Method for preparing high-resolution nano-pixel display array by using flexible nano-pillar pasting film

Abstract

This invention discloses a method for fabricating a high-resolution nanopixel display array using flexible nanopillar film. The method involves epitaxially etching GaN-based LED nanopillars on a substrate, transferring the nanopillars to a flexible temporary substrate, and removing the original substrate down to the N-type GaN layer to obtain a flexible nanopillar film. The surface of the N-type GaN layer of the flexible nanopillar film is then flip-chip bonded to a driving circuit substrate using In electrodes. Finally, the flexible temporary substrate is removed, resulting in the high-resolution nanopixel display array. This invention utilizes the flexible nanopillar film method to achieve massive nanopixel transfer. The high-density nanoarray avoids alignment problems inherent in mass transfer, enabling the control of light emission from multiple GaN nanopillars with a single In electrode without the need for photolithographic alignment, achieving sub-micron resolution.

Description

Technical Field

[0001] This invention relates to a method for fabricating a high-resolution nanopixel display array using flexible nanopillar films. Background Technology

[0002] Since the rise of Micro-LED display technology, efforts have been made to achieve smaller pixels and higher resolutions in this field. With the emergence of new industries such as the Internet of Things, 5G, and artificial intelligence, displays, which originally only had display functions, are gradually evolving into portable, wearable, and ultra-high-resolution near-eye devices. To make the light field on the display screen closer to the light field in the real world, achieving a near-identical representation of the object on the screen, ultra-low pixel sizes are urgently needed. In recent years, GaN-based micron-sized LEDs have been considered ideal candidate materials for achieving ultra-high-resolution displays due to their advanced manufacturing processes and potential advantages such as low dislocation density, low strain, tunable emission color, and high light extraction efficiency. However, limitations in manufacturing processes such as mass transfer, metal bonding, and pixel-level integration make it difficult to reduce pixel sizes to the sub-micron level using traditional techniques. Furthermore, traditional mass transfer processes suffer from difficulties such as alignment problems, crosstalk in emission signals, and low device yields. Therefore, high-resolution displays have always been a technological bottleneck in the display field. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a high-resolution nanopixel display array using flexible nanopillar films, which can produce a high-resolution nanopixel display array.

[0004] The technical solution adopted in this invention is as follows: a method for preparing a high-resolution nano-pixel display array using a flexible nanopillar film. GaN-based LED nanopillars are epitaxially etched on a substrate, and a dielectric film is filled to electrically isolate the nanopillars. An electrode is prepared on the top of the nanopillars using a P-type GaN layer to connect the nanopillars in parallel with a common P-electrode. The nanopillars are transferred to a flexible temporary substrate and the original substrate is removed down to the bottom of the nanopillars to obtain a flexible nanopillar film. The surface of the N-type GaN layer of the flexible nanopillar film is flip-chip bonded to the driving circuit substrate using an In electrode to obtain a high-resolution nano-pixel display array.

[0005] Preferably, the specific steps are as follows:

[0006] (1) Clean the Si substrate;

[0007] (2) Growth of GaN-based LED structures on a substrate;

[0008] (3) A nanopillar array with a depth of N-type GaN layer was etched on the GaN-based LED structure;

[0009] (4) Fill the space between the nanopillars with a dielectric film to achieve electrical isolation between the nanopillars;

[0010] (5) Etch the dielectric film at the top of the nanopillar to expose the P-type GaN layer of the nanopillar;

[0011] (6) Deposit metal electrodes or ITO transparent electrodes on the top of the nanopillars to make the common P electrodes of the nanopillars connected in parallel.

[0012] (7) A flexible thin film is spin-coated onto the metal electrode to form a flexible temporary substrate;

[0013] (8) Remove the original Si substrate;

[0014] (9) Remove the bottom of the nanopillars down to the N-type GaN layer to separate the bottoms of the nanopillars from each other, while the nanopillars still retain part of the N-type GaN layer, to obtain a flexible nanopillar film.

[0015] (10) The N-layer GaN surface of the flexible nanopillar film is flip-chip bonded to the driving circuit substrate with In electrode, so that each In electrode can contact several nanopillars to obtain a high-resolution nanopixel display array.

[0016] Preferably, in step (2), the GaN-based LED structure includes, from bottom to top, a GaN buffer layer, an N-type GaN layer, an InGaN / GaN quantum well layer, and a P-type GaN layer.

