A theoretical study on dielectric constants of Ta/sub 2/O/sub 5/ thin films deposited on Ru electrodes

Recently, Ta/sub 2/O/sub 5/ thin film deposited on Ru electrodes that have higher dielectric constants compared to those of bulk Ta/sub 2/O/sub 5/, has been attracting a lot of attention, because of their potential for 1G-bit and over 1G-bit DRAM memory-capacitor applications. However, the atomistic origin of high dielectric constants of the Ta/sub 2/O/sub 5/ film remains unclear. Since dielectric constants of materials generally have their origin in the electronic structures of the materials, a study on the electronic-structure of the Ta/sub 2/O/sub 5/ film is needed to clarify the origin of the dielectric constants of the film at atomic level. This paper is the first attempt to describe the atomistic origin of the high-dielectric constants of the Ta/sub 2/O/sub 5/ film. Using a molecular orbital (MO) method, we found that the one-dimensional TaO chains that exist in the Ta/sub 2/O/sub 5/ film had enhanced polarizabilities and that they were the origin of the high dielectric constants of the film. The MO analyses revealed that the TaO chains had one dimensionally-delocalized electronic-structures when an electric field was applied to the film. We believe that these delocalized electronic structures enhance the polarizabilities.