Micro light emitting diode display and method of forming the same

The present disclosure provides a micro light emitting diode display including a metal substrate, a plurality of micro light emitting diode chips on the metal substrate, a plurality of light absorbing layers on the metal substrate between the micro light emitting diode chips, a light conversion layer above the micro light emitting diode chips, and a cover plate above the light conversion layer, where sidewalls of the micro light emitting diode chips are separated by a gap, and where a contact angle of the light absorbing layers is between 0 degree and 30 degrees.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to China Application Serial Number 202111463507.7, filed on Dec. 2, 2021, which is herein incorporated by reference in its entirety.

BACKGROUND

Field of Invention

The present disclosure relates to the micro light emitting diode display and the method of forming the same.

Description of Related Art

In the development of the light emitting devices, the size of the light emitting chip in the devices gradually decreases. As such, the light emitting chip can become an individual cell of the light emitting device, which improves the performance of the device and reduces the power consumption of the device. For example, the micro light emitting diode (micro LED), as a digital cell of a display, can increase the definition and the contrast of the display, decrease the response time of the display, and reduce the power consumption of the display. However, the decreased size of the light emitting chip also reduces the width of the gap between the light emitting chips. As a result, the light emitting chips are easily interfered by each other, and the imaging performance of the display is affected. Therefore, it is an important development project for the light emitting device field to improve the optical performance of the light emitting chip and the imaging quality of the display.

SUMMARY

According to some embodiments of this disclosure, a micro light emitting diode display includes a metal substrate, a plurality of micro light emitting diode chips on the metal substrate, a plurality of light absorbing layers on the metal substrate between the micro light emitting diode chips, a light conversion layer above the micro light emitting diode chips, and a cover plate above the light conversion layer, where sidewalls of the micro light emitting diode chips are separated by a gap, and where a contact angle of the light absorbing layers is between 0 degree and 30 degrees.

In some embodiments, the light absorbing layers include a carbon black and anions from a thermal acid generator.

In some embodiments, a wavelength absorbed by the light absorbing layers is between 380 nm and 780 nm.

In some embodiments, the light absorbing layers have an absorbance no less than 99% in a wavelength range between 540 nm and 560 nm.

In some embodiments, a thickness of the light absorbing layers is between 1 μm and 2 μm.

In some embodiments, the light absorbing layers directly contact the sidewalls of the micro light emitting diode chips.

In some embodiments, the gap separating the micro light emitting diode chips is between 0.5 μm and 10 μm.

In some embodiments, the light absorbing layers do not cover the micro light emitting diode chips.

In some embodiments, the light conversion layer includes quantum dot layers and corresponding color filters.

In some embodiments, the quantum dot layers transfer a blue light emitted by the micro light emitting diode chips into a red light or a green light.

According to some embodiments of this disclosure, a method of forming a micro light emitting diode display includes the following steps. A plurality of micro light emitting diode chips are attached on a metal substrate, where sidewalls of the micro light emitting diode chips are separated by a gap. A light absorbing layer precursor is formed on the micro light emitting diode chips and the metal substrate, where the light absorbing layer precursor includes a thermal acid generator. The metal substrate is heated to let the thermal acid generator on the metal substrate release acids. The metal substrate is immersed in an organic solution, where a portion of the light absorbing layer precursor on the micro light emitting diode chips is dissolved in the organic solution, and a remained portion of the light absorbing layer precursor on the metal substrate forms a plurality of light absorbing layers between the micro light emitting diode chips. The metal substrate is dried, and a cover plate including a light conversion layer is attached above the micro light emitting diode chips, where the light conversion layer is aligned with the micro light emitting diode chips.

In some embodiments, before heating the metal substrate, a contact angle of the light absorbing layer precursor on the metal substrate is between 70 degrees and 90 degrees.

In some embodiments, after heating the metal substrate, a contact angle of the light absorbing layer precursor on the metal substrate is between between 0 degree and 30 degrees.

