RU2666165C1 - Method for forming a synaptic memristor based on a nanocomposite of metal-nonstechometric oxide - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to the field of micro- and nanoelectronics, namely the manufacturing technology of a synaptic memristor based on the metal-non-stoichiometric oxide nanocomposite, which has adaptive (neuromorphic) properties. Method for the formation of a synaptic memristor based on a metal-non-stoichiometric oxide nanocomposite is proposed, consisting in successive deposition of layers on a substrate. At the same time, the Cr/Cu/Cr layer, which is the lower electrode, the metal-non-stoichiometric oxide nanocomposite layer and the Cr/Cu/Cr layer, which is the upper electrode, are sequentially deposited on the glass-ceramic substrates by ion-beam sputtering method. In the metal-non-stoichiometric oxide nanocomposite, the ferroelectric material LiNbOis used as oxide, and the amorphous alloy CoFeB– as the metal. Deposition of the metal-non-stoichiometric oxide nanocomposite is carried out with a lack of oxygen 2.5–3.5 mcm in thickness and with a metal content of 2–4 at.% below the percolation threshold x≈ 15 at.% on substrates having a room temperature.EFFECT: creation of memristive structures Cr/Cu/Cr/(CoFeB)(LiNbO)/Cr/Cu/Cr using non-stoichiometric oxides capable of simulating the properties of biological synapses and simultaneously possessing increased resistance to cyclic resistive switching.5 cl, 6 dwg

Description

FIELD OF THE INVENTION

The invention relates to the field of micro- and nanoelectronics, and in particular to a manufacturing technology for a synaptic memristor based on a metal-non-stoichiometric metal nanocomposite, which has adaptive (neuromorphic) properties.

State of the art

The possibility of obtaining memristors with high degradation resistance during cyclic switching and the presence of more than two stable resistive states is an important task for the creation of multilevel (analog) elements of non-volatile resistive memory with random access (RRAM) and elements simulating the action of the synapse when constructing bio- similar processor devices.

Attempts to create such devices only on the basis of complementary metal-oxide-semiconductor structures by reducing the size of elements and using parallelism in information processing do not give the desired result. In particular, due to the complexity of the implementation of synaptic plasticity (variable efficiency of signal transmission between neurons) and the high enough power consumption.

To simulate the synapse, objects with memristive (memory) properties are required, which consist in changing the electrical resistance of the structure (its resistive switching) under the influence of the electric field and the leaking charge and storing the emerging resistive state after removing the external field effect.

Memristive metal-oxide-metal structures of an anion type, based on oxides (TiO ₂ or LiNbO ₃ ), with high values of dielectric constant, which can be used to simulate synapses when creating neuromorphic computing systems, are known. The disadvantage of their practical application is the low resistance to degradation with resistive switching N _max <5⋅10 ³ . The reason for the degradation of the memristive properties of metal-oxide-metal structures is the random (“filament”) nature of the transition to a conducting state that changes over time.

The main mechanisms of resistive switching of the above structure are the formation of conductive filament during electromigration of oxygen vacancies in the oxide layer, as well as the change in the Schottky barrier at the metal-oxide interface (Ielmini D. Resistive switching memories based on metal oxides: mechanisms, reliability and scaling // Semicond. Sci. Technol. - 2016 .-- V. 31. - P. 063002). In this type of structure (in particular, in Pt / Al ₂ O ₃ / TiO _2-x / Ti / Pt synaptic memristors (Prezioso M., Merrikh-Bayat F., Hoskins BD, Adam GC, Likharev K. K., and Strukov DB Training and operation of an integrated neuromorphic network based on metal-oxide memristors // Nature. - 2015. - V. 521. - P. 61.) a smooth change in resistance is possible, and according to the rules used in biological neural networks, in particular, according to the so-called “STDP” rule (spike-timing-dependent-plasticity-plasticity, depending on the time of arrival of the impulse) (M. Prezioso, F. Merrikh Bayat, B. Hoskins, K. Likharev, and D. Strukov. Self -Adaptive Spike-Time- Dependent Plasticity of Metal- Oxide Memristors. Sci. Rep.V.6, 21331; doi: 10.1038 / srep21331 (2016)) .Memrist The typical Pt / Al ₂ O ₃ / TiO _2-x / Ti / Pt structures were created using atomic layer deposition (ALD) at relatively low growth temperatures (<300 ° C). The structures have nanometer-thick oxide layers (d = 4 nm for Al ₂ O ₃ and d = 30 nm for TiO _2-x ) and have a fairly high resistance ratio R _oƒƒ / R _on > 10 ² . It is important that the low growth temperatures of Pt / Al ₂ O ₃ / TiO ₂ - _x / Ti / Pt structures made it possible to create cross-bars (12 × 12) based on them, integrated with a Si CMOS device for recording / erasing and reading information from a cross -bar of elements.

