Effect of Y-doping on the dielectric properties of BaTiO₃ films deposited in reducing atmospheres using pulsed laser deposition

BaTiO₃-based multilayer capacitors with Ni electrodes are fired at low Po₂ to prevent the oxidation of Ni. Amphoteric dopants such as Y, Ho and Dy are used to prevent electrical degradation due to oxygen vacancy migration. This paper describes use of this approach in preparing thin film BaTiO₃ capacitors. Tolerance of reducing atmospheres is particularly important in films which are co-processed with resistors such as TaN for integrated resistor-capacitor networks. To assess this approach, films with and without Y-doping were grown in pure N₂ atmospheres by pulsed laser deposition from undoped and 0.2wt% Y₂O₃ doped BaTiO₃ targets, respectively. Films were deposited onto Pt/Ti/SiO₂/Si substrates using a 5-10Hz laser repetition rate, an energy density of 4.2J/cm² and a working pressure of 100mTorr. It was found that polycrystalline perovskite films could be grown at 700°C and that Y-doped films had better crystallinity than the undoped ones. The dielectric constants of films without and with Y-doping are approx. 1100 and approx. 1300 at 1kHz, respectively. The dielectric losses of Y-doped films were lower than for undoped films, possibly because the concentration of mobile charges including oxygen vacancies was decreased. Y-doped films also have a smaller coercive field (25kV/cm) and higher maximum polarization (approx. 20μC/cm²) than undoped films. The defect chemistry of the system is also discussed.