DE102020125857A1 - System and method for fabricating a micro LED display - Google Patents

Abstract

Using chip-by-chip separation technology in particular, micro LED displays can be manufactured very accurately and efficiently. First, after an epitaxy process, the LED epi wafer is processed into micro LEDs. Second, bonding substrates with driver circuits for the LED epi-wafers are provided. Then, each LED chip can be mounted on the substrate chip-by-chip simultaneously or sequentially, and each LED chip can be transferred simultaneously or sequentially using the separation technique. The LED epi wafer itself can also be provided as an LED display substrate. A light-conversion layer and a color-determining layer can be patterned and formed individually on each LED chip in sequence to provide an LED display.

Description

FIELD OF THE INVENTION

The invention relates to a micro LED display panel and a method for manufacturing the micro LED display panel. The invention also relates to an apparatus for manufacturing the micro LED array. However, it is to be appreciated that the invention has a much broader scope of application.

BACKGROUND OF THE INVENTION

The micro-LED, after the conventional TFT-LCD display and the OLED display, is considered to be the next high-tech display. The advantages of micro-LED, inherited from conventional LED, include low power consumption, high brightness, short response time and long lifespan. The 55-inch crystal LED TV equipped with micro-LEDs was announced and manufactured by Sony in 2012, in which more than six million micro-LEDs were used as high-definition pixels with millions of levels of contrast, more than 140% NTSC, no response time issue compared to LCD displays, and also no lifespan issue compared to OLED displays. The technologies of micro LED display are reducing the size of LED chip to 1% of conventional LED chip, integrate single micro LED into high definition display, change the pitch between two micro LED from mm to micro -meter scale, address each pixel individually, and drive each individual micro-LED in a micro-LED array.

However, for each individual micro-LED, the conventional manufacturing process cannot be adapted for mass production, as millions of micro-LEDs in a display are difficult to efficiently transfer from the substrate to the display; this is the mass transfer problem.

To solve this problem, several approaches have been proposed. In a US patent with patent number U.S. 8,794,501 by Andreas Bibl et al. states that all of the micro-LEDs on an epi-substrate are completely transferred to a temporary or bonding substrate at one time, and then each individual micro-LED is phase-transformed from the bonding substrate to the receiving substrate of a display panel. The mass transfer problem of individually transferring millions of micro-LEDs from the bonding substrate to the receiving substrate remains; this is too time consuming and the yield is low. Some other solutions, such as the use of liquid filters or drop by gravity traps, are still not industrially and commercially available.

To solve the mass transfer problem, especially to transfer RGB LED chips to a bonding substrate, one solution is to transfer only nitride-based LED chips to the bonding substrate. However, nitride-based LEDs cannot provide red light, so the full color of a micro/mini LED display cannot be achieved.

Accordingly, there is a need to find an industrially and commercially viable solution to the mass transfer problem for the fabrication of micro LEDs.

BRIEF SUMMARY OF THE INVENTION

The aim of this invention is to provide a commercially and industrially practical solution for the manufacturing processes of a micro LED display, a micro LED display and an apparatus for manufacturing a micro LED display.

Accordingly, the invention therefore provides a method of manufacturing a display panel, comprising the steps of providing a first substrate having a first plurality of light emitting diode chips thereon, wherein for each first light emitting diode chip of the first plurality of light emitting diode chips, a pair of ohmic electrodes is formed on each of the first light emitting diode chips, each light emitting diode emitting light at a first wavelength; providing a second substrate having display panel driving circuits thereon and a plurality of mating bond pads; flipping the first substrate to connect the first plurality of light emitting diode chips to the plurality of mating bond pads; separating the first plurality of light emitting diode chips from the first substrate; and heating the second substrate such that the first plurality of light emitting diode chips are mounted on the second substrate.

In a preferred embodiment, the first substrate may be sapphire or SiC and the first plurality of light emitting diode chips contains III-Nitride for UV, blue or green light emission. The separation step is performed by LASER exposure when the first substrate is sapphire or SiC.

In a preferred embodiment, the first substrate may also be a tape and the first plurality of light emitting diode chips contains III arsenide or III phosphide to emit red light. the Separating step is performed by pressing the front side of the first substrate without the plurality of light emitting diode chips when the first substrate is the tape.

In a preferred embodiment, the second substrate may be PCB, silicon, silicon carbide, or ceramic. The ceramic substrate can contain AlN or aluminum oxide (Al2O3).

In a preferred embodiment, the second substrate may be GaAs and includes a second plurality of light emitting diode chips, wherein each second light emitting diode chip of the second plurality of light emitting diode chips emits light at a second wavelength that is longer than the first wavelength.

In a preferred embodiment, the driver circuit can be an active circuit array or a passive circuit array. The active circuit contains a multiplicity of transistors for driving the multiplicity of light-emitting diode chips.

In a preferred embodiment, a first pitch in the first plurality of light emitting diode chips on the first substrate is equal to a second pitch in the plurality of mating bond pads on the second substrate. The flipping step is performed to align the first plurality of light emitting diode chips with the plurality of paired ohmic electrodes. The separating step is performed in blocks for each of the first light-emitting diode chips.

In a preferred embodiment, a first pitch in the first plurality of light emitting diode chips on the first substrate is smaller than a second pitch in the plurality of mating bond pads on the second substrate. The turning step is performed to align one of the first plurality of light emitting diode chips with one of the plurality of paired ohmic electrodes, and then the separating step is performed.

In a preferred embodiment, a phosphor layer is formed on the first plurality of light emitting diode chips to provide light having a third wavelength longer than the first wavelength after the LED chips have been transferred to the bonding substrate.

In a preferred embodiment, light having the third wavelength and the first wavelength provides white light. The method may further comprise a step of depositing a third transparent substrate on the second substrate, with a color filter on top, after said reflowing step.

The present invention also provides a display panel comprising a GaAs substrate having display panel drive circuitry thereon and a plurality of mating bond pads, said GaAs substrate having a plurality of red light emitting diode chips and a plurality of GaN chips includes light emitting diodes electrically coupled to the plurality of mating bond pads.

The present invention also provides a display panel comprising a bonding substrate having driver circuits and a plurality of paired bonding electrodes thereon; a plurality of GaN light emitting diode chips electrically connected to the plurality of paired bonding electrodes, respectively; a phosphor layer structured as a plurality of regions capable of covering the plurality of GaN light emitting diode chips, respectively; and a transparent substrate having a color filter layer thereon to align with the plurality of GaN light emitting diode chips, respectively.

In a preferred embodiment, the bonding substrate may be PCB, silicon, silicon carbide, or ceramic. The ceramic substrate can contain AlN or aluminum oxide (Al2O3).

In a preferred embodiment, the driver circuit can be an active circuit array or a passive circuit array. The active circuit includes a multiplicity of transistors for driving the multiplicity of light-emitting diode chips.

The present invention also provides a method of manufacturing a display panel, comprising the steps of providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon, each of the plurality of GaN light emitting diode chips having a first electrode and a second electrode; providing a bonding substrate having driver circuits and a plurality of paired bonding electrodes thereon; transferring a plurality of GaN light emitting diode chips onto the plurality of paired bonding electrodes; providing a phosphor layer on each of the plurality of GaN light emitting diode chips; and applying a transparent substrate having a color filter thereon to the bonding substrate such that the color filter is aligned with the plurality of GaN light emitting diode chips.

In a preferred embodiment, the bonding substrate may be PCB, silicon, silicon carbide, or ceramic. The ceramic substrate can contain AlN or aluminum oxide (Al2O3).

In a preferred embodiment, the driver circuit can be an active circuit array or a passive circuit array. The active circuit contains a multiplicity of transistors for driving the multiplicity of light-emitting diode chips.

The present invention also provides a display panel comprising a sapphire substrate having a plurality of GaN light emitting diode chips thereon, each of the plurality of GaN light emitting diode chips having a first electrode and a second electrode; a first dielectric layer on said sapphire substrate with the first electrodes and the second electrodes exposed; a first transparent conductive layer patterned as a first plurality of signal lines on the first dielectric layer to electrically connect to a row of the first electrodes of the plurality of GaN light emitting diode chips; a second dielectric layer on said first dielectric layer and said first transparent conductive layer with the second electrode exposed; a second transparent conductive layer patterned as a second plurality of signal lines on the second dielectric layer to electrically connect to a column of the second electrodes of the plurality of GaN light emitting diodes; a passivation layer blanket covering said second dielectric layer and said second transparent conductive layer; a phosphor layer patterned as a plurality of regions adapted to cover the plurality of GaN light emitting diode chips on the passivation layer; and a transparent substrate having a color filter layer thereon to cover and align the plurality of GaN light emitting diode chips.

