CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U. S.C. § 119 of U.S.

Provisional Application Serial No. 62/472,121 filed on March 16, 2017, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

[0002] The disclosure relates generally to the field of micro-LED device fabrication, and specifically to a process for mass-transfer of micro-LEDs to a device, such as a display backplane. Generally, micro-LED material is grown on a growth substrate, such as sapphire. The micro-LED material is then etched, typically while on the growth substrate, to form micro-LEDs. To utilize the micro-LEDs in applications, such as display applications, the micro-LEDs are transferred to a display backplane. Due to the dense packing of micro-LEDs following etching and the need for sparse packing of micro-LEDs on the display backplane, efficient transfer of micro-LEDs particularly for large area displays, has proven difficult.

SUMMARY

[0003] One embodiment of the disclosure relates to a method of forming a micro-LED display. The method includes transferring a plurality of micro-LED material wafers onto a first major surface of a handling substrate. A first area is defined by a perimeter of the first major surface of the handling substrate, and a plurality of micro-LEDs are formed from each of the micro-LED material wafers. The method includes transferring a subset of the plurality of micro-LEDs from the handling substrate to a first major surface of a display backplane, and the display backplane has electrical contacts coupled to each of the plurality of transferred micro-LEDs. The subset of transferred micro-LEDs includes at least one micro- LEDs from each of the plurality of micro-LED material wafers, and the first area is equal to or greater than a second area defined by a perimeter of the first major surface of the display backplane.

[0004] An additional embodiment of the disclosure relates to a method of forming an LED device having a total number of micro-LEDs, m, arranged in an array on a selectively conductive substrate having an average separation pitch, The method includes supporting a densely packed array of micro-LEDs on a first major surface of a non-conductive support substrate. The densely packed array of micro-LEDS has an average separation pitch, p where > 10*/? _/ . The method includes moving the non-conductive support substrate such that the densely packed array of micro-LEDs are positioned opposing a first major surface of the selectively conductive substrate. While the non-conductive support substrate is positioned with the densely packed array of micro-LEDs positioned opposing the first major surface of the selectively conductive substrate, the method includes releasing a group of n number of non-adjacent micro-LEDs from the densely packed array of the support substrate and onto the conductive substrate, where n > 0.05*m.

[0005] An additional embodiment of the disclosure relates to a micro-LED support device. The micro-LED support device includes a glass or glass-ceramic substrate. The glass or glass-ceramic substrate includes a first major surface, a second major surface opposite the first major surface, at least 50 mol% S1O2, a width greater than 200 mm and a length greater than 200 mm. The micro-LED support device includes an array of at least 10 micro-LED material layers bonded to the first major surface of the glass or glass-ceramic substrate, and each micro-LED material layer is formed into an array of densely packed micro-LEDs. The array of densely packed micro-LEDs includes an average separation pitch of less than or equal to 100 μιτι and each micro-LED having a width of less than or equal to 100 μιτι. The total number of micro-LEDs supported by the glass substrate is greater than 10 million.

[0006] Additional features and advantages will be set forth in the detailed description that follows, and, in part, will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.

[0007] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.

[0008] The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and the operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic view of micro-LED wafers being bonded to a handling substrate, according to an exemplary embodiment. [0010] FIG. 2 is a schematic view showing release of growth substrates from micro-LED material layers following bonding to the handling substrate, according to an exemplary embodiment.

[0011] FIG. 3 is a schematic perspective view of a handling substrate supporting micro-LED material layers from multiple wafers prior to etching, according to an exemplary

embodiment.

[0012] FIG. 4 is a schematic perspective view of micro-LED material from multiple wafers etched into micro-LEDs while supported by the handling substrate, according to an exemplary embodiment.

[0013] FIG. 5 is a schematic plan view of the handling substrate supporting micro-LEDs etched from the material of multiple wafers, according to an exemplary embodiment.

[0014] FIG. 6 is a schematic view of the handling substrate of FIG. 5 positioned adjacent a display backplane, according to an exemplary embodiment.

[0015] FIG. 7 is a schematic view of select, non-adjacent micro-LEDs being released from the handling substrate and bonded to the display backplane, according to an exemplary embodiment.