In some embodiments, a concentration of the thermal acid generator in the light absorbing layer precursor is between 0.1 wt % and 5 wt %.

In some embodiments, the light absorbing layer precursor further includes a carbon black absorbing wavelength between 380 nm and 780 nm.

In some embodiments, heating the metal substrate includes heating the metal substrate with a temperature between 100° C. and 140° C.

In some embodiments, forming the light absorbing layer precursor includes spin coating the light absorbing layer precursor on upper surfaces of the micro light emitting diode chips and the metal substrate between the micro light emitting diode chips.

In some embodiments, the light absorbing layer precursor on the metal substrate between the micro light emitting diode chips has a width between 0.5 μm and 10 μm.

In some embodiments, attaching the micro light emitting diode chips on the metal substrate includes mass transferring the micro light emitting diode chips onto the metal substrate.

DETAILED DESCRIPTION

Generally, a micro light emitting diode display includes a metal substrate, micro light emitting diode chips on the metal substrate, and a light conversion layer above the micro light emitting diode chips. The current is provided to the micro light emitting diode chips by the metal substrate, so that the micro light emitting diode chips can emit light toward the light conversion layer. While the light pass through the light conversion layer, the incident light can be transferred into emissive light with different characteristics, such as different wavelengths, thereby allowing the micro light emitting diode display present colorful images.

For example,FIG.1Aillustrates the cross-sectional view of the micro light emitting diode display10, whileFIG.1Billustrates the enlarged schematic view and the corresponding spectrum of the micro light emitting diode display10emitting the red light. The micro light emitting diode display10includes a metal substrate100, a plurality of micro light emitting diode chips110on the metal substrate100, a transparent substrate120above the micro light emitting diode chips110, a light conversion layer130on the transparent substrate120, and a cover plate140above the light conversion layer130. The micro light emitting diode chips110on the metal substrate100emit the light toward the light conversion layer130. As such, the light sequentially passes through the transparent substrate120, light conversion layer130, and the cover plate140, where the light conversion layer130includes a transparent layer132, a green light conversion layer134, and a red light conversion layer136that respectively corresponds to different micro light emitting diode chips110. By the light conversion layer130that can transfer the light into various color lights, the light emitted by the micro light emitting diode chips110provides the imaging functionality of the micro light emitting diode display10.

As shown inFIG.1A, the light emitted by the micro light emitting diode chips110lacks directionality. As a result, a portion of the light emitted by the micro light emitting diode chips110reaches the metal substrate100. The light reaching the metal substrate100is reflected by the metal substrate100, which may be directed to undesired regions. In addition, the gap between the micro light emitting diode chips110are very small due to the small size of the micro light emitting diode chips110. For example, if the size of the micro light emitting diode chips110is no larger than 30 μm, the gap between the micro light emitting diode chips110may be no larger than 10 μm. As the gap between the micro light emitting diode chips110is small, the light emitted by one of the micro light emitting diode chips110may reach the light conversion layer130above other adjacent micro light emitting diode chips110after being reflected by the metal substrate100. As such, the light may be emitted from the undesired region of the light conversion layer130and may affect the imaging of the micro light emitting diode display10.

For example, as shown inFIG.1AandFIG.1B, when the light is emitted from the micro light emitting diode chip110below the red light conversion layer136, a portion of the light travels toward the red light conversion layer136and becomes the red light of the micro light emitting diode display10after passing through the red light conversion layer136. Meanwhile, another portion of the light of the micro light emitting diode chip110travels toward the metal substrate100. The light reaching the metal substrate100is reflected by the metal substrate100, thereby passing through the adjacent green light conversion layer134, which emits weak green light. Therefore, in the last imaging of the micro light emitting diode display10, the red light may be mixed with the green light, which affects the color tone and the imaging performance of the micro light emitting diode display10. This undesired interference of the emissive light is herein referred as light cross-talk.

