Microstructure evolution characteristics induced by oxygen vacancy generation in anatase TiO2 based resistive switching devices

In this work, first principle calculations are employed to study the microstructure characteristics of the anatase TiO2 resistive switching material associated with the generation of oxygen vacancy (V-o) based nanofilaments during the switching process. The calculations indicate that both the magneli phase Ti4O7 and Vo-defect phase of anatase TiO2 may be formed with the generation of oxygen vacancies during the forming and SET processes. Based on the calculations, a new physical insight is proposed to clarify the microstructure evolution characteristics of the anatase TiO2 resistive switching material and the correlation with resistive switching behaviors. During the forming or SET process, the anatase TiO2 is first excited to a transition state with the generation of oxygen vacancies, then fully relaxes to a stable Vo-defect state. This Vo-defect state may either recover to the original state with the recombination of the oxygen vacancies, which causes the reversible resistive switching behavior, or further transform to a much more stable state-the magneli phase Ti4O7, through a phase transition process with the generation of many more oxygen vacancies. The phase transition from Vo-defective anatase phase to magneli phase Ti4O7 causes the failure of the resistive switching due to the significantly reduced possibility of the reversible phase transition from the magneli phase to the anatase phase, compared with the possibility of the recombination from the V-o-defective anatase.