Transparent conductive circuit

Abstract

To provide a transparent conductive film (TCF) that can realize lower sheet resistance values for a transparent carbon nanotube (CNT) hybrid transparent circuit while maintaining high transparency.SOLUTION: A transparent conductive film (TCF) comprises: a substrate having a surface; a metal mesh layer over at least a portion of the surface of the substrate, where the metal mesh layer comprises a network of interconnected metal traces with open spaces between the metal traces, where the metal traces include two different metal trace layers such that one metal trace layer is atop the other metal trace layer; and a conductive layer encapsulating the metal mesh layer, and comprising carbon nanotubes (CNTs) and a binder.SELECTED DRAWING: Figure 2D

Description

Background Art

[0001] The present disclosure relates to a transparent conductive circuit.

[0002] A carbon nanotube (CNT) hybrid transparent conductive film (TCF) is applied to an electronic device. Some such TCFs include a silver nanowire (AgNW) layer and a printed CNT ink layer. To remove the 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] The present 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 the exposed MM region is advantageous when it is not practical to remove the MM using a wet wipe. For chemical etching to work, the printed CNT ink must also function as an etching mask. This makes the CNT ink a multifunctional material. The CNT ink enables the fabrication of a transparent conductive film that is superior to CNT or MM or AgNW alone, a CNT hybrid (either CNT + MM or CNT + AgNW, both using a polymer binder), and also enables the use of standard flexible printed circuit processing methods (using a chemical etching solution to dissolve conductive regions not covered by the etching mask).

[0006] Also, it can be beneficial to use a chemical etching solution to fabricate a circuit including an AgNW layer with CNT ink printed thereon. The wet wiping process is not generally accepted in the flexible printed circuit industry, which typically uses chemical etching agents sprayed or immersed thereon. In the wet wiping process, AgNW may remain on the circuit pattern, which can cause long-term reliability problems. Furthermore, the wet wiping process requires a certain amount of force to effectively perform wiping, which can damage finer circuit wiring, such as circuit wiring with a width of about 100 microns. Also, it is easier to etch a fine gap (100 microns or less) than to use wet wiping, and this etching method has a high possibility of completely removing AgNW from the gap region, preventing the risk of crosstalk between adjacent circuit functions.

[0007] All of the examples and features shown below can be combined in technically possible ways.

[0008] In one aspect, a 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, and the conductive layer includes carbon nanotubes (CNTs) and a binder.

[0009] Some examples include one or any combination of the above and / or the following 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 on the metal mesh layer. The sheet resistance of the TCF may be 1 Ω / sq (OPS) or less.

[0010] Some examples include one or any combination of the above and / or the following features. The combination of the metal mesh layer and the conductive layer may have a visible light transmittance (VLT) of at least 85%. The combination of the metal mesh layer and the 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 in a diamond, hexagonal, rectangular, or random pattern. The metal mesh layer may include at least 90% open space. The line width of the metal wiring may be 30 microns or less. The open space of the metal mesh layer may have a width of at least 15 times the width of the metal wiring. The TCF defines a circuit having conductive lines with a width that may be at least 10 times the width of the open space of the metal mesh. The metal mesh includes two different metals, a first metal and a second metal, and the second metal may be on the first metal. The first metal may include silver, and the second metal may include copper.

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

[0012] In another aspect, a method of manufacturing a TCF includes 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, the conductive layer including carbon nanotubes (CNTs) and a binder.

[0013] Some examples include one or more of the above and / or the following 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 an exposed metal mesh layer or nanowire layer not covered by the conductive layer. The etching may be achieved by spraying an etching solution onto the TCF. The etching solution may include ferric nitrate.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0015] The CNT - based hybrid TCF 10, FIG. 1, includes an MM layer 13 including metal wirings 14 - 16 and an overlying CNT ink layer 18 that is bonded to the upper surface of the substrate 12 and encapsulates the MM layer 13 with a conductive medium. 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.

