Low-stress al2o3 / yag transparent ceramic gradient film, preparation method and application
By depositing Al2O3/YAG transparent ceramic gradient films on sapphire substrates and utilizing magnetron sputtering and high-temperature sintering techniques, the problem of thermal stress concentration caused by the discontinuity of thermal expansion coefficients was solved, resulting in gradient films with high optical transmittance and strong adhesion, suitable for applications such as optical and high-temperature protective coatings.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF TECH
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-12
AI Technical Summary
Existing technologies struggle to effectively mitigate thermal stress concentration caused by discontinuous coefficients of thermal expansion while maintaining high optical transmittance, and the application of traditional gradient films in the optical field is limited.
Al2O3/YAG transparent ceramic gradient films were deposited on sapphire substrates using magnetron sputtering and high-temperature sintering techniques. By controlling the Y element content to gradually increase along the direction away from the substrate, a gradient film with a continuously changing coefficient of thermal expansion was formed. The combination of magnetron sputtering and high-temperature sintering enabled interdiffusion and reaction between the layers.
It achieves continuous variation of thermal expansion coefficient under low stress, suppresses interface cracking, maintains high optical transmittance, and improves the adhesion strength between the film and the substrate, making it suitable for high-performance optical components and high-temperature protective coatings.
Smart Images
Figure CN122187516A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of gradient film technology, specifically to a low-stress Al2O3 / YAG transparent ceramic gradient film, its preparation method, and its application. Background Technology
[0002] Multilayer gradient thin films, by creating a stepwise change in material composition and properties along the thickness direction, have demonstrated significant application value in multiple technological fields. For example, in high-temperature protective coatings, multilayer gradient structures can be used to adjust the matching of thermal expansion coefficients, improving the coating's thermal shock resistance and service life; in the field of optical thin films, gradient refractive index design helps reduce interface reflection, enhance transmittance, and improve the stability of the thin film under thermal effects; in electronic packaging, sensors, and energy devices, gradient layers are also frequently used to alleviate thermal stress and interface mismatch problems during the integration of heterogeneous materials, thereby improving the reliability and performance of the devices.
[0003] Currently, there are some studies on gradient films or stress buffer layers. For example, Chinese invention patent CN118390159A discloses a "method for preparing low-stress, high-quality AlN thin films," which uses the discontinuity of the physical structure to reduce dislocation density and disperse stress by sputtering AlN thin films with spaced holes and high / low distribution characteristics on a sapphire substrate. However, this stress buffering mechanism relies on abrupt changes and discontinuities in the microstructure, which may lead to stress reconcentration at the edges of holes or the roots of protrusions. Furthermore, its complex structure has an adverse effect on light transmittance, making it unsuitable for components or optical interfaces requiring high optical transmittance. Another example is Chinese invention patent CN118308699A, which discloses a "method for preparing ultra-low-stress metal thin films," which uses mixed magnetron sputtering power to deposit multiple nano-monometallic transition layers to disperse thermal stress and reduce residual stress. Although the technology smooths the stress gradient to some extent through multi-layer design, the internal composition of each layer is uniform, and there are still clear interfaces between layers with abrupt changes in the coefficient of thermal expansion. The stress buffering capacity is limited by the limited number of interfaces, and the inherent opacity of the metal material makes it completely unsuitable for optical applications that require light transmission.
[0004] In summary, there is currently a lack of thin films and their preparation methods that can solve the problem of thermal stress concentration caused by discontinuous coefficients of thermal expansion while also possessing high optical transmittance. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a low-stress Al2O3 / YAG transparent ceramic gradient film, its preparation method, and its applications.
[0006] This invention discloses a low-stress Al2O3 / YAG transparent ceramic gradient film, wherein the Al2O3 / YAG transparent ceramic gradient film is deposited on a sapphire substrate, and the content of yttrium (Y) in the Al2O3 / YAG transparent ceramic gradient film gradually increases in the direction away from the sapphire substrate.
[0007] As a further improvement of the present invention, the total thickness of the Al2O3 / YAG transparent ceramic gradient film is 140-630 nm.
