bluuebunny/crossref_metadata_2025 huggingface dataset:
(Ba, Sr)TiO3 Films Prepared by Liquid Source Chemical Vapor Deposition on Ru Electrodes
Authors: Kawahara Takaaki , Yamamuka Mikio , Akimasa Yuuki Akimasa Yuuki , Kouichi Ono Kouichi Ono
Published: October 2002

Electrical properties of (Ba, Sr)TiO3 [BST] films have been investigated on
RuO2/Ru and Ru electrodes instead of Pt, because they are easy to be etched. BST
films were deposited at a substrate temperature of T
s=420° C and a reactor pressure of
P=1.5 Torr by employing a two-step liquid source chemical vapor deposition (CVD)
process. BST films on RuO2/Ru were electrically shorted, which was considered to be
caused by surface roughening during BST film deposition and/or post-annealing. In
the case of Ru electrodes, an equivalent SiO2 thickness of t
eq=0.50 nm (a dielectric
constant of ε
r=190), a leakage current of J
L=4.6×10-8 A/cm2 at +1.1 V, and a
dielectric loss of tan
δ=0.018 were achieved at a total film thickness of 250 Å, by
restricting Ru surface oxidation and its surface roughening. Moreover, BST film
deposition on Ru storage nodes, 0.24 µ m wide, 0.6 µ m deep, 0.15 µ m high, and
each spaced by 0.3–0.14 µ m, verified that the storage capacitance can be successfully
increased by using sidewalls of the storage node, without a significant increase in the
leakage current.
Analysis of the Dependence of Ferroelectric Properties of Strontium Bismuth Tantalate (SBT) Thin Films on the Composition and Process Temperature
Authors: Noguchi Takehiro , Takashi Hase Takashi Hase , Yoichi Miyasaka Yoichi Miyasaka
Published: October 2002

Ferroelectric properties, crystal structure and microstructures were examined for various Sr/Bi/Ta atomic ratio strontium bismuth tantalate (SBT) films prepared by metalorganic decomposition at 700 and 800° C. The 20% Sr-deficient and 10% Bi-excess (0.8/2.2/2) composition showed maximum remanent polarization (P
r) values for both 700 and 800° C crystallization temperatures. From TEM analysis, the
P
r dependence on composition variation around the stoichiometric 1/2/2 composition was related to grain size and volume of voids. The effect of postannealing after Pt top electrode fabrication was also studied. On the films prepared at 800° C, postannealing markedly reduced the capacitor shorting rate. This was attributed to recrystallization of the Pt top layer, based on SEM analysis of the Pt layer and the Pt/SBT interface.
Piezoelectric Ceramic Oscillator Using Damped Capacitance Elimination Technique
Authors: Kazumasa Ohnishi Kazumasa Ohnishi , Katsutoshi Sakurai Katsutoshi Sakurai , Yoshiro Tomikawa Yoshiro Tomikawa , Chiharu Kusakabe Chiharu Kusakabe
Published: October 2002

The temperature stability of a piezoelectric ceramic oscillator is improved, using the damped capacitance elimination technique, which is performed using an operational amplifier circuit.
In order to improve the temperature stability, an electrostatic capacitance such that its temperature characteristic can cancel a change of the oscillation frequency is also applied in the circuit.
The theoretical principle of the damped capacitance elimination circuit and the experimental results are described.
The circuit proposed here is effective in improving the temperature stability of the piezoelectric ceramic oscillator.
Deflection of Light at the Boundaries between Ferroelectric and Antiferroelectric States in Chiral Smectic Liquid Crystals
Authors: Hiroyuki Uehara Hiroyuki Uehara , Shinji Ogawa Shinji Ogawa , Syuichi Tatemori Syuichi Tatemori , Jun Hatano Jun Hatano , Shin-ichi Saito Shin-ichi Saito , Hideo Saito Hideo Saito , Eiji Okabe Eiji Okabe
Published: October 2002

A light deflection phenomenon was observed at a field-induced phase transition point between an antiferroelectric state and ferroelectric one in antiferroelectric liquid crystals.
The dependence of the angle of deflection on the angle of incidence was numerically analyzed, and it was concluded that the light deflection is due to refraction and reflection at the boundaries between the states coexisting at the field-induced phase transition point.
A similar deflection phenomenon was also observed in the ferroelectric and ferrielectric phases at zero electric field.
Possible phases or domains coexisting in this condition were discussed.
Low-Temperature Sintering of Pb(Mg1/3Nb2/3)O3–PbTiO3 Ceramics with Addition of PbO–Bi2O3
Authors: Futakuchi Tomoaki , Tanino Katsumi , Furukawa Kazuhiro , Adachi Masatoshi , Kawabata Akira
Published: October 2002

The Low-temperature sintering has been examined in the
preparation process of Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics. The
sintering temperature could be reduced from 950° C to 800° C by
addition of PbO–Bi2O3 as a lower-melting-point sintering aid.
The dielectric constant of 16000 and loss tangent of 0.02 were
obtained for Pb[(Mg1/3Nb2/3)0.95Ti0.05]O3 ceramics fired at 800° C
with 2 mol% of PbO–Bi2O3. These low-temperature sintering
dielectric materials are very promising for use in fabrication of
printed thick-film capacitors.
Morphotropic Phase Boundary and Dielectric Properties of V 2O 5-Containing SrxBa 1-xNb 2O 6 ( 0.2 ≤x ≤ 0.4) Ferroelectrics
Authors: andMasayoshi Kishi Shiro Nishiwaki
Published: October 2002

