Study On Fabrication Of Microbridge Structure By Micropen Direct Writing Technique

With the rapid development of modern advanced manufacturing technologies, various new methods and new materials come forth continuously, which drive the study and application in the areas of Micro-Electro-Mechanical Systems ( MEMS) fabrication. The direct-write technique is advantageous over the mainstream fabrication techniques for its maskless and simple process, as well as high flexibility. Therefore, the study of application of direct-write technique in the area of MEMS device fabrication is of great significance.In this dissertation, the essential structure for most MEMS devices, microbridge structure, was chosen as the research object. Using polyimide (PI) and gold (Au) paste as sacrificial layer and structural materials respectively, a novel process flow for fabrication of microbridge structures based on micropen direct-write technique was established. The micropen direct writing process, the heat treatment of structural layer and the etching process of polyimide sacrificial layer were discussed in detail.In the micropen direct writing process, the effects of direct writing velocity, gas pressure, the distance between the tip of the micropen to the substrate, the deposition times, as well as the viscosity of polyimide on the width and thickness of the deposited patterns were studied. According to the results, the dimension of microbridge could be adjusted by direct writing velocity and gas pressure mainly.The heat treatment temperature of structural layer must be below the glass temperature of polyimide sacrificial layer, but above the minimum temperature that make the microbridge stand. The experimental results showed that the appropriate temperature was between 250oC and 350oC.In the etching process, the oxygen plasma was applied to eliminate the polyimide sacrificial layer. The influences of O2 flow and power on the etch rate were analyzed based on experiments. Typically, the etch rate of polyimide was 670 nm/min when the polyimide strips were 5μm in thickness and the gold strips were 200μm in width, with 250 W of power and 2 L/min of O2 flow.Using the optimized processing parameters, the microbridge structures in good shape were fabricated successfully when the microbridges were about 200μm in length, 7~13μm in Height and 10μm in thickness. The results proved that applying the micropen direct-write technique to fabricate MEMS devices is of feasibility.