PZT piezoelectric film and preparation method thereof

Abstract

The invention is suitable for the technical field of PZT piezoelectric ceramics, and provides a PZT piezoelectric film and a preparation method thereof.The preparation method comprises the following steps that PZT sol is prepared, specifically, the PZT sol is prepared from ethylene glycol monomethyl ether, lead acetate trihydrate, zirconium nitrate and tetrabutyl titanate; sol spin coating and heat treatment: carrying out spin coating and heat treatment on the prepared PZT sol; and annealing treatment: carrying out low-temperature and high-temperature annealing treatment on the basis of multiple times of spin coating and multiple times of annealing. The improved annealing process of low-temperature and high-temperature annealing is carried out on the basis of the multi-layer spin coating and multi-time annealing process, the PZT thin film subjected to low-temperature and high-temperature annealing is compact in structure and free of obvious boundary layers, gaps and cracks, and the remanent polarization of the thin film can reach 17.2 mu c / cm < 2 > at most and reaches the research level of peers at home and abroad.

Description

Technical Field

[0001] The present invention belongs to the technical field of PZT piezoelectric ceramics, and particularly relates to a PZT piezoelectric thin film and a preparation method thereof. Background Art

[0002] Piezoelectric ceramics are information functional ceramic materials that can convert mechanical energy and electrical energy into each other. In addition to piezoelectricity, they also have dielectricity, elasticity, etc., and are widely used in medical imaging, sound sensors, sound transducers, ultrasonic motors, etc.

[0003] The sol-gel process is a traditional method for preparing PZT thin films, but it has problems such as poor stability of the PZT sol, generation of annealing cracks, and obvious delamination layers generated by multiple annealings, which affect the performance of PZT piezoelectric ceramics. Summary of the Invention

[0004] An object of an embodiment of the present invention is to provide a preparation method of a PZT piezoelectric thin film, aiming to solve the problems raised in the above background art.

[0005] An embodiment of the present invention is implemented as follows. A preparation method of a PZT piezoelectric thin film includes the following steps:

[0006] Prepare a PZT sol: Prepare a PZT sol by using ethylene glycol monomethyl ether, lead acetate trihydrate, zirconium nitrate, and tetrabutyl titanate.

[0007] Sol spin coating and heat treatment: Spin coat and heat treat the prepared PZT sol.

[0008] Annealing treatment: Perform low-temperature and high-temperature annealing treatment on the basis of multiple spin coating and multiple annealing.

[0009] Preferably, in the step of the annealing treatment, spin coat six times, anneal five times at 500 - 550 °C, and anneal once at 650 °C.

[0010] Preferably, the step of preparing the PZT sol specifically includes the following process:

[0011] Weigh lead acetate trihydrate crystals, add ethylene glycol monomethyl ether, heat to completely dissolve it, stir in a water bath to make it uniformly mixed, and obtain solution one.

[0012] Weigh tetrabutyl titanate, add ethylene glycol monomethyl ether and acetylacetone, and make it uniformly mixed to obtain solution two.

[0013] Weigh zirconium nitrate, add it to ethylene glycol monomethyl ether, and make it uniformly mixed to obtain solution three.

[0014] After mixing solution one, solution two, and solution three, titrate with acetic acid to adjust the pH value.

[0015] Stir under water bath conditions to obtain a solution, and then seal and let the solution stand and age to obtain the PZT sol.

[0016] Preferably, the molar concentration ratio of Pb, Zr, and Ti in the solution is 1.15:0.53:0.47.

[0017] Preferably, the steps of spin coating and heat treatment of the sol specifically include the following process:

[0018] Drop the PZT sol onto the substrate and let it flow naturally until it covers the substrate;

[0019] Use a spin coater to evenly spin off the solution. The spin coating is divided into two gears. The first gear spins at 800 - 1000 rmp for 5 - 10 s, and the second gear spins at 2500 - 3000 rmp for 20 - 25 s;

[0020] Keep the substrate at 120 °C for 3 - 4 min to volatilize the solvent;

[0021] Keep the substrate at 300 °C for 4 - 6 min to pyrolyze the sol and remove the organic matter;

[0022] Repeat the above steps 8 - 10 times until the desired thickness is obtained.

