Gallium nitride thin film-based micro-display module integration device

Abstract

This application discloses a micro-display module integration device based on gallium nitride (GaN) thin film. The device comprises a composite substrate consisting of a substrate and a gradient buffer layer. The gradient buffer layer adopts a structure of at least two sub-layers stacked sequentially, and the material composition of each sub-layer changes in a stepwise manner away from the substrate to match the lattice constant of GaN. This stepwise gradient buffer layer structure can form a gradual transition of lattice constant between the substrate and the GaN functional thin film, gradually reducing the lattice difference between the substrate and GaN, thereby significantly reducing the stress caused by lattice mismatch. At the same time, the gradient buffer layer can effectively alleviate the mismatch problem, greatly reducing defects such as dislocations and stress inside the GaN functional thin film grown on its surface, improving the crystal quality of the GaN functional thin film, and thus helping to improve the luminous efficiency, brightness, reliability and other performance of the micro-display chip.

Description

Technical Field

[0001] This application relates to the field of display device technology, specifically to a micro-display module integration device based on gallium nitride thin film. Background Technology

[0002] In the current display technology field, with the rapid rise of emerging applications such as virtual reality (VR), augmented reality (AR), and wearable devices, increasingly higher demands are being placed on the performance of microdisplay modules. Traditional display technologies, such as liquid crystal displays (LCDs) and organic light-emitting diode (OLEDs), are gradually revealing many limitations when dealing with these emerging applications, such as insufficient brightness, slow response speed, and high power consumption. Therefore, developing new high-performance microdisplay technologies has become an urgent need for industry development. Gallium nitride (GaN), as a representative of third-generation semiconductor materials, possesses a series of excellent physical properties, including a large bandgap, high thermal conductivity, strong breakdown electric field, and fast saturated electron drift velocity. Compared with traditional display technologies, GaN-based microdisplay chips offer significant advantages such as high luminous efficiency, high brightness, fast response time, and long lifespan, better meeting the stringent display performance requirements of applications like VR and AR.

[0003] Currently, the common method for growing gallium nitride (GaN) thin-film-based micro-display modules is epitaxial growth on heterogeneous substrates using metal-organic chemical vapor deposition (MOCVD). Commonly used heterogeneous substrates include sapphire (Al₂O₃), silicon carbide (SiC), and silicon (Si). However, due to the significant lattice and thermal mismatch between the heterogeneous substrate and GaN, a large number of dislocations, stresses, and other defects are easily generated within the GaN thin film during growth. This not only affects the crystal quality of the GaN thin film but also reduces the luminous efficiency and reliability of the micro-display chip.

[0004] Therefore, how to alleviate the mismatch between heterostructures and gallium nitride is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a micro-display module integration device based on gallium nitride thin film.

[0006] This application provides a micro-display module integration device based on gallium nitride thin film, including: A composite substrate comprising: a substrate and a gradient buffer layer; wherein the gradient buffer layer is composed of at least two sublayers stacked sequentially, and the material composition of each sublayer changes in a stepwise manner along a direction away from the substrate to match the lattice constant of gallium nitride; A gallium nitride functional thin film, wherein the gallium nitride functional thin film is grown on the surface of the gradient buffer layer; The display driving layer is electrically connected to the gallium nitride functional thin film.

[0007] In one embodiment, the relationship between the number N of sublayers of the gradient buffer layer and the lattice mismatch δ between the substrate and gallium nitride satisfies: When δ≤5%, N=2; When 5% < δ ≤ 10%, N = 3; When 10% < δ ≤ 15%, N = 4; When δ > 15%, N = 5.

[0008] In one embodiment, the material composition of each sublayer varies independently and the composition difference between adjacent sublayers is ≤10%.

[0009] In one embodiment, the composition difference ΔC between adjacent sublayers is related to the lattice mismatch δ by the following condition: ΔC = δ / N × A, where A is a constant of 0.8-1.2.

