JP2004047814A - Piezoelectric element and its fabricating process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element in which high insulation performance and sufficient piezoelectric property can be obtained even with a thin film thereof and a density of a liquid exhausting head can be heightened. <P>SOLUTION: A piezoelectric body precursor film 41' is formed in a predetermined pattern on a lower electrode 32 to crystallize the patterned piezoelectric body precursor film, obtaining a piezoelectric body film 41. Consequently, the piezoelectric body film can be obtained which is possessed of crystal grains with a cross-sectional perimeter of 2,000 nm or more and of a crystal grain density of 4×10<SP>9</SP>[pieces/m<SP>2</SP>] or less. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piezoelectric element used as a driving element such as a liquid ejection head and a method for manufacturing the same. In addition, the present invention relates to a liquid discharge head such as an ink jet recording head and a liquid discharge device such as a printer provided with the above-mentioned piezoelectric element.
[0002]
[Prior art]
A piezoelectric element used for a liquid ejection head or the like includes a piezoelectric film such as PZT sandwiched between an upper electrode and a lower electrode. This piezoelectric film is manufactured as a polycrystal mainly from the viewpoint of easy film formation.
[0003]
[Problems to be solved by the invention]
However, since the polycrystalline piezoelectric film has grain boundaries, the insulating property may be reduced. Also, it was difficult to obtain sufficient piezoelectric characteristics. Therefore, there is a limit in reducing the thickness, and there is a limit in increasing the density of the piezoelectric element when manufacturing a liquid discharge head.
[0004]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a piezoelectric element which can obtain high insulating properties and sufficient piezoelectric characteristics even when thinned, and can increase the density of a liquid discharge head. It is another object of the present invention to provide a method for manufacturing such a piezoelectric element, a liquid ejection head including the piezoelectric element, and a method for manufacturing the same.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is a method for manufacturing a piezoelectric element including a piezoelectric thin film sandwiched between an upper electrode and a lower electrode, wherein a piezoelectric precursor film is formed on the lower electrode by a predetermined method. A step of forming a pattern in a shape, a step of crystallizing the patterned piezoelectric precursor film to obtain a piezoelectric thin film, and a step of forming an upper electrode on the piezoelectric film.
[0006]
In the above manufacturing method, the pattern formation of the piezoelectric precursor film may be performed by uniformly forming the piezoelectric precursor film on the lower electrode, and then etching the piezoelectric precursor film into a predetermined pattern. desirable. The pattern formation of the piezoelectric precursor film may be performed by forming a pattern of a sol containing the component of the piezoelectric precursor on the lower electrode by an inkjet method and gelling the sol.
[0007]
A method for manufacturing a liquid discharge head according to the present invention includes a step of forming a vibration plate on one surface of a substrate, a step of forming the piezoelectric element on the vibration plate by the above-described manufacturing method, and a step of etching the substrate to form a pressure chamber. And forming a.
[0008]
In the above manufacturing method, the liquid discharge head includes a plurality of piezoelectric elements, and the pattern formation of the piezoelectric precursor film in the step of forming the piezoelectric elements includes the step of forming a plurality of piezoelectric elements in each liquid discharge head. It is desirable to perform patterning so that the piezoelectric thin film to be formed is integrated.
[0009]
The piezoelectric element of the present invention is a piezoelectric element in which a piezoelectric thin film and an upper electrode are sequentially formed on a lower electrode, wherein the piezoelectric thin film includes crystal grains having a cross-sectional circumference of 2000 nm or more. Features.
[0010]
Further, the piezoelectric element of the present invention is a piezoelectric element in which a piezoelectric thin film and an upper electrode are sequentially formed on a lower electrode, and the piezoelectric thin film has a crystal grain density of 4 × 10 ⁹ [pieces / m ^2]. ] It is characterized by the following.
[0011]
Further, the piezoelectric element of the present invention is a piezoelectric element in which a piezoelectric thin film and an upper electrode are sequentially formed on a lower electrode, wherein the piezoelectric thin film is formed of a single crystal.
