Seed layer mediated growth of high dielectric and low leakage BaTiO₃ thin film using two-step sputtering process

In this study, we demonstrated the seed layer mediated growth of high-quality BaTiO₃ (BTO) thin films using a two-step radio frequency (RF) magnetron sputtering process. Since the as-grown BTO thin films obtained by RF magnetron sputtering at the deposition temperatures of 300–500 °C were amorphous with a low dielectric constant of 20, it is necessary to develop a fabrication process for obtaining crystalline high-k BTO thin films without sacrificing other film properties such as morphology and leakage current. First, it was revealed that ex-situ post-deposition annealing (PDA) at high temperatures in the 700–800 °C range led to the crystallization of BTO films and a high dielectric constant of 121. However, the film morphology deteriorated significantly during PDA, and consequently, a high leakage current was observed due to the rough and discontinuous surface containing voids and micro-cracks. To achieve an excellent leakage current characteristic as well as a high dielectric constant for a crystalline BTO thin film, in-situ crystallization was carried out through local epitaxial growth using a crystalline seed layer. The crystalline BTO seed layer was formed by annealing a 5-nm-thick amorphous BTO film at 700 °C on which the in-situ crystallized BTO main layer was deposited at 500 °C. The in-situ crystallization method resulted in a smooth and uniform surface and a high dielectric constant of 113. In addition, the in-situ crystallized BTO film exhibited a low leakage current density of 10⁻⁶ A/cm² (at 0.8 V) displaying an improvement by a factor of 10³ compared to the ex-situ crystallized BTO film.