Characterization of ferroelectric Ba0.6Sr0.4TiO3 thin films on different substrates for reconfigurable microwave application

This paper addresses the characterization of Ba_0.6Sr_0.4TiO₃ dielectric properties on different dielectric substrates using three different components. First, for low frequencies, metal-insulator-metal (MIM) capacitors are used to determine the BST dielectric constant, loss tangent and tunability for different biasing voltages from 0-30 V showing a tunability range of 66%. For microwave frequency ranges, coplanar waveguides (CPW), and interdigital capacitors (IDCs) are investigated on silicon, R-plane sapphire (Al₂O₃) and magnesium oxide (MgO) substrates. CPW is used to determine the complex propagation constant, while IDCs are used to determine the BST voltage tunability from 0-55 V over 1-20 GHz. Sapphire and MgO introduce low loss tangent values of 0.03, while sapphire gives better tunability (20% at 18 GHz) than MgO (8.3% at 18 GHz).