bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of RF Plasma Using a Magnetic Line-Cusp Field
Authors: Yabe Eiji , Takahashi Keiji , Takayama Kazuo
Published: October 2002

A large-volume cylindrical rf plasma source with a magnetic line-cusp field has been developed for large-scale plasma processing. In this type of plasma source, a capacitively-coupled 13.56 MHz rf plasma is produced in the presence of a magnetic line-cusp field. Two versions of the plasma source have been designed and tested. The first version has peripheral rf electrodes placed outside the ionization chamber, and is suitable for preparing a large-volume uniform plasma. This plasma source can attain a useful area of uniform plasma over a 30-cm-diameter region within 10% nonuniformity. The second version features doughnut-shaped parallel plate electrodes which form part of the chamber wall and serve as high-current sources. The electron density in such a version is proportional to the rf power, being equal to 4×1010 cm-3 at 400 W. The measured electron-energy distribution function showed a Maxwellian distribution function due to the electron-neutral particle collisions arising from drift motion in the magnetic line-cusp field.
Frequency Stabilization of a Semiconductor Laser under Direct Frequency Shift Keying Using the Saturated Absorption Signal
Authors: Sato Takashi , Mizumoto Jun'ichi , Kobayashi Yoshihisa , Ishiguro Makoto , Ohkawa Masashi , Shimba Takeo Maruyama
Published: October 2002

The oscillating frequency of a semiconductor laser was stabilized at the Rb-D2 absorption line under direct frequency shift keying (FSK). The control system equipped with a peak-hold circuit provided the frequency stability of 10-9>σ(2, τ)>10-12 at the averaging time 0.05 s<τ<40 s when the Doppler-limited absorption line was used as a frequency reference. This stability was better than that obtained by the traditional control system without the peak-hold circuit under direct FSK. Using the saturated absorption signal, the frequency stability was improved more than one order of magnitude in comparison with that obtained using the Doppler-limited absorption signal.
Frequency Stabilization of Diode Laser Using External Cavity and Doppler-Free Atomic Spectra
Authors: Utako Tanaka Utako Tanaka , Tsutomu Yabuzaki Tsutomu Yabuzaki
Published: October 2002

We report on the frequency stabilization of a diode laser, in which the long- and short-term stabilities are simultaneously improved. We use an external cavity whose resonance frequency is locked to the center of a Doppler-free spectrum of the 85Rb-D2 line without direct laser frequency modulation. The obtained linewidth of the diode laser is less than 100 kHz and the long-term stability (trackability) estimated from the variation of the error signal is between 2×10-12 and 2×10-14 at the averaging time τ between 100 ms and 100 s. We also propose a conventional method of stabilization of the magnetic field at the Rb cell used for the frequency stabilization.
Frequency Locking of 543 nm He–Ne Laser on Iodine Spectrum
Authors: Ishibashi Toshiaki , Yamashita Masafumi , Tako Toshiharu , Li Yong Chol , Hatakeyama Shigeo , Sakamoto Katsuhira , Inaba Hajime , Akimoto Yoshiaki
Published: October 2002

Frequency tuning of internal-mirror 543 nm He–Ne lasers was realized using a piezo-electric transducer (PZT) through an elastic deformation of the laser tube. Two 543 nm He–Ne lasers were locked on the saturated absorption lines of iodine with the third-derivative signal of a signal-to-noise ratio of about 50. From the beat signal between them the frequency stability was measured to be σ(τ, 2)=1.2×10-11τ-1/2(10-4 s<τ<10 s).
Optical Second-Harmonic Generation of Tetrazole Derivatives
Authors: Sahara Masahiko , Ichioka Hideki , Yano Shinichi , Fujimoto Fumihide , Ehara Masanao , Wakita Katsuya , Sonoda Nobuo
Published: October 2002

Second-harmonic generation (SHG) was investigated for 48 tetrazole compounds. Nine tetrazole compounds were found to generate second harmonic light upon irradiation with Nd:YAG laser light and to have an absorption edge of short wavelength below 350 nm.
Recent Experimental Results on Hydrogen Masers and Time and Frequency Service System at Shanghai Observatory
Authors: Zhai Zao-cheng , Hu Jin-lun , Lin Chuan-Fu , Guan-zong Wang Guan-zong Wang , Su-guang Jian Su-guang Jian
Published: October 2002

The recent activities and research progress on time and frequency (T/F) at Shanghai Observatory are summarized as follows.
  1.  Atomic frequency standards  The features and performance of the hydrogen masers constructed at Shanghai Observatory, and the research of a primary Cs standard are introduced.
  2.  Atomic time scale  The recent progress on Shanghai Observatory's atomic time scale AT(SO) are described. New devices and a new time-measuring system adopted in AT(SO) are also introduced.
  3.  Satellite T/F transfer  Experiments and preliminary results in time synchronization via Chinese communication satellite are discussed.
  4.  Time service and T/F applications  T/F applications in Shanghai Observatory's several research projects such as the very long baseline interferometer (VLBI) system and satellite laser ranging system are described.
Oxygen Clusters in Quenched Czochralski-Si Studied by Infrared Spectroscopy and Positron Annihilation
Authors: Ikari Atsushi , Haga Hiroyo , Uedono Akira , Ujihira Yusuke , Yoda Osamu
Published: October 2002

We studied the formation of oxygen clusters in quenched Czochralski (Cz)-grown silicon crystals. The formation and the dissociation of vacancy-oxygen complexes introduced by electron irradiation (3 MeV, 1×1018 e-/ cm2) were studied by infrared spectroscopy and the positron annihilation technique. From the annealing behavior of vacancy-oxygen complexes, it is found that oxygen clusters are introduced by quenching. These clusters are nuclei for enhanced oxygen precipitation in quenched Cz-grown silicon crystals.
Mechanism of Photostimulated Luminescence Process in BaFBr:Eu2+Phosphors
Authors: Iwabuchi Yasuo , Mori Nobufumi , Takahashi Kenji , Shionoya Terumi Matsuda
Published: October 2002

