Accumulation and relaxation of optically induced electric charge in ZrO2(Y) films with embedded single-layered arrays of Au nanoparticles (NPs) of 2-3 nm in diameter have been studied subject to the depth of the Au NPs in the ZrO2(Y) layers and the optical excitation power at the wavelengths of 473 and 633 nm by Scanning Kelvin Probe Microscopy (SKPM). Keywords: thin film systems, zirconia, nanoparticles, plasmon resonance.

The resistive switching effect in individual ferromagnetic filaments in memristive stacks based on ZrO2(Y)/Ni functional layers was studied experimentally. A conductive probe of an atomic force microscope played a role of a movable top electrode of a virtual memristive stack. The features of bipolar-type resistive switching found were related to the rapture and restoring of the filaments containing Ni atoms in the ZrO2(Y) dielectric films and are probably caused by different degree of metallization of the filaments. The filaments fromed were manifested in the images obtained by magnetic force microscopy as single-domain ferromagnetic particles. Keywords: memristor, resistive switching, atomic force microscopy, ferromagnetic filaments.

The effect of Gaussian noise on the switching of a ZrO 2 (Y) based memristor from the low resistance state (LRS) into the high resistance state (HRS) including transitions from the LRS into intermediate metastable states has been studied. The series of positive (with addition of the noise signal or without the one) and negative rectangular voltage pulses were used as the switching signals. The adding of noise to the switching signal initiated the switching of the memristor from the LRS into the HRS at smaller pulse magnitudes than in the case of switching by the rectangular pulses without adding the noise. A necessary (preset) HRS can be achieved passing the intermediate states by adding the noise with certain parameters to the rectangular switching pulses. The resistive switching is performed without application of adaptive switching protocols. The results of the present study can be applied in the development of innovative memristor switching protocols.

We report on the fabrication and investigation of prototype optically controlled memristors based on ZrO2(Y) (12% mol. Y2O3) with Au nanoparticles (NPs) of 2-3 nm in diameter formed by layer-by-layer magnetron deposition of ZrO2(Y)/Au/ZrO2(Y) stacks fol-lowed by annealing. The upper contacts of the memristor stacks were made from indium-tin oxide (ITO) to provide the access of photoexcitation to the active Au NP array. The cross -point memristor devices with the active region sizes of 2020 & mu;m2 were defined by standard photolithography with wet etching. A shift of the switching voltages from the high resistance state into the low resistance one and back has been observed under the photoexcitation at the wavelength of 650 nm corresponding to the collective plasmon resonance in the dense Au NP array. The effect was related to the charging of the Au NPs due to the internal photoemission of the electrons from the Au NPs into the ZrO2(Y) matrix enhanced by the plasmon resonance. It leads to the redistribution of the electric field near the Au NPs that, in turn, stimulates the switching process. The optically-controlled memristors investigated are promising for applica-tion in various fields of memristive photonics.

The effect of Gaussian noise on the switching of a ZrO2(Y) based memristor from the low resistance state (LRS) into the high resistance state (HRS) including transitions from the LRS into intermediate metastable states has been studied. The series of positive (with addition of the noise signal or without the one) and negative rectangular voltage pulses were used as the switching signals. The adding of noise to the switching signal initiated the switching of the memristor from the LRS into the HRS at smaller pulse magnitudes than in the case of switching by the rectangular pulses without adding the noise. A necessary (preset) HRS can be achieved passing the intermediate states by adding the noise with certain parameters to the rectangular switching pulses. The resistive switching is performed without application of adaptive switching protocols. The results of the present study can be applied in the development of innovative memristor switching protocols.

This report presents a method for controlling the synaptic plasticity of memristive devices based on changing not only the amplitude of control pulses, but also their duration. The object of study in this work is a ZrO 2 (Y)-based memristive device due to the demonstrated high stability of its resistive switching parameters. It is established that, when a sequence of pulses with varying duration and positive amplitude ≤ +1.0 V is applied, there is no change in the resistive state. At the amplitudes > +1.0 V, the resistance of memristive device increased significantly with increasing pulse duration. It is shown that the dependencies of the average current on the pulse duration can be satisfactorily approximated by an exponential decay function. The proposed protocol is demonstrated to be more efficient for controlling the synaptic plasticity of memristive devices.

