Abstract:
An anti-reflection structure includes a substrate including a planar portion, a protrusion portion disposed over the planar portion, and a coating layer, wherein the protrusion portion is integrated with the planar portion, and the coating layer conformably covers the planar portion and the protrusion portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 103126733, filed on Aug. 5, 2014, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an optical structure, and in particular to an anti-reflection structure suitable in multiple electronic devices such as displays and solar cells for providing, for example, anti-reflection and anti-smudge functions. 
     Description of the Related Art 
     When an electronic device, for example a mobile phone, is used in a bright environment, a reflection of the ambient light of the bright environment on the electronic device may be trigger a trouble like that making the content of the electronic device is difficult to read. In addition, reflection of the ambient light can occur at surfaces of electronic devices such as a display surface of a television, a display surface of a monitor or a solar cell, thereby making it hard for the user to read or degrading the electrical performance of the electronic device. 
     Accordingly, an anti-reflection coating technique is used in the art to improve the above reflection issues caused by ambient light. Usually one or two thin coating layers are formed on the surface of a transparent substrate in a vacuum chamber to reduce the interference of the reflection of the ambient light. However, since the anti-reflection coating is usually formed on a surface exposed to the environment, such that anti-reflection coating layer is easily affected by dirt and the operations of the users, and therefore defacement and damage can happen to the anti-reflection coating layer, thereby affecting the lifespan of the electronic device. It is desirable to provide an anti-reflection structure with improved mechanical strength and smudge-proof ability of the anti-reflection coating. 
     BRIEF SUMMARY OF THE INVENTION 
     An exemplary anti-reflection structure comprises a substrate comprising a planar portion and a protrusion portion disposed over the planar portion, and a coating layer disposed over the substrate. In one embodiment, the protrusion portion is integrated with the planar portion, and the coating layer covers the protrusion portion and the planar portion. 
     An exemplary electronic device comprises a first substrate, a second substrate disposed over the first substrate, and a liquid-crystal layer, a touch-sensing layer, or a photovoltaic element disposed between the first substrate and the second substrate. In one embodiment, the second substrate comprises the above anti-reflection structure. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIGS. 1-4  are schematic cross-sectional views showing a method for forming an anti-reflection structure according to an embodiment of the invention; 
         FIG. 5  is a schematic cross-sectional view showing an anti-reflection structure according to another embodiment of the invention; 
         FIG. 6  is a schematic cross-sectional view showing an anti-reflection structure according to yet another embodiment of the invention; 
         FIG. 7  is a schematic cross-sectional view showing an electronic device according to an embodiment of the invention, comprising the anti-reflection structure shown in  FIG. 4 ; 
         FIG. 8  is a schematic cross-sectional view showing an electronic device according to another embodiment of the invention, comprising the anti-reflection structure shown in  FIG. 4 ; 
         FIG. 9  is a schematic cross-sectional view showing an electronic device according to yet another embodiment of the invention, comprising the anti-reflection structure shown in  FIG. 4 ; and 
         FIG. 10  is a schematic cross-sectional view showing an electronic device according to another embodiment of the invention, comprising the anti-reflection structure shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the embodiment of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIGS. 1-4  are schematic cross-sectional views showing a method for forming an anti-reflection structure according to an embodiment of the invention. 
     As shown in  FIG. 1 , a substrate  100  is provided first. The substrate  100  may comprise transparent material such as glass, polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), or polyimide (PI). Next, a plurality of spheres  102  having the similar diameter D1 are disposed on a surface of the substrate  100  by methods such as Langmuir-Blodgett coating (LB coating), Langmuir-Schaefer coating (LS coating), dip coating, or self-assembly monolayers (SAMs), but they are not limited thereto. As shown in  FIG. 1 , the diameter D1 of the spheres  102  can be about 200-400 nm, and the spheres  102  may have a tolerance of plus or minus 25% on the diameter D1. The spheres  102  may comprise materials such as polystyrene (PS), polyethylene (PE), polyvinylchloride (PVC) or SiO 2 . The spheres  102  disposed on the substrate  100  are close to each other, such that the spheres  102  physically contact with each. 
     In  FIG. 2 , an etching process  104  is performed next on the structure shown in  FIG. 1 . The etching process  104  can be, for example, a dry etching such as a plasma etching, and the etchants (not shown) used in the etching process  104  can be adjusted according to the material of the spheres  102 . In one embodiment, the etching process  104  may use etchants comprising trifluoromethane (CHF 3 ) or tetrafluoromethane (CF 4 ) when the spheres  102  comprising polyvinylchloride (PVC). During the etching process  104 , the etchants not only penetrate space between the spheres  102  to isotropically remove portions of the substrate  100  under the spheres  102 , but also simultaneously isotropically removes portions of the spheres  102 . 
