Selective microdevice transfer to a recipient substrate and recipient substrate structure

Abstract

Method for transferring selected microdevices (102, 102a, 102b, 102c) in an array of microdevices (102, 102a, 102b, 102c), each of which is bonded to a donor substrate (100) by a donor force, the method comprising: Aligning the donor substrate (100) and a receiver substrate (200) such that each of the selected microdevices (102, 102a, 102b, 102c) is located on the receiver substrate (200) in alignment with a contact pad (206a, 206b, 206c); Moving the donor substrate (100) and the receiver substrate (200) towards each other until each of the selected microdevices (102, 102a, 102b, 102c) is in contact with or near a respective contact pad (206a, 206b, 206c) on the receiver substrate (200); Generating a receiver force by means of force modulation elements (204a, 204b, 204c), wherein the receiver force acts such that it holds each of the selected microdevices (102, 102a, 102b, 102c) to its respective contact pads (206a, 206b, 206c), wherein each of the selected microdevices (102, 102a, 102b, 102c) corresponds to one of the force modulation elements (204a, 204b, 204c), and wherein the receiver force is generated selectively to improve selectivity of the microdevice transfer, wherein the receiver force is modulated by heating the receiver substrate (200) by passing a current through the contact pads (206a, 206b, 206c); and Moving the donor substrate (100) and the receiver substrate (200) away from each other, leaving the selected microdevices (102, 102a, 102b, 102c) on the receiver substrate (200). wherein the force modulation elements (204a , 204b , 204c) are on the receiver substrate (200) and in direct contact with the contact pads (206a , 206b, 206c).

Description

AREA OF INVENTION

[0001] The present invention relates to the integration of devices into system substrates. In particular, the present invention relates to the selective transfer of microdevices from a donor substrate to a recipient substrate.

[0002] US Patent 2003 / 0162463A1 describes a method for selectively transferring components mounted on a first substrate to a second substrate on which an adhesive resin layer has been previously formed. The method comprises the steps of selectively heating the adhesive resin layer on the second substrate by laser irradiation from the back of the second substrate and curing the selectively heated sections of the adhesive resin layer, thereby bonding the devices to be transferred to the second substrate. At this point, sections of the adhesive layer corresponding to the devices are heated by laser irradiation from the back of the substrate, either directly or indirectly via the devices or wiring sections. The heated areas of the adhesive resin layer selectively exert adhesive forces.The heated areas of the adhesive layer are then cured so that only the components to be transferred are selectively transferred to the second substrate.

[0003] US Patent 2005 / 0211998 A1 discloses device structures for plates made of photoactive material. A first substrate has a transparent first conductive layer. A pattern of photoactive semiconductor elements is attached to the first substrate. The photoactive semiconductor elements have an n-side and a p-side. For each photoactive semiconductor element, either the n-side or the p-side is in electrical contact with the transparent conductive layer. A second substrate has a second conductive layer. An adhesive bonds the second substrate to the first substrate, such that the other side of the n-side or the p-side of each photoactive semiconductor element is in electrical contact with the second conductive layer. This creates a photoactive solid-state device. SUMMARY

[0004] According to one aspect, a method for transferring selected microdevices in an array of microdevices, each of which is bonded to a donor substrate by a donor force, is provided, the method comprising: aligning the donor substrate and a receiver substrate such that each of the selected microdevices is in alignment with a contact pad on the receiver substrate; moving the donor substrate and the receiver substrate relative to each other until each of the selected microdevices is in contact with or near a respective contact pad on the receiver substrate; generating a receiver force by means of force modulation elements, wherein the receiver force acts such that it holds each of the selected microdevices to its respective contact pads while not affecting other microdevices that are in contact with or near the receiver substrate;and moving the donor substrate and the receiver substrate away from each other, leaving the selected microdevices on the receiver substrate. Each of the selected microdevices corresponds to one of the force modulation elements, and the force modulation elements are on the receiver substrate and in direct contact with the contact pads. The receiver force is generated selectively to improve the selectivity of the microdevice transfer. The receiver force is modulated by heating the receiver substrate by passing a current through the contact pads.

[0005] Some embodiments further include weakening the donor force that bonds the microdevices to the donor substrate to aid microdevice transfer.

[0006] In some embodiments, the donor force for the selected microdevices is reduced to improve the selectivity of the microdevice transfer. In some embodiments, the receiver force is generated selectively to improve the selectivity of the microdevice transfer.

[0007] Some embodiments also include weakening the donor force using laser lift-off.

[0008] Some embodiments also include modulating the force by a magnetic field.

[0009] Some embodiments also include weakening the donor force by heating an area of ​​the donor substrate.

[0010] Some embodiments also include modulating the receiver force by heating the receiver substrate.

[0011] In some embodiments, heating is achieved by passing an electric current through the contact pads. In some embodiments, the receiving force is generated by a mechanical handle.

[0012] Some embodiments further include performing a process on the receiver substrate so that the contact pads are permanently bonded to the selected microdevices.

[0013] In some embodiments, the receiver force is generated by electrostatic attraction between the selected microdevices and the receiver substrate. In other embodiments, the receiver force is generated by an adhesive layer positioned between the selected microdevices and the receiver substrate.

[0014] Some embodiments further include removing the donor force; and applying a pressure force to selected microdevices to move the devices towards the recipient substrate.

[0015] In some embodiments, the pressure force is generated by a sacrificial layer deposited between the selected microdevices and the donor substrate.

[0016] According to another aspect, a receiver substrate structure is provided, comprising an array of landing surfaces for selectively holding microdevices from a donor substrate. Each landing surface includes at least one contact pad for coupling or connecting a microdevice to at least one circuit or potential in the receiver substrate; and at least one force modulation element for generating a receiver force to hold the microdevices on the receiver substrate. Each microdevice corresponds to at least one of the force modulation elements, and the at least one force modulation element is located on the receiver substrate and in direct contact with at least one contact pad. For clarity, the area where the microdevice sits on the receiver substrate is referred to as the landing surface.

[0017] In some embodiments, the force modulation element is an electrostatic structure. In some embodiments, the force modulation element is a mechanical handle. In some embodiments, the same element functions as the force modulation element and the contact pad for each landing surface.

