Refined model of electromigration of ag/pd electrodes in multilayer pzt ceramics under extreme humidity

The phenomenon of silver electromigration has been examined in multilayer structures comprised of a low-firing PZT-based ceramic with inner Ag _1-xPd _x electrodes (0<x<0.3). Under high humidity and dc bias, the time-to-failure was found to increase significantly with Pd content for x>0.1. Failed samples exhibited metallic-like transport properties including Ohmic behavior and a low temperature coefficient of resistance. Subsequently, electron microscopy of cross-sectioned samples revealed high concentrations of Ag in grain boundaries confirming Ag migration as the failure mechanism. Furthermore, it was found that the failure rate did not improve substantially by replacing a pure Ag anode with a higher Pd composition. This observation appears to conflict with previous conceptual models in which Ag migration originates mainly from the anode. It is suggested that Ag diffusion during sintering results in a background concentration of Ag within the ceramic which later contributes to the electrolytic flux of Ag ⁺ ions under high humidity. This effect may be more apparent in low temperature sintered materials where residual grain boundary phases become vulnerable pathways for moisture penetration.