Method and Apparatus of Forming Cracks as Masks for the Fabrication of Micro-Metal Mesh

Abstract

Methods and systems for forming cracks as masks for the fabrication of micro-metal mesh are disclosed, including depositing a composite film onto a substrate wherein the composite film comprises a brittle layer, a brittle layer atop a mediate layer, or a brittle layer atop a sacrificial layer; generating a tensile stress in the substrate and/or the composite film in order to form micro-cracks in the brittle layer; tuning widths of the micro-cracks; transferring pattern of the micro-cracks onto the sacrificial layer; depositing a conductive material onto the brittle layer and the area of the substrate or mediate layer exposed by the pattern of the micro-cracks; and performing a lift-off of the brittle layer and if present the sacrificial layer from the substrate or mediate layer, resulting in the micro-metal mesh atop the substrate or mediate layer. Other embodiments are described and claimed.

Description

I. BACKGROUND

The invention relates generally to the field of forming cracks as masks for the fabrication of micro-metal mesh. More particularly, the invention relates to a roll-to-roll compatible method and apparatus of forming cracks in a deposition layer for the fabrication of micro-metal mesh.

II. SUMMARY

In one respect, disclosed is a method for fabricating a micro-metal mesh, the method comprising: depositing a brittle layer onto a substrate; generating a tensile stress in the substrate and/or the brittle layer in order to form micro-cracks in the brittle layer; tuning widths of the micro-cracks; depositing a conductive material onto the brittle layer and the area of the substrate exposed by the pattern of the micro-cracks; and performing a lift-off of the brittle layer from the substrate, resulting in the micro-metal mesh atop the substrate.

In another respect, disclosed is a method for fabricating a micro-metal mesh, the method comprising: depositing a mediate layer onto a substrate; depositing a brittle layer onto the mediate layer; generating a tensile stress in the substrate, the mediate layer, and/or the brittle layer in order to form micro-cracks in the brittle layer; tuning widths of the micro-cracks; depositing a conductive material onto the brittle layer and the area of the mediate layer exposed by the pattern of the micro-cracks; and performing a lift-off of the brittle layer from the mediate layer, resulting in the micro-metal mesh atop the mediate layer.

In another respect, disclosed is a method for fabricating a micro-metal mesh, the method comprising: depositing a sacrificial layer onto a substrate; depositing a brittle layer onto the sacrificial layer; generating a tensile stress in the substrate, the sacrificial layer, and/or the brittle layer in order to form micro-cracks in the brittle layer; tuning widths of the micro-cracks; transferring pattern of the micro-cracks onto the sacrificial layer; depositing a conductive material onto the brittle layer and the area of the substrate exposed by the pattern of the micro-cracks transferred onto the sacrificial layer; and performing a lift-off of the sacrificial layer and the brittle layer from the substrate, resulting in the micro-metal mesh atop the substrate.

In yet another respect, disclosed is an apparatus for forming micro-cracks in a brittle layer, the apparatus comprising: a roller having a diameter; the apparatus configured to: drive a composite film around the roller to generate a tensile stress in the composite film, wherein the composite film comprises the brittle layer atop a substrate; and form cracks in the brittle layer, wherein the cracks are parallel to the axis of the roller and have a period dependent on the diameter of the roller.

Numerous additional embodiments are also possible.

III. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention may become apparent upon reading the detailed description and upon reference to the accompanying drawings.

FIGS. 1A and 1B are pictures of a metal mesh and a nanowire network, respectively.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional illustrations of the steps in fabricating a micro-metal mesh, in accordance with some embodiments.

FIG. 3 is a top-view illustration of the periodic metal nanowire structure illustrated in FIG. 2D, in accordance with some embodiments.

FIG. 4 is a top-view illustration of a metal nanowire mesh, in accordance with some embodiments.

FIG. 5 is a top-view illustration of a metal nanowire mesh, in accordance with some embodiments.

FIGS. 6A, 6B, 6C, and 6D are cross-sectional illustrations of the steps in fabricating a micro-metal mesh, in accordance with some embodiments.

FIG. 7 is a top-view illustration of the periodic metal nanowire structure illustrated in FIG. 6D, in accordance with some embodiments.

FIG. 8 is a cross-sectional view illustration of a roller setup used to generate cracks in a brittle layer, in accordance with some embodiments.

