Resonance of electrostatically actuated thin-film amorphous silicon microelectromechanical systems microresonators in aqueous solutions: Effect of solution conductivity and viscosity

Abstract

The resonance of electrostatically actuated thin-film hydrogenated amorphous silicon microbridges in air and immersed in aqueous solutions is measured and characterized. The detection of the resonance frequency of a microbridge operating in aqueous solutions with high electrical conductivities, up to 8 mS/cm, and high viscosities, up to 0.15 Pa s is demonstrated. The range of actuation voltages needed to excite resonance frequencies in the megahertz in these microstructures under aqueous solutions allows electrostatic actuation without electrode screening and electrolysis. Values of the quality factor between 1 and 10 in aqueous solutions will allow the detection of ∼1 pg of added mass to the resonators.

A Model for Electrostatic Actuation in Conducting Liquids

“…Both m l and b l depend on the density γ l and viscosity μ l of the liquid, as well as the drive frequency [8], [38]- [40]. The dynamic motion of the actuator is characterized by an amplitude magnification factor M , defined as the ratio of the displacement amplitude x p to the static displacement x st and given by…”

“…In addition, microactuators show promise in several other biomedical applications [5], [6], e.g., resonating structures for biochemical sensing [7], [8], microscale testing of single cells and biomaterials [9]- [12], cell manipulation [13], and microsurgical tools [14]. As a result, there is an increasing demand for integrating MEMS actuators into biomedical devices.…”

Modeling and characterization of electrostatic comb-drive actuators in conducting liquid media

“…A differential drive electrode design was demonstrated to overcome these parasitic impedance losses, achieving close to full scale actuation in conducting biological media [9, 10]. Other applications for liquid immersible actuators include resonant sensors [11, 12], parallel plate actuators [13, 14] and microfluidic pumps [15]. Adrega et al [12] used viscous damping models to estimate the viscous effects on a micro-bridge resonator operating in conducting ionic liquids.…”

Frequency-dependent stability of parallel-plate electrostatic actuators in conductive fluids

“…3,4 Electrostatic actuation in highdielectric media requires ac drive signals at frequencies f at least on the order of the critical actuation frequency f c to prevent electrode polarization and electrolysis, [5][6][7] but offers the advantage of lower actuation voltages, and is particularly important to microfluidic and bioMEMS development where it is desirable to integrate actuators into aqueous solutions and other conductive fluids. [8][9][10][11][12] For simplicity and to minimize the applied potential required for actuation, most applications of electrostatic actuators in conductive media have been operated in the high frequency limit, viz.,…”