JP2008042191A - Piezoelectric element and manufacturing method thereof, and ink jet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element having high piezoelectric characteristics and satisfactory durability, to provide a method for manufacturing the piezoelectric element, and to provide an ink jet head having the piezoelectric element, improved displacement controllability, and superior durability. <P>SOLUTION: The piezoelectric element has a piezoelectric film on a substrate and a pair of electrodes in contact with the piezoelectric film, and utilizes a bending mode. The piezoelectric element has a domain made of a tetragonal crystal. The domain has a domain (a) made of a crystal in which a (100) plane is arranged in parallel with the film surface of the piezoelectric film. The domain (a) comprises: a domain A having a normal axis of a (001) plane so that it becomes parallel to the deflection direction of the piezoelectric film within a tolerance of ±6 degrees; and a domain B having a normal axis of a (001) plane so that it orthogonally crosses the direction of the deflection of the piezoelectric film mainly within a tolerance of ±6 degrees. The volume ratio of the domain A to the total volume of the domains A and B is larger than 50 vol.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric element used in an ink jet recording apparatus, an ink jet head, and a method for manufacturing the piezoelectric element.

  Piezoelectric elements are elements that convert electrical energy into mechanical energy such as mechanical displacement, stress, and vibration, and vice versa, and there are types such as unimorph and bimorph types depending on the bending displacement that occurs. . Such piezoelectric elements are widely used, for example, in inkjet heads, microphones, sounding bodies (speakers, etc.), various vibrators and oscillators, sensors, and the like of inkjet recording apparatuses. In recent years, printers using inkjet heads are widely used as printing devices such as personal computers for reasons such as good printing performance and easy handling, and low cost. In this inkjet head, bubbles are generated in liquid such as ink by thermal energy, and droplets are ejected by pressure waves caused by the bubbles, droplets are sucked and discharged by electrostatic force, vibration like a piezoelectric element There are various methods such as those using pressure waves by the child.

  As an ink jet head using a piezoelectric element, for example, the one shown in FIG. 1 is known. In the ink jet head shown in FIG. 1, a piezoelectric film continuously formed on a base 41 on which a plurality of pressure chambers 61 are arranged to cover two or more pressure chambers 61 via a vibration plate 42. 45 is provided. At least one of the upper electrode 46 and the lower electrode 44 sandwiching the piezoelectric film 45 from above and below is formed separately for each pressure chamber 61, and piezoelectric driving is performed on the piezoelectric film 45 for each pressure chamber 61. A region is formed. This piezoelectric drive region is smaller than the corresponding pressure chamber 61 in the plane direction parallel to the piezoelectric film 45, and is arranged with a gap over the entire circumference between the periphery of the pressure chamber 61. Then, a predetermined voltage is applied to the piezoelectric film 45 to expand and contract the piezoelectric film 45, thereby causing the vibration plate 42 to bend and vibrate, pressurizing a liquid such as ink in the pressure chamber 61, and the liquid discharge port 53. A droplet is discharged from the nozzle.

  Recently, color ink jet printers have become widespread. However, improvement in printing performance, particularly high resolution and high speed printing, and further lengthening of the ink jet head are required. Therefore, it is required to realize a multi-nozzle head structure in which the ink jet head is miniaturized. In order to reduce the size of the liquid ejecting head, it is necessary to reduce the size of the piezoelectric element for discharging the liquid. Further, in order to reduce the size of the piezoelectric element, the driving capability is reduced even if the size is reduced. Therefore, a piezoelectric element having a high piezoelectric constant is required.

Conventionally, a piezoelectric film used in a piezoelectric element can be obtained by, for example, forming a green sheet by molding a paste of PbO, ZrO ₂ and TiO ₂ powder into a sheet shape, and then sintering the sheet. A PZT piezoelectric material is used. However, it is difficult to form a PZT oxide film by this method to a thickness of 10 μm or less, for example. Further, since the green sheet is sintered at a temperature of 1000 ° C. or higher, there is a problem that the piezoelectric film shrinks to about 70% during heating. Since it is difficult to align the piezoelectric film and the structure such as the ink chamber with a dimensional accuracy on the order of several microns, a satisfactory small piezoelectric element has not been obtained.

  Other methods for producing piezoelectric films other than those currently reported include sputtering, chemical vapor deposition (sometimes referred to as CVD), molecular beam epitaxy (sometimes referred to as MBE), sol-gel. There is a method of manufacturing an oxide piezoelectric film such as a method. When these methods are used, a piezoelectric film having a thickness of 10 μm or less can be obtained.

  However, a thin film formed by a film forming method such as a sputtering method, a CVD method, an MBE method, or a sol-gel method has a problem that characteristics equivalent to those of bulk ceramics are not obtained. In order to solve this problem, for example, Patent Document 1 discloses a method of controlling crystal orientation in the (001) plane, and Patent Document 2 discloses (100) plane and (001) plane orientation of a tetragonal structure. A method for producing a mixed domain structure epitaxial film has been proposed. Patent Document 3 proposes a method in which (100) plane orientation is performed by an orientation control layer, and the residual stress is made zero or compressive stress.

  However, even the method disclosed in Patent Document 1 is inferior in function as a piezoelectric element because the same characteristics as bulk ceramics do not appear on the high electric field side.

  Further, in the method disclosed in Patent Document 2, it is not possible to use a morphotropic phase boundary region (which may be referred to as an MPB region) having good characteristics, and (100) orientation and (001) orientation with good reproducibility. There is a problem that the ratio cannot be controlled. In addition, a film having an excessively high ratio of (100) orientation, that is, a ratio of the [100] axis has a large contribution of the 90-degree domain effect, and the thin film element has a problem that the durability of the film is inferior.

