Yuichi Sakai

Preparation of BaTiO3 thick films by inkjet printing on oxygen-plasma-modified substrates

Thick film patterns were prepared by an inkjet method with water-based ink containing BaTiO3 powder. An ethyl cellulose layer was made over Pt electrodes, and oxygen plasma modification was performed. After this modification, patterns on substrates were printed in shape. The measurement of the contact angle of ink on the ethyl cellulose layer and the X-ray photoelectron spectroscopy of the ethyl cellulose layer were carried out. From the obtained results, wettability was determined to be improved by increasing the number of hydrophilic functional groups on the surface of ethyl cellulose layer. Surface observation using a scanning electron microscope was carried out on a modified ethyl cellulose layer. Surface roughness due to the etching effect of oxygen plasma was observed to increase with modification time. After firing at 1340 °C for 1 h, the BaTiO3 film thickness was approximately 30 µm. The electric properties of BaTiO3 films were examined. The dielectric constant and tan δ were 2200 and 0.05 at 1 kHz, respectively. The remanent polarization and coercive field measured from a P–E hysteresis curve were 3.1 µC/cm2 and 1.1 kV/cm, respectively. These results indicate that an inkjet printing method using a modified EC layer is applicable to the fabrication of thick films on substrates.

Preparation of Ba(Ti,Zr)O3 Thick-Film Microactuators on Silicon Substrates by Screen Printing

BaTi0.975Zr0.025O3 thick-film microactuators were fabricated by combining screen printing and silicon micromachining. The electric properties of BaTi0.975Zr0.025O3 thick films with a small area on a Pt bottom electrode using silicon substrates prepared by screen printing were investigated. The thick films were fired in the temperature range from 1310 to 1370°C. The remanent polarization Pr and coercive field Ec were 6.2 µC/cm2 and 1.8 kV/cm at the firing temperature of 1350°C, respectively. The effective piezoelectric constant d33 calculated from a unipolar signal curve was approximately 120 pm/V for the thick film fired at 1350°C. After measuring the electric properties of BaTi0.975Zr0.025O3 thick films, microactuators were fabricated by etching the substrates. The displacement of a microactuator that has a 0.3×0.3 mm2 area membrane and is driven at 40 Vpp and 4 kHz was approximately 0.12 µm. This indicates the possibility of applying this microactuator in lead-free micropump or micromixer devices.

Photoelectrochemical hydrogen evolution using amorphous silicon electrodes having p-i-n or p-i-n-p-i-n junctions

Abstract Hydrogenated amorphous silicon (a-Si) films fabricated into p-i-n junctions were deposited on stainless steel plates and overcoated with platinum to make photoelectrodes for hydrogen conversion. The a-Si electrodes exhibited cathodic photocurrents associated with hydrogen evolution beginning at a potential 0.8 V more positive than the potential of the hydrogen electrode (UH). This was observed in aqueous solutions of 0.5 mol dm−3 H2SO4. None of the electrodes showed leakage current in the solution over a potential region from −0.3 to 0.6 V vs. SCE, where the hydrogen photoevolution occurred efficiently, although a considerable number of the p-i-n solid a-Si photocells, prepared in the same way, showed dark currents which probably arose due to current leakage through pin holes in the a-Si films. This implies that the a-Si electrodes generate an efficient photocurrent even if they have pin holes. The p-i-n-p-i-n a-Si electrode showed an onset potential for the cathodic photocurrent 1.6 V more positive than UH. This potential exceeds the equilibrium potential for the oxidation of water, indicating the usefulness of this electrode for water splitting without an aid of external bias.

Preparation of (Ba,Sr)TiO3 thick film on ZrO2 substrates by inkjet printing

The thick films were prepared by the inkjet method with ink containing BaTiO3 and SrTiO3 powders. The ink droplets from a piezoelectric-type inkjet head were observed. The velocity of ink droplets was increased with increasing applied voltage of the inkjet head. The dot and line patterns were formed by inkjet printing on a ZrO2 substrate with a Pt electrode. The lines printed on the substrate have 220 µm width. The thickness profiles were measured for the single dot and the 6.5×6.5 mm2 square pattern. The thickness was uniform over the printed thick film. The thick films printed by the inkjet method were fired in the temperature range from 900 to 1200°C. The grain growth advanced with increasing firing temperature. Ba0.7Sr0.3TiO3 was identified by X-ray diffraction patterns at firing temperatures of 1100 and 1200°C. The dielectric constant and tan δ of Ba0.7Sr0.3TiO3 thick films fired at 1200°C without DC bias voltage at 10 MHz were 350 and 11%, respectively. The dielectric constant decreased slightly with increasing frequency. The dielectric constant decreased with increasing DC bias voltage. It is expected that the inkjet method with ink containing several ceramic powders is applicable to the fabrication of thick film patterns.

