Dielectric constants of Ir, Ru, Pt, and IrO2: Contributions from bound charges

Abstract

We investigated the dielectric functions $\epsilon$($\omega$) of Ir, Ru, Pt, and IrO${}_2$, which are commonly used as electrodes in ferroelectric thin film applications. In particular, we investigated the contributions from bound charges ${\epsilon }^b$($\omega$), since these are important scientifically as well as technologically: the ${\epsilon }_1^b$(0) of a metal electrode is one of the major factors determining the depolarization field inside a ferroelectric capacitor. To obtain ${\epsilon }_1^b$(0), we measured reflectivity spectra of sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7 meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings to extract ${\epsilon }_1^b$(0) values. Ir, Ru, Pt, and IrO${}_2$ produced experimental ${\epsilon }_1^b$(0) values of 48$\pm$10, 82$\pm$10, 58$\pm$10, and 29$\pm$5, respectively, which are in good agreement with values obtained using first-principles calculations. These values are much higher than those for noble metals such as Cu, Ag, and Au because transition metals and IrO${}_2$ have such strong d-d transitions below 2.0 eV. High ${\epsilon }_1^b$(0) values will reduce the depolarization field in ferroelectric capacitors, making these materials good candidates for use as electrodes in ferroelectric applications.

arXiv comment26 pages, 6 figures, 2 tables

References in corpus (1)

• Polarization Relaxation Induced by Depolarization Field in Ultrathin Ferroelectric BaTiO${}_3$ Capacitors

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