A method for preparing a surface acoustic wave sensor with improved adhesion of the gate electrode
By using platinum as the electrode material and subjecting it to heat treatment, the problem of poor adhesion between lithium niobate and the metal grid electrode was solved, achieving stable electrode bonding force and low-cost sensor fabrication, making it suitable for surface acoustic wave sensors in harsh environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XI AN JIAOTONG UNIV
- Filing Date
- 2023-12-08
- Publication Date
- 2026-06-23
AI Technical Summary
In the prior art, lithium niobate has poor adhesion to the metal gate electrode, which makes the metal gate electrode easy to detach when removing the photoresist, increasing costs and potentially reducing sensor performance.
Platinum was used as the electrode material, and the adhesion between platinum and lithium niobate was improved by heating. The photoresist was removed by utilizing the principle of photoresist denaturation at high temperature, which avoided the introduction of external components and enhanced the bonding force between the electrode and the substrate.
A stable bond between the platinum gate electrode and the lithium niobate substrate was achieved, which improved the stability and bonding strength of the sensor, reduced the cost, and the process was simple and did not introduce external components that would affect the performance.
Smart Images
Figure CN117686010B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrical sensor technology, specifically relating to a method for fabricating a surface acoustic wave sensor that improves the bonding force of the gate electrode. Background Technology
[0002] Surface acoustic wave (SAW) sensors boast high precision, sensitivity, miniaturization, micro-scale design, and simple structure. They are technically feasible, even as passive wireless sensors, and are resistant to high temperatures and corrosion, making them suitable for harsh environments such as component structural health monitoring. Furthermore, with the development of MEMS technology, SAW sensors are being used in an increasing number of fields. Specific applications in safety and health monitoring include measuring parameters such as vibration modes, gas pressure distribution, crack germination and growth, and loss or damage to protective coatings. There are also sensors that can withstand the harsh operating conditions of gas turbines. Real-time measurement of these variables provides better data for diagnosing operational problems, validating and improving performance analysis models, and providing data on component material and structural health. While current engine sensors primarily consist of thermocouples and resistive strain gauges, which generally meet the above requirements, their instability in harsh environments, high temperatures, or oxidation leads to suboptimal sensing performance. SAW sensors, however, can operate stably for thousands of hours under the high temperatures of turbine engines. Therefore, SAW sensors have a very promising future and development potential in the safety and health monitoring of large machinery and various high-temperature and complex environments.
[0003] Lithium niobate, a piezoelectric material, is commonly used in surface acoustic wave (SAW) sensor materials. In the fabrication of SAW sensors, photoresist is spin-coated onto a lithium niobate substrate, followed by exposure and development, and then a metal gate electrode is magnetron sputtered. The sensor is then immersed in acetone to remove the photoresist. However, due to the poor adhesion between lithium niobate and the metal gate electrode (e.g., aluminum, gold), the metal gate electrode may detach during photoresist removal. In existing technologies, a transition layer is often added to improve the adhesion between the metal gate electrode and the substrate. The disadvantages of this are increased cost and the introduction of unnecessary components, potentially reducing the sensor's overall performance.
[0004] Therefore, the problem to be solved by this invention is how to improve the gate electrode bonding force in a simple way without introducing external impurities. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a method for fabricating a surface acoustic wave sensor that improves the bonding strength of the gate electrode. This invention uses platinum as the electrode material and improves the adhesion between platinum and lithium niobate through a heat treatment method, thus preventing the platinum gate electrode from falling off. Furthermore, the entire process does not introduce any external components and is low in cost.
[0006] The present invention is specifically implemented through the following technical solution.
[0007] A method for fabricating a surface acoustic wave sensor with improved grid electrode bonding strength includes the following steps:
[0008] After cleaning and drying, a pretreated lithium niobate substrate is obtained.
[0009] Photoresist was spin-coated onto the pretreated lithium niobate substrate, followed by a pre-baking treatment at 100–120°C.
[0010] Photolithography was performed by spin-coating 3510T photoresist onto the pre-baked substrate, followed by exposure and development.
[0011] The developed substrate is then post-baked at 120–140°C.