[0012]
A liquid ejection head according to the present invention includes the above-described piezoelectric element, a pressure chamber whose internal volume changes due to mechanical displacement of the piezoelectric element, and an ejection port that communicates with the pressure chamber to eject droplets. ing.
[0013]
According to another aspect of the invention, there is provided a liquid ejection apparatus including the above-described liquid ejection head.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
(Overall configuration of inkjet printer)
FIG. 1 is a perspective view illustrating the structure of a printer that is a liquid ejection device using the piezoelectric element and the liquid ejection head according to the present embodiment. In this printer, a tray 3, a discharge port 4 and an operation button 9 are provided on a main body 2. Further, inside the main body 2, an ink jet recording head 1, which is a liquid discharge head, a paper feed mechanism 6, and a control circuit 8 are provided.
[0016]
The ink jet recording head 1 includes a piezoelectric element manufactured by the manufacturing method of the present invention. The ink jet recording head 1 is configured to be able to discharge liquid ink from nozzles in accordance with a discharge signal supplied from the control circuit 8.
[0017]
The main body 2 is a housing of the printer, in which a paper feed mechanism 6 is arranged at a position where the paper 5 can be supplied from the tray 3, and the ink jet recording head 1 is arranged so as to be able to print on the paper 5. The tray 3 is configured so that the paper 5 before printing can be supplied by the paper feeding mechanism 6, and the discharge port 4 is an outlet for discharging the paper 5 on which printing has been completed.
[0018]
The paper feeding mechanism 6 includes a motor 600, rollers 601 and 602, and other mechanical structures (not shown). The motor 600 is rotatable in accordance with a drive signal supplied from the control circuit 8. The mechanical structure is configured to transmit the rotational force of the motor 600 to the rollers 601 and 602. The rollers 601 and 602 rotate when the rotational force of the motor 600 is transmitted. The rollers 601 and 602 pull in the paper 5 placed on the tray 3 by rotation, and supply the paper 5 so that the head 1 can print. I have.
[0019]
The control circuit 8 includes a CPU, a ROM, a RAM, an interface circuit, and the like (not shown). The control circuit 8 supplies a drive signal to the paper feeding mechanism 6 in accordance with print information supplied from a computer via a connector (not shown). A signal can be supplied to the ink jet recording head 1. The control circuit 8 can set an operation mode, perform a reset process, and the like in accordance with an operation signal from the operation panel 9.
[0020]
(Configuration of inkjet recording head)
FIG. 2 is an explanatory diagram of a structure of an ink jet recording head which is a liquid ejection head of the present embodiment. As shown in the drawing, the ink jet recording head 1 includes a nozzle plate 10, a pressure chamber substrate 20, and a vibration plate 30. This head constitutes an on-demand piezo jet type head.
[0021]
The pressure chamber substrate 20 includes a cavity (pressure chamber) 21, a side wall (partition wall) 22, a reservoir 23, and a supply port 24. The cavity 21 is a space for storing ink or the like formed by etching a substrate such as silicon for discharging. The side wall 22 is formed so as to partition between the cavities 21. The reservoir 23 is a common flow path for supplying ink to each cavity 21 via the supply port 24. The shape of the cavity 21 and the like can be variously changed by an ink jet method. For example, it may be a Kaiser shape having a planar shape or a Zoltan shape having a cylindrical shape. Further, the cavity may be configured for a one-chamber type or a two-chamber type.
[0022]
The nozzle plate 10 is attached to one surface of the pressure chamber substrate 20 so that the nozzles 11 are arranged at positions corresponding to the cavities 21 provided in the pressure chamber substrate 20, respectively. It is formed on the other surface of the chamber substrate 20. A head unit including the nozzle plate 10, the pressure chamber substrate 20, and the vibration plate 30 is housed in a housing 25 to constitute the ink jet recording head 1.
[0023]
The vibration plate 30 is provided with a piezoelectric element 40 (see FIG. 3). The vibration plate 30 is provided with an ink tank connection port (not shown) so that ink stored in an ink tank (not shown) can be supplied to the reservoir 23 of the pressure chamber substrate 20.
