JP7424113B2 - Piezoelectric body and liquid ejection head - Google Patents

Description

The present invention relates to a piezoelectric body and a liquid ejection head.

A liquid that consists of a diaphragm as a part of the pressure generation chamber that communicates with the nozzle opening that ejects ink, and deforms the diaphragm with a piezoelectric material to pressurize the ink inside the pressure generation chamber and eject the ink from the nozzle opening. Ejection heads, such as inkjet heads, utilize a piezoelectric actuator that deforms a piezoelectric material by linking it to a vibration plate by expanding and contracting in the thickness direction, and the deflection force generated by stretching and contracting in a direction perpendicular to the thickness direction. Two types of piezoelectric actuators that deform a diaphragm by deforming a diaphragm are already known.

Lead zirconate titanate (PZT), which is a perovskite-type ferroelectric material, is well known as a piezoelectric film material used in the piezoelectric actuator described above. This PZT material has extremely good piezoelectricity and ferroelectricity compared to other materials, and can be used in a wide temperature range, so it can be used not only for piezoelectric actuators but also for making use of its ferroelectricity. It is applied to a wide range of fields such as electronic devices.

When the PZT material is used in an inkjet head as a piezoelectric actuator that utilizes deflection force, a sputtering method, a CSD method such as a sol-gel method or a MOD method is applied to a silicon substrate on which a lower electrode is formed on the top of a diaphragm. (Chemical Solution Deposition) is a known method for forming a thin film of PZT material on the order of several micrometers.

The CSD method, which is typified by the sol-gel method, can easily change and control the (metal) component composition in the precursor liquid applied to the substrate, thereby making it possible to easily change and control the composition of the (metal) component in the precursor liquid applied to the substrate. It has the feature that the composition of the physical crystal film and the properties as a piezoelectric film can be controlled.

A method for forming a piezoelectric film (ferroelectric film) using the CSD method described above will be described below.
First, a precursor liquid synthesized according to the composite oxide composition of the piezoelectric film to be formed is applied onto the silicon substrate on which the lower electrode is formed by a spin coating method, and a coating film of the precursor liquid is applied onto the substrate. form (coating process).
Next, the precursor liquid coating film is heated to a first heating temperature (drying temperature) to evaporate the solvent remaining in the coating film, and a dry film is formed on the substrate by drying the precursor liquid coating film ( drying process).
Next, the dried film is heated to a second heating temperature (thermal decomposition temperature) higher than the first heating temperature (drying temperature) to decompose the organic components in the dried film, and the amorphous film of the composite oxide is formed on the substrate. (also called pyrolysis process or degreasing process) and then cooling (cooling process).
After repeating the steps of applying, drying, and thermally decomposing the precursor liquid film a predetermined number of times, an amorphous layer is formed on the substrate until the third heating temperature (crystallization temperature) is higher than the second heating temperature (thermal decomposition temperature). The film is crystallized by heating to form a composite oxide crystal film having piezoelectric properties (crystallization step).
Then, the steps from application of the precursor liquid to crystallization described above are repeated a predetermined number of times, and finally the composite oxide crystal film is cooled (cooling step) to obtain a piezoelectric film made of the composite oxide crystal film with a desired thickness. form.

The process flow of this CSD method is shown in FIG. In the process flow shown in Figure 1, the coating process, drying process, thermal decomposition process, and cooling process are repeated X times, and then the crystallization process is repeated Y times, that is, the precursor liquid is applied (X*Y). This step is repeated several times to form a piezoelectric film of a desired thickness.

In addition, in order to form a piezoelectric film with a desired thickness as described above, the crystallization process is repeated Y times and Y layers of thin composite oxide crystal films are stacked, so that the piezoelectric film obtained is There are (Y-1) thin interfaces between the composite oxide crystal films in the film.

In addition, when forming a piezoelectric film using the PZT material in the CSD process, the composition of zirconium (hereinafter referred to as Zr) and titanium (hereinafter referred to as Ti) in the thickness direction of the piezoelectric film obtained is It is known that the ratio (hereinafter referred to as Zr/Ti ratio) varies.

Regarding this Zr/Ti ratio variation in the thickness direction of the piezoelectric film, PZT materials generally consist of a solid solution of lead titanate crystals and lead zirconate crystals, but the crystallization temperature of lead titanate and the crystallization temperature of lead zirconate Comparing the temperatures, lead titanate crystallizes faster in one crystallization process because lead titanate is lower in temperature, and lead zirconate crystallizes later while both form a solid solution. , compositional segregation and fluctuations in the Zr/Ti ratio occur such that Ti is abundant on the lower electrode side of each composite oxide crystal film in which the Y layer is stacked, and Zr is abundant on the upper side of each composite oxide crystal film. It has been known.

