Electrical Properties And Failure Mechanisms Of Ultra-thin MLCCs With High Capacitance

Multilayer ceramic capacitors（MLCCs）are the most popular passive components used in electronic devices.In order to fulfill the increasing demands for high capacitance,high reliability and miniaturization,developing ultra-thin MLCCs with high capacitance has become imperative.In this thesis work,ultra-thin MLCCs with high capacitance fabricated with different barium titanate（BaTiO₃）powders were investigated and the effects of BaTiO3 powder characteristics and annealing oxygen partial pressure on the electrical properties and reliability of MLCCs were analyzed,and the mechanisms related to the degradation of insulation resistance and failure were discussed.The whole analysis method of the powder-ceramic-component was preliminarily established,and the strategy to improve the reliability of MLCCs was proposed,which will facilitate the development of ultra-thin MLCCs with improved performance.Results and conclusions are summarized as follows:The ultra-thin MLCCs with high capacitance were prepared using commercial BaTiO₃ powders with different physicochemical properties.For the MLCC using BaTiO₃ powders with low specific surface area（4.66 m~2/g）synthesized by oxalate method,as its layer thickness is 1μm and the grain size is 285 nm,it demonstrates the optimal performance,showing an insulation resistivity of～3×10~9Ω·m and meets the X6S requirements.It is revealed that the grain boundary concentration of BaTiO₃ceramic puts a strong influence on the breakdown voltage and degradation of insulation resistance.The BaTiO₃ powder prepared through oxalate method has a small specific surface area and a uniform particle size,which can be employed to fabricate ultra-thin layered MLCCs with high capacitance.Nextly,the ultra-thin X6T-type MLCCs were prepared under different oxygen partial pressures during annealing process.Under the annealing condition with oxygen partial pressure of～10^-4 atm,the MLCC with a thickness of～1.2μm demonstrates a dielectric constant of～5300,an insulation resistivity of 2×10~9Ω·m,a breakdown field of 52.7 V/μm and the estimated mean time to failure of about 53.0 years.Therefore,an annealing condition with high oxygen partial pressure could reduce the concentration of oxygen vacancies to achieve a high dielectric constant and a high insulation resistivity,increase the activation energy of grains and grain boundaries,and extend the degradation time of MLCCs.The failure mechanisms associated with insulation resistance degradation and breakdown were analyzed through impedance testing at high temperatures and transmission electron microscopy.The high direct current degradation dominated by inter-diffusion layer in MLCCs could be rationalized by the suppressed Schottky barrier due to the thick inter-diffusion layer between Ni and BaTiO₃.In summary,BaTiO₃ powder with low specific surface area synthesized by oxalate method helps to improve the insulation resistivity and breakdown strength of MLCCs,and high annealing oxygen partial pressure further enhances the insulation resistivity and dielectric constant,and can lengthen the degradation time of MLCC insulation resistance and avoid breakdown failure in degradation.