Stacked multicolor micro display device

Abstract

The invention discloses a stacked multicolor micro display device, comprising a substrate having a driving circuit; the LED semiconductor layer is arranged on the substrate, the LED semiconductor layer comprises a plurality of LED units which are electrically isolated, each LED unit comprises a first light-emitting unit, a second light-emitting unit and a third light-emitting unit which are stacked and have different light-emitting colors, and each light-emitting unit comprises a first semiconductor layer, an epitaxial light-emitting layer and a second semiconductor layer which are stacked; the light-emitting units of the same type share the same first semiconductor layer structure, and each first semiconductor layer is electrically connected with the driving circuit. The N-type layer or the P-type layer of each Micro LED pixel does not need to be independently etched and separated, so that the photoetching and etching processes can be greatly reduced, and the process complexity and the production cost are remarkably reduced. In addition, the first semiconductor layer of each LED unit does not need to be aligned with the substrate electrode independently, so that the positioning error tolerance to micron-sized pixels in the bonding process is reduced, and the bonding yield is improved.

Description

Technical Field

[0001] This invention relates to the field of light-emitting technology, and more specifically to a stacked multicolor microdisplay device. Background Technology

[0002] MicroLED display technology is widely regarded as the next-generation display technology with great potential in wearable devices, large-screen displays, and other fields. However, its color display still faces significant challenges, especially in terms of structural layout. The two mainstream schemes of horizontal distribution and coaxial vertical arrangement of red, green, and blue (RGB) subpixels both have obvious defects: The former uses three independent subpixels of red, green, and blue in the horizontal direction to form a color pixel unit. Since the three subpixels need to be arranged in the horizontal direction, even if the size of each subpixel is extremely small, the size of the overall color pixel unit after stacking is still relatively large, which directly leads to a low pixel density (PPI) in micro-display devices. This makes it difficult to meet the stringent requirements of "small pixel size + high PPI" in micro-display scenarios such as AR glasses and micro-projectors. The latter, in order to solve the pixel density problem of horizontal distribution, stacks RGB subpixels in the vertical direction to form a coaxial structure. Although this can effectively compress the horizontal pixel size and ensure high pixel density, since each subpixel needs to be independently set with N-type or P-type layers to lead out electrodes, it exacerbates the requirements for stacking accuracy during the bonding process. Interlayer alignment errors can easily cause short circuits or poor contact. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to propose a stacked multicolor microdisplay device to overcome the shortcomings of the prior art.

[0004] To achieve the aforementioned objective, the present invention proposes a stacked multicolor microdisplay device, comprising:

[0005] Substrate, with driving circuitry;

[0006] An LED semiconductor layer is disposed on the substrate. The LED semiconductor layer includes multiple electrically isolated LED units. Each LED unit includes a first light-emitting unit, a second light-emitting unit, and a third light-emitting unit that are stacked and emit different colors. Each light-emitting unit includes a stacked first semiconductor layer, an epitaxial light-emitting layer, and a second semiconductor layer. Light-emitting units of the same type share the same first semiconductor layer structure, and each first semiconductor layer is electrically connected to a driving circuit.

[0007] In some implementations, the first light-emitting unit is used to emit red light, and the area of ​​the light-emitting region of the first light-emitting unit is larger than the area of ​​the light-emitting regions of the other two light-emitting units. The second and third light-emitting units emit green or blue light, and their light-emitting regions are staggered.

[0008] In some implementations, the first light-emitting unit, the second light-emitting unit, and the third light-emitting unit adopt a common cathode connection structure.

[0009] In some embodiments, the substrate has a common cathode metal electrode and a plurality of anode metal electrodes electrically connected to the driving circuit. Each first semiconductor layer is electrically connected to the source / drain of the driving circuit through the common cathode metal electrode, and each second semiconductor layer is electrically connected to a constant voltage source through the anode metal electrodes.

[0010] In some embodiments, the length-to-size ratio of the epitaxial light-emitting layer of the light-emitting region of the second light-emitting unit and the third light-emitting unit is 1:M, where M ranges from 1 to 5.

[0011] In some embodiments, the first light-emitting unit is disposed close to the substrate, and the second light-emitting unit is located between the first light-emitting unit and the third light-emitting unit. The second light-emitting unit is used to emit green light, and the third light-emitting unit is used to emit blue light.

[0012] In some embodiments, the thickness of the first semiconductor layer of each light-emitting unit is 0.05μm-0.5μm, and the thickness of the second semiconductor layer is 1μm-5μm.

[0013] In some embodiments, a current spreading layer electrically connected to the anode metal electrode is provided on the second semiconductor layer of each light-emitting unit.

