Effect of post annealing on structural, optical and dielectric properties of MgTiO_3 thin films deposited by RF magnetron sputtering

摘要

MgTiO_3 (MTO) thin films have been deposited on to quartz and platinized silicon (Pt/TiO_2/SiO_2/Si) substrates by RF magnetron sputtering. The metal-MTO-metal (Ag-MTO-Pt/TiO_2/SiO_2/Si) thin film capacitors have been fabricated at different oxygen mixing percentage (OMP). The effects of OMP and post annealing on the structural, microstructural, optical and dielectric properties of MTO films were studied. The MTO target has been synthesized by mechanochemical synthesis method. The phase purity of the sputtering target was confirmed from X-ray diffraction pattern and refined to R3 space group with lattice parameters a=b = 5.0557(12) A, c=1 3.9003(9) A. The chemical composition of the deposited films was confirmed from EDS spectra and all the films exhibited the composition of the sputtering target. The XRD patterns of the as-deposited films are amorphous and annealing at 700℃ for 1 h induced nanocrystallinity with the improved optical and dielectric properties. The annealed films exhibit refractive index in the range of 2.12-2.19 at 600nm with an optical bandgap value in between 4.11 and 4.19eV. The increase in the refractive index and bandgap upon annealing can be attributed to the improvement in packing density, crystallinity, and decrease in porosity ratio. Both the dielectric constant and tan 8 decrease with the increase in frequency and were in the range of 13.7-31.11 and 0.006-0.124, respectively. The improvement in dielectric properties with the increase in OMP has been correlated to the reduction in oxygen vacancies, increase in crystallinity and grain size of the films.