Sr
x
Ba1-x
Nb2O6 (0.2 ≤x ≤0.4: SBN) ceramics were fabricated by pressureless sintering with the addition of V2O5 (1 mol%) which considerably accelerated grain growth.
X-ray diffraction analysis of elongated grains indicated that there is a morphotropic phase boundary between x=0.25 (tetragonal) and x=0.225 (orthorhombic) in the SBN system.
The sharpening of a ferroelectric phase transition peak was maximum at x=0.2.
This corresponded to a cation distribution in which the A2-sites in the tungsten bronze structure were fully occupied by Ba2+ ions.
A phase transition temperature diagram was developed for the present composition region.
Dielectric Properties of Ca1-xSm2x/3TiO3–Li1/2Ln1/2TiO3 Ceramics
Authors: Yoon Ki Hyun , Chang Yoon Hee , Kim Woo Sup , Kim Jae Beom Kim
Published: October 2002

The physical and microwave dielectric properties of Ca1-
x

Sm2
x
/3TiO3–Li1/2Ln1/2TiO3 (Ln=Sm, Nd)
have been investigated as a function of the degree of Sm substitution (x = 0.0 –1.0). As the
calcium vacancy concentration increased with increasing Sm substitution, high Q ·f values were
obtained due to the formation of a superlattice. The Q ·f values of the specimens with Nd increased
throughout the entire composition range, due to the formation of complete solid solutions, while
those of the specimens with Sm increased up to the solid solution limit x = 0.6, and then decreased
due to the formation of a secondary phase Sm2Ti2O7. Dielectric constant (K) and temperature
coefficient of resonant frequency (T
C
F) decreased linearly with increasing Sm substitution. In the
(1- y)Ca2/5Sm2/5TiO3– yLi1/2Sm1/2TiO3 system, the microwave dielectric properties could be controlled
by the variation of y. Typical values of K = 95.5, Q ·f = 7200 and T
C
F = 0 ppm/°C were
obtained for 0.67Ca2/5Sm2/5TiO3–0.33Li1/2Sm1/2TiO3.
Source/Drain Ion Implantation into Ultra-Thin-Single-Crystalline-Silicon-Layer of Separation by IMplanted OXygen (SIMOX) Wafers
Authors: Mitsutoshi Takahashi Mitsutoshi Takahashi , Yutaka Sakakibara Yutaka Sakakibara , Jyoji Nakata Jyoji Nakata
Published: October 2002

Problems associated with ion implantation into ultra-thin-film SIMOX (Separation by IMplanted OXygen) of SOI (silicon on insulator) structures are discussed. We realized n-type source/drain region with lower resistance by P+ ion implantation. To decrease the resistance of the implanted layer, the amorphized high-dose layer must be recrystallized by annealing. We show that the possibility of recrystallization can be predicted by TRIM simulation. Moreover, it was found that excess phosphorus above the solid solubility segregates in the Si/SiO2 interface.
Band Edge Disorder Producing Urbach's Tail and Enhanced Photochromic Efficiency Caused by Density of States inside Band Gap in Tungsten Oxide Films
Authors: Kubo Takaya , Nishikitani Yoshinori , Nobuyuki Kuroda Nobuyuki Kuroda , Mitsuo Matsuno Mitsuo Matsuno
Published: October 2002

The band gap of WO3 and its disorder at the band edge were evaluated, assuming Urbach's rule, and flat-band potentials (V
fb s) were also measured on WO3 films with high photochromic efficiency (HPE) and low photochromic efficiency (LPE). The main results are as follows: 1) the optical absorption of LPE- WO3 sets on at higher photon energy than that of HPE- WO3, 2) HPE- WO3 has the density of states deeper in the band gap than LPE- WO3 does, and 3) V
fb of HPE- WO3 is higher than that of HPE- WO3. These results indicate that the band edge disorder of WO3, which is closely related to Urbach's tail, determines the Fermi level position, and therefore makes V
fb high; they also imply that a high V
fb dissociates optically excited electrons and holes to make colors center resulting in photochromism at a high efficiency.
Electroreflectance Study of (AlxGa1-x)0.5In0.5P Alloys
Authors: Adachi Sadao , Ozaki Shunji , Sato Masahiro , Ohtsuka Kouji
Published: October 2002

Electroreflectance spectroscopy has been applied to the study of (Al

x

Ga1-
x

)0.5In0.5P quaternary systems lattice-matched to GaAs. The measurements are made at room temperature in the photon-energy range of 1.7–5.8 eV. The composition dependence of the E
0, E
0+Δ0, E
1, E
2 and E
2+δ gaps has been determined. The lowest direct band gap is found to be given by E
0(x)=1.90+0.57x+0.11×2 eV. The E
0+Δ0, and E
1 gaps are written as similar quadratic equations. On the other hand, the variation of the E
2 and E
2+δ gaps is found to be approximately linear. The lowest direct-to-indirect gap crossover is also estimated to occur at x∼0.63.
Formation of Columnar from Poly(p-Methylethynylbenzene) Polymerized Using [Rh(norbornadiene)Cl]2 as a Catalyst. An X-Ray and ESR Study
Authors: Tabata Masayoshi , Sadahiro Yoshikazu , Kazuaki Yokota Kazuaki Yokota , Shin Kobayashi Shin Kobayashi
Published: October 2002

Columnar polymers of p-methylethynylbenzene (MEB) were synthesized using [Rh(norbornadiene)Cl]2 as a catalyst in alcohol. Polymers having a cis-transoid structure were selectively formed at high yields. The structure and properties of the polymers were analyzed by means of X-ray diffraction and ESR methods. The data showed that the pristine amorphous polymer was converted to a pseudohexagonal columnar one when it was treated with toluene at room temperature. Formation of columnar polymers was also demonstrated by the increase in the linewidth in the ESR spectra of the polymer obtained by the toluene treatment of the pristine amorphous polymer, indicating that a magnetically inhomogeneous line broadening mechanism operates among the radical spins which are heterogeneously distributed in the columnar phase.
Investigation of Buffer Iayer of Cubic GaN Epitaxial Films on (100) GaAs Grown by Metalorganic-Hydrogen Chloride Vapor-Phase Epitaxy
Authors: Miura Yoshiki , Takahashi Naoyuki , Akinori Koukitu Akinori Koukitu , Hisashi Seki Hisashi Seki
Published: October 2002