[0016] Figures 2A to 2D show the results of the process for fabricating the TCF of the present disclosure. Note that the dimensions and other aspects of Figures 2A to 2D may not be to scale and may be exaggerated merely for the purpose of illustration. Practical examples are shown below. Assembly 20, Figure 2A, includes a substrate 22 carrying an MM that includes wirings 24 to 27. The MM can be fabricated on the substrate by various means described herein. Also, the MM may include various conductive materials (e.g., metals) as further described herein. The MM is composed of a series of thin electrically connected wirings (lines). The wirings are usually laid out in a regular pattern (such as the hexagonal pattern shown in Figure 4A), but this is not necessarily required.

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

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

[0019] Figure 2D shows the final TCF 60 in which the exposed wirings 40, 43 are removed by etching, as will be described in more detail elsewhere herein. Thereby, the conductor 49 remains on the substrate 22.

[0020] One exemplary method 70 for generating a TCF is shown in FIG. 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 on the metal mesh. Step 76 is optional and may not be necessary if the MM itself has an acceptable Rs and there is no need to increase the thickness (i.e., height) of the MM lines. The plated and added metal increases the volume of the MM wiring and thus reduces the resistance. It may also help to make the thin MM more robust and improve the bonding with the conductive ink. In step 78, a conductive medium (referred to as "ink") is printed in selected areas of the MM to form part of the circuit. In one example, the ink includes carbon nanotubes as its conductive medium and also includes a binder. CNT ink is further described 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] The present disclosure will be described in more detail in several non-limiting examples shown below. The examples illustrate a TCF and aspects of its manufacture. The parameters of the TCF and the method of manufacturing the TCF are as follows.

[0022] The metal mesh may be considered a metal grid composed of very fine lines that provide electrical conductivity through interconnected lines and at the same time allow for VLT through the spaces between the lines. The metal mesh can be fabricated on the surface of the substrate by any feasible method including, but not limited to, direct printing, embossing, photolithography followed by etching, and printing followed by plating. The metal mesh can be fabricated with a width sufficient for the final application of the TCF. The width can be up to 12 inches, 24 inches, or more.

[0023] The width of the metal line containing MM depends on the manufacturing method of MM (in some methods, a thinner line width 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 line width of about 2 - 10 μm. To make the width of the line relatively inconspicuous, 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 line width, and the metal grid pattern (for example, hexagonal, rectangular, random, etc.). The metal line has a thickness sufficient to have a substantially negligible VLT (that is, the metal line 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 lines can be calculated for different shapes of the metal grid pattern with respect to a given metal line width and VLT target. For a coarser MM with a line width of 30 μm and an aperture ratio of 90%, the spacing between metal lines is about 550 μm for both hexagonal and square grid patterns. For a finer MM with a line width of 5 μm and an aperture ratio of 90%, the spacing between metal lines 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 line width. These are examples and not limitations or definitions.

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] In the case of an MM with a metal volume resistivity of 4 μΩ·cm (a typical value of flexographic printed 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 / □. In order for the sheet resistance of the MM to be 1 Ω / □ or less (which is known to be strongly desired in antenna and RF shield applications), the thickness of this metal grid needs to be 0.9 μm or more. In the case of a metal grid with an aperture ratio of 85%, the thickness of the metal grid required to achieve a sheet resistance of 1 Ω / □ or less is 0.6 μm or more. In the case of a metal grid with an aperture ratio of 95%, the thickness of the metal grid required to achieve a sheet resistance of 1 Ω / □ or less is 1.8 μm or more.

[0028] The literature value of the volume resistivity of copper is 1.72 μΩ·cm, and in the case of silver, the volume resistivity is 1.59 μΩ·cm. Both of these are lower than the typical values achieved with electroplated copper and flexographic printed nano silver due to the porosity of the plated or printed lines. However, when achieving the literature value of copper for the volume resistivity of the manufactured metal grid, the thickness of the metal grid required 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 patterning followed by etching, etc. Most of the commercial methods for fabricating MM cannot achieve a metal thickness sufficient for the sheet resistance to be 1 Ω / □ or less in the case of 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 feasible processes.

