Sol-gel preparation of barium strontium titanate thin films

Barium strontium titanate, ((Ba_xSr_1-x)TiO ₃), thin films of various compositions were prepared by a spin coating technique. Processing parameters were optimized to develop stable solutions which yielded crack-free films with relatively low crystallization temperatures. XRD and thermal analysis techniques were used to characterize the films and gels. The dielectric constant and dissipation factor of the films were measured as a function of temperature and frequency. Leakage current was measured as a function of voltage and time. It was determined that ethylene glycol was a necessary component of the solution to increase stability and to decrease the crystallization temperature of the films. A dielectric constant of 400 and a dissipation factor of 0.04 was measured at 1 kHz for films of the approximate composition (Ba_0.8Sr_0.2)TiO₃ with a thickness of 400 nm. Films of this composition maintained low leakage current densities for extended time periods when measured at an applied field of 0.08 MV/cm. The BST thin films therefore exhibited properties sufficient for application as DRAM capacitors