JP2000263784A - Piezoelectric body thin film element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a layer of a low permittivity from being formed between a lower electrode and a PZT layer. SOLUTION: In forming a thin film piezoelectric body 16 on a substrate 10, a PZT precursor is formed by a sol-gel method to a lower electrode 14 on the substrate 10, and crystallized in a low temperature heating process. PZT crystals are further grown by a hydrothermal synthesis method with the crystallized PZT used as a seed crystal. A temperature of the low temperature heating process is in a range of 100-300 deg.C and the process is carried out in a hydrothermal process. According to the hydrothermal process, a solution not including PZT crystal components is heated, and the substrate is heated at the low temperature in the heated aqueous solution, thereby crystallizing the piezoelectric body precursor formed by the sol-gel method to use the precursor as the seed crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film piezoelectric element, and more particularly to an ink jet recording head used in an ink jet recording apparatus or the like. The present invention further relates to a method for manufacturing the piezoelectric element.

[0002]

2. Description of the Related Art Lead zirconate titanate (hereinafter referred to as "PZ").
T ". ) Is formed by a physical vapor deposition method (PVD) such as a sputtering method, a chemical vapor deposition method (CVD), a spin coating method such as a sol-gel method, and the like. It is formed by receiving a high-temperature heat treatment of about 1000 ° C.

However, at present, the film thickness is limited to 1 μm or less. Therefore, in order to increase the thickness of the piezoelectric thin film, the deposition time for film formation has been increased or the film formation has been repeated a plurality of times.

In addition, as a method for increasing the thickness of the piezoelectric thin film, use of a hydrothermal synthesis method (also referred to as a hydrothermal method), which allows the reaction to proceed in a low-temperature environment of 200 ° C. or less, is considered. Have been.

[0005] This hydrothermal method is described in, for example, "Preparation of PZT crystal film by hydrothermal synthesis method and its electrical characteristics" in the proceedings of the 15th Electronic Materials Research Seminar of the Ceramic Society of Japan, a recent research report. A seed crystal forming process for depositing a PZT seed crystal on a titanium metal substrate surface;
A crystal growth process for further depositing and growing a PZT crystal on the T seed crystal.

As a method of manufacturing an ink jet head using this hydrothermal synthesis method, for example, Japanese Patent Laid-Open No.
No. 8662 is described. In this conventional example, printing is performed in such a manner that a vibration plate made of a titanium plate is joined to a substrate, and PZT is deposited by hydrothermal synthesis at a position facing the pressure chamber of the vibration plate to provide a piezoelectric element. A head is disclosed.

[0007]

According to the inventor's intensive studies, the above-mentioned prior art has the following problems. In the process of forming PZT by hydrothermal synthesis, titanium is eluted, and titanium oxide (TiO _x ) is generated between the diaphragm made of titanium and PZT. This titanium oxide layer is formed between the diaphragm and the PZT with a thickness of 0.1 to 0.5 μm. Since the titanium oxide layer has low dielectric properties, there is a problem in that PZT cannot exhibit its original properties as a piezoelectric material.

Accordingly, the present inventor has disclosed in Japanese Patent Application No. 8-7766.
No. 8 proposed to form seed crystals in the hydrothermal synthesis method by the sol-gel method. In other words, the disclosure of this prior example discloses that the P
The present invention relates to a piezoelectric element in which a seed crystal of ZT is formed and a PZT crystal is grown based on the seed crystal in a solution for the hydrothermal synthesis method. According to this prior example, unlike the conventional example in which a seed crystal is grown on a titanium substrate, there is an advantage that formation of a low dielectric layer made of a titanium oxide film is prevented.

However, this method employs a step of heat-treating a PZT precursor at a high temperature to form a seed crystal, and thus has a problem that a substrate material that can withstand the high-temperature heat treatment must be used.

Accordingly, an object of the present invention is to provide an improved piezoelectric element in which a seed crystal of PZT is formed by a method other than the hydrothermal synthesis method. That is, an object of the present invention is to provide a piezoelectric element in which a heating step for forming a PZT precursor into a seed crystal by a sol-gel method can be performed at a lower temperature than before. Another object of the present invention is to
An object of the present invention is to provide a method for manufacturing a piezoelectric element that can use an electroformed substrate. Another object of the present invention is to provide an ink jet recording head having the piezoelectric element and an ink jet printer having the same.

