Characterization of acoustomigration with on-wafer measurement system

Developed an automated on-wafer measurement system and a suitable test device for the design-independent characterization of different metallization layers on piezoelectric substrates with respect to acoustomigration. With the measurement system we are able to measure the devices on the wafer without any additional manual handling. The test devices were fabricated on LiTaO₃ with Al and AlCu electrodes. The temperature and the applied stress level were kept constant during measurements with the help of our temperature and frequency controlled probing system. The observed reversible and irreversible shift in the test device resonance frequencies originates from self heating and migration in the metal layer, respectively. As a time-to-failure (TTF) criterion an irreversible frequency shift of 1 MHz is defined. The variations of TTF with respect to temperature and power can be interpreted in terms of an Eyring model, which assumes an Arrhenius law for the temperature dependence and a power law dependence for the applied power. As a result it was confirmed that the addition of Cu enhances the power durability of an Al film significantly