Taiji Tsuruoka

Structural properties of polycrystalline silicon films prepared at low temperature by plasma chemical vapor deposition

Evolution with thickness of the structure of the polycrystalline silicon (poly‐Si) films prepared at 300 °C has been studied by plasma decomposition of SiF4/SiH4/H2 source gases. The poly‐Si films with varied thickness are characterized mainly by Raman spectroscopy, x‐ray diffraction (XRD), and supplementarily by reflection high‐energy electron diffraction, transmission electron microscopy, Fourier‐transform infrared (FT‐IR) spectroscopy, electron‐spin resonance (ESR), and secondary‐ion‐mass spectroscopy (SIMS) measurements. The crystalline fraction of the film was calculated to be 87% by deconvoluting the Raman spectra. The grains indicated a strong 〈110〉 preferred orientation by XRD. The thickness (d) dependence of the diffracted (220) intensity is divided into three regions: an incubation region (d<200 nm, region 1), a linear region (200 nm ≤d<300–500 nm, region 2) where the deposition parameter (SiF4 flow rate, substrate temperature, and rf power) dependence is weak, and a linear region with steeper (...

Y-Ba-Cu-O Film Growth by OMCVD Using N2O

By using N2O gas as an oxygen source, Y-Ba-Cu-O films prepared at the growth temperature of 650°C on the SrTiO3(100) substrate showed zero resistance at 79 K, while by using O2 gas, a growth temperature of 800°C was required to obtain the same film quality. The deposition rate of Y-Ba-Cu-O films on MgO(100) substrates by using N2O gas was nearly one half of that using O2 gas. The deposition rate monotonically increased with increasing of the growth temperature from 600°C to 800°C. The electrical quality of films prepared on the substrate became poorer in the series of SrTiO3(100), MgO(100) and Si(100) substrates. X-ray diffraction patterns of Y-Ba-Cu-O films grown on SrTiO3(100) and MgO(100) substrates indicate c-axis orientation, but those of films on Si(100) substrates did not indicate c-axis orientation.

Y1Ba2Cu3O7-δ Film Formation by an OM-CVD Method

In this letter, we report further studies on Y-Ba-Cu-O film formation by OM-CVD (Organometallic Chemical Vapor Deposition). Without postannealing, Y-Ba-Cu-O films grown on MgO(100) single-crystal substrates at a substrate temperature of 780°C showed an onset temperature of 85 K and zero resistance at 65 K. X-ray diffraction (XRD) patterns showed well-ordered crystallinity for films grown at substrate temperatures higher than 700°C. XRD results indicated that Y-Ba-Cu-O films with (110) orientation were grown on SrTiO3(110) single-crystal substrates.

Mechanism of low‐temperature polycrystalline silicon growth from a SiF4/SiH4/H2 plasma

A model for the low‐temperature growth of poly‐Si by plasma‐enhanced chemical‐vapor deposition using SiF4/SiH4/H2 gases is presented. The model is based on the existing so‐called etching model in which growth and etching take place simultaneously. In this model a set of chemical reactions are postulated. The crucial factors to obtain high‐quality poly‐Si films are (1) the flux of precursors, (2) the concentration of F radicals in the vicinity of the growing surface which determines the etching rate, and (3) the H‐covered surface which ensures long diffusion length of precursors. The flow rate of SiH4 [factor (1)] determines whether the film becomes crystalline or amorphous, and variation in the other gas flow rates and plasma parameters affect factors (2) and (3). According to the model the electrode spacing and rf power predominantly determine the concentration of F radicals diffused to the growing surface, while the gas pressure changes the residence time of radicals which predominantly affects the etching reaction. Natural consequences of the model are that an excess supply of F radicals will in turn deteriorate the crystallinity by stripping the hydrogen covering the surface and increasing nucleation sites. The crystallinity of poly‐Si films prepared by changing the above plasma parameters are characterized by x‐ray diffraction, and their dependence on the above parameters are found to be consistent with the model. A high degree of hydrogen exchange between the growing surface and the plasma is observed by secondary‐ion‐mass spectroscopy for the film prepared with SiF4/SiH4/D2 gases.

