Memristors Based on (Zr, Hf, Nb, Ta, Mo, W) High‐Entropy Oxides

Abstract

medium, [15,16] have demonstrated successful integration into crossbar array structures with WO x , [9] TaO x /HfO x , [10] TiO 2 , [11] and Al 2 O 3 /TiO 2−x [17] However, memristor technology is still limited by variability, retention, reliability, and endurance issues, which are inherent in the random nature of ionic diffusion. [2] Here we suggest the use of highentropy oxides (HEOs), [18] which are multi-metallic (five or more typically) oxide systems stabilized by increased mixing entropy, as a switching medium for memristors to overcome these challenges. HEOs are derived from highentropy alloys (HEAs), which form stable single-phase solid solutions despite the different crystal structures of each element. [19] Depending on the atomic radius differences, HEAs can be in a crystalline or amorphous phase. [20,21] Recently, HEOs have displayed interesting material characteristics, including a colossal dielectric constant, [22] high Li-ion conductivity, [23,24] and low thermal conductivity. [15] HEO-based memristors offer an opportunity to engineer the oxygen vacancy migration through enhanced lattice distortion and sluggish diffusion effects. [25] Moreover, the ability of HEO materials to maintain charge neutrality when elements with different charge valences are mixed, [26] provides a means to generate a uniform distribution of oxygen vacancies, [23,27] and associated reduction in device variability. [28] In this work, materials with six transition metals (Zr, Hf, Nb, Ta, Mo, W) were selected in order to combine the successful characteristics of HfO 2 , Ta 2 O 5 , and WO 3 in memristors while using Zr, Nb, and Mo (elements one row higher in the periodic table) to stabilize the HEO system. WO 3 -based memristors exhibit forming-free behavior and good incremental conductance modulation (analog), but the retention is poor due to the high mobility of oxygen vacancies. [29] In contrast, HfO 2based memristors show good retention with abrupt conductance changes (digital) between on/off states. [30] Ta 2 O 5 -based memristors present moderate analog conductance changes and good retention, but with limited on/off ratios. [31] HEO systems using HfO 2 , Ta 2 O 5 , and WO 3 as switching mediums are expected to combine the favorable properties of these transition-metal-oxide-based memristors while overcoming the drawbacks of binary materials through the "cocktail effect" and high entropy. [25] Memristors have emerged as transformative devices to enable neuromorphic and in-memory computing, where success requires the identification and development of materials that can overcome challenges in retention and device variability. Here, high-entropy oxide composed of Zr, Hf, Nb, Ta, Mo, and W oxides is first demonstrated as a switching material for valence change memory. This multielement oxide material provides uniform distribution and higher concentration of oxygen vacancies, limiting the stochastic behavior in resistive switching. (Zr, Hf, Nb, Ta, Mo, W) high-entropy-oxide-based memristors manifest the "cocktail effect," exhibi...

High-entropy-alloy nanoparticles with 21 ultra-mixed elements for efficient photothermal conversion

“…It can be noted that the size of nanoparticles reduced noticeably when ultra-fast-cooling treatment was activated. The surface state of 21-HEA-NPs was characterized by X-ray photoelectron spectroscopy (XPS), and the result shows that the metals with an oxidation potential have already been oxidized under the storage process in ambient air (Figs S17–S19, Supplementary Data) [ 28–30 ].…”

Robust Memristive Fiber for Woven Textile Memristor

“…Such set voltage is lower than that for the majority of metal‐oxide memristors. [ 32–34 ] The resistances of both high resistance state (HRS) and low resistance state (LRS) for the memristor unit were well maintained in the repeated switching cycles (Figure 2c), accompanied by a high resistance ratio (>10 5 ) of HRS to LRS. In addition, as shown in Figure 2d, four discrete LRS states from 10 2 to 10 4 Ω were readily tuned by changing the compliance currents.…”

Fabrication of Graphene Oxide-Based Resistive Switching Memory by the Spray Pyrolysis Technique for Neuromorphic Computing

“…The most common methods are atomic layer deposition (ALD), 37 RF sputtering, 38 thermal evaporation, pulsed laser deposition (PLD), and e-beam evaporation. 39,40 In addition, these techniques are only applicable when a compressed target is available, so these are not suitable for solution-based materials, particularly organics and nanoparticles. Thus, several solution-based techniques are developed to take advantage of organic materials.…”

“…; , and (3) organic materials such as PEDOT:PSS, PVK, PANI, and carbon-based materials such as graphene oxide (GO) and reduced graphene oxide (rGO). , Until now, inorganic materials, particularly binary oxides, have shown significant characteristics in terms of stability, reproducibility, and CMOS process flow compatibility. ,, However, inorganic materials require high-vacuum techniques to produce such notable features. The most common methods are atomic layer deposition (ALD), RF sputtering, thermal evaporation, pulsed laser deposition (PLD), and e-beam evaporation. , In addition, these techniques are only applicable when a compressed target is available, so these are not suitable for solution-based materials, particularly organics and nanoparticles. Thus, several solution-based techniques are developed to take advantage of organic materials .…”