JP4513252B2 - Piezoelectric thin film element and actuator, ink jet head, and ink jet recording apparatus using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric thin film element, and more specifically to an actuator using the piezoelectric effect of a piezoelectric dielectric, an ink jet head using the same, and an ink jet recording apparatus including the ink jet head.
[0002]
[Prior art]
There are various applications of dielectrics in the electronics field, such as piezoelectric elements, infrared sensors, light modulation elements, and memory elements. With the development of micromachining technology and the demand for miniaturization and weight reduction of various devices, various thin film devices using these dielectric materials are being put into practical use by thinning technology and fine processing technology.
[0003]
12 is a cross-sectional view showing an example of a configuration of a conventional piezoelectric thin film element (I. Kanno et. Al: Appl. Phys. Let. 70 (1997) p1378-1380). That is, in the piezoelectric thin film element 90 of FIG. 12, a Pt lower electrode film 92, a PZT piezoelectric thin film 93 as a first electrode, and a Pt upper electrode film 94 as a second electrode are sequentially formed on an MgO single crystal substrate 91. It is a configuration. (See, for example, Non-Patent Document 1) For example, it is applied to actuators, pressure sensors, acceleration sensors, and the like by processing electrode films, piezoelectric films, and substrates.
[0004]
Usually, thinning a material has properties unique to the thin film. This is largely due to the difference in the formation process from the bulk and the influence of the substrate supporting the thin film. For example, crystal parameters such as crystal plane and lattice constant of the piezoelectric thin film are greatly influenced by the substrate. Ferroelectric PbTiO _Three Has been reported that the (001) plane is oriented on the (100) plane MgO single crystal substrate and the (111) plane is oriented on the c plane sapphire substrate. This is because it is greatly affected by the crystal plane of the substrate. In the case of a single crystal substrate, if the lattice constant is greatly different between the substrate and the piezoelectric film, the crystal plane to be oriented is also affected. Also, regardless of the type of substrate such as oxide single crystal, metal, glass, etc., the internal stress of the piezoelectric film produced changes due to the difference in the coefficient of thermal expansion of the substrate, which causes the lattice constant of the piezoelectric film, etc. The crystal parameters of
[0005]
Due to such changes in crystal parameters of the piezoelectric thin film, its electrical characteristics (relative dielectric constant, coercive electric field, spontaneous polarization, piezoelectric constant, pyroelectric coefficient, etc.), optical characteristics (refractive index, electro-optic coefficient, etc.), etc. The characteristics change greatly.
[0006]
[Non-Patent Document 1]
I. Kanno et. al: Appl. Phys. Let. 70 (1997) p1378-1380
[0007]
[Problems to be solved by the invention]
Here, the piezoelectric thin film element 90 needs to be crystallized at about 400 ° C. to 700 ° C. in forming the thin film. Therefore, during the process of cooling to room temperature, tensile or compressive internal stress is generated in the piezoelectric thin film 93 due to the difference in thermal expansion coefficient between the piezoelectric thin film 93 and the substrate 91 supporting the piezoelectric thin film 93.
[0008]
When the piezoelectric thin film 93 has an internal tensile stress, that is, when a tensile force is applied to the grain boundary of the film, the piezoelectric thin film 93 is always subjected to a stress that tends to be peeled off. As a result, the mechanical strength is reduced, and it becomes weak against bending when a voltage is applied, and a crack is generated in the piezoelectric thin film 93 or film breakage is induced.
[0009]
That is, in the case of film breakage due to the presence of a partial defect or foreign matter at the time of film formation, spot-like breakage is mainly, but in the case of breakage due to internal stress of the film, breakage such as cracks occurs. In the case of spot-like breakage, partial breakage is sufficient, and the entire film often functions. However, breakage such as cracks tends to break down the entire film and easily receive serious damage.
[0010]
Then, an object of this invention is to provide the technique which can prevent the crack and film destruction of a piezoelectric material thin film.
[0011]
[Means for Solving the Problems]
In order to solve this problem, a piezoelectric thin film element of the present invention includes a substrate, a first electrode formed on the substrate, a piezoelectric thin film formed on the first electrode by substrate heating, and a piezoelectric A piezoelectric thin film element having a second electrode formed on a body thin film, wherein the piezoelectric thin film and the substrate have different thermal expansion coefficients, and the piezoelectric thin film is a compression film depending on the substrate It is.