FIG. 9 is a block diagram illustrating a method for forming cracks as masks for the fabrication of a micro-metal mesh, in accordance with some embodiments.

FIG. 10 is a block diagram illustrating a method for forming cracks as masks for the fabrication of a micro-metal mesh, in accordance with some embodiments.

FIGS. 11A, 11B, 11C, 11D and 11E are cross-sectional illustrations of the steps in fabricating a micro-metal mesh, in accordance with some embodiments.

FIG. 12 is a top-view illustration of the random metal mesh structure illustrated in FIG. 11E, in accordance with some embodiments.

FIG. 13 is a block diagram illustrating a method for forming cracks as masks for the fabrication of a micro-metal mesh with a bi-layer composite film, in accordance with some embodiments.

While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiments. This disclosure is instead intended to cover all modifications, equivalents, and alternatives falling within the scope of the present invention as defined by the appended claims.

IV. DETAILED DESCRIPTION

One or more embodiments of the invention are described below. It should be noted that these and any other embodiments are exemplary and are intended to be illustrative of the invention rather than limiting. While the invention is widely applicable to different types of systems, it is impossible to include all of the possible embodiments and contexts of the invention in this disclosure. Upon reading this disclosure, many alternative embodiments of the present invention will be apparent to persons of ordinary skill in the art.

Transparent conductors are structures and materials that are electrically conductive and optically transparent or translucent. Transparent conductors are an essential part in many electronic devices, such as touch panels, flat screen displays, light emitting diodes, and solar cells and also in other applications such as in transparent heaters and in electromagnetic (EM) shielding. Presently, Indium Tin Oxide (ITO) is one of the prevailing materials used as transparent conductors in electronic devices. However, due to ITO's brittleness, high cost, high optical diffraction index, limited conductivity, and limited transparency, alternatives to the use of ITO are desirable. Alternatives such as metal mesh, metal nanowire, graphene, and carbon nanotube have attracted attention as alternatives to ITO. Of these alternatives, metal mesh and metal nanowire networks are especially attractive due to their excellent combination of high conductivity and high transparency.

FIGS. 1A and 1B are pictures of a metal mesh and a nanowire network, respectively.

FIG. 1A shows a typical metal mesh network manufactured by Unipixel, Inc. (www.unipixel.com). Unipixel utilizes an additive manufacturing process where micron sized copper lines 105 are printed on flexible printed electronics. The micron sized metal lines 105 are difficult to fabricate and relatively expensive to implement. FIG. 1B shows a typical nanowire network manufactured by Cambrios Technologies Corporation (www.cambrios.com). Cambrios utilizes a directly patternable, wet-processable transparent conductive film made from silver nanowires 110 to produce a network of nanowires to form a metal mesh. Although with the Cambrios nanowire network, narrow metal lines as narrow as 100 nm are possible, the tunable range of conductivity and transparency are relatively limited. Additionally, the Cambrios nanowire network is relatively expensive to implement. What is needed is a method of fabricating a metal mesh that is made up with metal lines that can be tuned with line widths between 20 nm to 5 μm and where the periodicity of the metal lines can also be tuned between 500 nm to 1 mm. A method of fabricating such a micro-metal mesh is disclosed in this invention.

FIGS. 2A, 2B, 2C, and 2D are cross-sectional illustrations of the steps in fabricating a micro-metal mesh, in accordance with some embodiments.