[0012] On the side of the substrate after post-baking, photoresist is spin-coated, and a platinum layer is sputtered by magnetron sputtering.
[0013] The substrate after magnetron sputtering is heated to 450-500℃ for heat treatment;
[0014] The photoresist in the substrate after heat treatment is removed to form a platinum gate electrode, thus obtaining the surface acoustic wave sensor.
[0015] In a preferred embodiment of the present invention, during the heat treatment process, the heating rate is 1-3°C / min, and the holding time at 450-500°C is 30-40min.
[0016] In a preferred embodiment of the present invention, the pre-baking time is 20 to 30 minutes.
[0017] In a preferred embodiment of the present invention, contact exposure is used, and the exposure time is 6 to 10 seconds.
[0018] In a preferred embodiment of the present invention, the developer formula is 300-26 and the developing time is 5 to 10 seconds.
[0019] In a preferred embodiment of the present invention, the post-baking time is approximately 20 to 30 minutes.
[0020] In a preferred embodiment of the present invention, the magnetron sputtering film thickness parameter is 200±50nm.
[0021] In a preferred embodiment of the present invention, the step of removing photoresist is as follows: after the heat-treated substrate has cooled naturally, it is immersed in acetone, and then cleaned with ethanol and water.
[0022] In a preferred embodiment of the present invention, the substrate pretreatment step is as follows: after polishing the lithium niobate substrate, it is first soaked in acetone, then cleaned with ethanol and water, and then dried.
[0023] Compared with the prior art, the present invention has the following advantages:
[0024] This invention first spin-coates photoresist onto a lithium niobate substrate, followed by pre-baking, exposure and development, and post-baking. After magnetron sputtering of platinum, the temperature is raised to 450-500℃ for heat treatment. High-temperature evaporation is used to remove the photoresist. This method utilizes the principle that the stability of the platinum electrode increases exponentially at high temperatures while the photoresist denatures, thus achieving the purpose of removing the photoresist and stabilizing the electrode. After removing the photoresist, the obtained platinum gate electrode has strong adhesion and high stability to the lithium niobate substrate.
[0025] The present invention employs a heat treatment method at 450–500°C after magnetron sputtering of platinum to remove the adhesive. This method not only improves the bonding strength between the platinum gate electrode and the lithium niobate substrate, but also, unlike traditional methods, eliminates the need for external components such as transition layers during the entire process, thus avoiding the impact of introducing external components on sensor performance.
[0026] This invention significantly reduces costs and improves the stability of electrode material adhesion, while the processing is simple and has broad application prospects. Attached Figure Description
[0027] Figure 1 Example 1 shows the bonding of platinum to the surface of lithium niobate.
[0028] Figure 2 Example 2 shows the bonding of platinum to the surface of lithium niobate.
[0029] Figure 3 Example 3 shows the bonding of platinum to the surface of lithium niobate.
[0030] Figure 4 Comparative Example 1: Platinum bonding on the surface of lithium niobate. Detailed Implementation
[0031] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.
[0032] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.
[0033] To improve the bonding force between lithium niobate and the gate electrode, platinum was chosen as the electrode material. Pure platinum is a lustrous, malleable, silvery-white metal. Platinum has the highest malleability of all pure metals, surpassing gold, silver, and copper. Furthermore, platinum is extremely corrosion-resistant, very stable at high temperatures, and has stable electrical properties. It also does not oxidize at any temperature, making platinum the preferred electrode material for high-temperature sensing.
[0034] First, the substrate is cleaned, followed by a complete process of photoresist homogenization, pre-baking, exposure and development, and heat treatment and resist removal after magnetron sputtering. During heat treatment, the temperature is raised to 450–500℃ for high-temperature photoresist evaporation. This utilizes the principle that while the photoresist denatures at high temperatures, the stability of the platinum electrode increases exponentially, achieving both resist removal and electrode stabilization. Afterwards, acetone immersion is used, which easily removes the photoresist while ensuring a tight bond between the electrode and the substrate.
[0035] This invention discloses a method for fabricating a surface acoustic wave sensor with improved grid electrode bonding force, comprising the following steps:
[0036] After cleaning and drying, a pretreated lithium niobate substrate is obtained.
