Patent Publication Number: US-2022231088-A1

Title: Method of integrating functional tuning materials with micro devices and structures thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Non-Provisional application Ser. No. 17/346,457, filed on Jun. 14, 2021, now allowed, which is a continuation of U.S. Non-Provisional patent application Ser. No. 16/901,828, filed on Jun. 15, 2020, which is a continuation of U.S. Non-Provisional patent application Ser. No. 16/420,580, filed on May 23, 2019, now U.S. Pat. No. 10,707,277, issued on Jul. 7, 2020, which is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 15/724,319, filed on Oct. 4, 2017, now U.S. Pat. No. 10,312,296, issued on Jun. 4, 2019, which claims priority to and the benefit of U.S. Provisional Patent Application No. 62/403,742, filed on Oct. 4, 2016, which are incorporated herein by reference in their entireties. U.S. Non-Provisional application Ser. No. 16/420,580, filed on May 23, 2019, also claims priority to U.S. Provisional Patent Application Ser. No. 62/768,771, filed Nov. 16, 2018, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an integration of color conversion layers into a display substrate. More particularly, the present invention relates to provide an encapsulation capsule to protect the color conversion layers from environmental agents. The present invention also relates to methods and structures to improve light extraction efficiencies of micro devices by mounting micro devices at a proximity of a corner of a pixel active area covered by color conversion layers. 
     BACKGROUND 
     System performance can be enhanced by integrating different micro devices into a system substrate. The challenge is that different micro devices can have different performance and also use different material systems. These material systems are in general sensitive to environmental agents (e.g., oxygen or water). Therefore, it is desirable to provide protection to these materials to enhance system performance. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a pixel structure comprising: a light source to generate light; a light conversion layer to convert the light to a desired color; and a light distribution structure to distribute 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., quantum dot (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. 
     Another aspect of this invention is creating an encapsulation capsule to protect color conversion materials. 
     According to one embodiment, there is provided an optoelectronic device comprising a plurality of semiconductor layers formed on a substrate that form a top surface and a bottom surface, wherein the plurality of semiconductor layers have isolated areas that form at least one side surface, one or more cover layers form a space around the isolated areas optically coupled to the at least one side surface; and functional tuning materials disposed in the space formed by the one or more cover layers. 
     According to one embodiment, a pixel structure for a display may be provided. The pixel structure may comprising a substrate, a light source (e.g., a micro device) mounted at the proximity of a corner of a pixel active area or pixel active side to generate light, a color conversion layer and/or color filters may be formed on the micro device to convert the light to a desired color and a top reflector mounted on the color conversion layer and extended over the top of the area of the micro device to reflect the light back toward and through the color conversion layer. The pixel active area is where the light generation or light conversion happens. The pixel active area can be the same as the pixel area. 
     According to other embodiments, a LED device structure may be provided. The structure may comprise optical layers coupling the LED lights into the structure and reflect the light created by QD layers towards the optical layers. 
    
    
     
       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 to reduce the effect of hotspots on the color conversion layer. 
         FIG. 5B  illustrates another light guide structure with an attenuator to reduce the effect of hotspots on the color conversion layer. 
         FIG. 5C  illustrates another light guide structure with an attenuator to reduce the effect of hotspots on the color conversion layer. 
         FIG. 5D  illustrates another light guide structure with an attenuator to reduce the effect of hotspots on the color conversion layer. 
         FIG. 5E  illustrates another light guide structure with an attenuator to reduce the effect of hotspots on the color conversion layer. 
         FIG. 5F  illustrates another light guide structure with an attenuator to reduce the effect of hotspots on the color conversion layer. 
         FIG. 6A  illustrates another light guide structure with an attenuator to reduce the effect of hotspots on the color conversion layer. 
         FIG. 6B  illustrates another light guide structure with an attenuator to reduce the effect of hotspots 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. 
         FIG. 12A  illustrates a cross-sectional view of the integration of a micro device with a color conversion layer in accordance with an embodiment. 
