CN110943063A

CN110943063A - Integrating micro devices into a system substrate

Info

Publication number: CN110943063A
Application number: CN201910895236.9A
Authority: CN
Inventors: 格拉姆雷扎·查济; 埃桑诺拉·法蒂
Original assignee: Vuereal Inc
Current assignee: Vuereal Inc
Priority date: 2018-09-21
Filing date: 2019-09-20
Publication date: 2020-03-31
Also published as: TW202030829A; KR20200034931A; TWI815968B

Abstract

The present application relates to integrating micro devices into a system substrate. In a microdevice integration process, a donor substrate is provided on which initial fabrication and pixelation steps will be performed to define a microdevice that includes a functional layer, such as a light emitting layer, sandwiched between top and bottom conductive layers. The micro device is then transferred to a system substrate for finalization and electronic control integration. The transfer may be facilitated by various means, including providing a continuous light emitting functional layer, a breakable anchor on the donor substrate, a temporary intermediate substrate implementing a heat transfer technique, or a temporary intermediate substrate with a breakable substrate bonding layer.

Description

Integrating micro devices into a system substrate

Cross Reference to Related Applications

This application is a partially-filed and priority-filed application No. 15/820,683, filed on 22/11/2017, and No. 15/820,683 claims priority and benefit from the following applications: united states provisional patent application No. 62/426,353 filed on 25/11/2016, united states provisional patent application No. 62/473,671 filed on 20/3/2017, united states provisional patent application No. 62/482,899 filed on 7/4/2017, united states provisional patent application No. 62/515,185 filed on 5/6/2017, and canadian patent application No. 2,984,214 filed on 30/10/2017, each of which is incorporated herein by reference in its entirety.

This application also claims the benefit of united states provisional patent application No. 62/734,679 filed on 21.9.2018 and No. 62/809,161 filed on 22.2.2019, which are incorporated herein by reference in their entirety.

The present application further claims the benefit of U.S. provisional patent application No. 62/746,300 filed on 16.10.2018, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to optoelectronic microdevices, and more particularly to integrating optoelectronic microdevices into system substrates with enhanced bonding and electrical conductivity capabilities.

Background

It is an object of the present invention to overcome the disadvantages of the prior art by providing a system and method for transferring a microdevice from a donor substrate to a system substrate.

Disclosure of Invention

According to one embodiment of the invention, a method of fabricating a pixelated structure comprises: providing a donor substrate; depositing a first conductive layer on the donor substrate; depositing a fully or partially continuous light-emitting functional layer on the first electrically conductive layer; depositing a second conductive layer on the functional layer; patterning the second conductive layer to form a pixelated structure; providing a bonding contact for each pixelated structure; securing the bonding contact to a system substrate; and removing the donor substrate.

In one embodiment, the micro devices are turned into an array using sequential pixelation.

In another embodiment, the devices are separated by filling the voids between the micro devices and transferred to an intermediate substrate.

In another embodiment, the micro device is post-processed after transfer to an intermediate substrate.

According to one embodiment, a bonding structure may be provided. The bonding structure may comprise a plurality of micro devices on a donor substrate, wherein each micro device comprises one or more conductive pads formed on a surface of the micro device; and a temporary material covers at least a portion of each micro device or the one or more conductive pads. In one case, the temporary material acts as an anchor that holds the plurality of microdevices inside a shell structure in a donor substrate.

According to one embodiment, there may be provided a method of integrating a micro device on a backplane, the method comprising: providing a microdevice substrate comprised of one or more microdevices; connecting pads on the micro devices and corresponding pads on the backplane to bond a set of selective micro devices from the substrate to the backplane; and separating the micro device substrates to leave a selected set of bonded micro devices on the backplane.

Drawings

The invention will be described in more detail with reference to the appended drawings showing preferred embodiments of the invention, in which:

FIG. 1A illustrates a cross-sectional view of a lateral functional structure on a donor substrate according to an embodiment of the present invention;

FIG. 1B illustrates a cross-sectional view of the lateral structure of FIG. 1A with a current distribution layer deposited thereon, in accordance with an embodiment of the present invention;

FIG. 1C shows a cross-sectional view of the lateral structure of FIG. 1B after patterning the top dielectric conductive layer and depositing a second dielectric layer, in accordance with an embodiment of the present invention;

FIG. 1D illustrates a cross-sectional view of a lateral structure after patterning a second dielectric layer, in accordance with an embodiment of the present invention;

FIG. 1E illustrates a cross-sectional view of a lateral structure after pad deposition and patterning in accordance with an embodiment of the present invention;

FIG. 1F illustrates a cross-sectional view of a lateral structure after bonding to a system substrate through a bonding region to form an integrated structure, in accordance with an embodiment of the present invention;

FIG. 1G illustrates a cross-sectional view of the integrated structure after removal of the donor substrate and the patterned bottom electrode, in accordance with an embodiment of the present invention;

FIG. 1H illustrates a cross-sectional view of the integrated structure after removal of the donor substrate and the patterned bottom electrode, in accordance with an embodiment of the present invention;

FIG. 2A shows a cross-sectional view of another embodiment of a lateral functional structure on a donor substrate with a pad layer;

fig. 2B illustrates a cross-sectional view of the lateral structure of fig. 2A after patterning the pad layer and the contact layer and the current distribution layer, in accordance with an embodiment of the present invention;

FIG. 2C illustrates a cross-sectional view of the lateral structure of FIG. 2A after filling the distance between patterned pads, in accordance with an embodiment of the present invention;

FIG. 2D illustrates a cross-sectional view of the lateral structure of FIG. 2A aligned and bonded to a system substrate through a patterned pad, in accordance with an embodiment of the present invention;

FIG. 2E illustrates a cross-sectional view of the lateral structure of FIG. 2A with the device substrate removed, in accordance with an embodiment of the present invention;

FIG. 3A shows a cross-sectional view of a mesa structure on a device (donor) substrate according to an embodiment of the present invention;

FIG. 3B illustrates a cross-sectional view of a step in accordance with an embodiment of the invention in which the empty spaces between the mesa structures of FIG. 3A are filled;

FIG. 3C shows a cross-sectional view of a step according to an embodiment of the invention in which the device (mesa structure) of FIG. 3B is transferred to a temporary substrate;

FIG. 3D illustrates a cross-sectional view of a step in which the device of FIG. 3C is aligned and bonded to a system substrate, in accordance with an embodiment of the present invention;

FIG. 3E shows a cross-sectional view of a step in which the device is transferred to a system substrate, in accordance with an embodiment of the present invention;

FIG. 3F illustrates a thermal profile of a thermal transfer step according to an embodiment of the invention;

FIG. 4A shows a cross-sectional view of a temporary substrate having a slot and a device transferred thereto, in accordance with an embodiment of the present invention;

FIG. 4B shows a cross-sectional view of the temporary substrate of FIG. 4A after cleaning of the filler material between the device space and the slot, in accordance with an embodiment of the present invention;

FIG. 4C shows a cross-sectional view of a step in which a device is transferred to a system substrate by breaking the released surface, in accordance with an embodiment of the present invention;

FIG. 5A illustrates a cross-sectional view of a microdevice having different anchors in a packed layer according to an embodiment of the invention;

FIG. 5B illustrates a cross-sectional view of a microdevice after post-processing a fill layer according to an embodiment of the invention;

FIG. 5C illustrates a top view of the micro device of FIG. 5B, according to an embodiment of the invention;

FIG. 5D shows a cross-sectional view of a transfer step for transferring a micro device to another substrate, in accordance with an embodiment of the present invention;

FIG. 5E shows a cross-sectional view of a micro device being transferred to a substrate, according to an embodiment of the invention;

fig. 6A shows a cross-sectional view of a mesa structure on a device (donor) substrate according to another embodiment of the present invention;

FIG. 6B shows a cross-sectional view of a step in which the empty spaces between the mesa structures of FIG. 6A are filled;

FIG. 6C shows a cross-sectional view of a step according to an embodiment of the invention in which the device (mesa structure) of FIG. 6B is transferred to a temporary substrate;

FIG. 6D shows a cross-sectional view of a step according to an embodiment of the invention, in which a portion of the bottom conductive layer of FIG. 6C is removed;

FIG. 6E illustrates a cross-sectional view of a microdevice having anchors in the fill layer according to an embodiment of the invention;

FIG. 6F illustrates a cross-sectional view of a microdevice having anchors in the fill layer according to an embodiment of the invention;

FIG. 6G illustrates a cross-sectional view of a microdevice having anchors in the fill layer according to an embodiment of the invention;

FIG. 6H illustrates a cross-sectional view of a preliminary step in another embodiment of the present invention;

FIG. 6I illustrates a cross-sectional view of an etching step in the embodiment of FIG. 6H, in accordance with an embodiment of the present invention;

FIG. 6J illustrates a cross-sectional view of a separation step in the embodiment of FIG. 6H, in accordance with an embodiment of the present invention;

FIG. 6K illustrates a top view of another embodiment of the present invention, according to an embodiment of the present invention;

FIG. 6L illustrates a cross-sectional view of the embodiment of FIG. 6K, in accordance with an embodiment of the present invention;

FIG. 6M illustrates a cross-sectional view of the embodiment of FIGS. 6K and 6L with a filler material, in accordance with an embodiment of the present invention;

FIG. 7 is a flow chart of a process of an embodiment of the present invention;

FIG. 8 is a flow chart of a microdevice installation process according to an embodiment of the invention;

FIG. 9 is a flow chart of a microdevice installation process according to an embodiment of the invention;

FIG. 10 is a flow chart of a microdevice installation process according to an embodiment of the invention;

FIG. 11 shows an example of a donor or temporary (box) substrate with different types of pixelated micro-devices, according to an embodiment of the invention;

FIG. 12 shows an example of a donor or temporary (box) substrate with different types of pixelated micro-devices, according to an embodiment of the invention;

FIG. 13 shows an example of a donor substrate for the same type of micro device but with different spacing between groups of micro devices, according to an embodiment of the invention;

FIG. 14A shows an example of a donor substrate or temporary substrate with non-uniform output over a block of micro devices according to an embodiment of the invention;

FIG. 14B shows an example of a recipient substrate or system substrate with non-uniform output across multiple micro device blocks, according to an embodiment of the invention;

FIG. 14C shows an example of a system substrate with a skewed micro device tile, according to an embodiment of the invention;

FIG. 14D shows an example of a system substrate with flipped micro device tiles in accordance with an embodiment of the invention;

FIG. 14E shows an example of a system substrate with flipped and alternating micro device blocks according to an embodiment of the invention;

FIG. 15A shows an example of a donor substrate with two different micro device blocks, according to an embodiment of the invention;

FIG. 15B shows an example of a system substrate with deflection blocks for different micro devices according to an embodiment of the present invention;

FIG. 16A shows an example of a donor substrate with three different types of pixelated micro-device blocks, according to an embodiment of the invention;

FIG. 16B shows an example of a system substrate with multiple different types of individual micro devices from each block, according to an embodiment of the invention;

FIG. 17A shows an example of a cassette substrate with multiple different types of pixelated micro-device blocks, according to an embodiment of the invention;

FIG. 17B shows an example of a cassette substrate with multiple different types of offset pixelated microdevice blocks, according to an embodiment of the invention;

figure 18 shows a donor substrate holding a micro device via a donor element, according to an embodiment of the invention.

FIG. 19 shows an example of a micro device having more than one contact pad on one side according to an embodiment of the invention.

20A1-20A2 illustrate examples of highlighted temporary conductive material covering micro devices according to some embodiments of the invention.

20B1-20B2 illustrate another example of a highlighted temporary conductive material covering a micro device, according to some embodiments of the invention.

20C1-20C2 illustrate another example of a highlighted temporary conductive material covering a micro device, according to some embodiments of the invention.

20D-20H illustrate another example of a highlighted temporary conductive material covering a micro device according to some embodiments of the invention.

20I1-20I2 illustrate another example of a highlighted temporary conductive material covering a micro device, according to some embodiments of the invention.

Fig. 21A illustrates the exemplary top view representation of fig. 20A, in accordance with embodiments of the present invention.

Fig. 21B1 illustrates an exemplary top view representation of fig. 20B1, in accordance with an embodiment of the present invention.

Fig. 21B2 illustrates another exemplary top view representation of fig. 20B2, in accordance with an embodiment of the present invention.

Fig. 21C illustrates the exemplary top view representation of fig. 20E, in accordance with embodiments of the present invention.

Fig. 21D illustrates the exemplary top view representation of fig. 20F in accordance with an embodiment of the present invention.

Fig. 22A-22C illustrate a micro device on a donor substrate, wherein the micro device can be selectively moved toward or away from a surface of the donor substrate, according to embodiments of the invention.

Fig. 23A-23B illustrate a micro device on a donor substrate, wherein the micro device can be selectively moved toward or away from a surface of the donor substrate, according to embodiments of the invention.

Fig. 24 shows another example of a micro device on a donor substrate, where the micro device can be selectively moved toward or away from the surface of the donor substrate, according to an embodiment of the invention.

Fig. 25A shows a cross-sectional view of an array of micro devices on a micro device substrate, according to one embodiment of the invention.

Fig. 25B illustrates a cross-sectional view of a micro device array having a patterned buffer layer, according to one embodiment of the invention.

Fig. 25C illustrates a cross-sectional view of a micro device array having a planarization layer, according to one embodiment of the present invention.

Figure 25D illustrates a cross-sectional view of a micro device array bonded to an intermediate substrate, according to one embodiment of the invention.

Fig. 25E shows a cross-sectional view of a micro device array having pads, according to one embodiment of the invention.

Figure 26 illustrates a cross-sectional view of a micro device array bonded to an intermediate substrate and a backplate, according to one embodiment of the invention.

FIG. 27A shows the process steps for extracting the location of a micro device according to one embodiment of the invention.

Figure 27B illustrates modifying the position/shape of an electrode based on the position of a microdevice according to one embodiment of the invention.

Fig. 27C shows an extension provided to an electrode according to one embodiment of the present invention.

If the same reference numbers are used in different drawings, similar or identical elements are indicated.

