bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation-Free Frequency Stabilization of a Grating-External-Cavity Diode Laser by Magnetically Induced sub-Doppler Dichroism in Cesium Vapor Cell
Authors: Wang Junmin , Yan Shubin , Wang Yanhua , Liu Tao , Zhang Tiancai
Published: February 2005

Thanks to the Zeeman effect and the saturation absorption spectroscopic technique, magnetically induced sub-Doppler dichroism has been experimentally demonstrated in a cesium vapor cell. A dispersion-like frequency-discriminating signal is obtained by this sub-Doppler dichroism. The phase-sensitive detection via lock-in is no longer required because there is no frequency dither on the laser. A grating-external-cavity 852 nm diode laser is frequency-stabilized to cesium 6 2S1/2 F = 4–6 2P3/2 F' = 4, 5 crossover by this modulation-free locking scheme. Compared with a frequency fluctuation of approximately 12 MHz under free-running conditions, a typical frequency jitter of less than +/- 260 kHz in 50 s was estimated in the preliminary stabilization. This locking scheme is relatively simple, and it can avoid extra noise due to the direct frequency dither on the laser source in the conventional saturation absorption locking technique.
High Sensitive X-ray Microcalorimeter Using Bi–Au Microabsorber for Imaging Applications
Authors: Kudo Hiroyuki , Arakawa Takahiro , Ohtsuka Shinichiro , Izumi Toshiyuki , Shoji Shuichi , Sato Hirotaka , Kobayashi Hideomi , Mori Kentaro , Homma Takayuki , Osaka Tetsuya , Iyomoto Naoko , Fujimoto Ryuichi , Mitsuda Kazuhisa , Yamasaki Noriko Y. , Oshima Tai , Futamoto Kazuo , Takei Yoh , Ichitsubo Taro , Fujimori Tamayuki , Ishisaki Yoshitaka , Morita Umeyo , Koga Takeo , Shinozaki Keisuke , Sato Kousuke , Ohashi Takaya , Kuroda Yoshikatsu , Onishi Mitsunobu , Otake Kunio , Beppu Fumiaki
Published: February 2005

An X-ray microcalorimeter is a cryogenic energy-dispersive spectrometer, which has an energy resolution almost comparable to that of conventional wavelength-dispersive spectrometers. Using a transition edge sensor (TES) as a temperature sensor, the energy resolution can be further improved. We have developed a new method of achieving an array of TES microcalorimeters for the purpose of X-ray imaging. To achieve this, mushroom-shaped X-ray microabsorbers formed using electrodeposition were applied. The temperature of the TES, which is easily degraded by thermal diffusion, was kept sufficiently low throughout the process to achieve practical use. On the bases of this new method, a 2×2 (× 4) array of TES microcalorimeters was fabricated and tested. A high energy resolution of 13.0 eV at 6 keV was achieved and the filling factor was improved to 83%. Although several issues still need to be investigated, we verified that our method is useful for fabricating a Ti–Au TES microcalorimeter array.
Optimization of Low-Energy Electron Beam Proximity Lithography Stencil Mask Structure Factors by Monte Carlo Simulation
Authors: Kim Chiho , Kang In-Yong , Chung Yong-Chae
Published: February 2005

Low-energy electron beam (e-beam) proximity lithography (LEEPL) is a notable next-generation lithography (NGL) technology. This study was performed to search for the most optimized structure of the LEEPL mask. The acceleration voltage of the e-beam and the angle of the pattern wall were taken as variables for our simulation. We calculated the energy and the coordinate of each electron with various possible combinations of these variables. Using this procedure, the count and angular distribution of electrons transmitted through a Si mask were analyzed. For the 50-nm-linewidth processing, the dependencies of the electron count distribution and the electron angular distribution on the pattern wall angle were very high in the case of using relatively high acceleration voltage such as higher than 2 keV.
Monte Carlo Study of X-ray Generation from Film/Substrate Structure by Electron Impact
Authors: Hibi Takaaki , Nagatomi Takaharu , Takai Yoshizo , Obori Ken-ichi , Awata Syogo , Yurugi Toshikazu
Published: February 2005

The Monte Carlo (MC) simulation of X-ray emission from film/substrate structures induced by electron impact was investigated. The developed MC simulation enables the calculation of the absolute X-ray spectrum consisting of continuous, characteristic K-line and fluorescent X-rays without any fitting parameters. The samples used were 40- and 78-nm-thick Ti films on Al, Cu and Zr substrates. These samples have atomic number combinations of Z
film<Z
sub, Z
film≈Z
sub and Z
film>Z
sub. An excellent agreement between the simulation and experimental X-ray spectra was observed for the wide range of the primary energy of electrons from the threshold energy of the K-shell ionization of each element to ∼30 keV.
Simultaneous Measurement of Growth and Movement of Cells Exploiting On-Chip Single-Cell Cultivation Assay
Authors: Umehara Senkei , Hattori Akihiro , Wakamoto Yuichi , Yasuda Kenji
Published: February 2005

We have developed an on-chip single-cell microcultivation assay as a means of simultaneously observing the growth and movement of single bacterial cells during long-term cultivation. This assay enables the direct observation of single cells captured in microchambers fabricated on thin glass slides and having semipermeable membrane lids, in which the cells can swim within the space without escape for the long periods. Using this system, the relationship between the cell cycle and the tendency of movement was observed and it was found that the mean free path length did not change during the cell cycle, and that the growth and the swimming were not synchronized. The result indicates that the ability of movement of the cells was independent of the cell cycle.
Manufacture of Dye Sensitized Solar Cell Using Titania Sol Prepared at Room Temperature by the Sol–Gel Method
Authors: So Won-Wook , Kim Kwang-Je , Lee Jung-Keun , Moon Sang-Jin
Published: February 2005

