Silver electrode and method for manufacturing the same

Abstract

The present invention provides: a silver electrode having a smaller change in resistivity due to temperature changes than in the prior art; and a method of manufacturing a silver electrode.　In the present invention, in an X-ray diffraction pattern measured by an X-ray diffractometer using a CuKα1 beam, there is one peak in a range in which a diffraction angle 2θ is 37.5° to 38.3°, and the rate of change of the diffraction angle of the peak when heating is carried out at 150°C for 30 minutes is 0.5% or less. Due to this configuration, realized is a silver electrode that has a smaller change in resistivity due to temperature changes as compared to the prior art.

Description

[Technical Field]

[0001] The present invention relates to a silver electrode and a method for producing the silver electrode. [Background technology]

[0002] Conventionally, electronic devices with built-in sensors, such as smartphones and smartwatches, have used silver electrodes, which have lower resistance than other metals, in sensors to ensure high detection speeds.

[0003] A method for forming a silver electrode is a vacuum deposition method (for example, Patent Document 1). Specifically, the vacuum deposition method uses a vacuum deposition device to evaporate silver, which is a deposition source, into a gaseous state in an evaporation chamber or a film-forming chamber, and deposits the gaseous silver onto the surface of a glass substrate from a nozzle facing the substrate in the film-forming chamber, thereby depositing a silver layer on the substrate and forming a silver electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-180351 Summary of the Invention [Problem to be solved by the invention]

[0005] Although silver electrodes with a silver layer formed by vacuum deposition have low resistivity at room temperature, their resistivity fluctuates with temperature changes. Therefore, resistivity can change due to body temperature or heat generated by the battery, resulting in errors in sensor sensitivity. In such cases, conventional electronic devices address this error by correcting it in software, but there are limits to how much software correction can be done, so it is preferable to minimize the error.

[0006] Therefore, an object of the present invention is to provide a silver electrode in which the change in resistivity due to temperature change is smaller than in the past, and a method for manufacturing the silver electrode. [Means for solving the problem]

[0007] One aspect of the present invention for solving the above-mentioned problems is a silver electrode having a silver layer laminated on a substrate, wherein an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation has one peak in the range of diffraction angle 2θ=37.5° to 38.3°, and when heated at 150°C for 30 minutes, the rate of change in the diffraction angle of the peak is 0.5% or less.

[0008] According to this aspect, the structure has little dependence on temperature changes and is excellent in thermal stability.

[0009] A preferred aspect is that the temperature coefficient at 70°C and the temperature coefficient at 190°C are both less than 0.00001.

[0010] A preferred aspect is that the temperature coefficient in the range of 70°C to 190°C is less than 0.00001.

[0011] A preferred aspect is that the resistivity at a frequency of 10 kHz is 1.1 times or less compared to the resistivity at a frequency of 1 kHz.

[0012] In a preferred aspect, the protective layer has a cross-sectional structure covering the surface of the silver layer, and the protective layer has at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group.

[0013] In a preferred embodiment, the silver layer further comprises silver particles having an average particle size larger than the average film thickness of the silver layer.

[0014] In a preferred aspect, the average thickness of the silver layer is 500 nm or less.

[0015] In a preferred aspect, an oxidizing agent containing silver is brought into contact with the substrate, and the oxidizing agent is reduced by a reducing agent containing an organic compound, resulting in a silver layer being laminated on the substrate, wherein the substrate is a copper body, an alloy layer containing a copper component and a silver component is formed at the interface between the substrate and the silver layer, and a protective layer containing a component of the reducing agent is laminated on the surface of the silver layer.

[0016] In a preferred aspect, the alloy layer has a ratio of silver to copper of 2 / 3 or more and 3 / 2 or less.

[0017] A preferred aspect is that when an electron beam diffraction image of the alloy layer is obtained, the pattern of the electron beam diffraction image matches the simulated pattern of an alloy in the space group Fm-3m with a 1:1 ratio of copper and silver components.

[0018] In a preferred aspect, the average thickness of the alloy layer is 30% to 60% of the average thickness of the silver layer.

[0019] In a preferred aspect, a residue layer containing components derived from the reducing agent is formed at the interface between the alloy layer and the silver layer.

[0020] The term "components derived from the reducing agent" as used herein includes not only reaction products that are generated when silver oxide is reduced by the reducing agent, but also unreacted components of the reducing agent. The same applies hereinafter.

[0021] In a preferred aspect, a void adjacent to the silver layer exists at the interface between the alloy layer and the silver layer, and at least a part of the inner wall of the void is constituted by the residue layer.

[0022] In a preferred aspect, the oxidizing agent is silver oxide.

[0023] The present inventors have conducted extensive research into silver layers formed by vacuum deposition and have found that when silver is deposited on a substrate, distortion occurs within the silver layer, which generates internal stress. They have also discovered that when the temperature of a silver layer formed by vacuum deposition is increased, the residual stress in the silver layer is alleviated, resulting in a tendency for the variation in resistivity to increase. Therefore, the inventors sought a method to form a silver layer by directly reducing silver oxide with a reducing agent, rather than by vacuum deposition. As a result, they discovered that by using a hindered amine light stabilizer, which has traditionally been used as a light stabilizer for resins but not as a reducing agent for inorganic metals, as a reducing agent, silver oxide can be reduced even at temperatures below 200°C, which is said to be the temperature at which silver oxide begins to decompose, and further that the resulting silver layer has small internal stress and small changes in resistivity due to temperature changes.

[0024] One aspect of the present invention, which was derived based on this discovery, is a method for producing a silver electrode, comprising: a mixing step of mixing a reducing agent and silver oxide to form a mixture; an application step of applying the mixture onto a substrate; and a heating step of heating the substrate, onto which the mixture has been applied, at a first heating temperature, wherein the reducing agent is a hindered amine compound having at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group.

[0025] According to this aspect, silver oxide can be reduced even at low temperatures, and a silver electrode can be produced in which the change in resistivity due to temperature change is small.

[0026] In a preferred aspect, the first heating temperature is less than 200°C.

[0027] According to this aspect, the silver layer can be formed at a temperature lower than the decomposition temperature of ordinary silver oxide.

[0028] However, when a silver layer is formed using a vacuum deposition method, the inside of the film formation chamber must be depressurized to a vacuum state every time the substrate is replaced, which results in a problem that film formation takes a long time. Furthermore, the silver layer formed by the vacuum deposition method has poor adhesion to the substrate and low strength, which means that the layer is easily peeled off from the substrate. Furthermore, the silver layer formed by the vacuum deposition method is easily oxidized by light and heat, and is prone to corrosion and discoloration.

[0029] Therefore, the inventors considered that by mixing silver oxide and a reducing agent as described above, and heating the mixture to directly reduce the silver oxide to silver, it would be possible to form a film in a shorter time than by vacuum deposition, and the density of the silver layer would be improved, thereby improving the film strength. The present inventors have conducted extensive research into methods for reducing silver oxide and have discovered that by subjecting silver oxide to a specific pretreatment, the rate of the reduction reaction can be increased compared to simply mixing silver oxide with a reducing agent and heating it.

