JPH1041464A - Variable capacitance capacitor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate miniaturization and improve the Q value. SOLUTION: A bottom electrode 3, first sacrifice layer 14, top electrode 4 and second sacrifice layers 16 and 17 are successively laminated on a quartz board 2. Then, an SiO2 , film 8a is formed at the top by sputtering. Through holes 12 are formed on the SiO2 film 8a, etching solution is applied into the sacrifice layers (ZnO) 14, 16 and 17 through the through holes 12 to remove the layers by etching and a space 11 is formed in the SiO2 film 8. Under the condition that the space 11 is evacuated of air, an SiO2 film 8b is formed at top of the SiO2 film 8a to cover the through holes 12, and a variable capacity capacitor 1 is completed. Since an outer shell 10 is formed by the SiO2 films 8a and 8b which have small dielectric loss, the Q value is improved, and moreover, the element of the variable capacitance capacitor 1 is easily miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a variable capacitor incorporated in a high-frequency modulation circuit or the like and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a variable capacitor. The variable capacitor 1 includes a substrate 2 formed of Si or Pyrex glass (trade name), a lower electrode 3 formed on the substrate 2, and a lower electrode 3.
And a second substrate 20 such as a Si substrate or a Pyrex glass substrate in which a recess 21 is formed in a region opposed to the upper side of the upper electrode 4 with an air gap therebetween.
The capacitor 5 formed by the lower electrode 3 and the upper electrode 4 is accommodated in a space 22 formed by joining the substrates 2 and 20.

The lower electrode 3 and the upper electrode 4 of the variable capacitor 1 are connected to through holes formed in a second substrate 20.
23 and a conductive pattern 24, which is electrically connected to an AC power supply (not shown). When a voltage is applied to the lower electrode 3 and the upper electrode 4 from the power supply, the lower A Coulomb force is generated between the electrode 3 and the upper electrode 4. The variable capacitor 1 utilizes this Coulomb force,
The upper electrode 4 is flexed and displaced upward and downward as shown in FIG. 4 to change the distance between the lower electrode 3 and the upper electrode 4 so that the capacitance between the lower electrode 3 and the upper electrode 4 (the capacitance of the capacitor 5). Capacity) can be variably controlled. And
An output corresponding to this capacitance is taken out through the through hole 23.

A variable capacitor 1 shown in FIG. 4 is incorporated in a high-frequency modulation circuit or the like, and includes a lower electrode 3 and an upper electrode 4.
The upper electrode 4 moves at a high frequency when a high-frequency AC voltage is applied to the lower electrode 3 and the upper electrode 4, that is, the space accommodating the capacitor 5.
Reference numeral 22 denotes a vacuum space, which is formed so as to prevent the high-frequency movable characteristics of the upper electrode 4 from deteriorating due to the viscous resistance of air.

[0005]

However, as shown in FIG. 4, since the two substrates 2 and 20 are overlaid, the thickness D of the element of the variable capacitor 1 is equal to the thickness of the two substrates. In addition, in order to securely join the substrate 2 and the substrate 20 and to seal the inside of the space 22 under vacuum, a large bonding area is required. There is a problem that is difficult.

A variable capacitor 1 shown in FIG.
Are the lower electrode 3, the upper electrode 4, and the conductor pattern on the substrate 2.
After the formation of 24, it is manufactured through a process of joining the substrate 2 and the substrate 20. In order to join the substrate 2 and the substrate 20, the substrates 2 and 20 are heated to a high temperature of 500 ° C. or more. This high-temperature heating may cause the metal forming the lower electrode 3 and the like on the substrate 2 to melt and diffuse, thereby damaging the lower electrode 3, the upper electrode 4, and the conductor pattern 24.

Further, the output of the capacitor 5 is guided to the outside through the through-hole 23. Since the through-hole 23 has a large electric resistance component and poor electric conductivity, the output of the capacitor 5 depends on the electric resistance component. That is, there is a problem that the Q value of the output of the variable capacitor 1 is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The first object of the present invention is to reduce the size of the element of the variable capacitor and to solve the problem of melting and diffusion of metal due to high-temperature heating of the substrate. A second object of the present invention is to provide a variable capacitor which avoids damage to electrodes and conductor patterns and the like and a method for manufacturing the same. A second object is to provide a variable capacitor capable of improving the Q value of the output of the variable capacitor. It is to provide a manufacturing method thereof.

