High-brightness red light Micro-LED structure and manufacturing method thereof

Abstract

The invention relates to design and optimization of a Micro-LED light-emitting structure, in particular to a high-brightness red light Micro-LED structure and a manufacturing method thereof, a bonding anode layer and a bonding cathode layer of a micro-cavity structure form two reflecting surfaces, the optical path length is determined by the thicknesses and refractive indexes of an energy level matching layer, an LED and the cathode layer, and the optical path length is determined by the refractive indexes of the energy level matching layer, the LED and the cathode layer. The purpose of adjusting the optical path length can be achieved by adjusting the thickness of the energy level matching layer, then the optical path length of the high-brightness red light Micro-LED structure is changed, the spectral width and angle output are reduced, and therefore the luminance, the output efficiency, the half-peak width and the visual angle characteristic of a device are improved.

Description

Technical Field

[0001] The present invention relates to the design and optimization of Micro-LED light-emitting structures, and more specifically, to a high-brightness red light Micro-LED structure and a manufacturing method thereof. Background Art

[0002] Micro-LED is a two-dimensional pixel matrix of miniaturized LEDs. With its advantages of self-luminescence, high brightness, high efficiency, and high stability, Micro-LED has become a major development direction for next-generation display technology.

[0003] Micro-LED, based on GaN inorganic materials, offers the advantage of ultra-high brightness, providing higher efficiency, brightness, contrast, and longer lifespan, while also enabling ultra-small pixels and compact device sizes. Its primary applications include high-brightness, high-PPI applications such as micro-projection, virtual reality, augmented reality, mixed reality, and HUD head-up displays. In the case of medium- and low-PPI displays, similar to small-sized wearable devices like smartwatches, which have small screen sizes and low pixel requirements, they don't require a very high PPI while still leveraging the advantages of Micro-LED's high brightness, reliability, and light weight. Furthermore, Micro-LED can be widely used in military infrared integrated smart helmet displays, allowing them to simultaneously display combat information and night vision images without affecting individual soldiers' observation of real-world scenes. This plays an important role in improving and upgrading the performance of individual soldier equipment in the future.

[0004] The electrodes of vertical Micro-LED chips are located at the top and bottom of the chip, allowing current to flow vertically through the LED chip. This overcomes the problem of uneven current density distribution in the chip's active area caused by lateral current expansion in horizontal and flip-chip LED chips. Furthermore, the vertical distribution of electrodes facilitates carrier injection and improves carrier recombination efficiency.

[0005] The electrodes with strong reflective properties at the upper and lower ends of the vertical Micro-LED structure will produce a strong microcavity effect. The optical properties of this strong resonant cavity structure will be significantly affected by wide-angle interference and multi-beam interference. The microcavity effect in vertical Micro-LED devices can redistribute the spatial and spectral distribution of light, thereby directly affecting the optical properties of the device.

[0006] The invention patent with publication number CN115863508 discloses a Micro-LED structure with a microcavity. The common anode is made of transparent conductive material and has optical semi-transmissive and semi-reflective properties. An optical microcavity structure is formed between the cathode and the common anode. The luminous efficiency of the LED is improved by adjusting the optical microcavity. The device adopts a flip-chip structure and adjusts the microcavity effect by adjusting the thickness of the doping layer. Summary of the Invention

[0007] In order to solve the problem that the microcavity effect of the vertical Micro-LED structure in the prior art may affect the optical properties of the device, the present invention proposes a high-brightness red light Micro-LED structure.

[0008] To achieve the above objectives, the present invention provides a high-brightness red light Micro-LED structure, characterized in that the structure is composed of a cathode layer, a passivation layer, a light-emitting pixel unit and a bonding anode in sequence, and the pixel light-emitting unit and the bonding anode form a stepped structure, wherein: The cathode layer adopts a common cathode structure, and the cathode layer covers the outside of the passivation layer; A first opening and a second opening are provided on the passivation layer. The first opening is located at the step structure so that the cathode layer is electrically connected to the light-emitting pixel unit. The second opening is located at the driving panel so that the cathode layer is electrically connected to the cathode ring on the driving panel. The red pixel unit is composed of a second doped semiconductor, an active multi-quantum well and a first doped semiconductor, wherein the second doped semiconductor is electrically connected to the cathode layer, and the first doped semiconductor is electrically connected to the bonding anode; The bonding anode is composed of an energy level matching layer, a high reflective layer, a first blocking layer, a first bonding layer, a second bonding layer, a second blocking layer and a panel compatible layer from top to bottom. The energy level matching layer is electrically connected to the first doped semiconductor, and the panel compatible layer is electrically connected to the first contact on the driving panel.

