JP2956356B2 - Lead-containing perovskite structure composite oxide ferroelectric thin film, its production method and material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a lead-containing perovskite structure composite oxide (PZT).
Or PLZT) ferroelectric thin film. PZT, PL
ZT ferroelectric thin films are used for infrared sensors, piezoelectric filters, vibrators, laser modulation elements, optical shutters, capacitor films, nonvolatile memories, and the like.

[0002]

2. Description of the Related Art In forming a ferroelectric thin film, it is necessary to finally perform a heat treatment to improve crystallinity in any film forming method in order to obtain good characteristics. However, as the crystallinity is increased, crystal grains grow at the same time, causing a problem of leakage current through the grain boundaries. Conventionally, there has been a limit in improving the characteristics of the ferroelectric thin film due to the conflicting phenomena. In the case of a PZT or PLZT ferroelectric thin film, in order to increase the ferroelectricity, it is necessary to increase the crystallinity by heat treatment. At this time, many of the impurities in the film are accompanied by the growth of crystal grain boundaries. Precipitates in the world.
This impurity region increases the leakage current through the grain boundary. Therefore, it is considered that the leakage current can be significantly reduced by removing the impurity region. However, Pb, La, Ti,
It is difficult to purify Zr or the like, and 1 ppm, especially 0.1 pp
It has been very difficult to reduce the impurity concentration to less than m. Conventionally, there is no report that the characteristics of a lead-containing ferroelectric thin film have been improved by high purification.

[0003]

The inventors of the present invention have studied the purification of each of these metal components, and as a result, have repeatedly distilled, sublimated, and recrystallized each metal component in the form of a metal organic compound. Can be used to obtain very high-purity metal component raw materials, and PZT or PLZ such as lead titanate, lead zirconate titanate, and lanthanum-containing lead zirconate titanate can be obtained from these raw materials.
T (hereinafter collectively referred to as a composite oxide) ferroelectric thin film was prepared. It was found that a ferroelectric thin film having extremely excellent characteristics was prevented by preventing impurities from being precipitated at grain boundaries during crystallization. Obtained knowledge that can be obtained.

[0004]

Formula _{Pb 1-x La x (Zr} y Ti 1-y) 1-x / 4 O 3 ( wherein x, according to the present invention: A solution means the configuration of the invention], y is less than 0 or 1 A ferroelectric thin film comprising a lead-perovskite structure composite oxide represented by (decimal number) and having a total content of Li, Na, and K of 1 ppm or less as impurities contained in the dielectric. . The ferroelectric thin film is, specifically, lead titanate (x = y = 0 in the general formula), lead zirconate titanate (x = 0 in the general formula, y is 0 <y <1), or lanthanum-containing titanate. Lead zirconate (x, y in the general formula
Are 0 <x, y <1) and the like.

The ferroelectric thin film of the present invention is obtained by purifying the constituent metal components of the thin film by repeating distillation, sublimation and recrystallization in the form of a metal-organic compound, or by purifying them in combination. These are dissolved in an organic solvent so as to have a predetermined composition to prepare a coating liquid for forming a film, and the coating liquid is applied to a substrate, and dried and fired.

Organic compounds that can be used include organic acid salts, alkoxides, β-diketonato complexes and the like. Specific examples of the organic acid salt include formate of Pb, Zr, La, and Ti, acetate propionate, butyrate, octanoate, and stearate. Specific examples of the alkoxides include ethoxides, propoxides, butoxides of these metals, and mixed alkoxides. Specific examples of the β-diketonato complex include an acetylacetonato complex and a dipivaloylmethanato complex.

The solvent that can be used for producing the ferroelectric thin film of the present invention may be any solvent that dissolves the above-mentioned metal organic compound and has an appropriate solubility for the compound.
Generally, it is appropriately selected from water, alcohol, ketone, ester and the like by experience or trial and error. These solvents are all referred to as electronic material grades, and water is referred to as ultrapure water (electrical resistance of 17.8 MΩ or more). The composition for producing a ferroelectric thin film of the present invention further comprises, as a stabilizer, at least one compound selected from β-diketones, ketones, ketoesters, oxyacids, higher carboxylic acids, and amines. Can be. The composition for producing the ferroelectric thin film of the present invention,
0.2 to 3 mol per mole of total metal atoms contained
It may be partially hydrolyzed by addition of 1 amount of water.
The composition for producing a ferroelectric thin film of the present invention may be provided in a state where the reaction is partially progressed by reflux heating.

