JP2010109035A - Variable capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable capacitor which reduces loss in conductivity as a component formed by combining a capacitor for cutting low frequency signal and a variable capacitor. <P>SOLUTION: The variable capacitor includes (a) a pair of electrode layers 22, 26, (b) a dielectric material layer held between the pair of electrode layers 22, 26 to change dielectric constant with application of a control voltage, and (c) a plurality of capacitors 6, 8 formed of the pair of electrode layers 22, 26 and the dielectric material layer. The capacitors 6, 8 respectively include at least one variable capacitor 6 changing capacitance with application of the control voltage and at least one capacitor 8 for cutting low frequency signal other than the variable capacitor 6. At least one capacitor 8 for cutting the low frequency signal is formed in the external side of the relevant variable capacitor 6 to surround the external circumference of at least one variable capacitor 6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a variable capacitor, and more particularly to a variable capacitor with a low frequency signal cut capacitor in which a low frequency signal cut capacitor and a variable capacitor are combined.

Conventionally, a variable capacitor having a dielectric layer whose dielectric constant is changed by application of a control voltage has been provided. A ferroelectric thin film material having a high capacitance change rate such as (Ba, Sr) TiO ₃ is used for the dielectric layer of the variable capacitor. In a variable capacitor having a parallel plate (MIM) type capacitor that sandwiches a dielectric layer between electrodes, the upper and lower electrodes are drawn through a single through hole and connected to an external circuit. For the upper and lower electrodes, a material such as Pt that is resistant to a high-temperature oxidizing atmosphere during formation of the dielectric thin film but has a high specific resistance is used.

When a variable capacitor is used as a variable filter, it must be used in combination with a low frequency signal (including DC) cut capacitor so that the control voltage does not affect the RF (Radio Frequency) circuit. . Therefore, it has been proposed that a low-frequency signal cut capacitor is formed at the same time as the variable capacitor element portion to form one component (see, for example, Patent Document 1).
JP-A-2005-64437

  That is, in the actual use circuit, in order to prevent the control voltage (DC voltage) from affecting the high frequency circuit, as shown in FIG. 1, a low frequency signal cut of about 1 nF is provided between the variable capacitor unit 6 and the high frequency circuit. Capacitor sections 8, 8a, 8b are required. In FIG. 1, terminal 2 is connected to the input terminal of the high frequency circuit, and terminal 3 is connected to the output terminal of the high frequency circuit. A control voltage (DC voltage) is applied to the terminals 4, 4a, 4b.

The capacity generating area of the high frequency variable capacitor is about several tens to several hundreds μm ² (<30 μm × 30 μm). While high processing accuracy is required, the occupied area is small, so other functions are formed simultaneously. It is easy.

  Therefore, it is useful to reduce the mounting area and volume since it is easy to make a low frequency signal cut capacitor of about 1 nF at the same time without requiring a large process change. In addition, the loss at high frequency of the variable capacitor is strongly influenced by the conductive loss as well as the dielectric loss. Therefore, by building the low-frequency signal cut capacitor on the same chip, there is an effect of reducing the conductive loss due to wiring. .

  Based on the background as described above, an element structure as in Comparative Example 1 described later is conceivable. That is, as shown in the plan view of FIG. 8, the low frequency signal cut capacitor unit 8 x is laid out between the variable capacitor unit 6 x and the external terminal 12. In such an element structure, the main cause of the conductive loss is a portion wired only by the electrode layer forming the upper electrode and the lower electrode of each capacitor portion 6x, 8x. The electrode layers constituting the upper and lower electrodes of the capacitor portions 6x and 8x are generally made of Pt, Pd, etc., which have high oxidation resistance at high temperatures, and lead electrodes 32x, 34x formed of a low resistance material such as Cu. The electric resistance is higher than that.

  In view of such a situation, the present invention intends to provide a variable capacitor in which a conductive loss is reduced as one component in which a low frequency signal cut capacitor unit and a variable capacitor unit are combined.

  In order to solve the above-described problems, the present invention provides a variable capacitor configured as follows.

