Method for fabricating sol-gel composite piezoelectric sensors

Abstract

To provide a sol-gel composite piezoelectric sensor production method that facilitates the production of a sol-gel composite piezoelectric sensor.SOLUTION: When producing a sol-gel composite piezoelectric sensor using a sol-gel solution and ceramic powder, a sol-gel solution in an amorphous state is used. For example, with a lead-free sol-gel solution and ceramic powder, it is possible to produce a lead-free sol-gel composite piezoelectric sensor that can operate from low to high temperatures even when polarization processes are performed at temperatures such as 0°C or more and 100°C or less (for example, room temperature). For example, by using a TiO2-Sr sol-gel solution, it is possible to achieve polarization at room temperature, 100°C or less, or 300°C or less even in a mixed piezoelectric film with lithium niobate powder, etc. whose polarization temperature is high.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a sol-gel composite piezoelectric sensor, and more particularly to a method for producing a sol-gel composite piezoelectric sensor. [Background technology]

[0002] The inventors have proposed a lead-free sol-gel composite piezoelectric sensor. For example, the inventors have used bismuth titanate or lithium niobate as powder and bismuth titanate-based or CaBi2Ta2O9 as sol-gel solution. For example, in Patent Document 1, CaBi2Ta2O9 powder and Bi4Ti3O 12 The formation of piezoelectric films from a mixture of sol-gel solutions was proposed.

[0003] In Patent Document 2, the inventors propose a sensor device suitable for wiring a sol-gel composite piezoelectric sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6829851 [Patent Document 2] Patent Application No. 2020-202072 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional sol-gel composite piezoelectric sensors have been difficult to fabricate.

[0006] Therefore, an object of the present invention is to propose a method for producing a sol-gel composite piezoelectric sensor that is suitable for easily producing a sol-gel composite piezoelectric sensor. [Means for solving the problem]

[0007] A first aspect of the present invention is a method for fabricating a sol-gel composite piezoelectric sensor, comprising the steps of fabricating the sol-gel composite piezoelectric sensor using a piezoelectric ceramic film formed from a mixture of a sol-gel solution and ceramic powder, wherein the sol-gel solution is amorphous.

[0008] A second aspect of the present invention is the method for producing a sol-gel composite piezoelectric sensor according to the first aspect, wherein neither the sol-gel solution nor the ceramic powder contains lead.

[0009] A third aspect of the present invention is the method for producing a sol-gel composite piezoelectric sensor according to the first or second aspect, wherein the polarization treatment of the piezoelectric ceramic film is carried out at 300° C. or less.

[0010] A fourth aspect of the present invention is the method for producing a sol-gel composite piezoelectric sensor according to any one of the first to third aspects, wherein the ceramic powder includes lithium niobate powder and / or bismuth titanate powder. [Effects of the Invention]

[0011] When conventional sol-gel composite piezoelectric sensors are produced, the polarization temperature must be high, for example, as is the case in Patent Document 1, where the polarization temperature is 400°C.

[0012] According to each aspect of the present invention, by using an amorphous sol-gel solution, for example, even when a lead-free sol-gel composite piezoelectric sensor is produced using a lead-free sol-gel solution and piezoelectric ceramic powder, the produced sol-gel composite piezoelectric sensor can operate at temperatures ranging from 0°C to 300°C (e.g., room temperature), and even at high temperatures such as 600°C or 1000°C, even when polarization treatment is performed at a temperature between 0°C and 300°C (e.g., room temperature).

[0013] Furthermore, the inventors confirmed that by using a TiO2-Sr sol-gel solution, polarization can be achieved at room temperature, below 100°C, below 300°C, etc., even in mixed piezoelectric films with lithium niobate powder, which has a high polarization temperature. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing an example of the configuration of a sensor device 1 according to an embodiment of the present invention. [Figure 2] 1A is a diagram showing an outline of the configuration of a sensor section 3, and FIG. 1B is a diagram showing a state in which the sensor section 3 and a heat-resistant wiring section 9 are joined at a joint 5. FIG. [Figure 3] The results of ultrasonic pulse echo waveform acquisition using the prototype sensor are shown below. [Figure 4] FIG. 1 shows data relating to amorphous. [Figure 5] FIG. 1 shows the experimental results of a piezoelectric film device produced by mixing and stirring lithium niobate powder and a sol-gel liquid and then spraying the mixture. [Figure 6] FIG. 2 shows the experimental results of a piezoelectric film device produced by mixing and stirring lithium niobate powder and a sol-gel liquid and then spraying the mixture. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, however, the present invention is not limited to this embodiment. [Example]

[0016] FIG. 1 is a diagram showing an example of the configuration of a sensor device 1 according to an embodiment of the present invention.

