Mass transfer method for micro light emitting diode display based on fluid assembly

Abstract

A mass transfer imprinting system for microLEDs includes an imprint substrate with an array of capture positions, each capture position configured with a columnar groove to temporarily secure a keel extending from the bottom surface of a microLED. For surface-mount microLEDs, the keel is non-conductive. In the case of vertical microLEDs, the keel serves as a conductive second electrode. The imprinting system also includes a fluid assembly carrier substrate with an array of wells having a spacing that separates adjacent wells, the spacing matching the spacing separating the capture positions on the imprint substrate. A display substrate includes an array of microLED connection pads with the same spacing as the capture positions. The top surface of the imprint substrate is pressed against the display substrate, each capture position is connected to a corresponding microLED position, and then the microLED is transferred. A fluid assembly imprint substrate for use with microLEDs having keels or axial orientation is also provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-light emitting diode (micro-LED) displays, and in particular to a system and method for mass transfer of micro-LEDs during display manufacturing. BACKGROUND

[0002] Red-green-blue (RGB) displays are composed of a plurality of pixels that emit light at three wavelengths corresponding to red, green and blue light in the visible spectrum. The RGB components of these pixels (each component is referred to as a sub-pixel) are energized in a systematic manner to superimpose colors in the visible spectrum. Different displays differ in the way they generate RGB images. Liquid Crystal Displays (LCDs) are currently the most popular technology, which generate RGB images by using a white light source (usually a white LED that emits fluorescent light) to illuminate color filters on the sub-pixels. Part of the wavelengths of light contained in the white light is absorbed and another part is transmitted through the color filters. Thus, the efficiency of an LCD display can be less than 4% and its contrast is limited by the light that leaks from the liquid crystal cells. Organic Light Emitting Diode (OLED) displays generate RGB light by exciting organic light emitting materials in each sub-pixel to directly emit light at the corresponding wavelength. OLED pixels are direct light emitters, thus the contrast of the display is high, but the organic materials deteriorate over time, causing image aging.

[0003] A third display technology, to which the present application relates, is the micro-LED display, which uses micro (5-150 micrometers (pm) in diameter) inorganic LEDs as sub-pixels and emits light directly. Inorganic micro-LED displays have many advantages over other displays. Compared to LCD displays, micro-LED displays have a contrast ratio of more than 50,000: 1 and are more efficient. Unlike OLED displays, inorganic LEDs do not age and can achieve significantly higher brightness.

[0004] Current mainstream High Definition Television (HDTV) resolution standards have two million pixels (or six million sub-pixels), with higher resolution 4K and 8K standards at eight million and thirty-three million pixels, respectively. Even relatively small displays used in tablets and cell phones have millions of pixels with resolutions exceeding six hundred pixels per inch (ppi). Thus, the manufacture of displays using micro-LEDs requires assembling large area micro-LED arrays with different pixel pitches at low cost so that displays of various sizes and resolutions can be manufactured. The most traditional micro-LED array assembly technique is known as pick-and-place, in which each micro-LED is individually picked from a carrier and placed on a substrate, as described below. Since each micro-LED is handled individually, the process is very slow.

[0005] Figures 1A-1C Cross-sectional diagrams of a Gallium Nitride (GaN) based LED stack Figure 1A ), a cross-sectional diagram of two fully fabricated vertical micro-LEDs Figure 1B ), and a cross-sectional diagram of a surface mount micro-LED Figure 1C ) (prior art) are depicted. Widely adopted GaN based high brightness LEDs for general lighting have created a complex manufacturing system, so micro-LEDs for displays are based on the investments already made in the industry. GaN based LEDs that emit blue (about 440 nanometers (nm)) wavelengths are fabricated in a series of complex high temperature Metal Organic Chemical Vapor Deposition (MOCVD) steps to produce vertical LED structures shown in cross-section in Figure 1A . The fabrication process is performed on polished sapphire, silicon or silicon carbide (SiC) substrates with diameters of 50-200 millimeters (mm). The surface is prepared by depositing undoped GaN and optionally an Aluminum Nitride (AIN) buffer layer to produce a surface with low defects and lattice constant of GaN. The thickness of high efficiency devices is higher than about 3 pm due to the need to adjust the initial deposition thickness and temperature to compensate for the lattice mismatch between the substrate and GaN, i.e., to increase the thickness to improve the surface quality. Since the MOCVD deposition process is complex and expensive, it is important to optimize the micro-LED process to make the most efficient use of the entire area of the growth wafer.

[0006] After the initial growth to form a crystalline GaN surface, a first LED layer is created by adding silicon doping to form n+ GaN for the cathode. Optionally, the stack can include layers adjusted for electron injection and hole blocking. Next, a layer of Gallium Indium Nitride (In x Ga1-x N) and GaN alternating layers (Multiple Quantum Well, MQW) structure, where the indium content and the thickness of the layers determine the emission wavelength of the device. Increasing the indium content shifts the emission peak to longer wavelengths, but also increases the stress due to lattice mismatch, and therefore high efficiency GaN devices cannot be made for red emission, and the efficiency of green LEDs is lower than for blue LEDs. After the MQW is formed, the stack can also include layers tailored for electron blocking and hole injection. The MOCVD layer sequence is completed by depositing Mg-doped GaN to form the p+ anode layer.

[0007] LEDs for general lighting (up to 3-4 mm per side) are much larger than micro-LEDs (5-150 μm in diameter) used in micro-LED displays, and therefore the requirements for patterning and electrodes are significantly different. Micro-LEDs need to be bonded to the substrate electrodes with solder or Asymmetric Conductive Film (ACF), while larger LEDs are typically wire-bonded or soldered to lead frames. Since micro-LEDs are very small, a large fraction of the area on the MOCVD wafer is removed during patterning, reducing the available light emitting area per wafer. LED wafers are relatively expensive, and the high resolution required for micro-LED fabrication further increases the cost, so it is important to use the light emitting area as efficiently as possible to minimize the material cost of the micro-LED display.

[0008] In the simplest process flow, a thin (few nm) layer of nickel oxide (NiO X ) is deposited to match the p+ GaN work function, and a layer of Indium Tin Oxide (ITO) with a thickness of 50-300 nm is deposited to form a transparent conductive electrode on the MOCVD stack. The deposited stack is then patterned and etched, typically using a chlorine (CI2) based reactive ion etch (RIE) process to produce individual micro-LEDs with minimum feature size and pitch. In particular when producing micro-LEDs with high efficiency, the thickness of the LED structure is only 3-5 μm, and therefore the thickness of the LED structure limits the minimum space that can be successfully etched.

[0009] As Figure 1CAfter the LED is etched to its profile, additional processing is performed to form electrodes on the anode, as shown schematically. To prevent electrical leakage and to etch openings for connecting the ITO layer, a passivation layer is typically provided, usually by Plasma-enhanced Chemical Vapor Deposition (PECVD) Silicon Dioxide (SiO2) or optionally including a thin Atomic Layer Deposition (ALD) Aluminum Oxide (Al2O3) layer on the surface. The anode structure is completed by depositing an electrode stack structure, including materials such as indium / tin (In / Sn) or gold, germanium (Au / Ge) alloys.

[0010] Figure 2A A process for removing micro light emitting diodes from a sapphire substrate using Laser Lift Off (LLO) is described. Figure 2B A pick-and-place process is described for moving and placing devices from a carrier wafer onto a display substrate. Figure 2C A connection of micro light emitting diode anodes to substrate electrodes (prior art) is described. In particular, in Figure 2A a finished micro light emitting diode is bonded to a carrier wafer by an adhesive layer and removed from a sapphire substrate by laser lift off. In Figure 2B a micro light emitting diode can be removed from a carrier by a pick-up head and placed on a sub-pixel with its anode electrically connected to a corresponding electrode on the substrate. A pixel is completed by coating the micro light emitting diode with a suitable dielectric (e.g. a photo-patternable polyimide) and connecting the cathode of the micro light emitting diode to an electrode on the substrate. Metal interconnects are deposited and patterned to form connections as shown in Figure 2C

[0011] LEDs emitting red light at a wavelength of about 630 nm, typically made of aluminum gallium indium phosphide (AlGaInP) grown on gallium arsenide (GaAs), cannot be lifted off from the GaAs substrate using the laser lift off technique because GaAs is opaque. Therefore, to lift off a red LED from the substrate, the substrate can be etched completely or selective etching (typically using hydrogen chloride (HC1): acetic acid) can be used to undercut and lift off the LED. The size (cross-section) of the LED is similar to GaN general illumination LEDs (size 150-1000 pm). The AlGaInP LED process is described more fully in patent US 10,804,426, which is incorporated herein by reference.

[0012] ​The aforementioned pick-and-place assembly process presents several significant challenges, leading to high costs and low yields. Specifically, the assembly process is inherently serial, making the assembly of millions of microLEDs time-consuming and costly. The small size of the microLEDs themselves makes the gripper head difficult to fabricate, and the edges of the gripper are likely to interfere with adjacent microLEDs during gripping or with the reflector structure between pixels during assembly. The single pick-and-place method described above can be extended to a parallel process by using a mass transfer head to simultaneously grip and transfer multiple microLEDs. However, the quality of this mass transfer method can be poor due to the presence of defective components in a simultaneously transferred group of microLEDs, and the spacing between each microLED is determined by the spacing of the components grown on the wafer.

[0013] Figures 3A-3H An example of a mass transfer method (prior art) is described. Mass transfer involves transferring an array of multiple miniature light-emitting diodes (LEDs) as a whole onto a display substrate. This method has been widely developed to address the low throughput problem of serial pick-and-place assembly. In the simplest mass transfer process, a rectangular imprinting stamp picks up a rectangular array of miniature LEDs from a carrier and presses the LEDs against the display substrate, so that each miniature LED is coupled to a corresponding electrode. Since the fabrication of RGB displays requires consideration of LEDs of different colors, the transfer imprinting stamp is arranged to pick up every three LEDs, thus leaving space for LEDs of the other two sub-pixel colors. Figure 2C The surface-mount miniature light-emitting diodes shown are assembled in the following order:

[0014] 1) Prepare individual MOCVD wafers for each color of micro-LED, with appropriate dimensions and spacing between each micro-LED. The gap between adjacent micro-LEDs is called the spacing. See [link to relevant documentation]. Figure 3A Each micro-LED has a cathode and an anode for connection to the display substrate. The micro-LED array is removed from the growth wafer by laser lift-off and held on a carrier substrate (not shown).

