JP6977570B2 - Manufacturing method of piezoelectric actuator unit - Google Patents

Description

The present invention relates to a method for manufacturing a piezoelectric actuator unit.

As an image forming apparatus such as a printer, a facsimile, a copying apparatus, and a multifunction device thereof, for example, an image forming apparatus (inkjet recording apparatus) using a liquid ejection head for ejecting ink droplets is known. This image forming apparatus forms an image by ejecting ink droplets from a liquid ejection head onto a recording medium.

The liquid ejection head includes a nozzle for ejecting ink droplets, a liquid chamber (also referred to as a pressurizing chamber, an ink flow path, a pressurized liquid chamber, a pressure chamber, a discharge chamber, etc.) through which the nozzles communicate, and the liquid chamber. There is known a configuration including an element for ejecting ink from a nozzle that communicates by changing the volume of the above.

As such an element, a configuration including an electromechanical conversion element such as a piezoelectric element and an electric heat conversion element such as a heater is known. However, a vibration plate is provided on a part of the wall of the pressure chamber, and the piezoelectric element is used. The former configuration (hereinafter, also referred to as "piezoelectric actuator"), which changes the volume of the pressure chamber by dislocating the vibrating plate and increases the pressure to eject the ink in the pressure chamber from the nozzle, can handle various droplets. In that respect, it has an advantage over the latter configuration (thermal method).

As a method for manufacturing a piezoelectric actuator, methods such as sheet bonding and ceramic molding have been adopted, but in recent years, in order to further reduce the size and increase the density, a so-called MEMS process applying semiconductor production technology was used. The method is being considered.
In a liquid discharge head equipped with such a piezoelectric actuator, it is necessary to apply a voltage when generating energy in the element, and a module in which wiring connecting the drive IC and the element is provided and these are protected by a protective member. (Hereinafter, also referred to as "piezoelectric actuator unit") is configured.

As the piezoelectric actuator unit, a diaphragm and a piezoelectric layer sandwiched between electrodes at the top and bottom are constructed on the surface of a silicon (Si) substrate, and the metal wiring layer, insulating film, and wiring layer for connecting the drive IC are oxidized. A protective film is constructed, a flow path for supplying ink is provided on the back surface of the silicon substrate, and a mechanism for ejecting ink is completed by connecting the nozzles (see FIG. 1).

Such a piezoelectric actuator unit needs to be machined without defects in the manufacturing process in order to obtain stable discharge performance of the applied liquid discharge head.
However, in the conventional method for manufacturing the piezoelectric actuator unit shown in FIG. 1, if a foreign substance is present during the processing of the liquid chamber 25 and the film formation of the wetted film 26, pinholes may occur. For example, if the substrate is exposed to the ink in the liquid chamber due to peeling of the wetted film 26 from the foreign matter when the piezoelectric actuator is driven, the silicon of the substrate component is eluted into the ink in the liquid chamber. There's a problem.

By the way, for the purpose of forming a smooth diaphragm, after forming the inner wall of the liquid chamber (pressure chamber) by forming a peripheral groove on the surface of the silicon substrate, the diaphragm, the electrode and the piezoelectric element are laminated, and then the pressure is applied. A method for manufacturing a droplet ejection head including a step of forming a chamber has been proposed (see Patent Document 1). Patent Document 1 discloses that a step of filling a filler after forming a peripheral groove is provided. By performing such a step, it is considered that the effect of suppressing the elution of the substrate component from the side wall of the liquid chamber can be obtained.

However, in the manufacturing method of Patent Document 1, depending on the method of filling the formed peripheral groove with a filler, a void may be generated in the center of the groove, or chipping may occur at the interface when the surface is ground and flattened. Or, the surface tension of the filled filler may cause protrusions or voids (see FIG. 2).

If the subsequent manufacturing process is performed in a state where the groove formed on the substrate has the above-mentioned defects, the flatness of the formed diaphragm and electrodes is impaired, which adversely affects the film formation of the piezoelectric film. May reduce crystallinity. Further, when the piezoelectric actuator is continuously driven in the manufactured liquid discharge head, the defect may become a source of cracks and the reliability may be impaired.

Therefore, the present invention is a piezoelectric actuator unit capable of achieving stable discharge performance in a liquid discharge head without impairing reliability while suppressing the generation of pinholes in the liquid chamber and the elution of substrate components. The purpose is to provide a manufacturing method.

