A nano-reducing agent for reducing the light transmittance of lithium tantalate wafers and a preparation method thereof

Abstract

The present invention provides a nano-reducing agent for reducing the light transmittance of lithium tantalate wafers and a preparation method thereof, belonging to the technical field of auxiliary materials for lithium tantalate wafer processing. The steps of the preparation method of the nano-reducing agent include: mixing silicon dioxide, carbon black, silicon powder, yttrium oxide with ethanol, ball-milling and drying, and then sintering in a nitrogen atmosphere to obtain porous silicon nitride; mixing ferrous sulfate and oxalic acid, and stirring until completely dissolved to obtain a ferrous oxalate suspension; soaking the porous silicon nitride in the ferrous oxalate suspension to obtain porous silicon nitride adsorbed with ferrous oxalate; mixing the porous silicon nitride adsorbed with ferrous oxalate with ethanol, ball-milling to the nanoscale, rinsing, and drying to obtain the nano-reducing agent. The above-prepared nano-reducing agent can be used in the blackening process of lithium tantalate wafers to reduce the light transmittance of lithium tantalate wafers.

Description

Technical Field

[0001] The present invention relates to the technical field of processing auxiliary materials for lithium tantalate wafers, and particularly relates to a nano-reducing agent for reducing the light transmittance of lithium tantalate wafers and a preparation method thereof. Background Art

[0002] Lithium tantalate (chemical formula LiTaO3) has excellent electro-optic, piezoelectric, and pyroelectric properties and is widely used in the field of surface acoustic wave devices (SAW). To fabricate a surface acoustic wave device, a lithium tantalate crystal must first be processed through multiple procedures such as cutting, grinding, and polishing to form a lithium tantalate wafer, and then metal comb-shaped electrodes are fabricated on the lithium tantalate wafer through other processes such as sputtering and photolithography. However, due to the high light transmittance of the lithium tantalate wafer, the light passing through the substrate during the photolithography process, one of the manufacturing processes of the surface acoustic wave device, is reflected back to the surface from the back of the substrate, resulting in a problem of reduced pattern resolution.

[0003] Through research, it has been found that the resistivity and color of lithium tantalate crystals can be changed through reduction treatment. During this reduction treatment process, the lithium tantalate wafer is placed in a reducing atmosphere such as hydrogen or nitrogen, so that the oxygen in the wafer reacts with the reducing agent, thereby increasing the concentration of oxygen vacancies. After these oxygen vacancies obtain electrons, they form color centers (such as F color centers), enhancing the conductivity. At the same time, the color centers absorb strongly in the visible light region, resulting in a change in the color of the wafer. Therefore, this reduction treatment is called "blackening". By blackening, the resistivity of the lithium tantalate wafer can be effectively reduced and the resolution of the subsequent pattern can be improved, significantly increasing the yield of SAW filter devices and thus reducing the manufacturing cost.

[0004] Currently, the blackening technology of lithium tantalate crystals mainly uses elemental reducing metal powders as reducing agents and is carried out by means such as slurry coating method, powder burial method, and vapor method. It can be seen that the types of reducing agents used in this field are single, and it is necessary to expand the variety of reducing agents to further meet the market demand. Summary of the Invention

[0005] To solve the problems mentioned in the background art, the present invention provides a nano-reducing agent. Ferrous oxalate is filled in the pores of porous silicon nitride, and the reducing gas is released by ferrous oxalate under the high temperature condition of blackening, thereby realizing the blackening process of lithium tantalate and reducing its light transmittance.

[0006] Specifically:

[0007] A preparation method of a nano-reducing agent, the steps include:

[0008] Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide according to a mass ratio of 9 - 12:3 - 5:1:2 - 6, and then mix the mixed powder with ethanol according to a mass ratio of 1:2 - 2.5. After ball milling and drying, sinter in a nitrogen atmosphere to obtain porous silicon nitride;

[0009] Step 2: Mix ferrous sulfate and oxalic acid at a molar ratio of 1:1 to 1.2, and stir until completely dissolved to obtain a ferrous oxalate suspension.

[0010] Step 3: Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2, control the pH value at 2.4 - 2.6, and soak for 16 - 30 h to obtain porous silicon nitride adsorbed with ferrous oxalate.

