Patent Publication Number: US-2022216366-A1

Title: Method for transferring light emitting elements, display panel, method for making display panel, and substrate

Description:
FIELD 
     The subject matter herein generally relates to display field, and particularly relates to a method for transferring light emitting elements, a display panel, a method for making the display panel, and a substrate. 
     BACKGROUND 
     The size of a light emitting element such as light emitting diode (LED) always tends towards being made smaller, and it becomes increasingly difficult to transfer a large number of light emitting elements to a receiving substrate. 
     Therefore, there is room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present disclosure will now be described, by way of embodiment, with reference to the attached figures. 
         FIG. 1  shows the result of step  11  as a cross-sectional view illustrating transferred light-emitting elements in an embodiment of a method. 
         FIG. 2  shows the result of step  12  as a cross-sectional view of light-emitting elements in the method of  FIG. 1 . 
         FIG. 3  shows the result of S 13  of the method. 
         FIG. 4  shows projections of a magnetic shielding layer and a receiving area shown in  FIG. 3 . 
         FIG. 5  shows a receiving substrate of  FIG. 3  made according to the method. 
         FIG. 6  is an arrangement diagram of coils of the receiving substrate shown in  FIG. 5 . 
         FIG. 7  is a schematic diagram of distribution of magnetic lines of force after the coils shown in  FIG. 5  is energized. 
         FIG. 8  shows projections of the electromagnetic unit and the receiving area of the receiving substrate shown in  FIG. 3  according to an embodiment on the substrate. 
         FIG. 9  shows projections of the electromagnetic unit and the receiving area of the receiving substrate shown in  FIG. 3  according to another embodiment on the substrate. 
         FIGS. 10, 11, 12  show the results of step  14  of the method as a cross-sectional view of transferred light emitting elements. 
         FIG. 13  shows the results of step  15  of the method as a cross-sectional view of transferred light emitting elements. 
         FIGS. 14 and 15  show the results of step  16  of the method as a cross-sectional view of transferred light emitting elements. 
         FIG. 16  shows a display panel in cross section made according to step  27  of the method. 
         FIG. 17  shows a display panel made according to step  28  of the method. 
         FIG. 18  shows a display panel in cross section made according to step  29  of the method. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the exemplary embodiments described herein may be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the exemplary embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one”. The term “circuit” is defined as an integrated circuit (IC) with a plurality of electric elements, such as capacitors, resistors, amplifiers, and the like. 
     A method for transferring light emitting elements is disclosed. The method is provided by way of embodiment, as there are a variety of ways to carry out the method. The method described below can be carried out using the configurations illustrated in  FIGS. 1 through 14  for example, and various elements of these figures are referenced in explaining the method. Each block in this method represents one or more processes, methods, or subroutines, carried out in the method. Additionally, the illustrated order of blocks is by example only and the order of the blocks can change. The method can begin at Block S 11 . 
     Block S 11 :  FIG. 1  shows a plurality of light emitting elements  10  provided. 
     As shown in  FIG. 1 , the light emitting elements  10  are spaced apart from each other on a carrier substrate  20 . Each light emitting element  10  includes a P-type doped inorganic light-emitting material layer  12 , an N-type doped inorganic light-emitting material layer  14 , and an active layer  13  between the P-type doped inorganic light-emitting material layer  12  and the N-type doped inorganic light-emitting material layer  14 . 
     In one embodiment, the carrier substrate  20  is a growth substrate such as sapphire or the like. In other embodiments, the carrier substrate  20  is a platform on which the light emitting elements  10  can be placed. 
     In one embodiment, a first electrode  11  and a second electrode  15  are connected to opposite ends of each light emitting element  10 . The first electrode  11  and the second electrode  15  may each be in the form of a magnetic material layer  16 , one layer of a certain magnetic pole and the other layer  16  of opposite polarity. The P-type doped inorganic light-emitting material layer  12  is electrically connected to the first electrode  11 , and the N-type doped inorganic light-emitting material layer  14  is electrically connected to the second electrode  15 . That is, the first electrode  11  and the second electrode  15  are of opposite magnetic poles. For example, the magnetic pole of the first electrode  11  is N pole, the magnetic pole of the second electrode  15  is S pole, or the magnetic pole of the first electrode  11  is S pole and the magnetic pole of the second electrode  15  is N pole. 
