JP5266654B2 - Switching element and method for manufacturing switching element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching device which does not require initialization operation prior to transition to an "on state", of a first time is excellent in repeating durability compared with before, reduced in the variation of a switching time, and to provide a rewritable integrated logic circuit using the switching device. <P>SOLUTION: The switching device is manufactured using an oxide ion conducting layer in which conducting metal is distributed previously. Metal ions are supplied also from the distributed metal when two electrodes are connected by a metal bridge using an electrochemical reaction. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a switching element using an electrochemical reaction and a method for manufacturing the same, which are used in electronic devices such as programmable logic and memory.

  In order to diversify the functions of the programmable logic and promote the mounting to electronic devices, it is necessary to reduce the size of the switch for connecting the logic cells to each other and to reduce the on-resistance. It is known that a switch using an electrochemical reaction has a smaller size and a lower on-resistance than a conventional semiconductor switch. Examples of the switching element using an electrochemical reaction include a two-terminal switch disclosed in Patent Document 1 and a three-terminal switch disclosed in Patent Document 2.

  The two-terminal switch has a structure in which an ion conductive layer is sandwiched between a second electrode that supplies metal ions and a first electrode that does not supply metal ions. When a voltage is applied between the two electrodes, if the second electrode is set to a higher potential than the first electrode, the metal is oxidized into metal ions on the surface of the second electrode, and the metal ions are supplied into the ion conductive layer. On the other hand, on the surface of the first electrode, metal ions in the ion conductive layer are reduced to metal, and metal is deposited. When the metal bridge that reaches the second electrode surface from the first electrode surface is formed by the deposited metal, the ion conduction in the ion conductive layer changes from the ionic conduction to the conductive state via the metal bridge. The resistance drops rapidly. That is, the switch is “ON”. Conversely, when the second electrode is set to a potential lower than that of the first electrode in a state where the metal bridge is formed, the metal is oxidized to metal ions on the metal bridge surface, which is equal to the first electrode surface, Metal ions are supplied into the ion conductive layer. On the other hand, on the surface of the second electrode, metal ions in the ion conductive layer are reduced to metal, and the metal is deposited. Accordingly, the metal bridge gradually becomes thinner, and at a certain point, the conduction path between the two electrodes via the metal bridge is interrupted. At this point, the electrical conduction between the two electrodes changes from the conductive state via the metal bridge to the ionic conduction in the ion conductive layer, so that the resistance between the two electrodes increases rapidly. That is, the switch is in the “off state”. Subsequently, when a voltage is continuously applied between both electrodes, the metal deposited on the surface of the first electrode is oxidized into metal ions, and the metal deposit disappears. The two-terminal switch performs switching between an “on state” and an “off state” by forming and eliminating a conduction path via the metal bridge. Since the two-terminal switch has a simple structure, the manufacturing process is simple, and the element size can be reduced to the nanometer order.

  The three-terminal switch has a configuration in which a third electrode for controlling the formation / disappearance of the metal bridge is provided in addition to the first electrode and the second electrode in which the conduction path is formed / disappeared via the metal bridge between them. . The thickness of the metal bridge can be controlled by changing the voltage applied between the third electrode, the first electrode, and the second electrode, and the three-terminal switch has excellent electromigration resistance.

  In addition, since the conduction path through the metal bridge is low resistance, when switching between the “on state” and the “off state”, the resistance between the first electrode and the second electrode rapidly increases, Indicates a decrease. Therefore, when the two-terminal switch is applied to logic, the voltage applied between the first electrode and the second electrode at the time of connection and disconnection causes a sudden change in the current flowing through the element. There is a risk of damaging the logic. In the three-terminal switch, there is a transmission device that transmits an electrical signal through a third electrode that controls the formation / extinction of metal bridges and a conduction path between the first electrode and the second electrode that are connected and disconnected. Since it exists separately, the current can be controlled. On the other hand, the three-terminal switch has a more complicated structure and a larger element size than the two-terminal switch.

In order to mount the switch using the above-described electrochemical reaction as a programmable logic wiring changeover switch, a switching voltage higher than the logic operating voltage and CMOS process compatibility are required. In particular, the switching characteristics of a switch using an electrochemical reaction largely depends on the material of the ionic conductor serving as a metal ion medium, so selection and optimization of the ionic conductor material is important. Oxides are promising as ionic conductors for switches utilizing electrochemical reactions because of their increased switching voltage and good compatibility with CMOS processes. An example of using an oxide for the ion conductive layer is tantalum oxide disclosed in Patent Document 3. Although the oxide ion conductor has a high switching voltage, it is a material that does not contain a metal that forms a metal bridge inside the ion conductor, so an initialization operation is required or the switching speed is increased when the switch is driven. There is a problem in reliability such as a large variation or a large variation in the number of repetitions between the “on state” and the “off state”.
Special Table 2002-536840 Publication International Publication No. 2006/070773 Pamphlet JP 2006-319028 A

  In the two-terminal switch or the three-terminal switch using the oxide ion conductive layer described above, a metal bridge is formed in the ion conductive layer from the electrode supplying the metal ion at the first transition to the “on state”. It is necessary to introduce metal ions to be used. For example, after the first transition to the “on state”, when the “off state” is set, a thin portion in the metal bridge formed between the first electrode and the second electrode disappears, and the metal The conduction path through the bridge is interrupted. Thereafter, the voltage application is continued for a little time, the metal constituting the metal deposit is oxidized into metal ions, and then the voltage application is stopped. At this point, metal precipitates that have formed metal bridges still remain on the electrode surface, and the ion conductive layer contains metal ions at a sufficient concentration. . Therefore, the transition to the “on state” for the second and subsequent times has already occurred on the surface of the metal precipitate remaining on the electrode surface in a state where the ion conductive layer contains a sufficient concentration of metal ions. Then, the reduced metal is precipitated from the metal ions, and the metal bridges partially disappeared are regenerated. That is, compared to the applied voltage used for the first transition to the “on state”, the transition to the “on state” for the second and subsequent times can be caused by using a somewhat lower applied voltage. On the other hand, the switching process from the “on state” to the “off state” is an operation of eliminating the thin portion in the metal bridge formed between the first electrode and the second electrode. After that, in principle, there is no difference in the required applied voltage.

  In other words, compared to the applied voltage used for the transition to the “on state” for the second and subsequent times, the applied voltage required for the transition to the “on state” for the first time is higher. In a two-terminal switch or a three-terminal switch using layers, an initialization operation is required before using the switch. For example, conventionally, when an operation for performing the first transition to the “on state” and then the transition from the “on state” to the “off state” is performed as the initialization operation, the subsequent switching operation is performed. The applied voltages required for the above are made substantially equal.

  When the switching operation is repeatedly performed, the supply time of the metal ions to the metal bridge is not sufficient, so that the switching time when switching from the “off state” to the “on state” varies. Furthermore, a sufficient number of repetitions cannot be obtained. As a result, when programmable logic is mounted, the reliability of the programmable logic may be reduced.

  The present invention has been made in order to solve the above-described problems of the prior art, and does not require an initialization operation prior to the first transition to the “on state” and is repeated more than before. It is an object of the present invention to provide a switching element that has excellent durability and little variation in switching time, and a rewritable logic integrated circuit using the switching element.

In order to achieve the above object, for example, when the switching element of the present invention is in the form of a two-terminal switch,
An ion conducting layer in which the same metal as the metal ion used for forming the metal bridge is dispersed in advance;
A first electrode provided in contact with the ion conductive layer, and a portion in contact with the ion conductive layer covered with a material that does not supply the metal ions;
And a second electrode that is provided in contact with the ion conductive layer and includes a material capable of supplying the metal ions.

  The switching element according to the present invention is characterized by using an ion conductive layer in which the same metal as a metal ion used for forming a metal bridge is dispersed in advance. When forming a metal bridge using an electrochemical reaction to electrically connect the two electrodes, metal ions are supplied also from a metal that is already dispersed in the ion conductive layer.

