SYNTHESIS AND CHARACTERIZATION OF ONE-DIMENSIONAL COPPER STRUCTURES

Abstract

Copper (Cu) nanowire (NW) arrays have potential applications in sensors, batteries, thermal and electrical management, and more. The performance and reliability of these devices depend on the robust bonding between the metal structures and the underlying substrates. Quantitative evaluation of the mechanical properties and bonding strength between the metal structures and substrates can provide guidance for device design, fabrication, and failure analysis. In the first part of the work, Cu NW arrays with different diameters, filling ratios, and spacings were prepared on Cu substrates. The effective Young’s modulus of the Cu NWs and the interfacial bonding strength between NWs and Cu substrates were evaluated using nanoindentation and nanoscratch tests, respectively. Our results showed that the effective Young's modulus of the Cu NW arrays decreased with their length, possibly due to the early buckling of some Cu NWs caused by their non-uniform length distribution and tilted angles. After correcting for full density, the effective Young’s modulus of Cu NWs was comparable to that of bulk Cu. On the other hand, the adhesion force and adhesion energy per unit area of the interface were found to be up to 67.62 mN and 544.87 J m-2, respectively, which are significantly higher compared to other one-dimensional (1D) nanostructure arrays evaluated using the same constant load scratch method. The constantly increasing power density of electronic devices necessitates the development of advanced thermal management solutions. TIMs play a crucial role in efficiently transferring heat from heat sources to heat sinks, ensuring that the device maintains a safe operating temperature and prevents thermal breakdowns. Likewise, electrical interconnects are vital in establishing low-resistance pathways for efficient electrical interconnection, thereby avoiding temperature rises caused by Joule heating. In the second part of the work, double-sided Cu NW arrays on Cu substrate were prepared and used as TIMs and electrical interconnect. The experimental results showed that the double-sided Cu NW arrays greatly reduced the thermal contact resistance (TCR), with reported values less than 5 mm2 K W-1, outperforming or comparable to double-sided nanostructural TIMs reported previously. The prepared double-sided Cu NW arrays were also used as electrical interconnects, resulting in a significant reduction in electrical contact resistance (ECR). Currently, the most widely used and commercially available templates are anodic aluminum oxide (AAO) and polycarbonate track etched (PCTE) templates. However, due to technical difficulties in the fabrication process, the thickness of these templates is limited to a few tens of microns. Some applications, such as advanced seal application, require structures that are longer, up to hundreds of microns. In the third part of the work, a polydimethylsiloxane (PDMS) template with a thickness of 200 to 300 μm was prepared and used for Cu MWs growth. The technical processes demonstrated here can be extended to prepare other 1D metal structures with customized geometries, lengths, diameters, and densities, paving the way for new applications of 1D metal structures.