     In another embodiment, the magnetic material layer  16  is not used as an electrode of the light emitting element  10 . The first electrode  11  and the second electrode  15  of each light emitting element  10  are of a magnetic material layer  16  of opposite magnetic properties. 
     In another embodiment, only the first electrode  11  or only the second electrode  15  of each light emitting element  10  is in the form of a magnetic material layer  16 . One end of each light emitting element  10  connected to the magnetic material layer  16  is arranged facing upward on the carrier substrate  20 . 
     In one embodiment, the magnetic material layer  16  may be made of a magnetic material, such as an aluminum-nickel-cobalt permanent magnet alloy, an iron-chromium-nickel permanent magnet alloy, a permanent magnet ferrite, other rare earth permanent magnet materials, or a composite permanent magnet material composed of the above materials. 
     In one embodiment, the light emitting element  10  is a conventional light emitting diode (LED), mini LED or micro LED. “Micro LED” means LED with grain size less than 100 microns. “Mini LED” is also a sub-millimeter LED, and its size is between conventional LED and micro LED. The mini LED generally means LED with grain size of about 100 microns to 200 microns. 
     Block S 12 :  FIG. 2  shows a first electromagnetic plate  30 . 
     The first electromagnetic plate  30  may be made of a material having magnetism when energized and having no magnetism when not energized. An insulating nonmagnetic material layer  31  is on a surface of the first electromagnetic plate  30 . The insulating nonmagnetic material layer  31  defines a plurality of through holes  33  spaced apart from each other, and the surface of the first electromagnetic plate  30  is exposed from the through holes  33 . Each through hole  33  is defined as one adsorption position  32 . Each adsorption position  32  is capable of magnetically attracting one light emitting element  10  on being energized. The adjacent through holes  33  are spaced apart from each other by the insulating nonmagnetic material layer  31 . 
     When the first electromagnetic plate  30  is energized, its positions correspond to each of the through holes  33  (i.e., the exposed surface of the first electromagnetic plate  30 ). The plate  30  can magnetically adsorb the magnetic material layer  16  at one end of the light emitting element  10 , thereby adsorbing one of the light emitting elements  10  in one of the through holes  33 , while other positions do not adsorb any light emitting element  10 . That is, when the first electromagnetic plate  30  is energized, only the positions corresponding to the through holes  33  have magnetic properties. A size of each through hole  33  is slightly larger than the size of one of the light emitting elements  10  but each of the through holes  33  is sized to adsorb only one of the light emitting elements  10 . 
     In one embodiment, the insulating nonmagnetic material layer  31  may be made of a polyimide-based composite material. 
     In one embodiment, a mechanical arm (not shown) is further provided on a side of the first electromagnetic plate  30  away from the insulating nonmagnetic material layer  31  to grasp and manipulate the first electromagnetic plate  30  in any orientation. 
     In one embodiment, a control circuit (not shown) is further provided corresponding to the first electromagnetic plate  30 . The control circuit is configured to supply a voltage or current to the first electromagnetic plate  30  to make the first electromagnetic plate  30  magnetic. In addition, a magnetic strength of the first electromagnetic plate  30  can be controlled by adjusting a magnitude of the voltage or current applied to the first electromagnetic plate  30  by the control circuit. 
     Block S 13 : a receiving substrate  40  is provided. 
     As shown in  FIG. 3 , the receiving substrate  40  includes a base layer  41 , an electromagnetic circuit layer  43  on a side of the base layer  41 , a magnetic shielding material layer  46  on a side of the electromagnetic circuit layer  43  away from the base layer  41 , and a bonding layer  45  on a side of the magnetic shielding material layer  46  away from the base layer  41 . The bonding layer  45  defines a plurality of receiving areas  450 , and each receiving area  450  is configured for receiving one of the light emitting elements  10 . In the first electromagnetic plate  30  shown in  FIG. 2 , the through holes  33  and the receiving areas  450  correspond to each other in number and position. 
     As shown in  FIGS. 3 and 4 , the magnetic shielding material layer  46  defines a plurality of openings  461 , and each opening  461  is arranged to correspond to one of the receiving areas  450 , to allow a magnetic field to pass through. 
