Multi-layer dissimilar material thermal bonding method based on assistance of SiO2 thin film interlayer

Abstract

The invention discloses a multi-layer dissimilar material thermal bonding method based on SiO2 thin film interlayer assistance. The method comprises the steps that S1, cutting and annealing destressing treatment are conducted on an Nd: YAG substrate and a cooling fin which need to be bonded; s2, finely regulating and controlling the surface shape and the roughness of the crystal bonding surface of the processed Nd: YAG substrate and the radiating fin to ensure that the bonding surface is flat and smooth; s3, the Nd: YAG substrate and the cooling fin which are subjected to grinding and polishing are cleaned; s4, the two sides of the cleaned Nd: YAG substrate are plated with SiO2 thin films; s5, gently attaching the coated Nd: YAG substrate and the cooling fin at room temperature by using Van der Waals force to complete primary optical cement; and S6, carrying out heat treatment on the Nd: YAG substrate and the cooling fin which are subjected to primary optical cement to obtain the multi-layer dissimilar material thermal bonding gain medium. According to the method, bonding is assisted through the SiO2 thin film intermediate layer, and the bonding stress caused by mismatching of thermal expansion coefficients during thermal bonding of multiple layers of dissimilar materials can be eliminated.

Description

Technical Field

[0001] The present invention relates to the field of solid laser technology, and particularly to a thermal bonding method for multi-layer dissimilar materials assisted by a SiO 2 thin film intermediate layer. Background Art

[0002] Distributed surface cooling structure lasers have both the high gain of rod structures and the efficient heat dissipation ability of thin sheet structures, and have great potential in realizing high-repetition-rate and high-pulse-energy laser output. Analyzing the problems of insufficient output power and beam quality degradation existing in the current distributed surface cooling crystal amplification of short pulses, these are caused by the preparation method of distributed surface cooling crystals.

[0003] Currently, the preparation of such distributed surface cooling crystals mainly uses room-temperature surface active bonding (SAB) technology. This technology uses an ion source to bombard the processed bonding interface in a vacuum, removing the surface absorption film layer and forming dangling bonds, and binding the bonding materials together through van der Waals forces. This technology can be realized at room temperature, can bond materials with different thermal expansion coefficients, and there is no bonding stress at the bonding interface. Since the interface bonded by van der Waals forces is prone to cracking in a liquid environment with a heat source, for the distributed surface cooling crystals prepared by surface active bonding technology, their cooling method cannot be cooled by liquid (such as water) circulation, and generally can only be cooled by metal (such as copper) conduction. However, the heat dissipation surface of transparent heat dissipation crystal materials is limited, thus restricting the average power and beam quality of amplified pulses.

[0004] Therefore, there is an urgent need for an efficient and reliable bonding method that can not only ensure high bonding strength and will not crack due to thermal expansion coefficient mismatch during temperature changes, but also will not crack in a liquid cooling environment with a heat source. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the present invention provides a thermal bonding method for multi-layer dissimilar materials assisted by a SiO 2 thin film intermediate layer, which can solve the problems faced by surface activation bonding technology. After heat treatment after photoresist coating, the hydroxyl groups on the photoresist surface undergo dehydration to form chemical bonds. The formed binding force is a molecular force or even an atomic force, with very high binding strength, capable of withstanding shear stresses of dozens of MPa, and can withstand side liquid flow cooling, providing a new possibility for high-pulse-energy and high-repetition-rate laser output.

[0006] The present invention provides a thermal bonding method for multi-layer dissimilar materials assisted by a SiO 2 thin film intermediate layer, and the method includes:

[0007] S1. Cut and anneal the Nd:YAG substrate and heat sink to relieve stress for bonding;

[0008] S2. Adopt a grinding and polishing process to finely control the surface shape and roughness of the crystal bonding surfaces of the processed Nd:YAG substrate and heat sink to meet the requirements of optical cementing, ensuring a flat and smooth bonding surface;

[0009] S3. Use a special solvent to clean the ground and polished Nd:YAG substrate and heat sink to remove organic and inorganic impurities on the polished surface;