[0010] In one embodiment, the substrate is sapphire, and when 5% < δ ≤ 10%, the gradient buffer layer includes a first sublayer, a second sublayer, and a third sublayer stacked sequentially. The first sublayer, located near the substrate, is made of aluminum gallium nitride with an aluminum content of 40%-60%; the second sublayer is made of aluminum gallium nitride with an aluminum content of 20%-40%; and the third sublayer, located near the gallium nitride functional film, is made of aluminum gallium nitride with an aluminum content of 0%-20%.

[0011] In one embodiment, the thickness of the first sublayer is 200nm-400nm, the thickness of the second sublayer is 300nm-500nm, the thickness of the third sublayer is 200nm-400nm, and the thickness ratio of each sublayer is 1:(1.2 to 1.5):1.

[0012] In one embodiment, a first transition interface is provided between the first sublayer and the second sublayer, and the component change rate at the first transition interface is ≤0.02% / nm; A second transition interface is provided between the second sublayer and the third sublayer, and the component change rate at the second transition interface is ≤0.01% / nm.

[0013] In one embodiment, the thickness of the first transition interface is 5nm-15nm, the thickness of the second transition interface is 10nm-20nm, and the thickness of the transition interface increases in the direction away from the substrate.

[0014] In one embodiment, both the first and second transition interfaces contain oxygen, with an atomic percentage of 0.5%-2%, and the oxygen content decreases symmetrically from the center of the transition interface to both sides.

[0015] In one embodiment, the doping element of the first sub-layer is silicon, with a doping concentration of 1×10⁻⁶. 18 cm -3 Up to 5×10 18 cm -3 The third sublayer is doped with magnesium at a concentration of 5 × 10⁻⁶. 17 cm -3 Up to 1×10 18 cm -3 The second sublayer is an undoped structure.

[0016] This application provides a micro-display module integration device based on gallium nitride (GaN) thin films. The device utilizes a composite substrate consisting of a substrate and a gradient buffer layer. The gradient buffer layer employs a structure with at least two sub-layers stacked sequentially, and the material composition of each sub-layer exhibits a step-like gradient away from the substrate to match the lattice constant of GaN. This step-like gradient buffer layer structure creates a gradual transition in lattice constant between the substrate and the GaN functional thin film, progressively reducing the lattice difference between them and significantly decreasing stress caused by lattice mismatch. Simultaneously, this structure also alleviates thermal mismatch between the substrate and GaN to some extent, reducing stress accumulation due to temperature changes. The gradient buffer layer effectively mitigates mismatch problems, significantly reducing defects such as dislocations and stress within the GaN functional thin film grown on its surface, improving the crystal quality of the GaN functional thin film, and thus contributing to improved luminous efficiency, brightness, and reliability of the micro-display chip.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A schematic diagram of the structure of the gallium nitride thin film-based micro-display module integration device provided in the embodiments of this application is shown. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the accompanying drawings and embodiments. Although the embodiments of this application provide method operation instruction steps as shown in the following embodiments or drawings, more or fewer operation instruction steps may be included in the method based on conventional or non-inventive effort. In steps where there is no logically necessary causal relationship, the execution order of these steps is not limited to the execution order provided in the embodiments of this application. In actual processing or when the device executes, the method may be executed sequentially or in parallel according to the method shown in the embodiments or drawings.

[0021] Example 1: This embodiment proposes a micro-display module integration device based on gallium nitride thin film. Please refer to [link / reference]. Figure 1 , Figure 1 A schematic diagram of the structure of the gallium nitride thin film-based micro-display module integration device provided in this embodiment is shown. Figure 1 As shown, the device mainly includes three functional components: a composite substrate, a gallium nitride functional thin film, and a display driving layer.

[0022] The composite substrate includes a substrate and a gradient buffer layer. The substrate serves as a supporting base, providing structural support for the entire device. In this embodiment, the substrate material is not limited and can be selected from materials such as sapphire (Al2O3), silicon carbide (SiC), and silicon (Si).

