Perpendicular stacking type full-color Micro-LED display device based on photonic crystal structure

Abstract

The invention discloses a vertically stacked full-color Micro-LED display device based on a photonic crystal structure, the vertically stacked full-color Micro-LED display device comprises a substrate layer, a red light Micro-LED layer, a two-dimensional photonic crystal connecting layer, a green light Micro-LED, a two-dimensional photonic crystal connecting layer, a blue light Micro-LED, a GaP connecting layer and an ITO / air interface layer from bottom to top in sequence, the two-dimensional photonic crystal is composed of indium bumps and air holes, the period of the two-dimensional photonic crystal is 100nm-2000nm, and the interval of the indium bumps and the air holes is 100nm-2000nm. The duty ratio is 20%-80%, and the height is 20 nm-500 nm. A two-dimensional photonic crystal structure is used and optimized, and red light and green light are reflected by adjusting the forbidden bandwidth of the photonic crystal, so that the light extraction efficiency of the bottom red light-emitting unit and the middle green light-emitting unit is improved, and the absorption loss of the red light and the green light is reduced; the problems that due to the fact that different-color connecting layers of an existing vertical stacking type Micro-LED display device absorb light seriously, the overall light emitting efficiency of the device is low, the chromaticity is not good, and use is affected are solved.

Description

Technical Field

[0001] The present invention relates to Micro-LED display, and in particular to a vertically stacked full-color Micro-LED display device based on a photonic crystal structure. Background Art

[0002] In recent years, with the development of portable electronic products, people have a demand for new micro-display devices. Micro-display devices with small size, long life, low energy consumption, high brightness, high resolution and easy to carry have become the focus of the development of the display industry. Compared with other micro-display devices on the market (such as LCoS, Mini-LED, OLED, etc.), Micro-LED, as a self-luminous micro-display device, has ultra-high luminous efficiency, luminous brightness and contrast, a larger color gamut range, faster response time, higher resolution, longer service life, and lower energy consumption. Therefore, Micro-LED is considered to be the most promising next-generation new display technology, and is currently used in large-screen display, wearable electronics, car display, AR / VR and other fields. The combination of Micro-LED + diffraction waveguide is considered to be the most competitive display solution for augmented reality equipment such as VR / AR glasses in the future, with broad market value.

[0003] Micro-LED is a miniaturized light-emitting diode. The size of a single pixel of an ordinary LED is usually around 300μm, and usually a light-emitting diode with a pixel size of less than 100μm is defined as a Micro-LED. The main difficulty of Micro-LED display technology at present is to achieve high resolution and full-color display. The resolution of a display device is usually measured by an important indicator parameter called PPI. The so-called PPI, or Pixels Per Inch, is also called pixel density. It represents the number of pixels per inch. Therefore, in display modules and display devices, the higher the PPI value, the higher the resolution of the display device. By reducing the size of a single pixel of Micro-LED, a higher resolution can be achieved on a display screen per unit area. An effective way to improve the display resolution of Micro-LED devices is to three-dimensionally stack and integrate the three-color RGB display pixels of Micro-LED, such as Figure 1 Shown are a traditional horizontal RGB arrangement of Micro-LED arrays (left) and a vertically stacked Micro-LED array (right).

[0004] The three-layer vertical stacking structure design (the three-layer structure corresponds to the three primary colors, usually red at the bottom, green in the middle, and blue at the top) improves the display resolution and full-color display capabilities of Micro-LED devices. However, the vertical stacking structure will cause absorption loss of the bottom red and the middle green, reduce the light extraction efficiency (external quantum efficiency is between 2%-6%), and reduce the color contrast. The main reasons are as follows: (1) The low light extraction efficiency at the interface between high-refractive-index semiconductor materials and low-refractive-index materials in vertically stacked Micro-LEDs is limited, and interface absorption causes losses; (2) Currently, the three-color Micro-LEDs in the vertically stacked Micro-LED structure are mainly bonded together by SU-8 epoxy resin. However, the light absorption of the SU-8 bonding layer will reduce the light output efficiency of the vertically stacked Micro-LED array.

[0005] An effective way to improve the light output efficiency and color contrast of full-color vertically stacked Micro-LEDs is to replace the traditional SU-8 epoxy resin bonding layer with a DBR reflector between the three-color Micro-LEDs. The applicant has improved the traditional DBR reflector and proposed to use a two-dimensional photonic crystal structure to achieve the same effect as the DBR reflector, improving the interface loss and external quantum efficiency of vertically stacked Micro-LEDs. Summary of the invention

[0006] The present invention provides a novel vertically stacked full-color Micro-LED device based on a photonic crystal structure, which solves the problem that the connection layers of different colors (red, green and blue primary colors) of the current vertically stacked Micro-LED display devices seriously absorb light, resulting in low overall light output efficiency of the device, poor color saturation and other problems that affect the use.

