Patent Publication Number: US-10312296-B2

Title: Color conversion layer integration into display substrate with high intensity light sources

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 62/403,742, filed Oct. 4, 2016, which is hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the reduction in the high stress points and direct lines of sight between a light source and a color conversion layer, such as quantum dots (QD), in an optical substrate system for pixels in color displays. 
     BACKGROUND 
     One method of creating a color display is to use color conversion material with a high energy light source. In some structures, the size of the color source is significantly smaller than the pixel size. As a result, the light generated by the light source is very high. For example, if the size of the pixel is Ap and the size of light source is Al, the light generated by the light source should be Ap/Al*L where L is the pixel required light. For example, if the pixel size is 100×100 um 2  and the light source is 10×10 um 2 , the light generated by the light source is at least 100× more than required for the pixel. Generally, the color conversion layers can degrade under such high direct light condition, i.e. a hot spot. 
     An object of the present invention is to overcome the shortcomings of the prior art by reducing the hot spot effect by distributing the light across the pixels using light distributing structures between the light source and the color conversion layer. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a pixel structure comprising: a light source for generating light; a light conversion layer for converting the light to a desired color; and a light distribution structure for distributing the light from the light source onto the conversion layer. 
     In one embodiment, other layers can be also integrated between the light distributor layer and light source. Also, other layers can be integrated after the light conversion, e.g. QD, layers. 
     In another embodiment, to avoid high stress points in the light conversion layer caused by high intensity light, an attenuator or blocking structure is used to reduce or block the light intensity from a direct line of sight between the light source and the light conversion, e.g. QD, layer. 
     In one embodiment, the light distributor is comprised of a light guide. 
     In another embodiment, the light distributor is comprised of reflective layers and a planarization layer. 
     In another embodiment, the light attenuator structure is also used as the light source electrode. 
     In another embodiment, the light attenuator structure is part of the light distributor structure reflective layers. 
     In an embodiment, the reflective layer is used as part of the light source contact. 
     In an embodiment, the light distribution structure comprises a thick transparent layer on top of the light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein: 
         FIG. 1  illustrates an embodiment of a color conversion layer on top of the light source in the pixel. 
         FIG. 2A  illustrates an example of implementing a light distribution structure between a light source and a color conversion layer. 
         FIG. 2B  illustrates another example of implementing a light distribution structure between a light source and a color conversion layer. 
         FIG. 2C  illustrates another example of implementing a light distribution structure between a light source and a color conversion layer. 
         FIG. 3A  illustrates an example of implementing a light distribution structure and a light attenuator between a light source and a color conversion layer. 
         FIG. 3B  illustrates another example of implementing a light distribution structure and a light attenuator between a light source and a color conversion layer. 
         FIG. 4A  illustrates a light guide structure to distribute the lights across a pixel. 
         FIG. 4B  illustrates another light guide structure to distribute the lights across a pixel. 
         FIG. 5A  illustrates a light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 5B  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 5C  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 5D  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 5E  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 5F  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 6A  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 6B  illustrates another light guide structure with an attenuator for reducing the hotspots effect on the color conversion layer. 
         FIG. 7  illustrates a flow diagram for a method in accordance with an embodiment of the present invention. 
         FIG. 8  illustrates a flow diagram for an alternative method in accordance with an embodiment of the present invention. 
         FIG. 9  illustrates a flow diagram for an alternative method in accordance with an embodiment of the present invention. 
         FIG. 10A  illustrates a flow diagram for alternative methods in accordance with embodiments of the present invention. 
         FIG. 10B  illustrates a flow diagram for alternative methods in accordance with embodiments of the present invention. 
         FIG. 11  illustrates various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. 
     Embodiments in the present disclosure are related to the integration of a color conversion layer, e.g. QDs, into an optical substrate system, typically used in color displays. The optical substrate may comprise one or more: micro light emitting diodes (LEDs), organic LEDs, sensors, solid state devices, integrated circuits, micro-electro-mechanical systems (MEMS), and other electronic components. The receiving substrate may be, but is not limited to, a printed circuit board (PCB), a thin film transistor backplane, an integrated circuit substrate, or, in one case of optical micro devices, such as LEDs, a component of a display, for example a driving circuitry backplane. 