[0017] The sensor device 1 is a sol-gel composite piezoelectric sensor (see Patent Document 2). The sensor device 1 includes a sensor section 3, a joint section 5, a crimping section 7, a heat-resistant wiring section 9, and a wiring connector section 11.

[0018] The sensor section 3 is realized by using a piezoelectric film layer.

[0019] The joint 5 joins the sensor part 3 and the heat-resistant wiring part 9 by the crimping part 7 .

[0020] The wiring connector portion 11 is for connecting the heat-resistant wiring portion 9 to external wiring (not shown).

[0021] 2(a) is a diagram showing an outline of the configuration of the sensor unit 3. In the sensor unit 3, a ground line attachment portion 29 is provided on a base material layer 27. A piezoelectric film layer 25 and an electrode layer 23 are formed on the base material layer 27 in a location different from the ground line attachment portion 29, in that order from closest to the base material layer 27. The piezoelectric film layer 25 and the electrode layer 23 are covered with a protective layer 21, except for a signal line attachment portion 22 provided on the electrode layer 23.

[0022] 2(b) is a diagram showing the state where the sensor unit 3 and the heat-resistant wiring unit 9 are joined at the joint 5. Joints 51 and 52 are the upper and lower parts of the joint 5, respectively.

[0023] The heat-resistant wiring section 9 includes a ground line 31 and a signal line 33. The ground line 31 is attached to a ground line attachment section 29 provided on the base layer 27 (see the ground line joint section 35 in the figure). A crimping tip 37 is provided at the tip of the signal line 33. The crimping tip 37 is located in the signal line attachment section 22 provided on the upper part of the electrode layer 23. The crimping section 7 applies force to the crimping tip 37 via the insulating layer 39 to crimp the crimping tip 37 to the electrode layer 23.

[0024] The present invention relates to a piezoelectric film layer 25. Sol-gel composite piezoelectric devices with practical performance can be efficiently fabricated by poling a piezoelectric ceramic film obtained by spraying and sintering a mixture of an amorphous sol-gel solution and ceramic powder. These devices can be used, for example, in ultrasonic probes (for industrial, medical, and biological applications) and pressure and vibration sensors. They offer features such as heat resistance of over 600°C (operational up to 1000°C), flexibility with a curvature radius of approximately 10 mm, and a thickness of less than 1 mm. Poling can be achieved at a process temperature of, for example, 0°C to 300°C (e.g., room temperature).

[0025] Sol-gel composite piezoelectric sensors are flexible and heat-resistant (thermal shock resistant) piezoelectric ceramic devices. They can be used for applications such as pipe thickness monitoring, pipe blockage detection, pressure / vibration monitoring, and as an acoustic emission (AE) sensor to monitor damage to structures. They are expected to be used as edge sensors, which are necessary for IoT implementation in factories, especially in places where conventional sensors are difficult to use, such as high-temperature areas and narrow spaces.

[0026] The inventors have proposed a sol-gel composite piezoelectric sensor fabrication process as a sol-gel spray method. Film coating: A mixture of a sol-gel solution, which is a precursor of the piezoelectric material, and ceramic powder is sprayed and heat-treated to form a piezoelectric ceramic film. Heat treatment: The coating film is heated to a temperature of 200 to 600° C. to dry it and crystallize the sol-gel liquid. Polarization: Polarization is performed by applying a strong electric field under corona discharge or by applying a high voltage to the piezoelectric film.

[0027] Sol-gel composite piezoelectric sensors and the sol-gel spray method are known for the following features: The porosity created by spraying the powder-mixed coating liquid allows for thermal shock resistance and flexibility. The spray coating process (= painting process) makes it possible to apply a sensor device (piezoelectric device) directly to the surface of a three-dimensional object to be measured, such as a pipe. Ultrasonic nondestructive testing under high-temperature conditions typically poses challenges in selecting a couplant (matching agent, typically glycerin or silicone oil) to ensure ultrasonic transmission between the object to be measured and the sensor. However, if the sensor is formed directly on the object to be measured using the sol-gel spray method, no couplant is required, eliminating this issue.