[0014] In some implementations, a reflective layer is provided on the bottommost light-emitting unit. The reflective layer is used to reflect the light emitted by the light-emitting unit above it and project the light emitted by the light-emitting unit below it.

[0015] In some embodiments, the transflective functional layer is a DBR functional layer consisting of alternating stacks of SiO2 and TiO2 thin films.

[0016] The full-color stacked multi-color micro-display device proposed in this invention has the following technical effects:

[0017] The MicroLED display device proposed in this invention allows light-emitting units of the same type to share the same first semiconductor layer structure. This eliminates the need for independent etching and separation of the N-type or P-type layer for each MicroLED pixel. For example, a continuous N-type layer can be formed through a single large-area epitaxial growth, and then the light-emitting layer and P-type layer can be directly fabricated on top of it. Compared to the process of "each pixel having an independent N-type layer" requiring individual etching and separation, this significantly reduces photolithography and etching steps, thereby significantly lowering process complexity and production costs. Furthermore, the first semiconductor layer of each LED unit does not need to be individually aligned with the substrate electrode, reducing the tolerance for positioning errors of micron-level pixels during bonding and improving bonding yield. Attached Figure Description

[0018] The preferred embodiments will now be described in a clear and easy-to-understand manner, in conjunction with the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages, and implementation methods of the present invention.

[0019] Figure 1 This is a schematic diagram of the structure of a stacked multicolor micro-display device in a typical embodiment of the present invention.

[0020] Reference numerals: Substrate 1; First light-emitting unit 2; Second light-emitting unit 3; Third light-emitting unit 4; Anode metal electrode 5; Cathode metal electrode 6; Current spreading layer 7; LED unit 8; Dielectric layer 9; Transmissive and reflective functional layer 10; First semiconductor layer 11; Epitaxial light-emitting layer 12; Second semiconductor layer 13. Detailed Implementation

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0022] As used in this embodiment of the invention, the term "layer" refers to a portion of material comprising a region of a certain thickness. A layer may extend over the entire lower or upper layer structure, or may have a extent smaller than that of the lower or upper layer structure. Furthermore, a layer may be a region of a homogeneous or heterogeneous continuous structure with a thickness less than the thickness of the continuous structure. For example, a layer may be located between the top and bottom surfaces of a continuous structure, or between any pair of horizontal planes therebetween. A layer may extend horizontally, vertically, and / or along a tapered surface. A single layer may comprise multiple layers. For example, a semiconductor layer may comprise one or more doped or undoped semiconductor layers, and may have the same or different materials.

[0023] The term MicroLED, as used in the embodiments of this invention, refers to a descriptive size of certain devices or structures according to embodiments of the invention, intended to indicate a scale from 0.1 to 100 μm. However, it should be understood that embodiments of the invention are not necessarily limited thereto, and certain aspects of the embodiments can be applied to larger and possibly smaller size scales.

[0024] Figure 1 A schematic diagram illustrating the structure of an illustrative MicroLED display device according to some embodiments of the present invention is shown. Please refer to... Figure 1The MicroLED display device disclosed in this invention is used in the display field, especially in the micro-display field. The MicroLED display device includes a substrate 1 and an LED semiconductor layer formed on the substrate 1. The LED semiconductor layer includes a plurality of electrically isolated LED units 8, each of which can be independently controlled.

[0025] The substrate 1 can be formed from semiconductor materials such as silicon, silicon carbide, gallium nitride, germanium, gallium arsenide, and indium phosphide, or from non-conductive materials such as glass, plastic, or sapphire. The substrate 1 can be a CMOS backplane or a TFT glass substrate, etc., and is not limited thereto. The substrate 1 contains a driving circuit, which, or semiconductor device, can be fabricated according to specific requirements, and is used to provide electrical signals to the LED unit 8 to control brightness. The driving circuit can include an active matrix driving circuit, with each individual LED unit 8 having its own independent driver. In some embodiments, the driving circuit can also include a passive matrix driving circuit.

