JP3937538B2 - Method for producing PZT fine particles and PZT thin film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, particles containing Pb, Zr, Ti or Pb, Ti obtained by reacting in an alkaline aqueous solution and Pb (Zr _x Ti _1-x ) O ₃ obtained therefrom (where 0 ≦ x <1 ) Fine particles or Pb (Zr _x Ti _1-x ) O ₃ (where 0 ≦ x <1) thin films.
[0002]
[Prior art]
Lead zirconate titanate (hereinafter referred to as PZT) has excellent properties as a piezoelectric material, pyroelectric material, and ferroelectric material, and includes an ultrasonic sensor, a pyroelectric infrared sensor, a nonvolatile memory, It is widely used in various devices such as condensers and actuators, and has been tried to be applied in many fields.
[0003]
When PZT is applied to a device, a method of sintering PZT particles to form a sintered body as an element and a method of forming a PZT thin film to form an element are generally used.
[0004]
PZT crystal particles are generally produced by a solid phase method in which TiO ₂ , ZrO ₂ and PbO are mixed and then fired. Sintered bodies used for various piezoelectric elements are obtained by further sintering these obtained PZT particles.
[0005]
However, since the PZT particles obtained by the above method have a large particle size, it is difficult to sinter, and a high sintering temperature condition of 1200 ° C. or higher is necessary, and the component Pb is scattered at a high temperature, There is a problem that the composition is shifted.
[0006]
Although the above problem can be solved by lowering the sintering temperature, it is desired to reduce the particle size of the PZT powder as a sintering raw material.
[0007]
As an example of PZT fine powder synthesis, PZT particles are synthesized by the hydrothermal synthesis method in the Journal of the Ceramic Society of Japan 98 [2] 150-55 (1990). Here, there is a description that the particle size tends to be smaller as the reaction temperature is higher, and particles of 1 μm to 3 μm are obtained under the temperature condition of 160 ° C. to 200 ° C., but the particle size is large and still satisfactory. Not. If the temperature is further increased, the pressure becomes high, which makes manufacturing difficult.
[0008]
As another method for synthesizing fine powder, there is a sol-gel method using an organometallic compound, but the raw material is expensive and the purity of the product is low.
[0009]
In addition, in order to improve the characteristics such as the piezoelectricity of the element, the orientation of crystal grains inside the ceramic is improved. As this means, anisotropic PZT crystal particles are used as a sintering raw material. Anisotropic PZT crystal particles are usually TiO ₂ , ZrO ₂ and flux (KCl, NaCl, K ₂ SO ₄ or Na ₂ SO ₄ ) after dry mixing and then firing to obtain acicular ZrTiO _4. After mixing with PbO, it is calcined to produce needle-shaped PZT (eg; Proceedings of Annual Conference of Ceramic Society of Japan in 1988, 348 (1988)). However, with this method, it is difficult to obtain fine acicular particles that can be sintered at a low temperature.
[0010]
On the other hand, as a conventional PZT film manufacturing method, a thin film composition is formed on a substrate mainly by a physical adsorption method (PVD method) represented by a sputtering method, thermal decomposition, oxidation, reduction, polymerization, etc. of an organic metal gas as a thin film material. A chemical vapor deposition method (CVD method) for forming a thin film by depositing on a substrate, a sol-gel method for forming an oxide film by applying an organic metal to a substrate, and a Ti substrate in an alkaline aqueous solution containing raw materials A method such as a hydrothermal method for hydrothermal treatment is used.
[0011]
However, each of these conventional forming methods has problems to be improved.
[0012]
That is, in the physical adsorption method, in general, in order to obtain a crystalline film, it is necessary to set the temperature of a base material such as a substrate to 500 ° C. or more, and thermal strain is accumulated in the process of cooling the base material, There is a problem that the formed PZT film is likely to be cracked or peeled off. In addition, since evaporation of the vapor deposition material is performed under a low oxygen partial pressure, the generated PZT often has oxygen defects, and there is a problem that characteristic deterioration and variation occur.