Therefore, in order to suppress the above-mentioned Zr/Ti ratio fluctuation, in the application of the precursor liquid and the formation of a coating film performed each X times in the crystallization process that is repeated Y times, the lower the coating film of the precursor liquid, the lower the Zr ratio. A method is known in which the Zr/Ti ratio in the precursor liquid is changed so that the Zr/Ti ratio becomes larger (the Ti ratio is smaller) and the Ti ratio becomes larger (the Zr ratio is smaller) toward the top (for example, see Patent Documents 1 and 2). .

However, all of the above-mentioned conventional techniques have the problem that the resulting actuators have large variations in performance, resulting in a decrease in yield.

Therefore, an object of the present invention is to provide a piezoelectric body that can reduce performance variations in the resulting actuators and improve yield.

The above problem is solved by the following configuration 1).
1) A piezoelectric body formed by laminating a plurality of crystal films containing at least Zr, Ti and Pb on an electrode,
Each of the plurality of laminated crystalline thin films has a variation width of Zr/Ti ratio of 5% or less in the lamination direction, and a variation width of Zr/Ti ratio of 5% or less before and after the lamination interface between the crystalline thin films. A piezoelectric body characterized by :

According to the present invention, it is possible to provide a piezoelectric body that can reduce performance variations of obtained actuators and improve yield.

This is a process flow of the CSD method. FIG. 2 is a plan view of an automatic film forming apparatus that can be used to manufacture the piezoelectric body of the present invention. This is a SEM cross-sectional image of a PZT crystal film. FIG. 3 is a diagram showing compositional fluctuations inside a crystal film. FIG. 2 is a diagram for explaining a spinner coating device that applies a precursor liquid onto a silicon substrate. 1 is a schematic cross-sectional view of an example of a piezoelectric element according to the present invention. FIG. 1 is a schematic cross-sectional view of an example of a liquid ejection head according to the present invention. FIG. 1 is a schematic diagram showing an example of a device for discharging liquid according to the present invention. It is a schematic diagram which shows another example of the apparatus which discharges the liquid based on this invention. FIG. 1 is a schematic diagram showing an example of a liquid ejection unit according to the present invention.

Embodiments of the present invention will be described in more detail below.
In the piezoelectric body of the present invention, a plurality of crystal films containing at least Zr, Ti, and Pb are laminated on an electrode, and each of the plurality of crystal films formed has a variation width of the Zr/Ti ratio in the thickness direction. It is characterized by being 5% or less.
With this configuration, the actuator performance is improved, and at the same time, the variation in the actuator performance is reduced, and the yield is improved.
In the piezoelectric body of the prior art, the Zr/Ti ratio of each of the plurality of formed crystal films varies greatly, and the effects of the present invention cannot be achieved.

In the present invention, the method for controlling the fluctuation width of the Zr/Ti ratio between the interfaces of the plurality of crystal films to 5% or less will be explained in detail below, but the process flow of the CSD method shown in FIG. There is a characteristic in the composition of the precursor used in the coating process when the coating process, drying process, thermal decomposition process, and cooling process are repeated X times. In other words, the amount of the Zr component, which is relatively difficult to crystallize, is increased in the lower layer (the side with fewer repetitions) of the laminated amorphous film formed by repeating the coating process, drying process, thermal decomposition process, and cooling process X times. (increased component ratio).

FIG. 2 is a plan view of an automatic film forming apparatus that can be used to manufacture the piezoelectric body of the present invention. The automatic film forming apparatus 100 shown in FIG. 2 is a single-wafer type apparatus that flows silicon substrates (not shown) on which lower electrodes are formed one by one. A transport device 102 that transports the substrate to each device, an aligner 103 that performs the substrate delivery position in the automatic film forming device 100, positioning and centering of the substrate in each device that makes up the automatic film forming device 100, and a precursor liquid for the ferroelectric film. A spinner coating device 104 that coats the precursor film onto the substrate, a hot plate 105 that dries the coated precursor film, an RTA (Rapid Thermal Annealing) device 106 that performs heat treatment for the thermal decomposition process and crystallization process of the dried film, and the RTA device. It consists of a cooling stage 107 that cools the wafer after the heat treatment in step 106.

In the automatic film forming apparatus 100 shown in FIG. 2, the thermal decomposition process and the crystallization process are performed using one common RTA apparatus, but the thermal decomposition process and the crystallization process are performed using two separate RTA apparatuses, or The structure may be such that the thermal decomposition step is performed on a hot plate, and the crystallization step is performed using an RTA apparatus.

