Patent Publication Number: US-2023161194-A1

Title: Light emitting device, backlight, and display panel

Description:
CROSS - REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of U.S. Application Serial No. 17/ 454, 820, field on Nov. 14, 2021, which claims priority of China Application Serial Number 202011306944.3, filed on Nov. 20, 2020, the entirety of which is incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Field of Invention 
     The present disclosure relates to a light emitting device, a backlight, and a display panel. 
     Description of Related Art 
     With the advancement of light emitting diode technologies and increasing market demand, novel display technologies represented by mini-light emitting diodes/micro-light emitting diodes (Mini-LEDs/Micro-LEDs) have emerged. 
     The Mini-LED packaging mainly includes chip on board (COB) technology and integrated mounted device (IMD) packaging technology. The COB technology is to directly mount the LED chip on the module substrate, and then mold each large unit as a whole. However, various existing COB packaging technology still have many problems such as high production costs, serious light loss, and poor product stabilities. 
     SUMMARY 
     In view of this, one goal of the present disclosure is to provide a light emitting device, a backlight, and a display panel capable of addressing the aforementioned issues. 
     One aspect of the present disclosure is to provide a light emitting device including a substrate, a conductive layer, a first reflective layer, a light emitting element, a second reflective layer, and an encapsulation layer. The conductive layer is disposed on the substrate. The first reflective layer covers the conductive layer and has an opening exposing a portion of the conductive layer. The light emitting element is disposed in the opening and electrically connects to the conductive layer. The second reflective layer is disposed on the first reflective layer and surrounds the light emitting element, and the second reflective layer has an outer diameter. The top surface of the second reflective layer is lower than a top surface of the light emitting element. The encapsulation layer covers the light emitting element. There is a height between a highest point of the encapsulation layer and an upper surface of the first reflective layer, and the height is 0.1 to 0.5 times the outer diameter. The encapsulating layer is in direct contact with the outer diameter of the second reflective layer. The present disclosure also provides a backlight and a display panel. 
     Another aspect of the present disclosure is to provide a backlight including a plurality of light emitting devices foregoing. Any two adjacent light emitting devices are separated by a distance, and the outer diameter is less than 0.5 times the distance. 
     Yet another aspect of the present disclosure is to provide a display panel including a backlight foregoing, a lower diffuser, a quantum dot layer, an optical film, an upper diffuser, and a liquid crystal panel. The lower diffuser is disposed on the backlight. The quantum dot layer is disposed on the lower diffuser. The optical film is disposed on the quantum dot layer. The upper diffuser is disposed on the optical film. The liquid crystal panel is disposed over the upper diffuser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows. 
         FIG.  1 A  illustrates a three-dimensional schematic view of a light emitting device according to one comparative example of the present disclosure. 
         FIG.  1 B  illustrates a cross-section schematic view of the light emitting device of  FIG.  1 A . 
         FIG.  2    illustrates a cross-section schematic view of a light emitting device according to another comparative example of the present disclosure. 
         FIG.  3    illustrates a cross-section schematic view of manufacturing a light emitting device according to yet another comparative example of the present disclosure. 
         FIG.  4    illustrates a cross-section schematic view of a light emitting device according to one embodiment of the present disclosure. 
         FIGS.  5 A,  5 B, and  5 C  illustrate a schematic top view of a second reflective layer according to various embodiments of the present disclosure. 
         FIG.  6    illustrates a cross-section schematic view of a light emitting device according to one embodiment of the present disclosure. 
         FIG.  7 A  is a diagram showing a path of light emitted by a light emitting device according to one embodiment of the present disclosure. 
         FIG.  7 B  is a schematic diagram showing the uniformity of light emitted by a light emitting device according to one embodiment of the present disclosure. 
         FIG.  7 C  is a diagram showing a path of light emitted by a light emitting device according to another embodiment of the present disclosure. 
         FIG.  7 D  is a schematic diagram showing the uniformity of light emitted by a light emitting device according to another embodiment of the present disclosure. 
         FIGS.  8 A,  8 B,  8 C, and  8 D  illustrate cross-section schematic views of a light emitting device according to various embodiments of the present disclosure. 
         FIGS.  9 A and  9 B  are schematic diagrams showing the light emission uniformity before and after processing the encapsulating layer of a light emitting device according to one embodiment of the present disclosure. 
         FIG.  10    illustrates a cross-section schematic view of a backlight according to one embodiment of the present disclosure. 