The present invention also provides a method of manufacturing a display panel, comprising the steps of: providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon, each of the plurality of GaN light emitting diode chips having a first electrode and a second electrode; forming a first dielectric layer on the sapphire substrate and the plurality of GaN light emitting diode chips; exposing the first electrodes and the second electrodes; forming a first transparent conductive layer on the first dielectric layer; patterning the first transparent conductive layer into a first plurality of signal lines to electrically connect to a row of the first electrodes of the plurality of GaN light emitting diode chips; forming a second dielectric layer on the first dielectric layer and the first patterned transparent conductive layer; exposing the second electrodes; forming a second transparent conductive layer on the second dielectric layer; patterning the second transparent conductive layer into a second plurality of signal lines to electrically connect to a column of the second electrodes of the plurality of GaN light emitting diode chips; forming a passivation layer to cover the second patterned transparent conductive layer and the second dielectric layer; providing a phosphor layer on the passivation layer; and attaching a transparent substrate having a color filter layer thereon to the sapphire substrate so that the color filter is aligned with the plurality of GaN light emitting diode chips.

The present invention also provides an apparatus comprising a platform for mounting a first substrate having a plurality of light emitting diode chips thereon; a first stage allowing a first movement with two mutually horizontal directions orthogonal to each other; a mounting stage on said first stage for mounting a second substrate having a driver circuit and a plurality of paired bonding pads, the plurality of light emitting diode chips facing the plurality of paired bonding pads; means for separating the plurality of light emitting diode chips from the first substrate; and a controller for controlling said platform, said first stage, said assembly stage and said separating means to form a display panel.

In a preferred embodiment, the apparatus may further comprise a second stage between said first stage and said mounting stage to allow vertical movement.

In a preferred embodiment, when the first substrate is sapphire or SiC, said separation means is an excimer laser.

In a preferred embodiment, said separating means is a pressing device for pressing the plurality of light emitting diode chips to the plurality of mating bonding pads when the first substrate is a tape.

The present invention also provides a display panel comprising a bonding substrate having driver circuits and a plurality of paired bonding electrodes thereon; a plurality of GaN light emitting diode chips electrically connected to the plurality of paired bonding electrodes, respectively; a light conversion layer structured as a plurality of regions adapted to cover the plurality of GaN light emitting diode chips, respectively; and a patterned color determination layer on the light conversion layer and disposed on the plurality of GaN light emitting diode chips, respectively.

The present invention also provides a display panel comprising a sapphire substrate having a plurality of GaN light emitting diode chips thereon; a patterned ohmic transparent conductive contact layer electrically connected to a first conductive type of the plurality of GaN light emitting diode chips; a patterned passivation layer covering the patterned first ohmic conductive transparent conductive contact layer and the plurality of GaN light emitting diode chips and exposing a second conductivity type of the plurality of GaN light emitting diode chips; and a patterned second ohmic transparent conductive contact layer electrically connected to the second conductor type of the plurality of GaN light emitting diode chips.

In a preferred embodiment, the patterned passivation layer is mixed with a light conversion material.

In a preferred embodiment, the display panel may further include a color definition layer over the plurality of GaN light emitting diode chips.

In a preferred embodiment, the color definition layer is a color filter, which defines the RGB in a pixel.

In a preferred embodiment, the display panel may further comprise a first metal line on the first ohmic transparent conductive contact layer and a second metal line on the second ohmic transparent conductive contact layer.

The present invention also provides a method of manufacturing a display panel, comprising the steps of providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon, each of the plurality of GaN light emitting diode chips having a first electrode and a second electrode; to provide a bonding substrate having driver circuits and a plurality of paired bonding electrodes thereon; transfer a plurality of GaN light emitting diode chips onto the plurality of paired bonding electrodes; provide a light conversion layer on the plurality of GaN light emitting diode chips; and form a patterned color determination layer on the light conversion layer aligned to the plurality of GaN light emitting diode chips.

The present invention also provides a method of manufacturing a display panel, comprising the steps of providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon; form a patterned first ohmic transparent conductive contact layer on a first conductor type of the plurality of GaN light emitting diode chips; form a pattern conforming passivation layer on the patterned first ohmic conductive transparent conductive contact layer and the plurality of GaN light emitting diode chips, wherein a second conductor type of the plurality of GaN light emitting diode chips is exposed; form a second ohmic transparent conductive layer electrically connected to the second conductor type of the plurality of GaN light emitting diode chips.

In a preferred embodiment, the method may further comprise a step of mixing a light-converting material into the passivation layer prior to said step of forming the pattern-conforming passivation layer.

In a preferred embodiment, the method may further comprise a step of forming a color determination layer over the plurality of GaN light emitting diode chips after said step of forming a second ohmic transparent conductive contact layer.

In a preferred embodiment, the color determination plane is a color filter, where RGB is specified in a pixel.

In a preferred embodiment, the method may further comprise steps of forming a patterned first metal line on the first ohmic transparent conductive contact layer, after said step forming the first ohmic transparent conductive contact layer; and forming a patterned second metal line on the second ohmic transparent conductive contact layer, after said step forming the second ohmic transparent conductive layer.

Other advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings which show by way of illustration and example certain embodiments of the present invention.

character list

• The present invention can be readily understood from the following detailed description when read in conjunction with the accompanying drawings, wherein like or similar reference numbers indicate like or similar structural elements, and in which:
• 1A-1D 12 are schematic representations of structures at various stages during the formation of LED chips on an epi-substrate in accordance with an embodiment of the present invention;
• 2A and 2 B 12 are schematic representations of structures at various stages during the preparation of transferring the micro-LED chips from the epi-substrate to the display, in accordance with an embodiment of the present invention;
• 3A ~ 3C 12 are schematic representations of structures at various stages during the LASER liftoff process in accordance with an embodiment of the present invention;
• 4A and 4B are schematic representations of structures at various stages during the separation between epi-substrate and binding substrate in accordance with an embodiment of the present invention;
• 5A-5D 12 are schematic representations of structures at various stages during the formation of another LED die on the bonding substrate in accordance with an embodiment of the present invention;
• 6A-6C 12 are schematic representations of phosphor on LED chips in accordance with an embodiment of the present invention;
• 7A ~ 7G 12 are schematic representations of structures at various stages during the formation of LED chips on the bonding substrate in accordance with another embodiment of the present invention;
• 8A ~ 8E 12 are schematic representations of structures at various stages during the formation of LED chips transferred to a temporary substrate in accordance with an embodiment of the present invention;
• 9 Fig. 12 is a flowchart showing the steps for fabricating red LED chips and driver circuitry on the bonding substrate in accordance with an embodiment of the present invention;
• 10A ~ 10M 12 are schematic representations of structures at various stages during the formation of red LED chips and driver circuits with blue/green LED chips transferred to the bonding substrate in accordance with another embodiment of the present invention;
• 11A and 11B 12 are schematic representations of LED display circuits in accordance with two embodiments of the present invention;
• 12A and 12B 12 are schematic representations of LED display layouts in accordance with two embodiments of the present invention;
• 13A Fig. 12 is a schematic representation of the cross-sectional view of an LED display employing color filter and phosphor on LED chip in an embodiment of the present invention;
• 13B Fig. 12 is another schematic representation of the cross-sectional view of an LED display employing color filter and phosphor on transparent substrate in an embodiment of the present invention;
• 13C Fig. 12 is another schematic representation of the cross-sectional view of an LED display employing color filters in an embodiment of the present invention;
• 14A Fig. 12 is a schematic representation of a top view of an LED display employing color filters in an embodiment of the present invention;
• 14B Fig. 12 is a schematic representation of the top view of an LED display employing black matrix color filters in an embodiment of the present invention;
• 15A ~ 15E 12 are schematic representations of structures at various stages during the formation of a passive GaN LED display on sapphire with coated phosphors and color filter substrate in accordance with another embodiment of the present invention;
• 16 Fig. 12 is a schematic representation of a cross-sectional view of a passive microlens array GaN LED display in accordance with another embodiment of the present invention;
• 17 Fig. 12 is a schematic representation of an apparatus for fabricating LED chips on the bonding substrate in accordance with an embodiment of the present invention;
• 18 Fig. 12 is a schematic representation of an apparatus for manufacturing LED chips on the bonding substrate in accordance with another embodiment of the present invention;
• 19A-19E 12 are schematic representations of cross-sectional structures at various stages during the formation of a GaN LED display on bonding substrate with coated phosphors and color filter substrate in accordance with another embodiment of the present invention;
• 20A-21H 12 are schematic representations of cross-sectional structures at various stages during the formation of a GaN LED display on sapphire with coated phosphors and color determination in accordance with an embodiment of the present invention;
• 21A-21G 12 are schematic representations of cross-sectional structures at various stages during the formation of a GaN-LED display on sapphire with coated phosphors and color definition in accordance with another embodiment of the present invention;
• 22A Figure 12 is a schematic representation of a cross-sectional structure showing a GaN LED chip on a sapphire substrate in a display, in accordance with a simplified embodiment of the present invention;
• 22B 12 is a schematic representation of a cross-sectional view illustrating a GaN LED chip on a sapphire substrate having a first transparent ohmic contact conductive layer in a display, in accordance with the embodiment of FIG 22A ;
• 22C 12 is a schematic representation of a cross-sectional view showing a GaN LED chip on a sapphire substrate having a second transparent ohmic contact conductive layer in a display, in accordance with the embodiment of FIG 2BA ;
• 23A 12 is a schematic representation of a top view showing a GaN LED chip on a sapphire substrate in a display, in accordance with the embodiment of FIG 22A ;
• 23B 12 is a schematic representation of a top view showing a GaN LED chip on a sapphire substrate with a first transparent ohmic contact conductor layer in a display, in accordance with the embodiment of FIG 23A ;
• 23C 12 is a schematic representation of a top view showing a GaN LED chip on a sapphire substrate with a second transparent ohmic contact conductor layer in a display, in accordance with the embodiment of FIG 23B ;
• 24A 12 is a schematic representation of a cross-sectional structure showing a GaN LED chip on a sapphire substrate in a display, in accordance with another simplified embodiment of the present invention;
• 24B 12 is a schematic representation of a top view showing a GaN LED chip on a sapphire substrate in a display, in accordance with the embodiment of FIG 24A ;
• 25A 12 is a schematic representation of a cross-sectional structure showing a GaN LED chip on a sapphire substrate in a display, in accordance with another simplified embodiment of the present invention; and
• 25B 12 is a schematic representation of a top view showing a GaN LED chip on a sapphire substrate in a display, in accordance with the embodiment of FIG 25A ;