[0030] In order to form a silver layer in a shorter time than conventional methods, a preferred aspect includes a pretreatment step of pretreating powdered silver oxide, in which the pretreated silver oxide is mixed with the reducing agent to form the mixture in the mixing step, and the silver oxide is exposed to a pretreatment solvent having a boiling point lower than the first heating temperature in the pretreatment step.

[0031] In a preferred aspect, the pretreatment step includes an immersion step of immersing the silver oxide in the pretreatment solvent, and a removal step of removing a part or all of the pretreatment solvent.

[0032] In a preferred aspect, the pretreatment solvent is a volatile organic solvent.

[0033] In a preferred aspect, the pretreatment solvent is at least one solvent selected from the group consisting of acetone, toluene, ethanol, acetonitrile, and water.

[0034] In a preferred aspect, the reducing agent is a hindered amine light stabilizer.

[0035] In a preferred aspect, the reducing agent includes a hindered amine compound having two or more of at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group and having a molecular weight of 700 or less.

[0036] In a preferred aspect, in the heating step, the silver oxide is reduced by the reducing agent to form a silver layer on the substrate, and the surface of the silver layer is further covered with a protective layer formed from a component derived from the reducing agent.

[0037] According to this aspect, during the heating process, the residue of the reducing agent bleeds out on the surface of the silver layer, forming a protective layer containing components derived from the reducing agent that covers the silver layer. This reinforces the strength of the layer, making it less likely to peel off from the substrate. [Effects of the Invention]

[0038] The silver electrode of the present invention is structurally stable, and therefore the change in resistivity due to temperature change can be made smaller than that of the prior art. According to the method for producing a silver electrode of the present invention, it is possible to produce a silver electrode whose resistivity changes less with temperature change than conventional methods. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 is a perspective view of a silver electrode according to a first embodiment of the present invention. [Figure 2] 2 is an explanatory diagram of the silver electrode of Fig. 1, where (a) is a cross-sectional view taken along line AA in Fig. 1, and (b) is a cross-sectional view taken along line BB in Fig. 1. Note that some hatching has been omitted to facilitate understanding. [Figure 3] 1 is a cross-sectional view of a silver electrode according to a second embodiment of the present invention, with some hatching omitted for ease of understanding. [Figure 4] 1 is a graph showing X-ray diffraction patterns before and after heating in Experimental Examples 1 and 2. [Figure 5] 10 is a graph showing temperature coefficients versus temperature in Experimental Examples 1 and 2. [Figure 6]10 is a graph showing the change in resistivity with respect to frequency in Experimental Examples 1 and 2. [Figure 7] 1 shows the results of SEM observation of Experimental Example 1, where (a) is an SEM image of Experimental Example 1, and (b) is a trace of (a). [Figure 8] 1 is a graph of resistance and temperature versus reaction time for Experimental Examples 3, 5, and 6. [Figure 9] 1 shows the results of STEM observation of Experimental Example 7, where (a) is a low-magnification secondary electron image and (b) is a trace of (a). [Figure 10] 1 shows the results of STEM observation of Experimental Example 7, where (a) is a high-magnification transmission electron image and (b) is a trace of (a). DETAILED DESCRIPTION OF THE INVENTION

[0040] Hereinafter, embodiments of the present invention will be described in detail. Note that physical properties are based on standard conditions of 25° C. and 1 atm unless otherwise specified.

[0041] The silver electrode 1 of the first embodiment of the present invention is suitable for use in semiconductor devices such as solar cell modules and power semiconductors, IoT devices such as smartphones and smart watches, analytical instruments such as X-ray detectors, optical detectors, and acoustic detectors, actuators such as artificial muscles, and the like. The silver electrode 1 can also be suitably used as a reflective film for organic EL displays, liquid crystal displays, and the like, conductive materials such as wiring and electrodes, decorative materials, recording materials, antibacterial materials, and the like.

[0042] As shown in FIG. 1, the silver electrode 1 is a substrate with a thin silver film, in which a thin silver film layer 3 (silver layer) is laminated on a substrate 2, and a silver particle layer 5 is locally formed. As shown in FIG. 2 , the silver electrode 1 has a cross-sectional structure in which the surface of the silver thin film layer 3 is covered with a protective layer 6, and the protective layer 6 extends from the surface of the silver thin film layer 3 to the surface of the silver particle layer 5 laminated on the silver thin film layer 3, covering the surfaces of the silver particles 10 that constitute the silver particle layer 5.

[0043] (Base material 2) The substrate 2 is a supporting substrate that extends in a planar shape and supports the silver thin film layer 3. The substrate 2 is in the form of a plate or film, and has a first main surface (surface on which a film is to be formed) and a second main surface. The substrate 2 is not particularly limited, and may be an insulating substrate such as a glass substrate or polyimide film, or a conductive substrate such as a metal substrate or metal film made of copper or the like.

[0044] (silver thin film layer 3) The silver thin film layer 3 is a silver thin film layer whose main component is silver. The term "major component" here refers to a component that accounts for more than 50% of the total. The silver thin film layer 3 preferably comprises 80% or more of silver as a whole, and more preferably 95% or more of silver. The average thickness of the silver thin film layer 3 is 1 μm or less, and from the viewpoint of ensuring sufficient conductivity while being easy to use in wiring, etc., it is preferably 50 nm or more and 500 nm or less, and more preferably 150 nm or more and 300 nm or less. The average film thickness of the silver thin film layer 3 can be determined, for example, by observing the cross section of the silver thin film layer 3 using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and calculating the arithmetic average value at any three points.

[0045] (Silver particle layer 5) 2(b), the silver particle layer 5 is a particle deposition layer in which silver particles 10 are deposited. In the silver particle layer 5, the silver particles 10 undergo crystal growth in a direction intersecting with the substrate 2, resulting in the silver particles 10 being stacked three-dimensionally. The average particle size of the silver particles 10 constituting the silver particle layer 5 is larger than the average film thickness of the silver thin film layer 3, and is preferably 10 μm or less. The average particle size refers to the number average particle size of secondary particles formed by aggregation of primary particles, and refers to the primary particles when secondary particles formed by aggregation of primary particles do not exist. The average particle size of silver particles 10 can be calculated, for example, by observing the silver particles 10 with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and calculating the arithmetic mean of the particle sizes of any 10 or more silver particles 10 that appear in the SEM or TEM image. The particle size of silver particles 10 refers to the diameter of the smallest encompassing circle that encompasses the silver particles 10 in the SEM or TEM image.

[0046] (Protective layer 6) The protective layer 6 is a layer that has light stability and heat stability and protects the silver thin film layer 3 from light and heat. The protective layer 6 in this embodiment is a layer derived from the reducing agent used to form the silver thin film layer 3 in the method for producing the silver electrode 1 described later, and is composed of a product of the reducing agent reacting with an oxidizing agent or an unreacted reducing agent. The protective layer 6 of this embodiment contains a compound having at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group. The number of 1,2,2,6,6-pentaalkylpiperidinyl groups and 2,2,6,6-tetraalkylpiperidinyl groups in this compound is not particularly limited. Furthermore, it is preferable that the alkyl groups in the 1,2,2,6,6-pentaalkylpiperidinyl group and 2,2,6,6-tetraalkylpiperidinyl group constituting this compound each independently have 1 to 4 carbon atoms.