The silicon substrates stored in the storage member 101 are transferred to the transfer device 102, and after the substrates are first positioned and centered by the aligner 103, each process in FIG. 1 is carried out according to the flowchart shown in FIG. Flow between each device. The silicon substrate that has been positioned and centered by the aligner 103 described above is first put into a spinner coating device 104 and coated with a precursor liquid, and then the substrate (not shown) on which a coating film of the precursor liquid is formed is The precursor coating film is loaded onto a hot plate 105 by the transport device 102 and subjected to heating and drying treatment. After the drying process, the silicon substrate is loaded into the RTA device 106 by the transport device 102, where the precursor dry film is heated and thermally decomposed, and then cooled by the cooling stage 107. Subsequently, after repeating the above-mentioned coating process or cooling process a predetermined number of times (X times), the laminated amorphous film formed on the silicon substrate is heated to a crystallization temperature higher than the thermal decomposition temperature using the RTA device 106. Crystallization is performed to form a thin PZT crystal thin film. Then, by repeating the above-mentioned coating process or crystallization process a predetermined number of times (Y times) to deposit thin PZT crystal thin films, a PZT crystal film with a desired thickness is formed, and this is further processed. , obtain the desired piezoelectric body. Incidentally, a SEM cross-sectional image of the PZT crystal film thus obtained is shown in FIG. Referring to the SEM cross-sectional image in Figure 3, as a result of repeatedly stacking thin PZT crystal thin films Y times, it is confirmed that there are (Y-1) number of interfaces between each stacked PZT crystal thin film. can.

FIG. 4 shows the results of an EDS analysis of the compositional variation inside the film in the thickness direction from the outermost surface of the film to the lower electrode for the above-mentioned PZT crystal film having an internal interface (conventional example). The left end of the graph's horizontal axis is the outermost surface of the membrane, and the right end of the graph's horizontal axis is the electrode side. As shown in Fig. 4, the crystal film (the whole), which has a structure in which a plurality of crystal thin films are stacked, has a large compositional variation of zirconium and titanium before and after the internal interface. The amount of zirconium is small (the amount of titanium is large), and the amount of zirconium is large (the amount of titanium is small) on the electrode side. In other words, when the surface facing the electrode side of the crystal film in the thickness direction is defined as the surface side, each of the individual crystal films in the crystal film formed by stacking a plurality of crystal thin films has its crystal interface. There is a compositional variation in which the Zr/Ti ratio is small on the surface side and large on the electrode side.
The variation in the Zr/Ti ratio shown in FIG. 4 is a phenomenon that occurs when a precursor liquid with the same PZT composition (Zr/Ti) ratio is used in the coating process or thermal decomposition process repeated (X times). This shows a compositional variation of more than 10%. On the other hand, in the present invention, since this compositional variation is suppressed to 5% or less, it has been revealed that the obtained PZT crystal film exhibits extremely good characteristics.

That is, in the piezoelectric body of the present invention, the variation width of the Zr/Ti ratio in the thickness direction of each of the plurality of crystal films formed is 5% or less.
In the present invention, as a specific means for reducing the fluctuation width of the Zr/Ti ratio in the thickness direction to 5% or less, the steps of coating, drying, thermal decomposition, and cooling are repeated a predetermined number of times (X times) before the crystallization step. Regarding the precursor liquid used in In addition to this, it is also important to optimize the degree of change in the Zr/Ti ratio that changes each time the number of coatings is applied to the temperature increase performance of the heating device (RTA device) used in the crystallization process. It will be done.
To explain in more detail, the temperature raising performance of the RTA equipment used in the crystallization process is particularly important from the temperature set in the pyrolysis process (usually around 380 to 500°C) to the crystallization temperature (usually around 680 to 750°C). The shorter the heating time to raise the substrate temperature, the smaller the degree of change in the Zr/Ti ratio for each number of coatings, and conversely, the longer the heating time, the more the degree of change in the Zr/Ti ratio for each number of coatings. By increasing , it is possible to minimize the Zr/Ti ratio fluctuation/segregation in the thickness direction that occurs during the crystallization process, which changes depending on the temperature raising performance of the RTA device.

In addition, the fluctuation range of the Zr/Ti ratio in the thickness direction refers to the amount of Zr at each position along the vertical axis drawn from the outermost surface of the crystal film to the lower electrode in the crystal film formed by stacking the plurality of crystal layers. (atomic%) and Ti amount (atomic%), calculate the Zr/Ti ratio at each position on the vertical axis, and obtain the difference between the maximum and minimum values of the calculated Zr/Ti ratio along the vertical axis. This is the value given.

Further, the amount of Zr (atomic%) and the amount of Ti (atomic%) at each position along the vertical axis in the thickness direction can be determined by EDS analysis. Details of the EDS analysis are as follows.
Measurements were performed using an energy dispersive X-ray spectrometer NSS212E equipped with an FIB-equipped Carl Zeiss SEM Model Nvision 40 and an EDX (Energy Dispersive X-ray Spectroscopy) unit manufactured by Thermo Fisher.
The energy conditions during the analysis were a maximum of 15 keV, the SEM aperture was adjusted so that the dead time was 20 or more, and line analysis was performed.

Further, when the surface of the crystal film facing the electrode side in the thickness direction is defined as the surface side, the Zr/Ti ratio of the interface on the electrode side formed between the crystal films is such that the Zr/Ti ratio is formed on the surface side. If the Zr/Ti ratio is made equal to the Zr/Ti ratio at the interface, the performance variation of the resulting actuator can be reduced the most.