[0028] Because the properties of piezoelectric materials improve when they contain lead, materials such as lead zirconate titanate (PZT) are widely used. Lead-free materials with performance equivalent to lead-containing materials are not currently in practical use, and piezoelectric materials are an exception to the lead exemption regulations in the RoHS Directive. Materials and processes for producing lead-free piezoelectric devices with practical performance not only reduce environmental impact, but are also a technology that could have a significant impact on the piezoelectric device market, which has previously been exempt from regulations.

[0029] The inventors have been working on a sol-gel spray method for lead-free materials, but when polarizing materials that can generally be used at high temperatures (the temperature at which they lose their piezoelectricity = Curie temperature is high), the process temperature must also be as high as 800°C, which has been a challenge in realizing a practical mass production process.

[0030] According to the present invention, by using an amorphous sol-gel solution (for example, titanate-strontium (TiO2-Sr sol-gel solution)), the polarization temperature can be reduced to room temperature or around 100°C or 300°C, and a process for fabricating a piezoelectric sensor with practical performance from room temperature to high temperatures has been successfully realized. Figure 3 shows the ultrasonic pulse echo waveform obtained using the prototype sensor.

[0031] Figure 4 shows data obtained by analyzing a sol-gel solution using X-ray diffraction (XRD). The horizontal axis indicates the angle of the X-ray beam, and the vertical axis indicates the intensity. A crystalline state is a solid in which atoms and other components are regularly arranged. An amorphous state is a state of matter that does not have a crystalline structure. In XRD analysis, a pronounced peak appears in a crystalline state. In an amorphous state, the peak is gentler because crystallization has not occurred. Figure 4 shows an example of analyzing strontium in a sol-gel solution. The data obtained by XRD shows that the peak is broadened and wide, indicating an amorphous state.

[0032] The inventors specifically created a piezoelectric ceramic film by mixing a TiO2-Sr sol-gel solution with lithium niobate powder, coating it on a titanium plate, and firing it. The film exhibited piezoelectricity even at room temperature, and successfully captured pulse echo waveforms within the titanium plate. In this case, the high-temperature operating limit temperature was 300°C.

[0033] Furthermore, a similar piezoelectric ceramic film poled at 100°C also exhibited piezoelectricity, enabling the pulse-echo waveform within the titanium plate to be successfully obtained. In this case, the high-temperature operating limit temperature was 600°C.

[0034] Furthermore, a piezoelectric ceramic film made by mixing a TiO2-Sr sol-gel solution with bismuth titanate powder, coating it on a titanium plate, and firing it exhibited piezoelectricity even at room temperature, enabling the successful acquisition of pulse-echo waveforms within the titanium plate. In this case, the high-temperature operating limit temperature was 670°C.

[0035] Figures 5 and 6 show the experimental results of a piezoelectric film device created by mixing and stirring lithium niobate powder and a sol-gel liquid using a spray method. The coating substrate was a titanium plate. Electrodes were attached, and high-temperature operation was evaluated using an ultrasonic pulse-echo test. The film thickness was approximately 50 μm.

[0036] Figure 5 is a graph showing temperature characteristics. The horizontal axis represents temperature (°C) and the vertical axis represents sensitivity (dB). Echo waveforms can be confirmed above 0°C. The presence of echo waveforms was confirmed at room temperature. Echo waveforms were confirmed by further increasing the temperature up to 600°C. Figures 6(a) and (b) show the echo waveforms confirmed at room temperature and 532°C, respectively. Sensitivity decreased above 600°C.

[0037] Polarization was possible at temperatures between 0°C and 300°C (for example, room temperature). [Explanation of symbols]

[0038] REFERENCE SIGNS LIST 1 sensor device, 3 sensor section, 5 joint section, 7 crimping section, 9 heat-resistant wiring section, 11 wiring connector section, 21 protective layer, 22 signal line attachment section, 23 electrode layer, 25 piezoelectric film layer, 27 substrate layer, 29 ground line attachment section, 31 ground line, 33 signal line, 35 ground line joint section, 37 crimping tip, 39 insulating layer

Claims

1. A method for fabricating a sol-gel composite piezoelectric sensor, comprising: fabricating the sol-gel composite piezoelectric sensor using a piezoelectric ceramic film formed from a mixture of a sol-gel solution and ceramic powder; the sol-gel solution is amorphous and contains strontium; the sol-gel solution contains TiO 2 ; The method for producing a sol-gel composite piezoelectric sensor comprises carrying out a polarization treatment on the piezoelectric ceramic film at a temperature of 300° C. or less.

2. The method for making a sol-gel composite piezoelectric sensor according to claim 1 , wherein the sol-gel solution and the ceramic powder are both lead-free.

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