Electron microscopy of heterogeneous interfaces in cofired noble and base metal electrode multilayer ceramic capacitors (MLCCS)

The compatibility of electrodes and dielectrics in cofired MLCCs with both Ni and Ag/Pd electrodes was characterized by transmission electron microscopy (TEM) using tripod polished samples. Tripod polishing procedures can reduce entire devices to a thickness of less than 1 mum. After low angle ion milling for a short time, many regions across several dielectric and electrode layers are electron transparent, which makes it possible to characterize the cofired interfacial microstructures. Analyzed by convergent beam electron diffraction (CBED) and energy dispersive X-ray spectrometry (EDS), NiO lamellae and P-rich intermediate layers were found in the highly accelerated life tested (HALT) MLCCs with Ni electrodes. CBED confirmed that the P-rich layers had Ba(4)Ti(13)O30 (B4T13) structures. Oxidized Ni layers containing Mn were also found in the HALT samples. It is believed that Mn ions were reduced by the Ni electrodes, as P-rich segregated layers were observed in the virginal (non-life tested) MLCCs. No silver diffusion was found in either the BaTiO3 based perovskite lattices or the flux phases in X7R type MLCCs fired in air.