JP6909421B2 - Manufacturing method of ferroelectric film - Google Patents

Description

The present invention relates to the production how the ferroelectric film.

Conventionally, a ferroelectric film used for a piezoelectric element or the like is formed on a substrate by using a chemical solution deposition method (CSD (Chemical Solution Deposition) method) such as a sol-gel method or a MOD method (metal organic compound decomposition method). A method for producing a dielectric film is known.

For example, Patent Document 1 discloses a production method for producing a PNbZT thin film (ferroelectric film) made of a zirconium niobate lead titanate-based composite perovskite by using a sol-gel method. In this manufacturing method, for the purpose of substantially uniform composition in the thickness direction of PNbZT film, composition formula _{Pb z Nb x Zr y Ti (} 1-y) O 3 (0 <x ≦ 0.05,0.40 ≦ Prepare a plurality of types of sol-gel solutions satisfying y ≦ 0.60, 1.05 ≦ z ≦ 1.25) and having different concentration ratios Zr / Ti of zirconium (Zr) and titanium (Ti). Then, the process of selecting a predetermined sol-gel solution from a plurality of types of sol-gel solutions, applying the solution on the substrate, and pre-baking is repeated two or more times so that the concentration ratio Zr / Ti becomes smaller stepwise. Two or more sol-gel films having a density ratio Zr / Ti smaller as the upper layer are laminated on the substrate. Then, these calcined films are fired together to obtain a single PNbZT thin film.

In recent years, as a ferroelectric film that compensates for the drawbacks of PZT (lead zirconate titanate) film, a ferroelectric film called PLZT crystal film in which a part of lead (Pb) of the PZT crystal film is replaced with lanthanum (La) is known. Has been done. However, when this PLZT crystal film is formed by a chemical solution deposition method such as a sol-gel method or a MOD method, there is a problem that the expected effect (effect compared with the PZT crystal film) cannot be sufficiently obtained. ..

In order to solve the above problems, the present invention provides a method of manufacturing a ferroelectric film for forming a ferroelectric film on a substrate using a chemical solution deposition method, the general formula _{Pb (1-x) La x} ( _{Zir y} Ti _(1-y) ) O ₃ (0 <x ≤ 0.08, 0.55 ≤ y ≤ 0.65) Zirconium (Zr) is used as a precursor liquid for the ferroelectric film of perovskite-type crystals. ) And titanium (Ti) concentration ratio Zr / Ti is lower in the upper layer as long as the magnitude relationship between Zr and Ti is maintained. It is characterized in that the ferroelectric film is formed by repeatedly carrying out the laminating and crystallization steps of crystallization.

According to the present invention, an excellent effect that a PLZT crystal film capable of sufficiently obtaining the expected effect can be formed by using a chemical solution deposition method is exhibited.

It is a schematic block diagram which shows one structural example of the liquid discharge part which is the basic component part of the liquid discharge head in embodiment. It is sectional drawing which shows an example of the layer structure of the diaphragm of the piezoelectric actuator and the piezoelectric element in the liquid discharge head. It is a flowchart of forming a PLZT crystal film of the same piezoelectric element by a sol-gel method. It is a graph which shows the EDS analysis result of the PLZT crystal film prepared using the precursor liquid which has the same concentration ratio Zr / Ti. It is an SEM cross-sectional image (drawing substitute photograph) of the PLZT crystal film prepared using the precursor liquid having the same concentration ratio Zr / Ti. It is a schematic block diagram of the automatic film forming apparatus which forms the PLZT crystal film which concerns on embodiment. It is a schematic diagram which shows an example of the spinner coating apparatus in the automatic film forming apparatus. The schematic block diagram of the spinner coating apparatus adopted for the automatic film forming apparatus of this embodiment. It is an SEM cross-sectional image (drawing substitute photograph) of the PLZT crystal film produced by Example. A piezoelectric actuator using the PLZT crystal film obtained in the examples and a piezoelectric actuator using a PLZT crystal film prepared using a precursor solution having the same concentration ratio Zr / Ti, and displacement over time when repeatedly driven. It is a graph which shows the change of quantity. It is a plane explanatory view of the main part which shows an example of the apparatus which discharges a liquid. It is a side explanatory view of the main part which shows an example of a liquid discharge unit. It is explanatory drawing of the main part plane which shows the other example of a liquid discharge unit. It is a front explanatory view which shows still another example of a liquid discharge unit.

Hereinafter, an embodiment in which the present invention is applied to the manufacture of a ferroelectric film of a piezoelectric element used in a piezoelectric actuator in a liquid discharge head of an inkjet recording device as an image forming device which is a device for discharging a liquid will be described.

FIG. 1 is a schematic configuration diagram showing a configuration example of a liquid discharge unit 10 which is a basic component of a liquid discharge head in the present embodiment.
FIG. 2 is a cross-sectional view showing an example of the layer structure of the diaphragm of the piezoelectric actuator and the piezoelectric element in the liquid discharge head.

In FIG. 1, the liquid discharge unit 10 is a liquid chamber substrate (hereinafter referred to as a liquid chamber substrate) in which a nozzle plate 12 having a nozzle hole 11 for ejecting a liquid such as ink and a liquid chamber 13 communicating with the nozzle hole 11 and accommodating the liquid are formed. It is simply referred to as a "board") 14. Further, on the substrate 14, a diaphragm 15 formed by a predetermined film forming method and a piezoelectric element 16 as an electromechanical conversion element for pressurizing the liquid in the liquid chamber 13 via the diaphragm 15 are formed. It is provided. As shown in FIGS. 1 and 2, in the piezoelectric element 16, the lower electrode 161 as the first driving electrode on the substrate 14 side, the PLZT crystal film 163, and the PLZT crystal film 163 on the side opposite to the substrate 14 side are the first. An upper electrode 162 as a two-drive electrode is laminated. In the liquid discharge unit 10 of FIG. 1, a driving voltage having a predetermined frequency and amplitude is applied between the lower electrode 161 and the upper electrode 162 of the piezoelectric element 16. The piezoelectric element 16 to which this drive voltage is applied vibrates so as to deform the vibrating plate 15 between the substrate 14 and the piezoelectric element 16, and the liquid in the liquid chamber 13 is pressurized by the deformation of the vibrating plate 15. Then, the droplet can be discharged from the nozzle hole 11.