[0009]

In order to achieve the above object, the present invention is configured as follows. That is, the invention of a variable capacitor includes a lower electrode formed on a substrate surface, and an upper electrode disposed above the lower electrode with a gap therebetween, and the upper electrode is provided with an insulator. The lower electrode and the upper electrode are housed in a vacuum space formed by the outer shell and the substrate, and are electrically connected to the lower electrode. The above object is achieved by a configuration in which a side connection electrode and an upper side connection electrode electrically connected to the upper electrode are drawn out from the vacuum space onto an external substrate surface.

According to a first aspect of a method for manufacturing a variable capacitor, a lower electrode and a lower connection electrode extending from the lower electrode are formed on a substrate surface, and a first electrode is formed above the lower electrode. A sacrificial layer is laminated and then the first
An upper electrode is formed on the upper surface of the sacrificial layer opposite to the lower electrode, and an upper connection electrode extending from the upper electrode is formed on the substrate surface. A second sacrifice layer covering the facing region of the electrode is formed by lamination, an outer shell made of an insulator film is formed on the second sacrifice layer, and then a through hole is formed to communicate with the second sacrifice layer. A hole is provided in the outer shell, and the first and second holes are formed through the through hole.
The first and second sacrificial layers are removed by etching by injecting an etchant into the sacrificial layer, forming a gap between the lower electrode and the upper electrode and forming a space inside the outer shell, The means for solving the above-mentioned problem has a configuration in which the through hole is closed to make the inside of the outer shell a vacuum space.

According to a second aspect of the method of manufacturing a variable capacitor, in addition to the configuration of the first aspect of the method of manufacturing a variable capacitor, an inner space of an outer shell that covers a region where the lower electrode and the upper electrode are opposed to each other is provided. After forming the vacuum space, the outer shell laminated on the lower connection electrode and the upper connection electrode outside the vacuum space is removed, and the lower connection electrode and the upper side on the substrate surface outside the vacuum space are removed. A configuration for exposing the connection electrode to the outside is a means for solving the above problem.

In a third aspect of the method for manufacturing a variable capacitor, the first and second sacrificial layers constituting the first or second aspect of the method for manufacturing a variable capacitor are formed of zinc oxide. The configuration is a means for solving the above problem.

In the invention having the above construction, the lower electrode and the upper electrode are covered with an outer shell formed of an insulating film, and the lower electrode and the upper electrode are accommodated in a vacuum space formed by the outer shell and the substrate.

Since the thickness of the insulator film can be made much thinner than the thickness of the substrate, the thickness of the film is lower than that in the case where the lower electrode and the upper electrode are housed in a vacuum space using two substrates. Further, the thickness of the element of the variable capacitor can be reduced, and the element of the variable capacitor can be reduced in size.

Further, the variable capacitor of the present invention comprises:
Manufacturing is completed through a manufacturing process of sequentially forming a lower electrode, a first sacrifice layer, an upper electrode, a second sacrifice layer, and an outer shell on a substrate surface. In the manufacturing process, the substrate is not heated to a high temperature of, for example, 500 ° C. or more, and there is no fear that the metal is melted and diffused by heating the substrate at a high temperature. This avoids the problem of damage to the lower and upper electrodes caused by the dissolution and diffusion of the metal.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1A is a perspective view of an embodiment of a variable capacitor according to the present invention, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A. ing. This variable capacitor 1
As shown in FIGS. 1A and 1B, an insulating substrate 2 such as a quartz substrate, a lower electrode 3, an upper electrode 4, and a lower connection extending from the lower electrode 3 are formed. An electrode 6 and an upper connection electrode 7 extended from the upper electrode 4
And a film 8a of silicon oxide (SiO ₂ ) as an insulator.
8b (the dielectric constant of this SiO ₂ film is very low, for example, 3.6).

As shown in FIG. 1, a lower electrode 3 is formed on a surface of a substrate 2, and an upper electrode 4 is disposed above the lower electrode 3 with a gap therebetween. The capacitor 5 constituted by the upper electrode 4 is covered by an outer shell 10 through a space, and the capacitor 5 is housed in a space 11 formed by the outer shell 10 and the substrate 2. This space 11 is in a vacuum state (for example, at a pressure of about 1 Pa) in which the high-frequency movable characteristics of the upper electrode 4 are improved when a high-frequency AC voltage is applied to the capacitor 5 to move the upper electrode 4 at high frequency.
State).

