High-performance dielectric thin film nanocomposites of barium titanate and cyanoethyl pullulan: Controlling the barium titanate nanoparticle size using a sol-gel method

A monodispersed BaTiO₃ nanoparticle sol was prepared by a sol-gel method, and the sizes of the obtained nanoparticles were successfully controlled from 15 to 60 nm by controlling the amount of H₂O introduced for the hydrolysis reaction. Cyanoethyl pullulan (CEP) was added to the BaTiO₃ sol to prepare a nanocomposite ink of BaTiO₃ and CEP. A thin film was fabricated by spin-coating the ink on a Pt/Ti/SiO₂/Si wafer. The device obtained from the 30 nm BaTiO₃/CEP nanocomposite ink demonstrated the highest dielectric constant, about 50 at 1 kHz, during the particle size range from 15 to 60 nm. The temperature dependence of the dielectric constant at approximately 120 °C is eliminated using our BaTiO₃ nanoparticles, because of their cubic crystal structure, which does not show a transformation at 120 °C. These improvements of the dielectric properties are important for the development of thin film-type capacitors for compact electric devices.