[0008] The ferroelectric thin film of the present invention can also be produced by a sputtering method using an oxide powder obtained from the metal organic compound purified as described above.

The impurities in the ferroelectric thin film of the present invention are Li,
The total content of Na and K is 1 ppm or less, preferably 0.1 ppm.
It is preferable that the content of U and Th is 1 ppm or less, the total content of U and Th is 10 ppb or less, and the total content of metal impurities is 1 ppm or less. Alkali metals are greatly involved in charge transfer and, when precipitated at the grain boundaries, tend to cause leakage current. Therefore, the total content of Li, Na, and K is 1 pp.
m or less.

[0010]

The ultrahigh-purity ferroelectric thin film of the present invention has a significantly reduced leakage current, which has been a problem in the prior art, and exhibits excellent dielectric properties. In addition, a stable film having very little change in characteristics depending on the portion of the film can be obtained, and can be widely used in the field of electronics and the like.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described with reference to Examples and Comparative Examples. The starting materials used were reagent grade commercial products, which were purified according to the present invention. Solvents were further purified from electronic grade commercial products.

Example 1 High purity was obtained by repeating recrystallization twice from ultrapure water twice to obtain highly purified lead acetate trihydrate, lanthanum acetate 1.5 hydrate and vacuum distillation twice. 25.18 g of tert-tert-butoxyzirconium and tetraisopropoxytitanium converted to 2-ethoxyethanol (refined distilled product)
3.45 g, 0.31 g, 2.43 g, and 0.45 g, respectively.
97 g each, Pb with a concentration of 10 wt% in terms of oxide
The _{0.91 La 0. 09 (Zr 0.65 Ti} 0.35) 0.9772 film-forming coating liquid of the proportion of O ₃ was produced. Ultrapure water was added to this solution, hydrolyzed, dried, and calcined. The oxide powder was analyzed for impurities by ICP.
The alkali metal content of each of Na, K and Li is 10 ppb
It was below. This solution was applied on a Pt substrate by spin coating to have a film thickness of 3000 ° and then fired in air at 700 ° C. for 1 hour. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 1] Relative dielectric constant Dielectric loss Leakage current density Dielectric strength (when 5 V is applied) 965 0.03 3.4 × 10 ⁻¹⁰ A / cm ² 872 kV / cm

Example 2 Recrystallization from ultrapure water was repeated twice to obtain highly purified lead acetate trihydrate and tetratertiary butoxyzirconium which was subjected to reduced pressure distillation twice to obtain highly purified tetratertiary butoxy zirconium. 3.79 g, 1.9 of tetraisopropoxy titanium was added to 25.42 g of 2-ethoxyethanol (distilled purified product).
9g and 1.36g are dissolved each, and 10wt% in oxide conversion
A coating solution for forming a PbZr _0.52 Ti _0.48 O ₃ film having a concentration of PbZr _0.52 Ti _0.48 O ₃ was prepared. This solution is hydrolyzed by adding ultrapure water, dried,
Impurity analysis of the composite oxide powder produced by firing by ICP method revealed that the amounts of alkali metals of Na, K, and Li were all 10 ppb or less. This solution was applied on a Pt substrate by a spin coating method, and a film thickness of 30
After the temperature was set to 00 °, firing was performed at 700 ° C. for 1 hour in air. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 2] Relative dielectric constant Dielectric loss Leakage current density Dielectric strength (when 5 V is applied) 928 0.02 8.2 × 10 ^-10 A / cm ² 892 kV / cm

Example 3 3.79 g of lead acetate trihydrate and tetraisopropoxytitanium purified by the same method as in Example 1 were added to 23.68 g of 2-ethoxymethanol (distilled refined product).
2.84 g of each was dissolved, and a coating solution for forming a PbTiO ₃ film having a concentration of 10 wt% in terms of oxide was prepared. Ultrapure water was added to this solution, hydrolyzed, dried, and calcined. Impurity analysis was performed by an ICP method on the produced oxide powder. The amounts of alkali metals of Na, K, and Li were all 10 ppb or less. there were. This solution was applied on a Pt substrate by spin coating to a thickness of 3000
Calcination was carried out in air at ℃ for 1 hour. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 3] Relative dielectric constant Dielectric loss Leakage current density Isolation voltage (when 5 V is applied) 174 0.06 6.8 × 10 ^-10 A / cm ² 816 kV / cm

