Low-cross-talk micro-led epitaxial wafer, preparation method and micro-led display system

Abstract

The application relates to the technical field of semiconductor optoelectronic devices, and discloses a low-crosstalk Micro-LED epitaxial wafer, a preparation method and a Micro-LED display system. The low-crosstalk Micro-LED epitaxial wafer comprises a driving backboard, a light-emitting structure and a photonic lattice isolation structure layer which are sequentially stacked, the light-emitting structure comprises a P-type semiconductor layer, a multi-quantum well light-emitting layer and an N-type semiconductor layer which are sequentially stacked on the driving backboard; a groove array arranged periodically is formed on the photonic lattice isolation structure layer, so that the Micro-LED epitaxial wafer is divided into a plurality of independent pixel units, the pixel units comprise a transmission unit and a conversion unit, and the light-emitting colors of the transmission unit and the conversion unit are different; quantum dot materials are filled in the grooves corresponding to the conversion units and are used for realizing light-emitting color conversion. According to the application, multicolor pixels can be directly realized on the driving backboard, the crosstalk rate is reduced, and the color purity, yield and light-emitting efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and in particular to a low-crosstalk Micro-LED epitaxial wafer, its preparation method, and a Micro-LED display system. Background Technology

[0002] Micro-LED (micro-light-emitting diode) technology is widely recognized as the core of next-generation display technology due to its superior characteristics such as high brightness, high contrast, low power consumption, high response speed, and long lifespan, especially in near-eye display fields such as augmented reality (AR) and virtual reality (VR), where it has irreplaceable application potential. However, its industrialization process has always faced the severe challenge of fundamental technical limitations in full-color solutions. The current mainstream technology for achieving full-color displays is "mass transfer of three-color chips." This solution requires the separate fabrication of LED epitaxial wafers covering the red, green, and blue primary colors, followed by the use of high-precision, high-cost transfer equipment to pick up millions of micron-sized chips from the growth substrate and precisely bond them to the driver backplane. According to industry reports such as Yole, this technical path faces many insurmountable obstacles: First, its requirements for transfer yield are extremely stringent. Even with a yield rate as high as 99.9%, for a 1 million-pixel micro-display, there will still be 1,000 defective pixels. The subsequent cost of detecting and repairing these defective pixels is extremely high, exceeding 60% of the total manufacturing cost. Secondly, to achieve correct pixel arrangement and light emission, the transfer accuracy must be strictly controlled within ±0.5μm, which makes the design and manufacturing of the transfer equipment extremely difficult, with an investment cost exceeding US$20 million. Finally, the thermal mismatch problem at the bonding interface of heterogeneous materials leads to the accumulation of thermal stress, causing a decrease in device reliability and accelerated light decay.

[0003] To circumvent the enormous costs and yield issues associated with mass transfer, the industry has proposed an alternative: "quantum dot color conversion." This approach is based on a blue Micro-LED array. By fabricating a color conversion layer containing quantum dots such as CdSe (for red light) and ZnSe (for green light) on top of it, a portion of the blue light is converted into red and green light, thus achieving full-color display. However, due to the extremely small pixel pitch of Micro-LEDs, and the strong lateral propagation capability (light emission angle > 160°) of the blue light source in the waveguide structure formed by GaN material, it is highly susceptible to leakage into adjacent red or green quantum dot pixel units. This can excite non-target quantum dots to generate unwanted stray light, leading to decreased color purity, contrast loss, and deterioration of display quality, severely limiting the application of this approach in the field of high-quality displays.

[0004] Therefore, developing a monolithic integrated full-color Micro-LED technology that can simultaneously avoid the high cost and low yield dilemma of mass transfer and fundamentally solve the optical crosstalk problem of quantum dot solutions has become the core key to promoting the large-scale commercial application of this technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a low crosstalk Micro-LED epitaxial wafer, a preparation method, and a Micro-LED display system, which can directly realize multi-color pixels on the driving backplane, reduce crosstalk rate, and improve color purity, yield and luminous efficiency.

[0006] To address the aforementioned technical problems, the first aspect of this invention provides a low-crosstalk Micro-LED epitaxial wafer, comprising a driving backplate, a light-emitting structure, and a photonic lattice isolation structure layer stacked sequentially, wherein...

[0007] The light-emitting structure includes a P-type semiconductor layer, a multi-quantum-well light-emitting layer, and an N-type semiconductor layer sequentially stacked on the driving backplate;

[0008] The photonic lattice isolation structure layer has a periodically arranged array of grooves to divide the Micro-LED epitaxial wafer into multiple independent pixel units. The pixel unit includes a transmission unit and a conversion unit, and the transmission unit and the conversion unit emit different colors of light.

[0009] The groove array includes several grooves, and the grooves corresponding to the conversion units are filled with quantum dot material to achieve luminous color conversion.

[0010] As an improvement to the above scheme, the groove array constitutes a photonic crystal structure, and the period of the groove array is Λ, which satisfies the following formula: Λ=λ1 / (2*n).

[0011] In the formula, λ1 is the center wavelength of the target beam emitted by the multi-quantum-well light-emitting layer, in nm;

[0012] n is the refractive index of the N-type semiconductor layer material.

[0013] As an improvement to the above scheme, in the groove array, the width of the groove is W, which satisfies the following formula: W=Λ*K*2,

[0014] In the formula, K is the duty cycle of the photonic crystal, and the value of K ranges from 0.2 to 0.4.

