Abstract:
Piezoelectric vibrating devices are disclosed that lack base through-holes and that can be manufactured on a wafer scale. Also disclosed are methods for making same. An exemplary piezoelectric device has a package base having first and second opposing main surfaces. On the second (outer) first main surface is formed a pair of external electrodes. The first (inner) main surface defines a first recess and a peripheral first bonding surface. A pair of connecting electrodes are provided for connecting to the respective external electrodes via respective edge surfaces of the package base that extend between the first and second main surfaces. A piezoelectric vibrating piece is mounted in and contained within the package base. The vibrating piece includes a pair of excitation electrodes electrically connected to respective connecting electrodes. A package lid comprises first and second main surfaces, of which the second (inner) main surface defines a second recess that is larger than the first recess. The second main surface also defines a second bonding surface that peripherally surrounds the second recess. A sealing material is applied, over the width of the second bonding surface, circumferentially between the first bonding surface and the second bonding surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Japan Patent Application No. 2010-184612, filed on Aug. 20, 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, methods for manufacturing piezoelectric devices, in which methods the piezoelectric vibrating piece is mounted onto a package manufactured as a lid wafer or base wafer. The disclosure also pertains to piezoelectric vibrating devices produced by such methods. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    As shown in Japan Unexamined Patent Publication No. 2005-333037, a surface-mountable type of piezoelectric device comprises a ceramic base having an insulating property. The base is fabricated of an alumina ceramic. A lid, fabricated of glass or of a kovar alloy, is affixed to the open portion of the ceramic base. The ceramic base and lid thus form a cavity that contains the piezoelectric vibrating piece sealed in the cavity. 
         [0004]    In Japan Unexamined Patent Publication No. 2005-057520, the base can be fabricated of glass instead of a ceramic, so as to achieve cost reduction. The glass base and lid are bonded together using a low-melting-point glass. 
         [0005]    Piezoelectric devices as disclosed in the JP &#39;037 reference comprise a base made of a ceramic. Consequently, manufacturing these devices requires performing a manufacturing step on each ceramic piece, which is disadvantageous from the perspective of cost reduction. In the JP &#39;520 reference, as noted, the piezoelectric device comprises a base made of glass; again, the manufacturing method for producing these devices requires performing a manufacturing step on each piece, which is disadvantageous for mass production. Also, the piezoelectric devices disclosed in JP &#39;520 require forming a through-hole on each glass base and forming a connecting electrode having a thickness of at least 30 μm on the main surface of the glass base to prevent the piezoelectric vibrating piece and the glass base from contacting each other. Consequently, the piezoelectric devices disclosed in the JP &#39;520 have higher manufacturing costs despite the fact that the base is fabricated of inexpensive glass. 
         [0006]    The present disclosure provides, inter alia, piezoelectric devices that do not require through-holes in their bases and that can be manufactured at a wafer scale (in which hundreds to thousands of bases can be manufactured simultaneously. The present disclosure also provides methods for manufacturing piezoelectric device, in which connecting electrode can be fabricated having a thickness (several hundred nm), formed by sputtering or vacuum-deposition. 
       SUMMARY 
       [0007]    A first aspect of the invention pertains to piezoelectric devices, of which a representative embodiment comprises a package base, a piezoelectric vibrating piece, and a package lid. The package base has a rectangular profile and includes an outer main surface including a pair of external electrodes and an inner main surface situated opposite the outer main surface. The inner main surface defines a first recess and a first bonding surface peripherally surrounding the first recess, and includes respective connecting electrodes electrically connected to the external electrodes. The piezoelectric vibrating piece is mounted to the inner main surface of the package base and includes respective excitation electrodes electrically connected to the connecting electrodes. The package lid defines a second recess and a second bonding surface. The second bonding surface has a width and peripherally surrounds the second recess. The second recess is larger than the first recess. The package lid covers the piezoelectric vibrating piece mounted to the package base. A sealing material, having a width substantial equal to the width of the second bonding surface, is disposed circumferentially between the first bonding surface and the second bonding surface, thereby sealing the package lid to the package base. 
