JPH1149567A - Dielectric thin film and ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dielectric thin film exhibiting a high relative dielectric constant even under applied DC bias, having a low temp. variation of capacitance and having a high relative dielectric constant even in a high frequency domain and to obtain a ceramic capacitor having the same characteristics. SOLUTION: The dielectric thin film is made of a perovskite type multiple oxide contg. Pb, Mg, Nb, Zr and Sn as metallic elements and has <=2 μm thickness. The compsn. of oxides of the metallic elements by molar ratio is represented by the formula (1-x-y)Pba (Mgb/3 Nb2/3 )-O3 .xPba ZrO3 .yPba SnO3 [where (x) and (y) are within the range defined by points A-B-C-D-E-A in the diagram, and further a is 1<=a<=1.10 and b is 1<=b<=1.15].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric thin film and a ceramic capacitor using the dielectric thin film.

[0002]

BACKGROUND OF THE INVENTION complex perovskite-type composite oxide of two or more metals, particularly _{Pb (Mg 1/3 Nb 2/3} ) O
₃ (hereinafter referred to as PMN) has a large relative dielectric constant at room temperature, and is therefore known to be useful as a capacitor material.

[0003] As such a PMN sintered body, conventionally,
There is known a solid phase sintering method in which bO powder, MgCO ₃ powder, and Nb ₂ O ₅ powder are collectively mixed, pulverized, and sintered. However, it is difficult to obtain a sintered body consisting essentially of a single perovskite phase in the production of a PMN sintered body by solid-phase sintering in which such a mixture is mixed and pulverized at once, and a pyrochlore phase that is stable at low temperatures is generated. Since the pyrochlore phase is easily formed and has a low relative dielectric constant, as a result, the relative dielectric constant of the sintered body becomes low, and it is often unsuitable as a capacitor material.

Therefore, in the solid-phase sintering method, synthesis is performed by a columbite method in which an MgNb oxide (MgNb ₂ O ₆ ) reacts with a Pb raw material and a Ti raw material. According to this method, it is possible to obtain a substantially single-phase perovskite sintered body, and the relative dielectric constant can be 15,000 or more. However, conventionally, it has been considered that these bulk materials have a large frequency dispersion of the relative dielectric constant, and have a low relative dielectric constant at a high frequency of 1 MHz or more, and do not function as a capacitor.

On the other hand, as electronic devices become smaller and thinner, there is a demand for smaller and thinner electronic components. In particular, miniaturization and thinning of capacitors, which are passive components, are essential. Electronic devices using high-speed digital circuits, such as computers, are in the trend of higher frequencies, and the operating frequency band from several tens of MHz to several hundreds of MHz is becoming important. Along with this, it has become essential that passive components such as capacitors also exhibit excellent characteristics with respect to high-frequency or high-speed digital pulses.

In recent years, it has been attempted to apply high dielectric constant materials such as PMN to thin films and apply them to thin film capacitors. However, in the conventional solid phase sintering method, the film thickness was at most about 10 μm. In addition, even in the case of a thin film, a pyrochlore phase that is stable at a low temperature is easily generated as in the case of a sintered body obtained by the solid phase sintering method, and it is difficult to obtain a film substantially composed of a perovskite single phase, which is often unsuitable as a capacitor material. . In particular, when a thin film is formed, it is said that there is a problem that a pyrochlore phase is easily generated due to lattice mismatch with the lower electrode and a difference in chemical bond (see, for example, JP-A-6-57437). Low perovskite single phase P
It was difficult to obtain an MN thin film.

As a method for solving the problem of the formation of the pyrochlore phase, a PMN thin film produced by a sol-gel method is subjected to a rapid heating baking method (see JP-A-2-177521) and a seeding method (see JP-A-6-177521). Various methods have been proposed, and a PMN thin film close to a perovskite single phase has been obtained.

[0008]

However, in the case of a PMN thin film formed by a rapid heating sintering method or a seeding method, a film substantially consisting of a perovskite single phase is obtained, but the relative dielectric constant at room temperature is still low, and the PMN-based At present, the original properties of the material have not been exhibited.

