Display device

Abstract

The present invention discloses a display device, comprising: a circuit board, a plurality of light-emitting elements, an adhesive layer, and a cover layer. The plurality of light-emitting elements are located on the circuit board and electrically connected to the circuit board, and each includes a light-emitting layer. The adhesive layer is located on the circuit board and between the circuit board and the plurality of light-emitting elements. The cover layer covers the plurality of light-emitting elements and the adhesive layer, wherein the adhesive layer has a real part of the complex refractive index n A , the cover layer has a real part of the complex refractive index n B , the light-emitting layer has a real part of the complex refractive index n LED , and (n A +n B ) / n LED is between 1.45 and 1.75.

Description

Technical Field

[0001] The present invention relates to a display device, and particularly to a display device with improved light extraction efficiency. Background Art

[0002] A micro light-emitting diode (Micro-LED) display device directly uses a micro light-emitting diode die as a light-emitting unit, and realizes the effect of displaying an image by encapsulating the micro light-emitting diode die on a circuit board. However, due to the relatively high refractive index of the micro light-emitting diode die itself, its light extraction efficiency is still relatively low. Summary of the Invention

[0003] The present invention provides a display device with improved light extraction efficiency.

[0004] An embodiment of the present invention provides a display device, including: a circuit board; a plurality of light-emitting elements located on the circuit board and electrically connected to the circuit board, and each including a light-emitting layer; a glue layer located on the circuit board and between the circuit board and the plurality of light-emitting elements; and a covering layer covering the plurality of light-emitting elements and the glue layer, wherein the glue layer has a real part of the complex refractive index n A , the covering layer has a real part of the complex refractive index n B , the light-emitting layer has a real part of the complex refractive index n LED , and (n A +n B ) / n LED is between 1.45 and 1.75.

[0005] In an embodiment of the present invention, the above n A / n LED is between 0.8 and 0.95.

[0006] In an embodiment of the present invention, the above n A <n B <n LED .

[0007] In an embodiment of the present invention, the upper surface of the above glue layer is not higher than the upper surface of the light-emitting element.

[0008] In an embodiment of the present invention, the above glue layer includes a dye, and the color of the dye is the same as the light color of the light-emitting element.

[0009] In an embodiment of the present invention, the above dye includes dye particles and a dyeing agent, and the real part of the complex refractive index of the dye particles is greater than the real part of the complex refractive index of the dyeing agent.

[0010] In an embodiment of the present invention, the imaginary part of the complex refractive index of the above covering layer is less than the imaginary part of the complex refractive index of the glue layer.

[0011] In an embodiment of the present invention, the above-mentioned cover layer includes a plurality of color filter structures.

[0012] In an embodiment of the present invention, the color of the above-mentioned color filter structure is the same as the light color of the corresponding light-emitting element.

[0013] In an embodiment of the present invention, the above-mentioned display device further includes an anti-reflection layer located on the cover layer.

[0014] In an embodiment of the present invention, the imaginary part of the complex refractive index of the above-mentioned anti-reflection layer is close to zero.

[0015] In an embodiment of the present invention, the above-mentioned anti-reflection layer includes a destructive interference anti-reflection layer or a graded refractive index anti-reflection layer.

[0016] To make the above features and advantages of the present invention more obvious and understandable, specific embodiments are hereinafter given and detailed descriptions are made in conjunction with the accompanying drawings as follows. Description of the Drawings

[0017] Figure 1A is a cross-sectional schematic view of a display device 10 according to an embodiment of the present invention;

[0018] Figure 1B is a simulated diagram of the light extraction efficiency of a display device 10 according to an embodiment of the present invention;

[0019] Figure 2 is a cross-sectional schematic view of a display device 20 according to an embodiment of the present invention;

[0020] Figure 3 is a cross-sectional schematic view of a display device 30 according to an embodiment of the present invention.