[0010] S4. Deposit SiO 2 thin films on both sides of the cleaned Nd:YAG substrate;

[0011] S5. Use the van der Waals force to gently bond the coated Nd:YAG substrate and heat sink at room temperature to complete preliminary optical cementing;

[0012] S6. Perform a heat treatment operation on the preliminarily optically cemented Nd:YAG substrate and heat sink. Raise the temperature of the overall structure and apply appropriate pressure in a vacuum hot pressing furnace. The bonded surfaces after optical cementing are tightly bonded together by hydroxyl groups. The heat treatment gradually intensifies the diffusion of ions and holes at the interface. After a period of lattice adjustment and reconstruction, stable Al - O bonds or Si - O bonds are finally formed, and the bonding strength increases rapidly. After cooling, a multi - layer dissimilar material thermally bonded gain medium, namely the Nd:YAG distributed surface cooling gain structure, can be obtained.

[0013] Preferably, the material of the heat sink is sapphire with a thermal conductivity of 36.9 W / m·K, and the multi - layer dissimilar material thermally bonded gain medium is the Nd:YAG and sapphire thermally bonded gain medium.

[0014] Preferably, the method uses a thermal bonding process. The SiO 2 thin film is used as an intermediate layer material to perform multi - layer thermal bonding of the Nd:YAG substrate and the sapphire heat sink. Among them, the SiO 2 thin film can react with YAG and alumina in sapphire to generate mullite 3Al 2 O 3 ·2SiO 2 . The thermal expansion coefficient and thermal conductivity of mullite are 5.3×10 -6 / K and 3.5 - 7 W / m·K respectively. Its thermal expansion coefficient is similar to that of YAG and sapphire, which can eliminate the bonding stress caused by the mismatch of thermal expansion coefficients between YAG and sapphire, has a high bonding strength, will not crack when the temperature changes, and will not disintegrate under side - flow liquid cooling.

[0015] Preferably, in step S6, the heat treatment includes the following three processes:

[0016] The first stage: heating to a first temperature range at a preset speed in a vacuum environment to cause the SiO 2 to react with alumina;

[0017] The second stage: keeping warm for a first preset time in a vacuum environment to cause the SiO 2 thin film to fully react with alumina;

[0018] The third stage: turning off the heating, rapidly cooling to a second temperature range in a vacuum environment, and maintaining for a second preset time.

[0019] Preferably, the first temperature is 1600 °C, the preset speed is 20 °C / min, the first preset time is 10 minutes, the second temperature is 25 °C, and the second preset time is 8 - 10 hours.

[0020] Preferably, the thickness of the sapphire is 2 mm.

[0021] Preferably, the thickness of the SiO 2 thin film is related to Fresnel loss, material bonding degree, and surface flatness of the substrate. Considering material bonding, 1 - 2 nm is sufficient; considering the surface flatness of the substrate, the currently processed surface shape can be less than 1 / 20 of a wavelength, and the thickness can be in the range of 15 - 30 nm.

[0022] Preferably, the thickness of the SiO 2 thin film is 15 nm, the single - time Fresnel loss is about one - thousandth, and the thickness of the SiO 2 thin film will decrease after melting and extrusion, and the Fresnel loss will be further reduced.

[0023] Preferably, the special solvent is sulfuric acid or hydrochloric acid.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The present invention adopts a thermocompression bonding process, using the SiO 2 thin film as an intermediate auxiliary layer for bonding. High - temperature heat treatment can cause the bonding interface to form a molecular force or even an atomic force to combine into a whole, with high bonding strength, not cracking during temperature changes, and not disintegrating even through liquid - cycle cooling, providing a new solution for high - energy, high - efficiency, and high - beam - quality laser output.

[0026] 2. The end face and side face of the convex part of the transparent heat - dissipating crystal material sapphire adopted in the present invention can both dissipate heat, increasing the heat - dissipating surface area, increasing the heat dissipation of the distributed - surface - cooled crystal, and providing a way for high - average - power output.