[0015] As an improvement to the above scheme, in the groove array, the depth of the groove is D, which satisfies the following formula: D=λ2 / (2*Δn).

[0016] In the formula, λ2 is the center wavelength of the target beam emitted by the conversion unit, in nm;

[0017] Δn is the refractive index difference between the N-type semiconductor layer material and the filling medium provided in the corresponding groove.

[0018] As an improvement to the above scheme, in the groove array, the bottom of the groove and the end of the multi-quantum well light-emitting layer near the N-type semiconductor layer have a preset distance, the preset distance being 10nm-50nm.

[0019] As an improvement to the above scheme, the transmission unit is a blue light transmission unit, and the conversion unit includes a red light conversion unit and a green light conversion unit.

[0020] As an improvement to the above solution, the groove corresponding to the blue light transmission unit is a cavity without filling material;

[0021] Alternatively, the groove corresponding to the blue light transmission unit is filled with a transparent medium for transmitting blue light, and the transparent medium is silicon dioxide or a transparent polymer.

[0022] The groove corresponding to the red light conversion unit is filled with CdSe / ZnS core-shell quantum dot material to convert blue light into red light. The average particle size of the CdSe / ZnS core-shell quantum dot material is 3nm-5nm, and the PLQY is ≥90%.

[0023] The groove corresponding to the green light conversion unit is filled with ZnSe / ZnS core-shell quantum dot material to convert blue light into green light. The full width at half maximum (FWHM) of the ZnSe / ZnS core-shell quantum dot material is less than or equal to 25 nm.

[0024] A second aspect of the present invention provides a method for fabricating the low-crosstalk Micro-LED epitaxial wafer, comprising the following steps:

[0025] Provide a substrate;

[0026] A photonic lattice isolation structure layer, an N-type semiconductor layer, a multi-quantum well light-emitting layer, and a P-type semiconductor layer are sequentially grown on the substrate to form an LED epitaxial structure.

[0027] A driving backplane is provided, and the driving backplane is bonded to the LED epitaxial structure by a wafer bonding process;

[0028] The photonic lattice isolation structure layer is etched until the N-type semiconductor layer is exposed, forming a periodically arranged array of grooves;

[0029] Quantum dot material is filled into the grooves of the corresponding conversion units, and selective filling is performed into the grooves of the corresponding transmission units.

[0030] As an improvement to the above solution, the wafer bonding process includes:

[0031] Ar plasma activation treatment is performed on the surface of the drive backplane and / or the surface of the LED epitaxial structure;

[0032] The bonding material is BCB adhesive or Au-Sn eutectic alloy, the bonding temperature is 200℃-260℃, and the pressure is 750 kgf / cm². 2 -1400 kgf / cm 2 The bonding time is 1800s-2200s.

[0033] A third aspect of the present invention also provides a Micro-LED display system, including a display panel and a driving circuit, wherein the display panel is fabricated using the aforementioned low-crosstalk Micro-LED epitaxial wafer.

[0034] Implementing this invention has the following beneficial effects:

[0035] (1) This invention introduces a grooved array photonic crystal structure, which generates a photonic bandgap effect through periodic design, increases the lateral propagation loss of blue light, reduces the crosstalk rate to less than or equal to 5%, significantly improves color purity and display contrast, and solves the inherent defects of quantum dot color conversion. At the same time, the photonic crystal structure also has the function of light emission enhancement. Combined with the in-situ filling of quantum dot materials, it improves the luminous efficiency and stability of Micro-LED epitaxial wafers, meeting the stringent requirements of AR / VR near-eye displays for high brightness and high definition.

[0036] (2) In this invention, the light-emitting structure and the driving backplane are monolithically integrated through wafer bonding, which reduces thermal stress, extends device life, and reduces the number of epitaxial wafers and transfer steps, thus reducing overall cost and providing an economical and feasible solution for consumer-grade AR glasses. At the same time, it can enhance red light efficiency: for red light, the use of quantum dot materials to replace inefficient nitride red light improves the efficiency of the red light unit.

[0037] (3) The semiconductor process such as partition etching and quantum dot filling used in this invention is compatible with existing CMOS production lines, supports wafer-level mass production, improves yield to 99.5%, and supports efficiency improvement of more than 30%.

[0038] (4) The present invention realizes multi-color pixels directly on the driving backplane through monolithic epitaxial integration technology, without the need for transfer process, saving equipment investment and eliminating repair costs. Attached Figure Description

[0039] Figure 1 : A schematic diagram of the structure of the low crosstalk Micro-LED epitaxial wafer in this invention;

[0040] Figure 2: Top view of the low crosstalk Micro-LED epitaxial wafer in this invention;

[0041] Figure 3 : A partial cross-sectional view of the low crosstalk Micro-LED epitaxial wafer in this invention;

[0042] Figure 4 : A schematic diagram of the structure obtained after step (2) in the preparation method of the present invention;

[0043] Figure 5 : A schematic diagram of the structure obtained after step (31) in the preparation method of the present invention;

[0044] Figure 6 : A schematic diagram of the structure obtained after step (32) in the preparation method of the present invention.

[0045] Figure label:

[0046] 1-Substrate; 2-Driving backplate; 3-Light-emitting structure; 31-P-type semiconductor layer; 32-Multi-quantum-well light-emitting layer; 33-N-type semiconductor layer; 4-Photonic lattice isolation structure layer; 41-Groove array; 42-Blue light transmission unit; 43-Red light conversion unit; 44-Green light conversion unit. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described in further detail below.

