Inverted structure red light micro-LED and optical optimization method thereof

Abstract

The invention relates to an inverted-structure red light micro-LED and an optical optimization method thereof, and the method specifically comprises the steps: designing a distributed Bragg reflector (DBR) at the top of the inverted-structure red light micro-LED, and achieving the reflection enhancement of the red light with a specific wavelength through controlling the number of layers of the DBR and the refractive index and thickness of each layer of material, meanwhile, a resonant cavity is formed by the Ag metal reflecting mirror and the Ag metal reflecting mirror located at the bottom, so that light emitting of the red light micro-LED in the vertical direction is effectively enhanced; the Ag metal reflecting mirror is arranged on the side wall of the micro-LED, so that the loss of light on the side wall is reduced, and the problem of light crosstalk between pixels is inhibited. Through the enhancement effect of the resonant cavity and the loss reduction effect of the side wall reflecting mirror, double improvement of the light emitting efficiency and the optical performance of the micro-LED is achieved, and the micro-LED is suitable for various micro-LED display and illumination applications needing high brightness, high contrast and low crosstalk.

Description

Technical Field

[0001] The present invention relates to the field of micro-LED display technology, and in particular to an optical optimization design scheme for a flip-chip structured red light micro-LED. Background Art

[0002] With the rapid development of microelectronics and optoelectronics, flip-chip red micro-LEDs have shown great application potential in the fields of display and lighting due to their advantages such as high brightness, low power consumption, and long life. However, traditional flip-chip red micro-LEDs still face some challenges in optical performance, especially in terms of light extraction efficiency and light directional control. These problems limit their performance in high-brightness, high-contrast display and precision lighting applications. In the traditional flip-chip red micro-LED design, light is prone to scattering, absorption, and reflection losses inside the chip and at the interface, resulting in low light extraction efficiency. To solve the above problems, the industry has begun to explore the optical optimization design of red micro-LEDs. Among them, the distributed Bragg reflector (DBR), as an effective optical structure, can achieve enhanced reflection of light of a specific wavelength by precisely controlling the number of layers and the refractive index and thickness of each layer of material, thereby improving light extraction efficiency. However, there are certain compatibility issues between the material system used in the current common DBR design and the industrial preparation system of red light micro-LEDs, and the use of DBR alone has limited improvement on the overall optical performance, especially in reducing sidewall light loss and suppressing optical crosstalk, which still needs further optimization. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to design an optical optimization design scheme for flip-chip red light micro-LED, design the material and structure of the distributed Bragg and combine it with Ag metal reflector to form a resonant cavity, so as to improve the light output efficiency and optical performance of the red light micro-LED.

[0004] Technical solution: The optical optimization method of an inverted structure red light micro-LED described in the present invention comprises the following steps: a top distributed Bragg reflector is arranged on the top of the inverted structure red light micro-LED, a bottom metal silver reflector is arranged on the bottom, and a side wall metal silver reflector is arranged on the side wall, wherein the top distributed Bragg reflector and the bottom metal silver reflector form a resonant cavity structure to enhance the light output of the micro-LED in the vertical direction.

[0005] The top distributed Bragg reflector is formed by alternately stacking two dielectric materials with different refractive indices, wherein the low refractive index material is AlN and the high refractive index material is GaN.

[0006] The thickness of the dielectric layer formed by stacking the dielectric materials satisfies the following optical relationship:

[0007]

[0008]

[0009] d AlN ,d GaN Respectively represent the thickness of AlN dielectric layer and GaN dielectric layer; λ center Represents the central wavelength of the micro-LED excitation light; n AlN 、n GaN They respectively represent the refractive indices of AlN and GaN materials in the micro-LED excitation light band.

[0010] The reflectivity of the distributed Bragg reflector is determined by the number of superposition periods of two dielectric materials with different refractive indices alternately superimposed, and there is the following relationship between the number of superposition periods and the reflectivity of the distributed Bragg reflector:

[0011]

[0012] R DBR represents the reflectivity of the distributed Bragg reflector; n AlN 、n GaN They respectively represent the refractive indices of AlN and GaN materials in the micro-LED excitation light band; T represents the number of superposition cycles of the two dielectric materials alternately superimposed.

