Abstract:
A quartz vibrator that includes a substrate, a quartz vibrating element, and a dome-shaped cap. The quartz vibrating element is mounted on the substrate. The cap is bonded to the substrate. The cap defines and forms a sealed space that seals the quartz vibrating element along with the substrate. The cap has a side wall portion, a ceiling portion, and a connecting portion. The side wall portion encloses the quartz vibrating element. The ceiling portion is positioned above the quartz vibrating element. The connecting portion connects the side wall portion and the ceiling portion. The connecting portion is thinner than the side wall portion and the ceiling portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of International application No. PCT/JP2013/063755, filed May 17, 2013, which claims priority to Japanese Patent Application No. 2012-113937, filed May 18, 2012, the entire contents of each of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to quartz vibrators. 
       BACKGROUND OF THE INVENTION 
       [0003]    Piezoelectric vibrating devices such as quartz vibrators have thus far been used as oscillators and the like. As an example of such a piezoelectric vibrating device, Patent Document 1 discloses a piezoelectric vibrating device that includes a substrate on which a piezoelectric vibrator is mounted and a metal cap that is bonded to the substrate and that seals the piezoelectric vibrator along with the substrate. In Patent Document 1, the metal cap and the substrate are connected by a sealing resin. 
         [0004]    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-245933 
       SUMMARY OF THE INVENTION 
       [0005]    The frequency characteristics of a quartz vibrating element change greatly due to external disturbances such as stress, for example. Accordingly, with a quartz vibrator that employs a quartz vibrating element, is extremely important to increase the frequency precision by making it difficult for external disturbances to act on the quartz vibrating element. 
         [0006]    However, according to the piezoelectric vibrating device disclosed in Patent Document 1, the sealing resin is water-absorbent, meaning that the humidity in the sealed space can change with ease; there is thus a problem in that the frequency precision of the quartz vibrator can drop. 
         [0007]    It is a primary object of the present invention to provide a quartz vibrator having high frequency precision. 
         [0008]    A quartz vibrator according to the present invention includes a substrate, a quartz vibrating element, and a dome-shaped cap. The quartz vibrating element is mounted on the substrate. The cap is bonded to the substrate. The cap defines and forms a sealed space that seals the quartz vibrating element along with the substrate. The cap includes a side wall portion, a ceiling portion, and a connecting portion. The side wall portion encloses the quartz vibrating element. The ceiling portion is positioned above the quartz vibrating element. The connecting portion connects the side wall portion and the ceiling portion. The connecting portion is thinner than the side wall portion and the ceiling portion. In the present invention, the cap and the substrate are bonded by an inorganic bonding material. 
         [0009]    According to a specific aspect of the quartz vibrator according to the present invention, the thickness of the connecting portion is not greater than 0.85 times the respective thicknesses of the side wall portion and the ceiling portion. 
         [0010]    According to another specific aspect of the quartz vibrator according to the present invention, the thickness of the connecting portion is not less than 0.5 times the respective thicknesses of the side wall portion and the ceiling portion. 
         [0011]    According to another specific aspect of the quartz vibrator according to the present invention, the side wall portion is vertical relative to a main surface of the substrate. The ceiling portion is parallel to the main surface of the substrate. 
         [0012]    According to yet another specific aspect of the quartz vibrator according to the present invention, the cap is made of a metal. 
         [0013]    According to another specific aspect of the quartz vibrator according to the present invention, the inorganic bonding material is bonded to the cap at an end surface and both side surfaces of a bonding area of the cap where the cap is bonded to the substrate. 
         [0014]    According to yet another specific aspect of the quartz vibrator according to the present invention, the inorganic bonding material has a fillet shape. 
         [0015]    According to yet another specific aspect of the quartz vibrator according to the present invention, a length, in the height direction of the cap, of an area where the inorganic bonding material and a side surface of the bonding area of the cap are bonded to each other is greater than a width of the end surface of the bonding area of the cap. 
         [0016]    According to another specific aspect of the quartz vibrator according to the present invention, the substrate includes a conductor formed in a frame shape on one main surface of the substrate, and the cap is mounted on the conductor. 
