Abstract:
Methods are disclosed for manufacturing piezoelectric vibrating devices that do not acquire unwanted gas or water vapor inside their respective packages during manufacture and that attain such end by methods suitable for mass-production. An exemplary manufacturing method includes preparing a piezoelectric wafer having multiple piezoelectric frames; on the piezoelectric wafer defining at least one first through-hole per frame; preparing a base wafer having multiple package bases alignable with the frames; on the base wafer defining at least one second through-hole; preparing a lid wafer having multiple package lids alignable with the frames; applying a sealing material between a first main surface of each frame and an inner main surface of the base wafer, and between a second main surface of each frame and an inner main surface of the lid wafer; and thereby bonding the three wafers together to form multiple packaged piezoelectric devices. To facilitate ventilation of gas from inside each package during bonding, each package includes at least one communicating groove extending from inside the package to the first or second through-hole. After venting, the communicating groove is sealed automatically with sealing material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Japan Patent Application No. 2010-170446, filed on Jul. 29, 2010, in the Japan Patent Office, the disclosure of which is incorporated herein by reference in its entirety. 
       FIELD 
       [0002]    This disclosure pertains to, inter alia, piezoelectric vibrating devices that, during their manufacture, automatically ventilate unwanted gas and water vapor from inside their respective packages, and to methods for manufacturing such devices. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    A surface-mount type piezoelectric device is one in which a piezoelectric vibrating piece is mounted on a package base that is not electrically conductive, and sealed in the package by a lid (which is also part of the package and typically not electrically conductive). During manufacture of a piezoelectric device, the package base and package lid are stacked in registration with each other, and a layer of sealing material, such as a polymeric resin or low-melting-point glass, is used to bond the package base and package lid either to each other or to an intervening structure to form a “package.” Using resin as a sealing material can cause problems because polymeric resins tend to release gas during exposure to elevated temperatures required for curing the resin. The released gas, especially if entrapped within the package, can adversely affect vibration of the piezoelectric vibrating piece inside the package. Even low-melting-point (LMP) glass can release unwanted gas from bubbles in the glass during an elevated-temperature sealing step. 
         [0004]    Japan Patent Publication No. JP 2005-026974A discusses a method for preventing released unwanted gas from entering a device package. On the entire edge surface of the no-conductive base, a first layer of LMP glass is applied for temporary hardening. Then, a layer of a second LMP glass is applied over the first layer and temporarily hardened. The second LMP glass is not applied to designated regions of the surface of the second LMP glass, particularly regions connected to inside the package. 
         [0005]    Disadvantageously, the method discussed JP &#39;974 requires two or more applications of LMP glass and respective temporary hardening steps, which is process-intensive. Also, if the second LMP glass has low viscosity, then the second LMP glass spreads tends to spread to regions where LMP glass is not wanted. Replacing the low-viscosity LMP glass with a higher-viscosity LMP glass poses difficulties in procedure used for applying the glass. Furthermore, the manufacturing methods discussed in JP &#39;974 require applying LMP glass on each piezoelectric device, which is unsuitable for mass-production. 
         [0006]    Therefore, there is a need for methods for manufacturing piezoelectric devices, as disclosed herein, that do not result in entrapment of unwanted gas or water vapor inside the package containing the piezoelectric vibrating device. There is also a need for piezoelectric vibrating devices that do not contain unwanted gas or water vapor. 
       SUMMARY 
       [0007]    Various aspects of the invention are summarized below. A first aspect is directed to methods for manufacturing piezoelectric devices. An exemplary embodiment of such a method comprises preparing a piezoelectric wafer having first and second main surfaces and including an array of multiple piezoelectric frames. Each piezoelectric frame includes a piezoelectric vibrating piece and a respective exterior frame that surrounds and supports the piezoelectric vibrating piece. The piezoelectric wafer also includes, for each piezoelectric frame in the array, at least a pair of first through-holes disposed between adjacent exterior frames in the array. Each first through-hole extends from the first main surface to the second main surface. Also prepared is a base wafer that has inner and outer main surfaces and includes an array of package bases that are co-alignable with the array of piezoelectric frames. Each package base includes at least one external electrode on the outer main surface and at least a pair of second through-holes disposed between adjacent package bases in the array. Each second through-hole extends from the inner main surface to the outer main surface. Also prepared is a lid wafer that includes an array of multiple package lids that are co-alignable with the array of piezoelectric frames. The lid wafer has an inner main surface and an outer main surface. For each piezoelectric frame in the array, at least one respective communicating groove is defined that extends from one main surface of the piezoelectric frame to the inner main surface of the package base, or that extends from the other main surface of the piezoelectric frame to the inner main surface of the package lid, such that the communicating groove opens into at least one of the first and second through-holes. A sealing material is placed between the second main surface of each exterior frame and the inner main surface of each respective package base, and between the first main surface of each exterior frame and the inner main surface of each respective package lid. The wafers are co-aligned and bonded together by bonding together each co-aligned package lid, piezoelectric frame, and package base using the placed sealing material to form respective packages each containing a respective piezoelectric vibrating piece. During bonding, each package automatically vents through the respective communicating groove, and the communicating groove(s) are automatically sealed with the sealing material so as to preserve the desired environment inside the packages. The sealing material desirably comprises an adhesive made of glass, epoxy resin, or polyimide resin. 