  Here, the “90-degree domain effect” uses a 90 ° domain in which a (100) orientation of a tetragonal structure is a domain and a (001) orientation is a c domain. This is the effect of the distortion of the difference of their lattice constants by reversibly changing the a domain to the c domain and the c domain to the a domain. Shows a large piezoelectric constant.

  Further, in Patent Document 3, it is impossible to control the (100) plane orientation and the (001) plane orientation, and it is impossible to form a 90 ° domain having in-plane anisotropy of the piezoelectric film.

JP-A-8-116103 JP 2000-332569 A JP 2005-119166 A

  The present invention has been made to solve the above problems, and has a piezoelectric element with high piezoelectric characteristics and good durability, and an inkjet head and a piezoelectric body having the same with excellent displacement controllability and durability. An object of the present invention is to provide a method for manufacturing an element.

  A piezoelectric element of the present invention that has solved the above-described problems is a piezoelectric element that uses a bending mode and includes a piezoelectric film provided on a substrate and a pair of electrodes provided in contact with the piezoelectric film. The piezoelectric film has a domain composed of tetragonal crystals, and the domain has a domain that is a domain composed of crystals in which a (100) plane is arranged in parallel to the film surface of the piezoelectric film. A domain, which is a domain having a normal axis of (001) plane so that the a domain is parallel within an allowable range of ± 6 degrees mainly with respect to the bending direction of the piezoelectric film, A B domain that is a domain having a normal axis of the (001) plane so as to be orthogonal within an allowable range of ± 6 degrees with respect to the bending direction of the piezoelectric film, and the volume of the A domain and the The body of the A domain relative to the sum of the B domain volumes It is characterized in that the product ratio is greater than 50% by volume.

  In addition, an ink jet head according to the present invention includes the piezoelectric element according to the present invention.

  The piezoelectric element manufacturing method of the present invention is a method for manufacturing a piezoelectric element having a piezoelectric film provided on a substrate and a pair of electrodes provided in contact with the piezoelectric film. A forming step of forming the piezoelectric film, an opening step of forming a rectangular opening on the surface of the base on which the piezoelectric film is not formed, and a temperature of the base during the forming step A heating step of heating the substrate to a high temperature in this order, and the substrate has a linear thermal expansion coefficient larger than that of the piezoelectric film at a time prior to the heating step.

  According to the present invention, a piezoelectric element having high piezoelectric characteristics, excellent displacement controllability, and good durability can be provided. Further, according to the present invention, it is possible to provide an ink jet head excellent in ink ejection stability and ejection force.

  Hereinafter, the present invention will be described in detail.

[Piezoelectric element]
As described above, the piezoelectric element of the present invention is a piezoelectric element using a bending mode, which includes a piezoelectric film provided on a substrate and a pair of electrodes provided in contact with the piezoelectric film. . The piezoelectric film has a domain composed of tetragonal crystals. In the present invention, a domain consisting of a crystal in which the (100) plane is arranged in parallel to the film surface of the piezoelectric film is a domain, and a crystal in which the (001) plane is arranged in parallel to the film surface of the piezoelectric film. The domain consisting of Further, among the a domains, a domain made of a crystal having a normal axis of (001) plane so as to be parallel within an allowable range of ± 6 degrees with respect to the bending direction of the piezoelectric film is defined as the A domain. . In addition, a domain made of a crystal having a normal axis of (001) plane so as to be orthogonal within an allowable range of ± 6 degrees with respect to a direction in which the piezoelectric film is mainly bent is defined as a B domain.

  The piezoelectric element of the present invention is characterized in that the piezoelectric film has a volume ratio of the A domain with respect to the sum of the volume of the A domain and the volume of the B domain of more than 50% by volume. Preferably, the piezoelectric film has a volume ratio of more than 60% by volume, more preferably a volume ratio of more than 80% by volume.

  Here, “mainly the direction in which the piezoelectric film bends” means the direction in which the curvature becomes highest when a voltage is applied to distort the piezoelectric element in the bending mode piezoelectric element shown in FIG. (Direction 1 in FIG. 2).

  The piezoelectric element is a bending mode piezoelectric element, and the piezoelectric film has at least a domain composed of a tetragonal crystal. In the piezoelectric film, the volume ratio of the A domain to the total volume of the A domain and the B domain is greater than 50% by volume. As a result, the piezoelectric element of the present invention has a very large amount of displacement. This is a method of forming a 90 ° domain by releasing compressive stress, and has a normal axis of the (001) plane so that it is parallel within an allowable range of ± 6 degrees with respect to the main bending direction of the piezoelectric element. It is considered that the ratio of the A domain increases, the amount of deflection in the direction increases, and the amount of displacement is very large.

  The piezoelectric element of the present invention is not particularly limited as long as it has the above configuration. FIG. 3 shows an example of an embodiment of the piezoelectric element of the present invention. The piezoelectric element of the embodiment shown in FIG. 3 has a laminated structure in which a base body 41, a diaphragm 42, a buffer layer 43, a lower electrode 44, a piezoelectric film 45, and an upper electrode 46 are sequentially laminated. A part of the base 41 may be formed by etching the back side of the base on which the piezoelectric film is not formed into a shape such as a rectangle to form an opening in a part of the base. Alternatively, as shown in FIG. 3, a thin-walled portion having a thickness of 2 to 10 μm that functions as a diaphragm of a piezoelectric element is formed on the base, and is added to the upper diaphragm 42 to function as a diaphragm. You may do it.