In order to achieve such an object, the method for manufacturing a piezoelectric actuator unit according to the present invention applies vibration to a liquid chamber communicating with a nozzle for ejecting droplets and a vibrating plate constituting a part of the liquid chamber. A method for manufacturing a piezoelectric actuator unit used for a liquid discharge head having a piezoelectric actuator that generates a pressure change in a liquid chamber.
The step of forming the diaphragm on the silicon substrate on which the liquid chamber is formed, and
A step of forming a plurality of grooves for forming a side wall for partitioning the liquid chamber from a surface facing the surface on which the diaphragm is formed with respect to the silicon substrate.
Said plurality of grooves the surface of the thermally oxidized, a step of filling the plurality of grooves by an oxide,
The process of forming electrodes on the diaphragm and
The process of forming a frame on the diaphragm and
A step of forming the liquid chamber side wall is constituted by the plurality of removing the silicon of the portion surrounded by the groove of the silicon substrate, the oxide filled in the step of filling the plurality of grooves,
It is characterized by including the step of forming a wetted film on the inner surface of the liquid chamber in this order.

According to the present invention, a piezoelectric actuator unit capable of suppressing the generation of pinholes in a liquid chamber and elution of substrate components, and achieving stable discharge performance in a liquid discharge head without impairing reliability. Production method can be provided.

It is explanatory drawing which shows an example of the manufacturing method of the conventional piezoelectric actuator unit. It is explanatory drawing which shows the example of the defect in the conventional manufacturing method. It is explanatory drawing which shows the formation and filling of the groove part in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is explanatory drawing which shows one step in the manufacturing method of this embodiment. It is a graph which shows the measurement result of the durability evaluation. It is an electron micrograph of the piezoelectric actuator unit of Comparative Example 1 which was destroyed. It is a perspective explanatory drawing which shows an example of the image forming apparatus provided with the piezoelectric actuator unit. It is a side explanatory view which shows an example of the image forming apparatus provided with the piezoelectric actuator unit.

FIG. 1 shows a conventional example of a process of manufacturing an actuator using a MEMS process.
In each of the steps (A) to (F) in FIG. 1, the upper row shows a sectional view in the lateral direction, and the lower row shows a sectional view in the longitudinal direction.

First, as shown in (A), a diaphragm 12, a lower electrode 15, a piezoelectric material 16, and an upper electrode 17 are formed on the substrate 11, and formed into a predetermined shape as shown in (B). Next, the protective film 18 and the wiring layer 19 are constructed as shown in (C), the insulating film 20 is formed as shown in (D), and the ink flow path 21 and the IC connection portion 22 are provided. Next, as shown in (E), the frame 23 is attached, and the drive IC 24 is mounted on the IC connection portion 22. After that, as shown in (F), the substrate 11 is ground to form a liquid chamber 25, and a liquid contact film 26 is formed on the inner side surface of the liquid chamber 25. The piezoelectric actuator is constructed by the above steps.

The piezoelectric actuator manufactured by the conventional method as described above has a problem that pinholes are generated at the time of driving and silicon as a substrate component is eluted into the ink in the liquid chamber.
To deal with this problem, it is preferable to carry out a step for preventing the substrate component from elution from the side wall of the liquid chamber 25. For example, as in Patent Document 1, a groove portion to be an inner wall portion of the liquid chamber is formed in advance to form a filler. A method of filling and heat treatment can be applied.
_{If the oxide film (SiO 2} ) is formed on the side wall of the liquid chamber by the heat treatment, the elution rate of silicon with respect to the ink becomes about 1/2000, and it is considered that elution can be suppressed.

However, when the step of filling the groove with the filler as in Patent Document 1, the flatness of the diaphragm directly under the actuator can be ensured, but the single crystal film forming property of the piezoelectric film is deteriorated depending on the filling method. It may cause defects such as cracks during driving.

An example that causes the above defect is shown in FIG. 2 (A) to 2 (C) schematically show an embodiment in which the filler 31 is filled in the groove 30 formed on the substrate 11.
As shown in FIG. 2A, when the filler 31 is formed into a film by spin coating or sputtering, a void 32 may be generated in the central portion of the groove portion 30. Further, as shown in FIG. 2B, when the filler 31 is formed into a film and then the surface is ground to be flat, chipping 33 is generated at the interface between the groove 30 and the filler 31, and the void is formed. May become. Further, as shown in FIG. 2C, when the filler 31 is directly inserted into the groove 30 by inkjet or the like, convex portions 34 and voids 32 may be generated due to the surface tension of the filler 31.

Hereinafter, a method for manufacturing a piezoelectric actuator according to the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments shown below, and can be modified within the range conceivable by those skilled in the art, such as other embodiments, additions, modifications, and deletions. However, as long as the action and effect of the present invention are exhibited, it is included in the scope of the present invention.