The main disadvantage of Pt / Al ₂ O ₃ / TiO _2-x / Ti / Pt structures is their low resistance to endurance during cyclic switching. The maximum number of switching cycles N _max from the high-resistance state to the low-resistance state and vice versa is about 5⋅10 ³ times. In addition, these structures require the use of a rather expensive ALD method for their synthesis.

Memristive Au / BiFeO ₃ / Pt / Ti structures (d = 600 nm for BiFeO ₃ ) are known, created by the relatively inexpensive pulsed laser deposition (PLD) method, which use the effect of modulating the height of the Schottky barrier at the BiFeO ₃ / Pt interface during ion electromigration (You T., Du N., Slesazeck S., Mikolajick T., Li G., Burger D., Skorupa I., Stocker H., Abendroth B., Beyer A., Volz K., Schmidt OG, and Schmidt H. Bipolar Electric-Field Enhanced Trapping and Detrapping of Mobile Donors in BiFe03 Memristors // ACS Appl. Mater. Interfaces. - 2014 .-- V. 6. - P. 19758-19765). These structures also have a resistance ratio R _oƒƒ / R _on ~ 10 ² , however, the switching cycles N _max ≈ 3⋅10 ⁴ are still not high enough. In addition, there is no information on the plasticity of structures, i.e. the ability to specify an arbitrary resistive state of structures in the range between R _on and R _oƒƒ , as well as their use for modeling synapses.

Quite large values of switching cycles N _max ≈ 1.7⋅10 ^{5 were} achieved for multilevel (analog) elements of non-volatile resistive memory with random access based on HfO ₂ layers grown by ALD (Balatti S, Ambrogio S, Wang ZQ, Sills S, Calderoni A, Ramaswamy N and Ielmini D Voltage-controlled cycling endurance of HfOx-based resistive-switching memory (RRAM) // IEEE Trans. Electron Devices-2015. - V.62. - P. 3365). In structures based on HfO _{2, it is} possible to obtain a set of intermediate resistive states (Brivio S., Covi E., Serb A., Prodromakis T., Fanciulli M., Spiga S. Experimental study of gradual / abrupt dynamics of Hf02-based memristive devices / / Appl. Phys. Lett. -2016. -V.109. -P. 133504), however, in this case, the ratio of electrical resistances in the most high-resistance and low-resistance states is small R _oƒƒ / R _on ≈ 6.

Recently, the possibility of using memristive structures Ti / Pt / LiNbO _3-y / LiNbO ₃ / Ti / Pt obtained by pulsed laser deposition (PLD) as synapses in neuromorphic computing systems (C. Yakopcic, S. Wang, W. Wang , E. Shin, J. Boeckl, G. Subramanyam, TM Taha. Filament formation in lithium niobate memristors supports neuromorphic programming capability // Neural Comput. & Applic. - 2017. DOI: 10.1007 / s00521-017-2958-z). These structures have a rather large resistance ratio R _oƒƒ / R _on ≈ 30, however, they have low resistance to resistive switching.

The well-known "Method of forming a memristor based on a solid state alloy Si: Me and the structure of a memristor based on a solid state alloy Si: Me" (Patent RU 2540237), which is characterized by the absence of "molding" when the structure is initially switched to a state with low resistance. A metal-insulator-metal structure memristor consists of an insulator layer of a solid state alloy Si: Me, which is formed with a predetermined metal concentration profile Me in thickness (in the direction from the lower electrode to the upper electrode within 1-25%). A memristor can have up to 5 different resistances.

The disadvantage of this method is that the resulting memristor is not resistant to degradation during cyclic switching, which makes it unsuitable for building bio-like processor devices.