[0011] Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 and ethanol at a mass ratio of 1:2 to 2.5, ball mill to the nanoscale, rinse, and dry to obtain a nano - reducing agent.

[0012] Further, in Step 1, the sintering process is as follows: First, pre - heat the reaction furnace for 40 - 50 min and evacuate; heat up at a rate of 20 - 25 °C / min to 1200 - 1300 °C and hold for 10 - 15 min; continue to heat up at a rate of 1.6 - 1.8 °C / min to 1590 - 1610 °C and hold for 30 - 35 min; continue to heat up at a rate of 0.5 - 0.7 °C / min to 1745 - 1755 °C and hold for 120 - 150 min; then cool down to complete sintering.

[0013] Further, in Step 1, when the temperature reaches 1200 °C during the sintering process, start to introduce nitrogen with a flow rate of 16 - 18 L / h and keep the nitrogen pressure in the furnace at 0.6 - 0.8 MPa; when the temperature drops to 1200 °C, close the nitrogen.

[0014] Further, the surface of the graphite crucible used in Step 1 is coated with boron nitride.

[0015] Further, in Step 3, 0.5 - 1 mL of ferrous oxalate suspension is required per gram of porous silicon nitride.

[0016] Further, in Step 3, the soaking temperature is controlled at 35 - 50 °C.

[0017] Further, in Step 4, deionized water is used for rinsing.

[0018] Further, in Step 4, a high - energy ball mill is used for ball milling, the ball - milling speed is 200 - 300 rpm, and the ball - milling time is 5 - 8 h.

[0019] The present invention also provides a nano - reducing agent for reducing the light transmittance of lithium tantalate wafers, which is prepared by the above - mentioned preparation method.

[0020] Compared with the prior art, the beneficial features of the present invention are as follows:

[0021] 1. The present invention prepares porous silicon nitride as a carrier, adsorbs ferrous oxalate in the pores of the porous silicon nitride. During use, ferrous oxalate can thermally decompose to form carbon monoxide, which will not be adsorbed by silicon nitride, and thus can penetrate from the pores of silicon nitride to the external environment to react with lithium tantalate, completing the blackening process of lithium tantalate; at the same time, the present invention also washes away most of the ferrous oxalate on the surface of the porous silicon nitride through rinsing, leaving the ferrous oxalate adsorbed in the pores of silicon nitride. The solid products after the decomposition of ferrous oxalate and the residues that have not fully reacted remain in the pores of silicon nitride, greatly reducing the influence of this part of the substances on the lithium tantalate wafer and reducing the probability of defects such as spots occurring on the lithium tantalate wafer.

[0022] 2. The porous silicon nitride of the present invention has good thermal stability and will not react with the lithium tantalate wafer during the treatment of lithium tantalate by the burial method, affecting subsequent processes; and ferrous oxalate can be bonded to silicon nitride through hydrogen bonds, reducing the loss rate of ferrous oxalate in the pores of silicon nitride. Specific Embodiments

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, 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.

[0024] To facilitate those skilled in the art to implement the present invention, some of the reagents used in the examples and comparative examples are described below:

[0025] Silica: Nanjing Xinhua Yuan Chemical;

[0026] Carbon black: Shandong Duoju Chemical;

[0027] Silicon powder: Nanjing Xinhua Yuan Chemical;

[0028] Yttrium oxide: Langfang Qianyao Technology;

[0029] Ethanol: Absolute ethanol, Jinan Jiewei Chemical;

[0030] Ferrous sulfate: Jinan Jibin Chemical;

[0031] Oxalic acid: Qidong Rongsheng Chemical.

[0032] Example 1

[0033] [[ID=३८]]A nano-reducing agent, the preparation steps include:

[0034] Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide in a mass ratio of 9:3:16. Then mix the mixed powder with ethanol in a mass ratio of 1:2, and ball-mill it in a nylon jar with silicon nitride balls for 12 h, followed by drying. Then put the mixture into a graphite crucible coated with boron nitride, transfer the graphite crucible to a multi-functional furnace, preheat the reaction furnace for 40 min, and evacuate. Heat it up at a rate of 20 °C / min to 1200 °C and hold for 10 min. When heated to 1200 °C, start to introduce nitrogen with a flow rate of 16 L / h and keep the nitrogen pressure in the furnace at 0.6 MPa. Continue to heat it up at a rate of 1.6 °C / min to 1590 °C and hold for 30 min. Then continue to heat it up at a rate of 0.5 °C / min to 1745 °C and hold for 120 min. Subsequently, cool it down to complete sintering. When the temperature drops to 1200 °C, turn off the nitrogen.

