Method for manufacturing a transparent electrode

Abstract

A method for manufacturing a transparent electrode comprises: a step for setting manufacturing conditions for manufacturing the transparent electrode; a step for forming a resist layer on a plate-shaped member including a transparent substrate; a step for irradiating the resist layer with a laser beam in a predetermined irradiation pattern in order to precipitate metal ions generated by a metal salt in the resist layer; and a step for removing a residual resin portion excluding the metal ions precipitated in the resist layer. The step for setting the manufacturing conditions includes a step for setting the thin wire thickness of a thin metal wire and a step for setting the resist thickness of the resist layer based on the thin wire thickness.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a transparent electrode and a transparent electrode. [Background technology]

[0002] Transparent electrodes, which are optically transparent and electrically conductive, are used as components of touch panels adopted in smartphones, tablet-type information terminals, etc. For example, transparent conductive films (ITO: Indium Tin Oxide) are used as transparent electrodes. However, several technical improvements have been pointed out for transparent conductive films.

[0003] For example, one area for improvement is the electrical resistivity (1.5 × 10 -6 Another area for improvement is the difficulty of increasing the size. Transparent conductive films are inorganic crystalline films and therefore have little flexibility. Therefore, making them flexible is also an area for improvement. Furthermore, indium, the main raw material for transparent conductive films, is a rare metal. Therefore, there are concerns about the future depletion of resources. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 030202 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-148082 Summary of the Invention [Problem to be solved by the invention]

[0005] Metal mesh transparent conductive films have attracted attention as transparent electrodes that can be made larger, more flexible, and with reduced material costs. Metal mesh transparent conductive films are formed by patterning a fine metal mesh structure on a transparent substrate. Patent Document 1 discloses a technique for fabricating metal meshes for touch panels using a plating method. Patent Document 2 discloses a technique for manufacturing thin film transistors (TFTs), which are semiconductor elements. The technique in Patent Document 2 uses an inkjet method to eject metal particles and organic resin in a predetermined pattern. The TFTs are then constructed by irradiating them with a laser.

[0006] Methods for manufacturing metal mesh transparent conductive films include the Super Nap method (SuPR-NaP method) and the silver nano inkjet method. The Super Nap method uses printing technology to create thin metal wires such as silver. Metal mesh transparent conductive films manufactured using the Super Nap method have characteristics such as a metal wire width of 2 μm, a sheet resistance of 21 Ω / sq, a light transmittance of 90%, and a film thickness of 100 nm or less. The silver nano inkjet method uses inkjet printing technology to create thin metal wires such as silver. Metal mesh transparent conductive films manufactured using the silver nano inkjet method have characteristics such as a metal wire width of 5 μm, a sheet resistance of 0.3 Ω / sq, a light transmittance of 83%, and a film thickness of 200 nm or less.

[0007] As described above, the performance of a transparent electrode is determined by its optical transparency and electrical conductivity, and therefore it is desirable to further improve the optical transparency and electrical conductivity of the transparent electrode.

[0008] The present invention provides a method for producing a transparent electrode that can further improve light transmittance and electrical conductivity, and a transparent electrode. [Means for solving the problem]

[0009] One aspect of the present invention is a method for manufacturing a transparent electrode including thin metal wires that are metal microstructures, the method comprising the steps of: setting manufacturing conditions for manufacturing the transparent electrode; forming a workpiece layer on a plate-like member including a light-transmitting substrate; irradiating the workpiece layer with laser light in a predetermined irradiation pattern, the workpiece layer being made of a resin material including a polyamic acid having a metal salt dissolved therein, to precipitate metal ions resulting from the metal salt; and removing residual resin in the workpiece layer except for the precipitated metal ions. The step of setting the manufacturing conditions includes the steps of setting the thickness of the thin metal wires and setting the thickness of the workpiece layer based on the thickness of the thin metal wires.

[0010] In this manufacturing method, a metal microstructure that constitutes a transparent electrode is deposited by irradiating a work layer with laser light. Deposition using laser light allows the shape of the metal microstructure to be miniaturized to the point where it is invisible to the naked eye. This further improves light transmittance. In this manufacturing method, the thickness of the work layer is set based on the thickness of the metal microstructure. The thickness of the metal microstructure is easily affected by the thickness of the work layer. As a result, by setting the appropriate thickness of the work layer, a metal microstructure having the desired thickness can be formed. In other words, conductivity can be further improved.

[0011] In one embodiment, in the step of setting the thickness of the processing layer, the thickness of the processing layer may be set to be equal to or greater than the thickness of the thin metal wire, thereby forming a transparent electrode having a sufficient thickness to achieve the desired conductivity.

[0012] In one embodiment, in the step of setting the thickness of the process layer, the thickness of the process layer may be set to 1 μm or more, which also allows the formation of a transparent electrode having a sufficient thickness to obtain the desired conductivity.