The invention is known as the “Nanometallic Resistive Element Switch” (Patent US 2012001146), which describes a non-volatile memory device comprising a lower electrode formed of metal and a resistive switching element deposited on top of this electrode. The resistive switching element is tungsten oxide WO _3-x . The device includes a top electrode made of precious metal. The resistance of this device can change when an increasing voltage is applied and, thus, information can be saved.

The disadvantage of this invention is that it does not demonstrate resistance to degradation during cyclic switching, which is unsuitable for building bio-like processor devices.

The closest in technical essence to the claimed invention is a memristor formed on the basis of mixed metal oxide (Patent RU 2524415). This device consists of an active layer located between two conductive layers, in electrical contact with them. The active layer has the property of resistive switching and is a two-layer oxide structure of HfA1 _x O _y / HfO ₂ . The HfAl _x O _y layer has a high solubility and a high equilibrium concentration of oxygen vacancies, and HfO ₂ is a layer with a low solubility of vacancies.

The conductive layers are made of titanium nitride or tungsten nitride. An ultrathin ruthenium oxide layer with a thickness of at least 0.5 nm is deposited at the HfO ₂ / TiN interface. When applying the layers were used: the method of pulsed laser deposition and the method of magnetron sputtering. Obtained during the implementation of this method, the memristor demonstrates the stability of the modes of switching resistance to low and high resistance state (at least 100 times).

The main significant drawback of the obtained memristor is that it demonstrates only two different resistive states (low and high), which is suitable only for constructing digital circuits. While the construction of bio-like processor devices and analog elements of non-volatile resistive memory with random access is critical, the possibility of realizing the synaptic plasticity of memristors, i.e. the presence of more than two stable resistive states.

Therefore, the possibility of obtaining memristors with high degradation resistance during cyclic switching (N _max > 10 ⁵ ) and the presence of more than two stable resistive states is an important task.

Disclosure of the invention

The technical result of the proposed invention is the creation of memristive structures Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr, capable of simulating the properties of biological synapses and at the same time possessing increased resistance to cyclic resistive switching.

To achieve a technical result, a method for the formation of a synaptic memristor based on a metal-non-stoichiometric oxide nanocomposite is proposed, which consists in sequentially depositing layers on a substrate, in this case, a layer of Cr / Cu / Cr, which is the lower electrode, is sequentially deposited onto the metal substrates by ion beam spraying a metal-non-stoichiometric oxide nanocomposite and a Cr / Cu / Cr layer, which is the upper electrode.

In addition, the nanocomposite-stoichiometric metal oxide is used as LiNbO ₃ ferroelectric oxide and metal as -amorfny alloy Fe ₄₀ Co ₄₀ B _20.

Also, the deposition of the metal-non-stoichiometric oxide nanocomposite with a thickness of 2.5-3.5 μm and with a metal content of 2-4 at.% Below the percolation threshold xp = 15 at.% Is carried out with a lack of oxygen.

A high-resistance interlayer with a thickness of 0.05-0.1 μm is formed near the surface of the lower electrode by adding at the initial stage of deposition of the nanocomposite layer of excess oxygen with a partial pressure of P _O2 = (1-3) 10-5 Torr for 5-10 minutes, after what is the deposition of layers with a lack of oxygen.

Also, layers are deposited on substrates having room temperature.

It is established that in the case of replacing the active oxide layer in the metal / oxide / metal structure with a metal-non-stoichiometric oxide nanocomposite, the transition to the conducting state at x <x _p is determined by percolation chains specified by the spatial position and concentration of the metal nanogranules, which ensures high stability of resistive switchings.

The method of ion-beam sputtering of composite targets of a nanocomposite is relatively inexpensive, well tested, and allows one to obtain nanocomposites of controlled composition, including those with a varying distribution of the metal and dielectric components (S.A. Gridnev, Yu.E. Kalinin, A.V. Sitnikov, OV Stogney, Nonlinear Phenomena in Nano- and Microheterogeneous Systems, Moscow: BINOM, Laboratory of Knowledge (2012), 352 p.

To create a non-stoichiometric oxide matrix with a high content of oxygen vacancies, an amorphous Co ₄₀ Fe ₄₀ B ₂₀ alloy is used as a metal. Boron atoms have a small size and high diffusion mobility. In this case, the low enthalpy of formation of the simplest BO oxide is E _e ≈ +0.04 eV / molecule (for comparison, in the case of TiO and NbO E _е ≈ +0.5 and + 1.9 eV / molecule), respectively, allow boron atoms to bind oxygen, which contributes to the formation of a non-stoichiometric oxide matrix with a significant excess of oxygen vacancies.