         FIG.  11    illustrates a cross-section schematic view of a display panel according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. The embodiments disclosed below may be combined or substituted with each other under beneficial circumstances, and other embodiments may also be added to an embodiment without further description. 
     It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these specific details. Furthermore, for simplifying the drawings, some of the conventional structures and elements are shown with schematic illustrations. 
       FIG.  1 A  illustrates a three-dimensional schematic view of a light emitting device  10  according to one comparative example of the present disclosure.  FIG.  1 B  illustrates a cross-section schematic view of the light emitting device  10  of  FIG.  1 A . Referring to  FIGS.  1 A and  1 B , the light emitting device  10  includes a printed circuit board  110 , a plurality of light emitting diodes  120 , and an encapsulating glue  130 . The light emitting diodes  120  are arranged on the printed circuit board  110  at intervals. The encapsulating glue  130  fully covers the printed circuit board  110  and the light emitting diodes  120 . It is noted that the encapsulating glue  130  fully covers the printed circuit board  110  and the light emitting diodes  120  by fully coating method. As a result, the surface flatness of the light emitting device  10  is greatly reduced, and the product specifications cannot be met. Furthermore, this method of fully coating the encapsulating glue  130  will also cover the non-light emitting area of the light emitting device  10  at the same time, and will increase the cost, thereby causing the reduction of the product competitiveness. 
       FIG.  2    illustrates a cross-section schematic view of a light emitting device  20  according to another comparative example of the present disclosure. Referring to  FIG.  2   , the light emitting device  20  includes a printed circuit board  210 , a light emitting diode  220 , a ring-shaped dam  230 , and an encapsulating glue  240 . It can be understood that the printed circuit board  210  includes a substrate  212 , a conductive layer  214  disposed on the substrate  212 , and a solder protection layer  216  disposed on the conductive layer  214 . The light emitting diode  220  is disposed on the conductive layer  214  of the printed circuit board  210  to electrically connect to the conductive layer  214 . The ring-shaped dam  230  is disposed on the solder protection layer  216  of the printed circuit board  210  and surrounds the light emitting diode  220 . Generally speaking, the ring-shaped dam  230  may be made of insulating material, and the insulating material is, for example, silicon. The encapsulating glue  240  is filled in the ring-shaped dam  230  and covers the light emitting diode  220 . Due to the higher viscosity material of the ring-shaped dam  230 , the width and height of the ring-shaped dam  230  formed therefrom are both larger than the width and height of the light emitting diode  220 . Therefore, the light emitting device  20  is likely to cause light loss and not suitable for forming a large-size light board. 
       FIG.  3    illustrates a cross-section schematic view of manufacturing a light emitting device  30  according to yet another comparative example of the present disclosure. The light emitting device  30  includes a printed circuit board  310 , a light emitting diode  320 , and a transparent cover  330 . The light emitting diode  320  is disposed on the printed circuit board  310 . The transparent cover  330  seals the single light emitting diode  320  disposed on the printed circuit board  310 . To be specific, the transparent cover  330  is formed by compression molding method. The materials of the transparent cover  330  include silicon resin, epoxy resin, and glass. However, the production and the operation of the compression molding equipment are very expensive, and the stability of the large-size molding products is also poor. 
       FIG.  4    illustrates a cross-section schematic view of a light emitting device  40  according to one embodiment of the present disclosure. Referring to  FIG.  4   , the light emitting device  40  includes a substrate  410 , a conductive layer  420 , a first reflective layer  430 , a light emitting element  440 , a second reflective layer  450 , and an encapsulating layer  460 . In some embodiments, the substrate  410  may be an insulating substrate, an aluminum composite substrate, a flexible substrate, or a ceramic substrate. The conductive layer  420  is disposed on the substrate  410 . In some embodiments, the conductive layer  420  may include conductive materials of copper, aluminum, nickel, silver, gold, palladium, or combinations thereof. The first reflective layer  430  covers the conductive layer  420 , and the first reflective layer  430  has an opening  432  exposing a portion of the conductive layer  420 . In some embodiments, the material of the first reflective layer  430  is a white ink. Specifically, the material of the white ink is a white text ink containing highly reflective titanium dioxide. This material not only has a highly reflectivity, but also has the effects of high heat resistance (for example, yellowing resistance and stress cracking resistance) and high reliability. 