To investigate the effect of the physical properties of titania particles on the photovoltaic performance of dye sensitized solar cells, various titania sols were prepared at room temperature by the sol–gel method. The subsequent aging treatment of this sol was carried out with and without hydrothermal treatment at higher temperatures. The dye adsorption amount of the titania particulate films and the power conversion efficiency of the solar cells thus fabricated were greatly affected by the physical properties of the particles such as crystalline form and the primary particle size. The power conversion efficiency of the solar cells made of the titania particles prepared even without the post-hydrothermal treatment reached up to approximately 6%, which was comparable to that of the cell fabricated with the particles treated hydrothermally at 200°C, indicating the possible skipping of this treatment step.
Crystal Defects in Epitaxial Layer on Nitrogen-doped Czochralski-grown Silicon Substrate (II) –Suppression of the Crystal Defects in Epitaxial Layer by the Control of Crystal Growth Condition and Carbon Co-doping–
Authors: Nakai Katsuhiko , Kitahara Koichi , Ohta Yasumitsu , Ikari Atsushi , Tanaka Masahiro
Published: February 2005

Two types of crystal defects, stacking fault induced by a nitrogen-doped substrate (N-SF) and elliptical pit (E-pit), are generated in the epitaxial layer due to grown-in defects in a nitrogen-doped Czochralski-grown silicon (CZ-Si) substrate. We investigate the dependence of N-SF and E-pit formation on the quality of nitrogen-doped substrates. It was revealed that the control of both nitrogen concentration and crystal growth parameter of the CZ-Si ingot is effective for suppressing N-SF and E-pit formation. We also examined crystal defect in the epitaxial layer on a nitrogen and carbon co-doped substrate, which is the other candidate for realizing the epitaxial wafer having a high intrinsic gettering ability. It was clarified that carbon co-doping in addition to nitrogen doping suppresses N-SF and E-pit generation.
Proposal and Analysis of a Traveling-Wave Amplifier in Terahertz Range Using Two-Dimensional Electron Gas
Authors: Asada Masahiro
Published: February 2005

A traveling-wave amplifier in the terahertz range using two-dimensional electron gas is proposed and analyzed using quantum mechanics including electron scattering. It is shown theoretically that the terahertz amplification is possible with high net gain coefficient at the temperature of 100 K.
Second Harmonic Generation in Barium Titanate Thin Films on Silica Glass by Corona Poling
Authors: Tsai Chun-An , Wu Adam Y. , Liou Wan-Rone , Lin Wen-Chung
Published: February 2005

Among potential inorganic thin films, perovskite-structured barium titanate (BaTiO3) is particularly attractive due to its large ferroelectric response and large optical nonlinear coefficients. SiO2 material is also important in semiconductor processing. Therefore, we study the nonlinear optical (NLO) thin film deposited on a SiO2 substrate. We report our investigation of a BaTiO3 thin film on a silica glass (SiO2) substrate grown by rf magnetron sputtering. We measured the second-harmonic generation (SHG) and calculated the second-order nonlinear optical coefficients from the BaTiO3/glass by using the Maker fringes technique. From our experimental results, we found that by applying corona poling, the nonlinear optical coefficients in BaTiO3/glass can be increased. The SHG of the nonlinear thin film by poling is dependent on temperature.
Photonic Crystal Slab Waveguides Fabricated by the Combination of Holography and Photolithography
Authors: Cho Chi-O , Roh Young-Geun , Park Yeonsang , Jeon Heonsu , Lee Beom-Seok , Kim Hye-Won , Choe Young-Ho
Published: February 2005

We have fabricated air-bridge type two-dimensional photonic crystal waveguides (2D-PCWs) using two high-throughput processes only: holography and photolithography. Despite the existence of misalignments of a defect line with respect to the air-hole arrays, waveguiding in both straight and 90°-bent PCWs was clearly observed at the wavelength of 1.55 µm. We also estimated the upper bound in propagation loss of our straight PCWs, which was measured to be about 40 cm-1.
Dielectric Relaxation Behavior of Ag(Ta,Nb)O3 Interdigital Capacitors on Oxide Substrates
Authors: Koh Jung-Hyuk , Song Jae-Sung , Lisauskas Alvydas , Grishin Alex
Published: February 2005

The time-dependent dielectric relaxation behavior of Ag(Ta,Nb)O3 interdigital capacitors was investigated for tunable device applications. Ag(Ta,Nb)O3 thin films, which have high k-factor (tunability/loss tangent), were deposited on the oxide substrates by pulsed laser deposition technique. Ag(Ta,Nb)O3 thin film on the LaAlO3 substrate has an epitaxial relationship with the substrate. The observed tunabilities and K-factors of Ag(Ta,Nb)O3/LaAlO3 and Ag(Ta,Nb)O3/Al2O3 interdigital capacitors were 5.9% and 17.8 and 3.8% and 9.9, respectively, at ±40 V (maximum electric field of 100 kV/cm), 300 K, and 1 MHz. Capacitance relaxation follows the power law C(t)=C
∞+C
0(t/1s)-β with a very small exponent negligibly fitted in the time domain. Due to this small exponent, the capacitance was changed by less than 0.05% in 2 V in 71 s. Time-dependent leakage current was measured by employing the Ag(Ta,Nb)O3(0.4 µm)/Al2O3 interdigital capacitor. The time-dependent relaxation current follows the power law j(t)=j
leak+j
0(t/1s)-α with an exponent α=0.98, j
leak=1.14×10-14, and j
0=11.42 s.
Preparation and Characterization of a- and b-Axes-Oriented Bi4Ti3O12 Thin Films Using TiO2 Anataze Buffer Layer
Authors: Nakamura Makoto , Higuchi Tohru , Hachisu Yuji , Tsukamoto Takeyo
Published: February 2005