A lower connection electrode 6 electrically connected to the lower electrode 3 and an upper connection electrode 7 electrically connected to the upper electrode 4 are respectively drawn out of the vacuum space 11 onto the surface of the external substrate 2. The upper portions of the lower connection electrode 6 and the upper connection electrode 7 which are formed and drawn out are coated with a metal such as Au and are exposed.

Further, a plurality of through holes 12 for evacuating the space 11 are formed in the SiO ₂ film 8a.
12 is filled with the material of the SiO ₂ film 8b, the through hole 12 is completely closed, and the space 11 is vacuum-sealed. Furthermore, SiO ₂ films 13 are formed on both front and back surfaces of the upper electrode 4.

The variable capacitor of this embodiment is configured as described above, and an example of a method of manufacturing the variable capacitor will be described below with reference to FIGS.

First, as shown in FIG. 2A, a lower electrode 3 is formed on an insulating substrate 2 made of quartz or the like and extended from the lower electrode 3 to the right side as shown in FIG. 2A. The lower connection electrode 6 is formed of a metal such as gold (Au), and zinc oxide (Zn) as a first sacrificial layer is formed on the lower electrode 3.
O) layer 14 is formed by lamination by sputtering (this Zn
The heating temperature of the substrate 2 during the sputter formation of the O layer 14 is about
100 ° C). Then, an SiO ₂ film 13 is formed on the substrate surface region on the upper side of the first sacrifice layer 14 and on the left side of the first sacrifice layer 14, and thereafter, aluminum (Al) or the like is formed on the upper side of the SiO ₂ film 13. Of the lower electrode 3
Is formed, and an upper-side connection electrode 7 electrically connected to the upper electrode 4 is formed.

Then, an SiO ₂ film 13 is formed on the upper side of the upper electrode 4 and on the upper side of the upper side connection electrode 7 in the portion inside the outer shell 10 shown in FIGS. 1 (a) and 1 (b). As shown in FIG. 1A, a metal 15 such as Au, which is a coating material, is laminated on the exposed lower connection electrode 6 and upper connection electrode 7.

Next, a ZnO layer is formed by lamination on the upper side of the substrate by a sputtering method, and thereafter, as shown in FIG. 2B, a portion (16) covering the facing region of the lower electrode 3 and the upper electrode 4 Excess ZnO layers other than the above are removed. And FIG.
As shown in (c), a ZnO layer 17 is formed on the remaining ZnO layer 16 by a sputtering method. The above Zn
A second sacrifice layer is constituted by the O layers 16 and 17, and the substrate 2 is heated to about 100 ° C. when the second sacrifice layer (ZnO layers 16 and 17) is formed by sputtering.

As described above, by forming the ZnO layers 16 and 17 separately, the thickness of the second sacrificial layers 17a and 17b other than the portion covering the opposing region of the lower electrode 3 and the upper electrode 4 is reduced. Can be formed to be thinner than the thickness of the second sacrifice layer covering the portion.

Further, as shown in FIG.
On top of the O layer 17, an SiO ₂ film 8a is laminated by sputtering. The substrate 2 is heated to about 150 ° C. when the SiO ₂ film 8a is formed by sputtering. Then, the SiO ₂ film 8 other than the portion where the outer shell 10 is formed as shown in FIGS.
a. Then, the remaining SiO ₂ film 8a is
As shown in (e), a through hole 12 communicating with the ZnO layer 17 (17a, 17b) is provided by RIE (reactive ion etching).

Thereafter, the ZnO layers 14 and 1
An etchant (etchant) is made to enter the layers 6 and 17, and the ZnO layers 14, 16 and 17 are removed by etching, as shown in FIG. 3F, to form a gap between the lower electrode 3 and the upper electrode 4. At the same time, a space 11 is formed inside the SiO ₂ film 8a.

The above-mentioned etching solution etches the first and second sacrificial layers (ZnO layers 14, 16, 17). The lower electrode 3, the upper electrode 4, the lower connection electrode 6, and the upper connection electrode 7 are etched.
(Eg, Au and aluminum)
Alternatively, the SiO ₂ films 13 and 8a are not etched. For example, concentrated nitric acid or acetylacetone is used as the etching solution.

