JPH1086365A - Thin film element for ferroelectric substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make handling easier and increase surface smoothness by preparing aqueous solutions of respective metallic oxides constituting a ferroelectric substance, using a solution prepared by mixing them together in the state of an aqueous solution as a precursor, and drying and burning the precursor after it is., applied on a predetermined base plate by spin coating or by dip coating. SOLUTION: An aqueous titanium solution is mixed with an aqueous zirconium solution at a room temperature. After stirring them sufficiently, an aqueous lead solution is mixed with this mixed solution and, after stirring both the solutions sufficiently at a room. temperature, they are refluxed and hydrolyzed at a predetermined temperature to obtain at titanate lead zirconate (PZT) precursor solution of a ferroelectric substance. Then, the PZT precursor solution is returned to the state of a room temperature and, after dropping water and a small amount of a hydroxypropyl cellulose thereinto, they are sufficiently stirred. Thereafter, a platinum electrode is formed on a high-rigid base plate such as ceramics by a sputtering process or by a sol-gel process and, after the PZT precursor solution is applied on the platinum electrode by spin coating or by dip coating, drying and burning are performed to form a thin PZT film on the platinum electrode. By this method, handling becomes easier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric or ferroelectric thin film element used as a piezoelectric element in an ink jet recording apparatus or the like.

[0002]

2. Description of the Related Art A technique for forming a ferroelectric lead zirconate titanate (PZT) thin film by a sol-gel method is well known. The sol-gel method is excellent in composition control system, and a film having high surface smoothness can be obtained by repeating spin coating and baking.

A method of forming a PZT thin film by a sol-gel method will be described. For example, as disclosed in JP-A-06-112550, lead acetate is dissolved in acetic acid and refluxed for 30 minutes. Zirconium tetrabutoxide and titanium tetraisopropoxide are dissolved in this solution, water and diethylene glycol are added dropwise, and the mixture is sufficiently stirred for hydrolysis.

[0004] Polyethylene glycol monomethyl ether is added at 10% by weight to PZT, and sufficiently stirred to obtain a homogeneous sol.

A platinum electrode is formed on a silicon substrate, the sol is spin-coated on the platinum electrode, and heated to 350 ° C. to form a crack-free porous gel thin film having a thickness of 2.5 μm. You.

The same raw material is hydrolyzed, and a sol to which polyethylene glycol monomethyl ether is not added is applied on the porous gel thin film by spin coating, and heated to 400 ° C.

This film is annealed in an oxygen atmosphere for 15 hours to obtain a PZT thin film having a perovskite structure.

As a method using a PZT aqueous solution as a precursor, a method called hydrothermal synthesis is also well known.

A method for forming a PZT thin film by a hydrothermal synthesis method will be described. For example, as disclosed in JP-A-6-112543, 0.2 mol of lead nitrate and 0.104 of zirconium oxychloride are used.
And 0.096 mol of titanium tetrachloride are dissolved in a 2 N aqueous solution of potassium hydroxide. A platinum electrode is formed on a silicon substrate, immersed in this solution, and
Heat at 0 ° C. for 30 hours.

The substrate is taken out of the autoclave and
When dried at 0 ° C for 1 hour, cubic P with an average particle size of 5 µm
A ZT thin film can be obtained.

[0011]

Problems to be Solved by the Invention JP-A-06-1125
In a method of forming a PZT thin film by a sol-gel method using a metal alkoxide as a main raw material such as 50, some metal alkoxides are not easy to handle, for example, raw materials must be mixed under a specific atmosphere.

Further, for example, a PZT thin film prepared by a hydrothermal synthesis method as disclosed in JP-A-6-112543 has a problem that the smoothness of the film surface is low because the average particle size is large.

An object of the present invention is to provide a ferroelectric thin film which is inexpensive, easy to handle, and has a high surface smoothness.

[0014]

In order to achieve the above object, the present invention employs a sol-gel method using a ferroelectric precursor aqueous solution as a starting solution. That is, the present invention creates an aqueous solution of each salt of lead, zirconium, and titanium,
The present invention relates to a method for producing a PZT thin film characterized by mixing these in an aqueous solution to form a PZT precursor aqueous solution and spin-coating or dip-coating a predetermined substrate.

Aqueous solutions of the respective salts of lead, zirconium and titanium are prepared and mixed to form a PZT precursor aqueous solution. The aqueous solution is spin-coated or dip-coated on a predetermined substrate, dried and fired to produce PZT. Produce a thin film. The aqueous solution is easy to handle, low cost, and has high surface smoothness.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a schematic view of an ink jet head using a ferroelectric thin film element according to the present invention. A method for manufacturing a ferroelectric element according to the present invention will be described with reference to FIG.