[0021] Symbol Description

[0022] 10, 20, 30: Display device

[0023] 110: Circuit board

[0024] 112: Bottom plate

[0025] 114: Driving circuit layer

[0026] 120: Light-emitting element

[0027] 120T: Upper surface

[0028] 130, 132: Adhesive layer

[0029] 130T: Upper surface

[0030] 140, 143: Cover layer

[0031] AR: Anti-reflection layer

[0032] BM: Light-shielding structure

[0033] C1, C2: Side

[0034] CF: Color filter structure

[0035] CH: Semiconductor layer

[0036] CS: Color filter substrate

[0037] CV: Light-transmitting cover plate

[0038] DE: Drain

[0039] DM: Dye

[0040] DP: Dye particles

[0041] DS: Dye

[0042] E1: First electrode

[0043] E2: Second electrode

[0044] EL: Light-emitting layer

[0045] GE: Gate

[0046] I1: Buffer layer

[0047] I2: Gate insulating layer

[0048] I3: Interlayer insulating layer

[0049] I4: Planarization layer

[0050] P1, P2: Pad

[0051] S1: First-type semiconductor layer

[0052] S2: Second-type semiconductor layer

[0053] SE: Source

[0054] SS: Light-emitting stack

[0055] T: Active device Detailed implementation mode

[0056] In the drawings, for clarity, the thickness of layers, films, panels, regions, etc. is enlarged. Throughout the specification, like reference numerals represent like elements. It should be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" or "connected to" another element, it can be directly on or connected to the other element, or intervening elements may also be present. Conversely, when an element is referred to as being "directly on" or "directly connected to" another element, no intervening elements are present. As used herein, "connected" can refer to physical and / or electrical connection. Further, "electrically connected" or "coupled" may have other elements present between two elements.

[0057] In addition, relative terms such as "lower" or "bottom" and "upper" or "top" may be used herein to describe the relationship of one element to another element, as shown in the figures. It should be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation shown in the figures. For example, if the device in one figure is flipped, an element described as being on the "lower" side of another element will be oriented on the "upper" side of the other element. Thus, the exemplary term "lower" can include both the "lower" and "upper" orientations, depending on the particular orientation of the figure. Similarly, if the device in one figure is flipped, an element described as being "under" or "below" another element will be oriented as being "above" the other element. Thus, the exemplary terms "under" or "below" can include both the upper and lower orientations.

[0058] Taking into account the particular amount of the measurements discussed and the errors associated with the measurements (i.e., the limitations of the measurement system), "about", "approximate", or "substantially" as used herein includes the stated value and the average value within an acceptable deviation range of the particular value determined by a person of ordinary skill in the art. For example, "about" can mean within one or more standard deviations of the stated value, or within ±30%, ±20%, ±10%, ±5%. Further, "about", "approximate", or "substantially" as used herein can select a more acceptable deviation range or standard deviation depending on optical properties, etching properties, or other properties, rather than applying one standard deviation to all properties.

[0059] Figure 1A is a cross-sectional schematic view of a display device 10 according to an embodiment of the present invention. Figure 1B is a simulation diagram of the light extraction efficiency of the display device 10 according to an embodiment of the present invention. The display device 10 includes: a circuit board 110; a plurality of light-emitting elements 120 located on the circuit board 110 and electrically connected to the circuit board 110, and each including a light-emitting layer EL; an adhesive layer 130 located on the circuit board 110 and between the circuit board 110 and the plurality of light-emitting elements 120; and a cover layer 140 covering the plurality of light-emitting elements 120 and the adhesive layer 130, wherein the adhesive layer 130 has a real part of the complex refractive index n A, the cover layer 140 has a real part of the complex refractive index n B , the light-emitting layer EL has a real part of the complex refractive index n LED , and (n A +n B ) / n LED can be between about 1.45 and 1.75.

[0060] In the display device 10 according to an embodiment of the present invention, by controlling the refractive indices of the adhesive layer 130 and the cover layer 140 around the light-emitting element 120, the light-emitting reflection of the light-emitting element 120 is reduced, and at the same time, the light-emitting transmission of the light-emitting element 120 is increased, thereby improving the light-emitting efficiency of the light-emitting element. Hereinafter, with reference to FIG. 1, the implementation manners of the respective elements of the display device 10 will be further described, but the present invention is not limited thereto.