         [0008]    Each piezoelectric frame desirably is formed so as to have at least one excitation electrode. During manufacture of such devices, a metal film is formed on the inside surfaces of the through-holes, and the metal film is formed so as to connect the excitation electrode(s) to respective external electrode(s). 
         [0009]    Some embodiments have a rectangular profile as viewed from above the package lid or below the package base. In these embodiments it is desirable that each first and second through-hole be located at a respective corner of the rectangular profile. Alternatively, each first and second through-hole can be located on a respective side of the rectangular profile. 
         [0010]    Another aspect of the invention is directed to piezoelectric devices. An exemplary embodiment of such a device comprises a piezoelectric frame including a piezoelectric vibrating piece having first and second main surfaces and a respective excitation electrode on each of the first and second main surfaces. The piezoelectric frame also includes an outer frame surrounding the piezoelectric vibrating piece. The device also includes a package base having an inner and an outer main surface. The outer main surface includes at least one external electrode, and the inner main surface is bonded to the second main surface of the piezoelectric frame. The device also includes a package lid having an inner and an outer main surface, wherein the inner main surface is bonded to the first main surface of the piezoelectric frame. A sealing material is disposed peripherally relative to the outer frame so as to be peripherally arranged relative to each of the first and second main surfaces of the piezoelectric frame. The sealing material thus bonds the piezoelectric frame to the package lid and to the package base to form a package defining a package cavity containing the piezoelectric vibrating piece. The device also has at least one communicating groove that extends from the cavity and that is defined in at least one of the first and second main surfaces of the outer frame, the inner main surface of the package base, and the inner main surface of the package lid. The at least one communicating groove is sealed with the sealing material. 
         [0011]    Some embodiments have a rectangular profile when viewed from above the package lid or below the package base. The rectangular profile includes four corners, and each corner includes a respective castellation defining a corresponding edge-surface. A first edge-surface can include a respective edge-surface electrode extending at least between the first and second main surfaces of the piezoelectric frame and being connected to one of the excitation electrodes. A second edge-surface can include a respective edge-surface electrode extending at least between the first and second main surfaces of the piezoelectric frame and being connected to the external electrode. 
         [0012]    Further with respect to packages having a rectangular profile, the rectangular profile includes four sides, and each side can include a respective castellation defining a corresponding edge-surface. A first edge-surface includes a respective edge-surface electrode extending at least between the first and second main surfaces of the piezoelectric frame and being connected to one of the excitation electrodes. A second edge-surface includes a respective edge-surface electrode extending at least between the first and second main surfaces of the piezoelectric frame and being connected to the external electrode. 
         [0013]    Another embodiment of a piezoelectric device comprises a package base comprising an inner main surface and an outer main surface. The inner main surface defines a cavity, and the outer main surface includes at least one external electrode. A piezoelectric vibrating piece is disposed in the cavity. The piezoelectric vibrating piece has a first main surface including a first excitation electrode and a second main surface including a second excitation electrode. The device includes a package lid having an inner main surface and an outer main surface. The inner main surface of the package lid is bonded to the package base by a sealing material, thereby forming a package containing the piezoelectric vibrating piece. At least one communicating groove is defined in the inner main surface of the package base or the inner main surface of the package lid. The communicating groove extends from the cavity to outside the package and is sealed with the sealing material. 
         [0014]    The embodiments summarized above, as well as other embodiments within the scope of the invention, have package cavities that do not contain any unwanted gas or water vapor. The subject devices are also suitable for mass-production. As a result of their having controlled environments inside their respective packages, the subject piezoelectric devices produce steady vibration accurately at a specified frequency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an exploded perspective view of a first embodiment of a piezoelectric device. 
           [0016]      FIG. 2A  is a cross-sectional view along the line A-A′ in  FIG. 1 , after bonding together a quartz-crystal frame, a package base, and a package lid. 
           [0017]      FIG. 2B  is a cross-sectional view along the line B-B′ in  FIG. 1 , after bonding together the quartz-crystal frame, a package base, and a package lid. 
           [0018]      FIG. 3  is a flow-chart of an embodiment of a method for manufacturing a piezoelectric device according to the first embodiment. 
           [0019]      FIG. 4  is a plan view of a quartz-crystal wafer. 
           [0020]      FIG. 5  is a plan view of a base wafer. 
           [0021]      FIG. 6  is a plan view of a lid wafer. 
           [0022]      FIG. 7  is an exploded perspective view of a second embodiment of a piezoelectric device. 
           [0023]      FIG. 8  is a cross-sectional view along the line C-C′ line in  FIG. 7 , after the quartz-crystal frame, package base, and package lid  22  have been bonded together. 
           [0024]      FIG. 9  is a plan view of a quartz-crystal wafer. 
           [0025]      FIG. 10  is a plan view of a base wafer. 
           [0026]      FIG. 11  is a plan view of a lid wafer. 
           [0027]      FIG. 12A  is a plan view of a ceramic package of a third embodiment of a piezoelectric vibrating device after removing the package lid. 
           [0028]      FIG. 12B  is a cross-sectional view of the third embodiment of a piezoelectric device  110 , along the line E-E′ in  FIG. 12A . 
           [0029]      FIG. 13  is a flow-chart of an embodiment of a method for manufacturing the third embodiment of a piezoelectric vibrating device. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Various embodiments are described in detail below, with reference to the accompanying drawings. 
