Selective transfer of micro LEDs

Abstract

1. A method of manufacturing a micro LED display (300), comprising: providing (102) a micro LED wafer (302) comprising an array of LEDs (304) deposited on a growth substrate (306); depositing (110) an adhesive layer (308) to cover the micro LED wafer (302) while leaving one or more selected LEDs exposed; depositing (112) a backplane (310) on the adhesive layer (308) such that the backplane (310) is aligned with and operably connected to the exposed one or more LEDs; and removing (114) the deposited backplane (310) and one or more LEDs connected to the display substrate (312).

Description

[Technical Field]

[0001] The present invention relates to a method for selectively transferring micro LEDs for flat panel displays, and more particularly for monolithic displays. [Background technology]

[0002] MicroLED displays are an emerging flat-panel display technology that uses tiny LED arrays to form individual pixels. MicroLED displays offer many advantages over traditional liquid crystal displays (LCDs). For example, because the LEDs are only lit when the pixel is lit and can be completely off at other times, microLED displays are much more energy efficient and have better contrast ratios. Furthermore, their fast response times make them suitable for augmented reality (AR) and virtual reality (VR) applications, where high pixel density and high frame rates are particularly useful.

[0003] Micro LED displays are often manufactured by transferring micro LEDs from a source wafer to a receiver substrate (display backplane). This allows RGB displays to be produced from separate red, green, and blue source micro LED wafers. The pitch of the micro LEDs on the source wafer is often different from the pixel pitch of the backplane, so techniques are required to transfer them in the correct position.

[0004] However, moving pixels individually requires a significant amount of time to manufacture a single display using expensive "pick-and-place" equipment, increasing the cost of the display. To reduce manufacturing time, researchers are considering using adhesive films to transfer multiple pixels onto the substrate at once.

[0005] However, the above process presents many challenges. In particular, the transfer process does not have a 100% yield, resulting in missing or misaligned pixels on the backplane. This requires additional rework to produce a fully functional display, significantly increasing the manufacturing cost of these components. Because displays have up to 24 million subpixels, a success rate of at least 99.99999% is required. Currently, the best success rate is around 99%. These issues are particularly pronounced when manufacturing displays with extremely high resolution, pixel density, and contrast ratio, such as those used in augmented reality (AR), virtual reality (VR) devices, or smartwatches. Given the potential increased demand for such devices in the future, a better method for manufacturing microLED displays is needed. Summary of the Invention [Problem to be solved by the invention]

[0006] One way to avoid transferring LEDs from a source wafer to a backplane is to fabricate a monolithic display by processing a backplane directly over the microLEDs on the source wafer. For example, a sapphire substrate may form the bottom layer of a monolithic display, with the microLEDs and thin-film transistors (TFTs) stacked on top. Because TFTs are typically opaque, the area of ​​each pixel must be shared between the TFT and the microLED, reducing the current that can be driven by the display. Furthermore, if high-mobility TFTs (such as LTPS) are used to reduce the TFT footprint, the high-temperature processing required to manufacture LTPS can significantly impair the performance of the microLEDs.

[0007] A further problem with the monolithic displays mentioned above is that the entire area of ​​the source wafer is used for each display, but this is not necessary as microLEDs are bright enough with only a small fraction of the source wafer area, for example around 5% of the source wafer area.

[0008] A further problem with the monolithic displays mentioned above is that because the backplane is processed directly above the micro LEDs on the source wafer, there is no way to repair defective micro LEDs on the source wafer.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome one or more of the problems set forth above. [Means for solving the problem]

[0010] According to a first aspect of the present invention, there is provided a method of manufacturing a micro LED display, the method comprising: providing a micro LED wafer including an array of LEDs deposited on a growth substrate; depositing an adhesive layer over the micro LED wafer leaving selected one or more LEDs exposed; depositing a backplane over the adhesive layer in alignment with and operative connection with the exposed one or more LEDs; and removing the deposited backplane and the one or more LEDs connected to the display substrate.

[0011] In other words, one or more LEDs are selectively transferred from the growth substrate to the display substrate. Therefore, the present invention differs from conventional methods for manufacturing monolithic displays, in which optoelectronic devices and thin-film transistors are grown on the same substrate (which may later be removed). In monolithic displays, each component is grown or deposited on a specific layer rather than being fabricated separately and bonded in a separate manufacturing step. In the present invention, LED components are grown or deposited on a specific layer, other components are deposited on selected LED components, and then the components connected to the selected LED components are removed and placed on a separate substrate.

[0012] A first aspect of the present invention advantageously fabricates a monolithic display by depositing a backplane onto a growth substrate, thereby avoiding the problems associated with transferring LEDs from a source wafer to a backplane. However, because the required brightness is met with only 5% of the light-emitting area of ​​each pixel, conventional monolithic displays do not efficiently utilize the LEDs and growth substrate because the typical density of LEDs on the growth substrate far exceeds that required for the display. The present invention addresses this issue by exposing only selected LEDs on the growth substrate for connection to the backplane, allowing LEDs to be selected at the appropriate pitch for the display. One or more selected and utilized LEDs are removed onto the display substrate to build the display, and the remaining LEDs on the source wafer are reused in another portion of the same or a new display.

[0013] As used herein, the terms "top," "bottom," "above," and "below" refer to the directions and relative positions shown in the figures. It will be understood that these terms do not require that the embodiments described herein be operable only in a particular orientation. The term "top" refers to the growth direction, i.e., the growth direction relative to the substrate (whether or not the device is detached from the substrate). In other words, the growth direction is perpendicular to the plane defined by the substrate, optoelectronic device, reflective layer, and / or thin film transistor.

[0014] "Micro LED display" refers to a display that includes an array of tiny LEDs, where the LEDs form the individual pixel elements. The LEDs themselves may have one or more dimensions on the micrometer scale, but may also have smaller or larger dimensions, such as, but not limited to, on the nanometer scale.

[0015] The term "backplane" is used to refer to circuitry for controlling the function of LEDs. For example, this circuitry may include one or more transistors configured to control the supply of current to the LEDs. The backplane may include, for example, one or more thin-film transistors and a capacitor. Alternatively, the backplane may include additional transistors, capacitors, and / or any additional circuitry for individually addressing each integrated circuit. The backplane may include two transistors and one capacitor (e.g., a switch TFT and a drive TFT), forming a 2T-1C backplane configuration. Processing the backplane on the LEDs refers to depositing the TFTs, followed by etching and depositing connections to connect the TFTs to the LEDs.

