Patent Publication Number: US-2015060251-A1

Title: Touch panel and method for making the same

Description:
This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Applications Application No. 201310389689.7, filed on Sep. 2, 2013, in the China Intellectual Property Office, disclosures of which are incorporated herein by references. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates touch panels and method for making the same, particularly to a carbon nanotube based capacitance-type touch panel and method for making the same. 
     2. Description of Related Art 
     In recent years, various electronic apparatuses such as mobile phones, car navigation systems have advanced toward high performance and diversification. There is continuous growth in the number of electronic apparatuses equipped with optically transparent touch panels in front of their display devices such as liquid crystal panels. A user of such electronic apparatus operates it by pressing a touch panel with a finger or a stylus while visually observing the display device through the touch panel. Thus a demand exists for such touch panels which superior in visibility and reliable in operation. Different types of touch panels, including a resistance-type, a capacitance-type, an infrared-type and a surface sound wave-type have been developed. 
     A conventional capacitance-type touch panel usually includes a first transparent conductive layer, an insulative substrate, and a second transparent conductive layer stacked with each other in that order. That is, the first transparent conductive layer and the second transparent conductive layer are located on opposite two surfaces of the insulative substrate. However, the insulative substrate is usually a glass plate or polymer plate with a relative high thickness, which cannot meet the requirement of lightweight and small thickness of electronic device development. Furthermore, in making process, it is difficult to form the first transparent conductive layer and the second transparent conductive layer on the same insulative substrate directly. Usually, the first transparent conductive layer and the second transparent conductive layer are formed on two different insulative substrates, and then the two different insulative substrates are bound together by an optically clear adhesive (OCA), however, the thickness of the touch panel is further increased. 
     What is needed, therefore, is to provide a touch panel and method for making the same which can overcome the short come described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic view of one embodiment of a touch panel. 
         FIG. 2  is a schematic, cross-sectional view, along a line II-II of  FIG. 1 . 
         FIG. 3  is a Scanning Electron Microscope (SEM) image of a carbon nanotube film. 
         FIG. 4  is a flow chart of one embodiment of a method for making a touch panel. 
         FIG. 5  is a schematic view of the other one embodiment of a touch panel. 
         FIG. 6  is a schematic, cross-sectional view, along a line VI-VI of  FIG. 5 . 
         FIG. 7  is a flow chart of the other one embodiment of a method for making a touch panel. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     References will now be made to the drawings to describe, in detail, various embodiments of the carbon nanotube based capacitance-type touch panel and method for making the same. 
     Referring to  FIGS. 1 and 2 , a capacitance-type multi touch panel  10  of one embodiment includes an insulative substrate  11 , a first adhesive layer  12  located on a surface of the insulative substrate  11 , a first transparent conductive layer  13  located on a surface of the first adhesive layer  12 , a second adhesive layer  14  located on a surface of the first transparent conductive layer  13 , a second transparent conductive layer  15  located on a surface of the second adhesive layer  14 , a plurality of first electrodes  16 , a first conductive trace  17 , a plurality of second electrode  18 , and a second conductive trace  19 . 
     The insulative substrate  11 , the first adhesive layer  12 , the first transparent conductive layer  13 , the second adhesive layer  14 , and the second transparent conductive layer  15  are stacked with each other in that order. That is, all the first adhesive layer  12 , the first transparent conductive layer  13 , the second adhesive layer  14 , and the second transparent conductive layer  15  are located on the same side of the insulative substrate  11 . Adjacent two of the insulative substrate  11 , the first adhesive layer  12 , the first transparent conductive layer  13 , the second adhesive layer  14 , and the second transparent conductive layer  15  are in contact with each other directly. That is, there is no other layer being located between the adjacent two of the insulative substrate  11 , the first adhesive layer  12 , the first transparent conductive layer  13 , the second adhesive layer  14 , and the second transparent conductive layer  15 . Thus, the touch panel  10  has a decreased thickness. The plurality of first electrodes  16  are located on at least one side of the first transparent conductive layer  13  and electrically connected with the first transparent conductive layer  13 . The plurality of first electrodes  16  are also electrically connected with a sensing circuit (not shown) via the first conductive trace  17 . The plurality of second electrodes  18  are located on at least one side of the second transparent conductive layer  15  and electrically connected with the second transparent conductive layer  15 . The plurality of second electrodes  18  are also electrically connected with a driving circuit (not shown) via the second conductive trace  19 . The sensing circuit and the driving circuit can be two printed circuit board (PCB) or integrated in the same PCB. 
