JP2004128492A - Piezoelectric thin-film element and actuator using it, ink jet head and ink jet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To relieve the internal stress of a dielectric thin-film, in a dielectric thin-film element. <P>SOLUTION: A dielectric thin-film element 16 is provided with a substrate 21, a first electrode 22 formed on the substrate 21, a dielectric thin-film 10 formed on the first electrode 22 and a second electrode 3 formed on the dielectric thin-film 10. The dielectric thin-film 10 has a structure having a piezoelectric layer 10a which has piezoelectric characteristics and a stress relieving layer 10b which is electrically isolated from the first electrode 22 and the second electrode 3, and whose Young's modulus is smaller than that of the piezoelectric layer 10a. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a piezoelectric thin film element used for a piezoelectric element, a pyroelectric infrared detecting element, a nonvolatile memory, an electro-optical effect element, and the like. More specifically, the present invention relates to an actuator using a piezoelectric effect of a piezoelectric dielectric, an ink jet head using the same, and an ink jet recording apparatus provided with the ink jet head.

応 用 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 to practical use by thinning technology and fine processing technology.

FIG. 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 dielectric thin film 93 as a first electrode, and a Pt upper electrode film 94 as a second electrode are formed on an MgO single crystal substrate 91. It is a structure formed sequentially. For example, it is applied to an actuator, a pressure sensor, an acceleration sensor, and the like by processing an electrode film, a dielectric film, and a substrate.
I. Kanno et. al: Appl. Phys. Let. 70 (1997) p1378-1380

Here, the piezoelectric thin film element 90 requires crystallization at 500 ° C. to 700 ° C. in forming the thin film. Therefore, during the process of cooling to room temperature, a compression or tensile internal stress is generated in the PZT dielectric thin film 93 due to a difference in thermal expansion coefficient between the PZT piezoelectric dielectric thin film 93 and the substrate 91 supporting the same.

Therefore, the mechanical strength is reduced, and there is a problem that when the piezoelectric film is continuously displaced, cracks are generated in the PZT piezoelectric dielectric thin film 93 or dielectric breakdown is induced.

Therefore, an object of the present invention is to provide a technique capable of relaxing the internal stress of a dielectric thin film.

In order to solve this problem, a piezoelectric thin film element according to the present invention includes a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a dielectric thin film formed on the first electrode. A piezoelectric thin-film element including a second electrode formed on the piezoelectric layer, wherein the dielectric thin film is electrically insulated from the piezoelectric layer having piezoelectricity and the first and second electrodes, And a stress relaxation layer having a smaller Young's modulus.

Further, the piezoelectric thin film element of the present invention comprises a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a second thin film formed on the dielectric thin film. Wherein the dielectric thin film has a piezoelectric function film having piezoelectricity and a stress relaxation function film having a different coefficient of thermal expansion from that of the piezoelectric function film.

Further, the piezoelectric thin film element of the present invention comprises a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a second thin film formed on the dielectric thin film. a piezoelectric thin-film element having the electrodes, the dielectric thin film has a composition represented by _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5), When the thermal expansion coefficient of the substrate is 20 to 40 × 10 ⁻⁷ (K ⁻¹ ), y is set to 0.4 to 0.5, and the thermal expansion coefficient of the substrate is 60 to 150 × 10 ⁻⁷ (K ^−1). In the case of ()), y = 0.5 to 0.7.

The piezoelectric thin film element of the present invention includes a substrate, a first electrode formed on the substrate, and a dielectric thin film containing a tetragonal phase of perovskite oxide formed on the first electrode. A piezoelectric thin-film element including a second electrode formed on a dielectric thin film, wherein the thermal expansion coefficient of the substrate is αs, the thermal expansion coefficient of the dielectric thin film is αf, and α = αs / αf. When 0.3 <α <0.7, the c-axis orientation ratio of the dielectric thin film is 10 to 40%, and when 1 <α <2.5, the c-axis orientation ratio of the dielectric thin film is 60% to 100%.

According to this, the internal stress of the dielectric thin film can be alleviated, the mechanical strength of the dielectric thin film can be maintained, and cracks and dielectric breakdown can be prevented.

As described above, according to the present invention, since the dielectric thin film has a multilayer structure or the composition of the dielectric thin film is adjusted according to the coefficient of thermal expansion of the substrate, internal stress is generated in the dielectric thin film. Even so, an effective effect that the internal stress can be relieved by the stress relieving layer can be obtained.

According to the actuator using such a piezoelectric thin film element, an effective effect that a stable displacement operation can be performed can be obtained.

According to the inkjet head using such an actuator, an effective effect that stable ink ejection can be performed can be obtained.

According to the ink jet recording apparatus having such an ink jet head, an effective effect that high quality printing can be performed by stable ink ejection can be obtained.

