Improved Tunability and Energy Storage Density Properties of Low-Loss, Lead-Free (Ba0.50Sr0.50)TiO3 and Ba(Zr0.15Ti0.85)O3 Bilayer Thin Film Stacks

Multilayer thin films of (Ba_0.50Sr_0.50)TiO₃ (BST) and Ba(Zr_0.15Ti_0.85)O₃ (BZT) were designed and grown using pulsed laser deposition technology. The periodic (BST/BZT)_n thin films were deposited on Pt‹111›/SiO₂/Si substrates. X-ray diffraction revealed the presence of a polycrystalline, perovskite structure corresponding to the bilayer thin film stacks. Scanning electron microscopy confirmed the multilayer structure without any interdiffusion across layers. It was also found that the dielectric and ferroelectric properties of the thin films were strongly influenced by the periodic heterostructures. The thin film stacks exhibited significantly higher tunability as compared with multilayer thin films grown on various single-crystal substrates such as LaAlO₃, MgO and SrTiO₃. Possible mechanisms explaining the other observed attributes such as improved dielectric properties and reduced leakage current are discussed. The effect of incorporating a comparatively lower-permittivity thin film in the multilayer stacks is presented. The observed properties of such multilayer structured films will aid in realizing low-loss and highly tunable applications.