Patent Publication Number: US-2021167751-A1

Title: Resonance device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT/JP2019/033731 filed Aug. 28, 2019, which claims priority to JP Application No. 2018-160026, filed Aug. 29, 2018, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to resonance devices. 
     BACKGROUND 
     In general, resonance devices fabricated using Micro-Electro-Mechanical Systems (MEMS) techniques are becoming more common. Such a resonance device includes, for example, a resonator, a lower cover (lower side substrate), and an upper cover (upper side substrate). 
     An existing resonance device of this kind is disclosed in Patent Document 1 (identified below). This device includes a resonator including a lower electrode, a plurality of upper electrodes, and a piezoelectric film formed between the lower electrode and the plurality of upper electrodes. Moreover, an upper cover having a first surface and a second surface is provided in which the first surface is provided in such a manner as to face the upper electrodes of the resonator and seal a first surface of the resonator; a lower cover is provided having a first surface and a second surface, with the first surface being provided in such a manner as to face the lower electrode of the resonator and seal a second surface of the resonator; a power supply terminal is provided that is electrically connected to the upper electrodes; and a ground terminal is provided on the second surface of the upper cover. Moreover, the lower electrode is electrically connected to the ground terminal with the upper cover interposed therebetween. 
     Patent Document 1: International Publication No. 2016/159018. 
     As in the resonance device of the Patent Document 1, in the case where a resonance device includes two power supply terminals and one ground terminal, a stray capacitance (hereinafter, simply referred to as “capacitance”) is formed both between one of the power supply terminals and the ground terminal and between the other power supply terminal and the ground terminal. 
     This capacitance is determined by the area of a wiring line routed inside the resonance device, the thickness of an insulating film formed on or in a substrate, and the like. Here, in the case where a resonator of the resonance device includes three or more upper electrodes, for convenience of electrode connection design, the capacitance formed between the one of the power supply terminals and the ground terminals and the capacitance formed between the other power supply terminal and the ground terminal are not in balance. In the resonator in which the capacitances are not in balance, for example, when voltage signals applied to the one of the power supply terminals and the other power supply terminal are reversed, the oscillation frequency may become different in some cases. 
     SUMMARY OF THE INVENTION 
     The exemplary embodiments of the present invention are provided in view of such circumstances. Specifically, it is an object thereof is to provide a resonance device constructed to suppress a capacitance imbalance. 
     Accordingly, a resonance device according to one exemplary includes a resonator including three or more upper electrodes, a lower electrode, and a piezoelectric film formed between the three or more upper electrodes and the lower electrode. Moreover; a substrate is provided in such a way that a first surface of the substrate faces the upper electrode of the resonator; a first power supply terminal is provided on a second surface of the substrate, the first power supply terminal being electrically connected to at least one of the three or more upper electrodes; a second power supply terminal is provided on the second surface of the substrate, the second power supply terminal being electrically connected to at least one of remaining upper electrodes of the three or more upper electrodes; and a ground terminal is provided on the second surface of the substrate, the ground terminal being electrically connected to the lower electrode. Moreover, an area of the first power supply terminal and an area of the second power supply terminal are different from one other in such a way that a capacitance formed between the first power supply terminal and the ground terminal is approximately equal to a capacitance formed between the second power supply terminal and the ground terminal. 
     According to the exemplary embodiments of the present invention, the capacitance imbalance is suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view schematically illustrating an exterior shape of a resonance device in a first exemplary embodiment. 
         FIG. 2  is an exploded perspective view schematically illustrating a structure of the resonance device illustrated in  FIG. 1 . 
         FIG. 3  is a plan view schematically illustrating a structure of a resonator illustrated in  FIG. 2 . 
         FIG. 4  is a cross-sectional view schematically illustrating a cross-sectional configuration along line IV-IV of the resonance device  1  illustrated in  FIG. 1  to  FIG. 3 . 
         FIG. 5  is a plan view schematically illustrating structures of power supply terminals and a ground terminal provided on an upper cover illustrated in  FIG. 1  and  FIG. 2 . 
         FIG. 6  is a plan view schematically illustrating the resonator and wiring lines in the vicinity of the resonator illustrated in  FIG. 1  to  FIG. 4 . 
         FIG. 7  is a plan view of a modified example schematically illustrating structures of the power supply terminals and the ground terminal provided on the upper cover illustrated in  FIG. 5 . 
         FIG. 8  is a cross-sectional view schematically illustrating a structure of a resonance device according to a second exemplary embodiment. 
         FIG. 9  is a cross-sectional view schematically illustrating a structure of a resonance device according to a third exemplary embodiment. 
         FIG. 10  is a cross-sectional view schematically illustrating a structure of a resonance device according to a fourth exemplary embodiment. 
         FIG. 11  is a plan view schematically illustrating a structure of a resonance device according to a fifth exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments of the present invention are described below. In the description of the following drawings, the same or similar reference characters are used for the same or similar constituent elements. The drawings are exemplifications, and the dimensions and the shape of each portion are schematically illustrated. Thus, it should not be understood that the technical scope of the present invention is limited to these embodiments. 
     First Exemplary Embodiment 
     First, referring to  FIG. 1  and  FIG. 2 , a schematic configuration of a resonance device  1  according to the first embodiment is described.  FIG. 1  is a perspective view schematically illustrating an exterior shape of the resonance device  1  in the first embodiment of the present invention.  FIG. 2  is an exploded perspective view schematically illustrating the structure of the resonance device  1  illustrated in  FIG. 1 . 
     As shown, the resonance device  1  includes a resonator  10 , a lower cover  20 , and an upper cover  30  configured such that the lower cover  20  and the upper cover  30  form a vibration space in which the resonator  10  vibrates therein. That is to say, the resonance device  1  is formed by stacking the lower cover  20 , the resonator  10 , a joint part  60  which will be described later, and the upper cover  30  in this order. It is noted that the upper cover  30  corresponds to one example of a “substrate” of the present disclosure. 
     In the following, each element of the resonance device  1  is described. In general, it is assumed that in the resonance device  1 , the side on which the upper cover  30  is provided is up (or top) and the side on which the lower cover  20  is provided is down (or back). 
     In an exemplary aspect, the resonator  10  is a MEMS oscillator fabricated using MEMS techniques. The resonator  10  and the upper cover  30  are joined with the joint part  60  interposed therebetween. Further, the resonator  10  and the lower cover  20  are each formed using a silicon (Si) substrate (hereinafter, referred to as “Si substrate”), for example, and these Si substrates are joined to each other. Alternatively, the resonator  10  and the lower cover  20  may be formed by using a SOI substrate, for example. 