Thereafter, the substrate 2 shown in FIG. 3 (f) is set in the exhaust chamber of the SiO ₂ film 8b film forming apparatus which is a vacuum apparatus, and the vacuum chamber is evacuated and the SiO ₂ film 8a is evacuated. The air in the internal space 11 is exhausted through the through hole 12.
Then, the vacuum state in the exhaust chamber and the internal space 11 of the SiO ₂ film 8a is suitable for the sputter deposition of the SiO ₂ film 8b, and the high-frequency movable characteristics of the upper electrode 4 are good (for example, the atmospheric pressure is about 1 Pa). 3), the SiO ₂ film 8a is formed on the upper side of the SiO ₂ film 8a as shown in FIG.
While forming the film 8b, the through hole 12 is closed with the material of the SiO ₂ film 8b. Thus, the SiO ₂ films 8a, 8
At the same time as the outer shell 10 made of b is formed, the through-hole 12 is closed and the inner space 11 of the outer shell 10 is sealed in a vacuum state in which the high-frequency movable characteristics of the upper electrode 4 are improved.

After that, the SiO ₂ film 8b (outer shell 10) formed on the lower connection electrode 6 and the upper connection electrode 7 on the substrate surface outside the vacuum space 11 is removed by the method shown in FIG. As shown in h), the variable capacitor 1 is completed by etching and removing.

According to this embodiment, the SiO ₂ film 8
The outer shell 10 is formed of an insulating film composed of a and 8b, and the capacitor 5 including the lower electrode 3 and the upper electrode 4 is accommodated in the inner space 11 of the outer shell 10. Since the thickness can be much smaller than the thickness of the substrate 20 of FIG. 4 shown in the conventional example, the thickness of the element of the variable capacitor 1 can be made extremely thin.

The SiO ₂ films 8a and 8b are formed by sputtering. The films formed by sputtering are the substrate 2, the lower connection electrode 6 and the upper connection electrode 7. a metal film or the like, due to the high adhesion between the insulating film and the like such as SiO _2, SiO ₂ film 8a is an outer shell 10, 8
Even if the bonding area between b and the substrate 2 to which the outer shell 10 is in close contact is reduced, a gap from the vacuum space 11 to the outside is formed at the bonding portion between the SiO ₂ films 8a and 8b and the substrate 2 side. Therefore, the SiO ₂ films 8a and 8b, that is, the outer shell 10 can be surely formed integrally with the upper side of the substrate 2 without any gap. Therefore, the coupling area between the outer shell 10 and the substrate 2 can be reduced.

As described above, since the coupling area of the outer shell 10 can be reduced and the thickness of the variable capacitor 1 can be reduced as described above, the size of the variable capacitor 1 can be reduced. Is easy, M
It can be incorporated in very small devices such as MIC (microwave monolithic integrated circuit).

Further, conventionally, as shown in FIG. 4, two substrates, a substrate 2 for supporting the capacitor and an upper substrate 20, were required to vacuum seal the capacitor 5, but in this embodiment, In the embodiment, since the outer shell film is formed on the substrate surface and the capacitor 5 is vacuum-sealed, the upper substrate 20 is not required, and the material cost can be reduced because the substrate 20 is not used.

Further, conventionally, the variable capacitor 1 was manufactured through a manufacturing process in which the upper substrate 20 was bonded to the upper side of the capacitor supporting substrate 2.
Since there is no technology for joining a substrate made of a low dielectric material such as SiO _{2 to} the upper side of the substrate, the substrate 20 cannot be formed of a low dielectric material, and the substrate 20 is made of a dielectric material such as Si or Pyrex glass (trade name). Had to be formed by the material. Since the above-mentioned Si and Pyrex glass have a large dielectric loss, the Q value of the output of the variable capacitor 1 has been reduced.

On the other hand, in this embodiment, the film of the outer shell 10 is formed on the substrate surface by using the sputtering method.
_The outer shell 10 can be formed of the film _{2 and} the dielectric loss of the SiO ₂ film is small, so that the Q value of the output of the variable capacitor 1 can be improved.

