variable capacitor

Abstract

To provide a variable capacitance capacitor capable of reducing a control voltage.SOLUTION: A variable capacitance capacitor 1 includes: a first electrode layer 11; an insulation layer 31 disposed on the first electrode layer; a second electrode layer 21 disposed in a first region RG1 on the insulation layer; a third electrode layer 22 disposed in a second region RG2 separated from the first region on the insulation layer; a dielectric layer 32 disposed in a third region RG3 at least between the first and second regions on the insulation layer; and a fourth electrode layer 12 disposed on the dielectric layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to variable capacitors. [Background technology]

[0002] Conventionally, there is a capacitor with variable capacitance in which a dielectric layer is disposed between a pair of electrodes for applying a DC bias (for example, Patent Document 1). In the conventional capacitor, a dielectric layer is disposed between an earth electrode and a DC bias electrode, and a capacitance acquisition electrode is disposed between the earth electrode and the DC bias electrode via the dielectric layer. When a DC bias is applied between the earth electrode and the DC bias electrode, the dielectric properties of the dielectric layer change, and the capacitance of the capacitor changes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-344845 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional capacitors, the earth electrode, DC bias electrode, and capacitance acquisition electrode are stacked in the same direction with a dielectric layer interposed between them, which makes it necessary to set the distance between the earth electrode and the DC bias electrode and the distance between the earth electrode and the capacitance acquisition electrode in conjunction with each other. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to one embodiment of the present disclosure, there is provided a variable capacitor (1) comprising: a first electrode layer (11), an insulating layer (31) disposed on the first electrode layer, a second electrode layer (21) disposed in a first region (RG1) on the insulating layer, a third electrode layer (22) disposed on the insulating layer in a second region (RG2) separate from the first region, a dielectric layer (32) disposed on the insulating layer in at least a third region (RG3) between the first region and the second region, and a fourth electrode layer (12) disposed on the dielectric layer.

[0007] According to this embodiment, for example, the direction of the electric field applied to the dielectric layer by applying a DC voltage between the second electrode layer and the third electrode layer can be made different from the direction of the electric field applied to the dielectric layer by applying an AC voltage between the first electrode and the fourth electrode. The distance between the first electrode layer and the fourth electrode layer and the distance between the second electrode layer and the third electrode layer can be set independently. Therefore, by shortening the distance between the second electrode layer and the third electrode layer, the electric field applied to the dielectric layer can be increased even with the same DC voltage, thereby reducing the DC voltage. Furthermore, since an insulating film is disposed between the first electrode layer and the second electrode layer, the first electrode layer and the third electrode layer can be effectively insulated from each other. Similarly, since an insulating film is disposed between the first electrode layer and the third electrode layer, the first electrode layer and the third electrode layer can be effectively insulated from each other. Furthermore, by using, for example, an oxide film as the insulating film, the oxide film can be resistant to chemicals used in the process of forming the upper layer of the insulating film layer, thereby improving manufacturability. Alternatively, the productivity can be improved by using, for example, a general-purpose polymer film as the insulating film layer. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. [Figure 2] 2 is a cross-sectional view of the variable capacitor shown in FIG. 1 taken along line II-II. [Figure 3] FIG. [Figure 4] A diagram explaining PVDF. [Figure 5] FIG. 10 is a diagram showing the relationship between a control electric field and a relative dielectric constant. [Figure 6] 5A and 5B are diagrams illustrating the relationship between the thickness of a dielectric layer and the electric field distribution. [Figure 7] FIG. 10 is a diagram illustrating the relationship between the thickness of a dielectric layer and the rate of change of capacitance value. [Figure 8] 10A and 10B are diagrams illustrating the relationship between the thickness of a control electrode layer and the electric field distribution. [Figure 9] 10A and 10B are diagrams illustrating the relationship between the thickness of a control electrode layer and the rate of change of capacitance value. [Figure 10] FIG. 10 is a diagram illustrating the relationship between the control electrode voltage, the extraction electrode voltage, and the electric field distribution. [Figure 11] FIG. 10 is a diagram showing the relationship between the control electrode voltage and the extraction electrode voltage and the rate of change of the capacitance value. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. Implementation: 1, the variable capacitor 1 has a first extraction electrode layer 11 as a first electrode layer, a second extraction electrode layer 12 as a fourth electrode layer, a first control electrode layer 21 as a second electrode layer, a second control electrode layer 22 as a third electrode layer, an insulating layer 31, a dielectric layer 32, a first extraction electrode common layer 41, and a second extraction electrode common layer 42. The first extraction electrode layer 11 and the second extraction electrode layer 12 are also collectively referred to as extraction electrode layers 10. The first control electrode layer 21 and the second control electrode layer 22 are also collectively referred to as control electrode layers 20.

