JP2011176211A - Switching element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-terminal switching element composed of a simpler structure and capable of stably performing switching operation. <P>SOLUTION: The switching element 100 includes an insulating substrate 10, a first electrode 20 and a second electrode 30 set on the insulating substrate, an inter-electrode clearance 40 formed between the first electrode and second electrode and having a nanometer order clearance making a switching phenomenon of resistance occur by applying a predetermined voltage between the first electrode and the second electrode, and a sealing member 50 sealing at least the inter-electrode clearance with gaseous oxygen filled in the inter-electrode clearance. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching element using a nanogap electrode.

At present, with the miniaturization and high density of electronic elements, further miniaturization of electric elements is desired, but various electronic elements are approaching the limit of miniaturization. For example, in the case of CMOS, which is the current main memory element, the minimum value of the channel length that exhibits its function is expected to be 6 nm. In order to exceed this limit, various new technology research and development have been promoted.
As an example, an element using two electrodes (nano-gap electrodes) separated by a fine gap and bridging the gap with a functional organic molecule has attracted attention. As this type of device, for example, a device in which catenane-based molecules are arranged in a gap between nanogap electrodes formed using platinum is known (for example, see Non-Patent Document 1). By applying a voltage to the electrode, the catenane molecule undergoes an oxidation-reduction reaction and can perform a switching operation.

  In addition, as a nanogap electrode, an element in which the gap is bridged with nano-particles is also attracting attention. For example, a nanogap electrode is prepared using silver sulfide and platinum, and silver particles are arranged in the gap (see, for example, Non-Patent Document 2). By applying a voltage to the electrodes, an electrochemical reaction takes place and the silver particles expand and contract, whereby the electrodes can be cross-linked and disconnected, and a switching operation is possible.

However, in any of the above switching elements, a special synthetic molecule or a complex metal complex system is required between the nanogap electrodes. In addition, since a chemical reaction is used for the switching operation, there is a problem that the element is likely to be deteriorated.
Therefore, the first and second electrodes are formed on the insulating substrate, and a spatial gap is formed between the electrodes, and the gap is maintained in a reduced pressure state or inert air such as dry air, nitrogen, rare gas, etc. A switching element that seals in a gas atmosphere has also been devised (see, for example, Patent Documents 1 and 2). In addition, such a spatial gap is formed by forming a second electrode by oblique vapor deposition using an end step of the first electrode on an insulating substrate, thereby eliminating the need for a fine processing technique. (For example, see Non-Patent Document 3).

JP 2007-123828 A JP 2008-235816 A

Science, 289 (2000) 1172-1175. Nature, 433 (2005) 47-50. Y. Naitoh, M. Horikawa, H. Abe, and T. Shimizu: Nanotechnology Vol. 17, pp. 5669-5674 (2006)

Each of the switching elements has a characteristic that the resistance value is switched by applying a predetermined voltage, and it is desired to use the switching element as an electronic device such as a nonvolatile memory.
However, the switching element described above has an operating voltage of about 3 V and an operating current of about 1 mA, causing a problem that its power consumption is too high for use as an electronic device.

  Accordingly, an object of the present invention is to provide a switching element in which power consumption is reduced.

  The invention according to claim 1 is provided between the first electrode and the second electrode, the first electrode and the second electrode provided on the insulating substrate, the first electrode and the second electrode, and the first electrode. An interelectrode gap having a gap on the order of nanometers in which a resistance switching phenomenon occurs by applying a predetermined voltage between the electrode and the second electrode, and at least in a state where the gap between the electrodes is filled with gaseous oxygen And a sealing member for sealing the gap between the electrodes.

  The invention described in claim 2 has the same configuration as that of the invention described in claim 1, and is characterized in that the first electrode and the second electrode are formed of gold, platinum, or an alloy thereof.

The invention described in claim 3 has the same configuration as that of the invention described in claim 1 or 2, and the sealing member seals oxygen at a pressure of at least 10 ² [Pa] or more.

  The invention according to claim 4 has the same configuration as that of the invention according to any one of claims 1 to 3, the insulating substrate has a step portion, and the first electrode and the second electrode Is arranged with a level difference due to the step of the step portion, and the inter-electrode gap portion is formed along the height direction of the step portion.

  The invention according to claim 5 has the same configuration as that of the invention according to any one of claims 1 to 3, and the insulating substrate has a hole portion that leads from the first electrode to the second electrode. The inter-electrode gap is formed in the hole, and the sealing member seals the hole.

In the present invention, a predetermined voltage is applied by forming an interelectrode gap having a spatial gap of nanometer order between the first electrode and the second electrode, and enclosing oxygen in the interelectrode gap. Thus, the switching operation in which the resistance value is switched between the electrodes is realized, so that the switching element does not require organic molecules or inorganic particles, and can be configured with a simpler structure.
Further, since the switching element does not include a substance that deteriorates between the electrodes, the switching operation can be stably repeated.
In addition, the switching element has non-volatility, and the operation state of the switching element 100 can be maintained even if there is no external input after the switching operation.