The material of the substrate in the piezoelectric element of the present invention is preferably a material having good crystallinity, for example, Si. Specifically, an SOI in which a SiO ₂ film is formed on Si can be given. SrTiO ₃ having a linear thermal expansion coefficient larger than that of the piezoelectric film is preferable. The thickness of the substrate can be, for example, 100 μm to 1000 μm.

The diaphragm is preferably provided to transmit the displacement of the piezoelectric film, has high lattice matching with the substrate, and has a sufficiently high Young's modulus to function as a diaphragm. As the material of the diaphragm, for example, stabilized zirconia or SrTiO ₃ is preferable. When SOI is used as the substrate, an SiO ₂ layer on the Si single crystal layer may be used as the diaphragm. Further, as described above, a layer obtained by adding a part of the substrate and the buffer layer may be used as the diaphragm. The thickness of the diaphragm is preferably 2 μm to 10 μm, for example.

The buffer layer is provided for the purpose of matching the lattice matching between the crystal lattice constant of the substrate and the crystal lattice constant of the piezoelectric film, and is omitted when the lattice matching between the substrate and the piezoelectric film is good. You can also Further, since it is important to apply a compressive stress to the piezoelectric film as a role of the buffer layer in the present invention, it is preferable to select a material that can apply the compressive stress. The buffer layer may have a single-layer structure or a stacked structure having a plurality of layers to achieve its function. The material of the buffer layer is preferably a material having high crystal lattice matching even with respect to the diaphragm provided immediately below. When the base material is Si, for example, stabilized zirconia YSZ (Y ₂ O ₃ —ZrO ₂ ), CeO ₂ , SrTiO _{3 and the} like are preferable. Further, when the material of the substrate is SrTiO ₃ , the buffer layer is not necessary because the lattice constant of the substrate is high in lattice matching with the piezoelectric film, but may be present.

The lower electrode may be provided immediately above the buffer layer 43 as shown in FIG. 3, or may be provided between the diaphragm 42 and the buffer layer 43. Further, when the buffer layer is not provided, the buffer layer may be provided. In this case, the lower electrode may be provided on the diaphragm via an adhesion layer for improving adhesion. . As the material of the lower electrode, platinum group metals and these oxide-based conductive materials are preferable. Specific examples of the material of the lower electrode include platinum group metals such as Ru, Rh, Pd, Os, Ir, and Pt, and oxide-based conductive materials such as SrRuO ₃ , LaScCoO ₃ , BaPbO ₃ , and RuO _2. Can do.

Examples of the material of the adhesion layer include metals such as Ti, Cr, and Ir, and oxides thereof such as TiO ₂ and IrO ₂ .

  Since such a lower electrode 44 affects the orientation crystal orientation of the piezoelectric film provided thereon, the preferred orientation crystal orientation on the lower electrode surface is any one of [100], [110], and [111]. Preferably there is. When the preferred orientation crystal orientation on the lower electrode surface is [100], [110] or [111], the preferred orientation crystal orientation of the piezoelectric film 45 formed thereon is [100], [001]. Are oriented parallel to the surface of the piezoelectric film.

  In such a lower electrode, the crystal orientation is preferably 80% or more. This crystal orientation ratio is the sum of the integrated intensities of the peaks in the (n00) peak in the preferentially oriented crystal direction [100] of the lower electrode as measured by XRD (X-ray diffraction) θ-2θ. It is the ratio to the sum. Similarly, the sum of the integrated intensities of the peaks at the (nn0) in the preferentially oriented crystal direction [110] is the ratio to the sum of the integrated intensities of the peaks at all the orientations, The sum of integrated intensities of peaks is a ratio to the sum of integrated intensities of peaks in all orientations. When the crystal orientation rate of the lower electrode is 80% or more, the lower electrode has good electrical characteristics, and the piezoelectric film 45 provided thereon has excellent crystallinity. The crystal orientation rate of the lower electrode is more preferably 90% or more.

  The thickness of the lower electrode is preferably 100 nm or more and 1000 nm or less. When the adhesion layer is provided, the thickness of the adhesion layer is preferably 5 nm or more and 300 nm or less, more preferably 10 nm or more and 70 nm or less.

The piezoelectric film in the piezoelectric element of the present invention has the following chemical formula (1)
_{(Pb 1-x M x)} xm (Zr y Ti 1-y) O z (1)
(In the formula, M represents any one element selected from La, Ca, Ba, Sr, Bi, Sb, W, and Nb. Also, x, xm, y, and z are each 0 ≦ (A real number satisfying the relationship of x <0.2, 1.0 ≦ xm ≦ 1.3, 0.40 ≦ y <0.65, 2.5 ≦ z ≦ 3.0 is shown.)
A piezoelectric film made of a piezoelectric material represented by Specifically, for example,
(Pb _0.94 La _0.06 ) _1.2 (Zr _0.45 Ti _0.55 ) O ₃ ,
(Pb _0.85 La _0.15 ) _1.2 (Zr _0.45 Ti _0.55 ) O ₃
And other piezoelectric materials.

  In the piezoelectric element of the present invention, it is preferable to select a material having a larger linear thermal expansion coefficient than that of the piezoelectric film as the substrate or buffer layer material. In this way, the piezoelectric film is etched on the back side of the substrate on which the piezoelectric film is not formed to form an opening or thin portion (thickness is preferably 1 to 10 μm) in a part of the substrate. When the diaphragm is formed, the compressive stress applied to the piezoelectric film before the etching is released.

  FIG. 6 is a block diagram showing a manufacturing process according to the present invention, and FIGS. 7A to 7E are cross-sectional views showing the manufacturing process according to the present invention. In the present invention, the back surface side of the substrate is etched to form openings or thin portions in a portion of the substrate (step (4) and FIG. 7 (d) in FIG. 6), and then the substrate temperature during the formation of the piezoelectric film. The piezoelectric film is heated at a higher temperature (step (5) in FIG. 6 and FIG. 7 (e)). As a result, a 90 ° domain in which the a domain and the c domain are mixed is formed in the piezoelectric film.