[0013] In one embodiment, the step of setting the manufacturing conditions further includes a step of setting the irradiation density of the laser beam, and in the step of setting the irradiation density of the laser beam, the irradiation density of the laser beam is set to 5 kJ / cm. 2 More than 1000kJ / cm2 The irradiation density of the laser light affects the conductivity of the metal microstructures. This setting makes it possible to form a transparent electrode that achieves the desired conductivity.

[0014] In one embodiment, the step of setting the manufacturing conditions may further include the step of setting a scanning speed of the laser beam, wherein the scanning speed of the laser beam may be set to 1 μm / sec or more and 1 mm / sec or less.

[0015] In one embodiment, the step of forming the processable layer may use a lamination method or a roll coating method, which can easily form the processable layer having the thickness set in the step of setting the thickness of the processable layer.

[0016] In one embodiment, the step of forming the processable layer in the manufacturing method may use a spin coating method. The method for manufacturing a transparent electrode may further include, after the step of setting the thickness of the processable layer and before the step of forming the processable layer, a step of setting at least one of the rotation speed of the spin coater and the viscosity of the resin material so that the processable layer has the thickness set in the step of setting the thickness of the processable layer. This setting allows the processable layer to be reliably formed with the set thickness.

[0017] Another embodiment of the present invention provides a transparent electrode comprising a light-transmitting substrate and an electrode network provided on the light-transmitting substrate and composed of fine metal wires that are metal microstructures. The fine metal wires may have a line width of 200 nm to 4 μm, a fine wire thickness of 200 nm to 4 μm, and a spacing between adjacent fine metal wires of 20 μm to 100 μm. A transparent substrate composed of fine metal wires having such a shape can further improve light transmittance and conductivity.

[0018] In another embodiment, the electrode mesh may include a plurality of first thin metal wires extending in a first direction and spaced apart from one another in a second direction perpendicular to the first direction, and second thin metal wires extending in the second direction and spaced apart from one another in the first direction. Even with this structure, good light transmittance and conductivity can be obtained. [Effects of the Invention]

[0019] According to the present invention, a method for producing a transparent electrode that can further improve light transmittance and conductivity, and the transparent electrode are provided. [Brief explanation of the drawings]

[0020] [Figure 1] Fig. 1(a) is a perspective view showing a schematic configuration of a device including a transparent electrode, and Fig. 1(b) is a perspective view showing an enlarged portion of the transparent electrode shown in Fig. 1(a). [Figure 2] FIG. 2 is a flow chart showing the main steps of the method for manufacturing a transparent electrode. [Figure 3] FIG. 3 is a diagram showing the irradiation step. [Figure 4] 4(a), 4(b), 4(c), 4(d), 4(e) and 4(f) are diagrams schematically illustrating the main steps of a method for producing a transparent electrode. [Figure 5] FIG. 5 is a diagram showing the relationship between the rotation speed of a spin coater when forming a resist layer and the thickness of a thin metal wire. [Figure 6] 6(a) and 6(b) are graphs showing the relationship between the irradiation intensity of the laser light and the line width of the thin metal wire. [Figure 7] 7(a) and 7(b) are graphs showing the relationship between the irradiation density of the laser light and the resistivity. [Figure 8] FIG. 8 is a graph for explaining the effect of the heating step. [Figure 9] FIG. 9 is a graph comparing the characteristics of a transparent electrode obtained by the manufacturing method of the embodiment with the characteristics of a transparent electrode obtained by the manufacturing method of the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0022] [Transparent electrode] As shown in FIG. 1( a), the transparent electrode 1 of this embodiment constitutes a display device 100 used in smartphones, tablets, and the like. The display device 100 includes the transparent electrode 1, a liquid crystal display panel 101, and a cover glass 103. The transparent electrode 1 is provided in close contact with the liquid crystal display panel 101. By pressing the transparent electrode 1 with a finger or the like, information regarding the two-dimensional position of the finger touching the liquid crystal display panel 101 is obtained. The transparent electrode 1 has a mesh-shaped or striped electrode network 10. The electrode network 10 generates changes in current and capacitance depending on the pressed position. The pressed position can be identified by utilizing the changes in current and capacitance, thereby obtaining information about the input position. Examples of devices that use the transparent electrode 1 include large touch panels such as digital signage, in-vehicle displays such as flexible displays, and small film touch panels for portable information terminals.

[0023] As shown in FIG. 1(b), the transparent electrode 1 has an electrode mesh 10 and a transparent substrate 21 (light-transmitting substrate). The transparent substrate 21 is a base of the transparent electrode 1. The transparent substrate 21 receives light emitted from the liquid crystal display panel 101 from the rear surface 21b of the substrate. The transparent substrate 21 emits the received light from the main surface 21a of the substrate toward the user. The transparent substrate 21 has rigidity according to the device to which it is applied. For example, the transparent substrate 21 has a predetermined rigidity so as not to bend even when operated by the user. When the transparent substrate 21 is applied to a device with a curved display or a device that is intended to be foldable, the transparent substrate 21 may have a desired flexibility.

