KR102556818B1 - Synapse and neuromorphic device including the same - Google Patents

Abstract

Synaptic and neuromorphic devices are provided. Synapse according to an embodiment of the present invention, the first electrode; a second electrode spaced apart from the first electrode; an oxygen retaining layer interposed between the first electrode and the second electrode and containing a P-type material; a reactive metal layer interposed between the oxygen retaining layer and the second electrode and capable of reacting with oxygen ions of the oxygen retaining layer; and an oxygen diffusion barrier layer interposed between the reactive metal layer and the oxygen retaining layer to prevent the movement of oxygen ions from the oxygen retaining layer to the reactive metal layer, and including an N-type material, The oxygen diffusion barrier layer can form a P-N junction.

Description

Synapses and neuromorphic devices including them {SYNAPSE AND NEUROMORPHIC DEVICE INCLUDING THE SAME}

This patent document relates to neuromorphic devices that mimic the human nervous system and their applications.

Recently, technology capable of efficiently processing a large amount of information is required due to miniaturization, low power consumption, high performance, and diversification of electronic devices. In particular, interest in neuromorphic technology that mimics the human nervous system is increasing. In the human nervous system, there are hundreds of billions of neurons and synapses, which are junctions between neurons. Neuromorphic technology aims to implement a neuromorphic device by designing a neuron circuit and a synapse circuit corresponding to these neurons and synapses, respectively. Neuromorphic devices can be used in various fields such as data classification and pattern recognition.

An object to be solved by embodiments of the present invention is to provide a synapse with improved symmetry and linearity and a neuromorphic device including the synapse.

Synapse according to an embodiment of the present invention for solving the above problems, the first electrode; a second electrode spaced apart from the first electrode; an oxygen retaining layer interposed between the first electrode and the second electrode and containing a P-type material; a reactive metal layer interposed between the oxygen retaining layer and the second electrode and capable of reacting with oxygen ions of the oxygen retaining layer; and an oxygen diffusion barrier layer interposed between the reactive metal layer and the oxygen retaining layer to prevent the movement of oxygen ions from the oxygen retaining layer to the reactive metal layer, and including an N-type material, The oxygen diffusion barrier layer can form a P-N junction.

In the above embodiment, the synapse, according to the voltage or current applied to the first electrode and the second electrode, at least one of the plurality of reactive metal layers reacts with the oxygen ions to the corresponding oxygen diffusion barrier layer When a reset voltage of a first polarity is applied through the first electrode and the second electrode, a reset operation is performed in which an insulating oxide layer is formed on the reactive metal layer or its thickness is increased at the interface with the oxygen diffusion barrier layer. And, when a set voltage of a second polarity different from the first polarity is applied through the first electrode and the second electrode, a set operation in which the insulating oxide layer disappears or its thickness is reduced may be performed. During the reset operation, a reverse voltage may be applied to the P-N junction, and during the set operation, a forward voltage may be applied to the P-N junction. A read operation may be performed by applying a read voltage of the first polarity while having a magnitude smaller than the reset voltage through the first electrode and the second electrode. During the read operation, a reverse voltage may be applied to the P-N junction. As the thickness of the insulating oxide layer increases, conductivity may decrease, and as the thickness of the insulating oxide layer decreases, conductivity may increase. During the reset operation, the thickness of the insulating oxide layer increases as the number of pulses of the reset voltage increases, and during the set operation, the thickness of the insulating oxide layer decreases as the number of pulses of the set voltage increases. there is. During the reset operation, the pulse of the reset voltage may have a constant width and a certain size, and during the set operation, the pulse of the set voltage may have a constant width and a certain size. The oxygen diffusion barrier layer may have a thickness that does not completely block the movement of the oxygen ions. The oxygen diffusion barrier layer may include an insulating material, a semiconductor material, or a combination thereof. When a suppression operation in which conductivity decreases as the number of electrical pulses of the first polarity applied through the first and second electrodes increases, as the number of electrical pulses of the second polarity different from the first polarity increases, A strengthening operation in which the conductivity increases may be performed. A conductivity during the reinforcing operation and a conductivity during the suppressing operation may be substantially symmetrical. In each of the strengthening operation and the suppressing operation, a rate of change in conductivity may be substantially constant. Each of the electric pulse of the first polarity and the electric pulse of the second polarity may have a constant width and a certain size. When at least one of a width and a size of each of the electric pulse of the first polarity and the electric pulse of the second polarity is less than a predetermined threshold value, conductivity may not change.

In addition, a neuromorphic device according to an embodiment of the present invention for solving the above problems includes a first neuron; second neuron; a first wire connected to the first neuron and extending in a first direction; a second wire connected to the second neuron and extending in a second direction to cross the first wire; and a synapse between the first wire and the second wire and located at an intersection of the first wire and the second wire, wherein the synapse comprises: an oxygen retaining layer containing a P-type material; a reactive metal layer interposed between the oxygen retaining layer and the second wire and capable of reacting with oxygen ions of the oxygen retaining layer; and an oxygen diffusion barrier layer interposed between the reactive metal layer and the oxygen retaining layer to prevent the movement of oxygen ions from the oxygen retaining layer to the reactive metal layer, and including an N-type material, The oxygen diffusion barrier layer can form a P-N junction.

In the above embodiment, when a reset voltage of a first polarity is applied to the synapse through the first wire and the second wire, an insulating oxide layer is formed on the reactive metal layer at the interface with the oxygen diffusion barrier layer, or When a reset operation is performed to increase the thickness, and a set voltage of a second polarity different from the first polarity is applied to the synapse through the first wire and the second wire, the insulating oxide layer disappears or the A set operation in which the thickness decreases may be performed. During the reset operation, a reverse voltage may be applied to the P-N junction, and during the set operation, a forward voltage may be applied to the P-N junction. A read operation may be performed by applying a read voltage of the first polarity having a magnitude smaller than the reset voltage and having the same polarity as the reset voltage to the synapse through the first wire and the second wire. During the read operation, a reverse voltage may be applied to the P-N junction. During the reset operation, as the number of pulses of the reset voltage increases, the thickness of the insulating oxide layer increases, and during the set operation, as the number of pulses of the set voltage increases, the thickness of the insulating oxide layer decreases. can do. During the reset operation, the pulse of the reset voltage may have a constant width and a certain size, and during the set operation, the pulse of the set voltage may have a constant width and a certain size.