         [0031]    In the described embodiments, an AT-cut quartz-crystal vibrating piece having thickness-shear vibrating mode is used as the piezoelectric vibrating piece. An AT-cut quartz-crystal vibrating piece has a principal surface (in the XZ plane) that is tilted by 35° 15′ about the Y-axis of the crystal coordinate system (XYZ) in the direction of the Y-axis from the Z-axis around the X-axis. Thus, in the following description, new axes tilted with respect to the axial directions of the quartz-crystal vibrating piece are denoted as the X′-axis, Y′-axis, and Z′-axis, respectively. Regarding a height in the Y′-axis direction, a positive (+) direction is denoted as high and a negative (−) direction is denoted as low. 
       First Embodiment 
       [0032]    The overall configuration of a piezoelectric device  100 A according to this embodiment is shown in FIGS.  1  and  2 A- 2 B.  FIG. 1  is an exploded perspective view of the piezoelectric device  100 A. Note that the view shown in  FIG. 1  is upside-down, with the package base  11  being shown uppermost.  FIG. 1  also does not show connection electrodes  118   a ,  118   b  (but see  FIG. 2A ).  FIG. 2A  is an elevational section along the line A-A′ in  FIG. 1 .  FIG. 2B  is an elevational section along the line B-B′ in  FIG. 1 . 
         [0033]    This embodiment of a piezoelectric vibrating device  100 A includes a quartz-crystal frame  10 , a package base  11 , and a package lid  12 . The package base  11  and package lid  12  can be made of a glass or quartz-crystal material. The quartz-crystal frame  10  and package base  11  are bonded together using a sealing material SL. Similarly, the quartz-crystal frame  10  and the package lid  12  are bonded together using the sealing material SL. A package cavity CT ( FIG. 2A ) is formed by bonding the package base  11  and package lid  12  to the quartz-crystal frame  10 . The package cavity CT is either at a particular vacuum level or filled with an inert gas. In either event the package cavity CT is sealed from the external environment. 
         [0034]    The quartz-crystal frame  10  is formed of AT-cut quartz-crystal material. The frame  10  includes a first bonding surface M 3  facing the +Y′-direction and a second bonding surface M 4  facing the −Y′-direction. The quartz-crystal frame  10  comprises a vibrating portion  101  and a frame portion  102  surrounding the vibrating portion  101 . Between the vibrating portion  101  and the frame portion  102  are a U-shaped first void  103  and a second void  103   a . A connecting portion  109  joins the vibrating portion  101  to the frame portion  102 . On the first and second (upper and lower) main surfaces of the vibrating portion  101  are respective excitation electrodes  104   a ,  104   b  (see  FIG. 2A ). On both main surfaces of the frame portion  102  are respective extraction electrodes  105   a ,  105   b  ( FIG. 2A ) that are electrically connected to the respective excitation electrodes  104   a ,  104   b.    
         [0035]    Each corner of the crystal frame  10  has a respective castellation  106   a ,  106   b , thereby providing two castellations  106   a  and two castellations  106   b . On the surface of each castellation  106   a  is a respective edge-surface electrode  107   a , and on the surface of each castellation  106   b  is a respective edge-surface electrode  107   b . Similarly, each corner of the package base  11  has a respective castellation  116   a ,  116   b , thereby providing two castellations  116   a  and two castellations  116   b . On the surface of each castellation  116   a  is a respective edge-surface electrode  117   a , and on the surface of each castellation  116   b  is a respective edge-surface electrode  117   b . The edge-surface electrodes  107   a  are connected to the extraction electrodes  105   a  and to the edge-surface electrodes  107   a . The edge-surface electrodes  107   b  are connected to the extraction electrodes  105   b  and to the edge-surface electrodes  117   b.    
         [0036]    The quarter-round castellations  106   a ,  106   b  are formed from corresponding full-round through-holes by perpendicular dicing cuts intersecting each other at the center of the respective through-hole ( FIG. 4 ). 
         [0037]    The package base  11  comprises an external main surface (“mounting surface”) M 1  and a bonding main surface (interior main surface) M 2 . On the external main surface M 1  are two pairs of external electrodes  115   a ,  115   b , respectively. As a result, four electrical connections can be made to the device  100 A. A respective castellation  116   a ,  116   b  is formed on each corner of the package base  11 , providing a total of four castellations. One of the castellations  116   a  has a respective edge-surface electrode  117   a , by which the respective external electrode  115   a  can be electrically connected to the respective edge-surface electrode  107   a . The other castellation  116   a  lacks the edge-surface electrode  117   a  and thus can be used as an electrical-ground terminal. Similarly, one of the castellations  116   b  has a respective edge-surface electrode  117   b , by which the respective external electrode  115   b  can be electrically connected to the respective side-surface electrode  107   b . The other castellation  116   b  lacks the edge-surface electrode  117   b  and thus can be used as an electrical-ground terminal. 
         [0038]    The quarter-round castellations  116   a ,  116   b  are formed from corresponding full-round through-holes by perpendicular dicing cuts intersecting each other at the center of the respective through-hole ( FIG. 4 ). 
