Akinori Nakayama

Resistance switching and retention behaviors in polycrystalline La-doped SrTiO3 ceramics chip devices

Resistance switching and retention behaviors in polycrystalline La-doped SrTiO3 ceramics have been investigated. La-doped SrTiO3 ceramics exhibits resistance switching as large as that of thin-film devices and exhibits a long-term memory effect of over 5 h. By means of a complex impedance analysis, it was clarified that these resistance changes can be reasonably attributed to the change in the electrical potential barrier at the interfaces and the resistance of the grain boundary changes remarkably by the application of voltage pulses. From the resistance retention properties at various temperatures, it was found that the high-resistance state is very stable even at 125 °C, whereas the resistance in the low-resistance state increases with time and its relaxation speed becomes remarkably faster with increasing temperatures. These results imply that the migration of the point defects could change the distribution of the space charge near the interface, resulting in a change in the interface resistances.

Improvement in Resistance Switching and Retention Properties of Pt ∕ TiO2 Schottky Junction Devices

Resistance switching and retention properties of Pt/TiO 2 Schottky junction devices are improved by doping anatase Ti0 2 thin films with Co ions. Co-doped TiO 2 devices exhibit excellent rectifying current―voltage characteristics and resistance switching compared to undoped TiO 2 devices. Conventional Schottky junction devices such as Pt/Nb:SrTi0 3 and Pt/TiO 2 devices exhibit very poor resistance retention properties in low resistance state (LRS); the resistance in LRS increases with time and the resistance relaxation accelerates with an increase in temperature. Co-doped Ti0 2 devices show excellent resistance retention properties even at 100°C. Experimental results indicate that in Schottky junction devices, resistance switching originates from the formation of local tunneling paths, and the oxygen vacancies near the electrode interface play an important role in resistance switching. These results are very important from the point of view of understanding the resistance switching mechanism and improving the resistance switching properties of Schottky junction devices.

Material Design for High Strength NTC Thermistor Ceramics

Various factors were investigated to decide the mechanical properties of (Mn1–xNix)3O4 ceramics, that are typical composition systems of NTC (negative temperature coefficient) thermistors. The strength of NTC thermistor ceramics can be improved by designing the material so that the compressive stress may remain at the surface of the ceramics. At high temperature, the thermal expansion coefficient of a rock salt phase segregated internally ceramic increases over that of the spinel phase, further, on the surface of the ceramics, this compressive stress remains below room temperature. Moreover, it was confirmed that the stress analysis result by the FEM corresponded well with the stress measurement result on the surface of the ceramics measured by μ -XRD.