JP2011187680A - Variable capacitance device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable capacity device which can suppress a variation of a Q value and has stable characteristics. <P>SOLUTION: The variable capacitance device includes a fixed electrode 12, a dielectric layer 13 formed on the fixed electrode, a capacitor electrode 14 formed on the dielectric layer, a movable electrode 15 provided facing the capacitor electrode and capable of approaching and separating from the capacitor electrode, and a projection 21 formed on the surface of the capacitor electrode 14. At indirect contact through the projection 21 between the capacitor electrode 14 and the movable electrode 15, contact resistance Rm and contact capacitance Cm are formed, and a resistance value of the contact resistance Rm is set so that, when the reciprocal of a dielectric dissipation factor tanδ=XCm/Rm by the resistance value of the contact resistance Rm and the reactance XCm of the contact capacitance Cm is defined as the Q value, the Q value becomes 10 or larger. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a variable capacitance device manufactured using, for example, MEMS technology.

  In recent years, with the spread of mobile communication devices such as mobile phones and the advancement of functions, there is an increasing demand for small variable capacitance devices that can be used at high frequencies of GHz or higher. There are MEMS (Micro Electro Mechanical Systems) or MEMS devices (micromachine devices) as technologies or devices that can meet such market demands.

  Conventionally, variable capacitance devices (MEMS capacitors) manufactured using MEMS technology have been proposed.

  That is, such a variable capacitance device includes a substrate, a fixed electrode and a movable electrode supported by the substrate, and a dielectric layer provided between the fixed electrode and the movable electrode. An air layer is formed between the dielectric layer and the movable electrode. When the movable electrode is driven by the actuator, the distance between the movable electrode and the fixed electrode changes, and the capacitance changes (Patent Document 1).

JP2004-6588

  In the conventional variable capacitance device described above, the surface of the dielectric layer and the surface of the movable electrode are in contact with each other during driving, but since there are many irregularities on each surface, the entire surface is in uniform contact. Instead, only a portion of them actually touch. For this reason, charges may be accumulated and charged in the contact portion of the dielectric layer, and in this case, the driving characteristics may change.

  In order to suppress this, a structure in which an electrode (capacitor electrode) is arranged on the surface of the dielectric layer and the charge movement of the dielectric layer is promoted to suppress the charge accumulation can be considered.

  That is, in the variable capacitance device 1K shown in FIG. 1, the fixed electrode 12K is formed on the substrate 11K, and the dielectric layer 13K and the capacitor electrode 14K are stacked on the fixed electrode 12K. Above the capacitor electrode 14K, a movable electrode 15K facing the capacitor electrode 14K is provided by being elastically supported by the substrate 11K.

  When a potential difference is applied between the fixed electrode 12K and the movable electrode 15K by the external power source GD, the movable electrode 15K is attracted by the electrostatic attractive force generated between them. Thereby, the distance between the fixed electrode 12K and the movable electrode 15K changes, and the electrostatic capacitance between them changes.

  Usually, in the digital variable capacitance device, the capacitance formed when the capacitor electrode 14K and the movable electrode 15K are separated from each other is the minimum (off state), and the capacitor electrode 14K and the movable electrode 15K are in contact with each other. The capacity becomes maximum (on state) and is used in these two states.

  However, in such a case, the contact resistance between the capacitor electrode 14K and the movable electrode 15K increases while the on / off operation is repeated, and the Q value of the variable capacitance device may fluctuate and stable characteristics may not be obtained.

  In addition, in the on / off operation (hot switch) with a signal flowing through the variable capacitance device, there is a possibility that the load on the contact portion between the capacitor electrode 14K and the movable electrode 15K increases and the electrodes melt and stick. is there.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a variable capacitance device that can suppress variation in the Q value and has stable characteristics.

  In the embodiment described herein, the variable capacitance device includes a fixed electrode, a dielectric layer formed on the fixed electrode, a capacitor electrode formed on the dielectric layer, and the capacitor electrode. And a movable electrode that can be brought into contact with and separated from the capacitor electrode. A contact resistance and a contact capacitance at the time of contact are formed between the capacitor electrode and the movable electrode, and a reciprocal of a dielectric loss tangent tan δ = XCm / Rm based on a resistance value Rm of the contact resistance and a reactance XCm of the contact capacitance The resistance value Rm is set so that the Q value is 10 or more, where is a Q value.