[0024] The electrode mesh 10 is a conductive portion composed of fine metal wires 11, which are metal microstructures. The electrode mesh 10 is composed of a combination of multiple fine metal wires 11 made of silver. The fine metal wires 11 are conductive. The fine metal wires 11 are thin enough to be invisible to the naked eye. For example, the line width W11 of the fine metal wires 11 is a value in the range of 200 nm to 4 μm. The line width W11 of the fine metal wires 11 is preferably a value in the range of 200 nm to less than 2 μm. The line width W11 of the fine metal wires 11 is more preferably a value in the range of 200 nm to 1 μm. For example, the line width W11 of the fine metal wires 11 is 1 μm. The fine wire thickness T11 is defined as the height of the fine metal wires 11 relative to the main surface 21a of the transparent substrate 21. The fine wire thickness T11 of the fine metal wires 11 may be considered to be the thickness of the electrode mesh 10. The wire thickness T11 of the metal wire 11 is a value within the range of 200 nm to 4 μm. For example, the wire thickness T11 of the metal wire 11 is 600 nm. When the wire has such dimensions, the electrical resistivity of the metal wire 11 is 0.5×10 -7 Ωm or more 10×10 -7 The electrical resistivity of the thin metal wire 11 is, for example, 2×10 -7 In this embodiment, the conductivity will be described using electrical resistivity. However, the indicator of conductivity is not limited to electrical resistivity. For example, the sheet resistance value (Ω / sq) may be used as the indicator of conductivity.

[0025] The electrode mesh 10 of the embodiment has a lattice shape. The electrode mesh 10 includes thin metal wires 11 (first thin metal wires) extending in a first direction and thin metal wires 11 (second thin metal wires) extending in a second direction. The spacing G11 between the thin metal wires 11 spaced apart from each other is a value within the range of 20 μm to 100 μm. The spacing G11 between the thin metal wires 11 is, for example, 40 μm. With such line width W11 and spacing G11, the electrode mesh 10 is not visible to the user. The electrode mesh 10 transmits light from the liquid crystal display panel 101 without blocking it. For example, the light transmittance of the electrode mesh 10 is a value within the range of 80% to 95%. The light transmittance of the electrode mesh 10 is more preferably a value within the range of more than 90% to 95%. The light transmittance of the electrode mesh 10 is, for example, 85%.

[0026] [Method for manufacturing transparent electrodes] A method for manufacturing the transparent electrode 1 will be described in detail below with reference to the flow chart shown in Fig. 2. The method for manufacturing the transparent electrode 1 mainly includes a setting step S10, a forming step S20, an irradiating step S30, a removing step S40, and a heating step S50.

[0027] <Setup steps> Several manufacturing conditions related to the manufacture of the transparent electrode 1 are set (setting step S10). In the setting step S10, conditions related to the forming step S20 and conditions related to the irradiating step S30 are mainly set. The conditions related to the forming step S20 include the cross-sectional shape of the thin metal wires 11, the resist thickness T51 of the resist layer 51 (see FIG. 3), the viscosity of the coating liquid, and the rotation speed of the spin coater. The conditions related to the irradiating step S30 include the irradiation intensity of the laser light, the irradiation density of the laser light, and the scanning speed of the laser light. In the setting step S10, conditions different from the conditions exemplified above may be set as necessary. For example, in the setting step S10, the irradiation pattern of the laser light may be set. The thin metal wires 11 that constitute the transparent electrode 1 are formed in the portions irradiated with the laser light. The irradiation pattern of the laser light corresponds to the arrangement of the thin metal wires 11 that constitute the transparent electrode 1.

[0028] The cross-sectional shape of the thin metal wire 11 is set (step S11). The cross-sectional shape of the thin metal wire 11 may be rectangular. The cross-sectional shape of the thin metal wire 11 may be approximately square. The cross-sectional shape of the thin metal wire 11 can be defined by the wire thickness T11 and the wire width W11.

[0029] The line width W11 affects light that is irradiated perpendicularly to the transparent substrate 21. For example, the larger the line width W11, the less light is transmitted. The smaller the line width W11, the more light is transmitted. The line width W11 and the line thickness T11 affect light that is irradiated obliquely to the transparent substrate 21. For example, the larger the line thickness T11, the less light is transmitted. The smaller the line thickness T11, the more light is transmitted. The cross-sectional area of the metal wire 11 is related to the resistance value of the metal wire 11. The line thickness T11 and line width W11 are related to the conductivity of the transparent electrode 1.

[0030] From the viewpoint of light transmittance, the smaller the wire width W11 and the wire thickness T11, the better. However, the smaller the wire width W11 and the wire thickness T11, the smaller the cross-sectional area. Therefore, the conductivity tends to decrease. Therefore, from the viewpoint of both light transmittance and conductivity, it is preferable to make the cross-sectional shape of the metal wire 11 approximately square, so that the cross-sectional area of the metal wire 11 is large and the shape does not hinder the propagation of light. The cross-sectional shape of the metal wire 11 has approximately the same wire width and thickness.