The invention according to claim 1 of the present invention is directed to a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a first electrode formed on the dielectric thin film. A piezoelectric thin-film element having two electrodes, wherein the dielectric thin-film is electrically insulated from the piezoelectric layer having piezoelectricity and the first and second electrodes, and has a Young's modulus higher than that of the piezoelectric layer. This is a piezoelectric thin film element having a small stress relaxation layer, and has an effect that even if internal stress occurs in the dielectric thin film, the internal stress can be relaxed by the stress relaxation layer.

According to a second aspect of the present invention, in the first aspect, the piezoelectric layer is represented by a chemical formula of ABO ₃ , wherein A is Pb, Ba, Nb, La, Li, Sr, Bi, Na, Perovskite-type oxidation containing at least one element selected from K and B as at least one element selected from Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W and Yb This is a piezoelectric thin film element that is a solid solution, and has an effect that even if an internal stress occurs in the dielectric thin film, the internal stress can be reduced by the stress relaxation layer.

The invention described in claim 3 of the present invention is the invention of claim 1, wherein the piezoelectric layer is represented by _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5) This is a piezoelectric thin film element that is a PZT film, and has an effect that even if internal stress occurs in the dielectric thin film, the internal stress can be reduced by the stress relaxation layer.

The invention according to claim 4 of the present invention is the piezoelectric thin film element according to claim 1, 2 or 3, wherein the stress relaxation layer is a metal containing a platinum-based noble metal as a main component or an oxide thereof. In addition, even if an internal stress is generated in the dielectric thin film, the internal stress can be alleviated by the stress relaxation layer.

The invention according to claim 5 of the present invention is directed to a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a first electrode formed on the dielectric thin film. A piezoelectric thin film element having two electrodes, wherein the dielectric thin film is a piezoelectric thin film element having a piezoelectric function film having piezoelectricity and a stress relaxation function film having a different coefficient of thermal expansion from the piezoelectric function film. In addition, even if an internal stress is generated in the dielectric thin film, the internal stress can be reduced by the stress relaxation function film.

According to a sixth aspect of the present invention, in the fifth aspect, the piezoelectric function film and the stress relaxation function film are represented by the chemical formula of ABO ₃ , and A represents Pb, Ba, Nb, La, Li, It contains at least one element selected from Sr, Bi, Na, and K, and at least one element selected from B, Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W, and Yb. This is a piezoelectric thin-film element that is a perovskite-type oxide solid solution containing, and has an effect that even if an internal stress occurs in the dielectric thin film, the internal stress can be reduced by the stress relaxation function film.

The invention according to claim 7 of the present invention is the invention of claim 5, wherein the piezoelectric functional film and the stress relaxation function _{film, Pb 1 + x (Zr y} + Ti 1-y) O 3 (x = 0~0 .5), the piezoelectric function film is a piezoelectric thin film element in which y = 0.5 to 0.6, and the stress relaxation function film is y = 0.1 to 0.3. Even if internal stress is generated in the body thin film, the internal stress can be reduced by the stress relaxation function film.

The invention according to claim 8 of the present invention is directed to a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a first thin film formed on the dielectric thin film. a piezoelectric thin-film element having a second electrode, the dielectric thin film has a composition expressed in _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5) When the thermal expansion coefficient of the substrate is 20 to 40 × 10 ⁻⁷ (K ⁻¹ ), y = 0.4 to 0.5, and the thermal expansion coefficient of the substrate is 60 to 150 × 10 ⁻⁷ (K ^In the case of ^-1 ), the piezoelectric thin film element in which y = 0.5 to 0.7, and the composition of the dielectric thin film is selected according to the coefficient of thermal expansion of the substrate. Has an effect that it is possible to reduce internal stress generated in the dielectric thin film when is cooled to room temperature.

The invention according to claim 9 of the present invention provides a dielectric thin film containing a substrate, a first electrode formed on the substrate, and a tetragonal phase of a perovskite oxide formed on the first electrode. And a piezoelectric thin-film element having a second electrode formed on the dielectric thin film, wherein the coefficient of thermal expansion of the substrate is αs, the coefficient of thermal expansion of the dielectric thin film is αf, and α = αs / αf. Then, when 0.3 <α <0.7, the c-axis orientation ratio of the dielectric thin film is 10 to 40%, and when 1 <α <2.5, the c-axis orientation ratio of the dielectric thin film is It is a piezoelectric thin film element having a ratio of 60 to 100%, and controls the coefficient of thermal expansion of the dielectric substrate itself by controlling the c-axis orientation rate of the dielectric thin film according to the coefficient of thermal expansion of the substrate. It is possible to reduce internal stress generated in dielectric thin film when substrate heated in thin film formation is cooled to room temperature It has the effect of that.

The invention according to claim 10 of the present invention is directed to a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a first thin film formed on the dielectric thin film. a piezoelectric thin-film element having a second electrode, the dielectric thin film, a _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5) in represented by tetragonal phase In the case where the thermal expansion coefficient of the substrate is 20 to 40 × 10 ⁻⁷ (K ⁻¹ ), the dielectric thin film has a c-axis orientation rate of 10 to 40%, and the thermal expansion coefficient of the substrate is 60 to 100%. In the case of × 10 ⁻⁷ (K ⁻¹ ), the piezoelectric thin film element has a c-axis orientation rate of the dielectric thin film of 60 to 100%, and the c-axis orientation of the dielectric thin film according to the thermal expansion coefficient of the substrate. The coefficient of thermal expansion of the dielectric substrate itself is controlled by controlling the coefficient of thermal expansion of the dielectric substrate itself. It has an effect of stress it is possible to alleviate.