Further, Ba, which is a typical capacitor material, is used.
A relaxor material such as TiO ₃ and Pb (Mg _1/3 Nb _2/3 ) O ₃ shows a large relative dielectric constant at a low frequency of about 1 KHz and is an excellent material for a capacitor, but has a large frequency dispersion. For this reason, it has been considered that the relative permittivity in the high-frequency region is greatly reduced and cannot be used as a high-permittivity material in the high-frequency region (see JP-A-6-77083).

[0010]

Means for Solving the Problems As a result of intensive studies on the solution to the above problems, the present inventor has found that the bulk does not have macro spontaneous polarization, so that the DC bias dependency is small and the relative dielectric constant is large. PbZrO _3, which has a small DC bias dependency due to being an antiferroelectric substance and has a large relative dielectric constant when dissolved in PMN, and PbZrO _{3
As in the case of 3} , a material having a solid solution of PbSnO _3, which can be expected to have a high dielectric constant and can be expected to be able to shift the peak of the dielectric constant shifted to a high temperature side due to solid solution of PbZrO ₃ to a low temperature side, thereby reducing the DC. The present inventors have found that a large relative dielectric constant is exhibited even under the application of a bias, and a decrease in the relative dielectric constant is reduced even in a high-frequency region.

That is, the dielectric thin film of the present invention is a dielectric thin film having a thickness of 2 μm or less and made of a perovskite-type composite oxide containing Pb, Mg, Nb, Zr and Sn as metal elements. the composition formula by molar ratio of the object, (1-x-y) Pb a (Mg b / 3 Nb 2/3) O 3 ·
When expressed as xPb _a ZrO ₃ .yPb _a SnO ₃ , the x and y are within a range surrounded by a point ABCDCA in FIG. 1, and a and b Where 1 ≦
a ≦ 1.10 and 1 ≦ b ≦ 1.15 are satisfied. The dielectric thin film of the present invention has a relative dielectric constant of 1000 or more at a measurement frequency of 1 kHz (room temperature) and a relative dielectric constant of 10 at a measurement frequency of 100 MHz (room temperature).
It has characteristics of 00 or more.

A ceramic capacitor according to the present invention comprises a pair of electrodes formed on both surfaces of the dielectric thin film so as to face each other.

[0013]

According to the dielectric thin film of the present invention, the DC thin film does not have macro spontaneous polarization and thus has excellent DC bias characteristics, and PMN having a high dielectric constant has a small DC bias dependency because it is an antiferroelectric material. PbZrO _3, which can be expected to improve relative dielectric constant by solid solution with PMN, and PMN and PbZrO ₃
Since it has the same structure as above and has a relative dielectric constant peak at room temperature and at a lower temperature side than PMN, the temperature at which the relative dielectric constant of the PMN-PbZrO ₃ solid solution having a relative dielectric constant peak at a higher temperature side than room temperature becomes the maximum near room temperature By dissolving PbSnO ₃ in a solid solution, the material can have a high dielectric constant and excellent DC bias characteristics at room temperature.

Further, by forming a thin film, the average crystal grain size of the perovskite-type composite oxide is reduced to the order of submicron, and the paraelectric property becomes more dominant. DC bias characteristics can be improved.

Further, even at a high frequency such as 100 MHz, since there is no macro spontaneous polarization which is the origin of ferroelectricity, the frequency dispersion of the dielectric constant caused by the spontaneous polarization is small.
It shows a large relative dielectric constant even at high frequencies.

In the ceramic capacitor of the present invention, for example, platinum (Pt) or gold (A) having a thickness of 0.05 μm or more is formed on both surfaces of the dielectric thin film having the excellent characteristics as described above.
u), by forming a pair of electrodes which are palladium (Pd) thin films facing each other, it is possible to obtain a ceramic capacitor excellent in high dielectric constant even at high frequencies.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dielectric thin film of the present invention has a thickness of 2 μm.
m, for example, a sol-gel method, PV
It is manufactured by the D method, the CVD method, or the like. Here, the reason why the dielectric thin film having a film thickness of 2 μm or less is that when the thickness is larger than this, the number of steps increases, and when a capacitor is formed, the capacitance decreases. The thickness of the dielectric thin film is desirably 1 μm or less in view of easiness of manufacturing and deterioration of film quality.
m is desirable.

