Variable capacitance capacitor and power supply device

Abstract

To provide a variable capacitance capacitor capable of reducing a control voltage.SOLUTION: An variable capacitance capacitor 1 includes: a first control electrode 21; a second control electrode 22 that faces the first control electrode; a dielectric layer 32 that is disposed at least between the first control electrode and the second control electrode; and a first extraction electrode 11 and a second extraction electrode 12 that face each other with the dielectric layer therebetween. The first extraction electrode and the second extraction electrode are positioned so as to generate an electric field in a direction that intersects an electric field vector generated between the first control electrode and the second control electrode when a control voltage is applied between the first control electrode and the second control electrode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a variable capacitor and a power supply device. [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] JP 2006-344845 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the capacitor described in Patent Document 1, the earth electrode, the DC bias electrode, and the capacitance acquisition electrode are laminated in the same direction with a dielectric layer interposed between them. This 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, a variable capacitor (1) is provided. This variable capacitor includes a first control electrode (21), a second control electrode (22) facing the first control electrode, a dielectric layer (32) disposed at least between the first control electrode and the second control electrode, and a first extraction electrode (11) and a second extraction electrode (12) facing each other across the dielectric layer, and the first extraction electrode and the second extraction electrode are disposed at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode and the second control electrode when a control voltage is applied between the first control electrode and the second control electrode.

[0007] According to this embodiment, the distance between the first control electrode and the second control electrode and the distance between the first extraction electrode and the second extraction electrode can be set independently, so that by shortening the distance between the first control electrode and the second control electrode, the electric field applied to the dielectric layer can be increased even with the same control voltage, thereby making it possible to reduce the control voltage. [Brief description of the drawings]

[0008] [Figure 1] FIG. [Diagram 2] 2 is a cross-sectional view of the variable capacitor shown in FIG. 1 taken along line II-II. [Diagram 3] A diagram explaining PVDF. [Figure 4] FIG. 13 is a graph showing the relationship between a control electric field and a relative dielectric constant. [Diagram 5] FIG. 11 is a perspective view of a variable capacitor according to a second embodiment. [Figure 6] FIG. 13 is a diagram showing the results of consideration of the number of placements. [Figure 7] FIG. 11 is a cross-sectional view of a variable capacitor according to a third embodiment. [Figure 8] FIG. 13 is a diagram showing the results of a study on the inter-electrode distance and the electrode length. [Figure 9] FIG. 13 is a circuit diagram of a contactless power supply system according to a fourth embodiment. [Figure 10] FIG. [Figure 11]A diagram comparing relaxors and ferroelectrics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: As shown in FIG. 1, the variable capacitor 1 has a first extraction electrode layer 11 as a first extraction electrode, a second extraction electrode layer 12 as a second extraction electrode, a first control electrode layer 21 as a first control electrode, a second control electrode layer 22 as a second control electrode, a first dielectric layer 31, a second dielectric layer 32 as a dielectric layer, a first extraction electrode common layer 41, and a second extraction electrode common layer 42.

[0010] In FIG. 1, three mutually orthogonal spatial axes, the XYZ axes, are depicted. The directions in which the X-axis, Y-axis, and Z-axis arrows point indicate the positive directions along the X-axis, Y-axis, and Z-axis, respectively. The positive directions along the X-axis, Y-axis, and Z-axis are the +X direction, +Y direction, and +Z direction, respectively. The directions opposite to the directions in which the X-axis, Y-axis, and Z-axis arrows point are the negative directions along the X-axis, Y-axis, and Z-axis, respectively. The negative directions along the X-axis, Y-axis, and Z-axis are the -X direction, -Y direction, and -Z direction, respectively. The directions along the X-axis, Y-axis, and Z-axis, regardless of whether they are positive or negative, are called the X direction, Y direction, and Z direction, respectively. The same 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 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] The second control electrode layer 22 faces the first control electrode layer 21. The second dielectric layer 32 is disposed at least between the first control electrode layer 21 and the second control electrode layer 22. The first extraction electrode layer 11 and the second extraction electrode layer 12 face each other with the second dielectric layer 32 in between. The first extraction electrode layer 11 and the second extraction electrode layer 12 are disposed at positions that generate an electric field along a direction intersecting with an electric field vector generated between the first control electrode layer 21 and the second control electrode layer 22 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22. In this embodiment, the first control electrode layer 21 and the second control electrode layer 22 face each other in the X direction as the first direction. The first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction as the second direction.

[0013] As shown in Fig. 2, the variable capacitor 1 has a laminated structure. Specifically, a first dielectric layer 31 is disposed on a first extraction electrode layer 11. A first control electrode layer 21, a second control electrode layer 22, and a second dielectric layer 32 are disposed on the first dielectric layer 31. The second dielectric layer 32 covers the first control electrode layer 21 and the second control electrode layer 22. A second extraction electrode layer 12 is disposed on the second dielectric layer 32. The film surface direction of each layer is the XY direction. The lamination direction in which each layer is laminated is the Z direction.

