JP2019216181A - Film structure and manufacturing method of the same - Google Patents

Abstract

To provide a film structure capable of improving a crimp characteristic of a crimp film containing lead zirconate titanate.SOLUTION: A film structure includes: a substrate 11 as a silicon substrate containing an upper surface 11a made of a (100) surface; an orientation film 12 formed on the upper surface 11a, having a cubic crystal structure, and containing a zirconium oxide film to be oriented (100); and a conductive film 13 formed on the orientation film 12, having the cubic crystal structure, and including a platinum film to be oriented (100). A mean boundary surface roughness of a boundary surface IF1 between the orientation film 12 and the conductive film 13 is larger than that of a boundary surface IF2 between the substrate 11 and the orientation film 12.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a film structure and a method for manufacturing the same.

  As a film structure having a substrate, a conductive film formed on the substrate, and a piezoelectric film formed on the conductive film, a substrate, a conductive film containing platinum formed on the substrate, And a piezoelectric film containing lead zirconate titanate (PZT) formed on the substrate.

WO 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. And a Pb (Zr _1-x Ti _x ) O ₃ film, wherein A and x satisfy 0 ≦ A ≦ 0.1 and 0.1 <x <1.

In JP-A-2014-84494 (Patent Document 2), a film of YSZ (8% Y ₂ O ₃ + 92% ZrO ₂ ), CeO ₂ , and LaSrCoO ₃ is sequentially laminated on a silicon substrate (Si). A technique for forming a PZT thin film on a buffer layer is disclosed. Patent Document 2 discloses a technique in which LaSrCoO ₃ (LSCO) is rotated by 45 ° lattice with respect to another film.

In Non-Patent Document 1, a buffer layer in which YSZ, CeO ₂ , La _0.5 Sr _0.5 CoO ₃ (LSCO), and SrRuO ₃ (SRO) are sequentially laminated on a silicon substrate is formed. A 0.06 Pb (Mn _1/3 , Nb _2/3 ) O ₃ -0.94 Pb (Zr _0.5 Ti _0.5 ) O ₃ (PMnN-PZT) epitaxial thin film having a c-axis orientation is formed thereon. The technology is disclosed. Non-Patent Document 1 discloses a technique in which the crystal lattice of PMnN-PZT is rotated by 45 ° with respect to Si in an in-plane direction.

Non-Patent Document 2 discloses a technology in which the relative dielectric constant of PbTiO ₃ grown by a flux method using a MgO single crystal crucible is 150 at room temperature, and 1.5 times the relative dielectric constant of pure PbTiO ₃ single crystal. Is disclosed.

International Publication No. WO 2016/009698 JP 2014-84494 A

S. Yoshida et al., “Fabrication and characterization of large figure-of-merit epitaxial PMnN-PZT / Si transducer for piezoelectric MEMS sensors”, Sensors and Actuators A 239 (2016) 201-208 Masafumi Kofuna, 1 other, "Growth and evaluation of PbTiO3 single crystal using MgO single crystal crucible", Journal of the Ceramic Society of Japan, 1987, Vol. 95, No. 11, p. 1053-1058

  In a piezoelectric film containing lead zirconate titanate, when the quality such as crystallinity of the piezoelectric film is not good, the piezoelectric characteristics of the piezoelectric film deteriorate. However, it is difficult to form a piezoelectric film containing, for example, lead zirconate titanate having good crystal quality, and it is difficult to improve the piezoelectric characteristics of the piezoelectric film.

  The present invention has been made to solve the above-described problems of the related art, and in a film structure for forming a piezoelectric film containing lead zirconate titanate, the piezoelectric characteristics of the piezoelectric film are improved. An object is to provide a film structure that can be improved.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  A film structure according to one embodiment of the present invention includes a silicon substrate including a main surface including a (100) plane, and a (100) -oriented silicon substrate formed over the main surface and having a cubic crystal structure. A first film including a zirconium monoxide film; and a conductive film formed on the first film and having a cubic crystal structure and including a (100) -oriented platinum film. The first average interface roughness of the first interface between the first film and the conductive film is larger than the second average interface roughness of the second interface between the silicon substrate and the first film.

  In another aspect, the first film includes a film portion formed on the main surface and a plurality of protrusions each protruding from an upper surface of the film portion, wherein the film portion has a cubic crystal structure. And a (100) -oriented second zirconium oxide film, wherein each of the plurality of protrusions has a cubic crystal structure and includes a (100) -oriented third zirconium oxide film. May be.

  Further, as another aspect, a cross-sectional shape of the protruding portion perpendicular to the first direction along the main surface is triangular, and a direction along the main surface of the protruding portion and perpendicular to the first direction. The width in the second direction may decrease from the film part side to the side opposite to the film part side.

  In another aspect, the thickness of the film portion may be 11 to 18 nm, and the height of each of the plurality of protrusions protruding from the upper surface of the film portion may be 4 to 8 nm.

  In another embodiment, the conductive film may cover the plurality of protrusions, and the conductive film may be embedded between two adjacent protrusions.

  In another aspect, the conductive film has a first tensile stress, and the first film has a first compressive stress or a second tensile stress smaller than the first tensile stress. Is also good.

  In another aspect, the upper layer of the first film has a second compressive stress, the lower layer of the first film has a third tensile stress, and the first film has a first compressive stress. At this time, the second compressive stress may be larger than the first compressive stress, and when the first film has the second tensile stress, the third tensile stress may be larger than the second tensile stress.

  In another embodiment, the film structure includes a piezoelectric film formed on a conductive film, having a tetragonal crystal structure, and including a (001) -oriented lead zirconate titanate film. You may.

  In another aspect, the first zirconium oxide film is configured such that a <100> direction along a main surface of the first zirconium oxide film is parallel to a <100> direction along a main surface of the silicon substrate. The platinum film may be oriented such that the <100> direction along the main surface of the platinum film is parallel to the <100> direction along the main surface of the silicon substrate.

  In another aspect, the first zirconium oxide film is configured such that a <100> direction along a main surface of the first zirconium oxide film is parallel to a <100> direction along a main surface of the silicon substrate. The platinum film may be oriented such that the <100> direction along the main surface of the platinum film is parallel to the <100> direction along the main surface of the silicon substrate. The lead zirconate titanate film is oriented such that the <100> direction along the main surface of the lead zirconate titanate film is parallel to the <100> direction along the main surface of the silicon substrate. You may.

In another aspect, the lead zirconate titanate film may include a composite oxide of lead zirconate titanate represented by the following general formula (Formula 1).
Pb (Zr _1-x Ti _x ) O ₃ (Formula 1)
x satisfies 0.32 ≦ x ≦ 0.52, and the ratio of the lattice constant of the second lattice constant in the c-axis direction to the first lattice constant in the a-axis direction of lead zirconate titanate is 1.010 to 1.0. 016 may be used.

  A method for manufacturing a film structure according to one embodiment of the present invention includes a step (a) of preparing a silicon substrate including a main surface including a (100) plane, and a cubic crystal structure on the main surface. And (b) forming a first film including a (100) -oriented first zirconium oxide film, and a (100) -oriented platinum film having a cubic crystal structure on the first film. (C) forming a conductive film containing The first average interface roughness of the first interface between the first film and the conductive film is larger than the second average interface roughness of the second interface between the silicon substrate and the first film.

  Further, as another aspect, in the step (b), a first film including a film portion formed on the main surface and a plurality of protrusions respectively protruding from the upper surface of the film portion is formed. Includes a second zirconium oxide film having a cubic crystal structure and (100) orientation, and each of the plurality of protrusions has a cubic crystal structure and is (100) oriented. A third zirconium oxide film may be included.

  Further, as another aspect, a cross-sectional shape of the protruding portion perpendicular to the first direction along the main surface is triangular, and a direction along the main surface of the protruding portion and perpendicular to the first direction. The width in the second direction may decrease from the film part side to the side opposite to the film part side.

  In another aspect, the thickness of the film portion may be 11 to 18 nm, and the height of each of the plurality of protrusions protruding from the upper surface of the film portion may be 4 to 8 nm.

  In another embodiment, in the step (c), a conductive film is formed to cover the plurality of protrusions. In the step (c), the conductive film may be buried between two adjacent protrusions. Good.

  In another aspect, the conductive film has a first tensile stress, and the first film has a first compressive stress or a second tensile stress smaller than the first tensile stress. Is also good.

  In another aspect, the upper layer of the first film has a second compressive stress, the lower layer of the first film has a third tensile stress, and the first film has a first compressive stress. At this time, the second compressive stress may be larger than the first compressive stress, and when the first film has the second tensile stress, the third tensile stress may be larger than the second tensile stress.

  In another aspect, the method for manufacturing a film structure includes forming a piezoelectric film having a tetragonal crystal structure and including a (001) -oriented lead zirconate titanate film on a conductive film. (D).

  In another aspect, the first zirconium oxide film is configured such that a <100> direction along a main surface of the first zirconium oxide film is parallel to a <100> direction along a main surface of the silicon substrate. The platinum film may be oriented such that the <100> direction along the main surface of the platinum film is parallel to the <100> direction along the main surface of the silicon substrate.

  In another aspect, the first zirconium oxide film is configured such that a <100> direction along a main surface of the first zirconium oxide film is parallel to a <100> direction along a main surface of the silicon substrate. The platinum film may be oriented such that the <100> direction along the main surface of the platinum film is parallel to the <100> direction along the main surface of the silicon substrate. The lead zirconate titanate film is oriented such that the <100> direction along the main surface of the lead zirconate titanate film is parallel to the <100> direction along the main surface of the silicon substrate. You may.

In another aspect, the lead zirconate titanate film may include a composite oxide of lead zirconate titanate represented by the following general formula (Formula 1).
Pb (Zr _1-x Ti _x ) O ₃ (Formula 1)
x satisfies 0.32 ≦ x ≦ 0.52, and the ratio of the lattice constant of the second lattice constant in the c-axis direction to the first lattice constant in the a-axis direction of lead zirconate titanate is 1.010 to 1.0. 016 may be used.

  By applying one embodiment of the present invention, in a film structure for forming a piezoelectric film containing lead zirconate titanate, the piezoelectric characteristics of the piezoelectric film can be improved.

It is a sectional view of a film structure of an embodiment. FIG. 4 is a cross-sectional view of the film structure in the case where 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 illustrated in FIG. 2. It is sectional drawing of another example of the film structure of embodiment. FIG. 5 is an enlarged sectional view showing a part of the film structure shown in FIG. 4. It is sectional drawing of the film structure shown in FIG. FIG. 5 is a cross-sectional view of the film structure in a step of manufacturing the film structure shown in FIG. 4. FIG. 4 is a diagram schematically illustrating a cross-sectional structure of two piezoelectric films included in the film structure according to the embodiment. 5 is a graph schematically showing electric field dependence of polarization of a piezoelectric film included in the film structure of the embodiment. FIG. 3 is a diagram illustrating a state in which a film of each layer included in the film structure of the embodiment has been epitaxially grown. It is a figure which shows the unit lattice of PZT typically. It is sectional drawing in the manufacturing process of the film structure of Embodiment. It is sectional drawing in the manufacturing process of the film structure of Embodiment. It is sectional drawing in the manufacturing process of the film structure of Embodiment. It is sectional drawing in the manufacturing process of the film structure of Embodiment. It is sectional drawing of the film structure of the modification of embodiment. It is a graph which shows the example of the (theta) -2 (theta) spectrum by the XRD method of the film structure of an Example. It is a graph which shows the example of the (theta) -2 (theta) spectrum by the XRD method of the film structure of an Example. 9 is a graph showing an example of a θ-2θ spectrum of a film structure of a comparative example by an XRD method. 9 is a graph showing an example of a θ-2θ spectrum of a film structure of a comparative example by an XRD method. It is a graph which shows the example of the pole figure by the XRD method of the film structure of an Example. It is a graph which shows the example of the pole figure by the XRD method of the film structure of an Example. It is a graph which shows the example of the pole figure by the XRD method of the film structure of an Example. It is a graph which shows the example of the pole figure by the XRD method of the film structure of an Example. FIG. 3 is a diagram for explaining a method of measuring the amount of warpage of a substrate by an XRD method. 5 is a graph showing a result of measuring a warpage amount of a substrate by an XRD method. It is a photograph which shows the HAADF image of the film structure of an example. It is a photograph which shows the BF image of the film structure of an example. It is a photograph which shows the BF image of the film structure of an example. It is a photograph which shows the HAADF image of the film structure of an example. 5 is a graph showing voltage dependence of polarization of a film structure of an example. 5 is a graph showing the voltage dependence of the displacement of the membrane structure of the example. 5 is a graph showing the temperature dependence of the remanent polarization value of the film structure of the example. 5 is a graph showing the temperature dependence of the coercive voltage value of the membrane structure of the example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of appropriate modifications while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, in order to make the description clearer, the width, thickness, shape, and the like of each part may be schematically illustrated as compared with the embodiment, but this is merely an example, and the interpretation of the present invention is not limited thereto. There is no limitation.

  In the specification and the drawings, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate.

  Further, in the drawings used in the embodiments, hatching (shading) for distinguishing structures may be omitted depending on the drawings.

  In the following embodiments, when a range is indicated as A to B, the range indicates A or more and B or less unless otherwise specified.

