JP2008258186A - Variable capacity device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact variable capacity device having a high continuously variable capacity ratio. <P>SOLUTION: The variable capacity device comprises a variable capacity capacitor employing a ferroelectric material, a capacitor connected in series with the variable capacity capacitor, and a switch connected in parallel with that capacitor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a variable capacitance device, and more particularly to a fine variable capacitance device used for an antenna device or the like that has a large continuous capacitance variable width and realizes both a wide band and high radiation efficiency.

  With the spread of information communication equipment such as wireless terminals, the frequency used for communications has increased from 400 MHz for digital television to 800 MHz for mobile phones and several GHz bands for wireless LANs. Yes. Currently, there are many situations where terminals compatible with various communication methods are used independently, but in the future, it is desired to realize a small terminal compatible with various communication methods with one wireless terminal.

  Therefore, in recent years, it is related to a tunable device that realizes high-sensitivity transmission / reception in a frequency band for each of a plurality of radio systems by using both antenna elements and amplifiers smaller than the number of on-board radio systems by coexistence of widening and high sensitivity of antennas. Research and development is ongoing. Some of the tunable devices are manufactured as MEMS devices that integrate mechanical element parts, various sensors, actuators, electronic circuits, and the like on a silicon substrate using MEMS (Micro Electro Mechanical Systems) technology. . In this tunable device, a variable capacitor, a switch, and a filter are formed on a silicon substrate (hereinafter, the capacitor, switch, and filter included in the tunable device are referred to as a MEMS capacitor, a MEMS switch, and a MEMS filter). In addition, a group of MEMS capacitors, MEMS switches, and MEMS filters are referred to as MEMS composite devices or composite devices), by controlling the capacitance (capacitance) value of any MEMS variable capacitor and the opening and closing of the MEMS switch, The inductance value and the capacitance value of the entire composite device are adjusted, and the antenna characteristics of the antenna elements connected to the tunable device are controlled. As a result, the antenna device including the tunable device and the antenna element can realize high-sensitivity transmission / reception in a plurality of frequency bands or a wide frequency band.

  For example, in a mobile terminal device typified by a mobile phone in recent years, a terrestrial digital broadcast (such as this) broadcasted by one segment out of 13 segments (bands) divided into frequencies allocated to one channel. Some terrestrial digital broadcasts are referred to as “One Seg.”). In order to receive terrestrial digital broadcasts broadcast on a plurality of channels, an antenna device mounted on a portable terminal device is required to secure a frequency band of about 470 to 770 [MHz]. On the other hand, a loop antenna often mounted on a mobile terminal device has a high sensitivity, but a frequency band that can be secured is as narrow as about 10 [MHz]. For this reason, by connecting a tunable device to the loop antenna and controlling the antenna characteristics of the loop antenna, a method of ensuring a high-bandwidth of about 300 [MHz] necessary for receiving digital terrestrial broadcasting with high sensitivity. Is being considered.

As a specific example of the tunable device as described above, for example, in Patent Document 1, a MEMS fixed capacitor C0, a MEMS variable capacitor C1 connected in series to the MEMS switch S1, and a MEMS switch S2 are connected in series. There has been proposed a variable capacitor system in which a MEMS variable capacitor C2 and a MEMS variable capacitor Cn connected in series to a MEMS switch Sn are connected in parallel.
JP 2004-327877 A

In the variable capacitor system disclosed in Patent Document 1, a MEMS variable capacitor is used, and the minimum value of the capacitance in a section where the capacitance continuously increases as the applied electric field increases (referred to as a continuous capacitance variable width). It is very difficult to increase the ratio between the maximum value and the maximum value (referred to as a continuous capacity variable ratio). Therefore, in Patent Document 1, transmission / reception in a plurality of frequency bands or a wide frequency band is realized by a configuration including a plurality of variable capacitors having a small continuous capacitance variable ratio. However, in this configuration, when the number of frequency bands to be transmitted / received by the antenna device increases or the bandwidth of the frequency band increases, it is necessary to increase the number of variable capacitors accordingly. When the number of MEMS variable capacitors that require a displacement region increases, not only the occupied area increases, but also the parasitic resistance increases, and the deterioration due to the repeated number of displacements also increases, and it is applied to the antenna device. In this case, the antenna performance is deteriorated.
Therefore, in order to provide a small antenna device capable of realizing high-sensitivity transmission / reception in a plurality of frequency bands or a wide frequency band, a small variable capacitance device having a large continuous capacitance variable ratio and low loss is required. . In addition to the antenna device, a high-frequency filter or the like is also strongly demanded for a small-sized variable capacitance device having a large continuous capacitance variable ratio in order to increase the bandwidth.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a small variable capacitance device having a large continuous capacitance variable ratio and a small loss.

The variable capacitance device of the present invention comprises a variable capacitance capacitor using a ferroelectric material, a capacitor connected in series with the variable capacitance capacitor, and a switch connected in parallel with the capacitor. To do.
According to this configuration, by using a capacitance variable capacitor using a ferroelectric material whose dielectric constant changes by applying an electric field, the continuous variable capacitance ratio can be increased, and this is connected in series to the capacitor. By doing so, it becomes possible to obtain a continuously variable capacity ratio of 2.7 or higher, which was not obtained conventionally. In addition, since it can be formed over the same substrate, it is possible to provide a variable capacitance device that is small and highly reliable with reduced parasitic capacitance and parasitic resistance. In addition, since the capacitance variable capacitor itself occupies a smaller area than the displacement type variable capacitance capacitor, it is possible to reduce the size even when a plurality of capacitance capacitors are connected. In addition, since a variable capacitance capacitor using a ferroelectric material does not have a displacement portion as compared with a displacement type variable capacitance capacitor, reliability can be maintained over a long period of time. Further, by connecting an antenna element to the capacity variable portion, it is possible to suppress deterioration of antenna performance.

According to the present invention, in the variable capacitance device, the variable capacitance capacitor is formed on the substrate, and a dielectric thin film made of a ferroelectric material is sandwiched between the first electrode and the second electrode. Including those composed of thin film elements.
According to the said structure, manufacture is easy and size reduction is attained.

According to the present invention, in the above variable capacitance device, the capacitor is formed on the substrate, and a thin film element in which a dielectric thin film made of a paraelectric material is sandwiched between a first electrode and a second electrode. Including those that are
According to the said structure, manufacture is easy and size reduction is attained. In addition, the first and second electrodes can be formed in the same process as the capacitance variable capacitor, and only the dielectric thin film needs to be changed. Therefore, manufacturing is easy and miniaturization is possible. Furthermore, since the resistance is lower than that of the ferroelectric thin film, the parasitic resistance can be reduced.

Further, the present invention includes the above variable capacitance device, wherein the continuous variable capacitance ratio of the variable capacitance capacitor is less than 2.7.
According to the above configuration, it is possible to form a capacitance variable section having a continuous capacitance variable ratio of 2.7 or more using a capacitance variable capacitor having a continuous capacitance variable ratio of less than 2.7 without causing an increase in size.

