JP2014157850A - Electromechanical conversion element, droplet discharge head, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromechanical conversion element that suppresses a deviation in composition ratio of a ferroelectric film and has good in-plane uniformity, a droplet discharge head including the electromechanical conversion element, and an image forming apparatus.SOLUTION: An electromechanical conversion element 18 includes: a diaphragm 12; an adhesion layer 13; a lower electrode 14 comprising a two-layer structure having a Pt metal layer 14a and a SRO(SrRuO) composite oxide layer 14b; a seed layer 15 comprising RST(PbSrTiO); a ferroelectric layer 16 comprising PZT(PbZrTiO); and an upper electrode 17 comprising pt, which are sequentially laminated on a substrate 11.

Description

The present invention is provided in an image forming apparatus (inkjet recording apparatus) such as an ink jet printer, facsimile, or copying machine, and is used as a drive source for a liquid droplet ejection head that ejects liquid droplets such as ink. The present invention relates to a conversion element, a droplet discharge head including an electromechanical conversion element, and an image forming apparatus including the droplet discharge head.

  A droplet discharge head of a printer, facsimile, or image forming apparatus (inkjet recording apparatus) includes a nozzle that discharges ink droplets and a pressure chamber (an ink flow path, a pressure liquid chamber, a pressure chamber, and a discharge chamber) that communicates with the nozzle. And an electromechanical transducer that pressurizes the ink in the pressurizing chamber, and deforms and displaces the diaphragm using energy generated by applying a voltage to the piezoelectric element. Ink droplets are ejected from the nozzles by pressurizing the ink in the pressure chamber.

  The pressure generating means as described above may be a piezo type that discharges ink droplets by deforming and displacing a diaphragm that forms the wall surface of the discharge chamber using an electromechanical transducer such as a piezoelectric element, or a discharge chamber There is a bubble type (thermal type) in which bubbles are generated by boiling an ink film using an electrothermal conversion element such as a heating resistor disposed in the nozzle to eject ink droplets. Further, the piezoelectric type includes a longitudinal vibration type using displacement in the d33 direction, a transverse vibration (bend mode) type using displacement in the d31 direction, and a shear mode type using shear deformation. Among these, thin film actuators have been devised in which liquid chambers and piezo elements are made directly on a Si substrate by utilizing semiconductor processes and MEMS (Micro Electro Mechanical System) technology with the aim of achieving higher definition of images. .

In recent years, various electromechanical transducers and methods for manufacturing the same have been proposed in order to improve electrical characteristics. For example, a conductive oxide such as RuO _x , SRO film (SrRuO _x film) or IrO _x is used as the material of the upper electrode or the lower electrode, and a PZT film (Pb (Zr _x Ti _1-x is used as the material of the ferroelectric layer). (2) A technique using (O ₃ film) has been proposed. By using these materials, it is possible to improve the fatigue characteristics of the capacitor. However, the specific resistance value of the metal oxide electrode is about 10 ¹ to 10 ³ times higher than that of the metal electrode. For this reason, in a configuration in which the lower electrode is provided in common for a plurality of piezoelectric elements, if a large number of ink droplets are ejected at the same time by driving a large number of piezoelectric elements at the same time, a voltage drop occurs and the piezoelectric element There is a problem that the amount of displacement becomes unstable and the ink ejection characteristics deteriorate.

Patent Document 1 discloses that an SRO film can be formed at a desired composition ratio by optimizing the temperature at which the SRO film is formed by sputtering and the Ar / O ₂ ratio of the atmospheric gas. ing. The PZT film deposited on the SRO film has little interdiffusion of component elements with the SRO film during the firing process, so that the amount of leakage is small and the residual polarization can have a large value. Is described.

  In Patent Document 2, when an SRO film is formed by sputtering, a Ru-rich SRO film is formed by optimizing the film formation temperature, the atmospheric gas, and the sputtering method on the barrier metal side of the SRO film. Is disclosed to be possible. According to this method, the contact resistance of the Ru-poor SRO film is 15 kΩ, whereas the contact resistance of the Ru-rich SRO film is 5 kΩ, and it is described that the contact resistance can be lowered.

  Patent Document 3 discloses a method of adding Pb or Bi, which is a component of a PZT film, into the SRO film when forming a PZT film on the SRO film in a method for manufacturing a ferroelectric RAM. Yes. According to this method, it is possible to suppress interdiffusion of component elements that occurs between the SRO film and the PZT film, and to reduce the amount of leakage of the ferroelectric film caused by the interdiffusion. Have been described.

  Patent Document 4 discloses a capacitor using an SRO film having a perovskite crystal structure as a lower electrode and a PZT film having a perovskite crystal structure as a ferroelectric film formed thereon. According to this structure, since the crystal orientations of the SRO film and the PZT film are aligned, it is described that an electromechanical conversion element having a large polarization can be obtained.

  Patent Document 5 discloses a droplet discharge head manufacturing apparatus that suppresses variations in the thermal history of a ferroelectric layer. In this manufacturing apparatus, a series of steps of forming a piezoelectric element ferroelectric precursor film, heating the ferroelectric film, and cooling the ferroelectric film is formed for each silicon wafer under predetermined conditions. Therefore, a control means is provided. According to this manufacturing apparatus, variations in ejection characteristics due to variations in the thermal history of the ferroelectric layer can be suppressed, and a high-quality liquid droplet ejection head can be provided.

