Patent Publication Number: US-11048032-B2

Title: Manufacturing method for metal grating, metal grating and display device

Description:
CROSS REFERENCE TO RELEVANT APPLICATION(S) 
     The present application claims the priority of the Chinese patent application No. 201710648516.0 filed on Aug. 1, 2017, the entire disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of display technologies, and in particular to a manufacturing method for a metal grating, a metal grating, and a display device. 
     BACKGROUND ART 
     At present, in a flat panel display, for fabricating a built-in polarizer, a dichroic dye is usually used as a main component of the polarizer, and applied inside a liquid crystal cell by spin-coating, so as to form the built-in polarizer. Due to limitations of the material, a polarizer formed in this way has only a polarization degree of 80%, which is far from the polarization degree of 99.99% as required by a display panel. Therefore, it cannot be applied in an actual product. 
     As an alternative formation approach, the built-in polarizer can also be formed by nano-imprinting. However, the nano-imprinting procedure has a lower yield rate and involves more complicated processes. This results in a higher fabricating cost and greater development difficulty. Besides, during the nano-imprinting procedure, the product yield rate drops rapidly as the resolution rises. 
     SUMMARY 
     According to one aspect of the present disclosure, a manufacturing method for a metal grating is provided in an embodiment. Specifically, the manufacturing method comprises: forming a peeling layer and an adhesive film layer sequentially on a base substrate; etching the adhesive film layer to form a plurality of grating strips parallel to each other; forming a metal thin film covering the plurality of grating strips and gaps between the grating strips, the metal thin film having a uniform thickness; covering the metal thin film with a filling material; performing a first topping process on the resulting structure, such that an exposed surface comprises grating strips, metal strips and filling strips arranged alternately and flush with each other; forming a base layer over the grating strips, the metal strips and the filling strips; peeling the base substrate by removing the peeling layer; and after flipping over, performing a second topping process on the resulting structure, such that an exposed surface comprises grating strips, metal strips and filling strips arranged alternately and flush with each other, thereby forming a metal grating. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, the thickness of the metal thin film is smaller than half of a pitch between adjacent grating strips. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, the width of each grating strip is smaller than the pitch between adjacent grating strips. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, the width of each grating strip is equal to that of each filling strip. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, the metal thin film covering the plurality of grating strips and the gaps between the grating strips is formed by atomic layer deposition or ion-assisted deposition. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, the filling material comprises a resin material with fluidity. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, during the first topping process, tops of the metal thin film and the filling material are removed simultaneously by dry etching. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, after the first topping process and prior to the second topping process, every two adjacent metal strips are connected with each other at one end via a metal thin film part. 
     According to a possible implementation, in the manufacturing method provided by an embodiment of the present disclosure, during the second topping process, tops of the grating strips, the metal strips and the filling strips, as well as the metal thin film parts, are removed simultaneously by dry etching. 
     According to a possible implementation, the manufacturing method provided by an embodiment of the present disclosure further comprises: forming a planarization layer over the metal grating. 
     According to another aspect of the present disclosure, a metal grating manufactured by the above manufacturing method is further provided in an embodiment. Specifically, the metal grating comprises: a base layer; a plurality of metal strips arranged on the base layer and parallel to each other; and grating strips and filling strips arranged alternately between adjacent metal strips. 
     According to a possible implementation, the metal grating provided by an embodiment of the present disclosure further comprises: a planarization layer arranged over the metal strips, the grating strips and the filling strips. 
     According to yet another aspect of the present disclosure, a display device is further provided in an embodiment. Specifically, the display device comprises: a display panel; and the metal grating arranged inside the display panel as a polarizer. 
     According to a possible implementation, in the display device provided by an embodiment of the present disclosure, the display panel is a liquid crystal display panel. Specifically, the liquid crystal display panel comprises: a counter substrate and an array substrate arranged opposite to each other; a liquid crystal layer arranged between the counter substrate and the array substrate; and the metal grating as mentioned above. The metal grating specifically comprises: a first metal grating arranged on one side of the array substrate facing the liquid crystal layer; and a second metal grating arranged on one side of the counter substrate facing the liquid crystal layer, wherein an extension direction of the first metal grating is perpendicular to that of the second metal grating. 