[0012]
The piezoelectric thin film element of the present invention is formed on a substrate, a first electrode formed on the substrate, a piezoelectric thin film formed by sputtering on the first electrode, and the piezoelectric thin film. A piezoelectric thin film element including a second electrode, wherein the piezoelectric thin film is a compression film.
[0013]
Furthermore, the piezoelectric thin film element of the present invention is formed on a substrate, a first electrode formed on the substrate, a piezoelectric thin film formed on the first electrode by substrate heating, and the piezoelectric thin film. A piezoelectric thin film element including the second electrode, wherein the piezoelectric thin film is an alignment film having a compressive stress.
[0014]
Furthermore, the actuator of the present invention is an actuator having a piezoelectric thin film that is bonded to a partition wall that forms a pressure chamber by an adhesive, and that causes displacement due to voltage application to the pressure chamber, and has a thermal expansion coefficient of the piezoelectric thin film Is αp and the thermal expansion coefficient of the adhesive is αb, the relationship of αp <αb is satisfied.
[0015]
The actuator of the present invention is an actuator having a piezoelectric thin film that is joined to a partition wall that defines a pressure chamber and causes displacement due to voltage application to act on the pressure chamber, and the coefficient of thermal expansion of the piezoelectric thin film is αp, When the thermal expansion coefficient of the partition wall is αa, the relationship αa> αp is satisfied.
[0016]
According to this, since the piezoelectric thin film becomes a compressed film having a compressive stress and can maintain the mechanical strength, it becomes possible to prevent cracks and film breakage due to tensile stress.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the present invention, there is provided a substrate, a first electrode formed on the substrate, a piezoelectric thin film formed on the first electrode by heating the substrate, and formed on the piezoelectric thin film. A piezoelectric thin film element including the second electrode, The piezoelectric thin film is an alignment film having a compressive stress, and satisfies the relationship ds <dp, where ds is the surface lattice spacing of the substrate and dp is the surface lattice spacing of the piezoelectric thin film. Since it is a piezoelectric thin film element and the piezoelectric thin film is a compressed film having a compressive stress, the mechanical strength is maintained, and cracks and film breakage due to tensile stress are prevented.
[0018]
According to a second aspect of the present invention, there is provided a substrate, an intermediate layer formed on the substrate, a first electrode formed on the intermediate layer, and a piezoelectric formed on the first electrode by substrate heating. A piezoelectric thin film element comprising a body thin film and a second electrode formed on the piezoelectric thin film, The piezoelectric thin film is an alignment film having a compressive stress, and satisfies the relationship ds <dp, where ds is the surface lattice spacing of the substrate and dp is the surface lattice spacing of the piezoelectric thin film. Since it is a piezoelectric thin film element and the piezoelectric thin film is a compressed film having a compressive stress, the mechanical strength is maintained, and cracks and film breakage due to tensile stress are prevented.
[0019]
The invention according to claim 3 of the present invention is the invention according to claim 1 or 2, The piezoelectric thin film is an epitaxial film. Since it is a piezoelectric thin film element and the piezoelectric thin film is a compressed film having a compressive stress, the mechanical strength is maintained, and cracks and film breakage due to tensile stress are prevented.
[0029]
Claims of the invention 4 The invention described in claim 2 In the described invention, a piezoelectric thin film element in which the surface lattice spacing between the intermediate layer and the first electrode is smaller than the surface lattice spacing of the piezoelectric thin film, and the piezoelectric thin film is a compressed film having compressive stress. The mechanical strength is maintained and cracks and film breakage due to tensile stress are prevented.
[0035]
The invention according to claim 5 of the present invention is An actuator in which the piezoelectric thin film element according to any one of claims 1 to 4 is used, and a stable displacement operation can be performed. It has the action.
[0039]
Claims of the invention 6 The invention described in claim 5 The ink jet head includes the actuator described above and a plurality of pressure chambers in which ink liquid is accommodated and the displacement of the actuator acts, and has an effect of enabling stable ink ejection.
[0040]
Claims of the invention 7 The invention described in claim 6 It is an ink jet recording apparatus provided with the ink jet head described above, and has the effect that high quality printing can be performed by stable ink ejection.
[0041]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.