Bi4Ti3O12 (BIT) thin films with TiO2 anataze buffer layer were deposited on the Pt/Ti/SiO2/Si substrates by metalorganic chemical vapor deposition (MOCVD) using Bi(CH3)3 and Ti(i-OC3H7)4 sources. When the substrate temperature was fixed at 500°C, the as-deposited BIT thin film exhibited highly a- and b-axes-oriented BIT single phase. The interface between the BIT thin film and the substrate was very smooth. The as-deposited BIT thin film consisted of small grain and exhibited a good P–E hysteresis loop. Subsequently, the remanent polarization (P
r) of the as-deposited BIT thin film with film thickness of 400 nm was 2P
r=44.4 µC/cm2.
Peculiar Hysteresis Loop of Pb(Mn1/3Nb2/3)O3–Pb(Ti, Zr)O3 Ceramics
Authors: Li BaoShan , Zhu ZhiGang , Li GuoRong , Yin QingRui , Ding AiLi
Published: February 2005

The P–E curves of Pb[Zr0.52Ti0.48(Mn1/3Nb2/3)]O3 ceramic with different sintering temperatures and variations of strontium (Sr) compositions have been investigated. It has been demonstrated that the polarization–field hysteresis curves show “pinched” shapes instead of the normal square-like P–E loops. In this paper we present the temperature dependence of the P–E curves for the ceramic with different firing temperatures and Sr dopants and show that the critical transitional temperature at which disappearance of the “pinched” shape occurs is highly dependent on the tetragonality (c/a ratio). In the meantime, the peculiar hysteresis loops are assumed to be the result of the pinning effect of the defect dipoles, which are slowly oriented antiparallel to the poling direction, and are finally broken down by the thermal activation.
Effect of EDTA on Growth of 4-Dimethylamino-N-Methyl-4-Stilbazolium Tosylate Crystals by Slope Nucleation Method
Authors: Wu Jer-I , Gopalakrishnan Rengasamy , Tai Clifford I-Der , Lan Chung-Wen
Published: February 2005

Nucleation experiments (metastable zone width) were carried out for 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) solutions at different saturation temperatures with and without the addition of a chelating agent. Using the results obtained from metastable zone width experiments, the slope nucleation method growth of DAST was performed. It was revealed that the addition of the chelating agent EDTA significantly suppresses spurious nucleation and cluster formation in the DAST solution, so that fewer, but larger, crystals can be easily obtained. With EDTA, the crystals grown also showed better crystallinity, hardness, and transparency in the visible/near-infrared region.
Properties of Ru Thin Films Fabricated on TiN by Metal-Organic Chemical Vapor Deposition
Authors: Sun Ho-Jung , Kim Younsoo , Song Han-Sang , Lee Jong-Min , Roh Jae-Sung , Sohn Hyun-chul
Published: February 2005

Ruthenium (Ru) thin films were fabricated on TiN, as well as on SiO2, by metal-organic chemical vapor deposition using tris(2,4-octanedionato)ruthenium. We characterized the Ru films grown on TiN, and compared them with the films prepared on SiO2. The Ru films deposited on TiN showed weak crystallinity and random grain orientation similar to the films on SiO2, but revealed notably rougher surfaces than the films on SiO2. Moreover, deposition rates on TiN were lower than those on SiO2. These properties of the Ru films grown on TiN originated from the difficulties in nucleation and growth at the initial stage of the deposition. The inferior surface flatness and deposition rate could cause structural instability and poor coverage of the Ru electrode at the bottom of a deep concave hole for a three-dimensional capacitor where the Ru film was in contact with a diffusion barrier metal TiN plug.
Pulsed Laser Deposition and Analysis for Structural and Electrical Properties of HfO2–TiO2 Composite Films
Authors: Honda Kazutaka , Sakai Akira , Sakashita Mitsuo , Ikeda Hiroya , Zaima Shigeaki , Yasuda Yukio
Published: February 2005

We have developed growth processes for HfO2–TiO2 composite films using a pulsed-laser-deposition (PLD) method and investigated the film structure which is characteristic to the growth sequences. Structural and electrical properties of the films sensitively depend on the growth conditions. It is observed that crystallization of the film is suppressed by increasing the TiO2 content. In the case that HfO2/TiO2 composition ratio is set to be 50/50, the film is completely in the amorphous phase and, after annealing, the film texture consisting of large HfTiO4 crystalline grains is formed. The dielectric constant of HfO2–TiO2 composite films increases with the increase in the TiO2 content in the film when the content is less than 50 at%. A marked change in the leakage property of the film is observed when comparing two films with 10 and 20 at% TiO2. We examine an optimum condition for the growth of HfO2–TiO2 composite film with both high dielectric constant and low leakage current.
Curvature Entropy Trapping of Long DNA under Hydrodynamic Flows in Microfluidic Devices
Authors: Ueda Masanori , Hayama Tetsuya , Takamura Yuzuru , Horiike Yasuhiro , Dotera Tomonari , Baba Yoshinobu
Published: February 2005

We investigated the curvature effect on the dynamics of long DNA using microfluidic devices. Long DNA has larger configurational entropy in a curved channel than in a straight channel. Under weak hydrodynamic flows, long DNA exhibited a curvature entropy trapping effect. The effect disappeared as the hydrodynamic flow was increased.
Eliminating the Threshold-Voltage Offset of p-Channel Metal-Oxide-Semiconductor Field Effect Transistors in High-Density Dynamic Random Access Memory
Authors: Takaura Norikatsu , Takemura Riichiro , Matsuoka Hideyuki , Nagai Ryo , Yamada Satoru , Asakura Hisao , Kimura Shin'ichiro
Published: February 2005

