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Highly elastic conductive polymeric MEMS

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ABSTRACT

Polymeric structures with integrated, functional microelectrical mechanical systems (MEMS) elements are increasingly important in various applications such as biomedical systems or wearable smart devices. These applications require highly flexible and elastic polymers with good conductivity, which can be embedded into a matrix that undergoes large deformations. Conductive polydimethylsiloxane (PDMS) is a suitable candidate but is still challenging to fabricate. Conductivity is achieved by filling a nonconductive PDMS matrix with conductive particles. In this work, we present an approach that uses new mixing techniques to fabricate conductive PDMS with different fillers such as carbon black, silver particles, and multiwalled carbon nanotubes. Additionally, the electrical properties of all three composites are examined under continuous mechanical stress. Furthermore, we present a novel, low-cost, simple three-step molding process that transfers a micro patterned silicon master into a polystyrene (PS) polytetrafluoroethylene (PTFE) replica with improved release features. This PS/PTFE mold is used for subsequent structuring of conductive PDMS with high accuracy. The non sticking characteristics enable the fabrication of delicate structures using a very soft PDMS, which is usually hard to release from conventional molds. Moreover, the process can also be applied to polyurethanes and various other material combinations.

No MeSH data available.


Laser-scanning images of (a) the Si master, (b) the PS/PTFE mold; and (c) the final conductive PDMS structure. The dimensions are as follows: line width, 140 μm; gap width, 40 μm; depth, 220 μm; and inner radius of the meanders, 48 μm.
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Figure 4: Laser-scanning images of (a) the Si master, (b) the PS/PTFE mold; and (c) the final conductive PDMS structure. The dimensions are as follows: line width, 140 μm; gap width, 40 μm; depth, 220 μm; and inner radius of the meanders, 48 μm.

Mentions: The process presented in this work allows the fabrication of PDMS structures with very high aspect ratios and minimal structures of 40 μm with a cost-efficient and easily adaptable benchtop approach. For test purposes, a capacitive strain gauge is fabricated. It consists of an interdigital finger structure with conductive lines with a width of 140 μm and gaps between parallel lines of 40 μm. A horseshoe design is used for the electrical connectors on both sides, forming a special stress-tolerant design. The accuracy of the molding process is displayed in figure 4. Using a laser scanning microscope (Axio LSM Pascal 510, Carl Zeiss AG, Oberkochen, Germany), the structural dimensions of the Si master are compared with those of both the PTFE/PS mold and the resulting conductive PDMS structure. The width of the gaps and lines of the structure were measured exemplarily. Within the measurement accuracy of +/− 1 μm, no difference in the dimensions of the Si master mold and the final PDMS structure were observed. Even tiny details, such as scratches or etching defects much smaller than 1 μm, were transferred from the Si master to the PS/PTFE mold.


Highly elastic conductive polymeric MEMS
Laser-scanning images of (a) the Si master, (b) the PS/PTFE mold; and (c) the final conductive PDMS structure. The dimensions are as follows: line width, 140 μm; gap width, 40 μm; depth, 220 μm; and inner radius of the meanders, 48 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036488&req=5

Figure 4: Laser-scanning images of (a) the Si master, (b) the PS/PTFE mold; and (c) the final conductive PDMS structure. The dimensions are as follows: line width, 140 μm; gap width, 40 μm; depth, 220 μm; and inner radius of the meanders, 48 μm.
Mentions: The process presented in this work allows the fabrication of PDMS structures with very high aspect ratios and minimal structures of 40 μm with a cost-efficient and easily adaptable benchtop approach. For test purposes, a capacitive strain gauge is fabricated. It consists of an interdigital finger structure with conductive lines with a width of 140 μm and gaps between parallel lines of 40 μm. A horseshoe design is used for the electrical connectors on both sides, forming a special stress-tolerant design. The accuracy of the molding process is displayed in figure 4. Using a laser scanning microscope (Axio LSM Pascal 510, Carl Zeiss AG, Oberkochen, Germany), the structural dimensions of the Si master are compared with those of both the PTFE/PS mold and the resulting conductive PDMS structure. The width of the gaps and lines of the structure were measured exemplarily. Within the measurement accuracy of +/− 1 μm, no difference in the dimensions of the Si master mold and the final PDMS structure were observed. Even tiny details, such as scratches or etching defects much smaller than 1 μm, were transferred from the Si master to the PS/PTFE mold.

View Article: PubMed Central - PubMed

ABSTRACT

Polymeric structures with integrated, functional microelectrical mechanical systems (MEMS) elements are increasingly important in various applications such as biomedical systems or wearable smart devices. These applications require highly flexible and elastic polymers with good conductivity, which can be embedded into a matrix that undergoes large deformations. Conductive polydimethylsiloxane (PDMS) is a suitable candidate but is still challenging to fabricate. Conductivity is achieved by filling a nonconductive PDMS matrix with conductive particles. In this work, we present an approach that uses new mixing techniques to fabricate conductive PDMS with different fillers such as carbon black, silver particles, and multiwalled carbon nanotubes. Additionally, the electrical properties of all three composites are examined under continuous mechanical stress. Furthermore, we present a novel, low-cost, simple three-step molding process that transfers a micro patterned silicon master into a polystyrene (PS) polytetrafluoroethylene (PTFE) replica with improved release features. This PS/PTFE mold is used for subsequent structuring of conductive PDMS with high accuracy. The non sticking characteristics enable the fabrication of delicate structures using a very soft PDMS, which is usually hard to release from conventional molds. Moreover, the process can also be applied to polyurethanes and various other material combinations.

No MeSH data available.