Patent Publication Number: US-2022231209-A1

Title: Led display

Description:
BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a display and, more particularly, to an LED display. 
     2. Related Prior Art 
     A light-emitting diode (“LED”) display includes light-emitting diodes attached to a substrate by glue. Each of the light-emitting diodes is in the form of a die cut from a wafer. The attachment of the light-emitting diodes to the substrate is called “die bonding.” 
     A light-emitting diode in the form of a flip chip includes a positive electrode P and a negative electrode N on a same side, and each of the positive and negative electrodes is covered by a block of solder. The light-emitting diode in the form of a flip chip is cut and bonded before it can be electrically connected to a circuit board. 
     Pixels-per-inch (“PPI”) is often used to describe the resolution of a display. However, the size of a micro light-emitting diode is smaller than 100 μm, about 1% of the size of a regular light-emitting diode. In the making of micro light-emitting diodes, problems are encountered. 
     For example, millions of micro light-emitting diodes are transferred to a glass substrate of a thin film transistor (“TFT”) or a circuit board from an original substrate made of sapphire or gallium arsenide for example. Transfer of such a large amount of micro light-emitting diodes is too difficult for conventional machines that are suitable for making average light-emitting diodes. 
     Moreover, an even larger amount of contact points have to be handled to attach such a large amount of micro light-emitting diodes to a circuit board. A display needs complicated wiring to connect micro light-emitting diodes at a high resolution. Such complicated wiring required a precise and expansive process and are not good for the transfer of such a large amount of micro light-emitting diodes. Hence, the rate of defects in the making of the displays equipped with micro light-emitting diodes is high. 
     The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art. 
     SUMMARY OF INVENTION 
     It is the primary objective of the present invention to provide an inexpensive and high-solution display. 
     To achieve the foregoing objective, the display includes micro light-emitting diodes connected to a color conversion layer and driver integrated circuits connected to the micro light-emitting diodes via an electrically connecting layer. Each of the micro light-emitting diodes includes an N pad and a P pad. The micro light-emitting diodes emit light beams of a same color. The color conversion layer converts the light beams into various colors. The electrically connecting layer includes elongated negative electrodes connected to the N pads and elongated positive electrodes connected to the P pads. Each of the driver integrated circuits includes a first group of bonding pads on a face, a second group of bonding pads on an opposite face, and conductors for connecting the first group of bonding pads to the second group of bonding pads. Some of the bonding pads in the first group are connected to the elongated negative electrodes. The remaining ones of the bonding pads in the first group are connected to the elongated positive electrodes. The circuit board is connected to the second group of bonding pads of each of the driver integrated circuits. 
     Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be described via detailed illustration of the preferred embodiment referring to the drawings wherein: 
         FIG. 1  is a perspective view of a driver IC according to the preferred embodiment of the present invention; 
         FIG. 2  is a perspective view of a wafer including light-emitting units; 
         FIG. 3  is a top view of an electrically connecting layer and the light-emitting units shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of the driver IC shown in  FIG. 1  electrically connected to the light-emitting units via the electrically connecting layer shown in  FIG. 3 ; 
         FIG. 5  is an enlarged, partial and cross-sectional view of a semi-product of a display equipped with the micro light-emitting diodes shown in  FIG. 4 ; 
         FIG. 6  is an enlarged, partial and cross-sectional view of a completed product of the display shown in  FIG. 5 ; 
         FIG. 7  is a sketch of a layout of one of the micro light-emitting diodes shown in  FIG. 2 ; and 
         FIG. 8  is a front view of a display equipped with the micro light-emitting diodes shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 through 7 , a display  10  includes at least one circuit board  20  and at least one group of micro light-emitting diodes  39  according to the preferred embodiment of the present invention. 
     Referring to  FIG. 1 , a driver integrated circuit (“IC”)  11  includes a base  12  formed with two opposite faces  13  and  14 . There are bonding pads  15  on the face  13  of the base  12 . There are bonding pads  17  on the face  14  of the base  12 . The bonding pads  17  are shaped and located corresponding to the bonding pads  15 . A through-silicon via (“TSV”) technique is used to make conductors  16  in the base  12 . Each of the conductors  16  connects a corresponding one of the bonding pads  15  to a corresponding one of the bonding pads  17 . Thus, the faces  13  and  14  of the base  12  of the driver IC  11  are electrically connected to each other. 
     Referring to  FIG. 2 , an original substrate  30  includes a crystal layer  31  of sapphire for example grown on an extensive layer  32  by an epitaxy technique. The extensive layer  32  includes structures of the micro light-emitting diodes  39 . The original substrate  30  is cut into light-emitting units  33  of a desired size, with some residual materials  34  and  35  to be disposed of. Each of the light-emitting units  33  includes light-emitting diodes  29  ( FIGS. 3 and 5 ). 
     Referring to  FIG. 3 , each of the light-emitting units  33  is electrically connected to a driver IC  11  through an electrically connecting layer  28 . The electrically connecting layer  28  includes two groups of pins  18 , a group of elongated negative electrodes  24  and a group of elongated positive electrodes  25 . Each of the elongated negative electrodes  24  and each of the elongated positive electrodes  25  extend like two skew lines, i.e., the elongated negative electrodes  24  are not electrically connected to the elongated positive electrodes  25 . The pins  18  in the first group are arranged along a line extending from the left top corner of the electrically connecting layer  28  to the right bottom corner. The pins  18  in the second group are arranged along a line extending from the right top corner of the electrically connecting layer  28  to the left bottom corner. The pins  18  in the first and second groups are electrically connected to the elongated negative electrodes  24 . 