While the invention is capable of various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. Drawings may not be to scale. It should be understood, however, that the drawings and their detailed description are not intended to limit the invention to the precise form disclosed, but on the contrary to cover all modifications, equivalents, and alternatives as may fall within the spirit and scope of the present invention as they may be are defined in the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term "substrate" generally refers to disks composed of a semiconductive or non-semiconductive material. Examples of such a semiconductor or non-semiconductor material include monocrystalline silicon, silicon carbide, gallium arsenide, indium phosphide, sapphire, ceramic, glass, and PCB, among others. Such substrates can be commonly found and/or processed in semiconductor manufacturing facilities. An epi-substrate refers to a slab intended for epitaxial growth in semiconductor manufacturing facilities. A bonding substrate refers to a board with circuits and Bond pads thereon for receiving electronic devices.

For the substrate, one or more layers may be formed on the substrate. Many different types of such layers are known in the art and the term substrate as used herein is intended to encompass a wafer on which all types of such layers can be formed. One or more layers formed on a substrate may be patterned. For example, a substrate may include a plurality of die/chips, each having repeatable patterned features. The formation and processing of such layers of material can eventually lead to finished semiconductor devices. Thus, a substrate may include a board on which not all layers of a complete semiconductor device have been formed, or a substrate on which all layers of a complete semiconductor device have been formed.

The substrate may also contain at least part of an integrated circuit (IC) or optoelectronic devices such as LED chips.

The term "LED" generally refers to light-emitting diodes that can emit red, green, blue, or UV light by operating on a specified DC current, with or without a package.

The term "LED chip" generally refers to LEDs formed by epitaxial growth on a substrate with paired ohmic contact electrodes, with or without separation from the epi-substrate. The LED chip in the present invention can be formed on the epi substrate or bonded to the bonding substrate.

A typical LED chip has a dimension of approximately 14×14 mil ² , which corresponds to 355.6×355.6 µm ² , and the micro LED chip has a dimension of generally less than 100×100 µm ² and a preferred dimension of less than 50x50 µm ² .

The term "circuit" in this invention can include resistors, diodes or transistors.

The term “index” in the present invention refers to a pitch between two LED chips on epi substrate or bond substrate.

The term "color filter" is used to filter light into a variety of wavelength bands. In the present invention, the term "color filter" refers to RGB filters that transmit red, green, and blue light, respectively.

Process flow steps in the present invention should generally be interchangeable unless a logical sequence is required.

The conductivity type of the semiconductor in the present invention, such as n-type or p-type conductivity in the semiconductor layer should be interchangeable.

Various example embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which some example embodiments of the invention are shown. Without limiting the scope of the present invention, all the descriptions and drawings of the embodiments are related to the micro LED display and its manufacturing method by way of example. However, the embodiments are not intended to limit the present invention to the micro-LED transmission method.

In the drawings, the relative dimensions of and between the individual components may be exaggerated for clarity. Throughout the following description of the drawings, the same or similar reference numbers refer to the same or similar components or units, and only the differences with respect to the individual embodiments will be described.

Accordingly, while the example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and are herein described in detail. However, it should be understood that the intention is not to limit example embodiments of the invention to the precise forms disclosed, but on the contrary, the example embodiments of the invention are intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention.

The present invention provides a method in which the micro-LED chips can be directly transferred onto a bonding substrate, where the bonding substrate not only includes driver circuits but is also dedicated to the display. First, for a III-nitride-based compound, GaN-based chips are formed by epitaxial growth on a sapphire, SiC, Si, GaN, or ZnO substrate to generate green, blue, or UV light. In a III-arsenide or III-phosphide compound, GaAs or AlInGaP is formed by epitaxial growth on a GaAs, GaSb, GaP or InP substrate to generate red light. After the epitaxial growth process, the epi-layers are processed with chip structures and placed on the p/n epi layers, ohmic contact electrodes are formed respectively. A bonding substrate having driver circuitry and bond pads formed thereon is provided for receiving the micro LED chips. III nitride micro LED chips can be transferred on a sapphire substrate with LASER lift-off technology, and III arsenide, III phosphide micro LED chips or III nitride micro LED chips can be transferred on SiC, Si, ZnO substrate are transferred using a mechanical pressing process. With the same index, the mass transfer method can be transferred in blocks at the same time or sequentially in chips if the index is not the same, or the entire substrate can be transferred directly. Then the bonding substrate with the transferred micro LED chips is reheated so that the bond pads and the micro LED chips can be connected by eutectic bonding, soldering or silver epoxy baking. With this, the mass transfer problem can be solved in industrial and commercial matters.

In one embodiment, a pixel of the display may include a blue micro-LED chip, a green micro-LED chip, and a red micro-LED chip. In another embodiment, a pixel of the display may include a blue micro-LED chip, a blue micro-LED chip coated with green phosphor, and a blue micro-LED chip coated with red phosphor. In another embodiment, a pixel of the display may include a blue micro-LED chip, a green micro-LED chip, and a blue micro-LED chip coated with red phosphor. In another embodiment, a pixel of the display may include three UV micro-LED chips with RGB phosphors, each coated with RGB phosphors. In another embodiment, a pixel of the display may include only a blue micro-LED chip for a monochromatic display. In one embodiment, a pixel of the display may include three micro-LED chips, each coated with yellow phosphor, followed by an RGB color filter that filters the white light into a full-color image. In this embodiment, the functions of the RGB filter are similar to those of the TFT-LCD. In this embodiment, red phosphor or quantum dot technologies can be adopted in this embodiment to meet a wide color spectrum. The red phosphor may contain nitride phosphor. Or white phosphor with enhanced red light, such as KSF (potassium fluoride silicon) phosphor and TriGain phosphor developed by GE. Sharp is also developing a WCG phosphor comprising β-SiAlON green phosphor and KSF phosphor.

In one embodiment, the bonding substrate may be GaAs, and red micro-LED chips and driver circuitry may be formed on the GaAs. So only blue and green micro LED chips have to be transferred to the binding substrate. Or blue micro LED chips with green phosphor such as silicate phosphor or β-SiAlON green phosphor are transferred onto the blue micro LED chips onto the bonding substrate.

Regarding the drawings, it should be noted that the present invention will be explained more clearly with the drawings.

In 1A Illustrated is a substrate 10 for epitaxial growth, which may be Si, SiC, ZnO, GaN, sapphire (Al ₂ O ₃ ), GaAs, GaSb, GaP, or InP. However, GaAs and sapphire are preferred as the epi-substrate in an embodiment of the present invention. For the III-Nitride compound, the epi-substrate 10 would be sapphire, SiC, Si, ZnO, or GaN, while for the III-Arsenide compound, the substrate 10 would be GaAs, GaSb, GaP, or InP. The orientation of the substrate 10 is chosen for the epitaxial growth of the III-arsenide, III-phosphide or III-nitride compound. In one embodiment, the sapphire substrate may be a patterned sapphire substrate to increase brightness.