[0015] 2) On the display substrate ( Figure 3B) sets of cathode and anode electrodes are provided, with the spacing between each set of electrodes being a multiple of the spacing between each micro-LED on the wafer, so that the electrodes and the positions of the micro-LEDs on the transfer stamp match each other. This spacing determines the final resolution of the display. The electrodes can be copper, indium tin oxide / aluminium (ITO / Al), gold or a solder such as tin / indium (Sn / In). An ACF film can also be used to cover the electrodes. By determining the materials of the electrodes and micro-LEDs on the display panel, an ohmic contact can be formed by a subsequent bonding process in step 5 below.

[0016] 3) The stamp is prepared by aligning the pick-up points with the positions on the display that match the pitch of the sub-pixels. The pick-up mechanisms currently used to secure each micro-LED include elastomers, adhesive tape, electrostatic and magnetic fields. Figure 3C A stamp of size 3*3 pixels is described, but in practice a stamp will typically hold hundreds of pixels.

[0017] 4) Referring to Figure 3D , the stamp is placed in alignment with the carrier substrate carrying the micro-LEDs of the first colour and brought into contact with the carrier substrate, so that the securing structures can pick up the micro-LEDs and remove them from the carrier substrate.

[0018] 5) Referring to Figure 3E , the filled stamp is placed in alignment with the electrodes on the first set of display substrates.

[0019] 6) Referring to Figure 3F , the stamp is pressed against and brought into contact with the display substrates, typically with heating to form the bond between the micro-LED electrodes and the electrodes on the display substrates. After the bond has formed and cooled sufficiently to secure the micro-LEDs, the stamp is removed for re-use.

[0020] 7) The same operations are performed for the micro-LEDs of the second and third colours, as shown in Figures 3G-3H , to form an RGB display array.

[0021] The above mass transfer method is feasible and has been used in the manufacture of displays, but there are still some problems that result in a low yield and high cost of the product. Firstly, in Figure 3BIn the figure, the pitch of the display in the x and y direction can only be an integer multiple of the pitch between the micro-LEDs on the MOCVD wafer, in the example 3*2. A perfect display manufacturing technology must be able to manufacture screens of different sizes according to industry standards, such as 4K (3840*2160 pixels), so a technology to change the pitch of the micro-LEDs on the stamp (pitch expansion) is needed. It is also possible to customize the size of the micro-LEDs on the MOCVD wafer for each display in terms of size and resolution, but this increases unnecessary costs. Secondly, the pick-up device must strike a balance in the size of the connection strength, if the connection strength is too small, some micro-LEDs will not be detached from the carrier substrate, leaving gaps in the array. Conversely, if the connection strength is too large, the micro-LEDs will also be forcibly removed after being soldered to the substrate. In both cases, the brightness of the sub-pixels will be reduced, which is not tolerable in a display. Finally, the structure of the transfer stamp is complex and difficult to manufacture. The connection points must be smaller than the pitch between the micro-LEDs to avoid the stamp interfering with adjacent micro-LEDs. This is difficult for complex fixation methods that require the generation of a local field (such as electrostatic or magnetic force). The stamp is also prone to contamination and damage, especially if it is made of elastomers such as polydimethylsiloxane (PDMS), so how to effectively clean it for repeated use of the stamp is also very important.

[0022] To illustrate the defects of the mass transfer imprinting process, Figure 3H Several possible failure cases are described:

[0023] Failure a: lack of micro-LEDs due to poor adhesion of the stamp during pick-up;

[0024] Failure b: misplacement of micro-LEDs due to contamination on the stamp;

[0025] Failure c: particles due to contamination of the transfer stamp;

[0026] Failure d: broken micro-LEDs;

[0027] Failure e: short-circuit of micro-LEDs due to defects of the MOCVD process:

[0028] Failure f: damage of the electrodes due to the micro-LEDs being forcibly removed by the stamp.

[0029] Figure 4A And Figure 4B It is described the use of a 14 mm stamp (14 mm x 14 mm) on a 100 mm wafer Figure 4A) with 20% of the micro-LEDs remaining on the wafer, with three defective micro-LEDs on each of the three imprint stamps. Another limitation of the above mass transfer process is the square shape of the imprint stamp, which does not match the circular shape of the wafer used to grow the LEDs by MOCVD. Figure 4A A typical arrangement is shown for a 100 mm wafer using 14*14 mm imprint stamps. Using large area imprint stamps increases the speed of assembly at the cost of leaving more micro-LEDs on the growth wafer. As a result of the requirement to fill all of the imprint stamps, there is a large area of the wafer that cannot be used for imprinting. In the above example, approximately 20% of the good micro-LEDs are discarded, which directly increases the cost. In addition, for defective micro-LEDs, the affected imprint stamp must be repaired or discarded. The above example describes three defects randomly for illustration purposes. If the defective imprint stamps are discarded in the example, only approximately 70% of the initial micro-LEDs can be used for display manufacturing.

[0030] A significant advantage of the mass transfer method is that the bonding process is performed under pressure on the micro-LEDs, so there is good mechanical contact between the two bonding electrodes. This ensures a large area of contact between the electrodes. The mechanical contact also breaks down the insulating oxide on the surface, improving the wetting of the solder material. ACF bonding also requires pressure to make a hard contact between the conductive filler material and the micro-LEDs and the electrodes on the display substrate.

[0031] It would be advantageous if there was a structure and method to fill the carrier substrate of the mass transfer assembly of micro-LED displays and to increase the flexibility and yield of the assembly in the following ways:

[0032] 1. Any display resolution can be achieved by simple pitch expansion;

[0033] 2. A series of micro-LEDs (known good dies) can be manufactured without device defects such as missing, broken or shorted micro-LEDs;

[0034] 3. The speed of mass transfer assembly can be increased by filling and transferring the imprint stamps in a large scale parallel transfer method;

[0035] 4. Simple transfer imprint stamps can be used with low manufacturing cost and can be reused by robust cleaning;

[0036] 5. A simple and non-damaging imprint mechanism can be used;

[0037] 6. Excess micro-LEDs can be recovered from defective imprint stamps. SUMMARY

[0038] The present application provides a method of fabricating micro light emitting diode arrays by fluidic assembly on a carrier substrate or a transfer stamp and related structures. The assembled micro light emitting diodes can be applied to a display substrate and bonded by a mass transfer method. The micro light emitting diodes are fabricated on a wafer by conventional MOCVD methods and are shaped to facilitate fluidic assembly and imprinting onto a display substrate.

[0039] Accordingly, the present application provides a micro light emitting diode mass transfer imprinting system including an imprint stamp substrate having a top surface. Formed on the top surface are arrayed imprint stamp capture locations each having a columnar recess for temporarily securing a keel extending from a bottom surface of a micro light emitting diode. When the micro light emitting diode is surface mount type, it has a planar top surface including a first electrode and a second electrode. When the micro light emitting diode is vertical type, it has a planar top surface with a first electrode, and the keel is a conductive second electrode. The imprint system further includes a fluidic assembly carrier substrate having a planar top surface with an array of wells formed thereon, the array of wells having a pitch separating adjacent wells that matches a pitch separating adjacent capture locations on the imprint stamp substrate.

[0040] A related micro light emitting diode mass transfer method includes providing the above fluidic assembly carrier substrate with the array of wells and providing the above imprint stamp substrate with each capture location in the array configured with a columnar recess that matches a well on the carrier substrate. The method uses a fluidic assembly process to fill the micro light emitting diodes into the wells of the carrier substrate. The method presses the top surface of the imprint stamp substrate against the top surface of the carrier substrate so that each capture location corresponds to a respective well, thereby transferring the micro light emitting diodes from the carrier substrate to the imprint stamp substrate. The recess of each capture location carries the keel extending from the bottom surface of the micro light emitting diode and secures the micro light emitting diode to the imprint stamp substrate by binding the keel. The use of the carrier substrate eliminates the restriction of the pitch between micro light emitting diodes on a MOCVD wafer, thereby allowing various imprint stamp substrate pitches to be applied to different display substrate sizes and resolutions.

[0041] The method also provides a display substrate having an array of micro-LED connection pads, wherein each micro-LED connection pad includes at least one electrode formed on a top surface, the electrode being electrically connected to a matrix of underlying column and row control lines. The connection pads have a pitch separating adjacent locations that matches a pitch separating adjacent capture locations in a stamp substrate. The method presses a top surface of the stamp substrate against a top surface of the display substrate, each capture location being connected to a corresponding micro-LED location, and transfers a plurality of micro-LEDs from the stamp substrate to the plurality of connection pads on the display substrate. In one aspect, the step of transferring the micro-LEDs to the connection pads on the display substrate includes heating the display substrate to bond the plurality of micro-LEDs to the plurality of connection pads. In the case of an RGB display, the method can press together stamp substrates having capture locations provided with micro-LEDs of a first wavelength, micro-LEDs of a second wavelength, and micro-LEDs of a third wavelength in sequence, or a single stamp substrate corresponding to micro-LEDs of one wavelength.

[0042] The present application also provides a method of micro-LED mass transfer, which uses a fluid-assembled stamp substrate having a planar top surface, the top surface having a plurality of capture locations formed thereon, each capture location having a first perimeter shape, a depth, and a planar bottom surface. Through a fluid-assembly process, the capture locations can be filled with micro-LEDs having the first perimeter shape, the micro-LEDs having a thickness greater than the depth of the capture locations, a bottom surface in contact with the bottom surface of the capture locations, a planar top surface, a first electrode extending out of the capture location, and a securing mechanism. In one aspect, the securing mechanism is a keel formed on the top surface of the micro-LED, the keel being either a conductive keel connected to the first electrode or a temporary non-conductive keel that is removed after the micro-LED is secured to the stamp substrate. In another aspect, the securing mechanism is a first component comprising a conjugate biomolecular pair disposed on the bottom surface of each micro-LED. In this case, the bottom surface of each capture location is provided with a second component comprising a conjugate biomolecular pair.

[0043] As described above, the method provides a display substrate having a planar top surface and an array of micro-LED connection pads, each micro-LED connection pad including a first electrode formed on the top surface that is electrically connected to a matrix of column and row control lines beneath the substrate. The display substrate has a pitch between adjacent wells that matches a pitch between adjacent capture sites on the imprint stamp substrate. The method imprints the top surface of the stamp substrate against the top surface of the display substrate such that each capture site is filled with a micro-LED, and transfers the plurality of micro-LEDs from the imprint stamp substrate to the micro-LED connection pads on the display substrate. Also, during the transfer, the display substrate can be heated to facilitate bonding of the electrodes.