According to the above-described embodiments of the present invention, symmetry and linearity of the synapse can be improved, and thus the operating characteristics of the neuromorphic device can be improved.

1 is a diagram for explaining a neuromorphic device and an operating method thereof according to an embodiment of the present invention.
2a to 2d are views for explaining characteristics required for each synapse of FIG. 1 .
3A is a cross-sectional view for explaining the synapse of Comparative Example, and FIGS. 3B and 3C are views for explaining the characteristics of the synapse of FIG. 3A.
4 is a cross-sectional view for explaining a synapse according to an embodiment of the present invention.
5A is a cross-sectional view illustrating a reset operation of the synapse of FIG. 4 , and FIG. 5B is a cross-sectional view illustrating a set operation of the synapse of FIG. 4 .
6A is a cross-sectional view illustrating a read operation when the synapse of FIG. 4 is in a high-resistance state, and FIG. 6B is a cross-sectional view illustrating a read operation when the synapse of FIG. 4 is in a low-resistance state.
7 is an example of a pattern recognition system according to an embodiment of the present invention.

Hereinafter, various embodiments are described in detail with reference to the accompanying drawings.

The drawings are not necessarily drawn to scale, and in some instances, the proportions of at least some of the structures shown in the drawings may be exaggerated in order to clearly show characteristics of the embodiments. When a multi-layered structure having two or more layers is disclosed in the drawings or detailed description, the relative positional relationship or arrangement order of the layers as shown only reflects a specific embodiment, so the present invention is not limited thereto, and the relative positioning of the layers Relationships or arrangement order may vary. Further, the drawings or detailed descriptions of multi-layer structures may not reflect all of the layers present in a particular multi-layer structure (eg, there may be one or more additional layers between two layers shown). For example, where a first layer is on a second layer or on a substrate in a multilayer structure in a drawing or description, it is indicated that the first layer may be formed directly on the second layer or directly on the substrate. In addition, cases where one or more other layers are present between the first layer and the second layer or between the first layer and the substrate may be indicated.

1 is a diagram for explaining a neuromorphic device and an operating method thereof according to an embodiment of the present invention.

Referring to FIG. 1 , a neuromorphic device according to an embodiment of the present invention includes a plurality of presynaptic neurons (10), a plurality of postsynaptic neurons (20), and a plurality of presynaptic neurons ( 10) and a plurality of post-synaptic neurons 20 may include synapses 30 providing respective connections.

The neuromorphic device of this embodiment includes 4 pre-synaptic neurons 10, 4 post-synaptic neurons 20 and 16 synapses 30, but these numbers may be variously modified. The number of pre-synaptic neurons 10 is N (where N is a natural number greater than or equal to 2), and the number of post-synaptic neurons 20 is M (where M is a natural number greater than or equal to 2), which may be the same as or different from N. In the case of), N * M synapses 30 may be arranged in a matrix form. To this end, a wiring 12 connected to each of the plurality of pre-synaptic neurons 10 and extending in a first direction, for example, in a horizontal direction, and a plurality of post-synaptic neurons 20 connected to each of the wires 12 crossing the first direction Wiring lines 22 extending in two directions, for example, in the vertical direction, may be provided. Hereinafter, for convenience of description, the wiring 12 extending in the first direction will be referred to as a row line, and the wiring 22 extending in the second direction will be referred to as a column line. The plurality of synapses 30 may be disposed at each intersection of the row wiring 12 and the column wiring 22 to connect the corresponding row wiring 12 and the corresponding column wiring 22 to each other.

The pre-synaptic neuron 10 serves to generate a signal, for example, a signal corresponding to specific data and send it to the row wiring 12, and the post-synaptic neuron 20 sends a synaptic signal that has passed through the synaptic element 30 to the column wiring It can play a role of receiving and processing through (22). The row wiring 12 may correspond to an axon of the pre-synaptic neuron 10, and the column wiring 22 may correspond to a dendrite of the post-synaptic neuron 20. However, whether a neuron is a pre-synaptic neuron or a post-synaptic neuron can be determined by its relative relationship with other neurons. For example, when the pre-synaptic neuron 10 receives synaptic signals in relation to other neurons, it may function as a post-synaptic neuron. Similarly, when the post-synaptic neuron 20 sends signals in relation to other neurons, it can function as a pre-synaptic neuron. The pre-synaptic neuron 10 and the post-synaptic neuron 20 may be implemented with various circuits such as CMOS.

A connection between the pre-synaptic neuron 10 and the post-synaptic neuron 20 may be made through a synapse 30 . Here, the synapse 30 is an element whose electrical conductance or weight changes according to an electrical pulse applied to both ends, for example, voltage or current.

The synapse 30 may include, for example, a variable resistance element. A variable resistance element is an element capable of switching between different resistance states depending on a voltage or current applied to both ends, and is composed of various materials capable of having a plurality of resistance states, such as transition metal oxides and perovskites. It may have a single-layer structure or a multi-layer structure including phase change materials such as metal oxides, chalcogenide-based materials, ferroelectric materials, ferromagnetic materials, and the like. An operation in which the variable resistance element and/or synapse 30 changes from a high resistance state to a low resistance state may be referred to as a set operation, and an operation in which the variable resistance element and/or synapse 30 may change from a low resistance state to a high resistance state may be referred to as a reset operation. .

