Selective transfer of micro LED

Abstract

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

Description

Technical Field

[0001] The present invention relates to a method for the selective transfer of micro-LEDs for flat panel displays, more particularly monolithic displays. Background Art

[0002] Micro-LED displays are an emerging flat-panel display technology that uses arrays of tiny LEDs to form individual pixels. Micro-LED displays have many advantages over earlier liquid crystal displays (LCDs). For example, because the LEDs are powered only when the pixels are emitting light and can be completely turned off at other times, Micro-LED displays are much more energy efficient and have better contrast. In addition, Micro-LED displays have faster response times, making them more suitable for augmented reality (AR) and virtual reality (VR) applications, where high pixel density and high frame rates are particularly useful.

[0003] MicroLED displays are typically made by transferring microLEDs from a source wafer onto a receiver substrate (display backplane). This allows RGB displays to be made from separate red, green, and blue source microLED wafers. The pitch of the microLEDs on the source wafer is typically different than the pitch of the backplane pixels, so technology is needed to transfer them to the correct position.

[0004] However, when pixels are moved individually, it can take considerable time to produce a single display using expensive "pick and place" machines, which increases the cost of the display. To reduce manufacturing time, the use of adhesive films to transfer multiple pixels to the substrate at once has also been considered.

[0005] However, there are many challenges with the above process. In particular, the transfer process does not have a 100% yield, resulting in backplanes with missing or misaligned pixels. This results in further repair work being required to produce a fully working display, significantly increasing the cost of manufacturing these parts. Since the displays may have up to 24 million sub-pixels, a success rate of at least 99.99999% is required. Currently, the best success rate may be around 99%. Such problems are particularly evident when producing displays with very high resolution, pixel density, and contrast, such as those used in augmented reality (AR) or virtual reality (VR) devices or smart watches. Given that the demand for such devices is likely to increase in the future, a better way to produce micro-LED displays is needed.

[0006] One way to avoid transferring the LEDs from the source wafer to the backplane is to process the backplane directly on top of the micro-LEDs on the source wafer, resulting in a monolithic display. For example, a sapphire substrate can form the bottom layer of a monolithic display, with the micro-LEDs and thin-film transistors (TFTs) deposited on top of it. Since TFTs are typically opaque to light, each pixel area needs to be shared by the TFT and the micro-LED, which reduces the current that can be driven from the display. In addition, if the TFT footprint is reduced by using higher mobility TFTs (such as LTPS), the high temperature process required for manufacturing with LTPS will severely compromise the performance of the micro-LEDs.

[0007] Another problem with the above monolithic displays is that for each display, all of the area of ​​the source wafer is used up. This is unnecessary because the micro-LEDs are bright enough even if only a small area of ​​the source wafer (e.g. 5% of the source wafer area) is illuminated.

[0008] Another problem with the above-mentioned monolithic display is that since the backplane is processed directly on top of the micro-LEDs on the source wafer, there is no way to repair defective micro-LEDs on the source wafer.

[0009] It is therefore an object of the present invention to overcome one or more of the problems set forth above. Summary of the invention

[0010] According to a first aspect of the present invention, there is provided a method for manufacturing a micro-LED display, the method comprising: providing a micro-LED wafer comprising an LED array deposited on a growth substrate; depositing an adhesive layer to cover the micro-LED wafer while keeping one or more selected LEDs exposed; depositing a backplane on the adhesive layer so that the backplane is aligned with and operably connected to the exposed one or more LEDs; and moving the deposited backplane and the connected one or more LEDs to a display substrate.

[0011] In other words, one or more LEDs are selectively transferred from a growth substrate to a display substrate. Thus, the present invention departs from conventional manufacturing methods for monolithic displays, in which optoelectronic devices and thin film transistors are grown on the same substrate (where the substrate can be removed later). In monolithic displays, components are grown or deposited on specific layers, rather than these components being manufactured separately and joined together during separate manufacturing stages. In contrast, in the present invention, LED components are grown or deposited on specific layers, other components are deposited on top of selected portions of the LED components, and then the selected portions of the LED components and the connected components are transferred to another substrate.

[0012] Advantageously, the first aspect of the invention produces a monolithic display due to the fact that the backplane is deposited on the growth substrate, thereby avoiding the problems associated with transferring the LEDs from the source wafer to the backplane. However, conventional monolithic displays do not efficiently utilize the LEDs and the growth substrate because the typical density of LEDs on the growth substrate is much greater than that required for a display where the required brightness is met with only 5% of the light emitting area of ​​each pixel. The present invention solves this problem by exposing only selected portions of the LEDs on the growth substrate for connection to the backplane, so that the LEDs can be selected with appropriate spacing to match the display. One or more of the selected and used LEDs are then moved to the display substrate to build the display, leaving the remaining LEDs of the source wafer to be used again in another segment of the same display or a new display.

[0013] As used herein, the terms "top", "bottom", "above", and "below" refer to directions and relative positions depicted in the figures. It will be understood that these terms do not require that any embodiment described herein can only operate in a specific orientation. The term "top" indicates the growth direction, that is, the growth direction relative to the substrate (the device may or may not have been removed 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] The phrase "micro-LED display" is used to refer to a display that includes an array of micro-LEDs, where the LEDs form individual pixel elements. The LEDs themselves can have one or more dimensions in the micrometer range, but are not limited thereto, and can also have smaller or larger dimensions, such as the nanometer range.

[0015] The phrase "backplane" is used to refer to the circuitry used to control the functionality of the LEDs. For example, the circuitry may include one or more transistors configured to control the current supply to the LEDs. The backplane may include, for example, one or more thin film transistors and capacitors. Alternatively, the backplane may include additional transistors, capacitors, and / or any other circuitry for individually addressing each integrated circuit. The backplane may include two transistors and one capacitor (e.g., a switching TFT and a driving TFT) to form a 2T-1C backplane arrangement. The processing of the backplane on the LEDs may refer to depositing the TFTs, and then etching and depositing connectors to connect them to the LEDs.