     The insulative substrate  11  can be flat or curved and configured to support other elements. The insulative substrate  11  can be transparent or opaque. The size and shape of the insulative substrate  11  can be selected according to need. In one embodiment, the thickness of the insulative substrate  11  is in a range from about 100 micrometers to about 500 micrometers. The insulative substrate  11  can be made of rigid materials such as glass, quartz, diamond, plastic or any other suitable material. The insulative substrate  11  can also be made of flexible materials such as polycarbonate (PC), polymethyl methacrylate acrylic (PMMA), polyimide (PI), polyethylene terephthalate (PET), polyethylene (PE), polyether polysulfones (PES), polyvinyl polychloride (PVC), benzocyclobutenes (BCB), polyesters, or acrylic resin. In one embodiment, the insulative substrate  11  is a flat PET plate with a thickness of 150 micrometers. 
     Both the first transparent conductive layer  13  and the second transparent conductive layer  15  are conductive film with resistance anisotropy. The first transparent conductive layer  13  defines a plurality of first conductive channels on a first surface of the first adhesive layer  12 , and the second transparent conductive layer  15  defines a plurality of second conductive channels on a second surface of the first adhesive layer  12  opposite to the first surface. The plurality of first conductive channels intercrosses the plurality of second conductive channels. The first transparent conductive layer  13  and the second transparent conductive layer  15  can be a patterned transparent conductive oxide (TCO) layer or a carbon nanotube film. In one embodiment, both the first transparent conductive layer  13  and the second transparent conductive layer  15  are continuous carbon nanotube film. 
     Referring to  FIG. 3 , the carbon nanotube film is a substantially pure structure consisting of a plurality of carbon nanotubes, with few impurities and chemical functional groups. The carbon nanotube film is a free-standing structure. The term “free-standing structure” includes, but is not limited to, the property that the carbon nanotube film can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. Thus, the carbon nanotube film can be suspended by two spaced supports. The majority of carbon nanotubes of the carbon nanotube film are joined end-to-end by van der Waals force therebetween so that the carbon nanotube film is a free-standing structure. The carbon nanotubes of the carbon nanotube film can be single-walled, double-walled, or multi-walled carbon nanotubes. The diameter of the single-walled carbon nanotubes can be in about 0.5 nm to about 50 nm. The diameter of the double-walled carbon nanotubes can be in about 1.0 nm to about 50 nm. The diameter of the multi-walled carbon nanotubes can be in about 1.5 nm to about 50 nm. 
     The carbon nanotubes of the carbon nanotube film are oriented along a preferred orientation. That is, the majority of carbon nanotubes of the carbon nanotube film are arranged to substantially extend along the same direction and in parallel with the surface of the carbon nanotube film. Each adjacent two of the majority of carbon nanotubes of the carbon nanotube film are joined end-to-end by van der Waals force therebetween along the extending direction. A minority of dispersed carbon nanotubes of the carbon nanotube film may be located and arranged randomly. However, the minority of dispersed carbon nanotubes have little effect on the properties of the carbon nanotube film and the arrangement of the majority of carbon nanotubes of the carbon nanotube film. The majority of carbon nanotubes of the carbon nanotube film are not absolutely form a direct line and extend along the axial direction, some of them may be curved and in contact with each other in microcosm. Some variations can occur in the carbon nanotube film. Because the electric conductivity of the carbon nanotubes along the axial direction is much better than the electric conductivity along the radial direction, and the majority of the carbon nanotubes of the carbon nanotube film are substantially arranged to extend along the same direction, the carbon nanotube film is conductivity anisotropy. 