         FIG. 12B  illustrates a cross-sectional view of the integration of a micro device with a color conversion layer in accordance with an embodiment. 
         FIG. 12C  illustrates a cross-sectional view of the integration of a micro device with a color conversion layer in accordance with an embodiment. 
         FIG. 13A  illustrates a cross-sectional view of the integration of micro devices with color conversion layers and contacts in accordance with an embodiment. 
         FIG. 13B  illustrates a cross-sectional view of the integration of micro devices with color conversion layers and encapsulation walls in accordance with an embodiment. 
         FIG. 13C  illustrates a cross-sectional view of the integration of micro devices with color conversion layers in accordance with an embodiment. 
         FIG. 13D  illustrates a cross-sectional view of the integration of micro devices with color conversion layers in accordance with an embodiment. 
         FIG. 13E  illustrates another embodiment with encapsulation walls that have a stack of different layers with different functionalities in accordance with the present invention. 
         FIG. 13F  illustrates another embodiment wherein a contact extends beyond the color conversion layer in accordance with the present invention. 
         FIG. 14A  illustrates a cross-sectional view of the integration of micro devices with color conversion layers in accordance with an embodiment. 
         FIG. 14B  illustrates a cross-sectional view of the integration of micro devices with color conversion layers in accordance with an embodiment. 
         FIG. 15A  shows a pixel structure with color conversion layer on top of a micro device in accordance with an embodiment of the present invention. 
         FIG. 15B  shows a cross-sectional view of integrating color conversion layers on a substrate in accordance with an embodiment of the present invention. 
         FIG. 15C  shows a cross-sectional view of integrating color conversion layers on a substrate in accordance with an embodiment of the present invention. 
         FIG. 15D  shows a cross-sectional view of integrating color conversion layers on a substrate in accordance with an embodiment of the present invention. 
         FIG. 16A  shows a configuration of a plurality of pixel structures having a common electrode in accordance with an embodiment of the present invention. 
         FIG. 16B  shows another configuration of a plurality of pixel structures having a common electrode in accordance with an embodiment of the present invention. 
         FIG. 16C  shows another configuration of a plurality of pixel structures having a common electrode in accordance with an embodiment of the present invention. 
         FIG. 17  shows an arrangement of color conversion films in a micro device structure, in accordance with an embodiment of the present invention. 
         FIG. 18A  shows an arrangement of QD films with optical layers in a micro device structure, in accordance with an embodiment of the present invention. 
         FIG. 18B  shows an arrangement of optical layers in a micro device structure, in accordance with an embodiment 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, microelectromechanical 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 (TFT) 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. 
     In this disclosure, the structure is described using microLED and color conversion layers. However, a similar structure can be used with other micro devices and other functional tuning materials. 
     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 a combination thereof. 
       FIG. 1  illustrates a pixel structure  10  in accordance with an embodiment of the present invention including a substrate  11  with three subpixels 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  12 - 1 ,  12 - 2 , or  12 - 3  may have no color conversion layer. For example, if a blue light source is used, the blue subpixel may not include 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, a color filter, or electrodes for a touch interface. The following description may use one subpixel  12 - 1 ,  12 - 2 , or  12 - 3  to explain the invention, but the invention may be easily extended to a plurality of subpixels (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 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 the location of the color conversion layers  14 - 1  and  14 - 2 . 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 to manufacture the pixel circuit comprises: step  702 , 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 , 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 , 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 μm. In another example, the side of the transparent layer may be blocked by an opaque or reflective layer(s)  18  for each pixel or subpixel. In another example, there may be a 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  to form a frusto-pyramidal or frusto-conical structure. The acute angle may be between 30° and 60°, but preferably between 40° and 50°, to let light 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 wavelength 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, 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 the 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 light conversion layer  36  and the light source  32 . 