[0027] 3. The distributed surface cooling structure prepared by the bonding method of the present invention can achieve an approximately one-dimensional thermal gradient distribution, and has a relatively low cost. It can solve the problem of serious thermal effects of the gain medium under high pump power, and can simultaneously achieve high-repetition-rate and high-pulse-energy laser output, meeting the requirements of small volume and large energy in engineering applications. Brief Description of the Drawings

[0028] Figure 1 FIG. is a schematic flow chart of a multi-layer dissimilar material thermal bonding method assisted by a SiO 2 thin film intermediate layer provided by the present invention;

[0029] Figure 2 FIG. is a physical diagram of a Nd:YAG distributed surface cooling gain structure provided by the present invention;

[0030] Figure 3 FIG. is a three-dimensional diagram of a Nd:YAG distributed surface cooling gain structure provided by the present invention;

[0031] Figure 4 FIG. is a schematic diagram of the simulation calculation results of the influence of the SiO 2 thin film thickness on Fresnel loss provided by the present invention;

[0032] Figures 5-7 FIG. is a schematic diagram of the simulation calculation results of the influence of the heat sink thickness on the heat conduction ability provided by the present invention;

[0033] Figures 8-10 FIG. is a schematic diagram of the simulation calculation results of the temperature and stress of a Nd:YAG distributed surface cooling gain structure provided by the present invention;

[0034] Figures 11-12 FIG. is a schematic diagram of the temperature and stress distribution of a traditional end-pumped structure under the same conditions provided by the present invention;

[0035] Figure 13 FIG. is a schematic diagram of the structure of a laser amplifier provided by the present invention;

[0036] In the drawings:

[0037] 1: Semiconductor pump source, 2: Pump shaping system, 3: Dichroic mirror DM2, 4: Second λ / 4 wave plate, 5: Total reflection mirror, 6: Nd:YAG and sapphire thermally bonded gain medium, 7: Dichroic mirror DM1, 8: Polarizer TFP2, 9: First λ / 4 wave plate, 10: 45° reflector, 11: Polarizer TFP1, 12: Seed source. Detailed Embodiments

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] The following further describes the present invention in detail with reference to the accompanying drawings.

[0040] As Figure 1 shown, the embodiments of the present invention provide a multi-layer dissimilar material thermal bonding method assisted by an SiO 2 thin film intermediate layer, including:

[0041] S1. Cut and anneal the Nd:YAG substrate and the heat sink to be bonded to remove stress.

[0042] S2. Adopt a grinding and polishing process to finely control the surface shape and roughness of the crystal bonding surfaces of the processed Nd:YAG substrate and the heat sink to meet the requirements of photo-resist, and ensure the flatness and smoothness of the bonding surface.

[0043] S3. Use a special solvent to clean the ground and polished Nd:YAG substrate and the heat sink to remove organic and inorganic impurities on the polished surface.

[0044] S4. Deposit SiO 2 thin films on both sides of the cleaned Nd:YAG substrate.

[0045] S5. Use the van der Waals force to gently bond the coated Nd:YAG substrate and the heat sink at room temperature to complete the preliminary photo-resist.

[0046] S6. Perform a heat treatment operation on the preliminarily photo-resisted Nd:YAG substrate and the heat sink. Raise the temperature of the overall structure and apply an appropriate pressure in a vacuum hot pressing furnace to cause the hydroxyl groups on the photo-resist surface to shrink and form chemical bonds. The formed bonding force is a molecular force or even an atomic force, and the bonding strength is very high. Cool down to obtain a multi-layer dissimilar material thermal bonding gain medium, that is, a Nd:YAG distributed surface cooling gain structure.

[0047] Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) is a neodymium-doped yttrium aluminum garnet crystal, which is a solid laser material widely used in laser technology.

