KR20220147565A - System and Method for Making Micro LED Display - Google Patents

Abstract

A micro LED display can be made very accurately and efficiently by mainly using chip-by-chip isolation technology. First, after an epitaxy process, an LED epitaxial wafer is processed into a micro LED. Second, a bonding substrate having a driving circuit on the LED epitaxial wafer is provided. Then, each LED chip can be simultaneously or sequentially fixed to the substrate on a chip-by-chip basis, and each LED chip can be simultaneously or sequentially transferred using isolation technology. The LED epitaxial wafer itself can be also provided as an LED display substrate. A light conversion layer and a color definition layer can be individually patterned and sequentially formed on each LED chip to provide an LED display.

Description

System and Method for Making Micro LED Display

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

Following the conventional TFT LCD display and OLED display, micro LED is considered as the next-generation advanced display. The advantages of micro LEDs inherited from conventional LEDs are low power consumption, high brightness, short response time, and long lifespan. A 55-inch crystal LED TV assembled with micro LEDs was announced and manufactured by Sony in 2012, with more than 6 million micro LEDs having a million-level contrast, over 140% NTSC, and no response time problems compared to LCD displays. High-resolution pixels that do not have a lifespan problem compared to OLED displays were used. The technology of micro LED display reduces the LED chip size to 1% of the conventional LED chip, applies a single micro LED to a high-resolution display, and reduces the pitch between two micro LEDs from mini-meter to micro-meter, each It treats the pixels individually and drives each micro LED in the micro LED array individually.

However, in the case of each single micro LED, it is difficult to efficiently transfer millions of micro LEDs in one display from the substrate to the display, so the conventional manufacturing process cannot be applied to mass production; That's the mass transfer problem.

Several approaches have been proposed to solve this problem. A US patent to Andreas Bibl et al., US Pat. No. US 8,794,501, states that all microLEDs on an epi-substrate are completely transferred to a temporary or bonding substrate at one time, after which each single microLED is bonded using a phase shift. It refers to being individually picked up from the bonding substrate to the receiving substrate of the display panel. The bulk transfer challenge is still that millions of microLEDs have to be individually picked up from the bonding substrate to the receiving substrate; It takes too much time, and a low yield is generated. Some other solutions, such as using fluid filters or dropping by gravity, are still not commercially or industrially available.

To solve the mass transfer problem, especially to transfer the RGB LED chip to the bonding substrate, the solution is to transfer only the nitride-based LED chip to the bonding substrate. However, since nitride-based LEDs cannot provide red light, they cannot realize the full color of micro/mini LED displays.

Therefore, there is a need to provide an industrially and commercially viable solution to the problem of mass transfer for micro LED fabrication.

It is an object of the present invention to provide a commercially and industrially viable solution for a method of manufacturing a micro LED display, a micro LED display and a device for manufacturing a micro LED display.

Accordingly, the present invention provides a method of forming a display panel, the method comprising: providing a first substrate having a plurality of first light emitting diode chips on a first substrate - each of the plurality of first light emitting diode chips for the first light emitting diode chip, a pair of ohmic electrodes are formed on the chip of each first light emitting diode emitting light of a first wavelength; providing a second substrate having a driving circuit for a display panel and a plurality of bonding pads forming a pair; flipping the first substrate to bond the plurality of first light emitting diode chips on the plurality of bonding pads forming a pair; separating the plurality of first light emitting diode chips from the first substrate; and reheating the second substrate so that the plurality of first light emitting diode chips are fixed on the second substrate.

In a preferred embodiment, the first substrate may be sapphire or SiC, and the plurality of first light emitting diode chips comprises III-nitride for emitting UV, blue or green light. The separating step is performed using laser exposure if the first substrate is sapphire or SiC.

In a preferred embodiment, the first substrate may be a tape, and the plurality of first light emitting diode chips comprises III-arsenic or III-phosphide for emitting red light. Separation is performed by pressing the front surface of the first substrate without a plurality of light emitting diode chips when the first substrate is a tape.

In a preferred embodiment, the second substrate may be a PCB, silicon, silicon carbide or ceramic. The ceramic substrate may include AlN or aluminum oxide (Al ₂ O ₃ ).

In a preferred embodiment, the second substrate may be GaAs, comprising a plurality of second light emitting diode chips, each second light emitting diode chip of the plurality of second light emitting diode chips having a second wavelength longer than the first wavelength emit light

In a preferred embodiment, the drive circuit may be an active circuit array or a passive circuit array. The active circuit includes a plurality of transistors for driving the plurality of light emitting diode chips.

In a preferred embodiment, the first pitch of the first plurality of light emitting diode chips on the first substrate is equal to the second pitch of the paired plurality of bonding pads on the second substrate. The inverting step is performed so that the plurality of first light emitting diode chips are aligned with the paired plurality of ohmic electrodes. Separation is performed in units of blocks for each of the first light emitting diode chips on the first substrate.

In a preferred embodiment, the first pitch of the first plurality of light emitting diode chips on the first substrate is smaller than the second pitch of the paired plurality of bonding pads on the second substrate. The flipping step is performed so that one of the plurality of first light emitting diode chips is aligned with one of the paired plurality of ohmic electrodes, and then the step of separating is performed.

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

In a preferred embodiment, the light having the third wavelength and the first wavelength provides white light. The method may further include, after the reflow step, providing a color filter on a third transparent substrate on the second substrate.

The present invention also includes a GaAs substrate having a driving circuit for a display panel and a plurality of paired bonding pads, wherein the GaAs substrate includes a plurality of red light emitting diode chips, and the GaAs substrate includes a plurality of paired bonding pads. and a plurality of GaN light emitting diode chips electrically secured to them.

The present invention also provides a bonding substrate having driving circuits and a plurality of bonding electrodes paired thereon; a plurality of GaN light emitting diode chips respectively electrically fixed to a plurality of paired bonding electrodes; a phosphor layer patterned as a plurality of regions suitable for individually covering a plurality of GaN light emitting diode chips; and a transparent substrate provided thereon with a color filter layer for aligning the plurality of GaN light emitting diode chips, respectively.

In a preferred embodiment, the bonding substrate may be a PCB, silicon, silicon carbide or ceramic. The ceramic substrate may include AlN or aluminum oxide (Al ₂ O ₃ ).

In a preferred embodiment, the drive circuit may be an active circuit array or a passive circuit array. The active circuit includes a plurality of transistors for driving the plurality of light emitting diode chips.

The present invention also provides a method of forming a display panel, comprising: providing a plurality of GaN light emitting diode chips on a sapphire substrate, each of the plurality of GaN light emitting diode chips having a first electrode and a second electrode; providing a bonding substrate having a driving circuit and a plurality of bonding electrodes paired thereon; transferring a plurality of GaN light emitting diode chips to a plurality of paired bonding electrodes; providing a phosphor layer on each of the plurality of GaN light emitting diode chips; and fitting the transparent substrate with the color filter to the bonding substrate such that the color filter is aligned with the plurality of GaN 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 the sapphire substrate to which the first electrode and the second electrode are exposed; a first transparent conductive layer patterned as a plurality of first signal lines on the first dielectric layer to be electrically connected to a column of first electrodes of the plurality of GaN light emitting diode chips; a second dielectric layer on the first transparent conductive layer to which the first dielectric layer and the second electrode are exposed; a second transparent conductive layer patterned as a second plurality of signal lines on the second dielectric layer to be electrically connected to the second row of electrodes of the plurality of GaN light emitting diodes; a passivation layer blanket covering the second dielectric layer and the second transparent conductive layer; a phosphor layer patterned as a plurality of regions suitable for covering a 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 forming a display panel, comprising the steps of providing a sapphire substrate having a plurality of GaN light emitting diode chips thereon, wherein the plurality of GaN light emitting diode chips each 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 electrode and the second electrode; forming a first transparent conductive layer on the first dielectric layer; patterning the first transparent conductive layer into a plurality of first signal lines to be electrically connected to a column of a first electrode 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 electrode; forming a second transparent conductive layer on the second dielectric layer; patterning a second transparent conductive layer into a plurality of second signal lines for electrically connecting to a row of second electrodes of the plurality of GaN light emitting diode chips; forming a passivation layer overlying the patterned second transparent conductive layer and the second dielectric layer; providing a phosphor layer over the passivation layer; and fitting the transparent substrate with the color filter layer to the sapphire substrate such 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 providing a first motion having two horizontal directions orthogonal to each other; a mounting stage on said first stage for fixing a driving circuit and a second substrate having a plurality of paired bonding pads, wherein a plurality of light emitting diode chips face a plurality of paired bonding pads; means for separating the plurality of light emitting diode chips from the first substrate; and a controller for controlling the platform, the first stage, the mounting stage, and the separating means such that a display panel is formed.

