Film structure and method for manufacturing the same

1. A film structure comprising:

a substrate;

a first film having tensile stress formed on the substrate and comprising a first composite oxide represented by a composition of formula (1) below,

Pb(Zr 1-x Ti x )O 3 ; and  (1)

a second film having compressive stress formed on the first film and comprising a second composite oxide represented by a composition of formula (2) below,

Pb(Zr 1-y Ti y )O 3 , wherein  (2)

the x satisfies 0.10<x≤0.20,

the y satisfies 0.35≤y≤0.55, and

a full width at half maximum is less than 0.8°.

2. The film structure according to claim 1 , wherein

the first film comprises a plurality of layers laminated on each other, and

the second film comprises a plurality of crystal grains integrally formed from a lower surface to an upper surface of the second film.

3. The film structure according to claim 2 , wherein

each of the plurality of crystal grains has spontaneous polarization,

the spontaneous polarization includes a polarization component parallel to a thickness direction of the second film, and

the polarization components included in the spontaneous polarization of each of the plurality of crystal grains are oriented in an identical direction.

4. The film structure according to claim 1 , wherein the substrate is a silicon substrate.

5. The film structure according to claim 4 , further comprising:

a third film formed on the silicon substrate; and

a conductive film formed on the third film, wherein

the silicon substrate has a main surface made of a (100) plane,

the third film comprises zirconium oxide having a cubic crystal structure and being (100) oriented,

the conductive film comprises platinum having a cubic crystal structure and being (100) oriented, and

the first composite oxide has a rhombohedral crystal structure and is (100) oriented.

6. The film structure according to claim 5 , wherein the second composite oxide has a rhombohedral crystal structure and is (100) oriented.

7. The film structure according to claim 5 , wherein the second composite oxide has a tetragonal crystal structure and is (001) oriented.

8. A method for manufacturing a film structure, comprising the steps of:

(a) preparing a substrate;

(b) forming a first film having tensile stress and comprising a first composite oxide represented by a composition of formula (1) below on the substrate,

Pb(Zr 1-x Ti x )O 3   (1),

wherein forming the first film comprising the steps of:

(b1) forming a third film comprising a first precursor of the first composite oxide by coating the substrate with a first solution comprising lead, zirconium, and titanium; and

(b2) heat-treating the third film; and

(c) forming a second film having compressive stress and comprising a second composite oxide represented by a composition of formula (2) below on the first film by a sputtering method,

Pb(Zr 1-y Ti y )O 3 , wherein  (2)

the x satisfies 0.10<x≤0.20,

they satisfies 0.35≤y≤0.55,

to obtain a film structure having a full width at half maximum of less than 0.8°.

9. The method for manufacturing a film structure according to claim 8 , wherein

the step (b1) further comprises a step (b3) of forming a fourth film comprising the first precursor by coating the substrate with the first solution,

in the step (b1), the step (b3) is repeated a plurality of times to form the third film including a plurality of the fourth films laminated on each other, and

in the step (c), the second film is formed to further comprise a plurality of crystal grains integrally formed from a lower surface to an upper surface of the second film.

10. The method for manufacturing a film structure according to claim 9 , wherein

each of the plurality of crystal grains has spontaneous polarization,

the spontaneous polarization includes a polarization component parallel to a thickness direction of the second film, and

the polarization components included in the spontaneous polarization of each of the plurality of crystal grains are oriented in an identical direction.

11. The method for manufacturing a film structure according to claim 8 , wherein

in the step (a), a silicon substrate is prepared.

12. The method for manufacturing a film structure according to claim 11 , further comprising the steps of:

(d) forming a fifth film comprising zirconium oxide on the silicon substrate, the zirconium oxide having a cubic crystal structure and being (100) oriented; and

(e) forming a conductive film comprising platinum on the fifth film, the platinum having a cubic crystal structure and being (100) oriented, wherein

in the step (b), the first film is formed on the conductive film,

the silicon substrate has a main surface made of a (100) plane, and

the first composite oxide has a rhombohedral crystal structure and is (100) oriented.

13. The method for manufacturing a film structure according to claim 12 , wherein the second composite oxide has a rhombohedral crystal structure and is (100) oriented.

14. The method for manufacturing a film structure according to claim 12 , wherein the second composite oxide has a tetragonal crystal structure and is (001) oriented.