[0010] Figure 1 depicts three mutually orthogonal spatial axes, the X, Y, and Z axes. The directions of the X, Y, and Z arrows indicate the positive directions along the X, Y, and Z axes, respectively. The positive directions along the X, Y, and Z axes are the +X direction, +Y direction, and +Z direction, respectively. The directions opposite to the directions of the X, Y, and Z arrows are the negative directions along the X, Y, and Z axes, respectively. The negative directions along the X, Y, and Z axes are the -X direction, -Y direction, and -Z direction, respectively. The directions along the X, Y, and Z axes, regardless of whether they are positive or negative, are called the X direction, Y direction, and Z direction, respectively. This also applies to the following figures and explanations.

[0011] 2, the first control electrode layer 21 and the second control electrode layer 22 are electrode layers for applying a control voltage to change the dielectric constant of the dielectric layer 32, and are electrode layers for adjusting the capacitance of the variable capacitor 1. The first extraction electrode layer 11 and the second extraction electrode layer 12 are electrode layers for utilizing the capacitance of the variable capacitor 1. Typically, the variable capacitor 1 is used by applying a control voltage, which is a DC voltage, to the first control electrode layer 21 and the second control electrode layer 22, and applying AC power between the first extraction electrode layer 11 and the second extraction electrode layer 12.

[0012] In this embodiment, the extraction electrode layer 10 and the control electrode layer 20 are made of gold (Au).

[0013] Alternatively, an AC voltage may be applied between the first control electrode layer 21 and the second control electrode layer 22, and a DC voltage may be applied between the first extraction electrode layer 11 and the second extraction electrode layer 12.

[0014] The variable capacitor 1 has a multilayer structure. As shown in FIG. 2, an insulating layer 31 is disposed on the first extraction electrode layer 11. The first control electrode layer 21 and the second control electrode layer 22 are disposed on the insulating layer 31. This insulates the first extraction electrode layer 11 from the first control electrode layer 21. The first extraction electrode layer 11 is also insulated from the second control electrode layer 22. As shown in FIG. 1, the first control electrode layer 21 is disposed in a first region RG1. The second control electrode layer 22 is disposed in a second region RG2 separated from the first region RG1. As shown in FIG. 2, a dielectric layer 32 is disposed on the insulating layer 31. The dielectric layer 32 is disposed in at least a third region RG3. The dielectric layer 32 covers the first control electrode layer 21 and the second control electrode layer 22. The third region RG3 is disposed between the first region RG1 and the second region RG2. The second extraction electrode layer 12 is disposed on the dielectric layer 32. The film surface direction of each layer is the XY direction, and the stacking direction of each layer is the Z direction.

[0015] 1, the first control electrode layer 21 and the second control electrode layer 22 each have a flat plate shape with the long axis in the Y direction. The first control electrode layers 21 and the second control electrode layers 22 are alternately arranged at intervals in the X direction. The -Y direction end of each first control electrode layer 21 is electrically connected to the first extraction electrode common layer 41. The +Y direction end of each second control electrode layer 22 is electrically connected to the second extraction electrode common layer 42.

[0016] As shown in FIG. 3, the variable capacitor 1 further includes a first extraction electrode common terminal 41a and a second extraction electrode common terminal 42a. The first extraction electrode common terminal 41a is electrically connected to the first extraction electrode common layer 41. The second extraction electrode common terminal 42a is electrically connected to the second extraction electrode common layer 42. The first control electrode layer 21 and the second control electrode layer 22 both have a comb-like shape. Specifically, as described above, the −Y direction end of each first control electrode layer 21 is electrically connected to the first extraction electrode common layer 41 extending in the X direction. Similarly, the +Y direction end of each second control electrode layer 22 is electrically connected to the second extraction electrode common layer 42 extending in the X direction. The first control electrode layers 21 and the second control electrode layers 22 are arranged alternately.