[0016] The phrase "deposition" may refer to deposition performed using chemical vapor deposition techniques (CVD) such as plasma enhanced chemical vapor deposition (PECVD) or metal organic chemical vapor deposition (MOCVD), or epitaxial techniques such as metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). These techniques allow the deposition of thin films (or "layers") of material on a substrate. Subsequently, parts of the layers may be selectively removed in a process known as patterning, which may be achieved by (dry) etching. In this way, adjacent parts of the layers may be electrically isolated from each other and channels for electrical paths through the layers may be formed.

[0017] The micro-LED preferably includes many semiconductor layers deposited sequentially, and the thin film transistor includes multiple layers deposited sequentially on the optoelectronic device.

[0018] In a method of manufacturing a micro LED display, the method step of depositing an adhesive layer may include: depositing an adhesive layer to cover the micro LED wafer; removing one or more sections of the adhesive layer to expose the one or more selected LEDs. By removing one or more specific sections of the adhesive layer to expose the one or more selected LEDs, after the adhesive layer has been deposited, the one or more selected LEDs can be precisely aligned with the removed sections of the adhesive layer, as opposed to aligning the adhesive layer with the removed sections with the one or more selected LEDs.

[0019] The bonding layer may include a photoresist. When the bonding layer includes a photoresist, the method of manufacturing a micro LED display may further include exposing the one or more sections of the bonding layer to light to expose the one or more selected LEDs. In this way, the one or more sections of the bonding layer may be removed more accurately and precisely to expose the one or more selected LEDs because it is easier to control the exposure of the one or more sections of the bonding layer to light.

[0020] In a method of manufacturing a micro-LED display, the method step of providing a micro-LED wafer may include depositing a series of semiconductor layers to form the LED array on the growth substrate. In this way, a monolithic micro-LED wafer can be provided, and thereby avoiding the transfer of the LED from the source wafer to the backplane. The LED may include any form and material for providing the desired light emission. For example, the LED may include a III-V nitride material, such as gallium nitride and / or indium gallium nitride. The LED may include one or more quantum wells and / or quantum dots.

[0021] In a method of manufacturing a micro-LED display, before depositing the bonding layer, the method may further include: depositing a wiring pattern on the micro-LED wafer to connect the LED array to a current source; applying a current to the wiring pattern to test the LEDs; and selecting one or more normally functioning LEDs as one or more selected LEDs to be connected to the backplane and transferred to the display substrate. In this way, all LEDs can be wired before backplane processing, and all pixels can be illuminated at the same time to determine which pixels are working and which pixels are not working. The image of the illuminated LEDs can then be used to determine which LEDs to avoid when building the display.

[0022] In the method of manufacturing a micro-LED display, the method step of selecting one or more working LEDs may further include: capturing an image of the micro-LED wafer while applying the current to the wiring pattern to cause the LED array to emit light; processing the image to identify the location of the normally working LEDs; and selecting one or more normally working LEDs as the one or more selected LEDs to be connected to the backplane and transferred to the display substrate. In this way, it is possible to identify which LEDs are working properly, so that only normally working LEDs are used to manufacture the micro-LED display and are bonded to the backplane, and non-normally working LEDs can be avoided.

[0023] In the method of manufacturing a micro LED display, the method may further include: removing the deposited wiring pattern from the one or more selected LEDs so that the one or more selected LEDs are not attached to the rest of the LED array. In this way, after testing the LEDs, the deposited backplane and one or more selected LEDs can be easily transferred to the display substrate without the connected wiring hindering the transfer.

[0024] In the method of manufacturing a micro LED display, the method step of removing the exposed deposited circuitry may further include wet etching the exposed deposited circuitry. In this way, the exposed deposited circuitry may be removed in an efficient and low-cost manner.

[0025] In the method of manufacturing a micro LED display, the method may further include removing the deposited adhesive layer from the backplane. In this way, there is no adhesive layer on the backplane, so that the backplane can be transferred and attached to the display substrate in a desired manner.

[0026] In the method of manufacturing a micro LED display, the method step of transferring the deposited backplane and the connected one or more LEDs to a display substrate may further include: attaching the display substrate to the deposited backplane; releasing the one or more selected LEDs from the growth substrate of the micro LED wafer; and lifting the display substrate with the attached backplane and the one or more connected LEDs. In this way, the deposited backplane and the connected one or more LEDs are effectively transferred to the display substrate.

[0027] In a method of manufacturing a micro-LED display, the method step of releasing the one or more selected LEDs from the growth substrate includes ablating the one or more LEDs with a laser. Laser ablation allows the LEDs to be removed from the growth substrate in a controlled manner without damaging the LEDs themselves. In particular, it allows very thin layers of material to be removed or converted to low melting point metals (e.g., converting GaN to Ga metal) to release the LEDs without the remaining LEDs absorbing significant energy.

[0028] In the method of manufacturing a micro LED display, the display substrate may include a laminated plastic substrate and / or a flexible substrate. In this way, a flexible micro LED display or device may be manufactured.

[0029] In a method of manufacturing a micro LED display, the display substrate may include a polymer 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 include one or more thin film transistors, TFTs. The method step of depositing the backplane on the adhesive layer may further include connecting the one or more TFTs to the exposed one or more LEDs.

[0031] In a method of manufacturing a micro-LED display, the one or more selected LEDs may include a sub-array of selected LEDs within an array of LEDs on the micro-LED wafer, wherein the spacing of the selected LEDs in the sub-array corresponds to the desired pixel spacing of the micro-LED display. By having the sub-array of selected LEDs have the desired pixel spacing of the micro-LED display, multiple LEDs can be transferred to the display substrate at one time while having the correct spacing when they are deposited on the display substrate. This reduces the number of individual transfers of LEDs that need to be made to the display substrate in order to manufacture the micro-LED display. More specifically, an array of LEDs can be selected that matches the desired spacing of the pixels of the display. Since LEDs are grown in an array with a much greater density than required for the pixels of the display, when the LEDs are exposed for transfer, multiple LEDs can be selected so that one (or more than one) LED is provided for each pixel of the display.