[0031] The cross-sectional shape of the thin metal wire 11 is not limited to a substantially square. The cross-sectional shape of the thin metal wire 11 may be, for example, rectangular, hemispherical dome-shaped, or circular. Ideally, the cross-sectional shape of the thin metal wire 11 is preferably rectangular, hemispherical dome-shaped, or circular. However, as long as the cross-sectional shape is such that the wire width and thickness are approximately the same, the thin metal wire 11 may have a complex shape, such as a rectangular shape with raised corners.

[0032] Next, the resist thickness T51 of the resist layer 51 is set (step S12). The resist thickness T51 is set based on the thin line thickness T11. At the very least, the resist thickness T51 is greater than the thin line thickness T11. The resist thickness T51 is set to a value equal to or greater than the thin line thickness T11. As an example, the resist thickness T51 may be set to 10 times the thin line thickness T11. For example, the resist thickness T51 may be set to 10 μm or more.

[0033] As a result of careful investigation, the inventors have found that the shape (thickness, width) of the deposited thin metal wires 11 is affected by the irradiation intensity and irradiation density of the laser light. The inventors have found that the thin wire thickness T11 is particularly susceptible to the influence of the resist thickness T51.

[0034] FIG. 4 is a diagram illustrating the main steps of forming the thin metal wire 11. In particular, FIGS. 4(b), 4(c), and 4(d) illustrate the precipitation of metal particles constituting the thin metal wire 11 by irradiation with laser light L. A plurality of metal ions 52 are dispersed in the resist layer 51 before irradiation with laser light L (see FIG. 4(a)). Laser light L is irradiated from the transparent substrate 21 side (see FIG. 4(b)). As a result, metal ions 52 resulting from metal salts are precipitated, forming precipitation nuclei 53. The precipitation nuclei 53 gradually grow while absorbing surrounding metal ions 52 (see FIGS. 4(c) and 4(d)). After irradiation with laser light L is completed, the residual resin portion 55 is removed (see FIG. 4(e)). Next, an annealing treatment is performed (see FIG. 4(f)). The annealing treatment effectively bonds the grown precipitation nuclei 53, resulting in the thin metal wire 11, which is a metal microstructure.

[0035] Noteworthy is the appearance and growth of precipitation nuclei 53 shown in Figures 4(c) and 4(d). The appearance and growth of precipitation nuclei 53 occur due to the presence of surrounding metal ions 52. For example, when a sufficient amount of metal ions 52 exists around the precipitation nuclei 53, the precipitation nuclei 53 can grow. However, when the resist thickness T51 is insufficient, a sufficient amount of metal ions 52 does not exist around the precipitation nuclei 53. As a result, the growth of the precipitation nuclei 53 may be inhibited. Therefore, it was found that the resist thickness T51 should be set so that a sufficient amount of metal ions 52 exists around the precipitation nuclei 53 to form the desired thin metal wires 11.

[0036] Next, the viscosity of the coating liquid, which is a resin material, is set (step S13).

[0037] Next, the operating conditions of the spin coater are set (step S14). More specifically, the rotation speed of the spin coater is set so that the resist thickness T51 becomes the value set in the previous step S12. It is assumed that when the transparent substrate 21 coated with the coating liquid that will become the resist layer 51 is rotated, the coating liquid is subjected to a balance between centrifugal force and viscous force. According to Newton's law of viscosity, the change in thickness of the coating liquid over time when a constant rotation speed is maintained is expressed by the following equation. Equation (1) is based on the assumption that the coating liquid is present over the entire substrate main surface 21a of the transparent substrate 21.

number

[0038] As an example, the following specific numerical values are given. Rotation speed: 500 rpm. Rotation time: 50 seconds. Kinematic viscosity: 17.2cSt (= viscosity 20cP / density 1.17g / cm3 ). Initial film thickness: 100 μm. Substituting these values into equation (1) gives a film thickness of 10.1 μm. The calculated value is the film thickness before pre-baking. The polymer solution used as the coating liquid contains a polymer and a solvent that is about 20 times the amount of silver nitrate. As a result, it is thought that the film thickness will be reduced to 1 / 10 to 1 / 20 of its original thickness when pre-baking is performed. Assuming that the film thickness after pre-baking will be 1 / 10, the film thickness will be 1 μm.

[0039] FIG. 5 shows experimental results in which coating liquids having the same properties were applied using a spin coater at different rotation speeds. Graph G5a shows the cross-sectional shape of the thin metal wires 11 formed when the rotation speed was 500 rpm. This cross-sectional shape was obtained using an atomic force microscope (AFM). Graph G5b shows the cross-sectional shape of the thin metal wires 11 formed when the rotation speed was 850 rpm. The height of the thin metal wires 11 at 500 rpm was greater than 0.5 μm. On the other hand, the height of the thin metal wires 11 at 850 rpm was less than 0.5 μm. In other words, the higher the rotation speed, the greater the centrifugal force. As a result, the resist layer 51 becomes thinner. Therefore, it is believed that the height of the thin metal wires 11 also becomes smaller.