[0048] The intermediate layer assisted thermal bonding process mainly includes: the pretreatment stage, where the materials to be bonded are precisely cut and annealed to remove stress, ensuring the optimal material state; subsequently, a grinding and polishing process is adopted to finely control the surface shape and roughness of the crystal bonding surface to meet the requirements of optical glue, ensuring the flatness and smoothness of the bonding surface; in the cleaning step, we use special solvents (sulfuric acid or hydrochloric acid) to effectively remove organic and inorganic impurities on the polished surface, ensuring the cleanliness of the interface; then, SiO 2 thin films are coated on both sides of the Nd:YAG substrate with good cleanliness; during the optical gluing process, the precisely polished and prepared Nd:YAG substrate and sapphire crystal are gently bonded at room temperature using van der Waals forces to complete the preliminary optical gluing; to further enhance the bonding effect, a heat treatment operation is carried out, raising the temperature of the overall structure and applying appropriate pressure in a vacuum hot press furnace. The bonded surface after optical gluing is tightly bonded together by hydroxyl groups. The heat treatment gradually intensifies the diffusion of ions and holes at the interface. After a period of lattice adjustment and reconstruction, stable Al-O bonds or Si-O bonds are finally formed, and the bonding strength increases rapidly.

[0049] In the embodiment of the present invention, the material of the heat sink is sapphire, and the multi-layer dissimilar material thermal bonding gain medium is the Nd:YAG and sapphire thermal bonding gain medium. The thickness of the sapphire is 2 mm. The end face and side face of the protruding part of the sapphire can dissipate heat. The main component of the sapphire is Al 2 O 3 。

[0050] In the embodiment of the present invention, in step S6, the heat treatment includes the following three processes:

[0051] The first stage: heating to the first temperature at a preset speed in a vacuum environment to react SiO 2 with alumina;

[0052] The second stage: maintaining the temperature for the first preset time in a vacuum environment to allow the SiO 2 thin film to fully react with sapphire alumina;

[0053] The third stage: turning off the heating and rapidly cooling to the second temperature in a vacuum environment and maintaining for the second preset time.

[0054] In the embodiment of the present invention, the first temperature is 1600 °C, the preset speed is 20 °C / min, the first preset time is 10 minutes, the second temperature is 25 °C, and the second preset time is 8 - 10 hours.

[0055] In step S4, SiO 2 thin film is selected as the intermediate layer material. The SiO 2 thin film reacts with alumina in the Nd:YAG substrate and sapphire to form mullite (3Al2O3 ·2SiO 2 ), the thermal expansion coefficient and thermal conductivity of mullite are 5.3×10-6 / K and 3.5-7 W / m·K respectively. Its thermal expansion coefficient is similar to that of the Nd:YAG substrate and sapphire. Stress relaxation will occur during the reaction process to eliminate the bonding stress caused by the mismatch of thermal expansion coefficients between the Nd:YAG substrate and sapphire.

[0056] In step S6, during the intermediate layer assisted bonding process, the bonded surfaces after photoresist rely on hydroxyl groups to be tightly bonded together. Heat treatment makes the diffusion of ions and holes at the interface gradually intensify. After a period of lattice adjustment and reconstruction, stable Al-O bonds or Si-O bonds are finally formed, and the bonding strength increases rapidly, making the bonded gain structure have a high bonding strength. It will not crack due to the mismatch of thermal expansion coefficients when the temperature changes, and can withstand side liquid flow cooling without disintegration.

[0057] In the embodiment of the present invention, considering the surface flatness of the substrate and the current processed surface profile can be less than 1 / 20 of a wavelength, SiO 2 The thickness range of the thin film is 15-30 nm. Considering factors such as Fresnel loss comprehensively, the thickness of the SiO 2 thin film is 15 nm.

[0058] Analyzing the factors affecting the thickness of the intermediate layer material, the following factors need to be considered: First, the influence of the intermediate layer thickness on Fresnel loss. When the intermediate layer is adopted, due to the difference in refractive index, Fresnel loss will be caused. It is calculated that when the thickness of SiO 2 is less than 15 nm, the single Fresnel loss is less than one-thousandth, which is within an acceptable range. Second, from the perspective of material bonding, the lattice constant of YAG is The lattice constant of sapphire is Considering from the perspective of material bonding, 1-2 nm is enough. Third, the intermediate layer needs to fill all positions of the surface. The surface flatness of the substrate needs to be considered. The current processed surface profile can be less than 1 / 20 of a wavelength. Therefore, the thickness can be in the range of 15-30 nm. Considering comprehensively, the thickness of the intermediate layer is determined to be 15 nm.