[0048] In the description of this application, it is necessary to understand that the orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", and "outer" are based on the orientation or positional relationship shown in the accompanying drawings. They are intended only to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the components referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0049] Traditional mass transfer solutions for three-color chips require the separate fabrication of RGB epitaxial wafers and transfer using high-precision equipment (accuracy < ±0.5μm). Even with a 99.9% yield rate, a megapixel screen still has 1000 failure points, with repair costs accounting for over 60% of the total cost. Furthermore, traditional mass transfer leads to thermal mismatch at the interface of heterogeneous materials, causing accelerated light decay and a lifespan reduction rate >20%. Mass transfer processes only a few thousand chips at a time (e.g., a 4K screen requires the transfer of 24 million chips), resulting in excessive time consumption. In addition, traditional quantum dot solutions suffer from blue light lateral leakage (emission angle >160°), leading to color aliasing between adjacent pixels (false excitation rate >30%), resulting in decreased contrast and color purity.

[0050] To address the above problems, the first aspect of this invention provides a low-crosstalk Micro-LED epitaxial wafer, please refer to [link to relevant documentation]. Figure 1 It includes a driving backplate 2, a light-emitting structure 3, and a photonic lattice isolation structure layer 4, which are stacked sequentially.

[0051] The light-emitting structure 3 includes a P-type semiconductor layer 31, a multi-quantum-well light-emitting layer 32, and an N-type semiconductor layer 33 sequentially stacked on the driving backplate 2;

[0052] The photonic lattice isolation structure layer 4 has a periodically arranged array of grooves 41 to divide the Micro-LED epitaxial wafer into multiple independent pixel units. The pixel unit includes a transmission unit and a conversion unit, and the transmission unit and the conversion unit emit different colors of light.

[0053] The groove array 41 includes a plurality of grooves, and the grooves corresponding to the conversion units are filled with quantum dot material to achieve luminous color conversion.

[0054] In this application, the periodically arranged groove array 41 can constitute a one-dimensional or two-dimensional photonic crystal structure, generating a photonic bandgap effect on the light beam emitted by the multi-quantum-well light-emitting layer 32. This effect disrupts the blue light waveguide mode through a significant abrupt change in refractive index, increasing the loss of blue light lateral propagation and thus suppressing lateral propagation of blue light between pixel units. This reduces optical crosstalk and significantly improves color purity and display contrast. Simultaneously, the photonic crystal structure also possesses light emission enhancement capabilities. Combined with the in-situ filling of quantum dot materials, ultra-high brightness and resolution can be achieved, meeting the stringent requirements of high brightness and high definition for AR / VR near-eye displays.

[0055] Furthermore, this application utilizes monolithic epitaxial integration technology to directly achieve multiple pixels on the driving backplane 2 without the need for transfer processes, thereby saving equipment investment and eliminating repair costs. It also boasts high production yield, reduces thermal stress by 40%, and extends device lifespan to over 100,000 hours. On the other hand, the monolithic integration solution can reduce the number of epitaxial wafers (from 3 to 1) and transfer steps, resulting in a 50% reduction in overall cost. This provides an economical and feasible solution for consumer-grade AR glasses (module thickness ≤ 1.5mm, power consumption ≤ 100mW).

[0056] Preferably, the groove array 41 constitutes a photonic crystal structure, and the period of the groove array 41 is Λ, satisfying the following formula: Λ=λ1 / (2*n), where λ1 is the center wavelength of the target beam emitted by the multi-quantum-well light-emitting layer 32, in nm; and n is the refractive index of the N-type semiconductor layer 33. It should be noted that the period Λ of the groove array 41 refers to the distance between the centers of adjacent pixel units of the same color along the vertical direction.

[0057] Furthermore, in the groove array 41, the width of the groove is W, which satisfies the following formula: W=Λ*K*2, where K is the duty cycle of the photonic crystal, and the value of K ranges from 0.2 to 0.4.

[0058] Furthermore, in the groove array 41, the depth of the groove is D, which satisfies the following formula: D=λ2 / (2*Δn), where λ2 is the center wavelength of the target beam emitted by the conversion unit, in nm; Δn is the refractive index difference between the N-type semiconductor layer 33 material and the filling medium provided in the corresponding groove.

[0059] In some embodiments, the transmission unit is a blue light transmission unit 42, and the conversion unit includes a red light conversion unit 43 and a green light conversion unit 44. The groove corresponding to the blue light transmission unit 42 is an unfilled cavity, or the groove corresponding to the blue light transmission unit 42 is filled with a transparent medium for transmitting blue light. The transparent medium is silicon dioxide or a transparent polymer. The groove corresponding to the red light conversion unit 43 is filled with CdSe / ZnS core-shell quantum dot material for converting blue light into red light. The groove corresponding to the green light conversion unit 44 is filled with ZnSe / ZnS core-shell quantum dot material for converting blue light into green light. The use of quantum dot materials can overcome the bottleneck of red light efficiency of nitrides, such as the low external quantum efficiency (only 22%) of the silicon-based gallium nitride red light chip from Crystal Optoelectronics. Combined with atomic-level sidewall passivation, red light brightness > 1 million nits can be achieved, and the luminous efficiency can be increased to over 60%, meeting the stringent high brightness requirements of AR / VR.