[0014] 1, the first control electrode layer 21 and the second control electrode layer 22 each have a flat plate shape with a long axis in the Y direction. The first control electrode layer 21 and the second control electrode layer 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.

[0015] An arrangement formed by alternately arranging the first control electrode layer 21 and the second control electrode layer 22 with the second dielectric layer 32 therebetween in the X direction is also referred to as a first arrangement ST1. By alternately arranging the first control electrode layer 21 and the second control electrode layer 22, the capacitors formed between the adjacent first control electrode layer 21 and second control electrode layer 22 are connected in parallel with each other, so that the capacitance value of the variable capacitor 1 can be increased.

[0016] 2, the second dielectric layer 32 is disposed at least between the first control electrode layer 21 and the second control electrode layer 22. Specifically, the second dielectric layer 32 is disposed in a control region RG1 sandwiched between the first control electrode layer 21 and the second control electrode layer 22 in the X direction. 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 control region RG1.

[0017] The first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction with the second dielectric layer 32 interposed therebetween. As a result, an electric field vector generated in the control region RG1 when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 intersects with a voltage vector generated in the control region RG1 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22. In this embodiment, the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction. The first control electrode layer 21 and the second control electrode layer 22 face each other in the X direction. Therefore, an electric field vector generated in the control region RG1 when an AC voltage is applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 is approximately perpendicular to a voltage vector generated in the control region RG1 when a control voltage is applied between the first control electrode layer 21 and the second control electrode layer 22.

[0018] 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 extraction electrode layer 11 and the second extraction electrode layer 12 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. Therefore, the control voltage can be reduced.

[0019] If the direction in which the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other is the same as the direction in which the first control electrode layer 21 and the second control electrode layer 22 face each other, the control voltage needs to be made larger than the voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12 in order to adjust the relative dielectric constant of the dielectric. In this regard, according to this embodiment, 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 can be set independently. Therefore, by shortening the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12, the control voltage can be reduced.

[0020] Also, for the above reasons, the voltage applied to the second dielectric layer 32 can be lowered compared to the case where the direction in which the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other is the same as the direction in which the first control electrode layer 21 and the second control electrode layer 22 face each other. Therefore, the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12 can be shortened to an extent that the second dielectric layer 32 can withstand the applied voltage. This allows the size of the variable capacitor 1 to be reduced. In addition, since the first control electrode layer 21 and the second control electrode layer 22 face each other in the X direction, an electric field can also be applied to the second dielectric layer 32 in a region outside the control region RG1. This allows the region of the second dielectric layer 32 in which the relative dielectric constant εr changes to be expanded.

[0021] The dielectric properties of the second dielectric layer 32 are anisotropic. Here, the anisotropy of the dielectric properties means that the relative dielectric constant εr when an AC voltage is applied to the second dielectric layer 32 in a state where a control voltage is applied thereto differs depending on the direction of the electric field vector generated by the application of the AC voltage. Since the dielectric properties of the second dielectric layer 32 are anisotropic, when the direction in which the control voltage is applied differs from the direction in which the AC voltage is applied, the relative dielectric constant εr changes characteristically depending on the magnitude of the control voltage, as will be described in detail later.

[0022] In this embodiment, the first dielectric layer 31 and the second dielectric layer 32 contain a ferroelectric material of the same material. In particular, the first dielectric layer 31 and the second dielectric layer 32 contain PVDF (polyvinylidene fluoride). Alternatively, the first dielectric layer 31 and the second dielectric layer 32 may contain a ferroelectric polymer such as a fluororesin such as P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)). The first dielectric layer 31 containing a ferroelectric material can also function as a variable capacitance capacitor.

[0023] As another embodiment of the first dielectric layer 31 and the second dielectric layer 32, the first dielectric layer 31 and the second dielectric layer 32 may include dielectric materials different from each other.

[0024] As shown in FIG. 3, in a PVDF molecule, hydrogen atoms and fluorine atoms are bonded to a carbon chain. Since hydrogen atoms are positively charged and fluorine atoms are negatively charged, the PVDF molecule has an electric dipole moment. When PVDF molecules are aggregated by intermolecular forces, the carbon chains of each PVDF molecule extend in the same direction. Hydrogen atoms and fluorine atoms are located in a direction perpendicular to the direction in which the carbon chains extend. Therefore, spontaneous polarization occurs in a PVDF crystal. When an electric field is applied to a PVDF crystal, the direction of polarization changes so as to rotate around the X-axis, which is the direction in which the carbon chains extend, as the central axis. Therefore, even when a control voltage is applied, the direction of polarization 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 second dielectric layer 32, it is possible to provide a variable capacitance capacitor 1 in which the relative dielectric constant εr changes significantly when the voltage value of the control voltage is changed.

[0025] 4 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] A ferroelectric material is spontaneously polarized when the control electric field is 0 V / m. When the control electric field is increased to the coercive electric field Ec, the polarization becomes zero and the relative dielectric constant εr becomes maximum. In the vicinity of 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, so it is considered that the relative dielectric constant εr becomes large.

