JP2001338839A - Variable capacitance capacitor - Google Patents

Abstract

(57) Abstract: Provided is a variable capacitor in which the rate of change in capacitance is large, the loss is sufficiently small even at a high frequency, and the frequency change when an oscillator is formed is linear with applied voltage. Kind Code: A1 A variable capacitor formed by forming electrodes on both surfaces of a dielectric film, wherein the thickness of the dielectric film is 1 μm or less, and the dielectric film is a metal element. A perovskite-type composite oxide containing at least Pb, Mg and Nb is used as a main crystal particle, and the average particle size of the main crystal particle is 0.3 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable capacitor whose capacitance changes in accordance with an applied voltage.
The present invention relates to a variable capacitor having a dielectric film having a high rate of change in dielectric constant and a small dielectric loss even at high frequencies.

[0002]

2. Description of the Related Art An oscillator (voltage-controlled oscillator, VCO) whose oscillation frequency can be controlled by an applied voltage is realized by changing the resonance frequency of an LC resonator constituting the oscillator according to a voltage. In order to change the resonance frequency of the LC resonator according to the voltage, an element whose capacitance changes according to the voltage is used as the capacitor C.

Conventionally, as an element whose capacitance changes according to a voltage, a diode called a varactor diode whose capacitance changes according to a reverse bias voltage is used.

[0004] Diodes are used in rectifier circuits and the like utilizing the fact that current flows when a forward bias is applied to a PN junction. At the junction surface, there is a region called a depletion layer where neither electrons nor holes exist.When a reverse bias is applied to the diode, both the electrons and holes are pulled away from the junction surface, so the depletion layer becomes thicker and depleted. The layer thickness varies depending on the magnitude of the reverse bias.

Since the depletion layer can be considered as a dielectric, when a reverse bias is applied to the diode, the thickness of the dielectric changes depending on the magnitude of the reverse bias, and as a result, the capacitance changes. Can be used as

A varactor diode has been standardized especially for use as a variable capacitance capacitor. A VCO using a varactor diode has been used as a local oscillator of a communication device such as a mobile phone, but in recent years it has been reduced in consumption. As power consumption increases, control of capacitance at a low voltage is also required for variable capacitance elements.

However, in a varactor diode, the depletion layer becomes thin at a low voltage, so that a leak current increases and it is theoretically difficult to use the varactor at a low voltage. In addition, since the capacitance of a diode changes greatly at a low voltage, and the subsequent change is smaller than that of a low voltage region, taking into account the problem of leakage current, the capacitance that can be actually used even if the entire capacitance variable range of the element is large. There is a problem that the variable range is limited, and as a result, there is a problem that the frequency variable range when an oscillator is configured is limited, and the variation width of the oscillation frequency is small.

Furthermore, since the change in capacitance at a low voltage is large, the change in resonance frequency obtained as a result of the change in capacitance of the varactor diode is not linear with respect to the applied voltage, so that it is difficult to control the frequency of the oscillator. There was also a problem.

For this reason, recently, (Ba, Sr) TiO ₃ (BST) has been used as an element replacing a varactor diode.
There has been proposed a variable capacitor using a dielectric film made of (see, for example, JP-A-10-3839).

In such a variable capacitor using BST, the BST itself is a dielectric material whose dielectric constant changes according to an applied voltage, and is a material having a small dielectric loss at high frequencies. The dielectric loss at a high frequency of BST is about 0.01 at 1 GHz, and the capacitance change rate is a bias voltage of 0 to 15 V.
Was about 35% at the maximum.

[0011]

However, the above B
In the variable capacitor using ST, although the dielectric loss at a high frequency is small, the change rate of the dielectric constant of BST is still small, so that the capacitor also has a small change rate of the capacitance, and the frequency is variable when an oscillator is formed. There was a problem that the range was limited.

The present invention provides a variable capacitor having a large capacitance change rate, a sufficiently small loss even at a high frequency, a wide frequency variable range when an oscillator is formed, and a frequency change linear with applied voltage. The purpose is to do.

[0013]

A variable capacitor according to the present invention is a variable capacitor having electrodes formed on both sides of a dielectric film, wherein the dielectric film has a thickness of 1 μm or less, The dielectric film has perovskite-type composite oxide containing at least Pb, Mg and Nb as metal elements as main crystal particles, and the average particle size of the main crystal particles is 0.3 μm or less.

