WO2018216225A1

WO2018216225A1 - Film structure and method for manufacturing same

Info

Publication number: WO2018216225A1
Application number: PCT/JP2017/020525
Authority: WO
Inventors: 健木島
Original assignee: アドバンストマテリアルテクノロジーズ株式会社
Priority date: 2017-05-26
Filing date: 2017-05-26
Publication date: 2018-11-29
Also published as: TWI758182B; JPWO2018216225A1; TW202134058A; JP7307302B2; TW201900415A; JP6881790B2; TWI728147B; JP2021121026A

Abstract

Provided is a film structure having a conductive film formed on a substrate and a piezoelectric film formed on the conductive film, wherein the piezoelectric constant of the piezoelectric film can be increased. A film structure 10 has a conductive film 13, a film 14, and a film 15 that are sequentially formed on a substrate 11. The conductive film 13 contains platinum that has a cubic crystal structure and that is (100)-oriented. The film 14 contains a first composite oxide that is represented by Pb(Zr1−xTix)O3 and that is (100)-oriented in the pseudocubic representation. The film 15 contains a second composite oxide that is represented by Pb(Zr1−yTiy)O3 and that is (100)-oriented in the pseudocubic representation. x and y satisfy 0 < x < 1, 0 ≤ y ≤ 0.1, and y < x.

Description

Membrane structure and manufacturing method thereof

The present invention relates to a membrane structure and a manufacturing method thereof.

As a film structure having a substrate, a conductive film formed on the substrate, and a piezoelectric film formed on the conductive film, the substrate, a conductive film containing platinum formed on the substrate, and the conductive film There is known a film structure having a piezoelectric film containing lead zirconate titanate (PZT) formed thereon.
International Publication No. 2016/009698 (Patent Document 1) discloses that a ferroelectric ceramic has a Pb (Zr _1-A Ti _A ) O ₃ film and a Pb (Zr _1-A Ti _A ) O ₃ film on the Pb (Zr _1-A Ti _A ) O ₃ film. And a formed Pb (Zr _1-x Ti _x ) O ₃ film, in which A and x satisfy 0 ≦ A ≦ 0.1 and 0.1 <x <1.

International Publication No. 2016/009698

In a piezoelectric film including PZT, for example, when an electric field is applied along a direction parallel to the polarization direction or a direction having a certain angle with the polarization direction, the piezoelectric constant is large. Therefore, even if most of the piezoelectric films are oriented in the same direction as each other, if a part of the piezoelectric film is oriented in a direction different from that direction, the polarization direction is not uniform in the entire piezoelectric film. The piezoelectric constant of the film cannot be increased, and the characteristics of the piezoelectric element deteriorate.
The present invention has been made to solve the above-described problems of the prior art, and includes a film structure having a conductive film formed on a substrate and a piezoelectric film formed on the conductive film. An object of the present invention is to provide a film structure capable of increasing the piezoelectric constant of the piezoelectric film.

Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.
A film structure as one embodiment of the present invention includes a silicon substrate including a main surface including a (100) plane, and a (100) -oriented oxide formed on the main surface and having a cubic crystal structure. A first film containing zirconium, and a first conductive film formed on the first film, having a cubic crystal structure, and containing (100) -oriented platinum. In addition, the film structure is formed on the first conductive film, is represented by the following general formula (Chemical Formula 1), and is a second film including the first composite oxide that is (100) -oriented in a pseudo cubic crystal display. And a third film that is formed on the second film, is represented by the following general formula (Chemical Formula 2), and includes a second composite oxide that is (100) -oriented in pseudo-cubic crystal display. The film structure includes a first piezoelectric film containing lead zirconate titanate formed on the third film.

x and y satisfy the following formula (Formula 1) to Formula (Formula 3).

As another aspect, the thicknesses of the second film and the third film may be thinner than the thickness of the first piezoelectric film.
As another aspect, the first piezoelectric film may have a tetragonal crystal structure and may include (001) -oriented lead zirconate titanate.
As another aspect, in the first diffraction pattern of the first piezoelectric film measured by the X-ray diffraction measurement using the θ-2θ method, the intensity of the diffraction peak on the (001) plane of lead zirconate titanate The ratio of the diffraction peak intensities of any of the (110) plane and (101) plane of lead zirconate titanate may be 4 × 10 ⁻⁵ or less, or (110) plane and (101) plane None of the diffraction peaks may be observed.
As another aspect, the full width at half maximum of the rocking curve measured for the diffraction peak of the (001) plane in the first diffraction pattern by X-ray diffraction measurement using the rocking curve method is 0.3 to 0.6. It may be °.
As another aspect, the first piezoelectric film is formed on the second piezoelectric film, the second piezoelectric film including the third composite oxide made of lead zirconate titanate formed on the third film, and the second piezoelectric film. A third piezoelectric film including a fourth composite oxide made of lead zirconate titanate, wherein the second piezoelectric film may have a compressive stress, and the third piezoelectric film may have a tensile stress. .
As another aspect, the second piezoelectric film includes a third composite oxide represented by the following general formula (Formula 3), and the third piezoelectric film is represented by the following general formula (Formula 4). A fourth composite oxide may be included.

a may satisfy 0.1 <a ≦ 0.48, and b may satisfy 0.1 <b ≦ 0.48.
As another aspect, the film structure includes a second conductive film formed on the first piezoelectric film, and an alternating current having a frequency of 1 kHz between the first conductive film and the second conductive film. The relative dielectric constant measured by applying a voltage may be 300 to 400.
A manufacturing method of a film structure as one embodiment of the present invention includes a step (a) of preparing a silicon substrate including a main surface made of a (100) plane, and a cubic crystal structure on the main surface, And (b) forming a first film containing (100) oriented zirconium oxide. The manufacturing method of the film structure includes a step (c) of forming a first conductive film having a cubic crystal structure and containing (100) -oriented platinum on the first film. In addition, the manufacturing method of the film structure includes a second composite oxide including the first composite oxide represented by the following general formula (Chemical Formula 1) and (100) -oriented in a pseudo-cubic crystal display on the first conductive film. A step (d) of forming a film, and a third film containing a second composite oxide represented by the following general formula (Chemical Formula 2) and having a (100) orientation in pseudo-cubic crystal representation on the second film: Forming (e). And the manufacturing method of the said film structure has a (f) process of forming the 1st piezoelectric film containing lead zirconate titanate on the 3rd film.

x and y satisfy the following formula (Formula 1) to Formula (Formula 3).

As another aspect, the method for manufacturing the film structure includes a step (g) of heat-treating the first conductive film at a temperature of 450 to 600 ° C. after the step (c) and before the step (d). You may have.
As another aspect, the step (d) includes the first precursor of the first composite oxide by applying a first solution containing lead, zirconium, and titanium on the first conductive film. A step (d1) of forming the fourth film and a step (d2) of forming the second film by heat-treating the fourth film may be included. The step (e) includes a second precursor of the second composite oxide by applying a second solution containing lead and zirconium or lead, zirconium and titanium on the second film. A step (e1) of forming five films and a step (e2) of forming a third film by heat-treating the fifth film may be included.
As another aspect, the thicknesses of the second film and the third film may be thinner than the thickness of the first piezoelectric film.
As another aspect, in the step (f), a first piezoelectric film having a tetragonal crystal structure and containing (001) -oriented lead zirconate titanate may be formed.
As another aspect, the method for manufacturing the film structure includes a step (h) of measuring a first diffraction pattern of the first piezoelectric film by X-ray diffraction measurement using a θ-2θ method. Also good. And in the 1st diffraction pattern measured at the (h) process, with respect to the intensity of the diffraction peak of the (001) plane of lead zirconate titanate, the (110) plane and (101) plane of lead zirconate titanate The intensity ratio of any diffraction peak may be 4 × 10 ⁻⁵ or less, or any diffraction peak on the (110) plane and the (101) plane may not be observed.
Moreover, as another aspect, the manufacturing method of the film structure includes a diffraction peak on the (001) plane in the first diffraction pattern measured in the step (h) by X-ray diffraction measurement using a rocking curve method. (I) The process of measuring the rocking curve about may be included. The full width at half maximum of the rocking curve measured in the step (i) may be 0.3 to 0.6 °.
As another aspect, the step (f) includes the step (j) of forming a second piezoelectric film including a third composite oxide made of lead zirconate titanate on the third film, and the second piezoelectric step. (K) forming a third piezoelectric film containing a fourth composite oxide made of lead zirconate titanate on the film. In the step (j), a second piezoelectric film having a compressive stress may be formed, and in the step (k), a third piezoelectric film having a tensile stress may be formed.
As another aspect, in the step (j), a second piezoelectric film containing a third composite oxide represented by the following general formula (Formula 3) is formed. In the step (k), the following general formula ( A third piezoelectric film containing a fourth composite oxide represented by Chemical formula 4) may be formed.

a may satisfy 0.1 <a ≦ 0.48, and b may satisfy 0.1 <b ≦ 0.48.
As another aspect, in the step (j), the second piezoelectric film may be formed by a sputtering method. In the step (k), a sixth film containing a third precursor of the fourth composite oxide is formed by applying a third solution containing lead, zirconium and titanium on the second piezoelectric film. (K1) Step and (k2) step of forming the third piezoelectric film by heat-treating the sixth film may be included.
As another aspect, the method for manufacturing the film structure includes a step (1) of forming a second conductive film on the first piezoelectric film, and 1 kHz between the first conductive film and the second conductive film. (M) step of measuring the relative dielectric constant by applying an AC voltage having a frequency of 300, and the relative dielectric constant measured in the step (m) may be 300 to 400.
By applying one embodiment of the present invention, the piezoelectric constant of a piezoelectric film can be increased in a film structure including a conductive film formed over a substrate and a piezoelectric film formed over the conductive film. .