[0023] The gradient buffer layer, serving as a transition structure between the substrate and the gallium nitride (GaN) functional thin film, is composed of at least two sublayers stacked sequentially. Along the direction away from the substrate, the material composition of each sublayer changes in a stepwise manner to match the lattice constant of GaN. The gradient buffer layer does not use a single, uniform material composition; instead, it combines multiple sublayers to allow the material composition to gradually change from the side closest to the substrate in a stepwise manner, ultimately approaching the lattice constant of GaN. This creates a gradual transition bridge in lattice constant between the substrate and the GaN functional thin film. The specific number of sublayers and the material composition of each sublayer are not limited in this embodiment and need to be set according to different substrate material types.

[0024] On the one hand, the stepped composition gradient of multiple sublayers can effectively reduce the lattice difference between the substrate and gallium nitride, avoiding severe stress concentration at the interface due to excessive lattice mismatch. This significantly reduces the probability of defects such as dislocations and cracks during the growth of gallium nitride functional films, thus improving the crystal quality of the gallium nitride functional films. On the other hand, this stepped gradient structure can also alleviate the thermal mismatch problem between the substrate and gallium nitride to a certain extent. Through the synergistic effect of each sublayer, the thermal stress generated by temperature changes is dispersed, reducing the adverse effects of thermal stress on the stability of the gallium nitride functional film and the entire device structure. This provides a reliable foundation for the high performance of subsequent micro-display chips, helping to improve the luminous efficiency, reliability, and lifespan of the entire micro-display module integrated device, making it better able to meet the high display performance requirements of emerging applications such as virtual reality and augmented reality.

[0025] Gallium nitride (GaN) functional thin films are grown on a gradient buffer layer, directly on the side of the gradient buffer layer away from the substrate. Because the gradient buffer layer achieves a gradual matching with the lattice constant of GaN through stepwise compositional changes, its surface lattice structure more closely resembles the lattice characteristics of GaN. This allows the GaN functional thin film to nucleate and grow with a more favorable crystal orientation during growth, reducing crystal defects caused by lattice mismatch. Simultaneously, the thermal mismatch problem alleviated by the gradient buffer layer provides a stable thermal environment for the growth of GaN functional thin films, preventing a decline in film growth quality due to temperature stress, thereby ensuring that the GaN functional thin film possesses excellent physical and optical properties.

[0026] The display driving layer is a functional layer used to drive gallium nitride (GaN) functional thin films to complete display operations. Its core function is to receive external control signals (such as image signals, timing signals, etc.) and convert these signals into electrical signals that can drive the GaN functional thin film to work, thereby realizing image display. The display driving layer typically includes the following parts: First, a driving circuit, composed of electronic components such as transistors (such as thin-film transistors, TFTs) and capacitors, which can realize functions such as signal amplification, conversion, and storage, and provide a stable driving current or voltage for the GaN functional thin film; Second, an electrode system, including lead-out electrodes electrically connected to the GaN functional thin film and connection electrodes inside the driving circuit, used to realize the transmission of electrical signals; Third, a timing control module, used to receive external timing signals, coordinate the working timing of various electronic components in the driving circuit, ensure that the GaN functional thin film can complete the light-emitting action according to the preset rhythm, and ensure the stability and continuity of the displayed image. In this embodiment, the specific types of devices included in the display driving layer are not limited, but only the above-mentioned functional parts are used as examples.

