Resistive switching characteristics of epitaxial NiO thin films affected by lattice strains and external forces

We investigated the resistive switching characteristics of NiO films grown epitaxially on two single-crystal Rh and Ni substrates. Two epitaxial NiO films were relatively small compressive strained on the Rh substrate, and confirmed by the x-ray diffraction experiments that the strain was relatively large compressive on the Ni substrate. Comparing the forming, SET, and RESET voltages of NiO resistive switching random access memory capacitors, NiO films grown on the Ni substrates showed relatively higher voltages than Rh substrates. We propose that this compressive strain has an effect on raising the forming, SET, and RESET voltages. Furthermore, we observed that the forming voltage decreases while reducing the compressive strain by applying pressure to the NiO thin film grown on the Ni substrate with an atomic force microscope tip. In addition, we showed that relaxation of compressive strain by external force by first-principles calculations can reduce the oxygen deficiency energy and lower the forming voltage and working voltages, which supports the experimental results well.