FIG. 1 is a cross-sectional view of the film structure according to the embodiment.
FIG. 2 is a cross-sectional view of the film structure when the film structure of the embodiment has a conductive film as an upper electrode.
FIG. 3 is a cross-sectional view of the film structure when the substrate and the alignment film are removed from the film structure shown in FIG.
FIG. 4 is a diagram schematically showing a pseudo-cubic unit cell and an orthorhombic unit cell when the composite oxide having a perovskite structure has an orthorhombic crystal structure.
FIG. 5 is a diagram schematically showing a cross-sectional structure of two piezoelectric films included in the film structure according to the embodiment.
FIG. 6 is a graph schematically showing the electric field dependence of the polarization of the piezoelectric film included in the film structure according to the embodiment.
FIG. 7 is a diagram illustrating a state in which the alignment film included in the film structure according to the embodiment has been epitaxially grown.
FIG. 8 is a cross-sectional view of the film structure of the embodiment during the manufacturing process.
FIG. 9 is a cross-sectional view during the manufacturing process of the film structure according to the embodiment.
FIG. 10 is a cross-sectional view of the film structure of the embodiment during the manufacturing process.
FIG. 11 is a cross-sectional view during the manufacturing process of the film structure according to the embodiment.
FIG. 12 is a cross-sectional view during the manufacturing process of the film structure according to the embodiment.
FIG. 13 is a cross-sectional view during the manufacturing process of the film structure according to the embodiment.
FIG. 14 is a cross-sectional view of a film structure according to a modification of the embodiment.
FIG. 15 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure in which the layers up to the PZO film are formed.
FIG. 16 is a graph showing an example of a θ-2θ spectrum by the XRD method of the film structure in which up to the PZO film is formed.
FIG. 17 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure in which up to the PZT film is formed.
FIG. 18 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure in which up to the PZT film is formed.
FIG. 19 shows the measurement result of the reciprocal lattice map of the film structure in which the layers up to the PZT film are formed.
FIG. 20 shows the measurement result of the reciprocal lattice map of the film structure formed up to the PZT film.
FIG. 21 shows the result of simulation of the PZT reciprocal lattice map.
FIG. 22 is a graph showing the voltage dependence of the polarization of the membrane structure.
FIG. 23 is a graph showing the voltage dependence of the polarization of the membrane structure.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.
In addition, the drawings may be schematically represented with respect to the width, thickness, shape, and the like of each part as compared with the embodiments for the sake of clarity of explanation, but are merely examples, and the interpretation of the present invention is not limited thereto. It is not limited.
In addition, in the present specification and each drawing, elements similar to those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description may be omitted as appropriate.
Furthermore, in the drawings used in the embodiments, hatching (shading) added to distinguish structures may be omitted depending on the drawings.
(Embodiment)
<Membrane structure>
First, a film structure according to an embodiment which is an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view of the film structure according to the embodiment. FIG. 2 is a cross-sectional view of the film structure when the film structure of the embodiment has a conductive film as an upper electrode. FIG. 3 is a cross-sectional view of the film structure when the substrate and the alignment film are removed from the film structure shown in FIG.
As shown in FIG. 1, the film structure 10 of the present embodiment includes a substrate 11, an alignment film 12, a conductive film 13, a film 14, a film 15, and a piezoelectric film 16. The alignment film 12 is formed on the substrate 11. The conductive film 13 is formed on the alignment film 12. The film 14 is formed on the conductive film 13. The film 15 is formed on the film 14. The piezoelectric film 16 is formed on the film 15.
As shown in FIG. 2, the film structure 10 of the present embodiment may have a conductive film 19. The conductive film 19 is formed on the piezoelectric film 16. At this time, the conductive film 13 is a conductive film as a lower electrode, and the conductive film 19 is a conductive film as an upper electrode. As shown in FIG. 3, the film structure 10 of the present embodiment does not have the substrate 11 (see FIG. 2) and the alignment film 12 (see FIG. 2), and the conductive film 13 as the lower electrode, It may have only the film 14, the film 15, the piezoelectric film 16, and the conductive film 19 as the upper electrode.
The substrate 11 is a silicon substrate made of silicon (Si) single crystal. The substrate 11 as a silicon substrate includes an upper surface 11a as a main surface made of a (100) plane. The alignment film 12 is formed on the upper surface 11a, has a cubic crystal structure, and includes (100) -oriented zirconium oxide. The conductive film 13 has a cubic crystal structure and contains (100) -oriented platinum. Thereby, when the piezoelectric film 16 includes a complex oxide having a perovskite structure, the piezoelectric film 16 can be (100) -oriented on the substrate 11.
Here, the alignment film 12 is (100) -oriented. The (100) plane of the alignment film 12 having a cubic crystal structure is mainly composed of the (100) plane of the substrate 11 which is a silicon substrate. It means that it is along the upper surface 11a as a surface, and preferably means that it is parallel to the upper surface 11a made of the (100) surface of the substrate 11 which is a silicon substrate. In addition, the (100) plane of the alignment film 12 is parallel to the upper surface 11 a made of the (100) plane of the substrate 11 only when the (100) plane of the alignment film 12 is completely parallel to the upper surface 11 a of the substrate 11. In addition, the case where the angle formed by the plane completely parallel to the upper surface 11a of the substrate 11 and the (100) plane of the alignment film 12 is 20 ° or less is included.
Alternatively, as the alignment film 12, an alignment film 12 made of a laminated film may be formed on the substrate 11 instead of the alignment film 12 made of a single layer film.
Preferably, the alignment film 12 is epitaxially grown on the substrate 11, and the conductive film 13 is epitaxially grown on the alignment film 12. Thereby, when the piezoelectric film 16 includes a complex oxide having a perovskite structure, the piezoelectric film 16 can be epitaxially grown on the conductive film 13.
Here, when two directions orthogonal to each other in the upper surface 11a as the main surface of the substrate 11 are an X-axis direction and a Y-axis direction, and a direction perpendicular to the upper surface 11a is a Z-axis direction, a film is epitaxially grown. The term “has” means that the film is oriented in any of the X-axis direction, the Y-axis direction, and the Z-axis direction.
The film 14 includes a complex oxide that is represented by the following general formula (Formula 1) and is (100) -oriented in a pseudo-cubic crystal display.

The film 15 includes a complex oxide that is represented by the following general formula (Formula 2) and is (100) -oriented in pseudo-cubic crystal display.

Here, x and y satisfy the following formula (Formula 1) to Formula (Formula 3).

In such a case, the piezoelectric film 16 formed on the film 15 can have a tetragonal crystal structure. Then, the content ratio of the lead zirconate titanate having a tetragonal crystal structure in the piezoelectric film 16 and the (110) orientation or the (101) orientation is set to a tetragonal crystal structure in the piezoelectric film 16. In addition, the content of lead (001) -oriented lead zirconate titanate can be made extremely small. Alternatively, the piezoelectric film 16 may be free from (110) -oriented or (101) -oriented lead zirconate titanate. Therefore, the polarization direction of each of the plurality of crystal grains included in the piezoelectric film 16 can be made uniform, so that the piezoelectric characteristics of the piezoelectric film 16 can be improved.
Suitably, x may satisfy | fill the following formula (Formula 4) instead of the said formula (Formula 1).

