Ferroelectric oxide structure, method for producing the structure, and liquid-discharge apparatus

Abstract

A ferroelectric oxide structure includes a substrate and a ferroelectric thin-film deposited on the substrate. The ferroelectric thin-film has a thickness of greater than or equal to 200 nm and a tetragonal crystal system. The ferroelectric thin-film has (100) single-orientation crystal orientation.

1 . A ferroelectric oxide structure comprising:
 a substrate; and   a ferroelectric thin-film having a thickness of greater than or equal to 200 nm and a tetragonal crystal system, the ferroelectric thin-film being deposited on the substrate, wherein the ferroelectric thin-film has (100) single-orientation crystal orientation.   
     
     
         2 . A ferroelectric oxide structure, as defined in  claim 1 , satisfying the following formulas (1) and (2):
   1.0<( c/a ) film ≦1.015  (1); and     α film −α sub (° C. −1 )≧3.0×10 −6   (2),   
       where (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film, α sub  is the thermal expansion coefficient of the substrate, and α film  is the thermal expansion coefficient of the ferroelectric thin-film in formulas (1) and (2). 
     
     
         3 . A ferroelectric oxide structure, as defined in  claim 1 , satisfying the following formulas (3) and (4):
   1.015<( c/a ) film ≦1.045  (3); and     α film −α sub (° C. −1 )≧9.0×10 −6   (4),   
       where (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film, α sub  is the thermal expansion coefficient of the substrate, and α film  is the thermal expansion coefficient of the ferroelectric thin-film in formulas (3) and (4). 
     
     
         4 . A ferroelectric oxide structure, as defined in  claim 1 , satisfying the following formulas (5) and (6):
   1.045<( c/a ) film ≦1.065  (5); and     α film −α sub (° C. −1 )≧12.0×10 −6   (6),   
       where (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film, α sub  is the thermal expansion coefficient of the substrate, and α film  is the thermal expansion coefficient of the ferroelectric thin-film in formulas (5) and (6). 
     
     
         5 . A ferroelectric oxide structure, as defined in  claim 1 , satisfying the following formula (7):
   (α film −α sub (° C. −1 ))×( Tg−Tc (° C.))/( c/a ) film )>25×10 −4   (7),   
       where α sub  is the thermal expansion coefficient of the substrate, α film  is the thermal expansion coefficient of the ferroelectric thin-film, Tg is the deposition temperature of the ferroelectric thin-film, Tc is a phase-transition temperature, and (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film in formula (7). 
     
     
         6 . A ferroelectric oxide structure, as defined in  claim 5 , satisfying the following formula (8):
   (α film −α sub (° C. −1 ))×( Tg−Tc (° C.))/( c/a ) film )>30×10 −4   (8),   
       where α sub  is the thermal expansion coefficient of the substrate, α film  is the thermal expansion coefficient of the ferroelectric thin-film, Tg is the deposition temperature of the ferroelectric thin-film, Tc is a phase-transition temperature, and (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film in formula (8). 
     
     
         7 . A ferroelectric oxide structure, as defined in  claim 2 , wherein the ferroelectric oxide thin-film contains at least one kind of perovskite-type oxide selected from the group consisting of barium titanate, barium strontium titanate, barium titanate zirconate, bismuth potassium titanate, and bismuth ferrites. 
     
     
         8 . A ferroelectric oxide structure, as defined in  claim 5 , wherein the ferroelectric oxide thin-film contains at least one kind of perovskite-type oxide selected from the group consisting of barium titanate, barium strontium titanate, barium titanate zirconate, bismuth potassium titanate, and bismuth ferrites. 
     
     
         9 . A ferroelectric oxide structure, as defined in  claim 6 , wherein the ferroelectric oxide thin-film contains at least one kind of perovskite-type oxide selected from the group consisting of barium titanate, barium strontium titanate, barium titanate zirconate, bismuth potassium titanate, and bismuth ferrites. 
     
     
         10 . A ferroelectric oxide structure, as defined in  claim 3 , wherein the ferroelectric oxide thin-film contains lead titanate zirconate. 
     
     
         11 . A ferroelectric oxide structure, as defined in  claim 5 , wherein the ferroelectric oxide thin-film contains lead titanate zirconate. 
     
     
         12 . A ferroelectric oxide structure, as defined in  claim 6 , wherein the ferroelectric oxide thin-film contains lead titanate zirconate. 
     
     
         13 . A ferroelectric oxide structure, as defined in  claim 4 , wherein the ferroelectric oxide thin-film contains lead titanate. 
     
     
         14 . A ferroelectric oxide structure, as defined in  claim 5 , wherein the ferroelectric oxide thin-film contains lead titanate. 
     
     
         15 . A ferroelectric oxide structure, as defined in  claim 6 , wherein the ferroelectric oxide thin-film contains lead titanate. 
     
     
         16 . A ferroelectric oxide structure, as defined in  claim 1 , wherein the substrate contains Si as a main component. 
     