[0011]

The summary of the present invention for achieving the above object is as follows. When a thin film piezoelectric material is formed on a substrate, P
A ZT precursor is formed, crystallized by low-temperature heat treatment, and the crystallized PZT is used as a seed crystal to further grow a PZT crystal by a hydrothermal synthesis method.

The optimum temperature for the low-temperature heat treatment is 100-degrees Celsius.
It is in the range of 300 degrees, preferably by hydrothermal treatment. Here, the hydrothermal treatment is to heat a solution containing no crystal component of PZT in the above-described hydrothermal synthesis method, heat the substrate at a low temperature in this heated aqueous solution, and form a precursor of the piezoelectric body formed by the sol-gel method. This is the process of crystallizing the body into seed crystals. After the seed crystal is formed, a PZT crystal is grown based on the seed crystal by a conventional hydrothermal synthesis method to form a thin film piezoelectric material.

In the present invention, since the seed crystal is formed by the sol-gel method, it is not necessary to use a titanium-containing substrate unlike the conventional hydrothermal synthesis method. Therefore, it is possible to avoid the problem that a titanium oxide film is formed between the thin film piezoelectric body and the substrate or between the thin film piezoelectric body and the vibration plate (lower electrode).

In the present invention, since a low-temperature heat treatment is performed in the process of forming a seed crystal of PZT, an electroformed substrate made of a heat-resistant substrate such as a silicon substrate or a nickel or the like having poor heat resistance is used as the substrate. Etc. can be used.

According to the present invention, since the thin-film piezoelectric material is formed without the intervention of a low-dielectric material such as a titanium oxide film, the problem of deterioration in distortion characteristics which cannot be avoided by the hydrothermal synthesis method is solved. It is possible to avoid. As a result of the study by the present inventors, it is possible to improve the distortion characteristics by 30%.

The present invention is also characterized in that the piezoelectric element is an ink jet recording head which is an actuator for discharging ink in an ink cavity provided on a substrate. Further, the present invention is an ink jet printer including the ink jet recording head.

[0017]

FIG. 1 shows the steps of the manufacturing method of the present invention. In the step (1), first, the nickel electroformed substrate 10 formed with the ink cavity 12 is formed.
On the lower electrode 1 made of platinum by sputtering
4 is formed with a thickness of about 0.1 to 0.8 μm.

Next, a PZT film as a piezoelectric thin film was formed on the lower electrode 14 by referring to “PZT Thin Film by the 2P-PA-11 Sol-Gel Method and Hydrothermal Treatment”, p. At low temperature ".

First, Pb (Zr _x Ti _1-x ) O ₃ + YPb
O (where 0.40 ≦ X ≦ 0.6, 0 ≦ Y ≦ 0.
The precursor 15 of the two-component PZT shown in 1) is formed by using the sol-gel method shown below. Known three-component PZT may be used.

In this manufacturing method, a hydrated complex of a hydroxide of a metal component capable of forming a PZT film, that is, a sol is dehydrated and gelled to form a precursor layer 15 of the PZT film.

The sol of the metal component constituting the PZT film is P
The alkoxide or acetate of a metal capable of forming a ZT film can be adjusted by, for example, hydrolysis with an acid.
By controlling the composition of the metal in the sol, the aforementioned PZT
The composition of the film can be obtained. That is, alkoxides or acetates of titanium, zirconium, lead, and other metal components are used as starting materials.

First, this sol composition is applied on the lower electrode 14 on which the PZT film is formed. The lower electrode is a common electrode and functions as a diaphragm. The coating method at this time is not particularly limited, and it can be performed by a commonly used method, for example, spin coating, dip coating, roll coating, bar coating, or the like. Further, it can be applied by flexographic printing, screen printing, offset printing or the like.

The PZT precursor comprising the sol composition is subjected to hydrothermal treatment to crystallize the precursor. This P
ZT functions as a seed crystal for growing a PZT crystal, as described later.

First, the thickness of the PZT precursor film formed by coating is determined by the thickness of the PZT precursor exhibiting the required piezoelectric strain characteristics.
This is an amount necessary for forming a film thickness of T. For example, when manufacturing an ink jet recording head,
0. 1 to 1 μm, especially 0.2 to 0.6
μm is preferred. The step of applying the sol composition is sequentially performed a plurality of times, preferably about 2 to 6 times.

