JP3599528B2 - Variable capacitance element and method of manufacturing the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a variable capacitance element that can be used as a capacitor for a high-frequency element and a method for manufacturing the same, and more particularly, to a variable capacitance element that can greatly change the capacitance by applying a voltage and a method for manufacturing the same.
[0002]
Problems to be solved by the prior art and the invention
Conventionally, as a variable capacitance element, (a) an element using a pn junction of Si or a GaAs semiconductor such as a varicap diode or a varactor, and (b) applying a voltage to a bulk ferroelectric to reduce the dielectric constant is used. Variable capacitors.
Of these variable capacitance elements, (a) is generally manufactured from a single crystal wafer of Si or GaAs, and cannot be monolithically formed by growing a single crystal of Si or GaAs on a ceramic substrate by thin film growth. Therefore, there is a problem that it cannot be formed as an integrated device on a ceramic substrate.
[0003]
As the variable capacitor (b), for example, there is a variable capacitor proposed in Japanese Patent Application Laid-Open No. 62-259417.
As shown in FIG. 7, this variable capacitor has a structure in which a bulk ferroelectric substance 14 (about 45 μm thick) is sandwiched between upper and lower electrodes, and a lower capacitance electrode 13 and a lower bias electrode 13 ′ as lower electrodes. And an upper capacitor electrode 16 and an upper bias electrode 16 ′ as upper electrodes. A DC bias is applied between the lower bias electrode 13 ′ and the lower capacitor electrode 13 and between the upper bias electrode 16 ′ and the upper capacitor electrode 16, thereby changing the dielectric constant of the ferroelectric 14. The capacitance between the lower bias electrode 13 'and the lower capacitance electrode 13 and the capacitance between the upper bias electrode 16' and the upper capacitance electrode 16 are made variable.
[0004]
In the above variable capacitor, a ferroelectric ceramic powder in the form of a sheet having a thickness of about 45 μm using a synthetic resin such as polyvinyl alcohol as a binder is used as the ferroelectric.
As described above, in the variable capacitor of (b), since a bulk ferroelectric ceramic material is used, it is difficult to reduce the size of the thin film device, and since the ferroelectric itself has a large thickness, the variable capacitor is applied. The voltage is large, and it is difficult to reduce the voltage. Further, since a ferroelectric substance is used, there is a drawback that it does not operate as a capacitor at a frequency of 1 GHz or more.
[0005]
On the other hand, a change in the dielectric constant of a strontium titanate (SrTiO ₃ ) thin film, which is a ferroelectric substance, due to voltage application has been reported (A. Walkenhorst et al., Appl. Phys. Lett. 60 (1992) 1744). There is a problem that the change in the dielectric constant in this case is smaller than that in the bulk. In the case of bulk strontium titanate, a large change in the dielectric constant can be obtained. However, in order to obtain such a large change in the dielectric constant, the temperature must be as low as 30 K. The reality is that you can't.
[0006]
The present invention has been made to solve the above-described problems, and can be easily formed on a ceramic substrate at low cost, and can obtain a large capacitance change with a small size, a low voltage, and a frequency of 10 GHz or more. However, an object of the present invention is to provide a variable capacitance element that does not deteriorate the capacitor characteristics.
[0007]
[Means for Solving the Problems]
According to the present invention, sequentially Bei example at least the lower electrode, dielectric thin film layer and an upper electrode on a substrate, Ri Do the dielectric thin film layer is a multilayer dielectric thin film, the substrate is a glass substrate, a resin substrate and There is provided a variable capacitance element which is formed of any one of the ceramic substrates and changes a capacitance by applying a voltage to at least one of the lower electrode and the upper electrode .
Further, the method for manufacturing the variable capacitance element,
(I) forming a lower electrode on the substrate,
(Ii) A plurality of steps of preparing a precursor solution of an element constituting a dielectric thin film by a sol-gel method, applying the solution on the lower electrode, drying the thin film, and decomposing and removing organic substances in the thin film by heat treatment are repeated a plurality of times. ,
( Iii ) There is provided a method for manufacturing a variable capacitance element, which comprises subjecting a heat treatment to crystallize the dielectric thin film before or after forming an upper electrode on the obtained multilayer dielectric thin film.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The variable capacitance element according to the present invention is mainly configured by sequentially forming a lower electrode, a dielectric thin film layer, and an upper electrode on a substrate.