     With reference to  FIG. 8 , the method to manufacture the pixel circuit comprises: step  802 , making at least one group of micro devices  32  on a donor substrate  30  according to a system substrate pattern; step  804 , covering or blocking undesired light paths from the micro devices  32  with opaque or reflective materials (e.g., light attenuator  38 ); step  806 , covering the light output (input) surface of the micro devices  32  with the color conversion layers  36  and/or color filters; and step  808 , 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  to reflect the light out through the top layer  44 - 3  or bottom layer  44 - 4  of the light distribution structure  44 - 1 . The light passes 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 . An 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 light conversion layer  46 - 1  and the light source  42 . 
     With reference to  FIG. 9 , the method to manufacture the pixel circuit comprises: step  902 , making at least one group of micro devices  42  on a donor substrate  40  according to a system substrate pattern; step  904 , covering or blocking undesired light paths from the micro devices  42  with opaque or reflective materials (e.g., light attenuator  48 ); step  906 , 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 , 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 subpixel  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°-60°), ideally 40°-50°, to the substrate  50  to form 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  to prevent 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 a 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 to manufacture the pixel circuit comprises: step  1002 , making at least one group of micro devices  52  on a donor substrate  50  according to a system substrate pattern; step  1004 , covering or blocking undesired light paths from the micro devices  52  with opaque or reflective materials (e.g., light attenuator  58 ); step  1006 , 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 , 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, to reflect 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 - 1 . In  FIG. 5F , at least a portion of the cover reflector  54 - 4  may contact the light source  52  directly, and act as a contact for the light source  52 . 
     With reference to  FIG. 10B , the method to manufacture the pixel circuit comprises: step  1002 , making at least one group of micro devices  52  on a donor substrate  50  according to a system substrate pattern; step  1004 , covering or blocking undesired light paths from the micro devices  52  with opaque or reflective materials (e.g., light attenuator  58 ); step  1006 , 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 , 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 subpixel structure  61  that includes a light distribution structure  64  with diverging sides in the direction of light transmission formed at an obtuse internal angle to a substrate  60  (acute external angle). 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 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 devices  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  to convert 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  to convert the light emitting from the micro device  1104  into a third color. Together, the three micro devices  1104  may comprise the three different colors (i.e., 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 to redirect 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  1114 . 
     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. 
     Encapsulating Functional Tuning Materials 
     One method to improve system performance is to integrate different micro devices into a system substrate. The challenge is that different micro devices can have different performance and also use different material systems. The embodiments described below are related to creating different functional micro devices (e.g., red, green, blue LED, or a sensor from a single blue LED) by integrating functional tuning materials (e.g., a color conversion layer). As functional tuning materials are in general sensitive to environmental agents (e.g., oxygen or water), encapsulation 
       FIG. 12A  shows a micro device  1200  embedded in functional tuning/alteration/modifying materials  1210 . The functional tuning/alternation materials are referred to as color conversion layers as an example in the rest of the description. In addition, the embodiment exemplarily illustrated one micro device  1200 , but the invention is not limited thereto. The number of micro devices  1200  may be changed. 
     Here, a plurality of semiconductor layers is formed/transferred into a substrate forming a top surface  1200 - 1  and a bottom surface  1200 - 2 . The plurality of the semiconductor layers are isolated in different areas forming microdevices (a micro device  1200  is shown as an example) with at least one side surface  1200 - 3  (or  1200 - 4 ). Here, the micro device  1200  can have at least one contact (via)  1202 ,  1204  on one side of the device (or just on one side). The contacts  1202 ,  1204  connect the device  1200  to pads  1206  and  1208 . The micro device  1200  may have a stack of different layers such as active layers sandwiched between charge blocking layers and doping layers. A space formed around the micro device  1200  created by at least one cover layer which is optically coupled to the at least one side surface  1200 - 3  (or  1200 - 4 ). There is a housing structure formed around the device consisting of cover walls  1212 ,  1214 ,  1216 , and  1218 . The top and bottom cover walls (layers)  1212  and  1214  extend beyond the top and bottom surface of the micro device  1200 . The functional tuning materials (e.g. color conversion materials)  1210  are inside the housing structure. The cover walls  1212 ,  1214 ,  1216 , and  1218  can be encapsulation layers to protect the color conversion materials from oxygen and moisture. The color conversion materials can be phosphor or quantum dots. In addition, the cover walls can include optical enhancement layers with some optical property to enhance the light coupling into the color conversion materials. In one case, the cover wall  1212  or  1216  can be reflective layers to reflect the light into the color conversion materials. In another case, the cover wall  1212  or  1216  are designed to only reflect small wavelengths (e.g., smaller than 450 nm) while allowing longer wavelength to go through. This allows the converted light to pass through the wall. In another case, the wall  1214  enhances the light extraction from the micro device  1200  into color conversion material  1210 . In one example, the wall  1218  is reflective to reflect back the lights. In another case, the wall  1218  is transparent to allow at least some wavelength to pass through. 