According to an eleventh aspect of the present invention, there is provided an actuator using the piezoelectric thin film element according to any one of the first to tenth aspects, and a stable displacement operation can be performed. Has an action.

According to a twelfth aspect of the present invention, there is provided an inkjet head including the actuator according to the eleventh aspect, and a plurality of pressure chambers in which an ink liquid is contained and the displacement of the actuator acts. It has the effect that it becomes possible to do so.

According to a thirteenth aspect of the present invention, there is provided an ink jet recording apparatus provided with the ink jet head according to the twelfth aspect, which has an effect that high quality printing can be performed by stable ink ejection.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment 1)
FIG. 1 is a perspective view illustrating 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 a cross-sectional view illustrating 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 section of the ink jet head of FIG. 2, and FIG. 5 is an example of a piezoelectric thin film element according to Embodiment 1 of the present invention. FIG. 6 is a sectional view showing another example of the piezoelectric thin film element according to the first embodiment of the present invention.

An ink jet recording apparatus 40 shown in FIG. 1 includes an ink jet head 41 of the present invention that performs recording by utilizing 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. The recording is performed on the recording medium 42 by landing.

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).

FIG. 2 is a cross-sectional view showing the overall configuration of the ink jet head in the ink jet recording apparatus of FIG. 1, and FIG. 3 is a perspective view showing a main part of FIG.

In FIG. 2 and FIG. 3, A is a pressure chamber component, and an opening 1 for the pressure chamber is formed. B is an actuator portion arranged so as to cover the upper end opening surface of the pressure chamber opening 1, and C is an ink liquid flow path component arranged so as to cover the lower end opening surface of the pressure chamber opening 1. The pressure chamber opening 1 of the pressure chamber component A is divided into an actuator portion B and an ink liquid flow channel component C located above and below the pressure chamber opening 1 to form a pressure chamber 2. In the actuator section B, a second electrode 3 which is an individual electrode located above the pressure chamber 2 is arranged. The pressure chambers 2 and the second electrodes 3 are arranged in a zigzag as shown in 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 communicating the common liquid chamber 5 with the pressure chamber 2, An ink flow path 7 through which the ink liquid flows out 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 denotes an IC chip, which supplies a voltage to a number of second electrodes 3 via bonding wires BW.

Next, the configuration of the actuator section B will be described with reference to FIG.

に お い て In the figure, the actuator section B is a sectional view in a direction orthogonal to the ink liquid supply direction shown in FIG. In the figure, a pressure chamber component A having four pressure chambers 2 arranged in an orthogonal direction is illustrated for reference.

The actuator section B is displaced and vibrated by the second electrode 3 located above each pressure chamber 2, the dielectric thin film 10 located immediately below the second electrode 3, and the piezoelectric effect of the dielectric thin film 10. A diaphragm / common electrode 11;

The diaphragm / common electrode 11 is formed of a conductive material, and also serves as a first electrode that is a common electrode common to the pressure chambers 2. Further, the actuator section B has a vertical wall 13 located above the partition wall 2a that partitions each pressure chamber 2 from each other. In the figure, reference numeral 14 denotes an adhesive for bonding the pressure chamber component A and the actuator B.

Each vertical wall 13 does not adhere to the diaphragm / common electrode 11 even when a part of the adhesive 14 protrudes outside the partition wall 2a at the time of bonding using the adhesive 14. In addition, it 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 expected displacement and vibration.

{Circle around (2)} The second electrode 3, the dielectric thin film 10, and the diaphragm / common electrode 11 constitute a piezoelectric thin film element. Although the diaphragm and the common electrode (first electrode) are used here as well, they may be separate bodies. FIG. 5 and subsequent figures show a state in which the first electrode is separate from the diaphragm.

The second electrode 3 is, for example, a metal mainly composed of a platinum-based noble metal such as Pt (platinum), Ir (iridium), Ru (ruthenium), Os (osmium), or Pd (palladium) or an oxide thereof. The common electrode 11 is formed of, for example, Pt (platinum), Cr (chromium), Cu (copper), Mo (molybdenum), or Ta (tantalum).

The structure described above is common to the second to fourth embodiments. Therefore, duplicate description in each embodiment will be omitted.

The piezoelectric thin film element 16 shown in FIG. 5 has a substrate 21 formed of, for example, silicon, and a Pt electrode film as a first electrode 22 disposed on the substrate 21, and the dielectric thin film 10 is formed thereon. And a Pt electrode film, for example, as the second electrode 3.

