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

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.