In-plane anisotropy in the microwave dielectric properties of SrTiO3 films

Abstract

Microwave tunable dielectric properties of strained (001) SrTiO3 thin films epitaxially deposited on (110) DyScO3 substrates were studied for in-plane film orientations ([100], [010], [110], and [−110]). A significant in-plane anisotropy in dielectric constant and tuning was observed in these SrTiO3 films. The highest dielectric constant and tuning at room temperature are observed along the [010] direction of the SrTiO3 film (1000 Å thick) (3500 and 70% at 1V∕μm, respectively), the lowest ones are observed along the [100] direction (i.e., 2000 and 50% at 1V∕μm, respectively). The dielectric constant and tuning along [−110] and [110] are about 2500 and 30% at 1V∕μm, respectively, which are intermediary to those along the [010] and [100] directions. The dielectric Q(=1∕tanδ) does not show any large difference for the four directions (i.e., Q∼10−20). Also, the phase-transition peak for the [−110] and [110] directions of the SrTiO3 film (300 Å thick) is observed at 275 K, which is lower than that for the [010] and [100] directions. The observed in-plane anisotropic dielectric properties have been interpreted based on the phenomenological thermodynamics of film strain.