Retardation of O diffusion through polycrystalline Pt by Be doping

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Abstract
A serious problem preventing the use of high dielectric oxide materials (e.g., barium-strontium-titanate) for capacitors as part of future dynamic random access memory is the oxidation of or the O diffusion through the electrodes. Platinum electrodes do not oxidize, but they allow for rapid O diffusion through the Pt film while the dielectric is deposited and annealed. This causes unwanted oxidation below the Pt film. Using first-principles electronic structure calculations, we first determine the O diffusion mechanism in polycrystalline Pt. We find that O diffuses as interstitial O along the grain boundary (GB) that we study. The calculated barrier is compatible with the experimental estimate. We screen nine elements for their potential to retard O diffusion if added to the Pt in small amounts. Beryllium is the most promising candidate. Be segregates to Pt GB’s at interstitial and substitutional sites. As GB interstitial Be diffuses at a rate comparable to that of O and it repels O. This leads to a stuffing of the GB. As substitutionally absorbed Be, Be has a high diffusion barrier, and it forms strong bonds to O. Thus O is trapped in the GB. Preliminary experimental results confirm our theoretical predictions.