In some embodiments, a brittle layer 205 is deposited onto a substrate 210 as illustrated in FIG. 2A. The brittle layer 205 may comprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or polymethyl methacrylate (PMMA). The substrate 210 may comprise any transparent and flexible film, such as polyethylene terephthalate (PET), polyimide (PI), cellulose, polyester, polyethylene, polyolefin, polycarbonate, flexible glass, or a combination or lamination thereof. A tensile stress may be generated in the brittle layer during its deposition or in a subsequent process such as during the heating, curing, or chemical crosslinking of the brittle layer. Next, micro-cracks 215 are generated in the brittle layer 205. Various methods, such as mechanical bending, stretching, squeezing, pressing, thermal shock, and quenching, may be used to generate micro-cracks 215 in the brittle layer 205 as shown in FIG. 2B. The micro-cracks 215 are generated as a result of the stress in the substrate 210 and the brittle layer 205. The density of the micro-cracks is determined by the stress in the brittle layer. The size of the micro-cracks may be adjusted by adjusting the thermal processing parameters, such as the drying temperature, the drying speed, and/or the drying time, or by etching. The width of the micro-cracks may range from about 20 nm to about 5 μm. Micro-cracks may also be generated in the brittle layer by adding nanoparticles in the brittle layer. The nanoparticles may comprise silver, copper, gold, iron, nickel, cobalt, platinum, palladium, titanium, aluminum, chromium, and/or molybdenum. After the micro-cracks have been generated, a layer of conductive material 220, comprising metals, alloys, and/or doped semiconductor, is deposited onto the micro-cracked brittle layer 205 as shown in FIG. 2C. The brittle layer with the micro-cracks is used as a mask during the deposition of the conductive material. Next, the brittle layer is lifted-off resulting in a structure of metal nanowires 225 atop the substrate 210 as illustrated in the periodic, one-dimensional metal nanowires 223 of FIG. 2D. FIG. 3 shows the top view of the periodic metal nanowire structure 225, comprising four one-dimensional metal nanowires 223, atop the substrate 210 as shown in FIG. 2D. In order to fabricate a two-dimensional metal nanowire mesh, a two-dimensional crack network may be generated in the step shown in FIG. 2B or in the alternative, the process steps as shown in FIG. 2A to FIG. 2D may be repeated but with a different orientation of the substrate. FIG. 4 illustrates a two-dimensional metal nanowire mesh network 405 where the cracks were substantially orthogonal to each other. Other more complicated metal nanowire mesh networks may be generated by using additional micro-crack directions. FIG. 5 illustrates a metal nanowire mesh 505 where the cracks were substantially sixty degrees relative to each other.

FIGS. 6A, 6B, 6C, and 6D are cross-sectional illustrations of the steps in fabricating a micro-metal mesh, in accordance with some embodiments.

In some embodiments, in order to control a larger range in the widths of the generated cracks, a mediate layer 602 is deposited onto a substrate 610, followed by the deposition of a brittle layer 605 onto the mediate layer 602 as illustrated in FIG. 6A. The more flexible and elastic mediate layer 602 relaxes the stress which is used to generate the cracks in the brittle layer 605. The mediate layer 602 may comprise PMMA, PS, polyvinyl chloride (PVC), rubber, silicone, polydimethylsiloxane (PDMS), nylon, or a combination thereof. The brittle layer 605 may comprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA. The substrate 610 may comprise any transparent and flexible film, such as PET, PI, cellulose, polyester, polyethylene, flexible glass, and/or other similar materials. A tensile stress may be generated in the brittle layer during its deposition or in a subsequent process such as during the heating, curing, or chemical crosslinking of the brittle layer. Next, micro-cracks 615 are generated in the brittle layer 605. Various methods, such as mechanical bending, stretching, squeezing, pressing, thermal shock, and quenching, may be used to generate micro-cracks 615 in the brittle layer 605 as shown in FIG. 6B. The micro-cracks 615 are generated as a result of the stress in the substrate 610, the mediate layer 602, and the brittle layer 605. The size of the micro-cracks is tunable by adjusting the stress in the brittle layer 605, the mediate layer 602, and/or the substrate 610. After the micro-cracks have been generated, a layer of conductive material 620, comprising metals, alloys, and/or doped semiconductor, is deposited onto the micro-cracked brittle layer 605 as shown in FIG. 6C. The brittle layer with the micro-cracks is used as a mask during the deposition of the conductive material. Next, the brittle layer is lifted-off resulting in a structure of metal nanowires 625 atop the mediate layer 602 as illustrated in the periodic, one-dimensional metal nanowires 623 of FIG. 6D. FIG. 7 shows the top view of the periodic metal nanowire structure 625, comprising four one-dimensional metal nanowires 623, atop the mediate layer 602 as shown in FIG. 6D. In order to fabricate a two-dimensional metal nanowire mesh, similar to the two-dimensional metal nanowire mesh networks illustrated in FIG. 4 and FIG. 5, a two-dimensional crack network may be generated in the step shown in FIG. 6B or in the alternative, the process steps as shown in FIG. 6A to FIG. 6D may be repeated but with a different orientation of the substrate.

FIG. 8 is a cross-sectional view illustration of a roller setup used to generate cracks in a brittle layer, in accordance with some embodiments.