     The carbon nanotube film can be made by the steps of: growing a carbon nanotube array on a wafer by chemical vapor deposition (CVD) method; and drawing the carbon nanotubes of the carbon nanotube array to from the carbon nanotube film. During the drawing step, the carbon nanotubes are joined end-to-end by van der Waals attractive force therebetween along the drawing direction. The carbon nanotube film has the smallest resistance along the drawing direction and the greatest resistance along a direction perpendicular to the drawing direction. Thus, the carbon nanotube film is resistance anisotropy. Furthermore, the carbon nanotube film can be etched or irradiated by laser. After being irradiated by laser, a plurality of parallel carbon nanotube conductive strings will be formed and the resistance anisotropy of the carbon nanotube film will not be damaged because the carbon nanotube substantially extending not along the drawing direction are removed by burning. Each carbon nanotube conductive string comprises a plurality of carbon nanotubes joined end-to-end by van der Waals attractive force. 
     In one embodiment, the carbon nanotube film includes a plurality of successively oriented carbon nanotube segments joined end-to-end by van der Waals attractive force therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes parallel to each other, and combined by van der Waals attractive force therebetween. The carbon nanotubes in the carbon nanotube film are oriented along a preferred orientation. The carbon nanotubes of the first transparent conductive layer  13  substantially extend along an X direction and form the plurality of first conductive channels along the X direction, and the carbon nanotubes of the second transparent conductive layer  15  substantially extend along a Y direction and form the plurality of second conductive channels along the Y direction. The X direction and the Y direction are perpendicular with each other. The first transparent conductive layer  13 , the first adhesive layer  12 , the second transparent conductive layer  15  and the second adhesive layer  14  are rectangular. The length and width of the first transparent conductive layer  13  are smaller than length and width of the first adhesive layer  12 . The length and width of the second transparent conductive layer  15  are smaller than length and width of the second adhesive layer  14 . The first transparent conductive layer  13  and the second transparent conductive layer  15  have the same shape and size. The first adhesive layer  12  and the second adhesive layer  14  have the same shape and size. 
     Both the first adhesive layer  12  and the second adhesive layer  14  are a layer of solidified electrically insulating glue. The first adhesive layer  12  is used to fix the first transparent conductive layer  13  on the insulative substrate  11 . The second adhesive layer  14  is used to bind the first transparent conductive layer  13  and the second transparent conductive layer  15  with each other, and electrically insulate the first transparent conductive layer  13  and the second transparent conductive layer  15  from each other. Because the first transparent conductive layer  13  and the second transparent conductive layer  15  are electrically insulated from each other only by the second adhesive layer  14 , the second adhesive layer  14  should have a certain thickness. The thickness of the first adhesive layer  12  can be in a range from about 10 nanometers to about 10 micrometers, for example, from about 1 micrometer to about 2 micrometers. The thickness of the second adhesive layer  14  can be in a range from about 5 micrometers to about 50 micrometers, for example, from about 10 micrometers to about 20 micrometers. The first adhesive layer  12  and the second adhesive layer  14  can be transparent or opaque. The first adhesive layer  12  and the second adhesive layer  14  can be made of materials such as thermal plastic glue, thermosetting glue or UV (Ultraviolet Ray) glue, for example PVC or PMMA. In one embodiment, the first adhesive layer  12  is an UV glue layer with a thickness of 1.5 micrometers and the second adhesive layer  14  is an UV glue layer with a thickness of 15 micrometers. The second adhesive layer  14  covers all the first transparent conductive layer  13 , the plurality of first electrodes  16  and the first conductive trace  17 . 