Example 4 The same operation as in Example 2 was performed to obtain 10 wt% in terms of oxide.
A coating solution for forming a PbZr _0.52 Ti _0.48 O ₃ film having a concentration of PbZr _0.52 Ti _0.48 O ₃ was prepared. This solution is hydrolyzed by adding ultrapure water, dried,
By firing, PZT powder was synthesized. Using this powder,
A sintered body was prepared by hot pressing, and used as a sputtering target. Impurity analysis of this sintered body by the ICP method revealed that the amounts of alkali metals of Na, K, and Li were all 10 ppb or less. This
After forming a thin film having a thickness of 3000 ° on a Pt substrate by a sputtering method using an R-get, firing was performed in air at 700 ° C. for 1 hour. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 4] Relative dielectric constant Dielectric loss Leakage current density Dielectric strength voltage (when 5 V is applied) 785 0.02 5.7 × 10 ^-10 A / cm ² 823 kV / cm

Example 5 PbTiO ₃ was prepared by MOCVD using dipivaloyl methanato lead purified by repeating sublimation twice and tetraisopropoxytitanium purified by repeating vacuum distillation twice.
A thin film was formed on a Pt substrate. Substrate temperature 700 ° C. Lead dipivaloylmethanato Vaporization temperature 130 ° C. Nitrogen carrier flow rate 200 sccm Tetraisopropoxy titanium Vaporization temperature 40 ° C. Nitrogen carrier flow rate 50 sccm Oxygen flow rate 500 sccm A thin film having a thickness of 3000 mm was formed under the conditions of a system pressure of 1 torr. This film was analyzed for impurities by ICP method.
The alkali metal contents of a, K, and Li were all 10 ppb or less. The composition of the film was also quantitatively analyzed by EPMA, and the stoichiometric ratio (Pb: Ti = 1: 1) was obtained.
1) It was confirmed that a PbTiO ₃ thin film was formed. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 5] Relative dielectric constant Dielectric loss Leak current density Dielectric breakdown voltage (when 5 V is applied) 155 0.04 5.7 × 10 ^-10 A / cm ² 843 kV / cm

Comparative Example 1 A coating liquid for forming a 10 wt% PLZT film formed in the same manner as in Example 1 is referred to as Liquid A. Also, Pb, La, Zr,
As a Ti compound and an organic solvent, commercially available lead acetate trihydrate, lanthanum acetate dihydrate, tetranormal butoxyzirconium, tetraisopropoxy titanium and 2-
A coating solution for forming a 10 wt% PLZT thin film was prepared in the same manner as in Example 1 except that ethoxyethanol was used.
This solution is designated as solution B. Pure water was added to a part of the solution B, hydrolyzed, dried and fired to obtain a powder for forming a PLZT thin film. When impurities in this powder were analyzed by ICP method, the total alkali metal content was about 25 ppm (Na; 1).
3 ppm K; 9 ppm; Li; 3 ppm).
It is considered that the film obtained from the solution B corresponds to a film having a conventional purity level. The solution A and the solution B were mixed at the following weight ratios to prepare coating solutions for film formation having various impurity concentrations. The amount of impurities shown below is the amount of impurities in the formed film.

[Table 6]

[Table 6]

[Table 6] -3

[Table 6] -4 This solution was applied on a Pt substrate by spin coating to have a thickness of 3000 °, and then baked in air at 700 ° C. for 1 hour to produce PLZT thin films having various impurity concentrations. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The average values of the relative dielectric constant and the dielectric loss were almost the same in all the samples as in Example 1, but there was a tendency that the higher the impurity concentration, the higher the leakage current density. The result is shown in FIG. As is clear from the figure, the amount of the alkali metal impurity was 1 ppm and 0.1 pp
The inflection point of the leak current density is around m.

