Transparent conductive circuit

Abstract

To provide a transparent conductive film (TCF) which is more likely to remove 100% of silver nanowires (AgNW's) from a gap area and prevents risk of having crosstalk between adjacent circuit features, and methods for creating the TCF.SOLUTION: A TCF10 comprises: a substrate 12 having a surface; a metal mesh (MM) layer 13 that includes metal traces 14 to 16 over at least a portion of the surface of the substrate; and a conductive layer (CNT ink layer 18) over the metal mesh layer. The conductive layer comprises carbon nanotubes (CNT's) and a binder.SELECTED DRAWING: Figure 1

Description

Background Art

[0001] This disclosure relates to a transparent conductive circuit.

[0002] Carbon nanotube (CNT) hybrid transparent conductive films (TCFs) are applied to electronic devices. Some such TCFs include a silver nanowire (AgNW) layer and a printed CNT ink layer. To remove exposed AgNW regions (i.e., regions where the CNT ink is not printed), a wet wiping method can be used.

Summary of the Invention

[0003] This disclosure relates to a CNT-based hybrid TCF including a metal mesh (MM) layer and a printed CNT ink layer. After the exposed MM (i.e., the region where the CNT ink is not printed) is removed by chemical etching, a circuit pattern is generated.

[0004] The advantage of using MM instead of AgNW is that a lower sheet resistance value can be achieved in a transparent CNT hybrid transparent circuit while maintaining high transparency. A low sheet resistance (Rs) is important for certain applications, particularly antennas. It is considered that Rs < 1 Ω / □ (OPS) is required for a printed transparent antenna to function like a printed opaque metal antenna. Also, high transparency is required, such as a visible light transmittance (VLT) of 85% for a printed transparent conductive film (excluding the substrate). More preferably, the VLT is > 90%.

[0005] Using a chemical etching solution to dissolve exposed MM areas is advantageous when removing MM using wet wipes is impractical. For chemical etching to work, the printed CNT ink must also function as an etching mask. This makes CNT ink a multifunctional material. Not only does CNT ink enable the creation of CNT hybrid (either CNT+MM or CNT+AgNW, both using a polymer binder) transparent conductive films that are superior to CNT, MM, or AgNW alone, CNT ink also allows the use of standard flexible printed circuit processing methods (using a chemical etching solution to dissolve conductive areas not covered by the etching mask).

[0006] Furthermore, using chemical etching solutions can be beneficial to fabricate circuits containing an AgNW layer with printed CNT ink on top. The wet wiping process is not generally accepted in the flexible printed circuit industry, which typically uses chemical etching agents that are sprayed on top or immersed in the circuit. With the wet wiping process, AgNW may remain on the circuit pattern, potentially leading to long-term reliability issues. In addition, the wet wiping process requires a certain amount of force to wipe effectively, which can damage finer circuit wiring, such as wiring with a width of around 100 microns. Moreover, etching fine gaps (less than 100 microns) is easier than using wet wiping, and this etching method is more likely to remove 100% of the AgNW from the gap area, preventing the risk of crosstalk between adjacent circuit functions.

[0007] All of the examples and features shown below can be combined in any way that is technically feasible.

[0008] In one embodiment, the transparent conductive film (TCF) includes a substrate having a surface, a metal mesh layer on at least a portion of the surface of the substrate, and a conductive layer on the metal mesh layer, wherein the conductive layer includes carbon nanotubes (CNTs) and a binder.

[0009] Some examples include one or any combination of the above and / or below features. The TCF may further include a second metal layer between the metal mesh layer and the conductive layer. The second metal layer may include a copper layer. The copper layer may be electroplated onto the metal mesh layer. The sheet resistance of the TCF may be 1Ω / □(OPS) or less.

[0010] Some examples include one or any combination thereof of the above and / or below features. The combination of a metal mesh layer and a conductive layer may have a visible light transmittance (VLT) of at least 85%. The combination of a metal mesh layer and a conductive layer may have a VLT of at least 90%. The metal mesh layer includes a network of interconnected metal wirings with open spaces between the wirings. The network can be rhombus, hexagonal, rectangular, or random patterns. The metal mesh layer may include at least 90% open space. The wire width of the metal wiring may be 30 microns or less. The open spaces in the metal mesh layer may be at least 15 times the width of the metal wiring. The TCF specifies a circuit having conductive wires of a certain width, the width of which may be at least 10 times the width of the open spaces in the metal mesh. The metal mesh includes two different metals, a first metal and a second metal, with the second metal on top of the first metal. The first metal may contain silver, and the second metal may contain copper.

[0011] Some examples include one or any combination of the above and / or below features. The CNTs in the conductive layer may consist of a network with a surface density of approximately 1 to 10 mg / m2. The binder:CNT ratio in the conductive layer may be greater than 120:1.

[0012] In another embodiment, a method for producing TCF comprises preparing a substrate having a surface, depositing a metal mesh layer or a nanowire layer on at least a portion of the surface of the substrate, and patterning a conductive layer on at least a portion of the metal mesh layer on the nanowire layer, wherein the conductive layer comprises carbon nanotubes (CNTs) and a binder.