The threshold voltage offsets of paired p+-gate p-channel metal-oxide-semiconductor field effect transistors in high-density dynamic random access memory is investigated. The threshold voltage offset is shown to be mainly due to segregation of phosphorus at the edges of the shallow trench isolation when the gate oxide is formed. A 20-mV threshold-voltage offset was experimentally eliminated through control of the phosphorus concentration and the layout of the cross-couplings of sense amplifiers. It is expected that reduction in the threshold voltage offset will improve the retention times of gigabit-scale dynamic random access memory.
Efficient Improvement of Hot-Carrier-Induced Device's Degradation for Sub-0.1 µm Complementary Metal-Oxide-Semiconductor Field-Effect-Transistor Technology
Authors: Lin Jung-Chun , Yeh Wen-Kuan , Lei Tan-Fu
Published: February 2005

The effect of post-thermal annealing (PA) after In-halo and As-halo implantation on the reliability of sub-0.1 µm complementary metal-oxide-semiconductor field-effect-transistors was investigated. We found that the control of annealing time is more efficient than that of annealing temperature with respect to improving hot-carrier-induced device's degradation. The optimal results of device performance as well as of reliability can be obtained with post-annealing treatment performed at medium temperatures (e.g., 900°C) for a longer time.
A Variable Channel-Size MOSFET with Lightly Doped Drain Structure
Authors: Nakanose Naoki , Arima Yutaka , Asano Tanemasa , Kosasayama Yasuhiro , Ueno Masashi , Kimata Masafumi
Published: February 2005

We propose a metal oxide semiconductor field-effect transistor (MOSFET) whose channel size can be modified by applying control voltage. The variable-channel-size MOSFET (VS-MOS) has a control gate between the main gate and the source/drain. The control gate possesses a gap at its end in the active region. Owing to this unique layout, the VS-MOS achieves continuous modulation of effective channel size and can be fabricated using the conventional complementary MOS (CMOS) fabrication process. Results of test device fabrication show that the channel size modulation can be enhanced by employing the lightly doped drain (LDD) structure. It is also shown that the logic threshold can be controlled in a CMOS inverter composed of the VS-MOS.
Highly Selective Etching of Tantalum Electrode to Thin Gate Dielectrics Using SiCl4-NF3 Gas Mixture Plasma
Authors: Shimada Hiroyuki , Maruyama Koichi
Published: February 2005

We have developed a new etching technology for a metal gate electrode with high selectivity to thin gate dielectrics. Dry etching of tantalum (Ta) and tantalum nitride (TaN
x
) electrodes, not only over thin silicon dioxide (SiO2) but also over thin silicon nitride (Si3N4) gate dielectrics, is achieved by employing an appropriate ratio of silicon tetrachloride (SiCl4) and nitrogen trifluoride (NF3) gas mixture plasma. We confirmed that the high selectivity is due to the formation of a deposition layer caused by plasma polymerization based on SiCl4-NF3 chemistry. In this paper, we also demonstrate excellent characteristics of metal oxide semiconductor field effect transistor (MOSFET) and metal nitride semiconductor field effect transistor (MNSFET) devices using a low-resistivity TaN
x
/bcc-Ta/TaN
x
stacked metal gate.
W-Polymetal Gate with Low W/Poly-Si Interface Resistance for High-Speed/High-Density Embedded Memory
Authors: Yamashita Tomohiro , Nishida Yukio , Hayashi Kiyoshi , Eimori Takahisa , Inuishi Masahide , Ohji Yuzuru
Published: February 2005

A new W-polymetal gate electrode with the structure of W/WN/WSi/poly-Si is proposed. The W-polymetal gate is suitable for high-density memories since it has low resistance and is compatible with the self-aligned contact process. In our study, however, it is found that the interface of W and poly-Si has non-ohmic and quite high resistance in the case wherein only WN is used as a barrier film. This resistance increases the delay in complementary metal-oxide-semiconductor (CMOS) logic circuits and prevents high-speed operation. Our new process includes the deposition of thin WSi on poly-Si, followed by rapid thermal annealing, which results in ohmic and sufficiently low contact resistance between W and poly-Si. It is also demonstrated that selective gate reoxidation is successfully applied for this new structure, and the insertion of thin WSi does not cause any adverse effect on the electrical characteristics of metal-oxide-semiconductor field-effect transistor (MOSFET). This process is promising for high-speed and high-density embedded memory.
Role of Frictional Force on the Polishing Rate of Cu Chemical Mechanical Polishing
Authors: Matsuo Hisanori , Ishikawa Akira , Kikkawa Takamaro
Published: February 2005

In the chemical mechanical polishing (CMP) of low-dielectric-constant (low-k) materials and Cu for ultralarge-scale integrated circuits, one of the major issues is the adhesion failure of the film caused by frictional force. An in situ quantitative measurement technique for frictional force during CMP has been developed. We have examined frictional force with respect to process parameters and slurries. A low frictional force and a high polishing rate (PR), which are desirable for a low-k/Cu CMP process, have been achieved simultaneously by optimizing slurry flow rate. The groove structures of the polishing pad did not affect frictional force at a low relative velocity. Frictional force and polishing rate increased with increasing glycine and H2O2 concentration in the slurry, and saturated at concentrations above 0.3 M and 3 vol%, respectively. A modified Preston's equation describing polishing rate as a function of frictional force instead of polishing pressure was proposed.
Halo Ion Implantation Effect on Extension Profile Studied by Scanning Capacitance Microscopy Using All-Metal Probe under FM Control
Authors: Naitou Yuichi , Ookubo Norio
Published: February 2005