In the ceramic powder, when x satisfies the above formula (formula 4) instead of the above formula (formula 1), the ceramic powder tends to have a rhombohedral crystal structure. On the other hand, in the film 14, when x satisfies the above formula (formula 4) instead of the above formula (formula 1), the film 14 has a tetragonal crystal structure mainly due to a binding force from the substrate 11. It becomes easy to have. This ensures that the piezoelectric film 16 formed on the film 14 via the film 15 has a tetragonal crystal structure and (110) -oriented or (101) -oriented lead zirconate titanate. Can be excluded.
That is, when x satisfies the above formula (formula 4) instead of the formula (formula 1), the crystal structure of the film 14 that should originally have a rhombohedral crystal structure is changed to a tetragonal crystal structure. Thereby, the orientation direction of the piezoelectric film 16 formed on the film 14 via the film 15 can be controlled more reliably.
The thickness of the film 14 can be 10 to 50 nm. In such a range, the piezoelectric film 16 formed on the film 14 via the film 15 has a tetragonal crystal structure and is (110) -oriented or (101) -oriented zirconate titanate. It is possible to further ensure that lead is not contained.
In the following, Pb (Zr when y satisfies y = 0) _1-y Ti _y ) O ₃ That is, PbZrO ₃ Is referred to as PZO, and Pb (Zr when y satisfies 0 <y ≦ 0.1 _1-y Ti _y ) O ₃ May be referred to as PZT.
The complex oxide represented by the above general formula (Chemical Formula 1) or (Chemical Formula 2) and having a perovskite structure has a (100) orientation in a pseudo cubic crystal representation means the following case.
First, it includes a unit cell arranged three-dimensionally and has the general formula ABO ₃ In the crystal lattice having a perovskite structure represented by the following, a case where the unit cell includes one atom A, one atom B, and three oxygen atoms is considered.
In such a case, the (100) orientation in pseudo-cubic crystal display means that the unit cell has a cubic crystal structure and is (100) oriented. At this time, the length of one side of the unit cell is expressed as a lattice constant a. _c And one angle of the unit cell is defined as a lattice constant α _c And α _c = 90 °.
On the other hand, for example, a case where a composite oxide having a perovskite structure has a rhombohedral crystal structure is considered. And the lattice constant a which is the length of one side of the two lattice constants of the rhombohedral crystal _r Is the pseudocubic lattice constant a _c Is a lattice constant α which is one angle of the two lattice constants of the rhombohedral crystal. _r Is the lattice constant α of the pseudo-cubic crystal _c Is considered to be approximately equal to In the present specification, the numerical value V1 and the numerical value V2 are substantially equal means that the ratio of the difference between the numerical value V1 and the numerical value V2 to the average of the numerical value V1 and the numerical value V2 is about 5% or less. means.
At this time, the (100) orientation in the pseudo-cubic crystal display means the (100) orientation in the rhombohedral crystal display.
Alternatively, for example, consider a case where a complex oxide having a perovskite structure has a tetragonal crystal structure. And the first lattice constant a of the two lattice constants of tetragonal crystal _t Is the pseudocubic lattice constant a _c The second lattice constant c of the two tetragonal lattice constants _t Is the pseudocubic lattice constant a _c Is considered to be approximately equal to
At this time, the (100) orientation in pseudo-cubic crystal display means (100) or (001) crystal orientation in tetragonal crystal display.
Specifically, an example is considered in which a composite oxide composed of lead zirconate or lead titanate zirconate represented by the above general formula (Formula 1) has a rhombohedral crystal structure. And the lattice constant a which is the length of one side of the two lattice constants of the rhombohedral crystal _r Is the pseudocubic lattice constant a _c Is a lattice constant α which is one angle of the two lattice constants of the rhombohedral crystal. _r Is the lattice constant α of the pseudo-cubic crystal _c Is considered to be approximately equal to
At this time, the (100) orientation in the pseudo-cubic crystal display means the (100) orientation in the rhombohedral crystal display.
Alternatively, a case is considered in which a composite oxide composed of lead zirconate or lead zirconate titanate represented by the above general formula (Formula 1) has a tetragonal crystal structure. And the first lattice constant a of the two lattice constants of tetragonal crystal _t Is the pseudocubic lattice constant a _c The second lattice constant c of the two tetragonal lattice constants _t Is the pseudocubic lattice constant a _c Is considered to be approximately equal to
At this time, the (100) orientation in pseudo-cubic crystal display means (100) or (001) crystal orientation in tetragonal crystal display.
FIG. 4 is a diagram schematically showing a pseudo-cubic unit cell and an orthorhombic unit cell when the composite oxide having a perovskite structure has an orthorhombic crystal structure.
As shown in FIG. 4, an example in which the complex oxide represented by the above general formula (Chemical Formula 1) or (Chemical Formula 2) and having a perovskite structure has an orthorhombic crystal structure is considered. And the first lattice constant a among the three lattice constants of orthorhombic crystal _o1 Is the pseudocubic lattice constant a _c And the second lattice constant b of the three orthorhombic lattice constants _o1 Is the pseudocubic lattice constant a _c Of 2 ^1/2 Approximately equal to twice, and the third lattice constant c of orthorhombic lattice constants _o1 Is the lattice constant a _c Of 2 ^1/2 Consider an example that is approximately equal to twice.
At this time, the (100) orientation in the pseudo cubic display means the (011) or (100) orientation in the orthorhombic display.
Alternatively, as an example different from the example shown in FIG. 4 (illustration is omitted), a complex oxide represented by the general formula (Chemical Formula 1) or (Chemical Formula 2) and having a perovskite structure is another orthorhombic crystal. Consider an example having the following crystal structure: And the first lattice constant a of the three lattice constants of the orthorhombic crystal _o2 Is the pseudocubic lattice constant a _c Of 2 ^1/2 Approximately equal to twice, the second lattice constant b of the three orthorhombic lattice constants _o2 Is the pseudocubic lattice constant a _c Of 2 ^3/2 Approximately equal to twice, and the third lattice constant c of the orthorhombic lattice constant _o2 Is the pseudocubic lattice constant a _c Consider an example that is approximately equal to twice.
At this time, the (100) orientation in the pseudo cubic display means the (120) or (002) orientation in the orthorhombic display.
The piezoelectric film 16 is formed on the film 15, has a tetragonal crystal structure, and contains (001) -oriented lead zirconate titanate. The piezoelectric film 16 may not be (001) oriented when it has a tetragonal crystal structure. Alternatively, the piezoelectric film 16 may not have a tetragonal crystal structure.
In this embodiment, in the diffraction pattern of the piezoelectric film 16 measured by X-ray diffraction measurement using the θ-2θ method, zirconate titanate with respect to the intensity of the diffraction peak of the (001) plane of lead zirconate titanate. The ratio of the intensity of diffraction peaks of (110) plane and (101) plane of lead is 4 × 10 ^-5 Or none of the diffraction peaks on the (110) plane and (101) plane are observed.
Accordingly, the content of the lead zirconate titanate having a tetragonal crystal structure in the piezoelectric film 16 and the (110) orientation or the (101) orientation is changed to a tetragonal crystal in the piezoelectric film 16. Compared to the content of lead zirconate titanate having a structure and (001) orientation, it can be made extremely small. Alternatively, the lead zirconate titanate having a tetragonal crystal structure and having (110) orientation or (101) orientation can be prevented from being included in the piezoelectric film 16. Therefore, the polarization direction of each of the plurality of crystal grains included in the piezoelectric film 16 can be made uniform, so that the piezoelectric characteristics of the piezoelectric film 16 can be improved.
This is considered to be because, for example, the crystallinity of Pt contained in the conductive film 13 is improved by forming the conductive film 13 and then heat-treating the conductive film 13 as will be described later with reference to FIG. . Alternatively, as will be described with reference to FIG. 7 described later, for example, the lattice constant of PZT contained in the film 14 is well matched with the lattice constant of Pt contained in the conductive film 13, so that the crystallinity of the film 14 is improved. It is considered that the crystallinity of the film 15 is improved because the lattice constant of PZO or the like contained in the film 15 is good with respect to the lattice constant of PZT contained in the film 14.
Preferably, when a diffraction peak of the (00n) plane (n is an integer of 1 or more) is observed in the diffraction pattern, a diffraction peak of the (00n) plane (n is an integer of 1 or more) is observed at an angle 2θ. The full width at half maximum of the rocking curve measured in a fixed state at a fixed angle is 0.3 to 0.6 °. That is, the full width at half maximum of the rocking curve measured for the diffraction peak on the (001) plane in the diffraction pattern by X-ray diffraction measurement using the rocking curve method is 0.3 to 0.6 °.
Thereby, the dispersion | variation in the orientation direction of each of the several crystal grain contained in the piezoelectric film 16 can be made small. Therefore, the direction of the polarization axis in each of the plurality of crystal grains included in the piezoelectric film 16 can be further aligned, so that the piezoelectric characteristics of the piezoelectric film 16 can be further improved.
Preferably, the piezoelectric film 16 includes a piezoelectric film 17 and a piezoelectric film 18. The piezoelectric film 17 includes a composite oxide made of lead zirconate titanate formed on the film 15. The piezoelectric film 18 includes a composite oxide made of lead zirconate titanate formed on the piezoelectric film 17. The piezoelectric film 17 has a compressive stress, and the piezoelectric film 18 has a tensile stress.
Consider the case where the piezoelectric film 17 has tensile stress and the piezoelectric film 18 has tensile stress. In such a case, when the upper surface 11a of the substrate 11 is the main surface, the film structure 10 is likely to warp so as to have a downwardly convex shape. Therefore, for example, the shape accuracy when the film structure 10 is processed using a photolithography technique is lowered, and the characteristics of the piezoelectric element formed by processing the film structure 10 are deteriorated.
Consider a case where the piezoelectric film 17 has a compressive stress and the piezoelectric film 18 has a compressive stress. In such a case, when the upper surface 11a of the substrate 11 is the main surface, the film structure 10 is likely to warp so as to have a convex shape upward. Therefore, for example, the shape accuracy when the film structure 10 is processed using a photolithography technique is lowered, and the characteristics of the piezoelectric element formed by processing the film structure 10 are deteriorated.
On the other hand, in the present embodiment, the piezoelectric film 17 has a compressive stress, and the piezoelectric film 18 has a tensile stress. Thereby, compared with the case where both the piezoelectric film 17 and the piezoelectric film 18 have tensile stress, the amount of warping of the film structure 10 can be reduced, and both the piezoelectric film 17 and the piezoelectric film 18 are compressed. Compared to the case where the film structure 10 has, the amount of warp of the film structure 10 can be reduced. Therefore, for example, the shape accuracy when the film structure 10 is processed using a photolithography technique can be improved, and the characteristics of the piezoelectric element formed by processing the film structure 10 can be improved.
The piezoelectric film 17 has a compressive stress and the piezoelectric film 18 has a tensile stress. For example, when the piezoelectric film 18 and the piezoelectric film 17 are sequentially removed from the film structure 10, before and after the removal of the piezoelectric film 18. Thus, it can be confirmed that the substrate 11 is deformed downward from the convex side to the convex side and the substrate 11 is deformed upward from the convex side to the convex side before and after the removal of the piezoelectric film 17.
Preferably, the piezoelectric film 17 includes a composite oxide represented by the following general formula (Formula 3).

Here, a satisfies 0.1 <a ≦ 0.48.
Preferably, the piezoelectric film 18 includes a composite oxide represented by the following general formula (Formula 4).

Here, b satisfies 0.1 <b ≦ 0.48.
When the ceramic powder contains a composite oxide represented by the above general formula (Formula 3) or the above general formula (Formula 4), it has a rhombohedral crystal structure. On the other hand, when the piezoelectric film 17 includes the composite oxide represented by the general formula (Chemical Formula 3) or the general formula (Chemical Formula 4), a tetragonal crystal structure is mainly formed by a binding force from the substrate 11. It becomes easy to have. Therefore, the polarization axis of the lead zirconate titanate contained in the piezoelectric film 17 can be oriented substantially perpendicular to the upper surface 11a, so that the piezoelectric characteristics of the piezoelectric film 17 can be improved. In addition, since the polarization axis of lead zirconate titanate contained in the piezoelectric film 18 can be oriented substantially perpendicular to the upper surface 11a, the piezoelectric characteristics of the piezoelectric film 18 can be improved.
That is, when a satisfies 0.1 <a ≦ 0.48 or b satisfies 0.1 <b ≦ 0.48, the piezoelectric film 17 that should originally have a rhombohedral crystal structure or The 18 crystal structure changes to a tetragonal crystal structure. This is considered to improve the piezoelectric response of lead zirconate titanate contained in the

piezoelectric film

17 or 18.
As will be described later with reference to FIG. 13, the piezoelectric film 17 having a compressive stress can be formed by, for example, a sputtering method. Further, when the manufacturing process of the film structure is described, the piezoelectric film 18 having tensile stress can be formed by a coating method such as a sol-gel method, as will be described with reference to FIG.
FIG. 5 is a diagram schematically showing a cross-sectional structure of two piezoelectric films included in the film structure according to the embodiment. FIG. 5 shows a cross section formed by cleaving the substrate 11 included in the film structure 10 of the embodiment shown in FIG. 1, that is, a fractured surface, was observed with a scanning electron microscope (SEM). Of the observed image, the piezoelectric film 17 and the piezoelectric film 18 are schematically shown.
FIG. 6 is a graph schematically showing the electric field dependence of the polarization of the piezoelectric film included in the film structure according to the embodiment. FIG. 6 shows the polarization of the piezoelectric film 16 when the electric field between the lower electrode (conductive film 13) and the upper electrode (conductive film 19) included in the film structure 10 of the embodiment shown in FIG. 2 is changed. It is a graph which shows typically the polarization electric field hysteresis curve which shows this change.
As shown in FIG. 5, when the piezoelectric film 17 is formed by a sputtering method, the piezoelectric film 17 includes a plurality of crystal grains 17 a that are integrally formed from the lower surface to the upper surface of the piezoelectric film 17. Further, voids or voids hardly remain between two crystal grains 17a adjacent to each other in the main surface of the substrate 11 (upper surface 11a in FIG. 1). Therefore, when a cross-section for observation with an SEM is formed on the piezoelectric film 17 by processing by a focused ion beam (FIB) method, the cross-section becomes easily visible as a single cross-section, and crystal grains 17a becomes difficult to observe.
On the other hand, when the piezoelectric film 18 is formed by a coating method, the piezoelectric film 18 includes a plurality of films 18 a as layers stacked on each other in the thickness direction of the piezoelectric film 18. The film 18a as each of the plurality of layers includes a plurality of crystal grains 18b integrally formed from the lower surface to the upper surface of the single-layer film 18a. In addition, holes or voids may remain between the two films 18 a adjacent to each other in the thickness direction of the piezoelectric film 18.
As shown in FIG. 5, each of the plurality of crystal grains preferably has spontaneous polarization. This spontaneous polarization includes a polarization component P1 parallel to the thickness direction of the piezoelectric film 17, and the polarization components P1 included in the spontaneous polarization of each of the plurality of crystal grains are oriented in the same direction.
As shown in FIG. 5, in the present embodiment, the polarization components P1 included in the spontaneous polarization included in each of the plurality of crystal grains 17a included in the piezoelectric film 17 are directed in the same direction. In such a case, as shown in FIG. 6, in the initial state, the piezoelectric film 17 has a large spontaneous polarization. Therefore, after the electric field is increased from the starting point SP where the electric field is 0 to the positive side and returned to 0 again, the electric field is decreased to the negative side and returned to the end point EP until 0 again. The hysteresis curve indicating the electric field dependency is a curve having a starting point SP at a point away from the origin. Therefore, when the film structure 10 of the present embodiment is used as a piezoelectric element, it is not necessary to subject the piezoelectric film 17 to polarization treatment before use.
Note that the thickness of each of the

