Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application of PCT/JP2007/070207 filed on Oct. 16, 2007 which claims priority from a Japanese Patent Application No. 2006-297100 filed on Oct. 31, 2006, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a variable capacitance element, a resonator, and a modulator. In particular, the present invention relates to a variable capacitance element, a resonator, and a modulator using MEMS (Micro Electro Mechanical System) technology. 
         [0004]    2. Related Art 
         [0005]    A variable capacitance element uses many electrical circuits such as a VFO (Variable Frequency Oscillator), a tuned amplifier, a phase shifter, and an impedance matching circuit. In recent years, variable capacitance elements are being increasingly used in portable devices, which creates a particular need for miniaturization and cost decrease. Use of variable capacitance elements at high frequency bands is also increasing. Variable capacitance elements manufactured using MEMS technology are expected to have less loss and a higher Q value than varactor diodes, which are widely used at present. 
         [0006]    Japanese Patent Application Publication No. 2004-172504 discloses a variable capacitor manufactured using MEMS technology and having an electrostatic actuator. This variable capacitor is provided with fixed capacitor electrodes and fixed actuator electrodes formed on a substrate, and with mobile actuator electrodes and mobile capacitor electrodes supported elastically on the fixed electrodes. The mobile actuator electrodes and mobile capacitor electrodes are formed integrally, and when the mobile actuator electrodes are moved by the electrostatic force between the fixed actuator electrodes and mobile actuator electrodes, the mobile capacitor electrodes are also moved. Accordingly, the intervals between the mobile capacitor electrodes and the fixed capacitor electrodes change, so that the capacitance also changes. 
         [0007]    Japanese Patent Application Publication No. 2004-127973 discloses a variable capacitor manufactured using MEMS technology and having actuators that use piezoelectric materials. This variable capacitor is provided with a pair of mobile electrodes that both have actuators, and the capacitance is changed by bringing these electrodes close together or moving them further apart to change the space therebetween. 
         [0008]    The above variable capacitor disclosed in Japanese Patent Application Publication No. 2004-172504 uses electrostatic actuators. In order for the electrostatic actuators to operate effectively, the actuator electrodes must have sufficient surface area. Therefore, the overall area of the variable capacitor including these electrodes is large. Furthermore, the electrostatic actuator has a drive force that changes greatly depending on the distance between the electrodes, and so it is difficult for the mobile electrodes to find a stroke. Yet further, a relatively high voltage around 10 V is desired for driving the electrostatic actuator, and so it is difficult to use this actuator in a circuit having a battery as a power source. 
         [0009]    The above variable capacitor disclosed in Japanese Patent Application Publication No. 2004-127973 has piezoelectric actuators, and can therefore be driven by a relatively low voltage. This variable capacitor also has a faster response than the capacitor having electrostatic actuators. However, in this variable capacitor, the dimensions of the mobile electrodes increase relative to the size of the capacitance. Therefore, the mass of the mobile electrodes, which are being moved by the actuator, increases, thereby slowing down the operation. The only way to maintain the same response speed is to increase the size of the actuators. 
       SUMMARY 
       [0010]    Therefore, it is an object of an aspect of the innovations herein to provide a variable capacitance element, a resonator, and a modulator, which are capable of overcoming the above drawbacks accompanying the related art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the innovations herein. 
         [0011]    According to a first aspect related to the innovations herein, one exemplary variable capacitance element may comprise a plurality of single capacitance elements that each include (i) a fixed electrode provided on a surface of a substrate, (ii) a floating electrode provided to be separate from the fixed electrode and facing the fixed electrode, and (iii) an actuator that moves the floating electrode closer to or farther from the fixed electrode; and a floating electrode driving section that supplies the actuators with drive power to move the floating electrodes, such that a combined capacitance of the plurality of single capacitance elements becomes a prescribed capacitance. 
         [0012]    According to a second aspect related to the innovations herein, one exemplary resonator may comprise the variable capacitance element according to claim  1 ; an inductance element that is electrically connected to the variable capacitance element to form a resonant circuit; and a resonance control section that controls the floating electrode driving section such that the combined capacitance of the plurality of single capacitance elements becomes a capacitance that causes the resonant circuit to resonate at a desired resonance frequency. 