     According to a possible implementation, in the display device provided by an embodiment of the present disclosure, the display panel is an organic electroluminescent display panel. Specifically, the organic electroluminescent display panel comprises: a base substrate; a light emitting device arranged on the base substrate; an encapsulation layer covering the light emitting device; the metal grating layer as mentioned above; and a quarter-wave plate. The metal grating is arranged between the encapsulation layer and the light emitting device, and the quarter-wave plate is arranged between the light emitting device and the metal grating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structure view for a typical metal grating; 
         FIGS. 2 a -2 d    are respectively schematic views for a structure at different stages during the manufacture of a metal grating by nano-imprinting; 
         FIG. 3  is an actual structure view for a metal grating manufactured by nano-imprinting; 
         FIG. 4  is a flow diagram of a manufacturing method for a metal grating according to an embodiment of the present disclosure; 
         FIGS. 5 a -5 j    are respectively schematic views for a structure at different stages during the manufacture of a metal grating according to an embodiment of the present disclosure; and 
         FIGS. 6 a  and 6 b    are respectively schematic structure views for a display device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Specific implementations of the manufacturing method for a metal grating, the metal grating and the display device provided in embodiments of the present disclosure will be described below in detail with reference to the drawings. 
     In the drawings, thicknesses and shapes of each thin film do not reflect the real ratio of the metal grating. But instead, they are only provided to illustrate contents of the present disclosure schematically. 
     Referring to  FIG. 1 , a schematic structure view for a typical metal grating is shown. Specifically, as shown in  FIG. 1 , the metal grating can be used as a built-in polarizer inside a display device. Next, the manufacturing process for the metal grating shown in  FIG. 1  will be described in detail with reference to  FIG. 2 . As an example, the manufacturing process can comprise steps of: ( 1 ) as shown in  FIG. 2 a   , depositing a metal film  2  on a base  1  and continuing to apply an adhesive film  3 ; ( 2 ) as shown in  FIG. 2 b   , patterning the adhesive film  3  by exposure or nano-imprinting, so as to form a shielding pattern  3 ′; ( 3 ) as shown in  FIG. 2 c   , subjecting the metal film  2  to a nanoscale high-resolution etching with shielding by the shielding pattern  3 ′, thereby forming a metal grating  2 ′; and ( 4 ) as shown in  FIG. 2 d   , removing the residual shielding pattern  3 ′. 
     When a metal grating with a period of 120 nm is manufactured by the above manufacturing method, only a 3-inch sample can be obtained due to the poor yield rate of nano-imprinting. This is particularly true for large-sized products, and thus is disadvantageous for applications in large-sized display panels. Moreover, a nano-imprinting procedure has a lower yield rate, and involves more complicated processes. So, the cost of templates is high, and the development is difficult. Besides, the nano-imprinting procedure belongs to a contact type of mechanical manufacture, which has high requirements for the smoothness of substrate. 
     Besides, a high-resolution metal grating is a huge challenge to the existing processes and devices. At present, the exposure can only reach the order of 1 μm, and cannot achieve resolution of 0.1 μm. Although the nano-imprinting procedure can barely reach the order of 100 nm at present, the product yield rate drops rapidly as the resolution rises. There is no mature process solution for that. So, nano-imprinting can only stagnate on low resolution for the time being. Apart from the difficulty for forming nanoscale patterns, another problem lies in etching the metal grating. A currently available etching device basically does not have homogeneity reaching the order of nanometers. So, the patterns formed are irregular. This can be seen clearly in  FIG. 3 . 
     In view of above, how to manufacture an erodible metal grating having high resolution and high yield rate is an urgent technical problem to be solved in the art. 
     To this end, a new manufacturing method for a metal grating is provided in an embodiment of the present disclosure. As shown in  FIG. 4 , the manufacturing method specifically comprises steps of: S 401 , forming a peeling layer and an adhesive film layer sequentially on a base substrate; S 402 , etching the adhesive film layer to form a plurality of grating strips parallel to each other; S 403 , forming a metal thin film covering the plurality of grating strips and gaps between the grating strips, the metal thin film having a uniform thickness, wherein the thickness d of the metal thin film is optionally smaller than half of a pitch a between adjacent grating strips; S 404 , covering the metal thin film with a filling material; S 405 , performing a first topping process on the resulting structure, such that an exposed surface comprises grating strips, metal strips and filling strips arranged alternately and flush with each other; S 406 , forming a base layer over the grating strips, the metal strips and the filling strips; S 407 , peeling the base substrate by removing the peeling layer; and S 408 , after flipping over, performing a second topping process on the resulting structure, such that an exposed surface comprises grating strips, metal strips and filling strips arranged alternately and flush with each other. 