         [0039]    The package lid  12  includes an external (outer) main surface and an internal (bonding main) M 5 . A respective castellation  126   a ,  126   b  is formed on each corner of the package lid  12 , providing a total of four castellations. On the bonding main surface M 5  are grooves  120  extending inboard of the respective castellations  126   a ,  126   b . One groove  120  provides communication between one of the castellations  126   a  and one of the castellations  126   b . The other groove  120  provides communication between the other of the castellations  126   a  and the other of the castellations  126   b.    
         [0040]    The quarter-round castellations  126   a ,  126   b  are formed from corresponding full-round through-holes by perpendicular dicing cuts intersecting each other at the center of the respective through-hole ( FIG. 6 ). 
         [0041]    In  FIG. 1  the sealing materials SL between the package base  11  and frame  10 , and between the frame  10  and the package lid  12 , are made of LMP glass, polyimide resin, or epoxy resin containing vanadium. The sealing materials SL are shown being formed as respective gaskets ( FIG. 1 ). More commonly, the sealing materials SL are applied by screen-printing or the like directly on the bonding surfaces M 3 , M 4 . The sealing material SL is normally not available in sheet format. 
         [0042]    LMP glass, polyimide resin, and epoxy resins are resistant to water and humidity. Consequently, when used as sealing materials SL, they prevent water vapor from entering the package and from damaging the hermetic seal of the package cavity. LMP glass is a lead-free vanadium-based glass that melts at 350° C. to 400° C. Vanadium-based glass can be formulated as a paste mixed with binder and solvent. This adhesive bonds to other materials by processes involving firing and cooling. Vanadium-based LMP glass seals are hermetic and have a reduced coefficient of thermal expansion as a result of control of the glass structure. 
         [0043]    In  FIG. 2B , the sealing material SL applied between the bonding surface M 2  of the package base  11  and the bonding surface M 3  of the frame portion  102  bonds the crystal frame  10  and the package base  11  together. Similarly, the sealing material SL applied between the bonding surface M 5  of the package lid  12  and the bonding surface M 4  of the frame portion  102  bonds the crystal frame  10  and the package lid  12  together. 
         [0044]    As noted above and shown in  FIGS. 2A and 2B , grooves  120  are defined on the bonding surface M 5 . During bonding, overflowing sealing material SL flows into the grooves  120  so that the cavity CT formed by bonding the crystal frame  10 , package base  11 , and package lid  12 , is hermetically sealed. 
         [0045]    In  FIG. 2A , the piezoelectric device  100 A has an outer surface that includes connection electrodes  118   a ,  118   b . The connection electrode  118   a  covers at least a portion of the exterior electrode  115   a , the edge-surface electrode  117   a , and the edge-surface electrode  107   a . Similarly, the connection electrode  118   b  covers at least a portion of the exterior electrode  115   b , the edge-surface electrode  117   b , and the edge-surface electrode  107   b . This structure allows the external electrodes  115   a ,  115   b , edge-surface electrodes  117   a ,  117   b , and the edge-surface electrodes  107   a ,  107   b  to be electrically connected. 
         [0046]    To stimulate vibration, an alternating voltage (voltage that alternates from positive to negative to positive . . . ) is applied across the external electrodes  115   a ,  115   b , and across the connection electrodes  118   a ,  118   b , all situated on the mounting surface M 1  of the package base  11  of the device  110 A. On the vibrating portion  101 , the external electrode  115   a , edge-surface electrode  117   a , connection electrode  118   a , inner electrode  107   a , and extraction electrode  105   a  all have the same instantaneous polarity, while the external electrode  115   b , edge-surface electrode  117   b , connection electrode  118   b , inner electrode  107   b , and extraction electrode  105   b , all have the same (but opposite) polarity. 
         [0047]    The piezoelectric device  100 A can be manufactured by a method depicted in  FIG. 3 .  FIG. 4  is a plan view of the crystal wafer  10 W,  FIG. 5  is a plan view of the base wafer  11 W, and  FIG. 6  is a plan view of the lid wafer  12 W. 
         [0048]    In protocol S 10  of the method, the quartz-crystal frame  10  is manufactured. Protocol S 10  includes steps S 101  to S 103 . In step S 101  the profile outlines of multiple quartz-crystal frames  10  are formed on a crystal wafer  10 W ( FIG. 4 ) by etching. I.e., the vibrating portion  101 , the exterior frame  102 , and the voids  103 ,  103   a  are formed. Also, as shown in  FIG. 4 , the first through-holes CH 1  are formed on the crystal wafer  10 W on each of the four corners of each crystal frame  10 . Dividing the first through-holes CH 1  into four respective quarter-round sections later in the method produces the castellations  106   a ,  106   b  ( FIG. 1 ). In step S 102 , a layer of chromium (Cr) is formed, followed by formation of an overlying layer of gold (Au), on the entire main surface of the quartz-crystal wafer  10 W, including in the through-holes CH 1 . These metal layers are formed by sputtering or vacuum-deposition. An exemplary thickness of the chromium foundation layer is in the range of 0.05 μm to 0.1 μm, and an exemplary thickness of gold layer is in the range of 0.2 μm to 2 μm. In step S 103  a photoresist is applied uniformly on the surface of the metal layer. Using an exposure tool (not shown), the profile outlines of the excitation electrodes  104   a ,  104   b , the extraction electrodes  105   a ,  105   b , and the edge-surface electrodes  107   a ,  107   b  are lithographically exposed onto the crystal wafer  10 W, followed by etching of the denuded regions of the metal layer. In  FIGS. 1 and 2 , the excitation electrodes  104   a ,  104   b , extraction electrodes  105   a ,  105   b , and edge-surface electrodes  107   a ,  107   b  are formed around the first through-holes CH 1 . 