  The ion conductive layer in which the metal is dispersed in advance is provided in contact with the ion conductive layer, and the metal is diffused from the metal layer into the ion conductive layer by heating and light irradiation, or by ion implantation, It is produced by implanting metal ions into the ion conductive layer.

(Function)
When metal bridges are formed using an electrochemical reaction, metal ions are supplied from the second electrode including a material capable of supplying metal ions, and also from the metal dispersed in advance in the ion conductive layer. If a metal bridge is formed in the ion conductive layer, a state where sufficient metal ions are present can be quickly achieved. Therefore, it is not necessary to use a voltage higher than the voltage applied at the time of the second and subsequent transitions to the “on state” as the voltage to be applied at the time of the first transition to the “on state”. Furthermore, after the transition from the “on state” to the “off state”, when the metal bridge is formed again and transitioned to the “on state”, the supply of metal ions used for forming the metal bridge is stabilized. For this reason, the number of times that switching can be repeated increases and the variation in switching time decreases.

  According to the present invention, before starting to use the switching element, an initialization operation for once writing and erasing, for example, a first transition to the “on state”, and then from the “on state” to the “off state” There is no need to perform an operation for making a transition to. Therefore, the rewritable logic integrated circuit using the switching element of the present invention does not require an initialization circuit used only for the initialization operation. In addition, since the switching element of the present invention performs “write / erase”, the number of repeatable operations increases when switching is repeated, and variations in switching time are reduced. Because of this advantage, when the switching element of the present invention is used as a “write / erase” switch in a rewritable logic integrated circuit, it is possible to provide a programmable logic having a simpler driving method and higher reliability than conventional ones.

  Hereinafter, the present invention will be described in more detail.

  The following forms can be mentioned as typical forms in the switching element using the electrochemical reaction according to the present invention.

First, a first embodiment in which the present invention is applied to a two-terminal switching element is as follows:
A two-terminal switching element using an electrochemical reaction, comprising a first electrode, a second electrode, and an ion conductive layer containing an oxide sandwiched between the first electrode and the second electrode,
The two-terminal switching element is
When applying a voltage between the first electrode and the second electrode so that the potential of the second electrode is higher than the potential of the first electrode,
Metal ions are supplied from the second electrode into the ion conductive layer,
The metal ions in the ion conductive layer receive electrons from the first electrode and precipitate as metals.
Due to the growth of the metal precipitate, a metal bridge reaching the second electrode surface from the first electrode surface is formed,
By adopting a switching operation method in which the resistance between the first electrode and the second electrode is changed by electrically connecting the metal bridge between the first electrode and the second electrode,
In the ion conduction layer, a metal having the same metal species as the metal ions is dispersed in advance.

In the two-terminal switching element of the first form, desirably,
When applying a voltage between the first electrode and the second electrode so that the potential of the second electrode is higher than the potential of the first electrode,
In addition to supplying metal ions from the second electrode into the ion conductive layer,
The metal ions are also supplied from a metal dispersed in advance in the ion conductive layer.

In the two-terminal switching element of the first form,
The ion conductive layer containing the oxide is
It is preferably a layer containing at least one oxide selected from the group consisting of tantalum oxide, tungsten oxide, molybdenum oxide, nickel oxide, titanium oxide, aluminum oxide, niobium oxide and silicon oxide.

The distribution of the metal dispersed in advance in the ion conductive layer is as follows:
A structure in which the metal is distributed in a part of the ion conductive layer may be employed. In that case, in the ion conductive layer containing the oxide sandwiched between the first electrode and the second electrode, metal is dispersed in advance in at least a region where the first electrode and the ion conductive layer are in contact with each other. Is one of the preferred configurations.

  In the above two-terminal switching element, the portion of the second electrode in contact with the ion conductive layer is made of a material capable of supplying metal ions. On the other hand, when a voltage is applied between the first electrode and the second electrode so that the potential of the second electrode is lower than the potential of the first electrode, the portion in contact with the ion conductive layer is The first electrode itself is made of a material that does not supply any metal ions.

  In the above two-terminal switching element, a metal of the same metal species as the metal ions is preliminarily dispersed in the ion conductive layer, but the dispersion concentration of the metal is an oxidization that constitutes the ion conductive layer. It is preferable to select within a range that does not exceed the solid solubility limit of the metal in the ion conductive material containing the product. In particular, the dispersion concentration of the metal is most preferably the solid solubility limit of the metal in an ion conductive material containing an oxide. That is, in order to fully exhibit the effects of the present invention, it is desirable that the dispersion concentration of the metal be higher in a range not exceeding the solid solubility limit of the metal, and therefore the upper limit is the solid solution of the metal. Degree limit. At least, the dispersion concentration of the metal is preferably 20% or more, usually 50% or more, with the solid solubility limit of the metal being 100%.

  On the other hand, as will be described later, the dispersion concentration of the metal may show a distribution in the film thickness direction in the ion conductive layer by means of dispersing the metal in the ion conductive material containing the oxide. When the metal dispersion concentration shows a distribution in the ion conductive layer, it is more preferable that the metal dispersion concentration (maximum value) in the region showing the concentration maximum be the solid solubility limit. When the concentration of the metal dispersed in the ion conductive layer exceeds the solid solubility limit, the portion exceeding the solid solubility limit precipitates and locally forms metal aggregates. When the distribution density of the locally formed metal aggregate is unnecessarily high, an increase in leakage current via the metal aggregate is caused. Therefore, although formation of local metal aggregates is suppressed, it is desirable that the metal dispersion concentration be in a state where the solid solubility limit is almost reached.

Moreover, the 2nd form which applies this invention to a 3 terminal switching element is as follows.
An ion conducting layer containing an oxide for conducting metal ions;
A first electrode and a second electrode which are provided in contact with the ion conductive layer and covered with a material which does not supply the metal ions at a portion in contact with the ion conductive layer;
A three-terminal switching element using an electrochemical reaction, comprising a third electrode provided in contact with the ion conductive layer and comprising a third electrode comprising a material capable of supplying the metal ions at a portion in contact with the ion conductive layer. There,
The three-terminal switching element is
The potential of the second electrode is between the third electrode and the first electrode so that the potential of the third electrode is higher than the potential of the first electrode, and between the third electrode and the second electrode. When applying a voltage so that the potential of the third electrode becomes higher,
Metal ions are supplied from the third electrode into the ion conductive layer,
The metal ions in the ion conductive layer receive electrons from the first electrode and precipitate as metals.
The metal ions in the ion conductive layer receive electrons from the second electrode and precipitate as metals.
Due to the growth of the metal precipitate, a metal bridge reaching the second electrode surface from the first electrode surface is formed,
By adopting a switching operation method in which the resistance between the first electrode and the second electrode is changed by electrically connecting the metal bridge between the first electrode and the second electrode,
In the ion conduction layer, a metal having the same metal species as the metal ions is dispersed in advance.

In the three-terminal switching element of the second form, desirably,
The potential of the second electrode is between the third electrode and the first electrode so that the potential of the third electrode is higher than the potential of the first electrode, and between the third electrode and the second electrode. When applying a voltage so that the potential of the third electrode becomes higher,
In addition to supplying metal ions from the third electrode into the ion conductive layer,
The metal ions are also supplied from a metal dispersed in advance in the ion conductive layer.

In the three-terminal switching element of the second form,
The ion conductive layer containing the oxide is
It is preferably a layer containing at least one oxide selected from the group consisting of tantalum oxide, tungsten oxide, molybdenum oxide, nickel oxide, titanium oxide, aluminum oxide, niobium oxide and silicon oxide.

The distribution of the metal dispersed in advance in the ion conductive layer is as follows:
A structure in which the metal is distributed in a part of the ion conductive layer may be employed. At that time, in the ion conductive layer, the region sandwiched between the first electrode and the second electrode, the vicinity of the interface where the first electrode and the ion conductive layer are in contact, and the second electrode and the ion conductive layer are in contact with each other. A configuration in which a metal is dispersed in the vicinity of the interface is a suitable configuration.

