Copper-Based Nanowires for Printable Memory and Stretchable Conductors
In the field of electronic materials, metal nanowires have been extensively studied for both their syntheses and their properties in electronic composites and devices. This dissertation addresses challenges in the field of electronic materials development with the use of copper nanowires synthesized in gram-scale syntheses, as well as provides analysis of devices and composites that could only be feasibly manufactured thanks to the large-scale syntheses.
In the field of printed electronics, there has been research into the development of fully printed memories. One of the challenges has been developing a memory that has switching characteristics that are on par with existing commercial memories, such as Flash memory. This can be achieved with a composite of Cu-SiO2 nanowires dispersed in ethylcellulose, which acts as a resistive switch when between printed Cu and Au electrodes. A 16-cell crossbar array of these memristors was printed with an aerosol jet. The memristors exhibited moderate operating voltages (~3 V), no degradation over 104 switching cycles, write speeds of 3 µs, and extrapolated retention times of 10 years. The low operating voltage enabled the programming of a fully printed 4-bit memristor array with an Arduino. The excellent performance of these fully printed memristors could help enable the creation of fully printed RFID tags and sensors with integrated data storage. Thanks to the large-scale synthesis of copper nanowires, this can allow for the expanded production of high-quality, fully printed memories.
Materials that retain a high conductivity under strain are essential for wearable electronics. I describe a new conductive, stretchable composite consisting of a Cu-Ag core-shell nanowire felt infiltrated with a silicone elastomer. This composite exhibits a retention of conductivity under strain that is superior to any composite with a conductivity greater than 1000 S cm-1. This work also shows how the mechanical properties, conductivity, and deformation mechanisms of the composite changes as a function of the stiffness of the silicone matrix. The retention of conductivity under strain was found to decrease as the Young’s modulus of the matrix increased. This was attributed to void formation as a result of debonding between the nanowire felt and the elastomer. The nanowire composite was also patterned to create serpentine circuits with a stretchability of 300%. Composites of this scale and density could only be feasibly manufactured thanks to large-scale syntheses of copper nanowires and the silver coating of copper nanowires. With the advances made in the quality of stretchable conductive composites, alternate methods were employed as to manufacture new composites and structures, such as the cofiltration of nanowires and waterborne rubber to accelerate production, or the manufacturing of Cu-Ag nanowire aerogels with density tunable via the aspect ratio of the nanowires.
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