JP2000094674A - Ink-jet type recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink-jet type recording head which has a superior ink discharge performance through the elimination of deflection of a diaphragm in manufacturing the head. SOLUTION: This ink-jet type recording head has a piezoelectric thin film element 60 arranged via a diaphragm 51 to at least one face of a pressure chamber substrate having a pressure chamber 10 filled with ink and also a bimetal layer 50 interposed between the diaphragm 51 and the piezoelectric thin film element 60. The bimetal layer 50 comprises a first thin film 52 formed to the side of the pressure chamber 10 and a second thin film 54 formed to the side of the piezoelectric thin film element. When a coefficient of linear expansion of the first thin film 52 is α1 and a coefficient of linear expansion of the second thin film 54 is α2, the bimetal layer is constituted to satisfy a relationship of α1>α2. When heat is applied to the bimetal layer 50, the diaphragm 51 displaces in a direction reducing a pressure of the pressure chamber 10, and therefore deflection of the diaphragm 51 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an on-demand type ink jet recording head which performs printing on recording paper by discharging ink droplets.

[0002]

2. Description of the Related Art An ink jet recording head used in an ink jet printer for selectively ejecting ink droplets onto recording paper in accordance with input print data to obtain a character or a desired image is provided with a driving source for ink ejection ( And a piezoelectric thin film element that functions as an actuator. This piezoelectric thin film element has a structure in which a piezoelectric ceramic thin film such as lead zirconate titanate, that is, a piezoelectric film is sandwiched between an upper electrode and a lower electrode. The piezoelectric film is deformed by applying a voltage and generates a voltage by applying a pressure, and thus functions as an electromechanical transducer. Many ceramics having a perovskite crystal structure exhibit this effect remarkably, and are therefore used as a material for a piezoelectric film.

Conventionally, in this ink jet recording head, after a silicon dioxide film functioning as a diaphragm is formed on a substrate surface, a lower electrode, a piezoelectric film, and an upper electrode are sequentially formed on the silicon dioxide film. This laminated structure is etched to form a piezoelectric thin-film element at a position where a pressure chamber is to be formed, and then formed by etching the pressure chamber on the opposite side of the substrate.

[0004]

However, when the present inventor manufactures an ink jet recording head by the above-described manufacturing method, after the formation of the pressurizing chamber, the vibrating plate is moved due to the residual stress inside the film. I found it to bend to the side. For example, as shown in FIG. 4A, after manufacturing the ink jet recording head, the diaphragm 51 is displaced dx ₁ toward the pressure chamber 10. Assuming that the maximum displacement of the diaphragm is 200 nm, dx
It was confirmed that ₁ was about 20 nm (in the figure, reference numeral 61 is a lower electrode, 62 is a piezoelectric film, 63 is an upper electrode, 11 is a side wall, and 2 is a nozzle plate). This is because non-uniform plastic deformation has occurred in the diaphragm to which heat has been applied, which remains even after heat has been removed, and local internal stresses having different sizes and directions have occurred. Conceivable. As described above, when the diaphragm bends toward the pressurizing chamber, the tensile stress of the piezoelectric film is relaxed, and there is a problem that the piezoelectric characteristics of the piezoelectric film deteriorate. Further, since the substantial displacement amount of the vibration plate is reduced, the displacement amount of the ink is also reduced. Further, as the number of ink ejections increases, the residual polarization in the piezoelectric thin film element increases, and a phenomenon may occur in which the diaphragm does not return to its original position (hereinafter referred to as “polarization fatigue”).

[0005] In view of the above problems, an object of the present invention is to provide an ink jet recording head which eliminates such deflection of the diaphragm and has excellent ink ejection characteristics.

[0006]

According to the ink jet recording head of the present invention, a piezoelectric thin film element is disposed via a diaphragm on at least one surface of a pressurizing chamber substrate having a pressurizing chamber filled with ink. In this ink jet recording head, two thin films (bimetal layers) having different linear expansion coefficients are laminated between the vibration plate and the piezoelectric thin film element.