Similarly,FIG.2Aillustrates the cross-sectional view of the micro light emitting diode display20, andFIG.2Billustrates the enlarged schematic view and the corresponding spectrum of the micro light emitting diode display20emitting green light. The micro light emitting diode display20is similar to the micro light emitting diode display10inFIG.1A, except the light is emitted from the micro light emitting diode chip110below the green light conversion layer134of the micro light emitting diode display20. As shown inFIG.2AandFIG.2B, a portion of the light travels toward the green light conversion layer134and becomes the green light of the micro light emitting diode display20after passing through the green light conversion layer134. Meanwhile, another portion of the light of the micro light emitting diode chip110travels toward the metal substrate100and is reflected by the metal substrate100. Since the gap between the micro light emitting diode chips110is small, the light reflected by the metal substrate100may pass through the adjacent red light conversion layer136, which emits weak red light. Therefore, in the last imaging of the micro light emitting diode display20, the green light may be mixed with the red light, which leads to the light cross-talk and affects the color tone and the imaging performance of the micro light emitting diode display20.

The present disclosure provides a micro light emitting diode display and the method of forming the micro light emitting diode display, which avoid the undesired light cross-talk. The micro light emitting diode display includes a metal substrate, a plurality of micro light emitting diode chips on the metal substrate, and a plurality of light absorbing layers on the metal substrate between the micro light emitting diode chips, where the light absorbing layers have a contact angle between 0 degree and 30 degrees. Since the light absorbing layers on the metal substrate between the micro light emitting diode chips can absorb the light, the metal substrate would not reflect the light emitted by the micro light emitting diode chips, and the light cross-talk would be avoided. Further, as the contact angle of the light absorbing layers is between 0 degree and 30 degrees, the patterning of the light absorbing layers may be performed by simple process operations, which avoid the application of high cost photolithography process.

According to some embodiments of this disclosure,FIG.3illustrates the cross-sectional view of the micro light emitting diode display30. The micro light emitting diode display30includes a metal substrate100, a plurality of micro light emitting diode chip110on the metal substrate100, light absorbing layers150on the metal substrate100between the micro light emitting diode chips110, a transparent substrate120above the micro light emitting diode chips110, a light conversion layer130on the transparent substrate120, and a cover plate140above the light conversion layer130. When the micro light emitting diode chips110receive the current provided by the metal substrate100and emit the light, the light pass through the transparent substrate120, the light conversion layer130, and the cover plate140to provide the imaging of the micro light emitting diode display30. Meanwhile, a portion of the light emitted by the micro light emitting diode chips110may travel toward the metal substrate100. Since the light absorbing layers150cover the metal substrate100between the micro light emitting diode chips110, the light absorbing layers150can absorb the light emitted toward the metal substrate100by the micro light emitting diode chips110, which avoids the light reflection from the metal substrate100. Therefore, the light absorbing layers150on the metal substrate100can avoid the light cross-talk, thereby increasing the color saturation of the micro light emitting diode display30and improving the color performance of the micro light emitting diode display30.

More specifically, the light absorbing layers150are hydrophilic so that a contact angle of the light absorbing layers150is between 0 degree and 30 degrees. For example, the contact angle of the light absorbing layers150may be 5 degrees, 10 degrees, 15 degrees, 20 degrees, or 25 degrees. As the light absorbing layers150have suitable contact angle, i.e., the light absorbing layers150have suitable hydrophilicity, the light absorbing layers150have low solubility corresponding to specific solvents (for example, non-polar organic solvents). Therefore, in the process of forming the micro light emitting diode display30, the patterning process of the light absorbing layers150may be simplified by the solubility characteristic of the light absorbing layers150, thereby decreasing the process cost of the micro light emitting diode display30. The advantages due to the suitable hydrophilicity of the light absorbing layers150will be further described in details in the following description related toFIG.5toFIG.9.

