JP6268966B2 - Method for forming ferroelectric film, electronic device, electronic device - Google Patents

Description

  The present invention relates to a method for forming a ferroelectric film, an electronic device including a ferroelectric film, and an electronic apparatus including the electronic device.

  An ink jet recording head in which a part of a pressure chamber communicating with a nozzle opening for discharging ink is constituted by a vibration plate, and the vibration plate is deformed by a piezoelectric element to pressurize ink in the pressure chamber and discharge ink from the nozzle opening. It has been known. Piezoelectric elements used in ink jet recording heads include those that expand and contract in the axial direction of the piezoelectric elements and those that use flexural forces. The piezoelectric films in piezoelectric elements that use flexural forces include zircon titanate. A ferroelectric film made of an oxide crystal film such as lead acid (PZT) is used.

  Such a ferroelectric film is formed on a silicon wafer substrate on which a lower electrode is formed by a CSD method (Chemical Solution Deposition) such as a sputtering method, a sol-gel method, or a MOD method. In the CSD method, it is possible to easily change and control the (metal) component composition in the precursor liquid to be coated on the substrate, thereby improving the composition of the obtained oxide crystal film and the characteristics as a ferroelectric film. It has controllable features.

  In addition, as a material for the lower electrode formed on the silicon wafer substrate, it has stability in a high temperature environment where it is exposed in the subsequent CSD process, and good conductivity required for the electrode. For this reason, noble metals or noble metal oxides such as platinum and iridium, especially platinum are usually employed.

  The platinum film used for the lower electrode is usually a polycrystalline film preferentially oriented in the (111) plane, and a ferroelectric film made of oxide crystals grown on the platinum film is quite preferentially oriented. Or a film with the same (111) preferential orientation as the lower electrode made of platinum by devising the film formation process.

  On the other hand, when the above ferroelectric film is used for a piezoelectric element used in an ink jet recording head or the like, if the (100) plane of the oxide crystal forming the ferroelectric film is preferentially crystallized, The ferroelectric film has the largest e31 piezoelectric constant. Therefore, it is preferable to form a (100) preferentially oriented oxide crystal ferroelectric film on the lower electrode.

  In order to form a (100) preferentially oriented ferroelectric crystal film on the lower electrode, for example, a (100) oriented orientation control layer is preliminarily formed on the lower electrode as a base of the ferroelectric film. A film is formed and crystallized. Then, a ferroelectric film may be formed on the crystallized orientation control layer and crystallized. Further, in order to increase the thickness of the ferroelectric film (crystal film), the process of forming a ferroelectric film thereon and crystallizing it may be repeated. In this case, as the orientation control layer, for example, a ferroelectric material having the same component as the material for forming the ferroelectric film can be used (see, for example, Patent Documents 1 and 2).

  However, the above method has a problem that the crystal orientation of the oxide crystal forming the obtained ferroelectric film is lowered as the thickness of the ferroelectric film is increased. This problem is particularly high when applied to the formation of a ferroelectric film (film thickness: approximately 1 μm to 2 μm) applied to a piezoelectric element used in an ink jet recording head or the like (compared to an electronic device such as FeRAM). ) It becomes very thick and appears prominently.

  Such a problem occurs for the following reason. That is, since the element types or composition ratios of the lower electrode, the orientation control layer, and the ferroelectric film are different, the lattice constants of the crystal lattices forming the layers are different. Therefore, crystal lattice mismatch occurs at the interface between the lower electrode and the orientation control layer and between the orientation control layer and the ferroelectric film. This crystal lattice mismatch causes strain and stress at the interface between the layers.

  The strain and stress generated at the interface between the layers increase as the thickness of the ferroelectric film is increased by stacking the ferroelectric film on the orientation control layer by the CSD process. And this distortion and stress become a factor which inhibits that the crystal orientation of the oxide crystal which forms a ferroelectric film aligns (it reduces orientation). Therefore, it becomes difficult to obtain a ferroelectric film of oxide crystal having a good orientation, particularly when a thick ferroelectric film applied to a piezoelectric element used in an ink jet recording head or the like is formed. . Furthermore, the interface between the orientation control layer and the ferroelectric film in which there is a crystal lattice mismatch is easily broken mechanically.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a method for forming a ferroelectric film having good crystal orientation using a chemical solution deposition method.

The method for forming a ferroelectric film is a method for forming a ferroelectric film using a chemical solution deposition method, the step of forming an amorphous orientation control layer, and the amorphous orientation Forming an amorphous ferroelectric film in contact with the control layer; and simultaneously crystallizing the amorphous orientation control layer and the amorphous ferroelectric film. Then, the thickness of the crystallized orientation control layer is 1/3 to 1/2 of the thickness of the crystallized ferroelectric film, and the crystallized orientation control layer is crystallized. It is necessary to include a ferroelectric material having the same crystal structure as that of the ferroelectric film and having a different composition ratio of constituent elements.

  According to the disclosed technology, it is possible to provide a method for forming a ferroelectric film having good crystal orientation using a chemical solution deposition method.

It is an example of the flowchart explaining the film-forming method by CSD method (chemical solution deposition method). It is a figure which illustrates the automatic film-forming apparatus which forms a ferroelectric film. It is an example of the flowchart which shows the film-forming method of the ferroelectric film which concerns on 1st Embodiment. It is a figure explaining the coupling | bonding of a crystal lattice. It is a figure explaining the mismatch of a crystal lattice. 6 is a cross-sectional view (part 1) illustrating a droplet discharge head using an electromechanical transducer. FIG. 6 is a cross-sectional view (part 2) illustrating a droplet discharge head using an electromechanical transducer. FIG. It is a perspective view which illustrates the inkjet recording device which concerns on 3rd Embodiment. It is a side view which illustrates the mechanism part of the inkjet recording device which concerns on 3rd Embodiment. It is a figure explaining film-forming of the ferroelectric film which concerns on a present Example. It is a figure which illustrates the result of having analyzed Pb, Zr, and Ti composition in the integrated crystal film by dynamic SIMS. It is a figure which illustrates the X-ray-diffraction result of the ferroelectric film which concerns on a present Example.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First Embodiment>
First, a film forming method by the CSD method (chemical solution deposition method) will be described. FIG. 1 is a flowchart for explaining a film forming method by the CSD method. In the case of forming a (composite) oxide crystal film, which is a ferroelectric film, by the CSD method, first, a precursor solution that matches the composition of the oxide is synthesized. Then, in step S1 of the flowchart of FIG. 1, a coating film of the precursor liquid is formed on the silicon wafer substrate on which the lower electrode, which is a conductive film, is formed by a technique such as spin coating (application process).

  Next, in step S2, the silicon wafer substrate having the precursor liquid coating film formed on the lower electrode is heated to the first heating temperature (drying temperature) to evaporate the solvent in the coating film and dry it. A body dry film is formed (drying step).