Исследованы электрические характеристики лабораторных макетов мемристоров на основе эпитаксиальных гетероструктур p-Si/p-Ge/n+-Si(001) с Ag- и Ru-электродами. Мемристоры с Ru-электродами демонстрируют меньшее напряжение электроформовки и большее отношение токов в состояниях с низким и высоким значениями сопротивления по сравнению с мемристорами с Ag-электродами. Также в мемристорах с Ru-электродами обнаружена инверсия полярности резистивного переключения. Указанные эффекты обусловлены большей подвижностью ионов Ru3+ в прорастающих дислокациях в слоях p-Si/p-Ge вследствие их меньшего ионного радиуса. Ключевые слова: мемристор, эпитаксиальные слои SiGe, резистивное переключение.

The electrical parameters of the prototype memristors based on p-Si/p-Ge/n + -Si(001) epitaxial heterostructures with Ag and Ru electrodes have been studied. The memristors with Ru electrodes demonstrated smaller electroforming voltage and greater ratio of currents in the low and high resistance values as compared to the memristors with Ag electrodes. Also, an inversion of the resistance switching polarity was observed in the memristors with Ru electrodes. Thses effects originate from a higher mobility of Ru 3+ ions in the threading dislocations in the p-Si/p-Ge layers due to smaller ion radius. Keywords: Memristor, SiGe epitaxial layers, resistance switching.

The effect of optical illumination in the visible band on the resistive switching in ITO/ZrO2(Y)/n-Si metal-oxide-semiconductor (MOS) structures (including those with Au nanoparticles embedded in the ZrO2(Y) layer) is studied. It is found that the dependence of the logical gap between the resistance states on the photoexcitation intensity had a threshold nature. The logical gap decreases with further increasing photoexcitation intensity above the threshold. This effect is ascribed to the heating of active layers of the MOS structure due to interband optical absorption in the Si substrate. The suppression of resistive switching by photoexcitation at a wavelength of 650 nm (corresponding to plasmon resonance in Au nanoparticles) due to plasmon optical absorption in nanoparticles is observed.

Accumulation and relaxation of optically induced electric charge in ZrO2(Y) films with embedded single-layered arrays of Au nanoparticles (NPs) of 2-3 nm in diameter have been studied subject to the depth of the Au NPs in the ZrO2(Y) layers and the optical excitation power at the wavelengths of 473 and 633 nm by Scanning Kelvin Probe Microscopy (SKPM).

The resonant activation of resistance switching (RS) of a memristor based on an yttria stabilized zirconia (YSZ) film with embedded Au nanoparticles (NPs) was investigated. The switching was made by triangular pulses with high frequency (HF) sinusoid added. A non-monotonous dependence a ratio of the electric current through the memristor in the low resistive state to the current in the high resistive one on the HF sinusoid frequency was found. The effect was explained by a finite electron tunneling time between the Pt electrode and Au NPs. This conclusion was supported by measuring a dependence of HF memristor capacitance on the probing signal frequency.

The effects of external digitally synthesized Gaussian noise on the resistive state relaxation time of a ZrO 2 (Y)-based memristive device when switching from a low resistance state to a high resistance state have been experimentally investigated. A nonmonotonic dependence of the resistive state relaxation time on the external noise intensity is found. This behavior is interpreted as a manifestation of the noise-enhanced stability effect previously observed in various complex systems with metastable states. It is shown that the experimental results agree satisfactorily with the theoretical ones. The presented results indicate the constructive role of external noise and its possible use as a mechanism for controlling the kinetics of resistive switching .

The memristor is a simple two-terminal device that can be realized as a capacitor-like thin film stack demonstrating the effect of resistive switching (resistive memory) due to atomic (defect) reconstruction, when a voltage of a certain polarity and magnitude is applied. The main physicochemical phenomena associated with the diffusion and drift of oxygen ions (vacancies), local processes of formation and reduction-oxidation of conducting channels (filaments) in different metal-oxide materials are considered in this chapter. The conclusions about the filamentary nature of resistive switching are supported by the local electrical characterization of thin oxide films with scanning probe microscopy techniques and multiscale simulation of electroforming and switching by using phenomenological approaches, ab initio, molecular dynamics and kinetic Monte Carlo methods.

