Magnetic Tunnel Junction
Authors: Lee Seungyeon , Lee Seungjun , Shin Hyungsoon , Kim Daejung
Published: July 2005

Magnetoresistive random access memory (MRAM) using a magnetic tunnel junction (MTJ) memory cell has the potential to revolutionize both high-density and high-speed memory applications with devices exhibiting non-volatility and good write endurance. This work presents a macromodel for an MTJ that is applicable to an HSPICE circuit simulator. The macromodel is realized as a five-terminal subcircuit that reproduces the characteristics of an MTJ including hysteresis and asteroid curves with thermal variation, and the R–V characteristics.
Distribution and Impact of Local Trapped Charges in Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) Memory
Authors: Sun Lei , Pan Liyang , Zeng Ying , Pang Huiqing , Wang Jimin , Zhang Zhaojian , Li Xiyou , Zhu Jun
Published: July 2005

In this paper we propose a two-transistor model with an R
PT for the punch-through resistor in the silicon-oxide-nitride-oxide-silicon (SONOS) memory cell. With this model, the subthreshold leakage current induced by the local trapped charges in silicon nitride and the impact on the cell's read characteristics are studied. Some solutions to decrease this leakage current and change the distribution of the trapped charges are proposed and analyzed, including programming condition optimization, the channel initiated secondary electron (CHISEL) programming, and cell structure optimization. Moreover, using the CHISEL or channel hot electron (CHE) programming, the influences on the programming and the erase characteristics of different charge distributions are investigated.
Al2O3/Si3N4 Insulated Gate Channel-Doped AlGaN/GaN Heterostructure Field-Effect Transistors with Regrown Ohmic Structure: Low Gate Leakage Current with High Transconductance
Authors: Maeda Narihiko , Makimura Takashi , Wang Chengxin , Hiroki Masanobu , Makimoto Toshiki , Kobayashi Takashi , Enoki Takatomo
Published: July 2005

An advanced structure of AlGaN/GaN heterostructure field-effect transistors (HFETs) has been proposed and fabricated, which is characterized by the following structural features: (i) a metal-insulator-semiconductor (MIS) structure using an Al2O3/Si3N4 bilayer gate insulator to reduce the gate leakage current, (ii) a thin AlGaN barrier with a doped channel to simultaneously obtain the high transconductance and high drain current, and (iii) a regrown ohmic structure to reduce the contact resistance. The fabricated devices have been proved to exhibit attractive characteristics such as low gate leakage current, low contact resistance, high drain current, and high transconductance. An HFET with a gate length of 0.1 µm has exhibited a gate leakage current density of below 10-4 A/mm even at a gate voltage of +3 V. It has also exhibited a low contact resistance of 0.3 Ωmm, a high maximum drain current density of 1.23 A/mm, and a high transconductance of 280 mS/mm, which is the highest transconductance ever reported in the category of MIS-HFETs. The cutoff frequency and maximum oscillation frequency, measured with the pad capacitances included, were 52 and 75 GHz, respectively. The proposed structure has thus been proved to be effective in further improving the device performance in GaN-based HFETs.
Pyramid Bumps for Fine-Pitch Chip-Stack Interconnection
Authors: Watanabe Naoya , Ootani Youhei , Asano Tanemasa
Published: July 2005

We propose pyramid bumps as one of the compliant bumps for realizing stacked chips with fine-pitch chip interconnections. The pyramid bumps, made of Au, are fabricated by the bump transfer method. The bump size is approximately 13 µm at the base and pitch is 20 µm. A comparative study between the pyramid bump and the conventional plated bump is carried out. It is demonstrated that the pyramid bump deforms more easily than the plated bump. This indicates that the pyramid bump has a significant advantage over the plated bump in compensating the bump height deviation and the nonuniformity in bonding pressure and that the bonding of a pyramid bump can be achieved at smaller pressing loads than those necessary for a plated bump. It is also found that the pyramid bump effectively excludes insulating resin, which is precoated on the chip surface, from the bonding interface and thereby suppresses bonding failure.
Connection Test of Area Bump Using Active-Matrix Switches
Authors: Watanabe Naoya , Hasegawa Satoshi , Asano Tanemasa
Published: July 2005

