JP2002012424A - Method of producing pzt thin film and pzt structure obtained thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a PZT thin film capable of making sufficient ionization of Ti at the surface of the substrate in a mixed alkaline aqueous solution in the beginning of hydrothermal synthesis, and to provide a PZT structure obtained by the method. SOLUTION: This method of producing a PZT film comprises immersing a substrate having titanium component on the surface in an alkaline aqueous solution of (A) or (B) below in advance of the hydrothermal synthesis. (A) an alkaline aqueous solution containing a lead compound and a zirconium compound. (B) an alkaline aqueous solution containing neither a lead compound, a zirconium compound nor a titanium compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a PZT thin film for forming a PZT thin film on a substrate surface by hydrothermal synthesis, and a PZT structure obtained by the method.

[0002]

2. Description of the Related Art Conventionally, a PZT thin film has been formed on a substrate surface by hydrothermal synthesis. This PZ
The method for producing a T thin film is a method in which the T thin film is formed in two stages of PZT crystal nucleus generation and PZT crystal growth (Japanese Patent Laid-Open No. 6-20678).
No. 7, JP-A-9-217178) and PZT.
Method of performing crystal nucleation and PZT crystal growth in one step (JP-A-9-217178, JP-A-9-2784)
No. 36).

The method of performing the above two steps is as follows.
In the first stage, as shown in FIGS. 5 and 6, for example,
Hydrothermal synthesis is performed under predetermined conditions while holding the titanium (Ti) substrate 51 in a mixed alkaline aqueous solution containing lead nitrate (Pb (NO ₃ ) ₂ ), zirconium oxychloride (ZrOCl), and potassium hydroxide (KOH). Thus, a PZT crystal nucleus is generated on the surface of the substrate 51, and the first film 52a including the PZT crystal nucleus is formed. Then, in the second stage, as shown in FIGS. 7 and 8, for example, Pb (NO
_{3) 2,} ZrOCl, by hydrothermal synthesis under prescribed conditions holds TiCl _4, substrate 51 KOH to the mixed alkali aqueous solution containing to form the first layer 52a,
A PZT crystal is grown around the PZT crystal nucleus (the surface of the PZT crystal nucleus and the gap between the PZT crystal nuclei) to form a second film 52b made of the PZT crystal. Thus, the first film 52a and the second film 5 are formed on the surface of the substrate 51.
2b is formed.

[0004] The method performed in one step is, for example, Pb
By holding the substrate 51 in a mixed alkaline aqueous solution containing (NO ₃ ) ₂ , ZrOCl, TiCl ₄ , and KOH and performing hydrothermal synthesis under predetermined conditions, the first surface is formed on the surface of the substrate 51.
A PZT crystal film of only the film 52a is formed.

[0005]

However, in the conventional formation of the PZT crystal film 52 by the hydrothermal synthesis, the ionization of Ti on the surface of the substrate 51 in the mixed alkaline aqueous solution at the start of the hydrothermal synthesis is not possible. P is sufficient
As the thickness of the first film 52a made of the ZT crystal nucleus increases, the Ti component in the surface portion of the first film 52a decreases significantly. Therefore, it has been difficult to sufficiently improve the piezoelectric constant of the PZT structure including the substrate 51 and the PZT crystal film 52 formed on the surface thereof. That is, in the PZT structure, Ti / Ti of the PZT crystal film 52 is used.
It is known that the piezoelectric constant is maximized when the composition of + Zr (molar ratio) is 0.48. However,
In the above-mentioned conventional hydrothermal synthesis, the composition of Ti / Ti + Zr (molar ratio) on the surface portion of the first film 52a is much lower than 0.48.
The composition of i + Zr (molar ratio) is significantly lower than 0.48,
The piezoelectric constant of the PZT structure does not become a sufficient value.

Therefore, it is conceivable that Ti ions are sufficiently contained in the mixed alkaline aqueous solution used for hydrothermal synthesis. In this case, PZT powder is formed in the mixed alkaline aqueous solution, and , First film 52
When forming a, Ti ions are not taken in.