[0027] The display driver layer, as the core component controlling the display function of the gallium nitride (GaN) functional thin film, establishes an electrical connection with the GaN functional thin film through conductive structures (such as metal wires and electrodes). It can transmit electrical signals to the GaN functional thin film to regulate its luminescence state (such as brightness, luminous area, and luminous time). Specific electrical connection methods can be found in related technologies and are not limited here. For example, bonding connections can be used, directly connecting the electrodes of the display driver layer to the lead-out electrodes of the GaN functional thin film through gold wire bonding, copper pillar bonding, etc., using metal bonding wires or bonding pillars to conduct electrical signals. Alternatively, flip-chip bonding can be used, where the electrodes of the display driver layer and the GaN functional thin film are soldered together using solder (such as tin-lead solder, lead-free solder, etc.) to form a tight electrical path. Further details will not be elaborated here.

[0028] Based on the above description, the gallium nitride (GaN) thin film-based micro-display module integration device provided in this embodiment utilizes a composite substrate composed of a substrate and a gradient buffer layer. The gradient buffer layer employs a structure with at least two sub-layers stacked sequentially, and the material composition of each sub-layer exhibits a step-like gradient away from the substrate to match the lattice constant of gallium nitride. This step-like gradient buffer layer structure creates a gradual transition in lattice constant between the substrate and the GaN functional thin film, progressively reducing the lattice difference between the substrate and GaN, thereby significantly reducing stress caused by lattice mismatch. Simultaneously, this structure can also alleviate the thermal mismatch problem between the substrate and GaN to some extent, reducing stress accumulation caused by temperature changes. The gradient buffer layer effectively alleviates the mismatch problem, significantly reducing defects such as dislocations and stress within the GaN functional thin film grown on its surface, improving the crystal quality of the GaN functional thin film, and thus contributing to improved luminous efficiency, brightness, reliability, and other performance characteristics of the micro-display chip.

[0029] Example 2: Since the lattice mismatch between the substrate and gallium nitride directly affects the stress between them and the growth quality of gallium nitride functional films, and different substrates have different degrees of lattice mismatch with gallium nitride, in order to adapt to different application scenarios and provide reliable assurance for the stable growth of gallium nitride functional films, this embodiment proposes a sublayer setting method for a gradient buffer layer.

[0030] Specifically, the relationship between the number of sublayers N of the gradient buffer layer and the lattice mismatch δ between the substrate and gallium nitride satisfies: When δ≤5%, N=2; When 5% < δ ≤ 10%, N = 3; When 10% < δ ≤ 15%, N = 4; When δ > 15%, N = 5.

[0031] When the lattice mismatch is small, the lattice difference between the substrate and gallium nitride is relatively small, and only a few sublayers are needed to achieve an effective transition of the lattice constant through a step-by-step transition. However, when the lattice mismatch is large, the lattice difference between the substrate and gallium nitride is significant, requiring more sublayers to refine the step-by-step transition process, gradually reducing the lattice difference and avoiding excessive stress due to too rapid a transition. The sublayer setting method provided in this embodiment sets different numbers of sublayers according to the different lattice mismatches between the substrate and gallium nitride. The smaller the lattice mismatch, the fewer the number of sublayers; the larger the lattice mismatch, the more sublayers, thus forming a sublayer number configuration adapted to the lattice mismatch.

[0032] By dynamically adjusting the number of sublayers based on the lattice mismatch, precise design of the gradient buffer layer structure can be achieved. This ensures effective mitigation of lattice mismatch while avoiding the increased process complexity and cost caused by too many sublayers, or insufficient stress relief caused by too few sublayers, thus optimizing resource allocation. Furthermore, this targeted sublayer number configuration allows the compositional gradient of each sublayer to closely match the actual lattice differences, further reducing stress concentration at the interface, minimizing defects such as dislocations and cracks in gallium nitride functional films, and improving their crystal quality. Simultaneously, this method enhances the adaptability of the gradient buffer layer to different substrate types. Regardless of the degree of lattice mismatch between the substrate and gallium nitride, a smooth lattice transition can be achieved through the corresponding sublayer number setting, providing a reliable guarantee for the stable growth of gallium nitride functional films. This contributes to improving the performance stability and reliability of the entire micro-display module integration device, better meeting the needs of various application scenarios.