[0044] The present application also provides a method for axial micro-LED mass transfer. The method provides a fluidically assembled imprint stamp substrate having a planar top surface with a plurality of capture sites formed thereon, each capture site having a first perimeter shape, a central portion having a planar first depth, a distal end having a planar second depth that is less than the first depth, and a proximal end having a planar second depth. Through a fluidic assembly process, the method fills the capture sites with axial micro-LEDs, each micro-LED occupying a respective capture site and having the first perimeter shape, a body connected to the central portion, and a vertical planar body having a body thickness that is greater than the first depth but less than twice the first depth. A distal electrode horizontally bisects the body and contacts the distal end of the capture site, the distal electrode having a vertical planar electrode thickness that is greater than the second depth of the capture site but less than twice the second depth. A proximal electrode has the same thickness as the distal electrode, horizontally bisects the body, and contacts the proximal end of the capture site.

[0045] The method provides a display substrate having a planar top surface and an array of micro-LED connection pads, each micro-LED connection pad including a pair of electrodes formed on the top surface and electrically connected to a matrix of column and row control lines beneath the substrate. The display substrate has a pitch separating adjacent wells that matches a pitch separating adjacent capture sites on the imprint stamp substrate. The method imprints the top surface of the stamp substrate against the top surface of the display substrate such that each capture site is in contact with a respective micro-LED, and transfers the micro-LEDs from the stamp substrate to the display substrate, typically with heating to facilitate bonding of the electrodes.

[0046] The above-described systems and methods will be described in detail in the following. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figures 1A-1C Cross-sectional view of a GaN LEDFigure 1A ), a cross-sectional view of two vertical micro-LEDs ( Figure 1B ), and a cross-sectional view of a surface mount micro-LED ( Figure 1C ) (prior art).

[0048] Figure 2A A process for removing micro-LEDs from a sapphire growth substrate using laser lift-off technology (prior art).

[0049] Figure 2B A pick-and-place process for moving devices from a carrier wafer and positioning them on a display substrate (prior art).

[0050] Figure 2C A process for connecting the anode of a micro-LED to a substrate electrode (prior art).

[0051] Figures 3A-3H A step in an exemplary mass transfer process (prior art).

[0052] Figures 4A-4B An example of the footprint for imprint pick-up using a 14 mm imprint stamp on a 100 mm wafer with 20% of the micro-LEDs left on the wafer and three of the micro-LEDs on the imprint stamp having defects (prior art). Figure 4A Figure 4B

[0053] Figure 5 A partial cross-sectional view showing a typical backplane arrangement of surface mount micro-LEDs and power transistors to control the brightness of the micro-LEDs.

[0054] Figures 6A-6B A top view and a cross-sectional view of a surface mount micro-LED for fluidic assembly, respectively.

[0055] Figure 7 A schematic of a micro-LED wafer after selective pick-up.

[0056] Figure 8 A brief description of the fluidic effect that enables 100% of the micro-LEDs to be assembled in the correct orientation with the electrodes facing down.

[0057] Figures 9A-9D A step in a micro-LED mass transfer imprint system.

[0058] Figures 10A-10D A cross-sectional view of a process for transferring micro-LEDs from a carrier substrate to a display substrate.

[0059] Figures 11A-11D ​​Schematic view of a press system, wherein the micro light emitting diodes are vertical micro light emitting diodes.

[0060] Figures 12A-12B Partial cross-sectional view of an attraction force generator for assisting the micro light emitting diodes to be fixed to the capture position of the carrier substrate.

[0061] Figures 13A-13K Schematic view of a step of a micro light emitting diode mass transfer press system using fluid assembly of a press stamp substrate.

[0062] Figure 14A and Figure 14B Schematic view of a micro light emitting diode mass transfer method using an electrostatic force generator and using a magnetic force generator as an assisting device, assisting the micro light emitting diodes to be fixed to the fluid assembly capture position.

[0063] Figures 15A-15I Schematic view of a micro light emitting diode mass transfer system using fluid press and axial micro light emitting diodes.

[0064] Figure 16 Flow chart of a micro light emitting diode mass transfer method corresponding to the system shown in Figures 9A-9D

[0065] Figure 17 Flow chart of a micro light emitting diode mass transfer method using fluid assembly of a press stamp substrate shown in Figures 13A-13K

[0066] Flow chart of an axial (lead) micro light emitting diode mass transfer method shown in Figure 18 Figures 15A-15I Flow chart of a micro light emitting diode transfer time span extension method.

[0067] Figure 19 Main element symbol explanation

[0068] Press stamp 900, 900a, 900b, 900c, 1300, 1500

[0069] Press stamp top surface 902, 1302, 1502

[0071] Capture position 904, 1304, 1504

[0072] Keel 906

[0073] Micro light emitting diode bottom surface 908

[0074] Micro light emitting diode 910

[0075]

[0076] ​​​Surface mount micro light emitting diode 910a, 910b, 910c

[0077] Micro light emitting diode top surface 912

[0078] First electrode 914, 1316

[0079] Second electrode 916, 1324

[0080] Display substrate 918, 1315, 1318, 1525

[0081] Carrier substrate 1000, 1000a, 1000b, 1000c

[0082] Carrier substrate top surface 1002

[0083] Well 1004

[0084] Pitch 1006

[0085] Carrier substrate bottom surface 1008

[0086] Heating device 1010

[0087] Vertical micro light emitting diode 1100

[0088] Vertical micro light emitting diode top surface 1102

[0089] Vertical micro light emitting diode first electrode 1104

[0090] Insulating layer 1106

[0091] Electrostatic force generator 1200, 1400

[0092] Magnetic force generator 1202, 1402

[0093] Depth 1306

[0094] Trapping location bottom surface 1308

[0095] Micro light emitting diode thickness 1310

[0096] Micro light emitting diode bottom surface 1312

[0097] Micro light emitting diode top surface 1314

[0098] Groove 1320

[0099] Thiol biotin bifunctional molecule / first component 1322

[0100] ACF 1325

[0101] Silicon dioxide film 1326

[0102] Streptavidin molecule / first component 1327

[0103] Central portion 1506

[0104] First depth 1508

[0105] Distal end 1510

[0106] Second depth 1512

[0107] Proximal end 1514

[0108] Axial micro-LED 1516

[0109] Body 1518

[0110] Body thickness 1520

[0111] Distal electrode 1522

[0112] Electrode thickness 1524

[0113] Proximal electrode 1526

[0114] Electrode 1528

[0115] Dielectric film 1530

[0116] Body recess 1532

[0117] P-connection pad 1534

[0118] N-connection pad 1536

[0119] First recess 1538

[0120] The following detailed description will further illustrate the present application in connection with the above-mentioned drawings. DETAILED DESCRIPTION

[0121] U.S. Patents 9,825,202 and 10,418,527 have reported the general process of fabricating micro-LED displays using inorganic LEDs and fluid assembly on a display backplane, which are incorporated herein by reference. In particular, U.S. 9,825,202 describes the process flow to fabricate a suitable display screen backplane starting with 13 columns by 26 rows as shown in Figure 17 The electrical requirements are described in the unpublished patent application 16 / 727,186, which is also incorporated herein by reference. The display substrate used here has the same column and row count as in patent 9,825,202, but with a different number of rows per column, as shown in Figure 14BThe same row and column arrangement and thin film transistor (TFT) circuit as described in FIG. 14C, but without the well layer because the macro transfer stamp sets the position of the micro light emitting diode.

[0122] Figure 5 A partial cross-sectional view of a typical backplane arrangement to show surface mount micro light emitting diodes and power transistors to control the brightness of the micro light emitting diodes.

[0123] The fluid assembly techniques presented in US Patents 9,825,202, 10,418,527 and 10,543,486 (incorporated herein) are suitable for low cost micro light emitting diode display manufacturing with direct random assembly. The same assembly techniques are used here to make a transfer stamp to sequentially bind micro light emitting diodes to the electrodes of a display substrate. The advantage of this approach compared to direct fluid assembly strategies is that by using a transfer stamp during the binding process and applying pressure, it helps to form an ohmic contact between the micro light emitting diode and the display. As used herein, the transfer stamp is configured to have an array of capture sites with a pitch that matches the pitch between the display pixels. The transfer stamp can be made of glass, quartz or single crystal silicon, and the capture sites (also referred to as wells) can be made by etching the transfer stamp or by providing a layer of film, such as patterned polyimide, on the transfer stamp and patterning the wells using photolithography techniques. The capture sites have the same shape as the micro light emitting diodes and can be slightly larger, as shown in US Patent 10,804,426 Figure 8 The uniqueness of the system described herein is that the depth of the capture sites can be less than at least one point of the micro light emitting diode thickness, so the micro light emitting diodes can contact the assembly tool or the display substrate without interference from the top surface of the transfer stamp. The wells (capture sites) etched on the transfer stamp can be more robust and can be cleaned more thoroughly, but the control of the depth of the capture sites becomes more difficult. Conversely, the depth of the capture sites formed on a polyimide or a deposited film can be controlled by the thickness of the film, but it is more susceptible to damage.

[0124] The transfer stamp system described in this application is compatible with micro light emitting diodes of various configurations, but the conventional LED structure shown in Figure 2C is not suitable because it lacks a means for positioning in fluid assembly, so the electrodes cannot be correctly positioned on the display substrate for binding. The disc-shaped surface mount micro light emitting diodes described in US Patent 10,804,426 are designed as a solution within a range of constraints for fluid assembly as described in US Patent 9,825,202, such as 12 columns by 56 rows and Figure 16microLEDs are shown, so these devices are applied to describe the imprint system described in this application. It is important to understand that other microLED shapes, such as square, rectangular, and triangular devices, such as those described in U.S. Patent 9,825,202, incorporated herein by reference, can be used in the same manner. Likewise, the imprint system is not limited to surface mount microLEDs. Vertical microLEDs can also be used with this method, using a single bottom electrode, and fabricating the top electrode after assembly. These variations will be apparent to those skilled in the art, and are not described in further detail in this application for the sake of brevity. Figure 8 and U.S. Patent 10,516,084, Figure 4, incorporated herein by reference, can be used in the same manner. Likewise, the imprint system is not limited to surface mount microLEDs. Vertical microLEDs can also be used with this method, using a single bottom electrode, and fabricating the top electrode after assembly. These variations will be apparent to those skilled in the art, and are not described in further detail in this application for the sake of brevity.

[0125] Figure 6A and Figure 6B A top view and a cross-sectional view of a surface mount microLED for fluidic assembly are shown in Figures 1 and 2, respectively. The device is typically 20-100 microns (pm) in diameter and 4-6 pm in thickness, and includes a keel that is 5-10 pm in height. In this case, the well depth is typically 3.5-4.5 pm to accommodate the microLED thickness. The detailed fabrication process flow can be found in U.S. Patent 10 / 804,426, column 8, line 56, and Figure 6. The disc shape matches the cylindrical shape of the capture site, which is typically less deep than the microLED thickness, and slightly larger in diameter than the microLED. The surface mount electrodes are typically made of solder, such as tin / indium or gold / germanium, and the bonding surfaces of the P and N connection pads must be in the same plane to facilitate contact.

