Effect of W impurity on resistance switching characteristics of NiOx films

In this work, we investigated the effect of W doping on the resistance switching behavior of NiOx films. The W doping is expected to produce cation-rich NiOx film because W has high valence state compared to Ni in NiOx. To measure resistance switching behavior, Pt/NiOx/Pt and Pt/NiOx/TiN MIM stacks were fabricated by reactive dc magnetron sputtering with various W doping contents in NiOx. Also, physical properties such as atomic density and chemical bonding states of NiOx were characterized in addition to the resistance switching characteristics.Increasing W doping into NiOx produced the higher resistance value of high resistance states (HRS) compared to the undoped NiOx films with large memory window. Even though Pt/NiOx with W/Pt stacks showed a unipolar resistance switching behavior, Pt/NiOx with W/TiN stacks showed bipolar resistance switching. Composition and chemical bonding states in the deposited films were investigated by x-ray photoelectron spectroscopy (XPS). W doping into NiOx films produced higher density of metallic Ni (Ni0) than that of NiOx films deposited at the same conditions. This work demonstrated that the resistive switching behavior of NiOx can be enhanced by doping NiOx with W of different oxidation valence.