[0016] The term "deposition" may refer to deposition performed using chemical vapor deposition (CVD) techniques such as plasma-enhanced chemical vapor deposition (PECVD) or metalorganic chemical vapor deposition (MOCVD), or epitaxy techniques such as metalorganic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). These techniques allow for the deposition of thin films (or "layers") of material on a substrate. Portions of the layer are then selectively removed in a process called patterning, which may be achieved by (dry) etching. In this way, it is possible to electrically isolate adjacent layers from each other and to form channels for electrical pathways through the layers.

[0017] Micro LEDs preferably comprise multiple semiconductor layers deposited sequentially, and thin film transistors comprise multiple layers deposited sequentially on an optoelectronic device.

[0018] In the method for manufacturing a micro LED display, the step of depositing an adhesive layer can include depositing a micro adhesive layer to cover the LED wafer and removing one or more portions of the adhesive layer to expose one or more selected LEDs. After depositing the adhesive layer, removing one or more specific portions of the adhesive layer to expose the one or more selected LEDs can precisely align the adhesive layer with the one or more selected LEDs, as opposed to aligning the adhesive layer with the one or more selected LEDs.

[0019] The adhesive layer may comprise a photoresist. When the adhesive layer comprises a photoresist, the method for manufacturing a micro LED display may further comprise exposing one or more portions of the adhesive layer to light to expose one or more selected LEDs. In this manner, the exposure of one or more portions of the adhesive layer may be more easily controlled, so that one or more portions of the adhesive layer may be more accurately and precisely removed to expose one or more selected LEDs.

[0020] In a method for manufacturing a micro LED display, providing a micro LED wafer may comprise depositing a series of semiconductor layers on a growth substrate to form an LED array. In this manner, a monolithic micro LED wafer may be provided, thereby avoiding the need to transfer the LEDs from a source wafer to a backplane. The LEDs may comprise any form and material to provide the required illumination. For example, the LEDs may comprise III-V nitride materials such as gallium nitride and / or indium gallium nitride. The LEDs may comprise one or more quantum wells and / or quantum dots.

[0021] The method for manufacturing a micro LED display may further include, prior to depositing the adhesive layer, depositing a wiring pattern on the micro LED wafer to connect the LED array to a current source, testing the LEDs by passing a current through the wiring pattern, and selecting one or more LEDs that are functioning properly as one or more selected LEDs to be connected to a backplane and removed from the display substrate. In this manner, all LEDs can be wired and all pixels can be simultaneously illuminated before backplane processing to determine which LEDs are working and which are not. Images of the illuminated LEDs can be used to determine which LEDs should be avoided when constructing the display.

[0022] In the method for manufacturing a micro LED display, the method steps of selecting one or more functional LEDs may further comprise taking images of the micro LED wafer while passing a current through the wiring pattern to illuminate the LED array, processing the images to identify the locations of the properly functioning LEDs, and selecting the properly functioning LEDs as the one or more selected LEDs to be connected to a backplane and removed from the display substrate. In this way, it is possible to identify which LEDs are properly functioning, and to fabricate a micro LED display using only the properly functioning LEDs and connect them to the backplane, thereby avoiding the incorrectly functioning LEDs.

[0023] The method for manufacturing a micro LED display may further include removing the deposited wiring pattern from the selected one or more LEDs so that the selected one or more LEDs are not attached to other portions of the LED array, so that after testing the LEDs, the deposited backplane and the selected one or more LEDs can be easily removed from the display substrate without the connected wiring interfering with removal.

[0024] In the method for manufacturing a micro LED display, the method step of removing the exposed deposited circuitry may further comprise wet etching the exposed deposited circuitry, thereby removing the exposed deposited circuitry in an efficient and low-cost manner.

[0025] In the method for manufacturing a micro LED display, the method may further comprise removing the deposited adhesive layer from the backplane, so that the adhesive layer can be removed and attached to the display substrate in a desired manner without leaving any adhesive layer remaining on the backplane.

[0026] In a method for manufacturing a micro LED display, the method steps of removing the deposited backplane and one or more LEDs connected to the display substrate may further comprise attaching a display substrate onto the deposited backplane, removing selected one or more LEDs from the growth substrate of the micro LED wafer, and lifting off the display substrate with the attached backplane and connected one or more LEDs. In this manner, the deposited backplane and connected one or more LEDs are effectively removed from the display substrate.

[0027] In a method for manufacturing a micro LED display, a method step for removing one or more selected LEDs from a growth substrate comprises laser ablating one or more LEDs. Laser ablation allows for controlled removal of the LEDs from the growth substrate without damaging the LEDs themselves. In particular, removing a very thin layer of material or converting it to a low-melting-point metal (e.g., converting GaN to Ga metal) can remove the LED without significant energy absorption by the remaining LEDs.

[0028] In the method for manufacturing a Micro LED display, the display substrate may comprise a laminated plastic substrate and / or a flexible substrate, and in this way a flexible Micro LED display or device may be manufactured.

[0029] In the manufacturing method of a Micro LED display, the display substrate does not comprise a polymer that is coated from a solution and cured to form a thick polymer film.

[0030] In the method of manufacturing a micro LED display, the backplane may comprise one or more thin film transistors (TFTs), and the method step of depositing the backplane onto the adhesive layer may further comprise connecting the one or more TFTs to the exposed one or more LEDs.

[0031] In a method for manufacturing a micro LED display, one or more selected LEDs comprise a subarray of selected LEDs within an LED array on a micro LED wafer, with the spacing of the selected LEDs within the subarray corresponding to the required pixel spacing of the micro LED display. By having a subarray of selected LEDs with the required pixel spacing of the micro LED display, multiple LEDs can be deposited onto the display substrate at once while maintaining the appropriate spacing when deposited onto the display substrate. This reduces the number of individual LED transfers required to fabricate the micro LED display. More specifically, an LED array can be selected that matches the required pitch of the display's pixels. Because the LEDs are grown in arrays with a much higher density than required for the display's pixels, when the LEDs are exposed for transfer, multiple LEDs can be selected to provide one (or more) LEDs per display pixel.