Example 6 Recrystallization from ultrapure water was repeated twice to obtain highly purified lead acetate trihydrate, lanthanum acetate 1.5 hydrate, and vacuum distillation was repeated twice to obtain high purity. 24.50 g of tert-tert-butoxyzirconium and tetraisopropoxytitanium converted to 2-ethoxyethanol (distilled purified product)
3.45 g, 0.31 g, 2.43 g, and 0.45 g, respectively.
The mixture was dissolved in 97 g portions, and refluxed at a solvent boiling point for 24 hours. Thereafter, 0.68 g of acetylacetone was added, and the mixture was refluxed again for one hour under the boiling point of the solvent, and was converted to 10 wt% in terms of oxide.
Concentration Pb _0.91 La _0.09 (Zr _0.65 Ti _0.35 ) _0.9772 O
_Three coating liquids for forming a film were prepared. Ultrapure water was added to this solution, hydrolyzed, dried, and calcined. Impurities were analyzed by an ICP method for an oxide powder.
The alkali metal content of each of Na, K and Li is 10 ppb
It was below. This solution was applied on a Pt substrate by spin coating to have a film thickness of 3000 ° and then fired in air at 700 ° C. for 1 hour. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 7] Relative dielectric constant Dielectric loss Leakage current density Dielectric withstand voltage (when 5 V is applied) 982 0.03 3.5 × 10 ^-10 A / cm ² 885 kV / cm Also, three months after preparing this solution, the same applies. The film was formed as described above, and the electrical characteristics were measured.

[Table 8] Relative dielectric constant Dielectric loss Leakage current density Dielectric strength (when 5 V is applied) 963 0.03 3.5 × 10 ^-10 A / cm ² 877 kV / cm This solution has little change with time and has good storage stability. You can see that you have.

Example 7 A highly purified lead acetate trihydrate obtained by repeating recrystallization twice from ultrapure water twice and a highly purified tetratertiary butoxy zirconium obtained by repeating vacuum distillation twice. 3.79 g, 1.9 of tetraisopropoxy titanium was added to 25.42 g of 2-ethoxyethanol (distilled purified product).
9g and 1.36g are dissolved each, and 10wt% in oxide conversion
A coating solution for forming a PbZr _0.52 Ti _0.48 O ₃ film having a concentration of PbZr _0.52 Ti _0.48 O ₃ was prepared. This solution is hydrolyzed by adding ultrapure water, dried,
Impurity analysis of the oxide powder produced by firing by ICP method revealed that the amounts of alkali metals of Na, K and Li were all 10 ppb or less. This solution is applied on a Pt substrate by a spin coating method, and a film thickness of 3000
Then, firing was performed in air at 700 ° C. for 1 hour.
A Pt electrode is formed on this film by sputtering,
The electrical characteristics were measured and were as follows.

[Table 9] Relative dielectric constant Dielectric loss Leakage current density Dielectric strength (when 5 V is applied) 928 0.02 8.2 × 10 ^-10 A / cm ² 892 kV / cm

Example 8 Lead acetate trihydrate and tetraisopropoxytitanium purified in the same manner as in Example 1 were 3.79 g each in 23.68 g of 2-ethoxymethanol (distilled purified product).
2.84 g of each was dissolved, and a coating solution for forming a PbTiO ₃ film having a concentration of 10 wt% in terms of oxide was prepared. Ultrapure water was added to this solution, hydrolyzed, dried, and calcined. Impurity analysis was performed by an ICP method on the produced oxide powder. The amounts of alkali metals of Na, K, and Li were all 10 ppb or less. there were. This solution was applied on a Pt substrate by spin coating to a thickness of 3000
Calcination was carried out in air at ℃ for 1 hour. A Pt electrode was formed on this film by sputtering, and the electrical characteristics were measured. The results were as follows.

[Table 10] Relative dielectric constant Dielectric loss Leakage current density Breakdown voltage (when 5 V is applied) 174 0.06 6.8 × 10 ^-10 A / cm ² 816 kV / cm

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a leakage current and an impurity concentration of a PZT thin film.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-35449 (JP, A) JP-A-48-38313 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 35/49

Claims (16)