     With reference to  FIG. 12B , the cover wall  1212  or  1216  can have two parts: a reflective part  1220  and a transparent part. The reflective layer  1220  is extended on top (or can be extended to the bottom) side of the device  1200 . In one case, the transparent part can also be transparent only to a portion of the wavelength to block the micro device light that goes out directly without being converted. 
     In another case shown in  FIG. 12C , color filter layers  1222  can be deposited on at least one of the walls to further prevent some of the wavelength from leaving the structure/device  1200  or enter the color conversion material  1210  from the outside. 
       FIG. 13A  shows a cross-sectional view of a micro device  1300  with contacts  1302  and  1304  on either the top or bottom side of the micro device. A pad  1306  can couple to the device  1300  through at least one of the contacts (e.g., the contact  1302  at the top side). In one case, a layer  1312  that can be a dielectric layer covers the part of the device surface that is not covered by the contact  1302 . There can be sidewall layers  1314  around the micro device which may have different functions such as a passivation layer, optical enhancement layer, or encapsulation layer. Here, a buffer layer or sacrificial layers  1332  may be provided between the micro device  1300  and a substrate  1330 . 
       FIG. 13B  shows a cross-sectional view where encapsulation walls  1312 A and  1312 B are formed around the micro device  1300 . The encapsulation layer  1312 A can be the same as sidewall layers  1314 . These sidewall layers  1314  can be deposited by different means such as printing, evaporation, sputtering or more. The sidewall layers can be patterned by traditional photolithography, liftoff, or printing. 
       FIG. 13C  shows a cross-sectional view of the color conversion materials are formed on top of the encapsulation walls  1312 A and  1312 B. The color conversion layers  1310  can cover the side of the device  1300  not facing the substrate  1330 . 
       FIG. 13D  shows a cross-sectional view of the micro device structure where the cover walls  1316  and  1318  are formed to enclose the color conversion material between the cover walls  1318 ,  1312 , and  1316 . 
       FIG. 13E  shows another cross-sectional view wherein a plurality of other walls can also be mounted on the micro device. The plurality of other layers may have a stack of different layers with different functionalities. In one case, the walls can include a reflective (e.g., total or selective) layer  1312 C and encapsulation layers  1312 B. 
     In another embodiment, the color conversion layer can be on a top or bottom surface of the micro device  1300 . In one example as shown in  FIG. 13F , if there is a contact on the same surface, the contact  1304  height will be increased to extend beyond the color conversion layer on that surface. It is possible to add walls  1320  to cover the side of the contact  1304  and the said surface of the micro device  1300 . 
       FIG. 14A  shows another embodiment wherein the contact  1404 A on one of the surfaces may be connected to a contact  1302  area on the opposite side of the device  1300  through a trace  1404 B. The trace can be separated from the device by a dielectric layer. The trace needs to be coupled with the color conversion layers, and transparent in some areas to allow the light to pass through it. In another case, the trace covers only part of the side of the micro device so that the light can pass through other areas. For better encapsulation, the wall layers  1312 A and  1312 B used for encapsulation are formed after the trace  1404 B. 