In some embodiments, an apparatus 800 comprises a mechanical bending used to generate the micro-cracks. A composite film 801 comprising a brittle layer 805 and a substrate 810 is wrapped around a roller 815 as illustrated in FIG. 8. The roller 815 has a diameter D. The composite film may be driven by the roller 815 or by an external roll-to-roll mechanical system (not shown). As the composite film is driven around the roller 815 in the direction shown by arrows 820 and 825, cracks 830 are formed in the brittle layer 805. The cracks 830 run along and are parallel to the axis 835 of the roller 815. The period between cracks P may be tuned by changing the diameter D of the roller 815. The larger the diameter D, the larger the period P between cracks. The composite film may also comprise a mediate layer or a sacrificial layer between the brittle layer and the substrate, resulting in a periodic crack structure as shown and described in FIGS. 6D and 11E, respectively. In order to fabricate more complicated metal nanowire, two-dimensional mesh networks, a two-dimensional micro-crack network may be generated by driving the composite film around the roller again but with a different orientation of the substrate. After formation of the periodic crack structure by wrapping the composite film around the roller, the widths of the cracks 830 may be tuned by adjusting the stress in the composite film. The stress may be adjusted by adjusting the thermal processing parameters, such as the drying temperature, the drying speed, and/or the drying time, or by etching. In an embodiment with a sodium silicide brittle layer, the width of the crack may be adjusted from 20 nm to 1 mm.

In one embodiment, a brittle layer of spin-on-glass, such as P-102F spin-on-glass from Filmtronics, was spun onto a substrate of cleaned PET film at a thickness between 75 μm to 100 μm using a rotation rate of 1,000 rpm for 40 seconds. The composite film of the spin-on-glass atop the PET film was subsequently dried in order to induce a tensile stress. The composite film may be dried at room temperature for a longer time or on a hot plate for shorter time. If dried at room temperature, the composite film is dried for two hours. Next, the dried composite film is mechanically bent at a constant stress of 2 MPa with rollers having different diameters. The diameter of the roller controls the period between cracks. For roller diameters of 1.6 mm, 2.4 mm, 3.2 mm, 4 mm, 4.8 mm, 5.6 mm, 10 mm, and 30 mm, periods of 500 nm-5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 30 μm, 200 μm, and 1 mm were formed, respectively. The range of periods from 500 nm to 5 μm for the 1.6 mm diameter roller was achieved by adjusting the stress in the composite film during the thermal drying process of the composite film. After formation of the periodic crack structure by wrapping the composite film around the roller, the widths of the cracks may be tuned by adjusting the stress in the composite film. The stress may be adjusted by adjusting the thermal processing parameters, such as the drying temperature, the drying speed, and/or the drying time, or by etching. The annealing may comprise a temperature ranging from about 40° C. to about 180° C. and a time ranging from about 10 seconds to about 1 hour. Using baking temperatures of 60° C., 80° C., 100° C., 110° C., 120° C., 130° C., 140° C., and 150° C. resulted in crack widths of 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 700 nm, and 1000 nm, respectively.

FIG. 9 is a block diagram illustrating a method for forming cracks as masks for the fabrication of a micro-metal mesh, in accordance with some embodiments. In some embodiments, the method illustrated in FIG. 9 may be performed by the device illustrated in FIG. 8.

Processing begins at 900 whereupon, at block 905, a brittle layer is deposited onto a substrate to form a composite film. In some embodiments, the brittle layer may comprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA and the substrate may comprise any transparent and flexible film, such as PET, PI, cellulose, polyester, polyethylene, flexible glass, and/or other similar materials. At block 910, a tensile stress is generated in the brittle layer and/or substrate. Depending on the brittle layer used, a tensile stress may be generated in the brittle layer during its deposition or in a subsequent process such as heating, curing, or chemical crosslinking of the brittle layer. Next, at block 915, micro-cracks are generated in the brittle layer. A one dimensional and/or two-dimensional micro-crack network may be generated by mechanical bending, stretching, squeezing, pressing, thermal shock, and/or quenching. After the micro-cracks have been formed, at block 920, the width of the micro-cracks may be tuned by adjusting the thermal processing parameters, such as the drying temperature, the drying speed, and/or the drying time, or by etching. The width of the micro-cracks may range from about 20 nm to about 5 μm. Next, at block 925, a conductive material is deposited onto the composite film. The brittle layer with the micro-cracks is used as a mask during the deposition of the conductive material. The conductive material may comprise metals, alloys, and/or doped semiconductor. At block 930, the brittle layer is lifted-off from the substrate resulting in a metal nanowire structure atop the substrate. The metal nanowire structure may comprise periodic, one-dimensional metal nanowires and/or a two-dimensional metal nanowire mesh with line widths between about 20 nm to about 5 μm with a spacing between metal lines between about 500 nm to about 1 mm. Processing subsequently ends at 999.

