An estimation method of the influence of interfaces on properties in perovskite-type oxide thin-film capacitors is presented. We proposed a modified Schottky model that can be employed to explain the electric properties of metal/perovskite-type oxide junctions. The modified model considers the electric field dependence of permittivity and the flow of electrons from metal to defect states located in the band gap of the perovskite oxide. The simulation based on this model could successfully describe the results of capacitance-voltage measurements of junctions between metals (Pt, Au, and Ag) and Nb-doped SrTiO3, which were not explained by the conventional Schottky model. Additionally, a simulation for a thin-film capacitor with hysteretic behavior could depict an asymmetric capacitance-voltage curve.
The behavior of hydrogen in (Ba,Sr)TiO3 (BST) thin film capacitors under electric fields was investigated by performing secondary ion mass spectroscopy (SIMS) analyses. It was clearly observed that the ingress of atmospheric hydrogen into BST thin film capacitors occurred through the anode and that it diffused toward the cathode under electric fields. In addition, it was found that the deterioration of the I-V properties of the BST thin film capacitors can be interpreted in terms of the distribution of hydrogen concentration in the BST thin films.
Novel sol-gel processing techniques of ceramic materials were developed for designing new functional environmental ion sensors. Wet-chemical preparation methods for metal-oxide thin-films, perovskite-type oxide thin-films, and solid-electrolyte discs could be developed by using solution techniques based on polymer precursors, etc. New electrochemical sensing techniques to hydrogen-phosphate ion with high sensitivity and selectivity were developed by the use of ceramic-based sensors. A sol-gel processing technique was developed for the preparation of La-based perovskite-type oxide thin-films using an acetylacetone (AcAc)-modified poly(vinyl alcohol) (PVA)-based polymeric precursor method. The AcAc modified PVA-based sol made it possible to deposit a thin-film as well as to lower the sintering temperatures. The La0.8Sr0.2CoO3 perovskite-type oxide thin-film electrode prepared at 500°C showed good properties of amperometric sensing to hydrogen-phosphate ion. A new solid-electrolyte ion sensor device using a Na+-ion conductor (Na5DySi4O12: NaDyCON) as an impedancemetric transducer and a perovskite-type oxide thin-film as a receptor has been further developed. The AC impedance of the device with a LaCoO3 receptor was found to vary logarithmically with increasing K2HPO4 concentration between 1.0 x 10-5 and 1.0 x 10-2 M at 10 kHz. The 90% response time was ca. 2 min at room temperature. The sensor showed a little sensitivity to NO3- at higher concentration, while no response was observed to the examined anions of Cl- and ClO4-.
The influence of metal/perovskite-type oxide interfaces on tunability of thin film capacitors