Next, a film forming method (method for producing the PLZT crystal film 163) for forming the PLZT crystal film 163 by the chemical solution deposition method (CSD method) will be described with reference to the drawings.
The sol-gel method, which represents the CSD method, is a weight having a metal-oxygen-metal (MO-M) bond by hydrolyzing an organic or inorganic compound of a metal in a solution and then advancing a polycondensation reaction. This is a method of producing ceramics by forming a coalescence and heating it. When the degree of polymerization of MOM is low, it is a liquid called "sol", but when polycondensation progresses, it becomes a solid called "gel". When a PLZT crystal film, which is a strong dielectric film, is to be produced by this sol-gel method, the metals forming the PLZT crystal, that is, the compounds of lead (Pb), lanthanum (La), zirconium (Zr), and titanium (Ti), respectively. Is hydrolyzed in one solution, followed by a polycondensation reaction, that is, a sol is prepared, which is applied onto a silicon wafer substrate on which a lower electrode is formed and heated. Incidentally, the sol serves as a precursor liquid for obtaining a PLZT crystal film.

FIG. 3 is a flowchart for forming a PLZT crystal film 163 by the sol-gel method.
On the electrode (lower electrode) on the silicon wafer substrate, a precursor liquid for forming a PLZT crystal film synthesized according to the composite oxide composition of the PLZT crystal film to be formed is applied by a spin coating method or the like, and the PLZT crystal film is applied. The precursor liquid coating film of No. 1 is formed on the substrate (coating step). The precursor liquid coating film of the PLZT crystal film is heated to the first heating temperature (drying temperature) to evaporate the solvent remaining in the coating film, and the dry film obtained by drying the precursor liquid coating film of the PLZT crystal film is obtained. Formed on a substrate (drying step). Then, the dry film is heated to a second heating temperature (pyrolysis temperature) higher than the first heating temperature (drying temperature) to decompose the organic components in the dry film, and the amorphous film of the composite oxide is placed on the substrate. Form (also referred to as a pyrolysis step or degreasing step). Next, the substrate is cooled to about room temperature (cooling step).

The steps of coating, drying, thermal decomposition, and cooling of the precursor liquid coating film are repeated a predetermined number of times (X times). After that, the amorphous film formed on the substrate is heated to a third heating temperature (crystallization temperature) higher than the second heating temperature (thermal decomposition temperature) to perform crystallization, and composite oxidation having ferroelectric properties is performed. Form a crystalline thin film of an object (crystallization step). By repeating such a coating step to a crystallization step a predetermined number of times (Y times), a PLZT crystal film having a desired thickness, which is a composite oxide crystal film, is formed on the lower electrode. By subjecting this to processing such as photolithography and etching, a target device such as a piezoelectric actuator element can be obtained.

The CSD method represented by the sol-gel method composed of the above-mentioned process flow can easily change and control the composition of the metal component in the precursor liquid applied on the substrate, thereby obtaining the metal component composition. It has the feature that the composition of the composite oxide crystal film and the characteristics as a piezoelectric element can be controlled. Therefore, even when forming a PLZT crystal film in which a part of lead (Pb) of the PZT crystal film is replaced with lanthanum (La) as in the present embodiment, a desired composition amount of the La compound is formed in the precursor liquid. A PLZT crystal film having a desired composition can be formed by preparing a precursor solution to which a component is added (the Pb compound component is reduced by that amount).

However, when a PLZT crystal film is formed by using such a CDS method, the characteristics as a piezoelectric element are improved as expected even though the PLZT crystal film having a desired composition is obtained. There wasn't. As a result of examining the cause, the composition of the entire PLZT crystal film obtained was as intended, and the added lanthanum (La) was distributed substantially uniformly throughout the PLZT crystal film. It was found that zirconium (Zr) and titanium (Ti) were not uniformly distributed in the film thickness direction of the PLZT crystal film. Then, it is concluded that the non-uniformity of the composition of the PLZT crystal film in this film thickness direction, particularly the non-uniformity of the concentration ratio Zr / Ti of zirconium (Zr) and titanium (Ti), hinders the expected effect. Got

The causes of non-uniformity of the composition of the PLZT crystal film in the film thickness direction (non-uniformity of the concentration ratio Zr / Ti) are as follows.
It is necessary to apply a piezoelectric crystal film (ferroelectric film) made of a composite oxide formed on a silicon wafer substrate to a piezoelectric element used for a liquid discharge head or the like to generate a required bending force. It is necessary to form a piezoelectric crystal film having a thickness (preferably a thickness of 1 to several μm). Here, in the CSD method consisting of a precursor liquid coating step, a drying step, a thermal decomposition step, and a crystallization step, the liquid of the precursor liquid charged into the process is a dry film, an amorphous film, and a crystal each time it passes through each step. It goes through a process that changes the state of the membrane with shrinkage of its volume. Therefore, when trying to obtain a thick piezoelectric film on the order of μm in one process flow, there arises a problem that innumerable cracks occur in the completed piezoelectric crystal film.

Therefore, when a piezoelectric crystal film having such a thickness is formed by the CSD method, a thin crystal film (crystal thin film) is formed on a silicon wafer substrate as if the coating to crystallization steps were repeated Y times in this embodiment. It is necessary to repeatedly form and stack the above to obtain a piezoelectric film having a thickness of, for example, about 1 μm. At this time, a CSD step of applying the precursor solution more than 10 times is set, and a piezoelectric film having a desired film thickness is formed by laminating a thin crystal thin film having a thickness of about 100 nm per application of the precursor solution. obtain.