Further, the composition formula based on the molar ratio is expressed as (1-x-
_{y) Pb a (Mg b /} 3 Nb 2/3) O 3 · xPb a ZrO
_When expressed as ₃ · yPb _a SnO ₃ , x and y are as shown in FIG.
Satisfies the range of the area surrounded by the points ABCDCEA, and a and b satisfy 1 ≦ a ≦ 1.10.
It satisfies b ≦ 1.15.

As described above, the molar ratio x indicating the amount of PbZrO ₃ is set to be equal to or less than the line segment CDE in FIG.
Since the relative permittivity at room temperature rapidly decreases when the relative permittivity exceeds −DE, the relative permittivity at 100 MHz becomes 100
This is because it becomes smaller than 0.

To improve the relative dielectric constant, the range of x is 0.0
It is desirable that 1 ≦ x ≦ 0.20.

The reason why the molar ratio y indicating the amount of PbSnO ₃ is set to be equal to or less than the line segment BCD is that when y is larger than the line segment BCD, the generated main crystal phase has a low dielectric constant. This is because it becomes a pyrochlore structure. To improve the relative dielectric constant, the range of y is desirably 0.01 ≦ y ≦ 0.05. Therefore, x and y in the above composition formula are 0.01 ≦ x ≦ 0.
20 and 0.01 ≦ y ≦ 0.05.

The reason why a is set to 1 to 1.1 is that a is 1
If it is smaller than this, a pyrochlore phase is generated and the relative permittivity decreases, and if it is larger than 1.1, PbO precipitates at the grain boundary and the relative permittivity decreases. a is 1.05 to 1.05 because the reproducibility of the characteristics is good.
1.1 is desirable.

Further, b is set to 1 to 1.15 because b
Is smaller than 1 or larger than 1.15, the relative dielectric constant decreases. b is desirably 1 to 1.1 because the reproducibility of characteristics is good.

Also, the ceramic capacitor of the present invention
A pair of electrodes are formed on both surfaces of the above-mentioned dielectric thin film so as to face each other, and a multilayer ceramic capacitor in which dielectric thin films and electrodes are alternately stacked is of course included.

The thickness of the capacitor electrode is 0.05
There are platinum (Pt), gold (Au), palladium (Pd) thin films and the like oriented at μm or more, and among these, oriented platinum (Pt) and gold (Au) thin films are most suitable. Pt, A
This is because u has low reactivity with the film and is hardly oxidized, so that a low dielectric constant phase is hardly formed at the interface with the film.

The reason why the film thickness is set to 0.05 μm or more is 0.0
This is because if it is less than 5 μm, the equivalent series resistance in the high frequency region increases. An oriented platinum (Pt) thin film is an oriented or single-crystal platinum (Pt) thin film, and an oriented Pt thin film has one of three crystal axes approximately perpendicular to the film surface. The single-crystal Pt thin film is a film in which all three crystal axes are aligned. Such an electrode has a substrate temperature of 45 degrees on which the electrode is formed in physical vapor deposition such as sputtering vapor deposition or laser vapor deposition.
It is obtained at a temperature of 0 ° C. or higher, and among these, sputter deposition at a substrate temperature of 450 ° C. or higher is desirable.

As a substrate on which a metal thin film is deposited,
Alumina, sapphire, MgO single crystal, SrTiO ₃ single crystal, titanium coated silicon, or copper (Cu), nickel (Ni), titanium (Ti), tin (Sn), stainless steel (SUS) thin film or thin plate is desirable.
In particular, alumina and sapphire are desirable in terms of low reactivity with the thin film, low cost, high hardness, and crystallinity of the metal thin film, and copper (C) is preferable in terms of low resistance in a high frequency region.
u) Thin or copper (Cu) thin films are preferred.

In the ceramic capacitor of the present invention, for example, Pt, Au, Pd, or the like is formed on a substrate by a method such as sputtering, vapor deposition, or gravure printing to form a lower electrode, and the surface of the lower electrode film is formed. Then, the dielectric thin film is formed by forming a film by the above method, and thereafter, an upper electrode is formed on the surface of the dielectric thin film in the same manner as the lower electrode. A multilayer ceramic capacitor is obtained by alternately stacking dielectric thin films and electrodes.