The first bimetal layer is formed on the side of the pressure chamber.
And a second thin film formed on the piezoelectric thin film element side, where a linear expansion coefficient of the first thin film is α ₁ , and a linear expansion coefficient of the second thin film is α ₂ , The film is formed so as to satisfy the relationship of α ₁ <α ₂ . As described above, by making the linear expansion coefficient of the second thin film larger than the linear expansion coefficient of the first thin film, if heat is applied to the bimetal layer, the pressure in the pressure chamber is reduced (the direction opposite to the direction of deflection). ) Because the diaphragm is displaced
The deflection of the diaphragm can be eliminated.

For example, the bimetal layer is formed by combining a combination of the second thin film and the first thin film with Ni / W, Cu / W, Cr /
W, Al / Cr, glass / W, Au / W, α-Al ₂ O ₃
/ W or TiO ₂ / W.

Preferably, a thin film (heating layer) for heating the two thin films is provided between the diaphragm and the piezoelectric thin film element. The heat generating layer is formed of, for example, tantalum nitride, rubidium oxide, a Ta-Al alloy, or the like, and plays a role of a heater. This heat generating layer may be interposed between the first thin film and the second thin film, or may be interposed between the lower electrode and the second thin film or between the diaphragm and the first thin film.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present embodiment will be described below with reference to FIGS.

(Structure of Inkjet Recording Head) The structure of the inkjet recording head will be described with reference to FIG. The exploded perspective view of the ink jet recording head shown in the figure is of a type in which an ink supply flow path is formed in a pressurizing chamber substrate. As shown in FIG. 1, the ink jet recording head mainly includes a pressure chamber substrate 1, a nozzle plate 2, and a base 3.

The pressure chamber substrate 1 is formed on a silicon single crystal substrate and then separated. The pressure chamber substrate 1 is provided with a plurality of strip-shaped pressure chambers 10 and has a common flow channel 12 for supplying ink to all the pressure chambers 10. The pressure chambers 10 are separated by side walls 11. Pressurizing chamber 10
Are arranged in two rows, and 128 are formed in one row, thereby realizing an ink jet recording head having a print density of 256 nozzles. On the substrate 3 side of the pressurizing chamber substrate 1, a diaphragm film and a piezoelectric thin film element (not shown) are formed. The wiring from each piezoelectric thin film element is converged on a wiring board 4 which is a flexible cable, and is connected to an ink discharge control circuit (not shown). The ink ejection control circuit is supplied with print data from a computer in the printer, and drives the piezoelectric thin film element at a predetermined timing to eject ink droplets and print on recording paper.

The nozzle plate 2 is joined to the pressure chamber substrate 1. At a position corresponding to the pressurizing chamber 10 in the nozzle plate 2, a nozzle 21 for extracting an ink droplet is formed. The nozzles 21 are formed in two rows at a predetermined arrangement pitch. The interval between each row is 1/180 inch, and the arrangement pitch of the nozzles 21 is 360 / inch.

The base 3 is a steel body such as plastic or metal, and serves as a mounting base for the pressurizing chamber substrate 1.

(Main parts of ink jet recording head)
FIG. 1 is a sectional view of a main part of the ink jet recording head. This figure corresponds to the AA cross-sectional view in FIG.