[0017] 1, a structure formed by alternately arranging first control electrode layers 21 and second control electrode layers 22 with dielectric layers 32 sandwiched therebetween in the X direction is also referred to as a first structure ST1. By alternately arranging the first control electrode layers 21 and the second control electrode layers 22, the capacitors formed between the first control electrode layers 21 and the second control electrode layers 22 are connected in parallel with each other, and therefore the capacitance value of the variable capacitor 1 can be increased.

[0018] 2, the dielectric layer 32 is disposed at least between the first control electrode layer 21 and the second control electrode layer 22. Specifically, the dielectric layer 32 is disposed in a third region RG3 sandwiched in the X direction between the first control electrode layer 21 and the second control electrode layer 22. As a result, when a control voltage that is a DC voltage is applied between the first control electrode layer 21 and the second control electrode layer 22, an electric field vector that is approximately parallel to the X direction is generated in the third region RG3.

[0019] 2 , the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction with the dielectric layer 32 sandwiched therebetween. As a result, an electric field vector generated in the third region RG3 when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 roughly intersects with a voltage vector generated in the third region RG3 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22. In this embodiment, the electric field vector generated in the third region RG3 when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 roughly intersects with a voltage vector generated in the third region RG3 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22.

[0020] The direction in which the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other is different from the direction in which the first control electrode layer 21 and the second control electrode layer 22 face each other. This allows the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 and the distance between the first control electrode layer 21 and the second control electrode layer 22 to be set independently. The distance between the first control electrode layer 21 and the second control electrode layer 22 can be shortened without shortening the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12. Therefore, by shortening the distance between the first control electrode layer 21 and the second control electrode layer 22 while maintaining a distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 that can withstand the voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12, the electric field applied between the first control electrode layer 21 and the second control electrode layer 22 can be increased. This allows the control voltage to be reduced.

[0021] Similarly, the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 can be set independently of the distance between the first control electrode layer 21 and the second control electrode layer 22, for example, so as to achieve a target capacitance value.

[0022] In this embodiment, the insulating layer 31 and the dielectric layer 32 contain different materials. Specifically, the insulating layer 31 contains an oxide film such as aluminum oxide or silicon dioxide. This makes it possible to prevent damage to the insulating layer 31 when an organic substance is used in a cleaning process before or after forming the first control electrode layer 21 and the second control electrode layer 22 during the manufacturing process of the variable capacitor 1. In this embodiment, silicon dioxide is used. The insulating layer 31 is formed on a conductive silicon substrate.

[0023] The dielectric layer 32 includes a ferroelectric polymer, for example a fluororesin such as PVDF (polyvinylidene fluoride) or P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)).

[0024] As shown in FIG. 4, a PVDF molecule has hydrogen and fluorine atoms bonded to a carbon chain. Because hydrogen atoms are positively charged and fluorine atoms are negatively charged, the PVDF molecule has an electric dipole moment. When PVDF molecules aggregate due to intermolecular forces, the carbon chains of each PVDF molecule align in the same direction. The hydrogen and fluorine atoms are positioned perpendicular to the carbon chain direction. Therefore, PVDF crystals undergo spontaneous polarization. When an electric field is applied to a PVDF crystal, the polarization direction changes so that the crystal rotates around the X-axis, which is the carbon chain direction. Therefore, even when a control voltage is applied, the polarization direction changes when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12. Therefore, by using PVDF for the dielectric layer 32, a variable capacitor 1 can be provided in which the relative dielectric constant εr changes significantly when the control voltage value is changed.

[0025] 5 is a diagram showing the relationship between the magnitude of the control electric field Ed generated by applying a control voltage between the first control electrode layer 21 and the second control electrode layer 22 and the relative dielectric constant εr when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12. The variable capacitor 1 has dielectric characteristics in which the relative dielectric constant εr has two peaks.