  Furthermore, in the present invention, for example, when a diaphragm is formed by etching the back side of the substrate and forming an opening or thin portion in a portion of the substrate after forming the piezoelectric film, the shape of the opening or thin portion is usually used. Is not a perfect circular isotropic in the in-plane direction, but has a short and long shape. When such an opening or a thin-walled portion is used, when a 90 ° domain is formed by heat treatment, compressive stress is released more in the lateral direction than in the longitudinal direction, and anisotropy occurs in the in-plane direction of the a domain. At this time, an a domain having a normal axis of the (001) plane in the same direction as the short direction is defined as an A domain. Further, a domain having a normal axis of (001) plane in the same direction as the longitudinal direction is defined as B domain.

  At this time, the volume of the A domain increases relative to the volume of the B domain. In such a piezoelectric element, the direction having a large piezoelectric constant that is dominant for large displacement is the short direction, and the contribution to the displacement of the A domain is greater than the isotropic one. Therefore, the piezoelectric film in the present invention has a larger number of 90 ° domains in a direction in which it is desired to be largely distorted in order to use a large piezoelectric constant due to the 90 ° domain.

  The a domain, c domain, twin structure and volume ratio of the piezoelectric film in the present invention can be confirmed by a reciprocal lattice mapping method of X-ray diffraction or a pole measurement method of a symmetry plane. Furthermore, it can also be measured by the method described in JP-A-2003-98124. The crystal phase can be determined by a reciprocal lattice mapping method of X-ray diffraction. The epitaxial single crystal film or the uniaxially oriented film can be confirmed by an X-ray diffraction θ-2θ method, a rocking curve method, or an asymmetric surface pole measurement method. As described above, the crystal structure of the piezoelectric film can be easily confirmed by X-ray diffraction, but may be confirmed by, for example, cross-sectional observation with a transmission electron microscope (sometimes referred to as TEM).

  In addition, the composition ratio of Zr / (Zr + Ti) or the like of the piezoelectric film can be confirmed by composition analysis (sometimes referred to as ICP composition analysis) using an inductively coupled plasma emission analyzer or fluorescent X-ray analysis.

  For example, the volume ratio of the A domain to the total volume of the A domain and the B domain can be calculated as follows. First, as shown in FIG. 4, the short side direction and the long side direction of the piezoelectric element viewed from the film thickness direction are determined. A domain consisting of a crystal having a c-axis parallel to the film thickness direction is a c-domain, a domain consisting of a crystal having a c-axis parallel to the short direction is an A-domain, and a crystal having a c-axis parallel to the longitudinal direction. Let the domain be the B domain.

  FIG. 5 is an explanatory diagram of reciprocal lattice mapping measurement of the (004) plane and the (204) plane of the PZT piezoelectric film by X-ray diffraction when the in-plane rotation angle Φ of the piezoelectric element shown in FIG. 4 is 0 °. It is. FIG. 5 shows how the c domain and the a domain can be separated. The relationship between the c domain and the a domain can be understood from the explanatory diagram of the reciprocal lattice mapping measurement of the (004) plane of the upper PZT piezoelectric film. Further, the relationship with the c domain, the A domain, and the B domain can be understood from the explanatory diagram of the reciprocal lattice mapping measurement of the (204) plane of the lower PZT piezoelectric film.

Based on the reciprocal lattice mapping measurement of the (204) plane of the PZT piezoelectric film, the volume ratio of the A domain to the sum of the volume of the A domain and the volume of the B domain is X _A (volume%), and the diffraction X-ray of the A domain The integrated intensity is O, and the integrated intensity of the B domain diffracted X-ray is P. X _A (volume%) is the following formula (1)
X _A = 100 × [O / (O + P)] (1)
Can be calculated.

From the above definition, the volume of the a domain is the sum of the volumes of the A domain and the B domain. Therefore, the volume ratio X _a (volume%) of the a domain with respect to the sum of the volume of the a domain and the volume of the c domain is also the reverse of the PZT (204) plane, where Q is the integrated intensity of the diffracted X-rays of the c domain. From lattice mapping measurement, the following formula (2)
X _a = 100 × [(O + P) / (O + P + Q)] (2)
Can be calculated.

  The film thickness of the piezoelectric film in the present invention is preferably 500 nm or more and 10,000 nm or less, and more preferably 500 nm or more and 8000 nm or less. When the film thickness of the piezoelectric film is 500 nm or more, when the piezoelectric element is used in an ink jet head, it has durability against stress generated by repeated driving, and when it is 10,000 nm or less, the occurrence of film peeling is suppressed. Can do.

  The upper electrode 46 is provided immediately above the piezoelectric film 45 and applies an electric field to the piezoelectric film together with the lower electrode. An adhesion layer made of the same material as the adhesion layer provided between the lower electrode and the diaphragm may be provided between the upper electrode and the piezoelectric film. As the material of the upper electrode 46, the same material as that of the lower electrode can be used.