[0013] Some examples include one of the above and / or below features, or any combination thereof. The method may further include depositing a second metal layer on the metal mesh layer before patterning the conductive layer. The method may further include etching the exposed metal mesh layer or nanowire layer that is not covered by the conductive layer. Etching may be achieved by spraying an etching solution onto the TCF. The etching solution may contain ferric nitrate. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic side view of the TCF. [Figure 2] Figures 2A to 2D show the method for preparing TCF. [Figure 3] The steps in the process of producing TCF are shown. [Figure 4] Figures 4A to 4C are three images of the TCF at different magnifications. [Figure 5] This figure shows the effect of copper plating on TCF metal mesh. [Modes for carrying out the invention]

[0015] A CNT-based hybrid TCF10, Figure 1, includes an MM layer 13 containing metal wiring 14-16 and an on top of it a CNT ink layer 18 bonded to the upper surface of a substrate 12 and encapsulating the MM layer 13 with a conductive medium. After the exposed MM (i.e., areas where the CNT ink is not printed) is removed by chemical etching, a circuit pattern is generated.

[0016] Figures 2A to 2D show the results of the process for fabricating the TCF of this disclosure. Note that the dimensions and other aspects in Figures 2A to 2D are not to scale and may be exaggerated for illustrative purposes only. A practical example is shown below. Assembly 20, Figure 2A, includes a substrate 22 supporting an MM including wirings 24-27. The MM can be fabricated on the substrate by various means described herein. The MM may also include various conductive materials (e.g., metals), as further described herein. The MM consists of a series of thin, electrically connected wires (lines). The wires are usually laid out in a regular pattern (such as the hexagonal pattern shown in Figure 4A), but this is not always necessary.

[0017] Figure 2B shows a further assembly 30 in which the MM is overplated with a second metal (in this non-limiting example, the second metal is copper). Thus, the wirings 24-27 are covered by a generally thicker second metal layer, including portions 34-37, producing thickened, less porous MM wirings 40-43, respectively.

[0018] Figure 2C shows a further assembly 50 in which the CNT ink 48 is printed on or otherwise positioned on part or all of the MM layer shown in Figure 2B. In this figure, the ink 48 is printed on the wiring 41, 42 but not on the wiring 40, 43. Thus, the wiring 41, 42 is covered by a conductive medium that forms a conductive wire or conductive area 49, while the wiring 40, 43 is exposed.

[0019] Figure 2D shows the final TCF60 after the exposed wiring 40,43 has been removed by etching, as will be described in more detail elsewhere in this specification. This leaves the conductor 49 on the substrate 22.

[0020] One exemplary method 70 for generating TCF is shown in Figure 3. In step 72, a suitable substrate is prepared. In step 74, a metal mesh is printed on the surface of the substrate. In step 76, a second metal (e.g., copper) is plated onto the metal mesh. Step 76 is optional and may not be necessary to increase the thickness (i.e., height) of the MM wires so that the MM itself has an acceptable Rs. The plated and added metal increases the volume of the MM wiring and therefore reduces resistance. It may also help to make thin MMs more robust and improve bonding with conductive ink. In step 78, a conductive medium (called "ink") is printed onto selected areas of the MM to form part of the circuit. In one example, the ink contains carbon nanotubes as its conductive medium and also contains a binder. CNT ink will be discussed further elsewhere in this specification. The final step 80 is intended to etch the exposed MM / copper to leave only the circuit on the substrate.

[0021] This disclosure is described in more detail in several non-limiting examples shown below, which illustrate TCF and embodiments of its production. Parameters of TCF and methods for producing TCF include the following:

[0022] A metal mesh can be thought of as a metal grid composed of extremely fine lines that provide electrical conductivity through interconnected lines while simultaneously enabling VLT through the spaces between the lines. Metal meshes can be fabricated on the surface of a substrate by any viable method, including, but not limited to, direct printing, embossing, photo-pattern formation followed by etching, and printing followed by plating. Metal meshes can be fabricated with sufficient width for the final application of TCF. Widths can be up to 12 inches, 24 inches, or more.

[0023] The width of the metal wire containing MM depends on the manufacturing method of MM (in some methods, thinner wire widths can be produced), and the requirements of the application (in some applications such as touchscreens, it needs to be made invisibly small to the naked eye). The width of the coarser MM is usually about 25 - 50 μm. The finer MM usually has a wire width of about 2 - 10 μm. To make the width of the wire less prominent, it needs to be less than about 6 μm. <(

[0024] The spacing between metal wirings depends on the desired visible light transmittance (VLT), the metal wire width, and the metal grid pattern (e.g., hexagonal, rectangular, random, etc.). The metal wire has a thickness sufficient to have a substantially negligible VLT (i.e., the metal wire absorbs or reflects almost all light). Therefore, the VLT of MM is mainly defined by the aperture ratio of the metal grid pattern. The spacing between metal wires can be calculated for different shapes of the metal grid pattern with respect to a given metal wire width and VLT target. For a coarser MM with a wire width of 30 μm and an aperture ratio of 90%, the spacing between metal wires is about 550 μm for both hexagonal and square grid patterns. For a finer MM with a wire width of 5 μm and an aperture ratio of 90%, the spacing between metal wires is about 91 μm for both hexagonal and square grid patterns.

[0025] Table 1 shows the calculation of the spacing for various combinations of aperture ratio and metal wire width. These are illustrative and not limiting or defining.

Table 1

[0026] The required thickness of the metal depends on the volume resistivity of the metal, the aperture ratio, and the target sheet resistance of MM.

[0027] For a metal MM with a volume resistivity of 4 μΩ·cm (typical value for flexographic printing nano silver ink), a metal grid thickness of 0.15 μm, and an aperture ratio of 90%, the sheet resistance of the MM is 6 Ω / □. For the sheet resistance of the MM to be 1 Ω / □ or less (known to be strongly desired in antenna and RF shielding applications), the thickness of this metal grid must be 0.9 μm or more. For a metal grid with an aperture ratio of 85%, the metal grid thickness required to achieve a sheet resistance of 1 Ω / □ or less is 0.6 μm or more. For a metal grid with an aperture ratio of 95%, the metal grid thickness required to achieve a sheet resistance of 1 Ω / □ or less is 1.8 μm or more.