The disclosure is susceptible to various modifications and alternative forms, and specific embodiments or implementations are shown by way of example in the drawings and will herein be described in detail. However, the disclosure is not intended to be limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.

Detailed Description

While the present teachings are described in conjunction with various embodiments and examples, the present teachings are not intended to be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those skilled in the art.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used in this specification and the claims, the singular form of "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

In this specification, the terms "device", "vertical device" and "microdevice" are used interchangeably. However, those skilled in the art will appreciate that the embodiments described herein are independent of device size.

In this specification, the terms "donor substrate" and "temporary substrate" are used interchangeably.

In this specification, the terms "receptor substrate", "system substrate" and "backplane" are used interchangeably.

Examples of optoelectronic devices are sensors and light emitting devices, such as Light Emitting Diodes (LEDs).

The present disclosure relates to a micro device array display device, wherein the micro device array may be bonded to a backplane using a reliable method. A micro device can be fabricated over a micro device substrate. The micro device substrate may include micro LEDs, inorganic LEDs, organic LEDs, sensors, solid state devices, integrated circuits, micro-electro-mechanical systems (MEMS), and/or other electronic components.

LEDs and LED arrays can be classified as vertical solid state devices. The micro device may be a sensor, an LED, or any other solid state device grown, deposited, or monolithically fabricated on a substrate. The substrate may be an intrinsic or acceptor substrate of the device layer to which the device layer or solid state device is transferred.

The receptor substrate may be any substrate and may be rigid or flexible. The receptor substrate may include, but is not limited to, a printed circuit board, a Thin Film Transistor (TFT) backplane, an integrated circuit substrate, or in one case of an optical micro device such as an LED, a component of a display such as a drive circuit backplane. Microdevice patterning on device donor and receptor substrates can be used in combination with different transfer techniques, such as pick and place, with different mechanisms (e.g., electrostatic transfer heads, elastomeric transfer heads) or direct transfer mechanisms (e.g., dual function pads).

In the present disclosure, a contact pad in a receptor substrate refers to a designated area in the receptor substrate to which a micro device is transferred. The contact pads may include a bonding material that permanently holds the micro device. The contact pads may be stacked in multiple layers to provide a mechanically more stable structure with improved bonding and conductive capabilities.

The system substrate may be made of glass, silicon, plastic or any other commonly used material. The system substrate may also have active electronic components such as, but not limited to, transistors, resistors, capacitors, or any other electronic components commonly used in system substrates. In some cases, the system substrate can be a substrate having rows and columns of electrical signals. The system substrate may be a backplane with circuitry to derive the micro LED devices.

FIG. 1A shows an embodiment of a donor substrate 110 having a lateral functional structure comprising a bottom planar or sheet-like conductive layer 112; functional layers 114, such as light-emitting quantum wells; and a top pixelated conductive layer 116.

Conductive layers

112 and 116 may be comprised of doped semiconductor material or other suitable type of conductive layer. The top conductive layer 116 may comprise several different layers. In one embodiment, as shown in FIG. 1B, a current distribution layer 118 is deposited on top of conductive layer 116. The current distribution layer 118 may be patterned. In one embodiment, the patterning may be performed by lift off. In another case, the patterning may be performed by photolithography. In an embodiment, the current distribution layer 118 may be patterned by first depositing and patterning a dielectric layer and then using it as a hard mask. After patterning the current distribution layer 118, the top conductive layer 116 may also be patterned to form a pixel structure. After patterning the current distribution layer 118 and/or the conductive layer 116, a final dielectric layer 120 may be deposited over and between the patterned conductive layer 116 and the current distribution layer 118, as shown in fig. 1C. The dielectric layer 120 may also be patterned to create an opening 130 as shown in fig. 1D to provide access to the current distribution layer 118. An additional leveling layer 128 may also be provided to level the upper surface, as shown in FIG. 1E.

As shown in fig. 1E, a pad 132 is deposited in each opening 130 on top of the current distribution layer 118. The resulting structure with bond pads 132 is bonded to a system substrate 150 with bond pads 154 as shown in fig. 1F. The pads 154 in the system substrate 150 may be separated by a dielectric layer 156. Other layers 152, such as circuitry, planarization layers, conductive traces, may be present between the system substrate pads 154 and the system substrate 150. The system substrate pad 154 may be bonded to the pad 132 by fusion bonding, anodic bonding, thermocompression bonding, eutectic bonding, or adhesive bonding. One or more other layers may also be deposited between the system device and the lateral device.

As shown in fig. 1G, donor substrate 110 can be removed from the lateral functional device, such as conductive layer 112. The conductive layer 112 may be thinned and/or partially or fully patterned. A reflective layer or black matrix 170 may be deposited and patterned to cover the regions of the conductive layer 112 between the pixels. After this stage, other layers may be deposited and patterned according to the function of the device. For example, a color conversion layer may be deposited to adjust the color of light produced by the lateral devices and pixels in the system substrate 150. One or more color filters may also be deposited before and/or after the color conversion layer. The dielectric layer in these devices, e.g., dielectric layer 120, may be an organic material such as polyamide or an organic material such as SiN or SiO₂、Al₂O₃And the like. The deposition can be performed with different processes, such as Plasma Enhanced Chemical Vapor Deposition (PECVD), Atomic Layer Deposition (ALD), and other methods. Each layer may be one deposited material or a combination of different materials deposited separately or together. The bonding material may be deposited only as a portion of pad 132 of donor substrate 110 or system substrate pad 154. For some of the layers, there may also be some annealing process. For example, the current distribution layer 118 may be annealed depending on the material. In one example, the current distribution layer 118 may be annealed at 500 ℃ for 10 minutes. Annealing may also be performed after the different steps.

Fig. 2A shows an exemplary embodiment of a donor substrate 210 having a lateral functional structure comprising a first top planar or sheet-like conductive layer 212; a functional layer 214, such as a light emitting layer; a second bottom pixelated conductive layer 216; a current-distributing layer 218; and/or bond pad layer 232. Fig. 2B shows all or one of the

patterned layers

216, 218, 232 to form a pixel structure. The

conductive layers

212 and 216 may be composed of a plurality of layers including a highly doped semiconductor layer. Some layers 228, such as a dielectric, may be used between

patterned post-layers

216, 218, and 232 to planarize the upper surface of the lateral functional structures, as shown in fig. 2C. The layer 228 may also have other functions, such as a black matrix. The resulting structure with pads 232 is bonded to a system substrate 250 with substrate pads 254, as shown in fig. 2D. The pads 254 in the system substrate may also be separated by a dielectric layer 256. Other layers 252, such as circuitry, planarization layers, and conductive traces, may be present between the system substrate pads 254 and the system substrate 250. The bonding may be performed, for example, by fusion bonding, anodic bonding, thermocompression bonding, eutectic bonding, or adhesive bonding. Other layers may also be deposited between the system means and the lateral means.

The donor substrate 210 may be removed from the lateral functional means. The conductive layer 212 may be thinned and/or patterned. A reflective layer or black matrix 270 may be deposited and patterned to cover the regions of the conductive layer 212 between the pixels. After this stage, other layers may be deposited and patterned according to the function of the device. For example, a color conversion layer may be deposited to adjust the color of light produced by the lateral devices and pixels in the system substrate 250. One or more color filters may also be deposited before and/or after the color conversion layer. The dielectric layers, e.g., 228 and 256, in these devices may be organic, e.g., polyamide, or of SiN, SiO₂、Al₂O₃And the like. The deposition can be performed by different processes, such as PECVD, ALD and other methods. Each layer may be one deposited material or a combination of different materials deposited separately or together. The material of bond pad 232 may be deposited as a portion of pad 232 of donor substrate 210 or system substrate pad 254. For some of the layers, there may also be some annealing process. For example, the current distribution layer 218 may be annealed depending on the material. In an example, it may be at 500 deg.CThe current-distributing layer was annealed for 10 minutes. Annealing may also be performed after the different steps.

In another embodiment, shown in fig. 3A, a mesa structure is created on a donor substrate 310. The microdevice structure is formed by etching through different layers, such as the first bottom conductive layer 312, the functional layer 314, and the second top conductive layer 316. Top contact 332 may be deposited before or after etching the top of top conductive layer 316. In another case, a multi-layer contact 332 may be used. In this case, a portion of the contact layer 332 may be deposited before etching and a portion of the contact layer may be deposited after etching. For example, an initial contact layer that creates an ohmic contact by annealing the conductive layer 316 may be first deposited. In one example, the initial contact layer may be gold or nickel. Other layers 372, such as dielectric or Metal Insulator Structures (MIS), may also be used between the mesa structures to isolate and/or insulate each structure. After the microdevice is formed, a filler layer 374, such as polyamide, may be deposited, as shown in fig. 3B. The filler layer 374 can be patterned if only selected micro devices are transferred to the cartridge (temporary) substrate 376 during the next steps. The filler layer 374 can also be deposited after the device is transferred to a temporary substrate. The filler layer 374 can serve as a shell for the microdevice. The lift-off process may be more reliable if a filler layer 374 is used prior to transfer.

The device is bonded to a temporary substrate (cassette) 376. For example, the bonding source may vary and may include one or more of the following: electrostatic bonding, electromagnetic bonding, adhesive bonding, Van Der Waals force (Van-Der-Waals force) bonding, or thermal bonding. For thermal bonding, a substrate bonding layer 378 having a melting temperature T1 may be used. Bonding layer 378 may be electrically conductive or may include an electrically conductive layer and a bonding layer, which may be an adhesive bond, a thermal bond, or a light assisted bond. The conductive layer can be used to bias devices on the substrate 376 to identify defects and characterize device performance. This structure may be used in other embodiments presented herein. To account for some surface profile non-uniformity, pressure may be applied during the bonding process. Temporary substrate 376 or donor substrate 310 may be removed and the device left on either. The process explained herein is based on leaving the device on temporary substrate 376, however, similar steps may be used when the device is left on donor substrate 310. After this, additional processes may be performed on the microdevice, such as thinning the device, creating contact bond layer 380 on bottom conductive layer 312, or removing filler layer 374. The device can be transferred to a system substrate 390 as shown in fig. 3D and 3E. Different techniques may be used to perform the transfer. In one case, the transfer is performed using thermal bonding. In this case, the melting point of the contact bonding layer 380 on the system substrate contact pad 382 is T2, where T2> T1. Here, a temperature above T2 will melt both the substrate bonding layer 378 and the contact bonding layer 380 on the pad 382.

In a subsequent step, the temperature is reduced to between T1 and T2. At this point, the device is bonded to the system substrate 390 through the contact bonding layer 380 such that the contact bonding layer 380 solidifies but the substrate bonding layer 378 melts. Thus, moving temporary substrate 376 leaves the micro devices on system substrate 390, as shown in FIG. 3E. The process can be made selective by applying localized heating to selected pads 382. Also, in addition to local heating, a global temperature may be used, such as placing

substrates

376 and 390 in an oven and performing the process by increasing the overall atmosphere therein, thereby increasing the transfer rate. Here, the global temperature on the temporary substrate 376 or the system substrate 390 may be such that the temperature is close to the melting point of the contact bonding layer 380, e.g., between 5 ℃ and 10 ℃ below the melting point, and the local temperature may be used to melt the contact bonding layer 380 and the substrate bonding layer 378 corresponding to the selected device. In another case, the temperature may be raised to near the melting point of substrate bonding layer 378 (above the melting point of contact bonding layer 378), e.g., between 5 ℃ and 10 ℃ below that melting point, and for devices in contact with heated pad 382, the temperature transfer from pad 382 through the device melts selected regions of substrate bonding layer 378.

Fig. 3F shows an example of a thermal profile with a melting temperature Tr melting the contact bonding layer 380 and the substrate bonding layer 378, and a curing temperature Ts curing the contact bonding layer 380 with the bond pad 382 while the substrate bonding layer 378 is still molten. The melting may be localized or may at least make the bonding layer soft enough to release the microdevice or activate the alloying process. Here, other forces may also be used in combination or alone to hold the device on the bond pad 382. In another case, the temperature profile may be generated by applying a current through the device. Because the contact resistance will be high prior to bonding, the power dissipated across the bond pad 382 and the device will be high, melting the contact bonding layer 380 and the substrate bonding layer 378. As the bond forms, the resistance will drop and the power dissipation will also drop, thereby lowering the local temperature. The voltage or current through the pad 382 can be used to indicate the quality of the bond and when to stop the process. Donor substrate 310 and temporary substrate 376 may be the same or different. After the device is transferred to the system substrate 390, different process steps may be performed. These additional processing steps may be planarization, electrode deposition, color conversion deposition and patterning, color filter deposition and patterning, and the like.

In another embodiment, the temperature used to release the micro devices from the cassette substrate 376 increases as the alloy begins to form. In this case, the temperature may be kept constant while the bonding alloy is formed on the bonding pad 382 of the receptor substrate 390 and the bonding layer is cured, thereby keeping the micro device in place on the receptor substrate 390. At the same time, the bonding layer 378 on the cartridge 376 connected to the selected micro device remains molten (or soft enough) to release the device. Here, a portion of the material needed to form the alloy may be on the microdevice and another portion deposited on the bond pad 382.

In another embodiment, a filler layer 374 may be deposited on top of the cartridge substrate 376 to form a polymer filler/bonding layer 374/378. The microdevice from donor substrate 310 may then be pushed into polymer filler/bonding layer 374/378. The microdevice can then be selectively or generally detached from the donor substrate 310. The polymer filler/bonding layer 374/378 may be cured before or after the microdevice is separated from the donor substrate 310. The polymer filler/bonding layer 374/378 may be patterned, particularly where a number of different devices are integrated into the cartridge substrate 376. In this case, the polymer filler/bonding layer 374/378 may be created for one type, with the microdevice buried in the layer and separated from its donor body 310. Another polymeric filler/bonding layer 374/378 is then deposited and patterned for the next type of microdevice. The second microdevice may then be buried in the associated layer 374/378. In all cases, the polymeric filler/bonding layer 374/378 may cover some or all of the microdevices.