[0032] In a method for manufacturing a micro LED display, where the deposited backplane is defined as a first backplane, after the method step of removing the deposited backplane and one or more LEDs connected to the display substrate, the method may further comprise depositing an adhesive layer to cover the micro LED wafer while leaving one or more additional LEDs exposed, depositing a second backplane aligned with and operatively connected to the exposed one or more additional LEDs, and removing the deposited second backplane and one or more additional LEDs connected to the display substrate. In this manner, the same micro LED wafer may be used multiple times, thereby reducing the overall manufacturing cost of the micro LED display. Also, each LED on the wafer may be transferred to the display substrate, further reducing the number of micro LED wafers required for production.

[0033] In the method of manufacturing a micro LED display, the deposited second backplane and one or more connected additional LEDs may be removed onto the same display substrate as the first backplane, which may reduce the overall manufacturing cost of the micro LED display since the same micro LED wafer may be used multiple times.

[0034] In the method for manufacturing a micro LED display, the LEDs may comprise one or more of micro LEDs, nano LEDs, and quantum dots. In particular, the size of the LEDs may be selected depending on the type of display required, taking into account, for example, the display size, pixel size, and / or required brightness.

[0035] In the method for manufacturing a micro LED display, the growth substrate may be a sapphire substrate, which provides a suitable lattice match for the growth of various semiconductor materials, particularly III-V nitrides, used to form the LED.

[0036] In a method for manufacturing a micro LED display, the method step of removing one or more portions of an adhesive layer to expose one or more selected LEDs may further comprise using digital lithography to define the one or more selected LEDs to be exposed. Digital lithography allows for the application of user-specified or automatically generated patterns of any shape to the adhesive layer. In particular, the method may comprise determining, on a growth substrate, a selection of functional LEDs having the correct pitch for the micro LED display, creating a mask pattern corresponding to the locations of the selected LEDs, and applying the mask pattern using digital lithography to expose the LEDs. By selecting the specific LEDs, the use of digital lithography allows for the avoidance of random distribution of defective LEDs.

[0037] According to another aspect of the present invention, there is provided a micro LED display comprising: a plurality of LEDs, each having an upper surface and an opposite lower surface; a backplane having an upper surface and an opposite lower surface, the backplane being formed on the upper surfaces of the LEDs, the lower surface of the backplane being deposited directly on and operatively connected to the LEDs; and a display substrate attached to the upper surface of the backplane.

[0038] The present invention distinguishes itself from conventional monolithic displays in which optoelectronic devices and thin-film transistors are grown on the same substrate (the substrate may later be removed). In monolithic displays, each component is grown or deposited on a specific layer rather than fabricated separately and bonded in a separate manufacturing step. In the present invention, the LED component is grown or deposited on a specific layer, other components are deposited on a portion of the LED component, and then the portion of the LED component and the other components are removed onto a separate substrate. This aspect of the present invention has the advantage of fabricating a monolithic display and avoiding the transfer of LEDs from a source wafer to a backplane.

[0039] In a micro LED display, the top surface of the LED may be aligned with the growth direction and the bottom surface may be removed from the growth substrate.

[0040] In a Micro LED display, the display substrate may comprise a laminated plastic substrate attached to the top surface of the backplane, which allows the Micro LED display or device to be flexible.

[0041] The micro LED display may further include a reflective layer formed between the top surface of one or more LEDs and the backplane. The reflective layer is arranged to reflect light emitted from the LEDs, and the reflected light emitted from the micro LED display is emitted in a direction corresponding to the bottom surface of the LEDs. By using the reflective layer, all or most of the light can be emitted in one direction from one side of the micro LED display. In this way, the reflective layer allows most of the light emitted from the LEDs to be emitted in one direction, improving the efficiency of the micro LED display.

[0042] According to another aspect of the present invention, there is provided a virtual reality or augmented reality headset comprising a micro LED display as described above.

[0043] According to another aspect of the present invention, there is provided a smart watch comprising the above-described micro LED display.

[0044] According to another aspect of the present invention, an integrated circuit for testing LEDs for a micro LED display is provided. The integrated circuit comprises a micro LED wafer having an LED array deposited on a growth substrate, and a wiring pattern deposited on the micro LED wafer for connecting each LED of the LED array to a current source for testing the LEDs prior to transfer to a micro LED display. In this way, all LEDs can be wired prior to backplane processing, and all pixels can be illuminated simultaneously to determine which LEDs are working and which are not. Images of the illuminated LEDs can be used to determine which LEDs to avoid when building the display.

[0045] Those skilled in the art will understand that any apparatus feature described herein may also be provided as a method feature, and vice versa, and that specific combinations of the various features described and defined in any aspect described herein may be implemented and / or provided and / or used independently.

[0046] Furthermore, it will be understood that the invention has been described herein purely by way of example and modifications of detail can be made within the scope of the invention.

[0047] One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0048] [Figure 1] FIG. 1 is a flow diagram illustrating a method for manufacturing a micro LED display according to an embodiment. [Figure 2] FIG. 2 is a flow diagram illustrating a method for selecting properly functioning LEDs as part of a method for manufacturing a micro LED display according to an embodiment. [Figure 3a] FIG. 3a is a schematic diagram illustrating a method for manufacturing a micro LED display according to one embodiment of the present invention. [Figure 3b]1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3c] 1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3d] 1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3e] 1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3f] 1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3g] 1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3h] 1A-1D are schematic diagrams illustrating a method for manufacturing a micro LED display according to an embodiment of the present invention. [Figure 3i] FIG. 3i is a schematic diagram illustrating a method for manufacturing a micro LED display according to one embodiment of the present invention. [Figure 4a] Figure 4a shows a schematic diagram of a microLED display. [Figure 4b] Figure 4b shows a schematic diagram of a display component formed from multiple pixels. [Figure 4c] Figure 4c shows a transistor array for a display backplane. [Figure 4d] Figure 4d shows an integrated circuit that may form part of the transistor array of Figure 4c. [Figure 5] FIG. 5 shows a schematic diagram of a backplane used in a method for manufacturing a micro LED display according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0049] In the following description and accompanying drawings, corresponding features are preferably identified using corresponding reference numerals to avoid describing common features in detail for each embodiment.

[0050] For clarity and conciseness, the terms "top," "bottom," "upper," and "lower" refer to the orientations and relative positions shown in the figures. It should be understood that these terms do not require that the embodiments described herein be operable only in a particular orientation. Furthermore, unless expressly specified otherwise, terms such as "located," "positioned," and "disposed" are intended to describe the relative position of two components or layers and do not exclude other components from being disposed between the two components.