[0026] Ferroelectrics are spontaneously polarized when the control electric field is 0 V / m. When the control electric field is increased up to the coercive electric field Ec, the polarization becomes zero and the relative dielectric constant εr becomes maximum. Near the coercive electric field Ec, the dipole moment tends to move in a direction corresponding to the AC voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12, which is thought to increase the relative dielectric constant εr.

[0027] When the control field Ed is larger than the coercive field Ec, the relative permittivity εr decreases. This is thought to be because the electric dipoles are constrained by the control field Ed and are less likely to move in response to the AC voltage.

[0028] In this embodiment, the direction of the control electric field Ed and the direction of the electric field generated by the application of an AC voltage intersect. Therefore, a peak in the relative permittivity εr appears even in a region where the control electric field Ed is smaller than the coercive electric field Ec. This is thought to be because the application of the control electric field Ed makes it easier for the electric dipoles to move in response to the application of the AC voltage than when the control electric field Ed is not applied.

[0029] The dielectric characteristics of the variable capacitor 1 have an assist region, a polarization inversion region, and a saturation region. When a control voltage in the assist region is applied, the polarization movement of the dielectric layer 32 is assisted. Specifically, the assist region is a region where the control electric field Ed is smaller than the coercive electric field Ec, and the relative dielectric constant εr is larger than the relative dielectric constant ε1 and smaller than the relative dielectric constant ε2. Here, the relative dielectric constant εr is the relative dielectric constant εr when the control electric field Ed is zero. The relative dielectric constant ε2 is the minimum point between the two peaks of the relative dielectric constant εr.

[0030] When a control voltage in the polarization inversion region including the voltage of the coercive field Ec is applied, the polarization of the dielectric layer 32 is more likely to be reversed in response to the AC voltage than in the assist region. Specifically, the polarization inversion region is an electric field range in which the control field Ed includes the coercive field Ec, and is a region in which the relative dielectric constant εr is larger than the peak value ε3 of the relative dielectric constant εr in the assist region.

[0031] When a control voltage in the saturation region is applied, the movement of polarization in the dielectric layer 32 is constrained. Specifically, the saturation region is a region where the control field Ed is greater than the coercive field Ec, and the control field Ed is greater than the coercive field Ec.

[0032] As described above, by applying the control electric field Ed in the assist region, it is possible to make the polarization move more easily than when the control electric field Ed is not applied. Therefore, by applying the control electric field Ed in the assist region to the variable capacitor 1, it is possible to make the capacitance of the variable capacitor 1 larger than the capacitance when the control electric field Ed is not applied.

[0033] Furthermore, by applying a control electric field Ed in the polarization inversion region, the polarization can be made to move more easily than in the assist region. Therefore, by applying a control electric field Ed in the polarization inversion region to the variable capacitor 1, the capacitance of the variable capacitor 1 can be made larger than the capacitance when a control electric field Ed in the assist region is applied.

[0034] Furthermore, applying a control electric field Ed in the saturation region makes it difficult for polarization to move. Therefore, by applying a control electric field Ed in the saturation region to the variable capacitor 1, the capacitance of the variable capacitor 1 can be made smaller than the capacitance when a control electric field Ed in the assist region is not applied. Therefore, with the variable capacitor 1, the capacitance value of the variable capacitor 1 can be set to a desired capacitance value by adjusting the magnitude of the control electric field Ed.

[0035] As described above, PVDF rotates around the direction of extension of the carbon chain as a central axis. Therefore, as in the present application, polarization is easily changed when an AC voltage is applied from a direction different from the direction of the control electric field Ed. Furthermore, since the relative dielectric constant εr of the dielectric layer 32 changes depending on the magnitude of the control electric field Ed, it is possible to provide a variable capacitor 1 with an excellent variability. Here, the variability refers to the amount of change in relative dielectric constant relative to the amount of change in the applied electric field.

[0036] The inventors investigated the relationship between the inter-electrode distance Dd between the first control electrode layer 21 and the second control electrode layer 22 and the thickness Td of the dielectric layer 32. Specifically, the thicknesses of the extraction electrode layer 10, the insulating layer 31, the control electrode layer 20, and the inter-electrode distance Dd were fixed, and the thickness Td of the dielectric layer 32 was varied between 300 nm and 1 μm, and the variable range of the capacitance value of the variable capacitor 1 was determined by simulation. The inter-electrode distance Dd was 1 μm.

