Structural, optical and microwave dielectric studies of Co doped MgTiO3 thin films fabricated by RF magnetron sputtering

Abstract

We report the structural, optical, and microwave dielectric characteristics of (Mg0.95Co0.05)TiO3 (MCT) thin films deposited onto amorphous SiO2 (a-SiO2) substrates by RF magnetron sputtering for the first time. The role of the oxygen mixing percentage (OMP) on the growth, morphology, optical, and microwave dielectric properties of MCT thin films has been investigated. The as-deposited MCT films were x-ray amorphous and crystallined after annealing at 700 °C for 1 h in air. A preferred orientation of grains along the (110) direction has been observed with increasing OMP. Such a textured growth is explained by calculating the orientation factors from the Lotgering model. The dispersion in a refractive index with wavelength has been explained using a single oscillator dispersion model. Both the refractive index and bandgap of the films increases on annealing. The annealed films exhibit refractive indices in the range of 1.88–2.08 at 600 nm with an optical bandgap value between 3.95–4.16 eV. The increase in the refractive index is attributed to the improvement in packing density and crystallinity, and decrease in the porosity ratio, whereas the increase in bandgap is due to the decrease in intermediary energy levels within the optical bandgap. (Mg0.95Co0.05)TiO3 thin films exhibited a progressive increase in the dielectric properties with OMP and a maximum dielectric constant of ϵr = 17.3 and low loss (tanδ ∼ 1.1 × 10−3) at a spot frequency of 10 GHz for the films deposited at 75% OMP, beyond which they decreased. The improvement in dielectric properties with an increase in OMP has been correlated to the preferred orientation growth, reduction in oxygen vacancies, and strain. The prepared MCT thin films are suitable candidates for anti-reflection coatings and complementary metal-oxide semiconductor (CMOS) applications.