         [0049]    In protocol S 11 , a package base  11  is manufactured. Protocol S 11  includes steps S 111 -S 113 . In step S 111 , a quartz-crystal wafer  11 W is prepared. Then, the through-holes BH 1  ( FIG. 5 ) are formed on the four corners of the package base  11  by etching so as to extend depthwise through the base wafer  11 W. The through-holes BH 1  form respective quarter-round castellations  116   a  or  116   b  ( FIG. 1 ) later in the method during dicing. 
         [0050]    In step S 112 , a layer of chromium (Cr) is formed, followed by formation of an overlying layer of gold (Au), on the mounting surface M 1  and the second through-holes BH 1  of the base wafer  11 W by sputtering or vacuum-deposition. An exemplary thickness of the chromium foundation layer is in the range of 0.05 μm to 0.1 μm, and an exemplary thickness of the gold layer is in the range of 0.2 μm to 2 μm. 
         [0051]    In step S 113 , a photoresist is applied uniformly on the surface of the metal layer. Using an exposure tool (not shown), the profile outlines of the external electrodes  115   a ,  115   b  and of the edge-surface electrodes  117   a ,  117   b  are exposed onto the base wafer  11 W. Then, the metal layer, exposed by patterning the photoresist, is etched. As shown in  FIGS. 1 and 2 , the external electrodes  115   a ,  115   b  are formed on the mounting surface M 1  of the base wafer  11 W, and the edge-surface electrodes  117   a ,  117   b  are formed on the second through-holes BH 1 . 
         [0052]    In protocol S 12 , package lids  12  are manufactured. Protocol S 12  includes a steps S 121 -S 122 . In step S 121 , a quartz-crystal lid wafer  12 W is prepared. Then, the through-holes DH 1  ( FIG. 6 ) are formed on the lid wafer  12 W by, etching on each of the four corners of each package lid  11  on the wafer. On the bonding surface M 5  of the lid wafer  12 W, communicating grooves  120  are formed that extend laterally from and communicate with the through-holes DH 1  on the lid wafer. The communicating grooves  120  extend from the through holes DH 1  at angles of 45°, 135°, 225°, and 315°, respectively ( FIG. 6 ). The width of each communicating groove  120  is in an exemplary range of 0.1 μm to 10 μm, and the depth of each communicating groove  120  is in an exemplary range of 0.1 μm to 10 μm. Each through-hole DH 1  forms four respective quarter-round castellations  126   a  or  126   b  ( FIG. 1 ) whenever the through holes are cut into four sections. Each communicating groove  120  is connected to a respective castellation  126 . 
         [0053]    The protocol S 10  for manufacturing quartz-crystal frames  10 , the protocol S 11  for manufacturing package bases  11 , and the protocol S 12  for manufacturing package lids  12  can be carried out in parallel. 
         [0054]    In step S 131 , a sealing material SL is applied uniformly on the surface M 3  of the exterior frame  102  on the quartz-crystal wafer  10 W ( FIG. 1 ). If the sealing material SL is LMP glass, it can be applied on the surface M 3  by screen-printing, followed by a preliminary curing step. If the sealing material SL is a polyimide resin, it can be applied as such on the surface M 3  of the exterior frame  102  followed by a temporary hardening step. The sealing material SL can be formed on the surface M 2  of the base wafer  11 W ( FIG. 1 ). 
         [0055]    In step S 132 , the quartz-crystal wafer  10 W and the base wafer  11 W are stacked in precise alignment with each other. Alignment is achieved by precisely checking the positions of the exterior profiles of the crystal frames on the quartz-crystal wafer  10 W, checking positions of the four corners formed by cutting through the through-holes CH 1  ( FIG. 4 ), and checking positions of the through holes BH 1  ( FIG. 5 ) formed on the base wafer  11 W. These positions can all be determined using a microscope. Upon achieving a desired alignment, the sealing material SL is heated to a temperature within an exemplary range of 350° C. to 400° C. while compressing the quartz-crystal wafer  10 W and the base wafer  11 W together. Thus, the quartz-crystal wafer  10 W and base wafer  11 W are bonded together. 
         [0056]    In step S 141 , sealing material SL is applied uniformly on the surface M 4  of each exterior frame  102  on the quartz-crystal wafer  10 W. After achieving a preliminary hardening of the sealing material SL the quartz-crystal wafer  10 W and lid wafer  12 W can be stacked precisely. 
         [0057]    Although the crystal wafer  10 W and the lid wafer  12 W are stacked, the sealing material SL does not yet flow into the communicating grooves  120 . Consequently, the cavity CT is in communication with the exterior environment through the communicating grooves  120  and the through-holes DH 1 . This communication allows the multiple package cavities defined by the package base wafer, the quartz-crystal wafer, and the lid wafer to be filled either with an inert gas (not shown) or to be evacuated to a desired vacuum level. Filling the package cavities with an inert gas or evacuating them is performed by placing the stacked wafers in a chamber evacuated to the desired level or filled with a desired inert gas. 