FIG. 10 is a block diagram illustrating a method for forming cracks as masks for the fabrication of a micro-metal mesh, in accordance with some embodiments. In some embodiments, the method illustrated in FIG. 10 may be performed by the device illustrated in FIG. 8.

Processing begins at 1000 whereupon, at block 1005, a mediate layer is deposited onto a substrate. In some embodiments, the mediate layer may comprise rubber, silicone, PDMS, and/or silicone rubber and the substrate may comprise any transparent and flexible film, such as PET, PI, cellulose, polyester, polyethylene, flexible glass, and/or other similar materials. Next, at block 1010, a brittle layer is deposited onto the mediate layer to form a composite film comprising the brittle layer, the mediate layer, and the substrate. The brittle layer may comprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA. At block 1015, a tensile stress is generated in the brittle layer, the mediate layer, and/or the substrate. Depending on the brittle layer and mediate layer used, a tensile stress may be generated in the brittle layer and mediate layer during its deposition or in a subsequent process such as heating, curing, or chemical crosslinking of the brittle layer and mediate layer. Next, at block 1020, micro-cracks are generated in the brittle layer. A one dimensional and/or two-dimensional micro-crack network may be generated by mechanical bending, stretching, squeezing, pressing, thermal shock, and/or quenching. After the micro-cracks have been formed, at block 1025, the width of the micro-cracks may be tuned by adjusting the thermal processing parameters, such as the drying temperature, the drying speed, and/or the drying time, or by etching. The width of the micro-cracks may range from about 20 nm to about 5 μm. Next, at block 1030, a conductive material is deposited onto the composite film. The brittle layer with the micro-cracks is used as a mask during the deposition of the conductive material. The conductive material may comprise metals, alloys, and/or doped semiconductor. At block 1035, the brittle layer is lifted-off from the mediate layer resulting in a metal nanowire structure atop the mediate layer. The metal nanowire structure may comprise periodic, one-dimensional metal nanowires and/or a two-dimensional metal nanowire mesh with line widths between about 20 nm to about 5 μm with a spacing between metal lines between about 500 nm to about 1 mm. Processing subsequently ends at 1099.

FIGS. 11A, 11B, 11C, 11D and 11E are cross-sectional illustrations of the steps in fabricating a micro-metal mesh with bi-layer composite film, in accordance with some embodiments.

In some embodiments, a sacrificial layer 1115 is deposited onto a substrate 1110, followed by the deposition of a brittle layer 1105 onto the sacrificial layer 1115 as illustrated in FIG. 11A. The sacrificial layer 1115 may be, but not limited to nylon and/or photo resists such as Shipley S1800 series. The thickness of sacrificial layer 1115 ranges from about 50 nm-1000 nm. The brittle layer 1105 may comprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA. The substrate 1110 may comprise any transparent and flexible film, such as PET, PI, cellulose, polyester, polyethylene, flexible glass, and/or other similar materials. Next, micro-cracks 1120 are generated in the brittle layer 1105. Various methods, such as mechanical bending, stretching, squeezing, pressing, thermal shock, quenching and adding nanoparticles in the brittle layer 1105, may be used to generate micro-cracks 1120 in the brittle layer 1105 as shown in FIG. 11B. The size of the micro-cracks is tunable by adjusting the thermal processing parameters after cracks are generated, such as the drying temperature, the drying speed, and/or the drying time, or by etching. The pattern of the micro-cracks 1125 in the sacrificial layer is copied or transferred by partially dissolving and/or reactive ion etching the uncovered area of the sacrificial layer 1115 as shown in FIG. 11C. After the micro-cracks 1125 have been generated, a layer of conductive material 1130, comprising metals, alloys, and/or doped semiconductor, is deposited onto the composite film as shown in FIG. 11D. Next, the bi-layer, comprising the brittle layer 1105 and the sacrificial layer 1115, is lifted-off resulting in a structure of micro-mesh 1135 atop the substrate 1110 as illustrated in the FIG. 11E. FIG. 12 shows the top view of the micro-mesh structure 1135 atop the substrate 1110 as shown in FIG. 11E.