To set a certain polarity of the switching voltage from the high-resistance R _oƒƒ to the low-resistance R _on state, to increase the electrical resistance ratio R _oƒƒ / R _on , as well as the storage time of the resistive states at the lower electrode, a high-resistance layer is created by adding excess oxygen with partial pressure at the initial nanocomposite growth process P _O2 ≈ (1-3) -10 ^-5 Torr for ≈ 5-10 minutes.

Brief Description of the Drawings

The invention is illustrated by the following figures:

In FIG. 1 schematically shows an implemented method for creating the structures Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _{3. Y} ) _100-x / Cr / Cu / Cr, where:

1- probes;

2- granular nanocomposite (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x ;

3- upper electrode Cr / Cu / Cr;

4- lower electrode Cr / Cu / Cr;

5-ceramic substrate.

In FIG. Figure 2 shows the current – voltage characteristic of memristor structures Cr / Cu / Cr / nanocomposite / Cr / Cu / Cr based on the nanocomposite (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x with the content of amorphous alloy x ≈ 13 and 16 at.% Obtained by adding oxygen nanocomposite at the initial stage of growth (P _O2 ≈ 2⋅10 ^-5 Torr). NK layer thickness d ≈ 3 μm.

In FIG. Figure 3 shows the time dependences of the resistance of the memristive structure Cr / Cu / Cr / nanocomposite / Cr / Cu / Cr based on the nanocomposite (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x (х ≈ 13 at.%) In various resistive states obtained by applying pulses of different polarity and amplitude, where:

1 - recording with a +5 V pulse for 10 s, then reading at 0.1 V with a frequency of ƒ = 1/20 s ^-1 ;

2 - erasing by a -5 V pulse with a duration of 10 s, then reading at 0.1 V s ƒ = 1/20 s ^-1 ;

3 - erasing by a -7 V pulse for 10 s, then recording with 10 voltage pulses of +3 V for 0.2 s, then reading at 0.1 V with ƒ = 1/20 s ^-1 .

In FIG. Figure 4 shows the shape of a voltage pulse (spike) on pre- and postsynaptic neurons.

In FIG. Figure 5 shows the dependence of the relative change in the conductivity ΔG of the CR / Сu / Сr / nanocomposite / Cr / Cu / Cr memristive structure based on the nanocomposite (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNb _3-y ) _100-x (х ≈ 13 at.% ) at different conductivity values (G _i = 1, 2, and 5 (kOhm) ^-1 ) according to the STDP rule of the delay time Δt between the spikes for different initial states of the memristor.

In FIG. Figure 6 shows the dependence of the electrical resistance of the memristive structure of Cr / Cu / Cr / nanocomposite / Cr / Cu / Cr based on the nanocomposite (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x (x ≈ 13 at.%) On number of write / erase cycles. Measurement procedure: write +5 V (100 ms), read 0.1 V (100 ms), erase -5 V (100 ms), read 0.1 V (100 ms).

The implementation of the invention

Structures Cr / Cu / Cr / (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr (Fig. 1) were obtained by ion beam sputtering of a composite target, which was a metal base from Co ₄₁ Fe ₃₉ B ₂₀ alloy with a size of 280 × 80 × 15 mm ³ with 14 LiNbO ₃ oxide plates 10 mm wide fixed on its surface, which were located unevenly on the base.

The sequence of deposition of the layers was as follows:

The 1 Cr / Cu / Cr layer, which is the lower electrode 4 with a thickness of d ≈ 1 μm, was deposited on the ceramic plates 5 having a room temperature of 60 × 48 × 0.6 mm ³ .

Layer 2 (nanocomposite 2 (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x was applied to layer 1 in an argon atmosphere (P _Ar ≈ 8-10 ^-4 Torr) through a metal mask with periodically arranged holes with a diameter ≈ 5 mm, Layer 2 of nanocomposite 2 was deposited with a lack of oxygen 2.5-3.5 μm thick and with a metal content of 2-4 at.% Below the percolation threshold x _p ≈ 15 at.%.