[0030] In the case of an MM with such a high % aperture ratio, to achieve such a low sheet resistance, the material constituting the grid needs to have a very low volume resistivity, which makes metal the only practical material. Table 2 shows the volume resistivity of various materials in units of Ω·m. To convert these values to μΩ·cm, it is necessary to multiply by 10 8 ​

Table 2

[0031] Among metals, there are some with a volume resistivity of less than about 10 μΩ·cm. As the volume resistivity increases, the thickness of the metal required to achieve a sheet resistance of 1 Ω / sq or less increases. Thus, an increase in volume resistivity will result in significant consequences. This will increase the manufacturing cost of MM and also increase the cost of etching MM when patterning the circuit. Metals with a literature value of volume resistivity exceeding twice that of copper are presumed to be less practical. Applying this selection criterion to the above table, the selected metals are only copper, silver, aluminum, and gold. Interestingly, all of these are metals commonly used in the manufacture of printed circuits.

[0032] Another selection criterion is the ability to etch MM with commercially viable etchants. Although it is technically possible to etch gold with aqua regia, it is not commercially practical. Silver is usually etched with ferric nitrate. Copper is usually etched with ferric chloride, but it is also possible to etch it with ferric nitrate (the same etchant used for silver). Aluminum is usually etched with sodium hydroxide or potassium hydroxide. Therefore, from the perspective of etching, silver, copper, and aluminum all seem to be commercially viable MM compositions. The CNT ink formulation used in the examples was also found to be suitable as an etching mask material for all of the typical etchants used for silver, copper, and aluminum. For reference, it is also described that an MM made by printing a nano-silver ink followed by electroplating of copper was successfully etched with ferric nitrate, which is a single etchant. 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 should 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 CNT and MM, and be chemically resistant to etching solutions that may be used for MM etching (i.e., the CNT ink should 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 the binder to the CNT in the CNT ink. If there is too little binder, the CNT ink may not be suitable as an etching mask. When the exposed MM area (the area not covered by the CNT ink) is being etched, it cannot adequately protect the underlying MM. If there is too much binder, the CNTs may be impaired in their ability to establish good electrical connections with each other, and / or with the underlying MM, and / or with the surface of the circuit (to achieve low contact resistance with the printed interconnects).

[0034] Using an ink vehicle chemistry similar to that of the international patent application incorporated herein by reference, a CNT ink prepared with a CNT concentration of 0.1 g / L and an acrylic copolymer binder (DSM B890) and printed with an ink coverage of 30 mg / m 2 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 fully acceptable (i.e., the underlying MM was etched). The ratio of 180:1 was at the limit (it may be okay but not always). Also, 240:1 did not appear to impair the electrical connectivity of the CNTs. Ratios higher than 240:1 are thought to be acceptable, and the upper limit is the penetration limit of CNTs in this binder system, which is estimated to be about 0.2 wt% CNT. This corresponds to a binder:CNT ratio of about 400:1.

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

[0036] < Comparison with the AgNW type of the MM type of 1 Ω / sq

[0037] <1 Ω / □ AgNW type: Transparent conductive films (TCFs) were fabricated using polyethylene terephthalate (PET) (125 μm) as a substrate, coated with a dispersion of 2.0 wt% silver nanowires (AgNWs) in isopropyl alcohol (IPA), and AgNWs with a diameter of approximately 40 nm and a length of 15 μm were used. The AgNW coating had a width of approximately 5 inches × a length of 7 inches. The AgNW dispersion was coated onto the PET film at an AgNW coverage rate of 632 mg / m2 using a Meyer rod (wet film thickness of 40 microns). The coating was dried for approximately 30 seconds with a handheld convection dryer set at 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 / sq. The AgNW coating was screen-printed with a carbon nanotube ink (a reformulated type of VC101 single-layer CNT ink manufactured by Cazm Advanced Materials, Inc., Canton, Massachusetts, USA) using a 305 polyester mesh screen (wet film thickness of approximately 30 μm) having a 2.5-inch block pattern. The ink was reformulated to a CNT concentration of 0.1 g / L and contained a polymer binder (e.g., a modified methacrylic acid copolymer). Other binders that can be used 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 all purposes. The printed CNT layer was dried for approximately 30 seconds with a handheld convection dryer set at 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 (about 25 °C). Next, using a wash bottle, 10% ferric nitrate (Fe(NO 3 ) 3)'s aqueous solution was sprayed for 30 seconds. Next, using another cleaning bottle, deionized water was sprayed on both sides of the sample membrane for 30 seconds. Next, the membrane 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 layers in this example were printed and etched at two different ratios of binder:CNT (120:1, 240:1).

