Patent Description:
Demand for light emitting diodes (LEDs) has expanded exponentially in terms of low power consumption and environmental friendliness. LEDs are used as backlights for lighting apparatuses and LCD devices and are widely applied to display devices.

LEDs are kinds of solid-state elements that convert electrical energy into light. LEDs are based on the principle that when a voltage is applied between two doped layers, i.e. an n-type semiconductor layer and a p-type semiconductor layer, between which an active layer is interposed, electrons and holes are injected into and recombine in the active layer to emit light. LEDs can be driven at relatively low voltage and have high energy efficiency. Due to these advantages, LEDs release a small amount of heat. LEDs can be produced in various types. Particularly, micro-LED array display devices are fabricated based on types of LEDs in which a plurality of micro-LED pixels are formed on one wafer. According to a conventional method for the fabrication of a micro-LED array display device in which a plurality of micro-LED pixels are formed on one wafer, a p-type terminal and an n-type terminal are formed in each pixel through a chip production process and are arrayed along the longitudinal and transverse axes of signal lines to drive the pixel. In this case, elements responsible for signal control in the micro-LED pixels should be disposed in the vicinity of the micro-LED pixels, resulting in an increase in the size of the micro-LED array display device. Further, data lines arrayed along the longitudinal and transverse axes should be connected to the micro-LED pixels by wire bonding, making the process complicated and inconvenient.

The formation of a plurality of micro-LED pixels on one substrate technically limits the production of structures emitting red, green, and blue light. Because of this technical difficulty, the use of LEDs as light sources in micro-LED array display devices inevitably leads to the emission of monochromatic light. Thus, there is a need in the art for an approach that can provide a solution to the problems of the prior art. <CIT>, <CIT> and <CIT> are examples of LED devices according to the prior art.

One object of the present invention is to provide a micro-LED array display device according to claim <NUM>, wherein micro-LED pixels are flip-chip bonded to corresponding CMOS cells formed on a CMOS backplane through bumps, thus avoiding the complexity and inconvenience of wire bonding for connecting micro-LED pixels to various data lines while enabling individual control of the micro-LED pixels.

A further object of the present invention is to provide a micro-LED array display device according to claim <NUM>, wherein micro-LED panels, each including a plurality of micro-LED pixels, are flip-chip bonded to a single CMOS backplane, thus overcoming the difficulties of the prior art in forming red, green, and blue light emitting structures including micro-LED pixels formed on one substrate.

According to the present invention, there is provided a micro-LED array display device including: a micro-LED panel including a plurality of micro-LED pixels; a CMOS backplane including a plurality of CMOS cells corresponding to the micro-LED pixels to individually drive the micro-LED pixels; and bumps electrically connecting the micro-LED pixels to the corresponding CMOS cells in a state in which the micro-LED pixels are arranged to face the CMOS cells, wherein the micro-LED pixels are flip-chip bonded to the corresponding CMOS cells formed on the CMOS backplane through the bumps so that the micro-LED pixels are individually controlled, wherin a first conductivity-type metal layer formed over a portion of the exposed portions of the first conductivity-type semiconductor layer, the first conductivity-type metal layer being spaced apart from the micro-LED pixels, wherein the first conductivity-type metal layer functions as a common electrode of the micro-LED pixels, wherein the first conductivity-type metal layer has the same height as the micro-LED pixels, wherein the first conductivity-type metal layer is formed along the periphery of the micro-LED panel on the first conductivity-type semiconductor layer.

According to one embodiment, the micro-LED pixels are formed by growing a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer in this order on a substrate and etching the layers, the micro-LED pixels have a vertical structure including the first conductivity-type semiconductor layer, the active layer, and the second conductivity-type semiconductor layer formed in this order, and the active layer and the second conductivity-type semiconductor layer are removed from the exposed portions of the first conductivity-type semiconductor layer where none of the micro-LED pixels are formed.

According to one embodiment, a first conductivity-type metal layer is formed over the portions of the first conductivity-type semiconductor layer where none of the micro-LED pixels are formed and is spaced apart from the micro-LED pixels.

According to the present invention, the first conductivity-type metal layer is formed along the periphery of the micro-LED panel on the first conductivity-type semiconductor layer.

According to the present invention, the first conductivity-type metal layer has the same height as the micro-LED pixels.

According to one embodiment, the first conductivity-type metal layer functions as a common electrode of the micro-LED pixels.

According to one embodiment, the CMOS backplane includes a common cell formed at a position corresponding to the first conductivity-type metal layer and the first conductivity-type metal layer is electrically connected to the common cell through a common bump.

According to one embodiment, the first conductivity-type is n-type and the second conductivity-type is p-type.

According to one embodiment, the substrate is made of a material selected from sapphire, SiC, Si, glass, and ZnO.