  The contact resistance Rm is set such that the Q value is 40 or more, for example. Further, the resistance value Rm is, for example, 1 KΩ or more.

  According to the present invention, it is possible to provide a variable capacitance device that can suppress fluctuations in the Q value and have stable characteristics.

It is a figure which shows the example of the basic structure of a variable capacity device. It is a figure which shows the example of the structure of the variable capacity device in 1st Embodiment. It is a figure which shows the equivalent circuit of a variable capacitance device. It is a Smith chart which shows the example of the characteristic of a variable capacity device. It is a figure which shows the example of the characteristic of a variable capacity device. It is a figure which shows the modification about the position which provides protrusion. It is a figure which shows the example of the shape and arrangement | positioning of a processus | protrusion. It is a figure which shows the example of the structure of the variable capacity device in 2nd Embodiment. It is a figure which shows the example of the shape of a resistance layer. It is a figure which shows the example of the arrangement | sequence of a resistance layer. It is a figure which shows the example of the structure of the variable capacity device in 3rd Embodiment. It is a figure explaining the example of the formation method of protrusion. It is a figure explaining the other example of the formation method of protrusion. It is a figure explaining the other example of the formation method of protrusion. It is a figure explaining the example of the formation method of a resistance layer. It is a figure explaining the other example of the formation method of a resistance layer.

[First Embodiment]
In FIG. 2, the variable capacitance device 1 includes a substrate 11, a fixed electrode 12 formed on the substrate 11, a dielectric layer 13 formed on the fixed electrode 12, and a capacitor electrode formed on the dielectric layer 13. 14 and the movable electrode 15.

  The substrate 11 is a ceramic substrate made of a metal oxide, an SOI (Silicon On Insulator) substrate, or the like.

  The fixed electrode 12 is formed by plating with a metal material. The fixed electrode 12 serves as one electrode in the variable capacitance device 1.

  The dielectric layer 13 is made of a dielectric material having an appropriate relative dielectric constant εr. The upper surface of the dielectric layer 13 is covered with a capacitor electrode 14. The capacitor electrode 14 has a function of suppressing the uneven distribution and accumulation of charges by promoting the movement of charges in the dielectric layer 13.

  Since the capacitor electrode 14 faces the fixed electrode 12 through the dielectric layer 13, an electrostatic capacitance (fixed capacitance) Cb is generated between the capacitor electrode 14 and the fixed electrode 12. The size of the capacitance Cb is a size according to the area and distance of the facing portion, the dielectric constant of the dielectric layer 13, and the like.

  A large number of protrusions 21 are formed on the surface of the capacitor electrode 14 to obtain contact resistance with the movable electrode 15. Such a protrusion 21 can be formed by, for example, ion milling using plasma.

  That is, when the capacitor electrode 14 is formed by, for example, stacking metal thin films, the surface can be close to a mirror surface, but fine processing is performed by irradiating the surface with an ion beam, A protrusion 21 is formed. That is, by performing removal processing on the surface of the capacitor electrode 14, the protrusion 21 that cannot be generated simply by forming the capacitor electrode 14 by plating or the like is formed. Here, ion milling as a removal process is illustrated, but the protrusion 21 may be formed by other various methods, and some examples will be described later.

  The movable electrode 15 has, for example, a bridge structure that is elastically supported by the substrate 11 at both ends thereof. FIG. 1 shows the central part of the bridge structure. Both ends of the movable electrode 15 are fixed with respect to the substrate 11, but the central portion has flexibility and is elastically bent, and can move in the vertical direction in the figure. The movable electrode 15 is the other electrode in the variable capacitance device 1.

  The fixed electrode 12 and the movable electrode 15 are drawn out by an electrode (not shown) or the like for applying a driving voltage and outputting a high-frequency signal.

  The capacitor electrode 14 and the movable electrode 15 are formed by plating with a metal material such as copper, gold, or aluminum. The movable electrode 15 may have a cantilever structure instead of a bridge structure.

  When an external power source GD is connected to such a variable capacitance device 1 and a potential difference (driving voltage) is applied between the fixed electrode 12 and the movable electrode 15, the movable electrode is generated by electrostatic attraction generated between them. 15 is sucked toward the fixed electrode 12. Thereby, the distance between the fixed electrode 12 and the movable electrode 15 changes, and the electrostatic capacitance C1 between them changes.