[0024]
(Layer structure)
FIG. 3 is a cross-sectional view illustrating a more specific structure of the ink jet recording head and the piezoelectric element. This cross-sectional view is an enlarged cross-section of one piezoelectric element. As shown in the figure, the diaphragm 30 is configured by laminating an insulating film 31 and a lower electrode 32, and the piezoelectric element 40 is configured by laminating a piezoelectric film 41, an upper electrode 42, and a lower electrode 32. . In particular, the ink jet recording head 1 is configured such that the piezoelectric elements 40, the cavities 21, and the nozzles 11 are continuously provided at a constant pitch. The design of the pitch between the nozzles can be changed as needed in accordance with the printing accuracy. For example, they are arranged to be 400 dpi (dot per inch).
[0025]
The insulating film 31 is made of a material that is not conductive, for example, silicon dioxide (SiO ₂ ) formed by thermally oxidizing a silicon substrate or the like. The insulating film 31 is deformed by deformation of the piezoelectric film layer and instantaneously changes the pressure inside the cavity 21. It is configured so as to be able to be increased as needed.
[0026]
Although the lower electrode 32 is formed on the insulating film 31, a titanium or titanium oxide film (adhesion layer) of about 20 nm may be formed between the insulating film 31 and the lower electrode 32.
[0027]
The lower electrode 32 is one electrode for applying a voltage to the piezoelectric film layer, and is made of a conductive material, for example, platinum (Pt). The lower electrode 32 is not limited to this, and may be made of iridium (Ir), which is a metal having the same FCC structure as platinum. The lower electrode 32 is formed in the same region as the insulating film 31 so as to function as an electrode common to a plurality of piezoelectric elements formed on the pressure chamber substrate 20. However, it is also possible to form the same size as the piezoelectric film 41, that is, the same shape as the upper electrode.
[0028]
The upper electrode 42 is the other electrode for applying a voltage to the piezoelectric film layer, and is made of a conductive material, for example, platinum (Pt) or iridium (Ir) having a thickness of 0.1 μm.
[0029]
The piezoelectric film 41 is, for example, a crystal of a piezoelectric ceramic having a perovskite structure manufactured by the manufacturing method of the present invention, and is formed in a predetermined shape on the vibration plate 30.
[0030]
The composition of the piezoelectric film 41, for example, lead zirconate titanate _{(Pb (Zr 0 56, Ti} 0 44) O 3:.. PZT) using a piezoelectric ceramics or the like. In addition, lead lanthanum titanate ((Pb, La) TiO ₃ ), lead lanthanum zirconate ((Pb, La) ZrO ₃ ), or lead zirconate titanate magnesium niobate (Pb (Mg, Nb) (Zr, Ti) O ₃ : PMN-PZT), barium zirconate titanate (Ba (Zr, Ti) O ₃ : BZT), barium titanate (BT), or the like may be used.
[0031]
(Printing operation)
A printing operation in the configuration of the ink jet recording head 1 will be described. When a drive signal is output from the control circuit 8, the paper feed mechanism 6 operates and the paper 5 is transported to a position where the head 1 can print. When the ejection signal is not supplied from the control circuit 8 and a driving voltage is not applied between the lower electrode 32 and the upper electrode 42 of the piezoelectric element 40, the piezoelectric film 41 does not deform. No pressure change occurs in the cavity 21 in which the piezoelectric element 40 to which the ejection signal is not supplied is provided, and no ink droplet is ejected from the nozzle 11.
[0032]
On the other hand, when a discharge signal is supplied from the control circuit 8 and a constant driving voltage is applied between the lower electrode 32 and the upper electrode 42 of the piezoelectric element 40, the piezoelectric film 41 is deformed. In the cavity 21 in which the piezoelectric element 40 to which the ejection signal is supplied is provided, the vibration plate 30 is largely bent. Therefore, the pressure in the cavity 21 increases instantaneously, and ink droplets are ejected from the nozzles 11. By supplying an ejection signal individually to the piezoelectric element at a position corresponding to the image data in the head, an arbitrary character or figure can be printed.
[0033]
(Production method)
Next, the method for manufacturing the piezoelectric element according to this embodiment will be described together with the method for manufacturing the ink jet recording head. 4 and 5 are cross-sectional views illustrating the steps of manufacturing the piezoelectric element and the ink jet recording head.