According to one embodiment, the bumps are formed on the CMOS cells and are melted by heating such that the CMOS cells are electrically connected to the corresponding micro-LED pixels.

According to an embodiment, there is provided a micro-LED array display device including: first, second, and third micro-LED panels emitting light of different wavelength bands, each of the micro-LED panels including a plurality of micro-LED pixels; a single CMOS backplane including a plurality of CMOS cells corresponding to the micro-LED pixels of the first, second, and third micro-LED panels to individually drive the micro-LED pixels; and bumps electrically connecting the micro-LED pixels of the first, second, and third micro-LED panels to the corresponding CMOS cells in a state in which the micro-LED pixels of the first, second, and third micro-LED panels are arranged to face the CMOS cells, wherein the micro-LED pixels of the first, second, and third micro-LED panels are flip-chip bonded to the corresponding CMOS cells formed on the CMOS backplane through the bumps so that the micro-LED pixels are individually controlled.

In the new concept of micro-LED array display device according to an embodiment, micro-LED pixels are flip-chip bonded to micro-LED pixels formed on a CMOS backplane through bumps, avoiding the complexity and inconvenience of wire bonding for connecting micro-LED pixels to various data lines while enabling individual control of the micro-LED pixels. The micro-LED array display device of an embodiment in which a plurality of micro-LED panels emitting red, green, and blue light are flip-chip bonded to a single CMOS backplane through bumps can focus three colors on the same area using an optical system to achieve full color. Therefore, the micro-LED array display device of the embodiment is effective in overcoming the technical difficulties of the prior art in forming red, green, and blue light emitting structures including a plurality of micro-LED pixels on one substrate.

These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:.

The present disclosure is directed to a micro-LED array display device in which micro-LED pixels are arrayed by MESA etching and are flip-chip bonded to a CMOS backplane, thus being applicable to a micro display, such as a head mounted display (HMD) or head up display (HUD). In the micro-LED array display device of the present disclosure, micro-LED pixels arrayed by MESA etching for the production of LED chips are flip-chip bonded to a CMOS backplane so that they can be individually driven. The present disclosure is also directed to a micro-LED array display device in which three red, green, and blue light emitting elements, i.e. micro-LED panels, are arrayed on a CMOS backplane to achieve full color.

Preferred embodiments will now be described with reference to the accompanying drawings. The drawings and embodiments described with reference to the drawings are simplified and illustrated such that those skilled in the art can readily understand the present invention. Accordingly, the drawings and the embodiments should not be construed as limiting the scope of the present invention.

<FIG> illustrates an exemplary micro-LED panel <NUM> of a micro-LED array display device according to one embodiment, <FIG> illustrates the micro-LED panel <NUM> including micro-LED pixels and a CMOS backplane <NUM> including a plurality of CMOS cells adapted to individually drive the micro-LED pixels of the micro-LED panel <NUM>, <FIG> illustrates a state in which the micro-LED panel <NUM> and the CMOS backplane <NUM> are electrically connected to each other through bumps <NUM> arranged on the CMOS backplane <NUM>, and <FIG> illustrates a state in which the micro-LED panel <NUM> and the CMOS backplane <NUM> are arranged to face each other through the bumps <NUM> to electrically connect the micro-LED pixels of the micro-LED panel <NUM> to the CMOS cells of the CMOS backplane <NUM>.

Referring first to <FIG>, a description will be given of a micro-LED array display device according to one embodiment. The micro-LED array display device includes a micro-LED panel <NUM>, a CMOS backplane <NUM>, and bumps <NUM>. The micro-LED panel <NUM> includes a plurality of micro-LED pixels <NUM>. The CMOS backplane <NUM> includes a plurality of CMOS cells <NUM> corresponding to the micro-LED pixels <NUM> to individually drive the micro-LED pixels <NUM>. The micro-LED pixels <NUM> are electrically connected to the corresponding CMOS cells <NUM> through the bumps <NUM> in a state in which the micro-LED pixels <NUM> are arranged to face the CMOS cells <NUM>. In <FIG>, only one of the micro-LED pixels and only one of the CMOS cells are denoted by reference numerals <NUM> and <NUM>, respectively, for the purpose of convenience. The micro-LED pixels <NUM> are flip-chip bonded to the corresponding CMOS cells <NUM> formed on the CMOS backplane <NUM> through the bumps <NUM>. Due to this construction, the micro-LED pixels <NUM> can be individually controlled.