An ink chamber 12 for storing ink is formed in the ink chamber forming member 11, and the ink chamber forming member 11 and the diaphragm 13 are bonded to each other or a diaphragm is formed.
Closely joined by an ink chamber integral formation method or the like.

The lower electrode 14 of the ferroelectric element 15 is formed at a position opposite to the ink chamber of the diaphragm 13 by sputtering, screen printing, a sol-gel method, or the like. The ferroelectric element 15 is formed thereon by a sol-gel method, and finally, the upper electrode 16 is formed by sputtering, screen printing, or a sol-gel method.

Next, an operation method of the ink jet head shown in FIG. 1 will be described.

By applying a voltage to the upper and lower electrodes 14, 16 sandwiching the ferroelectric element 15, the ferroelectric element is displaced by utilizing the piezoelectric characteristics of the ferroelectric element.
The diaphragm is pushed out toward the ink chamber, and the ink in the ink chamber is ejected.

Next, an example of a method for forming the ferroelectric element 15 will be described.

0.014 mol of tetraisopropoxytitanium is dissolved in 30 g of a 3N aqueous nitric acid solution to prepare an aqueous titanium solution. 0.156 mol of zirconium oxynitrate in 2
Dissolve in 0 g of water to obtain an aqueous zirconium solution. 0.03 mol of lead nitrate is dissolved in 20 g of water to obtain a lead aqueous solution.

The composition ratio of Zr and Ti in PZT is closely related to ferroelectric characteristics. Since this composition ratio is determined by the molar ratio of each metal salt, it is necessary to mix them at a desired molar ratio when each aqueous solution is prepared.

A titanium aqueous solution and a zirconium aqueous solution are mixed at room temperature, and after sufficiently stirring, a lead aqueous solution is mixed with the mixed solution. The order of mixing each metal ion aqueous solution is
This order is assumed. After sufficiently stirring at room temperature, the mixture is refluxed and hydrolyzed at 100 ° C. or higher. When each metal ion is mixed at room temperature, each metal ion only forms a metal hydroxide, and the degree of bonding between the metal ions is small. , Zirconium and lead ions can be linked to each other via oxygen. That is, here, Pb-O
-A Ti-O-Zr bond is formed and a sol state is formed. This solution is referred to as a PZT precursor aqueous solution.

FIGS. 2 and 3 are X-ray diffraction patterns of PZT powder prepared from the aqueous PZT precursor solution of the present invention. The PZT powder is prepared by placing a PZT precursor aqueous solution in a crucible and firing at a predetermined temperature for a certain period of time.

FIG. 2 is an X-ray diffraction pattern of a PZT powder prepared by using a solution obtained by mixing and stirring respective metal salts without hydrolyzing the aqueous PZT precursor solution.
FIG. 3 is an X-ray diffraction pattern of a PZT powder prepared after refluxing and hydrolyzing a PZT precursor aqueous solution.

The peak observed near the X-ray diffraction angle, 2θ = 29 °, is a peak called a pyrochlore phase which is observed when the crystallization of PZT is incomplete. The crystallinity of PZT can be quantitatively expressed by comparing the intensity of this peak with the peak intensity of the (101) plane having the highest diffraction intensity among the diffraction peaks of PZT. In FIG. 2, the ratio of the pyrochlore phase is 19.9%, and in FIG.
It was 0%. In other words, it can be seen that the more complete PZT crystal is obtained by refluxing and hydrolyzing.

As described above, the PZT precursor aqueous solution in the present invention can improve the crystallinity of PZT by mixing each metal salt, and then refluxing and hydrolyzing.

Next, the refluxed and hydrolyzed PZT precursor aqueous solution is returned to room temperature, water and a small amount of hydroxypropylcellulose are added dropwise, and the mixture is sufficiently stirred. Hydroxypropylcellulose is added to increase the viscosity of a relatively low-viscosity PZT precursor aqueous solution and increase the film thickness when dip coating or spin coating a substrate to form a film.

Also, hydroxypropyl cellulose is
In addition to increasing viscosity, Pb-O-Ti-O-Z
It also serves to strengthen the r-bond and shorten the distance of each ion. As a result, the firing temperature during film formation can be lowered and the crystallinity of the film is improved.

The above-mentioned hydroxypropylcellulose is an example, and the additive is not limited to hydroxypropylcellulose as long as it functions similarly.

The aqueous PZT precursor solution to which hydroxypropylcellulose is added is a homogeneous solution, and is a transparent solution free from cloudiness and precipitates.