We propose a new method of bump connection testing using active-matrix metal oxide semiconductor field-effect transistor (MOSFET) switches. One of the bump connections is electrically selected using the active-matrix switches and the current-voltage characteristic between chips is measured through the selected bump connection. In this method, the testing of the individual bumps and the investigation of the bonding failure mechanism are possible. This method can also be applied to the actual chip because the chip can be electrically separated from a test circuit using active-matrix MOSFET switches.
Separately Doped Structures for Red Organic Light-Emitting Diodes
Authors: Yang Chuan-Yi , Tsai Yu-Sheng , Juang Fuh-Shyang , Su Yan-Kuin , Lin David , Chu Chun-Hsun , Chiu Yi-Tai
Published: July 2005

This paper reports on the separately-doped structures of organic light-emitting diodes (OLED) in which red dye 4-(dicyanomethylene)-2-methyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJT) was doped into the host emitting layer of tris(8-hydroxyquinoline)aluminum (Alq3) by means of ultrathin separate doping (like quantum wells). The parameters in the ultrathin layer, including its width, position, number and spacing between separately doped layers, were changed to study their effects on electroluminescence (EL) characteristics. Thin doped layers increase the luminance efficiency. When the ultrathin separately doped layers were in the vicinity of the NPB/Alq3 interface, where N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) is used as a hole transport layer, luminance efficiency also increased. The highest luminance efficiency reaching 4 cd/A was achieved using a double ultrathin separately doped structure with optimum doping thickness and 2 nm of space between the two layers. The study also found that double ultrathin separately doped structures achieved better EL intensity than single or triple ultrathin separately doped structures.
Potential Behavior of Biochemically Modified Gold Electrode for Extended-Gate Field-Effect Transistor
Authors: Sakata Toshiya , Matsumoto Shinya , Nakajima Yoshio , Miyahara Yuji
Published: July 2005

We propose potentiometric detection of biomolecules using an extended-gate field-effect transistor (EGFET). Using a gold film electrode as the extended gate, the stability of the interface potential was characterized for a shift and a drift, and found to depend on the surface roughness of the gold electrode. The surface of the gold film was coated with self-assembled monolayers (SAMs) of various types of alkanethiol molecules with functional sites such as amino groups, carboxyl groups, hydroxyl groups and oligonucleotides. In all the alkanethiol molecules, the interface potential decreased drastically just after the introduction of each molecule because of the negative charges of thiol groups in aqueous solutions. Moreover, the complementary target deoxyribonucleic acid (DNA) has been introduced to the gold electrode modified with oligonucleotide probes and hybridized with them. The interface potential shifted in the negative direction due to the negative charges of the target DNA. Thus, the charge density change due to DNA hybridization as well as the adsorption of alkanethiol molecules on the gold electrode could be successfully detected using the biochemically modified EGFET.
Development of Piezoelectric Thin Film Resonator and Its Impact on Future Wireless Communication Systems
Authors: Satoh Yoshio , Nishihara Tokihiro , Yokoyama Tsuyoshi , Ueda Masanori , Miyashita Tsutomu
Published: July 2005

The bulk acoustic wave filter composed of piezoelectric thin film resonators has many features superior to those of other small filters such as a surface acoustic wave (SAW) filter and a ceramic filter. As it has no fine structure in its electrode design, it has a high Q factor that leads to low-loss and sharp-cut off characteristics and a high power durability particularly in the high-frequency range. Furthermore, it has the potentiality of integrated devices on a Si substrate. In this paper, we review the recent developments of piezoelectric thin film resonator filters in the world, including our development for mobile communication applications. After describing the feature and history of the piezoelectric thin film resonator filters, our technologies are introduced in focusing on the resonator structures, the piezoelectric thin film and electrode film materials, the cavity structures, the filter structure and its design rules and characteristics, comparing with SAW filters. The competition and coexistence between the piezoelectric thin film resonator filters and the SAW filters are also described. In this paper, we describe the development of a piezoelectric thin film resonator from the standpoint of researchers who have a long experience of SAW filter development.
Mechanical Stress Caused by Adsorption of O or N on Ga-terminated (100) GaAs Surface and InAl-terminated (100) InAlAs Surface: Degradation of Insulator/Semiconductor Interface
Authors: Seto Hiroki , Miyamura Satoshi , Inokuma Takao , Iiyama Koichi , Takamiya Saburo
Published: July 2005