The formation of photostimulated luminescence (PSL) centers in BaFBr:Eu2+single-crystal phosphors is studied in the 5–9 eV vacuum ultraviolet region. The centers are efficiently formed by the Eu2+photoionization absorption at 6.6 eV. The PSL excitation spectrum after the photoionization excitation is almost the same as that after X-ray excitation. Photoconductivity is generated in the PSL process after the photoionization excitation. These results present further confirmation of the PSL mechanism of Takahashiet al.. [J. Lumin. 31 & 32 (1984) 266]. The numerical analysis of the dependence of the PSL intensity on X-ray excitation intensity, assuming bimolecular kinetics in accord with this mechanism, gives the linear dependence over a very wide range of X-ray intensity under the practical conditions in the PSL applications. Thus the mechanism of Takahashiet al.. is definitely established.
Characterization of Si/SiGe Strained-Layer Superlattices Grown by an Ultrahigh Vacuum/Chemical Vapor Deposition Technique
Authors: Chang Ting-Chang , Chang Chun-Yen , Jung Tz-Guei , Tsai Wen-Chung , Wang Guo-Wei Huang
Published: October 2002

High-resolution double-crystal X-ray diffraction and cross-sectional transmission electron microscopy were used to characterize the Si/SiGe strained-layer superlattices grown by the ultrahigh vacuum/chemical vapor deposition (UHV/CVD) system. A dynamical X-ray simulation was employed to analyze the experimental rocking curves. Good matches between the experimental rocking curves and the simulated ones demonstrate that the high quality Si/SiGe strained-layer superlattices with abrupt interface and excellent thickness and composition uniformity have been achieved. Thickness uniformity was further confirmed by the cross-sectional transmission electron microscopy. In addition, high-resolution double-crystal X-ray diffraction was proven to be a powerful technique for determining the doping level and the thickness of heavily doped contact layer in Si/SiGe device structures prior to further processing. Good wafer-to-wafer uniformity can be simultaneously achieved by the UHV/CVD technique; as a result, the UHV/CVD technique is readily applicable to manufacturing.
Effects of the Variation in the Dose of the Injector Implant on the Endurance Characteristics of Floating Gate Electrically Erasable Programmable Read Only Memory Devices
Authors: Anjan Bhattacharyya Anjan Bhattacharyya
Published: October 2002

We have experimentally observed a dependence of the endurance characteristics of floating gate electrically erasable programmable read only memory (EEPROM) devices on the dose of the injector implant. With an increase in the implantation dose, the memory window closure is enhanced. This phenomenon is explained theoretically by calculating the change in threshold voltage and hence, the amount of charge injected through the tunnel oxide during write/erase cycles for different implantation doses in the injector region.
Novel Approach to Evaluation of Charging on Semiconductor Surface by Noncontact, Electrode-Free Capacitance/Voltage Measurement
Authors: Hirae Sadao , Kohno Motohiro , Okada Hiroshi , Matsubara Hideaki , Nakatani Ikuyoshi , Tatsufumi Kusuda Tatsufumi Kusuda , Takamasa Sakai Takamasa Sakai
Published: October 2002

This paper describes a novel approach to the quantitative characterization of semiconductor surface charging caused by plasma exposures and ion implantations. The problems in conventional evaluation of charging are also discussed. Following the discussions above, the necessity of unified criteria is suggested for efficient development of systems or processes without charging damage. Hence, the charging saturation voltage between a top oxide surface and substrate, V
s, and the charging density per unit area per second, ρ0, should be taken as criteria of charging behavior, which effectively represent the charging characteristics of both processes. The unified criteria can be obtained from the exposure time dependence of a net charging density on the thick field oxide. In order to determine V
s and ρ0, the analysis using the C-V curve measured in a noncontact method with the metal-air-insulator-semiconductor (MAIS) technique is employed. The total space-charge density in oxide and its centroid can be determined at the same time by analyzing the flat-band voltage (V
fb) of the MAIS capacitor as a function of the air gap. The net charge density can be obtained by analyzing the difference between the total space-charge density in oxide before and after charging. Finally, it is shown that charge damage of the large area metal-oxide-semiconductor (MOS) capacitor can be estimated from both V
s and ρ0 which are obtained from results for a thick field oxide implanted with As+ and exposed to oxygen plasma.
High-Pressure Synthesis and Electron Microscopic Study of 1212 Lead Cuprates (Pb, Cu)Sr2(Y, Ca)Cu2Oz
Authors: Akira Ono Akira Ono , Shigeo Horiuchi Shigeo Horiuchi
Published: October 2002

Superconducting 1212 lead cuprates, (Pb, Cu)Sr2(Y, Ca)Cu2O

z

(z>7.0), are synthesized under high pressures of oxygen. They crystallize in a tetragonal or orthorhombic structure, depending on temperature, oxidation state and Ca content. The orthorhombic phase is stable under higher oxidation states. Electron microscopic studies have revealed that an incommensurately modulated structure in the tetragonal phase changes to a nearly commensurate superstructure ( A=a, B=∼3b and C=2c) in the orthorhombic phase. The formation of the superstructure is due to the ordering of lead and copper atoms in the (Pb, Cu)–O sheets. High-pressure samples exhibit superconductivity below 20–60 K, depending on synthesis conditions. The superconductivity is suppressed by a slight increase in oxygen content and decrease in calcium content under the synthesis conditions used in the present study.
Polymer-C60 Composite with Ferromagnetism
Authors: Ata Masafumi , Machida Masataka , Haruo Watanabe Haruo Watanabe , Jun'etsu Seto Jun'etsu Seto
Published: October 2002