[0040] Meanwhile, in the above example, the rotation speed of the spin coater was selected as the parameter to be set. The viscosity of the coating liquid can also be set as a parameter to be set. For example, when the rotation speed of the spin coater is 2000 rpm, the viscosity of the coating liquid is 320 cP in order to make the film thickness of the coating liquid 10 μm. When the rotation speed of the spin coater is 5000 rpm, the viscosity of the coating liquid is 2000 cP in order to make the film thickness of the coating liquid 10 μm. The viscosity of the coating liquid can be estimated using equation (2).

number

[0041] Next, the irradiation conditions of the laser beam are set. More specifically, the process of setting the irradiation conditions includes a process of setting the irradiation intensity (irradiation power) of the laser beam (process S15), a process of setting the irradiation density of the laser beam (process S16), and a process of setting the scanning speed of the laser beam (process S17). According to the inventors' studies, the line width W11 depends on the magnitude of the irradiation intensity. The higher the irradiation intensity, the larger the line width W11. The irradiation conditions of the laser beam are set according to the line width W11. When it is desired to increase the line width W11, the irradiation intensity of the laser beam is set high. When it is desired to decrease the line width W11, the irradiation intensity of the laser beam is set low. For example, the irradiation intensity is set to a value of 2 mW or more and 5 mW or less. As an example, the irradiation intensity is 2 mW.

[0042] Graphs G6a, G6b, G6c, and G6d shown in FIG. 6(a) are experimental results confirming the relationship between the irradiation intensity of the laser light and the line width W11. Graph G6a shows the results when the irradiation intensity was 7 mW. Graph G6b shows the results when the irradiation intensity was 5 mW. Graph G6c shows the results when the irradiation intensity was 3 mW. Graph G6d shows the results when the irradiation intensity was 2 mW. As an example, if a line width W11 of about 5 μm is desired, the irradiation intensity of the laser light should be set to 7 mW (see graph G6a). If a line width W11 of about 1 μm is desired, the irradiation intensity of the laser light should be set to 2 mW (see graph G6d).

[0043] The graph shown in Figure 6(b) is also the result of another experiment confirming the relationship between the irradiation intensity of the laser beam and the line width W11. Graph G6e shows that there is a proportional relationship between the irradiation intensity of the laser beam and the line width W11. Graph G6e also shows that by setting the irradiation intensity of the laser beam between 1 mW and 5 mW, it is possible to obtain thin metal wires 11 with a line width W11 of 0.7 µm or more and 2.2 µm or less.

[0044] The irradiation conditions of the laser beam also include the irradiation density of the laser beam. The irradiation density is a parameter determined by the irradiation intensity and scanning speed of the laser beam. The irradiation density is proportional to the value obtained by dividing the irradiation intensity by the scanning speed. In other words, the irradiation density is the amount of photon energy given per unit time. For example, the irradiation density is 5 kJ / cm 2 More than 1,000kJ / cm 2 The irradiation density is set to the following value: 100 kJ / cm, for example. 2 is.

[0045] Graphs G7a, G7b, G7c, and G7d in FIG. 7(a) show experimental results confirming the relationship between the laser beam irradiation density and resistivity. Graph G7a shows the results when the irradiation intensity was 7 mW. Graph G7b shows the results when the irradiation intensity was 5 mW. Graph G7c shows the results when the irradiation intensity was 3 mW. Graph G7d shows the results when the irradiation intensity was 2 mW. As shown in graphs G7a, G7b, G7c, and G7d, it was found that the resistivity tends to decrease as the irradiation density increases. The irradiation intensity is constant for each of graphs G7a, G7b, G7c, and G7d. Therefore, the magnitude of the irradiation density depends on the scanning speed. For example, the higher the scanning speed, the lower the irradiation density. As a result, the resistivity tends to increase. On the other hand, the lower the scanning speed, the higher the irradiation density. As a result, the resistivity tends to decrease. This is thought to be because a higher irradiation density tends to result in better bonding of the precipitation nuclei 53. The good bonding between the precipitation nuclei 53 leads to good electrical conductivity, and therefore tends to decrease when evaluated by electrical resistivity.

[0046] FIG. 7(b) is a graph showing the scanning speed on the horizontal axis and the resistivity on the vertical axis. Graph G7e shows the results when the irradiation intensity is 3 mW. Graph G7f shows the results when the irradiation intensity is 2 mW. Graph G7g shows the results when the irradiation intensity is 1.5 mW. Graphs G7e, G7f, and G7g show that the resistivity decreases more gradually as the scanning speed decreases.

[0047] Then, after step S16, a step of setting the scanning speed of the laser light is carried out (step S17).

[0048] <Formation step> Next, a forming step (step S20) is performed. In the forming step, a plate-shaped member 50 is formed. The plate-shaped member 50 includes a transparent substrate 21 and a resist layer 51. The transparent substrate 21 functions as a base for the transparent electrode 1. After an irradiation step S30, a removal step S40, and a heating step S50, which will be described later, thin metal wires 11, which are electrode structures, are formed.