Cubic GaN epitaxial layers are grown with GaN buffer layers of various thicknesses on (100) GaAs substrate using (CH3)3Ga, HCI and NH3 as starting materials. The full width at half-maximum (FWHM) of the X-ray peak, the surface roughness and the PL spectra show that the optimum thickness of the GaN buffer layer ranges from 20 to 50 nm. It is found by high-resolution TEM and electron diffraction measurements that a GaN buffer layer grown at 500° C is a polycrystal and becomes a single crystal upon thermal annealing at 850° C for 10 min prior to the growth of a cubic GaN epitaxial layer.
Noncontact Measurement of Generation Lifetime
Authors: Kohno Motohiro , Hirae Sadao , Okada Hiroshi , Matsubara Hideaki , Nakatani Ikuyoshi , Imaoka Yasuhiro , Tatsufumi Kusuda Tatsufumi Kusuda , Takamasa Sakai Takamasa Sakai
Published: October 2002

In this paper, we discuss the measurement of minority carrier generation lifetime by the noncontact metal-insulator-semiconductor (MIS) method. This method enables electrical measurements on metal-air-insulator-semiconductor (MAIS) structure utilizing the air gap and is based on the conventional MIS theory. Capacitance-time ( C-t) measurement is employed for the lifetime evaluation in this method. The generation lifetime and the surface generation velocity are determined by Zerbst analysis, similar to the case of a conventional MIS capacitor formed with gate electrodes. For Si substrate with a long lifetime, the conventional MIS method has the disadvantage of long measurement time. However, MAIS structure reduces the measurement time by increasing the air gap distance. This is because the air gap is equivalent to a thick oxide film. In our experiment, metal-contaminated Si wafers were used to compare the MAIS method with the conventional MIS method in terms of the generation lifetime. The experimental results obtained from the two methods showed good agreement.
Determination of the Stokes-Poincaré Parameters for a Synchrotron X-Ray Beam by Multiple Bragg Scattering
Authors: Hirano Keiichi , Mori Takeharu , Iida Atsuo , Colella Roberto , Sasaki Satoshi , Shen Qun
Published: October 2002

Elliptically polarized X-rays were produced by means of a phase retardation plate. The Stokes-Poincaré parameters of the X-ray beam were determined by recording azimuthal scans of 3-beam diffraction profiles using a non-centrosymmetric crystal.
Ordering and Associated Domain Structures in Zinc and Silicon Doped Ga0.51In0.49P and GaxIn1-xAsyP1-y Layers Grown on GaAs by Metalorganic Vapour Phase Epitaxy
Authors: Seong Tae-Yeon , Kim Do Geun , Jang Dong Hoon , Lee Jung Kee
Published: October 2002

Transmission electron microscope (TEM) and transmission electron diffraction (TED) studies have been made of Zn- and Si-doped Ga0.51In0.49P and Ga

x

In1-
x

As

y

P1-
y

layers grown on (001) GaAs substrates to examine CuPt-type atomic ordering and associated domain structures. The ordering was dependent on the doping levels of Si and Zn atoms. The ordering was also found to depend on composition variations in GaInAsP layers. As for the GaInP layer, the ordered domains as viewed in [001] plan-view showed complicated structures with a density of antiphase boundaries (APBs) and were of width ∼0.5 to ∼1.2 µ m. It was suggested that surface steps associated with surface undulations have a major influence on the domain structures. Mechanisms were proposed to explain how the domain structures arise.
Preparation of High-Quality Undoped Microcrystalline Silicon with High Deposition Rate Using Mercury-Sensitized Photochemical Vapor Deposition Method
Authors: Jae Hoon Jang Jae Hoon Jang , Koeng Su Lim Koeng Su Lim
Published: October 2002

We prepared undoped microcrystalline silicon films (µ c- Si:H) using a mercury-sensitized photochemical vapor deposition system under various film deposition conditions of SiH4/(SiH4+H2) gas ratio and total gas flow rate, and investigated the dependence of the film quality on the deposition conditions in order to obtain high-quality undoped microcrystalline films at a high deposition rate. Up to a SiH4/(SiH4+H2) gas ratio of ∼0.1, the crystallite size of the µ c- Si:H films decreased linearly as the ratio increased, but the volume fraction of crystallites remained constant at about 80%. The dark conductivity of the films was very low, in the range of 10-7–10-6 Scm-1 under nearly all experimental conditions, and so a high photosensitivity of ∼550 was obtained without the addition of a dopant gas such as diborane. In addition, a high deposition rate of ∼30 Å/min was obtained at a low total flow rate of 21 sccm. No degradation of the microcrystallinity was observed for the low total flow rate.
High-Performance In0.5Al0.5As/In0.5Ga0.5As High Electron Mobility Transistors on GaAs
Authors: Kudo Katsuhiko Higuchi , Mitsuhiro Mori Mitsuhiro Mori , Tomoyoshi Mishima Tomoyoshi Mishima
Published: October 2002

InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-mismatched on GaAs substrates have been fabricated with a 0.6-µ m- thick step-graded In

y

Al1-
y

As buffer layer and a low-source-resistance triple cap layer. A peak extrinsic transconductance of 1060 mS/mm was obtained for a device with a 0.16-µ m- long gate due to both the low source resistance of 0.35 Ω mm brought by the triple cap layer and the high quality In0.5Ga0.5As channel brought by the step-graded In

y

Al1-
y

As buffer layer. This transconductance is comparable to or higher than that of HEMTs lattice-matched on InP substrates. A maximum oscillation frequency, f
max, of 127 GHz and a cutoff frequency, f
t, of 47 GHz were obtained for a fully-passivated device with a 0.66-µ m- long gate, giving a high f
max/f
t ratio of 2.7. This f
max is comparable to those of HEMTs lattice-matched on InP with the same gate length.
Proposal of New Interconnection Technique for Very High-Voltage IC's
Authors: Fujihira Tatsuhiko , Yano Yukio , Obinata Shigeyuki , Kumagai Naoki , Sakurai Kenya
Published: October 2002