         [0008]    The package base desirably has a rectangular plan profile, when viewed from above, that includes first and second opposing edges. Each edge has a length and defines a respective castellation having a length greater than half the length of the respective side. In certain embodiments each connecting electrode is situated in a respective one of said castellations, in which each connecting electrode has greater length than half the length of the respective castellation. 
         [0009]    According to another aspect, methods are provided for manufacturing a piezoelectric device. An embodiment of such a method comprises preparing a base wafer comprising multiple package bases each having a rectangular profile. Each package base comprises an outer main surface and an inner main surface situated opposite the outer main surface. On each package base, a pair of external electrodes is formed on the outer main surface and a first recess is formed on the inner main surface, wherein the first recess is surrounded by a peripheral first bonding surface of the inner main surface, and the peripheral first bonding surface has a respective width. On the base wafer, a pair of through-holes is formed between each pair of adjacent package bases on the base wafer. Each through-hole has a rectangular profile and extends from the inner main surface to the outer main surface. On the base wafer, respective connecting electrodes are formed and electrically connected to the external electrodes through the respective through-holes. With respect to each package base on the base wafer, a piezoelectric vibrating piece is mounted that has a pair of excitation electrodes. The piezoelectric vibrating pieces are mounted to the package base such that the excitation electrodes are electrically connected to the respective connecting electrodes on the package base. A lid wafer is prepared that comprises multiple package lids each having an inner main surface defining a second recess and an outer main surface situated opposite the inner main surface. The second recess is surrounded by a peripheral second bonding surface of the inner main surface. The second bonding surface has a respective width, and the second recess is larger than the first recess. The lid wafer and base wafer are aligned such that each first bonding surface is registered with each respective second bonding surface. A sealing material is applied on the respective first or second peripheral bonding surfaces of the base wafer or the lid wafer, wherein the sealing material is applied circumferentially at a width that is substantial equal to the width of the second bonding surface. The base wafer and lid wafer are heated and compressed together to bring respective registered first and second bonding surfaces together and to cause the sealing material to form a sealed bond between each respective first and second bonding surfaces, thereby forming a wafer sandwich containing multiple piezoelectric vibrating devices. 
         [0010]    In some embodiments the step of mounting the piezoelectric vibrating pieces comprises mounting the piezoelectric vibrating piece to the respective connecting electrodes using an electrically conductive adhesive. 
         [0011]    After heating and compressing the wafers together, the method desirably comprises the step of cutting the wafer sandwich along pre-established scribe lines after the heating and compression step, wherein the scribe lines extend through co-registered through-holes of adjacent piezoelectric vibrating devices on the wafer sandwich. 
         [0012]    The sealing material desirably is an adhesive made of glass that melts at temperature between 350° C. and 410° C. 
         [0013]    Before bonding the wafers together, the method can include the steps of contacting a respective probe of a frequency-measurement device to each connecting electrode or external electrode of a piezoelectric vibrating device and measuring a vibration frequency of each piezoelectric vibrating piece. 
         [0014]    In some embodiments each piezoelectric vibrating piece has respective sides on which the through-holes were formed, wherein each through-hole is formed as a respective elongated circle having length of ⅓ to ½ of the respective side. 
         [0015]    In some embodiments each connecting electrode has a width of at least half the length of the respective through-hole. 
         [0016]    As summarized above, the various aspects provide, inter alia, piezoelectric devices that can be manufactured at a wafer level, which allows reduction of manufacturing cost. Also, the absence of toxic gas or water vapor inside the piezoelectric device allows mass-production of the piezoelectric device. Further, due to the absence of toxic gas or water vapor, the piezoelectric vibrating piece vibrates or oscillates with high stability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an exploded perspective view of a first embodiment of a quartz-crystal vibrating device. 