     In one embodiment, the magnetic shielding material layer  46  may be made of a magnetic material, such as nickel, iron, cobalt, an aluminum-nickel-cobalt permanent magnet alloy, an iron-chromium-nickel permanent magnet alloy, a permanent magnet ferrite, other rare earth permanent magnet materials or a composite permanent magnet material composed of the above materials. 
     Since the magnetic shielding material layer  46  may be made of a magnetic material and has good magnetic permeability, the magnetic lines of force entering the magnetic shielding material layer  46  are mostly concentrated at the position where the magnetic shielding material layer  46  is provided with the opening  461 . That is, in the positions where the magnetic shielding material layer  46  has no opening  461 , the magnetic field is obstructed, and most of the magnetic lines of force are blocked; at the position of the opening  461  of the magnetic shielding material layer  46 , the magnetic field can pass through unobstructed. 
     In one embodiment, the receiving substrate  40  is a thin film transistor (TFT) substrate. The bonding layer  45  includes a TFT array layer  451  on a side of the magnetic shielding material layer  46  away from the base layer  41  and a pixel defining layer  452  on a side of the TFT array layer  451  away from the base layer  41 . The pixel defining layer  452  defines a plurality of contact holes  453  exposing the TFT array layer  451 , and each contact hole  453  is defined as one of the receiving areas  450 . 
     In one embodiment, the base layer  41  may be made of a rigid material, such as glass, quartz, silicon wafer. In other embodiments, the base layer  41  may be made of a flexible material such as polyimide (PI) or polyethylene terephthalate (PET). 
     In one embodiment, the receiving substrate  40  further includes an insulating layer  44  between the electromagnetic circuit layer  43  and the TFT array layer  451 . The insulating layer  44  electrically insulates the electromagnetic circuit layer  43  and the thin film transistor array layer  451  to prevent the TFT array layer  451  from affecting the electromagnetic circuit layer  43  during the transfer of the light emitting elements  10 . The insulating layer  44  may be made of a silicon oxide (SiOx) layer, a silicon nitride (SiNx) layer, or a multiple layer including the silicon oxide (SiOx) layer and the silicon nitride (SiNx) layer. 
     In one embodiment, the receiving substrate  40  further includes a barrier layer  42  between the base layer  41  and the electromagnetic circuit layer  43  to prevent moisture, oxygen, and the like from affecting the properties of the electromagnetic circuit layer  43  and the TFT array layer  451 . The barrier layer  42  may be made of a silicon oxide (SiOx) layer, a silicon nitride (SiNx) layer, or a multiple layer thereof including the silicon oxide (SiOx) layer and the silicon nitride (SiNx) layer. 
     As shown in  FIG. 5 , the steps involved in the process of making the TFT substrate are: sequentially forming the barrier layer  42 , the electromagnetic circuit layer  43 , the insulating layer  44  and the magnetic shielding material layer  46  on the base layer  41 , wherein forming the magnetic shielding material layer  46  includes a patterning process to define the openings  461 . Then, forming the TFT array layer  451  and the pixel defining layer  452 , wherein the TFT array layer  451  includes a first buffer layer  51 , a second buffer layer  52 , a plurality of TFTs  53  (only one is shown), a first interlayer dielectric layer  54 , a second interlayer dielectric layer  55 , an overcoat layer  56 , and a plurality of contact electrodes  57  (only one is shown). 
     In one embodiment, as shown in  FIG. 3 , the first buffer layer  51  fills the openings  461 . The first buffer layer  51 , the second buffer layer  52 , the first interlayer dielectric layer  54 , the second interlayer dielectric layer  55 , and the overcoat layer  56  may be made of a silicon oxide (SiOx) layer, a silicon nitride (SiNx) layer, or multiple layers including the silicon oxide (SiOx) layer and the silicon nitride (SiNx) layer. The contact electrode  57  may be made of a non-magnetic conductive material, such as indium tin oxide (ITO), indium zinc oxide (IZO), and zinc oxide (ZnO). 
     As shown in  FIG. 5 , each of the TFTs  53  includes a gate electrode GE, a semiconductor layer AS, a gate insulating layer GI, a source electrode SE, and a drain electrode DE. The overcoat layer  56  defines a plurality of vias  561 , each via  561  exposes the drain electrode DE of one TFT  53 . The drain electrode DE of each of the TFTs  53  is electrically connected to the corresponding contact electrode  57  through one of the vias  561 . The contact hole  453  (receiving area  450 ) defined on the pixel defining layer  452  exposes the contact electrode  57  for electrically connecting to one of the light emitting elements  10 . 