[0037] When a control electric field Ed is applied to the entire region from the first control electrode layer 21 to the second control electrode layer 22 in the X direction, as shown in "Td=1 μm" in Fig. 6, capacitances are formed between the first extraction electrode layer 11 and the second extraction electrode layer 12 in the order of first fixed capacitance Cf1, variable capacitance Cv, and second fixed capacitance Cf2 from the bottom. In this case, the combined capacitance Cs is expressed by the following equation (1). Cs=1 / (1 / Cf1+1 / Cv+1 / Cf2) ···(1) In equation (1), "Cf1" represents the capacitance value of the first fixed capacitance Cf1, "Cv" represents the capacitance value of the variable capacitance Cv, and "Cf2" represents the capacitance value of the second fixed capacitance Cf2. Therefore, the larger the value of "1 / Cv+1 / Cf2" relative to the value of "1 / Cf1," the more easily the rate of change of the variable capacitance Cv is reflected in the rate of change of the combined capacitance Cs. A larger rate of change of the combined capacitance Cs is preferable because it increases the variability of the variable capacitor 1.

[0038] The larger the capacitance value of the first fixed capacitance Cf1 is relative to the capacitance value of the variable capacitance Cv, the larger the value of "1 / Cv+1 / Cf2" relative to the value of "1 / Cf1". The first fixed capacitance Cf1 is a capacitance formed on the insulating layer 31, and the variable capacitance Cv and the second fixed capacitance Cf2 are capacitances formed on the dielectric layer 32. Therefore, by using a material with a large relative dielectric constant εr for the insulating layer 31, the capacitance value of the first fixed capacitance Cf1 can be made larger relative to the capacitance value of the variable capacitance Cv. Alternatively, by reducing the thickness of the insulating layer 31, the capacitance value of the first fixed capacitance Cf1 can be made larger relative to the capacitance value of the variable capacitance Cv.

[0039] As shown in "Td=400 nm" in FIG. 6, when the thickness Td of the dielectric layer 32 is small relative to the inter-electrode distance Dd, the distance between the control electrode layer 20 and the second extraction electrode layer 12 becomes short. Therefore, an electric field is generated between the second extraction electrode layer 12 and the control electrode layer 20, resulting in a region in the X direction between the first control electrode layer 21 and the second control electrode layer 22 where the control electric field Ed is not sufficiently applied. Therefore, a first variable capacitance Cv1, a second fixed capacitance Cf2, and a second variable capacitance Cv2 are formed between the first control electrode layer 21 and the second extraction electrode layer 12. The first variable capacitance Cv1 is a capacitance formed in a region Rcv1 close to the first control electrode layer 21. The second variable capacitance Cv2 is a capacitance formed in a region Rcv2 close to the second control electrode layer 22. The second fixed capacitance Cf2 is a capacitance formed in a region Rcf2 between the regions Rcv1 and Rcv2. By forming the second fixed capacitance Cf2, the variability of the capacitance of the variable capacitor 1 decreases.

[0040] As shown in FIG. 7, when the thickness Td of the dielectric layer 32 is 500 nm or greater, the capacitance of the variable capacitor 1 exhibits a large variability. The horizontal axis of FIG. 7 represents the rate of change in the dielectric constant εr of the dielectric layer 32. Specifically, it represents the rate of change in the dielectric constant εr when the control electric field Ed is 0 V / m and the dielectric constant εr is set to "10." For example, "1 / 10" indicates that the dielectric constant εr is one-tenth of the dielectric constant εr when the control electric field Ed is 0 V / m. The vertical axis of FIG. 7 represents the rate of change in the capacitance of the variable capacitor 1, i.e., the combined capacitance Cs. Specifically, like the horizontal axis, it represents the rate of change in the combined capacitance Cs when the control electric field Ed is 0 V / m and the combined capacitance Cs is set to "10." The steeper the slope of the characteristic line shown in FIG. 7, the greater the rate of change in the capacitance of the variable capacitor 1 with respect to the control electric field Ed, i.e., the greater the variability. The same applies to FIGS. 9 and 11, which will be described later. When the thickness Td of the dielectric layer 32 is 500 nm or more, the thicker the thickness Td, the larger the capacitance value of the variable capacitance Cv and therefore the larger the variability. For this reason, a thicker thickness Td is more preferable.