By using an all-metal probe under frequency modulation (FM) control, we developed a scanning capacitance microscope (FM-SCM), and applied it to a study of the halo ion implantation effect on two-dimensional (2D) extension profiles of cross-sectional p-channel metal-oxide-semiconductor field effect transistors. With the use of the all-metal probe under FM control, we attain sub-5-nm spatial resolution for the p-n junction in the ∂C/∂V image. The built-in depletion layer presumed by the ∂C/∂V image is narrower for the higher dose sample. The composition images of ∂C/∂V and topography allow us to determine extension depth X
J and extension-gate overlap length X
OV, both of which decrease with increase of the halo implant dose. Furthermore, the decrease of X
OV is steeper than that of X
J, clearly implying the anisotoropic effect of halo ion implantation.
Thermal Instability of Poly-Si Gate Al2O3 MOSFETs
Authors: Kim Woo Sik , Kawahara Takaaki , Itoh Hiroyuki , Horiuchi Atsushi , Muto Akiyoshi , Maeda Takeshi , Mitsuhashi Riichirou , Torii Kazuyoshi , Kitajima Hiroshi
Published: February 2005

The thermal stability of a SiO2/Al2O3 dielectric stack under high-temperature annealing after poly-Si gate deposition was examined. An interface reaction occurs when the activation temperature is higher than the post deposition annealing temperature, which results in the reduction of the interfacial oxide layer and hence silicate formation. As a result, the characteristics of metal oxide semiconductor field effect transistors (MOSFETs), such as mobility, reliability, and the distribution of capacitance are severely degraded. The formation of a SiON interfacial layer is found to be effective in suppressing the interface reaction.
Improving the Accuracy of Modified Shift-and-Ratio Channel Length Extraction Method Using Scanning Capacitance Microscopy
Authors: Eng Chee-Wee , Lau Wai-Shing , Jiang Yao-Yao , Vigar David , Tee Kheng-Chok , Chan Lap , Lim Vanissa Sei-Wei , Trigg Alastair
Published: February 2005

A modified shift-and-ratio (MS&R) method of extracting the effective channel length (L
eff) has been tested on metal oxide semiconductor (MOS) transistors fabricated by state-of-the-art CMOS technology. The value of L
eff generated by this method is more reasonable than the original shift-and-ratio method with much less computation time involved. We show the correctness of the MS&R method by comparing the L
eff extracted with the channel length obtained by cross-sectional scanning capacitance microscopy (SCM) measurement. In addition, we show that a higher off current corresponds to a smaller L
eff measured by our method.
Cross-Hatch Related Oxidation and Its Impact on Performance of Strained-Si MOSFETs
Authors: Nishisaka Mika , Hamasaki Yuichi , Shirata Osamu , Asano Tanemasa
Published: February 2005

The change in the morphology of thermally oxidized strained-Si layers on SiGe/Si substrates is studied using an atomic force microscope (AFM). The AFM observation was carried out before and after oxidation in an identical area of the sample. It was found that the oxidation rate of strained-Si was affected by the existence of the cross-hatch-related surface morphology. As the result, the surface roughness increased after oxidation. The roughness increase was more pronounced in a 30%-Ge-content sample than in a 15%-Ge-content sample. Strained-Si n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated and compared with unstrained Si devices. The enhancement of 58% of the transconductance was observed for the 15%-Ge-content wafer, while the 30%-Ge-content wafer exhibited a decrease of transconductance.
Visible Light Irradiation Effects on STM Observations of Hydrogenated Amorphous Silicon Surfaces
Authors: Arima Kenta , Kakiuchi Hiroaki , Ikeda Manabu , Endo Katsuyoshi , Morita Mizuho , Mori Yuzo
Published: February 2005

Scanning tunneling microscopy (STM) observations are performed on intrinsic hydrogenated amorphous silicon (a-Si:H) surfaces under monochromatic visible light irradiation. Tunneling spectroscopy results show rectifying behavior in the dark, and tunneling current increases dramatically at a negative (reverse) sample bias when the surface is continuously exposed to monochromatic visible light. It is elucidated that the increase of tunneling current under the irradiation is caused by the photoexcited electrons, which leads to the appearance of a larger voltage across the vacuum between the probe apex and the a-Si:H surface than that in the dark. A high tunneling current under the irradiation enables us to perform stable STM observations of the intrinsic a-Si:H surface. The current image at a negative sample bias under the irradiation was different from the topographic one at a positive sample bias, which may indicate that topographic images of a-Si:H surfaces reflect not only surface electronic structures but also subsurface information determined by the growth process of a-Si:H films.
Nucleation Control in Solid-Phase Crystallization of a-Si/SiO2 by Local Ge Insertion
Authors: Tsunoda Isao , Nagatomo Kei , Kenjo Atsushi , Sadoh Taizoh , Yamaguchi Shinya , Miyao Masanobu
Published: February 2005

The effects of local Ge insertion on the solid-phase crystallization (SPC) of a-Si films have been investigated. Three types of stacked structures, i.e., (a) a-Si/a-Ge/a-Si/SiO2, (b) a-Si/a-Ge/SiO2, and (c) SiO2/a-Ge/a-Si/SiO2, were annealed at 600°C. For structure (a) with thin (∼5 nm) Ge films, Ge atoms completely diffused into both sides of a-Si regions, and SPC was not enhanced. However, when Ge thickness was increased to more than 10 nm, Ge atoms were localized. Such localization became significant for structures (b) and (c) even for samples with thin Ge films. In addition, significant enhancement of SPC of a-Si was observed. These results indicated that crystal nucleation was initiated in Ge layers, and then propagated into a-Si layers. Therefore, interface-nucleation-driven SPC becomes possible using structures (b) and (c). This will be a useful tool in achieving oriented Si growth on SiO2.
Small-Signal Analysis of High Maximum Frequency of Oscillation 0.1-µm Off-Set Gamma-Shaped Gate InGaAs/InAlAs/GaAs Metamorphic High-Electron-Mobility Transistors
Authors: Lee Bok-Hyung , Kim Sam-Dong , Rhee Jin-Koo
Published: February 2005

