An Application of a Low-Loss MOD-Made BST Film Developed Especially with PLD Initial Nucleation Layer to a 20 GHz Tunable Phase Shifter

Abstract

ABSTRACTBarium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO substrate by combining preparation of initial layer by Pulsed Laser Deposition and main layer by Metal-Organic-Decomposition method. Films with an initial layer of 20, 30 and 40 nm thickness and final thickness of 400, 650 and 800 nm have been obtained. Physical and dielectric properties of the BST thin films have been characterized from the viewpoint of frequency-agile micro and millimeter wave circuit applications. The results reveal that Ba0.6Sr0.4TiO3 thin films have a good crystallinity with characteristic orientation that is affected by the deposition conditions of the initial layer. Interdigital capacitor with a gap of 10 μm has been characterized and the dielectric loss and tunability are as low as 0.002 to 0.004 and 12%, respectively, at frequency of 1 MHz for the applied voltage from -/+40V to +/-40V. At microwave frequencies, classical coplanar waveguide lines formed on BST/(100)MgO were investigated. A differential phase shift of 18 degree was obtained at 20 GHz with insertion loss of about −2 dB at 60 V for Au/Cr interconnection. Finally, a 3-stage LC-ladder-type phase shifter with variable capacitors of BST thin film has been fabricated considering the experimental results obtained for the coplanar waveguide lines and a maximum phase shift of 40 degrees is obtained at 20 GHz at 60 V.