Another method of increasing the temperature may be to use microwaves or lamps. Thus, layers may be deposited on: a bonding pad 382; a part of the pad 382; a micro device; or the cartridge 376 absorbs microwaves or light and locally heats a portion of the microdevice. Alternatively, the cartridge 376 and/or the receptor substrate 390 may contain heating elements that can selectively and/or globally heat the microdevice.

Other methods of separating the microdevice from temporary substrate 376 may also be used, such as chemical, optical, or mechanical forces. In one example, the microdevice can be covered with a sacrificial layer that can be debonded from the temporary substrate 376 by chemical, optical, thermal, or mechanical forces. The de-bonding process may be selective or global. The global debond transfer to the system substrate 390 is selective. If the device and temporary substrate (cassette) 376 debonding process is selective, a transfer force may be selectively or globally applied to the system substrate 390.

The transfer process from the cartridge 376 to the recipient substrate 390 can be based on different mechanisms. In one instance, the cartridge 376 has a bonding material that releases the device in the presence of light while the same light cures the bonding of the device to the receptor substrate.

In another embodiment, the temperature used to cure the bonding layer 380 of the device to the receptor substrate 390 releases the device from the cartridge 376.

In another case, the current or voltage cures the bonding layer 380 of the device to donor substrate 310. The same current or voltage may cause the device to release from the cartridge 376. Here, the release may be a function of the piezoelectric effect generated by the current or the temperature.

In another approach, after bonding of the curing device to the receptor substrate 390, the bonded device is pulled from the cassette 376. Here, the force holding the device to the cartridge 376 is less than the force bonding the device to the receptor substrate 390.

In another approach, the cartridge 376 has vias that can be used to push the device out of the cartridge 376 and into the recipient substrate 390. The pushing may be performed in different ways, such as using a micro-rod array or by pneumatic means. For a pneumatic configuration, the selected device is disconnected. For the micro-rods, the selected devices are moved toward the receptor substrate 390 by passing the micro-rods through their associated vias. The micron rods may have different temperatures to facilitate transfer. After the transfer of the selected device is complete, the micro-rods are retracted and the same rods are aligned with the vias of another set of micro-devices or a set of vias aligned with a new selected micro-device is used to transfer the new device.

In one embodiment, the cartridge 376 may be stretched to increase the device spacing in the cartridge 376 to increase throughput. For example, if the cartridge 376 is 1X 1cm²Where the device pitch is 5 microns and the pixel pitch of the receptor substrate 390 (e.g., display) is 50 microns, the cell 376 can fill 200 x 200(40,000) pixels at a time. However, if the cartridge 376 is stretched to 2X 2cm²Where the device pitch is 10 microns, the cartridge 376 can fill 400 x 400(160,000) pixels at a time. In another case, the cartridge 376 may be stretched such that at least two micro devices on the cartridge 376 become aligned with two corresponding locations in the recipient substrate. The stretching may be performed in one or more directions. The cartridge substrate 376 may include or consist of a stretchable polymer. The microdevice is also mounted in another layer or in the same layer as the cartridge substrate 376.

Combinations of the above-described methods may also be used to transfer the microdevice from the cartridge 376 to the recipient substrate 390.

During the production of the cartridge (temporary substrate) 376, the microdevice may be tested to identify different defects and device performance. In one embodiment, the device may be biased and tested prior to separation of the top electrode. If the device is an emissive device, a camera (or sensor) may be used to extract defects and device performance. If the device is a sensor, a stimulus can be applied to the device to extract defects and performance. In another embodiment, the top electrodes 332 may be patterned into groups for testing before being patterned into individual devices. In another example, a temporary common electrode between more than one device is deposited or coupled to the device to extract device performance and/or extract defects.

The methods described above with respect to fig. 3A-3D, including but not limited to separating, forming filler layers, different roles of filler layers, testing, and other structures, can be used with other structures including those described below.

The methods discussed herein for transferring a microdevice from a cartridge (temporary substrate) 376 to a receiver substrate 390 may be applied to all cartridge and receiver substrate configurations presented herein.

The device on the donor substrate 310 can be created with two

contacts

332 and 380 on the same side facing away from the donor substrate 310. In this embodiment, the conductive layer on the cartridge 376 may be patterned to independently bias the two

contacts

332 and 380 of the device. In one case, the device can be transferred directly from the cartridge substrate 376 to the receptor substrate 390. Here, the

contacts

332 and 380 may not be directly bonded to the receptor substrate 390, i.e., the receptor substrate 390 need not have special pads. In this case, a conductive layer is deposited and patterned to connect

contacts

332 and 380 to appropriate connections in receptor substrate 390. In another embodiment, the device may first be transferred from the cassette 376 to a temporary substrate before being transferred to the recipient substrate 390. Here,

contacts

332 and 380 may be bonded directly to receptor substrate pad 382. The device may be tested in the cassette 376 or in a temporary substrate.

In another embodiment, shown in fig. 4A, a mesa structure as described above is created on a donor substrate by etching through different layers, such as a first bottom conductive layer 412; a functional layer 414, for example, emitting light; and a second top conductive layer 416 is formed with a micro device structure. Top contact 432 may be deposited before or after etching on top of top conductive layer 416.

Temporary substrate 476 comprises a substrate that is initially filled with a filler material, for example, a soft material such as a polymer or a material such as SiO₂And a plurality of grooves 476-2 of a solid material such as SiN. The slot 476-2 is below the surface and/or substrate bonding layer 478. The device is transferred to a temporary substrate 476 on top of the slot 476-2 and the device includes contact pads 432. Also, each micro device may contain other passivation and/or MIS layers 472 surrounding each micro device for isolation and/or protection. The space between the devices may be filled with a filler material 474. After post-processing the device, another lower contact pad 480 may be deposited on the opposite surface of the device. Contact layer 412 may be thinned prior to depositing lower contact pad 480. The fill material 474 may then be removed and the grooves may be evacuated by various suitable means, such as, for example, chemical etching or evaporation, to cause or facilitate release of the surface and/or selected regions of the bonding layer 478. The device may be transferred to the system (receptor) substrate 490 using a process similar to that previously described hereinabove. Additionally, in another embodiment, a force applied from the pad 432, such as a pushing or pulling force, may damage the surface and/or the bonding layer 478 above the evacuated trench 476-2 while keeping the unselected mesa structures attached to the temporary substrate. This force may also release the device from the temporary substrate 476 as shown in fig. 4B and 4C. The depth of the slot 476-2 may be selected to manage some of the microdevice height differences. For example, if the height difference is H, the depth of the groove may be greater than H.

A device on the substrate 310 can be created with two

contacts

432 and 480 on the same side of the substrate 310 that faces away. In this case, the conductive layer on the cartridge 476 may be patterned to independently bias the two contacts of the device. In one case, the device can be transferred directly from the cartridge substrate 476 to a recipient substrate. Here,

contacts

432 and 480 will not be directly bonded to the receptor substrate (the receptor substrate need not have special pads). In this case, a conductive layer is deposited and patterned to connect

contacts

432 and 380 to appropriate connections in the receptor substrate. In another case, the device may first be transferred from the cassette 476 to a temporary substrate before being transferred to a recipient substrate. Here,

contacts

432 and 480 may be bonded directly to the receptor substrate pads. The device may be tested in a cassette or in a temporary substrate.

In another embodiment, shown in fig. 5A, a mesa structure as described above is created on a donor substrate 510 by etching through different layers, such as a first bottom conductive layer 512; a functional layer 514, such as a light emitting layer; and a second top conductive layer 516 is formed with a micro device structure. Top contact pads 532 may be deposited before or after etching on top of top conductive layer 516. Moreover, each micro device may contain additional passivation and/or MIS layers 572 surrounding each micro device for isolation and/or protection. In this embodiment, the device may be provided with different anchors, whereby the anchors hold the device to the donor substrate 510 after the device is lifted off. The lift-off may be performed by a laser. In an example, the laser scans only the device. In an embodiment, a mask may be used that has openings for devices only on the backside of the donor substrate 510 to block laser light from other areas. The mask may be separate from the donor substrate 510 or may be part of the donor substrate. In another case, another substrate may be connected to the device to hold the device prior to the lift-off process. In another case, a filler layer 574, such as a dielectric, can be used between the devices.

In the first shown case, a layer 592 is provided for holding the device to the donor substrate 510. Layer 592 can be a separate layer or part of a layer of a microdevice that is not etched during mesa creation. In another case, layer 592 can be a continuation of one of layers 572. In this case, layer 592 can be a metal layer or a dielectric layer (SiN or SiO)₂Or other material). In another instance, the anchor is created as a separate structure including the extension 594, the void/gap 596, and/or the bridge 598. Here, a sacrificial layer having the same shape as the void/gap 596 is deposited and patterned. Then, the anchoring layer is sunkAnd patterned to form bridges 598 and/or extensions 594. The sacrificial material may be later removed to create the void/gap 596. The extension 594 may also be avoided. Similar to the previous anchor 592, the other anchor may be constructed of a different structural layer. In another case, the fill layer 574 acts as an anchor. In this case, the filling layer 574 may be etched or patterned, or left as it is.

Figure 5B shows the sample after removing filler layer 574 and/or etching the filler layer to form anchors. In another case, the adhesion of the bridging layer 598 is sufficient to hold the device in place and act as an anchor after lift-off. The final device is shown on the right side of fig. 5B in one substrate 510 for illustration purposes only. One or a combination of the devices may be used in a substrate.

As shown in fig. 5C, the anchor may cover at least a portion of the perimeter of the device or the entire perimeter of the device, or it may be patterned to form

arms

594 and 592. Any of the structures may be used for any anchoring structure.

Fig. 5D shows one example of transferring the device to a receptor substrate 590. Here, the micro device is bonded to the pads 582 or placed in a predefined area without any pads. The pressure or separation force may release the anchor by breaking the anchor. In another case, temperature may also be used to release the anchor. The viscosity of the layer between the lift-off of the microdevice and the donor substrate 510 can be increased by controlling the temperature to act as an anchor. Fig. 5E illustrates the device after it is transferred to a receptor substrate 590 and shows possible release points 598-2 in the anchors. The anchors may also be connected to the donor substrate 510 directly or indirectly through other layers.

The device on the donor substrate 510 can be created with two

contacts

532 and 480 on the same side facing away from the donor substrate 510. In one case, the devices may be transferred directly from the donor substrate 510 to the acceptor substrate 590. Here,

contacts

532 and 480 may be bonded directly to receiver substrate pads 582. The device may be tested in the donor substrate 510 or in the cartridge. In another embodiment, the device may first be transferred from the donor substrate 510 to the cassette substrate before being transferred to the acceptor substrate 590. Here, the contacts 532 will not bond directly to the receptor substrate 590, i.e., the receptor substrate 590 need not have special pads 582. In this case, a conductive layer is deposited and patterned to connect contact 532 to the appropriate connection in receptor substrate 590.

The system or

acceptor substrates

390, 490, and 590 may include micro LEDs, organic LEDs, sensors, solid state devices, integrated circuits, MEMS (micro electro mechanical systems), and/or other electronic components. Other embodiments relate to patterning and placing micro devices with respect to pixel arrays to optimize micro device utilization in selective transfer processes. The system or

acceptor substrate

390, 490, 590 can be, but is not limited to, a Printed Circuit Board (PCB), a thin film transistor backplane, an integrated circuit substrate, or in the case of an optical micro device such as an LED, a component of a display, such as a drive circuitry backplane. The patterned micro device donor and receptor substrates may be used in combination with different transfer techniques, including but not limited to pick and place with different mechanisms (e.g., electrostatic transfer heads, elastomeric transfer heads) or direct transfer mechanisms such as dual function pads.

Fig. 6A shows an alternative embodiment of the mesa structure of fig. 3A-3F, where the mesa structure is not initially etched through all layers. Here, some portion of the buffer layer 312 and/or the contact layer 312 may remain during the initial step. A mesa structure is created on the donor substrate 310. The microdevice structure is formed by etching through different layers, such as the first bottom conductive layer 312, the functional layer 314, and the second top conductive layer 316. Top contact 332 may be deposited before or after etching the top of top conductive layer 316. The mesa structure may contain other layers 372 that will be deposited and patterned before or after the mesa structure is formed. These layers may be dielectrics, MIS, contacts, sacrifices, etc. After the mesa structure is created, one or more filler layers 374, such as dielectric materials, are used between and around the micro devices to hold the micro devices together. The micro device is bonded to a temporary substrate 376 by one or more substrate bonding layers 378. The one or more bonding layers 378 may provide one or more different forces, such as electrostatic, chemical, physical, thermal, and the like. After the devices are removed from donor substrate 310, additional portions of bottom conductive layer 312 may be etched away or patterned to separate the devices, as described above (fig. 6C). Other layers such as contact bonding layer 380 may be deposited and patterned. Here, the filler layer 374 may be etched to separate the micro devices, or the sacrificial layer may be removed to separate the devices. In another embodiment, temperature may be applied to separate the device from the filler layer 374 and prepare it for transfer to the receiver substrate 390. The separation may optionally be performed as described above. In another embodiment, filler layer 374 can be etched to form a shell, base, or anchor 375, e.g., in the shape of a truncated cone or a truncated pyramid, that at least partially surrounds each microdevice, as shown in fig. 6E. Another layer may be deposited over base 375 and may be used to form anchors 598-2. After additional layers 598-2 are formed, padding base layer 375 may be left behind or removed from the anchoring device. Fig. 6G shows a device with a sacrificial layer 372-2. The sacrificial layer 372-2 may be removed by etching or may be thermally deformed or removed.

In another embodiment, the anchors are identical to housing 375 and are constructed from a polymer layer, organic layer, or other layer after the microdevice is transferred to cartridge 376. The housing 375 may have different shapes. In one case, the housing may match the shape of the device. The housing sidewall may be shorter than the microdevice height. The housing sidewalls can be attached to the microdevice prior to the transfer cycle to provide support for the different microdevice post-processing in the cassette 376 and packaging of the microdevice cassette for shipping and storage. The housing sidewalls may be separated or the connections to the microdevice may be weakened from the device by different means such as heating, etching or exposure before or during the transfer cycle.