[0027] When the control electric field Ed becomes larger than the coercive electric field Ec, the relative dielectric constant εr becomes smaller. This is thought to be because the electric dipoles are restrained by the control electric 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 caused by the application of the AC voltage intersect. Therefore, even in the region of the control electric field Ed smaller than the coercive electric field Ec, a peak of the relative dielectric constant εr appears. It is considered that this is 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 include an assist region, a polarization inversion region, and a saturation region. When a control voltage for the assist region is applied, the movement of the polarization of the second 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 ε1 is the relative dielectric constant εr when the control electric field Ed is zero. The relative dielectric constant ε2 is the minimum point between two peaks of the relative dielectric constant εr.

[0030] When a control voltage for the polarization inversion region including the voltage of the coercive electric field Ec is applied, the polarization of the second dielectric layer 32 is more likely to be inverted 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 electric field Ed includes the coercive electric 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 the polarization of the second dielectric layer 32 is constrained. Specifically, the saturation region is a region in which the control electric field Ed is greater than the coercive electric field Ec, and the control electric field Ed is greater than the coercive electric field Ec.

[0032] As described above, by applying the control electric field Ed in the assist region, the polarization can be made to 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, the capacitance of the variable capacitor 1 can be made larger than the capacitance when the control electric field Ed is not applied.

[0033] Moreover, by applying the 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 the 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 the control electric field Ed in the assist region is applied.

[0034] Moreover, by applying a control electric field Ed in the saturation region, the polarization can be made less likely 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 the control electric field Ed in the assist region is not applied. Therefore, according to the variable capacitor 1, the capacitance value of the variable capacitor 1 can be set to a target capacitance value by adjusting the magnitude of the control electric field Ed.

[0035] As described above, PVDF rotates around the direction in which the carbon chain extends as a central axis. Therefore, as in the present application, when an AC voltage is applied from a direction different from the direction of the control electric field Ed, the polarization is likely to move. For this reason, the dielectric characteristics of the second dielectric layer 32 are anisotropic. The second dielectric layer 32 changes its relative dielectric constant εr depending on the magnitude of the control electric field Ed, so that a variable capacitor 1 having a good variability can be provided. Here, the variability refers to the amount of change in the relative dielectric constant relative to the amount of change in the applied electric field.

[0036] According to the first embodiment described above, the first extraction electrode layer 11 and the second extraction electrode layer 12 are arranged at positions that generate an electric field along a direction intersecting with an electric field vector generated when a control voltage is applied. 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. This allows the control voltage to be reduced.

[0037] In addition, the second dielectric layer 32 has a dielectric characteristic in which the relative dielectric constant εr when the control voltage for the assist region is applied is larger than the relative dielectric constant εr when the control voltage is not applied. Therefore, by applying the control voltage for the assist region to the second dielectric layer 32, the capacitance value of the variable capacitor 1 can be made larger than when the control voltage is not applied.

[0038] In addition, the second dielectric layer 32 has a dielectric characteristic in which the relative dielectric constant εr when a control voltage in the saturation region is applied is smaller than the relative dielectric constant εr when no control voltage is applied. Therefore, by applying a control voltage in the saturation region to the second dielectric layer 32, the capacitance value of the variable capacitor 1 can be made smaller than when no control voltage is applied.

[0039] In addition, the second dielectric layer 32 has a dielectric characteristic in which the relative dielectric constant εr when a control voltage for the polarization inversion region is applied is larger than the relative dielectric constant εr when no control voltage is applied. Therefore, by applying a control voltage for the polarization inversion region to the second dielectric layer 32, the capacitance value of the variable capacitor 1 can be made larger than when no control voltage is applied.

[0040] Moreover, the first control electrode layer 21 and the second control electrode layer 22 face each other in the X direction, and the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction perpendicular to the X direction. This makes it possible to uniformly apply the control electric field Ed to the second dielectric layer 32 regardless of the direction of the electric field generated by the AC voltage applied between the first extraction electrode layer 11 and the second extraction electrode layer 12.

[0041] Furthermore, the dielectric properties of the second dielectric layer 32 are anisotropic. Therefore, when an AC voltage is applied in a direction different from the control voltage, it is possible to provide a variable capacitor 1 whose capacitance value changes according to the voltage value of the control voltage. Furthermore, the second dielectric layer 32 includes a ferroelectric polymer. Since the second dielectric layer 32 includes a ferroelectric polymer, it is possible to provide a variable capacitor 1 having a good variability in capacitance value.

[0042] B. Second embodiment: 5, a variable capacitor 201 according to this embodiment has a first arrangement body ST1 and a second arrangement body ST2. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0043] The second arrangement ST2 is configured by arranging the first arrangement ST1 in the Z direction. The first extraction electrode layers 11 and the second extraction electrode layers 12 are arranged alternately in the Z direction. The first extraction electrode layers 11 are electrically connected to a first extraction electrode common layer (not shown). The second extraction electrode layers 12 are electrically connected to a second extraction electrode common layer (not shown). Since the first arrangement ST1 is stacked in the Z direction, the capacitors formed between the adjacent first extraction electrode layers 11 and second extraction electrode layers 12 are connected in parallel with each other, so that the capacitance value of the variable capacitance capacitor 201 can be increased.

