A study of love-wave acoustic sensors

Love-mode acoustic devices are very promising as biosensors in gaseous and liquid environments because of their high sensitivity. An experimental study of Love-wave devices based on SiO2/ST-cut quartz, over a wide range of SiO2 thickness, is presented in this paper. Devices with up to 7.3 mu m thick SiO2 guiding layers have been successfully manufactured via an r.f. sputtering technique. Mass sensitivity, velocity, insertion loss, oscillation frequency stability and temperature coefficient of the frequency have been studied as a function of layer thickness. The sensitivity increases with increasing layer thickness and reaches a maximum at around 5.5 mu m, for a wavelength of 40 mu m, in accordance with theory. Further increasing the thickness decreases the sensitivity dramatically. High sensitivity (greater than or equal to 300 cm(2) g(-1)) can be achieved at thicknesses between 3.5 and 6.5 mu m. The Love-wave dual-channel delay-line oscillators also demonstrate high frequency stability and low noise levels. The frequencies of the two channels track each other extremely well.