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Researchers Submit Patent Application, "Full-Color Led Display Device and Manufacturing Method Thereof", for Approval

May 28, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Do, Young-Rag (Seoul, KR); Sung, Yeon-Goog (Gyeonggi-do, KR), filed on April 27, 2012, was made available online on May 15, 2014.

The patent's assignee is Kookmin University Industry Academy Cooperation Foundation.

News editors obtained the following quote from the background information supplied by the inventors: "A Light-Emitting Diode (LED) TV, which has coming to the market, is an LCD TV adopting an LED backlight using white or three primary colors, more accurately an LCD TV using an LED backlight, instead of a Cold Cathode Fluorescent Lamp (CCFL) backlight of an existing LCD TV. As an LED full-color display presently available in the market, an ultra-large full-color outdoor electronic display board into which several ten thousands of three-color LED elements are inserted is known as a unique available product. Therefore, in an accurate conception, an LED full-color display is not yet adopted at the present as a home TV or a computer monitor. An existing LED element is not available as a display having a size of a TV or monitor due to the technical limits in relation to the manufacturing of an LED element and the full-color implementation technique. Presently, for an LED, an III-V group p-n light emitting diode is grown on a substrate of 2 to 8 inches by means of MOCVD and then cut into an appropriate size on which an electrode is wired, and then it is used as a unicolor or white LED element. In order to make a display for TV by using an III-V group wafer, in simple calculation, TV of 40 inches may be produced by attaching 5 to 20 wafers of 2 to 8 inches. In addition, in order to implement full-color with an LED, red-green-blue three-color LED elements should be put into a single pixel, and an LED full-color display may not be implemented by simply joining red-green-blue LED wafers. As another simple method for implementing an LED TV, a red-green-blue film or a nanorod-based LED element may be directly grown on a pixel of a large-area glass substrate for an actual display. However, this problem causes the same problems as when an LED is implemented by growing a high-quality III-V group film on a glass substrate by means of MOCVD. As well known in the art, the MOCVD for growing an III-V group film does not allow direct deposition on a substrate having a TV display size and also does not allow deposition of high-crystallinity and high-efficiency III-V group films or nanorods on a glass substrate. Due to such technical limits, there has not been proposed an effective technique for directly manufacturing a full-color display for a TV of 20 inches or above or a monitor of 14 inches or above by using an LED wafer.

"In spite of the limits in manufacturing techniques and realistic possibility, an LED TV must be developed due to low light emission efficiency of an existing LCD display. As known in the art, a full-color TFT-LCD, which is dominating the TV and monitor market at the present, emits just about 5% of the light emitted from a backlight to the front surface. An LCD uses two polarizers during an on/off procedure for penetration/blocking of light, a color filter to converting a white light passing through a liquid crystal into a three-color light, and a plurality of optical films while uniformly dispersing the light generated from a single backlight lamp, which causes an optical attenuation of about 95%. In detail, it is known that a light emission efficiency of a full-color LCD display is 2 to 3 lm/W in case of using a backlight lamp of 60 lm/W. Therefore, in case of an LED-LCD TV using LED as a backlight, even though the efficiency of the LED is greatly improved, there is a limit in improvement of efficiency of an actual display. It is reported that a white LED recently developed already has efficiency of 100 lm/W or above, which is expected to reach 200 lm/W in a few years. Therefore, it will be easily understood that directly manufacturing a full-color display by using high-efficiency LED is the most suitable method in aspect of light emission efficiency, in comparison to manufacturing a display by using high-efficiency LED as the LCD backlight.