  The variable capacitor includes: (a) a pair of electrode layers; (b) a dielectric layer that is sandwiched between the pair of electrode layers and changes a dielectric constant when a control voltage is applied; and (c) the pair of electrode layers. And a plurality of capacitor portions formed by the dielectric layer. The plurality of capacitor units include at least one variable capacitor unit whose capacitance is changed by application of a control voltage and one low frequency signal cut capacitor unit other than the variable capacitor unit. At least one of the low-frequency signal cut capacitor portions is formed outside the variable capacitor portion so as to surround an outer periphery of the at least one variable capacitor portion.

  In the above configuration, the variable capacitor portion is formed inside the low frequency signal cut capacitor portion, and the same electrode layer forming one electrode portion of each of the low frequency signal cut capacitor portion and the variable capacitor portion is The electrodes are connected at a short distance over the entire circumference. Therefore, the low frequency signal cut capacitor part and the variable capacitor part are formed side by side, and the same electrode layer forming one electrode part of each of the low frequency signal cut capacitor part and the variable capacitor part is provided for each electrode. Compared with a configuration in which the units are connected, the current path is shortened. Therefore, the conductive loss can be reduced.

  Preferably, 2n capacitor parts that are multiples of two or more natural numbers n are connected in series between a pair of external terminals formed on the same side with respect to the pair of electrode layers and the dielectric layer. .

  Unlike the above configuration, when 2n + 1 capacitor parts are connected in series between a pair of external terminals, the capacitor part is formed so as to be half a reciprocal half between a pair of electrode layers. Between the capacitor portion connected to the external terminal and the external terminal, it is necessary to form a wiring that extends halfway between the pair of electrode layers.

  On the other hand, when 2n capacitor parts are connected in series between a pair of external terminals, i = 2, 3,..., 2n−2, i-th from one external terminal side. The capacitor part connected to the i + 1 and the capacitor part connected to the (i + 1) th are connected on one electrode layer side, and the capacitor part connected to the (i + 1) th and the capacitor part connected to the (i + 2) th are on the other electrode layer side Since the capacitor portion can be connected in series so as to reciprocate between the pair of electrode layers, the current path between the pair of external terminals and the capacitor portion can be shortened.

  Therefore, the conductive loss can be further reduced.

  In the variable capacitor of the present invention, the conductive loss is reduced as one component in which the low frequency signal cut capacitor unit and the variable capacitor unit are combined.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  Example 1 A variable capacitor of Example 1 will be described with reference to FIGS.

  FIG. 2 is a plan view of the variable capacitor 10 according to the first embodiment. As shown in FIG. 2, a pair of external terminals 12 and 14 and a control voltage application unit 16 for applying a control voltage are formed on the upper surface of the variable capacitor 10 of the first embodiment, and the other part is the surface. Covered with a protective film 19.

  Inside the variable capacitor 10, a plurality of capacitor portions 6, 8 with diagonal lines are formed. That is, a thin dielectric layer 24 (not shown in FIG. 2) whose dielectric constant is changed by application of a control voltage is sandwiched between the upper electrode layer 26 and the lower electrode layer 22. The lower electrode layer 22 and the dielectric layer 24 are patterned to form the variable capacitor portion 6 and the low frequency signal cut capacitor portion 8. The low frequency signal cut capacitor unit 8 is formed outside the variable capacitor unit 6 so as to surround the outer periphery of the variable capacitor unit 6.

  The lower electrode layer 22 is formed in a circular shape, and a lower electrode of the variable capacitor unit 6 and a lower electrode of the low frequency signal cut capacitor unit 8 are formed by a part of the lower electrode layer 22. The lower electrode layer 22 is electrically connected to the control voltage application unit 16.

  The upper electrode layer 26 is formed such that a portion to be the upper electrode of the variable capacitor portion 6 with hatching is separated from a portion to be the upper electrode of the capacitor portion 8 for low frequency signal cutting with hatching, The external terminals 12 and 14 are connected to each other through the extraction electrodes 32 and 34.

  As in the equivalent circuit diagram of FIG. 1A, the variable capacitor 10 has a low-frequency signal cut capacitor unit 8 and a variable capacitor unit 6 connected in series between a pair of external terminals 12 and 14. A control voltage application unit 16 is connected to a connection point between the frequency signal cutting capacitor unit 8 and the variable capacitor unit 6. For example, one external terminal 12 is connected to the input terminal of the RF circuit, and the other external terminal 14 is grounded. Depending on the voltage applied to the control voltage application unit 16, the capacitance of the variable capacitor unit 6 changes.