[0042]
(Embodiment 1)
FIG. 1 is a perspective view showing an overall schematic configuration of an ink jet recording apparatus using a piezoelectric thin film element according to an embodiment of the present invention, and FIG. 2 is an overall configuration of an ink jet head in the ink jet recording apparatus of FIG. FIG. 3 is a perspective view showing a main part of FIG. 2, FIG. 4 is a cross-sectional view showing a configuration of an actuator part of the ink jet head of FIG. 2, and FIG. 5 is a piezoelectric thin film element according to Embodiment 1 of the present invention. FIG. 6 is an explanatory view showing the internal stress of the piezoelectric thin film due to the difference in thermal expansion coefficient between the piezoelectric thin film and the substrate, and FIG. 7 is based on the difference in thermal expansion coefficient between the piezoelectric thin film and the substrate. FIG. 8 is a cross-sectional view showing another example of the piezoelectric thin film element according to the first embodiment of the present invention.
[0043]
An ink jet recording apparatus 40 shown in FIG. 1 includes an ink jet head 41 of the present invention that performs recording using the piezoelectric effect of a piezoelectric thin film element, and ink droplets ejected from the ink jet head 41 are recorded on a recording medium 42 such as paper. Is recorded on the recording medium 42. The inkjet head 41 is mounted on a carriage 44 provided on a carriage shaft 43 arranged in the main scanning direction X, and reciprocates in the main scanning direction X as the carriage 44 reciprocates along the carriage shaft 43. Move. Further, the ink jet recording apparatus 40 includes a plurality of rollers (moving means) 45 for moving the recording medium 42 in the sub scanning direction Y substantially perpendicular to the width direction of the ink jet head 41 (that is, the main scanning direction X). .
[0044]
FIG. 2 shows the overall configuration of the inkjet head 41 according to the embodiment of the present invention, and FIG. 3 shows the configuration of the main part thereof.
[0045]
2 and 3, A is a pressure chamber component, and the pressure chamber opening 1 is formed. B is an actuator portion arranged to cover the upper end opening surface of the pressure chamber opening 1, and C is an ink liquid flow path component arranged to cover the lower end opening surface of the pressure chamber opening 1. The pressure chamber opening 1 of the pressure chamber part A is partitioned by an actuator part B and an ink liquid flow path part C positioned above and below to become a pressure chamber 2. In the actuator part B, a first electrode 3 which is an individual electrode located above the pressure chamber 2 is arranged. A large number of these pressure chambers 2 and first electrodes 3 are arranged in a staggered manner as can be seen from FIG. The ink liquid flow path component C includes a common liquid chamber 5 shared between the pressure chambers 2 arranged in the ink liquid supply direction, a supply port 6 that communicates the common liquid chamber 5 with the pressure chamber 2, An ink flow path 7 through which the ink liquid flows is formed. D is a nozzle plate, in which a nozzle hole 8 communicating with the ink flow path 7 is formed. In FIG. 2, E is an IC chip, which supplies a voltage to a large number of first electrodes 3 via bonding wires (BW).
[0046]
Next, the structure of the actuator part B is demonstrated based on FIG.
[0047]
In the figure, the actuator part B shows a cross-sectional view in a direction orthogonal to the ink liquid supply direction shown in FIG. In the drawing, a pressure chamber part A having four pressure chambers 2 arranged in the orthogonal direction is drawn for reference.
[0048]
The actuator portion B is displaced and vibrated by the first electrode 3 positioned above each pressure chamber 2, the piezoelectric thin film 10 positioned immediately below the first electrode 3, and the piezoelectric effect of the piezoelectric thin film 10. A diaphragm / common electrode 11 is included. The diaphragm / common electrode 11 is formed of a conductive material and also serves as a second electrode that is a common electrode common to the pressure chambers 2. Furthermore, the actuator part B has the vertical wall 13 located above the partition wall 2a which divides each pressure chamber 2 mutually. In the figure, reference numeral 14 denotes an adhesive for bonding the pressure chamber part A and the actuator part B together. Each vertical wall 13 does not adhere to the diaphragm / common electrode 11 even when a part of the adhesive 14 protrudes to the outside of the partition wall 2 a during bonding using the adhesive 14. The diaphragm / common electrode 11 has a role of increasing the distance between the upper surface of the pressure chamber 2 and the lower surface of the diaphragm / common electrode 11 so that the diaphragm / common electrode 11 causes the desired displacement and vibration.
[0049]
The first electrode 3, the piezoelectric thin film 10 and the diaphragm / common electrode 11 constitute a piezoelectric thin film element. Here, the diaphragm and the common electrode (second electrode) are used together, but they may be separated. In FIG. 5 and subsequent figures, the diaphragm and the common electrode as the second electrode are shown separately.
[0050]
The first electrode 3 is made of, for example, Pt (platinum), and the diaphragm / common electrode 11 is made of, for example, Pt (platinum), Cr (chromium), Cu (copper), Mo (molybdenum), or Ta (tantalum). Yes.