Furthermore, by sealing the interelectrode gap in an oxygen atmosphere with a sealing member, for example, compared to the case where an inert gas such as nitrogen that has been used in the past is sealed, the current voltage in the interelectrode gap is reduced. It is possible to reduce the peak voltage of the characteristic (see FIGS. 7 to 10). Further, since the peak current does not increase as compared with the case of nitrogen filling, the power consumption can be reduced even when the switching element is used as an electronic device.
Moreover, since the peak voltage and the peak current exhibit characteristics that decrease with an increase in the pressure of the oxygen gas to be sealed, the peak voltage and the peak current can be arbitrarily set by appropriately adjusting the oxygen gas pressure. It becomes possible to do.

It is sectional drawing which shows typically the principal part of the switching element illustrated as one Embodiment to which this invention is applied. It is a schematic diagram of the switching element which provided the sealing member in the structure of FIG. It is sectional drawing which shows typically the 1st vapor deposition process in the manufacturing process of the switching element of FIG. It is a principal part expanded sectional view which shows typically the principal part of the switching element of FIG. It is a diagram which shows an example of the current-voltage curve of the switching element which has a nano gap electrode. FIG. 6A shows the correspondence between the voltage applied between the nanogap electrodes of the switching element and the elapsed time, and FIG. 6B shows the correspondence between the current flowing between the nanogap electrodes and the elapsed time. . It is a diagram which shows the current-voltage characteristic at the time of making gas pressure into three steps, 10Pa, 1.5KPa, and 20KPa in oxygen atmosphere. It is a diagram which shows the change of the peak voltage at the time of changing the pressure of oxygen gas in the range to 1.0-10 < ⁵ > Pa. It is a diagram which shows the change of the peak electric current at the time of changing the pressure of oxygen gas in the range to 1.0-10 < ⁵ > Pa. The change of the peak voltage (equivalent to the voltage of the point A in FIG. 5) when the pressure of oxygen gas is changed in the range from 0.1 Pa to 2 × 10 ⁴ Pa for the switching element in which each electrode is formed of gold is shown. FIG. It is a diagram which shows the current-voltage characteristic at the time of making a gas pressure into three steps, 1KPa, 10KPa, and 100KPa about the comparative example with which the inside of the switching element was satisfy | filled with nitrogen gas. It is sectional drawing of the modification 1 of a switching element. It is sectional drawing of the modification 2 of a switching element.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.
Here, FIG. 1 is a cross-sectional view schematically showing a main part of a switching element 100 exemplified as an embodiment to which the present invention is applied. FIG. 2 is a schematic diagram showing an example in which a sealing member 50 is added to the configuration of FIG.

  For example, as shown in FIGS. 1 and 2, the switching element 100 according to the present embodiment includes an insulating substrate 10, and a first electrode 20 and a second electrode 30 provided on the upper surface (one surface) of the insulating substrate 10. An inter-electrode gap 40 provided between the first electrode 20 and the second electrode 30, and a sealing member 50 that seals the electrode forming surface of the insulating substrate 10 with the oxygen gas filled therein. have.

The insulating substrate 10 constitutes a holding body for providing, for example, the two electrodes 20 and 30 of the switching element 100 apart from each other. Further, the insulating substrate 10 is insulated from each of the first electrode 20 and the second electrode 30.
The structure and material of the insulating substrate 10 are not particularly limited. Specifically, for example, the surface shape of the insulating substrate 10 may be a flat surface or may have irregularities. Further, the insulating substrate 10 may be, for example, a substrate in which an oxide film or the like is provided on the surface of a semiconductor substrate such as Si, or the substrate itself may be insulative. Moreover, as a material of the insulating substrate 10, for example, glass, an oxide such as silicon oxide (SiO ₂ ), a nitride such as silicon nitride (Si ₃ N ₄ ), or the like is preferable, and among these, silicon oxide (SiO _2). ) Is preferable in terms of adhesion to the electrodes 20 and 30 described later and a large degree of freedom in manufacturing.

The first electrode 20 is, for example, for performing a switching operation of the switching element 100 in a pair with the second electrode 30.
The shape of the first electrode 20 is not particularly limited, and can be arbitrarily changed as appropriate.
The material of the first electrode 20 is not particularly limited. However, since the switching element is filled with an oxygen atmosphere as will be described later, a material that does not easily oxidize, such as gold, silver, platinum, copper, and the like. Is preferably at least one selected from those having a small value or an alloy thereof, particularly preferably gold or platinum. Here, in order to reinforce the adhesiveness with the insulating substrate 10, for example, two or more layers of different metals may be used. 1 and 2, the first electrode 20 is shown as a combination of the first electrode lower portion 21 and the first electrode upper portion 22 for convenience of description of the process described later.