     As shown in  FIG. 3 , after the etching process  104  shown in  FIG. 2  is performed, another etching process (not shown), for example a wet etching process, is then performed to remove the portions of the spheres  102  remaining on the substrate  100  and clean the substrate  100 . In one embodiment, etchants (not shown) such as sulfuric acid and hydrogen peroxide can be used to remove the portions of the sphere  102  remaining over the substrate  100  and clean the substrate  100  as the spheres  102  comprise polyvinylchloride (PVC). 
     As shown in  FIG. 3 , the substrate  100  being processed by the above etching processes now forms a substrate  100 ′, having a protrusion portion  100   b  and a planar portion  100   a  underlying the protrusion portion  100   b . The protrusion portion  100   b  comprises a plurality of first protrusions  101   a , and the protrusion portion  100   b  and the planar portion  100   a  underlying the protrusion portion  100   b  are formed of the same transparent materials and are integrated with each other. The first protrusion portions  101   a  may have a cross-section of a semicircular or semicircular-like configuration similar to portions of the surface of the spheres  102 . The first protrusion portions  101   a  may have a width (also entitled as D1) of about 195-400 nm similar with the diameter D1 of the spheres  102  and a height H1 of about 50-250 nm. It should be noted that the first protrusions  101   a  are closely proximate to each other, such that the first protrusions  101   a  physically contact with each other. 
     In  FIG. 4 , a coating layer  106  is next formed over the structure shown in  FIG. 3 . The coating layer  106  can be, for example, an anti-smudge layer. In one embodiment, the coating layer  106  may comprise materials such as per-fluorinated polyethers (PFPE), alkylflouride, or alkylhalide, and can be conformably formed over the exposed surface of the protrusion portion  100   b  and the planar portion  100   a  of the substrate  100 ′ shown in  FIG. 3  by methods such as dip coating, spray coating or evaporation. In addition, the coating layer  106  may have a thickness of about 1-100 nm. 
     Herein, as shown in  FIG. 4 , an exemplary anti-reflection structure is substantially fabricated.  FIG. 4  illustrates an exemplary anti-reflection structure, in which the adjacent first protrusions  101   a  formed over the substrate  100 ′ made of transparent material form an anti-reflection structure similar to a moth-eye structure, such that the anti-reflection structure is able to reduce reflection in the visible light wavelength band and has a reflectivity no greater than 0.65% in the visible light wavelength band (400-800 nm). 
     In addition, in the anti-reflection structure shown in  FIG. 4 , due to formation of the coating layer  106 , the surface of the coating layer  106  may have a contact angle greater than 110° and 55° to liquids such as water and n-hexadecane, respectively, thereby having anti-smudge and self-cleaning properties. 
     Moreover, since the protrusion portion  100   b  and the planar portion  100   a  of the substrate  100 ′ of the anti-reflection structure shown in  FIG. 4  are integrated with each other and are made of the same material, such that the protrusion portion  100   b  and the planar portion  100   a  are well connected and show a mechanical property greater than the conventional anti-reflection structure made of a transparent substrate and an anti-reflection coating of different materials formed thereon. Accordingly, the anti-reflection structure shown in  FIG. 4  also has good wear-resistance properties. 
       FIG. 5  is a schematic cross-sectional view showing an anti-reflection structure according to another embodiment of the invention. The anti-reflection structure shown in  FIG. 5  is modified from the anti-reflection structure shown in  FIG. 4 . For the purpose of simplicity, only differences between the anti-reflection structures shown in  FIGS. 4-5  are discussed bellow. 
     As shown in  FIG. 5 , the protrusion portion  100   b  is disposed over the planar portion  100   a  of the substrate  100 ′ of the anti-reflection structure, and comprises a plurality of first protrusions  101   a  and a plurality of second protrusions  101   b . The second protrusions  101   b  have a height H2 and a width D2 greater than that of the first protrusions  101   a . Fabrication of the second protrusions  101   b  can be formed by using the plurality of spheres  102  having two kinds of spheres of different sizes, and the spheres  102  may comprise a plurality of first spheres (not shown) having a diameter D1 of about 195-400 nm, and a plurality of second spheres (not shown) having a diameter D2 of about 280-400 nm, and the fabrications shown in  FIGS. 2-4  are performed to form the anti-reflection structure shown in  FIG. 5 . The first protrusions  101   a  may have a cross-section of semicircular or semicircular-like configuration substantially similar with the first spheres (not shown), and have a width (also shown as D1) of about 195-400 nm and a height H1 of about 50-250 nm. The second protrusions  101   b  may have a cross-section of a semicircular or semicircular-like configuration substantially similar with the second spheres (not shown) and have a width (shown as D2) of about 280-400 nm and a height H2 of about 50-250 nm. 
     It should be noted that the first protrusions  101   a  and the second protrusions  101   b  are closely proximate to each other, such that the first protrusions  101   a  and the second protrusions  101   b  physically contact with each other. 