[0037] Photoresist was spin-coated onto the pretreated lithium niobate substrate, followed by a pre-baking treatment at 100–120°C.
[0038] Photolithography is performed on the photoresist of the pre-baked substrate, followed by exposure and development.
[0039] The developed substrate is then post-baked at 120–140°C.
[0040] On the side of the substrate after post-baking, photoresist is spin-coated, and a platinum layer is sputtered by magnetron sputtering.
[0041] The substrate after magnetron sputtering is heated to 450-500℃ for heat treatment;
[0042] The photoresist in the substrate after heat treatment is removed to form a platinum gate electrode, thus obtaining the surface acoustic wave sensor.
[0043] In a preferred embodiment of the invention, during the heat treatment, the heating rate is 1–3 °C / min, and the holding time at 450–500 °C is 30–40 min. Because platinum and lithium niobate have extremely poor adhesion, direct photoresist removal would cause the electrode to detach. Therefore, we employ high-temperature evaporation photoresist removal, utilizing the principle that while the photoresist denatures at high temperatures, the stability of the platinum electrode increases exponentially at high temperatures. The sputtered substrate is placed in a tube furnace, a suitable temperature is set, and a holding time of 450–500 °C for 30–35 min is performed to achieve photoresist removal and electrode stabilization.
[0044] In a preferred embodiment of the present invention, the pre-baking time is 20-30 minutes. After the photoresist spin coating is completed without errors, we generally do not expose and develop immediately. A pre-baking treatment is required on the substrate coated with photoresist to reduce the viscosity of the photoresist, allowing it to better adhere to the lithium niobate substrate, and to evaporate the solvent. Pre-baking is generally performed at around 100-120°C for 20-30 minutes; specific parameters should be determined based on the photoresist type and specifications.
[0045] In a preferred embodiment of the present invention, contact exposure is used, and the exposure time is 6 to 10 seconds.
[0046] In a preferred embodiment of the present invention, the developer formula is 300-26 and the developing time is 5 to 10 seconds.
[0047] After pre-baking, the substrate is removed from the oven and allowed to cool before the photolithography step. Photolithography uses an optical system to transfer a fine pattern onto photoresist. Development removes the denatured areas of the photoresist under ultraviolet light, allowing for the formation of a preliminary patterned IDT and gate electrode. We use contact exposure with an exposure time of 6–10 seconds. The development process requires precise mixing of the developer solution. The development time must be carefully controlled to ensure complete pattern development without any detachment of the patterned areas.
[0048] In a preferred embodiment of the present invention, the post-baking time is approximately 20–30 minutes. The developed substrate is rinsed with distilled water to remove impurities from the developer, dried with nitrogen, and then placed in an oven at approximately 120–140°C for post-baking. The purpose of post-baking is to harden the film, making the patterned areas more stable and facilitating subsequent magnetron sputtering. The post-baked substrate is then allowed to cool naturally before being removed.
[0049] In a preferred embodiment of the present invention, the magnetron sputtering film thickness parameter is 200±50nm. The prepared substrate is subjected to magnetron sputtering to deposit a metal film. The substrate is placed in the magnetron sputtering chamber, and a platinum target is used to metallize the substrate by setting a certain sputtering time and power. After sputtering is completed, the substrate is taken out, and at this time, the front side of the substrate should have a platinum layer.
[0050] In a preferred embodiment of the present invention, the step of removing the photoresist is as follows: after the heat-treated substrate has cooled naturally, it is immersed in acetone, and then cleaned with ethanol and water. After the heat-treated substrate has cooled naturally, it is immersed in acetone solution for a few seconds, then cleaned with anhydrous ethanol, and then rinsed with distilled water. At this time, it will be found that except for the patterned area, all the platinum in other parts has been removed, thereby obtaining a platinum gate electrode with extremely high stability.