[0049] A transparent substrate 21 is prepared. The transparent substrate 21 may be a plate-shaped material made of glass, PET, polyimide, or the like. The transparent substrate 21 has optical transparency that allows the transmission of target light. The transparent substrate 21 may be flexible as needed.

[0050] Next, a resin material containing polyamic acid that will form the resist layer 51 is prepared. Using a known method, an acid anhydride and a diamine are dissolved in an organic solvent. Then, a polymerization reaction is carried out to obtain a polyamic acid resin. For example, pyromellitic dianhydride may be used as the acid anhydride. 4,4'-oxydianiline may be used as the diamine. 1-methyl-2-pyrrolidone may be used as the organic solvent. However, other materials may also be used, and the present invention is not limited to these.

[0051] When dissolving a metal salt in a polyamic acid resin, a coating solution containing a polyamic acid resin and a metal compound may be applied to the substrate. After applying a coating solution containing a polyamic acid resin to the substrate, the substrate may be impregnated with a solution containing a metal salt. The metal salt dissolved in the resist layer 51 may be a nitrate such as silver nitrate. Furthermore, the metal salt dissolved in the resist layer 51 may be a hydrochloride, acetate, oxalate, or citrate. Examples of metals constituting the metal salt include gold (Au), silver (Ag), copper (Cu), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), tin (Sn), rhodium (Rh), and iridium (Ir). The polyamic acid contained in the plate-shaped member 50 may be selected from heat-resistant resins made of polymers having imide groups in their structures, such as imidized polyimide, polyimide, polyamideimide, polybenzimidazole, polyimide ester, polyetherimide, and polysiloxaneimide. The polyamic acid contained in the plate-shaped member 50 is represented by the following chemical formula (1). [ka] [In the formula, n represents any integer.]

[0052] As shown in the following chemical formula (2), metal ions are bonded to the carboxyl groups of the polyamic acid contained in the resist layer 51. The bonding of the metal ions is based on an ion exchange reaction between the polyamic acid and the metal salt. -CO2 - H + →-CO2 - Ag + …(2) The above chemical formula (2) is an example of a reaction using silver nitrate as the metal salt.

[0053] Next, a polyamic acid resin is applied as a resist layer 51 to the substrate main surface 21a of the transparent substrate 21 (step S21). The polyamic acid resin is applied by spin coating. When a spin coater is used, the rotation speed obtained in the above-mentioned step S14 is used.

[0054] Next, the plate-shaped member 50 coated with the polyamic acid resin is pre-baked on a hot plate or the like at a predetermined temperature for a predetermined time. The pre-baking conditions may be, for example, a processing temperature of 80°C and a processing time of 10 minutes. Pre-baking heats the polyamic acid resin at a low temperature, which allows the metal ions contained in the polyamic acid to have fluidity. As a result, the metal ions bonded to the carboxyl groups are dispersed throughout the polyamic acid resin.

[0055] The "thickness of the work layer" refers to the thickness of the resist layer 51 in the irradiation step S30. In this embodiment, the resist layer 51 is formed by applying a polyamic acid resin by spin coating and then pre-baking. Therefore, the "thickness of the work layer" corresponds to the thickness of the resist layer 51 obtained after pre-baking. For example, once the fine line thickness is set, the thickness of the resist layer 51 after pre-baking can be set. Considering that the thickness of the applied resin decreases due to pre-baking, the target thickness of the polyamic acid resin applied by spin coating is, for example, about 10 times the thickness of the resist layer 51 after pre-baking.

[0056] By carrying out the above steps S10 and S20, the plate-shaped member 50 is obtained.

[0057] <Irradiation step> Next, an irradiation step S30 is performed (see FIGS. 4(b), (c), and (d)). In this irradiation step S30, metal is deposited on the plate-shaped member 50 using the apparatus shown in FIG. 3. The plate-shaped member 50 is mounted on an XY stage 201. The XY stage 201 moves the plate-shaped member 50 so as to correspond to the irradiation pattern of the laser light L. In other words, the scanning speed depends on the speed at which the XY stage 201 moves the plate-shaped member 50. The control device generates a control signal based on the conditions resulting from the setting step S10. The control device provides the control signal to the laser light source 202. The control signal includes a signal related to the irradiation intensity of the laser light L and a signal related to the scanning speed of the laser light L along the irradiation pattern.

[0058] Laser light L is irradiated onto the rear surface 21b of the transparent substrate 21. The laser light L passes through the transparent substrate 21 and reaches the resist layer 51 applied to the transparent substrate 21. Examples of the wavelength of the laser light L include 405 nm and 375 nm. When the resist layer 51 is irradiated with the laser light L, the metal (silver) contained in the resist layer 51 precipitates. The metal precipitation starts from a portion of the resist layer 51 that is in contact with the substrate main surface 21a of the transparent substrate 21. As a result, thin metal wires 11 that are electrode structures that are in contact with the substrate main surface 21a of the transparent substrate 21 are obtained. The laser light L is irradiated along an irradiation pattern. As a result, thin metal wires 11 that are metal microstructures are formed.

