Low Set Voltage Research Articles

Total ionizing dose (TID) effects of γ ray radiation on switching behaviors of Ag/AlO x /Pt RRAM device.

The total ionizing dose (TID) effects of 60Co γ ray radiation on the resistive random access memory (RRAM) devices with the structure of Ag/AlO x /Pt were studied. The resistance in low resistance state (LRS), set voltage, and reset voltage are almost immune to radiation, whereas the initial resistance, resistance at high resistance state (HRS), and forming voltage were significantly impacted after radiation due to the radiation-induced holes. A novel hybrid filament model is proposed to explain the radiation effects, presuming that holes are co-operated with Ag ions to build filaments. In addition, the thermal coefficients of the resistivity in LRS can support this hybrid filament model. The Ag/AlO x /Pt RRAM devices exhibit radiation immunity to a TID up to 1 Mrad(Si) and are highly suitable for radiation-hard electronics applications.

Electrode dependence of resistive switching in Au/Ni–Au nanoparticle devices

We synthesized Ni–Au nanoparticles (NPs) by a wet chemical method and fabricated sandwich structures of Au/Ni–Au NPs/Nb-doped SrTiO3 and Au/Ni–Au NPs/ITO (Indium Tin Oxide) glass. The Ni–Au NPs were identified as having a spindle-like nanostructure. Different bipolar resistive switching appeared. Linear fitting of I–V curves reveals that resistive switching follows the SCLC (Space Charge Limited Current) conduction mechanism. The switching behavior of Au/Ni–Au NPs/Nb-doped SrTiO3 is attributed to the electron trapping/detrapping of oxygen vacancies at the interface between NPs and Nb-doped SrTiO3, and that of Au/Ni–Au NPs/ITO glass which shows good switch characteristics such as high ON/OFF ratio, low SET voltage, can be ascribed to formation of a filament.

Room temperature resistive state switching with hysteresis in GdMnO3 thin film with low threshold voltage

In this paper, we report a room temperature resistive state switching with hysteresis, in a thin film of GdMnO3 grown on NdGaO3 substrate. The switched states have a resistance ratio ≈103. The switching is unipolar in nature, with a low set voltage <3 V, while the reset voltage <0.3 V. The switching occurs between a high resistance polaronic insulating state and a low resistance metallic state. The resistance state transition has been ascribed to an electronic mechanism that originates from co-existing phases (created by charge disproportionation) that can undergo a percolative transition enabled by the applied bias.

Low-power bipolar resistive switching TiN/HfO2/ITO memory with self-compliance current phenomenon

In this work, a TiN/HfO2/ITO memory device is fabricated, which shows stable bipolar resistive switching behavior, as well as excellent data retention and good endurance. Moreover, a very low SET voltage of 0.2 V is achieved with a self-compliance current effect. The result brings about an obvious reduction in SET power to 160 µW, which is crucial for future high-density resistive switching memories. On the basis of the conducting filament theory, a possible resistive mechanism is discussed to explain the low SET voltage and self-compliance current phenomenon.

High performance nonvolatile memory devices based on Cu2−xSe nanowires

We report on the rational synthesis of one-dimensional Cu 2−xSe nanowires (NWs) via a solution method. Electrical analysis of Cu 2−xSe NWs based memory device exhibits a stable and reproducible bipolar resistive switching behavior with a low set voltage (0.3–0.6 V), which can enable the device to write and erase data efficiently. Remarkably, the memory device has a record conductance switching ratio of 108, much higher than other devices ever reported. At last, a conducting filaments model is introduced to account for the resistive switching behavior. The totality of this study suggests that the Cu 2−xSe NWs are promising building blocks for fabricating high-performance and low-consumption nonvolatile memory devices.

Ion implantation synthesis and conduction of tantalum oxide resistive memory layers

In this paper, the ion implantation synthesis of tantalum oxide resistive memory material is introduced, the salient switching properties are described, and the results from an analysis of the off- and on-state conduction are presented. The tantalum oxide layers were synthesized by oxygen ion implanting (5 × 1016/cm2 O+ ions at 30 keV) tantalum metal. From composition-depth profiling, the oxygen implant profile is estimated to peak at ∼20 at. %. The properties of memory devices fabricated from the implantation-synthesized oxide were investigated through endurance testing. A stable 2× memory window was obtained for >103 switching cycles with low SET and RESET voltages 2 V, Frenkel-Poole emission current was identified; thus, trap states that may be induced by the implantation process impact high voltage conduction in this memory state.

A lithography-independent and fully confined fabrication process of phase-change materials in metal electrode nanogap with 16-μA threshold current and 80-mV SET voltage

In this paper,we fabricate a lateral phase change memory device composed of a Ge2Sb2Te5 nanowire (GST NW) fully confined in a tungsten electrode nanogap. A SiNx spacer is used not only as etch mask for the fabrication of the GST NW, but also as sacrificial layer for the lift-off process, which makes it feasible to fully confine the GST NW in the metal electrode nanogap. Electrical characterization shows that the device has unprecedentedly low threshold current and SET voltage of only 16 µA and 80 mV, respectively.

