CAPILLARY FORCES AT THE INTERFACE OF A MEMS ACTUATOR

A MEMS actuator has been designed, fabricated, and tested for the purpose of understanding capillary forces of liquids at the microscale. Experiments showed that this novel design method allows a MEMS plate, with dimensions of 100 μm x 20 μm x 4 μm thick, to be lowered by 10x its thickness into de-ionized water without inundation of the plate or the MEMS actuator's sensitive areas. The maximum force applied to the MEMS actuator during the lowering of the device was 5.2 μN, as recorded by the calibrated MEMS springs. In another experiment, the plate was extracted from the water's surface and a maximum force of 12.3 μN was applied to the plate. Movement of the plate during extraction was 40-50 μm. The novel design method utilizes the ability of sharp edges to prohibit the spreading of the de-ionized water. The mechanism by which the contact line between the water, air, and MEMS plate moves is described in detail. This mechanism also explains why the maximum force during the lowering of the plate was less than that of the plate being extracted from the water's surface.