In the prior art, the output of the variable capacitor 1 is taken out to the outside through the through hole 23. Since the through hole 23 has a large electric resistance component and poor electric conductivity, it is variable by the electric resistance component. Although the Q value of the output of the capacitor 1 was deteriorated, in the variable capacitor 1 of this embodiment, the through-hole was not provided, and the variable capacitor 1 was directly drawn from the lower electrode 3 and the upper electrode 4 to the outside of the vacuum space. The lower connection electrode 6 and the upper connection electrode 7 are provided, and the output of the variable capacitor 1 is connected to the upper connection electrode 7.
Alternatively, since the liquid crystal is directly guided to the outside via the lower connection electrode 6, the deterioration of the Q value of the output of the variable capacitor 1 can be prevented because of the absence of the through hole.

In addition, the variable capacitor 1 of this embodiment can be manufactured without heating the substrate 2 on which the lower electrode 3 and the upper electrode 4 and the like are formed to a high temperature of 500 ° C. or more (for example, The heating temperature of the substrate at the time of forming the first and second sacrificial layers 14, 16, 17 was about 100 ° C., and the SiO ₂ film 8a,
The heating temperature of the substrate during the formation of 8b is about 150 ° C.), and the lower electrode 3, the upper electrode 4, the lower connection electrode 6, and the upper connection electrode 7 are melted, diffused, and damaged due to the high temperature heating of the substrate. Further, since the electrode for taking out the output of the variable capacitor 1 to the outside (the upper connection electrode 7 in this embodiment) is formed of a metal such as aluminum having a small electric resistance component and good electric conductivity. In addition, it is possible to prevent deterioration of the Q value of the output of the variable capacitor 1 on the output path of the variable capacitor 1 due to the electric resistance component.

Further, as described above, in this embodiment, the SiO ₂ film 8 as the outer shell 10 is provided on the upper side of the substrate 2 instead of bonding the substrate 20 on the upper side of the substrate 2 as in the conventional example.
Since a and 8b are joined and formed by the sputtering method, the lower connection electrode 6 and the upper connection electrode 7 can be drawn out from the vacuum space 11 onto the external substrate surface. As described above, the coupling area between the outer shell 10 and the portion connecting the outer shell 10 may be small, that is, the coupling length L shown in FIG.
Can be very short, the length of the lower connection electrode 6 and the upper connection electrode 7 in the pull-out direction can be extremely short. By shortening the electrodes 6 and 7,
The electric resistance components of the electrodes 6 and 7 become smaller, and the Q value of the output of the variable capacitor 1 can be improved.

Further, in this embodiment, after the space 11 for accommodating the upper electrode 4 and the like is formed, the air in the space 11 is evacuated from the through hole 12 so that the state in the space 11 Since the through-hole 12 is closed in a vacuum state in which the high-frequency movable characteristics are good, the space 11 for accommodating the upper electrode 4 and the like is evacuated to a vacuum state in which the high-frequency movable characteristics of the upper electrode 4 become good. It is possible to avoid deterioration of the high-frequency movable characteristics of the upper electrode 4 due to the sealing and the viscous resistance of air.

[0040] Incidentally, the first and second sacrificial layers used in the process of manufacturing a variable capacitor 1 is considered to be formed by PSG (phosphosilicate-silicon glass) and SiO _2, but for these PSG or SiO ₂ The etchant must use an HF-based solution, and since the HF-based solution etches almost all metals such as aluminum and Ni, the material for forming the lower electrode 3 and the upper electrode 4 is HF-based. It is limited to a very small part of the noble metal such as Au which is not etched by the etching solution. The upper electrode 4 formed of a noble metal such as Au has a low resonance frequency due to the high density of the electrode material. When the variable capacitor 1 having the upper electrode 4 is used as a modulation element, the degree of freedom of the modulation speed ( (Variable range) is very narrow.

On the other hand, in this embodiment, the first
And the second sacrifice layer is made of ZnO.
Since nO can be removed by etching using a solution that does not etch metals such as aluminum as an etchant, the upper electrode 4 can be formed of aluminum. As described above, the resonance frequency of the upper electrode 4 formed of aluminum is increased, and the degree of freedom of the modulation speed of the variable capacitor as the modulation element can be increased.

Note that the present invention is not limited to the above-described embodiment, but can adopt various embodiments. For example, in the above embodiment, the outer shell 10 is made of the SiO ₂ film 8a,
8b, the insulator film forming the outer shell 10 can be formed without causing dissolution / diffusion of a metal when the outer shell 10 is formed, and has a small dielectric constant (for example, a dielectric constant). Rate 5 or less), and is not limited to a SiO ₂ film.