     Specifically, according to the manufacturing method for a metal grating provided by an embodiment of the present disclosure, after a plurality of grating strips are formed in parallel by an adhesive film layer, a metal thin film distributed continuously with a uniform thickness is formed over the plurality of grating strips and gaps between the grating strips. Furthermore, metal strips are formed by a metal thin film deposited over the grating strips. During this procedure, a line width of the metal strip depends on the thickness of the metal thin film. This helps to avoid subjecting the metal thin film to a nanoscale high-resolution etching, thereby reducing the etching difficulty and improving the manufacture yield rate. Besides, by forming filling strips over the metal thin film, e.g., in slits of the metal thin film, and removing a metal thin film part connecting adjacent metal strips, the metal strips are disconnected, and thus a final metal grating is formed. In the manufacturing method provided by an embodiment of the present disclosure, the line width of the metal strip in the metal grating is only relevant with the deposition thickness of the metal thin film. Thus, it will not be influenced by the etching accuracy of a metal-etching device. Therefore, the line width of the metal strip can be on the order of several tens of nanometers or even several nanometers, which is helpful for obtaining a high-resolution metal grating. 
     Steps in the manufacturing method provided by an embodiment of the present disclosure will be explained below in detail. 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 a   , in step S 401 , a peeling layer  200  and an adhesive film layer  300  are formed sequentially on the base substrate  100 . Specifically, the peeling layer  200  can be fabricated by using, for example, oxide materials that can be decomposed by laser irradiation. Besides, the thickness of the peeling layer  200  is generally controlled to be about several tens of nanometers. After that, the adhesive film layer  300  is formed on the peeling layer by using materials such as photoresist or resin. Generally, the thickness of the adhesive film layer  300  is controlled to be between 100 nm and 500 nm. 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 b   , in step S 402 , the adhesive film layer  300  is etched to form a plurality of grating strips  310  parallel to each other. Optionally, a width b of each grating strip  310  formed is smaller than a pitch a between adjacent grating strips  310 . Moreover, advantageously, a ratio between the width b of each grating strip  310  and the pitch a between adjacent grating strips  310  approximates 1:1. This helps to facilitate subsequent formation of metal strips having a same pitch therebetween, and ensures homogeneity in the grating period of the metal grating. 
     Optionally, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 d   , when the width b of each grating strip  310  formed is smaller than the pitch a between adjacent grating strips  310 , the width b of each grating strip  310  formed is further made equal to a width c of each filling strips  500  formed sequentially. This facilitates subsequent formation of metal strips  410  with the same pitch, and ensures homogeneity in the grating period of the metal grating. According to a specific embodiment, the advantageous effect such as the grating strips  310  and the filling strips having the same width can be achieved by adjusting a ratio relation between the width b of the grating strip  310 , the pitch a of adjacent grating strips  310 , and the thickness d of the metal thin film  400 , e.g., assuming that a−2*d=b. 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 c   , in step S 403 , a metal thin film  400  distributed continuously with a uniform thickness is formed over the plurality of grating strips  310  and the gaps between the grating strips  310 . Specifically, the metal thin film  400  can be formed by atomic layer deposition or ion-assisted deposition. As compared with a conventional deposition method such as chemical vapor deposition or physical vapor deposition, atomic layer deposition or ion-assisted deposition for example can ensure that not only metal thin film parts on top of each grating strip, but also metal thin film parts formed on a lateral side of each grating strip (i.e., the parts finally forming the metal strips of the metal grating), have the same thickness. This ensures a same size of each metal strip in the metal grating as formed finally, and facilitates obtaining a metal grating having a more prominent optical performance. 