         [0013]    According to a third aspect related to the innovations herein, one exemplary modulator may comprise the variable capacitance element according to claim  1 ; an inductance element that is electrically connected to the capacitance element to form an oscillation circuit; a carrier wave control section that controls the floating electrode driving section such that at least one of the plurality of single capacitance elements has a capacitance that causes the oscillation circuit to oscillate at a desired carrier wave frequency; and a modulation control section that controls the floating electrode driving section such that a different at least one of the plurality of single capacitance elements has a capacitance that changes an oscillation frequency of the oscillation circuit in accordance with a modulation signal supplied from an external source. 
         [0014]    The summary clause does not necessarily describe all necessary features of the embodiments of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view showing a stage in the process for manufacturing the floating electrode substrate  100 . 
           [0016]      FIG. 2  is a perspective view showing a stage in the process for manufacturing the floating electrode substrate  100 . 
           [0017]      FIG. 3  is a perspective view showing a stage in the process for manufacturing the floating electrode substrate  100 . 
           [0018]      FIG. 4  is a perspective view showing a stage in the process for manufacturing the floating electrode substrate  100 . 
           [0019]      FIG. 5  is a perspective view showing a stage in the process for manufacturing the floating electrode substrate  100 . 
           [0020]      FIG. 6  is a perspective view showing a stage in the process for manufacturing the spacer substrate  200 . 
           [0021]      FIG. 7  is a perspective view showing a stage in the process for manufacturing the spacer substrate  200 . 
           [0022]      FIG. 8  is a perspective view showing the floating electrode assembly  502 . 
           [0023]      FIG. 9  is a perspective view showing a stage in the process for manufacturing the fixed electrode substrate  300 . 
           [0024]      FIG. 10  is a cross-sectional view schematically showing the layered structure of the variable capacitance element  602 . 
           [0025]      FIG. 11  schematically shows the electrical function of the variable capacitance element  602 . 
           [0026]      FIG. 12  is a perspective view showing a stage in the process for manufacturing the fixed electrode substrate  300 . 
           [0027]      FIG. 13  schematically shows another embodiment of the variable capacitance element  710 . 
           [0028]      FIG. 14  schematically shows another embodiment of the variable capacitance element  720 . 
           [0029]      FIG. 15  is a perspective view showing a stage in the process for manufacturing the fixed electrode substrate  400 . 
           [0030]      FIG. 16  is a perspective view showing a stage in the process for manufacturing the fixed electrode substrate  400 . 
           [0031]      FIG. 17  is a perspective view showing a stage in the process for manufacturing the fixed electrode substrate  400 . 
           [0032]      FIG. 18  is a perspective view showing a stage in the process for manufacturing the spacer substrate  202 . 
           [0033]      FIG. 19  is a perspective view showing the structure of the fixed electrode assembly  504 . 
           [0034]      FIG. 20  is a cross-sectional view schematically showing the layered structure of the variable resonator  604 . 
           [0035]      FIG. 21  is a cross-sectional view schematically showing the electrical function of the variable capacitance element  602 . 
           [0036]      FIG. 22  schematically shows another embodiment of the variable resonator  730 . 
           [0037]      FIG. 23  schematically shows another embodiment of the variable resonator  740 . 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0038]    While the embodiments of the present invention are described below, the technical scope of the invention is not limited to the described embodiments. It is apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the invention. 
         [0039]    Hereinafter, some embodiments of the present invention will be described. The embodiments do not limit the invention according to the claims, and all the combinations of the features described in the embodiments are not necessarily essential to means provided by aspects of the invention. 
         [0040]      FIG. 1  is a perspective view showing one stage of a process for manufacturing a floating electrode substrate  100  with an Si wafer as a substrate. First, a plurality of hole patterns  110  are formed on a semiconductor substrate  102 . Each hole pattern  110  is L-shaped, and each set of four hole patterns  110  is formed to pass through to the bottom of the semiconductor substrate  102 . In this way, a pair of single variable capacitance element regions  142  and  144  are formed on the semiconductor substrate  102 . Each of the single variable capacitance element regions  142  and  144  includes a substantially square floating electrode region  120  and four actuator regions  130  that are continuous at the corners of the floating electrode region  120  and support the floating electrode region  120  from the semiconductor substrate  102 . 