[0126] Figure 7 A microLED wafer after selective pick-up is shown in Figure 3. Defects are identified by optical microscopy, scanning electron microscope (SEM) images, cathodoluminescence, or photoluminescence. The goal is to identify all defects that can cause a display pixel to fail, so that the defective products can be removed from the microLED suspension used for manufacturing. By combining the defect map with known patterns such as edge bead maps and array structure, the location of all known defective microLEDs can be determined. Using a printing process, the defective microLEDs are covered with a capture material to prevent them from being picked up. As shown, the selective pick-up imprint stamping process will result in all good microLEDs being picked up and leaving the defective microLEDs behind. Combining high utilization with the prevention of defective devices from being mixed in is a significant advantage of the fluidic assembly technique. The selective pick-up method is described in more detail in the non-public application number 16,875,994, incorporated herein by reference.

[0127] After the micro-LEDs are fabricated, the growth wafer is attached to a carrier wafer via an adhesive layer, the micro-LEDs are released from the sapphire wafer by laser lift-off (LLO) and the micro-LEDs are patterned with a keel on the bottom surface.

[0128] The micro-LED suspension is dispersed on the carrier substrate and assembled as described in U.S. Patent 10,418,527 and U.S. Patent 10,804,426. For mass transfer, it is important to avoid surface contaminants from interfering with the exposed surface of the micro-LEDs and the surface of the target location. Therefore, any un-assembled micro-LEDs on the surface are removed and recycled after assembly, so an effective cleaning method is also important. Figure 7

[0129] Figure 8 A brief overview of the fluidic effect is provided, which enables 100% of the micro-LEDs to be assembled in the correct orientation with the electrodes facing down. The assembled substrate is inspected, and if some of the wells are not filled, or there are other defects such as extra un-assembled micro-LEDs, the micro-LEDs are removed using a solvent cleaned stamp and the solvent is captured in a reservoir to recycle the micro-LEDs. The empty stamp is further cleaned, dried and inspected to ensure that there are no surface contaminants or residue on the capture locations. This capability is important for traditional stamps that use elastomers or adhesives to secure the micro-LEDs, as they are difficult to clean and re-use. With traditional techniques, stamps with contaminants or missing micro-LEDs are typically discarded, resulting in the loss of intact micro-LEDs on the stamp.

[0130] Figures 9A-9D The steps for using a micro-LED mass transfer stamping system are described. The system includes a stamp substrate 900 having a top surface 902. The top surface 902 has an array of stamp capture locations 904 formed thereon. Each capture location 904 is configured as a columnar recess to temporarily secure a keel 906 extending from a bottom surface 908 of a micro-LED 910. As shown, the micro-LEDs 910 are surface mount micro-LEDs, each including a planar top surface 912 having a first electrode 914 and a second electrode 916 disposed thereon. In this case, the keel 906 is not electrically conductive. In this particular example, as shown in FIG. 1, the second electrode is a full or partial ring around the first electrode. For other examples, the second electrode can be a full or partial ring around the first electrode, as shown in FIG. 2, or a full or partial ring around the perimeter of the micro-LED, as shown in FIG. 3. Figure 6A Figures 9A-9D Figures 11A-11D ​​​(See below) The system can use adhesive or elastomer to pattern the top surface 902 of the imprint substrate to cause the micro light-emitting diode to attach to a capture location.

[0131] The filled carrier substrate 1000 forms the basis for mass transfer to the display substrate 918 using an imprinting stamp substrate 900, illustrated in the figure as a single micro-LED. Although not explicitly shown in the figure, it is evident that the electrode pads of the display substrate are connected to a network of rows and columns to enable the micro-LEDs to operate; for details, please refer to U.S. Patent 9,825,202. In this case, the carrier substrate 1000 is a planar surface substrate with a well, allowing a localized protrusion (optionally adhesive or elastomer) near the imprinting stamp head capture position 904 to contact each micro-LED (e.g., ...). Figure 9B (As shown). Since micro LEDs are typically held in place by gravity alone, the relatively weak adhesion allows them to be removed from the carrier during transfer using optional adhesives or elastomers. An imprinting stamp is aligned with the electrodes on the display substrate and pressed together to create a hard contact between the electrodes of the micro LED and the electrodes on the display substrate, while solder bonding is formed through heating (as shown). Figure 9C In another embodiment, the connection can be made by an additional ACF film (not shown). Once bonding is complete, the transfer imprint stamp is retrieved and detached from the micro LED. Figure 9D The transfer head 900 and the carrier substrate 1000 are cleaned for reuse and cyclically operated to fill the entire area of ​​the display substrate 918.

[0132] Figures 10A-10D This is a cross-sectional view illustrating the process of transferring micro-light-emitting diodes (LEDs) from a carrier substrate to a display substrate. The system includes fluid assembly carrier substrates 1000a-1000c, each having a planar top surface 1002 and an array of wells 1004 arranged on the top surface 1002. Adjacent wells are spaced 1006, which matches the spacing between adjacent capture positions on an imprinting substrate. The wells 1004 of the carrier substrate have a first peripheral shape (circular in this embodiment) and a planar bottom surface 1008. Surface-mount micro-light-emitting diodes 910a-910c each have the first peripheral shape and a planar top surface 912, thereby contacting the bottom surface 1008 of the well via a first electrode 914 and a second electrode 916 (e.g., ...). Figure 9A (As shown).

[0133] In the case of RGB display, the imprinting system may further include a first fluid assembly carrier substrate 1000a, and an array of wells distributed on the top surface of the carrier substrate, with a spacing 1006 between adjacent wells to match the capture position of the imprinting stamp substrate.Figure 10B ). Micro light emitting diodes 910a are configured to emit light of a first wavelength, each micro light emitting diode occupying a respective well in the first carrier substrate 1000a. Similarly, the second fluidic assembly carrier substrate 1000b includes an array of wells disposed on the top surface of the carrier substrate with a pitch 1006 between adjacent wells to match the capture locations of the stamping stamp substrate. Micro light emitting diodes 910b are configured to emit light of a second wavelength, each micro light emitting diode occupying a respective well in the second carrier substrate 1000b. The third fluidic assembly carrier substrate 1000c includes an array of wells disposed on the top surface of the carrier substrate with a pitch 1006 between adjacent wells to match the capture locations of the stamping stamp substrate. Micro light emitting diodes 910c are configured to emit light of a third wavelength, each micro light emitting diode occupying a respective well in the third carrier substrate 1000c.

[0134] To manufacture the three colors needed for an RGB display, the three colors of micro light emitting diodes need to be assembled and stamped sequentially, as shown in Figures 10A-10D . The design of the array of capture locations on the three carrier substrates is spaced according to the pitch 1006 of the display pixels. It is likely that the process flow for the different colors of micro light emitting diodes or the performance gap of the LEDs determines that the different colors of micro light emitting diodes have different sizes and / or shapes. For example, red micro light emitting diodes can be made of aluminum indium gallium phosphide (AlInGaP), as described in U.S. Patent 10,804,426, in which case the red micro light emitting diodes can be thicker than the blue and green devices based on GaN. Since the blue and green micro light emitting diodes have different quantum efficiencies, and the human visual system is more sensitive to green, it can be desirable to manufacture the blue and green micro light emitting diodes with different emission areas. Examples of these differences are shown in Figure 10A , each carrier substrate is adjusted to meet the needs of the corresponding color of micro light emitting diodes. The stamping stamp substrate 900a captures an array of blue micro light emitting diodes 910a from the carrier substrate and is moved to the display substrate 918 so that the stamping stamp 900a is aligned with the vacant areas on the display substrate and the electrodes of the micro light emitting diodes are in physical contact with the matching electrodes on the display substrate Figure 10B . Pressure and heating devices 1010 are used to enhance the tight contact between the electrodes, causing the metal material to melt and form a solder bond. In Figure 10C and Figure 10DIn this case, green micro-LEDs 910b and red micro-LEDs 910c are transferred and bonded (stamps 900b, 900c) in the same manner. The bonding between the micro-LEDs and the connection pads can use materials such as gold / germanium to copper, indium / zinc to copper, and gold / ACF / copper. If ACF is used, the material of the display electrodes can have a wider selection, such as Mo / Al / Mo.

[0135] The fluidic assembly used in this application makes several improvements on the simple stamping process of the prior art:

[0136] 1) No gaps in the array pattern due to defective or missing micro-LEDs;

[0137] 2) Selective picking and fluidic assembly take full advantage of all the good micro-LEDs on a wafer;

[0138] 3) Recycling micro-LEDs from the assembly process and defective carrier substrates can prevent waste;

[0139] 4) Carrier substrates are made according to the distance of the capture location pieces on the display, and the expansion of the pitch can be easily completed.

[0140] Figures 11A-11D A stamping system is described in which the micro-LEDs are vertical micro-LEDs, each vertical micro-LED 1100 having a planar top surface 1102 with a first electrode 1104, and a conductive keel 906 as a second electrode. Like the surface mount micro-LEDs, the wells 1004 of the carrier substrate have a first perimeter shape (e.g., circular) and a planar well bottom surface 1008. Each vertical micro-LED 1100 has a first perimeter shape and a planar top surface 1102, which is in contact with the corresponding well bottom surface 1008 via the first electrode 1104.

[0141] For smaller micro-LEDs, there is not enough space to make two electrodes on the same surface as in the surface mount micro-LEDs, the same assembly process can also be applied to vertical micro-LEDs. In this case, the micro-LEDs are arranged with a single anode electrode on the top surface, and a cathode electrode on the bottom surface as a conductive post (keel) or electroplated gold or copper on the bottom surface. The conductive post can also serve as a keel when fluidically assembling on the carrier board (substrate).

[0142] The assembly and bonding sequence of a conductive keel vertical micro-LED is shown. The micro-LED suspension is prepared by the selective acquisition method described above and dispensed onto the surface of a carrier substrate provided with wells having a display pitch, then assembled in a conventional flow. The stamp is aligned with the carrier substrate and the micro-LEDs are removed from the carrier substrate as shown in Figure 11A The filled stamp is aligned with the display substrate and mechanical contact is made between the cathode electrode on the micro-LED and the P-connection pad electrode on the display substrate by applying pressure as shown in Figure 11B A heating device 1010 is used to form the solder bond, then the stamp is removed and cleaned and reused. An insulating layer 1106, such as polyimide, is used to fill the gap between the micro-LED and the reflective well to prevent shorting and to planarize the surface for metal deposition as shown in Figure 11C The keel protrudes from the insulating layer 1106, forming a self-aligned contact to each micro-LED. A portion of the insulating layer can be removed by a short O2 plasma etch to improve the contact. The conductive pillars of the micro-LED are connected to Vss (power supply) by a patterned metal as shown in Figure 11D

[0143] Figure 12A and Figure 12B are partial cross-sectional views of force generators used to assist in securing micro-LEDs to the capture sites of a carrier substrate. In Figure 12A is the use of an electrostatic force generator 1200, Figure 12B is the use of a magnetic force generator 1202. Although surface mount micro-LEDs are shown, the force generators described above can also be applied to vertical micro-LEDs.