[0032] In a method of manufacturing a micro-LED display, after the method step of moving the deposited backplane and the one or more connected LEDs to a display substrate, and wherein the deposited backplane is defined as a first backplane, the method may further include: depositing an adhesive layer to cover the micro-LED wafer while leaving one or more additional LEDs exposed; depositing a second backplane so that the second backplane is aligned with and operably connected to the exposed one or more additional LEDs; and moving the deposited second backplane and the connected one or more additional LEDs to the display substrate. In this way, the overall cost of manufacturing a micro-LED display can be reduced because the same micro-LED wafer can be used multiple times. This further reduces the number of micro-LED wafers that need to be produced because each LED on the wafer can be transferred to the display substrate.

[0033] In the method of manufacturing a micro-LED display, the deposited second backplane and the connected one or more additional LEDs can be moved to the same display substrate as the first backplane. In this way, the overall cost of manufacturing a micro-LED display can be reduced because the same micro-LED wafer can be used multiple times.

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

[0035] In the method of manufacturing a micro-LED display, the growth substrate may be a sapphire substrate. Sapphire provides a suitable lattice match for the growth of many different semiconductor materials to form LEDs, most preferably III-V nitrides.

[0036] In a method of manufacturing a micro-LED display, the method step of removing one or more sections of the bonding layer to expose the one or more selected LEDs may further include using digital lithography to define the one or more selected LEDs that are exposed. Digital lithography allows a pattern of arbitrary shape, specified by a user or automatically generated, to be applied to the bonding layer. In particular, the method may include: determining a selected portion of LEDs on a growth substrate that have the correct spacing for a micro-LED display and are functioning properly; creating a mask pattern corresponding to the location of the selected portion of the LEDs; and using digital lithography to apply the mask pattern to expose the LEDs. By selecting specific LEDs, the use of digital lithography enables the random distribution of defective LEDs to be avoided.

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

[0038] The present invention differs from conventional monolithic displays in which optoelectronic devices and thin film transistors are grown on the same substrate (where the substrate can be removed later). In monolithic displays, components are grown or deposited on specific layers, rather than these components being manufactured separately and joined together during separate manufacturing stages. In contrast, in the present invention, LED components are grown or deposited on specific layers, other components are deposited on top of a portion of the LED components, and then that portion of the LED components and other components are moved to another substrate. Advantageously, this aspect of the present invention produces a monolithic display and thereby avoids transferring the LEDs from the source wafer to the backplane.

[0039] In a micro-LED display, the top surface of the LEDs may correspond to the growth direction, and the bottom surface may be removed from the growth substrate.

[0040] In a micro LED display, the display substrate may include a laminated plastic substrate applied to the top surface of the backplane. In this way, a micro LED display or device may be flexible.

[0041] The micro LED display may further include a reflective layer formed between the top surface of the one or more LEDs and the backplane, the reflective layer being arranged to reflect light emitted by the LEDs so that the reflected light is emitted from the micro LED display in a direction corresponding to the bottom surface of the LEDs. The use of a reflective layer allows all or most of the light to be emitted in one direction through one side of the micro LED display. In this way, the reflective layer causes a greater proportion of the light from the LEDs to be directed in one direction, thereby 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 including the above-mentioned micro LED display.

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

[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 includes: a micro-LED wafer including an array of LEDs deposited on a growth substrate; and a wiring pattern deposited on the micro-LED wafer to connect each LED in the LED array to a current source so that the LEDs can be tested before being transferred to a micro-LED display. In this way, all LEDs can be wired before backplane processing, and all pixels can be illuminated at the same time to determine which pixels are working and which pixels are not working. The image of the illuminated LEDs can then be used to determine which LEDs to avoid when building a display.

[0045] The skilled person will understand that any device feature described herein can be provided as a method feature, and vice versa. It will also be understood that the specific combination of various features described and defined in any aspect described herein can be independently implemented and / or provided and / or used.

[0046] Moreover, it will be understood that the present invention has been described herein purely by way of example and modifications of detail can be made within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] One or more embodiments will now be described, purely by way of example, with reference to the accompanying drawings, in which:

[0048] Figure 1 A flow chart listing a method of manufacturing a micro LED display according to an embodiment is shown.

[0049] Figure 2 A flow chart is shown listing a method of selecting properly functioning LEDs as part of a method of manufacturing a micro LED display according to an embodiment.

[0050] Figures 3a to 3i A schematic diagram showing a method of manufacturing a micro LED display according to an embodiment is shown.

[0051] Figure 4a A schematic diagram of a micro-LED display is shown.

[0052] Figure 4b A schematic diagram showing a display element formed of a plurality of pixels is shown.

[0053] Figure 4c A transistor array for a display backplane is shown.

[0054] Figure 4d It shows that it can form Figure 4c The transistor array that is part of an integrated circuit.

[0055] Figure 5 A schematic diagram showing a backplane used in a method of manufacturing a micro LED display according to an embodiment. DETAILED DESCRIPTION

[0056] In the following description and drawings, corresponding reference numerals may preferably be used to identify corresponding features to avoid the need to describe the common features in detail for each embodiment.

[0057] For the sake of clarity and brevity, the terms "top", "bottom", "above", and "below" refer to directions and relative positions depicted in the figures. It will be understood that these terms do not require that any embodiment described herein can only operate in a specific orientation. In addition, unless otherwise expressly provided, terms such as "located", "positioned", and "disposed" are only used to indicate the relative position of two components or layers, and do not exclude that other components are located between the two components.