In 1B An epitaxial growth process for the formation of epi-layers is shown. A first epi layer 12 having a first conductivity is formed on the epi substrate 10 and a second epi layer 16 having a second conductivity is formed on the first epi layer 12 . The second conductivity is opposite to the first conductivity. In a preferred embodiment, the first conductivity is n-type and the second conductivity is p-type. A single quantum well layer or a multiple quantum well layer (not in 1B shown) is always formed between the first epi-layer 12 and the second epi-layer 16 using conventional methods. For sapphire, SiC, and Si epi substrate 10, a low temperature buffer layer 22 is formed prior to the formation of the first epi layer 12 to promote two-dimensional growth. In this invention, green, blue or UV light can be emitted from the III-Nitride compounds, while red light can be emitted from the III-Arsenide compound or III-Phosphide compounds. In one embodiment, the epi-layers 12 and 16 may be Al _x Ga _(1-x) As, (Al x Ga (1- _x) ) _y In _(1-y) P, y˜0.5 (lattice matching to GaAs), or Al _x In _{yGa (1-xy)} N. In one embodiment, epi layers 12 and 16 will emit blue light.

In 1C two electrodes are respectively formed on the first and second epi layers. A portion of the second epi-layer 16 is patterned by a conventional patterning technique which comprises a lithographic step and an etching step, and an anisotropic etching method would be preferable for the etching step. A first ohmic contact electrode 14 is then formed on the first epi layer 12 by a lift-off process, or an ohmic contact material layer is deposited on the first epi layer 12 and unnecessary portions of the ohmic contact layer are removed using a conventional patterning process comprising steps conventional lithography and etching steps. Materials of the first ohmic contact electrode 14 may be Ge/Au, Pd/Ge, CrAu, CrAl, Ti, TiN, Ti/Al, Ti/Al/Ni/Au, Ta/Ti/Ni/Au, V/Al/V/Au , V/Ti/Au, V/Al/V/Ag, IZO or ITO respectively for a III-nitride, III-phosphide or III-arsenide compound. A second ohmic contact electrode 18 is formed on the second epi layer 16 by a lift-off process, or an ohmic contact material layer is deposited on the second epi layer 18 and unnecessary portions of the ohmic contact layer are removed using a conventional patterning etch process including Steps of a lithographic process and an etching process. Second electrode 18 materials may be high work function metal such as Ni, Au, Ag, Pd, Pt, AuBe, AuZn, PdBe, NiBe, NiZn, PdZn, AuZn, Ru/Ni/ITO, Ni/Ag/Ru/Ni/Au , Ni/Au or ITO corresponding to III-nitride, III-phosphide or III-arsenide compound. In this embodiment, the lift-off method in the ohmic contact electrode formation process includes the steps of depositing photoresist layers first on the epi layers 12 or 16, exposing and developing the photoresist layers with patterns, depositing the ohmic contact material layer on the photoresist layer and the exposed epi layers 12 or 16 and subsequent direct removal of the photoresist layer. At the same time, the ohmic contact material layer on the photoresist layer is removed. The lift-off process has the advantage that an etching step is not required.

In 1D a mesa etch process is performed and scribe lines 20 are simultaneously formed using a conventional patterning etch process to differentiate each LED die 40 . The formation of the ohmic contact electrodes and the mesa is a so-called chip process, and the sequence of steps of forming the ohmic contact electrode in 1C and the mesa formation in 1D can be switched or reversed. A passivation layer with openings for the first/second ohmic contact electrodes can be formed on the micro LED chips to protect all the micro LED chips, although this is not shown in the figures in order to defocus the present invention to lose.

In 2A For example, a bonding substrate 50 is provided with driver circuitry 60 and mating bond pads 52 thereon. The bonding substrate 50 can be made of PCB, silicon, silicon carbide, AlN ceramic or alumina (Al2O3) ceramic, glass or GaAs. The methods of fabricating driver circuits 60 and mating bond pads 52 may be any conventional technique. The backside of the bonding substrate 50 is preferably flat. If LLO is to be performed later, the backside of the binding substrate 50 should be polished.

Micro LED chips are transferred to the binding substrate. In 2 B the processed epi-substrate 10 is made of 1D flipped over and each LED die 40 aligned with each mating bond pad 52 since the index on the epi substrate is the same as that on the bonding substrate. The bond pads 30 may include eutectic bonding, solder bonding, and epoxy paste with silver.

Then in 3A introduced a chip-by-chip LASER exposure. In this embodiment, only one chip for a given LED color is transferred at a time. However, a block of LEDs can be transmitted simultaneously if, in other applications or embodiments, all LEDs emit the same color. A first LED chip is irradiated by LASER exposure 32 down to the low temperature buffer layer 22 so that the GaN epi layer 12 is separated from the sapphire epi substrate 10 . In this way, the first LED chip is separated from the epi-substrate 10. Please note in 3A that ohmic contact electrodes are very close to the mating bond pads; however, they are not contacting right now. The epi-substrate 10 must be close enough to the bonding substrate 50 so that when the first LED die is exposed to the LASER, the first LED die is separated from the epi-substrate 10 and transferred directly onto the bonding substrate 50. In another conventional LASER lift-off process, the micro-LED chips are first connected to the mating bond pads and then irradiated by LASER exposure. In the present invention, the LASER exposure is performed first so that the micro LED chips can be bonded to the bonding substrate 50 selectively. Parameters such as wavelength, LASER power, beam size and shape, and exposure time can correspond to any conventional technique. In one embodiment, the KrF excimer laser can be used with a wavelength of 248 nm, a pulse of about 3-10 ns and an energy density of about 120-600 mJ/cm2. In another embodiment, the Nd:YAG laser with a wavelength of 355 nm, a pulse of about 20-50 ns and an energy density of about 250-350 mJ/cm2 can be used. Even if in this version tion form sapphire epi substrate is used, silicon carbide epi substrate can also be used in the LASER lift-off process, and details can be provided by Nakamura et al. published under US Patent No. 7,825,006.

In 3B a second LED chip is irradiated by LASER exposure 32 down to the low-temperature buffer layer 22 . In this way, the second LED chip is separated from the epi-substrate 10 and attached to the bonding substrate. And in 3C a third LED chip is irradiated by LASER exposure 32 down to the low-temperature buffer layer 22 . In this way, the third LED chip is separated from the epi-substrate 10 and transferred to the bonding substrate. Please note in 3 also that the first, second and third micro LED chips are not neighbors because some other micro LED chips that can emit different light can be bonded to this bonding substrate from another epi substrate. In one embodiment, the first, second, and third micro-LED chips can emit blue light, and other micro-LED chips on another epi-substrate that can emit green light should be bonded to this bonding substrate. Red LED chips can already be formed in the bonding substrate when the bonding substrate is made of GaAs. If red micro LED chips are to be connected to the bonding substrate and the bonding substrate itself is not GaAs, the distance between the blue micro LED chips should be doubled to the distance in 3 .

After all selected blue micro-LED chips are irradiated by LASER exposure, the selected blue micro-LED chips are transferred onto the bonding substrate. The remaining blue micro-LED chips on the epi-substrate can be processed on the next bonding substrate.

In 3 each micro LED chip can be transferred chip by chip sequentially or block by block.

In 4A the epi-substrate 10 is moved out of 34 while some micro-LED chips that have been irradiated by LASER exposure remain on the bonding substrate 50, while other LED chips that have not been irradiated by LASER exposure remain on the epi - Substrate 10 remain.

In 4B For example, the bonding substrate 50 can be reheated by eutectic bonding, solder bonding, or baked epoxy with silver so that the transferred micro-LED chips are connected to the mating bond pads. It is preferred that this step is performed when all micro LED chips have been transferred.

In 5A For example, a second epi-substrate 10-1 with other micro-LED chips 45, such as green LED chips, is flipped over and all of the micro-LED chips 45 are aligned with the remaining paired bond pads. In this embodiment, some green micro LED chips 45 on the epi substrate may have been processed on the other bonding substrate. Then, as in 5B shown, the epi-substrate 10-1 is placed sufficiently close to the bonding substrate 50, but the spacing between the epi-substrate 10-1 and the bonding substrate 50 should have a thickness greater than one chip thickness, e.g. several microns apart, to consider the chip pitch, and an LED chip 45 is irradiated by LASER exposure 32. In 5C another LED chip 45 is again irradiated by LASER exposure 32 down to the low-temperature buffer layer. In this way, all micro-LED chips are separated from the epi-substrate 10-1 and transferred to the bonding substrate 50 chip by chip. In 5D the epi-substrate 10-1 is moved away and all the LED chips are transferred. The bonding substrate 50 is reheated. The reheating step should conveniently be performed after all micro-LED chips have been transferred to the bonding substrate.

The bonding substrate 50 can be bonded, separated, or singulated into a display panel when the bonding substrate is small or large in size. For example, if the bonding substrate is a two inch by two inch panel and the display device is six inch by two inch, three bonding substrates must be bonded into a single display panel. If the binding substrate is a ten by twelve inch panel and the display device is six by three inches, the binding substrate must be separated or singulated into nine display panels.