"Therefore, a technique required for realizing a high-efficiency LED display becomes a main issue of this study. If technical or physical limits are not considered, developing a method for directly manufacturing LED pixels on a large-area display glass substrate will be the path of least resistance, which can be conceived by anyone. However, if the techniques for IIV-V growth are understood just a little, it will be figured out that this cannot be realized by the present techniques. Therefore, it will be reasonable in aspect of light emission efficiency to develop a new structure and technique for manufacturing a full-color LED display by using an existing high-efficiency III-V group LED wafer grown by means of MOCVD. Until now, the LED display manufacture and element techniques have been developed to implement a display by arranging one LED element at one pixel. For example, it has been reported that in case of a recently developed micro-sized LED display, a small micro LED display has been developed by fabricating one pixel with one micro LED. As another example, there is also reported a technique for manufacturing a display of a desired size by fabricating an LED of a micro size on a plastic substrate with great elasticity and then extending the substrate to increase its area. The technique for manufacturing a display in which a single micro LED array corresponds to a single pixel is easy to develop a subminiature micro LED display but has very high technical thresholds to be overcome in order to have a great area suitable for a TV or monitor. Moreover, if several LEDS are poor among several ten thousands of LEDS of the display, the entire display may be poor. Therefore, in order to implement a high efficiency LED display, there is needed a creative and simple structure and technique which may overcome the existing techniques."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present disclosure is directed to providing a full-color LED display device, which is suitable for manufacturing a large-area color-by-blue LED full-color display and allows a subminiature LED element to be accurately located on a sub-pixel (pixel site) of an LED display without lying or turning over, and a manufacturing method thereof. The present disclosure is also directed to providing a full-color LED display device, which is suitable for manufacturing a RGB LED full-color display and allows a subminiature LED element to be accurately located on a sub-pixel (pixel site) of an LED display without lying or turning over, and a manufacturing method thereof. Moreover, the present disclosure is also directed to providing a method for manufacturing a large-area LED display by using an LED wafer of a relatively smaller size, since the subminiature LEDs are located in less than 20% of the entire area of the display, preferably less than 10%.

"In one aspect to accomplish the first object, there is provided a manufacturing method of a full-color LED display device, comprising:

"1) forming a plurality of first electrodes on a substrate;

"2) attaching at least five subminiature blue LED elements to each unit pixel site formed on the first electrode;

"3) forming an insulation layer on the substrate;

"4) forming a plurality of second electrodes on the insulation layer; and

"5) successively patterning a green color conversion layer and a red color conversion layer on the second electrode corresponding to partial unit pixel sites selected from the unit pixel sites.

"In another aspect to accomplish the first object, there is provided a manufacturing method of a full-color LED display device, comprising:

"1) forming a plurality of first electrodes on a substrate;

"2) attaching at least one LED element among at least five subminiature blue, green and red LED elements to each unit pixel site formed on the first electrode;

"3) forming an insulation layer on the substrate; and

"4) forming a plurality of second electrodes on the insulation layer.

"According to an embodiment of the present disclosure, the first electrodes and second electrodes may be formed in a stripe shape to cross each other, and the unit pixel sites may be formed at portions corresponding to crossing points of the first electrodes and the second electrodes. According to another embodiment of the present disclosure, the unit pixel sites may have an area of 1.times.10.sup.4 .mu.m.sup.2 or less, more preferably 1.times.10.sup.2 .mu.m.sup.2 or less, and the unit pixel sites of the first electrodes may have grooves of a predetermined depth. According to another embodiment of the present disclosure, the subminiature LED elements may have a diameter of 50 to 3000 nm with a single or bundle form, and an insulation coating may be formed at the outer circumference of the LED elements. According to another embodiment of the present disclosure, the subminiature LED elements may be in a paste or ink form.

"According to another embodiment of the present disclosure, Step 2) may include:

"2-1) forming first coupling linkers, which are capable of being coupled to the unit pixel sites, on the unit pixel sites formed on the first electrode;

"2-2) adding metal micro powder capable of being coupled to the first coupling linkers;

"2-3) attaching at least five subminiature blue LED elements, to which second coupling linkers capable of being coupled to the metal micro powder are attached, to each unit pixel site; and

"2-4) forming a metallic ohmic layer between the unit pixel site and the subminiature blue LED element by soldering the metal micro powder.