Specific examples of the piezoelectric element of the present invention include the following layer structures. The display of this layer structure is
Upper electrode 46 // piezoelectric film 45 // lower electrode 44 // buffer layer 43 // vibrating plate 42 // substrate 41
And the stacked structure is indicated by /.
Example 1: Pt / Ti (upper electrode 46) // PbZrTiO ₃ (piezoelectric body 45) // Pt (lower electrode 44) // LaNiO ₃ / CeO ₂ / YSZ (Y ₂ O ₃ —ZrO ₂ ) (buffer layer 43 ) // Si / SiO _x (diaphragm 42) // Si (base 41)
Example 2: SrRuO ₃ (upper electrode 46) // PbZrTiO ₃ (piezoelectric body 45) // SrRuO ₃ (lower electrode 44) // LaNiO ₃ / CeO ₂ / YSZ (Y ₂ O ₃ —ZrO ₂ ) (buffer layer 43 )) // Si / SiO ₂ (diaphragm 42) // Si (base 41)
Example 3: Pt / Ti (upper electrode 46) // PbZrTiO ₃ (piezoelectric body 45) // SrRuO ₃ (lower electrode 44) // LaNiO ₃ / CeO ₂ / YSZ (Y ₂ O ₃ —ZrO ₂ ) (buffer layer) 43) // Si / SiO ₂ (diaphragm 42) // Si (base 41)
Example 4: Pt / Ti (upper electrode 46) // PbZrTiO ₃ (piezoelectric body 45) // Pt / SrRuO ₃ (lower electrode 44) // LaNiO ₃ / CeO ₂ / YSZ (Y ₂ O ₃ —ZrO ₂ ) ( Buffer layer 43) // Si / SiO ₂ (diaphragm 42) // Si (base 41)
In addition, since the function described in the layer of the above configuration example often overlaps, the function is not limited.

[Inkjet head]
The ink jet head of the present invention is characterized by having the piezoelectric element of the present invention, and is not particularly limited as long as it has the piezoelectric element of the present invention. An example of the form is shown in FIG. As shown in FIG. 1, the base 41, a plurality of pressure chambers (liquid chambers) 61 provided in parallel with the base 41, the liquid discharge ports (nozzles) 53 provided in communication with the pressure chambers 61, and the pressures An ink jet head composed of a piezoelectric element 51 provided corresponding to the chamber 61 may be mentioned. In this ink jet head, the liquid discharge ports 53 are formed at a predetermined interval in the nozzle plate 52 provided on the lower side of the substrate 41, but may be provided on the side surface side.

  As an example, the piezoelectric element 51 is positioned in an opening (not shown) on the upper surface of the base 41 provided corresponding to each pressure chamber 61 and is provided so as to close the opening. Examples of each piezoelectric element 51 include an element configured by a laminate in which a diaphragm 42, a buffer layer 43, a lower electrode 44, a piezoelectric film 45, and an upper electrode 46 are sequentially laminated.

In the ink jet head of the present invention, the diaphragm 42, the buffer layer 43, the lower electrode 44, the piezoelectric film 45, and the upper electrode 46 are sequentially formed on the substrate 41 as films having crystal orientations aligned as described above. It has a piezoelectric element. This piezoelectric element has a piezoelectric film composed of 90 ° domains having anisotropy as described above. Such an anisotropy 90 ° domain is parallel to the short direction (mainly the direction of deflection) of the pressure chamber of the substrate within an allowable range of ± 6 degrees in the inkjet head (001). It has an A domain made of a crystal having a normal axis of the surface. The volume ratio (X _A ) of the A domain is greater than 50% by volume and is parallel to the longitudinal direction (mainly perpendicular to the direction of bending) within an allowable range of ± 6 degrees (001) It is formed in many states with respect to the B domain made of a crystal having a normal axis of the surface. For this reason, the inkjet head of the present invention can mount a piezoelectric element having a larger displacement than a piezoelectric element having a piezoelectric film having an isotropic 90 ° domain, and ejects a large amount of energy. It becomes.

[Method for Manufacturing Piezoelectric Element]
The method for manufacturing a piezoelectric element according to the present invention includes the following steps in order.
(A) Formation step of forming a piezoelectric film on the substrate (b) Opening step of forming a rectangular opening on the surface of the substrate on which the piezoelectric film is not formed (c) Formation of the substrate during the formation step Heating step of heating the substrate to a temperature higher than the temperature Here, the substrate has a linear thermal expansion coefficient larger than that of the piezoelectric film at a point before the heating step.

  An example of a method for manufacturing the piezoelectric element of the present invention is a method using a thin film deposition technique.

  In manufacturing the piezoelectric element having the above-described configuration, a method for manufacturing the diaphragm 42 may be a thin film manufacturing method such as a sputtering method, a CVD method, a laser ablation method (sometimes referred to as a PLD method), or an MBE method. . In particular, in the sputtering method, the diaphragm 42 made of an oxide thin film epitaxially grown on the substrate 41 can be obtained by sufficiently heating the substrate during film formation.

  As a method for manufacturing the buffer layer 43 of the piezoelectric element, a method similar to the electrode manufacturing method described below using a buffer material can be used.

  As a method for producing the lower electrode 44 and the upper electrode 46 laminated on the substrate 41 in the production of the piezoelectric element, thin film production such as sputtering, CVD, PLD, sol-gel, MBE, hydrothermal synthesis, etc. Technology can be used. By these methods, it is possible to form films by orienting crystals of the electrode material of the upper and lower electrodes in a specific direction.

  In order to form the piezoelectric film 45 on the lower electrode 44, a method of forming a piezoelectric film and growing a crystal by a sputtering method, a CVD method, a sol-gel method, an MBE method, a hydrothermal synthesis method, or the like is used. be able to.

As a method for forming the piezoelectric film 45 in the present invention, a method of growing each crystal phase by a sputtering method can be mentioned as a preferable one. In the formation of the piezoelectric film 45 by the sputtering method, a piezoelectric material constituting a crystal phase, for example, a sintered product, preferably an oxide represented by the following chemical formula (2) is used as a target. Is preferred.
_{(Pb 1-x M x)} xm (Zr y Ti 1-y) O Z (2)
(In the formula, M represents any one element selected from La, Ca, Ba, Sr, Bi, Sb, W, and Nb. Also, x, xm, y, and z are each 0 ≦ (A real number satisfying the relationship of x <0.4, 1.0 ≦ xm ≦ 1.8, 0.30 ≦ y <0.75, 2.5 ≦ z ≦ 3.0 is shown.)