An increment of electron paramagnetic absorption was observed in a dimethylformamide (DMF) solution of polyvinylidenefluoride (PVDF) in which C60 was ultrasonically dispersed. A polymer film containing paramagnetic C60 was obtained by vacuum evaporation of the solvent DMF, and the film, which was free from metallic contaminations, exhibited ferromagnetic characteristics even at ambient temperatures. A transmission electron microscope (TEM) observation on thin slices of the sample film showed rod-shaped aggregates of fine crystalline C60 with cross sections of 2–8 µ m which were regularly arrayed and aligned in a certain direction. By laser desorption ionization time-of-flight mass spectroscopy (LDITOF-MS) on the samples, C60 adducts with R (R=H, F, CF3 and polymer fragments) were detected, which seemed to be formed as C60 radical adducts immediately after scission of the polymer chain by sonication. The observed magnetism seems to be carried out by the radical adducts represented as C60R

n

, where n is odd.
Electron Spin Resonance and Mössbauer Studies of CaS:Eu Synthesized Using the Flux Method
Authors: Pham-Thi Mai , Ruelle Nathalie , Tronc Elisabeth , Simons Danielle , Vivien Daniel
Published: October 2002

CaS:Eu phosphors were synthesized using the flux method. ESR and Mössbauer spectroscopies show the coexistence of Eu3+ and Eu2+. Eu3+ and Eu2+ are mainly observed in phosphors obtained with Na2S

z

((Na) phosphors) and K2S

z

fluxes ((K) phosphors), respectively. The Eu2+ fraction in (K) phosphors varies with total Eu content and temperature of synthesis. Under reducing thermal treatment, part of the Eu3+ is converted into Eu2+ in (Na) phosphors, and also in (K) phosphors with Eu content ≤10-3 mole. For the latter phosphors, addition of chloride ions in the flux enhances the Eu2+ level, and after reducing thermal treatment practically all europium ions are in the Eu2+ state. In similar conditions, (K) phosphors with more than 10-2 mole Eu exhibit nearly no Eu2+ level variation, and (Na) phosphors undergo a separation of phases to obtain CaS:Eu3+ and CaS:Eu3+Eu2+. Interpretation of the various features on the basis of Na (K), Eu codoping and dopant-induced lattice distortions is proposed. It is suggested that (K) phosphors are partially oxygenated, with Eu3+ ion charge balanced by K+ ions and/or Ca2+ vacancies.
Continuous Wave GaInAsP/InP Surface Emitting Lasers with a Thermally Conductive MgO/Si Mirror
Authors: Toshihiko Baba Toshihiko Baba , Yukiaki Yogo Yukiaki Yogo , Katsumasa Suzuki Katsumasa Suzuki , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga
Published: October 2002

We have fabricated continuous wave (cw) GaInAsP/InP vertical-cavity surface emitting lasers. For effective carrier confinement, we employed a planar buried heterostructure grown by a single-step maskless regrowth process. In addition, we introduced a novel multilayer mirror consisting of magnesia (MgO) and silicon (Si), which provides high reflectivity and high thermal conductivity simultaneously. Both threshold reduction and improvement of the highest cw temperature were clearly demonstrated by this new mirror; the highest cw temperature of 14° C was achieved with the threshold current of 22 mA. From the comparison of threshold current between cw and pulsed conditions, the increase of device temperature by the cw injection was estimated to be 8–15 K.
Dielectric, Elastic and Piezoelectric Properties of Li2B4O7Single Crystals in the Temperature Range from 4 K to 900 K
Authors: Maeda Masaki , Tachi Hironari , Koichi Honda Koichi Honda , Ikuo Suzuki Ikuo Suzuki
Published: October 2002

Dielectric, elastic and piezoelectric measurement was performed on Li2B4O7in the temperature range from 4 K to 900 K. Superionic properties along thec-axis above 400 K were reconfirmed by dielectric measurement. Temperature dependences of the elastic compliance coefficientss11ands22, the elastic stiffness constantc33, and the piezoelectric constantsd31,d32andd33were measured by the piezoelectric resonance-antiresonance method. Elastic anomalies were found at 375 K in boths11E(s11D) ands22E(s22D), while no anomaly was found inc33E(c33D). Piezoelectric constantd31showed a tiny steplike anomaly andd32exhibited a peak at 375 K, whereas no anomaly was found ind33. These elastic and piezoelectric anomalies are concluded to be caused by a phase transition.
Correlation between ZnSe Crystal Growth Conditions from Melt and Generation of Large-Angle Grain Boundaries and Twins
Authors: Rudolph Peter , Umetsu Kazuyuki , Han Jun Koh Han Jun Koh , Tsuguo Fukuda Tsuguo Fukuda
Published: October 2002

A series of ZnSe crystals for fundamental studies were grown by the vertical Bridgman method under 30 atm inert gas antipressure. A critical relationship between growth velocity and axial temperature gradient for the maintenance of a morphologically stable interface of 1.5×10-2cm2h-1K-1was determined. Furthermore, it has been shown that the number of twins is inversely proportional to the number of large-angle grain boundaries. Finally, the tendency of increasing improvement of the crystal quality with increasing superheating of the melt before the growth run was observed.
Growth of Epitaxial Co/Cu Superlattices with Surface Orientations of (111), (100) and (110) by DC Magnetron Sputtering
Authors: Kingetsu Toshiki , Yoshizaki Fukio
Published: October 2002