           [0018]      FIG. 2  is a perspective view of the first embodiment of a quartz-crystal vibrating piece after mounting a quartz-crystal vibrating piece  10  onto the package base  12  and before bonding a package lid  11  to the package base  12 .  FIG. 2  also shows the quartz-crystal vibrating piece  10  in a condition suitable for measuring its vibration frequency. 
           [0019]      FIG. 3A  is a cross-sectional view of the device shown in  FIG. 1 , along the line A-A in  FIG. 1 . 
           [0020]      FIG. 3B  is a plan view of the lower main surface of the first embodiment of a quartz-crystal vibrating device. 
           [0021]      FIG. 4  is a flow-chart of an embodiment of a method for manufacturing a quartz-crystal vibrating device  100  according to the first embodiment. 
           [0022]      FIG. 5  is a plan view of a quartz-crystal wafer on which multiple quartz-crystal vibrating pieces are manufactured simultaneously. 
           [0023]      FIG. 6  is a plan view of a lid wafer  11 W on which multiple lids are manufactured simultaneously. 
           [0024]      FIG. 7  is a plan view of base wafer  12 W on which multiple bases are manufactured simultaneously. 
           [0025]      FIG. 8A  is a perspective view of the first embodiment of a quartz-crystal vibrating device after mounting the quartz-crystal vibrating piece onto the package base and before bonding together the package lid and the package base. 
           [0026]      FIG. 8B  is a plan view of the lower main surface of the first embodiment of a quartz-crystal vibrating device. 
           [0027]      FIG. 9  is a plan view of the undersurface of a base wafer. 
           [0028]      FIG. 10  is an exploded perspective view of the second embodiment of a quartz-crystal vibrating device. 
           [0029]      FIG. 11  is a perspective view of the second embodiment of a quartz-crystal vibrating device after mounting a quartz-crystal vibrating device onto the package base but before bonding together the package lid and package base.  FIG. 11  also shows the vibration frequency of the piezoelectric vibrating piece being measured. 
           [0030]      FIG. 12A  is a cross-sectional view of the second embodiment along the line B-B in  FIG. 10 . 
           [0031]      FIG. 12B  is a plan view of the lower main surface of the second embodiment of a quartz-crystal vibrating device. 
           [0032]      FIG. 13  is a plan view of a quartz-crystal wafer  20 W on which multiple vibrating pieces can be manufactured simultaneously. 
           [0033]      FIG. 14  is a plan view of the base wafer on which multiple package bases can be manufactured simultaneously. 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment of Quartz-Crystal Vibrating Piece 
       [0034]    The general configuration of a first embodiment of a quartz-crystal vibrating device  100  is described below with reference to  FIGS. 1 ,  2  and  3 A- 3 B.  FIG. 1  is an exploded perspective view of the first embodiment of a quartz-crystal vibrating device  100 ;  FIG. 2  is a perspective view of the first embodiment of a quartz-crystal vibrating piece  100  as used in the first embodiment, after mounting the vibrating piece  10  onto the package base  12  and before bonding the package lid  11  to the package base  12 .  FIG. 3A  is a cross-sectional view of the first embodiment along the line A-A in  FIG. 1 , and  FIG. 3B  is a plan view of the lower main surface of the first embodiment of a quartz-crystal vibrating device  100 . 
         [0035]    In the embodiments described below, an AT-cut quartz-crystal vibrating piece  10  is used as the piezoelectric vibrating piece. An AT-cut quartz-crystal vibrating piece has a principal surface (in the YZ 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 first embodiment, new axes tilted with respect to the axial directions of the quartz-crystal vibrating piece are denoted as the Y′-axis and Z′-axis, respectively. Therefore, in the first embodiment, the longitudinal direction of the quartz-crystal vibrating device  100  is referred as the X-axis direction, the height direction of the vibrating device  100  is referred as the Y′-axis direction, and the direction normal to the X-axis and Y′-axis directions is referred as the Z′-axis direction, respectively. 