[0009] The bonding anode is located between the drive panel and the light-emitting pixel unit and is used to achieve electrical connection between the drive panel and the red light pixel unit; the transparent energy level matching layer has high transmittance for red light wavelengths; the high reflective layer has high reflectivity for red light wavelengths; the first barrier layer prevents chemical reaction or diffusion between the high reflective layer and the transparent energy level matching layer; the first bonding layer and the second bonding layer are used to physically and electrically connect the epitaxial material and the drive panel, ensuring the reliability of the bonding structure during high-temperature use, thereby extending the service life of the device; the second barrier layer is used to prevent chemical reaction or diffusion between the panel compatible layer and the second bonding layer; the panel compatible layer is used to ensure compatibility between the drive panel and the bonding anode, ensuring electrical connection between the drive panel and the microcavity structure. A passivation layer is deposited between the individual light-emitting pixel step structures to achieve mutual disconnection and electrical isolation, ultimately achieving independent driving of each Micro-LED structure.

[0010] The variables that affect the output characteristics of the high-brightness red light Micro-LED structure are mainly the reflection characteristics of the upper and lower electrodes and the structural parameters of the Micro-LED stacked between the upper and lower electrodes, mainly the emission wavelength and the refractive index and thickness of the material and its corresponding optical path length.

[0011] The bonded anode reflective layer and cathode layer of the Micro-LED structure form two reflective surfaces. The optical path length is determined by the thickness and material refractive index of the energy level matching layer, LED, and cathode layer. The optical path length is calculated as follows: L i =L anode +L LED +L Cathode Among them L anode Transparent energy level matching layer optical path length, L LED is the sum of the optical path lengths of the first doped semiconductor, the second doped semiconductor, and the active multi-quantum well, L Cathode is the optical path length into the cathode layer.

[0012] L i Designed to , where m is a positive integer, It is the wavelength of Micro-LED light emission.

[0013] Therefore, when the red light wavelength is 530nm, in order to adapt to the optimal optical path length, the material and thickness scheme of the red light Micro-LED structure is: The cathode layer is made of ITO with a thickness of 300nm; The passivation layer is made of AlGaN or GaN with a thickness of 190nm; The second doped semiconductor is GaN with a thickness of 900nm The active multi-quantum wells use InGaN or GaN with a thickness of 280nm; The high reflective layer is made of Al with a thickness of 30nm; The first and second barrier layers are made of Pt with a thickness of 100 nm; The first and second bonding layers are made of Au with a thickness of 500 nm; The energy level matching layer is made of ITO, and its suitable thickness is calculated by the red light emission wavelength. The optical path intensity is optimal when the thickness is 63nm or 231nm.

[0014] A method for manufacturing a high-brightness red light Micro-LED structure includes the following steps: 1) First, a transparent energy-level matching layer is prepared on the surface of the LED epitaxial material p-GaN and properly annealed at 600°C. Then, a high-reflection layer, a first barrier layer, and a first bonding layer are prepared. 2) sequentially preparing a panel compatible layer, a second barrier layer, and a second bonding layer on the driving panel; 3) The LED epitaxial wafer is interconnected and bonded to the driver panel through thermal compression bonding. After bonding, the LED epitaxial substrate, AlN transition layer, and u-GaN layer are removed. 4) Pixel formation and production: remove the second doped semiconductor, active multi-quantum well and first doped layer through photolithography and etching, and etch the bonding anode in the pixel pitch to form a stepped Micro-LED structure and form a cathode ring contact on the driving panel; 5) forming a passivation layer on the step structure and etching the passivation layer to form an opening in the passivation layer ring located on the cathode ring of the step structure; 6) A cathode layer is prepared on the passivation layer, and the cathode layer is electrically connected to the red pixel unit and the cathode ring of the driving panel through the openings.

[0015] The present invention utilizes the microcavity resonance of the Micro-LED structure to enhance the coupling strength to light, thereby improving the brightness and efficiency of the device. The optical path length of the bright red light Micro-LED structure is regulated by changing the position of the bonded anode reflection surface. By changing the Micro-LED structural parameters and the position of the electrode reflection interface, the optical path length of the high-brightness red light Micro-LED structure is changed, and the spectral width and angular output are reduced, thereby improving the device's luminous brightness, output efficiency, half-peak width and viewing angle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Enlarged schematic diagram of the high-brightness red light Micro-LED structure.