     Referring to  FIG.  4   , the light emitting element  440  is disposed in the opening  432  and electrically connected to the conductive layer  420 . In some embodiments, the light emitting element  440  may be a mini-LED or a micro-LED. For example, the light emitting element  440  may be a red mini-LED, a red micro-LED, a green mini-LED, a green micro-LED, a blue mini-LED, a blue micro-LED, a yellow mini-LED, a yellow micro-LED, a white mini-LED, or a white micro-LED. In some embodiments, the light emitting element  440  is flip-chip bonded to and in contact with the conductive layer  420 . 
     Referring to  FIG.  4   , the second reflective layer  450  is disposed on the first reflective layer  430  and surrounds the light emitting element  440 . More specifically, the second reflective layer  450  has an outer diameter Dout. In some embodiments, the outer diameter Dout ranges from 2.0 mm to 4.5 mm. For example, the outer diameter Dout may be 2.1 mm, 2.3 mm, 2.5 mm, 2.7 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.3 mm, 3.5 mm, 3.7 mm, 3.9 mm, 4.0 mm, 4.1 mm, or 4.3 mm. In some embodiments, the second reflective layer  450  has an inner diameter Din, and a difference between the outer diameter Dout and the inner diameter Din ranges from 0.05 mm to 0.6 mm, such as 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, or 0.55 mm. If the difference between the outer diameter Dout and the inner diameter Din is less than a certain value, such as 0.05 mm, the subsequent process of forming the encapsulating layer will cause insufficient cohesion of encapsulating glue, thereby causing the glue to overflow and the height of the encapsulating layer not easy to improve. On the other hand, if the difference between the outer diameter Dout and the inner diameter Din is greater than a certain a value, such as 0.6 mm, the amount of the encapsulating glue used will increase, and the process time for forming the encapsulating layer will also be prolonged. 
     In some embodiments, the material of the second reflective layer  450  is a white ink. Specifically, the material of the white ink is a white text ink containing highly reflective titanium dioxide. This material not only has a highly reflectivity, but also has the effects of high heat resistance (for example, yellowing resistance and stress cracking resistance) and high reliability. In some embodiments, a top surface of the second reflective layer  450  is lower than a top surface of the light emitting element  440 . In some embodiments, a thickness TH of the second reflective layer  450  ranges from 20 um to 60 um, such as 25 um, 30 um, 35 um, 40 um, 45 um, 50 um, or 55 um. If the thickness TH of the second reflective layer  450  is less than a certain value, such as 20 um, the subsequent process of forming the encapsulating layer will cause insufficient cohesion of encapsulating glue, thereby causing the glue to overflow and the height of the encapsulating layer not easy to improve. On the other hand, if the thickness TH of the second reflective layer  450  is greater than a certain a value, such as 60 um, the second reflective layer  450  will be not easy to form and easy to collapse. In some embodiments, the second reflective layer  450  may be formed by printing or coating, so that the expected position, the width, and the thickness of the second reflective layer  450  can be controlled more accurately. 
       FIGS.  5 A,  5 B, and  5 C  illustrate a schematic top view of the second reflective layer  450  according to various embodiments of the present disclosure. As shown in  FIG.  5 A , the shape of the second reflective layer  450  viewed in the top view direction may be a circle, in one embodiment. As shown in  FIG.  5 B , the shape of the second reflective layer  450  viewed in the top view direction may be a triangle having fillets, in another embodiment. As shown in  FIG.  5 C , the shape of the second reflective layer  450  viewed in the top view direction may be a square having fillets, in yet another embodiment. In other alternative embodiments, the shape of the second reflective layer  450  viewed in the top view direction may be a polygon having fillets. It is noted that regardless of the shape of the second reflective layer  450  observed in the top view direction, it has a virtual geometric circumscribed circle (as shown by the dashed line in  FIGS.  5 A- 5 C ) and a virtual geometric inscribed circle (as shown by the dashed line in  FIGS.  5 A- 5 C ). The geometric circumscribed circle has an outer diameter Dout and the geometric inscribed circle has an inner diameter Din, and a difference between the outer diameter Dout and the inner diameter Din ranges from 0.05 mm to 0.6 mm. 