  Next, in step S3, the precursor dry film is heated to a second heating temperature (thermal decomposition temperature) higher than the first heating temperature to decompose and burn organic components in the precursor dry film, and thereby the oxide. An amorphous film is obtained (thermal decomposition process or degreasing process). Next, in step S4, the amorphous film is cooled (cooling process).

  Subsequently, the cooling process shown in step S4 is repeated a predetermined number of times (X times: X ≧ 1) from the coating process shown in step S1. Thereafter, in step S5, the amorphous film formed on the silicon wafer substrate is heated up to a third heating temperature (crystallization temperature) higher than the thermal decomposition temperature to perform crystallization, and has ferroelectric characteristics. An oxide crystal film is formed (crystallization process). Next, in step S6, the oxide crystal film is cooled (cooling process).

  Subsequently, steps S1 to S4 are repeated a predetermined number of times (X times), and then steps S5 and S6 are repeated a predetermined number of times (Y times: Y ≧ 1) to stack an oxide crystal film and have a desired thickness. A (thickened) ferroelectric film is formed on the silicon wafer substrate. Then, an upper electrode as a conductive film is formed on the ferroelectric film on the obtained silicon wafer substrate, and fine processing such as photolithography / etching is performed to obtain a target piezoelectric element (piezoelectric actuator element), etc. Get the device.

  Next, a method for forming a ferroelectric film according to the present embodiment will be described. First, an automatic film forming apparatus for forming a ferroelectric film will be described with reference to FIG. 2. Next, a method for forming a ferroelectric film according to the present embodiment will be described with reference to FIG. explain.

  FIG. 2 is a diagram illustrating an automatic film forming apparatus for forming a ferroelectric film. The automatic film forming apparatus 10 is an apparatus for forming a ferroelectric film by the film forming method according to the present embodiment. More specifically, the automatic film forming apparatus 10 is, for example, a single-wafer type apparatus that flows the silicon wafer substrates 19 on which the lower electrode is formed one by one, and includes a storage member 11, a transfer device 12, and an aligner 13. A spinner coating device 14, a hot plate 15, an RTA (Rapid Thermal Annealing) device 16, and a cooling stage 17.

  The storage member 11 is a member that stores the silicon wafer substrate 19. The transfer device 12 is a device that transfers the silicon wafer substrate 19 to each device in the automatic film forming apparatus 10. The aligner 13 is a device for delivering and positioning the silicon wafer substrate 19 in the automatic film forming apparatus 10 and positioning and centering the silicon wafer substrate 19 in each apparatus constituting the automatic film forming apparatus 10.

  The spinner coating device 14 is a device having a mechanism (not shown) for individually controlling the ferroelectric film precursor liquid and the alignment control layer precursor liquid and applying the liquid onto the silicon wafer substrate 19. The hot plate 15 is an apparatus for drying the applied precursor liquid coating. The RTA apparatus 16 is an apparatus that performs heat treatment in the thermal decomposition process and the crystallization process of the precursor dry film. The cooling stage 17 is an apparatus that cools the silicon wafer substrate 19 after the heat treatment in the RTA apparatus 16.

  The silicon wafer substrate 19 stored in the storage member 11 is first positioned and centered by the aligner 13 by the transfer device 12, and then takes charge of each step in the flowchart according to the flowchart shown in FIG. Flows between each device.

  In the present embodiment, the thermal decomposition step and the crystallization step are performed by a common (one) RTA apparatus 16, but the present invention is not limited to this. For example, the pyrolysis step and the crystallization step may be performed by separate (two) RTA apparatuses. Alternatively, the pyrolysis process may be performed with a high-temperature hot plate different from that for the drying process, and the crystallization process may be performed with an RTA apparatus.

FIG. 3 is an example of a flowchart showing a method of forming a ferroelectric film according to the first embodiment. Examples of the ferroelectric material used for forming the ferroelectric film according to the present embodiment include perovskite structure oxidation such as barium titanate, lead titanate, lead zirconate titanate, and lead lanthanum zirconate titanate. Material can be selected. In particular, lead perovskites such as lead zirconate titanate (hereinafter also referred to as PZT; PbZr _x Ti _1-x O ₃ (x is an integer of 0 to 1 or a decimal)) having extremely good ferroelectricity and piezoelectric properties. A complex oxide having a structure can be preferably selected. However, it is possible to select an oxide other than the perovskite structure.

  The ferroelectric material used for forming the orientation control layer according to the present embodiment can be appropriately selected from the ferroelectric materials used for forming the ferroelectric film. That is, the ferroelectric material used for forming the orientation control layer according to the present embodiment has the same crystal structure as that of the ferroelectric material used for forming the ferroelectric film, and the composition ratio of the constituent elements. Different ferroelectric materials can be selected.

  In the present embodiment, PZT is adopted from among the above as the material of the ferroelectric film, and tetragonal titanium that is easily (100) oriented with an oxide having the same lead-based perovskite structure as PZT as the material of the orientation control layer. The following description will be given by taking lead acid (PT) as an example. Lead titanate (PT) is a ferroelectric material having the same crystal structure as lead zirconate titanate (PZT) and having a different composition ratio of constituent elements (Z composition ratio is zero).

  First, in step S21 of the flowchart of FIG. 3, a precursor liquid (PT precursor liquid) synthesized for forming an orientation control layer is applied on the lower electrode of the silicon wafer substrate 19 on which the lower electrode is formed. Note that the concentration of the precursor liquid (PT precursor liquid) is adjusted so that the desired composition and the thickness of the film formed by a single film formation flow become the desired thickness.

  Specifically, the silicon wafer substrate 19 on which the lower electrode housed in the housing member 11 of the automatic film forming apparatus 10 is formed is taken out by the transfer device 12 and placed in the aligner 13. Positioning and centering are performed. Then, the silicon wafer substrate 19 positioned and centered by the aligner 13 is loaded into the spinner coating device 14 by the transport device 12. And the precursor liquid synthesize | combined for alignment control layer film-forming on a lower electrode with the spinner coating device 14 is apply | coated by spin coating, and the coating film of a precursor liquid is formed into a film.

  A silicon wafer substrate is preferably used as the substrate, but a substrate made of magnesium oxide, stainless steel, alumina, glass, or the like can be used instead of the silicon wafer substrate. The thickness of the substrate is not particularly limited, but is preferably determined in consideration of the film forming process of the ferroelectric film and handling properties in the subsequent processing process.

  In addition, in order to provide a metal or metal oxide lower electrode on a substrate (if an insulating layer or an adhesion layer is provided on the substrate), a known method such as vacuum deposition, sputtering, or ion plating is used. Is adopted. Although there is no restriction | limiting in particular also about the film thickness of a lower electrode, Usually, about 0.05-1 micrometer, Preferably it is about 0.1-0.5 micrometer.