The present invention has been made in view of such circumstances, and a method of producing a PZT thin film capable of sufficiently ionizing Ti on a substrate surface in a mixed alkaline aqueous solution at the start of hydrothermal synthesis. The object is to provide a PZT structure obtained thereby.

[0008]

According to the present invention, a substrate having a titanium component on its surface is kept in an alkaline aqueous solution of the following (A) at 100 to 250 ° C.
PZT on the substrate surface by hydrothermal synthesis at a temperature of
A first aspect of the present invention is a method of producing a PZT thin film for forming a thin film, wherein the substrate is immersed in an alkaline aqueous solution of the following (A) or an alkaline aqueous solution of the following (B) prior to the hydrothermal synthesis. The PZT structure obtained thereby is referred to as a second gist. (A) An alkaline aqueous solution containing a lead compound and a zirconium compound. (B) An alkaline aqueous solution containing neither a lead compound, a zirconium compound nor a titanium compound.

That is, the method for producing the PZT thin film of the present invention comprises:
Prior to hydrothermal synthesis, the substrate having a titanium component on its surface is immersed in the aqueous alkali solution (A) or the aqueous alkali solution (B). Titanium on the surface is easily ionized. Therefore, when hydrothermal synthesis is started, titanium ionization on the substrate surface can be sufficiently performed in an alkaline aqueous solution used for hydrothermal synthesis.

In the method for producing a PZT thin film of the present invention, even when the aqueous alkali solution (A) contains a titanium compound, the ionization of titanium on the substrate surface can be promoted.

In the PZT structure obtained by the method for producing a PZT thin film of the present invention, titanium ions are sufficiently ionized on the substrate surface in the alkaline aqueous solution used for hydrothermal synthesis. The titanium component is also sufficiently contained in the surface portion of the first film composed of the nucleus.
Accordingly, the piezoelectric constant of the PZT structure has been sufficiently improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a method for producing a PZT thin film according to the present invention. In this embodiment, first, Pb (NO ₃ ) ₂ , ZrOCl, and K are placed in a pressure vessel 1 having an inner surface coated with polytetrafluoroethylene.
A mixed alkaline aqueous solution (first synthetic solution) containing OH is put in, and the Ti substrate 11 (see FIG. 2) washed with acetone is held in the first synthetic solution. On the other hand, silicone oil (heat medium) is placed in a stainless steel tank (heat-resistant vessel) 3 having a movable stage 2 for mounting the pressure vessel 1 thereon.
After the pressure vessel 1 has been put in and the pressure vessel 1 is closed with a lid 5, the pressure vessel 1 is hidden in the silicone oil 4 by gripping means 6. This latency is caused by moving the pressure vessel 1 in the direction parallel to the gravity.
This is performed at a temperature of 25 ° C. for a predetermined time while vibrating at a frequency of not less than Hz. Thus, the substrate 11 is immersed in the first synthesis liquid.

Subsequently, the silicone oil 4 is set to a predetermined temperature by a heating means (not shown), the pressure vessel 1 is vibrated at 3 Hz or more in a direction parallel to gravity, and the silicone oil 4 is stirred by the stirring means 7. Meanwhile, the hydrothermal synthesis process (first hydrothermal synthesis process) is performed for a predetermined time. In a state after the completion of the first hydrothermal synthesis process, a first film 12a (see FIG. 2) composed of PZT crystal nuclei is formed on the surface of the substrate 11. Then, after the first hydrothermal synthesis process, the substrate 11 on which the first film 12a is formed is taken out and subjected to ultrasonic cleaning with distilled water.

