Operation of electrothermal and electrostatic MUMPs microactuators underwater

Abstract

Surface-micromachined actuators made in multi-user MEMS processes (MUMPs) have been operated underwater without modifying the manufacturing process. Such actuators have generally been either electro-thermally or electro-statically actuated and both actuator styles are tested here for suitability underwater. This is believed to be the first time that thermal and electrostatic actuators have been compared for deflection underwater relative to air performance. A high-frequency ac square wave is used to replicate a dc-driven actuator output without the associated problem of electrolysis in water. This method of ac activation, with frequencies far above the mechanical resonance frequencies of the MEMS actuators, has been termed root mean square (RMS) operation. Both thermal and electrostatic actuators have been tested and proved to work using RMS control. Underwater performance has been evaluated by using in-air operation of these actuators as a benchmark. When comparing deflection per volt applied, thermal actuators operate between 5 and 9% of in-air deflection and electrostatic actuators show an improvement in force per volt applied of upwards of 6000%. These results agree with predictions based on the physical properties of the surrounding medium.

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.,…”

Design of a novel MEMS platform for the biaxial stimulation of living cells

“…As a matter of fact the displacement in water is much lower than one would expect. This is probably due to the fact that water is prevented from flowing under the PolyS 1 layer (which is the bottom part of the moving layer), since the silicon-water interface tension is high, which in turn causes the silicon surface to behave hydrophobically (Sameoto, 2004). Therefore the resulting stiction forces across water-air meniscus reduce device performance.…”

Viable cell handling with high aspect ratio polymer chopstick gripper mounted on a nano precision manipulator

“…1) was motivated by the necessity to optimize its performance in aqueous media in which the cell manipulation is performed. Chevron-type actuator was preferred over the conventional hot-arm cold-arm type, since the thermal gradient required to obtain optimum actuation of the latter is compromised in aqueous medium (Sameoto et al 2004). The long gripper arms were designed in the shape of a chopstick in order to ensure sufficient isolation of the cell handling tips from the metallic heater layer, which undergoes the maximum temperature change.…”