Mechanical stress at the surfaces of GaAs and InAlAs, caused by adsorption of O or N on their group III surfaces, was calculated using small cluster models and first-principles calculations. These elements adsorb at the bridge sites and give strong compressive stress to the crystal. Assuming that only the O and N at the interface generate the stress, i.e., the insulator does not give any stress, mechanical stress at the insulator/semiconductor interface were calculated. N at the insulator/GaAs interface does not give a strong stress, but O does. Calculation results were compared with various experimental results. The results do not contradict any of the examined experimental findings, and these findings are reasonably understandable when one takes the mechanical stress as a cause of the interface degradation.
Effects of Growth Interruption during Growth of InAs Wetting Layer on Formation of InAs Quantum Dots
Authors: Morishita Yoshitaka , Osada Koh , Hasegawa Tomoaki
Published: July 2005

The effects of growth interruption on the formation of InAs quantum dots (QDs) grown on GaAs substrates by molecular beam epitaxy were investigated. The growth interruption was carried out during the growth of InAs with a nominal thickness of 1.2 monolayers (ML). The number of growth interruptions was varied between 1 and 6, and the interruption time (t
INT) was varied between 5 and 15 s. After the growth interruption, a 2.8-ML-thick InAs was grown, and the total thickness was nominally 4 ML. The structural characterization was performed using an atomic force microscope. In the case of the growth with t
INT=5 s, the average size of QDs decreased and their density increased with increasing number of growth interruptions. On the other hand, the size of QDs increased and their density decreased with increasing number of growth interruptions for the growth with t
INT=10 or 15 s. These results suggested that the extremely uniform distribution of In adatoms in the wetting layer due to the migration of In atoms on the surface as well as the reduction of stress in the wetting layer due to the interchange of In and Ga atoms during the growth interruption affect the size and density of QDs.
Structural Characterization of Si0.75Ge0.25 Alloy Layers with Sb/Ge-Mediated Low Temperature-grown Si Buffers
Authors: Rahman Mohammad Mizanur , Zhang Shuqi , Tambo Toyokazu , Tatsuyama Chiei
Published: July 2005

SiGe has become a natural choice for the fabrication of low cost and high performance electronic devices. 2000-Å-thick Si0.75Ge0.25 alloy layers were grown on Si (001) substrate using (1 ML Sb)/(∼10 ML Ge)-mediated low temperature-grown Si (LT-Si) buffers by MBE process. After formation of 1 ML Sb on Si (001) a very thin Ge layer (∼10 ML) was grown just before the growth of LT-Si layer, which may be favorable for the creation of strain relaxing dislocation sites. High-resolution X-ray diffraction was used to determine the residual strain in the Si0.75Ge0.25 alloy layers. From the XRD data, it was seen that the residual strain of the alloy layers decreased with decreasing the growth temperature of the LT-Si buffer layers and reached to a lower value of about -0.06% at 300°C. Contact mode AFM observation of the same sample showed a smooth surface with rms roughness of about 13 Å.
Effect of CHF3 Addition on Reactive Ion Etching of Aluminum Using Inductively Coupled Plasma
Authors: Saito Shuichi , Sugita Kazuyuki , Tonotani Junichi
Published: July 2005

The role of CHF3 gas addition in reactive ion etching (RIE) processes using inductively coupled plasma for aluminum wirings were investigated. With increasing of the amount of CHF3 gas addition to the etching gas, the pattern profile changed from reverse to ordinary taper and the pattern width increased. It was considered that by adding CHF3 to the main etching gas, a larger amount of passivation layer deposited on the sidewall of the resist and Al pattern, which suppressed side etching of the pattern. To clarify the role of CHF3 addition, XPS, FT-IR and TDS analyses were carried out to study the structure of the passivation layer. Consequently, it is considered that the pattern sidewall is composed of AlF3, an organic polymerized film and a passivation layer including ammonium salt and B oxide. Due to the addition of CHF3 gas into the etching gas, AlF3 is additionally formed, which is deposited on the pattern sidewall, resulting in the change of the etched pattern profile and width.
Growth of Atomically Flat-Surface Aluminum Nitride Epitaxial Film by Metalorganic Chemical Vapor Deposition
Authors: Uehara Kensei , Aota Yuji , Kameda Suguru , Nakase Hiroyuki , Isota Yoji , Tsubouchi Kazuo
Published: July 2005