Improved endurance in ultrathin Al2O3 film with a reactive Ti layer based resistive memory

A 3-nm-thick Al2O3 based resistive memory with a Ti layer was prepared in this work. The Ti/HfOx devices with the same thickness were also fabricated for comparison. The oxygen gettering of Ti form Al2O3 is lower than that from HfOx. The Al2O3 devices with strong dielectric strength exhibit tight distribution of initial resistance state and high resistance state. The low resistance state, SET and RESET voltage of the devices seems insensitive to the dielectric film. Without an ideal current limiter, high forming voltage (VF) leads to the Al2O3 device with poor endurance (<100 cycles). Reduction of current overshoot by an external resistor of 800Ω during forming process, the endurance of the memory device can be improved and increase up to 104 cycles. The current overshoot and VF in the Al2O3 device with high operational temperature during forming step can be also suppressed.

Nonvolatile Memristive Switching Characteristics of TiO$_{\bm 2}$ Films Embedded With Nickel Nanocrystals

Nickel nanocrystal (Ni-NC)-embedded titanium dioxide films have been deposited for nonvolatile resistive switching memory devices. The polycrystalline behavior of the films has been observed from the X-ray diffraction spectra. Tiny isolated Ni-NCs with an average size of 4 nm are observed for the 1000 °C, 5-min annealed samples. Stable, bipolar, nonvolatile, and bistable resistive switching states are observed for the optimized annealed Ni-NC-embedded devices with a low SET and RESET voltage of 0.8 and −0.2 V, respectively. A high resistance ratio (>10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^3$</tex></formula> ), good stability, and retention properties are observed for the nanocrystal sample. The role of thin Ni-NC layer on memory switching stability is discussed.

Nanoscale resistive random access memory consisting of a NiO nanodot and Au nanowires formed by dip-pen nanolithography

We demonstrate the nanoscale resistive random access memory (RRAM) element consisting of an approximately 30nm diameter NiO nanodot and two bridging Au nanowires, formed by a dip-pen nanolithography technique using nickel carbonate (Ni2(CO3)(OH)2) and [AuCl4]− complex solutions, respectively. The Au/NiO/Au nanowire resistive switch exhibits typical unipolar switching characteristics with high performance at low Set and Reset voltages.

Temperature effects on the switching kinetics of a Cu–Ta2O5-based atomic switch

Voltage–current (I–V) measurements in a wide temperature range from 88 to 573 Kdemonstrated the effects of temperature on the switching behavior of aCu/Ta2O5/Pt resistive memory cell that is referred to as a gapless-type atomic switch. After the formingprocess, the cells were SET from the OFF state to the ON state at a positive bias to theCu electrode and then RESET from the ON state to the OFF state at a negative bias. In aprevious study (Tsuruoka et al 2010 Nanotechnology 21 425205), it was demonstrated thatthe SET process corresponds to the reformation of a metal filament between the electrodesby the inhomogeneous nucleation and subsequent growth of Cu whereas the RESETprocess can be attributed to the Joule-heating-assisted dissolution of the metal filament. Inthe work described here, we observed that the voltages at which the cells are SET andRESET (SET and RESET voltages) decreased in magnitude with an increase intemperature. From calculations of the nucleation rate of Cu nuclei based on theclassical nucleation theory, it was found that the observed temperature variationof the SET voltage is primarily determined by supersaturation in the vicinityof the Pt electrode, which is controlled by the application of positive bias. Thesupersaturation required for spontaneous growth of a Cu nucleus decreases withincreasing temperature, resulting in lower SET voltages at higher temperatures. TheRESET voltage is determined by the thermal stability of the metal filament formed.Moreover, using the temperature variation in cell resistances of the ON state, thegrowth speed of the Cu nucleus after the nucleation was found to decease withincreasing temperature. These results are consistent with our switching model.

Nonvolatile and unipolar resistive switching characteristics of pulsed laser ablated NiO films

Unipolar nonvolatile resistive switching memory properties of pulse laser ablated nickel oxide films have been studied. Grazing incidence x-ray diffraction and electron diffraction spectra of the oxide films reveal polycrystalline nature of deposited NiO films. Cross-sectional transmission electron micrograph shows a fairly uniform oxide surface. The rms surface roughnesses of deposited oxides have been studied as a function of annealing temperature using atomic force microscopy. By applying a proper voltage bias and compliance, Pt/NiO/Pt structures exhibited unipolar resistive switching having a very low SET and RESET voltages. The OFF state resistance and SET voltage are found to increase with the increase in annealing temperature. The ratio between the two resistance states can be as high as 1000. The current conduction phenomena at two resistance states have been studied. The switching phenomena have been explained using the rupture and formation of conducting filaments. The effect of postdeposition annealing on the resistance switching properties is discussed.