[0044] When the size of the variable capacitor 1 is fixed, there is a trade-off between the capacitance value of the variable capacitor 1 and the electric field resistance of the variable capacitor 1. For example, in the case of the first arrangement body ST1 shown in FIG. 6, if the first arrangement number of the first arrangement body ST1 is n1 and the applied voltage is V1, the capacitance value C1 is expressed by the following formula (1) using the formula for a parallel plate capacitor. Here, the first arrangement number is the number of pairs of the first control electrode layer 21 and the second control electrode layer 22. In other words, when the number of layers of the first control electrode layer 21 and the number of layers of the second control electrode layer 22 are the same, the first arrangement number is equal to (2×n-1) when the number of layers is n. C1 = ε0 ε r ·S1 / (D / n1)·n1 =ε0 ε r ·S1·n1 2 / D (1) The parameters in equation (1) are as follows: ε0: Dielectric constant of vacuum ε r : relative dielectric constant of dielectric S1: The area of ​​the capacitor formed by the first control electrode layer and the second control electrode layer D: Length in the stacking direction The inter-electrode distance d1 between the first control electrode layer 21 and the second control electrode layer 22 is d1=W / n1 Moreover, the electric field E1 applied to the dielectric body in the first arrangement body ST1 is expressed by the following formula (2). E1 = V1 / (W / n1) = V1 n1 / W (2) From formulas (1) and (2), if the first arrangement number n1 is increased, the capacitance value increases, but the applied electric field also increases. The magnitude of the applied electric field is limited by the electric field resistance, which is the electric field that can be applied to the dielectric. Therefore, the first arrangement number n1 is determined by the electric field resistance of the dielectric.

[0045] Similarly, for the second arranging bodies ST2, if the second arrangement number of the second arranging bodies ST2 is n2 and the applied voltage is V2, the capacitance value C2 is expressed by the following formula (3). C2 = ε0·ε r ·S2 / H·n2 2 (3) The parameters in equation (3) are as follows: S2: Area of ​​the capacitor formed by the first extraction electrode layer and the second extraction electrode layer H: Length in the stacking direction Moreover, the electric field E2 applied to the dielectric body in the second arrangement body ST2 is expressed by the following formula (4). E2 = V2 n2 / H (4)

[0046] The inventors have studied the optimum values ​​of the first arrangement number n1 and the second arrangement number n2 when the size of the variable capacitor 1 is fixed. The values ​​used in the study are as follows. Width of variable capacitor (W: length in Y direction): 20 mm Depth of variable capacitor (D: length in X direction): 20 mm Variable capacitor height (H: length in Z direction): 2mm First capacitance value (large capacitance value): 300nF Second capacitance value (smaller capacitance value): 60nF Control voltage (V1): 10V AC voltage (V2): 200V (effective value) As a result of the investigation, it was found that the electric field resistance condition is met and the target capacitance value can be obtained when the first arrangement number n1 is 20,000 or more and the second arrangement number n2 is 100 or more. Figure 6 shows the electric field E1 when the first arrangement number n1 is 20,000 and the electric field E2 when the second arrangement number n2 is 100. "H = ε0 ε r ·S2·n2 2 By substituting “ / C2” for “H” in equation (4), the electric field E2 is expressed by the following equation (5). E2=C2·V2 / (ε0·ε r S2 n2) (5) Therefore, as shown in FIG. 6, when the capacitance value C2, the voltage V2, the area S2, and the second arrangement number n2 are set to fixed values, the relative dielectric constant ε r The larger the electric field E2, the smaller it becomes.

[0047] Here, when P(VDF-TrFE) is used as the dielectric, the relative dielectric constant εr that satisfies the target capacitance value is "20." Point PO in Fig. 6 indicates the electric field withstandability of P(VDF-TrFE) when the relative dielectric constant εr is 20. As shown in Fig. 6, when the first arrangement number n1 is 20000 and the second arrangement number n2 is 100, both the electric field E1 and the electric field E2 are smaller than the electric field withstandability of the dielectric, so that the electric field withstandability condition of the dielectric can be satisfied.

[0048] According to the second embodiment described above, the variable capacitor 201 has the first arrangement body ST1 and the second arrangement body ST2, and therefore the capacitance value of the variable capacitor 201 can be increased compared to a capacitor that does not have a structure in which the electrodes are alternately arranged. In addition, the direction in which the first control electrode layer 21 and the second control electrode layer 22 of the first arrangement body ST1 are arranged is different from the direction in which the first extraction electrode layer 11 and the second extraction electrode layer 12 of the second arrangement body ST2 are arranged, so that it is possible to provide a variable capacitor 201 that satisfies both the electric field resistance and the capacitance value. In addition, by setting the first arrangement number n1 to 20,000 or more and the second arrangement number n2 to 100 or more, it is possible to provide a variable capacitor 201 with a desired capacitance value.