[0018] The preceding and additional aspects and embodiments of the present disclosure will be apparent to a person skilled in the art in view of the detailed description of the various embodiments and / or aspects, which is given with reference to the drawings, a brief description of which is provided next. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The preceding and other advantages of the revelation will become apparent upon reading the following detailed description and with reference to the drawings. Fig. Figure 1A shows a donor substrate and a recipient substrate before the transfer process begins. Fig. Figure 1B shows a donor substrate and a recipient substrate before the transfer process begins. Fig. Figure 2A shows a flowchart of the modulation of the donor and / or receiver forces after the donor and receiver substrates are in contact or close to each other. Fig. Figure 2B shows a flowchart of modulating donor forces in advance and modulating receiver forces as needed, after the donor and receiver substrates are in contact or close to each other. Fig. Figure 2C shows a flowchart of modulating the receiver forces in advance and modulating the donor forces as needed, after the donor and receiver substrates are in contact or close to each other. Fig. 3A shows the step of aligning the donor and receiver substrate. Fig. Figure 3B shows the step of moving the substrates relative to each other within a defined distance range. Fig. Figure 3C-1 shows an embodiment of modulating the forces by selectively applying receiver forces. Fig. Figure 3C-2 shows an embodiment of modulating the forces by selectively weakening the donor force and globally applying the receiver force. Fig. 3D shows one embodiment of modulating the forces by applying the receiver force and selectively attenuating the donor force. Fig. 3E shows the step of moving the substrate away. Fig. Figure 4A shows a donor substrate with various microdevices nested together and the corresponding contact pads in the receiver substrate are aligned with each microdevice, enabling simultaneous transfer of different microdevices. Fig. Figure 4B shows a donor substrate with various microdevices in groups, and the corresponding contact pads in the receiver substrate are aligned with each microdevice, thus enabling the simultaneous transfer of different microdevices. Figure 4C shows arrangements with different grid dimensions for the microdevices and the contact pads. Fig. Figure 4C shows a donor substrate with various microdevices nested inside, and only one set of the corresponding contact pads in the receiver substrate with one of the types of microdevices is aligned with each microdevice, so that multiple transfer processes are needed to transfer all the different types of microdevices. Fig. Figure 5A shows selective and global warming elements integrated into substrates. Fig. Figure 5B shows an embodiment for structuring selective and global warming elements integrated into substrates. Fig. Figure 5C demonstrates the use of external sources to selectively heat at least one substrate. Fig. Figure 6A shows a flowchart of a process 1100 for the selective transfer of microdevices from a donor substrate to a receiver substrate. Fig. Figure 6B shows the step of preparing the donor and recipient substrate for selective transfer. Fig. 6C shows the step of aligning the substrates. Fig. 6D shows the step of moving the substrates relative to each other within a defined distance range. Fig. Figure 6E shows the step of generating receiver forces by curing the adhesive (e.g., by applying pressure or heat). This can be done globally or selectively. Fig. 6F shows the step of reducing donor forces as needed. This can be done globally or selectively. Fig. 6G shows the step of moving the substrates away from each other. Fig. Figure 7A shows other possible arrangements of adhesive on the recipient substrate. Fig. Figure 7B shows a contact pad with a cutout before and after the application of an adhesive. Fig. Figure 8 shows a stamping process that can be used to apply adhesive to contact pads. Fig. Figure 9 shows a flowchart of a process 1200 for the selective transfer of microdevices from a donor substrate to a receiver substrate. Fig. Figure 10 shows a setup of a donor substrate and a recipient substrate for carrying out the procedure 1200. Fig. Figure 11A shows the step of aligning the donor and receiver substrate. Fig. Figure 11B shows the step of moving the donor and receiver substrate to a defined distance span while a mechanical force is applied. Fig. Figure 11C shows the step of increasing mechanical forces. Fig. Figure 11D shows the step of reducing donor forces when needed (this step can also be done in advance). Fig. Figure 11E shows the movement of the donor and recipient substrates away from each other. Fig. Figure 12A shows a flowchart of a process 1300 for the selective transfer of microdevices from a donor substrate to a receiver substrate. Fig. Figure 12B shows a setup of a donor substrate and a recipient substrate for carrying out procedure 1300. Fig. Figure 13A shows the step of aligning the donor and receiver substrate. Fig. Figure 13B shows the step of moving the substrates within a predefined distance range. Fig. Figure 13C shows the step of generating a receiver force by applying a potential to electrostatic elements. This can be done selectively or globally. Fig. Figure 13D shows the step of reducing the donor force as needed. This can be done globally or selectively. Fig. 13E shows the step of moving the substrates away. Fig. Figure 14A shows a different, alternative placement for the electrostatic layer. Fig. Figure 14B shows a different, alternative placement for the electrostatic layer. Fig. Figure 14C shows a different, alternative placement for the electrostatic layer. Fig. Figure 14D shows a different, alternative placement for the electrostatic layer. Fig. Figure 15A shows a different, alternative geometry for microdevices and contact pads. Fig. Figure 15B shows a different, alternative geometry for microdevices and contact pads. Fig. Figure 15C shows a different, alternative geometry for microdevices and contact pads. Fig. Figure 15D shows a different, alternative geometry for microdevices and contact pads. Fig. 15E shows a different, alternative geometry for microdevices and contact pads. Fig. Figure 16 shows a flow diagram of a process 1400 for the selective transfer of microdevices from a donor substrate to a receiver substrate. Fig. Figure 17A shows the step of aligning the donor and receiver substrate. Fig. Figure 17B shows the step of moving the substrates to a predefined distance from each other. Fig. Figure 17C shows an embodiment for the step of generating a receiver force on demand. This can be done globally or selectively. The force can be generated using various methods. Fig. Figure 17D shows the application of a pressure force to the microdevices of the donor substrate. The pressure force applied to the donor substrate should be selective. Fig. 17E shows the step of moving the substrate away. Fig. Figure 18A shows a platform for testing the donor substrate and / or the receiver substrate by biasing, enabling the microdevices to be tested for defects and performance. The output of the microdevice through the receiver substrate is shown here. Fig. Figure 18B shows a platform for testing the donor substrate and / or the receiver substrate by biasing, enabling the microdevices to be tested for defects and performance. The output of the microdevice through the donor substrate is shown here. Fig. Figure 19 shows a simplified bias state of the receiver substrate for testing the microdevices for defects and a performance analysis.

[0020] While the present disclosure is open to various modifications and alternative forms, specific embodiments or implementations have been shown in the drawings as examples and are described in detail here. It is understood, however, that the disclosure is not intended to be limited to the specific disclosed forms. Rather, the disclosure is intended to cover all modifications, equivalents, or alternatives that fall within the concept and scope of protection of the invention as defined by the accompanying claims. DETAILED DESCRIPTION

[0021] Many microdevices, including light-emitting diodes (LEDs), organic LEDs, sensors, solid-state devices, integrated circuits, MEMS (microelectromechanical systems), and other electronic components, are typically fabricated in batches, often on flat substrates. To form a functional system, microdevices must be selectively transferred from at least one donor substrate to a recipient substrate. Substrate and transfer structure

[0022] Fig. Figure 1 shows a donor substrate 100 and a receiver substrate 200 before the transfer process begins. Microdevices 102a, 102b, 102c start in an array attached to the donor substrate 100. The receiver substrate consists of an array of landing surfaces 202a, 202b, 202c on which the microdevices will be placed. The landing surfaces 202a, 202b, 202c each include at least one force modulation element 204a, 204b, 204c and at least one contact pad 206a, 206b, 206c. The force modulation element and the contact pads can be configured differently than shown in Figure 1. Fig. 1A may be shown or may have the same structure as in Fig. The microdevices 102 are shown in Figure 1B. The microdevices 102 can be coupled or connected to a circuit or potential on the receiver substrate 200 via the contact pads 206a, 206b, 206c. The force modulation elements 204a, 204b, 204c generate a transfer force to selectively hold the microdevice 102a, 102b, 102c on the receiver substrate 200 and separate it from the donor substrate 100. The donor substrate 100 is the substrate on which the microdevices 102 were fabricated or grown, or another temporary substrate onto which they were transferred. The microdevices 102 can be any microdevice typically manufactured in flat-surface batches, including LEDs, OLEDs, sensors, solid-state devices, integrated circuits, MEMS, and other electronic components. The donor substrate 100 is selected according to the manufacturing process for a specific type of microdevice 102.For example, in the case of conventional GaN LEDs, the donor substrate 100 is typically sapphire. Generally, the atomic spacing of the donor substrate 100 should match that of the growing material when growing GaN LEDs to avoid defects in the film. Each microdevice 102 is attached to the donor substrate 100 by a force, FD, which is determined by the fabrication process and the nature of the microdevices 102. FD will be essentially the same for each microdevice 102. The receiver substrate 200 can be any preferred location for the microdevices 102. For example, it can be a printed circuit board (PCB), a thin-film transistor backplane, an integrated circuit substrate, or, in the case of optical microdevices 102 such as LEDs, a component of a display, such as a driver circuit arrangement backplane. The landing area on the receiver substrate, as shown in... Fig. Figure 1B shows the location where the microdevice sits on the receiver substrate and can consist of at least one contact pad 101a and at least one force modulation element 101b. Although the landing area in some of the figures may be the same size as the contact pads 202, the contact pads 202 can also be smaller than the landing area. The contact pads 202 are the locations where the microdevices can be coupled to or directly connected to the receiver substrate 200. In this description, landing area and contact pads are used interchangeably.