(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 in the case where 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 cross-sectional view of another example of the film structure of the embodiment. FIG. 5 is an enlarged sectional view showing a part of the film structure shown in FIG. FIG. 6 is a cross-sectional view of the film structure shown in FIG. FIG. 6 schematically shows the stress of the film structure in addition to the cross-sectional view of the film structure shown in FIG. FIG. 7 is a cross-sectional view of the film structure in a step of manufacturing the film structure shown in FIG. FIG. 7 schematically shows a stress of the film structure in addition to a cross-sectional view of the film structure when the alignment film is formed on the substrate.

  As shown in FIG. 1, the film structure 10 according to the present embodiment includes a substrate 11, an alignment film 12, a conductive film 13, a film 14, and a piezoelectric film 15. 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 piezoelectric film 15 is formed on the film 14.

  As shown in FIG. 2, the film structure 10 of the present embodiment may have a conductive film 18. The conductive film 18 is formed on the piezoelectric film 15. At this time, the conductive film 13 is a conductive film as a lower electrode, and the conductive film 18 is a conductive film as an upper electrode. As shown in FIG. 3, the film structure 10 of the present embodiment does not include the substrate 11 (see FIG. 2) and the alignment film 12 (see FIG. 2), and includes a conductive film 13 as a lower electrode, It may have only the film 14, the piezoelectric film 15, and the conductive film 18 as the upper electrode.

  Further, as shown in FIG. 4, the film structure 10 of the present embodiment may have only the substrate 11, the alignment film 12, and the conductive film 13. In such a case, the film structure 10 can be used as an electrode substrate for forming the piezoelectric film 15, and the piezoelectric film 15 that is epitaxially grown on the conductive film 13 and has good piezoelectric characteristics can be easily formed. Can be formed.

  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 composed 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 (zirconium oxide film). The conductive film 13 has a cubic crystal structure and includes (100) -oriented platinum (platinum film). Accordingly, when the piezoelectric film 15 includes a composite oxide having a perovskite structure, the piezoelectric film 15 is oriented on the substrate 11 in (001) orientation in tetragonal system or (100) in pseudo-cubic system. be able to.

  Here, that the orientation film 12 is (100) oriented means that the (100) plane of the orientation film 12 having a cubic crystal structure is the main (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 of the substrate 11, which is a silicon substrate, having a (100) plane. Further, the expression that the (100) plane of the alignment film 12 is parallel to the upper surface 11a of the substrate 11 that is the (100) surface means that the (100) plane of the alignment film 12 is completely parallel to the upper surface 11a of the substrate 11. However, the case where the angle formed between 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 also included. The same applies to the orientation of the films of other layers as well as the orientation film 12.

  Alternatively, instead of the alignment film 12 formed of a single-layer film, the alignment film 12 formed of a laminated film may be formed on the substrate 11 as the alignment film 12.

  As shown in FIGS. 1, 2, 4 and 5, the alignment film 12 includes a film portion 12a formed on the upper surface 11a of the substrate 11 and a plurality of protrusions 12b protruding from the upper surface of the film portion 12a. And The film portion 12a has a cubic crystal structure and includes (100) -oriented zirconium oxide (zirconium oxide film). Each of the plurality of projections 12b has a cubic crystal structure and includes (100) -oriented zirconium oxide (zirconium oxide film).

  Thereby, the interface roughness (roughness) of the interface IF1 between the alignment film 12 and the conductive film 13 increases, and the average interface roughness of the interface IF1 between the alignment film 12 and the conductive film 13 increases. It becomes larger than the average interface roughness of the interface IF2 with the alignment film 12. Therefore, for example, the surface of the alignment film 12 becomes a surface other than the (100) plane of the zirconium oxide film included in the alignment film 12, and the surface of the zirconium oxide film other than the (100) plane is included in the conductive film 13. The epitaxial growth of the surface of the platinum film other than the (100) plane facilitates the epitaxial growth of the platinum film on the surface of the zirconium oxide film. Since the conductive film 13 including the platinum film is easily grown epitaxially, the film 14 and the piezoelectric film 15 are easily grown epitaxially, so that the piezoelectric characteristics of the piezoelectric film 15 can be improved.

  Alternatively, the average interface roughness of the interface IF1 between the alignment film 12 and the conductive film 13 may be larger than the average interface roughness of the interface IF2 between the substrate 11 and the alignment film 12, so that the alignment film 12 It is not necessary to have the plurality of protrusions 12b clearly, and for example, it may have a step terrace structure having a plurality of steps (steps) formed on the surface so as to be separated from each other in plan view.

The average interface roughness was obtained by capturing an image of a cross section of the membrane structure using a transmission electron microscope (TEM) so that the interface IF1 and the interface IF2 are captured in the same image. The calculation can be performed by performing arithmetic processing on the image using a computer. The type of the parameter indicating the average interface roughness of each of the interface IF1 and the interface IF2 may be the same type of parameter, and is not particularly limited. Therefore, the comparison can be performed using various parameters such as the arithmetic average roughness _Ra and the root mean square height _Rrms as parameters representing the average interface roughness. For example, when the protrusion heights HT1 of the plurality of protrusions 12b are all 6 nm and, for example, the arithmetic average roughness _Ra is used as the average interface roughness, the arithmetic average roughness _Ra is 3 nm.

  Preferably, the cross-sectional shape of the protrusion 12b perpendicular to the first direction along the upper surface 11a of the substrate 11 is triangular, and the protrusion 12b is along the upper surface 11a of the substrate 11 and in the first direction. The width in the second direction, which is a direction perpendicular to the direction of FIG. When the protrusion 12b has such a triangular shape, the platinum film included in the conductive film 13 is more easily epitaxially grown on the surface of the zirconium oxide film included in the alignment film 12.

  Preferably, the thickness TH1 of the film portion 12a (see FIG. 5) is 11 to 18 nm, and each of the plurality of protrusions 12b projects from the upper surface 12c of the film portion 12a (see FIG. 5). (See FIG. 5) is 4-8 nm. That is, preferably, the thickness TH2 (see FIG. 5) of the alignment film 12 is 13 to 22 nm.

  When the protrusion height HT1 of the protrusion 12b is 4 nm or more, the average interface roughness of the interface IF1 is surely larger than that of the interface IF2 as compared with the case where the protrusion height HT1 of the protrusion 12b is less than 4 nm. Therefore, platinum contained in the conductive film 13 formed on the alignment film 12 containing (100) -oriented zirconium oxide is easily oriented to (100). On the other hand, when the protrusion height HT1 of the protrusion 12b is equal to or less than 8 nm, the average interface roughness of the interface IF1 is not too large as compared with the case where the protrusion height HT1 of the protrusion 12b exceeds 8 nm. The flatness of the conductive film 13 formed on the oriented film 12 containing zirconium oxide can be improved.

  Further, when the thickness TH1 of the film portion 12a is 11 nm or more, the thickness TH2 of the alignment film 12 becomes somewhat thicker than when the thickness TH1 of the film portion 12a is less than 11 nm. , The alignment film 12 is formed uniformly, and the direct contact between the conductive film 13 and the substrate 11 can be prevented. Further, when the thickness TH1 of the film portion 12a is 11 nm or more, the thickness TH2 of the alignment film 12 becomes somewhat thicker than in the case where the thickness TH1 of the film portion 12a is less than 11 nm. HT1 is easily set to 4 nm or more, and the platinum contained in the conductive film 13 is easily oriented to (100). On the other hand, when the thickness TH1 of the film portion 12a is equal to or less than 18 nm, the average interface roughness of the interface IF1 is not too large as compared with the case where the thickness TH1 of the film portion 12a exceeds 18 nm. The flatness of the formed conductive film 13 can be improved.

  That is, when the thickness TH2 of the alignment film 12 is 13 nm or more, the alignment film 12 is formed uniformly over the entire upper surface 11a of the substrate 11 as compared with the case where the thickness TH2 of the alignment film 12 is less than 13 nm. The direct contact between the film 13 and the substrate 11 can be prevented. In addition, when the thickness TH2 of the alignment film 12 is 13 nm or more, the protrusion height HT1 of the protrusion 12b is more easily set to 4 nm or more than when the thickness TH2 of the alignment film 12 is less than 13 nm. Pt is easily (100) oriented. On the other hand, when the thickness TH2 of the alignment film 12 is 22 nm or less, the average interface roughness of the interface IF1 is not too large as compared with the case where the thickness TH2 of the alignment film 12 exceeds 22 nm. The flatness of the formed conductive film 13 can be improved.

  Preferably, the conductive film 13 covers the plurality of protrusions 12b, and the conductive film 13 is embedded between two adjacent protrusions 12b. When the conductive film 13 has such a shape, the area of the interface between the conductive film 13 and the alignment film 12 increases, and the adhesion force of the conductive film 13 to the alignment film 12 increases.

  Since the platinum film included in the conductive film 13 only needs to be able to epitaxially grow on the surface of the zirconium oxide film included in the alignment film 12, the cross section of the protrusion 12 b perpendicular to the first direction along the upper surface 11 a of the substrate 11. The shape need not be triangular. That is, the width of the protruding portion 12b in the second direction, which is along the upper surface 11a of the substrate 11 and is perpendicular to the first direction, is opposite to the film portion 12a, that is, from the substrate 11 side to the film portion 12a side. It does not have to decrease toward the side, that is, the side opposite to the substrate 11 side.

  In the film structure shown in FIG. 4, as shown in FIG. 6, preferably, the conductive film 13 has a tensile stress TS1, and the alignment film 12 has a compressive stress CS1 or a tensile stress TS1. It has a smaller tensile stress TS2.

  In the manufacturing process of the film structure shown in FIG. 4, the stress at the time when the alignment film 12 is formed on the substrate 11 as shown in FIG. 7 will be described. When the alignment film 12 is formed on the substrate 11, the alignment film 12 has a tensile stress TS4.

The linear expansion coefficient α _ZrO2 of zirconium oxide (ZrO ₂ ) is about 9 × 10 ⁻⁶ ° C. ⁻¹ , and the linear expansion coefficient α _Si of silicon (Si) is about 4 × 10 ⁻⁶ ° C. ⁻¹ , The linear expansion coefficient α _ZrO2 of zirconium oxide is larger than the linear expansion coefficient α _Si of silicon (Si). In such a case, after the alignment film 12 made of zirconium oxide is formed on the substrate 11 made of silicon at a temperature of, for example, 550 ° C., when the substrate 11 is cooled from 550 ° C. to room temperature (30 ° C.), Although 12 shrinks along the upper surface 11a of the substrate 11, the substrate 11 does not shrink as much as the alignment film 12, so the alignment film 12 is pulled by being restrained by the substrate 11, and cannot be completely shrunk. As a result, the alignment film 12 has a tensile stress TS4, the substrate 11 has a compressive stress, and the substrate 11 curves in a downwardly convex shape as shown in FIG.

On the other hand, the linear expansion coefficient α _Pt of platinum (Pt) is also about 9 × 10 ⁻⁶ ° C. ⁻¹ , and the linear expansion coefficient α _Pt of platinum (Pt) is larger than the linear expansion coefficient α _Si of silicon (Si). large. In such a case, after the conductive film 13 made of platinum is formed on the alignment film 12 at a temperature of, for example, 550 ° C., when the substrate 11 is cooled from 550 ° C. to room temperature (30 ° C.), the conductive film 13 Although it shrinks along the upper surface 11a of the substrate 11, the substrate 11 does not shrink as much as the conductive film 13, so the conductive film 13 is restrained and pulled by the substrate 11, and cannot be completely shrunk. Therefore, the conductive film 13 has a tensile stress TS1. The alignment film 12 is pulled from the substrate 11 but is compressed from the conductive film 13 or receives little force. Therefore, the alignment film 12 has a compressive stress CS1 or a tensile stress TS2 smaller than the tensile stress TS1.

  When the thickness of the conductive film 13 is larger than the thickness of the alignment film 12, the alignment film 12 is compressed from the conductive film 13. Therefore, as shown in FIG. 6, the upper layer 12d of the alignment film 12 has a compressive stress CS2, and the lower layer 12e of the alignment film 12 has a tensile stress TS3. When the alignment film 12 has a compressive stress CS1 as a whole, the compressive stress CS2 is larger than the compressive stress CS1, and when the alignment film 12 has a tensile stress TS2 as a whole, the tensile stress TS3 is larger than the tensile stress TS2.

  Preferably, the alignment film 12 is epitaxially grown on the upper surface 11a of the substrate 11, and the conductive film 13 is epitaxially grown on the alignment film 12. Accordingly, when the piezoelectric film 15 includes a composite oxide having a perovskite structure, the piezoelectric film 15 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 defined as an X-axis direction and a Y-axis direction, and a direction perpendicular to the upper surface 11a is defined as a Z-axis direction, a certain film epitaxially grows. Means that the film is oriented in any of the X-axis direction, the Y-axis direction, and the Z-axis direction. A preferred orientation direction in the upper surface 11a will be described with reference to FIG. Further, the above-described first direction corresponds to the Y-axis direction, and the above-described second direction corresponds to the X-axis direction.