[0058] Figure 1 A method of manufacturing the micro LED display 300 is listed. Figure 1 The method may be performed by a system for manufacturing a micro LED display. Figures 3a to 3i A schematic diagram showing a method for manufacturing a micro-LED display. Figures 3a to 3i Only an array with 16 LEDs is depicted, but it will be understood that any number of LEDs may be present in the array.

[0059] In step 102, a micro LED wafer 302 is provided. Figure 3a As shown, a micro LED wafer 302 may be provided. 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. Figure 3a An array of 16 LEDs is shown, but the skilled person will understand that this is for illustration only and that the array may include significantly more LEDs in reality. For example, there may be approximately one million LEDs in the LED array 304. The one or more LEDs in the LED array 304 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 one or more LEDs may be configured to emit light of a predetermined color, such as light of a specific wavelength or light within a specific 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. Optionally, a series of semiconductor layers may be deposited to form the LED array 304 on the growth substrate 306.

[0060] 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 can be connected to the anode test pad 316 and the cathode test pad 318, such as Figure 3b As shown. Anode test pad 316 may include gold connected to an indium tin oxide (ITO) layer on the anode of the LED, and cathode test pad 318 may include gold connected to an n-gallium nitride (n-GaN) layer forming the cathode of the LED. The cathode may be common to all LEDs, or the device may be isolated by etching so that a wiring pattern is required to connect the common cathode test pad to the cathode connector. Optionally, in step 106, a current is applied to wiring pattern 314 to test the LED. The current may have an appropriate amperage so that the LED array emits light when the current is applied between the anode and the cathode. Current may be applied to each LED to cause them all to emit light, thereby allowing imaging and image processing to determine the LED. Optionally, in step 108, one or more normally functioning LEDs are selected as one or more selected LEDs to be connected to backplane 310 and moved to display substrate 312. These one or more normally functioning LEDs may be connected to backplane 310 and moved to display substrate 312 individually or in the form of a group of one or more normally functioning LEDs. A properly functioning LED may be an LED that emits light as expected when current is applied to the wiring pattern 314 and the LED array 304. If the LED does not emit light when current is applied to the wiring pattern 314 and the LED array 304, the LED is not functioning properly. The optional steps of 104, 106, and 108 enable the LED array 304 to be wired prior to backplane processing. By providing current to the wiring pattern to test the LEDs, all of the LEDs are illuminated simultaneously, and then it can be determined which LEDs are functioning and which LEDs are not functioning.

[0061] Figure 2 A method of manufacturing the micro LED display 300 is listed, specifically a method for selecting one or more properly functioning LEDs as one or more selected LEDs to be connected to a backplane and transferred to a display substrate. Figure 2The method can be performed by a system for manufacturing a micro LED display. The step 108 of selecting one or more working LEDs can include capturing 202 an image of the micro LED wafer 302 while applying current to the wiring pattern 314 to cause the LED array 304 to emit light. The image of the micro LED wafer 302 can include the entire LED array 304 or a sub-section of the LED array 304. The image of the micro LED wafer 302 can be stored for future reference and processing. Step 108 can further include processing 204 the image to identify the location of the LEDs that are working properly. A properly functioning LED can be an LED that emits light as expected when current is applied to the wiring pattern 314 and the LED array 304. The location of the properly functioning LEDs can be stored for future reference and used to determine which LEDs will be selected for connection to the backplane 310 and transfer to the display substrate 312. Step 108 can further include selecting 206 one or more properly functioning LEDs as one or more selected LEDs to be connected to the backplane 310 and transferred to the display substrate 312. This operation enables defective LEDs to be avoided, which then means that the defective LEDs will not be transferred to the display substrate 312. Therefore, the number of defective LEDs on the display substrate 312 will be minimized.

[0062] Optionally, step 108 may further include 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 rest of the LED array 304. In step 208, removing the deposited wiring pattern 314 may include wet etching the deposited wiring pattern 314.

[0063] In step 110, an adhesive layer 308 is deposited to cover the micro LED wafer 302 while leaving one or more selected LEDs exposed. The adhesive layer 308 may be formed as shown in FIG. Figure 3c304. The deposition is performed as shown. The one or more selected LEDs may include 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. The step 110 of depositing the adhesive layer 308 may include depositing the adhesive layer 308 to cover the micro LED wafer 302. Step 110 may also include removing one or more sections of the adhesive layer 308 to expose the one or more selected LEDs. Optionally, the adhesive layer 308 may include a photoresist. When the adhesive layer 308 includes a photoresist, one or more sections of the adhesive layer 308 may be exposed to light to expose the one or more selected LEDs. Alternatively, the step of removing one or more sections of the adhesive layer 308 to expose the one or more selected LEDs may include using digital lithography to define the one or more selected LEDs that are exposed. The one or more selected LEDs that are exposed or remain exposed may be one or more working LEDs. This operation enables the random distribution of defective LEDs to be avoided, which then means that the defective LEDs will not be transferred to the display substrate 312. Therefore, the number of defective LEDs on the display substrate 312 will be minimized.

[0064] Optionally, if not already done in step 208, the deposited wiring pattern 314 may be removed from the one or more selected LEDs so that the one or more selected LEDs are not attached to the rest of the LED array 304. The deposited wiring pattern 314 may be removed from the one or more selected LEDs so that the one or more selected LEDs are not attached to the rest of the LED array 304. Figure 3d Removing the exposed deposited circuitry may include wet etching the exposed deposited circuitry.

[0065] In step 112, a backplane 310 is deposited on the adhesive layer 308 such that the backplane 310 is aligned with and operably connected to the exposed one or more LEDs. The backplane 310 may be deposited on the adhesive layer 308, such as Figure 3e As shown. Alignment of the backplane 310 with the exposed one or more LEDs ensures that the exposed one or more LEDs can be properly positioned and connected to the backplane 310. Operably connected can mean that the backplane and the exposed one or more LEDs are connected through one or more interlayer connectors, such as through one or more holes. The backplane 310 may include one or more thin film transistors (TFTs). When the backplane 310 includes one or more TFTs, the step of depositing 112 the backplane 310 on the adhesive layer 308 includes connecting the one or more TFTs to the exposed one or more LEDs. The backplane 310 may be as shown. Figure 5 Configure as shown.