The device on the donor substrate 310 can be created with two

contacts

332 and 380 on the same side facing away from the donor substrate 310. In this case, the conductive layer on the cartridge 376 may be patterned to independently bias the two

contacts

332 and 380 will not be directly bonded to the receptor substrate 390, i.e., the receptor substrate 390 need not have special pads. In this case, a conductive layer is deposited and patterned to connect

contacts

332 and 380 to appropriate connections in receptor substrate 390. In another embodiment, the device may first be transferred from the cassette 376 to a temporary substrate before being transferred to the recipient substrate 390. Thus,

contacts

332 and 380 may be bonded directly to the receptor substrate pads. The device may be tested in the cassette 376 or in a temporary substrate.

Due to the mismatch between the substrate lattice and the microdevice layer, the growth of the layer contains several defects such as dislocations, voids, and the like. To reduce defects, at least one first buffer layer 6114 and/or second buffer layer 6118 with a separation layer 6116 in between or near it can be deposited first on the donor substrate 6110 and then the active layer 6112 is deposited over the buffer layer 6114 and/or 6118. The thickness of the buffer layers 6114 and 6118 can be quite large, e.g., as thick as the donor substrate 6110. Buffer layer 6114/6118 may also be detached during detachment (lift-off) of the microdevice from donor substrate 6110. Therefore, the buffer layer deposition should be repeated each time. Fig. 6H shows a structure over the substrate 6110, where a separation layer 6116 is interposed between the first buffer layer 6114 and the actual device layer 6112. A second buffer layer 6118 may be present between the separation layer 6116 and the device layer 6112. The second buffer layer 6118 may also prevent contaminants from the separation layer 6116 from penetrating the device layer 6112.

Buffer layers

6114 and 6118 may each include more than one layer. The separation layer 6116 may also comprise a stack of different materials. In one example, the separating layer 6116 reacts to wavelengths of light to which the other layers are not responsive. This light source may be used to separate the actual device 6112 from one or more buffer layers 6114/6118 and the donor substrate 6110. In another example, the separation layer 6116 reacts to a chemical without the same chemical affecting the other layers. Such chemicals may be used to remove or alter the properties of the separation layer 6116 to separate the device from the one or more buffer layers 6114/6118 and substrate 6110. This method leaves the first buffer layer 6114 intact on the donor substrate 6110 and, therefore, can be reused for the next device generation. Some surface treatment such as cleaning or buffering may be performed before the next device deposition. In another example, the one or more buffer layers 6114/6118 may include zinc oxide.

The microdevice may be separated by a different etching process before the separation process (lift-off), as shown in fig. 6I. The etching can etch the second buffer layer 6118 (if present), and can etch a portion or all of the separation layer 6116 and the device layer 6112. In another example, the second buffer layer 6118 or the separation layer 6116 is not etched. After the etching step, the micro device is temporarily (or permanently) bonded to another substrate 6150, and the separation layer 6116 is removed or modified to separate the micro device from the first buffer layer 6114 and the second buffer layer 6118. As shown in fig. 6J, the first buffer layer 6114 may remain substantially intact on the donor substrate 6110.

In another embodiment shown in fig. 6K to 6M, layers may be formed on the donor substrate 6210 in the form of islands 6212, such as a first bottom conductive layer 312, a functional layer 314, and a second top conductive layer 316. Figure 6K shows a top view of islands 6212 formed in the micro device array. The island 6212 can be the same size as the box or a multiple of the box size. The islands 6212 may be formed starting from the buffer layer 6114/6118 or after the buffer layer. Here, a surface treatment or formation of

gaps

6262, 6263 may be performed on the surface to initiate film growth as islands (fig. 6L). To process the microdevice, the gap may be filled by a filler layer 6220, as shown in fig. 6M. The filler 6220 may be composed of a polymer layer, a metal layer, or a dielectric layer. The filler layer 6220 can be removed after the microdevice is processed.

Fig. 7 highlights the process of creating a microdevice cartridge. During a first step 702, a microdevice is fabricated on a donor substrate, e.g., 310 or 510. During this step, the device is formed and post-processing is performed on the device. During a second step 704, the device is prepared to be separated from the

donor substrate

310 or 510. This step may involve securing the microdevice by using anchors, e.g., 375, 476-1, 592, 594, 598, or 598-2, and fillers, e.g., 374, 472, and 574. During a third step 706, a cartridge or temporary substrate, such as 376 or 476, is formed by the pre-processed microdevices from the first step 702 and the second step 704. In one case, during this step, the microdevice is bonded directly or indirectly to the

cartridge substrate

376 or 476 by a bonding layer, such as 378 or 478. The microdevice is then separated from the

microdevice cartridge substrate

376 or 476. In another embodiment, the cartridge is formed on a microdevice donor substrate, such as 510. After the device is secured to the

cassette substrate

376, 476, or 510, other processing steps may be performed, such as removing some layers, e.g., 312, 374, 472, 574; or to add electrical layers (e.g., contacts 380 or 480) or optical layers (lenses, reflectors, etc.). During a fourth step 708, the

cartridge

376 or 476 moves to a recipient substrate, such as 390, 490 or 590 to transfer the device to the

recipient substrate

390, 490 or 590. Some of these steps may be rearranged or combined. While the microdevice is still on the cartridge substrate, e.g., 376 or 476, or after the microdevice has been transferred to a recipient substrate, e.g., 390, 490 or 590, a test step 707A may be performed on the microdevice to determine if the microdevice is defective. Defective micro devices may be removed or repaired in situ in step 707B. For example, a predetermined number of a group of micro devices may be tested, and if the number of defects exceeds a predetermined threshold, the entire group of micro devices may be removed, at least some of the defective micro devices may be removed, and/or at least some of the defective micro devices may be repaired.

FIG. 8 illustrates the step of transferring the device from the

cartridge

376, 476, or 510 to a

recipient substrate

390, 490, or 590. Here, during a first step 802, the

cartridge

376, 476, or 510 is loaded (or picked up), or in another embodiment, the spare equipment arm is pre-loaded with the

cartridge

376, 476, or 510. During a second step 804, the

cartridge

376, 476, or 510 is aligned with a portion (or all) of the receptor substrate. The alignment may be performed using dedicated alignment marks on the

cartridge

376, 476, or 510 and the

receptor substrate

390, 490, or 590 or using micro-devices and landing areas on the

receptor substrate

390, 490, or 590. During a third step, the micro device is transferred to a selected landing area. During a fourth step 808, if the

recipient substrate

390, 490 or 590 is completely filled, the

cartridge substrate

376, 476 or 510 is moved to a next step, such as another

recipient substrate

390, 490 or 590, in step 810. If the

current receiver substrate

390, 490 or 590 requires further filling, then one or more

additional cassettes

376, 476 or 510 are used to perform additional transfer steps. Before a new transfer cycle, if the

cartridge

376, 476 or 510 does not have sufficient means, the cycle starts with a first step 802. If the

cartridge

376, 476, or 510 has sufficient devices in step 812, the

cartridge

376, 476, or 510 is shifted (or moved and aligned) to a new area of the

recipient substrate

390, 490, or 590 in step 814 and the new loop continues to step 806. Some of these steps may be combined and/or rearranged.

Fig. 9 illustrates the step of transferring the device from a cartridge, e.g.,

temporary substrate

376, 476, or 510, to a recipient substrate, e.g., 390, 490, or 590. Here, during a first step 902, the

cartridge

376 or 476 is loaded (or picked up), or in another embodiment, the standby equipment arm is pre-loaded with a cartridge. During a second step 902-2, a set of micro devices is selected in the

cartridge

376, 476, or 510 such that the number of defects therein is less than a threshold. During a third step 904, the

cartridge

376, 476, or 510 and/or the

recipient substrate

390, 490, or 590 or using micro devices and landing areas on the

recipient substrate

390, 490, or 590. Then, during a third step 906, the micro device may be transferred to the selected landing area. In optional step 906-1, selected microdevices in the cartridge can be attached to the receptor substrate. In optional step 906-2, the micro device can be tested for connection to a receptor substrate, for example, by turning on the micro device by biasing through

receptor substrate

390, 490, or 590. If individual micro devices are found to be defective or non-functional, an additional adjustment step 906-3 may be performed to correct or repair some or all of the non-functional micro devices.

If the receptor substrate is completely filled, the

receptor substrate

390, 490, or 590 moves to the next step. If the

recipient substrate

390, 490 or 590 requires further filling, additional transfer steps from one or more

additional cassettes

376, 476 or 510 are performed. Before a new transfer loop, if 376, 476 or 510 does not have enough devices, the loop starts with a first step 902. If the

cartridge

376, 476, or 510 has sufficient devices, then in step 902-2, the

cartridge

376, 476, or 510 is shifted (or moved and aligned) to a new area of the

receptor substrate

390, 490, or 590.

FIG. 10 illustrates exemplary process steps for generating a

multi-type microdevice cartridge

376, 476, 510, or 1108. During a first step 1002, at least two different microdevices are fabricated on different donor substrates, e.g., 310 or 510. During this step, the device is formed and post-processing is performed on the device. During a second step 1004, the device is prepared to be separated from a donor substrate, e.g. 310 or 510. This step may involve securing the microdevice by using anchors, e.g., 375, 476-1, 592, 594, 598, and 598-2, and fillers, e.g., 374, 472, and 574. During a third step 1006, the first device is moved to the

cartridge

376, 476, 510, or 1108. During a fourth step 1008, at least a second microdevice is moved to a

cartridge

376, 476, 510, or 1108. In one case, during this step, the microdevice is bonded directly or indirectly to the

cartridge substrate

376, 476, 510, or 1108 through a bonding layer, such as 378 or 478. The microdevice is then separated from the

microdevice cartridge substrate

310 or 510. For direct transfer, different types of microdevices may have different heights. For example, the second type of micro device transferred to

cartridge

376, 476, 510, or 1108 may be slightly higher than the first type of micro device (or the position on

cartridge

376, 476, 510, or 1108 may be slightly higher for the second micro device type). Here, after the

cartridge

376, 476, 510, or 1108 is completely filled, the microdevice height may be adjusted to flatten the surface of the

cartridge

376, 476, 510, or 1108. This can be done by adding material to the shorter microdevice or removing material from the taller device. In another case, the landing areas on the

receptor substrate

390, 490, or 590 may have different heights associated with differences in the

cartridges

376, 476, 510, or 1108. Another method of filling the

cartridge

376, 476, 510, or 1108 is based on picking. The micro device may be moved to a

cartridge

376, 476, 510, or 1108 using a pick up process. Here, the force elements on the pick-up head may be uniform for the micro devices in one cluster in a

cartridge

376, 476, 510, or 1108, or a single force element may be used for each micro device. Also, the micro device may be moved to the

cartridge

376, 476, 510, or 1108 in other ways. In another embodiment, the additional devices are moved away from the

cartridge substrate

376, 476, 510, or 1108 of the first or second (or third or other) micro device and the other types of micro devices are transferred into blank areas on the

cartridge

376, 476, 510, or 1108. After the device is secured to the

cartridge substrate

376, 476, 510, or 1108, other processing steps may be performed, such as adding filler layers 374, 474, or 574; removing some of the layers; or to add electrical layers (e.g.,

contacts

380, 480, or 580) or optical layers (lenses, reflectors). The device may be tested after or before it is used to fill the

receptor substrate

390, 490 or 590. The test may be an electrical test or an optical test or a combination of both. The test may identify defects and/or performance of the devices on the cartridge. During a final step 1010, the

cartridge

376, 476, 510, or 1108 is moved to a

recipient substrate

390, 490, or 590 to transfer the device to the

recipient substrate

390, 490, or 590. Some of these steps may be rearranged or combined.

The transfer process described herein (e.g., fig. 7, 8, 9, and 10) may include a stretching step to increase the pitch of the micro devices on the

cartridges

376, 476, 510, or 1108. This step may be performed prior to alignment or may be part of the alignment step. This step may increase the number of micro devices aligned with the landing areas (or pads) on the

receptor substrate

390, 490, or 590. Further, the steps may match the pitch between the micro device arrays on the

cartridges

376, 476, 510, or 1108 that include at least two micro devices to match the pitch of the landing areas (or pads 382) on the

recipient substrates

390, 490, or 590.

FIG. 11 illustrates an example of a multi-type micro device cartridge 1108 that is similar to

temporary substrates

376, 476, or 510. The cartridge 1108 contains three different types of

micro devices

1102, 1104, 1106, for example, colors (red, green, and blue). There may be more device types. The distance x1, x2, x3 between micro devices is related to the pitch of the landing areas in the

receptor substrate

390, 490 or 590. After several devices, which may be related to the pixel pitch in the

receptor substrate

390, 490 or 590, there may be different pitches x4, y 2. This spacing compensates for the mismatch between the pixel pitch and the micro device pitch (landing area pitch). In this case, if pick-and-place is used to create the cartridge 1108, the force elements may take the form of columns corresponding to the columns of each microdevice type, or the force elements may be separate elements for each microdevice.

Fig. 12 illustrates one example of a multi-type micro device cartridge 1208 similar to

temporary substrates

376, 476, or 510. The cartridge 1208 contains three different types of

micro devices

1202, 1204, 1206, for example, colors (red, green, and blue). Other regions 1206-2 may be empty, filled with spare micro devices, or contain a fourth different type of micro device. The distance x1, x2, x3 between micro devices is related to the pitch of the landing areas in the

receptor substrate

390, 490 or 590. After several device arrays, possibly related to the pixel pitch in the

receptor substrate

390, 490 or 590, there may be different pitches x4, y 2. This spacing compensates for the mismatch between the pixel pitch and the micro device pitch (landing area pitch).

Fig. 13 shows one example of a microdevice 1302 prepared on a donor substrate 1304 similar to the

donor substrate

310 or 510 prior to transfer to a

multi-type microdevice cell

376, 476, 510, 1108, 1208. Here, the support layers 1306 and 1308 may be used for a single device or a group of devices. Here, the pitch may match the pitch in the

cartridges

376, 476, 510, 1108, 1208, or the pitch may be a multiple of the cartridge pitch.

In all of the above configurations, the microdevice may be moved from the first cassette to the second cassette before filling the substrate with the microdevice. Additional processing steps may be performed after the transfer, or some of the processing steps may be divided between the first and second cassette arrangements.

