Sub-1.0 V Low Voltage Resistive Random Access Memory Operations with Ag/VO_x/Pt Structure

Recently, as the importance of date-centric applications increases such as artificial intelligence which requires huge amount of real-time data processing, high performance non-volatile memories are highly required, particularly enabling high density integration and low voltage operations for stand-alone memory and computing elements in processing-in memory applications. Among various non-volatile memories, resistive random access memory (RRAM), which has a simple metal-insulator-metal (MIM) structure, has excellent scalability, easy fabrication also for 3D architecture, and has been reported to have potential for low voltage and high speed operations. In this study, the Ag/VO_x/Pt RRAM devices were demonstrated to show sub-1.0 V low voltage and high speed operation with low switching current, high endurance, and high memory window. Resistive switching was induced by the formation and rupture of silver filament through VO₂ layer by applied bias. The DC current-voltage curves showed average value of V_SET of +0.23 V, V_RESET of -0.07 V without electroforming step. In addition, highly stable cycle-to-cycle endurances up to 3000 cycles with on/off resistance ratio > 10² without any degradation. Voltage pulse measurements also revealed the low voltage and fast switching with V_SET < 1.0 V with the switching time < 1 μs in our measurement setup. Auger electron spectroscopy, Rutherford backscattering spectroscopy, and X-ray photoelectron spectroscopy analysis confirmed that the VO_x layer is composed of mixture of VO₂ and V₂O₅ phases. Transmission electron microscopy analysis revealed that VO_x layer is mostly in amorphous state with small fraction of crystallites. This amorphous structure of VO_x layer in addition to its inherent structural nature enabling to hold metallic elements within the lattice was advantageous in conductive-bridge random access memory of RRAM to achieve facilitated filament formation at low voltage thanks to the abundant oxygen vacancies in the amorphous phase. In addition, the homogeneous amorphous structure is desirable to achieve uniform device-to-device distribution. The presented results of highly stable, forming-free, low voltage and high speed switching operation of Ag/VO_x/Pt RRAM devices demonstrated their potential for stand-alone non-volatile memory and computing elements in the processing-in-memory applications.