A numerical method for calculating the dynamic stress in SAW devices

SAW-induced stress-migration, also known as acoustomigration is a well-known phenomenon in the field of surface acoustic wave (SAW) devices. In order to improve the power durability of SAW devices a better understanding of the acoustomigration mechanism as well as a detailed knowledge of the stress distribution in the SAW devices is essential. We present a numerical method to calculate the absolute values of the dynamic stress in the metallization for a given driving condition and frequency at each point in the metal structure. To present the device we use a P-matrix based model, which yields the acoustic power distribution and the resulting energy density in the device for a given driving level. For the calculation of the relative stress values we use the finite element method. To calculate quantitatively the distribution of the stress values we use the relationship between the energy density distribution and the sum of the strain-stress products. This method is a very flexible tool for the stress analysis and the detailed investigation of the driving forces of acoustomigration and the development of power durable SAW devices.