[0008] This invention discloses a method for preparing a low-stress Al2O3 / YAG transparent ceramic gradient film, comprising the following steps: Step 1, Substrate Pretreatment: Cut, polish and clean the sapphire substrate; Step 2, Target and Equipment Preparation: Provide Al2O3 ceramic target and YAG ceramic target, and load the pretreated sapphire substrate into the magnetron sputtering equipment; Step 3, magnetron sputtering gradient film: Under vacuum conditions, by controlling the sputtering process parameters, Al2O3 layer and YAG layer are sequentially and alternately deposited on the sapphire substrate to form a multilayer prefabricated structure; Step 4, High-temperature sintering: The sapphire substrate with the deposited multilayer prefabricated structure is sintered at high temperature in a vacuum or inert atmosphere, so that interdiffusion and reaction occur between the layers, and finally a ceramic gradient film with the proportion of Y2O3 gradually increasing along the direction away from the sapphire substrate is formed.
[0009] As a further improvement of the present invention, in step 2, the Al2O3 ceramic target and the YAG ceramic target are transparent ceramic targets containing sintering aids, wherein the sintering aids include at least one of MgO, SiO2, Y2O3 and La2O3.
[0010] As a further improvement of the present invention, in step 3, the multilayer prefabricated structure consists of a first Al2O3 layer, a first YAG layer, a second Al2O3 layer, and a second YAG layer in sequence; wherein the thickness of the first Al2O3 layer is 10-40 nm, the thickness of the first YAG layer is 20-50 nm, the thickness of the second Al2O3 layer is 10-40 nm, and the thickness of the second YAG layer is 100-500 nm; the magnetron sputtering process parameters are: substrate heating temperature of 150-300℃, sputtering power of 150-250 W, working gas of argon, and working gas pressure of 0.5-3.0 Pa.
[0011] As a further improvement of the present invention, in step 4, the high-temperature sintering temperature is 1200-1800℃ and the holding time is 1-5 hours.
[0012] This invention discloses a sapphire substrate with a ceramic gradient film, wherein the surface of the sapphire substrate has the aforementioned low-stress Al2O3 / YAG transparent ceramic gradient film, which is prepared by the aforementioned preparation method.
[0013] This invention discloses a laser gain medium comprising the aforementioned sapphire substrate.
[0014] This invention discloses a solid-state laser comprising the laser gain medium described above.
[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The Al2O3 / YAG transparent ceramic gradient film of the present invention has excellent optical transmittance and avoids optical loss caused by abrupt changes in refractive index through composition gradient design. Therefore, it can be applied to optical fields such as high-performance laser gain media.
[0016] 2. This invention prepares an Al2O3 / YAG transparent ceramic gradient film by magnetron sputtering and then sintersects it at high temperature to allow interdiffusion and reaction between the layers, ultimately forming a ceramic thin film with a continuously varying coefficient of thermal expansion. This can disperse the abrupt thermal stress at the interface of traditional dissimilar materials into a gradual stress, fundamentally suppressing stress-induced interface cracking.
[0017] 3. This invention employs magnetron sputtering technology combined with sintering, which enables the gradient film to form a good adhesion and diffusion bond with the sapphire substrate, resulting in high interfacial bonding strength.
[0018] 4. The thin film prepared by this invention is particularly suitable for applications with stringent requirements for thermal stress management, optical transmittance and interfacial bonding strength, such as high-performance optical components, semiconductor packaging and high-temperature protective coatings. Attached Figure Description
[0019] Figure 1 This is a graph showing the transmittance of a sapphire substrate to different wavelengths of light, obtained by measuring the transmittance of the film to different wavelengths using a spectrophotometer after a gradient thin film is sputtered onto the substrate by magnetron sputtering.
[0020] Figure 2 The surface profile is obtained by measuring the gradient thin film using a Zygo interferometer after high-temperature sintering at 1200℃-1800℃.
[0021] Figure 3 This is a scanning electron microscope (SEM) image showing the content distribution of Y, Al, and O at different locations along the thickness direction after high-temperature sintering of a gradient thin film.
[0022] Figure 4 These are grain boundary images taken under an optical microscope after the gradient film sample, which was sintered at high temperature using a hot etching method at 1100℃, was treated. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, not all embodiments. 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.
[0024] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a low-stress Al2O3 / YAG transparent ceramic gradient film, wherein the Al2O3 / YAG transparent ceramic gradient film is deposited on a sapphire substrate, and the content of yttrium (Y) in the Al2O3 / YAG transparent ceramic gradient film gradually increases in the direction away from the sapphire substrate; wherein the total thickness of the Al2O3 / YAG transparent ceramic gradient film is 140-630 nm.