In the method for manufacturing a piezoelectric actuator unit according to the present embodiment, vibration is applied to a liquid chamber communicating with a nozzle for ejecting droplets and a vibrating plate constituting a part of the liquid chamber to cause a pressure change in the liquid chamber. It is a method of manufacturing a piezoelectric actuator unit used for a liquid discharge head having a piezoelectric actuator to generate.
The manufacturing method of the present embodiment is a step of forming the diaphragm 12 on the substrate (silicon substrate) 11 on which the liquid chamber 25 is formed, and the liquid from the facing surface 11a of the diaphragm forming surface with respect to the silicon substrate 11. A step of forming the groove 13 for forming the side wall (liquid chamber side wall) 14 for partitioning the chamber 25 (FIG. 4) and a step of thermally oxidizing the surface of the groove 13 and filling the groove 13 with the oxide 13a (FIG. 4). 5), a step of forming an electrode on the diaphragm 12 (FIG. 6), a step of forming a frame 23 on the diaphragm 12, and a liquid chamber portion and a groove portion surrounded by a groove portion 13 of the silicon substrate 11. The step of removing the oxide 13a of 13 to form the liquid chamber 25 (FIG. 10) is included in this order.

As the overall flow, the diaphragm 12 is formed on the substrate 11 as shown in FIG. 4, the groove portion 13 for forming the side wall of the liquid chamber is formed by etching from the facing surface 11a, and the liquid is formed as shown in FIG. The chamber side wall 14 is formed. Next, as shown in FIG. 6, a lower electrode 15, a piezoelectric material 16 and an upper electrode 17 are formed on the diaphragm 12 and formed into the shape of FIG. 7. A protective film 18 and a wiring layer 19 are constructed on the protective film 18 as shown in FIG. 8, an insulating film 20 is formed as shown in FIG. 8, and an ink flow path 21 and an IC connection portion 22 are provided. After that, as shown in FIG. 9, the frame 23 is attached, and the drive IC 24 is mounted on the IC connection portion 22. Then, as shown in FIG. 10, the substrate 11 is ground to form the liquid chamber 25, and then the wetted film 26 is formed on the inner side surface of the liquid chamber. The piezoelectric actuator unit is completed by the above steps.

In the manufacturing method of the present embodiment, after the diaphragm 12 is formed on the substrate 11 as shown in FIG. 3A, the groove portion 13 is formed from the facing surface 11a of the diaphragm forming surface as shown in FIG. 3B. As shown in FIG. 3C, the surface of the groove 13 is thermally oxidized, and the groove 13 is filled with the oxide 13a.
Since the groove portion 13 is formed after the diaphragm 12 is formed, the entire surface of the diaphragm 12 is maintained in a flat state, the generation of voids and steps in the vicinity of the piezoelectric actuator as shown in FIG. 2 is improved, and the piezoelectricity is formed. It is possible to form a uniform single crystal film of the body, and the generation of cracks during driving is also suppressed.

Hereinafter, the process of the method for manufacturing the piezoelectric actuator unit according to the present embodiment will be described in detail with reference to FIGS. 4 to 10. The upper part of each figure shows a short cross section, and the lower part shows a long cross section.

First, the configuration of the process shown in FIGS. 4 and 5 will be described.
As the material of the substrate 11, it is preferable to use a silicon single crystal substrate, and it is usually preferable to have a thickness of 100 to 650 μm. There are three types of plane orientations, (100), (110), and (111), but (100) and (111) are generally widely used in the semiconductor industry, and (100) in the present embodiment. Use a substrate.

Since the diaphragm 12 is a member that receives the force generated by the piezoelectric material 16 and is deformed and displaced to eject the ink droplets of the liquid chamber 25, it is preferable that the diaphragm 12 has a predetermined strength.
Examples of the material of the diaphragm 12 include those made of Si, SiO ₂ , and Si ₃ N ₄ by the CVD method. Further, it is preferable to select a material having a high etching selectivity with Si and having a coefficient of linear expansion close to that of the actuator (lower electrode 15, piezoelectric material 16, and upper electrode 17).
In the present embodiment, since the interface with the substrate 11 is used as the etching stop layer in the diaphragm 12, it is preferable to use _{SiO 2} or Si ₃ N _{4 as the first layer.}

As the coefficient of linear expansion of the vibrating plate 12, since PZT is generally used as the material in the piezoelectric material 16, the ^{coefficient of linear expansion close to 8 × 10 −6} (1 / K) is 5 × 10. ^{A material having a linear expansion coefficient of -6} to 10 × 10 ^-6 is preferable, and a material having a linear expansion coefficient of 7 × 10 ^{-6 to} 9 × 10 ^-6 is more preferable.

The film thickness to be formed is preferably 0.1 to 10 μm, more preferably 0.5 to 3 μm. If the film thickness is less than 0.1 μm or more than 10 μm, it becomes difficult to deform and the ejection of ink droplets becomes unstable.

Further, the diaphragm 12 is preferably constructed by laminating a plurality of films having tensile stress or compressive stress by LPCVD. An example of a single-layer film is an SOI wafer, but the wafer cost is very high, and it is not possible to set an arbitrary film stress when trying to make the bending rigidity uniform. On the other hand, in the case of the laminated diaphragm, by optimizing the laminated configuration, the degree of freedom to set the rigidity and the film stress of the diaphragm 12 to desired values can be obtained. Since the overall rigidity and stress of the diaphragm 12 can be controlled by combining the stacking, the film thickness, and the laminated configuration, the material and film thickness of the layers constituting the piezoelectric actuator can be adjusted in a timely manner, and the diaphragm 12 can be adjusted according to the firing temperature. Fluctuations in rigidity and stress can be reduced. By forming the stable diaphragm 12 in this way, it is possible to realize highly accurate droplet ejection characteristics and stable ejection when applied to a liquid ejection head.