[0066] In step 114, the deposited backplane 310 and the attached one or more LEDs are moved to a display substrate 312. Figure 3g As shown, the deposited backplane 310 and the connected one or more LEDs can be moved to a display substrate 312. The display substrate 312 can be a laminated plastic substrate. Alternatively or additionally, the display substrate 312 can be a flexible substrate. If the display substrate 312 is a flexible substrate, this enables the production of a flexible device. The step 114 of moving the deposited backplane 310 and the connected one or more LEDs to the display substrate 312 can include attaching the display substrate 312 to the deposited backplane 310, such as Figure 3f as shown. The display substrate 312 can be attached to the deposited backplane by lamination with the help of an adhesive, or the substrate can be a coated polymer that is cured to form a thick polymer film. The coated polymer can be coated from a solution. Step 114 can also include releasing one or more selected LEDs from the growth substrate 306 of the micro LED wafer 302. The step of releasing one or more selected LEDs from the growth substrate 306 can be performed via any suitable etching technique, or by using a laser. For example, the release of one or more selected LEDs from the growth substrate 306 can be performed by ablating one or more LEDs with a laser. Step 114 can also include lifting the display substrate 312 with the attached backplane 310 and one or more connected LEDs. Since the display substrate 312 is already attached to the deposited backplane 310, the backplane 310 is already attached to one or more selected LEDs, and the one or more selected LEDs have been released from the growth substrate 306, the lifting step can include pulling the display substrate 312 and the growth substrate 306 in opposite directions to each other in the plane of the growth direction. Step 114 can produce the growth substrate 306 and the remaining LED array 304, as Figure 3h shown.

[0067] Some or all of the deposited adhesive layer 308 may remain attached to the deposited backplane 310 after it has been transferred 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 has been transferred 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 has been transferred 114 to the display substrate 312.

[0068] In step 116, an adhesive layer 308 is deposited to cover the micro LED wafer 302 while leaving one or more additional LEDs exposed. Figure 3iAs shown, an adhesive layer 308 may be deposited to cover the micro LED wafer 302 while keeping one or more additional LEDs exposed. The one or more selected LEDs may include 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 to cover the micro LED wafer 302. Step 116 may also include removing one or more sections of the adhesive layer 308 to expose the one or more selected LEDs. Optionally, the adhesive layer 308 may include a photoresist. When the adhesive layer 308 includes a photoresist, one or more sections of the adhesive layer 308 may be exposed to light to expose the one or more selected LEDs. Alternatively, the step of removing one or more sections of the adhesive layer 308 to expose the one or more selected LEDs may include using digital lithography to define the one or more selected LEDs that are exposed. The one or more selected LEDs that are exposed or remain exposed may be one or more working LEDs. This operation enables a random distribution of defective LEDs to be avoided, which subsequently means that defective LEDs will not be transferred to the display substrate 312. Therefore, the number of defective LEDs on the display substrate 312 will be minimized.

[0069] In step 118, the deposited backplane 310 is defined as the first backplane 310, and the second backplane is deposited so that the second backplane is aligned with the exposed one or more additional LEDs and is operably connected to the exposed one or more additional LEDs. The alignment of the second backplane with the exposed one or more LEDs ensures that the exposed one or more LEDs can be properly positioned and connected to the backplane 310. Operably connected can mean that the backplane and the exposed one or more LEDs are connected through one or more interlayer connectors, such as through one or more holes. The second backplane may include one or more thin film transistors (TFTs). When the second backplane includes one or more TFTs, the step of depositing 118 the second backplane on the adhesive layer 308 includes connecting the one or more TFTs to the exposed one or more LEDs. The second backplane may be as Figure 5 Configure as shown.

[0070] In step 120, the deposited second backplane and the connected one or more additional LEDs are moved to a display substrate 312. The deposited second backplane and the connected one or more additional LEDs can be moved to a display substrate 312 that is the same as the first backplane 310. The display substrate 312 can be a laminated plastic substrate. Alternatively or additionally, the display substrate 312 can be a flexible substrate. If the display substrate 312 is a flexible substrate, this enables the production of a flexible device. The step 120 of moving the deposited second backplane and the connected one or more LEDs to the display substrate 312 can include attaching the display substrate 312 to the second deposited backplane. The display substrate 312 can be attached to the deposited backplane by lamination with the help of an adhesive, or the substrate can be a coated polymer that is cured to form a thick polymer film. Step 120 can also include releasing one or more selected LEDs from the growth substrate 306 of the micro LED wafer 302. The step of releasing one or more selected LEDs from the growth substrate 306 can be performed via any suitable etching technique, or by using a laser. For example, releasing one or more selected LEDs from the growth substrate 306 can be performed by ablating one or more LEDs with a laser. Step 120 may also include lifting off the display substrate 312 with the attached second backplane and one or more connected LEDs. Since the display substrate 312 is already attached to the second deposited backplane, the second backplane is already attached to the one or more selected LEDs, and the one or more selected LEDs are already released from the growth substrate 306, the lifting step may include pulling the display substrate 312 and the growth substrate 306 in opposite directions from each other in the plane of the growth direction. Step 120 may result in the growth substrate 306 and the remaining LED array 304, as shown in FIG. Figure 3h shown.

[0071] Some or all of the deposited adhesive layer 308 may remain attached to the second deposited backplane after it has been transferred 114 to the display substrate 312. 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, some or all of the deposited adhesive layer 308 may remain attached to the micro LED wafer 302 after the second deposited backplane has been transferred 114 to the display substrate 312. The remaining deposited adhesive layer may be removed from the micro LED wafer 302 after the second deposited backplane has been transferred 114 to the display substrate 312.