[0013] The reflectivity of the bottom metal silver reflector and the side wall metal silver reflector conforms to the Fresnel equation. For light incident from medium 1 to medium 2, the reflection coefficients of vertical polarization and horizontal polarization satisfy the following relationship:

[0014]

[0015] r s 、r p They refer to the reflection coefficient of vertical polarization and the reflection coefficient of horizontal polarization respectively; n1 and n2 refer to the refractive index of medium 1 and medium 2 respectively, θ i ,θ t They refer to the angle of incidence and angle of refraction of the light respectively.

[0016] The angle of incidence and the angle of refraction satisfy Snell's law:

[0017] n1 sinθ i =n2 sinθ t

[0018] n1 and n2 refer to the refractive index of medium 1 and medium 2 respectively, θi ,θ t They refer to the angle of incidence and angle of refraction of the light respectively.

[0019] The reflectivity is the square of the reflection coefficient, and the reflectivity for vertical polarization and horizontal polarization are:

[0020] R s =|r s | 2

[0021] R p =|r p | 2

[0022] R s , R p Refers to the reflectivity of vertical polarization and horizontal polarization respectively; r s 、r p Refers to the reflection coefficient of vertically polarized light and horizontally polarized light respectively.

[0023] The thickness design of the bottom metal silver reflector and the side wall metal silver reflector takes into account the transmission of the micro-LED excitation light in the P-GaN layer, the metal silver film layer and the air medium in the micro-LED. The reflectivity and the thickness of the silver metal film meet the following relationship:

[0024]

[0025] R Ag Represents the reflectivity of metallic silver film; n pGaN 、n Ag and n Air Respectively refer to the refractive index of the P-GaN layer, the metal silver film layer and the air medium in the micro-LED; d Ag Refers to the thickness of the metallic silver film layer; center Indicates the central wavelength of the micro-LED excitation light.

[0026] Among them, in the resonant cavity structure composed of the top distributed Bragg reflector and the bottom metal silver reflector, the reflectivity of the distributed Bragg reflector needs to reach more than 80% in the micro-LED excitation light band, and the reflectivity of the bottom metal silver reflector needs to reach more than 90% in the micro-LED excitation light band.

[0027] The present invention also provides an inverted structure red light micro-LED, including a top distributed Bragg reflector, a bottom metal silver reflector, and a side wall metal silver reflector, wherein the top distributed Bragg reflector and the bottom metal silver reflector form a resonant cavity structure to enhance the light output of the micro-LED in the vertical direction.

[0028] The principle of the present invention is to comprehensively utilize the optical properties of the distributed Bragg reflector (DBR) and the Ag metal reflector to perform optical optimization design on the flip-chip structure red light micro-LED to achieve a significant improvement in light extraction efficiency and optical performance. Specifically, as a periodic multilayer thin film structure, DBR can form a strong reflection within a specific wavelength range by precisely controlling the number of layers, the refractive index and thickness of each layer of material, thereby enhancing the light extraction efficiency of the wavelength light. In the present invention, the DBR is designed and placed on the top of the red light micro-LED, and together with the Ag metal reflector at the bottom, it forms a resonant cavity. This resonant cavity can guide and enhance the propagation of red light in the vertical direction, effectively reducing the scattering and absorption losses of light inside the chip and at the interface, thereby improving the light extraction efficiency. At the same time, in order to further optimize the optical performance, the present invention also sets an Ag metal reflector on the side wall of the red light micro-LED. Ag metal has a high reflectivity, which can effectively reduce the loss of light on the side wall and suppress the problem of light crosstalk between pixels. Through the guidance of the side wall reflectors, more light is directed to emit in the vertical direction, further improving the light output efficiency and directional control of light.

[0029] Beneficial effects: Compared with the prior art, the present invention demonstrates significant superiority in the optical optimization of red light micro-LEDs, which is mainly reflected in three aspects: material selection and design, optical design and calculation, and innovative application of resonant cavity structure.