  As described above, in the technique of forming the PZT film as the ferroelectric film on the lower electrode made of the SRO film, when forming the PZT film as the ferroelectric film on the lower electrode made of the SRO film, It is known that interdiffusion of component elements occurs at the interface between the film and the PZT film. In particular, this is likely to occur when a composition ratio shift of the SRO film occurs and there is a portion that does not have a perovskite structure. If such interdiffusion occurs, a path that causes current leakage is created inside the PZT film, and the amount of leakage increases. This is not preferable for a PZT film that plays a role of capacitance.

  Further, there have been proposed a sputtering method for reducing the composition ratio shift of the SRO film by suppressing mutual diffusion of the component elements, and addition of Pb and Bi, which are components of the PZT film, into the SRO film. However, in order to eliminate the composition ratio deviation by the sputtering method, there is a problem that the system becomes complicated or the reproducibility is poor.

  Even if the composition ratio deviation of the SRO film can be reduced, in order to remove impurities such as carbon adhering to the surface before the PZT film is spin-coated, the wettability of the SRO surface is increased as a pretreatment to improve the adhesion. There is a need. Generally, wettability is enhanced by using oxygen plasma or UV plasma. However, it has been confirmed that this oxygen plasma also reduces Ru and causes a composition ratio shift on the surface of the SRO film.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide an electromechanical conversion element that suppresses a deviation in the composition ratio of the ferroelectric layer and has good in-plane uniformity of the crystallinity. To do.

  In order to solve the above problems and achieve the object, the present invention provides an electromechanical transducer provided on a substrate, in which a lower electrode, a seed layer, a ferroelectric layer, and an upper electrode are sequentially stacked. The seed layer is an electromechanical conversion element comprising a composite oxide having a perovskite crystal structure including at least Pb, Sr, and Ti.

  According to the electromechanical transducer of the present invention, the interdiffusion of component elements generated between the lower electrode and the ferroelectric layer can be suppressed, and the crystalline quality of the ferroelectric layer can be improved. There is an effect that the uniformity can be improved. Furthermore, since the crystal quality is good, there is an effect that the amount of leakage of the ferroelectric layer can be reduced.

It is sectional drawing which shows the structure provided with an example of the electromechanical conversion element on the board | substrate of this invention. It is a figure which shows a part of film-forming flow of an electromechanical conversion element. It is a graph which shows the XPS evaluation result of a seed layer (SRO) surface. It is a graph which shows the PE hysteresis curve of an electromechanical transducer. The graph which shows the VI evaluation result of an electromechanical transducer The graph which shows the XRD evaluation result of a ferroelectric layer (PZT) It is a schematic diagram which shows the structure of an example of the droplet discharge head of this invention. It is a schematic diagram which shows the structure of the droplet discharge head which has several electromechanical conversion elements. 1 is a perspective view illustrating an example of an ink jet recording apparatus that is an image forming apparatus of the present invention. It is a side view showing a mechanism part of an ink jet recording apparatus which is an image forming apparatus of the present invention.

  Hereinafter, embodiments of an electromechanical transducer, a droplet discharge head, and an image forming apparatus according to the present invention will be described with reference to the drawings.

(First embodiment)
An embodiment of the electromechanical transducer of the present invention will be described with reference to FIG. FIG. 1 shows a cross-sectional view of a structure 10 provided with an electromechanical transducer 18 on a substrate according to the present embodiment.
As shown in FIG. 1, the electromechanical transducer 18 is provided on the substrate 11, and has a lower electrode 14, a perovskite crystal containing at least Pb, Sr, and Ti via the diaphragm 12 and the adhesion layer 13. A seed layer 15 made of a complex oxide having a structure, a ferroelectric layer 16, and an upper electrode 17 are sequentially laminated. The lower electrode 14 has a two-layer structure having a composite oxide layer 14b on a metal layer 14a. The composite oxide layer 14 b is provided in contact with the seed layer 15.

The electromechanical transducer 18 is a transverse vibration (bend mode) type electromechanical transducer that utilizes deformation in the d31 direction. A voltage is applied to the ferroelectric layer 16 by the lower electrode 14 and the upper electrode 17, and the crystal of the ferroelectric layer 16 is deformed and displaced in a direction perpendicular to the electric field (direction d31).
Hereinafter, each layer will be described.

(Substrate 11)
As the substrate 11, it is preferable to use a silicon single crystal substrate, and it is preferable to have a thickness of 100 μm to 600 μm. There are three types of plane orientations, (100), (110), and (111), but (100) and (111) are generally widely used in the semiconductor industry. A single crystal substrate having a plane orientation of 100) is mainly used.

  After the electromechanical conversion element 18 is formed, the substrate 11 becomes a side wall of the pressurizing chamber 21 of the droplet discharge head formed integrally with the element by lithography as shown in FIG. Etching is used to process a silicon single crystal substrate. In this case, as an etching method, anisotropic etching is generally used. Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure. For example, in anisotropic etching immersed in an alkaline solution such as KOH, the (111) plane has an etching rate of about 1/400 compared to the (100) plane. Therefore, while a structure having an inclination of about 54 ° can be produced in the plane orientation (100), a deep groove can be removed in the plane orientation (110), so that the arrangement density is increased while maintaining rigidity. I know you can.