     In another embodiment, the color conversion layers can be on a top or bottom surface of the micro device  1300 . In one example as shown in  FIG. 14B , if there is a contact on the same surface, the contact  1404 A is transferred to another contact  1404 C on the other area with trace  1404 B. Here, a wall can cover the contact  1404 A, trace  1404 B, and the surface of the micro device for an optical or encapsulation function. 
     In the above embodiment, the cover walls on the top and bottom surface and the one on the side can be extensions of each other to offer better protection. In another case, the cover wall (layer) used on the side can extend over the bottom or top cover walls (layers). 
     In summary, the above embodiments provide many ways to encapsulate color conversion layers around the micro devices. 
     Improved Light Extraction Efficiencies 
     Further, various embodiments may be provided to improve light extraction efficiencies of micro devices by mounting micro devices at a proximity of a corner of a pixel active area. 
     According to one embodiment, a pixel structure for a display may be provided. The pixel structure may comprising a substrate, a light source (e.g., a micro device) mounted at the proximity of a corner of a pixel active area or pixel active side to generate light, a color conversion layer and/or color filters may be formed on the micro device to convert the light to a desired color and a top reflector mounted on the color conversion layer and extended over the top of the area of the micro device to reflect the light back toward and through the color conversion layer. The pixel active area is where the light generation or light conversion happens. The pixel active area can be the same as the pixel area. 
     In another case, a wall can surround part or all of the pixel area. A reflective layer covering the wall while the same or a different reflector layer is covering part of the micro device facing away from the pixel area to reflect the light toward the pixel area. The color conversion layer and/or color filter is formed on part or all of the pixel area. 
     In one aspect, the top reflector may act as a conductive electrode for coupling the micro device to a signal source such as a voltage or current source. In another embodiment, the reflective layer(s) can be also touch sensor electrodes. 
     In one embodiment, other layers may be used on top of color conversion layers such as encapsulation layers, color filters, or electrodes for a touch interface. 
     In another embodiment, a bottom reflector may be disposed between the micro device (pixel area) and the substrate for reflecting the light back from the micro device. This electrode can be another micro device electrode or a touch electrode. 
     In one case, the top reflector may be patterned to block escape the light from the pixel area. 
     In another case, if the bottom reflector is a metal, the bottom reflector may act as an electrode. In one embodiment, the bottom reflector may be patterned to open an area to let light be directed outwardly from the micro device. 
       FIG. 15A  shows a pixel structure with color conversion layer on top of a micro device in accordance with an embodiment of the present invention. A pixel structure  1502  comprising a substrate, a micro device  1510  may be mounted at the proximity of a corner of the pixel active area or pixel active side to generate light. The light output surface of the micro device  1510  may be covered by color conversion layers and/or color filters  1504 . The color conversion layers may comprise e.g. phosphor or quantum dots (QD). Here, other layers such as encapsulation layers, color filters, or electrodes may be used on top of the color conversion layers. A reflector/reflective layer  1508  may be mounted on the color conversion layers and extended over the top of the area of the micro device to reflect the light back toward and through the color conversion layer. The reflector  1508  may be patterned to block escaping the light out from the pixel area. Being micro device mounted at the proximity of a corner, this pixel structure can offer better light extraction, higher fill factor and better performance. 
     In one embodiment, a wall(s)  1506  can surround part or all of the pixel area. A reflective layer covering the wall while the same or a different reflector layer is covering part of the micro device facing away from the pixel area to reflect the light toward the pixel area. The color conversion layer and/or color filter is formed on part or all of the pixel area. 
     In one embodiment, pixel driving backplane can be integrated on top of the sample. In another case, the pixel driving backplane can be integrated before the color conversion layer. 
     Black matrix can be used on the surface facing away from the light to reduce the reflectivity of the surface for enhancing the contrast. 