         [0058]    The sealing material SL is heated to a temperature in the exemplary range of 350° C. to 400° C. while compressing the quartz-crystal wafer  10 W and the lid wafer  11 W together. During this heating step, the sealing material SL may release unwanted gas. This gas is ventilated through the communicating grooves  120  on the lid wafer  12 W and through the through-holes DH 1 . As the quartz-crystal wafer  10 W and the lid wafer  12 W are being compressed against each other while increasing the temperature of the sealing material, some of the sealing material SL melts and flows into the communicating grooves  120 . Thus, the communicating grooves  120  are filled and sealed with the sealing material SL. After cooling the sealing material SL room temperature, the crystal wafer  10 W and the lid wafer  12 W are bonded together. 
         [0059]    In step S 142 , outer connection electrodes  118   a ,  118   b  are formed. 
         [0060]    In step S 143 , the 3-wafer sandwich comprising the crystal wafer  10 W, base wafer  11 W, and lid wafer  12 W bonded together is separated into individual piezoelectric devices  100 A. This separation desirably is performed by cutting along cut-lines CL, denoted by dot-dash lines in  FIGS. 4 ,  5 , and  6 . Cutting can be performed using a dicing unit such as a laser beam or a dicing saw. Thus, several hundreds to several thousands of piezoelectric devices  100 A are produced, each producing an accurate vibration frequency when electrically energized. 
       Second Embodiment of Piezoelectric Device 
       [0061]    The second embodiment of a piezoelectric device  100 B is shown in  FIGS. 7 and 8 .  FIG. 7  is an exploded perspective view of the piezoelectric device  100 B, wherein the view in  FIG. 7  is upside-down, with the package base  21  being shown uppermost.  FIG. 8  is an elevational section of a portion of  FIG. 7  along the line C-C′, after the crystal frame  20 , package base  21 , and package lid  22  have been bonded together. Connection electrodes ( FIG. 2 ) are not shown in  FIGS. 7 and 8 . 
         [0062]    In this embodiment  100 B the castellations and communicating grooves  120  have different positions than corresponding features in the first embodiment  100 A. Also, the quartz-crystal vibrating portion  201  of the crystal frame  20  as a different configuration than in the previous embodiment. The thickness of the quartz-crystal vibrating portion  201  and of the exterior frame  202  are the same as in the previous embodiment. Respective recesses are defined on the inner main surface of the package base  21  and of the package lid  22 , thereby forming the package cavity CT. In this embodiment, components that are similar to corresponding components in the first embodiment have the same reference numerals. 
         [0063]    This embodiment of a piezoelectric device  100 B includes the quartz-crystal frame  20 , a package base  21 , and a package lid  22 . The package base  21  and package lid  22  are fabricated of either glass or a quartz-crystal material. The quartz-crystal frame  20  and package base  21  are bonded together using a sealing material SL, and the quartz-crystal frame  20  and package lid  22  are bonded together using the sealing material SL. After bonding together these components, the package cavity CT ( FIG. 8 ) is either evacuated or filled with an inert gas. 
         [0064]    The frame  20  includes the bonding surfaces M 3  and M 4 . The frame  20  includes an exterior frame portion  202  that surrounds the vibrating portion  201 . On the main surfaces of the exterior frame  202 , excitation electrodes  104   a ,  104   b  and electrically conductive extraction electrodes  205   a ,  205   b  are formed, respectively. Respective castellations  206   a ,  206   b  are formed on each side of the crystal frame  20 , in the Z′-axis direction. Castellations  206   a ,  206   b  are connected to the extraction electrodes  205   a ,  205   b , respectively. Similarly, edge-surface electrodes  207   a ,  207   b  (connected to the edge-surface electrodes  217   a ,  217   b , respectively, on the package base  21 ) are formed. The castellations  206  are formed when the rectangular through-holes CH 2  ( FIG. 9 ) are cut during dicing. 
         [0065]    The package base  21  includes an external main surface (mounting surface) M 1  and an internal main surface (bonding surface) M 2 . A pair of external electrodes  215   a ,  215   b  are formed on the mounting surface M 1 . A respective castellation  216   a ,  216   b  is formed on each opposing edge (in the Z′-axis direction) of the package base  21 . A respective edge-surface electrode  217   a ,  217   b  is formed on the inner surface of each castellation  216   a ,  216   b , respectively, and connected to the respective external electrode  215   a ,  215   b . A recess  219  ( FIGS. 8 and 10 ) is defined in the internal main surface M 2  of the package base  21 . The castellations  216   a ,  216   b  are formed when corresponding rectangular through-holes BH 2  ( FIG. 10 ) are diced. 
         [0066]    The package lid  22  includes an internal main surface (bonding surface) M 5 . A respective castellation  226   a ,  226   b  is formed on each opposing edge (in the Z′-axis direction) of the package lid  22 . A recess  229  ( FIGS. 8 and 11 ) is defined in the internal main surface M 5  of the package lid  22 . The main surface M 5  also defines a respective communicating groove  120  extending between the recess  229  and the respective castellation  216   a ,  216   b . The castellations  226   a ,  226   b  are formed when corresponding rectangular through-holes DH 2  ( FIG. 11 ) are diced. 
         [0067]    The second embodiment of a piezoelectric device  100 B shown in  FIG. 7  is manufactured by method depicted by a flow-chart that is substantially similar to the flow-chart of  FIG. 3 .  FIG. 9  is a plan view of the quartz-crystal wafer  20 W,  FIG. 10  is a plan view of the base wafer  21 W, and  FIG. 11  is a plan view of the lid wafer  22 W. 