The dielectric thin film 10 includes, for example, a piezoelectric layer 10a which is a piezoelectric PZT film having a composition of Pb (Zr _0.52 Ti _0.48 ) O ₃ and a stress relaxation layer 10b having a Young's modulus smaller than that of the piezoelectric layer 10a. The stress relaxation layer 10b is formed in two layers while being electrically insulated from the first electrode 22 and the second electrode 3, and has a thickness of, for example, 0.03 to 0.3 μm. However, the film thickness is not limited to this value, and the number of layers may be one or more.

{Circle around (4)} On the wall surface of the dielectric thin film 10, an insulating material 15 for preventing an electrical short circuit between the stress relaxation layers 10b is formed.

Here, including the case described below, the substrate 21 can be made of, for example, SUS (stainless steel), glass, MgO single crystal, or the like, in addition to silicon.

Further, the piezoelectric layer 10a is not limited to the PZT film described above, but is represented by the chemical formula of ABO ₃ , and A is at least one selected from Pb, Ba, Nb, La, Li, Sr, Bi, Na, and K. And a perovskite oxide solid solution containing at least one element selected from the group consisting of Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W and Yb. it can. Also, _{preferably, Pb 1 + x (Zr y} + Ti 1-y) O 3 and (x = 0~0.5) PZT film represented by, and more preferably, the use of Pb-based perovskite oxide solid solution Can be. Pb-based perovskite-type oxide solid solutions include Pb (Zr, Ti) O ₃ , (Pb, La) (Zr, Ti) O ₃ , Pb (Mg _1/3 , Nb _2/3 ) O ₃ , Pb (Mg _1/2 , W _1/2 ) O ₃ , Pb (Zn _1/3 , Nb _2/3 ) O ₃ , Pb (Cd _1/2 , W _1/2 ) O ₃ , Pb (Fe _2/3 , W _1/3 ) O ₃ , Pb (Yb _1/2 , Nb _1/2 ) O ₃ , PbTiO ₃ and their solid solutions, and PbZrO ₃ and their solid solutions.

{Circle around (4)} The stress relaxation layer 10b can be made of a metal mainly composed of a spreadable platinum-based noble metal such as Pt, Ir, Ru, Os, and Pd, or an oxide thereof.

Next, a method of forming the piezoelectric thin film element 16 will be described with reference to FIGS.

First, a Pt film of 0.2 μm and a PZT film of 1 μm are sequentially formed and laminated on the substrate 21 heated to, for example, about 600 to 650 ° C., and this is repeated twice more. Finally, a Pt film of 0.2 μm is formed.

ＲＦ An RF magnetron sputtering device is used as a film forming device. The Pt film is formed at about 0.3 Pa of Ar gas at a substrate temperature of about 650 ° C., and the PZT film is formed at about 0.3 Pa of Ar mixed gas with an oxygen partial pressure of 10% on Ar at a substrate temperature of about 620 ° C. .

The Pt film 10aa on the substrate 21 functions as the first electrode 22, the PZT films 10ba, 10bb, 10bc function as the piezoelectric layer 10a, and the Pt films 10ab, 10ac inside the laminated film function as the stress relaxation layer 10b.

Next, as shown in FIG. 16, the uppermost Pt film 10bd of the dielectric thin film 10 is subjected to photolithographic etching to form a plurality of second electrodes 3 independent of each other.

Further, as shown in FIGS. 6 and 17, the piezoelectric layer 10a and the stress relaxation layer 10b are etched to form a wall surface 10e on the piezoelectric layer 10a and the stress relaxation layer 10b, and as shown in FIG. An insulating material 15 is formed. The insulating material 15 is for preventing an electrical short circuit between the stress relaxation layers 10b, and is formed by a normal semiconductor manufacturing process using an organic resin such as a resist or polyimide, or an inorganic material such as SiO ₂ or Si ₃ N _4. Can be formed.

The electrical short circuit may be prevented by changing the film area shown in FIG.

In the embodiment described above, the piezoelectric thin-film element 16 is used for the substrate 2 heated in forming the thin film.
Even if an internal stress occurs in the dielectric thin film 10 due to a difference in thermal expansion coefficient from the substrate 21 in the process of cooling the substrate 1 to room temperature, the internal stress can be alleviated by the stress relaxation layer 10b. Thereby, the mechanical strength of the dielectric thin film 10 can be maintained, and cracks and dielectric breakdown can be prevented.

(Embodiment 2)
Figure 7 is a sectional view showing a piezoelectric thin film element according to the second embodiment of the present invention, FIG 8 is the composition and lattice constant at room temperature for PZT film represented by _{Pb (Zr y + Ti 1-} y) O 3 graph, Figure 10 showing the relationship between the temperature and the lattice constant of the graph, with y <0.6 for PZT film 9 is represented by _{Pb (Zr y + Ti 1-} y) O 3 showing the relationship between the is a graph showing the relationship between the _{pb (Zr y + Ti 1-} y) composition and thermal expansion coefficient of PZT film represented by O _3.