[0030] In terms of material selection and design, the present invention cleverly uses AlN / GaN as the material system of distributed Bragg reflectors (DBR). This choice is not only highly compatible with the production line and preparation system of gallium nitride-based micro-LEDs, reducing compatibility issues in the production process, but also the AlN / GaN material system has excellent physical and chemical stability, which can effectively improve the durability and reliability of DBR. This material selection strategy has laid a solid foundation for the efficient application of DBR in red light micro-LEDs.

[0031] In terms of optical design and calculation, the present invention has carried out precise optical design and calculation of DBR and silver reflector according to the emission wavelength of red light micro-LED. By optimizing the number of DBR layers, the refractive index and thickness of each layer of material, and the reflectivity of the silver reflector and other parameters, the present invention has achieved targeted optimization of the flip-chip structure red light micro-LED. This design not only significantly improves the reflection efficiency of DBR for red light, but also further enhances the directional control of light through the synergistic effect of the silver reflector, thereby effectively improving the light extraction efficiency of the red light micro-LED.

[0032] In addition, in terms of innovative application of resonant cavity structure, the present invention breaks through the limitation of traditional optical optimization that relies only on DBR. By constructing a resonant cavity structure with a top distributed Bragg reflector and a bottom silver reflector in the vertical direction, and using a silver reflector in the horizontal direction to reduce the side wall loss of light, the present invention can not only enhance the light output efficiency of the light output surface in the vertical direction, but also effectively suppress the scattering and absorption loss of light at the side wall and interface, thereby further improving the optical performance of the red light micro-LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a system structure diagram of the method of the present invention;

[0034] Figure 2 is the reflectivity of the distributed Bragg reflector of the embodiment at different light emission wavelengths;

[0035] Figure 3 The relationship between the reflectivity and thickness of the silver metal reflector at different luminous wavelengths in the embodiment;

[0036] Figure 4 The reflectivity of a silver metal reflector of specified thickness for different emission wavelengths is given in the examples. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with specific embodiments and drawings, but is not limited to the following contents.

[0038] like Figure 1 The flip-chip structure red light micro-LED of the present invention includes a top distributed Bragg reflector, a bottom metal silver reflector (Ag reflector (bottom)), and a side wall metal silver reflector (Ag reflector (side wall)), wherein the top distributed Bragg reflector and the bottom metal silver reflector form a resonant cavity structure to enhance the light output of the micro-LED in the vertical direction. The active layer is the light-emitting layer in the micro-LED. The top distributed Bragg reflector is formed by alternating two dielectric materials with different refractive indices, wherein the low refractive index material is AlN and the high refractive index material is GaN.

[0039] The present invention is directed to an optical optimization design scheme for a flip-chip structure red light micro-LED, and selects a flip-chip structure red light micro-LED with an excitation light center wavelength of 640nm as an implementation object. The optimization design scheme specifically includes the following steps:

[0040] Step 1: determine the thickness of the alternately stacked layers of two dielectric materials with different refractive indices in the distributed Bragg reflector.

[0041] The thickness of the dielectric layer formed by stacking the dielectric materials satisfies the following optical relationship:

[0042]

[0043] Among them, d AlN ,d GaN Respectively represent the thickness of AlN dielectric layer and GaN dielectric layer; λ center Represents the central wavelength of the micro-LED excitation light; n AlN 、n GaN They respectively represent the refractive indices of AlN and GaN materials in the micro-LED excitation light band.

[0044] Step 2: determine the number of superposition periods of the two dielectric materials with different refractive indices of the distributed Bragg reflector alternately superimposed, and calculate the reflectivity of the distributed Bragg reflector based on the number of superposition periods.

[0045] The reflectivity of the distributed Bragg reflector is determined by the number of superposition periods of two dielectric materials with different refractive indices alternately superimposed. There is the following relationship between the number of superposition periods and the reflectivity of the distributed Bragg reflector:

[0046]

[0047] Among them, R DBR represents the reflectivity of the distributed Bragg reflector; n AlN 、n GaN They respectively represent the refractive indices of AlN and GaN materials in the micro-LED excitation light band; T represents the number of superposition cycles of the two dielectric materials alternately superimposed.