  As a material of the lower electrode, for example, a noble metal such as platinum, gold, iridium or an oxide thereof can be used. In addition, an oxide electrode such as LNO or SRO formed on the lower electrode may be used. Note that platinum is particularly preferably used as the lower electrode.

  The orientation control layer includes a ferroelectric material having the same crystal structure as that of the ferroelectric film and having a different composition ratio of constituent elements. In other words, the material used for the orientation control layer is an oxide having the same crystal structure as the (composite) oxide that forms the ferroelectric film formed thereon, and a composition ratio different from that of the ferroelectric film material. An oxide material having the following is employed.

  In addition, the orientation control layer (crystal film) is 1/3 of the ferroelectric film (crystal film) obtained by drying, pyrolysis and crystallization of the coating film obtained by applying the precursor liquid once by the CSD method. The thickness is equivalent to 1/2. That is, the thickness of the orientation control layer (crystal film), which is typically about 5 nm and at most about 10 nm, is set to a thickness of about 30 to 50 nm when the orientation control layer is crystallized alone.

  Next, in step S22, the coating film of the precursor liquid for forming the orientation control layer formed on the lower electrode is dried. Specifically, a silicon wafer substrate 19 having a coating film of a precursor liquid for forming an orientation control layer formed on the lower electrode is placed on the hot plate 15 by the transport device 12, and the precursor liquid is applied by the hot plate 15. The precursor is dried to form the orientation control layer by heating and drying the film. The temperature of drying can be about 100-150 degreeC, for example.

  Next, in step S23, thermal decomposition (formation of an amorphous film) of the precursor dry film for forming the orientation control layer is performed. Specifically, the silicon wafer substrate 19 on which the precursor dry film for forming the orientation control layer is formed is loaded into the RTA apparatus 16 by the transfer device 12, and the precursor dry film is heated and pyrolyzed by the RTA apparatus 16. Then, an amorphous film of orientation control layer material (PT) is formed on the lower electrode. The temperature of thermal decomposition can be about 250-500 degreeC, for example.

  Next, in step S24, the silicon wafer substrate 19 in which the amorphous film of the orientation control layer material is formed on the lower electrode is transferred to the cooling stage 17 and cooled to room temperature.

  Next, in step S25, a ferroelectric film precursor liquid (PZT precursor liquid) is applied on the amorphous film of the orientation control layer material. Note that the concentration of the precursor liquid (PZT precursor liquid) is adjusted so that the desired composition and the thickness of the film formed in a single film formation flow become the desired thickness. Specifically, the silicon wafer substrate 19 on which the amorphous film of the orientation control layer material is formed is put into the spinner coating device 14 from the cooling stage 17 via the aligner 13. Then, the precursor liquid of the ferroelectric film is applied by spin coating on the amorphous film of the orientation control layer material by the spinner coating device 14 to form a coating film of the precursor liquid.

  Next, in step S26, the coating film of the precursor liquid of the ferroelectric film formed on the amorphous film is dried. Specifically, a silicon wafer substrate 19 having a ferroelectric film precursor liquid coating film formed on an amorphous film is loaded onto a hot plate 15 by a transfer device 12, and the precursor liquid coating film is formed on the hot plate 15. A precursor dry film of a ferroelectric film is formed by performing a heating / drying process. The temperature of drying can be about 100-150 degreeC, for example.

  Next, in step S27, pyrolysis (formation of an amorphous film) of the precursor dry film of the ferroelectric film is performed. Specifically, the silicon wafer substrate 19 on which the ferroelectric film precursor dry film is formed is loaded into the RTA apparatus 16 by the transfer apparatus 12. Then, the precursor dry film is heated and pyrolyzed by the RTA apparatus 16 to form a laminated amorphous film in which the amorphous film of the ferroelectric film material (PZT) is laminated on the amorphous film of the orientation control layer material (PT). Form. The temperature of thermal decomposition can be about 250-500 degreeC, for example.

  Next, in step S28, the silicon wafer substrate 19 in which the amorphous film of the ferroelectric film material is laminated on the amorphous film of the orientation control layer material is transferred to the cooling stage 17 and cooled to room temperature.

  Next, in step S29, the laminated amorphous film in which the amorphous film of the ferroelectric film material is laminated on the amorphous film of the orientation control layer material is crystallized. Specifically, the silicon wafer substrate 19 on which the laminated amorphous film is formed is put into the RTA apparatus 16 by the transfer device 12 and is continuously heated at a higher temperature to crystallize the laminated amorphous film.

  That is, the amorphous film of the orientation control layer material on the lower electrode and the amorphous film of the ferroelectric film material formed thereon are simultaneously crystallized. Thereby, the amorphous film of the orientation control layer material becomes an orientation control layer (crystal film), and the amorphous film of the ferroelectric film material becomes a ferroelectric film (crystal film). The crystallization temperature can be, for example, about 600 to 750 ° C.

As described above, in the first embodiment, the CSD method is used to crystallize the amorphous orientation control layer simultaneously with the amorphous ferroelectric film laminated thereon. This is because in the CSD method, the composition of the film to be formed can be easily controlled, and the orientation can be easily controlled by appropriately adjusting the temperature at which the thermal decomposition and crystallization are performed during the film formation. In addition, it is advantageous in that the orientation control layer can be formed by a one-step process.
Next, the silicon wafer substrate 19 in which the orientation control layer (crystal film) and the ferroelectric film (crystal film) are laminated on the lower electrode is cooled again to room temperature by the cooling stage 17, and then the conventional method shown in FIG. According to the process flow by the CSD method, the inside of the automatic film forming apparatus 10 flows.

  That is, the cooling process shown in step S4 is repeated a predetermined number of times (X times) from the coating process shown in step S1. Then, in step S5, the amorphous film formed on the silicon wafer substrate 19 is heated up to a third heating temperature (crystallization temperature) higher than the thermal decomposition temperature, and crystallization is performed. An oxide crystal film is formed (crystallization step). Next, in step S6, the oxide crystal film is cooled (cooling process).

  Subsequently, after repeating steps S1 to S4 a predetermined number of times (X times) and then repeating steps S5 and S6 a predetermined number of times (Y times), an oxide crystal film is stacked and has a desired thickness. A ferroelectric film is formed on the silicon wafer substrate 19.

  Then, a conductive film to be an upper electrode is formed on the ferroelectric film on the obtained silicon wafer substrate 19. The upper electrode can be formed by a known method such as vacuum deposition, sputtering, or ion plating. Although there is no restriction | limiting in particular about the film thickness of an upper electrode, For example, it is about 0.05-1 micrometer, Preferably it is about 0.1-0.5 micrometer.

  Furthermore, by putting the ferroelectric film on which the upper electrode is formed into a post-processing process (a fine processing process such as photolithography / etching), it can be processed into various electronic elements such as sensors and piezoelectric elements. The performance of various electronic devices obtained by processing the ferroelectric film formed by the film forming method according to the present embodiment is the crystal orientation (orientation) in which the characteristics required for the ferroelectric film are the best. Since it is preferentially oriented in the same crystal orientation as that of the control layer, good performance can be exhibited.

