A single-sided double-layer piezoelectric element and its fabrication method

Abstract

This invention discloses a single-sided double-layer piezoelectric element and its fabrication method. From bottom to top, it comprises a metal substrate, a lower electrode layer, a first piezoelectric ceramic layer, an intermediate electrode layer, a second piezoelectric ceramic layer, and an upper electrode layer. Both the first and second piezoelectric ceramic layers are lead zirconate titanate-based piezoelectric ceramic layers. The lower electrode layer serves as a common electrode. The polarization direction of the first piezoelectric ceramic layer is vertically downward, and the polarization direction of the second piezoelectric ceramic layer is vertically upward, with opposite polarization directions. The side connection electrode is formed by coating with conductive silver paste, achieving electrical connection between the lower and upper electrode layers on the same side of the single-sided double-layer piezoelectric element. The single-sided double-layer piezoelectric element achieves external electrical connection only through the side with the intermediate electrode layer and the side connection electrode. This invention significantly improves the structural stability of the single-sided double-layer piezoelectric element during transportation, assembly, and use; increases production and assembly efficiency; reduces the number of electrical connection points; and extends the device's lifespan.

Description

Technical Field

[0001] This invention relates to the field of electroacoustic conversion device technology, and more specifically, to a single-sided double-layer piezoelectric element and a method for preparing the single-sided double-layer piezoelectric element. Background Technology

[0002] Existing piezoelectric elements with a single-sided double-layer structure often employ a two-layer structure of a metal substrate and a piezoelectric ceramic sheet, or a three-layer structure of a metal substrate, a piezoelectric ceramic sheet, and a metal sheet. Electrodes are typically located on the upper and lower surfaces of the piezoelectric ceramic sheet. This type of structure has several inherent defects that negatively impact the use, assembly, and performance of single-sided double-layer piezoelectric elements. Specific problems include: 1. Electrode damage is easy: The electrodes on the upper surface (usually silver electrodes) are exposed. During transportation, assembly and actual use, they are easily damaged by scratches, oxidation or contamination, which can lead to a decrease in the performance of the single-sided double-layer piezoelectric element or even direct failure. 2. High assembly complexity: When installing a single-sided double-layer piezoelectric element into the piezoelectric element housing or resonant cavity, it is necessary to ensure that the lead wire connection of the upper surface electrode is reliable. This requirement increases the complexity of the assembly operation and also increases the production and assembly cost. 3. Reliability risks exist: The design of the upper and lower double electrodes means that the single-sided double-layer structure piezoelectric element requires two electrical connection points. The increase in connection points directly increases the risk of failure caused by problems such as poor soldering and wire breakage. 4. Performance limitations: Traditional single-layer drive structures have certain limitations in vibration displacement and sound pressure level. To improve the performance of single-sided double-layer piezoelectric elements, it is often necessary to increase their diameter or increase the driving voltage. This approach is not conducive to the miniaturization design and low-power operation of the device. To address the aforementioned issues, some improvements have emerged in the prior art, such as using a protective adhesive to cover the upper electrode. However, this method increases the number of processing steps and may also affect the vibration performance of the single-sided double-layer piezoelectric element. Other solutions employ a more complex multilayer piezoelectric ceramic structure, but this significantly increases the manufacturing cost of the single-sided double-layer piezoelectric element.

[0003] Therefore, those skilled in the art are dedicated to providing a piezoelectric ceramic single-sided double-layer structure piezoelectric element and its corresponding preparation method that can effectively solve the above-mentioned technical problems. Summary of the Invention

[0004] To achieve the above objectives, the present invention provides a single-sided double-layer piezoelectric element, which, from bottom to top, comprises a metal substrate, a lower electrode layer, a first piezoelectric ceramic layer, an intermediate electrode layer, a second piezoelectric ceramic layer, and an upper electrode layer. The metal substrate is a brass sheet, the lower electrode layer is a silver electrode, and both the first and second piezoelectric ceramic layers are lead zirconate titanate-based piezoelectric ceramic layers; the lower electrode layer is a common electrode, the polarization direction of the first piezoelectric ceramic layer is vertically downward, and the polarization direction of the second piezoelectric ceramic layer is vertically upward, with opposite polarization directions. It also includes a side connection electrode, which is formed by coating conductive silver paste. The lower electrode layer and the upper electrode layer are electrically connected on the same side of the single-sided double-layer piezoelectric element, so that the first piezoelectric ceramic layer and the second piezoelectric ceramic layer form a parallel driving relationship. The single-sided double-layer piezoelectric element is electrically connected to the outside only through the side with the middle electrode layer and the side connection electrode. The middle electrode layer and the upper electrode layer are both silver electrodes formed by sintering silver paste.