         [0036]    Turning first to  FIG. 1 , the first embodiment of a quartz-crystal vibrating device  100  comprises a package lid  11  defining a lid recess  111  configured as a concavity in the inner main surface of the package lid  11 , a package base  12 , and a quartz-crystal vibrating piece  10  mounted on the package base  12 . The quartz-crystal vibrating piece  10  comprises an AT-cut quartz-crystal piece  101 . A respective excitation electrode  102   a ,  102   b  is situated substantially in the center of the quartz-crystal piece  101  on both main surfaces thereof. Each excitation electrode  102   a ,  102   b  is connected to a respective extraction electrode  103   a ,  103   b  extending in a respective X-direction on the −Y′-side of the quartz-crystal piece  101 . 
         [0037]    An exemplary length L 6  of the quartz-crystal vibrating piece  10  in the X-axis direction is approximately 2,400 μm. An exemplary width W 6  in the Z′-axis direction is approximately 1,500 μm, and exemplary height H 6  in the Y′-axis direction is approximately 100 μm. Each excitation electrode and extraction electrode comprises a foundation layer of chromium (Cr) with an overlying layer of gold. An exemplary thickness of the chromium 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. 
         [0038]    The package base  12  comprises a first peripheral surface M 1  on the upper main surface (+Y′-side surface). The first peripheral surface circumscribes a base recess  121 . On both edges of the package base  12  in respective X-axis directions, respective base castellations  122   a ,  122   b  are formed. The castellations  122   a ,  122   b  are formed simultaneously with formation of the base through-holes BH 1  (refer to  FIG. 7 ), and extend in the Z′-axis direction. On the base castellations  122   a ,  122   b  are respective base edge-surface electrodes  123   a ,  123   b  (refer to  FIG. 3A ). A connecting electrode  124   a , situated on the first peripheral surface M 1  and extending in the −X-axis direction on the package base  12 , is electrically connected to the respective base edge-surface electrode  123   a . Similarly, a connecting electrode  124   b , situated on the first peripheral surface M 1  and extending in the +X-axis direction on the package base  12 , is electrically connected to the respective base edge-surface electrode  123   b . The package base  12  also comprises a pair of mounting terminals  125   a ,  125   b , which are electrically connected to respective base edge-surface electrodes  123   a ,  123   b.    
         [0039]    As shown in  FIG. 2 , an exemplary length L 1  of the package base  12  in the X-axis direction is approximately 3,200 μm. An exemplary width W 1  in the Z′-axis direction is approximately 2,500 μm, and an exemplary height H 3  in the Y′-axis direction is approximately 300 μm. The length W 2  of the base castellations  122   a , and  122   b  in the Z′-axis direction is approximately ⅓ to ½ of the width W 1  of the package base. Consequently, the length W 2  is approximately 800 μm to 1,300 μm. The length W 3  of the connecting electrodes  124   a ,  124   b  in the Z′-axis direction is between the same length to ½ of the length W 2  of the base castellations  122   a ,  122   b . Consequently, the length W 3  is approximately 700 μm to 1,300 μm. 
         [0040]    As shown in  FIG. 3A , the length L 5  of the base recess  121  in the X-axis direction is approximately 2,210 μm, which is shorter than the length L 6  of the quartz-crystal vibrating piece  10  in the X-axis direction. The depth of the base recess  121  is approximately 40 μm. The base edge-surface electrodes and respective connecting electrodes and mounting terminals have the same configurations as the respective excitation electrodes and extraction electrodes. 
         [0041]    In view of the foregoing, the length L 6  (2,400 μm) of the first embodiment of a quartz-crystal vibrating device  100  is greater than the length L 5  (2,210 μm) of the base recess  121 . As a result, when mounting the quartz-crystal vibrating piece  10  onto the package base  12  using electrically conductive adhesive  13 , both ends of the quartz-crystal vibrating piece  10  in the X-axis direction are mounted onto the first peripheral surface M 1  of the package base  12 . As shown in  FIG. 3A , during bonding, the extraction electrodes  103   a ,  103   b  on the quartz-crystal vibrating piece  10  are electrically connected to respective connecting electrodes  124   a ,  124   b  on the package base  12 . Thus, the mounting terminals  125   a ,  125   b  are electrically connected to the respective excitation electrodes  102   a ,  102   b  via the respective base edge-surface electrodes  123   a ,  123   b  and respective connecting electrodes  124   a ,  124   b , electrically conductive adhesive  13 , and extraction electrodes  103   a ,  103   b . Whenever an alternating voltage is applied across the mounting terminals  125   a ,  125   b , the quartz-crystal vibrating device  10  exhibits thickness-shear vibration. 