In such a variable capacitor, P
b, Mg, and Nb-containing perovskite-type composite oxide as main crystal particles, and the average particle size of the main crystal particles is 0.1 mm.
By using a dielectric film having a thickness of 3 μm or less and a film thickness of 1 μm or less, the rate of change of the dielectric constant by applying a voltage is large, the dielectric loss is sufficiently small even in a high frequency region, and the frequency variable range when configuring an oscillator is wide. Although the reason is not clear, the frequency change when the resonator is formed can be made linear with respect to the applied voltage.

That is, the series resistance of the dielectric is R, the capacitance is C,
If the frequency is ω, the loss of the dielectric at high frequency is Rω
It can be expressed as C. Here, assuming that the area of the dielectric is S and the thickness is d, RωC = ρ (d / S) ωε0εr (S / d) = ρω
ε0εr. Here, ρ is the resistivity of the dielectric, ε0 is the permittivity in a vacuum, and εr is the relative permittivity of the dielectric. From this, it can be seen that one way to reduce the dielectric loss at high frequencies is to reduce the relative dielectric constant of the dielectric while keeping the large change rate of the dielectric constant and the linearity of the resonance frequency change.

Therefore, in the present invention, by setting the average particle diameter of the main crystal grains to 0.3 μm or less, the relative permittivity of the dielectric can be reduced, and the large change rate of the capacitance and the linearity of the resonance frequency change can be achieved. , The dielectric loss at high frequencies can be reduced. Thus, since the dielectric loss can be reduced,
The resonance peak in the impedance characteristic becomes sharp, and it becomes easy to control the resonance peak to a desired oscillation frequency.

Further, the variable capacitor according to the present invention is a variable capacitor having electrodes formed on both surfaces of a dielectric film, wherein the dielectric film has a high dielectric constant dielectric film and a low dielectric constant dielectric film. Wherein the high dielectric constant dielectric film has perovskite-type composite oxides containing at least Pb, Mg and Nb as metal elements as main crystal grains.

In such a variable capacitor, since the dielectric film is formed by laminating a high-dielectric-constant dielectric film and a low-dielectric-constant dielectric film, capacitors composed of the respective dielectric films are connected in series. With this structure, dielectric loss at high frequencies can be further reduced. In addition, since the high dielectric constant dielectric film is made of a perovskite-type composite oxide containing Pb, Mg, and Nb as main crystal particles, a large capacitance change rate and linearity of resonance frequency change can be maintained.

Here, since the relative dielectric constant of the dielectric can be reduced by setting the average particle diameter of the main crystal grains of the high dielectric constant dielectric film to 0.3 μm or less, the dielectric loss at a high frequency can be further reduced. .

Further, by forming the low dielectric constant dielectric film only from crystal grains made of a pyrochlore type composite oxide containing at least Pb, Mg and Nb as metal elements, a large capacitance change rate and a resonance frequency change can be obtained. The dielectric loss at high frequencies can be further reduced while maintaining the linearity. In this case, the high dielectric constant dielectric film and the low dielectric constant dielectric film can be formed by using the same material and changing the manufacturing method.

Further, it is desirable that the low dielectric constant dielectric film is made of a perovskite-type composite oxide containing at least Pb and Ti as metal elements as main crystal grains. As a result, the rate of change of the capacitance of the low dielectric constant dielectric film can be changed by the applied voltage, and the dielectric loss at a high frequency is further reduced while maintaining the large rate of change of the capacitance and the linearity of the resonance frequency change. Can be.

Further, the thickness of the low dielectric constant dielectric film is set to 0.1 μm.
By setting m or less, the rate of change of the dielectric constant of the low dielectric constant dielectric film can be kept large.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A variable capacitor according to the present invention will be described below in detail with reference to FIG. FIG. 1 is a sectional view of a capacitor according to the present invention, wherein reference numeral 1 denotes an insulating substrate, 2 denotes a lower electrode, 3 denotes a dielectric film, and 5 denotes an upper electrode.

The insulating substrate 1 is a ceramic substrate such as alumina or a single crystal substrate such as sapphire, and the lower electrode 2 is formed on the insulating substrate 1.

The lower electrode 2 is made of Pt, Au, Ti or the like, has a thickness of 0.1 to 0.5 μm, and is made of, for example, an insulating sapphire single crystal such that the crystal plane of Pt is (111). It is formed by sputtering at 500 ° C. on the substrate 1. On this lower electrode 2, a dielectric film 3 is formed.