[0023] Another object of the embodiments of the present invention is to provide a PZT piezoelectric thin film prepared by the above preparation method.

[0024] The preparation method of a PZT piezoelectric thin film provided by the embodiments of the present invention is an improved annealing process of low - high temperature annealing based on the process of multi - layer spin coating and multi - step annealing. After low - high temperature annealing, the PZT thin film has a dense structure, no obvious boundary layer, voids, and cracks, and the remanent polarization intensity of the thin film can reach up to 17.2 μc / cm 2 , reaching the research level of domestic and foreign counterparts. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a physical diagram of the PZT sol prepared in Example 1 of the present invention;

[0026] Figure 2 It is the ferroelectric hysteresis loop result of the thin films prepared in Comparative Examples 1 - 3 of the present invention;

[0027] Figure 3 It is an interface schematic diagram of the thin film prepared in Comparative Example 1 of the present invention;

[0028] Figure 4 It is an interface schematic diagram of the thin films prepared in Examples 1 and 2 and Comparative Example 4 of the present invention;

[0029] Figure 5 The results of the polarization hysteresis loops of the thin films prepared in Example 1 and Example 2 of the present invention and Comparative Example 4. Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] A PZT piezoelectric thin film, and its preparation method includes the following steps:

[0032] (1) Prepare a PZT sol: The solute of the PZT sol is lead acetate, zirconium nitrate and tetrabutyl titanate, which are used as the sources of Pb, Zr, and Ti in PZT respectively. The composition of the PZT thin film is selected to be close to the morphotropic phase boundary (MPB) with Zr / Ti = 53:47. In order to make up for the volatilization loss of Pb during sintering, the molar concentration ratio of metal ions in the solution is Pb:Zr:Ti = 1.15:0.53:0.47. The colloidal solvent is ethylene glycol monomethyl ether, and the stabilizer is acetylacetone;

[0033] The amount of lead introduced has a great influence on the performance of the prepared PZT thin film. Under the action of high temperature for a long time during heat treatment, Pb is easily volatilized to form lead vacancies, making PZT a P-type conductive material with metal vacancies, reducing the insulation of the thin film and increasing the leakage current; the introduction of an appropriate amount of lead can compensate for the vacancies caused by the volatilization of lead. As the amount of lead introduced increases, the dielectric constant and remanent polarization increase; however, when too much Pb is introduced, too much Pb will segregate at the grain boundaries and domain boundaries, increasing the resistance to polarization reversal, resulting in an increase in the dielectric loss and coercive field of the thin film and a deterioration in performance. After experimental optimization, the excess amount of lead introduced is selected to be 15%;

[0034] The sol solvent is ethylene glycol monomethyl ether, and the stabilizer is acetylacetone;

[0035] The preparation process includes the following steps:

[0036] 1) Weigh a certain weight (0.3 - 0.8 mol) of lead acetate trihydrate crystals, add them to ethylene glycol monomethyl ether, heat to completely dissolve them, and then reflux at 120 °C for 1 h;

[0037] 2) Take tetrabutyl titanate in proportion, add ethylene glycol monomethyl ether and acetylacetone, and place it for 20 min under the conditions of 80 °C and ultrasonic oscillation to make it uniformly mixed;

[0038] 3) Weigh zirconium nitrate in proportion, add ethylene glycol monomethyl ether, stir evenly for 5 min, and place the mixed solution for 20 min under the conditions of 80 °C and ultrasonic oscillation to make it uniformly mixed;

[0039] 4) Mix the above three solutions, and place the mixed solution under the conditions of 80 °C and ultrasonic oscillation for 30 minutes to make it uniformly mixed;

[0040] 5) Titrate with acetic acid to make the pH value 2.7 - 3.0;