       FIG. 15B  shows a cross sectional view of pixel structure including a micro device and color conversion layers corresponding to  FIG. 15A . Here, a display substrate may be provided. The substrate  1524  may be an optical substrate that may comprises micro LED or a receiving substrate. The receiving substrate may be, but is not limited to, a printed circuit board (PCB), a thin-film transistor (TFT) 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. A bottom reflector  1526  may be disposed over the substrate used to reflect light back from the micro device. The micro device may be mounted at the proximity of a corner of the pixel area or pixel side to generate light. In one embodiment, an optional dielectric layer  1528  may be deposited over the bottom reflector  1526  to separate the bottom reflector from the micro device. 
     In one case, if the bottom reflector is a metal, the bottom reflector may act as an electrode to connect the pixel circuit to the micro device. In other embodiments, an optical stage  1530  may be provided on the side of the micro device with some optical property to enhance the light coupling into the color conversion materials. 
     The color conversion layers  1532  may be mounted on the micro device to convert the light to a desired color. A top reflector  1522  may also be disposed over the color conversion layers to reflect light back from the color conversion layer and may be patterned to open an area  1540  to let light be directed outwardly from the micro device. 
     In one embodiment, pixel driving backplane can be integrated on top of the sample. In another case, the pixel driving backplane can be integrated before the color conversion layer. 
     Black matrix can be used on the surface facing away from the light to reduce the reflectivity of the surface for enhancing the contrast. 
       FIG. 15C  shows another cross sectional view of pixel structure. Here, the top reflector  1522 -C may be fully disposed on and over on one side of the micro device  1520  and color conversion layers  1532  and the bottom reflector  1526 -C may be patterned to open an area to let light be directed outwardly from the micro device. 
       FIG. 15D  shows another cross sectional view of pixel structure. Here, the top reflector  1522 -D may be deposited over the micro device  1520  before disposition of the color conversion layers  1540 -D. The top reflector  1522 -D may be partially patterned and disposed to cover a part of the micro device. An additional plurality of walls/layers  1542  may be provided. These additional walls/layers  1542  may comprises a dielectric layer, a polymer, a stack of metals or another reflector. 
       FIG. 16A  shows a configuration of a plurality of pixel structures having a common electrode either as one of micro device electrode or a touch sensor in accordance with an embodiment of the present invention. Here, for an example, four different pixel structure may be used wherein respective micro device (e.g.,  1602 - 1 ,  1602 - 2 ,  1602 - 3  and  1602 - 4 ) is mounted on the proximity of a corner of each pixel structure. The pixel structures mounted in such a way that light output surface of each micro device is facing each other. The light output surface of each micro device may be covered by respective color conversion layers and/or color filters (e.g.,  1604 - 1 ,  1604 - 2 ,  1604 - 3  and  1604 - 4 ). The top reflector mounted on color conversion layer of each pixel structure may act as an electrode and may also act as a common electrode  1606  for each pixel structure to connect to the micro device. 
     In one case, the reflective layer(s) can be also touch sensor electrodes. The micro devices can be located in different corners of the pixels (or sub pixels). In this embodiment, the micro devices in one pixel for different sub pixels are located closer to each other. 
       FIG. 16B  shows another configuration of a plurality of pixel structures having a common electrode in accordance with an embodiment of the present invention. In this case, the micro devices in subpixels related to one pixel can be further away from each other as demonstrated in  FIG. 16B . The top reflector can cover part of the micro device specially if it only covering the micro device. 
       FIG. 16C  shows another configuration of a plurality of pixel structures having a common electrode in accordance with an embodiment of the present invention. In this case, the top reflector or an extra reflector covering QD layers can extend over the micro device. 
     In summary, the above embodiments provide many ways to mount micro devices at a proximity of a corner of a pixel active area to improve light extraction efficiencies of micro devices. 
     Optical Layer Integration with Micro Device Substrate 
     Furthermore, this disclosure is related to integration of optical layer(s) in a micro device structure. The micro device structure may comprise micro light emitting diodes (LEDs), organic LEDs, sensors, solid state devices, integrated circuits, MEMS, and/or other electronic components. 