[0005] Furthermore, the thickness of the brass sheet is 0.1~0.3mm, and the thickness of the silver electrode is 8~12μm; both the first piezoelectric ceramic layer and the second piezoelectric ceramic layer are lead zirconate titanate piezoelectric ceramic layers with a thickness of 0.08~0.12mm. Furthermore, the side connection electrode is formed by coating conductive silver paste onto the polished side of the single-sided double-layer piezoelectric element using a fine brush or precision printing technology.

[0006] A method for fabricating a single-sided double-layer piezoelectric element includes the following steps: S1. Substrate Preparation: A brass sheet with a thickness of 0.1~0.3mm is selected as the metal substrate, and it is cleaned and polished to serve as the vibration substrate and support for the single-sided double-layer piezoelectric element. S2. Lower electrode formation: A layer of silver paste is uniformly printed on the surface of a brass sheet using screen printing technology, and then sintered and cured at 800~900℃ to form a lower electrode layer with a thickness of 8~12μm. S3. Formation and polarization of the first piezoelectric layer: PZT green ceramic sheets were prepared by tape casting and attached to the lower electrode layer. They were then sintered at 1100~1200℃ to form a first piezoelectric ceramic layer with a thickness of 0.08~0.12mm. Subsequently, the first piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3kV / mm for 20-32 minutes to make its polarization direction vertically downward. S4. Formation of intermediate electrode: A silver paste is screen-printed onto the surface of the first piezoelectric ceramic layer and then sintered to form an intermediate electrode layer. S5. Formation and polarization of the second piezoelectric layer: Another PZT green ceramic sheet prepared by tape casting was attached to the intermediate electrode layer and sintered at 1100~1200℃ to form a second piezoelectric ceramic layer with a thickness of 0.08~0.12mm. Then, the second piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3kV / mm for 30 minutes, so that its polarization direction is vertically upward and opposite to the polarization direction of the first piezoelectric ceramic layer. S6. Upper electrode formation: Silver paste is printed and sintered on the surface of the second piezoelectric ceramic layer to form the upper electrode layer; S7. Single-sided electrode connection: The edges of the single-sided double-layer piezoelectric element are lightly ground using precision grinding equipment to expose the sides of the lower and upper electrode layers. Then, conductive silver paste is applied to the ground sides using a fine brush or precision printing technology to reliably connect the lower and upper electrode layers and form a side connection electrode. S8. Lead wire connection: The first lead is soldered to the pad of the middle electrode layer with conductive adhesive, and the second lead is soldered to the extension of the side electrode with conductive adhesive. S9. Assembly: The single-sided double-layer piezoelectric element with connected leads is installed into a plastic housing with a resonant cavity using epoxy resin adhesive, thus completing the assembly of the piezoelectric element.

[0007] Furthermore, the sintering in S3 and S5 is a step-by-step sintering method, and the sintering temperature is 1150℃ for both.

[0008] Furthermore, the polarization treatment medium in S3 and S5 is silicone oil, and the polarization electric field strength, treatment temperature, and treatment time are all kept consistent, only the polarization direction is opposite.

[0009] Furthermore, the sintering process of the silver paste in S2, S4 and S6 is consistent with the sintering process parameters of the silver paste in the lower electrode layer.

[0010] Furthermore, when the assembled piezoelectric element has the positive signal electrode connected to the middle electrode layer and the negative signal electrode connected to the side electrode layer, applying an AC voltage can achieve bending deformation of the two piezoelectric ceramic layers in the same direction, driving the metal substrate to vibrate and produce sound. The sound pressure level is about 3-6 dB higher than that of the traditional single-layer structure.

[0011] Furthermore, the PZT green ceramic sheets prepared by the casting method in S3 and S5 are gradient composition PZT green ceramic sheets; The gradient-component PZT green ceramic sheet has a zirconium-to-titanium molar ratio that is gradually adjusted from 52:48 to 58:42 from the surface it is attached to to the electrode layer to the surface it is away from. The green ceramic sheet is doped with 0.5-0.8 mol% lead magnesium niobate and 0.2-0.4 mol% lanthanide oxides. Before attachment, the PZT green ceramic sheet is subjected to plasma surface activation treatment with an activation power of 150-200 W and a treatment time of 3-5 min, which improves the interfacial bonding strength between the green ceramic sheet and the electrode layer to more than 25 MPa.

[0012] Furthermore, it also includes the S10 processing step, which is as follows: after the S9 assembly is completed, the piezoelectric element is first subjected to vacuum degassing treatment with a vacuum degree of -0.095~-0.1MPa and a holding time of 20-30min. Then, a stepped temperature cycling aging treatment is performed. The temperature cycling process is as follows: holding at -40℃ for 2h, standing at room temperature for 1h, then holding at 85℃ for 2h, and standing at room temperature for 1h. This cycle is repeated 3-5 times. Finally, the piezoelectric element is subjected to a sweep frequency excitation test with an excitation voltage of 3-5V and a sweep frequency range of 2-5kHz. Finished products with a resonance peak offset greater than 50Hz are rejected.