The main parts of the ink jet recording head are:
It mainly comprises a piezoelectric thin film element 60, a bimetal layer 50, a vibration plate 51, a pressure chamber 10, and a nozzle plate 2. The piezoelectric thin film element 60 includes an upper electrode 63 and a lower electrode 61.
And a piezoelectric film 62 sandwiched between them. Upper electrode 6
3 and the lower electrode 61 are made of a conductive material selected from platinum, iridium, iridium oxide, gold, aluminum, nickel and the like. A piezoelectric ceramic having piezoelectric characteristics is used as the composition of the piezoelectric film 60. For example, a PZT-based piezoelectric material or a material obtained by adding a metal oxide such as niobium oxide, nickel oxide, or magnesium oxide to this system is preferable. The composition of the piezoelectric film 60 is appropriately selected in consideration of the characteristics, use, and the like of the piezoelectric thin film element. Specifically, lead titanate (PbTiO ₃ ), lead zirconate titanate (Pb
(Zr, Ti) O ₃ ), lead zirconate (PbZr
O ₃ ), lanthanum lead titanate ((Pb, La), Ti
O ₃ ), lead lanthanum zirconate titanate ((Pb, L
a) (Zr, Ti) O ₃ ) or lead magnesium zirconium niobate titanate (Pb (Zr, Ti) (Mg,
Nb) O ₃ ) can be used.

The heating layer 5 is provided between the diaphragm 51 and the lower electrode 61.
3, a first thin film (tungsten) 52 and a second thin film (nickel) 54 having different linear expansion coefficients are formed to form a bimetal layer 50. The combination of these first thin film and second thin film is as follows, where the linear expansion coefficient of the first thin film is α ₁ and the linear expansion coefficient of the second thin film is α ₂ .
It is selected so as to satisfy the relationship of α ₁ <α ₂ . For example, the second
The combination of the thin film / the first thin film is not only the above-mentioned Ni / W combination but also Cr / W, Al / Cr, glass / W,
A combination of Au / W, α-Al ₂ O ₃ / W, and TiO ₂ / W may be used.

For example, the linear expansion coefficient of nickel is 12.7.
Since 9 × 10 ⁻⁶ deg ⁻¹ and the coefficient of linear expansion of tungsten is 1.43 × 10 ⁻⁶ deg ⁻¹ , nickel (second thin film) and tungsten (first thin film) are heated to 65 ° C. When heated, as shown in FIG. 4B, the pressure chamber 10 is displaced by dx ₂ in the direction of reducing the pressure. Here, dx ₂ is 20 nm
And the width L of the pressurizing chamber is 50 μm. With such a configuration, the deflection dx ₁ (≒ 20 μm) of the diaphragm 51 can be eliminated.

The heat generating layer 53 is a thin film that generates heat by passing an electric current, and plays a role of heating the first thin film and the second thin film to a predetermined temperature (for example, about 60 ° C.). For example, a film is formed using tantalum nitride, rubidium oxide, a Ta-Al alloy, or the like. The heat generating layer 53 is not limited to the space between the first thin film 52 and the second thin film 5, but may be interposed between the lower electrode 61 and the second thin film 54 or between the diaphragm 51 and the first thin film 52.

However, the heat generating layer 53 is not always required in the present invention, and the first thin film and the second thin film are formed by other means.
This heating layer 53 is unnecessary if the thin film can be heated.

The diaphragm 51 is formed of, for example, a silicon dioxide film and pressurizes the pressurizing chamber 10 and also has a role of insulating the lower electrode 61 from the silicon single crystal substrate 13 (pressurizing chamber substrate 1). Carry.

The pressure chamber substrate 1 has a pressure chamber 10, side walls 11 and the like formed by etching a silicon single crystal substrate 13. Ink is supplied to the pressurizing chamber 10, and the vibration of the piezoelectric thin film element 60 is transmitted to the pressurizing chamber 10 via the vibration plate 51, so that the inside of the pressurizing chamber 10 is pressurized and the ink droplets are Is discharged.

[0023] This step is a step of forming various thin films to be the diaphragm 51, the bimetal layer 50, and the piezoelectric thin film element 60 on the silicon single crystal substrate 13. As the silicon single crystal substrate 13,
For example, a silicon single crystal substrate having a diameter of 100 mm and a thickness of 220 μm is used. The vibration plate 51 is, for example, 1100 ° C.
In this furnace, dry oxygen is flowed and thermal oxidation is performed for about 22 hours to form a thermal oxide film having a thickness of about 1 μm.
Alternatively, a thermal oxide film having a thickness of about 1 μm may be formed by flowing oxygen containing water vapor in a furnace at 1100 ° C. and performing thermal oxidation for about 5 hours. Alternatively, a film may be formed by appropriately selecting a film forming method such as a CVD method. The vibration plate 51 electrically insulates between the silicon single crystal substrate 13 and the lower electrode 61,
It becomes a protective layer against the etching process. The vibration plate 51 is not limited to a silicon dioxide film, but may be a zirconium oxide film, a tantalum oxide film, a silicon nitride film, or an aluminum oxide film. Is also good.