Further, the present invention includes the above variable capacitance device, wherein a continuous capacitance variable ratio of the capacitance variable capacitor is 1.6 or more.
According to the above configuration, since the variable capacitance device can be realized with a simple configuration, the manufacturing process is simplified, high reliability can be realized, and a large continuous capacitance variable ratio can be provided with low loss.

In the variable capacitance device according to the present invention, the switch includes a switch body formed to be displaceable by a driving unit, a movable electrode formed on the switch body, and the substrate so as to face the movable electrode. Including a fixed electrode formed on the surface.
According to the above configuration, since the electromechanical switch is configured to perform switching between the movable electrode attached to the switch body and the fixed electrode facing the movable electrode, there is no OFF current and power consumption can be reduced. Can measure.

Further, the present invention includes the variable capacitance device, wherein the driving unit is a piezoelectric element attached to the switch body.
According to the above configuration, low voltage driving is possible, and the driving force is small and high.

In the variable capacitance device according to the present invention, the driving unit may include a first driving electrode formed on the switch body, a piezoelectric thin film formed on an upper layer of the first driving electrode, Including those composed of a second drive electrode formed on a piezoelectric thin film.
According to the above configuration, it can be very easily formed as a laminated structure of thin films.

The present invention includes the variable capacitance device, wherein the piezoelectric thin film is PZT.
According to the above configuration, a high driving force can be obtained at a low voltage due to the large piezoelectric effect of PZT.

The present invention includes the variable capacitance device, wherein the drive unit is an electrostatic drive element attached to the switch body.
According to the above configuration, the switch can be driven by driving the switch body toward the fixed electrode by electrostatic force.

Further, the present invention includes the above variable capacitance device, wherein the dielectric thin film is BST (barium strontium titanate).
According to the above configuration, it is possible to obtain a capacitance variable capacitor that can be easily thinned and has a high continuous capacitance change ratio.

Further, the present invention includes the above variable capacitance device, wherein the dielectric thin film is PZT (lead zirconium titanate).
According to the above configuration, it is possible to obtain a capacitance variable capacitor that can be easily thinned and has a high continuous capacitance change ratio.

The present invention includes the variable capacitance device, wherein the switch body is a cantilever.
According to the above configuration, a switch that can be driven at a low voltage with a simple structure can be obtained.

The present invention includes the variable capacitance device, wherein the switch body is a doubly supported beam.
According to the above configuration, a more stable switch can be obtained.

The present invention includes the variable capacitance device, wherein the switch body includes a fixed portion formed in a frame shape and a displacement portion extending from the fixed portion.
According to the said structure, the displacement part is reliably supported by the fixing | fixed part, and a stable operating characteristic can be acquired.

In the variable capacitance device according to the aspect of the invention, in the switch body, the displacement body is a cross-shaped beam extending from the fixed portion, and the contact point of the movable electrode is provided at the center of the cross-shape. Including things.
According to the above configuration, a stable and reliable displacement can be obtained.

Further, the present invention includes the variable capacitance device, wherein the switch body is a disk-shaped body having a fixed peripheral edge, and a contact point of the movable electrode is provided at the center of the disk-shaped body.
According to the above configuration, a stable and reliable displacement can be obtained.

In addition, the present invention includes the above-described variable capacitance device, in which a displacement assisting portion that assists the displacement of the displacement portion is provided at a boundary portion between the fixed portion and the displacement portion.
According to the said structure, the displacement auxiliary | assistant part was comprised, and a displacement can be assisted with a low voltage.

The present invention includes the variable capacitance device, wherein the displacement assisting portion is a through hole.
According to the said structure, the state which is easy to displace can be obtained by providing a through-hole in the boundary part of the said fixing | fixed part and the said displacement part.

In the variable capacitance device according to the present invention, the displacement assisting portion includes a thin portion.
According to the said structure, the state which is easy to displace can be obtained by providing a thin part in the boundary part of the said fixing | fixed part and the said displacement part.

In addition, the present invention includes the variable capacitance device described above, wherein the variable capacitance device is a monolithic device formed on the same substrate.
According to this configuration, since a connection pad or the like for inter-element connection is not necessary, a very fine and low resistance variable capacitance device can be realized.

In the present invention, an antenna element such as a loop antenna may be connected to the variable capacitance device. A loop antenna may be formed on the same substrate as the variable capacitance device.
According to the above configuration, there is a problem that the bandwidth is narrow particularly in the case of a loop antenna, but the bandwidth can be further increased by using the capacitance variable section using a ferroelectric capacitor.

Further, the present invention includes the above variable capacitance device, wherein the variable capacitance capacitor includes a series connection body of a plurality of variable capacitance capacitors.
According to the above configuration, since the capacitance value of a single variable capacitance capacitor can be increased, manufacturing can be facilitated.

According to the present invention, in the variable capacitance device, the variable capacitance capacitor is integrally formed on at least two first capacitance electrodes disposed at a predetermined interval and on an upper layer of the first capacitance electrode. A ferroelectric thin film, and at least two second capacitive electrodes formed on the ferroelectric thin film so as to partially overlap the first capacitive electrode.
According to the above configuration, the variable capacitance capacitor can be formed with a simple configuration. Since the ferroelectric thin film is integrally formed, only the first and second capacitor electrodes need to be patterned.

Further, the present invention includes the variable capacitance device, wherein the variable capacitance capacitor includes three or more capacitance electrodes and a ferroelectric thin film sandwiched between the capacitance electrodes.
According to the above configuration, since it can be configured by a laminated body, the occupied area can be reduced.

Moreover, the present invention is effective for an antenna device for a portable terminal, etc.
With this configuration, an antenna device having a small size, a wide band, and high reliability can be obtained, so that a portable terminal with good antenna performance can be provided.

  According to the variable capacitance device of the present invention, it is possible to obtain a variable capacitance that is small in size, has high reliability and low loss, and has a high continuous capacitance variable ratio.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 shows an equivalent circuit of the antenna apparatus using the variable capacitance device according to the first embodiment of the present invention. 4 is a top view and bottom view of the variable capacitance device of the antenna device, FIG. 5 is a cross-sectional view taken along the line AA of FIG. 4, and FIG. 6 is an enlarged plan view and a cross-sectional view of the main part of the switch.

  As shown in FIG. 1, the antenna device includes first and second variable capacitors C1 and C2 connected in series to each other, and a variable capacitor including a switch SW connected in parallel to the first variable capacitor C1. A variable capacitance device TD as a unit, and an antenna element ANT connected at both ends to the variable capacitance unit, one terminal of the antenna element is installed, and the other terminal is connected to the high frequency integrated processing circuit RFIC Has been. Here, this terminal may be connected to the high-frequency integrated processing circuit RFIC via the capacitor C.