  Here, the specific effect of the film forming method according to the first embodiment will be described in more detail. As described above, in the method of forming the orientation control layer on the lower electrode and forming the ferroelectric film of the composite oxide crystal on the lower electrode, as the thickness of the ferroelectric film increases, There is a problem that the orientation of the oxide crystal forming the ferroelectric film is lowered. This will be described in detail.

  It is known that device characteristics such as piezoelectric elements exhibit good device characteristics when the crystal orientation of the (composite) oxide crystal forming the ferroelectric film is aligned in a certain direction (single orientation). . However, crystal orientations exhibiting good characteristics differ depending on required device characteristics such as dielectricity, pyroelectricity, piezoelectricity, ferroelectricity, and electro-optical properties.

  In addition, the oxide crystal obtained through the crystallization process of the formation process of the ferroelectric film has no orientation because the individual crystals are arranged in an orderly manner in the film, or the oxide crystal film is laminated. It is customary that either the same orientation is exhibited following the crystal orientation of the underlying layer.

  In order to obtain a ferroelectric film composed of a (composite) oxide crystal that exhibits good device characteristics and has a crystal orientation oriented in a specific orientation, the following may be performed. That is, a lower electrode (crystal) film oriented on the target crystal orientation and having a lattice constant close to the lattice constant of the oxide crystal film forming the ferroelectric film is formed on the silicon wafer substrate. A ferroelectric film may be formed according to the CSD method shown in FIG. However, in order to align the ferroelectric film in the same crystal orientation as the lower electrode as intended, it is necessary to further elaborate the conditions for each step of coating, drying, pyrolysis, and crystallization of the precursor liquid. There is.

  However, since the CSD method shown in FIG. 1 is a method in which a workpiece is repeatedly exposed to a high temperature environment, the types of materials that can be selected as the lower electrode are limited (mainly noble metals and their oxide materials). It is not always possible to employ a lower electrode having an orientation in a target crystal orientation. For example, platinum widely used as the lower electrode of the CSD method has a very strong (111) orientation, and it is extremely difficult to change this to a (100) orientation (which increases the piezoelectricity of the ferroelectric film). is there.

  Therefore, in order to form a (100) -oriented ferroelectric film on the lower electrode employing platinum, it has the property of being easily (100) -oriented regardless of the orientation of platinum, and a ferroelectric film is formed. An orientation control layer having a lattice constant close to that of the (composite) oxide crystal to be formed is provided. A method of forming a ferroelectric film on the orientation control layer is employed.

  However, in the conventional method of providing a ferroelectric film on the orientation control layer formed on the lower electrode by the CSD method, an oxide crystal film that forms a ferroelectric film after crystallizing the orientation control layer A method of laminating a film is employed. Therefore, the existence of crystal lattice mismatch at the interface between the lower electrode and the orientation control layer, and the generation of strain and stress due to the mismatch cannot be avoided.

  FIG. 4A shows a general crystal lattice. As in the crystal lattice 200 shown in FIG. 4A, when the atoms 201 form a regular bond with each other with a strong force (202 indicates a bond between the atoms 201), a solid called “crystal” Form a state. In the crystalline state, the atoms 201 are arranged at regular intervals and are connected to each other with a strong force.

  In the crystal lattice 200, the distance between the atoms 201 is called “interatomic distance” or “lattice constant”. The “interatomic distance” or “lattice constant” is a unique value determined by the composition of the element or compound that forms the crystal. That is, the lattice constant of the crystal lattice varies depending on the composition of the compound.

  For example, as shown in FIG. 4B, when the ferroelectric film 220 is formed on the orientation control layer 210, the orientation control layer 210 is a composition of a compound on the orientation control layer 210 (crystal film). Therefore, the ferroelectric film 220 (crystal film) having different lattice constants is formed. Therefore, the crystal films (orientation control layer 210 and ferroelectric film 220) having different interatomic distances (lattice constants) are in contact with each other and bonded together with the interface between the two as a boundary. This is called a crystal lattice (lattice constant) mismatch. In FIG. 4B, A indicates the interatomic distance (lattice constant) of the orientation control layer 210, and B indicates the interatomic distance (lattice constant) of the ferroelectric film 220.

  As shown in FIG. 5 (a), the bonds between atoms having different lattice constants of crystal lattices cause a strong bond between atoms in the right arrangement, and a weak bond between atoms that are not so. Will do. However, in the bonding state between the layers as shown in FIG. 5 (a), the bonding force becomes weak, and peeling occurs at the interface or cracks occur, resulting in a very poor state.

  Therefore, as shown in FIG. 5B, normally, after forming the lower orientation control layer 210 (crystal film), the film formation conditions of the upper ferroelectric film 220 (crystal film) are devised. A crystal film having a strong upper and lower interlayer bonding state is produced. Specifically, by strongly combining the lattice constant of the ferroelectric film 220 (crystal film) near the interface with the lattice constant of the already formed lower orientation control layer 210 (crystal film), strong upper and lower interlayer coupling A crystalline film having a state is produced.

  As a result, the upper and lower interlayer bonds become strong, and problems such as delamination and generation of cracks are eliminated. On the other hand, in the upper ferroelectric film 220 (crystal film) formed later, the interatomic distance of atoms in the vicinity of the interface is matched with the interatomic distance of the lower orientation control layer 210 (crystal film). Since they are arranged narrower than they should be, the compressive stress is generated (arrow in FIG. 5B). This is the compressive stress due to crystal lattice mismatch. However, when the lattice constant of the lower crystal film is larger than the lattice constant of the upper crystal film, tensile stress due to crystal lattice mismatch is generated in the upper crystal film.

  Thus, with the conventional method, it is possible to avoid an increase in strain and stress at the interface between the orientation control layer and the ferroelectric film, or the presence of a crystal lattice mismatch at the interface and the generation of new strain and stress. There wasn't. In addition, a decrease in crystal orientation due to strain and stress that increases as the ferroelectric films are stacked cannot be avoided.

  Therefore, in the film forming method according to the present embodiment, the upper ferroelectric film (crystal film) is not formed on the already formed lower alignment control layer (crystal film), but both are crystallized simultaneously. Make it. This causes interdiffusion of each atom during the crystallization process at the interface between both layers, and gradually changes the chemical composition in the vicinity of the interface from the composition of the orientation control layer to the composition of the ferroelectric film (the lattice constant is changed). Gradually change).

  That is, when simultaneously crystallizing the amorphous orientation control layer material on the lower electrode and the amorphous ferroelectric film material formed so as to be in contact with the amorphous orientation control layer, each atom has Interdiffusion occurs. At that time, the crystallized orientation control layer is a (composite) oxide material having the same crystal structure as that of the crystallized ferroelectric film.