         [0042]    Since the connecting electrodes  124   a ,  124   b  on the package base  12  spread in width (dimension W 3 : over 700 μm), the extraction electrodes  124   a ,  124   b  can be more widely connected to the respective connecting electrodes  124   a ,  124   b . This ensures that the extraction electrodes  103   a ,  103   b  and connecting electrodes  124   a ,  124   b  are electrically connected together reliably and with low line resistance. As also shown in  FIG. 2 , the vibration frequency of the quartz-crystal vibrating piece  10  can be measured by contacting probes PB 1  and PB 2  of a frequency-measuring device to the connecting electrodes  124   a ,  124   b . Since the areas of the connecting electrodes  124   a ,  124   b  are relatively large, the vibration frequency of the quartz-crystal vibrating piece  10  can be measured easily and precisely. 
         [0043]    Turning now to  FIG. 3B , a respective mounting terminal  125  is situated on each of the four corners of the lower (mounting) main surface of the package base  12 . Of the four terminals, the mounting terminals  125   a ,  125   b  are electrically connected to the base edge-surface electrodes  123   a ,  123   b , respectively, and the remaining two mounting terminals are used as electrical-ground terminals. 
         [0044]    As shown in  FIGS. 1 ,  2 , and  3 A- 3 B, the quartz-crystal vibrating device  100  defines a cavity CT in which the quartz-crystal vibrating piece  10  is situated. The cavity CT is defined in part as a concavity in the inner main surface of the package lid  111  and in part by the base recess  121  of the package base  12 . The cavity CT is filled with an inert-gas or is under a vacuum. 
         [0045]    The package lid  11  comprises a second peripheral surface M 2  on the main surface thereof facing in the −Y′-axis direction. The surface M 2  extends around the periphery of the lid recess  111 . The second peripheral surface M 2  of the package lid  11  is bonded onto the first peripheral surface M 1  of the package base  12  using a non-electrically conductive adhesive, for example, a low-melting-point glass LG. 
         [0046]    Low-melting-point glass LG is a lead-free vanadium-based glass having an adhesive component that melts at 350° C. to 400° C. Vanadium-based glass can be formulated as a paste mixed with binder and solvent. Vanadium-based glass bonds to various materials by melting and solidification. The melting point of a vanadium-based glass is lower than the melting point of the package lid  11  or the melting point of the package base  12 . Low-melting-point glass forms a highly reliable air-tight seal and resists water and humidity. Vanadium-based glass resists incursion of atmospheric water vapor into the cavity CT and thus prevents moisture-caused damage to the airtightness of the cavity CT. Also, since the coefficient of thermal expansion of low-melting-point glass can be controlled effectively by controlling its glass structure, the low-melting-point glass can adjust to various coefficients of thermal expansion. 
         [0047]    Although similar to the package base  12 , the package lid  11  has an exemplary length L 1  in the X-axis direction of approximately 3,200 μm and a width W 1  (in the Z′-axis direction) of approximately 2,500 μm. The height H 2  in the Y′-axis direction is approximately 450 μm. The length L 4  of the lid recess  111  in the X-axis direction is approximately 2,600 μm, which is greater than the length L 6  of the quartz-crystal vibrating piece  10  in the X-axis direction. The depth of the lid recess  111  is approximately 250 μm. 