         [0068]    The method for manufacturing this second embodiment  100 B is described with reference to the flow-chart shown in  FIG. 3 . In the steps S 101 , S 111 , and S 121 , the rounded-rectangular through-holes CH 2 , BH 2 , and DH 2 , respectively, are formed. Also, the recess  219  is formed on the bonding surface of the package base  21 , and the recess  229  is formed on the bonding surface of the package lid  22 . 
         [0069]    Further with respect to step S 101 , as indicated in  FIG. 9 , the profile outlines of the multiple quartz-crystal frames  20  are defined by etching. A respective rounded-rectangular through-hole CH 2  is formed on each edge (Z′-axis direction) of each quartz-crystal frame  20 . Later, a dicing unit cuts through the quartz-crystal wafer  20 W and thus cuts the through-holes precisely in half. Each half forms a respective castellation  206   a ,  206   b  ( FIG. 7 ). 
         [0070]    In step S 111  (see  FIG. 10 ), a respective rounded-rectangular through-hole BH 2  is formed on each edge (Z′-axis direction) of each package base  21 . Later, a dicing unit cuts through the base wafer  21 W and thus cuts the through-holes DH 2  precisely in half. Each half forms a respective castellation  216   a ,  216   b  ( FIG. 7 ). Also, a recess  219  is defined in the bonding surface of the package base  21 . 
         [0071]    In step S 121  (see  FIG. 11 ), a respective rounded-rectangle through-hole DH 2  is formed on each edge (Z′-axis direction) of each package lid  22 . Later, a dicing unit cuts through the lid wafer  22 W while cutting the through-holes DH 2  precisely in half. Each half forms a respective castellation  226   a ,  226   b  ( FIG. 7 ). Also, a recess  229  is defined in the bonding surface of the package lid  22 . Communicating grooves  120  are defined in the bonding surface, extending between the recess  229  and the respective castellation  226   a ,  226   b.    
         [0072]    In both the first and second embodiments, although communicating grooves  120  are formed on the bonding surfaces of the respective package lids  12 ,  22 , the communicating grooves alternatively can be formed on the bonding surface M 4  of the quartz-crystal wafer. Also, in the flow-chart shown in  FIG. 3 , although the lid wafer and quartz-crystal wafer are bonded together after bonding together the base wafer and quartz-crystal wafer, the lid wafer and quartz-crystal wafer alternatively can be bonded together after bonding together the base wafer and quartz-crystal wafer. In this manufacturing step, the communicating grooves  120  can be formed on the bonding surface M 2  of the package base  11 ,  21 , or on the bonding surface M 3  of the quartz-crystal wafer. 
         [0073]    Further alternatively from the flow-chart of  FIG. 3 , the base wafer, quartz-crystal wafer, and lid wafer can be bonded together simultaneously. In such a method, the communicating grooves are formed in at least the bonding surface M 2  of the package base  11 ,  21 , the bonding surface M 5  of the package lid  12 ,  22 , or the bonding surface M 3  of the quartz-crystal wafer. 
       Third Embodiment of Piezoelectric Device 
       [0074]    A piezoelectric device  110  according to this embodiment is shown in  FIG. 12A  and a plan view with the package lid  50  removed.  FIG. 12B  is an elevational section along the line E-E′ in  FIG. 12A . The piezoelectric device  110  is a surface-mount type and comprises an insulative ceramic package  40  covered by a package lid  50 . The package lid  50  is fabricated of a kovar alloy or of glass. 
         [0075]    The ceramic package  40  includes a bottom-surface ceramic layer  41   a , a wall ceramic layer  41   b , and a mount ceramic layer  42 , all made of an alumina-based ceramic powder and green sheets including a binder. The ceramic package  40  comprises multiple ceramic layers  41   a ,  41   b . The package  40  defines a package cavity CT in which the AT-cut quartz-crystal vibrating piece  30  is mounted. Respective communicating grooves  120  extend on the upper main surface  41   c  of the ceramic wall  41   b , and communicate with the cavity CT. The ceramic package  40  is formed by stacking multiple, co-aligned ceramic layers, followed by exposing the stacked ceramic layers to a sintering condition. The ceramic package  40  includes surface-mountable external electrodes  115   a ,  115   b  located on the lower main surface BT. 
         [0076]    The AT-cut quartz-crystal vibrating portion  30  includes, on its first and second main surfaces, respective excitation electrodes  32   a ,  32   b . The vibrating portion  30  also includes respective connection electrodes  33 , on the first and second main surfaces, that are connected to respective excitation electrodes  32   a ,  32   b . The connection electrodes  33  are electrically connected to respective connection electrodes  43 ,  44 , and the AT-cut quartz-crystal vibrating piece  30  is bonded to a mount  42  (formed in the cavity CT) using electrically conductive adhesive  31 . 
         [0077]    This third embodiment  110  can be manufactured by an embodiment of a manufacturing method as shown in the flow-chart of  FIG. 13 . In protocol S 13 , the AT-cut quartz-crystal vibrating piece  30  is manufactured. Protocols S 40  (manufacturing the ceramic package  40 ) and S 50  (manufacturing the package lid  50 ) can be performed separately or in parallel. 
