A novel test device to characterize SAW acoustomigration

Acoustomigration is a well-known problem for SAW-filters used for front-end applications in modern mobile communications systems. Many different metallizations have been investigated so far to overcome this problem. Because of different test devices, testing conditions, and failure criteria it is difficult to compare and discuss the experimental results obtained by different research groups. Moreover, the electrical performance is changing during testing and thus the stress level in the metallization changes, too. In the present work, we propose a method to test metallizations independently of the influence of the SAW test device with defined and constant stressing of the metallization during the measurement campaigns. The device is a two-port resonator with a metallized area in the cavity. Migration patterns occur only in this fully metallized area whereas all electrodes remain unaffected. The irreversible shift of the resonance frequency due to acoustomigration can be evaluated as a function of temperature and input power during testing. Thus, the acoustomigration-related quality of different metallizations can be characterized in a well-defined manner.