As this configuration, a single crystal substrate having a (110) plane orientation can also be used. However, in this case, SiO ₂ which is a mask material is also etched, so this area is also used with attention.

(Vibration plate 12)
The diaphragm 12 may be a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a film in which these films are laminated, or a ceramic film such as an aluminum oxide film or a zirconia film in consideration of a thermal expansion difference from the upper layer. . These are insulators. Since the lower electrode formed on the upper part of the diaphragm functions as a common electrode when inputting a signal to the electromechanical transducer, the diaphragm is an insulator or is insulated if it is a conductor.

As shown in FIG. 7, the vibration plate 12 receives a force generated by the electromechanical conversion element, and the substrate and the vibration plate are deformed and displaced, and the liquid droplets contained in the pressurizing chamber 21 are discharged. Therefore, it is preferable to have a predetermined strength. That is, it is preferable to select a material close to the linear expansion coefficient of adhesion layer / lower electrode / ferroelectric layer. In particular, as a ferroelectric layer, since PZT is generally used as a material, a linear expansion coefficient close to 8 × 10 ⁻⁶ (1 / K) is 5 × 10 ⁻⁶ to 10 × 10. A material having a linear expansion coefficient of ⁻⁶ (1 / K) is preferable, and a material having a linear expansion coefficient of 7 × 10 ^{−6 to} 9 × 10 ⁻⁶ (1 / K) is more preferable.

The film thickness is preferably from 0.1 to 10 μm, more preferably from 0.5 to 3 μm. If it is smaller than this range, it becomes difficult to process the pressurizing chamber 21 as shown in FIG. 7, and if it is larger than this range, the substrate is difficult to deform and displace, and the discharge of the liquid droplets stored in the pressurizing chamber becomes unstable. Become.
As the silicon-based insulating film, a thermal oxide film or a CVD deposited film can be used, and the metal oxide film can be formed by a sputtering method.

(Adhesion layer 13)
The adhesion layer 13 is formed in order to improve the adhesion between the diaphragm 12 and the lower electrode 14. As the material of the adhesion layer, titanium, tantalum, titanium oxide, tantalum oxide, titanium nitride, tantalum nitride, or a laminated film thereof is effective.
The film thickness of the adhesion layer 13 is preferably 10 nm to 50 nm, and more preferably 15 nm to 30 nm. When the film thickness is thinner than the range of 10 nm to 50 nm, there is a concern about the adhesion, and when the film thickness is thicker than this range, the crystallinity of the layer formed thereon is affected.

  These films can be obtained by oxidizing a metal film by sputtering or rapid thermal oxidation (RTA). By providing the metal oxide as an adhesion layer, the adhesion between the substrate or the base film (for example, a diaphragm) and the lower electrode made of metal is improved, and the occurrence of cracks and the like is suppressed. Further, when the lower electrode has a structure having a composite oxide layer such as SRO on the metal layer, the crystallinity of SRO and the crystallinity of the ferroelectric layer can be improved. For example, when titanium oxide has a two-layer structure, platinum is used as the substrate-side material, and silicon oxide is used for the diaphragm, these adhesion properties can be maintained well. The material of the adhesion layer is appropriately selected depending on the material of the base film and the lower electrode.

(Lower electrode 14)
The lower electrode 14 functions as a common electrode when inputting a signal to the electromechanical transducer. The lower electrode 14 drives the element by applying a voltage to the ferroelectric layer together with the upper electrode 17 functioning as an individual electrode to displace and deform the ferroelectric layer 16. The lower electrode 14 has a two-layer structure in which a conductive complex oxide layer 14b is stacked on a metal layer 14a.

  The material of the metal layer 14a of the lower electrode 14 is mainly composed of a single metal such as platinum (Pt), rhodium (Rh), ruthenium (Ru), or iridium (Ir), or platinum such as platinum-rhodium (PtRh). Alloy materials with other platinum group elements are effective. The thickness of the metal layer 14a of the lower electrode is preferably 50 nm or more and 250 nm or less. 80 nm to 200 nm is more preferable. When the film thickness is thinner than 50 nm, there is a concern about the uniformity of the electrode film crystallinity in the substrate surface, and when the film thickness is thicker than 250 nm, there is a concern that the process time increases and the rigidity against the vibration system increases. .

The complex oxide layer 14b is formed in contact with the seed layer 15 on the metal layer 14a. As a material of the composite oxide layer 14b, a composite oxide containing two or more elements of Sr, Ru, La, and Ni can be used. For example, in addition to SRO (SrRuO ₃ : strontium ruthenate), LNO (LaNiO ₃ : nickel lanthanum oxide) can be used. As the film forming method, a sputtering method or the like is used. In this case, although the film quality changes depending on the sputtering conditions, the crystal orientation is particularly emphasized, and the crystal orientation of the metal layer 14a of the lower electrode is preferentially oriented. For example, in the case where the metal layer 14a is Pt, it is preferable that the crystal orientation of (111) is set as the preferential orientation following Pt (111). In order to make the crystal orientation of the SRO thin film have a (111) preferential orientation, it is preferable to form the film by heating the substrate at a film formation temperature of 500 ° C. or higher.