However, unlike the variable resistance element used in memory devices such as RRAM, PRAM, FRAM, and MRAM, the synapse 30 of the neuromorphic device does not have an abrupt change in resistance during the set operation and reset operation, and It can be implemented to have various characteristics that are distinguished from variable resistance elements in memories, such as exhibiting an analog behavior in which conductivity gradually changes according to the number of electrical pulses. This is because the characteristics required for the variable resistance element in the memory and the characteristics required for the synapse 30 in the neuromorphic device are different from each other. For reference, the variable resistance element used in the memory preferably maintains its own conductivity before a set operation or a reset operation is performed even when electrical pulses are repeatedly applied. This is to make the distinction between the low-resistance state and the high-resistance state clear to store different data. The characteristics of the synapse 30 suitable for a neuromorphic device will be described in more detail with reference to FIGS. 2A to 2D to be described later.

Meanwhile, the learning operation of the above neuromorphic device will be exemplarily described as follows. For convenience of description, the row wiring 12 is referred to as a first row wiring 12A, a second row wiring 12B, a third row wiring 12C, and a fourth row wiring 12D from above, and the column wiring 22 may be referred to as a first column wiring 22A, a second column wiring 22B, a third column wiring 22C, and a fourth column wiring 22D from the left.

In its initial state, all of the synapses 30 may be in a high resistance state. When at least some of the synapses 30 are in a low-resistance state, an initialization operation to make them into a high-resistance state may be additionally required. Each synapse 30 may have a predetermined threshold value. More specifically, when a voltage or current smaller than a predetermined threshold value is applied to both ends of each synapse 30, the conductivity of the synapse 30 does not change, and when a voltage or current greater than a predetermined threshold value is applied to the synapse 30 The conductance of the synapse 30 can vary.

In this state, in order to perform an operation of learning specific data to the specific column wiring 22, an input signal corresponding to specific data may be input to the row wiring 12. The input signal may appear as an application of an electrical pulse to each of the row wires 12 . As an example, when an input signal corresponding to data of '0011' is input to the row wire 12, an electrical voltage is applied to the row wire 12 corresponding to '0', for example, the first and second row wires 12A and 12B. An electrical pulse may be applied only to the row wires 12 corresponding to '1', for example, the third and fourth row wires 12C and 12D, without applying a pulse.

At this time, the column wiring 22 may be driven with an appropriate voltage or current for learning.

As an example, when the column wiring 22 to learn specific data is already determined, the synapse 30 located at the intersection of the column wiring 22 with the row wiring 12 corresponding to '1' performs a set operation may be driven so as to receive a voltage having a magnitude higher than or equal to a voltage required (hereinafter referred to as set voltage), and the remaining column wirings 22 may be driven so that the remaining synapses 30 receive a voltage smaller than the set voltage. For example, when the magnitude of the set voltage is Vset and the column wiring 22 to learn data of '0011' is determined as the third column wiring 22C, the third column wiring 22C and the third and fourth rows Magnitude of electrical pulses applied to the third and fourth row wires 12C and 12D so that the first and second synapses 30A and 30B located at the intersections with the wires 12C and 12D receive a voltage equal to or higher than Vset may be equal to or greater than Vset and the voltage applied to the third column wire 22C may be 0V. Accordingly, the first and second synapses 30A and 30B may be in a low resistance state. Conductivities of the first and second synapses 30A and 30B in the low resistance state may gradually increase as the number of electrical pulses increases. The remaining synapses 30 other than the first and second synapses 30A and 30B are applied to the remaining column wirings, that is, the first, second, and fourth column wirings 22A, 22B, and 22D so that a voltage smaller than Vset is applied. The applied voltage may have a value between 0V and Vset, for example, a value of 1/2Vset. Accordingly, the resistance state of the synapses 30 other than the first and second synapses 30A and 30B may not change.

When the row wiring 12 and the column wiring 22 are driven in the above manner, the synapses 30 receiving electrical pulses, for example, the third and fourth row wirings 12C and 12D and the third column wiring 22C As the conductivities of the first and second synapses 30A and 30B located at the intersection of the gradual increase, current flowing through them to the third column wire 22C may increase. The current flowing through the third column wiring 22C is measured, and when this current reaches a predetermined threshold current, the third column wiring 22C is a 'column wiring that has learned specific data', for example, data of '0011'. Column wiring can be

As another example, the column wires 22 to learn specific data may not be determined. In this case, while applying an electrical pulse corresponding to the specific data to the row wiring 12, the current flowing through each of the column wirings 22 is measured, and the column wiring 22 that reaches the predetermined threshold current first learns the specific data. Column wiring 22 may be.

According to the method described above, different data can be learned to different column wirings 22, respectively.

On the other hand, in the above learning process, only the set operation for changing the synapse 30 in the high resistance state to the low resistance state and the operation for increasing the conductivity have been described, but if necessary, the synapse 30 in the low resistance state A reset operation to change back to a high resistance state and an operation to reduce its conductivity may be required. For example, the aforementioned initialization operation is such. A polarity of a pulse applied during a set operation of the synapse 30 and an increase in conductivity may be opposite to a polarity of a pulse applied during a reset operation and a decrease in conductivity of the synapse 30 . An operation in which the conductivity of the synapse 30 increases may be referred to as a potentiation operation, and an operation in which the conductivity of the synapse 30 decreases may be referred to as a suppression operation.

On the other hand, the characteristics of the synapse 30 suitable for the above neuromorphic device will be described in more detail with reference to FIGS. 2A to 2D below.

2a to 2d are diagrams for explaining characteristics required for each synapse 30 of FIG. 1 .

Specifically, FIGS. 2A and 2B show the conductivity (G) of the synapse 30 according to the number of electrical pulses input to the synapse 30 . Figure 2c shows the weight change rate (ΔW) of the synapse according to the resistance (R) or conductivity (G) of the synapse (30). Figure 2d shows the weight change rate (ΔW) of the synapse 30 according to the magnitude of the voltage (V) applied to the synapse (30).