Characteristics of quenched Y‐Ba‐Cu‐O thin films on SrTiO3 (100),(110) grown by organometallic chemical vapor deposition

A thin Y‐Ba‐Cu‐O film was formed by the organometallic chemical vapor deposition (OMCVD) method. The substrates used were (100) and (110) SrTiO3. After forming Y‐Ba‐Cu‐O at 800 °C, it was cooled at a rate of 100 °C/min in O2 under 1 atm. This film was c‐axis oriented, with its (001) surface grown in parallel to the (100) surface of SrTiO3 and Tc =88 K. The (110) surface of Y‐Ba‐Cu‐O was grown in parallel to the substrate crystal and Tc =84 K on the (110) surface of SrTiO3. After forming, these films were quenched in air from 800 °C to room temperature. The change in resistance of the quenched sample with temperature was metallic, Tonset =75 K, and Tc =60 K.

Two-module stage optical switch network

A large-scale optical switch array based on guided-wave technology using two-module-stage network architecture is proposed. Networks are derived from a generalized three-stage switch network. Two types of architecture are demonstrated. In the first, building blocks in each module are 1/spl times/n, n/spl times/m nonblocking switches or n/spl times/r switch that can route limited numbers of input signal. In the second, crossbar, Banyan, or four-stage wide-sense nonblocking network is used as building blocks. The interconnection is simpler than for the first type. Network architectures that use Banyan or wide-sense nonblocking network building blocks are classed as thinned-out Banyan networks.

Phosphine Doping Effects in the Plasma Deposition of Polycrystalline Silicon Films

The effects of phosphine doping on the electronic and structural properties of polycrystalline silicon (poly-Si) films prepared by plasma chemical vapour deposition using SiF4/SiH4/H2 gases have been investigated. With increasing doping ratio, the conductivity rapidly increases and takes a maximum value of 80 Scm-1 at [PH3]/[SiH4](=γ)~1.7×10-2, while it decreases at larger doping ratios. This change is found to be caused mainly by the change in the carrier density, by Hall measurements. X-ray diffraction and transmission electron microscopy indicate that this electronic change is associated with the change in the preferred orientation of grains from to with a slight decrease in grain size, and the structural change from crystalline to amorphouslike with increasing γ.

High luminance white EL devices using SrS:Ce,Eu,K films deposited in a H2 atmosphere

Abstract White EL devices were fabricated using SrS:Ce, Eu, K phosphor films deposited in a reducing atmosphere of H 2 . The highest luminance of 1700 cd/m 2 was obtained under 1 kHz sinusoidal voltage drive. This value is 2.3 times larger than that of the devices without atmosphere of H 2 . Compared to phosphor films prepared without an atmosphere of H 2 gas, the residual oxygen concentration in the films had decreased by one half, additionally, the X-ray diffraction pattern showed a preferential (200) orientation.

Ta-Si-C High Resistivity Thin Films for Thermal Printing Heads

Ta-Si-C thin films have been developed for thermal printing heads, and the effect of composition on the film properties was studied. The results of these investigations show that (1) when Ta-Si-C thin films are formed, the composition of the film does not agree with the target composition, (2) addition of carbon to Ta/SiC mixtures suppresses recrystallization during high temperature treatment, (3) excellent characteristies are achieved with thermal printing heads using Ta-Si-C thin films formed using a target with more than 20-percent carbon in a SiC/C mixture, and (4) irreversible resistance changes are very small in thermal printing heads containing more than 20-percent carbon when external heat is applied. These results show that Ta-Si-C is an excellent material for use in thermal printing heads.

Reversed and Uniform Δβ Directional Coupler Optical Switch with Periodically Changing Coupling Strength

A new device structure for a reversed Δβ directional coupler is proposed to achieve the lower value of phase mismatch and device length product (ΔβL) required for switching or digital-like response. By decreasing the coupling coefficient in the middle of each electrode section, the ΔβL value required to drive the device is reduced to almost half of that for a conventional device. The response curve of the device can be modified to obtain a wide range of ΔβL values.