     The upper cover  30  expands in a flat-plate-like manner along the X-Y plane, and a depression part  31  having, for example, a flat rectangular parallelepiped shape is formed on a back surface of the upper cover  30 . The depression part  31  is surrounded by side walls  33  and forms part of the vibration space that is the space in which the resonator  10  vibrates. Alternatively, the upper cover  30  may have a flat-plate-like shape without the depression part  31 . Further, a getter layer for absorbing outgassed substances can be formed on a resonator  10  side surface of the depression part  31  of the upper cover  30 . 
     On a top surface of the upper cover  30 , two power supply terminals ST 1  and ST 2  and a ground terminal GT are provided. The power supply terminals ST 1  and ST 2  are electrically connected to upper electrodes  125 A,  125 B,  125 C, and  125 D of the resonator  10 , which will be described later, respectively. The ground terminal GT is electrically connected to a lower electrode  129  of the resonator  10 , which will be described later. 
     The lower cover  20  includes a bottom plate  22  that has a rectangular flat-plate-like shape and is provided along the X-Y plane and side walls  23  that extend from a perimeter part of the bottom plate  22  in the Z-axis direction, that is, the stacking direction of the lower cover  20  and the resonator  10 . In the lower cover  20 , a top surface of the bottom plate  22  and inner surfaces of the side walls  23  form a depression part  21  on a surface that faces the resonator  10 . The depression part  21  forms part of the vibration space of the resonator  10 . Alternatively, the lower cover  20  may have a flat-plate-like shape without the depression part  21 . Further, a getter layer for absorbing outgassed substances can be formed on a surface of the depression part  21  on the resonator  10  side of the lower cover  20 . 
     Next, referring to  FIG. 3 , a schematic configuration of the resonator  10  according to the first embodiment is described.  FIG. 3  is a plan view schematically illustrating the structure of the resonator  10  illustrated in  FIG. 2 . 
     As illustrated in  FIG. 3 , the resonator  10  is a MEMS oscillator fabricated using MEMS techniques and is constructed to make out-of-plane vibration in the X-Y plane in the orthogonal coordinate system of  FIG. 3 . However, it is noted that the resonator  10  is not limited to the resonator that uses an out-of-plane flexural vibration mode. The resonator of the resonance device  1  may be, for example, a resonator that uses an area expansion vibration mode, a thickness expansion vibration mode, a Lamb wave vibration mode, an in-plane flexure vibration mode, or a surface acoustic wave vibration mode. These oscillators are applied to, for example, timing devices, RF filters, duplexers, ultrasonic transducers, gyro sensors, acceleration sensors, and the like. Further, the resonators may also be used for piezoelectric mirrors with actuator capability, piezoelectric gyros, piezoelectric microphones with pressure sensor capability, ultrasonic vibration sensors, and the like. Furthermore, the resonators may also be applied to electrostatic MEMS elements, electromagnetic actuation MEMS elements, and piezoresistive MEMS elements. 
     The resonator  10  includes a vibration part  120 , a holding part  140 , and a holding arm  110 . 
     The holding part  140  (which can generally be considered a frame) is formed in a rectangular frame-like shape in such a manner as to surround the outside of the vibration part  120  along the X-Y plane. For example, the holding part  140  is formed as a single body from a rectangular column-shaped frame body. Note that the shape of the holding part  140  is not limited to a frame-like shape, as long as the holding part  140  is provided in such a manner as to surround the vibration part  120  at least partially. 
     The holding arm  110  is provided inside the holding part  140  and connects the vibration part  120  to the holding part  140 . 
     The vibration part  120  is provided inside the holding part  140 , and space is formed between the vibration part  120  and the holding part  140  in such a manner as to have a predetermined distance therebetween. In the example illustrated in  FIG. 3 , the vibration part  120  has a base part  130  and four vibration arms  135 A to  135 D (hereinafter, also collectively referred to as “vibration arms  135 ”). The vibration arms  135  contain four upper electrodes  125 A to  125 D (hereinafter, also collectively referred to as “upper electrodes  125 ”). In general, it is noted that the numbers of the vibration arms and the upper electrodes are not limited to four, and may be set to, for example, an arbitrary number greater than or equal to three. In the present embodiment, all the vibration arms  135 A to  135 D and the base part  130  are formed as a single body. 
     In the plan view, the base part  130  has long sides  131   a  and  131   b  in the X-axis direction and short sides  131   c  and  131   d  in the Y-axis direction. The long side  131   a  is one of sides of a front end surface (hereinafter, also referred to as “front end  131 A”) of the base part  130 , and the long side  131   b  is one of sides of a back end surface (hereinafter, also referred to as “back end  131 B”) of the base part  130 . In the base part  130 , the front end  131 A and the back end  131 B are provided in such a manner as to face each other. 
     The base part  130  is connected to the vibration arms  135  at the front end  131 A and is connected to the holding arm  110 , which will be described later, at the back end  131 B. It is noted that the base part  130  has a substantially non-square rectangular shape in the plan view in the example illustrated in  FIG. 3 . However, the shape of the base part  130  is not limited thereto. The base part  130  is only necessary to be formed to have approximate plane symmetry with respect to a hypothetical (or imaginary) plane P defined along a perpendicular bisector of the long side  131   a . For example, the base part  130  may alternatively be a trapezoid in which the long side  131   b  is shorter than the long side  131   a  or a semicircular shape whose diameter is the long side  131   a . Further, each surface of the base part  130  is not limited to a plane surface and may alternatively be a curved surface. Note that the hypothetical plane P is a plane that passes through the center of the direction along which the vibration arms  135  are lined up in the vibration part  120 . 
     According to an exemplary aspect, in the base part  130 , a base part length is about 35 μm, where the base part length is the longest distance between the front end  131 A and the back end  131 B in the direction from the front end  131 A to the back end  131 B. Further, a base part width can be about 265 μm, where the base part width is the longest distance between side ends of the base part  130  in the width direction orthogonal to the base part length direction. 
     The vibration arms  135  extend in the Y-axis direction and each have the same size. The vibration arms  135  are each provided between the base part  130  and the holding part  140  in parallel to the Y-axis direction. Each vibration arm  135  is connected to the front end  131 A of the base part  130  at one end portion to form a fixed end, and the other end portion of the vibration arm  135  forms an open end. Further, the vibration arms  135  are provided side by side in the X-axis direction at predetermined intervals. Note that the vibration arm  135  has, for example, a width of about 50 μm in the X-axis direction and a length of about 450 μm in the Y-axis direction. 
     In each of the vibration arms  135 , the width in the X-axis direction is wider, for example, at a part having a length of about 150 μm from the open end, compared with the other part of the vibration arm  135 . This part with a wider width is referred to as a weight part G. For example, the weight part G has a width of about 70 μm in the X-axis direction and is 10 μm wider in the width in the X-axis direction at each of left and right hand sides than the other part of the vibration arm  135 . The weight part G is formed as a single body by using the same process as the vibration arm  135 . By forming the weight part G, the vibration arm  135  has a heavier weight per unit length on the open-end side than the fixed end side. Accordingly, by having the weight part G on the open-end side of each of the vibration arms  135 , the amplitude of vertical vibration of each vibration arm can be increased. 