For example, the second electrode 30 is paired with the first electrode 20 to enable the switching operation of the switching element 100.
The shape of the 2nd electrode 30 is not specifically limited, It can change arbitrarily arbitrarily.
The material of the second electrode 30 is not particularly limited. As will be described later, the switching element is filled with an oxygen atmosphere so that the material is not easily oxidized, such as gold, silver, platinum, copper, and the like. It is preferable to use at least one selected from those having a small tendency or an alloy thereof, and it is particularly preferable to use gold or platinum. Here, in order to reinforce the adhesiveness with the insulating substrate 10, for example, two or more layers of different metals may be used.

The interelectrode gap 40 has, for example, a gap of nanometer order between the first electrode 20 and the second electrode 30, and has a role of expressing a switching phenomenon described later of the switching element 100.
The distance (interval) G between the first electrode 20 and the second electrode 30 (between nanogap electrodes) is preferably, for example, 0 nm <G ≦ 13 nm, and 0.8 nm <G <2.2 nm. More preferred.
Here, the reason why the upper limit value of the distance G is set to 13 nm is that, for example, when the gap G is formed by oblique deposition, switching does not occur when the gap interval is larger than 13 nm.
On the other hand, if the lower limit of the distance G is 0 nm, the first electrode 20 and the second electrode 30 are short-circuited, but the graph of Example 1 (see FIG. 5) described later changes around 0V. It is clear that there is a gap larger than 0 nm. Although it is difficult to determine the lower limit value by microscopic measurement, it can be said that it is the minimum distance at which a tunnel current can occur. That is, the lower limit value is a theoretical value of a distance at which a quantum mechanical tunnel effect is observed when the device is operated and the current-voltage characteristic does not follow Ohm's law.
Here, when a resistance value is substituted into the theoretical formula of the tunnel current, a range of 0.8 nm <G <2.2 nm is obtained as a calculation result of the gap width.

Further, the DC electric resistance of the interelectrode gap 40 (between the first electrode 20 and the second electrode 30) is preferably greater than 1 kΩ and less than 10 TΩ, and more preferably greater than 100 kΩ.
Here, the upper limit value of the resistance is set to 10 TΩ because switching does not occur when the resistance is 10 TΩ or more. On the other hand, the reason why the lower limit value of the resistance is set to 1 kΩ is the lower limit since it has never been lowered to 1 kΩ or less at present.
When used as a switch, the higher the resistance in the OFF state, the better. Therefore, the upper limit value is preferably higher. However, if the resistance in the ON state is 1 kΩ, a current in the order of mA is generated. The lower limit is preferably about 100 kΩ because it may easily flow and destroy other elements.

In addition, the nearest part between the 1st electrode 20 and the 2nd electrode 30 may be formed in the area | region where the 1st electrode 20 and the 2nd electrode 30 oppose, for example, one or more places.
Moreover, between the 1st electrode 20 and the 2nd electrode 30, the island part (Nakasu part) which consists of the constituent material of the said 1st electrode 20 and the 2nd electrode 30 etc. may be formed, for example. In this case, for example, a predetermined gap may be formed between the first electrode 20 and the island portion, between the second electrode 30 and the island portion, and the first electrode 20 and the second electrode 30 may not be short-circuited.
Further, lead wires L1 and L2 are connected to each of the first electrode 20 and the second electrode 30, and the lead wires L1 and L2 extend to the outside of the sealing member 50 (see FIG. 2). ).

The sealing member 50 is, for example, for operating the switching element 100 more stably in a state where the interelectrode gap 40 is not in contact with the air but is filled with an oxygen atmosphere. The sealing member 50 only needs to have a structure in which at least the interelectrode gap 40 is sealed so as to be exposed only to oxygen gas, but in the illustrated example, the entire electrode forming surface side of the insulating substrate 10 is sealed. The structure which stops is illustrated. Further, the entire switching element 100 may be sealed in an oxygen atmosphere.
The shape and material of the sealing member 50 can be arbitrarily changed as long as it has a function of preventing the inter-electrode gap 40 from coming into contact with the atmosphere and sealing the oxygen gas from leaking. As the material of the sealing member 50, for example, the same material as that of the insulating substrate 10 may be used, or a known semiconductor sealing material may be used. If necessary, a gas barrier layer made of a known substance is used. Etc. may be provided.

Here, since it is difficult to handle the pressure P if it deviates from a range of 10 ⁻⁶ Pa or more and 10 ⁵ Pa or less, it is desirable that the pressure P does not deviate from the range. More specifically, the pressure P inside the sealing member 50 is preferably, for example, 10 Pa or more, more preferably 1.5 × 10 ³ Pa or more, and more preferably 2 × 10 ⁴ Pa.
The effect of filling the periphery of the inter-electrode gap 40 with oxygen will be described based on actually measured data in the description of the above-described embodiments.

Next, a method for manufacturing the switching element 100 will be described.
The switching element 100 includes, for example, (1) a step of preparing the insulating substrate 10, (2) a first resist pattern forming step, (3) a first vapor deposition step, (4) a first lift-off step, and (5). It is manufactured by performing a second resist pattern forming step, (6) a second vapor deposition step, (7) a second lift-off step, (8) an electric field breaking step, and (9) a sealing step.