     The shape of the light sources used in the embodiments are for illustration purposes and may have different shapes and sizes. The light source devices may have one or more pads on the side that will contact the receiver substrate. The pads may be mechanical, electrical or a combination of both. The one or more pads may be connected to a common electrode or to a row/column of electrodes. The electrodes may be transparent or opaque. The light sources may have different layers. The light sources may be made of different materials, such as organic, inorganic, or combination thereof. 
       FIG. 1  illustrates a pixel structure  10  in accordance with an embodiment of the present invention including a substrate  11  with three sub-pixels defined by light sources  12 - 1 ,  12 - 2  and  12 - 3  mounted thereon with color conversion layers  14 - 1 ,  14 - 2 ,  14 - 3 , e.g. QD layers, mounted thereover. One of the light sources  14 - 1 ,  14 - 2  and  14 - 3  may have no color conversion layer. For example, if a blue light source is used, the blue sub-pixel may be without a color conversion layer. Here, other layers may be used on top of the color conversion layers  14 - 1 ,  14 - 2  and  14 - 3 , such as encapsulation, color filter, electrodes for touch interface. The following description may use one sub-pixel  12 - 1 ,  12 - 2  or  12 - 3  to explain the invention, but the invention may be easily extended to a plurality of sub-pixels, e.g. 2 to 5, and a plurality of pixels for an entire display. 
       FIGS. 2A to 2C  illustrate exemplary embodiments of the display substrate  11  that includes the light sources  12 - 1  and  12 - 2 , and respective light distribution structures  16 - 1  and  16 - 2  to distribute the light before reaching the respective color conversion layers  14 - 1  and  14 - 2 . The light distribution structures may comprise transparent polymer materials, such as: methyl methacrylate styrene (MS) resins with low density, low moisture absorption, and good moldability; methyl methacrylate butadiene styrene, (MBS) resins with a good balance of transparency, strength and fluidity; and transparent acrylonitrile butadiene styrene (ABS) resins. However, other high refractive index, e.g. &gt;1.5, transparent polymer materials may be used, ideally matching the index of the micro device material. 
     There may be pixel circuits (not shown) on the substrate  11 , which may include thin film transistors (TFTs). There may also be a planarization layer between the pixel circuits and the light sources  12 - 1  and  12 - 2 . An electrode or electrodes may connect the pixel circuits to the light source  12 - 1  and  12 - 2 . In one embodiment,  FIG. 2A , the light is distributed and directed away from the substrate  11  to where the color conversion layers  14 - 1  and  14 - 2  are located. In another embodiment,  FIG. 2B , the light is directed toward and through the substrate  11 , which comprises a material transparent to the particular wavelengths of the light. In this case, the light conversion layer  14 - 1  may be located on the substrate  11 , with the light distribution structure  16 - 1  on the light conversion layer  14 - 1 , and between the light source  12 - 1  and the light conversion layers  14 - 1 . The light conversion layer (or layers)  14 - 1  may be located on the other side of the substrate  11  opposite the light sources  12 - 1 . There may also be a planarization layer before the light distribution structures  16 - 1 . 
     With reference to  FIG. 7 , the method of manufacturing the pixel circuit comprises: step  702 , e.g. making at least one group of micro devices  12 - 1  and  12 - 2  on a donor substrate  11  according to a system substrate pattern; step  704 , e.g. covering the light output (input) surface of the micro devices  12 - 1  and  12 - 2  with the color conversion layers  14 - 1  and  14 - 2  and/or color filters; and step  706 , e.g. transferring at least one of the micro devices  12 - 1  and  12 - 2  in a group to a system substrate. 
     The light distribution structure  16 - 1  may be a thick transparent layer, as hereinabove described. In one example, the layer may be more than 3.mu.m. In another example, the side of the transparent layer may be blocked by an opaque or reflective layer(s)  18  for each pixel or sub-pixel. In another example, there may be reflective layer  19  behind or on top of the light source  12 - 1 . 
     With reference to  FIG. 2C , the sides of the light distribution structure  16 - 1  may be formed, e.g. etched, at an internal acute angle to the substrate  11  forming a frusto-pyramidal or frusto-conical structure. The acute angle may be between 30° and 60°, preferably between 40° and 50°, enabling light to be directed outwardly from the light source  12 - 1  at 180°. Similarly, the color conversion layer  14 - 1  would cover the angled sides and the top of the light distribution structure  16 - 1 . 
