Conformal Active Sheets

Abstract

Stretchable Electronics is an emerging class of electronics that allow electronics to be bent, conform, ex and stretch while still retaining its full functionality. Other than bending, existing and conforming, adding stretchability to electronic systems can open up a new frontier for a myriad of applications. Especially in the medical sector, these stretchable devices can increase the scope of monitoring and ease and comfort of the patient. All kinds of wearable devices can be based on these technologies to augment our daily lives. With the kind of state of art technology available to the common man today, the bar has already been set for the performance of such devices. Hence, its imperative that these stretchable devices perform at this level and should be capable of adapting to the market to serve the mass requirement. Hence, it becomes inevitable to use metal interconnects to provide very low resistance and easy adhesion to commercial electronic components. Another aspect of such devices is an adhesion ability with which we can attach it to various kinds of surfaces. In this thesis, we propose a new multi-layered PDMS structure approach to bring stretchability in the device. For all kinds of adhesion requirements, various ratios of PDMS: Cross-linker have been used. These different ratios of PDMS: Cross-linker changes the mechanical and adhesive properties of the cured PDMS. Hence, the same material can be used as the stretchable substrate as well as to serve various adhesion requirements. A soft adhesion allows us to attach it to the human body/other surfaces. The adhesion can be tailored to be quite conformal and strong, yet its removal is quite gentle to the skin. A higher curing ratio makes the PDMS very sticky and soft. Aluminum/Copper foils can be directly stuck upon it and tracks can be then etched out to get a printed circuit. Since this adhesive layer is quite soft, it acts as a cushion and reduces the amount of stress transferred to the metal interconnects. Hence, stretchable circuits with metal interconnects can be realized. The electronic components can be then attached upon it via normal soldering techniques/using conductive ink. Various devices that can be built with the proposed techniques have been coined the term CAS (Conformal Active Sheets) to allow easy reference to such kind of devices. Since the substrate is soft, physical handling of such devices becomes an issue as one tries to transfer the circuit pattern. Hence, direct etching of the metal foil was explored via high pulsed current discharge technique. A CNC machine was also designed to try various ways of direct etching of the metal foil in an accurate and repeatable fashion.