The illustrated piezoelectric thin film element 20 includes, for example, a substrate 21, a first electrode 22 disposed on the substrate 21, the dielectric thin film 10 disposed thereon, and a second thin film disposed thereon. Electrode 3. The first electrode 22 and the second electrode 3 are formed of a metal material such as Pt, Ir, Ru, Os, and Pd, or an alloy or oxide thereof.

The dielectric thin film 10 includes, for example, a piezoelectric function film 10c which is a piezoelectric PZT film having a composition of Pb (Zr _0.52 Ti _0.48 ) O ₃ and a stress relaxation function film 10d having a different coefficient of thermal expansion from the piezoelectric function film 10c. Become. The stress relaxation function film 10d is formed between the piezoelectric function film 10c and the first electrode 22, and has a thickness of, for example, 0.03 to 0.3 μm. However, the film thickness is not limited to this value, and the number of layers may be one or more.

Further, the piezoelectric function film 10c and the pressure relaxation function film 10d are not limited to the above-described PZT film, but are represented by the chemical formula of ABO ₃ , where A is Pb, Ba, Nb, La, Li, Sr, Bi, Na , K containing at least one element selected from the group consisting of Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W, and Yb. An oxide solid solution can be used. Also, _{preferably, Pb 1 + x (Zr y} + Ti 1-y) O 3 and (x = 0~0.5) PZT film represented by, and more preferably, the use of Pb-based perovskite oxide solid solution Can be. Pb-based perovskite-type oxide solid solutions include Pb (Zr, Ti) O ₃ , (Pb, La) (Zr, Ti) O ₃ , Pb (Mg _1/3 , Nb _2/3 ) O ₃ , Pb (Mg _1/2 , W _1/2 ) O ₃ , Pb (Zn _1/3 , Nb _2/3 ) O ₃ , Pb (Cd _1/2 , W _1/2 ) O ₃ , Pb (Fe _2/3 , W _1/3 ) O ₃ , Pb (Yb _1/2 , Nb _1/2 ) O ₃ , PbTiO ₃ and their solid solutions, and PbZrO ₃ and their solid solutions.

Here, when a PZT film represented by the piezoelectric functional film 10c and the stress relaxation function film _{10d Pb 1 + x (Zr y} + Ti 1-y) O 3 (x = 0~0.5), 8 As shown in FIG. 9, the lattice constant changes depending on the composition, and as shown in FIG. 9, the lattice constant also changes depending on the temperature. Therefore, as shown in FIG. 10, the thermal expansion coefficient of the randomly oriented PZT film continuously changes depending on the composition, and the polarity changes around y = 0.25. Taking advantage of this feature, the piezoelectric function film 10c and the stress relaxation function film 10d are set to y = 0.5 to 0.6 and y = 0.1 to 0.3, respectively. The coefficient of thermal expansion with the film 10d can be made different.

Next, a method for forming the piezoelectric thin film element 20 will be described.

First, a Pt film serving as the first electrode 22, a PZT film serving as the stress relaxation function film 10d, and a PZT film serving as the piezoelectric function film 10c are sequentially formed on the substrate 21 heated to, for example, 600 ° C. A Pt film to be the electrode 3 is formed.

ＲＦ An RF magnetron sputtering device is used as a film forming device. The Pt film is formed at an Ar gas of 0.3 Pa at a substrate temperature of 650 ° C., and the PZT film is formed on Ar at an Ar mixed gas of 10% oxygen partial pressure at 0.3 Pa at a substrate temperature of 620 ° C.

According to the piezoelectric thin film element 20 having such a configuration, even when internal stress is generated in the dielectric thin film 10 due to a difference in thermal expansion coefficient between the substrate 21 and the substrate 21 in the process of cooling the substrate 21 heated in forming the thin film to room temperature. The internal stress can be reduced by the stress relaxation function film 10d. Thereby, the mechanical strength of the dielectric thin film 10 can be maintained, and cracks and dielectric breakdown can be prevented.

The illustrated piezoelectric thin film element 30 has, for example, a silicon substrate 21, a Pt electrode film as a first electrode 22 disposed on the silicon substrate 21, a dielectric thin film 10 disposed thereon, and a For example, a Pt electrode film is disposed as the second electrode 3.

Here, the dielectric film 10 has a composition represented by _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5). When the coefficient of thermal expansion of the substrate 21 is 20 to 40 × 10 ⁻⁷ (K ⁻¹ ), the composition is y = 0.4 to 0.5, and the coefficient of thermal expansion of the substrate 21 is 60 to 150 × In the case of 10 ^-7 (K ^-1 ), the composition is y = 0.5 to 0.7.

That is, when the thermal expansion coefficient of the substrate 21 is 20 to 40 × 10 ⁻⁷ (K ⁻¹ ), the dielectric thin film 10 as a PZT film receives a tensile stress from the substrate 21. Therefore, if the composition is set to y = 0.4 to 0.5, the anisotropy (c / a) of the crystal in the crystal structure increases from the high temperature to the room temperature. Therefore, when a tensile stress is received from the substrate 21, the anisotropy changes in a direction to reduce the tensile stress, and the tensile stress applied to the dielectric thin film 10 is reduced.