     In one embodiment, the micro device may comprise at least one color conversion layers. In one embodiment, color conversion layers may include phosphor or quantum dots (QD). In another embodiment, the micro device may comprise one or more optical layers. 
     In yet another embodiment, a first optical layer may couple micro device light into the micro device structure and reflect the light created by a first color conversion layer towards a second optical layer. 
     In another embodiment, the second optical layer may couple remaining light from the LED and light generated by the first color conversion layer into a second color conversion layer. It may prevent the light from the second color conversion layer to go back to the first color conversion layer. 
     In one embodiment, the first color conversion layer may generate a higher wavelength light e.g, red and the second color conversion layer may generate a mid range wavelength light e.g, green. 
     In one case, color conversion layers may be color conversion layers embedded in a film (e.g. polymers). In another case, color conversion layers may be a continuous layer (e.g. mono layer) covered by passivation layer. 
     In another embodiment, the first color conversion layer may generate mid range wavelength (e.g. green) and the second color conversion layer may generate longer wavelengths (e.g. red). 
     In this case, the light generated by the first color conversion layer may also be converted by the second color conversion layer into longer wavelength light. Therefore, the second color conversion layer concentration may be controlled to only convert predefined percentage of the first color conversion layer light into the second color conversion layer light. 
     In yet another embodiment, the light entity of the first color conversion layer or a second color conversion layer light may also be modulated by adding a third optical film on top of the structure (for this structure, the first color conversion layer or a second color conversion layer can be mixed in one film as well). For example, for area where more red is needed, an optical film can be added on the top to reflect a percentage the light (either as selective by wavelength or general) back into the QD films. In such case, the mid wavelength (e.g. green) will be absorbed more by the QD films and generate more longer wavelength light (e.g. red). Various embodiments in accordance with the present structures and processes provided are described below in detail. 
       FIG. 17  shows an arrangement of color conversion films/color filters in a micro device structure, according to one embodiment of the invention. Here, a color conversion layer is used to convert the blue light of three subpixels to combine green and red color. The color filter is for each sub pixel to only allow the corresponding light out. To save power, one sub pixel has no color filter  1702 . In this case, if a pixel required a combination of red and green color, the sub pixel with no color filter can be used to generate all or part of the combined color. Furthermore, one sub pixel has no color conversion and therefore generate blue color only. 
       FIG. 18A  shows an arrangement of QD films with optical layers in a micro device structure, in accordance with an embodiment of the present invention. Here, the micro device  1820  may comprise one or more optical layers. A first optical layer  1802  may couple micro device  1820  light into the micro device structure and reflect the light created by a first color conversion layer  1802  towards a second optical layer  1804 . The second optical layer  1804  may couple remaining light from the LED and light generated by the first color conversion layer  1808  into a second color conversion layer  1810 . It may prevent the light from the second color conversion layer  1810  to go back to the first color conversion layer  1808 . 
     In one embodiment, the first color conversion layer  1808  may generate a higher wavelength light e.g, red and the second color conversion layer  1810  may generate a mid-range wavelength light e.g, green. In one case, color conversion layers may be color conversion layers embedded in a film (e.g. polymers). In another case, color conversion layers may be a continuous layer (e.g. mono layer) covered by passivation layer. In another embodiment, the first color conversion layer  1808  may generate mid-range wavelength (e.g. green) and the second color conversion layer  1810  may generate longer wavelengths (e.g. red). 
     In this case, the light generated by the first color conversion layer  1808  may also be converted by the second color conversion layer  1810  into longer wavelength light. Therefore, the second color conversion layer concentration may be controlled to only convert predefined percentage of the first color conversion layer light into the second color conversion layer light. 
