Resistive random access memory (RRAM) is a leading candidate in the race towards emerging nonvolatile memory technologies. The sneak path current (SPC) problem is one of the main difficulties in crossbar memory configurations. RRAM devices with desirable properties such as a selectorless, 1R-only architecture with self-rectifying behavior are potential SPC solutions. In this work, the intrinsic nonlinear (NL) characteristics and relaxation characteristics of bilayer high-k/low-k stacked RRAMs are presented. The intrinsic nonlinearity reliability of bilayer selectorless 1R-only RRAM without additional switches has been studied for their ability to effectively suppress SPC in RRAM arrays. The relaxation properties with resistive switching identification method by utilizing the activation energy (Ea) extraction methodology is demonstrated, which provides insights and design guidance for non-uniform bilayer selectorless 1R-only RRAM array applications.

Selectorless graphite-based resistive random-access memory (RRAM) has been demonstrated by utilizing the intrinsic nonlinear resistive switching (RS) characteristics, without an additional selector or transistor for low-power RRAM array application. The low effective dielectric constant value (k) layer of graphite or graphite oxide is utilized, which is beneficial in suppressing sneak-path currents in the crossbar RRAM array. The tail-bits with low nonlinearity can be manipulated by the positive voltage pulse, which in turn can alleviate variability and reliability issues. Our results provide additional insights for built-in nonlinearity in 1R-only selectorless RRAMs, which are applicable to the low-power memory array, ultrahigh density storage, and in-memory neuromorphic computational configurations.

In this work, the nonlinear (NL) characteristics of bi-layer high-k/low-k dielectrics structure, i.e. high-k layer with the low-k layer, are for selectorless oxide-based resistive random-access memories (RRAM) memory array application. It has been shown that such structure enhances the read currents at full read voltage (∼10-3 A) as compared to the bi-layer low-k/low-k structure (∼10-4 A), reduces low-voltage current, increases I-V nonlinearity and thereby suppresses the sneak path currents in the selectorless RRAM. Improved seasoning effect has also been demonstrated using the bilayer dielectric structure. The Fowler-Nordheim tunneling behavior has been found in the first RESET process (-0.45 to -1.25 V) as followed by the high self-rectifying characteristics that enlarge the immunity to the sneak path current and reduce the read errors in the array applications. The breakdown controllability of the forming process dominates the followed seasoning cycles which leads to two different performances in bilayer stacks i.e. efficient seasoning and inefficient seasoning, which provides an intrinsic design of selectorless RRAM devices. The device characteristics with current transport mechanisms have also been investigated. Our results provide additional insights into ways to achieve high performance and excellent reliability of built-in nonlinearity in selectorless RRAM (NL > 120, memory window > 100, sub-μs switching speed, and NL retention) for the future low-power RRAM memory array configurations.

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