Large dielectric constant (ε/ε0>6000) Ba0.4Sr0.6TiO3 thin films for high-performance microwave phase shifters

We deposited epitaxial Ba0.4Sr0.6TiO3 (BST) films via laser ablation on MgO and LaAlO3 (LAO) substrates for tunable microwave devices. Postdeposition anneals (similar to 1100 degrees C in O-2) improved the morphology and overall dielectric properties of films on both substrates, but shifted the temperature of maximum dielectric constant (T-max) up for BST/LAO and down for BST/MgO. These substrate-dependent T-max shifts had opposite effects on the room-temperature dielectric properties. Overall, BST films on MgO had the larger maximum dielectric constant (epsilon/epsilon(0)greater than or equal to 6000) and tunability (Delta epsilon/epsilon greater than or equal to 65%), but these maxima occurred at 227 K. 30 GHz phase shifters made from similar films had figures of merit (ratio of maximum phase shift to insertion loss) of similar to 45 degrees/dB and phase shifts of similar to 400 degrees under 500 V (similar to 13 V/mu m) bias, illustrating their utility for many frequency-agile microwave devices. (C) 2000 American Institute of Physics. [S0003-6951(00)02814-X].