  In the formed piezoelectric film, x, xm, y, and z in the above formula (2) are 0 ≦ x <0.2, 1.0 ≦ xm ≦ 1.3, and 0.40 ≦, respectively. It is preferably made of a crystal phase having a composition satisfying the relationship of y <0.65 and 2.5 ≦ z ≦ 3.0.

  In order to form the upper electrode 46 on the piezoelectric film 45, a sputtering method, a CVD method, a sol-gel method, an MBE method, a PLD method, a hydrothermal synthesis method, a vapor phase method such as a vapor deposition method, or a screen printing method. It is possible to use a coating method such as a liquid phase method such as a plating method.

  In order to form a 90 ° domain having anisotropy in the piezoelectric film, a recess is formed by etching on the surface of the substrate opposite to the surface on which the vibration plate 42 is provided, and then the piezoelectric film is formed. The piezoelectric film is heated at a temperature higher than the substrate temperature. As the etching method, wet etching using anisotropic etching, dry etching such as inductively coupled plasma method (sometimes referred to as ICP method), Liga process, Bosch process, or the like can be used. As a heating method, it is preferable to heat for several hours in an oxygen atmosphere using an electric furnace or a rapid heating apparatus (sometimes referred to as an RTA apparatus).

[Inkjet head manufacturing method]
A representative example of the method for producing an ink jet head of the present invention is a method for producing an ink jet head having the following steps.
(A) Piezoelectric element manufacturing process for manufacturing a piezoelectric element on a substrate (B) Pressure chamber forming step for providing a pressure chamber on the substrate (C) Ink supply path forming step for providing an ink supply path on the substrate (D) Liquid discharge port forming step for providing a liquid discharge port (E) Joining step for assembling an ink jet head by joining members constituting the ink jet head

  The method for manufacturing an ink jet head of the present invention is characterized in that the piezoelectric element manufacturing process is a piezoelectric element manufacturing process using the piezoelectric element manufacturing method of the present invention.

  Examples of the method for producing the ink jet head of the present invention include a method using a thin film deposition technique. In order to manufacture the ink jet head of the present invention, first, a piezoelectric element is produced on a substrate by the method for manufacturing a piezoelectric element of the present invention. Then, for example, a desired portion such as a pressure chamber 61 or an ink supply path is provided on the back surface side of the substrate surface on which the piezoelectric element is formed, and a nozzle plate 52 is manufactured by perforating a liquid discharge hole in a separate substrate. A method of assembling an ink jet head by joining them together can be given. In addition, a method of separately manufacturing a substrate provided with desired parts such as a pressure chamber, an ink supply path, a liquid discharge port, etc., and bonding them to the piezoelectric element manufactured by the piezoelectric element manufacturing method of the present invention, etc. Can be manufactured.

In the former method, a piezoelectric element is manufactured by the above-described method for manufacturing a piezoelectric element of the present invention, and a part of the base body 41 is removed at a constant pitch by a dry etching method to form a plurality of pressure chambers 61. A recess is formed. As the dry etching method, for example, wet etching using anisotropic etching, dry etching methods such as an ICP method, a liga process, and a Bosch process can be used. The shape of the pressure chamber can be selected as appropriate, such as a rectangle, a circle, and an ellipse, but is preferably a rectangle. In the case of a side shooter, the pressure chamber can be formed in a narrowed shape having a tapered portion toward the liquid discharge port. A nozzle plate 52 formed by punching the liquid discharge port 53 in a separate substrate is joined to the substrate in which the concave portion to be the pressure chamber 61 is formed, or the liquid discharge port 53 and the ink supply path are formed in another substrate. Ink jet heads can also be produced by joining the nozzle plates produced in this way. The material of the base for producing the nozzle plate or the like may be the same material as the base to be joined or a different material, for example, SUS, Ni or the like. The material of the substrate for producing the nozzle plate or the like is preferably a material having a difference in linear thermal expansion coefficient from that of the substrate to be bonded of 1 × 10 ⁻⁶ / ° C. or more and 1 × 10 ⁻⁸ / ° C. or less. Examples of the method for perforating the liquid discharge port in the substrate include methods such as etching, machining, and laser processing.

  The method for bonding the base body 41 and the nozzle plate 52 may be a method using an organic adhesive, but a method using solid phase bonding with an inorganic material is preferable. Examples of the material used for solid phase bonding include Si, In, Au, Cu, Ni, Pb, Ti, and Cr. For example, the bonding between the substrate and the nozzle plate is performed at a low temperature of 250 ° C. or less under a pressure of 2 MPa, or the bonding surfaces of the substrate and the nozzle plate are activated by Ar plasma or the like, and the bonding is performed in a high vacuum. There are some that can be joined firmly just by bonding at room temperature. Further, the solid phase bonding method is preferable because the difference in thermal expansion coefficient from the substrate is small, and problems due to warpage of the piezoelectric element are avoided when the length is increased, and damage to the piezoelectric element can be suppressed.

  Hereinafter, the piezoelectric element of the present invention and the ink jet head using the piezoelectric element of the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Example 1]
An ink jet head having the configuration shown in FIG. 1 was produced by the following method. First, using a sputtering apparatus, an epitaxially stabilized zirconia YSZ (Y ₂ O ₃ —ZrO ₂ ) film, an epitaxial CeO ₂ film, and an epitaxial SrTiO ₃ film are sequentially formed on a Si substrate, and a buffer layer (also serves as a vibration plate). ) Was produced.