[0041] From the above, it can be seen that when the inter-electrode distance Dd and the thickness Td of the dielectric layer 32 satisfy the formula (1), the capacitance value of the variable capacitor 1 has a good variability. Td≧Dd / 2 (1)

[0042] The inventors studied the thickness Te of the control electrode layer 20. Specifically, the thicknesses of the first extraction electrode layer 11, the insulating layer 31, the dielectric layer 32, and the second extraction electrode layer 12 were fixed, and the thickness Te of the control electrode layer 20 was varied to simulate the distribution of the electric field between the first extraction electrode layer 11 and the second extraction electrode layer 12. The thickness Td of the dielectric layer 32 was set to 500 nm. As a result, as shown in FIG. 8, the thicker the thickness Te of the control electrode layer 20, the closer the electric field is to the center. Then, as shown in FIG. 9, when the thickness Te of the control electrode layer 20 is 50 nm or more, the capacitance value of the variable capacitor 1 exhibits a good variability.

[0043] From the above, it can be seen that when the thickness Te of the control electrode layer 20 and the thickness Td of the dielectric layer 32 satisfy the following formula (2), the capacitance value of the variable capacitor 1 has a good variability. Te≧Td / 10 (2)

[0044] The inventors have investigated the relationship between the control voltage and the extraction voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12. Specifically, they have investigated how the distribution of the electric field changes depending on whether a voltage between a ground power supply and a positive power supply or a voltage between a negative power supply and a positive power supply is applied as the extraction voltage and the control voltage.

[0045] In FIG. 10, "Vd" indicates the control voltage and "Va" indicates the extraction voltage. As shown in FIG. 10, by matching the voltage ranges of the control voltage and the extraction voltage, an electric field can be applied to the dielectric layer 32 across the region from the first control electrode layer 21 to the second control electrode layer 22 in the X direction. This increases the rate of change in the capacitance value of the variable capacitor 1. Matching the voltage ranges of the control voltage and the extraction voltage specifically corresponds to "Case 1" and "Case 4" shown in FIG. 10. "Case 1" refers to the case where both the control voltage and the extraction voltage are applied in the range from negative to positive voltages. "Case 4" refers to the case where both the control voltage and the extraction voltage are applied in the range from ground voltage to positive voltages.

[0046] As shown in Figure 11, "Case 1" and "Case 4" have a better variability in the capacitance value of variable capacitor 1 than "Case 2" and "Case 3". Therefore, in "Case 1" and "Case 4", the variability in the capacitance value of variable capacitor 1 can be improved. Furthermore, "Case 4" is preferable to "Case 1" because it does not require a negative power supply and therefore allows for a simpler system configuration.

[0047] According to the embodiment described above, the variable capacitor 1 includes the first control electrode layer 21, the second control electrode layer 22, and the dielectric layer 32 disposed on the insulating layer 31, and the second extraction electrode layer 12 disposed on the dielectric layer 32. Therefore, the first control electrode layer 21 and the second control electrode layer 22 face each other in the direction along the insulating layer 31, and the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the stacking direction. By applying a control voltage to the first control electrode layer 21 and the second control electrode layer 22, the direction of the electric field applied to the dielectric layer 32 can be made different from the direction of the electric field applied to the dielectric layer 32 by applying a voltage to the first extraction electrode layer 11 and the second extraction electrode layer 12. By shortening the distance between the first control electrode layer 21 and the second control electrode layer 22, the control voltage Vd can be reduced. Furthermore, the insulating layer 31 can insulate the control electrode layer 20 from the first extraction electrode layer 11.

[0048] Furthermore, since the insulating layer 31 is an oxide film that is resistant to chemicals used in the process of forming the upper layer of the insulating film layer, manufacturability can be improved.

[0049] Furthermore, when the inter-electrode distance Dd in the X direction, which is the first direction, between the first control electrode layer 21 and the second control electrode layer 22 and the thickness Td of the dielectric layer 32 satisfy the formula (1), it is possible to provide a variable capacitor 1 with a good variability of the capacitance value. When the thickness Te of the first control electrode layer 21 and the second control electrode layer 22 and the thickness Td of the dielectric layer 32 satisfy the formula (2), it is possible to provide a variable capacitor 1 with a good variability of the capacitance value.

