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...

We present a new low cost microfabrication technology that utilizes a sacrificial conductive paint transfer method to realize thick film copper microstructures that are embedded in polydimethylsiloxane (PDMS). Several example structures are fabricated and characterized that demonstrate the potential application of this process in flexible electronics, wearable electronics, and novel microsensor and actuator designs. This process has reduced fabrication complexity and cost compared to existing metal-on-PDMS techniques, and enables large scale rapid prototyping of designs using minimal laboratory equipment. This technology differs from others in its use of a conductive copper paint seed layer and a unique transfer process that results in copper microstuctures embedded in PDMS rather than on top of the PDMS surface. The fabrication process begins with the deposition of the seed layer onto a flexible substrate via airbrushing. A dry film photoresist layer is laminated on top and patterned using standard techniques. Electroplated copper is grown on the seed layer through the photoresist mask and transferred to PDMS through a unique baking procedure. This baking transfer process releases the electroplated copper from the seed layer, permanently embedding it into the cured PDMS. The characterization of the copper microstructures is given in terms of feature size, film thickness, surface roughness, and resistivity. The resistivity is measured under static conditions as well as under conditions of flexing and stretching using various linear and 1-dimensional Peano curve structures [1]. To quantify the stability of a structure’s conductivity under flexing, linear structures are bent over curves having various radii and the response of the resistivity is measured against the number of iterations. To measure the response under stretching, 1-dimensional Peano curve structures are fabricated and stretched until failure, while the resistivity is measured against the strain. Results show that we can achieve films 25-75 micrometers in thickness, with reliable feature sizes down to 100 micrometers and a film resistivity of approximately 7.15 micro-Ω-cm [2]. Results from current experiments will be presented that characterize the resistivity response under flexing and stretching. Process variants and future work are discussed, as well as large scale adaptations and rapid prototyping. Finally, we outline the potential uses of this technology in flexible electronics and novel sensor and actuator designs. [1] J.A. Fan, W.-H. Yeo, Y. Su, Y. Hattori, W. Lee, S.-Y. Jung, Y. Zhang, Z. Liu, H. Cheng, L. Falgout, M. Bajema, T. Coleman, D. Gregoire, R. J. Larsen, Y. Huang, J. A. Rogers, “Fractal design concepts for stretchable electronics,” Nature Communications 5 (3266), 2014. [2] D. Hilbich, A. Khosla, L. Shannon, B. L. Gray, “A new low-cost, thick-film metallization transfer process onto PDMS using a sacrificial copper seed,” SPIE 9060, Nanosensors, Biosensors, and Info-Tech Sensors and Systems (906007), 2014