     The solidified electrically insulating glue is different from the widely used insulative layer, such as a previously prepared glass plate, or previously prepared polymer sheet. Usually, the carbon nanotube film is attached on the previously prepared glass plate or polymer sheet, and the glass plate or polymer sheet with the carbon nanotube film thereon is bound with the insulative substrate  11  by OCA. However, it is easy to result a stress difference between the two different insulative substrates during bounding process, which will cause the insulative substrates to be twisted or curled. Furthermore, the previously prepared glass plate or polymer sheet usually has a thickness greater than 100 micrometers, which cause the thickness of the touch panel is increased. If the previously prepared glass plate or polymer sheet has a too small thickness, the difficulty of bounding will be increased greatly. The touch panel  10  only has the second adhesive layer  14  located between the first transparent conductive layer  13  and the second transparent conductive layer  15 , which allows the making process to be simplified, and the second adhesive layer  14  have smaller thickness. 
     The plurality of first electrodes  16  are located at one side of the first transparent conductive layer  13  and on a surface of the first adhesive layer  12 . The plurality of first electrodes  16  are located along the Y direction and spaced from each other. The plurality of second electrodes  18  are located at one side of the second transparent conductive layer  15  and on a surface of the second adhesive layer  14 . The plurality of second electrodes  18  are located along the X direction and spaced from each other. When the area of the first adhesive layer  12  and the second adhesive layer  14  is less than the area of the insulative substrate  11 , the plurality of first electrodes  16  and the plurality of second electrodes  18  can be located on a surface of the insulative substrate  11  directly. The plurality of first electrodes  16 , the first conductive trace  17 , the plurality of second electrodes  18  and the second conductive trace  19  can be made of material such as metal, carbon nanotube, conductive silver paste, or TCO, and can be made by etching a metal film, etching an TCO film, or printing a conductive silver paste. In one embodiment, the plurality of first electrodes  16  and the plurality of second electrodes  18  are bar-shaped. The conductive silver paste can include about 50% to about 90% (by weight) of the metal powder, about 2% to about 10% (by weight) of the glass powder, and about 8% to about 40% (by weight) of the binder. 
     Referring to  FIG. 4 , a method of one embodiment for making the touch panel  10  comprises following steps: 
     step (S 10 ), forming a first adhesive layer  12  on a surface of an insulative substrate  11 ; 
     step (S 11 ), forming a first transparent conductive layer  13  on a surface of the first adhesive layer  12 ; 
     step (S 12 ), forming a plurality of first electrodes  16  and a first conductive trace  17  corresponding to the first transparent conductive layer  13 ; 
     step (S 13 ), forming a second adhesive layer  14  on a surface of the first transparent conductive layer  13  to cover the first transparent conductive layer  13 ; 
     step (S 14 ), forming a second transparent conductive layer  15  on a surface of the second adhesive layer  14 ; and 
     step (S 15 ), forming a plurality of second electrode  18  and a second conductive trace  19  corresponding to the second transparent conductive layer  15 . 
     In step (S 10 ), the first adhesive layer  12  can be formed by spin-coating, spraying, or brushing. The shape and size of the first adhesive layer  12  can be the same or different from the shape and size of the insulative substrate  11 . In one embodiment, the insulative substrate  11  is a flat and flexible PET plate with a thickness of 150 micrometers, and a UV glue layer with a thickness of 1.5 micrometers is formed on entire surface of the insulative substrate  11  by spin-coating. 
     In step (S 11 ), the first transparent conductive layer  13  is the free-standing carbon nanotube film of  FIG. 3 . The free-standing carbon nanotube film is drawn from a carbon nanotube array and then placed on the first adhesive layer  12  directly to cover part or entire surface of the first adhesive layer  12 . The carbon nanotube film can be infiltrated into the first adhesive layer  12  after being placed on the first adhesive layer  12 . In one embodiment, part of the carbon nanotube film is infiltrated into the first adhesive layer  12 , and part of the carbon nanotube film is exposed through of the first adhesive layer  12 . Furthermore, a step of pressing the carbon nanotube film can be performed after step (S 11 ) to allow more carbon nanotubes of the carbon nanotube film to infiltrate into the first adhesive layer  12 . In one embodiment, a single carbon nanotube film is placed on part surface of the first adhesive layer  12  with the carbon nanotubes substantially extending along the X direction. Each carbon nanotube of the carbon nanotube film has a first portion infiltrated into the first adhesive layer  12  and a second portion exposed through of the first adhesive layer  12 . 
