Mass sensitivity of love-mode acoustic sensors incorporating silicon dioxide and silicon-oxy-fluoride guiding layers

摘要

A detailed experimental study of the sensitivity to mass loading has been carried out for Love-mode acoustic sensors of frequency ～110 MHz and wavelength 40 μm, consisting of ST-cut quartz overlaid with various thicknesses of sputtered silicon dioxide guiding layers. Measurements of the sensitivity at various positions on the surfaces of the devices showed that the relative sensitivity of the IDT electrodes and 'sweet spot' (between' the IDTs) depends strongly on guiding layer thickness. The manufacture and properties of devices incorporating a versatile new guiding layer material based on silicon-oxy-fluorine has also been investigated. The characteristic velocity of shear acoustic waves in this material may be varied by controlling the fluorine content during deposition. A systematic study of the sensitivity and insertion loss has been carried out for devices incorporating guiding layers produced with various fluorine concentrations. Highly sensitive devices have been produced with guiding layer thickness ～2 to ～5.5 μm. Some preliminary results have also been obtained for devices incorporating multilayer or continuously graded silicon-oxy-fluoride guiding layers. The properties of most of the devices are extremely stable in air at room temperature.