Patent Publication Number: US-11380844-B2

Title: Semiconductor device including variable resistance element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application a divisional application of a U.S. patent application Ser. No. 16/868,429, filed on May 6, 2020, now U.S. Pat. No. 11,056,648, which claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0165406 filed on Dec. 12, 2019, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     Exemplary embodiments of the present disclosure relate to a variable resistance element and a semiconductor device including the same. 
     2. Discussion of the Related Art 
     With electronic devices trending toward miniaturization, low power consumption, high performance, diversification, and so on, technology capable of efficiently processing a large amount of information is in demand. In particular, there is a growing interest in neuromorphic technology for mimicking the human nervous system in electronic devices. The human nervous system contains hundreds of billions of neurons and synapses, which are connections between neurons. Neuromorphic technology is intended to realize neuromorphic devices by designing neuron circuits and synaptic circuits that correspond to biological neurons and synapses. The neuromorphic devices may be utilized in various applications including data classification, pattern recognition, and the like. 
     SUMMARY 
     Various embodiments are directed to a variable resistance element having a characteristic suitable for use as a synapse in a neuromorphic device, and a semiconductor device including the same. 
     In an embodiment, a semiconductor device includes at least one variable resistance element, the variable resistance element including: an ion-receiving layer having a top, a bottom and a sidewall connecting the top to the bottom; an ion supply layer having an inner sidewall connected to at least a portion of the sidewall of the ion-receiving layer; a gate pattern connected to an outer sidewall of the ion supply layer; and a source pattern connected to one of the top or bottom of the ion-receiving layer, and a drain pattern connected to the other one of the top or bottom of the ion-receiving layer, wherein a resistance of the ion-receiving layer varies depending on an amount of ions supplied from the ion supply layer based on a voltage applied to the gate pattern. 
     In another embodiment, a semiconductor device includes at least one variable resistance element, the variable resistance element including: an ion supply layer having a top, a bottom and a sidewall connecting the top to the bottom; an ion-receiving layer having an inner sidewall connected to at least a portion of the sidewall of the ion supply layer; a gate pattern connected to an outer sidewall of the ion-receiving layer; and a source pattern connected to one of the top or bottom of the ion supply layer, and a drain pattern connected to the other one or the top or bottom of the ion supply layer, wherein a resistance of the ion supply layer is varies depending on an amount of ions supplied from the ion supply layer to the ion-receiving layer in response to a voltage applied to the gate pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a conductivity of a synapse depending on the number of electrical pulses which are input to the synapse of a neuromorphic device. 
         FIGS. 2A and 2B  are a sectional view and plan view illustrating a variable resistance element according to an embodiment of the present disclosure. 
         FIG. 3  is a view illustrating a method of operating the variable resistance element illustrated in  FIGS. 2A and 2B . 
         FIGS. 4A and 4B  are a plan view and sectional view illustrating a semiconductor device according to an embodiment of the present disclosure. 
         FIG. 5  is a plan view illustrating a semiconductor device according to another embodiment of the present disclosure. 
         FIG. 6A  is a sectional view illustrating a variable resistance element according to another embodiment of the present disclosure. 
         FIG. 6B  is a sectional view illustrating a variable resistance element according to still another embodiment of the present disclosure. 
         FIG. 7  is a sectional view illustrating a variable resistance element according to yet another embodiment of the present disclosure. 
         FIG. 8  is a view illustrating a method of operating the variable resistance element of  FIG. 7 . 
         FIG. 9  is a sectional view illustrating a variable resistance element according to still yet another embodiment of the present disclosure. 
         FIG. 10  illustrates an example of a pattern recognition system according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described below in detail with reference to the accompanying drawings. 
     The drawings may not be necessarily to scale and in some instances, proportions of at least some of structures in the drawings may have been exaggerated in order to clearly illustrate certain features of the described embodiments. When a multilayer structure is disclosed in a drawing or the detailed description, the relative positioning relationship of such layers or the sequence of arranging the layers as shown reflects a particular implementation for the described or illustrated example, and thus the present disclosure is not limited thereto and the relative positioning relationship or sequence of arranging the layers may be changed. In addition, a described or illustrated example of a multi-layer structure may not reflect all layers present in the particular multilayer structure (e.g., one or more additional layers may be present between two illustrated layers). For example, when a first layer in a described or illustrated multi-layer structure is referred to as being “on” or “over” a second layer or “on” or “over” a substrate, it may not only represent a structure where the first layer may be directly formed on the second layer or the substrate but also represent a structure where one or more other intermediate layers may exist between the first layer and the second layer or between the first layer and the substrate. 
     Embodiments of the present disclosure are intended to provide a variable resistance element having a characteristic suitable for use as a synapse in a neuromorphic device. However, it is to be understood that variable resistance elements according to embodiments of the present disclosure may be used not only in neuromorphic devices, but also in various semiconductor devices such as memory devices. Before describing variable resistance elements according to embodiments of the present disclosure, characteristics of a device suitable for use as a synapse in a neuromorphic device will be described. 
     In general, a variable resistance element that is used as a memory element in a memory device may be able to switch between a high-resistance state and a low-resistance state through a set operation and a reset operation. The variable resistance element may preferably have a low-resistance state and a high-resistance state, which are clearly distinguished from each other due to the abrupt resistance change that occurs in the set operation and the reset operation. The variable resistance element may maintain its own resistance state until the set operation and the reset operation are performed, even if electrical pulses are repeatedly applied to the element. The variable resistance element may store different data using these characteristics. 