[0072] This method may be repeated multiple times until no more working LEDs remain in the LED array 304 on the growth substrate. In this case, the only remaining LEDs may be non-working LEDs.

[0073] Figure 4aA micro-LED display 300 is shown. The micro-LED display may include a plurality of LEDs, each having a top surface and an opposing bottom surface. The plurality of LEDs may be one or more of micro-LEDs, nano-LEDs, quantum dots, organic LEDs, or any other type of LED having any suitable size. The plurality of LEDs may be configured to emit light of a predetermined color, such as light having a particular wavelength or light 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 have been removed from the growth substrate 306. Although Figure 4a Only an array with one LED is depicted, but 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 spacing to provide a display suitable for a range of devices. For example, a high-density LED may be particularly suitable for a display in a VR or AR headset or a smart watch. The growth substrate 306 may be a sapphire substrate, or 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 may be formed above the top surface of the LED, and the bottom surface of the backplane 310 may be deposited directly on the LED and operably 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 applied to the top surface of the backplane 310. Alternatively or additionally, the display substrate 312 may be a flexible substrate.

[0074] The micro LED display 300 may also include a reflective layer ( Figure 4a). The reflective layer may be arranged to reflect light emitted by the LED so that the reflected light is emitted from the micro LED display 300 in a direction corresponding to the bottom surface of the LED. The reflective layer preferably covers at least 50% of the area of ​​the LED. The reflective layer may be a metal layer and may contain Al, Ag, Mo and / or Au. Alternatively, the reflective layer may include a distributed Bragg reflector having polarization properties that can be used to illuminate a liquid crystal display (LCD) located 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 is preferably at least 70% transparent. The display substrate 312 may be polished on the bottom surface so as not to affect the quality of the image from the micro LED display 300. Optionally, one or more lenses (not shown) and / or color filters may be provided on the bottom surface of the display substrate to collimate or focus the light or adjust the wavelength of the light leaving the display substrate 312. Optionally, the display substrate 312 may be thinned by back grinding or chemical etching before polishing to reduce the distance between the LED and the optical element.

[0075] The above-described embodiments provide a number of advantages. First, the use of a reflective layer to direct the upwardly emitted light back through the display substrate 312 means that the backplane 310 can cover a large area without blocking each LED. Therefore, compared to the prior art monolithic device in which the area of ​​the backplane 310 is limited, in the present invention, the backplane 310 can provide more current for each LED. Secondly, light emitted in a direction opposite to the intended emission direction is no longer wasted, but is reflected, so that a larger proportion of the light emitted by each LED is emitted in the intended emission direction, thereby producing a more efficient micro LED display 300. This means that the LEDs can operate at lower temperatures to produce the same light output; this reduces the stress on the backplane 310, which can improve the performance and life of the micro LED display 300.

[0076] One problem associated with manufacturing monolithic displays is that the metals used in the reflective layer and LEDs can be damaged by high temperatures, such as temperatures exceeding 150° C. For inorganic backplanes 310, such as amorphous silicon (a-Si), low temperature polycrystalline silicon (LTPS), and / or indium gallium zinc oxide (IGZO), a PECVD process is used to deposit high quality SiN x However, this operation is only effective at temperatures above 300°C, which would damage the LEDs and / or the reflective layers already present in the micro-LED display.

[0077] Therefore, it is particularly advantageous if the backplane 310 is an organic TFT (OTFT). OTFTs can be deposited onto the display 300 at much lower temperatures than those used when depositing inorganic TFTs, and thus damage to the reflective layer and / or LEDs can be avoided. For example, OTFTs can be processed at temperatures as low as 80°C, since heating is only required to remove the coating solvent from the formulated ink. The low temperature deposition process of OTFTs ensures that the reflective layer and LEDs are not damaged, so it is particularly advantageous to use OTFTs to form a monolithic device.

[0078] Suitable structures and materials for OTFTs are described in WO 2022 / 101644 and WO 2020 / 002914. For example, the OTFT may include an organic semiconductor (OSC) layer, an organic gate insulator (OGI) layer, a sputtered resistor layer (SRL), a substrate, and a base layer. The OSC layer may include at least one semiconductor ink comprising a small molecule organic semiconductor and an organic binder. The OGI layer of the OTFT may include a material as described in WO 2020 / 002914. The SRL may include a cross-linked organic layer as described in WO 2020 / 002914. The cross-linked organic layer may preferably be obtained by polymerization of a solution comprising at least one non-fluorinated multifunctional acrylate, a non-acrylate organic solvent, a cross-linkable fluorinated surfactant, and an organosilicon surfactant, wherein the organosilicon surfactant is preferably a cross-linkable organosilicon surfactant and may be a non-fluorinated surfactant. The organosilicon surfactant may be an acrylate and / or methacrylate functionalized organosilicon surfactant. The substrate may include glass or a polymer. The base layer may comprise an organic cross-linked layer having suitable materials as described in WO 2020 / 002914.

[0079] The micro LED display 300 can be combined with other components to provide a display device. For example, a protective layer, a frame, an electrical connector, and / or any other suitable component can be combined with the micro LED display 300. The micro LED display 300 can be used for a display in a VR or AR headset or a smart watch.

[0080] Each LED of the micro LED display 300 is individually addressable, wherein the state of each LED is controlled by a backplane 310, which may include one or more thin film transistors (TFTs). The TFTs may be used as switching devices for controlling the operation of each LED and / or as driver devices for driving the LEDs.