[0061] In the present embodiment, the circuit board 110 may include a bottom board 112 and a driving circuit layer 114. The bottom board 112 of the circuit board 110 may be a transparent substrate or a non-transparent substrate, and its material may be a quartz substrate, a glass substrate, a polymer substrate, or other suitable materials, but the present invention is not limited thereto. The driving circuit layer 114 may include pads P1 and P2, and the pads P1 and P2 may be electrically connected to the circuit board 110 and the light-emitting element 120. The pads P1 and P2 may have a single-layer structure or a structure in which conductive layers of multiple layers or more are stacked. For example, the pads P1 and P2 may have a structure in which a metal such as aluminum, molybdenum, titanium, or copper is stacked with an indium tin oxide (ITO), an indium zinc oxide (IZO), an indium gallium zinc oxide (IGZO), or other suitable conductive oxide, but the present invention is not limited thereto.

[0062] In some embodiments, the driving circuit layer 114 may further include components or circuits required by the display device 10, such as driving elements, switching elements, storage capacitors, power lines, driving signal lines, timing signal lines, current compensation lines, detection signal lines, and so on. For example, the driving circuit layer 114 may be formed on the bottom plate 112 by using thin film deposition manufacturing processes, photolithography manufacturing processes, and etching manufacturing processes. The driving circuit layer 114 may include an active element array, where the active element array may include a plurality of active elements T arranged in an array, and the active elements T may be electrically connected to the pad P1 or the pad P2. Specifically, the driving circuit layer 114 may include the active elements T, a buffer layer I1, a gate insulating layer I2, an interlayer insulating layer I3, a planarization layer I4, and pads P1 and P2. The active element T may be composed of a semiconductor layer CH, a gate GE, a source SE, and a drain DE. The region where the semiconductor layer CH overlaps the gate GE may be regarded as the channel region of the active element T. The gate insulating layer I2 is located between the gate GE and the semiconductor layer CH, and the interlayer insulating layer I3 is disposed between the source SE and the gate GE and between the drain DE and the gate GE. The gate GE and the source SE may respectively receive signals from, for example, driving elements, and the drain DE may be electrically connected to the pad P1 through a via hole in the planarization layer I4. When the gate GE receives a signal and turns on the active element T, the signal received by the source SE may be transmitted to the pad P1 through the drain DE. In other embodiments, the driving circuit layer 114 may further include more insulating layers and conductive layers as needed.

[0063] For example, the material of the semiconductor layer CH may include silicon-based semiconductor materials (such as polysilicon, amorphous silicon, etc.), oxide semiconductor materials, organic semiconductor materials, while the materials of the gate GE, the source SE, and the drain DE may include metals with good conductivity, such as aluminum, molybdenum, titanium, copper, and other metals or their laminates, but are not limited thereto. The materials of the buffer layer I1, the gate insulating layer I2, and the interlayer insulating layer I3 may include transparent insulating materials, such as silicon oxide, silicon nitride, silicon oxynitride, or laminates of the above materials, but the present invention is not limited thereto. The material of the planarization layer I4 may include transparent insulating materials, such as organic materials, acrylic materials, siloxane materials, polyimide materials, epoxy materials, etc., but are not limited thereto. The buffer layer I1, the gate insulating layer I2, the interlayer insulating layer I3, and the planarization layer I4 may also respectively have a single-layer structure or a multi-layer structure. The multi-layer structure is, for example, a laminate of any two or more of the above insulating materials, and can be combined and varied as needed.

[0064] In this embodiment, each light-emitting element 120 may include a first electrode E1, a second electrode E2, and a light-emitting stack SS, and the first electrode E1 and the second electrode E2 are electrically connected to different layers in the light-emitting stack SS, respectively. The light-emitting stack SS may include two semiconductor layers and a light-emitting layer sandwiched between the two semiconductor layers, and the first electrode E1 may be electrically connected to one of the two semiconductor layers, while the second electrode E2 may be electrically connected to the other of the two semiconductor layers. The materials of the first electrode E1 and the second electrode E2 may include metals, alloys, nitrides of metal materials, oxides of metal materials, oxynitrides of metal materials, or other suitable materials, or a stacked layer of a metal material and other conductive materials, or other materials with low resistance.