Epitaxial Co/Cu superlattices with three major surface orientations of (111), (100) and (110) were successfully grown by dc magnetron sputter deposition with a base pressure of an ultrahigh vacuum. X-ray diffraction profiles suggested that the structures of the interfaces between Co and Cu layers were different among the (111)-, (100)- and (110)-oriented superlattices even when prepared under the same conditions.
Far-Infrared Laser Interferometry Measurements on the STP-3(M) Reversed-Field Pinch
Authors: Shigeyuki Kubota Shigeyuki Kubota , Masaaki Nagatsu Masaaki Nagatsu , Takashige Tsukishima Takashige Tsukishima , Hideki Arimoto Hideki Arimoto , Koichi Sato Koichi Sato , Akio Matsuoka Akio Matsuoka
Published: October 2002

Far-infrared laser interferometry at 432 µm was carried out on the STP-3(M) reversed-field pinch. Measurements along two vertical chords showed a change from a parabolic-like to a flat-like electron density profile after field reversal. A density profile inversion and a correlated toroidal magnetic flux perturbation were also observed during the transition from the current rising to the current decay phase. Measurements of electron density fluctuations indicated relative fluctuation levels of ∼10% for both chords during the current rising phase and ∼5% and ∼15% during the current decay phase for the central and outer chords, respectively. Spectral analysis showed a ∼30 kHz mode consistent with poloidal mode number m=0 magnetic fluctuations, and a ∼90 kHz mode localized to the outer region of the plasma, which was strongly excited during the current decay phase and may be connected to particle and energy transport in STP-3(M).
Quantum Noise of Fourier-Coded Aperture Imaging System
Authors: King Chien Chou
Published: October 2002

The single-grating aperture (SGA) and Fourier aperture (FA) both behave as variable frequency gratings to record the object spectrum directly in a Fourier domain when quantum noise is originally generated in this region. This is in contrast to a stationary coded aperture in which the noise appears in the space domain in the shadow-casting images. The noise properties of SGA and FA imaging systems, using the summation filtered backprojection reconstruction algorithm, have been determined. They are proportional to the square root of the intensity distribution of the object. From the theoretical calculations, signal-to-noise ratios of SGA and FA show the same performance as the SNR of a pinhole camera for small objects. However, for larger objects, SGA and FA show better performance than the pinhole camera. The calculated SNRs of a point and a disc object agree with the experimental results.
Fabrication and Evaluation of Flexible Microgripper
Authors: Yoshihiko Suzuki Yoshihiko Suzuki
Published: October 2002

A new concept of a microgripper using Lorentz force actuation and electrothermal bimorph actuation is presented here. Design, theoretical consideration, fabrication process and characterization results are presented. Many free-standing fingers, ranging from 200 µ m to 1000 µ m in length, have been fabricated successfully by the micromachining process. We have observed the low driving voltage performance and the flexible finger motion of the flexible microgripper (FMG) under the microscope. A 210 µ m deflection of a 1000-µm-long finger was obtained at the input voltage of 1 V.
Highly Selective and Highly Anisotropic SiO2 Etching in Pulse-Time Modulated Electron Cyclotron Resonance Plasma
Authors: Seiji Samukawa Seiji Samukawa
Published: October 2002

A 10–100 µ s modulated electron cyclotron resonance (ECR) plasma is discharged to control the generation of reactive species in high-density, low-pressure plasma. The density ratio of CF2 radicals to F atoms in the CHF3 plasma correlates well with the pulse duration. This is because the generation of reactive species in the ECR plasma depends on time (10–100 µ s). Moreover, we found that a collimated ion flux was generated in the pulsed plasma. This method achieves a high ratio of SiO2 etching selectivity to Si etching and eliminates microloading effects during SiO2 contact hole etching.
Role of Transient Metastable Hexagonal Phase in the Formation of Extended Chain Single Crystals of Vinylidene Fluoride and Trifluoroethylene Copolymers
Authors: Hikosaka Masamichi , Sakurai Katsuyuki , Keller Hiroji Ohigashi
Published: October 2002

Crystallization of vinylidene fluoride and trifluoro-ethylene copolymer, P(VDF/TrFE), with higher VDF molar content (x) than the triple point x (x
tri=0.82) was studied. When the copolymer is crystallized at atmospheric pressure below the melting temperature from the melt, thick extended-chain crystals (ECCs) are formed. It is suggested that the ECCs were formed in the metastable hexagonal phase which appears transiently and then transforms into the stable orthorhombic phase, as has been shown on polyethylene (PE) previously by Rastogi et al.. [Macromolecules 24 (1991) 6384] This suggests the important role of the metastable hexagonal phase in the formation of ECCs, which is discussed by the the chain sliding diffusion theory presented by one of us (M. H.).
Fine Contact Hole Etching in Magneto-Microwave Plasma
Authors: Miyakawa Yasuhiro , Hashimoto Jun , Ikegami Naokatsu , Takayuki Matsui Takayuki Matsui , Jun Kanamori Jun Kanamori
Published: October 2002

Characteristics of fine contact hole etching have been investigated in hydro-fluorocarbon magneto-microwave plasma focusing on the z component of the gradient of magnetic field at 0.0875 T ( dB/ dz) and peak-to-peak voltage of RF bias (V
pp) as parameters. Decrease of dB/ dz drastically decreases the etch rate of boro-phospho silicate glass (BPSG), critical dimension loss (defined as diameter of the top of contact hole minus diameter of the bottom of resist) and selectivity over heavily doped n-type polycrystalline silicon ( n+ poly Si) and resist in fine contact holes. The changes of etching characteristics are correlated with neither F/C ratio nor C1s spectrum of deposited film, but with deposition rate in the region of high V
pp, which presumably reflects the change of incident CF

m

+ ion species with dB/ dz.
Analysis of Fluorocarbon Film Deposited by Highly Selective Oxide Etching
Authors: Akimoto Takeshi , Furuoya Shuichi , Keiichi Harasima Keiichi Harasima , Eiji Ikawa Eiji Ikawa
Published: October 2002

