Ferroelectric film and method for manufacturing the same

1. A method for manufacturing a ferroelectric film, comprising the steps of:

forming, by coating a sol-gel solution containing K, Na and Nb on a substrate by a spin-coating method, a coated film on said substrate;

forming, by calcining said coated film, a ferroelectric material film on said substrate;

forming a first material film for forming a crystalline oxide in an island shape or in a film shape directly on said ferroelectric material film; and

forming, by heat-treating said ferroelectric material film and said first material film for forming a crystalline oxide in an oxygen atmosphere, a ferroelectric film obtained by crystallizing said ferroelectric material film and said first material film for forming a crystalline oxide,

wherein a first crystalline oxide obtained by crystallizing said first material film for forming a crystalline oxide is preferentially oriented to (001);

wherein said first crystalline oxide is a bismuth layered-structure ferroelectric substance having a pseudo-perovskite structure or is a tungsten-bronze type ferroelectric substance; and

wherein the resulting crystallized ferroelectric material film is a (K 1-x Na x )NbO 3 film having a perovskite structure, and X satisfies the formula of 0<X<1.

2. The method for manufacturing a ferroelectric film according to claim 1 ,

wherein said bismuth layered-structure ferroelectric substance is Bi 4 Ti 3 O 12 or (Bi 4-x La x )Ti 3 O 12 , and x satisfies the formula below

0<x<1.

3. The method for manufacturing a ferroelectric film according to claim 1 , wherein:

before forming a coated film on said substrate, a second material film for forming a crystalline oxide preferentially oriented to (001) in an island shape or in a film shape is formed on said substrate;

said coated film is formed on said second material film for forming a crystalline oxide;

said ferroelectric material film, said first material film for forming a crystalline oxide, and said second material film for forming a crystalline oxide are heat-treated in an oxygen atmosphere; and

a second crystalline oxide obtained by crystallizing said second material film for forming a crystalline oxide is preferentially oriented to (001).

4. The method for manufacturing a ferroelectric film according to claim 1 ,

wherein the total concentration of said K, Na and Nb contained in said sol-gel solution is from 10 mol % to 50 mol %.

5. The method for manufacturing a ferroelectric film according to claim 1 ,

wherein, by repeating twice or more the formation of said coated film and said calcination when forming said ferroelectric material film, a ferroelectric material film including a plurality of coated films is formed, the first material film for forming a crystalline oxide being subsequently formed thereon.

6. The method for manufacturing a ferroelectric film according to claim 1 ,

wherein said heat treatment is carried out in a pressure range of 0.0993 to 1.986 MPa.

7. The method for manufacturing a ferroelectric film according to claim 1 ,

wherein said resulting crystallized ferroelectric material film is a (K 1-X Na X )NbO 3 film having a perovskite structure, and X satisfies the formula below

0.3≦X≦0.7.

8. A method for forming a ferroelectric film, comprising the steps of:

forming a first material film for forming a crystalline oxide in an island shape or in a film shape on a substrate;

forming, by coating a sol-gel solution containing K, Na and Nb on said first material film for forming a crystalline oxide by a spin-coating method, a coated film on said first material film for forming a crystalline oxide;

forming, by calcining said coated film, a ferroelectric material film on said first material film for forming a crystalline oxide;

forming a blocking film on said ferroelectric material film; and

forming, by suppressing separation of K and Na from said ferroelectric material film by said blocking film while heat-treating said ferroelectric material film and said first material film for forming a crystalline oxide in an oxygen atmosphere, a ferroelectric film obtained by crystallizing said ferroelectric material film and said first material film for forming a crystalline oxide,

wherein a first crystalline oxide obtained by crystallizing said first material film for forming a crystalline oxide is preferentially oriented to (001).

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

wherein the total concentration of said K, Na and Nb contained in said sol-gel solution is from 10 mol % to 50 mol %.

10. The method for manufacturing a ferroelectric film according to claim 8 ,

wherein, by repeating twice or more the formation of said coated film and said calcination when forming said ferroelectric material film, a ferroelectric material film including a plurality of coated films is formed, the first material film for forming a crystalline oxide being subsequently formed thereon.

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

wherein said heat treatment is carried out in a pressure range of 0.0993 to 1.986 MPa.

12. The method for manufacturing a ferroelectric film according to claim 8 ,

wherein said ferroelectric film is a (K 1-X Na X )NbO 3 film having a perovskite structure, and X satisfies the formula below

0.3≦X≦0.7.