Film structure and method for manufacturing the same
A film structure includes a substrate ( 11 ) which is a silicon substrate including an upper surface ( 11 a ) composed of a (100) plane, an alignment film ( 12 ) which is formed on the upper surface ( 11 a ) and includes a zirconium oxide film which has a cubic crystal structure and is (100)-oriented, and a conductive film ( 13 ) which is formed on the alignment film ( 12 ) and includes a platinum film which has a cubic crystal structure and is (100)-oriented. An average interface roughness of an interface (IF 1 ) between the alignment film ( 12 ) and the conductive film ( 13 ) is greater than an average interface roughness of an interface (IF 2 ) between the substrate ( 11 ) and the alignment film ( 12 ).
1. A film structure comprising:
a silicon substrate comprising a main surface composed of a (100) plane;
a first zirconium oxide film that is formed on the main surface and that has a cubic crystal structure and is (100)-oriented;
a conductive film that is formed on the first zirconium oxide film and comprises a platinum film which has a cubic crystal structure and is (100)-oriented; and
a first lead zirconate titanate film that is formed on the conductive film and that has a tetragonal crystal structure and is (001)-oriented, wherein
the first zirconium oxide film comprises:
a film portion formed on the main surface, and
a plurality of protrusion portions each protruded from an upper surface of the film portion,
the film portion comprises a second zirconium oxide film which has a cubic crystal structure and is (100)-oriented,
each of the plurality of protrusion portions comprises a third zirconium oxide film which has a cubic crystal structure and is (100)-oriented,
a thickness of the film portion comprising the second zirconium oxide film which has a cubic crystal structure and is (100)-oriented is 11 to 18 nm,
a protrusion height of each of the plurality of protrusion portions protruded from the upper surface of the film portion and comprising the third zirconium oxide film which has a cubic crystal structure and is (100)-oriented is 4 to 8 nm,
a first average interface roughness of a first interface between the first zirconium oxide film and the conductive film is greater than a second average interface roughness of a second interface between the silicon substrate and the first zirconium oxide film,
the first lead zirconate titanate film comprises a composite oxide comprising lead zirconate titanate represented by a formula (Chem. 1) as follows:
Pb(Zr 1-x Ti x )O 3 (Chem. 1)
wherein x is 0.32≤x≤0.52, and
x represents Ti/(Ti+Zr), and
a lattice constant ratio of a second lattice constant in a c-axis direction of the lead zirconate titanate to a first lattice constant in an a-axis direction of the lead zirconate titanate is 1.010 to 1.016 when the first lead zirconate titanate film is (001)-oriented, and x, which represents Ti/(Ti+Zr), is 0.32≤x≤0.52.
2. The film structure according to claim 1 , wherein
a cross-sectional shape of each one of the plurality of protrusion portions perpendicular to a first direction along the main surface is a triangular shape, and
a width of each one of the plurality of protrusion portions in a second direction that is a direction which is along the main surface and perpendicular to the first direction decreases from a film portion side toward a side opposite to the film portion side.
3. The film structure according to claim 1 , wherein
the conductive film covers the plurality of protrusion portions, and
the conductive film is embedded between two adjacent protrusion portions.
4. The film structure according to claim 1 , wherein
the first zirconium oxide film is oriented so that a <100> direction of the first zirconium oxide film, which is a direction along the main surface, is parallel to a <100> direction of the silicon substrate, which is a direction along the main surface, and
the platinum film is oriented so that a <100> direction of the platinum film, which is a direction along the main surface, is parallel to the <100> direction of the silicon substrate, which is a direction along the main surface.
5. The film structure according to claim 1 , wherein
the first zirconium oxide film is oriented so that a <100> direction of the first zirconium oxide film, which is a direction along the main surface, is parallel to a <100> direction of the silicon substrate, which is a direction along the main surface,
the platinum film is oriented so that a <100> direction of the platinum film, which is a direction along the main surface, is parallel to the <100> direction of the silicon substrate, which is a direction along the main surface, and
the first lead zirconate titanate film is oriented so that a <100> direction of the first lead zirconate titanate film, which is a direction along the main surface, is parallel to the <100> direction of the silicon substrate, which is a direction along the main surface.
6. The film structure according to claim 1 , comprising
a second lead zirconate titanate film that is formed on the first lead zirconate titanate film and that has a tetragonal crystal structure and is (001)-oriented, wherein
the first lead zirconate titanate film has a third compressive stress, and
the second lead zirconate titanate film has a fourth tensile stress.
7. The film structure according to claim 1 , wherein
x is 0.32≤x≤0.48.
8. The film structure according to claim 1 , wherein
x is 0.42, and
the lattice constant ratio of the second lattice constant in the c-axis direction of the lead zirconate titanate to the first lattice constant in the a-axis direction of the lead zirconate titanate is 1.016 when the first lead zirconate titanate film is (001)-oriented, and x, which represents Ti/(Ti+Zr), is 0.42.