The groove portion 13 forming the liquid chamber side wall 14 is formed by Si etching.
As the etching of Si, for example, wet etching and dry etching are generally used, but in consideration of the degree of freedom of the pattern shape, dry etching is preferable in this embodiment.

The width of the groove portion 13 can be appropriately selected, but if the aspect ratio is too high, the shape may become unstable and a film forming defect may occur when filling is performed in the subsequent process. Therefore, an appropriate aspect ratio should be selected. It is preferable to select.

The liquid chamber side wall 14 is made of a metal oxide or a Si oxide by performing a step of thermally oxidizing the surface of the groove portion 13 and filling the groove portion 13 with an oxide. Oxides are preferable because many of them exhibit stable behavior both in a steady state and in acids and bases.
By thermally oxidizing the surface of the groove portion 13, a dense silicon oxide film is formed. When the aspect ratio of the groove portion 13 is large, the groove portion 13 is filled due to the effect of increasing the film thickness of the surface by thermal oxidation. On the other hand, when the aspect ratio of the groove portion 13 is small, a separate filling step is required after the thermal oxidation step. Examples of the method of filling the groove portion 13 with an oxide include a film forming method typified by CVD, ALD, and sputtering.
When performing thermal oxidation, it is necessary to remove the residue inside the groove 13 with a chemical solution or the like.

Next, the configuration of the process shown in FIG. 6 will be described.
The lower electrode 15 and the upper electrode 17 are made of a metal material and an adhesion layer.
Examples of the metal material include Pt, Ir, Rh, which have excellent corrosion resistance, and alloy films thereof. These metals, due to poor adhesion to the underlying (in particular _{SiO 2), Ti, TiO2,} Ta, Ta 2 O 5, by laminating a _Ta 3 _{N 5} and the like previously, it is preferable that the electrode foundation layer ..

Examples of the method for manufacturing the lower electrode 15 and the upper electrode 17 include vacuum film formation such as a sputtering method and vacuum vapor deposition.
The film thickness to be formed is preferably 0.05 to 1 μm, more preferably 0.1 to 0.5 μm.

Further, due to concerns about the fatigue characteristics of the displacement of the piezoelectric material 16 over time, a conductive oxide such as strontium ruthenate may be laminated as an electrode portion between the lower electrode 15 and the upper electrode 17 and the piezoelectric material 16. preferable.

As the piezoelectric material 16, lead zirconate titanate (PZT) was mainly used.
PZT is a solid solution of lead zirconate (PbZrO ₃ ) and titanate (PbTiO ₃ ), and its characteristics differ depending on the ratio. In general, the composition showing excellent piezoelectric properties is such that _{the ratio of PbZrO 3} to PbTiO ₃ is 53:47, and the chemical formula shows Pb (Zr0.53, Ti0.47) O ₃ and general PZT (53 /). 47). In order to obtain a larger amount of displacement, Pb (Zr0.49, Ti0.51) can also be _{O 3.}

Examples of the composite oxide other than PZT include barium titanate. In this case, it is also possible to prepare a barium titanate precursor solution by using a barium alkoxide or a titanium alkoxide compound as a starting material and dissolving it in a common solvent.

These materials are _{described by the general formula ABO 3} , and correspond to a composite oxide containing Pb, Ba, Sr as A and Ti, Zr, Sn, Ni, Zn, Mg, and Nb as main components of B.
Specific descriptions include (Pb _1-x , Ba _x ) (Zr, Ti) O ₃ , (Pb) (Zr _x , T _y , Nb _1-x-y ) O _3, etc., and the former is A. When Pb of the site is partially replaced with Ba, the latter is a case where Zr and Ti of the B site are partially replaced with Nb. Such substitution is performed by material modification for the application of the deformation characteristic (displacement characteristic) of PZT.

Examples of the method for producing PZT include a method for producing PZT by a spin coater using a sputtering method and a sol-gel method. In this case, patterning is required, so a desired pattern can be obtained by photolithography etching or the like.

When PZT is prepared by the sol-gel method, a PZT precursor solution can be prepared by using lead acetate, zirconium alkoxide, and a titanium alkoxide compound as starting materials and dissolving them in methoxyethanol as a common solvent to obtain a uniform solution. Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of acetylacetone, acetic acid, diethanolamine or the like may be added as a stabilizer to the precursor solution.