     Specifically, the metal thin film  400  can be generally made of Ag, Al, Mo, Cu, and so on. Furthermore, the thickness of the metal thin film  400  deposited in the above manner can be controlled to be between several nanometers and several tens of nanometers. This can achieve good homogeneity. Besides, since the thickness d of the metal thin film  400  is associated with the width of each metal strip (wire)  410  in the metal grating as formed finally, with the manufacturing method provided by embodiments of the present disclosure, metal wires in the resulting metal grating can be reduced onto an order of several tens of nanometers, or even several nanometers. 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 d   , in step S 404 , a filling material, such as filling strip  500 , is formed over the metal thin film  400 , for example, in recessed slits of the metal thin film  400 . Specifically, a resin material with fluidity can be used to fill the recessed slits of the metal thin film, so as to obtain a good filling effect. Besides, in an actual operation, the resin material is not limited to fill only the recessed slits of the metal thin film. For example, the resin material may be left on top of the metal thin film unavoidably. That is, the resin material may be formed on the metal thin film parts in a top portion of the grating strips. 
     In view of above, according to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 e   , in step S 405 , top portions of the metal thin film  400  and the filling strips  500  are removed. Specifically, the top portions of the metal thin film  400  and the filling strips  500  can be removed simultaneously by dry etching, so as to form a plurality of metal strips  410  spaced from each other on an upper end and flush with upper ends of the filling strips  500 . Besides, the top portions of the metal thin film  400  and the filling strips  500  are removed directly. So, etching devices and etching techniques with high-resolution are not required. In other words, in step S 405 , the dry etching technique is not influenced by the accuracy of device. 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 f   , in step S 406 , a base layer  600  is formed over the metal thin film  500  and the filling strips  410 . Specifically, a coating process can be utilized with the help of materials such as PI or resin on the base layer  600 . 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 g   , in step S 407 , optionally, after the base substrate  100  is flipped over, the base substrate  100  can be peeled by removing the peeling layer  200 . Specifically, this can be done by irradiating the peeling layer  200  with laser from one side of the base substrate  100 . In this case, the peeling layer  200  will be decomposed into gases such as hydrogen and oxygen after being heated. Thus, the goal of peeling the base substrate  100  can be achieved. 
     According to a specific embodiment, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 5 h   , in step S 408 , the metal thin film parts connecting two adjacent metal strips  410  at one end are removed. Specifically, the metal thin film parts can be etched by wet etching, and thereby a metal grating can be obtained. In this case, the top portion of the grating strips  310  still protrudes from the metal strips, which is disadvantageous for the surface smoothness of the metal grating as obtained finally. Therefore, advantageously, as shown in  FIG. 5 i   , the top portions of the metal thin film parts and the grating strips  310  are removed simultaneously by dry etching, such that the metal strips  410  and the grating strips  310  are flush with each other on the upper ends. Then, a metal grating having better surface homogeneity is obtained. 
     Furthermore, in order to improve the surface homogeneity of the manufactured metal grating for connecting the metal grating with other film layer components inside the display panel in a better way, in the manufacturing method provided by an embodiment of the present disclosure, as shown in  FIG. 4 , the following steps can also be used. 
     Specifically, in step S 409 , a planarization layer  700  is formed over the metal grating. As shown in  FIG. 5 j   , a layer of resin greater than about 1 μm can be applied on a surface of the metal grating as a planarization layer  700 . In this way, better surface homogeneity of the metal grating can be obtained. Besides, the planarization layer can further function to protect the surface of the metal grating. 
     According to another aspect of the present disclosure, a metal grating manufactured by the above manufacturing method is further provided in an embodiment. As shown in  FIG. 5 j   , the metal grating can comprise: a base layer; a plurality of metal strips  410  arranged on the base layer  600  and parallel to each other; and grating strips  310  and filling strips  500  arranged alternately between adjacent metal strips  410 . 
     In the metal grating provided by an embodiment of the present disclosure, the line width of the metal strips  410  in the metal grating is only correlated with the deposition thickness of the metal thin film  400 . So, it will not be influenced by the etching accuracy of a metal-etching device. In this way, the line width of the metal strips  410  can be controlled on the order of several tens of nanometers, or even several nanometers, which is helpful for obtaining a high-resolution metal grating. 
