Combining Ta2O5 and Nb2O5 in Bilayered Structures and Solid Solutions for Use in MIM Capacitors

Binary systems of Ta 2 O 5 and Nb 2 O 5 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 Nb 2 O 5 film is crystallized in a hexagonal symmetry at a temperature of less than 500°C, which is more than 250°C lower than the corresponding temperature for a Ta 2 O 5 film. Using Nb 2 O 5 as a nucleation layer lowers the crystallization temperature for Ta 2 O 5 to less than 500°C. This is because hexagonal Ta 2 O 5 is stably formed on the hexagonal Nb 2 O 5 by heteroepitaxy. A Ta 2 O 5 /Nb 2 O 5 bilayer with a high dielectric constant of 50 can therefore be prepared by a 500°C fabrication process. Solid solutions of Nb 2 O 5 and Ta 2 O 5 are also investigated. The substitution of 10% Nb 2 O 5 in Ta 2 O 5 to form (Ta 0 . 9 Nb 0 . 1 ) 2 O 5 was found to decrease the temperature of crystallization from 700°C for pure Ta 2 O 5 to 550°C. The dielectric constant of the (Ta 0 . 9 Nb 0 . 1 ) 2 O 5 film is approximately 20% greater than that of the Ta 2 O 5 film. This is because the substitutional Nb 2 O 5 stabilizes the material in the hexagonal phase, which corresponds to a high dielectric constant, at lower temperatures.