The substrate that can be used for the variable capacitance element of the present invention is not particularly limited. For example, a glass substrate, a resin substrate, an insulating substrate such as a ceramic substrate, a semiconductor substrate, a compound semiconductor substrate, or the like may be used. Among them, a ceramic substrate is preferable in terms of strength, heat resistance, cost, and the like. In addition, the substrate used in the present invention has an insulating film such as SiN or SiO _{2 on} its surface, an element forming a desired circuit, an interlayer insulating film covering these elements, and an adhesive layer with an electrode layer formed on the substrate. An adhesive layer (for example, tantalum, titanium, titanium nitride, etc.) for improving the quality or a combination thereof may be formed.
[0009]
As the lower electrode in the variable capacitance element of the present invention, the material is not particularly limited as long as it can be generally used as an electrode material and can withstand heat treatment in a later step, for example, aluminum , Copper, silver, platinum; refractory metals such as titanium, tantalum, and tungsten; and various metals such as conductive oxides such as RuO ₂ and IrO ₂ . The thickness of the lower electrode is not particularly limited, and may be, for example, about 50 nm to 1 μm. The shape of the lower electrode can be appropriately adjusted according to the capacity, application, and the like to be obtained. Further, as described above, an adhesive layer or the like may be formed directly below the lower electrode in order to improve the adhesiveness and the like of the lower electrode.
[0010]
Examples of the dielectric thin film layer include a multilayer dielectric thin film. Here, the multilayer dielectric thin film is a dielectric thin film composed of two or three or more thin films, for example, about 2 to 6 layers, preferably about 3 or 4 layers. The thickness of the dielectric thin film layer can be appropriately adjusted according to the size of the variable capacitance element, applied voltage, application, forming method, etc., and the thickness of each dielectric thin film is, for example, about 50 nm to 100 nm, The total film thickness is preferably set to 100 nm to 1 μm. The thickness of each dielectric thin film may be a multilayer having substantially the same thickness, or a multilayer having different thicknesses. The dielectric thin film layer composed of two or more thin films may be the same as the elements and the proportions of the constituent elements of each layer, may be different in the kind and proportion, may be different in the kind and proportion, or Various combinations of multi-layered dielectric thin films, such as those in which all of the thin films having more than one layer are different and those in which only some of the layers are different, are all included. Specifically, a thin film in which about 2 to 6 layers of the same thin film are laminated, and a thin film in which about 2 to 6 layers are alternately repeated and two or more different thin films are laminated, and the like are given.
[0011]
Such a multilayer dielectric thin film can be formed by various methods such as a known method, for example, a sputtering method, a vapor deposition method, a sol-gel method, and an MOCVD method, and among them, it is preferable to form the dielectric thin film by the sol-gel method.
The type of the dielectric thin film is not particularly limited as long as high frequency characteristics can be obtained. For example, a dielectric that can be formed by a sol-gel method is preferable. For example, Ba _x Sr _1-x TiO ₃ (0 <x ≦ 0.8), (Pb _1−x La _x ) Zr _0.46 Ti _0.36 O ₃ (1 ≧ x ≧ 0.02), (Pb _1−x Er _x ) Zr _0.46 Ti _0.36 O ₃ (0.02 ≦ x ≦ 0.1). Specifically, SrTiO ₃ , SrBi ₂ Ta ₂ O ₉ , SrBi ₂ Nb ₂ O ₉ , SrBi ₂ (Ta, Nb) ₂ O ₉ , Bi ₄ Ti ₃ O ₁₂ , SrBi ₄ Ti ₄ O ₁₅ , SrBi ₄ ( Ti, Zr) ₄ O ₁₅ , CaBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , BaBi ₂ Nb ₂ O _{9 and the} like. Among them, SrTiO ₃ and Ba _0.7 Sr _0.3 TiO ₃ are more preferable.
