JPH11307832A - Piezoelectric thin film element, manufacturing method thereof, and ink jet recording head - Google Patents

Abstract

(57) [Problem] To provide a piezoelectric thin film element in which adhesion between a protective film and a substrate is not deteriorated. SOLUTION: A protection film 14 is formed on almost the entire surface of a substrate 12 of the piezoelectric thin film element. A base layer 16 formed on the protective film in accordance with the pattern of the PZT film and serving as a base when growing and forming the piezoelectric thin film, wherein the piezoelectric thin film is formed on the base layer. .

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 used as a microactuator such as an ink jet recording head and a micropump, and a method of manufacturing the same. The present invention relates to a thin-film piezoelectric element in which a piezoelectric thin film excellent in quality is selectively formed on a substrate.

[0002]

2. Description of the Related Art Conventionally, as an element for converting electric energy into mechanical energy, a piezoelectric thin film element having a structure in which a piezoelectric thin film is sandwiched between a lower electrode as a common electrode and an upper electrode as an individual electrode is known. Are known.

[0003] The piezoelectric thin film element is used, for example, as an actuator for an ink jet recording head or the like. When the piezoelectric thin film element is used, for example, as an actuator of an ink jet recording head or the like, the thickness of the piezoelectric thin film is usually required to be about 1 μm to 10 μm.

As a piezoelectric thin film, for example, a film made of lead zirconate titanate (hereinafter referred to as "PZT film") is generally used. This PZT film can be formed by physical vapor deposition (PVD) such as sputtering, chemical vapor deposition (CVD),
It is manufactured by a spin coating method such as a sol-gel method or a hydrothermal synthesis method.

Among these film forming methods, the reaction can proceed in a low-temperature environment of 200 ° C. or less, and the generation of cracks is suppressed. Therefore, the use of hydrothermal synthesis has been actively studied recently. ing.

[0006] This hydrothermal synthesis method is described in “Preparation of PZT Crystal Film by Hydrothermal Synthesis and Its Electrical Properties” in Proceedings of the 15th Electronic Materials Research Seminar of the Ceramic Society of Japan (published date 1
A seed crystal forming process of depositing a PZT seed crystal on the surface of a titanium metal substrate, as described on October 2, 995).
Next, another PZT crystal is deposited on the PZT seed crystal.
And a crystal growth process for growing.

Japanese Patent Application Laid-Open No. 8-306980 discloses a method for manufacturing a piezoelectric element unit using this hydrothermal synthesis method. First, a titanium layer is formed by a mask film forming method in which a film is formed only on a predetermined position of a substrate not containing titanium, or a titanium layer is formed on the entire surface of the substrate, and PZT is formed by photoetching. It is shown that a titanium layer is left only in a portion to be formed, and PZT is formed on the titanium layer.

Second, PZ on a substrate made of titanium
Platinum as a protective layer is formed on the portion where the T layer is not formed, or the protective layer formed on the entire surface of the substrate is
It is shown that the etching is performed in accordance with the pattern forming ZT.

[0009]

However, the piezoelectric unit element disclosed in Japanese Patent Application Laid-Open No. Hei 8-306980 has the following problems. First, when the protective film is patterned by etching, when a PZT element is formed using a hydrothermal reaction, an alkaline solution or an etchant used for the hydrothermal reaction is protected from the opening of the protective film. There is a possibility that the protective film is soaked into the film, the adhesion between the protective film and the substrate is deteriorated, and the protective film is separated from the substrate.

Second, in this conventional example, when the thickness of the platinum layer as the protective film is small, the function as the protective layer is impaired, and PZT seed crystals are deposited on platinum.
A fine pattern unlike an ink jet recording head is not formed.

Accordingly, an object of the present invention is to provide a piezoelectric thin-film element in which the adhesion between a protective film and a substrate is not deteriorated in order to solve such a problem. Another object of the present invention is to provide a piezoelectric thin film element having a fine piezoelectric thin film pattern formed thereon, such as an ink jet recording head. Another object of the present invention is to provide a manufacturing method for forming these piezoelectric thin film elements.