[0016] FIG. 8 is a schematic plan view of the handling substrate following release of select, non-adjacent micro-LEDs, according to an exemplary embodiment.

[0017] FIG. 9 is a schematic plan view of the display backplane following receipt of the select non-adjacent micro-LEDs from the handling substrate, according to an exemplary embodiment.

[0018] FIG. 10 is a schematic plan view showing population of gaps on a display backplane, according to an exemplary embodiment.

[0019] FIG. 11 shows etched micro-LEDs on a handling substrate having a small separation pitch, according to an exemplary embodiment.

[0020] FIG. 12 shows groups of three micro-LEDs on a display backplane having a large separation pitch, according to an exemplary embodiment.

DETAILED DESCRIPTION

[0021] Referring generally to the figures, various embodiments of a system and method for forming a micro-LED display backplane are shown and described. In various embodiments, the system and method discussed herein provides for the population of a micro-LED backplane utilizing a relatively small number of steps to transfer all of the desired micro- LEDs onto the display backplane. Micro-LEDs are typically formed by etching the individual micro-LEDs from deposited/grown micro-LED material into highly dense arrays while the micro-LED material is supported by the growth substrate (e.g., a sapphire growth substrate). The etched micro-LEDs are very small (e.g., dimensions less than 100 μιη, some as small as 12.5 μηι x 12.5 μηι or smaller) and have spacing between adjacent micro-LEDs in the as formed state (i.e., pitch) that is also very small (e.g. , pitch less than 100 μιτι, less than 15 μηι or smaller).

[0022] Display backplanes typically have spacing between adjacent micro-LEDs that is many times greater than the spacing between adjacent micro-LEDS in the as formed state on the growth wafers. Efficiently transferring micro-LEDs from the dense state following etching to the sparse state on the display backplane is a major challenge in the development of large area micro-LED devices or displays with most prior transfer methods of which Applicant is aware requiring hundreds of separate transfer steps to populate a large size display backplane (e.g. , displays having dimensions greater than about 300 mm x 300 mm or larger).

[0023] As discussed herein, the system and method discussed herein achieves sparse backplane population in a relatively low number of transfer steps (e.g., 20 or less and in specific embodiments, twelve transfer steps and in other embodiments, in four transfer steps). As will be discussed in more detail below, the highly efficient backplane population system and method discussed herein involves bonding the micro-LED material from a large number of growth wafers into an array (e.g. , tiled) onto a large handling substrate that is as large or larger than the size of the display backplane.

[0024] With the micro-LED material from multiple wafers supported by the handling substrate, the micro-LED material is etched into arrays of micro-LEDs. Applicant believes that by etching the micro-LEDs from multiple wafers at once while the micro-LED material of multiple wafers is supported by the backplane allows for the micro-LEDs to have a very low level of pitch variation across the whole handling substrate (at least compared to processes in which micro-LEDs are etched on the growth substrate and transferred to a common handling substrate after etching). This process creates a handling substrate supporting a densely packed array of micro-LEDs that is as large (or potentially larger) than the display backplane.

[0025] Next, the large, micro-LED supporting handling substrate is aligned with a display backplane, and a large number of non-adjacent micro-LEDs are released (e.g., via laser release) from the support substrate onto the display backplane. To provide the sparse micro- LED population on the display backplane, non-adjacent micro-LEDs from the handling substrate that are separated from each other by desired display backplane pitch are released from the handling substrate and bonded to the display backplane.

[0026] Thus, in this embodiment, a very large number of micro-LEDs (e.g., at least 5% of the total number of micro-LEDs for the display) are deposited on to the display backplane in a single transfer step. As will be understood, most micro-LED displays include groups of the micro-LEDs including a red micro-LED, a blue micro-LED and a green micro-LED at each position on the display backplane, and in such embodiments, the fully populated display backplane is formed from at least one transfer from a different handling substrate for each micro-LED color.

[0027] In specific embodiments, Applicant believes that the micro-LED wafers may be bonded to the handling substrate in a manner such that spaces or gaps in the form of empty rows and columns are formed between adjacent wafers on the handling substrate and these gaps are larger than the as-formed micro-LED pitch. As will be discussed below, in such embodiments, the system and method discussed herein includes use of additional micro-LED populated handling substrates that are used to populate "gaps" on the display backplane that result from the inter-wafer gap rows and columns on the primary handling substrates.