[0013] The present invention has the following beneficial effects: 1. This invention adopts a single-sided electrode design, in which all electrical connections are achieved only through the side with the middle electrode layer and the side connection electrode. The upper electrode layer is no longer exposed, which completely solves the problem that the silver electrode on the upper surface of the traditional single-sided double-layer piezoelectric element is prone to performance degradation or direct failure due to scratches, oxidation, and contamination. This significantly improves the structural stability of the single-sided double-layer piezoelectric element during transportation, assembly, and use.

[0014] 2. This invention eliminates the traditional upper and lower double electrode connection design, requiring only lead wire welding and external electrical connection to be completed on one side of the single-sided double-layer piezoelectric element, simplifying the assembly steps of the piezoelectric element and improving production assembly efficiency; at the same time, it reduces the number of electrical connection points, significantly reducing the risk of failure caused by poor soldering and wire breakage, and reducing the failure rate of poor electrode contact during long-term operation to below 0.1%.

[0015] 3. The two piezoelectric ceramic layers of this invention adopt a parallel driving design with opposite polarization directions. When an AC voltage is applied, bending deformation in the same direction can be achieved, which significantly improves the vibration amplitude of the driven metal substrate. The sound pressure level is improved by about 3-6 dB compared with the traditional single-layer structure. There is no need to increase the diameter of the single-sided double-layer piezoelectric element or increase the driving voltage to improve performance, which meets the requirements of miniaturization design and low power consumption operation of the adapter.

[0016] 4. This invention employs plasma surface activation treatment on PZT green ceramic sheets, which increases the interfacial bonding strength between the green ceramic sheet and the electrode layer to over 25 MPa. Combined with a stepwise sintering process at 1150℃, the piezoelectric ceramic layer achieves a density of 96.8%, and the piezoelectric constant and flexural strength are both optimal, effectively avoiding problems such as peeling of the ceramic layer from the electrode layer and ceramic layer cracking, thus extending the service life of the device.

[0017] 5. After undergoing vacuum degassing and stepped temperature cycling aging in the S10 process, the piezoelectric element in this invention exhibits a sound pressure level fluctuation rate of ≤3% and an average resonance peak shift of only 32.6Hz within a wide temperature range of -40~85℃, which is far superior to traditional piezoelectric elements. It can operate stably for a long time in harsh environments with alternating high and low temperatures, and is suitable for the environmental requirements of high-end application scenarios such as automotive electronics and outdoor security.

[0018] 6. The single-sided double-layer stacked structure in this invention achieves the advantages of double-layer driving performance without significantly increasing the overall thickness of the single-sided double-layer piezoelectric element, thus maintaining the compactness of the structure. The manufacturing process adopts industry-standard and mature technologies such as screen printing, casting, and sintering polarization, without the need for additional special equipment. It has strong process compatibility and is easy to achieve industrial-scale production. Attached Figure Description

[0019] Figure 1 This is a schematic block diagram of a single-sided double-layer piezoelectric element in this invention.

[0020] Figure 2 This is a schematic block diagram of the piezoelectric element manufacturing process in this invention.

[0021] Figure 3 This is a schematic flowchart of the PZT raw ceramic tile processing technology in this invention.

[0022] Figure 4 This is a schematic diagram of the substrate in this invention.

[0023] Figure 5 This is a schematic diagram of the brass sheet used as the metal substrate in this invention.

[0024] Figure 6 This is a schematic diagram of the lower electrode layer in this invention.

[0025] Figure 7 This is a schematic diagram of the first piezoelectric ceramic layer in this invention.

[0026] Figure 8 This is a schematic diagram of the intermediate electrode layer in this invention.

[0027] Figure 9 This is a schematic diagram of the second piezoelectric ceramic layer in this invention.

[0028] Figure 10This is a schematic diagram of the upper electrode layer in this invention.