     A protective film  235 , which will be described later, is formed on a top surface of the vibration part  120  (surface that faces the upper cover  30 ) in such a manner as to cover the whole area of the top surface. Further, a frequency adjustment film  236  is formed on a top surface of the protective film  235  at a top end portion on the open-end side of each of the vibration arms  135 A to  135 D. The protective film  235  and the frequency adjustment film  236  enable the adjustment of a resonant frequency of the vibration part  120 . 
     Note that in the present embodiment, substantially the whole area of a top surface of the resonator  10  (i.e., the surface on the side facing the upper cover  30 ) is covered by the protective film  235 . Note that the configuration of the protective film  235  is not limited to a configuration covering substantially the whole area of the resonator  10 , as long as the protective film  235  covers at least the vibration arms  135 . 
     Next, referring to  FIG. 4 , a multilayer structure of the resonance device  1  according to the first embodiment of the present invention is described.  FIG. 4  is a cross-sectional view schematically illustrating a cross-sectional configuration along line IV-IV of the resonance device  1  illustrated in  FIG. 1  to  FIG. 3 . 
     As illustrated in  FIG. 4 , in the resonance device  1 , the resonator  10  is joined onto the lower cover  20 , and furthermore, the resonator  10  and the upper cover  30  are joined together. As described above, by holding the resonator  10  between the lower cover  20  and the upper cover  30 , the lower cover  20 , the upper cover  30 , and the holding part  140  of the resonator  10  form the vibration space in which the vibration arms  135  vibrate. 
     The lower cover  20  is formed as a single body by using a silicon (Si) wafer (hereinafter, referred to as “Si wafer”) L 1 , for example. The thickness of the lower cover  20  defined in the Z-axis direction is, for example, about 150 μm. Note that Si wafer L 1  is formed using non-degenerate silicon and has a resistivity greater than or equal to 10 Ω·cm, for example. 
     According to an exemplary aspect, the holding part  140 , the base part  130 , the vibration arms  135 , and the holding arm  110  of the resonator  10  are formed as a single body using the same processes. In the resonator  10 , the lower electrode  129  is formed on a silicon (Si) substrate (hereinafter, referred to as “Si substrate”) F 2 , which is one example of the substrate, in such a manner as to cover the Si substrate F 2 . Moreover, a piezoelectric thin film F 3  is formed on the lower electrode  129  in such a manner as to cover the lower electrode  129 , and the upper electrodes  125 A,  125 B,  125 C, and  125 D are stacked on the piezoelectric think film F 3 . Furthermore, the protective film  235  is stacked on the upper electrodes  125 A,  125 B,  125 C, and  125 D in such a manner as to cover the upper electrodes  125 A,  125 B,  125 C, and  125 D. 
     The Si substrate F 2  is formed, for example, using a degenerate n-type silicon (Si) semiconductor having a thickness of about 6 μm and can contain phosphorus (P), arsenic (As), antimony (Sb), or the like as a n-type dopant. Moreover, the resistivity of the degenerate silicon (Si) to be used for the Si substrate F 2  is, for example, less than 16 mΩ·cm and more preferably less than or equal to 1.2 mΩ·cm. Note that as one example of a temperature characteristic compensation layer, a silicon oxide (for example, SiO 2 ) layer can be formed on at least one of an upper surface and a lower surface of the Si substrate F 2 . 
     Further, the thickness of each of the lower electrode  129  and the upper electrodes  125 A,  125 B,  125 C, and  125 D is, for example, greater than or equal to about 0.1 μm and less than or equal to about 0.2 μm. The lower electrode  129  and the upper electrodes  125 A,  125 B,  125 C, and  125 D are each patterned to a desired shape by etching and the like. For the lower electrode  129  and the upper electrodes  125 A,  125 B,  125 C, and  125 D, a metal whose crystalline structure is a body-centered cubic structure is used. Specifically, the lower electrode  129  and the upper electrodes  125 A,  125 B,  125 C, and  125 D are formed using Mo (molybdenum), tungsten (W), and the like. 
     The piezoelectric thin film F 3  is a thin film of piezoelectric substance that converts an applied voltage into a vibration. Moreover, in the exemplary aspect, the piezoelectric thin film F 3  is formed using a material whose crystalline structure is wurtzite-type hexagonal crystalline structure, and a main component thereof can be a nitride or an oxide such as, for example, aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), gallium nitride (GaN), indium nitride (InN), or the like. Note that scandium aluminum nitride is formed by substituting part of aluminum of aluminum nitride with scandium, and instead of scandium, this part of aluminum may be substituted with two elements such as magnesium (Mg) and niobium (Nb), magnesium (Mg) and zirconium (Zr), or the like. Further, the piezoelectric thin film F 3  has, for example a thickness of 1 μm. However, in one aspect, a piezoelectric thin film can also be used whose thickness is greater than or equal to about 0.2 μm and less than or equal to about 2 μm. 
     The piezoelectric thin film F 3  expands and contracts along an in-plane direction of the X-Y plane, that is, the Y-axis direction depending on an electric field applied to the piezoelectric thin film F 3  by using the lower electrode  129  and upper electrodes  125 A,  125 B,  125 C, and  125 D. This expansion and contraction of the piezoelectric thin film F 3  causes displacements of the free end toward inner surfaces of the lower cover  20  and the upper cover  30  (i.e., in the Z axis direction), thereby causing the vibration arm  135  to vibrate in an out-of-plane flexural vibration mode. 
     In the present embodiment, the phase of the electric field applied to the upper electrodes  125 A and  125 D of the vibration arms  135 A and  135 D on the outer side and the phase of the electric field applied to the upper electrodes  125 B and  125 C of the vibration arms  135 B and  135 C on the inner side are set to be opposite to each other. This causes the vibration arms  135 A and  135 D on the outer side and the vibration arms  135 B and  135 C on the inner side to be displaced in opposite directions. For example, when the free ends of the vibration arms  135 A and  135 D on the outer side are displaced toward the inner surface of the upper cover  30 , the free ends of the vibration arms  135 B and  135 C on the inner side are displaced toward the inner surface of the lower cover  20 . 
     The protective film  235  prevents oxidation of the upper electrodes  125 A,  125 B,  125 C, and  125 D. It is preferable that the protective film  235  is formed using a material whose mass reduction speed by etching is slower than that of the frequency adjustment film  236 . The mass reduction speed is expressed by the product of the etching speed, that is, the thickness to be removed per unit time and the density. The protective film  235  is formed of a piezoelectric film such as, for example, aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), gallium nitride (GaN), indium nitride (InN), or the like, or an insulation film such as, for example, silicon nitride (SiN), silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), or the like. The thickness of the protective film  235  is, for example, about 0.2 μm. 