[0028] The literature value for the volume resistivity of copper is 1.72 μΩ·cm, while for silver it is 1.59 μΩ·cm. Both of these values ​​are lower than typical values ​​achieved for electroplated copper and flexographically printed nanosilver due to the porosity of the plated or printed wires. However, to achieve the literature value for copper in terms of the volume resistivity of a fabricated metal grid, the required thickness of the metal grid to achieve a sheet resistance of 1 Ω / □ or less is 0.4 μm or more.

[0029] Commercial methods for fabricating metal grids include direct printing, embossing, and photo-pattern formation followed by etching. Most commercial methods for fabricating metal grids fail to achieve sufficient metal thickness for a sheet resistance of 1 Ω / □ or less for metal grids with an aperture ratio in the range of 85–95%. The thickness of the metal grid can be increased by electroplating or other viable processes.

[0030] For MMs with such high aperture ratios, achieving such low sheet resistance requires extremely low volume resistivity in the materials constituting the grid, making metal the only practical material. Table 2 shows the volume resistivity of various materials in Ω·m. To convert these values ​​to μΩ·cm, use 10 8 You need to multiply by . [Table 2]

[0031] Some metals have a volume resistivity of less than approximately 10 μΩ·cm. Higher volume resistivity has significant consequences because it increases the thickness of the metal required to achieve a sheet resistance of 1 Ω / □ or less. This increases the manufacturing cost of the MM (mechanical circuit board) and the cost of etching the MM when patterning circuits. Metals with a literature value of more than twice that of copper are presumably not very practical. Applying this selection criterion to the table above, the only metals selected are copper, silver, aluminum, and gold. Interestingly, these are all metals commonly used in the manufacture of printed circuits.

[0032] Another selection criterion is the ability to etch MM with commercially viable etching solutions. Etching gold with aqua regia is technically possible but not commercially viable. Silver is typically etched with ferric nitrate. Copper is typically etched with ferric chloride, but it can also be etched with ferric nitrate (the same etching solution used for silver). Aluminum is typically etched with sodium hydroxide or potassium hydroxide. Therefore, from an etching standpoint, silver, copper, and aluminum all appear to be commercially viable MM compositions. The CNT ink formulations used in the examples were found to be suitable as etching mask materials for all typical etching solutions used for silver, copper, and aluminum. For reference, it is also noted that MM produced by printing nanosilver ink followed by copper electroplating was successfully etched with a single etching solution, ferric nitrate. This makes the manufacturing process more cost-effective than requiring two separate etching processes.

[0033] Regarding the formulation of the CNT ink, the polymer binder type must be soluble in the ink vehicle (ideally soluble in alcohol), have high adhesion to the substrate, possess high VLT and low haze, be as colorless as possible, be able to encapsulate both CNTs and MMs, and be chemically resistant to etching solutions that may be used to etch the MMs (i.e., the CNT ink must be able to function as an etching mask). The ability of the CNT ink to function as an etching mask also depends on the ratio of binder to CNTs in the CNT ink. Too little binder may result in the CNT ink not being suitable as an etching mask. The underlying MMs will not be adequately protected when exposed MM areas (areas not covered by the CNT ink) are etched. Too much binder may impair the ability of the CNTs to establish good electrical connections with each other, and / or with the underlying MMs, and / or with the surface of the circuit (to achieve low contact resistance with printed interconnects).

[0034] Prepared using ink vehicle chemistry similar to that of the international patent application incorporated herein by reference, with a CNT concentration of 0.1 g / L and an acrylic copolymer binder (DSM B890), at a density of 30 mg / m². 2 CNT ink printed with this ink coverage rate was found to function well as an etching mask when the binder:CNT ratio was 240:1. Ratios of 60:1 and 120:1 were not entirely acceptable (i.e., the underlying MM was etched). A ratio of 180:1 was limiting (sometimes OK, but not always). Also, 240:1 did not appear to impair the electrical connectivity of the CNTs. Higher ratios than 240:1 are considered acceptable, with the upper limit being the penetration limit of CNTs in this binder system, which is estimated to be about 0.2 wt% CNTs. This corresponds to a binder:CNT ratio of about 400:1.

[0035] The following are some examples illustrating aspects of this disclosure.

[0036] < Comparison with MM type AgNW type with 1Ω / □

[0037] <1Ω / □AgNW type: TCFs were fabricated using polyethylene terephthalate (PET) (125 μm) as the substrate and coated with a dispersion of 2.0 wt% silver nanowires (AgNW) in isopropyl alcohol (IPA). AgNW with a diameter of approximately 40 nm and a length of 15 μm was used. The AgNW coating measured approximately 5 inches wide and 7 inches long. The AgNW dispersion was coated onto the PET film at a coverage rate of 632 mg / m2 AgNW using a Meyer rod (wet film thickness of 40 microns). The coating was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C, and then baked in a convection oven at 105°C for 3 minutes. After AgNW coating, the visible light transmittance (%VLT) was 45.6% (subtracting the VLT of the substrate), and the sheet resistance (Rs) of the assembly was 1 Ω / □. The AgNW coating was screen printed with carbon nanotube ink (using a recombined form of VC101 single-walled CNT ink manufactured by Chasm Advanced Materials, Inc., Canton, Massachusetts, USA) using a 305 polyester mesh screen (approximately 30 μm wet film thickness) with a 2.5-inch block pattern. The ink was recombined to a CNT concentration of 0.1 g / L and contained a polymer binder (e.g., modified methacrylate copolymer). Other binders usable in this TCF are disclosed in International (PCT) Patent Application Publication No. WO2016 / 172315, the entire disclosure of which is incorporated herein by reference for any purpose. The printed CNT layer was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C and then baked in a convection oven at 105°C for 5 minutes. The sample was cooled to ambient temperature (approximately 25°C). Next, using a wash bottle, the sample was sprayed with a 10% ferric nitrate (Fe(NO3)3) aqueous solution for 30 seconds. Then, using another wash bottle, deionized water was sprayed onto both sides of the sample film for 30 seconds. Next, the film was gently tapped with a lint-free cloth to remove large water droplets, and then baked in a convection oven at 105°C for 1 minute. The CNT layer in this example was printed and etched with two different binder:CNT ratios (120:1 and 240:1).

