Reliability of Bulk Acoustic Wave Resonators at High Power and High Frequency

We present the results of high-power reliability experiments performed in AlN thin-film piezoelectric bulk-acoustic-wave resonators. The experiments show that electromigration effects damage the aluminum electrodes of the device in a few hours of input power in the range of work of these devices. We have detected that this failure is very sensitive to the frequency of the input power, and we have quantified the damage using different techniques as atomic-force-microscope measurements, electrical measurements, and scanning-electron-microscope images. Due to the frequency selectivity of this effect, we present a high-power reliability experiment that allows us to compare different samples and is insensitive to the frequency of operation. We propose this technique as a standard procedure when testing for the high-power reliability of these devices. We have found that one solution to the problem is to deposit a Ti layer on top of the Al electrode to avoid the electromigration. Our results show that these improved devices can meet the expected power handling/lifetime requirement for duplexer filters in current wireless devices.