Satoshi Tanimoto

Investigation on Leakage Current Reduction of Photo‐CVD Tantalum Oxide Films Accomplished by Active Oxygen Annealing

Previously, the authors demonstrated that photo‐CVD films formed on a Si substrate using and acquire very low leakage current by active oxygen annealing. This paper investigates in detail the mechanism of the leakage current reduction. Low‐leakage‐current films are produced provided there is a sufficient UV‐activation of molecules during CVD, an abundant supply of electronically excited oxygen, O(1D) and , during annealing, and Si migration from the substrate into the films during annealing, or CVD. A phenomenological model of the leakage current reduction is proposed. In the model, a certain void in the Ta‐O network is compensated by chemically incorporating a Si atom and several excited oxygen species; O(1D) or . This model can consistently interpret a series of phenomena on leakage current reduction reported in this paper and in our previous papers.

Improvement of a Single‐Chamber Solid‐Oxide Fuel Cell and Evaluation of New Cell Designs

The performance of a single-chamber solid-oxide fuel cell (SOFC) made from an yttria-stabilized zirconia solid electrolyte with a 25 wt % Ce{sub 0.8}Gd{sub 0.2}O{sub 1.9} (GDC)-containing Ni anode and a 15 wt % MnO{sub 2}-containing La{sub 0.8}Sr{sub 0.2}MnO{sub 3} cathode was found to be significantly enhanced by the deposition of Mn, Ga, Cr, Ce, and Lu oxide layers on the YSZ surface. In particular, the deposition of the Mn oxide layer increased the maximum power density from 161 to 213 mW cm{sup {minus}2} in a mixture of methane and air having a volume ratio of methane to oxygen of 1/1 at a flow rate of 300 mL min{sup {minus}1} (methane 52 mL min{sup {minus}1}, oxygen 52 mL min{sup {minus}1}, nitrogen 196 mL min{sup {minus}1}), and at an operating temperature of 950 C. This effect was the result of the promoted anodic and cathodic reactions. Two types of cell designs were examined for the single-chamber SOFC; the two electrodes were deposited on opposite surfaces (A-type cell) and on the same face (B-type cell) of the solid electrolyte. The A-type cell showed an increasing power density with decreasing thickness of the solid electrolyte. The maximum power density was 256 mW cm{sup {minus}2}morexa0» at a solid electrolyte thickness of 0.3 mm. The B-type cell showed an increased power density for a decreased gap between the two electrodes. The maximum power density was 143 mW cm{sup {minus}2} for a gap of 0.5 mm between the two electrodes. In addition, the long-term stability of the single-chamber SOFC was also studied and found to have a direct relationship with the carbon deposition on the GDC-containing Ni electrode.«xa0less

Crystal and electrical characterizations of oriented yttria-stabilized zirconia buffer layer for the metal/ferroelectric/insulator/semiconductor field-effect transistor

Using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and X-ray pole figure measurements, we evaluated the crystallinities of yttria-stabilized zirconia (YSZ) thin films as an intermediate layer for metal/ferroelectric/insulator/semiconductor-structure field-effect transistors (MFIS-FETs). A highly oriented YSZ film was grown on a Si(100) substrate by the vacuum evaporation method. The [100] axes of the YSZ crystals were aligned parallel to [100] axes of Si crystals in the plane. In addition, electrical characterizations of the highly oriented YSZ thin films on Si(100) were evaluated from current–voltage ( I–V ) and capacitance–voltage ( C–V ) measurements. The I–V measurement indicated a breakdown field of about 3 MV/cm (at I=1 nA/cm2). The C–V measurement results suggest that mobile ions were present in the YSZ films. Oriented perovskite PbTiO3 films were deposited on YSZ crystal and YSZ/Si(100) substrates by the digital chemical vapor deposition (CVD) method. These PbTiO3 films included many PbTiO3 grains with their [100] axes parallel to the [100] or [110] axis of YSZ crystals in the plane of the PbTiO3/YSZ interface.

Synchronously excited discrete chemical vapor deposition of Ta[sub 2]O[sub 5]

A versatile chemical vapor deposition (CVD) technique is proposed which has two noteworthy technical features: (1) alternate or intermittent introduction of source vapors followed by evacuation and (2) one or more excitations synchronized with the sequences of vapor introduction. Since it can select and identify the place and time for the occurrence of reactions and excitation among source molecules, this technique also promises to be valuable in investigating the use of conventional CVD processes with unfamiliar materials. In this work, the technique is used to investigate the conventional photo and thermal CVD processes of tantalum pentoxide film using tantalum pentachloride and oxygen. The results indicate that significant deposition occurs even without the vapor phase reactions among source vapors and that photoexcitation of the substrate surface greatly enhances film deposition. In the course of the investigation, it was observed that temporary photoexcitation and ozone supply produced a high rate of film deposition even at temperature lower than 300 C.

c-Axis-Oriented Pb(Zr, Ti)O3 Thin Films Prepared by Digital Metalorganic Chemical Vapor Deposition Method

Tetragonal perovskite Pb(Zrx Ti1-x )O3 (PZT) film with single c-axis orientation was successfully fabricated on a single-crystalline MgO(100) substrate at a surface temperature as low as 480°C using a digital metalorganic chemical vapor deposition (digital MOCVD) method. In this method, each metalorganic source was supplied alternately into the MOCVD reactor to prevent the formation of unexpected phases such as pyrochlore due to gas phase reaction at the low processing temperature. For layer-by-layer growth in the MOCVD method, the introduction sequence and amount of metalorganic sources supplied were adjusted to correspond to the crystal structure and density of the fabricated film. This is the first report on the fabrication of tetragonal perovskite PZT film with single c-axis orientation using the digital MOCVD method.

A high rate of chemical vapor deposition of tantalum pentoxide film initiated by photoexcitation

Abstract It is demonstrated for the first time that, in CVD using TaCl 5 and O 2 , periodic photoexcitation produces a high rate of Ta 2 O 5 film deposition during the following interrupted photoexcitation intervals even at a temperature lower than 300°C. The experimental data indicate that this high rate of film deposition is self-sustaining, once photoexcited, but is obstructed if evacuation is performed just after the photoexcitation interval. A simple model incorporating a vapor phase reaction process between TaCl 5 and O( 3 P) is proposed as a possible explanation for this deposition mechanism.