A Latent Failure Mechanism for Surface Acoustic Wave Components Utilizing Lithium Niobate

A latent failure mechanism for surface acoustic wave components which utilize lithium niobate as the piezoelectric has been, identified. This failure mechanism involves the growth of aluminum oxide on the thin film aluminum metal which constitutes the interdigitated electrical/mechanical transducer structure. This failure mechanism has been successfully eliminated in high-reliability components by making certain that a necessary condition for the growth of the oxide does not exist. The necessary condition is the existence of a dc electric field within the transducer structure. The exact conditions necessary for the initiation of the oxide growth have not, as yet, been determined. It is known that electric field values of the order of 104 volts per centimeter with ambient temperature of 125°C for 168 hours can cause the growth. The effect of the growth is to reduce the effective electroacoustical coupling factor which results in the component exhibiting added insertion loss and a skewing of pass band RF characteristics as the growth progresses.