         [0041]    The patterning of the semiconductor substrate  102  described above can be implemented as etching using photolithography, for example. The etching may be wet etching that uses a chemical to dissolve the semiconductor substrate  102 , or may be dry etching such as ion milling. As another example, the hole pattern  110  can be drilled using physical processing such as a laser or a micro-drill. In addition to the above processing, a thinning process may be used to decrease the thickness of the semiconductor substrate  102  in a target region. The above processes decrease the mass of the floating electrode region  120  and facilitate deformation of the actuator regions  130 . 
         [0042]      FIG. 2  is a perspective view showing the next stage of the process for manufacturing the floating electrode substrate  100 . At this stage, a conduction layer  150  is formed over the single variable capacitance element regions  142  and  144  on the semiconductor substrate  102  having the hole pattern  110 . The conduction layer  150  forms a pattern that includes a floating electrode region  158  that covers the floating electrode region  120 , a connection portion  156  that connects the pair of single variable capacitance element regions  142  and  144  to each other, a terminal portion  154  that is used when the conduction layer  150  is connected to something outside of the semiconductor substrate  102 , a connection portion  152  that connects the terminal portion  154  to the single variable capacitance element region  144 , and an outer periphery  151  that wraps around the outer surface of the floating electrode region  158 . 
         [0043]    The method for forming the conduction layer  150  may be selected as desired from among evaporation techniques such as spattering that use photolithography. Using metal such as Au as the material for the conduction layer  150  leads to favorable electrical characteristics. If an Au thin film is evaporated on the semiconductor substrate  102 , favorable adhesive strength can be achieved and the diffusion of Au to the semiconductor substrate  102  can be prevented by laminating the thin layer of Au after forming a thin layer of Cr or the like. 
         [0044]      FIG. 3  is a perspective view showing the next stage of the process for manufacturing the floating electrode substrate  100 . At this stage, a piezoelectric material layer  160  is formed on each actuator region  130  of the semiconductor substrate  102 . Any material may be selected as the piezoelectric material, but PZT is selected here as being suitable for the intended application. The piezoelectric material layer  160  can be formed by evaporation techniques that use photolithography or the like. 
         [0045]      FIG. 4  is a perspective view showing the next stage of the process for manufacturing the floating electrode substrate  100 . At this stage, an insulation layer  170  is formed that includes an outer insulation layer  172  and an inner insulation layer  174 , which are connected to both ends of the region formed by the piezoelectric material layer  140 . The outer insulation layer  172  covers the outer periphery of the conduction layer  150 , and extends over the connection portions  152  and  156  of the conduction layer  150 . The material of the insulation layer  170  can be selected from among various types of oxides, nitrates, and the like. Photolithography can be used to simultaneously form the outer insulation layer  172  and the inner insulation layer  174 . 
         [0046]      FIG. 5  is a perspective view showing the next stage of the process for manufacturing the floating electrode substrate  100 . At this stage, another conduction layer  180  is formed on the floating electrode substrate  100  shown in  FIG. 4 . The conduction layer  180  includes a drive electrode region  186  that covers the top of the actuator region  130 , and covers the outer periphery  151 . At this point, the floating electrode substrate  100  is completed. 
         [0047]    It should be noted that the conduction layer  180  is not formed on the connection portion  156  that connects the pair of single variable capacitance element regions  142  and  144  to each other. Accordingly, as far as the conduction layer  180  is concerned, the single variable capacitance element region  142  is separate from the single variable capacitance element region  144 . Since the conduction layer  180  is formed on the piezoelectric material layer  160  or the insulation layer  170 , the conduction layer  180  is electrically separated from the conduction layer  150  formed directly on the semiconductor substrate  102 . 