[0048] pass Figure 2 It can be seen that the distributed Bragg reflector designed for red light micro-LED (central wavelength of 640nm) can maintain a reflectivity of more than 80% for light with a wavelength of 627nm-654nm when the number of superposition cycles of the two dielectric materials is 10.

[0049] Step 3: Calculate the reflectivity of the silver metal film for the micro-LED excitation light in the specified medium, and design the thickness of the bottom metal silver reflector and the sidewall metal silver reflector accordingly.

[0050] The reflectivity of the bottom metal silver reflector and the side wall metal silver reflector conforms to the Fresnel equation. For light incident from medium 1 to medium 2, the reflection coefficients of vertical polarization and horizontal polarization satisfy the following relationship:

[0051]

[0052]

[0053] r s 、r p They refer to the reflection coefficient of vertical polarization and the reflection coefficient of horizontal polarization respectively; n1 and n2 refer to the refractive index of medium 1 and medium 2 respectively, θ i ,θ t They refer to the angle of incidence and angle of refraction of the light respectively.

[0054] The angle of incidence and the angle of refraction satisfy Snell's law:

[0055] n1 sinθ i =n2 sinθ t

[0056] n1 and n2 refer to the refractive index of medium 1 and medium 2 respectively, θ i ,θ t They refer to the angle of incidence and angle of refraction of the light respectively.

[0057] The reflectivity is the square of the reflection coefficient, and the reflectivity for vertical polarization and horizontal polarization are:

[0058] R s =|r s | 2

[0059] R p =|r p | 2

[0060] R s , R p Refers to the reflectivity of vertical polarization and horizontal polarization respectively; r s 、r p Refers to the reflection coefficient of vertically polarized light and horizontally polarized light respectively.

[0061] The thickness design of the bottom metal silver reflector and the side wall metal silver reflector takes into account the transmission of the micro-LED excitation light in the P-GaN layer, the metal silver film layer and the air medium in the micro-LED. The reflectivity and the thickness of the silver metal film meet the following relationship:

[0062]

[0063] R Ag Represents the reflectivity of metallic silver film; n pGaN 、n Ag and n Air Respectively refer to the refractive index of the P-GaN layer, the metal silver film layer and the air medium in the micro-LED; d AgRefers to the thickness of the metallic silver film layer; center Indicates the central wavelength of the micro-LED excitation light.

[0064] pass Figure 3 It can be seen that for the silver metal reflector designed for red light micro-LED (central wavelength of 640nm), when the thickness of the silver metal film is greater than 50nm, the reflectivity of light with a wavelength of 627nm-654nm can be maintained above 90%.

[0065] Step 4: Check whether the reflectivity of the distributed Bragg reflector and the reflectivity of the bottom metal silver reflector meet the reflectivity requirements of the resonant cavity.

[0066] In the resonant cavity structure composed of the top distributed Bragg reflector and the bottom metal silver reflector, the reflectivity of the distributed Bragg reflector needs to reach more than 80% in the micro-LED excitation light band, and the reflectivity of the bottom metal silver reflector needs to reach more than 90% in the micro-LED excitation light band.

[0067] pass Figure 2 It can be seen that the distributed Bragg reflector designed for red light micro-LED (central wavelength of 640nm) has a reflectivity of more than 80% for light with a wavelength near 640nm;

[0068] pass Figure 4 It can be seen that the silver metal reflector designed for red light micro-LED (central wavelength of 640nm) can maintain a reflectivity of more than 90% for light with a wavelength near 640nm when the thickness of the silver metal film is 50nm.

Claims

1. An optical optimization method for a flip-chip structured red light micro-LED, characterized in that: The method comprises the following steps: a top distributed Bragg reflector is arranged on the top of the inverted structure red light micro-LED, a bottom metal silver reflector is arranged on the bottom, and a side wall metal silver reflector is arranged on the side wall, wherein the top distributed Bragg reflector and the bottom metal silver reflector form a resonant cavity structure to enhance the light output of the micro-LED in the vertical direction.