Here, the non-uniformity of the concentration ratio Zr / Ti of the PLZT crystal film in the film thickness direction described above is remarkably observed in the vicinity of the laminated interface of the thin crystal film (crystal thin film) described above. Specifically, from the analysis results of Energy Dispersive X-ray Spectroscopy (EDS) shown in FIG. 4, in each layer of the crystal thin film, the concentration ratio Zr / Ti is high on the upper surface side thereof, and the lower surface side thereof. It has been confirmed that the concentration ratio Zr / Ti is low. As a result, at the interface between the crystal thin films, the upper surface having a high concentration ratio Zr / Ti and the lower surface having a low concentration ratio Zr / Ti are adjacent to each other, and the non-uniformity (discontinuity) of the concentration ratio Zr / Ti becomes remarkable. .. It should be noted that the region where such compositional non-uniformity (discontinuity of concentration ratio Zr / Ti) occurs is the "interface", which is indicated by the scanning electron microscope (SEM) shown in FIG. It is confirmed from the cross-sectional image of.

In the CSD method, as described above, the coating-thermal decomposition steps of the precursor liquid synthesized according to the desired piezoelectric film composition are repeated X times, and then the obtained laminated amorphous composite oxide is heated and crystallized. Let me. At that time, first, each metal atom constituting the amorphous composite oxide moves in the film by the heat energy supplied during the heating process of the crystallization step, and is coordinated at a predetermined position in the composite oxide crystal structure. Crystallize with. At this time, the ease of movement (movement speed) differs depending on the metal atom.

For example, comparing the titanium (Ti) atom and the zirconium (Zr) atom in the PLZT crystal film, the titanium atom moves faster than the zirconium atom during the reaction. Therefore, during the crystallization process, a crystal structure is formed at a timing earlier than the zirconium atom, in other words, at a lower temperature region, and then at a later timing than the titanium atom, in other words, at a higher temperature region, the zirconium atom. Formes a crystal structure and dissolves in the previously formed crystal structure containing titanium atoms. That is, the PLZT crystal film is a solid solution of lanthanum-added lead titanate and lead zirconate.

If the crystallization process of such a PLZT crystal film can be carried out over a long period of time, or if it can be carried out at a sufficiently high process temperature, a crystal structure containing a zirconium atom to be formed later is formed first. It is possible to sufficiently dissolve in the crystal structure containing the titanium atom to be formed, and as a result, the concentration ratio Zr / Ti can be made uniform in any region in the film thickness direction. However, when the crystallization process is usually carried out for a short time or at a relatively low temperature by using a rapid heat treatment (RTA) apparatus or the like, the crystallization process carried out at such a relatively low temperature for a short time is performed. It is difficult to make the concentration ratio Zr / Ti in the PLZT crystal film uniform in the film thickness direction.

If the PLZT crystal film is crystallized at an extremely high process temperature to compensate for the short crystallization process time, lead deficiency and lead at a level that cannot be compensated for by the effect of adding lantern (La). Oxygen defects due to the defects occur in the crystal film, impairing the piezoelectric properties. This is because the vapor pressure of the lead element is low, so that the heat applied in the crystallization step volatilizes the lead atom into the atmosphere, causing lead deficiency.

In the film formation process of the piezoelectric film made of the composite oxide by the CSD method in the present embodiment, as described above, the precursor liquid is applied on the lower electrode film (conductive layer), and the coating film is heated, dried and dried. The process of degreasing to form an amorphous composite oxide film is repeated X times to laminate the amorphous composite oxide film, and then crystallization is performed. Therefore, the lower surface of the laminated amorphous composite oxide laminated film in the crystallization step is in contact with the lower electrode film or the already crystallized composite oxide crystal film (PLZT crystal film), while the upper surface faces the air layer. is doing.

Since the vicinity of the lower surface can follow the crystal structure and atomic arrangement of the adjacent lower electrode film (usually a Pt film having a certain crystal structure or a conductive oxide film), the atoms in the amorphous composite oxide film can be imitated. Is easy to align and form a crystal structure. This is even easier when the lower surface is a composite oxide crystal film that has already been crystallized. On the other hand, in the vicinity of the upper surface in contact with the air layer, it is difficult for the atoms in the amorphous composite oxide film to align and form a crystal structure. Therefore, when the amorphous composite oxide film in contact with layers having completely different properties on the upper surface and the lower surface is heated and crystallized, the easiness of crystallization (the temperature at which crystallization is performed) differs. In the PLZT film (before crystallization) containing an substance, an oxide (titanium (Ti)) that is easier to crystallize (crystallizes at a lower temperature) is more easily crystallized in a region near the lower surface where crystallization is easy. Crystallization of (oxides containing) is promoted and occupies most of the region. On the other hand, oxides (oxides containing zirconium (Zr)) that are more difficult to crystallize (crystallize at a higher temperature) are crystallized at a later timing, so that in the region near the lower surface. A crystal structure cannot be formed so much, and it occupies most of the region near the upper surface where crystallization is performed at a relatively late timing.

As a result, when the crystallization step is repeated Y times by the CSD method and the PLZT crystal thin film of the Y layer is laminated to obtain a PLZT crystal film having a desired thickness, the PLZT crystal thin film laminated with the Y layer is used. In the region near the lower surface of each layer, the crystal structure containing titanium (Ti), which is relatively easy to crystallize, occupies a large amount, and in the region near the upper surface of each layer, the crystal structure containing zirconium (Zr), which is relatively difficult to crystallize, occupies a large amount. become.

Therefore, in the present embodiment, the step of forming the laminated amorphous film (precursor liquid) performed before each crystallization step of forming each layer of the PLZT crystal thin film (Y times until a desired PLZT crystal film is obtained). The coating to thermal decomposition steps are repeated X times.) The zirconate atoms contained in the amorphous layer on the lowest layer side (silicon wafer substrate side) that forms a region near the lower surface where titanium atoms segregate in each layer of the PLZT crystal thin film. (Increase the concentration ratio Zr / Ti) and decrease the amount of zirconate atoms contained in each layer of the amorphous layer laminated on it (increase the concentration ratio Zr / Ti). Adopted the method of Specifically, a plurality of types of precursor liquids having different concentration ratios Zr / Ti are prepared, and the amorphous film forming steps from the coating to the thermal decomposition step are repeatedly carried out by using the precursor liquids having the highest concentration ratio Zr / Ti in order.

