Experimental characterization of Al/SiO2/45°-X-Z Li 2B4O7 SAW device parameters

SiO₂ under layer between Al electrodes and Li₂ B₄O₇ substrate has been shown to provide effective substrate protection both during device fabrication and for long-term device operation. To investigate the parametric dependencies of the basic SAW device parameters in the Al/SiO₂/45°-X-Z Li₂B₄O₇ structure, an experimental study was conducted. Isolated solid-electrode transducers and 2-electrode-per-wavelength reflection gratings of different metallization ratio and fabricated with different metal and SiO₂ layer thickness were measured and analyzed. This paper discusses the dependencies of the SAW velocity, the effective electromechanical coupling, the electrode reflectivity, the transducer static capacitance, and the SAW propagation loss on the metallization ratio and the metal and SiO₂ layer thickness, as well as versus ambient temperature. Several unexpected results are highlighted. Among these are (1) some unusual dependencies of the SAW velocity on electrode width and SiO₂ layer thickness, and (2) some rather strong temperature dependencies of the effective electromechanical coupling and the electrode reflectivity. Impact of these behaviors on practical device design, fabrication and performance is also discussed