Abstract:
An exemplary piezoelectric device includes a piezoelectric vibrating piece, on which excitation electrodes are formed, and a piezoelectric frame having a frame portion surrounding the piezoelectric vibrating piece. A plate (e.g., lid or base) is bonded to one surface of the frame portion. Fitting members are provided on both the frame and the plate. When the piezoelectric frame and plate are brought together for assembly, the fitting members fit together (e.g., interdigitate) to provide quick and error-free alignment. Then, the fitting members are bonded together by a bonding material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Japan Patent Application No. 2009-213926, filed on Sep. 16, 2009, in the Japan Patent Office, the disclosure of which is incorporated herein by reference in its entirety. 
       FIELD 
       [0002]    This disclosure relates to, inter alia, piezoelectric vibrating devices and methods for manufacturing them, particularly in a manner suitable for mass-production. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Nowadays, crystal vibrating devices used in mobile communications devices and/or OA equipment must increasingly be miniaturized, provided with a thinner profile, and/or made to operate at a higher frequency so as to be correspondingly accommodated in electronic devices that likewise are increasingly miniaturized, provided with a thinner profile, and/or made to operate at a higher frequency. Also, for economic viability, devices satisfying these criteria must be mass-producible at increasingly lower cost. 
         [0004]    Certain methods for manufacturing piezoelectric vibrating devices are disclosed in Japan Unexamined Patent Application No. 2008-182468. Each device includes a “package” including a lid. Each lid is mounted on a respective guiding portion on a “package wafer” on which a plurality of packages has been formed, wherein each package accommodates a respective piezoelectric vibrating piece. During manufacture each lid and package are fitted together by the guiding portion, and each package is hermetically sealed. Then, each package is cut from the package wafer, thereby producing multiple individual piezoelectric devices. The method disclosed in JP &#39;468 can prevent misalignment of the package base and lid. However, in the method of JP &#39;468ed in JP &#39;468, multiple packages are formed integrally on a single wafer, whereas the lids are formed individually. As a result, each lid must be mounted individually on its respective package on the wafer, which imposes additional manufacturing steps to produce the piezoelectric vibrating devices. 
         [0005]    In view of the above, methods as disclosed herein increase productivity of piezoelectric vibrating devices while providing such devices that exhibit high stability of vibrational frequency for long periods. 
       SUMMARY 
       [0006]    A first aspect of the invention pertains to piezoelectric vibrating devices. An exemplary device comprises a piezoelectric frame that includes a piezoelectric vibrating piece on which excitation electrodes are formed and a frame portion surrounding the piezoelectric vibrating piece. The device also includes a plate (e.g., a base plate or lid plate) bonded to one surface of the frame portion of the piezoelectric frame. A respective fitting member is formed on the frame portion and on the plate. The fitting members are configured to engage each other (e.g., interdigitate or fit one within the other) whenever the piezoelectric frame and plate are aligned and brought together for assembly. In the device the respective fitting members are bonded together by a bonding material. The fitting members can include respective metal films, in which event the bonding material can comprise a metal material. Alternatively, the bonding material can be a resin material (e.g., an epoxy resin), in which event the metal films are not required in the fitting members. Desirably a corrosion-resistant film is formed on the exterior of the piezoelectric vibrating device. The corrosion-resistant film comprises an inorganic oxide film, a nitride film, or a nitric oxide film, or a combination thereof. 
         [0007]    The plate can comprise glass, ceramic, or a piezoelectric material. The piezoelectric vibrating piece can be an AT-cut crystal vibrating piece or a tuning-fork type crystal vibrating piece. 
         [0008]    In a representative embodiment of a method for manufacturing the subject piezoelectric devices, a piezoelectric wafer is prepared that defines multiple piezoelectric vibrating pieces and respective frame portions surrounding each piezoelectric vibrating piece. Each piezoelectric vibrating piece comprises at least one excitation electrode, and each frame portion defines first fitting members. Also prepared is a plate wafer that defines multiple plates sized substantially similarly to respective frame portions on the piezoelectric wafer. Each plate defines second fitting members configured to physically engage (e.g., interdigitate with or fit one within the other) with respective first fitting members whenever the plate wafer is aligned with and brought together with the piezoelectric wafer. A bonding material is placed between the first fitting members and the second fitting members. The piezoelectric wafer and the plate wafer are aligned and bonded them together using the placed bonding material, thereby forming a package wafer. 