However, in such embodiments, the total number of LED transfer steps required is less than 20 and may specifically be 12: one primary transfer for each of the three micro-LED colors, one row gap filing transfer for each of the three micro-LED colors, one column gap filing transfer for each of the three micro-LED colors, and one intersection gap filing transfer for each of the three micro-LED colors. Even in embodiments accounting for the inter-wafer gaps on the handling substrate, display backplanes can be populated in less than 20 steps as compared to hundreds of transfer steps of typical backplane population processes.

[0028] Referring to FIGS. 1-10, a method of efficiently populating a display backplane is shown and described. As shown in FIG. 1 , a plurality (e.g., at least 10, at least 30, at least 100) of micro-LED wafers 10 are bonded, adhered or transferred to a handling substrate 12. As shown in FIG. 1 , an outer surface of each micro-LED wafer 10 is bonded to a first major surface 14 of handling substrate 12. In particular embodiments, each micro-LED wafer 10 includes a layer of micro-LED material 16 (e.g., GaN for blue and green micro-LEDs, InP for red micro-LEDs) supported on a growth substrate 18. In this embodiment, the layer of micro-LED material 16 of each wafer is bonded (e.g., through an adhesive material) to major surface 14 of handling substrate. As shown in FIG. 2, following bonding to substrate 12, each growth substrate 18 is released (e.g., via a laser release process represented by arrow 19 or an alternative method such as grind and polish), leaving each of the layers of micro-LED material 16 from each of the wafers 10 bonded to handling substrate 12.

[0029] It should be understood the for illustration purposes, FIG. 1 shows removal of growth substrates 18 from the micro-LED layers 16 in one step. However, in some embodiments, each growth substrate 18 may be removed after its micro-LED layer 16 is adhered to handling substrate 12 and before attachment of the next, adjacent micro-LED layer 16. In such embodiments, Applicant believes that, by removing growth substrates 18 before attaching an adjacent micro-LED layer 16, the gap between the adjacent micro-LED layers 16 may be formed to be very small (about 1 mm).

[0030] In a specific embodiment, handling substrate 12 has an adhesive which is initially uncured and later cured once the micro-LED material layers 16 is brought in contact with the adhesive. In one embodiment, the adhesive is a UV curing adhesive, for example, with the UV light passing through handling substrate 12 to cure the adhesive. Select removal of micro-LEDs will be discussed in more detail below, selective release of individual micro- LEDs may be achieved by using a laser to warm that adhesive back into a liquid-like state at the location of the micro-LED to be released. The heat from a laser also may be used to heat solder on the display backplane (discussed below) that is later cooled and frozen so that the micro-LED is bonded to the display backplane and able to release from the handling substrate 12.

[0031] Referring to FIGS. 1-3, micro-LED wafers 10 are bonded both along the width and length dimension (in the orientation of the figures) such that the LED material 16 from micro-LED wafers 10 form an array or tiled arrangement on handling substrate 12. As can be seen best in FIG. 3, following removal of growth substrates 18, a large number micro-LED material layers 16 from wafers 10 are arranged in the array or tiled pattern along major surface 14 of handling substrate 12.

[0032] As shown in FIG. 3, handling substrate 12 has a width dimension, Wl , and a length, LI . As can be seen from FIGS. 1 and 3, handling substrate 12 is substantially larger than wafers 10 such that multiple wafers 10 (and the micro-LED material layers 16 of multiple wafers 10) fit within the perimeter of handling substrate 12. In such embodiments, handling substrate has a perimeter of 2W1 + 2L1, and in specific embodiments, 2W1 + 2L1 is greater than 3 times, specifically greater than 5 times, more specifically greater than 10 times the length of the outermost perimeter of wafer 10. Similarly, as can be seen in FIG. 3, the area of first major surface 14 of handling substrate 12 is at least 10 times greater than area of each micro-LED material layer 16. These sizing differentials as described allow micro-LED material layers 16 from multiple wafers 10 to be supported on a single handling substrate 12, such as a monolithic, continuously connected sheet of a single material or a group of such sheets connected together to form a single handling substrate for example. It should be understood that FIG. 3 shows 20 micro-LED material layers 16 bonded to handling substrate 12 for illustration purposes, and in many applications, where handling substrate 12 is configured for populating large display backplanes (e.g., 50 inch displays, 65 inch displays, 75 inch displays, etc.) or multiple display backplanes, handling substrate 12 is as large or larger than the display backplane and includes enough micro-LED material layers 16 to fill the area of surface 14.