[0049] C. Third embodiment: 7, the variable capacitor 301 according to the third embodiment differs from the first embodiment in the opposing direction of the first extraction electrode layer 11 and the second extraction electrode layer 12, and in the opposing direction of the first control electrode layer 21 and the second control electrode layer 22. The same components as those in the above embodiments are denoted by the same reference numerals, and detailed explanations will be omitted as appropriate.

[0050] As shown in FIG. 7, the variable capacitor 301 has a first extraction electrode layer 11, a second extraction electrode layer 12, a first control electrode layer 21, a second control electrode layer 22, a second dielectric layer 32, a first insulating layer 51, and a second insulating layer 52. The first insulating layer 51 is disposed on the first control electrode layer 21. The first extraction electrode layer 11, the second extraction electrode layer 12, and the second dielectric layer 32 are disposed on the first insulating layer 51. The first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the X direction with the second dielectric layer 32 interposed therebetween. The second insulating layer 52 is disposed on the second dielectric layer 32. The second insulating layer 52 covers the first extraction electrode layer 11, the second dielectric layer 32, and the second extraction electrode layer 12. The second control electrode layer 22 is disposed on the second insulating layer 52. The first control electrode layer 21 and the second control electrode layer 22 face each other in the Z direction, with the second dielectric layer 32 sandwiched therebetween.

[0051] In this embodiment, the first insulating layer 51 and the second insulating layer 52 contain the same material. For example, an oxide film such as aluminum oxide (Al2O3) or silicon dioxide (SiO2) can be used as the first insulating layer 51 and the second insulating layer 52. Note that, in another embodiment, the first insulating layer 51 and the second insulating layer 52 may be realized by containing different materials.

[0052] By disposing the first insulating layer 51 between the second dielectric layer 32 and the first control electrode layer 21, and by disposing the second insulating layer 52 between the second dielectric layer 32 and the second control electrode layer 22, the electric field generated when a control voltage is applied can be applied evenly to the second dielectric layer 32. This is because by disposing the first insulating layer 51 and the second insulating layer 52, the influence of the electric field generated by applying an AC voltage between the first control electrode layer 21 and the second control electrode layer 22 can be suppressed.

[0053] The inventors have studied the optimum values ​​of the inter-electrode distance Lc between the first extraction electrode layer 11 and the second control electrode layer 22 of the variable capacitance capacitor 301, and the electrode length Le, which is the length of the second control electrode layer 22. The variable capacitance region Rcv shown in FIG. 8 is a region in which the relative dielectric constant εr changes depending on the control voltage applied between the first control electrode layer 21 and the second control electrode layer 22, making the capacitance variable. The fixed capacitance region Rcf is a region in which the relative dielectric constant εr does not change, that is, the capacitance is fixed, because an electric field is unlikely to be applied even when a control voltage is applied. The capacitor formed in the variable capacitance region Rcv is called the variable capacitance capacitor Cv, and the capacitor formed in the fixed capacitance region Rcf is called the fixed capacitance capacitor Cf. A capacitor in which the fixed capacitance capacitor Cf, the variable capacitance capacitor Cv, and the fixed capacitance capacitor Cf are connected in series is formed between the first extraction electrode layer 11 and the second extraction electrode layer 12. The capacitance value of the capacitor formed between the first extracting electrode layer 11 and the second extracting electrode layer 12, that is, the combined capacitance Cs, is expressed by the following formula (6). Cs=1 / (1 / Cf+1 / Cv+1 / Cf) ···(6) In equation (6), "Cf" represents the capacitance value of the fixed capacitor Cf, and "Cv" represents the capacitance value of the variable capacitor Cv.

[0054] The horizontal axis of the graph shown in FIG. 8 is the variability of the variable capacitor Cv, and the vertical axis is the variability of the composite capacitance Cs. The variability is the amount of change in capacitance relative to the amount of change in the electric field, i.e., (ΔC / ΔE). FIG. 8 is a graph plotting the variability calculated by setting the distance between the first extraction electrode layer 11 and the second extraction electrode layer 12, i.e., (Lc+Le+Lc), to a fixed value and changing the ratio of the inter-electrode distance Lc to the electrode length Le. As shown in FIG. 8, the variability of the composite capacitance Cs can be increased by decreasing the ratio of the inter-electrode distance Lc to the electrode length Le.

[0055] D. Fourth embodiment: The variable capacitor 1 according to the fourth embodiment shown in Fig. 9 is used in a power supply device 70 included in a contactless power supply system 400. The same components as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0056] As shown in Fig. 9, the contactless power supply system 400 includes a power supply device 70 and a power receiving device 80. In this embodiment, the power supply device 70 is buried under a road. The power receiving device 80 is mounted on a vehicle as a mobile body that travels on the road. When the vehicle is traveling, power is supplied to the power receiving device 80 from the power supply device 70. Here, "traveling" includes a case where the vehicle VE is moving and a case where the vehicle is stopped while waiting for a traffic light or the like.