[0051] In a preferred embodiment of the present invention, the substrate pretreatment steps are as follows: After polishing the lithium niobate substrate, it is first soaked in acetone, then cleaned with ethanol and water, and finally dried. First, the polished lithium niobate substrate is cleaned by initially cleaning it with acetone solution and soaking it for 2-3 minutes. Then, the substrate is further treated with anhydrous ethanol, followed by rinsing with distilled water. After rinsing, it is placed in an oven for preliminary drying. The purpose of this process is to remove impurities from the substrate, facilitating the subsequent acquisition of a clean and smooth surface conducive to metal deposition.
[0052] After the substrate is cleaned, it is removed from the oven and allowed to cool naturally. The specific operation of spin coating is to fix the substrate on a rotating chuck, and then apply an appropriate amount of liquid photoresist starting from the center of the substrate to ensure that the entire substrate is coated with photoresist without any omissions. Centrifugation is used to evenly coat the photoresist on the substrate surface. The parameters are 600 r / min for 12 seconds and then 4000 r / min for 40 seconds. The resulting spin-coated photoresist is about 2 μm in size.
[0053] The method of this invention can improve the bonding force between the electrode and the substrate, and is simple to operate, does not require the introduction of a process layer, and reduces costs.
[0054] The invention will now be described in detail through the following specific embodiments and comparative examples.
[0055] Example 1
[0056] A method for fabricating a surface acoustic wave sensor with improved grid electrode bonding strength includes the following steps:
[0057] (1) Cleaning treatment: First, the polished lithium niobate substrate is cleaned. The substrate is initially cleaned with acetone solution and soaked for 3 minutes. Then, the substrate is further treated with anhydrous ethanol. After that, it is rinsed with distilled water and placed in an oven for preliminary drying. The purpose of this process is to remove impurities from the substrate so that a clean and smooth surface that is easy for metal deposition can be obtained in the future.
[0058] (2) Coating process: After the substrate is cleaned, it is taken out of the oven and allowed to cool naturally. The specific operation of coating is to fix the substrate on the rotating chuck, and then apply an appropriate amount of liquid photoresist starting from the center of the substrate to ensure that the entire substrate is coated with photoresist without any omissions. Centrifugation is used to make the photoresist evenly coated on the surface of the substrate. The parameters are 600 r / min for 12s, and then 4000 r / min for 40s. The coated colloid is about 2um in size.
[0059] (3) Pre-baking: After the photoresist spin coating is completed without error, we generally do not expose and develop it immediately. We need to pre-bake the substrate coated with photoresist to reduce the viscosity of the photoresist, so that it can be better adsorbed on the lithium niobate substrate, and to evaporate the solvent in it. Generally, the pre-baking is carried out at about 110°C for 20 minutes. The specific parameters also need to be referred to the photoresist type and parameters.
[0060] (4) Exposure and Development: After pre-baking, the substrate is removed from the oven and allowed to cool before photolithography. Photolithography uses an optical system to transfer a fine pattern onto the photoresist. The purpose of development is to remove the denatured areas of the photoresist under ultraviolet irradiation in the exposed areas, so as to obtain a preliminary patterned IDT and gate electrode after development. We use contact exposure with an exposure time of 8 seconds. During development, the developer solution and distilled water need to be mixed in a 1:2 ratio before development. The development time is generally 8 seconds, and the timing needs to be precisely controlled to ensure that the pattern is fully developed and that the patterned areas do not peel off.
[0061] (5) Post-baking: After development, the substrate is rinsed with distilled water to remove impurities from the developer, and then dried with nitrogen before being placed in an oven at 130°C for post-baking. The purpose of post-baking is to harden the film and make the patterned area more stable, which facilitates subsequent magnetron sputtering. The substrate can be removed after natural cooling after post-baking.
[0062] (6) Magnetron sputtering: The prepared substrate is subjected to magnetron sputtering to prepare for metal film deposition. The substrate is placed in the magnetron sputtering chamber, and a platinum target is used to metallize the substrate by setting the sputtering parameters to a film thickness of 200nm. After sputtering is completed, the substrate is taken out. At this time, the front side of the substrate should have a platinum layer of about 200nm.