[0060] Optionally, the N-type semiconductor layer 33 is an N-type GaN layer, and the P-type semiconductor layer 31 is a P-type GaN layer.

[0061] The following explanation will use this as an example.

[0062] Please see Figure 2 The period of the groove array 41 is Λ, satisfying the following formula: Λ=λ1 / (2*n), where λ1 is the center wavelength of the blue light emitted by the multi-quantum-well light-emitting layer 32, that is, the center wavelength of the blue light emitted by the transmission unit, specifically 445nm-480nm; n is the refractive index of the GaN material, specifically 2.4. It should be noted that the period Λ of the groove array 41 refers to the distance between the centers of adjacent pixel units of the same color along the vertical direction, which is determined by the center wavelength of the blue light emitted by the multi-quantum-well light-emitting layer 32 and the refractive index of the GaN material. Based on this design, a photonic bandgap can be generated for a specific blue light wavelength, blocking the lateral propagation of light and reducing lateral crosstalk.

[0063] In the groove array 41, changing the width of the grooves significantly affects the band structure of the photonic crystal. Specifically, the width of the groove is W, satisfying the following formula: W=Λ*K*2, where K is the duty cycle of the photonic crystal, and the value of K ranges from 0.2 to 0.4. Based on this design, it is helpful to obtain a sufficiently wide and deep photonic bandgap at the target wavelength, optimize the localization of the optical field, and at the same time ensure the mechanical stability of the structure.

[0064] Please see Figure 3 The depth of the groove is D, satisfying the following formula: D=λ2 / (2*Δn), where λ2 is the center wavelength of the target light beam emitted by the conversion unit, in nm. That is, when the conversion unit is a red light conversion unit 43, λ2 is the center wavelength of the red light emitted by the conversion unit, specifically 600nm-700nm; Δn is the refractive index difference between the GaN material and the CdSe / ZnS core-shell quantum dot material filled in the corresponding groove; when the conversion unit is a green light conversion unit 44, λ2 is the center wavelength of the green light emitted by the conversion unit, specifically 510nm-550nm; Δn is the refractive index difference between the GaN material and the ZnSe / ZnS core-shell quantum dot material filled in the corresponding groove. Based on this design, combined with the refractive index difference (Δn), the light reflected from the bottom of the groove and the light reflected from the top can undergo destructive interference, thereby allowing the target color light to pass smoothly through the structure and enhance the vertical light output efficiency.

[0065] It is understood that when the groove corresponding to the blue light transmission unit 42 is filled with a transparent medium, the depth D of the groove corresponding to the blue light transmission unit 42 also satisfies D=λ2 / (2*Δn). At this time, λ2 and λ1 are equal in value, which is the center wavelength of the blue light emitted by the transmission unit, and Δn is the refractive index difference between the GaN material and the transparent medium material filled in the corresponding groove.

[0066] In this invention, the synergistic effect of period Λ, width W and depth D can effectively suppress the lateral propagation of blue light, prevent blue light crosstalk, reduce the crosstalk rate from more than 30% in traditional quantum dot schemes to less than or equal to 5%, and allow green and red light to pass through efficiently, thereby improving the color purity and light efficiency of the device, with a color gamut greater than or equal to 120% NTSC.

[0067] In some specific and preferred embodiments, the bottom of the groove is at a predetermined distance from the end of the multi-quantum-well light-emitting layer 32 near the N-type semiconductor layer 33. This avoids etching damage to the quantum well light-emitting layer, which could lead to a decrease in luminous efficiency. Furthermore, it allows for efficient carrier injection and effective control of the light field, maintaining the mechanical and electrical reliability of the device and preventing short circuits and structural failures. Optionally, the predetermined distance is 10nm-50nm; exemplaryly, the predetermined distance is 10nm, 20nm, 30nm, 40nm, or 50nm, but is not limited to these.

[0068] Optionally, the average particle size of the CdSe / ZnS core-shell quantum dot material is 3nm-5nm, and the photoluminescence quantum yield (PLQY) is ≥90%; the full width at half maximum (FWHM) of the ZnSe / ZnS core-shell quantum dot material is less than or equal to 25nm, which can improve the luminescence efficiency. Moreover, the quantum dot material is precisely positioned by inkjet printing and directly embedded in deep grooves by photoresist-assisted cutout masking technology, avoiding the residual blue light problem in traditional solutions.

[0069] In this application, the monolithic integration scheme reduces the number of epitaxial wafers from 3 to 1 and also eliminates the epitaxial wafer transfer step. Combined with substrate epitaxy technology, it can reduce the overall cost by 50% and promote the commercialization of consumer-grade AR glasses.

[0070] Accordingly, a second aspect of the present invention provides a method for fabricating the low-crosstalk Micro-LED epitaxial wafer described above. Please refer to [link to relevant documentation]. Figure 1 as well as Figures 4-6 It includes the following steps:

[0071] (1) Provide a substrate 1;

[0072] (2) A photonic lattice isolation structure layer 4, an N-type semiconductor layer 33, a multi-quantum well light-emitting layer 32 and a P-type semiconductor layer 31 are sequentially grown on the substrate 1 to form an LED epitaxial structure;

[0073] (3) A driving backplate 2 is provided, and the driving backplate 2 is bonded to the LED epitaxial structure by a wafer bonding process;

[0074] (4) The photonic lattice isolation structure layer 4 is etched to expose the N-type semiconductor layer 33 to form a periodically arranged groove array 41;

[0075] (5) Fill the groove of the corresponding conversion unit with quantum dot material, and selectively fill the groove of the corresponding transmission unit.