The film 14 includes a composite oxide represented by the following general formula (Formula 2) and oriented in (100) orientation in pseudo cubic expression.
_{Sr (Ti 1-z Ru z} ) O 3 ··· ( of 2)
Here, z satisfies 0 ≦ z ≦ 1. In the following, _Sr when z satisfies _{z = 0 (Ti 1-z} Ru z) a _{O 3} i.e. SrTiO _3, referred to as STO, z is 0 <Sr when satisfying z <1 _{(Ti 1-} the _z Ru _{z) O 3,} referred to as STRO, the _{Sr (Ti 1-z Ru z} ) O 3 i.e. SrRuO ₃ when z satisfies z = 1, may be referred to as SRO.

  SRO has metal conductivity, and STO has semiconducting or insulating properties. Therefore, the conductivity of the film 14 is improved as z approaches 1, so that the film 14 can be used as a part of the lower electrode including the conductive film 13.

  Here, when the film 14 is formed by a sputtering method, z preferably satisfies 0 ≦ z ≦ 0.4, and more preferably satisfies 0.05 ≦ z ≦ 0.2. If z exceeds 0.4, the composite oxide represented by the general formula (Formula 2) may become powder and may not be sufficiently hardened, which makes it difficult to manufacture a sputtering target.

  On the other hand, when the film 14 is formed by a coating method such as a sol-gel method, it can be easily formed even if z> 0.4.

  The complex oxide having a perovskite structure represented by the general formula (Formula 2) and being (100) -oriented in a pseudo-cubic representation means the following cases.

First, in a crystal lattice having a perovskite structure represented by the general formula ABO ₃ including a unit cell arranged three-dimensionally, the unit cell is composed of one atom A, one atom B, and three oxygen atoms. Consider the case.

In such a case, being (100) oriented in pseudo cubic means that the unit cell has a cubic crystal structure and is (100) oriented. In this case, the length of one side of the unit lattice, and the lattice constant a _c.

On the other hand, consider the case where the composite oxide represented by the general formula (Formula 2) and having a perovskite structure has an orthorhombic crystal structure. The second of the substantially equal and the three lattice constants of orthorhombic first lattice constant a _o to 2 ^1/2 times the lattice constant a _c of the pseudo cubic of the three lattice constant of orthorhombic lattice constant b _o is approximately equal to twice the lattice constant a _c of the pseudo cubic of 2 ¹ of the third lattice constant c _o is the lattice constant a _c of the pseudo cubic of the three lattice constant of orthorhombic Consider the case of approximately equal to ^{/ 2} times. In the specification of the present application, the expression that 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, being (100) oriented in pseudo cubic display means being (101) or (020) oriented in orthorhombic display.

Film 14 is represented by the above general formula (Formula 2), by satisfying 0 ≦ z ≦ 1, the lattice constant _{a c} of the pseudo-cubic is to meet the 0.390nm ≦ _{a c} ≦ 0.393nm, later As described with reference to FIG. 10, the film 14 can be (100) -oriented on the conductive film 13 in pseudo-cubic display.

  The piezoelectric film 15 is formed on the conductive film 13 with the film 14 interposed therebetween, has a tetragonal crystal structure, and is a lead oxide zirconate titanate (PZT) (PZT) as a (001) -oriented composite oxide. Including membrane. Alternatively, when the PZT included in the piezoelectric film 15 includes a portion having a tetragonal crystal structure and a portion having a rhombohedral crystal structure, the piezoelectric film 15 , And may include lead zirconate titanate (PZT) as a composite oxide oriented in (100) orientation in pseudo cubic notation.

That the piezoelectric film 15 contains PZT means that the piezoelectric film 15 contains a composite oxide represented by the following general formula (Formula 3).
Pb (Zr _1-u Ti _u ) O ₃ (Formula 3)
u satisfies 0 <u <1.

In the case where the piezoelectric film 15 has a tetragonal crystal structure and includes (001) -oriented PZT, in the present embodiment, the X-ray of the piezoelectric film 15 is determined by the θ-2θ method using CuKα radiation. In the diffraction pattern, assuming that the diffraction angle of the diffraction peak of the (004) plane in the tetragonal expression of lead zirconate titanate is 2θ ₀₀₄ , 2θ ₀₀₄ satisfies the following equation (Equation 1).
2θ ₀₀₄ ≦ 96.5 ° (Equation 1)

  Thereby, the interval of the (004) plane in the tetragonal display of lead zirconate titanate becomes long. Alternatively, the content of the (001) -oriented (c-axis oriented) lead zirconate titanate having a tetragonal crystal structure in the piezoelectric film 15 may be adjusted to the tetragonal crystal structure in the piezoelectric film 15. And the content of lead zirconate titanate having a (100) orientation (a-axis orientation) can be increased. Therefore, the polarization direction of each of the plurality of crystal grains included in the piezoelectric film 15 can be made uniform, so that the piezoelectric characteristics of the piezoelectric film 15 can be improved.

  On the other hand, when the piezoelectric film 15 includes PZT oriented in (100) orientation in pseudo cubic expression, it can be considered as follows.

PZT contained in the piezoelectric film 15 has a tetragonal crystal structure, the two lattice constants of tetragonal is _{a t} and _{c t, a t} and _{c t} satisfies _c t> _{a t,} the unit cell but consider a case where the length of the three sides which are perpendicular to each other is a rectangular parallelepiped is a _t, a _t and c _t. The lattice constant a _t tetragonal substantially equal to the lattice constant a _c of the pseudo-cubic lattice constant c _t tetragonal Consider the case substantially equal to the lattice constant a _c of the pseudo-cubic. In such a case, PZT being (100) oriented in pseudo cubic notation means that PZT is (100) oriented (a-axis oriented) or (001) oriented (c-axis oriented) in tetragonal notation. Means

On the other hand, _let us consider a case where PZT included in the piezoelectric film 15 has a rhombohedral crystal structure and the lattice constant of the rhombohedral is ar. Then, the lattice constants a _r rhombohedral Consider the case substantially equal to the lattice constant a _c of the pseudo-cubic. In such a case, that PZT is (100) -oriented in pseudo cubic expression means that PZT is (100) -oriented in rhombohedral expression.

In such a case, in the present embodiment, in the X-ray diffraction pattern of the piezoelectric film 15 by the θ-2θ method using CuKα radiation, the diffraction peak of the (400) plane in the pseudo cubic display of lead zirconate titanate is shown. when the diffraction angle was 2 [Theta] _400, 2 [Theta] _400, in the above-mentioned formula (formula 1) will satisfy the equation (2 [Theta] ₄₀₀ ≦ 96.5 °) was replaced with 2 [Theta] ₄₀₀ instead of the 2 [Theta] _004. As a result, the interval between the (400) planes in the pseudo cubic display of lead zirconate titanate becomes longer. Therefore, in the piezoelectric film 15, the content of the (001) -oriented lead zirconate titanate having a tetragonal crystal structure is adjusted to the tetragonal crystal structure in the piezoelectric film 15, and , (100) -oriented lead zirconate titanate. Therefore, the polarization direction of each of the plurality of crystal grains included in the piezoelectric film 15 can be made uniform, so that the piezoelectric characteristics of the piezoelectric film 15 can be improved.

Further, in the present embodiment, when the relative dielectric constant of the piezoelectric film 15 and epsilon _r, epsilon _r satisfies the following formula (Formula 2).
ε _r ≤450 (Equation 2)

  Thus, when the film structure 10 is used as, for example, a pressure sensor using the piezoelectric effect, the detection sensitivity can be improved, and the detection circuit of the pressure sensor can be easily designed. Alternatively, when the film structure 10 is used as, for example, an ultrasonic vibrator using an inverse piezoelectric effect, an oscillation circuit can be easily designed.

  In a film structure having a piezoelectric film containing lead zirconate titanate, for example, due to a low film density or a low content of lead zirconate titanate, the quality such as crystallinity of the piezoelectric film is good. If not, the piezoelectric characteristics of the piezoelectric film deteriorate. On the other hand, in a film structure having a piezoelectric film containing lead zirconate titanate, for example, due to a high film density or a high content of lead zirconate titanate, the quality of the piezoelectric film such as crystallinity is high. Is good, the piezoelectric characteristics of the piezoelectric film are improved, but the relative permittivity of the piezoelectric film may not be reduced.

  As described above, in a film structure having a piezoelectric film containing lead zirconate titanate, the relative dielectric constant of the piezoelectric film may not be reduced when the piezoelectric characteristics of the piezoelectric film are improved. If the relative permittivity of the piezoelectric film does not decrease, for example, when the piezoelectric film is used as a pressure sensor, the detection sensitivity of the pressure sensor decreases due to, for example, an increase in the capacity of the pressure sensor. May be difficult to design the detection circuit.

In the film structure 10 of the present embodiment, 2θ ₀₀₄ satisfies the above equation (Equation 1), and ε _r satisfies the above equation (Equation 2). When 2θ ₀₀₄ satisfies the above formula (Equation 1), the content of the (001) -oriented lead zirconate titanate having a tetragonal crystal structure in the piezoelectric film 15 is increased. Characteristics can be improved. In addition, when ε _r satisfies the above expression (Equation 2), the relative dielectric constant decreases, so that the detection sensitivity of the pressure sensor can be increased. Therefore, according to the film structure 10 of the present embodiment, the piezoelectric characteristics can be improved, and the detection sensitivity of the sensor using the piezoelectric effect can be improved. That is, in a film structure having a piezoelectric film containing lead zirconate titanate, the piezoelectric characteristics of the piezoelectric film can be improved, and the detection sensitivity of a pressure sensor using the piezoelectric film can be improved.

As described in Non-Patent Document 2, PbTiO ₃ becomes a single crystal, and when the crystallinity including the orientation is improved, the relative dielectric constant decreases. Therefore, it is considered that the relative dielectric constant of PZT is also reduced by improving the crystallinity including the orientation of the thin film, similarly to PbTiO ₃ . That is, the relative dielectric constant ε _r of the film structure 10 being lowered to 450 or less indicates that the piezoelectric film 15 which is a piezoelectric film containing lead zirconate titanate has a single crystal shape.

Preferably, when the film structure 10 has the conductive film 18, the relative dielectric constant of the piezoelectric film 15 measured by applying an AC voltage having a frequency of 1 kHz between the conductive film 13 and the conductive film 18 is ε. when the _r, epsilon _r of the piezoelectric layer 15 satisfy the above expression (expression 2). By reducing the relative dielectric constant at an AC voltage having such a frequency, for example, the clock frequency of the detection circuit can be increased, and the response speed of the pressure sensor using the membrane structure 10 can be improved.

When the film structure 10 has the conductive film 18, the conductive film 13, the piezoelectric film 15, and the conductive film 18 form the ferroelectric capacitor CP1. Then, ε _{r of the} piezoelectric film 15 is calculated based on the capacitance of the ferroelectric capacitor CP1 when an AC voltage having a frequency of 1 kHz is applied between the conductive film 13 and the conductive film 18.

Preferably, when the residual polarization value of the piezoelectric film 15 was set to P _r, P _r satisfies the following formula (Equation 3).
^{_{P r ≧ 28μC / cm 2 ···}} ( number 3)

The remanent polarization value is a value that serves as an index of the ferroelectric properties of a piezoelectric substance that is also a ferroelectric substance. In general, a piezoelectric film having excellent ferroelectric properties also has excellent piezoelectric properties. Therefore, by P _r of the piezoelectric film 15 satisfies the above expression (Expression 3), it is possible to improve the ferroelectric characteristic of the piezoelectric film 15, it is possible to improve the piezoelectric characteristics of the piezoelectric film 15.

Incidentally, _{P r} preferably satisfies _{P r} ≧ _40μC / cm ^2, it is more preferable to satisfy _{P r} ≧ _50μC / cm ^2, it is more preferred to satisfy the _{P r} ≧ _55μC / cm ^2. As the value of _Pr increases, the ferroelectric characteristics of the piezoelectric film 15 can be further improved. Therefore, the piezoelectric characteristics of the piezoelectric film 15 can be further improved.

When the film structure 10 has the conductive film 18, a polarization voltage hysteresis curve indicating a change in polarization of the piezoelectric film 15 when a voltage applied between the conductive film 13 and the conductive film 18 is changed (see FIG. 9), the polarization value when the voltage applied between the conductive film 13 and the conductive film 18 is increased from 0 to the positive side and returned to 0 again is the remanent polarization of the piezoelectric film 15. Value _Pr . Further, the polarization value when returning the voltage applied between the conductive film 13 and the conductive film 18 from 0 to 0 again reduced to the negative side, the residual polarization value -P _r of the piezoelectric film 15.

That is, when measuring the polarization electric field hysteresis curve indicating the change in the polarization of the piezoelectric film 15 when the electric field applied to the piezoelectric film 15 is changed, the voltage applied to the piezoelectric film 15 is increased from 0 to the positive side. polarization when returned to 0 again Te is a remanent polarization P _r of the piezoelectric film 15. Further, the polarization when returned to 0 again reduces the electric field applied to the piezoelectric layer 15 from 0 to a negative side, the residual polarization value -P _r of the piezoelectric film 15.

As shown in FIG. 2, when the film structure 10 includes the conductive film 18, the conductive film 13, the piezoelectric film 15, and the conductive film 18 form a ferroelectric capacitor CP1. In this case, P _r of the piezoelectric film 15, the residual polarization value of the ferroelectric capacitor CP1.