[0033] To flexibly address the lattice differences between different substrates and gallium nitride (GaN), the material composition of each sublayer in the gradient buffer layer can be designed and adjusted individually according to actual needs, without being limited by the composition of other sublayers. Furthermore, the difference in material composition between any two adjacent sublayers is controlled within 10%. This independent variation in the composition of each sublayer endows the gradient buffer layer structure with flexibility and adaptability, enabling it to adapt to various substrate types and expanding the application range of the device. Limiting the composition difference between adjacent sublayers effectively reduces interfacial stress, decreases the generation and propagation of defects such as dislocations and cracks between sublayers, and improves the overall structural stability of the gradient buffer layer. Through this precise composition control, lattice matching between the substrate and GaN can be achieved more efficiently, providing a superior interfacial environment for the high-quality growth of GaN functional thin films.

[0034] To further achieve a precise correlation between the composition difference between adjacent sublayers and the lattice mismatch and the number of sublayers, the composition difference ΔC between any two adjacent sublayers in the gradient buffer layer can be determined by the lattice mismatch δ between the substrate and gallium nitride and the number of sublayers N. Specifically, ΔC = δ / N × A, where A is a constant between 0.8 and 1.2. By establishing a clear quantitative formula and constant range to define the correspondence between the composition difference between adjacent sublayers and the lattice mismatch and the number of sublayers, the gradient buffer layer design is made more precise and standardized. This avoids the blindness of composition difference design and ensures the effectiveness of lattice transition. This precise control of composition difference can further optimize the lattice matching effect, minimize interfacial stress, and reduce defects in gallium nitride functional films. Example 3: Sapphire is chemically stable in high-temperature environments (typically 900-1200℃ for gallium nitride growth) and various reactive gases (such as NH3 and H2), and does not chemically react with epitaxial materials or reaction sources. It also exhibits reliable mechanical properties, high hardness, and optical transmittance, making it a common substrate material for gallium nitride growth. Considering sapphire's primary application as a substrate material, and addressing the relatively common lattice mismatch range of 5% to 10%, this embodiment proposes a specific material configuration for the gradient buffer layer.

[0035] When the substrate is sapphire and the lattice mismatch between the substrate and gallium nitride is in the range of 5% < δ ≤ 10%, the gradient buffer layer is composed of three sub-layers, and all three sub-layers are made of aluminum gallium nitride. From the first sub-layer close to the sapphire substrate to the third sub-layer close to the gallium nitride functional film, the aluminum composition is distributed in the range of 40%-60%, 20%-40%, and 0%-20% respectively, showing a step-like gradual change trend of gradually decreasing aluminum composition.

[0036] In this embodiment, aluminum gallium nitride (AlGaN) is selected as the sublayer material. The lattice constant can be effectively adjusted by varying its aluminum composition. The lattice constant of AlGaN increases with increasing aluminum composition (aluminum atoms have a larger atomic radius than gallium atoms). By decreasing it in a stepwise manner from 40%-60% → 20%-40% → 0%-20%, the lattice constant of each sublayer can gradually transition from being close to that of the sapphire substrate (with a larger lattice constant) to being close to that of gallium nitride (with a smaller lattice constant). This gradient design can disperse the total lattice mismatch (5% < δ ≤ 10%) between sapphire and gallium nitride across the three sublayer interfaces. The local mismatch at each interface is controlled within 3%-5%, avoiding stress concentration at a single interface and significantly reducing dislocation density.

[0037] The core function of the gradient buffer layer is to alleviate the lattice mismatch stress between the sapphire substrate and the gallium nitride functional film. To ensure the comprehensive optimization of stress release, crystal quality control, and film growth stability of the gradient buffer layer, in addition to material selection, stress gradient dispersion can be further achieved by adjusting the thickness of each sublayer. Specifically, one possible sublayer thickness setting is as follows: the thickness of the first sublayer is 200nm-400nm, the thickness of the second sublayer is 300nm-500nm, and the thickness of the third sublayer is 200nm-400nm, with a thickness ratio of 1:(1.2 to 1.5):1.

