Preparation method of tantalum pentoxide / silicon nitride gradient composite infrared antireflection film

Abstract

The invention relates to a preparation method of a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film, and belongs to the field of antireflection film materials. A five-layer gradient structure is designed, the thickness of each layer is 0.4-0.8 [mu] m, nano Ta2O5, nano Y2O3 and nano Si3N4 powder are mixed in proportion, and the material is prepared through planetary ball milling, cold isostatic pressing, segmented pressure-controlled sintering and graded polishing. Segmented pressure control is adopted for sintering, densification and interface fusion are ensured, and finally a low-roughness film layer is obtained through diamond suspension liquid polishing. According to the method, the problems of defects, weak adhesive force, discontinuous gradient refractive index, difficult high-temperature densification, insufficient mechanical property and the like are solved, the optical property, the mechanical property and the environmental adaptability are remarkably improved, and the method is suitable for high-performance infrared optical elements.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of antireflection films, in particular to a preparation method of a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film. BACKGROUND

[0002] Infrared antireflection films play an important role in optical systems, mainly used to reduce the reflection loss of the surface of optical elements, thereby improving the transmittance and imaging quality of the system. Traditional preparation methods mainly include physical vapor deposition (PVD, such as magnetron sputtering, evaporation) and chemical vapor deposition (CVD) techniques. Although these techniques have made significant progress in the field of optical thin films, they still face many challenges in preparing complex structures (such as gradient refractive index films), such as interlayer defects, weak adhesion, difficulty in achieving continuous gradient refractive index, low efficiency and high cost, difficulty in densification of high-temperature materials, and insufficient mechanical properties of the film layer.

[0003] The limitations of the prior art mainly manifest in the following aspects: first, the layer-by-layer deposition method (such as PVD or CVD) is prone to produce defects such as residual stress, micropores and microcracks at the interface when depositing materials with large differences in thermal expansion coefficient, resulting in weak adhesion and decreased optical performance. Second, traditional coating methods have difficulty in accurately controlling complex refractive index profiles, and sol-gel methods can prepare gradient films, but the densification and mechanical strength of the film layer are usually insufficient. In addition, the preparation of multi-layer or gradient films requires multiple depositions and complex process switching, resulting in long production cycle, low equipment utilization rate and high cost. Densification of high-melting-point materials is difficult, and traditional sintering methods cannot accurately control the complex structure of multiple layers.

[0004] Therefore, in view of the limitations of the above-mentioned related art, there is an urgent need to develop a preparation method of a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film. SUMMARY

[0005] Therefore, in view of the limitations of the above-mentioned related art, there is an urgent need to develop a preparation method of a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A preparation method of a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film, comprising the following preparation steps:

[0008] Step S1: design a gradient structure, each layer thickness 0.4-0.8 μm, wherein the content of nano Ta2O5 decreases from 100% to 0%, the content of nano Si3N4 increases in the opposite direction; nano Y2O3 is only added to the layer with Ta2O5 content ≥40%, and the addition amount is 0.1-0.5wt%, wherein 0.4wt%-0.5wt% of nano Y2O3 is added to layer 1, 0.2wt%-0.4wt% of nano Y2O3 is added to layer 2, and 0.1wt%-0.3wt% of nano Y2O3 is added to layer 3;

[0009] Step 2: mix nano Ta2O5, nano Y2O3 and nano Si3N4 in proportion by planetary ball milling to obtain nano powder for each layer;

[0010] Step S3: stack each layer of powder in gradient order, pre-press into a preform by cold isostatic pressing;

[0011] Step S4: put the preform into a vacuum sintering furnace for segmented pressure control sintering to obtain a sintered body:

[0012] Step S5: cut and polish the sintered body to obtain an anti-reflection film.

[0013] Preferably, the gradient structure is 5 layers:

[0014] Layer 1: 100% nano Ta2O5, thickness 0.6-0.8 μm;

[0015] Layer 2: 70%-80% nano Ta2O5+20%-30% nano Si3N4, thickness 0.6-0.8 μm;

[0016] Layer 3: 40%-60% nano Ta2O5 powder+40%-60% nano Si3N4, thickness 0.5-0.6 μm;

[0017] Layer 4: 20%-30% nano Ta2O5 powder+70%-80% nano Si3N4, thickness 0.4-0.6 μm;

[0018] Layer 5: 100% nano Si3N4, thickness 0.4-0.6 μm.

[0019] Preferably, the particle size of the nano Ta2O5 powder is 45-55 nm, the particle size of the nano Y2O3 powder is 17-23 nm, and the particle size of the nano Si3N4 powder is 60-80 nm.