[0023] The goal of a selective transfer is to transfer some selected microdevices 102 from the donor substrate 100 to the recipient substrate 200. For example, the transfer of microdevices 102a and 102b to the contact pads 206a and 206b without transferring microdevice 102c is described. Transfer process

[0024] The following steps describe a method for transferring selected microdevices in an array of microdevices, each of which is bonded to a donor substrate by a donor force, to contact pads in an array on a receiver substrate: a. Aligning the donor substrate and the receiver substrate so that each of the selected microdevices is in alignment with a contact pad on the receiver substrate; b. Moving the donor substrate and the receiver substrate towards each other until each of the selected microdevices is in contact with or near at least one contact pad on the receiver substrate; c. Generating a receiving force that acts in such a way as to hold the selected microdevices to their contact pads; d. Moving the donor substrate and the recipient substrate away from each other, leaving the selected microdevices on the recipient substrate, while other non-selected microdevices remain on the donor substrate despite possible contact or proximity with the system substrate during steps b and c.

[0025] If the donor force is too strong to be overcome by the receiver force to transfer the microdevice to the receiver substrate, the donor force is reduced for the microdevices to facilitate the transfer. Furthermore, if the receiver force is applied globally, or if a selective receiver force is insufficient for selective microdevice transfer, the donor force is selectively reduced for the selected microdevices to improve the selectivity of the microdevice transfer.

[0026] Fig. 2A-2C show exemplary flowcharts for selective transfer processes 1000A-1000C. Fig. Figure 1 shows a donor substrate 100 and a recipient substrate 200 suitable for carrying out any one of the processes 1000. Process 1000A is described with reference to Fig. Procedures 3A-3E are described. Procedures 1000B and 1000C are analogous variations of procedure 1000A. The combination of procedures 1000A-1000C can be used to further improve the transfer process.

[0027] In 1002A, the donor substrate 100 and the receiver substrate 200 are aligned such that selected microdevices 102a, 102b are in alignment with corresponding contact pads 202a, 202b, as shown in Fig. Figure 3A shows that the microdevice 102c is not to be transferred, so although it is shown as aligned, it may or may not be aligned with the contact pad 202c.

[0028] In 1004A, the donor substrate 100 and the receiver substrate 200 are moved towards each other until the selected microdevices 102a, 102b are positioned at a defined distance to the contact pads 202a, 202b, as shown in Fig. Figure 3B shows that the defined distance can correspond to full or partial contact, but is not limited to this. In other words, it may not be strictly necessary for the selected microdevices 102a, 102b to actually touch the corresponding contact pads 202a, 202b, but they must be close enough so that the forces described below can be manipulated.

[0029] In 1006A, forces between the selected microdevices 102, the donor substrate 100 and the receiver substrate 200 (and the contact pads 202) are modulated such that a resultant force for the selected microdevices towards the receiver substrate 200 and a resultant force for the other microdevices 102c towards the donor substrate 100 (or a resultant force of zero) is generated.

[0030] The forces acting on one of the selected microdevices 102 are considered. There is a pre-existing force, FD, that holds it to the donor substrate 100. There is also a force, FR, generated between the microdevice 102 and the receiver substrate 200, which acts such that it pulls the microdevice 102 toward or holds it to the receiver substrate 200, thus causing a transfer. When the substrates are moved away from each other, for any given microdevice 102, the microdevice 102 will move with the receiver substrate 200 if FR exceeds FD, while the microdevice 102 will remain with the donor substrate 100 if FD exceeds FR. There are several ways to generate FR, which are described in later sections. However, once FR has been generated, there are at least four (4) possible ways to modulate FR and FD to achieve a transfer of the selected microdevices. 1. Attenuation of FD so that it is lower than FR for microdevices selected for transfer. 2. Increase FR so that it is greater than FD for microdevices selected for transfer. 3. Attenuation of FR so that it is lower than FD for microdevices NOT selected for transfer. 4. Increase FD so that it is greater than FR for microdevices NOT selected for transfer.

[0031] Various combinations and arrangements of the above are also possible. The use of combinations may be desirable in some cases. For example, if the required change in FD or FR is very high, a combination of modulation of FD and FR can be used to achieve the desired resultant forces for the selected and unselected microdevices. Preferably, FR can be generated selectively and therefore act only on the selected microdevices 102a, 102b, as shown in Fig. 3C-1 is shown. FR can also be generated globally and applied over the entire receiver substrate 200 and can therefore be applied to the microdevices 102a, 102b, 102c, as shown in Fig. Figure 3C-2 shows how donor forces can be selectively attenuated. The landing surface on the receiver substrate can include a force modulation element to effect FR force modulation completely or partially. Methods for selectively and globally generating FR, including adhesive, mechanical, electrostatic, and magnetic techniques, are described below. Furthermore, examples of force modulation elements in the landing surface are described below. However, those skilled in the art know that various variations of force modulation elements are possible, which are not listed here. It is also understood that the shapes and structures of the contact pads and force modulation elements are used for illustrative purposes and are not limited to those used in this description.

[0032] In one embodiment, the donor force FD for the selected microdevices 102a, 102b is selectively weakened so that FD' is less than FR, as shown in Fig. 3D is shown. This can be done, for example, using laser lift-off techniques, lapping, or wet / dry etching. In some cases, it may be desirable to use selective and global FR generation simultaneously. For example, it may not be feasible to generate a selective FR of sufficient size to overcome FD' on its own. In this case, the global component of FR should preferably remain small, ideally smaller than FD', while the sum of the global and selective components of FR is larger than FD' but smaller than FD.

[0033] It should also be noted that actions performed during steps 1002A-1006A can be combined. For example, selective or global attenuation of FD could take place before the substrates are brought together.

[0034] In 1008A, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding contact pads 202a, 202b, as shown in Fig. Figure 3E shows that once the donor substrate 100 is separated from the receiver substrate 200, further processing steps can be performed. For example, the donor substrate 100 and the receiver substrate 200 can be realigned, and steps 1002A to 1008A can be repeated to transfer another set of microdevices 102 to another set of contact pads 202. Additional layers can also be deposited on or between the microdevices 102; for example, transparent electrode layers, fillers, planarization layers, and other optical layers can be deposited during the fabrication of an LED display.

[0035] Fig. Figure 2B shows method 1000B; an alternative embodiment of method 1000A.

[0036] In 1002B, the forces between the microdevices 102a, 102b and the donor substrate 100 are modulated globally (for all devices in a region of the donor substrate) or selectively (only for selected microdevices 102a, 102b) so that a donor force, FD, is attenuated.

[0037] In 1004B, the donor substrate 100 and the receiver substrate 200 are aligned such that selected microdevices 102a, 102b are in coordination with corresponding contact pads 202a, 202b.

[0038] In 1006B, the donor substrate 100 and the receiver substrate 200 are moved towards each other until the selected microdevices 102a, 102b touch the contact pads 202a, 202b. It may not be strictly necessary for the selected microdevices 102a, 102b to actually touch the corresponding contact pads 202a, 202b, but they must be close enough so that the forces described below can be manipulated.

[0039] In 1008B, the forces between the selected microdevices 102 and the receiver substrate 200 (and the contact pads 202) are modulated as needed to generate a resultant force for the selected microdevices towards the receiver substrate 200 and a resultant force for the other microdevices 102c towards the donor substrate 100 (or a resultant force of zero).

[0040] In 1010B, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding contact pads 202a, 202b.

[0041] In step 1012B, an optional post-processing step is applied to selected microdevices 102a and 102b. Once the donor substrate 100 is separated from the recipient substrate 200, further processing steps can be performed. Additional layers can be deposited on or between the microdevices 102a and 102b; for example, transparent electrode layers, fillers, planarization layers, and other optical layers can be deposited during the fabrication of an LED display. Step 1012B is optional and can also be applied at the end of process 1000A or 1000C.

[0042] Fig. Figure 2C shows method 1000C; an alternative embodiment of method 1000A.

[0043] In 1002C, contact pads 202a, 202b, corresponding to the selected microdevices 102a, 102b, are treated to generate extra force upon contact. For example, an adhesive layer can be applied, as described in more detail below.

[0044] At 1004C, the donor substrate 100 and the receiver substrate 200 are aligned such that selected microdevices 102a, 102b are in alignment with corresponding contact pads 202a, 202b.

[0045] At 1006C, the donor substrate 100 and the receiver substrate 200 are moved towards each other until the selected microdevices 102a, 102b touch the contact pads 202a, 202b.