In one embodiment, a sacrificial layer of PMMA from MicroChem, is coated onto a substrate of cleaned PET film at a thickness between 75 μm and 150 μm by a micro-gravure roll-to-roll coater from MIRWEC Film, Inc. Next, a brittle layer of spin-on-glass, such as P-102F from filmtronic, is coated onto the PMMA film by the same roll-to-roll coater. The composite film is subsequently dried in air at room temperature for 2 hours. Next, the dried composite film is thermal shocked and annealed by baking on a hot plate. The density of the micro-cracks increases when the baking temperature is increased from 50° C. to 150° C. The size of the micro-cracks increases from 200 nm to 700 nm when the baking time is increased from 30 seconds to 3 minutes at 110° C. Next, the micro-cracks pattern is copied to the PMMA layer by immersing the film in Acetone for 10 seconds. Next, 100 nm of silver is deposited onto the micro-cracked composite film by e-beam evaporation or sputtering. Next, the PMMA and spin-on-glass layer bi-layer is lifted-off from the substrate resulting in a metal mesh structure atop the PET substrate.

FIG. 13 is a block diagram illustrating a method for forming cracks as masks for the fabrication of a micro-metal mesh, in accordance with some embodiments. In some embodiments, the method illustrated in FIG. 13 may be performed by the device illustrated in FIG. 8.

Processing begins at 1300 whereupon, at block 1305, a sacrificial layer and a brittle layer are deposited onto a substrate to form a composite film. In some embodiments, the sacrificial layer can be, but not limited to polymers such as PMMA, PS, PVC, rubber, silicone, PDMS, nylon and/or photo resists such as Shipley S1800 series. The brittle layer may comprise spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA and the substrate may comprise any transparent and flexible film, such as PET, PI, cellulose, polyester, polyethylene, flexible glass, and/or other similar materials. At block 1310, micro-cracks are generated by various methods, such as mechanical bending, stretching, squeezing, pressing, thermal shock, quenching and adding nanoparticles in the brittle layer. After the micro-cracks have been formed, at block 1315, the width of the micro-cracks may be tuned by adjusting the annealing processing parameters, such as anneal temperature and time. The width of the micro-cracks may range from about 20 nm to about 5 μm. Then the micro-cracks pattern is transferred or copied to the sacrificial layer at block 1320. The pattern of the micro-cracks in the sacrificial layer is copied or transferred by partially dissolving and/or reactive ion etching the uncovered area of the sacrificial layer. Next, at block 1325, a conductive material is deposited onto the composite film. The bi-layer, comprising the sacrificial layer and the brittle layer, is used as a mask during the deposition of the conductive material. The conductive material may comprise metals, alloys, and/or doped semiconductor having a material selected from the group consisting of silver, copper, gold, iron, nickel, cobalt, platinum, palladium, titanium, aluminum, chromium, molybdenum, or a combination thereof. At block 1330, the bi-layer is lifted-off from the substrate resulting in a metal mesh structure atop the substrate. The metal mesh structure has a line width between about 200 nm to 1000 nm with a spacing between metal lines. Processing subsequently ends at 1399.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The benefits and advantages that may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment.

While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions, and improvements fall within the scope of the invention as detailed within the following claims.

Claims

1. A method for fabricating a micro-metal mesh, the method comprising:

depositing a mediate layer onto a substrate;

depositing a brittle layer onto the mediate layer;

generating a tensile stress in the substrate, the mediate layer, and/or the brittle layer in order to form micro-cracks in the brittle layer;

tuning widths of the micro-cracks;

depositing a conductive material onto the brittle layer and the area of the mediate layer exposed by the pattern of the micro-cracks; and

performing a lift-off of the brittle layer from the mediate layer, resulting in the micro-metal mesh atop the mediate layer.

2. The method of claim 1, wherein tuning the widths of the micro-cracks comprises etching the brittle layer or annealing the substrate, the mediate layer, and the brittle layer.

3. The method of claim 2, wherein the annealing comprises a temperature ranging from about 40° C. to about 180° C.

4. The method of claim 2, wherein the annealing comprises a time ranging from about 10 seconds to about 1 hour.

5. The method of claim 1, wherein the substrate comprises a transparent and flexible film having a material selected from the group consisting of polyethylene terephthalate, polyimide, cellulose, polyester, polyethylene, polyolefin, polycarbonate, glass, or a combination or lamination thereof.