  In the above three-terminal switching element, the potential of the third electrode is higher than the potential of the first electrode between the third electrode and the first electrode, and the third electrode and the second electrode When the voltage is applied so that the potential of the third electrode is higher than the potential of the second electrode during this period, the potential of the first electrode is usually equal to the potential of the second electrode.

  In the above three-terminal switching element, the third electrode is made of a material capable of supplying metal ions at the portion in contact with the ion conductive layer. On the other hand, the first electrode and the second electrode are arranged between the third electrode and the second electrode so that the potential of the third electrode is lower than the potential of the first electrode between the third electrode and the first electrode. In addition, when a voltage is applied so that the potential of the third electrode is lower than the potential of the second electrode, the portion in contact with the ion conductive layer is supplied with some metal ions from the first electrode and the second electrode itself. Consists of a material that does not occur.

  In the above-described three-terminal switching element, a metal of the same metal type as the metal ions is preliminarily dispersed in the ion conductive layer, and the dispersion concentration of the metal is an oxidation constituent that constitutes the ion conductive layer. It is preferable to select within a range that does not exceed the solid solubility limit of the metal in the ion conductive material containing the product. In particular, the dispersion concentration of the metal is most preferably the solid solubility limit of the metal in an ion conductive material containing an oxide. That is, in order to fully exhibit the effects of the present invention, it is desirable that the dispersion concentration of the metal be higher in a range not exceeding the solid solubility limit of the metal, and therefore the upper limit is the solid solution of the metal. Degree limit. At least, the dispersion concentration of the metal is preferably 20% or more, usually 50% or more, with the solid solubility limit of the metal being 100%.

  On the other hand, as will be described later, the dispersion concentration of the metal may show a distribution in the film thickness direction in the ion conductive layer by means of dispersing the metal in the ion conductive material containing the oxide. When the metal dispersion concentration shows a distribution in the ion conductive layer, it is more preferable that the metal dispersion concentration (maximum value) in the region showing the concentration maximum be the solid solubility limit. When the concentration of the metal dispersed in the ion conductive layer exceeds the solid solubility limit, the portion exceeding the solid solubility limit precipitates and locally forms metal aggregates. When the distribution density of the locally formed metal aggregate is unnecessarily high, an increase in leakage current via the metal aggregate is caused. Therefore, although formation of local metal aggregates is suppressed, it is desirable that the metal dispersion concentration be in a state where the solid solubility limit is almost reached.

  On the other hand, the process of manufacturing the two-terminal switching element of the first embodiment may include at least the following processes (i) to (iv), for example.

(I): forming the second electrode on the underlayer;
(Ii): forming the ion conductive layer on the second electrode;
(iii): A metal of the same metal species as the metal ions is dispersed in the ion conductive layer in advance;
(Iv): forming the first electrode on an ion conductive layer in which the metal is dispersed in advance;

During the process of manufacturing the two-terminal switching element of the first embodiment, for example,
The step of predispersing a metal of the same metal species as the metal ions in the ion conductive layer,
This can be done by ion implanting the metal into the ion conducting layer.

  Alternatively, the step can be performed by thermally diffusing the metal into the ion conductive layer. Alternatively, the step can be performed by light diffusing the metal into the ion conductive layer.

  Moreover, the process of manufacturing said 3 terminal switching element of a 2nd form shall include the following process (i)-(v) at least, for example.

(I): forming the first electrode on the underlayer;
(Ii): forming the ion conductive layer on the first electrode;
(iii): A metal of the same metal species as the metal ions is dispersed in the ion conductive layer in advance;
(Iv): forming the second electrode on an ion conductive layer in which the metal is previously dispersed.
(V): forming the third electrode on the ion conductive layer at a position where direct electrical contact with the second electrode is not achieved.

During the process of manufacturing the three-terminal switching element of the second embodiment, for example,
The step of predispersing a metal of the same metal species as the metal ions in the ion conductive layer,
This can be done by ion implanting the metal into the ion conducting layer.

  Alternatively, the step can be performed by thermally diffusing the metal into the ion conductive layer. Alternatively, the step can be performed by light diffusing the metal into the ion conductive layer.

  The switching element according to the present invention can be used for a switch used for the rewriting operation in a rewritable logic integrated circuit. For example, a rewritable logic integrated circuit using the above-described two-terminal switching element of the first form or the three-terminal switching element of the second form as a switch can be provided.

(Embodiment 1)
A configuration of the two-terminal switch according to the first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing an example of the configuration of the two-terminal switch element according to the first exemplary embodiment of the present invention.

  The two-terminal switching element shown in FIG. 1 includes a first electrode 11, an ion conductive layer 13 in which a metal 14 is dispersed, and a second electrode 12 provided via the ion conductive layer 13. When a voltage is applied between the first electrode 11 and the second electrode 12, the ion conductive layer 13 serves as a medium for conducting metal ions. When the voltage is applied between the first electrode 11 and the second electrode 12 so that the potential of the second electrode is higher than that of the first electrode 11, the second electrode has a metal in the ion conductive layer 13. It is made of a material capable of supplying ions. On the other hand, when a voltage is applied between the first electrode 11 and the second electrode 12 so that the potential of the second electrode is lower than that of the first electrode 11, the first electrode 11 It is desirable that the material 11 is made of a material that does not supply metal ions from itself. The metal 14 is desirably the same metal species as the metal ions supplied from the second electrode into the ion conductive layer 13.

  The metal 14 is dispersed in the ion conductive layer 13 by thermal diffusion, light diffusion, or ion implantation. It is preferable that the dispersion concentration of the metal 14 in the ion conductive layer 13 is as high as possible. When the solid solubility limit of the metal in the material constituting the ion conductive layer 13 is exceeded, the amount exceeding the solid solubility limit aggregates with each other in the ion conductive layer 13 to form a metal lump. Considering this point, it is preferable that the dispersion concentration of the metal 14 in the ion conductive layer 13 is as high as possible within a range not exceeding the solid solubility limit.

  On the other hand, due to the dispersion of the metal 14 in the ion conductive layer 13, the leakage current between the first electrode 11 and the second electrode 12 via the ion conductive layer 13 in the “off state” increases more than necessary. There is also a case where it ends up. Therefore, it is necessary to adjust the demerit of an increase in leakage current and the effect (merit) of the present invention, and to select the dispersion concentration of the metal 14 in the ion conductive layer 13.

  A driving method of the two-terminal switch according to the first embodiment of the present invention will be described with reference to FIG.

  In the two-terminal switch according to the first embodiment shown in FIG. 2, the second electrode 22 is made of a conductive material containing the same metal as the metal 24 dispersed in the ion conductive layer 23.

  When the first electrode 21 is grounded and a positive voltage is applied to the second electrode 22, the metal of the second electrode 22 becomes metal ions 26 and dissolves in the ion conductive layer 23. Along with this, at least a part of the metal 24 dispersed in the ion conductive layer 23 also becomes the metal ions 26. Then, the metal ions 26 in the ion conductive layer 23 are reduced to a metal and deposited by electrons supplied from the surface of the first electrode 21. A metal bridge 25 is formed from the surface of the first electrode 21 by the deposited metal. The first electrode 21 and the second electrode 22 are connected by a metal bridge 25 formed by the deposited metal. The first electrode 21 and the second electrode 22 are electrically connected by the conduction path through the metal bridge 25, so that the two-terminal switch is turned on.

  On the other hand, when the first electrode 21 is grounded and a negative voltage is applied to the second electrode 22 with respect to the two-terminal switch transitioned to the “ON state”, the metal constituting the metal bridge 25 is ion-conductive layer. 23 is dissolved as metal ions 26. As this dissolution proceeds, a part of the metal bridge 25 that connects the first electrode 21 and the second electrode 22 is cut. At that time, the concentration of the metal ions 26 contained in the ion conductive layer 23 locally shows a transient increase due to dissolution of the metal constituting the metal bridge 25. Thereafter, surplus metal ions 26 are reduced to a metal and recovered by being deposited as a metal 24 dispersed in the ion conductive layer 23 or as a metal deposited on the surface of the second electrode 22. Through this process, the electrical connection between the first electrode 21 and the second electrode 22 is broken, and the two-terminal switch is turned off.