When the coefficient of thermal expansion of the substrate 21 is 60 to 150 × 10 ⁻⁷ (K ⁻¹ ), the dielectric thin film 10 as a PZT film receives a compressive stress. In this case, since there is no need to adjust the stress, y = 0.5 to 0.7, which has the highest piezoelectricity of the PZT film, may be used.

Next, a method of forming the piezoelectric thin film element 30 will be described.

First, for example, on the substrate 21 was heated to 600 ° C., Pt film serving as the first electrode _{22, Pb 1 + x (Zr} y + Ti 1-y) O 3 as a dielectric thin film 10 (x = 0~0. The PZT film formed in 5) is formed while adjusting “y” in accordance with the coefficient of thermal expansion of the substrate 21, and a Pt film serving as the second electrode 3 is sequentially formed.

ＲＦ An RF magnetron sputtering device is used as a film forming device. The Pt film is formed at an Ar gas of 0.3 Pa at a substrate temperature of 650 ° C., and the PZT film is formed on Ar at an Ar mixed gas of 10% oxygen partial pressure at 0.3 Pa at a substrate temperature of 620 ° C. At this time, the method of controlling Y can be performed by changing the composition ratio of Ti or Zr in the target material according to the thermal expansion coefficient of the substrate 21.

According to the piezoelectric thin film element 30 having such a configuration, since the composition of the dielectric thin film 10 is selected according to the coefficient of thermal expansion of the substrate 21, the dielectric thin film is heated when the substrate 21 is cooled to room temperature. The internal stress generated in the body thin film 10 can be reduced. Thereby, the mechanical strength of the dielectric thin film 10 can be maintained, and cracks and dielectric breakdown can be prevented.

(Embodiment 3)
The structure of the piezoelectric thin-film element 30 of the present embodiment is the same as the structure of the piezoelectric thin-film element of the above-described third embodiment, and a description thereof will be omitted.

Dielectric film 10 in this embodiment, for example, _{Pb 1 + x (Zr y +} Ti 1-y) O 3 perovskite oxide containing tetragonal phase represented by (x = 0 to 0.5) It is a polycrystalline PZT film (random orientation).

When the thermal expansion coefficient of the substrate 21 is αs, the thermal expansion coefficient of the dielectric thin film 10 is αf, and α = αs / αf, when 0.3 <α <0.7, the dielectric thin film 10 The c-axis orientation ratio is 10 to 40%, and when 1 <α <2.5, the c-axis orientation ratio of the dielectric thin film 10 is 60 to 100%.

The coefficient of thermal expansion αf of the dielectric thin film 10 greatly differs depending on the material composition, and takes a value of αf = about 30 to 110 × 10 ⁻⁷ (K ⁻¹ ). For example, αf = about 80 × 10 ⁻⁷ (K ⁻¹ ) for Pb (Zr _0.52 , Ti _0.48 ) O _{3 and} αf = about 40 × 10 ^{−7 for} Pb (Mg _1/3 , Nb _2/3 ) O _3. For (K ⁻¹ ) and Pb (Zn _1/3 , Nb _2/3 ) O ₃ , αf = about 50 × 10 ⁻⁷ (K ⁻¹ ).

The dielectric thin film 10 is characterized in that its coefficient of thermal expansion differs depending on the axial direction. That is, the thermal expansion coefficient is negative on the c-axis and positive on the a-axis. By utilizing this, the coefficient of thermal expansion of the dielectric thin film oriented in a certain direction can be controlled.

That is, when the thermal expansion coefficient αf of the dielectric thin film 10 is larger than the thermal expansion coefficient αs of the substrate 21, that is, when 0.3 <α <0.7, the c-axis orientation rate is set to 10 to 40%. If the c-axis is larger than the a-axis in the plane of the dielectric thin film 10 and the coefficient of thermal expansion αf of the dielectric thin film 10 is reduced, the stress can be relaxed.

When the coefficient of thermal expansion αs of the substrate 21 is larger than the coefficient of thermal expansion αf of the dielectric thin film 10, that is, when 1 <α <2.5, the c-axis orientation ratio is set to 60 to 100% and the in-plane If the a-axis is larger than the c-axis and the thermal expansion coefficient αf of the dielectric thin film 10 is increased, the stress can be reduced.

More specifically, when the thermal expansion coefficient of the substrate 21 is, for example, 20 to 40 × 10 ⁻⁷ (K ⁻¹ ), the thermal expansion coefficient of the dielectric thin film Since the coefficient of thermal expansion of the substrate 21 is smaller than the coefficient, the c-axis orientation rate of the dielectric thin film 10 is set to 10 to 40%, and the stress of the dielectric thin film 10 is reduced by reducing the coefficient of thermal expansion.

When the thermal expansion coefficient of the substrate 21 is, for example, 60 to 100 × 10 ⁻⁷ (K ⁻¹ ), the thermal expansion coefficient of the substrate 21 is larger than that of the dielectric thin film 10. The c-axis orientation ratio of the dielectric thin film 10 is set to 60 to 100%, and the thermal expansion coefficient of the dielectric thin film 10 is increased to reduce stress.