"According to another embodiment of the present disclosure, Step 2) may include:

"2-5) forming first coupling linkers, which are capable of being coupled to the unit pixel sites, on the unit pixel sites formed on the first electrode;

"2-6) adding metal micro powder capable of being coupled to the first coupling linkers;

"2-7) attaching at least five LED elements among the subminiature blue, green and red LED elements, to which second coupling linkers capable of being coupled to the metal micro powder are attached, to each unit pixel site; and

"2-8) forming a metallic ohmic layer between the unit pixel site and the subminiature blue LED element by soldering the metal micro powder. According to another embodiment of the present disclosure, the manufacturing method may further include forming a short wavelength penetration filter (SWPF) between Step 4) and Step 5); and forming a long wavelength penetration filter (LWPF) after Step 5).

"In an aspect to accomplish the second object, there is provided a full-color LED display device, comprising:

"1) a plurality of first electrodes formed on a substrate;

"2) at least five subminiature blue LED elements attached to each unit pixel site formed on the first electrode;

"3) an insulation layer formed on the substrate and the blue LED element;

"4) a plurality of second electrodes formed on the insulation layer; and

"5) a green color conversion layer and a red color conversion layer formed on the second electrode corresponding to partial unit pixel sites selected from the unit pixel sites.

"In another aspect to accomplish the second object, there is provided a full-color LED display device, comprising:

"1) a plurality of first electrodes formed on a substrate;

"2) at least one LED element among at least five subminiature blue, green and red LED elements attached to each unit pixel site formed on the first electrode;

"3) an insulation layer formed on the substrate; and

"4) a plurality of second electrodes formed on the insulation layer.

"According to an embodiment of the present disclosure, the subminiature blue, green and red LED elements may have a diameter of 50 to 3000 nm with a single or bundle type, and an insulation coating may be formed at an outer circumference of the LED elements. According to another embodiment of the present disclosure, a metallic ohmic layer may be formed between the unit pixel site and the subminiature LED element. According to another embodiment of the present disclosure, the unit pixel site may have an area of 1.times.10.sup.4 .mu.m.sup.2 or below, and grooves of a predetermined depth may be formed at the unit pixel sites of the first electrodes.

"According to another embodiment of the present disclosure, the first electrodes and second electrodes may be formed in a stripe shape to cross each other, and the unit pixel sites may be formed at portions corresponding to crossing points of the first electrodes and the second electrodes. According to another embodiment of the present disclosure, a short wavelength penetration filter may be formed between the second electrode and the subminiature red or green LED elements, and a long wavelength penetration filter may be formed on the subminiature red or green LED elements.

"Hereinafter, terms used in the present disclosure will be described. The term 'pixel sites' is also called 'sub-pixels' and represents a plurality of regions formed at the first electrode of the LED display, which means locations to which the subminiature LED elements are attached. A plurality of 'pixel sites' may be formed along the first electrode, and if the first electrode is arranged with a stripe shape, the pixel sites may be formed at regular intervals along the first electrode. The term 'unit pixel site' means a single pixel site.

"Since at least five subminiature LED elements are coupled on each unit pixel site of the full-color LED display according to the present disclosure, it is possible to minimize a defect rate and manufacture a large-area high-efficiency full-color LED display. In addition, since the subminiature LED elements of the present disclosure may be freely assembled into a desired pixel pattern by using the coupling linkers, and the subminiature LED element may be accurately located on the sub-pixel of the LED display without lying or turning over, thereby greatly improving the efficiency of the LED display. Moreover, in the full-color LED display of the present disclosure, the optical loss problem caused by polarizers, color filters or the like decreases in comparison to an existing LCD display based on an LED backlight, which reduces the limit in efficiency and greatly improves an energy loss. In addition, the subminiature LED element of the present disclosure is a technique capable of overcoming the limit in productivity and size, which may occur in an existing LED display, and a true LED display of a TV size may be implemented since a small-sized LED wafer substrate may be expanded to a display of a TV size.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a perspective view for illustrating a step of patterning a first electrode on a surface of an LED display substrate according to the present disclosure.

