Improved substrate selection for lateral field TSM sensors

In recent years there have been several motivations away from thickness field excitation and toward lateral field excitation for thickness shear mode (TSM) fluid phase sensors. Lateral field excitation offers an unmetallized sensor surface for electrical interactions while still providing for hermetic packaging of the driven electrodes. Historical substrate selections have supported both thickness field and lateral field excitation, incurring a hybrid operating mode and a significant issue with spurious signals. This effect is not conducive to a commercially-viable, mass-producible sensor. The objectives of this paper are to present a ground-up analysis of the ideal symmetry properties for lateral field excitation and to recommend classes of materials and proper orientations through which to obtain low-spurious lateral field excitation.