The dielectric thin film of the present invention is produced, for example, as follows. First, at least one selected from organic acid salts, inorganic salts, and alkoxides of Mg and Nb.
Kind of Mg compound and Nb compound is Mg: Nb = b: 2 (1
≦ b ≦ 1.15) in a molar ratio of R ₁ OH, R ₂ OC ₂ H ₄
OH and R ₃ COOH (R ₁ , R ₂ , R ₃ : an alkyl group having 1 or more carbon atoms) are mixed in a solvent. After mixing, in order to obtain a high relative dielectric constant, a predetermined operation is performed, and an Mg-based compound having an absorption near 656 cm ^{-1 in} the IR spectrum and stable even in the presence of another nucleophilic organometallic compound is obtained.
A MgNb composite alkoxide molecule having an O-Nb bond is synthesized.

In order to obtain a MgNb composite alkoxide molecule having an absorption near 656 cm ^{-1 in the} IR spectrum, there are the following methods.

A first method is to mix the alkoxide raw materials of Mg and Nb with a solvent, raise the temperature of the solution to the boiling point of the solvent, and perform a reflux operation.

As a second method, the alkoxide raw materials of Mg and Nb are mixed with a solvent as described above, the temperature of the solution is raised to the boiling point of the solvent, and complexation is performed by a reflux operation. A method of adding a stabilizer represented by amine, acetylacetone and the like.

As a third method, a deesterification reaction in a molecule is promoted by a reflux operation of a carboxylate of Mg and an alkoxide of Nb.

As a fourth method, Mg hydroxide and Nb
A alkoxide of Mg or an alkoxide of Mg and a hydroxide of Nb to promote an intramolecular dealcoholization reaction.

A fifth method is to add a stabilizer such as acetic anhydride, ethanolamine or acetylacetone to the lead precursor in order to reduce the nucleophilicity of the lead precursor.

By using any of the above methods, a MgNb composite alkoxide molecule having a stable Mg—O—Nb bond can be synthesized even in the presence of another nucleophilic organometallic compound. Of these, the first or second method is most desirable.

Further, a mixed solution of water and a solvent is appropriately applied to the synthesized MgNb composite alkoxide solution, and partial hydrolysis is carried out to form the above-mentioned MgNb composite alkoxide polycondensed MgNb sol. The partial hydrolysis is a method in which a part of an alkoxyl group in a molecule is substituted with a hydroxyl group, and polycondensation is performed by dehydration or dealcoholation reaction in the substituted molecule.

Next, at least one Sn compound selected from organic acid salts, inorganic salts and alkoxides of Sn is converted to R ₁ O
H, R ₂ OC ₂ H ₄ OH, R ₃ COOH (R ₁ , R ₂ ,
R ₃ : an alkyl group having 1 or more carbon atoms) to prepare a Sn solution.

One kind of Zr compound selected from organic acid salts, alkoxides and the like of Zr is represented by R ₁ OH, R ₂ OC ₂ H ₄ O
It is mixed with a solvent represented by H and R ₃ COOH (R ₁ , R ₂ , R ₃ : an alkyl group having 1 or more carbon atoms) to prepare a Zr solution.

The prepared Mg—Nb solution, Zr solution and Sn
The solution was treated with Mg-Nb: Zr: Sn = (1-xy): x:
After mixing at a molar ratio of y and refluxing at 124 ° C, the mixture was cooled to room temperature, and a chelating agent such as acetylacetone was added to Mg-Nb-
Add and mix at least 0.5 times the amount of metal in the Zr-Sn solution.

Next, at least one lead compound selected from an organic acid salt, an inorganic salt and an alkoxide of lead (Pb) is converted to R ₁ OH, R ₂ OC ₂ H ₄ OH, R ₃ COOH (R ₁ ,
R ₂ and R ₃ : an alkyl group having 1 or more carbon atoms) to prepare a Pb precursor solution. When the lead compound contains water of crystallization, dehydration treatment is performed so that water does not exist in the produced Pb precursor solution.