In some embodiments, the hydrophilicity of the light absorbing layers150may come from the acidic substances in the light absorbing layers150. Specifically, the light absorbing layers150may include hydron which provide the acidic surface material of the light absorbing layers150, leading to the increased hydrophilicity of the surfaces of the light absorbing layers150. In some embodiments, the hydron in the light absorbing layers150may come from a thermal acid generator (TAG). When the thermal acid generator is heated, the thermal acid generator may produce hydron that provides the hydrophilicity of the surfaces of the light absorbing layers150. For example, the thermal acid generator may be a salt composed of a cation and a corresponding anion, where the cation produces hydron after being heated. In such embodiments, the light absorbing layers150may include the anion from the thermal acid generator. For example, when the thermal acid generator is Diphenyl(4-(phenylthio)phenyl)sulfonium perfluorobutane sulfonate, the light absorbing layers150may include the hydron produced by heating the thermal acid generator and the corresponding perfluorobutane sulfonate ion.

In some embodiments, the light absorbing layers150may include carbon black, so that the light absorbing layers150can absorb the light emitted by the micro light emitting diode chips110. For example, the carbon black may absorb the wavelength between 380 nm and 780 nm such that the light absorbing layers150may absorb the visible light emitted by the micro light emitting diode chips110. In some embodiments, the light absorbing layers150including carbon black may have a suitable thickness, so that the light absorbing layers150have a high absorbance in a wavelength range between 540 nm and 560 nm. Specifically, the thickness of the light absorbing layers150may be between 1 μm and 2 μm, and the light absorbing layers150have an absorbance no less than 99% in a wavelength range between 540 nm and 560 nm. For example, when the thickness of the light absorbing layers150is about 1 μm, the light absorbing layers150may have an absorbance about 99% at a wavelength about 550 nm. When the thickness of the light absorbing layers150is about 2 μm, the light absorbing layers150may have an absorbance about 99.9% at a wavelength about 550 nm. If the thickness of the light absorbing layers150is smaller than 1 μm, the absorbance of the light absorbing layers150may be too low to avoid the light emitted by the micro light emitting diode chips110from being reflected by the metal substrate100below the light absorbing layer150. If the thickness of the light absorbing layers150is larger than 2 μm, the absorbance of the light absorbing layers150may not be significantly improved with the increased thickness while the process cost is rather increased.

In some embodiments, the light absorbing layers150may only cover the upper surface of the metal substrate100without covering the micro light emitting diode chips110. As shown inFIG.3, the light absorbing layers150cover the upper surface of the metal substrate100between the micro light emitting diode chips110, while the light absorbing layers150do not cover the upper surfaces or the side surfaces of the micro light emitting diode chips110. As such, the light absorbing layers150absorb the light emitted toward the metal substrate100by the micro light emitting diode chips110, and the light emitted toward the light conversion layer130by the micro light emitting diode chips110is not affected. In some embodiments, the light absorbing layers150may directly contact the sidewalls of the micro light emitting diode chips110. Specifically, the sidewalls of the micro light emitting diode chips110may be separated from each other by a gap W1, so that a portion of the metal substrate100in the gap W1is not covered by the micro light emitting diode chips110. In contrast, the light absorbing layers150cover the metal substrate100between the micro light emitting diode chips110and directly contact the sidewalls of the micro light emitting diode chips110. Therefore, the light absorbing layers150between the micro light emitting diode chips110have a width equal to that of the gap W1. For example, the gap W1separating the micro light emitting diode chips110may have a width between about 0.5 μm and 10 μm, so the light absorbing layers150between the micro light emitting diode chips110have a width between about 0.5 μm and 10 μm.