  The film thickness of the composite oxide layer 14b is preferably 20 nm or more and 100 nm or less, and more preferably 30 nm or more and 80 nm or less. If the thickness is less than 20 nm, sufficient characteristics cannot be obtained with respect to initial displacement and displacement deterioration after continuous driving. If the thickness exceeds 100 nm, the dielectric breakdown voltage of the ferroelectric layer 16 is very poor and leaks easily. If the lower electrode has a structure in which a metal layer and a conductive complex oxide are laminated, the specific resistance can be lowered as compared with a conductive oxide-only electrode, and further, a ferroelectric layer formed thereon. The perovskite type crystal can be made of high quality.

(Seed layer 15)
The seed layer 15 is made of a complex oxide having a perovskite crystal structure containing at least Pb, Sr, and Ti. This is a perovskite complex oxide having the same crystal structure as PZT (Pb (Zr, Ti) O ₃ ), which is often used in ferroelectric layers, and is therefore provided between the electrode and the ferroelectric layer. However, the ferroelectric properties are maintained. The thickness of the seed layer is preferably 60 nm or more and 150 nm or less, and more preferably 80 nm or more and 120 nm or less. When the film thickness is thinner than 60 nm, there is a concern about the invalidation of the seed effect due to voids generated during firing, and when the film thickness is larger than 150 nm, the epitaxial growth is inhibited and the orientation control may not be possible. There is.

As a complex oxide having a perovskite crystal structure containing at least Pb, Sr, and Ti, for example, (Pb, Sr) TiO ₃ (hereinafter referred to as PST) can be given. Other examples include (Ba, Sr) TiO ₃ .
When PST is used as a method for producing the seed layer, a PST precursor solution using lead acetate trihydrate, isopropoxide titanium, isopropoxide strontium as a starting material is formed by spin coating, etc. It can be obtained by applying heat treatments for drying, pre-baking (thermal decomposition), and crystallization.

(Ferroelectric layer 16)
The material of the ferroelectric layer 16 is composed of a complex oxide having a perovskite crystal structure represented by the general formula ABO ₃ , wherein A is mainly composed of Pb, Ba, or Sr, and B is Ti, Zr, Sn. , Ni, Zn, Mg, or Nb as a main component. As specific examples, PZT (Pb (Zr, Ti) O ₃ ), PbTiO ₃ , PbZrO ₃ , Pb at the A site is partially replaced with Ba or Sr, and Zr at the B site is replaced with Ti (Pb _{1− x, Ba x) (Zr 1} -y, Ti y) O 3, and the like _{(Pb 1-x, Sr x} ) (Zr 1-y, Ti y) O 3, BaTiO 3, SrTiO 3. Such substitution is possible with a divalent element, and the effect thereof has an effect of reducing characteristic deterioration due to evaporation of lead during heat treatment.
The ferroelectric layer 16 is deformed and displaced by applying a voltage to the ferroelectric layer 16 by the lower electrode 14 and the upper electrode 17.

The material of the ferroelectric layer 16 is PZT, which is a solid solution of lead zirconate (PbZrO ₃ ) and lead titanate (PbTiO ₃ ), and the characteristics differ depending on the ratio. In general, the composition exhibiting excellent piezoelectric characteristics has a ratio of PbZrO ₃ and PbTiO ₃ of 53:47. When expressed by a chemical formula, Pb (Zr _0.53 , Ti _0.47 ) O ₃ , generally PZT ( 53/47). It can be formed by the sol-gel method using the following materials.

  Lead acetate, zirconium alkoxide, and titanium alkoxide compounds are used as starting materials and dissolved in methoxyethanol as a common solvent to obtain a uniform solution. This homogeneous solvent is called a PZT precursor solution. The lead acetate, zirconium alkoxide, and titanium alkoxide compound materials are weighed according to the desired chemical formula. Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of a stabilizer such as acetylacetone, acetic acid or diethanolamine may be added to the precursor solution as a stabilizer.

Using this precursor solution, a coating film is formed on a base electrode by a solution coating method such as spin coating, and then subjected to solvent heat treatment, pre-baking (thermal decomposition), and crystallization heat treatment. The positioning of the pre-baking is aimed at “thermal decomposition of organic matter” in the PZT precursor which exists even after solvent drying. Since transformation from the coating film to the crystallized film is accompanied by volume shrinkage, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a film free from cracks.
When used as an electromechanical conversion element of a liquid ejecting apparatus such as an ink jet recording apparatus, the thickness of the PZT film is required to be 1 μm to 2 μm. In order to obtain this film thickness by the above method, the process is repeated ten times.

In the case of barium titanate (BaTiO ₃ ), a barium titanate precursor solution can be prepared by using barium alkoxide and a titanium alkoxide compound as starting materials and dissolving them in a common solvent.

  The film thickness of the ferroelectric layer 16 is preferably 0.5 μm to 5 μm, more preferably 1 μm to 2 μm. If the film thickness is thinner than this range, sufficient displacement cannot be generated. If the film thickness is thicker than this range, many layers are stacked, so that the number of processes increases and the process time becomes longer.