         [0048]    In other words, by creating a potential difference between the conduction layers  150  and  180 , a voltage can be applied to the piezoelectric material layer  160 . The conduction layer  180 , which is the top layer, is formed separately for the single variable capacitance element region  142  and the single variable capacitance element region  144 , and so voltage is applied separately to the piezoelectric material layer  160  of the single variable capacitance element region  142  and the single variable capacitance element region  144 , causing the actuator to function. Furthermore, in each of the pair of single variable capacitance element regions  142  and  144 , the actuators are connected at uniform intervals and arranged symmetrically with respect to the center of the floating electrode region  158 . Accordingly, each entire floating electrode region  158  can be moved effectively. 
         [0049]    In the same manner as the conduction layer  150 , the conduction layer  180  may be formed by a method selected as desired from among evaporation techniques such as spattering that use photolithography. Any conductive material may be selected for the conduction layer  180 , but noble metals such as Au and Pt are desirable due to high chemical stability and superior electrical characteristics. 
         [0050]      FIG. 6  is a perspective view showing a stage in the process of manufacturing the spacer substrate  200  that is sandwiched between the floating electrode substrate  100  and a fixed electrode substrate  300 , described further below, to maintain a space therebetween. The depth D 1  of the semiconductor substrate  230  is less than the depth D 0  of the semiconductor substrate  102 , and the terminal portions  154  and  184  of the conduction layers  150  and  180  are exposed on the outside when the spacer substrate  200  is laminated onto the floating electrode substrate  100 . 
         [0051]    The spacer substrate  200  can be manufactured by processing the square semiconductor substrate  230  in the same manner as the floating electrode substrate  100 . As shown in  FIG. 6 , the spacer substrate  200  includes a pair of hole patterns  232  that are positioned to surround the pair of single variable capacitance element regions  142  and  144 . The shape of the hole patterns  232  can be formed by various types of etching using photolithography, laser processing, or machining processing. 
         [0052]      FIG. 7  is a perspective view showing the next stage of the process for manufacturing the spacer substrate  200 . At this stage, fixed electrode notches  222  and  224  are formed on the top of the spacer substrate  200 , and floating electrode notches  212 ,  214 , and  216  are formed on the bottom of the spacer substrate  200 . The fixed electrode notch  224  and the floating electrode notches  212  and  216  pass through the hole pattern  232  from the inside to the outside. The fixed electrode notch  222  and the floating electrode notch  214  pass through between the hole patterns  232 . The floating electrode notches  212 ,  214 , and  216  and the fixed electrode notches  222  and  224  can be formed by various types of etching using photolithography, laser processing, or machine processing. 
         [0053]      FIG. 8  is a perspective view showing a floating electrode assembly  502  resulting from the lamination of the floating electrode substrate  100  and the spacer substrate  200 . The spacer substrate  200  is positioned on the floating electrode substrate  100  such that the hole patterns  232  surround the single variable capacitance element regions  142  and  144 , and is then laminated to be adhered to the floating electrode substrate  100 . 
         [0054]    The connection portions  152  and  182  on the floating electrode substrate  100  pass through the floating electrode notches  212  and  216  on the bottom of the spacer substrate  200 , respectively, and extend to the outside of the spacer substrate  200 . Accordingly, the terminal portions  154  and  184  of the conduction layer  150  are exposed on the outside of the spacer substrate  200 . The connection portion  156  of the conduction layer  150  passes through the floating electrode notch  214  on the bottom of the spacer substrate  200  to connect the pair of single variable capacitance element regions  142  and  144  to each other. 
         [0055]      FIG. 9  is a perspective view showing a process for manufacturing a fixed electrode substrate  300  that is laminated on the floating electrode assembly  502 . The fixed electrode substrate  300  is formed by loading a conduction layer  310  onto a square semiconductor substrate  302  having the same dimensions as the spacer substrate  200 . 
         [0056]    The conduction layer  310  includes a pair of fixed electrode regions  312 , a connection portion  314  that connects the fixed electrode regions  312  to each other, a terminal portion  318  that connects the fixed electrode regions  312  to the outside, and a connection portion  316  that connects the terminal portion  318  to the fixed electrode regions  312 . The fixed electrode regions  312  correspond respectively to the single variable capacitance element regions  142  and  144 . 
