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

Abstract

Lead-free ferroelectric sol-gel thin films derived from barium strontium titanate (Ba0.85Sr0.15Zr0.1Ti0.9O3, 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.