Subsequently, after discharging the first synthetic solution, a mixed alkaline aqueous solution (second synthetic solution) containing Pb (NO ₃ ) ₂ , ZrOCl, TiCl ₄ and KOH is added, and the above-mentioned hydrothermal synthesis is performed. The processed substrate 11 is held in the second synthetic solution. Next, after the pressure vessel 1 is sealed with a lid 5, the silicone oil 4
Latent within. Then, the silicone oil 4 is set at a predetermined temperature, the pressure vessel 1 is vibrated at 3 Hz or more in a direction parallel to gravity, and the silicone oil 4 is stirred by the stirring means 7 while the hydrothermal synthesis processing (second water Thermal synthesis) for a predetermined time to grow a PZT crystal and
A second film 12b made of ZT crystal is formed. In this way, as shown in FIG. 2, a PZT crystal film (thin film) 12 composed of the first film 12a and the second film 12b is formed on the surface of the substrate 11, and is formed on the substrate 11 and the surface thereof. A PZT structure 10 composed of the PZT crystal film 12 thus obtained is obtained.

According to the above embodiment, since the Ti substrate 11 is immersed in the first synthetic solution prior to the first hydrothermal synthesis processing, the substrate 11 is chemically etched and Of the substrate 11 becomes uneven, and Ti of the substrate 11 is easily ionized. Therefore, when the first hydrothermal synthesis process is started, it is possible to sufficiently ionize Ti on the surface of the substrate 11 in the first synthetic solution. Therefore, the Ti component is sufficiently contained even in the surface portion of the first film 12a made of the PZT crystal nucleus, and Ti / Ti +
The composition of Zr (molar ratio) is a value close to 0.48. Therefore, according to the above embodiment, the obtained P
The piezoelectric constant of the ZT structure 10 can be sufficiently improved.

In another embodiment of the method for producing a PZT thin film of the present invention, first, an aqueous alkali solution (Pb compound, Zr compound and Ti) having a predetermined concentration containing KOH is placed in a container (not shown).
Aqueous alkali solution that does not contain any of the compounds)
The Ti substrate 11 washed with acetone is kept in the above-mentioned alkaline aqueous solution and immersed at 25 ° C. for a predetermined time.

Subsequently, in the same manner as in the above embodiment,
The first synthetic solution is placed in a pressure vessel 1 and the immersed substrate 1
1 is held in the first synthesis solution. On the other hand, a silicone oil 4 is put in a stainless steel tank 3 provided with a movable stage 2 for mounting the pressure vessel 1, and is set at a predetermined temperature by a heating means. After sealing, it is hidden in the silicone oil 4 by the gripping means 6. Then, while the pressure vessel 1 is vibrated at 3 Hz or more in a direction parallel to the gravity, the hydrothermal synthesis treatment (first
Hydrothermal synthesis treatment) for a predetermined time. After that, it is the same as the above embodiment.

According to the other embodiment, the Ti substrate 11 is immersed in an alkaline aqueous solution prior to the first hydrothermal synthesis process. Are uneven, and Ti of the substrate 11 is easily ionized. For this reason, when starting the first hydrothermal synthesis process, the substrate 11
Can sufficiently perform ionization of Ti on the surface. Therefore, the first film 12a made of PZT crystal nuclei
In the surface portion, the Ti component is sufficiently contained, and T
The composition of i / Ti + Zr (molar ratio) is close to 0.48. Therefore, similarly to the above embodiment, the piezoelectric constant of the obtained PZT structure 10 can be sufficiently improved.

Next, examples will be described together with comparative examples.

[0021]

Example 1 Example 1 is a production method similar to that of the above-described embodiment. Specifically, the first synthesis solution contains Pb (N
10 mmol of O ₃ ) ₂ and 5.2 mmol of ZrOCl
1 and 30 ml of KOH using 136.8 mmol, and the substrate 11 made of Ti is 30 mm × 40 mm × 50 μm
(Thickness). Then, the immersion of the substrate 11 in the first synthetic solution was performed at 25 ° C. for 1 hour. Further, the first hydrothermal synthesis treatment was performed for 24 hours at a set temperature of the silicone oil 4 of 180 ° C.

The second synthetic solution is Pb (NO ₃ ) ₂
10 mmol, ZrOCl 5.2 mmol, TiC
The l ₄ 4.8 mmol, 30 ml made using 136.8mmol the KOH, second hydrothermal synthesis treatment was carried out setting the temperature of the silicone oil 4 in the 120 ° C. 24 hours. Then, a PZT structure 10 having the PZT crystal film 12 formed on the surface of the substrate 11 was obtained (see FIG. 2).