[0033] In specific embodiments, handling substrate 12 is sized to populate relatively large display backplanes in a small number of micro-LED transfer steps. In specific embodiments, Wl and/or LI may be at least 200 mm, at least 300 mm, at least 700 mm, at least 1270 mm, at least 1650 mm, at least 1900 mm, at least 2200 mm, etc. In these embodiments, major surface 14 of handling substrate 12 has an area greater than 300 cm ² , greater than 1000 cm ² , greater than 5000 cm ² , greater than 1000 cm ² , etc.

[0034] In specific embodiments, handling substrate 12 is a non-conductive support substrate that does not include the electrical connections for powering micro-LEDs as are present on a display backplane. In various embodiments, substrate 12 is a sheet of glass or glass-ceramic material. In some such embodiments, the material of substrate 12 is at least 50 mol% S1O2, and in specific embodiments, is between 67 mol% and 70 mol% S1O2. In specific embodiments, substrate 12 may be Eagle XG glass available from Corning Inc.

[0035] In various embodiments, in addition to having a large perimeter and area, substrate 12 may be relatively thin and light facilitating handling during processing as discussed herein. As shown in FIG. 2, substrate 12 has a second major surface 26 opposing first major surface 14. Substrate 12 has a thickness, Tl, defined between surfaces 14 and 26. In specific embodiments, Tl is between 0.25 mm and 1 mm. [0036] As shown in FIG. 3, in some embodiments, the arrangement of micro-LED wafers 10 onto handling substrate 12 creates a plurality of horizontally oriented gap rows 20, a plurality of vertically oriented gap columns 22, and a plurality of intersection gaps 24 at the intersections between rows 20 and columns 22. In some embodiments, Applicant believes that due to constraints imposed by the dimensions of micro-LED wafers 10 and/or the bonding and release processes for bonding micro-LED material layers 16 to handling substrate 12, there may be a limit to how close to each other micro-LED wafers 10 can be when attached to handling substrate 12. This limitation results in gaps 20, 22 and 24 between adjacent zones of micro-LED material layers 16.

[0037] As can be seen in FIG. 3, gaps 20, 22 and 24 are fairly large compared to the size of micro-LED material layers 16 and are very large compared to the size of the micro-LEDs that will be formed from micro-LED material layers 16. In various embodiments, gaps 20 and 22 generally have a gap size, shown as Gl . In specific embodiments, Gl is greater than 0.5 mm, specifically is between 0.5 mm and 1.5 mm, and more specifically is about 1 mm. It should be understood that gap size Gl is exaggerated in FIG. 3 for ease of illustration. As an example, the dimensions of micro-LED material layers typically will be on the order of about 100 mm, and in such embodiments, at least 90%, specifically at least 95% and more specifically at least 99% of the surface area of handling substrate 12 is occupied by micro- LED material layers 16. As will be explained in more detail below regarding FIG. 10, various display backplane population methods discussed herein utilize three additional handling substrates for each color micro-LED that are used to populate spaces on the display backplane corresponding to gaps 20 and 22 and intersections 24.

[0038] As shown in FIG. 4, once growth substrates 18 are removed leaving micro-LED material layers 16 supported from handling substrate 12, micro-LEDs 30 are formed from the multiple micro-LED layers 16 located on substrate 12. As shown in FIG. 4, micro-LEDs 30 are formed from multiple micro-LED material layers 16 while supported by handling substrate 12, and in specific embodiments, all micro-LEDs 30 are formed from all micro- LED material layers 16 while supported on handling substrate 12.

[0039] In particular embodiments, micro-LEDs 30 are formed by etching all of the micro- LED material layers 16 to form the plurality of micro-LEDs 30 while the micro-LED material layers 16 are supported by handling substrate 12. In some embodiments, etching to form micro-LEDs 30 includes applying a photoresist coating onto all of the micro-LED material layers 16 while supported on first major surface 14 of handling substrate 12.