     The light-emitting units  33  are electrically connected to the electrically connecting layer  28  by various etching techniques such as mask techniques or reticle techniques. A so-called etching technique is a technique that produces or deposits layers of different materials and etches each of the layers into a circuit. 
     Referring to  FIG. 4 , the face  13  of the driver IC  11  is electrically connected to some of the pins  18  so that the driver IC  11  is electrically connected to the elongated negative electrodes  24 . The face  13  of the driver IC  11  is electrically connected some of the pins  18  so that the driver IC  11  is electrically connected to the elongated positive electrodes  25 . The bonding pads  17 , which are formed on the face  14  of the driver IC  11 , are electrically connected to the light-emitting units  33  through the conductors  16 . 
     The micro light-emitting diodes  39  are formed in the extensive layer  32 , which is grown on the crystal layer  31 . The extensive layer  32  is supported on the driver IC  11 . 
     Referring to  FIG. 5 , each of the micro light-emitting diodes  39  includes an N pad  36  and a P pad  37 . The N pad  36  and the P pad  37  are pointed at the driver IC  11 . The N pads  36  of the micro light-emitting diodes  39  are electrically connected to the elongated negative electrodes  24 . The P pads  37  of the micro light-emitting diodes  39  are electrically connected to the elongated positive electrodes  25 . The bonding pads  17  are electrically connected to the circuit board  20  so that the light-emitting units  33 , the electrically connecting layer  28 , the driver IC  11  and the circuit board  20  together form an electric loop to energize the micro light-emitting diodes  39 . 
     The circuit board  20  is a printed circuit board (“PCB”), a printed wiring board (“PWB”), a polyimide (“PI”) board or a glass substrate. At least one cable  21  is used to electrically connect the circuit board  20  to at least one controller  22 . The controller  22  is programmable to turn on and off the driver IC  11  through the electrically connecting layer  28 . 
     Referring to  FIG. 6 , a Laser-Lift-Off (“LLO”) technique is used to separate the extensive layer  32  from the crystal layer  31 . Thus, the group of micro light-emitting diodes  39  is still connected to the driver IC  11  after the separation. 
     A color conversion layer  40  is laid on the micro light-emitting diodes  39 . The color conversion layer  40  is preferably a quantum dot color filter (“QDCF”). 
     The micro light-emitting diodes  39  emit light beams to the color conversion layer  40  as indicated by an arrow head  41  when the circuit board  20  is turned on. The color conversion layer  40  turns the light beams of a color into light beams of red, green and blue. The light beams of red, green and blue then go out of the display  10 . The controller  22  is used to correct brightness of the micro light-emitting diodes  39  so that the display shows desired colors and brightness. 
     Referring to  FIG. 7 , each of the elongated negative electrodes  24  extends parallel to an X-axis so that the elongated negative electrodes  24  are not connected to one another. Each of the elongated positive electrodes  25  extends parallel to a Y-axis so that the elongated positive electrodes  25  are not connected to one another. Some of the micro light-emitting diodes  39  do not emit light beams even if one of the elongated negative electrodes  24  transmits electricity to the N pads  36  of these micro light-emitting diodes  39 . Similarly, some of the micro light-emitting diodes  39  do not emit light beams even if one of the elongated positive electrodes  25  transmits electricity to the P pads  37  of these micro light-emitting diodes  39 . Thus, only a micro light-emitting diode  39  that is connected to one of the elongated negative electrodes  24  and one of the elongated positive electrodes  25  cast a light beam. The layout of the display  10  helps control a current or voltage through each of the light-emitting diodes  39 . 
     Referring to  FIG. 8 , several light-emitting units  33  are used together to provide a display of a large size. Due to the use of the above-mentioned layout, multiple light-emitting units  33  are electrically connected to the faces  13  of the bases  12  of multiple driver ICs  11 . The face  13 . The face  14  of the bases  12  of the driver ICs  11  are electrically connected to the bonding pads  17 . Thus, the driver ICs  11  can control a current or voltage through each of the light-emitting diodes  39 . 
     For example, multiple light-emitting units  33  are used together to provide a value of PPI of 180×180 and each driver IC  11  provides a value of PPI of 30×30. Thus, it takes only six driver ICs  11  that are arranged along a diagonal line of the array of light-emitting units  33  to control all the micro light-emitting diodes  39  of the display equipped  10 . 
     In another embodiment, the display  10  does not include any color conversion layer  40 , i.e., QDCF. Instead, each driver IC  11  of the display  10  is electrically connected to three groups of micro light-emitting diodes. The micro light-emitting diodes in the first group emit red light. The micro light-emitting diodes in the second group emit green light. The micro light-emitting diodes in the third group emit blue light. Each driver IC  11  is electrically connected to the circuit board  20 . The color conversion layer  40  is not essential when techniques for massive transfer of micro light-emitting diodes mature. The display  10  is reduced by omitting the color conversion layer  40 . 
     As discussed above, the display  10  is advantageous in several aspects. Firstly, the light-emitting units  33 , each of which includes multiple micro light-emitting diodes  39 , are cut from the wafer. There is no need to cut the micro light-emitting diodes  39 , one by one, from the wafer. There is no need to transfer a very large number of separated micro light-emitting diodes  39 . There is no need to precisely locate the micro light-emitting diodes  39 , one by one. 
     Secondly, the process for electrically connecting the driver ICs  11  to the micro light-emitting diodes  39  is simplified. The related cost is reduced. 
     Thirdly, the precision of connecting the micro light-emitting diodes  39  to the electrode strips  24  and  25  is improved. The yield of the making of displays is increased. 
     The present invention has been described via the illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.