In some embodiments, the light conversion layer130may include a plurality of sub light conversion layers having different materials, where the light emitted by the micro light emitting diode chips110can be transferred into different color lights in each sub light conversion layers. For example, the micro light emitting diode chips110may be the blue light emitting diodes, and the light conversion layer130may include a transparent layer132, a green light conversion layer134, and a red light conversion layer136separated from each other. When the blue light emitted by the micro light emitting diode chips110reaches the transparent layer132, the blue light may directly pass through the transparent layer132to let the micro light emitting diode display30emit the blue light. When the blue light emitted by the micro light emitting diode chips110respectively reaches the green light conversion layer134and the red light conversion layer136, the blue light may be absorbed by the green light conversion layer134and the red light conversion layer136emitting the corresponding green light and red light after the absorption. In some embodiments, the green light conversion layer134and the red light conversion layer136may be a quantum dot layer including semiconductor particles with suitable radius, thereby respectively transferring the blue light emitted by the micro light emitting diode chip110into the green light and the red light. In some embodiments, the light conversion layer130may further include corresponding color filters to improve the optical quality of the light passing through the light conversion layer130. For example, the light conversion layer130may include a green color filter135on the green light conversion layer134, so that the green light produced from the light sequentially passing through the green light conversion layer134and the green color filter135has higher color saturation. Similarly, the light conversion layer130may include a red color filter137on the red light conversion layer136, so that the red light produced from the light sequentially passing through the red light conversion layer136and the red color filter137has higher color saturation.

As mentioned above, the structure inFIG.3is provided as an example. Other embodiments may include the structures different from that ofFIG.3. In fact, compared with the structure shown inFIG.3, there may be additional devices and/or material layers, fewer devices and/or material layers, different devices and/or material layers, or different arrangements of devices and/or material layers. For example, one or more interlayer dielectric layers or wires may be disposed in the structure shown inFIG.3.

According to some embodiments of this disclosure,FIG.4illustrates the flow diagram of the method400of forming the micro light emitting diode display. In some embodiments, the method400may be used to form the micro light emitting diode display30inFIG.3.FIG.5,FIG.6,FIG.7A,FIG.8, andFIG.9illustrate the cross-sectional views of the intermediate stages of forming the micro light emitting diode display according to the method400. It should be noted that the process operations illustrated inFIG.5toFIG.7A,FIG.8, andFIG.9are merely examples, and that those skilled in the art may add additional operations before, during, or after the illustrated process, or may substitute, reduce, or logically alter the sequence of the illustrated process operations.

Referring to operation402inFIG.4andFIG.5, a plurality of micro light emitting diode chips110are attached on a metal substrate100. The metal substrate100includes conductive elements. The electrical connection may be formed between the micro light emitting diode chips110and the metal substrate100when the micro light emitting diode chips110are attached on the metal substrate100. As shown inFIG.5, the sidewalls of the micro light emitting diode chips110are separated by the gap W1, so that the micro light emitting diode chips110are not contacted to each other. In some embodiments, when the micro light emitting diode chips110are attached on the metal substrate100, the micro light emitting diode chips110may have the gap W1with a suitable width to decrease the interference between the micro light emitting diode chips110or to satisfy the process tolerance. For example, when the size of the micro light emitting diode chips110are between 3 μm and 30 μm, the gap W1separating the micro light emitting diode chips110may have a width between 0.5 μm and 10 μm.

In some embodiments, the micro light emitting diode chips110may be attached on the metal substrate100by the mass transfer technique. Specifically, the micro light emitting diode chips110may first be formed on an additional substrate, such as a sapphire substrate with a flat upper surface. Then, the micro light emitting diode chips110on the additional substrate are attached to the metal substrate100, so that the micro light emitting diode chips110are between the additional substrate and the metal substrate100. The micro light emitting diode chips110are then detached from the additional substrate by using a power source (such as radiation), leading to the formation of the micro light emitting diode chips110on the metal substrate100.

Referring to operation404inFIG.4andFIG.6, a light absorbing layer precursor155is formed on the micro light emitting diode chips110and the metal substrate100, where the light absorbing layer precursor155includes a thermal acid generator. Specifically, the light absorbing layer precursor155including the thermal acid generator is formed on the upper surfaces of the micro light emitting diode chips110and the exposed upper surface of the metal substrate100. As a result, the light absorbing layer precursor155covers the upper surfaces of the micro light emitting diode chips110and the upper surface of the metal substrate100between the micro light emitting diode chips110. Therefore, the micro light emitting diode chips110and the metal substrate100may be covered by the light absorbing layer precursor155in a top view. In the following process, the thermal acid generator in the light absorbing layer precursor155may be heated to produce hydron, so that the surface of the light absorbing layer precursor155is acidic, and the hydrophilicity of the light absorbing layer precursor155is increased.

