The current density is measured as a function of time for thin (⩽1000 Å) barium strontium titanate (BST) capacitors with platinum electrodes. The current density curve shows a peak prior to the onset of resistance degradation. The peak position on the time axis varies with applied voltage and temperature. The data are explained by the theory for space-charge-limited (SCL) current transients, and the measured current is identified as ionic current associated with oxygen vacancies. Using the SCL analysis, the mobility of the oxygen vacancies is measured as a function of temperature. The mobility obtained from current measurements is shown to be compatible with the Einstein relation for mobility and diffusivity. In summary, the ionic current associated with oxygen vacancies is shown to be an important component of the measured current in thin BST films.
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The effect of hydrogen on strontium bismuth tantalate (SrBi2Ta2O9; SBT) ferroelectric capacitors is investigated. Using several analytical techniques such as x-ray diffraction, electron diffraction, Auger electron, scanning and transmission electron microscopies, the structural and compositional changes in the ferroelectric film are studied as a function of annealing gas and temperature. The mechanism for hydrogen induced damage to the capacitor is identified. Measurements show that the hydrogen induces both structural and compositional changes in the ferroelectric film. Hydrogen reacts with the bismuth oxide to form bismuth and the reduced bismuth diffuses out of the SBT film causing the electrodes to peel.
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