In a preferred embodiment, the apparatus may further comprise a second stage between the first stage and the mounting stage to provide vertical motion.

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

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

The present invention also provides a display panel, comprising: a bonding substrate having a driving circuit and a plurality of bonding electrodes forming a pair thereon; a plurality of GaN light emitting diode chips each electrically fixed to a plurality of bonding electrodes forming a pair; a light conversion layer patterned into a plurality of regions suitable for respectively covering a plurality of GaN light emitting diode chips; and a patterned color definition layer on the light conversion layer and each aligned with the plurality of GaN 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; a patterned first ohmic contact transparent conductive layer electrically connected to a first conductivity type of the plurality of GaN light emitting diode chips; a patterned passivation layer covering the patterned first ohmic conductive transparent conductive 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 second patterned ohmic contact transparent conductive layer electrically connected to a second conductivity type of the plurality of GaN light emitting diode chips.

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

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

In a preferred embodiment, the color definition layer is a color filter for defining RGB in one pixel.

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

The present invention also provides a method of forming 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 a driving circuit and a plurality of bonding electrodes forming a pair thereon; transferring a plurality of GaN light emitting diode chips to a plurality of bonding electrodes forming a pair; providing a light conversion layer on each of the plurality of GaN light emitting diode chips; and forming a patterned color definition layer on the light conversion layer aligned with the plurality of GaN light emitting diode chips.

The present invention also provides a method of forming a display panel, comprising: providing a plurality of GaN light emitting diode chips on a sapphire substrate; forming a patterned first ohmic contact transparent conductive layer on a first conductivity type of the plurality of GaN light emitting diode chips; forming a patterned first ohmic conductive transparent conductive layer having a second conductivity type of the exposed plurality of GaN light emitting diode chips and a patterned conformal passivation layer on the plurality of GaN light emitting diode chips; and forming a second ohmic contact transparent conductive layer electrically connected to a second conductivity type of the plurality of GaN light emitting diode chips.

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

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

In a preferred embodiment, the color definition layer is a color filter for defining RGB in one pixel.

In one preferred embodiment, the method further comprises: forming a patterned first metal line on the first ohmic contact transparent conductive layer after the step of forming the first ohmic contact transparent conductive layer; and forming the patterned second metal line on the second ohmic contact transparent conductive layer after the step of forming the second ohmic contact transparent conductive layer.

Other advantages of the present invention will become apparent in conjunction with the accompanying drawings from the following description, which is illustrated by way of illustration and specific embodiments of the invention by way of illustration and example.

This display panel may be well suited for a wearable display device.

The present invention provides advantages including the industrial and commercial availability of mass transfer micro LEDs. Since all the micro LED chips are transferred directly from the epitaxial substrate to the bonding substrate, the throughput can be improved. In addition, mass production of micro LED displays may be possible. In the present invention, structure and fabrication can be applied to phosphors. In addition, when the bonding substrate is GaAs, a quaternary red LED chip may be directly formed on the bonding substrate. When color filters and phosphors can be applied to LED displays, only GaN LED chips are configured in LED displays. For some specific configurations, no bulk transfer is required for passive LED displays in which signal lines are formed directly on a GaN LED chip and a sapphire substrate. In the present invention, there is no packaging process.

In the present invention, the light intensity of the current display is significantly improved compared to the conventional LCD due to the liquid crystal layer, the diffuser, and the polarizer, and while other transparent films modulate the light intensity of the backlight module, in the present invention, modulating the GaN LED chip is nothing. It offers the advantage of not having

Since all of the materials of the present invention can be integrated into the bonding substrate or the sapphire substrate, there is no need for a separate color filter process on another transparent substrate. In the case of the embodiment in which the GaN LED chips are formed on a sapphire substrate, a mass transfer problem does not occur compared to all other micro or mini LED displays, and thus the display manufacturing yield can be very good.

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

The present invention has the advantage of maturing all stages of the manufacturing process and maturing equipment and equipment. Accordingly, there is no need to develop other processes, equipment or facilities.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be readily understood by the following detailed description taken in conjunction with the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar structural elements, wherein:
1A-1D are schematic diagrams of structures at various stages during formation of LED chips on an epi-substrate according to an embodiment of the present invention;
2A and 2B are schematic diagrams of structures at various stages during preparation for transferring a micro LED chip from an epi-substrate to a display according to an embodiment of the present invention;
3A-3C are schematic diagrams of structures at various stages during a laser lift-off process in accordance with an embodiment of the present invention;
4A and 4B are schematic diagrams of structures at various stages during separation between an epi-substrate and a bonding substrate according to an embodiment of the present invention;
5A-5D are schematic diagrams of structures at various stages during formation of further LED chips on a bonding substrate according to an embodiment of the present invention;
6A-6C are schematic diagrams of a phosphor on LED chips according to an embodiment of the present invention;
7A-7G are schematic diagrams of structures at various stages during formation of LED chips on a bonding substrate according to another embodiment of the present invention;
8A-8E are schematic diagrams of structures at various stages during formation of LED chips transferred to a temporary substrate according to an embodiment of the present invention;
9 is a flowchart showing the steps of forming red LED chips and driving circuits on a bonding substrate according to an embodiment of the present invention;
10A-10M are schematic diagrams of structures at various stages during forming drive circuits with red LED chips and blue/green LED chips transferred onto a bonding substrate according to another embodiment of the present invention;
11a and 11b are schematic diagrams of LED display circuits according to two embodiments of the present invention;
12a and 12b are schematic diagrams of an LED display layout according to two embodiments of the present invention;
13A is a schematic diagram of a cross-sectional view of an LED display using a color filter and phosphor on LED chips in one embodiment of the present invention;
13B is another schematic diagram of a cross-sectional view of an LED display using a color filter and phosphor on a transparent substrate in one embodiment of the present invention;
13C is another schematic diagram of a cross-sectional view of an LED display using a color filter in one embodiment of the present invention;
14A is a schematic diagram of a top view of an LED display using color filters in one embodiment of the present invention;
14B is a schematic diagram of a top view of an LED display using a color filter with a black matrix in one embodiment of the present invention;
15A-15E are schematic diagrams of structures at various stages during formation of a passive GaN LED display on sapphire with coated phosphors and a color filter substrate according to another embodiment of the present invention;
16 is a schematic diagram of a cross-sectional view of a passive GaN LED display having a micro lens array according to another embodiment of the present invention;
17 is a schematic diagram of an apparatus for forming LED chips on a bonding substrate according to an embodiment of the present invention;
18 is a schematic diagram of an apparatus for forming LED chips on a bonding substrate according to another embodiment of the present invention;
19A-19E are schematic diagrams of cross-sectional structures at various stages during formation of a GaN LED display on a bonding substrate having a coated phosphor and a color filter substrate according to another embodiment of the present invention;
20A-21H are schematic diagrams of cross-sectional structures at various stages during formation of a GaN LED display on a sapphire with a color definition and a coated phosphor according to an embodiment of the present invention;
21A-21G are schematic diagrams of cross-sectional structures at various stages during formation of a GaN LED display on sapphire with a coated phosphor and color definition according to another embodiment of the present invention;
22A is a schematic diagram of a cross-sectional structure showing GaN LED chips on a sapphire substrate of a display according to a simplified embodiment of the present invention;
22B is a schematic cross-sectional view showing a GaN LED chip on a sapphire substrate having a first ohmic contact transparent conductive layer of a display according to the embodiment of FIG. 22A;
22C is a schematic diagram of a cross-sectional view showing a GaN LED chip on a sapphire substrate with a second ohmic contact transparent conductive layer of a display according to the embodiment of FIG. 22A;
23A is a schematic diagram of a top view showing a GaN LED chip on a sapphire substrate of a display according to the embodiment of FIG. 22A;
23B is a schematic diagram of a top view showing a GaN LED chip on a sapphire substrate with a first ohmic contact transparent conductive layer of a display according to the embodiment of FIG. 23A ;
23C is a schematic diagram of a top view showing a GaN LED chip on a sapphire substrate with a second ohmic contact transparent conductive layer of a display according to the embodiment of FIG. 23B;
24A is a schematic diagram of a cross-sectional structure showing a GaN LED chip on a sapphire substrate of a display according to another simplified embodiment of the present invention;
24B is a schematic diagram of a top view showing a GaN LED chip on a sapphire substrate of a display according to the embodiment of FIG. 24A;
25A is a schematic diagram of a cross-sectional structure showing a GaN LED chip on a displayer sapphire substrate according to another simplified embodiment of the present invention;
25B is a schematic diagram of a top view showing a GaN LED chip on a sapphire substrate of a display according to the embodiment of FIG. 25A ;
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may be described in detail herein. The drawings may not be to scale. However, the drawings and detailed description thereof are not intended to limit the invention to the specific form disclosed, but, on the contrary, cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. should be understood as intended to include