[0063] (7) Heat treatment: Due to the extremely poor adhesion between platinum and lithium niobate, direct photoresist removal would cause the electrode to detach. Here, we use high-temperature evaporation photoresist removal, taking advantage of the principle that the stability of the platinum electrode increases exponentially at high temperatures while the photoresist denatures. The sputtered substrate is placed in a tube furnace, the parameters are set appropriately, and a heat treatment is performed at 450°C for 30 minutes to achieve the purpose of photoresist removal and electrode stabilization.
[0064] (8) Removal of adhesive: After the heat-treated substrate is cooled naturally, it is soaked in acetone solution for a few seconds, then cleaned with anhydrous ethanol, and then rinsed with distilled water. At this time, it will be found that except for the patterned part, all the platinum in other parts has fallen off, thus obtaining a platinum gate electrode with extremely high stability.
[0065] Example 2
[0066] A method for fabricating a surface acoustic wave sensor with improved grid electrode bonding strength includes the following steps:
[0067] (1) Cleaning treatment: First, the polished lithium niobate substrate is cleaned. The substrate is initially cleaned with acetone solution and soaked for 2 minutes. Then, the substrate is further treated with anhydrous ethanol. After that, it is rinsed with distilled water and then placed in an oven for preliminary drying.
[0068] (2) Coating process: After the substrate is cleaned, it is taken out of the oven and allowed to cool naturally. The specific operation of coating is to fix the substrate on a rotating chuck, and then apply an appropriate amount of liquid photoresist starting from the center of the substrate to ensure that the entire substrate is coated with photoresist without any omissions. Centrifugation is used to make the photoresist evenly coated on the surface of the substrate. The parameters are 600 r / min for 12s, and then 4000 r / min for 40s. The coated colloid is about 2um in size.
[0069] (3) Pre-baking: After the photoresist spin coating is completed without error, the substrate coated with photoresist is pre-baked at 100°C for 20 minutes.
[0070] (4) Exposure and Development: After pre-baking, the substrate is removed from the oven and allowed to cool before photolithography. Contact exposure is used, with an exposure time of 7 seconds. During development, the developer and distilled water are mixed in a 1:2 ratio and then developed for 10 seconds to ensure that the pattern is fully developed and does not peel off.
[0071] (5) Post-baking: Rinse the developed substrate with distilled water to remove impurities from the developer, and dry it with nitrogen gas before placing it in an oven at 100°C for post-baking. After post-baking, the substrate can be taken out after natural cooling.
[0072] (6) Magnetron sputtering: The prepared substrate is subjected to magnetron sputtering to prepare for metal film deposition. The substrate is placed in the magnetron sputtering chamber, and a platinum target is used to metallize the substrate by setting the sputtering parameters to a film thickness of 250nm. After sputtering is completed, the substrate is taken out. At this time, the front side of the substrate should have a platinum layer of about 250nm.
[0073] (7) Heat treatment: Due to the extremely poor adhesion between platinum and lithium niobate, direct photoresist removal would cause the electrode to detach. Here, we use high-temperature evaporation photoresist removal, taking advantage of the principle that the stability of the platinum electrode increases exponentially at high temperatures while the photoresist denatures. The sputtered substrate is placed in a tube furnace, the parameters are set appropriately, and a heat treatment is performed at 450°C for 40 minutes to achieve the purpose of photoresist removal and electrode stabilization.
[0074] (8) Removal of adhesive: After the heat-treated substrate is cooled naturally, it is soaked in acetone solution for a few seconds, then cleaned with anhydrous ethanol, and then rinsed with distilled water. At this time, it will be found that except for the patterned part, all the platinum in other parts has fallen off, thus obtaining a platinum gate electrode with extremely high stability.
[0075] Example 3
[0076] A method for fabricating a surface acoustic wave sensor with improved grid electrode bonding strength includes the following steps:
[0077] (1) Cleaning treatment: First, the polished lithium niobate substrate is cleaned. The substrate is initially cleaned with acetone solution and soaked for 2 minutes. Then, the substrate is further treated with anhydrous ethanol. After that, it is rinsed with distilled water and then placed in an oven for preliminary drying.