[0017] Preferably, the method further includes step (11): when the P electrode is a metal thin film, removing the flexible temporary substrate.

[0018] Preferably, dry etching is used in step (3), and the etching conditions are: Cl2 / BCl3 gas: 48 / 6, gas pressure 1-10 mtorr, power 30 / 200.

[0019] Preferably, in step (4), SOG is spin-coated to fill the space between the nanopillars as a dielectric film.

[0020] Preferably, in step (6), a P-type metal thin film is deposited on the P-type GaN side of the nanopillar, and the metal thin film contacts the exposed P-type GaN layer, and annealing is performed to form an ohmic contact.

[0021] Preferably, in step (7), PI adhesive is spin-coated onto the metal thin film to form a flexible temporary substrate.

[0022] Preferably, in step (8), the device is immersed in a solution of HF:HNO3:H2O = 1:1:1 to remove the Si substrate.

[0023] Preferably, in step (9), ICP dry etching is used to remove excess GaN at the bottom of the nanopillars, so that the bottoms of the nanopillars are isolated from each other.

[0024] Another preparation process of the present invention is as follows:

[0025] (1) Clean the sapphire substrate;

[0026] (2) Growth of GaN-based LED structures on a substrate;

[0027] (3) A nanopillar array extending deep into a sapphire substrate was etched onto a GaN-based LED structure;

[0028] (4) Fill the space between the nanopillars with a dielectric film to achieve electrical isolation between the nanopillars;

[0029] (5) Etch the dielectric film at the top of the nanopillar to expose the P-type GaN layer of the nanopillar;

[0030] (6) Deposit metal electrodes or ITO transparent electrodes on the top of the nanopillars to make the common P electrodes of the nanopillars connected in parallel.

[0031] (7) A flexible thin film is spin-coated onto the metal electrode to form a flexible temporary substrate;

[0032] (8) The original sapphire substrate is removed by laser lift-off, so that the bottom of the nanopillars are separated from each other, and the nanopillars still retain part of the N-type GaN layer, thus obtaining a flexible nanopillar film.

[0033] (9) The N-layer GaN surface of the flexible nanopillar film is flip-chip bonded to the driving circuit substrate with In electrode, so that each In electrode can contact several nanopillars to obtain a high-resolution nanopixel display array.

[0034] Preferably, the method further includes step (10): when the P electrode is a metal thin film, removing the flexible temporary substrate.

[0035] This invention utilizes a flexible nanopillar film-coating method to achieve massive nanopixel transfer. By using a high-density nanoarray, it avoids the alignment problem in the massive transfer. Without the need for photolithography alignment, it achieves the goal of controlling the light emission of several GaN nanopillars with a single In electrode, thus achieving submicron resolution.

[0036] The beneficial effects of this invention are as follows:

[0037] (1) A large-area flexible nanopillar light-emitting pixel film is obtained, which has a wide range of applications and can meet the application requirements of flexible display. It is compatible with the driving backplate of existing display technology. The flexible nanopillar film can greatly alleviate the stress accumulation problem between the light-emitting unit and the driving backplate. Furthermore, the flexible nanofilm can reduce the contact effect caused by unevenness and defects on the surface of the driving backplate, which is of great help to improve the yield of the device.

[0038] (2) The manufacturing process is simple. No photolithography and alignment processes are required in the fabrication of flexible nanopillar films, which greatly reduces the problem of pixel unit alignment accuracy caused by photolithography and alignment processes, and is also conducive to improving the pixel unit yield.

[0039] (3) The flexible nanopillar film proposed in this invention can solve the problem of precise alignment between the driving circuit and the display pixel. By interconnecting a single electrode with multiple nanopillars, the cumbersome process required for precise alignment is significantly simplified.

[0040] (4) The pixels of the present invention are compatible with existing large-size driving circuits. In addition, the film application method of the present invention can be used to repair damaged pixels. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the process flow. In the diagram, 1 represents Si, 2 represents GaN nanopillars, 3 represents dielectric film, 4 represents metal thin film, 5 represents flexible temporary substrate, 6 represents In pillars, and 7 represents driving circuit substrate.

[0042] Figure 2 This is a scanning electron microscope (SEM) bird's-eye view of the periodic nanomask fabricated on an LED chip by nanoimprinting in Example 1.