The influence of fluorocarbon film composition on oxide etching selectivity have been studied in a CHF3/CO mixture-gas plasma, using a magnetron-enhanced reactive ion etching system. The Fluorocarbon-film deposition rate dependence on CO concentration was measured. The Sputtering rate and carbon concentration of fluorocarbon films, which were deposited under various CO concentrations, were investigated. With CO addition, the carbon concentration in the fluorocarbon film increases, and the sputtering rate of the deposited film is reduced. High carbon concentration in a deposited polymer can enhance the selectivity of etching by protecting the Si surface from ion bombardment. In addition, an adequate CO mixing can yield a high selectivity of polymer deposition on a Si surface as compared to an oxide surface, which, in turn, achieves a high selectivity in oxide etching on Si.
Radiation Damage of SiO2 Surface Induced by Vacuum Ultraviolet Photons of High-Density Plasma
Authors: Tatsumi Tetsuya , Seiichi Fukuda Seiichi Fukuda , Shingo Kadomura Shingo Kadomura
Published: October 2002

The formation of a surface-damaged layer of gate SiO2 induced by exposure to plasma for gate etching led to the increase in etch rate of SiO2 during HF wet treatment. The effects of vacuum ultraviolet (VUV) photons from various gas plasmas generated by an electron cyclotron resonance (ECR) plasma system and a helicon plasma system were evaluated. It was found that the depth of the damaged layer depends on the energy and penetration depth of VUV radiation. The damaged layer grew exponentially with distance from the surface and was extremely disordered, making it more susceptible to the HF etchant.
The Radical Transport in the Narrow-Gap-Reactive-Ion Etcher in SF6by the Relaxation Continuum Model
Authors: Nobuhiko Nakano Nobuhiko Nakano , Zoran Lj. Petrović  Zoran Lj. Petrović  , Toshiaki Makabe Toshiaki Makabe
Published: October 2002

We have established a selfconsistent modeling of a narrow-gap reactive ion etcher (N-gap-RIE) with parallel-plate geometry in SF6. Using the discharge structure of the relaxation continuum model, we have numerically predicted the radical transport to the surface of N-gap-RIE in SF6under two different surface reactions. The spatiotemporal profiles of radicals and neutrals are demonstrated for a long time scale (0–1 s) at between 0.05 Torr and 1.0 Torr at 13.56 MHz. The estimated etch rate of Si wafer with F radicals agrees reasonably well with the previous experimental value obtained under a low-power condition. It is stressed from the present result that the ion-molecule reactions for the generation of F radicals as well as the electron impact dissociation of SF6are of great importance.
Impact of High-Precision RF-Plasma Control on Very-Low-Temperature Silicon Epitaxy
Authors: Hirayama Masaki , Shindo Wataru , Ohmi Tadahiro
Published: October 2002

A technique for formation of abrupt and arbitrary carrier depth profile in epitaxial silicon film deposited at temperatures as low as 300° C has been developed utilizing an RF-DC coupled-mode bias sputtering system. The effect of ion bombardment energy and ion flux density on the quality of silicon film has been investigated. It was found that the activation level of dopants in the grown silicon film can be widely varied by appropriately controlling the ion bombardment energy while maintaining excellent crystallinity. For controlling the carrier concentrations in the deposited silicon film with an appropriate degree of accuracy, the ion bombardment energy must be precisely controlled with a degree of accuracy higher than 0.5 V, since the properties of the deposited films are very sensitive to the ion bombardment energy. For this purpose, a technique for measurement of the plasma potential is required. While the Langmuir probe technique has been applied to the measurements in DC and also RF discharges, its use in RF discharges has been hindered by the problem of RF interference. Therefore, we have developed advanced Langmuir probes for plasma diagnoses in RF discharges at the plasma excitation frequency of 200 MHz.
Low-Temperature Epitaxial Growth of Si/Si1-xGex/Si Heterostructure by Chemical Vapor Deposition
Authors: Junichi Murota Junichi Murota , Shoichi Ono Shoichi Ono
Published: October 2002

By ultraclean low-pressure chemical vapor deposition (CVD) using SiH4 and GeH4 gases, low-temperature epitaxial growth of Si/Si1-
x

Ge

x

/Si heterostructures at high Ge fractions on Si(100) is achieved. The deposition rate and Ge fraction are controlled by the SiH4 and GeH4 partial pressures and the deposition temperature. Atomically flat surfaces and interfaces for the heterostructures containing Si0.8Ge0.2, Si0.5Ge0.5 and Si0.3Ge0.7 layers are obtained by deposition at 550, 500 and 450° C, respectively. Cross-sectional transmission electron microscope (TEM) images and Raman spectra show that these samples have excellent epitaxial qualities. It is also found that the Si0.5Ge0.5-channel metal-oxide-semiconductor field-effect transistor (MOSFET) has the highest peak field-effect mobility. Moreover, the atomic-layer growth of Si and Ge is achieved by the separation of surface adsorption and reaction of reactant gases. The adsorption processes of SiH4 and GeH4 are found to be described by the Langmuir adsorption-type equation.
High Field Transport of Hot Electrons in Strained Si/SiGe Heterostructure
Authors: Miyatsuji Kazuo , Ueda Daisuke , Masaki Kazuo , Yamakawa Shinya , Hamaguchi Chihiro
Published: October 2002