As a result, the multi-layered amorphous film forming the PLZT crystal thin film has a higher concentration ratio Zr / Ti as the lower amorphous film (the amount of zirconium atoms is relatively larger), and the concentration ratio Zr / Ti increases toward the upper layer side. Is low (the amount of zirconium atoms is relatively low). Even when such a laminated amorphous film is put into the crystallization step, a phenomenon in which a large amount of titanium atoms are segregated in a region near the lower surface of the obtained PLZT crystal thin film and a large amount of zirconium atoms are segregated in a region near the upper surface, as in the normal case. However, in the amorphous layer located near the lower surface in advance, the number of titanium atoms is reduced (more zirconium atoms), and conversely, in the amorphous layer located near the upper surface, the number of zirconium atoms is reduced (more titanium atoms). Therefore, the segregation phenomenon in the crystallization step is canceled out, and a PLZT crystal thin film having improved composition uniformity in the film thickness direction can be obtained.

Then, the PLZT crystal film obtained by laminating the PLZT crystal thin films having improved composition uniformity in the film thickness direction by repeating such a process Y times is formed in spite of the fact that the film is formed by the CSD method. However, the composition uniformity in the film thickness direction is high, and the non-uniformity (discontinuity) of the concentration ratio Zr / Ti near the interface of the PLZT crystal thin film is eliminated, and the expected effect of the PLZT crystal film is good. Can be obtained.

Next, an automatic film forming apparatus 600 as a film forming apparatus (manufacturing apparatus) for the PLZT crystal film 163 in the embodiment will be described.
FIG. 6 is a schematic configuration diagram of an automatic film forming apparatus 600 for forming the PLZT crystal film 163 according to the present embodiment.
The automatic film forming apparatus 600 is a single-wafer type apparatus in which a silicon wafer substrate (not shown in FIG. 2) on which a lower electrode is formed is flowed one by one. The automatic film forming apparatus 600 includes a storage member 601 for accommodating the silicon wafer substrate, a conveying device 602 for transporting the silicon wafer substrate to each apparatus of the automatic film forming apparatus 600, a substrate delivery position, and positioning of the substrate in each apparatus. It is equipped with an aligner 603 for centering. Further, a spinner coating device 604 for coating the precursor liquid of the PLZT crystal film 163 on a silicon wafer substrate, a hot plate 605 for drying the applied precursor liquid coating film, a thermal decomposition step of the dried film, and a heat treatment for the crystallization step are performed. It is equipped with an RTA device 606 to perform. Further, it is provided with a cooling stage 607 that cools the wafer after the heat treatment in the RTA apparatus 606.

The silicon wafer substrate stored in the storage member 601 is transported by the transport device 602, and is positioned and centered by the aligner 603. After that, the transfer device 602 flows between the devices in charge of each process in the flowchart according to the flowchart of the film forming process shown in FIG.

The silicon wafer substrate positioned and centered by the aligner 603 is first charged into the spinner coating device 604 to be coated with the precursor liquid. Subsequently, the substrate on which the coating film of the precursor liquid is formed is put into the hot plate 605 by the transport device 602, and the coated precursor coating film is heated and dried. The silicon wafer substrate that has completed the drying step is put into the RTA device 606 by the transfer device 602, and the precursor drying film is heated and thermally decomposed. Subsequently, after repeating the above-mentioned coating step to thermal decomposition step a predetermined number of times (X times), a thin film was formed on the silicon wafer substrate (on the silicon wafer substrate) to a crystallization temperature higher than the thermal decomposition temperature by the RTA apparatus 606. The laminated amorphous film) is heated to crystallize it to form a PLZT crystal thin film.

Then, the PLZT crystal thin film is laminated and formed by repeating such a coating step to a crystallization step a predetermined number of times (Y times) to form a PLZT crystal film having a desired thickness, which is further processed. To obtain the target device such as a piezoelectric element.

FIG. 7 is a schematic view showing an example of the spinner coating device 604 used in the present embodiment.
The spinner coating device 604 rotates the spinner chuck 611 that sucks and holds the silicon wafer substrate 204, and the silicon wafer substrate 204 that is connected to the spindle motor and sucked and held by the spinner chuck 611 according to the program input to the control device. Consists of a pressurizing container 614 that stores the precursor fluid and pressurizes the precursor fluid with a pressurized gas, and a liquid feed line 617 that feeds the pressurized precursor fluid to a nozzle 616 mounted on the tip of the arm 615. ..

In the present embodiment, as a coating system from the pressure vessel 614 to the nozzle 616 for dropping the PLZT precursor liquid onto the silicon wafer substrate 204, the number of coating steps to thermal decomposition steps performed before the crystallization step ( It is equipped with X coating systems equivalent to (X times). In each of the pressure containers 614-1, 614-2, ..., 614-X, PLZT precursor liquids having different compositions among the pressure containers are stored. In the present embodiment, the coating system is switched by the coating system switching means for each X coating process performed before the crystallization step, and for each coating process (first, second ..., X). , PLZT precursor liquids having different composition components are used. Specifically, the PLZT precursor liquid to be applied for the first time has the highest concentration ratio Zr / Ti, and the PLZT precursor liquid in which the concentration ratio Zr / Ti is sequentially lowered as the number of coatings increases is dropped and applied onto the silicon wafer substrate 204. To obtain a PLZT thin film (before crystallization) of the X layer.

The PLZT thin film (before crystallization) of the X layer obtained by such a process cancels (supplements) the segregation phenomenon in the film thickness direction that occurs in the heating process in the crystallization step (before crystallization). Since the film is formed with different compositions (concentration ratio Zr / Ti), the composition uniformity in the film thickness direction is high, and good ferroelectric properties and piezoelectric properties can be obtained.