[0144] Figures 13A-13K The steps of a micro-LED mass transfer stamping system using fluidic assembly to assemble the stamp substrate are described. To further simplify the assembly process, the stamp can be filled directly using fluidic assembly, thus eliminating the carrier substrate. The micro-LEDs shown in Figure 6 use a keel structure on the bottom surface, hereafter referred to as a securing mechanism, to secure the micro-LEDs to the electrodes of the fluidic assembly capture sites. For the direct assembly process, the electrode sites must be “up” in the stamp, so the keel structure is fabricated on the top surface of the micro-LED as shown in Figure 13A Fluidic assembly is performed in the conventional manner, assembling the micro-LEDs in an array in the capture sites with the keel structure and electrodes both up. The material used to fabricate the keel structure is typically a photo-sensitive polyimide, which can be removed using a solvent or etched using an oxygen plasma. After assembly and drying, the keel is removed as shown in Figure 13B ​As shown), this facilitates the bonding of electrodes to the display substrate. The fabrication method of the imprinting stamp is the same as in the aforementioned embodiment, but the trap structure must not be affected by the removal of the keel; therefore, organic thin films cannot be used. A preferred solution is to directly etch the substrate to form the trapping position structure. Under the influence of gravity and van der Waals forces, the imprinting stamp can accommodate miniature light-emitting diodes. If the imprinting stamp is inverted, the miniature light-emitting diodes will fall out of the imprinting stamp. Therefore, during heating, the surface of the imprinting stamp needs to be facing upwards for transfer assembly and bonding, and the display substrate needs to be pressed down onto the imprinting stamp. Figure 13C ).

[0145] The fluid-assembled embossing stamp substrate 1300 has a planar top surface 1302. An array of trapping positions 1304 are formed on the top surface 1302 of the embossing stamp substrate. Each trapping position has a first peripheral shape, a depth 1306, and a planar trapping position bottom surface 1308. As in the aforementioned embodiment, the first peripheral shape is circular, but the system is not limited to this shape. A micro-light-emitting diode 910 is disposed in the trapping position 1304, having a first peripheral shape, a thickness 1310 greater than the trapping position depth 1306, a planar bottom surface 1312 contacting the bottom surface 1308, a planar top surface 1314 having a first electrode 1316 extending out of the trapping position, and a protective mechanism (see explanation below). The micro-light-emitting diode has the same electrical connection as the vertical micro-light-emitting diode 1100, which has a second electrode formed on the bottom surface 1312 (e.g., ...). Figure 13D (As shown) or has the same electrical connection as a surface-mount micro LED 910, the surface-mount micro LED 910 having a first electrode 1316 and a second electrode 1324 formed on the surface 1314 (see figure) Figure 13A and Figure 13E ).

[0146] like Figure 13A As shown, the fixing mechanism is a keel 906 formed on the top surface of the micro-LED. The keel 906 is a temporary, non-conductive keel, and it is removed before the micro-LED contacts the display substrate 1315. Alternatively, as... Figure 13D and Figure 13E As shown, the fixing mechanism can be a conductive keel 906 connected to the first electrode 1316. Figure 13D In this example, the miniature light-emitting diode is a vertical miniature light-emitting diode 1100.

[0147] In another embodiment, a conductive center post is used instead of a non-conductive keel during the direct imprint transfer process, so that the structure can serve as both the keel in the fluid assembly process and as the anode electrode. Figure 13E). In this case, the stamp is a simple disk with an array of capture sites, with the same pitch as the display pixels. In the display substrate 1318, the P-connection pad electrodes are below the N-connection pad electrodes, leaving room for the conductive posts that form the anode electrode on the micro-LEDs Figure 13F Due to process variations, the height of the conductive posts and the depth of the P-connection pad recesses can vary. This can be compensated by using an ACF 1325 to connect the micro-LEDs to the display substrate.

[0148] Thus, Figure 13E The micro-LEDs in FIG. 10a are surface-mounted micro-LEDs 910a, while Figure 13F The display substrate 1318 in FIG. 13 includes recesses 1320 for receiving the conductive keel 906.

[0149] Another mechanism for positioning and securing micro-LEDs in the transfer stamp is to use preferential binding between conjugate pairs of biomolecules, such as the pair of streptavidin and biotin. As shown in FIG. 13, after LLO, the micro-LEDs are functionalized by depositing a thin layer of silicon dioxide 1326 on the back surface of the device 1312. The surface of the micro-LEDs is exposed to a hydrogen ion or a basic compound, and then reacted with an amine-terminated molecule such as 3-aminepropyl-trimethoxysilane to silanize. The surface is cleaned with a streptavidin solution to bind streptavidin molecules 1327 to the amine termini, resulting in a streptavidin-functionalized micro-LED (as shown in FIG. 13). Before assembly, the capture sites on the transfer stamp can be similarly treated with biotin-terminated ligands, or the bottom surface of the well can be a gold surface and exposed to thiol-biotin bifunctional molecules 1322, as shown in FIG. 13. Figure 13H Figure 13I

[0150] Thus, Figures 13G-13K A micro-LED using conjugate pairs of biomolecules as a "securing mechanism" is described. In this case, the stamp substrate bottom surface 1308 is coated with a first component 1322 containing a conjugate pair of biomolecules. The micro-LED securing mechanism is a second component 1327 containing a conjugate pair of biomolecules coated on the bottom surface 1312 of each micro-LED. During assembly, the relatively low capture site depth (about 1 μm) can more easily remove misoriented micro-LEDs by fluid disturbance, while correctly oriented micro-LEDs can be chemically bound to the bottom surface of the capture site and better labeled by being constrained in the capture site. Figure 13J ​​In some embodiments, the biological conjugate bond is shown with an exaggerated z scale to illustrate the binding effect. In reality, the binding layer is very thin, and the Figure 13K more accurate representation in FIG. 1 1. Alternative chemical pairs for the biotin-streptavidin system, such as thiol-maleimide and azide-alkyne, can have advantages in stability and ease of processing, but the sequence of preparation is similar.

[0151] Figure 14A and Figure 14B FIGS. 1 1 and 12 respectively describe the use of electrostatic force generators 1400 and magnetic force generators 1402 as auxiliary mechanisms for assisting in the securing of micro-LEDs in fluidic assembly capture locations (with or without keels). In Figure 14A and Figure 14B the primary securing mechanism can be gravity. Additionally, in Figure 14A the securing mechanism is a conjugate biological molecule (not shown). In other embodiments (not shown), Figure 14A the force generator in Figure 14B can also be a magnetic force generator, Figure 14A and Figure 14B only fluidic assembly stamp substrates are shown, but it should be understood that force generators can also be used for stamp substrates with groove configurations in Figures 9B-9D and Figures 11A-11B .

[0152] As a cost of added complexity, some securing structures can be added to the stamp structure to prevent micro-LEDs from dislodging from the capture locations when the stamp is inverted. Since the securing mechanism can be removed from the micro-LED after binding, the use of adhesives for binding is not attractive. Vacuum conditions can be introduced into the stamping system by placing a porous layer between the substrate bearing surface and the capture location forming layer, but fluidic assembly liquids can flow into the porous layer, preventing the drying operation. The most practical structures for securing micro-LEDs in a stamp are magnetic or electrostatic. For electrostatic securing, the micro-LED has a dielectric film deposited on the surface corresponding to the surface mount electrode (i.e., the bottom surface), and the stamp includes a power electrode beneath the capture location structure. For magnetic securing, the micro-LED electrode structure can contain a magnetic material, such as nickel, and the stamp has a permanent magnet or electromagnet.

[0153] These securing mechanisms are independently controllable on a point-by-point basis in the array, so a procedure can be used to repair stamps with defective micro-LEDs as follows:

[0154] 1) Inspect the stamp for micro-LEDs with defects;

[0155] 2) Fixing mechanism for all good micro-LEDs is activated;

[0156] 3) Defective micro-LEDs are removed by rinsing;

[0157] 4) Additional micro-LED suspension is placed and assembly proceeds.

[0158] In one aspect, the stamp can include a light sensor that activates all the capture sites temporarily electrically connected to the micro-LEDs on the stamp (simultaneously or sequentially) when pressed onto the display substrate. The stamp and associated drive circuitry are connected to a system that records which micro-LEDs are good. The fixing mechanism on the stamp is activated to hold the good micro-LEDs in the capture sites and assembly proceeds until all micro-LEDs are tested good, as shown in the above flowchart 2)-4). The binding process then proceeds.

[0159] Figures 15A-15I A micro-LED mass transfer stamping system is described that uses a fluid stamp substrate and axial micro-LEDs. The hybrid fluidic assembly mass transfer method can also be applied to the axial micro-LEDs described in application No. 16 / 846,493. To reduce cost and increase density, the micro-LEDs are configured as vertical devices with a 5*8 pm light emitting area, as shown in Figure 15G The blade-shaped micro-LED electrodes can be plated copper or gold. The dimensions of all the above features are adjustable, but the relative shapes are important to facilitate fluidic assembly into an oriented array.

[0160] Figures 15A-15C The fabrication of an axial micro-LED display substrate 1525 is described. Electrodes 1528 are deposited and patterned from a conductive material, such as molybdenum / copper (Mo / Cu), to form connection pads for the cathode and anode of the micro-LEDs. A dielectric film 1530 is deposited over the electrodes, which can be silicon dioxide, silicon nitride (Si3N4), or polyimide, and contact openings are patterned and etched into the dielectric film 1530, as shown in Figure 15B A body recess 1532 is etched to accommodate the body of the micro-LED using the metal electrodes as a hard mask, as shown in Figure 15B Finally, N and P connection pads 1536 and 1534 are formed by plating, sputtering, or evaporation, as shown in Figure 15C

[0161] For the shape of the axial micro-LEDs, the fabrication of the stamp is more complex, requiring two different depths of capture sites. As shown in Figure 15D ​As shown, a first recess 1538 is etched into the substrate, the first recess 1538 having a depth and profile for receiving a micro-LED body protruding below the surface of the axial electrode. Figure 15E In some embodiments, a second recess 1504 is formed by etching to receive the axial electrode. The second recess can also be formed from a thin film material (e.g., photoresist polyimide) after the first recess 1538 is formed.

