Breakdown Sites in MIM Structures

Metal-aluminum oxide-metal structures are prepared by physical vapour deposition on silicon wafers. Their final breakdown field is 4.5 MV/cm. Above 1 MV/cm partial breakdown spots appear on the electrodes. The spots are not only restricted to the volume of the oxide films with thickness 200 nm, but they extend down into the silicon substrate. Crater-like holes with depths of about 1.5 μm are formed as revealed by an atomic force microscope. An amount of energy 50 times higher than stored electrostatically in the structure is necessary to burn these craters by a melting process. It is supposed, that the hot breakdown channels trigger a second process, which delivers the missing energy. In this second process hydrogen ions might be involved.