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

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

Table 3

[0040] <1 Ω / □ MM type:The 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 500 - micron pitch) at 120 feet per minute using an anilox roll, and baked in a convection oven at 170 °C for 5 seconds. Next, the hexagonally patterned film was electroplated with copper (Cu). The thickness of the upper copper layer was approximately 0.5 - 1.5 microns (thus, about 5 - 10 times the thickness of the MM layer). Using a 305 polyester mesh screen with a 2.5 - inch block pattern (wet film thickness of approximately 30 μm), the Ag - patterned film was screen - printed with carbon nanotube ink (VC101 single - layer CNT ink manufactured by Cazum Advanced Materials, Inc.). The ink was re - formulated to a CNT concentration of 0.1 g / L and contained the above - mentioned binder. The CNT layers in this example were printed and etched at two different ratios of binder:CNT (120:1, 240:1). The printed CNT layer was dried with a handheld convection dryer set at an outlet air temperature of 177 °C for approximately 30 seconds and baked in a convection oven at 105 °C for 5 minutes. The sample was cooled to ambient temperature (about 25 °C). Next, using a wash bottle, an aqueous solution of 40% ferric nitrate (Fe(NO 3 ) 3 ) was sprayed onto the sample for 15 seconds to etch the exposed Ag - patterned film. Next, using another wash bottle, deionized water was sprayed onto both sides of the sample film for about 30 seconds to remove the etching solution. Next, the film 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.

[0041] After flexographically printing the Ag hexagonal pattern, the visible light transmittance (%VLT) was 90.6% (subtracting the VLT of the substrate), and the sheet resistance (Rs) was 5 Ω / sq. After electroplating with Cu, the %VLT was 90.2% (the value after subtracting the substrate), and the Rs was <1 Ω / sq. After screen printing and etching a 240:1 binder:CNT ink, in the 2.5-inch CNT pattern area, the %VLT and Rs were 90.6% (subtracting the substrate) and <1 Ω / sq, respectively. In the exposed area outside the 2.5-inch CNT pattern area, both the %VLT and Rs increased to 99.6% (the value after subtracting the base) and infinity, respectively. After screen printing and etching a 120:1 binder:CNT ink, there was clear evidence that the etching solution had eaten into the 2.5-inch CNT square area and was advancing from the outer boundary towards the center of the 2.5-inch square. 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.

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

Table 4

[0043] A comparison of the results of the MM type vs. the AgNW type with <1 Ω / sq using a 240:1 binder:CNT ink at 0.1 g / L is shown in Table 5 below.

Table 5

[0044] MM flexographically printed nano Ag + CNT ink + etching solution / each condition:

[0045] Square AgMM + CNT etching time:The TCF sample was fabricated using PET (125 μm) as the substrate, flexographically printed with silver (Ag) ink in a square mesh pattern at 120 feet per minute using an anilox roll, and baked in a convection oven at 170 °C for 5 seconds. A 305 polyester mesh screen (wet film thickness of approximately 30 μm) with a 2.5-inch block pattern was used to screen-print the carbon nanotube ink (VC101 single-layer CNT ink manufactured by Cazm Advanced Materials, Inc.) onto the Ag pattern film. The ink was re-formulated to a CNT concentration of 0.1 g / L and contained the above binder at a binder:CNT ratio of 240:1. The printed CNT layer was dried with a handheld convection dryer set to an outlet air temperature of 177 °C for approximately 30 seconds and baked in a convection oven at 105 °C for 5 minutes. The sample was cooled to ambient temperature (approximately 25 °C). Next, the sample was immersed in a 40 wt% solution of ferric nitrate (Fe(NO 3 ) 3 ) in deionized (DI) water and rinsed with deionized water on both sides of the film for approximately 30 seconds using a wash bottle. Next, 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 CNT before etching were 88.7% (subtracting the substrate) and 4 Ω / □, respectively. The TCF of this example was immersed in a 40 wt% solution of ferric nitrate (Fe(NO 3 ) 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, and the %VLT remained the same at 88.7% (subtracting the substrate). The measured values of %VLT and Rs for etching times of 45 seconds and 10 seconds remained the same as the initial 88.7% (subtracting the substrate) and 4 Ω / □, respectively.