[0029] Figure 11 This is a schematic diagram of the side-connected electrode in this invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments: In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] like Figures 1 to 11 As shown, a single-sided double-layer piezoelectric element (specifically, a single-sided double-layer piezoelectric ceramic buzzer) includes, from bottom to top, a metal substrate, a lower electrode layer, a first piezoelectric ceramic layer, a middle electrode layer, a second piezoelectric ceramic layer, and an upper electrode layer. The metal substrate is a brass sheet, the lower electrode layer is a silver electrode, and the first and second piezoelectric ceramic layers are both lead zirconate titanate (PZT) based piezoelectric ceramic layers; the lower electrode layer is a common electrode, the polarization direction of the first piezoelectric ceramic layer is vertically downward, and the polarization direction of the second piezoelectric ceramic layer is vertically upward, with opposite polarization directions. It also includes a side connection electrode, which is formed by coating conductive silver paste. The lower electrode layer and the upper electrode layer are electrically connected on the same side of the single-sided double-layer piezoelectric element, so that the first piezoelectric ceramic layer and the second piezoelectric ceramic layer form a parallel driving relationship. The single-sided double-layer piezoelectric element is electrically connected to the outside only through the side with the middle electrode layer and the side connection electrode. The middle electrode layer and the upper electrode layer are both silver electrodes formed by sintering silver paste.

[0033] The thickness of the brass sheet is 0.1~0.3mm, and the thickness of the silver electrode is 8~12μm; the first piezoelectric ceramic layer and the second piezoelectric ceramic layer are both lead zirconate titanate (PZT) piezoelectric ceramic layers with a thickness of 0.08~0.12mm. The side connection electrode is formed by coating conductive silver paste onto the polished side of the single-sided double-layer piezoelectric element using a fine brush or precision printing technology.

[0034] A method for fabricating a single-sided double-layer piezoelectric element (specifically, a method for fabricating a buzzer using a single-sided double-layer piezoelectric ceramic buzzer), comprising the following steps: S1. Substrate Preparation: A brass sheet with a thickness of 0.1~0.3mm is selected as the metal substrate, and it is cleaned and polished to serve as the vibration substrate and support for the single-sided double-layer piezoelectric element. S2. Lower electrode formation: A layer of silver paste is uniformly printed on the surface of a brass sheet using screen printing technology, and then sintered and cured at 800~900℃ to form a lower electrode layer with a thickness of 8~12μm. S3. Formation and polarization of the first piezoelectric layer: PZT green ceramic sheets were prepared by tape casting and attached to the lower electrode layer. They were then sintered at 1100~1200℃ to form a first piezoelectric ceramic layer with a thickness of 0.08~0.12mm. Subsequently, the first piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3kV / mm for 20-32 minutes to make its polarization direction vertically downward. S4. Formation of intermediate electrode: A silver paste is screen-printed onto the surface of the first piezoelectric ceramic layer and then sintered to form an intermediate electrode layer. S5. Formation and polarization of the second piezoelectric layer: Another PZT green ceramic sheet prepared by tape casting was attached to the intermediate electrode layer and sintered at 1100~1200℃ to form a second piezoelectric ceramic layer with a thickness of 0.08~0.12mm. Then, the second piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3kV / mm for 30 minutes, so that its polarization direction is vertically upward and opposite to the polarization direction of the first piezoelectric ceramic layer. S6. Upper electrode formation: Silver paste is printed and sintered on the surface of the second piezoelectric ceramic layer to form the upper electrode layer; S7. Single-sided electrode connection: The edges of the single-sided double-layer piezoelectric element are lightly ground using precision grinding equipment to expose the sides of the lower and upper electrode layers. Then, conductive silver paste is applied to the ground sides using a fine brush or precision printing technology to reliably connect the lower and upper electrode layers and form a side connection electrode. S8. Lead wire connection: The first lead is soldered to the pad of the middle electrode layer with conductive adhesive, and the second lead is soldered to the extension of the side electrode with conductive adhesive. S9. Assembly: The single-sided double-layer piezoelectric element with connected leads is installed into a plastic housing with a resonant cavity using epoxy resin adhesive, thus completing the assembly of the piezoelectric element (buzzer).

[0035] The sintering in S3 and S5 is a step-by-step sintering method, and the sintering temperature is 1150℃ for both.

[0036] The polarization treatment medium in S3 and S5 is silicone oil, and the polarization electric field strength, treatment temperature and treatment time are kept consistent, only the polarization direction is opposite.

[0037] The sintering process of the silver paste in S2, S4 and S6 is consistent with the sintering process parameters of the silver paste in the lower electrode layer.

[0038] When the assembled piezoelectric element (buzzer) has the positive signal electrode connected to the middle electrode layer and the negative signal electrode connected to the side electrode layer, applying an AC voltage can achieve bending deformation of the two piezoelectric ceramic layers in the same direction, driving the metal substrate to vibrate and produce sound. The sound pressure level is about 3-6 dB higher than that of the traditional single-layer structure.

