Micro light emitting diode pixel current injection impedance regulation structure and preparation method thereof

Abstract

This invention discloses a micro-LED pixel current injection impedance control structure and its fabrication method, comprising a CMOS backplane, a cathode electrode and an anode electrode located in the central region of the pixel, a MicroLED epitaxial structure disposed on the anode electrode, and an n-type transparent electrode layer electrically connected above the MicroLED epitaxial structure via an array of conductive elements. This invention achieves structured control of the equivalent current injection impedance through differences in the geometric diameters of the conductive pillars. While maintaining a constant number of conductive pillars, it achieves passive balancing of the current injection weight within the pixel, thereby effectively suppressing current concentration and localized overheating in the central region of the MicroLED pixel, improving the spatial uniformity of pixel brightness and overall luminous efficiency. Furthermore, it eliminates the need for active compensation circuits or complex driving strategies, resulting in a simple structure and high reliability.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic devices and MicroLED display technology, specifically relating to a microLED pixel current injection impedance control structure. This invention also relates to a method for fabricating the microLED pixel current injection impedance control structure. Background Technology

[0002] As MicroLED displays develop towards higher pixel density and higher brightness, the size of individual MicroLED pixels continues to shrink, and the current injection area inside the pixel tends to be concentrated, leading to the following problems becoming increasingly prominent: the current density in the central region of the pixel is too high, which easily causes local overheating; different spatial regions inside the pixel have different responses to the injected current; uneven current injection leads to uneven distribution of light emission brightness and reduced luminous efficiency; although simply increasing the number of injection points can disperse the current, it will significantly increase the process complexity and introduce parasitic effects.

[0003] In existing technologies, pixel-internal current equalization is typically achieved by increasing the number of conductive pillars, changing the position of injection holes, or introducing active drive compensation circuits. However, these solutions generally suffer from problems such as complex structures, limited pixel sizes, high manufacturing costs, or difficulties in system integration, making them particularly unsuitable for large-scale applications in micrometer-level pixels.

[0004] Therefore, there is an urgent need for a structural solution that allows for the design and controllability of the spatial distribution of current injection within a MicroLED pixel, without increasing the number of conductive pillars or introducing additional active devices. Summary of the Invention

[0005] The purpose of this invention is to provide a current injection impedance control structure for micro-light-emitting diode pixels, which solves the problem that the current injection weight within existing micro-light-emitting diode pixels is difficult to control.

[0006] Another objective of this invention is to provide a method for fabricating a micro-light-emitting diode pixel current injection impedance control structure.

[0007] The first technical solution adopted in this invention is: a micro-light-emitting diode pixel current injection impedance control structure, including a CMOS backplane, a cathode electrode and an anode electrode located in the center region of the pixel are disposed on the CMOS backplane, a MicroLED epitaxial structure is disposed on the anode electrode, and an n-type transparent electrode layer is electrically connected above the MicroLED epitaxial structure through an array of conductive materials.

[0008] The first technical solution of this invention is further characterized by: The conductor is a rectangular array of conductive pillars arranged along a transverse plane, including a conductive pillar body that is electrically connected to an n-type transparent electrode layer at the top, and a conductive pillar contact layer that contacts the MicroLED epitaxial structure at the bottom of the conductive pillar body.

[0009] Equivalent injection impedance of conductive pillar Set as:

[0010] In the formula, The resistivity of the conductive pillar body. The length of the conductive column body. This represents the cross-sectional area of ​​the conductive pillar.

[0011] The diameter of the conductive pillars gradually decreases from the center of the pixel towards the edge.

[0012] The diameter of the conductive pillars in the non-pixel center region of the conductive pillar array Set as:

[0013] In the formula, The diameter of the conductive pillar in the center region of the pixel. This is the diameter adjustment coefficient. The distance between the conductive pillars in the non-pixel center region and the conductive pillars in the pixel center region of the conductive pillar array.