  Therefore, from the composition of the material of the orientation control layer in contact with the lower electrode including the interface between the crystallized orientation control layer and the crystallized ferroelectric film, the composition of the material above the ferroelectric film Until then, the composition ratio of the oxide material (composition ratio of the constituent elements) changes continuously. Then, the interface between the orientation control layer and the ferroelectric film becomes unclear and they are integrated. Further, in the integrated orientation control layer and the ferroelectric film, the composition ratio of the oxide material (composition ratio of the constituent elements) changes continuously, and at the same time, the crystal lattice constant continuously changes according to the composition change. Change.

  Thereby, it is possible to avoid generating a compressive stress in the ferroelectric film due to a crystal lattice mismatch at the interlayer interface. That is, in the usual method, the generation of strain and stress caused by the lattice constant mismatch at the interface between the orientation control layer and the ferroelectric film is eliminated. In addition, the strain and stress caused by the mismatch of the lattice constant at the interface between the lower electrode and the orientation control layer are alleviated by the continuous change of the internal crystal lattice constant.

  As a result, when a ferroelectric film is laminated on the integrated orientation control layer and the lowermost ferroelectric film to obtain a thicker ferroelectric film intended for application to piezoelectric elements. Also good results can be obtained. Specifically, since the generation of strain and stress that hinders the function of aligning crystal orientation is avoided, a ferroelectric film having good crystal orientation and piezoelectric characteristics can be formed.

  In addition, as described above, the ferroelectric film obtained by the film forming method according to the present embodiment has the alignment control layer and the ferroelectric film integrated together, as well as strain and The stress is in a relaxed state. Therefore, the adhesiveness at each interface becomes strong, and the mechanical strength required for the device used for the application of the piezoelectric element can be increased.

  Note that the conventional technique (for example, see Patent Document 1) in which the orientation control layer material and the ferroelectric material are the same can also eliminate the mismatch of crystal lattices at the interface between them and relax the strain and stress generated in the same part. However, this technique cannot provide an effect of relaxing strain and stress generated at the interface between the lower electrode and the orientation control layer.

  In addition, the conventional technique for crystallizing the orientation control layer in the non-crystallized / non-oriented state at the same time as the ferroelectric film in contact therewith (4 or 5 nm as usual) For example, Patent Document 2) reports that there is no orientation control effect. The reason for this result is that under the condition that the film thickness of the alignment control layer is only about 4 or 5 nm as usual, the alignment control layer material is all diffused into the ferroelectric film during the crystallization process, and the alignment control is performed. It can be considered that the orientation control layer showing the function of has disappeared.

  In the film forming method according to the present embodiment, the thickness of the orientation control layer is set to 1/3 to 1/2 of the thickness of the ferroelectric film directly stacked on the orientation control layer and simultaneously crystallized (about 30 to 50 nm), which is thicker than usual. For this reason, an orientation control layer having a sufficient thickness control effect is formed on the lower electrode even after the interdiffusion of the orientation control layer material and a continuous change in the composition centering on the interface occur during the crystallization process. The As a result, a good alignment control effect can be obtained.

  As described above, in the film forming method according to the first embodiment, the crystallization process of the orientation control layer and the ferroelectric film, which are partially the same material, is simultaneously performed. As a result, the lattice constant of the crystal at the interface between the orientation control layer crystal and the ferroelectric film crystal changes continuously (from the lattice constant of the orientation control layer crystal to the lattice constant of the ferroelectric film crystal). As a result, compared to the conventional method of individually crystallizing the orientation control layer and the upper ferroelectric film in contact therewith, it is possible to eliminate the compressive stress caused by crystal lattice mismatch, and there is no internal stress. Can be formed.

  Further, in the film forming method according to the present embodiment, the orientation control layer is made thicker than usual, from 1/3 to 1/2 (about 30 to 50 nm) of the thickness of the upper ferroelectric film in contact therewith. . As a result, even if the interface between the orientation control layer and the ferroelectric film becomes unclear, the orientation control layer is not formed in the lower layer portion (the vicinity in contact with the lower electrode) of the laminated film of the orientation control layer and the ferroelectric film. Existing. In other words, the crystallization process is performed so that the material that becomes the orientation control layer exists in the lower layer portion of the laminated film.

  Therefore, the orientation control layer existing in the lower layer portion of the laminated film can maintain the function of controlling the crystal orientation of the ferroelectric film. That is, when the thickness of the precursor liquid coating film that becomes the orientation control layer is reduced and the orientation control layer is integrated with the ferroelectric film as in the conventional case, the presence of the orientation control layer itself is not clarified, and the orientation control layer is aligned at the same time. The control function is lost. On the other hand, in this embodiment, such a problem (disappearance of the function of orientation control) can be avoided. Note that the orientation control layer according to the present embodiment has a property as a ferroelectric, and the interface between the portion showing the property of the ferroelectric film and the portion showing the property as the orientation control layer is not clear. Absent.

<Second Embodiment>
In the second embodiment, a droplet discharge head using an electromechanical conversion element, which is an example of an electronic element having a ferroelectric film formed by the film forming method according to the first embodiment, is illustrated. To do.

  FIG. 6 is a cross-sectional view illustrating a droplet discharge head using an electromechanical transducer. Referring to FIG. 6, the droplet discharge head 30 includes a nozzle plate 31, a pressure chamber substrate 34, a vibration plate 35, and an electromechanical conversion element 40. The nozzle plate 31 is formed with nozzles 32 that eject ink droplets. The nozzle plate 31, the pressure chamber substrate 34, and the vibration plate 35 may be referred to as a pressure chamber 33 (an ink channel, a pressurized liquid chamber, a pressurized chamber, a discharge chamber, a liquid chamber, or the like) communicating with the nozzle 32. ) Is formed. The diaphragm 35 forms a part of the wall surface of the ink flow path.

The electromechanical conversion element 40 includes an adhesion layer 41, a lower electrode 42, an electromechanical conversion film 43, and an upper electrode 44, and has a function of pressurizing ink in the pressure chamber 33. The adhesion layer 41 is a layer made of, for example, Ti, TiO ₂ , TiN, Ta, Ta ₂ O ₅ , Ta ₃ N _{5, and the} like, and has a function of improving adhesion between the lower electrode 42 and the diaphragm 35. However, the adhesion layer 41 is not an essential component of the electromechanical conversion element 40.

  The electromechanical conversion film 43 is a typical example of the ferroelectric film described in the first embodiment. The electromechanical conversion film 43 is formed by the film forming method according to the first embodiment using, for example, PZT. Therefore, since the electromechanical conversion film 43 has a preferential orientation (100) that exhibits good piezoelectricity, it exhibits good piezoelectric characteristics.