         [0057]    The pattern of the conduction layer  310  can be formed with conductive material deposition achieved from any evaporation technique and patterning using photolithography. Any conductive material can be selected as the material of the conduction layer  310 , but noble metals such as Au and Pt are desirable due to high chemical stability and superior electrical characteristics. Improved adhesive strength of the conduction layer  310  can be achieved and the diffusion of the material used for the conduction layer  310  to the semiconductor substrate  302  can be prevented by forming a thin undercoating of Cr or the like on the surface of the semiconductor substrate  302  prior to forming the conduction layer  310 . 
         [0058]      FIG. 10  is a cross-sectional view showing the layered structure of a variable capacitance element  602  manufactured as described above. The variable capacitance element  602  is formed by laminating the fixed electrode substrate  300  shown in  FIG. 9  onto the floating electrode assembly  502  shown in  FIG. 8 . Here, the fixed electrode substrate  300  is laminated onto the floating electrode assembly  502  after flipping the fixed electrode substrate  300  over the dotted line A 1  in  FIG. 9  in a direction of the arrow T 1 . Therefore, the floating electrode region  158  of the conduction layer  150  on the floating electrode substrate  100  faces the fixed electrode region  312  of the conduction layer  310  on the fixed electrode substrate  300 . 
         [0059]    In the variable capacitance element  602  having the above structure, a voltage is applied between the conduction layers  150  and  180  to move the floating electrode region  158 , so that the space between the floating electrode region  158  and the fixed electrode region  312  changes, thereby changing the capacitance between the floating electrode region  158  and the fixed electrode region  312 . The pair of single variable capacitance element regions  142  and  144  are connected to each other in parallel by the connection portion  156  of the conduction layer  150  and the connection portion  314  of the conduction layer  310 . Therefore, the combined capacitance of the pair of single variable capacitance element regions  142  and  144  is created between the terminal portion  154  of the conduction layer  150  and the terminal portion  318  of the conduction layer  310 . 
         [0060]    Furthermore, in the variable capacitance element  602 , the actuator region  130  extends to the outside from the outer periphery of the floating electrode region  158 , so that the space between the conduction layer  150  in the floating electrode region  158  and the conduction layer  310  in the fixed electrode region  312  is almost completely filled with air. As a result, the floating electrode region  158  can be moved with a large stroke and the single variable capacitance element regions  142  and  144  can be set to have a high capacitance, and so the resulting variable capacitance element  602  has a large rate of change. 
         [0061]      FIG. 11  schematically shows the electrical function of the variable capacitance element  602 . The variable capacitance element  602  has an electrical structure in which the pair of single variable capacitance element regions  142  and  144  are connected to each other. Drive voltages can be applied separately to the actuator region  130  in the single variable capacitance element region  142  and the actuator region  130  in the single variable capacitance element region  144 , via the terminal portion  184 . Accordingly, by applying a drive voltage to the piezoelectric material layer  140  from a floating electrode driving section formed as the voltage source, the floating electrode region  120  can be brought near or moved away from the fixed electrode region  312 . In this way, the capacitances of the single variable capacitance element regions  142  and  144  can be individually changed. 
         [0062]    The overall capacitance C of the variable capacitance element  602  is a combination of the capacitances of the single variable capacitance element regions  142  and  144 . Therefore, the capacitance C of the variable capacitance element  602  can be changed by selecting suitable drive voltages Vd 1  and Vd 2 . In this case, the drive voltages Vd 1  and Vd 2  may be changed separately or simultaneously. Instead, one of the drive voltages may be fixed while the other is changed. In this way, the rate of change of the capacitance C of the variable capacitance element  602  can be increased, so that small adjustments become easier. Furthermore, the overall maximum capacitance of the variable capacitance element  602  is increased due to the combination of the plurality of single variable capacitance element regions  142  and  144 . 