[0046] In 1008C, the forces between the selected microdevices 102 and the donor substrate 100 are modulated as needed to generate a resultant force for the selected microdevices towards the receiver substrate 200 and a resultant force for the other microdevices 102c towards the donor substrate 100 (or a resultant force of zero).

[0047] In 1010B, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding contact pads 202a, 202b. Multiple applications

[0048] Any of the methods 1000A, 1000B, 1000C can be applied multiple times to the same receiver substrate 200 using different or the same donor substrates 100, or to the same donor substrate 100 using different receiver substrates 200. For example, consider the case of assembling a display from LEDs. Each pixel can comprise red, green, and blue LEDs in a cluster. However, LEDs are more easily manufactured in batches of a single color and on substrates that are not always suitable for integration into a display. Accordingly, the LEDs must be removed from the donor substrate 100, where they may have been grown, and placed in RGB clusters on a receiver substrate, which can be the backplane of a display.This is easiest if the grid spacing of the array of pixels can be set to match the grid spacing of the array of LEDs on the donor substrate.

[0049] If this is not possible, the grid dimensions of each array can be set proportionally. Fig. 4A and Fig. Figure 4B shows arrangements where the grid spacing of the LEDs on the donor substrate is one seventh of the grid spacing of the contact pads on the receiver substrate.

[0050] In general, matching the grid spacing of an array of pixels with the donor substrate is highly unlikely to be feasible. For example, the general approach is to fabricate LEDs with the smallest possible grid spacing on the donor substrate to maximize yield, but the grid spacing of the pixels and the array of contact pads on the receiver substrate is designed based on desired product specifications, such as the size and resolution of a display. In this case, it may not be possible to transfer all of the LEDs in one step, and a repetition of any one of the procedures 1000A, 1000B, or 1000C will be required. Conversely, it may be possible to design the donor substrate and the receiver substrate contact pad array such that a portion of each pixel can be occupied during each repetition of any one of the procedures 1000A, 1000B, or 1000C, as shown in Fig. Figure 4C shows that in step I, the recipient substrate and the donor substrate are not aligned. In step II, all red LEDs are transferred. In step III, all green LEDs are transferred. In step IV, all blue LEDs are transferred. Repositioning of the donor substrate and the recipient substrate is required between each transfer step.

[0051] A person skilled in the art will understand that additional variations and combinations of methods 1000A, 1000B, and 1000C are also possible. Specific techniques and considerations are described below that apply to any one of the methods 1000, alone or in combination. Using heat for force modulation

[0052] Selective and global heating can be used in several ways to support method 1000A. For example, heat can be used in step 1008A to attenuate FD, or after step 1008A to create a permanent bond between the microdevices 102 and the contact pads 202. In one embodiment, heat can be generated using resistive elements integrated into the donor substrate 100 and / or the receiver substrate 200.

[0053] Fig. Figure 5A shows selective and global heating elements integrated into the substrates. Selective heating elements 300 and a global heating element 302 can be integrated into the donor substrate 100, while selective heating elements 304 and a global heating element 306 can be integrated into the recipient substrate 200. In another embodiment, selective heating can be achieved using a structured global heater, which is shown in a top view in Fig. 5B is shown, can be achieved.

[0054] FD can be attenuated by applying heat to the interface between a microdevice 102 and the donor substrate 100. Preferably, the selective heating elements 300 are sufficient to heat the interface to a temperature above a threshold at which the microdevices 102 will detach. However, if this is not feasible, the global heater 302 can be used to raise the temperature to a point below the threshold, while the selective heaters 300 further raise the temperature above the threshold only for the selected microdevices 102a, 102b. An ambient heat source, for example, a hot room, can replace the global heater.

[0055] Heat can also be used to create a permanent bond between the microdevices 102 and the contact pads 202. In this case, the contact pads 202 should be constructed of a material that cures upon heating, thereby creating a permanent bond. Preferably, the selective heating elements 304 are sufficient to heat the contact pads 202 above a threshold temperature to induce curing. However, if this is not feasible, the global heater 306 can be used to raise the temperature to a point below the curing threshold, while the selective heaters 304 raise the temperature for the selected contact pads 202a, 202b above the threshold. An ambient heat source, for example, a hot room, can replace the global heater. Pressure can also be applied to aid in creating a permanent bond.

[0056] Other variations are possible. In some cases, it may be feasible for the microdevices 102 or the contact pads 202 themselves to function as the resistive elements in the selective heaters 300, 304. Heat can also be applied selectively using lasers. In the case of lasers, it is likely that the donor substrate 100 and / or the receiver substrate 200 will need to be constructed of a material that is at least semi-transparent to the laser used. As in Fig. As shown in Figure 5C, a shadow mask can be used in one case to selectively block the laser for the unselected devices. Here, the shadow mask 501 is aligned with the receiver substrate or the donor substrate depending on the laser direction. The laser can then either partially or completely cover the substrate. In the case of partial coverage, raster scanning or step-and-repeat scanning can be used to cover the entire intended area of ​​the substrate. To further improve heat transfer from the laser, a layer with a high laser absorption rate can be added to the force modulation element. It is possible to use the contact pad as the force modulation element in the receiver substrate. Adhesive force modulation

[0057] In another embodiment of selective transfer, FR is generated by an adhesive. Here, FR is modulated either by selectively applying an adhesive to the landing area of ​​the recipient substrate (or to selected microdevices) or by selectively curing an adhesive layer. This method can be used in combination with selective or global donor force attenuation and is compatible with any of methods 1000A, 1000B, and 1000C, or any combination thereof. Although the following description is based on 1000A, similar approaches can be used for 1000B, 1000C, and combinations of the methods. Furthermore, the order of the donor force attenuation step 1110 can be changed with respect to other steps without affecting the results.

[0058] Fig. Figure 6A shows a flowchart of Process 1100, a modified version of Process 1000, which is specified to use an adhesive to produce FR. Fig. Figure 6B shows a setup of a donor substrate 100 and a receiver substrate 200 for carrying out the method 1100. The donor substrate 100 is shown in cross-section, and the receiver substrate 200 is shown in cross-section and top view. The donor substrate 100 has an attached array of microdevices 102. The donor force FD acts such that it holds the microdevices 102 to the donor substrate 100.

[0059] The receiver substrate 200 has an attached array of contact pads 212. Although Fig. 6B shows the force modulation element 500 connected to the contact pads 212, they can be physically separated.

[0060] As in Fig. As shown in Figure 6B, the contact pads 212a, 212b are surrounded by a ring of adhesive 500. The adhesive 500 was selectively applied to the contact pads 212 where a transfer of a microdevice is desired, so that when the donor substrate 100 and the receiver substrate 200 are moved towards each other, the microdevices 102a, 102b make contact with the adhesive 500 as well as with the contact pads 212a, 212b.

[0061] Procedure 1100 is carried out with reference to the Fig. 6B-6F explained. At 1102, the adhesive is applied selectively, as shown in Fig. 6B is shown.

[0062] In 1104, the donor substrate 100 and the receiver substrate 200 are aligned such that the selected microdevices 102a, 102b are in alignment with corresponding selected contact pads 212a, 212b, as shown in Fig. 6C is shown.

[0063] At 1106, the donor substrate 100 and the recipient substrate 200 are moved towards each other until the selected microdevices 102a, 102b are in contact with the corresponding selected contact pads 212a, 212b and the adhesive 500, as shown in Fig. 6D is shown.

[0064] At 1108, a receiver force, FR, is generated, as in Fig. Figure 6E shows that FR is generated by adhesion between the microdevices 102a, 102b, the adhesive 500, and at least one of the contact pads 212a, 212b and the receiving substrate 200. FR acts such that the selected microdevices 102 are held against corresponding selected contact pads 212. Preferably, FR can be generated selectively by selectively applying the adhesive 500, as shown.

[0065] At 1110, the donor force FD for the selected microdevices 102a, 102b is selectively (or globally) attenuated so that FD' is less than FR, as in Fig. 6F is shown. This can be achieved, for example, using laser lift-off techniques, lapping, or wet / dry etching. In another case, the donor force FD can be attenuated for all microdevices. In this case, force modulation is performed by selectively applying adhesive to the selected force element on the recipient substrate. The order of the FD and FR modulation can be changed. This step can be omitted if the adhesive force modulation is selective and FR is greater than FD.