Referring to FIGS. 2A and 2B , when a voltage pulse of a first polarity having a predetermined threshold value or more, for example, a negative voltage pulse is repeatedly applied to the synapse 30 in a low resistance state, the synapse 30 Conductivity (G) may gradually increase. The direction in which the conductivity (G) of the synapse 30 increases may be referred to as the G+ direction or the potentiation direction.

When a voltage pulse of the second polarity having a magnitude greater than or equal to the reset voltage, for example, a positive voltage pulse is applied to the synapse 30, a reset operation in which the resistance state of the synapse 30 changes to a high resistance state may be performed.

For the synapse 30 in a high-resistance state, when a voltage pulse of the second polarity is repeatedly applied, the conductivity (G) of the synapse 30 may gradually decrease. A direction in which the conductivity (G) of the synapse 30 decreases may be referred to as a G- direction or a depression direction.

When a voltage pulse of the first polarity equal to or higher than the set voltage is applied to the synapse 30 again, a set operation in which the resistance state of the synapse 30 changes to a low resistance state may be performed.

At this time, even if the size and width of the pulse are constant, it may be preferable that the conductivity (G) of the synapse 30 is substantially symmetrical and the rate of change of the conductivity (G) is substantially constant in the reinforcing operation and the inhibition operation. In other words, it may be desirable for the conductance G of the synapse 30 to have linearity and symmetry in the reinforcing action and the inhibiting action. This is to prevent a rapid resistance change of the synapse 30 during the set operation and the reset operation. It is also possible to consider securing the linearity and symmetry of the synapse 30 as described above by varying the size and/or width of the pulse, but it is disadvantageous in terms of area or power because additional circuit implementation is required to generate various pulses. can do. Therefore, it is preferable that the amplitude and width of the pulse are constantly controlled during driving of the synapse 30 .

In the reinforcing and inhibiting actions, it is required that the conductance (G) of the synapse 30 has linearity and symmetry regardless of the case where the rate of change of weights is small (see ΔW1) or the rate of change of weights is large (see ΔW2). It can be. However, if the size or width of the pulse is not sufficient, the conductivity (G) of the synapse 30 may not change regardless of the number of pulses.

Referring to FIG. 2C, regardless of the current state of the synapse 30, that is, regardless of the current resistance (R) or current conductivity (G) of the synapse 30, the weight change rate (ΔW) of the synapse 30 may be preferably substantially constant.

Referring to FIG. 2D , the weight and/or conductivity of the synapse 30 may not be varied at a voltage below a predetermined threshold value, that is, V3. That is, the weight change rate (ΔW) of the synapse 30 may be zero. On the other hand, the weight change rate (ΔW) of the synapse 30 may increase at a voltage greater than a predetermined threshold value, for example, at a voltage greater than or equal to V4. At this time, the weight change rate (ΔW) of the synapse 30 may increase substantially in proportion to the magnitude of the voltage.

In summary, the synapse 30 of the neuromorphic device has a characteristic that the conductivity (G) increases or decreases substantially in proportion to the number of electrical pulses, regardless of the current state of the synapse 30, and during the reinforcement operation It is preferred that the conductance (G) and the conductance (G) during suppression operation are substantially symmetrical. Here, the change in conductivity (G) of the synapse 30 is preferably possible only at or above a predetermined threshold value. This is because the closer the characteristics of the synapse 30 are to this, the better the learning and recognition accuracy of the neuromorphic device and other operational characteristics can be improved.

In this embodiment, it is intended to implement a synapse that can satisfy the above characteristics as much as possible. Prior to the description of this embodiment, the synapse of the comparative example will be described first.

3A is a cross-sectional view for explaining the synapse of Comparative Example, and FIGS. 3B and 3C are views for explaining the characteristics of the synapse of FIG. 3A.

Referring to FIG. 3A , the synapse 100 of the comparative example includes a first electrode 110, a second electrode 140, and an oxygen retaining layer 120 interposed between the first electrode 110 and the second electrode 140. ), and a reactive metal layer 130 interposed between the oxygen retaining layer 120 and the second electrode 140 and capable of reacting with oxygen of the oxygen retaining layer 120 .

The first and second electrodes 110 and 140 are ends of the synapse 100 for applying voltage or current, and may be formed of various conductive materials such as metal and metal nitride. The first electrode 110 may be connected to any one of the row wiring 12 and the column wiring 22 of FIG. 1, and the second electrode 140 may be connected to the row wiring 12 and the column wiring 22 of FIG. By being connected to the other one of, the synapse 100 can be driven by an electrical pulse. At least one of the first and second electrodes 110 and 140 may be omitted. In this case, the row wiring 12 or the column wiring 22 replaces the first electrode 110 or the second electrode 140. can do.

The oxygen holding layer 120 is a layer containing oxygen, and may include oxides of various metals, such as oxides of transition metals such as Ti, Ni, Al, Nb, Hf, and V, and perovskite oxides such as PCMO and LCMO. can

The reactive metal layer 130 is a layer capable of forming an insulating oxide by reacting with oxygen ions, and may include a metal such as Al, Ti, Ta, Mo, or a nitride of the metal.

In the initial state, the synapse 100 may be in a relatively low resistance state. An initialization operation to make the synapse 100 into a high-resistance state may be required for the operation of the neuromorphic device described above.

When a voltage pulse of a predetermined polarity is applied to the synapse 100 in a low-resistance state through the first and second electrodes 110 and 140, oxygen ions in the oxygen holding layer 120 move toward the reactive metal layer 130, thereby increasing the reactive metal layer 130. An insulating oxide layer may be formed at an interface with the reactive metal layer 130 by reacting with the metal included in the metal layer 130 . As a result, the resistance state of the synapse 100 may be changed to a high resistance state. Since the thickness of the insulating oxide layer increases as the number of voltage pulses increases, the conductivity of the synapse 100 may gradually decrease.