         [0009]    By this method, a plurality of devices can be manufactured simultaneously on a single package wafer, thereby improving manufacturing efficiency. 
         [0010]    After bonding, the bonded wafer can be cut along the outside periphery of the frame portion. A slit can be formed that extends between the first fitting member and the second fitting member. A corrosion-resistant film can be formed on the slit. The corrosion-resistant film desirably includes at least one of an inorganic oxide, a nitride, or a nitric oxide. At least one of the films is formed by chemical vapor deposition or sputtering. 
         [0011]    The bonded wafer (“package wafer”) can be cut along the slit using a narrower blade than used to cut the slit. 
         [0012]    Using the subject methods, multiple devices can be formed simultaneously on a single package wafer while improving the stability and durability of the piezoelectric devices thus produced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a plan view of the inner surface of a lid for use in the package of a first embodiment of a crystal vibrating device. 
           [0014]      FIG. 1B  is a plan view of a crystal frame of the first embodiment, the crystal frame including a tuning-fork type crystal vibrating piece. 
           [0015]      FIG. 1C  is a plan view of the inner surface of a base for use in the package of a first embodiment of a crystal vibrating device. 
           [0016]      FIG. 1D  is an elevational section along the line A-A in  FIGS. 1A-1C . 
           [0017]      FIG. 2  is a plan view of a package wafer comprising multiple crystal vibrating devices, as viewed from the lid side, according to the first embodiment. 
           [0018]      FIG. 3  is an enlarged elevational section along the line B-B of  FIG. 2 , showing a portion of the package wafer before actually bonding the three constituent wafers together. 
           [0019]      FIG. 4  is a plan view of a package wafer according to a second embodiment, as viewed from the lid side. 
           [0020]      FIG. 5  is an enlarged elevational section along the line C-C of  FIG. 4 , showing a portion of the package wafer before actually bonding the three constituent wafers together. 
           [0021]      FIG. 6A  is an enlarged elevational section along the line D-D of  FIG. 4 . 
           [0022]      FIG. 6B  is the same as  FIG. 6A  but after a cut has been made between two adjacent crystal vibrating devices. 
           [0023]      FIG. 6C  is the same as  FIG. 6B  but after a corrosion-resistant film has been formed. 
           [0024]      FIG. 6D  is the same as  FIG. 6C  but after a cut has been made that completely separates the devices from each other. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The invention is described below in the context of representative embodiments that are not intended to be limiting in any way. 
       First Embodiment of a Crystal Vibrating Device 
       [0026]      FIG. 1A  is a plan view of the inner surface of a lid  10  of this embodiment of a crystal vibrating device  100 .  FIG. 1B  is a plan view of the crystal frame  20  of this embodiment, wherein the crystal frame  20  comprises a tuning-fork type crystal vibrating piece  30 .  FIG. 1C  is a plan view of the inner surface of a base  40  of this embodiment.  FIG. 1D  is an elevational section along the line A-A in  FIGS. 1A-1C , showing the crystal vibrating device  100 . The crystal vibrating device  100  comprises a package including the crystal frame  20  sandwiched between the lid  10  and the base  40 . 
         [0027]    The lid  10  and base  40  are each made of glass, ceramic, or crystal (quartz crystal) material. The crystal frame  20  includes the tuning-fork type crystal vibrating piece  30 , which has an outline profile formed by etching. 
         [0028]    As shown in  FIG. 1A , the lid  10  has a concavity  17  that faces the crystal frame  20 . Around the periphery of the lid  10 , facing the crystal frame  20 , is a fitting concavity  73 . The fitting concavity  73  includes a metal film  15  formed herein. 
         [0029]    As shown in  FIG. 1B , the crystal frame  20  comprises a tuning-fork type crystal vibrating piece  30 , an outer frame  29 , and a pair of supporting arms  26 . These components are formed integrally, with the same thickness, on the crystal wafer  20 W (see  FIG. 2 ). The tuning-fork type crystal vibrating piece  30  comprises a pair of vibrating arms  21  and a base portion  23 . Around the periphery of the outer frame  29  on the surface shown in  FIG. 1B  is a fitting convexity  72 . Similarly, around the periphery of the outer frame  29  on the opposing surface is a fitting concavity  73 . Thus, both major surfaces of the crystal frame  20  have respective fitting concavities. Each fitting concavity  72 ,  73  has a respective metal film  25  formed therein. 
