Ferroelectric thin films and solutions: compositions and processing

Abstract

The ferroelectric thin film is formed from a liquid composition by the sol-gel processing which has a large amount of polarization, remarkably improved retention and imprint characteristics as compared with a PZT, minute grains and fine film quality, homogeneous electrical properties, and low leakage currents and which is suited for nonvolatile memories. The ferroelectric thin film of the present invention comprising a metal oxide represented by the general formula: (Pb V Ca W Sr X La Y )(Zr Z Ti 1−Z )O 3 , wherein 0.9≦V≦1.3, 0≦W≦0.1, 0≦X≦0.1, 0<Y≦0.1, 0<Z≦0.9 and at least either of W and X is not 0, is formed from a solution where thermally decomposable organometallic compounds of respective metals constituting said metal oxide, hydrolyzable organometallic compounds thereof, and partially hydrolyzed products and/or polycondensation products of said hydrolyzable organometallic compounds are dissolved in an organic solvent in such a proportion as to provide the metal atom ratio represented by the above-mentioned formula.

What is claimed is:  
     
         1 . A liquid composition for the formation of a ferroelectric thin film comprising: 
 a metal oxide represented by the general formula    (Pb V  Ca W  Sr X  La Y )(Zr Z  Ti 1−Z )O 3      wherein 0.9≦V≦1.3, O≦W≦0.1, O≦X≦0.1, O<Y≦0.1, O<Z≦0.9 and at least either of W and X is not 0, said composition comprising a solution wherein thermally decomposable organometallic compounds of respective metals constituting said metal oxide, hydrolyzable organometallic compounds thereof, partially hydrolyzed products and/or polycondensation products of said hydrolyzable organometallic compounds are dissolved in an organic solvent in such a proportion as to provide the metal atom ratio represented by said formula.    
     
     
         2 . The liquid composition for the formation of a ferroelectric thin film according to    claim 1   , wherein the organometallic compound is a compound an organic radical of which is bound to a metal through an oxygen atom or nitrogen atom thereof.  
     
     
         3 . The liquid composition for the formation of a ferroelectric thin film according to    claim 2   , wherein the organometallic compound is selected from the group consisting of a metal alkoxide, a metal carboxylate, a metal β-diketonato complex, a metal β-diketoester complex, a β-iminoketo complex, and a metal amino complex.  
     
     
         4 . The liquid composition for the formation of a ferroelectric thin film according to    claim 1   , wherein the organometallic compound is a compound that changes into a metal oxide at a temperature not more than 500° C.  
     
     
         5 . The liquid composition for the formation of a ferroelectric thin film according to    claim 2   , wherein the organometallic compound is a compound that changes into a metal oxide at a temperature not more than 500° C.  
     
     
         6 . The liquid composition for the formation of a ferroelectric thin film according to    claim 3   , wherein the organometallic compound is a compound that changes into a metal oxide at a temperature not more than 500° C.  
     
     
         7 . The liquid composition for the formation of a ferroelectric thin film according to    claim 1   , wherein the organometallic compound is selected from the group consisting of a metal alkoxide and a metal carboxylate, and the solution contains a stabilizer selected from the group consisting of a β-diketone, a β-ketonic acid, a β-keto ester, an oxy-acid, a diol, a higher carboxylic acid, an alkanolamine, and a polyamine in a proportion of 0.2 to 3 mol per one mol of the total amount of metals in said composition.  
     
     
         8 . The liquid composition for the formation of a ferroelectric thin film according to    claim 2   , wherein the organometallic compound is selected from the group consisting of a metal alkoxide and a metal carboxylate, and the solution contains a stabilizer selected from the group consisting of a β-diketone, a β-ketonic acid, a β-keto ester, an oxy-acid, a diol, a higher carboxylic acid, an alkanolamine, and a polyamine in a proportion of 0.2 to 3 mol per one mol of the total amount of metals in said composition.  
     
     
         9 . The liquid composition for the formation of a ferroelectric thin film according to    claim 3   , wherein the organometallic compound is selected from the group consisting of a metal alkoxide and a metal carboxylate, and the solution contains a stabilizer selected from the group consisting of a β-diketone, a β-ketonic acid, a β-keto ester, an oxy-acid, a diol, a higher carboxylic acid, an alkanolamine, and a polyamine in a proportion of 0.2 to 3 mol per one mol of the total amount of metals in said composition.  
     
     
         10 . The liquid composition for the formation of a ferroelectric thin film according to    claim 4   , wherein the organometallic compound is selected from the group consisting of a metal alkoxide and a metal carboxylate, and the solution contains a stabilizer selected from the group consisting of a β-diketone, a β-ketonic acid, a β-keto ester, an oxy-acid, a diol, a higher carboxylic acid, an alkanolamine, and a polyamine in a proportion of 0.2 to 3 mol per one mol of the total amount of metals in said composition.  
     
     
         11 . A method for forming a ferroelectric thin film comprising the steps of: 
 coating a substrate with a liquid composition comprising: a liquid composition for the formation of a ferroelectric thin film comprising: a metal oxide represented by the general formula    (Pb V  Ca W  Sr X  La Y )(Zr Z  Ti 1−Z )O 3      wherein 0.9≦V≦1.3, O≦W≦0.1, O≦X≦0.1, O<Y≦0.1, O<Z≦0.9 and at least either of W and X is not 0;    heating the coated substrate to form the thin film of a metal oxide on the substrate; and    subjecting the substrate to heat treatment at a temperature below 700° C. to crystallize the thin film of said metal oxide.    
     
     
         12 . The method according to    claim 11   , wherein the coating and heating steps or the coating, heating, and crystallizing steps are repeated until the thin film reaches to a desired thickness.  
     
     
         13 . A ferroelectric thin film formed from the liquid composition according to    claim 1   .  
     
     
         14 . A ferroelectric thin film formed from the liquid composition according to    claim 2   .  
     
     
         15 . A ferroelectric thin film formed from the liquid composition according to    claim 3   .  
     
     
         16 . A ferroelectric thin film formed from the liquid composition according to    claim 4   .  
     
     
         17 . A ferroelectric thin film formed from the liquid composition according to    claim 7   .  
     
     
         18 . The ferroelectric thin film according to    claim 17   , having <111> orientation in not less than 70% volume fraction of the thin film.  
     
     
         19 . The ferroelectric thin film according to    claim 8   , further including: 
 a capacitor.    
     
     
         20 . The ferroelectric thin film according to    claim 19   , further including: 
 a nonvolatile memory.