Conversely, when a voltage pulse of opposite polarity is applied to the synapse 100 in a high-resistance state, oxygen ions in the oxygen holding layer 120 move to the opposite side of the reactive metal layer 130, so that the thickness of the pre-formed insulating oxide layer is thin. can lose As a result, the resistance state of the synapse 100 may be changed to a low resistance state. Since the thickness of the insulating oxide layer decreases as the number of voltage pulses increases, the conductivity of the synapse 100 may gradually increase.

In this way, since the thickness of the oxide layer gradually increases or decreases by the voltage pulse while the synapse 100 switches between the high resistance state and the low resistance state, the synapse 100 in the high resistance state and the low resistance state, respectively An analog behavior of a gradual change in the conductivity of β can be seen. However, it may be insufficient to satisfy the synaptic properties described in FIGS. 2a to 2d. This will be described with reference to FIGS. 3B and 3C.

Referring to FIG. 3B, when a voltage pulse of the first polarity is applied to the synapse 100 in a low resistance state, it can be seen that the conductivity (G) of the synapse 100 gradually increases as the number of voltage pulses increases. there is. However, it can be seen that the increase rate of the conductivity (G) is very large at the beginning of the set operation, which is changed to a low resistance state, and decreases as time passes. Therefore, there is a problem that the linearity of the synapse 100 is not satisfied.

In addition, when a voltage pulse of the second polarity having a magnitude greater than or equal to the reset voltage is applied to the synapse 100 in the low resistance state, a reset operation in which the resistance state of the synapse 100 changes to the high resistance state may be performed. As the number of voltage pulses applied to the synapse 100 in the high resistance state increases, the conductivity G of the synapse 100 may gradually decrease. However, it can be seen that a rapid decrease in conductivity (G) occurs during the reset operation. In addition, it can be seen that the rate of decrease of the conductivity (G) is very large at the beginning of the reset operation and decreases with time. The degree of decrease in conductivity G at the beginning of the reset operation may be much greater than the degree of increase in conductivity G at the beginning of the set operation. Therefore, there is a problem that the linearity and symmetry of the synapse 100 are not satisfied.

Referring to FIG. 3C , it can be seen that the weight change rate (ΔW) of the synapse 100 is not constant according to the current resistance (R) of the synapse 100 . In the G+ direction, when the current resistance (R) of the synapse 100 is relatively large, for example, when it has a value of R5 or R6, the weight change rate (ΔW) of the synapse 100 may increase. In other words, the conductivity change rate of the synapse 100 may be large at the beginning of the set operation when the resistance R is relatively large. Conversely, in the G- direction, when the current resistance (R) of the synapse 100 is relatively small, for example, when it has a value of R1, the weight change rate (ΔW) of the synapse 100 may increase. In other words, the conductivity change rate of the synapse 100 may be large at the beginning of the reset operation when the resistance R is relatively small. This shows that the linearity of the synapse 100 is not satisfied.

In addition, it can be seen that the weight change rate (ΔW) in the G- direction is greater than the weight change rate (ΔW) in the G+ direction at the beginning of the operation. That is, it shows that the symmetry of the synapse 100 is not satisfied.

The above problem occurs because the resistance change rate of the synapse 100 according to the number of pulses is large at the beginning of each set operation and reset operation, and the interface oxide layer is generated compared to the set operation in which the interface oxide layer disappears. Because the speed is much greater.

In this embodiment, it is intended to provide a synapse that can solve the problems of the comparative example.

4 is a cross-sectional view for explaining a synapse according to an embodiment of the present invention.

Referring to FIG. 4 , the synapse 200 according to an embodiment of the present invention is interposed between a first electrode 210, a second electrode 240, and a first electrode 210 and a second electrode 240. oxygen retaining layer 220, a reactive metal layer 230 interposed between the oxygen retaining layer 220 and the second electrode 240, and an oxygen diffusion interposed between the reactive metal layer 230 and the oxygen retaining layer 220. A stop layer 250 may be included.

The first and second electrodes 210 and 240 are ends of the synapse 200 for applying voltage or current, and may be formed of various conductive materials such as metal and metal nitride. The first electrode 210 may be connected to any one of the row wiring 12 and the column wiring 22 of FIG. 1 , and the second electrode 240 may be connected to the row wiring 12 and the column wiring 22 of FIG. 1 By being connected to the other one of, the synapse 200 can be driven by an electrical pulse. At least one of the first and second electrodes 210 and 240 may be omitted. In this case, the row wiring 12 or the column wiring 22 replaces the first electrode 210 or the second electrode 240. can do.

The oxygen retaining layer 220 may be a layer containing oxygen. For example, the oxygen holding layer 220 may include oxides of various metals, such as transition metal oxides such as Ti, Ni, Al, Nb, Hf, and V, and perovskite-based oxides such as PCMO and LCMO. In particular, in this embodiment, the oxygen retaining layer 220 may include a P-type material.

The reactive metal layer 230 is a layer capable of forming an insulating oxide by reacting with oxygen ions, and may include a metal such as Al, Ti, Ta, Mo, or a nitride of the metal.

The oxygen diffusion barrier layer 250 may serve to block the movement of oxygen ions from the oxygen retention layer 220 to the reactive metal layer 230 between the oxygen retention layer 220 and the reactive metal layer 230 . The oxygen diffusion barrier layer 250 may be formed of various insulating materials or semiconductor materials such as oxide, nitride, or a combination thereof. In particular, in this embodiment, the oxygen diffusion barrier layer 250 may include an N-type material. The oxygen diffusion barrier layer 250 hinders the movement of oxygen ions on the premise that it does not completely block the movement of oxygen ions, so that the insulating oxide layer is formed on the reactive metal layer 230 at the interface with the oxygen diffusion barrier layer 250. can reduce the rate of formation of The oxygen diffusion barrier layer 250 may have a thin thickness that does not completely block the movement of oxygen ions, for example, less than 10 nm.

