Modification of a hybrid sol-gel dielectric and barium titanate for capacitors with ultrahigh energy density
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Capacitors have been widely used in diverse areas owing to their strengths such as high power and fast charge/discharge capability. However, their lack of high energy density has been considered a significant disadvantage that limits their use in energy storage systems. In an effort to conquer the intrinsic weakness, many research efforts have been dedicated to improving the energy density of capacitors by developing new dielectric materials and improving conventional dielectrics via proper modification. In this study, three different approaches were investigated to enhance the electrical properties of thin film capacitors. First, self-assembled monolayers (SAMs) of phosphonic acids were prepared on a hybrid sol-gel dielectric, 2-cyanoethlytrimethoxysilane (CNETMS), to provide a higher energy barrier to the dielectric. With the help of monolayers, leakage currents were reduced and higher energy densities were obtained. Second, thin films of metal oxides including titanium dioxide (TiO2) and zirconium dioxide (ZrO2) were introduced as charge blocking layers into the CNETMS capacitor structure by atomic layer deposition (ALD). TiO2 exhibited a large contribution to the high permittivity of the multilayer structure and in turn to the high energy density. Lastly, barium titanate (BaTiO3) nanoparticles were coated with ZrO2 to form core-shell nanoparticles to smooth the transition between local electric fields applied to the BaTiO3 nanoparticles and the host matrix. The breakdown strength increased with the coating but the rough surface of the coating must be addressed to achieve improved performance in the other electrical characteristics.