[0051]
The structure described above is common to the following embodiments. Therefore, redundant description in each embodiment is omitted.
[0052]
In the piezoelectric thin film element 16 shown in FIG. 5, a substrate 21 and, for example, a Pt electrode film as the first electrode 3 is disposed on the substrate 21, the piezoelectric thin film 10 is disposed thereon, and the first thin film 10 is disposed thereon. For example, a Cr electrode film is disposed as the second electrode 22.
[0053]
Here, as a material of the substrate 21, for example, alumina (thermal expansion coefficient: 68 × 10 ^-7 / K), 860 crystallized glass (thermal expansion coefficient: 108 × 10 ^-7 / K), 863 crystallized glass (thermal expansion coefficient: 142 × 10 ^-7 / K), SUS304 (thermal expansion coefficient: 173 × 10 ^-7 / K), magnesium oxide (thermal expansion coefficient: 120 × 10 ^-7 / K) or the like.
[0054]
The piezoelectric thin film 10 is a PZT film having a perovskite structure containing Pb, Zr, Ti, for example, Pb (Zr _0.53 Ti _0.47 ) O _Three Piezoelectric PZT film having the following composition (thermal expansion coefficient: 60 × 10 ^-7 / K) is used. Note that the PZT film has a property that the thermal expansion coefficient is small and the stress can be easily controlled, and that the orientation (epitaxial growth) can be easily performed and the composition can be easily controlled.
[0055]
The piezoelectric thin film 10 has a thickness of 0.2 to 10 μm, and the substrate 21 has a thickness of 0.15 to 1.5 mm. However, the film thickness is not limited to this value.
[0056]
A method for forming the piezoelectric thin film element will be described. In addition, the formation method of a piezoelectric thin film element is not limited to the following description.
[0057]
After setting the substrate 21 of the above-described material in the vacuum chamber and evacuating, the substrate 21 is heated to 600 ° C., and a 4-inch Pt target is used by RF magnetron sputtering, with Ar gas as the sputtering gas, A Pt electrode film to be the first electrode 3 was formed at a gas pressure of 1 Pa and an RF power of 100 W.
[0058]
Next, a 6-inch PZT sintered body target (added with 20 mol% of PbO) is used on the first electrode 3 made of a Pt film by RF magnetron sputtering, and the substrate temperature is 580 ° C., Ar and O ₂ Mixed sputtering gas (gas ratio Ar: O ₂ = 19: 1), a piezoelectric thin film 10 made of a PZT film was formed at a gas pressure of 0.4 Pa and an RF power of 500 W.
[0059]
Thereafter, a Cr electrode film was formed as the second electrode 22 by DC sputtering using a 4-inch Cr target without heating the substrate with 100 W power in an atmosphere of Ar gas of 0.7 Pa of sputtering gas.
[0060]
Here, as described above, the piezoelectric thin film 10 and the substrate 21 have different thermal expansion coefficients, and the thermal expansion coefficient (αs) of the substrate 21 is larger than the thermal expansion coefficient (αp) of the piezoelectric thin film 10. Is larger (αp <αs). Thereby, the piezoelectric thin film 10 is a compressed film by the substrate 21.
[0061]
That is, as shown in FIG. 6, when the thermal expansion coefficient of the formed piezoelectric thin film 10 and the thermal expansion coefficient of the substrate 21 supporting the piezoelectric thin film 10 are different, Compressive or tensile stress acts on the piezoelectric thin film 10.
That is, as shown in FIG. 6A, when αp <αs (when the thermal expansion coefficient of the substrate 21 is larger than the thermal expansion coefficient of the piezoelectric thin film 10), the piezoelectric thin film 10 becomes a compression film. Further, as shown in FIG. 6B, when αp> αs (when the thermal expansion coefficient of the piezoelectric thin film 10 is larger than the thermal expansion coefficient of the substrate 21), the piezoelectric thin film 10 becomes a tensile film.
[0062]
Therefore, as shown in FIG. 6A, adjustment is made so that the thermal expansion coefficient of the substrate 21 is larger than the thermal expansion coefficient of the piezoelectric thin film 10 (αp <αs), and the piezoelectric thin film 10 is compressed. If the compressed film has, mechanical strength is maintained, and cracks and film breakage due to tensile stress are prevented.
[0063]
FIG. 7 shows the defective rate of piezoelectric actuators due to the difference in thermal expansion coefficient between the piezoelectric thin film and the substrate.