(1) Preparation Step of Insulating Substrate 10 As the insulating substrate 10, for example, a Si substrate with an oxide film, a substrate having an insulating surface, or the like is used. Specifically, for example, when a conductive substrate such as Si is used, a desired insulating film is provided on the surface by a known method such as heat treatment, oxidation treatment, vapor deposition, sputtering, etc., and the insulating film is insulative. The substrate 10 is used. In addition, for example, when an insulating substrate such as glass is used as the insulating substrate 10, it is not necessary to form an insulating film.

(2) First Resist Pattern Formation Step The first resist pattern formation step is performed using, for example, photolithography, and forms a resist pattern 60 for forming the first electrode lower portion 21 on the insulating substrate 10. (See FIG. 3).
Note that the thickness of the resist pattern 60 can be arbitrarily changed, for example, and is specifically set to 1 μm.

(3) 1st vapor deposition process A 1st vapor deposition process is performed using a predetermined vapor deposition apparatus, and forms the 1st electrode lower part 21, for example.
The deposition surface of the insulating substrate 10 is disposed so as to be inclined when facing the deposition surface from a deposition source, for example. That is, for example, as shown in FIG. 3, the insulating substrate 10 has an angle of 0 ° <θ1 <90 °, where θ1 is an angle formed by the deposition surface and the flying direction of particles evaporated from the vapor deposition source. (The vapor deposition method is hereinafter referred to as “tilted vapor deposition”). As a result, the first electrode lower portion 21 is formed in a shape in which the tip portion is inclined with respect to the insulating substrate 10 (deposition surface).
Note that the angle θ1 ′ formed between the inclination direction of the tip of the first electrode lower portion 21 and the surface of the insulating substrate 10 is, for example, the shape and the angle at which the metal on the surface of the insulating substrate 10 is deposited. It can be changed depending on the magnitude of θ1.

In the first vapor deposition step, for example, at least one substance selected from gold, silver, platinum, copper, or an alloy thereof is deposited once or a plurality of times. Specifically, as the plurality of times of vapor deposition, for example, the first electrode lower part 21 having a two-layer structure may be formed by changing the metal for each vapor deposition.
The thickness of the first electrode lower portion 21 can be arbitrarily changed, for example, and is set to 5 nm or more here.

(4) First lift-off process The first lift-off process is performed using, for example, a stripping solution suitable for the material of the resist pattern 60. As a result of the process, the first electrode lower portion 21 is formed, and the resist pattern The sacrificial electrode 21a formed on 60 is removed.

(5) Second resist pattern forming step The second resist pattern forming method is performed using, for example, photolithography, and a resist pattern (not shown) for forming the second electrode 30 and the first electrode upper portion 22. ).

(6) Second vapor deposition step The second vapor deposition step is performed using, for example, a predetermined vapor deposition apparatus to form the second electrode 30 and incidentally form the first electrode upper portion 22 (FIG. 4). reference).
Further, the second vapor deposition step is performed by, for example, inclined vapor deposition, for example, as shown in FIG. 4, when the angle formed between the vapor deposition surface and the flying direction of particles evaporated from the vapor deposition source is θ2, When θ1 ′ <90 °, the insulating substrate 10 is set such that 0 ° <θ2 <θ1 ′ <90 °, and when 90 ° ≦ θ1 ′, 0 ° <θ2 <90 °. Is placed.
Further, in the second vapor deposition step, for example, at least one substance selected from gold, silver, platinum, copper, or an alloy thereof is vapor-deposited once or a plurality of times.

In addition, the inter-electrode gap portion 40 having a nanometer-order gap is formed between the first electrode 20 and the second electrode 30 by the second vapor deposition step.
That is, the formation of the inter-electrode gap 40 utilizes, for example, the shadow of the first electrode lower portion 21 formed by vapor deposition particles in the gradient vapor deposition of the second vapor deposition step. Accordingly, by adjusting at least one of the thickness of the first electrode lower portion 21 and the angle θ2 of the inclined vapor deposition in the second vapor deposition step, the interelectrode gap portion 40 having a desired interelectrode distance G is obtained. be able to.

(7) Second lift-off process The second lift-off process is performed using, for example, a stripping solution that matches the material of the resist pattern. As a result of the process, the first electrode 20 and the second electrode 30 are formed, A gap electrode is obtained.

(8) Electric field breaking process Since the nanogap electrode may be short-circuited, it is preferable to perform the electric field breaking process as needed.
In the electric field breaking step, for example, a variable resistance, a fixed resistance, and a power source (all not shown) are connected in series with the short-circuited electrode, and a voltage is applied. Then, the resistance value of the variable resistor is adjusted from the initial value (large resistance) so that the resistance slowly decreases, and is stopped when the current stops flowing, thereby obtaining a nanogap electrode having a desired interelectrode distance G. Can do.

(9) Sealing step The sealing step is performed using, for example, a predetermined hermetic sealing technique, and in an oxygen atmosphere, by ceramic sealing, glass sealing, plastic sealing, sealing with a metal cap, or the like. Done.