The prepared Pb precursor solution or lead acetate
Organic acid salt of lead (Pb) such as trihydrate and Mg-Nb-
A Zr—Sn solution or a Mg—Nb—Zr—Sn sol is converted into Pb: (Mg + Nb + Zr + Sn) = a: [(b +
2) / 3 + [(1-b) / 3] (x + y)] (1 ≦ a ≦
1.10, 1 ≦ b ≦ 1.15) at a molar ratio of PM
This is an N-PZ-PS precursor solution.

The prepared coating solution is formed on a substrate by a method such as spin coating, dip coating, or spraying.

After the film formation, a heat treatment is performed at a temperature of 300 ° C. to 400 ° C. for 1 minute, and the organic matter remaining in the film is burned to form a gel film. The thickness of each film is preferably 0.1 μm or less.

After the film formation and heat treatment are repeated until the film thickness reaches a predetermined value, baking is performed at 750 ° C. to 850 ° C. to produce the crystalline dielectric thin film of the present invention. The thickness of the obtained dielectric thin film is 2 μm or less. If the thickness is larger than this, the number of steps increases, and if a capacitor is formed, the capacitance decreases.

[0046]

EXAMPLES Mg ethoxide and Nb ethoxide were added in an amount of 1.0.
The mixture was weighed in a molar ratio of 5: 2, refluxed in 2-methoxyethanol (17 hours at 124 ° C.), and 1M (mol
/ L) MgNb composite alkoxide solution of concentration was synthesized. In the IR spectrum, Mg around 656 cm ⁻¹
Absorption due to -O-Nb bond was observed.

Next, Zr propoxide was dissolved in 2-methoxyethanol at room temperature to prepare a 1M Zr solution.

Next, Sn propoxide was mixed with 2-methoxyethanol at room temperature to prepare a 1M Sn solution.

A 1M Sn solution and a Zr solution were mixed with Mg
In an Nb composite alkoxide solution, (Mg + Nb): Zr:
After mixing at a ratio of Sn = 1-xy: x: y, acetylacetone was added in an amount of 1 times the total metal amount of the Mg-Nb-Zr-Sn solution, and then stirred at room temperature for 10 minutes to stabilize. Was.

Pb: (Mg + Nb) was added to a Mg—Nb—Zr—Sn solution by adding lead acetate trihydrate and 2-methoxyethanol.
+ Zr + Sn) = 1.05: [3.05 / 3] (1-x
-Y) + (x + y), and stirred for 1 hour at room temperature to obtain 1M Pb _1.05 (Mg _{1.05 / 3}
Nb _2/3 ) _(1-xy) Zr _x Sn _y O ₃ precursor solution was synthesized.

The coating solution was applied by a spin coater to the surface of the Pt electrode on a sapphire single crystal substrate on which Pt (111) to be an electrode was sputter deposited at 650 ° C.
After drying, a heat treatment was performed at 380 ° C. for 1 minute to produce a gel film. After repeating the operation of coating and heat treatment of the coating solution 11 times, calcination was performed at 820 ° C. for 0.5 minute (in air) by rapid temperature rise baking to obtain a 0.82 μm-thick Pb _1.05 (Mg
_{1.05 / 3} Nb _2/3 ) _(1-xy) Zr _x Sn _y O ₃ thin film was obtained. From the X-ray diffraction result of the obtained thin film, the perovskite generation rate was calculated to be about 95%.

A gold electrode having a diameter of 0.2 mm was formed on the surface of the formed thin film having a thickness of 0.82 μm by sputter deposition to prepare a ceramic capacitor, and then heat-treated at 500 ° C. for 10 minutes. Using an LCR meter (4284A manufactured by Hewlett-Packard Co.), 25 ° C., 1 kHz (AC10
The relative dielectric constant was determined under the condition of 0 mV).

Further, the DC bias characteristics are defined as a relative dielectric constant K ₀ when no voltage is applied at room temperature, a DC electric field of 3 V
When the relative dielectric constant at the time of applying a voltage of / μm is K ₁ , the relative dielectric constant was determined by (K ₀ −K ₁ ) / K ₀ × 100, and is shown in Table 1.