The effect of interposing thin oxide layers on the photovoltaic properties of a‐Si:H solar cells II between the middle n and p layers of a tandem‐type cell

The properties of the p/n junction of hydrogenated amorphous silicon (a‐Si) were studied by use of some kinds of a‐Si cells. It was concluded that the photoelectromotive force generated at the p/n junction reduces the photovoltage of the tandum‐type solar cells, and the rate of the electron‐hole recombination lowers their fill factor. However, by interposing a 2‐nm‐thick TiO2 layer between p and n layers of the tandem‐type solar cells, the open‐circuit photovoltage was raised from 1.50 to 1.64 V, the fill factor from 0.705 to 0.775, and the energy conversion efficiency was improved ∼10%. Among the metal oxides examined i.e., V2O5, TiO, TiOx, TiO2, NiO, WO3, ITO, Fe2O3, and SiO2, the TiOx (x=1.7) layer showed the best result. In addition, it was observed that the thickness of the p and n layers, which was necessary to form the p/n junction, could be reduced by interposing a metal‐oxide layer.

Preparation of Inkjet-Printed NiO Films for Ba(Ti,Zr)O3-Based Ceramics and Application to Multilayer Ceramics with Ni Electrodes

The possibility of fabricating a lead-free multilayer ceramic (MLC) actuator with Ni inner electrodes prepared by inkjet printing has been investigated. Inkjet ink containing NiO powder was prepared. NiO films were prepared on [(BaO)1.00(CaO)0.01](Ti0.95Zr0.05)O2 green sheets by the inkjet method and co-fired in a reducing atmosphere. After co-firing, the NiO films were reduced to metal Ni films, which acted as electrodes. The remanent polarization Pr and coercive field Ec of the ceramics were 2.5 µC/cm2 and 3.0 kV/cm, respectively. The Curie temperature, orthorhombic–tetragonal transition temperature, and rhombohedral–orthorhombic transition temperature were 110, 45, and 0 °C, respectively. The [(BaO)1.00(CaO)0.01](Ti0.95Zr0.05)O2 MLCs with Ni inner electrodes were prepared using NiO ink. The diffusion and reaction of Ni to ceramic layers were not observed. The displacement of the MLCs with seven active layers was approximately 0.17 µm when the electric field was 20 kV/cm. It is expected that inkjet printing using NiO ink will be applicable to the fabrication of lead-free MLC actuators with Ni inner electrodes.

Preparation of Ba(Ti,Zr)O3 Thick Films on Silicon Substrate by Screen Printing

BaTi0.975Zr0.025O3 thick films were prepared by a screen-printing method on Pt bottom electrodes using silicon substrates in the firing temperature range from 1330°C to 1370°C. The high-temperature sintering of Pt bottom electrodes and Ba(Ti,Zr)O3 thick films was successfully achieved using silicon substrates with a fairly thick oxide layer. The ferroelectric and piezoelectric properties of the thick films were examined. The remanent polarization of the thick films increased with increasing firing temperature. A remanent polarization of 13.8 µC/cm2 for a Ba(Ti,Zr)O3 thick film was obtained at a firing temperature of 1370°C. The longitudinal piezoelectric constant d33 calculated from a unipolar signal (10 kV/cm, 1 Hz) curve was 610 pC/N for the thick film fired at 1370°C.

Preparation of solder plated patterns on paper and applying to RFID tags

In this study, we investigate the preparation of radio frequency identification tags on paper by using screen printing, solder plating, and self-alignment attachment. Waste-fluids are not produced in the proposed process. In addition, the process of preparing the tags involves fewer steps compared to the general process. Moreover, the prepared tags are heat resistant at temperatures greater than 200 °C.

Preparation of (Ba,Sr)TiO3 Thick Films with Ni Electrodes by Screen Printing

The effects of doping MgO into (Ba0.6Sr0.4)TiO3 (BST) fired under a reducing atmosphere were investigated in order to prepare BST thick films with Ni electrodes by the screen-printing method. MgO-doped BST thick films fired under a reducing atmosphere showed insulation resistance. Grain growth in the thick films was advanced by MgO doping. The dielectric constant near TC of the bulk ceramics and thick films increased with increasing MgO concentration up to 2 and 10 mol %, respectively. Mg ion substitution to the B-site was also observed up to these concentrations. The tunability and tan δ of thick films with MgO concentrations of 2 and 4 mol % at an electric field of 10 V/µm were approximately 77 and 0.3%, respectively. It is expected that thick films prepared by screen printing will be applicable to tunable devices with Ni electrodes.

Preparation of (1-x)(Ba,Sr)TiO3–xMgTiO3 Based Thick Films by Inkjet Printing

(1-x)(Ba0.6Sr0.4)TiO3–xMgTiO3 (x=0–0.01) thick film patterns were prepared by the inkjet method. The dielectric properties and tunabilities of the thick films were examined. The Curie temperature was shifted to a lower temperature by adding MgTiO3. The value of tan δ was improved by adding a small amount of MgTiO3. In order to improve the electric properties of the thick films, the effects of adding SiO2 to 0.995(Ba0.6Sr0.4)TiO3–0.005MgTiO3 thick films were investigated. The dielectric constant without DC electric field and the tunability at 10 V/µm DC electric field were approximately 2300 and 70%, respectively, when 0.5 wt % SiO2 was added to the thick films. When the amount of SiO2 added was too large, the Ba2TiSi2O8 phase appeared and the electric properties deteriorated. These results indicate that the MgTiO3 solute and the addition of SiO2 were effective for improving the electric properties of the thick films prepared by the inkjet method.