〔Example〕
Next, a PLZT crystal film 163 in which 8% of lead (Pb) of PZT (lead zirconate titanate), which is known to have the best ferroelectric properties and piezoelectric properties, is replaced with lanthanum (La) is applied as a base. An example of forming a film on the orientation control film of PT (lead titanate) by the CSD method will be described.

The PLZT crystal film 163 produced in this example is lead lanthanum-added lead zirconate titanate having a composition ratio of lead: lanthanum: zirconium: titanium = 92: 8: 60: 40, and has a general formula Pb _{(1-x). ) La x (Zr y Ti (} 1-y)) O 3 ( where, x = 0.08, is represented by the y = 0.60). The PLZT crystal film 163 of this example had a thickness of 2.0 μm, and was manufactured under the process conditions of X = 3 and Y = 24 in the flow chart of the film forming process shown in FIG.

Under the above process conditions, the lead: lanthanum: zirconium: titanium ratio in the precursor liquid is 110: 8: 66: 34 at X = 1 (application of the precursor liquid in the first process) and 110: 8 at X = 2. : 60:40, X = 3, 110: 8: 54: 46. The lead: lanthanum: zirconium: titanium = 92: 8: 60: 40 PLZT crystal film is formed, whereas the lead composition ratio in the precursor liquid is 110 because the precursor liquid is a silicon wafer substrate. This is the result of adding "excess lead" to compensate for the so-called "lead loss" that occurs during the heat treatment performed after dropping and coating on 204.

[Synthesis of precursor fluid]
In order to prepare the precursor solution having the PZT composition described above, lead acetate trihydrate, lanthanum acetate hydrate, zirconium propoxide, titanium isopropoxide was used as a starting material, and 2-methoxyethanol was used as a common solvent. , The following three types of precursor solutions (stock solutions) were synthesized.
(1) Precursor solution of lead: lanthanum: zirconium: titanium ratio = 110: 8: 66: 34 (Zr concentration + Ti concentration = 0.5 mol / L)
(2) Precursor solution of lead: lanthanum: zirconium: titanium ratio = 110: 8: 60: 40 (Zr concentration + Ti concentration = 0.5 mol / L)
(3) Precursor solution of lead: lanthanum: zirconium: titanium ratio = 110: 8: 54: 46 (Zr concentration + Ti concentration = 0.5 mol / L)

In the synthesis of the precursor solution described above, first, a predetermined amount of lead acetate trihydrate and lanthanum acetate hydrate are dissolved in 2-methoxyethanol for each of the above three types of precursor solutions, and then in a dry atmosphere. The mixture was heated at a solution temperature exceeding the boiling point (125 ° C.) of 2-methoxyethanol, preferably a solution temperature of 130 to 135 ° C. for 12 hours. During this period, the water of crystallization is distilled and dehydrated together with 2-methoxyethanol, and the reaction of replacing the acetic acid group of lead acetate and lanthanum acetate with the methoxyethoxy group of 2-methoxyethanol proceeds. Next, after the dehydration step of the lead acetate trihydrate and lanthanum acetate was completed, a predetermined amount of zirconium propoxide and titanium isopropoxide were added in a state where the solution temperature was lowered to 80 ° C. or lower, and 2 again. The mixture was heated at a solution temperature exceeding the boiling point (125 ° C.) of −methoxyethanol, preferably a solution temperature of 128 to 130 ° C. for 12 hours. During this period, an alcohol exchange reaction in which the propyl group of zirconium propoxide and the isopropyl group of titanium isopropoxide and the methoxyethoxy group of 2-methoxyethanol are substituted, and an esterification reaction between the acetate group and the alcohol group of lead acetate occur. These side reaction products are fractionated together with 2-methoxyethanol, and the polymerization reaction proceeds between the lead compound, the lanthanum compound and the zirconium compound, and the titanium compound in the solution. Then, when the reaction is completed, 2-methoxyethanol is added to the synthetic solution cooled to room temperature by stopping heating so as to have a predetermined concentration to complete the precursor solution.

[Film formation of PLZT crystal film]
The three types of precursor liquids synthesized as described above are set in the respective pressure containers 614-1, 614-2, 614-3 of the spinner coating device 604 shown in FIG. 7 (X = 3). Then, the silicon wafer substrate 204 housed in the storage member 601 of the automatic film forming apparatus 600 shown in FIG. 6 is first positioned and centered by the aligner 603 by the transport device 602, and then applied with a spinner. It is charged into the apparatus 604, and the coating system including the first pressure vessel 614-1 is operated to drop the precursor liquid (1) for the first time. Then, the spindle 612 is rotated at a maximum speed of 3000 rpm to form a coating film of the precursor liquid (1) on the silicon wafer substrate 204 (the coating step of X = 1 in the flowchart shown in FIG. 3).

Next, the silicon wafer substrate 204 on which the coating film of the precursor liquid (1) was formed was charged into the hot plate 605 heated to 140 ° C., which is higher than the boiling point of the main solvent, by the transfer device 602 for 1 minute, and the silicon wafer substrate was charged. A dry film is formed on the 204 (the drying step of X = 1 in the flowchart shown in FIG. 3).

Subsequently, the silicon wafer substrate 204 on which the dry film was formed was put into the RTA device 606 by the transfer device 602 and heated at a thermal decomposition temperature of 480 ° C. for 5 minutes to decompose organic components in the dry film, and 1 An amorphous film of the layer is obtained (the thermal decomposition step of X = 1 in the flowchart shown in FIG. 3).

After that, the silicon wafer substrate 204 on which the first layer amorphous film is formed is moved to the cooling stage 607 by the transfer device 602 and kept on the cooling stage 607 for 2 minutes or more to raise the temperature of the silicon wafer substrate 204. Cool to room temperature (cooling step of X = 1 in the flowchart shown in FIG. 3).

The process from the coating process to the cooling process as described above is repeated twice more (three times in total). However, in the second process, the precursor fluid (2) is used, and in the third process, the precursor fluid (3) is used. That is, the precursor liquid is dropped, coated, and dried so that the concentration ratio Zr / Ti is gradually reduced to obtain an amorphous film in which three layers are laminated.