We examined the effects of gate recess process conditions on the electrical characteristics of 0.1-µm-gate-length metamorphic high-electron-mobility transistors (MHEMTs) by the comparative analysis of small-signal parameters. When the wide-gate-recess method is adopted, significant reductions in gate-to-drain conductance and gate-to-drain capacitance were obtained compared with those obtained by the of narrow-gate-recess method. These differences in small-signal parameters are due to the removal of the entire n+ cap layer and corresponding dissimilarity in gate structure when the wide-gate-recess method is used. The wide-gate-recess method produced ∼1/2 drain-source saturation current and extrinsic transconductance compared with the narrow-gate-recess method. In contract to the DC performances, a markedly enhanced S21 gain of 3.5 dB and an f
max of 447 GHz were obtained from the MHEMTs processed by the wide-gate-recess method. This high f
max is responsible for the proper selection of the gate recess method for what and is one of the best data thus far reported for 0.1-µm-gate-length MHEMTs.
Extrinsic Base Regrowth of p-InGaN for Npn-Type GaN/InGaN Heterojunction Bipolar Transistors
Authors: Makimoto Toshiki , Kumakura Kazuhide , Kobayashi Naoki
Published: February 2005

The regrowth of p-InGaN as the extrinsic base layer of Npn-type GaN/InGaN heterojunction bipolar transistors (HBTs) significantly improves the ohmic characteristics of the base layer. The specific contact resistance is 7.8×10-4 Ω·cm2 even after the dry etching. This value for a non-alloyed ohmic contact is much better than that for as-grown p-GaN (1.7×10-3 Ω·cm2) and decreased turn-on voltage in the emitter-base diodes, which results in high current gains of up to 2000 and reduced offset voltages in the GaN/InGaN HBTs. These results show that the p-InGaN extrinsic base regrowth is an effective way to improve nitride HBT characteristics.
Fabrication of GaN/Alumina/GaN Structure to Reduce Dislocations in GaN
Authors: Hiroki Masanobu , Kumakura Kazuhide , Makimōto Toshiki , Kobayashi Naoki , Kobayashi Takashi
Published: February 2005

GaN/Alumina/GaN structures were fabricated to reduce dislocation density in GaN. Alumina films were deposited on GaN templates by electron cyclotron resonance plasma sputtering. GaN was regrown on the alumina films by metalorganic vapor phase epitaxy. It was found that GaN on alumina selectively regrown from pinholes in alumina by annealing prior to GaN regrowth. Hardly any of the dislocations in the GaN template propagated through the interlayer. Most of dislocations were terminated or bent at the interface between the alumina and regrown GaN. On the other hand, new vertical dark lines and horizontal dislocations were generated in regrown layer. The vertical lines were found to correspond to an inversion domain from convergent beam electron diffraction analysis.
Fabrication of InP-based Optoelectronic Integrated Circuit (OEIC) Photoreceivers Using Shared Layer Integration of Heterojunction Bipolar Transistors and Refracting-Facet Photodiodes
Authors: Lee Bangkeun , Yang Kyounghoon
Published: February 2005

InP-based monolithic photoreceivers have been fabricated using a shared layer integration scheme of refracting-facet photodiodes (RFPDs) and heterojunction bipolar transistors (HBTs). An HBT was fabricated using a self-aligned emitter-base process and nonalloyed metallization of the emitter, base and collector ohmic contacts. The fabricated 2×10 µm2 emitter HBT exhibited a maximum current gain of 40. The maximum cutoff frequencies of this HBT were measured to be f
T=79 GHz and f
max=143 GHz at I
C=19 mA and V
CE=1.5 V, respectively. An RFPD was fabricated using the base-collector junction layers of the HBT based on the selective wet chemical etching characteristics of InP and InGaAs layers. The fabricated RFPD showed a 37% increased optical responsivity of 0.48 A/W compared to the fabricated surface-illuminated photodiode using the same photoreceiver epitaxial layer. The full width at half maximum (FWHM) of the fabricated RFPD was determined to be 24 ps using the standard 50 Ω system load. The fabricated three-stage transimpedance amplifier (TIA) showed a transimpedance gain of 46 dBΩ and a -3 dB bandwidth of 12 GHz. The fabricated monolithic RFPD/HBT photoreceiver has demonstrated a -3 dB optical bandwidth of 6.9 GHz.
Local Change of Carbon Nanotube-Metal Contacts by Current Flow through Electrodes
Authors: Maki Hideyuki , Suzuki Masaki , Ishibashi Koji
Published: February 2005

The new processes of current flow through electrodes at carbon nanotube (CNT)-electrode junctions were carried out to change the contact resistance of CNT conductors and the tunnel barriers of CNT quantum dots. When the current flow process was applied to CNT conductors with the Au/Ti electrodes deposited on multiwall CNTs (MWNTs), the contact resistance markedly decreased. This is caused by the formation of titanium carbide (TiC) at the electrode-nanotube junction due to the strong interaction between Ti and nanotubes. This process is useful for obtaining the CNT conductor with low contact resistance. Meanwhile, when the current flow process was applied to single-wall CNT (SWNT) quantum dots with Au-Ag alloy electrodes, the contact resistance hardly changed due to the weak nanotube-Au-Ag interaction. However, in the electrical measurement of these samples at low temperatures, a quantum dot with a strong confinement was obtained after the current flow process. Therefore, this process can be also used for the change of tunnel junctions of CNT quantum dots.
A Novel Comb-Type Differential Pressure Sensor with Silicon Beams Embedded in a Silicone Rubber Membrane
Authors: Seo Chang-Taeg , Kim Young-Min , Shin Jang-Kyoo , Lee Jong-Hyun
Published: February 2005