[0007] The technical solution adopted by the present invention is: a vertically stacked full-color Micro-LED display device based on a photonic crystal structure, which includes, from bottom to top, a substrate layer, a red light Micro-LED layer, a two-dimensional photonic crystal connection layer, a green light Micro-LED, a two-dimensional photonic crystal connection layer, a blue light Micro-LED, a GaP connection layer and an ITO / air interface layer. The two-dimensional photonic crystal is composed of indium columns and air holes, with a period of 100nm to 2000nm, a duty cycle of 20% to 80%, and a height of 20nm to 500nm.

[0008] The vertically stacked full-color Micro-LED display device based on a photonic crystal structure has three light-emitting units. The first light-emitting unit is a red light-emitting unit, which includes a first N-type layer, a red light quantum well, and a first P-type layer from bottom to top; the second light-emitting unit is a green light-emitting unit, which includes a second N-type layer, a green light quantum well, and a second P-type layer from bottom to top; the third light-emitting unit is a blue light-emitting unit, which includes a third P-type layer, a red light quantum well, and a third N-type layer from bottom to top.

[0009] The blue light Micro-LED has a surface composed of a one-dimensional photonic crystal that enhances the efficiency of coupling out light.

[0010] The epitaxial sizes of the red light Micro-LED, the green light Micro-LED, and the blue light Micro-LED decrease in a step-like manner.

[0011] The epitaxial sizes of the red light Micro-LED, the green light Micro-LED, and the blue light Micro-LED decrease in a step-like manner by no less than 20%.

[0012] The two-dimensional photonic crystal is circular in shape.

[0013] Preferably, the period of the two-dimensional photonic crystal is 500 nm.

[0014] Preferably, the duty cycle of the two-dimensional photonic crystal is 50%.

[0015] Preferably, the height of the two-dimensional photonic crystal is 200 nm.

[0016] The present invention adopts a vertically stacked full-color Micro-LED display device based on a photonic crystal structure designed using the above-mentioned technical solution. A two-dimensional photonic crystal structure is used and optimized at the connection between the red light-emitting unit and the green light-emitting unit structure and the connection between the green light-emitting unit and the blue light-emitting unit in the vertically stacked Micro-LED. The band gap width of the photonic crystal is adjusted to reflect red light and green light, thereby improving the light extraction efficiency of the bottom red light-emitting unit and the middle green light-emitting unit and reducing the absorption loss of red and green light.

[0017] (1) Compared with the vertical stacked Micro-LED method of achieving full-color operation using the traditional SU-8 bonding layer, the present invention greatly reduces the absorption rate of the bottom red and middle green light, improves the red and green light extraction efficiency, and the overall color performance of the device is better; and the photonic crystal connection layer has more parameters available for design, and the overall device functionality and flexibility are better.

[0018] (2) Compared with the vertical stacked Micro-LED that uses DBR reflectors (i.e., Bragg grating reflector layers) to connect layers to achieve full-color operation, the photonic crystal layer used in the present invention has a simple manufacturing process and does not require multiple epitaxy to manufacture a multi-layer structure (DBR reflectors are different refractive index layers made by multiple epitaxial growths, and each layer is thin and the process is difficult). The process tolerance is large and the cost is low. Moreover, the two-dimensional photonic crystal layer has more design parameters, and the design is more flexible and changeable, which can achieve better output efficiency and other device performance. In addition, the production of the two-dimensional photonic crystal layer does not require precise epitaxial layer thickness control technology, which is suitable for large-scale commercial applications.

[0019] (3) The vertically stacked Micro-LED with a two-dimensional photonic crystal structure proposed in the present invention is based on a traditional vertically stacked Micro-LED structure. The manufacturing process steps of the device provided by the present invention are almost the same as the manufacturing process steps of mature Micro-LED devices, and only one step of manufacturing a two-dimensional photonic crystal connecting layer is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Represents the traditional horizontal RGB arrangement of Micro-LED arrays and vertically stacked Micro-LED arrays; Figure 2 A schematic diagram showing the structure of a vertically stacked Micro-LED having a two-dimensional photonic crystal structure provided by an embodiment of the present invention; Figure 3 A schematic transverse cross-sectional view of a two-dimensional photonic crystal provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The following is a detailed description of a vertically stacked full-color Micro-LED display device based on a photonic crystal structure of the present invention in conjunction with the accompanying drawings.