  Next, a method for manufacturing the variable capacitor 10 will be described with reference to FIGS. 3 and 4 are cross-sectional views showing the manufacturing process for the cross section cut along the line AA in FIG.

  First, as shown in FIG. 3A, an adhesion layer 21, a lower electrode layer 22, a dielectric layer 24, and an upper electrode layer 26 are formed on the surface 20a of the substrate 20 to form a laminate.

Specifically, on the surface 20a of the SiO ₂ / Si substrate 20 on which the SiO ₂ film is formed on the surface 20a, Ba _0.7 Sr _0.3 TiO ₃ (as the adhesion layer 21 is formed by a chemical solution deposition (CSD) method. BST) A thin film is formed. Specifically, a BST raw material solution having a stoichiometric composition is applied onto a SiO ₂ film, dried on a hot plate at 350 ° C., and crystallized by a heat treatment at 650 ° C. for 30 minutes to obtain a BST thin film. Next, a 300 nm-thickness Pt film is formed on the BST thin film of the adhesion layer 21 by RF magnetron sputtering to form the lower electrode layer 22. Next, a BST thin film is formed on the Pt film of the lower electrode layer 22 by the CSD method in the same manner as the BST thin film of the adhesion layer 21 to form a dielectric layer 24. That is, the raw material solution is applied onto the lower electrode layer 22, dried on a hot plate at 350 ° C., and crystallized by a heat treatment at 650 ° C. for 30 minutes to obtain the dielectric layer 24 of the BST thin film. Next, a 300 nm-thickness Pt film is formed on the BST thin film of the dielectric layer 24 by RF magnetron sputtering to form a first upper electrode layer. Next, the obtained laminated structure is heat-treated at 800 ° C. for 30 minutes. Next, in order to reduce the resistance of the upper electrode layer 26, a second upper electrode layer is formed on the first upper electrode layer. Specifically, Ti (10 nm) and Cu (500 nm) are sequentially formed by RF magnetron sputtering. That is, the upper electrode layer 26 is made of Pt / Ti / Cu.

  Next, as shown in FIG. 3 (b), the upper electrode layer 26, the dielectric layer 24, the lower electrode layer 22 and the adhesion layer 21 of the laminate are patterned, so that the variable capacitor portion 6 and the low frequency signal cut capacitor are processed. The capacitor structure of part 8 is formed.

  At this time, the upper electrode 26p of the variable capacitor unit 6 and the upper electrode 26q of the low frequency signal cut capacitor unit 8 are formed by patterning the upper electrode layer 26. 5, the upper electrode 26p of the variable capacitor unit 6 is formed in a circular shape, and the upper electrode 26q of the low frequency signal cut capacitor unit 8 is the outer periphery of the upper electrode 26p of the variable capacitor unit 6. 26a is formed in a donut shape surrounding the entire circumference by providing a gap 26b.

  Specifically, after a resist mask is formed on the upper electrode layer 26 of the laminated body by a photolithography method, the upper electrode layer 26 and the dielectric layer 24 and the lower electrode layer 22 below the upper electrode layer 26 are formed by an Ar ion milling method. By sequentially performing dry etching, as shown in FIG. 3B, two capacitor structures of a variable capacitor portion 6 and a low frequency signal cut capacitor portion 8 are formed.

  Next, as shown in FIG. 3C, an insulating protective film 28 covering the surface 20a of the substrate 20 and the capacitor structure is formed, and an organic protective film 29 having openings 29a and 29b is formed thereon.

Specifically, as the insulating protective film 28, a silicon nitride (SiN _x ) film is formed to a thickness of 300 nm by a sputtering method. Next, an organic protective film 29 made of polyimide resin is formed on the SiNx film. Specifically, a photosensitive resin material is applied by spin coating, heated at 125 ° C. for 5 minutes, subjected to exposure and development steps, and heated at 350 ° C. for 1 hour. As shown in FIG. An organic insulating film 29 of a polyimide film having a film thickness of 2 μm having 29b is formed.

  Next, as shown by an arrow 29x in FIG. 3D, etching is performed through the organic protective film 29, and the insulating protective film 28 is communicated with the openings 29a and 29b of the organic protective film 29 so that the variable capacitor unit 6 The openings 29a and 29b are formed through which the upper electrode 26p or the upper electrode 26q of the low frequency signal cut capacitor portion 8 is exposed.

