Highly conductive stretchable electrically conductive composites for electronic and radio frequency devices
Agar, Joshua Carl
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The electronics industry is shifting its emphasis from reducing transistor size and operational frequency to increasing device integration, reducing form factor and increasing the interface of electronics with their surroundings. This new emphasis has created increased demands on the electronic package. To accomplish the goals to increase device integration and interfaces will undoubtedly require new materials with increased functionality both electrically and mechanically. This thesis focuses on developing new interconnect and printable conductive materials capable of providing power, ground and signal transmission with enhanced electrical performance and mechanical flexibility and robustness. More specifically, we develop: 1.) A new understanding of the conduction mechanism in electrically conductive composites (ECC). 2.) Develop highly conductive stretchable silicone ECC (S-ECC) via in-situ nanoparticle formation and sintering. 3.) Fabricate and test stretchable radio frequency devices based on S-ECC. 4.) Develop techniques and processes necessary to fabricate a stretchable package for stretchable electronic and radio frequency devices. In this thesis we provide convincing evidence that conduction in ECC occurs predominantly through secondary charge transport mechanism (tunneling, hopping). Furthermore, we develop a stretchable silicone-based ECC which, through the incorporation of a special additive, can form and sinter nanoparticles on the surface of the metallic conductive fillers. This sintering process decreases the contact resistance and enhances conductivity of the composite. The conductive composite developed has the best reported conductivity, stretchability and reliability. Using this S-ECC we fabricate a stretchable microstrip line with good performance up to 6 GHz and a stretchable antenna with good return loss and bandwidth. The work presented provides a foundation to create high performance stretchable electronic packages and radio frequency devices for curvilinear spaces. Future development of these technologies will enable the fabrication of ultra-low stress large area interconnects, reconfigurable antennas and other electronic and RF devices where the ability to flex and stretch provides additional functionality impossible using conventional rigid electronics.