Further, in the above embodiment, the S
The iO ₂ film was formed by a sputtering method.
The film forming method of the film is appropriately set according to the material of the outer shell 10. For example, the film of the outer shell 10 is formed by a film forming method other than the sputtering method, such as a CVD method or an evaporation method. Sometimes.

As described above, the film of the outer shell 10 formed by the CVD method, the vapor deposition or the like has good adhesion, similarly to the film of the outer shell 10 formed by the sputtering method as in the above embodiment. Therefore, the effect of reducing the size of the variable capacitor 1 and the ability to form a film of the outer shell 10 made of a low dielectric substance allow the Q of the output of the variable capacitor 1 to be reduced.
Values can be improved, and an effect that a film can be formed at a substrate heating temperature at which metal dissolution / diffusion does not occur, thereby eliminating damage to electrodes and the like due to high-temperature heating of the substrate, etc. be able to.

Further, in the above embodiment, the through holes 12
Is closed using the SiO ₂ film 8b, but may be closed with another closing material. In such a case, the outer shell 10 is S
It is not necessary to form the iO ₂ films 8a and 8b separately.

In the above embodiment, the first and second sacrificial layers are made of ZnO. However, the first and second sacrificial layers are made of a material other than ZnO which can be etched with a solution that does not etch metals such as aluminum. First and second sacrificial layers may be formed. For example, one of the first and second sacrificial layers may be made of ZnO and the other may be made of a material other than ZnO. Both the second sacrificial layer is ZnO
Alternatively, one of the first and second sacrificial layers may be formed of a material other than ZnO, and the other may be formed of a material other than ZnO. Is also good.

Further, in the above embodiment, the first and second sacrificial layers are formed by the sputtering method.
It may be formed by a forming method other than a sputtering method such as a method or vapor deposition.

Further, in the above embodiment, a quartz substrate is used as the substrate 2, but of course, a substrate other than the quartz substrate may be used.

[0049]

According to the present invention, the outer shell is formed of an insulating film, and the lower electrode and the upper electrode are accommodated in a vacuum space formed by the outer shell and the substrate. Since the thickness of the film can be significantly thinner than the thickness of the substrate, compared to the case where a vacuum space is formed using two substrates as shown in the conventional example, the element of the variable capacitor is The thickness can be made very thin.

The film of the outer shell can be formed by sputtering, vapor deposition, or the like. The film formed by sputtering, vapor deposition, or the like can be formed on the side of the substrate on which the film is laminated. Even if the bonding area between the outer shell and the substrate side is reduced due to the high adhesion to the part, there is no gap at the bonding part from the vacuum space inside the outer shell to the outside. The outer shell can be formed integrally with the coupling region on the substrate side without any gap. That is, the coupling area between the outer shell and the substrate can be reduced.

As described above, the coupling area can be reduced, and as described above, the thickness of the variable capacitor can be reduced, so that the size of the variable capacitor can be easily reduced. The downsizing of the element makes it possible to incorporate it into a small device such as an MMIC.

Further, as described above, the outer shell film is formed on the substrate surface to create a vacuum space for accommodating the lower electrode and the upper electrode. Therefore, as shown in the conventional example, the lower electrode is formed by using two substrates. And a space for accommodating the upper electrode,
Material costs can be kept low.

Further, since the outer shell can be formed by using a sputtering method, vapor deposition, or the like, the outer shell can be formed of a film of a low dielectric material, and the dielectric of the film of the low dielectric material can be formed. Since the loss is small, the Q value of the output of the variable capacitor can be improved.

Further, as described above, the outer shell is formed of an insulator film, and the outer shell film can be formed by a film forming technique such as a sputtering method. The upper connection electrode electrically connected to the upper electrode can be drawn out of the vacuum space containing the lower electrode and the upper electrode onto an external substrate surface. From this, the output of the variable capacitor can be taken out to the outside through the lower connection electrode or the upper connection electrode, the electric resistance component on the output path is small, and the electric resistance component on the output path is large. Accordingly, it is possible to prevent the Q value of the output of the variable capacitor from deteriorating.

In addition, as described above, since the outer shell film has good adhesion to the bonding region on the substrate side, the lower connection electrode and the upper connection electrode at the bonding portion between the outer shell film and the substrate side. It is possible to reduce the length of the lower connection electrode or the upper connection electrode in the pull-out direction, thereby reducing the electrical resistance on the output path. The components can be smaller. From this, the Q value of the output of the variable capacitor can be further improved.