         [0063]      FIG. 12  is a perspective view showing another embodiment of the process for manufacturing the fixed electrode substrate  300 . In this embodiment, a dielectric layer  320  is formed on the fixed electrode region  312 . By using the fixed electrode substrate  300  provided with the dielectric layer  320  to form the variable capacitance element  602 , a short between the fixed electrode region  312  of the conduction layer  310  and the conduction layer  150  of the floating electrode substrate  100  can be prevented. The dielectric layer  320  can be provided on the surface of the floating electrode region  158 , but providing the dielectric layer  320  on the fixed electrode region  312 , which is not moved, is beneficial for improving the response time of the variable capacitance element  602 . The dielectric layer  320  can be made of any material and formed by photolithography. 
         [0064]      FIG. 13  schematically shows the structure of a variable capacitance element  710  according to another embodiment. The variable capacitance element  710  includes a plurality of single variable capacitance elements  141 , and all of the single variable capacitance elements  141  receive a common drive voltage Vd 3  to be driven simultaneously. As a result, the variable capacitance element  710  has an extremely large overall capacitance C, and the rate of change of the capacitance C is also extremely large. Furthermore, since each single variable capacitance element  141  includes an independent actuator region  130 , the operating speed when displacing the floating electrode region  120  is the same for a large capacitance C as it is for a small capacitance. Therefore, regardless of an increase in the capacitance C, the response speed to a change in the drive voltage Vd 3  is the same as that of the single variable capacitance element  141 . 
         [0065]      FIG. 14  schematically shows the structure of a variable capacitance element  720  according to another embodiment. The variable capacitance element  720  includes a combination of a single variable capacitance element  148  and a large single variable capacitance element  146  having greater dimensions than the single variable capacitance element  148 . As a result, the capacitance C, which is roughly determined by driving the floating electrode of the large single variable capacitance element  146  with a drive voltage Vd 4 , can be more finely adjusted by independently driving the single variable capacitance element  148  with a drive voltage Vd 5 . Therefore, the variable capacitance element  720  has both a large capacitance C and a function for fine capacitance adjustment. 
         [0066]      FIG. 15  is a perspective view showing a stage in a process for manufacturing a fixed electrode substrate  400  when forming a variable resonator  604  according to another embodiment. The fixed electrode substrate  400  includes, in addition to a conduction layer  410  that includes a pattern forming fixed electrodes, a conduction layer  420  having a coil  422 . 
         [0067]    The conduction layer  410  includes a pair of fixed electrode regions  412 , a terminal portion  418  that connects the fixed electrode regions  412  to the outside, and a connection portion  414  that connects the fixed electrode regions  412  to each other and connects the terminal portion  418  to the fixed electrode regions  412 . The conduction layer  410  further includes a terminal portion  416  that is used when connecting to the coil  422 , described further below. In the conduction layer  410 , the fixed electrode regions  412  correspond respectively to the single variable capacitance element regions  142  and  144 . 
         [0068]    The conduction layer  420  includes a pair of terminal portions  424  and  428 , the coil  422 , and a connection portion  426  that connects the terminal portions  424  and  428  and the coil  422  to each other. The terminal portion  428  is used when connecting the variable resonator  604  to the outside. The terminal portion  424  is used when connecting the fixed electrode substrate  400  to the floating electrode substrate  100 , as described further below. 
         [0069]    The pattern of the conduction layer  410  can be formed with conductive material deposition achieved from any evaporation technique and patterning using photolithography. Any conductive material can be selected as the material of the conduction layer  410 , but noble metals such as Au and Pt are desirable due to high chemical stability and superior electrical characteristics. Improved adhesive strength of the conduction layer  310  can be achieved and the diffusion of the material used for the conduction layer  410  to the semiconductor substrate  402  can be prevented by forming a thin undercoating of Cr or the like on the surface of the semiconductor substrate  402  prior to forming the conduction layer  410 . 
         [0070]      FIG. 16  is a perspective view showing the next stage in the process for manufacturing the fixed electrode substrate  400 . At this stage, an insulation layer  430  is formed over a portion of the conduction layer  410  and the conduction layer  420 . In other words, The insulation layer  430  formed on top of the conduction layer  420  prevents the cross-over formed by the conduction layer  440 , described further below, from forming a short with the coil  422  of the conduction layer  420 . 