[0162] A known good suspension of axial micro-LEDs is applied to the stamp and assembled into an array of micro-LEDs (as shown in Figure 15F The assembled stamp is inspected and pressed together with a display substrate after matching the electrodes of the LED to the electrodes on the display substrate (as shown in Figure 15I After binding, the stamp is retracted and cleaned and inspected for reuse.

[0163] Thus, the system includes a fluidic assembly stamp substrate 1500 having a planar top surface 1502. An array of capture sites 1504 formed in the top surface 1502 of the stamp substrate includes a first perimeter shape (a substantially rectangular shape), a central portion 1506 having a first depth 1508 that is planar, a distal end 1510 having a second depth 1512 that is planar, the second depth 1512 being less than the first depth 1508, and a proximal end 1514 having a second depth 1512 that is planar.

[0164] Referring also to Figure 15F and 15G an axial micro-LED 1516 occupying a corresponding capture site 1504 and having the first perimeter shape, a body 1518 in contact with the central portion 1506 of the capture site, a vertical planar portion thickness 1520 that is greater than the first depth 1508 of the capture site but less than twice the first depth 1508 of the capture site, a distal electrode 1522 horizontally bisecting the body 1518 and in contact with the distal end 1510 of the capture site, the distal electrode 1522 having a vertical electrode thickness 1524 that is greater than the second depth 1512 of the capture site but less than twice the second depth 1512 of the capture site, and a proximal electrode 1526 horizontally bisecting the body 1518 and in contact with the proximal end 1514 of the capture site, the proximal electrode 1526 having the electrode thickness 1524.

[0165] As shown in Figure 15I the process of transferring the micro-LED to a display substrate is similar to Figure 13CThe process is similar, the aligned display substrate is pressed down onto the fluidic assembly stamping substrate, causing the electrodes of the micro light emitting diodes to contact the corresponding electrodes on the display substrate. The transfer and bonding is accomplished by heating the solder while pressure is applied. Optionally, an ACF film (not shown) can be inserted between the corresponding electrodes to enable electrical and mechanical connection without the need for a metal phase change.

[0166] Although not explicitly shown, the stamping substrate of the present embodiment can include an electrostatic or magnetic force generator as shown in Figure 14A and Figure 14B

[0167] Figure 16 is a flow chart depicting a micro light emitting diode mass transfer method corresponding to the system shown in Figures 9A-9D . Although for ease of understanding the method is described as comprising a series of steps with numbers, the numbers do not necessarily indicate the order of the steps. It is to be understood that some steps can be skipped, performed simultaneously or can not need to be performed in strict order. However, the method can generally be performed in the order of the numbers. The method begins at step 1600.

[0168] Step 1602 provides a stamping substrate having a planar top surface and an array of capture sites formed on the top surface, each capture site configured as a columnar recess. In one aspect, step 1603a patterns the top surface of the stamping substrate with an adhesive material or elastomer. In step 1604, each capture site is recessed to accommodate a keel extending from a bottom surface of a micro light emitting diode and in step 1606, the micro light emitting diode is secured to the stamping substrate by constraining the keel of each micro light emitting diode. Step 1606 can use additional electrostatic or magnetic forces to secure the micro light emitting diode to the stamping substrate.

[0169] In one aspect, constraining the keel in step 1604 includes constraining a surface mount LED having a non-conductive keel, including a planar surface having a first electrode and a second electrode. In another aspect, step 1604 constrains a conductive keel and connects to the second electrode, the vertical LED including a planar surface having a first electrode (i.e. the keel is the second electrode).

[0170] ​In one aspect, step 1602 provides a stamp substrate having spaced capture locations. Step 1601a provides a fluidic assembly carrier substrate having a planar top surface and a plurality of wells arranged in an array on the top surface of the carrier substrate, the spacing between adjacent wells matching the spacing between adjacent capture locations on the stamp substrate. In step 1601b, micro light emitting diodes are filled into the wells of the carrier substrate by a fluidic assembly process. In one aspect, step 1601b can use electrostatic forces or magnetic forces to secure the micro light emitting diodes into the wells. Step 1603b presses the top surface of the stamp substrate against the top surface of the carrier substrate, each capture location in contact with a corresponding well, and step 1603c mass transfers the micro light emitting diodes from the carrier substrate to the stamp substrate.

[0171] In particular, step 1601a can provide a carrier substrate having a plurality of wells including a first perimeter shape and a planar well floor. Then, in step 1601b, micro light emitting diodes are filled into each well, wherein the surface mount micro light emitting diode filled into the well has the first perimeter shape, a planar top surface in contact with the well floor, and including a first electrode and a second electrode. In other embodiments, step 1601b fills into the well a vertical micro light emitting diode having the first perimeter shape, a planar top surface in contact with the well floor, and including a first electrode.

[0172] In the case of an RGB display, the carrier substrate provided in step 1601a includes:

[0173] a first fluidic assembly carrier substrate including an array of wells disposed on a top surface of the carrier substrate, the distance between adjacent wells matching the spacing between adjacent capture locations on the stamp substrate;

[0174] a second fluidic assembly carrier substrate including an array of wells disposed on a top surface of the carrier substrate, the distance between adjacent wells matching the spacing between adjacent capture locations on the stamp substrate;

[0175] a third fluidic assembly carrier substrate including an array of wells disposed on a top surface of the carrier substrate, the distance between adjacent wells matching the spacing between adjacent capture locations on the stamp substrate. Then, the process of filling the wells of the carrier substrate in step 1601b includes:

[0176] filling the wells on the first carrier substrate with first micro light emitting diodes configured to emit a first wavelength of light;

[0177] filling the wells on the second carrier substrate with second micro light emitting diodes configured to emit a second wavelength of light; and

[0178] A third micro light emitting diode is used to fill a third well on a third carrier substrate, which is configured to emit light of a third wavelength. The transferring of the micro light emitting diodes from the carrier substrates to the stamp substrate in step 1603c includes transferring the micro light emitting diodes from the first, second, and third carrier substrates to the corresponding stamp substrates. As shown in FIGS. 16A and 16B, the micro light emitting diodes are transferred from the carrier substrates to the stamp substrates in a manner that the micro light emitting diodes are aligned with the corresponding wells on the stamp substrates. Figure 10A and Figure 10B As shown in FIGS. 16A and 16B, different sizes of the carrier substrates are necessary for the RGB micro light emitting diodes with different shapes. In addition, if the diameters of the RGB micro light emitting diodes are equal, one carrier substrate can be used to fill the micro light emitting diodes of different wavelengths and to transfer them to the stamp substrates, respectively.

[0179] Step 1608 provides a display substrate having a planar top surface and an array of micro light emitting diode connection pads, each of which includes at least one electrode formed on the top surface and electrically connected to a matrix of underlying column and row control lines. The display substrate has a pitch between adjacent connection pads that matches a pitch between adjacent capture locations on the top surface of the stamp substrate, which is the same as a pitch between adjacent wells on the carrier substrate. In step 1610, the top surface of the stamp substrate is pressed against the top surface of the display substrate, with each capture location in contact with a corresponding micro light emitting diode connection pad. In step 1612, the micro light emitting diodes are mass transferred from the stamp substrate to the micro light emitting diode connection pads on the display substrate. In one aspect, the micro light emitting diodes are bonded to the micro light emitting diode connection pads by heating the display substrate in step 1612.

[0180] In the case of an RGB display, the display substrate in step 1608 includes a plurality of connection pads for the first micro light emitting diodes for emitting light of the first wavelength, a plurality of connection pads for the second micro light emitting diodes for emitting light of the second wavelength, and a plurality of connection pads for the third micro light emitting diodes for emitting light of the third wavelength. The pressing of the top surface of the stamp substrate against the top surface of the display substrate in step 1610 includes pressing the stamp substrates filled with the first, second, and third micro light emitting diodes, respectively. The micro light emitting diodes of each wavelength can use a stamp substrate, or if the shapes of all the micro light emitting diodes are similar, the same substrate can be used to fill the micro light emitting diodes of different wavelengths and to transfer them to the display substrate.

[0181] Figure 17 For Figures 13A-13KA flow chart of a micro light emitting diode mass transfer method using a fluidic assembly imprint stamp substrate is shown. The method starts at step 1700. A fluidic assembly imprint stamp substrate having a planar top surface with capture sites disposed thereon is provided in step 1702. The capture sites have a first perimeter shape, a depth, and a planar capture site bottom surface. In a fluidic assembly process, micro light emitting diodes filled into the capture sites in step 1704 have a first perimeter shape, a thickness greater than the depth of the capture sites, a planar bottom surface in contact with the capture site bottom surface, and a planar top surface with a first electrode extending out of the capture site. The micro light emitting diodes also include a securing mechanism. Micro light emitting diodes with a second electrode on the bottom surface can be used in step 1704, or surface mount micro light emitting diodes with a first electrode and a second electrode on the top surface can be used to fill into the capture sites.

[0182] In one aspect, the providing of the imprint stamp substrate in step 1702 includes providing an imprint stamp substrate having spaced capture sites. The display substrate provided in step 1706 has a planar bottom surface and an array of micro light emitting diode connection pads disposed thereon. Each micro light emitting diode connection pad includes a first electrode formed on a top surface and is electrically connected to a matrix of underlying column and row control lines. The pitch between adjacent connection pad sites on the display substrate is matched to the pitch between adjacent capture sites on the imprint stamp substrate. In step 1708, the top surface of the imprint stamp substrate is pressed onto the top surface of the display substrate so that each capture site is in contact with a micro light emitting diode connection pad. The micro light emitting diodes on the imprint stamp substrate are mass transferred to the micro light emitting diode connection pads on the display substrate in step 1710. Step 1710 can include using heat to facilitate the bonding of the micro light emitting diodes to the connection pads on the display substrate.

[0183] In one aspect, the providing of the micro light emitting diodes in step 1704 includes forming a keel-shaped securing mechanism on the top surface of the micro light emitting diodes. The keel can be a conductive keel connected to the first electrode (e.g. Figure 13D and Figure 13E ) or a temporary (removable) non-conductive keel (e.g. Figure 13A ). In another aspect, the imprint stamp substrate provided in step 1702 has the bottom surface of each capture site coated with a first component of a conjugate biomolecular pair. The securing mechanism mentioned in step 1704 is then a second component of the conjugate biomolecular pair that coats the bottom surface of each micro light emitting diode. Examples of conjugate biomolecular pairs include biotin-streptavidin, thiol-maleimide, and azide-alkyne. The imprint stamp substrate can also be further provided with an electrostatic or magnetic force generator as shown in Figure 14A and Figure 14B .