  In this variable capacitance device, one end of the switch SW is connected to one end of the variable capacitor C1, and the other end of the switch SW is connected to one end of a loop antenna constituting the antenna element ANT. The other ends of the variable capacitors C1 and C2 are connected to the other end of the loop antenna ANT. The two end portions of the loop antenna are connected to high frequency integrated circuits RFIC and GND that process high frequency signals, respectively. In the first embodiment of the present invention, the antenna element is a loop antenna. However, the antenna element applicable to the antenna device of the present invention is not limited to the loop antenna, and other types of antenna elements such as slots Even with an antenna, a helical antenna, a monopole antenna, a dipole antenna, a patch antenna, a microstrip antenna, an inverted F antenna, and an inverted L antenna, transmission / reception in a wide frequency band can be realized.

For example, in order to secure a frequency band of about 470 to 770 [MHz] of terrestrial digital TV (One Seg), the capacity of the variable capacitance device TD needs to change in the range of 1.26 to 3.39 [pF]. There is. For this purpose, variable capacitors C1 and C2 whose capacities change as follows when the applied voltage Vt is simultaneously changed from 0.5 [V] to 2 [V] are used.
[Variable capacitor C1]
3. The capacitance changes from 20 to 5.38 [pF]. The capacitance of the variable capacitor C2 is 5.38 [pF] when the applied voltage Vt is 1 [V], and the capacitance of the variable capacitor C2 is 3.20 [pF] when the applied voltage Vt is 2 [V]. Become. At this time, the continuous capacity variable ratio is 5.38 / 3.20≈1.68.
[Variable capacitor C2]
The capacitance changes from 2.08 to 3.39 [pF]. The capacitance of the variable capacitor C1 is 3.39 [pF] when the applied voltage Vt is 1 [V], and the capacitance of the variable capacitor C1 is 2.08 [pF] when the applied voltage Vt is 2 [V]. Become. At this time, the continuous capacity variable ratio is 3.39 / 2.08≈1.63.
First, when the switch SW is opened and the applied voltage Vt is set to 2 [V], C1 = 3.2 [pF] and C2 = 2.08 [pF], and the combined capacitance is 1.26 [pF]. Become. If the applied voltage Vt is gradually decreased and set to 0.5 [V], C1 = 5.38 [pF], C2 = 3.39 [pF], and the combined capacitance becomes 2.08 [pF]. . Next, when the switch SW is closed, the capacitive element is only the variable capacitor C2, and if the applied voltage Vt is set to 2 [V], C2 = 2.08 [pF] and the combined capacitance is 2.08 [pF]. become. If the applied voltage Vt is gradually lowered and set to 0.5 [V], C2 = 3.39 [pF] and the combined capacitance is 3.39 [pF]. That is, the capacitance of the variable capacitance device TD is changed in the range of 1.26 to 3.39 [pF].

For this reason, if the continuous capacitance variable ratio of the variable capacitors C1 and C2 is 1.6 or more, preferably 1.7 or more, the switches SW1 and SW2 are selectively short-circuited, and one of the variable capacitors C1 and C2 is selected. Is connected to the loop antenna ANT, so that a frequency bandwidth of 470 M to 600 MHz can be secured when the variable capacitor C1 is connected, and a frequency bandwidth of 600 M to 770 MHz can be secured when the variable capacitor C2 is connected. .
In this way, a broadband antenna device can be provided.

  It has been stated that the capacity of the tunable device TD needs to be changed in the range of 1.26 to 3.39 [pF] in order to secure a frequency band of about 470 to 770 [MHz]. Here, when the tunable device TD realizes the change in capacitance within this range with one capacitance variable capacitor C0, the continuous capacitance variable ratio required for the capacitance variable capacitor C0 will be considered.

  FIG. 2 shows an equivalent circuit of a tunable device composed of one variable capacitor as a reference example for explaining the present invention. In FIG. 2, the tunable device TD is formed by one capacitance variable capacitor C0, and two ends of the loop antenna ANT are connected to both ends of the capacitance variable capacitor C0. Further, the two end portions of the loop antenna ANT are connected to high frequency integrated circuits RFIC and GND that process high frequency signals, respectively.

  In order to secure a frequency band of about 470 to 770 [MHz], the capacitance variable capacitor C0 needs to continuously change its capacitance at a value of 1.26 to 3.39 [pF] according to the applied voltage Vt. (The variable capacitance capacitor C0 has a capacitance of 470 [MHz] when its capacitance is 3.39 [pF] and 770 [MHz] when its capacitance is 1.26 [pF]). At this time, the continuous capacitance variable ratio of the capacitance variable capacitor C0 must be 3.39 / 1.26≈2.7. However, since it is difficult to manufacture a variable capacitance capacitor that realizes a high continuous capacitance variable ratio of 2.7, it is possible to realize the tunable device including one capacitance variable capacitor shown in FIG. It is also difficult. Therefore, like the antenna device according to the first embodiment of the present invention, a tunable device including two capacitance variable capacitors C1 and C2 having a continuous capacitance variable ratio of 1.6 or more (preferably 1.7 or more). It came to assume. According to the antenna device of the first embodiment of the present invention, the tunable device is configured by at least two capacitance variable capacitors, so that the circuit scale increases as the bandwidth of the frequency band required for the antenna element increases. The circuit scale can be further reduced as compared with the conventional system.

  If the number of capacitance variable capacitors is increased to three or four, the continuous capacitance variable ratio required for the capacitance variable capacitor is reduced accordingly. For this reason, according to the continuous capacitance variable ratio of a capacitance variable capacitor, you may increase / decrease the number of the capacitance variable capacitors connected in series with a switch, respectively.

  In addition, the dielectric used in the two capacitance variable capacitors C1 and C2 in the antenna device according to the first embodiment of the present invention realizes a continuous capacitance variable ratio of about 1.6 or more (preferably 1.7 or more). There are BST (barium strontium titanate) and PZT (lead zirconate titanate). BST and PZT are ferroelectrics whose permittivity ε changes according to the applied electric field. A capacitance variable capacitor disclosed in Japanese Patent Application Laid-Open No. 2004-327877 (Patent Document 1) that obtains a desired capacitance by changing the distance between electrodes by electrostatic force (electrostatic method) generates the static electricity. Therefore, a BST capacitor using BST as a dielectric material or a PZT capacitor using PZT as a dielectric material requires a dielectric constant at a driving voltage of less than 3 [V], compared with the case where a driving voltage of several tens [V] is required. A desired capacity can be obtained by changing ε. For this reason, it can be said that a tunable device having a configuration including a BST capacitor or a PZT capacitor is a device suitable for mounting for a portable terminal device that is required to operate with a driving voltage as low as about 3 [V]. The antenna device tunable device according to the first embodiment of the present invention includes a BST capacitor or a PZT capacitor as a variable capacitance capacitor. If the continuous capacitance variable ratio is a ferroelectric material of 1.6 or more, the tunable device of the antenna device of the present invention can be configured by a capacitance variable capacitor using the ferroelectric material.