A high c-axis-oriented and atomically flat-surface aluminum nitride (AlN) film has been successfully deposited on a (0001)sapphire substrate by metalorganic chemical vapor deposition. We evaluated the dependences of surface roughness, tilted mosaicity and twisted mosaicity on the conditions of AlN deposition. It was found that the atomically flat-surface AlN film was deposited under the diffusion-limited area with suppression of vapor phase reaction at a substrate temperature of 1200°C and a V/III ratio of 800. It was also recognized that surface roughness was controlled by gas flow velocity, which is determined by both gas flow rate and pressure in reactor. Mean surface roughness (R
a) of the deposited AlN films was approximately 1 Å. The full width at half maximum of X-ray rocking curve for (0002) and (1012)AlN were approximately 100 and 2300 arcsec, respectively.
Annealing Characteristics of Zn-Doped InN films on Sapphire Substrates by Reactive Magnetron Sputtering
Authors: Chen Lung-Chien , Chen Hung-Chang
Published: July 2005

Zinc-doped indium nitride (InN:Zn) films were deposited on (0001) sapphire substrates by radio-frequency reactive magnetron sputtering. All as-deposited InN:Zn film samples exhibit n-type conductivity, with a measured carrier concentration of at least 5.6×1020 cm-3. Rapid thermal annealing (RTA) at 500°C for 20 min, was used to deposit the sample at a sputtering power of 100 W, and transformed the n-type InN film into a p-type In2O3. The compensated carrier concentration and the Hall mobility at sputtering power of 50 W were 1.28×1017 cm-3 and 1.24 cm2/V·s, respectively. Two emission peaks in 20 K photoluminescence (PL) spectrum of the p-type In2O3 films were identified to correspond to the near band-to-band and conduction band-to-acceptor recombination.
Crystallization Behavior of Co32Fe48B20 Electrode Layers in Annealed Magnetic Tunnel Junctions
Authors: Bae Ji Young , Lim Woo Chang , Kim Hyun Jeong , Kim Tae Wan , Lee Taek Dong
Published: July 2005

The magnetoresistance (MR) ratio of magnetic tunnel junctions (MTJs) depends on the structure and characteristics of the interface between the ferromagnetic electrode and insulating layer. In order to understand the role of the amorphous CoFeB layer, the MTJs of the following three different pinned layers (PLs) were used: CoFeB (PL1), CoFe/CoFeB/CoFe (PL2) and CoFe (PL3). The MTJs with PL1 and PL2 showed almost the same maximum MR ratio after annealing. This indicates that a smooth or sharp interface has an increased MR ratio. The crystallization temperature of the CoFeB layer showed different dependence on the structure and lattice parameters of the adjacent layer.
Pulse Width Reduction in Diode-Pumped Nd:GdVO4 Laser with AO and GaAs Double Q-Switches
Authors: Li Guiqiu , Zhao Shengzhi , Yang Kejian , Wu Wei
Published: July 2005

By considering the Gaussian spatial distribution of the intracavity photon density, we introduce the rate equations of a diode-pumped Nd:GdVO4 laser doubly Q-switched by acoustic-optic (AO) modulator and GaAs saturable absorber. These rate equations are solved numerically, and the dependence of pulse width on incident pump power is obtained. Meanwhile, a diode-pumped doubly Q-switched Nd:GdVO4 laser with AO and GaAs is realized. This laser can generate a shorter and more symmetric pulse when compared with purely AO and passive Q-switching. The experimental results are in agreement with the theoretical calculations.
Synthesis and Third-Order Optical Nonlinearities of Conjugated Polymer-Bonded Carbon Nanotubes
Authors: Yi Wenhui , Feng Wei , Xu Youlong , Wu Hougcai
Published: July 2005