[0012]

According to the present invention, in order to achieve the above object, a piezoelectric thin film is formed through a base film such as a titanium layer without etching a protective film formed on a substrate. It is characterized by being selectively grown on a film. With such features, the present invention can provide an element having a piezoelectric thin film formed in a fine pattern without impairing the adhesion between the substrate and the protective film.

A second feature of the present invention is that a protective film is formed with a thickness of 50 nm or more to make the film structure dense, and, for example, a piezoelectric material substantially formed on this protective film by a hydrothermal method. This is to prevent seed crystals of the thin film element from being deposited. As a result, the present invention can provide a piezoelectric thin film element having a fine piezoelectric thin film element pattern.

That is, according to the present invention, a piezoelectric thin film is formed on a substrate in a predetermined pattern, and the piezoelectric thin film is deformed by energizing the piezoelectric thin film through a common electrode and an individual electrode. A protective layer for protecting the substrate so that the piezoelectric thin film is not formed directly on the substrate, on the substantially entire surface of the substrate, and the piezoelectric thin film formed on the protective film in accordance with the pattern; A base layer that forms the basis for growing and forming
And the piezoelectric thin film is formed on the base layer.

Considering the structure of the piezoelectric thin film element, it is preferable that this protective film is a common electrode. The base film is, for example, a film for forming a seed crystal for the piezoelectric thin film. Preferably, the piezoelectric thin film is composed of a PZT film formed by using a hydrothermal synthesis method, and the base film is formed of the PZT film.
It consists of a titanium film for forming a seed crystal for the film.
When the piezoelectric thin film is made of a PZT film, the protective film is selected from gold, platinum, and iridium. Particularly preferred is platinum. It is preferable that the protective film is formed to have a thickness such that seed crystals of the piezoelectric thin film are not substantially formed on the surface thereof. The protective film is made of platinum, and 50
The thickness is preferably not less than nm.

The present invention is further directed to a mechanical actuator such as an ink jet recording head using the piezoelectric thin film element as a driving source for discharging ink. Still further, the present invention provides a method of manufacturing a piezoelectric thin film element, wherein a piezoelectric thin film is formed with a predetermined pattern on a substrate, and further, a common electrode and an individual electrode for the piezoelectric thin film are formed. Forming a protective layer on almost the entire surface of the substrate to protect the substrate so that the piezoelectric thin film is not formed directly on the substrate; and growing the piezoelectric thin film on the protective film according to the pattern. And a step of selectively forming the piezoelectric thin film on the base film.

In the present invention, "entire surface" is not to be construed as limiting as meaning all surfaces on the substrate.
This is within the range where the piezoelectric thin film is formed on the substrate.
In addition, the base film is a film for assisting when selectively forming the piezoelectric thin film on the protective film, for example,
It is as described in the claims.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a sectional structure of a thin film piezoelectric element. This piezoelectric element 10
Is used for an ink jet recording head. A piezoelectric thin film 18 is disposed on an ink cavity 20. Hereinafter, the structure of the piezoelectric element will be described with reference to the manufacturing process of the thin film piezoelectric element.

On a substrate (for example, a nickel electroformed substrate) 12, a protective film 14 made of platinum is formed on the entire surface of the substrate.
This protective film 14 is preferably formed with a thickness of 50 nm or more. In particular, the thickness is preferably 100 nm or more. The upper limit of the thickness of the protective film is preferably 1 μm or less, where the film stress of platinum is small. This protective film is formed, for example, by sputtering. The specific conditions of the sputtering are as follows. In a DC sputtering apparatus, the substrate is heated at 150 ° C. and the output is 1000 W, and the film thickness is 200 nm.

Next, a base layer 16 made of titanium is formed on the entire surface of the protective layer 14 made of platinum. Platinum prevents a PZT seed crystal described later from being formed on a substrate beyond a predetermined pattern. Titanium precipitates a seed crystal of PZT and further grows and forms a PZT film using the seed crystal as a nucleus. As a seed crystal of PZT, PZT
T in which a part of Pb is substituted with Sr or Ba can also be used. The formation of the titanium layer can also depend on sputtering, as in the case of the protective layer. The thickness of the titanium layer is 0.5 to 1 μm.
m.