[0025] This invention utilizes magnetron sputtering and high-temperature sintering to deposit an Al2O3 / YAG transparent ceramic gradient film on a sapphire substrate. The sapphire single crystal is composed of Al2O3, and selecting Al2O3 as one of the components of the gradient film allows for good lattice matching and chemical compatibility with the substrate, laying the foundation for a strong bond between the film and the substrate. YAG ceramic itself is a compound composed of Y2O3 and Al2O3 (chemical formula 3Y2O3·5Al2O3), sharing the same anionic groups and good chemical compatibility with Al2O3. Therefore, sintering allows yttrium ions in the YAG film and aluminum ions in the Al2O3 film to interdiffuse, resulting in a gradual increase in the Y2O3 content in the Al2O3 / YAG transparent ceramic gradient film away from the substrate.
[0026] The above-described design of the present invention has the dual advantages of achieving thermal stress relief and maintaining optical transparency: In terms of stress relief, this design utilizes the interdiffusion of interfacial atoms to form a transition zone with a slowly changing coefficient of thermal expansion. This transforms the concentrated thermal stress caused by the abrupt change in the coefficient of thermal expansion at the interface into a gradually distributed stress over a wider area, thus solving the problem of thermal stress concentration caused by the discontinuity of the coefficient of thermal expansion in traditional gradient films.
[0027] In terms of optical transparency, both Al₂O₃ and YAG are isotropic transparent ceramic materials with good optical transmittance even before sintering, which lays the foundation for preparing gradient films with low optical loss. After high-temperature sintering, Y³⁺ diffuses into the Al₂O₃ lattice. Since YAG and Al₂O₃ have the same oxygen ion sublattice framework, the diffusion process achieves the gradual substitution of cation lattice sites while maintaining the anionic framework essentially unchanged, without destroying the long-range ordered structure of the material. Therefore, the intrinsic transparency of the film is completely preserved. In addition, sintering further improves the density of the film layer, almost completely eliminating pore scattering. At the same time, the interdiffusion of interfacial atoms transforms the original abrupt interface into a gradient interface with continuously changing composition, thereby eliminating interfacial reflection loss caused by abrupt changes in refractive index.
[0028] The above mechanisms work together to enable the Al2O3 / YAG transparent ceramic gradient film to maintain high optical transmittance, comparable to that of bulk transparent ceramics.
[0029] This invention provides a method for preparing a low-stress Al2O3 / YAG transparent ceramic gradient film, comprising the following steps: Step 1, Substrate pretreatment: The sapphire substrate is cut and polished to make its surface shape accuracy better than λ / 20, where λ=632.8nm, and then it is cleaned to remove surface contaminants; Step 2, Preparation of Sputtering Targets and Equipment: A sputtering target is used to fix the substrate and ensure the uniformity of the coating area; high-purity transparent Al2O3 ceramic targets and transparent YAG ceramic targets are used as sputtering sources, and the pretreated sapphire substrate is placed into the vacuum chamber of the magnetron sputtering equipment; wherein, the Al2O3 ceramic targets and YAG ceramic targets are transparent ceramic targets containing sintering aids, and the sintering aids include at least one of MgO, SiO2, Y2O3 and La2O3; Step 3: Magnetron sputtering gradient film: Under vacuum conditions, controlling the sputtering process parameters, Al2O3 layers and YAG layers are sequentially and alternately deposited on the sapphire substrate to form a multilayer prefabricated structure; wherein the multilayer prefabricated structure consists of a first Al2O3 layer, a first YAG layer, a second Al2O3 layer, and a second YAG layer; wherein the thickness of the first Al2O3 layer is 10-40 nm, the thickness of the first YAG layer is 20-50 nm, the thickness of the second Al2O3 layer is 10-40 nm, and the thickness of the second YAG layer is 100-500 nm, preferably 100-200 nm; the magnetron sputtering process parameters are: substrate heating temperature 150-300℃, sputtering power 150-250 W, working gas argon, and working pressure 0.5-3.0 Pa; Step 4, High-temperature sintering: The sapphire substrate with the deposited multilayer prefabricated structure is sintered at high temperature in a vacuum or inert atmosphere, so that interdiffusion and reaction occur between the layers, and finally a ceramic gradient film with the proportion of Y2O3 gradually increasing along the direction away from the sapphire substrate is formed; wherein, the high-temperature sintering temperature is 1200-1800℃, and the holding time is 1-5 hours.