The thickness of the dielectric film 3 is 1 μm or less, and a perovskite-type composite oxide containing at least Pb, Mg and Nb as metal elements is used as main crystal particles, and the average particle size of the main crystal particles is 0 μm. 0.3 μm or less.

The reason why the thickness of the dielectric film 3 (hereinafter, sometimes referred to as PMN dielectric film 3) is set to 1 μm or less is that when the thickness is larger than 1 μm, the number of manufacturing steps of the thin film dielectric film is reduced. This is because, when a variable capacitor is configured, the applied voltage for changing the capacitance increases. The thickness of the dielectric film 3 is desirably 0.3 to 1 μm for the above reason.

The average particle size of the main crystal particles is 0.3 μm.
The reason for the following is to reduce the dielectric constant of the dielectric film and reduce the dielectric loss. On the other hand, if it is larger than 0.3 μm, there is almost no effect of reducing the dielectric loss.

A dielectric film having a perovskite-type composite oxide containing at least Pb, Mg and Nb as metal elements as main crystal grains is a ferroelectric substance, has a high relative permittivity and a small dielectric loss. For this reason, the permittivity changes according to the applied voltage, and the change rate is large.

That is, the dielectric constant of the dielectric film changes according to the applied voltage. In order to obtain a large change rate of the dielectric constant, a pyrochlore phase which is a paraelectric substance does not exist (Pb, Mg and Nb). Of a perovskite-type composite oxide containing When an oscillator is configured using a variable capacitor, the loss of the capacitor is required to be low. However, the loss at a high frequency of the capacitor is RωC = ρ (d / S) ωε0ε as described above.
r (S / d) = ρωε0εr.

In order to obtain a variable capacitor, it is necessary to use a ferroelectric as a dielectric. However, in a ferroelectric having a high dielectric constant, a loss at a high frequency becomes large in principle. Since the dielectric constant of a bulk ferroelectric decreases as the particle diameter decreases, the dielectric constant of the thin film can be reduced by making the crystal grains fine, and the loss can be reduced.

An upper electrode 5 is formed on the high dielectric constant dielectric film 3. The upper electrode 5 is formed, for example, by sputtering Pt, Ti, Au or the like on the dielectric film 3.

The dielectric film 3 is made of Pb or M as a metal element.
It is formed by applying a coating solution by spin coating or the like so as to obtain a perovskite-type composite oxide containing g and Nb, and then subjecting the dried gel film to heat treatment.

Specifically, the dielectric film 3 is manufactured, for example, as follows. First, Pb as a coating solution,
A precursor solution in which organometallic compounds of Mg and Nb are uniformly dissolved is prepared.

That is, at least one type of Mg selected from organic acid salts, inorganic salts, and alkoxides of Mg and Nb.
The compound and the Nb compound are represented by Mg: Nb = b: 2 (1.00 ≦
b ≦ 1.15) in a molar ratio of R ₁ OH, R ₂ OC ₂ H ₄ OH,
It is mixed with a solvent represented by R ₃ COOH (R ₁ , R ₂ , R ₃ : an alkyl group having 1 or more carbon atoms).

After mixing, predetermined operations are performed to obtain an Mg—O— salt having an absorption near 656 cm ⁻¹ in the IR spectrum and stable even in the presence of another nucleophilic organometallic compound.
A MgNb composite alkoxide molecule having an Nb bond is synthesized.

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

As a first method, an alkoxide raw material of Mg and Nb is mixed with a solvent, the temperature of the solution is raised to the boiling point of the solvent, and a reflux operation is performed in the presence of a catalyst such as an acid to obtain an intramolecular compound. To promote the deetherification reaction in water.

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.

A third method is to accelerate the intramolecular deesterification reaction by refluxing the carboxylate of Mg and the 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 the above-mentioned stabilizing agent such as acetic anhydride, ethanolamine or acetylacetone 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. Among these, the method of adding a stabilizer after the second reflux operation is most desirable.

Further, a mixed solution of water and a solvent is appropriately applied to the synthesized MgNb composite alkoxide solution to partially hydrolyze to form the MgNb sol in which the above-mentioned MgNb composite alkoxide is polycondensed.

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 lead compound selected from an organic acid salt, an inorganic salt and an alkoxide of lead (Pb) is converted into R ₁ OH, 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).