Multiwalled carbon nanotubes (MWNTs) bonded with an amino-moiety-containing nonlinear optical (NLO) polymer, poly{[3-octylthiophene-2,5-diyl]-[p-aminobenzylidenequinomethane]} (POTABQ), were synthesized via amidiation reaction and were characterized using transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) spectroscopy, ultraviolet-visible absorption spectroscopy (UV-vis), and fluorescence (FL) spectroscopy. The micrograph of POTABQ-MWNTs showed a “bead-shaped structure”, which indicated that the polymer was attached to the tubes by chemical linkage rather than as a homogenous coating. POTABQ-MWNTs showed fluorescence quenching, which is involved in the intramolecular photoinduced charge transfer process. A broad absorption band appeared at over 800 nm, indicating the ground-state interaction between POTABQ and MWNTs. Third-order NLO properties were studied by nanosecond degenerate four-wave mixing (DFWM) techniques. The resulting POTABQ-MWNTs exhibited large third-order NLO responses mainly due to the formation of an intramolecular photoinduced charge transfer system of polymers and carbon nanotubes.
Composite Dielectric Ceramics Based on BaO–Ln2O3–TiO2 (Ln = Nd, La)
Authors: Zheng Hong , Reaney Ian M. , Muir Duncan , Price Tim , Iddles David M.
Published: July 2005

BaLa4Ti4O15 (BLT) is a hexagonal perovskite-related compound with a temperature coefficient of resonant frequency (τf) of -2 ppm/°C, relative permittivity (ε
r)∼44 and figure of merit (Q·f)∼44000 GHz. Ba4Nd9.333Ti18O54 (BNT) has a tungsten-bronze-related structure with ε
r∼78, Q·f≈11000 GHz and τf of +47 ppm/°C. The microstructures and microwave dielectric properties of xBNT–(1-x)BLT (0≤x≤1) composite ceramics have been studied. X-ray diffraction analysis and scanning electron microscopy revealed that there was limited inter-reaction between the two phases and that samples were composed largely of BNT and BLT, although some deterioration in measured ε
r with respect to calculated values was observed. The optimum compositions were x=0.55 and 0.75 for which ε
r∼63, τf∼-20 ppm/°C and Q·f>10,000 GHz.
Temperature and Polarization Dependence of Transient Gratings in Azo-Dye-Doped Liquid Crystals
Authors: Kuo Chie-Tong , Huang Shuan-Yu , Kuo Ming-Syun , Jang Der-Jun
Published: July 2005

The dynamic behavior of transient gratings (TGs) formed in a planar-aligned azo-dye-doped liquid crystal film is investigated. The temporal profile of the diffraction efficiency of TGs reveals two components corresponding to the fast photoinduced isomerization of azo dye molecules and the slow dye-induced reorientation of liquid crystals. The polarization dependence of diffraction efficiency shows a strong anisotropy of excitation. The temperature dependence of diffraction efficiency and the corresponding relaxation time of decay in the slow component of diffraction reveal a thermal effect on grating formation.
A Novel Fringe Field Switching Mode with 3-partition Pixel Slit
Authors: Kim Mi Sook , Jung Youn Hak , Seen Seung Min , Kim Hyang Yul , Kim Seo Yoon , Lim Young Jin , Lee Seung Hee
Published: July 2005

We proposed a novel fringe field switching (FFS) liquid crystal (LC) mode with a 3-partition pixel slit. In this mode, a pixel branch is partitioned into 3 areas, namely, two edges and a center, where the edge slit angle is larger than the center slit angle. Thus the reverse twist region in the pixel edge is reduced and the LC dynamics in this region becomes very stable. Also, when an external pressure is applied to the panel at the operating voltage, the disclination line is barely extended into the active area. Consequently, this mode exhibits a high external pressure resistance with a wide viewing angle and is attractive for pen-based touch panels such as personal digital assistants (PDAs) and tablet personal computers (PCs).
Induced Smectic Phase in a (Nematic and Discotic) Liquid Crystal Composite System
Authors: Chen Wen-Ren , Chen Chia-Ming , Hwang Jenn-Chiu , Liaw Ben-Ruey
Published: July 2005

The phase behavior and aggregation states of a binary composite system constructed from a nematic and a discotic liquid crystal have been investigated. The nematic liquid crystal E44 with a strong polar terminal group was miscible with the discotic liquid crystal R45C8 that possesses a flat core and eight soft side chains. This binary mixture showed an induced smectic phase in the range of 80/20–30/70 weight fractions. The d-spacing of this induced smectic phase is about 33–34 Å and the layer-stacking structure of a binary composite is proposed.
Active Noise Control Systems for Broad-band Disturbance
Authors: Tseng Wen-Kung
Published: July 2005