[0038] After screen printing and etching with CNT ink, the %VLT and Rs in the 2.5-inch CNT printed area were 32.2% (subtracting the substrate's VLT) and 1Ω / □, respectively. After etching the exposed area outside the 2.5-inch CNT printed area, the %VLT increased to 90.0% (subtracting the substrate's VLT), and the sheet resistance could not be measured.

[0039] The results are summarized in Table 3 below. [Table 3]

[0040] <1Ω / □MM type:TCF was fabricated using PET (125 μm) as the substrate and flexographically printed with silver (Ag) ink in a hexagonal pattern (30 micron lines with a thickness of approximately 0.1–0.15 microns and a spacing of 500 microns) using an anilox roll at 120 feet per minute. It was then baked in a convection oven at 170°C for 5 seconds. Next, the hexagonally patterned film was electroplated with copper (Cu) in a bath. The thickness of the upper copper layer was approximately 0.5–1.5 microns (thus approximately 5–10 times the thickness of the MM layer). The Ag pattern film was screen printed with carbon nanotube ink (VC101 single-walled CNT ink from Chasm Advanced Materials, Inc.) using a 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm). The ink was reformulated to a CNT concentration of 0.1 g / L and contained the above binder. In this example, the CNT layer was printed and etched at two different binder:CNT ratios (120:1 and 240:1). The printed CNT layer was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C, and then baked in a convection oven at 105°C for 5 minutes. The sample was cooled to ambient temperature (approximately 25°C). Next, using a wash bottle, the sample was sprayed with a 40% ferric nitrate (Fe(NO3)3) aqueous solution for 15 seconds to etch the exposed Ag patterned film. Next, using another wash bottle, deionized water was sprayed on both sides of the sample film for approximately 30 seconds to remove the etching solution. Finally, the film was gently tapped with a lint-free cloth to remove large water droplets, and then baked in a convection oven at 105°C for 1 minute.

[0041] After flexographic printing of an Ag hexagonal pattern, the visible light transmittance (%VLT) was 90.6% (subtracting the substrate's VLT), and the sheet resistance (Rs) was 5Ω / □. After electroplating with Cu, the %VLT was 90.2% (subtracting the substrate's VLT), and Rs was <1Ω / □. After screen printing and etching with a 240:1 binder:CNT ink, in a 2.5-inch CNT pattern area, the %VLT and Rs remained at 90.6% (subtracting the substrate) and <1Ω / □, respectively. In the exposed area outside the 2.5-inch CNT pattern area, both the %VLT and Rs increased to 99.6% (subtracting the base) and infinity, respectively. After screen printing and etching with a 120:1 binder:CNT ink, there was clear evidence that the etching solution penetrated a 2.5-inch CNT square area, starting from the outer boundary and progressing toward the center of the 2.5-inch square. In the exposed areas outside the 2.5-inch CNT pattern area, both %VLT and Rs increased to 99.6% (subtracting base) and infinity, respectively.

[0042] The results are summarized in Table 4 below. [Table 4]

[0043] Table 5 below shows a comparison of the results for MM type versus AgNW type with <1Ω / □ using 0.1g / L 240:1 binder:CNT ink. [Table 5]

[0044] MM flexographically printed with nano-Ag+CNT ink + etching solution / Conditions:

[0045] Etching time for square AgMM+CNTs:TCF samples were prepared using PET (125 μm) as the substrate and flexographically printed with silver (Ag) ink in a square mesh pattern at 120 feet per minute using an anilox roll. The samples were then baked in a convection oven at 170°C for 5 seconds. The Ag pattern film was screen printed with carbon nanotube ink (VC101 single-walled CNT ink from Chasm Advanced Materials, Inc.) using a 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm). The ink was reformulated to a CNT concentration of 0.1 g / L and contained the above-mentioned binder in a binder:CNT ratio of 240:1. The printed CNT layer was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C and then baked in a convection oven at 105°C for 5 minutes. The samples were then cooled to ambient temperature (approximately 25°C). Next, the sample was immersed in a 40 wt% solution of ferric nitrate (Fe(NO3)3) in deionized (DI) water, and both sides of the membrane were rinsed with deionized water for about 30 seconds using a washing bottle. Then, the sample was gently tapped with a lint-free cloth to remove large water droplets, and baked in a convection oven at 105°C for 1 minute.

[0046] The initial sheet resistance (Rs) and visible light transmittance (%VLT) of the square Ag mesh printed with CNTs before etching were 88.7% (subtracting substrate) and 4 Ω / □, respectively. The TCFs in this example were immersed in a 40 wt% solution of ferric nitrate (Fe(NO3)3) in deionized (DI) water for various etching times (120, 60, 45, and 10 seconds).