Fig. 14A shows an embodiment of a micro device in a donor substrate 1480 similar to

donor substrate

310 or 510. Due to manufacturing and material defects, the output power of the micro device may gradually decrease or increase, i.e., there is non-uniformity, on the donor substrate 1480, as shown by the coloring from dark to light. Neighboring devices in the

receptor substrate

390, 490, or 590 gradually degrade because the devices may be transferred together into a block, such as block 1482, or may be transferred one or more devices at a time in sequence into the

receptor substrate

390, 490, or 590. However, where one block, e.g., 1482 or a series of adjacent blocks, ends and another block, e.g., 1483 or another series of blocks begins, e.g., along intersection line 1484, a worse problem may arise which may result in an abrupt change in output performance, as shown in fig. 14B. Such abrupt changes may result in visual artifacts of optoelectronic devices such as displays.

To address the issue of non-uniformity, one embodiment shown in FIG. 14C includes using blocks above and below

separate blocks

1482 and 1483 in the display to skew or interleave the separate blocks so that the edges or crosshairs of the blocks are not sharp lines, eliminating the crosshairs 1484, and thereby the device blocks form a skewed pattern on the display. Thus, the average effect of sharp transitions is significantly reduced. The skew may be random and may have different profiles.

Fig. 14D illustrates another embodiment in which the micro-device devices in adjacent blocks are flipped so that devices with similar performance are adjacent to each other, e.g., the performance in a first block 1482 decreases from a first outer side a to a first inner side B, while the performance of a second adjacent block 1483 increases from a second inner side B adjacent to the first inner side B to a second outer side a, which can keep the changes and transitions between blocks very smooth and eliminate long sharp intersections 1484.

FIG. 14E shows an exemplary combination of flipping devices, e.g., alternating high and low performance devices on the inside and skewing the edges to further improve the average uniformity. In the illustrated embodiment, the device performance alternates between high and low in both directions, i.e., in adjacent horizontal blocks and adjacent vertical blocks.

In one case, the performance of the micro devices at the tile edges are matched for adjacent transferred tiles (arrays) prior to transfer to the

receptor substrate

390, 490 or 590.

Fig. 15A shows the use of two or

more blocks

1580, 1582 to fill in blocks in an acceptor substrate 1590. In the illustrated embodiment, the average uniformity may be further improved using a skew or flip approach, as shown in FIG. 15B. The higher (or lower) output power sides B and C from

blocks

1580 and 1582, respectively, may be positioned adjacent to each other, in addition to which the connections of the blocks above and below the blocks are used to skew or interleave the connections between the blocks. Also, a random or defined pattern can be used to fill a cassette or receptor substrate 1590 having more than one patch.

Fig. 16A shows a sample with more than one

block

1680, 1682, and 1684.

Blocks

1680, 1682, and 1684 may be from the

same donor substrate

310 or 510 or from

different donor substrates

310 or 510. Fig. 16B shows an example of filling the box 1690 with

different blocks

1680, 1682, and 1684 to eliminate any non-uniformities found in the blocks.

Fig. 17A and 17B illustrate a structure having a plurality of cassettes 1790. As described above, the location of the cassette 1790 is selected in a manner that eliminates overlap of the same area in the

recipient substrate

390, 490, 590, or 1590 with a cassette 1790 having the same micro-devices during different transfer cycles. In one example, the cassettes 1790 can be independent, meaning that a separate arm or controller processes each cassette independently. In another embodiment, the alignment may be performed independently, but other operations may be performed simultaneously. In this embodiment, the

receptor substrate

390, 490, 590 or 1590 may be moved for ease of transfer after alignment. In another example, the cassettes 1790 move together for easy transfer after alignment. In another example, both the cassette 1790 and the

recipient substrate

390, 490, 590, or 1590 can be moved for ease of transfer. In another case, the cartridge 1790 may be assembled in advance. In this case, the frame or substrate may hold the assembled case 1790.

The distances X3, Y3 between cassettes 1790 may be multiples of the width X1, X2 or length Y1, Y2 of cassette 1790. The distance may be a function of the step size of the movement in different directions. For example, X3 ═ KX1+ HX2, where K is the step of moving to the left (directly or indirectly) to fill the

receiver substrate

390, 490, 590, or 1590 and H is the step of moving to the right (directly or indirectly) to fill the receiver substrate. The same reasoning can be used for the distance Y3 between cassettes 1790 and for the lengths Y1 and Y2. As shown in fig. 17A, the cassette 1790 can be aligned in one or two directions. As shown in fig. 17B, in another example, the cassette 1790 is misaligned in at least one direction. Each cassette 1790 can have independent controls for applying pressure and temperature to the

receptor substrate

390, 490, 590, or 1590. Other arrangements are possible depending on the direction of movement between the

recipient substrate

390, 490, 590 or 1590 and the cassette 1790.

In another example, the cassette 1790 may have different devices and thus fill different areas in the

recipient substrate

390, 490, 590, or 1590 with different devices. In this case, the relative positions of the cassette 1790 and the

recipient substrate

390, 490, 590 or 1590 are changed after each transfer cycle to fill different areas with all required microdevices from different cassettes 1790.

In another embodiment, several cartridge arrays 1790 are prepared. Here, after transferring the device from the first cartridge array to the

acceptor substrate

390, 490, 590, or 1590, the

acceptor substrate

390, 490, 590, or 1590 moves to the next micro device array to fill the remaining area in the

acceptor substrate

390, 490, 590, or 1590 or receive a different device.

In another example, the cassette 1790 may be on a curved surface, and thus the circular movement will provide a point of contact to transfer the micro device into the

recipient substrate

390, 490, 590 or 1590.

The vertical optoelectronic stack comprises a substrate, an active layer, at least one buffer layer between the active layer and the substrate, and at least one separation layer between the buffer layer and the active layer, wherein the active layer can be physically removed from the substrate by changing the properties of the separation layer while the buffer layer remains on said substrate.

In one embodiment, the process of altering the properties of the one or more separation layers includes chemical reactive etching or deforming the separation layer.

In another embodiment, the process of altering the properties of the one or more separation layers comprises exposure to an optoelectronic wave, thereby deforming the separation layers.

In another embodiment, the process of changing the property of the one or more separation layers comprises changing the temperature, thereby deforming the separation layer.

In one embodiment, reusing the buffer layer to create a new optoelectronic stack layer includes surface treatment.

In one embodiment, the surface treatment uses chemical or physical etching or buffing.

In another embodiment, the surface treatment uses the deposition of an additional thin layer or buffer layer to reform the surface.

In one embodiment, the optoelectronic device is an LED.

In one embodiment, the separation layer is zinc oxide.

Embodiments of the invention include continuous pixelated structures comprising fully or partially continuous active layers, pixelated contact layers and/or current spreading layers.

In this embodiment, a pad layer and/or a bonding layer may be present on top of the pixelated contact layer and/or the current spreading layer.

In the above embodiments, there may be a dielectric opening on top of each pixelated contact layer and/or current spreading layer.

Another embodiment includes a donor substrate including micro devices having bond pads and a filler layer filling spaces between the micro devices.

Another embodiment includes a temporary substrate including a bonding layer to which micro devices from a donor substrate are bonded.

Another embodiment includes a heat transfer technique comprising the steps of:

1) aligning the micro device on the temporary substrate with a bond pad of a system substrate;

2) verifying that a melting point of a bonding pad on the system substrate is higher than a melting point of a bonding layer in the temporary substrate;

3) creating a thermal profile that melts both the bond pad and the bond layer and thereafter holds the bond layer molten and the bond pad solidified; and

4) separating the temporary substrate from the system substrate.

In another embodiment of the transfer technique, the thermal profile is generated by a local or global heat source or both.

Another embodiment includes a microdevice structure in which at least one anchor holds the microdevice to a donor substrate after the microdevice is released from the donor substrate by a lift-off process.

Another embodiment includes a transfer technique for a micro device structure in which an anchor releases the micro device after or during bonding of the micro device to a pad in a receptor substrate by a pushing or pulling force.

In another embodiment, the anchors according to the microdevice structure are comprised of at least one layer extending from the side of the microdevice to the substrate.

In another embodiment, the anchors according to the microdevice structure are composed of a void or at least one layer on top of a void.

In another embodiment, the anchors according to the microdevice structure are comprised of a filler layer surrounding the device.

Another embodiment includes a structure according to a microdevice structure in which the viscosity of a layer lifted off between the microdevice and the donor substrate is increased by controlling the temperature to act as an anchor.

Another embodiment includes a release process for anchors in a microdevice structure, wherein the temperature is adjusted to reduce the force between the anchor and the microdevice.

Another embodiment includes a process of transferring a microdevice into a receptor substrate, wherein the microdevice is formed in a cartridge; aligning the cartridge with a selected landing area in a recipient substrate; and transferring the micro device associated with the selected landing area in the cartridge to a recipient substrate.

Another embodiment includes a process of transferring a microdevice into a receptor substrate, wherein the microdevice is formed in a cartridge; selecting a group of micro devices having a defective micro device less than a threshold; aligning a selected set of micro devices in the cartridge with a selected landing area in the recipient substrate; and transferring the micro device associated with the selected landing area in the cartridge to a recipient substrate.

Embodiments include cartridges having multiple types of microdevices transferred thereto.

Embodiments include microdevice cartridges in which a sacrificial layer separates at least one side of the microdevice from a filler layer or a bonding layer.

In an embodiment, the sacrificial layer is removed to release the micro device from the filler layer or the bonding layer.

In embodiments, the sacrificial layer releases the microdevice from the filler under some conditions, such as high temperature.

The microdevice may be tested to extract information related to the microdevice including, but not limited to, defects, uniformity, operating conditions, and the like. In one embodiment, one or more microdevices are temporarily bonded to a cartridge having one or more electrodes for testing the microdevice. In one embodiment, the other electrode is deposited after the microdevice is positioned in the cartridge. This electrode can be used to test the microdevice before or after patterning. In one embodiment, the cartridge is placed in a predefined position (which may be a holder). The cassette and/or the recipient substrate are moved for alignment. At least one selected device is transferred to a recipient substrate. If more micro devices are available on/in the cartridge, the cartridge or the recipient substrate is moved to align with a new area in the same recipient substrate or a new recipient substrate, and at least another selected device is transferred to a new location. This process may continue until the cartridge does not have enough micro devices, at which point a new cartridge may be placed in a predefined location. In one example, the transfer of the selected device is controlled based on information extracted from the cartridge. In one example, the defect information extracted from the cassette may be used to limit the number of defective devices transferred to the recipient substrate to below a threshold number by eliminating the transfer of a group of devices having a number of defects that exceeds a threshold, or the cumulative number of defects transferred will exceed a threshold. In another example, the boxes will be binned based on one or more extracted parameters, and each bin will be used for a different application. In another case, cells having similar properties based on one or more parameters will be used in a receptor substrate. The examples presented herein can be combined to improve cassette transfer performance.

In embodiments, physical contact and pressure and/or temperature may be used to transfer the device from the cartridge into the receptor substrate. Here, the pressure and/or temperature may generate a bonding force (clamping force) for holding the micro device to the recipient substrate, and/or also the temperature may reduce a contact force between the micro device and the cartridge. Thus, transfer of the microdevice to the receptor substrate is achieved. In this case, the locations assigned to the micro devices on the receiver substrate may have a higher profile than the rest of the receiver to enhance the transfer process. In embodiments, the cartridge is free of micro devices in areas that may come into contact with unwanted areas of the recipient substrate, such as locations assigned to other types of micro devices during the transfer process. The two instances may be combined. In embodiments, the dispensed locations of the microdevices on the substrate may have been wetted with an adhesive or may have been covered with a bonding alloy, or additional structures may be placed on the dispensed locations. In the stamping process, a separate cartridge, printing or other process may be used. In an embodiment, selected micro devices on the cassette may be moved closer to the recipient substrate to enhance selective transfer. In another case, the receiver substrate exerts a pulling force to assist or initiate transfer of the microdevice from the cartridge. The pulling force may be combined with other forces.

In one embodiment, the housing may support a microdevice in a cartridge. The housing can be fabricated around the microdevice on the donor substrate or the cassette substrate or separately, and then the microdevice is moved inside and bonded to the cassette. In one embodiment, at least one polymer (or another type of material) may be deposited on top of the cassette substrate. The microdevice from the donor substrate is pushed into the polymer layer. The microdevice is selectively or generally separated from the donor substrate. The layer may be cured before or after the device is separated from the donor substrate. This layer can be patterned, especially if a plurality of different devices are integrated into the cartridge. In this case, the layer may be created for a type in which the microdevice is buried and separated from its donor. Another layer is then deposited and patterned for the next type of micro device. The second microdevice is then buried in the associated layer. In all cases, this layer may cover some or all of the microdevices. In another case, the housing is constructed from a polymer layer, an organic layer, or other layer after the transfer of the microdevice to the cartridge. The housing may have different shapes. In one case, the housing may match the shape of the device. The housing sidewall may be shorter than the microdevice height. The housing sidewalls can be attached to the microdevice prior to the transfer cycle to provide support for different microdevice reprocessing in the cassette and microdevice cassette packaging for shipping and storage. The housing sidewalls may be separated or the connections to the microdevice may be weakened from the device by different means such as heating, etching or exposure before or during the transfer cycle. There may be a contact point holding the microdevice to the cartridge substrate. The contact point to the cartridge may be the bottom side or the top side of the device. The contact points may be weakened or eliminated by different means such as heating, chemical processes or exposure before or during transfer. This process may be performed for some selected devices or may be performed globally for all of the micro devices on the cartridge. The contacts may also be conductive to enable testing of the microdevice by biasing the device at the contacts and other electrodes connected to the microdevice. During the transfer cycle, the cartridge may be under the receptor substrate to prevent the microdevice from falling out of the housing with the contact points globally removed or weakened.

In one embodiment, the microdevice cartridge may include at least one anchor that holds the microdevice to the cartridge surface. The cassette and/or the receptor substrate are moved such that some of the micro devices in the cassette are aligned with some of the locations in the receptor substrate. This anchor may break under pressure during the pushing of the cassette and the receptor substrate towards each other or the pulling of the device through the receptor substrate. The micro device may be permanently resting on the receptor substrate. The anchors can be on the sides of the microdevice or on the top (or bottom) of the microdevice.

