We adopted (111)-oriented Cu with high surface diffusivity to achieve low-temperature and low-pressure Cu/SiO₂ hybrid bonding. Electroplating was employed to fabricate arrays of Cu vias with 78% (111) surface grains. The bonding temperature can be lowered to 200 °C, and the pressure is as low as 1.06 MPa. The bonding process can be accomplished by a 12-inch wafer-to-wafer scheme. The measured specific contact resistance is 1.2 × 10⁻⁹ Ω·cm², which is the lowest value reported in related literature for Cu-Cu joints bonded below 300 °C. The joints possess excellent thermal stability up to 375 °C. The bonding mechanism is also presented to provide more understanding on hybrid bonding.

Rotary electroplating was employed to fabricate high-strength nanotwinned copper (nt-Cu) foils serving as a current collector for high energy-density lithium ion batteries (LIBs). The effect of Cu ion concentration on the microstructural and mechanical properties of the nt-Cu foils was then investigated. Formation of nano-scaled grains was found at the bottom. Its size gradually increases toward the top surface to form a microstructural mixture of gradient nano-scaled and columnar grains in the upper region. Experimental results show that the grains and elongation of the nt-Cu foils increase with increasing concentration of Cu ions. However, a trade-off between tensile strength and elongation is present. The elongation of nt-Cu foils has been enhanced by 22% (from 3.1% to 3.8%) while 8.3% and 3.9% reductions in ultimate tensile strength (UTS) and yield stress (YS) are seen. The current study shows a promising method to tune and optimize the microstructure and mechanical properties of such nt-Cu foils for various applications.

The objective of this study is to investigate the effect of long-term static bending on the conductive characteristics of indium tin oxide (ITO) thin film in flexible optoelectronics. Two types of substrate are considered, namely ITO on polyethylene naphthalate (ITO/PEN) and ITO on polyethylene terephthalate (ITO/PET). Electrical properties of the ITO/PEN and ITO/PET sheets are measured in situ under static bending at various radii of curvature. Experimental results indicate that no significant change in electrical resistance of the ITO/PEN and ITO/PET sheets is found for compressive bending after 1000 h at a curvature radius of 10 mm or larger. However, the ITO/PEN and ITO/PET sheets are seriously damaged under a tensile bending of 10 mm radius and 5 mm radius, respectively. The given ITO/PET sheet exhibits a greater resistance to long-term mechanical bending than the ITO/PEN one, which is attributed to the effect of stiffness and thickness of substrate. As the given PET substrate has a lower stiffness and thickness than the PEN one, ITO thin film in the ITO/PET sheet has a smaller stress given a bending radius. Consequently, a smaller extent of change in the electrical conductance of ITO thin film is found in the ITO/PET sheet.