Kenichi Onisawa

Change in crystalline morphologies of polycrystalline silicon films prepared by radio‐frequency plasma‐enhanced chemical vapor deposition using SiF4+H2 gas mixture at 350 °C

Polycrystalline silicon films have been deposited on glass substrates at 350 °C by radio‐frequency plasma‐enhanced chemical vapor deposition using a SiF4+H2 gas mixture. Crystalline fraction decreased abruptly with increasing gas flow ratio. Film structure drastically changed by increasing gas pressure from 0.4 to 2.0 Torr. At lower gas pressure, columnar crystals 30 nm in diameter grew from the glass substrates, while at higher gas pressure larger columnar crystals with a maximum diameter of approximately 100 nm grew on an amorphous Si layer approximately 170 nm thick.

Transferred Charge in the Active Layer and EL Device Characteristics of TFEL Cells

The relationship between transferred charge in the active layer of a thin-film electroluminescent (TFEL) cell and EL device characteristics has been investigated electrically. Making use of a charge density-voltage characteristic measuring system based on a Sawyer-Tower circuit, a general formula for the input power density was found to be given by twice the product of the frequency, the threshold voltage of the active layer, and the transferred-charge density. From this formula, the luminous efficiency could be estimated, once the dependence of the luminance upon the frequency and the transferred charge density was found. At a frequency smaller than the inverse of twice the luminous decay time, e.g. 500 Hz in the ZnS:Mn case, the luminance was found to be proportional to the product of frequency and transferred charge density. Hence, the luminous efficiency becomes constant with a value 2–2.5 times larger than that for 5 or 1 kHz drive conditions.

Dielectric properties of rf‐sputtered Y2O3 thin films

Yttrium oxide (Y2O3) thin films were deposited on indium‐tin‐oxide(ITO)‐coated glass substrates by the radio‐frequency‐sputtering method using an Y2O3‐sintered target. The relative dielectric constant er and the dielectric strength EBD of the Y2O3 films were studied. It was found that er and EBD have a maximum value and a minimum value, respectively, at 1.3 Pa when the pressure of the sputtering gas, Ar+10% O2, is varied from 0.67 to 9.3 Pa. The x‐ray diffraction study showed that the Y2O3 films deposited at 1.3 Pa are predominantly oriented along the 〈332〉 direction and their grain size is the smallest. Ion mass analysis showed impurity diffusion from ITO in the films deposited at 1.3 Pa. Furthermore, the dielectric properties of the Y2O3 films deposited at 1.3 Pa are related to the structural properties, such as the 〈332〉 orientation, grain size, and impurity diffusion.

Crystalline Fraction of Microcrystalline Silicon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition Using Pulsed Silane Flow

Microcrystalline silicon (?c-Si) films have been prepared at 200?C by radio-frequency (rf: 13.56 MHz) plasma-enhanced chemical vapor deposition using pulsed silane flow. The crystalline fraction, Xc(Raman), of ?c-Si films approximately 200 nm thick is quantitatively determined by decomposing Raman spectra into three peaks: crystalline, intermediate (small-grain-size-crystalline), and amorphous. The effects of rf power on Xc(Raman) and hydrogen content, CH, have been studied. Xc(Raman) increases with increasing rf power and tends to saturate; the maximum value of Xc(Raman) is 71%. With increasing rf power CH decreases to a minimum value of 4.5% and then increases. Hydrogen introduction into Si films overlapped with hydrogen elimination is responsible for the increase and saturation of Xc(Raman) with rf power.

Structural Change during Annealing of Amorphous Indium-Tin Oxide Films Deposited by Sputtering with H2O Addition

This paper describes the effects of annealing on electric properties and structure of amorphous indium-tin oxide (ITO) films deposited by sputtering at room temperature and with H2O addition. The film resistivity was increased by annealing at 150–200° C; in this temperature range the growth of ITO crystallites dispersed in the amorphous ITO phase was observed. This increased resistivity was found to be due to decreases in both Hall mobility (µ H) and carrier density (n) of the films. Measurements of thermal desorption spectroscopy revealed that two different adsorption states, in terms of H2O molecules which are due to the hydrogen-bonded H2O and OH species, were formed in amorphous ITO films during film deposition and the subsequent annealing process. Factors in the decreases of µ H and n were discussed on the basis of the experimental results obtained.