6. The method of claim 1, wherein the brittle layer comprises spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA.

7. The method of claim 1, wherein the mediate layer comprises a material selected from the group consisting of PMMA, PS, PVC, rubber, silicone, PDMS, nylon, or a combination thereof.

8. The method of claim 1, wherein the conductive material comprises a metal, alloy, and/or doped semiconductor having a material selected from the group consisting of silver, copper, gold, iron, nickel, cobalt, platinum, palladium, titanium, aluminum, chromium, molybdenum, or a combination thereof.

9. The method of claim 1, wherein the micro-cracks comprise a width ranging from about 20 nm to about 5 μm.

10. The method of claim 1, wherein generating a tensile stress comprises mechanical bending, stretching, squeezing, pressing, thermal shock, quenching, and/or adding nanoparticles in the brittle layer.

11. The method of claim 10, wherein the nanoparticles comprise silver, copper, gold, iron, nickel, cobalt, platinum, palladium, titanium, aluminum, chromium, and/or molybdenum.

12. The method of claim 1, wherein the method is roll-to-roll compatible.

13. A method for fabricating a micro-metal mesh, the method comprising:

depositing a sacrificial layer onto a substrate;

depositing a brittle layer onto the sacrificial layer;

generating a tensile stress in the substrate, the sacrificial layer, and/or the brittle layer in order to form micro-cracks in the brittle layer;

tuning widths of the micro-cracks;

transferring pattern of the micro-cracks onto the sacrificial layer;

depositing a conductive material onto the brittle layer and the area of the substrate exposed by the pattern of the micro-cracks transferred onto the sacrificial layer; and

performing a lift-off of the sacrificial layer and the brittle layer from the substrate, resulting in the micro-metal mesh atop the substrate.

14. The method of claim 13, wherein tuning the widths of the micro-cracks comprises etching the brittle layer or annealing the substrate, the sacrificial layer, and the brittle layer.

15. The method of claim 14, wherein the annealing comprises a temperature ranging from about 40° C. to about 180° C.

16. The method of claim 14, wherein the annealing comprises a time ranging from about 10 seconds to about 1 hour.

17. The method of claim 13, wherein transferring the pattern of the micro-cracks onto the sacrificial layer comprises dissolving and/or reaction ion etching the sacrificial layer exposed by the pattern of the micro-cracks in the brittle layer.

18. The method of claim 13, wherein the substrate comprises a transparent and flexible film having a material selected from the group consisting of polyethylene terephthalate, polyimide, cellulose, polyester, polyethylene, polyolefin, polycarbonate, glass, or a combination or lamination thereof.

19. The method of claim 13, wherein the brittle layer comprises spin-on-glass, liquid glass, ceramic, salt, carbon, and/or PMMA.

20. The method of claim 13, wherein the sacrificial layer comprises a polymer selected from the group consisting of PMMA, PS, PVC, rubber, silicone, PDMS, nylon, and photo resist.

21. The method of claim 13, wherein the conductive material comprises a metal, alloy, and/or doped semiconductor having a material selected from the group consisting of silver, copper, gold, iron, nickel, cobalt, platinum, palladium, titanium, aluminum, chromium, molybdenum, or a combination thereof.

22. The method of claim 13, wherein the micro-cracks comprise a width ranging from about 20 nm to about 5 μm.

23. The method of claim 13, wherein generating a tensile stress comprises mechanical bending, stretching, squeezing, pressing, thermal shock, quenching, and/or adding nanoparticles in the brittle layer.

24. The method of claim 23, wherein the nanoparticles comprise silver, copper, gold, iron, nickel, cobalt, platinum, palladium, titanium, aluminum, chromium, and/or molybdenum.

25. The method of claim 13, wherein the method is roll-to-roll compatible.

26. An apparatus for forming micro-cracks in a brittle layer, the apparatus comprising:

a roller having a diameter;

the apparatus configured to: drive a composite film around the roller to generate a tensile stress in the composite film, wherein the composite film comprises the brittle layer atop a substrate; and form cracks in the brittle layer, wherein the cracks are parallel to the axis of the roller and have a period dependent on the diameter of the roller.

27. The apparatus of claim 26, wherein the composite film further comprises a mediate layer or a sacrificial layer between the brittle layer and the substrate.

28. The apparatus of claim 26, wherein the roller the diameter ranges from about 1.6 mm to about 30 mm.