A new, cost-effective, high-voltage interconnection technique for very high-voltage IC's, called the “self-shielding technique”, is proposed. To avoid reduction of the breakdown voltage of high-voltage devices due to the electric potential of overlying interconnections, only the self-PN-junction structures of the high-voltage devices themselves are utilized in the self-shielding technique. No additional shielding structure is required, even to realize a very high-voltage IC above 1000 V. The design concept and device structures are presented with the experimental results on the electrical characterictics of self-shielded interconnections and on the operations of self-shielded 1200-V level shifters. Comparison between self-shielded and conventional high-voltage IC's (HVIC's) and the process and the devices of self-shielded HVIC technology are also described.
Improvement of Threshold Voltage Uniformity in Ion-Implanted GaAs-Metal-Semiconductor Field-Effect Transistors on Si
Authors: Moritani Akihiro , Tachikawa Akiyoshi , Jono Aiji , Aigo Takashi , Ikematsu Yoichi , Sano Yoshiaki , Yamagishi Chouho , Akiyama Masahiro
Published: October 2002

The macroscopic and microscopic threshold-voltage (V
th) uniformities in GaAs-metal-semiconductor field-effect transistors (MESFET's) fabricated by ion implantation to metal-organic chemical vapor deposition (MOCVD)-grown GaAs-on-Si wafers are extensively evaluated for their application to integrated circuits. A novel technique has been adopted to reduce the dislocation density in a confined region around the gate electrode of each FET by annealing under the stress generated between GaAs epilayers and a SiO2 passivation film with a window in the confined region. Reduction of the dislocation density in this area due to the stress annealing is clearly discovered in cross-sectional and planview transmission electron microscope (TEM) measurements. A combination of the stress annealing and the formation of buried p-layers markedly reduces the scatter of threshold voltage to as low as 20 mV in 0.5-µm-gate self-aligned MESFET's on 3′′ GaAs-on-Si wafers.
Anomalous Photoinduced Change in Threshold Voltage of Current-Controlled Negative Resistance in Si p-i-n Diodes Doped with Gold
Authors: Ma Laina , Kimura Hideki , Akiba Yukio , Tateki Kurosu Tateki Kurosu , Masamori Iida Masamori Iida
Published: October 2002

An anomalous photoinduced change in the threshold voltage of silicon p-i-n diodes doped with gold atoms has been studied. Under photoillumination, it was observed that the threshold voltage of current-controlled negative resistance was larger than that in darkness. Using several gold-doped samples, the current-voltage characteristics were measured under photoillumination at various ambient temperatures. It was found that the anomalous phenomenon is observed under constant photoillumination in a particular range of ambient temperature, i.e., at this temperature the density of thermally generated carriers is less than that of optically generated carriers.
A Broadband Passive Optical Network with Low Multiple Optical Carrier Interference
Authors: Wen-Piao Lin Wen-Piao Lin
Published: October 2002

In this paper, we report a method for obtaining low multiple optical carrier interference noise in a broadband passive optical network (BPON). The technique for reducing the optical interference involves a laser diode at each subscriber loop with strong sine wave modulation. The results show that the optical interference can be reduced to a low level even when the spectra of all the optical sources overlap. Other significant experimental results are as follows. (1) The end-to-end optical power budget of a network for bidirectional transmission is as high as 24.45 dB when three upstream signals are transmitted. (2) The network can be extended to at least 20 optical network units (ONUs).
Epitaxial Stress Effect on Crystallographic Properties of Bi4Ti3O12 Heterostructures and Their Leakage Current Behaviors
Authors: Watanabe Yukio , Matsumoto Yasuaki , Tanamura Mitsuru
Published: October 2002

Three dimensionally aligned epitaxial Bi4Ti3O12 films were grown on SrTiO3 (001) and LaAlO3 (001) substrates with and without a semiconductive La2CuO4 bottom layer. The leakage current and crystallographic properties of Bi4Ti3O12 were found to be markedly different from ABO3-type ferroelectric such as Pb(Zr, Ti)O3, BaTiO3, and SrTiO3. The d-spacings of Bi4Ti3O12 depend markedly on the substrate material, suggesting that the amount of misoriented domains formed to relieve epitaxial stress was less than that in ABO3-type ferroelectrics. This epitaxial stress effect was observed even in relatively thick films 1500 Å thick. Furthermore, the time dependence of the leakage current in Bi4Ti3O12 was substantially reduced compared to those in the ABO3-type ferroelectrics.
Chemical Treatment Effect of Si(111) Surfaces in H2SO4:H2O2 Solution
Authors: Kobayashi Kazuyuki , Unno Hiroyuki , Takizawa Hidekazu , Sadao Adachi Sadao Adachi
Published: October 2002

Chemically treated Si(111) surfaces in an H2SO4:H2O2=4:1 (sulphuric peroxide mixture; SPM) solution at 80° C have been studied using spectroellipsometry (SE), ex situ atomic force microscopy (AFM) and contact-angle measurement techniques. The SE data clearly indicate that the solution causes in surface chemical oxidation. The oxidation occurs immediately upon immersing the sample in the solution. The thickness of the chemical oxide layer shows a nearly saturated value of ∼14 Å. The SE data also indicate that the chemical oxidation and subsequent HF etching result in surface smoothing, in reasonable agreement with the AFM results. The SPM-treated surface is found to be highly hydrophilic.
Synthesis and Magnetic Properties of Non-Equilibrium Eu-Rich EuO Thin Films
Authors: Konno Toyohiko J. , Ogawa Norihiro , Wakoh Kimio , Kenji Sumiyama Kenji Sumiyama , Kenji Suzuki Kenji Suzuki
Published: October 2002

