Tham khảo tài liệu 'micro electronic and mechanical systems 2009 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fabrication of High Aspect Ratio Microcoils for Electromagnetic Actuators 131 Fig. 10. SEM image of coil line width of 10 pm. Fig. 11. SEM image of coil line width of 30 pm. Formation of seed layer Since an acrylic pipe is non-conductive material a conductive seed layer is required for electroforming. We formed a seed layer on pipe surface using sputtering. In order to realize a circumferentially flat seed layer we have performed sputtering rotating the pipe at 3 rpm and sputtering at three hours. First it was found that a resistance of seed layer between both ends was very high. To solve this problem we moved the position of pipe along its axis Noda et al. 2007 . As this result we successfully produced an approximately 300 nm thick seed layer which was level in the circumferential direction of the pip surface. Copper electroforming Following a seed layer deposition we immersed an acrylic pipe in a copper sulphate solution bath including a levelling agent to uniform electroforming. To form plating film growth uniformity over the all coil line patterns the pipe was connected to mixer and rotated in the plating solution. Figure 12 shows the plating bath. In first plating it is not good result to be due to voids that has generated inside the plating film. It was confirmed that these voids were produced inside coil line patterns had prevented the formation of satisfactory coil lines. Since high aspect ratio structure had been formed to be electroplated it was estimated that air bubbles would remain inside high aspect ratio structure due to surface tension when the pipe was dipped in the plating 132 Micro Electronic and Mechanical Systems Fig. 12. Image diagram of copper electroforing bath. solution. By cleaning air bubbles from spiral structures a vacuum deforming was used before electroforming. In addition the pipe was lifted out of the bath a few times circulating the plating liquid in the patterned area during the plating. After these improvements we .
