JPH0318281B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is directed to dielectric thin films, especially those with a thickness of 1000 to
This invention relates to a method for producing a lead titanium zirconate dielectric thin film of 15,000㎥. Dielectric films are conventionally manufactured by pressure molding and sintering a powdery dielectric composition, but in this method, the thickness can be reduced to less than 10 microns, which is a condition for an excellent thin film capacitor. It is extremely difficult to produce a thin film with a high dielectric constant, and the sintering temperature is extremely high, so expensive metals must be used as electrodes. Sputtering method, vacuum evaporation method, gas phase reaction method, etc. are being considered as methods for manufacturing dielectric films suitable for excellent thin film capacitors, but stoichiometry control is extremely difficult with these methods. However, it has not been put to practical use because only extremely thin films can be obtained and conduction easily occurs. Apart from these methods, a solution containing an organometallic compound is applied onto a glass substrate by a dropping method or a dipping method, and then heated at 110°C for 30 minutes in air at room temperature.
After drying in a constant temperature bath for 30 minutes to complete the hydrolysis reaction, the dielectric thin film is produced by heating and baking at a temperature of 200°C to 800°C while forcing steam into an electric furnace. The method was published in 1983.
This is proposed in Publication No. 28408. however,
In this method, it is difficult to obtain a homogeneous coating film because the exemplified organometallic compound solution absorbs moisture in the atmosphere and is easily hydrolyzed and is extremely unstable. In addition, because it is extremely difficult to control the atmosphere during hydrolysis and heating and baking, especially the partial pressure of water vapor, defects such as cracks and pinholes occur in the formed thin film, resulting in conductivity. It is difficult to obtain a dielectric thin film having properties, particularly dielectric properties, and the publication does not specifically describe electrical properties. Generally, in order to obtain a high dielectric constant, it is necessary to crystallize the dielectric composition, but in the case of thin films,
It is generally accepted that a dielectric thin film with a high dielectric constant cannot be obtained because conduction due to grain boundaries occurs due to crystallization of the thin film composition. The present invention has a high dielectric constant and a film thickness of 1000㎓.
The purpose of the present invention is to provide a homogeneous and transparent lead titanium zirconate dielectric thin film with a thickness of ~15,000㎓ and a method for manufacturing the same. As a result of intensive research to achieve the above objective, the present inventors applied an acetylacetone solution of a titanium-zirconium-lead composite organometallic compound onto a heat-resistant substrate and heated it as a precursor solution for forming lead titanium zirconate. The inventors have completed the present invention by discovering that a laminate of lead titanium zirconate thin films obtained by firing, repeating coating and heating and firing has a high dielectric constant. In the present invention, the titanium lead zirconate dielectric thin film is produced by a β-diketone solution of a mixture of an organic titanium compound, an organic zirconium compound, and a lead compound in a predetermined ratio, or a composite organic metal obtained by reacting these. A β-diketone solution of the compound is applied as a precursor solution for producing lead titanium zirconate on a heat-resistant substrate, and then heated and baked to form a lead titanium zirconate thin film, and the precursor solution is applied and heated and baked. Manufactured by repeating. As the organic titanium compound, any compound can be used as long as it is soluble in β-diketone. For example, tetraethoxytitanium, tetraisopropoxytitanium, tetrabutoxytitanium,
Titanium alkoxides such as diethoxydiisopropoxytitanium and polymers produced by their hydrolysis, some or all of the alkoxy groups of titanium alkoxides can be substituted with acetylacetone, β-diketones such as benzoylacetone, acetoacetic acid, propionylbutyric acid, Ketone acids such as benzoyl formic acid, lower alkyl esters of said ketone acids, oxyacids such as lactic acid, glycolic acid, α-oxybutyric acid, salicylic acid, lower alkyl esters of said oxyacids, oxyketones such as diacetone alcohol, acetoin, etc. Examples include titanium alkoxide derivatives substituted with residues of chelating agents such as α-amino acids such as , glycine and alanine, and amino alcohols such as aminoethyl alcohol. Further, as the organic zirconium compound, a compound having the same type of substituent as the organic titanium compound can be used. Lead compounds include lead oxide,
Inorganic compounds such as lead hydroxide and lead chloride, and lead carboxylates such as lead acetate can be used. In the present invention, a solution of β-diketone, such as acetylacetone or benzoylacetone, which is a mixture of the above-described organic titanium compound, an organic zirconium compound, and a lead compound in a predetermined ratio, or a solution of an organic titanium compound, an organic zirconium compound, and a lead compound, such as acetylacetone, benzoylacetone, etc. A lead-containing complex organometallic compound obtained by reacting at a predetermined ratio, preferably,
It is obtained by reacting titanium alkoxide with zirconium alkoxide and lead carboxylate, which was proposed by the present applicant in JP-A-58-41723. Composition formula (1) Pb・MO ₂ (OR) _n・(COOR′) _o ...(1) (Here, M is titanium and zirconium atom, R and R′ represent the same or different alkyl group or aryl group. , m and n are 0, 1 or 2, and m+
n is 2. ) of the lead-containing complex organometallic compound represented by β
- Using a diketone solution as a precursor solution for lead titanium zirconate production. The concentration of the metal compound in the precursor solution is 5 to 20% by weight in terms of composite metal oxide, that is, lead titanium zirconate. If the concentration of the metal compound is too low, the thickness of the lead titanium zirconate thin film formed by one coating and heating and baking will be too thin, and the number of repetitions of coating and heating and baking will have to be increased, and it will also be too high. , the coating thickness of the precursor formed by one application becomes thicker,
This is not preferred because cracks are likely to occur during heating and firing. In addition to β-diketone, methanol,
Lower alcohols such as ethanol, isopropanol, and butanol, and lower esters such as methyl formate, methyl acetate, ethyl acetate, methyl acetoacetate, and propyl acetoacetate can also be used, but β-diketones are preferred from the viewpoint of stability of the precursor solution. Particularly preferred is acetylacetone. In the present invention, a glass plate, a ceramic plate, a glass plate or ceramic plate coated with a conductive thin film, a metal plate, a metal foil, etc. can be used as the heat-resistant substrate on which the lead titanium zirconate thin film is formed.