  After the transition to the “off state”, in order to perform “switching” for transition from the “off state” to the “on state” again, the first electrode 21 is grounded again and the second electrode 22 is positively connected. A voltage may be applied.

  Note that the transition from the “off state” to the “on state” indicates that the voltage between the first electrode 21 and the second electrode 22 is such that the potential of the second electrode 22 is higher than that of the first electrode 21. Occurs by applying. Accordingly, the second electrode 22 may be grounded, a negative voltage may be applied to the first electrode 21, and the two-terminal switch may be changed to the “on state”. The transition from the “on state” to the “off state” is a voltage between the first electrode 21 and the second electrode 22 such that the potential of the second electrode 22 is lower than that of the first electrode 21. Occurs by applying. Therefore, the second electrode 22 may be grounded, a positive voltage may be applied to the first electrode 21, and the two-terminal switch may transition to the “ON state”.

  In the process in which the two-terminal switch is changed from the “on state” to the “off state”, the metal constituting the metal bridge 25 is dissolved as the metal ion 26 in the ion conductive layer 23, so that the electrical connection is established. The resistance between the first electrode 21 and the second electrode 22 increases from the stage before it is completely cut. At the same time, the interelectrode capacitance between the first electrode 21 and the second electrode 22 changes. Due to such a change in electrical characteristics, the electrical connection is eventually broken.

  FIG. 3 is a graph showing changes in electrical characteristics with respect to the operation of a two-terminal switch having a conventional structure (FIG. 4) using an ion conductive layer in which metal is not dispersed.

  When the first electrode 41 is grounded and a positive voltage is applied to the second electrode 42, the switch changes from “OFF state” (high resistance state) to “ON state” (low resistance state) at 2.6V. (A shown in FIG. 3). At this time, the current flowing through the two-terminal switching element is limited so that the upper limit is 1 milliampere. Next, when the first electrode 41 is grounded and a negative voltage is applied to the second electrode 42, the current decreases at 0.4 V and transitions to an “off state” (B shown in FIG. 3). At this time, the current flowing through the two-terminal switching element is controlled so that the upper limit is 50 milliamperes. Next, when the first electrode 41 is grounded again and a positive voltage is applied to the second electrode 42, the state transits to the “on state” again at 1.4 V (A ′ shown in FIG. 3). Therefore, the applied voltage that causes the second transition to the “on state” is different from the applied voltage that causes the first transition to the “on state”.

  After the second transition to the “on state”, the first electrode 41 is grounded and a negative voltage or a positive voltage is applied to the second electrode 42, so that the “on state” and the “off state” are changed. Transitions can be made alternately. At the time of the switching, in the second and subsequent switching operations, the applied voltage that causes the transition to the “on state” is the same applied voltage as the second transition to the “on state”. In the two-terminal switch according to the first embodiment of the present invention shown in FIG. 1, metal ions are supplied from the second electrode 12 to the ion conductive layer 13 in the process of the first transition to the “on state”. Since the metal ions are also supplied from the metal 14 dispersed in the ion conductive layer 13 in advance, the applied voltage causing the transition to the “on state” is compared with the two-terminal switch having the conventional structure shown in FIG. Thus, the applied voltage becomes remarkably low. When the dispersion concentration of the metal 14 previously dispersed in the ion conductive layer 13 is sufficiently high, the applied voltage at which the first transition to the “on state” occurs is the second voltage in the conventional two-terminal switch. The applied voltage (A ′ shown in FIG. 3) causing the transition to the “on state” after the first time can be made substantially the same value.

  In general, in the conventional two-terminal switch shown in FIG. 4, in the first transition to the “on state”, first, metal deposition starts on the surface of the first electrode 41, and the island-like switch Metal precipitates are formed. As the electric field concentrates on the tip of the island-shaped metal deposit, metal deposition due to reduction of the metal ions selectively proceeds at the tip of the metal deposit. Initially, a plurality of island-like metal deposits are generated, but as the metal deposition progresses to the tip of the metal deposit, the electric field is further concentrated on the tip growing faster. As a result, finally, the tip portion of one metal precipitate is overwhelmed with the other and is extended by metal deposition. Due to this phenomenon, in principle, only one metal bridge reaching the second electrode 42 from the first electrode 41 is formed.

  At this time, the ion conductive layer composed of the oxide is microscopically in a state where the oxide particles are aggregated, and the elongation of the metal precipitate proceeds along the grain boundary. Therefore, it is presumed that the entire metal bridge grows in a state where a dendrite (dendritic) structure is formed.

  On the other hand, in the ion conductive layer in which the oxide particles are in an aggregated state, the metal dispersed in the ion conductive layer in advance is also present along the grain boundary in a considerable proportion. In the present invention, when the metal bridge is formed in the first transition to the “on state”, the metal bridge is supplied from the surface of the second electrode and moves toward the first electrode along the grain boundary. In addition to metal ions, it is presumed that the growth of metal bridges showing a dendrite (dendritic) structure proceeds by utilizing a pre-dispersed metal present along the grain boundary.

  As long as the dispersion concentration of the metal dispersed in advance in the ion conductive layer does not reach the solid solubility limit, the dispersed metal exists in a dispersed state along the grain boundaries of the oxide particles. On the other hand, when the solubility limit is exceeded, metal aggregates are locally formed, and the metal existing along the surrounding grain boundaries is used for the formation of these aggregates. As a result, the local density | concentration of the metal which exists along the grain boundary becomes a low area | region around the site | part in which the metal aggregate formation occurred. In order to avoid this phenomenon, it is preferable to keep the dispersion concentration of the metal dispersed in advance in the ion conductive layer within a range not reaching the solid solubility limit.

Example 1
As an example of the best mode of the two-terminal switch according to the first embodiment of the present invention, the two-terminal switching element of the first embodiment and the manufacturing method thereof will be described. A manufacturing process of the two-terminal switching element of Example 1 will be described with reference to FIG.

  [Step 1] A silicon oxide film 56 having a thickness of 300 nm is formed on the surface of the low resistance silicon substrate 55. A platinum film is formed to a thickness of 100 nm on the oxide film by vacuum deposition or sputtering to form the first electrode 51.

[Step 2] As the ion conductive layer 53, tantalum oxide having a thickness of 20 nm is deposited by sputtering. At that time, the composition of tantalum oxide is made as close as possible to the stoichiometric tantalum pentoxide (Ta ₂ O ₅ ). Specifically, the amount of oxygen to be supplied is optimized when sputtering of tantalum oxide is performed. The inventors made tantalum oxide under the film forming conditions of an oxygen flow rate of 0.5 sccm and an oxygen partial pressure of 0.5 Pa, and the composition ratio of oxygen and tantalum (O: Ta atom number ratio) was 2.5. A film is formed.

[Step 3] In the ion conductive layer 53, copper which is a metal used for forming a metal bridge is dispersed. In order to disperse copper into the ion conductive layer 53, a 100 nm thick copper is deposited on the ion conductive layer 53 as a metal supply layer 57 by vacuum deposition or sputtering. Thereafter, copper is thermally diffused from the surface of the tantalum oxide film of the ion conductive layer 53 by heating in a nitrogen atmosphere. The heating temperature is selected to be 600 ° C. or lower at which the crystal state of the formed tantalum oxide film does not change. It is desirable to disperse copper in the ion conductive layer 53 up to 7 × 10 ²⁰ atoms / cm ³ which is the limit of solid solubility of copper in tantalum oxide. The inventors set the concentration of copper dispersed in the 20 nm tantalum oxide film to reach the solid solubility limit of copper in tantalum oxide by heating at 300 ° C. for about 20 minutes. After the metal is dispersed in the ion conductive layer 53 by applying the thermal diffusion method, the metal supply layer 57 is removed by an etching technique.

  [Step 4] The insulating layer 54 is formed of silicon oxide. A silicon oxide film having a thickness of 100 nm is formed on the ion conductive layer 53 by sputtering or CVD. A resist is spin-coated thereon, and the resist is patterned by a lithography technique. After the patterning, the silicon oxide is etched to form the insulating layer 54.