[0066] In 1112, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding selected contact pads 212a, 212b, as shown in Fig. Figure 6G shows that once the donor substrate 100 is separated from the receiver substrate 200, further processing steps can be performed. For example, the donor substrate 100 and the receiver substrate 200 can be realigned, and the steps can be repeated to transfer another set of microdevices 102 to the contact pads 212. Additional layers can also be deposited on or between the microdevices 102; for example, transparent electrode layers, fillers, planarization layers, and other optical layers can be deposited during the fabrication of an LED display.

[0067] A possible additional step in 1114 is curing the adhesive 500. Curing can create a permanent bond between the microdevices 102 and the contact pads 212. In another embodiment, curing takes place as part of step 1108 and is part of generating FR. If several sets of selected microdevices 102 are to be transferred to a common receiving substrate 200, curing can be performed after all transfers are complete or after each set has been transferred.

[0068] The adhesive 500 can be applied in many ways. For example, the adhesive 500 can be applied to any or all of the microdevices 102, the contact pads 212, or the receiver substrate 200. Often, it will be desirable to have electrical coupling between a microdevice 102 and its corresponding contact pad 202. In this case, the adhesive can be chosen based on its conductivity. However, suitable conductive adhesives are not always available. In any case, but especially when a conductive adhesive is not available, adhesives can be applied close to the contact pads or can cover only a portion of the contact pad. Fig. Figure 7A shows some other possible arrangements of an adhesive on the receiver substrate 200, including (I) four corners, (II) opposite sides, (III) in the center and (IV) one-sided geometries.

[0069] In another embodiment, one or more cutouts can be provided for the adhesive 500. Fig. Figure 7B shows a contact pad 212 with a cutout (I) before and (II) after the application of an adhesive.

[0070] The adhesive 500 can be stamped, printed, or textured onto the contact pads 212, the microdevices 102, or the receiver substrate 200 using any standard lithography techniques. For example, shows Fig. 8. A stamping process that can be used to apply the adhesive 500, for example, to contact pads 212. Selectivity in generating FR can be achieved by selecting which contact pads 212 receive the adhesive 500. An analogous procedure can be used to apply an adhesive to the microdevices 102 or the receiving substrate 200. In (I), a stamp with a profile corresponding to the desired distribution of the adhesive 500 is wetted. In (II), the stamp is brought into contact with the receiving substrate 200 and the selected microdevices 102. In (III), the receiving substrate is now wetted with the adhesive and ready to receive a transfer from the selected microdevices 102. Depending on the process requirements, stamps with reversed profiles can also be used.In another embodiment, both the microdevices 102 and the contact pads 212 can be wetted with adhesive.

[0071] The adhesive 500 can be selected to cure when heat is applied. Any of the heating techniques described can be appropriately applied by a qualified professional according to the requirements of a specific application. Mechanical force modulation

[0072] In another embodiment of selective transfer, FR is generated by a mechanical force. Here, FR is modulated by applying mechanical forces between the landing area on the receiver substrate and the microdevice. This method can be used in combination with selective or global attenuation of the donor force and is compatible with any of methods 1000A, 1000B, and 1000C, or any combination thereof. Although the following description is based on 1000A, similar approaches can be used for 1000B, 1000C, and combinations of the methods. Furthermore, the order of the donor force attenuation step 1210 can be changed relative to other steps without affecting the results.

[0073] In one example, a differential thermal expansion or pressure force can be used to achieve an interference fit that holds the microdevices 102 to the contact pads 202.

[0074] Fig. Figure 9 shows a flow diagram of a process 1200, a modified version of process 1000A, which is suitable for the mechanical production of FR. Fig. Figure 10 shows a setup of a donor substrate 100 and a receiver substrate 200 for carrying out the method 1200. The donor substrate 100 is shown in cross-section, and the receiver substrate 200 is shown in cross-section and top view. The donor substrate 100 has an attached array of microdevices 102. The donor force FD acts such that it holds the microdevices 102 to the donor substrate 100. The microdevices 102 and the donor substrate 100 are shown connected by mass 244.

[0075] The receiver substrate 200 has an attached array of contact pads 222. In the embodiment shown, the array of contact pads 222 has the same grid dimension as the array of microdevices 102; that is, there is one microdevice 102 for each contact pad 222. As discussed above, this need not be true, although it is preferred that the grid dimension of the array of contact pads 222 and the grid dimension of the array of microdevices 102 are proportional to each other, as this facilitates the simultaneous transfer of multiple devices.

[0076] Procedure 1200 is carried out with reference to the Fig. Described in Figures 11A-11E. In Figure 1202, the substrates are prepared for mechanical force modulation. In the case of a mechanical handle, the handle is opened by various means. In one example, heat is applied to the force modulation element 222, which can be the same as a contact pad on the landing surface. Here, the mechanical handle and contact pads are used interchangeably. However, it is obvious to a person skilled in the art that the mechanical handle and the contact pad can be different. It is also possible to integrate the mechanical handle into the microdevices. The heat can be applied globally or selectively using heaters 304, causing the handle to open, as indicated by the double arrows in Figure 1202. Fig. Figure 11A shows that the contact pads 222 are designed with a central recess 224 and peripheral walls 226. It should also be noted that a combination of selective heaters 304 and global heaters 306, or a combination of selective heaters 304 and an ambient heat source or an external heat source, can be used in combination or alone.

[0077] In 1204, the donor substrate 100 and the recipient substrate are aligned such that the selected microdevices 102a, 102b are in alignment with corresponding contact pads 222a, 222b, as shown in Fig. 11B is shown.

[0078] In 1206, a donor substrate 100 and a receiver substrate 200 are moved towards each other until the selected microdevices 102a, 102b fit into the space defined by the peripheral walls of the corresponding mechanical handle, as shown in Fig. Figure 11B shows that each contact pad 222 is constructed with a central recess 224 and peripheral walls 226. These features of the contact pads 222 are dimensioned to fit precisely around a microdevice 102. The material of the mechanical handles is chosen partly for its thermal properties; specifically, the mechanical handles have a higher coefficient of thermal expansion than the microdevices 102. When heat is applied to the mechanical handles, they expand correspondingly more than a microdevice 102 would expand at the same temperature, so that the central recess and peripheral walls are able to accommodate a microdevice 102 with a gap 228. The extended size of the mechanical handle allows the microdevices 102 to fit easily inside.

[0079] At 1208, a receiver force, FR, is generated. FR is generated by selectively cooling the contact pads 222 corresponding to the selected microdevices 102, causing the peripheral walls 226 around the selected microdevices 102 to contract, thereby closing the gap 228 and exerting a compressive force on the microdevice 102, which holds it in position, as shown in Fig. 11C is shown. Selectivity can be achieved by selectively switching off selective heaters 304.

[0080] At 1210, the donor force FD for the selected microdevices 102a, 102b is selectively (or globally) attenuated so that FD' is less than FR, as in Fig. Figure 11D shows this. This can be achieved, for example, using laser lift-off techniques, lapping, or wet / dry etching. In some embodiments, FD is weaker than FR, in which case selective attenuation of FD is not required. This step can be omitted if the mechanical force modulation is selective and FR is greater than FD.

[0081] In 1212, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding contact pads 222a, 222b, as shown in Fig. Figure 11E shows that once the donor substrate 100 is separated from the receiver substrate 200, further processing steps can be performed. For example, the donor substrate 100 and the receiver substrate 200 can be realigned, and the steps can be repeated to transfer another set of microdevices 102 to the contact pads 222. Additional layers can also be deposited on or between the microdevices 102; for example, transparent electrode layers, fillers, planarization layers, and other optical layers can be deposited during the fabrication of an LED display. Electrostatic force modulation

[0082] In another embodiment of selective transfer, FR is generated by an electrostatic or a magnetic force. In the case of a magnetic force, a current flows through a conductive layer instead of charging a conductive layer for an electrostatic force. Although the structures used here are to describe the electrostatic force, similar structures can be used for a magnetic force. Here, FR is modulated by applying selective electrostatic forces between the landing area on the receiver substrate and the microdevice. This method can be used in combination with selective or global attenuation of the donor force and is compatible with any of methods 1000A, 1000B, and 1000C, or any combination thereof.Although the following description is based on 1000A, similar approaches can be used for 1000B, 1000C, and combinations of the procedures. Furthermore, the order of the donor force attenuation step 1410 can be changed relative to other steps without affecting the results.

