Characteristics of Surface Acoustic Waves on Proton-Exchanged and Annealed Proton-Exchanged Z-Cut LiNbO3 Using Pyrophosphoric Acid

The characteristics of surface acoustic waves (SAWs) on proton-exchanged (PE) and annealed proton-exchanged (APE) Z-cut Y-propagated LiNbO3 waveguides using pure pyrophosphoric acid are investigated and compared. The distribution of hydrogen in the PE samples measured by secondary-ion mass spectrometry (SIMS) shows a step-like profile with the diffusion constant D 0 and the activation energy Q of about 9×107 µ m2/ h and 82.18 kJ/mol, respectively. The velocity (V p) of SAW on PE samples decreases with the increase of k d, where k is 2π/λ and d is the waveguide depth, and almost exhibits an exponential decay. However, post-annealing will result in a restoration of the decreased velocity and an improvement of the SAW insertion loss (IL). On the other hand, the electromechanical coupling coefficient (K 2) almost decreases with the increase of k d and shows greater sample-to-sample discrepancy.