Low temperature (<100°C) hydrothermal synthesis of high K-low loss BaTiO3 films for integral capacitors

Integration of passive components like resistors, inductors and capacitors into the substrate offers a number of advantages including better electrical performance, miniaturization, reliability and reduced part counts. The integral capacitor requirements in today´s systems vary widely from 1-20 pF for signal capacitors in RF applications to 0.01- 0.1 μF for digital, RF and power decoupling. Ferroelectric thin films can provide this wide range of properties but their integration has been rendered impossible due to either high temperatures involved in processing or high cost associated with thin film deposition techniques. In this paper we report synthesis of low loss hydrothermal BaTiO₃ thin films via a low temperature process - hydrothermal synthesis at 95°C on laminated titanium foils. The films grown on Titanium foils were subsequently treated with oxygen plasma to improve the yield and reduce the dielectric loss. The films were characterized systematically using X-Ray Diffraction analysis, SEM and capacitance measurements. Films synthesized on thinner foils revealed nanograins under SEM and upon treating in oxygen plasma demonstrated dielectric loss of 0.06 at 100 kHz, which is the lowest loss reported on hydrothermal films synthesized at these temperatures. The effect of titanium source, hydrothermal conditions and the post hydrothermal treatment on the dielectric constant and loss of the synthesized films is discussed. Films with capacitance of more than 1.5 μF/cm² and thickness of 300 nm (corresponding to a dielectric constant of above 350) were integrated into standard Printed Wiring Board processes using Ti foil lamination, patterning, hydrothermal treatment and electroless plating of copper for top metallization. These films are suitable candidate materials for digital decoupling applications.