If all LED chips can be UV light LEDs, red 70 phosphors, green 71 phosphors and blue 72 phosphors can be formed on the back of micro LED chips, as in 6A shown. In 6B only blue LED chips are provided, while green phosphor 71 and red phosphor 70 are formed or coated on the LED chips. The phosphors 70 can be produced by spraying, lithography, taping or printing. Another embodiment is in 6C shown, when blue and green micro-LED chips are present, only red phosphor 70 is formed and applied to some of the blue LED Chips applied. In this way a display is made.

In another embodiment, if the index of the micro LED chips on the epi substrate is not the same as that on the bonding substrate, the LED chips should be transferred from the epi substrate piece by piece. First, the first micro-LED die is aligned on the epi-substrate to specific paired bond pads, as shown in 7A shown. Then in 7B , the epi-substrate is brought close enough to the binding substrate.

Then in 7C the first micro-LED chip is irradiated by LASER exposure 32. In this way, in 7D the first micro-LED chip is separated from the epi-substrate 10 and mounted on the bonding substrate 50 while the other micro-LED chips still remain on the epi-substrate.

Then be in 7E moving the epi-substrate 10 and bonding substrate so that the second LED chip is aligned with other mated bond pads and illuminated by the LASER exposure 32. In 7F the second LED chip is transferred to the bonding substrate 50 . In 7G the epi-substrate 10 and the bonding substrate are moved so that the third LED chip is aligned with further mated bond pads and irradiated by the LASER exposure 32 again. In this way, the process can continue until all of the given micro-LED chips are transferred to the bonding substrate. In this embodiment, the index of the micro-LED chips on the epi-substrate is less than that of the mating bond pads on the bonding substrate.

In the present invention, the sapphire substrate can be separated using the LASER lift-off process. However, for some other epi-substrates such as silicon, silicon carbide and GaAs, it is not easy to separate the epi-substrate from the epi-layers by LASER lift-off. Therefore, another method is provided. In one embodiment, micro red LED chips may be formed on GaAs substrate and then the micro red LED chips are transferred to a temporary substrate. The GaAs substrate is removed by a selective etching process, and then all the micro LED chips are re-transferred onto a tape substrate. Because the tape is soft and the adhesive strength between the micro LED chips and the tape is not so strong, the micro LED chips can be pressed directly onto the bonding substrate using a tip. This means that the previous LASER lifting process can now be replaced by a mechanical pressing process. The adhesion of the tape can be controlled so that the transfer can be optimized.

In order to explain this embodiment, some drawings should be presented for clarity.

In one embodiment, a GaAs epi substrate 10 is first provided. Then, an etch selective layer 23 such as AlAs is formed on the GaAs substrate by a conventional epitaxial growth method as shown in FIG 8A shown. Subsequently, the first epi-layer 12 and the second epi-layer 16 are sequentially formed by epitaxial growth, and individual LED chip structures are later formed. A p-ohmic contact layer 18 is formed on the second epi-layer 16 by evaporation techniques. Then the top of the epi-substrate 10 is attached to a temporary substrate 80 with a specific adhesive that can lose its adhesion when illuminated with UV light or heated to a certain temperature, as in 8B shown.

Next, the epi-substrate 10 is removed by etching the etch-selective layer 23 (details of this method can be found in US Publication No. 2006/0286694), and LED chips with n ohmic contact electrode 14 and p ohmic contact electrode 18 are formed on the epi- layer formed as in 8C shown. The temporary substrate 80 is turned over. Then the top of the n ohmic contact electrode 14 is attached to a tape 81 as in FIG 8D shown. The adhesiveness of the tape is not too sticky or tacky, so each micro LED chip can be dropped later with a simple mechanical push. The temporary substrate 80 is then removed by heating or exposure to UV light and the tape with the LED chips is cut as in FIG 8E shown reversed. Another embodiment to remove the GaAs substrate is to directly etch the GaAs substrate with an etch stop layer such as AlAs formed directly on the GaAs substrate. The process flow of this embodiment is the same as described above.

For other epi substrates such as Si, SiC, GaN, ZnO, GaP and GaSb, a corresponding selective etching layer should be formed before forming the epi layers, and the former method can be used. A transition metal nitride layer is suitable as a selective etching layer for an epi-substrate made of silicon carbide.

Epi substrate can be used as bonding substrate with driver circuits, and AlGaInP red LED structure growing on GaAs substrate sen are provided to illustrate this embodiment. In 9 A process flow is shown to illustrate this embodiment. First, a substrate such as GaAs or InP for the epitaxial growth of red micro-LED chip structures and as a bonding substrate for blue/green micro-LED chips is provided as shown in step S9-1. Then, as an optional step S9-2, a DBR layer for reflecting red light is formed on the substrate, and the red LED structure is epitaxially grown on the DBR layer as step S9-3. Next, red micro LED chips are fabricated on the DBR layer as step S9-4. Then, a p-well is formed in the GaAs substrate by conventional ion implantation and/or diffusion as step S9-5. In this embodiment, since the substrate is n-type, a p-well is formed. If a p-type MISFET is preferred, an n-well should be formed in this step. Subsequently, a plurality of isolation regions are formed in the p-well as step S9-6 for isolating the subsequently formed transistors from the paired bond pads. The insulation zones can be silicon nitride, silicon oxide, aluminum oxide or aluminum nitride, for example. The transistors, in this embodiment MISFET (Metal Insulator Semiconductor Field Effect Transistor), are formed in the p-well as step S9-7. The GaAs substrate is incorporated into the MISFET as a semiconductor layer. Then, an ohmic contact matrix is formed for ohmically contacting micro LED chips as step S9-8, and mating bond pads are formed on the isolation devices as step S9-9. Blue and green micro-LED chips can then be transferred to the mated bond pads as step S9-10. An ILD (inter-level dielectric) layer such as silicon oxide or silicon nitride is formed on the substrate as step S9-11, and multiple contacts are formed in the ILD layer as step S9-12. Then, a metal layer is formed on the ILD layer to electrically connect to the contact as step S9-13. A passivation layer such as silicon oxide or silicon nitride is formed to cover all transistors, micro-LED chips and the metal layer as step S9-14, and the back side of the substrate is optionally metallized as step S9-15.

Detailed steps of the in 9 illustrated process flow can 10A 10M can be taken. First, a GaAs or InP substrate 51 is provided as in FIG 10A shown. A DBR layer 53 may be formed on the substrate 51 to improve red light extraction, and then an n epi layer 12 and a p epi layer 16 are sequentially formed on the DBR layer 53 by MOCVD. A chip process is used to form individual red micro-LED chips 47 on the substrate 51, as shown in FIG 10B shown using conventional patterning and etching processes. To form driver circuits, a p-well 55 is formed using conventional ion implantation and/or diffusion steps as shown in FIG 10C shown. In one embodiment of this process, the dopants can be Mg or Zn. A plurality of isolation zones 56 are then formed in the substrate 51 to electrically isolate the micro-LED chips from the transistors, as shown in FIG 10D shown. The isolation zones can be dielectric, such as silicon oxide, silicon nitride, aluminum oxide or aluminum nitride. In this step, the formation of the isolation zones includes an etching process and refilling of the dielectric layer in etched areas.

In 10E n-type MISFETs 90 are formed in and on p-well 55 using conventional methods. In one embodiment, gate dielectric layer 92 and gate 93 are sequentially deposited on substrate 51 and then etched, and then source/drain regions 91 are formed in p-well 55 by doping, implanting, or diffusing made of silicon. Gate dielectric layer 92 may be silicon oxide or silicon nitride, or other dielectric material, and gate 93 may be polysilicon, aluminum, or suitable metals. Spacers 94, which may be silicon oxide, are then optionally formed on the sidewall of the gate and the red micro-LED chips 47 to protect the gate and the red micro-LED chips 47, as in FIG 10F shown. The formation of the spacers 94 includes depositing a conformal layer on the substrate 51 and directly etching the conformation layer. Then, a transparent ohmic contact layer 18 is formed on the substrate 51 to electrically connect the red micro LED chips 47 and the later transferred blue/green micro LED chips to the transistors 90 . The transparent ohmic contact layer 18 may be ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), IGO (Indium Gallium Oxide), AZO (Aluminum Zinc Oxide), or IGZO (Indium Gallium Zinc Oxide) oxide). Then, mated bond pads 52 are formed on the isolation devices 56 and electrically connected to the transparent ohmic contact layer 18 as shown in FIG 10G shown. Then the blue micro LED chip 40 and the green micro LED chip 45 are transferred to the paired bond pads as shown in FIG 10H shown.