[0047] The average thickness of the protective layer 6 is preferably 1 nm or more and 20 nm or less, in order to adequately protect the silver thin film layer 3 from light and heat. The average film thickness of the protective layer 6 can be determined, for example, by observing the cross section of the protective layer 6 using an SEM image or a TEM image and calculating the arithmetic average value at any three points.

[0048] Next, the physical properties of the silver electrode 1 of this embodiment will be described.

[0049] In the X-ray diffraction pattern of the silver electrode 1 measured by an X-ray diffractometer using CuKα1 radiation, the silver electrode 1 has one peak in the range of diffraction angle 2θ=37.5° to 38.3°, and the rate of change in the diffraction angle 2θ of this peak when heated at 150°C for 30 minutes is 0% or more and 0.5% or less. The silver electrode 1 preferably has a crystallite diameter of 0.3 nm or more and 0.4 nm or less. When the silver electrode 1 is heated at 150° C. for 30 minutes, the rate of change in crystallite size after heating relative to before heating is preferably 1 or more and 1.15 or less. The silver electrode 1 preferably has a lattice constant of 0.235 nm or more and 0.245 nm or less. When the silver electrode 1 is heated at 150° C. for 30 minutes, the rate of change in lattice constant after heating relative to before heating is preferably 0.95 or more and 1.05 or less. The silver electrode 1 preferably has a temperature coefficient in the range of 70°C to 190°C of less than 0.00001, and more preferably less than 0.000001. The silver electrode 1 preferably has a resistivity at a frequency of 10 kHz that is 0.9 to 1.1 times that at a frequency of 1 kHz. Silver electrode 1 is 1.0 x 10 -18 Hz~1.0×10 3 In the kHz range, 7.0 x 10 -5 It is preferably Ωcm or less.

[0050] Next, a method for manufacturing the silver electrode 1 of the first embodiment will be described.

[0051] The method for producing the silver electrode 1 of the first embodiment mainly comprises a pretreatment step, a mixing step, a coating step, a heating step, and a washing step.

[0052] First, a pretreatment step is carried out in which silver oxide is pretreated with a pretreatment solvent. The pretreatment step is carried out by carrying out an immersion step and a removal step in this order.

[0053] In the immersion process, powdered silver oxide and a pretreatment solvent are placed in a sealed container, and the silver oxide is immersed in the pretreatment solvent and stirred.

[0054] At this time, the maximum particle size of the silver oxide introduced into the closed vessel is preferably 0.5 μm or more and 10 μm or less. The maximum particle size of silver oxide can be determined by sieving it through a sieve with a known opening size to exclude particles larger than the opening size. The pretreatment solvent is not particularly limited as long as it has a boiling point lower than the first heating temperature in the heating step described below. By using a pretreatment solvent with a boiling point lower than the first heating temperature, even if the pretreatment solvent cannot be sufficiently removed in the removal step, it can be vaporized in the heating step, and the solvent is less likely to remain in the silver thin film layer 3. The pretreatment solvent may be at least one selected from the group consisting of acetone, toluene, ethanol, acetonitrile, and water. By using such a solvent, residues of the pretreatment solvent are less likely to remain in the heating step described below. The pretreatment solvent preferably has a boiling point of 50°C or higher and 120°C or lower. The pretreatment solvent is preferably an organic solvent that is volatile at room temperature. By using an organic solvent that is volatile at room temperature, the pretreatment solvent can be removed by natural drying at room temperature in the removal step described below, and the reaction time can be further shortened.

[0055] Next, most of the pretreatment solvent is separated from the silver oxide immersed in the pretreatment solvent in the sealed container and removed (removal step). In this embodiment, the pretreatment solvent is removed by decantation one or more times, and then the pretreatment solvent is substantially removed by drying in a dryer at a predetermined drying temperature.

[0056] The drying temperature is not particularly limited as long as it is a temperature at which the pretreatment solvent volatilizes, but is preferably 100° C. or less from the viewpoint of suppressing aggregation of silver oxide.

[0057] After the pretreatment step is performed and the pretreatment of the silver oxide is completed, the pretreated silver oxide is mixed with a reducing agent to form a mixture (mixing step).

[0058] In this case, the reducing agent is an amine-based reducing agent, and is preferably a hindered amine-based light stabilizer having at least one of a 1,2,2,6,6-pentaalkylpiperidinyl group and a 2,2,6,6-tetraalkylpiperidinyl group, and more preferably an N-CH3-type or NH-type hindered amine-based light stabilizer. By using a hindered amine light stabilizer as a reducing agent, the silver thin film layer 3 can have a surface corrosion suppression effect. As the N-CH3 type hindered amine light stabilizer, Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate or the like can be used. Examples of the NH-type hindered amine light stabilizer that can be used include Tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, Tetrakis(2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, and Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate. From another perspective, the reducing agent preferably contains a hindered amine compound having two or more of at least one of 2,2,6,6-tetraalkylpiperidinyl groups and 1,2,2,6,6-pentaalkylpiperidinyl groups and having a molecular weight of 700 or less. In this hindered amine compound, the carbon atom at the 4-position of the piperidine ring of the 1,2,2,6,6-pentaalkylpiperidinyl group or 2,2,6,6-tetraalkylpiperidinyl group preferably forms an ester bond with a carboxylic acid. The number of 1,2,2,6,6-pentaalkylpiperidinyl groups and 2,2,6,6-tetraalkylpiperidinyl groups in this hindered amine compound is not particularly limited. Furthermore, it is preferable that the alkyl groups in the 1,2,2,6,6-pentaalkylpiperidinyl group and the 2,2,6,6-tetraalkylpiperidinyl group each independently have 1 to 4 carbon atoms. The reducing agent may be solid or liquid at room temperature, but preferably has a melting point lower than the first heating temperature in the heating step described below. If the melting point of these amine compounds is lower than the first heating temperature, when the reducing agent is heated together with silver oxide in the heating step described below, even if the reducing agent is solid, the reducing agent will melt and become liquid before the first heating temperature is reached, thereby increasing the contact area with silver oxide and enabling efficient reduction of silver oxide. In this embodiment, the reducing agent contains an amine compound having the following structural formula (1):

[0059] [ka]

[0060] In the above structural formula (1), R 1 and R 2 are each independently a hydrogen atom or a methyl group, and p is a positive integer of 1 or more and 18 or less.

[0061] Subsequently, the mixture obtained in the mixing step is applied to a desired area on the first main surface of the substrate 2 (application step).

[0062] The coating method is not particularly limited, and examples thereof include casting, roll coating, bar coating, die coating, spin coating, spray coating, and dip coating.

[0063] Subsequently, the substrate 2 coated with the mixture is placed in a heating device and heated at a first heating temperature, and the silver oxide serving as the oxidizing agent is reduced with the reducing agent to form a thin silver layer 3 on the substrate 2 (heating step).