In some embodiments, the thermal acid generator in the light absorbing layer precursor155may include a sulfonium salt, such as Diphenyl(4-(phenylthio)phenyl)sulfonium. The sulfonium ion in the sulfonium salt may produce hydron after being heated, thereby increasing the hydrophilicity of the light absorbing layer precursor155. In some embodiments, the thermal acid generator may include Diphenyl(4-(phenylthio)phenyl)sulfonium and the corresponding anion. For example, the thermal acid generator may be selected from Diphenyl(4-(phenylthio)phenyl)sulfonium perfluorobutane sulfonate, Diphenyl(4-(phenylthio)phenyl)sulfonium 4-adamantanecarboxy-1,1,2,2,-tetrafluorobutane sulfonate, Diphenyl(4-(phenylthio)phenyl)sulfonium 3-hydroxy-4-adamantanecarboxyl-1,1,2,2-tetrafluorobutane sulfonate, Diphenyl(4-(phenylthio)phenyl)sulfonium adamantanyl-methoxycarbonyl-difluoromethane sulfonate, Diphenyl(4-(phenylthio)phenyl)sulfonium 3-hydroxyadamantanyl-methoxycarbonyl-difluoromethane sulfonate, or Diphenyl(4-(phenylthio)phenyl)sulfonium 4-dehydrocholate-1,1,2,2-tetrafluorobutane sulfonate. In some embodiments, the light absorbing layer precursor155may have a suitable concentration of the thermal acid generator, so that the required amount of hydron may be produced in the light absorbing layer precursor155in the subsequent process. For example, the concentration of the thermal acid generator in the light absorbing layer precursor155may be between 0.1 wt % and 5 wt %. If the concentration of the thermal acid generator is lower than 0.1 wt %, the thermal acid generator in the light absorbing layer precursor155may be too low to produce sufficient hydron and to increase the hydrophilicity of the light absorbing layer precursor155. If the concentration of the thermal acid generator is higher than 5 wt %, it may affect the viscosity or the absorbance of the light absorbing layer precursor155.

In some embodiments, the light absorbing layer precursor155may have a relative hydrophobicity, so that the light absorbing layer precursor155has a relative high contact angle. For example, the contact angle of the light absorbing layer precursor155may be between 70 degrees and 90 degrees. As the light absorbing layer precursor155is relative hydrophobic and a portion of the light absorbing layer precursor155is heated, the thermal acid generator in the heated portion of the light absorbing layer precursor155can produce hydron, thereby increasing the hydrophilicity of the light absorbing layer precursor155. In contrast, the unheated portion of the light absorbing layer precursor155remains its relative hydrophobicity. Therefore, the unheated portion of the light absorbing layer precursor155and the heated portion of the light absorbing layer precursor155may have a significant difference of hydrophobicity/hydrophilicity. In the subsequent process, this characteristic difference may simplify the differentiation between the unheated portion of the light absorbing layer precursor155and the heated portion of the light absorbing layer precursor155(as shown inFIG.8).

In some embodiments, the light absorbing layer precursor155may further include carbon black, so that the light absorbing layer precursor155absorbs the light emitted by the micro light emitting diode chips110. For example, the carbon black in the light absorbing layer precursor155may absorb the wavelength between 380 nm and 780 nm, so the light absorbing layer precursor155absorbs the visible light emitted by the micro light emitting diode chips110.