         [0017]    According to another specific aspect of the quartz vibrator according to the present invention, the conductor is configured of a base layer and a plating layer formed on the base layer, and the base layer is covered by the plating layer so that the base layer is not exposed to the exterior. 
         [0018]    According to yet another specific aspect of the quartz vibrator according to the present invention, a width of the conductor is greater than the width of the end surface of the bonding area of the cap. 
         [0019]    According to yet another specific aspect of the quartz vibrator according to the present invention, the conductor contains Au on an outer surface thereof, the cap contains Au on an outer surface thereof, and the inorganic bonding material contains Au. 
         [0020]    According to yet another specific aspect of the quartz vibrator according to the present invention, the conductor has a Au plating layer in an outermost layer of the conductor, the cap has a Au plating layer in an outermost layer of the cap, and the inorganic bonding material is a Au/Sn alloy. 
         [0021]    According to the present invention, a quartz vibrator having high frequency precision can be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic perspective view illustrating a quartz vibrator according to an embodiment of the present invention. 
           [0023]      FIG. 2  is a schematic plan view illustrating a quartz vibrator according to an embodiment of the present invention. 
           [0024]      FIG. 3  is a schematic cross-sectional view taken along a III-III line shown in  FIG. 2 . 
           [0025]      FIG. 4  is a schematic cross-sectional view illustrating a quartz vibrator according to a reference example. 
           [0026]      FIG. 5  is a graph illustrating a relationship between a thickness ratio and a maximum principal stress. 
           [0027]      FIG. 6  is an exploded perspective view illustrating a quartz vibrator according to another embodiment of the present invention. 
           [0028]      FIG. 7  is a partially cut-out cross-sectional view illustrating an area where a cap and a substrate are bonded in the quartz vibrator illustrated in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Examples of preferred embodiments for carrying out the present invention will be described hereinafter. Note, however, that the following embodiments are merely examples. The present invention is not intended to be limited to the following embodiments in any way. 
         [0030]    Furthermore, in the drawings referred to in the embodiments and the like, members having functions that are substantially identical are given identical reference numerals. The drawings referred to in the embodiments and the like are schematic depictions, and as such the ratios of dimensions and so on of objects depicted in the drawings may differ from the actual ratios of dimensions and so on of those objects. The ratios of dimensions and so on of the objects may differ from drawing to drawing as well. The specific ratios of dimensions and so on of objects should be understood from the following descriptions. 
         [0031]      FIG. 1  is a schematic perspective view illustrating a quartz vibrator  1  according to the present embodiment.  FIG. 2  is a schematic plan view illustrating the quartz vibrator  1  according to the present embodiment.  FIG. 3  is a schematic cross-sectional view illustrating the quartz vibrator  1  according to the present embodiment. 
         [0032]    As shown in  FIGS. 1 to 3 , the quartz vibrator  1  includes a substrate  10 . The substrate  10  can be configured of a ceramic material such as alumina, for example. 
         [0033]    A quartz vibrating element  11  is mounted on the substrate  10 . The quartz vibrating element  11  has an approximately rectangular plate shape. The quartz vibrating element  11  is supported on the substrate  10  in a cantilever state by support members  12  provided on one side thereof in a lengthwise direction. The support members  12  are provided at both corner areas of the quartz vibrating element  11  in the widthwise direction thereof, at one side end portion of the quartz vibrating element  11  in the lengthwise direction thereof. The support members  12  can be configured of a conductive adhesive that has set, or the like, for example. 
         [0034]    A cap  20  is disposed on the substrate  10 . The cap  20  has a dome shape. The cap  20  has a recessed portion  20   a . The cap  20  is disposed so that the open side of the recessed portion  20   a  faces the substrate  10 . A sealed space  30  in which the quartz vibrating element  11  is disposed is defined and formed by the cap  20  and the substrate  10 . The cap  20  is bonded to the substrate  10  at an end surface  20   b  thereof. The cap  20  and the substrate  10  are bonded to each other using an inorganic bonding material  40  such as metal, glass, or the like. Accordingly, moisture, gases, and the like can be suppressed from entering into the sealed space  30 . A Au/Sn alloy can be given as an example of a preferred material to be used as the inorganic bonding material  40 . 