     In one embodiment, the amount of first spheres (not shown) used for forming the anti-reflection structure shown in  FIG. 5  is about 0.1-99% of the total amount of the spheres  102 , and the amount of second spheres (not shown) used for forming the anti-reflection structure shown in  FIG. 5  is about 0.1-99% of the total amount of spheres  102 , such that the first protrusions  101   a  in the anti-reflection structure occupy about 0.1-99.9% of the total surface of a total area, and the second protrusions  101   b  of the anti-reflection structure occupy about 0.1-99.9% of the total surface of the total area. 
       FIG. 6  is a schematic cross-sectional view showing an anti-reflection structure according to yet another embodiment of the invention. The anti-reflection structure shown in  FIG. 6  is modified from the anti-reflection structure shown in  FIG. 4 . For the purpose of simplicity, only differences between the anti-reflection structures shown in  FIGS. 4 and 6  are discussed bellow. 
     As shown in  FIG. 6 , the protrusion portion  100   b  is disposed over the planar portion  100   a  of the substrate  100 ′ of the anti-reflection structure, and comprises a plurality of first protrusions  101   a , a plurality of second protrusions  101   b , and a plurality of third protrusions  101   c . The third protrusions  101   c  have a height H3 and a width D3 greater than that of the first protrusions  101   a  and the second protrusion  101   b , and the second protrusions  101   b  have a height H2 and a width D2 greater than that of the first protrusions  101   a.    
     Fabrication of the first protrusions  101   a , the second protrusions  101   b , and the protrusions  101   c  can be formed by using the plurality of spheres  102  having three kinds of spheres of different sizes, and the spheres  102  may comprise a plurality of first spheres (not shown) having a diameter D1 of about 195-245 nm, a plurality of second spheres (not shown) having a diameter D2 of about 280-330 nm, and a plurality of third spheres (not shown) having a diameter D3 of about 350-400 nm, and the fabrications shown in  FIGS. 2-4  are performed next to form the anti-reflection structure shown in  FIG. 6 . 
     The first protrusions  101   a  may have a semi-sphere or semi-sphere like cross-sectional configuration substantially similar with the first spheres (not shown), and have a width (also shown as D1) of about 195-245 nm and a height H1 of about 50-250 nm. The second protrusions  101   b  may have a cross-section of a semicircular or semicircular-like configuration substantially similar with the second spheres (not shown) and have a width (shown as D2) of about 280-330 nm and a height H2 of about 50-250 nm. The third protrusions  101   c  may have a cross-section of a semicircular or semicircular-like configuration substantially similar with the third spheres (not shown) and have a width (shown as D3) of about 350-400 nm and a height H3 of about 50-250 nm. It is noted that the first protrusions  101   a , the second protrusions  101   b , and the third protrusions  101   c  are closely proximate to each other, such that the first protrusions  101   a , the second protrusions  101   b , and the third protrusions  101   c  physically contact with each other. 
     In one embodiment, an amount the first spheres (not shown) used for forming the anti-reflection structure shown in  FIG. 6  is about 60-98% of the total amount of the spheres  102 , the second spheres (not shown) used for forming the anti-reflection structure shown in  FIG. 6  is about 1-20% of the total amount of the spheres  102 , and the third spheres (not shown) used for forming the anti-reflection structure shown in  FIG. 6  is about 1-20% of the total amount of the spheres  102 , such that the first protrusions  101   a  in the anti-reflection structure occupy about 60-98% of the total surface of a total area, the second protrusions  101   b  of the anti-reflection structure occupy about 1-20% of the total surface of the total area, and the third protrusions  101   c  of the anti-reflection structure occupy about 1-20% of the total surface of the total area. 
     Similarly, the anti-reflection structures shown in  FIG. 5-6  also have the properties of low reflection rate, anti-smudge and self-clean as that of the anti-reflection structure shown in  FIG. 4 , and have a mechanical strength greater than the conventional anti-reflection structure made of a transparent substrate and an anti-reflection coating of different materials formed thereon. 
       FIG. 7  is a schematic cross sectional view showing an electronic device  200  according to an embodiment of the invention, using the anti-reflection structure shown in  FIG. 4 . 
     As shown in  FIG. 7 , the electronic device  200  can be used in applications such as display devices and comprises a first substrate  210 , a second substrate  240 , a liquid crystal layer  220  disposed between the first substrate  210  and the second substrate  240 , and a color filter layer  230  disposed on a surface of second substrate  240  adjacent to the liquid crystal layer  220 . 