     In yet another embodiment, the light entity of the first color conversion layer or a second color conversion layer light may also be modulated by adding a third optical film  1806  on top of the structure (for this structure, the first color conversion layer or a second color conversion layer can be mixed in one film as well). For example, for area that more red is needed, an optical film can be added on the top to reflect a percentage the light (either as selective by wavelength or general) back into the QD films. In such case, the mid wavelength (e.g. green) will be absorbed more by the QD films and generate more longer wavelength light (e.g. red). 
       FIG. 18B  shows an arrangement of optical layers in a micro device structure, in accordance with an embodiment of the present invention. Here, the sub pixel with no optical layer 3  1840  creates more of higher wavelength (green) color, while the sub pixel with optical layer 3  1820  creates more lower wavelength (red) color. 
     According to one embodiment, an optoelectronic device is provided. The optoelectronic device comprises a plurality of semiconductor layers formed on a substrate to form a top surface and a bottom surface, wherein the plurality of semiconductor layers have isolated areas that form at least one side surface; one or more cover layers form a space around the isolated areas optically coupled to the at least one side surface; and functional tuning materials are disposed in the space formed by the one or more cover layers. 
     According to another embodiment, the one or more cover layers comprises one or more of: a passivation layer, a dielectric layer, an optical enhancement layer, an encapsulation layer, a reflective layer, and a color filter layer, and functional tuning materials comprises color conversion materials. 
     According to some embodiments, the functional tuning materials are further disposed on one of: the top surface or the bottom surface of the optoelectronic device. 
     According to further embodiments, the at least one contact is disposed on at least one of: the top surface or the bottom surface of the optoelectronic device and a pad is coupled to the optoelectronic device through the at least one contact. 
     According to another embodiment, the height of the at least one contact is extendable beyond the functional tuning materials disposed on a same side of the at least one contact and wherein the at least one contact on one of: the top surface or the bottom surface of the optoelectronic device is connected to a least another contact on another surface of the optoelectronic device through a trace. The trace is separated from the optoelectronic device by a dielectric layer. 
     According to some embodiments, the encapsulation layer protects the color conversion materials from oxygen and moisture, the optical enhancement layer reflects the light into the color conversion materials, the reflective layer enhances the light coupling into the color conversion materials, and the reflective layer is extended on one of: the top surface or the bottom surface of the optoelectronic device. The reflective layer comprises a reflective part and a transparent part. 
     According to other embodiments, the plurality of cover layers is deposited by one of: printing, evaporation, or sputtering and patterned by one of: photolithography, liftoff, or printing. 
     According to further embodiments, the one or more cover layers encircling the functional tuning materials between the at least one side surface and the one or more cover layers. 
     According to one embodiment, a display may be provided. The display may comprising: a substrate, at least one pixel structure disposed on or over the substrate, each pixel structure including at least one micro device mounted in proximity of a corner of the pixel structure, at least one color conversion layer mounted on the at least one micro device; and a top reflector mounted on the color conversion layer extended over the top of the area of the micro device. 
     According to another embodiment, the display may further comprise at least a wall surrounding a part or a whole of the pixel structure, a reflective layer covering the wall to reflect back the light towards the pixel structure. The top reflector is a conductive electrode for coupling the micro device to a signal source and the reflective layer is a touch sensor electrode. 
     According to yet another embodiment, the display may further comprise a bottom reflector disposed between the micro device and the substrate for reflecting the light back from the micro device. The bottom reflector is used as an electrode. The top reflector is patterned to open an area to let light be directed outwardly from the pixel area. The bottom reflector is patterned to open an area to let light be directed outwardly from the micro device. The wall comprises a dielectric layer, a polymer, a stack of metals or another reflector. 
     According to one embodiment, a plurality of optical layers may be coupled with the micro device. The optical layers are disposed in between color conversion layers. 
     In summary, the disclosure is related to creating different functional micro devices by integrating functional tuning materials and creating an encapsulation capsule to protect these materials. Various embodiments of the present disclosure also related to improve light extraction efficiencies of micro devices by mounting micro devices at a proximity of a corner of a pixel active area and arranging QD films with optical layers in a micro device structure. 
     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 teachings. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.