[0034]
Insulating film forming step (S1)
The insulating film forming step is a step of forming an insulating film 31 on a silicon substrate to be the pressure chamber substrate 20. A silicon substrate having a thickness of, for example, 200 μm and a diameter of about 10 cm is used, and a plurality of ink jet recording heads as shown in FIG. The insulating film 31 is formed to a thickness of, for example, about 1 μm. For the production of the insulating film, a known thermal oxidation method or the like is used to form a silicon dioxide film. Note that a titanium film or a titanium oxide film (adhesion layer: not shown) having a thickness of preferably 5 nm to 40 nm, more preferably about 20 nm may be further formed on the insulating film 31. This adhesion layer improves the adhesion between the insulating film 31 and the lower electrode 32.
[0035]
Lower electrode forming step (S2)
This lower electrode forming step is a step of forming the lower electrode 32 on the insulating film 31 or the adhesion layer. The lower electrode 32 is formed by stacking, for example, platinum or iridium with a thickness of 200 nm. For manufacturing these layers, a known electron beam evaporation method, sputtering method, or the like is used.
[0036]
Further, on the platinum film, a seed layer of titanium (Ti) is formed with a thickness of preferably 3 nm to 25 nm, more preferably 5 nm. For forming the titanium seed layer, for example, a known direct current sputtering method or the like is used. This seed layer is formed with a uniform thickness, but may be in an island shape in some cases.
[0037]
In this embodiment, the lower electrode 32 is formed on the entire surface of the substrate. However, the present invention is not limited to this, and the following piezoelectric film may be formed after the lower electrode is patterned into a predetermined shape. By patterning the lower electrode, the warpage of the substrate is further reduced.
[0038]
Formation of piezoelectric precursor film (S3)
Next, a piezoelectric precursor film 41 'is formed on the lower electrode 32. The piezoelectric precursor film is configured as an amorphous film before being crystallized by a process described below to become the piezoelectric film 41. In this embodiment, a precursor film such as lead zirconate titanate (PZT) is formed by a sol-gel method. The method of forming the PZT film is not limited to the sol-gel method, but may be a MOD (Metal-Organic Deposition) method or the like.
[0039]
In the sol-gel method, a metal organic compound such as a metal alkoxide is hydrolyzed and polycondensed in a solution system. Specifically, first, a solution (sol) containing a metal organic compound is applied on a substrate and dried (S3). Examples of the metal organic compound to be used include alkoxides such as methoxide, ethoxide, propoxide and butoxide of metal constituting the inorganic oxide and acetate compounds. Inorganic salts such as nitrates, oxalates and perchlorates may be used.
[0040]
This mixed solution is applied on the lower electrode to a thickness of, for example, 20 nm. At the stage of application, each metal atom constituting PZT is dispersed as an organometallic complex.
[0041]
After the application, the sol is dried at a fixed temperature for a fixed time to evaporate the solvent of the sol. For example, the drying temperature is set to, for example, 150 ° C. or more and 200 ° C. or less. Preferably, it is dried at 180 ° C. The drying time is, for example, 5 minutes or more and 15 minutes or less. Preferably, it is dried for about 10 minutes.
[0042]
After drying, further degreasing is performed at a constant degreasing temperature in an air atmosphere for a predetermined time. The degreasing temperature is preferably in the range of 400 ° C to 600 ° C. This is because crystallization starts at a temperature higher than this range, and sufficient degreasing cannot be performed at a temperature lower than this range. Preferably, the temperature is set at about 450 ° C. to 550 ° C. The degreasing time is, for example, 5 minutes or more and 90 minutes or less. This is because crystallization starts in a time longer than this range, and is not sufficiently degreased in a time shorter than this range. It is preferably defatted for about 10 minutes. The organic matter coordinated to the metal is dissociated from the metal by degreasing, causing an oxidative combustion reaction, and is scattered into the atmosphere. Through the above steps, the piezoelectric precursor film 41 'is formed.
