ENHANCED DIELECTRIC PROPERTIES OF (Ba, Sr)TiO3 THIN FILMS FOR HIGH-PERFORMANCE MICROWAVE PHASE SHIFTERS†

Abstract

ABSTRACT Barium strontium titanate (BST) thin films have been intensively studied as a frequency and phase agile materials for the tunable microwave devices such as tunable filter, phase shifter and phased array antennas. The dielectric properties of BST thin films, including the dielectric constant, dielectric loss and tunability of capacitance are affected by many factors, such as Ba/Sr ratio, growth temperature, crystallographic orientation, grain size, defect chemistry, oxygen vacancies, strain and stress, and dopants. In this work, we report on the enhanced dielectric properties of (Ba0.6, Sr0.4)TiO3 (BST) thin films for high-performance microwave tunable device applications. Epitaxial BST thin films were deposited on MgO substrates by the insertion of thin BaTiO3 [BT] seed layers with intermediate lattice mismatch between the BST films and the MgO substrate using a pulsed laser ablation. Dielectric measurements were carried out using planar interdigitated (IDT) capacitor in ranges of RF/microwave frequency. IDT capacitor based on epitaxial BST film exhibited the large capacitance tunability of 77% at a frequency of 100 kHz and applied electric field of 80 kV/cm. CPW phase shifter showed the large phase tuning of 153° at 10 GHz and 40 V. These results indicate that it is a promising candidate for high-performance microwave phase shifters at room temperature. †Originally presented at 2004 ISIF, Kyung Ju, Korea, April 5-8, 2004.