Next, hydrothermal treatment is performed on the electroformed substrate on which the applied sol composition has been formed. The substrate containing the PZT precursor is immersed in an aqueous alkaline solution (which contains almost no raw material components for forming PZT), for example, 0.5 MBa (OH) ₂ , and heated in an autoclave at 0.8 MPa and 160 ° C. As a result, the PZT precursor is heated and crystallized to form a perovskite-type PZT seed crystal.

Next, as shown in FIG. 1B, unnecessary portions of PZT are removed by ion milling and patterned. The patterning method is not particularly limited.
Further, as shown in (3), a hydrothermal synthesis method is applied to this substrate, so that PZT
A crystal of ZT is grown. That is, a PZT film (layer) 16 is grown on the PZT seed crystal 15 obtained by the sol-gel method by a hydrothermal reaction. The reaction solution used in the hydrothermal reaction is adjusted by mixing an aqueous solution of lead acetate Pb (NO ₃ ) _{2, an} aqueous solution of zirconium oxychloride ZrOCl _{2, an} aqueous solution of titanium chloride TiCl ₄ , and an aqueous solution of potassium hydroxide KOH. This gives P
ZT16 grew to 3 μm. Next, the upper electrode 4 is selectively formed on the PZT 16 by using a technique such as an electron beam evaporation method or a sputtering method, as shown in FIG.
Form 2 As a material for the upper electrode, platinum (Pt) / gold (Au) or the like is used. The thickness is about 100 nm.

The PZT crystal may be grown without patterning the PZT seed crystal to form an upper electrode, and unnecessary portions of the piezoelectric body and the upper electrode may be removed by etching.

Thereafter, a desired process such as joining a nozzle plate having nozzles for ink ejection to the open side of the ink chamber obtained in this manner is completed to complete an ink jet recording head.

According to this manufacturing method, the PZT film is crystallized based on the seed crystal in the course of the hydrothermal reaction, so that the effect of improving the crystallization rate can be achieved. Therefore, the time required for the hydrothermal reaction can be shortened, so that the substrate is prevented from being damaged by the alkaline aqueous solution. Further, at this time, by controlling the seed crystal orientation and the film forming conditions, the crystal of the PZT film becomes (10
It is oriented to the 0) plane or the (111) plane. When the degreasing temperature is 350 ° C. or lower, the (111) orientation is obtained, and when the degreasing temperature is 400 ° C. or higher, the (100) orientation is obtained.

The crystal grain size of the piezoelectric thin film is 0.05 μm or more and 0.5 μm or less. If the thickness of the piezoelectric thin film is 1 μm or more, for example, the required piezoelectric characteristics in an ink jet recording head can be obtained, and if it is 10 μm or less, the piezoelectric elements can be formed with high density. It is preferably 1 to 5 μm, more preferably 2 μm.
m.

If the crystal grain size is 0.05 μm or more, required piezoelectric characteristics can be exhibited. 1μm crystal grain size
If it is below, fine patterning of the piezoelectric thin film element becomes possible. This numerical value is realized by a structure in which a fine seed crystal of the piezoelectric thin film is used as a nucleus and the piezoelectric thin film is further crystallized. Further, by setting the surface roughness to 1 μm or less in Rmax, the upper electrode can sufficiently cover the piezoelectric thin film.

The ink jet recording head 1 shown in FIG.
Is a type in which an ink supply flow path is formed in a pressure chamber substrate. As shown in the drawing, the ink jet recording head mainly includes a pressure chamber substrate 20A, a nozzle unit 2, and a base 25.

The pressure chamber substrate 20A is formed on a silicon single crystal substrate and then separated. Pressurizing chamber substrate 20A
Is provided with a plurality of strip-shaped pressure chambers 21, and has a common flow path 23 for supplying ink to all the pressure chambers 21.
Reference numeral 24 denotes a supply port for supplying ink to each ink chamber. The pressurizing chambers 21 are separated by side walls 22.
A vibrating plate 30A is provided on the base 25 side of the pressure chamber substrate 21. The wiring from each piezoelectric thin film element is converged on a wiring board which is a flexible cable, and is connected to an external circuit of the base.

The nozzle plate 10A is a pressure chamber substrate 20A
Joined to. A nozzle 11 for extracting an ink droplet is formed at a position corresponding to the pressure chamber 21 in the nozzle plate. The base 25 is a steel body such as a metal and serves as a mount for the pressurizing chamber substrate 20A.