[0051] Figure 1 illustrates a method for manufacturing a micro LED display 300. The method of Figure 1 can be performed by a micro LED display manufacturing system. Figures 3a-3i are schematic diagrams of a method for manufacturing a micro LED display. Although Figures 3a-3i show only a 16 LED array, it will be understood that any number of LEDs may be arranged in the array.

[0052] In step 102, a micro LED wafer 302 is provided. The micro LED wafer 302 may be provided as shown in FIG. 3a. The micro LED wafer 302 may include an LED array 304 deposited on a growth substrate 306. The LED array 304 may include one or more LEDs. While FIG. 3a shows an array of 16 LEDs, this is for illustrative purposes only, and those skilled in the art will appreciate that an actual array may include many more LEDs. For example, the LED array 304 may include approximately one million LEDs. The one or more LEDs in the LED array 304 may be one or more micro LEDs, nano LEDs, quantum dot LEDs, organic LEDs, or any other type of LED of any suitable size. The one or more LEDs may be configured to emit light of a predetermined color, such as light of a particular wavelength or within a particular wavelength band. The growth substrate 306 may be a sapphire substrate or may be made of other suitable materials, such as zinc oxide or silicon carbide. If desired, a series of semiconductor layers may be deposited on the growth substrate 306 to form the LED array 304.

[0053] Optionally, in step 104, a wiring pattern 314 is deposited on the micro LED wafer 302 to connect the LED array 304 to a current source. The wiring pattern 314 may be connected to an anode test pad 316 and a cathode test pad 318, as shown in FIG. 3b. The anode test pad 316 may comprise gold connected to an indium tin oxide (ITO) layer on the anode of the LED, and the cathode test pad 318 may comprise gold connected to an N-type gallium nitride (N-GAN) layer forming the cathode of the LED. The cathode may be common to all LEDs, or the devices may be etched apart, requiring a wiring pattern to connect the common cathode test pad to the cathode connection. Optionally, in step 106, a current is applied to the wiring pattern 314 to test the LEDs. The current may be of an appropriate amperage to illuminate the LED array when applied between the anode and cathode. The current is applied to all LEDs, illuminating all LEDs so that they can be identified by imaging and image processing. Optionally, in step 108, one or more properly functioning LEDs are selected as one or more selected LEDs to be connected to the backplane 310 and removed to the display board 312. These properly functioning LEDs may be connected to the backplane 310 individually or as a group of one or more properly functioning LEDs to be removed to the display board 312. A properly functioning LED may be an LED that lights up as expected when current is applied to the wiring pattern 314 and the LED array 304. An LED that does not light up when current is applied to the wiring pattern 314 and the LED array 304 is not functioning properly. Optional steps 104, 106, and 108 allow wiring of the LED array 304 prior to backplane processing. Testing the LEDs by applying current to the wiring pattern allows all of the LEDs to light up simultaneously, thereby determining which LEDs are working and which are not.

[0054] FIG. 2 illustrates a method for manufacturing a micro LED display 300, specifically, a method for selecting one or more functional LEDs as one or more selected LEDs to be connected to a backplane and removed to a display substrate. The method of FIG. 2 can be performed by a system for manufacturing a micro LED display. Step 108 of selecting one or more functional LEDs may include taking 202 an image of the micro LED wafer 302 while applying current to the wiring pattern 314 to illuminate the LED array 304. The image of the micro LED wafer 302 may include the entire LED array 304 or a subsection of the LED array 304. The image of the micro LED wafer 302 may be stored for future reference and processing. Step 108 may further include processing 204 the image to identify locations of functional LEDs. A functional LED may be an LED that illuminates as expected when current is applied to the wiring pattern 314 and the LED array 304. The locations of the functional LEDs may be stored for future reference and to determine the selection of LEDs to be connected to the backplane 310 and removed to the display substrate 312. Step 108 may further include selecting 206 one or more functioning LEDs as the one or more selected LEDs to be connected to backplane 310 and removed onto display substrate 312. This allows for the avoidance of defective LEDs, meaning that defective LEDs are not transferred onto display substrate 312. Thus, the number of defective LEDs on display substrate 312 is minimized.

[0055] Step 108 may optionally further include removing 208 the deposited wiring pattern 314 from the selected one or more LEDs such that the selected one or more LEDs are not attached to the remainder of the LED array 304. In step 208, removing the deposited wiring pattern 314 may include wet etching the deposited wiring pattern 14.

[0056] In step 110, an adhesive layer 308 is deposited over the micro LED wafer 302, while leaving one or more selected LEDs exposed. The adhesive layer 308 may be deposited as shown in FIG. 3c. The selected one or more LEDs may comprise a subarray of selected LEDs within the LED array 304 on the micro LED wafer 302. The spacing of the selected LEDs in the subarray may correspond to the required pixel spacing of the micro LED display 300. Step 110 of depositing the adhesive layer 308 may include depositing the adhesive layer 308 over the micro LED wafer 302. Step 110 may include removing one or more portions of the adhesive layer 308 to expose the selected one or more LEDs. Optionally, the adhesive layer 308 may comprise photoresist. If the adhesive layer 308 comprises photoresist, one or more portions of the adhesive layer 308 may be exposed to light to expose the selected one or more LEDs. Alternatively, removing one or more portions of adhesive layer 308 to expose the selected one or more LEDs may include using digital lithography to define the selected one or more LEDs to be exposed. The selected one or more LEDs that are exposed or left exposed may be one or more functioning LEDs. This avoids random distribution of defective LEDs, which means that defective LEDs are not transferred to display substrate 312. Therefore, the number of defective LEDs on display substrate 312 is minimized.

[0057] Optionally, if not already completed in step 208, the deposited wiring pattern 314 may be removed from the selected one or more LEDs to prevent the selected one or more LEDs from being attached to the remainder of the LED array 304. The deposited wiring pattern 314 may be removed from the selected one or more LEDs, leaving the selected one or more LEDs as shown in Figure 3d. Removal of exposed deposited circuitry may include wet etching of the exposed deposited circuitry.

