Research on high-resolution/low-resistive interconnectors and their display application

Abstract

The hybrid platform, which is the combination of rigid islands and stretchable interconnectors is one of the most promising approaches in the field of stretchable electronics, but it is criticized for its limited resolution compared to conventional electronics due to the large footprint occupied by essential wiring areas because of its horse-shoe shape. Furthermore, when using multiple interconnectors, a broader wiring area is required, imposing significant constraints on achieving high resolution. Additionally, reducing the size of interconnector to address these issues results in higher interconnector resistance, posing practical limitations. In this research, a new stretchable interconnector structure has been developed that allows for higher resolution and lower resistance while utilizing existing semiconductor fabrication processes. Firstly, to achieve stable low-resistance interconnector in stretchable electronics, metal wiring was realized using aluminum, which has a low Young’s modulus and resistivity. The insertion of molybdenum thin films between aluminum and polyimide layers resolved manufacturing defects caused by the high reactivity between the two layers. Based on molybdenum-aluminum bilayer structure, highly stretchable and low-resistive stretchable interconnector was successfully fabricated. These bilayered interconnectors were then applied to oxide thin-film transistors to validate their practical applicability. Secondly, the limitations of existing stretchable interconnector structures that utilize only the upper surface of the wires were structurally analyzed. To overcome these limitations, a novel stretchable interconnector structure was proposed, utilizing the sidewalls of the interconnector named “SWE” (sidewall wrapping electrode). This approach wrapping the sidewalls allows for reduced wiring size while maintaining low resistance, enabling high-resolution integration. The implementation of a high aspect ratio stretchable interconnector structure ensures improved stretchability and allows for the implementation of multiple signal lines even when required. Numerical simulations were used to analyze the stretchability of wiring, and a mask-less self-patterning process was newly introduced to implement the stretchable interconnector using both top surface and sidewall of the wire. Theoretical and experimental evidence showed that this approach increases display integration by several times while achieving even lower wiring resistance under the same design rules. Finally, for practical applications of this high-resolution, low-resistive stretchable interconnector, a high-resolution stretchable display was implemented by adopting microLEDs to a stretchable display backplane based on this technology. The stretchable array exhibited a significantly higher FOM at the level of 4500 compared to existing technologies. By this way, high resolution and high stretchability were achieved simultaneously by adopting SWE structure.