Development of High Dielectric Constant Ceramic Films Using Multilayer Electrophoretic Deposition of BaTiO3 Berkan Harari

Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Canada Introduction Barium Titanate (BaTiO3) is a common ferroelectric material used in energy storage devices known as capacitors. Due to its perovskite structure and high dielectric constant it is widely used in the electronics industry. Electrophoretic deposition is a cost-effective technique to prepare homogenous BaTiO3 green films on various substrates [1]. This colloidal forming technique has processing parameters that are difficult to control therefore void formation and cracking are a common occurrence. These anomalies significantly degrade the material’s electrical properties. The coating normally experiences 10-15% linear shrinkage during sintering which also contributes to the presence of defects. Currently there are several methods that can reduce this problem such as liquid phase sintering using glass enamel, matching the thermal expansion coefficient of the substrate with the film and by using a reaction-bonding technique [2]. These methods are difficult to reproduce and do not tackle the problem of void formation very well. In this study a novel multilayer electrophoretic deposition technique is introduced. Methods and Results The particle size distribution of advanced Barium Titanate powder was determined using an LA-910 Horiba Laser Scattering Particle Size Analyzer. The mean particle size was found to be 0.903µm. A Rigaku X-ray diffractometer was used to confirm the composition of the powder and it’s lack of contaminants. 0.225g of powder was ultrasonically mixed in a 30ml Ethanol/Acetone suspension medium with a 2:1 ratio. Two substrates were cut out from Ni foil (125µm), etched, and cathodic electrophoretic deposition was performed on them. One sample was deposited on continuously while the other underwent three deposition/sintering steps. A constant potential of 10V was applied throughout this process. The sintering steps involved drying the samples at 140°C for 30min then heating to 1250°C at a rate of 5°C/min and holding for 1hr in reducing atmosphere. The absence of NiO was confirmed using X-ray diffraction. Further peak broadening analysis comparing the multilayer film to the single layer film of the same thickness showed the existence of larger grains in the multilayer film due to repeated sintering. SEM images (Figure 1) were used to determine the average grain size near the Ni/BaTiO3 interface. A value of 20µm and 1.5µm was found for the multilayer and single layer films respectively. Dielectric measurements were carried out on a Solartron 1260 Impedance Analyzer. The results showed a significantly lower dielectric constant for the multilayer film that was due to the presence of larger grains along the interface. The dielectric losses for the single layer film were higher due to the presence of defects (Figure 2). It is clear that multilayer electrophoretic deposition is an affective way of preventing cracking and covering voids. However, this technique results in lower dielectric constants.

Figure 1: SEM images of BaTiO3 grains for Figure 2: Dielectric constant (top) and Dissipation Factor (bottom) 1 layer film (top) and 3 layer film (bottom) vs. Frequency for 1 layer film and 3 layer film References [1] Yaseen, Hanady, Sioma Baltianski, and Yoed Tsur. "Cathodic Electrophoretic Deposition of Barium Titanate Films from Aqueous Solution." Journal of Materials Science 42.23 (2007): 9679-683. [2] Boccaccini, Aldo R., and Jan B. Talbot. Electrophoretic Deposition, Fundamentals and Applications: Proceedings of the International Symposium. Pennington, NJ: Electrochemical Society, 2002.