A reduced high-resistance state (HRS) current assists in obtaining high ON/OFF ratio and is beneficial to operation flexibility. This study proposes that less difference in the atomic radius of alkaline earth oxide-based memory devices is beneficial to reduce the HRS current. Forming-free resistive-switching behavior in the alkaline earth oxide-based memory device using magnesium titanate (MTO), strontium titanate (STO), and barium titanate (BTO) thin films is fabricated by sol-gel method. The dependence of HRS current on the difference in atomic radius was predicted by the Hume–Rothery rule and confirmed experimentally. The hydrolyzed particles, surface roughness, and density of oxygen vacancy were decreased when the difference in atomic radius between the Ti element and alkaline earth metal was less. Compared with the BTO thin film, the MTO thin film has fewer particles, smoother surface, and less density of oxygen vacancy, resulting in lower HRS current. Thus, suitable element selection for the alkaline earth oxide-based memory devices can reduce the HRS current.
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