Next, a gold electrode having a diameter of 0.05 mm was formed on the surface of the formed film having a thickness of 0.82 μm by sputter deposition to form a ceramic capacitor, and then heat-treated at 500 ° C. for 10 minutes. About this ceramic capacitor, an impedance analyzer (HP4291A, fixture HP16092, manufactured by Hewlett-Packard Company)
A) and 1 MHz to 1.8 using a microprobe
The characteristics were evaluated at GHz. By measuring the impedance-frequency characteristics, the equivalent series capacitance at 100 MHz was evaluated, and the relative permittivity was determined. Table 1 shows these results.
It describes in.

[0055]

[Table 1]

As can be seen from Table 1, the dielectric thin film of the present invention has a high dielectric constant of 1000 or more at 100 MHz, while the comparative examples all have a dielectric constant of 100 MHz.
It can be seen that the relative dielectric constant at is lower than 1000.

Further, the ratio of Mg ethoxide to Nb ethoxide was set to b (0.9 to 1.2): 2, and an MgNb composite alkoxide solution was synthesized, and lead acetate trihydrate and 2-methoxyethanol were converted to Mg- Pb in Nb-Zr-Sn solution:
(Mg + Nb + Zr + Sn) = a (0.9-1.2):
[[B (0.9-1.2) +2] / 3] (1-xy)
A dielectric thin film was prepared in the same manner as in the above example, except that mixing was performed so that + (x + y) was obtained, and the characteristics were measured in the same manner as in the above example. The results are also shown in Samples Nos. 17 to 25 in Table 1.

From Table 1, it can be seen that the dielectric thin film of the present invention
It has a high dielectric constant of 1000 or more at 00 MHz, and the relative dielectric constant decreases by less than 30% even when an electric field of 3 V / μm is applied.
It can be seen that the relative dielectric constant at kHz is lower than 1000.

The capacitance change rate TCC at −25 ° C.
(%) Is the capacitance of -25 ° C. and C _{-2 5,} when the electrostatic capacitance of 25 ° C. was _{C 25, (C -25 -C 25} ) × 100 /
Determined by C _25, the change rate of the capacitance 85 ° C. (%) is 85
The capacitance of ° C. and C _85, when the electrostatic capacitance of 25 ° C. was C _25, obtained in the _{(C 85 -C 25) × 100} / C 25.

Further, the inventor of the present invention prepared a composition consisting of sample No. 6 in the same manner as described above except that the number of repetitions of the coating solution application-heat treatment operation was changed so that the thickness was 1 μm and 2 μm. A dielectric thin film was prepared, and its characteristics were measured in the same manner as described above. The case where the thickness was 1 μm was described as Sample No. 26, and the case where the thickness was 2 μm was described as Sample No. 27.

[0061]

As described in detail above, the dielectric thin film of the present invention has excellent DC bias characteristics and temperature characteristics, and has a large relative dielectric constant even at a high frequency such as 100 MHz. And I
It can be widely applied as a capacitor used at a high frequency such as a decoupling capacitor around C.

[Brief description of the drawings]

FIG. 1 is a view showing a range of x and y in the above composition formula.

Claims (3)

[Claims] 1. A dielectric thin film having a thickness of 2 μm or less made of a perovskite-type composite oxide containing Pb, Mg, Nb, Zr, and Sn as metal elements, wherein a composition formula based on a molar ratio of the metal element oxide is (1-x-y) Pb a (Mg b / 3 Nb 2/3) O 3 · xP
When expressed as b _a ZrO ₃ .yPb _a SnO ₃ , the x and y are points ABC- in FIG.
A dielectric thin film which is within a range surrounded by D-E-A, and wherein a and b satisfy 1 ≦ a ≦ 1.10.1 ≦ b ≦ 1.15. 2. The dielectric constant at a measurement frequency of 1 kHz (room temperature) is 1000 or more, and the measurement frequency is 100 M
2. The dielectric thin film according to claim 1, wherein a relative dielectric constant at Hz (room temperature) is 1000 or more. 3. A ceramic capacitor comprising a pair of electrodes formed on both surfaces of the dielectric thin film according to claim 1 so as to face each other.