Enhanced electrical conductivity and reliability for flexible copper thin-film electrode by introducing aluminum buffer layer

Great demands for flexible conducting electrodes (FCEs) are promoted considering the rapid development of flexible electronics. Conventional thin-film FCE, however, has limits of low conductivity, poor mechanical reliability and requires complicated fabrication process due to the use of nanowires and nanoparticles. In this work, aluminum-copper bilayer FCEs were fabricated via facile thermal evaporation. Aluminum buffer layer is introduced to improve copper crystallinity and reduce internal thermal stress in the electrode films, resulting in enhanced electrical conductivity and reliability. The preparation condition and thickness of buffer layer (Al) has been optimized. The lowest electrical resistivity of 3.05 μΩ·cm was achieved for Al(0.86 μm)-Cu bilayer FCE, which is comparable to that of the bulk material (1.77 μΩ·cm). Additionally, the Al-Cu films exhibited excellent adhesion and flexibility under a bending radius of larger than 6 mm (ε = 1.82%) over 1000 cycles. And nanoindenter test was also conducted to describe the elastic characteristics of the flexible electrode and explain the mechanism of crack evolution. Meanwhile, superior reliability with negligible resistance changes was observed for Al-Cu FCEs after thermal shock tests.