The room temperature resistive switching behavior in 50 keV O+-ion irradiated TiO2-x layers at an ion fluence of 5 × 1016 ions cm-2 is reported. A clear transformation from columnar to layered polycrystalline films is revealed by transmission electron microscopy with increasing ion fluence, while the complementary electron energy loss spectroscopy suggests an evolution of oxygen vacancy (OV) in TiO2-x matrix. This is further verified by determining electron density with the help of x-ray reflectivity. Both local and device current-voltage measurements illustrate that the ion-beam induced OVs play a key role in bistable resistive switching mechanism. © 2018 IOP Publishing Ltd.

Sajal Kumar Ghosh

Physics

(SoNS) School of Natural Sciences

Sankar Dhar

Aloke Kanjilal

Barman A.

Saini C.P.

Sarkar P.K.

Bhattacharjee G.

Bhattacharya G.

Srivastava S.

Satpati B.

Kanjilal D.

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Shiv Nadar University

Journal of Physics D: Applied Physics

The application of a NiO y /NiO x bilayer in resistive switching (RS) devices with x &gt; y was studied for its ability to achieve reliable multilevel cell (MLC) characteristics. A sharp change in resistance brought about by sweeping the voltage, along with an improved on/off ratio (&gt;103) and endurance (104) were achieved in the bilayer structure as compared to the single NiO x layer devices. Moreover, it was found that nonvolatile and stable resistance levels, especially the multiple low-resistance states of Cu/NiO y /NiO x /Pt memory devices, could be controlled by varying the compliance current. All the multilevel resistance states of the Cu/NiO y /NiO x /Pt bilayer devices were stable for up to 500 consecutive dc switching cycles, as compared to the Cu/NiO x /Pt single layer devices. The temperature-dependent variation of the high and low resistance states of both the bilayer and single layer devices was further investigated to elucidate the charge conduction mechanism. Finally, based on a detailed analysis of the experimental results, comparisons of the possible models for RS in bilayer and single layer memory devices have also been discussed. © 2016 IOP Publishing Ltd.

Nanotechnology

Multilevel programming in Cu/NiO y /NiO x /Pt unipolar resistive switching devices

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

An improved temperature dependent uniformity and reliability is investigated in La2O3/Pt-based memory devices with Cu top electrode. The microstructural investigation suggested the formation of polycrystalline La2O3 layer with stoichiometric chemical composition confirmed by X-ray photoelectron spectroscopy. Besides showing a forming-free resistive switching (RS) behaviour, the device also exhibited excellent multilevel capability with low switching voltage. A uniformity in the SET/RESET process was observed indicating enhanced switching stability. In addition, endurance with a high ON/OFF ratio of the order 103 and satisfactory data retention time over 104 s at 85 °C temperature confirmed the reliability of memory cells. Intrinsic tailoring of switching mechanism has been discussed in the framework of electric field-induced creation and annihilation of the reproducible Cu filaments in switching layer. The metallic nature of conducting filament has further been confirmed by temperature-dependent RS characterization. © 2016, Springer Science+Business Media New York.

Journal of Materials Science

Multilevel resistance state of Cu/La2O3/Pt forming-free switching devices

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.