[0043]
Patterning of piezoelectric precursor film (S4)
Next, the piezoelectric precursor film 41 'is patterned into a predetermined shape for constituting an individual ink jet recording head. As a specific method, for example, a resist is applied on the piezoelectric precursor film 41 ', and is patterned by exposing and developing according to the position where the piezoelectric element is formed. Using the remaining resist as a mask, the piezoelectric precursor film 41 'is etched by ion milling or the like.
[0044]
The method of forming the pattern of the piezoelectric precursor film 41 'is not limited to the methods shown in S3 and S4, and may be a method of applying a sol of a metal organic compound containing a component of the piezoelectric precursor in a predetermined pattern by an inkjet method. Good. By performing drying and degreasing after the application, the piezoelectric precursor film 41 'is formed.
[0045]
Crystallization step (S5)
The piezoelectric precursor film 41 ′ obtained by the above process is crystallized by heat treatment to form the piezoelectric film 41. Although the sintering temperature varies depending on the material, for example, heating is performed at 650 ° C. for 5 to 30 minutes. As the heating device, an RTA (Rapid Thermal Annealing) device, a diffusion furnace, or the like can be used.
[0046]
By this crystallization, the piezoelectric film 41 is formed. In particular, according to the method of the present embodiment, since the piezoelectric precursor film 41 ′ is patterned on the substrate and then crystallized, the single crystal film is easily grown uniformly. As a result, even if a crystal grain boundary is generated, a piezoelectric film having crystal grains whose cross-sectional peripheral length of the crystal grains is 2000 nm or more, or a piezoelectric film having a crystal grain density of 4 × 10 ⁹ [pieces / m ² ] or less It becomes. As a result, insulating properties and piezoelectric properties comparable to those of a single crystal can be obtained, and a thinner film and a higher density of the liquid discharge head can be obtained. In this embodiment, the piezoelectric film 41 is formed by performing the steps of sol application, drying, degreasing, patterning, and crystallization once. However, the present invention is not limited to this. The film 41 may be made thicker.
[0047]
Upper electrode forming step (FIG. 5: S6, S7)
The upper electrode 42 is formed on the piezoelectric film 41 formed as described above. Specifically, an amorphous fluororesin layer 50 is formed by patterning in a region where the piezoelectric film 41 is not formed (S6), and then an upper electrode 42 is formed on the piezoelectric film 41 and the amorphous fluororesin layer 50. The film is formed, and the upper electrode is removed together with the amorphous fluororesin layer (S7). The upper electrode 42 is formed of platinum (Pt), iridium (Ir) or another metal, and is formed to a thickness of 100 nm by a DC sputtering method.
[0048]
Next, the piezoelectric thin film 43 and the upper electrode 44 are patterned into a predetermined shape of the piezoelectric element. Specifically, after a resist is spin-coated on the upper electrode 42, patterning is performed by exposing and developing to a position where a pressure chamber is to be formed. Using the remaining resist as a mask, the upper electrode 42 and the piezoelectric thin film 41 are etched by ion milling or the like. Through the above steps, a piezoelectric element is formed.
[0049]
Formation of inkjet recording head (S8, S9)
Further, the cavity 21 is formed in the pressure chamber substrate 20, and the nozzle plate 10 is formed. Specifically, an etching mask is applied to the pressure chamber substrate 20 in accordance with the position where the cavity 21 is to be formed, and is predetermined by dry etching using an active gas such as parallel plate reactive ion etching. The cavity 21 is formed by etching the pressure chamber substrate 20 to the depth. The portion left without being etched becomes the side wall 22. Thereafter, the laminated body such as the substrate 20 is cut so as to have the size of each ink jet recording head.
[0050]
Finally, the nozzle plate 10 is joined to the pressure chamber substrate 20 using a resin or the like. When joining the nozzle plate 10 to the pressure chamber substrate 20, the nozzles 11 are aligned so that the nozzles 11 are arranged corresponding to the respective spaces of the cavity 21. Through the above steps, an ink jet recording head is formed.
[0051]
(Other modifications)
The piezoelectric element manufactured according to the present invention is applicable not only to the pressure generating source of the ink jet recording head, but also to piezoelectric element devices such as a piezoelectric fan, an ultrasonic motor, and an ultrasonic transducer, and to the manufacture of such an apparatus. be able to.
