Understanding the influence of surface chemical states on the dielectric tunability of sputtered Ba < inf > 0.5 < /inf > Sr < inf > 0.5 < /inf > TiO < inf > 3 < /inf > thin films

Abstract

The surface chemical states of RF-magnetron sputtered Ba0.5Sr0.5TiO3 (BST5) thin films deposited at different oxygen mixing percentage (OMP) was examined by x-ray photoelectron spectroscopy. The O1s XPS spectra indicate the existence of three kinds of oxygen species (dissociated oxygen ion O2-, adsorbed oxide ion O-and lattice oxide ion O2-) on the films' surface, which strongly depends on OMP. The presence of oxygen species other than lattice oxygen ion makes the films' surface highly reactivity to atmospheric gases, resulting in the formation of undesired surface layers. The XPS results confirm the formation of surface nitrates for the films deposited under oxygen deficient atmosphere (OMP-25%), whereas the films deposited in oxygen rich atmosphere (OMP-75%) show the presence of metal-hydroxide. The influence of a surface dead layer on the tunable dielectric properties of BST5 films have been studied in detail and are reported. Furthermore, our observations indicate that an optimum ratio of Ar:O2 is essential for achieving desired material and dielectric properties in BST5 thin films. The films deposited at 50% OMP have the highest dielectric tunability of ~65% (@280 kV cm-1), with good E curve symmetry of 98% and low tan of 0.018. The figure of merit for these films is about 35, which is promising for frequency agile device applications.