[0043] Figure 3 This is a SEM bird's-eye view of the LED nanopillars formed after ICP etching in Example 1.

[0044] Figure 4 This is a SEM cross-sectional view of the LED nanopillars formed after ICP etching in Example 1.

[0045] Figure 5 This is a SEM bird's-eye view of the SOG-filled LED nanopillars with the P-type GaN layer exposed by reverse etching, as shown in Example 1.

[0046] Figure 6 This is a photograph of the flexible LED nanopillar film of Example 1.

[0047] Figure 7 This is a display diagram of the flexible LED film after bonding in Example 1.

[0048] Figure 8 The image shows the IV electrical characteristic curve of the pixel unit obtained in Example 1.

[0049] Figure 9 The electroluminescence spectra of the pixel unit obtained in Example 1 under different currents are shown. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] like Figure 1 As shown in the structure, the specific steps of achieving high-resolution display using flexible nanopillar films in this invention include:

[0053] 1) Clean the Si substrate sequentially with acetone, alcohol and water using ultrasonic cleaning for 5 min, then clean it in BOE for 5 min.

[0054] 2) Place the Si substrate in MOCVD and grow N-type GaN, InGaN / GaN quantum well and P-type GaN respectively at a temperature of 760℃~1200℃ using TMGa as Ga source, TMIn as In source, NH3 as N source, SiH4 as Si source and Mg dicerocene as Mg source to form LED structures.

[0055] 3) Nanopillars were formed using nanoimprinting and ICP etching. A Cl2 / BCl3 gas mixture of 48 / 6 ohms was used at a pressure of 6 mtorr and a power of 30 / 200 ohms for both nanoimprinting and dry etching. The etching time was calculated based on the required nanopillar height, and etching was required up to the N-type GaN layer. The SEM images of the obtained samples are shown below. Figure 2-4 As shown (in this embodiment, the etching time is 8 minutes. The nanopillar depth is 2.3 micrometers);

[0056] 4) SOG was spin-coated onto the surface of the nanopillars using a spin-coating method. The SOG adhesive was spun at 4000 rpm for 30 seconds, filling the gaps between the nanopillars. The nanopillars were then baked at 180°C for 24 hours. Dry etching was performed using RIE (Reverse Etching) at CF430 sccm, 4 Pa ​​pressure, and 120 W power. The etching time was calculated based on the thickness of the SOG film at the top of the nanopillars. Excess silicon oxide film at the top of the nanopillars was removed, exposing the p-type GaN layer. The resulting SEM image is shown below. Figure 5 As shown (in this implementation example, the etching time is 3 minutes and 30 seconds);

[0057] 5) P-type metal (Ni / Au, 100 / 500nm) is deposited on the P-type GaN side of the nanopillar by magnetron sputtering, and annealing is performed to form an ohmic contact (baking at 570℃ for 5 minutes in air atmosphere) to form a metal film. The metal film is connected to the exposed P-type GaN layer (in this embodiment, the annealing equipment is Aowei AW410 model).

[0058] 6) Spin-coat PI adhesive onto the metal film to form a flexible temporary substrate at 3000 rpm for 40 seconds. The PI adhesive thickness is approximately 5 micrometers. Then bake on a hot plate at 100°C for 30 minutes, 160°C for 30 minutes, and 230°C for 30 minutes to form a PI film. (See photograph). Figure 6 As shown;

[0059] 7) Soak in a solution of HF:HNO3:H2O = 1:1:1 at room temperature for 30 minutes, then rinse with water and dry with a nitrogen gun;

[0060] 8) The excess GaN layer at the bottom of the nanopillar is removed by ICP dry etching. Cl2 / BCl3 gas: 48 / 6 sccm, gas pressure 6 mtorr, power 30 / 200W. The etching time is calculated based on the residual thickness at the bottom of the nanopillar (in this implementation case, the ICP etching time is 5 minutes and 30 seconds).

[0061] 9) Perform flip-chip bonding of the flexible nanopillar film to the prepared driving circuit substrate. Solder: In, thickness 3-4 micrometers, heating conditions: 150℃ for 1 minute, then increase to 220℃ for 3 minutes and 30 seconds, pressure 5-10N; 10) Immerse in a 1:1 alkaline solution of KOH or NaOH for 30 minutes to remove the PI substrate. The display image after flexible film bonding is shown below. Figure 7 As shown.