  The tunable device TD of the antenna device according to the first embodiment of the present invention has a configuration in which two variable capacitance capacitors are connected in series. Since it is easy to make two capacitors connected in series with each other in a laminated structure, the mounting area of the tunable device can be suppressed.

  Further, when the tunable device TD is formed by the BST capacitors C1 and C2 and the switch SW, it is necessary to consider the equivalent series resistance Rs of the BST capacitors C1 and C2 and the switch SW. FIG. 3 shows the relationship between radiation efficiency and equivalent series resistance. In FIG. 3, the equivalent series resistance Rs of the entire tunable device connected to the plate-shaped loop antenna (outer circumference 40 [mm] × 6 [mm], plate-shaped width 8 [mm]) is changed from 0 to 800 [mΩ]. The radiation efficiency η by the plate loop antenna in the case of changing is shown. Note that the shape of the plate-like loop antenna is assumed to be mounted on a portable terminal device, and the plate-like loop antenna having such a shape is, for example, an end of a casing of a portable terminal device, When the terminal device is composed of two housings, the terminal device is disposed at an end portion different from an end portion where the two housings are joined.

  The plate-like loop antenna connected to the tunable device TD can secure the frequency band 470 to 770 [MHz] used for digital terrestrial broadcasting and suppress the decrease in the radiation efficiency η to about 1 [dB]. preferable. According to FIG. 3, it can be seen that if the equivalent series resistance Rs is less than 200 [mΩ], the decrease in the radiation efficiency η can be suppressed to less than 1 [dB]. For this reason, it is necessary to select the BST capacitors C1 and C2 and the switch SW used for the tunable device so that the equivalent series resistance Rs of the entire tunable device is less than 200 [mΩ].

  For example, when a varactor diode or a Pin diode that has been used in a tunable device so far is selected as the switch SW, these diodes have a large equivalent series resistance Rs of 500 [mΩ] or more, and the radiation efficiency η is It decreases by 1 [dB] or more. In the first embodiment of the present invention, the tunable device is formed by the BST capacitor connected in series. Therefore, the equivalent series resistance of the BST capacitor is added, and the equivalent series resistance Rs of the entire tunable device tends to increase. In addition, as a conventionally used switch having a small resistance value, there is a relay having an electromagnetic driving means and a mechanical contact. This relay has a problem in that the physical volume is larger than that of a physically small antenna element, so that the performance of the antenna is affected, and the wiring portion becomes longer, so that the inductance increases and the antenna efficiency deteriorates. Yes, it is inappropriate as a switch for small antenna elements.

Next, a specific configuration of the variable capacitance device including the variable capacitance capacitors 110a and 110b (C1 and C2) and the electromechanical (MEMS) switch 120 (SW) will be described.
The variable capacitance device is formed on the same silicon substrate 100. The first capacitance electrodes 111a and 111b formed by the first layer wiring and the BST (BaSrTiO ₃ : barium strontium titanate) formed on the upper layer are formed. And ferroelectric capacitor layers 112a and 112b, and second capacitor electrodes 113a and 113b composed of a second-layer wiring formed on the upper layer, and the first and second capacitor electrodes 111a and 111b. A region between the ferroelectric layers 112a and 112b constitutes the first and second capacitance variable capacitors 110a and 110b. In these second layer wirings, the second capacitance electrodes 113a and 113b of the first and second variable capacitance capacitors are interconnected by the wiring 113, and the fixed electrode 123 of the MEMS switch 120 constituting the switch SW is connected to this connection portion. Is connected. The ferroelectric layers 112a and 112b are integrally formed, but may be separately formed.

  In addition, as shown in FIG. 6, the MEMS switch SW includes a MEMS switch main body 122 formed of a single rod beam formed of an insulating layer such as a silicon dioxide layer formed on the silicon substrate 100, and A drive unit 130 formed of a piezoelectric element that is formed on the MEMS switch body 122 and displaces the MEMS switch body 122 according to the drive electric field, and the MEMS switch body 122 is displaced according to the drive electric field, Opening / closing (ON / OF) is realized. In this MEMS switch, a movable electrode 121 is formed on the lower surface of the MEMS switch main body 122 of the capacitance variable capacitor, and a fixed electrode 123 is disposed opposite to the movable electrode 121. The fixed electrode 123 is connected to the wiring 113 at the connection portion of the second capacitance electrodes 113a and 113b of the first and second capacitance variable capacitors C1 and C2. The movable electrode 121 is formed on the lower surface of the MEMS switch body 122, and is connected to a signal electrode 123b made of a conductive layer formed on the surface of the silicon substrate 100 as the same layer as the fixed electrode 123. 123 b is connected to the second capacitance electrode 113 a of the first variable capacitance capacitor 110. ON / OFF of the first capacitance variable capacitor is controlled by ON / OFF of the MEMS switch.

  The driving unit 130 includes a lower layer electrode 131 formed on the upper surface of the beam-shaped MEMS switch body 122 and an upper layer electrode 133 with a piezoelectric thin film 132 made of PZT or the like sandwiched between the lower layer electrode 131 and the upper layer electrode 133. The piezoelectric thin film is stretched in the length direction when a voltage is applied between the lower layer electrode 131 side and the upper layer electrode 133. The force displaces the MEMS switch body 122, and the protrusion 121 </ b> S formed at the tip of the movable electrode 121 is in contact with the fixed electrode 123, so that the switch is turned on. The piezoelectric thin film 132 is formed so as to avoid the tip and the root portion 122n of the beam constituting the MEMS switch body 122 in order to increase driving efficiency and improve reliability. Here, the root portion n refers to the boundary between the fixed portion and the MEMS switch body 122 that is a movable portion.

Also, on the surface of the silicon substrate, as shown in FIGS. 4A and 4B, an input terminal 100T for inputting an input signal to the variable capacitance device, and a drive unit 130 made of a piezoelectric element of a MEMS switch. Are connected to the switch drive terminal 130T for inputting the drive signal, the output terminal 113T of the variable capacitance device, and the first capacitance electrodes 111a and 111b, which are the lower layer electrodes of the first and second capacitance variable capacitors, respectively. First and second capacitance control terminals 111Ta and 111Tb are formed.
Here, the input signal input from the input terminal 100T is output from the output terminal 113T. However, in the present embodiment, the voltages applied to the first and second capacitance control terminals 111Ta and 111Tb are made common, but they may be individually provided. By making them separate, it is possible to control the individual capacitance values of the variable capacitance capacitors C1 and C2.

  The variable capacitance device is connected to both ends of the antenna element ANT via the input terminal 100T and the output terminal 113T (FIG. 1).

Next, the operation of this variable capacitance device will be described.
Prior to the description of the operation, the characteristics of the dielectric constituting the variable capacitance capacitor will be described.
In BST, as shown in FIG. 7 showing the relationship between the voltage V and the relative permittivity ε, the relative permittivity changes by about 200 to about 400 by applying an electric field. Therefore, the relative permittivity ε1 and ε2 of each capacitance variable capacitor can be similarly changed from about 200 to about 400 by changing the relative permittivity.