Then, the silicon wafer substrate 204 on which the three-layer laminated amorphous film is formed is again put into the RTA device 606 by the transport device 602, heated at a crystallization temperature of 750 ° C. for 6 minutes, and the three-layer laminated amorphous film is collectively put together. To crystallize, a PLZT crystal thin film having a thickness of about 80 nm was obtained (the crystallization step of Y = 1 in the flowchart shown in FIG. 3). Further, the process from the coating step to the crystallization step as described above was repeated 24 times to obtain a PLZT crystal film having a thickness of about 2 μm.

FIG. 8 is a cross-sectional image of the cross section of the PLZT crystal film produced in this example taken by a scanning electron microscope (SEM). Comparing with the example shown in FIG. 5 using the precursor liquid having the same concentration ratio Zr / Ti, it can be seen that the interface between the PLZT crystal thin films is not recognized and a uniform composition is obtained in the film thickness direction. ..

FIG. 9 is a graph showing changes in the amount of displacement over time when the PLZT crystal film obtained in this example is further processed to produce a membrane vibrating element (piezoelectric actuator) and the membrane vibrating element (piezoelectric actuator) is repeatedly driven. ..
This graph also shows the results for the PLZT crystal film of the example shown in FIG. 5 (an example of a precursor solution having the same concentration ratio Zr / Ti). Comparing the two, in this example, in which the composition uniformity in the film thickness direction was improved, the decrease in the displacement amount with time was suppressed and the piezoelectricity was improved, as compared with the example in FIG. 5, in which the composition uniformity in the film thickness direction was poor. The durability of the actuator is high.

Next, an example of the device for discharging the liquid according to the present invention will be described with reference to FIGS. 10 and 11. FIG. 10 is a plan view of the main part of the device, and FIG. 11 is a side view of the main part of the device.

This device is a serial type device, and the carriage 403 is reciprocated in the main scanning direction by the main scanning moving 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 is bridged over the left and right side plates 491A and 491B to movably hold the carriage 403. Then, the carriage 403 is reciprocated in the main scanning direction by the main scanning motor 405 via the timing belt 408 bridged between the drive pulley 406 and the driven pulley 407.

The carriage 403 is equipped with a liquid discharge unit 440 in which the liquid discharge head 404 and the head tank 441 according to the present invention are integrated. The liquid discharge head 404 of the liquid discharge unit 440 discharges liquids of, for example, yellow (Y), cyan (C), magenta (M), and black (K). Further, the liquid discharge head 404 is mounted by arranging a nozzle array composed of a plurality of nozzles in the sub-scanning direction orthogonal to the main scanning direction and directing the discharge direction downward.

The liquid stored in the liquid cartridge 450 is supplied to the head tank 441 by the supply mechanism 494 for supplying the liquid stored outside the liquid discharge head 404 to the liquid discharge head 404.

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

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

The transport belt 412 attracts the paper 410 and transports it at a position facing the liquid discharge head 404. The transport belt 412 is an endless belt, and is hung between the transport roller 413 and the tension roller 414. Adsorption can be performed by electrostatic adsorption, air suction, or the like.

Then, the transport belt 412 orbits in the sub-scanning direction by rotationally driving the transport roller 413 via the timing belt 417 and the timing pulley 418 by the sub-scanning motor 416.

Further, on one side of the carriage 403 in the main scanning direction, a maintenance / recovery mechanism 420 for maintaining / recovering the liquid discharge head 404 is arranged on the side of the transport belt 412.

The maintenance / recovery mechanism 420 is composed of, for example, a cap member 421 that caps the nozzle surface (the surface on which the nozzle is formed) of the liquid discharge 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 / recovery mechanism 420, and the transport mechanism 495 are attached to a housing including the side plates 491A and 491B and the back plate 491C.

In this device configured in this way, the paper 410 is fed onto the transport belt 412 and sucked, and the paper 410 is transported in the sub-scanning direction by the orbital movement of the transport belt 412.

Therefore, by driving the liquid discharge head 404 in response to the image signal while moving the carriage 403 in the main scanning direction, the liquid is discharged to the stopped paper 410 to form an image.

As described above, since this device includes the liquid discharge head according to the present invention, it is possible to stably form a high-quality image.

Next, another example of the liquid discharge unit according to the present invention will be described with reference to FIG. FIG. 12 is an explanatory plan view of a main part of the unit.

This liquid discharge unit includes a housing portion composed of side plates 491A, 491B and a back plate 491C, a main scanning movement mechanism 493, a carriage 403, and a liquid among the members constituting the device for discharging the liquid. It is composed of a discharge head 404.

A liquid discharge unit may be configured in which at least one of the above-mentioned maintenance / recovery mechanism 420 and the supply mechanism 494 is further attached to, for example, the side plate 491B of the liquid discharge unit.

Next, still another example of the liquid discharge unit according to the present invention will be described with reference to FIG. FIG. 13 is a front explanatory view of the unit.

This liquid discharge unit includes a liquid discharge head 404 to which the flow path component 444 is attached, and a tube 456 connected to the flow path component 444.

The flow path component 444 is arranged inside the cover 442. A head tank 441 may be included instead of the flow path component 444. Further, a connector 443 that electrically connects to the liquid discharge head 404 is provided on the upper part of the flow path component 444.

In the present application, the "device for discharging a liquid" is a device provided with a liquid discharge head or a liquid discharge unit and driving the liquid discharge head to discharge the liquid. The device for discharging the liquid includes not only a device capable of discharging the liquid to a device to which the liquid can adhere, but also a device for discharging the liquid toward the air or the liquid.

The "device for discharging the liquid" may include means for feeding, transporting, and discharging paper to which the liquid can be attached, as well as a pretreatment device, a posttreatment device, and the like.

For example, as a "device that ejects a liquid", an image forming apparatus that ejects ink to form an image on paper, and a three-dimensional object (three-dimensional object) are formed in layers in order to form a three-dimensional object. There is a three-dimensional modeling device (three-dimensional modeling device) that discharges the modeling liquid into the powder layer.

