OXYGEN VACANCY MOBILITY DETERMINED FROM CURRENT MEASUREMENTS IN THIN BA0.5SR0.5TIO3 FILMS

The current density is measured as a function of time for thin (less t han or equal to 1000 Angstrom) barium strontium titanate (BST) capacit ors with platinum electrodes. The current density curve shows a peak p rior to the onset of resistance degradation. The peak position on the time axis varies with applied voltage and temperature. The data are ex plained by the theory for space-charge-limited (SCL) current transient s, and the measured current is identified as ionic current associated with oxygen vacancies. Using the SCL analysis, the mobility of the oxy gen vacancies is measured as a function of temperature. The mobility o btained from current measurements is shown to be compatible with the E instein relation for mobility and diffusivity. In summary, the ionic c urrent associated with oxygen vacancies is shown to be an important co mponent of the measured current in thin BST films. (C) 1998 American I nstitute of Physics.