The operation of this variable capacitance device will be described in detail.
When an electric field is applied between the lower layer electrode 131 of the piezoelectric element constituting the driving unit 130 of the MEMS switch 120 and the upper layer electrode 133, the piezoelectric thin film 132 is displaced, and a piece formed on the silicon substrate 100 as a base. The tip of the MEMS switch main body 122 which is a cantilever is displaced in the direction of arrow a, the protrusion 121S of the movable electrode 121 contacts the fixed electrode 123, and the movable electrode 121 and the fixed electrode 123 are short-circuited.
On the other hand, if the voltage application between the lower layer electrode 131 that is the drive electrode of the piezoelectric element and the upper layer electrode 133 is stopped, the tip of the MEMS switch constituting the cantilever moves in the direction opposite to the arrow A, Returning to the state, the protrusion 121S is separated from the fixed electrode 123, and the contact between the fixed electrode and the movable electrode is released.

  In this way, since the sum of the capacitances of the two capacitance variable capacitors is C1 · C2 / (C1 + C2), it can be changed from C1 · C2 / (C1 + C2) to C2. Therefore, as described above, a frequency bandwidth of 470 to 700 can be obtained. In addition, power consumption at the time of OFF is extremely small, and a highly reliable variable capacitance device can be formed. Accordingly, it is possible to obtain a small antenna with a wide band and high sensitivity.

  In the above embodiment, as shown in FIG. 6B, the piezoelectric thin film 132 is formed avoiding the tip of the beam and the root portion 122n constituting the MEMS switch main body 122. Reliability can be improved and displacement can be performed with a small force.

In addition, this variable capacitance device can be formed by integrating a capacitance variable capacitor and a MEMS switch on a single silicon substrate 100, and is easy to manufacture and highly reliable. Further, since the two capacitance variable capacitors and the MEMS switch are integrated, the transmission loss is small, the size is extremely fine, and the mounting workability is high.
The hybrid antenna device can be formed by mounting on a substrate on which a silicon substrate (semiconductor chip) antenna circuit constituting the variable capacitance device is formed.

Although the hybrid antenna device is formed in the above embodiment, it is possible to form a monolithic structure antenna device by forming a loop antenna element on a silicon substrate.
Furthermore, only the switch may be configured by MEMS, and the capacitance variable capacitor chip may be mounted on the substrate on which the antenna element is formed, and may be mounted by MEMS.

  In the above-described embodiment, the piezoelectric thin film 132 is formed so as to avoid the tip and the root portion 122n of the beam constituting the MEMS switch body 122. However, the piezoelectric thin film 132 may be formed on the entire MEMS switch body 122. Depending on the material, the MEMS switch main body 122 can be formed so as not to disturb the displacement, and in this case, a larger driving force can be generated.

(Embodiment 2)
Next, as a second embodiment of the present invention, a modification of the MEMS switch used in the variable capacitance device of the present invention will be described.
As shown in FIGS. 9A to 9C, the MEMS switch 120 constituting the variable capacitance device for an antenna device according to the second embodiment of the present invention is provided with a MEMS switch body 122D having a double-supported beam structure. The movable electrode 121 is disposed on this. Here, FIG. 9A is a top view of the MEMS switch used in the second embodiment, FIG. 9B is a cross-sectional view taken along line AA of FIG. 9A, and FIG. 9C is FIG. It is BB sectional drawing of).

  The constituent elements are the same as those of the variable capacitance device shown in the first embodiment, except that the MEMS switch body 122D is supported at both ends by the circular frame 130, and has a doubly supported beam stretched along the diameter direction. It differs from the MEMS switch of the said embodiment by the point which comprises.

  The movable electrode 121 is formed on the back side of the MEMS switch main body 122D by a radius from the frame portion to the center position along the beam, and has a protrusion 121S at the tip. The fixed electrode extends from the position facing the protrusion 121S by a radius in the direction opposite to the movable electrode 121.

  The drive unit 130 is also formed on the MEMS switch main body 122D, and although detailed description is omitted, the piezoelectric thin film 132 is sandwiched between the lower layer electrode 131 and the upper layer electrode 133.

  Also in this MEMS switch, the OFF current is small as in the MEMS switch used in the first embodiment, so that a small and wideband antenna device can be obtained.

  Moreover, the MEMS switch having this structure can be easily mounted as a switching device chip. Since the connection can be made without selecting the direction, the layout is easy even when the antenna device is configured with a hybrid structure.

  Although not shown here, other elements constituting the variable capacitance device are the same as those in the first embodiment.

(Embodiment 3)
Next, as a third embodiment of the present invention, a modification of the MEMS switch used in the variable capacitance device will be described.
As shown in FIGS. 10A to 10C, the MEMS switch 120 constituting the variable capacitance device for an antenna device according to the third embodiment of the present invention has a both-end supported beam structure fixed at the center. A MEMS switch main body 122Q is disposed, and a movable electrode 121 is disposed thereon. Here, FIG. 10A is a top view of the MEMS switch used in the third embodiment, FIG. 10B is a cross-sectional view taken along line AA of FIG. 10A, and FIG. 10C is FIG. It is BB sectional drawing of).

  The components are the same as those of the variable capacitance device shown in the first and second embodiments, but the MEMS switch main body 122Q is supported at both ends by the circular frame 130 and is stretched along the diametrical direction. This is different from the MEMS switch of the above embodiment in that a beam is formed.

  Two movable electrodes 121 are formed on the back surface side of the MEMS switch main body 122Q from the frame portion to the center position along the beam by a radius, and a protrusion 121S is provided at the tip. In addition, the fixed electrode extends by two radii from the position facing the protrusion 121S in the direction opposite to the movable electrode 121.

  The drive unit 130 is also formed on the MEMS switch main body 122Q, and detailed description is omitted in the same manner, but the piezoelectric thin film 132 is sandwiched between the lower layer electrode 131 and the upper layer electrode 133.

  Also in this MEMS switch, the OFF current is small as in the MEMS switch used in the first embodiment, so that a small and wideband antenna device can be obtained.

  Moreover, the MEMS switch having this structure can be easily mounted as a switching device chip. Since the connection can be made without selecting the direction, the layout is easy even when the antenna device is configured with a hybrid structure.

  Although not shown here, other elements constituting the variable capacitance device are the same as those in the first embodiment.

(Embodiment 4)
Next, as a fourth embodiment of the present invention, a modification of the MEMS switch used in the antenna device will be described.
As shown in FIGS. 11A and 11B, the MEMS switch 120 constituting the variable capacitance device for the antenna device according to the fourth embodiment of the present invention is a MEMS having a doubly-supported beam structure as in the second embodiment. The switch body 122D is disposed, and the movable electrode 121 is disposed on the switch body 122D. However, in the present embodiment, one hole 125 is formed in each of the root portions 122n of the beam, and the frame portion which is a fixed portion is formed. It is characterized by forming a structure that increases elasticity and is easily displaced. Here, FIG. 11A is a top view of the MEMS switch used in the fourth embodiment, and FIG. 11B is a cross-sectional view taken along line AA of FIG.