  Preferably, the piezoelectric film 15 includes a piezoelectric film 16 and a piezoelectric film 17. The piezoelectric film 16 includes a composite oxide made of lead zirconate titanate formed on the film 14. The piezoelectric film 17 includes a composite oxide made of lead zirconate titanate formed on the piezoelectric film 16. The piezoelectric film 16 has a compressive stress, and the piezoelectric film 17 has a tensile stress.

  Consider a case where the piezoelectric film 16 has a tensile stress and the piezoelectric film 17 has a tensile stress. In such a case, the film structure 10 easily warps so as to have a downwardly convex shape when the upper surface 11a of the substrate 11 is used as a main surface. Therefore, for example, when the film structure 10 is processed by using the photolithography technology, the shape accuracy is reduced, and the characteristics of the piezoelectric element formed by processing the film structure 10 are reduced.

  It is also assumed that the piezoelectric film 16 has a compressive stress and the piezoelectric film 17 has a compressive stress. In such a case, the film structure 10 is likely to be warped so as to have an upwardly convex shape when the upper surface 11a of the substrate 11 is used as a main surface. Therefore, for example, when the film structure 10 is processed by using the photolithography technology, the shape accuracy is reduced, and the characteristics of the piezoelectric element formed by processing the film structure 10 are reduced.

  On the other hand, in the present embodiment, the piezoelectric film 16 has a compressive stress, and the piezoelectric film 17 has a tensile stress. Accordingly, the warpage of the film structure 10 can be reduced as compared with the case where both the piezoelectric films 16 and 17 have a tensile stress, and both the piezoelectric films 16 and 17 have a compressive stress. , The amount of warpage of the film structure 10 can be reduced. Therefore, for example, when the film structure 10 is processed using the photolithography technique, the shape accuracy can be improved, and the characteristics of the piezoelectric element formed by processing the film structure 10 can be improved.

  The fact that the piezoelectric film 16 has a compressive stress and the piezoelectric film 17 has a tensile stress means that, for example, when the piezoelectric film 17 and the piezoelectric film 16 are sequentially removed from the film structure 10, before and after the piezoelectric film 17 is removed. Thus, it can be confirmed that the substrate 11 is deformed from the downward convex side to the upward convex side, and the substrate 11 is deformed from the upward convex side to the downward convex side before and after the removal of the piezoelectric film 16.

Preferably, the piezoelectric film 16 includes a composite oxide represented by the following general formula (Formula 4) and made of lead zirconate titanate (PZT).
Pb (Zr _1-x Ti _x ) O ₃ (Formula 4)
Here, x satisfies 0.32 ≦ x ≦ 0.52. The general formula (Formula 4) represents the same composite oxide as that of the general formula (Formula 1).

  When x satisfies 0.32 ≦ x ≦ 0.48, PZT contained in the piezoelectric film 16 has a rhombohedral crystal structure, but mainly due to the binding force from the substrate 11 or the like. It has a tetragonal crystal structure and is easy to be oriented (001). Then, the piezoelectric film 16 containing PZT is epitaxially grown on the film 14. When x satisfies 0.48 <x ≦ 0.52, PZT contained in the piezoelectric film 16 has a tetragonal crystal structure because PZT originally has a tetragonal crystal structure, and (001) orientation. Then, the piezoelectric film 16 containing PZT is epitaxially grown on the film 14. Thereby, the polarization axis of the lead zirconate titanate contained in the piezoelectric film 16 can be oriented substantially perpendicular to the upper surface 11a, so that the piezoelectric characteristics of the piezoelectric film 16 can be improved.

Further, preferably, the piezoelectric film 17 is represented by the following general formula (Formula 5) and includes a composite oxide made of lead zirconate titanate (PZT).
Pb (Zr _1-y Ti _y ) O ₃ (Formula 5)
Here, y satisfies 0.32 ≦ y ≦ 0.52.

  When y satisfies 0.32 ≦ y ≦ 0.48, PZT contained in the piezoelectric film 17 has a composition having a rhombohedral crystal structure, but mainly due to a binding force from the substrate 11 or the like. It has a tetragonal crystal structure and is easy to be oriented (001). Then, the piezoelectric film 17 containing PZT is epitaxially grown on the piezoelectric film 16. When y satisfies 0.48 <y ≦ 0.52, PZT contained in the piezoelectric film 17 has a tetragonal crystal structure because the PZT originally has a tetragonal crystal structure. (001) orientation. Then, the piezoelectric film 17 containing PZT is epitaxially grown on the piezoelectric film 16. Thereby, 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.

  As described below with reference to FIG. 15, the piezoelectric film 16 having a compressive stress can be formed by, for example, a sputtering method. Further, when describing the manufacturing process of the film structure, as described with reference to FIG. 1, the piezoelectric film 17 having a tensile stress can be formed by a coating method such as a sol-gel method.

  FIG. 8 is a diagram schematically illustrating a cross-sectional structure of two piezoelectric films included in the film structure of the embodiment. FIG. 8 shows a section formed by cleaving the substrate 11 included in the film structure 10 of the embodiment shown in FIG. 1, that is, a fracture section, observed by a scanning electron microscope (Scanning Electron Microscope: SEM). In the observation image, the piezoelectric films 16 and 17 are schematically illustrated.

  FIG. 9 is a graph schematically showing the electric field dependence of the polarization of the piezoelectric film included in the film structure of the embodiment. FIG. 9 shows the polarization of the piezoelectric film 15 when the electric field between the lower electrode (conductive film 13) and the upper electrode (conductive film 18) included in the film structure 10 of the embodiment shown in FIG. 2 is changed. 5 is a graph schematically showing a polarization electric field hysteresis curve showing a change in the electric field.

  As shown in FIG. 8, when the piezoelectric film 16 is formed by a sputtering method, the piezoelectric film 16 includes a plurality of crystal grains 16g integrally formed from the lower surface to the upper surface of the piezoelectric film 16. Further, holes or voids are unlikely to remain between two adjacent crystal grains 16g in the main surface of the substrate 11 (the upper surface 11a in FIG. 1). Therefore, when a cross section to be observed by the SEM is formed on the piezoelectric film 16 by processing by a focused ion beam (FIB) method, the cross section is easily seen as a single cross section, and the crystal grains are easily observed. It becomes difficult to observe 16 g.

  On the other hand, when the piezoelectric film 17 is formed by a coating method, the piezoelectric film 17 includes a plurality of films 17f as layers stacked on each other in the thickness direction of the piezoelectric film 17. The film 17f as each of the plurality of layers includes a plurality of crystal grains 17g integrally formed from the lower surface to the upper surface of the one-layer film 17f. In addition, holes or voids may remain between two adjacent films 17f in the thickness direction of the piezoelectric film 17.

  As shown in FIG. 8, preferably, each of the plurality of crystal grains has spontaneous polarization. The spontaneous polarization includes a polarization component P1 parallel to the thickness direction of the piezoelectric film 16, and the polarization components P1 included in the spontaneous polarization of each of the plurality of crystal grains are oriented in the same direction.

  In such a case, as shown in FIG. 9, the piezoelectric film 15 has a large spontaneous polarization in an initial state. Therefore, the electric field of the polarization of the piezoelectric film 15 when the electric field increases from the starting point SP of 0 to the positive side and returns to 0 again, and then decreases to the negative side and returns to the end point EP of 0 again. The hysteresis curve showing the dependency is a curve having a point away from the origin as a starting point SP. Therefore, when the film structure 10 of the present embodiment is used as a piezoelectric element, it is not necessary to perform a polarization process on the piezoelectric film 15 before use.

Incidentally, when the hysteresis curve shown in FIG. 9 intersects the field axis, i.e. the electric field value at which the polarization becomes 0, referred to as the coercive field value E _c. In the graph of the hysteresis curve, when the polarization is expressed by the voltage dependence of the polarization instead of the electric field dependence, the voltage value when the hysteresis curve intersects the voltage axis, that is, when the polarization becomes 0, is determined by the resistance. referred to as the voltage value _{V c.}

  FIG. 10 is a diagram illustrating a state in which the films of the respective layers included in the film structure of the embodiment have been epitaxially grown. Note that FIG. 10 schematically illustrates each layer of the substrate 11, the alignment film 12, the conductive film 13, the film 14, and the piezoelectric film 15.

The lattice constant of Si contained in the substrate 11, the lattice constant of ZrO ₂ contained in the alignment film 12, the lattice constant of Pt contained in the conductive film 13, the lattice constant of SRO contained in the film 14, and the lattice constant of the piezoelectric film 15 Table 1 shows the lattice constants of PZT.

As shown in Table 1, the lattice constant of Si is 0.543 nm, the lattice constant of ZrO ₂ is 0.511 nm, and the mismatch between the lattice constant of ZrO _{2 and} the lattice constant of Si is 6.1%. Therefore, the lattice constant of ZrO ₂ matches well with the lattice constant of Si. Therefore, as shown in FIG. 10, the orientation film 12 containing ZrO ₂ can be epitaxially grown on the upper surface 11a as the main surface composed of the (100) plane of the substrate 11 containing silicon single crystal. Therefore, the orientation film 12 containing ZrO ₂ can be (100) oriented in a cubic crystal structure on the (100) plane of the substrate 11 containing silicon single crystal, and the crystallinity of the orientation film 12 is improved. be able to.

  It is assumed that the alignment film 12 has a cubic crystal structure and includes a (100) -oriented zirconium oxide film 12f. In such a case, the <100> direction of the zirconium oxide film 12f along the upper surface 11a as the main surface of the substrate 11 made of the silicon substrate is <100 along the upper surface 11a of the substrate 11 itself. > Orient so as to be parallel to the direction.

  Note that the <100> direction of the zirconium oxide film 12f along the upper surface 11a of the substrate 11 is parallel to the <100> direction along the upper surface 11a of the silicon substrate 11 itself. <100> direction of the zirconium oxide film 12f and the <100> direction of the <100> direction along the upper surface 11a of the substrate 11 itself. > Includes the case where the angle with the direction is 20 ° or less. The same applies to the in-plane orientation of the film of other layers as well as the zirconium oxide film 12f.

On the other hand, as shown in Table 1, although the lattice constant of ZrO ₂ is 0.511 nm and the lattice constant of Pt is 0.392 nm, when Pt is rotated by 45 ° in the plane, the length of the diagonal is , 0.554 nm, and the mismatch of the length of the diagonal line with the lattice constant of ZrO ₂ is as small as 8.1%. Therefore, the conductive film 13 containing Pt is placed on the (100) plane of the orientation film 12 containing ZrO _2. It is also considered that epitaxial growth can be performed. For example, Patent Document 2 and Non-Patent Document 1 disclose a <100> direction in a plane of an LSCO film made of LSCO, which is not a Pt film but has a lattice constant (0.381 nm) substantially equal to the lattice constant of Pt. Are reported to be oriented so as to be parallel to the <110> direction in the main surface of the silicon substrate.

However, although the present inventors have found that the mismatch between the lattice constant of Pt and the lattice constant of ZrO ₂ is as large as 26%, the Pt-containing conductive film 13 is not rotated by 45 ° in a plane, and the silicon substrate is not rotated. It has been found for the first time that epitaxial growth can be performed thereon. That is, the conductive film 13 includes a platinum film 13a having a cubic crystal structure and (100) orientation. In such a case, in the platinum film 13a, the <100> direction of the platinum film 13a along the upper surface 11a of the substrate 11 made of a silicon substrate is parallel to the <100> direction along the upper surface 11a of the substrate 11 itself. Orientation. In this manner, the conductive film 13 containing Pt can be (100) oriented in a cubic crystal structure on the (100) plane of the alignment film 12 containing ZrO _2, and the crystallinity of the conductive film 13 can be improved. It became clear that it could be improved.

By adjusting the conditions for forming ZrO ₂ or the conditions for forming Pt, the conductive film 13 containing Pt is rotated in a plane by 45 °, that is, the substrate 11 is rotated. Can be epitaxially grown on the (100) plane of the orientation film 12 containing ZrO _{2 in} a state where the <100> direction of Pt is along the <110> direction of Si in the main surface of (1).

  Also, as shown in Table 1, the lattice constant of Pt is 0.392 nm, the lattice constant of SRO is 0.390 to 0.393 nm, and the mismatch between the lattice constant of PZT and the lattice constant of Pt is Since it is as small as 0.5% or less, the matching between the lattice constant of SRO and the lattice constant of Pt is good. Therefore, as shown in FIG. 10, the film 14 containing SRO can be epitaxially grown on the (100) plane of the conductive film 13 containing Pt. Therefore, the film 14 containing SRO can be oriented (100) in 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.

  It is assumed that the film 14 has a pseudo-cubic crystal structure and includes a (100) -oriented SRO film 14a. In such a case, in the SRO film 14a, the <100> direction of the SRO film 14a along the upper surface 11a of the silicon substrate 11 is parallel to the <100> direction of the SRO film 14a along the upper surface 11a of the substrate 11 itself. Orientation.

  Further, as shown in Table 1, the lattice constant of SRO is 0.390 to 0.393 nm, the lattice constant of PZT is 0.411 nm, and the mismatch between the lattice constant of PZT and the lattice constant of SRO is Since it is as small as 4.5 to 5.2%, the matching between the lattice constant of PZT and the lattice constant of SRO is good. Therefore, as shown in FIG. 10, the piezoelectric film 15 containing PZT can be epitaxially grown on the (100) plane of the film 14 containing SRO. Accordingly, the piezoelectric film 15 containing PZT can be oriented on the (100) plane of the film 14 containing SRO in the (001) orientation in tetragonal system or the (100) orientation in pseudo-cubic system. Crystallinity can be improved.