     According to a specific embodiment, the metal grating provided by an embodiment of the present disclosure can further comprise, as shown in  FIG. 5 j   , a planarization layer  700  arranged over the metal strips  410 , the grating strips  310  and the filling strips  500 . The planarization layer  700  can not only endow the surface of the metal grating with better homogeneity, but also function to protect the surface of the metal grating. 
     Based on a same concept, an embodiment of the present disclosure further provides a display device. The display device can be any product or component having a display function, such as a cellphone, a tablet computer, a television, a display, a notebook computer, a digital photo frame, a navigator and the like. For implementations of the display device, the above embodiments of the metal grating can be referred to, which will not be repeated here for simplicity. 
     Specifically, an embodiment of the present disclosure provides a display device. The display device can comprise: a display panel; and the metal grating arranged inside the display panel as a polarizer. 
     Specifically, in the display device provided by an embodiment of the present disclosure, the thickness of the display device can be greatly reduced by using the metal grating as a polarizer and arranging it inside the display panel. 
     According to a specific embodiment, in the display device provided by an embodiment of the present disclosure, as shown in  FIG. 6 a   , the display panel can be a liquid crystal display panel. Specifically, the liquid crystal display panel comprises: a counter substrate  01  and an array substrate  02  arranged opposite to each other; a liquid crystal layer  03  between the counter substrate  01  and the array substrate  02 ; and a metal grating. Furthermore, the metal grating comprises: a first metal grating  04  arranged on one side of the array substrate  02  facing the liquid crystal layer  03 ; and a second metal grating  05  arranged on one side of the counter substrate  01  facing the liquid crystal layer  03 , wherein an extension direction of the first metal grating  04  is perpendicular to that of the second metal grating  05 . In this way, a polarizer allowing passage of polarized light having a first direction and a second direction respectively is obtained, wherein the first direction and the second direction are perpendicular to each other. 
     According to a specific embodiment, in the display device provided by an embodiment of the present disclosure, as shown in  FIG. 6 b   , the display panel can further be an organic electroluminescent display panel. The organic electroluminescent display panel can comprise: a base substrate  01 ; a light emitting device  20  arranged on the base substrate  10 ; an encapsulation layer  30  covering the light emitting device  20 ; a metal grating  40 ; and a quarter-wave plate  50 . Specifically, the metal grating  40  is arranged between the encapsulating layer  30  and the light emitting device  20 , and the quarter-wave plate  50  is arranged between the light emitting device  20  and the metal grating  40 . The quarter-wave plate  50  and the metal grating  40  serving as a circular polarizer cooperate with each other to achieve an anti-reflection function. 
     Embodiments of the present disclosure provide a manufacturing method for a metal grating, a metal grating, and a display device. Specifically, after a plurality of grating strips are formed in parallel by using an adhesive film layer, a metal thin film distributed continuously with a uniform thickness is formed over the plurality of grating strips and the gaps between the grating strips. Furthermore, optionally, the thickness of the metal thin film is smaller than half of a pitch between adjacent grating strips. In this way, metal strips are formed by depositing a metal thin film, wherein the line width of each metal strip depends on the thickness of the metal thin film. This can avoid subjecting the metal thin film to a nanoscale high-resolution etching, thereby reducing the etching difficulty, and improving the manufacture yield rate. Besides, by forming filling strips in recessed slits of the metal thin film, and removing the metal thin film part connecting adjacent metal strips, the metal strips are disconnected, and thus a final metal grating is formed. The metal grating formed by the above manufacturing method can comprise: a base layer; a plurality of metal strips arranged on the base layer and parallel to each other; and grating strips and filling strips arranged alternately between adjacent metal strips. In such a metal grating, the line width of each metal strip is only correlated with the deposition thickness of the metal thin film. So, it will not be influenced by the etching accuracy of a metal-etching device. Therefore, the line width of the metal strips can be on the order of several tens of nanometers, or even several nanometers, which is helpful for obtaining a high-resolution metal grating. 
     Obviously, those skilled in the art can make various modifications and variations to the present disclosure without departing from the spirit and scope of the present disclosure. Thus, if modifications and variations to the present disclosure fall within the scope of claims of the present disclosure and the equivalent techniques thereof, the present disclosure is intended to include them too.