EuO thin films have been formed by reactive evaporation, in which O2 gas was introduced in the form of a molecular beam directed toward a substrate. In order to optimize preparation conditions, we varied the substrate temperature, T
s, and the ratio of the Eu vapor to O2 gas deposition rates, R. The structure and magnetic properties of the films were measured by X-ray diffraction and a super-conducting interference device (SQUID) magnetometer. Non-stoichiometric EuO films can be produced more easily at T
s=200° C than at T
s=300° C. Choosing an appropriate value of R at T
s=200° C, we obtain Eu-rich EuO films with the Curie temperature of about 150 K. The present method is based on the control of reaction kinetics, and is superior to the post-oxidation method of Eu-metals with respect to the formation of Eu-rich EuO films.
Evaluation of Hyperpolarizability of Nonlinear Optical Organic Molecules by Hyper-Rayleigh Scattering
Authors: Kodaira Takuo , Watanabe Akira , Ito Osamu , Matsuda Minoru , Clays Koen , Persoons Andre
Published: October 2002

The hyperpolarizability β of nonlinear optical (NLO) organic molecules was determined by the hyper-Rayleigh scattering (HRS) technique. The β values obtained by using the HRS technique were compared with the values calculated using a semiempirical molecular orbital (MO) method, and good agreement between these values was obtained. The solvent dependence in the HRS measurements was also investigated for NLO organic molecules using p-dioxane and methanol. A specific interaction between the solute and solvent was concluded to influence the β value.
On the Theory of Optical Gain of Strained-Layer Hexagonal and Cubic GaN Quantum-Well Lasers
Authors: Park Doyeol Ahn
Published: October 2002

The optical gains of strained-layer hexagonal and cubic GaN quantum wells are calculated within the multiband effective mass approximation. The 6×6 multiband effective-mass Hamiltonians are used to calculate the band structures of hexagonal and cubic quantum wells. Non-Markovian relaxation is taken into account in the optical gain calculation. Calculated results show that the optical gains of the cubic quantum well are larger in magnitudes than those of the hexagonal GaN quantum well over the wide range of carrier densities.
Characterization of Residual Stress in Active Region due to AlAs Native Oxide of Vertical-Cavity Surface-Emitting Lasers
Authors: Hatori Nobuaki , Mukaihara Toshikazu , Abe Makoto , Ohnoki Noriyuki , Mizutani Akimasa , Matsutani Akihiro , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga
Published: October 2002

The stress effect of an AlAs oxide layer which is formed near the active region to confine carriers in vertical-cavity surface-emitting lasers (VCSELs) has been discussed. From the result of micro-photoluminescence measurement, it has been shown that there is no significant residual stress to the active region originating from the AlAs oxide layer.
Optical Properties of Fluorescent Polyimide Langmuir-Blodgett Films Containing 2,5-Distyrylpyrazine
Authors: Wu Aiping , Akagi Tsutomu , Jikei Mitsutoshi , Kakimoto Masa-aki , Imai Yoshio
Published: October 2002

UV-visible absorption and photoluminescence, originating from the 2,5-distyrylpyrazine (DSP) chromophore incorporated into the polymer backbone of polyamic acid and polyimide were demonstrated in the Langmuir-Blodgett (LB) films. The formation of an aggregated structure with a large Stokes shift and a weak emissive intensity was observed in the cases of the polyamic acid 1 and the polyimide 3 LB films. In-plane anisotropic optical properties manifested by the polymer LB films indicated that the DSP chromophores were highly oriented parallel to the dipping direction. Meanwhile, photo-polymerization of the DSP chromophores was observed in the polyimide 3 LB film. This suggested that a three dimensional network structure was formed in the polymer LB film.
Etching Studies of Solution-Grown Crystals: (100) Faces of Mixed Crystals of Potassium Dihydrogen Orthophosphate and Ammonium Dihydrogen Orthophosphate (KDP-ADP)
Authors: Suparna Sen Gupta Suparna Sen Gupta , Siba Prasad Sen Gupta Siba Prasad Sen Gupta
Published: October 2002

We have critically examined the growth conditions to obtain transparent and moderate single crystals of K1-
x

(NH4)

x

H2PO4 over the entire range of composition by several tests. Defect configurations of as-grown mixed crystals have been studied by chemical etch technique with greater details. Various interesting patterns like growth hillocks, pyramids, trisection of boundaries and branching of dislocations were clearly observed on the etched surfaces of mixed crystals. Optical and scanning electron micrographs show a good correspondence between etch pits and dislocations.
Smectic Layer Rotation in the Smectic A Phase of Ferroelectric and Antiferroelectric Liquid Crystals
Authors: Keizo Nakayama Keizo Nakayama , Masanori Ozaki Masanori Ozaki , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

Smectic layer rotation in the smectic A phase of ferroelectric and antiferroelectric liquid crystals has been observed by applying asymmetric voltage pulses. The layer rotates over the field-induced tilt angle due to the electroclinic effect. The rotation is reversible. Namely, the layer rotates in the opposite direction upon applying pulses of opposite polarity. The electroclinic effect plays an important role in this phenomenon.
Effects of Multiple Shock and Thermal Conduction on Mixing Layer Evolution in a Stagnating High-Gain Inertial Confinement Fusion Target
Authors: Sunahara Atsushi , Takeuchi Hajime , Hideaki Takabe Hideaki Takabe , Kunioki Mima Kunioki Mima
Published: October 2002

We have investigated the effects of multiple shock waves and electron thermal conduction coupled with the Richtmyer-Meshkov instability in a stagnating system of inertial confinement fusion (ICF) by 2D simulations. We found that the multiple shock waves enhance the small wave number perturbation modes due to the inverse-cascade process from large wave number modes, and the final spectra are almost independent of the initial spectra. Due to the Richtmyer-Meshkov instability, the mixing layer of the interface grows and enhances the cooling of the hot spark region by an inflow of cool and dense fuel material. The cooling effect is compatible to that by electron thermal conduction. However, the ablation of the fuel material caused by the thermal conduction suppresses the growth of the large wave number modes. Therefore, although both cooling effects is present in the stagnating system, the cooling of the hot spark region are not markedly enhanced.
Experimental Study of Conventional and Multipass Thomson Scattering Diagnostic Systems
Authors: O. Campos Delton , A. Berni Munemasa Machida , Michail Kantor Michail Kantor , Stanislav A. Moshkalyov Stanislav A. Moshkalyov , Sergei V. Lebedev Sergei V. Lebedev
Published: October 2002