The constituent elements are the same as those of the variable capacitance device shown in the second embodiment.
According to this configuration, in addition to the effect of the second embodiment, each hole 125 is formed in the root portion 122n of the beam that constitutes the MEMS switch main body 122D. And can be easily displaced.

(Embodiment 5)
Next, as a fifth embodiment of the present invention, a modification of the MEMS switch used in the antenna device will be described.
As shown in FIGS. 12A and 12B, the MEMS switch 120 constituting the variable capacitance device for an antenna device according to the fifth embodiment of the present invention is different from the first to fourth embodiments described above. In this embodiment, the MEMS switch body 126 is configured by a disk-shaped plate connected to the frame portion 130. Then, the MEMS switch body 126 made of this plate-like body is disposed, and the movable electrode 121 is disposed on the MEMS switch body 126. In the present embodiment, a plurality of members are provided along the circumferential direction at the root portion 122n of the beam. Each of the holes 125 is formed to increase the elasticity of the frame portion, which is a fixed portion, and to form a structure that is easily displaced. Here, FIG. 12A is a top view of the MEMS switch used in the fifth embodiment, and FIG. 12B is a cross-sectional view taken along line AA of FIG.

The constituent elements are the same as those of the variable capacitance device shown in the first embodiment.
According to this configuration, in addition to the effects of the first embodiment, the MEMS switch main body 126 has one hole 125 in the root portion 122n, so that the elasticity of the frame portion that is the fixing portion is increased and the displacement is increased. It is possible to make it easy to do.

Note that the movable electrode and the fixed electrode are arranged to face each other in the radial direction, as in the second embodiment.
According to this configuration, a stable displacement can be obtained, and a highly accurate and reliable MEMS switch can be provided.

(Embodiment 6)
Next, as a sixth embodiment of the present invention, a modification of the MEMS switch used in the antenna device will be described.
As shown in FIGS. 13A and 13B, the MEMS switch 120 constituting the variable capacitance device for an antenna device according to the sixth embodiment of the present invention is similar to the fifth embodiment in the present embodiment. The MEMS switch body 126 is constituted by a disk-shaped plate connected to the frame portion 130. Then, the MEMS switch main body 126 made of this plate-like body is provided, and the movable electrode 121 is provided thereon. In this embodiment, a belt-like groove is formed along the circumferential direction on the beam 122n. 127 to form a structure that is easy to displace by increasing the elasticity of the frame portion, which is a fixed portion. Here, FIG. 13A is a top view of the MEMS switch used in the sixth embodiment, and FIG. 13B is a cross-sectional view taken along line AA of FIG.

The constituent elements are the same as those of the variable capacitance device shown in the fifth embodiment.
According to this configuration, in addition to the effects of the first embodiment, since the MEMS switch body 126 forms the band-shaped groove 127 along the circumferential direction in the root portion 122n, the frame portion which is a fixed portion Therefore, it is possible to provide a structure that is more easily displaced.

  In this case as well, the movable electrode and the fixed electrode are arranged so as to face each other in the radial direction as in the second embodiment.

(Embodiment 7)
Next, as a seventh embodiment of the present invention, a modified example of the variable capacitance capacitor of the variable capacitance device used in the antenna device will be described.
The variable capacitance device for an antenna device according to the seventh embodiment of the present invention is the same as that of the conventional variable capacitance device shown in FIG. 14A, as shown in FIGS. 14A and 14B. As shown in FIG. 14B, the variable capacitance capacitor C1 is composed of a series connection body of five variable capacitance capacitors C11, C12, C13, C14, and C15, and a fine capacitance variable capacitor having a large continuous capacitance variable ratio is formed. It is characterized by providing.

  That is, the dielectric constant of a ferroelectric such as BST or PZT changes depending on the applied DC voltage. Accordingly, it is possible to configure a variable capacitance capacitor that controls the capacitance value with the applied DC voltage. However, these ferroelectrics have a large dielectric constant, and in order to reduce the voltage value that controls the capacitance value, Since the thickness must be reduced, it may be difficult to obtain a small capacitance value when it is difficult to reduce the area. In such a case, a small capacitance value can be obtained by connecting a plurality of capacitance variable capacitors in series.

  For example, if the capacitance variable capacitor C1 using BST as a dielectric layer is variable in the range of 5 to 10 pF, for example, if it is desired to obtain a capacitance value of 1/5, the electrode area is reduced to 1/5. There is a need. However, when it is difficult to form a smaller pattern by photolithography, as shown in FIG. 14B, a series connection body of five capacitance variable capacitors C11, C12, C13, C14, and C15 is used. Constitute. Thereby, the continuous capacitance variable ratio 2 can be obtained with a fine capacitance of 1 to 2 pF.

(Embodiment 8)
Next, as an eighth embodiment of the present invention, the structure of a variable capacitance capacitor constituting the antenna device of the seventh embodiment will be described.
The first variable capacitance capacitor constituting the variable capacitance device for an antenna device according to the eighth embodiment of the present invention has three first capacitances formed at predetermined intervals as shown in the conceptual cross-sectional explanatory diagram of FIG. One capacitive electrode 111a, 111b, 111c, a dielectric layer 112 made of BST integrally formed on the first capacitive electrode 111a, 111b, 111c, and the first capacitive electrode 111a, 111b, 111c. And second capacitive electrodes 113a, 113b, 113c formed so as to overlap each other by a predetermined width a, and are connected in series in regions R1 to R5 where the first capacitive electrode and the second capacitive electrode overlap. The connected variable capacitance capacitors C11, C12, C13, C14, and C15 are configured.

According to this configuration, it is possible to easily and efficiently form a variable capacitance capacitor having a fine capacity.
In manufacturing, since the BST formation process is only required once, a highly reliable device can be formed very easily.

  That is, the dielectric constant of a ferroelectric such as BST or PZT changes depending on the applied DC voltage. Therefore, it is possible to construct a variable capacitance capacitor that controls the capacitance value with the applied DC voltage. However, it is difficult to obtain a small capacitance value when these ferroelectrics have a large dielectric constant and it is difficult to reduce the area. It may become. In such a case, a fine capacitance can be obtained by connecting a plurality of variable capacitance capacitors in series.

  For example, if the capacitance variable capacitor C1 using BST as a dielectric layer is variable in the range of 5 to 10 pF, for example, if it is desired to obtain a capacitance value of 1/5, the electrode area is reduced to 1/5. There is a need. However, when it is difficult to form a smaller pattern by photolithography, as shown in FIG. 14B, a series connection body of five capacitance variable capacitors C11, C12, C13, C14, and C15 is used. Constitute. Thereby, the continuous capacitance variable ratio 2 can be obtained with a fine capacitance of 1 to 2 pF.