     Referring to  FIG.  4    again, the encapsulating layer  460  covers the light emitting element  440 . More specifically, there is a height H between a highest point of the encapsulating layer  460  and an upper surface of the first reflective layer  430 , and the height H is 0.1 to 0.5 times the outer diameter Dout. For example, the height H may be 0.2, 0.3, or 0.4 times the outer diameter Dout. In some embodiments, the encapsulating layer  460  covers the light emitting element  440  and a portion of the first reflective layer  430 , but not covers the second reflective layer  450 . In other words, the encapsulating layer  460  is merely disposed within an inner edge of the second reflective layer  450 . To put it another way, the range covered by the encapsulating layer  460  only covers the inner diameter Din of the second reflective layer  450 . In some embodiments, the encapsulating layer  460  has an arc-shaped outer surface. In some embodiments, the encapsulating layer  460  may be formed by dispensing or jetting. In some embodiments, the encapsulating layer  460  may include an organic packaging material, an inorganic packaging material, or combinations thereof. For example, the organic packaging material includes silicon rubber, acrylic and epoxy resin, while the inorganic packaging material includes silicon dioxide and fluorine adhesive. However, the present disclosure is not limited thereto. The encapsulating layer  460  can increase the area capable to block moisture and protect the light emitting element  440  from moisture, thereby increasing the reliability and service life of the product. In addition, the encapsulating layer  460  may also act as a lens to change the light emitting angle of the light emitting element  440 . 
       FIG.  6    illustrates a cross-section schematic view of a light emitting device  60  according to one embodiment of the present disclosure. In order to facilitate the comparison with the aforementioned embodiments and simplify the description, the same reference numbers are used in the following embodiments to refer to the same or like parts. Also, the differences between embodiments are discussed below, and similar parts will not be repeated. The difference between the light emitting device  60  and the light emitting device  40  is that the encapsulating layer  460  of the light emitting device  60  completely covers the second reflective layer  450 . Compared with the light emitting device  40 , the light emitting device  60  has more uniform light emission and can improve the visual effect of applications thereof. 
       FIG.  7 A  is a diagram showing a path of light emitted by the light emitting device  60  according to one embodiment of the present disclosure.  FIG.  7 B  is a schematic diagram showing the uniformity of light emitted by the light emitting device  60  according to one embodiment of the present disclosure.  FIG.  7 C  is a diagram showing a path of light emitted by the light emitting device  60  according to another embodiment of the present disclosure.  FIG.  7 D  is a schematic diagram showing the uniformity of light emitted by the light emitting device  60  according to another embodiment of the present disclosure. It is noted that  FIGS.  7 A and  7 B  show the light emission path and uniformity of the light emitting device  60  under the design where the height H between the highest point of the encapsulating layer  460  and the upper surface of the first reflective layer  430  is 0.1 times the outer diameter Dout.  FIGS.  7 C and  7 D  show the light emission path and uniformity of the light emitting device  60  under the design where the height H between the highest point of the encapsulating layer  460  and the upper surface of the first reflective layer  430  is 0.5 times the outer diameter Dout. In various embodiments where the height H is 0.1 times to 0.5 times the outer diameter Dout, it can be understood that when the height H is closer to 0.5 times the outer diameter Dout, the light emission uniformity of the light emitting device  60  is better. 
       FIGS.  8 A and  8 B  illustrate cross-section schematic views of a light emitting device  80   a  and  80   b  according to various embodiments of the present disclosure. As shown in  FIGS.  8 A and  8 B , the encapsulating layer  460  of the light emitting device  80   a  and  80   b  has a width gradually decreasing by a constant amount from bottom to top and has an arc-shaped top surface. From the schematic cross-sectional view, the slope of the sidewalls of the light emitting device  80   a  and  80   b  is a certain value. The difference between the light emitting device  80   a  and the light emitting device  80   b  is that a radius of curvature of the arc-shaped top surface of the encapsulating layer  460  of the light emitting device  80   a  is smaller than that of the encapsulating layer  460  of the light emitting device  80   b . Compared with the light emitting device  80   a , the arc-shaped top surface of the encapsulating layer  460  of the light emitting device  80   b  is a relatively smooth arc-shaped top surface. In some embodiments, the sidewalls of the encapsulating layer  460  of the light emitting device  80   a  and  80   b  may be flattened by post-processing. 