Next, the titanium film is etched by a mixed solution of aqueous hydrogen peroxide and ammonia into a specific pattern, that is, a pattern in which the titanium layer remains on the ink cavity 20, based on a photolithography method using a resist. Next, a PZT seed crystal is formed on the titanium film 16 on the substrate 12 by the following method.

The lead nitrate (Pb _{(NO 3) 2)} aqueous solution of zirconium oxychloride (ZrOCl ₂ · _{8H 2} O) aqueous solution, titanium tetrachloride (TiCl ₄₎ aqueous solution, and aqueous potassium hydroxide, strontium nitrate as necessary or The above-described substrate is immersed in a reaction solution prepared by mixing an aqueous barium chloride solution, and a hydrothermal treatment is performed at 140 ° C.

In this reaction, the Ti source eluted from the titanium film 16, the Ti source in the reaction solution, the Pb source in the reaction solution,
PZT seed crystal (piezoelectric thin film seed crystal) by reacting with r source
Was formed with a thickness of 0.1 μm on the surface of the titanium layer. At this time, PZT seed crystal 6 is formed only on titanium film 16 because platinum, which is a protective film, does not react with the reaction solution.

Next, a PZT film 18 is grown on the PZT seed crystal by hydrothermal synthesis. As a reaction solution used in the hydrothermal reaction, a lead nitrate (Pb (NO ₃ ) ₂ ) aqueous solution, a zirconium oxychloride (ZrOCl ₂ ) aqueous solution,
A mixture of an aqueous solution of titanium tetrachloride (TiCl ₄ ) and an aqueous solution of potassium hydroxide (KOH) can be used.

The back surface of the substrate 12 on which the PZT seed crystal 6 was formed was coated with a fluororesin, charged into the reaction solution at 150 ° C., and subjected to a hydrothermal treatment for 12 hours.
The T film grew to 10 μm.

In this series of steps, since the step of etching the protective film has not been performed, the etching solution or the alkaline solution used in the hydrothermal synthesis method does not penetrate through the opening of the protective film. There is no loss of adhesion to Therefore, the PZT film can be selectively formed only on the titanium layer.

An individual electrode (upper electrode) 22 is formed on the PZT film.
Are formed, an ink jet recording type printer head is completed. The lower electrode in this head is platinum having conductivity, that is, the protective film 14. That is, in this piezoelectric thin film element, the protective film also serves as the lower electrode.

As the substrate 12, a nickel electroformed substrate is used. However, the present invention is not limited to this. For example, a silicon substrate, another metal or ceramic processed, or a molded product of a polymer material such as polysulfone may be used. it can.

An ink jet recording head is completed by bonding a nozzle plate having a nozzle port for discharging ink in the ink cavity to the ink cavity side of the substrate.

When the protective film on the titanium-containing substrate is etched in a predetermined pattern using etching ion milling, and the PZT film is formed by applying the same hydrothermal synthesis method as described above, A hydrothermal reaction enters the gap between the protective film and the substrate, and the protective film is peeled off or a PZT film is formed at an unnecessary portion, which makes it difficult to form a desired fine piezoelectric thin film.

On the other hand, without etching the protective film, a titanium layer is formed in a predetermined pattern.
In the piezoelectric thin film on which the T film is formed, the Pt film thickness is 100 nm.
FIG. 2 is a plane in which a PZT film is formed on a protective film.
As shown in (200 × image photograph), it can be seen that peeling does not occur between the protective film and the substrate, and that the PZT film is not formed in unnecessary portions.

Next, the thickness of the protective film Pt is set to 50 nm.
In the case of FIG. 3 (200 × image photograph), which is a plane in which a PZT film is formed by applying a hydrothermal synthesis method to a smaller 30 nm, a PZT film was partially formed on the protective film. It is considered that the reason for this is that if the platinum film thickness is small, the platinum may react with the hydrothermal reaction solution under the influence of the unstable layer at the time of sputtering.