  [Step 5] Copper having a film thickness of 100 nm is deposited on the patterned insulating layer 54 by vacuum vapor deposition or sputtering. A resist is spin-coated thereon, and the resist is patterned by a lithography technique. After the patterning, copper is etched to form the second electrode 52.

  When the thermal diffusion method is applied, the metal is uniformly diffused in the ion conductive layer 53 covered with the metal supply layer 57. As a result, in the produced two-terminal switching element of Example 1, the distribution of the dispersed copper in the in-plane direction is not limited to the region where the second electrode 52 and the ion conductive layer 53 are in contact with each other but the surrounding ions. In the conductive layer 53, dispersed copper is present. Further, the concentration distribution in the film thickness direction of the dispersed ion conduction layer 53 of copper indicates a concentration distribution by thermal diffusion. That is, a concentration distribution is formed in which the dispersion concentration of copper is highest and the concentration gradually decreases in the film thickness direction at the surface side of the ion conductive layer 53 and at the interface where the second electrode 52 and the ion conductive layer 53 are in contact with each other. Has been.

  In the two-terminal switch of Example 1, the first transition to the “on state” is that when the first electrode 51 is grounded and a positive voltage is applied to the second electrode 52, the applied voltage is 1.0 V. Occurs in the range of ~ 1.5V. The second transition to the “on state” occurs when the first electrode 51 is grounded and a positive voltage is applied to the second electrode 52, and the applied voltage is in the range of 1.0V to 1.5V. The applied voltage at which the transition to the “on state” after the second time occurs is in the range of 1.0 V to 1.5 V.

(Example 2)
As another example of the best embodiment of the two-terminal switch according to Embodiment 1 of the present invention, a two-terminal switching element of Example 2 and a manufacturing method thereof will be described. A manufacturing process of the two-terminal switching element according to the second embodiment will be described with reference to FIG.

  In the two-terminal switching element of the second embodiment, the light diffusion method is applied in step 3 in which copper, which is a metal used for forming a metal bridge, is dispersed in the ion conductive layer 53. The other steps are the same as the manufacturing steps shown in the first embodiment. Step 3 of applying this light diffusion method will be described in detail.

[Step 3] In order to disperse copper into the ion conductive layer 53, copper is deposited as a metal supply layer 57 on the ion conductive layer 53 by vacuum deposition or sputtering to a thickness of 100 nm. Thereafter, light having an energy larger than the optical gap of tantalum oxide (for example, a wavelength of less than 500 nanometers) is irradiated. It is desirable to disperse copper in the ion conductive layer 53 to which this light diffusion method is applied up to 7 × 10 ²⁰ atoms / cm ^3, which is the solid solubility limit of copper in tantalum oxide. For example, when using light having a wavelength λ = 436 nm, the light intensity to be irradiated is selected to be 6.3 MW / cm ² , and the irradiation time is selected to be 10 minutes. After the metal is dispersed in the ion conductive layer 53 by applying the light diffusion method, the metal supply layer 57 is removed by an etching technique.

  Note that the temperature of the low-resistance silicon substrate 55 is adjusted to room temperature (25 ° C.) when the tantalum oxide film is irradiated with light. The light irradiation itself is performed from the side of the metal supply layer 57 formed on the surface of the tantalum oxide film. As a result, the local temperature of the site irradiated with light has increased. However, as described above, by adjusting the temperature of the low resistance silicon substrate 55, this local temperature rise is 600 ° C. or less, particularly 300 ° C. or less, in which the crystal state of the formed tantalum oxide film does not change. Is suppressed.

  When this light diffusion method is applied, selective diffusion of metal is caused only in a region to which light irradiation is applied in the ion conductive layer 53 covered with the metal supply layer 57. As a result, in the two-terminal switching element of Example 2 to be manufactured, the distribution in the in-plane direction of the dispersed copper is a uniform distribution in the region where the light irradiation is performed, but the surrounding area is made of copper. The dispersion concentration rapidly decreases. Therefore, when the region where the second electrode 52 and the ion conductive layer 53 are in contact with the region where the light irradiation is performed, the distribution of the dispersed copper in the in-plane direction is the same as the second electrode 52 and the ion conductive layer. The area where the layer 53 is in contact is selectively and uniformly dispersed with copper, and the periphery thereof has a shape in which the copper dispersion concentration rapidly decreases. Further, in the region where the light irradiation is performed, the concentration distribution in the film thickness direction of the dispersed ion conduction layer 53 of copper shows a concentration distribution by light diffusion. That is, a concentration distribution is formed in which the dispersion concentration of copper is highest and the concentration gradually decreases in the film thickness direction at the surface side of the ion conductive layer 53 and at the interface where the second electrode 52 and the ion conductive layer 53 are in contact with each other. Has been.

  In the two-terminal switch of Example 2, the first transition to the “ON state” is that when the first electrode 51 is grounded and a positive voltage is applied to the second electrode 52, the applied voltage is 1.0 V. Occurs in the range of ~ 1.5V. The second transition to the “on state” occurs when the first electrode 51 is grounded and a positive voltage is applied to the second electrode 52, and the applied voltage is in the range of 1.0V to 1.5V. The applied voltage at which the transition to the “on state” after the second time occurs is in the range of 1.0 V to 1.5 V.

(Example 3)
As another example of the best embodiment of the two-terminal switch according to Embodiment 1 of the present invention, a two-terminal switching element of Example 3 and a manufacturing method thereof will be described. A manufacturing process of the two-terminal switching element of Example 3 will be described with reference to FIG.

  In the two-terminal switching element of the third embodiment, an ion implantation method is applied in step 3 in which copper, which is a metal used for forming a metal bridge, is dispersed in the ion conductive layer 53. The other steps are the same as the manufacturing steps shown in the first embodiment. Step 3 to which this ion implantation method is applied will be described in detail.

[Step 3] In order to disperse copper into the ion conductive layer 53, copper ions are ion-implanted into the ion conductive layer 53. Ion implantation is performed with an energy of about 10 KeV. The dispersion of copper into the ion conductive layer 53 to which this ion implantation method is applied is desirably performed up to 7 × 10 ²⁰ atoms / cm ^3, which is the solid solubility limit of copper in tantalum oxide. For example, the acceleration energy of the implanted copper ions is selected to be 10 keV, the implantation angle is set to 7 °, and the implantation amount is set to 2 × 10 ¹³ atoms / cm ² .

  When this ion implantation method is applied, selective metal dispersion is performed only in a region where ion implantation is performed in the ion conductive layer 53. As a result, in the manufactured two-terminal switching element of Example 3, the distribution in the in-plane direction of the dispersed copper is a uniform distribution in the region where the ion implantation is performed, but the periphery thereof is made of copper. The dispersion concentration rapidly decreases. Therefore, when the region where the second electrode 52 and the ion conductive layer 53 are in contact with the region where the ion implantation is performed, the distribution of the dispersed copper in the in-plane direction is the same as the second electrode 52 and the ion conductive layer. The area where the layer 53 is in contact is selectively and uniformly dispersed with copper, and the periphery thereof has a shape in which the copper dispersion concentration rapidly decreases. Further, in the region where the ion implantation is performed, the concentration distribution of the dispersed copper ion conduction layer 53 in the film thickness direction is a distribution showing a concentration peak depending on the acceleration energy of ions. That is, a concentration peak depending on the acceleration energy of ions exists in the ion conductive layer 53, and the copper side of the surface of the ion conductive layer 53, the interface where the second electrode 52 and the ion conductive layer 53 are in contact with each other The dispersion concentration is lower than the peak concentration. When the concentration peak is exceeded, a concentration distribution is formed in which the concentration decreases rapidly as the film thickness increases.

  In the two-terminal switch of Example 3, the first transition to the “on state” is that when the first electrode 51 is grounded and a positive voltage is applied to the second electrode 52, the applied voltage is 1.0 V. Occurs in the range of ~ 1.5V. The second transition to the “on state” occurs when the first electrode 51 is grounded and a positive voltage is applied to the second electrode 52, and the applied voltage is in the range of 1.0V to 1.5V. The applied voltage at which the transition to the “on state” after the second time occurs is in the range of 1.0 V to 1.5 V.