[0020] Preferably, the nano Ta2O5 powder, nano Y2O3 powder and nano Si3N4 powder are mixed by planetary ball milling, wherein the ball milling parameters are: medium is anhydrous ethanol, powder liquid mass ratio is 1:2-3; rotation speed is 350-450 rpm, ball milling time is 4-6 h; grinding ball is zirconia, grading is 3 / 6 / 10 mm.

[0021] Preferably, the cold isostatic pressing preforming pressure is 250-300 MPa, the pressure maintaining time is 30-50 min, and the pressure releasing rate is 1-2 MPa / min.

[0022] Preferably, the segmented pressure control sintering is as follows:

[0023] First stage: 1x10 -3 Pa from room temperature to 800℃ at a heating rate of 1-3℃ / min;

[0024] Second stage: 5x10 -3 Pa from 800℃ to 1300℃ at a heating rate of 3-5℃ / min;

[0025] Third stage: 0.1 Pa from 1300℃ to 1550℃ at a heating rate of 1-3℃ / min;

[0026] Fourth stage: 0.1 Pa at 1550℃ for 60-120 min.

[0027] Preferably, the sintered body polishing adopts diamond suspension liquid grading polishing, and the specific steps are as follows:

[0028] Coarse polishing: using 3 μm particle size diamond suspension liquid to preliminarily polish the surface of the sintered body for 10-12 min;

[0029] Medium polishing: using 0.5 μm particle size diamond suspension liquid to secondarily polish the surface of the sintered body for 15-30 min;

[0030] Fine polishing: using 0.1 μm particle size diamond suspension liquid to finally polish the surface of the sintered body for 20-40 min.

[0031] The beneficial effects of the present application are as follows:

[0032] 1. The present application realizes the continuous transition from high refractive index tantalum pentoxide to low refractive index silicon nitride through the carefully designed gradient structure. This gradient change can effectively reduce the reflection loss of the optical interface, significantly improve the transmittance and imaging quality of the optical system, and make the infrared antireflection film have more excellent optical performance in the infrared optical field.

[0033] 2. In the preparation process, a proper amount of nano yttrium oxide Y2O3 is added only in the specific layer with high tantalum pentoxide content, which not only plays a role of sintering aid and promotes the densification of the film layer, but also avoids the negative impact on the entire film structure. At the same time, the optimized sintering process ensures the hardness and wear resistance of the film layer, so that it can better resist external mechanical damage and prolong the service life.

[0034] 3. The use of segmented pressure control sintering process and cold isostatic pressing pre-pressing technology enables the film layer to be uniformly densified during high temperature sintering, reducing defects caused by temperature changes or stress concentration. After various environmental adaptability tests such as high and low temperature tests and immersion tests, the film layer shows good stability without peeling, blistering, cracking, and delamination, and can meet the use requirements in complex environments. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0036] Embodiment 1

[0037] A preparation method of a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film, comprising the following preparation steps:

[0038] Step S1: a 5-layer gradient structure is constructed, layer 1 is 100% nano Ta2O5+0.45wt% nano Y2O3, thickness 0.7μm; layer 2 is 75% nano Ta2O5+25% nano Si3N4+0.3wt% nano Y2O3, thickness 0.7μm; layer 3 is 50% nano Ta2O5+50% nano Si3N4+0.2wt% nano Y2O3, thickness 0.6μm; layer 4 is a combination of 25% nano Ta2O5+75% nano Si3N4, thickness 0.5μm; layer 5 is 100% nano Si3N4, thickness 0.5μm; nano Ta2O5 particle size 50nm, nano Y2O3 particle size 20nm, nano Si3N4 particle size 70nm;

[0039] Step S2: after the powders of each layer are weighed according to the ratio, planetary ball milling is performed with anhydrous ethanol as the medium. The powder-liquid mass ratio is 1:2.5, the ball milling speed is 400rpm, the ball milling time is 5h, the milling balls are zirconia, and the grading is 3 / 6 / 10mm. The powder and ethanol are added to the ball milling tank and mixed uniformly;

[0040] Step S3: the mixed powders of each layer are stacked in the mold in gradient order, and cold isostatic pressing pre-pressing is performed. The forming pressure is 275MPa, the pressure holding time is 40min, and the pressure relief rate is 1.5MPa / min, to obtain a preformed body;

[0041] Step S4: the preformed body is subjected to segmented pressure control sintering in a vacuum sintering furnace. In the first stage, the vacuum degree is 10 -3Pa, the temperature is raised to 800℃ at a rate of 2℃ / min; the second stage, the vacuum degree is 5x10 -3 Pa, the temperature is raised to 800℃ at a rate of 2℃ / min; the second stage, the vacuum degree is 5x10

[0042] Step S5: After the sintered body is cut, it is polished by stages. Coarse polishing is performed using 3 μm diamond suspension for 10 min; medium polishing is performed using 0.5 μm diamond suspension for 22 min; and fine polishing is performed using 0.1 μm diamond suspension for 30 min, thereby obtaining the gradient composite tantalum pentoxide / silicon nitride infrared antireflection film.