     In one embodiment, each of the gate electrode GE, the source electrode SE, and the drain electrode DE may be made of one of molybdenum (Mo), aluminum (Al), gold (Au), titanium (Ti), copper (Cu), or a combination thereof. In other embodiments, each of the gate electrode GE, the source electrode SE, and the drain electrode DE are multiple layers formed of one of molybdenum (Mo), aluminum (Al), gold (Au), titanium (Ti), neodymium (Nd), copper (Cu), or a combination thereof. For example, each of the gate electrode GE, the source electrode SE, and the drain electrode DE is formed as a double layer of Mo/Al. In one embodiment, the gate electrode GE, the source electrode SE, and the drain electrode DE may be made of non-magnetic conductive materials. The gate insulating layer GI may be made of a silicon oxide (SiOx) layer, a silicon nitride (SiNx) layer, or multiple layers including the silicon oxide (SiOx) layer and the silicon nitride (SiNx) layer. The semiconductor layer AS may be made of a silicon semiconductor or an oxide semiconductor. 
     In one embodiment, the TFT substrate defines a plurality of pixels, and each pixel includes sub-pixels emitting light of different colors. Each sub-pixel corresponds to one light emitting element  10 . 
     In one embodiment, each pixel includes a red (R) sub-pixel, a green (G) sub-pixel, and a blue (B) sub-pixel. The R, G, and B sub-pixels correspond to a light emitting element  10  emitting red, green and blue light, respectively. 
     In other embodiments, each pixel may include R, B, and W (white) sub-pixels. The W sub-pixel corresponds to one light emitting element  10  emitting white light. Each pixel may further include multi-color sub-pixels, and each multi-color sub-pixel corresponds to one light emitting element  10  emitting multiple colors. 
     The electromagnetic circuit layer  43  includes a plurality of coils  4311  (labeled in  FIG. 6 ). The coils  4311  are arranged on the same plane and are in one same layer. Each of the coils  4311  generates a magnetic field upon energization, and generates an attractive or repulsive force to a magnet (e.g., the magnetic material layer  16  of the light emitting element  10 ) within the magnetic field. 
     In one embodiment, the material of each layer between the receiving areas  450  and the electromagnetic circuit layer  43  (e.g., the insulating layer  44 , the first buffer layer  51 , the second buffer layer  52 , the first interlayer dielectric layer  54 , the second interlayer dielectric layer  55 , the TFTs  53 , the overcoat layer  56 , and the contact electrodes  57 ) are made of a non-magnetic material. Therefore, the magnetic field lines of the magnetic field generated when the coils  4311  are energized can pass through the openings  461 , and reach each receiving area  450  without obstruction; corresponding to the positions where the magnetic shielding material layer  46  having no opening  461 , the magnetic lines are obstructed by the magnetic shielding material layer  46 , and are concentrated at the positions of the receiving areas  450 . Thus, during the transfer process, the alignment accuracy of the subsequent light emitting elements  10  is improved, and the transfer error is reduced. 
     In one embodiment, the electromagnetic circuit layer  43  further includes a power supply (not shown) for supplying power to the coils  4311 . The coils  4311  are electrically connected to the power supply. When a current is applied to the coils  4311  by the power supply, the coils  4311  generate a magnetic field. By adjusting the current direction flowing through the coils  4311 , the magnetic pole direction of the magnetic field generated by the coils  4311  can be adjusted, thereby the direction of the magnetic force generated between the coils  4311  and the magnetic material layer  16  of each light emitting elements  10  can be controlled. By adjusting the magnitude of the current flowing through the coils  4311 , the magnitude of the magnetic force generated between the coils  4311  and the magnetic material layer  16  of each light emitting element  10  can be adjusted. 
     In other embodiments, the electromagnetic circuit layer  43  does not include the power supply, and the coils  4311  are electrically connected to an external power supply from which the current is applied to the coils  4311 . 
     As shown in  FIG. 6 , the coils  4311  are spaced apart from each other. Each coil  4311  includes an annular portion  4311   a  and two connecting portions  4311   b  extending from ends of the annular portion  4311   a . The connecting portions  4311   b  of each coil  4311  are electrically connected to the power supply of the electromagnetic circuit layer  43  or to the external power supply. 
