Combining Ta2O5 and Nb2O5 in bilayered structures and solid solutions for use in MIM capacitors

Binary systems of Ta2O5 and Nb2O5 are investigated as dielectric materials that allow low-temperature fabrication and are suitable for use in metal-insulator-metal (MIM) capacitors. This investigation shows that a Nb2O5 film is crystallized in a hexagonal symmetry at a temperature of less than 500 degrees C, which is more than 250 degrees C lower than the corresponding temperature for a Ta2O5 film. Using Nb2O5 as a nucleation layer lowers the crystallization temperature for Ta2O5 to less than 500 degrees C. This is because hexagonal Ta2O5 is stably formed on the hexagonal Nb2O5 by heteroepitaxy. A Ta2O5/Nb2O5 bilayer with a high dielectric constant of 50 can therefore be prepared by a 500 degrees C fabrication process. Solid solutions of Nb2O5 and Ta2O5 are also investigated. The substitution of 10% Nb2O5 in Ta2O5 to form (Ta0.9Nb0.1)(2)O-5 was found to decrease the temperature of crystallization from 700 degrees C for pure Ta2O5 to 550 degrees C. The dielectric constant of the (Ta0.9Nb0.1)(2)O-5 film is approximately 20% greater than that of the Ta2O5 film. This is because the substitutional Nb2O5 stabilizes the material in the hexagonal phase, which corresponds to a high dielectric constant, at lower temperatures. (c) 2005 The Electrochemical Society.