[0035] Step 2: Mix ferrous sulfate and oxalic acid in a molar ratio of 1:1, and stir until completely dissolved to obtain a ferrous oxalate suspension.

[0036] Step : Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2. 0.5 mL of ferrous oxalate suspension is required per gram of porous silicon nitride. Control the pH value at 2.4 and the temperature at 35 °C, and soak for 16 h, then dry to obtain porous silicon nitride adsorbed with ferrous oxalate.

[0037] Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 with ethanol in a mass ratio of 1:2, transfer it to a high-energy ball mill, use boron nitride balls for ball milling at a ball milling speed of 200 rpm for 5 h until it reaches the nanoscale, wash it with deionized water, and dry to obtain a nano-reducing agent.

[0038] Example 2

[0039] A nano-reducing agent, the preparation steps include:

[0040] Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide in a mass ratio of 12:5:1:2. Then mix the mixed powder with ethanol in a mass ratio of 1:2.5, and ball-mill it in a nylon jar with silicon nitride balls for 12 h, followed by drying. Then put the mixture into a graphite crucible coated with boron nitride, transfer the graphite crucible to a multi-functional furnace, preheat the reaction furnace for 50 min, and evacuate. Heat it up at a rate of 25 °C / min to 1300 °C and hold for 10 - 15 min. When heated to 1200 °C, start to introduce nitrogen with a flow rate of 18 L / h and keep the nitrogen pressure in the furnace at 0.8 MPa. Continue to heat it up at a rate of 1.8 °C / min to 1610 °C and hold for 35 min. Then continue to heat it up at a rate of 0.7 °C / min to 1755 °C and hold for 15 min. Subsequently, cool it down to complete sintering. When the temperature drops to 1200 °C, turn off the nitrogen.

[0041] Step 2: Mix ferrous sulfate and oxalic acid at a molar ratio of 1:1.2 and stir until completely dissolved to obtain a ferrous oxalate suspension;

[0042] Step 3: Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2. 1 mL of ferrous oxalate suspension is required for each gram of porous silicon nitride. Control the pH value at 2.6 and the temperature at 50 °C, soak for 30 h, and then dry to obtain porous silicon nitride adsorbed with ferrous oxalate;

[0043] Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 and ethanol at a mass ratio of 1:2.5, transfer to a high-energy ball mill, use boron nitride balls for ball milling, with a ball milling speed of 300 rpm and ball milling for 8 h until it reaches the nanoscale, rinse with deionized water, and dry to obtain the nano-reducing agent.

[0044] Example 3

[0045] A nano-reducing agent, the preparation steps include:

[0046] Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide at a mass ratio of 10:4:1:5, then mix the mixed powder and ethanol at a mass ratio of 1:2.1, use silicon nitride balls to ball mill in a nylon pot for 12 h, and then dry; then put the mixture into a graphite crucible coated with boron nitride, transfer the graphite crucible to a multi-functional furnace, preheat the reaction furnace for 40 min, and evacuate; heat up to 1200 °C at a rate of 20 °C / min, hold for 10 min. When heated to 1200 °C, start to introduce nitrogen with a flow rate of 16 L / h and keep the nitrogen pressure in the furnace at 0.6 MPa; continue to heat up to 1590 °C at a rate of 1.6 °C / min and hold for 30 min; continue to heat up to 1745 °C at a rate of 0.5 °C / min and hold for 120 min; then cool down to complete sintering. When the temperature drops to 1200 °C, turn off the nitrogen;

[0047] Step 2: Mix ferrous sulfate and oxalic acid at a molar ratio of 1:1.1 and stir until completely dissolved to obtain a ferrous oxalate suspension;

[0048] Step 3: Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2. 0.8 mL of ferrous oxalate suspension is required for each gram of porous silicon nitride. Control the pH value at 2.5 and the temperature at 40 °C, soak for 20 h, and then dry to obtain porous silicon nitride adsorbed with ferrous oxalate;

[0049] Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 and ethanol at a mass ratio of 1:2.2, transfer to a high-energy ball mill, use boron nitride balls for ball milling, with a ball milling speed of 250 rpm and ball milling for 6 h until it reaches the nanoscale, rinse with deionized water, and dry to obtain the nano-reducing agent.