     However, the thickness of the light distribution structure  16 - 1  may be too large, if the ratio of pixel area to light source area is too big. To eliminate the need for a thick light distribution structure  16 - 1 ,  FIGS. 3A and 3B  illustrate embodiments including a light distribution structure  34  with a light attenuator  38  mounted thereon for reducing the hot spot effect. The light attenuator  38  reduces the light intensity from a direct line of sight from a light source  32 . In the illustrated embodiment, the attenuator  38  may be comprised of a material opaque to the wavelengths of the light thereby blocking direct light from the light source from hitting the light conversion layer  36 . The attenuator structure  38  may act as the contact or electrode of the light source  32 . The light attenuator  38  may include at least one of a semi-transparent, an opaque, and a reflective layer. The attenuator  38  may also be an optical structure that redirects the light. The light attenuator  38  may be a part of the light distribution layer  34 . The light attenuator structure  38  may be directly on top of the light source  32  or there may be other layers between the light source  32  and the light attenuator structure  38 . There may be layers, e.g. of the light distribution structure  34 , between light attenuator structure  38  and the light conversion layer  36 . The attenuator  38  may be directly on or connected to the light conversion layer  36 . Also, the light conversion layer  36  may cover the whole or part of the area over the light attenuator structure  38 .  FIG. 3B  illustrates an alternate embodiment, in which the light source  32  directs the light through the substrate  30 , which is transparent to wavelengths in the light, whereby the light conversion layer  36  may be mounted directly on or over the substrate  30 , with the light distribution layer  34  and the attenuator  38  mounted between the lighter conversion layer  36  and the light source  32 . 
     With reference to  FIG. 8 , the method of manufacturing the pixel circuit comprises: step  802 , e.g. making at least one group of micro devices  32  on a donor substrate  30  according to a system substrate pattern; step  804 , e.g. covering or blocking undesired light paths from the micro devices  32  with opaque or reflective materials, e.g. light attenuator  38 ; step  806 , e.g. covering the light output (input) surface of the micro devices  32  with the color conversion layers  36  and/or color filters; and step  808 , e.g. transferring at least one of the micro devices  32  in a group to a system substrate. 
     There are several ways to implement the attenuator structure  38  and/or the light distribution structure  34 .  FIGS. 4A and 4B  illustrate embodiments in which the light is guided to the sides from a light source  42  and either a top layer  44 - 3  ( FIG. 4A ) or bottom layer  44 - 4  ( FIG. 4B ) of a light distribution structure  44 - 1  enables the light to pass through. A reflector (or a blocking layer)  44 - 2  extending along the sides of the light distribution structure  44 - 1  is used to reflect the light back through the light distribution structure  44 - 1 . The reflector  44 - 2  may be at an acute angle to the substrate  40  for reflecting the light out through the top  44 - 3  layer or bottom layer  44 - 4  of the light distribution structure  44 - 1 . The light pass through the top layer  44 - 3  ( FIG. 4A ) or the bottom layer  44 - 4  ( FIG. 4B ) and then passes through the light conversion layer  46 - 1 . A attenuator structure  48  mounted on or over the light source  42  is used to reduce hot spots caused by direct line of sight transmission of light from the light source  42 . The attenuator structure  48  may also comprise a connection electrode for the light source  42 . There can be layers before  46 - 2  and after  46 - 3  the light conversion layer  46 - 1 . These layers can have different functionalities.  FIG. 4B  illustrates an alternate embodiment, in which the light source  42  directs the light through the substrate  40 , which is transparent to wavelengths in the light, whereby the light conversion layer  46 - 1  may be mounted directly on or over the substrate  40 , with the light distribution layer  44 - 1  and/or the attenuator  48  mounted between the lighter conversion layer  46 - 1  and the light source  42 . 
     With reference to  FIG. 9 , the method of manufacturing the pixel circuit comprises: step  902 , e.g. making at least one group of micro devices  42  on a donor substrate  40  according to a system substrate pattern; step  904 , e.g. covering or blocking undesired light paths from the micro devices  42  with opaque or reflective materials, e.g. light attenuator  48 ; step  906 , e.g. covering the light output (input) surface of the micro devices  42  with the color conversion layers  46 - 1  and/or color filters; step  908 , depositing layers  46 - 2  and  46 - 3  before and/or after the color conversion layers  46 - 1  for encapsulation and/or heat dissipation; and step  910 , e.g. transferring at least one of the micro devices  42  in a group to a system substrate. 
