Daniel S. Krueger

Supercritical extraction of binder containing poly(vinyl butyral) and dioctyl phthalate from barium titanate–platinum multilayer ceramic capacitors

Supercritical extraction using carbon dioxide was examined for the removal of binder from multilayer ceramic capacitors. The binder contained poly(vinyl butyral) (PVB) and dioctyl phthalate (DOP), and the dielectric and metal electrode materials were barium titanate and platinum, respectively. At 40 MPa of carbon dioxide at 95 °C, approximately 55 wt % of the binder could be removed, and this was mainly the dioctyl phthalate component. The use of entrainers such as 2-propanol, methyl isobutyl ketone, and n-hexane was seen to have negligible effect on the degree of binder removal. The dielectric constant, loss tangent, and breakdown voltage of devices processed by supercritical extraction were similar as compared to devices processed by thermal oxidation alone. Although it was not possible to extract all of the binder with supercritical carbon dioxide, removal of the DOP fraction increases the pore space in the body by a factor of two. Transport model calculations indicate this partial removal of binder mitigates the buildup of pressure in the subsequent thermal processing step and can reduce the processing time for thermal removal of the remaining binder by a factor of 25.

Effect of porosity on the electrical properties of Y2O3-doped SrTiO3 internal boundary layer capacitors

Compositions of 0.8 mole % Y2O3-doped SrTiO3 were sintered over a range of temperatures of 1450–1550 °C for times of 1–15 h, and the resulting internal boundary layer capacitors had relative densities ranging from 92% to 98%. The effective dielectric constant and effective conductivity were highly correlated with each other, and both electrical properties decreased strongly with increasing porosity. To account for the effect of porosity on the two electrical properties, a scaling law model was developed, which takes into account the grain size, the thickness of the grain boundary region, the pore size, and the pore aspect ratio. The model predicts a strong decrease in effective dielectric constant and effective conductivity with porosity for internal boundary layer capacitors, which is in accord with the observed trends.