Specifically, using the organic protective film 29 of polyimide film as a mask, the insulating protective film 28 of SiN _X film is dry-etched using CHF ₃ gas, and as shown in FIG. To expose a part of

  Next, as shown in FIG. 4E, the openings 28a and 28b of the insulating protective film 28 and the organic protective film are connected to the upper electrode 26p of the variable capacitor section 6 or the upper electrode 26q of the low frequency signal cut capacitor section 8. Lead electrodes 32 and 34 extending from the openings 29 a and 29 b of the 29 to the upper surface 29 s of the organic protective film 29 are formed.

  Specifically, Ti (100 nm) and Cu (2000 nm) are sequentially formed by RF magnetron sputtering, then a resist mask is formed by photolithography, and etching is performed by Ar ion milling to form Cu / Ti. Lead electrodes 32 and 34 are formed.

  Next, as shown in FIG. 4 (f), the surface protective film 19 having openings 19 a and 19 b covering the upper surface 29 s of the organic protective film 29 and the extraction electrodes 32 and 34, and exposing part of the extraction electrodes 32 and 34. Form.

  Specifically, a photosensitive resin material is applied by spin coating, heated at 125 ° C. for 5 minutes, cured by exposure and development steps at 350 ° C. for 1 hour, and a polyimide film having a thickness of 2 μm having openings 19a and 19b. A surface protective film 19 of the film is formed.

  Finally, the external terminals 12 and 14 are formed on the lead electrodes 32 and 34 exposed from the openings 19a and 19b of the surface protective film 19 by plating or the like, and the variable capacitor 10 is completed.

The control voltage application unit 16 is also formed in the same manner as the external terminals 12 and 14. That is, when the upper electrode, dielectric film, and lower electrode shown in FIG. 3B are processed, a control voltage applying external electrode connecting portion is provided in which the lower electrode 22 is the outermost layer. Then, the SiN _X protective film formation → polyimide film formation → opening part formation → Cu / Ti lead electrode formation → surface protective film formation → external connection terminal formation are performed together with the variable capacitance portion. As described above, since only the pattern change is performed without changing the process, the control voltage application unit is formed.

  Next, a modified example and a comparative example of Example 1 will be described. In the following, the same reference numerals are used for the same components as in the first embodiment, and differences from the first embodiment will be mainly described.

  FIG. 6 is a plan view of the variable capacitor 10a of the first modification. As shown in FIG. 6, the variable capacitor 10 a of Modification 1 has a low-frequency signal cut capacitor unit 8 a and a control voltage application unit 18 added to the configuration of Example 1, and two low-frequency signals. Cut capacitor portions 8 and 8 a and one variable capacitor portion 6 are provided.

  The added low frequency signal cut capacitor section 8a has a configuration in which a dielectric layer (not shown) is sandwiched between the upper electrode layer 26s and the lower electrode layer 22s, like the low frequency signal cut capacitor section 8. It is. The upper electrode layer 26s that forms the upper electrode of the low-frequency signal cut capacitor unit 8a is connected to the upper electrode of the variable capacitor unit 6 via the lead electrode 36s. The added control voltage application unit 18 is connected to the upper electrode of the variable capacitor unit 6 through the extraction electrode 36s. The lower electrode layer 22s that forms the lower electrode of the added low frequency signal cut capacitor portion 8a is connected to the other external terminal 14 via the lead electrode 34a.

  As in the equivalent circuit diagram of FIG. 1 (b), the variable capacitor 10 a of Modification 1 has a variable capacitor unit 6 connected in series between the low frequency signal cut capacitor units 8, 8 a. Both ends are connected to the control voltage application units 16 and 18, respectively.

  FIG. 7 is a plan view of the variable capacitor 10b of the second modification. As shown in FIG. 7, in the variable capacitor 10b of the second modification, a variable capacitor unit 6t, a low frequency signal cut capacitor unit 8b, and a control voltage application unit 18 are added to the configuration of the first embodiment. That is, two low frequency signal cut capacitor portions 8 and 8b and two variable capacitor portions 6 and 6t are provided.