         [0035]    The cap  20  and the substrate  10  are bonded to each other via the inorganic bonding material  40  in a largely depressurized state. Accordingly, the sealed space  30  is in a depressurized state, or in other words, is in a so-called vacuum state. Because the sealed space  30  is in the so-called vacuum state, it is difficult for vibrations of the quartz vibrating element  11  to be inhibited. Accordingly, the frequency precision can be effectively increased. 
         [0036]    If the sealed space  30  is depressurized, it becomes easier for the aforementioned moisture, gases, and so on to enter. However, the cap  20  and the substrate  10  are bonded to each other by the inorganic bonding material  40 , and thus the entrance of moisture, gases, and so on can be effectively suppressed as described above. 
         [0037]    It is preferable for the cap  20  to be configured of an elastic material. It is preferable for the cap  20  to be made of a metal, for example. Specifically, the cap  20  can be configured of nickel, a nickel alloy such as iron/nickel alloy, Kovar, stainless steel, or the like, for example. 
         [0038]    The cap  20  has a side wall portion  21 , a ceiling portion  22 , and a connecting portion  23 . The side wall portion  21  is provided in a frame shape so as to enclose the quartz vibrating element  11  when viewed from above. The side wall portion  21  extends from a main surface of the substrate  10 , in a direction vertical relative to the main surface of the substrate  10 . The ceiling portion  22  is positioned above the quartz vibrating element  11 . The ceiling portion  22  is parallel to the main surface of the substrate  10 . The side wall portion  21  and the ceiling portion  22  are connected by the connecting portion  23 . The connecting portion  23  has a curved structure. The connecting portion  23  configures ridge areas and corner areas of the cap  20 . 
         [0039]    Caps and substrates generally have different thermal expansion coefficients. Accordingly, when the temperature of the quartz vibrator changes, stress arises in both the cap and the substrate due to the difference in the thermal expansion coefficients between the cap and the substrate. Stress remaining in the substrate is exerted on the quartz vibrating element mounted on the substrate, and furthermore, the magnitude of the stress exerted on the quartz vibrating element varies when the stress remaining in the substrate varies. There are thus cases where the frequency precision of the quartz vibrator drops. 
         [0040]    Here, according to the quartz vibrator  1 , the connecting portion  23  is thinner than the side wall portion  21  and the ceiling portion  22 . It is thus easier for the cap  20  to deform when stress is exerted on the cap  20 , as compared to, for example, a quartz vibrator  100  according to a reference example shown in  FIG. 4 , in which a connecting portion  123  has the same thickness as a side wall portion  121  and a ceiling portion  122 . Accordingly, the remaining stress exerted on the cap  20  is reduced, and the stress remaining in the substrate  10  is also reduced. This in turn reduces the stress exerted on the quartz vibrating element  11  from the substrate  10 . As a result, a high frequency precision can be realized. 
         [0041]      FIG. 5  is a graph illustrating a relationship between a thickness ratio and a maximum principal stress. To be more specific, in  FIG. 5 , the thickness ratio on the horizontal axis is a ratio of the thickness of the connecting portion  23  relative to the thickness of the ceiling portion  22  ((connecting portion  23  thickness)/(ceiling portion  22  thickness)). When measuring the thickness of the ceiling portion  22 , the thickness of a central area of the ceiling portion  22  was measured, whereas when measuring the thickness of the connecting portion  23 , the thickness of the thinnest part of the connecting portion  23  was measured. Note that in the present embodiment, the side wall portion  21  and the ceiling portion  22  have the same thickness, and thus the thickness ratio that is the ratio of the thickness of the connecting portion  23  relative to the side wall portion  21  takes on the same values as those shown in  FIG. 5 . The maximum principal stress on the vertical axis is a maximum value of tension stress exerted on a point A indicated in  FIG. 3  when the quartz vibrator  1  is cooled from a temperature of 300° C. to −40° C. 
         [0042]    Note that the data indicated in  FIG. 5  is data obtained under the following conditions. 
         [0043]    Substrate  10 : alumina ceramic substrate (thermal expansion coefficient: 5.4×10 −6 /° C.; Young&#39;s modulus: 220×10 9  Pa) 
         [0044]    Cap  20 : 42Ni alloy (thermal expansion coefficient: 5.0×10 −6 /° C.; Young&#39;s modulus: 200×10 9  Pa) 
         [0045]    Support members  12 : silicone-based conductive adhesive that has set (thermal expansion coefficient: 100×10 −6 /° C.; Young&#39;s modulus: 0.1×10 9  Pa) 
         [0046]    The numerical values of the points plotted in  FIG. 5  are shown in Table 1. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 CAP THICKNESS 
                 MAXIMUM PRINCIPAL 
               
