A Multilayer Template Stripping Based Microtransfer Printing Process for Stretchable Electronics

The development of flexible and stretchable electronics is essential for advancing wearable healthcare and biomedical devices. These technologies demand sophisticated mechanical design and integration strategies to improve durability and form factor. Moreover, scalability is important to support the high-volume manufacturing necessary to satisfy increasing market demands [1].<br/><br/>In this work, we describe a novel method for fabricating stretchable electronics utilizing a multilayer template stripping based microtransfer printing process, which builds upon published work [2]. Notably, once the master template is produced, this method does not rely on photolithography, etching, or other specialized equipment beyond metal evaporation, making it a simple process to carry out. The process involves four key steps: metal deposition, template stripping and transfer, and carrier substrate dissolution.<br/><br/>Initially, metal is deposited onto Si wafer etched template. The top metal layer is then stripped using a polyethylene naphthalate (PEN)-supported polyvinyl alcohol (PVA) layer. This flexible PVA sheet is gently laminated onto the template, ensuring no air is trapped, and negating the need for a vacuum chamber. The pressureless lamination ensures that the metal is only stripped from the top of the structured template, despite the adhesive sheet's flexibility. This procedure is conducted at 120°C, above the glass transition temperature of PVA, which increases its adhesive strength. Once cooled to room temperature, the two sheets are separated without applying any shearing forces. The metal pattern on the adhesive sheet is then transferred onto a stretchable substrate (PDMS). The sheet is laminated under pressure and further stabilized by applying pressure from above with a soft stamp at 120°C. The final step involves dissolving the remaining PVA in boiling water. This entire process can be repeated (using the same template or a new one) to create a multilayer structure of metallic features.<br/><br/>Finite Element Analysis (FEA) is conducted to optimize the structural performance of the interconnects, helping to identify design strategies that enhance device stretchability before failure. Devices can then be fabricated based on these design rules. Preliminary results indicate that our designs can achieve stretchability up to 100%, and withstand 1000 cycles at 50% strain. Ongoing research aims to further characterize devices and increase this stretchability by improving the interfacial properties between different layers.<br/><br/>The promising preliminary results indicate potential applications in a variety of fields, including for example strain sensors, stretchable electrodes, and cochlear implants.<br/><br/>References:<br/>1. Gillan, L., Hiltunen, J., Behfar, M. H., & Rönkä, K. (2022). Advances in design and manufacture of stretchable electronics. <i>Japanese Journal of Applied Physics</i>, <i>61</i>(SE), SE0804. https://doi.org/10.35848/1347-4065/ac586f<br/>2. Tiefenauer, R. F., Tybrandt, K., Aramesh, M., & Vörös, J. (2018). Fast and Versatile Multiscale Patterning by Combining Template-Stripping with Nanotransfer Printing. <i>ACS Nano</i>, <i>12</i>(3), 2514–2520. https://doi.org/10.1021/acsnano.7b08290