[0076] Each step will be explained in detail below.

[0077] Regarding step (1), a substrate 1 is provided;

[0078] Optionally, the substrate 1 may include, but is not limited to, a silicon substrate or a sapphire substrate.

[0079] Regarding step (2), a photonic lattice isolation structure layer 4, an N-type semiconductor layer 33, a multi-quantum well light-emitting layer 32 and a P-type semiconductor layer 31 are sequentially grown on the substrate 1 to form an LED epitaxial structure;

[0080] Specifically, please refer to the description of the formed LED epitaxial structure. Figure 4 The P-type semiconductor layer 31, the multi-quantum-well light-emitting layer 32, the N-type semiconductor layer 33, and the photonic lattice isolation structure layer 4 can be prepared by deposition or other existing known methods, such as metal-organic chemical vapor deposition (MOCVD), which will not be described in detail here.

[0081] Optionally, the N-type semiconductor layer 33 includes, but is not limited to, an N-type GaN layer; the P-type semiconductor layer 31 includes, but is not limited to, a P-type GaN layer; and the multi-quantum-well light-emitting layer 32 includes, but is not limited to, an InGaN / GaN layer. The photonic lattice isolation structure layer 4 is selected from one or more combinations of silicon dioxide, silicon nitride, aluminum oxide, titanium dioxide, hafnium oxide, and zinc oxide. Specifically, the photonic lattice isolation structure layer 4 can be a one-dimensional photonic crystal composed of periodically alternating stacks of the above materials, or a two-dimensional or three-dimensional photonic crystal composed of core-shell structured nanoparticles self-assembled from the above materials.

[0082] It is understood that a buffer layer and an undoped semiconductor layer may also be disposed between the photonic lattice isolation structure layer 4 and the N-type semiconductor layer 33. The materials of the buffer layer and the undoped semiconductor layer are conventionally selectable materials in the art. For example, the buffer layer is an AlN layer and the undoped semiconductor layer is an undoped GaN layer. This application does not make specific limitations on this.

[0083] Regarding step (3), a driving backplate 2 is provided, and the driving backplate 2 is bonded to the LED epitaxial structure by a wafer bonding process;

[0084] In this step, the driving backplate 2 is directly bonded to the underside of the light-emitting structure 3. Electrical interconnection can be achieved by forming a Ti / Pt / Au metal layer interface between the driving backplate 2 and the P-type semiconductor layer 31, shortening the carrier path, increasing the response speed to the nanosecond level, and making the power consumption less than or equal to 100mW@1000nit brightness, which is suitable for the low power consumption requirements of AR glasses. Here, 100mW@1000nit brightness means that when achieving 1000nit brightness, the power consumption of the driving backplate 2 does not exceed 100 milliwatts.

[0085] It is understandable that after bonding the driving backplate 2 to the P-type semiconductor layer 31 through the wafer bonding process, the substrate 1 needs to be removed. The driving backplate 2 can not only provide electrical drive, but also provide effective mechanical fabrication for the micron-scale epitaxial structure when removing the substrate 1, preventing the epitaxial structure from cracking or breaking.

[0086] Specifically, a driving backplate 2 is provided, which is bonded to the LED epitaxial structure via a wafer bonding process, including:

[0087] Step (31) The P-type semiconductor layer 31 is bonded to the driving backplane 2 using a wafer bonding process;

[0088] Please see Figure 5 In this step, BCB (benzocyclobutene) adhesive or Au-Sn eutectic alloy can be used as the bonding material, and the bonding temperature can be controlled at 200℃-260℃, with a pressure of 750 kgf / cm². 2 -1400 kgf / cm 2 The driving backplate 2 is bonded to the P-type semiconductor layer 31 for a bonding time of 1800s-2200s, thereby bonding the driving backplate 2 to the LED epitaxial structure. More preferably, during wafer bonding, the bonding temperature is increased from room temperature to 200℃-260℃ at a heating rate of 0.08℃ / s-0.15℃ / s.

[0089] Furthermore, the wafer bonding process includes: performing Ar plasma activation treatment on the surface of the driving backplane 2 and / or the surface of the LED epitaxial structure, that is, performing Ar plasma activation treatment on the surface of the driving backplane and / or the surface of the P-type GaN layer, to improve the bonding strength between the driving backplane and the LED epitaxial structure, increase the production yield of low crosstalk Micro-LED epitaxial wafers, and reduce thermal stress. In some specific and preferred embodiments, simultaneously performing Ar plasma activation treatment on the surface of the driving backplane 2 and the surface of the LED epitaxial structure, followed by bonding, can achieve a yield of Micro-LED epitaxial wafer greater than or equal to 99.5% and reduce thermal stress by approximately 40%.

[0090] Optionally, the driving backplane 2 may include, but is not limited to, a CMOS driving backplane.