[0083] In another embodiment of selective transfer, FR is generated by an electrostatic force. Here, FR is modulated by applying selective electrostatic forces between the landing area on the receiver substrate and the microdevice. This method can be used in combination with selective or global attenuation of the donor force and is compatible with any of methods 1000A, 1000B, and 1000C, or any combination thereof. Although the following description is based on 1000A, similar approaches can be used for 1000B, 1000C, and combinations of the methods. Furthermore, the order of the donor force attenuation step 1410 can be changed with respect to other steps without affecting the results.

[0084] Fig. Figure 12A shows a flowchart of a process 1300, a modified version of process 1000, which is suitable for electrostatic generation of FR.

[0085] Fig. Figure 12B shows a setup of a donor substrate 100 and a receiver substrate 200 for carrying out the method 1300. The donor substrate 100 is shown in cross-section, and the receiver substrate 200 is shown in cross-section and top view. The donor substrate 100 has an attached array of microdevices 102. The donor force FD acts such that it holds the microdevices 102 to the donor substrate 100. The microdevices 102 and the donor substrate 100 are shown connected by mass 244.

[0086] The landing surface on the receiver substrate 200 has at least one attached contact pad 232 and a force modulation element 234.

[0087] The contact pads 232 are surrounded by a ring of a conductor / dielectric bilayer composite, hereinafter referred to as the electrostatic layer 234. The shape and position of the force modulation element 234 can be modified in the landing area and relative to the contact pad. The electrostatic layer 234 comprises a dielectric part 236 and a conductive part 238. The dielectric part 236 comprises a material selected partly for its dielectric properties, including a dielectric constant, dielectric leakage loss, and breakdown voltage. The dielectric part may also be part of the microdevice or a combination of the receiver substrate and the microdevice. Suitable materials may include SiN, SiON, SiO, HfO, and various polymers. The conductive part 238 is selected partly for its conductive properties.There are many suitable single metals, double layers, and triple layers that may be used, including Ag, Au, and Ti / Au. Each conductive part 238 is coupled to a voltage source 240 via a switch 242. It should be noted that, although the conductive parts 238 are shown as being connected in parallel to a single voltage source 240 via simple switches 242, this is to be understood as an illustrative example. The conductive parts 238 can be connected in parallel to a single voltage source 240. Different subsets of conductive parts 238 can be connected to different voltage sources. Simple switches 242 can be replaced with more complex arrangements.The desired functionality is the ability to selectively connect a voltage source 240, which has a different potential than the microdevice 102, to selected conductive parts 238 as required, in order to cause an electrostatic attraction between the selected conductive parts 238 and corresponding selected microdevices 102.

[0088] Procedure 1300 is used in connection with Fig. 13A-13E explained. In 1302, the donor substrate 100 and the recipient substrate are aligned such that the selected microdevices 102a, 102b are in alignment with corresponding contact pads 232a, 232b, as shown in Fig. 13A is shown.

[0089] At 1304, the donor substrate 100 and the receiver substrate 200 are moved towards each other until the microdevices 102 come into contact with the contact pads 232, as shown in Fig. 13B is shown.

[0090] At 1306, a receiver force, FR, is generated, as in Fig. Figure 13C shows that FR is generated by closing switches 242a and 242b, which connect the conductive parts 238 of the electrostatic layers 234 to the voltage source 240, thereby generating charged conductive parts 238 at the potential of the voltage source 240. The selected microdevices 102a and 102b, which are at a different potential, e.g., at ground potential (or another relative potential), are electrostatically attracted to the conductive parts 238. The electrostatic charge can be generated by different potential levels. For example, for a 300 nm dielectric, a voltage difference of 20 V to 50 V may need to be applied to the electrostatic force element to obtain a suitable grip on a microdevice. However, this voltage can be modified depending on the device, the gap size, and the dielectric constant.

[0091] At 1308, the donor force FD for the selected microdevices 102a, 102b is selectively attenuated so that FD' is less than FR, as in Fig. 13D is shown. This can be done, for example, using laser lift-off techniques, lapping, or wet / dry etching.

[0092] At 1310, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding contact pads 232a, 232b, as shown in Fig. Figure 13E shows that once the donor substrate 100 is separated from the receiver substrate 200, further processing steps can be performed and the mass 244 can be removed. For example, the donor substrate 100 and the receiver substrate 200 can be realigned, and the steps can be repeated to transfer another set of microdevices 102 to the contact pads 232. Additional layers can also be deposited on or between the microdevices 102; for example, transparent electrode layers, fillers, planarization layers, and other optical layers can be deposited during the fabrication of an LED display. It should be noted that FR ceases to function if the connection to the voltage source 240 is removed. Accordingly, further processing steps to create a permanent bond between the microdevices 102 and the contact pads 232 are desirable.Curing the contact pads 232, as described above, is a suitable further processing step that will create such a bond and will enable further work or transport of the receiver substrate 200.

[0093] In other embodiments, the electrostatic layer 234 can assume other configurations. Fig. Figure 14 shows some alternative placements for the electrostatic layer 234. Possible alternative placements of the electrostatic layer 234 relative to each contact pad 232 include: (A) four corners, (B) opposite sides, (C) the center, and (D) one side. A person skilled in the art can now design a configuration suitable for specific applications.

[0094] In other embodiments, the geometry of the contact pads 232, the electrostatic layer 234 and the microdevices 102 can be changed with varying effect. Fig. Figure 15 illustrates some possible alternative geometries. Fig. Figure 15A shows an embodiment in which the electrostatic layer 234 extends above the top of the contact pad 232 to form a cavity 240, and the microdevice 102 has a mesa 242 that fits into the cavity 240. Fig. Figure 15B shows an embodiment in which the electrostatic layer 234 extends above the top surface of the contact pad 232 to form a cavity 240, and the microdevice 102 has an extension 244 attached to it that fits into the cavity 240. The extension 240 can be made of the same material 232 as the contact pad 232, so that curing later fuses the extension 244 and the contact pad 232. Angled geometries, as shown in Fig. As shown in Figure 15E, geometries with a mesa 242 or an extension 244 can help guide the microdevices 102 into the contact pads 232, ensuring a suitable fit and preventing tilting of the microdevices 102 when they are detached from the donor substrate 100. Preferably, the geometry of the microdevices 102 and the contact pads 232 is chosen to fit together in order to maximize the electrostatic force.

[0095] Fig. Figure 15C shows an embodiment in which the electrostatic layer 234 forms a cavity 240, but the conductive part 238 remains in the same plane as the contact pad 232. Fig. Figure 15D shows an embodiment in which the electrostatic layer 234 forms a cavity 240, but also overlaps with the contact pad 232, and the conductive part 238 is located in a different plane than the contact pad 232, thereby enabling fine-tuning of the electrostatic force. Transfer of microdevices with different heights

[0096] In another embodiment of selective transfer, the force on the donor substrate is modulated to press the device toward the receiver substrate. In one example, other forces, such as electrostatic forces, can be used after the donor force is removed to press the device toward the receiver substrate. In another case, a sacrificial layer can be used to generate a pressing force in the presence of heat or light sources. To selectively generate the pressing force, a shadow mask can be used to apply a light source (e.g., a laser) to the selected microdevices. Furthermore, FR can be generated by one of the aforementioned methods (e.g., mechanical, heating, adhesive, electrostatic). For example, FR can be modulated by applying selective electrostatic forces between a landing area on the receiver substrate and the microdevice.This procedure is compatible with any of procedures 1000A, 1000B, and 1000C, or any combination thereof. Although the following description is based on 1000A, similar approaches can be used for 1000B, 1000C, and combinations of these procedures. Furthermore, the order of the donor force modulation step 1410' can be changed relative to other steps without affecting the results. However, the most reliable results can be obtained by applying FR first and then applying the pressure force to the microdevice.