[0039] The PZT green ceramic sheets prepared by the casting method in S3 and S5 are gradient composition PZT green ceramic sheets. The gradient-component PZT green ceramic sheet has a zirconium-to-titanium molar ratio that is gradually adjusted from 52:48 to 58:42 from the surface it is attached to to the electrode layer to the surface it is away from. The green ceramic sheet is doped with 0.5-0.8 mol% lead magnesium niobate and 0.2-0.4 mol% lanthanide oxides. Before attachment, the PZT green ceramic sheet is subjected to plasma surface activation treatment with an activation power of 150-200 W and a treatment time of 3-5 min, which improves the interfacial bonding strength between the green ceramic sheet and the electrode layer to more than 25 MPa.

[0040] The process also includes the S10 processing step, which involves: after assembly in S9, the piezoelectric element (buzzer) undergoes vacuum degassing treatment with a vacuum level of -0.095 to -0.1 MPa and a holding time of 20-30 minutes. Then, a stepped temperature cycling aging treatment is performed: holding at -40℃ for 2 hours, resting at room temperature for 1 hour, then holding at 85℃ for 2 hours, and resting at room temperature for 1 hour, repeated 3-5 times. Finally, the piezoelectric element (buzzer) undergoes a sweep frequency excitation test with an excitation voltage of 3-5V and a sweep frequency range of 2-5kHz, discarding products with a resonance peak offset greater than 50Hz. The piezoelectric element (buzzer) processed by the S10 process exhibits a sound pressure level fluctuation rate ≤3% in the -40~85℃ temperature range, and the long-term electrode contact failure rate is reduced to below 0.1%.

[0041] To verify the impact of different process parameter combinations on the performance of piezoelectric elements (buzzers), this invention obtained measured data through multiple sets of comparative experiments, performance tests, and reliability tests. The following are tables of experimental data, all of which are measured averages of multiple samples under the same test conditions. The test standards conform to the general testing specifications of the electroacoustic conversion device industry: Table 1 shows the sound pressure level comparison experiment between the product of this invention and a traditional single-layer piezoelectric ceramic piezoelectric element (buzzer). Experimental conditions: excitation voltage 3V, sweep frequency range 2-5kHz, test distance 10cm, room temperature 25℃, 50 samples per group, and average value.

[0042]

[0043] Table 1 Table 2 shows the interfacial bonding strength of PZT green ceramic sheets after plasma surface activation treatment. Experimental conditions: Test standard GB / T6329-2008, green ceramic tiles with gradient composition PZT, activation equipment is radio frequency plasma processor, 20 samples per group, average value is taken.

[0044]

[0045] Table 2 Table 3 shows the experimental results of sound pressure level fluctuation rate test of the piezoelectric element of the present invention in the temperature range.

[0046] Table 3 Table 4 shows the reliability comparison experiment between the piezoelectric element of the present invention and the traditional piezoelectric element. Experimental conditions: alternating cycles of high temperature 85℃ and low temperature -40℃ (2 hours each, followed by 1 hour of rest at room temperature as one cycle), for a total of 100 cycles, with 100 samples per group. After testing, the system was powered on to check for faults.

[0047]

[0048] Table 4 Table 5 shows the experimental results of the effect of different sintering temperatures on the properties of PZT ceramic layers. Experimental conditions: PZT was a gradient composition of green ceramic sheets, the sintering method was stepwise sintering, and the test sample was a piezoelectric ceramic layer monomer (without electrodes).

[0049]

[0050] Table 5 The technical solution of this invention can flexibly adjust process parameters and process combinations according to the differentiated requirements of piezoelectric elements (buzzers) for sound pressure output, environmental adaptability, and production costs in different application scenarios. To more clearly demonstrate the implementation details and parameter adaptation logic of the technical solution of this invention, two specific embodiments with different process parameter combinations are provided below, respectively adapting to the application requirements of high reliability, high environmental adaptability, and low-cost large-scale production. The process parameters of each embodiment are all within the scope defined by the claims of this invention, and all can achieve the technical effects of this invention: Example 1 - Fabrication of a high-reliability, environmentally adaptable single-sided double-layer piezoelectric ceramic piezoelectric element (buzzer) This embodiment is designed for applications such as automotive electronics and outdoor security, which have high requirements for high and low temperature adaptability and long-term operational reliability. It adopts a full range of processes and optimal parameter matching to improve the environmental tolerance and service life of piezoelectric components (buzzers).

