High power durable SAW antenna duplexers for W-CDMA with epitaxially grown aluminum electrodes

We have fabricated surface acoustic wave antenna duplexers for W-CDMA with epitaxial aluminum electrodes. Devices with epitaxial electrodes have achieved 2.5 × 10⁶ hours estimated lifetime at an input power of 0.8 W and in an ambient temperature of 50°C, which is several orders longer than those with polycrystalline electrodes. Since stress migration is attributed to self-diffusion of aluminum atoms mainly ruled with the grain boundary region in the film, the epitaxial aluminum film that is highly oriented and has extremely less grain boundary makes it possible to suppress stress migration and improve power durability. A new epitaxial relationship has been found to be Al(111)<011> // Ti(001)<100> // LiNbO₃(001)<100>, not based on the rotation angles between 63° to 70° of θ rotated Y-X LiNbO₃ substrates. The titanium intermediate layer plays an important role to relax the lattice mismatch between LiNbO₃(001) and Al(111) planes and to form epitaxially grown aluminum films. The intriguing crystal growth mechanism is discussed in detail.