(Upper electrode 17)
The upper electrode 17 is made of a conductive material and functions as an individual electrode of an element selected according to an input signal. A voltage is applied together with the lower electrode 14 to deform and displace the ferroelectric layer 16. The material of the upper electrode 17 is a single metal such as platinum (Pt), rhodium (Rh), ruthenium (Ru), iridium (Ir), or platinum-rhodium (PtRh), as in the metal layer 14a of the lower electrode. An alloy material with other platinum group elements mainly composed of platinum is effective.

  The thickness of the metal layer 14a of the upper electrode 17 is desirably 30 nm or more and 150 nm or less. More preferably, it is 50 nm or more and 80 nm or less. When the film thickness is less than 30 nm, there is a concern about a voltage drop due to an increase in electrical resistance, and when the film thickness is greater than 150 nm, there is a concern that the rigidity with respect to the vibration system increases. As a method for manufacturing the electrode, a general sputtering method or vacuum film formation such as vacuum deposition can be applied.

  Thereafter, a photoresist is formed by a spin coating method, a resist pattern is formed by a normal photolithography technique, and then a pattern is formed by using an ICP etching apparatus or the like to produce an electromechanical conversion element.

According to the electromechanical transducer of the present invention, since the composite oxide of the seed layer 15 has a perovskite structure having the same crystal structure as that of the composite oxide of the ferroelectric layer 16, the ferroelectric layer 16 grows epitaxially, The crystal orientations of the layer 15 and the ferroelectric layer 16 are aligned. Thereby, the crystal structure of the ferroelectric layer 16 can be made high quality with high in-plane uniformity.
In addition, by providing the seed layer 15 made of a composite oxide, the composition ratio shift of the ferroelectric material due to the diffusion of the constituent elements occurring between the lower electrode 14 and the ferroelectric layer 16 is suppressed. Thus, a high-quality crystal with high in-plane uniformity can be obtained. At the same time, leakage of the ferroelectric layer caused by diffusion of the metal element from the lower electrode can be prevented. In particular, since the PST film contains Sr and Pb, when the SRO film is used for the composite oxide layer 14b of the lower electrode 14 and the PZT film is used for the ferroelectric layer 16, the SRO film This is effective in suppressing Sr diffusion of Pb and Pb diffusion from the PZT film.

(Second Embodiment)
Next, a droplet discharge head according to a second embodiment of the present invention will be described. FIG. 7 is a schematic diagram showing the structure of an example of a droplet discharge head of the present invention, and FIG. 8 is a cross-sectional view of a droplet discharge head 40 in which a plurality of droplet discharge heads of the present invention are arranged.
The droplet discharge head 30 according to the present invention includes a droplet discharge nozzle 20 that discharges droplets, a pressurization chamber 21 that communicates with the droplet discharge nozzle, and a pressure generating unit that pressurizes liquid contained in the pressurization chamber. The pressure generating means is composed of the diaphragm 12 provided in the pressurizing chamber and the electromechanical transducer 18 of the present invention provided on the diaphragm 12, and the electromechanical transducer is By driving and deforming and displacing the diaphragm 12, the liquid contained in the pressurizing chamber is pressurized and the liquid is discharged to the outside of the pressurizing chamber 21.
The pressurizing chamber 21 is manufactured by removing a part of the silicon substrate 11 from the back surface by a lithography method and joining a nozzle plate 19 having nozzle holes. Thereafter, the droplet discharge head 30 is manufactured by bonding so as to cover the electromechanical conversion element with a protective substrate (not shown). According to this, the electromechanical conversion element can be formed by a simple manufacturing process (having performance equivalent to that of bulk ceramics). The droplet discharge head is provided with a liquid supply means (not shown) for supplying a liquid to the pressurizing chamber 21, a flow path (not shown), and a fluid resistance (not shown).

  As shown in FIG. 8, the droplet discharge head 40 is formed by arranging a plurality of droplet discharge heads manufactured as described above in parallel.

  If the droplet discharge head is configured using the electromechanical conversion element of the present invention, the droplet discharge characteristic can be satisfactorily maintained by the driving force equivalent to that of a ceramic sintered body, and stable droplet discharge characteristics even when continuously discharged. Can be maintained. In addition, if a droplet discharge device provided with this droplet discharge head, for example, an ink jet recording apparatus, there is no ink droplet discharge failure due to vibration plate drive failure, and image quality is improved by stable ink droplet discharge characteristics.

(Third embodiment)
Next, an ink jet recording apparatus of an image forming apparatus according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 9 shows a perspective view of an ink jet recording apparatus provided with a droplet discharge head (ink jet head), and FIG. 10 shows a side view of a mechanism part of the ink jet recording apparatus.

  An ink jet recording apparatus 80 according to the present invention includes the liquid droplet ejection head according to the present invention. As shown in FIGS. 9 and 10, the ink jet recording apparatus includes a carriage (93) movable in the main scanning direction inside the recording apparatus main body (81), and a recording comprising an ink jet head mounted on the carriage and embodying the present invention. A print mechanism unit including an ink cartridge (95) for supplying ink to the head (94) and the recording head (94) is accommodated, and a large number of sheets are provided from the front side in the lower part of the apparatus main body (81). A paper feed cassette (84) (or a paper feed tray) on which (83) can be loaded can be removably mounted, and a manual feed tray (85) for manually feeding paper (83) is also provided. ), The paper (83) fed from the paper feed cassette (84) or the manual feed tray (85) is taken in, and a required image is recorded by the printing mechanism. After it is discharged to the discharge tray mounted on the rear side (86).