The top side is the side of the device facing the cartridge and the bottom is the opposite side of the microdevice. The other sides are referred to as sides or sidewalls.

In one embodiment, the microdevice may be tested to extract information related to the microdevice including, but not limited to, defects, uniformity, operating conditions, and the like. The cartridge may be placed in a predefined position (which may be a holder). The cassette and/or the receptor substrate may be moved to perform alignment. At least one selected device may be transferred to a recipient substrate. If more micro devices are available on/in the cartridge, the cartridge or the recipient substrate can be moved to align with a new area in the same recipient substrate or a new recipient substrate, and at least another selected device can be transferred to a new location. This process may continue until the cartridge does not have enough micro devices, at which point a new cartridge will be placed in the predefined location. In one case, the transfer of the selected device may be controlled based on information extracted from the cassette. In one case, the defect information extracted from the cartridge may be used to limit the number of defective devices transferred to the recipient substrate to below a threshold number, or the cumulative number of defects transferred exceeds a threshold, by eliminating the transfer of a group of devices having a number of defects that exceeds a threshold. In another case, the cartridges would be binned based on one or more extracted parameters, and each bin could be used for a different application. In another case, cells having similar properties based on one or more parameters may be used in a receiver substrate. The examples presented herein can be combined to improve cassette transfer performance.

One embodiment includes a method of transferring a device to a receptor substrate. The method comprises the following steps:

a) preparing a cartridge having a substrate, wherein a micro device is positioned on at least one surface of the cartridge substrate, and the substrate has more micro devices in an area outside of a same sized micro device location corresponding to an area in a recipient substrate.

b) The device on the cartridge is tested by extracting at least one parameter.

c) Pick up the cassette or transfer the cassette to a position with the micro device facing the recipient substrate.

d) The test data is used to select a set of micro devices on the cartridge.

e) A selected set of micro devices on the cartridge is aligned with selected locations on the receptor substrate. Transferring the set of micro devices from the cartridge to a recipient substrate.

f) Processes d and e may continue until the cartridge does not have any useful devices or the receptor substrate is completely filled.

One embodiment includes a cassette having more than one type of microdevice positioned in the cassette at the same pitch as in the recipient substrate.

One embodiment includes a cartridge having a substrate with micro devices positioned (directly or indirectly) on a surface thereof, and the micro devices are skewed in any row or column such that an edge of at least any one row or column is not aligned with an edge of at least another row or column.

One embodiment is a method of transferring a device to a recipient substrate. The method includes transferring an array of micro devices into a substrate, wherein an edge of a transferred micro device of at least any one row or column is not aligned with an edge of a transferred device of at least another row or column.

One embodiment includes a method of transferring a device to a receptor substrate. The method includes transferring an array of devices from a donor substrate to a recipient substrate, where in any area on the recipient substrate similar in size to the transferred array, there is at least any one row or column of micro devices having two different areas from the donor substrate corresponding to the transferred array.

One embodiment includes a process of transferring an array of micro devices into a recipient substrate, where the micro devices are deflected at the edges of the array to eliminate abrupt changes.

Another embodiment includes a process of transferring an array of micro devices into a receptor substrate, wherein the performance of the micro devices at adjacent edges of two arrays of micro devices are matched prior to transfer.

Another embodiment includes a process of transferring a micro device array into a receptor substrate, wherein the micro device array is filled from at least two different regions of a micro device donor substrate.

Another embodiment includes a process for transferring an array of micro devices from a cartridge to a receiver substrate, wherein a number of micro device cartridges are placed in different positions corresponding to different areas of the receiver substrate, then the cartridge is aligned with the receiver substrate, and the micro devices are transferred from the cartridge to the receiver substrate.

Different anchor schemes for securing microdevices on donor substrates

The process of integrating the microdevice into the system substrate involves creating and preparing a donor substrate, transferring a preselected array of microdevices to a recipient substrate, and subsequently (or simultaneously) electrically or mechanically bonding the microdevices to the system substrate. During bonding between the two substrates, the application of a curing agent before or after alignment of the microdevice and the system substrate assists in forming a strong bond. The curing agent comprises one of the following: polyamide, SU8, PMMA, BCB film layer, epoxy and UV curable adhesive, and curing is performed in one of the following: electrical current, light, heat or mechanical force or chemical reaction. However, the current/voltage requirements for curing may be higher than the current/voltage requirements that the microdevice can withstand.

To avoid damage to the microdevice, structures and methods are needed to integrate the microdevice into a system substrate with enhanced bonding and conductive capabilities. Also, another/alternative current/voltage path may be formed to avoid damage to the micro device.

According to one embodiment, a bonding structure may be provided. The bonding structure may comprise a plurality of micro devices on a donor substrate, each micro device comprising one or more conductive pads formed on a surface of the micro device; and a temporary material covers at least a portion of each micro device or the one or more conductive pads.

In one case, the temporary material acts as an anchor that holds the plurality of microdevices inside a shell structure in a donor substrate.

In another case, all or part of the micro device may be covered by a temporary conductive material, which may redirect current through the temporary conductive material rather than the micro device and thus avoid damaging the micro device.

In one case, the micro device may have one conductive pad on each side of the micro device. In another case, the micro device may have more than one conductive pad on one side.

Fig. 18 shows a donor substrate 1802 holding a plurality of micro devices via a donor element, according to an embodiment of the present invention. The donor substrate 1802 can be a growth substrate (where the microdevice is being fabricated or grown) or another temporary substrate to which it has been transferred. The following is described with reference to gallium nitride (GaN) based LEDs, however the presently described structure may be used for any type of LED having a different material system.

In general, GaN-based micro LEDs are fabricated by depositing a stack of materials on a sapphire substrate. Conventional GaN led devices include a substrate such as sapphire, an n-type GaN layer or a buffer layer (e.g., GaN) formed on the substrate, an active layer/semiconductor layer such as a Multiple Quantum Well (MQW) layer and a p-type GaN layer.

As shown in fig. 18, the plurality of micro devices on the donor substrate 1802 can have

conductive pads

1814, 1816 on both the top and bottom of the stack 1806 of semiconductor layers. The receiver substrate 1808 has at least one receiver force element 1818 for each selected micro device selected to be transferred to the receiver substrate 1808. In one instance, the receptor force element is a current/voltage curable component. Here, a current/voltage 1810 is applied to a selected receptor force element (e.g., 1818), causing it to harden and hold the microdevice in place. In one example, the receptive force element may comprise a monomer that forms a polymer under an applicable charge. In another example, the receptor force element is a medium with a high resistance trace that generates heat at an applicable current/voltage, and the generated heat locally cures the medium.

Donor substrate 1802 has at least one donor element 1804. The donor force element 1804 is an element that loses its adhesive properties under current or voltage. Here, a voltage/current 1812 is applied to the donor force element 1804 holding the selected device for transfer. In one example, the donor force element is a polymer that decomposes (oxidizes) under the application of a charge. In another example, the donor force element is a highly resistive trace that burns at an applicable current/voltage.

FIG. 19 illustrates a microdevice having more than one conductive pad on one side according to an embodiment of the invention. Here, in one example, the micro device may have two conductive/

contact pads

1904, 1906 at the bottom of the semiconductor layer stack on the donor substrate 1902. The receiver substrate 1908 has one receiver element 1918 corresponding to the contact pads for each micro-device selected for transfer to the receiver substrate 1908. The receptor force element is a current/voltage curable component. Here, a current/voltage 1910 is applied to a selected receptor force element (e.g., 1918), causing it to harden and holding the micro device in place.

Voltage/current 1910, 1912 may be applied to selected receptor force elements (e.g., 1918) to cure them, causing them to harden and hold the micro device in place.

In one case, the microdevice can be used as part of a bias loop. Here, a voltage/current 1914 may be applied via the donor substrate 1902, or a voltage/current 1910, 1912 may be applied to the acceptor substrate 1908, which passes through the microdevice and through either the donor substrate 1902 or the acceptor substrate 1908.

However, the current/voltage requirements of the curing receiver element may be higher than the current/voltage requirements that the microdevice can withstand. To avoid damage to the micro device, another/alternative current/voltage path may be formed. In another case, a portion or the entire microdevice of the microdevice may be covered with a temporary conductive material, which may redirect current flow through the temporary conductive material rather than the microdevice and avoid damaging the microdevice.

Fig. 20A-20I illustrate examples of micro devices partially/completely covered by temporary conductive material according to some embodiments of the invention.

Some or all of the micro device may be covered with a temporary conductive material, which may redirect current through the temporary conductive material rather than the micro device and thus avoid damaging the micro device. In one case, the temporary material may be a temporary conductive material. The conductive material may be connected as a sheet or trace with the same conductive material or a different conductive material on the donor substrate.

In one embodiment, the microdevice can be inside the housing structure. Some sacrificial layer may be present between the housing wall and the microdevice. In another embodiment, there may also be bonding material between the donor substrate and the micro device and conductive pads (a similar material to the housing walls) or a combination thereof.

In one embodiment, the temporary layer may also serve as an anchor to hold the device in place. In another embodiment, there may be anchors that hold the microdevice into the donor substrate. The anchor may be the same or different material as the shell material. In one case, the housing may extend almost to the edge of the microdevice. In another case, the housing wall is shorter than the microdevice. It is also possible to have a housing that is taller than the microdevice.

In another case, the temporary conductive material may be replaced with a non-conductive material.

For the case of having both conductive and non-conductive temporary materials, the temporary material can hold the microdevice in place after the sacrificial layer is removed or released. The micro device may be transferred to another substrate. During the transfer process, the temporary material is removed or separated from the shell structure. The separation process may be mechanical (e.g., push or pull), optical, thermal, or chemical.

The micro device may be covered by a temporary material/layer prior to transfer to the recipient substrate, or it may be covered after transfer to the recipient substrate. In one case, the housing material is coated on the substrate between the microdevices. It can be bonded to the donor substrate and then the shell material can be cured. In another case, there may be different materials used on the surface of the donor substrate that can be electrically coupled to the microdevice or temporary layer. In another case, the shell material is coated on top of the donor substrate. The microdevice is then bonded and pushed into the material, and the material is then cured. The housing material may be an epoxy, polymer, or other type of material. In one case, BCB or polyamide may be used as the shell material.

The temporary material may be patterned to form an opening on top of the donor substrate. This opening may facilitate some processing, such as removal of the sacrificial layer, to separate the micro device from the housing sidewall.

20A1-20A2 illustrate examples of protruding temporary conductive material covering the surface of a microdevice according to some embodiments of the invention.

Referring to fig. 20a1, here the microdevice is inside a shell structure 2006 a. There may be some sacrificial layer between the housing structure/wall 2006a and the micro device 2016. In one case, the sacrificial layer 2008a may be a patterned sacrificial layer to cover the length to the housing. In another case, the sacrificial layer 2008b may be set to the length of the microdevice. Between the donor substrate and the micro device may be a bonding material 2010a, conductive pads 2004a, or a material similar to the housing wall, or a combination thereof. Also, anchors 2014a may hold the micro device in the donor substrate. The anchor may be the same or different material as the shell material. The temporary conductive material 2002a can cover the surface of the microdevice 2016 including the conductive pads 2004a and the housing 2006 a. This structure facilitates transfer of the micro devices to inspect the system substrate for defective micro devices.

In another embodiment, the housing wall may extend almost to the edge of the microdevice.

Fig. 20a2 shows a cross-sectional view of a micro device on a device (donor) substrate where the temporary conductive material does not cover the entire surface of the micro device, according to an embodiment of the invention. Here, the housing 200b and sacrificial layer 2008b may extend almost to the edge of the micro device 2016. Temporary conductive material 2002a may include conductive pads 2004 a. Traces on the donor substrate or the conductive layer between the donor substrates can couple the conductive material to a current/voltage source.

Fig. 20B1 shows a cross-sectional view of a micro device on a device (donor) substrate with temporary conductive material covering a portion of a conductive pad of the micro device, according to an embodiment of the invention. Here, the conductive pads such as 2004c are patterned conductive pads, and the sacrificial layer 2008c is also a patterned sacrificial layer deposited around the micro device and the conductive pads. The temporary conductive material 2002a can cover a surface of the micro device 2016 that includes the conductive pads 2004a and a portion of the housing 2006 a. In another case, the sacrificial layer may extend only to a portion of the microdevice. The temporary conductive material 2002a may be coupled to a current source/voltage to facilitate curing or debonding. Traces on the donor substrate or the conductive layer between the donor substrates can couple the conductive material to a current/voltage source.

Fig. 20B2 shows a cross-sectional view of a micro device on a device (donor) substrate where the temporary conductive material does not cover the entire surface of the micro device, according to an embodiment of the invention. Here, the housing 2006b can extend almost at the edge of the microdevice. Temporary conductive material 2002a may comprise a portion of conductive pad 2004 b.

Fig. 20C1 shows an example of temporary conductive material forming a current/voltage path between conductive pads 2004C, 2006C, which may be on the top and bottom or the same side of the micro device. Here, the temporary conductive material 2002c also covers the micro devices, which facilitates selective transfer of the micro devices to the system substrate. This structure helps redirect current through the temporary conductive material, rather than the micro device, and thus avoids damaging the micro device.

Fig. 20C2 shows an example where no bonding material is present between the donor substrate and the microdevice. The temporary conductive material forms a current/voltage path between the

conductive pads

2004c, 2006c, which may be on the top and bottom or the same side of the microdevice. The temporary conductive material 2002c also covers one of the surfaces of the microdevice. Here, the temporary conductive material acts as a bonding material to the microdevice.

Fig. 20D illustrates another example of a temporary conductive material 2002D forming a current/voltage path between the conductive pads 2004D, 2006D of the micro device when the temporary conductive material 2002D and the conductive pads do not cover the entire surface of the micro device. Here, the conductive pads, such as 2004d, are patterned conductive pads, and the temporary material is deposited on the patterned conductive pads.