[0058] In step 112, a backplane 310 is deposited on the adhesive layer 308, and the backplane 310 is aligned with and operably connected to the exposed LED(s). The backplane 310 may be deposited on the adhesive layer 308 as shown in FIG. 3e. Aligning the backplane 310 with the exposed LED(s) allows the exposed LED(s) to be properly positioned and connected to the backplane 310. By operably connected, it is meant that the backplane and the exposed LED(s) are connected by one or more interlayer connections, for example, one or more vias. The backplane 310 may include one or more thin film transistors (TFTs). If the backplane 310 includes one or more TFTs, step 112 of depositing the backplane 310 on the adhesive layer 308 includes connecting the one or more TFTs to the exposed LED(s). The backplane 310 may be configured as shown in FIG. 5.

[0059] In step 114, the deposited backplane 310 and the connected one or more LEDs are removed to a display substrate 312. The deposited backplane 310 and the connected one or more LEDs can be removed to the display substrate 312, as shown in FIG. 3g. The display substrate 312 may be a laminated plastic substrate. Alternatively, or additionally, the display substrate 312 may be a flexible substrate. When the display substrate 312 is a flexible substrate, a flexible device can be manufactured. Step 114 of removing the deposited backplane 310 and the connected one or more LEDs to the display substrate 312 may include attaching the display substrate 312 onto the deposited backplane 310, as shown in FIG. 3f. The display substrate 312 may be attached to the deposited backplane by lamination using an adhesion promoter, or the substrate may be a coated polymer that is cured to form a thick polymer film. The coated polymer may be coated from a solution. Step 114 may also include removing one or more selected LEDs from the growth substrate 306 of the micro LED wafer 302. Removing the selected LED(s) from the growth substrate 306 may be performed using any suitable etching technique or may be achieved using a laser. For example, removing the selected LED(s) from the growth substrate 306 may be performed by ablating the LED(s) using a laser. Step 114 may also include lifting off the backplane 310 and the display substrate 312 with the attached LED(s). With the display substrate 312 attached to the deposited backplane 310, the backplane 310 attached to the selected LED(s), and the selected LED(s) removed from the growth substrate 306, the lifting off may include pulling the display substrate 312 and the growth substrate 306 away from each other in opposite directions within the plane of the growth direction. Step 114 may yield the growth substrate 306 and the remaining LED array 304, as shown in FIG. 3h.

[0060] Some or all of the deposited adhesive layer 308 may remain attached to the deposited backplane 310 after the deposited backplane 310 is removed (114) to the display substrate 312. The remaining deposited adhesive layer 308 may be removed from the backplane 310 before the backplane 310 is placed on the display substrate 312. Alternatively, or additionally, some or all of the deposited adhesive layer 308 may remain attached to the micro LED wafer 302 after the deposited backplane 310 is removed (114) to the display substrate 312. The remaining deposited adhesive layer may be removed from the micro LED wafer 302 after the deposited backplane 310 is removed (114) to the display substrate 312.

[0061] In step 116, an adhesive layer 308 is deposited over the micro LED wafer 302, leaving one or more additional LEDs exposed. The adhesive layer 308 may be deposited over the micro LED wafer 302, leaving one or more additional LEDs exposed, as shown in FIG. 3i. The selected one or more LEDs may comprise a subarray of selected LEDs within the LED array 304 on the micro LED wafer 302. The spacing of the selected LEDs in the subarray may correspond to the desired pixel spacing of the micro LED display 300. Step 116 of depositing the adhesive layer 308 may include depositing the adhesive layer 308 over the micro LED wafer 302. Step 116 may include removing one or more portions of the adhesive layer 308 to expose the selected one or more LEDs. Optionally, the adhesive layer 308 may comprise photoresist. If the adhesive layer 308 comprises photoresist, one or more portions of the adhesive layer 308 may be exposed to light to expose the selected one or more LEDs. Alternatively, removing one or more portions of adhesive layer 308 to expose the selected one or more LEDs may include using digital lithography to define the selected one or more LEDs to be exposed. The selected one or more LEDs that are exposed or left exposed may be one or more functioning LEDs. This avoids random distribution of defective LEDs, which means that defective LEDs are not transferred to display substrate 312. Therefore, the number of defective LEDs on display substrate 312 is minimized.

[0062] In step 118, the deposited backplane 310 is defined as the first backplane 310, and a second backplane is deposited so as to be aligned with and operably connected to one or more additional exposed LEDs. Aligning the second backplane with the exposed LEDs allows the exposed LEDs to be properly positioned and connected to the backplane 310. Operatively connected may mean that the backplane and the exposed LEDs are connected by one or more interlayer connections, such as one or more vias. The second backplane may include one or more thin film transistors (TFTs). If the second backplane includes one or more TFTs, step 118 of depositing the second backplane on the adhesive layer 308 includes connecting the one or more TFTs to the exposed LEDs. The second backplane may be configured as shown in FIG. 5.

[0063] In step 120, the deposited second backplane and the connected one or more additional LEDs are removed to the display substrate 312. The deposited second backplane and the connected one or more additional LEDs may be removed to the same display substrate 312 as the first backplane 310. The display substrate 312 may be a laminated plastic substrate. Alternatively, or additionally, the display substrate 312 may be a flexible substrate. When the display substrate 312 is a flexible substrate, a flexible device can be manufactured. Step 120 of removing the deposited second backplane and the connected one or more LEDs to the display substrate 312 may include attaching the display substrate 312 to the deposited second backplane. The display substrate 312 may be attached to the deposited backplane by lamination using an adhesion promoter, or the substrate may be a coated polymer that is cured to form a thick polymer film. Step 120 may also include removing one or more selected LEDs from the growth substrate 306 of the micro LED wafer 302. Removing one or more selected LEDs from growth substrate 306 may be performed by any suitable etching technique or may be accomplished using a laser. For example, removing one or more selected LEDs from growth substrate 306 may be performed by laser ablating one or more LEDs. Step 120 may also include lifting off display substrate 312 with the attached second backplane and one or more connected LEDs. With display substrate 312 attached to the second deposition backplane, the second backplane attached to one or more selected LEDs, and one or more selected LEDs removed from growth substrate 306, the lifting off may include pulling display substrate 312 and growth substrate 306 in opposite directions in the plane of the growth direction. Step 120 may result in growth substrate 306 and remaining LED array 304, as shown in FIG. 3h.