In this study we evaluated the performance of an active noise control system for a broad-band disturbance using the method of acoustic pressure minimization at various spaces and frequencies. The technique is squared acoustic pressure minimization. The theory and simulations of pressure minimization over space and frequency using single-channel and two-channel systems are presented. The work presented in this paper is the first part of the study and we only focus on a plane wave primary field with one and two secondary sources for simplicity. A constrained minimization of pressure is introduced, to control pressure at various spaces and frequencies. The results show that a good attenuation is achieved at the microphone location or desired range over space and frequency using a single-channel system. However, a better performance could be achieved using a two-channel system. In the next part of the study more realistic sound fields such as a diffuse field will be investigated.
Shape and Thermal Effects of Metal Films on Stress-Induced Bending of Micromachined Bilayer Cantilever
Authors: Kuo Ju-Nan , Lee Gwo-Bin , Pan Wen-Fung , Lee Huei-Huang
Published: July 2005

In this study, the shape and thermal effects of metal films on the stress-induced bending of micromachined bilayer cantilever are systematically investigated. The cantilever makes use of residual stresses in thin films to induce the bending of microstructures by applying preloads. The characterization of the bilayer cantilever with different Au distribution has been performed to observe out-of-plane deformation. A finite-element model has been established to analyze such a deformation using experimental and theoretical results. It indicates that the commonly used formula for predicting the deformation of the cantilever is not valid for these devices. When the percentage of the area deposited with a metal is increased, deflection angle also increases. Furthermore, the influence of postprocessing temperature on the residual stress of the metal films is examined. Postprocessing temperature and residual stress reveal a close relationship. As postprocessing temperature increases, the residual stress of the metal increases, resulting in a larger out-of-plane deformation of the cantilever. Residual stress increases to a saturation value while the temperature reaches a critical value. This new finding could greatly affect the performance of a stress-induced bilayer cantilever. Finally, a switchable micromachined corner mirror is demonstrated using the bilayer cantilever.
Scanning Tunneling Microscopy/Spectroscopy of La2@C72 Multilayer Islands on Si(100)-2×1-H Surfaces
Authors: Taninaka Atsushi , Kato Haruhito , Shino Kazuhiro , Sugai Toshiki , Heike Seiji , Terada Yasuhiko , Suwa Yuji , Hashizume Tomihiro , Shinohara Hisanori
Published: July 2005

We have investigated structural and electronic properties of La2@C72 multi layer islands grown on a hydrogen-terminated Si(100)-2×1-H surface using ultra-high-vacuum scanning tunneling microscopy/spectroscopy (STM/STS) and theoretical calculations based on first principles. The La2@C72 molecules are observed by STM as ellipsoids, consistent with the NMR results [H. Kato et al.: J. Am. Chem. Sci. 125 (2003) 7782], indicating that, out of 24 isomers only two, with D
2 symmetry and with a non-IPR (isolated pentagon rule) structure are possible. The energy gap for the carbon cage of the La2@C72 multi layer islands is measured by STS as 1.4 eV, suggesting that the C72 carbon cage is stabilized by a charge transfer from the encaged La atoms to the fullerene cage. The La-atom derived LUMO states are localized near the encapsulated La atoms and observed as a midgap-like density of states by STS.
Aerosol Plasma Deposition Method for Preparation of Lead Zirconate Titanate Thick Films
Authors: Peng Cheng-Jien , Wang Shih-Chieh , Wang Sea-Fue , Chang Chih-Shiang , Lin Tzer-Sheng
Published: July 2005

Lead zirconate titanate (PZT) thick films were grown by a novel aerosol plasma deposition (APD) method, which combines aerosol deposition (AD) and low-temperature microwave plasma. In our set-up, the deposition rate used in the APD method was about one order of magnitude higher than that in the AD method, which can be attributed to the charging and decomposition effects of the plasma on moving agglomerates to form a trapped jet. While an as-grown APD film deposited at 200°C with a thickness of ∼10 µm showed no ferroelectric hysteresis loop, a PZT film annealed at 600°C showed a remanent polarization of ∼26 µC/cm2 and a coercive field of ∼110 kV/cm.
Crystal Structures and Photoluminescence Properties of Gd2O3:Eu3+ Phosphor Thin Films Prepared by Laser Ablation
Authors: Tanaka Isao , Ishii Norihiko , Sato Ryuji , Tamaki Takahiko
Published: July 2005