A low-cost, simple and effective multipass structure was built and tested for the first time in a theta-pinch device, the compact torus TC-1. A detailed analysis of the gain in the scattered signal produced by the multipass system is presented. The use of a multipass geometry for Thomson scattering experiments in theta-pinch devices or in more dense plasmas as well as in plasmas with higher Z
eff is recommended for increasing the relationship between scattered and bremsstrahlung signals.
Rational Function Approximation of Nuclear Scattering Cross-Section Function
Authors: Shyh-Wei Wang Shyh-Wei Wang , Shuang-Fa Guo Shuang-Fa Guo
Published: October 2002

The one-variable scattering cross-section function f(η) proposed by Lindhard, Nielsen and Scharff (LNS) is approximated by a rational function using the minimax algorithm in this work. Taking an ingenious transformation of the variable η, this approximation is about one order of magnitude faster than other approximations in the literature. To maintain a reasonable accuracy, we divide the wide variable range into two regions. In addition, an adaptive integration method is adopted to compute the scattering angle and the nuclear stopping power in order to get accurate f(η) data.
Electron Beam Direct Writing Techniques for the Development of Sub-Quarter-Micron Devices
Authors: Fujino Takeshi , Maeda Hiroshi , Kimura Yoshika , Horibe Hideo , Imanaga Yuji , Shinkawata Hiroki , Nakao Shuji , Kato Takaaki , Matsui Yasuji , Makoto Hirayama Makoto Hirayama , Akihiko Yasuoka Akihiko Yasuoka
Published: October 2002

Novel techniques for electron beam (EB) direct writing are established for the development of sub-quarter micron devices. These techniques include 1) use of highly stable processes for positive and negative chemical amplification resists, 2) precise pattern size control by way of proximity effect correction using the pattern-area-density method, 3) a practical improvement technique for pattern size error at the exposure-field boundary, and 4) a novel alignment technique for a substrate covered with a heavy metal film. Successful fabrication of sub-quarter-micron test devices indicates that variable-shaped EB direct writing using these techniques is the best tool for research and development of advanced devices.
Reducing Proximity Effects in Optical Lithography
Authors: Chris A. Mack Chris A. Mack
Published: October 2002

Using simulation, the influence of stepper parameters on optical proximity effects is explored. In particular, numerical aperture and partial coherence will be examined for a variety of feature sizes and types. Both one-dimensional and two-dimensional mask features will be studied. The impact of resist contrast will also be explored. In addition to the iso-dense print bias as a metric of proximity effects, the depth of focus as an overlapping of two focus-exposure process windows, one for the isolated line and one for the dense line, will be used. The optimum NA and σ will give the maximum depth of focus calculated from the overlapped process window. Finally, the statistical CD distribution methodology will be used to find the stepper settings that minimize the linewidth distribution spread for a given process.
Precision Improvement in Optical Proximity Correction by Optimizing Second Illumination Source Shape
Authors: Akihiro Nakae Akihiro Nakae , Kazuya Kamon Kazuya Kamon , Tetsuro Hanawa Tetsuro Hanawa , Koichi Moriizumi Koichi Moriizumi , Shuji Nakao Shuji Nakao
Published: October 2002

We have achieved precision improvement by optimizing the second illumination source shape in our optical proximity correction system. Based on the consideration that the optical proximity effect is significantly dependent on interference conditions, we have applied a new type of modified illumination to projection optics in order to improve the correction accuracy. A new second illumination source is formed by an illumination aperture with a spindle-shaped opaque region, whose curvature is the same as that of the projection lens pupil. Through use of this aperture, pattern edges can be definitely classified according to the interference condition, and resultant improvement of the pattern size accuracy, within ±0.01 µm, which is nearly the same level as the detection limit, can be achieved.
Printing Isolated Features with k 1= 0.2 Using Multiple-Pupil Exposure
Authors: Rudolf M. von Bünau Rudolf M. von Bünau , Hiroshi Fukuda Hiroshi Fukuda
Published: October 2002

Recently, we have investigated the effects of radially non-symmetric pupil filters and multiple-pupil exposure sequences in optical lithography [to appear in: Proc. SPIE 2726 (1996)]. Based on numerical simulations we predicted that extremely narrow lines could be delineated using the superposition of exposures with symmetric and anti-symmetric pupil functions. Here, we present experimental results verifying this prediction. Using conventional masks and a pupil filtering i-line stepper with a numerical aperture of 0.4, we were able to achieve linewidths of 0.18 µm in 1.0 µm thick positive photoresist, with a depth of focus of 1 µm.
Fabrication of High-Resolution Fresnel Zone Plates by a Single Layer Resist Process
Authors: Hiroshima Hiroshi , Komuro Masanori , Gentili Massimo , Grella Luca , Fabrizio Enzo Di , Maggiora Romano
Published: October 2002

In this work, fabrication of a high-resolution Fresnel zone plate (ZP) by a single layer electron beam (EB) resist process combined with a gold electroplating process is described. The ZP designed has a diameter of 80 µm and is composed of 250 rings (499 zones) of which the width of the outermost ring is nominally 40 nm. In order to fabricate a 150-nm-thick gold layer which acts as a phase-shifter for X-rays, a 200-nm-thick polymethylmethacrylate (PMMA) is used as a single layer resist. A 50 kV EB lithography system with a probe diameter of 3 nm is employed for high-resolution patterning. To prevent resist patterns with an aspect ratio of 5 from collapsing, we reinforce the ZP patterns by combining neighboring rings with ribs. It is demonstrated that a modified ZP pattern with a 40-nm-wide outermost ring which will not collapse can be fabricated whereas the original ZP pattern collapses at a high aspect ratio. Although control of the width of the gold phase shifter should be improved, the outermost ring with the nominal width of 40 nm can be electroplated.
Fabrication of InAlAs/InGaAs High-Electron-Mobility Transistors Using ArF-Excimer-Laser-Assisted Damage-Free Highly Selective InGaAs/InAlAs Etching
Authors: Takazawa Hiroyuki , Takatani Shinichiro , Katsuhiko Higuchi Katsuhiko Higuchi , Makoto Kudo Makoto Kudo
Published: October 2002