[0030] The present invention provides a sapphire substrate with a ceramic gradient film, wherein the surface of the sapphire substrate has the aforementioned low-stress Al2O3 / YAG transparent ceramic gradient film, which is prepared by the aforementioned preparation method.
[0031] The present invention provides a laser gain medium comprising the sapphire substrate described above.
[0032] The present invention provides a solid-state laser comprising the laser gain medium described above. Example:
[0033] This embodiment provides a method for preparing an Al2O3 / YAG transparent ceramic gradient film with high optical transmittance, including: S1, Substrate preparation and cleaning: Select a sapphire single crystal substrate with a size of 17mm×17mm, and clean it by ultrasonic cleaning with acetone, ethanol and deionized water for 30 minutes each, and then dry it with nitrogen gas for later use.
[0034] S2, Magnetron Sputtering Deposition: An RF magnetron sputtering system was used, with YAG ceramic targets and Al2O3 ceramic targets (both 76.2 mm in diameter) mounted. Both the YAG and Al2O3 targets were transparent ceramic targets containing sintering aids. The Al2O3 target contained 0.05 wt% MgO, and the YAG target contained 0.1 wt% MgO to suppress abnormal grain growth and improve film density. Under conditions of a substrate temperature of 200℃, sputtering power of 200W, Ar gas flow rate of 50 sccm, and a base vacuum of 1.5 Pa, the following four gradient film structures were deposited sequentially: First layer: Al2O3, approximately 15 nm thick; Second layer: YAG, approximately 30 nm thick; Third layer: Al2O3, approximately 15 nm thick; Fourth layer: YAG, approximately 150 nm thick; Total film thickness approximately 210 nm.
[0035] S3, High-temperature sintering: The prepared gradient film sample is sintered at high temperature. The sample is placed in a tungsten crucible and then placed in a tungsten wire vacuum furnace. At room temperature of 20°C, the temperature is increased to 1200°C-1800°C at a rate of 10°C / min. The temperature is held at this temperature for 120 min, then decreased to 600°C at a rate of 10°C / min, and finally allowed to cool naturally to room temperature.
[0036] Sputtered gradient thin film performance testing: 1. Optical performance testing: After sintering, the sample is visually transparent, the film layer is intact, and there is no peeling or flaking. (See reference...) Figure 1 The transmittance curves of the samples to different wavelengths of light were measured using a spectrophotometer. The results showed that the transmittance of the unsintered samples was 68.32%-87.9% in the wavelength range of 250-2000 nm. After high-temperature sintering at 1200℃-1800℃, the transmittance increased to 81.82%-84.47%. The transmittance after sintering was significantly improved and tended to be stable, which confirmed that the high-temperature sintering treatment eliminated the defects and scattering centers of the film, significantly improved the film quality, and the sintered Al2O3 / YAG transparent ceramic gradient film has excellent optical transparency.
[0037] 2. Surface Shape and Stress Assessment: The surface shape of the sample was tested using a Zygo laser interferometer. (See reference...) Figure 2 The results showed that the surface accuracy (RMS) of the film region was better than 0.05λ, indicating that the prepared Al2O3 / YAG transparent ceramic gradient film still maintained extremely low residual stress after high-temperature sintering and did not cause obvious warping of the substrate, proving that the gradient film has a significant buffering effect on thermal stress.
[0038] 3. Measurement of Y, Al, and O elemental composition: Line scanning analysis of the cross-section of the gradient thin film after high-temperature sintering was performed using scanning electron microscopy (SEM). Figure 3 In the figure, the horizontal axis represents the scanning position along the substrate to the thin film direction, and the vertical axis represents the characteristic X-ray intensity of each element (YKα1 line for Y element, AlKα1 line for Al element, and OKα1 line for O element). The intensity value directly reflects the relative change in the content of that element. The results show that at a distance of approximately 0-290 nm, which corresponds to the sapphire substrate, the Y element content is approximately 0, while the Al and O element contents remain unchanged. The theoretical film thickness is 210 nm, therefore, at a distance of approximately 290-500 nm, which corresponds to the sintered gradient film, the Y element content gradually increases as the measurement distance moves away from the sapphire substrate, the Al element content decreases accordingly, and the O element content remains relatively stable. The concentration curves of the three elements show a smooth transition without obvious plateaus or steep interfaces, proving that sintering causes yttrium ions in the YAG film and aluminum ions in the Al2O3 film to diffuse into each other, thereby causing the Y2O3 content in the Al2O3 / YAG transparent ceramic gradient film to gradually increase in the direction away from the substrate.