[0014] The n-type transparent electrode layer material is selected from ITO, IZO or ZnO, the conductive pillar body is selected from Cu, W, Al, ITO, IZO or ZnO or Ti / Al / TiN composite metal, and the conductive pillar contact layer is selected from TiN / TaN.

[0015] The conductor is a conductive ring arranged concentrically along a transverse plane.

[0016] The wall thickness of the conductive ring gradually decreases from the inside to the outside.

[0017] The microLED epitaxial structure includes a p-type semiconductor layer that forms a p-type contact with the anode electrode, an InGaN or GaN multi-quantum-well light-emitting layer disposed on the p-type semiconductor layer, and an n-type semiconductor layer disposed on the light-emitting layer that contacts the bottom of the conductor.

[0018] The second technical solution adopted in this invention is: a method for fabricating a micro-light-emitting diode pixel current injection impedance control structure, comprising the following steps: Step 1: Provide a Si-based GaN epitaxial structure and bond it to a CMOS backplane; Step 2: Thin the GaN epitaxial structure to the predetermined thickness; Step 3: Deposit a hard mask layer; Step 4: Forming a photoresist microarray pattern; Step 5: Etching to form a MESA pixel array; Step 6: Isolate the MESA pixel array and deposit a passivation layer; Step 7: Form a pixel array pattern with conductive pillars of different diameters; Step 8: Etch to form conductive pillar patterns; Step 9: Deposit a transparent conductive film layer to fill the conductive pillars.

[0019] The beneficial effects of this invention are as follows: The micro-LED pixel current injection impedance control structure and its fabrication method solve the problems of uneven current distribution, decreased brightness uniformity, and increased risk of local overheating caused by the high concentration of current injection regions within the pixel after the reduction of MicroLED pixel size, and the difficulty in controlling the current injection weights in different spatial regions. This invention achieves structured control of the equivalent current injection impedance through the difference in the geometric diameter of the conductive pillars. While maintaining the same number of conductive pillars, it achieves passive balancing of the current injection weights within the pixel, effectively suppressing current concentration and local overheating in the central region of the MicroLED pixel, improving the spatial uniformity of pixel brightness and overall luminous efficiency. Furthermore, it eliminates the need for active compensation circuits or complex driving strategies, resulting in a simple structure with high reliability. It is particularly effective for micron-sized pixels and suitable for high-density MicroLED arrays. Attached Figure Description

[0020] Figure 1 This is a cross-sectional schematic diagram of the micro-light-emitting diode pixel current injection impedance control structure of the present invention; Figure 2 This is a schematic diagram of the distribution of the conductive pillar array in the micro-light-emitting diode pixel current injection impedance control structure of the present invention; Figure 3 This is a schematic diagram of the distribution of the conductive ring array in the micro-light-emitting diode pixel current injection impedance control structure of the present invention; Figure 4 This is a schematic diagram comparing the equivalent injection impedance and current formed by conductive pillars of different diameters. Figure 5 This is a schematic diagram comparing the current distribution within a pixel before and after adopting the structure of this invention.

[0021] In the figure, 1. CMOS backplane, 2. Cathode electrode, 3. Anode electrode, 4. MicroLED epitaxial structure, 5. n-type transparent electrode layer, 6. Conductive pillar; 41. n-type semiconductor layer; 42. Light-emitting layer; 43. p-type semiconductor layer; 61. Conductive post body; 62. Conductive post contact layer. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] Example 1 This invention provides a current injection impedance control structure for micro LED pixels. By setting an array of conductive pillars with different geometric diameters in the current injection region of the MicroLED pixel, and while keeping the number of conductive pillars constant, the diameter of the conductive pillars corresponds to their spatial position or functional area inside the pixel, thereby structurally designing the equivalent current injection impedance corresponding to each conductive pillar and realizing passive control of the current injection weight in different regions inside the pixel.