The deposition of nanocomposite 2 (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _{100-x was} carried out simultaneously on four sitallic substrates 5 (with a previously deposited layer 1), which were aligned with the target at a distance of 200 mm from it in the form of a strip . The uneven arrangement on the surface of the Co ₄₁ Fe ₃₉ B ₂₀ wafer from LiNbO ₃ made it possible to form nanocomposites with a different ratio of the metal phase along the length of the metal substrate 5 in a single cycle in the range x = 5 - 48 at.%. The elemental composition of the nanocomposite was determined using an Oxford INCA Energy 250 energy dispersive X-ray attachment using a JEOL JSM-6380 LV scanning electron microscope. The accuracy of determining the composition of the samples was determined by their size and discreteness of location on the ceramic 5 substrates and was δх ≈ ± 1 at.%.

Layer 2 of nanocomposite 2 (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x at the initial stage of growth can be deposited with oxygen with a partial pressure P _O2 ≈ (1-3) ⋅10 ^-5 Torr for ≈ 5-10 minutes The deposition rate of nanocomposite 2 was about 0.25 nm / s, and the thickness was d ≈ 3 μm. In this case, a high-resistance layer with a thickness of d ≈ 0.05-0.1 μm is created at the lower electrode 4.

Layer 3 Cr / Cu / Cr, serving as the upper electrode 3 with a thickness of d ≈ 1 μm, was applied to layer 2 through a metal mask with a hole size of 0.5 × 0.2 mm ² .

Studies of memristic properties of structures

Cr / Cu / Cr / (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr were performed at room temperature using a multifunctional source meter NI PXI-4130 (National Instruments) and PM5 analytical probe station (Cascade Microtech) equipped with a specialized PSM-100 system (Motic) with an optical microscope, which allows micrometric movement of probes 1.

The current – voltage characteristics of Cr / Cu / Cr / (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structures were measured with a grounded lower electrode 4 and a linear voltage sweep U of the upper electrode law in the sequence from 0 → +5 → -5 → 0 V in 0.1 V increments. The period of the sawtooth voltage sweep is T = 12 s.

Experiments to study the possibility of selecting an arbitrary resistive state (plasticity) of the Cr / Cu / Cr / (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structure and its storage over time (retention time ) were performed in two ways:

1) by applying pulses of different polarity and amplitude;

2) according to the STDP rule, including the impact on the structure of two consecutive voltage pulses of the same shape, simulating spikes from neurons.

The resulting difference voltage pulse from the spikes was determined programmatically and applied to the Cr / Cu / Cr / (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structure, after which its resistance was measured at reading voltage U _r = 0.1 V.

The stability of the Cr / Cu / Cr / (Co ₄₁ Fe ₃₉ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structure to degradation during cyclic switching (endurance) was studied by applying successive voltage pulses of 100 ms duration : U _set → U _r → U _res → U _r , where:

U _set = ⁺ (5-7) V is the write voltage (set), which transfers the structure to a low-impedance state;

U _r = 0.1 V - read voltage;

U _res = - (5-7) V - voltage to erase (reset) or return the structure to its original state (U _res ≈ - U _set ).

It was found that the hysteresis in the current – voltage characteristic, characteristic of the effect of resistive switching, is most strongly observed at a certain optimal content of the amorphous alloy x = x _opt , lower by 2-3 at.% Percolation threshold. This fact is illustrated in FIG. 2, which shows the current – voltage characteristics for the structures Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr with an amorphous alloy content (x ≈ 13 and 16 at.%) below and above the percolation threshold x _p ≈ 15 at.%, obtained in the current limit mode at 0.1 A. It can be seen that a sufficiently strong hysteresis in the current-voltage range is observed below the threshold at x ≈ 13 at.% characteristic, whereas in the metallic mode (x ≈ 16 at.%) hysteresis is absent. Note that in the high-resistance and low-resistance states of the structure, its current-voltage characteristic is linear up to voltage bias U ≈ 0.4 V; the ratio R _oƒƒ / R _on ≈ 32.4 and 31.5 at U = 0.1 and 0.4 V, respectively.

In FIG. Figure 3 presents the results of experiments to study the possibility of selecting an arbitrary resistive state of the Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x Cr / Cu / Cr structure and its storage in time (at least 1 hours). It can be seen that when the structure is exposed to voltage pulses with an amplitude of +5 V for 10 s (line 1 in Fig. 3), its transition from the initial high-resistance state (R _h ≈ 2900 Ohms) to the lowest-resistance state (R _l ≈ 300-350 Ohms) is achieved . However, after affecting the structure of Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x Cr / Cu / Cr (line 3 in Fig. 3) with 10 pulses of lower amplitude ( +3 For a duration of 0.2 s), its resistance is in the intermediate state R _int ≈ 1600 Ohm, and the difference between the initial and intermediate states ΔR ≈ 1300 Ohm is preserved with an accuracy of better than 10%.