films

14 and 15 is smaller than the thickness of the piezoelectric film 16. In such a case, the thickness of the piezoelectric film 16 functioning as a piezoelectric film can be made thicker than any of the thicknesses of the

films

14 and 15, so that the characteristics of the film structure 10 as a piezoelectric element can be improved. Can be improved.
FIG. 7 is a diagram illustrating a state in which the alignment film included in the film structure according to the embodiment has been epitaxially grown. In FIG. 7, each layer of the substrate 11, the alignment film 12, the conductive film 13, the

films

14 and 15, and the piezoelectric film 16 is schematically illustrated. Hereinafter, the case where the film 15 is PZO will be described as an example.
The lattice constant of Si contained in the substrate 11 and ZrO contained in the alignment film 12 ₂ Table 1 shows the lattice constant of Pt included in the conductive film 13, the lattice constant of PZT included in the film 14, the lattice constant of PZO included in the film 15, and the lattice constant of PZT included in the piezoelectric film 16. Show.

As shown in Table 1, the lattice constant of Si is 0.543 nm, and ZrO ₂ Has a lattice constant of 0.511 nm, and ZrO relative to the lattice constant of Si. ₂ Since the mismatch of the lattice constant of Si is as small as 5.9%, ZrO with respect to the lattice constant of Si ₂ The lattice constant consistency of is good. Therefore, as shown in FIG. ₂ The alignment film 12 containing can be epitaxially grown on the main surface made of the (100) plane of the substrate 11 containing a silicon single crystal. Therefore, ZrO ₂ The alignment film 12 containing can be (100) oriented with a cubic crystal structure on the (100) plane of the substrate 11 containing silicon single crystal, and the crystallinity of the alignment film 12 can be improved.
As shown in Table 1, ZrO ₂ Although the lattice constant of Pt is 0.511 nm and the lattice constant of Pt is 0.392 nm, when Pt rotates 45 ° in the plane, the length of the diagonal becomes 0.554 nm, and ZrO ₂ The mismatch of the diagonal length with respect to the lattice constant of ZrO is as small as 8.4%. ₂ The lattice constant of Pt matches the lattice constant of. Therefore, as shown in FIG. 7, the conductive film 13 containing Pt is made of ZrO. ₂ On the (100) plane of the alignment film 12 containing, (100) orientation can be achieved with a cubic crystal structure, and the crystallinity of the conductive film 13 can be improved.
Further, as shown in Table 1, the lattice constant of Pt is 0.392 nm, the lattice constant of PZT is 0.411 nm, and the mismatch of the lattice constant of PZT with respect to the lattice constant of Pt is 4.8%. Therefore, the PZT lattice constant is consistent with the Pt lattice constant. Therefore, the film 14 containing PZT can be (100) oriented in a pseudo-cubic crystal display on the (100) plane of the conductive film 13 containing Pt, and the crystallinity of the film 14 can be improved.
Further, as shown in Table 1, the lattice constant of PZT is 0.411 nm, the lattice constant of PZO is 0.412 nm, and the mismatch of the lattice constant of PZO with respect to the lattice constant of PZT is 0.2%. Therefore, the consistency of the lattice constant of PZO with that of PZT is good. Therefore, the film 15 containing PZO can be (100) -oriented in a pseudo-cubic crystal display on the (100) plane of the film 14 containing PZT, and the crystallinity of the film 15 can be improved.
Further, as shown in Table 1, the lattice constant of PZO is 0.412 nm, the lattice constant of PZT is 0.411 nm, and the mismatch of the lattice constant of PZT with respect to the lattice constant of PZO is 0.2%. Therefore, the PZT lattice constant is consistent with the PZO lattice constant. Therefore, the piezoelectric film 16 containing PZT can be (001) oriented with a tetragonal crystal structure on the (100) plane of the film 15 containing PZO, and the crystallinity of the piezoelectric film 16 can be improved. .
Preferably, as shown in FIG. 2, when the film structure includes the conductive film 19, the relative dielectric constant measured by applying an AC voltage having a frequency of 1 kHz between the conductive film 13 and the conductive film 19. Is 300 to 400.
Thereby, when using the film | membrane structure 10 as a sensor using the piezoelectric effect, for example, detection sensitivity can be improved. Alternatively, when the film structure 10 is used as, for example, an ultrasonic vibrator using the inverse piezoelectric effect, the oscillation circuit can be easily designed.
<Method for producing membrane structure>
Next, a method for manufacturing the film structure of the present embodiment will be described. 8 to 13 are cross-sectional views during the manufacturing process of the film structure according to the embodiment.
First, as shown in FIG. 8, a substrate 11 is prepared (step S1). In step S1, a substrate 11 which is a silicon substrate made of silicon (Si) single crystal is prepared. Preferably, the substrate 11 made of silicon single crystal has a cubic crystal structure and has an upper surface 11a as a main surface made of a (100) plane. Further, when the substrate 11 is a silicon substrate, the upper surface 11a of the substrate 11 has SiO 2 ₂ An oxide film such as a film may be formed.
Note that various substrates other than a silicon substrate can be used as the substrate 11, for example, an SOI (Silicon on Insulator) substrate, a substrate made of various semiconductor single crystals other than silicon, and various oxide single crystals such as sapphire. A substrate or a substrate made of a glass substrate with a polysilicon film formed on the surface thereof can be used.
As shown in FIG. 8, two directions orthogonal to each other in the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal are defined as an X-axis direction and a Y-axis direction, and a direction perpendicular to the upper surface 11a is defined as Z. Axial direction.
Next, as shown in FIG. 9, an alignment film 12 is formed on the substrate 11 (step S2). In the following, the case where the alignment film 12 is formed using the electron beam evaporation method in step S2 will be described as an example. However, the alignment film 12 can be formed using various methods such as a sputtering method.
In step S2, the substrate 11 is first heated to, for example, 700 ° C. with the substrate 11 placed in a certain vacuum atmosphere.
Next, in step S2, Zr is evaporated by an electron beam vapor deposition method using a zirconium (Zr) single crystal vapor deposition material. At this time, the evaporated Zr reacts with oxygen on the substrate 11 heated to, for example, 700 ° C., whereby zirconium oxide (ZrO ₂ ) To form a film. And ZrO as a single layer film ₂ An alignment film 12 made of a film is formed.
The alignment film 12 is epitaxially grown on the upper surface 11a as the main surface made of the (100) plane of the substrate 11 made of silicon single crystal. The alignment film 12 has a cubic crystal structure and (100) -oriented zirconium oxide (ZrO ₂ )including. In other words, (100) -oriented zirconium oxide (ZrO) is formed on the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal. ₂ An alignment film 12 made of a single layer film is formed.
As described with reference to FIG. 8 described above, two directions orthogonal to each other in the upper surface 11a of the (100) plane of the substrate 11 made of silicon single crystal are the X-axis direction and the Y-axis direction, and the upper surface 11a The vertical direction is taken as the Z-axis direction. At this time, that a certain film is epitaxially grown means that the film is oriented in any of the X-axis direction, the Y-axis direction, and the Z-axis direction.
The thickness of the alignment film 12 is preferably 2 to 100 nm, and more preferably 10 to 50 nm. By having such a film thickness, it is possible to form an alignment film 12 that is epitaxially grown and extremely close to a single crystal.
Next, as shown in FIG. 10, a conductive film 13 is formed (step S3).
In this step S 3, first, a conductive film 13 is formed as a part of the lower electrode, which is epitaxially grown on the alignment film 12. The conductive film 13 is made of metal. For example, a conductive film containing platinum (Pt) is used as the conductive film 13 made of metal.
When a conductive film containing Pt is formed as the conductive film 13, the conductive film 13 epitaxially grown on the alignment film 12 at a temperature of 450 to 600 ° C. is formed as a part of the lower electrode. The conductive film 13 containing Pt is epitaxially grown on the alignment film 12. Pt contained in the conductive film 13 has a cubic crystal structure and is (100) -oriented.
For example, a conductive film containing iridium (Ir) can be used as the conductive film 13 made of metal instead of the conductive film containing platinum (Pt).
In this step S3, next, the conductive film 13 is heat-treated at a temperature of 450 to 600 ° C. Specifically, it is preferable that the conductive film 13 is formed by sputtering at a temperature of 450 to 600 ° C., and subsequently heat-treated while being held at a temperature of 450 to 600 ° C. for 10 to 30 minutes.
When the temperature at which the conductive film 13 is heat-treated is less than 450 ° C., the temperature is too low, so that the crystallinity of platinum contained in the conductive film 13 cannot be improved. The crystallinity of the formed piezoelectric film 16 cannot be improved. When the temperature at which the conductive film 13 is heat-treated exceeds 600 ° C., the temperature is too high, and platinum crystal grains contained in the conductive film 13 grow, so that the crystallinity of platinum cannot be improved. The crystallinity of the piezoelectric film 16 formed on the film 13 via the

films

14 and 15 cannot be improved. On the other hand, when the conductive film 13 is heat-treated at a temperature of 450 to 600 ° C., the crystallinity of platinum contained in the conductive film 13 can be improved, and the piezoelectric film formed on the conductive film 13 via the

films

14 and 15. The crystallinity of the film 16 can be improved.
Further, when the conductive film 13 is heat-treated at a temperature of 450 to 600 ° C., the heat treatment is preferably performed by holding for 10 to 30 minutes. When the time for heat-treating the conductive film 13 is less than 10 minutes, the time is too short to improve the crystallinity of platinum contained in the conductive film 13 and is formed on the conductive film 13 via the