[0017] Figure 2 Schematic diagram before bonding the LED epitaxial wafer and driver panel.

[0018] Figure 3 Schematic diagram of the LED epitaxial wafer and driver panel after bonding.

[0019] Figure 4 Schematic diagram of LED epitaxial side substrate peeling and second doped semiconductor thinning.

[0020] Figure 5 Schematic diagram of the high-brightness red light Micro-LED structure.

[0021] Figure 6 Schematic diagram of sidewall passivation of high-brightness red Micro-LED structure.

[0022] Figure 7 Schematic diagram of the cathode layout of the high-brightness red light Micro-LED structure.

[0023] Among them: cathode layer 1, passivation layer 2, red light pixel unit 3, second doped semiconductor 3-1, active multi-quantum well 3-2, first doped semiconductor 3-3, bonding anode 4, energy level matching layer 4-1, high reflective layer 4-2, first blocking layer 4-3, first bonding layer 4-4, second bonding layer 4-5, second blocking layer 4-6, panel compatible layer 4-7, driving panel 5, first contact 5-1, second contact 5-2, transition layer 6, substrate 7. DETAILED DESCRIPTION

[0024] Example 1: See Figure 1 The driving panel can be, but is not limited to, a CMOS driving panel or a TFT glass substrate. The high-brightness red light Micro-LED structure adopts a common cathode layout, and the peak emission wavelength of the red light pixel unit is 530nm.

[0025] In this embodiment, an energy-level matching layer is first formed on the surface of the LED epitaxial p-GaN material and annealed at 600°C to minimize internal stress and metal bonding voids, thereby improving the contact characteristics of the electrode P-GaN interface. A high-reflectivity layer, a first barrier layer, and a first bonding layer are then formed on the surface of the LED epitaxial p-GaN material. A panel-compatible layer, a second barrier layer, and a second bonding layer are then sequentially formed on the driver backplane. ITO (tin-doped indium oxide) is used for the energy-level matching layer. To ensure optimal energy-level matching and compatibility, maximize the red light interference-enhanced coupling effect, and effectively reduce the device's turn-on voltage, the transparent energy-level matching layer is controlled at 63nm, 231nm, and other wavelengths based on microcavity optimization calculations.

[0026] The LED epitaxial wafer and the driver panel are interconnected and bonded through hot compression bonding. After the bonding is completed, the LED epitaxial side substrate, AlN transition layer and u-GaN layer are effectively removed by combining physical and chemical stripping methods, and the second doped semiconductor is appropriately thinned. The final thickness of the second doped semiconductor is determined by the optical path difference calculation of the high-brightness Micro-LED structure.

[0027] The MESA pattern is designed using a patterned mask. The second doped semiconductor, active multi-quantum well, and first doped layer are etched away, and the bonding anode in the pixel pitch is etched away. This fully separates the LED light-emitting pixels, forming a stepped structure and a second contact on the cathode ring surface of the driver panel. Given the pixel size characteristics of silicon-based Micro-LED microdisplays, the pixel size of the embodiments of this patent is controlled within the range of 1 to 10µm.

[0028] After the step structure is formed, PCEVD or ALD is used to form a dense passivation layer on the surface of the light-emitting pixel step to achieve side wall protection and electrical isolation of the red light pixel unit.

[0029] The passivation layer on the surface of the step structure is etched with photolithography and etching methods to form a first opening of the step structure and a second opening at the cathode ring of the driving panel.

[0030] A transparent common cathode is prepared on the step structure, and the cathode layer is in contact with the first opening and the second opening.

[0031] Following the above fabrication process, the fabrication of a vertical microcavity stacked Micro-LED pixel structure and pixel array can be achieved. The optical path length of the device is determined by the distance between the anode reflective layer and the cathode layer. Considering the need to balance the device's electrical performance with the MOCVD growth characteristics of the epitaxial LED structure, the thicknesses of the energy-level matching layer, first doped semiconductor, active multi-quantum well, and cathode layer in this embodiment are determined by the device's electrical performance. The optical path length in this embodiment of the present invention is primarily achieved by adjusting the thickness of the energy-level matching layer to achieve optimal optical interference-enhanced coupling.