In this embodiment, since the oxygen retention layer 220 includes a P-type material and the oxygen diffusion barrier layer 250 in contact with the oxygen retention layer 220 includes an N-type material, the oxygen retention layer 220 and the oxygen diffusion barrier Stop layer 250 may form a P-N junction.

A method of operating the synapse 200 as described above will be described with reference to FIGS. 5A to 6B below.

5A is a cross-sectional view illustrating a reset operation of the synapse of FIG. 4 , and FIG. 5B is a cross-sectional view illustrating a set operation of the synapse of FIG. 4 . Before the synapse 200 of FIG. 4 starts operating, that is, in the initial state, since the insulating oxide layer is not formed between the oxygen retaining layer 220 and the reactive metal layer 230, the synapse 200 has low resistance. may be in a state

Referring to FIG. 5A, when a voltage pulse of a predetermined polarity having a magnitude greater than or equal to the reset voltage is applied to the synapse 200 in a low resistance state through the first and second electrodes 210 and 240, the Oxygen ions may move toward the reactive metal layer 230 via the oxygen diffusion barrier layer 250 . As a result, since the insulating oxide layer 260 is formed in the reactive metal layer 230 at the interface with the oxygen diffusion barrier layer 250, a reset operation in which the resistance state of the synapse 200 is changed to a high resistance state can be performed. there is. Since the thickness of the insulating oxide layer 260 increases as the number of voltage pulses increases, the conductivity of the synapse 200 may gradually decrease. A resistance component formed by the insulating oxide layer 260 is marked with a resistance symbol on the right side of the synapse 200 .

At this time, when the voltages applied to the first electrode 210 and the second electrode 240 of the synapse 200 are referred to as the first voltage V1 and the second voltage V2, respectively, the second voltage for the reset operation. (V2) may be a relatively positive voltage compared to the first voltage (V1). For example, the second voltage V2 may be a positive voltage having a magnitude greater than or equal to the reset voltage, and the first voltage V1 may be a ground voltage. On the other hand, when such a voltage is applied, a reverse voltage (see the arrow on the right side of the synapse 200) is applied to the P-N junction (see the diode symbol on the right side of the synapse 200) formed by the oxygen diffusion barrier layer 250 and the oxygen retaining layer 220. this may be authorized. Effects in this case will be described in more detail with reference to FIGS. 6A and 6B to be described later.

Referring to FIG. 5B , when a voltage pulse having a magnitude equal to or higher than the set voltage and having a polarity opposite to that applied during a reset operation is applied to the synapse 200 in a high resistance state, oxygen ions are released from the reactive metal layer 230. It can move towards the retention layer 220 . As a result, the thickness of the pre-formed insulating oxide layer 260 in the reactive metal layer 230 is reduced or the insulating oxide layer 260 disappears, resulting in a set operation in which the resistance state of the synapse 200 is changed to a low resistance state. can be performed Since the thickness of the insulating oxide layer 260 decreases as the number of voltage pulses increases, the conductivity of the synapse 200 may gradually increase. When the insulating oxide layer 260 disappears, a resistance component caused by the insulating oxide layer 260 may disappear.

At this time, when the voltages applied to the first electrode 210 and the second electrode 240 of the synapse 200 are referred to as the third voltage V3 and the fourth voltage V4, respectively, the fourth voltage for the set operation (V4) may be a relatively negative voltage compared to the third voltage (V3). For example, the fourth voltage V4 may be a negative voltage having a level greater than or equal to the set voltage, and the third voltage V3 may be a ground voltage. Accordingly, a forward voltage (refer to the arrow on the right side of the synapse 200) may be applied to the P-N junction (see the diode symbol on the right side of the synapse 200) formed by the oxygen diffusion barrier layer 250 and the oxygen retaining layer 220. there is. Effects in this case will be described in more detail with reference to FIGS. 6A and 6B to be described later.

In this way, since the thickness of the insulating oxide layer 260 is varied by the voltage pulse while the synapse 200 switches between the high resistance state and the low resistance state, the synapse 200 in the high resistance state and the low resistance state, respectively An analog behavior of a gradual change in the conductivity of β can be seen. In particular, since the rate of formation of the insulating oxide layer 260 is reduced by the oxygen diffusion barrier layer 250, a sudden change in resistance at the initial stage of the reset operation can be prevented, and the overall speed of the reset operation can be reduced. As a result, a phenomenon in which the conductivity of the synapse 200 rapidly changes during the reset operation compared to the set operation is prevented, and thus the symmetry of the synapse 200 can be improved.

6A is a cross-sectional view illustrating a read operation when the synapse of FIG. 4 is in a high-resistance state, and FIG. 6B is a cross-sectional view illustrating a read operation when the synapse of FIG. 4 is in a low-resistance state.

Referring to FIG. 6A , first and second electrodes ( A read voltage pulse may be applied through 210 and 240). A magnitude of the read voltage pulse may be smaller than that of the reset voltage pulse, and a polarity thereof may be substantially the same as that of the reset voltage pulse. This is to allow a reverse voltage to be applied to the P-N junction formed by the oxygen retaining layer 220 and the oxygen diffusion barrier layer 250 . In other words, when the voltages applied to the first electrode 210 and the second electrode 240 of the synapse 200 are the fifth voltage V5 and the sixth voltage V6, respectively, the sixth voltage V6 may be a relatively positive voltage compared to the fifth voltage V5. For example, the sixth voltage V6 may be a predetermined positive voltage smaller than the reset voltage, and the fifth voltage V5 may be a ground voltage.