[0057] The moving body on which the power receiving device 80 is mounted is not limited to a vehicle that travels on a road, and may be, for example, an AGV (automated guided vehicle) or a traveling robot.

[0058] The power supply device 70 includes an AC power source 71, a plurality of primary resonant circuits 72, and a plurality of control voltage application circuits 76. The AC power source 71 supplies power to the plurality of primary resonant circuits 72. The primary resonant circuit 72 is a series resonant circuit having a primary coil L1 and a variable capacitor 1. The primary coils L1 are arranged along the direction in which the road extends. The control voltage application circuit 76 changes the voltage value of the control voltage applied to the variable capacitor 1, thereby changing the capacitance value of the variable capacitor 1.

[0059] The power receiving device 80 includes a secondary resonant circuit 81 and a power receiving circuit 83. The secondary resonant circuit 81 is a series resonant circuit having a secondary coil L2 and a capacitor 82. The power receiving circuit 83 is a circuit that utilizes the received power. The power receiving circuit 83 includes a rectifier circuit and a battery (not shown).

[0060] The AC power source 71 applies AC power of a predetermined operating frequency to the primary side resonant circuit 72. In this embodiment, the operating frequency is 85 kHz. The variable capacitor 1 has a function of making the primary side resonant circuit 72 resonate at the operating frequency and making the primary side resonant circuit 72 non-resonate at the operating frequency. In this embodiment, the variable capacitor 1 is configured to be switchable between a first capacitance value and a second capacitance value smaller than the first capacitance value. The capacitance value of the variable capacitor 1 is switched between the first capacitance value and the second capacitance value by a control voltage output from a control voltage application circuit 76. When the primary side coil L1 and the secondary side coil L2 are magnetically coupled and the variable capacitor 1 has the first capacitance value, the primary side resonant circuit 72 resonates at the operating frequency. That is, the first capacitance value of the variable capacitor 1 is set to a value at which the resonant frequency of the primary side resonant circuit 72 coincides with the operating frequency. On the other hand, when the variable capacitor 1 has the second capacitance value, the resonant frequency of the primary resonant circuit 72 deviates from the operating frequency, and the primary resonant circuit 72 is in a non-resonant state at the operating frequency. Since the second capacitance value is smaller than the first capacitance value, when the variable capacitor 1 is set to the second capacitance value, the impedance of the primary resonant circuit 72 becomes large and the current flowing through the primary coil L1 becomes small.

[0061] The state in which the variable capacitor 1 is set to a first capacitance value, a transmission current flows through the primary coil L1, and power is being supplied is called a power supply state. The state in which the variable capacitor 1 is set to a second capacitance value, a standby current smaller than the transmission current flows through the primary coil L1, and power is not being supplied is called a standby state.

[0062] When the primary coil L1 and the secondary coil L2 are magnetically coupled, the resonant frequency of the primary resonant circuit 72 and the resonant frequency of the secondary resonant circuit 81 are set to be substantially the same. This allows contactless power supply to the power receiving device 80 by magnetic field resonance between the primary coil L1 and the secondary coil L2.

[0063] The primary coils L1 are arranged in the direction in which the road extends, and the secondary coils L2 receive power from the nearest primary coil L1 in a non-contact manner. In a standby state, a standby current flows through the primary coil L1, causing the primary coil L1 to generate magnetic flux. The power receiving device 80 includes a magnetic sensor (not shown). When the power receiving device 80 approaches the target primary resonant circuit 72, the magnetic sensor detects the magnetic flux generated by the primary coil L1. When the power receiving device 80 detects the magnetic flux, it passes an AC current through the secondary coil L2 to generate magnetic flux. The power supply device 70 includes a magnetic sensor (not shown). When the magnetic sensor detects the magnetic flux generated by the secondary coil L2, the control voltage application circuit 76 changes the voltage value of the control voltage to switch the variable capacitor 1 to a first capacitance value. This causes the primary resonant circuit 72 to enter a resonant state, and power supply is started.

[0064] The method by which the power supply device 70 detects the presence of the secondary coil L2 is not limited to the above. As another embodiment, the power supply device 70 may detect a current flowing through the primary coil L1 and detect an increase in the current, or may detect a voltage of the primary coil L1 and detect an increase in the voltage.

[0065] As shown in FIG. 10, in the power supply state, the control voltage application circuit 76 sets the control voltage to 0V. As a result, the control electric field Ed applied to the second dielectric layer 32 becomes 0V / m. The capacitance value of the variable capacitor 1 is set to the first capacitance value. The relative dielectric constant εr is represented by the amount of change in polarization relative to the amount of change in the electric field, that is, the slope of the hysteresis curve. In the standby state, the control voltage application circuit 76 sets the control voltage to a voltage value in the saturation region. As a result, the relative dielectric constant εr becomes smaller than in the power supply state, and the capacitance value of the variable capacitor 1 becomes a second capacitance value smaller than the capacitance value in the power supply state. In the standby state, the area of ​​the hysteresis curve becomes smaller, so that low loss can be achieved.