[0041] 6) Stir the above solution under the water bath condition, the stirring speed is 220 - 280 rpm, and the stirring time is 4 - 6 h;

[0042] 7) Supplement the volatilized ethylene glycol monomethyl ether in the solution, and adjust the solution concentration to 0.4 - 0.6 mol / L;

[0043] 8) Naturally cool, stand still and seal, and age for 40 - 80 h under natural conditions to produce the Tyndall phenomenon, indicating that the sol has been formed, as Figure 1 shown;

[0044] (2) Sol spin coating and heat treatment: After the colloid is aged, use a CHEMAT KW-4A spin coater to spin coat the colloid on the substrate. Before annealing, the film needs to be heat treated to remove the solvent and organic matter in the sol. If the solvent is not removed completely, it will burn violently at high temperature, rendering the film useless and even endangering the safety of the experimental equipment; if the organic matter is not removed completely, holes will be left in the film after burning, affecting the film performance. Therefore, after spin coating, use a baking machine to heat treat the substrate. The spin coating and heat treatment steps are as follows:

[0045] 1) Drop the above-prepared solution onto the substrate and let it flow naturally until it covers the substrate;

[0046] 2) Use a spin coater to evenly spread the solution; the spin coating is divided into two gears. The first gear is spin-coated at 800 - 1000 rmp for 5 - 10 seconds, and the second gear is spin-coated at 2500 - 3000 rmp for 20 - 25 seconds;

[0047] 3) Keep the substrate at 120 °C for 3 - 4 min to volatilize the solvent;

[0048] 4) Keep the substrate at 300 °C for 4 - 6 min to pyrolyze the sol and remove the organic matter;

[0049] 5) Repeat steps 1) - 4) 8 - 10 times until the required thickness (> 1 μm);

[0050] (3) Annealing treatment: The PZT thin film treated by thermal decomposition at 300 °C is in an amorphous state of thermodynamic imbalance and has a relatively high energy. Under annealing treatment or other effects, this system will release energy and transform into a crystalline state, becoming a polycrystalline thin film or even a single-crystalline thin film. The annealing process has a great influence on the performance and structure of the thin film. The amorphous original film first transforms into a metastable pyrochlore phase structure (400 - 550 °C), and then crystallizes into a stable perovskite phase (500 - 700 °C). The chemical stoichiometry of the pyrochlore phase is Pb2(Zr1-xTi x )O 7-x , which can be expressed as A2B2O7 and is a centrosymmetric face-centered cubic structure. Like the amorphous thin film, it has a low dielectric constant and poor ferroelectric properties, which need to be avoided in the preparation of PZT thin films. There are two methods to eliminate the pyrochlore phase: The first is to use a rapid heating method to shorten the residence time of the amorphous PZT thin film in the low-temperature stage (400 - 550 °C) to prevent the formation of the pyrochlore phase to the greatest extent; the other is to appropriately increase the annealing temperature to convert the unstable intermediate-phase pyrochlore phase into the perovskite phase. However, with the increase of the annealing temperature, the volatilization of Pb accelerates. In the perovskite ABO3, the ratio of lead atoms in the A site is 20%, while in the pyrochlore phase A2B2O7, the ratio of lead atoms is only 18.18%. Therefore, the volatilization of lead will also lead to the formation of the pyrochlore phase structure; moreover, when Pb is insufficient, the formation of a Zr-rich pyrochlore-type structure has greater stability and cannot be completely transformed into the perovskite structure even at a higher temperature (650 °C). In addition to considering the PZT structure, too high a sintering temperature causes serious interdiffusion between the substrate, electrode, and PZT thick film, resulting in a decrease in the adhesion between the substrate, electrode, and PZT thick film, affecting the piezoelectric properties of the thick film. In the traditional sol-gel preparation process of PZT, the annealing process of multi-layer spin coating and single annealing or multi-layer spin coating and multi-annealing is adopted. The prepared PZT thin film has a certain piezoelectricity in the ferroelectric hysteresis loop, but there are obvious boundary layers, voids, and even cracks. Therefore, in the embodiment of the present invention, an improved annealing process of low-high temperature annealing is carried out on the basis of the multi-layer spin coating and multi-annealing process. The specific process is as follows: spin coat six times, anneal five times at 500 - 550 °C, and anneal once at 650 °C, with an annealing time of 1 h for each time.

