Acoustic Wave Conductometric Sensors

The article presents outcomes of a finite element study of the acousto-electric (AE) effect associated with the propagation of acoustic waves in c-ZnO piezoelectric films subjected to electric conductivity changes. ZnO is a well-known wide-bandgap semiconductor: if illuminated by ultraviolet (UV) light, it changes its electrical conductivity which alters the electrostatic potential travelling in synchronous with the acoustic waves. As the mechanical and electrical field waves are inter-coupled in piezoelectric materials, as a result the wave velocity and propagation loss change thus revealing the in-progress photoconductivity process. The electroacoustic device’ response (the wave velocity and insertion loss changes) to the external stimulus can be utilized for applications to highly sensitive UV detectors based on the acoustic-waves propagation. The AE effect associated with the propagation of surface acoustic waves and Lamb modes in ZnO (i.e. the waves velocity and propagation loss shifts induced by the ZnO bulk conductivity changes) are theoretically studied for different ZnO thicknesses and wavelengths. The calculated conductometric sensitivities (i.e., the relative velocity change per unit conductivity change) demonstrate the suitability of the ZnO-based surface acoustic wave (SAW) and Lamb-mode devices to design a multi-mode sensing structure with high sensitivity and wide dynamic range.