         [0071]    Although not displayed, an insulation layer may be formed on the conduction layer  410  to serve the same function as the dielectric layer  320  formed on the conduction layer  310  in  FIG. 12 . Therefore, in the variable resonator  604 , the conduction layer  410  of the fixed electrode substrate  400  can be prevented from forming a short with the conduction layer  150  in the floating electrode substrate  100 . The insulation layer can be provided on the surface of the floating electrode region  158 , but providing the insulation layer on the fixed electrode region  412 , which is not moved, is beneficial for improving the response time of the variable resonator  604 . 
         [0072]      FIG. 17  is a perspective view showing the next stage in the process for manufacturing the fixed electrode substrate  400 . At this stage, a conduction layer  440  is formed on the insulation layer  430 , which is formed on the coil  422  of the conduction layer  420 . One end of the conduction layer  440  overlaps the terminal portion  423  formed at the end of the inner side of the coil  422 , and the other end of the conduction layer  440  overlaps the terminal portion  416  of the conduction layer  410 . As a result, the one end of the coil  422  can be connected to the connection portion  414  of the conduction layer  410 . 
         [0073]    Furthermore, at this stage, a removed portion  450  is formed on the upper left side of the semiconductor substrate  402 , as shown in  FIG. 17 . The removed portion  450  is formed to facilitate connection of the terminal portion  184  onto the floating electrode substrate  100  when the variable resonator  604  is in an assembled state. 
         [0074]      FIG. 18  is a perspective view showing a stage in the process for manufacturing the spacer substrate  202  with a shape differing from that of the spacer substrate  200  shown in  FIG. 7 . The shapes of the spacer substrate  202  differs from that of the spacer substrate  200  in regards to the arrangement of the fixed electrode notches  252  and  254  on one surface, and therefore the spacer substrate  200  can be used up until the stage at which the fixed electrode notches  252  and  254  are formed. The fixed electrode notches  252  and  254  formed on the bottom of the spacer substrate  202  pass through to the connection portion  414  of the conduction layer  410  on the fixed electrode substrate  400 . 
         [0075]      FIG. 19  is a perspective view showing a fixed electrode assembly  504  formed by adhering the spacer substrate  202  to the floating electrode substrate  100 . The spacer substrate  202  is positioned on the fixed electrode substrate  400  such that the hole patterns  232  surround the single variable capacitance element regions  142  and  144 , and is then laminated to be adhered to the fixed electrode substrate  400 . 
         [0076]    Here, the connection portion  414  on the fixed electrode substrate  400  passes through the fixed electrode notches  252  and  254  formed on the bottom of the spacer substrate  202 . The coil  422  of the conduction layer  420  is positioned outside of the spacer substrate  202 . At this stage, the solder ball  270  is provided on the terminal portion  424  of the conduction layer  420 . As a result, when the floating electrode substrate  100  is laminated onto the fixed electrode assembly  504 , the terminal portion  154  of the conduction layer  150  is connected to the terminal portion  424 . The floating electrode substrate  100  shown in  FIG. 5  is then laminated onto the fixed electrode assembly  504  described above to form the variable resonator  604 . 
         [0077]      FIG. 20  is cross-sectional view showing the layered structure of a variable resonator  604  manufactured as described above. The variable resonator  604  is formed by laminating the floating electrode substrate  100  shown in  FIG. 5  onto the fixed electrode assembly  504  shown in  FIG. 19 . Here, the floating electrode substrate  100  is laminated onto the fixed electrode assembly  504  after flipping the floating electrode substrate  100  over the dotted line A 2  in  FIG. 5  in a direction of the arrow T 2 . Therefore, the fixed electrode region  412  of the conduction layer  410  on the fixed electrode substrate  400  faces the floating electrode region  158  of the conduction layer  150  on the floating electrode substrate  100 . 
