The effect of stress on the dielectric properties of barium strontium titanate thin films

Barium strontium titanate thin films are being developed as capacitors in dynamic random access memories. These films, grown on silicon substrates, are under tensile residual stress. By a converse electrostrictive effect, the in-plane tensile stress reduces the capacitance in the thickness direction of the film. We measured the substrate curvature change upon the removal of the film, and found the magnitude of the residual stress to be 610 MPa. In a separate experiment, we applied a force to vary the stress in a film on a substrate, and simultaneously recorded the capacitance change of the film. The measurements quantify the effect of stress on thin film capacitance. The stress free capacitance was found to be 23% higher than the capacitance under residual stress.