The first thin film 52, the heat generating layer 53 and the second thin film 52 are formed on the vibration plate 51 by using a thin film forming method such as a sputtering film forming method.
Are sequentially formed. The first thin film is selected from tungsten, chromium, and the like, and the second thin film is selected from nickel, copper, chromium, aluminum, glass, gold, α-Al ₂ O ₃ , titanium oxide, and the like. The heat generation layer 53 may be appropriately selected from tantalum nitride, rubidium oxide, a Ta-Al alloy, or the like. Next, after the lower electrode 61 is formed on the second thin film, the piezoelectric film 62 is formed.

When the piezoelectric film 62 is formed by the sol-gel method, first, a hydrated complex of a hydroxide of a metal component capable of forming the piezoelectric film, that is, the sol is dehydrated to form a gel, Further, by heating and firing, an inorganic oxide (piezoelectric film) is obtained. Specifically, the molar mixing ratio of lead titanate and lead zirconate is 44
%: The precursor of the PZT-based piezoelectric film is adjusted to 56% by a sol-gel method by a desired number (for example, three times) of filling / drying / drying until the final film thickness becomes 0.4 μm. A film is formed by repeating degreasing. The drying step may be performed by natural drying or heating to a temperature of 200 ° C. or less. The degreasing step is performed by heating the sol composition film at a temperature and for a sufficient period of time and at a temperature sufficient to remove the organic substances from the film. In this step, a porous gel thin film made of an amorphous metal oxide substantially free of residual organic matter is obtained. After forming the piezoelectric film precursor, the entire substrate is heated after the third degreasing to crystallize the piezoelectric film precursor. In this step, the substrate is kept at 650 ° C. for 5 minutes in an oxygen atmosphere from both sides of the substrate using an infrared radiation light source (not shown), heated at 900 ° C. for 1 minute, and then cooled naturally. In this step, the piezoelectric film precursor is crystallized and sintered with the above composition, and becomes the piezoelectric film 62 having a perovskite crystal structure. As described above, when the film is formed by the sol-gel method, the piezoelectric film 62 can be formed by appropriately adjusting the application amount of the PZT-based piezoelectric film precursor.

After the piezoelectric film 62 is formed, the upper electrode 63 is made of platinum or the like using a technique such as electron beam evaporation or sputtering.
Is formed.

Step of Separating Piezoelectric Thin Film Element (FIG. 2B) This step is a step of separating the piezoelectric thin film element 60 by etching the upper electrode 63 and the piezoelectric film 62.
An appropriate etching mask (not shown) is applied to the upper electrode 63 and the piezoelectric film 62 in accordance with the position where the pressure chamber 10 is to be formed, and is formed into a predetermined separated shape by using ion milling.

Pressurizing Chamber Forming Step (FIG. 2C) This step is a step of forming the pressurizing chamber 10 on the silicon single crystal substrate 13. An etching mask (not shown) is provided in accordance with the position where the pressure chamber is to be formed, and the pressure chamber 10 is formed by dry anisotropic etching using an active gas such as parallel plate reactive ion etching. The portion left without being etched becomes the side wall 11.

Nozzle Plate Joining Step (FIG. 2D) This step is a step of joining the nozzle plate to the pressurizing chamber substrate. The nozzle plate 2 is bonded to the etched silicon single crystal substrate 13 using a resin or the like. At this time, the nozzles 21 are aligned so as to be arranged corresponding to the respective spaces of the pressurizing chamber 10. When the silicon single crystal substrate 13 to which the nozzle plate 2 is bonded is attached to the base 3, an ink jet recording head is completed.