[0064]
In FIG. 7, a voltage of 35 V DC was applied between two electrodes for 200 pins (elements) of the ink jet head, and the defective rate of the piezoelectric actuators was determined. As shown in the figure, it can be seen that when 1.0 <αs / αp, that is, αp <αs, the defective product rate drastically decreases.
[0065]
If excessive compressive stress is generated in the piezoelectric thin film 10, problems such as operational stability may occur. In addition, electrical characteristics such as relative permittivity and piezoelectric characteristics may change, causing variations in characteristics. Considering this, an appropriate internal stress can be obtained when the condition 1 <αs / αp ≦ 1.2 is satisfied.
[0066]
The materials of the piezoelectric thin film 10 and the substrate 21 are not limited to those described above, and it is sufficient that the thermal expansion coefficient of the substrate 21 is larger than the thermal expansion coefficient of the piezoelectric thin film 10.
[0067]
Here, as shown in FIG. 8, an intermediate layer 23 may be formed on the substrate 21, and the first electrode 3 may be formed on the intermediate layer 23. As the intermediate layer 23, a rock salt type crystal structure oxide film such as MgO can be applied.
[0068]
A method for forming a piezoelectric thin film element configured as shown in FIG. 8 will be described. For example, after setting an alumina substrate as the substrate 21 in the vacuum chamber and evacuating it, the substrate 21 is heated to 400 ° C., and an intermediate layer of an MgO film having a rock salt type crystal structure crystallized in the (100) plane by plasma MOCVD. Layer 23 was formed to a thickness of about 700 nm. For this film formation, magnesium acetylacetonate gas vaporized at 215 ° C. as a CVD source gas and O 2 ₂ A gas pressure of 30 Pa and an RF power of 400 W were used.
[0069]
Next, the substrate 21 is placed in another vacuum chamber, heated to 600 ° C., and a 4-inch Pt target is used by an RF magnetron sputtering method. Ar gas is sputtered to a gas pressure of 1 Pa and RF power of 100 W. Thus, a Pt electrode film serving as the first electrode 3 was formed.
[0070]
Subsequently, a 6-inch PZT sintered target (added with 20 mol% of PbO) was used on the first electrode 3 made of a Pt film by RF magnetron sputtering, and the substrate temperature was 580 ° C., Ar and O ₂ Mixed sputtering gas (gas ratio Ar: O ₂ = 19: 1), a piezoelectric thin film 10 made of a PZT film was formed at a gas pressure of 0.4 Pa and an RF power of 500 W.
[0071]
Thereafter, a Cr electrode film was formed as the second electrode 22 by DC sputtering using a 4-inch Cr target without heating the substrate with 100 W power in an atmosphere of Ar gas of 0.7 Pa of sputtering gas.
[0072]
(Embodiment 2)
In FIG. 5, the piezoelectric thin film element of the present embodiment includes a substrate 21, a first electrode 3 formed on the substrate 21, a piezoelectric thin film 10 formed on the first electrode 3, and a piezoelectric film. A second electrode 22 formed on the body thin film 10 is provided, and the piezoelectric thin film 10 is formed on the compression film by sputtering.
[0073]
That is, in this embodiment, the deposition rate of the piezoelectric thin film 10 during sputtering is 0.8 μm / h to 10 μm / h, preferably 2.0 μm to so that the piezoelectric thin film 10 has a compressive stress after film formation. It is as high as 7 μm / h (hi-rate film formation).
[0074]
The deposition rate can be adjusted by, for example, sputtering gas pressure for forming a perovskite layer at a substrate temperature of 600 ° C., sputtering gas flow rate, oxygen partial pressure ratio (in the case of mixed gas with argon), target substrate distance, input power (cathode RF power). ) Can be performed by changing each condition.
[0075]
A method for forming the piezoelectric thin film element will be described. In addition, the formation method of a piezoelectric thin film element is not limited to the following description.
[0076]
After setting the substrate 21 of the above-described material in the vacuum chamber and evacuating, the substrate 21 is heated to 600 ° C., and a 4-inch Pt target is used by RF magnetron sputtering, with Ar gas as the sputtering gas, A Pt electrode film to be the first electrode 3 was formed at a gas pressure of 1 Pa and an RF power of 100 W.