     In contrast, a variable resistance element that is used as a synapse in a neuromorphic device preferably does not undergo an abrupt resistance change between the set operation and the reset operation, but instead exhibits analog behavior in which conductivity and/or electrical resistance gradually changes depending on the number of input electrical pulses. This analog behavior improves various operating characteristics of the neuromorphic device, such as increasing the accuracy of learning and recognition. Hereinafter, a more detailed description will be made with reference to  FIG. 1 . 
       FIG. 1  shows a conductivity of a synapse depending on the number of electrical pulses which are input to the synapse of a neuromorphic device. 
     Referring to  FIG. 1 , when first-polarity voltage pulses, for example, negative voltage pulses that have a voltage equal to or higher than a certain critical value, are repeatedly applied to a synapse that is in a low-resistance state, the electrical conductivity (G) of the synapse may gradually increase. A direction in which the electrical conductivity (G) of the synapse increases may be referred to as a G+ direction or a potentiation direction. 
     When second-polarity voltage pulses, for example, positive voltage pulses that have a voltage equal to or higher than a reset voltage, are applied to this synapse, a reset operation may be performed in which the resistance state of the synapse changes to a high-resistance state. 
     When the second-polarity voltage pulses are repeatedly applied to the synapse that is in the high-resistance state, the electrical conductivity (G) of the synapse may gradually decrease. A direction in which the electrical conductivity (G) of the synapse decreases may be referred to as a G− direction or a depression direction. 
     When first-polarity voltage pulses having a voltage equal to or higher than a set voltage are applied again to the synapse, the set operation may be performed and the resistance state of the synapse changes to the low-resistance state. 
     It may be preferable that the rate of change of electrical conductivity (G) of the synapse is substantially constant in the potentiation operation and the depression operation, and that the synapse exhibits substantially symmetrical electrical conductivity (G) characteristics around the set or reset points as illustrated in  FIG. 1 . 
     In summary, it may be preferable that the electrical conductivity (G) of the synapse is variable gradually, that is, with three or more multiple levels, in comparison to variable resistance elements that abruptly switch between high and low resistance states. The electrical conductivity (G) of the synapse in the potentiation operation and the depression operation may preferably have linearity and symmetry. 
     Hereinafter, a variable resistance element having a structure suitable for use as a synapse having the above-described characteristics, and a method of operating the variable resistance element, will be described with reference to  FIGS. 2A, 2B and 3 . 
       FIGS. 2A and 2B  are a sectional view and plan view illustrating a variable resistance element according to an embodiment of the present disclosure.  FIG. 2B  is a plan view taken along line H 1 -H 1 ′ of  FIG. 2A . 
     Referring to  FIGS. 2A and 2B , a variable resistance element according to an embodiment may include: a pillar-shaped ion-receiving layer  120  extending in a vertical direction; an ion supply layer  130  surrounding a sidewall of the ion-receiving layer  120 ; a gate pattern  140  surrounding a sidewall of the ion supply layer  130 ; a source pattern  110  connected to a bottom of the ion-receiving layer  120 ; and a drain pattern  150  connected to a top of the ion-receiving layer  120 . 
     The ion-receiving layer  120  may include a material that may enter an oxygen-deficient state to form oxygen vacancies when receiving cations, particularly metal cations, from the ion supply layer  130 . For example, the ion-receiving layer  120  may include at least one of electrolyte materials, electro-chromic materials, lithium (Li)-based oxides, transition metal oxides such as LiPON, LiCoO 2 , LiFePO 4 , LiMn 2 O 4  and M 2 O x , perovskite-like materials such as WO 3 , MoO 3  and SrTiO 3 , and so on. The oxygen vacancies act as donor defects. Thus, as the amount of the oxygen vacancies increases, the electrical conductivity of the ion-receiving layer  120  may increase, and as the amount of the oxygen vacancies decreases, the electrical conductivity of the ion-receiving layer  120  may decrease. That is, the resistance of the ion-receiving layer  120  may be variable depending on the amount of the oxygen vacancies in the ion-receiving layer  120 .
     The ion supply layer  130  may include a material that supplies cations, particularly metal cations, to the ion-receiving layer  120 . For example, the ion supply layer  130  may include at least one of Li-based oxides, transition metal oxides such as LiPON, LiCoO 2 , LiFePO 4 , LiMn 2 O 4  and M 2 O x , perovskite-like materials such as WO 3 , MoO 3  and SrTiO 3 , and so on. In particular, the ion supply layer  130  may be formed of a material different from that of the ion-receiving layer  120 , and may include a material having a greater metal ion content than that of the ion-receiving layer  120 . In an embodiment, the ion supply layer  130  may have a shape that surrounds the outer sidewall of the ion-receiving layer  120 . However, this present disclosure is not limited thereto, and the shape of the ion supply layer  130  may be variously modified such that the ion supply layer  130  is in contact with at least a portion of the sidewall of the ion-receiving layer  120  and provides a smooth or uninterrupted supply of ions to the ion-receiving layer  120 .   

     The gate pattern  140  may function to control ion movement from the ion supply layer  130  to the ion-receiving layer  120  in response to certain received voltages. The gate pattern  140  may include various electrically conductive materials, such as metals, metal nitrides, or combinations thereof. In an embodiment, the gate pattern  140  may have a shape surrounding the outer sidewall of the ion supply layer  130 ; the inner sidewall of the ion supply layer  130  may mean a sidewall coming in contact with the sidewall of the ion-receiving layer  120 , and the outer sidewall of the ion supply layer  130  may mean a sidewall opposite the inner sidewall. However, the present disclosure is not limited thereto, and in other embodiments the shape of the gate pattern  140  may be variously modified so that the gate pattern  140  is in contact with at least a portion of the outer sidewall of the ion supply layer  130  and the gate pattern  140  controls ion movement from the ion supply layer  130  to the ion-receiving layer  120  to allow smooth transitions between a plurality of resistance states. 