[0023]

[Embodiment 2] In Embodiment 2, the immersion time of the substrate 11 in the first synthetic solution in the above-mentioned Embodiment 1 was set to 8 hours. Other than that is the same as the first embodiment.

[0024]

[Embodiment 3] In Embodiment 3, the immersion time of the substrate 11 in the first synthetic solution in Embodiment 1 is set to 24 hours. Other than that is the same as the first embodiment.

[0025]

Fourth Embodiment In a fourth embodiment, the immersion time of the substrate 11 in the first synthetic solution in the first embodiment is set to 48 hours. Other than that is the same as the first embodiment.

[0026]

Fifth Embodiment A fifth embodiment is a manufacturing method similar to that of the other embodiments. Specifically, the concentration of the aqueous alkali solution (KOH) for immersing the substrate 11 was 6 mol / l, and the immersion was performed at 25 ° C. for 1 hour. Also, the substrate 11,
The first synthesis solution, the first hydrothermal synthesis process, the second synthesis solution, and the second hydrothermal synthesis process were the same as in Example 1 above.

[0027]

[Embodiment 6] In Embodiment 2, the immersion time of the substrate 11 in the alkaline aqueous solution is set to 8 hours in Embodiment 5. Other than that is the same as the fifth embodiment.

[0028]

Seventh Embodiment In the seventh embodiment, the immersion time of the substrate 11 in the alkaline aqueous solution is set to 24 hours in the fifth embodiment. Other than that is the same as the fifth embodiment.

[0029]

Eighth Embodiment In an eighth embodiment, the immersion time of the substrate 11 in the alkaline aqueous solution is set to 48 hours in the fifth embodiment. Other than that is the same as the fifth embodiment.

[0030]

Comparative Example 1 Comparative Example 1 is the same as Example 1 except that the step of immersing the substrate 11 in the first synthetic solution (immersing at 25 ° C. for 1 hour) is omitted. Other than that is the same as the first embodiment.

Then, the above Examples 1 to 8 and Comparative Example 1
The piezoelectric constant of the PZT structure 10 obtained by the above method was calculated. That is, first, after the second hydrothermal synthesis treatment, the PZT structure 10 was taken out, ultrasonically washed with distilled water, and dried at 100 ° C. Next, a 30 mm × 10 mm PZT structure 10 is cut out from the PZT structure 10, and the cut PZT structure 10 is cut out.
(25mm × 10m) using silver paste on both sides of
m) was formed. Next, as shown in FIG. 3, one end of the PZT structure 10 on which the electrode is formed is
mm, and fixed with a jig 21 with electrodes.
The other end was a free end. And PZT on which electrodes are formed
The DC voltage is increased by 1 V from 1 V to 20 V intermittently at intervals of 1 second in the structure 10 via a jig 21 with electrodes to reduce the DC voltage to 1
For 2 seconds (see FIG. 4), the displacement of the free end 10a one second after the start of the application of each voltage was measured by a laser displacement meter. Then, from each measurement result, the displacement amount (μm) / voltage (V) from 1 to 20 V was calculated, and the average value thereof was obtained. Further, the thickness of the PZT structure 10 (excluding the electrodes) and the thickness of the substrate 11 of the PZT structure 10 were measured with a micrometer, and the PZT structure 10 was measured.
The thickness of the PZT crystal film 12 was calculated by dividing the difference by two. Further, the Young's modulus of the substrate 11 and the Young's modulus of the PZT structure 10 were measured according to JIS Z 2241. By substituting these values and the length of the PZT structure 10 on which the electrodes are formed from the jig 21 with electrodes into the following equations (1) and (2), the Young's modulus of the PZT crystal film 12 is calculated, and the PZT structure is obtained. The piezoelectric constant of the body 10 was determined. The results are shown in Table 1 below.