[0059] <Removal step> Next, a removal step S40 is performed (see FIG. 4(e)). In step S40, the resist layer 51 remaining on the main surface of the transparent substrate 21 is removed. More specifically, when step S40 is performed, the resist layer 51 includes the thin metal wires 11 and a residual resin portion 55 which is a polyamic acid resin. Therefore, the residual resin portion 55 is removed from the resist layer 51. In other words, in the removal step S40, the thin metal wires 11 are not removed from the resist layer 51. Specifically, the plate-like member 50 is immersed in an alkaline solution. As a result, the residual resin portion 55 is removed from the resist layer 51, and the thin metal wires 11 remain.

[0060] <Heating step> Next, the intermediate product 56 including the transparent substrate 21 and the thin metal wires 11 is heated (step S50). In step S50, the intermediate product 56 is heated at a high temperature (for example, 300°C) using an oven. Step S50 is an annealing treatment. The heat treatment improves the bonding state of the silver that has been precipitated as particles. As a result, the conductivity of the thin metal wires 11 can be increased.

[0061] FIG. 8 shows the results of an experiment comparing the resistivity before and after the heating step S50. Graph G8a shows the resistivity before the heating step S50 when the irradiation intensity is 7 mW. Graph G8b shows the resistivity before the heating step S50 when the irradiation intensity is 5 mW. Graph G8c shows the resistivity before the heating step S50 when the irradiation intensity is 3 mW. Graph G8d shows the resistivity after the heating step S50 when the irradiation intensity is 7 mW. Graph G8e shows the resistivity after the heating step S50 when the irradiation intensity is 5 mW. Graph G8f shows the resistivity after the heating step S50 when the irradiation intensity is 3 mW.

[0062] 8, it was found that in either case, the resistivity was reduced by performing the heating step S50. It was found that the execution of the heating step S50 improved the bonding state of the silver that had been precipitated as particles, and as a result, the conductivity of the thin metal wire 11 could be increased.

[0063] <Action and effect> In the method for manufacturing a transparent electrode, laser light L is irradiated onto a resist layer 51, which is a layer to be processed, to deposit the thin metal wires 11 that constitute the transparent electrode 1. Deposition using laser light L allows the shape of the thin metal wires 11 to be made so fine that they are invisible to the naked eye. This further improves light transmittance. Furthermore, in the method for manufacturing a transparent electrode, the resist thickness T51 is set based on the thin metal wire thickness T11 of the thin metal wires 11. The thin wire thickness T11 is easily affected by the resist thickness T51. Therefore, by setting the appropriate resist thickness T51, thin metal wires 11 having the desired thickness can be formed. This means that conductivity can be further improved.

[0064] The effects of the method for producing a transparent electrode according to this embodiment can be explained specifically by the following three points.

[0065] The first point of interest is the thinning of the line width W11 of the metal microstructure. If the line width W11 is 4 μm or more, it is visible to the naked eye. Therefore, by setting the line width W11 to 3 μm or less, the light transmittance of the transparent electrode 1 is improved and the line width W11 becomes invisible to the naked eye. In a method for manufacturing a transparent electrode, a mixed solution of a polyamic acid with a metal salt dissolved therein and a solvent is applied to a transparent substrate 21 to a uniform thickness, and then laser light L is irradiated onto the mixed solution, thereby making it possible to produce a line width W11 of 1 μm.

[0066] The second point of interest is the thickening of the thin metal wires 11. In other words, thickening the thin metal wires 11 reduces their electrical resistance. Thinning the wire width W11 reduces the cross-sectional area of the thin metal wires 11. Therefore, the conductivity of the thin metal wires 11 tends to decrease. As a result, it becomes difficult to increase the size of panels that use the transparent electrode 1. In the method for manufacturing a transparent electrode, we devised a method for increasing the thickness of the thin metal wires 11, thereby increasing the cross-sectional area of the thin metal wires 11 and improving the conductivity of the thin metal wires 11. The resist material used in conventional semiconductor processes is intended to be thin. In other words, its low viscosity makes it unsuitable for thicker films. In this embodiment, the viscosity of the coating material is increased by adjusting the ratio of polyamic acid, metal salt, and solvent. Furthermore, the rotation speed of the spin coater is adjusted when uniformly applying the coating material using the spin coater. In other words, the combination of viscosity and rotation speed is optimized in the method for manufacturing a transparent electrode.

