Effect of the thermal expansion matching on the dielectric 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 rf sputtered (100)-one-axis-oriented polycrystalline (Ba0.5Sr0.5)TiO3 films. These films were grown on various substrates with different thermal expansion coefficients [α(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 α(sub) by enhancement of the surface-normal lattice spacing of (Ba0.5Sr0.5)TiO3 and Pt. Dielectric tunability of the films also linearly increased with the increase in α(sub). These results clearly demonstrate that dielectric tunability tailoring of the (Ba0.5Sr0.5)TiO3 films can be achieved by using residual thermal strain.