Adhesive sintered Cu nanoparticles (NPs) with low resistivity (41.0 µΩ cm) were formed on polyimide (PI) substrates using well-dispersed Cu NP inks containing polyvinylpyrrolidone (PVP), and their flexibilities were improved by combining the Cu NPs with Cu nanowires (NWs). PVP functioned as a dispersant for the Cu inks and as a binder at interfaces between the substrates and sintered Cu NP surfaces. Although the PVP led to cracks on the Cu NP films after the inks were dried, the films without PVP easily peeled off and broke after the films were repeatedly deformed, demonstrating that PVP is essential for attaining adhesive and flexible films. After a repeated bending test, the electrical resistance of the sintered Cu NPs with PVP rapidly increased in the early stages of the test and then increased gradually thereafter. During the bending test, cracks propagated and the sintered Cu NP surfaces newly exposed to air oxidized, resulting in the observed rapid increase in the film's resistance. In addition, regions where sintered Cu NPs were connected around cracks were continuously broken, leading to the observed gradual increase in resistance. To prevent the resistance increases, Cu NWs were dispersed in the Cu NP inks, which were subsequently dried and sintered. The Cu NWs retarded the crack initiation and propagation and provided conductive paths even between cracks, suppressing both the rapid and gradual increases in resistance. The flexible and adhesive sintered films of Cu NPs and Cu NWs with PVP are expected to be used in printed electronics on flexible substrates.
|Colloids and Surfaces A: Physicochemical and Engineering Aspects
|Published - 2021 Sept 20