Love-Mode MEMS Devices for Sensing Applications in Liquids

Abstract

Love-wave-based MEMS devices are theoretically investigated in their potential role as a promising technological platform for the development of acoustic-wave-based sensors for liquid environments. Both single- and bi-layered structures have been investigated and the velocity dispersion curves were calculated for different layer thicknesses, crystallographic orientations, material types and electrical boundary conditions. High velocity materials have been investigated too, enabling device miniaturization, power consumption reduction and integration with the conditioning electronic circuits. The electroacoustic coupling coefficient dispersion curves of the first four Love modes are calculated for four dispersive coupling configurations based on a c-axis tilted ZnO layer on wz-BN substrate. The gravimetric sensitivity of four Love modes travelling at a common velocity of 9318 m/s along different layer thicknesses, and of three Love modes travelling at different velocity along a fixed ZnO layer thickness, are calculated in order to design enhanced-performance sensors. The phase velocity shift and attenuation due to the presence of a viscous liquid contacting the device surface are calculated for different thicknesses of a c-axis inclined ZnO layer onto BN half-space.

Mathematical modelling of Love waves propagation in viscoelastic waveguide loaded with complex fluids

“…which was previously obtained by [6,13,21]. A last comparison can be drawn between the present generalized complex dispersion equation ( 19) and those of literature in the case of Love waves propagating in viscoelastic waveguide without any fluid on its surface.…”

Viscoelastic fluid effect on the surface wave propagation

“…Three detailed dispersion relations were established, (i) viscoelastic fluid with finite substrate, (ii) viscoelastic fluid with semi-infinite substrate, and (iii) Newtonian fluid with semi-infinite substrate. The last dispersion relation was previously obtained by [6,18]. Finally, the new original theoretical resolution proposed in this work can be used to develop and design the Love wave sensors.…”

Guided acoustic wave sensors for liquid environments

“…The IDTs can be located only onto the piezoelectric substrate surface, under the overlayer, and thus they are isolate from the liquid environment. ZnO antibody-antigen immunoreactions in aqueous solutions [66] The LMs also propagate along a non-piezoelectric halfspace (such as Si, glass, BN, a-SiC,...) covered by a piezoelectric layer (such as c-axis tilted ZnO or AlN) [58,[67][68][69].…”

“…The K 2 dispersion curves for the a) LM1, b) LM2, c) LM3 and d) LM4 modes in 90°tilted c-axis ZnO/wBN, for the four coupling configurations[68].…”