     The annular portions  4311   a  extend to form a plurality of concentric circles. Inner diameters R 1  of the annular portions  4311   a  sequentially increase in a direction away from the center of the concentric circle, and the annular portions  4311   a  are equally spaced. The line width D of each coil  4311  may be the same, for example, 3.5 microns. The line pitch L of adjacent coils  4311  may be the same, for example, 5 microns. In one embodiment, the inner diameter R 1  of the annular portion  4311   a  of each coil  4311  is at least 13 microns and the outer diameter R 2  of the annular portion  4311   a  of each coil  4311  is not more than 50 microns. In other embodiments, the inner diameter R 1  of the annular portion  4311   a  of each coil  4311  is at least 16 microns and the outer diameter R 2  of the annular portion  4311   a  of each coil  4311  is not more than 90 microns. The parameters such as the line width D, the line pitch L, the inner diameter R 1 , and the outer diameter R 2  can be adjusted according to the demand for the strength of the magnetic field. 
     In addition, the density of the coils  4311  can also be adjusted according to the demand for the strength of the magnetic field. That is, the coils  4311  may be arranged at unequal intervals as required by actual needs. For example, if a strong magnetic field is required, the arrangement of the coils  4311  is dense, and the line pitch L of the adjacent coils  4311  is small; if a weak magnetic field is required, the arrangement of the coils  4311  is sparse, and the line pitch L of the adjacent coils  4311  is large. 
     It should be noted that in the electromagnetic circuit layer  43 , each coil  4311  keeps the plane of its annular portion  4311   a  perpendicular to a thickness direction of the receiving substrate  40 , so that the direction of the magnetic field generated by each coil  4311  is approximately the thickness direction of the receiving substrate  40 . 
     As shown in  FIG. 7 , when the coil  4311  (only one is shown) is fed with the current, the magnetic field generated by the coil  4311  is perpendicular to the plane of the annular portion  4311   a  of the coil  4311 . That is, the direction of the magnetic field generated by the coil  4311  is approximately along the thickness direction of the receiving substrate  40 . 
     In one embodiment, the electromagnetic circuit layer  43  is arranged over an entire surface. That is, the coils  4311  are not only arranged to correspond to the receiving areas  450 , but are also arranged to correspond to positions between adjacent two receiving areas  450 . The insulating layer  44  fills gaps between the adjacent coils  4311  to electrically insulate the adjacent two coils  4311 . 
     In another embodiment, as shown in  FIGS. 8 and 9 , the electromagnetic circuit layer  43  is not arranged over the entire surface. The electromagnetic circuit layer  43  includes a plurality of electromagnetic units  431  spaced apart from each other. Each of the electromagnetic units  431  includes a plurality of coils  4311  (labeled in  FIG. 6 ). Each of the electromagnetic units  431  corresponds to at least one of the receiving areas  450 . The insulating layer  44  fills gaps between any adjacent two coils  4311  in one electromagnetic unit  431  and gaps between adjacent two electromagnetic units  431  to electrically insulate the coils  4311 . 
     As shown in  FIG. 8 , each electromagnetic unit  431  corresponds to and aligns with one of the receiving areas  450 . A projection of each electromagnetic unit  431  on the base layer  41  completely covers a projection of its corresponding receiving area  450  on the base layer  41 . That is, each electromagnetic unit  431  is arranged to correspond to one sub-pixel. 
     As shown in  FIG. 9 , each electromagnetic unit  431  corresponds to three adjacent receiving areas  450 . The projection of each electromagnetic unit  431  on the base layer  41  completely covers the projection of its corresponding three receiving areas  450  on the base layer  41 . That is, each electromagnetic unit  431  is arranged to correspond to three or more than three sub-pixels. 
     A shape of each electromagnetic unit  431  is not limited, for example, it may be circular as shown in  FIG. 8  or rectangular as shown in  FIG. 9 . 
     Block S 14 : as shown in  FIGS. 10 through 12 , the first electromagnetic plate  30  is energized to magnetically adsorb one light emitting element  10  at each adsorption position  32 . 
     As shown in  FIG. 10 , the first electromagnetic plate  30  is moved above the carrier substrate  20 , and the through holes  33  are aligned with the light emitting elements  10  on the carrier substrate  20  one by one, each of through holes  33  being aligned with one of the light emitting elements  10 . 