[0013]
Furthermore, when forming a thin film of a complex oxide such as PZT, the deposition rate varies depending on the element, so that it is difficult to obtain a complex oxide having a target composition by controlling the film composition. There is a point. Also, the slow growth rate of the film is a serious drawback of this method.
[0014]
In addition, in the chemical vapor deposition method, there is a problem that the deposition temperature of the organic metal is relatively high and a large-scale facility is required, and the composition of the film is controlled as in the case of the above physical vapor deposition method. However, it is difficult to form a film having a target composition. Furthermore, there is a disadvantage that the organometallic compound as a raw material is extremely expensive.
[0015]
In addition, in the organic metal coating method, it is necessary to perform baking at a high temperature of 500 ° C. or higher in order to oxidize the organic metal applied to the base material to form an oxide film. There is a problem that large shrinkage occurs in the coating film, and the formed film tends to crack or peel off. Further, there is a problem that it is difficult to obtain a porous and dense film due to evaporation or combustion of the organic substance during the baking process.
[0016]
Furthermore, the hydrothermal method has a problem that the surface roughness of the film formed on the substrate is large.
[0017]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described circumstances of PZT thin films, and has been made to solve the above-described problems of PZT particles, and enables low-temperature sintering in which composition change is unlikely to occur. An object is to provide fine PZT particles or fine acicular particles. Furthermore, an object of the present invention is to provide a PZT thin film having a small surface roughness that can be easily formed on various substrates at a low temperature by eliminating the drawbacks of the conventional method for forming a PZT thin film.
[0018]
[Means for Solving the Problems]
As a result of intensive research on a method for producing a low-temperature sinterable fine powder and a method for producing a high-quality PZT thin film that hardly cause composition changes, the present inventors have devised a raw material for hydrothermal synthesis, thereby achieving the above object. Has been found to achieve the present invention.
[0019]
In the present invention, the Pb-containing raw material compound is 50 mmol / l to 500 mmol / l, the Zr-containing raw material compound is 0 mmol / l to 500 mmol / l, and the Ti-containing raw material compound is 0.002 mmol / l to 500 mmol / l. Hydrothermal synthesis at a temperature of 130 ° C. to 250 ° C. in an aqueous alkali solution using Pb, Zr and Ti obtained by reacting in the temperature range of 0 ° C. to 100 ° C. or particles containing Pb and Ti as raw materials Pb (Zr _x Ti _1-x ) O ₃ (where 0 ≦ x <1) fine particle manufacturing method
About.
[0020]
Further, the present invention is alkaline under the conditions that the Pb-containing raw material compound is 50 mmol / l to 500 mmol / l, the Zr-containing raw material compound is 0 mmol / l to 500 mmol / l, and the Ti-containing raw material compound is 0.002 mmol / l to 500 mmol / l. Pb, Zr and Ti obtained by reacting in an aqueous solution within a temperature range of 0 ° C. to 100 ° C. or particles containing Pb and Ti as raw materials are dispersed in an alkaline aqueous solution. The present invention relates to a method for producing a Pb (Zr _x Ti _1-x ) O ₃ (where 0 ≦ x <1) thin film formed on a substrate, characterized by hydrothermal synthesis at a temperature of 200 ° C.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The particles containing Pb, Zr, Ti or Pb, Ti used in the present invention (hereinafter referred to as precursor particles) are obtained by the following method.
[0023]
The alkali concentration is 166 mmol / l to 8066 mmol / l, the Pb-containing raw material compound is 50 mmol / l to 500 mmol / l, the Zr-containing raw material compound is 0 mmol / l to 500 mmol / l, and the Ti-containing raw material compound is 0.002 mmol / l to 500 mmol / l. The mixed solution adjusted to 1 is mixed with stirring.
[0024]
Alternatively, it is possible to react the components other than the Pb-containing raw material compound first, and then add the Pb-containing raw material compound to cause the reaction.
[0025]
As the raw material compound containing Pb, Zr and Ti used in the present invention, chloride, oxychloride, hydroxide and oxide are preferable. Examples of the alkali compound used include alkali metal hydroxides such as KOH and NaOH.