     Moreover, in an exemplary aspect, the frequency adjustment film  236  is formed only on a predetermined area using processes such as etching and the like after being formed over substantially the whole area of the vibration part  120 . The frequency adjustment film  236  is formed using a material whose mass reduction speed by etching is faster than that of the protective film  235 . Specifically, the frequency adjustment film  236  is formed using a metal such as molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), or the like. 
     It is noted that the magnitude relationship between the etching speeds in the protective film  235  and the frequency adjustment film  236  is arbitrary as long as the mass reduction speeds of the protective film  235  and the frequency adjustment film  236  are in the relationship described above. 
     An electrically conductive layer CL is formed in such a manner as to come into contact with the lower electrode  129 . Specifically, at the time of connecting the electrically conductive layer CL and the lower electrode  129 , part of the piezoelectric thin film F 3  stacked on the lower electrode  129  is removed to form a via in such a manner as to expose the lower electrode  129 . The lower electrode  129  and the electrically conductive layer CL are connected by filling the inside of this via with a material similar to the lower electrode  129 . 
     Upper wiring lines UW 1  and UW 2  are electrically connected to the upper electrodes  125 A,  125 B,  125 C, and  125 D. Specifically, the upper wiring line UW 1  is electrically connected to the upper electrodes  125 B and  125 C of the vibration arms  135 B and  135 C on the inner side via lower wiring lines that are not illustrated. The upper wiring line UW 2  is electrically connected to the upper electrodes  125 A and  125 D of the vibration arms  135 A and  135 D on the outer side via lower wiring lines that are not illustrated. In one aspect, the upper wiring lines UW 1  and UW 2  can be formed using a metal such as, for example, aluminum (Al), gold (Au), tin (Sn), or the like. 
     The joint part  60  is formed in a rectangular ring shape along the X-Y plane in between the resonator  10  and the upper cover  30 . The joint part  60  joins the resonator  10  and the upper cover  30  in such a manner as to seal the vibration space of the resonator  10 . Because of this, the vibration space is hermetically sealed, and a vacuum state is maintained. 
     Moreover, the joint part  60  can be formed using a metal such as, for example, aluminum (Al), germanium (Ge), an alloy formed by eutectic bonding of aluminum (Al) and germanium (Ge), or the like. 
     The upper cover  30  is formed using the Si wafer L 3  having a predetermined thickness. The upper cover  30  is joined to the resonator  10  using the joint part  60 , which will be described later, at the circumferential part of the upper cover  30  (e.g., side walls  33 ). It is preferable that in the upper cover  30 , an upper surface on which the power supply terminals ST 1  and ST 2  and the ground terminal GT are provided, a lower surface that faces the resonator  10 , side surfaces of penetration electrodes V 1  and V 2  are covered with a silicon oxide film L 31 . The silicon oxide film L 31  is formed on a top surface of the Si wafer L 3  by oxidization of the top surface of the Si wafer L 3  or chemical vapor deposition (CVD), for example. 
     The penetration electrodes V 1  and V 2  are each formed by filling a through hole formed in the upper cover  30  with an electrically conductive material. The electrically conductive material to be filled is, for example, polycrystalline silicon doped with impurities (Poly-Si), copper (Cu), gold (Au), monocrystalline silicon doped with impurities, or the like. The penetration electrode V 1  serves as a wiring line that electrically connects the power supply terminal ST 1  and a terminal T 1 ′, and the penetration electrode V 2  serves as a wiring line that electrically connects the power supply terminal ST 2  and a terminal T 2 ′. 
     The power supply terminals ST 1  and ST 2  and the ground terminal GT are formed on an upper surface of the upper cover  30  (surface on the side opposite to the surface facing the resonator  10 ). Further, the terminals T 1 ′ and T 2 ′ and a ground wiring line GW are formed on a lower surface of the upper cover  30  (i.e., a surface facing the resonator  10 ). The power supply terminal ST 1 , the penetration electrode V 1 , and the terminal T 1 ′ are electrically insulated from the Si wafer L 3  by the silicon oxide film L 31 . On the other hand, at the time of joining the upper cover  30  and the resonator  10 , by connecting the terminal T 1 ′ and the upper wiring line UW 1 , the power supply terminal ST 1  is electrically connected to the upper wiring line UW 1 . As described above, the upper wiring line UW 1  is electrically connected to the upper electrodes  125 B and  125 C, and thus the power supply terminal ST 1  is electrically connected to the upper electrodes  125 B and  125 C of the resonator  10 . 
     The power supply terminal ST 2  is electrically connected to the upper wiring line UW 2  via the penetration electrode V 2  and the terminal T 2 ′. Moreover, the power supply terminal ST 2 , the penetration electrode V 2 , and the terminal T 2 ′ are electrically insulated from the Si wafer L 3  by the silicon oxide film L 31 . On the other hand, at the time of joining the upper cover  30  and the resonator  10 , by connecting the terminal T 2 ′ and the upper wiring line UW 2 , the power supply terminal ST 2  is electrically connected to the upper wiring line UW 2 . As described above, the upper wiring line UW 2  is electrically connected to the upper electrodes  125 A and  125 D, and thus the power supply terminal ST 2  is electrically connected to the upper electrodes  125 A and  125 D of the resonator  10 . 
     The ground terminal GT provided on the X-axis positive direction side is formed in such a manner as to come into contact with the Si wafer L 3 . Specifically, part of the silicon oxide film L 31  is removed by processing such as etching and the like, and the ground terminal GT is formed on the exposed Si wafer L 3 . Similarly, the ground wiring line GW is formed in such a manner as to come into contact with the Si wafer L 3 . Specifically, part of the silicon oxide film L 31  is removed by processing such as etching and the like, and the ground wiring line GW is formed on the exposed Si wafer L 3 . 
     The ground terminal GT and the ground wiring line GW are formed using a metal such as, for example, gold (Au), aluminum (Al), or the like. By annealing (e.g., thermal treatment) the formed metal, ohmic contacts of the ground terminal GT and the ground wiring line GW to the Si wafer L 3  are formed. This process allows the ground terminal GT and the ground wiring line GW to be electrically connected to each other via the Si wafer L 3 . 
     At the time of joining the upper cover  30  and the resonator  10 , by connecting the ground wiring line GW and the electrically conductive layer CL, the ground terminal GT is electrically connected to the electrically conductive layer CL. As described above, the electrically conductive layer CL is electrically connected to the lower electrode  129 , and thus the ground terminal GT is electrically connected to the lower electrode  129  of the resonator  10 . 
     Here, a stray capacitance is formed between the power supply terminal ST 1  and the ground terminal GT, and a stray capacitance is also formed between the power supply terminal ST 2  and the ground terminal GT. For example, the area of a wiring line routed from the power supply terminal ST 1  is different from the area of a wiring line routed from the power supply terminal ST 2 , and thus there is a possibility that the stray capacitance between the power supply terminal ST 1  and the ground terminal GT and the stray capacitance between the power supply terminal ST 2  and the ground terminal GT are not in balance. 
