Micro-structural and dielectric properties of porous TiO₂ films synthesized on titanium alloys by micro-arc discharge oxidization

Titanium oxide (TiO₂) has stable dielectric properties characterized by a high relative dielectric constant and low dielectric loss, and the materials have attracted much attention in microelectronics and microwave applications. In this work, the dielectric properties of porous TiO₂ films formed on TC11 titanium alloys by micro-arc discharge oxidization (MDO) using different current densities were investigated. The micro-structures, compositions, and dielectric constant of the films were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and vector analysis. The growth rates, composition phases, and properties of the pores in the films are found to strongly depend on the electrical current density. The acquired complex permittivity values are correlated to the structural and compositional changes. At a frequency of 10.80 GHz, the dielectric constants of the film with a thickness of approximately 10 μm prepared under different current densities of 18, 12 and 6 A dm^-2 were 12.20, 14.61, and 16.91, respectively, and the tangential losses were 1.1 × 10^-2, 1.3 × 10^-2, and 1.4 × 10^-2, respectively. The relationship between the dielectric properties of the MDO TiO₂ with the structure and composition is discussed. © 2005 Elsevier B.V. All rights reserved.