Improving the Electrical Performance of Printed Stretchable Interconnects by Local Modification of Stiffness

Abstract

For the production of stretchable electronics, the development of advanced materials which can be adaptable to deformation, as well as tailoring of the structural designs, fabrication and characterization strategies for soft materials are all needed. The major challenge is the ability of the device to maintain both the mechanical and electrical performance during the deformation for a desired number of cycles, and each of the aforementioned requirements are essential to respond to this challenge. From the fabrication point of view, although printing is heavily employed for stretchable electronics, fully printed circuit devices still need further improvements due to their response time, low integration density, etc. To overcome these limitations, heterogonous integration is a potential solution combining the advantages of printing techniques found in the production of large area electronics with the high performance of conventional inorganic electronic devices. In this regard, the island-bridge concept provides links between miniaturized functional units using stretchable interconnects on compliant substrates. Therefore, the development of reliable, stretchable interconnections is highly sought after.

This thesis focuses on an investigation of the practical approaches to improving the electromechanical performance of screen-printed, stretchable interconnects based on carbon and silver inks. Initially, stretchable carbon interconnects were screen-printed, and then methods and tools for the electromechanical characterization of the samples were tested and verified. After this stage, the concept of a “sacrificial zone” was introduced in this thesis where it was shown to improve the stretching performance of interconnections from 44% to 54%.

In the following studies, the “local tuning of the stiffness” by adding and removing material was investigated. This approach had positive effects on the rigidsoft interface by mitigating the strain in this location and improving the homogenous distribution of the stress in the system. The approach can be used in heterogenous integrations, where it was demonstrated to improve the stretching performance from 22% to 43% in the case of passive component attachments.