[0048] MM Flexographic Printing Nano Ag+Cu Plating+CNT Ink+Etching Solution / Each Condition:

[0049] Cu-plated MM etching solution type: The TCF sample was 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) at 120 feet per minute using an anilox roll, and baked in a convection oven at 170 °C for 5 seconds. Next, copper (Cu) was electroplated to a thickness of 1.0 micron onto the hexagonal patterned film while stirring. A 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm) was used to screen-print the Ag pattern film with carbon nanotube ink (VC101 single-walled CNT ink manufactured by Cazm Advanced Materials, Inc.). The ink was re-formulated to a CNT concentration of 0.1 g / L and contained the above binder at a binder:CNT ratio of 240:1. The printed CNT layer was dried with a handheld convection dryer set to an outlet air temperature of 177 °C for approximately 30 seconds and 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 CNT printed before etching were 90.6% (value after subtracting the substrate) and <1 Ω / sq, respectively.

[0050] The TCF of this example was etched using two different etching solutions (40% ferric nitrate, 20% ferric chloride) and their combination. Next, the sample was rinsed with deionized (DI) water on both sides of the film for approximately 30 seconds using a wash bottle, gently tapped with a lint-free cloth to remove large water droplets, and 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 pattern area, %VLT and Rs remained at 90.6% (subtracting the substrate) and <1 Ω / sq, respectively. In the exposed area outside the 2.5-inch CNT pattern area, both %VLT and Rs increased to 99.6% (subtracting the base) and infinity, respectively. There was also an approximately 2-mm halo of unetched material at the outer ends of the 2.5-inch CNTs.

[0052] Sample B was immersed in 20% ferric chloride for 10 seconds. In the 2.5-inch CNT pattern area, %VLT and Rs remained at 90.6% (subtracting the substrate) and <1 Ω / sq, respectively. In the exposed area outside the 2.5-inch CNT pattern area, %VLT increased to 92.9% (subtracting the base), 6.7% lower than that of Sample A. This means that even though Rs was infinity, the exposed mesh area was not completely removed. Ferric chloride removed the halo effect seen 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 the substrate) and <1 Ω / sq, respectively. In the exposed area outside the 2.5-inch CNT pattern area, both %VLT and Rs increased to 99.6% (value after subtracting the base) and infinity, respectively. The post-treatment with ferric chloride removed the halo effect seen after the initial ferric nitrate etching.

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

[0055] Coating method of Cu-plated MM etching solution: The TCF was fabricated using PET (125 μm) as the substrate, flexographically printed with silver (Ag) ink in a hexagonal pattern (30-micron lines, 500-micron spacing) at 120 feet per minute using an anilox roll, and baked in a convection oven at 170 °C for 5 seconds. Next, copper (Cu) was electroplated onto the hexagonal-patterned film to a thickness of 1.0 micron while stirring. A 305 polyester mesh screen with a 2.5-inch block pattern (wet film thickness of approximately 30 μm) was used to screen-print the carbon nanotube ink (VC101 single-layer CNT ink manufactured by Cazm Advanced Materials, Inc.) onto the Ag pattern film. The ink was re-formulated to a CNT concentration of 0.1 g / L and contained the above binder at a binder:CNT ratio of 240:1. The printed CNT layer was dried with a handheld convection dryer set to 177 °C outlet air for approximately 30 seconds and 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 CNT printed before etching were 90.6% (subtracting the substrate) and <1 Ω / □, respectively.