In some embodiments, the light absorbing layer precursor155may be formed by spin coating the light absorbing layer precursor155on the micro light emitting diode chips110and the metal substrate100between the micro light emitting diode chips110. More specifically, the light absorbing layer precursor155may cover the upper surfaces of the micro light emitting diode chips110and the exposed upper surface of the metal substrate100, while the light absorbing layer precursor155do not cover the side surfaces of the micro light emitting diode chips110. In some embodiments, the light absorbing layer precursor155on the metal substrate100between the micro light emitting diode chips110may directly contact the sidewalls of the micro light emitting diode chips110, so that the width of the light absorbing layer precursor155equals to that of the gap, such as the gap W1inFIG.5, between the micro light emitting diode chips110. For example, the light absorbing layer precursor155on the metal substrate100between the micro light emitting diode chips110may have a width between 0.5 μm and 10 μm.

Referring to operation406inFIG.4andFIG.7A, the metal substrate100is heated to let the thermal acid generator in the light absorbing layer precursor155on the metal substrate100release acids. Specifically, the metal substrate100is heated to heat a portion of the light absorbing layer precursor155on the metal substrate100. The thermal acid generator in the light absorbing layer precursor155is heated to produce hydron, which provides the acidic substances in the surface of the light absorbing layer precursor155on the metal substrate100. In contrast, the other portion of the light absorbing layer precursor155on the micro light emitting diode chips110is not heated and remained the composition of the light absorbing layer precursor155. As a result, the light absorbing layer precursor155on the metal substrate100is more acidic than the light absorbing layer precursor155on the micro light emitting diode chips110after the heating operation. Therefore, the light absorbing layer precursor155on the metal substrate100forms the relative hydrophilic light absorbing layers150, where the composition of the light absorbing layers150is different from that of the light absorbing layer precursor155on the micro light emitting diode chips110.

According to some embodiments,FIG.7Billustrates the schematic view of the acid release reaction of the thermal acid generator, where Diphenyl(4-(phenylthio)phenyl)sulfonium salt is presented as an example of the thermal acid generator. As shown inFIG.7B, Diphenyl(4-(phenylthio)phenyl)sulfonium salt includes Diphenyl(4-(phenylthio)phenyl)sulfonium ion and its corresponding anion X−. Diphenyl(4-(phenylthio)phenyl)sulfonium ion produces sulfur-containing anion after being heated, and the sulfur-containing anion reacts with H2O in the environment to produce hydron. As a result, the thermal acid generator in the light absorbing layer precursor155may release acids after being heated, thereby increasing the hydrophilicity of the light absorbing layer precursor155.

In some embodiments, after heating the metal substrate100, the light absorbing layer precursor155on the metal substrate100(or referred as the light absorbing layers150) may have suitable hydrophilicity, so that the light absorbing layers150on the metal substrate100and the light absorbing layer precursor155on the micro light emitting diode chips110have a significant difference of hydrophilicity/hydrophobicity. For example, the contact angle of the light absorbing layers150on the metal substrate100may be between 0 degree and 30 degrees.

In some embodiments, heating the metal substrate100may include heating the metal substrate100with suitable temperature and short time period, so that the light absorbing layer precursor155on the metal substrate100forms the light absorbing layers150. For example, the metal substrate100may be heated about 30 seconds to 300 seconds with a temperature between about 100° C. and 140° C. In some preferred embodiments, the metal substrate100may be heated about 60 seconds with a temperature about 120° C. If the metal substrate100is heated with a temperature lower than 100° C., the temperature of the metal substrate100may be too low to promote the acid release reaction of the thermal acid generator. If the metal substrate100is heated with a temperature higher than 140° C., the light absorbing layer precursor155may deteriorate due to the high temperature, which affects the optical quality of the micro light emitting diode chips110.

Referring to operation408inFIG.4andFIG.8, the metal substrate100is immersed in an organic solution. When the metal substrate100is immersed in the organic solution, the light absorbing layer precursor155on the micro light emitting diode chips110is redissolved in the organic solution and removed from the micro light emitting diode chips110. In contrast, the light absorbing layers150on the metal substrate100are insoluble in the organic solution, so that the light absorbing layers150are remained on the metal substrate100, especially on the metal substrate100between the micro light emitting diode chips110. Therefore, the light absorbing layer precursor155on the metal substrate100(or referred as the light absorbing layers150) forms the plurality of the light absorbing layers150between the micro light emitting diode chips110.