[0078] (2) Coating process: After the substrate is cleaned, it is taken out of the oven and allowed to cool naturally. The specific operation of coating is to fix the substrate on a rotating chuck, and then apply an appropriate amount of liquid photoresist starting from the center of the substrate to ensure that the entire substrate is coated with photoresist without any omissions. Centrifugation is used to make the photoresist evenly coated on the surface of the substrate. The parameters are 600 r / min for 12s, and then 4000 r / min for 40s. The coated colloid is about 2um in size.
[0079] (3) Pre-baking: After the photoresist spin coating is completed without errors, the substrate coated with photoresist needs to be pre-baked. The purpose is to reduce the viscosity of the photoresist, so that it can be better adsorbed on the lithium niobate substrate, and to evaporate the solvent in it. Pre-baking is performed at about 120°C for 20 minutes. The specific parameters also need to be referred to the photoresist type and parameters.
[0080] (4) Exposure and Development: After pre-baking, the substrate is removed from the oven and allowed to cool before photolithography. Contact exposure is used, with an exposure time of 8 seconds. During development, the developer and distilled water are mixed in a 1:2 ratio and then developed for 7 seconds to ensure that the pattern is fully developed and does not peel off.
[0081] (5) Post-baking: Rinse the developed substrate with distilled water to remove impurities from the developer, and dry it with nitrogen gas before placing it in an oven at 140°C for post-baking. After post-baking, the substrate can be removed after natural cooling.
[0082] (6) Magnetron sputtering: The prepared substrate is subjected to magnetron sputtering to prepare for metal film deposition. The substrate is placed in the magnetron sputtering chamber, and a platinum target is used to metallize the substrate with a film thickness of 150nm. After sputtering, the substrate is taken out. At this time, the front side of the substrate should have a platinum layer of about 150nm.
[0083] (7) Heat treatment: We use high-temperature evaporation to remove the photoresist, taking advantage of the principle that the stability of the platinum electrode increases exponentially at high temperatures while the photoresist denatures at high temperatures. The sputtered substrate is placed in a tube furnace and held at 500°C for 30 minutes to remove the photoresist and stabilize the electrode.
[0084] (8) Removal of adhesive: After the heat-treated substrate is cooled naturally, it is soaked in acetone solution for a few seconds, then cleaned with anhydrous ethanol, and then rinsed with distilled water. At this time, it will be found that except for the patterned part, all the platinum in other parts has fallen off, thus obtaining a platinum gate electrode with extremely high stability.
[0085] Comparative Example 1
[0086] (1) Prepare a substrate with a single-sided polished surface, and use organic solvent acetone, anhydrous alcohol and pure water to perform ultrasonic cleaning for 4 minutes in sequence to remove surface dust and impurities.
[0087] (2) After cleaning, use compressed air to blow dry the water stains on the substrate surface and place it in a 90°C oven to dry the moisture for about 15 minutes.
[0088] (3) Spin coat the substrate surface with 3510T positive photoresist using a spin coater. Spin the photoresist slowly at 600r / min for 12s, and then quickly at 3000r / min to thin the photoresist thickness for 40s. At this time, the photoresist thickness on the substrate surface is about 1.5um. After the photoresist coating is completed, place the silicon wafer in an oven and set it to 90℃ for 20min.
[0089] (4) Use an ultraviolet exposure machine and a mask with a pre-etched sensor pattern to expose the silicon wafer after the pre-baking and return to room temperature for 6.5s. After exposure, bake at 90℃ for 2min. Develop with 300-26 developer for about 30s. After development, immediately rinse the substrate with pure water and dry it with nitrogen.
[0090] (5) Place the developed and dried substrate into an oven and bake at 90°C for about 20 minutes to harden the film.
[0091] (6) Use a magnetron sputtering instrument to sputter the platinum layer according to the preset program to remove the photoresist and the metal film on it. Soak the substrate with the film grown on it in acetone solution for about 20 minutes. After removing the photoresist, rinse the substrate with anhydrous alcohol and pure water and dry it.
[0092] Figure 1 This shows the bonding of the platinum gate electrode on the lithium niobate substrate in Example 1. Figure 1 The portion marked in the Chinese box is platinum prepared on a lithium niobate substrate. As can be seen, the platinum layer is continuous and stable, without any peeling off, which indicates that the prepared platinum can be stably bonded to the substrate.