  The added variable capacitor unit 6t and the low frequency signal cut capacitor unit 8b have the same configuration as the variable capacitor unit 6 and the low frequency signal cut capacitor unit 8, and are provided between the upper electrode layer 26t and the lower electrode layer 22t. A dielectric layer (not shown) is sandwiched between the low-frequency signal cut capacitor portion 8b and surrounds the outer periphery of the variable capacitor portion 6t.

  The upper electrodes of the variable capacitor sections 6 and 6t are connected via the extraction electrode 36t. The added control voltage application unit 18 is electrically connected to the extraction electrode 36t.

  The added lower electrode of the variable capacitor unit 6t and the added lower electrode of the low frequency signal cut capacitor unit 8b are formed by a common lower electrode layer 22t and are electrically connected to each other. The upper electrode layer 26t that forms the upper electrode of the added low frequency signal cut capacitor portion 8b is connected to the other external terminal 14 via the lead electrode 34b.

  The control voltage application unit 16 is also electrically connected to the lower electrode layer 22t that forms the lower electrode of the added variable capacitor unit 6t.

  FIG. 8 is a plan view of the capacitor 10x of the first comparative example. As shown in FIG. 8, the variable capacitor 10x of Comparative Example 1 includes one variable capacitor unit 6x and one low frequency signal cut capacitor unit 8x. Unlike the first embodiment, the variable capacitor 10x of the comparative example 1 has a variable capacitor portion 6x formed outside the low frequency signal cut capacitor portion 8x.

  FIG. 9 is a plan view of the variable capacitor 10y of the second comparative example. As shown in FIG. 9, the variable capacitor 10y of Comparative Example 2 includes one variable capacitor unit 6x and two low frequency signal cut capacitor units 8x and 8y. The variable capacitor of Comparative Example 2 is different from Modification 1 of FIG. 6 in that the variable capacitor unit 6x is formed outside the low frequency signal cut capacitor units 8x and 8y.

可変コンデンサ部の面積は２２５μｍ^２、低周波信号カット用コンデンサ部の面積は２２５００μｍ^２とし、メッシュサイズは５μｍで計算した。 The following Table 1 shows the comparative example 1 (FIG. 8) and the comparative example 2 (FIG. 10) of the conventional structure in which the variable capacitor unit is arranged outside the low frequency signal cut capacitor unit, and the low frequency signal cut capacitor unit. With respect to the first embodiment (FIG. 2), the first modification (FIG. 6), and the second modification (FIG. 7) of the structure of the present invention in which the variable capacitor portion is arranged, the resistance between the external terminals at 2 GHz by the finite element method. The result of calculating Rs is shown. Although the shape of the low frequency signal cut capacitor portion is different between FIG. 2 and FIG. 8, there is almost no influence on the calculation of the resistance value.

The area of the variable capacitor was 225 μm ² , the area of the low frequency signal cut capacitor was 22500 μm ² , and the mesh size was 5 μm.

  From Table 1, it can be seen that the structures (Example 1, Modification 1 and Modification 2) of the present invention can reduce the resistance Rs between the external terminals as compared with the conventional structures (Comparative Examples 1 and 2). .

  7 includes two low-frequency signal cut capacitor sections, and two variable capacitor sections are connected in series in Modification 2 in which the element structure of the present invention is used for both low-frequency signal cut capacitor sections. Even in this case, Rs hardly increases, and the area of the capacitor portion can be increased, so that the fabrication becomes easy. Further, as shown in FIG. 7, by connecting the control voltage application units 16 and 18 to the two variable capacitor units 6 and 6a, the capacitance change amount of the variable capacitor units 6 and 6a with respect to the control voltage is changed to the external terminals 12 and 14 respectively. Even if the voltage between them changes, it does not change.

  In the variable capacitors of Example 1 and Modifications 1 and 2, the low frequency signal cut capacitor part is arranged so as to surround the periphery of the variable capacitor part, and the lower electrode layer causes the lower electrode lead part of the variable capacitor part to Directly connected to the lower electrode of the low frequency signal cut capacitor section. Therefore, the current path between the variable capacitor unit and the low frequency signal cut capacitor unit increases, and the resistance Rs between the external terminals decreases.