[0050] Furthermore, a variable capacitor 1 having a good variability of capacitance can be provided by supplying a negative power supply voltage to the first control electrode layer 21, a positive power supply voltage to the second control electrode layer 22, a negative power supply voltage to the first extraction electrode layer 11, and a positive power supply voltage to the second extraction electrode layer 12. Further, a variable capacitor 1 having a good variability of capacitance can be provided by supplying the first control electrode layer 21 with a ground, a positive power supply voltage to the second control electrode layer 22, a grounded first extraction electrode layer 11, and a positive power supply voltage to the second extraction electrode layer 12.

[0051] B. Other Embodiments: (B1) In the above embodiment, the insulating layer 31 includes an oxide film. Alternatively, the insulating layer 31 may include a dielectric having a dielectric constant of 10 or more. Examples of dielectrics having a dielectric constant of 10 or more include PVDV and inorganic high-dielectric materials such as barium titanate. If the difference between the dielectric constants of the insulating layer 31 and the dielectric layer 32 is large, polarization movement is hindered near the boundary between the insulating layer 31 and the dielectric layer 32. Therefore, by using an insulating layer 31 with a high dielectric constant, polarization movement is less likely to be hindered near the interface between the insulating layer 31 and the dielectric layer 32, thereby improving the variability of the capacitance value of the variable capacitor 1. Furthermore, using a general-purpose high-dielectric film as the insulating layer 31 improves the manufacturability of the variable capacitor 1.

[0052] (B2) In the above embodiment, the insulating layer 31 includes an oxide film. Alternatively, the insulating layer 31 may include a ferroelectric polymer. This allows the insulating layer 31 to function as a variable capacitor whose relative dielectric constant εr changes when a control electric field Ed is applied, thereby improving the variability of the capacitance value of the variable capacitor 1.

[0053] (B3) In the above embodiment, the variable capacitor 1 is formed on a conductive silicon substrate. In other embodiments, the variable capacitor 1 may be formed on a silicon dioxide layer, an aluminum oxide layer, or an aluminum electrode layer formed on a silicon substrate.

[0054] The present disclosure is not limited to the above-described embodiments and modifications, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and modifications corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0055] Other forms: The features of the present disclosure are as follows: (Form 1) A variable capacitor (1), The first electrode layer (11), an insulating layer (31) disposed on the first electrode layer; a second electrode layer (21) disposed in a first region (RG1) on the insulating layer; a third electrode layer (22) disposed on the insulating layer in a second region (RG2) separate from the first region; a dielectric layer (32) disposed on the insulating layer in at least a third region (RG3) between the first region and the second region; a fourth electrode layer (12) disposed on the dielectric layer, (Form 2) The variable capacitor according to aspect 1, The variable capacitor, wherein the insulating layer is an oxide film. (Form 3) The variable capacitor according to aspect 1 or 2, the second electrode layer and the third electrode layer are electrode layers for applying a control voltage to change the dielectric constant of the insulating layer, the first electrode layer and the fourth electrode layer are electrode layers for extracting capacitance, the dielectric layer is disposed to cover the second electrode layer and the third electrode layer; A variable capacitance capacitor, wherein the inter-electrode distance Dd between the second electrode layer and the third electrode layer in a first direction along the film surface direction of the insulating layer and the thickness Td of the dielectric layer satisfy the following formula (1): Td≧Dd / 2 (1) (Form 4) The variable capacitor according to any one of aspects 1 to 3, the dielectric layer is disposed to cover the second electrode layer and the third electrode layer; the second electrode layer and the third electrode layer have the same thickness; a thickness Te of the second electrode layer; The thickness Td of the dielectric layer is a variable capacitance capacitor that satisfies the following formula (2): Te≧Td / 10 (2) (Form 5) The variable capacitor according to any one of aspects 1 to 4, a negative power supply voltage is supplied to either the second electrode layer or the third electrode layer; a positive power supply voltage is supplied to the other of the second electrode layer and the third electrode layer; a negative power supply voltage is supplied to either the first electrode layer or the fourth electrode layer; A variable capacitor, wherein the other of the first electrode layer and the fourth electrode layer is supplied with a positive power supply voltage. (Form 6) The variable capacitor according to any one of aspects 1 to 5, One of the second electrode layer and the third electrode layer is grounded, a positive power supply voltage is supplied to the other of the second electrode layer and the third electrode layer; one of the first electrode layer and the fourth electrode layer is grounded; A variable capacitor, wherein the other of the first electrode layer and the fourth electrode layer is supplied with a positive power supply voltage. (Form 7) The variable capacitor according to any one of aspects 1 to 6, The insulating layer includes a dielectric having a relative dielectric constant of 10 or more. (Form 8) The variable capacitor according to any one of aspects 1 to 7, The variable capacitor wherein the insulating layer comprises a ferroelectric polymer. (Form 9) The variable capacitor according to any one of aspects 1 to 8, the second electrode layer and the third electrode layer both have a comb-tooth shape, The variable capacitor, wherein the second electrode layers and the third electrode layers are alternately arranged in a first direction along the film surface direction of the insulating layer. [Explanation of symbols]