Monte Carlo simulation of two-dimensional electron gas in strained Si/SiGe heterostructures has been carried out to investigate the high electric field transport phenomena. In the Monte Carlo simulation we take into account the intervalley scattering due to the f-type phonons between twofold and fourfold valleys of Si well layer split by the tensile strain in addition to the g-phonon scattering. We obtained the electron drift velocity at room temperature of as high as 1×107 cm/s at 10 kV/cm. Calculated results at 4.2 and 77 K show negative differential mobility beyond 10 kV/cm. At 77 K, transient response of the drift velocity shows a marked overshoot reaching about 3×107 cm/s at 0.2 ps and 10 kV/cm. Ohmic mobility calculated using self-consistent wave functions is also demonstrated. Results are given for the strained Si well width of 10 nm. Obtained low field electron mobility at high temperatures shows a good agreement with the experimental results reported so far.
Vertical Si-Metal-Oxide-Semiconductor Field Effect Transistors with Channel Lengths of 50 nm by Molecular Beam Epitaxy
Authors: Harald Gossner Harald Gossner , Ignaz Eisele Ignaz Eisele , Lothar Risch Lothar Risch
Published: October 2002

The growth conditions in molecular beam epitaxy (MBE) were studied for the fabrication of vertical Si-metal-oxide-semiconductor field effect transistors (MOSFET) with channel lengths down to 50 nm. The short channel length imposes severe constraints on the doping profile. MBE growth provided a steepness of 10 nm/dec for boron and 2 nm/dec for antimony. The sharpness of the doping profile was sustained throughout the process by keeping all process temperatures below 700° C. The high crystal quality and the well-defined doping profile was verified by the good performance of a triangular barrier diode. A vertical n-MOSFET with an estimated channel length of 50 nm was grown. The drain and gate characteristics were discussed for a source drain voltage regime from U
sd=0 V to 1 V.
Schottky/Two-Dimensional Hole Gas Silicon Barrier Diodes with Single and Coupled Delta-Doped Wells
Authors: Wang Shui Jinn , Wu San Lein , Fang Yuh Yeh Fang Yuh Yeh , Ching Yuan Cheng Ching Yuan Cheng
Published: October 2002

A Schottky/two-dimensional hole gas (2DHG) barrier diode based on boron δ-doped silicon grown by molecular beam epitaxy has been fabricated for the first time. The advantages of the coupled δ-doped well structure over the single δ-doped well structure have been investigated both theoretically and experimentally. Preliminary measurements on the single and coupled δ-doped well devices including the current-voltage ( I-V ) and capacitance-voltage ( C-V ) characteristics are reported. Reverse breakdown voltages of over 50 V and 35 V were obtained for the single and coupled δ-doped devices, respectively. The coupled δ-doped layer diode exhibits a lower series resistance and a larger C-V nonlinearity as compared to those of the single δ-doped device, which is favorable for higher RC cutoff frequency Schottky/2DHG barrier diode fabrication.
Semi-Insulating Substrate Effects on Pure GaAs Epilayers
Authors: Hwang Yun Taek , Cha Sang Suk , Lee Byung Chul , Lee Young Hee , Lim Kee Young , Suh Eun-Kyung , Choi Choon Tae , Hyung Jae Lee Hyung Jae Lee
Published: October 2002

Unintentionally doped GaAs layers were grown on semi-insulating GaAs substrates by metal-organic chemical vapor deposition. Temperature-dependent electrical transport measurements were performed and the layer characteristics were derived by a two-layer analysis. The substrate begins to affect the layer transport properties at low temperatures, depending on the carrier density and the layer thickness. The p-type samples show two conductivity-type conversions at two different temperatures. One is a combined transport phenomenon of the layer and substrate, and the other occurs in the layer but is still influenced by the substrate. A two-band model involving light- and heavy-hole bands was adopted in analyzing the hole transport in the layer, and the light hole was determined to play a crucial role even with its very small effective mass compared to the heavy hole.
Preparation of Some Rare-Earth Borates (R, Bi)(Al, Ga)3(BO3)4 with Huntite Structure by Flux Method
Authors: Chani Valery I. , Shimamura Kiyoshi , Inoue Keiji , Sasaki Takatomo , Tsuguo Fukuda Tsuguo Fukuda
Published: October 2002

Huntite structure crystals with a basic formula (R, Bi)(Al, Ga)3(BO3)4 (R=Yb, Er, Ho and its combinations) have been grown by spontaneous crystallization in molten fluxes based on the Bi2O3–B2O3. X-ray powder diffraction patterns and cell parameter data are reported. In (Ho, Bi)(Al, Ga)3(BO3)4, (Yb, Er, Bi)(Al, Ga)3(BO3)4 and Cr:(Er, Bi)(Al, Ga)3(BO3)4 crystals, the second harmonic generation effect was observed.
GaAs/AlGaAs Quantum Well Infrared Detectors with an Integral Silicon Grating
Authors: Gou-Chung Chi Gou-Chung Chi , Cheng Juang Cheng Juang
Published: October 2002

Single quantum well GaAs/AlGaAs infrared photodetectors (QWIPs) with an integral silicon grating have been fabricated. An enhancement of radiation coupling efficiency over a 45° bevel device is observed at 77 K. In addition, this technology enables the device to detect normally incident infrared radiation from the substrate side and makes possible the practical packaging of detector arrays.
Temperature Influence on the Generalized Einstein Relation for Degenerate Semiconductors with Arbitrary Band Structures
Authors: Chyan Yih-Feng , Sze Simon Ming , Chang Chun-Yen , Liao Kenneth , Reif Rafael
Published: October 2002