At this time, when the lead compound contains water of crystallization, dehydration treatment is performed so that water does not exist in the prepared Pb precursor solution.

The prepared Pb precursor solution and the MgNb composite alkoxide solution or the MgNb sol were mixed with Pb: (Mg
+ Nb) = a: (b + 2) / 3 (1.00 ≦ a ≦ 1.1
5, 1.00 ≦ b ≦ 1.15) in a molar ratio of PM
This is an N precursor solution.

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

After the film formation, the temperature is set between 1 and 250 ° C.
Heat treatment for minutes, burn the organic matter remaining in the film,
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 thickness, baking is performed at 700 to 800 ° C. to produce the crystalline high dielectric constant dielectric film of the present invention.

In such a variable capacitor, by using the dielectric film 3 made of PMN having high dielectric constant and low loss and having a film thickness of 1 μm or less and an average particle diameter of 0.3 μm or less, the capacitance change rate can be reduced by the conventional BST. In addition, since the dielectric loss at high frequencies is small, when a variable capacitor is manufactured, it is easy to control the resonance peak to the oscillation frequency, the capacitance change rate is small, and the LC resonator or oscillator is The frequency change when configured can be linear with applied voltage.

Another variable capacitor according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view of the capacitor of the present invention, wherein reference numeral 11 denotes an insulating substrate, 12 denotes a lower electrode, 13 denotes a dielectric film, and 15 denotes an upper electrode.

Insulating substrate 11, lower electrode 12, upper electrode 1
5 is the same as above. In this example, the dielectric film 13 includes the high dielectric constant dielectric film 13a and the low dielectric constant dielectric film 1a.
3b.

The high-dielectric-constant dielectric film 13a is formed in the same manner as described above, and has a thickness of 1 μm or less, particularly, 0.1 μm or less.
It is 5 μm or less. Note that the average particle size of the main crystal particles made of the perovskite-type composite oxide of the high dielectric constant dielectric film 13 is not necessarily required to be 0.3 μm or less. Is preferably 0.3 μm or less.

On the upper surface of the high dielectric constant dielectric film 13a, a low dielectric constant dielectric film 13b is formed.

The low dielectric constant dielectric film 13b is formed by, for example,
It is formed from pyrochlore-type composite oxide crystal particles containing Pb, Mg, and Nb as metal elements. The dielectric constant and the loss of the high dielectric constant dielectric film 13a are reduced by reducing the size of crystal grains. However, the effect is limited by reducing the size of the crystal grains.

By forming the low dielectric constant dielectric film 13b on the high dielectric constant dielectric film 13a, the capacitors composed of the respective thin films are connected in series, and a further lower dielectric constant and lower loss are achieved. it can.

Since the pyrochlore phase constituting the low dielectric constant dielectric film 13b is a paraelectric material and does not change its dielectric constant with an applied voltage, the variable range of the dielectric constant of the dielectric film 13 (entire multilayer thin film) also decreases. . Therefore, as described later, as the low dielectric constant dielectric film 13b, a dielectric film mainly composed of a perovskite-type composite oxide that is a ferroelectric having a low dielectric constant and contains at least Pb and Ti as metal elements is used. Is used, the variable range of the dielectric constant can be expanded.

After forming the high dielectric constant dielectric film 13a as described above, the low dielectric constant dielectric film 13b is formed on the high dielectric constant dielectric film 13a. In the case of pyrochlore, the same solution as in the case of perovskite is used, and a film is formed by a method such as spin coating, dip coating, or spraying, as in the case of perovskite.

After film formation, at a temperature between 250 and 350 ° C.,
Heat treatment for minutes, burn the organic matter remaining in the film,
Gel film. The thickness of each film is preferably 0.1 μm or less. After repeating the film formation-heat treatment until the film thickness reaches a predetermined value, baking is performed at 600 to 700 ° C. to produce a low dielectric constant dielectric film of the present invention.

By performing the heat treatment and firing at such a low temperature, at least Pb, Mg and Nb are used as metal elements.
The low dielectric constant dielectric film 13b composed of only the crystal grains composed of the pyrochlore-type composite oxide containing the same can be formed.