[0038] The first sublayer, close to the substrate, bears the main initial stress buffer. Its thickness of 200nm-400nm ensures a stable lattice anchor at the sapphire interface, avoiding stress concentration due to excessive thinness. The second sublayer, as an intermediate transition layer, has a thickness of 300nm-500nm (20%-50% thicker than the first and third sublayers) to further disperse residual stress and reduce dislocation multiplication by increasing the fault tolerance space for crystal growth. The thickness of the third sublayer returns to 200nm-400nm, which can achieve precise stress convergence when approaching the gallium nitride functional film, avoiding a decrease in compositional uniformity due to excessive thickness.

[0039] While lattice mismatch can be mitigated simply by varying the composition, it may not be possible to control the electrical properties of the gradient buffer layer. To enable the gradient buffer layer to not only provide stress buffering but also optimize the electrical conductivity of the entire device, targeted doping can be applied to each sublayer to provide a suitable electrical environment for the electrical connection between the gallium nitride functional film and the display driving layer. Specifically, one doping configuration and concentration setting is as follows: the dopant element of the first sublayer is silicon, with a doping concentration of 1×10⁻⁶. 18 cm -3 Up to 5×10 18 cm -3 The third sublayer is doped with magnesium at a concentration of 5 × 10⁻⁶. 17 cm -3 Up to 1×10 18 cm -3 The second sublayer is an undoped structure.

[0040] Silicon, as an n-type dopant, can provide free electrons to aluminum gallium nitride, 1×10 18 cm -3 Up to 5×10 18 cm -3 High concentrations of doping can significantly improve the conductivity of the first sublayer, reduce the contact resistance with the sapphire substrate, and at the same time weaken the electrostatic field caused by lattice mismatch through the electron shielding effect, thereby reducing the probability of carrier capture at defects.

[0041] Magnesium, as a p-type dopant, can provide hole carriers, 5 × 10⁻⁶17 cm -3 Up to 1×10 18 cm -3 Medium concentration doping and the common doping range of gallium nitride functional thin films (typically 1 × 10⁻⁶) 17 Up to 5×10 18 cm -3 This design, when matched with the buffer layer, can effectively modulate the interface barrier between the third sublayer and the gallium nitride functional film, promoting the injection of charge carriers from the buffer layer to the functional film.

[0042] Undoped structures can serve as isolation layers between n-type and p-type doped regions, reducing interdiffusion between silicon and magnesium atoms and preventing the formation of compensation centers. Simultaneously, their intrinsic semiconductor properties can mitigate abrupt changes in carrier concentration at both ends of the highly doped regions, reducing uneven current distribution caused by differences in longitudinal resistance. Furthermore, undoped structures have higher crystal quality, further filtering dislocation defects and improving the overall structural integrity of the buffer layer.

[0043] The n-type-intrinsic-p-type doping distribution forms a vertical electrical gradient, which, together with the stepwise gradient of the aluminum composition, creates a synergistic effect of structural and electrical gradients. This design can alleviate lattice mismatch through compositional gradient and achieve efficient carrier transport through doping control, while reducing the driving voltage of the display driving layer, reducing device power consumption, and providing electrical assurance for the high-performance operation of the micro-display module.

[0044] It should be noted that this embodiment only uses sapphire as a substrate. Other materials as substrates can be designed and adjusted accordingly by referring to parameters such as the lattice constant of sapphire, which will not be elaborated here.

[0045] Example 4: Based on Example 3, even if there are compositional differences between adjacent sublayers, if an abrupt interface is formed, stress concentration may still occur due to the sudden change in the crystal structure, becoming a source of defects such as dislocations and cracks. In order to achieve a slow transition of composition, this example proposes to disperse the lattice differences between sublayers over a wider area to avoid excessive local stress, thereby reducing the density of interface defects.

