Sensitivity of a Lamb wave sensor with 2 microm AlN membrane.

Anti-symmetrical Lamb wave mode A0 presents a large sensitivity to mass loading and can be used in contact with liquids with a small attenuation. The advantages of this system are the possibility to get a large mass sensitivity. The sensitivity increases when the thickness of membrane decreases. Therefore the problem is to obtain thin piezoelectric membranes. A membrane of AlN with a thickness of 2 microm has been made. The measured mass sensitivity with a fluid is 200 cm(2) g(-1). In a practical use point of view, the problem in this kind of sensor is its temperature sensitivity. In order to reduce effective temperature sensitivity, a device with thin metallic strips is presented. On the same membrane two different waves with perpendicular propagating directions are produced. Experimentally, temperature sensitivity is rather different depending on the propagation direction but mass sensitivity is almost the same, this allows distinguishing temperature effects from those due to mass loading on the frequency shift measurements.