Thickness and strain effects on RF/microwave properties of BST thin films on NdGaO ₃ substrates

Ba _0.60Sr _0.40TiO ₃ thin films were deposited on 〈100〉 oriented NdGaO ₃ substrates by pulsed-laser deposition. Film thickness ranged from 20 nm to 800 nm. Microstructural features, as evaluated with AFM and FESEM, have exhibited high quality thickness dependent topography. X-ray analyses have shown consistently 〈110〉 textured films of high crystallinity. Permittivity, Q-factor, and tunability, were investigated using interdigitated capacitors in the 0.1-20 GHz range. Effect of film thickness on dielectric properties and tunability in polycrystalline 〈110〉 textured films exhibited strong thickness dependence in their elasto-dielectric properties. Tunability up to 45% was observed at moderate field levels (∼ 7 MV/m), while the Q-factors remained ≤40.