In this paper, resistive random-access memory (RRAM) with InGaO (IGO) as an active layer was fabricated by radio-frequency (RF) sputtering system and the resistive switching mechanism with the different top electrode (TE) of Pt, Ti, and Al were investigated. The Pt/IGO/Pt/Ti RRAM exhibits typical bipolar resistive switching features with an average set voltage of 1.73 V, average reset voltage of −0.60 V, average high resistance state (HRS) of 54,954.09 Ω, and the average low resistance state (LRS) of 64.97 Ω, respectively. Ti and Al were substituted for Pt as TE, and the conductive mechanism was different from TE of Pt. When Ti and Al were deposited onto the switching layer, both TE of Ti and Al will form oxidation of TiOx and AlOx because of their high activity to oxygen. The oxidation will have different effects on the forming of filaments, which may further affect the RRAM performance. The details of different mechanisms caused by different TE will be discussed. In brief, IGO is an excellent candidate for the RRAM device and with the aids of TiOx, the set voltage, and reset voltage, HRS and LRS become much more stable.

The stability of a resistive random-access memory (RRAM) device over long-term use has been widely acknowledged as a pertinent concern. For investigating the stability of RRAM devices, a stacked In x Ga 1– x O structure is designed as its switching layer in this study. Each stacked structure in the switching layer, formed via sputtering, consists of varying contents of gallium, which is a suppressor of oxygen vacancies; thus, the oxygen vacancies are well controlled in each layer. When a stacked structure with layers of different contents is formed, the original gradients of concentration of oxygen vacancies and mobility influence the set and reset processes. With the stacked structure, an average set voltage of 0.76 V, an average reset voltage of −0.66 V, a coefficient of variation of set voltage of 0.34, and a coefficient of variation of reset voltage of 0.18 are obtained. Additionally, under DC sweeps, the stacked RRAM demonstrates a high operating life of more than 4000 cycles. In conclusion, the performance and stability of the RRAM are enhanced herein by adjusting the concentration of oxygen vacancies via different compositions of elements.