  The piezoelectric film 15 has a tetragonal crystal structure and includes a (001) -oriented lead zirconate titanate film 15a. In such a case, in the lead zirconate titanate film 15a, the <100> direction of the lead zirconate titanate film 15a along the upper surface 11a of the substrate 11 made of a silicon substrate is along the upper surface 11a of the substrate 11 itself. Orient so as to be parallel to the <100> direction.

  Thus, the present inventors have found for the first time that the piezoelectric film 15 containing lead zirconate titanate can be epitaxially grown on a silicon substrate without rotating the lead zirconate titanate by 45 ° in a plane. Was. This is a completely different relationship from the in-plane orientation described in Patent Document 2 and Non-Patent Document 1, for example.

Note that a film containing lead zirconate titanate may be formed between the film 14 and the piezoelectric film 15. The film may include a composite oxide represented by the following general formula (Formula 6) and oriented in (100) orientation in pseudo cubic crystal.
_{Pb (Zr 1-v Ti v} ) O 3 ··· ( of 6)
Here, v satisfies 0 ≦ v ≦ 0.1.

  Thereby, the piezoelectric film 15 containing PZT can be more easily oriented on the (100) plane of the film 14 containing SRO in (001) orientation in tetragonal display or (100) orientation in pseudo cubic display, The crystallinity of the piezoelectric film 15 can be more easily improved.

  FIG. 11 is a diagram schematically showing a unit cell of PZT. FIG. 11 shows lead (Pb), zirconium (Zr), or titanium (Ti) among the elements contained in the unit cell of PZT contained in the piezoelectric film 15.

  As shown in FIG. 11, when the PZT included in the piezoelectric film 15 has a (001) orientation in a tetragonal system, that is, a c-axis orientation, the tetragonal PZT preferably has a square with respect to the lattice constant a in the a-axis direction. The lattice constant ratio of lattice constant c in the c-axis direction of crystalline PZT is 1.010 to 1.016.

  The lattice constant ratio (c / a ratio) of the lattice constant c in the c-axis direction of tetragonal PZT to the lattice constant a in the a-axis direction of ordinary tetragonal PZT is less than 1.010. On the other hand, the c / a ratio of tetragonal PZT in the piezoelectric film 15 included in the film structure of the present embodiment is 1.010 or more. The piezoelectric properties of tetragonal PZT depend on the c / a ratio of tetragonal PZT. Therefore, according to the piezoelectric film 15 included in the film structure of the present embodiment, it is possible to realize a piezoelectric film having piezoelectric characteristics superior to ordinary PZT. In the piezoelectric film 16 of the piezoelectric film 15, the ratio of the lattice constant c in the c-axis direction of tetragonal PZT to the lattice constant a in the a-axis direction of tetragonal PZT is 1.010 to 1.016. There may be.

<Method of manufacturing membrane structure>
Next, a method for manufacturing the film structure of the present embodiment will be described. 12 to 15 are cross-sectional views of the film structure of the embodiment during a manufacturing process.

First, as shown in FIG. 12, the substrate 11 is prepared (Step S1). In step S1, a substrate 11 which is a silicon substrate made of, for example, silicon (Si) single crystal is prepared. Substrate 11 made of silicon single crystal has a cubic crystal structure, and has upper surface 11a as a main surface made of a (100) plane. When the substrate 11 is a silicon substrate, an oxide film such as a SiO ₂ film may be formed on the upper surface 11a of the substrate 11.

  In addition, 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, a substrate formed of a glass substrate having a surface on which a polysilicon film is formed, or the like can be used.

  As shown in FIG. 12, two directions orthogonal to each other in an upper surface 11a formed of a (100) plane of a 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 direction. Axial direction.

  Next, as shown in FIG. 13, an alignment film 12 is formed on the substrate 11 (Step S2). In the following, in the step S2, the case where the alignment film 12 is formed using an electron beam evaporation method 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, first, the substrate 11 is heated to, for example, 700 ° C. in a state where the substrate 11 is placed in a constant vacuum atmosphere.

In step S2, next, Zr is evaporated by an electron beam evaporation method using a zirconium (Zr) single crystal evaporation material. At this time, the evaporated Zr reacts with oxygen on the substrate 11 heated to, for example, 700 ° C. to form a zirconium oxide (ZrO ₂ ) film. Then, an alignment film 12 made of a ZrO ₂ film as a single-layer film is formed.

The alignment film 12 is epitaxially grown on the upper surface 11a as a main surface composed of the (100) plane of the substrate 11 made of silicon single crystal. The alignment film 12 has a cubic crystal structure, and contains (100) -oriented zirconium oxide (ZrO ₂ ). That is, an alignment film 12 made of a single-layer film containing (100) -oriented zirconium oxide (ZrO ₂ ) is formed on an upper surface 11a made of a (100) plane of a substrate 11 made of a silicon single crystal.

  As described with reference to FIG. 12 described above, two directions orthogonal to each other in the upper surface 11a made of the (100) plane of the substrate 11 made of silicon single crystal are defined as the X-axis direction and the Y-axis direction. A perpendicular direction is defined as a 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.

  It is assumed that the alignment film 12 has a cubic crystal structure and includes a (100) -oriented zirconium oxide film 12f (see FIG. 10). In such a case, the <100> direction of the zirconium oxide film 12f along the upper surface 11a as the main surface of the substrate 11 made of the silicon substrate is <100 along the upper surface 11a of the substrate 11 itself. > Orient so as to be parallel to the direction.

  As shown in FIG. 13, preferably, the alignment film 12 includes a film portion 12a formed on the upper surface 11a of the substrate 11, and a plurality of protrusions 12b each protruding from the upper surface of the film portion 12a. The film portion 12a has a cubic crystal structure and includes (100) -oriented zirconium oxide (zirconium oxide film). Each of the plurality of projections 12b has a cubic crystal structure and includes (100) -oriented zirconium oxide (zirconium oxide film).

  Thereby, the interface roughness (roughness) of the interface IF1 (see FIG. 4) between the alignment film 12 and the conductive film 13 (see FIG. 4) formed in step S3 described below increases. The average interface roughness of the interface IF1 with the conductive film 13 is larger than the average interface roughness of the interface IF2 between the substrate 11 and the alignment film 12 (see FIG. 4). Therefore, for example, the surface of the alignment film 12 becomes a surface other than the (100) plane of the zirconium oxide film included in the alignment film 12, and the surface of the zirconium oxide film other than the (100) plane is included in the conductive film 13. The epitaxial growth of the surface of the platinum film other than the (100) plane facilitates the epitaxial growth of the platinum film on the surface of the zirconium oxide film. Since the conductive film 13 including the platinum film is easily grown epitaxially, the film 14 and the piezoelectric film 15 are easily grown epitaxially, so that the piezoelectric characteristics of the piezoelectric film 15 can be improved.

  Alternatively, the average interface roughness of the interface IF1 between the alignment film 12 and the conductive film 13 may be larger than the average interface roughness of the interface IF2 between the substrate 11 and the alignment film 12, so that the alignment film 12 It is not necessary to clearly have the plurality of protrusions 12b, and for example, it may have a step terrace structure having a plurality of steps (steps) formed on the surface so as to be separated from each other in plan view.

  Preferably, the cross-sectional shape of the protrusion 12b perpendicular to the first direction along the upper surface 11a of the substrate 11 is triangular, and the protrusion 12b is along the upper surface 11a of the substrate 11 and in the first direction. The width in the second direction, which is a direction perpendicular to the direction of FIG. When the protrusion 12b has such a triangular shape, the platinum film included in the conductive film 13 is more easily epitaxially grown on the surface of the zirconium oxide film included in the alignment film 12.

  Preferably, the thickness TH1 of the film portion 12a (see FIG. 5) is 11 to 18 nm, and each of the plurality of protrusions 12b projects from the upper surface 12c of the film portion 12a (see FIG. 5). (See FIG. 5) is 4-8 nm. That is, preferably, the thickness TH2 (see FIG. 5) of the alignment film 12 is 13 to 22 nm.

  When the protrusion height HT1 of the protrusion 12b is 4 nm or more, the average interface roughness of the interface IF1 is surely larger than that of the interface IF2 as compared with the case where the protrusion height HT1 of the protrusion 12b is less than 4 nm. Therefore, platinum contained in the conductive film 13 formed on the alignment film 12 containing (100) -oriented zirconium oxide is easily oriented to (100). On the other hand, when the protrusion height HT1 of the protrusion 12b is equal to or less than 8 nm, the average interface roughness of the interface IF1 is not too large as compared with the case where the protrusion height HT1 of the protrusion 12b exceeds 8 nm. The flatness of the conductive film 13 formed on the oriented film 12 containing zirconium oxide can be improved.

  Further, when the thickness TH1 of the film portion 12a is 11 nm or more, the thickness TH2 of the alignment film 12 becomes somewhat thicker than when the thickness TH1 of the film portion 12a is less than 11 nm. , The alignment film 12 is formed uniformly, and the direct contact between the conductive film 13 and the substrate 11 can be prevented. Further, when the thickness TH1 of the film portion 12a is 11 nm or more, the thickness TH2 of the alignment film 12 becomes somewhat thicker than in the case where the thickness TH1 of the film portion 12a is less than 11 nm. HT1 is easily set to 4 nm or more, and the platinum contained in the conductive film 13 is easily oriented to (100). On the other hand, when the thickness TH1 of the film portion 12a is equal to or less than 18 nm, the average interface roughness of the interface IF1 is not too large as compared with the case where the thickness TH1 of the film portion 12a exceeds 18 nm. The flatness of the formed conductive film 13 can be improved.

  That is, when the thickness TH2 of the alignment film 12 is 13 nm or more, the alignment film 12 is formed uniformly over the entire upper surface 11a of the substrate 11 as compared with the case where the thickness TH2 of the alignment film 12 is less than 13 nm. The direct contact between the film 13 and the substrate 11 can be prevented. In addition, when the thickness TH2 of the alignment film 12 is 13 nm or more, the protrusion height HT1 of the protrusion 12b is more easily set to 4 nm or more than when the thickness TH2 of the alignment film 12 is less than 13 nm. Pt is easily (100) oriented. On the other hand, when the thickness TH2 of the alignment film 12 is 22 nm or less, the average interface roughness of the interface IF1 is not too large as compared with the case where the thickness TH2 of the alignment film 12 exceeds 22 nm. The flatness of the formed conductive film 13 can be improved.

  Next, as shown in FIG. 4, the conductive film 13 is formed (Step S3).

  In this step S3, first, a conductive film 13 as a part of a lower electrode, which is epitaxially grown on the alignment film 12, is formed. The conductive film 13 is made of a metal. As the conductive film 13 made of metal, for example, a conductive film containing platinum (Pt) is used.

  When a conductive film containing Pt is formed as the conductive film 13, the conductive film 13 epitaxially grown is formed as a part of the lower electrode on the alignment film 12 by a sputtering method at a temperature of 450 to 600 ° C. The conductive film 13 containing Pt grows epitaxially on the alignment film 12. Further, Pt contained in the conductive film 13 has a cubic crystal structure and is (100) oriented.

  It is assumed that the conductive film 13 has a cubic crystal structure and includes a (100) -oriented platinum film 13a (see FIG. 10). In such a case, in the platinum film 13a, the <100> direction of the platinum film 13a along the upper surface 11a of the substrate 11 made of a silicon substrate is parallel to the <100> direction along the upper surface 11a of the substrate 11 itself. Orientation.

  Note that, as the conductive film 13 made of metal, for example, a conductive film containing iridium (Ir) can be used instead of the conductive film containing platinum (Pt).

  Preferably, in step S3, a conductive film 13 covering the plurality of protrusions 12b is formed, and the conductive film 13 is buried between two adjacent protrusions 12b. When the conductive film 13 has such a shape, the area of the interface between the conductive film 13 and the alignment film 12 increases, and the adhesion force of the conductive film 13 to the alignment film 12 increases.

  In the film structure shown in FIG. 4, as shown in FIG. 6, preferably, the conductive film 13 has a tensile stress TS1, and the alignment film 12 has a compressive stress CS1 or a tensile stress TS1. It has a smaller tensile stress TS2.

  First, as shown in FIG. 13, when the alignment film 12 is formed on the substrate 11, the alignment film 12 has the tensile stress TS4 as described with reference to FIG.

The linear expansion coefficient α _ZrO2 of zirconium oxide (ZrO ₂ ) is about 9 × 10 ⁻⁶ ° C. ⁻¹ , and the linear expansion coefficient α _Si of silicon (Si) is about 4 × 10 ⁻⁶ ° C. ⁻¹ , The linear expansion coefficient α _ZrO2 of zirconium oxide is larger than the linear expansion coefficient α _Si of silicon (Si). In such a case, after the alignment film 12 made of zirconium oxide is formed on the substrate 11 made of silicon at a temperature of, for example, 550 ° C., when the substrate 11 is cooled from 550 ° C. to room temperature (30 ° C.), Although 12 shrinks along the upper surface 11a of the substrate 11, the substrate 11 does not shrink as much as the alignment film 12, so the alignment film 12 is pulled by being restrained by the substrate 11, and cannot be completely shrunk. As a result, the alignment film 12 has a tensile stress TS4, the substrate 11 has a compressive stress, and the substrate 11 curves in a downwardly convex shape as shown in FIG.