     The source pattern  110  and the drain pattern  150  are connected to the bottom and top of the ion-receiving layer  120 , respectively, and a change in the resistance of the ion-receiving layer  120  may be read through these patterns. The source pattern  110  and the drain pattern  150  may include various electrically conductive materials, such as metals, metal nitrides, or combinations thereof. In an embodiment, the source pattern  110  and the drain pattern  150  are shown to have a rectangular sectional shape, but in other embodiments the shape of the drain and source patterns may be variously modified. Source pattern  110  and drain pattern  150  may be connected to the bottom and top of the ion-receiving layer  120  through a source contact  115  and a drain contact  155 , respectively. As will be described later, for easy processing and the like, the source contact  115  and the drain contact  155  may be interposed between the source pattern  110  and the ion-receiving layer  120 , and between the drain pattern  150  and the ion-receiving layer  120 , respectively. The source contact  115  and the drain contact  155  may have a pillar-like shape. However, the present disclosure is not limited thereto, and in other embodiments, the source contact  115  and the drain contact  155  may be omitted, and the source pattern  110  and the drain pattern  150  may directly contact the bottom and top of the ion-receiving layer  120 , respectively. In addition, although this embodiment illustrates a case in which the source pattern  110  is positioned below the ion receiving layer  120  and the drain pattern  150  is positioned above the ion-receiving layer  120 , in other embodiments positions of the source pattern  110  and the drain pattern  150  may be reversed or positioned relative to each other in different configurations. 
     A method of operating a variable resistance element described above will be described in detail below with reference to  FIG. 3 . 
       FIG. 3  is a view illustrating a method of operating a variable resistance element illustrated in  FIGS. 2A and 2B , namely, a view illustrating a program method.  FIG. 3  shows only a portion of the variable resistance element illustrated in  FIG. 2A . 
     Referring to  FIG. 3 , in an embodiment, the ion supply layer  130  may include LiCoO 2 , and the ion-receiving layer  120  may include WO 3 . 
     When a positive program voltage is applied to the gate pattern  140 , the metal cations, that is, Li +  ions, in the ion supply layer  130  may move to the ion-receiving layer  120 . The Li +  ions that have moved to the ion-receiving layer  120  may meet electrons supplied from the source pattern  110  and/or the drain pattern  150  and react with WO 3  as shown in the following chemical reaction equation 1, thereby forming oxygen vacancies in the ion-receiving layer  120 :
 
xLi + +xe − +WO 3 →Li x WO 3-x   Chemical Reaction Equation 1
 
     For the source pattern  110  and/or the drain pattern  150  to supply electrons, a ground voltage may be applied to at least one of these patterns. As an example, a ground voltage may be applied to the source pattern  110 , and the drain pattern  150  may be in a floating state in which no voltage is applied. Alternatively, the source pattern  110  may be in a floating state, and a ground voltage may be applied to the drain pattern  150 . Alternatively, a ground voltage may be applied to both the source pattern  110  and the drain pattern  150 . 
     The oxygen vacancies act as donor defects as described above. Thus, when a positive program voltage is applied, the electrical conductivity of the ion-receiving layer  120  may increase, that is, the electrical resistance may decrease. 
     Here, as the number of the program voltage pulses increases, the amount of Li +  ions moving from the ion supply layer  130  to the ion-receiving layer  120  may gradually increase, and accordingly, the amount of oxygen vacancies in the ion-receiving layer  120  may gradually increase. 
     As a result, the electrical conductivity of the ion-receiving layer  120  may gradually increase, that is, the electrical resistance may gradually decrease. 
     In contrast, although not shown in the figures, when a negative erase voltage is applied to the gate pattern  140 , Li +  ions may be returned from the ion-receiving layer  120  to the ion supply layer  130 , and thus the electrical conductivity of the ion-receiving layer  120  may decrease, that is, the electrical resistance may increase. This decrease in electrical conductivity and/or increase in electrical resistance may be gradual depending on the number of erase voltage pulses. In addition, a positive voltage may be applied to at least one of the source pattern  110  and the drain pattern  150 . As an example, a positive voltage may be applied to the source pattern  110 , and the drain pattern  150  may be in a floating state. Alternatively, the source pattern  110  may be in a floating state, and a positive voltage may be applied to the drain pattern  150 . Alternatively, a positive voltage may be applied to both the source pattern  110  and the drain pattern  150 . 
     As a result, the variable resistance element including the ion-receiving layer  120 , the ion supply layer  130  and the gate pattern  140  may be characterized by resistance that gradually changes depending on the amount of ions moving between the ion-receiving layer  120  and the ion supply layer  130 , and thus this variable resistance element is suitable for use as a synapse in a neuromorphic device. 
     The resistance state of this variable resistance element may be read using the source pattern  110  and the drain pattern  150 . That is, the resistance state of the variable resistance element may be understood or determined by applying a predetermined read voltage between the source pattern  110  and the drain pattern  150  and reading the current flowing therebetween, that is, the current flowing in the ion-receiving layer  120 . 
     Meanwhile, a plurality of the variable resistance elements may be arranged to form an array. This will be described below by way of examples with reference to  FIGS. 4A, 4B and 5 . 
       FIGS. 4A and 4B  are a plan view and sectional view illustrating a semiconductor device according to an embodiment of the present disclosure.  FIG. 4B  is a sectional view taken along line X 2 -X 2 ′ of  FIG. 4A . 
     Referring to  FIGS. 4A and 4B , a semiconductor device according to an embodiment of the present disclosure may include: a substrate  200 ; source lines  210  formed on the substrate  200  and extending in a first direction; bit lines  250  extending in a second direction intersecting with the first direction; an ion-receiving layer  220  disposed between the source lines  210  and the bit lines  250 , and located at intersections between the source lines  210  and the bit lines  250 ; an ion supply layer  230  surrounding a sidewall of the ion-receiving layer  220 ; and word lines  240  surrounding a sidewall of the ion supply layer  230  and extending in the second direction. 