films

14 and 15. The crystallinity of the piezoelectric film 16 to be applied cannot be improved. When the time for heat-treating the conductive film 13 exceeds 30 minutes, the temperature is too high, and the crystal grains of platinum contained in the conductive film 13 grow, so that the crystallinity of platinum cannot be improved. The crystallinity of the piezoelectric film 16 formed on the film 13 via the

films

14 and 15 cannot be improved.
Next, as shown in FIG. 11, a film 14 is formed (step S4). In this step S4, the film 14 containing the composite oxide (PZT) represented by the general formula (Formula 1) is formed on the conductive film 13 by a coating method such as a sol-gel method. Hereinafter, a method for forming the film 14 by the sol-gel method will be described.
In step S4, first, a film containing a precursor of the composite oxide (PZT) represented by the above general formula (Chemical Formula 1) is applied on the conductive film 13 by applying a solution containing lead, zirconium and titanium. Form. Note that the step of applying the solution containing lead, zirconium, and titanium may be repeated a plurality of times, whereby a film including a plurality of films stacked on each other may be formed.
In step S4, next, the film is heat treated to oxidize and crystallize the precursor, thereby forming the film 14 containing the complex oxide represented by the above general formula (Formula 1).
Next, as shown in FIG. 12, a film 15 is formed (step S5). In this step S5, the film 15 containing the complex oxide (PZO) represented by the above general formula (Formula 2) is formed on the film 14 by a coating method such as a sol-gel method. Hereinafter, a method for forming the film 15 by the sol-gel method will be described.
In step S5, first, a film containing a precursor of the composite oxide (PZT) represented by the above general formula (Chemical Formula 2) is applied on the film 14 by applying a solution containing lead, zirconium and titanium. Form. Note that the step of applying the solution containing lead, zirconium, and titanium may be repeated a plurality of times, thereby forming a film including a plurality of films stacked on each other.
In step S5, next, the film is heat-treated to oxidize and crystallize the precursor, thereby forming the film 15 containing the complex oxide represented by the above general formula (Formula 2).
Here, x and y satisfy the above formula (Formula 1) to Formula (Formula 3). At this time, the PZT contained in the film 14 is (100) oriented in the pseudo-cubic crystal display, and the PZO contained in the film 15 is (100) oriented in the pseudo-cubic crystal display. The film 14 containing PZT is epitaxially grown on the conductive film 13, and the film 15 containing PZO is epitaxially grown on the film 14.
Preferably, x may satisfy the following equation (Equation 4) instead of the above equation (Equation 1).
In step S4 and step S5, for example, the film 14 and the film 15 are formed by the evaporation of the solvent in the solution during the heat treatment or the film contraction when the precursor is oxidized and crystallized. , Have tensile stress.
Next, as shown in FIG. 13, the piezoelectric film 17 is formed (step S6). In this step S6, the piezoelectric film 17 containing the composite oxide (PZT) represented by the above general formula (Formula 3) is formed on the film 15 by the sputtering method. In the above general formula (Formula 3), a satisfies 0.1 <a ≦ 0.48. In such a case, the PZT included in the piezoelectric film 17 has a tetragonal crystal structure and (001) orientation, although it has a composition having a rhombohedral crystal structure. The piezoelectric film 17 containing PZT is epitaxially grown on the film 15.
For example, when the piezoelectric film 17 is formed by sputtering, each of the plurality of crystal grains 17a (see FIG. 5) included in the piezoelectric film 17 can be polarized by plasma. Therefore, each of the plurality of crystal grains 17a included in the formed piezoelectric film 17 has spontaneous polarization. The spontaneous polarization of each of the plurality of crystal grains 17 a includes a polarization component parallel to the thickness direction of the piezoelectric film 17. And the polarization component contained in the spontaneous polarization which each of the some crystal grain 17a has has faced the same direction mutually. As a result, the formed piezoelectric film 17 has spontaneous polarization as a whole of the piezoelectric film 17 before the polarization process is performed.
That is, in step S6, when the piezoelectric film 17 is formed by sputtering, the piezoelectric film 17 can be polarized by plasma. As a result, as described with reference to FIG. 6, when the film structure 10 of the present embodiment is used as a piezoelectric element, it is not necessary to subject the piezoelectric film 17 to polarization treatment before use.
In step S6, when the piezoelectric film 17 is formed by the sputtering method, for example, the sputtered particles and the argon (Ar) gas are incident on the piezoelectric film 17, and the piezoelectric film 17 expands. , Have compressive stress.
Next, as shown in FIG. 1, the piezoelectric film 18 is formed (step S7). In this step S7, the piezoelectric film 18 containing the composite oxide (PZT) represented by the above general formula (Formula 4) is formed on the piezoelectric film 17 by a coating method such as a sol-gel method. Hereinafter, a method for forming the film 15 by the sol-gel method will be described.
In step S7, first, a film containing PZT precursor is formed on the piezoelectric film 17 by applying a solution containing lead, zirconium and titanium. Note that the step of applying the solution containing lead, zirconium, and titanium may be repeated a plurality of times, thereby forming a film including a plurality of films stacked on each other.
In step S7, next, the film is heat-treated to oxidize and crystallize the precursor, thereby forming the piezoelectric film 18 containing PZT. Here, in the above general formula (Formula 4), b satisfies 0.1 <b ≦ 0.48. In such a case, the PZT contained in the piezoelectric film 18 has a tetragonal crystal structure and (001) orientation, although it has a composition having a rhombohedral crystal structure. The piezoelectric film 18 containing PZT is epitaxially grown on the film 15.
When PZT having a tetragonal crystal structure is (001) oriented, the polarization direction parallel to the [001] direction and the electric field direction parallel to the thickness direction of the piezoelectric film 16 are parallel to each other. Improved characteristics. That is, in PZT having a tetragonal crystal structure, large piezoelectric constants d33 and d31 are obtained when an electric field along the [001] direction is applied. Therefore, the piezoelectric constant of the piezoelectric film 16 can be further increased.
In step S7, the piezoelectric film 18 has a tensile stress, for example, when the solvent in the solution evaporates during the heat treatment or when the film contracts when the precursor is oxidized and crystallized. .
Thus, the piezoelectric film 16 including the

piezoelectric films

17 and 18 is formed, and the film structure 10 shown in FIG. 1 is formed. That is, step S6 and step S7 are included in the process of forming the piezoelectric film 16 containing lead zirconate titanate on the film 15. As described above, the thickness of each of the

films

14 and 15 is thinner than the thickness of the piezoelectric film 16.
Next, the diffraction pattern of the piezoelectric film 16 is measured by X-ray diffraction measurement using the θ-2θ method (step S8).
Preferably, in the diffraction pattern measured in step S8, any of the (110) plane and (101) plane of lead zirconate titanate with respect to the intensity of the diffraction peak of (001) plane of lead zirconate titanate The intensity ratio of diffraction peaks is also 4 × 10 ^-5 Or none of the diffraction peaks on the (110) plane and (101) plane are observed.
In such a case, the content of the lead zirconate titanate having a tetragonal crystal structure in the piezoelectric film 16 and (110) orientation or (101) orientation is set to the tetragonal crystal in the piezoelectric film 16. Compared with the content of lead (001) -oriented lead zirconate titanate having a crystal structure of Alternatively, the lead zirconate titanate having a tetragonal crystal structure and having (110) orientation or (101) orientation can be prevented from being included in the piezoelectric film 16. Therefore, the direction of the polarization axis in each of the plurality of crystal grains included in the piezoelectric film 16 can be made uniform, so that the piezoelectric characteristics of the piezoelectric film 16 can be improved.
Next, the rocking curve for the diffraction peak of the (00n) plane (n is an integer of 1 or more) in the diffraction pattern measured in step S8 is measured by X-ray diffraction measurement using the rocking curve method (step S9). ).
Preferably, the full width at half maximum of the rocking curve measured in step S9 is 0.3 to 0.6 °.
In such a case, the variation in the orientation direction of each of the plurality of crystal grains included in the piezoelectric film 16 can be reduced. Therefore, the direction of the polarization axis in each of the plurality of crystal grains included in the piezoelectric film 16 can be further aligned, so that the piezoelectric characteristics of the piezoelectric film 16 can be further improved.
After forming the piezoelectric film 18, a conductive film 19 (see FIG. 2) as an upper electrode may be formed on the piezoelectric film 18 (step S10). Thereby, an electric field can be applied to the piezoelectric film 18 in the thickness direction.
Further, after forming the conductive film 19, an AC voltage having a frequency of 1 kHz may be applied between the conductive film 13 and the conductive film 19 to measure the relative dielectric constant (step S11).
Preferably, the relative dielectric constant measured in step S11 is 300 to 400. In such a case, when the film structure 10 is used as a sensor using a piezoelectric effect, for example, the detection sensitivity can be improved. Alternatively, when the film structure 10 is used as, for example, an ultrasonic vibrator using the inverse piezoelectric effect, the oscillation circuit can be easily designed.
<Modification of Embodiment>
In the embodiment, as shown in FIG. 1, the piezoelectric film 16 including the

piezoelectric films

17 and 18 is formed. However, the piezoelectric film 16 may include only the piezoelectric film 17. Such an example will be described as a modification of the embodiment.
FIG. 14 is a cross-sectional view of a film structure according to a modification of the embodiment.
As shown in FIG. 14, the film structure 10 of the present modification includes a substrate 11, an alignment film 12, a conductive film 13, a film 14, a film 15, and a piezoelectric film 16. The alignment film 12 is formed on the substrate 11. The conductive film 13 is formed on the alignment film 12. The film 14 is formed on the conductive film 13. The film 15 is formed on the film 14. The piezoelectric film 16 is formed on the film 15. The piezoelectric film 16 includes a piezoelectric film 17.
That is, the film structure 10 of the present modification is the same as the film structure 10 of the embodiment except that the piezoelectric film 16 does not include the piezoelectric film 18 (see FIG. 1) but includes only the piezoelectric film 17. It is.
When the piezoelectric film 16 includes the piezoelectric film 17 having compressive stress but does not include the piezoelectric film 18 having tensile stress (see FIG. 1), the piezoelectric film 16 has the piezoelectric film 17 having compressive stress and the tensile stress. Compared with the case where any of the piezoelectric films 18 (see FIG. 1) is included, the amount of warping of the film structure 10 is increased. However, for example, when the thickness of the piezoelectric film 16 is thin, the amount of warping of the film structure 10 can be reduced. Therefore, even when the piezoelectric film 16 includes only the piezoelectric film 17, for example, the shape accuracy when the film structure 10 is processed using a photolithography technique can be improved, and the film structure 10 is formed by processing. The characteristics of the piezoelectric element can be improved.
Note that the film structure 10 of the present modification may also include the conductive film 19 (see FIG. 2), similarly to the film structure 10 of the embodiment.

Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.
(Example 1 to Example 7, Comparative Example 1 to Comparative Example 5)
In the following, the film structure 10 described with reference to FIG. 1 in the embodiment was formed as the film structures of Examples 1 to 7. The film structures of Examples 1 to 7 were formed while changing the heat treatment temperature and the heat treatment time after the platinum (Pt) film as the conductive film 13 was formed. On the other hand, a film structure formed while changing the heat treatment temperature and heat treatment time after the Pt film formation to a heat treatment temperature and heat treatment time different from the heat treatment temperature and heat treatment time after the Pt film formation in Example 1 to Example 7, The film structures of Comparative Examples 1 to 5 were obtained.
First, as shown in FIG. 8, a wafer having a top surface 11a as a main surface made of (100) plane and made of 6-inch silicon single crystal was prepared as a substrate 11.
Next, as shown in FIG. 9, a zirconium oxide (ZrO ₂ ) film was formed as an alignment film 12 on the substrate 11 by an electron beam evaporation method. The conditions at this time are shown below.
Apparatus: Electron beam vapor deposition apparatus Pressure: 7.00 × 10 ⁻³ Pa
Vapor deposition source: Zr + O ₂
Acceleration voltage / emission current: 7.5kV / 1.80mA
Thickness: 24nm
Deposition rate: 0.005 nm / s
Oxygen flow rate: 7 sccm
Substrate temperature: 500 ° C
Next, as shown in FIG. 10, a platinum (Pt) film was formed as the conductive film 13 on the alignment film 12 by a sputtering method. The conditions at this time are shown below.
Apparatus: DC sputtering apparatus Pressure: 1.20 × 10 ⁻¹ Pa
Deposition source: Pt
Power: 100W
Thickness: 150nm
Deposition rate: 0.14 nm / s
Ar flow rate: 16sccm
Substrate temperature: 450-600 ° C
Next, the Pt film was heat treated. The conditions at this time are shown below.
Equipment: DC sputtering equipment Substrate temperature (heat treatment temperature): 450-600 ° C
Heat treatment time: 10 to 30 minutes Here, Table 2 shows the heat treatment temperature and the heat treatment time after forming the Pt film in each of Examples 1 to 7 and Comparative Examples 1 to 5. In addition, the thing which does not perform the heat processing after Pt film formation is set as the comparative example 1.

Next, as shown in FIG. 11, a Pb (Zr _0.58 Ti _0.42 ) O ₃ film (PZT film) was formed as a film 14 on the conductive film 13 by a coating method. The conditions at this time are shown below.
An organometallic compound of Pb, Zr, and Ti is mixed so as to have a composition ratio of Pb: Zr: Ti = 100 + δ: 58: 42, and Pb (Zr _{0. 0 is} added to a mixed solvent of ethanol and 2-n-butoxyethanol _{. The} raw material solution was prepared so that the concentration as ₅₈ Ti _0.42 ) O ₃ was 0.35 mol / l. Here, δ is the surplus Pb amount in consideration of the volatilization of the Pb oxide in the subsequent heat treatment process, and in this example, δ = 20. Further, 20 g of polypyrrolidone having a K value (viscosity characteristic value) of 27 to 33 was dissolved in the raw material solution.
Next, 3 ml of the prepared raw material solution is dropped onto the substrate 11 made of a 6-inch wafer, rotated at 3000 rpm for 10 seconds, and the precursor solution is applied onto the substrate 11 to thereby apply the precursor. A containing film was formed. Then, the substrate 11 is placed on a hot plate at a temperature of 200 ° C. for 30 seconds, and further, the substrate 11 is placed on a hot plate at a temperature of 450 ° C. for 30 seconds to evaporate the solvent and form a film. Dried. Thereafter, the precursor is oxidized and crystallized by heat treatment at 600 to 700 ° C. for 60 seconds in an oxygen (O ₂ ) atmosphere of 0.2 MPa, thereby forming a PZT film having a film thickness of 20 nm. did.
Next, as shown in FIG. 12, a laminated film in which a PbZrO ₃ film (PZO film) was laminated on the film 14 as a film 15 was formed by a coating method. The conditions at this time are shown below.
An organometallic compound of Pb and Zr is mixed so as to have a composition ratio of Pb: Zr = 100 + δ: 100, and the concentration of PbZrO ₃ is 0.35 mol / l in a mixed solvent of ethanol and 2-n-butoxyethanol. The raw material solution dissolved was adjusted as follows. For δ, δ = 20. Further, 20 g of polypyrrolidone having a K value of 27 to 33 was dissolved in the raw material solution.
Next, 3 ml of the prepared raw material solution is dropped onto the substrate 11 made of a 6-inch wafer, rotated at 3000 rpm for 10 seconds, and the precursor solution is applied onto the substrate 11 to thereby apply the precursor. A containing film was formed. Then, the substrate 11 is placed on a hot plate at a temperature of 200 ° C. for 30 seconds, and further, the substrate 11 is placed on a hot plate at a temperature of 450 ° C. for 30 seconds to evaporate the solvent and form a film. Dried. Thereafter, the precursor was oxidized and crystallized by heat treatment at 650 ° C. for 60 seconds in an oxygen (O ₂ ) atmosphere of 0.2 MPa, thereby forming a PZO film having a thickness of 30 nm.
For Example 1 to Example 7 and Comparative Example 1 to Comparative Example 5, the θ-2θ spectrum by the XRD method of the film structure in which the layers up to the PZO film were formed was measured. That is, X-ray diffraction measurement by the θ-2θ method was performed for Examples 1 to 7 and Comparative Examples 1 to 5. X-ray diffraction measurement was performed using a fully automatic horizontal multipurpose X-ray diffractometer SmartLab manufactured by Rigaku Corporation.
FIGS. 15 and 16 are graphs showing examples of the θ-2θ spectrum by the XRD method of the film structure in which the layers up to the PZO film are formed. The horizontal axis of the graphs of FIGS. 15 and 16 indicates the angle 2θ, and the vertical axis of the graphs of FIGS. 15 and 16 indicates the intensity of X-rays. FIG. 15 shows the results for Example 3, and FIG. 16 shows the results for Comparative Example 1.
In the example shown in FIG. 15 (Example 3), in the θ-2θ spectrum, a peak corresponding to the (200) plane of ZrO _{2 in} pseudo-cubic crystal display, corresponding to the (200) plane of Pt having a cubic crystal structure. And peaks corresponding to the (100) plane and (200) plane were observed in a pseudo cubic representation of PZO. Therefore, in the example (Example 3) shown in FIG. 15, the alignment film 12 includes ZrO ₂ that is (100) -oriented in pseudo-cubic display, and the conductive film 13 is Pt that is (100) -oriented in cubic display. In addition, the film 15 was found to contain (100) -oriented PZO in pseudocubic display.
Also in the example shown in FIG. 16 (Comparative Example 1), in the θ-2θ spectrum, the peak corresponding to the (200) plane of ZrO ₂ in the pseudo-cubic crystal display and the (200) plane of Pt having a cubic crystal structure. And peaks corresponding to the (100) plane and (200) plane were observed in a pseudo cubic representation of PZO. However, in the example shown in FIG. 16 (Comparative Example 1), unlike the example shown in FIG. 15 (Example 3), a peak corresponding to the (101) plane was observed in the pseudo cubic display of PZO. Therefore, in the example shown in FIG. 16 (Comparative Example 1), the alignment film 12 contains ZrO ₂ that is (100) -oriented in pseudo-cubic display, and the conductive film 13 is Pt that is (100) -oriented in cubic display. In addition, although the film 15 includes (100) -oriented PZO in the pseudo-cubic crystal display, the film 15 also includes (110) -oriented PZO in the pseudo-cubic crystal display.
That is, in the example shown in FIG. 15 (Example 3), it was found that the film 15 does not contain (110) -oriented PZO in pseudo cubic display. Further, in the example (Example 3) shown in FIG. 15, it was found that the conductive film 13 did not contain (111) -oriented Pt in the cubic display.
Next, as shown in FIG. 13, a Pb (Zr _0.55 Ti _0.45 ) O ₃ film (PZT film) having a film thickness of, for example, 2 μm is sputtered on the film 15 as the piezoelectric film 17. Formed by. The conditions at this time are shown below.
Equipment: RF magnetron sputtering equipment Power: 2500W
Gas: Ar / O ₂
Pressure: 0.14 Pa
Substrate temperature: 475 ° C
Deposition rate: 0.63 nm / s
Next, as shown in FIG. 1, a Pb (Zr _0.55 Ti _0.45 ) O ₃ film (PZT film) was formed as a piezoelectric film 18 on the piezoelectric film 17 by a coating method. The conditions at this time are shown below.
An organometallic compound of Pb, Zr and Ti is mixed so as to have a composition ratio of Pb: Zr: Ti = 100 + δ: 55: 45, and a mixed solvent of ethanol and 2-n-butoxyethanol is mixed with Pb (Zr _0.55 A raw material solution was prepared so that the concentration as Ti _0.45 ) O ₃ was 0.35 mol / l. For δ, δ = 20. Further, 20 g of polypyrrolidone having a K value of 27 to 33 was dissolved in the raw material solution.
Next, 3 ml of the prepared raw material solution is dropped onto the substrate 11 made of a 6-inch wafer, rotated at 3000 rpm for 10 seconds, and the precursor solution is applied onto the substrate 11 to thereby apply the precursor. A containing film was formed. Then, the substrate 11 is placed on a hot plate at a temperature of 200 ° C. for 30 seconds, and further, the substrate 11 is placed on a hot plate at a temperature of 450 ° C. for 30 seconds to evaporate the solvent and form a film. Dried. Thereafter, the precursor was oxidized and crystallized by heat treatment at 600 to 700 ° C. for 60 seconds in a 0.2 MPa oxygen (O ₂ ) atmosphere to form a piezoelectric film 18 having a thickness of 30 nm.
For each of Examples 1 to 7 and Comparative Examples 1 to 5, the θ-2θ spectrum was measured by the XRD method of the film structure in which the PZT film as the piezoelectric film 18 was formed. That is, X-ray diffraction measurement by the θ-2θ method was performed for each of Examples 1 to 7 and Comparative Examples 1 to 5.
Each of FIGS. 17 and 18 is a graph showing an example of the θ-2θ spectrum by the XRD method of the film structure in which the layers up to the PZT film are formed. The horizontal axis of each graph in FIGS. 17 and 18 indicates the angle 2θ, and the vertical axis in each graph in FIGS. 17 and 18 indicates the intensity of X-rays. FIG. 17 shows the results for Example 3, and FIG. 18 shows the results for Comparative Example 1.
In the example shown in FIG. 17 (Example 3), in the θ-2θ spectrum, a peak corresponding to the (200) plane of Pt having a cubic crystal structure, and (001) of PZT having a tetragonal crystal structure. A peak corresponding to the plane and the (002) plane was observed. Therefore, in the example shown in FIG. 17 (Example 3), the conductive film 13 has a cubic crystal structure and includes (100) -oriented Pt, and the piezoelectric film 16 has a tetragonal crystal structure. It was found to contain P001T with (001) orientation.
Also in the example shown in FIG. 18 (Comparative Example 1), in the θ-2θ spectrum, a peak corresponding to the (200) plane of Pt having a cubic crystal structure, and (001) of PZT having a tetragonal crystal structure. A peak corresponding to the plane and the (002) plane was observed. However, in the example shown in FIG. 18 (Comparative Example 1), unlike the example shown in FIG. 17 (Example 3), there is a peak corresponding to the (110) plane or (101) plane of PZT having a tetragonal crystal structure. Observed. Therefore, in the example shown in FIG. 18 (Comparative Example 1), the conductive film 13 has a cubic crystal structure and contains (100) -oriented Pt, and the piezoelectric film 16 has a tetragonal crystal structure. However, the piezoelectric film 16 has a tetragonal crystal structure and includes (110) -oriented or (101) -oriented PZT.
That is, in the example shown in FIG. 17 (Example 3), it was found that the piezoelectric film 16 does not contain (110) -oriented PZT in tetragonal display.
Table 2 shows the results of measuring PZT (110) / PZT (001) in the θ-2θ method. Here, PZT (110) / PZT (001) is the (110) plane or (101) plane of PZT having a tetragonal crystal structure with respect to the peak intensity of the (001) plane of PZT having a tetragonal crystal structure. Means the ratio of the stronger peak intensity. When neither the (110) plane nor the (101) plane of PZT is observed, the background level at the angle 2θ (2θ≈31 °) at which the PZT (110) plane is observed is set to (110) of PZT. It was defined as the stronger peak intensity of the plane or (101) plane.
As shown in Table 2, for example, none of the PZT (110) plane and the (101) plane is observed, and in Examples 1 to 7 where the crystallinity is good, PZT (110) / PZT (001) Was 4 × 10 ⁻⁵ or less. On the other hand, for example, PZT (110) / PZT (001) is 1 × 10 ⁻⁴ or more in Comparative Examples 1 to 5 where the PZT (110) plane or (101) plane is observed and the crystallinity is not good. Met.
A wide area reciprocal lattice map measurement was performed on each of the film structures of Examples 1 to 5 and Comparative Examples 1 to 5. The wide area reciprocal lattice map was measured by attaching a hybrid multidimensional pixel detector HyPix-3000 to a fully automatic horizontal multipurpose X-ray diffractometer SmartLab manufactured by Rigaku Corporation.
19 and 20 are measurement results of the reciprocal lattice map of the film structure in which the layers up to the PZT film are formed. FIG. 19 shows the results for Example 3, and FIG. 20 shows the results for Comparative Example 1. FIG. 21 shows the result of simulation (calculation) of the reciprocal lattice map of PZT. By comparing FIGS. 19 and 20 with FIG. 21, it is determined whether or not the piezoelectric film 16 is epitaxially grown, that is, oriented in any of the X-axis direction, the Y-axis direction, and the Z-axis direction (see FIG. 1). Can be evaluated.
In the measurement of the reciprocal lattice map, first, a scan by the ω-2θ method (ω-2θ scan) similar to the scan by the θ-2θ method (θ-2θ scan) is performed, and the intensity of the angle ω, the angle 2θ, and the X-ray intensity A plurality of first numerical value groups consisting of the three numerical values are acquired. In the measurement of the reciprocal lattice map, the reciprocal lattice space is obtained by substituting two numerical values of the angle ω and the angle 2θ among the three numerical values included in each of the plurality of first numerical value groups into the following equation (Equation 4). The coordinate q _x is obtained, and two numerical values of the angle ω and the angle 2θ are substituted into the following equation (Equation 5) to obtain the reciprocal lattice space coordinate q _z . Then, each first group of numerical values, and converts reciprocal space coordinate q _x, the second numerical value group consisting of three numbers of the intensity of the reciprocal lattice space coordinates q _z and X-ray. In the measurement of the reciprocal lattice map, among the three numerical values included in each of the plurality of second numerical groups, the X-ray intensity is represented by the reciprocal space coordinate q _x as the horizontal coordinate and the reciprocal space coordinate. q _z at the coordinates the plane of the longitudinal axis, to contour lines.

