By employing a precise method for locating and directly imaging the active switching region in a resistive random access memory (RRAM) device, a nanoscale conducting channel consisting of an ...amorphous Ta(O) solid solution surrounded by nearly stoichiometric Ta2O5 is observed. Structural and chemical analysis of the channel combined with temperature‐dependent transport measurements indicate a unique resistance switching mechanism.
Titanium dioxide memristive devices have been non‐destructively characterized using x‐ray absorption spectromicroscopy and TEM. These techniques allow direct identification of the chemistry and ...structure of the conducting channel responsible for the bipolar resistance switching seen in these devices. Within the TiO2 matrix, we observe the formation of a Ti4O7 Magnéli phase possessing metallic properties and ordered planes of oxygen vacancies.
We experimentally demonstrate and present an analytical model for a nanoscale metal/oxide/metal device that simultaneously exhibits memristance, based on oxygen vacancy drift, and current‐controlled ...negative differential resistance, based on a metal‐insulator transition instability. We show that this oxide nanodevice can be used to fabricate a continuously tunable voltage‐controlled oscillator.
We report sub-nanosecond switching of a metal-oxide-metal memristor utilizing a broadband 20 GHz experimental setup developed to observe fast switching dynamics. Set and reset operations were ...successfully performed in the tantalum oxide memristor using pulses with durations of 105 and 120 ps, respectively. Reproducibility of the sub-nanosecond switching was also confirmed as the device switched over consecutive cycles.
Twisted bilayer graphene is created by slightly rotating the two crystal networks in bilayer graphene with respect to each other. For small twist angles, the material undergoes a self-organized ...lattice reconstruction, leading to the formation of a periodically repeated domain
. The resulting superlattice modulates the vibrational
and electronic
structures within the material, leading to changes in the behaviour of electron-phonon coupling
and to the observation of strong correlations and superconductivity
. However, accessing these modulations and understanding the related effects are challenging, because the modulations are too small for experimental techniques to accurately resolve the relevant energy levels and too large for theoretical models to properly describe the localized effects. Here we report hyperspectral optical images, generated by a nano-Raman spectroscope
, of the crystal superlattice in reconstructed (low-angle) twisted bilayer graphene. Observations of the crystallographic structure with visible light are made possible by the nano-Raman technique, which reveals the localization of lattice dynamics, with the presence of strain solitons and topological points
causing detectable spectral variations. The results are rationalized by an atomistic model that enables evaluation of the local density of the electronic and vibrational states of the superlattice. This evaluation highlights the relevance of solitons and topological points for the vibrational and electronic properties of the structures, particularly for small twist angles. Our results are an important step towards understanding phonon-related effects at atomic and nanometric scales, such as Jahn-Teller effects
and electronic Cooper pairing
, and may help to improve device characterization
in the context of the rapidly developing field of twistronics
.
The logical relationship between two previously defined “memory resistors” is revealed by constructing and experimentally demonstrating a three‐terminal memistor equivalent circuit using two ...two‐terminal memristors. A technique is then presented, using nanoimprint lithography in combination with angle evaporation, to fabricate a single nanoscale device with a footprint of 4F2, where F is the minimum lithographic feature size, that can be operated as either a two‐terminal lateral memristor or a three‐terminal memistor inside a crossbar structure. These devices exhibit repeatable bipolar nonvolatile switching behavior with up to 103 ON/OFF conductance ratios, as well as the desired three‐terminal behavior.
A single nanoscale device that can be operated as either a two‐terminal lateral memristor or a three‐terminal memistor inside a crossbar structure is fabricated using a technique based on nanoimprint lithography and angle evaporation.
A key requirement for using memristors in circuits is a predictive model for device behavior that can be used in simulations and to guide designs. We analyze one of the most promising materials, ...tantalum oxide, for high density, low power, and high-speed memory. We perform an ensemble of measurements, including time dynamics across nine decades, to deduce the underlying state equations describing the switching in Pt/TaO x /Ta memristors. A predictive, compact model is found in good agreement with the measured data. The resulting model, compatible with SPICE, is then used to understand trends in terms of switching times and energy consumption, which in turn are important for choosing device operating points and handling interactions with other circuit elements.
Tantalum oxide memristors can switch continuously from a low-conductance semiconducting to a high-conductance metallic state. At the boundary between these two regimes are quantized conductance ...states, which indicate the formation of a point contact within the oxide characterized by multistable conductance fluctuations and enlarged electronic noise. Here, we observe diverse conductance-dependent noise spectra, including a transition from 1/f(2) (activated transport) to 1/f (flicker noise) as a function of the frequency f, and a large peak in the noise amplitude at the conductance quantum GQ=2e(2)/h, in contrast to suppressed noise at the conductance quantum observed in other systems. We model the stochastic behaviour near the point contact regime using Molecular Dynamics-Langevin simulations and understand the observed frequency-dependent noise behaviour in terms of thermally activated atomic-scale fluctuations that make and break a quantum conductance channel. These results provide insights into switching mechanisms and guidance to device operating ranges for different applications.
Thermal diffusion of Ti through Pt electrode forms Ti atom channels of 1 nm diameter along Pt grain boundaries, seeding switching centers and controlling nanoscale memristive switching. The image ...shows EFTEM maps of Ti overlaid on HRTEM images for a Si/SiO2 100 nm/Ti 5nm/Pt 15 nm sample in‐situ annealed in ultrahigh vacuum at 250 °C for 1 hour.
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