     Next, referring to  FIG. 5 , schematic configurations of the power supply terminal ST 1 , the power supply terminal ST 2 , and the ground terminal GT according to the first embodiment are shown and described.  FIG. 5  is a plan view schematically illustrating structures of the power supply terminals ST 1  and ST 2  and the ground terminal GT provided on the upper cover  30  illustrated in  FIG. 1  and  FIG. 2 . 
     As illustrated in  FIG. 5 , the power supply terminal ST 1  includes a power supply pad PD 1  and a power supply wiring line LN 1 . The power supply pad PD 1  is arranged on the top surface of the upper cover  30  in a corner part of the X-axis positive direction side and the Y-axis positive direction side. Further, when the top surface of the upper cover  30  is seen in a plan view (hereinafter, referred to simply as “plan view”), the power supply pad PD 1  has a substantially rectangular shape. The power supply wiring line LN 1  is connected to the power supply pad PD 1  at one end portion (e.g., as shown as the rightmost part in  FIG. 5 ) and extends close to a ground pad PD 4 , which will be described later. Further, at the other end portion of the power supply wiring line LN 1  (e.g., as shown as the leftmost part in  FIG. 5 ), the penetration electrode V 1  illustrated in  FIG. 4  is formed. 
     The power supply terminal ST 2  includes a power supply pad PD 2 . The power supply pad PD 2  is arranged on the top surface of the upper cover  30  in a corner part of the X-axis negative direction side and the Y-axis negative direction side. Further, in the plan view, the power supply pad PD 2  has a substantially rectangular shape. Furthermore, the power supply pad PD 2  has a part that protrudes in the X-axis positive direction. At this part, the penetration electrode V 2  illustrated in  FIG. 4  is formed. 
     The ground terminal GT includes ground pads PD 3  and PD 4  and a ground wiring line LN 3  that connects the ground pads PD 3  and PD 4 . On the top surface of the upper cover  30 , the ground pad PD 3  is arranged in a corner part of the X-axis negative direction side and the Y-axis positive direction side, and the ground pad PD 4  is arranged in a corner part of the X-axis positive direction side and the Y-axis negative direction side. Further, in the plan view, the ground pads PD 3  and PD 4  each has a substantially rectangular shape. The ground wiring line LN 3  is connected to the power supply pad PD 3  at one end portion (e.g., as shown as the rightmost part in  FIG. 5 ) and is connected to the ground pad PD 4  at the other end portion (e.g., as shown as the leftmost part in  FIG. 5 ). Further, a penetration electrode V 3 , which is similar to the penetration electrodes V 1  and V 2  illustrated in  FIG. 4 , is formed on the power supply wiring line LN 1 . 
     As is evident from  FIG. 5 , whereas the power supply terminal ST 1  includes the power supply pad PD 1  and the power supply wiring line LN 1 , the power supply terminal ST 2  includes only the power supply pad PD 2 , and thus the areas (relative to the plan view) of the power supply terminal ST 1  and the power supply terminal ST 2  are different from each other. More specifically, the areas of the power supply terminal ST 1  and the power supply terminal ST 2  are different from each other in such a way that the capacitance formed between the power supply terminal ST 1  and the ground terminal GT is approximately equal to the capacitance formed between the power supply terminal ST 2  and the ground terminal GT. It is noted that the term “approximately” takes into account minor differences in the respective capacitance values due to manufacturing variances, for example. More specifically, the capacitances are approximately equal to the extent the resulting configuration reduces the absolute value of the difference between the capacitance formed between the power supply terminal ST 1  and the ground terminal GT and the capacitance formed between the power supply terminal ST 2  and the ground terminal GT. Accordingly, the imbalance between the capacitance formed between the power supply terminal ST 1  and the ground terminal GT and the capacitance formed between the power supply terminal ST 2  and the ground terminal GT can be suppressed. 
     Specifically, the capacitance formed between the power supply terminal ST 1  and the ground terminal GT is preferably in the range from −50% to +50% of the capacitance formed between the power supply terminal ST 2  and the ground terminal GT. This configuration provides a favorable oscillation, for example, even after reversing the voltage signals applied to the power supply terminal ST 1  and the power supply terminal ST 2 . 
     Further, it is more preferable that the capacitance formed between the power supply terminal ST 1  and the ground terminal GT is in the range from −20% to +20% of the capacitance formed between the power supply terminal ST 2  and the ground terminal GT. In the present embodiment, for example, the capacitance formed between the power supply terminal ST 1  and the ground terminal GT is 6.5 pF, and the capacitance formed between the power supply terminal ST 2  and the ground terminal GT is 7.3 pF. This configuration provides a more favorable oscillation, for example, even after reversing the voltage signals applied to the power supply terminal ST 1  and the power supply terminal ST 2 . 
     Next, modified examples of the foregoing first embodiment are described. Note that the same or similar reference characters are used for elements that are the same as or similar to those of the resonance device  1  illustrated in  FIG. 1  to  FIG. 5 , and the descriptions thereof are omitted if appropriate. Further, similar actions and effects caused by similar constituent elements are not repeated. 
     First Modified Example 
       FIG. 6  is a plan view schematically illustrating the resonator  10  and the wiring lines in the vicinity of the resonator  10  illustrated in  FIG. 1  to  FIG. 4 . 
     As illustrated in  FIG. 6 , the terminal T 1 ′ electrically connects the penetration electrode V 1  formed at the power supply terminal ST 1  of the upper cover  30  and the upper wiring line UW 1  formed on the protective film  235  of the resonator  10 . The upper wiring line UW 1  is electrically connected to a lower wiring line LW 1  covered by the protective film  235 . The lower wiring line LW 1  is routed and electrically connected to the upper electrode  125 B of the vibration arm  135 B and the upper electrode  125 C of the vibration arm  135 C. 
     The terminal T 2 ′ electrically connects the penetration electrode V 2  formed at the power supply terminal ST 2  of the upper cover  30  and the upper wiring line UW 2  formed on the protective film  235  of the resonator  10 . The upper wiring line UW 2  is electrically connected to lower wiring lines LW 21  and LW 22  covered by the protective film  235 . The lower wiring line LW 21  is routed and electrically connected to the upper electrode  125 D of the vibration arm  135 D. The lower wiring line LW 22  is routed and electrically connected to the upper electrode  125 A of the vibration arm  135 A. 
     The penetration electrode V 3  formed at the ground terminal GT of the upper cover  30  is connected to the joint part  60  formed in a ring-like shape on the resonator  10 . 