When a PZT film is obtained on the entire surface of the underlying substrate, it is obtained by forming a coating film by a solution coating method such as spin coating and performing heat treatments of solvent drying, thermal decomposition, and crystallization. Since the transformation from the coating film to the crystallized film is accompanied by volume shrinkage, it is necessary to adjust the concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a crack-free film.

The film thickness is preferably 0.5 to 5 μm, more preferably 1 μm to 2 μm. If it is smaller than 0.5 μm, sufficient displacement cannot be generated, and if it exceeds 5 μm, the number of laminating steps increases and the process time becomes long.

Next, the configuration of the process shown in FIG. 7 will be described.
As the material of the protective film 18, it is preferable to use an oxide or a nitride. In particular, Al ₂ O ₃ has excellent weather resistance and chemical resistance, and is particularly suitable as a material for the protective film 18.
The thickness of the protective film 18 is preferably thick for the purpose of protection, but if the protective film is thickly deposited on the PZT which is the driving part of the actuator, the characteristics of the actuator will be impaired. Therefore, the film thickness is basically preferably 30 nm to 100 nm, and more preferably 60 nm to 90 nm. Further, when Al ₂ O ₃ is used as the protective film 18, the film needs to be very dense. Therefore, it is preferable to use the ALD method instead of the sputtering method as the production method.

As the material of the wiring layer 19, it is preferable to use a precious metal material. Al, Cu, and alloys of Al and Cu are often used in semiconductors and MEMS devices, but in this embodiment, a part of the wiring is exposed to the etching solution during wet etching, so the etching solution is used. Noble metals such as Au and Pt that do not dissolve are used.
The film thickness of the wiring layer 19 needs to be a film thickness sufficient to cover the step of the actuator formed in the step of FIG. 6, and is preferably 100 nm or more.

Next, the configuration of the process shown in FIG. 8 will be described.
As the insulating film 20, an oxide film and a nitride film are preferable as in the protective film 18 formed in the step of FIG. The film thickness is preferably 20 nm to 50 nm.

The ink flow path 21 is formed by dry etching. By forming the liquid chamber 25 from the back surface facing the ink flow path 21, the actuator can function as an inkjet. A fluid resistance that controls the ink flow rate may be formed in the ink flow path 21 and the liquid chamber 25.
The IC connection portion 22 can be formed by processing at the same time as the ink flow path 21.

Next, the configuration of the process shown in FIG. 9 will be described.
The frame 23 is formed by using a silicon substrate. Specifically, a portion penetrating the substrate 11 such as the ink flow path 21 and the IC connection portion 22 and a gap for sealing the actuator are formed by etching, and then the surface is protected by _{SiO 2.} To make.

The drive IC 24 is electrically connected to the IC connection portion 22 formed by the process of FIG.
In the present embodiment, gold bumps are formed in the driving IC 24 and the IC connection portion 22 by the stud bumps, and then electrically connected by the flip chip bonder.

Next, the configuration of the process shown in FIG. 10 will be described.
The liquid chamber 25 is formed by dry etching. _{Specifically, it is formed by removing the SiO 2} on the outermost surface of the substrate 11 by dry etching and then removing the internal Si surrounded by the groove 13 by dry etching.

Examples of the dry etching method include a Bosch process. By using the Bosch process, it is possible to perform pseudo anisotropic etching, and holes corresponding to the resist pattern can be formed perpendicularly to the substrate.

The wetted film 26 is preferably made of a dense film of a metal oxide, and preferably contains at least one of tantalum and zirconium.
Examples of the method for forming a dense film include a method using ALD in which metal atoms and oxygen atoms are alternately formed to form an oxide film.

By the manufacturing method having the above steps, the generation of pinholes in the liquid chamber and the elution of substrate components are suppressed, the reliability is not impaired, and stable discharge performance can be realized in the liquid discharge head. A piezoelectric actuator unit can be obtained.

Hereinafter, specific examples will be described together with comparative examples.

[Example 1]
On a (100) silicon wafer having a thickness of 300 μm as the substrate 11, SiO ₂ (thickness 600 nm), Si ₃ N ₄ (thickness 250 nm), SiO ₂ (thickness 600 nm), Si (thickness 200 nm), SiO ₂ A diaphragm 12 made of a laminated film (thickness 500 nm) was formed.

After that, the groove portion 13 (width 5 μm) for forming the liquid chamber side wall 14 was patterned on the facing surface of the diaphragm 11 from the diaphragm forming surface, and the groove portion 13 was formed by dry etching.

Then, thermal oxidation was performed for 24 hours in a thermal oxidation furnace. The silicon on the surface of the groove 13 was thermally oxidized to form a thermal oxide film made of an oxide having a thickness of 2.5 μm, and the groove 13 was filled. The surface of the substrate (opposite surface of the diaphragm forming surface) was polished and flattened with the groove portion 13 buried.