[0043] Example 2

[0044] A method for preparing a gradient composite tantalum pentoxide / silicon nitride infrared antireflection film, comprising the following preparation steps:

[0045] Step S1: a 5-layer gradient structure is designed, layer 1 is 100% nano Ta2O5+0.4wt% nano Y2O3, the thickness is 0.6 μm; layer 2 is 70% nano Ta2O5+30% nano Si3N4+0.2wt% nano Y2O3, the thickness is 0.6 μm; layer 3 is 40% nano Ta2O5+60% nano Si3N4+0.1wt% nano Y2O3, the thickness is 0.5 μm; layer 4 is 20% nano Ta2O5+80% nano Si3N4, the thickness is 0.4 μm; and layer 5 is 100% nano Si3N4, the thickness is 0.4 μm. The nano Ta2O5 particle size is 45 nm, the nano Y2O3 particle size is 17 nm, and the nano Si3N4 particle size is 60 nm.

[0046] Step S2: the nano Ta2O5, nano Y2O3 (added according to layer requirements) and nano Si3N4 powders required for each layer are mixed by planetary ball milling with anhydrous ethanol as the medium. The powder-liquid mass ratio is 1:2, the ball milling speed is set to 350 rpm, the ball milling time lasts for 4 h, the grinding balls are made of zirconia material, and the gradation is 3 / 6 / 10 mm;

[0047] Step S3: the powders of each layer after ball milling are sequentially stacked in order according to the gradient, and then put into a mold for cold isostatic pressing pre-pressing. The forming pressure is 250 MPa, the pressure holding time is 30 min, and the pressure relief rate is controlled at 1 MPa / min, thereby finally obtaining a preformed body;

[0048] Step S4: the preformed body is put into a vacuum sintering furnace for segmented pressure control sintering. The first stage is sintering at a vacuum degree of 10 -3Pa, the temperature is raised to 800℃ at a rate of 1℃ / min; the second stage, the vacuum is maintained at 5x10 -3 Pa, the temperature is raised to 1300℃ at a rate of 3℃ / min; the third stage, the vacuum is adjusted to 0.1Pa, the temperature is raised to 1550℃ at a rate of 1℃ / min; the fourth stage, the vacuum is maintained at 0.1Pa, the sintering is completed at 1550℃ for 60min, and the sintered body is cooled and taken out;

[0049] Step S5: After cutting the sintered body, diamond suspension is used for grading polishing. Coarse polishing uses 3μm particle size diamond suspension, polishing time is 10min; medium polishing selects 0.5μm particle size diamond suspension, polishing time is 15min; fine polishing uses 0.1μm particle size diamond suspension, polishing time is 20min, and finally the five-tantalum pentoxide / silicon nitride gradient composite infrared antireflection film is obtained.

[0050] Example 3

[0051] Step S1: a 5-layer gradient structure is designed, layer 1 is 100% nano Ta2O5+0.5wt% nano Y2O3, thickness is 0.8μm; layer 2 is 80% nano Ta2O5+20% nano Si3N4+0.4wt% nano Y2O3, thickness is 0.8μm; layer 3 is 60% nano Ta2O5+40% nano Si3N4+0.3wt% nano Y2O3, thickness is 0.6μm; layer 4 is 30% nano Ta2O5+70% nano Si3N4, thickness is 0.6μm; layer 5 is 100% nano Si3N4, thickness is 0.6μm, nano Ta2O5 particle size is 55nm, nano Y2O3 particle size is 23nm, and nano Si3N4 particle size is 80nm;

[0052] Step S2: nano powder is weighed according to the proportion of each layer, and planetary ball milling is carried out with anhydrous ethanol as medium. The powder-liquid mass ratio is 1:3, the ball milling speed is 450rpm, the ball milling time is 6h, the grinding ball is zirconia, and the grading is 3 / 6 / 10mm. The powder and ethanol are added into the ball milling tank and mixed thoroughly;

