Reduction of density of subgrain boundaries and misfit dislocations in epitaxial (001) SrTiO3 thin films: Effect on dielectric tunability

The effect of a YBa2Cu3O7−x buffer layer on the quality of rf magnetron sputtered epitaxial (001) SrTiO3 thin films on a LaAlO3 substrate has been investigated using high resolution transmission electron microscopy. Magnetron sputtered SrTiO3 films generally exhibit a columnar subgrain morphology. By using a 75 nm thick YBa2Cu3O7-x buffer layer the subgrain boundary area was reduced considerably compared to single layer films. Subgrain widths around 130 nm were observed, which corresponded to an 80% reduction of the subgrain boundary area. The density of misfit dislocations was also reduced by 80%. By using a YBa2Cu3O7−x buffer layer, the dielectric tunability increased 30%, to a value of 1.43 (at U=16.5 V/μm, 2 MHz, 77 K). The influence of interfacial strain and misfit dislocations on the subgrain structure, and corresponding effect on the dielectric constant εr, is elucidated.