  In addition, the manufacturing method of said switching element 100 is an example, Comprising: It is not restricted to this.

  Next, an example of the operation of the switching element 100 of this embodiment will be described below. FIG. 5 schematically shows an example of a current-voltage curve of the switching element 100. The horizontal axis in FIG. 5 corresponds to the voltage applied between the nanogap electrodes of the switching element 100, and the vertical axis corresponds to the current. In FIG. 5, symbols from A to H and 0 are given for the sake of explanation.

  As shown in FIG. 5, the current-voltage curve of the switching element 100 is point-symmetric with respect to the zero point, and thus the voltage and current applied to the switching element 100 do not depend on the polarity of the switching element 100. For this reason, in the following description, FIG. 5 illustrates the right half, that is, the portion where the voltage is positive, and the description regarding the portion where the voltage is negative is omitted. The switching operation for the negative voltage portion will be read by reversing the polarity in the following description as appropriate. In the region between point A (voltage having the minimum resistance value) passing through point B in FIG. 5 and point C, the switching element 100 exhibits a negative resistance effect in which the resistance increases as the applied voltage is increased. In this region, the state of the switching element 100 changes depending on the applied voltage. Hereinafter, this voltage region is referred to as a transition region. The voltage in this transition region is instantaneously changed from a state where it is applied to the element to a value in the vicinity of the 0 point (practically, a value between the vicinity of the A point and the vicinity of the E point). The operation of changing the voltage value to near the zero point is referred to as “voltage cut”), and a resistance value corresponding to the voltage value applied immediately before the voltage is cut can be obtained. As the voltage in the transition state that determines the resistance value at this time is set closer to the point A, the resistance value of the element decreases, and as the voltage is set higher than the point A, the resistance value increases. . Here, point B in the transition region is an intermediate state between a low resistance state (hereinafter referred to as “ON state”) and a high resistance state (hereinafter referred to as “OFF state”) after the voltage is cut. It shows the point where the state can be obtained. The end of the transition region on the low voltage side, that is, the voltage near the point A is called a threshold voltage. Here, the threshold value is defined as a value in the vicinity of the point A because the threshold value, which is a voltage at which the minimum element resistance can be obtained in the transition region, depends on the operating voltage, the measurement environment, and the like. This is because it does not always coincide with the point A, and in some cases, it is slightly shifted.

FIG. 6A is a diagram schematically showing the correspondence between the voltage applied between the nanogap electrodes and the elapsed time, and FIG. 6B shows the current flowing between the nanogap electrodes and the elapsed time. It is a figure which shows typically the correspondence of these.
First, an ON voltage of a rectangular pulse I (a voltage close to A between AB in FIG. 5) is applied between the nanogap electrodes, and then a read voltage R1 is applied (see FIG. 6A). ), A large current flows between the nanogap electrodes, and it is confirmed that the switching element 100 is turned on (see FIG. 6B).
Next, an OFF voltage of a rectangular pulse J (a voltage close to C between B and C in FIG. 5) is applied between the nanogap electrodes, and then a read voltage R2 is applied (FIG. 6A). It is confirmed that no current flows between the nanogap electrodes, and the switching element 100 is turned off (see FIG. 6B).

  After that, when the ON voltage K and the OFF voltage L are repeatedly applied in the same manner, the switching element 100 repeats the switching operation in the ON state and the OFF state in the same manner. And

(Example)
In the switching element 100 as an example, a silicon substrate covered with a silicon oxide layer having a thickness of 300 nm was used as the insulating substrate 10. The thickness of the first resist pattern was 1 μm. The first resist pattern was formed so that the horizontal width of the first electrode lower portion 22 was 100 μm. The first electrode lower portion 22 was vapor-deposited with platinum so that its thickness was 25 nm. The angle θ1 during the inclined vapor deposition in the first vapor deposition step was set to 75 °. The thickness of the second resist pattern was 1 μm. The second resist pattern was formed so that the horizontal width of the second electrode 30 was 2 μm. The second electrode 30 was formed by depositing platinum and having a thickness of 15 nm. Therefore, the total thickness of the first electrode 20 was about 40 nm. The angle θ2 during the inclined vapor deposition in the second vapor deposition step was 60 °. Next, a second lift-off process was performed. Since the switching element 100 included the first electrode 20 and the second electrode 30 that are short-circuited in the above state, an electric field breaking step was performed to remove the short-circuit portion. The conditions for electric field rupture were an additional voltage of 1 V, a resistance Rc value of 100Ω, and the variable resistance Rv was gradually decreased from 100 kΩ to 0Ω to gradually increase the amount of current. When the electric field breakage occurred, the amount of current was about 4 mA. The switching element 100 was obtained as described above.
Then, the switching element 100 was placed in a vacuum prober, the pressure was reduced to 0.1 Pa with a vacuum pump, and oxygen gas was introduced therein, thereby realizing an oxygen atmosphere while maintaining an arbitrary vacuum pressure. The current-voltage characteristics of the switching element under such an oxygen atmosphere were measured with a semiconductor parameter analyzer (Keithley 4200). In order to perform the above measurement by arbitrarily changing the oxygen pressure, the switching element 100 is not provided with the sealing member 50 for convenience, but the entire switching element 100 including the interelectrode gap 40 is placed in an oxygen atmosphere. Since it is exposed and the outside air is shut off, it can be regarded as equivalent to a switching element in which oxygen is sealed by a sealing member.

