Ba0.6Sr0.4TiO3 and BaZr0.3Ti0.7O3 thick films as tunable microwave dielectrics

Thick films have been investigated for application in frequency and phase agile microwave devices. Since Ba0.6Sr0.4TiO3 (BST) and BaZr0.3Ti0.7O3 (BZT) bulk ceramics exhibit high tunability (τ=ε0−εEmaxε0) near room temperature, both compositions have been chosen for preparation of screen printed thick films. Low frequency dielectric properties have been characterized using metal-insulator-metal capacitor structures in a temperature range of −120 °C to +160 °C. Measurements of the bias dependent permittivity show a hysteresis effect in both materials in the whole investigated temperature range. BZT thick films exhibit a more diffuse phase transition than BST and therefore a lower temperature dependence. Permittivity, dielectric loss and tunability have also been determined at microwave frequencies from 4 to 90 GHz. Temperature and frequency dependence of the dielectric losses and tunability of both materials have been compared.