[0047] After etching, the Rs measurements for etching times of 120 seconds and 60 seconds increased to 15 and 7 Ω / □, respectively, indicating degradation of the patterned TCF film, while the %VLT remained the same at 88.7% (substrate subtraction). The %VLT and Rs measurements for etching times of 45 seconds and 10 seconds remained the same as the initial 88.7% (substrate subtraction) and 4 Ω / □, respectively.

[0048] MM flexographic printing, nano-Ag+Cu plating + CNT ink + etching solution / various conditions:

[0049] Cu plating MM vs. etching solution type: TCF samples were fabricated using PET (125 μm) as the substrate and flexographically printed with silver (Ag) ink in a hexagonal mesh pattern (30 micron lines, 500 micron spacing) using an anilox roll at 120 feet per minute. The samples were then baked in a convection oven at 170°C for 5 seconds. Next, the hexagonal patterned film was electroplated with copper (Cu) to a thickness of 1.0 micron while stirring. The Ag pattern film was screen printed with carbon nanotube ink (VC101 single-walled CNT ink from Chasm Advanced Materials, Inc.) using a 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm). The ink was reformulated to a CNT concentration of 0.1 g / L and contained the above-mentioned binder in a binder:CNT ratio of 240:1. The printed CNT layer was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C, and then baked in a convection oven at 105°C for 5 minutes. The sample was cooled to ambient temperature (approximately 25°C). The initial visible light transmittance (%VLT) and sheet resistance (Rs) of the Cu-plated Ag mesh with printed CNTs before etching were 90.6% (substrate subtracted) and <1Ω / □, respectively.

[0050] The TCF in this example was etched using two different etching solutions (40% ferric nitrate, 20% ferric chloride) and combinations thereof. Next, the sample was rinsed on both sides of the film with deionized (DI) water for about 30 seconds using a wash bottle, large water droplets were removed by gently patting with a lint-free cloth, and the sample was baked in a convection oven at 105°C for 1 minute.

[0051] Sample A was immersed in 40% ferric nitrate for 15 seconds. In the 2.5-inch CNT patterned area, %VLT and Rs remained at 90.6% (subtracting substrate) and <1Ω / □, respectively. In the exposed area outside the 2.5-inch CNT patterned area, both %VLT and Rs increased to 99.6% (subtracting base) and infinity, respectively. There was also a halo of approximately 2 mm of unetched material at the outer edge of the 2.5-inch CNT.

[0052] Sample B was immersed in 20% ferric chloride for 10 seconds. In the 2.5-inch CNT patterned area, %VLT and Rs remained at 90.6% (substrate subtraction) and <1Ω / □, respectively. In the exposed area outside the 2.5-inch CNT patterned area, %VLT increased to 92.9% (base subtraction), which was 6.7% lower than sample A. This means that even with Rs at infinity, the exposed mesh area was not completely removed. Ferric chloride eliminated the halo effect observed in sample A.

[0053] Sample C was first immersed in 40% ferric nitrate for 15 seconds, rinsed and dried as described above, then immersed in 20% ferric chloride for 10 seconds, and finally rinsed and dried again as described above. In the 2.5-inch CNT pattern area, %VLT and Rs remained at 90.6% (subtracting substrate) and <1Ω / □, respectively. In the exposed area outside the 2.5-inch CNT pattern area, both %VLT and Rs increased to 99.6% (subtracting base) and infinity, respectively. Post-treatment with ferric chloride eliminated the halo effect observed after the initial ferric nitrate etching.

[0054] Sample D was first immersed in 20% ferric chloride for 10 seconds, rinsed and dried as described above, then immersed in 40% ferric nitrate for 15 seconds, finally rinsed and dried again as described above. In the 2.5-inch CNT patterned area, %VLT and Rs remained at 90.6% (subtracting substrate) and <1Ω / □, respectively. In the exposed area outside the 2.5-inch CNT patterned area, %VLT increased to 96.0% (subtracting base), which was 3.6% lower than sample A. This means that even with Rs at infinity, the exposed mesh area was not completely eliminated. Ferric chloride eliminated the halo effect observed in sample A.

[0055] Method of applying etching solution to Cu-plated MM: TCF was fabricated using PET (125 μm) as the substrate and flexographically printed with silver (Ag) ink in a hexagonal pattern (30 micron lines, 500 micron spacing) using an anilox roll at 120 feet per minute. It was then baked in a convection oven at 170°C for 5 seconds. Next, copper (Cu) was electroplated to a thickness of 1.0 micron while stirring onto the hexagonal patterned film. The Ag pattern film was screen printed with carbon nanotube ink (VC101 single-walled CNT ink from Chasm Advanced Materials, Inc.) using a 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm). The ink was reformulated to a CNT concentration of 0.1 g / L and contained the above binder in a binder:CNT ratio of 240:1. The printed CNT layer was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air of 177°C, and then baked in a convection oven at 105°C for 5 minutes. The sample was cooled to ambient temperature (approximately 25°C). The initial %VLT and sheet resistance (Rs) of the CNT-printed Cu-plated Ag mesh with printed CNTs before etching were 90.6% (substrate subtraction) and <1Ω / □, respectively.

[0056] In this example, the TCF was etched for 15 seconds with an aqueous solution of 40% ferric nitrate (Fe(NO3)3) using two different application methods (spray and immersion). Next, using a separate wash bottle, deionized water was sprayed onto both sides of the sample film for approximately 30 seconds. Then, the film was lightly tapped with a lint-free cloth to remove large water droplets, and baked in a convection oven at 105°C for 1 minute. In both cases, the %VLT and Rs of the 2.5-inch CNT square area remained 90.6% (subtracting substrate) and <1Ω / □, respectively. Both samples showed good etching of the mesh pattern of the unprotected exposed Cu plating on the 2.5-inch CNT square, although the immersion sample had a halo of approximately 2 mm around the periphery of the 2.5-inch printed square and was not completely etched. The sprayed ferric nitrate sample showed no signs of this halo at all.