[0081] Figure 4b A schematic diagram of a display element 41 including a pixel array 45 is shown. Figure 4bOnly an array with 40 pixels 45 is depicted, but it will be understood that any number of pixels 45 may be present in the array to provide a particular resolution. As will be described in more detail later, the pixels 45 may include sub-pixels that may be configured to emit light of a predetermined color, for example to provide an RGB display. In addition, the pixels may be arranged to have a specific pixel density and / or pixel pitch to provide a display suitable for a range of devices. For example, a high density of pixels 45 may be particularly suitable for displays in VR or AR headsets or smart watches. Other components may be combined with the display component 41 to provide a display device. For example, a protective layer, a frame, an electrical connector, and / or any other suitable component may be combined with the display component 41.

[0082] Each pixel 45 (or sub-pixel) of the display component 41 is individually addressable, wherein the state of each pixel 45 is controlled by one or more thin film transistors (TFTs). The TFT is used as a switching device for controlling the operation of each pixel, and / or as a driver device for driving the pixel. For example, the TFT can be used as a switch and current driver for 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 a substrate 412. For example, one integrated circuit 410 can provide a pixel 45 of the display component 41, or a plurality of integrated circuits 410 can be used to provide a plurality of sub-pixels of the display component 41. Figure 4b As shown for an exemplary pixel 45, three integrated circuits 410 are provided for each pixel 45. TFTs can also be used to operate LEDs that provide a backlighting zone for a liquid crystal display (LCD), where each LED provides backlighting for multiple LCD pixels. By dividing the backlight into multiple backlighting zones, each of which is controlled by a separate TFT, the energy efficiency and contrast of the LCD can be improved because the zones can be completely turned off when not needed. For example, one TFT can be used to switch the LED backlighting for a zone with about one hundred LCD pixels. Therefore, the term "integrated circuit 410" as used herein can refer to a single pixel 45 of a display, and can also refer to a backlighting zone provided by an LED, where each backlighting zone corresponds to multiple LCD pixels.

[0083] Figure 4bThe display component 41 in is a monolithic display component 41, in which the integrated circuit 410 is deposited (or "grown") on a substrate 412, rather than being transferred to the substrate 412 from a separate ("source wafer"). In this way, the substrate 412 of the display component 41 can also be called a source wafer. In a monolithic display, the integrated circuit 410 can be produced by forming multiple layers on top of the substrate 412. This operation can be achieved using chemical vapor deposition (CVD) techniques such as plasma enhanced chemical vapor deposition (PECVD) or metal organic chemical vapor deposition (MOCVD), or epitaxial techniques such as metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). These techniques allow a thin film of material (or "layer") to be deposited on the substrate 412 to form each integrated circuit 410. Subsequently, part of the layer can be selectively removed in a process called patterning, which can be achieved by (dry) etching. In this way, adjacent integrated circuits can be electrically isolated from each other, and channels for electrical paths through these layers can be formed.

[0084] Now refer to Figure 4c and Figure 4d The process for individually addressing the pixels 5 is described in more detail. Figure 4c A transistor array 400 for a display backplane is shown, wherein the transistor array 400 includes a plurality of integrated circuits 402 arranged in a regular array of rows and columns. Each integrated circuit 402 includes a thin film transistor (TFT) 408. As in a conventional active matrix display, each TFT acts as a switch for controlling the application of current to a corresponding pixel capacitor 401, wherein each integrated circuit 402 may include 2T-1C or other combinations of transistors and capacitors.

[0085] The backplane includes a series of row (scan or gate) lines 403 connected to the gate of each TFT 408 in a common row, wherein 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 (or data) line 405. A row driver 406 is connected to each gate line 405, and a column driver 406 is connected to each data line 405. Each integrated circuit 402 can be individually addressed by providing a voltage pulse to the row driver 404 to turn on each TFT 408 in the row, while providing the required data voltage to the source or drain terminal of each TFT 408. By sequentially scanning each row and applying a data voltage to each data line 405, a data signal can be written to the pixel capacitor 401 of the matrix. In this way, the transistors and capacitors of each integrated circuit 402 can maintain the state of a pixel while addressing other pixels.

[0086] Figure 4dAn example of a 2T-1C integrated circuit 402 is depicted, which includes a selection or switching TFT 408, a drive TFT 520, and a storage capacitor 401. When the row (scan) line is turned on, the data signal V 数据 A voltage can be written to the storage capacitor 401, which is also connected to the gate of the driving TFT 520. If V DD and V SS If a voltage is applied to the gate of the drive TFT 520, the change in resistance of the drive TFT 520 will cause a current to flow through the LED 515 relative to the voltage applied to the gate of the drive TFT 520, thereby adjusting the amount of light emitted from the display.

[0087] Figure 5 A single pixel design is shown forming part of a backplane used in the above method. The backplane is formed from a repeating unit of this pixel according to the number of rows and columns required in the backplane array matrix.

[0088] Figure 3b An integrated circuit for testing LEDs for a micro LED display 300 is shown. 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 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, such as Figure 3b As shown. Anode test pad 316 may comprise gold connected to an indium tin oxide (ITO) layer on the anode of the LED, and cathode test pad 318 may comprise gold connected to an n-gallium nitride (n-GaN) layer forming the cathode of the LED. The cathode may be common to all LEDs, or the devices may be isolated by etching so that a wiring pattern is required to connect the common cathode test pad to the cathode connection. Wiring pattern 314 may connect each LED in the LED array to a current source to test the LEDs before moving to a micro LED display, such as Figure 2 The current may have an appropriate amperage to cause the LED array to emit light when the current is applied between the anode and cathode. The integrated circuit may be configured so that current can be applied to each LED to cause them all to emit light, thereby allowing imaging and image processing to determine which LEDs are operational and which are inoperative.

[0089] Although the foregoing is directed to exemplary embodiments of the present invention, it will be understood that the present invention is described herein purely by way of example, and that modifications may be made to the details within the scope of the present invention. Furthermore, it will be understood by those skilled in the art that the present invention may not be limited to the embodiments disclosed herein, or to any details shown in the accompanying drawings that are not described in detail herein or defined in the claims. In fact, such redundant features may be removed from the accompanying drawings without affecting the present invention.

