Micro-EIS of anodic thin oxide films on titanium for capacitor applications

The present work focuses on the investigation of the effect of the different crystallographic orientation of titanium grains on the formation of anodic oxide films and consequently their dielectric and semiconductive properties. By using a microcapillary cell the formation process and the electrochemical impedance spectroscopy (EIS) can be performed at high lateral resolution on variously orientated single grains of polycrystalline titanium. The oxide films were potentiodynamically formed by cyclovoltammetry. EIS measurements immediately followed by the oxide formation were used for a detailed investigation of the film properties, in particular, the relative permittivity ɛr and the donor concentration ND. In contrast to the most publications it was found that under the chosen conditions the crystallographic orientation of titanium substrate has no significant influence on the oxide thickness d, the relative permittivity ɛr or on the donor concentration ND of the oxide films. The relative permittivity ɛr is approximately 50. The donor concentration depends on the film thickness and amounts to approximately 3 × 1018 cm−3 in minimum.