[0050] Example 4

[0051] A nano-reducing agent, the preparation steps include:

[0052] Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide in a mass ratio of 11:3:1:4, then mix the mixed powder with ethanol in a mass ratio of 1:2.4, use silicon nitride balls to ball mill in a nylon jar for 12 h, and then dry; put the mixture into a graphite crucible coated with boron nitride, transfer the graphite crucible to a multi-functional furnace, preheat the reaction furnace for 45 min, and evacuate; heat up to 1250 °C at a rate of 22 °C / min, hold for 13 min, start to introduce nitrogen when heated to 1200 °C, with a flow rate of 17 L / h, and keep the nitrogen pressure in the furnace at 0.7 MPa; continue to heat up to 1600 °C at a rate of 1.7 °C / min, hold for 32 min; continue to heat up to 1750 °C at a rate of 0.6 °C / min, hold for 130 min; then cool down to complete sintering, close the nitrogen when the temperature drops to 1200 °C;

[0053] Step 2: Mix ferrous sulfate and oxalic acid in a molar ratio of 1:1, stir until completely dissolved to obtain a ferrous oxalate suspension;

[0054] Step 3: Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2. Each gram of porous silicon nitride requires 0.7 mL of ferrous oxalate suspension, control the pH value at 2.5, control the temperature at 35 °C, soak for 25 h, and dry to obtain porous silicon nitride adsorbed with ferrous oxalate;

[0055] Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 with ethanol in a mass ratio of 1:2, transfer to a high-energy ball mill, use boron nitride balls for ball milling, with a ball milling speed of 300 rpm, ball mill for 8 h, ball mill to the nanoscale, rinse with deionized water, and dry to obtain the nano-reducing agent.

[0056] Example 5

[0057] A nano-reducing agent, the preparation steps include:

[0058] Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide in a mass ratio of 10:3:1:4.5. Then mix the mixed powder with ethanol in a mass ratio of 1:2, and ball mill it in a nylon jar with silicon nitride balls for 12 h, and then dry it. Then put the mixture into a graphite crucible coated with boron nitride, transfer the graphite crucible to a multi-functional furnace, preheat the reaction furnace for 40 min, and evacuate. Heat it up to 1200 °C at a rate of 20 °C / min, hold for 10 min. When heated to 1200 °C, start to introduce nitrogen with a flow rate of 16 L / h and keep the nitrogen pressure in the furnace at 0.6 MPa. Continue to heat it up to 1600 °C at a rate of 1.6 °C / min and hold for 30 min. Then continue to heat it up to 1750 °C at a rate of 0.5 °C / min and hold for 120 min. Then cool it down to complete sintering. When the temperature drops to 1200 °C, turn off the nitrogen.

[0059] Step 2: Mix ferrous sulfate and oxalic acid in a molar ratio of 1:1.05, stir until completely dissolved to obtain a ferrous oxalate suspension.

[0060] Step 3: Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2. 1 mL of ferrous oxalate suspension is required for each gram of porous silicon nitride. Control the pH value at 2.4 and the temperature at 35 °C, soak for 24 h, and dry to obtain porous silicon nitride adsorbed with ferrous oxalate.

[0061] Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 with ethanol in a mass ratio of 1:2.2, transfer it to a high-energy ball mill, use boron nitride balls for ball milling, the ball milling speed is 200 rpm, ball mill for 7 h until it reaches the nanoscale, wash it with deionized water, and dry to obtain a nano-reducing agent.

[0062] Comparative Example 1

[0063] A reducing agent for lithium tantalate blackening, the preparation steps are as follows:

[0064] Step 1: Mix iron powder and graphene powder evenly in a mass ratio of 99∶1:

[0065] Step 2: Mechanically ball mill the mixed powder in Step 1 and lithium carbonate powder in a mass ratio of 5∶95 to obtain.