[0040] It should be understood that FIG. 4 shows the micro-LED material layer 16 from each wafer 10 etched in 16 micro-LEDs for ease of depiction. While, the exact number of micro- LEDs 30 formed from each micro-LED material layer 16 will depend on the size of wafer 10 and the final size of each micro-LED 30, each micro-LED material layer 16 forms a large number of micro-LEDs 30. In specific embodiments, each micro-LED material layer 16 forms more than 1 ,000,000 micro LEDs 30, at least 10 million micro-LEDs 30, at least 30 million micro-LEDs 30, etc. Thus, in various embodiments, each handling substrate 12 may support more than 10 million micro-LEDs, more than 100 million micro-LEDs 30, more than 500 million micro-LEDs, more than 800 million micro-LEDs, etc.

[0041] Still referring to FIG. 4, the number of micro-LEDs 30 formed from each micro-LED material layer 16 depends on the size, shown as W2, of each micro-LED 30, on the size, shown as W3, of each micro-LED layer 16 and the separation or pitch, shown as PI , between adjacent micro-LEDs 30 within each micro-LED material layer 16. In various embodiments, W2 is less than or equal to 100 μιτι, and PI is less than or equal to 100 μιτι. In various embodiments, W3 is between 50 mm and 150 mm and more specifically is about 100 mm. In some embodiments, micro-LEDs 30 may be very small or densely packed micro-LEDs. Specifically in some embodiments, micro-LEDs 30 may be rectangular and have dimensions of about 1 1.5 x 1 1.5μιη, and in some such embodiments, have pitch, PI of about 12.5 μιτι. In some embodiments, W2 may be as small as 5 μπι

[0042] Referring to FIGS. 5-9, population of one or more display backplane 40 is shown utilizing handling substrate 12. FIG. 5 shows handling substrate 12 with additional areas of micro-LED material 16 etched into micro-LEDs 30 for purposes of illustrating display backplane population utilizing the system and method discussed herein. For ease of illustration, FIG. 5 shows gap rows 20 and gap columns 22 as lines.

[0043] In general, referring to FIG. 6, a selectively conductive substrate, such as an insulating substrate with conductive traces, shown as display backplane 40, is a support device configured to receive micro-LEDs 30 and to support micro-LEDs 30 in a display application. In particular applications, display backplane 40 is a support device that includes one or more conductive layer/element and electrical contacts that will be coupled to each of the micro-LEDs 30 transferred to display backplane 40. [0044] Referring to FIG. 6 and FIG. 7, handling substrate 12 is moved and positioned such that micro-LEDs 30 are facing a first major surface 42 of display backplane 40. As will be understood, the desired micro-LED separation pitch, P2, on display backplane 40 is greater than the etched, separation pitch, PI , in the dense, etched state of micro-LEDs 30 on handling substrate 12. Referring to FIG. 7, to accommodate the greater micro-LED separation pitch, P2, needed for display backplane 40, a subset of micro-LEDs 30 are transferred (e.g., via selective laser release) from handling substrate 12 to display backplane 40. As shown in FIG. 7, the separation pitch needed on display backplane 40 is accommodated by transferring non- adjacent micro-LEDs 44 that are spaced from each other substrate 12 by the desired backplane pitch, P2.

[0045] Further, to decrease or minimize the number of transfer steps needed, the area of surface 14 of handling substrate 12 is greater than or equal to the area of surface 42 of display backplane 40. Thus, because substrate 12 is as large or larger than display backplane 40, when in the facing arrangement shown in FIGS. 6 and 7, one micro-LED 30 on substrate 12 will be facing most or all of the desired LED locations on display backplane 40. Thus, the selective release of each non-adjacent micro-LEDs 30 that are separated from each other by display pitch P2 forms transferred micro-LEDs 44 on display backplane 40 having pitch P2. In this manner, most or all of the display backplane 40 is populated as needed with micro- LEDs 30 in a single transfer step.