Next, an embodiment of the coating process in the PZT crystal film forming process will be described.
FIG. 5 shows a spinner coating device 144 for coating a precursor liquid onto a silicon substrate. The spinner coating device 144 is connected to a spinner chuck 111 that holds the silicon substrate 5 by suction, and a spindle motor (not shown) to rotate the silicon wafer substrate 5 held by the spinner chuck 111 according to a program input to a control device (not shown). It is composed of a spindle 112, a pressurized container 114 that stores a precursor liquid and pressurizes this precursor liquid with pressurized gas, and a liquid feeding line 117 that flows the pressurized precursor liquid to a nozzle 116 attached to the tip of an arm 115. be done. In particular, in this embodiment, a pressurized tank 114, a liquid supply line 117, an arm 115, and a nozzle 116 for dropping the precursor liquid onto the silicon substrate 5 are used in a coating process or a thermal decomposition process performed before the crystallization process. There are X pressurized containers 114 corresponding to a predetermined number of steps (X times), and each pressurized container 114 stores a PZT precursor liquid having a different composition among the containers.
The composition of the PZT components dispersed in the precursor liquid varies depending on the number of times of application (first time, second time, . . . , Xth time). Specifically, as mentioned above, the amount of zirconium component (Zr/Ti ratio) in the PZT precursor liquid applied for the first time is the highest, and as the number of times of application increases, the amount of zirconium component (Zr/Ti ratio) in the liquid increases. A precursor solution having a sequentially lowered ratio) is dropped and applied onto the silicon substrate 5, and then introduced into the film forming process shown in the process flow of FIG. 1 to form a PZT crystal film having a desired thickness.
The PZT crystal film obtained by such a process changes its composition according to the number of times the amorphous film is laminated before the crystallization process, so as to compensate for the compositional segregation in the film thickness direction that occurs during the heating process in the crystallization process. Since the film is formed using a precursor liquid that is Body characteristics can be obtained.

The crystal film of the present invention is preferably a PZT crystal film made of lead zirconate titanate, and the PZT crystal film is represented by PbZr _X Ti _(1-X) O ₃ (0.40<x≦0.60). A perovskite-type crystal film is preferred, and one having an MPB composition of PbZr _0.53 Ti _0.47 O ₃ is optimal.

Next, a crystal film, a piezoelectric body, and an electronic device using the piezoelectric body of the present invention will be explained.
The crystal film of the present invention is made of a crystallized product of the precursor liquid.
The piezoelectric body of the present invention has electrodes provided on the upper and lower surfaces of the crystal film of the present invention, respectively.
Examples of the electronic device of the present invention include a liquid discharge head, a liquid discharge device such as a printer/printing device equipped with the liquid discharge head, a liquid discharge unit, etc., which are operated by driving the piezoelectric body of the present invention.
Hereinafter, as an example of the electronic device, a liquid ejection head, a liquid ejection device, and a liquid ejection unit will be described, particularly taking the form of an inkjet head as an example.

An embodiment of a crystal film (hereinafter referred to as a PZT crystal film stacked structure) according to the present invention will be described using FIG. 6. FIG. 6 is a schematic cross-sectional view of an example of a piezoelectric body according to the present invention. The piezoelectric body of the present invention has electrodes provided on the upper and lower surfaces of the crystal film of the present invention, and the crystal film of the present invention is made of a crystallized product of the precursor liquid. Further, a liquid ejection head having a PZT crystal film stacked structure of this embodiment will be explained using FIG. 7. 6 and 7 schematically show cross sections.
FIG. 6 shows a substrate 10, a diaphragm 11, a base film 20 (adhesive layer 21, a lower electrode 22, an orientation control layer 23), a piezoelectric film 30 (PZT crystal film), an upper electrode 40 (a conductive oxide layer 41) , an upper electrode layer 42), and a protective layer 50. Further, FIG. 7 shows a nozzle hole 79, a nozzle substrate 80, and a pressurized liquid chamber 70. Each configuration will be explained.

<Substrate>
A silicon single crystal substrate is preferably used as the substrate 10, and preferably has a thickness of 100 to 600 μm. There are three types of plane orientation: (100), (110), and (111), and (100) and (111) are generally widely used in the semiconductor industry. In this embodiment, a single crystal substrate mainly having a (100) plane orientation is used.

Furthermore, when producing a pressurized liquid chamber 70 as shown in FIG. 7, a silicon single crystal substrate is processed using etching, and anisotropic etching is generally used as the etching method in this case. It is.