[0026]
The reaction temperature is preferably 100 ° C. or less which does not require the use of an autoclave. Moreover, since it can also be made to react at room temperature, there exists an advantage that the apparatus for a heating is not required in that case. Although the reaction time varies depending on the reaction temperature, at 25 ° C., precursor particles can be obtained in about 24 hours. When reacted at a high temperature, not only the precursor particles of the present invention but also PZT particles having a large particle size are formed. The reaction is slow at low temperatures, so 0 ° C. or lower is not preferable.
[0027]
Most of the precursor particles obtained are amorphous particles, but some of them contain crystalline particles, and are composed of fine particles or needle-like particles of several hundred nm or less. Although the components of individual particles cannot be specified, the aggregate of particles contains Pb, Zr, Ti, O, and H, or Pb, Ti, O, and H, and Pb, Zr, and Ti contain Pb (Zr _x Ti _{1-x) O 3} (where included at the rate required to construct the 0 ≦ x <1).
[0028]
In order to obtain acicular precursor particles, the raw materials, alkali components and their amounts are the same as described above, but first, the components other than the Pb-containing raw material compound are reacted at 20 ° C. to 60 ° C. for 10 hours to 48 hours. After that, a Pb-containing raw material compound is added and reacted at the same temperature for about 48 hours. If the reaction time before the addition of the Pb-containing raw material compound is long, larger acicular particles can be obtained.
[0029]
Next, a method for producing a PZT fine powder that can be sintered at low temperature from the precursor particles will be described.
[0030]
Fine PZT particles can be obtained by hydrothermally treating precursor particles at a temperature of 130 ° C. to 250 ° C. in an alkaline aqueous solution. Or you may utilize for a PZT particle synthesis | combination as it is, without taking out a precursor from the solution which synthesize | combined precursor particle | grains. In that case, an alkali compound may be added as needed.
[0031]
Examples of the alkali compound used in the PZT particle synthesis include alkali metal hydroxides such as KOH and NaOH. The concentration of alkali at the time of synthesis is preferably in the range of 0.1 mol / l to 8.0 mol / l. When the concentration is low, the reaction does not proceed, and when the concentration is high, the alkali compound is wasted.
[0032]
When the reaction temperature is lower than the above temperature range, the reaction rate is slow, and when the temperature is high, the reaction pressure becomes high and the apparatus becomes expensive.
[0033]
The obtained PZT particles are very fine PZT crystal particles having a specific surface area of 10 m ² / g or more and a particle diameter of 0.05 μm or less.
[0034]
Fine PZT crystal particles can also be obtained by heat treatment at about 800 ° C. in the atmosphere. In this case, the particles have a specific surface area of about 5 m ² / g and a particle size of about 0.1 μm.
[0035]
PZT needle crystal particles obtained from a needle-like precursor by hydrothermal synthesis are crystal particles having a specific surface area of 2 m ² / g or more and a longitudinal direction of several tens of μm or less.
[0036]
Next, a dense PZT thin film having a small surface roughness obtained from the precursor particles will be described.
[0037]
A dense PZT thin film having a small surface roughness is obtained by dispersing PZT precursor particles in an alkaline aqueous solution, dipping the substrate, and then hydrothermally treating at a temperature of 100 ° C. to 200 ° C. Alternatively, the precursor particles can be used as they are for thin film synthesis without being taken out from the reaction solution obtained by synthesizing the precursor particles. In that case, an alkali compound may be added as needed.
[0038]
Examples of the alkali compound used in the thin film synthesis include alkali metal hydroxides such as KOH and NaOH. The concentration of alkali during thin film synthesis is preferably in the range of 0.1 mol / l to 8.0 mol / l. When the concentration is low, the reaction does not proceed, and when the concentration is high, the alkali compound is wasted.
[0039]
The substrate used in the present invention is not particularly limited. In addition to Ti or Ni metal, a crystal is used to increase the adhesion between the crystal film and the substrate due to the reaction between the substrate and metal ions in the solution during crystal nucleus formation. A substrate containing at least one constituent element of the film is preferable. In addition, a substrate coated with an element constituting the crystal film can be used.