Highly selective etching of InGaAs/InAlAs assisted by a 193 nm ArF excimer laser in HBr and F2 atmosphere is used as a gate-recess technique to fabricate InAlAs/InGaAs high-electron-mobility transistors (HEMTs). The HEMT with an Al/Ti gate shows a gate ideality factor of 1.2 and an effective Schottky barrier height of 0.55 eV. For a 0.7 µ m×18 µ m device, a maximum extrinsic transconductance of 610 mS/mm is obtained. The extrinsic transconductance of the HEMT is stable for more than 6 weeks, whereas degradation of the extrinsic transconductance is observed in a device fabricated by etching using citric acid. Enhancement of InGaAs/InAlAs selectivity is caused by formation of a nonvolatile AlF

x

thin layer on the InAlAs surface, as shown by the X-ray photoemission spectroscopy (XPS) measurements. The good gate electrical characteristics and long-term transconductance stability are attributed to the Al deficiency of the etched surface after the postetching wash. These results demonstrate that this excimer-laser-assisted selective-etching technique is useful for fabricating damage-free, high-performance InAlAs/InGaAs HEMTs.
Micropatterning of Ferroelectric Bi 4Ti 3O 12 Using Electron-Beam-Induced Reaction of Metal Octylate Films
Authors: Soichiro Okamura Soichiro Okamura , Yukie Yagi Yukie Yagi , Shizutoshi Ando Shizutoshi Ando , Takeyo Tsukamoto Takeyo Tsukamoto , Katsumi Mori Katsumi Mori
Published: October 2002

Micropatterning of ferroelectric Bi4Ti3O12 was carried out using an electron-beam-induced reaction of metal octylate films. Bismuth and titanium octylates were used as starting materials. Precursor solutions were prepared by mixing the octylates at a Bi:Ti molar ratio of 5.2:3.0 and diluting with acetone. The metal octylates exhibited negative exposure characteristics upon electron beam irradiation: a sensitivity of 1.5 ×10-4 C/cm2 and a gamma value of 2. Precursor micropatterns were formed by electron beam irradiation on the spin-coated octylate films and successive development with toluene. The precursor micropatterns were calcined at 450°C for 10 min and sintered at 800°C for 30 min in air. A 65 ×80 µm2 precursor micropattern was crystallized into the single-phase of Bi4Ti3O12 by the heat treatment. Crystallized square micropatterns 1 µm in size consisted of small platelike crystals.
Fabrication of a New Si Field Emitter Tip with Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) Structure
Authors: Hirano Takayuki , Kanemaru Seigo , Hisao Tanoue Hisao Tanoue , Junji Itoh Junji Itoh
Published: October 2002

A current-controllable silicon field emitter tip with a metal-oxide-semiconductor field-effect transistor (MOSFET) structure is fabricated. The device has a simple structure in which a conical Si tip is made in the drain region of a MOSFET. The gate performs two roles; one is that of a conventional extraction gate and the other is that of a control gate for the drain current supplied to the tip. The fabrication process is very simple. In order to form n-type regions for the source and drain, only two steps including a self-aligned ion implantation were added to the conventional silicon tip fabrication process. Experimental results showed that the emission current was well controlled and stabilized by the drain current of the MOSFET. Stable emission of about 0.8 µA was obtained with a single tip. We also discuss a dual-gate MOSFET for further extension of the fabrication process introduced.
Site Control of Ga Droplet Array on CaF 2 by Surface Modification Using a Focused Electron Beam
Authors: Koji Kawasaki Koji Kawasaki , Kazuya Uejima Kazuya Uejima , Kazuo Tsutsui Kazuo Tsutsui
Published: October 2002

Site-controlled Ga droplet formation on CaF2 film by means of focused electron beam exposure was applied to the fabrication of a two-dimensional ordered nanostructure array. The proximity effect of this method was investigated as a function of the period of the dot array and the electron dose per dot site. A two-dimensional Ga droplet array, in which the diameter of each droplet was approximately 20 nm, with a 100 nm period was obtained. The minimum period which can control the formation site was found to be related to the exposed region at the As/CaF2 interface, and may be reduced by improving the process conditions such as by using a small beam spot and a thinner As film.
Thermal Desorption Spectroscopy of (Ba, Sr)TiO3 Thin Films Prepared by Chemical Vapor Deposition
Authors: Yamamuka Mikio , Kawahara Takaaki , Makita Tetsuro , Akimasa Yuuki Akimasa Yuuki , Kouichi Ono Kouichi Ono
Published: October 2002

Thermal desorption characteristics of (Ba, Sr)TiO3 [BST] thin films prepared by metalorganic chemical vapor deposition (CVD) using liguid sources have been studied, together with their crystallinity and electrical properties. Thermal desorption was observed for CO2 at 400° C and 900° C, and CO at 600° C. The intensities of the CO2 peaks at 400° C and 900° C increased with the increasing atomic composition ratio of (Ba+Sr)/Ti, in relation to the excess Ba and Sr in the BST films; in particular, the CO2 peak at 900° C may originate from BaCO3 and/or SrCO3 lumps formed in the films, and the CO2 peak at 400° C may be attributed to gases adsorbed on the sites of contaminants such as BaO

x

and/or SrO

x

in films, due to excess Ba and Sr coming from the atmosphere after deposition. On the other hand, the CO peak at 600° C occurred most strongly from BST films with high dielectric constants at (Ba+Sr)/Ti∼1, or perovskite crystalline structures having large grains. Moreover, the desorption of CO at 600° C was also observed from films kept in the atmosphere after annealed above 600° C in vacuum. These results imply that the BST crystalline perovskite grains may have adsorption sites for CO from the atmosphere.
Monte Carlo Simulation of RF Plasmas and Trial Investigation of Similarity Rule
Authors: Yoshiomi Kondoh Yoshiomi Kondoh , Atsushi Onozato Atsushi Onozato , Akio Matsuoka Akio Matsuoka , Masayoshi Ishii Masayoshi Ishii , Makoto Goto Makoto Goto , Minoru Sugawara Minoru Sugawara
Published: October 2002