[0064] The first heating temperature is not particularly limited as long as it is a temperature at which the reaction between silver oxide and the reducing agent proceeds, but from the viewpoint of reducing silver oxide in a short time, it is preferably 100°C or higher and lower than 200°C, and more preferably 120°C or higher and 180°C or lower.

[0065] Subsequently, the substrate 2 on which the silver thin film layer 3 has been formed in the heating step is washed with a washing solvent (washing step), and the silver electrode 1 is formed.

[0066] The cleaning solvent used here is not particularly limited as long as it does not substantially react with silver, and for example, a volatile organic solvent such as acetone can be used.

[0067] According to the silver electrode 1 of this embodiment, when heated at 150°C for 30 minutes, the rate of change in the peak diffraction angle is 0.5% or less, so that the structure is less dependent on temperature changes and has excellent thermal stability.

[0068] According to the silver electrode 1 of this embodiment, the temperature coefficients at both 70°C and 190°C are less than 0.00001, and therefore thermal stability can be achieved at both 70°C and 190°C.

[0069] The silver electrode 1 of this embodiment has a temperature coefficient of less than 0.00001 in the range of 70°C to 190°C, and therefore exhibits thermal stability, high thermal conductivity, and thermal diffusivity in the range of 70°C to 190°C.

[0070] According to the silver electrode 1 of this embodiment, the resistivity at a frequency of 10 kHz is 1.1 times or less that at a frequency of 1 kHz, and the variation in resistivity with respect to the change in frequency is small. Therefore, the silver electrode 1 has excellent stability with respect to frequency and can exhibit low frequency dependency.

[0071] In the silver electrode 1 of this embodiment, the surface of the silver thin film layer 3 is covered with the protective layer 6, which reinforces the strength of the layer and improves the bonding strength with the substrate 2, making the silver thin film layer 3 less likely to peel off from the substrate 2. In addition, oxidation of the silver thin film layer 3 can be suppressed. In the silver electrode 1 of this embodiment, the surface of the silver thin film layer 3 is covered with the protective layer 6 containing a compound having a 2,2,6,6-tetraalkylpiperidinyl group or a 1,2,2,6,6-pentaalkylpiperidinyl group. Therefore, compared to when the silver thin film layer 3 is exposed, the protective layer 6 has a greater effect of inhibiting surface corrosion against heat and light, has excellent corrosion resistance, and is more durable than conventional electrodes.

[0072] According to the silver electrode 1 of this embodiment, since the protective layer 6 is a layer derived from a reducing agent, there is no need to provide a separate protective layer, and the effect of suppressing oxidation of the silver thin film layer 3 can be achieved at low cost.

[0073] According to the method for producing the silver electrode 1 of this embodiment, a hindered amine compound having at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group is used as the reducing agent, which allows silver oxide to be reduced even at low temperatures, making it possible to produce a silver electrode 1 whose resistivity changes little with temperature changes.

[0074] According to the method for producing the silver electrode 1 of this embodiment, the silver thin film layer 3 can be formed by reducing silver oxide at a temperature lower than the decomposition temperature of general silver oxide, and the silver electrode 1 can be easily formed.

[0075] According to the method for producing the silver electrode 1 of this embodiment, the first heating temperature is less than 200°C, which is a low temperature below the decomposition temperature of general silver oxide, and the reducing agent and silver oxide are reacted with each other. Therefore, the reducing agent is less likely to be thermally decomposed by heating.

[0076] According to the method for producing the silver electrode 1 of this embodiment, silver oxide and a reducing agent are mixed and heated to reduce the silver oxide to form the silver thin film layer 3. Therefore, compared to forming a silver thin film layer by vacuum deposition, the apparatus is not complicated and the silver thin film layer 3 can be easily formed in a short period of time. According to the method for manufacturing the silver electrode 1 of this embodiment, in the pretreatment step, silver oxide is exposed to a pretreatment solvent whose boiling point is lower than the first heating temperature. Therefore, compared to the case where the pretreatment step is not performed, the silver thin film layer 3 can be formed in a shorter time, and solvent residue is less likely to remain in the heating step.

[0077] According to the method for producing the silver electrode 1 of this embodiment, the pretreatment step includes an immersion step in which silver oxide is immersed in a pretreatment solvent, and a removal step in which part or all of the pretreatment solvent is removed. Therefore, even if the viscosity of the pretreatment solvent is low or the pretreatment solvent separates from the reducing agent, the pretreatment solvent is removed, so that the presence of the pretreatment solvent is unlikely to interfere with application of the mixture to the substrate 2, making it easier to apply the mixture to the substrate 2.

[0078] Next, a silver electrode 101 according to a second embodiment of the present invention will be described. Note that the same components as those of the silver electrode 1 according to the second embodiment will be denoted by the same reference numerals and will not be described again. The same applies hereinafter.

[0079] 3, the silver electrode 101 of the second embodiment is a multilayer structure in which an alloy layer 103 and a silver thin film layer 3 are laminated in this order on a copper plate 102 (copper body, base material). That is, in the silver electrode 101, the alloy layer 103 is interposed between the copper plate 102 and the silver thin film layer 3. 3, the silver electrode 101 has a residue layer 106 formed on the surface of the alloy layer 103 at the interface between the alloy layer 103 and the silver thin film layer 3, and a protective layer 6 formed on the surface of the silver thin film layer 3. As shown in the enlarged view of FIG. 3, the silver electrode 101 has a plurality of voids 108 formed at the interface between the alloy layer 103 and the silver thin film layer 3.

[0080] (Copper plate 102) The copper plate 102 is a copper plate-like body that extends in a planar shape, has a first main surface 110 and a second main surface 111, and serves as a support substrate that supports the silver thin film layer 3 on the first main surface 110. The copper plate 102 has different surface roughness between the first main surface 110 and the second main surface 111, with the first main surface 110 having surface irregularities and the surface roughness of the first main surface 110 being greater than the surface roughness of the second main surface 111.

[0081] (Alloy layer 103) The alloy layer 103 is formed on the copper plate 102 and is a copper-silver alloy layer containing a copper component and a silver component. In the alloy layer 103, the ratio of the silver component to the copper component is preferably 2 / 3 or more and 3 / 2 or less. The average thickness of the alloy layer 103 is thinner than that of the silver thin film layer 3, and is preferably 10% to 90%, more preferably 20% to 60%, of the average thickness of the silver thin film layer 3. The average film thickness of the alloy layer 103 can be determined, for example, by observing the cross section of the alloy layer 103 using a scanning electron microscope (SEM) image or a transmission electron microscope (TEM) image and calculating the arithmetic average value at any three points. The alloy layer 103 preferably contains a copper component and a silver component in a 1:1 ratio and has a crystal structure of the space group Fm-3m.

[0082] (Residue layer 106) The residue layer 106 is a layer formed on the surface of the alloy layer 103 . The residue layer 106 contains a component derived from a reducing agent used in the manufacturing method of the silver electrode 101 described later, and is mainly composed of residue generated during the manufacturing process of the silver electrode 101. The residue layer 106 of this embodiment contains carbon elements derived from the reducing agent. The average thickness of the residual layer 106 is preferably 1 nm or more and 20 nm or less, in which case electrical conduction between the alloy layer 103 and the silver thin film layer 3 is less likely to be impeded.