"FIG. 2a is a perspective view for illustrating a step of forming coupling linkers at surfaces of pixel sites formed on the first electrode of the present disclosure, FIG. 2b is a perspective view for illustrating a step of coating the coupling linkers formed on the surface of the pixel sites with metal micro powder, FIG. 2c is a perspective view for illustrating a step of attaching a plurality of subminiature blue LED elements to the pixel sites coated with the metal micro powder, FIG. 2d is a perspective view showing a coupling linker formed at a pixel site and a coupling relation formed between the metal micro powder and the coupling linker formed at one surface of a subminiature LED element, and FIG. 2e is a perspective view showing a metallic ohmic layer formed between the pixel sites and the subminiature LED elements after a soldering process.

"FIG. 3 is a perspective view for illustrating a step of coupling a subminiature LED element bundle to the sub-pixel of the present disclosure.

"FIG. 4 is a perspective view for illustrating a step of forming an insulation layer on the subminiature LED element of the present disclosure.

"FIG. 5 is a perspective view for illustrating a step of forming a second electrode on the insulation layer of the present disclosure.

"FIG. 6 is a perspective view for illustrating a step of forming a short wavelength penetration filter on the second electrode of the present disclosure.

"FIG. 7 is a perspective view for illustrating a step of forming a plurality of green conversion layers on the second electrode which correspond to partial pixel sites selected from the pixel sites on the short wavelength penetration filter of the present disclosure.

"FIG. 8 is a perspective view for illustrating a step of forming a plurality of red conversion layers on the second electrode which correspond to partial pixel sites selected from the pixel sites on the short wavelength penetration filter of the present disclosure.

"FIG. 9 is a perspective view for illustrating a step of forming a long wavelength penetration filter on the red and/or green LED elements of the present disclosure.

"FIG. 10a is a perspective view for illustrating a step of coupling at least five red subminiature LED element to partial sub-pixels of the present disclosure, FIG. 10b is a perspective view for illustrating a step of coupling at least five green subminiature LED elements to partial sub-pixels, and FIG. 10c is a perspective view for illustrating a step of coupling at least five blue subminiature LED elements to partial sub-pixels.

"FIG. 11 is a perspective view for illustrating a step of forming an insulation layer on the subminiature red, green and blue LED elements of the present disclosure.

"FIG. 12 is a perspective view for illustrating a step of forming a second electrode on the insulation layer of the present disclosure.

"FIG. 13 is an electron microscope photograph showing a section of the LED basic element layer of the present disclosure.

"FIG. 14 is an electron microscope photograph showing sections of the present disclosure in which an insulation layer and a metal mask layer are formed on the second conductive semiconductor layer.

"FIG. 15a is an electron microscope photograph showing a section of the present disclosure in which a nano-sphere monolayer is formed on the metal mask layer, and FIG. 15b is an electron microscope photograph showing a plane thereof.

"FIG. 16a is an electron microscope photograph showing a section of the present disclosure in which the nano-sphere monolayer has been ashed under an O.sub.2 gas circumstance, and FIG. 16b is an electron microscope photograph showing a plane thereof.

"FIG. 17a is an electron microscope photograph showing a section of the present disclosure in which the metal mask layer has been etched under a Cl.sub.2 gas circumstance while using a nano-sphere of a reduced size as a mask, and FIG. 17b is an electron microscope photograph showing a plane thereof.

"FIG. 18a is an electron microscope photograph showing a section of the metal mask layer pattern of the present disclosure, which has been transferred according to a shape of polystyrene by the etching process, and FIG. 18b is an electron microscope photograph showing a plane thereof.

"FIG. 19a is an electron microscope photograph showing a section of the present disclosure in which SiO.sub.2 (the insulation layer) has been etched under a CF.sub.4 and O.sub.2 gas circumstance by using the metal mask layer pattern, and FIG. 19b is an electron microscope photograph showing a plane thereof.

"FIG. 20a is an electron microscope photograph showing a section of the present disclosure which has been etched under a SiCl.sub.4 and Ar gas circumstance by means of inductively coupled plasma (ICP) by using the etched insulation layer, and FIG. 20b is an electron microscope photograph showing a plane thereof.