A platinum electrode is sputtered on a substrate such as a ceramic having high rigidity, which is a member for forming the diaphragm 13,
Alternatively, it is formed by a sol-gel method, and the above-mentioned aqueous solution of the PZT precursor is applied thereon by spin coating or dip coating.

The PZT precursor solution applied to the substrate is not crystallized into PZT as it is.
After drying at 0 ° C for 10 minutes, it is fired once at 500 ° C or more,
Decompose the added hydroxypropylcellulose.

Next, firing is performed at 650 ° C. for 1 hour to obtain a perovskite PZT structure. Thus, a PZT thin film was formed on the platinum electrode.

The PZT thin film formed as described above is
It has good adhesion to the diaphragm and lower electrode, and can be formed integrally without using an adhesive.

Further, since the sol-gel method is used, the firing temperature can be made relatively low as compared with the solid-phase method, so that there is a wide range of choices for the substrate as the diaphragm.

(Embodiment 2) The following method is also available for forming the ferroelectric element 15.

0.014 mol of titanium tetrachloride is dissolved in an aqueous ammonia solution, and the generated titanium hydroxide is filtered, washed and taken out, and dissolved in a 3N nitric acid solution to obtain an aqueous titanium solution.

0.156 mol of zirconium oxynitrate is dissolved in 20 g of water to obtain an aqueous zirconium solution. 0.03 mol of lead nitrate is dissolved in 20 g of water to obtain a lead aqueous solution.

A titanium aqueous solution and a zirconium aqueous solution are mixed at room temperature, and after sufficiently stirring, a lead aqueous solution is mixed into the mixed liquid. The order of mixing each metal ion aqueous solution is
This order is assumed. After sufficiently stirring at room temperature, the mixture is refluxed and hydrolyzed at 100 ° C. or higher.

After returning to room temperature, water and a small amount of hydroxypropylcellulose are added dropwise, and the mixture is sufficiently stirred to obtain a uniform PZT solution.

A platinum electrode is sputtered on a substrate made of a highly rigid ceramic or the like, which is a member for forming the diaphragm 13,
Alternatively, it is formed by a sol-gel method, and the above-mentioned aqueous solution of the PZT precursor is applied thereon by spin coating or dip coating. After drying at 150 ° C. for 10 minutes, it is calcined once at 500 ° C. or higher to decompose the added hydroxypropylcellulose. Finally, bake at 650 ° C for 1 hour, and use perovskite P
Obtain a ZT structure. Thus, PZT on the platinum electrode
A thin film was formed.

[0044]

According to the present invention, an aqueous solution of each of the metal oxides constituting the ferroelectric material which is easy to handle is prepared, and a mixture obtained in the state of the aqueous solution is used as a precursor, which is then applied to a predetermined substrate. By spin-coating or dip-coating, and drying and firing, a ferroelectric thin film that is easy to prepare, has a small particle size, and has a high surface smoothness can be provided at a lower cost than before.

[Brief description of the drawings]

FIG. 1 is a perspective view of an ink jet head using a ferroelectric thin film element according to the present invention.

FIG. 2 is an X-ray diffraction pattern of a PZT powder prepared from an aqueous solution of a PZT precursor according to the present invention. Those that do not reflux or hydrolyze.

FIG. 3 is an X-ray diffraction pattern of a PZT powder prepared from an aqueous solution of a PZT precursor according to the present invention. Refluxed and hydrolyzed.

[Explanation of symbols]

 11 Ink chamber forming member 12 Ink chamber 13 Diaphragm 14 Lower electrode 15 Ferroelectric 16 Upper electrode

Claims (5)

[Claims] An aqueous solution is prepared by using each metal salt constituting a ferroelectric as a starting material, and a mixture of the aqueous solutions is used as a ferroelectric precursor aqueous solution, and a thickener is added to the ferroelectric precursor aqueous solution. A ferroelectric thin-film element characterized by being prepared by adding an element. 2. The ferroelectric thin-film element according to claim 1, wherein the thickener added to the ferroelectric precursor aqueous solution according to claim 1 decomposes at a certain temperature or higher when forming the ferroelectric element. 3. The ferroelectric thin-film device according to claim 1, wherein the aqueous solution of a ferroelectric precursor according to claim 1 is refluxed and hydrolyzed after mixing the respective aqueous metal salt solutions. 4. A ferroelectric thin film device, wherein the aqueous metal salt solution according to claim 1 is acidic. 5. A ferroelectric thin-film element prepared by applying the ferroelectric precursor aqueous solution according to claim 1 on a fixed substrate, drying and firing.