_{Next, after surface-treating the SiO 2} layer on the surface of the diaphragm 12 _{with plasma, a 20 nm film of Ti was formed on the SiO 2 layer as an electrode base layer, and a TiO 2} film was formed at 700 ° C. by RTA (rapid heat treatment). Made. The TiO ₂ film has _{a role as an adhesion layer between SiO 2} and the electrode (Pt film).
Next, a Pt film (thickness 160 nm) was formed as the lower electrode 15, and then a 7 nm PbTiO ₃ was formed as a seed layer for controlling the orientation of the piezoelectric material 16 by a spin coating method.

As a material for the PZT film constituting the piezoelectric material 16, a coating liquid prepared with a composition ratio of Pb: Zr: Ti = 150: 49: 51 was prepared.
Lead acetate trihydrate, isopropoxide titanium, and isopropoxide zirconium were used as starting materials. The water of crystallization of lead acetate was dissolved in methoxyethanol and then dehydrated. The amount of lead is excessive for the composition of both chemistry. This is to prevent a decrease in crystallinity due to so-called lead loss during heat treatment. A PZT precursor solution was synthesized by dissolving isopropoxide titanium and isopropoxide zirconium in methoxyethanol, proceeding with an alcohol exchange reaction and an esterification reaction, and mixing with a methoxyethanol solution in which lead acetate was dissolved. The PZT concentration was 0.3 mol / L.

After applying the obtained solution by a spin coating method, drying at 120 ° C. → thermal decomposition at 500 ° C. was performed on a hot plate.
After the thermal decomposition treatment of the third layer, a crystallization heat treatment (temperature 730 ° C.) was performed by RTA. At this time, the film thickness of PZT was 250 nm.
This step was carried out a total of 8 times (24 layers) to obtain a PZT film thickness of about 2.0 μm.

Next, as the upper electrode 17, an SrRuO ₃ film (film thickness 40 nm) and a Pt film (film thickness 125 nm) were sequentially sputtered. The substrate temperature at the time of sputter film formation was 300 ° C. The SrRuO ₃ membrane was post-annealed at 550 ° C./300 s in an oxygen atmosphere by RTA treatment.

Next, a photoresist was formed into a film by a spin coating method, a resist pattern was formed by ordinary photolithography, and then PZT and electrodes were etched using an ICP etching apparatus.

After that, 50 nm Al ₂ O ₃ as the protective film 18, 5 μm Al as the wiring layer 19, and 50 μm SiO ₂ as the insulating film 20 are formed by sequentially forming and etching, and then the ink flow path 21 is etched. Formed by.

The frame 23 is divided into a penetrating portion and a non-penetrating portion. After forming a hard mask for forming the non-penetrating portion on a 400 μm Si substrate, a resist mask for the penetrating portion is formed, and the penetrating portion is formed first. After that, the resist mask was removed, and a non-penetrating portion was formed with a hard mask.

The frame 23 is bonded to the wafer provided with the actuator previously manufactured by the above method with an adhesive, the wiring layer 19 and the driving IC 24 are flip-chip connected, and the connection portion is embedded with resin, and then the wafer is used. Grinding was performed from the back surface (the surface facing the diaphragm forming surface of the substrate 11) to a height of 75 μm.

Next, the liquid chamber 25 was formed by dry etching.
_{A 50 nm Ta 2} O ₅ film was formed as a wetted film 26 on the inside of the formed liquid chamber 25 by ALD to complete the piezoelectric actuator unit.

[Comparative Example 1]
In the method for manufacturing the piezoelectric actuator unit of Example 1, the groove portion 13 (width 5 μm) for forming the liquid chamber side wall 14 with the photoresist is patterned on one surface of the substrate 11, and the groove portion 13 is formed by dry etching. Then, thermal oxidation was performed for 24 hours in a thermal oxidation furnace to fill the groove 13 with an oxide so that the groove 13 was buried, and then a vibrating plate 12 was formed in the same manner as in Example 1. The piezoelectric actuator unit was manufactured.

[Comparative Example 2]
In the method for manufacturing the piezoelectric actuator unit of Example 1, the piezoelectric actuator unit was manufactured in the same manner as in Example 1 except that the groove portion 13 for forming the liquid chamber side wall 14 was not formed.

〔evaluation〕
The following tests were conducted to evaluate the performance of the piezoelectric actuator units manufactured according to Example 1, Comparative Example 1 and Comparative Example 2 described above.

(1) Substrate component elution test The inner wall surface of the liquid chamber of the manufactured piezoelectric actuator unit was scratched to cause pinholes. After immersing in each of yellow, cyan, magenta, and black inks for 72 hours so that the pinholes were immersed, the thickness of the partition partition for partitioning the liquid chamber was measured and compared with the thickness before immersion. It is considered that the partition wall thickness is attenuated by the elution of the substrate component from the pinhole location.
If the attenuation of the thickness of the partition wall after immersion was less than 5 nm, it was evaluated as acceptable (evaluation: ◯), and if the attenuation was 5 nm or more, it was rejected (evaluation: ×). The results are shown in Table 1.