(Modification) As another configuration of the bimetal layer, the second thin film is a metal layer of iridium, silver, titanium, iron, palladium or the like, and the first thin film is cordierite,
Ceramic layers such as zircon and tin oxide can also be used.

(Operation) As described above, according to the present embodiment, since the bimetal layer is interposed between the diaphragm and the piezoelectric thin film element, the bimetal layer exists inside the film at the time of manufacturing the ink jet recording head. It is possible to eliminate the deflection of the diaphragm due to the residual stress. Thereby, the relaxation of the tensile stress of the piezoelectric film can be prevented, and the deterioration of the piezoelectric characteristics of the piezoelectric thin film element can be prevented. Accordingly, it is possible to improve the ink ejection characteristics as compared with the related art.

Further, by displacing the vibration plate in the direction of reducing the pressure in the pressurizing chamber at the time of standby for ink discharge (FIG. 4B),
Polarization fatigue can be eliminated. As a result, it is possible to effectively prevent a decrease in the ink ejection characteristics due to a substantial decrease in the amount of displacement of the diaphragm. Further, since the bimetal layer is heated by the heat generating layer or the like, the heat is transmitted to the ink through the pressurized chamber substrate, and the viscosity of the ink is reduced. For this reason, ejection of extremely small ink droplets can be realized. Accordingly, high-definition printing and image quality can be achieved.

[0033]

According to the ink jet recording head of the present invention, the first thin film formed on the pressurizing chamber side and the film formed on the piezoelectric thin film element are provided between the diaphragm and the piezoelectric thin film element. The second thin film is laminated, and the linear expansion coefficient of the first thin film is α ₁ ,
When the linear expansion coefficient of the second thin film is α ₂ , the configuration is such that the relationship α ₁ <α ₂ is satisfied. By applying heat to these thin films, the deflection of the diaphragm during manufacture of the ink jet recording head is eliminated. can do. Therefore, it is possible to prevent a decrease in the piezoelectric characteristics of the piezoelectric film and improve the ink ejection characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an ink jet recording head of the present invention.

FIG. 2 is a cross-sectional view illustrating a manufacturing process of a main part of the ink jet recording head of the present invention.

FIG. 3 is an exploded perspective view of the ink jet recording head of the present invention.

FIG. 4 is an explanatory diagram of deflection of a diaphragm of the ink jet recording head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pressurization chamber substrate 2 Nozzle plate 3 Base 4 Wiring board 10 Pressurization chamber 11 Side wall 12 Common channel 13 Silicon single crystal substrate 21 Nozzle 50 Bimetal layer 51 Vibration plate 52 First thin film 53 Heat generation layer 54 Second thin film 60 Piezoelectric thin film element 61 Lower electrode 62 Piezoelectric film 63 Upper electrode

Claims (4)

[Claims] 1. An ink jet recording head in which a piezoelectric thin-film element is arranged via a diaphragm on at least one surface of a pressure chamber substrate having a pressure chamber filled with ink. An ink jet recording head in which two thin films having different linear expansion coefficients are laminated between body thin film elements. 2. The two-layered thin film is composed of a first thin film formed on a pressure chamber side and a second thin film formed on a piezoelectric thin film element side. linear expansion coefficient alpha ₁ of the the linear expansion coefficient of the second thin film and alpha _2, satisfying the alpha ₁ <alpha ₂ relationship ink jet recording head according to claim 1. 3. The method according to claim 2, wherein the combination of the second thin film and the first thin film is Ni / W, Cu / W, C
r / W, Al / Cr, glass / W, Au / W, α-Al
_{2. The method according to} claim 1, wherein the material is any one of ₂ O ₃ / W and TiO ₂ / W.
Or the inkjet recording head according to claim 2. 4. The ink jet type according to claim 1, further comprising a thin film between said diaphragm and said piezoelectric thin film element for heating said two layers of thin films. Recording head.