As used herein, the term “substrate” generally refers to a plate formed of a semiconductor or non-semiconductor material. Examples of such semiconductor or non-semiconductor materials include, but are not limited to, single crystal silicon, silicon carbide, gallium arsenide, indium phosphide, sapphire, ceramic, glass, and PCB. Such substrates may generally be found and/or processed in semiconductor manufacturing facilities. An epi-substrate refers to a plate provided for epitaxial growth in a semiconductor manufacturing facility. A bonding substrate refers to a plate having circuits for accommodating an electronic device and bonding pads thereon.

In the case of a 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 include a wafer on which all types of such layers may be formed. One or more layers formed on the substrate may be patterned. For example, a substrate may include a plurality of dies/chips each having a repeatable patterned feature. The formation and processing of the material layers can ultimately result in finished semiconductor devices. As such, the substrate may include a plate on which not all layers of the finished semiconductor device are formed, or a substrate on which all layers of the finished semiconductor device are formed.

The substrate may further include at least some integrated circuits (ICs), or optoelectronic devices such as LED chips.

The term "LED" generally refers to a light emitting diode capable of emitting red, green, blue, or UV light by driving a specific direct current, which may or may not be packaged.

The term "LED chip" generally refers to an LED formed by epitaxial growth on a substrate having paired Ohmic contact electrodes, which may or may not be separated from the episubstrate. The LED chip of the present invention may be formed on an epitaxial substrate or connected to a bonding substrate.

A typical LED chip has a size of about 14x14 mil ² , which is 355.6x355.6 μm ² , a micro LED chip typically has a size less than 100X100 μm ² , with a preferred size less than 50X50 μm ² .

The term “circuit” may include resistors, diodes or transistors in the present invention.

The term "index" in the present invention refers to a pitch between two LED chips on an epi substrate or a bonding substrate.

The term "color filter" is used to filter light in a plurality of wavelength bands. In the present invention, the color filter refers to an RGB filter that passes red, green, and blue light, respectively.

The steps of the process flow of the present invention should generally be interchangeable unless a logical order is required.

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

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various exemplary embodiments of the present invention will now be more fully described with reference to the accompanying drawings in which several exemplary embodiments are shown. Without limiting the protection scope of the present invention, all descriptions and drawings of the embodiments will be referred to by way of example as a micro LED display and a manufacturing method thereof. However, the examples are not used to limit the present invention to a micro LED transfer method.

In the drawings, the relative dimensions between each component and all components may be exaggerated for clarity. In the following description of the drawings, the same or similar reference numbers refer to the same or similar components or entities, and only differences for individual embodiments are described.

Accordingly, while exemplary embodiments of the present invention are possible in various modifications and alternative forms, the embodiments are shown by way of example in the drawings and will be described in detail herein. However, there is no intention to limit the exemplary embodiments of the present invention to the specific form disclosed, but on the contrary, it is to be understood that the exemplary embodiments of the present invention cover all modifications, equivalents and alternatives falling within the scope of the present invention. .

The present invention provides a method in which micro LED chips can be directly transferred to a bonding substrate, wherein the bonding substrate includes a driving circuit as well as being provided for a display. First, for III-nitride based compounds, GaN based compounds are formed using epitaxial growth on sapphire, SiC, Si, GaN or ZnO substrates to provide green, blue or UV light. In the case of III-arsenic or III-phosphide compounds, a GaAs-based compound or AlInGaP is formed using epitaxial growth on a GaAs, GaSb, GaP or InP substrate to provide red light. After the epitaxial growth process, the epi-layers are processed into chip patterns and ohmic contact electrodes are respectively formed on the p/n epi-layers. A bonding substrate is provided having drive circuits and bonding pads formed thereon for accommodating micro LED chips. III-nitride micro LED chips on sapphire substrate can be transferred using LASER lift-off technology, III-arsenic, III-phosphide micro LED chips or III-nitride micro LED on SiC, Si, ZnO substrate The chips may be transferred using a mechanical pressing method. The mass transfer procedure can be performed block-by-block for the same index, sequentially chip-by-chip for unequal indexes, or directly as a whole substrate transfer. Subsequently, the bonding substrate with the transferred micro LED chips is reheated so that the bonding pads and the micro LED chips can be bonded using eutectic bonding, soldering bonding or silver epoxy baking. have. Therefore, the mass transfer problem can be solved in industrial and commercial problems.

In one embodiment, one 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, one pixel of the display may include a blue micro LED chip, a blue micro LED chip coated thereon with a green phosphor, and a blue micro LED chip coated thereon with a red phosphor. In another embodiment, one pixel of the display may include a blue micro LED chip, a green micro LED chip and a blue micro LED chip coated thereon with a red phosphor. In another embodiment, one pixel of the display may include three UV micro LED chips each coated thereon with an RGB phosphor. In another embodiment, one pixel of the display may include only one blue micro LED chip for a monochromatic display. In one embodiment, one pixel of the display may contain three micro LED chips with yellow phosphor all coated thereon, after which the RGB color filter will filter the white light into a full color image. In this embodiment, the function of the RGB filter will be similar to that in the TFT LCD. In this embodiment, in order to meet a wide color gamut, a red phosphor or quantum dot technology can be applied in this embodiment. The red phosphor may include a nitride phosphor, or a white phosphor that is enhanced with red light, such as GE's Potassium Fluoride Silicon (KSF) phosphor and TriGain phosphor. Sharp also develops WCG phosphors, including β-SiAlON green phosphors and KSF phosphors.

In one embodiment, the bonding substrate may be GaAs and the driving circuits as well as the red micro LED chips may be formed on GaAs. Therefore, only the blue and green micro LED chips need to be transferred to the bonding substrate. Alternatively, a blue micro LED chip with a green phosphor such as silicate phosphor or β-SiAlON green phosphor on top of the blue micro LED chips is transferred to the bonding substrate.

It is noted that turning now to the drawings, the present invention will be more clearly described with reference to the drawings.

In FIG. 1A , a substrate 10 for epitaxial growth is provided, which may be Si, SiC, ZnO, GaN, sapphire (Al ₂ O ₃ ), GaAs, GaSb, GaP or InP. However, GaAs and sapphire are preferred in one embodiment of the present invention as epi substrates. In the case of the III-nitride compound, the epi substrate 10 may be sapphire, SiC, Si, ZnO or GaN, and in the case of the III-arsenic compound, the substrate 10 may be GaAs, GaSb, GaP or InP. The orientation of the substrate 10 is selected for epitaxial growth of III-arsenic, III-phosphide, or III-nitride compounds. In one embodiment, the sapphire substrate may be a sapphire substrate patterned to enhance brightness.

1B, an epitaxial-growth process is provided to form epilayers. A first epitaxial layer 12 having a first conductivity is formed on the epitaxial substrate 10 , and a second epitaxial layer 16 having a second conductivity is formed on the first epitaxial layer 12 . The second conductivity is opposite to the first conductivity. In one preferred embodiment, the first conductivity is n-type and the second conductivity is p-type. A single quantum well layer or multiple quantum well layer (not shown in FIG. 1B ) is always prepared using the prior art for the first epitaxial layer 12 and the second epitaxial layer 16 . ) is formed between In the case of the sapphire, SiC and Si epitaxial substrate 10 , the low-temperature buffer layer 22 is formed before the first epitaxial layer 12 is formed to promote two-dimensional growth. In the present invention, green, blue or UV light may be emitted by a III-nitride compound, whereas red light may be emitted by a III-arsenic compound or a III-phosphide compound. In one embodiment, epilayers 12 and 16 are Al _x Ga _(1-x) As, (Al _x Ga _(1-x))y In _(1-y) P, y-0.5 (for GaAs) lattice match) or Al _x In _y Ga _(1-xy) N. In one embodiment, epilayers 12 and 16 will emit blue light.