Further, the "device for discharging a liquid" is not limited to a device in which a significant image such as characters and figures is visualized by the discharged liquid. For example, those that form patterns that have no meaning in themselves and those that form a three-dimensional image are also included.

The "liquid-attachable" means a liquid to which the liquid can adhere at least temporarily, such as one that adheres and adheres, and one that adheres and permeates. Specific examples include paper, recording paper, recording paper, film, recording media such as cloth, electronic substrates, electronic components such as piezoelectric elements, powder layers (powder layers), organ models, and media such as inspection cells. Yes, including anything to which the liquid adheres, unless otherwise specified.

The material of the "material to which liquid can adhere" is temporary liquid such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, building materials such as wallpaper and flooring, and textiles for clothing. However, it is sufficient if it can be attached.

The "liquid" also includes inks, treatment liquids, DNA samples, resists, pattern materials, binders, modeling liquids, or solutions and dispersions containing amino acids, proteins, and calcium.

Further, the "device for discharging the liquid" includes, but is not limited to, a device in which the liquid discharge head and the device to which the liquid can adhere move relatively. Specific examples include a serial type device that moves the liquid discharge head, a line type device that does not move the liquid discharge head, and the like.

In addition, as a "device for ejecting liquid", a treatment liquid coating device for ejecting a treatment liquid to the paper in order to apply the treatment liquid to the surface of the paper for the purpose of modifying the surface of the paper, raw materials. There is an injection granulation device that granulates fine particles of raw materials by injecting a composition liquid in which the above-mentioned material is dispersed in a solution through a nozzle.

The "liquid discharge unit" is a liquid discharge head integrated with functional parts and a mechanism, and is an aggregate of parts related to liquid discharge. For example, the "liquid discharge unit" includes a combination of at least one of a head tank, a carriage, a supply mechanism, a maintenance / recovery mechanism, and a main scanning movement mechanism with a liquid discharge head.

Here, "integration" means, for example, a liquid discharge head and a functional component, a mechanism in which the mechanism is fixed to each other by fastening, adhesion, engagement, etc., or one in which one is movably held with respect to the other. include. Further, the liquid discharge head, the functional parts, and the mechanism may be detachably attached to each other.

For example, as a liquid discharge unit, there is a liquid discharge head and a head tank integrated, such as the liquid discharge unit 440 shown in FIG. In addition, there are cases in which the liquid discharge head and the head tank are integrated by being connected to each other by a tube or the like. Here, a unit including a filter can be added between the head tank of these liquid discharge units and the liquid discharge head.

Further, as a liquid discharge unit, there is a liquid discharge head and a carriage integrated.

Further, as a liquid discharge unit, there is a liquid discharge head in which the liquid discharge head and the scanning movement mechanism are integrated by holding the liquid discharge head movably by a guide member forming a part of the scanning movement mechanism. Further, as shown in FIG. 12, there is a liquid discharge unit in which a liquid discharge head, a carriage, and a main scanning movement mechanism are integrated.

Further, as a liquid discharge unit, there is a carriage to which a liquid discharge head is attached, in which a cap member which is a part of the maintenance / recovery mechanism is fixed, and the liquid discharge head, the carriage, and the maintenance / recovery mechanism are integrated. ..

Further, as a liquid discharge unit, as shown in FIG. 13, a tube is connected to a liquid discharge head to which a head tank or a flow path component is attached, and the liquid discharge head and a supply mechanism are integrated. ..

The main scanning movement mechanism shall also include a single guide member. Further, the supply mechanism includes a single tube and a single loading unit.

Further, the pressure generating means used for the "liquid discharge head" is not limited. For example, in addition to the piezoelectric actuator (which may use a laminated piezoelectric element) as described in the above embodiment, it is composed of a thermal actuator using an electrothermal conversion element such as a heat generating resistor, a vibrating plate, and a counter electrode. An electrostatic actuator or the like may be used.

In addition, image formation, recording, printing, printing, printing, modeling, etc. in the terms of the present application are all synonymous.