The printing mechanism unit slidably holds the carriage (93) in the main scanning direction by 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). A carriage (93) is provided with a plurality of ink discharge heads (94) comprising an inkjet head according to the present invention for discharging ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). Outlets (nozzles) are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.
Each ink cartridge (95) for supplying ink of each color to the head (94) is replaceably mounted on the carriage (93).
The ink cartridge (95) has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside. The ink supplied to the inkjet head is maintained at a slight negative pressure by capillary force. Further, although the heads 94 of the respective colors are used here as the recording heads, a single head having nozzles for ejecting ink droplets of the respective colors may be used.

  Here, the carriage (93) is slidably fitted to the main guide rod (91) on the rear side (downstream side in the paper conveyance direction), and the front side (upstream side in the paper conveyance direction) is attached to the secondary guide rod (92). It is slidably mounted. 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) rotated by a main scanning motor (97) and a driven pulley (99). The timing belt (100) is fixed to the carriage (93), and the carriage (93) is reciprocated by forward and reverse rotation of the main scanning motor (97).

  On the other hand, in order to convey the paper (83) set in the paper feed cassette (84) to the lower side of the head (94), a paper feed roller (101) for separating and feeding the paper (83) from the paper feed cassette (84). ) And a friction pad (102), a guide member (103) for guiding the paper (83), a transport roller (104) for transporting the fed paper (83) in an inverted manner, and the transport roller (104) A conveyance roller (105) pressed against the peripheral surface of the sheet and a leading end roller (106) for defining a feed angle of the sheet (83) from the conveyance roller (104) are provided. The transport roller (104) is rotationally driven through a gear train by a sub-scanning motor (107).

  Then, a printing receiving member which is a paper guide member for guiding the paper (83) fed from the transport roller (104) corresponding to the moving range of the carriage (93) in the main scanning direction on the lower side of the head (94). (109) is provided. 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 the sheet (83) in the sheet discharge direction are provided. ) Are delivered to a paper discharge tray (86), and a paper discharge roller (113) and a spur (114), and guide members (115) and (116) forming a paper discharge path are disposed.

  At the time of recording, the recording head (94) is driven according to the image signal while moving the carriage (93), thereby ejecting ink onto the stopped sheet (83) to record one line. 83) After the predetermined amount is conveyed, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper (83) has reached the recording area, the recording operation is terminated and the paper (83) is discharged.

  A recovery device (117) for recovering defective ejection of the head (94) is disposed 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 head (94) is capped by the capping means, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. . Further, by ejecting ink that is 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 a discharge failure occurs, the discharge port (nozzle) of the head (94) is sealed with a capping unit, and bubbles and the like are sucked out from the discharge port with a suction unit through the tube. Dust and the like are 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.

  Thus, since this ink jet recording apparatus is equipped with a liquid droplet ejection head (ink jet head) that ejects liquid droplets by driving the electromechanical transducer of the present invention, ink droplets due to vibration plate drive failure There is no ejection failure, stable ink droplet ejection characteristics are obtained, and image quality is improved.

  That is, the droplet discharge head including the electromechanical transducer of the present invention and the droplet discharge apparatus including the droplet discharge head are excellent in discharge stability and durability. In addition to application to inkjet printers such as printers and MFPs used, it is also possible to apply to three-dimensional molding techniques.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples at all. Any modification of these embodiments as appropriate without departing from the gist of the present invention is within the scope of the present invention.
Hereinafter, embodiments of the present invention will be described with reference to FIGS.

Example 1
FIG. 1 is a cross-sectional view illustrating an example in which the electromechanical transducer of the present invention is provided on a substrate, and FIG. 2 is a diagram illustrating a part of a film formation flow of the electromechanical transducer of the present embodiment. These are the graphs which show the XPS (X-ray photoelectron spectroscopy) evaluation result of the SRO film | membrane surface which is a lower electrode.
As shown in FIG. 1, a vibration plate 12 made of a silicon oxide film is formed on a silicon wafer to be a substrate 11 by thermal oxidation (film thickness 1 μm), and a titanium film (film thickness 50 nm) is formed thereon as an adhesion layer 13. Was sputtered. Subsequently, the lower electrode 14 is formed on the adhesion layer 13. The lower electrode is formed by laminating a platinum film 14a and a composite oxide layer 14b made of SRO (SrRuO ₃ ). First, a platinum film 14a (film thickness 200 nm) was formed by sputtering. Further, an SRO film 14b (film thickness 60 nm) was formed by sputtering on the platinum film 14a. The composition ratio of the surface of the SRO film 14b at this time was evaluated by an X-ray photoelectron spectroscopy (XPS) method. The result is shown in FIG. As shown in FIG. 3, the composition ratio of sputtered SRO was generated, and the composition ratio was Sr: Ru = 60: 40.