[0083] (Gap 108) The voids 108 are voids originating from gaps between the silver particles that make up the silver thin film layer 3 and gaps between the silver particles and the residue layer 106 . Each void 108 is biased toward the silver thin film layer 3 and is provided adjacent to the silver thin film layer 3 . The gap 108 in this embodiment is preferably 0.5 nm or more and 30 nm or less.

[0084] Next, a method for manufacturing the silver electrode 101 of the second embodiment will be described.

[0085] The method for manufacturing the silver electrode 101 of the second embodiment involves reducing an oxidizing agent containing silver with a reducing agent containing an organic compound while the oxidizing agent is in contact with a copper plate 102, and laminating a silver thin film layer 3 on the copper plate 102. The oxidizing agent is not particularly limited as long as it contains silver and functions as an oxidizing agent in relation to the reducing agent, and examples of the oxidizing agent that can be used include silver oxide, silver carbonate, silver acetate, and silver acetylacetonate complex. In the following description, a case where silver oxide is used as an example of an oxidizing agent will be described.

[0086] The method for producing the silver electrode 101 of the second embodiment mainly comprises a mixing step, a coating step, a heating step, and a cleaning step, and may include a pretreatment step as required, similar to the first embodiment.

[0087] First, silver oxide is mixed with a reducing agent to form a mixture (mixing step).

[0088] In this case, the reducing agent is an amine-based reducing agent, and the same reducing agent as that used in the mixing step of the first embodiment can be used.

[0089] Subsequently, the mixture obtained through the mixing step is applied to a desired area on the first main surface of the copper plate 102 (application step).

[0090] Subsequently, the copper plate 102 coated with the mixture is placed in a heating device and heated at a first heating temperature, and the silver oxide is reduced with a reducing agent to form a thin silver layer 3 on the copper plate 102 (heating step).

[0091] At this time, on the surface of the copper plate 102, the copper component diffuses toward the silver thin film layer 3, forming an alloy layer 103 with the silver thin film layer 3, and a residue layer 106 of part of the reducing agent that has reacted with the oxidizing agent is formed on the surface of the alloy layer 103. In addition, at the interface between the alloy layer 103 and the silver thin film layer 3, voids 108 are formed that correspond to the gaps between the silver particles that make up the silver thin film layer 3 and the gaps between the silver particles and the copper plate 102. A protective layer 6 is formed on the surface of the silver thin film layer 3 by covering a part of the reducing agent that has reacted with the oxidizing agent or by the unreacted reducing agent.

[0092] Next, the copper plate 102 on which the silver thin film layer 3 has been formed is washed with a washing solvent (washing step).

[0093] The cleaning solvent used at this time may be the same as the cleaning solvent used in the cleaning step of the first embodiment.

[0094] According to the silver electrode 101 of the second embodiment, the alloy layer 103 is formed at the interface between the copper plate 102 and the silver thin film layer 3. Therefore, the interface resistance between the copper plate 102 and the silver thin film layer 3 can be reduced.

[0095] In the first embodiment described above, a plate-like or film-like body is used as the substrate 2, and the silver thin film layer 3 is formed on the first main surface of the substrate 2, but the present invention is not limited to this. The substrate 2 may be a housing of a personal computer or the like, and the silver thin film layer 3 may be formed on the surface on which the film is to be formed.

[0096] In the first embodiment described above, the silver thin film layer 3 is formed on the first main surface of the substrate 2, but the present invention is not limited to this. The silver thin film layer 3 may be formed on both sides of the substrate 2. That is, the silver thin film layer 3 may be formed on both the first and second main surfaces of the substrate 2. Similarly, in the second embodiment described above, the silver thin film layer 3 is formed on the first main surface 110 of the copper plate 102, but the present invention is not limited to this. The silver thin film layer 3 may be formed on both surfaces 110, 111 of the copper plate 102. That is, the silver thin film layer 3 may be formed on both the first main surface 110 and the second main surface 111 of the copper plate 102.

[0097] In the first embodiment described above, most of the pretreatment solvent is removed by decantation in the removal step, and then the pretreatment solvent is substantially removed by drying in a dryer. However, the present invention is not limited to this. The method for removing the pretreatment solvent is not particularly limited. For example, if the pretreatment solvent is a volatile solvent, it may be removed by drying in a dryer alone, or it may be removed by volatilizing it in the air or in a vacuum chamber at room temperature.

[0098] In the first embodiment described above, the silver oxide is exposed to the pretreatment solvent by immersing and stirring the silver oxide in the pretreatment solvent, but the present invention is not limited to this, and the method of exposing the silver oxide to the pretreatment solvent is not particularly limited. For example, the silver oxide may be exposed to the pretreatment solvent by spraying the pretreatment solvent onto the silver oxide.

[0099] In the first embodiment described above, a pre-treatment step is carried out, but the present invention is not limited to this, and the pre-treatment step may be omitted.

[0100] In the second embodiment described above, the copper plate 102 is used as the copper body supporting the silver thin film layer 3, but the present invention is not limited to this. The copper body may be a copper layer laminated on a support. For example, the copper body may be a glass substrate on which a copper layer is laminated.

[0101] In the second embodiment described above, a case where the copper plate 102 is used as the copper body supporting the silver thin film layer 3 has been described, but the present invention is not limited to this. A film-like or sheet-like body such as a copper foil or a copper sheet may also be used.

[0102] In the above-described embodiments, each component can be freely substituted or added between the respective embodiments as long as it falls within the technical scope of the present invention. [Example]

[0103] The present invention will be specifically explained below by way of experimental examples as examples, but the present invention is not limited to these experimental examples.

[0104] (Experimental Example 1) In Experimental Example 1, 100 parts by weight of silver oxide powder (special grade silver oxide, manufactured by Tokyo Chemical Industry Co., Ltd.) and 100 parts by mass of liquid bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (ADEKA CORPORATION, ADK STAB LA-72) were mixed to obtain a paste-like mixture. The resulting mixture was applied to a 5 cm x 5 cm area on a glass substrate and held at 150°C for 60 minutes. The surface of the mixture on the substrate was then washed with acetone to obtain a thin silver layer with an average film thickness of 100 nm to 200 nm adhered to the substrate. The silver electrode thus obtained was used as Experimental Example 1.

[0105] (Experimental Example 2) In Experimental Example 2, a silver thin film layer was formed on a glass substrate using a silver target in a vacuum deposition apparatus so that the average film thickness was 150 nm. The silver electrode thus obtained was used as Experimental Example 2.

[0106] (Powder X-ray diffraction measurement) XRD measurements were performed on the silver electrodes of Experimental Examples 1 and 2 at room temperature, and then they were heated at 150° C. for 30 minutes, after which XRD measurements were performed again at room temperature. Powder X-ray diffraction measurements (hereinafter also referred to as XRD measurements) were carried out using a powder X-ray diffractometer (manufactured by BRUKER, model number: D2 PHASER 2nd Gen) under conditions of CuKα radiation, output of 40 kV, and 40 mA.