[0077]
Next, a 6-inch PZT sintered body target (added with 20 mol% of PbO) is used on the first electrode 3 made of a Pt film by RF magnetron sputtering, and the substrate temperature is 580 ° C., Ar and O ₂ Mixed sputtering gas (gas ratio Ar: O ₂ = 19: 1), sputtering gas pressure 0.1 Pa to 5.0 Pa, preferably 0.1 Pa to 2.0 Pa, input power RF power 0.25 kW to 5.0 kW, preferably 5 kW to 3.0 kW A piezoelectric thin film 10 made of a PZT film was formed.
[0078]
As described above, the deposition rate of the piezoelectric thin film 10 at this time is a deposition rate of 0.8 μm / h to 10 μm / h, preferably 2.0 μm to 7 μm / h.
[0079]
Thereafter, a Cr electrode film was formed as the second electrode 22 by DC sputtering using a 4-inch Cr target without heating the substrate with 100 W power in an atmosphere of Ar gas of 0.7 Pa of sputtering gas.
[0080]
When the piezoelectric thin film 10 is formed as a compression film by sputtering as in the present embodiment, the substrate 21 is not limited to those listed in the first embodiment, for example, quartz (thermal expansion coefficient: 5.6). × 10 ^-7 / K), silicon (thermal expansion coefficient: 27 × 10 ^-7 / K), 7059 glass (thermal expansion coefficient: 46 × 10 ^-7 / K) or the like can be used, and no consideration is necessary for the thermal expansion coefficient. The materials described in Embodiment 1 can be used for the first electrode 3, the piezoelectric thin film 10, and the second electrode 22.
[0081]
As described above, according to the present embodiment, since the piezoelectric thin film 10 has a compressive stress by increasing the film forming speed of the strong piezoelectric thin film 10 formed by sputtering, the mechanical strength is high. It is held and cracks and film breakage due to tensile stress are prevented.
[0082]
(Embodiment 3)
FIG. 9 is an explanatory diagram showing the lattice spacing between the substrate of the piezoelectric thin film element and the piezoelectric thin film according to the third embodiment of the present invention.
[0083]
The structure of the piezoelectric thin film element is the same as that shown in FIG. 5 or FIG. The materials described in the first and second embodiments can be used for the first electrode 3, the piezoelectric thin film 10, and the second electrode 22.
[0084]
Here, in the present embodiment, the piezoelectric thin film 10 is an alignment film such as an epitaxial film having a compressive stress. When the surface lattice spacing of the substrate 21 is ds and the surface lattice spacing of the piezoelectric thin film 10 is dp, the relationship satisfies ds <dp. Specifically, when the piezoelectric thin film 10 in the present embodiment is a PZT film, since the a-axis lattice constant is 4.04 mm, the material of the substrate 21 has a smaller lattice constant, for example, SrTiO _Three (A-axis lattice constant: 3.905) is used.
[0085]
That is, when the piezoelectric thin film 10 is epitaxially grown on the substrate 21 under heating, the piezoelectric thin film 10 receives a compressive or tensile force reflecting the surface lattice spacing of the substrate 21.
[0086]
That is, as shown in FIG. 9A, when the surface lattice spacing of the piezoelectric thin film 10 epitaxially grown is larger than the surface lattice spacing of the substrate 21 (ds <dp), when viewed in one lattice unit of the film, This means that the substrate 21 is restrained, and compression internal stress acts inside the piezoelectric thin film 10.
[0087]
Further, as shown in FIG. 9B, when the plane lattice spacing of the piezoelectric thin film 10 epitaxially grown is smaller than the plane lattice spacing of the substrate 21 (ds> dp), no tension is generated inside the piezoelectric thin film 10. Internal stress works.
[0088]
Therefore, as shown in FIG. 9A, the surface lattice spacing of the piezoelectric thin film 10 is made larger than the surface lattice spacing of the substrate 21 (ds <dp), and the piezoelectric thin film 10 has a compressive film having compressive stress. Then, the mechanical strength is maintained, and cracks and film breakage due to tensile stress are prevented.
[0089]
Although the first electrode 3 is between the substrate 21 and the piezoelectric thin film 10, the first electrode 3 is overwhelmingly thinner than the substrate 21, and has little influence in terms of the restraining force of the piezoelectric thin film 10. Alternatively, the piezoelectric thin film 10 may be grown directly on the substrate 21 (in the case of an actuator, the first electrode 3 is formed after the substrate 21 is removed, and an electrode or buffer layer that does not inhibit epitaxial growth is used. ). As a method for forming the piezoelectric thin film 10, sputtering, a sol-gel method, a CVD method, or the like can be used.
