Low-loss Ba0.5Sr0.5TiO3 thin films by inverted cylindrical magnetron sputtering

The structural and electrical characteristics of Ba0.5Sr0.5TiO3 (BST) thin films deposited by inverted cylindrical magnetron rf sputtering have been i nvestigated. This unconventional sputter deposition technique consisting of a hollow cylindrical composite target of BST, high argon/oxygen gas pressu re 53.2 Pa (400 mu m), and 750 degrees C substrate temperature was employed for depositing low-loss BST thin films. The films were postannealed in a t ube furnace at 780 degrees C for 8 h in flowing oxygen. Atomic-force micros copy revealed anisotropic grain growth with a columnar grain structure prot ruding from the surface with a 0.25 mu m grain size. X-ray diffractometry s hows the films to be purely (h00) oriented for certain deposition parameter s. The lattice parameter of the best film was slightly larger than that for bulk BST. Other deposition conditions yielded films having many of the BST powder peaks. Capacitance versus voltage characteristics have been measure d from 50 MHz to 20 GHz. Device Q values > 600, beyond the resolution of th e device/measurement system, were realized with a 6.7% tunability at 10 GHz for the best films. [S0021-8979(00)01119-1].