Low-Temperature Hydrothermal Deposition of (BaxSr1-x)TiO3 Thin Films on Flexible Polymeric Substrates for Embedded Applications

The fabrication of ferroelectric thin films on flexible metal foils or polymeric substrates is of particular interest for embedded capacitors integrated into Printed Circuit Boards (PCB). In this work, BaxSr1-xTiO3 (x = 1, 0.9, 0.7, 05, 0.3, 0.1, and 0) polycrystalline thin films were fabricated at low temperature (120 degrees C) and for a short time (1 h) by a hydrothermal process on commercial flexible polymeric Kapton films. Microstructural analysis showed that dense BaTiO3 thin films comparable to those derived from long time hydrothermal processes were achieved with the present synthesis conditions. With increasing strontium content, BaxSr1-xTiO3 film thickness decreased and grain size increased. For x = 0, i.e., SrTiO3, the films displayed a monolayer of coarse grains. The variation of the film morphology with the composition suggests a faster nucleation and reaction kinetics for BaTiO3 than SrTiO3. Electrical characterization showed high capacitance densities and acceptable dielectric loss for the films after postannealing in oxygen. Existence of polar domains in the hydrothermally synthesized BaTiO3 thin films was proved by piezo-response force microscopy (PFM). All the used processes were compatible with commercial Kapton films, showing the technological value of this work for the deposition of large area capacitors onto flexible printed circuits.