Effect of internal residual stress on the dielectric properties and microstructure of sputter-deposited polycrystalline (Ba,Sr)TiO3 thin films

Abstract

The role of internal residual stress in the dielectric properties of sputter-deposited polycrystalline (Ba,Sr)TiO3 thin films was studied experimentally using test samples in the form of parallel-plate capacitors on platinized silicon substrate. Different deposition-pressure conditions provided a systematic change in the film stress and we found that a reduction in the in-plane tensile stress of the films (primarily originating from the thermal expansion mismatch) was effective for increasing the dielectric constant in the out-of-plane direction. On the other hand, a large in-plane tensile stress (exceeding 1GPa) cannot be elastically accommodated in a 250-nm-thick (Ba,Sr)TiO3 thin film and the film relaxes through the optically visible microcrack formation. The relationship between the internal residual stress and the dielectric constant of the crack-free (Ba,Sr)TiO3 thin films could be well explained by the phenomenological thermodynamic theory of Landau–Ginsburg–Devonshire, without a transition to the in-plane polar axis phase.