A PZT piezoelectric ceramic and a preparation method of an electrode thereof

Abstract

The application discloses a PZT piezoelectric ceramic electrode and a preparation method of the electrode, and belongs to the technical field of piezoelectric ceramics. The method comprises the following steps: step one, taking a ceramic sheet with printed electrodes, passing air and heating to 450-550 DEG C, and keeping the temperature for 45-90 min; step two, increasing the air flow and continuously heating to 750-850 DEG C, and keeping the temperature for 10-30 min; step three, after the temperature keeping, cooling to 550-650 DEG C, passing nitrogen, and keeping the temperature for 3-5 min; and step four, reducing the nitrogen flow, cooling to normal temperature with the furnace, and taking out. The PZT piezoelectric ceramic electrode is prepared by using air and nitrogen, the number of oxygen vacancies in the ceramic crystal is increased by using nitrogen, the defects caused by the oxidation of the electrode surface and the micro defects in the glass phase are reduced, the dielectric loss of the ceramic is reduced, the electromechanical coupling coefficient of the ceramic is increased, the electrical characteristics of the piezoelectric ceramic sheet are improved, and the high-temperature stability and the silver layer adhesion of the piezoelectric ceramic are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of piezoelectric ceramics, and in particular to a PZT piezoelectric ceramic and a method for preparing its electrodes. Background Technology

[0002] Piezoelectric ceramics possess advantages such as direct and inverse piezoelectric effects, fast response, low power consumption, and high displacement resolution, leading to their widespread application in various fields including bioengineering, electronics, precision machinery, and communication technology. With the development of the precision machinery industry, higher demands are being placed on the miniaturization and performance of piezoelectric ceramic devices. As a core component of products, piezoelectric ceramics play a crucial role in converting electrical and mechanical energy. PZT piezoelectric ceramic sheets are widely used in high-tech fields such as optics, electronics, and acoustics due to their numerous superior properties, including high capacitance, high Curie temperature, large planar electromechanical coupling coefficient, and low dielectric loss. They show particularly promising application prospects in piezoelectric pumps and underwater acoustic transducers.

[0003] In the design of miniature piezoelectric pumps for the medical industry, piezoelectric ceramics operate at high-frequency resonant points for extended periods, with vibration displacements exceeding 40µm. This places high demands on ceramic heating and reliability. During the manufacturing process of piezoelectric pumps, multiple high-temperature baking processes are required, which impacts the stability of the ceramic Kp. Currently, the conventional production process of screen printing, baking, and high-temperature silver firing results in a Kp decrease of approximately 20% after baking at 120 degrees Celsius, failing to meet product design requirements and functional implementation. This severely restricts the technological advancement and application of precision micropumps in China, currently relying mainly on imports from Japan and Germany.

[0004] While traditional piezoelectric ceramic manufacturing processes offer numerous advantages, they often struggle to control the influence of airborne substances on the ceramic surface electrodes during firing. This results in metal electrodes with poor density and numerous defects, which can lead to incomplete polarization and stress concentration on the ceramic surface during polarization, thereby compromising the electromechanical coupling properties of the piezoelectric ceramic and increasing dielectric loss. Conventional nitrogen-fired silver processes do not significantly improve Kp and greatly affect the adhesion of the silver layer, making welding impossible. Therefore, these processes have significant defects and are difficult to mass-produce. Summary of the Invention

[0005] To overcome the above-mentioned technical defects, the present invention provides a method for preparing a PZT piezoelectric ceramic electrode to solve the problems involved in the background art.

[0006] This invention provides a method for preparing a PZT piezoelectric ceramic electrode, comprising:

[0007] Step 1: Take a ceramic sheet with printed electrodes, introduce air and heat it to 450-550℃, and keep it at that temperature for 45-90 minutes.

[0008] Step 2: Increase the airflow and continue to heat to 750-850℃, and keep it at that temperature for 10-30 minutes;

[0009] Step 3: After the heat preservation is completed, cool down to 550-650℃, introduce nitrogen gas, and maintain for 3-5 minutes;

[0010] Step 4: Reduce the nitrogen flow rate and cool the furnace to room temperature before removing the furnace.

[0011] Preferably or optionally, in step one, the air flow rate is not less than 2L / min; in step two, the air flow rate is not less than 10L / min.

[0012] Preferably or optionally, in step one, the heating rate is 8-12°C / min; in step two, the heating rate is 18-25°C / min.

[0013] Preferably or optionally, in step 3, the nitrogen flow rate is 12 to 18 L / min; in step 4, the nitrogen flow rate is 5 to 8 L / min.

[0014] Preferably or optionally, the purity of the nitrogen gas is 99.99% or higher.

[0015] Preferably or optionally, the ceramic sheet is a PZT piezoelectric ceramic with a thickness of 2 mm;

[0016] Preferably or optionally, the PZT piezoelectric ceramic has the molecular formula PbZr. x Ti 1-x O3, x = 0 to 0.8.