In FIG. 1C , two electrodes are respectively formed on the first and second epitaxial layers. A portion of the second epitaxial layer 16 is removed using a conventional patterning method comprising a lithography step and an etching step, and for the etching step, an anisotropic etching method will be preferred. Thereafter, the first ohmic contact electrode 14 is formed on the first epitaxial layer 12 by a lift-off method or by depositing an ohmic contact material layer on the first epitaxial layer 12 . and removing unnecessary portions of the ohmic contact layer using a conventional patterning method including a conventional lithography step and an etching step. The material of the first ohmic contact electrode 14 is Ge/Au, Pd/Ge, CrAu, CrAl, Ti, TiN, Ti/Al, Ti/Al/ for III-nitride, III-phosphide or III-arsenic compound, respectively. Ni/Au, Ta/Ti/Ni/Au, V/Al/V/Au, V/Ti/Au, V/Al/V/Ag, IZO, or ITO. The second ohmic contact contact electrode 18 is formed on the second epitaxial layer 16 by a lift-off method or by depositing an ohmic contact material layer on the second epitaxial layer 18, Unnecessary portions of the ohmic contact layer are removed using conventional patterning in an etching method including a lithographic method and an etching method including an etching method. The material of the second electrode 18 is Ni, Au, Ag, Pd, Pt, AuBe, AuZn, PdBe, NiBe, NiZn, PdZn, AuZn, Ru/ for III-nitride, III-phosphide or III-arsenic compound, respectively. It may be a metal having a high work function, such as Ni/ITO, Ni/Ag/Ru/Ni/Au, Ni/Au, or ITO. The lift-off method in the process of forming the ohmic contact electrodes of the present embodiment includes first depositing photoresist layers on the epitaxial layers 12 or 16, exposing and developing a photoresist layer having a pattern, and a photoresist layer. depositing a layer of ohmic contact material on the overexposed epilayers 12 or 16, followed by direct removal of the photoresist layer. The ohmic contact material layer of the photoresist layer will be removed at the same time. The lift-off method has the advantage of omitting one etching step.

In FIG. 1D , a mesa etching process is performed and scribe lines are formed simultaneously using a conventional patterning to etch method to distinguish all LED chips 40 . Forming the ohmic contact electrodes and the mesa is referred to as a chip process, and the order of the steps of forming the ohmic contact electrode in FIG. 1C and forming the mesa in FIG. 1D may be reversed or reversed. Although not shown in the drawings in order not to defocus the present invention, a passivation layer having openings for the first and second ohmic contact electrodes is formed on the micro LED chip to protect all the micro LED chips. can be

In FIG. 2A , the bonding substrate 50 is provided with driving circuits 60 and paired bonding pads 52 thereon. The bonding substrate 50 may be a PCB, silicon, silicon carbide, AlN ceramic or aluminum oxide (Al ₂ O ₃ ) ceramic, glass, or GaAs. The method of forming the driving circuits 60 and the paired bonding pads 52 may be any conventional technique. The back surface of the bonding substrate 50 is preferably flat. If LLO is to be performed later, the back side of the bonding substrate 50 must be polished.

The micro LED chips are transferred to the bonding substrate. In Fig. 2b, the processed episubstrate 10 of Fig. 1d is inverted, and each LED chip 40 has respective paired bonding pads 52 such that the index on the epi substrate is the same as the index on the bonding substrate. are sorted on The bonding pads 30 may include eutectic bonding, solder bonding, and an epoxy paste using silver.

A chip-by-chip LASER exposure is then introduced in FIG. 3A . In this embodiment, only one chip is transferred at a time for a particular LED color. However, a block of LEDs may be transferred simultaneously if all LEDs emit the same color in different applications or embodiments. The first LED chip is irradiated by laser exposure 32 for the low temperature buffer layer 22 so that the GaN epitaxial layer 12 is separated from the sapphire epitaxial substrate 10 . Accordingly, the first LED chip is separated from the epi-substrate 10 . In Figure 3a the ohmic contact electrodes are very close to the paired bonding pads; But they don't make exact contact. When the first LED chip is exposed to a laser, the epi substrate 10 is sufficiently close to the bonding substrate 50 so that the first LED chip can be separated from the epi substrate 10 and directly transferred to the bonding substrate 50 . . In the case of other conventional laser lift-off processes, micro LED chips are first adhered to paired bonding pads and then irradiated by laser exposure. In the present invention, laser exposure is first performed so that the micro LED chip can be selectively bonded to the bonding substrate 50 . Recipes such as wavelength, laser power, beam size and shape, and exposure time may be of any conventional technique. In one embodiment, the KrF excimer laser may be applied with a wavelength of 248 nm, a pulse of about 3-10 ns, and an energy density of about 120-600 mJ/cm ² . In another embodiment, the Nd:YAG laser may be applied with a wavelength of 355 nm, a pulse of about 20-50 ns, and an energy density of about 250-350 mJ/cm ² . In this embodiment, a sapphire episubstrate is used but a silicon carbide episubstrate can be applied for laser lift-off, see Nakamura et al. can refer to

In FIG. 3B , the second LED chip is irradiated by laser exposure 32 to the low temperature buffer layer 22 . Accordingly, the second LED chip is separated from the epi-substrate 10 and falls on the bonding substrate. And in FIG. 3C , the third LED chip is irradiated by laser exposure 32 for the low temperature buffer layer 22 . Accordingly, the third LED chip is separated from the epi-substrate 10 and transferred onto the bonding substrate. Also in FIG. 3 , the first, second, and third micro LED chips are not adjacent because several different micro LED chips capable of emitting different light from several different epi substrates may be bonded to this bonding substrate. . In one embodiment, the first, second and third micro LED chips are capable of emitting blue light, and other micro LED chips on different epi-substrates capable of emitting green light must be bonded to this bonding substrate. If the bonding substrate is GaAs, red LED chips can already be formed on the bonding substrate. When the red micro LED chips are to be bonded to the bonding substrate and the bonding substrate itself is not GaAs, the spacing between the blue micro LED chips should be double that of FIG. 3 .

After all the selective blue micro LED chips are irradiated by laser exposure, the selective blue micro LED chips are transferred to the bonding substrate. The blue micro LED chips remaining on the epi substrate can be processed on the next bonding substrate.

In FIG. 3 , each micro LED chip may be sequentially transferred on a chip-by-chip basis or on a block basis.

In FIG. 4A, the epi substrate 10 is moved to the outside 34 while some micro LED chips irradiated by laser exposure stay on the bonding substrate 50, and other LED chips not irradiated by laser exposure are epitaxial. It remains on the substrate 10 .

In Figure 4b, the bonding substrate 50 can be reheated using eutectic bonding, solder bonding or baked epoxy with silver so that the transferred micro LED chips are bonded to the paired bonding pads. This step is preferably performed when all the micro LED chips have been transferred.

In FIG. 5A , the second epi-substrate 10-1 having other micro LED chips 45 such as a green LED chip is flipped, and all the micro LED chips 45 are attached to the remaining paired bonding pads. are sorted In this embodiment, several green micro LED chips 45 on the epi-substrate can be processed on another bonding substrate. Thereafter, as shown in FIG. 5B , the epitaxial substrate 10-1 is positioned sufficiently close to the bonding substrate 50, but the distance between the epitaxial substrate 10-1 and the bonding substrate 50 is considered for chip clearance. Therefore, it should have a thickness greater than the chip thickness, for example, several micrometers apart, and one LED chip 45 is illuminated by the laser exposure 32 . In Fig. 5c, another LED chip 45 is again irradiated by laser exposure 32 to the low temperature buffer layer. Accordingly, all the micro LED chips are separated from the epi-substrate 10 - 1 and transferred to the bonding substrate 50 in a chip unit. In Fig. 5d, the epi-substrate 10-1 is moved away and all the LED chips are transferred (34). The bonding substrate 50 is reheated again. Conveniently, the reheat step should be processed after all the micro LED chips have been transferred to the bonding substrate.