FIG. 7 is a diagram showing current-voltage characteristics when the gas pressure is set to three stages of 10 Pa, 1.5 KPa, and 20 KPa in the oxygen atmosphere, and FIG. 8 shows oxygen in the range of 1.0 to 10 ⁵ Pa. FIG. 9 is a diagram showing changes in peak voltage (corresponding to the voltage at point A at which the current value in FIG. 5 is maximum) when the gas pressure is changed, and FIG. 9 shows oxygen in the range of 1.0 to 10 ⁵ Pa. It is a diagram which shows the change of the peak electric current (equivalent to the electric current of A point in FIG. 5) at the time of changing the pressure of gas. For comparison, FIG. 11 shows current-voltage characteristics when the above-described switching element has three stages of gas pressures of 1 KPa, 10 KPa, and 100 KPa in a nitrogen atmosphere.

According to FIGS. 7 to 9, the switching element of Example 1 has a peak voltage that varies between approximately 2 V and 1.5 V at 1 KPa, 10 KPa, and 100 KPa, and a peak current that is between approximately 0.7 mA and 1.0 mA. Has changed. On the other hand, in the comparative example, as shown in FIG. 11, the peak voltage varies between about 3.0 V and 3.4 V at 1 KPa, 10 KPa, and 100 KPa, and the peak current varies between about 0.6 mA and 0.9 mA. is doing.
According to these comparisons, it was observed that the effect of reducing the peak voltage was obtained by oxygen sealing in the switching element as compared with the conventional nitrogen sealing switching element.
Furthermore, according to FIG. 8, it was observed that the peak voltage decreases as the pressure of the oxygen gas to be sealed increases. Further, according to FIG. 9, when the pressure of the enclosed oxygen gas exceeds 10 ⁵ Pa, a part of the pressure rises, but the peak voltage decreases as the pressure of the oxygen gas increases in a lower pressure range. Observed.

Further, the peak voltage can be greatly reduced by setting the pressure of the oxygen gas to 10 ² Pa or more as shown in FIG. That is, in the atmosphere of nitrogen gas, as shown in FIG. 11, the peak voltage drops only to about 3 V at each pressure, but in the atmosphere of oxygen gas, the pressure is set to 10 ² Pa or more. Then, it is possible to reduce the peak voltage to a level of 2V, far below 3V. In addition, as shown in FIG. 10, the electrode is not limited to platinum, and the same applies when it is formed of gold. Note that the measurement test is performed only to a pressure of 10 ⁵ Pa (≈atmospheric pressure), but the internal pressure of the switching element 100 may be considered as the upper limit up to about atmospheric pressure so as not to cause leakage of oxygen gas.

In addition, although the switching element of the said Example illustrated what formed each electrode with platinum, when the electrode is formed with gold | metal | money, it is possible to aim at reduction of a peak voltage similarly. FIG. 10 shows the peak voltage (corresponding to the voltage at point A in FIG. 5) when the pressure of the oxygen gas is changed in the range from 0.1 Pa to 2 × 10 ⁴ Pa for the switching element in which each electrode is formed of gold. It is a diagram which shows a change. As shown in this figure, it was observed that the peak voltage can be reduced to the same level or lower when the electrode is made of gold than when it is made of platinum.

(Technical effects in switching elements)
As described above, according to the switching element 100 of the present embodiment, the structure of the switching element 100 can be made simpler, and the switching operation can be stably repeated. That is, since it is composed of the nano gap electrodes (first electrode 20 and second electrode 30) and the sealing member 50 arranged with a spatial gap of nanometer order, organic molecules, inorganic particles, etc. Is unnecessary, and can be configured with a simpler structure.
Furthermore, since the switching element 100 does not include a substance that deteriorates, the switching operation can be stably repeated.
In addition, the switching element 100 has non-volatility and can maintain the operating state of the switching element 100 even if there is no external input after the switching operation.

Further, by sealing one side of the insulating substrate 10 including the gap between the nano-gap electrodes in an oxygen atmosphere by the sealing member 50, for example, compared with a case where an inert gas such as nitrogen used conventionally is sealed. Thus, the peak voltage can be reduced. Further, since the peak current does not increase as compared with the case of nitrogen filling, the power consumption can be reduced even when the switching element is used as an electronic device.
Moreover, since the peak voltage and the peak current exhibit characteristics that decrease with an increase in the pressure of the oxygen gas to be sealed, the peak voltage and the peak current can be arbitrarily set by appropriately adjusting the oxygen gas pressure. It becomes possible to do.