         [0030]    A first base electrode  31  and a second base electrode  32  are formed on the outer frame  29 , the base  23 , and the supporting arms  26  of the crystal frame  20 . The vibrating arms  21  have a respective first excitation electrode  33  (on one vibrating arm) and a respective second excitation electrode  34  (on the other vibrating arm). On each vibrating arm  221 , the respective excitation electrodes are provided on the upper, lower, and side surfaces thereof. The first excitation electrode  33  is connected to a first base electrode  31 , and the second excitation electrode  34  is connected to a second base electrode  32 . The tuning-fork type crystal vibrating piece  30  is very small, and oscillates at 32.768 kHz. 
         [0031]    Each of the first base electrode  31 , second base electrode  32 , first excitation electrode  33 , and second excitation electrode  34  comprises respective metal layers. Example metal layers are 400-2000 Ångstroms of gold (Au) layered on 150-700 Ångstroms of chromium (Cr). 
         [0032]    The supporting arms  26  extend parallel to the vibrating arms  21  (in the Y-direction) from one end of the base  23 , and connect to the outer frame  29 . The supporting arms  26  reduce leakage of oscillations from the vibrating arms  21 , oscillating inside of the package, to the exterior of the crystal vibrating device  100 . The supporting arms  26  protect the device from adverse influences such as changes in external temperature and/or physical impacts from dropping the package. 
         [0033]    As shown in  FIG. 1C , the base  40  defines a concavity  47  that faces the crystal frame  20  in the package. The concavity  47 , a first through-hole  41 , and a second through-hole  43  are all formed concurrently by etching. The base  40  also includes step portions  49  used for connecting electrodes, specifically a first connecting electrode  42  and a second connecting electrode  44 , formed thereon. On the under-surface of the base  40  are a first external electrode EX 1  and a second external electrode EX 2 , both of which are metalized. Just inboard of the periphery of the base  40 , facing the crystal frame  20 , is a fitting convexity  72  that includes a metal film  45  formed therein. 
         [0034]    The first and second through-holes  41 ,  43  each include an interior metal film. Each metal film is formed, simultaneously with formation of the first and second connecting electrodes  42 ,  44 , by photolithography. The first connecting electrode  42  connects to the first external electrode EX 1  on the under-surface of the base  40  via the first through-hole  41 . The second connecting electrode  44  connects to the second external electrode EX 2  on the under-surface of the base  40  via the second through-hole  43 . 
         [0035]    The first base electrode  31  and second base electrode  32 , formed on the under-surface of the outer frame  29 , connect respectively to the first connecting electrode  42  and second connecting electrode  44  formed on the upper surface of the base  40 . I.e., the first base electrode  31  is electrically connected to the first external electrode EX 1 , and the second base electrode  32  is electrically connected to the second external electrode EX 2 . 
         [0036]    The metal film  25  formed on the crystal frame  20  comprises a layer of gold (Au; 400 to 1500 Å thick) that may be formed on a layer of chromium (Cr; 150 to 700 Å thick). Specifically, whenever the lid and base are made of a crystal material, the metal films  15 ,  45  each include a gold layer formed on a chromium layer. Whenever the lid and base are made of glass or ceramic, the metal films  15 ,  45  each include only the gold layer. 
         [0037]    As shown in  FIG. 1D , a crystal vibrating device  100  is formed by layering together the lid  10  of  FIG. 1A , the crystal frame  20  of  FIG. 1B , and the base  40  of  FIG. 1C . These parts, exclusive of the tuning-fork type crystal vibrating piece  30 , are called the “package”  80 . In  FIG. 1D , each of these parts is illustrated separately for clarity of depiction. The first and second through-holes  41 ,  43  of the package  80  are sealed by a sealing material  70 . 
         [0038]    Further with respect to  FIG. 1D , fitting steps are formed on the bonding faces of the lid  10 , base  40 , and crystal frame  20 . More specifically, the fitting concavity  73  of the lid  10  fits into the fitting convexity  72  of the crystal frame  20 , and the fitting convexity  72  of the base  40  fits into the fitting concavity  73  of the crystal frame  20 . 