Next, a method of forming the piezoelectric thin film element 30 will be described.

In FIG. 11, a Pt film (first electrode 22) of 0.2 μm and a PZT film (dielectric thin film 10) of 1 μm are sequentially formed and laminated on a (001) MgO single crystal substrate (substrate 21). A film (second electrode 3) of 0.2 μm is formed. All films are formed by sputtering, and an RF magnetron sputtering device is used as a film forming device. The first and second electrodes 21 and 3 are not limited to Pt, but may be Al, Ti / Au, or the like.

The crystal structure of a Pt film or a PZT film varies depending on sputtering conditions. For example, if a Pt film is formed at an Ar gas of 0.3 Pa and a substrate temperature of 650 ° C., and a PZT film is formed of Ar at an Ar mixed gas of 10% oxygen partial pressure, 0.3 Pa and a substrate temperature of 620 ° C., (001) A Pt film and a PZT film epitaxially grown in the (001) direction on the MgO single crystal substrate are obtained.

Here, when the PZT film has a tetragonal crystal structure, the (001) direction is separated into the c-axis and the a-axis, and the c-axis domain and the a-axis domain are formed. When analyzed by the powder X-ray diffraction method, the diffraction intensity Ic from the c-axis domain and the diffraction intensity Ia from the a-axis domain are obtained, and Ic / (Ic + Ia) × 100 (%) is defined as the c-axis orientation ratio.

Ｃ The c-axis orientation of the PZT film can be controlled by the cooling rate of the substrate temperature after film formation. That is, when the substrate 21 is cooled after the PZT film formation, the c-axis orientation rate is 10 to 40% when the cooling rate when the substrate temperature is lowered from 620 ° C. to 400 ° C. is 1 ° C./min or less. Become. On the other hand, when the cooling rate is also rapidly cooled at 20 ° C./min or more, the c-axis orientation ratio becomes 60 to 100%.

Therefore, the cooling rate of the substrate temperature after film formation is controlled so that the c-axis orientation ratio becomes a desired ratio from the relationship between the thermal expansion coefficient of the substrate 21 and the dielectric thin film 10 described above.

(4) Although the mechanism by which the c-axis orientation ratio can be controlled by the cooling rate is not clear, the following may be considered. That is, the cubic PZT film undergoes a phase transition to the tetragon at the Curie temperature during cooling during growth. At this time, in the case of slow cooling, the c-axis of each crystal grain is randomly oriented in the film thickness direction and the in-plane direction so as to relax the internal stress, so that the c-axis orientation decreases.

According to the piezoelectric thin film element 30 having such a configuration, the coefficient of thermal expansion of the dielectric thin film 10 is controlled by controlling the c-axis orientation rate of the dielectric thin film 10 according to the thermal expansion coefficient of the substrate 21. Therefore, it is possible to reduce the internal stress generated in the dielectric thin film 10 when the substrate 21 heated in forming the thin film is cooled to room temperature. Thereby, the mechanical strength of the dielectric thin film 10 can be maintained, and cracks and dielectric breakdown can be prevented.

In the present embodiment described above, 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, but a temperature sensor utilizing the pyroelectricity, an electro-optical The present invention can be applied to various other uses such as a light modulation device utilizing the effect, an optical actuator utilizing the photoelastic effect, and a SAW device.

According to the actuator using the piezoelectric thin film element described above, a stable displacement operation can be performed. According to the inkjet head using such an actuator, stable ink ejection can be performed. Will be possible. And according to the ink jet recording apparatus provided with such an ink jet head, it becomes possible to perform high quality printing by stable ink ejection.

The structures and methods described in Embodiments 1 to 3 can be appropriately combined.

INDUSTRIAL APPLICABILITY The present invention can be applied to an actuator used for ink ejection of an ink jet recording apparatus, a temperature sensor utilizing the pyroelectricity, a light modulation device utilizing the electro-optic effect, an optical actuator utilizing the photoelastic effect, a SAW The present invention can be applied to various other uses such as a device.

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. FIG. 2 is a cross-sectional view illustrating an overall configuration of an inkjet head in the inkjet recording apparatus of FIG. 1. The perspective view which shows the principal part of FIG. FIG. 2 is a cross-sectional view illustrating a configuration of an actuator unit of the inkjet head of FIG. 2. Sectional drawing which shows an example of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows another example of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows the piezoelectric thin film element in Embodiment 2 of this invention. Graph showing the relationship between the _{Pb (Zr y + Ti 1-} y) composition and lattice constant at room temperature for PZT film represented by O ₃ Graph showing the relationship between the temperature and the lattice constant in y <0.6 for PZT film represented by _{Pb (Zr y + Ti 1-} y) O 3 Graph showing the relationship between the _{Pb (Zr y + Ti 1-} y) composition and thermal expansion coefficient of PZT film represented by O ₃ Sectional drawing which shows the piezoelectric thin film element in Embodiment 3 of this invention. Sectional drawing which shows an example of the structure which shows the conventional piezoelectric thin film element. Sectional drawing which shows the formation procedure of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows the formation procedure of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows the formation procedure of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows the formation procedure of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows the formation procedure of the piezoelectric thin film element in Embodiment 1 of this invention. Sectional drawing which shows the formation procedure of the piezoelectric thin film element in Embodiment 1 of this invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 3 2nd electrode 10 Dielectric thin film 10a Piezoelectric layer 10b Stress relaxation layer 10c Piezoelectric function film 10d Stress relaxation function film 16 Piezoelectric thin film element 20 Piezoelectric thin film element 21 Substrate 22 First electrode 30 Piezoelectric thin film element