     Another configuration for a light distribution and a light attenuator structure is demonstrated in  FIGS. 5A to 5F . In  FIGS. 5A and 5B , a sub-pixel  51  includes a base reflector layer  54 - 3  mounted on a substrate  50  with a light source  52  mounted thereon. A light distribution layer  54 - 1  is disposed over the light source  52  and the base reflector layer  54 - 3 . The light distribution layer  54 - 1  includes sides formed, e.g. etched, at an acute angle, e.g. 30.degree.-60.degree., ideally 40.degree.-50.degree., to the substrate  50  forming a frusto-pyramidal or frusto-conical shape. The angled sides of the light distribution layer  54 - 1  are then covered, e.g. coated, with angled side reflectors  54 - 2  at the same angle to the substrate  50 . An attenuator  58  is mounted on or over the light source  52  for preventing a direct line of sight from the light source  52  to a light conversion layer  56 - 1  disposed over the light distribution layer  54 - 1 . Additional layers  56 - 2  and  56 - 3  may also be provided. The base reflector  54 - 3  and the angled side reflectors  54 - 2  redirect the light from the light source  52 , perhaps multiple times, back through the light conversion layer  56 - 1  and then finally out through the light conversion layer  56 - 1 . The attenuator layer  58  may also act as reflecting layer and reflect the light from the light source  52  toward the base reflector  54 - 3 . The combination of reflectors  54 - 3 ,  54 - 2  and  58  reduces the hot spot problem, i.e. the high light intensity at a direct line of sight from the light source  52  to the light conversion layer  56 - 1 , and distributes the light across the pixel  51 .  FIG. 5B  illustrates an embodiment in which the light distribution layer  54 - 1  is mounted, e.g. coated, over the entire base reflector  54 - 3  with the angled side reflectors  54 - 2  extending down to the substrate  50 , in contrast to  FIG. 5B , in which the base reflector  54 - 3  extends the entire width of the pixel  51 , whereby the angled side reflectors  54 - 2  extend proximate to the base reflector  54 - 3 . 
       FIGS. 5C and 5D  are substantially identical to  FIGS. 5A and 5B , except that the attenuator  58  is mounted directly on the light source  52 , and acts as a contact layer therefor. The contact  58  may be electrical or just mechanical. The contact  58  may be connected to some other structure, e.g. electrical traces or mechanical structure, through a via. The contact  58  may also be connected to the angled side reflectors  54 - 2  through a patterned trace or through a common electrode. The contact  58  may also be connected to a common electrode. In this case, the common electrode can be deposited on top of the attenuator  58  after a possible dielectric layer with an opening at the attenuator  58 . The common electrode may be either patterned into rows or columns or a single layer that connects an array of the pixels  51 C or  51 D in the display. The base reflector layer  54 - 3  may be extended beyond the angled side reflector layer  54 - 2 , as hereinbefore discussed. In the case where the base reflector layer  54 - 3  is not extended beyond the angled side layer  54 - 2 , the angled side layer  54 - 2  may cover the whole pixel structure  51 , as demonstrated in  FIGS. 5B and 5D . 
     With reference to  FIG. 10A , the method of manufacturing the pixel circuit comprises: step  1002 , e.g. making at least one group of micro devices  52  on a donor substrate  50  according to a system substrate pattern; step  1004 , e.g. covering or blocking undesired light paths from the micro devices  52  with opaque or reflective materials, e.g. light attenuator  58 ; step  1006 , e.g. covering the light output (input) surface of the micro devices  52  with the color conversion layers  56 - 1  and/or color filters, wherein the color conversion layers may include a dielectric layer for passivation; step  1008 , depositing layers  56 - 2  and  56 - 3  before and/or after the color conversion layers  56 - 1  for encapsulation and/or heat dissipation; and step  1010 , e.g. transferring at least one of the micro devices  52  in a group to a system substrate. 
