Nanoscale evidence of self-recovery in resistive switching (RS) behavior was found in TiO2-x film by conductive atomic force microscopy when exposed to Ar+-ions above a threshold fluence of 1 × 1016 ions cm-2. This revealed an evolution and gradual disappearance of bipolar RS-loops, followed by reappearance with increasing number of voltage sweep. This was discussed in the realm of oxygen vacancy (OV) driven formation, dissolution and reformation of conducting filaments. The presence of OVs in ion-beam irradiated TiO2-x films was evidenced by decreasing trend of work function in scanning-Kelvin probe microscopy, and was further verified by x-ray absorption near edge spectroscopy at Ti and O-K edges. © 2017 IOP Publishing Ltd.

Sankar Dhar

Physics

(SoNS) School of Natural Sciences

Aloke Kanjilal

Barman A.

Saini C.P.

Sarkar P.K.

Das D.

Singh M.

Sinha A.K.

Kanjilal D.

Gupta M.

Phase D.M.

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Journal of Physics D: Applied Physics

The controlled incorporation of defect species in amorphous oxide (AO) for regulating charge transport properties is highly demanding and challenging, especially for resistive switching (RS) memories. Here, we use pulsed electron beam deposition technique to engineer the growth of AO films, which show a large decrease (â33\%) in the t2g-eg gap. Our collective experiments and density functional theory (DFT) based ab initio simulations reveal the presence of undercoordinated TiO5 units, causing a decrease in the t2g-eg gap. Further, the importance of TiO5 in facilitating excess electron localization is demonstrated, showing an evolution of a broad defect band within the energy gap. The origin of this band (singly charged oxygen vacancy) is resolutely established by X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements and is also supported by calculated partial charge density and Bader charge analysis. The preeminence of singly charged oxygen vacancies cause a low-current level (up to 1-5 nA) RS operation with a gradual change of resistance states, which could set their path for the energy-efficient neuromorphic computing application. Finally, a new model based on probabilistic Markov chain algorithm is also developed to unfold the gradual change of resistance states from the fundamental defect interaction perspective. © 2019 American Chemical Society.

Journal of Physical Chemistry C

Synergistic Effect of Singly Charged Oxygen Vacancies and Ligand Field for Regulating Transport Properties of Resistive Switching Memories

The variation of electron density in TiO2-x nanochannels, exhibiting resistive switching phenomenon, produced by Ar+ ion-irradiation at the threshold fluence of 5 × 1016 ions/cm2 is demonstrated by X-ray reflectivity (XRR). The transmission electron microscopy reveals the formation of nanochannels, while the energy dispersive X-ray spectroscopy confirms Ti enrichment near the surface due to ion-irradiation, in consistent with the increase in electron density by XRR measurements. Such a variation in Ti concentration indicates the evolution of oxygen vacancies (OVs) along the TiO2-x nanochannels, and thus paves the way to explain the operation and performance of the Pt/TiO2-x/Pt-based memory devices via OV migration. © 2016 Author(s).

Fulltext

Applied Physics Letters

Probing electron density across Ar+ irradiation-induced self-organized TiO2- x nanochannels for memory application

Transformation of self-assembled crystalline TiO2 nanorods to amorphous layer, and the corresponding impact on optical-bandgap (Eg) on Si pyramids are investigated by irradiating with 50 keV Ar+-ions. Initially, Eg is found to be reduced from 3.23 to 2.94 eV up to a fluence of 1 × 1016 ions/cm2, and discussed in terms of the rise in oxygen vacancies (VO). However, a sudden increase in Eg to 3.38 eV is detected at a fluence of 1 × 1017 ions/cm2 through evolution of voids by over-saturating VO, manifesting the appearance of degenerate states by shifting the Fermi level above the conduction band minimum via Burstein-Moss effect. © 2016 AIP Publishing LLC.

Defect-engineered optical bandgap in self-assembled TiO2 nanorods on Si pyramids

Towards developing next generation scalable TiO2-based resistive switching (RS) memory devices, the efficacy of 50 keV Ar+-ion irradiation to achieve self-organized nano-channel based structures at a threshold fluence of 5 × 1016 ions/cm2 at ambient temperature is presented. Although x-ray diffraction results suggest the amorphization of as-grown TiO2 layers, detailed transmission electron microscopy study reveals fluence-dependent evolution of voids and eventual formation of self-organized nano-channels between them. Moreover, gradual increase of TiO/Ti2O3 in the near surface region, as monitored by x-ray photoelectron spectroscopy, establishes the upsurge in oxygen deficient centers. The impact of structural and chemical modification on local RS behavior has also been investigated by current-voltage measurements in conductive atomic force microscopy, while memory application is manifested by fabricating Pt/TiO2/Pt/Ti/SiO2/Si devices. Finally, the underlying mechanism of our experimental results has been analyzed and discussed in the light of oxygen vacancy migration through nano-channels. © 2015 AIP Publishing LLC.

Journal of Applied Physics

Self-organized titanium oxide nano-channels for resistive memory application

Nature Communications

Direct observation of oxygen vacancy-driven structural and resistive phase transitions in La2/3Sr1/3MnO3

Oxygen migration during resistance switching and failure of hafnium oxide memristors

Nanoscale self-recovery of resistive switching in Ar+ irradiated TiO2-x films