[0056] 1...variable capacitor, 11...first extraction electrode layer, 12...second extraction electrode layer, 21...first control electrode layer, 22...second control electrode layer, 31...insulating layer, 32...dielectric layer, RG1...first region, RG2...second region, RG3...third region

Claims

1. A variable capacitor (1), A first electrode layer (11); an insulating layer (31) disposed on the first electrode layer; a second electrode layer (21) disposed in a first region (RG1) on the insulating layer; a third electrode layer (22) disposed on the insulating layer in a second region (RG2) separated from the first region; a dielectric layer (32) disposed on the insulating layer in at least a third region (RG3) between the first region and the second region; a fourth electrode layer (12) disposed on the dielectric layer.

2. 2. The variable capacitor according to claim 1, The variable capacitor, wherein the insulating layer is an oxide film.

3. 3. The variable capacitor according to claim 1, the second electrode layer and the third electrode layer are electrode layers for applying a control voltage to change the dielectric constant of the insulating layer, the first electrode layer and the fourth electrode layer are electrode layers for extracting capacitance, the dielectric layer is disposed to cover the second electrode layer and the third electrode layer; A variable capacitance capacitor, wherein an inter-electrode distance Dd between the second electrode layer and the third electrode layer in a first direction along the film surface direction of the insulating layer and a thickness Td of the dielectric layer satisfy the following formula (1): Td≧Dd / 2 (1)

4. 3. The variable capacitor according to claim 1, the dielectric layer is disposed to cover the second electrode layer and the third electrode layer; the second electrode layer and the third electrode layer have the same thickness; a thickness Te of the second electrode layer; The thickness Td of the dielectric layer is a variable capacitance capacitor that satisfies the following formula (2): Te≧Td / 10 (2)

5. 2. The variable capacitor according to claim 1, a negative power supply voltage is supplied to either the second electrode layer or the third electrode layer; a positive power supply voltage is supplied to the other of the second electrode layer and the third electrode layer; a negative power supply voltage is supplied to either the first electrode layer or the fourth electrode layer; A variable capacitor, wherein the other of the first electrode layer and the fourth electrode layer is supplied with a positive power supply voltage.

6. 2. The variable capacitor according to claim 1, one of the second electrode layer and the third electrode layer is grounded; a positive power supply voltage is supplied to the other of the second electrode layer and the third electrode layer; one of the first electrode layer and the fourth electrode layer is grounded; A variable capacitor, wherein the other of the first electrode layer and the fourth electrode layer is supplied with a positive power supply voltage.

7. 2. The variable capacitor according to claim 1, The insulating layer includes a dielectric having a relative dielectric constant of 10 or more.

8. 2. The variable capacitor according to claim 1, The variable capacitor wherein the insulating layer comprises a ferroelectric polymer.

9. 2. The variable capacitor according to claim 1, the second electrode layer and the third electrode layer both have a comb-tooth shape, The variable capacitor, wherein the second electrode layers and the third electrode layers are alternately arranged in a first direction along a film surface direction of the insulating layer.

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