  Note that RF blocks 31 and 32 for preventing leakage of high-frequency signals are provided between the external power supply GD and the electrodes of the variable capacitance device 1.

  In the variable capacitance device 1, when the external power source GD is not connected, the movable electrode 15 is in a free state, and the protrusion 21 of the capacitor electrode 14 and the movable electrode 15K are separated [state in FIG. 2 (a)]. . When an external power source GD is connected and a driving voltage is applied, the movable electrode 15 is attracted and bent by the fixed electrode 12, and the surface of the movable electrode 15 comes into contact with the tip portion of the protrusion 21 (see FIG. 2B). Status〕.

  In this way, when the external power supply GD is connected and a predetermined drive voltage is applied, the movable electrode 15 contacts the capacitor electrode 14, but does not contact directly, but via the protrusion 21, the capacitor electrode 14. Contact with. Therefore, the contact area at the time of contact between the movable electrode 15 and the capacitor electrode 14 does not increase, and a contact resistance Rm is generated here. The magnitude of the contact resistance Rm is determined according to the material, shape, dimension, area, contact pressure, etc. of the protrusion 21.

  Further, a contact capacitance Cm is generated between the movable electrode 15 and the capacitor electrode 14 in a state where the movable electrode 15 is in contact with the capacitor electrode 14 through the protrusion 21. The size of the contact capacitance Cm is a size according to the area and distance of the facing portion and the dielectric constant of the substance therebetween. The contact capacitance Cm is expressed in parallel with the contact resistance Rm in the equivalent circuit.

  Next, an equivalent circuit of the variable capacitance device 1 will be described. In this specification, the term “contact resistance Rm” is used for both “contact resistance Rm” as an object or circuit element and “resistance value Rm” for contact resistance. However, when the “resistance value Rm” is expressed, it may be described as “the magnitude of the contact resistance Rm”. The same applies to other elements such as the contact capacitance Cm and the capacitance Cb.

  FIG. 3 shows an equivalent circuit of the variable capacitance device 1 when the movable electrode 15 is driven, that is, when the movable electrode 15 and the protrusion 21 are in contact with each other.

  In the equivalent circuit shown in FIG. 3, the contact resistance Rm and the contact capacitance Cm between the capacitor electrode 14 and the movable electrode 15 are connected in parallel to each other, and the electrostatic resistance between the capacitor electrode 14 and the fixed electrode 12 is connected. A capacitor Cb is connected in series. In addition, a parasitic inductance Lp and a parasitic resistance Rp are connected in series to each other.

  In the present embodiment, the magnitude of the contact resistance Rm (resistance value Rm) is set so that the Q value of the variable capacitance device 1 is 10 or more. Preferably, the magnitude of the contact resistance Rm is set so that the Q value is 40 or more, or the Q value is 50 or more. A specific example of the contact resistance Rm is, for example, 250Ω or more, and preferably, for example, 1KΩ or more.

  Here, the Q value of the variable capacitance device 1 indicates good performance of the variable capacitance device 1, and the higher the Q value, the smaller the loss.

  In the present embodiment, the Q value of the variable capacitance device 1 is expressed by the following equation (1), which is the reciprocal of the dielectric tangent tan δ = XCm / Rm based on the magnitude of the contact resistance Rm and the reactance XCm of the contact capacitance Cm.

Q value = Rm / XCm (1)
That is, the dielectric loss tangent tan δ = XCm / Rm represents the loss of the contact capacitance Cm as a capacitor when the contact resistance Rm is a resistance component (real part) of the contact capacitance Cm. Therefore, the larger the contact resistance Rm, the smaller the loss and the higher the Q value. However, in the variable capacitance device 1, it cannot be infinite due to the function of the capacitor electrode 14, and is a finite value. For example, the Q value is usually about 40 to 50, or 50 or more, about 100 is sufficient, and about 1000 at the maximum.

  For example, when it is considered that the protrusion 21 is not provided between the capacitor electrode 14 and the movable electrode 15 and the contact resistance between the capacitor electrode 14 and the movable electrode 15 is set as low as possible, the contact resistance is usually 0. About 5Ω.