[0097] Fig. Figure 16 shows a flowchart of a process 1400 based on an electrostatic flow rate. However, other flow rates can be applied in the same way. The process 1400 is a modified version of the process 1300 and is particularly suitable for the simultaneous transfer of microdevices 102 with different heights. In 1402, the donor substrate 100 and the receiver substrate are aligned such that the selected microdevices 102a, 102b are in alignment with corresponding contact pads 232a, 232b, as shown in Figure 16. Fig. Figure 17A shows that microdevice 102a has a different height than microdevice 102b.

[0098] In 1404, the donor substrate 100 and the receiver substrate 200 are moved towards each other until the microdevices 102 are close enough for electrostatic FR to act on the microdevices 102. The donor substrate 100 and the receiver substrate 200 can be held such that no microdevice 102 makes contact with the contact pads 232, or, as in Fig. As shown in Figure 17B, the substrates 100, 200 can stop approaching each other when some microdevices 102 make contact with the contact pads 232.

[0099] At 1406, a receiving force, FR, is generated, as in Fig. Figure 17C shows that FR is generated by closing switches 242a and 242b, which connect the conductive parts 238 of the electrostatic layers 234 to the voltage source 240, thereby generating charged conductive parts 238 at the potential of the voltage source 240. The selected microdevices 102a and 102b, which are at a different potential, e.g., at ground potential, are electrostatically attracted to the conductive parts 238.

[0100] At step 1408, the donor force FD for the selected microdevices 102a, 102b is selectively attenuated so that FD' is less than FR. This can be achieved, for example, using laser lift-off techniques, lapping, or wet / dry etching. At this point, the devices 102a, 102b will detach from the donor substrate 100. The microdevice 102b will bridge the gap to its corresponding contact pads 232a, 232b on the receiver substrate 200.

[0101] At 1410, the donor substrate 100 and the receiver substrate 200 are moved away from each other, leaving the selected microdevices 102a, 102b attached to corresponding contact pads 232a, 232b, as shown in Fig. Figure 17E shows that once the donor substrate 100 is separated from the receiver substrate 200, further processing steps can be performed. For example, the donor substrate 100 and the receiver substrate 200 can be realigned, and the steps can be repeated to transfer another set of microdevices 102 to the contact pads 232. Additional layers can also be deposited on or between the microdevices 102; for example, transparent electrode layers, fillers, planarization layers, and other optical layers can be deposited during the fabrication of an LED display. It should be noted that FR ceases to function if the connection to the voltage source 240 is removed. Accordingly, further processing steps to create a permanent bond between the microdevices 102 and the contact pads 232 are desirable.Curing the contact pads 232, as described above, is a suitable further processing step that will create such a bond and will enable further work or transport of the receiver substrate 200.

[0102] One application of this method is the development of displays based on micro-LED devices. An LED display consists of RGB (or another pixel pattern) pixels made from individual color LEDs (such as red, green, blue, or any other color). The LEDs are manufactured separately and then transferred to a backplane. The backplane circuit drives these LEDs actively or passively. In the active form, each subpixel is driven by a transistor circuit by controlling either the current, the on-time, or both. In the passive form, each subpixel can be addressed by selecting the respective row and column and driving it through an external driver.

[0103] LEDs are conventionally manufactured as single-color LEDs on a wafer and structured into individual microdevices through various processes, such as etching. Since the LED pitch on their substrate differs from the pitch on a display, a method is required to selectively transfer them from the substrate to the backplane. The LED pitch on the substrate is the minimum possible to maximize LED fabrication yield on a wafer, while the LED pitch on the backplane is dictated by the display size and resolution.

[0104] According to the methods implemented here, the force between the LED substrate and the micro-LEDs can be modulated, and any of the techniques presented here can be used to increase the force between the selected LED and the backplane substrate. In one case, the force for the LED wafer is modulated first. In this case, the force between the LED devices and the substrate is reduced either by a laser, backplane etching, or other methods. The process can selectively weaken the bonding force between LEDs selected for transfer and the LED substrate, or it can be applied to all devices to reduce the bonding force of all LED devices to the LED substrate. In one embodiment, this is achieved by transferring all LEDs from their native substrate to a temporary substrate.Here, the temporary substrate is applied to the LEDs from the top side, and the first substrate is then removed either by polishing and / or etching or by laser lift-off. The force between the temporary substrate and the LED devices is weaker than the force that the system substrate can selectively apply to the LEDs. To achieve this, a buffer layer can first be deposited on the temporary substrate. This buffer layer can be a polyamide layer. If the buffer layer is non-conductive, to allow the devices to be tested after transfer to the temporary and system substrates, an electrode is deposited and patterned either before or after the buffer layer. If the electrode is deposited before the buffer layer, the buffer layer can be patterned to create an opening for contact.

[0105] In another method, the LED connection force modulation takes place after the LED substrate and the backplane substrate are in contact and the system substrate forces to the LED have been selectively modulated by the methods presented here. The LED substrate force modulation can also be performed before the backplane substrate force modulation.

[0106] Since the force holding the LEDs to the backplane substrate after transfer is temporary in most of the aforementioned methods, a post-processing step may be necessary to increase the bond reliability to the backplane substrate. In one embodiment, high temperature (and / or pressure) can be used. Here, a flat surface is used to apply pressure to the LEDs while the temperature is increased. The pressure is increased gradually to prevent cracking and displacement of the LED devices. Furthermore, the selective force of the backplane substrate can remain active during this process to aid bonding.

[0107] In one case, the two connections required for the LED are located on the transfer side, and the LED is in full contact with the backplane after the transfer process. In another case, a top electrode is deposited and patterned as needed. In one case, a polarizing layer can be used prior to electrode deposition. For example, a polyamide layer can be applied to the backplane substrate. After deposition, the layer can be patterned to create an opening for connecting the top electrode layer to the system substrate contacts. The contacts can be separate or shared for each LED. Furthermore, optical enhancement layers can also be deposited before or after the top electrode. Test process

[0108] Identifying defective microdevices and characterizing the microdevices after they have been transferred are an essential part of developing a high-yield system, as this can enable the use of repair and compensation techniques.

[0109] During a Fig. In the embodiment shown in Figure 18, the receiver substrate is placed in a test mode during a transfer process. If necessary, the donor substrate can be biased for the test mode. If the microdevice is an optoelectronic device, a sensor 1810 (or a sensor array) can be used to extract the optical characteristics of the transferred devices. Here, the receiver substrate is biased so that only the selected device 1802 is activated by selected contact pads 1804. The unselected devices 1806 remain deactivated, and the unselected pads 1808 remain inactive to prevent any interference. For connectivity testing, the microdevice is biased so that it is active (in the LED case, it emits light). If a microdevice is not active, the device can be marked as defective.In another test, the microdevice is biased so that it is inactive (in the case of an LED, it emits no light). If a microdevice is active, the device can be marked as defective. Fig.Figure 19 shows an example of a pixel bias state for activating or deactivating a microdevice. Here, microdevice 1906 is coupled to a bias voltage 1910 (supply voltage) 1908, thus activating it. To deactivate microdevice 1906, it is disconnected from the voltages. Here, the donor substrate 1900 can be biased to enable testing. In another case, the microdevices are tested during post-processing. While a surface is used to apply pressure to the devices to create a permanent bond, the circuit is biased to activate the microdevices. The surface can be conductive so that it can (if needed) act as another electrode for the microdevices. The pressure can be adjusted if a device is inactive to improve any interference in the bond with the receiving substrate.Similar testing can be performed to check for open defects in the devices. For performance testing, the microdevice is biased with different levels and its performance (in the case of LEDs, its output light and color point) is measured.

[0110] In one case, the defective devices are replaced or repaired before any post-processing is applied to permanently bond the device to the receiver substrate. Here, the defective devices can be removed before being replaced with a functioning device. In another embodiment, the landing area on the receiver substrate corresponding to the microdevices comprises at least one contact pad and at least one force modulation element.