Next, the structure of a printer using the ink jet recording head having the piezoelectric element shown in FIG. 2 will be described with reference to FIG. The printer is provided with a tray 3, a discharge port 4, and various operation buttons 9 on the main body 2 so as to function as a line printer. Further, an ink jet recording head, a supply mechanism 6, and a control circuit 8 are provided inside the main body.

The ink jet recording head includes the above-described piezoelectric element. This head is particularly a head for a line printer, and is formed to have a length covering the width of a sheet that can be supplied. The ink jet recording head is configured to be able to discharge ink from nozzles provided over the entire width of the sheet in response to a discharge signal supplied from a control circuit.

The supply mechanism includes a motor 600, a roller 60
1, 602 and the like. The motor is rotatable in accordance with the drive signal Sd supplied from the control circuit. The mechanical structure is configured to transmit the rotational force of the motor to the rollers. The roller is configured to rotate when the rotational force of the motor is transmitted, draws the sheet placed on the tray by rotation, and supplies the sheet so as to be printable by the head.

The control circuit includes a CPU, a ROM, a RAM, an interface circuit, and the like. The control circuit supplies a drive signal to a supply mechanism in accordance with print information supplied from a computer via a connector, and supplies an ejection signal to an ink jet type. It can be supplied to a recording head. Further, the control circuit can set an operation mode, perform a reset process, and the like in accordance with an operation signal from the operation panel.

[0039]

As described above, according to the present invention,
Since a layer having a low dielectric constant is not formed on a substrate or a lower electrode on which PZT is formed, a piezoelectric element having excellent piezoelectric characteristics can be provided. Further, according to the present invention, the PZT precursor formed by the sol-gel method is crystallized by low-temperature heat treatment to grow the PZT crystal as a seed crystal. It is possible to use a substrate that is not suitable for the above.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a manufacturing process of an ink jet recording head according to the present invention.

FIG. 2 is a configuration diagram of an inkjet recording head.

FIG. 3 is a perspective view of an ink jet printer using the ink jet recording head.

[Explanation of symbols]

10: nickel electroformed substrate, 12: ink chamber, 14: lower electrode, 15: PZT precursor, 16: PZT crystal growth layer

Claims (12)

[Claims] 1. A piezoelectric element comprising a thin film piezoelectric body formed on an electroformed substrate, wherein a low dielectric layer is not present between the piezoelectric body and the vibration plate formed on the substrate. A piezoelectric element in which the piezoelectric substance is formed. 2. The piezoelectric element according to claim 1, wherein a low dielectric layer made of titanium oxide does not exist between the diaphragm and the piezoelectric body. 3. The piezoelectric element according to claim 1, wherein the diaphragm contains substantially no titanium. 4. A piezoelectric element including the piezoelectric body obtained by depositing a crystal of a piezoelectric body on an electroformed substrate, wherein the low dielectric layer is not formed between the substrate and the piezoelectric body. A piezoelectric element in which the piezoelectric substance is directly deposited on a substrate. 5. An actuator using a deformation of the piezoelectric element according to claim 1 as a drive source. 6. An ink jet recording head using the piezoelectric element according to claim 5 as a driving source for discharging ink. 7. An ink jet printer using the recording head according to claim 6. 8. In a method for manufacturing a thin film piezoelectric material, a PZT precursor is formed by a sol-gel method, a low-temperature heat treatment is performed to crystallize the precursor, and the crystallized PZT is used as a seed crystal. Using hydrothermal synthesis method based on crystal
A method of manufacturing a piezoelectric film, comprising growing a crystal of ZT. 9. A method for manufacturing a piezoelectric element using the manufacturing method according to claim 8, wherein a step of forming a lower electrode on a substrate and a step of forming a seed crystal of the PZT on the lower electrode. A piezoelectric element comprising: a step of patterning the seed crystal according to a pattern of an upper electrode; a step of growing PZT on the seed crystal; and a step of growing the upper electrode on a PZT crystal. Manufacturing method. 10. The method according to claim 8, wherein the piezoelectric body is formed on a substrate that does not include an element that causes a low dielectric layer to be formed. 11. The method according to claim 8, wherein the low-temperature heat treatment is performed by a hydrothermal treatment. 12. The method according to claim 10, wherein the piezoelectric body is formed on a titanium-free substrate.