"FIG. 21a is an electron microscope photograph showing a section of the present disclosure after the insulation layer used as a mask is removed, and FIG. 21b is an electron microscope photograph showing a plane thereof.

"FIGS. 22a and 22b are diagrams showing contact angles measured before (22a) and after (22b) coating the semiconductor layer having an insulation coating (Al.sub.2O.sub.3) with a hydrophobic coating (octadecyltrichlorosilane (OTS)) according to the present disclosure.

"FIGS. 23a and 23b are electron microscope photographs showing a section of the present disclosure in which a lift-off process is performed toward a buffer layer to which a support film is not attached or toward an undoped semiconductor layer and a sapphire substrate.

"FIGS. 24a and 24b are electron microscope photographs showing a section of the present disclosure in which the buffer layer or the undoped semiconductor layer is further etched by means of ICP to expose the first conductive semiconductor layer.

"FIGS. 25a and 25b are electron microscope photographs showing a section of the present disclosure in which etching is further performed by means of ICP.

"FIG. 26a is an electron microscope photograph showing a section of the present disclosure in which etching is performed by means of ICP to expose the first conductive semiconductor layer, and FIG. 26b is an electron microscope photograph showing a plane thereof.

"FIG. 27 is an electron microscope photograph showing a section of the present disclosure in which an electrode (Ti) is deposited to the first conductive semiconductor layer of the subminiature LED by means of sputtering.

"FIG. 28 is an electron microscope photograph showing a subminiature LED in an independent state after removing the support film with acetone according to the present disclosure.

"FIG. 29 is an electron microscope photograph showing a single independent subminiature LED of FIG. 28.

"FIG. 30 is an electron microscope photograph showing that independent subminiature LED elements of FIG. 28 are arranged on an electrode substrate.

"FIG. 31 shows a spectrum measured after the subminiature LED elements of the present disclosure are arranged on the electrode substrate.

"FIGS. 32a to 32c are photographs observed by naked eyes, showing that the subminiature LED of the present disclosure emits light in blue.

"FIG. 33 is a diagram showing a blue light emission peak measured when fifty subminiature LED elements of the present disclosure are attached and when one hundred subminiature LED elements are attached.

"FIG. 34 is a diagram showing transmittance of the short wavelength penetration filter of the present disclosure.

"FIG. 35 is a diagram showing a light emission peak of the green color conversion layer of the present disclosure.

"FIG. 36 is a diagram showing a light emission peak of the red color conversion layer of the present disclosure.

"FIG. 37 is a diagram showing transmittance of the long wavelength penetration filter of the present disclosure.

"FIG. 38 is a diagram respectively showing transmittance of the short wavelength penetration filter of the present disclosure, a blue light emission peak of the standardized subminiature LED element, and light emission peaks of the green and red color conversion layers.

"FIG. 39 is a diagram respectively showing transmittance of the long wavelength penetration filter of the present disclosure, a blue light emission peak of the standardized subminiature LED element, and light emission peaks of the green and red color conversion layers.

"FIG. 40 is a diagram showing the change of intensity of the light emission peak of the green color conversion layer according to the short wavelength penetration filter and the long wavelength penetration filter of the present disclosure.

"FIG. 41 is a diagram showing the change of intensity of the light emission peak of the red color conversion layer according to the short wavelength penetration filter and the long wavelength penetration filter of the present disclosure.

"FIG. 42 is a diagram showing light emission ratios and spectrums of the subminiature blue LED and the green and red color conversion layers of the present disclosure at a color temperature of 12000K."

For additional information on this patent application, see: Do, Young-Rag; Sung, Yeon-Goog. Full-Color Led Display Device and Manufacturing Method Thereof. Filed April 27, 2012 and posted May 15, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5420&p=109&f=G&l=50&d=PG01&S1=20140508.PD.&OS=PD/20140508&RS=PD/20140508

Keywords for this news article include: Electronics, Semiconductor, Light-emitting Diode, Kookmin University Industry Academy Cooperation Foundation.

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