  Further, in the switching element 100, the interelectrode gap 40 is sealed in an oxygen atmosphere by forming the first electrode 20 and the second electrode 30 from a material that is difficult to oxidize, particularly gold, platinum, or an alloy thereof. Even when stopped, the oxidation of the electrodes 20 and 30 can be more effectively suppressed, and the switching operation between the electrodes can be performed satisfactorily. Further, durability can be improved by preventing oxidation, and good operation can be maintained for a long time.

(Variation of switching element [1])
The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.
Below, the modification of the switching element which concerns on this invention is demonstrated. In addition, about the some modification demonstrated below, the same code | symbol shall be attached | subjected about the structure which is common in the switching element 100 mentioned above, and description shall be abbreviate | omitted.

For example, as shown in FIG. 12, the switching element 200 of Modification 1 includes an insulating substrate 10, an insulator 260 provided on the upper surface of the insulating substrate 10, and a first electrode provided on the upper surface of the insulating substrate 10. One electrode 220, a second electrode 230 provided above the first electrode 220, an interelectrode gap 240 provided between the first electrode 220 and the second electrode 230, and an electrode of the insulating substrate 10 And a sealing member 50 for sealing in a state where the formation surface side is filled with oxygen gas.
Specifically, the insulator 260 is provided on the upper surface of the insulating substrate 10 to form a stepped portion. The insulator 260 causes the first electrode 220 and the electrode 230 on the base to have a difference in height. Is placed on top. The first electrode 220 is provided in contact with the upper surface of the insulating substrate 10 and the lower portion of the side surface 261 of the insulator 260, and the second electrode 230 is connected to the upper surface of the insulator 260 and the insulator 260. It is provided in contact with the upper portion of the side surface 261. The interelectrode gap 240 is provided between the first electrode 220 provided in the lower portion of the side surface 261 of the insulator 260 and the second electrode 230 provided in the upper portion of the side surface 261 of the insulator 260. ing. That is, the gap G between the electrodes 240 is formed along the height direction of the step formed by the insulator 260.

In addition, as for the material of the 1st electrode 220 and the 2nd electrode 230, it is desirable to select the thing similar to the 1st electrode 20 and the 2nd electrode 30 mentioned above.
In addition, the insulator 260 is disposed so that the facing portion of the first electrode 220 and the facing portion of the second electrode 230 that form the interelectrode gap 240 are aligned along the height direction with respect to the plane of the substrate 10. Is. Therefore, other structures may be adopted as long as the above functions are provided.
The insulator 260 may be, for example, a part of the insulating substrate 10 provided with an oxide film or the like, or an oxide film or the like provided on the whole surface of the insulating substrate 10 and removing a part thereof. It may be formed. Moreover, as a material of the insulator 260, for example, glass, an oxide such as silicon oxide (SiO ₂ ), a nitride such as silicon nitride (Si ₃ N ₄ ), or the like is preferable. Among these, silicon oxide (SiO ₂ ) is preferable. However, it is suitable in that the adhesion between the first electrode 220 and the second electrode 230 and the degree of freedom in manufacturing the electrode are large.

  The inter-electrode gap 240 has substantially the same substantial structure except that the orientation of the plane formed is different from that of the inter-electrode gap 40 described above. Therefore, the design conditions such as the dimensions of the interelectrode gap 240 and the operation method thereof are the same as those of the interelectrode gap 40 described above.

The switching element 200 according to Modification 1 has the same technical effect as the switching element 100 described above,
The first electrode 220 and the second electrode 230 are arranged with a height difference by a step formed by the insulator 260 with respect to the upper surface of the insulating substrate 10, and an interelectrode gap 240 is formed along the height direction. Therefore, the interelectrode gap 240 occupies the area of the insulating substrate 10 in plan view as compared with the case where the first electrode 220, the second electrode 230, and the interelectrode gap 240 are arranged side by side on the same plane. It becomes possible to reduce. Accordingly, for example, when a memory element is formed by integrating a large number of switching elements 200 while sharing a single insulating substrate 10, it is advantageous for integration, and the memory element can be reduced in size. Is possible.

(Modification of switching element [2])
Modification 2 of the switching element according to the present invention will be described. In addition, about the some modification demonstrated below, the same code | symbol shall be attached | subjected about the structure which is common in the switching element 100 mentioned above, and description shall be abbreviate | omitted.

  For example, as shown in FIG. 13, the switching element 300 of Modification 2 is in contact with the insulating substrate 10, the first electrode 320 provided in contact with the upper surface of the insulating substrate 10, and the upper surface of the first electrode 320. Provided between the first electrode 320 and the second electrode 330, the second electrode 330 disposed above the first electrode 320 and in contact with the upper surface of the insulator 360. The inter-electrode gap portion 340 and the sealing member 350 provided in contact with the upper surface of the second electrode 330 are mainly provided.