An ILD layer 64 such as silicon oxide, TEOS (tetraethylorthosilicate), epoxy or silicone [org. silicone], is applied to the substrate 51 by conventional spin coating, such as in 10I shown. Then contacts 68 are formed in the ILD layer 64 to electrically connect to the n-wells 91 of the transistors 90, as in FIG 10y shown. Fabrication of the contact 68 involves etching the ILD layer 64 to first form a contact hole and then filling the contact hole with a metal. A metal layer 62 is then formed on the ILD layer 64 and electrically connected to the contacts 68 by conventional methods, as shown in FIG 10K shown. The metal layer 62 provides a brightness signal to the micro LED chips 40, 45 and 47 via the transistors 90, and one of the micro LED chips emits a predetermined light brightness upon turning on the corresponding transistors. A passivation layer 65, such as epoxy, silicon, or MEMS materials, is formed to cover the transistors 90, the micro LED chips, and the metal layer 62, as shown in FIG 10L shown. Optionally, a metal layer 66 is formed on the back of the substrate 51, as in FIG 10M is shown so that all n-electrodes of the micro LED chips can be grounded via the metal layer 66. The red micro-LED chip 47 can have the n-electrode grounded through the substrate 51, while the blue/green micro-LED chip 40/45 can have the n-electrode grounded through vias in the substrate 51. Fabrication of the via may include etching through the substrate 51 to form via holes and filling the metal in the via holes using conventional methods.

In order to understand the pixel design of the micro LED display, it would be better to have a top view to illustrate this invention. In 11A An active electrical schematic of two pixels in a micro LED display panel is shown. A pixel 100 includes three micro LED chips 106 and three transistors 104. All gates of the transistors 104 are connected to the control signal 110 and all sources of the transistor 104 are connected to the brightness signal 112. FIG. Control signal 110 provides signals to turn micro LED chip 106 on/off via transistor 104 . The brightness signal 112 supplies signals with which the micro-LED chip 106 should have a specific brightness. The functions of the transistors 104 are similar to those of the TFT (Thin Film Transistor) in an LCD panel. A black matrix 102 comprising each pixel 10 can improve contrast and reduce interference between all pixels 100. The p-electrode (anode) of the micro-LED chip 106 is connected to the drain of the transistor 104, and the n-electrode (cathode) of the micro-LED chip is grounded.

In 11B Figure 1 shows a passive electrical schematic with two pixels in a micro LED display. Only three micro-LED chips 106 are provided in one pixel 100, and all the p-electrodes (anode) of the micro-LED chip 106 are connected to the image pickup signal 120, and all the n-electrodes (cathode) of the micro-LED chips Chips 106 are connected to switching signal 122 . The image sensing signal 120 provides image information directly to the micro LED chips 106, and the switching signal determines which micro LED chip 106 is turned on/off. When the switching signal is an open circuit, the connected micro LED chip is turned off. The switching signal 122 will be open circuit in turn so that the image signal 120 provides correct signal information to each micro LED chip 106 . The micro LED array can be driven in interlaced or non-interlaced mode to show image and motion. Please note that the GaAs substrate is not applicable in this embodiment.

A pixel design layout of the active electrical schematic in 11A on the binding substrate can on the 12A and 12B be obtained. In 12A the RGB layout is a sequence and would be easy to make. Area 108 will accommodate micro LED chips and the two bond pads 52 are provided. The zener diode can also be integrated into the driver circuits as a protection circuit. Transistor 104 may be an NMIS, PMIS, CMIS transistor, or a BJT. In a preferred embodiment, NMIS transistors are used. In this embodiment, a common cathode electrode would be optional. In 12B Another design layout is provided in a pixel when RGB micro-LED chips are to be lined up closely together for contrast enhancement.

In 13A Another embodiment of the present invention for micro LED chips is shown. For blue, green and red LED chips, the drive voltage and lifetime may differ due to the structures and materials of these LEDs. A simple and easy way or method of manufacturing micro LED display can only comprise blue micro LED chips coated with phosphor 73 . The phosphor 73 emits yellow light, and white light can be provided after the yellow light is mixed with the blue light of the micro-LED. Then, a transparent substrate 200 is provided with color filter 130 and black matrix 102 thereon. Therefore, when each micro LED chip is driven by an image signal, after the color filter 130, an image can be displayed. The phosphor 73 can produce a high color rendering index or color spectrum. That Substrate 200 with the color filter 130 and the black matrix is then fitted or attached to the LED chip to form an LED display as in 13C shown. In another embodiment, phosphor 73 and color filter 130 may first be formed on transparent substrate 200, as in FIG 13B shown. In this embodiment, the substrate 200 with the color filter 130, the phosphor 73 and the black matrix 102 is then fitted or attached to the LED chip, also as in FIG 13C shown. In another embodiment, the phosphor 73 can emit green and red together. In another embodiment, the micro LED chips may emit UV light and the phosphor 73 will emit RGB light. In this embodiment, the function of the color filter 200 is similar to that of the color filter in the TFT-LCD display, but there is no longer a liquid crystal layer. With the TFT-LCD panel, even if the image is completely dark, some white light will leak out of the LCD panel because the liquid crystal cannot completely turn off the backlight. On the other hand, in the present invention of the LED display panel, the LED can be turned off completely, so that the black image can be compared with a conventional CRT monitor or plasma display panel with excellent quality. 14A FIG. 12 is the plan view of the transparent substrate 100 to show four pixels 100. FIG. The black matrix 102 can be formed around a pixel as in FIG 14B shown.

In this invention, another embodiment is provided in which all LED chips in a passively driven LED display panel are not transferred to a bonding substrate. Please look 15A , the LED chips 40 already being formed on the sapphire substrate 10 with corresponding n/p ohmic contact electrodes 14/18. In this embodiment, the LED chips 40 emit blue light. The design of the configuration of the LED chips should be defined in accordance with the display pixel, and in this embodiment, the left three LED chips are grouped into one pixel while the right three LED chips are grouped into another pixel. Then a dielectric layer 210 is formed to cover the LED chips 40 and n/p ohmic contact electrodes 14/18 are exposed as in FIG 15B shown. Dielectric layer 210 may be silicon oxide, silicon nitride, TEOS, epoxy, or silicon. A transparent conductive layer such as ITO, IGO, IZO, IGZO, or AZO is formed and patterned as an image pickup signal line 120 to electrically contact each p-ohmic conductive electrode individually, as in FIG 15C shown. The image pickup signal line 120 can also be on 11B be obtained. Then another dielectric layer 212 such as silicon oxide, silicon nitride, epoxy or silicon is formed to cover the LED chips and the image pickup signal line 120. FIG. Multiple holes are formed in dielectric layer 212 to expose each n ohmic contact electrode 14, and another transparent conductive layer, such as ITO, IGO, IZO, IGZO, or AZO, is filled in each hole and placed on dielectric layer 212 as switch signal lines 122 structured as in 15D shown. The switch signal line 122 can also be on 11B be obtained. A passivation layer 65 is formed to cover the switch signal line 122 and high color rendering index phosphor 73 emitting yellow light to generate white light together with the blue GaN LED chip 40 . If the LED chip emits 40 UV, RGB mixed phosphors can be applied. A transparent substrate 200 coated with color filter 130 and black matrix 102 is intended to mount the micro LED chip 40 onto the epi substrate 10 as shown in FIG 15E shown. This creates a passive LED display with GaN LED chip.

Another embodiment for passive LED display panels is also given. Please refer 16 wherein the sapphire substrate 10 is formed with LED chips and flipped over to bond to the bonding substrate 50 with mating bond pads 52 . Similar to the previous embodiment, the configuration of the LED chips should be defined in accordance with the display pixel. Then, a microlens array 220 is formed on the back of the epi-substrate 10 as shown in FIG 15B shown. The microlens can be a single element with a plane surface and a spherical convex surface for refraction, or it must have two plane and parallel surfaces and focusing is achieved by varying the refractive index across the lens, which is a graded index lens. The microlens array 220 may be formed by molding or embossing from a master lens array. Then, a transparent substrate 200 with phosphor 73, color filter 130 and black matrix 102 is sequentially formed thereon to match each LED chip.

In 17 An apparatus for fabricating a micro LED display is shown. An xy stage 300 offers two directions that are horizontally orthogonal to each other. The xy stage 300 is used to provide a bonding substrate that moves along the xy directions so that the bond pads to be connected can be moved to a specific position. A z stage 302 on the xy stage 300 provides a direction orthogonal to the xy stage in the vertical direction. The purpose of z-stage 302 is to adjust the height of the binding substrate so that the LASER is at a desired position the epi-substrate can be focused. A chuck 304, such as an electrostatic chuck or a vacuum chuck, is provided on the z-stage 302 for attachment of the bonding substrate. Then, the bonding substrate 50 is held on the E-chuck 50 . An xy platform 310 having two similar orthogonal directions that run horizontally moves between the bonding substrate 50 and the LASER 320. The epi-substrate 10 is mounted on the xy platform 310 such that a desired LED chip can be placed in the desired position so that the LED chip can be irradiated by the LASER 320 and separated from the epi-substrate 10 to the bonding substrate 50. The xy platform 310 maintains the same pitch to the z-stage. The excimer LASER 320 is used to irradiate the epi-substrate so that the LED chip or chips can be separated from the epi-substrate 10. A controller 300 electrically connected to the xy stage 300, the z stage 302, the chuck 304, the xy platform 310 and the LASER 320.

