Impact of electrode materials on microstructure, leakage current and dielectric tunable properties of lead-free BSZT thin films

Lead-free ferroelectric sol-gel thin films derived from barium strontium titanate (Ba_0.85Sr_0.15Zr_0.1Ti_0.9O₃, BSZT) were deposited onto two types of electrode: (i) noble metallic Pt- and (ii) conductive oxides LaNiO₃- and SrRuO₃-coated silicon substrates. The present studies demonstrate that electrode materials impact significantly on morphology, crystallographic orientation, lattice mismatch-induced microstrains and electrical properties of BSZT thin films. Highly (100)-textured BSZT thin films with the highest crystallinity and lowest microstrain were found on conductive oxide electrodes, whereas Pt electrodes showed polycrystalline. Capacitors with oxide LaNiO₃ electrode display predominated Schottky emission with a rather low leakage current density ~4.68 × 10⁻⁸ A/cm², while Pt electrode capacitors indicate space-charge limited conduction. Dielectric characterizations in the frequency range of 10³–5 × 10⁶ Hz and the dc electric field up to ±800 kV/cm show that the permittivity, loss tangent, and tunability of BSZT films also strongly depend on the electrode materials used. The optimal dielectric tunability with a large figure of merit (FOM ≈ 22.53) and low dielectric loss (tanδ ≈ 2.9%), was found to be 66% for BSZT thin films on the conductive LaNiO₃ electrode, suggesting that the as-deposited ferroelectric films are promising candidates for applications in tunable microwave elements and related electronic devices.