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...
Single crystal (010) β-Ga2O3 was irradiated by a Ti:sapphire ultrafast laser (150 fs pulse width) with varying fluences and a number of pulses in air ambient. Femtosecond laser-induced damage threshold of β-Ga2O3 is reported. Single pulse exposure results in surface morphological changes above a threshold laser fluence of 1.11 J/cm2. Laser-induced straight cracks aligned to the [001] crystallographic direction are observed in the laser irradiated regions, which are believed to be caused by laser-induced thermal stress, due to the unique low thermal conductivity and anisotropy associated with β-Ga2O3. Multiple pulse irradiation below the single pulse damage threshold fluence exhibited the formation of high spatial frequency laser-induced periodic surface structures. Electron backscattering diffraction and Raman spectroscopy suggested that there was no apparent phase transition of the irradiated β-Ga2O3 material for either single pulse or multiple pulse irradiation. This work serves as a starting point to further understanding the material properties of β-Ga2O3 and to unlock the potential for ultrafast laser material processing of β-Ga2O3.
The electrical properties of 4H-SiC under ultrafast laser irradiation in the low fluence regime (<0.50 J/cm2) are presented. The appearance of high spatial frequency laser induced periodic surface structures is observed at a fluence near 0.25 J/cm2 and above, with variability in environments like in air, nitrogen, and a vacuum. In addition to the formation of periodic surface structures, ultrafast laser irradiation results in possible surface oxidation and amorphization of the material. Lateral conductance exhibits orders of magnitude increase, which is attributed to either surface conduction or modification of electrical contact properties, depending on the initial material conductivity. Schottky barrier formation on ultrafast laser irradiated 4H-SiC shows an increase in the barrier height, an increase in the ideality factor, and sub-bandgap photovoltaic responses, suggesting the formation of photo-active point defects. The results suggest that the ultrafast laser irradiation technique provides a means of engineering spatially localized structural and electronic modification of wide bandgap materials such as 4H-SiC with relatively low surface damage via low temperature processing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.