9. The film structure according to claim 1 , wherein
an upper layer portion of the third zirconium oxide film is more stretched and distorted in a horizontal direction as compared with a lower layer portion of the third zirconium oxide film.
10. The film structure according to claim 1 , wherein
the conductive film has a first tensile stress, and
the first zirconium oxide film has a first compressive stress or a second tensile stress weaker than the first tensile stress.
11. The film structure according to claim 10 , wherein
an upper layer portion of the first zirconium oxide film has a second compressive stress,
a lower layer portion of the first zirconium oxide film has a third tensile stress,
the second compressive stress is stronger than the first compressive stress when the first zirconium oxide film has the first compressive stress, and
the third tensile stress is stronger than the second tensile stress when the first zirconium oxide film has the second tensile stress.
12. A method for manufacturing a film structure, comprising the steps of:
(a) preparing a silicon substrate comprising a main surface composed of a (100) plane;
(b) forming a first zirconium oxide film which has a cubic crystal structure and is (100)-oriented on the main surface, wherein the first zirconium oxide film comprises a film portion on the main surface and a plurality of protrusion portions each protruded from an upper surface of the film portion, and
the film portion comprises a second zirconium oxide film which has a cubic crystal structure and is (100)-oriented, and
each of the plurality of protrusion portions comprises a third zirconium oxide film which has a cubic crystal structure and is (100)-oriented,
a thickness of the film portion composed of the second zirconium oxide film which has a cubic crystal structure and is (100)-oriented is 11 to 18 nm,
a protrusion height of each of the plurality of protrusion portions protruded from the upper surface of the film portion and composed of the third zirconium oxide film which has a cubic crystal structure and is (100)-oriented is 4 to 8 nm; and
(c) forming a conductive film comprising a platinum film which has a cubic crystal structure and is (100)-oriented on the first zirconium oxide film and a first lead zirconate titanate film having a tetragonal crystal structure and is (001)-oriented, wherein
a first average interface roughness of a first interface between the first zirconium oxide film and the conductive film is greater than a second average interface roughness of a second interface between the silicon substrate and the first zirconium oxide film,
the first lead zirconate titanate film comprises a composite oxide comprising lead zirconate titanate represented by a formula (Chem. 1) as follows:
Pb(Zr 1-x Ti x )O 3 (Chem. 1)
wherein x is 0.32≤x≤0.52, and
x represents Ti/(Ti+Zr), and
a lattice constant ratio of a second lattice constant in a c-axis direction of the lead zirconate titanate to a first lattice constant in an a-axis direction of the lead zirconate titanate is 1.010 to 1.016 when the first lead zirconate titanate film is (001)-oriented, and x, which represents Ti/(Ti+Zr), is 0.32≤x≤0.52.
13. The method for manufacturing a film structure according to claim 12 , wherein
a cross-sectional shape of each one of the plurality of protrusion portions perpendicular to a first direction along the main surface is a triangular shape, and
a width of each one of the plurality of protrusion portions in a second direction that is a direction which is along the main surface and perpendicular to the first direction decreases from a film portion side toward a side opposite to the film portion side.
14. The method for manufacturing a film structure according to claim 12 , wherein
in the step (c), the conductive film covering the plurality of protrusion portions is formed, and
in the step (c), the conductive film is embedded between two adjacent protrusion portions.
15. The method for manufacturing a film structure according to claim 12 , wherein
the conductive film has a first tensile stress, and
the first zirconium oxide film has a first compressive stress or a second tensile stress weaker than the first tensile stress.
16. The method for manufacturing a film structure according to claim 12 , further comprising the step of:
(d) forming a piezoelectric film comprising a lead zirconate titanate film which has a tetragonal crystal structure and is (001)-oriented on the conductive film.
17. The method for manufacturing a film structure according to claim 12 , wherein
the first zirconium oxide film is oriented so that a <100> direction of the first zirconium oxide film, which is a direction along the main surface, is parallel to a <100> direction of the silicon substrate, which is a direction along the main surface, and
the platinum film is oriented so that a <100> direction of the platinum film, which is a direction along the main surface, is parallel to the <100> direction of the silicon substrate, which is a direction along the main surface.
18. The method for manufacturing a film structure according to claim 16 , wherein
the first zirconium oxide film is oriented so that a <100> direction of the first zirconium oxide film, which is a direction along the main surface, is parallel to a <100> direction of the silicon substrate, which is a direction along the main surface,
the platinum film is oriented so that a <100> direction of the platinum film, which is a direction along the main surface, is parallel to the <100> direction of the silicon substrate, which is a direction along the main surface, and
the first lead zirconate titanate film is oriented so that a <100> direction of the first lead zirconate titanate film, which is a direction along the main surface, is parallel to the <100> direction of the silicon substrate, which is a direction along the main surface.