     As shown in  FIG. 6 , the upper wiring line UW 1  and the lower wiring line LW 1  that electrically connect the power supply terminal ST 1  to the upper electrodes  125 B and  125 C are different from the upper wiring line UW 2  and the lower wiring lines LW 21  and LW 22  that electrically connect the power supply terminal ST 2  to the upper electrodes  125 A and  125 D in the routing length (i.e., the distance), and therefore are different in the area. 
     In the first modified example, the lower wiring line LW 1  includes a dummy wiring line DW. In this embodiment, the dummy wiring line DW is not for electrical connection, but for increasing the area of the lower wiring line LW 1  while making symmetry with the lower wiring line LW 1 . This configuration maintains symmetry of vibrations of the vibration arms  135  and also enables adjusting the imbalance among the capacitances formed by the areas of the upper wiring line UW 1 , the lower wiring LW 1 , the upper wiring line UW 2 , and the lower wiring lines LW 21  and LW 22  by using the area of the dummy wiring line DW. 
     Second Modified Example 
       FIG. 7  is a plan view of a modified example schematically illustrating structures of the power supply terminals ST 1  and ST 2  and the ground terminal GT provided on the upper cover  30  illustrated in  FIG. 5 . 
     As illustrated in  FIG. 7 , the power supply terminal ST 1  is different from the power supply terminal ST 1  illustrated in  FIG. 5  in the shape of the power supply pad PD 1  and the line width of the power supply wiring line LN 1 . 
     Specifically, in the plan view, while the power supply pad PD 2  of the power supply terminal ST 2  has a substantially rectangular shape, the power supply pad PD 1  of the power supply terminal ST 1  has a shape including a cut part (or chamfered portion) CO. In this way, because of the difference between the shape of the power supply terminal ST 1  and the shape of the power supply terminal ST 2 , it becomes possible to provide a configuration in which the power supply terminal ST 1  and the power supply terminal ST 2  have different areas. 
     Further, while the power supply terminal ST 2  includes only the power supply pad PD 2 , the power supply terminal ST 1  includes the power supply wiring line LN 1  in addition to the power supply pad PD 1 , and the line width of the power supply wiring line LN 1  is wider than the one illustrated in  FIG. 5 . In this way, because of the difference between the width of the power supply terminal ST 1  and the width of the power supply terminal ST 2 , it becomes also possible to provide the power supply terminal ST 1  and the power supply terminal ST 2  to have different areas. 
     Alternatively, instead of the shape and the width, or in addition to the shape and the width, the length (i.e., the distance) of the power supply terminal ST 1  and the length (i.e., the distance) of the power supply terminal ST 2  may be different from each other. This configuration also facilitates the realization of the power supply terminal ST 1  and the power supply terminal ST 2  that have different areas. 
     Second Exemplary Embodiment 
     Next, referring to  FIG. 8 , a resonance device according to the second embodiment is described. Note that in the following embodiments, the same or similar reference characters are used for constituent elements that are the same as or similar to those of the first embodiment, and the difference from the first embodiment is described. 
     Further, similar actions and their effects caused by similar constituent elements are not repeated. 
       FIG. 8  is a cross-sectional view schematically illustrating the structure of a resonance device  200  according to the second embodiment. Note that  FIG. 8  is a cross-sectional view along the Y-axis of the resonance device  200 . 
     The resonance device  200  of the second embodiment is different from the resonance device  1  of the first embodiment in that a first metal layer  61  of the joint part  60  and the lower electrode  129  are electrically connected to each other. 
     As illustrated in  FIG. 8 , the power supply terminal ST 2  and the upper electrode  125  are electrically connected to each other via the penetration electrode V 2 , a connection wiring line  70 A, and a contact electrode  76 A. Note that although it is not illustrated in  FIG. 8 , the power supply terminal ST 1  and the penetration electrode V 1  illustrated in  FIG. 4  are similarly formed. On the other hand, the ground terminal GT and the lower electrode  129  are electrically connected to each other via a penetration electrode V 4 , a connection wiring line  70 C, and a contact electrode  76 B. The penetration electrode V 4  is formed in the upper cover  30  as is the case with the penetration electrodes V 1  and V 2 . 
     As shown, a stray capacitance reduction film  240  is stacked on the protective film  235 . The stray capacitance reduction film  240  is composed of tetraethyl orthosilicate (TEOS). The thickness of the stray capacitance reduction film  240  is about 1 μm. The stray capacitance reduction film  240  reduces a stray capacitance in a wiring line routing part and also serves as an insulation layer when wiring lines having different electrical potentials cross over and a capability of serving as a standoff structure for expanding the vibration space. 
     On the lower surface of the Si substrate F 2 , as one example of the temperature characteristic compensation layer, for example, a silicon oxide layer F 21  that is silicon dioxide (SiO 2 ) is formed. This enables the improvement of the temperature characteristic. Alternatively, the silicon oxide layer F 21  may be formed on the upper surface of the Si substrate F 2  or may be formed on both the upper surface and the lower surface of the Si substrate F 2 . 
     The joint part  60  includes the first metal layer  61  formed on the resonator  10  and a second metal layer  62  formed on the upper cover  30  and joins the resonator  10  and the upper cover  30  together by eutectic bonding of the first metal layer  61  and the second metal layer  62 . The first metal layer  61  is, for example, a layer whose main component is aluminum (Al), and the second metal layer  62  is, for example, a layer whose main component is germanium (Ge). 
     Note that in the example illustrated in  FIG. 8 , the first metal layer  61  and the second metal layer  62  are each illustrated as an independent layer. However, in practice, eutectic bonding is formed at the interface between the first metal layer  61  and the second metal layer  62 . That is to say, the joint part  60  is formed in such a way that a main component of the joint part  60  is formed as a eutectic alloy of a first metal whose main component is aluminum (Al) and a second metal whose main component is germanium (Ge). 
     The connection wiring line  70 A is electrically connected to the power supply terminal ST 2  via the penetration electrode V 2  and is also electrically connected to the contact electrode  76 A. Further, the connection wiring line  70 C is electrically connected to the ground terminal GT via the penetration electrode V 4  and is also electrically connected to the contact electrode  76 B. 
     The contact electrode  76 A is formed to contact the upper electrode  125  of the resonator  10  and electrically connects the connection wiring line  70 A and the resonator  10 . Specifically, at the time of connecting the contact electrode  76 A and the upper electrode  125 , parts of the stray capacitance reduction film  240  and the protective film  235  stacked on the upper electrode  125  are removed to form a via V 5  in such a manner as to expose the upper electrode  125 . The upper electrode  125  and the contact electrode  76 A are connected by filling the inside of the formed via V 5  with a material similar to the contact electrode  76 A. The contact electrode  76 B is formed in such a manner as to come into contact with the lower electrode  129  of the resonator  10  and electrically connects the connection wiring line  70 C and the resonator  10 . Specifically, at the time of connecting the contact electrode  76 B and the lower electrode  129 , parts of the stray capacitance reduction film  240  and the piezoelectric thin film F 3  stacked on the lower electrode  129  are removed to form a via V 6  in such a manner as to expose the lower electrode  129 . The lower electrode  129  and the contact electrode  76 B are connected by filling the inside of the formed via V 6  with a material similar to the contact electrode  76 B. The contact electrodes  76 A and  76 B are formed using a metal such as, for example, aluminum (Al), gold (Au), tin (Sn), or the like. Note that a connecting part of the upper electrode  125  and the contact electrode  76 A and a connecting part of the lower electrode  129  and the contact electrode  76 B are preferably located in an area outside of the vibration part  120 . In the present embodiment, the upper electrode  125  and the contact electrode  76 A and the lower electrode  129  and the contact electrode  76 B are connected at the holding part  140 . 