         [0078]    In the variable resonator  604  having the above structure, a voltage is applied between the conduction layers  150  and  180  to move the floating electrode region  158 , so that the space between the floating electrode region  158  and the fixed electrode region  412  changes, thereby changing the capacitance between the floating electrode region  158  and the fixed electrode region  412 . The pair of single variable capacitance element regions  142  and  144  are connected to each other in parallel by the connection portion  156  of the conduction layer  150  and the connection portion  414  of the conduction layer  410 . Therefore, the combined capacitance of the pair of single variable capacitance element regions  142  and  144  is created between the terminal portion  154  of the conduction layer  150  and the terminal portion  418  of the conduction layer  410 . 
         [0079]    In the variable resonator  604 , the actuator region  130  on the floating electrode substrate  100  side extends to the outside from the outer periphery of the floating electrode region  158 , as described above. Accordingly, the space between the conduction layer  150  in the floating electrode region  158  and the conduction layer  410  in the fixed electrode region  412  is almost entirely filled with air. As a result, the floating electrode region  158  can be moved with a large stroke and the single variable capacitance element regions  142  and  144  can be set to have a large capacitance, so that the variable resonator  604  has a large rate of change. 
         [0080]      FIG. 21  schematically shows the electrical function of the variable resonator  604 . The variable resonator  604  has an electrical structure in which the pair of single variable capacitance element regions  142  and  144  and the inductance element  460  formed by the coil  422  are connected to each other in parallel. Accordingly, this circuit resonates with respect to a specific frequency that is determined by the combined capacitance of the single variable capacitance element regions  142  and  144  and the impedance of the inductance element  460 . 
         [0081]    Separate drive voltages can be applied to the actuator region  130  in the single variable capacitance element region  142  and the actuator region  130  in the single variable capacitance element region  144 , via the terminal portion  184 . Accordingly, by applying a drive voltage to the piezoelectric material layer  140  from a floating electrode driving section formed as the voltage source, the floating electrode region  120  can be brought near or moved away from the fixed electrode region  412 . In this way, the capacitances of the single variable capacitance element regions  142  and  144  can be individually changed. Therefore, the resonance frequency of the variable resonator  604  can be changed according to the change in the capacitance. 
         [0082]    Furthermore, the variable resonator  604  can operate as a CL resonator. In this case, one of the drive voltages Vm 1  and Vm 2  applied to the single variable capacitance element regions  142  and  144  is selected such that the oscillation frequency becomes the carrier frequency, and the other drive voltage is changed according to a modulation signal. As a result, the variable resonator  604  can function as a frequency modulator having a simple configuration. 
         [0083]      FIG. 22  schematically shows the structure of a variable resonator  730  according to another embodiment. The variable resonator  730  includes a plurality of single variable capacitance elements  141 . The two drive voltages Vm 1  and Vm 2 , one of which is the drive voltage applied to determine the carrier frequency and the other of which is the drive voltage applied to determine the modulation frequency, are applied to the single variable capacitance elements  141 . As a result, both frequencies can be determined using a large capacitance and a large rate of change. Furthermore, since each single variable capacitance element  141  includes an independent actuator region  130 , the response speed for a change in the drive voltage determining the modulation frequency is particularly high. 
         [0084]      FIG. 23  schematically shows another embodiment of the variable resonator  740 . The variable resonator  740  includes a combination of a single variable capacitance element  148  and a large single variable capacitance element  146  having greater dimensions than the single variable capacitance element  148 . Therefore, by using the large single variable capacitance element  146  to determine the carrier frequency and the single variable capacitance element  148  to determine the modulation frequency, for example, the resulting frequency modulator has a high response speed. 
         [0085]    As described above, the variable capacitance element, and the variable resonator and modulator using this variable capacitance element, can be formed of a thin metal film having low conduction loss to obtain a high Q value and low conduction loss. By providing a plurality of single variable capacitance elements that can be changed simultaneously or individually, the response speed does not drop even when the capacitance increases. Furthermore, using photolithography for the manufacturing enables industrial mass production with high precision and yield. Yet further, the variable capacitance elements can be integrated with other circuit elements. Accordingly, these variable capacitance elements can be used is many electrical circuits, such as variable frequency oscillators (VFOs), tuned amplifiers, phase shifters, impedance matching circuits, and the like. 
         [0086]    The operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by “prior to,” “before,” or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as “first” or “next” in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order.

Technology Category: 5