[0107] The diffraction spectrum obtained by the XRD measurement was subjected to Rietveld analysis using the crystal structure analysis software DIFFRAC.SUITE to calculate the lattice constants. The crystal structure was a cubic crystal structure with space group number 225 and space group Fm-3m. The crystallite diameter D was calculated using the Scherrer equation from the half-width of the peak near 2θ=37.90° in the diffraction spectrum obtained by XRD measurement. The Scherrer formula is expressed as D=0.94λ / (βcosθ), where λ is the measurement X-ray wavelength (0.15418 nm), β is the half-width, and θ is the Bragg angle.

[0108] (Temperature coefficient test) For the silver electrodes of Experimental Examples 1 and 2, the electrical resistivity was measured at 1°C increments from room temperature to 190°C, and the temperature coefficient at each measurement temperature was calculated by differentiating the resistivity at each measurement temperature. The temperature coefficients at each measurement temperature were also arithmetically averaged to calculate the average temperature coefficient. The electrical resistivity was calculated as follows. Using a stylus-type profilometer (ET3000i, manufactured by Kosaka Laboratory Co., Ltd.), the step height at the boundary between the substrate and the silver thin film layer was measured at three arbitrary measurement points within a range of 100 μm from the boundary with the substrate on the side of the silver thin film layer within the sample, and the arithmetic mean of the film thickness of the silver thin film layer at these three measurement points was calculated. Next, the sheet resistance at each of these three measurement points was measured using the four-point probe method, and the arithmetic mean of the sheet resistance was calculated. The electrical resistivity (Ω·cm) was calculated by multiplying the calculated arithmetic mean of the sheet resistance (Ω / □) by the arithmetic mean of the film thickness (nm).

[0109] (Spectroscopic ellipsometry measurement) 1.0 x 10 by spectroscopic ellipsometry -18 Hz~1.0×10 3 The dielectric function in the kHz frequency range was obtained, and the obtained dielectric function was fitted using the Drude model to calculate the resistivity in each frequency range.

[0110] The diffraction peaks in the powder X-ray diffraction measurement are shown in FIG. 4, the temperature coefficients at each measurement temperature in the temperature coefficient test are shown in FIG. 5, and the electrical resistivity at each frequency in the spectroscopic ellipsometry measurement is shown in FIG. Table 1 also shows the lattice constants and crystallite sizes before and after heating obtained by powder X-ray diffraction measurement, and the average temperature coefficients obtained by temperature coefficient tests.

[0111] [Table 1]

[0112] In Experimental Examples 1 and 2, as shown in Figure 4, peaks originating from the (111) plane of Ag were detected in the range of 37.50° to 39.50°, indicating that a thin silver layer was formed on the glass substrate. As shown in FIG. 4, the peak of the (111) plane in Experimental Example 1 was shifted to the lower angle side compared to the peak of the (111) plane in Experimental Example 2. Furthermore, the peak of the (111) plane of Experimental Example 1 after heating had a higher peak intensity and was slightly shifted to a lower angle compared to the peak of the (111) plane of Experimental Example 1 before heating, whereas the peak of the (111) plane of Experimental Example 2 after heating had a slightly higher peak intensity and was shifted to a higher angle compared to the peak of the (111) plane of Experimental Example 2 before heating.

[0113] In Experimental Example 1, the lattice constant was constant before and after heating, and the crystallite size increased, as shown in Table 1. This increase in crystallite size is thought to be due to particle growth, and the constant lattice constant suggests that the structure is stable against heat. On the other hand, in Experimental Example 2, the lattice constant and crystallite size decreased before and after heating, as shown in Table 1. This is thought to be due to the influence of thermal distortion caused by residual stress.

[0114] The temperature coefficients of Experimental Example 1 are distributed as shown by the circles in Figure 5, and are less than 0.00001 in any temperature range from 70°C to 190°C. In any temperature range from 70°C to 190°C, the temperature coefficient is the same as that of bulk silver at room temperature (4 × 10 -3 Ω / K), and the average temperature coefficient is smaller than that of bulk silver (4×10 -3 Ω / K) is 1.7×10 -4 It was twice as small. This suggests that compared to bulk silver at room temperature, the temperature coefficient is small and the silver has thermal stability in any temperature range from 70°C to 190°C.

[0115] In addition, the average temperature coefficient of Experimental Example 1 is 7.14 × 10 as shown in Table 1. -7 Ω / K, which is an extremely low value of 0.02 times the average temperature coefficient of Experimental Example 2. From this, it was confirmed that Experimental Example 1 had a smaller change in resistivity with respect to temperature change than Experimental Example 2, and had thermal stability.

[0116] In Experimental Example 2, as shown in FIG. 6, the resistivity increased significantly as the frequency increased from around 1 kHz, whereas in Experimental Example 1, the resistivity remained roughly constant even as the frequency increased. In Experimental Example 1, 7.0 × 10 -6 The resistance was reduced to Ωcm or less. In addition, in Experimental Example 1, the resistivity at 10 kHz was 1.1 times or less compared to the resistivity at 1 kHz. This shows that in Experimental Example 1, the resistivity is less affected by changes in frequency and has low frequency dependency.

[0117] The above can be summarized as follows: (1) From the results of XRD measurement, a peak derived from silver on the (111) plane was confirmed in Experimental Example 1, and it was found that silver oxide could be reduced even at a low temperature of 150°C to form a silver layer with high thermal conductivity and thermal diffusivity. (2) The results of XRD measurements showed that the lattice constant remained constant and the crystallite size increased only slightly after heating at 150°C for 30 minutes, suggesting that the structure was stable against heat. (3) The results of the temperature coefficient test showed that the temperature coefficient in the range of 70°C to 190°C was extremely small compared to bulk silver, being less than 0.00001 in all cases, indicating that the resistivity is almost independent of temperature and has high thermal stability. (4) The results of spectroscopic ellipsometry measurements showed that the resistivity was almost constant with respect to changes in frequency, and that the resistivity at 10 kHz was less than 1.1 times that at 1 kHz, indicating that the resistivity had low-frequency dependence even in the high-frequency range.

[0118] (Experimental Example 3) In Experimental Example 1, first, as a pretreatment step, toluene (Wako Co., Ltd., ultra-dehydrated) and silver oxide powder (FUJIFILM Wako Pure Chemical Industries, Ltd., special grade silver oxide, maximum particle size 10 μm) were placed in a sealed container and stirred. Thereafter, decantation was carried out three times to extract the toluene, and then the silver oxide was placed in a dryer and dried at 100°C to volatilize and substantially remove the toluene. Subsequently, 100 parts by weight of silver oxide from which the toluene had been removed and 100 parts by mass of liquid bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (ADEKA CORPORATION, Adekastab LA-72) were mixed to obtain a paste-like mixture. Other than these, the same procedure as in Experimental Example 1 was followed, and this was designated Experimental Example 3.

[0119] (Experimental Example 4) Experimental Example 4 was conducted in the same manner as in Experimental Example 3, except that solid bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (ADEKA CORPORATION, Adeka STAB LA-77Y, melting point 82°C to 87°C) was used as the reducing agent.

