Capacitors are in numerous electronic systems, ranging in application from medical, telecommunications, computational, consumer electronics, transportation, and military. In development of modern day capacitors, long-term reliability is often limited by electrochemical processes within the capacitive materials that ultimately lead to material and device failure. With continued miniaturization of devices and electronic components, reliability becomes a more critical issue in maintaining yields and insuring electrical system longevity. This research aims to understand the statistical nature of material failure in capacitor materials using unique characterization techniques to identify local defects within a device that ultimately evolve to limit the lifetime of the component. This research program is collaborative endeavor between Kemet Corporation (Greenville, SC), who has vast experience in producing commercial multilayer ceramic capacitors and Penn State University who has an established history of research in capacitor materials and the analytical tools necessary to understand the physical origins of material degradation. Beyond providing a new experimental methodology for assessing and understanding degradation and failure, the program will foster greater university-industrial interaction and provide students with a dual industrial/academic perspective on a scientifically rich and technologically significant materials science research program.
This research program focuses on material degradation phenomena in BaTiO3-based multilayer ceramic capacitors, with the specific aim of understanding scaling laws for degradation as the dielectric layers are reduced to submicron thickness. Generally, it is agreed that the loss of insulation resistance (increase in leakage current) in BaTiO3 is associated with the migration of oxygen vacancies under a DC bias. The kinetics of this degradation process, however, are a function of many processing variables, including dielectric and electrode formulations, layer thicknesses and lay-down, processing temperatures and PO2, all of which affect the microstructure and distribution of dopants and point defects within the material. Moreover, for each of these processes there are significant scaling issues encountered as the dielectric layer thickness is reduced below 1 mm, which need to be quantitatively and statistically evaluated and scientifically understood. Utilizing electron probe techniques that are sensitive to voltage and current imaging, we identify locations of high leakage current in capacitive devices. Applying these methods in-situ within a focused ion beam system, samples are extracted from the weak points of capacitors for more detailed electrical and structural analysis. A statistical approach is applied and modeled to better understand the onset of total leakage of a device from its microscopic origins. This research is timely, given the fact that within the next ten years, multilayer capacitors based on barium titanate will reduce to thicknesses of the order of 0.2 micrometers, and with layers approaching the many hundreds.