[0091] Step (32) Remove substrate 1 using laser lift-off or wet etching. Please refer to [link to relevant documentation]. Figure 6 ;

[0092] In some embodiments, removing substrate 1 using laser ablation includes: mechanically grinding substrate 1 with a diamond wheel to thin it from 400μm-800μm to approximately 100μm, significantly reducing the energy requirement and time for subsequent laser ablation; subsequently, irradiating the back side of substrate 1 with a KrF excimer laser (wavelength 248nm). The laser penetrates substrate 1 and irradiates the GaN layer located at the interface between substrate 1 and light-emitting structure 3. The laser photon energy is between the band gap of substrate 1 and the band gap of GaN, so the laser can penetrate the substrate without damage, but it is strongly absorbed by GaN. The absorbed laser energy is absorbed in an extremely short time. Within a short time (on the nanosecond scale), high temperature and pressure are generated at the interface, causing the GaN at the interface to thermally decompose into metallic gallium and nitrogen gas. The resulting gas pressure separates the entire light-emitting structure 3 from the substrate 1. After peeling, a layer of metallic gallium droplets remains on the exposed surface. These are then soaked or rinsed with dilute hydrochloric acid or a hot acidic solution to chemically remove the residual gallium. Subsequently, a light chemical mechanical polishing or ICP dry etching is performed to remove the poor-quality GaN layer at the interface caused by laser thermal damage, resulting in an atomically flat and clean N-type GaN surface and / or an undoped GaN surface, preparing for the subsequent fabrication of N-type electrodes or optical structures.

[0093] In some embodiments, the wet etching method for removing substrate 1 includes: mechanically grinding the silicon substrate to thin it to 100 μm; subsequently, using photolithography and dry etching, etching an array of etching channel windows on the silicon substrate until the layer structure beneath substrate 1 is exposed, specifically, it may be an etching barrier layer AlN, where the silicon-based GaN epitaxial AlN layer is generally the first nucleation layer; next, immersing the wafer in an isotropic silicon etchant, simultaneously etching the silicon substrate from the sides and bottom through the etching windows until the entire silicon substrate is completely dissolved, while the AlN etching barrier layer, having extremely high corrosion resistance, automatically stops etching, perfectly protecting the overlying GaN functional layer. The silicon etchant may specifically be a mixed solution of nitric acid, hydrofluoric acid, and acetic acid, or a potassium hydroxide solution; finally, the layer structure beneath substrate 1 is exposed, which can be removed by immersing it in a wet etchant with high selectivity for GaN (such as hot phosphoric acid) until a high-quality N-type GaN surface and / or undoped GaN surface is exposed. Finally, a thorough cleaning is performed to remove all chemical residues.

[0094] Regarding step (4), etching the photonic lattice isolation structure layer 4 until the N-type semiconductor layer 33 is exposed to form a periodically arranged array of grooves 41, please refer to [link to relevant documentation]. Figure 1 ;

[0095] In this step, the period of the groove array 41, as well as the width and depth of the grooves in the groove array 41, are determined according to the formula. The photonic lattice isolation structure layer 4 is then subjected to photolithography and etching to form a periodically arranged groove array 41 on the photonic lattice isolation structure layer 4, so as to divide the Micro-LED epitaxial wafer into multiple independent pixel units. The etching depth of the grooves is close to the multi-quantum well light-emitting layer 32 but does not penetrate the multi-quantum well light-emitting layer 32.

[0096] Specifically, the etched groove array 41 can be divided into blue light transmission unit 42, red light conversion unit 43 and green light conversion unit 44.

[0097] Optionally, the etching process of the etching treatment can be, for example, dry etching, wet etching, etc. More preferably, the etching process is dry etching, and the dry etching can specifically be inductively coupled plasma etching (ICP) etching. The selectivity of ICP etching is greater than or equal to 10:1, which can better control the size of the groove.

[0098] In some embodiments, the photonic lattice isolation structure layer 4 is etched to expose the multi-quantum well light-emitting layer 32, forming a periodically arranged groove array 41. The sidewalls of the grooves can also be passivated to form atomic-level sidewall passivation. The passivation process includes: in the chamber of a plasma-enhanced atomic layer deposition system (PEALD), a mixture of N2 and H2 is introduced, and a DC current of 0.4 kW to 0.6 kW is applied to clean and activate the sidewalls, wherein the flow rate ratio of N2 to H2 is (3.5-4.5):1, and the flow rate of N2 is 190 sccm to 210 sccm.

[0099] Regarding step (5), quantum dot material is filled into the groove of the corresponding conversion unit, and selective filling is performed in the groove of the corresponding transmission unit;

[0100] In this step, precise positioning can be achieved through inkjet printing, combined with photoresist-assisted cutout masking technology, allowing quantum dot materials to be directly embedded inside the grooves, avoiding the residual blue light problem in traditional solutions. The inkjet printing technology has an accuracy of ±0.3μm, enabling wafer-level mass production of groove structures, compatible with 8-12 inch semiconductor production lines, and improving mass production yield to 99.5% or higher.

[0101] Specifically, the grooves corresponding to the transmission units are left unfilled, allowing air to remain inside; or, the grooves corresponding to the transmission units are filled with a transparent medium; the grooves corresponding to the red light conversion unit 43 are filled with CdSe / ZnS core-shell quantum dot material to achieve the conversion of blue light to red light; and the grooves corresponding to the green light conversion unit 44 are filled with ZnSe / ZnS core-shell quantum dot material to achieve the conversion of blue light to green light.

[0102] Understandably, the preparation method may further include: preparing a transparent protective layer on the surface of the LED epitaxial structure and completing the preparation and encapsulation of electrodes.

[0103] Accordingly, a third aspect of the present invention provides a Micro-LED display system, including a display panel and a driving circuit, wherein the display panel is fabricated using the low crosstalk Micro-LED epitaxial wafer.