[0064] After the second deposition backplane is removed 114 from the display substrate 312, some or all of the deposited adhesive layer 308 may remain attached to the second deposition backplane. The remaining deposited adhesive layer 308 may be removed from the second backplane before the second backplane is placed on the display substrate 312. Alternatively, or additionally, after the second deposition backplane is removed 114 from the display substrate 312, some or all of the deposited adhesive layer 308 may remain attached to the micro LED wafer 302. After the second deposition backplane is removed 114 from the display substrate 312, the remaining deposited adhesive layer may be removed from the micro LED wafer 302.

[0065] This method may be repeated multiple times until there are no functioning LEDs left in the LED array 304 on the growth substrate, in which case the only LEDs remaining may be non-functioning LEDs.

[0066] FIG. 4a illustrates a micro LED display 300. The micro LED display may include multiple LEDs, each having a top surface and an opposite bottom surface. The multiple LEDs may be one or more of micro LEDs, nano LEDs, quantum dots, organic LEDs, or any other type of LED of any suitable size. The multiple LEDs may be configured to emit light of a predetermined color, such as light of a particular wavelength or within a particular wavelength band. The top surface of the LED may correspond to the growth direction, and the bottom surface of the LED may be removed from the growth substrate 306. While FIG. 4a illustrates an array including only one LED, it will be understood that any number of LEDs may be present in the array to provide a particular resolution. The LEDs may be arranged at a particular LED density and / or pitch to provide a display suitable for various devices. For example, a high density of LEDs may be particularly suitable for displays in VR or AR headsets or smartwatches. The growth substrate 306 may be a sapphire substrate or may be made of other suitable materials, such as zinc oxide or silicon carbide. The micro LED display 300 may also include a backplane 310 having a top surface and an opposite bottom surface. The backplane 310 may include one or more thin film transistors (TFTs). The backplane 310 is formed on the top surface of the LEDs, and the bottom surface of the backplane 310 is deposited directly on and operatively connected to the LEDs. The micro LED display 300 may also include a display substrate 312 attached to the top surface of the backplane 310. The display substrate 312 may be a laminated plastic substrate attached to the top surface of the backplane 310. The display substrate 312 may alternatively or additionally be a flexible substrate.

[0067] The micro LED display 300 may also include a reflective layer formed between the top surface of one or more LEDs and the backplane 310 (not shown in FIG. 4a). The reflective layer is positioned to reflect light emitted from the LEDs, and the reflected light is emitted from the micro LED display 300 in a direction corresponding to the bottom surface of the LEDs. The reflective layer preferably covers at least 50% of the area of ​​the LEDs. The reflective layer may be a metal layer and may include Al, Ag, Mo, and / or Au. Alternatively, the reflective layer may comprise a distributed Bragg reflector with polarizing properties that may be useful for illuminating a liquid crystal display (LCD) positioned below the LED display device. When the micro LED display 300 includes a reflective layer, the display substrate 312 may be at least partially transparent. If the display substrate 312 is partially transparent, it preferably has a transparency of at least 70%. The display substrate 312 may have a polished bottom surface so as not to affect the image quality from the micro LED display 300. Optionally, one or more lenses (not shown) and / or color filters may be provided on the underside of the display substrate to collimate or focus or tune the wavelength of the light exiting the display substrate 312. Optionally, prior to polishing, the display substrate 312 may be thinned by backgrinding or chemical etching to reduce the distance between the LEDs and the optical elements.

[0068] The above-described embodiment has several advantages. First, the use of a reflective layer that reflects upward-emitted light back through the display substrate 312 allows the backplane 310 to cover a large area without blocking each LED. Therefore, compared to conventional monolithic devices where the area of ​​the backplane 310 is limited, the backplane 310 can deliver more current to each LED. Second, a more efficient micro LED display 300 is achieved because a greater percentage of the light emitted from each LED is reflected back toward the intended direction of emission, rather than wasting light emitted in a direction opposite to the intended emission direction. This means that the LEDs can operate at a lower temperature to produce the same light output, reducing stress on the backplane 310 and potentially improving the performance and lifetime of the micro LED display 300.

[0069] One challenge with manufacturing monolithic displays is that the metals used in the reflective layer and LEDs can be damaged by temperatures exceeding 150°C. Inorganic backplanes 310, such as amorphous silicon (A-Si), low temperature polycrystalline silicon (LTPS), and indium gallium zinc oxide (IGZO), require high-quality SiN x A PECVD process is used to deposit the dielectric layer, but this process is only effective at temperatures above 300°C and can damage the LEDs and reflective layers already present in the microLED display.

[0070] This is particularly advantageous when the backplane 310 is an organic TFT (OTFT). OTFTs may be deposited on the display 300 at much lower temperatures than inorganic TFTs, avoiding damage to the reflective layer or LEDs. For example, OTFTs can be processed at temperatures as low as 80°C because heating is required only to remove the coating solvent from the formulated ink. The low-temperature deposition process for OTFTs ensures that the reflective layer and LEDs are not damaged, making it particularly advantageous for forming monolithic devices using OTFTs.

[0071] Suitable structures and materials for OTFTs are described in WO 2022 / 101644 and WO 2020 / 002914. For example, an OTFT may comprise an organic semiconductor (OSC) layer, an organic gate insulator (OGI) film, a sputtered resistive layer (SRL), a substrate, and a base layer. The OSC layer may comprise at least one semiconductor ink containing a small molecule organic semiconductor and an organic binder. The OGI layer of the OTFT may comprise a material such as that described in WO 2020 / 002914. The SRL may comprise a crosslinked organic layer such as that described in WO 2020 / 002914. The crosslinked organic layer is preferably obtained by polymerization of a solution comprising at least one non-fluorinated multifunctional acrylate, a non-acrylate organic solvent, a crosslinkable fluorinated surfactant, and a silicone surfactant. The silicone surfactant is preferably a crosslinkable silicone surfactant, but may also be a non-fluorinated surfactant. The silicone surfactant may be an acrylate-functionalized silicone surfactant and / or a methacrylate-functionalized silicone surfactant. The substrate may comprise glass or a polymer. The base layer may comprise an organic cross-linked layer using suitable materials as described in WO2020 / 002914.

[0072] The micro LED display 300 may be combined with other components to provide a display device. For example, a protective layer, a frame, electrical connections, or other suitable components may be combined with the micro LED display 300. The micro LED display 300 may be used as a display for a VR or AR headset or a smartwatch.

[0073] Each LED in the micro LED display 300 is individually addressable, and the state of each LED is controlled by the backplane 310, which may include one or more thin film transistors (TFTs). The TFTs may be used as switching devices to control the operation of each LED and / or as driving devices to drive the LEDs.

