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Lead zirconate titanate thin films directly on copper electrodes for ferroelectric, dielectric and piezoelectric applications

Abstract

Replacement of noble metal electrodes by base metals significantly lowers the cost of ferroelectric, piezoelectric and dielectric devices. Here, we demonstrate that it is possible to process lead zirconate (Pb(Zr0.52Ti0.48)O3, or PZT) thin films directly on base metal copper foils. We explore the impact of the oxygen partial pressure during processing, and demonstrate that high-quality films and interfaces can be achieved through control of the oxygen partial pressure within a narrow window predicted by thermodynamic stability considerations. This demonstration has broad implications, opening up the possibility of the use of low-cost, high-conductivity copper electrodes for a range of Pb-based perovskite materials, including PZT films in embedded printed circuit board applications for capacitors, varactors and sensors; multilayer PZT piezoelectric stacks; and multilayer dielectric and electrostrictive devices based on lead magnesium niobate–lead titanate. We also point out that the capacitors do not fatigue on repeated switching, unlike those with Pt noble metal electrodes. Instead, they appear to be fatigue-resistant, like capacitors with oxide electrodes. This may have implications for ferroelectric non-volatile memories.

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Figure 1: Thermodynamic representation of Cu-Cu2O, Cu2O-CuO and Pb-PbO stability conditions.
Figure 2: X-ray diffraction pattern (Cu K radiation) of PZT thin film on Cu foil.
Figure 3: Atomic force microscopy topography image of PZT thin-film surface on copper foil.
Figure 4
Figure 5: Polarization–electric field hysteresis loops of PZT thin-film capacitor on copper foil.
Figure 6: Fatigue characteristics of a typical Cu/PZT capacitor (Cu as the top electrode) on Cu foil, in comparison with a Pt/PZT capacitor on Pt foil.
Figure 7: Leakage-current dependence on applied voltage of PZT thin film on copper foil.

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Acknowledgements

The authors acknowledge important discussions and experimental support from Jon-Paul Maria, as well as experimental support from Taeyun Kim, Thomas Blair, Jon Ihlefeld and Dan Lichtenwalner. The authors also acknowledge financial support from the National Science Foundation through contract no. 0113350, as well as a Sidney Stein grant from the International Microelectronics and Packaging Society.

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Correspondence to Angus I Kingon.

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Kingon, A., Srinivasan, S. Lead zirconate titanate thin films directly on copper electrodes for ferroelectric, dielectric and piezoelectric applications. Nature Mater 4, 233–237 (2005). https://doi.org/10.1038/nmat1334

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