[0051] The following specifically describes the specific implementation of the present invention in combination with specific embodiments.

[0052] Example 1. A PZT piezoelectric thin film, and its preparation method includes the following steps:

[0053] (1) Prepare PZT sol:

[0054] Weigh 0.3 mol of lead acetate trihydrate crystals, add them to ethylene glycol monomethyl ether, heat to completely dissolve them, and then reflux at 120 °C for 1 h;

[0055] Weigh tetrabutyl titanate in the molar concentration ratio of metal ions of Pb:Zr:Ti = 1.15:0.53:0.47, add ethylene glycol monomethyl ether and acetylacetone, and place it for 20 min under the conditions of 80 °C and ultrasonic oscillation to make it uniformly mixed;

[0056] Weigh zirconium nitrate in the molar concentration ratio of metal ions of Pb:Zr:Ti = 1.15:0.53:0.47, add ethylene glycol monomethyl ether, and stir evenly for 5 min. Place the mixed solution for 20 min under the conditions of 80 °C and ultrasonic oscillation to make it uniformly mixed;

[0057] Mix the above three solutions, and place the mixed solution for 30 minutes under the conditions of 80 °C and ultrasonic oscillation to make it uniformly mixed;

[0058] Use acetic acid titration to make the pH value 2.7 - 3.0;

[0059] Stir the above solution under water bath conditions, with a stirring speed of 220 rpm and a stirring time of 6 h;

[0060] Supplement the volatilized ethylene glycol monomethyl ether in the solution and adjust the solution concentration to 0.5 mol / L;

[0061] Cool naturally, seal and stand still, and age for 48 h under natural conditions to produce the Tyndall phenomenon, indicating that the sol has been formed;

[0062] (2) Sol spin coating and heat treatment:

[0063] Drop the above-prepared solution onto the substrate and let it flow naturally until it covers the substrate;

[0064] Use a spin coater to evenly spread the solution; the spin coating is divided into two gears. The first gear is spin-coated at 800 rmp for 10 seconds, and the second gear is spin-coated at 3000 rmp for 25 seconds;

[0065] Keep the substrate at 120 °C for 4 min to volatilize the solvent;

[0066] Keep the substrate at 300 °C for 5 min to pyrolyze the sol and remove the organic matter;

[0067] Repeat the above steps until the required thickness (>1 μm);

[0068] (3) Annealing treatment: Spin coat six times, anneal five times at 550 °C, and anneal once at 650 °C.

[0069] The difference between Example 2 and Example 1 is only that the parameters of the annealing treatment in step (3) are adjusted to spin coat six times, anneal five times at 500 °C, and anneal once at 650 °C.

[0070] Comparative Example 1: The only difference from Example 1 is that the parameters of the annealing treatment in step (3) are adjusted to spin coating six times, annealing twice, and the temperature is 650°C.

[0071] Comparative Example 2: The only difference from Example 1 is that the parameters of the annealing treatment in step (3) are adjusted to spin coating four times, annealing three times, and the temperature is 650°C.

[0072] Comparative Example 3: The only difference from Example 1 is that the parameters of the annealing treatment in step (3) are adjusted to spin coating five times, annealing twice, and the temperature is 650°C.

[0073] Comparative Example 4: The only difference from Example 1 is that the parameters of the annealing treatment in step (3) are adjusted to spin coating six times, annealing six times, and the temperature is 650°C.

