Investigation of acoustomigration effects in Al-based metallizations

In contrast to other investigations on power durability where the over-all time-to-failure (TTF) of commercial filter devices is measured for comparison of different metallizations we extrapolate the TTF values in a steady-state of acoustomigration. The filters were driven in a cw-mode at their center frequency at constant power level and fixed ambient temperature. Within short terms the frequency characteristic was regularly probed to track the shift of center frequency in order to secure constant loading conditions. The TTF value calculated from the slope of a middle-term linear frequency shift over time was taken as a measure of power durability. The electrical measurements were assisted by scanning electron (SEM) and ion (FIB) microscopic techniques to investigate the structural changes in the metallization layer at different states of degradation. In addition, we have used for the first time very thin (thickness in the nm scale) protective layers for electrode cladding. The influence of these layers on the device characteristics was studied as well as their power capability enhancement.