(Embodiment 9)
Next, as a ninth embodiment of the present invention, a structure of a variable capacitance capacitor constituting the antenna device of the seventh embodiment will be described.
The first variable capacitance capacitor constituting the variable capacitance device for an antenna device according to the ninth embodiment of the present invention has five capacitance variable capacitors formed in a laminated structure as shown in the conceptual cross-sectional explanatory diagram of FIG. Is.
That is, in the eighth embodiment, five capacitance variable capacitors are arranged side by side to form a series connection body, but in this structure, five capacitance variable capacitors are stacked to form a series connection body.
According to this configuration, the occupied area can be reduced. Further, since the adjacent electrodes can be shared, a compact structure can be obtained.

In all of the above-described embodiments, BST, PZT, or the like can be applied as a material constituting the dielectric layer.
In addition, PZT, PLZT, AlN, ZnO, or the like can be applied as the piezoelectric thin film constituting the driving unit.
In addition, SiO ₂ , SiN, or the like can be used as an insulating film material that covers the substrate surface. When used as a sacrificial layer that is removed by etching in the MEMS process, it is necessary to select the material in consideration of the etching selectivity. .
Furthermore, it is desirable to use silicon (Si) as the substrate, but a compound semiconductor substrate such as GaAS may be used.

  Moreover, in the said embodiment, although the connection part of the movable electrode 121 and fixed electrode 123 in a MEMS switch was performed with metal, either a silicon oxide film or silicon nitride on the surface of the movable electrode 121 and the fixed electrode 123 is carried out. A thin insulating film such as a film may be formed.

  Moreover, in the said embodiment, although the drive part of the MEMS switch was comprised by the piezoelectric element, you may use an electrostatic force.

(Embodiment 10)
Next, as a tenth embodiment of the present invention, a modification of the antenna device of the first embodiment will be described. In the first embodiment, the control unit connected to the first and second capacitance variable capacitors is controlled with the same potential, but a separate voltage generation circuit is provided and controlled independently by the first and second control units. You may do it.

  In the above embodiment, an example using two capacitance variable capacitors has been described. However, for example, three or more capacitance variable capacitors are used, such as using n capacitance variable capacitors and n−1 MEMS switches. It is also applicable when

  As described above, as a result of forming the variable capacitance device by the BST capacitors C1 and C2 and the switch SW manufactured by using the MEMS technology, the radiation efficiency η by the plate loop antenna is shown in the frequency band 470 to 770 [MHz]. The relationship shown in FIG. FIG. 8 shows the relationship between the radiation efficiency and the frequency band used for the terrestrial digital method. The radiation efficiency η by the plate loop antenna decreases at 600 [MHz]. This is because the switch SW in the variable capacitance device is opened and the BST capacitors C1 and C2 are connected in series. This is because the entire equivalent series resistance Rs increases. However, since the decrease in the radiation efficiency η is extremely small, there is no influence on the transmission / reception of digital terrestrial broadcast waves by the antenna device according to the embodiment of the present invention.

  As described above, according to the antenna device of the embodiment of the present invention, transmission / reception in a wide frequency band can be realized by a variable capacitance device having a configuration in which BST capacitors are connected in series. The antenna device according to the embodiment of the present invention that achieves frequency matching with a low drive voltage and can reduce the mounting area satisfies the requirements for an antenna device mounted on a mobile terminal device, Very useful.

(Embodiment 11)
In the first to tenth embodiments, a variable capacitance device having a configuration in which BST capacitors are connected in series is used. In this embodiment, one BST capacitor is a fixed capacitance capacitor Cs using a paraelectric thin film. It is characterized by doing so.
Next, FIG. 15 shows an equivalent circuit of the antenna device according to the eleventh embodiment of the present invention. In the variable capacitance device of the present embodiment, instead of the variable capacitance capacitor C1 using a ferroelectric thin film as the capacitive insulating film of the first embodiment, a fixed capacitance capacitor Cs using a paraelectric thin film is used. It is characterized by that. That is, the fixed capacitor Cs includes a thin film element that is formed on the substrate and sandwiches a dielectric thin film made of a paraelectric material between a first electrode and a second electrode.

  As shown in FIG. 15, this antenna device includes a variable capacitor as a variable capacitor including a fixed capacitor Cs and a variable capacitor C2 connected in series to each other, and a switch SW connected in parallel to the fixed capacitor Cs. A device TD and an antenna element ANT having both ends connected to the variable capacitance section are provided. One terminal of the antenna element is installed, and the other terminal is connected to the high-frequency integrated processing circuit RFIC.

  In order to secure a frequency band of about 470 to 770 [MHz], the capacity of the tunable device TD needs to change in the range of 1.26 to 3.39 [pF]. For this purpose, when the applied voltage Vt is changed from 1 [V] to 2 [V], the fixed capacitance capacitor Cs fixed to the next capacitance and the capacitance variable capacitor C2 whose capacitance changes as follows. Use.

[Fixed capacitance capacitor Cs]
The fixed capacitor Cs has a fixed capacitance of 4.00 [pF].
[Capacitance variable capacitor C2: When switch SW is short-circuited]
The capacitance changes from 1.82 to 3.39 [pF]. The capacitance of the variable capacitance capacitor C2 is 3.39 [pF] when the applied voltage Vt is 1 [V], and the capacitance of the variable capacitance capacitor C2 is 1.82 [pF] when the applied voltage Vt is 2 [V]. 〕become. At this time, the continuous capacity variable ratio becomes 3.39 / 1.82≈1.86.
[Combined capacitance of fixed capacitor Cs and variable capacitor C2: When switch SW is opened]
The capacitance changes from 1.26 to 1.82 [pF]. When the applied voltage Vt is 1 [V], the combined capacity is 1.82 [pF], and when the applied voltage Vt is 2 [V], the combined capacity is 1.26 [pF].

  For this reason, if the continuous capacitance variable ratio of the capacitance variable capacitor C2 is 1.8 or more, the switch SW is short-circuited or opened, and only the fixed capacitance capacitor Cs and the capacitance variable capacitor C2, or the capacitance variable capacitor C2 is a loop antenna. By connecting to the ANT, the frequency bandwidth of 470 to 650 MHz is obtained when only the capacitance variable capacitor C2 is connected, and the frequency bandwidth of 650 to 770 is obtained when the capacitance variable capacitor C1 and the capacitance variable capacitor C2 are connected. Can be secured. In this way, a broadband antenna device can be provided.

  According to this structure, manufacture is easy and size reduction is attained. In addition, the first and second electrodes can be formed in the same process as the capacitance variable capacitor, and only the dielectric thin film needs to be changed. Therefore, manufacturing is easy and miniaturization is possible. Furthermore, since the resistance is lower than that of the ferroelectric thin film, the parasitic resistance can be reduced.