  Furthermore, the variable capacitor portion and the low frequency signal cut capacitor portion can be patterned and formed simultaneously. For this reason, the interval between the variable capacitor portion and the low frequency signal cut capacitor portion does not depend on the mask alignment, facilitating fabrication, and reducing the cost.

  As described above, by adopting the element structure in which the variable capacitor part is disposed inside the low frequency signal cut capacitor part, not only the element characteristics can be improved but also the cost can be reduced.

  <Example 2> The variable capacitor of Example 2 will be described with reference to FIGS.

  FIG. 10 is a plan view of the variable capacitor 11 according to the second embodiment. As shown in FIG. 10, the variable capacitor 11 according to the second embodiment includes two variable capacitor portions 6a and 6b in addition to the variable capacitor portion 6 and the low frequency signal cut capacitor portion 8 having the same configuration as the first embodiment. Yes. In other words, the variable capacitor unit 6 according to the first embodiment is different from the variable capacitor 10 in that the variable capacitor units 6, 6 a, and 6 b are provided.

  The variable capacitor sections 6, 6 a, 6 b are connected in series, and the added variable capacitor sections 6 a, 6 b are farther from one external terminal 12 than the variable capacitor section 6 having the same configuration as that of the first embodiment. A low frequency signal cut capacitor unit 8 is connected in series between the variable capacitor unit 6 closest to the one external terminal 12 and the one external terminal 12. The low frequency signal cut capacitor unit 8 is formed outside the variable capacitor unit 6 so as to surround the outer periphery of the variable capacitor unit 6.

  One external terminal 12 is connected to the upper electrode of the low frequency signal cut capacitor unit 8 through the lead electrode 32. The lower electrode of the low frequency signal cut capacitor unit 8 and the lower electrode of the first variable capacitor unit 6 are formed by a common lower electrode layer 22 and are electrically connected. The control voltage application unit 16 is electrically connected to the lower electrode layer 22.

  Unlike the first embodiment, the upper electrode of the first variable capacitor section 6 is connected to the upper electrode of the adjacent second variable capacitor section 6a via the lead electrode 36a. The lower electrode of the second variable capacitor portion 6a and the lower electrode of the third variable capacitor portion 6b adjacent thereto are formed by a common lower electrode layer 22a and are electrically connected. The upper electrode of the third variable capacitor unit 6 b is connected to the other external terminal 14 through the extraction electrode 35.

  Next, a modified example and a comparative example of Example 2 will be described.

  FIG. 11 is a plan view of the variable capacitor 11a of the third modification. As shown in FIG. 11, the variable capacitor 11a of the third modification has substantially the same configuration as the variable capacitor 11 of the second embodiment. However, unlike the variable capacitor 11 of the second embodiment, the third variable capacitor section 6b and the other A fourth variable capacitor portion 6c connected in series with the external terminal 14 is added. The upper electrode of the fourth variable capacitor portion 6c is formed by the common upper electrode layer 36b together with the upper electrode of the third variable capacitor portion 6b, and is electrically connected. The lower electrode layer 22b that forms the lower electrode of the fourth variable capacitor portion 6c and the other external terminal 14 are connected via an extraction electrode 35a.

  FIG. 12 is a plan view of the variable capacitor 11b of the fourth modification. As shown in FIG. 12, the variable capacitor 11b of the fourth modification has substantially the same configuration as the variable capacitor 11a of the third modification, but unlike the variable capacitor 11a of the third modification, the fourth variable capacitor section 6c and the other A fifth variable capacitor portion 6d connected in series with the external terminal 14 is added. The lower electrode of the fifth variable capacitor portion 6d is formed by the lower electrode layer 22t together with the lower electrode layer of the fourth variable capacitor portion 6c, and is electrically connected. The upper electrode of the fifth variable capacitor portion 6d is connected to the other external terminal 14 via the lead electrode 35b.

  FIG. 13 is a plan view of the variable capacitor 11x of the third comparative example. As shown in FIG. 13, the variable capacitor 11 x of Comparative Example 3 is similar to the variable capacitor 11 of Example 2 in that one low frequency signal cut capacitor unit 8 x is provided between one terminal 12 and the other external terminal 14. And three variable capacitor sections 6x, 6p, 6q are connected in series and are configured in substantially the same manner.

  Unlike the variable capacitor 11 according to the second embodiment, the variable capacitor 11x according to the third comparative example has a variable capacitor portion 6x that is closest to one of the external terminals 12 outside the low frequency signal cut capacitor portion 8x.