     As shown in  FIG. 11 , after the through holes  33  and the light emitting elements  10  are aligned one by one, the control circuit in the first electromagnetic plate  30  is turned on, and a voltage or current is applied to the first electromagnetic plate  30  by the control circuit. When the voltage or current is applied to the first electromagnetic plate  30 , the first electromagnetic plate  30  generates magnetism opposite to the magnetic pole of the first electrode  11  (i.e., magnetic material layer  16 ) of each light emitting element  10 . 
     As shown in  FIG. 12 , the light emitting elements  10  are attracted to the corresponding through holes  33  due to the magnetic force between the light emitting element  10  and the first electromagnetic plate  30 . The positions of the first electromagnetic plate  30  corresponding to each through hole  33  can adsorb one of the light emitting elements  10 . The positions of the first electromagnetic plate  30  having no through holes  33  do not absorb any of the light emitting elements  10  due to the insulating non-magnetic material layer  31 . 
     Block S 15 : A surface of the first electromagnetic plate  30  on which the light emitting elements  10  are magnetically adsorbed is opposite to a surface of the receiving substrate  40  defining the receiving areas  450 , and the light emitting elements  10  are aligned with the receiving areas  450  one by one. 
     As shown in  FIG. 13 , after the first electromagnetic plate  30  corresponding to the position of each of the through holes  33  adsorbs one light emitting element  10 , the first electromagnetic plate  30  remains energized, and moves over the receiving substrate  40 , so that each of the light emitting elements  10  adsorbed on the first electromagnetic plate  30  is aligned one-to-one with the corresponding receiving area  450  on the receiving substrate  40 . 
     Block S 16 : a current is applied to the coils  4311  to form a magnetic field, and the first electromagnetic plate  30  is switched off so that each of the light emitting elements  10  can be detached from the first electromagnetic plate  30  by the magnetic field and transferred to a corresponding receiving area  450  of the receiving substrate  40 . 
     As shown in  FIG. 14 , after aligning each light emitting element  10  adsorbed on the first electromagnetic plate  30  with the corresponding receiving area  450  on the receiving substrate  40 , the first electromagnetic plate  30  is moved toward the receiving substrate  40  so that each light emitting element  10  abuts and contacts the corresponding receiving area  450 . At the same time, the current is applied to the coils  4311  in the electromagnetic circuit layer  43  to generate a magnetic field. A magnetic force between the magnetic material layer  16  of each light emitting element  10  and the coils  4311  in the electromagnetic circuit layer  43  is generated. The magnetic lines of the magnetic field pass through the openings  461  to reach the receiving areas  450 , and are blocked at the positions of the magnetic shielding material layer  46  which do not have the openings  461 . That is, the magnetic lines of the magnetic field generated by the coils  4311  are concentrated at the receiving areas  450 . 
     As shown in  FIG. 15 , the first electromagnetic plate  30  is powered off, and each of the light emitting elements  10  and its first and second electrodes  11  and  15  are detached from the first electromagnetic plate  30  under the magnetic field and transferred to the corresponding receiving area  450 . Then, the first electromagnetic plate  30  and the insulating nonmagnetic material layer  31  are removed. 
     It should be noted that after the current is applied to the coils  4311  in the electromagnetic circuit layer  43 , the direction of the magnetic field generated by the coils  4311  is perpendicular to the plane in which the annular portion  4311   a  of each coil  4311  is located. That is, the magnetic pole direction of the magnetic field is directed from the receiving substrate  40  to the first electromagnetic plate  30  or from the first electromagnetic plate  30  to the receiving substrate  40 . 
     The direction of the magnetic field generated by the coils  4311  is established by the direction of the current flowing through the coils  4311 , to cause a mutual attraction magnetic force between the coils  4311  and the magnetic material layer  16  of each of the light emitting elements  10 . The magnitude of the magnetic force generated between the coils  4311  and the magnetic material layer  16  of each of the light emitting elements  10  can be adjusted by adjusting the magnitude of the current flowing through the coils  4311 . 
     It should be noted that, in this method, a color of light emitted from each light emitting element  10  is not limited. In this method, after the first electromagnetic plate  30  is energized, the surface of the first electromagnetic plate  30  can magnetically adsorb a large number of light emitting elements  10  at one time, the transfer a mass of the light emitting elements  10  is achieved. 