In FIG. Figure 4 shows the shape of the spikes on the pre- and postsynaptic neuron, which were used to test the applicability of the STDP rules. FIG. 5 shows the possibility of changing the resistive state of the memristive structure Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr using the STDP rule. According to this rule, the conductivity of the ΔG structure should increase (the connection between neurons is strengthened) if the difference Δt between the time of arrival of 2 voltage pulses that imitate the pre- and postsynaptic commissures of biological neurons at the memristor is negative (see Fig. 4). Conversely, when Δt> 0 (the postsynaptic spike arrives before the presynaptic spike), the conductivity decreases (the connection between neurons is weakened). Note that the spike-pulse shapes we have chosen are often used to test the STDP rule. We simulated the spike with two triangular bipolar pulses having durations and amplitudes sufficient to change the resistive states in the created memristor structures: at the beginning, the voltage U _s in the spikes increases from 0 to +4 V over 200 ms, then it is inverted and changes from -2 up to 0 V during 500 ms. The resulting pulse was programmatically subtracted from the pre-synaptic spike and applied from the NI PXI-4130 meter to the memristor structure.

The resistance of Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structures to degradation upon cyclic switching (endurance) turned out to be rather high. We could not observe noticeable degradation effects when the number of write / erase cycles exceeding 10 ⁵ times (Fig. 6), which is more than for Si Flash memory and is not inferior to the elements of multilevel (analog) elements of non-volatile resistive memory with random access (RRAM) memory based on HfO ₂ layers with a small ratio R _oƒƒ / R _on ≈ 6.

In studies of the resistance of Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structures to resistive switching, the following sequence of measurement operations was used: recording +5 V for 100 ms, reading 0.1 V (100 ms), erasing -5 V (100 ms), reading 0.1 V (100 ms). The greatest stability and accuracy of measuring low-resistance and high-resistance states over time was observed for Cr / Cu / Cr / (Co ₄₀ Fe ₄₀ B ₂₀ ) _x (LiNbO _3-y ) _100-x / Cr / Cu / Cr structures with Cr / Cu / Cr / electrodes 3 and 4, in which, after the first 10 ⁴ write / erase cycles, the state levels R _oƒƒ and R _on turn out to be constant with an accuracy of better than 10% at a ratio R _0ƒƒ / R _on ≈ 20 (see Fig. 6).

Thus, the proposed method allows to obtain memristive structures capable of simulating the properties of biological synapses and at the same time possessing increased stability (N _max > 10 ⁵ ) during cyclic resistive switching, sufficient for their practical application.

Claims (5)

1. A method of forming a synaptic memristor based on a metal-non-stoichiometric oxide nanocomposite, which consists in sequentially depositing layers on a substrate, characterized in that a Cr / Cu / Cr layer, which is the lower electrode, is a metal lower layer electrode, a metal nanocomposite layer is sequentially deposited onto the metal substrates non-stoichiometric oxide and a Cr / Cu / Cr layer, which is the upper electrode. 2. The method according to p. 1, characterized in that in the metal-non-stoichiometric oxide nanocomposite, LiNbO ₃ ferroelectric is used as the oxide, and the amorphous alloy Co ₄₀ Fe ₄₀ B _{20 is} used as the metal. 3. The method according to p. 1, characterized in that the deposition of the metal-non-stoichiometric metal nanocomposite oxide with a thickness of 2.5-3.5 μm and a metal content of 2-4 at.% Below the percolation threshold x _p = 15 at.% Is carried out with lack of oxygen. 4. The method according to p. 1, characterized in that a high-resistance layer with a thickness of ≈0.05-0.1 μm is formed at the surface of the lower electrode by adding at the initial stage of deposition of the nanocomposite layer of excess oxygen with a partial pressure P _O2 = (1-3) 10 ^-5 Torr for 5-10 minutes, after which the deposition of oxygen-deficient layers is carried out. 5. The method according to p. 1, characterized in that the layers are deposited on substrates having room temperature.

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