Doctor of Philosophy (PhD)
Engineering Science (Interdepartmental Program)
Polymer based micro-transducers have many advantages over the traditional silicon based micro-transducers, such as easy integration with metal structures, design flexibility, and low fabrication costs. The characteristics of micro-transducers include converting electrical signals to/from mechanical response, the ability to sustain loading, sensitivity to external excitation, and etc. Some of the difficulties in realizing these characteristics include: characterizing material mechanical properties, techniques for producing electrically conductive polymer structures, and reliable fabrication procedures. In this dissertation, research addressing these difficulties is presented. The developed techniques are demonstrated in the design and fabrication of a SU-8 polymer based comb-drive micro-actuator. The micro-actuator used SU-8 polymer as the main structural material and gold coating film for realizing electrical conduction. It was fabricated with multi-layer, multi-step UV-lithography technology and metallized with titled E-beam deposition and selectively electroless plating techniques. The adhesion properties between metallic surface and SU-8 polymer were measured firstly. After comparing different metals, Au was chosen as the base material for electroplating for its good adhesion to SU-8. Customized micro-fracture toughness measurement procedure was then designed based on ASTM standards to measure the fracture toughness of Ni micro-structures. The difficulties in micro-fabrication were then addressed. Two different approaches were evaluated for fabricating the SU-8 micro-structure: (1) multilayer processing using modified SU-8 with reduced PAG; (2) multilayer processing using normal SU-8 with copper as sacrificial layer. The second method was shown more reliable. The polymer structures were surface metallized using two methods: (1) titled E-beam deposition; (2) selectively electroless plating. The latter was proven to be more suitable for high aspect ratio sidewalls. The proper UV exposure dosage, duration, and other parameters were also established. A novel structural design of comb drive micro-actuator was studied using analytical and finite element analysis. The design was realized with the developed fabrication technologies. Finally, the resulted micro-actuators were tested to prove the feasibility of the design and fabrication.
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Dai, Wen, "Design and fabrication of micro transducers using cured SU-8 polymer as main structural material" (2006). LSU Doctoral Dissertations. 2058.