Example 4
As an example of the best mode of the two-terminal switch according to the first embodiment of the present invention, a two-terminal switching element of Example 4 and a manufacturing method thereof will be described. The manufacturing process of the two-terminal switching element of Example 4 will be described with reference to FIG. In the fourth embodiment, the two-terminal switching element is configured as a switching element provided between two wirings in a semiconductor integrated circuit. In particular, a two-terminal switching element is formed in a multilayer wiring layer structure used for the configuration of a semiconductor integrated circuit.

  [Step 1] A substrate 61 including a semiconductor element or the like formed using a conventional technique on a silicon substrate is prepared. Thereafter, a first protective insulating film 62, a first interlayer insulating film 63, and a first stop insulating film 64 are formed.

  [Step 2] An opening to be a wiring is formed by using a photolithography technique and an etching technique. Sputtering of the first barrier metal 65 and a copper seed layer that becomes a part of copper is performed on the formed opening. The thickness of the copper seed layer may be about 20 to 100 nm. Copper plating is performed on the sputter deposited film as described above. The thickness of the copper to be plated may be about 300 to 800 nm. The unnecessary first barrier metal 65 and copper outside the opening of the first interlayer insulating film 63 and the stop insulating film 64 are scraped off by a technique such as chemical mechanical polishing (CMP, chemical / mechanical polishing). As a result, the first wiring layer 66 in which the first barrier metal 65 and copper are embedded in the first protective insulating film 62, the first interlayer insulating film 63, and the first stop insulating film 64 is completed.

  [Step 3] Tantalum 50 nm, tantalum oxide 20 nm, and copper 50 nm are sputtered on the first wiring layer 66, the first barrier metal 65, and the first stop insulating film 64, and the first electrodes are respectively formed by a general lithography technique. 65, the ion conductive layer 66, and the metal supply layer 67 are processed. Thereafter, heating is performed at 300 ° C. for 20 minutes in a nitrogen atmosphere, and copper is thermally diffused from the metal supply layer 67 covering the ion conductive layer 66 into the ion conductive layer 66. After the heating, the metal supply layer 67 is removed by an etching technique. As a result, copper is dispersed in the ion conductive layer 66 by the thermal diffusion treatment.

  [Step 4] On the ion conductive layer 66 in which the copper is dispersed, copper is again sputtered by 50 nm and processed by a lithography technique to form the second electrode 68. A second protective insulating film 69, a second interlayer insulating film 70, a third protective insulating film 71, a third interlayer insulating film 72, and a second stop insulating film are formed on the second electrode 68 and the first stop film 64.

  [Step 5] Connection of the second electrode 69 of the two-terminal switching element and the second wiring layer to the insulating layer composed of the third protective insulating film 71, the third interlayer insulating film 72, and the second stop insulating film 73 An opening is formed that is used to form a wiring via. The opening (connection hole 74) may be formed by general lithography. For example, a photoresist is formed on the second stop insulating film and patterned by optical exposure. An opening can be formed by etching through the resist pattern. For example, in the 90 nm generation lithography technology, the diameter of the opening is about 80 to 200 nm.

  [Step 6] In the insulating layer formed of the third protective insulating film 71, the third interlayer insulating film 72, and the second stop insulating film 73, a wiring groove used for manufacturing the via wiring and the second wiring layer of the two-terminal switching element 75 is formed. The formation of the wiring groove 75 is performed by the same technique as the formation of the connection hole 74. When the wiring trench 75 is formed, the connection hole 74 (opening) formed in step 5 is transferred to the insulating layer composed of the second interlayer insulating film 70 and the second protective insulating film 69, and becomes a wiring via.

  [Step 7] Sputtering of the second barrier metal 76 and the copper seed layer that becomes a part of copper is performed. The thickness of the copper seed layer may be about 20 to 100 nm. Next, copper plating is performed on the sputter deposited film. The thickness of the copper to be plated may be about 300 to 800 nm. The unnecessary second barrier metal 76 and copper other than the connection groove 74 (wiring via) and the wiring groove 75 on the second stop insulating film 73 are formed by a method such as chemical mechanical polishing (CMP, chemical / mechanical polishing). Scrape off. A second wiring layer 77 other than the two-terminal switching element and the wiring connected to the switching element is formed, and an upper layer wiring 78 is formed on the second wiring layer.

  The first protective insulating film 62, the second protective insulating film 69, and the third protective insulating film 71 are made of, for example, silicon nitride (SiN) or a material in which an arbitrary amount of carbon is mixed (SiNC). It is preferable to use a material that suppresses the diffusion of copper into the oxide film.

  On the other hand, each of the first interlayer insulating film 63, the second interlayer insulating film 70, and the third interlayer insulating film 72 is a compound of silicon and oxygen, and has a low dielectric constant added with any amount of hydrogen, fluorine, and carbon. An insulating film is preferred. It is known that a dielectric constant can be further reduced in a film including a void in an insulating film. The size of “holes” formed in the interlayer insulating film is preferably 2 nanometers or less.

  The first stop insulating film 64 and the second stop insulating film 73 may be silicon oxide films, and may have a thickness of about 50 to 200 nanometers. Each insulating film can be formed by a conventional sputtering method or a CVD method. The first barrier metal 65 and the second barrier metal 76 may be, for example, a laminated structure of tantalum nitride (TaN) and tantalum (Ta), and are formed so as to cover the bottom surface and the side wall of the opened opening. The first barrier metal 65 serves to prevent copper in the first wiring from diffusing into the first interlayer insulating film 63. The second barrier metal 76 serves to prevent the copper of the second wiring from diffusing into the second interlayer insulating film 70 and the third interlayer insulating film 72. The film thickness of tantalum nitride (TaN) and tantalum may be about 5 to 30 nm.

  In the two-terminal switching element of the fourth embodiment, since the thermal diffusion method is applied, metal diffusion is uniformly caused in the ion conductive layer 66 portion covered with the metal supply layer 67. As a result, in the two-terminal switching device of Example 4 to be manufactured, the distribution in the in-plane direction of the dispersed copper is in the ion conductive layer 53 in the entire region where the second electrode 68 and the ion conductive layer 53 are in contact. The copper dispersed in is uniformly present. In addition, the concentration distribution in the film thickness direction of the dispersed ion conduction layer 66 of copper indicates a concentration distribution by thermal diffusion. That is, a concentration distribution in which the copper dispersion concentration is the highest and the concentration gradually decreases in the film thickness direction at the surface side of the ion conductive layer 66 and the interface where the second electrode 68 and the ion conductive layer 66 are in contact is formed. Has been.

  In the two-terminal switch of Example 4, the first transition to the “on state” is that when the first electrode 65 is grounded and a positive voltage is applied to the second electrode 68, the applied voltage is 1.0 V. Occurs in the range of ~ 1.5V. The second transition to the “on state” occurs when the first electrode 65 is grounded and a positive voltage is applied to the second electrode 68, and the applied voltage is in the range of 1.0V to 1.5V. The applied voltage at which the transition to the “on state” after the second time occurs is in the range of 1.0 V to 1.5 V.

(Embodiment 2)
The configuration of the three-terminal switch according to the second embodiment of the present invention will be described. FIG. 7 is a cross-sectional view schematically showing an example of the configuration of the three-terminal switch according to the second embodiment of the present invention.

  The three-terminal switch shown in FIG. 7 includes a second electrode 82 and a first electrode 81 and a third electrode 83 provided via an ion conductive layer 84 in which the second electrode 82 and the metal 85 are dispersed. . The first electrode 81 and the second electrode 82 are formed of a metal that does not supply metal ions, and the third electrode 83 is formed of a metal that supplies metal ions. The metal 85 is desirably the same metal as the metal material used for forming the third electrode 83 and supplying metal ions. The ion conductive layer 84 serves as a medium for conducting metal ions.

