A synapse and a neuromorphic device including the same are provided. The synapse includes: a first electrode; a second electrode spaced apart from the first electrode; an oxygen-containing layer disposed between the first electrode and the second electrode; a reactive metal layer disposed between the oxygen-containing layer and the second electrode and capable of reacting with oxygen ions from the oxygen-containing layer; and an oxygen diffusion-retarding layer provided between the oxygen-containing layer and the reactive metal layer, the oxygen diffusion-retarding layer hindering movement of oxygen ions from the oxygen-containing layer to the reactive metal layer.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A synapse comprising: a first electrode; a second electrode spaced apart from the first electrode; an oxygen-containing layer disposed between the first electrode and the second electrode; a reactive metal layer disposed between the oxygen-containing layer and the second electrode and capable of reacting with oxygen ions from the oxygen-containing layer; and an oxygen diffusion-retarding layer provided between the oxygen-containing layer and the reactive metal layer, the oxygen diffusion-retarding layer hindering movement of oxygen ions from the oxygen-containing layer to the reactive metal layer. 2. The synapse of claim 1, wherein electrical conductivity of the synapse changes depending on a thickness of a dielectric layer generated by a reaction between the oxygen-containing layer and the reactive metal layer. 3. The synapse of claim 1, wherein a thickness of a dielectric layer generated by a reaction between the oxygen-containing layer and the reactive metal layer increases with an increase in a number of electrical pulses having a first polarity, which are applied through the first and second electrodes, and the thickness of the dielectric layer decreases with an increase in a number of electrical pulses having a second polarity opposite to the first polarity, which are applied through the first and second electrodes. 4. The synapse of claim 3, wherein the electrical pulses having the first polarity and the electrical pulses having the second polarity have a constant width or constant magnitude, or both. 5. The synapse of claim 1, wherein the oxygen diffusion-retarding layer has a thickness that does not completely block the movement of the oxygen ions. 6. The synapse of claim 1, wherein the oxygen diffusion-retarding layer comprises a dielectric material or a semiconductor material. 7. The synapse of claim 1, further comprising a resistance layer located between the first electrode and the oxygen-containing layer and/or between the second electrode and the reactive metal layer, the resistance layer increasing a resistance value of the synapse. 8. The synapse of claim 1, wherein a potentiation operation is performed so that electrical conductivity of the synapse progressively increases with an increase in a number of electrical pulses having a second polarity, which are applied through the first and second electrodes, and a depression operation is performed so that the electrical conductivity of the synapse progressively decreases with an increase in a number of electrical pulses having a first polarity opposite to the second polarity, which are applied through the first and second electrodes. 9. The synapse of claim 8, wherein the electrical conductivity of the synapse in the potentiation operation is substantially symmetric with the electrical conductivity of the synapse in the depression operation. 10. The synapse of claim 8, wherein a rate of change in the electrical conductivity of the synapse in each of the potentiation operation and the depression operation is substantially constant. 11. The synapse of claim 8, wherein the electrical pulses having the first polarity and the electrical pulses having the second polarity have a constant width or a constant magnitude, or both. 12. The synapse of claim 8, wherein the electrical conductivity of the synapse does not change if at least one of width and magnitude of each of the electrical pulses having the first polarity and the electrical pulses having the second polarity is less than a certain critical value. 13. A neuromorphic device comprising: a first neuron; a second neuron; a first line connected to the first neuron and extending in a first direction; a second line connected to the second neuron and extending in a second direction intersecting with the first line; and a synapse disposed between the first line and the second line and located at an intersection between the first line and the second line, wherein the synapse comprises: an oxygen-containing layer; a reactive metal layer disposed between the oxygen-containing layer and the second line and capable of reacting with oxygen ions from the oxygen-containing layer; and an oxygen diffusion-retarding layer provided between the oxygen-containing layer and the reactive metal layer, the oxygen diffusion-retarding layer hindering movement of oxygen ions from the oxygen-containing layer to the reactive metal layer. 14. The neuromorphic device of claim 13, wherein the first neuron is configured to derive the first line by selectively providing electrical pulses having a first polarity and electrical pulses having a second polarity opposite to the first polarity; a thickness of a dielectric layer generated by a reaction between the oxygen-containing layer and the reactive metal layer increases with an increase in the number of the electrical pulses having the first polarity, the electrical conductivity of the synapse decreasing as the thickness of the dielectric layer increases; and the thickness of the dielectric layer decreases with an increase in the number of the electrical pulses having the second polarity, the electrical conductivity of the synapse increasing as the thickness of the dielectric layer decreases. 15. The neuromorphic device of claim 13, wherein the synapse further comprises a resistance layer located between the first line and the oxygen-containing layer and/or between the second line and the reactive metal layer, the resistance layer increasing a resistance value of the synapse. 16. A synapse comprising: first and second electrodes configured to receive electrical pulses; and a variable resistance material layer interposed between the first electrode and the second electrode, wherein the variable resistance material layer includes a plurality of layers through which a potentiation operation and a depression operation are performed, wherein the potentiation operation is performed so that electrical conductivity of the synapse progressively increases with an increase in a number of electrical pulses having a second polarity, which are applied through the first and second electrodes, and wherein the depression operation is performed so that the electrical conductivity of the synapse progressively decreases with an increase in a number of electrical pulses having a first polarity opposite to the second polarity, which are applied through the first and second electrodes. 17. The synapse of claim 16, wherein the electrical conductivity of the synapse in the potentiation operation is substantially symmetric with the electrical conductivity of the synapse in the depression operation. 18. The synapse of claim 16, wherein a rate of change in the electrical conductivity of the synapse in each of the potentiation operation and the depression operation is substantially constant. 19. The synapse of claim 16, wherein the first-polarity electrical pulses and the second-polarity electrical pulses have a constant width or constant magnitude, or both. 20. The synapse of claim 16, wherein the electrical conductivity of the synapse does not change if at least one of the width and magnitude of each of the first-polarity electrical pulses and the second-polarity electrical pulses is less than a certain critical value.