Further, in the method for manufacturing a variable capacitor according to the present invention, the substrate on which the lower electrode, the upper electrode, and the like are formed is used.
It does not heat to a high temperature of 500 ° C or more, and the melting and diffusion of metals such as the lower electrode and upper electrode due to the high temperature heating of the substrate does not occur, and the lower and upper electrodes due to the melting and diffusion of metal do not occur. Can be eliminated.

Further, after a space for accommodating the upper electrode and the like is formed in the outer shell, air in the space is evacuated from the through hole of the outer shell, and the inside of the space has good high-frequency movable characteristics of the upper electrode. Because the through hole is closed in a vacuum state, the space inside the outer shell can be sealed in a vacuum state in which the high-frequency movable characteristics of the upper electrode are good, and the viscosity of air can be reduced. Deterioration of high-frequency movable characteristics of the upper electrode due to resistance can be avoided.

In the invention, after forming a vacuum space for accommodating the lower electrode and the upper electrode, the outer shell laminated above the lower connection electrode and the upper connection electrode outside the vacuum space is removed. However, the lower connection electrode and the upper connection electrode on the substrate surface outside the vacuum space can be exposed to the outside, and the output of the variable capacitor is taken out through the through hole as in the conventional example. The output of the variable capacitor can be taken out to the outside by the lower connection electrode or the upper connection electrode, and the Q value of the output of the variable capacitor is reduced by the amount that does not pass through a portion having a large electric resistance component such as a through hole. Can be improved.

Further, in the invention of the method for manufacturing a variable capacitor in which the first and second sacrificial layers are formed of zinc oxide, the zinc oxide is etched using a solution which does not etch metals such as aluminum as an etching solution. Since the upper electrode can be removed, the upper electrode can be formed of a metal having good electric conductivity and low density, such as aluminum. As described above, the upper electrode formed of a metal having good electric conductivity and low density has a high resonance frequency, and when a variable capacitor is used as a modulation element, the variable range of the modulation speed of the variable capacitor is widened. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a variable capacitor according to the present invention.

FIG. 2 is an explanatory view showing one example of a method for manufacturing a variable capacitor according to the present invention.

FIG. 3 is an explanatory view showing an example of a method of manufacturing a variable capacitor following FIG. 2;

FIG. 4 is an explanatory diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable capacitor 2 Substrate 3 Lower electrode 4 Upper electrode 6 Lower connection electrode 7 Upper connection electrode 10 Outer shell 11 Space 12 Through hole 14 First sacrificial layer 16, 17 ZnO film

Claims (4)

[Claims] 1. A semiconductor device comprising: a lower electrode formed on a substrate surface; and an upper electrode disposed above the lower electrode with a gap therebetween, the upper electrode being formed of an insulating film. The lower electrode and the upper electrode are housed in a vacuum space formed by the outer shell and the substrate, and the lower electrode and the lower electrode are electrically connected to the lower electrode. And an upper connection electrode electrically connected to the upper electrode, which is drawn out from the vacuum space onto an external substrate surface. 2. A lower electrode and a lower connection electrode extending from the lower electrode are formed on the substrate surface, and a first sacrificial layer is formed on the lower electrode by lamination. An upper electrode is laminated on the first sacrificial layer at a position facing the lower electrode, and an upper connection electrode extending from the upper electrode is formed on the substrate surface. And a second sacrifice layer that covers the opposing region of the upper electrode, and an outer shell made of an insulator film is formed on the second sacrifice layer, and then a second sacrifice layer is formed on the second sacrifice layer. A through hole is formed in the outer shell, and an etchant is introduced into the first and second sacrifice layers from the through hole to etch away the first and second sacrifice layers. A void is formed between the shells and a space is formed inside the outer shell. A method for manufacturing a variable capacitor, characterized in that a through hole is closed to make a vacuum space inside an outer shell. 3. A vacuum space is defined as an inner space of an outer shell that covers a region where a lower electrode and an upper electrode face each other, and an outer layer formed over the lower connection electrode and the upper connection electrode outside the vacuum space. 3. The method according to claim 2, wherein the shell is removed to expose the lower connection electrode and the upper connection electrode on the substrate surface outside the vacuum space to the outside. 4. The method according to claim 2, wherein the first and second sacrificial layers are formed of zinc oxide.