  The metal 85 is dispersed in the ion conductive layer 84 by thermal diffusion, light diffusion, or ion implantation. It is preferable that the dispersion concentration of the metal 85 in the ion conductive layer 84 is as high as possible. When the solid solubility limit of the metal in the material constituting the ion conductive layer 84 is exceeded, the amount exceeding the solid solubility limit aggregates with each other in the ion conductive layer 84 to form a metal lump. Considering this point, it is preferable that the dispersion concentration of the metal 85 in the ion conductive layer 84 is as high as possible within a range not exceeding the solid solubility limit.

  On the other hand, due to the dispersion of the metal 85 in the ion conductive layer 84, the leakage current between the first electrode 81 and the second electrode 82 via the ion conductive layer 84 in the “off state” increases more than necessary. There is also a case where it ends up. Therefore, it is necessary to adjust the demerit of an increase in leakage current and the effect (merit) of the present invention, and to select the dispersion concentration of the metal 65 in the ion conductive layer 84.

  A driving method of the three-terminal switch according to the second embodiment of the present invention will be described with reference to FIG.

  In the three-terminal switch according to the second embodiment shown in FIG. 8, the third electrode 93 is made of the same metal material as the metal 95 dispersed in the ion conductive layer 94.

  When the first electrode 91 and the second electrode 92 are grounded and a positive voltage is applied to the third electrode 93, the metal of the third electrode 93 becomes metal ions 96 and dissolves in the ion conductive layer 94. Along with this, at least a part of the metal 95 dispersed in the ion conductive layer 94 also becomes the metal ions 96. Then, the metal ions 96 in the ion conductive layer 95 are reduced to metal and deposited by electrons supplied from the surface of the first electrode 91 and the surface of the second electrode 91. By the deposited metal, metal bridges 97 are formed from the surface of the first electrode 91 and the surface of the second electrode 91, respectively. The first electrode 91 and the second electrode 92 are connected by the metal bridge 97 formed by the deposited metal. The first electrode 91 and the second electrode 92 are electrically connected by the conduction path via the metal bridge 97, so that the three-terminal switch is turned on.

  On the other hand, when the first electrode 91 and the second electrode 92 are grounded and a negative voltage is applied to the third electrode 93 with respect to the three-terminal switch that has transitioned to the “on state”, a metal bridge 97 is formed. The metal dissolves in the ion conductive layer 94 as metal ions 96. As this dissolution proceeds, a part of the metal bridge 97 that connected the first electrode 91 and the second electrode 92 is cut. At this time, the concentration of the metal ions 96 contained in the ion conductive layer 94 locally shows a transient increase due to dissolution of the metal constituting the metal bridge 97. Thereafter, surplus metal ions 96 are reduced to a metal and recovered by being deposited as a metal 95 dispersed in the ion conductive layer 94 or as a metal deposited on the surface of the third electrode 93. Through this process, the first electrode 91 and the second electrode 92 are disconnected from each other, and the three-terminal switch is turned off.

  After the transition to the “off state”, in order to perform “switching” for transition from the “off state” to the “on state” again, the first electrode 91 and the second electrode 92 are grounded again, A positive voltage may be applied to the three electrodes 93.

  The transition from the “off state” to the “on state” causes the third electrode 93 and the first electrode so that the potential of the third electrode 93 is higher than that of the first electrode 91 and the second electrode 92. This is caused by applying a voltage between 91 and the second electrode 92. Therefore, the third electrode 93 may be grounded, a negative voltage may be applied to the first electrode 91 and the second electrode 92, and the three-terminal switch may transition to the “on state”. Further, the transition from the “on state” to the “off state” causes the third electrode 93 and the first electrode so that the potential of the third electrode 93 is lower than that of the first electrode 91 and the second electrode 92. This is caused by applying a voltage between 91 and the second electrode 92. Therefore, the third electrode 93 may be grounded, a positive voltage may be applied to the first electrode 91 and the second electrode 92, and the three-terminal switch may transition to the “on state”.

  In the configuration example shown in FIG. 7, the first electrode 91 and the second electrode 92 are in contact with the ion conductive layer 94 on one surface of the conductor layer constituting the electrode. As described above, in the three-terminal switch according to the second embodiment of the present invention, the first electrode 91 and the second electrode 92 are not entirely in contact with the ion conductive layer 94 but on the outer surface of the electrode. Among them, a part of the surface can be in contact with the ion conductive layer 94. In that case, it is not necessary that all of the outer surfaces of the first electrode 91 and the second electrode 92 be made of a material that does not supply metal ions, and at least the surface portion that is in contact with the ion conductive layer 94 supplies metal ions. Any material can be used. For example, in the configuration example shown in FIG. 7, the upper surface of the first electrode 91 and the lower surface of the second electrode 92 that are in contact with the ion conductive layer 94 are made of a material that does not supply metal ions, while the ion conductive layer It is also possible to select a form in which the lower surface of the first electrode 91 and the upper surface of the second electrode 92 that do not come in contact with 94 are made of a material that supplies metal ions.

(Example 5)
As an example of the best mode of the three-terminal switch according to the second embodiment of the present invention, a three-terminal switching element of Example 5 and a manufacturing method thereof will be described. A manufacturing process of the three-terminal switching element according to the fifth embodiment will be described with reference to FIG.

  [Step 1] A silicon oxide film 107 having a thickness of 300 nm is formed on the surface of the low resistance silicon substrate 106. A platinum film with a thickness of 100 nm is formed on the oxide film by vacuum deposition or sputtering to form the first electrode 101.

[Step 2] As the ion conductive layer 104, tantalum oxide having a thickness of 20 nm is deposited by sputtering. At that time, the composition of tantalum oxide is made as close as possible to the stoichiometric tantalum pentoxide (Ta ₂ O ₅ ). Specifically, the amount of oxygen to be supplied is optimized when sputtering of tantalum oxide is performed. The inventors made tantalum oxide under the film forming conditions of an oxygen flow rate of 0.5 sccm and an oxygen partial pressure of 0.5 Pa, and the composition ratio of oxygen and tantalum (O: Ta atom number ratio) was 2.5. A film is formed.

[Step 3] In the ion conductive layer 104, copper which is a metal used for forming a metal bridge is dispersed. In order to disperse copper into the ion conductive layer 104, copper is deposited as a metal supply layer 108 on the ion conductive layer 104 by vacuum deposition or sputtering to a thickness of 100 nm. Thereafter, copper is thermally diffused from the surface of the tantalum oxide film of the ion conductive layer 104 by heating in a nitrogen atmosphere. The heating temperature is selected to be 600 ° C. or lower at which the crystal state of the formed tantalum oxide film does not change. It is desirable to disperse copper in the ion conductive layer 104 up to 7 × 10 ²⁰ atoms / cm ^3, which is the limit of solid solubility of copper in tantalum oxide. The inventors set the concentration of copper dispersed in the 20 nm tantalum oxide film to reach the solid solubility limit of copper in tantalum oxide by heating at 300 ° C. for about 20 minutes. After the metal is dispersed in the ion conductive layer 104 by applying the thermal diffusion method, the metal supply layer 108 is removed by an etching technique.

  [Step 4] An insulating layer 105 is formed of silicon oxide on a part of the ion conductive layer 104. On the ion conductive layer 104 (tantalum oxide film), 100 nm of silicon oxide is formed by sputtering. A resist is spin-coated thereon, and the resist is patterned by a lithography technique. After patterning, the silicon oxide is etched to form the insulating layer 105.

  [Step 5] Platinum having a thickness of 100 nm is deposited on the patterned insulating layer 105 and on the ion conductive layer 104 not covered with the insulating layer 105 by vacuum deposition or sputtering. A resist is spin-coated thereon, and the resist is patterned by a lithography technique. After the patterning, the second electrode 102 is formed by dry etching of platinum. In dry etching of platinum, a mixed gas of chlorine, oxygen and argon is used as an etching gas.

  [Step 6] Copper having a film thickness of 100 nm is deposited on the patterned insulating layer 105, the ion conductive layer 104 not covered with the insulating layer 105, and the second electrode 102 by vacuum evaporation or sputtering. A resist is spin-coated thereon, and the resist is patterned by a lithography technique. After the patterning, the third electrode 103 is formed by etching copper.