[0184] Figure 18 ForFigures 15A-15I A flowchart of an axial micro-LED mass transfer method of the system shown. The method begins at step 1800. Step 1802 provides a fluidic assembly stamp substrate having a planar top surface with a plurality of capture sites formed thereon, each capture site having a first perimeter shape, a central portion having a planar first depth, a distal end having a planar second depth less than the first depth, and a proximal end having the second depth. Under fluidic assembly, step 1804 populates the capture sites with axial micro-LEDs, each micro-LED occupying a respective capture site and having the first perimeter shape and a body portion conforming to the central portion, the body portion having a vertical body thickness greater than the first depth but less than twice the first depth. The micro-LED also has a distal electrode horizontally bisecting the body portion, the distal electrode conforming to the distal portion of the capture site, the distal electrode having a vertical electrode thickness greater than the second depth but less than twice the second depth. The micro-LED also has a proximal electrode horizontally bisecting the body portion, the proximal electrode conforming to the proximal portion of the capture site, and having an electrode thickness. In one aspect, the stamp electrodes can also include electrostatic or magnetic force generators, as shown in Figure 14A and Figure 14B as shown.

[0185] In one aspect, the providing of the stamp substrate in step 1802 includes providing a stamp substrate having capture sites with a pitch. In step 1806, a display substrate is provided having a planar top surface and an array of micro-LED connection pads, each micro-LED connection pad including first and second electrodes formed on the top surface, the plurality of electrodes electrically connected to a matrix of underlying column and row control lines. The display substrate includes a plurality of connection pads spaced apart by a pitch that matches the pitch by which the capture sites on the stamp substrate are spaced apart. In step 1808, the top surface of the stamp substrate is pressed onto the top surface of the display substrate so that each capture site is aligned with a micro-LED connection pad. In step 1810, the micro-LEDs are mass transferred from the stamp substrate to the micro-LED connection pads on the display substrate. Optionally, the bonding between the micro-LEDs and the display substrate connection pad electrodes can be facilitated by heating.

[0186] Figure 19A flow chart of a method for pitch expansion of micro-LED transfer. The method starts at step 1900. Step 1902 provides a micro-LED MOCVD wafer having a first pitch between adjacent micro-LEDs. Step 1904 releases the micro-LEDs into a fluid assembly suspension. Step 1906 provides a carrier substrate having an array of wells arranged with a second pitch between adjacent wells, and the second pitch is different from the first pitch. The micro-LEDs are filled into the wells of the carrier substrate by a fluid assembly process in step 1908. Step 1910 provides a stamp pad substrate including an array of capture sites, adjacent capture sites are spaced apart by the second pitch. In step 1912, a top surface of the stamp pad substrate is pressed against a top surface of the carrier substrate so that each capture site is in contact with a corresponding well. In step 1914, the micro-LEDs are massively transferred from the carrier substrate to the stamp pad substrate.

[0187] Step 1916 provides a display substrate having an array of micro-LED connection pads, each micro-LED connection pad includes at least one electrode formed on a top surface and electrically connected to a matrix of underlying column and row control lines. Adjacent connection pad sites on the display substrate are spaced apart by the second pitch. In step 1918, a top surface of the stamp pad substrate is pressed against a top surface of the display substrate so that a capture site is in contact with a corresponding micro-LED connection pad. In step 1920, the micro-LEDs are massively transferred from the stamp pad substrate to the micro-LED connection pads of the display substrate. Optionally, the micro-LEDs are encouraged to form bonds with the electrodes of the display substrate connection pads by heating.

[0188] In one aspect, steps 1906, 1908, 1912 and 1914 are bypassed, and the micro-LEDs are filled directly into the capture sites of the stamp pad substrate using a fluid assembly process in an additional step 1911.

[0189] The present application provides systems and methods for micro-LED massive transfer. Examples of specific LED, carrier substrate and stamp pad substrate structures are given to illustrate the present application. However, the present application is not limited to the above examples. Other variants and embodiments of the present application can be conceived by those skilled in the art.

Claims

1. A micro light emitting diode mass transfer imprint system, characterized in that, comprising: a stamp substrate having a top surface; and forming an array of capture sites on the top surface of the stamp substrate, each capture site configured as a columnar recess to temporarily secure a keel extending from a bottom surface of a micro light emitting diode; the array of capture sites of the stamp substrate having a pitch separating adjacent capture sites; the micro light emitting diode mass transfer stamping system further comprising: a fluid assembly carrier substrate comprising: a planar top surface; and an array of wells formed on the top surface of the fluid assembly carrier substrate having a pitch separating adjacent wells matching the pitch separating the capture sites of the stamp substrate; 2. The micro light emitting diode mass transfer imprint system of claim 1, wherein, the micro light emitting diodes are surface mount micro light emitting diodes each comprising a planar top surface having a first electrode and a second electrode; and the keels are non-conductive.

3. The micro light emitting diode mass transfer imprint system of claim 1, wherein, the micro light emitting diodes are vertical micro light emitting diodes each comprising a planar top surface having a first electrode; and the keels are conductive second electrodes.

4. The micro light emitting diode mass transfer stamping system of claim 1, wherein: the wells of the fluid assembly carrier substrate have a first perimeter shape and a planar well bottom surface; and the micro light emitting diodes are surface mount micro light emitting diodes each having the first perimeter shape and a planar top surface having a first electrode and a second electrode for contact with a corresponding well bottom surface.

5. The micro light emitting diode mass transfer stamping system of claim 1, wherein: the wells of the fluid assembly carrier substrate have a first perimeter shape and a planar well bottom surface; and the micro light emitting diodes are vertical micro light emitting diodes each having the first perimeter shape and a planar top surface having a first electrode for contact with a corresponding well bottom surface.

6. The micro light emitting diode mass transfer imprint system of claim 1, wherein, further comprising: a first fluid assembly carrier substrate having a first array of wells formed on a top surface of the first fluid assembly carrier substrate, the first array of wells having a pitch separating adjacent wells matching the pitch separating the capture sites of the stamp substrate; a second fluid assembly carrier substrate having a second array of wells formed on a top surface of the second fluid assembly carrier substrate, the second array of wells having a pitch separating adjacent wells matching the pitch separating the capture sites of the stamp substrate; a third fluid assembly carrier substrate having a third array of wells formed on a top surface of the third fluid assembly carrier substrate, the third array of wells having a pitch separating adjacent wells matching the pitch separating the capture sites of the stamp substrate; a plurality of micro light emitting diodes configured to emit a first wavelength of light each occupying a corresponding well in the first fluid assembly carrier substrate; a plurality of micro light emitting diodes configured to emit a second wavelength of light each occupying a corresponding well in the second fluid assembly carrier substrate; and a plurality of micro light emitting diodes configured to emit a third wavelength of light each occupying a corresponding well in the third fluid assembly carrier substrate. a plurality of micro light emitting diodes configured to emit light of a third wavelength, each occupying a corresponding well in the third fluid assembly carrier substrate.

7. The micro light emitting diode mass transfer imprint system of claim 1, wherein, The top surface of the embossing stamp substrate has a patterned material selected from the group of materials consisting of adhesives and elastomers.

8. The micro light emitting diode mass transfer imprint system of claim 1, wherein, Also included is: An attractive force generator located beneath the embossing stamp substrate, the attractive force generator selected from the group consisting of electrostatic force generators and magnetic force generators.

9. The micro light emitting diode mass transfer imprint system of claim 1, wherein, Also included is: An attractive force generator located beneath the well of the fluid assembly carrier substrate, the attractive force generator selected from the group consisting of electrostatic force generators and magnetic force generators.

10. A micro light emitting diode mass transfer imprint system, comprising: Included is: A fluid assembly embossing stamp substrate having a planar top surface; An array of capture sites formed on the top surface of the fluid assembly embossing stamp substrate, the capture sites having a first perimeter shape, a depth, and a planar capture site bottom surface; And Each of the capture sites is configured to be occupied by a corresponding micro light emitting diode having the first perimeter shape, a thickness greater than the depth of the capture site, a planar bottom surface for contact with the capture site bottom surface, a planar top surface having a first electrode for extending from the capture site, and a securing mechanism.

11. The micro light emitting diode mass transfer imprint system of claim 10, wherein, The securing mechanism is a keel formed on the top surface of the micro light emitting diode, the keel selected from the group consisting of a conductive keel connected to the first electrode and a non-conductive temporary keel.

12. The micro light emitting diode mass transfer imprint system of claim 10, wherein, The capture site bottom surface of the fluid assembly embossing stamp substrate is coated with a first component comprising a pair of conjugated biomolecules; Wherein the securing mechanism is a second component comprising a second component of the pair of conjugated biomolecules coating the bottom surface of each micro light emitting diode.

13. The micro light emitting diode mass transfer imprint system of claim 12, wherein, The conjugated biomolecules are selected from the group consisting of biotin-streptavidin, thiol-maleimide, and azide-alkyne.

14. The micro light emitting diode mass transfer imprint system of claim 10, wherein, The micro light emitting diode has an electrical interface selected from the group consisting of a vertical micro light emitting diode having a second electrode formed on the bottom surface and a surface mount micro light emitting diode having first and second electrodes formed on the top surface.

15. A micro light emitting diode mass transfer imprint system, comprising: Included is: A fluid assembly embossing stamp substrate having a planar top surface; And An array of capture sites formed on the top surface of the fluid assembly embossing stamp substrate, each capture site having a first perimeter shape, a central portion having a planar first depth, a distal end having a planar second depth less than the first depth, and a proximal end having the planar second depth; Each of the capture sites is configured to be occupied by a corresponding axial micro light emitting diode having the first perimeter shape, a body for contact with the central portion of the capture site, a distal electrode horizontally bisecting the body for contact with the distal end of the capture site, and a proximal electrode horizontally bisecting the body for contact with the proximal end of the capture site.

16. The micro light emitting diode mass transfer imprint system of claim 15, wherein, The body has a vertical planar body thickness greater than a first depth of the capture locations but less than 2 times the first depth of the capture locations, the distal electrode has a vertical planar electrode thickness greater than a second depth of the capture locations but less than 2 times the second depth of the capture locations, the proximal electrode has the vertical planar electrode thickness.