         [0078]    In protocol S 30 , an AT-cut quartz-crystal vibrating piece  30  is manufactured. Protocol S 30  includes steps S 301  to S 303 . In step S 301  multiple AT-cut quartz-crystal vibrating pieces  30  are formed on a quartz-crystal wafer  30 W (not shown) by lithography and etching. In step S 302  a layer of chromium (Cr) and an overlying layer of gold (Au) are formed on the entire main surface of a quartz-crystal wafer  30 W by sputtering or vacuum-deposition. The thickness of chromium foundation layer is in an exemplary range of 0.05 μm to 0.1 μm, and the thickness of gold layer is in an exemplary range of 0.2 μm to 2 μm. 
         [0079]    In step S 303 , a photoresist is applied uniformly on the surface of the metal film. Using an exposure tool (not shown), the outline pattern of the excitation electrodes  32   a ,  32   b , and of the connection electrodes  33  is exposed on the quartz-crystal wafer  30 W. Afterword, portions of the metal layer not protected by the photoresist are etched. As shown in  FIGS. 1 ,  2 A, and  2 B, the excitation electrodes  32   a ,  2   b  and the connection electrodes  33  are formed on the quartz-crystal wafer  30 W. The AT-cut quartz-crystal vibrating piece  30  is cut away from the quartz-crystal wafer  30 W. 
         [0080]    In protocol S 40 , the ceramic package  40  is manufactured according to steps S 401  to S 403 . In step S 401  layers are made of ceramic green sheets, including a bottom-surface ceramic layer  41   a , a wall-surface ceramic layer  41   b , and a mount ceramic layer  42  (see  FIG. 12 ). On the top surface  41   c  of the wall ceramic layer  41   b , communicating grooves  120  are formed that communicate with the cavity CT. On the ceramic layer  41   a  including the mount  42 , tungsten metal is printed on the ceramic green sheet thereof, destined for use as external electrodes  115 ,  115   b  and extraction electrodes  43 ,  44 . In step S 402 , a ceramic package  40  is formed by stacking multiple green ceramic layers and sintering them at a temperature over 1,300° C. After sintering, the ceramic package  40  is cut to predetermined sizes. In step S 403 , on the ceramic package  40 , a film of nickel is formed over a tungsten layer, and a film of gold is applied atop the tungsten layer. The extraction electrodes  43 ,  44  are formed on the lower main surface BT of the ceramic package  40  and the mount  42 . The external electrodes  115   a ,  115   b  are formed outside the ceramic package  40 . Extraction electrodes  43 ,  44  are connected to the respective external electrodes  115   a ,  115   b.    
         [0081]    In protocol S 50 , the package lid  50  is manufactured. Protocol S 50  includes steps S 501  to S 502 . In step S 501 , a package lid  50  made of glass or kovar alloy is formed. In step S 502 , a sealing material SL is prepared and uniformly applied so as to extend peripherally around the package lid  50 . For example, if the sealing material SL is low-melting-point (LMP) glass, the LMP glass is applied peripherally around the package lid  50  by screen-printing, for example, and preliminarily cured. If the sealing material SL is polyimide resin, the resin is applied peripherally around the package lid  50  and preliminarily cured. 
         [0082]    In step S 151  the AT-cut quartz-crystal vibrating pieces  30  are disposed on respective extraction electrodes  43  on the mount  42  of the ceramic package  40 , and bonded thereto using electrically conductive adhesive  31 . In step S 152  the package lid  50  is placed inside the ceramic package  40  in the package chamber CT. Before completion of packaging, the package chamber CT will be either evacuated or filled with an inert gas. The ceramic package  40  and package lid  50  are heated in a vacuum or in an inert gas environment at a temperature in the exemplary range of 350° C. to 400° C. while simultaneously compressing the lid and ceramic package together. 
         [0083]    Whenever the ceramic package  40  and package lid  50  are stacked precisely relative to each other, the sealing material SL does not flow into the communicating grooves  120 , which can allow the cavity CT to communicate with the outside environment. This property is exploited during bonding by placing a wafers in a chamber filled with inert gas (not shown) or evacuated to a desired vacuum level (not shown). In the chamber the sealing material SL is heated to a temperature in the exemplary range of 350° C. to 400° C. while compressing the ceramic package  40  and package lid  50  together. During heating, unwanted gas released from the sealing material SL does not remain in the cavity CT; rather, the gas is ventilated through the communicating grooves  40  in the ceramic package  40 . As the ceramic package  40  and package lid  50  are being compressed against each other while the temperature of the sealing material SL is rising, molten sealing material SL flows into the communicating grooves  120 . Thus, the communicating grooves  120  are sealed by the sealing material SL in this method. After cooling the sealing material SL to room temperature, the ceramic package  40  and the package lid  50  are bonded firmly together. 
         [0084]    Representative embodiments have been described in detail above. As evident to those skilled in the art, the present invention may be changed or modified in various ways within the technical scope of the invention. For example, as an alternative to AT vibrating pieces, the present invention may be directed to the manufacture of tuning-fork type vibrating pieces. In this specification, although the various embodiments have been described in the context of AT-cut quartz-crystal vibrating pieces, it will be understood that the embodiments can be applied with equal facility to piezoelectric materials such as lithium tantalite and lithium niobate. Furthermore, the present disclosure can be applied to piezoelectric oscillators that also include an IC configured as an oscillating circuit mounted inside the package on the package base.