     Further, the contact electrode  76 B extends over the stray capacitance reduction film  240  and is connected to the first metal layer  61  formed at an outer perimeter part of the resonator  10 . Alternatively, the contact electrode  76 B and the first metal layer  61  may be formed on the stray capacitance reduction film  240  as a single body. In this way, the first metal layer  61  of the joint part  60  is electrically connected to the lower electrode  129  via the contact electrode  76 B. Because of this configuration, the joint part  60  and the lower electrode  129  are short-circuited, and thus it becomes possible to cancel a stray capacitance that can be formed due to the piezoelectric thin film F 3  or the stray capacitance reduction film  240  arranged between the joint part  60  and the lower electrode  129 . As a result, although it becomes more susceptible to the capacitance imbalance, as described above, influences caused by the capacitance imbalance can be suppressed by making the area of the power supply terminal ST 1  and the area of the power supply terminal ST 2  different from each other in such a way that the capacitance formed between the power supply terminal ST 1  and the ground terminal GT is approximately equal to the capacitance formed between the power supply terminal ST 2  and the ground terminal GT. 
     Third Exemplary Embodiment 
     Next, referring to  FIG. 9 , a resonance device according to the third embodiment is described. Note that in each of the following embodiments, the same or similar reference characters are used for constituent elements that are the same as or similar to those of the first embodiment or the second embodiment, and the difference from the first embodiment and the second embodiment is described. Further, similar actions and effects caused by similar constituent elements are not repeated. 
       FIG. 9  is a cross-sectional view schematically illustrating a structure of a resonance device  300  according to the third embodiment. Note that  FIG. 9  is a cross-sectional view along the Y-axis of the resonance device  300 . 
     The resonance device  300  of the third embodiment is different from the resonance device  1  of the first embodiment and the resonance device  200  of the second embodiment in that the second metal layer  62  of the joint part  60  is electrically connected to the lower electrode  129 . 
     As illustrated in  FIG. 9 , the contact electrode  76 B of the resonance device  300  is not connected to the first metal layer  61 , which is different from the resonance device  200  of the second embodiment illustrated in  FIG. 8 . 
     On the other hand, part of the connection wiring line  70 C is connected to the second metal layer  62  that is formed at an outer perimeter part of the upper cover  30  and extends over the silicon oxide film L 31  formed on the lower surface of the upper cover  30 . Alternatively, the part of the connection wiring line  70 C and the second metal layer  62  may be formed on the stray capacitance reduction film  240  as a single body. In this way, the second metal layer  62  of the joint part  60  is electrically connected to the lower electrode  129  via the connection wiring line  70 C and the contact electrode  76 B. Because of this configuration, as is the case with the second embodiment, it becomes possible to cancel a stray capacitance that can be formed due to the piezoelectric thin film F 3  or the stray capacitance reduction film  240  arranged between the joint part  60  and the lower electrode  129 . 
     Fourth Exemplary Embodiment 
     Next, referring to  FIG. 10 , a resonance device according to the fourth embodiment is described. 
       FIG. 10  is a cross-sectional view schematically illustrating a structure of a resonance device  400  according to the fourth embodiment. Note that  FIG. 10  is a cross-sectional view along the Y-axis of the resonance device  400 . 
     The resonance device  400  of the fourth embodiment is different from the resonance device  1  of the first embodiment and the resonance device  200  of the second embodiment in that a ground part  50  is provided therein. 
     As illustrated in  FIG. 10 , the contact electrode  76 B extends over the stray capacitance reduction film  240  and is connected to part of the joint part  60 , or the contact electrode  76 B is formed together with part of the joint part  60  as a single body. 
     The ground part  50  comes into contact with the contact electrode  76 B formed on the resonator  10  and is electrically connected to the lower electrode  129  via the contact electrode  76 B. The ground part  50  is connected to the contact electrode  76 B when eutectic bonding of the upper cover  30  and the resonator  10  is formed using the joint part  60 . 
     At a location of the upper cover  30  where the ground part  50  is to be formed, the silicon oxide film L 31  is removed by processing such as etching and the like, and the ground part  50  is formed on the exposed Si wafer L 3 . The ground part  50  is joined to the Si wafer L 3  in such a manner as to form ohmic bonding therebetween by thermal annealing after forming a metal such as, for example, gold (Au), aluminum (Al), or the like on the Si wafer L 3 . This configuration allows the ground terminal GT and the ground part  50  to be electrically connected to each other via the Si wafer L 3  of the upper cover  30 . Furthermore, by joining the ground part  50  and the contact electrode  76 B, the lower electrode  129  is electrically connected to the ground terminal GT. Accordingly, it also becomes possible to cancel a stray capacitance that can be formed due to the silicon oxide film L 31  arranged between the joint part  60  and the Si wafer L 3  of the upper cover  30 . 
     Fifth Exemplary Embodiment 
     Next, referring to  FIG. 11 , a resonance device according to the fifth embodiment is described. 
       FIG. 11  is a plan view schematically illustrating a structure of a resonance device  500  according to the fifth embodiment.  FIG. 11  is a plan view that corresponds to  FIG. 6  in the first embodiment. 
     The resonance device  500  of the fifth embodiment is different from the resonance device  1  of the first embodiment and the resonance device  200  of the second embodiment in that the joint part  60  and the lower electrode  129  are electrically connected to each other by an electrically conductive part  237  and a wiring line  238 . 
     As illustrated in  FIG. 10 , the electrically conductive part  237  is formed on the holding part  140  along an inner edge of the holding part  140 . Specifically, the electrically conductive part  237  is provided at such a location where, in the plan view, an inner edge of the electrically conductive part  237  substantially matches an inner edge of the holding part  140  and an outer edge of the electrically conductive part  237  is positioned in between the inner edge and an outer edge of the holding part  140 . The width from the inner edge to the outer edge of the electrically conductive part  237  is, for example, about 10 μm. Note that it is only necessary to form the electrically conductive part  237  at least in a maximum displacement area where the displacement of the vibration part  120  caused by vibration becomes maximum, that is to say, at least in an area that faces the open ends of the vibration arms  135 . 