         [0039]    In  FIG. 1D  the lid  10 , base  40 , and crystal frame  20  are not yet bonded together, but the figure indicates how these parts are aligned with each other for bonding. During actual manufacture, a single crystal wafer  20 W on which hundreds or thousands, of crystal frames  20  are formed (see  FIG. 2 ), one lid wafer  10 W on which hundreds or thousands of lids  20  are formed (see  FIG. 3 ), and a base wafer  40 W on which hundreds or thousands of bases  40  are formed (see  FIG. 3 ) are aligned, layered (with the crystal wafer being sandwiched between the base and lid wafers), and bonded together to form hundreds or thousands of crystal vibrating devices  100  simultaneously. The three-layer sandwich thus formed is called a package wafer  80 W. 
         [0040]      FIG. 2  is a top plan view of a package wafer  80 W, as viewed from the lid wafer side. The lid wafer  10 W is depicted as if it were transparent, and the figure mainly shows the tuning-fork type crystal vibrating pieces  30  formed on the crystal wafer  20 W. For comprehension, an area corresponding to the section of one crystal vibrating device  100  is denoted with a virtual line (two-dotted chain line) on the package wafer  80 W. Also, voids  22  are depicted as meshed zones to distinguish the tuning-fork type vibrating piece  30  and the outer frame  29 . 
         [0041]    Further with respect to  FIG. 2 , cutting grooves  60  are formed on the lid wafer  10 W. Cutting grooves  60  are also formed on the base wafer  40 W (see  FIG. 3 ) aligned (in the X-Y plane) with the cutting grooves on the lid wafer  10 W (X-Y plane). The package wafer  80 W is affixed to a dicing film, not shown, and cut using a dicing saw. The cutting grooves  60  are used for preventing formation of cracks on the crystal vibrating device  100  whenever the lid wafer  10 W and the base wafer  40 W are being cut by the dicing saw. During cutting the dicing saw moves linearly between the walls of the cutting grooves  60  of the lid wafer  10 W and the base wafer  40 W. The depth of each cutting groove  60  is in the range of 20 to 40 μm. 
         [0042]    Continuing further with  FIG. 2 , the metal film  15  formed on the lid wafer  10 W, the metal film  25  formed on the crystal wafer  20 W, and the metal film  45  formed on the base wafer  40 W are situated so as to become layered with each other in the X-Y plane. Thus, the fitting concavity  73  of the lid  10  fits within the fitting convexity  72  of the crystal frame  20 . The metal films  15 ,  25 , and  45  are positioned so that they do not extend into the cutting grooves  60 . This avoids the cutting saw from cutting into the metal forms, which prevents formation of metal chips that could attach to the blade of dicing saw. 
         [0043]      FIG. 3  is an enlarged elevational section, along the line B-B, of a portion of the package wafer  80 W. For comprehension, an area corresponding to the size of one crystal vibrating device  100  is illustrated within a virtual line (two-dotted line) on the package wafer  80 W. The package wafer  80 W comprises a lid wafer  10 W on which lids  10  are formed, a crystal wafer  20 W on which crystal frames  20  are formed, and a base wafer  40 W on which bases  40  are formed.  FIG. 3  shows these portions of the package wafer  80 W aligned with each other but not yet bonded together. In  FIG. 3  the lid wafer  10 W is situated below and the base wafer  40 W is situated above so that they sandwich the crystal wafer  20 W. On the lid wafer  10 W and the base wafer  40 W are respective cutting grooves  60  that are positioned according to the size of the crystal vibrating devices  100  formed between them. 
         [0044]    On the inner surface of the lid wafer  10 W a concavity  17  is formed by wet-etching. Also formed at the same time by wet-etching is the fitting concavity  73  on the lid wafer  10 W, facing the crystal wafer  20 W. On the outer (upper) surface of the lid wafer  10 W, the cutting grooves  60  are formed. On the inner surface of the base wafer  40 W, a concavity  47  and fitting convexity  72  are formed by wet-etching. On the outer surface (under-surface) of the base wafer  40 W are formed the cutting grooves  60 . 
         [0045]    On the surface of the crystal wafer  20 W facing the lid wafer  10 W, the fitting convexity  72  is formed by wet-etching. On the surface of the crystal wafer  20 W facing the base wafer  40 W, the fitting concavity  73  is formed by wet-etching. The fitting concavity  73  formed on the lid wafer  10 W fits with the fitting convexity  72  of the crystal wafer  20 W. Similarly, the fitting convexity  72  formed on the base wafer  40 W fits with the fitting concavity  73  of the crystal wafer  20 W. 