[0026] Taking one LED unit 8 as an example, LED unit 8 includes a first light-emitting unit 2, a second light-emitting unit 3, and a third light-emitting unit 4 stacked together. The first light-emitting unit 2 is closer to the substrate 1 than the second light-emitting unit 3 and the third light-emitting unit 4, and the second light-emitting unit 3 is located between the first light-emitting unit 2 and the third light-emitting unit 4. In this embodiment, the first light-emitting unit 2 can be a red light-emitting unit, or the second light-emitting unit 3 or the third light-emitting unit 4 can be a red light-emitting unit. This embodiment does not specifically limit the position of the red light-emitting unit. As an example, the first light-emitting unit 2 is a red light-emitting unit, and the second light-emitting unit 3 is a green light-emitting unit or a blue light-emitting unit. The second light-emitting unit 3 and the third light-emitting unit 4 emit different colors of light. When the second light-emitting unit 3 is a green light-emitting unit, the third light-emitting unit 4 is a blue light-emitting unit; when the second light-emitting unit 3 is a blue light-emitting unit, the third light-emitting unit 4 is a green light-emitting unit. For ease of description, the first light-emitting unit 2 will be referred to as a red light-emitting unit, the second light-emitting unit 3 as a green light-emitting unit, and the third light-emitting unit 4 as a blue light-emitting unit in the following text.

[0027] MicroLED devices exhibit a size effect. When the length dimension of the device is around 20µm, the device efficiency decreases sharply as the device size decreases, with the size effect being most pronounced in red light. In this embodiment, the first light-emitting unit 2, the second light-emitting unit 3, and the third light-emitting unit 4 are stacked along the thickness direction of the substrate 1. One of them can emit red light outward. Therefore, the size of the red light-emitting unit can be enlarged without increasing the size of the device in the first direction, thereby reducing the size effect of the entire device and improving the overall luminous efficiency.

[0028] In this embodiment, the length ratio of the epitaxial light-emitting layer 12 of the light-emitting region of the second light-emitting unit 3 to the third light-emitting unit 4 is 1:M, where M ranges from 1 to 5. Under the same intensity conditions, the human eye generally perceives green light as brighter than other colors, meaning the human eye is more sensitive to green light and relatively less sensitive to blue and red light. To maintain a balanced lifespan for the light-emitting units, the area of ​​the blue light-emitting unit's light-emitting region can be set larger than that of the green light-emitting unit's light-emitting region. As an example, the length of the epitaxial light-emitting layer 12 of the light-emitting region of the second light-emitting unit 3 is approximately 1.5 μm, and the length of the epitaxial light-emitting layer 12 of the light-emitting region of the third light-emitting unit 4 is approximately 3 μm. Thus, compared to the traditional horizontal arrangement structure of red, green, and blue light-emitting units, the stacked structure of the LED units 8 occupies less horizontal space, allowing the display to have a higher PPI (pixel density), which is more suitable for the high PPI requirements of AI AR (augmented reality) glasses. Furthermore, by designing the second light-emitting unit 3 as a green light-emitting unit, the length dimension of the epitaxial light-emitting layer 12 of the light-emitting area of ​​the second light-emitting unit 3 can be reduced. The reduced second light-emitting unit 3 does not need to maintain the original power, and the driving current can be appropriately reduced, which can reduce the heat generation and power consumption of the second light-emitting unit 3 and indirectly improve the device life.

[0029] In this embodiment, the epitaxial light-emitting layer 12 of the light-emitting region of the third light-emitting unit 4 is located to the side of the epitaxial light-emitting layer 12 of the light-emitting region of the second light-emitting unit 3. Thus, since the epitaxial light-emitting layers 12 of the respective light-emitting regions of the second light-emitting unit 3 and the third light-emitting unit 4 are staggered, there is no need to worry about brightness loss due to light shading. Furthermore, the size of the epitaxial light-emitting layer 12 of the light-emitting region of the second light-emitting unit 3 can be appropriately reduced, and the size of the epitaxial light-emitting layer 12 of the light-emitting region of the third light-emitting unit 4 can be increased accordingly, so that the entire device achieves maximum operating efficiency at the same PPI (pixel density).

[0030] The first light-emitting unit 2, the second light-emitting unit 3, and the third light-emitting unit 4 each include a first semiconductor layer 11, an epitaxial light-emitting layer 12, and a second semiconductor layer 13 stacked sequentially. The difference between the above light-emitting units is that the color of the light emitted by the epitaxial light-emitting layer 12 is different. For example, the epitaxial light-emitting layer 12 of the first light-emitting unit 2 can emit red light, the epitaxial light-emitting layer 12 of the second light-emitting unit 3 can emit green light, and the epitaxial light-emitting layer 12 of the third light-emitting unit 4 can emit blue light.

[0031] The first semiconductor layer 11 and the second semiconductor layer 13 can be either P-type or N-type semiconductor layers, without limitation. It should be noted that the different doping types of the first semiconductor layer 11 and the second semiconductor layer 13 result in opposite electrical characteristics. For example, if the first semiconductor layer 11 is a P-type semiconductor layer, then the second semiconductor layer 13 is an N-type semiconductor layer; conversely, if the first semiconductor layer 11 is an N-type semiconductor layer, then the second semiconductor layer 13 is a P-type semiconductor layer. For ease of explanation, the following description will use an example where the first semiconductor layer 11 is an N-type semiconductor layer and the second semiconductor layer 13 is a P-type semiconductor layer.