Fig. 20E shows another example, where temporary conductive material 2002E forms current/voltage paths for more than one pad on the surface of the micro device. Here, the conductive material shorts the conductive pad to the surface of the micro device. The conductive material covers

pads

2004e, 2006e or is connected to

pads

2008e, 2010 e. Also, traces (directly or indirectly) on the donor substrate may connect some of the conductive materials together. Here, the conductive material may partially or completely cover the conductive pads depending on the voltage and current requirements.

Fig. 20F shows an example of conductive pads 2008F, 2010F on surfaces that are not shorted together by the conductive layer 2002F. Here, the pads may be completely or partially covered by the conductive layer 2002f, as shown. Also, no bonding material is present between the donor substrate and the microdevice. The temporary conductive material serves as a bonding material for the microdevice.

Fig. 20G shows another example, where temporary conductive material 2002G forms current/voltage paths for more than one pad on the surface of the micro device. Here, the conductive material forms a via between a surface facing the donor substrate and a surface facing away from the donor substrate. And, in one case, it shorts the pad to the surface. Here, the conductive material covers the

conductive pads

2012g, 2014g or is connected to the

conductive pads

2008g, 2010 g.

Fig. 20H shows an example of conductive pads 2008H, 2010H on surfaces that are not shorted together by the conductive layer 2002H. Here, the

conductive pads

2012h, 2014h may be completely covered, or the

conductive pads

2008h, 2010h may be partially covered, as shown. In all cases, the conductive material 2004h can directly couple the surface remote from the donor substrate to the conductive layer at the donor substrate. In another case, it indirectly couples the surface remote from the donor substrate to the conductive layer 2006h at the donor substrate.

Fig. 20I1 and 20I2 show examples in which there are no conductive pads on the surface remote from the donor substrate. Here, no conductive pads are present on the surface of the microdevice remote from the donor substrate. In this case, the temporary material 2002h holds the device in place after the

sacrificial layers

2006a, 2008a are removed. The temporary material is removed or separated from the housing after the micro device is transferred into another substrate, such that the micro device is released from the donor substrate.

Fig. 21A-21D illustrate top views of different microdevices constructed with temporary material (conductive or non-conductive) according to embodiments of the invention. The temporary material may be patterned to form an opening on top of the donor substrate. This opening may facilitate some processing, such as removal of the sacrificial layer, to separate the micro device from the housing sidewall. This processing may be performed before or after the transfer of the microdevice into the receptor substrate. In one case, a chemical etch may be used to remove (or modify) the sacrificial layer. In another case, an electromagnetic signal (e.g., microwave or light) may be used to release the device by removing/modifying the sacrificial layer. Here, the temporary layer may also serve as an anchor to hold the device in place. If the temporary layer does not assist the bonding process, it does not need to connect (or cover) pads on the microdevice.

Fig. 21A illustrates the exemplary top view representation of fig. 20A, in accordance with embodiments of the present invention. Here, a micro device 2102 on a donor substrate 2104 has a conductive pad 2106 surrounded by a temporary conductive material 2108 and a sacrificial layer 2110. Here, the traces of conductive material on top of the donor substrate may be connected as a net, row or column. There may be access points on top of the donor substrate to bias the temporary layer via traces.

Fig. 21B1 illustrates an exemplary top view representation of fig. 20B. Here, the traces on top of the donor substrate may be connected as a net, row, or column. There may be access points on top of the donor substrate to bias the temporary layer via traces. Micro device 2102 on donor substrate 2104 has patterned conductive pad 2106-1 surrounded by sacrificial layer 2110. The traces of temporary conductive material on top of the donor substrate may be connected as a net, row or column. There may be access points on top of the donor substrate to bias the temporary layer via traces.

Fig. 21B2 shows an example in which the temporary material is not connected to the pad. The micro device 2102 on the donor substrate 2104 has conductive pads 2106-2 surrounded by sacrificial layer 2110 and traces of temporary conductive material on top of the donor substrate can be connected as a net, row or column. This can be used in other embodiments or related structures in this disclosure.

FIG. 21C illustrates an exemplary top view representation of FIG. 20E, where micro device 2102 has one or more pads (2106-3, 2106-4) on donor substrate 2104 surrounded by temporary conductive material 2108 and sacrificial layer 2110. Here, the traces on top of the donor substrate 2104 can be connected as a net, row, or column. Also, the traces for each pad may be processed in separate connection groups. There may be access points on top of the donor substrate to bias the temporary layer via traces.

Fig. 21D illustrates an exemplary top view representation of fig. 20F, where the micro device 2102 has one or more patterned conductive pads (2106-3, 2106-4) on a donor substrate 2104 surrounded by a temporary conductive material 2108 and a sacrificial layer 2110. Here, the traces on top of the donor substrate 2104 can be connected as a net, row, or column. Also, the traces for each pad may be processed in separate connection groups. There may be access points on top of the donor substrate to bias the temporary layer via traces.

Release of microdevices from donor substrates via breakable anchors

Some embodiments of the present disclosure show that the micro device can be provided with different temporary anchors, whereby after lifting off the device, the temporary anchors hold the device to the donor substrate and can be selectively moved toward or away from the surface of the donor substrate. Thus, when the donor substrate becomes proximate to the acceptor substrate, some selected devices are proximate to or connected with the acceptor substrate, while other micro devices are still a significant distance from the acceptor substrate. The temporary anchor releases the micro device after or during bonding of the micro device to a pad in the recipient substrate by either a pushing or pulling force. The anchors can break under pressure during pushing of the donor substrate and the recipient substrate toward each other or pulling of the microdevice through the recipient substrate. The microdevice may be permanently held on the receptor substrate. The anchor may be on one side of the microdevice or at the top (or bottom) of the microdevice.

Referring to fig. 22A, according to one embodiment, the stack includes

electrodes

2204, 2206 and an Electroactive Polymer (EPE) layer 2208 formed under a microdevice, such as 2210, 2212 on top of a donor substrate 2214. The donor substrate and/or the receiver substrate are moved so that some micro devices in the donor substrate become aligned with some locations in the receiver substrate. In one case, applying a voltage to the stack causes the stack to thin, and thus the device to be closer to the surface of the receptor substrate.

Referring to fig. 22B, according to another embodiment, the stack includes

electrodes

2208, 2206 and an Electroactive Polymer (EPE) layer 2222 formed under the microdevice (e.g., 2210, 2212 on top of the donor substrate 2214). In one case, the electrodes may be disposed around the EPE layer. The EPE layer may be thin or thick as desired. When a voltage is applied to the stack comprising the electrodes and the EPE layer, the stack becomes thicker. In one instance, the housing and anchors may also hold the

microdevices

2210, 2212 in place.

Fig. 22C shows another example, where the stacked electrodes and

microdevices

2210, 2212 structure on top of the

EPEs

2222, 2220 are surrounded by a housing structure 2226. In addition, the anchors 2234 hold the

microdevices

2210, 2212 inside the housing structure 2226. In another case, the bonding layer may hold the micro device on top of the stacked EPEs. The housing may have different shapes. In one case, the housing may match the shape of the device. The housing sidewall may be shorter than the microdevice height. The housing sidewalls can be attached to the microdevice prior to the transfer cycle to provide support for various post-processing of the microdevice.

During transfer of the

micro devices

2210, 2212 from the donor substrate 2214 to the recipient substrate, the EPE stack 2222 pushes the micro device 2210 forward. The pushing force releases anchors 2234 and the microdevice can be placed on the surface of the receptor substrate.

Fig. 23A-23B illustrate another embodiment of a micro device on a donor substrate, wherein the micro device can be selectively moved toward or away from the surface of the donor substrate.

In fig. 23A, a stack of

different materials

2304, 2308, 2310 with different coefficients of thermal expansion are formed on top of a donor substrate 2320 under the

micro devices

2312, 2314, 2318, respectively, according to another embodiment. As the temperature of the stack 2308 changes, the stack 2308 becomes distorted and pushes the device 2314 farther away from the surface of the donor substrate. In one case, applying a current through the stack changes the temperature. Here, the

electrodes

2302, 2306 may carry current. In another case, the light absorbing layer as part of the stack converts light into thermal energy. In another case, the stack may resonate to a particular signal frequency, such as microwave or ultrasonic. This resonance can increase the temperature or directly deform the stack.

Fig. 23B illustrates another example, where the

micro device

2312, 2314, 2318 structure on top of the

stacked layers

2304, 2308, 2310 is surrounded by a housing 2322. Further, the

anchors

2332, 2326 hold the

devices

2312, 2314 and 2318 inside the housing structure. The anchor may be connected to the microdevice or the housing. During transfer of the device 2314 from the donor substrate 2320 to the recipient substrate, the stack 2308 pushes the micro device 2314 forward. The pushing force releases anchor 2326 and microdevice 2314 may be placed on the surface of a recipient substrate.

Here, the

micro device

2410, 2414, 2418 structure on top of the stack layer 2404 is surrounded by a housing 2422. Additionally, anchors 2426, 2428

hold devices

2410, 2414, and 2418 inside the shell structure. During transfer of the device 2414 from the donor substrate to the receptor substrate, the electroactive polymer layer becomes a gas 2456 and the pressure created by the change pushes the micro device 2414 forward. The push/pull releases anchors 2426 and microdevice 2414 may be placed on the surface of the recipient substrate. Thermal, optical, electrical, or chemical forces may change layer 2404 into a gas. In one instance, the absorbing layer 2458 can absorb light and heat layer 2404-1 and create a gas pressure that pushes the micro device forward.

Micro device box structure

Some embodiments of the present invention also disclose methods of integrating monolithic micro device arrays into system substrates or selectively transferring micro device arrays to system substrates.

According to one embodiment, there may be provided a method of integrating a micro device on a backplane, comprising: providing a microdevice substrate comprising one or more microdevices; bonding a set of selective micro devices from a substrate to a backplane by connecting pads on the micro devices and corresponding pads on the backplane; and leaving the bonded selective set of micro devices on the backplane by separating the micro device substrates.

In one embodiment, an array of micro devices may be created on a micro device substrate, where the micro devices may be created by etching one or more planar layers.

In another embodiment, one or more planarization layers may be formed on the microdevice substrate and cured by temperature, light, or other sources.

In one embodiment, an intermediate substrate may be provided, wherein, in one case, one or more bonding layers may be formed on the intermediate substrate or on the planarization layer.

In another embodiment, the microdevice substrate may be removed by laser or chemical lift-off.

In one embodiment, there may be openings in the buffer layer that connect the micro devices to the planarization layer. In one case, the electrode may be disposed on the top or bottom of the planarization layer.

In another embodiment, after removing the micro device substrate, additional processes may occur, such as removing additional common layers, or thinning the planarization layer and/or the micro devices.

In one case, more pads may be added to the microdevice. The pads may be conductive or purely for bonding to the system substrate. In one case, the buffer layer may connect at least one micro device to the test pad. The test pads may be used to bias the micro device and test its functionality. Testing may be performed at the wafer level or at the intermediate (box) level. The pads are accessible at an intermediate level after the removal of the multilayers.

In one case, the micro device may have more than one contact at the top side, and the buffer layer may be patterned to connect the contact of at least one of the micro devices to the test pad.

In one embodiment, a back plate may be provided. In one case, the backplane may have transistors and other elements for the pixel circuitry to drive the micro devices. In another case, the backplate may be a substrate with no components.

In one embodiment, one or more pads may be disposed on the backplane for the bonding process. In one case, the pads on the backplane or on the micro device may create a force to pull out the micro device.

After the micro device is transferred to the backplane, it is possible to detect the position/location of the micro device and adjust the patterning of the other layers to match the alignment during the transfer. In one case, different means may be used to detect the position of the microdevice, such as a camera or a probe tip. In another case, an offset in the transfer setting can be used to identify a misalignment of the position of the micro device on the system substrate. In yet another case, a color filter or conversion layer may also be adjusted based on the position of the micro device. In one case, some random offset may be induced in the micro device locations to reduce optical artifacts.

In one embodiment, the pattern on the micro device may be modified (e.g., electrodes coupling the micro device to a signal, a functionally tunable layer such as a color filter or color conversion, vias opened in a passivation/planarization layer, or a backplane layer).

In one case, the position/shape of the electrodes may be modified based on the position of the microdevice. In another case, there may be some extension of each electrode that may be modified in position or length based on the position of the microdevice.

Fig. 25A shows a cross-sectional view of an array of micro devices on a micro device substrate, according to one embodiment of the invention. Here, a microdevice substrate 2502 is provided. The micro device array 2504 may be produced on a micro device substrate 2502. In one case, the micro device may be a micro LED. In another case, the micro device may be any micro device, including LEDs, OLEDs, sensors, solid state devices, integrated circuits, MEMS, and/or other electronic components, typically manufactured in a flat batch.

In one case, one or more planar active layers may be formed on the substrate. The planar active layer may include a first bottom conductive layer, a functional layer (e.g., a light emitting layer), and a second top conductive layer. The micro-devices may be created by etching a planar active layer. In one case, the etch can reach all the way to the microdevice substrate. In another case, there may be partial etching on the planar layer to leave some on the surface of the microdevice substrate. Other layers may be deposited and patterned before or after the formation of the microdevice.

Fig. 25B shows a cross-sectional view of a micro device array with a buffer layer according to one embodiment of the invention. Here, a buffer layer 2506 may be formed on the micro device array 2504. The buffer layer 2506 may extend over the surface of the microdevice substrate 2502. The buffer layer may be electrically conductive. In one case, the buffer layer may be a patterned buffer layer. In another case, the buffer layer may be a common buffer layer. In one embodiment, the buffer layer 2506 may include an electrode that may be patterned or used as a common electrode.

Fig. 25C illustrates a cross-sectional view of a micro device array having a planarization layer, according to one embodiment of the present invention. A planarization layer 2508 can be deposited around each micro device 2504 on top of the micro device substrate 2502. The planarization layer 2508 can be used for isolation and/or protection of the microdevice. The planarization layer may comprise a polymer such as polyamide, SU8, or BCB. The planarization layer may be cured. In one case, the planarization layer may be cured via temperature, light, or some other source.