  Assuming that the impedance Z1 of the variable capacitance device 1 is set to, for example, 50Ω, which is a commonly used characteristic impedance Z0, and assuming that a half of 25Ω is a reactance XCm due to the contact capacitance Cm, the Q value in this case is simply If it sees, it will be about 50 (25ohm / 0.5ohm).

  In the variable capacitance device 1 of this embodiment, an equivalent circuit is shown in FIG. 3, and the contact resistance Rm is increased to about 1 KΩ instead of about 0.5Ω. Therefore, in the parallel connection body of the contact resistance Rm and the contact capacitance Cm, the reactance XCm of the contact capacitance Cm is sufficiently lower than the contact resistance Rm.

  Therefore, it can be considered that the contact resistance Rm hardly affects the Q value for the capacitance Cb connected in series with the parallel connection body. Further, when the contact resistance Rm is set as high as about 1 KΩ, even if the contact resistance Rm slightly changes with the value as a base point, the contact resistance Cm and the capacitance Cb are hardly affected. It can be regarded as.

  That is, the capacitance C1 of the variable capacitance device 1 is almost similar to the capacitance Cb when the contact resistance Rm is small, and when the contact resistance Rm is large, the capacitance Cb and the contact capacitance Cm are connected in series. Close to the combined capacity.

  In general, the contact resistance of a switch formed by the MEMS technology is about 0.5Ω, and thus the Q value is about 40. In the variable capacitance device 1 of the present embodiment, the contact resistance Rm is increased and a combined capacitance of the capacitance Cb and the contact capacitance Cm is used to obtain a high Q value.

  That is, for example, the impedance Z1 at the operating frequency of the variable capacitance device 1 is set to about 50Ω as described above, and the reactances XCm and XCb of the contact capacitance Cm and the capacitance Cb are set to about 25Ω to match this. That is, the contact capacitance Cm is set to the same size as the electrostatic capacitance Cb. In this case, when the contact resistance Rm is the same value around 25Ω as the reactances XCm and XCb, the Q value is expected to be the lowest.

  Therefore, in order to increase the Q value, it is necessary to make the contact resistance Rm sufficiently higher than 25Ω, and it is considered that a minimum of about 10 times 250Ω is necessary, and usually 40 times 1 kΩ, 50 times, for example. 1.25 kΩ, 100 times 2.5 kΩ, etc. Further, it can be set to about 10 kΩ, 100 kΩ, or 1 MΩ.

  FIG. 4 is a Smith chart showing the results obtained by simulating the reflection characteristics of the variable capacitance device 1 according to the contact resistance Rm when the frequency is varied in the range of 0.5 to 8 GHz in the circuit shown in FIG. It is shown.

  In the simulation, both the contact capacitance Cm and the capacitance Cb in FIG. 3 were set to 2.5 pF, the parasitic inductance Lp was set to 0.163 nH, and the parasitic resistance Rp was set to 0.288Ω.

  In FIG. 4, the horizontal axis represents the real part of the complex reflection coefficient, and the vertical axis represents the imaginary part. The real number component (resistance component) of the impedance is constant on each circle in the figure, and the imaginary number component (reactance component) of the impedance is constant on the circle bent up and down. In the figure, the Q value increases as it approaches the outer circumference.

  FIG. 4 shows the case where the contact resistance Rm is 0.1Ω, 1Ω, 10Ω, 100Ω, 1 kΩ, and 10 kΩ. In the curve by each contact resistance Rm, the right end of each curve has a frequency of 0.5 GHz and the left end has a frequency of 8 GHz.

  According to FIG. 4, when the contact resistance Rm is 0.1Ω, 1Ω, 1 kΩ, and 10 kΩ, the curve approaches the outer circumference, and it can be seen that the Q value is high. When the contact resistance Rm is 10Ω or 100Ω, the contact resistance Rm is far from the outer circumference and the Q value is low.

  FIG. 5 shows a static capacitance of the variable capacitance device 1 according to the contact resistance Rm when the contact capacitance Cm and the capacitance Cb are both set to 2.5 pF and the frequency is 2.0 GHz, as in FIG. The electric capacity C1 and the Q value are obtained by simulation.