[0033]

As described above, according to the present invention,
Provided is a piezoelectric thin film element in which the adhesion between a protective film and a substrate is not deteriorated. Provided is a piezoelectric thin film element on which a dense piezoelectric thin film pattern is formed, such as an ink jet recording head.

[Brief description of the drawings]

FIG. 1 is a sectional view of a piezoelectric thin film element.

FIG. 2 shows a Pt film having a Pt film thickness of 100 nm and a PZT film formed on a protective film.
It is a 200 times electron microscope photograph which shows the state in which the film was formed.

FIG. 3 is a similar photomicrograph when the Pt film thickness is 30 nm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Piezoelectric element 12 Substrate 14 Protective film 16 Base layer 18 Piezoelectric thin film 20 Ink cavity

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuo Hashimoto, Inventor, Ube City, Ube City, Yamaguchi Prefecture, 5, 1978 Kobe, Ube Research Institute (72) Inventor Toshihiko Abu, 1978 Kobe, Ube City, Yamaguchi Prefecture, 1978, 5 Ube, Ube City Kosan Co., Ltd.

Claims (14)

[Claims] 1. A piezoelectric thin film element in which a piezoelectric thin film is formed with a predetermined pattern on a substrate, and the piezoelectric thin film is deformed by energizing the piezoelectric thin film via a common electrode and an individual electrode. A protective layer for protecting the substrate so that the piezoelectric thin film is not formed directly on the substrate, on substantially the entire surface of the substrate; and forming the piezoelectric thin film on the protective film in accordance with the pattern. A piezoelectric thin film element, comprising: a base layer that is a base for molding; and the piezoelectric thin film is formed on the base layer. 2. The piezoelectric thin-film element in which the protective film is the common electrode and the individual electrodes are formed on the piezoelectric thin-film element. 3. The piezoelectric thin film element according to claim 2, wherein the base film is a film for forming a seed crystal for the piezoelectric thin film. 4. The piezoelectric thin film comprises a PZT film formed by using a hydrothermal synthesis method, and the base film comprises a PZT film.
4. The piezoelectric thin film element according to claim 3, comprising a titanium film for forming a seed crystal for the film. 5. The piezoelectric thin-film element according to claim 1, wherein the protective film is made of gold, platinum, or iridium. 6. The piezoelectric thin film element according to claim 3, wherein the protective film is formed on the surface with a thickness such that seed crystals of the piezoelectric thin film are not substantially formed. 7. The protective film is made of platinum and has a thickness of 50.
7. The piezoelectric thin film element according to claim 6, which is formed with a thickness of at least nm. 8. An ink jet recording head using the piezoelectric thin film element according to claim 1 as a driving source for discharging ink. 9. A method of manufacturing a piezoelectric thin film element, wherein a piezoelectric thin film is formed on a substrate with a predetermined pattern, and further, a common electrode and an individual electrode for the piezoelectric thin film are formed. Forming a protective layer on almost the entire surface of the substrate to protect the substrate so that the piezoelectric thin film is not directly formed on the substrate; and growing and molding the piezoelectric thin film on the protective film according to the pattern. A step of forming a base layer that serves as a base when performing the method, and a step of selectively forming the piezoelectric thin film on the base film. 10. The base film is formed from a film for forming a seed crystal when forming the piezoelectric thin film.
The described method. 11. The piezoelectric thin film is formed using a hydrothermal synthesis method, and the base film is formed from a titanium film that forms a seed crystal for a PZT film formed by a hydrothermal synthesis method. The described method. 12. The method according to claim 9, wherein said protective film is formed of gold, platinum, or iridium. 13. The method according to claim 9, wherein said protective film is formed to a thickness such that a seed crystal of said piezoelectric thin film is not substantially formed on its surface. 14. The protective film is formed of platinum, and
14. The method according to claim 13, which is formed from a film thickness of 50 nm or more.