         [0046]    As shown in  FIG. 3 , the fitting concavity  73  of the lid wafer  10 W includes the metal film  15 . Similarly, the fitting convexity  72  and the fitting concavity  73  of the crystal wafer  20 W include the metal film  25 , and the fitting convexity  72  of the base wafer  40 W includes the metal film  45 . 
         [0047]    A eutectic metal ball  75  can be placed in the fitting concavity  73  to maintain a temporary space between the metal layers  25 ,  45 . After inserting the fitting convexity  72  into the fitting concavity  73 , as the eutectic metal ball  75  melts, the molten eutectic metal flows along the metal films  15 ,  25 ,  45 . I.e., the molten eutectic metal wets the surfaces of the metal film  15 ,  25 ,  45  by capillary action. When the molten eutectic metal cools, it hardens, resulting in bonding the metal films  15 ,  25  together and the metal films  25 ,  45  together. Thus, the package of the crystal vibrating device  100  of this embodiment is formed by interaction of the metal films  15 ,  25 ,  45 . 
         [0048]    The eutectic metal ball  75  desirably comprises a gold-silicon alloy (Au 3.15 Si, wherein the percent w/w of Si is 3.15), a gold-germanium alloy (Au 12 Ge), or a gold-tin alloy (Au 20 Sn). The melting temperature of the gold-silicon alloy is 363° C., of the gold-germanium alloy is 356° C., and of the gold-tin alloy is 280° C. 
         [0049]    The first through-hole  41  and second through-hole  43  are sealed using a sealing material  70 . The sealing material  70  can be a eutectic, similar to the bonding material discussed above, namely a gold-silicone alloy, a gold-germanium alloy, or a gold-tin alloy. If the same eutectic is used for both sealing and bonding, both can be done simultaneously. For example, sealing of the through-holes and bonding together of respective wafers can be done at the same temperature by placing the packaged wafer  80 W in a reflow furnace under a preselected vacuum or filled with a desired inert gas. 
         [0050]    Alternatively, the sealing material and bonding material can be different. For example, a eutectic metal having a high melting temperature can be used first (e.g., for bonding), followed by use of a eutectic metal having a lower melting temperature (e.g., for sealing), since use of the second eutectic will not result in melting of the first eutectic. 
         [0051]    Note that the cut regions between adjacent crystal vibrating devices  100  (indicated in  FIG. 3  by two-dotted chain lines) do not extend into the metal films  15 ,  25 ,  45 . Thus, the regions occupied by melted eutectic do not extend into cut regions, either. Hence, whenever the crystal vibrating devices  100  are being cut into individual devices by a dicing saw, the dicing saw does not cut the metal films. As a result, the dicing saw blade does not form chips or cracks on the package wafer  80 W that otherwise would be caused by friction of the dicing saw with metals. 
         [0052]    Since the lid wafer  10 W and the base wafer  40 W are provided with cutting grooves  60 , the cutting load otherwise imposed on the dicing saw is reduced, which improves work efficiency. During dicing the lid wafer  10 W and base wafer  40 W are affixed to a dicing tape and then diced. The cutting grooves prevent metal chips from interfering with the lid wafer  10 W and base wafer  40 W. 
       Second Embodiment of a Crystal Vibrating Device 
       [0053]      FIG. 4  is a top plan view of a package wafer  85 W as viewed from the lid wafer  10 WA. The lid wafer  10 WA is shown as if it were transparent, revealing the underlying tuning-fork type crystal vibrating pieces  30  formed on the crystal wafer  20 WA. For comprehension, the area corresponding to the profile of one crystal vibrating device  110  is delineated with a virtual line (two-dotted chain line) on the packaged wafer  85 W. Also the voids  22  are denoted as meshed regions to distinguish them from the tuning-fork type vibrating piece  30  and the outer frame  29 . 
         [0054]    As shown in  FIG. 4 , cutting grooves  60  are provided on the lid wafer  10 WA and on the base wafer  40 WA at corresponding locations in the X-Y plane (see  FIG. 5 ) as on the lid wafer  10 WA. Fitting concavities  68  and fitting convexities  69  are denoted by solid lines in a region corresponding to the profile of one crystal vibrating device  110 . 
         [0055]      FIG. 5  is an enlarged elevational section, along the line C-C in  FIG. 4 , of a package wafer  85 W including a crystal vibrating device  110 . In  FIG. 5  the wafers are aligned but not yet brought into contact with each other. In this embodiment a resin (e.g., epoxy resin) is used as a bonding material for forming the package of the crystal vibrating device  110 . For comprehension of  FIG. 5 , areas corresponding to the size of respective crystal vibrating devices  110  are delineated with virtual lines (two-dotted chain lines) on the package wafer  85 W. 