[0120] (SEM observation) The cross sections of the silver electrodes of Experimental Examples 3 and 4 were subjected to SEM observation using a field emission scanning electron microscope (FE-SEM) (JSM6700F, manufactured by JEOL Ltd.).

[0121] FIG. 7(a) shows an SEM image of Experimental Example 3, and FIG. 7(b) shows a trace of the SEM image of FIG. 7(a). In Experimental Example 3, as shown in FIG. 7, a uniform thin silver layer of about 220 nm to 280 nm was confirmed, and a silver particle layer in which silver particles of about several μm were locally deposited was also confirmed. Similarly, in Experimental Example 4, SEM observation was performed, and a thin silver film layer was confirmed, as well as a silver particle layer in which silver particles of about several μm in size were locally deposited. These results confirmed that the use of an N-CH3-type hindered amine light stabilizer or an NH-type hindered amine light stabilizer as a reducing agent can reduce silver oxide on a glass substrate to form a nanometer-order thin silver film layer. Furthermore, a silver particle layer consisting of locally deposited silver particles of a few micrometers was confirmed, suggesting that silver oxide particles larger than a certain particle size do not melt to form a thin silver film layer, but are reduced to silver while maintaining their shape, resulting in crystal growth.

[0122] (Experimental Example 5) Experimental Example 5 was conducted in the same manner as Experimental Example 3, except that distilled water was used as the pretreatment solvent.

[0123] (Experimental Example 6) Experimental Example 6 was conducted in the same manner as Experimental Example 3, except that the pretreatment step was not carried out.

[0124] (Reaction time test) In Experimental Examples 3, 5, and 6, the temperature change and resistance change during the heating process were measured, and the reaction time from the start of heating and the change in the resistance value were observed. The resistance change was measured using a Loresta GP (MCP-T610) manufactured by Mitsubishi Chemical Analytech Co., Ltd., using a four-terminal four-point probe method.

[0125] The results of the reaction time test are shown in FIG. In Experimental Example 3, the resistance value became nearly 0 after a reaction time of approximately 1090 seconds, suggesting that the silver oxide had decomposed and a thin silver film layer had been formed, as shown in Figure 8. In Experimental Example 3, it was also suggested that a thin silver film layer had been formed when the heating temperature rose to approximately 143°C. In Experimental Example 5, the resistance value became nearly 0 after a reaction time of about 1680 seconds, suggesting that the silver oxide had decomposed and a thin silver layer had been formed. In Experimental Example 6, the resistance value became nearly 0 after a reaction time of about 1760 seconds, suggesting that silver oxide had decomposed and a thin silver layer had been formed. In Experimental Example 3, in which pretreatment was performed with an organic solvent, the time required for the silver thin film layer to form was reduced by approximately 38% compared to Experimental Example 6, in which no pretreatment was performed. In Experimental Example 5, in which pretreatment was performed with water, the time required for the silver thin film layer to form was reduced by approximately 5% compared to Experimental Example 6, in which no pretreatment was performed. In addition, in Experimental Example 3, in which pretreatment was performed with an organic solvent, the time required for the formation of a thin silver layer was reduced by approximately 35% compared to Experimental Example 5, in which pretreatment was performed with water. These findings indicate that immersing silver oxide in a pretreatment solvent removes impurities from the surface of the silver oxide, accelerating the start of silver particle growth compared to when the silver oxide is not pretreated, and improving the overall rate at which the silver thin film layer is formed. In particular, the use of an organic solvent as a pretreatment solvent dramatically improves the rate at which the silver thin film layer is formed. It was also suggested that the use of an organic solvent as a pretreatment solvent would enable the formation of a thin silver layer at a lower heating temperature.

[0126] (Experimental Example 7) Vacuum degree 1×10 -4 Silver was evaporated onto the glass substrate at a deposition rate of approximately 0.1 to 0.3 nm / sec under reduced pressure of 100 Pa or more to form a thin silver film layer. The silver electrode thus obtained was used as Experimental Example 7.

[0127] (Corrosion resistance test) Experimental Examples 3 and 7 were heated in the atmosphere at 190° C. for 1 hour, and the changes before and after were confirmed.

[0128] Discoloration was observed at the edge in Experimental Example 7, whereas no discoloration was observed in Experimental Example 3. From this, it is considered that in Experimental Example 3, the presence of a protective layer having 1,2,2,6,6-pentaalkylpiperidinyl groups derived from the reducing agent suppressed surface corrosion. Furthermore, when the silver thin film layer of the silver electrode of Experimental Example 7 was scraped with a fingernail, the silver thin film easily peeled off from the glass substrate, whereas when the silver thin film layer of the silver electrode of Experimental Example 3 was scraped with a fingernail with the same amount of force, the silver thin film did not peel off from the glass substrate. From this, it is believed that the presence of the protective layer improved the adhesion between the silver thin film layer and the glass substrate, and also improved the layer strength of the silver thin film layer.

[0129] (Experimental Example 8) Experimental Example 8 was conducted in the same manner as in Experimental Example 1, except that a copper substrate was used as the base material instead of the glass substrate.

[0130] (Experimental Example 9) Experimental Example 9 was conducted in the same manner as Experimental Example 2, except that a copper substrate was used as the base material instead of the glass substrate.

[0131] (STEM observation) In Experimental Example 8, cross-section processing was performed using a focused ion beam (FIB), and the cross-section was observed using a scanning transmission electron microscope (STEM) (Hitachi High-Technologies Corporation, HD-2700) and elemental analysis was performed using energy dispersive X-ray analysis (EDX). In addition, in Experimental Example 8, an electron beam diffraction image was observed, and a simulation of the electron beam diffraction image was performed based on the crystal database of Mat Navi (https: / / mits.nims.go.jp / ). The electron beam diffraction image of Example 7 was superimposed on the simulation pattern for identification.

[0132] FIG. 9(a) shows a low-magnification STEM secondary electron image (hereinafter also referred to as SE image) in Experimental Example 8, and FIG. 9(b) shows a trace of the SE image in FIG. 9(a). FIG. 10(a) shows a high-magnification STEM transmission electron image (hereinafter also referred to as a TE image) in Experimental Example 8, and FIG. 10(b) shows a trace of the TE image in FIG. 10(a).