[0046] Referring to FIG. 7 and FIG. 8, the transfer of micro-LEDs 30 from substrate 12 is shown in more detail. Release of the subset of micro-LEDs 30 from substrate 12 forms a partially depopulated substrate 46 that has an ordered pattern of spaces 48 that were occupied by the micro-LEDs 30 that were released to become transferred micro-LEDs 44 located on display backplane 40. As shown in FIG. 9, the transferred micro-LEDs 44 on display backplane 40 are the mirror image of spaces 48 vacated by the transferred micro-LEDs from substrate 12.

[0047] In addition, as shown in FIGS. 7-9, at least one micro-LED 30 from each of micro- LED layers 16 is transferred to display backplane 40, and in such embodiments, because only a subset of micro-LEDs 30 from substrate 12 are transferred to populate display backplane 40, substrate 12 may be used to populate multiple display backplanes. For example, FIGS. 7- 9 show 25% of the micro-LEDs 30 from each micro-LED layer 16 being transferred, and as such substrate 12 could be used to populate four display backplanes 40. However, as noted above, each micro-LED layer 16 typically will include millions of micro-LEDs 30 and because the ratio of P2 to PI will be very large, only a small portion of the total number of LEDs from substrate 12 (e.g., less than 5% of micro-LEDs 30, less 3% micro-LEDs 30, less than 1 % of micro-LEDs 30, etc.) will be transferred to a backplane 40 in each transfer step. As such, each substrate 12 can be used in multiple transfer steps with multiple backplanes 40 in order to populate a large number of display backplanes.

[0048] As will be understood, because many display backplanes 40 include 3 micro-LEDs (one red, one blue and one green, see FIG. 12) at each LED location, the process discussed regarding FIGS. 7-9 will be repeated with three different substrates, each with micro-LEDs of one of the three colors. In addition, in specific embodiments, the process includes ordering the handling substrate depopulation in a way that accounts for size and space occupied by micro-LEDs 30. For example, in one embodiment, a full handling substrate 12 with the green of micro-LEDs may not be positionable as shown in FIG. 7 relative to a display backplane 40 that has already been populated with blue micro-LEDs due to interference between the micro- LEDs on the full substrate 12 and the blue micro-LEDs already on backplane 40. Thus, in such embodiments, a partially depopulated green micro-LED bearing substrate 12 is used when blue micro-LEDs 30 are already on the backplane 40. Thus, some backplanes 40 may be first populated with green micro-LEDs to provide partially depopulated substrates 12 to populate those backplanes 40 that received blue micro-LEDs first, and some backplanes 40 may be first populated with blue micro-LEDs 30 to provide partially depopulated blue substrates 12 to populate substrates that received green micro-LEDs first.

[0049] In some embodiments, red micro-LEDs are formed from a material that has a thickness (e.g., height from substrate 12) that is greater than the height of the material of blue or green micro-LEDs. Thus in such embodiments, because of this greater height, populating backplane 40 with red micro-LEDs 30 first or second would cause interference with the subsequent backplane population of green or blue micro-LEDs 30. Thus, in such

embodiments, in the various methods discussed herein red micro-LEDs 30 are populated after all green and blue micro-LEDs 30 have been populated onto backplane 40.

[0050] Thus, referring to FIGS. 5-9, the process discussed herein allows for formation of an LED device, such as a display device, that has a total number of micro-LEDs, m, arranged in an array on backplane 40, having an average separation pitch P2. The micro-LEDs 30 are supported in a densely packed array on substrate 12 having an average separation pitch, PI . In various embodiments, P2 is greater than 10 times PI and more specifically P2 is greater than 30 times PI . In such embodiments, a large proportion of the total number of micro- LEDS, m, of display backplane 40 are transferred in a single step. In various embodiments, a n number of micro-LEDs 30 are released forming released micro-LEDs 44 on backplane 40 in each release step. In specific embodiments, the large number of transferred micro-LEDs 30, n, transferred in a single transfer step follows one or more of the following relationships: n > 0.05*m, n > 0A *m, n > 0.2*m, or n > 0.3*m. Thus, as can be seen, even utilizing substrates with gaps 20, 22 and 24, the process described in relation to FIGS. 5-9 allows for a very large percentage of the final number of LEDs needed for display backplane 40 to be transferred with each transfer step.

