Anisotropic tuning behavior in epitaxial Ba0.5Sr0.5TiO3 thin films

The tuning properties of epitaxial ${\mathrm{Ba}}_{\mathrm{0.5}}{\mathrm{Sr}}_{\mathrm{0.5}}{\mathrm{TiO}}_{\mathrm{3}}$ (BST) thin films were investigated by a scanning microwave microscope (SMM) and an LCR meter. Although the BST films on ${\mathrm{LaAlO}}_{\mathrm{3}}$ and MgO substrates showed similar tuning behavior when measured by the LCR meter at 1 MHz, remarkably different tuning properties were observed in the planar capacitors measured by SMM. The BST films on ${\mathrm{LaAlO}}_{\mathrm{3}}$ substrates were hardly tuned when measured by SMM, while the BST films on MgO showed significant tuning behavior between the electrodes. We attribute these different tuning properties to the anisotropic tuning caused by the strain in BST films. This will enable the design of much improved tunable devices while minimizing the loss associated with the dielectric.