Ni/NiO/HfO₂ Core/Multishell Nanowire ReRAM Devices with Excellent Resistive Switching Properties

Abstract

magnetic random-access memory, [3] ferroelectric random-access memory, [4] and resistive random-access memory (ReRAM). [5] Among them, ReRAM is one of the most powerful candidates due to its higher endurance, higher retention, faster write and read speeds, and lower power consumption. In addition, it has a simple sandwich structure of metal-insulator-metal (MIM) for data storage and information compilation. [6][7][8][9] The resistive switching behavior in ReRAM devices is generally understood as the reversible formation and disruption of conducting filaments (CFs). In addition, the SET process was defined as the resistance switching from the high-resistance state (HRS) to the low-resistance state (LRS); by contrast, the RESET process operates inversely. [10] CFs are commonly categorized according to their formation types, including electrochemical metallization [5,11,12] and valence change mechanism. When the top electrode is the active metal (such as Ag or Cu), the metal would be oxidized to anionic specie and then diffuse into the insulator layer due to the external electric field. The anions in the insulator layer would accept electrons, resulting in a reduction process to form CFs. On the other hand, when the top electrode is the inert metal (such as Au or Pt), the oxygen ions would migrate toward high electric potential and form oxygen vacancies in the insulator layer. The oxygen vacancies would connect the electrodes, causing resistive switching from the HRS to LRS. Moreover, the insulator layer plays an essential role in ReRAM devices and has significantly influence on ReRAM performance. Hence, a variety of materials for the insulator layer, such as Ta 2 O 5 , [13] NiO, [14,15] CuO, [16] TiO 2 , [17][18][19][20] Al 2 O 3 , [21,22] ZnO, [11] and HfO x , [23][24][25][26] have been studied to show their resistive switching behavior. To overcome the problem of scaling down, 1D nanowires have been applied to ReRAM fabrication. However, the endurance and reliability of nanowire devices are still not sufficient for commercial production. Although many kinds of nanowires have been widely discussed, core/shell nanowires provide a strategy to reach nanoscale MIM structure and have exhibited high potential for applications in ultrahigh density ReRAM devices because the switching behavior could be controlled within the few-nanometer shell. [7,8,15,27,28] More research about performance enhancement and the switching mechanism are still needed. Owing to the excellent resistive switching characteristics in HfO 2 -based Resistive random-access memory (ReRAM) is one of the most promising types of nonvolatile memory because it has several important advantages, for example, a simple metal-insulator-metal structure, fast operating speed, high endurance, high retention, and low energy consumption. However, the reliability of ReRAM nanodevices is not persistent, and the complete switching mechanism is not fully understood. In this study, a unique 1D Ni/NiO/HfO 2 core/multishell ReRAM nanodevice is designed and fabricated. The d...

Selective Dual‐Ion Modulation in Solid‐State Magnetoelectric Heterojunctions for In‐Memory Encryption

“…This region is featured with ordered lattice fringes, suggesting its crystallization nature. Further analysis shows that the interplanar spacing (≈0.177 nm) and the fast Fourier transformed images of the crystallized region, as shown in Figure 1d(ii),(iii), agree well with that of metallic Hf nanocrystals, [26,27] implying the reduction of HfO 2−x into Hf owing to O 2− ions' removal. The observation of the electrode deformation with bubblelike protrusions indicates O 2− ions turned into oxygen gas that accumulates at the Pt/HfO 2−x interface (Figure S1, Supporting Information).…”

“…[28] Apparent morphology changes were not detected in the NiO y layer, suggesting that the O 2− ions' movement mainly occurs in the HfO 2−x layer, likely caused by the bearing of a higher divided voltage by the high-k HfO 2−x film than the NiO y film. [26] These results suggest that, positive voltages selectively drive O 2− ions in HfO 2−x film and create a Pt/Hf-CF/NiO y /Ni nanostructure in the solid-state device (Figure 1e).…”