Characterization of Stretchable Interconnects Fabricated Using a Low Cost Metallization Transfer Process onto PDMS

Abstract

The growing number of applications requiring conformal electronic devices incorporated into unconventional and dynamic surfaces has led to an increase in the development of stretchable electronics. Together with novel materials and fabrication processes, innovative conductive patterns are being developed in order to meet the needs of modern applications. Here, we present the design, fabrication, and characterization of first-order curved Peano structures fabricated using a newly developed thick film copper metallization transfer process onto PDMS. In order to maximize the stretchability of these structures, we present a characterization and analysis of the relationship between relative resistance and tensile strain in fabricated devices while systematically varying the geometric parameters of various curve designs. The response of the structures to cyclic failure and recovery is also characterized. These results demonstrate that the newly developed transfer process can be used to fabricate stretchable Peano curves and provide insight into the geometric optimization of these curves in stretchable electronics applications. Stretchable electronics is an emerging technology enabling new devices that cannot be fabricated using traditionally rigid substrates. The particular advantages of stretchable devices over their rigid counterparts are the ability to conform to a curved surface (for example, the human body), the ability to be folded within a constrained volume, and the ability to otherwise be physically flexed or stretched without failing. Example applications are particularly prevalent in biomedicine and include wearable monitoring devices, 1,2 implantable neural or muscular stimulators, 3 implantable drug delivery systems, 4 fluid control systems, 4 flexible sensors and actuators, 5-7 and flexible integrated circuit technology. 8 In an effort to further the development of these devices, there are two primary areas of improvement; the first area is in fabrication process technologies, and the second is in investigating new geometries that enable more effective stretchable structures.With respect to fabrication technologies, there are several existing processes suitable for the development of stretchable electronics, including the direct metallization of polymers, nanocomposite polymer (NCP) fabrication, 9 fabrication using conductive polymers, 10 and inkjet printing of conductive inks.11 While many of these methods can produce impressive flexible features, the conductivity of non-metallic structures is generally poorer than deposited pure metals. Therefore, the metallization of polymers is commonly used due to high electrical performance and relatively low cost. In previous work, 12 we have shown a new process for low-cost, large-scale, thick-film metallization of PDMS; in this work, we demonstrate the application of this process to stretchable electronics.Using a given process, stretchable metal patterns on polymers can generally be achieved with pre-stressed, thin-film, metal conductors that form stretchable m...

Stretchable electronics for wearable and high-current applications

“…In this case, a strain of 21.9% is applied before the device experiences conductive failure. This is comparable to the previous result of 18.3% +/-3% strain before failure found using the same structure with the base process [23] .…”

“…This fabric is used due to its popularity and well-known stretchable properties. The deposited curvilinear pattern shown in Figure 3 has been studied previously by our group in stretchable applications, and accommodates the most strain among all tested structures [23] . Each segment in the curve has a 300µm trace width, an arc angle of 270º, and a radius of curvature of 1.37mm.…”

“…The trace width, w, and spacing between fins are both 500µm, while the radius, r, is 2.3mm. A relatively large 500µm trace width is chosen in order to reduce the mechanical stress in the coil during magnetic field generation [20] , while the radius is calculated according to the radiusto-trace width ratio that is used in our previous study [23] . The laser-etched alignment hole in the transparency substrate must have a slightly smaller radius than the electroplated coil (Figure 4(d)), and is designed with 80% of the coil radius to allow a degree of tolerance.…”

A Low-Cost, Micropattern Transfer Process for Thick-Film Metallization of PDMS

“…Characterization of additional mechanical properties relevant to applications in flexible and stretchable electronics, such as stretchability, are presented previously. 47 Other experiments demonstrating the application of this process to wearable fabrics and multi-layer devices are also presented previously. 44 This section contains the experimental procedure used to acquire the measurement data, while the Results and analysis section contains the measurement results and analysis.…”

From stretchable to reconfigurable inorganic electronics

“…This design has also been successfully applied using other metal thin films, such as gold [170] , aluminum [171] , silver [172] , AgNWs [173] and ITO [174,175] . The mechanics of bending, stretching and stress strain distribution along the length of springs have been well studied for the meandering spring architecture [178][179][180][181] . In 2014, Rahimi et al directly sewed copper wires onto a stretchable substrate in a meandering pattern.…”