[0059] For the selection of the heat sink material and the confirmation of its thickness, we choose white YAG, sapphire, and diamond as alternative materials for the heat sink. Through analysis and calculation, it is found that the thermal expansion coefficient and refractive index difference between white YAG and Nd:YAG are very small, and the bonding stress and Fresnel loss of thermal bonding can also be ignored. However, the thermal conductivity of white YAG is low, and its axial heat conduction ability as a heat sink is limited. Although the thermal conductivity of diamond is as high as 2000 W / (m·K), its refractive index difference from Nd:YAG reaches 0.6, and the Fresnel loss per single pass is as high as 2.5%, which is unacceptable as the gain medium for multi-layer bonding. Therefore, considering the axial heat conduction ability of the heat sink and the Fresnel loss comprehensively, sapphire is the best choice. When the thickness of the heat sink increases from 0.5 mm to 4 mm, the temperature gradually decreases. When it continues to increase from 4 mm, the temperature basically remains unchanged, indicating that a 4-mm heat sink can conduct all the heat. However, the greater the thickness of the heat sink, the longer the overall length of the bonded structure. And when the thickness increases from 2 mm to 3 mm, the temperature only decreases by 1 °C. Considering the temperature and the overall length comprehensively, 2-mm sapphire is selected as the heat sink.

[0060] As Figures 2-3 shown, the embodiment of the present invention also provides a multi-layer dissimilar material thermally bonded gain medium, which is prepared by a multi-layer dissimilar material thermal bonding method assisted by a SiO 2 thin film intermediate layer.

[0061] As Figure 13 shown, the embodiment of the present invention also provides a laser amplifier, which uses a multi-layer dissimilar material thermally bonded gain medium.

[0062] Figure 2 This is a physical diagram of the distributed surface cooling structure successfully prepared by the multi-layer dissimilar material thermal bonding method assisted by the SiO 2 thin film intermediate layer provided by the embodiment of the present invention. The polished Nd:YAG thin slice that has been cleaned with a special solution is coated with a 15-nm SiO 2 thin film, and the polished sapphire crystal and the coated Nd:YAG thin slice are combined together by van der Waals force. Then, through high-temperature heat treatment and annealing, the high-temperature heat treatment can cause the bonding interface to form a whole by molecular force or even atomic force. The annealing method is to reduce the oxygen vacancies by rapid heating and cooling. ① The first stage: rapidly heat to 1600 °C (20 °C / min) in a vacuum environment to make SiO 2 react with alumina; ② The second stage: keep it warm for 10 minutes in a vacuum environment to make the SiO 2 thin film react fully with alumina; ③ The third stage: turn off the heating and rapidly cool (water cooling) to 25 °C in a vacuum environment, which takes about 8 - 10 hours. Finally, through cooling, the successfully prepared thermally bonded structure can be obtained.

[0063] Figure 3 For the three-dimensional diagram of the Nd:YAG distributed surface cooling gain structure assisted by intermediate layer bonding based on SiO 2 Among them, the gain medium is a Nd:YAG crystal with a doping concentration of 1.0%, the size is Ф7mm, the thickness is 0.6mm, and there are 10 pieces in total. The heat sink is made of sapphire crystal, its thermal conductivity is 36.9 W / (m·K), the thickness of each piece is 2mm, the size is 8mm×8mm, and there are 11 pieces in total. The intermediate layer assisted bonding technology is adopted, and SiO 2 film is selected as the intermediate layer material. SiO 2 film can react with alumina in YAG and sapphire to generate mullite. Stress relaxation will occur during the reaction process to eliminate the bonding stress caused by the mismatch of the thermal expansion coefficients between YAG and sapphire. After intermediate layer assisted bonding, stable Al-O bonds or Si-O bonds are formed, and the bonding strength increases rapidly, which can bond Nd:YAG and sapphire into a firm integrated structure. The pump light and the seed light enter from the end face of the gain medium. It can be known from COMSOL simulation that the pump light absorption is uniform.