We prepared red-light-emitting europium-doped gadolinium oxide (Gd2O3:Eu3+) phosphor thin films by laser ablation using a KrF excimer laser, and characterized the correlation between the crystal structures and the photoluminescence properties of the ablated targets and the prepared thin films. The crystal structures of the Gd2O3:Eu3+ targets were changed from a cubic type to a monoclinic one by evaporation for the laser ablation. The prepared Gd2O3:Eu3+ thin films exhibited not only the cubic phase but also the monoclinic one on the quartz substrate heated at 500°C for the thin-film deposition. The thin films also showed photoluminescence spectra that were superpositions of the individual cubic and monoclinic spectra. By increasing the laser fluence during the deposition of thin films, the monoclinic phase was more efficiently formed in the prepared Gd2O3:Eu3+ thin films.
Improvement of Charging Performance of Corona Charger in Electrophotography by Irradiating Ultrasonic Wave to Surrounding Region of Corona Electrode
Authors: Choi Kwang-Seok , Nakamura Satoshi , Murata Yuji
Published: July 2005

In order to improve the performance of a corona charger in charging the photoreceptor in electrophotography, the effect of an ultrasonic wave on the process was investigated experimentally. An ultrasonic wave of 28 kHz was supplied from an ultrasonic generator at five different strengths ranging from 0 to 50 W. Instead of a photoreceptor drum, a coated aluminum drum containing a thin insulator film was used in this study. It was confirmed that the ultrasonic wave had a marked effect on the charging performance of the corona charger; namely, the ultrasonic wave increased the charge density on the insulator layer of the drum. The charge density depended on the magnitude of the ultrasonic wave and the distance between the ultrasonic generator and the wire electrode. These results were attributed to the activation of the corona discharge by the ultrasonic wave and the blowing off of the suppression gas near the corona wire electrode by the ultrasonic wave.
Highly Reliable Piezoelectric Actuator for Precision Stage System
Authors: Hashiguchi Hiroyuki , Egashira Yoshiya , Furukawa Hiroyuki , Endo Taishi , Kosaka Tetsuya , Kosaka Koji , Uozumi Kiyohiko , Watanabe Masayuki , Yamakawa Takahiro , Miyata Noboru , Nakada Akira , Kubota Hiroshi , Ohmi Tadahiro
Published: July 2005

A highly reliable nonresonant ultrasonic motor (NRUSM) made of cylindrical piezoelectric material is proposed in this paper. The high reliability is characterized by long lifetime and no outer gas in the vacuum environment, which are ensured by not using stack adhesives as the source of the gas emission. Positioning and tracking accuracy was better than below ±2 nm. The structural design is discussed in terms of the application to a high-speed high-precision stage system which has stable response to frequent biases without interference from resonant phenomena and the required mechanical strength.
Formation Procedure and Microstructural Analysis of Pb7Bi3 (Pb–Bi) Alloy Nanowires
Authors: Kuo Chin-Guo , Lo Shen-Chuan , Chen Jung-Hsuan , Chiang Cheng-Cheng , Chao Chuen-Guang
Published: July 2005

Pb7Bi3 nanowires with a diameter of 80 nm have been fabricated by a centrifugal process, in which the Pb–Bi alloy nanowires formed as the melt was forced into the pores of an anodic aluminum oxide (AAO) template. The nanowires inside the pores of the anodic alumina template could be separated from the remaining metal by a quenching process. X-ray diffraction analysis and energy dispersive X-ray spectroscopy were carried out to determine the composition of the lead-bismuth alloy nanowires. Selected-area electron diffraction and high-resolution electron microscopy investigations indicate that the Pb–Bi alloy nanowire is a single crystal without dislocations and has a hexagonal structure.
Readout Power Dependence of Signal Distribution Observed in Fourier Plane of Focus Spot
Authors: Nakano Takashi , Mashimo Emi , Shima Takayuki , Yamakawa Yuzo , Tominaga Junji
Published: July 2005