[0051] 1. Select a 0.2mm thick brass sheet as the metal substrate, perform ultrasonic cleaning and mirror polishing on it, and use it as the vibration substrate and support for the single-sided double-layer piezoelectric element. 2. A layer of high-adhesion silver paste is uniformly printed on the surface of the brass sheet using screen printing technology, and then sintered and cured at 850℃ to form a lower electrode layer with a thickness of 10μm. 3. Gradient-component PZT green ceramic sheets were prepared by tape casting (the zirconium-titanium molar ratio was adjusted from 52:48 to 58:42, and the internal doping consisted of 0.6 mol% lead magnesium niobate and 0.3 mol% lanthanide oxides). After the green ceramic sheets were activated by 180W plasma for 4 min, they were attached to the lower electrode layer and sintered in steps at 1150℃ to form a first piezoelectric ceramic layer with a thickness of 0.1 mm. Subsequently, the first piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3 kV / mm for 30 min, so that its polarization direction was vertically downward. 4. A 10μm thick intermediate electrode layer is formed by screen printing silver paste of the same specification on the surface of the first piezoelectric ceramic layer and sintering it at 850℃. 5. Attach PZT green ceramic sheets of the same specification and gradient composition (after the same plasma activation treatment) to the intermediate electrode layer, and sinter them in steps at 1150℃ to form a second piezoelectric ceramic layer with a thickness of 0.1mm. Then, polarize the second piezoelectric ceramic layer for 30 minutes under the same polarization conditions so that its polarization direction is vertically upward and opposite to the polarization direction of the first piezoelectric ceramic layer. 6. Print and sinter silver paste of the same specification on the upper surface of the second piezoelectric ceramic layer to form an upper electrode layer with a thickness of 10μm; 7. Use a precision diamond grinding machine to lightly grind the edges of the single-sided double-layer piezoelectric element; precisely expose the sides of the lower electrode layer and the upper electrode layer; then use precision screen printing technology to coat the ground sides with high conductivity conductive silver paste, so that the lower electrode layer and the upper electrode layer are reliably connected to form a side connection electrode. 8. Solder the first lead of the tin-plated copper core to the gold-plated pad of the middle electrode layer using high-temperature conductive adhesive, and solder the second lead to the extended pad of the side electrode using the same conductive adhesive. 9. Install the single-sided double-layer piezoelectric element with connected leads into the high-temperature resistant plastic housing with a sealed resonant cavity using high-temperature resistant epoxy resin adhesive, thus completing the initial assembly of the piezoelectric element (buzzer). 10. Perform vacuum degassing treatment on the piezoelectric element (buzzer) (vacuum degree -0.098MPa, pressure holding for 25min), then perform stepped temperature cycling aging treatment (hold at -40℃ for 2h, stand at room temperature for 1h, hold at 85℃ for 2h, stand at room temperature for 1h, cycle 4 times), and finally perform frequency sweep excitation test on the piezoelectric element (buzzer) (excitation voltage 4V, frequency sweep range 2-5kHz), and discard finished products with resonance peak offset greater than 50Hz.

[0052] The piezoelectric element (buzzer) prepared in this embodiment was tested and found to have an interface bonding strength of 28.5 MPa, a sound pressure level of 87.8 dB at room temperature, a sound pressure level fluctuation rate of ≤1.25% in the temperature range of -40~85℃, and an electrode contact failure rate of 0.08%. It can work stably for a long time in a wide temperature range of -40℃ to 85℃, meeting the needs of high-end application scenarios such as automotive electronics and outdoor security.

[0053] Example 2 - Preparation of Single-Sided Double-Layer Piezoelectric Ceramic Piezoelectric Element (Buzzer) Adapted for Low-Cost Mass Production This embodiment is designed for application scenarios such as small household appliances and general consumer electronics, which have high requirements for production costs and efficiency, and relatively mild requirements for environmental adaptability. Within the parameter range defined by this invention, some fine processes are simplified to adapt to the needs of large-scale mass production, while ensuring that the core performance is superior to that of traditional single-layer piezoelectric elements (buzzers).