Anisotropic etching utilizes the property that the etching rate differs depending on the plane orientation of the crystal structure. For example, in anisotropic etching performed by immersion in an alkaline solution such as KOH, the etching rate for the (111) plane is about 1/400 of that for the (100) plane.
Therefore, in the plane orientation (100), a structure with an inclination of approximately 54.74° can be fabricated, whereas in the plane orientation (110), deep grooves can be cut, so while maintaining more rigidity, the arrangement density is can be made higher. In this embodiment, it is also possible to use a single crystal substrate with a (110) plane orientation. However, in this case, SiO ₂ which is a mask material may also be etched, so it is preferable to use this with consideration.

<Vibration plate>
As shown in FIG. 76, the diaphragm 11 is deformed and displaced by the force generated by the piezoelectric film 30, causing the ink droplets in the pressurized liquid chamber 70 to be ejected. Therefore, it is preferable that the diaphragm 11 has a predetermined strength.
Note that the diaphragm 11 may be made of a single material, or may be made of a plurality of laminated films made of a plurality of materials.

Examples of methods for forming the diaphragm 11 include sputtering, a combination of sputtering and thermal oxidation, and MOCVD (Metal Organic Chemical Vapor Deposition). In this embodiment, when laminating layers, those produced by the LPCVD (Low Pressure CVD) method are used. A diaphragm made of a film formed by the LPCVD method is a film that has been commonly used in semiconductors and MEMS devices, and is easy to process, so it is preferable because it does not introduce new process issues. . Furthermore, a stable diaphragm can be obtained without using an expensive substrate such as SOI (Silicon on Insulator).

The surface roughness of the diaphragm 11 is preferably 4 nm or less in terms of arithmetic mean roughness. If this range is exceeded, the dielectric strength of the PZT film formed thereafter will be very poor, and leakage may occur easily.
Examples of the material for the diaphragm 11 include polysilicon, silicon oxide film, silicon nitride film, and combinations thereof.

An example of the diaphragm 11 will be explained.
First, a silicon oxide film (for example, 200 nm thick) is formed as a diaphragm constituent film on a silicon single crystal substrate with a (100) plane orientation by, for example, the LPCVD method (or heat treatment film forming method), and then polysilicon A film (eg, 500 nm thick) is formed. It is desirable that the polysilicon layer has a thickness of 0.1 to 3 μm and a surface roughness of 5 nm or less in terms of arithmetic mean roughness. Next, a silicon nitride film is formed as a diaphragm constituent film by the LPCVD method.

<Base film>
Next, the base film 20 formed on the diaphragm 11 will be explained. As shown, the adhesion layer 21, the lower electrode 22, and the orientation control layer 23 form the base film 20, and the orientation control layer 23 is particularly important because it influences the crystallinity of the piezoelectric film 30. .

The adhesion layer 21 does not necessarily need to be laminated, but when using platinum (Pt) or the like for the lower electrode 22, considering the adhesion with the diaphragm 11, Ti, TiO ₂ , Ta, It is preferable to laminate an adhesive layer 21 made of Ta ₂ O ₅ , Ta ₃ N ₅ or the like. As a method for producing the adhesive layer 21, a vacuum film formation method such as a sputtering method or a vacuum evaporation method is generally used.

The thickness of the base film 20 is preferably 20 to 500 nm, more preferably 100 to 300 nm.
The thickness of the adhesive layer 21 is preferably 50 to 90 nm.
The thickness of the lower electrode 22 is preferably 140 to 200 nm.
The thickness of the orientation control layer 23 is preferably 5 to 10 nm.

Further, as the material for the lower electrode 22, Pt having a high (111) orientation is preferable, and a Pt film having a high peak intensity when the crystallinity of Pt is evaluated by X-ray diffraction can be obtained.

An orientation control layer 23 is formed on the lower electrode 22 . As the orientation control layer, titanium oxide or lead titanate is preferable. A titanium oxide film is preferable because it can cause a reaction with PZT in the sol-gel solution laminated thereon to produce a Ti-rich PZT crystal film. The Ti-rich film acts as a PZT (100) crystal source and can form the (100) or (001) main orientation of the PZT crystal film to be further laminated.

The orientation control layer 23 does not have to be a titanium oxide film, but may be directly made of lead titanate. Lead titanate is preferable because it directly acts as a PZT (100) crystal source and can form the (100) or (001) main orientation of the PZT crystal film to be laminated.

<PZT crystal film>
Next, the piezoelectric film 30 (PZT crystal film) according to this embodiment will be explained.
The piezoelectric film 30 can be produced from the precursor liquid of the present invention.

The piezoelectric film 30 can be manufactured using a spin coater using a sputtering method or a sol-gel method. In that case, patterning is required, so a desired pattern is obtained by photolithography etching or the like.