     The substrate  200  may include certain necessary underlying structures (not shown), such as for example, transistors for controlling the source lines  210 , the word lines  240  and/or the bit lines  250 . 
     The plurality of source lines  210  may be arranged to be spaced apart from each other in the second direction, which is at an angle to the first direction, while extending in the first direction on the substrate  200 . Although not shown in the figures, an interlayer dielectric layer may fill in a space between the source lines  210 . The source line  210  may include various electrically conductive materials such as metals, metal nitrides, or combinations thereof. 
     On an interlayer dielectric layer (not shown) between the source lines  210  and the ion-receiving layer  220 , a pillar-shaped source line contact  215  may be disposed. The source line contact  215  may be disposed at each of intersections between the source lines  210  and the bit lines  250  and may have a pillar-like shape. A space between the source line contacts  215  may be filled with a first interlayer dielectric layer ILD 1 . 
     On a first layer including the source line contact  215  and the first interlayer dielectric layer ILD 1 , the ion-receiving layer  220 , the ion supply layer  230  and the word lines  240  may be disposed. 
     The ion-receiving layer  220  may be disposed at each of intersections between the source lines  210  and the bit lines  250  and may have a pillar shape. A bottom of the ion-receiving layer  220  may be connected to the source line contact  215 . The width of the ion-receiving layer  220  in a horizontal direction parallel to the surface of the substrate  200  may be equal to or greater than the width of the source line contact  215  in the same direction. As a result, the source line contact  215  does not unintentionally connect with the ion supply layer  230  and/or the word line  240 . 
     The ion supply layer  230  may completely surround a sidewall of the ion-receiving layer  220 . In other embodiments, the ion supply layer  230  may be in contact with a portion of the outer sidewall of the ion-receiving layer  220 , as long as the contact area ensures a smooth supply of ions to the ion-receiving layer  220 . As used herein, “a portion of the sidewall of the ion-receiving layer  220 ” may mean a portion of the sidewall in the horizontal direction and/or the vertical direction. That is, the ion supply layer  230  may have a shape which is in contact with a portion of the ion-receiving layer  220  in the horizontal direction and does not surround the ion-receiving layer  220  in the plan view. Alternatively, the ion supply layer  230  may completely surround a sidewall of the ion-receiving layer  220  in a plan view, but only a portion of the ion-receiving layer  220  in the sectional view, i.e., the ion supply layer  230  may have a smaller thickness than the ion-receiving layer  220  in the vertical direction. Alternatively, both may be possible. That is, the ion supply layer  230  may partially contact the ion-receiving layer  220  in the horizontal direction and the vertical direction. A sidewall of the ion supply layer  230 , which is in contact with the sidewall of the ion-receiving layer  220 , will be referred to as an inner sidewall, and the sidewall of the ion supply layer  230  that is located opposite to the inner sidewall of the ion supply layer  230  will be referred to as an outer sidewall. 
     The word line  240  may completely surround the outer sidewall of the ion supply layer  230 . However, in other embodiments, the word line  240  may be in contact with a portion of the outer sidewall of the ion supply layer  230 , as long as the contact area is of a magnitude for ensuring a sufficient voltage to the ion supply layer  230 . As used herein, “a portion of the outer sidewall of the ion supply layer  230 ” may mean a portion of the outer sidewall in the horizontal direction and/or the vertical direction. That is, the word line  240  may have a shape which is contact with a portion of the outer sidewall of the ion supply layer  230  in the horizontal direction and does not surround the ion supply layer  230  in the plan view. Alternatively, the word line  240  may be in contact with a portion of the outer sidewall of the ion supply layer  230  in the vertical direction, with a smaller thickness than the thickness of the ion supply layer  230  in the vertical direction, while surrounding the outer sidewall of the ion supply layer  230  in the plan view. Alternatively, both may be possible. That is, the word line  240  may partially contact the ion supply layer  230  in the horizontal direction and the vertical direction. In addition, the word line  240  may be formed to extend in the second direction and surround the plurality of ion supply layers  230  which are arranged in the second direction. However, the direction in which the word line  240  extends may be variable. For example, word line  240  may extend in a direction and is connected to the plurality of ion supply layers  230  that are arranged in the same direction. For example, the word line  240  may extend in the first direction and surround the plurality of ion supply layer  230  that are arranged in the first direction. 
     Referring back to  FIG. 4B , a space between the ion-receiving layer  220 , the ion supply layer  230  and the word line  240  may be filled with a second interlayer dielectric layer ILD 2 . 
     The ion-receiving layer  220 , the ion supply layer  230 , the word line  240  and the second interlayer dielectric layer ILD 2  may be included in a second layer. The bit line contact  255  may be disposed at each intersection between the source line  210  and the bit line  250 , and may have a pillar or pillar-like shape. A bottom of the bit line contact  255  may be connected to a top of the ion-receiving layer  220 . The width of the ion-receiving layer  220  in a horizontal direction parallel to the surface of the substrate  200  may be equal to or greater than the width of the bit line contact  255  in the same direction. A space between the bit line contact  255  will may be filled with a third interlayer dielectric layer ILD 3 . 
     The bit line contact  255  and the third interlayer dielectric layer ILD 3  may form a third layer on which bit lines  250  may be disposed, and arranged to be spaced from each other in the first direction while extending in the second direction. 