[0111] It is understood that various embodiments are provided in accordance with and as variations of the above.

[0112] In another embodiment, the resulting transfer forces are modulated by attenuating the donor force using laser lift-off. In another embodiment, the resulting transfer forces are modulated by attenuating the donor force using selective heating of the area of ​​the donor substrate near each of the selected microdevices. In another embodiment, the resulting transfer forces are modulated by selectively applying an adhesive layer to the microdevices. In another embodiment, a casting device is used to selectively apply the adhesive layer. In another embodiment, printing is used to selectively apply the adhesive layer. In another embodiment, post-processing is performed on the recipient substrate so that the contact pads are permanently bonded to the selected microdevices.In another embodiment, the post-processing includes heating the receiver substrate. In another embodiment, the heating is performed by passing a current through the contact pads. In another embodiment, the method is repeated using at least one additional set of selected microdevices and corresponding contact pads. In another embodiment, the contact pads are located within a recess in the receiver substrate, and each selected microdevice fits into such a recess. In another embodiment, the grid spacing of the array of microdevices is the same as the grid spacing of the array of contact pads. In another embodiment, the grid spacing of the array of microdevices is proportional to the grid spacing of the array of contact pads.In another embodiment, each of the selected microdevices includes a protrusion, and the contact pads include a recess dimensioned to match the protrusion on each microdevice. In another embodiment, the resulting transfer forces are modulated by generating an electrostatic attraction between the selected microdevices and the receiver substrate. In another embodiment, the electrostatic forces are applied to the entire array of microdevices on the donor substrate by a force element on or behind the receiver substrate. In yet another embodiment, the electrostatic forces are selectively generated by the force modulation element of the landing surface.In another embodiment, the force modulation element of the landing surface on the receiver substrate comprises a conductive element near each contact pad, each conductive element being capable of being connected to a voltage source to maintain an electrostatic charge. In another embodiment, each conductive element comprises one or more sub-elements. In another embodiment, the sub-elements are distributed around the contact pad. In another embodiment, each conductive element surrounds a contact pad. In yet another embodiment, the force modulation element of the landing surface on the receiver substrate comprises a conductive layer and a dielectric layer extending through a substantial portion of the landing surface, the conductive layer being capable of being connected to a voltage source to maintain an electrostatic charge.In another embodiment, the donor substrate and the receiver substrate are brought close to each other, but the selected microdevices and the contact pads do not touch until after the resulting transfer forces have been modulated, whereupon the selected microdevices move across the small gap to the contact pads. In another embodiment, the height of the selected microdevices differs. In another embodiment, the contact pads are concave. In another embodiment, the force modulation element of the receiver substrate generates a mechanical clamping force. In another embodiment, the mechanical force modulation element forms part of at least one contact pad. In another embodiment, the mechanical force modulation elements are separate from the contact pad.In another embodiment, the mechanical force modulation is generated by thermal expansion or contraction of the force modulation element and / or the microdevice. In another embodiment, each contact pad has a concave portion, and each selected microdevice is inserted into a concave portion of a contact pad.

[0113] In another embodiment, the receiver substrate is heated before the donor substrate and the receiver substrate are moved towards each other, so that the concave part of the contact pads expands to be larger than a selected microdevice, and the receiver substrate is cooled before the donor substrate and the receiver substrate are moved away from each other, so that the concave part of the contact pads contracts around the selected microdevices and provides the receiver force by mechanically clamping the selected microdevices.

[0114] In another embodiment, the force modulation element in the landing area of ​​the receiver substrate is an adhesive layer positioned between the selected microdevices and the receiver substrate. In another embodiment, the adhesive layer is conductive. In another embodiment, a portion of each of the contact pads on the receiver substrate is coated with an adhesive layer. In another embodiment, a portion of each of the selected microdevices is coated with an adhesive layer. In another embodiment, a portion of the area near the contact pads is coated with an adhesive layer.

[0115] In another embodiment, the resulting transfer force is modulated both on the donor substrate using at least one of the aforementioned methods and on the recipient substrate using at least one of the described methods.

Claims

[1] Method for transferring selected microdevices (102, 102a, 102b, 102c) in an array of microdevices (102, 102a, 102b, 102c), each of which is bonded to a donor substrate (100) by a donor force, the method comprising: Aligning the donor substrate (100) and a receiver substrate (200) such that each of the selected microdevices (102, 102a, 102b, 102c) is located on the receiver substrate (200) in alignment with a contact pad (206a, 206b, 206c); Moving the donor substrate (100) and the receiver substrate (200) towards each other until each of the selected microdevices (102, 102a, 102b, 102c) is in contact with or near a respective contact pad (206a, 206b, 206c) on the receiver substrate (200); Generating a receiver force by means of force modulation elements (204a, 204b, 204c), wherein the receiver force acts such that it holds each of the selected microdevices (102, 102a, 102b, 102c) to its respective contact pads (206a, 206b, 206c), wherein each of the selected microdevices (102, 102a, 102b, 102c) corresponds to one of the force modulation elements (204a, 204b, 204c), and wherein the receiver force is generated selectively to improve selectivity of the microdevice transfer, wherein the receiver force is modulated by heating the receiver substrate (200) by passing a current through the contact pads (206a, 206b, 206c); and Moving the donor substrate (100) and the receiver substrate (200) away from each other, leaving the selected microdevices (102, 102a, 102b, 102c) on the receiver substrate (200). wherein the force modulation elements (204a , 204b , 204c) are on the receiver substrate (200) and in direct contact with the contact pads (206a , 206b, 206c). [2] The method of claim 1, further comprising weakening the donor force that bonds the microdevices to the donor substrate (100) to assist the microdevice transfer. [3] Method according to claim 2, wherein the donor force for the selected microdevices (102, 102a, 102b, 102c) is reduced to improve the selectivity of the microdevice transfer. [4] Method according to claim 1, further comprising reducing the donor force using laser lift-off. [5] Method according to claim 1, further comprising weakening the donor force by heating a region of the donor substrate (100). [6] Method according to claim 1, wherein the receiving force is generated by a mechanical handle. [7] Method according to claim 1, further comprising performing a process on the receiver substrate (200) such that the contact pads (206a, 206b, 206c) are permanently bonded to the selected microdevices (102, 102a, 102b, 102c). [8] Method according to claim 1, wherein the receiver force is generated by electrostatic attraction between the selected microdevices (102, 102a , 102b , 102c) and the receiver substrate (200). [9] Method according to claim 1, wherein the receiver force is generated by an adhesive layer positioned between the selected microdevices (102, 102a , 102b , 102c) and the receiver substrate (200). [10] The method of claim 1, further comprising: Removal of donor force; and Applying a pressure force to the selected microdevices (102, 102a, 102b, 102c) to move the devices towards the receiver substrate (200). [11] Method according to claim 10, wherein the pressure force is generated by a sacrificial layer deposited between the selected microdevices (102, 102a, 102b, 102c) and the donor substrate (100). [12] Recipient substrate structure, which includes the following: an array of landing surfaces for selectively holding microdevices (102, 102a, 102b, 102c) from a donor substrate, each landing surface comprising: at least one contact pad (206a, 206b, 206c) for coupling a microdevice (102, 102a, 102b, 102c) to a circuit or a potential in the receiver substrate (200); and at least one force modulation element (204a , 204b , 204c) for generating a receiver force for holding a microdevice (102, 102a, 102b, 102c) on the receiver substrate (200), wherein the force modulation element (204a , 204b , 204c) is a mechanical handle, wherein each of the microdevices (102, 102a, 102b, 102c) corresponds to at least one of the force modulation elements (204a, 204b, 204c), and wherein the at least one force modulation element (204a, 204b, 204c) is on the receiver substrate (200) and in direct contact with at least one contact pad (206a, 206b, 206c). [13] Receiver substrate structure according to claim 12, wherein the force modulation element (204a , 204b , 204c) is an electrostatic structure. [14] Receiver substrate structure according to claim 12, wherein for each landing area the same element functions as the force modulation element (204a , 204b , 204c) and the contact pad (206a, 206b, 206c).

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