On the other hand, the linear expansion coefficient alpha _Pt platinum (Pt), a 9 × ^{10 -6} ° C. of about ^-1, linear expansion coefficient alpha _Pt platinum (Pt), than the linear expansion coefficient alpha _Si of silicon (Si) large. In such a case, after the conductive film 13 made of platinum is formed on the alignment film 12 at a temperature of, for example, 550 ° C., when the substrate 11 is cooled from 550 ° C. to room temperature (30 ° C.), the conductive film 13 Although it shrinks along the upper surface 11a of the substrate 11, the substrate 11 does not shrink as much as the conductive film 13, so the conductive film 13 is restrained and pulled by the substrate 11, and cannot be completely shrunk. Therefore, the conductive film 13 has a tensile stress TS1. The alignment film 12 is pulled from the substrate 11 but is compressed from the conductive film 13 or receives little force. Therefore, the alignment film 12 has a compressive stress CS1 or a tensile stress TS2 smaller than the tensile stress TS1.

  When the thickness of the conductive film 13 is larger than the thickness of the alignment film 12, the alignment film 12 is compressed from the conductive film 13. Therefore, as shown in FIG. 6, the upper layer 12d of the alignment film 12 has a compressive stress CS2, and the lower layer 12e of the alignment film 12 has a tensile stress TS3. When the alignment film 12 has a compressive stress CS1 as a whole, the compressive stress CS2 is larger than the compressive stress CS1, and when the alignment film 12 has a tensile stress TS2 as a whole, the tensile stress TS3 is larger than the tensile stress TS2.

  Next, as shown in FIG. 14, the film 14 is formed (Step S4). In this step S4, the film 14 containing the complex oxide represented by the general formula (Formula 2) is formed on the conductive film 13. As the composite oxide represented by the general formula (Formula 2), for example, a conductive film containing strontium titanate (STO), strontium ruthenate titanate (STRO), or strontium ruthenate (SRO) can be formed. . In the case where a conductive film containing SRO is formed as the composite oxide represented by the general formula (Formula 2), a film 14 as a conductive film as a part of the lower electrode is formed on the conductive film 13 in Step S4. Will be. In the general formula (Formula 2), z satisfies 0 ≦ z ≦ 1.

  When a conductive film containing STO, STRO, or SRO is formed as the film 14, the epitaxially grown film 14 is formed as a part of the lower electrode on the conductive film 13 at a temperature of about 600 ° C. by a sputtering method. The film 14 containing STO, STRO, or SRO is epitaxially grown on the conductive film 13. The STO, STRO, or SRO included in the film 14 is (100) -oriented in pseudo-cubic or cubic.

  It is assumed that the film 14 has a pseudo-cubic crystal structure and includes a (100) -oriented SRO film 14a (see FIG. 10). In such a case, in the SRO film 14a, the <100> direction of the SRO film 14a along the upper surface 11a of the silicon substrate 11 is parallel to the <100> direction of the SRO film 14a along the upper surface 11a of the substrate 11 itself. Orientation.

  Further, the film 14 can be formed by a coating method such as a sol-gel method instead of the sputtering method. In such a case, in step S4, first, strontium and ruthenium, strontium, titanium and ruthenium, or a solution containing strontium and titanium is applied on the film 14 to obtain the compound represented by the general formula (Formula 2). A film containing the precursor of the composite oxide to be formed is formed. In the case where the film 14 is formed by the coating method, in step S4, the film is heat-treated to oxidize and crystallize the precursor, thereby obtaining the composite oxide represented by the general formula (Formula 2). Is formed.

  Next, as shown in FIG. 15, the piezoelectric film 16 is formed (Step S5). In this step S5, a piezoelectric film 16 represented by the general formula (Formula 4) and containing a composite oxide made of lead zirconate titanate (PZT) is formed on the film 14 by a sputtering method. Here, in the above general formula (Formula 4), x satisfies 0.32 ≦ x ≦ 0.52.

  When x satisfies 0.32 ≦ x ≦ 0.48, PZT contained in the piezoelectric film 16 has a rhombohedral crystal structure, but mainly due to the binding force from the substrate 11 or the like. It has a tetragonal crystal structure and is easy to be oriented (001). Then, the piezoelectric film 16 containing PZT is epitaxially grown on the film 14. When x satisfies 0.48 <x ≦ 0.52, PZT contained in the piezoelectric film 16 has a tetragonal crystal structure because PZT originally has a tetragonal crystal structure, and (001) orientation. Then, the piezoelectric film 16 containing PZT is epitaxially grown on the film 14. Thereby, the polarization axis of the lead zirconate titanate contained in the piezoelectric film 16 can be oriented substantially perpendicular to the upper surface 11a, so that the piezoelectric characteristics of the piezoelectric film 16 can be improved.

  It is assumed that the piezoelectric film 16 has a tetragonal crystal structure and includes a (001) -oriented lead zirconate titanate film 16a (see FIG. 10). In such a case, in the lead zirconate titanate film 16a, the <100> direction of the lead zirconate titanate film 16a along the upper surface 11a of the substrate 11 made of a silicon substrate is along the upper surface 11a of the substrate 11 itself. Orient so as to be parallel to the <100> direction.

  For example, when forming the piezoelectric film 16 by a sputtering method, each of a plurality of crystal grains 16g (see FIG. 8) included in the piezoelectric film 16 can be polarized by plasma. Therefore, each of the plurality of crystal grains 16g included in the formed piezoelectric film 16 has spontaneous polarization. The spontaneous polarization of each of the plurality of crystal grains 16g includes a polarization component P1 (see FIG. 8) parallel to the thickness direction of the piezoelectric film 16. The polarization components P1 included in the spontaneous polarization of each of the plurality of crystal grains 16g are oriented in the same direction. As a result, the formed piezoelectric film 16 has spontaneous polarization as a whole before the polarization process.

  That is, in step S5, when the piezoelectric film 16 is formed by the sputtering method, the piezoelectric film 16 can be polarized by the 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 perform a polarization process on the piezoelectric film 16 before use.

  In step S5, when the piezoelectric film 16 is formed by the sputtering method, for example, sputtered particles and argon (Ar) gas enter the piezoelectric film 16 and the piezoelectric film 16 expands. , Has a compressive stress.

  Next, as shown in FIG. 1, the piezoelectric film 17 is formed (Step S6). In step S6, a piezoelectric film 17 represented by the general formula (Formula 5) and containing a composite oxide made of lead zirconate titanate (PZT) is applied on the piezoelectric film 16 by a coating method such as a sol-gel method. Form. Hereinafter, a method for forming the piezoelectric film 17 by the sol-gel method will be described.

  In step S6, first, a film containing a PZT precursor is formed on the piezoelectric film 16 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, whereby a film including a plurality of films stacked with each other is formed.

  In step S6, the piezoelectric film 17 containing PZT is formed by heat-treating the film to oxidize and crystallize the precursor. Here, in the above general formula (Formula 5), y satisfies 0.32 ≦ y ≦ 0.52.

  When y satisfies 0.32 ≦ y ≦ 0.48, PZT contained in the piezoelectric film 17 has a composition having a rhombohedral crystal structure, but mainly due to a binding force from the substrate 11 or the like. It has a tetragonal crystal structure and is easy to be oriented (001). Then, the piezoelectric film 17 containing PZT is epitaxially grown on the piezoelectric film 16. When y satisfies 0.48 <y ≦ 0.52, PZT contained in the piezoelectric film 17 has a tetragonal crystal structure because the PZT originally has a tetragonal crystal structure. (001) orientation. Then, the piezoelectric film 17 containing PZT is epitaxially grown on the piezoelectric film 16. Thereby, 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.

  The piezoelectric film 17 has a tetragonal crystal structure and includes a (001) -oriented lead zirconate titanate film 17a (see FIG. 10). In such a case, in the lead zirconate titanate film 17a, the <100> direction of the lead zirconate titanate film 17a along the upper surface 11a of the substrate 11 made of a silicon substrate is along the upper surface 11a of the substrate 11 itself. Orient so as to be parallel to the <100> direction.

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 15 are parallel to each other. The characteristics are improved. That is, the PZT has a crystal structure of tetragonal, when the electric field along the [001] direction is applied, a large piezoelectric constant d ₃₃ and d ₃₁ of the absolute value is obtained. Therefore, the piezoelectric constant of the piezoelectric film 15 can be further increased. In this specification, the piezoelectric constant d ₃₁ is essentially though the sign is negative, it may be expressed in absolute value by omitting the sign.

  In step S6, the piezoelectric film 17 has a tensile stress, for example, by evaporating the solvent in the solution during the heat treatment, or by shrinking the film when the precursor is oxidized and crystallized. .

  Thus, the piezoelectric film 15 including the piezoelectric films 16 and 17 is formed, and the film structure 10 shown in FIG. 1 is formed. That is, Steps S5 and S6 include the lead zirconate titanate which is (001) oriented in tetragonal system or (100) oriented in pseudocubic system and epitaxially grown on the conductive film 13 via the film 14. This is included in the step of forming the piezoelectric film 15.

  As described with reference to FIG. 11 described above, when the PZT included in the piezoelectric film 15 has the (001) orientation in the tetragonal system, that is, the c-axis orientation, preferably, the PZT in the a-axis direction of the tetragonal PZT is in the a-axis direction. The lattice constant ratio of the lattice constant c in the c-axis direction of the tetragonal PZT to the lattice constant a is 1.010 to 1.016.

  The lattice constant ratio (c / a ratio) of the lattice constant c in the c-axis direction of tetragonal PZT to the lattice constant a in the a-axis direction of ordinary tetragonal PZT is less than 1.010. On the other hand, the c / a ratio of tetragonal PZT in the piezoelectric film 15 included in the film structure of the present embodiment is 1.010 or more. The piezoelectric properties of tetragonal PZT depend on the c / a ratio of tetragonal PZT. Therefore, according to the piezoelectric film 15 included in the film structure of the present embodiment, it is possible to realize a piezoelectric film having piezoelectric characteristics superior to ordinary PZT.

  After forming the piezoelectric film 17, a conductive film 18 (see FIG. 2) as an upper electrode may be formed on the piezoelectric film 17 (Step S7).

  Further, a film containing lead zirconate titanate may be formed between the film 14 and the piezoelectric film 15. The film may include a composite oxide represented by the general formula (Formula 6) and oriented in (100) orientation in pseudo cubic expression.

<Modification of Embodiment>
In the embodiment, as shown in FIG. 1, the piezoelectric film 15 including the piezoelectric films 16 and 17 is formed. However, the piezoelectric film 15 may include only the piezoelectric film 16. Such an example will be described as a modification of the embodiment.

  FIG. 16 is a cross-sectional view of a film structure according to a modification of the embodiment.

  As shown in FIG. 16, the film structure 10 of the present modification includes a substrate 11, an alignment film 12, a conductive film 13, a film 14, and a piezoelectric film 15. 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 piezoelectric film 15 is formed on the film 14. The piezoelectric film 15 includes a piezoelectric film 16.

  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 15 does not include the piezoelectric film 17 (see FIG. 1) but includes only the piezoelectric film 16. It is.

  When the piezoelectric film 15 includes the piezoelectric film 16 having a compressive stress but does not include the piezoelectric film 17 having a tensile stress (see FIG. 1), the piezoelectric film 15 has the piezoelectric film 16 having a compressive stress and the tensile film. The amount of warpage of the film structure 10 is increased as compared with the case where both of the piezoelectric films 17 (see FIG. 1) are included. However, for example, when the thickness of the piezoelectric film 15 is small, the amount of warpage of the film structure 10 can be reduced. Therefore, even when the piezoelectric film 15 includes only the piezoelectric film 16, for example, it is possible to improve the shape accuracy when the film structure 10 is processed by using the photolithography technique, and the film structure 10 is formed by processing the film structure 10. The characteristics of the piezoelectric element can be improved.

  Note that the film structure 10 of the present modification may also have the conductive film 18 (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 by the following examples.

(Examples and Comparative Examples)
Hereinafter, the film structure 10 described in the embodiment with reference to FIG. 1 was formed as the film structure of the example. In the film structure of the embodiment, the alignment film 12 has the protrusion 12b. On the other hand, in the film structure of the comparative example, the alignment film 12 does not have the protrusion 12b.

  Hereinafter, a method for forming the film structure of the embodiment will be described. First, as shown in FIG. 12, as the substrate 11, a wafer made of a 6-inch silicon single crystal having an upper surface 11a as a main surface made of a (100) plane was prepared.