     Furthermore, the first adhesive layer  12  is solidified to fix the carbon nanotube film. The method for solidifying the first adhesive layer  12  depends on the material of the first adhesive layer  12 . The thermoplastic first adhesive layer  12  can be solidified by cooling, the thermosetting first adhesive layer  12  can be solidified by heating, and the UV glue first adhesive layer  12  can be solidified by irradiating with ultraviolet light. Because part of the carbon nanotube film is infiltrated into the first adhesive layer  12 , the carbon nanotube film is fixed by the first adhesive layer  12  during solidifying the first adhesive layer  12 . In one embodiment, the first adhesive layer  12  is UV glue layer and solidified by ultraviolet light irradiating for about 2 seconds to about 30 seconds, for example, irradiating for about 4 seconds. 
     In step (S 12 ), the plurality of first electrodes  16  and the first conductive trace  17  can be made by a method such as screen printing, chemical vapor deposition, or magnetron sputtering. The plurality of first electrodes  16  can be entirely formed on the surface of the first adhesive layer  12 , entirely formed on the surface of the first transparent conductive layer  13 , or have a part formed on the surface of the first adhesive layer  12  and the other part formed on the surface of the first transparent conductive layer  13 . The first conductive trace  17  is formed only on the surface of the first adhesive layer  12 . 
     In one embodiment, the plurality of first electrodes  16  and the first conductive trace  17  are made of conductive silver paste and made by printing conductive silver paste concurrently. That is, the plurality of first electrodes  16  and the first conductive trace  17  are made by the same screen printing process once time. At least part of each first electrode  16  is formed on the surface of the first transparent conductive layer  13  so the first electrode  16  can permeate into the carbon nanotube film before backing and form a composite after backing. Because the carbon nanotube film has a plurality of gaps between the carbon nanotubes, the materials of the first electrode  16  can permeate into the carbon nanotube film easily. The plurality of first electrodes  16  are located at one side of the first transparent conductive layer  13  and on a surface of the first adhesive layer  12 . The plurality of first electrodes  16  are located along the Y direction and spaced from each other. The plurality of first electrodes  16  are electrically connected to the first transparent conductive layer  13 . The first conductive trace  17  is electrically connected to the plurality of first electrodes  16 . 
     In step (S 13 ), the method for making the second adhesive layer  14  is the same as the method for making the first adhesive layer  12 . In one embodiment, the shape and size of the second adhesive layer  14  is the same as the shape and size of the first adhesive layer  12 . The second adhesive layer  14  is an UV glue layer with a thickness of 15 micrometers and cover all the first transparent conductive layer  13 , the plurality of first electrodes  16  and the first conductive trace  17 . 
     In step (S 14 ), the method for making the second transparent conductive layer  15  and solidifying the second adhesive layer  14  is the same as the method for making the first transparent conductive layer  13  and solidifying the first adhesive layer  12 . In one embodiment, a single carbon nanotube film is placed on part surface of the second adhesive layer  14  with the carbon nanotubes substantially extending along the Y direction. 
     In step (S 15 ), the method for making the plurality of second electrodes  18  and the second conductive trace  19  is the same as the method for making the plurality of first electrodes  16  and the first conductive trace  17 . In one embodiment, both the plurality of second electrodes  18  and the second conductive trace  19  are made of conductive silver paste and made by printing conductive silver paste concurrently. The plurality of second electrodes  18  are located at one side of the second transparent conductive layer  15  and on a surface of the second adhesive layer  14 . The plurality of second electrodes  18  are located along the X direction and spaced from each other. The plurality of second electrodes  18  are electrically connected to the second transparent conductive layer  15 , and the second conductive trace  19  is electrically connected to the plurality of second electrodes  18 . 