[0065] For example, the light-emitting stack SS may include a first-type semiconductor layer S1, a second-type semiconductor layer S2, and a light-emitting layer EL sandwiched between the first-type semiconductor layer S1 and the second-type semiconductor layer S2. One of the first-type semiconductor layer S1 and the second-type semiconductor layer S2 may be an N-type doped semiconductor, and the other may be a P-type doped semiconductor. In addition, the first-type semiconductor layer S1 and the second-type semiconductor layer S2 may include II-VI group materials (e.g., zinc selenide (ZnSe)) or III-V nitride materials (e.g., gallium nitride (GaN), gallium arsenide, indium nitride (InN), indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), aluminum indium gallium nitride (AlInGaN)) or aluminum gallium indium phosphide (AlGaInP). For example, in this embodiment, the first-type semiconductor layer S1 is, for example, an N-type doped semiconductor layer, the material of the N-type doped semiconductor layer is, for example, N-type gallium nitride (n-GaN), the second-type semiconductor layer S2 is, for example, a P-type doped semiconductor layer, and the material of the P-type doped semiconductor layer is, for example, P-type gallium nitride (p-GaN), but the present invention is not limited thereto. In addition, the structure of the light-emitting layer EL is, for example, a multiple quantum well structure (Multiple Quantum Well, MQW). The multiple quantum well structure may include multiple layers of indium gallium nitride (InGaN) and multiple layers of gallium nitride (GaN) stacked alternately. By designing the ratio of indium or gallium in the light-emitting layer EL, the emission wavelength range of the light-emitting layer can also be adjusted, but the present invention is not limited thereto.

[0066] The light-emitting element 120 may be manufactured on a growth substrate (e.g., a sapphire substrate) and then transferred onto the circuit substrate 110 through a mass transfer manufacturing process. The first electrode E1 may be electrically connected to the pad P1, and the second electrode E2 may be electrically connected to the pad P2. In some embodiments, solder, conductive adhesive, or other conductive materials may also be included between the first electrode E1 and the pad P1 and between the second electrode E2 and the pad P2.

[0067] After the mass transfer manufacturing process, the adhesive layer 130 can be coated on the circuit board 110 around the light-emitting element 120, and then the adhesive layer 130 can also flow between the light-emitting element 120 and the circuit board 110. Considering the feasibility of the actual manufacturing process, the upper surface 130T of the adhesive layer 130 may not be higher than the upper surface 120T of the light-emitting element 120. For example, in this embodiment, the upper surface 130T of the adhesive layer 130 may be lower than the upper surface 120T of the light-emitting element 120, but it is not limited thereto. In some embodiments, the upper surface 130T of the adhesive layer 130 may be substantially flush with the upper surface 120T of the light-emitting element 120.

[0068] Generally speaking, the so-called refractive index refers to the real part of the complex refractive index of the material, and the imaginary part of the complex refractive index can be called the extinction coefficient, which represents the attenuation amount of light after entering the material. In this embodiment, the light-emitting layer EL of the light-emitting element 120 can be defined to have a real part of the complex refractive index n LED , and the adhesive layer 130 has an average real part of the complex refractive index n A . Since the refractive index of the light-emitting layer EL may be as high as 2.4 to 3.6, it is designed that n A is less than n LED , and the ratio of n A / n LED is preferably above 0.8. For example, n A / n LED can be between 0.8 and 0.95 to avoid total reflection of the light emitted by the light-emitting layer EL.

[0069] In this embodiment, the cover layer 140 can cover the upper surface 120T of the light-emitting element 120 and the adhesive layer 130, and the cover layer 140 can have an average real part of the complex refractive index n B . In some embodiments, n B can be between n A and n LED , that is, n A <n B <n LED , which is beneficial to improving the light extraction efficiency of the light-emitting element 120. In addition, from Figure 1B the simulation results of the light extraction efficiency, it can be seen that when (n A + n B ) / n LED is between 1.45 and 1.75, the light extraction efficiency of the light-emitting element 120 can be increased to more than 11.5%; when (n A + n B ) / n LED is between 1.47 and 1.71, the light extraction efficiency of the light-emitting element 120 can reach more than 12%; and when (nA +n B ) / n LED When it is between 1.5 and 1.67, the light extraction efficiency of the light-emitting element 120 can also exceed 12.5%.