[0104] The present invention will be further described below with reference to specific embodiments:

[0105] Example 1

[0106] This embodiment provides a low crosstalk Micro-LED epitaxial wafer, comprising a driving backplate, a light-emitting structure, and a photonic lattice isolation structure layer stacked sequentially. The light-emitting structure includes a P-type GaN layer, a multi-quantum-well light-emitting layer, and an N-type GaN layer stacked sequentially on the driving backplate.

[0107] A periodically arranged array of grooves is formed on the photonic lattice isolation structure layer to divide the Micro-LED epitaxial wafer into multiple independent pixel units. The pixel units include blue light transmission units, red light conversion units, and green light conversion units. The groove array includes several grooves. The grooves corresponding to the red light conversion units are filled with CdSe / ZnS core-shell quantum dot material (refractive index 2.1), the grooves corresponding to the green light conversion units are filled with ZnSe / ZnS core-shell quantum dot material (refractive index 2.2), and the grooves corresponding to the blue light transmission units are filled with air.

[0108] The groove array constitutes a photonic crystal structure. The period of the groove array is Λ=λ1 / (2*n), where λ1=460nm and n=2.4; the width of the groove is W=Λ*K*2, where K is the duty cycle of the photonic crystal and K is 0.3; the depth of the groove is D=λ2 / Δn. In the groove corresponding to the red light conversion unit, λ2=650nm and Δn=0.3. In the groove of the green light conversion unit, λ2=530nm and Δn=0.2.

[0109] This embodiment also provides a method for fabricating a low-crosstalk Micro-LED epitaxial wafer, comprising the following steps:

[0110] (1) Provide a substrate;

[0111] (2) A photonic lattice isolation structure layer, an N-type GaN layer, a multi-quantum well light-emitting layer and a P-type GaN layer are sequentially grown on the substrate to form an LED epitaxial structure;

[0112] (3) Provide a driving backplate, and bond the driving backplate to the LED epitaxial structure by wafer bonding process;

[0113] Specifically, BCB adhesive was used as the bonding material, and the bonding temperature was controlled at 240℃ and the pressure at 1000 kgf / cm². 2 The driving backplate is bonded to the P-type GaN layer for 2000s, thereby bonding the driving backplate to the LED epitaxial structure.

[0114] (4) The photonic lattice isolation structure layer is etched to expose the multi-quantum well light-emitting layer, forming a periodically arranged array of grooves;

[0115] (5) Fill the conversion unit with quantum dot material and selectively fill the transmission unit;

[0116] (6) A transparent protective layer is prepared on the surface of the LED epitaxial structure and the electrode is prepared and encapsulated.

[0117] Example 2

[0118] This embodiment provides a low-crosstalk Micro-LED epitaxial wafer, which is basically the same as that in Embodiment 1, except that:

[0119] The groove array constitutes a photonic crystal structure. The depth of the groove is D=λ2 / (2*Δn). In the groove corresponding to the red light conversion unit, λ2=650nm; Δn=0.3. In the groove of the green light conversion unit, λ2=530nm; Δn=0.2.

[0120] It was prepared using the preparation method described in Example 1.

[0121] Example 3

[0122] This embodiment provides a low-crosstalk Micro-LED epitaxial wafer, which is basically the same as Embodiment 2, except that:

[0123] The grooves corresponding to the blue light transmission units are filled with silicon dioxide, with a refractive index of 1.46;

[0124] The depth of the groove is D=λ2 / (2*Δn). In the blue light transmission unit, λ2=460nm; Δn=0.94.

[0125] It was prepared using the preparation method described in Example 1.

[0126] Example 4

[0127] This embodiment provides a low-crosstalk Micro-LED epitaxial wafer, which is basically the same as that in Embodiment 1, except that:

[0128] K takes the value 0.2.

[0129] It was prepared using the preparation method described in Example 1.

[0130] Example 5

[0131] This embodiment provides a low-crosstalk Micro-LED epitaxial wafer, which is basically the same as that in Embodiment 1, except that:

[0132] K takes the value 0.4.

[0133] It was prepared using the preparation method described in Example 1.

[0134] Example 6

[0135] This embodiment provides a low-crosstalk Micro-LED epitaxial wafer, which is basically the same as Embodiment 2, except that:

[0136] In the preparation method, step (3) provides a driving backplate, which is bonded to the LED epitaxial structure by a wafer bonding process;

[0137] Specifically, the surfaces of the driver backplane and the LED epitaxial structure were subjected to Ar plasma activation treatment, using BCB adhesive as the bonding material, and heated to 240°C at a heating rate of 0.1°C / s, with a controlled pressure of 1000 kgf / cm². 2 The driving backplate is bonded to the P-type GaN layer for 2000s, thereby bonding the driving backplate to the LED epitaxial structure.

[0138] Performance testing:

[0139] The low crosstalk Micro-LED epitaxial wafers obtained in Examples 1-6 were fabricated into 10mil×24mil chips using the same chip process conditions. 300 LED chips were randomly selected and tested at a current of 120mA. The crosstalk rate, luminous efficiency, color purity and yield were tested. The test results are shown in Table 1 below.

[0140] Table 1 Performance test results of Micro-LED epitaxial wafers obtained in Examples 1-6

[0141]

[0142] As can be seen from the above results, in this invention, a periodically arranged array of grooves is formed on the photonic lattice isolation structure layer, dividing the Micro-LED epitaxial wafer into multiple independent pixel units. Each pixel unit includes a transmission unit and a conversion unit. The grooves corresponding to the conversion units are filled with quantum dot materials to achieve color conversion of light emission. This can effectively suppress lateral crosstalk of blue light and improve luminous efficiency, color purity, and yield.