In this case, as described above, a reverse voltage may be applied to the P-N junction formed by the oxygen diffusion barrier layer 250 and the oxygen retaining layer 220 . Accordingly, the resistance value of the synapse 200 in the high-resistance state may further increase overall. Accordingly, the resistance change rate of the synapse 200 according to the number of pulses may decrease. As a result, a phenomenon in which the resistance value of the synapse 200 rapidly increases at the beginning of the reset operation can be further prevented, and the linearity of the synapse 200 can be improved.

Referring to FIG. 6B, the first and second electrodes of the synapse 200 in a low resistance state, that is, when the insulating oxide layer 260 does not exist at the interface between the reactive metal layer 230 and the oxygen diffusion barrier layer 250. A read voltage pulse may be applied through (210, 240). The magnitude and polarity of the read voltage pulse may be constant regardless of the resistance state of the synapse 200 . That is, the aforementioned fifth voltage V5 and sixth voltage V6 may be respectively applied to the first electrode 210 and the second electrode 240 of the synapse 200 .

In this case, unlike the set operation, a reverse voltage (refer to the arrow on the right of the synapse 200) may be applied to the P-N junction formed by the oxygen diffusion barrier layer 250 and the oxygen retention layer 220. Accordingly, the resistance value of the synapse 200 in the low-resistance state may also increase overall. Accordingly, the resistance change rate of the synapse 200 according to the number of pulses may decrease. As a result, a phenomenon in which the resistance value of the synapse 200 rapidly decreases at the beginning of the set operation can be further prevented, and the linearity of the synapse 200 can be improved.

In summary, since a reverse voltage is commonly applied to the P-N junction of the synapse 200 during a read operation regardless of the resistance state of the synapse 200, the resistance value of the synapse 200 may increase overall. Accordingly, the resistance change rate of the synapse 200 according to the number of pulses decreases, and thus the linearity of the synapse 200 can be further improved.

The neuromorphic device of the above-described embodiments may be used in various devices or systems. This will be exemplarily described with reference to FIG. 7 .

7 is an example of a pattern recognition system according to an embodiment of the present invention. The pattern recognition system of this embodiment may be a system for recognizing various types of patterns, such as a speech recognition system and an imaging recognition system. The pattern recognition system of this embodiment can be implemented with the neuromorphic device of the above-described embodiments.

Referring to FIG. 7 , the pattern recognition system 400 of this embodiment includes a central processing unit (CPU) 410, a memory device 420, a communication control unit 430, a network 440, a pattern output unit 450, It may include a pattern input device 460, an analog-to-digital converter (ADC, 470), a neuromorphic device 480, a bus line 490, and the like.

The central processing unit 410 generates and transmits various signals for learning of the neuromorphic device 480, and performs various processes for recognizing patterns such as voice and video according to output from the neuromorphic device 480. and functions. The central processing unit 410 supplies a bus line 490 to a memory device 420, a communication control device 430, a pattern output device 450, an analog-to-digital converter 470, and a neuromorphic device 480. can be connected through

The memory device 420 may store various information required to be stored in the pattern recognition system 400, and may include different types of memories for this purpose. For example, the memory device 420 may include a ROM (ROM) 422, a RAM (RAM) 424, and the like. The ROM 422 may perform a function of storing various programs or data used in the central processing unit 410 to process and control learning, pattern recognition, and the like of the neuromorphic device 480 . The ROM 424 may download and store programs or data of the ROM 422 or may store data such as audio and video converted and analyzed by the analog-to-digital converter 470 .

The communication control device 430 may exchange data such as recognized voice and video with other communication control devices through the network 440 .

The pattern output device 450 may output data such as recognized voice and video in various ways. For example, the pattern recognition device 450 may include a printer, a display unit, and the like, and may display voice as a waveform or display an image.

The pattern input device 460 is a part that receives an analog type of voice, image, and the like, and may include a microphone, a camera, and the like.

The analog-to-digital converter 470 may convert analog data input from the pattern input device 460 into digital data and may analyze the digital data.

The neuromorphic device 480 may perform learning and recognition using the data output from the analog-to-digital converter 470 and output data corresponding to the recognized pattern. The neuromorphic device 480 may include one or more of the neuromorphic devices and synapses of the above-described embodiments. For example, the neuromorphic device 480 may include a plurality of synapses, each of which includes a first electrode; a second electrode spaced apart from the first electrode; an oxygen retaining layer interposed between the first electrode and the second electrode and containing a P-type material; a reactive metal layer interposed between the oxygen retaining layer and the second electrode and capable of reacting with oxygen ions of the oxygen retaining layer; and an oxygen diffusion barrier layer interposed between the reactive metal layer and the oxygen retaining layer to prevent the movement of oxygen ions from the oxygen retaining layer to the reactive metal layer, and including an N-type material, The oxygen diffusion barrier layer can form a P-N junction. Through this, symmetry and linearity of the synapse can be secured. Accordingly, operating characteristics of the neuromorphic device 480 may be improved, and accordingly, operating characteristics of the pattern recognition system 400 may be improved.

In addition, the pattern recognition system 400 may further include other components required to properly perform its functions. For example, as an input unit for inputting various parameters or setting conditions for driving the pattern recognition system 400, a keyboard, a mouse, and the like may be further included.

Although various embodiments for the problem to be solved have been described above, it is clear that a person skilled in the art can make various changes and modifications within the scope of the technical idea of the present invention. .