(57) [Claims] 1. A lead-containing perovskite structure composite formula _{Pb 1-x La x (Zr} y Ti 1-y) 1-x / 4 O 3 ( wherein x, y is 0 or less than 1 point) represented by An oxide having a total content of Li, Na, and K of 1 ppm
A ferroelectric thin film characterized by the following. 2. The lead-containing perovskite structure composite oxide is lead titanate (x = y = 0 in the general formula), lead zirconate titanate (x = 0 in the general formula, y is 0 <y <1).
2. The ferroelectric thin film according to claim 1, wherein lanthanum-containing lead titanate zirconate (x, y in the general formula is 0 <x, y <1). 3. The ferroelectric thin film according to claim 1, wherein the total content of Li, Na, and K contained in the composite oxide is 0.1 ppm or less. 4. A metal organic compound selected from the group consisting of organic acid salts, alkoxides and β-diketonato complexes of Pb, La, Zr and Ti by distillation, recrystallization or sublimation.
Purification alkali metal content of interest _{Pb 1-x La x (Zr} y Ti 1-y) 1-x / 4 O 3 is to some extent at 1ppm or less, these objectives _{Pb 1-x La x (Zr} y Ti _{1 -y) 1-x / 4} and O ₃ and the composition of the same stoichiometric composition with respect to metals, the composition was coated on a desired substrate, preparation of a ferroelectric thin film which comprises drying and firing. 5. The metal organic compound of Pb, La, Zr, Ti is formate, acetate, octanoate, stearate,
5. An ethoxide, propoxide, butoxide, acetylacetonato complex, dipivaloylmethanato complex.
3. The method for producing a ferroelectric thin film according to item 1. 6. Purpose _{Pb 1-x La x (Zr} y Ti 1-y)
_{1-x / 4} method of the ferroelectric thin film according to claim 4 or 5 alkali metal content of O ₃ is purified to some extent 0.1ppm or less. 7. A metal organic compound selected from the group consisting of organic acid salts, alkoxides and β-diketonato complexes of Pb, La, Zr, and Ti, by distillation, recrystallization or sublimation.
Purification alkali metal content of interest _{Pb 1-x La x (Zr} y Ti 1-y) 1-x / 4 O 3 is to some extent at 1ppm or less, these objectives _{Pb 1-x La x (Zr} y Ti _{1 -y) 1-x / 4} and O ₃ and the composition of the same stoichiometric composition with respect to the metal, forming a film by sputtering a powder or sintered body of the composite oxide obtained by drying and firing as the target consisting _{Pb 1-x La x (Zr} y Ti 1-y) 1-x / 4 O 3 ferroelectric preparation of thin films. 8. The metal organic compound of Pb, La, Zr, Ti is formate, acetate, octanoate, stearate,
8. An ethoxide, propoxide, butoxide, acetylacetonate complex or dipivaloylmethanato complex.
3. The method for producing a ferroelectric thin film according to item 1. 9. Purpose _{Pb 1-x La x (Zr} y Ti 1-y)
_{1-x / 4} method of the ferroelectric thin film according to claim 7 or 8 alkali metal content of O ₃ is purified to some extent 0.1ppm or less. 10. Pb, La, Zr and Ti metal-organic compounds are distilled, recrystallized or sublimated to obtain the target Pb _{1-x
La x (Zr y Ti 1-} y) alkali metal content of _{1-x /} 4 O ₃ is purified to some extent 1ppm or less, these objectives _{Pb 1-x La x (Zr} y Ti 1-y) 1 _{-x / 4} O ₃ and at the same stoichiometric proportions with respect to the metal containing in a solvent Pb _1-x La _x (Zr
_y Ti _1-y ) _{1-x / 4} O ₃ A composition for producing a ferroelectric thin film. 11. The ferroelectric thin film according to claim 10, wherein the metal organic compound of Pb, La, Zr, and Ti is a metal organic compound selected from the group consisting of an organic acid salt of the metal, an alkoxide, and a β-diketonato complex. Production composition. 12. The ferroelectric substance according to claim 10, further comprising at least one compound selected from β-diketones, ketones, ketoesters, oxy acids, higher carboxylic acids, and amines as a stabilizer. A composition for producing a thin film. 13. The composition for producing a ferroelectric thin film according to claim 10, wherein the composition is partially hydrolyzed by adding 0.2 to 3 mol of water to 1 mol of total metal atoms contained therein. 14. obtain _{Pb 1-x La x (Zr} y T
i _1-y ) _{1-x / 4} O ₃ composite oxide having an alkali metal content of 0.1 ppm or less and purified to some extent.
14. The composition for producing a ferroelectric thin film according to 0, 11, 12 or 13. 15. The organometallic compound of Pb, La, Zr, Ti is formate, acetate, octanoate, stearate, ethoxide, propoxide, butoxide, acetylacetonato complex, dipivaloylmethanato complex. The composition for producing a ferroelectric thin film according to claim 10, 11, 12, 13, or 14. 16. The reaction according to claim 10, 11, 12, 13, 14 or 1 in which the reaction partially proceeds by reflux heating.
6. The composition for producing a ferroelectric film according to 5. [0001]