[0133] In Experimental Example 8, when the SE image was observed as shown in Figure 9, a silver-copper alloy layer was confirmed between the copper substrate and the silver thin film layer, and multiple voids were formed on the silver thin film layer side of the alloy layer. Similarly, in Experimental Example 9, when the SE image was observed, a silver-copper alloy layer was confirmed between the copper substrate and the silver thin film layer, and multiple voids were formed on the silver thin film layer side of the alloy layer. In Experimental Example 8, when a high-magnification TE image was observed as shown in Figure 10, a silver-copper alloy layer was confirmed between the copper substrate and the silver thin film layer, and a protective layer of several to several tens of nanometers thick derived from the reducing agent was confirmed on the surface of the silver thin film layer. In addition, a residue layer (light metal layer) was confirmed between the alloy layer and the silver thin film layer. Elemental analysis by EDX was performed at measurement points 1 to 6 shown in Figure 10(b). At measurement point 2, which corresponds to the position of the silver thin film layer, a silver peak was detected, but no carbon or nitrogen peaks were detected. However, at measurement point 1, which corresponds to the position of the protective layer, not only a silver peak but also carbon and nitrogen peaks were detected. At measurement point 4, which corresponds to the alloy layer, peaks for silver, copper, and carbon were detected, but no nitrogen peak was detected. At measurement point 3, which corresponds to the position of the residue layer, peaks for silver, copper, and carbon were detected, as at measurement point 4, but no nitrogen peak was detected. In addition, a larger carbon peak was detected than at measurement point 4, and the amount detected was greater. At measurement point 5, which corresponds to the position of the interface between the alloy layer and the copper substrate, and measurement point 6, which corresponds to the position of the copper substrate, a copper peak was detected, but no nitrogen peak was detected.

[0134] In Experimental Example 8, electron beam diffraction was performed at measurement point 4 shown in FIG. 10(b) and the electron beam diffraction image was observed. The pattern of the electron beam diffraction image roughly matched the simulation pattern of a copper-silver alloy with a copper component and silver component ratio of 1:1. The simulation pattern of this copper-silver alloy was calculated based on the crystal structure (space group number 225, crystal structure of space group Fm-3m (a=0.38765 nm, b=0.38765 nm, c=0.38765 nm, α=90°, β=90°, γ=90°)).

[0135] In the results at measurement point 1, a nitrogen peak and a carbon peak were detected, suggesting that heating caused the reducing agent residue to bleed out from the surface of the silver thin film layer, forming a protective layer on the silver thin film layer containing a compound with a 1,2,2,6,6-pentaalkylpiperidinyl group derived from the reducing agent. The results at measurement point 4 showed that large amounts of carbon were detected in the adjacent silver thin film layer and alloy layer, and that areas between the alloy layer and silver thin film layer were confirmed in the TE image that were lighter in color than the alloy layer and silver thin film layer. This suggested that a light metal layer had formed between the silver thin film layer and the alloy layer as a residue layer due to the oxidation and decomposition of the reducing agent.

[0136] The above can be summarized as follows: (1) The results of SEM and STEM observations revealed that by using an N-CH3-type hindered amine light stabilizer having a 1,2,2,6,6-pentaalkylpiperidinyl group or an NH-type hindered amine light stabilizer having a 2,2,6,6-tetraalkylpiperidinyl group as a reducing agent, it is possible to reduce silver oxide on a copper substrate and form a nanometer-order silver thin film layer. (2) The results of the reaction time test showed that the reaction time for forming the silver thin film layer could be shortened by pre-treating with a pre-treatment solvent before the heating step. In particular, the reaction time was significantly shortened by using an organic solvent as the pre-treatment solvent. (3) The results of the corrosion resistance test showed that the use of a hindered amine light stabilizer as a reducing agent resulted in the formation of a silver thin film with higher corrosion resistance than a silver thin film layer formed by vacuum deposition. (4) The results of STEM observation confirmed that the use of a hindered amine light stabilizer as a reducing agent reduces silver oxide on the copper substrate to form a thin silver film layer, and also forms a protective layer on the surface of the thin silver film layer and a residue layer on the surface of the alloy layer. The results of EDX analysis suggested that the protective layer on the surface of the thin silver film layer and the residue layer at the interface between the thin silver film layer and the alloy layer were derived from the reducing agent. [Explanation of symbols]

[0137] 1,101 silver electrode 2. Substrate 3. Silver thin film layer (silver layer) 5 layers of silver particles 6. Protective layer 10 silver particles 102 Copper Plate (Copper Body, Substrate) 103 alloy layer 106 Residue Layer 108. Void

Claims

1. A silver electrode in which a silver layer is laminated on a substrate, In an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation, there is one peak in the range of diffraction angle 2θ=37.5° to 38.3°, the rate of change in the diffraction angle of the peak when heated at 150°C for 30 minutes is 0.5% or less; A protective layer is provided. the protective layer has a cross-sectional structure that covers the surface of the silver layer, The protective layer has at least one of a 1,2,2,6,6-pentaalkylpiperidinyl group and a 2,2,6,6-tetraalkylpiperidinyl group.

2. 2. The silver electrode according to claim 1, wherein the temperature coefficient at 70°C and the temperature coefficient at 190°C are both less than 0.00001.

3. 3. The silver electrode according to claim 2, having a temperature coefficient in the range of 70°C to 190°C of less than 0.00001.

4. The silver electrode according to any one of claims 1 to 3, wherein the resistivity at a frequency of 10 kHz is 1.1 times or less relative to the resistivity at a frequency of 1 kHz.

5. The silver electrode according to any one of claims 1 to 4, further comprising, on the silver layer, silver particles having an average particle size larger than the average film thickness of the silver layer.

6. The silver electrode according to any one of claims 1 to 5, wherein the silver layer has an average film thickness of 500 nm or less.

7. A silver electrode in which an oxidizing agent containing silver is in contact with a substrate, the oxidizing agent is reduced by a reducing agent containing an organic compound, and a silver layer is laminated on the substrate, In an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation, there is one peak in the range of diffraction angle 2θ=37.5° to 38.3°, the rate of change in the diffraction angle of the peak when heated at 150°C for 30 minutes is 0.5% or less; the substrate is a copper body, an alloy layer containing a copper component and a silver component is formed at the interface between the substrate and the silver layer, A silver electrode, wherein a protective layer containing a component of the reducing agent is laminated on the surface of the silver layer.

8. The silver electrode according to claim 7 , wherein a residue layer containing a component derived from the reducing agent is formed at the interface between the alloy layer and the silver layer.

9. A pretreatment step of pretreating powdered silver oxide; mixing the pretreated silver oxide with a reducing agent to form a mixture; a coating step of coating the mixture onto a substrate; a heating step of heating the substrate coated with the mixture at a first heating temperature; the reducing agent is a hindered amine compound having at least one of a 1,2,2,6,6-pentaalkylpiperidinyl group and a 2,2,6,6-tetraalkylpiperidinyl group, In the pretreatment step, the silver oxide is exposed to a pretreatment solvent having a boiling point lower than the first heating temperature.

10. The method for producing a silver electrode according to claim 9 , wherein the first heating temperature is less than 200° C.

11. The method for producing a silver electrode according to claim 9 or 10, wherein the pretreatment step includes an immersion step of immersing the silver oxide in the pretreatment solvent, and a removal step of removing a part or all of the pretreatment solvent.

12. The method for producing a silver electrode according to any one of claims 9 to 11, wherein the pretreatment solvent is at least one solvent selected from the group consisting of acetone, toluene, ethanol, acetonitrile, and water.

13. The method for producing a silver electrode according to any one of claims 9 to 12, wherein in the heating step, the silver oxide is reduced with the reducing agent to form a silver layer on the base material, and the surface of the silver layer is further covered with a protective layer formed from a component derived from the reducing agent.

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