     In this embodiment, the second substrate  240  can be a transparent substrate contacting the surroundings and may thus have the anti-reflection structure shown in  FIG. 4 , such that the electronic device  200  having the anti-reflection structure shown in  FIG. 4  may have the properties of low reflection rate, anti-smudge and self-clean as that of the anti-reflection structure shown in  FIG. 4 , and have a mechanical property greater than the conventional anti-reflection structure made of a transparent substrate and an anti-reflection coating of different materials formed thereon. Herein, due to the purpose of simplicity, components in the second substrate  240  are similar with that shown in  FIG. 4  and are not described in detail. Other components in the electronic device  200  can be components used in a conventional liquid crystal display device, and are not described here in detail. 
       FIG. 8  is a schematic cross sectional view showing an electronic device  300  according to another embodiment of the invention, using the anti-reflection structure shown in  FIG. 4 . 
     As shown in  FIG. 8 , the electronic device  300  can be used in applications such as touch-sensing type display devices and comprises a first substrate  310 , a second substrate  360 , a third substrate  350  disposed between the first substrate  310  and the second substrate  360 , a liquid crystal layer  320  disposed between the first substrate  310  and the third substrate  350 , a plurality of touch-sensing elements  330  disposed over a surface of the first substrate  310  adjacent to the liquid crystal layer  320 , and a color filter layer  340  disposed over a surface of the third substrate  350  adjacent to the liquid crystal layer  320 . The space between the second substrate  360  and the third substrate  350  is filled with air or optical glues to separate the second substrate  360  and the third substrate  350 . 
     In this embodiment, the second substrate  360  can be a transparent substrate contacting the surroundings and may thus have the anti-reflection structure shown in  FIG. 4 , such that the electronic device  300  having the anti-reflection structure shown in  FIG. 4  may have the properties of low reflection rate, anti-smudge and self-clean as that of the anti-reflection structure shown in  FIG. 4 , and have a mechanical property greater than the conventional anti-reflection structure made of a transparent substrate and an anti-reflection coating of different materials formed thereon. Herein, for the purpose of brevity, components in the second substrate  360  are similar with that shown in  FIG. 4  and are not described in detail here. Other components in the electronic device  300  can be components used in conventional touch-sensing type liquid crystal display device, and are not described here in detail. 
       FIG. 9  is a schematic cross sectional view showing an electronic device  400  according to an embodiment of the invention, using the anti-reflection structure shown in  FIG. 4 . 
     As shown in  FIG. 9 , the electronic device  400  can be used in applications such as solar cell devices and comprises a first substrate  414 , a second substrate  402 , and an electrode layer  412 , a photovoltaic element  450  and a transparent conductive layer  404  sequentially disposed on the first substrate  414  and located between the first substrate  414  and the second substrate  402 . In one embodiment, the photovoltaic element  450  comprises an n-type amorphous silicon layer  410 , and intrinsic amorphous silicon layer  408 , and a p-type amorphous silicon layer  406  sequentially stacked over the electrode layer  412 . 
     In this embodiment, the second substrate  402  can be a transparent substrate contacting the surroundings and may thus have the anti-reflection structure shown in  FIG. 4 , such that the electronic device  400  having the anti-reflection structure shown in  FIG. 4  may have the properties of low reflection rate, anti-smudge and self-clean as that of the anti-reflection structure shown in  FIG. 4 , and have a mechanical property greater than the conventional anti-reflection structure made of a transparent substrate and an anti-reflection coating of different materials formed thereon. Herein, due to the purpose of simplicity, components in the second substrate  402  are similar with that shown in  FIG. 4  and are not described in detail here. Other components in the electronic device  400  that are components used in conventional solar cell devices are not described here in detail. 
       FIG. 10  is a schematic cross sectional view showing an electronic device  500  according to yet another embodiment of the invention, using the anti-reflection structure shown in  FIG. 4 . 
     As shown in  FIG. 10 , the electronic device  500  can be used in applications such as touch-sensing modules and comprises a first substrate  502 , a second substrate  506 , and a touch-sensing layer  504  disposed between the first substrate  502  and the second substrate  506 . In this embodiment, the second substrate  506  can be a transparent substrate contacting the surroundings and may thus have the anti-reflection structure shown in  FIG. 4 , such that the electronic device  500  having the anti-reflection structure shown in  FIG. 4  may have the properties of a low reflection rate, anti-smudge and self-clean as that of the anti-reflection structure shown in  FIG. 4 , and have a mechanical property greater than the conventional anti-reflection structure made of a transparent substrate and an anti-reflection coating of different materials formed thereon. Herein, due to the purpose of simplicity, components in the second substrate  506  are similar with that shown in  FIG. 4  and are not described in detail here. 
     The anti-reflection structure used in the electronic devices  200 ,  300 ,  400 , and  500  shown in  FIGS. 7-10 , respectively, is not limited to that shown in  FIG. 4 . In other embodiments, the anti-reflection structure shown in  FIGS. 5-6  can be also used in the electronic devices  200 ,  300 ,  400 , and  500  shown in  FIGS. 7-10 . 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.