     Because the first adhesive layer  12 , the first transparent conductive layer  13 , the second adhesive layer  14 , and the second transparent conductive layer  15  are stacked on the same side of the insulative substrate  11  with each other in that order, the method of making the touch panel  10  can only need the process of coating adhesive layer, laying carbon nanotube film, and printing conductive silver paste. Thus, there is no need to bound two different insulative substrates by an OCA, and the method of making the touch panel  10  is simple and cost less. 
     Referring to  FIGS. 5 and 6 , a capacitance-type multi touch panel  20  of one embodiment includes an insulative substrate  21 , a first transparent conductive layer  23  located on a surface of the insulative substrate  21 , a second adhesive layer  24  located on a surface of the first transparent conductive layer  23 , a second transparent conductive layer  25  located on a surface of the second adhesive layer  24 , a plurality of first electrodes  26 , a first conductive trace  27 , a plurality of second electrode  28 , and a second conductive trace  29 . 
     The insulative substrate  21 , the first transparent conductive layer  23 , the second adhesive layer  24 , and the second transparent conductive layer  25  are stacked with each other in that order. That is, all the first transparent conductive layer  23 , the second adhesive layer  24 , and the second transparent conductive layer  25  are located on the same side of the insulative substrate  21 . The touch panel  20  is similar as the touch panel  10  except that the first transparent conductive layer  23  is a patterned TCO layer located on a surface of the insulative substrate  21  directly. That is, the touch panel  20  does not have any adhesive layer between the first transparent conductive layer  23  and the insulative substrate  21 . 
     The first transparent conductive layer  23  includes a plurality of strap-shaped TCO layers spaced from and in parallel with each other. The plurality of strap-shaped TCO layers extend along the X direction. The pattern of the first transparent conductive layer  23  is not limited, as long as it can form a conductive film with resistance anisotropy. The thickness, width, and gaps of the plurality of strap-shaped TCO layers can be selected according to need. The material of the TCO layer can be indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO) or tin oxide (TO). In one embodiment, the first transparent conductive layer  23  includes a plurality of strap-shaped ITO layers with each electrically connected to one of the plurality of first electrodes  26 . 
     The second adhesive layer  24  is located on the insulative substrate  21  and covers the entire patterned TCO layer. Part of the second adhesive layer  24  permeates the gaps between the adjacent strap-shaped TCO layers. 
     Because the first transparent conductive layer  23  is a patterned TCO layer, the touch panel  20  can omit the first electrodes  26 . That is the first conductive trace  27  can be in contact with and electrically connected to the patterned TCO layer directly. 
     Referring to  FIG. 7 , a method of one embodiment for making the touch panel  20  comprises following steps: 
     step (S 20 ), forming a patterned TCO layer on a surface of an insulative substrate  21  as a first transparent conductive layer  23 ; 
     step (S 21 ), forming a plurality of first electrodes  26  and a first conductive trace  27  corresponding to the first transparent conductive layer  23 ; 
     step (S 22 ), forming a second adhesive layer  24  on a surface of the first transparent conductive layer  23  to cover the first transparent conductive layer  23 ; 
     step (S 23 ), forming a second transparent conductive layer  25  on a surface of the second adhesive layer  24 ; and 
     step (S 24 ), forming a plurality of second electrode  28  and a second conductive trace  29  corresponding to the second transparent conductive layer  25 . 
     In step (S 20 ), the insulative substrate  21  is a glass plate with a thickness in a range from about 100 micrometers to about 300 micrometers. In one embodiment, the forming the patterned TCO layer on the surface of the insulative substrate  21  includes following steps: 
     step (S 201 ), providing an ITO glass including a glass plate and an ITO layer on a surface of the glass plate; and 
     step (S 202 ), patterning the ITO layer by laser etching. 