  In the electromechanical conversion element 40, when a voltage is applied between the lower electrode 42 and the upper electrode 44, the electromechanical conversion film 43 is mechanically displaced. Along with the mechanical displacement of the electromechanical conversion film 43, the diaphragm 35 made of silicon or the like is deformed and displaced in the lateral direction (d31 direction), for example, and pressurizes the ink in the pressure chamber 33. Thereby, ink droplets can be ejected from the nozzle 32.

  As shown in FIG. 7, a plurality of droplet discharge heads 30 can be arranged in parallel to form a droplet discharge head 50.

  In the present embodiment, an example in which the electromechanical conversion element 40 is used as a component of the droplet discharge head 30 or 50 has been described. However, the electromechanical transducer 40 may be used as a component such as a micro pump, an ultrasonic motor, an acceleration sensor, a two-axis scanner for a projector, an infusion pump, or the like.

<Third Embodiment>
In the third embodiment, as an application example, an ink jet recording apparatus is illustrated as an example of a liquid droplet ejection apparatus provided with a liquid droplet ejection head 50 (see FIG. 7). FIG. 8 is a perspective view illustrating an ink jet recording apparatus according to the third embodiment. FIG. 9 is a side view illustrating the mechanism unit of the ink jet recording apparatus according to the third embodiment.

  Referring to FIGS. 8 and 9, an inkjet recording apparatus 60 is an inkjet that is an embodiment of a droplet 93 that is movable in the main scanning direction inside a recording apparatus main body 81 and a droplet discharge head 50 that is mounted on the carriage 93. The recording head 94 is accommodated. Further, the ink jet recording apparatus 60 houses a printing mechanism portion 82 and the like that are configured by an ink cartridge 95 that supplies ink to the ink jet recording head 94.

  A paper feed cassette 84 (or a paper feed tray) on which a large number of sheets 83 can be stacked can be detachably attached to the lower portion of the recording apparatus main body 81. Further, the manual feed tray 85 for manually feeding the paper 83 can be turned over. The paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken in, and after a required image is recorded by the printing mechanism unit 82, the paper is discharged to a paper discharge tray 86 mounted on the rear side.

  The printing mechanism 82 holds the carriage 93 slidably in the main scanning direction with a main guide rod 91 and a sub guide rod 92 which are guide members horizontally mounted on left and right side plates (not shown). An ink jet recording head 94 is mounted on the carriage 93 such that a plurality of ink discharge ports (nozzles) are arranged in a direction intersecting the main scanning direction and the ink droplet discharge direction is directed downward. The inkjet recording head 94 ejects ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). Further, the carriage 93 is mounted with replaceable ink cartridges 95 for supplying ink of each color to the ink jet recording head 94.

  The ink cartridge 95 has an air port (not shown) that communicates with the atmosphere above, an air port (not shown) that supplies ink to the ink jet recording head 94 below, and a porous body (not shown) filled with ink inside. ing. The ink supplied to the inkjet recording head 94 is maintained at a slight negative pressure by the capillary force of the porous body. Further, although the respective color heads are used here as the ink jet recording head 94, one head having nozzles for ejecting ink droplets of each color may be used.

  The carriage 93 is slidably fitted to the main guide rod 91 on the downstream side in the paper conveyance direction, and is slidably mounted on the sub guide rod 92 on the upstream side in the paper conveyance direction. In order to move and scan the carriage 93 in the main scanning direction, a timing belt 100 is stretched between a driving pulley 98 and a driven pulley 99 that are rotationally driven by the main scanning motor 97, so that the main scanning motor 97 is forward / reverse. The carriage 93 is reciprocated by the rotation. The timing belt 100 is fixed to the carriage 93.

  Further, the inkjet recording apparatus 60 conveys the fed sheet 83 by reversing the sheet feeding roller 101 for separating and feeding the sheet 83 from the sheet feeding cassette 84, the friction pad 102, the guide member 103 for guiding the sheet 83, and the like. A conveying roller 104 is provided. Further, the inkjet recording apparatus 60 is provided with a conveyance roller 105 that is pressed against the circumferential surface of the conveyance roller 104 and a leading end roller 106 that defines a feeding angle of the paper 83 from the conveyance roller 104. As a result, the paper 83 set in the paper feed cassette 84 is conveyed to the lower side of the ink jet recording head 94. The transport roller 104 is rotationally driven by a sub-scanning motor 107 through a gear train.

  The printing receiving member 109 which is a paper guide member guides the paper 83 sent out from the conveying roller 104 corresponding to the movement range of the carriage 93 in the main scanning direction on the lower side of the ink jet recording head 94. On the downstream side of the printing receiving member 109 in the sheet conveyance direction, a conveyance roller 111 and a spur 112 that are rotationally driven to send out the sheet 83 in the sheet discharge direction are provided. Further, a paper discharge roller 113 and a spur 114 for sending the paper 83 to the paper discharge tray 86, and guide members 115 and 116 for forming a paper discharge path are provided.

  During image recording, the inkjet recording head 94 is driven in accordance with the image signal while moving the carriage 93, thereby ejecting ink onto the stopped paper 83 to record one line and transporting the paper 83 by a predetermined amount. After that, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing end of the paper 83 reaches the recording area, the recording operation is terminated and the paper 83 is discharged.

  A recovery device 117 for recovering defective ejection of the inkjet recording head 94 is provided at a position outside the recording area on the right end side in the movement direction of the carriage 93. The recovery device 117 includes a cap unit, a suction unit, and a cleaning unit. The carriage 93 is moved to the recovery device 117 side during printing standby, and the ink jet recording head 94 is capped by the capping unit, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting ink not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant, and stable ejection performance is maintained.

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

  As described above, the ink jet recording apparatus 60 includes the ink jet recording head 94 that is an embodiment of the droplet discharge head 50. Since the droplet discharge head 50 includes the electromechanical conversion film 43 that has a preferential orientation (100) that expresses good piezoelectricity and that expresses good piezoelectric characteristics, ink droplet discharge failure due to vibration plate drive failure And stable ink droplet ejection characteristics can be obtained, and the image quality can be improved. The ink jet recording apparatus 60 is a typical example of an electronic apparatus according to the present invention.

<Example>
In this example, a silicon wafer substrate in which an orientation control layer using PT (lead titanate) is formed on the lower electrode (platinum) is used, and the best piezoelectric property is exhibited on the orientation control layer. An example of forming a (100) preferentially oriented ferroelectric film will be described. As the ferroelectric film, PZT (lead zirconate titanate) having good ferroelectric characteristics and piezoelectric characteristics was used.

[Synthesis of precursor liquid]
First, a PZT precursor liquid for forming a PZT (lead zirconate titanate) ferroelectric film by a CSD method and a PT precursor liquid for forming a PT (lead titanate) orientation control layer were prepared. Starting materials include lead acetate trihydrate Pb (CH ₃ COO) ₂ .3H ₂ O, zirconium tetranormal propoxide Zr (OCH ₂ CH ₂ CH ₃ ) ₄ , titanium tetraisopropoxide Ti [OCH (CH ₃ ) ₂ ] ₄ was used.