In the present invention, a CSD method including a sol-gel method is particularly preferred. For example, when forming a PZT crystal film by the sol-gel method, a precursor liquid for the PZT crystal film is applied to the orientation control layer 23 and baked to form the film, and then the precursor liquid is applied by spin coating or the like. A coating film is formed on the substrate (coating process).
Next, the precursor liquid coating film is heated to a first heating temperature (drying temperature) to evaporate the solvent remaining in the coating film, and a dry film is formed on the substrate by drying the precursor liquid coating film ( drying process).
Next, the dried film is heated to a second heating temperature (thermal decomposition temperature) higher than the first heating temperature (drying temperature) to decompose the organic components in the dried film, and the amorphous film of the composite oxide is formed on the substrate. (also called pyrolysis process or degreasing process) and then cooling (cooling process).
After repeating the steps of applying, drying, and thermally decomposing the precursor liquid film a predetermined number of times, an amorphous layer is formed on the substrate until the third heating temperature (crystallization temperature) is higher than the second heating temperature (thermal decomposition temperature). The film is crystallized by heating to form a composite oxide crystal thin film having piezoelectric properties (crystallization step).

Then, the steps from application of the precursor liquid to crystallization described above are repeated a predetermined number of times, and finally the composite oxide crystal film is cooled (cooling step) to obtain a piezoelectric film made of the composite oxide crystal film with a desired thickness. form.

When producing a PZT crystal film by the sol-gel method, a PZT precursor liquid can be produced by using lead acetate, zirconium alkoxide, and titanium alkoxide compounds as starting materials and dissolving them in methoxyethanol as a common solvent to obtain a homogeneous solution.
Since metal alkoxide compounds are easily hydrolyzed by moisture in the atmosphere, an appropriate amount of a stabilizer such as acetylacetone, acetic acid, or diethanolamine may be added to the precursor liquid as a stabilizer.
The alkoxide is preferably methoxy ethoxide, and the precursor liquid preferably contains lead acetate, Ti methoxy ethoxide, and Zr methoxy ethoxide.

When obtaining a PZT crystal thin film on the entire surface of the base, a coating film is formed by a solution coating method such as spin coating, and a PZT crystal thin film is obtained by performing heat treatments such as solvent drying, thermal decomposition, and crystallization. Since the transformation from a coating film to a crystallized film is accompanied by volumetric contraction, in order to obtain a crack-free film, it is preferable to adjust the concentration of the precursor liquid so that a film thickness of 100 nm or less can be obtained in one step.

The thickness of the PZT crystal film is preferably 0.5 to 5 μm, more preferably 1 μm to 2 μm. If it is smaller than the above range, sufficient displacement cannot be generated, and if it is larger than the above range, the number of steps will increase and the process time will become longer when laminating many layers.

<Top electrode>
The upper electrode 40 of this embodiment is composed of a conductive oxide layer 41 and an upper electrode layer 42. The upper electrode is not particularly limited, and may include materials commonly used in semiconductor processes, such as Al and Cu, and combinations thereof. Although the conductive oxide layer 41 and the upper electrode layer 42 are not particularly limited, the conductive oxide layer 41 may be made of SRO (SrRuO3), which has good adhesion to PZT and has the same perovskite structure. ) is preferable, and as the upper electrode layer 42, Pt is preferable.
Further, the thickness of the conductive oxide layer 41 is preferably 35 to 50 nm.
Further, the thickness of the upper electrode layer 42 is preferably 100 to 150 nm.

<Protective layer>
Examples of the material for the protective layer 50 include aluminum oxide, tantalum oxide, and the like.
The thickness of the protective layer 50 is preferably 40 to 70 nm.
The protective layer 50 can be formed, for example, by an ALD (Atomic Layer Deposition) method.

(liquid discharge device, liquid discharge unit)
Next, an example of a liquid ejection device according to the present invention will be described with reference to FIGS. 8 and 9. FIG. 8 is an explanatory plan view of the main part of the apparatus, and FIG. 9 is a side view of the main part of the apparatus.

This device is a serial type device, and a carriage 403 is reciprocated in the main scanning direction by a main scanning movement mechanism 493. The main scanning movement mechanism 493 includes a guide member 401, a main scanning motor 405, a timing belt 408, and the like. The guide member 401 spans between the left and right side plates 491A and 491B, and movably holds the carriage 403. Then, the carriage 403 is reciprocated in the main scanning direction by the main scanning motor 405 via a timing belt 408 stretched between a driving pulley 406 and a driven pulley 407 .

This carriage 403 is equipped with a liquid ejection unit 440 that integrates a liquid ejection head 404 and a head tank 441 according to the present invention. The liquid ejection head 404 of the liquid ejection unit 440 ejects liquid of each color, for example, yellow (Y), cyan (C), magenta (M), and black (K). Further, the liquid ejection head 404 has a nozzle array made up of a plurality of nozzles 11 arranged in a sub-scanning direction perpendicular to the main scanning direction, and is mounted with the ejection direction facing downward.

A supply mechanism 494 for supplying liquid stored outside the liquid ejection head 404 to the liquid ejection head 404 supplies the liquid stored in the liquid cartridge 450 to the head tank 441 .