[0032] The first semiconductor layer 11 can be one or more layers formed of II-VI materials (such as ZnSe or ZnO) or III-V nitride materials (such as GaN, AlN, InN, InGaN, GaP, AlInGaP, AlGaAs, and their alloys), with a thickness of 1 μm-5 μm, preferably 1.5 μm-3 μm. The first semiconductor layer 11 can be N-type GaN formed by doping GaN with elements such as phosphorus or arsenic. The first semiconductor layer 11 can also be N-type GaN, N-type InGaN, N-type AlGaInP, etc., without specific limitations.

[0033] The epitaxial light-emitting layer 12 has a single quantum well structure, a multi-quantum well structure, or an alternating stacked structure of well layers and barrier layers, with a thickness of 0.05µm-0.5µm, preferably 0.1µm. The epitaxial light-emitting layer 12 is disposed between the first semiconductor layer 11 and the second semiconductor layer 13, and is used to recombine the holes and electrons provided by the first semiconductor layer 11 and the second semiconductor layer 13, respectively, to output light of a specific wavelength. For example, the epitaxial light-emitting layer 12 of the first light-emitting unit 2 is used to output red light, the epitaxial light-emitting layer 12 of the second light-emitting unit 3 is used to output green light, and the epitaxial light-emitting layer 12 of the third light-emitting unit 4 is used to output blue light.

[0034] In this embodiment, the epitaxial light-emitting layer 12 of the light-emitting region of the second light-emitting unit 3 is located on the side of the epitaxial light-emitting layer 12 of the light-emitting region of the third light-emitting unit 4, and is arranged in parallel with it. It can be understood that "parallel" in this embodiment means that the two light-emitting units are arranged in one direction. For example, the second light-emitting unit 3 and the second light-emitting unit 322 are arranged in parallel, which means that the second light-emitting unit 3 and the second light-emitting unit 322 are arranged along the length direction of the substrate 1.

[0035] The second semiconductor layer 13 can be one or more layers formed of II-VI materials (such as ZnSe or ZnO) or III-V nitride materials (such as GaN, AlN, InN, InGaN, GaP, AlInGaP, AlGaAs, and alloys thereof), with a thickness of 0.05 μm to 0.5 μm, preferably 0.2 μm to 0.35 μm. The second semiconductor layer 13 can be P-type GaN formed by doping GaN with elements such as magnesium or boron, or it can be P-type InGaN or P-type AlGaInP, etc., without specific limitations.

[0036] Because the P-type layer has poor conductivity and uneven current distribution, a current spreading layer 7 can be provided on the second semiconductor layer 13 to enhance its conductivity. The current spreading layer 7 includes an ohmic contact layer and a current transport layer. The ohmic contact layer is preferably made of ITO material, which can form a good ohmic contact with the first semiconductor layer 11. It is understood that the current transport layer can be made of ITO, or it can be made of metals with good conductivity such as Al or Ag, and is not limited to these. If it is made of metal, it is required to have high transparency so that it does not block the light emitted upwards from the bottom epitaxial light-emitting layer 12 during operation.

[0037] In some implementations, a reflective layer 10 can be disposed on the surface of the first light-emitting unit 2. The reflective layer 10 can completely cover the first light-emitting unit 2 or extend to the edge areas of the second and third light-emitting units. This invention does not impose specific limitations on this. The reflective layer 10 is configured to reflect blue-green light while transmitting red light. That is, the first light-emitting unit 2 can emit light upwards through the reflective layer 10 and pass through the second and third light-emitting units 3 and 4. After the second and third light-emitting units 3 and 4 are driven, blue and green light will not be transmitted towards the red light-emitting unit. Therefore, it can prevent the first light-emitting unit 2 from absorbing blue and green light energy and re-emitting red light, thus ensuring the color quality of the entire device. The reflective layer 10 can be a DBR functional layer, which achieves precise control of light transmission and reflection by alternating stacks of multiple transparent films with different refractive indices, such as alternating stacks of SiO2 and TiO2 films, so that the entire device has excellent performance in terms of efficiency and display color gamut.