     In a semiconductor device of an embodiment described above, a variable resistance element may be formed at each of the intersections (see the dotted line in  FIG. 4A ) between the source lines  210  and the bit lines  250 . This variable resistance element may be substantially the same as the above-described variable resistance element shown in  FIGS. 2A and 2B . In other words, the source line  210 , the source line contact  215 , the ion-receiving layer  220 , the ion supply layer  230 , the word line  240 , the bit line contact  255  and the bit line  250 , which are included in the dotted line region of  FIG. 4A , may respectively correspond to the source pattern  110 , the source contact  115 , the ion-receiving layer  120 , the ion supply layer  130 , the gate pattern  140 , the drain contact  155  and the drain pattern  150 , which are shown in  FIGS. 2A and 2B . Accordingly, each variable resistance element in the semiconductor device of this embodiment may operate in the same manner as described above with reference to  FIG. 3 , as an example. 
     A method of fabricating the semiconductor device of an embodiment will be described below by way of example. 
     First, a conductive material may be formed on a substrate  200  and patterned to form source lines  210 . Then, a dielectric material covering the source lines  210  may be deposited and a planarization process may be performed until the upper surfaces of the source lines  210  are exposed, thereby forming an interlayer dielectric layer (not shown) filling a space between the source lines  210 . Next, a first interlayer dielectric layer ILD 1  covering the source lines  210  and the interlayer dielectric layer therebetween may be formed, and then the first interlayer dielectric layer ILD 1  may be selectively etched to provide spaces in which a source line contact  215  is to be formed. The spaces may be filled with a conductive material to form the source line contacts  215 . Then, a conductive material may be formed on the first interlayer dielectric layer ILD 1  and the source line contacts  215  and patterned to form word lines  240 , and a second interlayer dielectric layer ILD 2  filling the space between the word lines  240  may be formed. Then, the word lines  240  may be selectively etched to form, in the word lines  240 , holes H 1  which provide spaces in which an ion-receiving layer  220  and an ion supply layer  230  are to be formed. The hole H 1  may be formed to have a larger width than that of each source line contact  215  while exposing each of the source line contacts  215 . Next, a material layer for forming the ion supply layer  230  may be formed along the sidewalls and bottom surfaces of the holes H 1  up to a thickness that does not completely fill the holes H 1 , and then the material layer may be blanket-etched to form the ion supply layer  230  on the sidewalls of the holes H 1 . By this blanket etching, the bottom surface of the hole H 1  may be exposed. The thickness and extent of blanket etching of the material layer may be adjusted such that the width of the exposed bottom surface of the hole H 1  is equal to or larger than the width of the source line contact  215 . Next, an ion-receiving layer  220  may be formed, which fills the remaining space of the hole H 1  having the ion supply layer  230  formed therein. Next, a third interlayer dielectric layer IDL 3  may be formed over the ion-receiving layer  220 , the ion supply layer  230 , the word lines  240  and the second interlayer dielectric layer ILD 2 , and then the third interlayer dielectric layer ILD 3  may be selectively etched to provide spaces in which bit line contacts  255  are to be formed, and the spaces may be filled with a conductive material to form the bit line contacts  255 . Thereafter, a conductive material may be formed over the bit line contacts  255  and the third interlayer dielectric layer ILD 3  and patterned to form bit lines  250 . 
       FIG. 5  is a plan view illustrating a semiconductor device according to another embodiment of the present disclosure. This embodiment will be described with a focus on differences from the embodiment described above with reference to  FIGS. 4A and 4B . 
     Referring to  FIG. 5 , a semiconductor device of this embodiment may include: source lines  310  extending in a first direction; bit lines  350  extending in a second direction intersecting with the first direction; an ion-receiving layer  320  disposed between the source lines  310  and the bit lines  350  and located at intersections between the source lines  310  and the bit lines  350 ; an ion supply layer  330  surrounding a sidewall of the ion-receiving layer  320 ; and word lines  340  extending in a third direction and surrounding a sidewall of the ion supply layer  330 . 
     This embodiment may be substantially the same as the above-described embodiment, except for the directions in which the source line  310 , the bit line  350  and the word line  340  extend. 
     The source line  310 , the bit line  350  and the word line  340  extend in directions that intersect with one another at angles that need not be perpendicular. In  FIG. 5 , an area having a substantially triangular shape is defined by the source line  310 , the bit line  350  and the word line  340 . As an example, the angle formed by the source line  310  and the bit line  350  may be about 60°, the angle formed by the bit line  350  and the word line  340  may be about 60°, and the angle formed by the word line  340  and the source line  310  may be about 60°. In this example, an area defined by the source line  310 , the bit line  350 , and the word line  340  has an equilateral triangle shape. 
     The ion-receiving layer  320  and the ion supply layer  330  may be disposed at each intersection of the source lines  310 , the bit lines  350  and the word lines  340 . As a result, a variable resistance element may be formed at each intersection of the source lines  310 , the bit lines  350  and the word lines  340 . 
     According to this embodiment, the degree of integration of the semiconductor device can be further increased as compared to embodiments described with reference to  FIGS. 4A and 4B . 
       FIG. 6A  is a sectional view illustrating a variable resistance element according to another embodiment of the present disclosure, and  FIG. 6B  is a sectional view illustrating a variable resistance element according to still another embodiment of the present disclosure. These embodiments will be described with a focus on differences from the embodiment described above with reference to  FIGS. 2A and 2B . 
     Referring to  FIG. 6A , a variable resistance element of an embodiment may further include a selection element pattern  160  in addition to the components of the variable resistance element shown in  FIGS. 2A and 2B . 