  According to the variable capacitance device of the present invention, since the continuous capacitance variable ratio is high, and it is fine and highly reliable, transmission / reception in a plurality of frequency bands or a wide frequency band can be realized. It is useful in the field of filters and antenna devices in information communication equipment such as wireless terminals for the purpose of realizing high radiation efficiency.

1 is an equivalent circuit diagram illustrating an antenna device using the variable capacitance device according to the first embodiment of the present invention. Equivalent circuit of a tunable device composed of one variable capacitor (reference example) Relationship between radiation efficiency and equivalent series resistance The figure which shows the semiconductor chip which comprises the variable capacitance device of the apparatus, (a) is a top view, (b) is a bottom view AA sectional view of FIG. 4A and 4B are views showing a MEMS switch of the variable capacitance device of FIG. 4, FIG. The figure which shows the relationship between the relative dielectric constant of the dielectric layer of the capacitance variable capacitor used for the variable capacitance device, and the applied electric field Relationship between radiation efficiency and frequency band used for terrestrial digital method The figure which shows the MEMS switch of the variable capacity device of Embodiment 2 of this invention, (a) is a top view, (b) is AA sectional drawing of (a), (c) is BB of (a). Cross section The figure which shows the MEMS switch of the variable capacity device of Embodiment 3 of this invention, (a) is a top view, (b) is AA sectional drawing of (a), (c) is BB of (a). Cross section The figure which shows the MEMS switch of the variable capacitance device of Embodiment 4 of this invention, (a) is a top view, (b) is AA sectional drawing of (a). The figure which shows the MEMS switch of the variable capacitance device of Embodiment 5 of this invention, (a) is a top view, (b) is AA sectional drawing of (a). The figure which shows the MEMS switch of the variable capacitance device of Embodiment 6 of this invention, (a) is a top view, (b) is AA sectional drawing of (a). Explanatory drawing which shows the MEMS switch of the variable capacitance device of Embodiment 7 of this invention, (a) is a circuit schematic diagram, (b) is a principal part detail drawing of (a). Sectional drawing which shows the MEMS switch of the variable capacitance device of Embodiment 8 of this invention Conceptual sectional view showing the MEMS switch of the variable capacitance device according to the ninth embodiment of the present invention. Equivalent circuit diagram showing an antenna apparatus using the variable capacitance device according to the eleventh embodiment of the present invention.

ANT Loop antenna C1, C2 Capacitance variable capacitor TD Variable capacitance device SW MEMS switch 100 Silicon substrates 110a, 110b Capacitance variable capacitors 111a, 111b First capacitance electrodes 112a, 112b Ferroelectric layers 113a, 113b Second capacitance electrodes 120 switches 121 Movable electrode 121S Protrusion (bump)
122 MEMS switch body 122n Root part 123 Fixed electrode 130 Drive part

Claims (25)

A variable capacitance capacitor using a ferroelectric material;
A capacitor connected in series with the variable capacitance capacitor;
A variable capacitance device comprising a switch connected in parallel with the capacitor. The variable capacitance device according to claim 1,
The variable capacitance device, wherein the capacitance variable capacitor is formed on the substrate, and includes a thin film element in which a dielectric thin film made of a ferroelectric material is sandwiched between a first electrode and a second electrode. The variable capacity device according to claim 1 or 2,
The capacitor is a variable capacitance device which is a thin film element formed on the substrate and sandwiching a dielectric thin film made of a paraelectric material between a first electrode and a second electrode. The variable capacity device according to any one of claims 1 to 3,
The variable capacitance device wherein a continuous capacitance variable ratio of the capacitance variable capacitor is less than 2.7. The variable capacitance device according to claim 4,
A variable capacitance device having a continuous capacitance variable ratio of the capacitance variable capacitor of 1.6 or more. A variable capacitance device according to any one of claims 1 to 5,
The switch includes a switch main body formed to be displaceable by a driving unit, a movable electrode formed on the switch main body, and a fixed electrode formed on the substrate surface so as to face the movable electrode. Capacity device. The variable capacitance device according to claim 6,
The drive unit is a variable capacitance device that is a piezoelectric element attached to the switch body. The variable capacity device according to claim 7,
The drive unit includes a first drive electrode formed on the switch body, a piezoelectric thin film formed on an upper layer of the first drive electrode, and a second drive formed on the piezoelectric thin film. A variable capacitance device composed of electrodes. The variable capacitance device according to claim 8, wherein
The piezoelectric thin film is a variable capacitance device that is PZT. The variable capacitance device according to claim 6,
The drive unit is a variable capacitance device that is an electrostatic drive element attached to the switch body. The variable capacitance device according to any one of claims 2 to 10,
The dielectric thin film is a variable capacitance device which is BST (barium strontium titanate). The variable capacitance device according to any one of claims 2 to 10,
The dielectric thin film is a variable capacitance device which is PZT (lead zirconate titanate). The variable capacitance device according to claim 6,
The switch body is a variable capacitance device that is a cantilever. )
The variable capacitance device according to claim 6,
The switch body is a variable capacitance device that is a doubly supported beam. The variable capacitance device according to claim 6,
The switch body is a variable capacitance device including a fixed portion formed in a frame shape and a displacement portion extending from the fixed portion. The variable capacitance device according to claim 15,
The switch body is a variable capacitance device in which the displacement portion is a cross-shaped beam portion extending from the fixed portion, and a contact point of the movable electrode is provided at the center of the cross-shape. The variable capacitance device according to claim 6,
The switch body is a disk-shaped body having a fixed peripheral edge, and a variable capacitance device in which a contact point of the movable electrode is provided at the center of the disk-shaped body. The variable capacitance device according to any one of claims 15 to 17,
A variable capacitance device comprising a displacement assisting part for assisting displacement of the displacement part at a boundary part between the fixed part and the displacement part. The variable capacitance device according to claim 18, comprising:
The displacement assisting unit is a variable capacitance device that is a through hole. The variable capacitance device according to claim 18, comprising:
The displacement assisting part is a variable capacitance device that is a thin part. The variable capacitance device according to any one of claims 1 to 20,
The variable capacitance device is a variable capacitance device that is a monolithic device formed on the same substrate. The variable capacitance device according to claim 1,
The variable capacitance capacitor is a variable capacitance device configured by connecting a plurality of variable capacitance capacitors in series. The variable capacitance device according to claim 22,
The capacitance variable capacitor includes at least two first capacitance electrodes arranged at a predetermined interval, a ferroelectric thin film integrally formed on an upper layer of the first capacitance electrode, and the ferroelectric thin film A variable capacitance device comprising at least two second capacitance electrodes formed on the upper layer so as to overlap the first capacitance electrode in a partial region. The variable capacitance device according to claim 22,
The variable capacitance capacitor is a variable capacitance device including three or more capacitance electrodes and a ferroelectric thin film sandwiched between the capacitance electrodes.   A mobile terminal comprising the variable capacitance device according to claim 1.