Any known coating method such as dipping method, spray method, spinner method, printing method, or brush coating method can be used to apply the precursor solution onto the heat-resistant substrate. A dipping method that easily provides a homogeneous coating film is preferred, and a hot dipping method in which dipping is carried out while maintaining the temperature of the precursor solution at 40 to 95° C. is more preferred. The heating and firing temperature of the heat-resistant substrate coated with the precursor solution varies depending on the type and concentration of the metal compound in the precursor solution, the type of solvent, the type of the heat-resistant substrate, etc., but is at least the crystallization temperature of lead titanium zirconate. Must be heated to a temperature of 450-800℃, preferably 500-700℃
It is. The lead titanium zirconate dielectric thin film of the present invention is manufactured to have a predetermined total thickness by repeating the application of the precursor solution and heating and baking a plurality of times. The number of repetitions of coating and heating and baking is 2 to 10 times, preferably 5 to 10 times.
If the coating is applied and fired once, thin film defects such as pinholes remain and conduction occurs, and if the coating is repeated more than once, no further improvement in electrical properties is observed, which is not preferable. The composition of the lead titanium zirconate dielectric thin film obtained by the present invention is not particularly limited, but the preferred range is the composition formula (2) Pb(Zr _x Ti _y ) O ₃ ... (2) (where x is 0.7 ~0.45 y is 0.3 to 0.55 and x+y=1), preferably the total thickness is
It is a thin film with a thickness of 1,000 to 15,000, and has particularly excellent electrical properties. The titanium lead zirconate dielectric thin film of the present invention has excellent electrical properties and can be used not only as a thin film capacitor but also as a pyroelectric material and a piezoelectric material. The reason why the lead titanium zirconate dielectric thin film of the present invention has a high relative dielectric constant is that, surprisingly, the crystal axes of the lead titanium zirconate crystals are oriented in a certain direction, and the lead titanium zirconate thin film has a high dielectric constant. This is because the multilayer structure repairs thin film defects such as pinholes, and at the same time prevents electrical conduction through grain boundaries. The present invention provides a lead titanium zirconate dielectric thin film having excellent electrical properties and a thickness that has been conventionally considered difficult to manufacture, and a method for manufacturing the same, and has extremely great industrial significance. Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the scope of the present invention is not limited in any way by the following examples. Example 1 Preparation of lead titanium zirconate precursor solution: Lead oxide: PbO, zirconium acetylacetonate: Zr・(CH ₃ COCHCOCH ₃ ) ₄ and tetrabutoxytitanium: Ti・(OC ₄ H ₉ ) ₄ , and PbTiO ₃ /
PbZrO ₃ was weighed and placed in acetylacetone so that the molar ratio was 45/55.
The mixture was heated to a temperature of 0.degree. C. to react, thereby preparing a titanium lead zirconate precursor solution having a concentration of 12.5% by weight in terms of composite metal oxide. The prepared precursor solution was heated to dry up the solvent, and then thermally decomposed at a temperature of 500°C to obtain a yellow powder. As a result of performing X-ray diffraction on the obtained yellow powder, it was confirmed that it was a crystal of lead titanium zirconate. The X-ray diffraction pattern of the obtained yellow powder is shown in FIG. Production of lead titanium zirconate dielectric thin film: A glass substrate coated with a tin-doped indium oxide transparent conductive film (ITO film) is immersed in the prepared lead titanium zirconate precursor solution kept at 50 to 60°C. Then, a coating film of lead titanium zirconate precursor was formed by pulling at a speed of 47 cm/min. Next, in an electric furnace heated to a temperature of 500°C,
It was heated and baked for 30 minutes. This dipping and heating baking were repeated to obtain a transparent thin film body. As a result of performing X-ray diffraction on the obtained thin film body, it was confirmed that it was a thin film body of lead titanium zirconate. Table 1 shows the number of repetitions of dipping and heating and firing and the electrical properties of the obtained lead titanium zirconate thin film body. Moreover, the X-ray diffraction pattern of the obtained lead titanium zirconate thin film body is shown in FIG.