In some embodiments, the metal substrate100may be immersed in the organic solution such as non-polar organic solution. As such, the relative hydrophobic light absorbing layer precursor155on the micro light emitting diode chips110is soluble in the organic solution, while the relative hydrophilic light absorbing layers150on the metal substrate100are relatively insoluble in the organic solution. For example, the organic solution immersing the metal substrate100may include propylene glycol methyl ether acetate (PGMEA). Therefore, the light absorbing layer precursor155with the contact angle no lower than 70 degrees is dissolved in the organic solution, and the light absorbing layers150with the contact angle no higher than 30 degrees are remained on the metal substrate100.

It should be noted that, combining the operation406and operation408of the method400, the patterning of the light absorbing layers150is completed by using the simplified process operations. In particular, the gap between the micro light emitting diode chips110is very small since the size of the micro light emitting diode chips110is also very small. For example, when the size of the micro light emitting diode chips110is no larger than 30 μm, the gap between the micro light emitting diode chips110may be no larger than 10 μm. In general, as the gap between the micro light emitting diode chips is small, the patterning of the light absorbing layer requires the photolithography process with high accuracy. However, the metal substrate of the micro light emitting diode display might reflect the light used in the photolithography process, leading to the reflective light reaching the undesired exposed region nearby. As a result, the reflective light in the photolithography process induces the cross-linking reaction of the light absorbing layer in the undesired exposed region, which reduces the patterning accuracy. In contrast, due to the different solubility of the relative hydrophobic light absorbing layer precursor155and the relative hydrophilic light absorbing layers150in the organic solution, the light absorbing layer precursor155on the micro light emitting diode chip110may be removed while remaining the light absorbing layers150on the metal substrate100in the operation406and operation408. Therefore, the method400may pattern the light absorbing layers150in the small gaps between the micro light emitting diode chips110by the simplified heating operation and redissolving operation.

Referring to operation410and operation412inFIG.4andFIG.9, the metal substrate100is dried, and a cover plate140including a light conversion layer130is attached above the micro light emitting diode chips110. Specifically, the patterned light conversion layer130may first be formed on the cover plate140, where the light conversion layer130includes separated sub light conversion layers. After the metal substrate100is dried, a transparent substrate120is attached above the micro light emitting diode chips110, so that the cover plate140including the light conversion layer130may be attached above the micro light emitting diode chips110. After the cover plate140is attached above the micro light emitting diode chips110, the light conversion layer130is disposed between the cover plate140and the micro light emitting diode chips110, and each of the sub light conversion layers of the light conversion layer130is aligned with the corresponding micro light emitting diode chip110. Therefore, the light emitted by the micro light emitting diode chips110may sequentially pass through the transparent substrate120, the light conversion layer130, and the cover plate140.

According to the above-mentioned embodiments of this disclosure, the micro light emitting diode display of the disclosure includes a metal substrate, a plurality of micro light emitting diode chips on the metal substrate, and a plurality of light absorbing layers on the metal substrate between the micro light emitting diode chips. The light absorbing layer absorbs the light emitted toward the metal substrate by the micro light emitting diode chips, thereby avoiding the light reflection toward the region above the adjacent micro light emitting diode chip by the metal substrate. Therefore, the light absorbing layers on the metal substrate between the micro light emitting diode chips can avoid the light cross-talk. In addition, the method of forming the micro light emitting diode display of this disclosure includes forming the light absorbing layer precursor with the thermal acid generator, heating the light absorbing layer precursor on the metal substrate, and redissolving the light absorbing layer precursor on the micro light emitting diode chip. Due to the relative hydrophilic light absorbing layers formed after the heating operation and the relative hydrophobic light absorbing layer precursor not being heated, the light absorbing layer precursor or the light absorbing layers may be patterned by simplified redissolving operation, which reduces the process cost.