[0090] Moreover, other and further embodiments of the present invention will be apparent to those skilled in the art from consideration of this specification, and such embodiments may be devised without departing from the basic scope of the invention, which is determined by the following claims.

Claims

1. A method for manufacturing a micro LED display (300), the method comprising: Providing (102) a micro LED wafer (302) comprising an LED array (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 backing plate (310) on the adhesive layer (308) such that the backing plate (310) is aligned with and operably connected to the exposed one or more LEDs; as well as The deposited backplane (310) and attached one or more LEDs are transferred (114) to a display substrate (312).

2. The method of claim 1, wherein: The step of depositing (110) an adhesive layer (308) comprises: Depositing an adhesive layer (308) to cover the micro LED wafer (302); One or more sections of the adhesive layer (308) are removed to expose the one or more selected LEDs.

3. The method of claim 2, wherein: The adhesive layer (308) comprises a photoresist, and the method comprises: The one or more sections of the bonding layer (308) are exposed to light to expose the one or more selected LEDs.

4. A method as claimed in any preceding claim, wherein: The step of providing (102) a micro LED chip (302) comprises: A series of semiconductor layers are deposited to form the LED array (304) on the growth substrate (306).

5. A method as claimed in any preceding claim, wherein: Prior to depositing (110) the adhesion layer (308), the method includes: Depositing (104) a wiring pattern (314) on the micro LED wafer to connect the LED array (304) to a current source; applying (106) a current to the wiring pattern (314) to test the LEDs; One or more properly functioning LEDs are selected (108) as one or more selected LEDs to be connected to the backplane (310) and transferred to the display substrate (312).

6. The method of claim 5, wherein: The step of selecting (108) one or more operating LEDs comprises: capturing an image of the micro LED wafer while applying the current to the wiring pattern to cause the LED array to emit light; processing the image to identify the locations of properly functioning LEDs; One or more properly functioning LEDs are selected as the one or more selected LEDs to be connected to the backplane and transferred to the display substrate.

7. The method according to claim 5 or 6, wherein: The method includes: The deposited wiring pattern (314) is removed (208) from the one or more selected LEDs such that the one or more selected LEDs are not attached to the rest of the LED array (304).

8. The method of claim 7, wherein: Removing (208) the exposed deposited circuitry includes wet etching the exposed deposited circuitry.

9. The method according to any preceding claim, further comprising: The deposited adhesion layer (308) is removed from the backing plate (310).

10. A method as claimed in any preceding claim, wherein: Transferring (114) the deposited backplane (310) and connected one or more LEDs to a display substrate (312) includes: attaching the display substrate (312) to the deposited backplane (310); releasing the one or more selected LEDs from a growth substrate (306) of the micro LED wafer (302); The display substrate (312) with attached backplane (310) and one or more connected LEDs is lifted off.

11. The method of claim 10, wherein: Releasing the one or more selected LEDs from the growth substrate (306) includes ablating the one or more LEDs with a laser.

12. A method as claimed in any preceding claim, wherein: The display substrate (312) includes a laminated plastic substrate.

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

14. A method as claimed in any preceding claim, wherein: The display substrate (312) is a flexible substrate.

15. A method as claimed in any preceding claim, wherein: The backplane (310) includes one or more thin film transistors (TFT), wherein the step of depositing (112) the backplane (310) on the adhesive layer includes connecting the one or more TFTs to the exposed one or more LEDs.

16. A method as claimed in any preceding claim, wherein: The one or more selected LEDs include a subarray of selected LEDs within an LED array (304) on the micro LED wafer (302), wherein a spacing of the selected LEDs in the subarray corresponds to a desired pixel spacing of the micro LED display (300).

17. A method as claimed in any preceding claim, wherein: After transferring (114) the deposited backplane (310) and the one or more connected LEDs to a display substrate (312), wherein the deposited backplane (310) is defined as a first backplane (310), the method further comprises: depositing (116) an adhesive layer (308) to cover the micro LED wafer (302) while leaving one or more additional LEDs exposed; depositing (118) a second backing plate such that the second backing plate is aligned with and operably connected to the exposed one or more additional LEDs; and The deposited second backplane and connected one or more additional LEDs are transferred (120) to a display substrate (312).

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

19. A method as claimed in any preceding claim, wherein: These LEDs include one or more of micro-LEDs, nano-LEDs, and quantum dots.

20. A method as claimed in any preceding claim, wherein: The growth substrate (306) is a sapphire substrate.

21. The method according to any one of claims 2 to 20, wherein: Removing one or more sections of the adhesive layer (308) to expose the one or more selected LEDs includes: Digital lithography is used to define one or more selected LEDs that are exposed.

22. A micro LED display (300), comprising: a plurality of LEDs, each LED having a top surface and an opposing bottom surface; a backplane (310) having a top surface and an opposing bottom surface, the backplane (310) being formed over the top surface of the LEDs, wherein the bottom surface of the backplane (310) is directly deposited on and operably connected to the LEDs; A display substrate (312) is attached to the top surface of the backplane (310).

23. The micro LED display of claim 22, wherein: The top surfaces of the LEDs correspond to the growth direction, wherein the bottom surface has been removed from the growth substrate (306).

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

25. The micro LED display as described in any one of claims 22 to 24 further comprises a reflective layer formed between the top surface of the one or more LEDs and the back panel (310), the reflective layer being arranged to reflect light emitted by the LEDs so that the reflected light is emitted from the micro LED display (300) in a direction corresponding to the bottom surface of the LEDs.

26. An integrated circuit for testing LEDs for a micro LED display (300), the integrated circuit comprising: A micro LED wafer (302) comprising an LED array (304) deposited on a growth substrate (306); A wiring pattern (314) is deposited on the micro LED wafer (302) to connect each LED in the LED array to a current source to test the LEDs before transferring to a micro LED display (300).

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