What has been described above is an example, and each of the following aspects produces a unique effect.
(Aspect A)
The method of manufacturing a ferroelectric film for forming a ferroelectric film on a substrate such as a silicon wafer substrate 204 using a chemical solution deposition method such as the sol-gel technique, the general formula _{Pb (1-x) La x} (Zr y As a precursor liquid of a PLZT crystal film, which is a ferroelectric film of a perovskite-type crystal represented by _{Ti (1-y)} ) O _{3 (0 <x ≦ 0.08, 0.55 ≦ y ≦ 0.65),} After laminating a plurality of amorphous layers using a zirconium (Zr) and titanium (Ti) having a lower concentration ratio Zr / Ti as the upper layer, a step of crystallizing the plurality of amorphous layers is carried out. It is characterized by forming a ferroelectric film.
The PZT crystal film (ferroelectric film) generally used as a piezoelectric material for a piezoelectric element has a problem that a so-called fatigue phenomenon occurs in which the piezoelectric characteristics gradually deteriorate due to the repeated operation of the piezoelectric element. Various mechanisms have been considered for the cause of this fatigue phenomenon, but one of the most promising causes is "lead deficiency" existing in the crystal of the PZT crystal film, and it is caused by lead deficiency. Examples include "oxygen defects" in the crystal that occur to eliminate the charge imbalance in the crystal.
As a method for eliminating such defects due to lead deficiency and oxygen deficiency, Pb ions are added to a part of the site (a site of the perovskite crystal structure) in which lead (Pb) ions in the crystal of the PZT crystal film are coordinated. A method of substituting with another metal ion having a close ionic radius and a valence higher than that of Pb ion (+2) is known.
The present inventors consider La ion (+3) as a promising metal ion to be substituted, and a method of substituting a part of lead (Pb) in the crystal of the PZT crystal film with lanthanum (La) is ferroelectric. We are studying the realization by a chemical solution deposition method (CSD method) such as the sol-gel method and the MOD method, which are known as simple and inexpensive film forming methods for body membranes. However, even if an attempt is made to form a PLZT crystal film in which a part of lead (Pb) of the PZT crystal film is replaced with lanthanum (La) by using a usual chemical solution deposition method, the expected effect cannot be sufficiently obtained. It has been found.
As a result of examining the cause, as described above, the composition of the entire PLZT crystal film obtained was as intended, and the added lantern (La) was distributed substantially uniformly throughout the PLZT crystal film. Was. However, it was found that zirconium (Zr) and titanium (Ti) were not uniformly distributed in the film thickness direction of the PLZT crystal film. Specifically, it was confirmed that the PLZT crystal film formed by the chemical solution deposition method had a higher concentration ratio Zr / Ti as it was closer to the upper surface in the stacking direction. This is because, in the crystallization step, the region closer to the lower surface of the PLZT crystal film has a relatively large number of titanium atoms, and the region closer to the upper surface has a relatively large amount of zirconium atoms segregated. Then, it was concluded that the expected effect of the PLZT crystal film was inhibited due to the non-uniformity of the concentration ratio Zr / Ti.
Therefore, tables in the present embodiment, the general formula _{Pb (1-x) La x} (Zr y Ti (1-y)) O 3 (0 <x ≦ 0.08,0.55 ≦ y ≦ 0.65) In forming the PLZT crystal film, which is a ferroelectric film of the perovskite type crystal, a plurality of amorphous layers are laminated and then crystallized, and as a precursor liquid used when forming each layer of the amorphous layer. , The density ratio Zr / Ti is lower as the upper amorphous layer is used. As a result, in the plurality of amorphous layers constituting the PLZT film (before crystallization), the lower amorphous layer has a higher concentration ratio Zr / Ti, and the upper amorphous layer has a lower concentration ratio Zr / Ti. ..
Even when crystallizing such a plurality of amorphous layers, a phenomenon occurs in which the region closer to the lower surface of the PLZT film has a relatively large number of titanium atoms, and the region closer to the upper surface has a relatively large number of zirconium atoms segregated. However, in this embodiment, as described above, the amorphous layer located in the region near the lower surface has relatively few titanium atoms (relatively many zirconium atoms), and conversely, the amorphous layer located in the region near the upper surface. The layer has relatively few zirconium atoms (relatively many titanium atoms). Therefore, the segregation phenomenon in the crystallization step is canceled out, and a PLZT crystal film having improved composition uniformity in the film thickness direction can be obtained.

(Aspect B)
In the aspect A, a series of steps including a coating step of applying the precursor liquid, a drying step of drying the applied precursor liquid, and a thermal decomposition step of thermally decomposing the precursor dry film obtained by drying are repeated a plurality of times. , The present invention is characterized in that the plurality of amorphous layers are laminated.
According to this, it is possible to easily prepare a plurality of laminated amorphous layers by using a precursor liquid having a concentration ratio Zr / Ti lower in the upper layer.

(Aspect C)
In the aspect A or B, the ferroelectric film is formed on a substrate on which a lower electrode 161 of a piezoelectric element is formed.
According to this, it is possible to manufacture a piezoelectric element using a PLZT crystal film having improved composition uniformity in the film thickness direction, and it is possible to obtain a highly durable piezoelectric element. The ferroelectric film is not limited to the case where the ferroelectric film is directly formed on the lower electrode 161 of the piezoelectric element, but the ferroelectric film is formed on the lower electrode 161 via the orientation control film. May be good.

(Aspect D)
A general formula Pb _(1- coating a precursor solution of the perovskite-type crystal represented by _{x) La x (Zr y Ti} (1-y)) O 3 (0 <x ≦ 0.08,0.55 ≦ y ≦ 0.65) on a substrate Coating means such as a coating system including a pressurized container 614, an arm 615, and a nozzle 616, and coating for changing the concentration ratio Zr / Ti of zirconium (Zr) and titanium (Ti) in the precursor liquid to be coated by the coating means. It has a precursor liquid changing means such as a system switching means, and after laminating a plurality of amorphous layers using a precursor liquid having a concentration ratio Zr / Ti lower in the upper layer, the plurality of amorphous layers are crystallized. , The ferroelectric film is formed.

11 Nozzle hole 12 Nozzle plate 13 Liquid chamber 14 Liquid chamber substrate 15 Vibration plate 16 Piezoelectric element 161 Lower electrode 162 Upper electrode 163 PLZT Crystal film 204 Silicon wafer substrate 600 Automatic film forming device 601 Storage member 602 Conveyor device 603 Aligner 604 Spinner coating device 605 Hot plate 606 RTA device 607 Cooling stage 611 Spinner chuck 612 Spindle 614 Pressurized container 615 Arm 616 Nozzle 617 Liquid transfer line

Japanese Unexamined Patent Publication No. 2015-65430

Claims (3)

In a method for producing a ferroelectric film, which forms a ferroelectric film on a substrate by using a chemical solution deposition method.
Strong perovskite crystal represented by the general formula _{Pb (1-x) La x} (Zr y Ti (1-y)) O 3 (0 <x ≦ 0.08,0.55 ≦ y ≦ 0.65) As a precursor liquid for the dielectric film, a plurality of amorphous layers are formed by using a solution in which the concentration ratio Zr / Ti of zirconium (Zr) and titanium (Ti) is lower in the upper layer as long as the magnitude relationship between Zr and Ti is maintained. A method for producing a ferroelectric film, which comprises repeatedly performing a lamination / crystallization step of crystallizing the plurality of amorphous layers after laminating to form the ferroelectric film. In the method for producing a ferroelectric film according to claim 1,
A series of steps including a coating step of applying the precursor liquid, a drying step of drying the applied precursor liquid, and a thermal decomposition step of thermally decomposing the precursor dry film obtained by drying are repeated a plurality of times to obtain the plurality of layers. A method for producing a ferroelectric film, which comprises laminating amorphous layers. In the method for producing a ferroelectric film according to claim 1 or 2.
A method for producing a ferroelectric film, which comprises forming the ferroelectric film on a substrate on which a lower electrode of a piezoelectric element is formed .

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