Next, as shown in FIG. 13, 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 evaporation apparatus Pressure: 7.00 × 10 ⁻³ Pa
Evaporation source: Zr + O ₂
Acceleration voltage / emission current: 7.5 kV / 1.80 mA
Thickness: 24 nm
Substrate temperature: 500 ℃

Next, as shown in FIG. 4, a platinum (Pt) film was formed as a 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
Evaporation source: Pt
Power: 100W
Thickness: 150nm
Substrate temperature: 450-600 ° C

Next, as shown in FIG. 14, an SRO film was formed as a film 14 on the conductive film 13 by a sputtering method. The conditions at this time are shown below.
Equipment: RF magnetron sputtering equipment Power: 300W
Gas: Ar
Pressure: 1.8 Pa
Substrate temperature: 600 ° C
Thickness: 20 nm

Next, as shown in FIG. 15, a Pb (Zr _0.58 Ti _0.42 ) O ₃ film (PZT film) having a thickness of 0.91 μm is formed as a piezoelectric film 16 on the film 14 by sputtering. It was formed by a method. The conditions at this time are shown below.
Equipment: RF magnetron sputtering equipment Power: 1750W
Gas: Ar / O ₂
Pressure: 1Pa
Substrate temperature: 380 ° C

  In the formed piezoelectric film 16, the distance from the center in the radial direction is 0 mm, 5 mm, 15 mm, 25 mm, 35 mm, 45 mm, 55 mm, 65 mm, 75 mm, 85 mm, and 95 mm. The values were 0.91 μm, 0.91 μm, 0.92 μm, 0.92 μm, 0.92 μm, 0.91 μm, 0.91 μm, 0.91 μm, 0.90 μm, and 0.89 μm. Therefore, the piezoelectric film 16 having a uniform film thickness over the entire surface of the substrate 11 could be formed.

Next, as shown in FIG. 1, a Pb (Zr _0.58 Ti _0.42 ) O ₃ film (PZT film) was formed as a piezoelectric film 17 on the piezoelectric film 16 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 _0.58 ) is added to a mixed solvent of ethanol and 2-n-butoxyethanol. A raw material solution dissolved so as to have a concentration of Ti _0.42 ) O ₃ of 0.35 mol / l was prepared. For δ, δ = 20. Then, 20 g of polypyrrolidone having a K value of 27 to 33 was further dissolved in the raw material solution.

Next, 3 ml of the raw material solution of the prepared raw material solution was dropped on the substrate 11 composed of a 6-inch wafer, and rotated at 3000 rpm for 10 seconds to apply the raw material solution on the substrate 11, thereby forming a precursor. The film containing was formed. Then, the substrate 11 is placed on a hot plate at a temperature of 200 ° C. for 30 seconds, and the substrate 11 is further placed on a hot plate at a temperature of 450 ° C. for 30 seconds, thereby evaporating the solvent to form a film. Let dry. Thereafter, the precursor was oxidized and crystallized by heat treatment at 600 to 700 ° C. for 60 seconds in an oxygen (O ₂ ) atmosphere of 0.2 MPa to form a piezoelectric film 17 having a thickness of 30 nm.

  For each of the example and the comparative example, a θ-2θ spectrum of the film structure on which the PZT film as the piezoelectric film 17 was formed was measured by an X-ray diffraction (XRD) method. That is, the X-ray diffraction measurement by the θ-2θ method was performed for each of the examples and the comparative examples.

  Each of FIGS. 17 to 20 is a graph showing an example of the θ-2θ spectrum of the film structure formed up to the PZT film by the XRD method. The horizontal axis of each graph of FIGS. 17 to 20 indicates the angle 2θ, and the vertical axis of each graph of FIGS. 17 to 20 indicates the intensity of X-rays. 17 and 18 show the results for the example, and FIGS. 19 and 20 show the results for the comparative example. 17 and 19 show a range of 20 ° ≦ 2θ ≦ 50 °, and FIGS. 18 and 20 show a range of 90 ° ≦ 2θ ≦ 110 °.

  In the examples (examples) shown in FIGS. 17 and 18, peaks corresponding to the (200) plane and the (400) plane of Pt having a cubic crystal structure, and PZT in the tetragonal crystal display, in the θ-2θ spectrum Peaks corresponding to the (001), (002) and (004) planes were observed. Therefore, in the example (example) shown in FIGS. 17 and 18, the conductive film 13 has a cubic crystal structure and contains (100) -oriented Pt, and the piezoelectric film 15 has a tetragonal crystal display. It was found to contain (001) oriented PZT.

In the example shown in FIG. 18 (Example), when the diffraction angle of the diffraction peak of the (004) plane in the tetragonal crystal display of PZT is 2θ ₀₀₄ , 2θ ₀₀₄ = 96.5 °. Therefore, in the example shown in FIGS. 17 and 18 (Example), 2 [Theta] ₀₀₄ satisfies 2 [Theta] ₀₀₄ ≦ 96.5 °, was found to satisfy the above equation (Equation 1).

  In the example (comparative example) shown in FIGS. 19 and 20, similarly to the example (example) shown in FIGS. 17 and 18, in the θ-2θ spectrum, the (200) plane of Pt having a cubic crystal structure and Peaks corresponding to the (400) plane and peaks corresponding to the (001), (002), and (004) planes of PZT in tetragonal crystal display were observed. Therefore, in the example (comparative example) shown in FIGS. 19 and 20, similarly to the example (example) shown in FIGS. 17 and 18, the conductive film 13 has a cubic crystal structure and (100). ) It was found that the piezoelectric film 15 contained oriented Pt and that the piezoelectric film 15 contained (001) -oriented PZT in tetragonal crystal representation.

However, in the example (comparative example) shown in FIG. 20, unlike the example (example) shown in FIG. 18, when the diffraction angle of the diffraction peak of the (004) plane in the tetragonal crystal display of PZT is 2θ ₀₀₄ , 2θ ₀₀₄ = 96.7 °. Therefore, in the example shown in FIGS. 19 and 20 (Comparative Example), 2 [Theta] ₀₀₄ may not satisfy the 2 [Theta] ₀₀₄ ≦ 96.5 °, it was found that not satisfy the above expression (Expression 1).

In the examples, the pole figure was measured by the XRD method, and the relationship of the in-plane orientation of the film of each layer was examined. Each of FIGS. 21 to 24 is a graph showing an example of a pole figure of the film structure of the example by the XRD method. FIG. 21 is a pole figure of a Si (220) plane, FIG. 22 is a pole figure of a ZrO ₂ (220) plane, FIG. 23 is a pole figure of a Pt (220) plane, and FIG. It is a pole figure of a PZT (202) plane.

  As described above, the alignment film 12 has a cubic crystal structure and includes the (100) -oriented zirconium oxide film 12f (see FIG. 10). In such a case, as shown in FIG. 21 and FIG. 22, the zirconium oxide film 12f is formed such that the <100> direction of the zirconium oxide film 12f along the upper surface 11a as the main surface of the silicon substrate 11 is It has been clarified that the film is oriented so as to be parallel to the <100> direction along the upper surface 11a of the film itself. In other words, in the zirconium oxide film 12f, the <110> direction of the zirconium oxide film 12f along the upper surface 11a as the main surface of the silicon substrate 11 is the <110> direction along the upper surface 11a of the substrate 11 itself. It was clarified that they were oriented so as to be parallel.

  It is also assumed that the conductive film 13 has a cubic crystal structure and includes a platinum film 13a oriented in (100) (see FIG. 10). In such a case, as shown in FIG. 21 and FIG. 23, the platinum film 13a is such that the <100> direction of the platinum film 13a along the upper surface 11a of the substrate 11 made of a silicon substrate is on the upper surface 11a of the substrate 11 itself. The orientation was found to be parallel to the <100> direction. In other words, the platinum film 13a is oriented such that the <110> direction of the platinum film 13a along the upper surface 11a of the silicon substrate 11 is parallel to the <110> direction along the upper surface 11a of the substrate 11 itself. It turned out that they were oriented.

  The piezoelectric film 15 has a tetragonal crystal structure and includes a (001) -oriented lead zirconate titanate film 15a (see FIG. 10). In such a case, as shown in FIGS. 21 and 24, the lead zirconate titanate film 15a has a <100> direction along the upper surface 11a of the silicon substrate 11 of the lead zirconate titanate film 15a. It was revealed that the substrate 11 was oriented so as to be parallel to the <100> direction along the upper surface 11a of the substrate 11 itself. In other words, in the lead zirconate titanate film 15a, the <110> direction of the lead zirconate titanate film 15a along the upper surface 11a of the substrate 11 made of a silicon substrate is <110 along the upper surface 11a of the substrate 11 itself. > It became clear that they were oriented so as to be parallel to the direction.

  In the example, when forming the alignment film 12, the conductive film 13, the film 14, and the piezoelectric film 15 on the substrate 11, the amount of warpage of the substrate 11 was measured in order to measure the stress of each layer. FIG. 25 is a diagram for explaining a method of measuring the amount of warpage of the substrate by the XRD method. FIG. 26 is a graph showing the result of measuring the amount of warpage of the substrate by the XRD method.

  As shown in FIG. 25, regarding the amount of warpage of the substrate 11, a distance along the upper surface 11a of the substrate 11 from the center 11b of the upper surface 11a of the substrate 11 to the measurement portion 11c is defined as a distance ΔX, and a rocking curve (ω) by the XRD method is used. When the difference (shift amount) of the peak angle of (scan) with respect to the reference angle is an angle Δω, the radius of curvature R indicating the degree of the amount of warpage of the substrate 11 is calculated by a calculation formula of R = ΔX / sin (Δω). Can be.

Therefore, at each position on a certain straight line that passes through the center 11b of the upper surface 11a of the substrate 11 and along the upper surface 11a of the substrate 11, the rocking curve (ω scan) is measured by the XRD method, and the peak of the rocking curve is measured. The dependence of the angle ω on the distance from the center 11b of the upper surface 11a of the substrate 11 was determined. FIG. 26 shows the result. In FIG. 26, for example, the measurement result at the time when the ZrO ₂ film is formed is described as “ZrO ₂ ”.

As shown in FIG. 26, when the alignment film 12 was formed on the substrate 11 (“ZrO ₂ ” in FIG. 26), the substrate 11 had a compressive stress. Therefore, when the alignment film 12 was formed on the substrate 11, the alignment film 12 had a tensile stress. The radius of curvature R was 66.1 mm.

  Further, as shown in FIG. 26, when the conductive film 13 was formed on the alignment film 12 (“Pt” in FIG. 26), the compressive stress of the substrate 11 increased. The radius of curvature R was 46.7 mm. Therefore, when the conductive film 13 is formed on the alignment film 12, as described with reference to FIG. 6, the conductive film 13 has the tensile stress TS1 and the alignment film 12 has the compressive stress CS1. It was found to have or have a tensile stress TS2 smaller than the tensile stress TS1.

  As shown in FIG. 26, after the conductive film 13 is formed on the alignment film 12, when the film 14 and the piezoelectric film 15 are formed on the conductive film 13 ("SRO" and "PZT" in FIG. 26) In (), the compressive stress of the substrate 11 hardly changed. The curvature radii R were 45.4 mm and 44.1 mm, respectively. Therefore, even when the film 14 and the piezoelectric film 15 are formed on the conductive film 13, the conductive film 13 has the tensile stress TS1, and the alignment film 12 has the compressive stress CS1 or the tensile stress TS1. It was found to have a smaller tensile stress TS2.

  With respect to the crystal structure of the film structure of the example, an image of a cross section perpendicular to the upper surface 11a of the substrate 11 (cross-sectional TEM image) was taken with a transmission electron microscope (TEM). As a cross-sectional TEM image, a high angle annular dark field (HAADF) image and a bright field (Bright Field: BF) image were taken. Note that an image of a cross section perpendicular to the <110> direction of Si of the substrate 11 was taken as a cross section perpendicular to the upper surface 11a of the substrate 11.

  FIG. 27 is a photograph showing a HAADF image of the film structure of the example. 28 and 29 are photographs showing BF images of the film structure of the example. FIG. 30 is a photograph showing a HAADF image of the film structure of the example.

FIG. 27 shows a cross-sectional area near the interface IF1 (see FIG. 5) between the ZrO ₂ film included in the alignment film 12 (see FIG. 5) and the Pt film included in the conductive film 13 (see FIG. 5). Indicates the same cross-sectional area as the cross-sectional area shown in FIG. FIG. 29 shows a cross-sectional area near the interface IF1 (see FIG. 5), which is a cross-sectional area slightly apart from the cross-sectional areas shown in FIGS. 27 and 28. FIG. 30 shows a cross-sectional area of the PZT film included in the piezoelectric film 15.

As shown in FIGS. 27 and 28, since the interface IF1 between the ZrO ₂ film and the Pt film is not flat, as described with reference to FIG. 5, the alignment film 12 is formed by the film portion 12a and the protrusion 12b. It became clear that it included. In the cross-sectional areas shown in FIGS. 27 and 28, the height of the protrusion 12b is 6 nm, and when including other cross-sectional areas, the average height of the protrusions 12b is 6 nm. The value of 3σ, which is three times the standard deviation of the height, was 2 nm. Therefore, the height of the protrusion 12b was 4 to 8 nm.

When the region RG5 in FIG. 28 is enlarged, about 5.5 or about 6 unit lattices of ZrO ₂ per 2 nm are arranged in a horizontal direction, that is, in a direction parallel to the upper surface 11a of the substrate 11. Was observed. In the cross-sectional area near the character “6” in FIG. 29, about 5.5 or about 6 unit cells of ZrO ₂ per 2 nm are arranged along the horizontal direction. in the cross-sectional area near letter 5 ", along the horizontal direction, are arranged the unit lattice of ZrO ₂ of about five per 2 nm, the upper portion of the ZrO ₂ film, compared with the lower part of the ZrO ₂ film It was stretched and distorted in the horizontal direction. This has revealed that the upper layer of the alignment film 12 has a compressive stress CS2 and the lower layer of the alignment film 12 has a tensile stress TS3.