[0040]
If the reaction temperature is less than 100 ° C., the film growth rate is slow and lacks practicality, and if it exceeds 200 ° C., the formation of PZT particles takes precedence over the film growth, which is not preferable.
[0041]
The electrode used when the PZT film obtained in the present invention is made into an element is not particularly limited, but an optimum electrode is selected in consideration of cost and mass productivity. For example, there are Ni by sputtering, Ni by electroless plating, and baking type Ag. In addition, Al by vapor deposition, Pt or Au by sputtering, or the like is also used. In addition, when using resin for a board | substrate, since it cannot heat at high temperature, a baking type Ag electrode is unpreferable.
[0042]
【Example】
Examples relating to the method for producing PZT particles of the present invention are shown in Examples 1 to 4 below. Specific examples of the synthesis of the PZT thin film are shown in Examples 5 and 6.
[0043]
Example 1
Pb (NO ₃ ) ₂ aqueous solution 77 mmol / l, ZrOCl ₂ aqueous solution 30.8 mmol / l, TiCl ₄ aqueous solution 30.8 mmol / l and KOH aqueous solution 1388.8 mmol / l (total solution amount 700 ml, filling rate 70%) Precursor particles A of several nm or less containing all of Pb, Zr, Ti, O and H as shown in FIG. 1 were formed by stirring and mixing at 25 ° C. for about 24 hours. The electron beam diffraction pattern of the precursor particle A thus obtained was amorphous as shown in FIG. Further, as shown in the results of Tg-DTA analysis in FIG. 3, the precursor particles A completed the reaction at 400 ° C. or lower, and a high-purity oxide could be formed. Next, the precursor particles were hydrothermally treated in a KOH aqueous solution of 1388.8 mmol / l at 180 ° C. for 4 hours to obtain a specific surface area of 10.0 m ² / g and an average particle size of 0.05 μm. PZT single phase crystal particles showing an X-ray diffraction pattern were obtained. Also, the PZT powder similar to the above was obtained by subjecting the precursor powder synthesis solution before taking out the precursor powder to a hydrothermal treatment at 180 ° C. for 4 hours as it was.
[0044]
Example 2 (Reference Example 1)
A solution of Pb (NO ₃ ) ₂ aqueous solution 80 mmol / l, ZrOCl ₂ aqueous solution 40.4 mmol / l, TiCl ₄ aqueous solution 20.2 mmol / l and KOH aqueous solution 1339.2 mmol / l (total solution amount 700 ml, filling rate 70%). Precursor particles B of several nm or less containing all of Pb, Zr, Ti, O and H as shown in FIG. 5 were formed by stirring and mixing at room temperature for 72 hours or more. The electron beam diffraction pattern of the precursor particle B thus obtained was crystalline as shown in FIG. Further, as shown in the result of Tg-DTA analysis in FIG. 7, this precursor particle B was able to form a high-purity oxide at a low temperature. Next, this precursor particle B is heat-treated at 800 ° C. for 5 hours in an air atmosphere to give a PZT showing the X-ray diffraction pattern of FIG. 8 having a specific surface area of 5.0 m ² / g and a particle size of about 0.1 μm. Single-phase crystal particles were obtained.
[0045]
Example 3
A solution of ZrOCl ₂ aqueous solution 20.2 mmol / l, TiCl ₄ aqueous solution 40.4 mmol / l and KOH aqueous solution 1392.8 mmol / l (total solution amount 400 ml, filling rate 70%) was stirred and mixed at 25 ° C. for 10 hours, and then Pb ( A precursor having an average particle size of 0.1 μm or less containing all of Pb, Zr, Ti, O and H as shown in FIG. 9 by adding 77 mmol / l of NO ₃ ) ₂ aqueous solution and further stirring and mixing at room temperature for 48 hours Acicular particles C were formed. The electron beam diffraction pattern of the precursor particle C thus obtained was amorphous as shown in FIG. Further, this precursor particle C is hydrothermally treated at 130 ° C. for 3 hours to give a PZT single-phase needle-like shape having an X-ray diffraction pattern of FIG. 11 having a specific surface area of 2.0 m ² / g and an average length of about 5 μm. Crystal particles were obtained.