[0070] In some embodiments, the adhesive layer 130 may have an imaginary part k of the average complex refractive index A , and the cover layer 140 may have an imaginary part k of the average complex refractive index B , and k B may be slightly smaller than k A , that is, k B < k A , so as to reduce the interface reflection between the adhesive layer 130 and the cover layer 140.

[0071] Hereinafter, use Figures 2 to 3 to continue to describe other embodiments of the present invention, and, following Figure 1A the component numbers and related content of the embodiments, wherein, the same reference numerals are used to represent the same or similar components, and the description of the same technical content is omitted. For the description of the omitted part, reference can be made to Figure 1A the embodiments, and will not be repeated in the following description.

[0072] Figure 2 is a schematic cross-sectional view of a display device 20 according to an embodiment of the present invention. The display device 20 includes a circuit board 110, a light-emitting element 120, pads P1, P2, an adhesive layer 132, and a cover layer 140, and the light-emitting element 120 includes a first electrode E1, a second electrode E2, and a light-emitting stack SS. Among them, the light-emitting layer in the light-emitting stack SS has a real part n of the complex refractive index LED , the adhesive layer 132 has an average real part n of the complex refractive index A , the cover layer 140 has an average real part n of the complex refractive index B , and (n A + n B ) / n LED is between 1.45 and 1.75. Compared with the display device 10 shown in Figure 1A , Figure 2 the difference between the display device 20 shown and the above is that: the adhesive layer 132 of the display device 20 further includes a dye DM.

[0073] For example, in the present embodiment, the color of the dye DM is preferably the same as the light color of the light-emitting element 120, and the dye DM may include dye particles DP and a dyeing agent DS. The dyeing agent DS can help the dye particles DP to be dispersed in the glue layer 132. In addition, the real part of the complex refractive index of the dye particles DP may be slightly greater than the real part of the complex refractive index of the dyeing agent DS to improve the light color uniformity. In some embodiments, the cover layer 140 may also include a dye, and the color of the dye in the cover layer 140 is also the same as the light color of the light-emitting element 120.

[0074] In some embodiments, the display device 20 further includes an antireflection layer AR, and the antireflection layer AR may be located on the cover layer 140. The antireflection layer AR can reduce the reflectivity and is used to improve the light transmittance and the light extraction efficiency. In certain embodiments, the imaginary part of the complex refractive index of the antireflection layer AR may be close to zero to improve the light extraction rate by reducing the attenuation amount of the incident light.

[0075] In some embodiments, the antireflection layer AR may be a destructive interference antireflection layer. For example, the thickness of the antireflection layer AR may be half of the light wavelength. In this way, the phase of the light reflected by the antireflection layer AR after passing through the antireflection layer AR may be opposite to that of the incident light, so that the reflected light and the incident light generate destructive interference, thereby reducing the reflectivity.

[0076] In some embodiments, the antireflection layer AR may be a gradient refractive index antireflection layer. For example, the antireflection layer AR may include a material with a lower refractive index, such as air bubbles or other suitable materials. When the distribution concentration of the air bubbles increases from the side C1 of the antireflection layer AR close to the cover layer 140 to the opposite side C2, a refractive index decreasing from the side C1 to the side C2 can be formed in the antireflection layer AR, which is beneficial to light extraction. In certain embodiments, the antireflection layer AR may include a multi-layer structure with a gradually changing refractive index.

[0077] Figure 3 is a cross-sectional schematic diagram of a display device 30 according to an embodiment of the present invention. The display device 30 includes a circuit board 110, a light-emitting element 120, pads P1, P2, a glue layer 130, and a cover layer 143. The light-emitting element 120 includes a first electrode E1, a second electrode E2, and a light-emitting stack SS. Among them, the light-emitting layer in the light-emitting stack SS has a real part of the complex refractive index n LED , the glue layer 130 has an average real part of the complex refractive index n A , the cover layer 143 has an average real part of the complex refractive index n B , and (n A + n B ) / n LED is between 1.45 and 1.75. Compared with the display device 10 as shown in Figure 1A Figure 3The difference of the display device 30 shown is that the cover layer 143 of the display device 30 may include a plurality of color filter structures CF, and the upper surface 130T of the glue layer 130 may be substantially flush with the upper surface 120T of the light-emitting element 120.