[0053] Step S3: the mixed powder of each layer is laid in the mold in gradient order, and cold isostatic pressing pre-pressing is carried out. The molding pressure is 300MPa, the pressure maintaining time is 50min, the pressure relief rate is 2MPa / min, and the pre-formed body is obtained;

[0054] Step S4: the pre-formed body is put into a vacuum sintering furnace for staged pressure control sintering. The first stage is 10 -3 Pa, the temperature is raised to 800℃ at a rate of 3℃ / min; the second stage, the vacuum is maintained at 5x10 -3Pa, heating rate 5℃ / min, heating to 1300℃; third stage, vacuum degree 0.1Pa, heating rate 3℃ / min, heating to 1550℃; fourth stage, vacuum degree 0.1Pa, heat preservation at 1550℃ for 120min, and remove the sintered body after cooling;

[0055] Step S5: After the sintered body is cut, it is polished in stages. A 3μm diamond suspension is used for coarse polishing for 12 minutes; a 0.5μm diamond suspension is used for medium polishing for 30 minutes; and a 0.1μm diamond suspension is used for fine polishing for 40 minutes. Finally, a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film is produced.

[0056] Comparative Example 1

[0057] Compared with Example 1, this comparative example does not add nano-Y2O3 to all layers, and the remaining steps and parameters are the same, which will not be repeated in this comparative example. Finally, a tantalum pentoxide / silicon nitride gradient composite infrared anti-reflection film is obtained.

[0058] Comparative Example 2

[0059] Compared with Example 1, in this comparative example, nano-Y2O3 is added to all layers, among which 0.2 wt% of nano-Y2O3 is added to layers 4 and 5. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, a tantalum pentoxide / silicon nitride gradient composite infrared anti-reflection film is obtained.

[0060] Comparative Example 3

[0061] Compared with Example 1, this comparative example has the following characteristics: layer 1: 100% nano-Ta2O5 + 0.45wt% Y2O3; layer 2: 50% nano-Ta2O5 + 50% nano-Si3N4 + 0.2wt% Y2O3; layer 3: 100% nano-Si3N4, each layer has a thickness of 1.0μm, and the addition rules are the same as those in Example 1.

[0062] Comparative Example 4

[0063] Compared with Example 1, step S4 of this comparative example is changed to normal pressure (101 kPa) sintering throughout, and the remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film is obtained.

[0064] Comparative Example 5

[0065] Compared with Example 1, the entire process of step S4 in this comparative example was changed to normal pressure (1×10 -3 The remaining steps and parameters are the same and will not be repeated in this comparative example, and finally a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film is obtained.

[0066] Further effect detection was made on the gradient composite infrared antireflection films of tantalum pentoxide / silicon nitride prepared in Examples 1-3 and Comparative Examples 1-5 of the present application. The test reference standard was GJB2485-95 General Specification for Optical Film Layer, and the detection method was as follows:

[0067] High and low temperature test: The film sample was put into a high and low temperature test box, and was kept at a low temperature of (-62±2) ℃ for 2 h and at a high temperature of (70±2) ℃ for 2 h, respectively, for 5 cycles, with the temperature rising and falling rate being <2 ℃ / min. It was observed whether the film layer had peeling, blistering, cracking or film peeling.

[0068] Abrasion resistance test: The outer surface of the rubber friction head was wrapped with 2 layers of dry degreasing gauze, and the composite infrared antireflection film was rubbed along the same track under a pressure of 4.9 N for 40 times. It was observed whether the film layer had scratches.

[0069] Soaking test: The composite infrared antireflection film was completely immersed in distilled water or deionized water. After 96 hours, no new peeling, peeling, cracking or blistering occurred in the film layer.

[0070] Reflectivity test: The average reflectivity of the composite infrared antireflection film in the range of 3-5 μm was tested by using an FTIR spectrometer. The test reference standard was ASTM E903.

[0071] Film layer hardness test: The film layer hardness of the composite infrared antireflection film was tested by using a nano indentation method, with a load of 50 mN. The test reference standard was ISO 14577.

[0072] The test results of the gradient composite infrared antireflection films of tantalum pentoxide / silicon nitride prepared in Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

[0073] Table 1: Test results

[0074]

[0075]

[0076] According to the data in Table 1, the gradient composite infrared antireflection films of tantalum pentoxide / silicon nitride prepared in the examples had excellent optical performance, mechanical properties and environmental adaptability.

[0077] In Comparative Example 1, no nano Y2O3 was added, and the sintering aid was missing, which weakened the densification of Ta2O5, resulting in a decrease in the hardness of the composite infrared antireflection film.