The embodiment in 18 is an LED transmission device when LASER take off is not applicable. A pressing device 322 with a tip 323 replaces the Excimer LASER 320 in 14 . When the micro LED die on the tape is to be transferred to the bonding substrate, the tip of the presser extends or protrudes to knock the micro LED die down onto the bonding substrate.

The present invention also provides an embodiment of manufacturing a simplified display panel. Please refer 19A , a bonding substrate 50 is provided with mating bond pads 52 thereon. The wiring circuits 60, with or without active devices, are formed on the bonding substrate 50. FIG. The bonding substrate 50, rigid or flexible, can be PCB, silicon, SiC, ceramic, glass, or polyimide, and can be any substrate such that the circuitry can be placed thereon.

Please refer 19B , a plurality of GaN LED chips 40 are respectively transferred to the paired bonding pads by the flip-chip method mentioned above. Then, as in 19C 1, a black matrix 102 is formed on the bonding substrate 50. As shown in FIG. The black matrix 102 can be formed to isolate each GaN LED chip 40 instead of a pixel if required.

The patterned light-converting layer 72 is formed to cover each GaN LED chip to produce white light with or without diffusers, as in FIG 19D shown. The light conversion layer 72 may include phosphor or quantum dot, yellow phosphor (YAG or TAG), red phosphor, KSF (potassium fluoride silicon) phosphor and TriGain phosphor, WCG phosphor comprising β-SiAlON green phosphor, and KSF phosphor. In one embodiment, the light-converting layer 74 can cover three GaN LED chips or be formed within a pixel.

Please refer 19E , a color determination layer 132 such as color filter to define RGB in a pixel is formed directly on the light conversion layer 72 or 74 and aligned with each GaN LED chip 40 . The color determination layer 132 is formed in a conventional method by patterning steps three times for each color.

In the conventional LCD display, the light intensity emitted from the backlight module is first modulated by the liquid crystal panel, such as a liquid crystal, a polarizer, an alignment film, etc., while in the present invention of this embodiment, there is nothing to block the light from to modulate the GaN LED chips. The light intensity is significantly higher in this embodiment.

In this embodiment, the GaN LED chips are transferred from the epi substrate to the bonding substrate, and the current mass transfer problem is not yet solved. A further embodiment is thus provided to solve the mass transfer problem. to avoid mass transfer issuers].

Please refer 20A , an epi-substrate 10 such as sapphire or SiC is provided with a plurality of LED chips 40 formed thereon. Each LED chip 40 includes an n epi layer 12, a p epi layer 16, an n ohmic contact electrode 14 and a p ohmic contact electrode 18. Both the n ohmic contact electrode 14 and the p ohmic contact electrode 18 are transparent.

Then, a first insulating layer 64 is formed on the epi-substrate 10 and a plurality of contact holes are formed to expose the plurality of p ohmic contact electrodes 18 as shown in FIG 20B shown. The insulating layer 64 may be silicon oxide, silicon nitride, silicon oxynitride, BPSG (boron phosphosilicate glass), PSG (phosphosilicate glass), or other transparent dielectric materials. The formation of the insulating layer 64 can be done by chemical vapor deposition or by spin coating, depending on the materials of the insulating layer 64 . The multiplicity of contact holes can be achieved by a con conventional patterning etching process can be formed.

Please refer 20c , a first patterned transparent conductive layer 66 is formed on the first insulating layer 64 and filled in the plurality of contact holes so that each p ohmic contact electrode 18 can be electrically contacted with the first transparent conductive layer 66 . The first patterned transparent conductive layer 66 is patterned as a first plurality of signal lines on the first insulating layer to electrically connect to a row of the first electrodes of the plurality of GaN light emitting diode chips. In this embodiment, the first electrodes are p ohmic contact electrodes 18. Materials of the first transparent conductive layer 66 can be ITO (indium tin oxide), IGO (indium germanium oxide), IZO (indium zinc oxide), AZO (aluminum zinc oxide), and the first transparent conductive layer 66 can be formed first and later patterned by the sputtering or evaporation methods. The first transparent conductive layer 66 can also be patterned with the lift-off method, which is easier than the conventional patterning etching method.

Please note 20D , a second insulation layer 65 is formed to cover the first insulation layer 64 and the first transparent conductive layer 66 . Materials and formation of the second insulation layer 65 can be similar to the first insulation layer 64 . In this embodiment, the second insulating layer 65 is formed by conformal plating. In a simplified embodiment, the formation of the second insulating layer is identical to the formation of the first insulating layer 64. A plurality of contact holes can then be formed using a conventional patterning etch process, and then a second transparent conductive layer 67 is formed on the second insulating layer 65 and filled in the plurality of contact holes 68 so that each n ohmic contact electrode 14 can be electrically contacted with the second transparent conductive layer. The second transparent conductive layer 67 is patterned as a second plurality of signal lines on the second insulating layer to electrically contact a column of the second electrodes of the plurality of GaN light emitting diodes. In this embodiment, the second electrodes are the n ohmic contact electrodes 14. The material and configuration of the second transparent conductive layer 67 may be similar to the first transparent conductive layer 66. In a simplified embodiment, the formation of the second transparent conductive layer 67 can be identical to the first transparent conductive layer 66 .

Then, a passivation layer 90 is formed on the second insulating layer 65 and the second transparent conductive layer 67 by chemical vapor deposition, evaporation or spin coating, as in FIG 20E shown. Passivation layer 90 materials may be silicon oxide, silicon nitride, silicon oxynitride. In this embodiment, the top surface of the passivation layer 90 is flat, which is more suitable for the following steps. However, a conformal passivation layer 90 is also acceptable in the present invention.

Please refer 20F , a black matrix 102 is formed on the passivation layer 90 to define each pixel and prevent image blur between pixels. The materials and configuration for forming the black matrix 102 can be referred to conventional processes in the LCD art. The black matrix layer 102 in this embodiment is for isolating pixels. However, the black matrix layer 102 can be formed to isolate each GaN LED chip 40 .

Then a patterned light conversion layer 70 aligned with each GaN LED chip 40 is formed on the passivation as shown in FIG 20G shown. In another embodiment, the light-converting layer 72 is formed on the passivation layer 90 without aligning with each GaN LED die 40 . The light conversion layer 70 or 72, with or without diffusers, combined with each GaN LED chip 40 provides white light. The light conversion layer 70 or 72 may include phosphor or quantum dot, yellow garnet phosphor (YAG or TAG), red phosphor, KSF (potassium fluoride silicon) phosphor and TriGain phosphor, WCG phosphor, β-SiAlON green phosphor and KSF phosphor , include. In a simplified embodiment, when the black matrix 102 and the color determination layer 70 or 72 are dielectric or insulating, it is not necessary to form the passivation layer 90. FIG. In an alternative embodiment, phosphors can be mixed with epoxy or silicon and provided as the passivation layer 90 . Thus, it is not necessary to form a light conversion layer 70 or 72 after forming the passivation layer 90.

Please refer 20H , a patterned, color-determining layer 130, such as a color filter, is formed on the color conversion layer 70 or 72 using any conventional method, such as from LCD technology, to define RGB in one pixel at a time by one step . This creates a display with micro or mini LED chips on it.

In another embodiment, a black matrix may be formed on the sapphire substrate after each GaN LED die is formed. Please refer 21A , an epi-substrate 10, such as sapphire or SiC, is provided with a plurality of LED chips 40 formed thereon. Each LED chip 40 includes an n epi layer 12, a p epi layer 16, an n ohmic contact electrode 14 and a p ohmic contact electrode 18. A black matrix 102 has therefore been formed to define each pixel.

Please refer 21B , a first insulating layer 64 is formed on the epi-substrate 10 and each GaN LED chip 40, exposing the n contact ohmic electrode 14 and the p contact ohmic electrode 18 with the polishing process. Then, a first transparent conductive layer 66 is formed on each p ohmic contact electrode 18 so that each p ohmic contact electrode 18 is electrically contacted with the first transparent conductive layer 66 as shown in FIG 21C shown.

Please refer 21D , a second insulating layer 65 is formed on the first insulating layer 64 and the first transparent conductive layer 66 with a plurality of contact holes 68 to expose each n ohmic contact electrode 14 . A second transparent conductive layer 67 is formed on the second insulating layer 65 and is filled in each contact hole so that each n ohmic contact electrode 14 is electrically contacted with the second transparent conductive layer 67 .