[0078] In this embodiment, the orthographic projections of the plurality of color filter structures CF on the circuit board 110 may respectively overlap the orthographic projections of the plurality of light-emitting elements 120 on the circuit board 110 to filter the light from the corresponding light-emitting elements 120 respectively, and the color of the color filter structure CF may be the same as the light color of the corresponding light-emitting element 120. For example, when the corresponding light-emitting element 120 is a blue light-emitting diode, the color filter structure CF may be a blue filter; when the corresponding light-emitting element 120 is a green light-emitting diode, the color filter structure CF may be a green filter; and when the corresponding light-emitting element 120 is a red light-emitting diode, the color filter structure CF may be a red filter.

[0079] In this embodiment, the display device 30 may further include a plurality of light-shielding structures BM and a light-transmitting cover plate CV. The color filter structures CF and the light-shielding structures BM may be alternately formed on the surface of the light-transmitting cover plate CV close to the light-emitting element 120, and the color filter structures CF, the light-shielding structures BM and the light-transmitting cover plate CV may form a color filter substrate CS. By making the light-shielding structures BM be respectively located between the color filter structures CF and the orthographic projections of the light-shielding structures BM on the circuit board 110 be outside the orthographic projections of the light-emitting elements 120 on the circuit board 110, the light output can be prevented from being affected, and at the same time, the dark state brightness can be reduced and the color contrast can be improved.

[0080] In summary, the display device of the present invention can effectively improve the light extraction efficiency of the light-emitting element by controlling the complex refractive index of the glue layer and the cover layer around the light-emitting element.

[0081] Although the present invention is disclosed in combination with the above embodiments, it is not intended to limit the present invention. Any person with ordinary knowledge in the technical field can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be defined by the appended claims.

Claims

1. A display device, comprising: Circuit substrate; A plurality of light-emitting elements located on and electrically connected to the circuit substrate, and each including a light-emitting stack, a first electrode, and a second electrode. The light-emitting stack includes a first-type semiconductor layer, a second-type semiconductor layer, and a light-emitting layer located between the first-type semiconductor layer and the second-type semiconductor layer. The first electrode is electrically connected to the first-type semiconductor layer, and the second electrode is electrically connected to the second-type semiconductor layer; An adhesive layer located on the circuit substrate and between the circuit substrate and the plurality of light-emitting elements and around the first-type semiconductor layer and the second-type semiconductor layer of each of the plurality of light-emitting elements. Wherein the second-type semiconductor layer is located between the first-type semiconductor layer and the circuit substrate, and the upper surface of the adhesive layer is not higher than the upper surface of the first-type semiconductor layer and not lower than the lower surface of the first-type semiconductor layer; And A cover layer covering the plurality of light-emitting elements and the adhesive layer, wherein the cover layer covers and contacts the upper surface of the light-emitting stack of the plurality of light-emitting elements, Among them, the adhesive layer has a real part of the complex refractive index n A , the cover layer has a real part of the complex refractive index n B , the light-emitting layer has a real part of the complex refractive index n LED , and (n A + n B ) / n LED is between 1.45 and 1.75, where n A / n LED is between 0.8 and 0.95, where n A < n B < n LED , and the imaginary part of the complex refractive index of the cover layer is less than the imaginary part of the complex refractive index of the adhesive layer.

2. The display device according to claim 1, wherein the adhesive layer comprises a dye, and the color of the dye is the same as the light color of the light-emitting element.

3. The display device according to claim 2, wherein the dye comprises dye particles and a dyeing agent, and the real part of the complex refractive index of the dye particles is greater than the real part of the complex refractive index of the dyeing agent.

4. The display device according to claim 1, wherein the cover layer comprises a plurality of color filter structures.

5. The display device according to claim 4, wherein the color of the color filter structure is the same as the light color of the corresponding light-emitting element.

6. The display device according to claim 1, further comprising an anti-reflection layer located on the cover layer.

7. The display device according to claim 6, wherein the anti-reflection layer comprises a gradient refractive index anti-reflection layer, and the gradient refractive index anti-reflection layer comprises air bubbles, wherein the distribution concentration of the air bubbles increases from the side of the anti-reflection layer close to the cover layer to the opposite side.

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