[0066] According to the fourth embodiment described above, the variable capacitor 1 is used in the power supply device 70. The control voltage application circuit 76 applies a voltage in the saturation region when the power supply device 70 is in a standby state, thereby making the capacitance value of the variable capacitor 1 smaller than the capacitance value in the power supply state. This makes it possible to reduce loss occurring in the variable capacitor 1 in the standby state.

[0067] E. Other embodiments: (E1) In the first embodiment, the second dielectric layer 32 includes a ferroelectric polymer. In another embodiment, the second dielectric layer 32 may include an inorganic ferroelectric such as barium titanate (BaTiO3). As with ferroelectric polymers, the inorganic ferroelectric changes its relative dielectric constant εr depending on the magnitude of the control voltage. This allows a variable capacitor 1 to be provided. It is even better if the inorganic ferroelectric has anisotropic dielectric properties. This is because, even when the direction in which the control voltage is applied is different from the direction in which the AC voltage is applied, the relative dielectric constant changes depending on the magnitude of the control voltage, allowing a variable capacitor 1 with a good variability to be provided. Note that barium titanate can be polarized in each of the three axes of the crystal structure, so the dielectric properties of barium titanate are anisotropic.

[0068] (E2) In the first embodiment, the second dielectric layer 32 includes a ferroelectric polymer. In another embodiment, the second dielectric layer 32 may include a ferroelectric relaxor. A ferroelectric relaxor is a polymer in which domains in which the polarizations of the molecules are aligned are formed locally, as shown in FIG. 11. A ferroelectric relaxor has a property that the polarization can be changed locally, and therefore the polarization moves with a small electric field. By using a ferroelectric relaxor as the second dielectric layer 32, the variability of the capacitance of the variable capacitor 1 can be improved. In addition, since the area of ​​the hysteresis curve is smaller than that of the ferroelectric, a variable capacitor 1 with low loss can be provided. A specific example of a ferroelectric relaxor is a copolymer obtained by copolymerizing a third monomer such as CTFE or CFE with P(VDF-TrFE) as a base, for example, P(VDF-TrFE-CTFE) or P(VDF-TrFE-CTE). Alternatively, ferroelectric relaxors can be fabricated by creating defects in ferroelectric polymers, such as P(VDF-TrFE), using an electron beam.

[0069] (E3) In the above fourth embodiment, the control voltage application circuit 76 applies a control voltage in the saturation region when the power supply device 70 is in a standby state, and does not apply a control voltage when the power supply device 70 is in a power transmission state. As another embodiment, the control voltage application circuit 76 may apply a control voltage in the polarization inversion region or the assist region when the power supply device 70 is in a standby state, and may not apply a control voltage when the power supply device 70 is in a power transmission state.

[0070] (E4) In the first embodiment, the first control electrode layer 21 and the second control electrode layer 22 are alternately arranged in the X direction. In another embodiment, a configuration having one each of the first control electrode layer 21 and the second control electrode layer 22 may be used. In the first embodiment, the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the Z direction, and the first control electrode layer 21 and the second control electrode layer 22 face each other in the X direction. The facing direction is not limited to this. For example, a structure in which the first extraction electrode layer 11 and the second extraction electrode layer 12 face each other in the X direction, and the first control electrode layer 21 and the second control electrode layer 22 face each other in the Z direction may also be used.