[0024] Specifically, N conductive pillars (N≥2) are set in a MicroLED pixel. The conductive pillars are electrically connected to the upper or lower layer electrodes through metal vias or metal pillar structures, serving as current injection channels for the MicroLED pixel. Each conductive pillar has a preset geometric diameter. Its typical diameter range is 0.2–5 μm, preferably 0.5–3 μm. The conductive pillar material can be Cu, W, Al, ITO, IZO, ZnO, Ti / Al / TiN composite metal or other conductive metal systems.

[0025] Since the equivalent current injection impedance of a conductive post is related not only to its contact area, but also to its conductive path length, cross-sectional area, and three-dimensional current propagation behavior, changing the diameter of the conductive post can effectively change its corresponding equivalent injection impedance, rather than simply changing the contact area.

[0026] Equivalent injection impedance of conductive pillar Approximately satisfies:

[0027] in, The resistivity of the conductive pillar material. This is the length of the conductive path. This represents the cross-sectional area of ​​the conductive pillar. By changing the diameter of the conductive pillar... It can directly change its cross-sectional area. This allows for the design of structures with different injection impedances.

[0028] By associating the diameter of the conductive pillars with their spatial location or functional partitioning within the pixel—such as radial location, partition location, or brightness compensation requirements—different regions within the pixel can exhibit different equivalent injection impedances for the conductive pillars, thus pre-setting the current injection weight ratio for each region at the structural level. For example, a larger diameter conductive pillar (e.g., 1–3 μm) can be used in the central region of the pixel, while a smaller diameter conductive pillar (e.g., 0.5–1 μm) can be used in the edge regions. This results in a lower current injection impedance in the central region compared to the edge regions, compensating for current diffusion losses in the central region of the MicroLED.

[0029] Larger diameter conductive pillars have lower equivalent injection impedance and thus higher injection current weighting; smaller diameter conductive pillars have higher equivalent injection impedance and thus lower injection current weighting. The conductive pillar array can be arranged according to the radial distance within the pixel. Perform diameter mapping, for example, satisfying the following relationship:

[0030] in, The diameter of the central conductive post, This is the diameter adjustment coefficient, which is changed by... The size of the current injection weight can be adjusted to determine the radial distribution.

[0031] Through the aforementioned structured design, without increasing the number of conductive pillars or introducing active driving or compensation circuits, the current distribution within a pixel can be transformed from a concentrated type to a preset uniform or zoned distribution, thereby effectively suppressing local current concentration and improving the spatial uniformity of pixel brightness. When the pixel size is reduced to the micrometer level, due to the limited current diffusion capability within the pixel, this structure based on the equivalent injection impedance control of conductive pillars is particularly effective in suppressing current concentration and improving brightness uniformity.

[0032] Example 2 In Example 1, in terms of specific structure, such as Figure 1 and Figure 2 As shown, the conductive pillars can be formed by semiconductor processes such as photolithography, etching, metal deposition and chemical mechanical polishing (CMP), and their height can be 0.2μm to 10μm. They are electrically connected to the MicroLED pixel electrodes through a metal interconnect layer.

[0033] Example 3 In addition to using a conductive pillar array, the current injection structure of this invention can also be used in other ways, such as... Figure 1 and Figure 3 As shown, it can also be achieved using multiple concentric conductive ring structures.

[0034] Specifically, multiple concentric ring-shaped conductive structures are set in the current injection region of the MicroLED pixel, each ring having a different ring width. or ring radius This forms a multi-layered conductive ring structure. The conductive rings are electrically connected to the pixel electrodes through metal layers or conductive vias, enabling current injection into different radial regions within the pixel.

[0035] In this structure, the equivalent injection impedance of different rings is determined by their ring width, ring radius, and conductive path length. This is achieved by adjusting the width of each ring. The thickness of the metal can be adjusted to achieve different current injection weights in different radial regions. For example, the inner ring can be designed to be wider (e.g., 1–3 μm), while the outer ring can be designed to be narrower (e.g., 0.3–1 μm), so that the injection impedance in the central region is lower than that in the edge region.

