Effect of Palladium Electrode Patterns on Hydrogen Response Characteristics from a Sensor Based on Ta2O5 Film on SiC at High Temperatures

Our study aims to fabricate a hydrogen sensor based on thermal stability analysis of Ta2O5 film, and to determine the effect of Pd electrodes on the hydrogen sensor at high temperatures. First, in order to ensure high-temperature stability of silicon carbide (SiC)-based hydrogen sensors, the thermal stability of Ta2O5 dielectric thin film at temperatures above 900 °C was studied. The sensor structure consisted of a metal-insulator-semiconductor (MIS) and a tantalum oxide (Ta2O5) dielectric film was formed by rapid thermal oxidation (RTO). The Ta2O5 film was assessed through SEM, TEM, SIMS, and dielectric breakdown strength to observe thermal stability. Secondly, hydrogen sensors using a SiC substrate were fabricated, with the process considering thermal stability. The response characteristics for hydrogen were evaluated using three types of sensors with different Pd electrode patterns. The patterns of the Pd electrode were designed as squares or grid shapes, and were characterized by 100%, 75%, and 50% area ratios of Pd electrodes covering the Ta2O5 layer. The results showed that the sensor with a 100% area ratio of the Pd electrode had better sensitivity and linear response characteristics compared to sensors with a 50% area ratio of the Pd electrode.

Electrochemical Behaviour for Europium Doped Tantalum Oxide Coated Glass Carbon Electrode

Europium doped tantalum oxide (europium-Ta2O5) particles were synthesized with a low temperature hydrothermal method. The electrochemical behaviour of an europium-Ta2O5 film electrode in 0.1 mol dm-3KCl solution containing 5 mmol dm-3K3Fe(CN)6was investigated using cyclic voltgrammetry (CV). The CV results indicated that the europium-Ta2O5film electrode exhibited good stable and reversible electrochemistry properties. The electrochemical reaction of K3Fe(CN)6was a diffusion-controlling process on the europium-Ta2O5film electrode. The europium-Ta2O5particles might have potential applications in electrochemical fields.

Change in Radiative Optical Properties of Tantalum Pentoxide Thin-Films Due to Material Compositional Changes at High Temperature

Thin films (0.85μm, 3μm) of Ta2O5 deposited on Si and SiO2 were heated to 900°C. Their reflectance in the infrared was measured using an FTIR (Fourier Transform Infrared Spectrometer) equipped with a multiple angle reflectometer before and after exposure to high temperature. An interfacial layer (TaSixOy) formed by the diffusion of Si from the substrate into the deposited film was observed using Auger depth profiling, and the effect of this interfacial layer on the reflectance was measured. Using a least squares optimization technique coupled with an optical admittance algorithm, the multiple angle reflectance data was used to calculate the optical constants of the as deposited Ta2O5 film, crystalline Ta2O5, and the interfacial layer in the 1.6μm to 10μm range. The interfacial layer formed due to exposure to high temperature was found to be more absorptive than the crystalline Ta2O5.

Fluorescence property and dissolution site of Er3+ in Ta2O5 film prepared by sol-gel method and dip-coating technique

Ta2O5–xEr2O3 (TE) films were produced by a sol-gel method and a dip-coating technique with heat treatment at 600–1000 °C. Their powders were also prepared from the same sol. The Er3+ fluorescence property of the TE films containing various contents of Er3+ was measured as a function of the heat-treatment temperature. In crystallized films, the Er3+ fluorescence was observed because water-related residues (Ta–OH and H2O) and carbon-related residues (–CH3, –CH2–, –(C ⁼ O)–, and C≡C–H) were removed from the films. It is shown from infrared absorption spectroscopy that Ta–O− and Ta ⁼ O structures dissolve the Er3+ ions selectively and play a role in dispersing the Er3+. The strongest Er3+ fluorescence is observed in the TE film with 2 mol% of Er2O3 because of its highest ability to disperse the Er3+ ions.