Strain effects on the dielectric properties of epitaxial SrTiO3 thin films grown by pulsed laser deposition

SrTiO3 (STO) thin films 1 mu m thick were deposited on conducting SrRuO3 (SRO) bottom electrodes. The films were grown epitaxially on SrTiO3 and LaAlO3 substrates, respectively using a KrF-248 nm laser. The thickness of the SRO buffer (electrode) layer was varied between 150 nm-500 nm in order to study its effect on the dielectric properties of STO. Loss peaks were observed as a function of temperature at various frequencies and these are explained on the basis of the possible relation to the strain in the thin films. The possible effects of the lattice mismatch at the interfaces, thermal expansion coefficient differences and oxygen vacancies generated in the films during growth, on the loss factor are explained. The extremely low losses and reasonably high tunability in these samples are very encouraging, from the perspective of their possible application in microwave device applications.