The article discusses a memristive neuromorphic system consisting of two analog memristive neurons, Fitzhugh-Nagumo, connected through a memristive device Au/Zr/SiO2/TiN/Ti/SiO2/Si. Such a system, on one hand, imitates the biologically plausible dynamics of ion channels in neurons, and on the other hand, the interneuronal synaptic connections. It has been established that the memristive device, under the influence of a signal from the presynaptic electrical neuron, exhibits synaptic plasticity. Experimental results have shown forced synchronization modes with frequency ratios of 1:1, 2:1, N:1. The developed system effectively reproduces the dynamics of synaptic connections in neural networks of the brain. From an applied point of view, due to the adaptive properties of the memristor, it can be used for the development of neurosensory devices.

A technology was developed for activating ion-implanted dopants in silicon-on-insulator layers at a low annealing temperature (600°C) using the pre-amorphization technique of a silicon device layer. In the case of phosphorus implantation, silicon was amorphized directly by dopant ions. In the case of boron implantation for pre-amorphization, the layers were preliminary irradiated with argon or fluorine ions. Complex diagnostics of the implanted layers was carried out using secondary ion mass spectrometry, X-ray diffractometry, and small-angle X-ray reflectometry. The combination of methods made it possible to characterize the impurity distribution, the degree of silicon crystallinity, the layer thicknesses, and the interface widths in structures. The results of diagnostics of the structure and composition correlate well with calculations in the SRIM software package and the electrophysical characteristics of the layers after annealing. It was shown that the use of argon for pre-amorphization of silicon interfered with the recrystallization process and did not make it possible to achieve acceptable electrical characteristics of the doped layer. Amorphization with phosphorus and pre-amorphization with fluorine during boron implantation allowed obtaining the required values of the resistance of the doped layers after annealing at a temperature of 600°C. The use of a complex approach rendered it possible to optimize the modes of amorphization, ion doping, and annealing of silicon-on-insulator structures at low temperatures necessary for the creation of light-emitting device structures based on silicon-germanium nanoislands.

A transition is made from piecewise continuous functions of the memristor model with threshold type switching to differentiable functions described by a single formula. Systems of equations are obtained and numerically solved for circuit sections in which the memristive device is connected in series with other discrete elements, a conventional resistor, diode, inductor, and capacitor. For the case of a serial connection of a memristor and a resistor, the calculated data are compared with the experiment. The case of series connection of a memristor and a semiconductor diode has been studied in detail. The assumptions concerning the mathematical description and physical interpretation of the influence of the molding process on the memristive system are presented.

Magnetotransport measurements were carried out for YBa_2Cu_3O_{7-x} (YBCO) thin films in external perpendicular magnetic fields of H. The studies were performed both for the virgin samples and for the irradiated ones. Xenon ions were used as an external irradiation. Thus we studied features of the broadening of superconducting transition in YBCO films (virgin and irradiated). The broadening of superconducting drop was analyzed depending on an external magnetic field H, as well as on an irradiation dose n_D. When processing the experimental data R(H, T), we studied a criterion for determination of temperature dependence of the upper critical field H_{c2}(T). The criterion was analyzed depending on the defect concentration in the film corresponding to a certain value of n_D. It was found out that for a virgin sample, H_{c2} should be determined by the resistance level R = 0.4R_N inside the superconducting transition, where R_N = R(T = 100 K). With a gradual increase in n_D, this resistance level decreases. At sufficiently high radiation doses n_D > 7·10^{12} cm^{-2}, the H_{c2}(T) phase transition line should be determined by the level R ≈ 0.

The disorder effect on superconducting properties of thin-film YBCO nanostructures in external magnetic fields is experimentally studied. The disorder was produced by irradiation with xenon ions. The research included transport measurements of narrow bridges based on HTSC YBCO films (thickness 50 nm) in strong magnetic fields (up to 12 T). Thus, for samples with different degrees of disorder, critical dependencies have been studied, i.e. the Hc2(T) phase transition line, the Hirr(T) irreversibility line, etc. The dependences of the mean-free path and critical temperature on the concentration of defects created by ion irradiation have been experimentally studied. The experimental data are described using formulas obtained within the framework of well-known models, such as the Ginzburg-Landau theory, the Drude theory and the Gorkov equations.

Предложен новый подход к созданию энергоэффективных нейроморфных систем на основе многомерных нейронов с синапсами на основе мемристивных устройств. Такие системы могут имитировать функции пространственной памяти гиппокампа и предназначены для решения сложно формализуемых задач искусственного интеллекта.

Рассмотрен процесс разработки многослойного персептрона на основе мемристивных устройств для двунаправленного адаптивного нейроинтерфейса. Предложен общий подход к обеспечению точности его функционирования с учетом влияния дестабилизирующих факторов.

It is shown that self-forming GeSi nanoislands built into the dielectric–semiconductor interface in the Si(001)-based metal–oxide–semiconductor (MOS) structures with the SiOx and ZrO2(Y) dielectric layers obtained by magnetron sputtering initiate bipolar resistive switching without preliminary electroforming. The I–V characteristics and electrical parameters of the MOS structures in the high- and low-resistance states have been investigated. The change in the charge incorporated in the dielectric at the dielectric–semiconductor interface during resistive switching has been established, which is related to the formation and destruction of conducting filaments. The optically stimulated switching of the MOS structures with the ZrO2(Y) dielectric layer from the high- to low-resistance state has been observed, which is caused by an increase in the conductivity of the space charge region in the Si substrate due to the interband optical absorption in Si leading to the voltage redistribution between Si and ZrO2(Y). A difference between the shapes of the low-signal photovoltage spectra of the MOS structures in the spectral region of the Si intrinsic photosensitivity in the high- and low-resistance states related to the leakage of photoexcited carriers from Si into a metal electrode through filaments has been found.