[0064] Figure 4 Shows the influence of different thicknesses of the intermediate layer SiO 2 film on Fresnel loss. When the intermediate layer is adopted, due to the difference in refractive index, Fresnel loss will be caused. It is calculated that when the thickness of the SiO 2 film is 15nm, considering that the maximum error of the coating machine is ±3%, the thickness range of the 15nm SiO 2 film is 14.55nm - 15.45nm. The Fresnel loss at a wavelength of 1064nm is at most 0.001, the Fresnel loss at a wavelength of 885nm is 0.00134, and the Fresnel loss at a wavelength of 808nm is 0.00155. The single Fresnel loss is about one-thousandth, which is within the acceptable range. And the thickness of the SiO 2 film will decrease after melting and extrusion, and the Fresnel loss will decrease.

[0065] Figures 5-7 Shows the influence of different thicknesses of the sapphire heat sink on the heat conduction ability. When the thickness of the heat sink increases from 0.5mm to 4mm, the temperature gradually decreases. When it continues to increase from 4mm, the temperature basically remains unchanged, indicating that a 4mm heat sink can export all the heat. However, the greater the thickness of the heat sink, the longer the overall length of the distributed surface cooling structure. And when the thickness increases from 2mm to 3mm, the temperature only decreases by 1℃. Considering the temperature and the overall length comprehensively, 2mm sapphire is selected as the heat sink.

[0066] To ensure that this structure does not cause the gain medium structure to fracture due to excessive temperature and thermal stress, the temperature and stress inside the Nd:YAG distributed surface cooling gain structure are simulated and calculated, and compared with the traditional non-bonded end-pumped structure. As Figures 8-9 shown, using the COMSOL finite element analysis software, the water cooling method is adopted, the water cooling temperature is 293K, and its conversion coefficient is 10000W·m -2 k -1 . It can be seen that when the pump power is 500W, the maximum temperature in the gain medium is 51.7°C, and the maximum stress is 28.8MPa, which is much less than the stress fracture limit of YAG, 196MPa. Pumping at 500W will not cause damage to the structure. Refer to Figures 10-12 . Compared with the traditional non-bonded end-pumped structure, bonding sapphire crystals with high thermal conductivity reduces the overall temperature by 104.3°C, reduces the stress by 59.1MPa, and at the same time, the internal heat distribution in the gain medium is more uniform, enabling an approximately one-dimensional thermal gradient distribution, with a maximum radial temperature difference of 26°C, and the absorption efficiency can reach 55%.

[0067] Figure 13 Figure 12 is a schematic diagram of the laser amplifier structure of the Nd:YAG distributed surface cooling gain structure assisted by SiO2 intermediate layer bonding. Based on the successfully fabricated distributed surface cooling structure of the present invention, it can be applied to a laser amplifier to achieve high-repetition-rate and high-energy short-pulse laser output. This laser is composed of a semiconductor pump source 1, a pump shaping system 2, a dichroic mirror DM2 3, a second λ / 4 wave plate 4, a total reflection mirror 5, a thermally bonded Nd:YAG and sapphire gain medium 6 (fabricated by the present invention), a dichroic mirror DM1 7, a polarization plate TFP2 8, a first λ / 4 wave plate 9, a 45° reflector 10, a polarization plate TFP1 11, and a seed source 12. The pump source 1 is a semiconductor fiber-coupled pump source, with a central wavelength of 885nm, a maximum output power of 200W, NA = 0.22 (divergence half-angle 12.7°), and a fiber core diameter of 105μm. The seed source 12 is a laser with a pulse width of 5.5ns, a single-pulse energy of 300μJ, a beam quality M 2 of 1.3, an output wavelength of 1064nm, and an output energy stability of 10%. The polarization state is changed by the TFP polarization plate, and a λ / 4 wave plate is added to change the polarization direction of the 1064nm light to prevent the amplified light from damaging the seed source.

[0068] Compared with the prior art, the present invention has the following advantages:

[0069] The present invention can solve many defects existing in the current technology for preparing a distributed surface cooling structure. The successfully prepared distributed surface cooling structure fundamentally solves the problem of severe internal thermal effects in the gain medium, making its thermal distribution approximately one-dimensional, having high gain and efficient heat dissipation capabilities, enabling the laser output with high repetition rate and high pulse energy, which cannot be compared with the traditional non-bonded end-pumping structure, and can be widely used in the fields of basic science, industrial processing, national defense construction, etc., to meet the application requirements of high repetition rate, small volume and large energy.