[0074] FIG. 4b shows a schematic diagram of a display component 41 comprising an array of pixels 45. While FIG. 4b shows an array of only 40 pixels 45, it will be understood that any number of pixels 45 may be present in the array to provide a particular resolution. As described in more detail below, the pixels 45 may comprise subpixels configured to emit light of predetermined colors, for example, to provide an RGB display. Furthermore, the pixels may be arranged at a particular pixel density and / or pixel pitch to provide a display suitable for various devices. For example, a high density of pixels 45 may be particularly suitable for displays in VR or AR headsets and smartwatches. Other components may be combined with the display component 41 to provide a display device. For example, protective layers, frames, electrical connections, and / or other suitable components may be combined with the display component 41.

[0075] Each pixel 45 (or subpixel) of the display component 41 is individually addressable, and the state of each pixel 45 is controlled by one or more thin film transistors (TFTs). The TFTs are used as switching devices to control the operation of each pixel and / or as driving devices to drive the pixel. For example, TFTs function as switches and current drivers in a micro LED display, an organic LED (OLED) display, or a quantum dot light-emitting diode (QD-LED) display. Each pixel of the display component 41 is provided by one or more integrated circuits 410 disposed on the substrate 412. For example, one integrated circuit 410 may provide a pixel 45 of the display component 41, or multiple integrated circuits 410 may be used to provide multiple subpixels of the display component 41. As shown in the example pixel 45 of FIG. 4b, three integrated circuits 410 are provided for each pixel 45. The TFTs may also be used to drive LEDs that provide backlight zones in a liquid crystal display (LCD), with each LED providing backlight for multiple LCD pixels. By dividing the backlight into multiple backlight zones, each controlled by a separate TFT, unnecessary zones may be turned off completely, improving the energy efficiency and contrast ratio of the LCD. For example, a single TFT may be used to switch the LED backlight for a zone of approximately 100 LCD pixels. Thus, as used herein, the term "integrated circuit 410" may refer to individual pixels 45 of the display, as well as to backlight zones provided by LEDs, each backlight zone corresponding to multiple LCD pixels.

[0076] The display component 41 of FIG. 4b is a monolithic display component 41, in which the integrated circuits 410 are deposited (or "grown") on the substrate 412 rather than transferred to the substrate 412 from another substrate (a "source wafer"). As such, the substrate 412 of the display component 41 is also referred to as the source wafer. In a monolithic display, the integrated circuits 410 may be fabricated by forming multiple layers on the substrate 412. This may be achieved using chemical vapor deposition (CVD) techniques, such as plasma-enhanced chemical vapor deposition (PECVD) or metalorganic chemical vapor deposition (MOCVD), or epitaxy techniques, such as metalorganic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). These techniques allow thin films (or "layers") of material to be deposited on the substrate 412 to form each integrated circuit 410. Portions of the layers may then be selectively removed in a process known as patterning, which is accomplished by dry etching. This can electrically isolate adjacent integrated circuits and create channels for electrical pathways through the layers.

[0077] The process of individually addressing the pixels 5 will now be described in more detail with reference to Figures 4c and 4d. Figure 4c shows a transistor array 400 for a display backplane. The transistor array 400 comprises a plurality of integrated circuits 402 arranged in a regular array of rows and columns. Each integrated circuit 402 contains a thin film transistor (TFT) 408. As in conventional active matrix displays, each TFT acts as a switch that controls the application of current to a corresponding pixel capacitor 401, and each integrated circuit 402 may comprise a 2T-1C type or other combination of transistors and capacitors.

[0078] The backplane includes a series of row (scan or gate) lines 403 connected to the gates of each TFT 408 in a common row, and each row line 403 is connected to a row driver 404 for applying a voltage to the gate of each TFT in a particular row. The source or drain terminal of each TFT 408 in a particular column is connected to a column (data) line 405. A row driver 406 is connected to each gate line 405, and the column driver 406 is connected to each data line 405. Each integrated circuit 402 can be individually addressed by applying a voltage pulse with the row driver 404 to turn on each TFT 408 in the row, while simultaneously applying the required data voltage to the source or drain terminal of each TFT 408. By scanning each row in turn and applying a data voltage to each data line 405, a data signal can be written to the pixel capacitors 401 of the matrix. In this way, the transistors and capacitors of each integrated circuit 402 may maintain the state of the pixel while other pixels are being addressed.

[0079] 4d shows an example of a 2T-1C integrated circuit 402 with a select or switch TFT 408, a drive TFT 520, and a storage capacitor 401. When a row (scan) line is turned on, a data signal V DATA can write a voltage to the storage capacitor 401, which is also connected to the gate of the driving TFT 520. V DD Voltage and V SS When a voltage is applied, the change in resistance of the drive TFT 520 causes a current to flow through the LED 515 according to the voltage applied to the gate of the drive TFT 520, modulating the amount of light emitted from the display.

[0080] Figure 5 shows the design of a single pixel that forms part of a backplane that can be utilized in the above manner. The backplane is constructed from a repeating unit of this pixel according to the number of rows and columns required for the backplane array matrix.

[0081] FIG. 3b shows an integrated circuit for testing LEDs for a micro LED display 300. The integrated circuit may include a micro LED wafer 302. The micro LED wafer 302 may include an LED array 304 deposited on a growth substrate 306. The growth substrate 306 may be a sapphire substrate or may be made of other suitable materials, such as zinc oxide or silicon carbide. The integrated circuit may also include a wiring pattern 314 deposited on the micro LED wafer 302. The wiring pattern 314 may be connected to an anode test pad 316 and a cathode test pad 318, as shown in FIG. 3b. The anode test pad 316 may comprise gold connected to an indium tin oxide (ITO) layer on the anode of the LED, and the cathode test pad 318 may comprise gold connected to an N-type gallium nitride (N-GAN) layer forming the cathode of the LED. The cathode may be common to all LEDs, or the devices may be separated by etching, requiring a wiring pattern to connect the common cathode test pad to the cathode connection. The wiring pattern 314 may connect each LED in the LED array to a power source to test the LEDs before transfer to a micro LED display, as shown in FIG. 2. The current may be of an appropriate amperage to illuminate the LED array when applied between the anode and cathode. The integrated circuit may be configured to pass current through all of the LEDs, illuminating all of the LEDs, and to enable imaging and image processing to determine which LEDs are functional and which are not.