  Further, as shown in FIG. 30, the PZT film included in the piezoelectric film 15 was confirmed to be a single crystal without any disorder of the crystal lattice such as dislocation. The crystal lattice shown in FIG. 30 shows the crystal lattice when viewed from the <110> direction of PZT. When the crystal lattice of PZT in FIG. 11 is viewed from the direction of arrow AR1 in FIG. 11, that is, (110) of PZT. 2 shows a crystal lattice in a plane PLU as a plane.

  The lattice constant a in the a-axis direction and the lattice constant c in the c-axis direction of tetragonal PZT of tetragonal PZT were determined from the cross-sectional TEM image of FIG. As a result, the lattice constant a was 0.410 nm, the lattice constant c was 0.415 nm, and the lattice constant ratio (c / a ratio) was 1.016. On the other hand, when the lattice constant a and the lattice constant c were obtained from the X-ray diffraction pattern by the θ-2θ method, the lattice constant a was 0.408 nm, the lattice constant c was 0.414 nm, and the lattice constant ratio ( c / a ratio) was 1.015. Therefore, the lattice constant obtained from the cross-sectional TEM image substantially coincided with the lattice constant obtained from the X-ray diffraction pattern by the θ-2θ method.

  For example, in the above-described general formula (Formula 3) calculated from the PDF (Powder Diffraction File) of the International Center for Diffraction Data (ICDD) using the Vegard rule, the composition of u = 0.42 (Zr / Ti = 58) / 42) has a lattice constant a of 0.4081 nm in rhombohedral PZT. Therefore, it is apparent that the lattice constant of the PZT film included in the piezoelectric film 15 included in the film structure of the present embodiment is completely different from the lattice constant a of rhombohedral PZT at normal Zr / Ti = 58/42. became.

  The lattice constant ratio (c / a ratio) of ordinary tetragonal PZT is less than 1.010. On the other hand, it was found that the c / a ratio of tetragonal PZT in the piezoelectric film 15 of the film structure of the present embodiment is 1.010 or more, and can be improved to a maximum of 1.016.

  Further, with respect to the film structure of the example, a voltage was applied between the conductive film 13 and the conductive film 18 to measure the voltage dependency of polarization. FIG. 31 is a graph showing the voltage dependence of the polarization of the film structure of the example. A cantilever was formed for the film structure of the example, and the voltage dependence of the displacement of the film structure of the example was measured using the formed cantilever. FIG. 32 is a graph showing the voltage dependence of the displacement of the film structure of the example.

According to FIG 31, in the film structure of Example, the dielectric constant epsilon _r is 216, the residual polarization value _{P r} was 57μC / cm ^2. In addition, according to FIG. 32, the piezoelectric constant _{d 31} was 230pm / V.

Here, when the voltage dependence of polarization and displacement was measured also for the film structure of the comparative example in which the alignment film 12 did not have the protrusion 12b, the relative dielectric constant ε _r was 580, and the residual polarization value _Pr was a 18μC / cm ^2, the piezoelectric constant _{d 31} was 178pm / V. That is, the film structure of the example had extremely excellent remanent polarization characteristics and piezoelectric characteristics as compared with the film structure of the comparative example. Therefore, it became clear that the piezoelectric characteristics of the film structure were improved when the alignment film 12 had the protrusions 12b.

Further, in the temperature range of 30 to 200 ° C., and measuring the voltage dependence of the polarization by applying a voltage between the conductive film 13 and the conductive film 18 while changing the temperature, the residual polarization value P _r, and anti It was measured the temperature dependence of the voltage values V _c. FIG. 33 is a graph showing the temperature dependence of the remanent polarization value of the film structure of the example. FIG. 34 is a graph showing the temperature dependence of the coercive voltage value of the membrane structure of the example. The vertical axis of FIG. 33 shows the square of the residual polarization value _{P r,} the vertical axis of FIG. 34 shows a 2/3 square of the coercive voltage value _{V c.}

As shown in FIG. 33, squares the temperature dependence of the remanent polarization P _r has a linear, as shown in FIG. 34, the temperature dependence of the two-thirds power of the coercive voltage value V _c is It showed linearity. The remnant polarization value in FIG. 33 was not used in the evaluation of the Curie temperature _Tc in consideration of the influence of leakage at a high temperature, but the coercive voltage value in FIG. calculated by the calculated approximate line calculated temperature that intersects the temperature axis, the calculated temperature was evaluated as the Curie temperature T _c, the Curie temperature T _c will become 587 ° C., it showed a very high value .

  Therefore, according to the film structure of the example in which the alignment film 12 has the protruding portion 12b, it has become clear that the film has a high Curie temperature extremely close to the theoretical value of the Curie temperature of PZT. Therefore, according to the film structure of the present embodiment, it was clarified that the PZT included in the piezoelectric film 15 was a single crystal, and that the piezoelectric characteristics were improved.

  As described above, the invention made by the inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and can be variously modified without departing from the gist thereof. 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 skilled in the art may add, delete, or change the design of components, or add, omit, or change the conditions of the above-described embodiments. As long as it has the gist, it is included in the scope of the present invention.

Reference Signs List 10 film structure 11 substrate 11a, 12c upper surface 11b center 11c measuring portion 12 alignment film 12a film portion 12b projecting portion 12d upper layer portion 12e lower layer portion 12f zirconium oxide film 13, 18 conductive film 13a platinum film 14 film 14a SRO film 15, 16 , 17 Piezoelectric films 15a, 16a, 17a Lead zirconate titanate films 16g, 17g Crystal grains 17f Film AR1 Arrow CP1 Ferroelectric capacitors CS1, CS2 Compressive stress EP End point HT1 Projection height IF1, IF2 Interface P1 Polarization component PLU Plane RG5 Region SP Starting points TS1 to TS4 Tensile stress

Claims (22)

A silicon substrate including a main surface composed of a (100) plane;
A first film formed on the main surface, having a cubic crystal structure, and including a (100) -oriented first zirconium oxide film;
A conductive film formed on the first film, having a cubic crystal structure, and including a (100) -oriented platinum film;
Have
A film, wherein a first average interface roughness of a first interface between the first film and the conductive film is larger than a second average interface roughness of a second interface between the silicon substrate and the first film. Structure. The membrane structure according to claim 1,
The first film includes:
A film portion formed on the main surface;
A plurality of protrusions each protruding from the upper surface of the film portion,
Including
The film portion has a cubic crystal structure and includes a (100) -oriented second zirconium oxide film,
Each of the plurality of protrusions has a cubic crystal structure and includes a (100) -oriented third zirconium oxide film. The membrane structure according to claim 2,
The cross-sectional shape of the protrusion, which is perpendicular to the first direction along the main surface, is a triangular shape,
The width of the protruding portion in the second direction along the main surface and perpendicular to the first direction decreases from the film portion side to the opposite side to the film portion side. Membrane structure. The membrane structure according to claim 2 or 3,
The thickness of the film portion is 11 to 18 nm,
The film structure, wherein a protrusion height of each of the plurality of protrusions from the upper surface of the film portion is 4 to 8 nm. The film structure according to any one of claims 2 to 4,
The conductive film covers the plurality of protrusions,
A film structure in which the conductive film is buried between two adjacent protrusions. The membrane structure according to any one of claims 1 to 5,
The conductive film has a first tensile stress,
The film structure, wherein the first film has a first compressive stress or a second tensile stress smaller than the first tensile stress. The membrane structure according to claim 6,
An upper layer of the first film has a second compressive stress,
A lower layer of the first film has a third tensile stress;
When the first film has the first compressive stress, the second compressive stress is larger than the first compressive stress,
The film structure, wherein the third tensile stress is greater than the second tensile stress when the first film has the second tensile stress. The membrane structure according to any one of claims 1 to 7,
A film structure comprising a piezoelectric film formed on the conductive film and having a tetragonal crystal structure and including a (001) -oriented lead zirconate titanate film. The film structure according to any one of claims 1 to 8,
The first zirconium oxide film is oriented such that a <100> direction along the main surface of the first zirconium oxide film is parallel to a <100> direction along the main surface of the silicon substrate. ,
The film structure, wherein the platinum film is oriented such that a <100> direction along the main surface of the platinum film is parallel to a <100> direction along the main surface of the silicon substrate. . The membrane structure according to claim 8,
The first zirconium oxide film is oriented such that a <100> direction along the main surface of the first zirconium oxide film is parallel to a <100> direction along the main surface of the silicon substrate. ,
The platinum film is oriented such that a <100> direction along the main surface of the platinum film is parallel to a <100> direction along the main surface of the silicon substrate;
The lead zirconate titanate film is formed such that a <100> direction along the main surface of the lead zirconate titanate film is parallel to a <100> direction along the main surface of the silicon substrate. Oriented membrane structure. The membrane structure according to claim 8, wherein
The lead zirconate titanate film has a composite oxide of lead zirconate titanate represented by the following general formula (Formula 1),
Pb (Zr _1-x Ti _x ) O ₃ (Formula 1)
X satisfies 0.32 ≦ x ≦ 0.52,
A film structure, wherein the ratio of the lattice constant of the second lattice constant in the c-axis direction to the first lattice constant in the a-axis direction of the lead zirconate titanate is 1.010 to 1.016. (A) preparing a silicon substrate including a main surface composed of a (100) plane;
(B) forming a first film having a cubic crystal structure and including a (100) -oriented first zirconium oxide film on the main surface;
(C) forming a conductive film having a cubic crystal structure and including a (100) -oriented platinum film on the first film;
Have
A film, wherein a first average interface roughness of a first interface between the first film and the conductive film is larger than a second average interface roughness of a second interface between the silicon substrate and the first film. The method of manufacturing the structure. The method for manufacturing a film structure according to claim 12,
In the step (b), the first film including a film portion formed on the main surface and a plurality of protrusions respectively protruding from an upper surface of the film portion is formed;
The film portion has a cubic crystal structure and includes a (100) -oriented second zirconium oxide film,
Each of the plurality of protrusions has a cubic crystal structure and includes a (100) -oriented third zirconium oxide film. The method for manufacturing a film structure according to claim 13,
The cross-sectional shape of the protrusion, which is perpendicular to the first direction along the main surface, is a triangular shape,
The width of the protruding portion in the second direction along the main surface and perpendicular to the first direction decreases from the film portion side to the opposite side to the film portion side. A method for manufacturing a membrane structure. The method for producing a film structure according to claim 13 or 14,
The thickness of the film portion is 11 to 18 nm,
The method of manufacturing a film structure, wherein a height of each of the plurality of protrusions protruding from an upper surface of the film part is 4 to 8 nm. The method for manufacturing a film structure according to any one of claims 13 to 15,
In the step (c), the conductive film covering the plurality of protrusions is formed,
In the step (c), a method for manufacturing a film structure, wherein the conductive film is buried between two adjacent protrusions. The method for producing a film structure according to any one of claims 12 to 16,
The conductive film has a first tensile stress,
The method for manufacturing a film structure, wherein the first film has a first compressive stress or has a second tensile stress smaller than the first tensile stress. The method for manufacturing a film structure according to claim 17,
An upper layer of the first film has a second compressive stress,
A lower layer of the first film has a third tensile stress;
When the first film has the first compressive stress, the second compressive stress is larger than the first compressive stress,
The method of manufacturing a film structure, wherein when the first film has the second tensile stress, the third tensile stress is larger than the second tensile stress. The method for manufacturing a film structure according to any one of claims 12 to 18,
(D) forming a piezoelectric film having a tetragonal crystal structure and including a (001) -oriented lead zirconate titanate film on the conductive film;
A method for producing a film structure, comprising: The method for manufacturing a film structure according to any one of claims 12 to 19,
The first zirconium oxide film is oriented such that a <100> direction along the main surface of the first zirconium oxide film is parallel to a <100> direction along the main surface of the silicon substrate. ,
The film structure, wherein the platinum film is oriented such that a <100> direction along the main surface of the platinum film is parallel to a <100> direction along the main surface of the silicon substrate. Manufacturing method. The method for manufacturing a film structure according to claim 19,
The first zirconium oxide film is oriented such that a <100> direction along the main surface of the first zirconium oxide film is parallel to a <100> direction along the main surface of the silicon substrate. ,
The platinum film is oriented such that a <100> direction along the main surface of the platinum film is parallel to a <100> direction along the main surface of the silicon substrate;
The lead zirconate titanate film is formed such that a <100> direction along the main surface of the lead zirconate titanate film is parallel to a <100> direction along the main surface of the silicon substrate. A method for producing an oriented film structure. The method for manufacturing a film structure according to claim 19 or 21,
The lead zirconate titanate film has a composite oxide of lead zirconate titanate represented by the following general formula (Formula 1),
Pb (Zr _1-x Ti _x ) O ₃ (Formula 1)
X satisfies 0.32 ≦ x ≦ 0.52,
A method for producing a film structure, wherein the ratio of the lattice constant of the second lattice constant in the c-axis direction to the first lattice constant in the a-axis direction of the lead zirconate titanate is 1.010 to 1.016.