[0071] The present disclosure is not limited to the above-mentioned embodiments and modifications, and can be realized in various configurations without departing from the spirit of the present disclosure. 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 column can be appropriately replaced or combined in order to solve some or all of the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0072] Other forms: The features of the present disclosure are as follows: (Form 1) A variable capacitor (1, 201, 301), A first control electrode (21), a second control electrode (22) facing the first control electrode; a dielectric layer (32) disposed at least between the first control electrode and the second control electrode; a first extracting electrode (11) and a second extracting electrode (12) facing each other with the dielectric layer interposed therebetween; a variable capacitance capacitor, wherein the first extraction electrode and the second extraction electrode are arranged at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode and the second control electrode when a control voltage is applied between the first control electrode and the second control electrode. (Form 2) The variable capacitor according to aspect 1, A variable capacitor, wherein the dielectric layer has dielectric properties such that the dielectric constant of an assist region for assisting polarization movement when the control voltage is applied is greater than the dielectric constant when the control voltage is not applied. (Form 3) The variable capacitor according to aspect 1 or 2, A variable capacitor, wherein the dielectric layer has dielectric properties in which the dielectric constant when the control voltage in a saturation region for constraining polarization movement is applied is smaller than the dielectric constant when the control voltage is not applied. (Form 4) The variable capacitor according to any one of aspects 1 to 3, A variable capacitor, wherein the dielectric layer has a dielectric characteristic in which the relative dielectric constant of a polarization inversion region when the control voltage including the voltage value of a coercive electric field is applied is greater than the relative dielectric constant when the control voltage is not applied. (Form 5) The variable capacitor according to any one of aspects 1 to 4, the first control electrode and the second control electrode face each other in a first direction, and the first extraction electrode and the second extraction electrode face each other in a second direction perpendicular to the first direction; (Form 6) 6. The variable capacitor according to any one of aspects 1 to 5, a first arrangement (ST1) in which the first control electrodes and the second control electrodes are alternately arranged with the dielectric layer interposed therebetween; a second arrangement body (ST2) in which the first control electrodes and the second control electrodes are arranged alternately with the first arrangement body therebetween, the variable capacitor having a capacitance of 100 Ω / s. (Form 7) A variable capacitor according to claim 6, A variable capacitor, wherein the number of the first array is 20,000 or more, and the number of the second array is 100 or more. (Form 8) The variable capacitor according to any one of the first to seventh aspects, A variable capacitor, wherein the dielectric properties of the dielectric layer are anisotropic. (Form 9) The variable capacitor according to any one of the first to eighth aspects, The variable capacitor, wherein the dielectric layer comprises one of a ferroelectric polymer and an inorganic ferroelectric. (Form 10) The variable capacitor according to any one of the first to ninth aspects, The variable capacitor, wherein the dielectric layer includes a ferroelectric relaxor. (Form 11) A power supply device (70) having a variable capacitor according to any one of aspects 1 to 10, the dielectric layer includes a ferroelectric material; the power supply device includes a resonant circuit (72) formed of the variable capacitor and a primary coil (L1), and a control voltage application circuit (76) that applies the control voltage between the first control electrode and the second control electrode, The control voltage application circuit applies a voltage in a saturation region for constraining a movement of polarization when the power supply device is in a standby state. [Explanation of symbols]

[0073] 1, 201, 301...variable capacitor, 11...first extraction electrode, 12...second extraction electrode layer, 21...first control electrode layer, 22...second control electrode layer, 31...first dielectric layer, 32...second dielectric layer

Claims

1. A variable capacitor (1, 201, 301), A first control electrode (21); a second control electrode (22) facing the first control electrode; a dielectric layer (32) disposed at least between the first control electrode and the second control electrode; a first extraction electrode (11) and a second extraction electrode (12) facing each other with the dielectric layer interposed therebetween; a variable capacitance capacitor, wherein the first extraction electrode and the second extraction electrode are arranged at positions that generate an electric field along a direction intersecting an electric field vector generated between the first control electrode and the second control electrode when a control voltage is applied between the first control electrode and the second control electrode.

2. 2. The variable capacitor according to claim 1, A variable capacitor, wherein the dielectric layer has dielectric properties such that the dielectric constant of an assist region for assisting polarization movement when the control voltage is applied is greater than the dielectric constant when the control voltage is not applied.

3. 2. The variable capacitor according to claim 1, A variable capacitor, wherein the dielectric layer has dielectric properties in which the dielectric constant when the control voltage in a saturation region for constraining polarization movement is applied is smaller than the dielectric constant when the control voltage is not applied.

4. 2. The variable capacitor according to claim 1, A variable capacitor, wherein the dielectric layer has a dielectric characteristic in which the relative dielectric constant of a polarization inversion region when the control voltage including the voltage value of a coercive electric field is applied is greater than the relative dielectric constant when the control voltage is not applied.

5. 2. The variable capacitor according to claim 1, the first control electrode and the second control electrode face each other in a first direction, and the first extraction electrode and the second extraction electrode face each other in a second direction perpendicular to the first direction.

6. 2. The variable capacitor according to claim 1, a first arrangement (ST1) in which the first control electrodes and the second control electrodes are alternately arranged with the dielectric layer interposed therebetween; a second arrangement (ST2) in which the first extraction electrodes and the second extraction electrodes are alternately arranged with the first arrangement interposed therebetween, the variable capacitor having a capacitance of 100 Ω / s.

7. 7. A variable capacitor according to claim 6, A variable capacitor, wherein the number of the first arrangements is 20,000 or more, and the number of the second arrangements is 100 or more.

8. 2. The variable capacitor according to claim 1, A variable capacitor, wherein the dielectric properties of the dielectric layer are anisotropic.

9. 2. The variable capacitor according to claim 1, The variable capacitor, wherein the dielectric layer comprises one of a ferroelectric polymer and an inorganic ferroelectric.

10. 2. The variable capacitor according to claim 1, The variable capacitor, wherein the dielectric layer includes a ferroelectric relaxor.

11. A power supply device (70) having a variable capacitor according to claim 1, the dielectric layer includes a ferroelectric material; the power supply device includes a resonant circuit (72) formed of the variable capacitor and a primary coil (L1), and a control voltage application circuit (76) that applies the control voltage between the first control electrode and the second control electrode, The control voltage application circuit applies a voltage in a saturation region for constraining a movement of polarization when the power supply device is in a standby state.

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