  In the three-terminal switching element of the fifth embodiment, since the thermal diffusion method is applied, metal diffusion is uniformly caused in the ion conductive layer 104 portion covered with the metal supply layer 108. As a result, in the manufactured three-terminal switching element of Example 5, the distribution of the dispersed copper in the in-plane direction is a region where the third electrode 103 and the ion conductive layer 104 are in contact with each other, and the second electrode 102 and the ion conductive layer. In all regions including the region in contact with the layer 104, the copper dispersed in the ion conductive layer 104 exists uniformly. Further, the concentration distribution in the film thickness direction of the dispersed ion conduction layer 104 of copper shows a concentration distribution by thermal diffusion. That is, the copper dispersion concentration is highest at the surface side of the ion conductive layer 104, the contact interface between the second electrode 102 and the ion conductive layer 104, and the contact interface between the third electrode 103 and the ion conductive layer 104, and the film thickness A density distribution in which the density gradually decreases in the direction is formed.

  In the three-terminal switch of Example 5, the transition to the “on state” is a state in which a metal bridge is formed between the first electrode 101 and the second electrode 102 and electrical connection is achieved. Of course, a metal bridge connecting the first electrode 101 and the second electrode 102 is formed, but no metal bridge is formed between the first electrode 101 and the third electrode 103.

  The switching element of the present invention can be used as a switching element used for changing a wiring path in a programmable logic circuit.

It is sectional drawing which shows typically an example of a structure of the 2 terminal switching element concerning Embodiment 1 of this invention. It is sectional drawing which shows typically the function of the metal currently disperse | distributed in the ion conductive layer at the time of switching operation | movement of the 2 terminal switching element concerning Embodiment 1 of this invention. It is a graph which shows an example of the switching characteristic of the 2 terminal switching element of the conventional structure, and shows the difference in switching voltage in the transition to the "on state" for the first time and the transition to the "on state" for the second time and thereafter. It is a graph. It is sectional drawing which shows typically the structure of the 2 terminal switching element of a conventional structure. 3 is a cross-sectional view schematically showing a manufacturing process of the two-terminal switching element of Example 1. It is a cross section which shows typically the first half process 1-process 4 in the manufacturing process of the 2 terminal switching element of Example 2. FIG. It is a cross section which shows typically the latter half process 5-process 8 in the manufacturing process of the 2 terminal switching element of Example 2. FIG. It is sectional drawing which shows typically an example of a structure of the 3 terminal switching element concerning Embodiment 2 of this invention. It is sectional drawing which shows typically the function of the metal currently disperse | distributed in the ion conduction layer at the time of switching operation | movement of the 3 terminal switching element concerning Embodiment 1 of this invention. 10 is a cross section schematically showing a manufacturing process of a two-terminal switching element of Example 5.

Explanation of symbols

11, 21, 41, 51, 65, 81, 91, 101 First electrode 12, 22, 42, 52, 68, 82, 92, 102 Second electrode 83, 93, 103 Third electrode 13, 23, 43, 53, 66, 84, 94, 104 Ion conductive layer 54, 105 Insulating layer 14, 24, 85, 95 Metal 26, 96 Metal ion 24, 97 Metal bridge 57, 67, 108 Metal supply layer 56, 107 Silicon oxide film 55 106 low resistance silicon substrate 61 substrate 62 first protective insulating film 63 first interlayer insulating film 64 first stop insulating film 65 first barrier metal 66 first wiring layer 69 second protective insulating film 70 second interlayer insulating film 71 first 3 protective insulating film 72 third interlayer insulating film 73 second stop insulating film 74 connection groove 75 wiring groove 76 second barrier metal 77 second wiring layer 78 upper layer wiring

Claims (10)

A two-terminal switching element using an electrochemical reaction, comprising a first electrode, a second electrode, and an ion conductive layer containing an oxide sandwiched between the first electrode and the second electrode,
The two-terminal switching element is
When applying a voltage between the first electrode and the second electrode so that the potential of the second electrode is higher than the potential of the first electrode,
Metal ions are supplied from the second electrode into the ion conductive layer,
The metal ions in the ion conductive layer receive electrons from the first electrode and precipitate as metals.
Due to the growth of the metal precipitate, a metal bridge reaching the second electrode surface from the first electrode surface is formed,
By adopting a switching operation method in which the resistance between the first electrode and the second electrode is changed by electrically connecting the metal bridge between the first electrode and the second electrode,
A switching element, wherein a metal of the same metal type as the metal ion is dispersed in the ion conductive layer in advance. When applying a voltage between the first electrode and the second electrode so that the potential of the second electrode is higher than the potential of the first electrode,
In addition to supplying metal ions from the second electrode into the ion conductive layer,
The switching element according to claim 1, wherein the metal ions are also supplied from a metal dispersed in advance in the ion conductive layer. The ion conductive layer containing the oxide is
A layer containing at least one oxide selected from the group consisting of tantalum oxide, tungsten oxide, molybdenum oxide, nickel oxide, titanium oxide, aluminum oxide, niobium oxide and silicon oxide;
The switching element according to claim 1. The distribution of the metal previously dispersed in the ion conductive layer is as follows:
The switching element according to claim 1, wherein the metal is distributed in a part of the ion conductive layer. A method for manufacturing a two-terminal switching element according to claim 1, comprising:
The step of predispersing a metal of the same metal species as the metal ions in the ion conductive layer,
A method of manufacturing a switching element, which is performed by ion-implanting the metal into the ion conductive layer. A method for manufacturing a two-terminal switching element according to claim 1, comprising:
The step of predispersing a metal of the same metal species as the metal ions in the ion conductive layer,
A method for manufacturing a switching element, which is carried out by thermally diffusing the metal into the ion conductive layer. A method for manufacturing a two-terminal switching element according to claim 1, comprising:
The step of predispersing a metal of the same metal species as the metal ions in the ion conductive layer,
A method of manufacturing a switching element, which is performed by light diffusing the metal into the ion conductive layer. A rewritable logic integrated circuit using the switching element according to claim 1 as a switch. An ion conducting layer containing an oxide for conducting metal ions;
A first electrode and a second electrode which are provided in contact with the ion conductive layer and covered with a material which does not supply the metal ions at a portion in contact with the ion conductive layer;
A three-terminal switching element using an electrochemical reaction, comprising a third electrode provided in contact with the ion conductive layer and comprising a third electrode comprising a material capable of supplying the metal ions at a portion in contact with the ion conductive layer. There,
The three-terminal switching element is
The potential of the second electrode is between the third electrode and the first electrode so that the potential of the third electrode is higher than the potential of the first electrode, and between the third electrode and the second electrode. When applying a voltage so that the potential of the third electrode becomes higher,
Metal ions are supplied from the third electrode into the ion conductive layer,
The metal ions in the ion conductive layer receive electrons from the first electrode and precipitate as metals.
The metal ions in the ion conductive layer receive electrons from the second electrode and precipitate as metals.
Due to the growth of the metal precipitate, a metal bridge reaching the second electrode surface from the first electrode surface is formed,
By adopting a switching operation method in which the resistance between the first electrode and the second electrode is changed by electrically connecting the metal bridge between the first electrode and the second electrode,
In the ion conductive layer, a metal of the same metal type as the metal ion is dispersed in advance,
The ion conductive layer comprises two surfaces having a front and back relationship with each other,
The third electrode is in contact with only one of the two surfaces of the ion conductive layer;
Either one of the first electrode and the second electrode is in contact with only one of the two surfaces that the ion conductive layer is in contact with the third electrode,
Of the first electrode and the second electrode, the other is in contact with only the other of the two surfaces, which is different from one of the two surfaces with which the third electrode is in contact with the ion conductive layer,
At least a part of the surface of the first electrode in contact with the ion conductive layer and a part of the surface of the second electrode in contact with the ion conductive layer have an arrangement facing each other across the ion conductive layer. A switching element characterized by comprising:   A rewritable logic integrated circuit using the switching element according to claim 9 as a switch.

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