A numerical study of forming voltage and switching polarity dependence on Ti top electrode thickness in Zr _{O 2} RRAM

The authors investigate the conduction filament (CF) formation voltage and reset polarity dependence of a Ti/Zr_{O 2}/Pt resistive switching memory device on the Ti top electrode (TE) thickness by means of numerical simulation. A calculation method which accounts for both the initial statistical nature of the resistive switching layer (RSL) and the interaction of oxygen vacancies with oxygen species (O) on the overall conductance is used. The results show a correlation between the TE thickness and the density profile of O species both along the RSL–TE interface and within the TE, and indentify the causes for the previously observed not yet fully comprehended TE thickness dependent functionality of this device. The authors demonstrate that accumulation and reduction of O, during forming, result in a charged interfacial layer which decreases the effective oxide thickness and determines the forming voltage and switching polarity. In addition, local temperature profiles within the CF during forming promote O diffusion into the TE material which reduces the local conductivity and affects the forming voltage magnitude as well. In addition the authors provide forming and reset calculations for TE thicknesses of 5, 20 and 40 nm which are in good agreement with published experimental data.