[0074] Performance test: The PZT thin films prepared in Comparative Examples 1 - 3 were tested, and the ferroelectric hysteresis loops of the thin films were obtained as Figure 2 shown. The ferroelectric hysteresis loop is used to characterize the magnitude of the remanent polarization (positive value) when the electric field strength is 0. The larger this value, the better the piezoelectric performance. Among them, 2*6 represents spin coating 6 times and annealing 2 times, 3*4 represents spin coating 4 times and annealing 3 times, 5*2 represents spin coating 5 times and annealing 2 times. According to Figure 2 it can be seen that in the traditional sol - gel process for preparing PZT, using the annealing process of multi - layer spin coating with single annealing or multi - layer spin coating with multiple annealings, the ferroelectric hysteresis loops of the prepared PZT thin films have certain piezoelectricity. However, through the observation of their interfaces (the thin film prepared in Comparative Example 1), as Figure 3 shown, it can be seen that there are obvious boundary layers, voids and even cracks.

[0075] The PZT thin films prepared in Examples 1 - 2 and Comparative Example 4 were tested, and the interfaces were observed. The results are as Figure 4 shown (from left to right are Comparative Example 4, Example 1, Example 2). It can be seen that there is obvious delamination between the thin film layers in Comparative Example 4, while the delamination between the thin film layers in Example 1 is improved, and the thin film structure in Example 2 is dense, without obvious boundary layers, voids and cracks; in addition, the ferroelectric hysteresis loop results are as Figure 5 shown. In the figure, 650°C*6 is the ferroelectric hysteresis loop of Comparative Example 4, 550°C*5 - 650°C*1 is the ferroelectric hysteresis loop of Example 1, and 500°C*5 - 650°C*1 is the ferroelectric hysteresis loop of Example 2. It can be seen that the remanent polarization intensity of the PZT thin films prepared in the examples of the present invention can reach up to 17.2 μc / cm 2 .

[0076] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a PZT piezoelectric thin film, characterized in that It includes the following steps: Prepare PZT sol: Use ethylene glycol monomethyl ether, lead acetate trihydrate, zirconium nitrate and tetrabutyl titanate to prepare PZT sol; Spin coating and heat treatment of sol: Spin coat and heat treat the prepared PZT sol; Annealing treatment: Based on multiple spin coating and multiple annealing, perform low and high temperature annealing treatment.

2. The preparation method of the PZT piezoelectric thin film according to claim 1, wherein, In the step of the annealing treatment, spin coat six times, anneal at 500 - 550 °C five times, and anneal at 650 °C once.

3. The preparation method of the PZT piezoelectric thin film according to claim 1, characterized in that, The step of preparing the PZT sol specifically includes the following processes: Weigh lead acetate trihydrate crystals, add ethylene glycol monomethyl ether, heat to completely dissolve it, then stir in a water bath to make it uniformly mixed to obtain Solution 1; Weigh tetrabutyl titanate, add ethylene glycol monomethyl ether and acetylacetone, and make it uniformly mixed to obtain Solution 2; Weigh zirconium nitrate, add it to ethylene glycol monomethyl ether, and make it uniformly mixed to obtain Solution 3; After mixing Solution 1, Solution 2 and Solution 3, titrate with acetic acid to adjust the pH value; Stir under water bath conditions to obtain a solution, and then seal and let the solution stand and age to obtain the PZT sol.

4. The preparation method of the PZT piezoelectric thin film according to claim 3, wherein, The molar concentration ratio of Pb, Zr and Ti in the solution is 1.15:0.53:0.

47.

5. The preparation method of the PZT piezoelectric thin film according to claim 1, wherein, The step of spin coating and heat treatment of the sol specifically includes the following processes: Drop the PZT sol onto the substrate and let it flow naturally until it covers the substrate; Use a spin coater to evenly spin off the solution. The spin coating is divided into two gears. The first gear spins at 800 - 1000 rmp for 5 - 10 s, and the second gear spins at 2500 - 3000 rmp for 20 - 25 s; Keep the substrate at 120 °C for 3 - 4 min to volatilize the solvent; Keep the substrate at 300 °C for 4 - 6 min to pyrolyze the sol and remove organic substances; Repeat the above 8 - 10 times until the required thickness is obtained.

6. A PZT piezoelectric thin film, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 5.

Images