[0038] In this embodiment, the connection structure of each LED unit can be a common cathode, a common anode, or each unit can be independent. As an example, the first light-emitting unit 2, the second light-emitting unit 3, and the third light-emitting unit 4 adopt a common cathode structure. Specifically, the substrate 1 has a common cathode metal electrode 6 and multiple anode metal electrodes 5 corresponding to the positions of the first light-emitting unit 2, the second light-emitting unit 3, and the third light-emitting unit 4, respectively. The LED semiconductor layer has three electrically connected first semiconductor layers. For ease of distinction, these three first semiconductor layers are defined as the first lower semiconductor layer, the first middle semiconductor layer, and the first upper semiconductor layer according to their relative positions. The first semiconductor layer of each first light-emitting unit 2 corresponds to the first lower semiconductor layer, the first semiconductor layer of each second light-emitting unit 3 corresponds to the first middle semiconductor layer, and the first semiconductor layer of each third light-emitting unit 4 corresponds to the first upper semiconductor layer. That is, light-emitting units of the same type share the same first semiconductor layer structure. Each first semiconductor layer is electrically connected to the source / drain of the driving circuit through the common cathode metal electrode 6. Each second semiconductor layer 13 is electrically connected to a constant voltage source one-to-one through the anode metal electrodes 5, thereby achieving the purpose of independent control of the epitaxial light-emitting layer 12 of the first light-emitting unit 2, the third light-emitting unit 4, and the second light-emitting unit 3. The materials of the anode metal electrode 5 and the common cathode metal electrode 6 can be metals or metal alloys, such as Cu, Al, Au, Pt, Ti, Cr, Ag, Ta, Ni, etc., and are not limited to these.

[0039] As described above, since the same type of light-emitting units share the same first semiconductor layer structure, there is no need to independently etch and separate the N-type or P-type layer of each Micro LED pixel. For example, a continuous N-type layer can be formed through a single large-area epitaxial growth, and then the light-emitting layer and P-type layer can be directly fabricated on it. Compared with the process of "each pixel having an independent N-type layer" which requires individual etching and isolation, this significantly reduces photolithography and etching steps, thereby significantly reducing process complexity and production costs. In addition, the first semiconductor layer of the LED unit does not need to be individually aligned with the substrate electrode, reducing the tolerance for positioning errors of micron-level pixels during the bonding process and improving the bonding yield.

[0040] It should be noted that the above embodiments can be freely combined as needed. The above are merely preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A stacked multicolor microdisplay device, characterized in that, The application relates to a stacked multicolor micro display device. The application relates to a stacked multicolor micro display device.

2. The stacked multicolor micro display device according to claim 1, wherein: the first light emitting unit is used for emitting red light, the area of the light emitting region of the first light emitting unit is larger than the areas of the light emitting regions of the other two light emitting units, the second light emitting unit and the third light emitting unit emit green light or blue light, and the light emitting regions of the second light emitting unit and the third light emitting unit are arranged staggeredly.

3. The stacked multicolor micro display device according to claim 1, wherein: the first light emitting unit, the second light emitting unit and the third light emitting unit adopt a common cathode connection structure.

4. The stacked multicolor micro display device according to claim 3, wherein: the substrate has a common cathode metal electrode and a plurality of anode metal electrodes which are electrically connected with the driving circuit, each first semiconductor layer is electrically connected with the source / drain of the driving circuit through the common cathode metal electrode, and each second semiconductor layer is electrically connected with a constant voltage source through the anode metal electrode one by one.

5. The stacked multicolor micro display device according to claim 2, wherein: the length dimension ratio of the epitaxial light emitting layers of the light emitting regions of the second light emitting unit and the third light emitting unit is 1:M, and the value range of M is 1-5.

6. The stacked multicolor micro display device according to claim 2, wherein: the first light emitting unit is arranged close to the substrate, the second light emitting unit is located between the first light emitting unit and the third light emitting unit, the second light emitting unit is used for emitting green light, and the third light emitting unit is used for emitting blue light.

7. The stacked multicolor micro display device according to claim 1, wherein: the thickness of the first semiconductor layer of each light emitting unit is 0.05-0.5 mu m, and the thickness of the second semiconductor layer is 1-5 mu m.

8. The stacked integrated Micro LED display chip according to claim 4, wherein: a current expansion layer which is electrically connected with the anode metal electrode is arranged on the second semiconductor layer of each light emitting unit.

9. The stacked multicolor micro display device according to claim 1, wherein: a transmissive and reflective functional layer is arranged on the bottommost light emitting unit, and the transmissive and reflective functional layer is used for reflecting the light emitted by the light emitting unit above the transmissive and reflective functional layer and projecting the light emitted by the light emitting unit below the transmissive and reflective functional layer.

10. The stacked multicolor micro display device according to claim 9, wherein: the transmissive and reflective functional layer adopts a DBR functional layer formed by alternately stacking SiO2 and TiO2 thin films. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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