The effects of temperature on the switching kinetics of an yttrium-stabilized zirconia-based memristor from a low-resistance state to a high-resistance state have been experimentally investigated. It was found that the memristor relaxation time depends on the temperature in a non-monotonous way, with a maximum observed at the temperature close to 55 degrees C. This nonmonotonic behavior is a signature of the noise-enhanced stability phenomenon observed in all physical and complex systems characterized by metastable states. (c) 2022 Elsevier Ltd. All rights reserved.

We report on a comparative study of resistive switching in the memristors based on ZrO 2 (Y) films and on ZrO 2 (Y)/Ta 2 O 5 bilayer stacks by triangle voltage pulses with superimposed high-frequency sinusoidal signal. The dependencies of the current difference in the low resistance state and in the high resistance one on the sinusoidal signal frequency for the ZrO 2 (Y)-based memristor and for the ZrO 2 (Y)/Ta 2 O 5 -stack based one manifested one and two maxima, respectively attributed to the resonant activation of the migration of the oxygen ions via the oxygen vacancies by the alternating external electric field in ZrO 2 (Y) and in Ta 2 O 5 .

Conducting ferromagnetic nanosized filaments consisting of Ni atoms are formed in thin ZrO2(Y)/Ni films using an atomic force microscope probe. The contact of the probe to such films (a virtual composite memristor device) exhibits resistive switching of the bipolar type associated with the destruction and restoration of Ni filaments in the ZrO2(Y) film. The region in which the conductive filament emerges onto the surface of the ZrO2(Y) film manifests itself in the magnetic force image as a single-domain ferromagnetic particle.

A mechanism of effect of optical excitation on resistive switching of dielectric films with embedded metal nanoparticles (MNPs) has been proposed. The mechanism is related to a charging of the MNPs due to internal photoemission of electrons from the MNPs, which results in an increasing of the electric field strength at the MNP surfaces that, in turn, promotes the rupture and restoring of the conductive filaments in the dielectric film. The increasing of the electric filed strength due to the MNP charging as a function of the MNP sizes and positions inside the dielectric films was evaluated using a simple model taking into account the mirror charges on the conductive electrodes of a memristor stack. The single electron charging was found to be essential at small MNP radii (∼1 nm). The proposed mechanism was confirmed experimentally by studying the photoexcitation-induced charging of Au MNPs (with average radius 1.6–1.8 nm) embedded into a 10 nm thick ZrO2(Y) film by Kelvin probe force microscopy.

The stochastic resonance phenomenon has been studied experimentally and theoretically for a state-of-art metal-oxide memristive device based on yttria-stabilized zirconium dioxide and tantalum pentoxide, which exhibits bipolar filamentary resistive switching of anionic type. The effect of white Gaussian noise superimposed on the sub-threshold sinusoidal driving signal is analyzed through the time series statistics of the resistive switching parameters, the spectral response to a periodic perturbation and the signal-to-noise ratio at the output of the nonlinear system. The stabilized resistive switching and the increased memristance response are revealed in the observed regularities at an optimal noise intensity corresponding to the stochastic resonance phenomenon and interpreted using a stochastic memristor model taking into account an external noise source added to the control voltage. The obtained results clearly show that noise and fluctuations can play a constructive role in nonlinear memristive systems far from equilibrium.

Исследовано влияние оптического излучения видимого диапазона на резистивное переключение в МДП-структурах ITO/ZrO2(Y)/n-Si, в том числе с наночастицами Au, встроенными в слой ZrO2(Y). Обнаружено, что зависимость ширины логического коридора резистивных состояний от интенсивности фотовозбуждения имеет пороговый характер. При увеличении интенсивности фотовозбуждения выше порогового значения наблюдалось уменьшение ширины логического коридора, предположительно, связанное с разогревом активных слоев МДП-структуры при межзонном поглощении излучения в Si-подложке. Обнаружено подавление резистивных переключений при фотовозбуждении на длине волны 650 нм (соответствующей плазмонному резонансу в наночастицах Au) за счет плазмонного оптического поглощения в наночастицах. Ключевые слова: мемристор, резистивное переключение, МДП-структуры, стабилизированный диоксид циркония, наночастицы Au, фоточувствительность.