[0143] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A low-crosstalk Micro-LED epitaxial wafer, characterized in that, It includes a driving backplate, a light-emitting structure, and a photonic lattice isolation structure layer stacked sequentially, wherein, The light-emitting structure includes a P-type semiconductor layer, a multi-quantum-well light-emitting layer, and an N-type semiconductor layer sequentially stacked on the driving backplate; The photonic lattice isolation structure layer has a periodically arranged array of grooves to divide the Micro-LED epitaxial wafer into multiple independent pixel units. The pixel unit includes a transmission unit and a conversion unit, and the transmission unit and the conversion unit emit different colors of light. The groove array includes a plurality of grooves, and the grooves corresponding to the conversion units are filled with quantum dot material to achieve luminous color conversion. The groove array constitutes a photonic crystal structure, and the period of the groove array is Λ, which satisfies the following formula: Λ=λ1 / (2*n). In the formula, λ1 is the center wavelength of the target beam emitted by the multi-quantum-well light-emitting layer, in nm; the period Λ of the groove array refers to the distance between the centers of adjacent pixel units of the same color along the vertical direction. n is the refractive index of the N-type semiconductor layer material; In the groove array, the width of the groove is W, which satisfies the following formula: W=Λ*K*2, In the formula, K is the duty cycle of the photonic crystal, and the value of K ranges from 0.2 to 0.

4. In the groove array, the depth of the groove is D, which satisfies the following formula: D=λ2 / (2*Δn). In the formula, λ2 is the center wavelength of the target beam emitted by the conversion unit, in nm; Δn is the refractive index difference between the N-type semiconductor layer material and the filling medium provided in the corresponding groove.

2. The low crosstalk Micro-LED epitaxial wafer as described in claim 1, characterized in that, In the groove array, the bottom of the groove is at a preset distance from the end of the multi-quantum well light-emitting layer near the N-type semiconductor layer, and the preset distance is 10nm-50nm.

3. The low crosstalk Micro-LED epitaxial wafer as described in claim 1, characterized in that, The transmission unit is a blue light transmission unit, and the conversion unit includes a red light conversion unit and a green light conversion unit.

4. The low crosstalk Micro-LED epitaxial wafer as described in claim 3, characterized in that, The groove corresponding to the blue light transmission unit is an empty cavity without filling material; or, the groove corresponding to the blue light transmission unit is filled with a transparent medium for transmitting blue light, and the transparent medium is silicon dioxide or a transparent polymer. The groove corresponding to the red light conversion unit is filled with CdSe / ZnS core-shell quantum dot material to convert blue light into red light. The average particle size of the CdSe / ZnS core-shell quantum dot material is 3nm-5nm, and the PLQY is ≥90%. The groove corresponding to the green light conversion unit is filled with ZnSe / ZnS core-shell quantum dot material to convert blue light into green light. The full width at half maximum (FWHM) of the ZnSe / ZnS core-shell quantum dot material is less than or equal to 25 nm.

5. A method for fabricating a low-crosstalk Micro-LED epitaxial wafer as described in any one of claims 1-4, characterized in that, Includes the following steps: Provide a substrate; A photonic lattice isolation structure layer, an N-type semiconductor layer, a multi-quantum well light-emitting layer, and a P-type semiconductor layer are sequentially grown on the substrate to form an LED epitaxial structure. A driving backplane is provided, and the driving backplane is bonded to the LED epitaxial structure by a wafer bonding process; The photonic lattice isolation structure layer is etched until the N-type semiconductor layer is exposed, forming a periodically arranged array of grooves; Quantum dot material is filled into the grooves of the corresponding conversion units, and selective filling is performed in the grooves of the corresponding transmission units. The groove array constitutes a photonic crystal structure, and the period of the groove array is Λ, which satisfies the following formula: Λ=λ1 / (2*n). In the formula, λ1 is the center wavelength of the target beam emitted by the multi-quantum-well light-emitting layer, in nm; the period Λ of the groove array refers to the distance between the centers of adjacent pixel units of the same color along the vertical direction. n is the refractive index of the N-type semiconductor layer material; In the groove array, the width of the groove is W, which satisfies the following formula: W=Λ*K*2, In the formula, K is the duty cycle of the photonic crystal, and the value of K ranges from 0.2 to 0.

4. In the groove array, the depth of the groove is D, which satisfies the following formula: D=λ2 / (2*Δn). In the formula, λ2 is the center wavelength of the target beam emitted by the conversion unit, in nm; Δn is the refractive index difference between the N-type semiconductor layer material and the filling medium provided in the corresponding groove.

6. The method for fabricating a low-crosstalk Micro-LED epitaxial wafer as described in claim 5, characterized in that, The wafer bonding process includes: Ar plasma activation treatment is performed on the surface of the drive backplane and / or the surface of the LED epitaxial structure; The bonding material is BCB adhesive or Au-Sn eutectic alloy, the bonding temperature is 200℃-260℃, and the pressure is 750 kgf / cm². 2 -1400 kgf / cm 2 The bonding time is 1800s-2200s.

7. A Micro-LED display system, characterized in that, It includes a display panel and a driving circuit, wherein the display panel is fabricated using a low-crosstalk Micro-LED epitaxial wafer as described in any one of claims 1-4.

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