Composition-control of magnetron-sputter-deposited (BaxSr1-x)Ti1+yO3+z thin films for voltage tunable devices

Precise control of composition and microstructure is critical for the produ ction of (BaxSr1-x)Ti1+yO3+z (BST) dielectric thin films with the large dep endence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into t unable high-frequency devices. Here, we present results on composition-micr ostructure-electrical property relationships for polycrystalline BST films produced by magnetron-sputter deposition, that are appropriate for microwav e and millimeter-wave applications such as varactors and frequency triplers . Films with controlled compositions were grown from a stoichiometric Ba0.5 Sr0.5TiO3 target by control of the background processing gas pressure. It w as determined that the (Ba+Sr)/Ti ratios of these BST films could be adjust ed from 0.73 to 0.98 by changing the total (Ar+O-2) process pressure, while the O-2/Ar ratio did not strongly affect the metal ion composition. Film c rystalline structure and dielectric properties as a function of the (Ba+Sr) /Ti ratio are discussed. Optimized BST films yielded capacitors with low di electric losses (0.0047), among the best reported for sputtered BST, while still maintaining tunabilities suitable for device applications. (C) 2000 A merican Institute of Physics. [S0003-6951(00)01705-8].