[0056] The TCF in this example was etched using two different application methods (spraying, dipping) with 40% ferric nitrate (Fe(NO 3 ) 3) was etched for 15 seconds with an aqueous solution. Next, using another wash bottle, deionized water was sprayed onto both sides of the sample film for approximately 30 seconds. Next, the film 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. In both cases, the %VLT and Rs of the 2.5-inch CNT square region remained 90.6% (subtracting the substrate) and <1 Ω / □, respectively. Both samples showed good etching of the exposed Cu plating mesh pattern in the 2.5-inch CNT square, but in the immersed sample, there was a halo of approximately 2 mm around the 2.5-inch printed square and it was not fully etched. The sprayed ferric nitrate showed no sign of this halo.

[0057] Chemical Etching of the AgNWs Type of AgeNT:

[0058] Etching of AgeNT-75:The TCF was fabricated using PET (125 μm) as the substrate and coated with a dispersion of a 0.3 wt% silver nanowire solution using an aqueous silver nanowire ink (diameter of about 40 nm and length of 15 μm). The AgNW coating was approximately 5 inches wide by 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 using 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 with a carbon nanotube ink (VC101 single layer CNT ink manufactured by Cazum Advanced Materials, Ink) using a 305 polyester mesh screen (wet film thickness of approximately 30 μm) having a 2.5-inch block pattern. The ink was reconstituted to a CNT concentration of 0.1 g / L and contained the above binder at a binder:CNT ratio of 120:1. The printed CNT layer was dried for approximately 30 seconds using 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 (about 25 °C). The initial %VLT and sheet resistance (Rs) of the CNT printed AgNW film before etching were 99.3% (subtracting the substrate) and 60 Ω / sq, respectively.

[0059] The TCF in this example was sprayed with an aqueous solution of 10% ferric nitrate (Fe(NO 3 ) 3 ) for 15 seconds. Next, using a different wash bottle, DI 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 baked in a convection oven at 105 °C for 1 minute.

[0060] After screen printing and etching the CNT ink, in the 2.5-inch CNT printed area, %VLT and Rs remained at 99.3% (subtracting the VLT of the substrate) and 60 Ω / sq, respectively. After etching, in the exposed area outside the 2.5-inch CNT printed area, %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. So far, the best form for etching AgNW or MM has been to use ferric nitrate as the etching solution and the spraying method or the dipping method. This does not exclude other etching solutions or other etching methods that are currently known or will be developed in the future.

[0062] Review of Cu and Ag etching technologies:

[0063] Copper etching solution: For the etching of Cu, many wet chemical systems (Table 6) are used. Important parameters for the control and optimization of the etching process are pH, temperature, replenishment of the etching solution, and the degree of stirring.

[0064] One of the most commonly used and least expensive chemical systems is ferric chloride. This mechanism involves oxidizing copper to cuprous chloride. Other chemical species such as HCl may be added to improve the etching performance by enhancing the reaction kinetics of cuprous chloride formation, which can be the rate-limiting step in the overall reaction kinetics of the etching process.

[0065] Another commonly used etching solution is cupric chloride. Since copper is reduced to cuprous chloride, which degrades the performance of the etching solution, the regeneration of CuCl 2 is important. Similar to the case of ferric chloride, other chemicals (HCl, KCl, NaCl) are usually added to improve the performance.

Table 6

[0066] Alkaline etching solutions such as ammonium hydroxide form copper-ammonium complex ions that bind to copper ions and stabilize the dissolved Cu in the solution.

[0067] Ammonium persulfate is an excellent etching solution for Cu, but a heat exchanger is required because the process is exothermic. Furthermore, the etching rate is lower than some of the more aggressive chemical systems, which makes it more easily controllable but suitable for processes where rate control may be done in the overall process scheme.

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

Table 7

[0069] Additional examples:

[0070] There are numerous ways to create the MM layer using various combinations of Rs and VLT characteristics. One method involves flexographic printing of MM using nano Ag ink. This method appears to be suitable for creating MM with Rs of about 10 Ω / □ and VLT of about 90%. To reduce the Rs of the MM without sacrificing VLT, Cu is electroplated on the printed AgMM to create Ag / CuMM. Other materials may be used for both the printed layer and the plating layer on top.