               
                   
                 RATIO 
                 STRESS (TENSION) (MPa) 
               
               
                   
                   
               
             
             
               
                   
                 0.55 
                 12.37 
               
               
                   
                 0.59 
                 12.37 
               
               
                   
                 0.73 
                 12.37 
               
               
                   
                 0.86 
                 12.38 
               
               
                   
                 0.94 
                 12.55 
               
               
                   
                 0.99 
                 12.55 
               
               
                   
                 1.03 
                 12.61 
               
               
                   
                 1.16 
                 12.61 
               
               
                   
                 1.20 
                 12.61 
               
               
                   
                 1.25 
                 12.61 
               
               
                   
                 1.29 
                 12.61 
               
               
                   
                 1.34 
                 12.61 
               
               
                   
                   
               
             
          
         
       
     
         [0047]    From the results shown in  FIG. 5 , it can be seen that the maximum principal stress can be reduced by setting the thickness of the connecting portion  23  to not more than 0.85 times the thickness of the side wall portion  21  and the thickness of the ceiling portion  22 . Accordingly, it can be seen that the frequency precision can be further improved by setting the thickness of the connecting portion  23  to not more than 0.85 times the thickness of the side wall portion  21  and the thickness of the ceiling portion  22 . However, if the connecting portion  23  is too thin, the rigidity of the connecting portion  23  may decrease too much. Accordingly, it is preferable for the thickness of the connecting portion  23  to not less than 0.5 times the thickness of the side wall portion  21  and the thickness of the ceiling portion  22 . 
         [0048]    Meanwhile, because the bonding material  40  that bonds the cap  20  and the substrate  10  to each other is an inorganic bonding material, the bonding material is less water-absorbent than a sealing resin, which makes it possible to improve the seal of the sealed space. From the standpoint of providing a better seal, it is desirable to employ, of the inorganic bonding materials mentioned above, a metal, which is more dense. Furthermore, because an inorganic bonding material fixes more strongly to the cap  20  and the substrate  10  than a sealing resin, which provides an increased bonding strength between the cap  20  and the substrate  10 . Meanwhile, the inorganic bonding material itself is harder than a sealing resin and bonds the cap  20  and the substrate  10  strongly to each other, making it easy for stress to arise between the cap  20  and the substrate  10 , which increases the stress remaining in the substrate  10  and by extension the stress exerted on the quartz vibrating element  11 . It is precisely for this reason that the connecting portion  23  is made thinner than the side wall portion  21  and the ceiling portion  22  and the remaining stress is dissipated. 
         [0049]    Note that the thickness ratio between the side wall portion  21  and the ceiling portion  22  is not particularly limited. For example, the side wall portion  21  and the ceiling portion  22  may be set to the same thickness. The side wall portion  21  may be set thicker than the ceiling portion  22 , or thinner than the ceiling portion  22 . 
         [0050]      FIGS. 6 and 7  are diagrams illustrating the configuration of a quartz vibrator according to another embodiment of the present invention in more detail, where  FIG. 6  is an exploded perspective view illustrating an overview of the quartz vibrator  1  and  FIG. 7  is a partially cut-out cross-sectional view illustrating an area where the substrate  10  and the cap  20  are bonded in the quartz vibrator. 