     In step (S 21 ), the plurality of first electrodes  26  and the first conductive trace  27  can be made by a method such as screen printing, chemical vapor deposition, or magnetron sputtering. The plurality of first electrodes  26  can be entirely formed on the surface of the first transparent conductive layer  23 , entirely formed on the surface of the insulative substrate  21 , or have a part formed on the surface of the insulative substrate  21  and the other part formed on the surface of the first transparent conductive layer  23 . The first conductive trace  27  is formed only on the surface of the insulative substrate  21 . In one embodiment, the plurality of first electrodes  26  and the first conductive trace  27  are made of conductive silver paste and made by printing conductive silver paste concurrently. The plurality of first electrodes  26  are located along the Y direction and spaced from each other. The plurality of first electrodes  26  are electrically connected to the first transparent conductive layer  23 . The first conductive trace  27  is electrically connected to the plurality of first electrodes  26 . 
     Because the first transparent conductive layer  23  is a patterned TCO layer, the touch panel  20  can omit the first electrodes  26 , and the first conductive trace  27  can be in contact with and electrically connected to the patterned TCO layer directly. That is, the plurality of first electrodes  26  and the first conductive trace  27  can be made during the process of laser etching the ITO layer in step (S 20 ). 
     In step (S 22 ), the second adhesive layer  24  can be formed by spin-coating, spraying, or brushing. The second adhesive layer  24  covers at least the first transparent conductive layer  23 . In one embodiment, the shape and size of the second adhesive layer  24  is the same as the shape and size of the insulative substrate  21 . The second adhesive layer  24  is a UV glue layer with a thickness of 40 micrometers and covers all the first transparent conductive layer  23 , the plurality of first electrodes  26 , and the first conductive trace  27 . 
     In step (S 23 ), the second transparent conductive layer  25  is the free-standing carbon nanotube film of  FIG. 3 . The free-standing carbon nanotube film is drawn from a carbon nanotube array and then placed on the second adhesive layer  24  directly to cover part or entire surface of the second adhesive layer  24 . The carbon nanotube film can be infiltrated into the second adhesive layer  24  after being placed on the second adhesive layer  24 . In one embodiment, part of the carbon nanotube film is infiltrated into the second adhesive layer  24 , and part of the carbon nanotube film is exposed through of the second adhesive layer  24 . Furthermore, a step of pressing the carbon nanotube film can be performed after step (S 23 ) to allow more carbon nanotubes of the carbon nanotube film to infiltrate into the second adhesive layer  24 . In one embodiment, a single carbon nanotube film is placed on part surface of the second adhesive layer  24  with the carbon nanotubes substantially extending along the Y direction. Each carbon nanotube of the carbon nanotube film has a first portion infiltrated into the second adhesive layer  24  and a second portion exposed through of the second adhesive layer  24 . 
     In step (S 24 ), the method for making the plurality of second electrode  28  and the second conductive trace  29  is the same as the method for making the plurality of first electrodes  26  and the first conductive trace  27 . In one embodiment, both the plurality of second electrodes  28  and the second conductive trace  29  are made of conductive silver paste and made by printing conductive silver paste concurrently. The plurality of second electrodes  28  are located at one side of the second transparent conductive layer  25  and on a surface of the second adhesive layer  24 . The plurality of second electrodes  28  are located along the X direction and spaced from each other. The plurality of second electrodes  28  are electrically connected to the second transparent conductive layer  25 , and the second conductive trace  29  is electrically connected to the plurality of second electrodes  28 . 
     Because only the adhesive layer is located between the first transparent conductive layer and the second transparent conductive layer, the touch panel has small thickness, which can meet the requirement of lightweight and small thickness of electronic device development. The touch panel with such structure is easy to fabricate. Furthermore, there is no need to bound two different insulative substrates by an OCA, and the method of making the touch panel is simple and low cost. 
     It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Any elements described in accordance with any embodiments is understood that they can be used in addition or substituted in other embodiments. Embodiments can also be used together. Variations may be made to the embodiments without departing from the spirit of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure. 
     Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.