[0012]
As the upper electrode in the variable capacitance element of the present invention, the same material as the lower electrode can be used. However, the upper electrode material does not need to be the same as the lower electrode material. Further, as described above, an adhesive layer or the like may be formed immediately below the upper electrode in order to improve the adhesiveness and the like of the upper electrode. Further, the shape of the upper electrode can be appropriately adjusted depending on the capacity, application, applied voltage, and the like to be obtained, and the shape in which the entire surface of the upper electrode is in contact with the dielectric thin film and the shape in which the entire surface of the dielectric is covered And various shapes such as a shape having an air bridge in a part between the dielectric and the dielectric.
[0013]
The variable capacitance element in the present invention is not particularly limited as long as it has a shape and a structure that can operate as a variable capacitance element up to the GHz band. For example, the lower electrode, the dielectric thin film, and the upper electrode Various shapes and structures such as a general capacitor structure, a vertical capacitor structure, and a structure in which an air bridge is formed at least at one end of an upper electrode are included.
[0014]
The variable capacitance element according to the present invention can change the capacitance by applying a bias voltage to at least one of the upper and lower electrodes, and furthermore, by applying the bias voltage, the relative dielectric constant of the dielectric thin film can be changed. The rate can be changed according to a change in voltage. The voltage applied to the upper and lower electrodes can be appropriately adjusted depending on the dielectric material, film thickness, application, etc., for example, from the viewpoint of dielectric leakage current, practicality, and the like, about 20 V or less, preferably about 16 V. Hereinafter, more preferably, about −16 to +16 V is used. Further, the capacitance that changes in response to the applied voltage is preferably as large as possible, for example, about -50% or more, and more preferably about -100%. Further, the relative permittivity of the dielectric, which changes according to the applied voltage, varies depending on the dielectric material and the like, and is, for example, about 50 to 1,000.
[0015]
In the step (i) of the method of manufacturing a variable capacitance element according to the present invention, a lower electrode is formed on a substrate. At this time, the above-mentioned electrode material can be formed into a desired film thickness by a known method, for example, various methods such as a vacuum evaporation method, a sputtering method, and an electron beam evaporation method, for example, photolithography and etching. It can be patterned into a desired shape by a method, a lift-off method, or the like.
[0016]
In the step (ii), first, a precursor solution of an element constituting the dielectric thin film is prepared by a sol-gel method. The precursor solution may be, for example, a carboxylate or alkoxide such as Ba, Bi, Sr, Ta, Nb, Ti, Zr, Ca, Pb, or Er at an appropriate concentration, at an appropriate temperature, and in an appropriate blending ratio. It can be prepared by dissolving in an aqueous medium or an organic solvent. At this time, examples of the organic solvent that can be used include lower alcohols such as methanol, ethanol, and propanol, xylene, and acetate. The preparation of the precursor solution depends on, for example, the composition of the ferroelectric to be finally obtained from each solution of the metal element constituting the ferroelectric, but is about 0.1 to 5 mol / L, preferably 0 to 5 mol / L. Prepared separately at about 1 to 2 mol / L, for example, sufficiently heated at about 200 ° C. or lower, preferably about 150 ° C. or lower, and appropriately mixed with stirring for about 5 hours, preferably about 1 to 3 hours. For example, a method of stirring the mixture for about 1 hour to 1 day and night can be used. It is preferable that the precursor solution is optionally subjected to filtration, distillation of a solvent, adjustment of concentration, and the like.
[0017]
Next, the obtained precursor solution can be applied to the lower electrode with a film thickness of about 20 to 200 nm per layer by various methods such as a spin coating method, a printing method, and a roll coating method. However, if the thickness per layer is large, cracks are likely to occur in the drying step. Therefore, the thickness to be applied per layer is more preferably about 100 nm or less. In particular, in the case of the printing method, the precursor solution is appropriately mixed with an organic binder resin such as an acrylic resin, a phenol resin, an alkyd resin, ethyl cellulose, and polyvinyl alcohol, and an organic solvent such as an alcohol-based, ether-based, and ester-based resin. Thereby, the viscosity can be adjusted. Further, a glass component such as silicate glass, borosilicate glass, or alumina silicate glass may be mixed in order to enhance the adhesiveness to the lower electrode.
[0018]
Further, the applied precursor solution is dried. The drying method can be appropriately selected depending on the type of the organic solvent used as the precursor solution, the composition of the precursor solution, and the like. For example, a temperature range of about 80 ° C to 300 ° C, preferably about 100 ° C to 200 ° C. The heat treatment can be performed in the atmosphere for 10 seconds to 60 minutes, preferably for about 15 minutes or less. The heat treatment may be performed at a uniform temperature for a fixed time using a known method, for example, an infrared heating furnace, a resistance heating furnace, or the like, or at different temperatures.