[0093] Figure 2 This shows the bonding of the platinum gate electrode on the lithium niobate substrate in Example 2. Figure 2 The portion marked in the Chinese box is platinum prepared on a lithium niobate substrate. As can be seen, the platinum layer is continuous and stable, without any peeling off, which indicates that the prepared platinum can be stably bonded to the substrate.
[0094] Figure 3 The figure shows the bonding of the platinum gate electrode on the lithium niobate substrate in Example 3. As can be seen, the platinum layer is continuous and stable, without any peeling, which indicates that the prepared platinum can be stably bonded to the substrate.
[0095] Comparative Example 1 shows a device obtained using a conventional method without heat treatment. Compared to the device obtained using the method of this invention, its electrodes show obvious detachment. Figure 4 In the image, the area marked in the box represents the portion where platinum detached, causing the electrode to fail to attach.
[0096] By comparing the surface acoustic wave (SAW) sensors prepared in the embodiments of this invention with those prepared in Comparative Example 1, it can be seen that in Comparative Example 1, without the heat treatment process of this invention, the electrode eventually detaches. However, the electrode prepared after heat treatment in this invention is uniformly distributed on the substrate surface and does not detach, proving the feasibility of this invention. In this invention, after magnetron sputtering the metal gate electrode, the temperature is first raised to 450–500°C for heat treatment. High-temperature evaporation is used to remove the photoresist. Utilizing the principle that the photoresist denatures at high temperatures while the stability of the platinum electrode increases exponentially at high temperatures, the purpose of removing the photoresist and stabilizing the electrode is achieved. After removing the photoresist, the obtained platinum gate electrode and lithium niobate substrate have strong adhesion and high stability. Furthermore, this process does not introduce transition layers or other components, resulting in low cost and avoiding the problem of device impact caused by the introduction of external components. This invention's method is simple, improves the adhesion between the gate electrode and the substrate, and is suitable for widespread use.
[0097] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, it is intended to include any modifications and variations that fall within the scope of the claims and their equivalents.
Claims
1. A method for fabricating a surface acoustic wave sensor with improved grid electrode bonding force, characterized in that, Includes the following steps: After cleaning and drying, a pretreated lithium niobate substrate is obtained. Photoresist was spin-coated onto the pretreated lithium niobate substrate, followed by a pre-baking treatment at 100~120℃; Photolithography is performed on the photoresist of the pre-baked substrate, followed by exposure and development. The developed substrate is then post-baked at 120~140℃. On the side of the substrate after post-baking, photoresist is spin-coated and then a platinum layer is deposited by magnetron sputtering. The substrate after magnetron sputtering is heated to 450~500℃ for heat treatment; The photoresist in the substrate after heat treatment is removed to form a platinum gate electrode, thereby obtaining the surface acoustic wave sensor; During the heat treatment process, the heating rate is 1~3℃ / min, and the holding time at 450~500℃ is 30~35min; The steps to remove photoresist are as follows: After the heat-treated substrate has cooled naturally, it is immersed in acetone, and then cleaned with ethanol and water. High-temperature evaporation is used to remove the photoresist, taking advantage of the principle that the stability of the platinum electrode increases exponentially at high temperatures while the photoresist denatures at high temperatures, thus achieving the purpose of removing the photoresist and stabilizing the electrode.
2. The preparation method according to claim 1, characterized in that, The pre-baking time is 20-30 minutes.
3. The preparation method according to claim 1, characterized in that, Contact exposure is used, with an exposure time of 6-10 seconds.
4. The preparation method according to claim 1, characterized in that, The development time is 5~10 seconds.
5. The preparation method according to claim 1, characterized in that, The post-drying time is 20-30 minutes.
6. The preparation method according to claim 1, characterized in that, The platinum layer thickness is 200±50nm.
7. The preparation method according to claim 1, characterized in that, The substrate pretreatment steps are as follows: after polishing the lithium niobate substrate, soak it in acetone, then clean it with ethanol and water, and then dry it.