     In one embodiment, by applying a current to the coils  4311  in the electromagnetic circuit layer  43 , the magnetic field is generated, thereby generating the magnetic force between the magnetic material layer  16  of each of the light-emitting elements  10  and the coils  4311 . The positions of the magnetic shielding material layer  46  which do not have the openings  461  block the magnetic field, but, at the positions of the opening  461 , the magnetic field can pass through. Therefore, after the first electromagnetic plate  30  is powered off, each of the light emitting elements  10  is magnetically attracted by the coils  4311  of the receiving substrate  40  in addition to its own gravity. In addition, interference from magnetic lines of force around the receiving area  450  can be avoided, thereby avoiding the problem of displacement of the light emitting elements  10  during the transfer process. The alignment accuracy of the light emitting elements  10  is improved, and the transfer error is reduced. 
     In one embodiment, a method for making a display panel  100  is also disclosed. The method includes the following Blocks. 
     Block S 21 : the light emitting elements  10  are provided. 
     Block S 22 : the first electromagnetic plate  30  is provided. 
     Block S 23 : the receiving substrate  40  is provided. 
     Block S 24 : the first electromagnetic plate  30  is energized to magnetically adsorb one light emitting element  10  at each adsorption position  32 . 
     Block S 25 : a surface of the first electromagnetic plate  30  on which the light emitting elements  10  are magnetically adsorbed is opposite to a surface of the receiving substrate  40  defining the receiving areas  450 , and the light emitting elements  10  are aligned with the receiving areas  450  one by one. 
     Block S 26 : a current is applied to the coils  4311  to form a magnetic field, and the first electromagnetic plate  30  is powered off so that each of the light emitting elements  10  is detached from the first electromagnetic plate  30  by the magnetic field and transferred to a corresponding receiving area  450  of the receiving substrate  40 . 
     Blocks S 21  to S 26  are the same as Blocks S 11  to S 16  above, and will not be described here. 
     Block S 27 : a planarization layer  60  is formed on a side of the pixel defining layer  452  away from the base layer  41 . 
     As shown in  FIG. 16 , the first electrode  11  of each light emitting element  10  is electrically connected to the TFT array layer  451  through one contact electrode  57 , and the planarization layer  60  fills gaps between adjacent light emitting elements  10  and exposes the first electrode  11  of each light emitting element  10 . 
     Block S 28 : a common electrode layer  70  is formed on the planarization layer  60 . 
     As shown in  FIG. 17 , the common electrode layer  70  is electrically connected to the first electrode  11  of each of the light emitting elements  10 . The common electrode layer  70  may be connected to a driving circuit (not shown) through wires to apply a voltage to the first electrode  11  of the light emitting element  10 . When there is a forward bias between the first electrode  11  and the second electrode  15  of the light emitting element  10 , the light emitting element  10  emits light. 
     Block S 29 : as shown in  FIG. 18 , an encapsulating layer  80  is formed on a side of the common electrode layer  70  away from the planarization layer  60 , thereby obtaining the display panel  100 . 
     In one embodiment, the light emitting elements  10  provided in Block S 21  are light emitting elements which emit one color of light, such as some light emitting elements emitting red, some emitting green, some emitting blue etc., such display panel  100  is a monochrome display panel. The monochrome display panel  100  can be applied to advertising signs, indicator lights, and the like. 
     In one embodiment, the light emitting elements  10  provided in Block S 21  are light emitting elements which emit more than one color of light, such display panel  100  is a color display panel. The color display panel  100  can be applied to mobile phones, tablet computers, smart watches and the like. 
     It should be noted that the electromagnetic circuit layer  43  is only used in the process of transferring the light emitting element  10  to the receiving substrate  40 . When the display panel  100  displays images, the electromagnetic circuit layer  43  does not function, and the electromagnetic circuit layer  43  and the TFT array layer  451  are electrically insulated by the insulating layer  44 , so that the electromagnetic circuit layer  43  does not affect the light emission of the light emitting elements  10 . 
     In one embodiment, a substrate used in a display panel is disclosed. The substrate is the receiving substrate  40 , and will not be described here again. 
     In one embodiment, a display panel is disclosed. The display panel is the display panel  100 , and will not be described again here. 
     It is to be understood, even though information and advantages of the present exemplary embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present exemplary embodiments, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present exemplary embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.