[0046]
Example 4
Crystalline PZT fine particles obtained from the precursor particles A were molded into pellets having a diameter of 20 mm at ² t / cm ² . It was calcined at 900 ° C. for 12 hours in a PbO atmosphere. The relative density of the sintered body was 95%. On the other hand, the density of the sintered body fired under the same conditions by the solid phase method is 80%, and it can be understood that low-temperature sintering can be performed by using the PZT fine particles obtained from the precursor particles of the present invention.
[0047]
Example 5
Pb (NO ₃ ) ₂ aqueous solution 77 mmol / l, ZrOCl ₂ aqueous solution 30.8 mmol / l, TiCl ₄ aqueous solution 30.8 mmol / l and KOH aqueous solution 1388.8 mmol / l (total solution amount 700 ml, filling rate 70%) PZT precursor particles were formed by stirring and mixing at room temperature for 24 hours.
[0048]
Next, the precursor particles were dispersed in a 1388.8 mmol / l aqueous solution of KOH, and after immersion of the Ti substrate, a PZT thin film having a thickness of 2 μm was obtained by hydrothermal treatment at 130 ° C. for 12 hours.
[0049]
FIG. 12 shows an X-ray diffraction pattern of the synthesized PZT thin film.
[0050]
FIG. 13 shows a surface SEM photograph of the synthesized PZT thin film.
[0051]
FIG. 14 shows the surface roughness of the synthesized PZT thin film. The vertical axis represents the surface roughness, and the horizontal axis represents the measured length of the sample. It can be seen that the surface state of the thin film formed from the precursor as a raw material is improved as compared with the surface roughness of the thin film shown in FIG. 15 which is produced by direct hydrothermal synthesis without passing through the precursor.
[0052]
Comparative Example 1
For comparison, a film was directly produced by hydrothermal synthesis as follows without going through the precursor.
A solution of Pb (NO ₃ ) ₂ aqueous solution 106.67 mmol / l, ZrOCl ₂ aqueous solution 53.33 mmol / l, TiCl ₄ aqueous solution 0.53 mmol / l and KOH aqueous solution 2000.0 mmol / l (total solution amount 700 ml, filling rate 70% The Ti substrate was placed in the middle, and hydrothermal treatment was carried out at 180 ° C. for 12 hours without any special stirring operation to form a PZT thin film on the substrate surface. The surface roughness of the PZT thin film at this time is shown in FIG.
[0053]
Example 6
A solution of 20.2 mmol / l ZrOCl ₂ aqueous solution, 40.4 mmol / l TiCl ₄ aqueous solution and 1392.8 mol / l KOH aqueous solution (total solution amount 400 ml, filling rate 70%) was stirred and mixed at room temperature for 10 hours or more, and then Pb ( It added NO _{3) 2} aqueous solution 77 mmol / l, to form a further 48 hours of stirring Pb in mixed by, Zr, Ti, O and number including all H tens nm or less of the precursor acicular particles at room temperature.
[0054]
Next, the precursor particles are dispersed in a KOH aqueous solution of 1388.8 mmol / l, and a Si substrate on which a PZT thin film having a thickness of 1 μm is formed by a sol-gel method is immersed, and then hydrothermally treated at 130 ° C. for 12 hours. A PZT thin film having a thickness of 2 μm was obtained. The same PZT can also be obtained by using a precursor synthesis reaction solution before taking out the precursor powder as it is, dipping a 1 μm-thick PZT thin film by a sol-gel method and then hydrothermally treating it at 130 ° C. for 12 hours. A thin film was obtained.
[0055]
FIG. 16 shows an X-ray diffraction pattern of the synthesized PZT thin film.
[0056]
FIG. 17 shows a surface SEM photograph of the synthesized PZT thin film.
[0057]
FIG. 18 shows the surface roughness of the synthesized PZT thin film. It can be seen that the surface state of the thin film formed from the precursor as a raw material is improved as compared with the surface roughness of the thin film shown in FIG. 15 which is produced by direct hydrothermal synthesis without passing through the precursor.