[0032]

(Equation 1)

[0033]

(Equation 2)

[0034]

[Table 1]

From the results shown in Table 1, the PZT structure 10 manufactured by the method of Examples 1 to 8 is different from the PZT structure manufactured by the method of Comparative Example 1.
It can be seen that the piezoelectric constant is larger than that of the T structure 10.

[0036] In the embodiments and examples of the above embodiments, but was included TiCl ₄ in the second synthesis solution, is not limited to this, if titanium salt, TiCl ₄
May be replaced by titanium sulfate or a titanium compound.

In each of the above embodiments and examples, the method of manufacturing the PZT crystal film is performed in two steps.
The first synthesis solution may include a titanium salt such as TiCl ₄ , and may be performed in one step.

In each of the above embodiments and examples, the first synthetic solution or the like or the second synthetic solution in which the Ti substrate 11 is immersed prior to the first hydrothermal synthesis process contains KOH. Although it is an alkaline aqueous solution, any other alkaline aqueous solution may be used.

In each of the above embodiments and examples, the substrate 11 is immersed in the first synthesis solution or the alkaline aqueous solution at 25 ° C., but is preferably immersed in the range of 5 to 100 ° C. Also, the immersion time is 1 to
Preferably it is in the range of 48 hours. Further, it is preferable that the above-mentioned immersion is performed while stirring the first synthetic solution or the alkaline aqueous solution used for the immersion.

[0040]

As described above, according to the method for producing a PZT thin film of the present invention, prior to hydrothermal synthesis, a substrate having a titanium component on its surface is treated with an alkaline aqueous solution of the following (A) or an alkaline aqueous solution of the following (B). Because the substrate is immersed in the substrate, the substrate is chemically etched, and the surface of the substrate is made uneven, so that titanium on the substrate surface is easily ionized. Therefore, when hydrothermal synthesis is started, titanium ionization on the substrate surface can be sufficiently performed in an alkaline aqueous solution used for hydrothermal synthesis. (A) An alkaline aqueous solution containing a lead compound and a zirconium compound. (B) lead compounds,
An alkaline aqueous solution containing neither a zirconium compound nor a titanium compound.

In the method for producing a PZT thin film of the present invention, even when the aqueous alkali solution (A) contains a titanium compound, the ionization of titanium on the substrate surface can be promoted.

In the PZT structure obtained by the method for producing a PZT thin film of the present invention, the titanium ion is sufficiently ionized on the substrate surface in the aqueous alkali solution used for hydrothermal synthesis. The titanium component is also sufficiently contained in the surface portion of the first film composed of the nucleus.
Accordingly, the piezoelectric constant of the PZT structure has been sufficiently improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a method for producing a PZT thin film of the present invention.

FIG. 2 is an explanatory diagram showing a PZT structure obtained by the above manufacturing method.

FIG. 3 is an explanatory diagram showing a method for calculating a piezoelectric constant of the PZT structure.

FIG. 4 is a graph showing a method of applying a DC voltage to the PZT structure.

FIG. 5 shows SE showing a state in which PZT crystal nuclei are generated on a substrate.
It is an M photograph.

FIG. 6 is an explanatory diagram schematically showing a state in which a first film is formed on a substrate.

FIG. 7 is an SEM showing a state in which a PZT crystal has grown on a substrate.
It is a photograph.

FIG. 8 is an explanatory diagram schematically showing a state in which a second film is formed on a substrate.

Claims (3)

[Claims] 1. A substrate having a titanium component on its surface is held in an alkaline aqueous solution of the following (A) at 100 to 250 ° C.
PZT on the substrate surface by hydrothermal synthesis at a temperature of
A method for producing a PZT thin film for forming a thin film, wherein the substrate is immersed in the following alkaline aqueous solution (A) or alkaline aqueous solution (B) prior to the hydrothermal synthesis. (A) An alkaline aqueous solution containing a lead compound and a zirconium compound. (B) An alkaline aqueous solution containing neither a lead compound, a zirconium compound nor a titanium compound. 2. The method for producing a PZT thin film according to claim 1, wherein the aqueous alkali solution (A) contains a titanium compound. 3. A PZT structure obtained by the method for producing a PZT thin film according to claim 1.