[0071] MM can be created using other methods. This includes using more advanced flexographic printing plates to achieve MM line widths up to about 3 microns. This example has an MM line width of about 30 microns. Reducing the MM line width makes the MM less visible at the same VLT value. Also, thin lines enable thinner line widths in the CNT hybrid circuit. As a general rule of thumb, for the % opening area of the MM to be higher than about 90%, the width of the opening area of the mesh needs to be about 15 - 20 times the MM line width. The % opening area determines the maximum VLT value of the printed CNT hybrid circuit. Thus, an MM line width of 30 microns needs to have an opening area width of about 500 microns. Another general rule of thumb is that for sufficient conductive material to be placed in the circuit wiring, the minimum line width of the printed CNT hybrid circuit needs to be more than 10 times the width of the opening area segment of the MM. Thus, the minimum line width of the circuit must be greater than about 5 mm. This minimum line width is expected to be about 0.5 mm if the MM line width can be reduced to 3 microns.

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

[0073] The MM can also be created using lithographic etching methods or various lift-off patterning methods that are being developed in the printed circuit industry. It is also possible to create the MM using laser ablation of a metal thin film.

[0074] Figures 4A - 4C, 5A, and 5B include images illustrating a printed CNT hybrid (MM type), where MM was flexographically printed Ag (without subsequent Cu electroplating). The SEM image (magnification 50x) of Figure 4A shows an MM hexagonal pattern with an Ag line width of approximately 30 μm and an overall width of the hexagonal open space of approximately 500 μm. The SEM image (magnification 50k x) of Figure 4B shows how CNTs form a well - connected network in a space that normally has no conductive material. The areal density of the CNT network is sufficiently low (about 1 - 10 mg / m 2 ) and transparent, but a sufficiently high areal density enables charge diffusion in the open space, resulting in a more uniform electrode. The SEM image (magnification 100k x) of Figure 4C shows how the CNT network helps strengthen the porous AgMM lines and can provide redundant conductive paths to enhance reliability. Note that the CNT ink printed on top of the AgMM shown in Figure 4A did not contain a polymer binder in them, so the CNT network was only visible in the SEM images of Figures 4B and 4C. Usually, the polymer binder is at a level sufficient to encapsulate the MM and CNTs, and the CNT network self - organizes within the polymer matrix. This makes it impossible to see the CNT network by SEM imaging.

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

[0076] Figures 5A and 5B show only the flexographically printed AgMM, which is plated with copper. Figure 5A includes images at both 10k and 25k magnifications, and Figure 5B includes images at both 50k and 100k magnifications. Still, the porous appearance of the flexographically printed AgMM can be "filled" after Cu electroplating to reduce porosity. The thickness of the Cu electroplating is about 0.5 - 1.5 microns, while the thickness of the flexographically printed Ag can be about 0.1 - 0.15 microns. The SEM images in Figures 5A and 5B clearly show this. It is believed that Cu plating not only reduces sheet resistance (without sacrificing 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 serves to enhance the environmental stability and adhesion of the printed CNT hybrid circuits. It also serves to protect the MM or AgNW from chemical etching (i.e., it is a component for providing an etching mask function). The binder must have excellent environmental stability, adhesion properties, high transparency, and low haze.

[0078] It is reasonable to expect that many different binders can be used. The selection criteria for suitable polymer binder candidates include the following. · Good 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 treatment requirements compatible with plastic film substrates (<120°C). · Solubility compatible with ink formulation (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 CNTs. However, it is reasonable to expect that good results can also be obtained by replacing them with two-layer, few-layer, or multi-layer CNTs.