[0066] The lithium tantalate blackening process steps adopted by the present invention include:

[0067] S1: First cut the lithium tantalate crystal according to a predetermined size, remove the dirt on the surface of the lithium tantalate wafer, dry it and set it aside;

[0068] S2. Alternately spread the reducing agent and lithium tantalate wafers at the bottom of the crucible, and place the crucible containing the reducing agent and several lithium tantalate wafers into a vacuum reduction furnace; evacuate the furnace chamber, increase the temperature in the furnace at a rate of 50 °C / h, raise the temperature to 550 °C, keep it warm for 30 h, then cool down. When the temperature is lower than 100 °C, stop evacuating. After the air pressure in the furnace is equal to the outside, take out the crucible from the vacuum reduction furnace, and take out the reduced lithium tantalate wafers.

[0069] According to the above lithium tantalate blackening process, use the reducing agents of Examples 1-5 and Comparative Example 1 respectively to blacken the lithium tantalate wafers, and then test the transmittance of the blackened lithium tantalate wafers at a wavelength of 365 nm. Use the unblackened lithium tantalate wafers as the blank group. The test results are shown in the following table:

[0070]

[0071] From the above test data, it can be seen that compared with the blank group, the transmittance of Examples 1-5 has a significant decrease, and the effect of reducing the transmittance of lithium tantalate wafers can be achieved. Moreover, the transmittance effects of Examples 1-5 and Comparative Example 1 are similar. The lithium tantalate reducing agent used in Comparative Example 1 is a commonly used reducing agent combination in the current industry. It shows that the reducing agent of the present invention can achieve the same effect as the current market reducing agents.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a nano reducing agent for reducing the light transmittance of a lithium tantalate wafer, characterized in that the steps Comprising: Step 1: Mix silicon dioxide, carbon black, silicon powder, and yttrium oxide in a mass ratio of 9 - 12:3 - 5:1:2 - 6, then mix the mixed powder with ethanol in a mass ratio of 1:2 - 2.5, ball-mill and dry it, and sinter it under a nitrogen atmosphere to obtain porous silicon nitride; Step 2: Mix ferrous sulfate and oxalic acid in a molar ratio of 1:1 - 1.2, stir until completely dissolved to obtain a ferrous oxalate suspension; Step 3: Immerse the porous silicon nitride prepared in Step 1 in the ferrous oxalate suspension prepared in Step 2, control the pH value at 2.4 - 2.6, and immerse for 16 - 30 h to obtain porous silicon nitride adsorbed with ferrous oxalate; Step 4: Mix the porous silicon nitride adsorbed with ferrous oxalate obtained in Step 3 with ethanol in a mass ratio of 1:2 - 2.5, ball-mill it to the nanoscale, rinse it, and dry it to obtain a nano-reducing agent.

2. The preparation method according to claim 1, characterized in that, In Step 1, the sintering process is as follows: First, preheat the reaction furnace for 40 - 50 min and evacuate it; heat it up at a rate of 20 - 25 °C / min to 1200 - 1300 °C and hold for 10 - 15 min; continue to heat it up at a rate of 1.6 - 1.8 °C / min to 1590 - 1610 °C and hold for 30 - 35 min; continue to heat it up at a rate of 0.5 - 0.7 °C / min to 1745 - 1755 °C and hold for 120 - 150 min; then cool it down to complete the sintering.

3. The preparation method according to claim 2, characterized in that, In the sintering process of Step 1, when heated to 1200 °C, start to introduce nitrogen with a flow rate of 16 - 18 L / h and keep the nitrogen pressure in the furnace at 0.6 - 0.8 MPa; when the temperature drops to 1200 °C, close the nitrogen.

4. The preparation method according to claim 1, wherein The surface of the graphite crucible used for sintering in Step 1 is coated with boron nitride.

5. The preparation method according to claim 1, wherein In Step 3, 0.5 - 1 mL of ferrous oxalate suspension is required per gram of porous silicon nitride.

6. The preparation method according to claim 1, characterized in that, In Step 3, the immersion temperature is controlled at 35 - 50 °C.

7. The preparation method according to claim 1, characterized in that, In Step 4, deionized water is used for rinsing.

8. The preparation method according to claim 1, characterized in that, In Step 4, a high-energy ball mill is used for ball-milling with a ball-milling speed of 200 - 300 rpm and ball-milling for 5 - 8 h.

9. A nano-reducing agent for reducing the light transmittance of lithium tantalate wafers, characterized in that, Prepared by the preparation method described in any one of claims 1 - 8.

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