     
         17 . A ferroelectric oxide structure, as defined in  claim 1 , wherein the substrate is a single-crystal substrate, and the ferroelectric thin-film is an epitaxial layer. 
     
     
         18 . A ferroelectric oxide structure, as defined in  claim 1 , wherein a crystal plane at a surface of the substrate is formed by off-cutting the substrate from a low-index plane of the substrate, and wherein the ferroelectric thin-film has substantially uniform crystal orientation in a plane parallel to the crystal plane. 
     
     
         19 . A ferroelectric oxide structure, as defined in  claim 1 , wherein the ferroelectric oxide structure is a ferroelectric element having electrodes that apply an electric field to the ferroelectric thin-film in the direction of the thickness of the ferroelectric thin-film. 
     
     
         20 . A liquid discharge apparatus comprising:
 a piezoelectric element composed of the ferroelectric oxide structure as defined in  claim 19 ; and   a liquid discharge member provided next to the piezoelectric element, wherein the liquid discharge member includes a liquid reservoir for storing liquid and a liquid outlet for discharging the liquid from the liquid reservoir to the outside of the liquid reservoir based on the electric field applied to the piezoelectric element.   
     
     
         21 . A method for producing a ferroelectric oxide structure that has a substrate and a ferroelectric thin-film deposited on the substrate, wherein the crystal structure of the ferroelectric thin-film undergoes phase-transition at a predetermined temperature, and wherein the ferroelectric thin-film has a thickness of greater than or equal to 200 nm and a tetragonal crystal system when the temperature of the ferroelectric thin-film is less than or equal to the predetermined temperature, the method comprising the steps of:
 preparing the substrate that satisfies the following formula (2) based on the thermal expansion coefficient of the ferroelectric thin-film when the ferroelectric thin-film satisfies the following formula (1);   preparing the substrate that satisfies the following formula (4) based on the thermal expansion coefficient of the ferroelectric thin-film when the ferroelectric thin-film satisfies the following formula (3);   preparing the substrate that satisfies the following formula (6) based on the thermal expansion coefficient of the ferroelectric thin-film when the ferroelectric thin-film satisfies the following formula (5); and   depositing the ferroelectric thin-film on the substrate at a temperature higher than or equal to the predetermined temperature, wherein the formulas (1) through (6) are
   1.0<( c/a ) film ≦1.015  (1), 
   α film −α sub (° C. −1 )≧3.0×10 −6   (2), 
   1.015<( c/a ) film ≦1.045  (3), 
   α film −α sub (° C. −1 )≧9.0×10 −6   (4), 
   1.045<( c/a ) film ≦1.065  (5), 
   α film −α sub (° C. −1 )≧12.0×10 −6   (6), 
   
       where (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film, α sub  is the thermal expansion coefficient of the substrate, and α film  is the thermal expansion coefficient of the ferroelectric thin-film in formulas (1) through (6). 
     
     
         22 . A method for producing a ferroelectric oxide structure that has a substrate and a ferroelectric thin-film deposited on the substrate, wherein the crystal structure of the ferroelectric thin-film undergoes phase-transition at a predetermined temperature, and wherein the ferroelectric thin-film has a thickness of greater than or equal to 200 nm and a tetragonal crystal system when the temperature of the ferroelectric thin-film is less than or equal to the predetermined temperature, the method comprising the steps of:
 preparing the substrate that satisfies the following formula (7) based on the thermal expansion coefficient of the ferroelectric thin-film and the lattice constant ratio of the crystal axes of the ferroelectric thin-film; and   depositing the ferroelectric thin-film on the substrate at a temperature higher than or equal to the predetermined temperature, wherein the formula (7) is
   (α film −α sub (° C. −1 ))×( Tg−Tc (° C.))/( c/a ) film )>25×10 −4   (7), 
   
       where α sub  is the thermal expansion coefficient of the substrate, α film  is the thermal expansion coefficient of the ferroelectric thin-film, Tg is the deposition temperature of the ferroelectric thin-film, Tc is a phase-transition temperature, and (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film in formula (7). 
     
     
         23 . A method for producing a ferroelectric oxide structure, as defined in  claim 22 , the method comprising the steps of:
 preparing the substrate that satisfies the following formula (8) based on the thermal expansion coefficient of the ferroelectric thin-film and the lattice constant ratio of the crystal axes of the ferroelectric thin-film; and   depositing the ferroelectric thin-film on the substrate at a temperature higher than or equal to the predetermined temperature, wherein the formula (8) is
   (α film −α sub (° C. −1 ))×( Tg−Tc (° C.))/( c/a ) film )>30×10 −4   (8), 
   
       where α sub  is the thermal expansion coefficient of the substrate, α film  is the thermal expansion coefficient of the ferroelectric thin-film, Tg is the deposition temperature of the ferroelectric thin-film, Tc is a phase-transition temperature, and (c/a) film  is the lattice constant ratio of the crystal axes of the ferroelectric thin-film in formula (8).