[0090]
Here, in the case where the intermediate layer 23 is formed between the substrate 21 and the first electrode 3 (see FIG. 8), in order to make the piezoelectric thin film 10 a compressed film with certainty, the intermediate layer 23 and the first electrode 3 The surface lattice spacing with the electrode 3 is made smaller than the surface lattice spacing of the piezoelectric thin film 10.
[0091]
(Embodiment 4)
FIG. 10 is an explanatory view continuously showing a state in which the actuator according to the fourth embodiment of the present invention is bonded to the partition wall.
[0092]
The actuator according to the present embodiment is bonded to the partition wall 2 a that forms the pressure chamber 2 and the adhesive 14, and is a piezoelectric thin film by applying a voltage to the first electrode 3 and the second electrode 22. 10 displacements are applied to the pressure chamber 2, and the ink filled in the pressure chamber 2 is ejected.
[0093]
In such an actuator, when the thermal expansion coefficient of the piezoelectric thin film 10 is αp and the thermal expansion coefficient of the adhesive 14 is αb, the relationship of αp <αb is satisfied. As a result, the piezoelectric thin film 10 becomes a compressed film by the adhesive 14.
[0094]
That is, when the thermal expansion coefficient of the piezoelectric thin film 10 is different from the thermal expansion coefficient of the adhesive 14 used for bonding, compressive or tensile stress acts on the piezoelectric thin film 10. That is, when αp <αb (when the thermal expansion coefficient of the adhesive 14 is larger than the thermal expansion coefficient of the piezoelectric thin film 10), the piezoelectric thin film 10 becomes a compression film. In addition, when αp> αb (when the thermal expansion coefficient of the piezoelectric thin film 10 is larger than the thermal expansion coefficient of the adhesive 14), the piezoelectric thin film 10 becomes a tensile film.
[0095]
Therefore, the actuator shown in FIG. 10A and the partition wall 2a are bonded using the adhesive 14 having a thermal expansion coefficient larger than that of the piezoelectric thin film 10 (αp <αb) (FIG. 10). (B)). After bonding the partition wall 2a and the actuator, the substrate 21 is removed (FIG. 10C).
[0096]
In addition, as the adhesive 14, an inorganic material having a large thermal expansion coefficient (metal material such as silver solder or solder) is used, and adhesion is performed under heating. As a result, the adhesive 14 having a large coefficient of thermal expansion shrinks after bonding, so that compressive stress is applied to the piezoelectric thin film.
[0097]
Thus, in the piezoelectric thin film 10 constituting the actuator and the adhesive 14 for bonding the actuator to the partition wall 2a, the thermal expansion coefficient of the adhesive 14 is larger than the thermal expansion coefficient of the piezoelectric thin film 10. (Αp <αb) and the piezoelectric thin film 10 is a compressed film having a compressive stress, so that the mechanical strength is maintained and cracks and film breakage due to tensile stress are prevented.
[0098]
(Embodiment 5)
FIG. 11 is a sectional view showing an actuator according to the fifth embodiment of the present invention.
[0099]
The actuator according to the present embodiment is joined to the partition wall 2a that forms the pressure chamber 2 without using an adhesive, that is, the substrate is partially removed to form the partition wall 2a. In the case shown in FIG. 11 as well, as in the case shown in FIG. 10, the displacement of the piezoelectric thin film 10 due to the voltage application to the first electrode 3 and the second electrode 22 is applied to the pressure chamber 2 to Ink filled in the chamber 2 is ejected.
[0100]
In such an actuator, when the thermal expansion coefficient of the piezoelectric thin film 10 is αp and the thermal expansion coefficient of the partition wall 2a is αa, the relationship of αa> αp is satisfied. Thereby, the piezoelectric thin film 10 becomes a compression film by the partition wall 2a.
[0101]
Specifically, the piezoelectric thin film 10 is, for example, Pb (Zr _0.53 Ti _0.47 ) O _Three Piezoelectric PZT film having the following composition (thermal expansion coefficient: 60 × 10 ^-7 / K), the material of the partition wall 2a includes, for example, 860 crystallized glass (thermal expansion coefficient: 108 × 10 ^-7 / K) and 863 crystallized glass (thermal expansion coefficient: 142 × 10 ^-7 / K).
[0102]
Thus, the thermal expansion coefficient of the partition wall 2a is set to be larger than the thermal expansion coefficient of the piezoelectric thin film 10 constituting the actuator (αa> αp), and the piezoelectric thin film 10 is compressed with compressive stress. Since it is a film, mechanical strength is maintained, and cracks and film breakage due to tensile stress are prevented.
