Investigation On Electrohydrodynamic Jet Forming Deposition Of BTO Thin Films With High Dielectric Constant

Barium titanate, BaTiO₃ （BTO）, known as "the pillar of the electronic ceramic industry", has been widely used as electronic ceramic material in many fields such as energy storage devices and microwave communication, because of its excellent properties including the high dielectric constant, low dielectric loss, good ferroelectricity, piezoelectricity and insulating property. This paper mainly focused on processing the BTO thin film and by comparing electrohydrodynamic jet （E-jet） deposition with electrophoretic deposition, the former was chosen because of its better film deposition performance. The E-jet deposition of BTO thin film was developed and the BTO suspension was firstly formulated. The effects of the electrical parameters of the E-jet deposition on the BTO thin film morphology were studied and the effect of way of heat treatment on the BTO crystalline phase was also discussed. Combining the E-jet deposition and electrospinning process preliminaryly, three-layer structure of BTO fiber-film-fiber was prepared, and its capacitance value was tested. Finally, this structure was simulated by COMSOL.The stable solution and suspension of BTO were used and the BTO thin film was deposited on the silicon substrate by E-jet deposition. The influences of the deposition height and line-to-line pitch of the scanning were studied. It was concluded that reducing E-jet deposition height and optimizing of the line-to-line pitch contributed to less film cracks and density improvement. The impact of the way of heat treatment on BTO crystalline phase was also studied and discussed. From the viewpoint of prevention from cracks, the methods of ladder preheation to release the stress and appropriate annealing were raised. The annealing temperature and the annealing time of BTO films were compared and based on XRD analysis results, the optimal annealing temperature and time to BTO film were obtained. E-jet deposition showed its advantage over the electrophoretic deposition in processing the BTO thin film. The dielectric constant of BTO thin film made by technology above is 2940 at 1kHz at room temperature.To construct the micro-structure on the BTO film surface, electrospinning was applied and the influences of experimental parameters on BTO fiber diameter were also studied. Larger electrospinning height and smaller flow rate were discovered to reduce the BTO fiber diameter and increase the specific surface area. Then the BTO fibers were double-sided deposited on BTO film substrate and its dielectric property was tested and compared. Combining with COMSOL numerical simulation, the influence of microstructure on the capacitor was studied. The results showed that the add of microstructure on the BTO film surface can increase the capacitance value indeed.