可変コンデンサ部の面積は２２５μｍ^２、低周波信号カット用コンデンサ部の面積は２２５００μｍ^２とし、メッシュサイズは５μｍで計算した。 Table 2 below shows Example 2 (FIG. 10), Modification 3 (FIG. 11), and Modification 4 (FIG. 12) of the structure of the present invention in which the variable capacitor part is arranged inside the low frequency signal cut capacitor part. And the result of having calculated resistance Rs between the external terminals in 2 GHz by the finite element method about the comparative example 3 (FIG. 13) of the conventional structure which arrange | positions a variable capacitor part outside the capacitor part for low frequency signal cut is shown.

The area of the variable capacitor was 225 μm ² , the area of the low frequency signal cut capacitor was 22500 μm ² , and the mesh size was 5 μm.

  Comparing Example 2 in which the total number of capacitor parts connected in series is four and Modification 3 in which the total number of capacitor parts connected in series is five, the difference in Rs is 0.14Ω. It is. On the other hand, when the modification 3 in which the total number of capacitor parts connected in series is five and the modification 4 in which the total number of capacitor parts connected in series is six are compared, The difference is 0.06Ω, which is smaller than 0.14Ω.

  From this, it is possible to reduce Rs in the high-frequency band at a lower cost and with a higher yield compared to the case where the total number of capacitor units connected in series is 2n (n ≧ 2) is 2n + 1, and the loss can be reduced. I understand.

  That is, when 2n + 1 capacitor parts are connected in series between a pair of external terminals, the capacitor part is formed so as to have n reciprocal halves between a pair of electrode layers, and connected in series. Between the capacitor portion and the external terminal, it is necessary to form a wiring that extends half a round trip between the pair of electrode layers.

  On the other hand, when 2n capacitor parts are connected in series between a pair of external terminals, the capacitor part can be formed so as to reciprocate between a pair of electrode layers. The current path between the capacitor portion can be shortened.

  Therefore, Rs in the high frequency band can be reduced at a lower cost and with a higher yield as compared with the case where the total number of capacitor portions connected in series is 2n (n ≧ 2) is 2n + 1, and the loss can be reduced.

  Next, a modified example including the two control voltage application units 16 and 18 will be described with reference to FIGS.

  FIG. 14 is a plan view of the variable capacitor 11p of the fourth modification. As shown in FIG. 14, the variable capacitor 11p of Modification 4 has a control voltage application unit 18 added to the configuration of the variable capacitor 11 of Embodiment 2. The added control voltage application unit 18 is electrically connected to an extraction electrode 36p that connects the upper electrodes of the variable capacitor units 6 and 6a. In addition to the lower electrode layer 22 that forms the lower electrode of the variable capacitor unit 6, the control voltage application unit 16 is also electrically connected to the lower electrode layer 22p that forms the lower electrodes of the variable capacitor units 6a and 6b. Yes.

  FIG. 15 is a plan view of a variable capacitor 11q according to the sixth modification. As shown in FIG. 15, the variable capacitor 11q of Modification 6 has a variable capacitor section 6c added to the configuration of Modification 4. The other control voltage application unit 18 is also electrically connected to the extraction electrode 36q connected to the upper electrodes of the variable capacitor units 6b and 6c. The lower electrode layer 22q forming the lower electrode of the variable capacitor 6c and the other external terminal 14 are connected by an extraction electrode 35q.

  FIG. 16 is a plan view of the variable capacitor 11r of Modification 7. As shown in FIG. 16, the variable capacitor 11r of Modification 7 has a variable capacitor portion 6d added to the configuration of Modification 6. One control voltage application unit 16 is also electrically connected to a lower electrode layer 22q that forms a lower electrode of the variable capacitor units 6c and 6d. The lower electrode layer 22q that forms the lower electrode of the variable capacitor 6d and the other external terminal 14 are connected by an extraction electrode 35q.