If the size of the bonding substrate is small or large, the bonding substrate 50 may be merged, separated, or individualized in the display panel. For example, when the bonding substrate is a 2x2 inch plate and the display device is 6x2 inch, three bonding substrates must be merged into one display panel. If the bonding substrate is a 10x12 inch plate and the display is 6x3 inch, the bonding substrate must be separated or individualized into 9 display panels.

If all the LED chips can be UV light LEDs, the red phosphor 70 , the green phosphor 71 and the blue phosphor 72 can be formed on the back side of the micro LED chip as shown in FIG. 6A . In FIG. 6B , only blue LED chips are provided and a green phosphor 71 and a red phosphor 70 are formed or coated on the LED chips. The phosphor 70 may be formed by spraying, lithography, taping, or printing. In another embodiment shown in Figure 6c, where blue and green micro LED chips are provided, only a red phosphor 70 is formed and coated on some of the blue LED chips. Accordingly, a display is manufactured.

In another embodiment, if the index of the micro LED chip on the epi substrate is not the same as the index on the bonding substrate, the LED chip on the epi substrate must be transferred one-by-one. First, the first micro LED chip of the epi-substrate is aligned to specific paired bonding pads as shown in FIG. 7A . Then, in Fig. 7B, the epi-substrate is moved close enough to the bonding substrate.

Then, in FIG. 7C , the first micro LED chip is irradiated by laser exposure 32 . Accordingly, in FIG. 7D , the first micro LED chip is separated from the epi-substrate 10 and attached to the bonding substrate 50, while the other micro-LED chip still remains on the epi-substrate.

Thereafter, in FIG. 7E , the epitaxial substrate 10 and the bonding substrate are moved so that the second LED chip is aligned with another paired bonding pad and irradiated by the laser exposure 32 . In FIG. 7F , the second LED chip is transferred to the bonding substrate 50 . In FIG. 7G , the epitaxial substrate 10 and the bonding substrate are moved so that the third LED chip is aligned with the other paired bonding pad and irradiated again by the laser exposure 32 . Accordingly, the process can continue until all the specified micro LED chips are transferred to the bonding substrate. In this embodiment, the index of the micro LED chips on the epi substrate is smaller than the index of the paired bonding pads on the bonding substrate.

In the present invention, the sapphire substrate can be separated using a laser lift-off method. However, in the case of some other epi-substrates such as silicon, silicon carbide, and GaAs, it is not easy to separate the epi-substrate from the epi-layers using laser lift-off. Therefore, another method is provided. In one embodiment, the red micro LED chips may be formed on a GaAs substrate, after which the red micro LED chips are transferred to a temporary substrate. The GaAs substrate is removed using a selective etching method, after which all micro LED chips are transferred to tape as a substrate. Since the tape is soft and the adhesion between the micro LED chips and the tape is not too tight, the micro LED chips can be pressed directly to the bonding substrate using the tip. Accordingly, the previous laser lift-off method can now be replaced by a mechanical press method. The tackiness of the tape can be adjusted to optimize the transfer.

To explain this embodiment, several drawings should be introduced for better clarity.

In one embodiment, a GaAs episubstrate 10 is first provided. Then, an etch selective layer 23 such as AlAs is formed on the GaAs substrate using a conventional epitaxial growth method as shown in Fig. 8A. Thereafter, the first epitaxial layer 12 and the second epitaxial layer 16 are sequentially formed by epitaxial growth and individual LED chip patterns are formed later. A p-ohmic contact layer 18 is formed on the second epitaxial layer 16 using an evaporating method. Thereafter, as shown in FIG. 8B , the upper surface of the epi-substrate 10 is fixed to the temporary substrate 80 using a specific adhesive that may lose its adhesiveness when irradiated by UV or heated to a specific temperature.

Next, the epi-substrate 10 is removed by etching the etch selective layer 23 (the detailed procedure of this process can be referred to US Publication No. 2006/0286694), the n-ohmic contact electrode 14 and the p-ohmic contact electrode 14 LED chips with contact electrodes 18 are formed in the epi layer as shown in FIG. 8C. The temporary substrate 80 is flipped. Then, the upper surface of the n-ohmic contact electrode 14 is fixed to the tape 81 as shown in FIG. 8D. The adhesiveness of the tape is not too sticky or glutinous, so each micro LED chip can later be removed by simple mechanical pressing. The temporary substrate 80 is then removed by being irradiated by heating or UV light, and the tape with the LED chips is flipped as shown in Fig. 8E. Another embodiment for removing a 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 similar to that described above.

In the case of other epitaxial substrates such as Si, SiC, GaN, ZnO, GaP, and GaSb, each selective etching layer must be formed before the epitaxial layers are formed, and the former method can be applied. In the case of a silicon carbide epitaxial substrate, a transition metal nitride layer is suitable as a selective etching layer.

The epi-substrate may be used as a bonding substrate having a driving circuit, and an AlGaInP red LED structure grown on a GaAs substrate is provided to explain this embodiment. In Figure 9, a process flow is provided for explaining this embodiment. First, as shown in step S9-1, a substrate such as GaAs or InP is provided for epitaxially grown red micro LED chip structures and as a bonding substrate for blue/green micro LED chips. Then, in optional step S9-2, a DBR layer is formed on the substrate to reflect red light, and a red LED structure is epitaxially grown on the DBR layer in step S9-3. Next, in step S9-4, red micro LED chips are made on the DBR layer. A p-well is then formed in the GaAs substrate in step S9-5 using conventional ion implantation and/or diffusion. In this embodiment, a p-well is formed because the substrate is n-type. If a p-type MISFET is preferred, an n-well should be formed at this stage. Thereafter, a plurality of isolation regions are formed in the p-well in step S9-6 to isolate the next formed transistors from the paired bonding pads. The isolation regions may be, for example, silicon nitride, silicon oxide, aluminum oxide or aluminum nitride. Then, the transistors in this embodiment are metal-insulator-semiconductor field effect transistors (MISFETs), which are formed in the p-well in steps S9-7. The GaAs substrate serves as the semiconductor layer in the MISFET. Then, in step S9-8 an ohmic contact matrix is formed on the ohmic contact micro LED chips, and in step S9-9 paired bonding pads are formed on the isolation elements. In step S9-10 the blue and green micro LED chips may then be transferred to the paired bonding pads. In step S9-11, an inter-level dielectric (ILD) layer such as silicon oxide or silicon nitride is formed on the substrate, and in step S9-12 several contacts are formed in the ILD layer. A metal layer is then formed on the ILD layer to electrically connect to the contact in step S9-13. A passivation layer such as silicon oxide or silicon nitride is formed to cover all transistors, micro LED chips and metal layer in step S9-14, and the back surface of the substrate is optionally metallized in step S9-15.

Detailed steps of the process flow shown in FIG. 9 may refer to FIGS. 10A and 10M . First, a GaAs or InP substrate 51 is provided as shown in Fig. 10A. A DBR layer 53 may be formed on the substrate 51 to enhance red light extraction, after which an n epitaxial layer 12 and a p epitaxial layer 16 are subsequently formed on the DBR layer 53 by MOCVD. is formed negatively. A chip process is used to form individual red micro LED chips 47 on a substrate 51 , as shown in FIG. 10B , using conventional patterning and etching processes. To form the driving circuits, a p-well 55 is formed using a conventional ion implantation and/or diffusion step as shown in Fig. 10C. In one embodiment of this process, the dopant may be Mg or Zn. Thereafter, as shown in FIG. 10D , several isolation regions 56 are formed in the substrate 51 to electrically isolate the micro LED chips from the transistors. The isolation regions may be a dielectric such as silicon oxide, silicon nitride, aluminum oxide or aluminum nitride. In this step, the formation of the isolation regions includes an etching process and refilling the dielectric layer with the etched area.