       FIGS.  8 C and  8 D  illustrate cross-section schematic views of a light emitting device  80   c  and  80   d  according to various embodiments of the present disclosure. As shown in  FIGS.  8 C and  8 D , the encapsulating layer  460  of the light emitting device  80   c  and  80   d  has a width gradually decreasing by a constant amount from bottom to top, and the encapsulating layer has a flat top surface. From the schematic cross-sectional view, the slope of the sidewalls of the encapsulating layer  460  of the light emitting device  80   c  and  80   d  is a certain value. The difference between the light emitting device  80   c  and the light emitting device  80   d  is that the area of the flat top surface of the encapsulating layer  460  of the light emitting device  80   c  is smaller than that of encapsulating layer  460  of the light emitting device  80   d . In some embodiments, the arc-shaped top surfaces of the light emitting device  80   a  and  80   b  may be processed into flat top surfaces by a post-processing planarization process, such as grinding or flat polishing. 
       FIGS.  9 A and  9 B  are schematic diagrams showing the light emission uniformity before and after processing the encapsulating layer of a light emitting device according to one embodiment of the present disclosure.  FIG.  9 A  is a schematic diagram of the light emission uniformity of the encapsulating layer of the light emitting device without post-processing.  FIG.  9 B  is a schematic diagram of the light emission uniformity of the encapsulating layer of the light emitting device after post-processing. It can be seen from  FIGS.  9 A and  9 B  that the light emitting device after post-processing has better light emission uniformity than the light emitting device without post-processing. 
       FIG.  10    illustrates a cross-section schematic view of a backlight  90  according to one embodiment of the present disclosure. As shown in  FIG.  10   , the backlight  90  includes a plurality of light emitting devices ( 40 ,  60 ,  80   a ,  80   b ,  80   c ,  80   d , or combinations thereof) foregoing. It is noted that any two adjacent light emitting devices are separated by a distance P, and the outer diameter Dout is less than 0.5 times the distance P. This design may reduce the amount encapsulating glue of the backlight  90  overall. For example, the amount encapsulating glue may be reduced by more than 80%, thereby reducing costs and enhancing the market competitiveness of products. 
       FIG.  11    illustrates a cross-section schematic view of a display panel  1000  according to one embodiment of the present disclosure. As shown in  FIG.  11   , the display panel  1000  includes the backlight  90  foregoing, a lower diffuser  1010 , a quantum dot layer  1020 , an optical film  1030 , an upper diffuser  1040 , and a liquid crystal panel  1050 . To be specific, the lower diffuser  1010  is disposed on the backlight  90 . The lower diffuser  1010  is used to increase a brilliancy of the display panel  1000 . 
     Referring to  FIG.  11   , the quantum dot layer  1020  is disposed on the lower diffuser  1010 . In some embodiments, the quantum dot layer  1020  includes a red quantum dot, a green quantum dot, a blue quantum dot, or combinations thereof. The quantum dot layer  1020  can make the display panel  1000  have higher color purity and stronger color expression. 
     Referring to  FIG.  11   , the optical film  1030  is disposed on the quantum dot layer  1020 . In some embodiments, the optical film  1030  includes a prism sheet or a brightness enhancement film (BEF). It can be understood that the number of the optical film  1030  is not limited to one as shown in  FIG.  11   , and the number of the optical film  1030  may be two or more depending on design requirements. The main function of the optical film  1030  is to achieve light collection, enhancement of the front light emission, and increase of the brightness through the refraction and reflection of light. When the light diffuses out through the lower diffuser, the travelling direction of the light is not concentrated and the directivity of the light is poor. Using the optical film  1030  to correct the travelling direction of the light may greatly increase the overall brightness of the display panel  1000 . 
     Referring to  FIG.  11   , the upper diffuser  1040  is disposed on the optical film  1030 . The upper diffuser  1040  may improve the light distribution to expand the field of view. The upper diffuser  1040  may also make the light emitted by the subsequent liquid crystal panel more uniform, so that the display panel  1000  may have a soft and uniform surface light source. 
     Referring to  FIG.  11   , the liquid crystal panel  1050  is disposed over the upper diffuser  1040 . In other embodiments, the display panel  1000  may further include other optical components commonly used in this field to better enhance the visual performance of the display panel  1000 . 
     In summary, the second reflective layer of the light emitting device of the present disclosure can control and divide accurately each light emitting element. By effectively adjusting the height of the encapsulating layer to control the amount of glue materials to achieve the purpose of reducing production costs and improving product market competitiveness. In addition, precisely controlling the relative relationship between the outer diameter of the second reflective layer and the height of the encapsulating layer can further improve the visual effects of the light emitting device and applications thereof (for example, backlights and display panels). 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.