A flexural plate wave (FPW) device with low insertion loss and high electromechanical coupling coefficient

For micro mass sensing applications, this paper aims to reduce the insertion loss and enhance the electromechanical coupling coefficient of conventional flexural plate wave (FPW) devices utilizing MEMS technology. Four sputtering process parameters (e.g. substrate temperature, sputtering power and pressure, Ar/O₂ flow rate) were modulated to achieve a high C-axis (002) orientated piezoelectric ZnO film and a high electromechanical coupling factor of the FPW device. Under the optimized sputtering condition in this work, a high X-Ray diffraction (XRD) intensity (20,944 a.u) of the ZnO thin-film at 34.2° diffraction angle and a very narrow full-width at half-maximum (FWHM = 0.573°) can be demonstrated. Furthermore, as the optimized ZnO layer integrated on the bulk-micromachined FPW sensor, very low insertion loss (14dB) and high electromechanical coupling coefficient (11.62%) can be obtained at a very low operation frequency.