  In FIG. 5, when the contact resistance Rm is low, the capacitance C1 is about 2.7 pF, which is a value close to 2.5 pF of the capacitance Cb. When the contact resistance Rm exceeds 10Ω, the capacitance C1 decreases, and when the contact resistance Rm reaches about 100Ω, the capacitance C1 becomes about 1.8 pF.

  Even if the contact resistance Rm is greater than 100Ω, there is no significant change in the capacitance C1. When the contact resistance Rm is about 10 kΩ, the capacitance C1 is about 1.75 pF, which is half the value of the contact capacitance Cm and the capacitance Cb of 2.5 pF.

  In FIG. 5, when the contact resistance Rm is about 0.5Ω, the Q value is about 50. However, as the contact resistance Rm increases, the Q value decreases, and when the contact resistance Rm becomes about 10Ω, the Q value decreases. The value drops to about 1. When the contact resistance Rm is between 10Ω and 100Ω, the Q value is about 1, and when the contact resistance Rm exceeds 100Ω, the Q value increases accordingly.

  For example, when the contact resistance Rm is about 1000Ω, the Q value is about 50. When the contact resistance Rm is about 10 kΩ, the Q value is increased to about 160.

  According to these FIG. 4 and FIG. 5, the Q value is the lowest when the contact resistance Rm is between 10Ω and 100Ω, and the contact resistance Rm is made sufficiently low or high to obtain a high Q value. There is a need. A certain Q value is obtained when the contact resistance Rm is greater than 100Ω. When the contact resistance Rm is about 1 kΩ, a Q value 50 equivalent to that when the contact resistance Rm is about 0.5Ω is obtained.

  In the variable capacitance device 1 of the present embodiment, the contact resistance Rm is set to about 1 kΩ, and a Q value of 50 is obtained. The electrostatic capacity C1 is a combined capacity of the electrostatic capacity Cb and the contact capacity Cm.

  Since the contact resistance Rm is as high as about 1 kΩ, even if the contact and separation between the capacitor electrode 14 and the movable electrode 15 are repeated by use, the contact resistance Rm hardly changes and the Q value hardly changes. Further, since the contact capacitance Cm and the capacitance Cb hardly change, the capacitance C1 of the variable capacitance device 1 hardly changes.

  In the equivalent circuit shown in FIG. 3, the actual numerical value of each element may be different from the above-described values, and factors not shown in the equivalent circuit may be included. The simulation results shown may be different.

  Thus, in the variable capacitance device 1 of the present embodiment, fluctuations in the Q value can be suppressed and the characteristics are stabilized.

  In addition, since the contact resistance Rm is as high as about 1 kΩ, the current flowing through the variable capacitance device 1 is suppressed even when the on / off operation is performed with the signal current flowing through the variable capacitance device 1, that is, even when the variable capacitance device 1 is operated as a hot switch. Further, welding between the capacitor electrode 14 and the movable electrode 15 can be prevented.

  In the above embodiment, the protrusion 21 is provided on the surface of the capacitor electrode 14. However, such a protrusion 21 may be provided in another part.

  That is, unlike the variable capacitance device 1B shown in FIG. 6A, the protrusion 21B is provided on the surface (lower surface) of the movable electrode 15 opposed to the surface of the capacitor electrode 14 instead of being provided on the surface of the capacitor electrode 14. .

  Further, like the variable capacitance device 1C shown in FIG. 6B, the protrusions 21 and 21B are provided on the opposing surfaces of both the surface of the capacitor electrode 14 and the surface of the movable electrode 15.

  As shown in FIG. 7A, the shapes of the protrusions 21 and 21B can be conical. Further, as shown in FIG. 7B, the conical protrusions 21 and 21B can be arranged in a matrix in the vertical direction and the horizontal direction.

  The shape of the protrusions 21 and 21B may be various shapes other than the conical shape, and the array may be various arrays other than the matrix shape.

The protrusion 21 can be formed by roughening the surface by various ion milling or other methods.
[Second Embodiment]
In the first embodiment described above, an appropriate contact resistance Rm is obtained by bringing the capacitor electrode 14 and the movable electrode 15 into contact with each other via the protrusion 21. In the second embodiment, a resistance layer is used instead of the protrusion 21.