2. The optical optimization method of the flip-chip structure red light micro-LED according to claim 1, characterized in that: The top distributed Bragg reflector is formed by alternately stacking two dielectric materials with different refractive indices, wherein the low refractive index material is AlN and the high refractive index material is GaN.

3. The optical optimization method of the flip-chip structure red light micro-LED according to claim 2, characterized in that: The thickness of the dielectric layer formed by stacking the dielectric materials satisfies the following optical relationship: Among them, d AlN d GaN Respectively represent the thickness of AlN dielectric layer and GaN dielectric layer; λ center Represents the central wavelength of the micro-LED excitation light; n AlN 、n GaN They respectively represent the refractive indices of AlN and GaN materials in the micro-LED excitation light band.

4. The optical optimization method of the flip-chip structure red light micro-LED according to claim 2, characterized in that: The reflectivity of the distributed Bragg reflector is determined by the number of superposition periods of two dielectric materials with different refractive indices alternately superimposed. There is the following relationship between the number of superposition periods and the reflectivity of the distributed Bragg reflector: Among them, R DBR represents the reflectivity of the distributed Bragg reflector; n AlN 、n GaN They respectively represent the refractive indices of AlN and GaN materials in the micro-LED excitation light band; T represents the number of superposition cycles of the two dielectric materials alternately superimposed.

5. The optical optimization method of the flip-chip structure red light micro-LED according to claim 1, characterized in that: The reflectivity of the bottom metal silver reflector and the side wall metal silver reflector conforms to the Fresnel equation; for light incident from medium 1 to medium 2, the reflection coefficients of vertical polarization and horizontal polarization satisfy the following relationship: Among them, r s 、r p They refer to the reflection coefficient of vertical polarization and the reflection coefficient of horizontal polarization respectively; n1 and n2 refer to the refractive index of medium 1 and medium 2 respectively, θ i ,θ t They refer to the angle of incidence and angle of refraction of light respectively; The angle of incidence and the angle of refraction satisfy Snell's law: n1 sinθ i =n2 sinθ t Where n1 and n2 refer to the refractive index of medium 1 and medium 2 respectively, θ i ,θ t They refer to the angle of incidence and angle of refraction of light respectively; The reflectivity is the square of the reflection coefficient, and the reflectivity for vertical polarization and horizontal polarization are: R s ＝|r s | 2 R p ＝|r p | 2 Among them, R s , R p Refers to the reflectivity of vertical polarization and horizontal polarization respectively; r s 、r p Refers to the reflection coefficient of vertically polarized light and horizontally polarized light respectively.

6. The optical optimization method of flip-chip structure red light micro-LED according to claim 1, characterized in that: The thickness design of the bottom metal silver reflector and the side wall metal silver reflector takes into account the transmission of the micro-LED excitation light in the P-GaN layer, the metal silver film layer and the air medium in the micro-LED. The reflectivity and the thickness of the silver metal film meet the following relationship: Among them, R Ag Represents the reflectivity of metallic silver film; n pGaN 、n Ag and n Air Respectively refer to the refractive index of the P-GaN layer, the metal silver film layer and the air medium in the micro-LED; d Ag Refers to the thickness of the metallic silver film layer; center Indicates the central wavelength of the micro-LED excitation light.

7. The optical optimization method of flip-chip structure red light micro-LED according to claim 1, characterized in that: In the resonant cavity structure composed of the top distributed Bragg reflector and the bottom metal silver reflector, the reflectivity of the distributed Bragg reflector reaches more than 80% in the micro-LED excitation light band, and the reflectivity of the bottom metal silver reflector reaches more than 90% in the micro-LED excitation light band.

8. A flip-chip structure red light micro-LED based on the optical optimization method according to any one of claims 1 to 7, characterized in that: It includes a top distributed Bragg reflector, a bottom metal silver reflector, and a side wall metal silver reflector, wherein the top distributed Bragg reflector and the bottom metal silver reflector form a resonant cavity structure to enhance the light output of the micro-LED in the vertical direction.

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