At this time, the film formation conditions of the epitaxially stabilized zirconia YSZ (Y ₂ O ₃ —ZrO ₂ ) film are as follows: the Si substrate temperature is 800 ° C., Ar and O ₂ are used as process gases, and the applied power between the Si substrate and the target is The pressure in the apparatus was set to 60 Pa and 1.0 Pa. Thus, an epitaxially stabilized zirconia YSZ (Y ₂ O ₃ —ZrO ₂ ) film having a thickness of 200 nm was obtained.

Next, the conditions for forming the epitaxial CeO ₂ film were as follows: the Si substrate temperature was 800 ° C., Ar and O ₂ were used as process gases, the applied power between the Si substrate and the target was 80 W, and the pressure in the apparatus was 0.5 Pa. . Thereby, an epitaxial CeO ₂ film having a thickness of 200 nm was obtained.

Next, the film formation conditions of the epitaxial SrTiO ₃ are as follows: Si substrate temperature is 600 ° C., Ar and O ₂ are used as process gases, the applied power between the Si substrate and the target is 100 W, and the pressure in the apparatus is 0.3 Pa. . As a result, an epitaxial SrTiO ₃ film having a thickness of 2000 nm was obtained.

  Next, on the buffer layer (also serving as the diaphragm), Pt was used as a target, and a lower electrode was fabricated by the same method as the method for fabricating the buffer layer (also serving as the diaphragm) (step (1) in FIG. ) And FIG. 7 (a)). At this time, the production conditions of the lower electrode were as follows: the substrate temperature was 600 ° C., Ar was used as the process gas, the applied power between the buffer layer and the target was 100 W, and the pressure in the apparatus was 0.5 Pa. As a result, a single highly oriented Pt film (lower electrode) having a thickness of 400 nm was obtained.

Thereafter, a piezoelectric film was formed on the lower electrode using the sputtering apparatus (step (2) in FIG. 6 and FIG. 7 (b)). At this time, the production conditions of the piezoelectric film were as follows: the substrate temperature was 550 ° C., Ar and O ₂ were used as process gases, the applied power between the lower electrode and the target was 100 W, and the pressure in the apparatus was 0.5 Pa. Moreover, the target which has a composition represented by following Chemical formula (3) was used as a target.
_{(Pb 1-x M x)} xm (Zr y Ti 1-y) O 3 (3)
(In the formula, M represents La. Further, x = 0.06, xm = 1.10, and y = 0.52.)

Then, the upper electrode was produced by the method similar to the production method of the said lower electrode (process (3) of FIG. 6, and FIG.7 (c)). Next, a dry etching method using ICP was performed from the surface of the Si base opposite to the surface on which the diaphragm 42 was provided to remove the central portion to form a thin portion (sometimes referred to as a recess) (step (FIG. 6 ( 4) and FIG. 7 (d)). The thin portion has a depth of 200 μm, a width of 70 μm (equivalent to 180 dpi, 141 μm pitch), a length of 3 mm, and a thin thickness of 3 μm. At this time, the temperature of the substrate is 20 ° C., the gases used are SF ₆ and C ₄ F ₈ , the dielectric of the high frequency coil is performed at a high frequency (sometimes referred to as RF) with an output of 1800 W, and the pressure in the apparatus is 4.0 Pa. It was.

  Thereafter, heat treatment is performed in an oxygen atmosphere using an RTA apparatus at 700 ° C., which is a substrate temperature higher than the film forming temperature at the time of forming the piezoelectric film (step (5) in FIG. 6 and FIG. Thus, a piezoelectric element was obtained.

Here, the domain of the piezoelectric film after the heat treatment of the piezoelectric element was evaluated. The domain was evaluated by measuring the reciprocal lattice mapping of the (004) plane and the (204) plane of the piezoelectric film crystal by X-ray diffraction as described above. The volume ratio (X _A (volume%)) of the A domain to the sum of the volume of the A domain and the volume of the B domain was calculated using the following mathematical formula (1).
X _A = 100 × [O / (O + P)] (1)
The X _A of the piezoelectric film of the piezoelectric element was 80% by volume.

  Next, a Si nozzle plate provided with a liquid outlet 53 by drilling a liquid discharge port with a diameter of 30 μm in the Si substrate was prepared. This nozzle plate is formed on a Si base having a recess formed on the back surface side by applying a Si-Si bonding method (conditions are room temperature and Si surface activated in the same manner as the Si surface activated by Ar plasma at 10-6 Pa. Bonding was performed by bonding in a high vacuum), and a bonded inkjet head was manufactured. The obtained ink jet head had a pressure chamber having a length (longitudinal direction) of 3 mm and a width (short side direction) of 70 μm.

  An applied voltage of 20 V and a frequency of 10 kHz is applied to the obtained piezoelectric element (in the absence of ink when the inkjet head is manufactured), and the center position of the concave portion of the piezoelectric element (center of width 70 μm, center of length 3 mm) The amount of displacement was measured with a laser Doppler displacement meter. In addition, the obtained inkjet head was synchronized with the ejected droplet and the input signal, the droplet was observed with a CCD, and the size was observed to determine the ejection amount, and the ejection speed was measured. At this time, a voltage having a voltage of 20 V and a frequency of 10 kHz was applied to the inkjet head, as in the case of the piezoelectric element. The obtained results are shown in Tables 1 and 2.