17. A method of mass transfer of micro light emitting diodes, the method comprising: providing a stamp substrate having a planar top surface and an array of capture locations formed on the top surface, each capture location configured as a columnar recess; each of the capture location recesses tethering a keel extending from a bottom surface of a micro light emitting diode; and securing the micro light emitting diodes to the stamp substrate by tethering the keel of each micro light emitting diode; providing the stamp substrate includes providing the stamp substrate having a pitch separating adjacent capture locations; the method of mass transfer of micro light emitting diodes further comprising: providing a fluidic assembly carrier substrate having a planar top surface and an array of wells formed on the top surface of the fluidic assembly carrier substrate, the array of wells having a pitch separating adjacent wells matching the pitch separating the capture locations of the stamp substrate; populating the wells of the fluidic assembly carrier substrate with micro light emitting diodes using a fluidic assembly process; pressing the top surface of the stamp substrate against the top surface of the fluidic assembly carrier substrate with each capture location in contact with a corresponding well; and mass transferring the micro light emitting diodes from the fluidic assembly carrier substrate to the stamp substrate.

18. The micro light emitting diode mass transfer method of claim 17, wherein, tethering the keel includes each capture location recess tethering a non-conductive keel of a surface mount light emitting diode having a planar top surface with a first electrode and a second electrode.

19. The micro light emitting diode mass transfer method of claim 17, wherein, tethering the keel includes each capture location recess tethering a conductive keel connected to a second electrode of a vertical light emitting diode having a planar top surface with a first electrode.

20. The micro light emitting diode mass transfer method of claim 17, wherein, providing the fluidic assembly carrier substrate includes providing wells having a first perimeter shape and a planar well bottom surface; and populating the wells of the fluidic assembly carrier substrate with micro light emitting diodes includes populating the wells with surface mount micro light emitting diodes having the first perimeter shape and a planar top surface in contact with a corresponding well bottom surface, the top surface of the surface mount micro light emitting diode having a first electrode and a second electrode.

21. The micro light emitting diode mass transfer method of claim 17, wherein, providing the fluidic assembly carrier substrate includes providing wells having a first perimeter shape and a planar well bottom surface; and populating the wells of the fluidic assembly carrier substrate with micro light emitting diodes includes populating the wells with vertical micro light emitting diodes having the first perimeter shape and a planar top surface in contact with a corresponding well bottom surface, the top surface of the vertical micro light emitting diode having a first electrode.

22. The micro light emitting diode mass transfer method of claim 17, wherein, providing the fluidic assembly carrier substrate includes providing: a first fluid assembly carrier substrate having a first array of wells formed on a top surface of the first fluid assembly carrier substrate, the first array of wells having a pitch separating adjacent wells, the pitch of the first array of wells matching the pitch separating the imprint stamp substrate capture locations; a second fluid assembly carrier substrate having a second array of wells formed on a top surface of the second fluid assembly carrier substrate, the second array of wells having a pitch separating adjacent wells, the pitch of the second array of wells matching the pitch separating the imprint stamp substrate capture locations; a third fluid assembly carrier substrate having a third array of wells formed on a top surface of the third fluid assembly carrier substrate, the third array of wells having a pitch separating adjacent wells, the pitch of the third array of wells matching the pitch separating the imprint stamp substrate capture locations; filling the wells of the fluid assembly carrier substrates includes: filling the wells of the first fluid assembly carrier substrate with first micro light emitting diodes configured to emit a first wavelength of light; filling the wells of the second fluid assembly carrier substrate with second micro light emitting diodes configured to emit a second wavelength of light; filling the wells of the third fluid assembly carrier substrate with third micro light emitting diodes configured to emit a third wavelength of light; and mass transfer of the micro light emitting diodes from the fluid assembly carrier substrates to the imprint stamp substrates includes transferring micro light emitting diodes from the first fluid assembly carrier substrate, the second fluid assembly carrier substrate, and the third fluid assembly carrier substrate to respective imprint stamp substrates.

23. The micro light emitting diode mass transfer method of claim 17, wherein the micro light emitting diode mass transfer method further comprises: Also included are: patterning a top surface of the imprint stamp substrate, the material of the imprint stamp substrate top surface selected from the group consisting of an adhesive and an elastomer.

24. The micro light emitting diode mass transfer method of claim 17, wherein the micro light emitting diode mass transfer method further comprises: securing the micro light emitting diodes to the imprint stamp substrate includes additionally using an attractive force selected from the group consisting of an electrostatic force and a magnetic force to secure the micro light emitting diodes.

25. The micro light emitting diode mass transfer method of claim 17, wherein the micro light emitting diode mass transfer method further comprises: filling the wells of the fluid assembly carrier substrates with the micro light emitting diodes includes using an attractive force selected from the group consisting of an electrostatic force and a magnetic force to secure the micro light emitting diodes in the wells.

26. The method of mass transfer of micro light emitting diodes of claim 17, providing the imprint stamp substrate includes providing the imprint stamp substrate having a pitch separating adjacent capture locations; The method of mass transfer of micro light emitting diodes further includes: providing a display substrate having a planar top surface and an array of micro light emitting diode connection pads, each micro light emitting diode connection pad including at least one electrode formed on the top surface of the display substrate, the electrode electrically connected to a matrix of underlying column and row control lines, and the display substrate having a pitch separating adjacent connection pad sites, the pitch separating adjacent connection pad sites matching the pitch separating the imprint stamp substrate capture locations; pressing a top surface of the imprint stamp substrate against the top surface of the display substrate, each capture location interfacing with a respective micro light emitting diode site; and mass transferring the micro light emitting diodes from the stamp substrate to micro light emitting diode connection pads of the display substrate.

27. The micro light emitting diode mass transfer method of claim 26, wherein the micro light emitting diode mass transfer method further comprises: mass transferring the micro light emitting diodes from the stamp substrate to micro light emitting diode connection pads of the display substrate. 28.The micro light emitting diode mass transfer method of claim 26, wherein providing the display substrate includes providing connection pads for a plurality of first micro light emitting diodes that emit light of a first wavelength, connection pads for a plurality of second micro light emitting diodes that emit light of a second wavelength, and connection pads for a plurality of third micro light emitting diodes that emit light of a third wavelength; and pressing a top surface of the stamp substrate against a top surface of the display substrate includes sequentially pressing the stamp substrate so that the trapping sites are occupied by the first micro light emitting diodes, followed by the second micro light emitting diodes, followed by the third micro light emitting diodes.

29. A method of mass transfer of micro light emitting diodes, the method comprising: providing a fluidic assembly stamp substrate having a planar top surface with trapping sites formed thereon having a first perimeter shape, a depth, and a planar bottom surface; filling the trapping sites with micro light emitting diodes using a fluidic assembly process, the micro light emitting diodes having the first perimeter shape, a thickness greater than the depth of the trapping sites, a planar bottom surface in contact with the trapping site bottom surface, a planar top surface having a first electrode extending therefrom, and a securing mechanism; providing the stamp substrate includes providing the stamp substrate having a pitch separating adjacent trapping sites; the method of mass transfer of micro light emitting diodes further comprising: providing a display substrate having a planar top surface and an array of micro light emitting diode connection pads, each micro light emitting diode connection pad including a first electrode formed on the top surface of the display substrate that is electrically connected to a matrix of underlying column and row control lines, and the display substrate having a pitch separating adjacent connection pad sites that matches the pitch separating the stamp substrate trapping sites; pressing a top surface of the stamp substrate against a top surface of the display substrate, each trapping site interfacing with a corresponding micro light emitting diode site; and mass transferring the micro light emitting diodes from the stamp substrate to micro light emitting diode connection pads of the display substrate.

30. The micro light emitting diode mass transfer method of claim 29, wherein the micro light emitting diode is a micro light emitting diode on a substrate. the securing mechanism is a keel formed on the top surface of the micro light emitting diode, the keel selected from the group consisting of a conductive keel connected to the first electrode and a temporary non-conductive keel.

31. The micro light emitting diode mass transfer method of claim 29, wherein the micro light emitting diode mass transfer method further comprises: providing the stamp substrate includes providing the stamp substrate with each trapping site bottom surface coated with a first component of a conjugate pair of biomolecules; and the securing mechanism of the micro light emitting diode is a second component of the conjugate pair of biomolecules that coats the bottom surface of each micro light emitting diode.

32. The micro light emitting diode mass transfer method of claim 31, wherein the micro light emitting diode is a micro light emitting diode on a substrate. the conjugate pair of biomolecules is selected from the group consisting of biotin-streptavidin, thiol-maleimide, and azide-alkyne. the securing mechanism of the micro light emitting diode is a second component of the conjugate pair of biomolecules that coats the bottom surface of each micro light emitting diode. the conjugate pair of biomolecules is selected from the group consisting of biotin-streptavidin, thiol-maleimide, and azide-alkyne.

33. The micro light emitting diode mass transfer method of claim 29, wherein the micro light emitting diode mass transfer method further comprises: Filling the capture sites with the micro light emitting diodes includes the micro light emitting diodes having electrical interfaces, the micro light emitting diodes selected from the group consisting of vertical micro light emitting diodes having a second electrode formed on a bottom surface and surface mount micro light emitting diodes having first and second electrodes formed on a top surface.

34. A method of mass transfer of micro light emitting diodes, the method comprising: providing a fluid assembly stamp substrate having a planar top surface with a plurality of capture sites formed thereon, each capture site having a first perimeter shape, a central portion having a planar first depth, a distal end having a planar second depth less than the first depth, and a proximal end having the planar second depth; and, filling the capture sites with axial micro light emitting diodes using a fluid assembly process, each axial micro light emitting diode occupying a respective capture site and having the first perimeter shape, a body in contact with the central portion of the capture site, a distal electrode horizontally bisecting the body and in contact with the distal end of the capture site, and a proximal electrode horizontally bisecting the body and in contact with the proximal end of the capture site; the body having a vertical planar body thickness greater than the first depth of the capture site but less than 2 times the first depth of the capture site, the distal electrode having a vertical planar electrode thickness greater than the second depth of the capture site but less than 2 times the second depth of the capture site, and the proximal electrode having the vertical planar electrode thickness.

35. The micro light emitting diode mass transfer method of claim 34, wherein the micro light emitting diode mass transfer method further comprises: providing the stamp substrate includes providing the stamp substrate having a pitch separating adjacent capture sites; the method of mass transfer of micro light emitting diodes further comprising: providing a display substrate having a planar top surface and an array of micro light emitting diode connection pads, each micro light emitting diode connection pad including a first electrode formed on the top surface of the display substrate and a second electrode formed on the top surface of the display substrate, the first and second electrodes electrically connected to a matrix of underlying column and row control lines, and the display substrate having a pitch separating adjacent connection pad sites that matches the pitch separating the stamp substrate capture sites; pressing the top surface of the stamp substrate against the top surface of the display substrate, each capture site interfacing with a respective micro light emitting diode site; and mass transferring the micro light emitting diodes from the stamp substrate to the micro light emitting diode connection pads of the display substrate.

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