Detailed properties of RF plasmas sustained by an RF external source of 13.56 MHz and 270 V are presented using self-consistent Monte Carlo simulations in an Ar-like model gas. It is shown that most of the RF external electric field is absorbed in the sheath regions and ions cannot follow the RF field. The time-dependent distribution of the number of excitation collisions is shown to give a physical picture of the moving sheath boundary which oscillates with the RF electric field. It is shown that a lower gas pressure yields a distribution with a wider sheath region which gives dominantly the capacitive component of impedance. A trial investigation of the similarity rule for the bulk region of RF plasmas is presented with respect to the electric field, the electron density, the conduction current density, and the mean electron velocity in the direction of the current.
Determination of Optical Constants of Polyquinoxalines as Electroluminescent Materials
Authors: Fukuda Takashi , Kanbara Takaki , Yamamoto Takakazu , Nakao Satoru , Ishikawa Ken , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: October 2002

We have determined the optical constants of poly(quinoxaline-5,8-diyl) and five of its 2,3-disubstituted derivatives using the pseudo-Brewster angle technique at six wavelengths (457.9, 488.0, 514.5, 632.8, 800.0 and 1064 nm). The refractive indices are fitted to Sellmeier's dispersion formula to estimate the wavelength dispersions of the refractive index in these polymers. The differences in the refractive indices of the six polymers were interpreted based on linear polarizability and free volume. The free volume of the repeating unit for each polymer estimated using Lorentz-Lorenz's relation is consistent with the size of the side chain. These polyquinoxalines with low refractive indices are promising for use as electroluminescent materials.
New Optical-Waveguide Pockels Sensor for Measuring Electric Fields
Authors: Tsuguhiro Takahashi Tsuguhiro Takahashi , Kunihiko Hidaka Kunihiko Hidaka , Teruya Kouno Teruya Kouno
Published: October 2002

An optical electric field sensor using a Pockels crystal which has the advantage of directly measuring the electric field in a space with limited disturbance of its distribution has been studied. We present an optical waveguide technique which has been developed to miniaturize the sensor. In a prototype sensor a light beam is propagated along a z-direction waveguide in a y-cut LiNbO3 crystal. The width of the waveguide is 7 µ m and its length is 4.39 mm. The sensor is not based on an interferometer but on a single waveguide. The sensor has a simple and optimum configuration, and its output has good linearity to applied electric fields. Its frequency and temperature characteristics are presented. A new and smaller sensor with a waveguide 1 mm in length has been developed. It has almost the same configuration as the prototype sensor except for a smaller size. Results of measurement of ac and step electric fields using this sensor are presented.
Impact of Nitrogen Implantation on Highly Reliable Sub-Quarter-Micron Metal Oxide Field-Effect Transistors (MOSFETs) with Lightly Doped Drain Structure
Authors: Shimizu Satoshi , Kuroi Takashi , Kusunoki Shigeru , Okumura Yoshinori , Masahide Inuishi Masahide Inuishi , Hirokazu Miyoshi Hirokazu Miyoshi
Published: October 2002

We studied the effects of nitrogen implantation in the SiO2 sidewall spacer in detail in order to improve in the reliability of lightly doped drain (LDD) metal oxide field-effect transistors (MOSFETs), since the hot carrier degradation of LDD MOSFETs remains one of major issues even in the sub-quarter-micron region. It was found that nitrogen implantation in the SiO2 sidewall spacer can effectively suppress the hot carrier degradation of the LDD structure because the nitrogen atoms are segregated at the interface between the sidewall SiO2 and the Si substrate. This segregation can reduce the generation of interface states or electron traps in the sidewall spacer without causing gate depletion or an increase in gate resistance. Highly reliable sub-quarter-micron LDD N-MOSFETs can be realized using this nitrogen implantation technique.
Large 1/f Noise in Polysilicon TFT Loads and its Effects on the Stability of SRAM Cells
Authors: Aoki Masaaki , Hashimoto Takashi , Nagano Toshiaki Yamanaka
Published: October 2002

We have observed very large drain current fluctuations over time in polysilicon thin film transistors (TFTs). The noise with 1/f power spectra in TFTs is found to be about 104 times larger than that in single-crystalline Si metal oxide semiconductor (MOS) transistors. The influence of 1/f noise in TFTs on static random access memory (SRAM) cell stability is clarified for the first time. Maintaining a high on-current and lowering of the grain-boundary barrier are found to be essential for increasing stability.
Influence of Statistical Spatial-Nonuniformity of Dopant Atoms on Threshold Voltage in a System of Many MOSFETs
Authors: Tomohisa Mizuno Tomohisa Mizuno
Published: October 2002

We have experimentally and analytically studied the influence of the statistical spatial-nonuniformity of dopant atoms on the threshold voltage V
th in a system of many metal-oxide-semiconductor field-effect-transistors (MOSFETs). According to experimental results and our analytical model, it is found that the nonuniformity of dopant atoms along the channel (the lateral nonuniformity) causes the unstable drain bias V
d dependence of V
th, whereas the standard deviation of V
th has weak dependence of V
d. Moreover, the substrate bias dependence of V
th fluctuates due to the vertical nonuniformity of dopant atoms which is perpendicular to the channel. Consequently, V
th fluctuation is caused by the statistical spatial-nonuniformity of dopant atoms as well as their total-number variation in the channel depletion volume.