  In FIG. 8, the variable capacitance devices 1 </ b> D to 1 </ b> F are formed on the substrate 11, the fixed electrode 12 formed on the substrate 11, the dielectric layer 13 formed on the fixed electrode 12, and the dielectric layer 13. The capacitor electrode 14 and the movable electrode 15 are included. On the surface of the capacitor electrode 14 or the movable electrode 15, a plurality of resistance layers 22 and 22 </ b> B formed using a resistance material for forming the contact resistance Rm are provided.

  That is, in the variable capacitance device 1D shown in FIG. 8A, a plurality of resistance layers 22 are provided on the surface (lower surface) of the movable electrode 15. In the variable capacitance device 1E shown in FIG. 8B, a plurality of resistance layers 22B are provided on the surface (upper surface) of the capacitor electrode. In the variable capacitance device 1F shown in FIG. 8C, a plurality of resistance layers 22 and 22B are provided on both the surface (lower surface) of the movable electrode 15 and the surface (upper surface) of the capacitor electrode 14.

  As shown in FIG. 9A, the resistance layers 22 and 22B are circular in plan view (front view). The resistance layers 22 and 22B have a thickness (height) of, for example, about 50 to 100 nm and a diameter of, for example, about 3 to 10 μm.

  Further, as shown in FIG. 9B, the resistance layers 22 and 22B may be formed so that the plan view (front view) is a square or a rectangle. In that case, the length of one side is, for example, about 3 to 10 μm.

  The resistance layers 22 and 22B may have various shapes other than these. For example, a regular polygon, a trapezoid, a polygonal pyramid, a truncated cone, a spherical surface, a hemispherical surface, or other curved surface may be used.

  The arrangement of the resistance layers 22 and 22B may be a matrix arrangement, an oblique arrangement, a concentric arrangement, a spiral arrangement, or the like. In the example shown in FIG. 10, a plurality of resistance layers 22 are arranged in a matrix on the lower surface of the movable electrode 15.

  Nb—SiO 2, ruthenium oxide, Cu—Mn alloy, Ni—Cu alloy, Ni—Cr alloy, or the like is used as the material of the resistance layers 22 and 22B. Moreover, what disperse | distributed metal conductor particles, such as Ag or Cu, in resin can be used.

  The resistance layers 22 and 22B can also be formed using a semiconductor material such as Si. For example, a Si thin film having a high resistivity may be formed by vacuum evaporation or sputtering to form the resistance layers 22 and 22B.

Thus, by forming the contact resistance Rm and the contact capacitance Cm by the resistance layers 22 and 22B, the design of the contact resistance Rm and the contact capacitance Cm is easy, and the contact resistance Rm and the contact capacitance Cm having accurate values can be obtained. Obtainable. For example, by setting the thickness, height, area, volume, and the like of the resistance layers 22 and 22B to appropriate values, the magnitude of the contact resistance Rm can be easily set. Further, the values of the contact resistance Rm and the contact capacitance Cm are stable over a long period of use.
[Third Embodiment]
In the first and second embodiments described above, one capacitor electrode 14 and one movable electrode 15 are opposed to each other. In the third embodiment, a plurality of capacitor electrodes 14 a to 14 c are provided to face one movable electrode 15.

  11, the variable capacitance devices 1G to 1J include a substrate 11, a fixed electrode 12 formed on the substrate 11, a plurality of dielectric layers 13a to 13c formed on the fixed electrode 12, and each dielectric layer 13a to 13c. a plurality of capacitor electrodes 14a to 14c formed on c, a movable electrode 15 and the like.

  One or a plurality of protrusions 21 or resistance layers 22 and 23 for forming the contact resistance Rm are provided on the surface of each capacitor electrode 14a to 14c or the movable electrode 15.

  That is, in the variable capacitance device 1G shown in FIG. 11A, a plurality of protrusions 21 are provided on the surface (lower surface) of the movable electrode 15. In the variable capacitance device 1H shown in FIG. 11B, a plurality of resistance layers 22 are provided on the surface (lower surface) of the movable electrode 15. In the variable capacitance device 1 </ b> J shown in FIG. 11C, a long resistance layer 23 integrated with the surface (lower surface) of the movable electrode 15 is provided.

  The protrusions 21 and the resistance layers 22 and 23 are the same as those described in the first or second embodiment, respectively.