Then, on the second insulation layer 65 and the second transparent conductive layer 67, a passivation layer 90 is formed as in FIG 21E shown. A color conversion layer 70 is formed on the passivation layer 90 and aligned on each GaN LED chip 40 . In another embodiment, a color conversion layer 72 is formed on the passivation layer 90 without aligning it on each GaN LED die 40 . Next, a color determination layer 130 is formed on the color conversion layer 70 or 72 as in FIG 21G shown.

For a simplified embodiment showing a GaN LED chip on a sapphire substrate, see FIG 22A until 22C are referenced showing cross-sectional views at various stages while the 23A until 23C a plan view in different stages corresponding to that in FIGS 22A until 22C shown embodiments show. The GaN LED chip comprising an n epi layer 12 and a p epi layer 16 is fabricated sequentially as shown in FIGS 22A and 23A shown. Then a patterned, transparent, conductive, n ohmic contact layer 14 is formed on the n epi layer 12, which is also electrically connected to other GaN LED chips in the same column as in FIGS 22B and 23B shown. Next, a patterned, conformal passivation layer 64 is formed on the GaN LED chip and the sapphire substrate 10 with the p epi layer 18 exposed, as in FIG 22C shown. The passivation layer 64, in a simplified embodiment, may be epoxy or silicon mixed with or without a phosphor. Then a patterned, transparent, conductive, p-ohmic contact layer 18 is formed on the p-epi layer 16, which is also electrically connected to other GaN LED chips in the same row, as in FIGS 22C and 23C shown. The p-ohmic, transparent, conductive contact layer 18 can be formed as a lift-off process or as a structuring etching process. In this embodiment, both the n ohmic transparent conductive contact layer 14 and the p ohmic transparent conductive contact layer 18 may be ITO, IZO, IGO, IGZO, AZO, or a combination thereof. Please note that the conformal passivation layer is 64 in 23C is not shown to show the relationship between the n ohmic transparent conductive layer 14 and the p ohmic transparent conductive layer 18 .

For another embodiment showing a GaN LED chip on a sapphire substrate, reference can be made to FIG 24A and 24B be referred to, where 24A a cross-sectional view and 24B a top view of the 24A indicates. In this embodiment, the n ohmic transparent contact layer 14 and the p ohmic transparent contact layer 18 are only used specifically for the GaN LED chip. A patterned conductive metal line 68 is formed on the n-ohmic transparent conductive contact layer 14 and electrically connects other n epi layers of GaN LED chips in the same column. On the other hand, a patterned conductive metal line 67 is formed on the p ohmic transparent conductive contact layer 18 and electrically connects other p epi layers of GaN LED chips in the same row. Although two conductive metal lines 67 and 68 are formed in this embodiment to increase manufacturing complexity, they can provide better electrical conductivity.

For another embodiment showing a GaN LED chip on a sapphire substrate, reference can be made to FIG 25A and 25B be referred to, where 25A a cross-sectional view and 25B a top view of the 25A indicates. The p ohmic transparent contact layer 18 is formed on the p epi layer 16 and is shared with other GaN LED chips in the same column electrically connected. Next, a patterned conformal passivation layer 64 is formed to cover the sapphire substrate 10, the p epi layer 16 and the p ohmic transparent conductive contact layer 18 with the n epi layer 12 exposed. The passivation layer 64, in a simplified embodiment, may be epoxy or silicon mixed with or without a phosphor. Then an n ohmic transparent conductive contact layer 14 is formed to electrically contact the n epi layer 12 to cover the conformal passivation layer 64 and is electrically connected to other GaN LED chips in the same row. The n-ohmic, transparent, conductive contact layer can be formed as a lift-off process or as a structuring etching process. In this embodiment, both the transparent conductive n ohmic contact layer 14 and the transparent conductive p ohmic contact layer 18 may be ITO, IZO, IGO, IGZO, AZO, or a combination thereof. In this embodiment, the order of formation of the n ohmic contact transparent conductive layer 14 and the p ohmic contact transparent conductive layer 18 can be reversed without affecting the performance of the display. If the color determination layer is non-conductive and no phosphor is mixed into the passivation layer 64, the color determination layer 130 can be formed directly on the n ohmic transparent conductive contact layer 14. FIG.

For the above embodiments, this display panel is very suitable for a portable display device.

The present invention offers advantages including the mass transfer of micro-LEDs being industrially and commercially available first. All micro-LED chips are transferred directly from the epi-substrate to the bonding substrate, thus increasing throughput. Also, mass production for micro LED display may be possible. In this invention, the structure and fabrication can be adapted to phosphors. In addition, quaternary red LED chips can be formed directly on a bonding substrate when the bonding substrate is GaAs. If color filter and phosphor can be applied to LED display, only GaN LED chips are used for LED display. For some specific configurations, mass transfer is not required in passive LED displays with signal lines formed directly on the GaN LED chip and sapphire substrate. In the present invention, there is no packaging process.

The present invention also offers advantages in that the light intensity in the present display is significantly increased compared to conventional LCDs, due to which in these the light intensity of the backlight module is modulated by a liquid crystal layer and diffuser, polarizer and other transparent films, while in the present invention nothing modulates the GaN LED chip.

All of the materials in the present invention can be integrated on the binding substrate or sapphire substrate, so there is no separate color filter process on another transparent substrate. For the embodiment that the GaN LED chips are formed on the sapphire substrate, there is no mass transfer problem compared to any other micro or mini LED displays, so the yield in manufacturing the display can be very high .

The manufacturing process of a display is simplified, and the manufacturing cost is thus reduced with high yield.

The present invention takes advantage of the fact that all the steps in the manufacturing process are mature and the equipment and facilities are also mature. Therefore, there is no need to develop other processes, equipments or facilities.

Although the present invention has been described in accordance with the illustrated embodiments, those skilled in the art will recognize that there could be variations on the embodiments and such variations would be within the spirit and scope of the present invention. Accordingly, many modifications can be made by one skilled in the art without departing from the spirit and scope of the appended claims.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US8794501 [0004]

Claims (12)

A scoreboard comprising: a bonding substrate having driver circuits and a plurality of paired bonding electrodes thereon; a plurality of GaN light emitting diode chips each electrically fixed to the plurality of paired bonding electrodes; a light conversion layer structured as a plurality of regions each covering the plurality of GaN light emitting diode chips; and a patterned color definition layer on the light conversion layer and respectively aligned to the plurality of GaN light emitting diode chips. A scoreboard comprising: a sapphire substrate having a plurality of GaN light emitting diode chips thereon; a patterned first ohmic contact transparent conductive layer electrically connected to a first conductor type of the plurality of GaN light emitting diode chips; a patterned passivation layer covering the patterned first ohmic transparent conductive contact layer and the plurality of GaN light emitting diode chips and exposing a second conductivity type of the plurality of GaN light emitting diode chips; and a patterned second ohmic transparent conductive contact layer electrically connected to the second conductor type of the plurality of GaN light emitting diode chips. The scoreboard after claim 2 , wherein the patterned passivation layer is mixed with a light conversion material. The scoreboard after claim 3 , further comprises a color definition layer over the plurality of GaN light emitting diode chips. The scoreboard after claim 1 or 4 , where the color definition layer is a color filter to define RGB in a pixel. the scoreboard claim 2 , further comprising a first metal line on the first ohmic contact transparent conductive layer; and a second metal line on the second transparent conductive contact layer. A method of forming a display panel, comprising: providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon, each of the plurality of GaN light emitting diode chips having a first electrode and a second electrode; providing a bonding substrate having driver circuits and a plurality of paired bonding electrodes thereon; transferring the plurality of GaN light emitting diode chips onto the plurality of paired bonding electrodes; providing a light conversion layer on each of the plurality of GaN light emitting diode chips; and Formation of a patterned color definition layer on the light conversion layer aligned with the plurality of GaN light emitting diode chips. A method of forming a display panel, comprising: providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon; forming a patterned first ohmic transparent conductive contact layer on a first conductor type of the plurality of GaN light emitting diode chips; forming a patterned conformal passivation layer on the patterned first ohmic conductive transparent conductive contact layer and the plurality of GaN light emitting diode chips, wherein a second conductor type of the plurality of GaN light emitting diode chips is exposed; forming a second ohmic transparent conductive contact layer electrically connected to the second conductor type of the plurality of GaN light emitting diode chips. The procedure after claim 8 further comprising a step of mixing a light conversion material into the passivation layer prior to said step of forming the patterned, conformal passivation layer. The procedure after claim 8 further comprises a step of forming a color determination layer over the plurality of GaN light emitting diode chips after said step of forming a second ohmic transparent conductive contact layer. The procedure after claim 7 or 10 , wherein the color determination layer is a color filter to define RGB in a pixel. The procedure after claim 8 further comprises the steps of forming a patterned first metal line on the first ohmic transparent conductive contact layer after said step of forming a first ohmic transparent conductive contact layer; and forming a patterned second metal line on the second ohmic transparent conductive contact layer after said step a to form second ohmic transparent conductive contact layer.

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