In the switching element 300, the first electrode 320 and the second electrode 330 are arranged side by side along a direction (vertical direction) orthogonal to the plane of the substrate 10, and the first electrode 320 constituting the interelectrode gap 340. And the second electrode 330 are also opposite to each other in common with the switching element 200 described above in that they are arranged side by side in the vertical direction.
Specifically, in the switching element 300, an insulator 360 is interposed between the first electrode 320 and the second electrode 330, and a hole 361 as a hole penetrating from the first electrode 320 to the second electrode 330 is formed as an insulator. The inter-electrode gap 340 is formed in the inner space of the hole 361.
The inter-electrode gap 340 extends from the first electrode 320 along the inner surface of the hole 361 toward the second electrode 330 and from the second electrode 330 along the inner surface of the hole 361. And an extending end 331 extending toward the first electrode 320. Further, the point that a predetermined gap G is formed at the tip of each extended end is the same as that of the switching element 100 described above.

  The second electrode 330 is formed with an opening 332 that opens the internal space of the hole 361 upward, and the sealing member 350 is formed on the upper surface of the second electrode 330 so as to close the opening 332. As a result, oxygen gas is sealed inside the hole 361.

In the switching element 300, it is desirable to select the same material as the first electrode 20 and the second electrode 30 described above as the material of the first electrode 320 and the second electrode 330.
The insulator 360 is for supporting the first electrode 320 and the second electrode 330 so as to be arranged side by side in a direction (vertical direction) orthogonal to the plane of the substrate 10. Other structures may be adopted as long as the structure is a support structure for realizing the above.
The insulator 360 functions to hold the electrodes 320 and 330 together with the insulating substrate 10, and can be regarded as a part of the insulating substrate 10 functionally.
The insulator 360 may be, for example, a part of the insulating substrate 10 provided with an oxide film or the like, or an oxide film or the like provided on the whole surface of the insulating substrate 10 and removing a part thereof. It may be formed. Further, as the material of the insulator 360, for example, glass, oxides such as silicon oxide (SiO ₂ ), nitrides such as silicon nitride (Si ₃ N ₄ ), and the like are preferable, and among these, silicon oxide (SiO ₂ ) However, it is suitable in that the adhesion between the first electrode 320 and the second electrode 330 and the degree of freedom in manufacturing the electrode are large.

  The inter-electrode gap 340 has substantially the same substantial structure except that the orientation of the plane formed is different from that of the inter-electrode gap 40 described above. Therefore, the design conditions such as the dimensions of the interelectrode gap 340 and the operation method thereof are the same as those of the interelectrode gap 40 described above.

The switching element 300 according to the second modification has the same technical effect as the switching element 100 described above, and a hole 361 is provided in the insulator 360 provided in the insulating substrate 10, and the inter-electrode is provided in the hole 361. Since the gap 340 is formed, when the first electrode 320 and the second electrode 330 are arranged in the vertical direction, the interelectrode gap 340 can be arranged between them. As a result, the first electrode 320, the interelectrode gap 340, and the second electrode 330 can be arranged side by side along the vertical direction with respect to the flat surface of the insulating substrate 10. Thus, the area occupied by each of the electrodes 320 and 330 in the plan view of 10 can be reduced. Accordingly, for example, when a memory element is manufactured by forming a large number of switching elements 300 by sharing a single insulating substrate 10, it is advantageous for integration, and the memory element can be reduced in size. It becomes possible to plan.
In addition, since the first electrode 320 and the second electrode 330 can be arranged along the direction (vertical direction) intersecting the plane of the insulating substrate 10, for example, a memory element is manufactured. In this case, when the switching elements 300 are arranged in a plane along two directions intersecting (orthogonal) with each other along the plane of the insulating substrate 10, the first one of the two directions intersecting each other is first. The electrodes 320 can be integrated in common, and the second electrode 330 can be integrated in other directions out of the two directions intersecting each other, thereby taking a further advantageous structure for integration. It becomes possible.

DESCRIPTION OF SYMBOLS 10 Insulating board | substrate 20,220,320 1st electrode 30,230,330 2nd electrode 40,240,340 Interelectrode gap | interval part 50,350 Sealing member 100,200,300 Switching element 260 Insulator (step part)
361 hole

Claims (5)

An insulating substrate;
A first electrode and a second electrode provided on the insulating substrate;
Between electrodes having a gap on the order of nanometers provided between the first electrode and the second electrode and causing a switching phenomenon of resistance when a predetermined voltage is applied between the first electrode and the second electrode A gap,
A sealing member that seals at least the interelectrode gap in a state where the interelectrode gap is filled with gaseous oxygen;
A switching element comprising:   The switching element according to claim 1, wherein the first electrode and the second electrode are made of gold, platinum, or an alloy thereof. The switching element according to claim 1, wherein the sealing member seals oxygen at a pressure of at least 10 ² [Pa] or more. The insulating substrate has a step portion, and the first electrode and the second electrode are arranged with a height difference due to a step of the step portion,
The switching element according to claim 1, wherein the inter-electrode gap is formed along a height direction of the stepped portion. The insulating substrate has a hole that leads from the first electrode to the second electrode;
4. The switching element according to claim 1, wherein the inter-electrode gap is formed in the hole, and the sealing member seals the hole. 5.

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