Processing of rf-sputtered lead zirconate titanate thin films on copper foil substrates

• Published in: Journal of materials science Vol. 50; no. 19; pp. 6420 - 6426
• Main Authors: Walenza-Slabe, J., Gibbons, B. J.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-10-2015; Springer; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Copper; Copper oxides; Copper products; Crystallization; Crystallography and Scattering Methods; Dielectric films; Dielectric relaxation; Diffusion barriers; Film thickness; Gettering; Interlayers; Lead compounds; Lead zirconate titanates; Magnetron sputtering; Materials Science; Metal foils; Original Paper; Oxidation; Oxygen; Partial pressure; Polymer Sciences; Solid Mechanics; Substrates; Temperature dependence; Thermal expansion; Thermodynamic equilibrium; Thermodynamics; Thin films; Zirconium; PbO2; Thick Film; Copper Foil; Crystallization Temperature; Cu2O
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-015-9196-5

Pb(Zr
0.52
Ti
0.48
)O
3
(PZT) thin films on copper foils were fabricated via rf magnetron sputtering and ex situ crystallized in a forming gas atmosphere. The PZT/Cu system is interesting due to the low oxygen partial pressure (
p
O
2
) required during crystallization to prevent Cu oxidation, as well as the mismatch of substrate and film coefficients of thermal expansion. The formation of a Cu
2
O interlayer at
p
O
2
levels not thermodynamically predicted suggests that the film and substrate cannot be thought of as being in equilibrium. It was expected that thicker films would provide a stronger barrier to oxygen diffusion from the ambient to the substrate, but instead Cu
2
O formation was found to increase with PZT film thickness. Therefore, the PZT film likely plays an active role in substrate oxidation, perhaps as a source of oxygen. Cu oxidation was significantly minimized by wrapping the films in a sacrificial copper envelope during crystallization. This likely resulted in a gettering of oxygen, which buffered the local
p
O
2
inside the envelope near the—Cu–Cu
2
O thermodynamic equilibrium curve during heating. Two distinct mechanisms may be responsible for the oxidation of the Cu substrate. These can explain the film thickness and crystallization temperature dependence of the Cu
2
O interlayer formation, as well as justify the use of a Cu envelope. The dielectric response and hysteresis are shown for samples with varying amounts of the Cu
2
O interlayer. A dielectric relaxation near 1 kHz was correlated to the presence of the interlayer.