Grain Boundary Passivation via Balancing Feedback of Hole Barrier Height Modulation in HfO_2-x for Flexible Electronics

Flexible electronics has attracted considerable attention owing to its enormous potential for practical applications in various fields. However, the vast strain produced during bending degrades the device, especially at grain boundaries, where many defects accumulate to form local leakage current channels. Here, we propose an HfO_2-<i>x</i> thin film that can be used as an excellent material for flexible electronics with versatile functionality, especially for grain boundary passivation. Various electrical phases of HfO_2-<i>x</i> thin films with conducting to insulating behavior, which originates from oxygen deficiency, have been fabricated on flexible substrates. Furthermore, owing to the most stable charge state of oxygen vacancies, oxygen-deficient HfO_2-<i>x</i> shows <i>p</i>-type conductivity. Current mapping by conductive atomic force microscopy reveals that current flow is hindered at grain boundaries because of the formation of potential barriers. This phenomenon is also observed in bent flexible thin films on convex and concave molds, leading to tensile and compressive strains, respectively. Although the defect concentration increases because of lattice deformation during bending, more holes are trapped at the grain boundaries, resulting in an increased hole barrier height. We believe that grain boundary passivation through hole barrier modulation during bending would pave the way for advances in hafnia-based flexible electronics.