  By the way, a potential difference is applied between the fixed electrode 12 and the movable electrode 15 by the external power source GD, and when they come into contact with each other, the capacitance Cb between the fixed electrode 12 and the capacitor electrode 14 is charged. In this state, when the movable electrode 15 is separated from the capacitor electrode 14 by eliminating the potential difference, a discharge may occur between the capacitor electrode 14 and the movable electrode 15 due to the charged charge.

On the other hand, according to the variable capacitance devices 1G to 1J of the third embodiment, the capacitance Cb which is a fixed capacitance is subdivided by providing a plurality of capacitor electrodes 14a to 14c facing one movable electrode 15. did. Thereby, the electrostatic capacitances Cba to c formed in the respective capacitor electrodes 14a to 14c are subdivided, and the charge amount for the individual electrostatic capacitances Cba to c is reduced. Therefore, it is difficult for discharge to occur, and even if discharge occurs, the discharge becomes small, and it is difficult to cause electrode damage and welding. Thereby, reliability can be further improved.
[Method of forming protrusion and resistance layer]
Next, an example of a method for forming the protrusions 21 and 21B and the resistance layers 22 and 23 will be described.

  FIGS. 12 to 14 show examples of methods for forming the protrusions 21 and 21B, and FIGS. 15 to 16 show examples of methods for forming the resistance layers 22 and 23, respectively.

  As shown in FIG. 12A, a sacrificial layer 31 is formed on the upper surface of the capacitor electrode 14. As a material of the sacrificial layer 31, for example, SiO2, MgO or the like is used. As shown in FIG. 12B, a mask 32 having a large number of holes 32a is disposed on the sacrificial layer 31, and the sacrificial layer 31 is partially etched as shown in FIG. The sacrificial layer 31 is undercut, and a space KK is formed under each hole 32a.

  As shown in FIG. 12D, sputtering or the like is performed using a metal material or a semiconductor material to form a conical protrusion 21 in a space KK portion on the surface of the capacitor electrode 14. At this time, a material such as sputtering is also deposited on the mask 32. As shown in FIG. 12E, protrusions 21 are formed on the surface of the capacitor electrode 14 by removing the sacrificial layer 31 by etching or the like.

  As shown in FIG. 13A, a sacrificial layer 31 is formed on the upper surface of the capacitor electrode 14. As shown in FIGS. 13B and 13C, the surface of the sacrificial layer 31 is pressed and molded using a press die 33 made of metal having a large number of conical protrusions 33a formed on the surface. As a result, as shown in FIG. 13D, a large number of conical recesses 31 a are formed on the surface of the sacrificial layer 31.

  As shown in FIG. 13E, a metal layer 34 is formed on the sacrificial layer 31 by plating or the like. As shown in FIG. 13F, by removing the sacrificial layer 31, the movable electrode 15 having a large number of protrusions 21B on the surface is formed.

  As shown in FIG. 14A, a sacrificial layer 31 is formed on the upper surface of the capacitor electrode 14. As a material of the sacrificial layer 31, for example, SiO2, MgO or the like is used. As shown in FIG. 14B, a mask 35 having a large number of holes 35a is disposed on the sacrificial layer 31, and the sacrificial layer 31 is half-etched as shown in FIG. 14C. Thereby, a recess 31 b is formed in the sacrificial layer 31.

  The mask 35 is removed as shown in FIG. 14D, and a metal layer 36 is formed on the sacrificial layer 31 by plating or the like as shown in FIG. As shown in FIG. 14F, by removing the sacrificial layer 31, the movable electrode 15 having a large number of protrusions 21B on the surface is formed.

  As shown in FIG. 15A, a sacrificial layer 31 is formed on the upper surface of the capacitor electrode 14. A resin or the like can be used as the material of the sacrificial layer 31. As shown in FIGS. 15B and 15C, the surface of the sacrificial layer 31 is pressed and molded using a press die 37 made of metal having a large number of conical protrusions 37a formed on the surface. As a result, a large number of conical recesses 31 c are formed on the surface of the sacrificial layer 31 as shown in FIG.

  As shown in FIG. 15E, a resistor 38 is applied on the sacrificial layer 31 by screen printing or the like. As shown in FIG. 15F, the resistor 38 is etched back to remove the resistor 38a applied in the recess 31c. As shown in FIG. 15G, a metal layer 39 is formed on the sacrificial layer 31 and the resistor 38a by sputtering or the like. The metal layer 39 and the resistor 38a are integrated by an anchor effect. As shown in FIG. 15H, by removing the sacrificial layer 31, the movable electrode 15 having a large number of resistance layers 22 on the surface is formed.