  Here, consider the case where the number of capacitors connected in series is 2n (n ≧ 2), 2n + 1, 2 (n + 1), and there is one low-frequency signal cut capacitor. When n = 2, the number of connections 2n (FIG. 10) and 2n + 1 (FIG. 11) are compared. In the case of 2n + 1, the portion wired only by the lower electrode layer 22b increases, so Rs increases. In addition, in order to reduce the increase in the conductive loss due to the addition of the capacitance generating portion, it is necessary to draw out the wiring (leading electrode) from the lower electrode layer 22b as close as possible to the capacitance generating portion. Accurate patterning and suppression of over-etching of the lower electrode portion are required.

  On the other hand, comparing 2n + 1 (FIG. 11) and 2 (n + 1) (FIG. 12), in 2 (n + 1), the portion wired only by the lower electrode layer does not change (is not added), so Rs does not change. In addition, since the lower electrode layer through which the high-frequency signal flows is entirely covered with the dielectric layer, the element characteristics do not increase due to over-etching or change in characteristics due to pattern deviation. Therefore, it is easy to process the dielectric layer. In addition, since the number of series connections increases, the area per variable capacitor portion for obtaining the same capacitance value increases, and the process margin increases, which facilitates manufacture. Even when the control voltage is independently applied to the variable capacitor portions connected in series, as shown in FIGS. 14 to 16, only the wiring relating to the added control voltage application portion 18 is increased. Hardly changes. Further, the area of the capacitor portion including the electrode lead portion with respect to the entire chip hardly changes between 2n + 1 and 2 (n + 1).

  From the above points, an element can be obtained more efficiently when the number of capacitors connected in series is 2n (n ≧ 2). This is the same even when there are two low frequency signal cut capacitors.

  <Summary> By forming the low frequency signal cut capacitor part so as to surround the entire outer periphery of the upper electrode of the variable capacitor part, the portion wired only by the electrode layers that form the upper and lower electrodes of the high resistance capacitor part is reduced as much as possible. As a result, the conductive loss can be reduced, and a low-loss element can be provided.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications.

It is an equivalent circuit diagram of a variable capacitor. (Example 1) It is a top view of a variable capacitor. (Example 1) It is sectional drawing which shows the manufacturing process of a variable capacitor. (Example 1) It is sectional drawing which shows the manufacturing process of a variable capacitor. (Example 1) It is a principal part top view which shows the manufacturing process of a variable capacitor. (Example 1) It is a top view of a variable capacitor. (Modification 1) It is a top view of a variable capacitor. (Modification 2) It is a top view of a variable capacitor. (Comparative Example 1) It is a top view of a variable capacitor. (Comparative Example 2) It is a top view of a variable capacitor. (Example 2) It is a top view of a variable capacitor. (Modification 3) It is a top view of a variable capacitor. (Modification 4) It is a top view of a variable capacitor. (Comparative Example 3) It is a top view of a variable capacitor. (Modification 5) It is a top view of a variable capacitor. (Modification 6) It is a top view of a variable capacitor. (Modification 7)

Explanation of symbols

6, 6a, 6b, 6c, 6d, 6p, 6q, 6t, 6x Variable capacitor section 8, 8a, 8b, 8t, 8x, 8y Low frequency signal cut capacitor section 10, 10a, 10b, 10x, 10y Variable capacitor 11 , 11a, 11b, 11p, 11q, 11r, 11x, 11y Variable capacitor 12 External terminal 14 External terminal 19 Surface protective film 20 Substrate 21 Adhesion layer 22, 22a, 22b, 22p, 22q, 22s, 22t Lower electrode layer 24 Dielectric Layer 26, 26s, 26t, 26x, 26y Upper electrode layer 28 Insulating protective film 29 Organic protective film

Claims (2)

A pair of electrode layers;
A dielectric layer sandwiched between the pair of electrode layers, the dielectric constant of which changes by application of a control voltage;
A plurality of capacitor portions formed by the pair of electrode layers and the dielectric layer;
With
The plurality of capacitor units include at least one variable capacitor unit whose capacitance is changed by application of a control voltage and one low frequency signal cut capacitor unit other than the variable capacitor unit,
The variable capacitor according to claim 1, wherein at least one of the low frequency signal cut capacitor portions is formed outside the variable capacitor portion so as to surround an outer periphery of the at least one variable capacitor portion.   Between the pair of external terminals formed on the same side with respect to the pair of electrode layers and the dielectric layer, 2n capacitor parts that are multiples of a natural number n of 2 or more are connected in series. The variable capacitor according to claim 1.

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