Chemical sensors using surface acoustic wave devices on proton-exchanged LiNbO₃

Waveguides provide several advantages such as acoustic beam confinement, prolongation of delay time, and high acoustic intensity to acoustic devices. Using proton exchange, waveguides on Z-cut and Y128°-cut LiNbO₃ crystals were applied to investigate chemical detection in a dilute conductive solution. The changes in velocity and the attenuation as a function of conductivity of the solution are discussed. Theoretical calculations obtained through perturbation theory are compared with experimental results. From the measurement, it is clearly indicated that the surface acoustic wave can be used to detect the conductivity of the dilute electrolyte. For Z-cut LiNbO₃, proton-exchanged devices exhibit higher sensitivity than unexchanged devices. The dielectric constant of proton-exchanged layer is not easily directly measured; however, it can be calculated from the critical conductivity