[0046] Specifically, instead of abrupt interfaces between adjacent sublayers, there exists a transition region where the composition changes slowly, namely the first transition interface and the second transition interface. The rate of change of material composition at the first transition interface does not exceed 0.02% per nanometer, and the rate of change of composition at the second transition interface does not exceed 0.01% per nanometer. By limiting the gradient of composition change at the interface, a smooth connection between sublayers is achieved.

[0047] The first transition interface connects the first sublayer with a high aluminum composition (40%-60%) to the second sublayer with a medium aluminum composition (20%-40%). The composition difference between the two is relatively large (about 20%), and a slightly higher rate of change (≤0.02% / nm) is allowed to achieve an effective transition. The second transition interface connects the second sublayer with a medium aluminum composition (20%-40%) to the third sublayer with a low aluminum composition (0%-20%). It needs to be directly docked with the gallium nitride functional film. Using a lower rate of change (≤0.01% / nm) can further reduce lattice abrupt changes and provide a smoother interface environment for gallium nitride growth.

[0048] Furthermore, to ensure effective transition of components between sublayers while avoiding expansion of high-aluminum component regions due to excessive thickness, this embodiment proposes a thickness setting for the transition interface. Specifically, the thickness of the first transition interface is 5nm-15nm, the thickness of the second transition interface is 10nm-20nm, and the thickness of the transition interface increases in the direction away from the substrate.

[0049] The first transition interface (with a thickness range of 5nm-15nm) can effectively transition the composition between the first sublayer (aluminum composition 40%-60%) and the second sublayer (aluminum composition 20%-40%), while avoiding the expansion of the high-aluminum composition region due to excessive thickness (which may increase thermal mismatch with the substrate). When the thickness is controlled within 5nm-15nm, the dislocation density of the first transition interface can be controlled below 2×10⁸ cm⁻², which is more than 40% lower than that of the structure without a transition interface.

[0050] The second transition interface (10nm-20nm) is relatively thick, which is compatible with the characteristics of the low aluminum composition (0%-20%) of the third sublayer, enabling a more complete transition to the gallium nitride lattice. The 10nm-20nm thickness allows the composition change rate of the second transition interface to be stably controlled at ≤0.01% / nm, ensuring the formation of a nearly continuous lattice structure with the gallium nitride functional thin film.

[0051] The increasing trend from 5nm-15nm to 10nm-20nm synergizes with the gradual change in aluminum composition from high to low, allowing the adjustment rhythm of the lattice constant to gradually match the stress release requirements, thus avoiding the local stress accumulation that may be caused by a single thickness design.

[0052] To optimize the crystal structure and stress state of the transition interface, this embodiment further proposes to introduce oxygen as a dopant in the materials of both the first and second transition interfaces, with the atomic percentage of oxygen controlled within the range of 0.5% to 2%. At the same time, the oxygen content exhibits a specific spatial distribution pattern, with the peak value at the geometric center of the transition interface and gradually decreasing towards the adjacent sublayers on both sides, forming a symmetrical concentration gradient distribution.

[0053] Oxygen atoms have a radius (approximately 0.074 nm) between that of aluminum (0.143 nm) and gallium (0.122 nm). By filling the lattice gaps through interstitial doping or substitutional doping (replacing some nitrogen atoms), the lattice mismatch stress caused by the compositional differences between adjacent sublayers can be alleviated. In addition, oxygen has a chemical affinity with oxygen atoms in the sapphire substrate, which can enhance the interfacial bonding force between the transition interface and the substrate and reduce the risk of interfacial peeling.

[0054] By controlling the atomic percentage of oxygen within the range of 0.5% to 2%, it can effectively fill the interstitial spaces in the crystal lattice while avoiding the formation of oxygen donor defects or oxygen-vacancy complexes, which would lead to enhanced carrier scattering and reduced electrical conductivity at the transition interface.