[0051] Referring to FIG. 10, in embodiments where substrate 12 includes gap rows 20, gap columns 22 and gap intersections 24, additional transfer steps may be needed to populate the corresponding gaps formed on display backplane 40. As shown in FIG. 10, transfer of micro- LEDs from substrate 12 creates gaps on display backplane 40 that correspond to gap rows 20, columns 22 and intersections 24 present on substrate 12. Specifically, following the initial transfer from substrate 12 display backplane 40 includes gap rows 50 that correspond with substrate gap rows 20, gap columns 52 that correspond with substrate gap columns 22 and gap intersections 54 that correspond to substrate gap intersections 24. As will be understood, because substrate 12 includes gaps 20, 22 and 24, when micro-LEDs are released from substrate 12 the areas of gaps 20, 22, and 24 without LEDs are not able to transfer LEDs to the opposing sections of display backplane 40 creating the corresponding backplane gaps 50, 52 and 54.

[0052] As shown in FIG. 10, the size of gaps 50, 52 and 54 are greater than the desired pitch, P2, on display backplane 40 and further, the size of gaps 50, 52 and 54 results in a nonuniform distribution of micro-LEDs 44 on display backplane 40, before the gap-filling transfer steps. To eliminate these gaps and non-uniformity, three additional handling substrates, shown as substrates 60, 62 and 64 are provided. Substrates 60, 62 and 64 are formed in the same manner and have the same arrangement as substrate 12 discussed above. However, when substrates 60, 62 and 64 are aligned with display backplane 40 (in a manner similar to that shown in FIG. 7), only select spaced apart micro-LEDs 30 are released in order to fill in the gaps 50, 52 and 54. As shown in FIG. 10, substrate 60 is an "intersection" substrate, and select micro-LEDs (identified with the number 1) are released onto display backplane 40 to populate all of the intersections 54 on display backplane 40. Substrate 62 is a "row" substrate, and select micro-LEDs (identified with the number 2) are released onto display backplane 40 to populate gap rows 50. Substrate 64 is a "column" substrate, and select micro-LEDs (identified with the number 3) are released onto display backplane 40 to populate gap columns 52. In a particular embodiment, intersections 54 are filled before gap rows 50 or gap columns 52.

[0053] Thus, as shown in FIG. 10, in this embodiment, all micro-LEDs of a given color are populated onto display backplane 40 with four transfers, one from "intersection" substrate 60, one from "row" substrate 62, one from "column" substrate 64 and one from substrate 12. In a specific embodiment, display backplane 40 is populated with transfer from "intersection" substrate 60 first and the transfer from substrate 12 last. In such embodiments, 12 total transfers are needed to fully populate backplane 40 because the four transfers are repeated for each of the three micro-LED colors.

[0054] As noted above, FIGS. 5-10, show pitch, PI , on substrates 12, 60, 62 and 64 as only being one half of pitch P2 on backplane 40 for ease of depiction. FIGS. 11 and 12 illustrate an example of the pitch differential typical between etched micro-LEDs 30 and display backplane 40. In this embodiment, pitch PI of micro-LEDs 30 on substrate 12 is 12.5 μιτι, and pitch P2 of micro-LEDS on display backplane 40 is 375 μπι Thus in this example, every 30th micro-LED 30 from substrate 12 will be transferred to display backplane 40 to provide the display backplane pitch of 375 μιτι.

[0055] In addition, by way of example, FIG. 12 shows each LED group 70 including three micro-LEDs. In one embodiment, each LED group 70 includes a blue micro-LED 72, a green micro-LED 74 and a red micro-LED 76. In another embodiment, each LED group 70 may include three LEDs of the same color, and in such embodiments, display backplane 40 may be used in conjunction with a color conversion device to form a final display device.

[0056] In addition to the handling and efficiency advantages discussed above, the method described herein may provide other advantages over other micro-LED etching and transfer methods. For example, lateral shifting of micro-LEDs during release from the growth wafer has been reported as stress from lattice mismatch is relieved during etching on the growth substrate. Applicant hypothesizes that lateral shifting of the micro-LEDs may be reduced or avoided by etching micro-LEDs 30 on substrate 12 as discussed herein, rather than etching on the growth substrate. [0057] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein, the article "a" is intended to include one or more component or element, and is not intended to be construed as meaning only one.

[0058] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.