[0032] See also Figure 1 In the vertical micro-cavity stacked Micro-LED light-emitting structure, the light generated by the electron-hole recombination is emitted from the active multi-quantum well. Since the active multi-quantum well is close to the bonded anode high reflective layer, the light emitted by the active multi-quantum well will interfere with the light reflected by the metal reflective layer. According to the previous optical path difference theory calculation, the two interfering light will produce destructive and constructive phenomena. These two lights are the light emitted directly upward by the electric dipole into the air and the light emitted into the air after being reflected by the bonded anode reflective layer. The optical path difference in the vertical direction satisfies the half wavelength. , two-way light , where: n is the refractive index of the bonded anode reflective layer, transparent energy level matching layer, first doped semiconductor, active multi-quantum well, second doped semiconductor and semi-transparent composite cathode respectively; is the wavelength of the outgoing light; m is an integer. When m is an even number, the two beams interfere constructively, while when m is an odd number, the two beams interfere destructively. This embodiment achieves enhanced interference between the two beams by precisely controlling the thickness of the transparent energy level matching layer to precisely adjust the optical path difference or phase difference between the two beams.

[0033] In summary, through this embodiment, the design and manufacture of vertical microcavity stacked Micro-LED light-emitting diodes can be successfully completed, and the phase difference length can be changed by changing the material thickness between the two reflective surfaces, thereby realizing the optimized design of the vertical microcavity stacked Micro-structure, reducing the spectral width and angular output, and improving the device's luminous brightness and efficiency.

Claims

1. A high-brightness red light Micro-LED structure, characterized by The structure is composed of a cathode layer, a passivation layer, a light-emitting pixel unit and a bonding anode in sequence. The pixel light-emitting unit and the bonding anode form a step structure, wherein: The cathode layer adopts a common cathode structure, and the cathode layer covers the outside of the passivation layer; A first opening and a second opening are provided on the passivation layer. The first opening is located at the step structure so that the cathode layer is electrically connected to the light-emitting pixel unit. The second opening is located at the driving panel so that the cathode layer is electrically connected to the cathode ring on the driving panel. The red pixel unit is composed of a second doped semiconductor, an active multi-quantum well and a first doped semiconductor, wherein the second doped semiconductor is electrically connected to the cathode layer, and the first doped semiconductor is electrically connected to the bonding anode; The bonding anode is composed of an energy level matching layer, a high reflective layer, a first blocking layer, a first bonding layer, a second bonding layer, a second blocking layer and a panel compatible layer from top to bottom. The energy level matching layer is electrically connected to the first doped semiconductor, and the panel compatible layer is electrically connected to the first contact on the driving panel.

2. A high-brightness red Micro-LED structure according to claim 1, characterized in that When the red light wavelength is 450nm, the material and thickness scheme of the red light Micro-LED structure is: The cathode layer is made of ITO with a thickness of 300nm; The passivation layer is made of AlGaN or GaN with a thickness of 190nm; The second doped semiconductor is GaN with a thickness of 900nm The active multi-quantum wells use InGaN or GaN with a thickness of 280nm; The high reflective layer is made of Al with a thickness of 30nm; The first and second barrier layers are made of Pt with a thickness of 100 nm; The first and second bonding layers are made of Au with a thickness of 500 nm; The energy level matching layer is made of ITO, and its suitable thickness is calculated by the red light emission wavelength. The optical path intensity is optimal when the thickness is 63nm or 231nm.

3. A method for manufacturing a high-brightness red light Micro-LED structure, characterized in that The following steps are involved: First, a transparent energy-level matching layer is prepared on the surface of the LED epitaxial material p-GaN and properly annealed at 600°C. Then, a high-reflection layer, a first barrier layer, and a first bonding layer are prepared. sequentially preparing a panel compatible layer, a second barrier layer, and a second bonding layer on the driving panel; 3) The LED epitaxial wafer is interconnected and bonded to the driver panel through thermal compression bonding. After bonding, the LED epitaxial substrate, AlN transition layer, and u-GaN layer are removed. 4) Pixel formation and production: remove the second doped semiconductor, active multi-quantum well and first doped layer through photolithography and etching, and etch the bonding anode in the pixel pitch to form a stepped Micro-LED structure and form a cathode ring contact on the driving panel; 5) forming a passivation layer on the step structure and etching the passivation layer to form an opening in the passivation layer ring located on the cathode ring of the step structure; 6) A cathode layer is prepared on the passivation layer, and the cathode layer is electrically connected to the red pixel unit and the cathode ring of the driving panel through the openings.

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