     Although it is not illustrated in the drawing, as is the case with the contact electrode  76 B illustrated in  FIG. 8 , part of the electrically conductive part  237  is connected to the lower electrode  129  by removing parts of the piezoelectric thin film F 3  and the stray capacitance reduction film  240  stacked on the lower electrode  129  and filling the inside of a formed via with the electrically conductive part  237 . 
     The wiring line  238  is a wiring line routed from the joint part  60  to the electrically conductive part  237  and connects the joint part  60  and the electrically conductive part  237 . Because of this, the joint part  60  and the lower electrode  129  are electrically connected and short-circuited via the wiring line  238  and the electrically conductive part  237 , and thus it becomes possible to cancel a stray capacitance that can be formed due to the piezoelectric thin film F 3  or the stray capacitance reduction film  240  arranged between the joint part  60  and the lower electrode  129 . 
     Exemplary embodiments of the present invention have been described above. In a resonance device according to an exemplary embodiment, the area of a first power supply terminal and the area of a second power supply terminal are different from each other in such a way that the capacitance formed between the first power supply terminal and a ground terminal is approximately equal to the capacitance formed between the second power supply terminal and the ground terminal. This configuration reduces the absolute value of the difference between the capacitance formed between the first power supply terminal and the ground terminal and the capacitance formed between the second power supply terminal and the ground terminal. Accordingly, an imbalance between the capacitance formed between the first power supply terminal and the ground terminal and the capacitance formed between the second power supply terminal and the ground terminal can be suppressed. 
     Further, in the foregoing resonance device, the length of the first power supply terminal and the length of the second power supply terminal are different from each other. This configuration facilitates the realization of the first power supply terminal and the second power supply terminal that have different areas. 
     Further, in the foregoing resonance device, the width of the first power supply terminal and the width of the second power supply terminal are different from each other. This configuration facilitates the realization of the first power supply terminal and the second power supply terminal that have different areas. 
     Further, in the foregoing resonance device, the shape of the first power supply terminal and the shape of the second power supply terminal are different from each other. This configuration facilitates the realization of the first power supply terminal and the second power supply terminal that have different areas. 
     As noted above, the capacitance formed between the first power supply terminal and the ground terminal is approximately equal to the capacitance formed between the second power supply terminal and the ground terminal. In one exemplary aspect of the foregoing resonance device, the capacitance formed between the first power supply terminal and the ground terminal is in the range from −50% to +50% of the capacitance formed between the second power supply terminal and the ground terminal. This configuration allows to have a favorable oscillation, for example, even after reversing voltage signals applied to the first power supply terminal and the second power supply terminal. 
     Further, in the foregoing resonance device, the capacitance formed between the first power supply terminal and the ground terminal is preferably in the range from −20% to +20% of the capacitance formed between the second power supply terminal and the ground terminal. This configuration allows to have a more favorable oscillation, for example, even after reversing the voltage signals applied to the first power supply terminal and the second power supply terminal. 
     Further, in the foregoing resonance device, a dummy wiring line is included either in an upper wiring line and a lower wiring line that electrically connect the first power supply terminal and an upper electrode or in an upper wiring line and a lower wiring line that electrically connect the second power supply terminal and an upper electrode. This configuration enables to keep symmetry of vibrations of vibration arms and also enables to adjust an imbalance among the capacitances formed by the areas of the upper wiring line and the lower wiring line that electrically connect the first power supply terminal and the upper electrode and the areas of the upper wiring line and the lower wiring line that electrically connect the second power supply terminal and the upper electrode by using the area of the dummy wiring line. 
     Further, in the foregoing resonance device, a voltage signal applied to the first power supply terminal and a voltage signal applied to the second power supply terminal are in opposite phases. This configuration suppresses the capacitance imbalance and also facilitates the realization of a resonance device that vibrates in a flexural vibration mode. 
     Further, in the foregoing resonance device, a joint part is electrically connected to the lower electrode. Because of this configuration, the joint part and the lower electrode are short-circuited, and thus it becomes possible to cancel a stray capacitance that can be formed due to a piezoelectric thin film or a stray capacitance reduction film arranged between the joint part and the lower electrode. As a result, although this makes the resonance device more susceptible to the capacitance imbalance, as described above, it becomes possible to suppress influences caused by the capacitance imbalance by making the area of the first power supply terminal and the area of the second power supply terminal different from each other in such a way that the capacitance formed between the first power supply terminal and the ground terminal is approximately equal to the capacitance formed between the second power supply terminal and the ground terminal. 
     In general, it is noted that each of the exemplary embodiments described above is provided to facilitate understanding of the present invention and is not to be construed as limiting the present invention. The exemplary embodiments can be modified or improved without departing from its spirit, and the present invention also includes equivalents thereof. That is to say, ones obtained by suitably modifying designs of the respective embodiments by those skilled in the art are also included within the scope of the present invention as long as they include features of the present invention. For example, each element included in each embodiment as well as its arrangement, material, vibration mode, condition, shape, size, and the like are not limited to those exemplified, and may be suitably changed. Needless to say, each embodiment is for illustrative purposes only, and constituent elements illustrated in different embodiments may be combined or partially exchanged, which are also included in the scope of the present invention so long as the characteristic features of the present invention are included. 
     REFERENCE SIGNS LIST 
       1 : Resonance device,  10 : Resonator,  20 : Lower cover,  21 : Depression part,  22 : Bottom plate,  23 : Side wall,  30 : Upper cover,  31 : Depression part,  33 : Side wall,  60 : Joint part,  70 A,  70 C: Connection wiring line,  76 A,  76 B: Contact electrode,  110 : Holding arm,  120 : Vibration part,  125 ,  125 A,  125 B,  125 C,  125 D: Upper electrode,  129 : Lower electrode,  130 : Base part,  131   a : Long side,  131 A: Front end,  131   b : Long side,  131 B: Back end,  131   c : Short side,  131   d : Short side,  135 ,  135 A,  135 B,  135 C,  135 D: Vibration arm,  140 : Holding part,  235 : Protective film,  236 : Frequency adjustment film, CL: Electrically conductive layer, DW: Dummy wiring line, F 2 : Si substrate, F 3 : Piezoelectric thin film, G: Weight part, GT: Ground terminal, GW: Ground wiring line, L 1 , L 3 : Si wafer, L 31 : Silicon oxide film, LN 1 : Power supply wiring line, LN 3 : Ground wiring line, LW 1 : Lower wiring line, LW 21 , LW 22 : Lower wiring line, P: Hypothetical plane, PD 1 : Power supply pad, PD 2 : Power supply pad, PD 3 , PD 4 : Ground pad, ST 1 : Power supply terminal, ST 2 : Power supply terminal, T 1 ′, T 2 ′: Terminal, UW 1 : Upper wiring line, UW 2 : Upper wiring line, V 1 , V 2 , V 3 : Penetration electrode.