[0057] AgNWs type chemical etching of AgeNT:

[0058] Etching of AgeNT-75:TCF was fabricated using PET (125 μm) as a substrate and coated with a dispersion of 0.3 wt% silver nanowire solution using aqueous silver nanowire ink (approximately 40 nm in diameter and 15 μm in length). The AgNW coating was approximately 5 inches wide x 7 inches long. The AgNW dispersion was coated onto the PET film using a Meyer rod (wet film thickness of 12 microns) at an AgNW coverage rate of 28 mg / m2. The coating was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C and then baked in a convection oven at 105°C for 3 minutes. The AgNW coating was screen printed using carbon nanotube ink (VC101 single-walled CNT ink from Chasm Advanced Materials, Inc.) on a 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm). The ink was reformulated to a CNT concentration of 0.1 g / L and contained the above-mentioned binder in a binder:CNT ratio of 120:1. The printed CNT layer was dried for approximately 30 seconds in a handheld convection dryer set to an outlet air temperature of 177°C, and then baked in a convection oven at 105°C for 5 minutes. The sample was cooled to ambient temperature (approximately 25°C). The initial %VLT and sheet resistance (Rs) of the CNT printed AgNW film before etching were 99.3% (substrate subtraction) and 60 Ω / □, respectively.

[0059] In this example, the TCF was sprayed with a 10% ferric nitrate (Fe(NO3)3) aqueous solution for 15 seconds. Next, using a separate wash bottle, both sides of the sample membrane were sprayed with DI water for 30 seconds. Then, the membrane was gently patted with a lint-free cloth to remove large water droplets, and baked in a convection oven at 105°C for 1 minute.

[0060] After screen printing and etching with CNT ink, the %VLT and Rs remained at 99.3% (subtracting the substrate's VLT) and 60Ω / □ in the 2.5-inch CNT printed area, respectively. After etching, in the exposed area outside the 2.5-inch CNT printed area, the %VLT increased to 91.0% (the same value as the bare substrate), and the sheet resistance could not be measured.

[0061] The following is an overview of various chemical etching solutions that can be used for etching copper (Cu) or silver (Ag) materials. To date, the best form for etching AgNW or MM has been the use of ferric nitrate as the etching solution, employing either spraying or immersion methods. This does not exclude other etching solutions or methods currently known or to be developed in the future.

[0062] Review of etching techniques for Cu and Ag:

[0063] Copper etching solution: Numerous wet chemical systems (Table 6) are used for etching Cu. Key parameters for controlling and optimizing the etching process include pH, temperature, replenishment of the etching solution, and the degree of agitation.

[0064] One of the most commonly used and inexpensive chemical systems is ferric chloride. This mechanism involves the oxidation of copper to cuprous chloride. Other chemical species, such as HCl, may be added to improve etching performance by enhancing the kinetics of cuprous chloride production, which can be a rate control step in the overall kinetics of the etching process.

[0065] Another commonly used etching solution is cupric chloride. Since copper is reduced to cuprous chloride, which degrades the etching solution's performance, the regeneration of CuCl2 is important. As with ferric chloride, other chemicals (HCl, KCl, NaCl) are usually added to improve performance. [Table 6]

[0066] Alkaline etching solutions such as ammonium hydroxide combine with copper ions to form copper-ammonium complex ions, which stabilize the dissolved Cu in the solution.

[0067] Ammonium persulfate is an excellent etching agent for copper, but the process is exothermic, requiring a heat exchanger. Furthermore, its etching rate is lower than some more aggressive chemical systems, making it suitable for processes that are easier to control but where rate control may be desirable within the overall process scheme.

[0068] Silver etching solution: While silver and copper are commonly used in many of the same electrical and electronic applications, the number of etching solutions used for Ag (Table 7) is far fewer compared to Cu due to the extreme cost difference. Typical etching solutions for silver include nitric acid-aqueous and sulfuric acid-aqueous systems in various concentrations. [Table 7]

[0069] Additional examples:

[0070] There are numerous methods that can be used to create MM layers using various combinations of Rs and VLT properties. One method involves flexographic printing of MM using nano-Ag ink. This method appears suitable for creating MM with an Rs of approximately 10 Ω / □ and a VLT of approximately 90%. To reduce the Rs of the MM without sacrificing VLT, Cu has been electroplated onto the printed AgMM to create Ag / CuMM. Other materials may be used for both the printed layer and the overlaid plating layer.

[0071] MM can be created using other methods. This includes using more advanced flexographic printing plates to achieve MM line widths down to approximately 3 microns. This embodiment has an MM line width of approximately 30 microns. Reducing the MM line width makes the MM less visible at the same VLT value. Also, thinner lines allow for thinner line widths in CNT hybrid circuits. As a general rule of thumb, to achieve a % aperture area of ​​MM higher than approximately 90%, the width of the mesh's aperture area needs to be approximately 15 to 20 times the MM line width. The % aperture area determines the maximum VLT value of the printed CNT hybrid circuit. Therefore, a 30-micron MM line width requires an aperture area width of approximately 500 microns. Another general rule of thumb is that the minimum line width of a printed CNT hybrid circuit needs to be at least 10 times the width of the MM's aperture area segment in order to allow sufficient conductive material for circuit wiring. Therefore, the minimum line width of the circuit must be greater than approximately 5 mm. This minimum line width is expected to be around 0.5 mm if the MM line width can be reduced to 3 microns.

