ABSTRACT
The resistive random-access memory (RRAM) with multi-level storage capability has been considered one of the most promising emerging devices to mimic synaptic behavior and accelerate analog computations. In this study, we investigated the reset-first bipolar resistive switching (RS) and multi-level characteristics of a LaNiO3-x thin film deposited using a reactive magnetron co-sputtering method. Polycrystalline phases of LaNiO3 (LNO), without La2O3 and NiO phases, were observed at similar fractions of Ni and La at a constant partial pressure of oxygen. The relative chemical proportions of Ni3+ and Ni2+ ions in LaNiO3-x indicated that it was an oxygen-deficient LaNiO3-x thin film, exhibiting RS behavior, compared to LNO without Ni2+ ions. The TiN/LaNiO3-x/Pt devices exhibited gradual resistance changes under various DC/AC voltage sweeps and consecutive pulse modes. The nonlinearity values of the conductance, measured via constant-pulse programming, were 0.15 for potentiation and 0.35 for depression, indicating the potential of the as-fabricated devices as analog computing devices. The LaNiO3-x-based device could reach multi-level states without an electroforming step and is a promising candidate for state-of-the-art RS memory and synaptic devices for neuromorphic computing.
ABSTRACT
Reset-first resistive random access memory (RRAM) devices were demonstrated for off-stoichiometric Ni1-xO thin films deposited using reactive sputtering with a high oxygen partial pressure. The Ni1-xO based RRAM devices exhibited both unipolar and bipolar resistive switching characteristics without an electroforming step. Auger electron spectroscopy showed nickel deficiency in the Ni1-xO films, and X-ray photoemission spectroscopy showed that the Ni3+ valence state in the Ni1-xO films increased with increasing oxygen partial pressure. Conductive atomic force microscopy showed that the conductivity of the Ni1-xO films increased with increasing oxygen partial pressure during deposition, possibly contributing to the reset-first switching of the Ni1-xO films.
ABSTRACT
Threshold switching in chalcogenides has attracted considerable attention because of their potential application to high-density and three-dimensional stackable cross-point array structures. However, despite their excellent threshold switching characteristics, the selectivity and endurance characteristics of such selectors should be improved for practical application. In this study, the effect of Ag on the threshold switching behavior of a Ga2Te3 selector was investigated in terms of selectivity and endurance. The Ag-Ga2Te3 selector exhibited a high selectivity of 108 with low off-state current of < 100 fA, steep turn-on slope of 0.19 mV/dec, and high endurance of 109 cycles. The transient response was verified to depend on the pulse input voltage and measurement temperature. Considering its excellent threshold switching characteristics, the Ag-Ga2Te3 selector is a promising candidate for applications in cross-point array structures.
ABSTRACT
Chalcogenide materials of the amorphous phase with low band gaps were reported to show Ovonic threshold switching (OTS), making them suitable for selection devices in cross-point memory arrays. Herein, we report that ZnTe films with polycrystalline structures show OTS behavior. Nearly stoichiometric ZnTe thin films were deposited by an RF sputtering method. X-ray diffraction analysis indicated that the films were polycrystalline. The optical band gaps of the ZnTe films were estimated as 2.2 eV from UV-visible spectroscopy transmittance measurements. Photoluminescence measurements indicated the existence of deep-level defects in the ZnTe thin films. Although these ZnTe films have a polycrystalline structure with a relatively high band gap, I-V profiles show OTS characteristics, with a selectivity of over 104, fast threshold switching time in the sub-10 ns scale, and thermal stability up to 400 °C. ZnTe also shows switching endurance for more than 109 cycles without Vth drift, maintaining its selectivity of 104. Thus, we improved the threshold switching characteristics by using a wide band-gap and polycrystalline-structured ZnTe-based chalcogenide material. Post-annealing experiments indicated that the thermal budget of the ZnTe thin film was sufficient for stacked cross-point array structures, thereby overcoming a previous limitation of chalcogenide switching materials. This material is promising for application in high-density cross-point memory arrays as the selection device.
ABSTRACT
The electrical characteristics of tunnel barrier engineered-charge trap flash (TBE-CTF) memory devices with junctionless (JL) source and drain (S/D) were investigated. The JL structure is composed of an n(+)-poly-Si based ultra-thin channel and S/D with identical doping concentrations. The band engineered Hf-silicate/Al2O3 tunnel barrier stack was applied to a JL-TBE-CTF memory device in order to enhance the field sensitivity. The Hf-silicate/Al2O3 tunnel barrier, HfO2 trap layer, and Al2O3 blocking layer were deposited by atomic layer deposition. The fabricated device exhibited a large memory window of 9.43 V, as well as high programming and erasing speeds. Moreover, it also showed adequate retention times and endurance properties. Hence, the JL-TBE-CTF memory (which has a low process complexity) is expected to be an appropriate structure for 3D stacked ultra-high density memory applications.