[0052]
In addition, the liquid discharge head of the present invention includes, besides a head that discharges ink used in an ink jet recording apparatus, a head that discharges a liquid containing a color material used for manufacturing a color filter for a liquid crystal display or the like, and an organic EL. For heads that eject various liquids, such as a head that ejects a liquid containing an electrode material used for forming electrodes in displays and FEDs (surface emitting displays), and a head that ejects a liquid that contains biological organic substances used in the production of biochips. It is possible to apply.
[0053]
【The invention's effect】
According to the present invention, it is possible to provide a piezoelectric element capable of obtaining high insulating properties and sufficient piezoelectric characteristics even when thinned, and capable of increasing the density of a liquid ejection head. Further, it is possible to provide a method for manufacturing such a piezoelectric element, a liquid ejection head including the piezoelectric element, and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating a structure of a printer (liquid ejection device) using a piezoelectric element and a liquid ejection head according to an embodiment.
FIG. 2 is an explanatory diagram of a structure of an ink jet recording head which is a liquid ejection head of the embodiment.
FIG. 3 is a cross-sectional view illustrating a specific structure of the ink jet recording head and the piezoelectric element.
FIG. 4 is a cross-sectional view illustrating a manufacturing process of the piezoelectric element.
FIG. 5 is a cross-sectional view illustrating a manufacturing process of the piezoelectric element and the ink jet recording head.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Nozzle plate, 20 ... Pressure chamber substrate, 30 ... Vibration plate, 31 ... Insulating film, 32 ... Lower electrode, 40 ... Piezoelectric element, 41 ... Piezoelectric thin film layer, 42 ... Upper electrode, 21 ... Cavity

Claims (10)

A method for manufacturing a piezoelectric element including a piezoelectric thin film sandwiched between an upper electrode and a lower electrode,
A step of patterning the piezoelectric precursor film in a predetermined shape on the lower electrode,
Crystallizing the patterned piezoelectric precursor film to obtain a piezoelectric thin film,
Forming an upper electrode on the piezoelectric film,
The manufacturing method of the piezoelectric element provided with. In claim 1,
The pattern formation of the piezoelectric precursor film is performed by uniformly forming the piezoelectric precursor film on the lower electrode and then etching the piezoelectric precursor film into a predetermined pattern. . In claim 1,
The method of manufacturing a piezoelectric element, wherein the pattern formation of the piezoelectric precursor film is performed by forming a sol containing the component of the piezoelectric precursor on the lower electrode by an ink jet method and gelling the sol. A method for manufacturing a liquid ejection head including a piezoelectric element manufactured by the manufacturing method according to claim 1, wherein:
Forming a diaphragm on one surface of the substrate;
Forming the piezoelectric element on the diaphragm,
Forming a pressure chamber by etching the substrate. In claim 4,
The liquid discharge head includes a plurality of piezoelectric elements, and the pattern formation of the piezoelectric precursor film in the step of forming the piezoelectric elements includes forming a plurality of piezoelectric elements in each of the liquid discharge heads. A method for manufacturing a liquid discharge head, wherein patterning is performed so that a body thin film is integrated. A piezoelectric element in which a piezoelectric thin film and an upper electrode are sequentially formed on a lower electrode, wherein the piezoelectric thin film includes crystal grains having a cross-sectional peripheral length of 2000 nm or more. A piezoelectric element in which a piezoelectric thin film and an upper electrode are sequentially formed on a lower electrode, wherein the piezoelectric thin film has a crystal grain density of 4 × 10 ⁹ [pieces / m ² ] or less. A piezoelectric element in which a piezoelectric thin film and an upper electrode are sequentially formed on a lower electrode, wherein the piezoelectric thin film is formed of a single crystal. A piezoelectric element according to any one of claims 6 to 8, a pressure chamber whose internal volume is changed by a mechanical displacement of the piezoelectric element, and a droplet which is discharged in communication with the pressure chamber. A liquid ejection head having an ejection port. A liquid ejection device comprising the liquid ejection head according to claim 9.

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