We describe the readout-power dependence of the properties optical readout signals, and discuss the super-resolution mechanism in platinum-oxide super-resolution near-field structure (super-RENS) disks. From the Fourier analysis of a focused spot, it is clear that a low-reflectivity region within the beam spot during readout above the threshold readout power is generated in a special-temperature region, which, in turn, is associated with the readout mechanism. These phenomena suggest that such readout is related to a large change in the optical properties of a phase change layer, as proposed in the ferroelectric catastrophe model.
Design of Slider and Suspension for 4×1 Probe Array Type Near-Field Scanning Optical Microscope
Authors: Hong Eo-Jin , Oh Woo-Seok , Park No-Cheol , Yang Hyun-Seok , Park Young-Pil , Lee Sung-Q , Kim Eun-Kyung , Park Kang-Ho
Published: July 2005

Many information storage devices have been introduced and developed in recent years. The trend for these devices is toward high capacity, compact size, low power consumption, reliability, and removability for data interchange with other devices. In addressing these trends, the near-field scanning microscope (NSOM) technique is in the spotlight as the next generation device. In order for a near-field device to be successfully implemented in a system, a slider and suspension must be introduced as actuating mechanisms. Consequently, a suitable slider and suspension needed to be designed. The optical slider should be designed considering near-field optics with the probe structure. The suspension should function generally to support slider performance and track servo capacity in hard disk drives (HDDs). Moreover, the suspension for an optical slider must meet optical requirements, and is also required to satisfy criteria for shock performance in the mobility of the actuator. In this study, the optical slider and the suspension for a near-field probe array are designed and analyzed.
High Response Twin-Objective Actuator with Radial Tilt Function for Blu-ray Disc Recorder
Authors: Kim Seok Jung , Heor Tae Youn , Kim Tae Kyung , Ahn Young Man , Chung Chong Sam , Park Soo Han
Published: July 2005

We have developed Blu-ray Disc (BD) optical pick-up with a twin-objective lens actuator which is compatible with compact disc (CD) and digital versatile disc (DVD) in the high-speed BD-read only memory (ROM) and BD Recorder. In order to readout CD and DVD in BD Recorder, we adopted twin-objective lens actuator in consideration of optical utilization efficiency, optical performance and insurance of sufficient working distance (WD). This twin-objective lens actuator has two objectives in radial direction, one is for CD/DVD and the other is for BD. Through our careful investigation in design process, this actuator has extremely high AC sensitivities and good 2nd resonance characteristics in consideration of twin-objective actuator. Also, this actuator has linearity in wide focus range, that is to say, more than ±1.0 mm and has radial tilt function which is tilt range more than 7 deg.
Photoluminescence Study of the Sol–Gel Derived (Ba0.5Sr0.5) TiO3 Thin Films for the Characterization of Trap States
Authors: Roy Somnath Chanda , Bhatnagar Mukesh Chander , Sharma Ganpat Lal , Karar Nirmalya , Chander Harish
Published: July 2005

Room temperature photoluminescence (PL) spectroscopy was done to investigate luminescent trap states in sol–gel deposited (Ba,Sr)TiO3 thin films. The pre-sintered films showed three distinct PL peaks. Increase in the peak intensity was observed with increase in pre-sintering temperature. These PL peaks were assigned to (a) singly charged oxygen vacancies (b) TiO2 networks and (c) the contribution from the substrate. In contrast, the sintered samples showed only a band-edge luminescence with an intense peak near the band-gap energy. Identification of such observed trap states are important in understanding the results of dielectric measurements because they contribute to the leakage currents and loss mechanisms.
Radial and Tangential-Tilt Servo Using Four-Axis Actuator
Authors: Kawasaki Toshiyuki , Akanuma Goichi , Maeda Ikuo , Kitazawa Tomofumi , Andoh Shunichi
Published: July 2005

A two-axis tilt servo using a four-axis object-lens actuator was developed. The four-axis actuator can tilt the object lens in the radial and tangential directions, and can move it to allow axial tracking or radial tracking. The tilt servo was applied on an optical disc system for next-generation digital versatile discs using a blue-violet laser, and the effect of disc-tilt compensation was determined experimentally. These experiments show that the tilt servo with the four-axis object lens actuator reduces tilt by 0.1 deg in the cases of a disc tangential tilt to 0.43 deg and a disc radial tilt to 0.47 deg.