[0103]
In the above-described embodiment, the case where the piezoelectric thin film element of the present invention is applied to an actuator used for ink ejection of an ink jet recording apparatus has been described. However, a temperature sensor using the pyroelectric property, The present invention can be applied to various other uses such as a light modulation device utilizing an optical effect, an optical actuator utilizing a photoelastic effect, and a SAW device.
[0104]
In addition, according to the actuator using the piezoelectric thin film element described above, it is possible to perform a stable displacement operation, and according to the ink jet head using such an actuator, it is possible to perform stable ink ejection. It becomes possible. According to the ink jet recording apparatus provided with such an ink jet head, it is possible to perform high quality printing by stable ink ejection.
[0105]
【The invention's effect】
As described above, according to the present invention, since the piezoelectric thin film is a compressed film having compressive stress, the mechanical strength is maintained, and an effective effect that cracks and film breakage due to tensile stress are prevented can be obtained. .
[0106]
According to the actuator using such a piezoelectric thin film element, an effective effect that a stable displacement operation can be performed is obtained.
[0107]
According to the ink jet head using such an actuator, it is possible to obtain an effective effect of enabling stable ink discharge.
[0108]
In addition, according to the ink jet recording apparatus including such an ink jet head, an effective effect that high quality printing can be performed by stable ink ejection is obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an overall schematic configuration of an ink jet recording apparatus using a piezoelectric thin film element according to an embodiment of the present invention.
2 is a cross-sectional view showing the overall configuration of an ink jet head in the ink jet recording apparatus of FIG. 1;
FIG. 3 is a perspective view showing a main part of FIG.
4 is a cross-sectional view showing a configuration of an actuator part of the ink jet head of FIG. 2;
FIG. 5 is a cross-sectional view showing an example of a piezoelectric thin film element in the first embodiment of the present invention.
FIG. 6 is an explanatory diagram showing the internal stress of the piezoelectric thin film due to the difference in thermal expansion coefficient between the piezoelectric thin film and the substrate.
FIG. 7 is a graph showing the rate of defective piezoelectric actuators due to the difference in thermal expansion coefficient between the piezoelectric thin film and the substrate.
FIG. 8 is a cross-sectional view showing another example of the piezoelectric thin film element in the first embodiment of the present invention.
FIG. 9 is an explanatory diagram showing a lattice interval between a substrate of a piezoelectric thin film element and a piezoelectric thin film according to a third embodiment of the present invention.
FIG. 10 is an explanatory view continuously showing a state where an actuator according to a fourth embodiment of the present invention is bonded to a partition wall.
FIG. 11 is a sectional view showing an actuator according to a fifth embodiment of the present invention.
FIG. 12 is a cross-sectional view showing an example of a configuration showing a conventional piezoelectric thin film element
[Explanation of symbols]
2 Pressure chamber
2a partition wall
3 First electrode
10 Piezoelectric thin film
14 Adhesive
21 Substrate
22 Second electrode
23 Middle layer

Claims (7)

A substrate; a first electrode formed on the substrate; a piezoelectric thin film formed on the first electrode by heating the substrate; and a second electrode formed on the piezoelectric thin film. A piezoelectric thin film element,
The piezoelectric thin film is an alignment film having a compressive stress, and satisfies a relationship of ds <dp, where ds is a lattice spacing of the substrate and dp is a lattice spacing of the piezoelectric thin film. Piezoelectric thin film element. A substrate, an intermediate layer formed on the substrate, a first electrode formed on the intermediate layer, a piezoelectric thin film formed on the first electrode by substrate heating, and the piezoelectric thin film A piezoelectric thin film element having a second electrode formed on the substrate,
The piezoelectric thin film is an alignment film having a compressive stress, and satisfies a relationship of ds <dp, where ds is a lattice spacing of the substrate and dp is a lattice spacing of the piezoelectric thin film. Piezoelectric thin film element. 3. The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film is an epitaxial film. 3. The piezoelectric thin film element according to claim 2, wherein a surface lattice spacing between the intermediate layer and the first electrode is smaller than a surface lattice spacing of the piezoelectric thin film. An actuator comprising the piezoelectric thin film element according to any one of claims 1 to 4 . An actuator according to claim 5 ;
An ink-jet head comprising: a plurality of pressure chambers in which ink liquid is stored and the displacement of the actuator acts. An ink jet recording apparatus comprising the ink jet head according to claim 6 .

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