     Although  FIG. 6A  illustrates the selection element pattern  160  interposed between a drain pattern  150  and a drain contact  155 , the present disclosure is not limited thereto. The selection element pattern  160  may be positioned between the drain pattern  150  and the ion-receiving layer  120 , and/or between the source pattern  110  and the ion receiving layer  120 . The selection element pattern  160  may control access from the drain pattern  150  to the ion-receiving layer  120  or from the source pattern  110  to the ion-receiving layer  120 . For example, the selection element pattern  160  may be interposed between the drain contact  155  and the ion-receiving layer  120 , between the source pattern  110  and the source contact  115 , and/or between the source contact  115  and the ion-receiving layer  120 . 
     In addition, although  FIG. 6A  illustrates a selection element pattern  160  that has the same shape as the drain pattern  150 , the present disclosure is not limited thereto, and the selection element pattern  160  may have various shapes. For example, the selection element pattern  160  may have the same outline, outer contour or island-like shape as the drain contact  155  and/or the source contact  115  when viewed in the plan view. Alternatively, or additionally, the selection element pattern  160  may also have the same shape as the source pattern  110 . In other embodiments, the selection element pattern  160  may also have a line shape that overlaps with the bit line or the source line when viewed in the plan view. 
     The selection element pattern  160  may have a selection element characteristic in that when the magnitude of the voltage or current applied thereto is equal to or lower than a certain critical value, the selection element pattern  160  passes little or no current therethrough, and when the magnitude of the voltage or current applied thereto is higher than a certain critical value, the selection element pattern  160  passes a current that rapidly increases in proportion to the magnitude of the applied voltage or current. Selection element pattern  160  may include, for example, an MIT (Metal Insulator Transition) element such as NbO 2  or TiO 2 , an MIEC (Mixed Ion-Electron Conducting) element such as ZrO 2 (Y 2 O 3 ), Bi 2 O 3 —BaO or (La 2 O 3 )x(CeO 2 )1-x, an OTS (Ovonic Threshold Switching) element including a chalcogenide-based material such as Ge 2 Sb 2 Te 5 , As 2 Te 3 , As 2  or As 2 Se 3 , a rectifying element such as a diode, or a tunneling dielectric layer, which is composed of various dielectric materials such as silicon oxides, silicon nitrides or metal oxides. The tunneling dielectric layer may have a small or minimal thickness to permit electron tunneling at a certain voltage or current. 
     The selection element pattern  160  may have either a monolayer structure or a multilayer structure, which is composed of a combination of two or more layers and exhibits selection element characteristics. 
     When the selection element pattern  160  is used in the variable resistance element, it may reduce and/or block leakage current between adjacent variable resistance elements that are disposed in an array structure such as those illustrated in  FIGS. 4A, 4B and 5 . 
     Referring to  FIG. 6B , a variable resistance element of an embodiment may further include, in addition to the components of the variable resistance element shown in  FIGS. 2A and 2B , an isolation layer interposed between the ion-receiving layer  120  and the ion supply layer  130  to physically isolate them from each other. 
     The isolation layer  170  may function to prevent a mixed layer from being unnecessarily formed due to ion movement at the interface between the ion-receiving layer  120  and the ion supply layer  130 . In addition, the isolation layer  170  may permit the movement of metal ions when an operating voltage such as a program voltage or an erase voltage is applied to the gate pattern  140 . On the other hand, the isolation layer  170  may block electron movement at other voltages. An electrolyte material may be used in the isolation layer  170 . 
     When the isolation layer  170  is used, it may efficiently control metal ion movement between the ion supply layer  130  and the ion-receiving layer  120 , and may prevent a mixed layer from being formed between the ion supply layer  130  and the ion-receiving layer  120 . The isolation layer  170  thus contributes to the reliability of the variable resistance element. 
       FIG. 7  is a sectional view illustrating a variable resistance element according to yet another embodiment of the present disclosure. 
     Referring to  FIG. 7 , the variable resistance element of an embodiment may include: a pillar-shaped ion supply layer  420  extending in a vertical direction; an ion-receiving layer  430  surrounding a sidewall of the ion supply layer  420 ; a gate pattern  440  surrounding a sidewall of the ion-receiving layer  430 ; a source pattern  410  connected to a bottom of the ion supply layer  420 ; and a drain pattern  450  connected to a top of the ion supply layer  420 . A source contact  415  may be interposed between the source pattern  410  and the ion supply layer  420 , and a drain contact  455  may be interposed between the drain pattern  450  and the ion supply layer  420 . 
     An embodiment illustrated in  FIG. 7  differs from an embodiment shown in  FIGS. 2A and 2B  in the position of the ion supply layer and the ion-receiving layer in the different embodiments. An embodiment shown in  FIGS. 2A and 2B  illustrates a variable resistance element in which the ion supply layer  130  surrounds the outer sidewall of the pillar-shaped ion-receiving layer  120 , but  FIG. 7  shows a variable resistance element in which the ion-receiving layer  430  surrounds an outer sidewall of a pillar-shaped ion supply layer  420 . Although only the positions of the ion-receiving layers and the ion supply layers are reversed in the different embodiments, the material forming the ion supply layer  420  may be the same as the material forming the ion supply layer  130 , and the material forming the ion-receiving layer  430  may be the same as the material forming the ion-receiving layer  120 . 
     In this embodiment, the ion supply layer  420  may develop a metal ion deficient state by supplying cations, particularly metal cations, to the ion-receiving layer  430 , thus forming holes. The holes in the ion supply layer  420  act as acceptor defects. Thus, as the amount of the holes increases, the electrical conductivity of the ion supply layer  420  may increase, and as the amount of the holes decreases, the electrical conductivity of the ion supply layer  420  may decrease. That is, the resistance of the ion supply layer  420  may be variable depending on the amount of holes in the ion supply layer  420 . Accordingly, in the variable resistance element according to embodiments shown in  FIGS. 2A and 2B , the ion-receiving layer  120  functions as a resistance change element, but in the present embodiment, the ion supply layer  420  may function as a resistance change element. 