In synthesizing PZT precursor liquid, Pb (Zr _0.53 Ti _0.47 ) O ₃ , generally indicated as PZT (53/47), the stoichiometric amount of lead zirconate titanate that exhibits particularly good piezoelectric properties The starting material was weighed so that the lead content was 10 mol% excess relative to the theoretical composition. That is, the starting material was weighed so as to be Pb _1.10 (Zr _0.53 Ti _0.47 ) O ₃ . This is to prevent the deterioration of crystallinity caused by so-called “lead loss” that occurs during the heat treatment of the coating film of the applied precursor liquid.

Similarly, in the weighing of the starting material when synthesizing the PT precursor solution, in consideration of a decrease in crystallinity due to “lead loss” during the heat treatment, a composition in which the lead amount is excessive by 10 mol%, that is, Pb _1.10. The starting material was weighed so as to be TiO ₃ .

  The precursor liquid synthesis process after the weighing is performed by separate independent synthesis apparatuses for the PZT precursor liquid and the PT precursor liquid, but the flow of the synthesis process is almost the same. Hereinafter, the flow of the synthesis process will be described focusing on the PZT precursor liquid.

After weighing the starting material, first lead acetate trihydrate was dissolved in ₂ -methoxyethanol CH ₃ OCH ₂ CH ₂ OH, and then heated and refluxed at a solution temperature not lower than the boiling point (125 ° C.) of the solvent for 18 hours. Water dehydration, removal of by-products, and production of lead alkoxide compounds were performed.

  Subsequently, zirconium tetranormal propoxide and titanium tetraisopropoxide were added to the 2-methoxyethanol solution of the lead compound subjected to dehydration and alkoxide compound generation (in the PT precursor solution, only titanium tetraisopropoxide). Then, this solution was heated and refluxed to advance an alcohol exchange reaction and an esterification reaction (polycondensation reaction), and the by-product ester was removed. The retention time after reaching the solvent boiling point was 18 hours.

Finally, a solvent is added so that the PZT concentration in the precursor liquid is 0.5 mol / l (PT concentration in the PT precursor liquid is 0.3 mol / l), the concentration is adjusted, and 2.5 vol% as a stabilizer. Appropriate acetic acid CH ₃ COOH was added to obtain a PZT precursor solution.

[Formation of integrated film of PT orientation control layer and PZT ferroelectric film]
As a substrate on which a ferroelectric film is formed, a Ti layer (film thickness: 50 nm) is formed as an adhesion layer 152 on a silicon wafer substrate 151, and a platinum film (film thickness: 160 nm) is formed as a lower electrode 153 through the adhesion layer 152. A film was formed by a sputtering method. Then, according to the flow shown in the flowchart of FIG. 3, a laminated amorphous film including the amorphous film 154 of the PT alignment control layer material and the amorphous film 155 of the PZT ferroelectric film material is formed on the lower electrode 153 (FIG. 10A )). The lower electrode 153, which is a platinum film, has a strong crystal orientation in the (111) direction, as shown in FIG.

  Specifically, the silicon wafer substrate 151 on which the lower electrode 153 housed in the housing member 11 of the automatic film forming apparatus 10 shown in FIG. 2 is formed is taken out by the transfer device 12 and placed in the aligner 13. The silicon wafer substrate 151 was positioned and centered. Then, the silicon wafer substrate 151 positioned and centered by the aligner 13 was put into the spinner coating device 14 by the transport device 12. Then, while dropping the prepared PT precursor solution, the silicon wafer substrate 151 was rotated at a maximum of 3000 rpm by the spinner coating device 14 to form a coating film of the PT precursor solution on the lower electrode 153 (application step).

  Next, the silicon wafer substrate 151 is placed on the hot plate 15 by the transfer device 12, and the precursor liquid coating film is heated and dried on the hot plate 15 to form a precursor dry film for forming the orientation control layer. . Specifically, it was put into a hot plate 15 heated to 140 ° C. higher than the boiling point of the main solvent for 1 minute, and a precursor dry film for forming an orientation control layer was formed on the lower electrode 153 (drying process).

  Next, the silicon wafer substrate 151 is loaded into the RTA apparatus 16 by the transfer apparatus 12, and the precursor dry film is heated and pyrolyzed by the RTA apparatus 16, and the orientation control layer material (PT) is amorphous on the lower electrode 153. A film 154 was formed. Specifically, it was heated at a thermal decomposition temperature of 380 ° C. for 5 minutes to decompose the organic component in the PT precursor dry film to obtain an amorphous film 154 of the PT precursor material (thermal decomposition step).

  Next, the silicon wafer substrate 151 was transferred to the cooling stage 17 by the transfer device 12, and left on the cooling stage 17 for 2 minutes (or more) to cool the silicon wafer substrate 151 to room temperature (cooling step).

  Next, the silicon wafer substrate 151 on which the orientation control layer material amorphous film 154 was formed was put into the spinner coating apparatus 14 from the cooling stage 17 via the aligner 13. Then, while dropping the prepared PZT precursor liquid, the silicon wafer substrate 151 was rotated at a maximum of 3000 rpm by the spinner coating apparatus 14 to form a coating film of the PZT precursor liquid on the amorphous film 154 of the PT precursor material (application process) ).

  Next, the silicon wafer substrate 151 was put into the hot plate 15 by the transfer device 12, and the precursor liquid coating film was heated and dried by the hot plate 15 to form a precursor dry film of the ferroelectric film. Specifically, the precursor was dried on the amorphous film 154 on the hot plate 15 heated to 140 ° C., which is higher than the boiling point of the main solvent, for 1 minute (drying process).

  Next, the silicon wafer substrate 151 is put into the RTA apparatus 16 by the transfer device 12, and the precursor dry film is heated and pyrolyzed by the RTA apparatus 16, and the ferroelectric film material (PZT) is formed on the amorphous film 154. An amorphous film 155 was formed. Specifically, it was heated at a thermal decomposition temperature of 380 ° C. for 5 minutes to decompose organic components in the dry PZT precursor film, and an amorphous film 155 of PZT precursor material was obtained (thermal decomposition step).

  Next, the silicon wafer substrate 151 was transferred to the cooling stage 17 by the transfer device 12, and left on the cooling stage 17 for 2 minutes (or more) to cool the silicon wafer substrate 151 to room temperature (cooling step).

  Next, the silicon wafer substrate 151 on which the amorphous films 154 and 155 (laminated amorphous film) were formed was loaded into the RTA apparatus 16 via the aligner 13 by the transfer apparatus 12. Then, an operation of heating at a higher temperature was continuously performed with the RTA apparatus 16 to simultaneously crystallize the laminated amorphous film. Specifically, heating is performed at a crystallization temperature of 680 ° C. for 5 minutes, and the amorphous film 154 of the PT precursor material that becomes the orientation control layer and the amorphous film 155 of the PZT precursor material that becomes the ferroelectric film are crystallized at the same time. A film 156 was formed (crystallization step).