A novel differential pressure sensor has been developed with silicon beams embedded in a silicone rubber membrane. The transducer is usable for most applications involving exposure to harsh media. A piezoresistive differential pressure sensor using silicone rubber membrane has been fabricated on the selectively diffused (100)-oriented n/n+/n silicon substrates by a unique silicon micro-machining technique using porous silicon etching. The pressure sensitivity is about 4.75 mV/kPa and the non-linearity is less than 1.05% FS (full scale).
Structure of Atomically Smoothed LiNbO3 (0001) Surface
Authors: Saito Akira , Matsumoto Hideo , Ohnisi Shuji , Akai-Kasaya Megumi , Kuwahara Yuji , Aono Masakazu
Published: February 2005

LiNbO3 (LN) is a substrate material used extensively for various optical or piezoelectric devices. We investigated an atomic-scale smoothing process of a LN single-crystal (0001) surface. Atomic force microscopy (AFM) observation revealed a surface morphology flattened from threefold symmetry to a step-terrace structure. The marked change of the surface was found to be dominated by a balance of surface diffusion and crystal growth within a period of 1–5 hours. An atomically flat surface with a straight and single-step height of 0.22 nm was obtained for a conventional LN substrate on the market. Next, we evaluated the surface composition and structure of the atomically flat LN (0001) surface by coaxial-impact collision ion scattering spectroscopy (CAICISS). We found that the atomically smoothed surface was terminated by a Nb atomic layer in which the Nb atoms were not shifted from the bulk position.
Spin Depolarization via Tunneling Effects in Asymmetric Double Quantum Dot Structure
Authors: Sasakura Hirotaka , Adachi Satoru , Muto Shunichi , Song Hai Zhi , Miyazawa Toshiyuki , Usuki Tatsuya
Published: February 2005

Time-resolved photoluminescence experiments have been performed to investigate exciton spin relaxation processes at low temperatures in InAlAs-InGaAs asymmetric double quantum dots embedded in AlGaAs layers. By decreasing the thickness of the AlGaAs barrier between the dots, the spin relaxation times decreased from 3 ns to 1 ns. The observed spin relaxation as a function of barrier thickness was reasonably described by two components: one was a constant and the other was exponentially depended on barrier thickness. The origin of the latter component is discussed in connection with spin-flip tunneling.
Control of GaSb/GaAs Quantum Nanostructures by Molecular Beam Epitaxy
Authors: Nakai Takanori , Iwasaki Seiki , Yamaguchi Koichi
Published: February 2005

GaSb quantum wells (QWs) and quantum dots (QDs) were fabricated on GaAs(001) surfaces by molecular beam epitaxy. By scanning transmission electron microscopy and photoluminescence (PL) measurements, their nanostructures were evaluated. One-monolayer-thick GaSb was precisely formed by the surface exchange reaction between As and Sb atoms, which was monitored by reflection high-energy electron-beam diffraction. In the Stranski-Krastanov growth of the GaSb QDs, low growth rate and low Sb4 pressure were effective conditions for suppressing size fluctuation. As a result, we could obtain the narrowest PL linewidth of 67 meV for GaSb/GaAs QDs.
Investigation of Ultrafast Carrier Dynamics in Quantum Wire by Terahertz Time-Domain Spectroscopy
Authors: Morohashi Isao , Komori Kazuhiro , Hidaka Takehiko , Wang Xue-Lun , Ogura Mutsuo , Watanabe Masanobu
Published: February 2005

We have investigated ultrafast carrier dynamics in a semiconductor crescent-shaped quantum wire by terahertz (THz) wave time-domain spectroscopy (THz-TDS). THz waves are generated by the motion of photoexcited carriers in semiconductor nanostructures, so that the time evolution of coherent polarization in the nanostructures is obtained by integration of observed THz waves. THz waves were generated by ultrashort optical pulse excitation of the quantum wire and detected using a free-space electrooptic (EO) sampling method. The dephasing time of coherent polarization in the quantum wire was varied by increasing the excitation energy. It was estimated that the dephasing time of coherent polarization is 300 fs at an excitation energy of 1.534 eV.
CMOS Application of Schottky Source/Drain SOI MOSFET with Shallow Doped Extension
Authors: Matsumoto Sumie , Nishisaka Mika , Asano Tanemasa
Published: February 2005

The silicon-on-insulator metal-oxide-semiconductor field-effect transistor (SOI MOSFET) whose source/drain is composed of Schottky contacts and a shallow-doped extension is investigated. It is demonstrated that the incorporation of the shallow-doped extension into the Schottky source/drain can increase the current drive and reduce the leakage current under reverse bias for both n-channel and p-channel devices. The shallow doping is performed by implanting Sb for n-channel devices, and BF2 or Ga for p-channel devices. The effect of Schottky contacts on the floating body effect (FBE) is investigated by analyzing the lateral bipolar characteristics of these devices. By employing the shallow-doped extension, a complementary MOS (CMOS) of the Schottky source/drain can be fabricated using single metal (cobalt, in this work) silicide. The stability of CMOS operation with the proposed devices under a high supply voltage is demonstrated by comparing it with a conventional pn-junction SOI MOSFET. It is also demonstrated from the characteristics of the CMOS-inverter ring oscillator that the proposed device operates at speeds as high as or even higher than that of the conventional SOI MOSFET.
A Low-Dielectric-Constant Sr2(Ta1-x,Nbx)2O7 Thin Film Controlling the Crystal Orientation on an IrO2 Substrate for One-Transistor-Type Ferroelectric Memory Device
Authors: Takahashi Ichirou , Sakurai Hiroyuki , Yamada Atsuhiko , Funaiwa Kiyoshi , Goto Tetsuya , Hirayama Masaki , Teramoto Akinobu , Sugawa Shigetoshi , Ohmi Tadahiro
Published: February 2005