The supply mechanism 494 includes a cartridge holder 451, which is a filling section into which the liquid cartridge 450 is mounted, a tube 456, a liquid feeding unit 452 including a liquid feeding pump, and the like. Liquid cartridge 450 is removably attached to cartridge holder 451. Liquid is fed from the liquid cartridge 450 to the head tank 441 by a liquid feeding unit 452 via a tube 456 .

This device includes a transport mechanism 495 for transporting paper 410. The conveyance mechanism 495 includes a conveyance belt 412 that is a conveyance means, and a sub-scanning motor 416 for driving the conveyance belt 412.

The conveyance belt 412 attracts the paper 410 and conveys it to a position facing the liquid ejection head 404 . This conveyance belt 412 is an endless belt, and is stretched between a conveyance roller 413 and a tension roller 414. Adsorption can be performed by electrostatic adsorption, air suction, or the like.

The conveyance belt 412 rotates in the sub-scanning direction by rotationally driving the conveyance roller 413 via the timing belt 417 and timing pulley 418 by the sub-scanning motor 416.

Further, a maintenance and recovery mechanism 420 that maintains and recovers the liquid ejection head 404 is arranged on one side of the carriage 403 in the main scanning direction and on the side of the conveyor belt 412.

The maintenance and recovery mechanism 420 includes, for example, a cap member 421 that caps the nozzle surface (the surface on which the nozzles 11 are formed) of the liquid ejection head 404, a wiper member 422 that wipes the nozzle surface, and the like.

The main scanning movement mechanism 493, the supply mechanism 494, the maintenance and recovery mechanism 420, and the transport mechanism 495 are attached to a housing including side plates 491A, 491B and a back plate 491C.

In this apparatus configured in this manner, the paper 410 is fed onto the conveyor belt 412 and adsorbed, and the paper 410 is conveyed in the sub-scanning direction by the rotational movement of the conveyor belt 412.

Therefore, by driving the liquid ejection head 404 according to the image signal while moving the carriage 403 in the main scanning direction, liquid is ejected onto the stationary paper 410 to form an image.

In this manner, since this apparatus includes the liquid ejection head according to the present invention, it is possible to stably form high-quality images.

EXAMPLES Hereinafter, the present invention will be further explained with reference to examples, but the present invention is not limited to the following examples.

1) Synthesis of precursor liquids Lead acetate trihydrate, zirconium propoxide, and titanium isopropoxide are used as starting materials, and 2-methoxyethanol is used as a common solvent to synthesize the following three types of precursor liquids (undiluted solutions). did.
1-1) Lead: zirconium: titanium ratio (molar ratio) = 110:59:41 precursor solution (Zr concentration + Ti concentration = 0.5 mol/L)
1-2) Lead: zirconium: titanium ratio (molar ratio) = 110:53:47 precursor solution (Zr concentration + Ti concentration = 0.5 mol/L)
1-3) Lead: zirconium: titanium ratio (molar ratio) = 110:47:53 precursor solution (Zr concentration + Ti concentration = 0.5 mol/L)

The synthesis of the precursor liquid described above is as follows.
For each of the above three types of precursor liquids, first, a predetermined amount of lead acetate trihydrate weighed according to the target stoichiometric composition was dissolved in 2-methoxyethanol, and then 2-methoxyethanol was dissolved in 2-methoxyethanol in a dry atmosphere. The solution was heated for 12 hours at a solution temperature above the boiling point of ethanol (125°C), preferably between 130°C and 135°C. During this time, the water of crystallization is fractionally distilled and dehydrated together with 2-methoxyethanol, and a reaction proceeds in which the acetate group of lead acetate is substituted with the methoxyethoxy group of 2-methoxyethanol (dehydration step).
Next, after the above dehydration step of lead acetate trihydrate was completed, a predetermined amount of zirconium propoxide and titanium isopropoxide were added while the solution temperature was lowered to 80°C or less, and 2-methoxyethanol was added again. The solution was heated for 12 hours at a solution temperature above the boiling point (125°C), preferably between 128°C and 130°C. During this time, an alcohol exchange reaction in which the propyl group of zirconium propoxide and the isopropyl group of titanium isopropoxide are substituted with the methoxyethoxy group of 2-methoxyethanol, and an esterification reaction between the acetate group of lead acetate and the alcohol group occur. These side reaction products are fractionally distilled together with 2-methoxyethanol, and a polymerization reaction also proceeds between the lead compound, zirconium compound, and titanium compound in the solution.
After the reaction was completed, heating was stopped and the synthesis solution was cooled to room temperature. 2-methoxyethanol was added to the synthesis solution to a predetermined concentration to complete a precursor solution.

