High sensitivity quartz cantilever gas sensors

This paper introduces the use of thickness shear mode (TSM) resonators fabricated upon quartz micro cantilevers as a means for highly sensitive gas detection. Background literature is reviewed and clearly indicates the existence of various gas/film interactions that lend themselves to a variety of gas detection schemes. Among these are mass loading, film elasticity and stress-induced frequency changes. The following work clearly demonstrates the use of film stress-induced frequency change as a detection mechanism. Several cantilever and micro bridge designs have been devised to utilize frequency response change due to film stress-induced reactions. Using gaseous mercury and gold sensing films as a test case, the cantilever test results clearly show as much as a factor of 2.4 times the sensor response over a simple mass loaded inverted mesa structure. Additionally, the micro bridge sensor results demonstrate that film stress due to gas film interactions can be coupled into an active acoustic region even if the sensing film is isolated from the active acoustic area. Finally, preliminary results are shown for palladium coated cantilever responses to hydrogen gas.