[0019]
Subsequently, the organic matter in the thin film is decomposed and removed by heat treatment. The heat treatment method at this time is preferably performed at a temperature at which organic substances present in the thin film are sufficiently decomposed, and at a temperature range in which crystallization does not start. Specifically, a temperature range of about 400 ° C. to 550 ° C. This can be performed in the atmosphere or in an inert gas atmosphere for about 10 to 60 minutes.
The above step (ii) is repeated at least twice depending on the number of dielectric thin films to be obtained. The step (ii) at this time may be repeated under exactly the same conditions in order to obtain a dielectric thin film having the same type and composition ratio, or the conditions and the like may be changed according to the type and composition ratio of the dielectric thin film. It may be adjusted appropriately and repeated.
[0020]
In step (iv), an upper electrode is formed on the obtained dielectric thin film layer. The method for forming the upper electrode can be the same as that for the lower electrode.
The formation of the upper electrode may be performed after the step (iii) and before the crystallization of the dielectric thin film described later, or may be performed after the crystallization of the dielectric thin film layer.
The crystallization of the dielectric thin film is performed in an oxygen atmosphere, an inert atmosphere such as argon or nitrogen, at normal pressure or reduced pressure, preferably at normal pressure, in a temperature range of 550 ° C. to 800 ° C. or less for about 30 seconds to 60 minutes. be able to. As the heat treatment method at this time, an RTA method or the like can be used in addition to the above-described method.
[0021]
In the method of manufacturing the variable capacitance element according to the present invention, the heat treatment for decomposing and removing organic substances in the thin film and the heat treatment for crystallization can be performed by appropriately selecting appropriate conditions. . For example, after applying the precursor solution in the step (ii), the precursor solution is dried in the air at a temperature of about 100 ° C. for about 5 to 20 minutes, and subsequently, in a temperature range of about 600 ° C., at normal pressure and in the air, and then dried. There is a method in which heat treatment is performed for about 60 minutes to crystallize the dielectric thin film layer, and a method in which this is repeated two or more times is exemplified. However, it is necessary to select conditions under which organic substances in the thin film can be sufficiently decomposed and removed before crystallization proceeds.
[0022]
The operation of the variable capacitance element according to the present invention is considered as follows.
Generally, in a paraelectric (or paraelectric phase) such as SrTiO ₃ or (Ba _0.7 Sr _0.3 ) TiO ₃ , the relationship between the electric field E, the polarization P, and the relative permittivity εr is as follows.
ε ₀ εrE = εE + P (1)
Holds. Here, ε ₀ represents a dielectric constant in a vacuum.
[0023]
In general, in a paraelectric (or paraelectric phase),
E = aP (a is a constant) (2)
(However, the phase transition temperature (105 K) or more of SrTiO ₃ is satisfied).
Therefore, the relative permittivity is constant without depending on the electric field from the equations (1) and (2).
However, when the dielectric thin films are stacked in multiple layers as in the present invention, the contribution of the interfacial energy to the whole free energy is larger than that of a bulk or a single thin film. Does not hold, and includes a non-linear component of P, for example, as in equation (3).
[0024]
E = aP + bP ³ + cP ⁵ (a, b and c are constants) (3)
As a result, the relative dielectric constant has an electric field dependency according to the equation (1).
Further, the dielectric thin film in the method for manufacturing a variable capacitance element of the present invention is a step of applying a sol-state dielectric precursor solution, drying and then decomposing and removing organic substances in the thin film by heat treatment using a sol-gel method. Is repeated two or more times, and then heat treatment is performed for crystallization to form a multilayer, so that an interface that does not exist in a bulk or a single thin film is formed between the dielectric thin films. Therefore, the contribution of the interface energy is further increased.
[0025]
As described above, in the variable capacitance element of the present invention, the capacitance of the entire element can be greatly changed by the bias voltage applied to the upper electrode, and when the capacitance affects the characteristics of the high-frequency circuit, for example, a high-frequency filter, an impedance antenna, By changing the capacitance such as the above, it becomes possible to change the filter transmission characteristics, the detection frequency, and the like, and it can be applied to various high-frequency devices.