The thickness of the obtained low dielectric constant dielectric film 13b is desirably 0.1 μm or less. Thereby, the low dielectric constant can be maintained, and the capacitance change rate of the capacitor can be maintained high. On the other hand, if the thickness is more than 0.1 μm, the loss becomes small because the capacitance becomes small, but the rate of change of the capacitance becomes too small, and the merit as a variable capacitance capacitor is reduced. The thickness of the low dielectric constant dielectric film 13b is desirably 0.08 μm or less.

At least Pb and Ti as metal elements
Is used as the low dielectric constant dielectric film 13b using a dielectric film containing a perovskite-type composite oxide containing as a main crystal particle, one selected from an organic acid salt of Ti, an alkoxide, or the like.
Kind of Ti compound and the above-mentioned Pb precursor solution with Pb: T
After mixing at a molar ratio of i = a: 1 (1.00 ≦ a ≦ 1.15), a refluxing operation was performed to synthesize a PT precursor solution, and the PT precursor solution was synthesized by a method such as spin coating, dip coating, or spraying. Form a film.

After film formation, at a temperature between 250 and 350 ° C.,
Heat treatment for minutes, burn the organic matter remaining in the film,
Gel film. The thickness of each film is preferably 0.1 μm or less.

After the film formation-heat treatment is repeated until the film thickness reaches a predetermined value, baking is performed at 700 to 800 ° C. to produce a low dielectric constant dielectric film of the present invention. The thickness of the obtained low dielectric constant dielectric film 13b is desirably 0.1 μm or less for the above reason. Desirably, it is composed of only perovskite-type composite oxide.

In the variable capacitor as described above, the dielectric constant and the loss can be reduced by reducing the crystal grains of the high dielectric constant dielectric film 13a, and the low dielectric constant is formed on the high dielectric constant dielectric film 13a. By forming the dielectric constant film 13b, capacitors composed of the respective dielectric films are connected in series, further lowering the dielectric constant and lowering the loss can be achieved, and the capacitance change rate is large as a variable capacitance capacitor. The loss is sufficiently small even at a high frequency, and the frequency change when the oscillator is formed can be made linear with respect to the applied voltage.

[0068]

EXAMPLES Mg ethoxide and Nb ethoxide were added in an amount of 1.0.
The mixture was weighed at a molar ratio of 5: 2, and refluxed in 2-methoxyethanol (17 hours at 130 ° C.) to obtain 1M (mol)
/ L) MgNb composite alkoxide solution of concentration was synthesized.

In the IR spectrum, absorption due to the Mg—O—Nb bond was observed at around 656 cm ⁻¹ . Then T
Each of i-propoxide was dissolved in 2-methoxyethanol at room temperature to prepare a 1M concentration Ti solution.

Pb: (Mg + Nb) = 1.0 in a Mg—Nb solution by adding lead acetate trihydrate and 2-methoxyethanol.
The mixture was mixed at a ratio of 5: 1 and stirred at room temperature for 1 hour to obtain 1M Pb _1.05 (Mg _{1.05 / 3} Nb _2/3 ) O _3.
A precursor solution was synthesized. This is designated as solution 1.

Lead acetate trihydrate and 2-methoxyethanol
Mixed with Ti solution so that Pb: Ti = 1: 1
And stirred at room temperature for 1 hour to obtain 1M Pb
TiO _ThreeA precursor solution was synthesized. This is designated as solution 2.

The solution 1 was applied on the surface of the lower electrode on a sapphire single crystal substrate on which Pt (111) to be an electrode was sputtered at 500 ° C. by a spin coater, dried, and then heated to a temperature shown in Table 1. For 1 minute, and the operation of coating and heat-treating the coating solution was repeated 5 times. Then, the film was subjected to rapid temperature heating for 0.5 minutes (in air) at the temperature shown in Table 1 to obtain a film having a thickness of 0.4 μm. A high dielectric constant dielectric film was obtained.

In the case of multilayering, the above-mentioned solution 1 or solution 2 is applied on the high-dielectric-constant dielectric film which has been baked by a spin coater, dried, and then heat-treated at a temperature shown in Table 1 for 1 minute. A low-permittivity dielectric film having a film thickness shown in Table 1 was formed by performing rapid temperature rise baking at a temperature shown in Table 1 for 0.5 minutes (in the air) to obtain a multilayer dielectric film.

The average grain size of the high dielectric constant dielectric film was determined by an intercept method based on the result of SEM observation. The electrical characteristics were measured using an impedance analyzer. The rate of change of the capacitance is such that the bias voltage is 0.
It was measured by changing to 〜15V.