  In the above description, the amorphous film 155 of PZT precursor material is stacked on the amorphous film 154 of PT precursor material, the silicon wafer substrate 151 is once cooled by the cooling stage 17, and then charged into the RTA apparatus 16 again. Then, crystallization is performed. However, the heating and crystallization process may be performed continuously with the thermal decomposition process of the PZT precursor material performed in the same RTA apparatus 16 (without removing the silicon wafer substrate 151 from the RTA apparatus 16 and cooling it once).

  A crystal film 156 (a film obtained by simultaneously crystallizing a laminated amorphous film) obtained by laminating an orientation control layer and a ferroelectric film obtained in this example is as shown in a schematic cross-sectional view of FIG. , The interface between the two became unclear, resulting in an integrated crystal film. The thickness of this integrated crystal film 156 was about 100 nm.

  FIG. 11 is a diagram illustrating the results of analyzing the Pb, Zr, and Ti compositions in the integrated crystal film by dynamic SIMS. As shown in FIG. 11, the composition in the vicinity of the surface layer of the integrated crystal film 156 is a ferroelectric PZT composition. The amount of Zr continuously decreases toward the lower portion of the crystal film 156, and at the same time, the amount of Ti increases. Furthermore, it can be seen that the composition in the vicinity of the interface with the lower electrode of the lower layer is the PT composition of the orientation control layer. With the PT crystal layer remaining in the region near the interface with the lower electrode, the crystal orientation of the PZT ferroelectric film laminated thereon can be controlled to the same crystal orientation (100) as the PT orientation control layer. .

[Thickening of PZT ferroelectric film by stacking PZT ferroelectric film]
After forming the integrated crystal film as described above, the PZT precursor liquid is dropped onto the integrated crystal film according to the process flow of the usual CSD method shown in FIG. 1 to obtain a PZT ferroelectric film. The laminated film was formed (thickened) until the thickness became.

  In this example, in FIG. 1, X = 3, Y = 8, that is, the process of performing the crystallization process was repeated 8 times each time the PZT precursor solution coating process to the thermal decomposition process were repeated 3 times. As a result, a PZT ferroelectric film having a thickness of about 2 μm was obtained on the lower electrode. In this case, the coating, drying, thermal decomposition, and crystallization processing conditions are the same as those for the PZT ferroelectric film described above in this embodiment.

  FIG. 12B shows the X-ray diffraction result of the obtained PZT ferroelectric film having a thickness of about 2 μm. FIG. 12B shows that the obtained PZT ferroelectric film exhibits good piezoelectricity controlled by the orientation control layer, even though the platinum film of the lower electrode has (111) orientation ( 100) It turns out that it has a preferential orientation.

  Subsequently, a platinum film (thickness: 100 nm) serving as an upper electrode was formed on the obtained PZT ferroelectric film having a thickness of about 2 μm by a sputtering method. Then, a piezoelectric element applied to an inkjet head or the like was obtained by performing predetermined fine processing such as photolithography and etching. The piezoelectric element exhibits good piezoelectric characteristics because the PZT ferroelectric film that drives the piezoelectric element has a preferential orientation (100) that expresses good piezoelectricity.

  The preferred embodiments and examples have been described in detail above, but the present invention is not limited to the above-described embodiments and examples, and the above-described embodiments are not deviated from the scope described in the claims. Various modifications and substitutions can be made to the embodiments.

DESCRIPTION OF SYMBOLS 10 Automatic film-forming apparatus 11 Storage member 12 Conveyance apparatus 13 Aligner 14 Spinner coating apparatus 15 Hot plate 16 RTA apparatus 17 Cooling stage 19, 151 Silicon wafer substrate 30, 50 Droplet discharge head 31 Nozzle plate 32 Nozzle 33 Pressure chamber 34 Pressure chamber Substrate 35 Diaphragm 40 Electromechanical conversion element 41, 152 Adhesion layer 42, 153 Lower electrode 43 Electromechanical conversion film 44 Upper electrode 60 Inkjet recording apparatus 81 Recording apparatus main body 82 Printing mechanism section 83 Paper 84 Paper feed cassette 85 Manual feed tray 86 Exhaust Paper tray 91 Main guide rod 92 Sub guide rod 93 Carriage 94 Inkjet recording head 95 Ink cartridge 97 Main scan motor 98 Drive pulley 99 Driven pulley 100 Timing belt 101 Paper feed roller 10 Friction pad 103 Guide member 104 Conveying roller 105 Conveying roller 106 Leading end roller 107 Sub-scanning motor 109 Printing receiving member 111 Conveying roller 112 Spur 113 Discharge roller 114 Spur 115, 116 Guide member 117 Recovery device 154, 155 Amorphous film 156 Crystal film 200 Crystal lattice 201 Atom 202 Bond between atoms 210 Orientation control layer 220 Ferroelectric film

Japanese Patent No. 4122430 JP 2002-367985

Claims (8)

A method of forming a ferroelectric film using a chemical solution deposition method,
Forming an amorphous orientation control layer;
Forming an amorphous ferroelectric film in contact with the amorphous orientation control layer;
Crystallization of the amorphous orientation control layer and the amorphous ferroelectric film simultaneously,
The thickness of the crystallized orientation control layer is 1/3 to 1/2 of the thickness of the crystallized ferroelectric film;
The ferroelectric film characterized in that the crystallized orientation control layer includes a ferroelectric material having the same crystal structure as that of the crystallized ferroelectric film and having a different composition ratio of constituent elements. The film forming method. 2. The method of forming a ferroelectric film according to claim 1, wherein the crystallized orientation control layer has a thickness of 30 to 50 nm.   2. The composition ratio of the constituent elements of the ferroelectric material continuously changes at the interface between the crystallized orientation control layer and the crystallized ferroelectric film. Alternatively, the method of forming a ferroelectric film according to 2. The ferroelectric material is PbZr _x
4. The method for forming a ferroelectric film according to claim 1, wherein Ti _1-x O ₃ (x is an integer of 0 to 1 or a decimal number). 5. After the crystallizing step,
A first step of forming an amorphous ferroelectric film on the crystallized ferroelectric film;
A second step of crystallizing the amorphous ferroelectric film formed in the first step,
5. The ferroelectric film according to claim 1, wherein the first process and the second process are repeated a predetermined number of times to thicken the crystallized ferroelectric film. 6. The film forming method. The orientation control layer is formed on the lower electrode,
6. The method for forming a ferroelectric film according to claim 5, further comprising a step of forming an upper electrode on the crystallized ferroelectric film after the thick film formation.   An electronic device comprising a ferroelectric film formed by the method for forming a ferroelectric film according to claim 1.   An electronic device comprising the electronic device according to claim 7.

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