[0072] It should also be possible to create MM by printing a suitable catalyst (e.g., palladium) and using electroless Cu to create the MM. Other metals besides Cu are also possible. If Rs is not low enough, Cu electroplating can be used after electroless Cu deposition.

[0073] MMs can also be fabricated using lithography etching methods or various lift-off pattern formation methods, which are widely used in the printed circuit industry. It is also possible to fabricate MMs using laser ablation of thin metal films.

[0074] Figures 4A–4C, 5A, and 5B contain images illustrating printed CNT hybrids (MM type), where MM was flexographically printed Ag (without subsequent Cu electroplating). The SEM image in Figure 4A (50x magnification) shows an MM hexagonal pattern with an Ag linewidth of approximately 30 μm and an overall hexagonal open space width of approximately 500 μm. The SEM image in Figure 4B (50kx magnification) shows how CNTs form a well-connected network in a space that normally does not contain conductive material. The surface density of the CNT network is sufficiently low (approximately 1–10 mg / m²). 2 ), although transparent, its sufficiently high surface density allows for charge diffusion in open spaces, resulting in a more uniform electrode. The SEM image (100kx magnification) in Figure 4C shows how the CNT network helps enhance porous AgMM lines and provides redundant conductive paths to increase reliability. Note that the CNT ink printed on AgMM shown in Figure 4A did not contain polymer binder, so the CNT network was only visible in the SEM images of Figures 4B and 4C. Normally, the polymer binder is present at a level sufficient to encapsulate the MM and CNTs, and the CNT network self-assembles within the polymer matrix. This prevents the CNT network from being seen in SEM imaging.

[0075] Furthermore, the CNT network within the polymer matrix also provides electrical connectivity from the surface of the printed CNT hybrid circuit to the underlying MM layer. This enables reliable and easy electrical connection to the circuit. This situation also occurs when the CNT ink is printed on top of the AgNW. In both cases, good electrical connectivity is achieved from the circuit surface to the underlying MM or AgNW layer.

[0076] Figures 5A and 5B show only flexographically printed AgMMs, which are copper-plated. Figure 5A includes images at both 10kx and 25kx magnifications, and Figure 5B includes images at both 50kx and 100kx magnifications. Furthermore, the porous appearance of flexographically printed AgMMs can be reduced by "filling" after Cu electroplating. The thickness of the Cu electroplating is approximately 0.5 to 1.5 microns, while the thickness of the flexographically printed Ag can be approximately 0.1 to 0.15 microns. The SEM images in Figures 5A and 5B clearly demonstrate this. It is believed that the Cu plating not only reduces the sheet resistance (without compromising the VLT), but also improves reliability because the porosity of the Ag / CuMM structure is lower than that of the AgMM structure alone.

[0077] The polymer binder plays a role in enhancing the environmental stability and adhesion of printed CNT hybrid circuits. It also protects MM or AgNW from chemical etching (i.e., it is a component that provides etching mask functionality). The binder must possess excellent environmental stability and adhesion properties, high transparency, and low haze.

[0078] It is reasonable to expect that many different binders will be available. The selection criteria for a suitable polymer binder candidate include the following: • Excellent optical properties (high transparency, low haze, low coloration, refractive index equivalent to PET). • Good adhesion to commonly used plastic film substrates (PET, PC, acrylic, etc.). • Temperature processing requirements suitable for plastic film substrates (<120°C). • Solubility suitable for ink formulations (e.g., good solubility in alcohol and / or amine components). • Chemical resistance to common etching solutions used for Ag and Cu.

[0079] The type of CNT used in this disclosure was single-walled carbon nanotubes (WNTs). However, it is reasonable to expect that good results can be obtained by replacing them with two-walled, multi-walled, or multi-walled CNTs.