Figure 25D illustrates a cross-sectional view of a micro device array bonded to an intermediate substrate, according to one embodiment of the invention. In one embodiment, one or more bonding layers 2512 may be formed on the planarization layer 2508. The bonding layer 2512 may be the same or different layer as the planarization layer. In another case, the bonding layer may be formed on top of the intermediate substrate (box) 2510. The bonding layer may provide one or more different forces, such as electrostatic, chemical, physical, or thermal. Bonding layer 2512 may contact planarization layer 2508. To form a contact between the planarization layer and the bonding layer, the bonding layer is cured by pressure, temperature, light, or other source.

In one embodiment, after forming the intermediate substrate 2510 over the bonding layer, the micro device substrate 2502 may be removed, which may be by laser or chemical lift-off.

In one case, there may be openings in the buffer layer 2506 that allow the micro devices 2504 to connect to the planarization layer 2508. This connection may act as an anchor. In one case, the buffer layer can be etched to form a shell, substrate, or anchor at least partially surrounding each microdevice. After lift-off, the anchors can hold the microdevice to the substrate. In another case, the buffer layer can couple at least one of the microdevice pads to the electrode. The electrodes may be placed on the top or bottom of the planarization layer.

Fig. 25E shows a cross-sectional view of a micro device array having pads, according to one embodiment of the invention. The microdevice substrate may be removed to enable a flexible system or for post-processing steps performed on the substrate-facing side of the system. After the substrate is removed, additional processes may be performed. These processes include one of the following: removing additional common layers or thinning the planarization layer and/or the micro devices. In one case, one or more pads 2520 may be added to micro device 2504. In one case, the pads may be electrically conductive. In another case, these pads are used purely for bonding to the system substrate. In one instance, the buffer layer 2506 can be electrically conductive.

In one embodiment, the buffer layer 2506 may connect one or more micro devices to a test pad. The test pads may be used to bias the microdevice and test its functionality. In one case, testing may be performed at the wafer/substrate level. In another case, testing may be performed at the middle (box) level. The pads are accessible at an intermediate level after the removal of the multilayers.

In one case, if the micro device has more than one contact at the top side, the buffer layer may be patterned to connect the contacts of at least one of the micro devices to the test pads.

Figure 26 illustrates a cross-sectional view of a micro device array bonded to an intermediate substrate and a backplate, according to one embodiment of the invention. Here, a back plate 2630 may be provided. In one case, the backplane may be fabricated using a TFT process. In another case, the backplane may be fabricated utilizing a chiplet (chiplet) or other process fabricated in Complementary Metal Oxide Semiconductor (CMOS).

In one embodiment, the backplane may have transistors and other elements for the pixel circuitry to drive the micro devices. In another embodiment, the backplate may be a substrate without elements. One or more pads 2622 may be formed on the backplane 2630 to bond the backplane to the micro device array. In one case, the one or more pads on the backplane may be electrically conductive.

In one embodiment, the buffer layer 2606 can be removed or deformed to release the microdevice. The pads 2622 on the backplane or the pads 2620 on the micro devices may create a force to pull out a selected micro device 2640. In another embodiment, the buffer layer 2606 or the housing can be etched back, reduced, or removed. The housing can be removed from the empty LED spot.

FIG. 27A shows the process steps for extracting the location of a micro device according to one embodiment of the invention. After the micro devices are transferred to the backplane, the micro device locations on the backplane can be detected, and if there is misalignment during the transfer, the patterning of other layers can be adjusted to match this transfer misalignment. The process comprises the following steps: step 2702, place the microdevice on the system substrate; step 2704, extract the position of the micro device on the system substrate using a camera, surface profiler (optical, ultrasonic, electrical) or other means; at step 2706, a pattern for the micro device may be modified, wherein the pattern may comprise one of: electrodes coupling the micro device to a signal, a functionally tunable layer (e.g., a color conversion or color filter), vias opened in a passivation/planarization layer, or a backplane layer. Some reference structure may be present on the system substrate to first calibrate the tool used to extract the position of the micro device, or the reference may be used to find the relative position of the micro device.

In one embodiment, different means may detect the position of the microdevice. For example, a camera, probe tip, surface profiler (optical, ultrasonic, electrical), or other means can detect/extract the position/location of the micro device. In another embodiment, an offset in the transfer setup may identify a misalignment of the position of the micro devices on the system substrate/backplane.

For example, in one case, metallization patterning can avoid shorting. In another case, the color filters or color conversion may also be adjusted based on the position of the micro device. This may reduce the tolerance required to place the microdevice. Some random offset may also be induced in the micro device locations to reduce optical artifacts.

Figure 27B illustrates modifying the position/shape of an electrode based on the position of a microdevice according to one embodiment of the invention. One or more of the

microdevices

2710, 2712, or 2714 may have contact pads 2706. In one case, the location/shape of the

electrodes

2702, 2704 can be modified based on the location of the

micro devices

2710, 2712, 2714. In another case, the position/shape of the electrode may be modified based on the position of the via. In another case, the location of the via in the planarization/passivation layer may be modified according to the microdevice location.

Fig. 27C shows an extension provided to an electrode according to one embodiment of the present invention. In one case, the position of the electrode 2702 can be modified. Also, there may be some extension 2720 for each electrode so that its position or length can be modified based on the position of the

microdevice

2710, 2712, or 2714. This may be for a common electrode or for individual electrodes.

According to one embodiment, a bonding structure may be provided. The bonding structure may include a plurality of micro devices on a donor substrate, each micro device including one or more conductive pads formed on a surface of the micro device; and a temporary material to cover at least a portion of each micro device or the one or more conductive pads, wherein the temporary material is coupled to a current/voltage source to redirect current to the one or more conductive pads through the temporary material. The temporary material comprises a conductive material or a non-conductive material, and wherein the temporary conductive material further completely or partially covers the one or more conductive pads.

According to a further embodiment, the method may further comprise a conductive layer at the donor substrate to couple the temporary conductive material to the current/voltage source; a housing structure to cover at least a portion of each micro device on the donor substrate, wherein the temporary material acts as an anchor to hold the plurality of micro devices inside the housing structure in the donor substrate.

According to a further embodiment, the method may further comprise at least one sacrificial layer between the casing structure and each micro device, wherein the temporary material is patterned to form an opening on a top surface of the donor substrate. An opening at the top surface of the donor substrate is used to release the micro device from the sidewalls of the housing structure by removing the sacrificial layer. After the sacrificial layer is removed, a temporary material holds each micro device in place and the sacrificial layer is removed by using a chemical etching process or an electromagnetic signal.

According to other embodiments, the temporary material is separated from the housing structure after each micro device is transferred to the receptor substrate by one of the following processes: mechanical processes, optical processes, thermal processes and chemical processes. The conductive traces on the top surface of the donor substrate are connected as one of: a net, a row, or a column.

According to some embodiments, a plurality of access points on the top surface of the donor substrate are used to bias the temporary material via the conductive traces. The temporary material forming a via between a surface facing the donor substrate and a surface facing away from the donor substrate; .

According to one embodiment, a method of bonding at least one micro device to a receptor substrate is provided. The method comprises the following steps: forming a stack comprising an electrode and an electroactive polymer layer on a donor substrate under the at least one micro device; a voltage is applied to the stack to bring at least one micro device within contact/proximity of a surface of a receptor substrate.

According to some embodiments, the method may further comprise: providing a housing structure around the at least one microdevice; and providing an anchor to hold the at least one microdevice inside the housing structure.

According to another embodiment, the anchor releases the micro device on the surface of the receptor substrate by one of a pushing force or a pulling force, the stack further comprises an absorption layer that converts light into a thermal change, and the electroactive polymer layer becomes a gas, and the pressure resulting from the change pushes the at least one micro device to the surface of the receptor substrate.

According to one embodiment, there may be provided a method of integrating a micro device on a backplane, comprising: forming a buffer layer on or over the one or more micro devices extending over a substrate; forming a planarization layer on the buffer layer, the planarization layer comprising a polymer, and wherein the polymer comprises one of polyamide, SU8, or BCB; and depositing a bonding layer between the planarization layer and the intermediate substrate.

According to a further embodiment, the method may further comprise curing the bonding layer after contacting the planarization layer, and removing the micro device substrate by laser or chemical lift-off. Curing the bonding layer by pressure, temperature or light.

According to a further embodiment, the method may further comprise removing the micro device substrate by one of laser or chemical lift-off, and wherein bonding a set of selective micro devices from the substrate to the backplane comprises the steps of: aligning and contacting the microdevice and the backing plate; removing the buffer layer to release the microdevice; creating a force to pull out the selected set of micro devices; and bonding the selected set of micro devices to the backplane.

According to a further embodiment, the method may further comprise providing an opening in the buffer layer to connect the micro device to the planarization layer. The buffer layer is electrically conductive, wherein the buffer layer connects the at least one micro device to the test pad.

According to a further embodiment, the method may further comprise: providing an electrode on either the top or the bottom of the planarization layer; coupling at least one micro device to the electrode via a buffer layer; extracting the position of the micro device on the back plate; and extending the position of the electrode to extract the position of the micro device on the backplate, wherein the position of the micro device is extracted by a camera, a probe tip, or a surface profiler.

In view of the foregoing, the present disclosure provides a microdevice integration process that is transferred to a system substrate for completion, and electronic control integration. The transfer can be facilitated by various means, including providing a temporary material, a breakable anchor on the donor substrate, or a temporary intermediate substrate.

The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

1. A bonding structure, comprising:

a plurality of micro devices on a donor substrate, each micro device comprising one or more conductive pads formed on a surface of the micro device; and

a temporary material to cover at least a portion of each micro device or the one or more conductive pads, wherein the temporary material is coupled to a current/voltage source to redirect current to the one or more conductive pads through the temporary material.

2. The bonded structure of claim 1, wherein the temporary material comprises a conductive material or a non-conductive material.

3. The bonded structure of claim 1, further comprising:

a conductive layer at the donor substrate coupling the temporary conductive material to the current/voltage source.

4. The bonding structure of claim 2, wherein the temporary conductive material further completely or partially covers the one or more conductive pads.

5. The bonded structure of claim 1, further comprising:

a housing structure to cover at least a portion of each micro device on the donor substrate.

6. The bonding structure of claim 5, wherein the temporary material acts as an anchor that holds the plurality of micro devices inside the shell structure in the donor substrate.

7. The bonded structure of claim 1, further comprising:

at least one sacrificial layer between the housing structure and each micro device.

8. The bonded structure of claim 1, wherein the temporary material is patterned to form an opening on a top surface of the donor substrate.

9. The bonded structure of claim 8, wherein the opening at the top surface of the donor substrate is used to release the micro device from a sidewall of the housing structure by removing the sacrificial layer.

10. The bonded structure of claim 9, wherein the temporary material holds each micro device in place after removing the sacrificial layer, and wherein the sacrificial layer is removed by using a chemical etching process or an electromagnetic signal.

11. The bonded structure of claim 8, wherein the temporary material is separated from the housing structure after each micro device is transferred to a recipient substrate by one of the following processes: mechanical processes, optical processes, thermal processes and chemical processes.

12. The bonded structure of claim 11, wherein a conductive trace on the top surface of the donor substrate connects as one of: a net, a row, or a column.

13. The bonded structure of claim 11, wherein a plurality of access points on the top surface of the donor substrate are used to bias the temporary material via the conductive traces.

14. The bonded structure of claim 1, wherein the temporary material forms a via between a surface facing the donor substrate and a surface facing away from the donor substrate.

15. A method of placing at least one micro device to a receptor substrate, the method comprising:

forming a stack comprising an electrode and an electroactive polymer layer on a donor substrate under the at least one micro device;

applying a voltage to the stack to bring at least one micro device within contact/proximity of the surface of the acceptor substrate.

16. The method of claim 15, further comprising:

providing a housing structure around the at least one microdevice; and

providing an anchor to hold the at least one microdevice inside the housing structure.

17. The method of claim 15, wherein the anchors release the micro device on the surface of the receiver substrate by one of a pushing force or a pulling force.

18. The method of claim 15, wherein the stack further comprises an absorption layer that converts light into a thermal change.

19. The method of claim 15, wherein the electroactive polymer layer becomes a gas and the pressure resulting from the change pushes the at least one micro device to the surface of the receptor substrate.

20. A method of integrating a micro device on a backplane, the method comprising:

providing a microdevice substrate comprising one or more microdevices;

bonding a set of selective micro devices from the substrate to the backplane by connecting contact pads on the micro devices and corresponding pads on the backplane;

leaving the bonded set of selective micro devices on the backplane by separating the micro device substrates.

21. The method of claim 20, further comprising:

forming a buffer layer on or over the one or more micro devices extending over the substrate;

forming a planarization layer on the buffer layer, the planarization layer comprising a polymer, and wherein the polymer comprises one of polyamide, SU8, or BCB; and

a bonding layer is deposited between the planarization layer and an intermediate substrate.

22. The method of claim 21, further comprising

Curing the bonding layer after contacting the planarization layer, wherein the bonding layer is cured by any one of pressure, temperature, or light.

23. The method of claim 20, further comprising

Removing the micro device substrate by one of laser or chemical lift-off.

24. The method of claim 20, wherein pads on the micro device and corresponding pads on the backplane are electrically conductive.

25. The method of claim 20, wherein bonding the selective set of the micro devices from the substrate to the backplane comprises:

aligning and contacting the micro device and the backplane;

removing the buffer layer to release the micro device;

generating a force to pull out the selected set of micro devices; and

bonding the selected set of micro devices to the backplane.

26. The method of claim 20, further comprising

Providing an opening in the buffer layer to allow the micro device to be connected to the planarization layer.

27. The method of claim 21, wherein the buffer layer is electrically conductive.

28. The method of claim 21, wherein the buffer layer connects at least one micro device to a test pad.

29. The method of claim 21, further comprising

Providing an electrode on either the top or bottom of the planarization layer; and

at least one micro device is coupled to the electrode via the buffer layer.

30. The method of claim 21, further comprising

Extracting the position of the micro device on the back plate; and

extending a position of the electrode to extract a position of a micro device on the backplate, wherein the position of the micro device is extracted by one of a camera, a probe tip, or a surface profiler.