         [0056]    As shown in  FIG. 5 , the package wafer  85 W comprises a lid wafer  10 WA, on which individual lids  10 A are formed, a crystal wafer  20 WA, on which individual crystal frames  20 A are formed, and a base wafer  40 WA on which bases  40 A are formed. For comprehension,  FIG. 5  depicts shows the package wafer  85 WA in which the constituent wafer are aligned but not yet bonded together. In  FIG. 5 , the lid wafer  10 WA is at the bottom and the base wafer  40 WA at the top, with the crystal wafer  30 WA being sandwiched therebetween. On the lid wafer  10 WA and base wafer  40 WA are cutting grooves  60  placed according to the sizes of the crystal vibrating devices. 
         [0057]    A concavity  17  is formed by wet-etching the inner surface of the lid wafer  10 WA. At the same time, the fitting concavity  68  facing the crystal wafer  20 WA can also be formed on the lid wafer  10 WA by wet-etching. On the opposite surface of the lid wafer  10 WA (i.e., on the outer surface) are the cutting grooves  60 . Also on the base wafer  40 WA, a concavity  47  and the fitting convexity  69  are formed by wet etching. The cutting grooves  60  are spaced apart according to the size of the crystal vibrating device  110 , and are formed by wet-etching the base wafer  40 WA as well. 
         [0058]    On the surface of the crystal wafer  20 WA facing the lid wafer  10 WA, fitting convexities  69  are formed by wet-etching. Similarly, on the opposite surface, fitting concavities  68  are formed by wet-etching. The fitting concavity  68  on the lid wafer  10 WA receives the fitting convexity  69  formed on the crystal wafer  20 WA. Similarly, the fitting convexity  69  formed on the base wafer  40 WA fits into the fitting concavity  68  formed on the crystal wafer  20 WA. Metal films are not formed on the fitting convexities  69  or fitting concavities  68  because bonding the wafers of the crystal vibrating devices  110  together is simply performed using a resin (e.g., epoxy resin). Other resins that could be used include silicone resins and polyimide resins, or combinations thereof. 
       Method for Manufacturing Crystal Vibrating Device of Second Embodiment 
       [0059]      FIGS. 6A ,  6 B,  6 C, and  6 D are enlarged elevational sections along the line D-D in  FIG. 4 . These figures are of a package wafer  85 W including the crystal vibrating device  110 .  FIGS. 6A-6D  also show respective manufacturing steps for making the crystal vibrating device  110 . Areas corresponding to the size of the crystal vibrating device  110  are delineated with virtual lines (two-dotted chain lines) on the package wafer  85 W. 
         [0060]    In  FIG. 6A  the lid wafer  10 WA is shown on which the lids  10 A are formed, the crystal wafer  20 WA is shown on which crystal frames  20 A having respective tuning-fork type crystal vibrating pieces  30  are formed, and the base wafer  40 WA is shown on which the bases  40 A are formed. The wafers are shown as respective layers that are aligned but not yet bonded together. The fitting concavities  68  of the wafers receive respective fitting convexities  69  and are bonded thereto. An adhesive is applied on the fitting concavities  68  so as not to be separated, resulting in layering of the three wafers. 
         [0061]    On the lid wafer  10 WA and base wafer  40 WA are formed respective cutting grooves  60 . The cutting grooves  60  are not required, but when present prevent cracking of the package wafer  85 W during dicing. 
         [0062]    The concavity  17  and the cutting grooves  60  on the lid  10 A are formed by etching prior to bonding of the wafers together. Similarly, the concavity  47  and the cutting grooves  60  can be formed simultaneously by wet-etching. Also formable by wet-etching are the first connecting electrode  42  and second connecting electrode  44 . 
         [0063]    To bond together the mating surfaces of the lid wafer  10 WA, crystal wafer  20 WA, and base wafer  40 WA, the wafers are first aligned, then bonded. Bonding is performed by application of epoxy resin on the bonding surfaces and bringing the wafers together to form a sandwich. During bonding the layered wafers desirably are pressed (in an air environment) to achieve strong bonds by the epoxy, thereby forming a package wafer  85 W. During bonding, the first and second base electrodes  31 ,  32  ( FIG. 5 ) and the first and second connecting electrodes  42 ,  44  are also bonded together strongly. 