Claims (13)

A piezoelectric thin film including a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a second electrode formed on the dielectric thin film An element,
The dielectric thin film,
A piezoelectric layer having piezoelectricity;
A piezoelectric thin film element comprising: a stress relaxation layer that is electrically insulated from the first electrode and the second electrode and has a Young's modulus smaller than that of the piezoelectric layer. The piezoelectric layer is represented by a chemical formula of ABO ₃ , wherein A contains at least one element selected from Pb, Ba, Nb, La, Li, Sr, Bi, Na, and K, and B contains Cd, Fe, Ti. 2. The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film element is a perovskite oxide solid solution containing at least one element selected from the group consisting of, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W, and Yb. The piezoelectric _{layer, Pb 1 + x (Zr y} + Ti 1-y) O 3 piezoelectric thin-film element according to claim 1, characterized in that the PZT film represented by (x = 0 to 0.5) . 4. The piezoelectric thin film element according to claim 1, wherein the stress relaxation layer is a metal mainly composed of a platinum-based noble metal or an oxide thereof. A piezoelectric thin film including a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a second electrode formed on the dielectric thin film An element,
The dielectric thin film,
A piezoelectric functional film having piezoelectricity,
A piezoelectric thin film element comprising: the piezoelectric function film; and a stress relaxation function film having a different coefficient of thermal expansion. The piezoelectric function film and the stress relaxation function film are represented by the chemical formula of ABO ₃ , and A contains at least one element selected from Pb, Ba, Nb, La, Li, Sr, Bi, Na, and K; 6. A perovskite oxide solid solution containing at least one element selected from the group consisting of Cd, Fe, Ti, Ta, Mg, Mo, Ni, Nb, Zr, Zn, W and Yb. The piezoelectric thin film element as described in the above. The piezoelectric functional film and the stress relieving feature film is a PZT film represented by _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5), the piezoelectric functional film y 6. The piezoelectric thin film element according to claim 5, wherein y = 0.1 to 0.3 and y = 0.1 to 0.3 for the stress relaxation function film. A piezoelectric thin film including a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a second electrode formed on the dielectric thin film An element,
Wherein the dielectric thin _{film, Pb 1 + x (Zr y} + Ti 1-y) O 3 has a composition represented by (x = 0~0.5), the thermal expansion coefficient of 20 to 40 × 10 of the substrate ^-7 (K ^-1 ), y = 0.4 to 0.5; and when the thermal expansion coefficient of the substrate is 60 to 150 × 10 ^-7 (K ^-1 ), y = 0. A piezoelectric thin-film element having a ratio of 5 to 0.7. A substrate, a first electrode formed on the substrate, a dielectric thin film containing a tetragonal phase of a perovskite oxide formed on the first electrode, and a dielectric thin film formed on the dielectric thin film. A piezoelectric thin film element comprising a second electrode,
When the thermal expansion coefficient of the substrate is αs, the thermal expansion coefficient of the dielectric thin film is αf, and α = αs / αf,
When 0.3 <α <0.7, the c-axis orientation ratio of the dielectric thin film is 10 to 40%. When 1 <α <2.5, the c-axis orientation ratio of the dielectric thin film. Is 60 to 100%. A piezoelectric thin film including a substrate, a first electrode formed on the substrate, a dielectric thin film formed on the first electrode, and a second electrode formed on the dielectric thin film An element,
Wherein the dielectric thin film is represented by _{Pb 1 + x (Zr y +} Ti 1-y) O 3 (x = 0~0.5) containing tetragonal, the thermal expansion coefficient of the substrate is 20 to 40 In the case of × 10 ⁻⁷ (K ⁻¹ ), the dielectric thin film has a c-axis orientation ratio of 10 to 40%, and the substrate has a thermal expansion coefficient of 60 to 100 × 10 ⁻⁷ (K ⁻¹ ). In some cases, the dielectric thin film has a c-axis orientation ratio of 60 to 100%. An actuator using the piezoelectric thin-film element according to claim 1. An actuator according to claim 11,
An ink jet head, comprising: a plurality of pressure chambers in which an ink liquid is accommodated and in which the displacement of the actuator acts. An ink jet recording apparatus comprising the ink jet head according to claim 12.

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