Next, a PST (PbSrO ₃ ) film as the seed layer 15 was formed on the SRO film 14 b of the lower electrode 14. A PST precursor solution was spin-coated using a sol-gel method. In order to spin coat the PST film, the precursor coating solution was synthesized using lead acetate trihydrate, isopropoxide titanium, and isopropoxide strontium as starting materials. Crystal water of lead acetate was dissolved in methoxyethanol and then dehydrated. The amount of lead was excessive by 10 mol% relative to the stoichiometric composition. This is to prevent crystallinity deterioration due to so-called lead loss during heat treatment.

  Next, isopropoxide titanium and isopropoxide strontium are dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction are advanced, and the PST precursor solution is mixed with the methoxyethanol solution in which the lead acetate is dissolved. Synthesized. The PST concentration was 0.1 mol / liter. This PST precursor solution was spin-coated on the SRO film. After the spin coat film formation, the drying step was performed at 120 ° C. This drying step is desirably performed at a temperature lower than the boiling point of methoxyethanol, which is a solvent.

  Next, temporary baking was performed as shown in FIG. Temporary firing is a step for removing organic components contained in the PST precursor, and this is fired by RTA (Rapid Thermal Annealing). Pre-firing for the PST film precursor was performed at 400 ° C. for 3 minutes. In order to crystallize as it is, the main baking was performed at 450 ° C. for 1 minute. When the film thickness of the PST film was examined after carrying out the main baking, it was 100 nm.

  Next, a PZT film as the ferroelectric layer 16 is formed on the seed layer 15 made of PST. For the synthesis of the precursor solution of the PZT film, the same synthesis method as that for the PST precursor solution was used. As starting materials, lead acetate trihydrate, isopropoxide titanium, isopropoxide zirconium were used. Crystal water of lead acetate was dissolved in methoxyethanol and then dehydrated. The lead amount is 10 mol% excess relative to the stoichiometric composition.

  Isopropoxide titanium and isopropoxide zirconium were dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction were advanced, and the PZT precursor solution was synthesized by mixing with the methoxyethanol solution in which the lead acetate was dissolved. The PZT concentration was 0.1 mol / liter. This PZT precursor solution was spin-coated on the PST film as the seed layer 15. After the spin coat film formation, the drying step was performed at 120 ° C. After the drying process, the calcination process is started. The apparatus used for baking as in the PST film formation is RTA. The pre-baking temperature was set to 480 ° C.

  Thereafter, as shown in FIG. 2, the PZT precursor solution, which is the ferroelectric layer 16, was spin-coated on the wafer that had undergone the provisional firing step, and the drying step and the provisional firing step were performed. This wafer is subjected to the main baking process for the wafer subjected to three cycles of the spin coating and the temporary baking process. The main baking temperature was set to 700 ° C. with an RTA apparatus. The total film thickness of the PST film and the PZT film subjected to the main baking process was 400 nm. A process flow such as “PZT precursor coating, drying process, and calcining process is performed for 3 cycles and the main firing process is performed” is repeatedly performed until a desired film thickness is obtained. In this example, coating was repeated until the main firing step for the PZT film was performed six times. The total film thickness of the PST film and PZT film at that time was 1900 nm. A Pt film (200 nm) was formed as an upper electrode on the obtained PZT film by sputtering. The upper electrode 17 was patterned using photolithography.

  After patterning the upper electrode, the electrical characteristics were evaluated. FIG. 4 shows a graph of the PE hysteresis curve of the electromechanical transducer manufactured according to this example. The relative dielectric constant of the ferroelectric layer 15 made of PZT is 1220, the dielectric loss is 0.02, the remanent polarization is 19.3 μC / cm 2, and the coercive electric field is 36.5 kV / cm, which is the same as a normal ceramic sintered body It was found to have the characteristics of That is, since the crystal structure of the seed layer 15 made of PST is a perovskite type, it was found that the ferroelectric characteristics of the ferroelectric layer can be maintained even if a seed layer is provided.

  Further, the breakdown voltage of the ferroelectric layer 16 made of PZT was evaluated. FIG. 5 shows a graph of the VI evaluation results. In FIG. 5, the solid line shows the VI characteristic when the seed layer 15 made of PST is provided. Moreover, the broken line in FIG. 5 shows the VI characteristic of the element without a seed layer as a comparative example. As shown in FIG. 5, when there is no seed layer, conduction occurs at around 60 V, but when the seed layer 15 made of PST is provided, it can be confirmed that it has high breakdown voltage characteristics up to around 100 V. did it. Since the seed layer is made of PST, it is possible to suppress Sr diffusion from the SRO layer 14b and Pb diffusion from the PZT film of the ferroelectric layer 16, so that a high quality crystal can be obtained and the breakdown voltage characteristics can be improved. It was found that it contributed to.

(Example 2)
Next, as Example 2, an element in which the surface of the SRO layer of the electromechanical conversion element of the present invention was irradiated with oxygen plasma was produced, and the electrical characteristics were evaluated.
If the PST precursor solution is spin-coated immediately after sputtering of the SRO film, it can be formed with improved wettability on the surface of the SRO film. Ingredients adhere and its wettability deteriorates. In order to improve the wettability of the surface of the SRO film having deteriorated wettability, it is necessary to remove the organic component with oxygen plasma. When oxygen plasma irradiation is performed, Ru is reduced to form a Ru-poor film, and the contact resistance increases. Originally, the ratio of Sr and Ru in the SRO film is most preferably 50:50. In Example 1, the composition ratio of Sr and Ru was different when the SRO film was formed by sputtering. The composition ratio of Sr and Ru of the target was adjusted, the composition ratio of Sr and Ru was set to Sr: Ru = 50: 50, and the change in electrical characteristics due to the composition ratio shift between Sr and Ru due to oxygen plasma irradiation was evaluated.