Specifically, the ω-2θ scan was performed by changing the angle 2θ in the range of 10 to 120 ° and changing the angle ω in the range of 10 to 90 °. In the ω-2θ scan, the rotation surfaces of the angle 2θ and the angle ω are parallel to the Si (110) plane of the substrate 11.
In the measurement of a wide area reciprocal lattice map using a fully automatic horizontal multi-purpose X-ray diffractometer SmartLab manufactured by Rigaku Co., Ltd., measurement is performed at two angles φ of 0 ° and 45 ° when the φ axis is the in-plane rotation axis. is doing. Further, as described above, the angle ω and the angle 2θ obtained by the ω-2θ scan are substituted into the above equations (Equation 4) and (Equation 5), and the reciprocal space coordinate q _x and the reciprocal space coordinate q _z are obtained. The reciprocal lattice map is measured by the calculation, but it is also possible to measure different components of the polarization domain by superimposing the reciprocal lattice maps measured for multiple angles χ when the χ axis is the turning axis. It is.
When the measurement result of the reciprocal lattice map shown in FIG. 19 (Example 3) is compared with the calculation result of the reciprocal lattice map shown in FIG. 21, the measurement result of the reciprocal lattice mapping shown in FIG. It agrees with the calculation result. Therefore, it can be seen that the PZT film of Example 3 is a good single crystal film.
On the other hand, when the measurement result of the reciprocal lattice map shown in FIG. 20 (Comparative Example 1) is compared with the calculation result of the reciprocal lattice map shown in FIG. 21, the measurement result of the reciprocal lattice map shown in FIG. Although substantially coincident with the map calculation result, each point is wider than the measurement result of the reciprocal lattice map shown in FIG. Therefore, it can be seen that the PZT film of Comparative Example 1 has lower crystallinity than the PZT film of Example 3.
Further, with respect to each of the film structures of Examples 1 to 7 and Comparative Examples 1 to 5, the diffraction peak on the (001) plane in the diffraction pattern measured by X-ray diffraction measurement using the θ-2θ method. When the angle 2θ was observed, the rocking curve was measured with the angle 2θ fixed at the angle at which the diffraction peak of the (001) plane was observed. Table 2 shows the full width at half maximum (FWHM) of the rocking curve measured in this rocking curve measurement for each of the film structures of Examples 1 to 7 and Comparative Examples 1 to 5. Shown in
As shown in Table 2, for example, none of the PZT (110) plane and (101) plane is observed, and in Examples 1 to 7 where the crystallinity is good, the half value in the rocking curve of PZT (100) The total width was 0.3 to 0.6 °. On the other hand, for example, in Comparative Examples 1 to 5 where the PZT (110) plane or (101) plane is observed and the crystallinity is not good, the full width at half maximum in the rocking curve of PZT (100) is 1.0 to 2 0.0 °.
The full width at half maximum of the rocking curve for each diffraction peak of the (001) plane, (002) plane, (003) plane, and (004) plane in the diffraction pattern measured by X-ray diffraction measurement by the θ-2θ method is This is synonymous with the full width at half maximum of the reciprocal lattice point corresponding to each of the (001) plane, (002) plane, (003) plane, and (004) plane of the reciprocal lattice map.
Further, the spread of each spot in the measurement result of the reciprocal lattice map in FIG. 19 (Example 3) is smaller than the spread of each spot in the measurement result of the reciprocal lattice map in FIG. 20 (Comparative Example 1). This is because the full width at half maximum of the rocking curve of PZT (001) in each of the film structures of Examples 1 to 7 corresponds to the rocking curve of PZT (001) in each of the film structures of Comparative Examples 1 to 5. This is consistent with being less than the full width at half maximum.
That is, the full width at half maximum in the rocking curve of PZT (00n) (n is an integer of 1 or more) in each of the film structures of Examples 1 to 7 is the same as that of each of the film structures of Comparative Examples 1 to 5. It is smaller than the full width at half maximum in the rocking curve of PZT (00n) (n is an integer of 1 or more).
In the peripheral region of the PZT (113) plane (see FIG. 21) in the reciprocal lattice map of FIG. 19, the spot corresponding to the reciprocal lattice point of the (113) plane of PZT having a tetragonal crystal structure is divided into three spots. However, the reciprocal space coordinates q _x of each of these three spots are different. Therefore, it is considered that the stress is relaxed between the portions represented by each of these three spots in the piezoelectric film 16. The phenomenon in which the reciprocal lattice points on the (113) plane of PZT are divided into three spots and the reciprocal space coordinate q _x of each of these three spots is different is described in Examples 1 to 7. Was observed in each of the membrane structures.
On the other hand, in the θ-2θ spectrum of FIG. 17, a peak that is considered to be, for example, the (100) plane of PZT having a tetragonal crystal structure is observed on the high angle side of the (001) plane of PZT having a tetragonal crystal structure. Has been. Further, a peak considered to be, for example, the (200) plane of PZT having a tetragonal crystal structure is observed on the high angle side of the (002) plane of PZT having a tetragonal crystal structure. Accordingly, considering that the reciprocal lattice map of FIG. 19 suggests that the stress is relaxed between the portions of the piezoelectric film 16 represented by each of these three spots. For example, it is considered that the (100) -oriented portion of PZT having a tetragonal crystal structure is present in a small amount, and the portion functions as a stress relaxation layer.
Next, as shown in FIG. 2, a platinum (Pt) film was formed as a conductive film 19 on the piezoelectric film 16 by a sputtering method. Thereafter, a voltage was applied between the conductive film 13 and the conductive film 19 to measure the voltage dependence of polarization.
Each of FIG. 22 and FIG. 23 is a graph showing the voltage dependence of the polarization of the membrane structure. The horizontal axis of each graph of FIG. 22 and FIG. 23 shows a voltage, and the vertical axis | shaft of each graph of FIG.22 and FIG.23 shows polarization. FIG. 22 shows the results for Example 3, and FIG. 23 shows the results for Comparative Example 1. Since the thicknesses of the piezoelectric films 16 included in the film structures of Example 3 and Comparative Example 1 are equal to each other, when the horizontal axis of each graph in FIGS. 22 and 23 is an electric field instead of a voltage, Can be compared in the same manner.
According to the voltage dependence of the polarization in Example 3 shown in FIG. 22, the relative dielectric constant εr, the remanent polarization value Pr, and the coercive voltage Vc were as follows.
εr = 300
Pr = 50 μC / cm ²
Vc=23.2V@2.7 μm
Further, according to the voltage dependence of the polarization of Comparative Example 1 shown in FIG. 23, the relative dielectric constant εr, the remanent polarization value Pr, and the coercive voltage Vc were as follows.
εr = 500
Pr = 20 μC / cm ²
Vc=19.5V@2.7 μm
Similarly, Table 2 shows the relative dielectric constant εr measured by measuring the voltage dependence of this polarization for each of the film structures of Examples 1 to 7 and Comparative Examples 1 to 5. The relative dielectric constant εr is a relative dielectric constant measured by applying an AC voltage having a frequency of 1 kHz between the conductive film 13 and the conductive film 19.
As shown in Table 2, for example, none of the PZT (110) plane and the (101) plane is observed, and in Examples 1 to 7 where the crystallinity is good, the relative dielectric constant εr is 300 to 400. Met. On the other hand, in Comparative Examples 1 to 5 where, for example, PZT (110) plane or (101) plane is observed and the crystallinity is not good, the relative dielectric constant εr is 450 to 500.
As described above, in each of the film structures of Examples 1 to 7, the relative dielectric constant of the piezoelectric film 16 is lower than that of the conventional PZT film. Thereby, when each film structure of Example 1 to Example 7 is used as a sensor using the piezoelectric effect, for example, the detection sensitivity can be improved. Alternatively, when each of the film structures of Examples 1 to 7 is used as, for example, an ultrasonic vibrator using the inverse piezoelectric effect, the oscillation circuit can be easily designed.
For the film 14 included in each of the film structures of Examples 1 to 7 and Comparative Examples 1 to 5, Pb (Zr _1-x Ti _x when x satisfies x = 0.42) ) O ₃ film, ie, Pb (Zr _0.58 Ti _0.42 ) O ₃ film, Pb (Zr _1-x Ti _x ) O ₃ film, ie, PZT film, when x satisfies 0 <x ≦ 0.48 Similar results were obtained when forming. Also, even when a PZT film is formed when x satisfies 0.48 <x <1, there is a difference in the direction in which the characteristics slightly decrease compared to a PZT film when x satisfies 0 <x ≦ 0.48. However, almost the same results were obtained.
In addition, for the film 15 included in each of the film structures of Examples 1 to 7 and Comparative Examples 1 to 5, Pb (Zr _1-y Ti _y ) O when y satisfies y = 0. Similar results were obtained when a Pb (Zr _1-y Ti _y ) O ₃ film, that is, a PZT film when y satisfies 0 <y ≦ 0.1, was formed instead of the ₃ film, that is, the PZO film.
As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.
In the scope of the idea of the present invention, those skilled in the art can conceive various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention.
For example, those in which the person skilled in the art appropriately added, deleted, or changed the design of the above-described embodiments, or those in which the process was added, omitted, or changed the conditions are also included in the present invention. As long as the gist is provided, it is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Film structure 11 Substrate 11a Upper surface 12 Orientation film 13