The compounds of the Sr2Nb2O7 (SNO) family are suitable for use as ferroelectric materials for ferroelectric memory field-effect transistors (FETs), because these substances have a low dielectric constant and high heat-resistance. A very low dielectric constant ferroelectric Sr2(Ta1-x
,Nb
x
)2O7 (STN) film formation technology, which can be applied to a floating-gate-type ferroelectric random access memory (FFRAM), has been developed. Furthermore, a new technology that controls the orientation and the properties (a low dielectric constant and large coercive field) of STN has been developed. An MFMIS structure device with a large memory bias window (1.3 V) under ±5 V operation and a long retention time (>10 h) has successfully been fabricated.
Variable RF Inductor on Si CMOS Chip
Authors: Sugawara Hirotaka , Yokoyama Yoshisato , Gomi Shinichiro , Ito Hiroyuki , Okada Kenichi , Hoshino Hiroaki , Onodera Hidetoshi , Masu Kazuya
Published: February 2005

We propose a novel variable inductor on a Si complementary metal oxide semiconductor (CMOS) chip, whose inductance is of nH-order, for GHz applications. The inductance value can be varied by moving a metal plate above the inductor. The magnetic flux penetrating the spiral inductor continuously varies depending on the position of the metal plate. The metal plate is slid horizontally using a micro electro mechanical system (MEMS) actuator. We present the measured and simulated results. At 2.45 GHz, the inductance is varied from 6.6 nH to 5.7 nH, i.e., the variable range is 13%. These results show that the effect of parasitic capacitance between the spiral inductor and the metal plate can be ignored. The proposed variable inductor can be applied to RF circuits.
Fabrication and Photoelectrochemical Properties of Polythiophene-Porphyrin Composite Films
Authors: Akiyama Tsuyoshi , Kakutani Keitaro , Yamada Sunao
Published: February 2005

Polythiophene-porphyrin composite films consisting of bithiophene and meso-tetrathienylporphyrin were prepared on transparent indium tin oxide (ITO) electrodes. First, a polythiophene film was fabricated on the ITO electrode by electrochemical polymerization in the bithiophene solution with repeated oxidation-reduction cycles in the 0–+2 V region. Then, porphyrin was assembled on the polythiophene-modified electrode by using the same electrochemical polymerization in the porphyrin solution, to give polythiophene-porphyrin modified electrodes. The amount of porphyrin increased with increasing number of scanning cycles for electrochemical polymerization. In the presence of oxygen, irradiation of the polythiophene-porphyrin modified electrodes resulted in stable cathodic photocurrents. Photocurrent increased with increasing amount of porphyrin. Large cathodic photocurrents were observed in the negatively applied potentials. The photocurrent action spectra of modified electrodes strongly suggested the photochemical cooperation of porphyrin and polythiophene for photocurrent generation. The combination of polythiophene and porphyrin in the electrochemically modified electrode is quite effective for generating large photocurrents.
Flow Condition in Resist Spray Coating and Patterning Performance for Three-Dimensional Photolithography over Deep Structures
Authors: Singh Vijay Kumar , Sasaki Minoru , Hane Kazuhiro , Esashi Masayoshi
Published: February 2005

Spray coating of the photoresist is an attractive technique that offers new processes for realizing three-dimensional structures in a manner compatible with well-established planar photolithography. There are, however, many hurdles to overcome for its development, including the analysis of coating mechanism. Essentially, this is because the method used is the complex gas-liquid two-phase flow. In this paper, the detailed results relating to the resist film deposition inside microstructures of the Si wafer are described, while focusing on the pinhole distribution, which is a serious drawback of the application. In addition, the performance of the pattern transfer over deep (>1 mm) structures is investigated using a projection-type aligner.
Spectral Effects of a Single-Junction Amorphous Silicon Solar Cell on Outdoor Performance
Authors: Nakajima Akihiko , Ichikawa Mitsuru , Kondo Masataka , Yamamoto Kenji , Yamagishi Hideo , Tawada Yoshihisa
Published: February 2005

The device current–voltage (I–V) parameters of single-junction amorphous Si (a-Si) solar cells in natural sunlight at various locations have been investigated over three years. The effective efficiency was compared among testing locations from the latitude of 12.8 degrees to 43.8 degrees. The effective efficiency was varied periodically and the most advantageous performance was obtained in summer at all locations. The increase of output current dominantly contributed to the excellent performance. The output current of single-junction a-Si modules depended not only on module temperature and the annealing effect but also the seasonal variation of the air mass and the atmospheric conditions, such as turbidity and water vapor at each location. The annual performance ratio to initial efficiency measured under standard test conditions reached 82% in Hamamatsu, Japan.
Impact of Self-Aligned Metal Capping Method on Submicron Copper Interconnections
Authors: Saito Tatsuyuki , Noguchi Junji , Kubo Maki , Imai Toshinori , Ito Yuko
Published: February 2005

Novel copper (Cu) interconnection technology using self-aligned metallic cap was developed to reduce effective dielectric constant (k-value) as well as to improve reliability. Tungsten (W) was preferentially deposited on Cu wiring by chemical vapor deposition (CVD) using tungsten hexa-fluoride (WF6) and hydrogen (H2). Though W selectivity loss occurred without additional cleaning because of Cu contamination on the dielectric film during the chemical mechanical polishing (CMP) process, this problem was solved by surface cleaning prior to W-CVD combined with lift-off process just after it, resulting in improved yield in the test element group (TEG) during a short check. Using these processes, we fabricated a large-scale integration (LSI) with 4-level Cu interconnections eliminating capping barrier dielectrics such as silicon nitride (SiN), which had a relatively high k-value, and confirmed that there was no degradation in LSI yield. We also confirmed effective k-value was reduced by comparing propagation delay in conventional and metal-capped interconnections.