The original research results for thin disordered HTSC films based on YBCO are presented in this article. Several experiments have been carried out to confirm a theoretical prediction that the s-phase of superconducting pairing in disordered d-type superconductors can occur with a gradual decrease in the mean free path. The YBa_2Cu_3O_{7-x} films were used as samples which possess a d-type of superconducting state that was experimentally confirmed. A gradual decrease in the mean free path was achieved by both thermal annealing and ion irradiation. The experiments included measurements of temperature dependence of the London penetration depth λ and resistive studies.

The electrophysical characteristics of a multilayer memristive Au/Ta/ZrO 2 (Y)/TaO x /TiN structure have been studied. Electron and ion electret effects due to charge carrier trapping and ion migration polarization in the dielectric have been discovered. The influence of traps on electroforming processes and resistive switching has been established. The values of activation energy and ion and trap concentrations have been determined. The effect of resistive switching stabilization has been found, which is associated with the specific bilayer structure of TaO x and self-forming tantalum nanoclusters. The nanoclusters serve as electric field concentrators in the course of electroforming and subsequent resistive switching.

The electrophysical characteristics of multilayer memristive structure Au/Ta/ZrO2(Y)/TaOx/TiN have been studied. The effects of electron and ion electrification associated with carrier trapping on traps and ion migration polarization in a dielectric are found. The effect of traps located in dielectrics on the effects of electroforming and resistive switching is established. The values of activation energy and concentrations for traps and ions are determined. The phenomenon of stabilization of resistive switching, which is associated with the features of the two-layer structure of YSZ/TaOx and self-assembled Ta nanoclusters, is found. Nanoclusters play the role of electric field concentrators in the process of electroforming and subsequent resistive switching.

Рассмотрены основные явления на микро- и макроскопическом уровне, ответственные за динамический отклик металл-оксидных мемристивных устройств, важный для их применения в новых нейросетевых архитектурах. Результаты проведенных экспериментов показывают конструктивную роль шума в мемристивном эффекте.

The self-assembled GeSi nanoislands built into the semiconductor-insulator interface of the MOS-structures based on Si(001) with SiOx and ZrO2(Y) oxide layers deposited by magnetron sputtering have been shown to initiate bipolar resistive switching without preliminary electroforming. The current-voltage curves and electrical parameters of the MOS-structures in the high-resistance state and in the low-resistance state have been studied. A change in the built-in charge in the dielectric near the insulator-semiconductor interface during resistive switching is established and associated with the formation and destruction of conductive filaments. The light-stimulated resistive switching of MOS-structures with ZrO2(Y) layer from the high-resistance to the low-resistance state is observed, which is associated with an increase in the conductivity of the space-charge region in the Si substrate due to interband optical absorption in Si, which causes a voltage redistribution between Si and ZrO2(Y) layer. A difference in the shape of the small signal photo-voltage spectra of MOS-structures is found in the spectral region of intrinsic photosensitivity of Si in the high and low resistance states due to the leakage of photo-excited charge carriers from Si to the metal electrode through filaments.

Resistive switching of memristive structures based on films of yttria stabilized zirconia (40 nm), irradiated with Si+ ions with an energy of 6 keV and a dose of 5.4∙1015 cm-2, was studied. It is established that ion irradiation leads to an increase in the stability of the parameters of resistive switching. This improvement is due to the fact that the diameter of the filaments as a result of irradiation is limited to the lateral size of the region of the individual cascades of displacement. Oxidation of such filaments in the process of resistive switching occurs more efficiently, which leads to an increase in resistance in a high resistance state.

AbstractThe peculiarities of resistive switching in capacitors with yttria-stabilized hafnia layers were studied. The characteristics of current transport in the initial state and after electroforming and resistive switching at different temperatures were examined. The parameters of a small-signal equivalent circuit of a capacitor were determined for switching into low- and high-resistance states. These parameters suggest that the resistance of filaments changes after each successive switching. This provides an opportunity to use such measurements to determine the nature of resistive switching and verify the reproducibility of its parameters. The contribution of electron traps to switching was revealed. Ion migration polarization was observed at temperatures above 500 K, and the activation energy of ion migration and the ion concentration were determined. The effect of resistive switching under the influence of temperature was observed and interpreted for the first time.

An unusual decrease in the slope of the upper critical field near Tc0 at a gradual increase in the ion implantation dose has been experimentally observed in narrow bridges formed on the base of thin HTSC YBa2Cu3O7 – x films, while an increase in the defect concentration usually leads to an increase in the local slope of the phase transition line Hc2(T). In addition, it has been found that the temperature dependence of the upper critical field has a positive curvature near Tc0. A possible theoretical interpretation of the results is proposed. It is based on the modified Ginzburg–Landau theory with a nonuniform length of superconducting correlations.

AbstractAn unusual decrease in the slope of the upper critical field near T _ c 0 at a gradual increase in the ion implantation dose has been experimentally observed in narrow bridges formed on the base of thin HTSC YBa_2Cu_3O_7 – _ x films, while an increase in the defect concentration usually leads to an increase in the local slope of the phase transition line H _ c 2( T ). In addition, it has been found that the temperature dependence of the upper critical field has a positive curvature near T _ c 0. A possible theoretical interpretation of the results is proposed. It is based on the modified Ginzburg–Landau theory with a nonuniform length of superconducting correlations.