Fabrication of borosilicate-glass-coated CuAg inner electrode for multilayer ceramic actuator

Abstract

This study introduces a new process for the fabrication of an electrode/ceramic multilayer device that uses a mixture of base and noble metals (Cu and Ag) as the inner electrode and is co-fired in air. In order to protect the Cu base metal when exposed to air, the Cu powder was sequentially coated with Ag nanoparticles using a wet process, and borosilicate glass using a sol-gel process. The degrees of oxidation and shrinkage of the glass-coated CuAg during the co-firing process were investigated. The glass-coated CuAg survived without the formation of copper oxide during the binder-burnout process in air at 500 °C. The CuAg was stable and unoxidized even when further heated to 950 °C, which is ascribable to the protection provided by the Ag layer to the Cu exposed to the oxidative atmosphere. The glass-coated CuAg exhibited complicated shrinkage behavior that was similar to that of glass at low temperatures, and to Ag and Cu densification at high temperatures. To examine the electrical performance of the glass-coated CuAg as an inner electrode, a CuAg/(Bi0.37Na0.37Sr0.26)TiO3 (CuAg/BNST) multilayer-ceramic material was prepared using a conventional tape-casting and stacking procedure. The CuAg-paste binders were evaporated at 500 °C in air, and the CuAg electrode was then sintered at 950 °C in air. The electromechanical performance of the CuAg/BNST ceramic device is similar to that of a AgPd/BNST device, indicating that it can potentially be used as the inner electrode in a multilayer device.