Oxygen in SrS Phosphor Powder and Its Effects on Performance of Thin Film Electroluminescent Devices

This paper reports on oxygen and oxidation effects in SrS powder that were investigated in order to improve luminance of SrS-based thin-film electroluminescent devices, XPS analysis revealed that the SrS powder surface was oxidized by the adsorption of water, giving the surface products SrSO{sub 3} and free S. Adsorption of water on the surface proceeded rapidly when exposed to a moist atmosphere, and oxidation of the surface occurred when heated in a nitrogen atmosphere as well as in a vacuum. Higher luminance and a better build-up characteristic in the luminance-voltage curve of the EL cells were obtained through heat-treatment of evaporation sources in an H{sub 2}S atmosphere.

Effect of microstructures on nanocrystallite nucleation and growth in hydrogenated amorphous indium–tin–oxide films

Hydrogenated amorphous indium–tin–oxide (ITO) films were prepared by a sputtering method at room temperature with H2O addition. The initial stage of thermal crystallization of the amorphous films was investigated after annealing at 150 °C, just below the crystallization temperature. With increasing H2O addition, the growth of crystallites dispersed in the amorphous matrix was suppressed, while the nucleation of crystallites was sharply enhanced. The amount of bonded hydrogen increased and that of oxygen vacancies decreased at the same time, with introducing inhomogeneites in the amorphous matrix. The effect of these microstructural changes on the nucleation and growth process of crystallites embedded in the amorphous solids was discussed based on these experimental results taking into account a recently proposed theoretical prediction to describe the crystallization of disordered solids.

TiO2 / SiO2 Multilayer Insulating Films for ELDs

Dielectric properties and the optical energy gap of TiO 2 /SiO 2 multilayer films prepared by sputtering were measured. The thickness ratio, TiO 2 /SiO 2 , was fixed at 1/3, and TiO 2 monolayer thickness, dt, was varied from 0.3 to 60 nm. The peak of the maximum charge density, which is the product of the dielectric constant and the breakdown field strength, was observed at dt=1 nm. The optical energy gap was constant for dt>2 nm, and increased as dt dropped below 2 nm

Temperature Dependence in Emission Characteristics of an Organic EL Cell with 8‐hydroxyquinoline Aluminum Emitting Layer

Current density-voltage characteristics, luminance, and emission spectra of an organic electroluminescent (EL) cell were measured at temperatures between -160 and 20 o C. An aromatic diamine and 8-hydroxyquinoline aluminum (Alq 3 ) were used as the hole transport and the emitting layers, respectively. The EL luminance at a constant current density of 1 mA/cm 2 was found to decrease with increasing temperature, and the photoluminescence intensity of the Alq 3 powder was also found to show a similar temperature dependence

White‐light emitting thin film electroluminescent devices with stacked SrS:Ce/CaS:Eu active layers

By stacking blue‐green emitting SrS:Ce and red‐emitting CaS:Eu active layers, white‐light emitting electroluminescent (EL) devices were fabricated. Luminance improvement and EL characteristics of SrS:Ce and CaS:Eu EL devices were discussed. The electrooptical characteristics of white‐light emitting EL devices with stacked SrS:Ce/CaS:Eu active layers were presented. Color changed from blue‐green to white by changing the voltage or frequency. Finally, feasibility of multicolor EL devices by using the fabricated white‐light emitting EL devices with color filters were discussed. UFpg5523,5527 UFid992922JAP UFttIn situ ac magnetic susceptibility of gadolinium thin films UFauF. H. Salas