[0078] In Comparative Example 2, nano Y2O3 was added in the whole layer. The Y2O3 weakened the Si3N4 grain boundary, resulting in a decrease in the hardness of the composite infrared antireflection film.

[0079] Comparative Example 3 is a 3-layer gradient structure, and the insufficient gradient layers result in a refractive index mutation and an increase in reflectivity, highlighting the role of the 5-layer gradient design in ensuring optical performance.

[0080] Comparative Example 4 is sintered under normal pressure, and impurity pollution destroys optical uniformity, resulting in an increase in reflectivity.

[0081] Comparative Example 5 is sintered under constant high vacuum, and the composition deviates due to the volatilization of Ta2O5, resulting in an increase in reflectivity.

[0082] The above is merely an example and a description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present claims.

Claims

1. A method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film, characterized in that: The method comprises the following preparation steps: Step S1: Designing a gradient structure with a thickness of 0.4-0.8 μm per layer, wherein the content of nano-Ta2O5 decreases from 100% to 0%, and the content of nano-Si3N4 increases in the opposite direction; nano-Y2O3 is added only to the layer with a Ta2O5 content of ≥40%, and the addition amount is 0.1-0.5wt%, wherein 0.4wt%-0.5wt% nano-Y2O3 is added to layer 1, 0.2wt%-0.4wt% nano-Y2O3 is added to layer 2, and 0.1wt%-0.3wt% nano-Y2O3 is added to layer 3; Step 2: Nano-Ta2O5, nano-Y2O3 and nano-Si3N4 are mixed in proportion by planetary ball milling to obtain nano-powders of each layer; Step S3: stacking the layers of powder in a gradient order and pre-forming by cold isostatic pressing to obtain a preform; Step S4: placing the preform into a vacuum sintering furnace for staged controlled pressure sintering to obtain a sintered body: Step S5: The sintered body is cut and polished to obtain an antireflection film.

2. The method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film according to claim 1, characterized in that: The gradient structure consists of 5 layers: Layer 1: 100% nano-Ta2O5, thickness 0.6-0.8μm; Layer 2: 70%-80% nano-Ta2O5 + 20%-30% nano-Si3N4, thickness 0.6-0.8μm; Layer 3: 40%-60% nano-Ta2O5 powder + 40%-60% nano-Si3N4, thickness 0.5-0.6μm; Layer 4: 20%-30% nano-Ta2O5 powder + 70%-80% nano-Si3N4, thickness 0.4-0.6μm; Layer 5: 100% nano-Si3N4, thickness 0.4-0.6 μm.

3. The method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film according to claim 1, characterized in that: The particle size of the nano-Ta2O5 powder is 45-55nm, the particle size of the nano-Y2O3 powder is 17-23nm, and the particle size of the nano-Si3N4 powder is 60-80nm.

4. The method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film according to claim 1, characterized in that: The nano-Ta2O5 powder, nano-Y2O3 powder and nano-Si3N4 powder are mixed by planetary ball milling, wherein the ball milling parameters are: the medium is anhydrous ethanol, the powder-liquid mass ratio is 1:2-3; the rotation speed is 350-450rpm, the ball milling time is 4-6h; the grinding balls are zirconia with a gradation of 3 / 6 / 10mm.

5. The method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film according to claim 1, characterized in that: The cold isostatic pressing pre-molding pressure is 250-300 MPa, the pressure is maintained for 30-50 minutes, and the pressure release rate is 1 MPa / min-2 MPa / min.

6. The method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film according to claim 1, characterized in that: The segmented controlled pressure sintering: Stage 1: 1×10 -3 Pa from room temperature to 800 ° C, with a heating rate of 1-3 ° C / min; Second stage: 5×10 -3 Pa from 800 ° C to 1300 ° C, the heating rate is 3-5 ° C / min; The third stage: from 1300°C to 1550°C at 0.1 Pa, with a heating rate of 1-3°C / min; The fourth stage: keep warm at 1550℃ for 60-120min at 0.1Pa.

7. The method for preparing a tantalum pentoxide / silicon nitride gradient composite infrared antireflection film according to claim 1, characterized in that: The sintered body is polished by diamond suspension graded polishing, and the specific steps are as follows: Rough polishing: Use a 3μm particle size diamond suspension to perform preliminary polishing on the sintered surface for 10-12 minutes; Medium polishing: Use a diamond suspension with a particle size of 0.5 μm to perform secondary polishing on the sintered surface for 15-30 minutes; Fine polishing: Use a diamond suspension with a particle size of 0.1 μm to perform final polishing on the sintered surface for 20-40 minutes.

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