[0036] Two to five concentric conductive rings can be set, and the ring width can be gradually varied radially or designed according to a preset functional relationship to achieve radial uniformity of the current density inside the pixel.

[0037] Example 4 In Example 3, the conductive ring structure can be formed by conventional semiconductor processes, such as defining the ring pattern by photolithography, metal deposition, and subsequent etching or CMP planarization steps.

[0038] Example 5 This invention provides a micro-light-emitting diode pixel current injection impedance control structure, such as... Figure 1 As shown, it includes: a CMOS backplane 1, a cathode electrode 2 and an anode electrode 3 disposed on the CMOS backplane 1, a MicroLED epitaxial structure 4 disposed on the anode electrode 3, and an n-type transparent electrode layer 5 disposed above the MicroLED epitaxial structure 4, wherein an array of conductive pillars 6 is disposed between the MicroLED epitaxial structure 4 and the n-type transparent electrode layer 5.

[0039] The CMOS backplane 1 serves as the driving circuit for the MicroLED microdisplay, providing pixel driving signals and current control. Multiple metal interconnect layers and via structures are formed on the CMOS backplane 1, and cathode electrodes 2 and anode electrodes 3 are formed thereon to connect the MicroLED pixels. The anode electrode 3 is located in the center region of the pixel, while the cathode electrode 2 is located on either side of the pixel. The anode electrode 3 is connected to the CMOS pixel driving circuit via metal interconnects to provide driving current to the MicroLED; the cathode electrode 2 provides a return current path.

[0040] A MicroLED epitaxial structure 4 is formed on the anode electrode 3. The MicroLED epitaxial structure 4 includes an n-type semiconductor layer 41, a light-emitting layer 42, and a p-type semiconductor layer 43. The light-emitting layer 42 is an InGaN / GaN multiple quantum well structure, and the p-type semiconductor layer 43 forms a p-type contact with the anode electrode 3. Therefore, the driving current is transmitted from the anode electrode 3 → p-type semiconductor layer 43 → light-emitting layer 42 → n-type semiconductor layer 41.

[0041] An n-type transparent electrode layer 5 is formed above the n-type semiconductor layer 41. The n-type transparent electrode layer 5 can be ITO, IZO, ZnO or other transparent conductive oxides. The transparent electrode is used for lateral current diffusion and to provide a current injection interface.

[0042] A conductive pillar array is disposed between the n-type semiconductor layer 41 and the n-type transparent electrode layer 5. The conductive pillar array consists of multiple conductive pillars 6, which are distributed in a predetermined array pattern within the pixel area. Each conductive pillar 6 includes a conductive pillar body 61 and a bottom conductive pillar contact layer 62. The conductive pillar body 61 passes through the insulating layer and is electrically connected to the upper n-type transparent electrode layer 5. The conductive pillar body 61 can be Cu, W, Al, ITO, IZO, ZnO, Ti / Al / TiN composite metal, or other conductive metal systems, preferably the same material as the n-type transparent electrode layer 5. The bottom of the conductive pillar contact layer 62 can make ohmic contact with the n-type semiconductor layer 41 to reduce contact resistance. The conductive pillar contact layer 62 is preferably TiN / TaN, thereby forming the n-side current injection channel of the MicroLED.

[0043] A conductive pillar array is disposed above the MicroLED pixel and covers at least part of the n-type transparent electrode layer 5. Multiple conductive pillars 6 form a two-dimensional array structure along the pixel plane. The conductive pillar array can be a rectangular array, a ring array, or a radial array.