[0082] While the foregoing relates to exemplary embodiments of the present invention, it will be understood that the invention is described herein by way of example only and that modifications of detail may be made within the scope of the present invention. Moreover, those skilled in the art will understand that the present invention is not limited to the embodiments disclosed herein or by details shown in the accompanying drawings that are not specifically described herein or defined in the claims. In fact, such unnecessary features may be omitted from the drawings without detracting from the invention.

[0083] Furthermore, other and further embodiments of the invention will be apparent to those skilled in the art from consideration of this specification and may be devised without departing from the basic scope of the invention as defined by the appended claims.

Claims

1. Providing (102) a micro LED wafer (302) comprising an LED array (304) deposited on a growth substrate (306); depositing (110) an adhesive layer (308) over the micro LED wafer (302) leaving one or more selected LEDs exposed; depositing (112) a backplane (310) on the adhesive layer (308) such that the backplane (310) is aligned with and operatively connected to the exposed one or more LEDs; A method of manufacturing a micro LED display (300) comprising removing (114) one or more LEDs connected to the deposited backplane (310) and display substrate (312).

2. depositing (110) the adhesive layer (308), depositing the adhesive layer (308) to cover the micro LED wafer (302); The method of claim 1 , comprising removing one or more portions of the adhesive layer (308) to expose one or more selected LEDs.

3. the adhesion layer (308) comprises a photoresist, and the method comprises:

3. The method of claim 2, comprising exposing the one or more portions of the adhesive layer (308) to expose the one or more selected LEDs.

4. providing (102) the micro LED wafer (302), 10. The method of any preceding claim, comprising depositing a sequence of semiconductor layers onto the growth substrate (306) to form the LED array (304).

5. Prior to depositing (110) the adhesion layer (308), the method further comprises: depositing a wiring pattern (314) on the micro LED wafer to connect the LED array (304) to a current source (104); applying a current to the wiring pattern (314) to test the LED (106); 10. The method of claim 1, further comprising selecting (108) one or more functional LEDs to connect to the backplane (310) and remove from the display substrate (312).

6. Selecting one or more functioning LEDs (108) taking an image of the micro LED wafer while applying a current to the wiring pattern to light up the LED array; processing the image to identify locations of functional LEDs; 6. The method of claim 5, further comprising selecting one or more functioning LEDs to connect to a backplane and to be removed from the display substrate.

7. The method comprises:

7. The method of claim 5 or 6, comprising removing (208) the deposited wiring pattern (314) from the one or more selected LEDs such that the one or more selected LEDs are not attached to the remainder of the LED array (304).

8. The method of claim 7 , wherein removing (208) the exposed deposited circuitry comprises wet etching the exposed deposited circuitry.

9. 10. The method of any preceding claim, further comprising removing the deposited adhesion layer (308) from the backplane (310).

10. removing (114) one or more LEDs connected to the deposited backplane (310) and display substrate (312); attaching a display substrate (312) onto the deposited backplane (310); removing the selected one or more LEDs from the growth substrate (306) of the micro LED wafer (302); 10. The method of any preceding claim, comprising lifting the display substrate (312) with the attached backplane (310) and one or more connected LEDs.

11. 11. The method of claim 10, wherein removing the one or more selected LEDs from the growth substrate comprises laser ablating the one or more LEDs.

12. The method of claim 1 , wherein the display substrate (312) comprises a laminated plastic substrate.

13. The method of any one of claims 1 to 11, wherein the display substrate (312) comprises a polymer that is coated from a solution and cured to form a thick polymer film.

14. 10. The method of any preceding claim, wherein the display substrate (312) is a flexible substrate.

15. 10. The method of claim 1, wherein the backplane (310) comprises one or more thin film transistors (TFTs), and wherein depositing the backplane (310) on the adhesive layer (112) comprises connecting the one or more TFTs to the exposed one or more LEDs.

16. 10. The method of any preceding claim, wherein the one or more selected LEDs comprise a sub-array of selected LEDs within the LED array (304) on the micro LED wafer (302) having a spacing of the selected LEDs within the sub-array that corresponds to a required pixel spacing of the micro LED display (300).

17. After removing (114) the deposited backplane (310), defining the deposited backplane (310) as a first backplane (310), and one or more LEDs connected to a display substrate (312), the method includes: depositing (116) an adhesion layer (308) over the micro LED wafer (302) while exposing one or more additional LEDs; depositing (118) a second backplane aligned with and operatively connected to the exposed one or more additional LEDs; and 10. The method of any preceding claim, further comprising removing (120) one or more further LEDs connected to the deposited second backplane and display substrate (312).

18. 18. The method of claim 17, wherein the deposited second backplane and the connected one or more additional LEDs are removed (120) to the same display substrate (312) as the first backplane (310).

19. 10. The method of any preceding claim, wherein the LED comprises one or more of a micro LED, a nano LED, or a quantum dot.

20. 10. The method of any preceding claim, wherein the growth substrate (306) is a sapphire substrate.

21. removing one or more portions of the adhesive layer (308) to expose the one or more selected LEDs; A method according to any one of claims 2 to 20, comprising defining the one or more selected LEDs to be exposed using digital lithography.

22. a plurality of LEDs, each having a top surface and an opposite bottom surface; a backplane (310) having an upper surface and an opposite lower surface, the backplane (310) being formed on the upper surface of the LEDs, the lower surface of the backplane (310) being laminated directly on the LEDs and operatively connected to the LEDs; a display substrate (312) attached to the top surface of the backplane.

23. 23. The micro LED display of claim 22, wherein a top surface of the LED corresponds to the growth direction and the bottom surface is removed from the growth substrate (306).

24. 24. The micro LED display of claim 22 or 23, wherein the display substrate (312) comprises a laminated plastic substrate attached to the top surface of the backplane (310).

25. 25. The micro LED display of claim 22, further comprising a reflective layer formed between the top surface of the one or more LEDs and the backplane (310), the reflective layer being arranged to reflect light emitted by the LEDs, such that the reflected light is emitted from the micro LED display (300) in a direction corresponding to the bottom surface of the LED.

26. a micro LED wafer (302) comprising an LED array (304) deposited on a growth substrate (306); and a wiring pattern (314) deposited on the micro LED wafer (302) for connecting each LED of the LED array to a power source and testing the LEDs prior to transfer to the micro LED display (300).

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