We present a systematic study of the temperature influence on the generalized Einstein relation for degenerate semiconductors with different band structures. The conventional Einstein relation is still a good approximation at very high temperatures for most carrier concentrations but becomes invalid at low temperatures for highly degenerate semiconductors. As the temperature rises, higher energy bands with small minimum energy separations ( e.g., from Γ band to L band) and large density-of-state effective masses will have a larger fraction of carriers, because the minimum energy separations become comparable to the thermal energy. Thus, from 500 K to 1200 K, in n-type GaAs and n-type Ge, we observe kinks in the D/µ versus carrier concentration curves. However, no such kinks are observed in n-type Si due to its large minimum energy separations. Similarly, p-type Ge and p-type GaAs show no kinks, because the energy of the spin-orbit splitting in these semiconductors is large compared to the thermal energy.
Chemical Treatment Effect of Si Surfaces in 1NH4OH:XH2O2:5H2O Solutions Studied by Spectroscopic Ellipsometry
Authors: Takahiro Suzuki Takahiro Suzuki , Sadao Adachi Sadao Adachi
Published: October 2002

Chemically treated Si(111) surfaces in 1NH4OH: X H2O2:5H2O ( X=0.025–2.0) solutions at 80°C have heen studied using spectroscopic ellipsometry (SE). The SE data clearly indicate that the solutions cause in surface chemical oxidation. The oxidation occurs immediately upon immersing the samples in the solutions. The thickness of the chemical oxide shows a saturated value of ∼11.5 Å, independent of the H2O2 concentration, within our experimental X range.
Epitaxial Growth of CeO2 Films on Si(111) by Sputtering
Authors: Yaegashi Seiji , Kurihara Toshiya , Hideo Hoshi Hideo Hoshi , Hideo Segawa Hideo Segawa
Published: October 2002

CeO2 films were epitaxially grown on Si(111) substrates by reactive sputtering following the single-crystal CeO2 seed layer formation by oxygen-reactive solid-phase epitaxy. Formation of metallic Ce layers and oxidation of the layers prior to reactive sputtering was found to be the key process for epitaxial growth of CeO2 on Si substrates. An Auger electron spectroscopy depth profiling analysis showed that the Ce–Si interlayer was formed after the Ce metal deposition. Reflection high-energy electron diffraction and transmission electron microscopy proved that epitaxial CeO2 films were grown by reactive sputtering on the seed layers formed by oxidation of Ce metal layers with thickness of 5 to 10 nm. Crystalline quality of the films depended on the sputtering conditions, especially on total sputtering pressure and oxygen concentration. The optimization of the conditions for seed layer formation by oxygen-reactive solid-phase epitaxy and reactive sputtering was an important factor for improving the crystalline quality of epitaxially grown CeO2 film.
Structural Characteristics of Combination Oxide Consisting of Dry Thermal SiO2 and Sputtered SiO2
Authors: Bhan Rajinder Kumar , Mathur Renganathan Ashokan
Published: October 2002

The infrared transmission characteristics of “combination oxides” consisting of initially growing a thin thermal SiO2 layer (to achieve interface properties equivalent to thermal SiO2) followed by sputter deposited SiO2, for bulk oxide growth (a low temperature deposition process), are studied to see the feasibility of substituting these oxides for dry thermal silicon oxides. In this study, “combination oxides”, grown on both p- and n-type silicon substrates were compared with dry thermal oxides of identical thicknesses. The infrared transmission results indicate that the vibration frequency (v) and full-width at half-maximum (FWHM) of dominant IR active mode of combination oxides differ only by ≈7 cm-1 from those of dry thermal oxides, thereby indicating a comparable stoichiometery of the former oxides to the latter.
A Very Low Level DC Current Amplifier Using Photocoupler Negative Feedback Circuit
Authors: Ikuo Nakamura Ikuo Nakamura , Hiroki Higa Hiroki Higa
Published: October 2002

In order to improve the response speed of a very low level dc current amplifier, we propose a novel method in which a photocoupler, instead of a high resistor (1010 Ω), is employed for the negative feedback circuit. In this paper, it is shown experimentally that with the proper use of positive feedback, the rise time t
r of 10 µs is obtained for this circuit at the current sensitivity of 10 pA. In comparison, the t
r with the use of the high resistor with the shielding plate is 120 µs. (Here, the current sensitivity is the minimum measurable input signal current that produces an output signal voltage of a very low level dc current amplifier equal to its output noise voltage, or that leads to a signal-to-noise ratio of unity.)
Generalized Ultrasonic Percussion: Imaging of Ultrasonic Nonlinear Parameters and Its Medical and Industrial Applications
Authors: Takuso Sato Takuso Sato
Published: October 2002

Imaging of parameters of nonlinearity in ultrasonic waves is considered as a generalization of doctor's percussion, where some kinds of perturbations are given and the responses are observed by means of ultrasonic detection. The concept and possibilities of its application are reviewed, and details of two examples of practical measuring systems are shown. One is a new medical diagnostic system and the other is a nondestructive testing system of characterizing the states of metal.
Sonochemical Application of Ultrasound to Tumor Treatment
Authors: Shin-ichiro Umemura Shin-ichiro Umemura
Published: October 2002

We recently found that chemical agents such as hematoporphyrin can be activated by ultrasound, producing significant antitumor effects. This was demonstrated with plane wave insonation at 2 MHz in experiments of killing isolated tumor cells. The efficacy of focal ultrasound at 750 kHz to localize sonochemical reactions was also demonstrated in insonation of a specially developed agarose gel phantom and in treatments of inoculated experimental tumors.
Ultrasonic Absorption Anomaly of Brain Tissue
Authors: Etoh Akinori , Mitaku Shigeki , Yamamoto Jun , Okano Koji
Published: October 2002