Hereinafter, a variable capacitance element and a method for manufacturing the same according to the present invention will be described with reference to the drawings.
[0026]
Embodiment 1
FIG. 1 is a schematic sectional view of a variable capacitance element according to the present invention. In this variable capacitance element, a Ta lower electrode adhesive layer 2, a Pt lower electrode layer 3, a dielectric multilayer thin film 4, an air bridge 5, a Ta lower electrode adhesive layer 6, and the Pt electrode layer 7 are sequentially formed on a ceramic substrate 1. Be done.
[0027]
Hereinafter, a method for manufacturing the above variable capacitance element will be described.
First, a lower electrode resist pattern is formed on a ceramic substrate 1 by using a lift-off method based on ordinary photolithography, and a Ta lower electrode adhesive layer 2 and a Pt lower electrode layer 3 are formed to a thickness of 20 nm and 100 nm, respectively, by sputtering. After the formation, the lower electrode resist pattern was lifted off to form a lower electrode pattern including the Ta lower electrode adhesive layer 2 and the Pt lower electrode layer 3.
[0028]
Next, on the Pt lower electrode layer 3 thus formed, a sol-state precursor solution composed of a metal alkoxide of SrTiO ₃ is spin-coated (process 1), and dried by a heat treatment at 100 ° C. for 10 minutes. A dry gel thin film was prepared (Process 2).
Next, in order to thermally decompose the organic substance in the thin film of the dried gel thus produced, a heat treatment was performed at 400 ° C. for 10 minutes in the atmosphere at atmospheric pressure (process 3).
[0029]
After repeating the above processes 1 to 3 three times, a heat treatment was performed at 600 ° C. for 30 minutes in an oxygen atmosphere at 1 atm in order to crystallize the multilayer film from which organic substances were removed. As a result, a dielectric multilayer thin film 4 made of SrTiO _{3 having} a thickness of 210 nm was obtained. This dielectric multilayer thin film 4 was processed into a predetermined shape by etching.
[0030]
Next, after forming an air bridge resist pattern on the dielectric multilayer thin film 4 using an air bridge forming resist, an upper electrode resist pattern is formed using a lift-off method similar to the lower electrode pattern forming method, and sputtering is performed. The Ta upper electrode adhesive layer 6 and the Pt upper electrode layer 7 were formed to a thickness of 20 nm and 500 nm, respectively, by using the method. Thereafter, by lifting off the air bridge resist pattern and the upper electrode resist pattern, an upper electrode pattern including the Ta upper electrode adhesive layer 6 and the Pt upper electrode layer 7 was formed.
[0031]
A bias voltage was applied between the Pt upper electrode layer 6 and the Pt lower electrode layer 3 of the variable capacitance element manufactured by the above method, and the bias voltage dependence of the capacitance at 10 GHz at room temperature was measured. FIG. 2 shows the measurement results.
The relative dielectric constant of the obtained dielectric multilayer thin film 4 is 160, and at an applied voltage of 16 V, a capacitance change characteristic of 67 capacitance change rate Cv / Co × 100 [%] = − 62% is obtained. The ratio was 67 (where Cv represents the capacity when a voltage was applied, and Co represents the capacity when no voltage was applied).
[0032]
Comparative Example 1
For comparison, a variable capacitance element was manufactured in the same manner as in the first embodiment except that an SrTiO ₃ thin film produced by a sputtering method was used as a dielectric thin film.
[0033]
The SrTiO ₃ thin film was formed by using a ceramic sintered body of SrTiO ₃ as a sputtering target, using only O ₂ gas as a sputtering gas, forming a 210 nm film at a sputtering gas pressure of 2 Pa and a substrate temperature of 400 ° C.
The capacitance change characteristics of the variable capacitance element manufactured as described above were measured. The result is shown in FIG.
[0034]
The relative dielectric constant of the obtained SrTiO ₃ thin film was 150, and the capacitance change rate was -9% even at an applied voltage of 16 V, which was lower than that of the variable capacitance element shown in the first embodiment.