     In the embodiment illustrated in  FIGS. 5E and 5F , the light distribution layer  54 - 1  is substantially the same as in  FIGS. 5A to 5D , but the light conversion layer  56 - 1  is mounted, e.g. coated, proximate to the substrate  50 , whereby the light is directed from the light source  52  through the substrate  50 , which is transparent to wavelengths in the light. The attenuator  58  is positioned on or above the light conversion layer  56 - 1  between the light source  52  and the light conversion layer  56 - 1 . A cover reflector  54 - 4 , e.g. a reflective coating, is disposed over the entire light distribution layer  54 - 1 , including the angled sides, for reflecting the light back toward and through the color conversion layer  56 - 1 , and the substrate  50 . There may be layers before  56 - 2  and after  56 - 3  the light conversion layer  56 - 2 . In  FIG. 5F , at least a portion of the cover reflector  54 - 2  may contact the light source  52  directly, and act as a contact for the light source  52 . 
     With reference to  FIG. 10B , the method of manufacturing the pixel circuit comprises: step  1002 , e.g. making at least one group of micro devices  52  on a donor substrate  50  according to a system substrate pattern; step  1004 , e.g. covering or blocking undesired light paths from the micro devices  52  with opaque or reflective materials, e.g. light attenuator  58 ; step  1006 , e.g. covering the light output (input) surface of the micro devices  52  with the color conversion layers  56 - 1  and/or color filters, wherein one of the color conversion layers or the light attenuator  58  may include a conductive layer acting as an electrode for the micro device  52 ; step  1008 , depositing layers  56 - 2  and  56 - 3  before and/or after the color conversion layers  56 - 1  for encapsulation and/or heat dissipation; and step  1010 , e.g. transferring at least one of the micro devices  52  in a group to a system substrate. 
       FIGS. 6A and 6B  illustrate another embodiment of a sub-pixel structure  61  including a light distribution structure  64  with diverging sides in the direction of light transmission formed at an internal obtuse angle to a substrate  60  (acute angle externally). A base reflector layer  64 - 2 , provided on the bottom and angled side surfaces of the light distribution layer  64 , also at the same angle as the sides of the light distribution structure  64 , reflects the light from a light source  62  away from the substrate  60  and up through a light conversion layer  66 - 1 . A light attenuator  68  mounted over the light source  62 , e.g. on a top surface of the light distribution layer  64 , eliminates hot spot effects on the light conversion layer  66 - 1 . The embodiment illustrated in  FIG. 6B  is substantially the same as the one in  FIG. 6A , except that the light attenuator structure  68  extends into contact with the light source  62 , and thereby may act as a contact for the light source  62  to an external source of electricity. 
     In all the structures, the conversion layer  66 - 1  may be deposited over a bank structure  66 - 2 , in which a layer generally organic or dielectric layer is deposited. The bank structure layer  66 - 2  may be patterned to open the layer in the area where light conversion layer  66 - 1  will be deposited. 
     With reference to  FIGS. 11 a  to 11 c   , the transfer process is illustrated, in which a donor substrate  1102  initially includes three micro devices  1104 . Each of the micro device  1104  includes an electrode  1106 , which may be transparent, but ideally comprises an opaque or reflective material providing a light attenuator function. The middle micro device  1104  includes, e.g. is coated with, a first color conversion or filter layer  1108  for converting the emitted light from the micro device  1104  into a different color. The left micro device  1104  includes, e.g. is coated with, a second color conversion or filter layer  1110  for converting the emitting light from the micro device  1104  into a third color. Together the three micro devices  1104  may comprise the three different colors, e.g. red, green and blue, required to form a pixel for a display device. 
     In a first embodiment, the three micro devices  1104  are transferred to a cartridge substrate, and provided with a second electrode  1116  mounted on the opposite end of the micro device  1104  as the electrode  1106 . The second electrode  1116  may be comprised of an opaque or reflective material for redirecting any light from the micro device  1104  back through any light distribution material, around any light attenuator structure and through any color conversion layer  1108  or  1110 . Each of the micro devices  1104  are then mounted on pads  1114  on a receiver substrate  1112  ( FIG. 11 b   ), with the second electrode  1116  in electrical contact with the pad  114 . 
     Alternatively, as illustrated in  FIG. 11 c   , the three micro devices  1104  may be directly transferred to the receiver substrate  1112  with the electrode  1106  in contact with the pads  1114 . In this embodiment, the receiver substrate  1112  and the pads  1114  may be transparent to the light emitted from the micro devices  1104  and any subsequent conversion. 
     The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.