Improved resistive switching characteristics by O₂ plasma treatment in bi-layer Ti/ZnO/OPT-ZnO/ITO RRAM

This paper presents the effect of oxygen plasma process to the ZnO switching layer of Ti/ZnO/ITO resistive random access memory (RRAM). ZnO thin film was formed by spin-coating of the precursor solution and oxygen plasma process was carried out in three different cases: Case 1) Single ZnO film with no oxygen plasma treatment; Case 2) Single ZnO film with oxygen plasma treatment on the top; Case 3) Two ZnO layers and oxygen plasma treatment on the bottom layer. The best resistive switching characteristics were obtained from the case 3) with stable endurance over 1000 DC cycles and stable retention up to 10⁴ s, while the case 2) showed better endurance cycle (∼350 cycles) than that (<100) of the case 1). This result may be attributed to the prevention of oxygen ion absorption of Ti layer. XPS analysis indicates that the oxygen plasma process increases the oxygen contents in ZnO film, increasing metal-oxygen bonds and reducing the oxygen vacancies.