[0044] In this invention, the conductive pillars 6 in the conductive pillar array have different geometric diameters. Specifically, as shown... Figure 2 As shown, the diameter of the conductive post 6 located in the center region of the pixel is D1, and the diameter of the conductive post 6 located in the edge region of the pixel is D2. Where D1 = (1 / 8)·D mesa D2=(1 / 32)·D mesa For example: D1 = 1~3μm, D2 = 0.5~1μm. Different current injection impedances are formed by using conductive pillars 6 with different diameters. Figure 4 As shown, as the diameter of the conductive post 6 increases, its corresponding equivalent injection impedance decreases, and the injection current weight increases accordingly. By presetting the diameter distribution of the conductive posts 6, the structured control of the current distribution within a pixel can be achieved.

[0045] The current path of a MicroLED pixel is as follows: CMOS backplane 1 driving circuit → anode electrode 3 → p-type semiconductor layer 43 → light-emitting layer 42 → n-type semiconductor layer 41 → conductive pillar contact layer 62 → conductive pillar body 61 → n-type transparent electrode layer 5 → external electrode or common electrode → cathode electrode 2. After flowing through the n-type transparent electrode layer 5, the current can also enter the cathode electrode 2 on the CMOS backplane 1 through the metal pillar connected to the cathode electrode 2 on the uLED side, or directly into the common cathode ring. Since different conductive pillars 6 have different geometric dimensions, the current injection impedance corresponding to each conductive pillar 6 is different. The MicroLED pixel is divided into multiple injection functional areas, and the diameter of the conductive pillars 6 in different functional areas is set to different ranges, so that the current injection weight of each area meets a preset ratio, thereby achieving spatial balance of brightness within the pixel. Figure 5 As shown, after adopting the structure of the present invention, the current within the pixel changes from a centrally concentrated distribution to a spatially uniform distribution.

[0046] Example 6 This invention provides a method for fabricating a micro-light-emitting diode pixel current injection impedance control structure. Taking an array of 8μm×8μm pixels and a pixel pitch of 4μm as an example, the specific implementation steps are as follows: (1) The total thickness of the GaN epitaxial layer is 4.9 μm. From bottom to top, it consists of a U-type GaN layer, an N-type GaN layer, a quantum well, a P-type GaN layer, and a P-ITO layer. The Si-based GaN epitaxial layer is reversed and bonded to the CMOS backplane using metal bonding. The GaN epitaxial layer is the bonding surface.

[0047] (2) After bonding, the Si substrate of GaN epitaxy is thinned to 100μm by grinding with a grinding machine. Then, the remaining Si on the GaN epitaxial surface is etched clean with Si etching solution (nitric acid / HF / glacial acetic acid). Then, the U-shaped GaN layer on the surface is etched away and the N-type GaN layer is exposed by ICP etching machine. At this time, the total epitaxial thickness is 1.2μm.

[0048] (3) A 500 nm thick SiO2 film was deposited by PECVD as a hard mask for etching GaN.

[0049] (4) A positive photoresist is spin-coated on the GaN epitaxial layer. The photomask pattern is a pixel array pattern with a pixel size of 8μm×8μm and a pixel pitch of 4μm. The wafer is exposed using an ultraviolet contact exposure machine, the Mark points on the CMOS are aligned, and after development, a photoresist microarray consistent with the photomask pattern is obtained.

[0050] (5) Etch SiO2 with photoresist as a mask, then etch GaN with SiO2 as a hard mask. The etching stop layer is P-ITO. After removing the photoresist and removing and cleaning the hard mask SiO2, the MESA pixel array is obtained.

[0051] (6) The P-ITO and bonding metal between each MESA pixel array are etched apart by photolithography and etching technology, that is, each MESA pixel is isolated, and a 500nm thick SiO2 film is deposited by PECVD as a passivation layer.

[0052] (7) Spin-coat photoresist onto the wafer surface with the above structure. The photomask pattern is a pixel array pattern with conductive pillars of different diameters inside. The pixel size is the same as the MESA above, which is 8μm×8μm. The pixel pitch is 4μm. The conductive pillars inside the pixels are circular, such as... Figure 2 As shown, the diameter of the conductive pillars near the center of the pixel is 1.5 μm, and the diameter of the conductive pillars increases towards the edge. The diameter of the second conductive pillar is 1 μm, and the diameter of the outermost third layer of conductive pillars is 0.6 μm. The spacing between each layer of conductive pillars is 0.4 μm. The wafer is exposed using an ultraviolet contact exposure machine, and after development, a pixel array with conductive pillars of different diameters is obtained, which is consistent with the photomask pattern.