The micro-LED pixels <NUM> of the micro-LED panel <NUM> are formed by growing a first conductivity-type semiconductor layer <NUM>, an active layer <NUM>, and a second conductivity-type semiconductor layer <NUM> in this order on a substrate <NUM> and etching the layers. The micro-LED pixels have a vertical structure including the first conductivity-type semiconductor layer <NUM>, the active layer <NUM>, and the second conductivity-type semiconductor layer <NUM> formed in this order on the substrate <NUM>. The substrate <NUM> may be made of a material selected from sapphire, SiC, Si, glass, and ZnO. The first conductivity-type semiconductor layer <NUM> may be an n-type semiconductor layer and the second conductivity-type semiconductor layer <NUM> may be a p-type semiconductor layer. The active layer <NUM> is a region where electrons from the first conductivity-type semiconductor layer <NUM> recombine with holes from the second conductivity-type semiconductor layer <NUM> when power is applied.

The second conductivity-type semiconductor layer <NUM> and the active layer <NUM> are removed from the etched portions <NUM> of the micro-LED panel <NUM> where none of the micro-LED pixels <NUM> are formed, and as a result, the first conductivity-type semiconductor layer is exposed in the etched portions. The micro-LED panel <NUM> includes a first conductivity-type metal layer <NUM> formed over the portions <NUM> of the first conductivity-type semiconductor layer <NUM> where none of the micro-LED pixels <NUM> are formed. The first conductivity-type metal layer <NUM> is spaced apart from the micro-LED pixels <NUM>. According to the present invention, the first conductivity-type metal layer <NUM> is formed with a predetermined width along the periphery of the micro-LED panel <NUM> on the first conductivity-type semiconductor layer <NUM>. According to the present invention, the first conductivity-type metal layer <NUM> has the same height as the micro-LED pixels <NUM>. The first conductivity-type metal layer <NUM> is electrically connected to the CMOS backplane <NUM> through the bumps <NUM>. As a result, the first conductivity-type metal layer <NUM> functions as a common electrode of the micro-LED pixels <NUM>. For example, the first conductivity-type metal layer <NUM> may be a common ground.

The plurality of CMOS cells <NUM> of the CMOS backplane <NUM> serve to individually drive the micro-LED pixels <NUM>. The CMOS cells <NUM> are electrically connected to the corresponding micro-LED pixels through bumps <NUM>. The CMOS cells <NUM> are integrated circuits for individually driving the corresponding micro-LED pixels. The CMOS backplane <NUM> may be, for example, an active matrix (AM) panel. Specifically, each of the CMOS cells <NUM> may be a pixel driving circuit including two transistors and one capacitor. When the micro-LED panel <NUM> is flip-chip bonded to the CMOS backplane <NUM> through the bumps <NUM>, each of the micro-LED pixels may be arranged between a drain terminal and a common ground terminal (e.g., reference numeral <NUM>) of a transistor of the pixel driving circuit to form an equivalent circuit.

The CMOS backplane <NUM> includes a common cell <NUM> formed at a position corresponding to the first conductivity-type metal layer <NUM>. The first conductivity-type metal layer <NUM> is electrically connected to the common cell <NUM> through a common bump <NUM>. Herein, the bumps <NUM> is often intended to include the bumps <NUM> electrically connecting the plurality of CMOS cells to the micro-LED pixels and the common bump <NUM> electrically connecting the first conductivity-type metal layer <NUM> to the common cell <NUM>.

As illustrated in <FIG>, the CMOS backplane <NUM> on which the CMOS cells <NUM> are arranged faces the micro-LED panel <NUM>. After the CMOS cells <NUM> are brought into contact with the micro-LED pixels <NUM> in a one-to-one relationship, the bumps <NUM> and the common bump <NUM> are melted by heating. As a result, the CMOS cells <NUM> are electrically connected to the corresponding micro-LED pixels <NUM>, as illustrated in <FIG>.

Referring next to <FIG>, a description will be given of a micro-LED array display device capable of achieving full color according to a further embodiment. <FIG> illustrates a state in which red, green, and blue micro-LED panels <NUM>, <NUM>, and <NUM>, a single CMOS backplane <NUM> having CMOS cell areas <NUM>, <NUM>, and <NUM> where the micro-LED panels <NUM>, <NUM>, and <NUM> are to be electrically connected to CMOS cells, and bumps <NUM> arranged on the CMOS cells to achieve full color in a micro-LED array display device according to one embodiment and <FIG> illustrates a state in which the red, green, and blue micro-LED panels <NUM>, <NUM>, and <NUM> are electrically connected to the single CMOS backplane <NUM> through the bumps <NUM>.