The internal friction of bovine brain tissue has been studied by the measurements of longitudinal ultrasonic propagation in the megahertz region and Young's modulus in the frequency region from 10 to 1000 Hz. The ultrasonic absorption of bovine brain tissue increased monotonously as the frequency was decreased. The imaginary part of Young's modulus appeared to have a finite value at the lower frequency limit. The results of the two kinds of mechanical measurements led to the conclusion that apparent viscosity of brain tissue increased anomalously as the frequency decreased from 5 MHz to 10 Hz. There are two possible mechanisms for the ultrasonic behaviors of brain tissue: anomalous absorption due to the existence of lamellar structures and very broad distribution of relaxation phenomena. Experimental methods to determine the contribution of the two mechanisms were discussed based upon the essential difference in the expected behaviors of the real part of moduli.
Measurement of Static and Dynamic Elastic Moduli of Shape Memory Alloys
Authors: Tonokawa Takashi , Morito Shigekazu , Nakajima Yoichi , Ooishi Akira , Otsuka Kazuhiro , Tetsuro Suzuki Tetsuro Suzuki
Published: October 2002

The mechanism of the so-called rubberlike elasticity in shape memory alloys such as Au–Cd and Cu–Au–Zn alloys is investigated using the measurement of static and dynamic elastic moduli. A large difference between the static and dynamic elastic moduli is found. While the dynamic modulus remains almost unchanged during room-temperature annealing for 3 days, the static modulus increases appreciably during the same annealing, corresponding to the appearance of the rubberlike elasticity. These experimental results are discussed in terms of the pseudoelasticity due to twin boundary motion.
Bulk Acoustic Wave Filter Using Piezoelectrically Coupled Resonators
Authors: Takehiko Uno Takehiko Uno
Published: October 2002

New configurations for bulk acoustic wave (BAW) filters suitable for the ultra high frequency (UHF) band are proposed. In contrast with a monolithic crystal filter, the resonators of the proposed filter are electrically coupled through a piezoelectric film deposited on the filter substrate. Equivalent circuit analysis and simulation results are described. The simulation results suggest the possibility of BAW filters in the UHF band. Because the proposed filter is suitable for the silicon diaphragm structure, development of highly sophisticated integrated electronic circuits with piezoelectric filters is expected.
Epitaxially Grown Aluminum Film on 36° -Rotated Y-Cut Lithium Tantalate for High-Power Surface Acoustic Wave Devices
Authors: Sakurai Atsushi , Yukio Yoshino Yukio Yoshino , Hideharu Ieki Hideharu Ieki
Published: October 2002

Epitaxially grown Al film was obtained on 36°-rotated Y-cut LiTaO3 substrate by an IBS system. The epitaxial relation was (111)<10 1̄>Al//(012)<100>LiTaO3. The Al film had very high resistance to stress migration. In SAW filters, time to failure caused by stress migration was improved by more than 100 times over an ordinary polycrystalline Al–Cu film.
Nanometer Electrode Fabrication Technology Using Anodic Oxidation Resist and Application to Unidirectional Surface Acoustic Wave Transducers
Authors: Kazuhiko Yamanouchi Kazuhiko Yamanouchi , Toshiyasu Meguro Toshiyasu Meguro , Yasuo Wagatsuma Yasuo Wagatsuma , Hiroyuki Odagawa Hiroyuki Odagawa , Keiichi Yamamoto Keiichi Yamamoto
Published: October 2002

Nanometer lithography technology is very important for high density integrated circuits and higher-frequency-range surface acoustic wave (SAW) devices. The frequency ranges of SAW devices extend to around 10 GHz; therefore a sub-micron technology below 0.1 µm is required. In this paper, we propose new lithography techniques for nanometer fabrication using very thin anodic oxidation films. Since very thin resists (less than 50 nm) can be used in this process, a narrow resist pattern and electrodes can be obtained. The results show the 75 nm width of an interdigital transducer (IDT) made of aluminum with thickness of 30 nm on 128° Y-X LiNbO3. SAW experimental results show the 17 GHz-range characteristics. Also, new lithography technologies are applied to 2 GHz low-loss filters using a unidirectional transducer.
Surface Acoustic Wave Multiple Phase Shift Keying Modulator-Demodulator Circuits
Authors: Araki Nobushige , Komine Kenji , Hara Motoaki , Ueno Hiroaki , Hohkawa Kohji
Published: October 2002

Multiple phase shift keying technology is effectively used in various communication systems because of its high-capacity data transmission capability along a restricted passband. This-paper proposes a high-performance offset quadri-pulse shift keying modulator and demodulator with a new simple circuit configuration employing surface acoustic wave (SAW) devices. We propose two types of modulators (modulation and pulse pattern generation method) and a demodulator with a differential-operation SAW device. A fundamental experiment verified the feasibility of the circuits.
Welding Characteristics of Ultrasonic Wire Bonding Using High-Frequency Vibration Systems
Authors: Tsujino Jiromaru , Takahiro Mori Takahiro Mori , Koichi Hasegawa Koichi Hasegawa
Published: October 2002

Welding characteristics of ultrasonic wire bonding using 60 kHz, 90 kHz and 120 kHz complex vibration as well as 190 kHz linear vibration welding systems are studied. The locus shapes of the complex vibration welding tip are controlled from linear to elliptical or circular. Aluminum wire specimens of 0.1 mm diameter are welded successfully using complex and high-frequency welding equipment. The required vibration amplitudes of these complex vibration systems are about one-half to one-third and required weld time is shorter than those of a conventional system of linear vibration. The required vibration velocity of a high-frequency system is lower than that of a low-frequency system. The deformations of the welded specimens under adequate welding conditions are almost the same, even if the welding tip vibration locus is altered from linear to elliptical or circular, or the vibration frequency used is changed from 60 kHz to 190 kHz in the case where the same wire specimens are used. Using these methods, the weld strength of wire bonding becomes independent of the difference in the directions of the welding tip vibration and wire length.