Conductive film

14, 15

Film

16, 17 Piezoelectric film 17a Crystal grain 18 Piezoelectric film 18a Film 18b Crystal grain 19 Conductive film EP End point P1 Polarization SP Starting point

Claims

A silicon substrate including a main surface consisting of (100) planes;
A first film formed on the main surface, having a cubic crystal structure and containing (100) oriented zirconium oxide;
A first conductive film formed on the first film, having a cubic crystal structure and containing (100) -oriented platinum;
A second film comprising a first composite oxide formed on the first conductive film, represented by the following general formula (Chemical Formula 1), and (100) oriented in a pseudo-cubic crystal representation:

A third film formed on the second film, represented by the following general formula (Chemical Formula 2), and including a second composite oxide having a pseudo cubic crystal representation (100) orientation;

A first piezoelectric film comprising lead zirconate titanate formed on the third film;
Have
The x and y are film structures satisfying the following formula (formula 1) to formula (formula 3).
The membrane structure according to claim 1, wherein
A film structure in which each of the second film and the third film is thinner than the first piezoelectric film.
The membrane structure according to claim 1 or 2,
The first piezoelectric film has a tetragonal crystal structure and includes (001) -oriented lead zirconate titanate.
The membrane structure according to claim 3,
In the first diffraction pattern of the first piezoelectric film measured by the X-ray diffraction measurement using the θ-2θ method, lead zirconate titanate with respect to the diffraction peak intensity of the (001) plane of lead zirconate titanate The intensity ratio of any diffraction peak on the (110) plane and the (101) plane is 4 × 10 −5 or less, or any diffraction peak on the (110) plane and the (101) plane is observed. Not a membrane structure.
The membrane structure according to claim 4,
Film structure in which the full width at half maximum of the rocking curve measured for the diffraction peak of the (001) plane in the first diffraction pattern is 0.3 to 0.6 ° by X-ray diffraction measurement using the rocking curve method body.
In the film structure according to any one of claims 1 to 5,
The first piezoelectric film is
A second piezoelectric film including a third composite oxide made of lead zirconate titanate formed on the third film;
A third piezoelectric film including a fourth composite oxide made of lead zirconate titanate formed on the second piezoelectric film;
Including
The second piezoelectric film has a compressive stress,
The third piezoelectric film is a film structure having a tensile stress.
The membrane structure according to claim 6,
The second piezoelectric film includes the third composite oxide represented by the following general formula (Formula 3):

The third piezoelectric film includes the fourth composite oxide represented by the following general formula (Formula 4):

A satisfies 0.1 <a ≦ 0.48,
The b is a film structure satisfying 0.1 <b ≦ 0.48.
The film structure according to any one of claims 1 to 7,
A second conductive film formed on the first piezoelectric film;
A film structure having a relative dielectric constant of 300 to 400 measured by applying an AC voltage having a frequency of 1 kHz between the first conductive film and the second conductive film.
(A) a step of preparing a silicon substrate including a main surface made of a (100) plane;
(B) forming a first film having a cubic crystal structure and containing (100) oriented zirconium oxide on the main surface;
(C) forming a first conductive film containing platinum having a cubic crystal structure and (100) orientation on the first film;
(D) forming a second film containing the first composite oxide represented by the following general formula (Chemical Formula 1) and having a (100) orientation in a pseudo cubic display on the first conductive film;

(E) forming on the second film a third film containing a second composite oxide represented by the following general formula (Chemical Formula 2) and having a (100) orientation in pseudo-cubic crystal representation;

(F) forming a first piezoelectric film containing lead zirconate titanate on the third film;
Have
Said x and y are the manufacturing method of a film | membrane structure which satisfy | fills following formula (Formula 1)-Formula (Formula 3).
In the manufacturing method of the membrane structure according to claim 9,
(G) a step of heat-treating the first conductive film at a temperature of 450 to 600 ° C. after the step (c) and before the step (d);
A method for producing a membrane structure, comprising:
In the manufacturing method of the membrane structure according to claim 9 or 10,
The step (d)
(D1) forming a fourth film containing the first precursor of the first composite oxide by applying a first solution containing lead, zirconium and titanium on the first conductive film;
(D2) forming the second film by heat-treating the fourth film;
Including
The step (e)
(E1) A fifth film containing the second precursor of the second composite oxide is applied on the second film by applying a second solution containing lead and zirconium or lead, zirconium and titanium. Forming step,
(E2) forming the third film by heat-treating the fifth film;
A method for producing a membrane structure, comprising:
In the manufacturing method of the film structure according to any one of claims 9 to 11,
The method of manufacturing a film structure, wherein the thickness of each of the second film and the third film is thinner than the thickness of the first piezoelectric film.
In the manufacturing method of the membrane structure according to any one of claims 9 to 12,
In the step (f), the first piezoelectric film having a tetragonal crystal structure and containing (001) -oriented lead zirconate titanate is formed.
In the manufacturing method of the membrane structure according to claim 13,
(H) a step of measuring a first diffraction pattern of the first piezoelectric film by X-ray diffraction measurement using a θ-2θ method;
Have
In the first diffraction pattern measured in the step (h), the (110) plane and (101) plane of lead zirconate titanate with respect to the intensity of the diffraction peak of the (001) plane of lead zirconate titanate. The ratio of the intensity of any diffraction peak is 4 × 10 −5 or less, or the diffraction peak of any of the (110) plane and the (101) plane is not observed.
In the manufacturing method of the membrane structure according to claim 14,
(I) a step of measuring a rocking curve for a diffraction peak of the (001) plane in the first diffraction pattern measured in the step (h) by X-ray diffraction measurement using a rocking curve method;
Have
The method for producing a membrane structure, wherein the full width at half maximum of the rocking curve measured in the step (i) is 0.3 to 0.6 °.
In the manufacturing method of the film structure according to any one of claims 9 to 15,
The step (f)
(J) forming a second piezoelectric film containing a third composite oxide made of lead zirconate titanate on the third film;
(K) forming a third piezoelectric film including a fourth composite oxide made of lead zirconate titanate on the second piezoelectric film;
Including
In the step (j), the second piezoelectric film having a compressive stress is formed,
In the step (k), the third piezoelectric film having a tensile stress is formed.
In the manufacturing method of the membrane structure according to claim 16,
In the step (j), the second piezoelectric film containing the third composite oxide represented by the following general formula (Formula 3) is formed,

In the step (k), the third piezoelectric film containing the fourth composite oxide represented by the following general formula (Formula 4) is formed.

A satisfies 0.1 <a ≦ 0.48,
Said b is a manufacturing method of a film structure satisfying 0.1 <b ≦ 0.48.
In the manufacturing method of the membrane structure according to claim 16 or 17,
In the step (j), the second piezoelectric film is formed by a sputtering method,
The step (k)
(K1) forming a sixth film containing a third precursor of the fourth composite oxide by applying a third solution containing lead, zirconium and titanium on the second piezoelectric film;
(K2) forming the third piezoelectric film by heat-treating the sixth film;
A method for producing a membrane structure, comprising:
In the manufacturing method of the membrane structure according to any one of claims 9 to 18,
(L) forming a second conductive film on the first piezoelectric film;
(M) measuring a relative dielectric constant by applying an alternating voltage having a frequency of 1 kHz between the first conductive film and the second conductive film;
Have
The method for producing a film structure, wherein the relative dielectric constant measured in the step (m) is 300 to 400.