[0080] Numerous implementations have been described. Nevertheless, additional changes can be made without departing from the scope of the inventive concept described herein, and thus, other examples are within the scope of the claims. Also, the present invention can be implemented with the following configurations. (1) A substrate having a surface, A metal mesh layer on at least a part of the surface of the substrate, A transparent conductive film (TCF) including a conductive layer containing carbon nanotubes (CNTs) and a binder on the 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, wherein the second metal layer includes a copper layer. (4) The transparent conductive film according to (3) above, wherein the copper layer is electroplated on the metal mesh layer. (5) The transparent conductive film according to (1) above, wherein the sheet resistance of the transparent conductive film is 1 Ω / □ (OPS) or less. (6) The transparent conductive film according to (1) above, wherein 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, wherein 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 in a hexagonal, rectangular, or random pattern. (10) The transparent conductive film according to (8) above, wherein the metal mesh layer includes at least 90% open space. (11) The transparent conductive film according to (8) above, wherein the line width of the metal wiring is 30 microns or less. (12) The transparent conductive film according to (8) above, wherein the open space of the metal mesh layer has 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 lines with a certain width, and the width of the conductive lines is at least 10 times the width of the open space of the metal mesh. (14) The transparent conductive film according to (1) above, wherein the metal mesh includes two different metals, a first metal and a second metal, and the second metal is on the first metal. (15) The transparent conductive film according to (14) above, wherein the first metal includes silver and the second metal includes copper. (16) The carbon nanotubes in the conductive layer include a network with a surface density of about 1 - 10 mg / m 2 of the transparent conductive film according to (1) above. (17) The transparent conductive film according to (1) above, wherein the ratio of binder:carbon nanotubes in the conductive layer is greater than 120:1. (18) Preparing a substrate having a surface, Depositing a metal mesh layer or a nanowire layer on at least a part of the surface of the substrate, Patternizing a conductive layer on at least a part of the metal mesh layer or the nanowire layer, and the conductive layer includes carbon nanotubes (CNT) and a binder, a method for manufacturing a transparent conductive film (TCF). (19) The method according to (18) above, further including depositing a second metal layer on the metal mesh layer before patternizing the conductive layer. (20) The method according to (18) above, wherein the nanowire layer includes silver nanowires. (21) The method according to (18) above, further comprising etching an exposed metal mesh layer or nanowire layer not covered by a conductive layer. (22) The method according to (21) above, wherein the etching is achieved by spraying an etching solution onto the transparent conductive film. (23) The method according to (22) above, wherein the etching solution contains ferric nitrate.

Claims

1. a substrate having a surface; a metal mesh layer on at least a portion of a surface of the substrate, the metal mesh layer including a network of interconnected metal wiring having open spaces between the metal wiring, the metal wiring including two separate metal wiring layers, one metal wiring layer overlying the other metal wiring layer; A transparent conductive film (TCF) comprising: a conductive layer encapsulating a metal mesh layer and comprising carbon nanotubes (CNTs) and a binder.

2. The transparent conductive film according to claim 1 , wherein the metal wiring layers are made of different metals.

3. The transparent conductive film according to claim 2 , wherein the upper metal wiring layer comprises a copper layer.

4. The transparent conductive film according to claim 3 , wherein the copper layer is electroplated on the lower metal wiring layer.

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

6. 10. The transparent conductive film of claim 1, wherein the combination of the metal mesh layer and the conductive layer has a visible light transmittance (VLT) of at least 85%.

7. 10. The transparent conductive film of claim 1, wherein 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 of claim 1 , wherein the network is a hexagonal, rectangular, or random pattern.

9. 10. The transparent conductive film of claim 1, wherein the metal mesh layer comprises at least 90% open space.

10. 2. The transparent conductive film according to claim 1, wherein the line width of the metal wiring is 30 microns or less.

11. 2. The transparent conductive film according to claim 1, wherein the open spaces of the metal mesh layer have a width at least 15 times the width of the metal wiring.

12. 10. The transparent conductive film of claim 1 defining a circuit having conductive lines having a width, the width of the conductive lines being at least 10 times the width of the open spaces of the metal mesh.

13. 2. The transparent conductive film of claim 1, wherein the metal mesh comprises two different metals, a first metal and a second metal, the second metal being on top of the first metal.

14. 14. The transparent conductive film according to claim 13, wherein the first metal comprises silver and the second metal comprises copper.

15. The carbon nanotubes in the conductive layer have a surface density of 1 to 10 mg / m ２ The transparent conductive film according to claim 1 , comprising a network of

16. 2. The transparent conductive film of claim 1, wherein the ratio of binder:carbon nanotubes in the conductive layer is greater than 120:

1.

17. A transparent conductive film (TCF) in which the ratio of binder to carbon nanotubes in the conductive layer is at least 240:1 or greater.

Images