[0022] The present invention is described below in conjunction with the accompanying drawings. Figure 2 , which from bottom to top are substrate layer 1, red light Micro-LED layer 2, two-dimensional photonic crystal connection layer 3, green light Micro-LED 4, two-dimensional photonic crystal connection layer 5, blue light Micro-LED 6, GaP connection layer 7 and ITO / air interface layer 8. Substrate layer 1 is an epitaxially grown substrate, and the ITO layer is used for current injection. Blue light Micro-LED 4 has a surface composed of one-dimensional photonic crystals to enhance the efficiency of coupled output light. The epitaxial sizes of red light Micro-LED, green light Micro-LED, and blue light Micro-LED decrease in a step-like manner, and the reduction is not less than 20%.

[0023] In the present invention, two-dimensional photonic crystals are distributed in the connecting layer between the red light layer and the green light layer, and in the connecting layer between the green light layer and the blue light layer. The two-dimensional photonic crystals are composed of indium columns and air holes, and the photon bandgap is used to form a high-efficiency coupling output of light in a specific wavelength band and a transparent transmission effect for light in other wavelength bands. Figure 2 The photonic crystal is composed of a two-dimensionally periodically arranged cylindrical indium column 9. The material selected for the photonic crystal is indium (In) material. The shape is circular. The period is 100nm to 2000nm, preferably 500nm. The duty cycle is 20% to 80%, preferably 50%. The height is 20nm to 500nm, preferably 200nm.

[0024] The vertically stacked full-color Micro-LED display device based on the photonic crystal structure of the present invention has three light-emitting units. The first light-emitting unit is a red light-emitting unit, which includes a first N-type layer, a red light quantum well and a first P-type layer from bottom to top; the second light-emitting unit is a green light-emitting unit, which includes a second N-type layer, a green light quantum well and a second P-type layer from bottom to top; the third light-emitting unit is a blue light-emitting unit, which includes a third P-type layer, a red light quantum well and a third N-type layer from bottom to top (N-type layer and P-type layer are common terms in this field, referring to N-type doping and P-type doping of semiconductor materials so that different epitaxial layers inside the semiconductor device have different conductive properties).

[0025] The red, green and blue Micro-LED layers emit red, green and blue light respectively, forming the RGB three primary colors of the full-color Micro-LED device. Unlike traditional vertically stacked Micro-LED devices, the Micro-LED device is designed with two sections of two-dimensional photonic crystal connection layers. In order to ensure the best monochromatic light coupling effect, these two sections of two-dimensional photonic crystals are placed on both sides of the middle green light-emitting layer to achieve the best red and green light coupling effect. The epitaxial sizes of the red, green and blue Micro-LEDs decrease in a step-like manner, ensuring that the absorption of the green and blue light reflected by the bottom two-dimensional photonic crystal layer gradually decreases to avoid poor color of the overall Micro-LED device.

Claims

1. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure, characterized in that From bottom to top, they are substrate layer, red light Micro-LED layer, two-dimensional photonic crystal connection layer, green light Micro-LED, two-dimensional photonic crystal connection layer, blue light Micro-LED, GaP connection layer and ITO / air interface layer. The two-dimensional photonic crystal is composed of indium columns and air holes, with a period of 100nm to 2000nm, a duty cycle of 20% to 80%, and a height of 20nm to 500nm.

2. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The vertically stacked full-color Micro-LED display device based on a photonic crystal structure has three light-emitting units. The first light-emitting unit is a red light-emitting unit, which includes a first N-type layer, a red light quantum well, and a first P-type layer from bottom to top; the second light-emitting unit is a green light-emitting unit, which includes a second N-type layer, a green light quantum well, and a second P-type layer from bottom to top; the third light-emitting unit is a blue light-emitting unit, which includes a third P-type layer, a red light quantum well, and a third N-type layer from bottom to top.

3. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The blue light Micro-LED has a surface composed of a one-dimensional photonic crystal that enhances the efficiency of coupling out light.

4. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The epitaxial sizes of the red light Micro-LED, the green light Micro-LED, and the blue light Micro-LED decrease in a step-like manner.

5. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 4, characterized in that The epitaxial sizes of the red light Micro-LED, the green light Micro-LED, and the blue light Micro-LED decrease in a step-like manner by no less than 20%.

6. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The two-dimensional photonic crystal is circular in shape.

7. A vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The period of the two-dimensional photonic crystal is 500nm.

8. The vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The duty cycle of the two-dimensional photonic crystal is 50%.

9. The vertically stacked full-color Micro-LED display device based on a photonic crystal structure according to claim 1, characterized in that The height of the two-dimensional photonic crystal is 200 nm.

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