10E, n-type MISFET 90 is formed in and on p-well 55 using conventional methods. In one embodiment, gate dielectric layer 92 and gate 93 are subsequently deposited on substrate 51 , after which source/drain regions 91 are p-well by silicon doping, implantation or diffusion. (55) is formed. The gate dielectric layer 92 may be silicon oxide or silicon nitride or other dielectric materials, and the gate 93 may be polysilicon, aluminum or suitable metals. Thereafter, as shown in FIG. 10F , spacers 94 , which may be silicon oxide, are selectively placed on the gate and sidewalls of the red micro LED chip 47 to protect the gate and the red micro LED chip 47 . is formed Forming the spacers 94 includes depositing a conformal layer on the substrate 51 and etching the conformal layer directly. A transparent ohmic contact layer 18 is formed on the substrate 51 to make electrical contact with the red micro LED chip 47 and later the blue/green micro LED chips are transferred to the transistors 90 . The transparent ohmic contact layer 18 may be indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium oxide (IGO), aluminum zinc oxide (AZO), or indium gallium zinc oxide (IGZO). Thereafter, as shown in FIG. 10G , paired bonding pads 52 are formed on the isolation elements 56 and electrically connected to the transparent ohmic contact layer 18 . Thereafter, as shown in FIG. 10H , the blue micro LED chip 40 and the green micro LED chip 45 are transferred to paired bonding pads.

As shown in Figure 10i, an ILD layer 64 such as silicon oxide, tetra-ethyl-ortho-silicate (TEOS), epoxy or silicon is deposited on the substrate 51 using conventional spin-on coating. . Then, as shown in FIG. 10J , contacts 68 are formed in the ILD layer 64 to electrically connect to the n-wells 91 of the transistors 90 . The formation of the contacts 68 includes first etching the ILD layer 64 to form the contact holes, which are then filled with metal inside the contact holes. A metal layer 62 is then formed over the ILD layer 64 and connected to the contacts 68 using a conventional method, as shown in FIG. 10K . Metal layer 62 will provide a brightness signal to micro LED chips 40 , 45 , 47 via transistors 90 , one of which emits a predetermined brightness of light when the corresponding transistors are turned on. something to do. As shown in FIG. 101 , a passivation layer 65 , such as an epoxy, silicon or MEMS material, is formed to cover the transistors 90 , the micro LED chips and the metal layer 62 . As shown in FIG. 10M , a metal layer 66 is selectively formed on the back surface of the substrate 51 , so that all n-electrodes of the micro LED chips can be grounded through the metal layer 66 . In the case of the red micro LED chip 47 , the n-electrode can be grounded through the substrate 51 , whereas in the case of the blue/green micro LED chip 40/45 , the n-electrode is connected to the via of the substrate 51 . ) can be grounded through The formation of the via may include etching through the substrate 51 to form the via-holes and filling the via-holes with metal using a conventional method.

In order to understand the pixel design of a micro LED display, it is better to look at the floor plan to illustrate the present invention. 11A, an active electrical circuit diagram of two pixels of a micro LED display panel is provided. Pixel 100 includes three micro LED chips 106 and three transistors 104 . All gate electrodes of transistors 104 are connected to control signal 110 , and all source electrodes of transistors 104 are connected to brightness signal 112 . Control signal 110 will provide a signal that micro LED chip 106 should be turned on/off via transistor 104 . The brightness signal 112 will provide a signal that the micro LED chip 106 should have a certain brightness. The function of the transistors 104 is similar to a thin film transistor (TFT) of an LCD panel. A black matrix 102 including each pixel 100 may improve contrast and reduce interference between all pixels 100 . The p-electrode (anode) of the micro LED chip 106 is connected to the drain electrode of the transistor 104, and the n-electrode (cathode) of the micro LED chip is grounded.

In FIG. 11B , a passive electrical circuit diagram of two pixels of a micro LED display is provided. In one pixel 100 , only three micro LED chips 106 are provided, and all p electrodes (anode) of the micro LED chip 106 are connected to the image scanning signal 120 , and the micro LED chips 106 are connected to the image scanning signal 120 . All n electrodes (cathode) of n are connected to the switch signal 122 . The image scanning signal 120 provides image information directly to the micro LED chips 106, and the switch signal determines which micro LED chip 106 will be turned on/off. When the switch signal is an open circuit, the connected micro LED chip will be turned off. The switch signal 122 will in turn open circuit such that the image signal 120 provides accurate signal information to each of the micro LED chips 106 . The micro LED array can be driven in an interlace or non-interlace manner to display images and motion. In this embodiment, a GaAs substrate cannot be applied.

One pixel design layout of the active electrical circuit diagram of FIG. 11A on a bonding substrate may be referred to as FIGS. 12A and 12B . In Fig. 12a, the RGB layout is a sequence and is easy to manufacture. Area 108 houses the micro LED chip and is provided with two bonding pads 52 . The Zener diagram may be included in the driving circuit as a protection circuit. Transistor 104 may be a NMIS, PMIS, CMIS transistor or BJT. In a preferred embodiment, NMIS transistors are used. In this embodiment, the common cathode electrode will be optional. In FIG. 12B , another design layout of one pixel is provided when RGB micro LED chips want to be closely designed for improvement of contrast.

13A, another embodiment of the present invention is provided in micro LED chips. In the case of blue, green, and red LED chips, the driving voltage and lifespan may be different depending on the structures and materials of the LED. A simple and easy method or scheme for manufacturing a micro LED display may include only blue micro LED chips coated with phosphor 73 . The phosphor 73 emits yellow light, and after the yellow light is mixed with the blue light of the micro LED, white light may be provided. Thereafter, the transparent substrate 200 is provided with a color filter 130 and a black matrix 102 thereon. Accordingly, when each micro LED chip is driven by an image signal, an image may be displayed after the color filter 130 . Phosphor 73 can produce a high color rendering index or color gamut. As shown in FIG. 13C , a substrate 200 having a color filter 130 and a black matrix is fitted or matched to an LED chip to form an LED display. In another embodiment, as shown in FIG. 13B , the phosphor 73 and the color filter 130 may be first formed on the transparent substrate 200 . In this embodiment, as shown in FIG. 13C , a substrate 200 having a color filter 130 , a phosphor 73 and a black matrix 102 is fitted or matched to an LED chip. In another embodiment, the phosphor 73 may 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 will be similar to the color filter of the TFT LCD display panel, but there is no more liquid crystal layer. In the case of a TFT LCD display panel, even if a completely dark image is provided, some white light leaks from the LCD panel because the liquid crystal cannot completely turn off the backlight. However, the LED display panel of the present invention can be compared to a conventional CRT monitor or plasma display of excellent quality with the LED completely turned off, resulting in a dark image. In FIG. 14A , it is a plan view of the transparent substrate 100 showing four pixels 100 . A black matrix 102 may be formed around the pixels as shown in FIG. 14B .

In the present invention, another embodiment is provided in which not all LED chips are transferred to the bonding substrate in the passive mode LED display panel. Referring to FIG. 15A , here the LED chips 40 are already formed on a sapphire substrate 10 having n/p ohmic contact electrodes 14/18, respectively. In this embodiment, the LED chips 40 emit blue light. The formation of the LED chip configuration should be defined according to the display pixel, in this embodiment, the left three LED chips are grouped into one pixel and the right three LED chips are grouped into another pixel. Thereafter, as shown in FIG. 15B , a dielectric layer 210 is formed to cover the LED chip 40 , and the n/p ohmic contact electrodes 14/18 are exposed. The dielectric layer 210 may be silicon oxide, silicon nitride, TEOS, epoxy, or silicon. In order to electrically connect each p-ohmic contact electrode individually as shown in FIG. 15C , a transparent conductive layer such as ITO, IGO, IZO, IGZO, or AZO is formed and patterned as the image scanning signal line 120 . The image scanning signal line 120 may also be referred to as FIG. 11B . Then, another dielectric layer 212 such as silicon oxide, silicon nitride, epoxy or silicon is formed to cover the LED chips and the image scanning signal line 120 . Several holes are formed in the 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 all the holes, Fig. 15d The dielectric layer 212 is patterned with a switch signal line 122 as shown in FIG. The switch signal line 122 may also be referred to as FIG. 11B . A passivation layer 65 is formed over the switch signal line 122 and a phosphor 73 that emits yellow light having a high color rendering index and coupled with a blue GaN LED chip 40 to produce white light. If the LED chip 40 emits UV, RGB mixed phosphors may be applied. As shown in FIG. 15E , the transparent substrate 200 coated with the color filter 130 and the black matrix 102 is fitted to the micro LED chip 40 on the epitaxial substrate 10 . Accordingly, an LED display with a GaN LED chip is formed.