     The ion-receiving layer  430  may receive cations, particularly metal cations, from the ion supply layer  420 . In this embodiment, the ion-receiving layer  430  may have a shape that surrounds an outer sidewall of the ion supply layer  420 . However, the present disclosure is not limited thereto, and the shape of the ion-receiving layer  430  may be variously modified so that the ion-receiving layer  430  is in contact with at least a portion of the sidewall of the ion supply layer  420  to provide a smooth or uninterrupted ion supply from the ion supply layer  420  to the ion-receiving layer  430 . 
     The gate pattern  440  may function to control ion movement from the ion supply layer  420  to the ion-receiving layer  430  in response to receiving a predetermined voltage. The gate pattern  440  may have a shape that surrounds an outer sidewall of the ion-receiving layer  430 . However, the present disclosure is not limited thereto, and in other embodiments, the shape of the gate pattern  440  may be variously modified so that gate pattern  440  is in contact with at least a portion of the outer sidewall of the ion-receiving layer  430 , and ion movement from the ion supply layer  420  o the ion-receiving layer  430  is smooth and uninterrupted. 
     The source pattern  410  and the drain pattern  450  may be connected to the bottom and top of the ion supply layer  420 , respectively, and a change in the resistance of the ion supply layer  420  may be read through these patterns. 
     A method of operating the variable resistance element shown in  FIG. 7  will be described in detail below with reference to  FIG. 8 . 
       FIG. 8  is a view illustrating a method of operating the variable resistance element shown in  FIG. 7 , particularly a program method.  FIG. 8  shows only a portion of the variable resistance element shown in  FIG. 7 . 
     Referring to  FIG. 8 , the ion supply layer  420  may include LiCoO 2 , and the ion-receiving layer  430  may include WO 3 . 
     When a negative program voltage is applied to the gate pattern  440 , the metal cations, that is, Li +  ions, in the ion supply layer  420  may move to the ion-receiving layer  430 . When Li +  ions are released from the ion supply layer  420 , holes may be formed in the ion supply layer  420  as shown in the following chemical reaction equation 2:
 
LiCoO 2 →Li 1-x CoO 2 +xLi+ + xh  Chemical Reaction Equation 2
 
     In this case, a ground voltage may be applied to at least one of the source pattern  410  and the drain pattern  450 . As an example, a ground voltage may be applied to the source pattern  410 , and the drain pattern  450  may be in a floating state. Alternatively, the source pattern  410  may be in a floating state, and a ground voltage may be applied to the drain pattern  450 . Alternatively, a ground voltage may be applied to both the source pattern  410  and the drain pattern  450 . 
     As described above, the holes act as acceptor defects. Thus, when a negative program voltage is applied, the electrical conductivity of the ion supply layer  420  may increase, that is, the electrical resistance may decrease. 
     Here, as the number of the program voltage pulses increases, the amount of Li +  ions moving from the ion supply layer  420  to the ion-receiving layer  430  may gradually increase, and accordingly, the amount of holes in the ion supply layer  420  may gradually increase. 
     As a result, the electrical conductivity of the ion supply layer  420  may gradually increase, that is, the electrical resistance may gradually decrease. 
     In contrast, although not shown in the figures, when a positive erase voltage is applied to the gate pattern  440 , Li +  ions may be returned from the ion-receiving layer  430  to the ion supply layer  420 , and thus the electrical conductivity of the ion supply layer  420  may decrease, that is, the electrical resistance may increase. This decrease in electrical conductivity and/or increase in electrical resistance may be gradual depending on the number of erase voltage pulses. In addition, a negative voltage may be applied to at least one of the source pattern  410  and the drain pattern  450 . As an example, a negative voltage may be applied to the source pattern  410 , and the drain pattern  450  may be in a floating state. Alternatively, the source pattern  410  may be in a floating state, and a negative voltage may be applied to the drain pattern  450 . Alternatively, a negative voltage may be applied to both the source pattern  410  and the drain pattern  450 . 
     As a result, the variable resistance element including the ion supply layer  420 , the ion-receiving layer  430  and the gate pattern  440  may be characterized by resistance that gradually changes depending on the amount of ions moving between the ion supply layer  420  and the ion-receiving layer  430 , and thus this variable resistance element is suitable for use as a synapse in a neuromorphic device. In the above-described embodiment, the change in resistance of the variable resistance element through changes in oxygen vacancies in a layer is possible, but the present embodiment differs from the above-described embodiment in that the change in resistance of the variable resistance element results from changes in the numbers of holes. 
     This resistance state of the variable resistance element may be read using the source pattern  410  and the drain pattern  450 . That is, the resistance state of the variable resistance element may be understood or determined by reading the current or voltage difference between the source pattern  410  and the drain pattern  450 . 
     Meanwhile, it is to be understood that the variable resistance element of the present embodiment may be used in the above-described semiconductor devices shown in  FIGS. 4A, 4B and 5 , or may further include a selection element pattern, similar to the variable resistance element shown in  FIG. 6A , and/or may further include an isolation layer, similar to the variable resistance element shown in  FIG. 6B . 
       FIG. 9  is a sectional view illustrating a variable resistance element according to still yet another embodiment of the present disclosure. This embodiment will be described with a focus on differences from the embodiment shown in  FIGS. 2A and 2B . 
     Referring to  FIG. 9 , an ion-receiving layer  120 ′ of a variable resistance element according to an embodiment may have a hollow pillar shape, for example, a cylinder-like shape, unlike the ion-receiving layer  120  of the variable resistance element shown in  FIGS. 2A and 2B , which has a solid pillar shape. The space in the ion-receiving layer  120 ′ may be filled with a dielectric pattern  180 . In other words, a pillar-shaped dielectric pattern  180  may be further formed, and the ion-receiving layer  120 ′ may have a shape surrounding the dielectric pattern  180 . 