200: synapse 210: first electrode
220: oxygen holding layer 230: reactive metal layer
240: second electrode 250: oxygen diffusion barrier layer

Claims (22)

a first electrode;
a second electrode spaced apart from the first electrode;
an oxygen retaining layer interposed between the first electrode and the second electrode and containing a P-type material;
a reactive metal layer interposed between the oxygen retaining layer and the second electrode and capable of reacting with oxygen ions of the oxygen retaining layer; and
An oxygen diffusion barrier layer interposed between the reactive metal layer and the oxygen retaining layer to prevent the movement of oxygen ions from the oxygen retaining layer to the reactive metal layer and containing an N-type material;
The oxygen retention layer and the oxygen diffusion barrier layer form a PN junction
Synapse.
◈Claim 2 was abandoned when the registration fee was paid.◈ According to claim 1,
When a reset voltage of a first polarity is applied through the first electrode and the second electrode, a reset operation is performed in which an insulating oxide layer is formed on the reactive metal layer or its thickness is increased at the interface with the oxygen diffusion barrier layer. become,
When a set voltage of a second polarity different from the first polarity is applied through the first electrode and the second electrode, a set operation in which the insulating oxide layer disappears or its thickness is reduced is performed
Synapse.
◈Claim 3 was abandoned when the registration fee was paid.◈ According to claim 2,
During the reset operation, a reverse voltage is applied to the PN junction;
During the set operation, a forward voltage is applied to the PN junction
Synapse.
◈Claim 4 was abandoned when the registration fee was paid.◈ According to claim 2,
A read operation is performed by applying a read voltage of the first polarity while having a magnitude smaller than the reset voltage through the first electrode and the second electrode.
Synapse.
◈Claim 5 was abandoned when the registration fee was paid.◈ According to claim 4,
During the read operation, a reverse voltage is applied to the PN junction
Synapse.
◈Claim 6 was abandoned when the registration fee was paid.◈ According to claim 2,
The conductivity decreases as the thickness of the insulating oxide layer increases, and the conductivity increases as the thickness of the insulating oxide layer decreases.
Synapse.
◈Claim 7 was abandoned when the registration fee was paid.◈ According to claim 2,
During the reset operation, the thickness of the insulating oxide layer increases as the number of pulses of the reset voltage increases,
During the set operation, the thickness of the insulating oxide layer decreases as the number of pulses of the set voltage increases.
Synapse.
◈Claim 8 was abandoned when the registration fee was paid.◈ According to claim 7,
During the reset operation, the pulse of the reset voltage has a constant width and a constant size,
During the set operation, the pulse of the set voltage has a constant width and a constant size.
Synapse.
◈Claim 9 was abandoned when the registration fee was paid.◈ According to claim 1,
The oxygen diffusion barrier layer,
Having a thickness that does not completely block the movement of the oxygen ions
Synapse.
◈Claim 10 was abandoned when the registration fee was paid.◈ According to claim 1,
The oxygen diffusion barrier layer,
Including an insulating material, a semiconductor material, or a combination thereof
Synapse.
◈Claim 11 was abandoned when the registration fee was paid.◈ According to claim 1,
When a suppression operation in which conductivity decreases as the number of electrical pulses of the first polarity applied through the first and second electrodes increases, as the number of electrical pulses of the second polarity different from the first polarity increases, A reinforcing operation in which the conductivity increases is performed.
Synapse.
delete delete ◈Claim 14 was abandoned when the registration fee was paid.◈ According to claim 11,
Each of the electric pulse of the first polarity and the electric pulse of the second polarity has a constant width and a constant size.
Synapse.
◈Claim 15 was abandoned when the registration fee was paid.◈ According to claim 11,
When at least one of the width and size of each of the electrical pulse of the first polarity and the electrical pulse of the second polarity is less than a predetermined threshold value, the conductivity does not change
Synapse.
first neuron;
second neuron;
a first wire connected to the first neuron and extending in a first direction;
a second wire connected to the second neuron and extending in a second direction to cross the first wire; and
A synapse positioned at an intersection between the first wiring and the second wiring between the first wiring and the second wiring;
The synapse,
an oxygen retaining layer comprising a P-type material;
a reactive metal layer interposed between the oxygen retaining layer and the second wire and capable of reacting with oxygen ions of the oxygen retaining layer; and
An oxygen diffusion barrier layer interposed between the reactive metal layer and the oxygen retaining layer to prevent the movement of oxygen ions from the oxygen retaining layer to the reactive metal layer and containing an N-type material;
The oxygen retention layer and the oxygen diffusion barrier layer form a PN junction
neuromorphic device.
◈Claim 17 was abandoned when the registration fee was paid.◈ According to claim 16,
When a reset voltage of a first polarity is applied to the synapse through the first wiring and the second wiring, a reset in which an insulating oxide layer is formed or its thickness increases on the reactive metal layer at the interface with the oxygen diffusion barrier layer. action is performed,
When a set voltage of a second polarity different from the first polarity is applied to the synapse through the first wire and the second wire, a set operation in which the insulating oxide layer disappears or its thickness is reduced is performed
neuromorphic device.
◈Claim 18 was abandoned when the registration fee was paid.◈ According to claim 17,
During the reset operation, a reverse voltage is applied to the PN junction;
During the set operation, a forward voltage is applied to the PN junction
neuromorphic device.
◈Claim 19 was abandoned when the registration fee was paid.◈ According to claim 17,
A read operation is performed by applying a read voltage of the first polarity equal to the reset voltage and having a magnitude smaller than the reset voltage to the synapse through the first wiring and the second wiring
neuromorphic device.
◈Claim 20 was abandoned when the registration fee was paid.◈ According to claim 19,
During the read operation, a reverse voltage is applied to the PN junction
neuromorphic device.
◈Claim 21 was abandoned when the registration fee was paid.◈ According to claim 17,
During the reset operation, as the number of pulses of the reset voltage increases, the thickness of the insulating oxide layer increases,
During the set operation, as the number of pulses of the set voltage increases, the thickness of the insulating oxide layer decreases.
neuromorphic device.
◈Claim 22 was abandoned when the registration fee was paid.◈ According to claim 21,
During the reset operation, the pulse of the reset voltage has a constant width and a constant size,
During the set operation, the pulse of the set voltage has a constant width and a constant size.
neuromorphic device.

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