Another embodiment for a passive LED display panel is also provided. Referring to FIG. 16 , here a sapphire substrate 10 having LED chips is formed and flipped to bond with a bonding substrate 50 having paired bonding pads 52 . Similar to the previous embodiment, the LED chip configuration should be defined according to the display pixels. Thereafter, as shown in FIG. 15B , the micro lens array 220 is formed on the rear surface of the epi-substrate 10 . A microlens may be a single element with one planar surface and one spherical convex surface for refracting light, or it may be a single element with two flat, parallel surfaces and the focusing action of the refractive index across the lens being a gradient-index lens. obtained by change. Formation of the micro lens array 220 may be molding or embossing from the master lens array. Thereafter, a transparent substrate 200 having a phosphor 73 , a color filter 130 , and a black matrix 102 is sequentially formed thereon for each LED chip.

17 , an apparatus for manufacturing a micro LED display is provided. The x-y stage 300 provides two directions orthogonal to each other horizontally. The x-y stage 300 is used to provide a bonding substrate that moves along the x-y direction so that bonding pads to be bonded can be moved to a specific position. The z-stage 302 on the x-y stage 300 provides a direction orthogonal to the x-y stage, a vertical direction. The purpose of providing the Z-stage 302 is to adjust the height of the bonding substrate so that the laser can be focused on the epi-substrate at a desired position. A chuck 304, such as an electrostatic chuck or a vacuum chuck, is provided on the z-stage 302 to hold the bonding substrate. Thereafter, the bonding substrate 50 is fixed to the E-chuck 50 . An x-y platform 310 providing two similar directions orthogonal to each other in the horizontal direction will move between the bonding substrate 50 and the laser 320 . The epi-substrate 10 is mounted on the x-y platform 310 so that a desired LED chip can be moved to a specific position, the LED chip is irradiated by a laser 320 and separated from the epi-substrate 10 into a bonding substrate 50 can be The x-y platform 310 will maintain the same pitch for 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 . Controller 300 electrically coupled to x-y stage 300 , z-stage 302 , chuck 304 , x-y platform 310 and laser 320 .

In FIG. 18 , the LED transport device is provided when no laser lift off is applied. A pressing device 322 with a tip 323 replaces the excimer laser 320 of FIG. 14 . When the micro LED chip on the tape is to be transferred to the bonding substrate, the tip will extend or stretch from the pressing device to strike the micro LED chip down onto the bonding substrate.

The present invention further provides an embodiment of manufacturing a simplified display panel. Referring to FIG. 19A , the bonding substrate 50 is provided with paired bonding pads 52 thereon. Wiring circuits 60 with and without active elements are formed on the bonding substrate 50 . Bonding substrate 50 may be rigid or flexible, PCB, silicon, SiC, ceramic, glass, or polyimide, and may be any substrate upon which circuitry may be disposed.

Referring to FIG. 19B , a plurality of GaN LED chips 40 are transferred to correspond to the paired bonding pads using the aforementioned flip-chip process. Thereafter, as shown in FIG. 19C , a black matrix 102 is formed on the bonding substrate 50 . If necessary, a black matrix 102 may be formed to isolate each GaN LED chip 40 instead of a pixel.

As shown in FIG. 19D , a patterned light converting layer 72 is formed to cover each GaN LED chip with or without a diffuser to provide white light. The light conversion layer 72 may include phosphors or WCG phosphors including quantum dots, yellow phosphors (YAG or TAG), red phosphors, Potassium Fluoride Silicon (KSF) phosphors and TriGain phosphors, ß-SiAlON green phosphors, and KSF phosphors. have. In one embodiment, the light conversion layer 74 may cover three GaN LED chips or be formed within one pixel.

Referring to FIG. 19E , a color definition layer 132 such as a color filter for defining RGB in one pixel is directly formed on the light conversion layer 72 or 74 and aligned with each GaN LED chip 40 . . In one prior art color definition layer 132 is formed using three patterning steps for each color.

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

In this embodiment, the GaN LED chips are transferred from the epi substrate to the bonding substrate, and the current mass transfer problem still occurs. Accordingly, another embodiment is provided to avoid mass delivery problems.

Referring to FIG. 20A , the 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.

Thereafter, as shown in FIG. 20B , a first insulating layer 64 is formed on the epitaxial substrate 10 , and a plurality of contact holes are formed to expose the p-ohmic contact electrode 18 . The insulating layer 64 may be silicon oxide, silicon nitride, silicon oxynitride, borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), or other transparent dielectric materials. Formation of the insulator 64 may be chemical vapor deposition or spin on a coating, depending on the materials of the insulator 64 . The plurality of contact holes may be formed by a conventional patterning-etching method.

Referring to FIG. 20C , a patterned first 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 is first transparent. It may be in electrical contact with the conductive layer 66 . The patterned first transparent conductive layer 66 is patterned on the first insulating layer as a plurality of first signal lines to be electrically connected to the column of 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 may be Indium Tin Oxide (ITO), Indium Germanium Oxide (IGO), Indium Zinc Oxide (IZO), or Aluminum Zinc Oxide (AZO), and the first transparent conductive layer 66 . may be first formed by sputtering or evaporative methods and later patterned. The first transparent conductive layer 66 may also be patterned using a lift-off method that is simpler than conventional patterning-etch.

Referring to FIG. 20D , a second insulating layer 65 is formed to cover the first insulating layer 64 and the first transparent conductive layer 66 . The materials and formation of the second insulating layer 65 may be similar to that of the first insulating layer 64 . In this embodiment, the second insulating layer 65 is formed by conformal coating. In one simplified embodiment, the formation of the second insulating layer is identical to the formation of the first insulating layer 64 . Then, a plurality of contact holes may be formed by using a conventional patterning-etch method, and then a second transparent conductive layer 67 is formed on the second insulating layer 65 and the plurality of contact holes ( 68), so that each n-ohmic contact electrode 14 can be in electrical contact with the second transparent conductive layer. The second transparent conductive layer 67 is patterned with a plurality of second signal lines on the second insulating layer to be electrically connected to the second row of electrodes of the plurality of GaN light emitting diodes. In this embodiment, the second electrodes are n-ohmic contact electrodes 14 . The material and formation of the second transparent conductive layer 67 may be similar to that of the first transparent conductive layer 66 . In a simplified embodiment, the formation of the second transparent conductive layer 67 may be the same as that of the first transparent conductive layer 66 .

Thereafter, as shown in FIG. 20E , a passivation layer 90 is formed on the second insulating layer 65 and the second transparent conductive layer 67 using a chemical vapor deposition method, evaporation, or spin-on-coating. do. Materials of the passivation layer 90 may be silicon oxide, silicon nitride, or silicon oxynitride. In this embodiment, the top surface of the passivation layer 90 is flat, which will be better in the next step. However, conformal passivation layer 90 is also acceptable in the present invention.

Referring to FIG. 20F , a black matrix 102 is formed on the passivation layer 90 to define each pixel and prevent image blur between pixels. Materials and formation for forming the black matrix 102 may refer to conventional processes in LCD technology. In this embodiment, the black matrix layer 102 is for separating pixels. However, the black matrix layer 102 may be formed to isolate each GaN LED chip 40 .

Thereafter, a patterned light conversion layer 70 aligned to each GaN LED chip 40 is formed on the passivation, as shown in FIG. 20G . In another embodiment, the light converting layer 72 is formed on the passivation layer 90 without being aligned with each GaN LED chip 40 . A light conversion layer 70 or 72 associated with each GaN LED chip 40, with or without a diffuser, will provide white light. The light conversion layer 70 or 72 comprises phosphor or quantum dots, yellow garnet phosphor (YAG or TAG), red phosphor, potassium fluoride silicon (KSF) phosphor and WCG phosphor including TriGain phosphor, ß-SiAlON green phosphor and KSF phosphor. may include In one simplified embodiment, if the black matrix 102 and the color conversion layer 70 or 72 are dielectric or insulating, there is no need to form the passivation layer 90 . In an alternative embodiment, the phosphor may be mixed with an epoxy or silicone to serve as the passivation layer 90 . Accordingly, it is not necessary to form the light conversion layer 70 or 72 after the formation of the passivation layer 90 .

Referring to FIG. 20H , in order to define RGB of one pixel as one step, a patterned color definition layer 130 such as a color filter is formed on the color conversion layer 70 or 72 according to a conventional method such as LCD technology. formed using the method. Accordingly, a display with micro or mini LED chips thereon is provided.