         [0064]    A unit of sealing material  70  is placed on each of the first and second through-holes  41 ,  43  of the package wafer  85 W. The package wafer  85 W is placed in a vacuum reflow furnace (not shown) providing a vacuum or inert-gas environment for sealing. The sealing material  70  can be gold-germanium alloy (Au 12 Ge), which melts at 356° C. 
         [0065]      FIG. 6B  is an elevational section showing formation of a slit  87 . The package wafer  85 W is cut, using a dicing saw, along the cutting grooves, which forms the slit  87 . The depth of the slit  87  extends through the region in which the fitting convexity  69  and fitting concavity  68  have been layered and bonded together. Considering the crystal vibrating device  110  not as a wafer but as an individual device, the slit  87  can be cut to the lower surface of the package wafer  85 W, thereby releasing the crystal vibrating device  110 . 
         [0066]      FIG. 6C  is an elevational section depicting formation of a corrosion-resistant film  90 . The corrosion-resistant film  90  is formed on the package wafer  85 W on the upper surface of the lids and in regions in which the slits  87  have been formed. The corrosion-resistant film  90  is formed by chemical vapor deposition (CVD) and physical vapor deposition (PVD) on the side surfaces and top surface of the package wafer  85 W. The corrosion-resistant film  90  desirably is applied thickly to the side surfaces of the fitting convexity  69  and fitting concavity  68 . 
         [0067]    The corrosion-resistant film  90  can be formed of at least one of an inorganic oxide film, a nitride film, or a nitric oxide film. The film can be formed as a double-layer of inorganic oxide and nitride, respectively. The inorganic oxide film can be, for example, a silica (SiO 2 ) film, a titanium oxide (TiO 2 ) film, or an aluminum oxide (Al 2 O 3 ) film. The nitride film can be a silicon nitride (Si 3 N 4 ) film or an aluminum nitride (AlN) film. The nitride oxide film can be a silicone oxide nitride (Si 2 ON 2 ) film. 
         [0068]    The fitting convexity  69  and fitting concavity  68  of the crystal vibrating device  110  are bonded together using an adhesive, such as a resin (e.g., epoxy resin). Adhesives such as these tend to exhibit adhesion degradation over time. This results in difficulty of keeping the interior of the crystal vibrating device  110  in a vacuum state or filled with a desired concentration of inert gas for long periods of time. Use of the corrosion-resistant film  90  overcomes this problem so that the inside of the crystal vibrating device  110  can be kept at a vacuum or at a desired concentration of inert gas for long periods. 
         [0069]    Chemical vapor deposition (CVD) is a method by which a thin film is deposited through deposition, reaction, and desorption on a surface of a substrate after applying energy, such as plasma, to components of thin films provided as gases to form intermediate products of the gas. Physical vapor deposition (PVD) is a method by which a thin film can be deposited on a substrate by evaporating a material to be deposited with energy, such as heat or plasma. Typical PVD methods include vacuum deposition and sputtering. 
         [0070]      FIG. 6D  is an elevational section of crystal vibrating devices  110  that have been cut into individual devices. A cut region  96  is formed by a dicing saw that is narrower than the slit  87  along the length of the slit  87 . Thus, the package wafer  85 W is cut into many individual crystal vibrating devices  110  by dicing. 
         [0071]      FIGS. 6A and 6B  show that the slit  87  is formed on the package wafer  85 W after the first and second through-holes  41 ,  43  have been sealed by the sealing material  70 . But, this is not intended to be limiting. Alternatively, for example, the package wafer  85 W can be sealed in a vacuum or inert-gas atmosphere after the slit  87  and the corrosion-resistant film  90  have been formed. 
         [0072]    Preferred embodiments of the present invention, including the crystal vibrating devices  100  and  110 , are described above. According to these embodiments, the air-tightness of the devices is improved by forming the package with fitting members on the lid, the piezoelectric frame, and the base. Also, the embodiments are described in the context of tuning-fork type crystal resonator having vibrating arms on which grooves are not formed. However, it will be understood that the resonator alternatively can have vibrating arms with grooves or can be configured as crystal resonator using AT-cut crystal units exhibiting “thickness shear vibration.” Furthermore, any of various combinations of shapes of bonding surfaces, fitting members, and bonding materials can be used.