Dielectric Properties of (Ba_xSr_1-x)TiO₃ Thin Films Prepared by RF Sputtering for Dynamic Random Access Memory Application

Abstract

Dielectric properties of (Ba 0.5 Sr 0.5 )TiO 3 and (Ba 0.75 Sr 0.25 )TiO 3 thin films have been investigated, focusing on the effects of film structure and Ba/Sr compositions on the dielectric properties. Dielectric constant of the films increased with increasing grain size and with improvement in film crystallinity. For the 50-nm-thick films deposited at 660° C, the dielectric constant of 400 for the (Ba 0.5 Sr 0.5 )TiO 3 film is larger than that of 320 for the (Ba 0.75 Sr 0.25 )TiO 3 film. This indicated that dielectric constant is affected by the ratio of Ba/Sr composition. Leakage current density of less than 1×10 -7 A/cm 2 at 1 V and SiO 2 equivalent thickness of 0.38 nm are measured at 120° C for 660° C-deposited (Ba 0.5 Sr 0.5 )TiO 3 film of 30 nm in thickness. The (Ba 0.5 Sr 0.5 )TiO 3 film has the possibility for application to generations beyond 256 Mbit dynamic random access memories.