  The SRO film 14b was similarly formed in the same manner as in Example 1, and after the surface of the SRO film 14b was irradiated with oxygen plasma, the composition ratio of the surface was evaluated by XPS analysis. As a result, it was found that Ru was reduced by oxygen plasma, the ratio of Sr and Ru became Sr: Ru = 70: 30, and the composition ratio changed. A seed layer 15 made of PST, a ferroelectric layer 16 made of PZT, and an upper electrode 17 were formed on the SRO film in the same manner as in Example 1, and the electrical characteristics were evaluated. The characteristics could be obtained.

  From Example 2, it was found that a PZT film having high withstand voltage characteristics can be formed even when the ratio of Sr: Ru is significantly changed from 50:50 to 70:30. In other words, by providing a seed layer made of PST, even if there is a portion whose composition ratio has changed due to oxygen plasma, it is not affected by it, and is formed on the seed layer while improving the wettability of the SRO surface. It was found that the ferroelectric layer formed can be epitaxially grown to improve the crystal orientation, and the same electrical characteristics as in Example 1 can be obtained.

(Example 3)
Next, the crystal orientation rate of the PZT ferroelectric layer when the main firing temperature of the seed layer 15 made of PST was changed was evaluated. In Example 1, the PST film as the seed layer 15 was temporarily fired at 400 ° C. and main baking was performed at 450 ° C. In this example, the main baking temperature of the seed layer 15 was 420 ° C., 450 ° C., And 480 ° C. A PZT film, which is the ferroelectric layer 16, was formed on each seed layer 15 with different main firing temperatures in the same manner as in Example 1. With respect to the formed PZT film | membrane, each crystal orientation rate was evaluated using the X-ray diffraction (XRD: X-Ray Diffraction) apparatus. The result is shown in FIG.

  From FIG. 6, the (100) orientation of the PZT film has priority at 420 ° C., and conversely, the (111) orientation has priority at 450 ° C. and 480 ° C. Although the use of the PZT film varies depending on the orientation ratio of the PZT film, it can be controlled by the firing conditions of the PST film. That is, when the orientation of the PST film is changed by firing, the information of the PZT film formed thereon can be inherited by epitaxial growth, and a good crystal structure can be obtained. In order to obtain a desired orientation, the crystal orientation of the seed layer may be controlled by the main firing temperature.

11 Silicon substrate 12 Diaphragm 13 Adhesion layer 14 Lower electrode 14a Metal layer 14b Composite oxide layer 15 Seed layer 16 Ferroelectric layer 17 Upper electrode 18 Electromechanical transducer 20 Droplet discharge nozzle 21 Pressurizing chamber 30 Droplet discharge head 40 Liquid droplet ejection head 80 Inkjet recording device 94 Recording head

JP 2001-284541 A Japanese Patent Application Laid-Open No. 2001-077326 JP 2001-196547 A Patent No. 3769276 JP 2012-192573 A

Claims (7)

An electromechanical transducer provided on a substrate,
A lower electrode, a seed layer, a ferroelectric layer, and an upper electrode are sequentially laminated,
The seed layer is made of a complex oxide having a perovskite crystal structure including at least Pb, Sr, and Ti.   2. The electricity according to claim 1, wherein the lower electrode has a layer made of a complex oxide containing at least two elements of Sr, Ru, La, and Ni in contact with the seed layer. Mechanical conversion element.   The lower electrode is formed by sequentially laminating a metal layer made of a single metal of Pt, Rh, Ru, or Ir, or an alloy with another platinum group element mainly containing Pt, and a layer made of the complex oxide. The electromechanical transducer according to claim 2, wherein the electromechanical transducer has a two-layer structure. The ferroelectric layer is made of a complex oxide having a perovskite crystal structure represented by the general formula ABO ₃ , wherein A is mainly composed of Pb, Ba, or Sr, and B is Ti, Zr, Sn, Ni, The electromechanical transducer according to any one of claims 1 to 3, comprising Zn, Mg, or Nb as a main component.   The lower electrode is formed on the substrate via an adhesion layer, and the adhesion layer is made of at least one of titanium, tantalum, titanium oxide, tantalum oxide, titanium nitride, and tantalum nitride. The electromechanical transducer according to any one of claims 1 to 4, wherein A droplet discharge nozzle for discharging droplets;
A pressurizing chamber to which the droplet discharge nozzle communicates;
Pressure generating means for pressurizing the liquid contained in the pressure chamber,
The pressure generating means includes a diaphragm provided in the pressurizing chamber,
The electromechanical transducer according to any one of claims 1 to 5 provided on the diaphragm,
A liquid characterized in that the electromechanical transducer is driven to deform and displace the diaphragm so as to pressurize the liquid contained in the pressurizing chamber and discharge the liquid to the outside of the pressurizing chamber. Drop ejection head.   An image forming apparatus comprising the droplet discharge head according to claim 6.

Images