  As shown in FIG. 16A, a sacrificial layer 31 is formed on the upper surface of the capacitor electrode 14. As shown in FIG. 16B, a mask 40 having a large number of holes 40a is disposed on the sacrificial layer 31, and the sacrificial layer 31 is half-etched as shown in FIG. Thereby, a recess 31 d is formed in the sacrificial layer 31.

  The mask 40 is removed as shown in FIG. 16D, and a resistor 41 is applied on the sacrificial layer 31 by screen printing or the like as shown in FIG. As shown in FIG. 16 (F), the resistor 41 is etched back, and the rest is removed while leaving the resistor 41a applied in the recess 31d. As shown in FIG. 16G, a metal layer 42 is formed on the sacrificial layer 31 and the resistor 41a by sputtering or the like. The metal layer 42 and the resistor 41a are integrated by an anchor effect. As shown in FIG. 16H, by removing the sacrificial layer 31, the movable electrode 15 having a large number of resistance layers 22 on the surface is formed.

  In each of the forming methods described above, the shape, size, number, and arrangement of the holes 32a, 35a, 40a, the protrusions 33a, 37a, the recesses 31a, 31b, 31c, 31d, the resistor 38a, the protrusions 21, 21B, and the resistance layer 22 are used. In addition to the above, various changes can be made. Various formation methods other than those described above can be employed.

  In each of the above embodiments, the Q value, the contact resistance Rm, the contact capacitance Cm, the electrostatic capacitance Cb, the parasitic inductance Lp, the parasitic resistance Rp, and the like are the purpose of use of the variable capacitance device, the characteristic impedance Z0 of the transmission line, etc. Various changes can be made according to the usage conditions.

  In each of the above embodiments, the variable capacitance device 1, 1B to J that applies a potential difference between the fixed electrode 12 and the movable electrode 15 by the external power source GD and contacts the capacitor electrode 14 and the movable electrode 15 by electrostatic attraction. An example of However, the variable capacitance device is not limited to this structure, and can be applied to a device on which a mechanism for bringing the capacitor electrode 14 and the movable electrode 15 into contact is mounted. Further, a drive electrode for driving the movable electrode 15 may be provided separately.

  In addition, each part of the fixed electrode 12, the dielectric layer 13, the capacitor electrode 14, the movable electrode 15, the protrusion 21, the resistance layers 22, 22B, 23, and the variable capacitance devices 1, 1B to J, or the entire configuration, structure, circuit, shape The number, material, arrangement, manufacturing method, and the like can be changed as appropriate in accordance with the gist of the present invention.

1, 1B to J Variable capacitance device 12 Fixed electrode 13 Dielectric layer 14 Capacitor electrode 15 Movable electrode 21 Protrusion 22, 22B Resistance layer 23 Resistance layer Rm Contact resistance Cm Contact capacitance Cb Capacitance (fixed capacitance)
C1 Capacitance (combined capacity)
XCm reactance

Claims (6)

A fixed electrode;
A dielectric layer formed on the fixed electrode;
A capacitor electrode formed on the dielectric layer;
A movable electrode provided facing the capacitor electrode and capable of contacting and separating from the capacitor electrode;
A contact resistance and a contact capacitance at the time of contact are formed between the capacitor electrode and the movable electrode,
The resistance value Rm is set so that the Q value becomes 10 or more when the reciprocal of the dielectric loss tangent tan δ = XCm / Rm based on the resistance value Rm of the contact resistance and the reactance XCm of the contact capacitance is defined as a Q value. ing,
Variable capacity device. The resistance value Rm is set so that the Q value is 40 or more.
The variable capacitance device according to claim 1. The resistance value Rm is 1 KΩ or more,
The variable capacitance device according to claim 1. A plurality of protrusions for forming the contact resistance is provided on the surface of the capacitor electrode or the movable electrode.
The variable capacitance device according to claim 1. A resistance layer formed using a resistance material for forming the contact resistance is provided on the surface of the capacitor electrode or the movable electrode.
The variable capacitance device according to claim 1. A plurality of the capacitor electrodes are provided facing one movable electrode,
The variable capacitance device according to claim 1.

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