Galvano-Diffusion Effect in Thin Film Metal Dielectric Structures

THIS paper describes further studies of galvano-diffusion phenomena as first reported at the 1963 Failure Mechanism Symposium. It has been found that a voltage is generated between the metal electrodes of a thin film metal-dielectric-metal sandwich. A necessary requirement for the phenomenon is ionic diffusion through the dielectric accompanied by an oxidation of one of the metal films. The ionic diffusion is characterized by an activation energy which is characteristic of the dielectric material. The process involves the diffusion of metal ions through the dielectric which then results in a chemical reaction. The electrical circuit is completed by an external load resistor which provides a path for electron flow. It has beeb possible to experimentally correlate the rate of consumption of metal ions (increase in dielectric thickness) with the integrated electron flow through the load resistor. This was accomplished by recording both capacitance and current flow as a function of time while the structure was held at a constant elevated temperature. The test vehicle has consisted primarily of Al-A12O3-Au devices. In these experiments, the Au film acts as an oxygen collector while the Al film is the electrode that is oxidized. Tests have been performed to determine the effect of electrode thickness (both Au and Al) and dielectric thickness on the diffusion rate. The theoretical model that has been proposed and which agrees qualitatively with experiment can be used to predict the life of electronic devices that are susceptible to this phenomenon.