[0080] Many implementations have been described. Nevertheless, additional modifications can be made without departing from the scope of the inventive concept described herein, and therefore other examples are within the scope of the claims. The present invention can be implemented in the following configurations (1) to (23). (1) A substrate having a surface, A metal mesh layer on at least a portion of the surface of the substrate, A transparent conductive film (TCF) comprising a conductive layer containing carbon nanotubes (CNTs) and a binder on a metal mesh layer. (2) The transparent conductive film according to (1) above, further comprising a second metal layer between the metal mesh layer and the conductive layer. (3) The transparent conductive film according to (2) above, characterized in that the second metal layer includes a copper layer. (4) The transparent conductive film according to (3) above, characterized in that the copper layer is electroplated onto a metal mesh layer. (5) The transparent conductive film according to (1) above, characterized in that the sheet resistance of the transparent conductive film is 1Ω / □(OPS) or less. (6) The transparent conductive film according to (1) above, characterized in that the combination of the metal mesh layer and the conductive layer has a visible light transmittance (VLT) of at least 85%. (7) The transparent conductive film according to (6) above, characterized in that the combination of the metal mesh layer and the conductive layer has a visible light transmittance of at least 90%. (8) The transparent conductive film according to (1) above, wherein the metal mesh layer includes a network of interconnected metal wirings and has open spaces between the wirings. (9) The transparent conductive film according to (8) above, wherein the network is characterized by being hexagonal, rectangular, or a random pattern. (10) The transparent conductive film according to (8) above, characterized in that the metal mesh layer includes at least 90% open space. (11) The transparent conductive film described in (8) above, characterized in that the wire width of the metal wiring is 30 microns or less. (12) The transparent conductive film according to (8) above, characterized in that the open spaces in the metal mesh layer have a width of at least 15 times the width of the metal wiring. (13) The transparent conductive film according to (8) above, which defines a circuit having conductive wires having a certain width, characterized in that the width of the conductive wires is at least 10 times the width of the open space of the metal mesh. (14) The transparent conductive film according to (1) above, characterized in that the metal mesh comprises two different first metals and second metals, with the second metal on top of the first metal. (15) The transparent conductive film according to (14) above, characterized in that the first metal contains silver and the second metal contains copper. (16) The transparent conductive film according to (1) above, characterized in that the carbon nanotubes in the conductive layer include a network with a surface density of approximately 1 to 10 mg / m2. (17) The transparent conductive film according to (1) above, characterized in that the ratio of binder to carbon nanotubes in the conductive layer is greater than 120:1. (18) Prepare a substrate having a surface, Depositing a metal mesh layer or nanowire layer on at least a portion of the surface of the substrate, A method for producing a transparent conductive film (TCF) comprising patterning a conductive layer on at least a portion of a metal mesh layer or a nanowire layer, wherein the conductive layer comprises carbon nanotubes (CNTs) and a binder. (19) The method according to (18), further comprising depositing a second metal layer on a metal mesh layer before patterning the conductive layer. (20) The method according to (18) above, characterized in that the nanowire layer contains silver nanowires. (21) The method according to (18), further comprising etching an exposed metal mesh layer or nanowire layer that is not covered by a conductive layer. (22) The method according to (21) above, characterized in that etching is achieved by spraying an etching solution onto a transparent conductive film. (23) The method according to (22) above, characterized in that the etching solution contains ferric nitrate.

Claims

1. A substrate having a surface, The substrate includes an etched circuit pattern on its surface, The circuit pattern is, A first material layer on at least a portion of the surface of a substrate, comprising metal elements much longer than the width, arranged such that the metal elements are interconnected, and having open spaces between the metal elements, A transparent conductive film (TCF) comprising a first material layer encapsulating a second material layer containing carbon nanotubes (CNTs) and a binder, wherein the binder:CNT ratio is at least 180:

1.

2. The transparent conductive film according to claim 1, characterized in that each metal element comprises two metal layers, one of which is located on the other metal layer.

3. The transparent conductive film according to claim 2, characterized in that the upper metal layer includes a copper layer.

4. The transparent conductive film according to claim 2, characterized in that the upper metal layer is electroplated onto the other metal layer.

5. The transparent conductive film according to claim 1, characterized in that the sheet resistance of the transparent conductive film is 1 Ω / □ (OPS) or less.

6. The transparent conductive film according to claim 1, characterized in that the first material layer includes a metal mesh consisting of a network of interconnected metal wirings, with open spaces between the wirings.

7. The transparent conductive film according to claim 6, characterized in that the network is hexagonal, rectangular, or a random pattern.

8. The transparent conductive film according to claim 6, characterized in that the metal mesh includes at least 90% open space.

9. The transparent conductive film according to claim 6, characterized in that the wire width of the metal wiring is 30 microns or less.

10. The transparent conductive film according to claim 6, characterized in that the open spaces in the metal mesh have a width at least 15 times the width of the metal wiring.

11. A transparent conductive film according to claim 6, characterized in that it defines a circuit having conductive wires having a certain width, wherein the width of the conductive wires is at least 10 times the width of the open space of the metal mesh.

12. The transparent conductive film according to claim 6, characterized in that the metal mesh comprises two different first and second metals, with the second metal on top of the first metal.

13. The transparent conductive film according to claim 12, characterized in that the first metal contains silver and the second metal contains copper.

14. The transparent conductive film according to claim 1, characterized in that the combination of the first material layer and the second material layer has a visible light transmittance (VLT) of at least 90%.

15. The carbon nanotubes in the second material layer have a surface density of approximately 1 to 10 mg / m². ２ The transparent conductive film according to claim 1, characterized by including a network.

16. A substrate having a surface, The substrate includes an etched circuit pattern on its surface, The circuit pattern is, A first material layer on the surface of a substrate, comprising a metal mesh consisting of a network of interconnected metal wirings, with open spaces between the wirings, wherein the metal wiring comprises two metal layers, one of which rests on the other metal layer, and A transparent conductive film (TCF) comprising a metal mesh encapsulated and a second material layer containing carbon nanotubes (CNTs) and a binder, wherein the binder:CNT ratio is at least 180:

1.

17. The transparent conductive film according to claim 16, characterized in that the upper metal layer includes a copper layer.

18. The carbon nanotubes in the second material layer have a surface density of approximately 1 to 10 mg / m². ２ The transparent conductive film according to claim 17, characterized in that it includes a network.

19. The transparent conductive film according to claim 18, characterized in that the sheet resistance of the transparent conductive film is 1 Ω / □ (OPS) or less.

20. A method for producing a transparent conductive film (TCF), To prepare a substrate having a surface, A metal mesh layer is deposited on at least a portion of the surface of the substrate, comprising a network of interconnected metal wirings with open spaces between the wirings. Depositing a second metal layer on a metal mesh layer, Patterning a conductive layer containing carbon nanotubes (CNTs) and a binder, wherein the binder:CNT ratio is at least 180:1, on at least a portion of the metal mesh layer on which the second metal layer is deposited, This includes etching to remove the metal mesh layer on which the exposed second metal layer not covered by the conductive layer has been deposited, thereby forming a circuit pattern. A method for achieving a sheet resistance of 1 Ω / □ (OPS) or less for a transparent conductive film.

Images