[Example 2]
As a target, the following chemical formula (4)
_{(Pb 1-x M x)} xm (Zr y Ti 1-y) O 3 (4)
(In the formula, M represents La. Moreover, x = 0.06, xm = 1.10, and y = 0.40.)
A piezoelectric element and an ink jet head were produced in the same manner as in Example 1 except that those represented by In the same manner as in Example 1, the volume ratio X _A of the A domain with respect to the total volume of the A domain and the B domain of the piezoelectric film, and the ejection amount and ejection speed of the droplets of the inkjet head were measured. X _A of the piezoelectric film was 80% by volume. Tables 1 and 2 show the measurement results of the ejection amount and ejection speed of the droplets of the inkjet head.

[Comparative Example 1]
As a target, the following chemical formula (5)
_{(Pb 1-x M x)} xm (Zr y Ti 1-y) O 3 (5)
(In the formula, M represents La. Moreover, x = 0.06, xm = 1.10, and y = 0.40.)
This was carried out except that a material represented by the following was used, and after the heat treatment using the RTA apparatus, the center portion was removed from the Si substrate surface opposite to the vibration plate 42 by ICP to remove the central portion and form a recess. A piezoelectric element and an inkjet head were produced in the same manner as in Example 1. In the same manner as in Example 1, the volume ratio X _A of the A domain with respect to the total volume of the A domain and the B domain of the piezoelectric film, and the ejection amount and ejection speed of the droplets of the inkjet head were measured. X _{A of the} piezoelectric film was 50% by volume. Tables 1 and 2 show the measurement results of the ejection amount and ejection speed of the droplets of the inkjet head.

As shown in Table 1, in the piezoelectric films of the piezoelectric elements of Examples 1 and 2, the volume ratio (X _A ) of the A domain to the total of the volume of the A domain and the volume of the B domain was 80% by volume. . The piezoelectric film of the piezoelectric element of Comparative Example 1 to which X _A was 50% by volume. The displacement amount of the piezoelectric elements of Examples 1 and 2 having a large volume ratio (X _A ) of the A domain was larger than the displacement amount of the piezoelectric element of Comparative Example 1 and showed excellent performance.

  As shown in Table 2, the ink jet heads of Examples 1 and 2 have a large discharge amount when the applied voltage of 20 V and 10 kHz is applied, and the discharge speed is large and excellent in comparison with the ink jet head of Comparative Example 1. showed that.

It is a schematic diagram which shows the cross-section of one Embodiment of the inkjet head of this invention. It is a schematic diagram for demonstrating the direction (direction 1) mainly bent in one Embodiment of the piezoelectric element of this invention. It is a schematic diagram which shows the cross-sectional structure of one Embodiment of the piezoelectric element of this invention. It is a top view which shows the definition of each domain structure of the piezoelectric element of this invention. It is explanatory drawing of the profile of each domain structure by the reciprocal lattice space map of this invention. It is a block diagram which shows the manufacturing process which concerns on this invention. It is sectional drawing which shows the manufacturing process which concerns on this invention.

Explanation of symbols

41 Base 42 Diaphragm 43 Buffer Layer 44 Lower Electrode 45 Piezoelectric Film 46 Upper Electrode 51 Piezoelectric Element 52 Nozzle Plate 53 Liquid Discharge Port 61 Pressure Chamber (Liquid Chamber)

Claims (7)

In a piezoelectric element using a bending mode, having a piezoelectric film provided on a substrate and a pair of electrodes provided in contact with the piezoelectric film,
The piezoelectric film has a domain composed of tetragonal crystals,
The domain has an a domain that is a domain made of a crystal having a (100) plane arranged in parallel to the film surface of the piezoelectric film;
The A domain, which is a domain having a normal axis of (001) plane so that the a domain is parallel within an allowable range of ± 6 degrees with respect to the bending direction of the piezoelectric film, A B domain that is a domain having a normal axis of the (001) plane so as to be orthogonal to the direction of deflection of the piezoelectric film within an allowable range of ± 6 degrees;
The ratio of the volume of the A domain to the total volume of the A domain and the B domain is more than 50% by volume.   2. The piezoelectric element according to claim 1, wherein the domain composed of tetragonal crystals further has a c domain composed of crystals in which a (001) plane is arranged in parallel with the film surface of the piezoelectric film.   2. The piezoelectric element according to claim 1, wherein a direction in which the piezoelectric film is mainly bent is a short direction of the piezoelectric film. The piezoelectric film has the following formula (1):
_{(Pb 1-x M x)} xm (Zr y Ti 1-y) O z (1)
(In the formula, M represents any one element selected from La, Ca, Ba, Sr, Bi, Sb, W, and Nb. Also, x, xm, y, and z are each 0 ≦ (A real number satisfying the relationship of x <0.2, 1.0 ≦ xm ≦ 1.3, 0.40 ≦ y <0.65, 2.5 ≦ z ≦ 3.0 is shown.)
The piezoelectric element according to claim 1, wherein the piezoelectric element is made of   2. The piezoelectric element according to claim 1, wherein the piezoelectric film has a thickness of 500 nm or more and 10,000 nm or less.   An ink jet head comprising: a liquid chamber communicating with an ejection port for ejecting ink; and a piezoelectric element according to claim 1 that is provided corresponding to the liquid chamber and generates energy for ejecting ink. In a method for manufacturing a piezoelectric element having a piezoelectric film provided on a substrate and a pair of electrodes provided in contact with the piezoelectric film,
Forming the piezoelectric film on the substrate;
An opening step of forming a rectangular opening on the surface of the base on which the piezoelectric film is not formed;
A heating step of heating the substrate to a temperature higher than the temperature of the substrate during the forming step;
In this order, and the substrate has a coefficient of linear thermal expansion greater than that of the piezoelectric film before the heating step.

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