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Highly elastic conductive polymeric MEMS

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.


Detailed picture of a C-PDMS structure impressively demonstrating the high aspect ratio achievable with the presented fabrication process.
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Figure 9: Detailed picture of a C-PDMS structure impressively demonstrating the high aspect ratio achievable with the presented fabrication process.

Mentions: The conductive properties of the described materials partly limit their use for resistive sensor and actuator principles. However, a suitable application is a capacitive sensor, where the absolute value of the resistance of the conductive material does not play an important role. For example, a capacitive strain gauge has been designed and fabricated with the described process. Figure 8 shows an interdigital structure (IDC) that forms such a capacitive strain gauge. The IDC has 216 μm-wide fingers and 46 μm-wide gaps and was fabricated using C-PDMS. The high degree of accuracy is impressively demonstrated in figure 9, where details such as the type number of the master mold are replicated with excellent precision. The sensor shows a base capacitance of 49.5 pF. An analytical value for the capacitance can be obtained by conformal mapping [28], which leads to a value of 49.1 pF. The sensor can be easily calibrated by absolute strain measurements. For this, the capacitive strain gauge was elongated with a maximum strain of 125 % at a speed of 1 mm S−1 as shown in figure 10. At 125 % strain, the capacitance is decreased by 59.2 % down to 20.2 pF. A calibration curve can be obtained by fitting the measured results to the original description of the simple plate capacitor by assuming constant volumes:1where ϵ is the linear strain and c0 and c1 are fit parameters.


Highly elastic conductive polymeric MEMS
Detailed picture of a C-PDMS structure impressively demonstrating the high aspect ratio achievable with the presented fabrication process.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: Detailed picture of a C-PDMS structure impressively demonstrating the high aspect ratio achievable with the presented fabrication process.
Mentions: The conductive properties of the described materials partly limit their use for resistive sensor and actuator principles. However, a suitable application is a capacitive sensor, where the absolute value of the resistance of the conductive material does not play an important role. For example, a capacitive strain gauge has been designed and fabricated with the described process. Figure 8 shows an interdigital structure (IDC) that forms such a capacitive strain gauge. The IDC has 216 μm-wide fingers and 46 μm-wide gaps and was fabricated using C-PDMS. The high degree of accuracy is impressively demonstrated in figure 9, where details such as the type number of the master mold are replicated with excellent precision. The sensor shows a base capacitance of 49.5 pF. An analytical value for the capacitance can be obtained by conformal mapping [28], which leads to a value of 49.1 pF. The sensor can be easily calibrated by absolute strain measurements. For this, the capacitive strain gauge was elongated with a maximum strain of 125 % at a speed of 1 mm S−1 as shown in figure 10. At 125 % strain, the capacitance is decreased by 59.2 % down to 20.2 pF. A calibration curve can be obtained by fitting the measured results to the original description of the simple plate capacitor by assuming constant volumes:1where ϵ is the linear strain and c0 and c1 are fit parameters.

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.