2) Formation of PZT film The three types of precursor liquids synthesized in 1) above were each set in a pressurized precursor liquid container 114 shown in FIG. 5 (X=3).
The silicon substrate stored in the storage member 101 of the automatic film forming apparatus 100 shown in FIG. The coating line connected to the pressurized container 114 is operated to drip the first precursor liquid 1-1), and then the spin coating device 104 is rotated at a maximum speed of 3000 rpm to coat the precursor liquid 1-1). A coating film was formed on the silicon substrate 5 (coating step of X=1 in the flow diagram of FIG. 1).

Next, the transfer device 102 placed the solvent on a hot plate 105 heated to 140°C, which is higher than the boiling point of the main solvent, for 1 minute to form a dry film on the silicon substrate 5 (the drying temperature of process).

Next, the silicon substrate 5 is loaded into the RTA device 106 by the transfer device 102, and heated at a thermal decomposition temperature of 480° C. for 5 minutes to decompose the organic components in the dry film of the precursor, and form the first amorphous film. (The thermal decomposition step of X=1 in the flow diagram of Figure 1) was obtained.

Subsequently, the silicon substrate 5 was moved to the cooling stage 107 by the transfer device 102, and was left on the cooling stage 107 for 2 minutes (or more) to cool the wafer temperature to room temperature (X = 1 in the flow diagram of Fig. 1). cooling process).

Then, the process from the coating step to the cooling step described above was repeated two more times (total three times). However, in the second process, the precursor liquid 1-2), and in the third process, the precursor liquid 1-3), that is, the precursor liquid is dropped so that the amount of zirconium component (Zr/Ti ratio) contained decreases sequentially. After coating and drying to obtain a three-layered amorphous film, the wafer was again placed into the RTA device 106 by the transfer device 102, and the temperature was raised from room temperature to the crystallization temperature = 750° C. in a heating time of 80 msec. After that, the temperature was maintained and heated for 6 minutes to crystallize the three-layer laminated amorphous film to obtain a PZT crystal thin film with a thickness of approximately 80 nm (the crystal with X = 3 and Y = 1 in the flow diagram of Figure 1). process).

Furthermore, the process from the coating process to the crystallization process described above was repeated 24 times to obtain a PZT film with a thickness of approximately 2 μm.

In each of the plurality of crystalline thin films obtained by the above-described process, the variation range of the Zr/Ti ratio in the thickness direction was 4.7%, which satisfied the variation range of 5% or less specified in the present invention. At the same time, the PZT film (the Zr/Ti Compared to the drive voltage of an inkjet head that uses an inkjet head with a ratio variation of 11%, we confirmed that ink droplets can be ejected with an 11% lower drive voltage (improved actuator performance).

100 Automatic film forming apparatus 101 Storage member 102 Transport device 103 Aligner 104 Spinner coating device 105 Hot plate 106 RTA device 107 Cooling stage 5 Silicon substrate 111 Spinner chuck 112 Spindle 114 Pressure container 115 Arm 116 Nozzle 117 Liquid feeding line 10 Substrate 11 Vibration Plate 20 Base film 21 Adhesion layer 22 Lower electrode 23 Orientation control layer 30 Piezoelectric film 40 Upper electrode 41 Conductive oxide layer 42 Upper electrode layer 50 Protective layer 70 Pressurized liquid chamber 79 Nozzle hole 80 Nozzle substrate 201 Substrate 202 Vibration Plate 203 Pressure sealing plate 204 Pressure chamber 205 First electrode 206 Actuator 207 Second electrode 401 Guide member 403 Carriage 404 Liquid ejection head 405 Main scanning motor 406 Drive pulley 407 Followed pulley 408 Timing belt 410 Paper 412 Conveyance belt 413 Conveyance roller 414 Tension roller 421 Cap member 422 Wiper member 440 Liquid discharge unit 441 Head tank 442 Cover 443 Connector 444 Channel parts 450 Liquid cartridge 451 Cartridge holder 452 Liquid feeding unit 456 Tubes 491A, 491B Side plate 491C Back plate 493 Main scanning movement mechanism 494 Supply mechanism 495 Transport mechanism

Japanese Patent Application Publication No. 2013-12655 Japanese Patent Application Publication No. 2003-17421

Claims (4)

A piezoelectric body made of a crystal film formed by laminating a plurality of crystal thin films containing at least Zr, Ti, and Pb,
Each of the plurality of laminated crystalline thin films has a variation width of Zr/Ti ratio of 5% or less in the lamination direction, and a variation width of Zr/Ti ratio of 5% or less before and after the lamination interface between the crystalline thin films. A piezoelectric body characterized by : The piezoelectric body according to claim 1, wherein each of the plurality of laminated crystal thin films has a thickness of 100 nm or less. The piezoelectric body according to claim 1 or 2 , wherein the piezoelectric body has a thickness of 0.5 to 5 μm. a nozzle that discharges liquid;
a liquid chamber communicating with the nozzle;
a piezoelectric body that pressurizes the liquid in the liquid chamber,
A liquid ejection head, wherein the piezoelectric body is the piezoelectric body according to any one of claims 1 to 3.

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