[0055] Meanwhile, the oxygen content decreases symmetrically from the center of the transition interface to both sides. The higher oxygen content in the central region can effectively alleviate the lattice mismatch in the core area of ​​the interface, while the gradually decreasing concentration towards the two sub-layers can reduce interference with the original composition and electrical properties of the adjacent sub-layers. This results in a balanced adaptation of oxygen to the sub-layers on both sides of the interface.

[0056] This embodiment further optimizes the stepped gradient structure of the gradient buffer layer. By refining the component transition characteristics at the interface, it minimizes stress concentration and defect transmission between sublayers, providing a more reliable structural basis for the high-quality growth of gallium nitride functional films.

[0057] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the foregoing disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A micro-display module integration device based on gallium nitride thin film, characterized in that, include: A composite substrate comprising: a substrate and a gradient buffer layer; wherein the gradient buffer layer is composed of at least two sublayers stacked sequentially, and the material composition of each sublayer changes in a stepwise manner along a direction away from the substrate to match the lattice constant of gallium nitride; A gallium nitride functional thin film, wherein the gallium nitride functional thin film is grown on the surface of the gradient buffer layer; The display driving layer is electrically connected to the gallium nitride functional thin film.

2. The apparatus as claimed in claim 1, characterized in that, The relationship between the number N of the gradient buffer layer and the lattice mismatch δ between the substrate and gallium nitride satisfies: When δ≤5%, N=2; When 5% < δ ≤ 10%, N = 3; When 10% < δ ≤ 15%, N = 4; When δ > 15%, N = 5.

3. The apparatus as described in claim 2, characterized in that, The material composition of each sublayer varies independently and the composition difference between adjacent sublayers is ≤10%.

4. The apparatus as described in claim 3, characterized in that, The composition difference ΔC between adjacent sublayers is related to the lattice mismatch δ by the following condition: ΔC = δ / N × A, where A is a constant of 0.8-1.

2.

5. The apparatus as described in claim 2, characterized in that, The substrate is sapphire, and when 5% < δ ≤ 10%, the gradient buffer layer includes a first sublayer, a second sublayer, and a third sublayer stacked sequentially. The first sublayer, located near the substrate, is made of aluminum gallium nitride with an aluminum content of 40%-60%; the second sublayer is made of aluminum gallium nitride with an aluminum content of 20%-40%; and the third sublayer, located near the gallium nitride functional film, is made of aluminum gallium nitride with an aluminum content of 0%-20%.

6. The apparatus as claimed in claim 5, characterized in that, The thickness of the first sublayer is 200nm-400nm, the thickness of the second sublayer is 300nm-500nm, the thickness of the third sublayer is 200nm-400nm, and the thickness ratio of each sublayer is 1:(1.2 to 1.5):

1.

7. The apparatus as claimed in claim 5, characterized in that, A first transition interface is provided between the first sublayer and the second sublayer, and the component change rate at the first transition interface is ≤0.02% / nm; A second transition interface is provided between the second sublayer and the third sublayer, and the component change rate at the second transition interface is ≤0.01% / nm.

8. The apparatus as claimed in claim 7, characterized in that, The thickness of the first transition interface is 5nm-15nm, the thickness of the second transition interface is 10nm-20nm, and the thickness of the transition interface increases in the direction away from the substrate.

9. The apparatus as claimed in claim 7, characterized in that, Both the first and second transition interfaces contain oxygen, with an atomic percentage of 0.5%-2%, and the oxygen content decreases symmetrically from the center of the transition interface to both sides.

10. The apparatus as claimed in claim 5, characterized in that, The first sublayer is doped with silicon at a concentration of 1×10⁻⁶. 18 cm -3 Up to 5×10 18 cm -3 The third sublayer is doped with magnesium at a concentration of 5 × 10⁻⁶. 17 cm -3 Up to 1×10 18 cm -3 The second sublayer is an undoped structure.

Images