Analysis of Capillary Forces in Electrowetting and Precision Self Assembly

Developments in micro and nano technology have great potential in many applications. Two applications that will be addressed in this work are self assembly of microdevices and Electrowetting in microfluidics. Capillary forces are the most critical factor in both of these techniques and need proper characterization. This thesis describes a detailed study of these forces and explains how they were utilized as an effective source of drive in high end applications. Self assembly is a promising alternative to conventional pick and place robotic assembly of micro components. Its benefits include parallel integration of parts with low equipment costs. Various approaches to self assembly have been demonstrated, yet demanding applications like assembly of micro-optical devices require increased positioning accuracy. This thesis proposes a new method for design of self assembly bonds that addresses this need. Current methods have zero force at the desired assembly position and low stiffness. The proposed method uses a substrate assembly feature to provide a high accuracy alignment guide to the part. The capillary bond region of the part and substrate are then modified to create a non-zero positioning force to maintain the part in the desired assembly position. Capillary force models show that this force aligns the part to the substrate assembly feature and reduces the sensitivity of part position to process variation. Thus, the new configuration analyzed proves substantial improvement in positioning accuracy of capillary self assembly. Guidelines are proposed for the design of an effective assembly bond using this new approach. Electrowetting is another application that has been successfully demonstrated as a means of drop manipulations in digital micro-fluidic devices. These demonstrations show that electrowetting actuation holds great promise, but there are also reports of erratic behavior and system degradation. While a method for electrowetting force measurement to track the degradation of the electrowetting response was demonstrated, this thesis analyzes some adverse effects in the electrowetting response due to variations during measurement of electrowetting forces, specially the variation of volume, the tilt in the part considered for measurements, and defective layer response