Improvement in Power Durability of Al Electrode Films Used in SAW Devices by Zr Additive and Ti Underlayer
In order to improve the power durability of Al electrode films and obtain fine-dimensional control in high-frequency surface acoustic wave (SAW) devices, two-layered Al-Zr/Ti electrode films were investigated on 128°Y−X LiNbO3 substrates by sputter deposition. The results indicated that Al-Zr/Ti electrode films had improved electromigration (EM) reliability compared to Al/Ti electrode films and their lifetime was strongly dependent on the microstructure and Zr concentration. Al-Zr/Ti electrode films with a strong Al (111) texture exhibited longer EM lifetime than polycrystalline films. The Al-Zr/Ti electrode film with an ideal Zr concentration of 0.2 wt.% and a sputtering pressure of 0.25 Pa had a strong Al (111) texture, and its lifetime was approximately four times longer than that of Al/Ti films tested at a current density of 5 × 107 A/cm2 at 200°C. Furthermore, the Al-Zr/Ti films were easily etched in reactive ion etching and fine-dimensional control was realized during pattern replication for high-frequency SAW devices.