As shown in Table 1, in the piezoelectric actuator units manufactured by the methods of Example 1 and Comparative Example 1 in which the side wall of the liquid chamber is made of SiO _{2, the attenuation is less than 5 nm for any of the inks.} Met. On the other hand, it was found that the piezoelectric actuator units manufactured by the method of Comparative Example 2 had an attenuation of 5 nm or more, and there was a risk of elution of the substrate component into the ink.

(2) Crystallinity evaluation The piezoelectric material constituting the manufactured piezoelectric actuator unit was measured by the θ-2θ method of X-ray diffraction, and the orientation rate of PZT was evaluated.
The definition of the orientation rate is to calculate the percentage of the diffraction intensity of the (100) plane, (110) plane, and (111) plane of PZT, and pass if the orientation ratio of (100) is 98% or more (evaluation: ○). If it was less than 98%, it was rejected (evaluation: ×). The results are shown in Table 2.

As shown in Table 2, in the piezoelectric actuator units manufactured by the methods of Example 1 and Comparative Example 2, the orientation ratio of PZT (100) was 98% or more, whereas the method of Comparative Example 1 was used. In the piezoelectric actuator unit manufactured by the above, the orientation ratio of PZT (100) was about 88%. It was found that the production method of Comparative Example 1 did not form a PZT film having high-quality crystallinity.

(3) Durability evaluation Durability is evaluated by continuously driving the manufactured piezoelectric actuator unit using a pulse waveform with an applied electric field of 150 kV / cm, rising edge of 1 μs, falling edge of 1 μs, pulse width of 4 μs, and 100 kHz. rice field. The displacement was measured using a laser Doppler vibrometer.
Evaluation of driving durability, the number of times of driving until breakdown occurs is measured, pass if more than 10 ⁸ times (Evaluation: ○), if it is less than 10 ⁸ times fail (rating: ×) and the. The results are shown in Table 3.

As shown in Table 3, in the piezoelectric actuator unit manufactured by the method of Example 1 and Comparative Example 2, while the number of times of driving until the destruction was more than 10 ⁸ times, the method of Comparative Example 1 the piezoelectric actuator unit manufactured by was less than 10 ⁸ times.

FIG. 12 shows an electron micrograph around the actuator after the piezoelectric actuator unit manufactured by the method of Comparative Example 1 which was destroyed the number of times less than the acceptance criteria. It can be seen that cracks have occurred around the actuator.

From the above test results, it was found that only the piezoelectric actuator unit manufactured by the manufacturing method of Example 1 according to the present embodiment satisfies the acceptance criteria in all the evaluations.
According to the method for manufacturing the piezoelectric actuator unit of the present embodiment, the generation of pinholes in the liquid chamber and the elution of substrate components are suppressed, the reliability is not impaired, and stable discharge performance is achieved in the liquid discharge head. It is possible to manufacture a piezoelectric actuator unit that can be realized.

Next, an example of an image forming apparatus provided with a liquid discharge head including a piezoelectric actuator unit manufactured by the manufacturing method according to the present invention will be described with reference to FIGS. 13 and 14.
13 and 14 are an inkjet recording device equipped with an inkjet head which is a liquid ejection head, FIG. 13 is a perspective explanatory view, and FIG. 14 is a side explanatory view of a mechanism portion.

This inkjet recording device includes a carriage that can move in the main scanning direction inside the recording device main body 81, a recording head composed of an inkjet head according to the present invention mounted on the carriage, an ink cartridge that supplies ink to the recording head, and the like. A paper cassette (or a paper tray) 84 capable of loading a large number of sheets of paper 83 from the front side is freely mounted on the lower part of the apparatus main body 81 to accommodate the printing mechanism unit 82 or the like. In addition, the manual feed tray 85 for manually feeding the paper 83 can be opened and closed, and the paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken in by the printing mechanism unit 82. After recording the required image, the paper is discharged to the paper ejection tray 86 mounted on the rear surface side.

The printing mechanism unit 82 slidably holds the carriage 93 in the main scanning direction by the main guide rod 91 and the slave guide rod 92, which are guide members laid horizontally on the left and right side plates (not shown), and the carriage 93 is yellow. A head 94 composed of an inkjet head that ejects ink droplets of each color of (Y), cyan (C), magenta (M), and black (Bk) is placed in a direction in which a plurality of ink ejection ports (nozzles) intersect the main scanning direction. They are arranged and mounted with the ink droplet ejection direction facing downward. Further, each ink cartridge 95 for supplying ink of each color to the head 94 is replaceably mounted on the carriage 93.
The head 94 includes a piezoelectric actuator unit manufactured by the manufacturing method of the present invention.

The ink cartridge 95 has an atmosphere port that communicates with the atmosphere above, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body. Keeps the ink supplied to the inkjet head at a slight negative pressure. Further, although the head 94 of each color is used here as the recording head, one head having a nozzle for ejecting ink droplets of each color may be used.