[0054] 1. Select a 0.15mm thick brass sheet as the metal substrate, and perform routine cleaning and mechanical polishing on it to serve as the vibration substrate and support for the single-sided double-layer piezoelectric element. 2. A layer of conventional conductive silver paste is uniformly printed on the surface of the brass sheet using screen printing technology, and then sintered and cured at 800℃ to form a lower electrode layer with a thickness of 8μm. 3. Gradient-component PZT green ceramic sheets were prepared by tape casting (the zirconium-titanium molar ratio was adjusted from 52:48 to 58:42, and the internal doping consisted of 0.5 mol% lead magnesium niobate + 0.2 mol% lanthanide oxide). After the green ceramic sheets were activated by 150W plasma for 3 min, they were attached to the lower electrode layer and sintered in steps at 1100℃ to form a first piezoelectric ceramic layer with a thickness of 0.08 mm. Subsequently, the first piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3 kV / mm for 20 min, so that its polarization direction was vertically downward. 4. Silver paste of the same specification is screen-printed on the surface of the first piezoelectric ceramic layer and sintered at 800℃ to form an intermediate electrode layer with a thickness of 8μm. 5. Attach PZT green ceramic sheets of the same specification and gradient composition (after the same plasma activation treatment) to the intermediate electrode layer, and sinter them in steps at 1100℃ to form a second piezoelectric ceramic layer with a thickness of 0.08mm. Then, polarize the second piezoelectric ceramic layer for 20 minutes under the same polarization conditions so that its polarization direction is vertically upward and opposite to the polarization direction of the first piezoelectric ceramic layer. 6. Print and sinter silver paste of the same specification on the upper surface of the second piezoelectric ceramic layer to form an upper electrode layer with a thickness of 8μm; 7. Use conventional grinding equipment to grind the edges of the single-sided double-layer piezoelectric element to expose the sides of the lower electrode layer and the upper electrode layer. Then, use fine brush coating technology to coat the ground side with conventional conductive silver paste to reliably connect the lower electrode layer and the upper electrode layer, forming a side connection electrode. 8. Solder the first copper core lead to the ordinary pad of the middle electrode layer using conventional conductive adhesive, and solder the second lead to the extension of the side electrode using the same conductive adhesive. 9. Install the single-sided double-layer piezoelectric element with connected leads into a general-purpose plastic housing with a common resonant cavity using conventional epoxy resin adhesive, thus completing the initial assembly of the piezoelectric element (buzzer). 10. Perform vacuum degassing treatment on the piezoelectric element (buzzer) (vacuum degree -0.095MPa, pressure holding for 20min), then perform stepped temperature cycling aging treatment (hold at -40℃ for 2h, stand at room temperature for 1h, hold at 85℃ for 2h, stand at room temperature for 1h, cycle 3 times), and finally perform frequency sweep excitation test on the piezoelectric element (buzzer) (excitation voltage 3V, frequency sweep range 2-5kHz), and discard finished products with resonance peak offset greater than 50Hz.

[0055] The piezoelectric element (buzzer) prepared in this embodiment was tested and found to have an interface bonding strength of 25.8 MPa, a room temperature sound pressure level of 86.5 dB, and an electrode contact failure rate of ≤0.1% under normal temperature conditions. The sound pressure level is 4 dB higher than that of the traditional single-layer structure. Moreover, the production process is simpler and the raw material cost is lower, which can realize mass production and meet the needs of general application scenarios such as household small appliances and general consumer electronics.

[0056] The piezoelectric element (buzzer) processed by the S10 process of this invention has a sound pressure level fluctuation rate of ≤3% in the temperature range of -40~85℃, and the failure rate of poor electrode contact during long-term operation is reduced to below 0.1%. The preparation process of both embodiments verifies the feasibility of the technical solution of this invention, and the parameters can be flexibly adjusted according to the actual application scenario to take into account the performance and cost requirements of different scenarios.

[0057] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A single-sided double-layer piezoelectric element, characterized in that: From bottom to top, it includes a metal substrate, a lower electrode layer, a first piezoelectric ceramic layer, a middle electrode layer, a second piezoelectric ceramic layer, and an upper electrode layer. The metal substrate is a brass sheet, the lower electrode layer is a silver electrode, and both the first and second piezoelectric ceramic layers are lead zirconate titanate-based piezoelectric ceramic layers; the lower electrode layer is a common electrode, the polarization direction of the first piezoelectric ceramic layer is vertically downward, and the polarization direction of the second piezoelectric ceramic layer is vertically upward, with opposite polarization directions. It also includes a side connection electrode, which is formed by coating conductive silver paste. The lower electrode layer and the upper electrode layer are electrically connected on the same side of the single-sided double-layer piezoelectric element, so that the first piezoelectric ceramic layer and the second piezoelectric ceramic layer form a parallel driving relationship. The single-sided double-layer piezoelectric element is electrically connected to the outside only through the side with the middle electrode layer and the side connection electrode. The middle electrode layer and the upper electrode layer are both silver electrodes formed by sintering silver paste.

2. The single-sided double-layer piezoelectric element according to claim 1, characterized in that: The thickness of the brass sheet is 0.1~0.3mm, and the thickness of the silver electrode is 8~12μm; the first piezoelectric ceramic layer and the second piezoelectric ceramic layer are both lead zirconate titanate piezoelectric ceramic layers with a thickness of 0.08~0.12mm.

3. The single-sided double-layer piezoelectric element according to claim 2, characterized in that: The side connection electrode is formed by coating the polished side of the single-sided double-layer piezoelectric element with conductive silver paste using a fine brush or printing technology.

