Preparation and characterization of barium titanate dielectric thin/thick films for MLCC applications

Miniaturization in microelectronic devices mandates much smaller multilayer ceramic capacitors with higher volumetric efficiency. One of the major efforts is to produce a much thinner (<3 μm) BaTiO₃ (BT) dielectric layers. Although some chemical processes such as sol-gel, hydrothermal, and chemical vapor deposition have proven to be useful methods to prepare thin films, the difficulty for preparing thick films is well recognized. As ceramic nanopowders are widely available, electrophoretic deposition and sol-gel powder coating processes tend to be effective methods to prepare particle films which have potential applications not only in electronic, magnetic, and electro-optic thick films devices, but also in thermal, chemical, and wear-resistant coatings. The most important advantage is that these processes can easily achieve an intermediate thickness (1∼5 μm) which other processes have difficulty in meeting.; This research investigated an electrophoretic deposition process to prepare dielectric ceramic thick films. Uniform and relatively dense BaTiO₃ thick films of 1∼5 μm were prepared by using submicron BaTiO₃ powders (∼0.2 μm). The thickness can be controlled by keeping the applied voltage and current drop constant for a given concentration BaTiO ₃ suspension in an ethanol/acetone medium. The microstructural examination indicated that the BaTiO₃ thick films deposited by EPD have a uniform and dense microstructure due to the selective movement of BaTiO₃ particles under the uniform DC electric field. Dielectric properties were characterized in terms of the sintering temperature.; A highly stable, water-based BaTiO₃ sol system (BTLA) was developed using a chelate acetate sol-gel process. XRD, FT-IR and DTA/TGA were used to investigate the structure evolution of BaTiO₃ gels. The BaTiO₃ thin films prepared from BTLA sol have the cubic perovskite structure. The resulting microstructures indicated that the BaTiO₃ thin films consisted of nanocrystallites with a grain size of 30–60 nm. The dielectric constant vs. temperature curve exhibited no dielectric peak at the Curie temperature.; A sol-gel particle coating process was investigated to prepare BaTiO ₃ composite thick films by mixing BTLA sol and dry X7R powder without introducing any other organic additives such as binder or dispersants. The dispersing and binding mechanisms of BaTiO₃ sol will be discussed. The film quality was evaluated in terms of solids concentration and mixing time. The rheology of the BaTiO₃ suspension and the film density were also characterized. The microstructure and sintering behavior of BaTiO ₃ composite thick films were investigated by SEM and AM. The dielectric properties of BaTiO₃ composite thick films sintered at different temperatures and times were measured.; The BaTiO₃ thick film samples with different BaTiO₃ gel fractions were prepared by using different concentrations of BaTiO ₃ sol and solid content. The effect of BaTiO₃ gel volume fraction on the dielectric constant was investigated. Different models were used to evaluate the dielectric mixing effect. A dielectric mixing model software package was developed to demonstrate visual illustration of theoretical dielectric mixing models, and provides a function to predict the dielectric constant of the BaTiO₃ composite thick films at different volume fractions.