[0062] Figure 8 This is the IV electrical characteristic curve of a pixel unit controlled by an In electrode, from Figure 8 It can be seen that the pixel unit turns on at approximately 2.4V, and the reverse leakage current is less than 0.1nA.

[0063] Figure 9 It is an electroluminescence spectrum of a pixel unit controlled by an In electrode under different currents, with the emission peak at a wavelength of 453nm.

[0064] The metal thin film can be replaced with an ITO transparent electrode, in which case the flexible temporary substrate does not need to be removed.

[0065] The substrate can also be replaced with a sapphire substrate. When using a sapphire substrate, the nanopillars must be etched down to the sapphire substrate and the sapphire substrate is removed by laser lift-off, so that the bottoms of the nanopillars are separated from each other.

Claims

1. A method for fabricating a high-resolution nanopixel display array using flexible nanopillar films, characterized in that... The specific steps are as follows: (1) Clean the Si substrate; (2) Growth of GaN-based LED structures on a substrate; (3) A nanopillar array with a depth of N-type GaN layer was etched on the GaN-based LED structure; (4) Fill the space between the nanopillars with a dielectric film to achieve electrical isolation between the nanopillars; (5) Etch the dielectric film at the top of the nanopillar to expose the P-type GaN layer of the nanopillar; (6) Deposit metal electrodes or ITO transparent electrodes on the top of the nanopillars to make the nanopillars have common P electrodes in parallel. (7) A flexible thin film is spin-coated onto the metal electrode to form a flexible temporary substrate; (8) Remove the original Si substrate; (9) Remove the bottom of the nanopillars down to the N-type GaN layer to separate the bottoms of the nanopillars from each other, while the nanopillars still retain part of the N-type GaN layer, to obtain a flexible nanopillar film. (10) The N-layer GaN surface of the flexible nanopillar film is flip-chip bonded to the driving circuit substrate with In electrode, so that each In electrode can contact several nanopillars to obtain a high-resolution nanopixel display array.

2. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 1, characterized in that: In step (2), the GaN-based LED structure includes, from bottom to top, an N-type GaN layer, an InGaN / GaN quantum well layer, and a P-type GaN layer.

3. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 1, characterized in that: It also includes step (11): when the P electrode is a metal thin film, remove the flexible temporary substrate.

4. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 1, characterized in that: In step (4), SOG is spin-coated to fill the space between the nanopillars as a dielectric film.

5. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 1, characterized in that: In step (6), a P-type metal thin film is deposited on the P-type GaN side of the nanopillar, and the metal thin film contacts the exposed P-type GaN layer, and annealing is performed to form an ohmic contact.

6. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 1, characterized in that: In step (7), PI adhesive is spin-coated onto the metal thin film to form a flexible temporary substrate.

7. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 3, characterized in that: In step (8), the device is immersed in a solution of HF:HNO3:H2O = 1:1:1 to remove the Si substrate.

8. A method for fabricating a high-resolution nanopixel display array using flexible nanopillar films, characterized in that... The specific steps are as follows: (1) Clean the sapphire substrate; (2) Growth of GaN-based LED structures on a substrate; (3) A nanopillar array extending deep into a sapphire substrate was etched onto a GaN-based LED structure; (4) Fill the space between the nanopillars with a dielectric film to achieve electrical isolation between the nanopillars; (5) Etch the dielectric film at the top of the nanopillar to expose the P-type GaN layer of the nanopillar; (6) Deposit metal electrodes or ITO transparent electrodes on the top of the nanopillars to make the nanopillars have common P electrodes in parallel. (7) A flexible thin film is spin-coated onto the metal electrode to form a flexible temporary substrate; (8) The original sapphire substrate is removed by laser lift-off method, so that the bottom of the nanopillars are separated from each other, and the nanopillars still retain part of the N-type GaN layer, thus obtaining a flexible nanopillar film. (9) The N-layer GaN surface of the flexible nanopillar film is flip-chip bonded to the driving circuit substrate with In electrode, so that each In electrode can contact several nanopillars to obtain a high-resolution nanopixel display array.

9. The method for preparing a high-resolution nanopixel display array using flexible nanopillar films according to claim 8, characterized in that: It also includes step (10): when the P electrode is a metal thin film, remove the flexible temporary substrate.

Images