[0035]
Embodiment 2
A variable capacitance element is manufactured by using a barium strontium titanate ((Ba _0.7 Sr _0.3 ) TiO ₃ ) multilayer thin film formed by a sol-gel method instead of the dielectric multilayer thin film made of SrTiO _{3 in the} first embodiment. did.
The method for manufacturing a variable capacitance element according to this embodiment is different from the method for manufacturing a variable capacitance element according to the first embodiment in that the sol-state precursor solution composed of metal alkoxide in Process 1 is not SrTiO ₃ but (Ba _{0 0.7} Sr _0.3 ) The only difference is that a sol-state precursor solution made of a metal alkoxide of TiO ₃ is used. Otherwise, a method similar to the method of manufacturing the variable capacitance element of the first embodiment is used. Was.
[0036]
The bias voltage dependence of the capacitance at 10 GHz of the variable capacitance element manufactured by the above method was measured. FIG. 4 shows the measurement results.
The relative dielectric constant of the obtained (Ba _0.7 Sr _0.3 ) TiO ₃ multilayer thin film is 180, and a capacitance change characteristic of −60% is obtained at an applied voltage of 16 V. The rate was 67.
[0037]
Comparative Example 2
For comparison, a variable capacitance element was manufactured in the same manner as in the first embodiment except that a (Ba _0.7 Sr _0.3 ) TiO ₃ thin film produced by a sputtering method was used as the dielectric thin film.
[0038]
(Ba _0.7 Sr _0.3 ) TiO ₃ thin film is prepared by using a ceramic sintered body of (Ba _0.7 Sr _0.3 ) TiO ₃ as a sputtering target and using only O ₂ gas as a sputtering gas. A film thickness of 210 nm was formed at a sputtering gas pressure of 2 Pa and a substrate temperature of 400 ° C.
The capacitance change characteristics of the variable capacitance element manufactured as described above were measured. The relative dielectric constant of the obtained (Ba _0.7 Sr _0.3 ) TiO ₃ thin film is 170, and the capacitance change rate is -10% even at an applied voltage of 16 V, which is lower than that of the variable capacitance element shown in the second embodiment. It was a change characteristic.
[0039]
Embodiment 3
Instead of the dielectric multilayer thin film made of SrTiO _{3 in the} first embodiment, an SrTiO ₃ thin film formed by a sol-gel method and barium strontium titanate ((Ba _0.7 Sr _0.3 ) TiO ₃ ) were alternately laminated. A variable capacitance element was fabricated using the multilayer thin film.
[0040]
The method for manufacturing the variable capacitance element according to the third embodiment is the same as the method for manufacturing the variable capacitance element according to the first and second embodiments except for the method for forming the dielectric multilayer thin film.
The dielectric multilayer thin film of the variable capacitance element according to the third embodiment was manufactured as follows.
On the Pt lower electrode layer 3, a sol-state precursor solution composed of a metal alkoxide of SrTiO ₃ is spin-coated (process 1) and dried by heat treatment at 100 ° C. for 10 minutes to produce a dry gel thin film ( Process 2). Next, heat treatment was performed at 400 ° C. for 10 minutes in the atmosphere at atmospheric pressure (process 3).
[0041]
Next, a precursor solution in a sol state composed of a metal alkoxide of (Ba _0.7 Sr _0.3 ) TiO ₃ is spin-coated (process 4), and dried by heat treatment at 100 ° C. for 10 minutes. A thin film is formed (process 5). Next, the dried gel thus produced was subjected to a heat treatment at 400 ° C. for 10 minutes in the atmosphere at atmospheric pressure (process 6).
[0042]
Further, a precursor solution in a sol state composed of a metal alkoxide of SrTiO ₃ is spin-coated (process 7), and dried by heat treatment at 100 ° C. for 10 minutes to produce a dry gel thin film (process 8). Next, heat treatment was performed at 400 ° C. for 10 minutes in the atmosphere at atmospheric pressure (process 9).
Thereafter, a heat treatment was performed at 600 ° C. for 30 minutes in an oxygen atmosphere at 1 atm. As a result, a dielectric multilayer thin film 4 having a structure in which SrTiO ₃ and (Ba _0.7 Sr _0.3 ) TiO ₃ having a total film thickness of 210 nm were alternately laminated was obtained.