In order to separate the loss of the electrode from the loss of the dielectric, the loss of the dielectric near the measurement location is removed by acid treatment, the loss of only the lower electrode is measured, and the loss is subtracted from the measurement result of the entire capacitor. I asked. The subtraction was calculated using | Z | and the resistance R and the reactance X obtained from the measurement results of the phase. The measurement frequency was 1 GHz. The results are shown in Table 1.

The PMN of the high dielectric constant dielectric film is formed only of the perovskite type composite oxide, and the PMN of the low dielectric constant dielectric film is formed only of the pyrochlore type composite oxide. On the other hand, the PT of the low dielectric constant dielectric film was formed only from the perovskite-type composite oxide.

[0077]

[Table 1]

From Table 1, it can be seen that the dielectric constant of the examples (Samples Nos. 1 to 5) was lower than that of the dielectric film composed of coarse perovskite having an average particle size of 0.5 μm in the comparative example (Sample No. 6). It can be seen that the loss has decreased. When the dielectric film has a laminated structure (Sample Nos. 2 to 5), the single-layer sample N
o. It can be seen that although the capacitance change rate is smaller than that of No. 1, the dielectric loss is small.

FIG. 3 (a) shows the sample No. 1 and the rate of change of the capacitance of the varactor diode, and (b) shows the rate of change of the oscillation frequency. From FIG. 3, it can be seen that the change rate of the capacity change rate is 80%, and the change rate of the transmission frequency is linear.

[0080]

According to the variable capacitor of the present invention, P
b, Mg, and Nb-containing perovskite-type composite oxide as main crystal particles, and the average particle size of the main crystal particles is 0.1 mm.
By using a dielectric film having a thickness of 3 μm or less and a film thickness of 1 μm or less, the rate of change in capacitance due to voltage application is large, the dielectric loss is sufficiently small even in a high frequency region, and the frequency variable range when configuring an oscillator is wide. The frequency change when the resonator is formed can be made linear with respect to the applied voltage.

Further, since the dielectric film is formed by laminating a high dielectric constant dielectric film and a low dielectric constant dielectric film, a structure in which capacitors made of the respective dielectric films are connected in series is obtained. The loss can be further reduced, and the high dielectric constant dielectric film is made of Pb, Mg and N
Since the perovskite-type composite oxide containing b is used as the main crystal particles, a large capacitance change rate and linearity of the resonance frequency change can be maintained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a variable capacitor according to the present invention.

FIG. 2 is a sectional view of another variable capacitor according to the present invention.

FIG. 3 (a) shows a sample No. 1 is a graph showing the change rate of the capacitance of the varactor diode, and (b) is a graph showing the change rate of the oscillation frequency.

[Explanation of symbols]

 1, 11: insulating substrate 2, 12: lower electrode 3, 13: dielectric film 5, 15: upper electrode 13a: high dielectric constant dielectric film 13b: low dielectric constant Dielectric film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference)

Claims (6)

[Claims] 1. A variable capacitor having electrodes formed on both surfaces of a dielectric film, wherein said dielectric film has a thickness of 1 μm.
And the dielectric film has a main crystal particle of a perovskite-type composite oxide containing at least Pb, Mg and Nb as metal elements, and the main crystal particle has an average particle size of 0.3 μm or less. A variable capacitor. 2. A variable capacitor having electrodes formed on both surfaces of a dielectric film, wherein the dielectric film is formed by laminating a high dielectric constant dielectric film and a low dielectric constant dielectric film, and A variable-capacitance capacitor, wherein a dielectric constant dielectric film is made of a perovskite-type composite oxide containing at least Pb, Mg and Nb as metal elements as main crystal grains. 3. The variable capacitor according to claim 2, wherein the average grain size of the main crystal grains of the high dielectric constant dielectric film is 0.3 μm or less. 4. The variable dielectric material according to claim 2, wherein the low dielectric constant dielectric film is composed of only crystal grains composed of a pyrochlore-type composite oxide containing at least Pb, Mg and Nb as metal elements. Capacitive capacitors. 5. The variable capacitor according to claim 2, wherein the low dielectric constant dielectric film is made of a perovskite-type composite oxide containing at least Pb and Ti as metal elements as main crystal grains. 6. The variable capacitor according to claim 2, wherein the low dielectric constant dielectric film has a thickness of 0.1 μm or less.