[0058]
【The invention's effect】
According to the present invention, by using the precursor for producing PZT as a raw material, it is possible to easily obtain a PZT powder having a small particle size that can be sintered at a low temperature and can be sintered with a small composition change. In addition, by immersing various substrates in an alkaline raw material liquid containing PZT precursor particles and performing hydrothermal treatment, a uniform and low surface roughness PZT thin film can be easily and reliably formed at a low temperature of 100 to 200 ° C. be able to.
[Brief description of the drawings]
FIG. 1 is a photographic diagram instead of a drawing, showing a particle structure of precursor particles A obtained in Example 1. FIG.
2 is an X-ray photograph instead of a drawing showing a diffraction pattern of precursor particles A obtained in Example 1. FIG.
3 is a diagram showing a Tg-DTA pattern of precursor particles A obtained in Example 1. FIG.
4 is a diagram showing an XRD (powder X-ray diffraction) pattern of a product produced by hydrothermal treatment of precursor particles A obtained in Example 1 in an aqueous KOH solution. FIG.
5 is a photographic diagram instead of a drawing showing the particle structure of precursor particles B obtained in Example 2. FIG.
6 is an X-ray photographic diagram instead of a drawing showing a diffraction pattern of precursor particles B obtained in Example 2. FIG.
7 is a diagram showing a Tg-DTA pattern of precursor particles B obtained in Example 2. FIG.
8 is a diagram showing an XRD (powder X-ray diffraction) pattern of a product produced by hydrothermally treating the precursor particles B obtained in Example 2 in a KOH aqueous solution. FIG.
9 is a photographic diagram instead of a drawing, showing a particle structure of precursor particles C obtained in Example 3. FIG.
10 is an X-ray photographic diagram instead of a drawing showing a diffraction pattern of precursor particles C obtained in Example 3. FIG.
11 is a diagram showing an XRD (powder X-ray diffraction) pattern of a product produced by hydrothermally treating the precursor particles C obtained in Example 3 in an aqueous KOH solution. FIG.
12 is an XRD pattern diagram showing the crystal structure of the PZT thin film obtained in Example 5. FIG.
FIG. 13 is a SEM photograph showing a surface of a PZT thin film obtained in Example 5 instead of a drawing.
14 is a view showing the surface roughness of the PZT thin film obtained in Example 5. FIG.
FIG. 15 is a comparative view showing the surface roughness of a PZT thin film directly formed by a hydrothermal synthesis method without passing through the precursor of the present invention.
16 is an XRD pattern diagram showing the crystal structure of the PZT thin film obtained in Example 6. FIG.
FIG. 17 is a SEM photograph showing a surface of a PZT thin film obtained in Example 6 instead of a drawing.
18 is a view showing the surface roughness of the PZT thin film obtained in Example 6. FIG.

Claims (2)

Pb-containing raw material compound is 50 mmol / l to 500 mmol / l, Zr-containing raw material compound is 0 mmol / l to 500 mmol / l, and Ti-containing raw material compound is 0.002 mmol / l to 500 mmol / l. Characterized in that hydrothermal synthesis is performed at a temperature of 130 ° C. to 250 ° C. in an alkaline aqueous solution using as a raw material particles containing Pb, Zr and Ti, or Pb and Ti obtained by reacting within a temperature range of to _{Pb (Zr x Ti 1-x} ) O 3 ( however, 0 ≦ x <1) production method of fine particles. Pb-containing raw material compound is 50 mmol / l to 500 mmol / l, Zr-containing raw material compound is 0 mmol / l to 500 mmol / l, and Ti-containing raw material compound is 0.002 mmol / l to 500 mmol / l. The particles containing Pb, Zr and Ti obtained by reacting within the temperature range of ° C or particles containing Pb and Ti are dispersed in an alkaline aqueous solution as a raw material , and after immersing the substrate, water is heated at a temperature of 100 ° C to 200 ° C. Pb formed on the substrate, characterized in that the thermal synthesis _{(Zr x Ti 1-x)} O 3 ( however, 0 ≦ x <1) the method of manufacturing the thin film.

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