Here, the carriage 93 is slidably fitted on the main guide rod 91 on the rear side (downstream side in the paper transport direction) and slidably mounted on the slave guide rod 92 on the front side (upstream side in the paper transport direction). is doing. Then, in order to move and scan the carriage 93 in the main scanning direction, a timing belt 100 is stretched between the drive pulley 98 and the driven pulley 99 which are rotationally driven by the main scanning motor 97, and the timing belt 100 is mounted on the carriage 93. The carriage 93 is reciprocated by the forward and reverse rotation of the main scanning motor 97.

On the other hand, in order to convey the paper 83 set in the paper cassette 84 to the lower side of the head 94, the paper 83 is guided to the paper feed roller 101 and the friction pad 102 that separate and supply the paper 83 from the paper feed cassette 84. A tip that defines a guide member 103, a transport roller 104 that inverts and transports the fed paper 83, and a transport roller 105 that is pressed against the peripheral surface of the transport roller 104 and a feed angle of the paper 83 from the transport roller 104. A roller 106 is provided. The transfer roller 104 is rotationally driven by the sub-scanning motor 107 via the gear train.

A printing receiving member 109, which is a paper guide member for guiding the paper 83 sent out from the transport roller 104 on the lower side of the recording head 94 corresponding to the movement range of the carriage 93 in the main scanning direction, is provided. On the downstream side of the imprint receiving member 109 in the paper transport direction, a transport roller 111 and a spur 112 that are rotationally driven to feed the paper 83 in the paper discharge direction are provided, and further, the paper 83 is fed to the paper discharge tray 86. A roller 113, a spur 114, and guide members 115 and 116 forming a paper ejection path are arranged.

At the time of recording, by driving the recording head 94 in response to the image signal while moving the carriage 93, ink is ejected to the stopped paper 83 to record one line, and the paper 83 is conveyed in a predetermined amount and then next. Record the line of. When the recording end signal or the signal that the rear end of the paper 83 reaches the recording area is received, the recording operation is ended and the paper 83 is ejected.

Further, a recovery device 117 for recovering the ejection failure of the head 94 is arranged at a position outside the recording area on the right end side in the moving direction of the carriage 93. The recovery device 117 has a cap means, a suction means, and a cleaning means. The carriage 93 is moved to the recovery device 117 side during the printing standby, and the head 94 is capped by the capping means, and the ejection port portion is kept in a wet state to prevent ejection defects due to ink drying. In addition, by ejecting ink that is not related to recording during recording, the ink viscosities of all the ejection ports are kept constant, and stable ejection performance is maintained.

When a ejection failure occurs, the ejection port (nozzle) of the head 94 is sealed by the capping means, air bubbles, etc. are sucked out from the ejection port by the suction means through the tube, and ink, dust, etc. adhering to the ejection port surface are sucked out. Is removed by cleaning means and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed in the lower part of the main body, and is absorbed and held by an ink absorber inside the waste ink reservoir.

11 Substrate (silicon substrate)
12 Diaphragm 13 Groove 14 Liquid chamber side wall 15 Lower electrode 16 Piezoelectric material 17 Upper electrode 18 Protective film 19 Wiring layer 20 Insulating film 21 Ink flow path 22 IC connection 23 Frame 24 Drive IC
25 Liquid chamber 26 Wetting membrane

Japanese Unexamined Patent Publication No. 2007-331175

Claims (4)

It is used for a liquid discharge head having a liquid chamber communicating with a nozzle for ejecting droplets and a piezoelectric actuator that applies vibration to a vibrating plate constituting a part of the liquid chamber to generate a pressure change in the liquid chamber. It is a method of manufacturing a piezoelectric actuator unit.
The step of forming the diaphragm on the silicon substrate on which the liquid chamber is formed, and
A step of forming a plurality of grooves for forming a side wall for partitioning the liquid chamber from a surface facing the surface on which the diaphragm is formed with respect to the silicon substrate.
Said plurality of grooves the surface of the thermally oxidized, a step of filling the plurality of grooves by an oxide,
The process of forming electrodes on the diaphragm and
The process of forming a frame on the diaphragm and
A step of forming the liquid chamber side wall is constituted by the plurality of removing the silicon of the portion surrounded by the groove of the silicon substrate, the oxide filled in the step of filling the plurality of grooves,
A method for manufacturing a piezoelectric actuator unit, which comprises a step of forming a wetted film on the inner surface of the liquid chamber in this order. The method for manufacturing a piezoelectric actuator unit according to claim 1, wherein the groove is formed by dry etching. The method for manufacturing a piezoelectric actuator unit according to claim 1 or 2 , wherein the wetted film contains at least one of tantalum and zirconium. The method for manufacturing a piezoelectric actuator unit according to any one of claims 1 to 3, wherein the step of forming the liquid chamber is performed by dry etching.

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