Copper Compatible Barium Titanate Thin Films for Embedded Passives

• Published in: Journal of electroceramics 2005-03, Vol.14 (2), p.95-102
• Main Authors: Ihlefeld, Jon, Laughlin, Brian, Hunt-Lowery, Alisa, Borland, William, Kingon, Angus, Maria, Jon-Paul
• Format: Article
• Language: English
• Subjects: Barium; Point defects; Thin films
• ISSN: 1385-3449; 1573-8663
• DOI: 10.1007/s10832-005-0866-6

Barium titanate thin films were prepared by chemical solution deposition on 18 micron thick, industry standard copper foils in the absence of chemical barrier layers. The final embodiment exhibited randomly oriented BaTiO3 grains with diameters between 0.1 and 0.3 micron, and an equiaxed morphology. The average film thickness was 0.6 micron and the microstructure was free from secondary or interfacial phases. The BaTiO3 films were sintered in a high temperature reducing atmosphere such that copper oxidation is avoided. Subsequent lower-temperature, higher oxygen pressure anneals were used to minimise oxygen point defects. Permittivities of 2500 were seen at zero bias and room temperature, with permittivities > 3000 at the coercive field. Loss tangents < 1.5% were shown at high fields. The BaTiO3 phase exhibited pronounced ferroelectric switching and coercive field values near 10 kV/cm. Temperature dependent measurements indicated a ferroelectric transition near 100 C with very diffuse character. Combining the approaches of the multilayer capacitor industry with traditional solution processed thin films has allowed pure barium titanate to be integrated with copper. The high sintering temperature, compared to typical film processing, provides for large grained films and properties consistent with well-prepared ceramics. Integrating BaTiO3 films on copper foil represents an important step towards high capacitance density embedded passive components and elimination of economic constraints imparted by traditional noble metallisation. 33 refs.