         [0051]    As shown in  FIG. 6 , in the quartz vibrating element  11 , electrodes  11   a  are formed on the front and rear surfaces of a quartz chip (the electrode on the rear surface is not shown). The electrodes  11   a  oppose each other in the thickness direction of the quartz chip. The electrodes formed on the quartz vibrating element  11  are electrically connected to conductors  43   a  and  43   a  formed on one main surface of the substrate  10  via conductive adhesives  42  and  42 . The conductor  43   a  is electrically connected to an outer electrode formed on another main surface of the substrate  10  via a via conductor (not shown) formed in the substrate  10 . 
         [0052]    The conductor  43  has a contour that conforms to a bonding area  20   c  of the cap  20  on the one main surface of the substrate  10 . Specifically, the conductor  43  is formed having a frame shape. 
         [0053]    As shown in  FIG. 7 , the conductor  43  has a long, semi-oval shape when viewed as a cross-section. Here, the conductor  43  is formed of a base layer  44  containing Mo, a Ni plating layer  45 , a Pd plating layer  46 , and a Au plating layer  47 , in that order from the bottom. The base layer is covered by the plating layers formed thereabove, and as such is not exposed to the exterior. Note that the conductor  43   a  and the outer electrode can be configured having the same layer structure as the conductor  43 . 
         [0054]    As shown in  FIG. 7 , the bonding area  20   c  of the cap  20  has a shape in which a tip thereof extends in a rounded shape. This shape provides an effect of smoothing the wet-rising of the inorganic bonding material  40 , which will be mentioned later. The cap  20  has a metallic layer  20   d  on a surface thereof, and the metallic layer  20   d  is configured of a plating layer configured of Au or a Au alloy. 
         [0055]    As shown in  FIGS. 6 and 7 , the substrate  10  and the cap  20  are bonded to each other via the inorganic bonding material  40 . The bonding material is configured of a Au/Sn alloy. As described earlier, the inorganic bonding material  40  is temporarily melted when bonding the cap  20 , and is then set. The metallic layer  20   d  of the cap  20 , the outermost plating layer of the conductor  43 , and the inorganic bonding material  40 , each contain Au, and thus are easily wetted to each other. The inorganic bonding material  40  thus takes on a fillet shape after setting. The inorganic bonding material  40  wet-rises up to the side surfaces of the cap  20 , in addition to the end surface thereof. Furthermore, the inorganic bonding material  40  spreads out to cover the plating layer of the conductor  43 . 
         [0056]    Accordingly, the base layer  44  of the conductor  43 , which is relatively porous, is covered by a plating layer. As such, the base layer  44  is not exposed to the exterior, which makes it difficult for moisture to enter via the base layer. The inorganic bonding material  40  is itself configured of a metal, and thus is denser and less water-absorbent than an adhesive containing a resin. A border between the inorganic bonding material  40  and the cap  20  and a border between the inorganic bonding material  40  and the conductor  43  are widely sealed as a result of the inorganic bonding material  40  spreading out. A path through which moisture enters is lengthened as a result, which makes it difficult for moisture to enter. 
         [0057]    Accordingly, the sealed space formed by the substrate  10 , the conductor  43 , the inorganic bonding material  40 , and the cap  20  is sealed with more certainty. The frequency precision of the quartz vibrator  1  stabilizes as a result. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  quartz vibrator 
               10  substrate 
               11  quartz vibrating element 
               12  support member 
               20  cap 
               20   a  recessed portion 
               20   b  end surface 
               21  side wall portion 
               22  ceiling portion 
               23  connecting portion 
               30  sealed space 
               40  inorganic bonding material