[0017] Preferably or optionally, the printed electrode ceramic sheet is formed by screen printing silver paste onto the upper, lower, or side surfaces of the sintered ceramic sheet to form the electrode.

[0018] The present invention also provides a PZT piezoelectric ceramic obtained based on the preparation method of the PZT piezoelectric ceramic electrode described above.

[0019] This invention relates to a method for preparing PZT piezoelectric ceramic electrodes, which has the following advantages compared to existing technologies: This invention uses air and nitrogen to prepare lead zirconate titanate piezoelectric ceramic electrodes. Nitrogen gas is used to increase the number of oxygen vacancies in the ceramic crystal, reducing defects caused by oxidation on the electrode surface and microscopic defects in the glass phase. This reduces the dielectric loss of the ceramic, increases the electromechanical coupling coefficient of the ceramic, improves the electrical properties of the piezoelectric ceramic sheet, enhances the high-temperature stability of the piezoelectric ceramic and the adhesion of the silver layer, thereby promoting the application of PZT piezoelectric ceramics in precision machining, precision transmission, and fine flow control. Detailed Implementation

[0020] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention. Invention Overview

[0022] Traditional piezoelectric ceramics suffer from difficulties in controlling the influence of airborne substances on the ceramic surface electrodes during sintering, especially during high-temperature sintering of metal electrodes. Air infiltration leads to microscopic defects in the underlying glass phase and oxidation of the metal surface. The resulting metal electrodes exhibit poor density and numerous defects, easily causing incomplete polarization and stress concentration on the ceramic surface during polarization, thus compromising the electromechanical coupling properties of the piezoelectric ceramic and increasing dielectric loss. Conventional nitrogen-fired silver processes do not significantly improve Kp and greatly affect the adhesion of the silver layer, making welding impossible. Therefore, they exhibit significant defects and are not suitable for mass production.

[0023] This invention introduces a specific amount of air and nitrogen during the electrode firing process, at controlled temperatures during heating and cooling. This ensures the full oxidation and removal of organic matter in the silver paste during firing, normal electrode-ceramic penetration, and strong adhesion between the electrode and ceramic. The principle behind this invention is to increase oxygen vacancies within the ceramic crystals through nitrogen introduction, thereby improving the product's Kp performance and adhesion. It is a process and method that is completed in one step alongside electrode firing, by controlling the firing curve, the time and flow rate of air introduction, and the time and flow rate of nitrogen introduction to achieve the desired electrode firing. The equipment is simple, the consumables are inexpensive, and it allows for control over the size of the ceramic flakes and the uniformity of the glass phase on the ceramic surface. Moreover, nitrogen is non-toxic and harmless, making this method risk-free and environmentally friendly during production.

[0024] The present invention will be further described below with reference to the embodiments. The examples described are intended to explain the present invention and should not be construed as limiting the present invention.

[0025] Example 1: Silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Then, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After the holding period, the temperature was reduced to 600 °C, and the nitrogen flow rate was increased to 15 L / min and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0026] In Example 2, silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Nitrogen gas was then introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After the holding period, the temperature was reduced to 600 °C, and the nitrogen flow rate was increased to 15 L / min and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0027] In Example 3, silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Nitrogen gas was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. At this time, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After the holding period, the temperature was reduced to 600 °C, the nitrogen flow rate was increased to 15 L / min, and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0028] Example 4: Silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Then, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After holding, the temperature was reduced to 600 °C, and the air flow rate was increased to 15 L / min and held for 4 min. The air flow rate was then reduced to 5 L / min and held at room temperature before the air was turned off.

[0029] In Example 5, silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Then, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After the holding period, the temperature was reduced to 700 °C, and the nitrogen flow rate was increased to 15 L / min and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0030] Example 6: Silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Then, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After holding, the temperature was reduced to 650 °C, and the nitrogen flow rate was increased to 15 L / min and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0031] In Example 7, silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Then, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After the holding period, the temperature was reduced to 550 °C, and the nitrogen flow rate was increased to 15 L / min and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0032] Example 8: Silver paste was screen-printed onto the upper and lower surfaces of a sintered ceramic sheet (2 mm thick) to form electrodes (120 μm thick). Air was introduced at a rate of 2 L / min, and the temperature was increased to 500 °C at a rate of 10 °C / min and held for 60 min. Then, air was introduced at a rate of 10 L / min, and the temperature was increased to 800 °C at a rate of 20 °C / min and held for 20 min. After the holding period, the temperature was reduced to 500 °C, and the nitrogen flow rate was increased to 15 L / min and held for 4 min. The nitrogen flow rate was then reduced to 5 L / min and held at room temperature before the nitrogen was turned off.

[0033] Example 1: The PZT piezoelectric ceramics and their electrodes obtained in the above embodiments of the present invention were evaluated as follows: Kp: the electromechanical coupling coefficient, was obtained by impedance analysis. The specific testing method was as follows: the center of the piezoelectric ceramic sheet (within the diameter range of φ3) was fixed by clamping it with a pin, and two pins were connected to the impedance analyzer for testing. The frequency sweep range was 150kHz~300kHz. Kp before high temperature refers to the test value after the piezoelectric ceramic was polarized and placed for 24 hours; Kp after high temperature refers to the test value after placing for 24 hours, baking at 120 degrees Celsius for 90 minutes, and cooling to room temperature.

