Balancing the Source and Sink of Oxygen Vacancies for the Resistive Switching Memory

Abstract

The high nonuniformity and low endurance of the resistive switching random access memory (RRAM) are the two major remaining hurdles at the device level for mass production. Incremental step pulse programming (ISPP) can be a viable solution to the former problem, but the latter problem requires material level innovation. In valence change RRAM, electrodes have usually been regarded as inert (e.g., Pt or TiN) or oxygen vacancy (V) sources (e.g., Ta), but different electrode materials can serve as a sink of V. In this work, an RRAM using a 1.5 nm-thick TaO switching layer is presented, where one of the electrodes was V-supplying Ta and the other was either inert TiN or V-sinking RuO. Whereas TiN could not remove the excessive V in the memory cell, RuO absorbed the unnecessary V. By carefully tuning (balancing) the capabilities of V-supplying Ta and V-sinking RuO electrodes, an almost invariant ISPP voltage and a greatly enhanced endurance performance can be achieved.

Electroforming-Free, Flexible, and Reliable Resistive Random-Access Memory Based on an Ultrathin TaOx Film

“…For example, the number of defective ions cannot be effectively controlled, which induces the uncontrolled formation and rupture of the CFs during the subsequent RS operations. Further, the additional EF process increases the complexity of the design of the driving circuit. , In most oxide-based RRAMs, the CFs are constituted by the aggregation of defects, most typically V O ’s, and the thermal diffusion of such defects into the insulating matrix causes the degradation of the performance of the memory device . Although the negative effects of the EF process on Si-based RRAM were reported, they could show a reasonable resistive switching performance even while undergoing the EF process. − For the flexible RRAM, however, the EF process should increase the uneven distribution of the defects in oxide film due to the randomly generated defects.…”

“…16,17 most typically V O 's, and the thermal diffusion of such defects into the insulating matrix causes the degradation of the performance of the memory device. 18 Although the negative effects of the EF process on Si-based RRAM were reported, they could show a reasonable resistive switching performance even while undergoing the EF process. 19−22 For the flexible RRAM, however, the EF process should increase the uneven distribution of the defects in oxide film due to the randomly generated defects.…”

Defect-Engineered Electroforming-Free Analog HfOx Memristor and Its Application to the Neural Network

“…EF corresponds to a soft-breakdown of the insulating layer, which usually induces several CFs in the insulating matrix, such as HfO 2 , as in this work. In insulating oxides, the CFs are usually composed of oxygen-deficient phases, such as Magnéli in TiO 2 , − or oxygen vacancy (V O ) clusters, as in HfO 2 and Ta 2 O 5 . − However, such an EF process also induces several unwanted side effects, which largely deteriorate the memristor performances of uniformity, endurance, and retention. Also, from the driving circuit point of view, incorporating an EF control circuit into the system is highly undesirable.…”

“…Another crucial ingredient that might contribute to the improvement in device performance is the electrode. For many resistive switching random access memories (ReRAMs) using an oxide switching layer, the electrodes must play the role of oxygen reservoir or oxygen transport layer. − ,, In several cases, an additional oxygen reservoir layer has been adopted, especially for the cases where the electrodes can hardly take the role, such as TiN . Whereas the standard memory applications can take the industry-standard test protocol, that is, incremental step pulse programming, to achieve the desired (multiple) target resistance values, it can hardly be used for the neural network, especially when the system was intended to be used for applications requiring online learning or training-intensive tasks.…”

What Will Come After V‐NAND—Vertical Resistive Switching Memory?

“…The problems include limited reliability (in terms of rewriting endurance and data retention) and nonuniform switching of the memory cell as well as low performance of the selectors in the CBA. [8] The retention issue in nonvolatile memories (NVMs) is generally becoming a lesser concern as the lifetime of a given device is currently being shortened. The significance of nonuniform switching can also be lessened by actively adopting incremental step pulse programming and error correction codes (ISPP-ECC).…”