In another embodiment, the black matrix may be formed on the sapphire substrate after each GaN LED chip is formed. Referring to FIG. 21A , the 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 . Accordingly, a black matrix 102 is formed to define each pixel.

Referring to FIG. 21B , a GaN LED chip 40 having an n-ohmic contact electrode 14 and a p-ohmic contact electrode 18 in which a first insulating layer 64 is formed on the epitaxial substrate 10 is subjected to a polishing method. exposed by Thereafter, as shown in FIG. 21C , a first transparent conductive layer on each p ohmic contact electrode 18 such that each p ohmic contact electrode 18 is in electrical contact with the first transparent conductive layer 66 . (66) is formed.

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

Thereafter, as shown in FIG. 21E , a passivation layer 90 is formed on the second insulating layer 65 and the second transparent conductive layer 67 . A color conversion layer 70 is formed on the passivation layer 90 and aligned with each GaN LED chip 40 . In another embodiment, a color conversion layer 72 is formed on the passivation layer 90 without alignment with each GaN LED chip 40 . Next, as shown in FIG. 21G , the color definition layer 130 is formed on the color conversion layer 70 or 72 .

For a simplified embodiment showing a GaN LED chip on a sapphire substrate, reference may be made to FIGS. 22A-22C showing cross-sectional views of various stages, wherein FIGS. 23A-23C are plan views at various stages according to the embodiment shown in FIGS. 22A-22C. shows As shown in FIGS. 22A and 23A , a GaN LED chip including an n epitaxial layer 12 and a p epitaxial layer 16 is sequentially formed. Then, as shown in FIGS. 22b and 23b, a patterned n-ohmic contact transparent conductive layer 14 is formed on the n epi-layer 12 and will also electrically connect other GaN LED chips in the same row. Next, as shown in FIG. 22C , a conformal passivation layer 64 patterned with the p epitaxial layer 18 exposed is formed on the GaN LED chip and the sapphire substrate 10 . In a simplified embodiment, passivation layer 64 may be epoxy or silicone mixed with or without phosphor. Then, a patterned p-ohmic contact transparent conductive layer 18 will be formed on the p-epi layer 16 and electrically connected to another GaN LED chip in the same row, as shown in FIGS. 22c and 23c. The formation of the p-ohmic contact transparent conductive layer 18 may be a lift-off method or a patterning-etch. In this embodiment, both the n-ohmic contact transparent conductive layer 14 and the p-ohmic contact transparent conductive layer 18 may be ITO, IZO, IGO, IGZO, AZO, and combinations thereof. The conformal passivation layer 64 is not shown in FIG. 23C to show the relationship between the n ohmic contact transparent conductive layer 14 and the p ohmic contact transparent conductive layer 18 .

Another embodiment showing a GaN LED chip on a sapphire substrate may be referred to as FIGS. 24A and 24B , where FIG. 24A shows a cross-sectional view and FIG. 24B shows the top view of FIG. 24A . In this embodiment, the n-ohmic contact transparent layer 14 and the p-ohmic contact transparent layer 18 are dedicated to the GaN LED chip. A patterned conductive metal line 68 is formed on the n-ohmic contact transparent conductive layer 14 and will electrically connect the other n epilayers of the GaN LED chip in the same row. On the other hand, a patterned conductive metal line 67 is formed on the p ohmic contact transparent conductive layer 18 and will electrically connect the other p epilayers of the GaN LED chip in the same row. In this embodiment, although two conductive metal lines 67 and 68 are formed increasing manufacturing complexity, they may provide better electrical conductivity.

Another embodiment showing a GaN LED chip on a sapphire substrate may be referred to as FIGS. 25A and 25B , where FIG. 25A shows a cross-sectional view and FIG. 25B shows the top view of FIG. 25A . A P ohmic contact transparent layer 18 is formed on the p epilayer 16 and will be electrically connected to another GaN LED chip in the same row. Next, a conformal passivation layer 64 patterned to cover the sapphire substrate 10 , the p epitaxial layer 16 , and the p ohmic transparent conductive layer 18 in a state where the n epitaxial layer 12 is exposed is formed . In a simplified embodiment, passivation layer 64 may be epoxy or silicone mixed with or without phosphor. Then, an n-ohmic contact transparent conductive layer 14 is formed to make electrical contact with the n-epi layer 12 and cover the conformal passivation layer 64, which will electrically connect other GaN LED chips in the same row. The formation of the n-ohmic contact transparent conductive layer may be a lift-off method or patterning-etch. In this embodiment, both the n-ohmic contact transparent conductive layer 14 and the p-ohmic contact transparent conductive 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 definition layer is non-conductive and no phosphor is mixed with the passivation layer 64 , the color definition layer 130 may be formed directly on the n-ohmic contact transparent conductive layer 14 .

In the above-described embodiments, this display panel may be very suitable for a wearable display device.

The present invention firstly provides advantages including the industrial and commercial availability of mass transfer micro LEDs. Since all the micro LED chips are transferred directly from the epitaxial substrate to the bonding substrate, the throughput can be improved. In addition, mass production of micro LED displays may be possible. In the present invention, structure and fabrication can be applied to phosphors. In addition, when the bonding substrate is GaAs, a set of four red LED chips may be directly formed on the bonding substrate. When color filters and phosphors can be applied to LED displays, only GaN LED chips are configured in LED displays. For some specific configurations, a passive LED display with signal lines formed directly on a GaN LED chip and a sapphire substrate does not require mass transfer. In the present invention, there is no packaging process.

In the present invention, the light intensity of this display is significantly improved compared to the conventional LCD due to the liquid crystal layer, the diffuser and the polarizer, and while other transparent films modulate the light intensity of the backlight module, in the present invention, modulating the GaN LED chip is nothing. It offers the advantage of not having

Since all the materials of the present invention can be integrated into the bonding substrate or the sapphire substrate, there is no need for a separate color filter process on another transparent substrate. In the case of the embodiment in which the GaN LED chips are formed on a sapphire substrate, a mass transfer problem does not occur compared to all other micro or mini LED displays, and thus the display manufacturing yield can be very good.

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

The present invention has the advantage that all stages of the manufacturing process are mature and the equipment and equipment are mature. Accordingly, there is no need to develop other processes, equipment or facilities.

While the present invention has been described in accordance with the illustrated embodiments, those skilled in the art will readily recognize that there may be variations to the embodiments and such variations will fall within the spirit and scope of the invention. Accordingly, many modifications may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Claims (8)

a sapphire substrate having a plurality of GaN light emitting diode chips thereon;
a patterned n-ohmic contact transparent conductive layer electrically connected to a first conductivity type of the plurality of GaN light emitting diode chips;
a patterned passivation layer covering the patterned n-ohmic contact transparent conductive 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 p ohmic contact transparent conductive layer electrically coupled to the second conductivity type of the plurality of GaN light emitting diode chips.
According to claim 1,
wherein the patterned passivation layer is mixed with a light conversion material.
3. The method of claim 2,
A display panel further comprising a color definition layer on the plurality of GaN light emitting diode chips.
According to claim 1,
a first metal line on the n-ohmic contact transparent conductive layer; and
and a second metal line on the p-ohmic contact transparent conductive layer.
providing a sapphire substrate with a plurality of GaN light emitting diode chips thereon;
forming a patterned n-ohmic contact transparent conductive layer on a first conductivity type of the plurality of GaN light emitting diode chips;
forming a patterned conformal passivation layer on the patterned n-ohmic contact transparent conductive layer and the plurality of GaN light emitting diode chips, exposing a second conductivity type of the plurality of GaN light emitting diode chips;
and forming a p-ohmic contact transparent conductive layer electrically coupled to a second conductivity type of the plurality of GaN light emitting diode chips.
6. The method of claim 5,
and mixing a light converting material into the passivation layer prior to said step of forming a patterned conformal passivation layer.
6. The method of claim 5,
and forming a color definition layer over the plurality of GaN light emitting diode chips after the step of forming the p ohmic contact transparent conductive layer.
6. The method of claim 5,
forming a patterned first metal line on the n ohmic contact transparent conductive layer after the step of forming the n ohmic contact transparent conductive layer; and
After the step of forming the p ohmic contact transparent conductive layer, the method further comprising the step of forming a patterned second metal line on the p ohmic contact transparent conductive layer.

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