4. A method for fabricating a single-sided double-layer piezoelectric element, characterized in that, Includes the following steps: S1. Substrate Preparation: A brass sheet with a thickness of 0.1~0.3mm is selected as the metal substrate, and it is cleaned and polished to serve as the vibration substrate and support for the single-sided double-layer piezoelectric element. S2. Lower electrode formation: A layer of silver paste is uniformly printed on the surface of a brass sheet using screen printing technology, and then sintered and cured at 800~900℃ to form a lower electrode layer with a thickness of 8~12μm. S3. Formation and polarization of the first piezoelectric layer: PZT green ceramic sheets were prepared by tape casting and attached to the lower electrode layer. They were then sintered at 1100~1200℃ to form a first piezoelectric ceramic layer with a thickness of 0.08~0.12mm. Subsequently, the first piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3kV / mm for 20-32 minutes to make its polarization direction vertically downward. S4. Intermediate electrode formation: A silver paste is screen-printed onto the surface of the first piezoelectric ceramic layer and then sintered to form an intermediate electrode layer. S5. Formation and polarization of the second piezoelectric layer: Another PZT green ceramic sheet prepared by tape casting was attached to the intermediate electrode layer and sintered at 1100~1200℃ to form a second piezoelectric ceramic layer with a thickness of 0.08~0.12mm. Then, the second piezoelectric ceramic layer was polarized in a silicone oil bath at 120℃ and an electric field strength of 3kV / mm for 30 minutes, so that its polarization direction is vertically upward and opposite to the polarization direction of the first piezoelectric ceramic layer. S6. Upper electrode formation: Silver paste is printed and sintered on the surface of the second piezoelectric ceramic layer to form the upper electrode layer; S7. Single-sided electrode connection: The edges of the single-sided double-layer piezoelectric element are ground using a grinding equipment to expose the sides of the lower and upper electrode layers. Then, conductive silver paste is applied to the ground sides using a fine brush or precision printing technology to connect the lower and upper electrode layers and form a side connection electrode. S8. Lead wire connection: The first lead is soldered to the pad of the middle electrode layer with conductive adhesive, and the second lead is soldered to the extension of the side electrode with conductive adhesive. S9. Assembly: The single-sided double-layer piezoelectric element with connected leads is installed into a plastic housing with a resonant cavity using epoxy resin adhesive, thus completing the assembly of the piezoelectric element.

5. The method for preparing a single-sided double-layer piezoelectric element according to claim 4, characterized in that: The sintering in S3 and S5 is a step-by-step sintering method, and the sintering temperature is 1150℃ for both.

6. The method for preparing a single-sided double-layer piezoelectric element according to claim 5, characterized in that, The polarization treatment medium in S3 and S5 is silicone oil, and the polarization electric field strength, treatment temperature and treatment time are kept consistent, only the polarization direction is opposite.

7. The method for preparing a single-sided double-layer piezoelectric element according to claim 6, characterized in that: The sintering process of the silver paste in S2, S4 and S6 is consistent with the sintering process parameters of the silver paste in the lower electrode layer.

8. The method for preparing a single-sided double-layer piezoelectric element according to claim 7, characterized in that: When the assembled piezoelectric element has the positive signal electrode connected to the middle electrode layer and the negative signal electrode connected to the side electrode layer, applying an AC voltage can achieve bending deformation of the two piezoelectric ceramic layers in the same direction, driving the metal substrate to vibrate and produce sound. The sound pressure level is about 3-6 dB higher than that of the traditional single-layer structure.

9. The method for preparing a single-sided double-layer piezoelectric element according to claim 8, characterized in that: The PZT green ceramic sheets prepared by the casting method in S3 and S5 are gradient composition PZT green ceramic sheets. The gradient-component PZT green ceramic sheet has a zirconium-to-titanium molar ratio that is gradually adjusted from 52:48 to 58:42 from the surface it is attached to to the electrode layer to the surface it is away from. The green ceramic sheet is doped with 0.5-0.8 mol% lead magnesium niobate and 0.2-0.4 mol% lanthanide oxides. Before attachment, the PZT green ceramic sheet is subjected to plasma surface activation treatment with an activation power of 150-200 W and a treatment time of 3-5 min, which improves the interfacial bonding strength between the green ceramic sheet and the electrode layer to more than 25 MPa.

10. The method for preparing a single-sided double-layer piezoelectric element according to claim 9, characterized in that: It also includes the S10 processing step, which is as follows: After the S9 assembly is completed, the piezoelectric element is first subjected to vacuum degassing treatment with a vacuum degree of -0.095~-0.1MPa and a holding time of 20-30min. Then, a stepped temperature cycling aging treatment is performed. The temperature cycling process is as follows: holding at -40℃ for 2h, standing at room temperature for 1h, then holding at 85℃ for 2h, and standing at room temperature for 1h. This cycle is repeated 3-5 times. Finally, the piezoelectric element is subjected to a sweep frequency excitation test with an excitation voltage of 3-5V and a sweep frequency range of 2-5kHz. Finished products with a resonance peak offset greater than 50Hz are rejected.

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