[0053] (8) Use ICP to etch SiO2 to etch the conductive pillar pattern on the pixel.

[0054] (9) A 500nm thick ITO transparent conductive film layer is deposited using Ebeam to fill conductive pillars of different diameters, so that the equivalent current injection impedance can be controlled when the current passes through the conductive pillars of different diameters, thus solving the problem of the current injection area inside the pixel tending to be concentrated.

Claims

1. A micro-light-emitting diode pixel current injection impedance control structure, characterized in that, The CMOS backplate (1) is provided with a cathode electrode (2) and an anode electrode (3) located in the center region of the pixel. A MicroLED epitaxial structure (4) is provided on the anode electrode (3). An n-type transparent electrode layer (5) is electrically connected above the MicroLED epitaxial structure (4) through an array of conductive materials.

2. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 1, characterized in that, The conductor is a conductive pillar (6) arranged in a rectangular array along a transverse plane, including a conductive pillar body (61) whose top is electrically connected to an n-type transparent electrode layer (5), and a conductive pillar contact layer (62) that contacts the MicroLED epitaxial structure (4) is provided at the bottom of the conductive pillar body (61).

3. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 2, characterized in that, The equivalent injection impedance of the conductive pillar (6) Set as: In the formula, The resistivity of the main body (61) of the conductive pillar, The length of the conductive post body (61) is... The cross-sectional area of ​​the conductive column body (61).

4. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 2, characterized in that, The diameter of the conductive pillar (6) gradually decreases from the center region of the pixel to the edge region.

5. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 4, characterized in that, The diameter of the conductive pillars (6) in the non-pixel center region of the conductive pillar (6) array Set as: In the formula, The diameter of the conductive pillar (6) in the center region of the pixel is [missing information]. This is the diameter adjustment coefficient. The distance between the conductive pillars (6) in the non-pixel center region and the conductive pillars (6) in the pixel center region of the conductive pillar (6) array.

6. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 2, characterized in that, The n-type transparent electrode layer (5) is made of one of ITO, IZO or ZnO, the conductive pillar body (61) is made of one of Cu, W, Al, ITO, IZO or ZnO or Ti / Al / TiN composite metal, and the conductive pillar contact layer (62) is made of TiN / TaN.

7. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 1, characterized in that, The conductor is a conductive ring arranged concentrically along a transverse plane.

8. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 7, characterized in that, The wall thickness of the conductive ring gradually decreases from the inside to the outside.

9. The micro-light-emitting diode pixel current injection impedance control structure as described in claim 1, characterized in that, The MicroLED epitaxial structure (4) includes a p-type semiconductor layer (43) that forms a p-type contact with the anode electrode (3), an InGaN or GaN multi-quantum-well structure light-emitting layer (42) is disposed on the p-type semiconductor layer (43), and an n-type semiconductor layer (41) that contacts the bottom of the conductor is disposed on the light-emitting layer (42).

10. The method for fabricating the micro-light-emitting diode pixel current injection impedance control structure as described in claim 1, characterized in that, Includes the following steps: Step 1: Provide a Si-based GaN epitaxial structure and bond it to a CMOS backplane; Step 2: Thin the GaN epitaxial structure to the predetermined thickness; Step 3: Deposit a hard mask layer; Step 4: Forming a photoresist microarray pattern; Step 5: Etching to form a MESA pixel array; Step 6: Isolate the MESA pixel array and deposit a passivation layer; Step 7: Form a pixel array pattern with conductive pillars of different diameters; Step 8: Etch to form conductive pillar patterns; Step 9: Deposit a transparent conductive film layer to fill the conductive pillars.

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