[0043]
The bias voltage dependence of the capacitance of 10 GHz of the variable capacitance element manufactured by the above method was measured. FIG. 6 shows the measurement results. The relative dielectric constant of the obtained multilayer thin film having a structure in which SrTiO ₃ and (Ba _0.7 Sr _0.3 ) TiO ₃ are alternately stacked is 170, and the capacitance change rate is −60% at an applied voltage of 16 V. The capacitance change characteristic was obtained, and the relative dielectric constant at this time was 67.
[0044]
【The invention's effect】
According to the variable capacitance element of the present invention, at least a lower electrode, a dielectric thin film, and an upper electrode are sequentially provided on a substrate, and the dielectric thin film is formed of a multilayer dielectric thin film. In addition to being possible, a reduction in size and weight can be realized. Further, since it is not necessary to use a single crystal material of Si or GaAs, it can be formed easily and inexpensively on a ceramic substrate.
[0045]
In addition, when a multilayer dielectric thin film is formed by a sol-gel method, a specific interface state is formed at the interface of each layer during crystallization, so that a remarkable change in capacitance can be obtained.
Further, when the dielectric thin film is made of a multilayer strontium titanate, barium strontium titanate or a combination thereof, since these are paraelectric or paraelectric phases, the capacitance does not deteriorate even at a frequency of 10 GHz or more. A variable element can be obtained.
[0046]
In addition, since the variable capacitance element changes the capacitance by applying a voltage to at least one of the lower electrode and the upper electrode, a tunable high-frequency filter that can control the magnitude of the capacitance with the voltage, a delay, It can be widely applied to high frequency devices such as elements, array antennas, and coupled strip lines.
Further, according to the variable capacitance element manufacturing method of the present invention, it is possible to provide a manufacturing method capable of easily realizing the variable capacitance element having the special functions and functions as described above.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a main part showing a variable capacitance element of the present invention.
FIG. 2 is a diagram illustrating a capacitance change characteristic of the variable capacitance element according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating a capacitance change characteristic of a variable capacitance element according to Comparative Example 1 of the present invention.
FIG. 4 is a diagram illustrating a capacitance change characteristic of a variable capacitance element according to a second embodiment of the present invention.
FIG. 5 is a diagram illustrating a capacitance change characteristic of a variable capacitance element according to a second embodiment of the present invention.
FIG. 6 is a diagram illustrating a capacitance change characteristic of a variable capacitance element according to a third embodiment of the present invention.
FIG. 7 is a schematic sectional view of a main part showing a conventional variable capacitance element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic substrate 2 Ta lower electrode adhesive layer 3 Pt lower electrode layer 4 Dielectric multilayer thin film 5 Air bridge 6 Ta upper electrode adhesive layer 7 Pt upper electrode layer

Claims (7)

At least a lower electrode on a substrate, e sequentially Bei a dielectric thin film layer and an upper electrode, Ri Do a dielectric thin film of the dielectric thin film layer is a multilayer,
The substrate is made of any one of a glass substrate, a resin substrate, and a ceramic substrate,
A capacitance variable element that changes a capacitance by applying a voltage to at least one of the lower electrode and the upper electrode . 2. The variable capacitance element according to claim 1, wherein the dielectric thin film is formed by a sol-gel method. 2. The variable capacitance element according to claim 1, wherein the dielectric thin film layer comprises a multilayer strontium titanate film. 2. The variable capacitance element according to claim 1, wherein the dielectric thin film layer comprises a multilayer barium strontium titanate film. 2. The variable capacitance element according to claim 1, wherein the dielectric thin film layer is a multilayer in which strontium titanate films and barium strontium titanate films are alternately stacked. The capacitance variable element according to any one of claims 1 to 5, wherein an air bridge is formed at at least one end of the upper electrode . A method for manufacturing a variable capacitance element according to claim 1,
(I) forming a lower electrode on the substrate,
(Ii) A plurality of steps of preparing a precursor solution of an element constituting a dielectric thin film by a sol-gel method, applying the solution on the lower electrode, drying the thin film, and decomposing and removing organic substances in the thin film by heat treatment are repeated a plurality of times. ,
( Iii ) A method for manufacturing a variable capacitance element, which comprises subjecting a heat treatment to crystallize the dielectric thin film before or after forming an upper electrode on the obtained multilayer dielectric thin film.

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