Referring to these figures, the micro-LED array display device capable of achieving full color includes a first micro-LED panel <NUM>, a second micro-LED panel <NUM>, and a third micro-LED panel <NUM>, each of which includes a plurality of arrayed micro-LED pixels. The first <NUM>, second <NUM>, and third micro-LED panels <NUM> emit light of different wavelength bands. For example, the first, second, and third micro-LED panels <NUM>, <NUM>, and <NUM> may be constructed to emit red light, green light, and blue light, respectively. The micro-LED array display device capable of achieving full color includes a single CMOS backplane <NUM> adapted to individually drive the micro-LED pixels of the first, second, and third micro-LED panels <NUM>, <NUM>, and <NUM>. The single CMOS backplane <NUM> includes a plurality of CMOS cells corresponding to the micro-LED pixels of the first, second, and third micro-LED panels <NUM>, <NUM>, and <NUM>. CMOS cell areas <NUM>, <NUM>, and <NUM> are formed in the CMOS backplane <NUM> such that the micro-LED panels <NUM>, <NUM>, and <NUM> are arranged on the CMOS backplane <NUM>. The CMOS cell areas <NUM>, <NUM>, and <NUM> are formed corresponding to the micro-LED panels <NUM>, <NUM>, and <NUM>, respectively. The micro-LED panels <NUM>, <NUM>, and <NUM> are flip-chip bonded to the CMOS cell areas <NUM>, <NUM>, and <NUM>, respectively. A plurality of CMOS cells corresponding to the micro-LED pixels of the micro-LED panels <NUM>, <NUM>, and <NUM> are formed in the CMOS cell areas <NUM>, <NUM>, and <NUM>, respectively. With this arrangement, the micro-LED panels <NUM>, <NUM>, and <NUM> are flip-chip bonded to the single CMOS backplane <NUM> to electrically connect the micro-LED pixels to the CMOS cells. The CMOS cells are electrically connected to the micro-LED pixels through bumps <NUM>. The flip-chip bonding of the micro-LED panels <NUM>, <NUM>, and <NUM> to the single CMOS backplane <NUM> is performed in the same manner as that of the micro-LED panel <NUM> to the CMOS backplane <NUM> explained with reference to <FIG>.

Common cells are formed in the CMOS cell areas <NUM>, <NUM>, and <NUM> on the single CMOS backplane <NUM> and are electrically connected to first conductivity-type metal layers of the micro-LED panels <NUM>, <NUM>, and <NUM> through common bumps.

As described before, the micro-LED array display device in which the plurality of independently fabricated micro-LED panels emitting light of different wavelength bands, i.e. red, light, and blue light, are flip-chip bonded to the single CMOS backplane <NUM> can focus three colors on the same area using an optical system to achieve full color, thus overcoming the technical difficulties of the prior art in forming red, green, and blue light emitting structures on one substrate in the fabrication of micro-LEDs. In addition, the micro-LED array display device can avoid the inconvenience or difficulty of wire bonding for connecting LED chips to various data lines, which run along the longitudinal and transverse axes and are responsible for the control of the LED chips. Furthermore, the micro-LED array display device can eliminate the need to dispose elements responsible for signal control in LED chips at positions away from the LED chips, contributing to a reduction in the overall size of the display device.

Claim 1:
A micro-LED array display device including:
a micro-LED panel(<NUM>) including a plurality of micro-LED pixels(<NUM>) formed on a substrate(<NUM>), the micro-LED pixels(<NUM>) have a vertical structure including a first conductivity-type semiconductor layer(<NUM>), an active layer(<NUM>), and a second conductivity-type semiconductor layer(<NUM>) in this order on the substrate(<NUM>), and the active layer(<NUM>) and the second conductivity-type semiconductor layer(<NUM>) are removed from exposed portions of the first conductivity-type semiconductor layer(<NUM>) where none of the micro-LED pixels(<NUM>) are formed;
a CMOS backplane (<NUM>) including a plurality of CMOS cells (<NUM>) corresponding to the micro-LED pixels (<NUM>);
bumps(<NUM>) electrically connecting the micro-LED pixels(<NUM>) to the corresponding CMOS cells(<NUM>) in a state in which the micro-LED pixels(<NUM>) are arranged to face the CMOS cells(<NUM>); and
wherein the micro-LED pixels are flip-chip bonded to the corresponding CMOS cells formed on the CMOS backplane through the bumps so that the micro-LED pixels are individually controlled, characterized by comprising
a first conductivity-type metal layer(<NUM>) formed over a portion of the exposed portions of the first conductivity-type semiconductor layer(<NUM>), the first conductivity-type metal layer(<NUM>) being spaced apart from the micro-LED pixels(<NUM>), wherein the first conductivity-type metal layer(<NUM>) functions as a common electrode of the micro-LED pixels(<NUM>), wherein the first conductivity-type metal layer(<NUM>) has the same height as the micro-LED pixels(<NUM>), wherein the first conductivitytype metal layer(<NUM>) is formed along the periphery of the micro-LED panel(<NUM>) on the first conductivity-type semiconductor layer(<NUM>).