     The ion-receiving layer  120 ′ needs to be electrically connected to the source pattern  110  and the drain pattern  150 . Thus, a portion of a bottom of the ion-receiving layer  120 ′ may be in contact with the source contact  115  (or the source pattern  110  if the source contact  115  is omitted), and a portion of a top of the ion-receiving layer  120 ′ may be in contact with the drain contact  155  (or the drain pattern  150  if the drain contact  155  is omitted). In addition, the width of the dielectric pattern  180  in the horizontal direction may be smaller than the width of each of the source contact  115  (or the source pattern  110  if the source contact  115  is omitted) and the drain contact  155  (or the drain pattern  150  if the drain contact  155  is omitted). 
     According to this embodiment, the overall width of the ion-receiving layer  120 ′ in the horizontal direction may be decreased because of the inclusion of dielectric pattern  180 . Consequently, the path of metal ion movement may be shortened in the horizontal direction, and hence the rate of oxygen vacancy formation in the ion-receiving layer  120 ′ may increase. As a result, the rate of change in resistance of the ion-receiving layer  120 ′ may increase, and thus the operating speed of the variable resistance element may also increase. 
     Similarly, although not shown in the figures, the shape of the ion supply layer  420  in the variable resistance element shown in  FIG. 7  may be modified into a hollow pillar shape, and the empty space of the ion supply layer  420  may be filled with a dielectric material. Such an embodiment also supports an increased operating speed. 
     The variable resistance element and/or semiconductor device according to each of the above-described embodiments may be used in various devices or systems, for example, a neuromorphic device. This will be described by way of example with reference to  FIG. 10 . 
       FIG. 10  shows an example of a pattern recognition system  1000  according to an embodiment of the present disclosure. The pattern recognition system according to this embodiment may be a system for recognizing various patterns, such as a speech recognition system or an image recognition system. The pattern recognition system according to this embodiment may be configured to have a neuromorphic device including embodiments of variable resistance elements and/or semiconductor devices described above. 
     Referring to  FIG. 10 , the pattern recognition system  1000  according to this embodiment may include a central processing unit (CPU)  1010 , a memory device  1020 , a communication control device  1030 , a network  1040 , a pattern output device  1050 , a pattern input device  1060 , an analog-digital converter (ADC)  1070 , a neuromorphic device  1080 , a bus line  1090 , and the like. 
     The central processing unit  1010  may generate and transmit various signals used in a learning operation of the neuromorphic device  1080 , and may perform various processing operations and functions for recognizing patterns of sound, images or the like based on an output from the neuromorphic device  1080 . This central processing unit  1010  may be connected, via the bus line  1090 , to the memory device  1020 , the communication control device  1030 , the pattern output device  1050 , the analog-digital converter (ADC)  1070 , and the neuromorphic device  1080 . 
     The memory device  1020  may store various information required for the pattern recognition system  1000 . To this end, the memory device  1020  may include different kinds of memory devices. For example, the memory device  1020  may include a ROM device  1022 , a RAM device  1023 , and the like. The ROM device  1022  may function to store various programs or data, which are used in the central processing unit  1010  in order to perform the learning operation of the neuromorphic device  1080 , pattern recognition, etc. The RAM device  1023  may store the program or data downloaded from the ROM device  1022 , or store data, such as sound or images, which were converted and analyzed by the analog-digital converter (ADC)  1070 . 
     The communication control device  1030  may exchange recognized data (e.g., sound or images) with other communication control devices through the network  1040 . 
     The pattern output device  1050  may output the recognized data (e.g., sound or images) in various manners. For example, the pattern output device  1050  may include a printer, a display unit, and the like, and may output sound waveforms or display images. 
     The pattern input device  1060  may receive analog-type sound, images, etc., and may include a microphone, a camera, etc. 
     The analog-digital converter (ADC)  1070  may convert analog data, provided by the pattern input device  1060 , to digital data, and may also analyze the digital data. 
     The neuromorphic device  1080  may perform learning, recognition, and the like using data provided by the analog-digital converter (ADC)  1070 , and may output data corresponding to recognized patterns. The neuromorphic device  1080  may include one or more of the variable resistance elements and semiconductor devices according to the above-described embodiments. For example, the neuromorphic device  1080  may include a plurality of synapses, and each of the plurality of synapses may include: an ion-receiving layer having a top, a bottom and a sidewall connecting the top and the bottom; an ion supply layer having an inner sidewall connected to at least a portion of an outer sidewall of the ion-receiving layer; a gate pattern connected to an outer sidewall of the ion supply layer; and a source pattern connected to one of the top or bottom of the ion-receiving layer, and a drain pattern connected to the other one of the top or bottom of the ion-receiving layer, wherein a resistance of the ion-receiving layer varies depending on an amount of ions supplied from the ion supply layer based on a voltage applied to the gate pattern. Through this configuration, the symmetry and linearity of synapses may be ensured. Accordingly, the operating characteristics of the neuromorphic device  1080  may be improved, and thus operating characteristics of the pattern recognition system  1000  may also be improved. 
     In addition, the pattern recognition system  1000  may further include other components required for properly performing its function. For example, it may further include a keyboard, a mouse and the like, as input units for receiving various parameters or setting conditions for operations of the pattern recognition system  1000 . 
     According to the embodiments described above, it is possible to provide a variable resistance element having characteristics suitable for use as a synapse in a neuromorphic device, and a semiconductor device including the same. 
     Although various embodiments have been described for illustrative purposes, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure as defined in the following claims.