[0067] A third point of interest is the relationship between thickening the line width W11 and the irradiation conditions of the laser beam L. When laser beam L is irradiated onto a coating material of polyamic acid containing a metal salt to deposit metal, if the coating material (resist layer 51) is thick, the laser beam L does not reach the bottom of the coating material. As a result, the metal at the bottom of the coating material may not be completely deposited. Therefore, it is necessary to increase the output of the laser beam L or slow down the scanning speed of the laser beam L so that the laser beam L reaches the bottom of the coating material. However, if the irradiation intensity of the laser beam L is too high, it becomes difficult to reduce the line width W11 of the thin metal wires 11. If the scanning speed of the laser beam L is slowed, the throughput for forming the thin metal wires 11 increases. In this embodiment, by adjusting the power (irradiation intensity) of the laser beam L, the scanning speed, the coating material, and the film thickness, it is possible to produce thin metal wires 11 with a desired thickness.

[0068] The characteristics of the transparent electrode 1 obtained by the manufacturing technique of this embodiment are compared with those of a transparent electrode obtained by a manufacturing technique of a comparative example. Line width W11 and resistivity are selected as the characteristics of the transparent electrode. In the graph of FIG. 9, the horizontal axis represents line width W11, and the vertical axis represents resistivity. Graphs G9a and G9b show the characteristics of the transparent electrode 1 obtained by the manufacturing technique of this embodiment. Graph G9a shows the experimental results when the scanning speed of the laser light L was 100 μm / sec. Graph G9b shows the experimental results when the scanning speed of the laser light L was 5 μm / sec. Plots P9a, P9b, P9c, and P9d show the characteristics of the transparent electrode obtained by the manufacturing technique of the comparative example. Plot P9a shows the transparent electrode produced by the reverse printing silver ink method, and plot P9b shows the transparent electrode produced by the imprinting silver paste method. Plot P9c shows the transparent electrode produced by the gravure printing silver paste method, and plot P9d shows the transparent electrode produced by the letterpress printing silver ink method. Plots P9a to P9d show that the manufacturing techniques of these comparative examples can provide transparent electrodes that are excellent in either line width or resistivity. The thinnest line width W11 of these comparative examples is 4 μm (see plot P9d).

[0069] On the other hand, the manufacturing technique of this embodiment can produce a transparent electrode with a minimum line width W11 of 1 μm. The manufacturing technique of this embodiment can produce a transparent electrode with a line width W11 of 1 μm or more and 5 μm or less. As shown in FIG. 9, the manufacturing technique of this embodiment can produce a line width W11 that falls within the invisible region E, exemplified as 3 μm or less. The resistivity is 1×10 -7 Ωm or more 10×10 -7 The resistance can be kept within the range of Ω / sq or less. For example, according to the manufacturing technique of this embodiment, it is possible to obtain a transparent electrode 1 having a line width W11 of 1 μm, a spacing G11 between the thin metal wires 11 of 30 μm, an electrode thickness of 1 μm, a light transmittance of 90%, and a sheet resistance of 21.4 Ω / sq. In other words, it is clear that the light transmittance and the resistance can be further improved.

[0070] The transparent electrode and the method for producing the transparent electrode of the present invention are not limited to the configurations and methods of the above-described embodiments.

[0071] For example, in the step of forming the workpiece layer, a lamination method or a roll coating method may be used instead of a spin coating method. That is, in the above embodiment, a spin coating method is exemplified as a method for applying a polyamic acid resin as the resist layer 51 to the substrate main surface 21a of the transparent substrate 21 (step S21). The method for applying the polyamic acid resin is not limited to a spin coating method. For example, a lamination method or a roll coating method may be used instead of a spin coating method. Parameters for controlling the thickness of the resist layer 51 include the pressing pressure of the roll and the rotation speed of the roll. A step of setting the pressing pressure is performed corresponding to step S13 so that the resist layer 51 has a set thickness. [Explanation of symbols]

[0072] 1...transparent electrode, 10...electrode mesh, G11...spacing, W11...line width, 21...transparent substrate (light-transmitting substrate), 50...plate-shaped member, 51...resist layer (processable layer), 52...metal ions, 55...residual resin portion, L...laser light.

Claims

1. A method for manufacturing a transparent electrode including thin metal wires that are metal microstructures, comprising: setting manufacturing conditions for manufacturing the transparent electrode; forming a processable layer on a plate-like member including a light-transmitting substrate; a step of irradiating a laser beam in a predetermined irradiation pattern onto the work layer made of a resin material containing a polyamic acid having a metal salt dissolved therein, in order to precipitate metal ions resulting from the metal salt on the work layer; removing a residual resin portion excluding the metal ions precipitated in the processed layer; and The step of setting the manufacturing conditions includes: setting the thickness and resistivity of the thin metal wire; setting the thickness of the work layer based on the thickness of the thin metal wire; and setting the irradiation density of the laser light based on the resistivity of the thin metal wire. , a method for manufacturing a transparent electrode.

2. In the step of forming the processing layer, a spin coating method is used, The step of setting the manufacturing conditions includes: setting the rotation speed of a spin coater and the viscosity of the resin material based on the thickness of the workpiece layer; setting the light intensity of the laser light based on the thickness of the processing layer; The method for manufacturing a transparent electrode according to claim 1 , further comprising the step of: setting the irradiation density and scanning speed of the laser light based on the light intensity of the laser light.

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