[Table] Example 2 Synthesis of lead-containing complex organometallic compound: Lead propionate: Pb (OCOC ₂ H _s ) ₂ , tetrabutoxyzirconium: Zr (OC ₄ Hg) ₄ and tetrabutoxytitanium: Ti (OC ₄ Hg) ₄ and PbTiO ₃ /
PbTiO ₃ was weighed out so that the molar ratio was 50/50, and reacted by heating it to a temperature of 130 to 140°C in decalin. Low-boiling substances were distilled off under reduced pressure to obtain a powdery reaction product. From the IR analysis, elemental analysis of Pb, Ti, and Zr, and the distilled amounts of butanol and butyl acetate, the average composition of the reaction product obtained was:
Pb・Ti _0.5・Zr _0.5・O ₂ (OC ₄ Hg) _1.4・(OCOC ₂ H ₅ ) _0.
I admitted that it was ₆ . The resulting reaction product powder was thermally decomposed at a temperature of 600° C., and the resulting powder was subjected to X-ray diffraction, which confirmed that it was lead titanium zirconate. Production of lead titanium zirconate dielectric thin film: The lead-containing composite organometallic compound powder obtained above was dissolved in acetylacetone to prepare a lead titanium zirconate forming precursor solution having a concentration of 12.5% by weight in terms of composite oxide. After applying the precursor by dipping a glass substrate coated with an ITO film under the same conditions as in Example 1 to the prepared lead titanium zirconate forming precursor solution heated and maintained at a temperature of 50 to 60 ° C. ,
Heat and bake by holding at a temperature of 500℃ for 30 minutes,
The dipping and heating and baking process was repeated four times to obtain a five-layer laminated thin film body. The electrical properties of the obtained laminated thin film body were as follows. Film thickness: d6000Å Capacitance: C0.71μF/ ^cm2 Relative dielectric constant: ε480 Dielectric loss: tanδ0.054 Specific resistance: 4×10 ¹⁰ Comparative Example 1 The lead titanium zirconate forming precursor solution prepared in Example 1 A glass substrate coated with an ITO film was dipped and heated and fired under the same conditions as in Example 1 to obtain a single-layer thin film body of lead titanium zirconate. The electrical properties of the obtained thin film could not be measured because of conductivity.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction diagram of the lead titanium zirconate powder obtained in Example 1, and FIG. 2 is an X-ray diffraction diagram of the lead titanium zirconate thin film obtained in Example 1.

Claims (1)

[Scope of Claims] 1. A β-diketone solution of a mixture consisting of an organic titanium compound, an organic zirconium compound, and a lead compound or a reaction product of an organic titanium compound, an organic zirconium compound, and a lead compound is used as a precursor for producing lead titanium zirconate. forming a lead titanium zirconate thin film in multiple layers on the heat-resistant substrate by applying the precursor solution to a heat-resistant substrate, heating and baking it, and repeating the application and heating and baking the precursor solution. A method for producing a titanium lead zirconate dielectric thin film characterized by: 2. Titanium zirconium acid according to claim 1, wherein the organic titanium compound and the organic zirconium compound are at least one of alkoxides of the metal and compounds in which part or all of the alkoxy groups of the alkoxides are substituted with a chelating agent. Method for producing lead dielectric thin film. 3. Claim 1, wherein the lead compound is at least one of lead oxide, lead hydroxide, and lead carboxylate.
A method for producing a lead titanium zirconate dielectric thin film as described in . 4. The method for producing a lead titanium zirconate dielectric thin film according to claim 1, wherein the β-diketone is acetylacetone. 5. The method for producing a lead titanium zirconate dielectric thin film according to claim 1, wherein the precursor solution has a concentration of 5 to 20% by weight in terms of lead titanium zirconate. 6. The method for producing a lead titanium zirconate dielectric thin film according to claim 1, wherein the method for applying the precursor solution to the heat-resistant substrate is a dipping method. 7 The coating temperature of the precursor solution on the heat-resistant substrate is 40~
A method for producing a lead titanium zirconate dielectric thin film according to claim 1, wherein the temperature is 90°C. 8. The method for producing a lead titanium zirconate dielectric thin film according to claim 1, wherein the heating and firing temperature of the heat-resistant substrate coated with the precursor solution is 450 to 800°C, preferably 500 to 700°C.