Effect of the Strain from the Substrate on Tunability of(100) One-axis Oriented (Ba0.5Sr0.5)TiO3 Thin Films

The impact of the residual strain induced by the thermal strain on the dielectric tunability was systematically studied for (100)-one-axis-oriented polycrystalline (Ba_0.5Sr_0.5)TiO₃ films. These films were grown on various substrates with different thermal expansion coefficients [a_(sub.)] covered with a stack of (100)_cSrRuO₃/(100) _cLaNiO₃/(111)Pt layers. The residual strain was ascertained to linearly increase with the increase in a_(sub.) by enhancement of the surface-normal lattice spacing of (Ba_0.5Sr_0.5)TiO₃ and Pt. Dielectric tunability of the films also linearly increased with the increase in a_(sub.). These results clearly demonstrate that dielectric tunability tailoring of the (Ba_0.5Sr_0.5)TiO₃ films can be achieved by using residual thermal strain.