[0034] Silver layer adhesion: A cross-cut adhesion test is used. The specific testing method is as follows: Use a cross-cut adhesion tester to make 10×10 1mm×1mm small grids on the electrode surface, and each line should penetrate to the bottom layer of the electrode layer; use a brush to clean the debris in the test area; firmly stick the test grids with 3M 600 tape or equivalent adhesive tape, and rub the tape vigorously with an eraser to increase the contact area and adhesion between the tape and the test area; after standing for 3-5 minutes, grab one end of the tape and quickly tear it off vertically. Perform the same test twice at the same location. The results were divided into 6 levels, from 0 to 5B; Level 5B: The edges of the scribing are smooth, and there is no silver layer peeling at the edges and intersections of the scribing; Level 4B: Small patches of silver layer peeling occur at the intersections of the scribing, and the total peeling area is less than 5%; Level 3B: Small patches of silver layer peeling occur at the edges and intersections of the scribing, and the total peeling area is between 5% and 15%; Level 2B: Large areas of silver layer peeling occur at the edges and intersections of the scribing, and the total peeling area is between 15% and 35%; Level 1B: Large areas of silver layer peeling occur at the edges and intersections of the scribing, and the total peeling area is between 35% and 65%; Level 0B: Large areas of silver layer peeling occur at the edges and intersections of the scribing, and the total peeling area is greater than 65%.

[0035] Table 1:

[0036]

[0037] Discussion 1, referring to Table 1, firstly, it can be seen that repeatedly oxidizing the organic matter in the silver paste with air and then volatilizing it, followed by timely introduction of nitrogen, can effectively reduce defects caused by oxidation on the electrode surface and microscopic defects in the glass phase, thereby reducing the dielectric loss of the ceramic and increasing its electromechanical coupling coefficient. Secondly, the temperature at which nitrogen is introduced during the cooling process should not be too high, otherwise it will reduce the adhesion of the silver layer; if the nitrogen temperature is too low, the nitrogen cannot effectively increase the oxygen vacancies inside the piezoelectric ceramic, thus affecting the electromechanical coupling coefficient of the ceramic.

[0038] Example 2 shows the changes in electromechanical coupling coefficients of the PZT piezoelectric ceramics prepared in Example 1 after pretreatment following polarization (96 hours or baking at 120°C for 1 hour) using the conventional air-firing silver process (the conventional air-firing silver process involves placing the product in the furnace, closing the furnace door, setting the air flow rate to 7 L / min, keeping the silver firing temperature at 800°C, firing in the same atmosphere for 20 minutes). See Table 2 below for details.

[0039] Table 2

[0040]

[0041] Discussion 2, as shown in Table 2, reveals that the new process in this application can improve the electromechanical coupling coefficient by approximately 20%, significantly enhancing product performance, high-temperature stability, and reliability. The silver layer adhesion meets the requirement of ≥4B in a 1mm*1mm cross-cut adhesion test.

[0042] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A method of preparing a PZT piezoelectric ceramic electrode, characterized by, It comprises the following steps: Step one, take the printed electrode ceramic sheet, air flow is not less than 2L / min, and the temperature is raised to 450-550℃, the heating rate is 8-12℃ / min, and the temperature is kept for 45-90min; Step two: increase the air flow and the air flow is not less than 10L / min, and continue to raise the temperature to 750-850℃, the heating rate is 18-25℃ / min, and the temperature is kept for 10-30min; Step three: after the temperature keeping, the temperature is lowered to 550-650℃, nitrogen is introduced and the nitrogen flow is 12-18L / min, and the temperature is kept for 3-5min; Step four: reduce the nitrogen flow and the nitrogen flow is 5-8L / min, and the furnace is cooled to room temperature.

2. The method of claim 1, wherein the PZT piezoelectric ceramic electrode is prepared by the steps of: The purity of the nitrogen is more than 99.99%.

3. The method of claim 1, wherein the PZT piezoelectric ceramic electrode is prepared by the steps of: The ceramic sheet is PZT piezoelectric ceramic with a thickness of 2mm; the printed electrode is silver film with a thickness of 120um.

4. The method of claim 3, wherein the PZT piezoelectric ceramic electrode is prepared by the steps of: The PZT piezoelectric ceramic has a molecular formula of PbZr x Ti 1-x O3, x = 0-0.

8.

5. The method of claim 1, wherein the PZT piezoelectric ceramic electrode is prepared by the steps of: The printed electrode ceramic sheet is printed with silver paste on the upper surface, lower surface or side surface of the sintered ceramic sheet by screen printing process to form the electrode.

6. A PZT piezoelectric ceramic obtained by the preparation method of the PZT piezoelectric ceramic electrode according to any one of claims 1-5.

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