[0070] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-layer heterogeneous material thermal bonding method based on SiO2 thin film intermediate layer, characterized in that: The method comprises: S1. Cut and anneal the Nd:YAG substrate and heat sink to be bonded to relieve stress; S2. Using a grinding and polishing process, finely control the surface shape and roughness of the crystal bonding surface of the Nd:YAG substrate and the heat sink after treatment, so that they meet the requirements of optical adhesive and ensure that the bonding surface is flat and smooth; S3, using a special solvent to clean the Nd:YAG substrate and the heat sink after grinding and polishing to remove organic and inorganic impurities on the polished surface; S4, coating SiO2 thin films on both sides of the cleaned Nd:YAG substrate; S5. Using van der Waals force, gently bond the coated Nd:YAG substrate and the heat sink to each other at room temperature to complete preliminary photobonding. S6. Perform heat treatment on the Nd:YAG substrate and the heat sink after preliminary photobonding. Raise the temperature of the overall structure and apply appropriate pressure in a vacuum hot press furnace. The bonding surfaces after photobonding are tightly bonded together by hydroxyl groups. Heat treatment gradually intensifies the diffusion of ions and holes on the interface. After a period of lattice adjustment and reconstruction, a stable Al-O bond or Si-O bond is finally formed, and the bonding strength increases rapidly. After cooling, a multi-layer heterogeneous material thermally bonded gain medium, i.e., a Nd:YAG distributed surface cooled gain structure, can be obtained.

2. The method according to claim 1, characterized in that: The heat sink is made of sapphire with a thermal conductivity of 36.9 W / m·K. The multi-layer heterogeneous material thermal bonding gain medium is a Nd:YAG and sapphire thermal bonding gain medium.

3. The method according to claim 2, characterized in that The method adopts a thermal bonding process, wherein SiO2 film is used as an intermediate layer material to perform multi-layer thermal bonding on the Nd:YAG substrate and the sapphire heat sink, wherein the SiO2 film can react with the aluminum oxide in YAG and sapphire to generate mullite 3Al2O3·2SiO2, and the thermal expansion coefficient and thermal conductivity of mullite are 5.3×10 -6 / K, 3.5-7W / m·K, its thermal expansion coefficient is similar to that of YAG and sapphire, which can eliminate the bonding stress caused by the mismatch of thermal expansion coefficients between YAG and sapphire. It has high bonding strength and will not crack when the temperature changes, and will not disintegrate when cooled by side liquid flow.

4. The method according to claim 2, characterized in that: In step S6, the heat treatment includes the following three processes: The first stage: heating to a first temperature at a preset speed in a vacuum environment to react SiO2 with aluminum oxide; The second stage: keeping the temperature in a vacuum environment for a first preset time to allow the SiO2 film to fully react with the aluminum oxide; The third stage: turn off the heating, and quickly cool down to the second temperature in the vacuum environment for a second preset time.

5. The method according to claim 4, characterized in that The first temperature is 1600° C., the preset speed is 20° C. / min, the first preset time is 10 minutes, the second temperature is 25° C., and the second preset time is 8-10 hours.

6. The method according to claim 2, characterized in that The thickness of the sapphire is 2 mm.

7. The method according to claim 1, characterized in that The thickness of the SiO2 film is related to the Fresnel loss, the degree of material bonding and the surface flatness of the substrate. From the perspective of material bonding, 1-2nm is sufficient. Considering the surface flatness of the substrate, the surface currently processed can be less than 1 / 20 of a wavelength, and the thickness can be within the range of 15-30nm.

8. The method according to claim 7, characterized in that The thickness of the SiO2 film is 15 nm, and the single Fresnel loss is about one thousandth. The thickness of the SiO2 film will decrease after melting and extrusion, and the Fresnel loss will be further reduced.

9. The method according to any one of claims 1 to 8, characterized in that: The special solvent is sulfuric acid or hydrochloric acid.

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