[0039] 4. Thermal corrosion method for verifying crystallinity: Utilizing the difference in energy and chemical stability between grain boundaries and the interior of grains, water vapor or oxygen in the air reacts with rare earth elements (such as yttrium) at the grain boundaries, generating volatile or easily migrating compounds (e.g., Y(OH)3), thus exposing the grain boundaries. The temperature is increased to 1100℃ at 10℃ / min from room temperature (20℃), held at 1100℃ for 2 hours, and finally allowed to cool naturally to room temperature (20℃). See also... Figure 4 Under an optical microscope, grain boundaries can be observed, indicating that a polycrystalline structure has been formed. Therefore, Y, Al, and O atoms in the YAG layer and Al and O atoms in the Al2O3 layer can diffuse rapidly along these grain boundaries, thereby achieving a large-scale material exchange across the interface. This indicates that a transition zone with continuously changing Y2O3 composition was eventually formed.
[0040] This embodiment successfully fabricated an Al2O3 / YAG transparent ceramic gradient film on a sapphire substrate. Testing verified that the fabricated Al2O3 / YAG transparent ceramic gradient film exhibits good optical transmittance, low residual stress after sintering, and interdiffusion of elements between the film grain boundaries forms a gradual transition region with a progressively changing composition. This results in a continuous and smooth change in the coefficient of thermal expansion, enabling the gradient film prepared in this invention to effectively disperse thermal stress.
[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A low-stress Al2O3 / YAG transparent ceramic gradient film, characterized in that, The Al2O3 / YAG transparent ceramic gradient film is deposited on a sapphire substrate, and the yttrium content in the Al2O3 / YAG transparent ceramic gradient film gradually increases in the direction away from the sapphire substrate.
2. The low-stress Al2O3 / YAG transparent ceramic gradient film according to claim 1, characterized in that, The total thickness of the Al2O3 / YAG transparent ceramic gradient film is 140-630 nm.
3. A method for preparing a low-stress Al2O3 / YAG transparent ceramic gradient film according to claim 1 or 2, characterized in that, Includes the following steps: Step 1, Substrate Pretreatment: Cut, polish and clean the sapphire substrate; Step 2, Target and Equipment Preparation: Provide Al2O3 ceramic target and YAG ceramic target, and load the pretreated sapphire substrate into the magnetron sputtering equipment; Step 3, magnetron sputtering gradient film: Under vacuum conditions, by controlling the sputtering process parameters, Al2O3 layer and YAG layer are sequentially and alternately deposited on the sapphire substrate to form a multilayer prefabricated structure; Step 4, High-temperature sintering: The sapphire substrate with the deposited multilayer prefabricated structure is sintered at high temperature in a vacuum or inert atmosphere, so that interdiffusion and reaction occur between the layers, and finally a ceramic gradient film with the proportion of Y2O3 gradually increasing along the direction away from the sapphire substrate is formed.
4. The preparation method according to claim 3, characterized in that, In step 2, the Al2O3 ceramic target and the YAG ceramic target are transparent ceramic targets containing sintering aids, and the sintering aids include at least one of MgO, SiO2, Y2O3 and La2O3.
5. The preparation method according to claim 3, characterized in that, In step 3, the multilayer prefabricated structure consists of a first Al2O3 layer, a first YAG layer, a second Al2O3 layer, and a second YAG layer, in sequence. The thickness of the first Al2O3 layer is 10-40 nm, the thickness of the first YAG layer is 20-50 nm, the thickness of the second Al2O3 layer is 10-40 nm, and the thickness of the second YAG layer is 100-500 nm. The magnetron sputtering process parameters are: substrate heating temperature of 150-300℃, sputtering power of 150-250 W, working gas of argon, and working pressure of 0.5-3.0 Pa.
6. The preparation method according to claim 3, characterized in that, In step 4, the high-temperature sintering temperature is 1200-1800℃, and the holding time is 1-5 hours.
7. A sapphire substrate, characterized in that, The surface of the sapphire substrate has a low-stress Al2O3 / YAG transparent ceramic gradient film as described in claim 1 or 2, wherein the low-stress Al2O3 / YAG transparent ceramic gradient film is prepared by the preparation method described in any one of claims 3 to 6.
8. A laser gain medium, characterized in that, It includes the sapphire substrate as described in claim 7.
9. A solid-state laser, characterized in that, It includes the laser gain medium as described in claim 8.