         [0048]    In view of the foregoing, the length L 4  of the lid recess  111  (2,600 μm) is greater than the length L 6  (2,600 μm) of the quartz-crystal vibrating piece  10  and the length L 5  (2,210 μm) of the package base  121 . Therefore, as shown in  FIGS. 1 and 3A , the low-melting-point glass LG bonds the package lid  11  and the package base  12  on the outer portions of the first peripheral surface M 1  (having a width of approximately 300 μm) of the package base  12 . 
       Method for Manufacturing the First Embodiment of Quartz-Crystal Vibrating Piece 
       [0049]      FIG. 4  is a flow-chart of an embodiment of a method for manufacturing the first embodiment of a quartz-crystal vibrating device  100 . In  FIG. 4 , the protocol S 10  for manufacturing the quartz-crystal vibrating piece  10 , the protocol S 11  for manufacturing the package lid  11 , and the protocol S 12  for manufacturing the package base  12  can be carried out separately or in parallel.  FIG. 5  is a plan view of the quartz-crystal wafer  10 W,  FIG. 6  is a plan view of the lid wafer  11 W, and  1 G.  7  is a plan view of the base wafer  12 W. 
         [0050]    In protocol S 10 , the quartz-crystal vibrating piece  10  is manufactured. The protocol S 10  includes steps S 101  to S 103 . In step S 101  (see  FIG. 5 ) the profile outlines of a plurality of quartz-crystal vibrating pieces  10  are formed on a planar quartz-crystal wafer  10 W by etching. Each quartz-crystal vibrating piece  10  is connected to the quartz-crystal wafer  10 W by a respective joining portion  104 . 
         [0051]    In step S 102  a layer of chromium is formed, followed by formation of an overlying layer of gold, on both main surfaces and side surfaces of the entire quartz-crystal wafer  10 W by sputtering or vacuum-deposition. Then, 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 and of the extraction electrodes are lithographically exposed onto the crystal wafer  10 W. Next, regions of the metal layer are denuded by etching. As shown in  FIG. 5 , etching forms the excitation electrodes  102   a ,  102   b  and extraction electrodes  103   a ,  103   b  on both main surfaces and side surfaces of the quartz-crystal wafer  10 W (refer to  FIG. 1 ). 
         [0052]    In step S 103  the quartz-crystal vibrating pieces  10  on the crystal wafer are cut to separate individual devices. During cutting, cuts are made along cut lines CL (denoted by dot-dash lines in  FIG. 5 ) using a dicing unit such as a laser beam or dicing saw. 
         [0053]    In protocol S 11 , the package lid  11  is manufactured. Protocol S 11  includes steps S 111  and S 112 . In step S 111  several hundreds to several thousands of lid recesses  111  are formed on a main surface of a lid wafer  11 W, the latter being a circular, uniformly planar plate of quartz-crystal material. The lid recesses  111  are formed in the lid wafer  11 W by etching or mechanical processing, leaving the first peripheral surfaces M 1  around the lid recesses  111 . 
         [0054]    As shown in  FIG. 6 , in step S 112  low-melting point glass LG is printed on the second peripheral surface M 2  of the lid wafer  11 W by screen-printing. A film of low-melting-point glass is formed on the second peripheral surface M 2  of the lid wafer  11 W and preliminarily cured. 
         [0055]    In protocol S 12 , package bases  12  are manufactured. Protocol S 12  includes steps S 121  and S 122 . In step S 121 , as shown in  FIG. 7 , several hundreds to several thousands of base recesses  121  are formed on the base wafer  12 W, the latter being a circular, uniformly planar plate of quartz-crystal material. On the base wafer  12 W, multiple base recesses  121  are formed by etching or mechanical processing. The first peripheral surfaces M 1  circumscribe the respective base recesses  121 . Also formed are respective rounded-rectangular through-holes BH 1  on each edge of the package base  12  in respective X-axis directions. The through-holes extend depthwise through the base wafer  12 W. Whenever a base through-hole BH 1  is cut in half during dicing, it forms a respective base castellation  122   a ,  122   b  (refer to  FIG. 1 ). 
         [0056]    In step S 122 , as shown in  FIG. 7 , the mounting terminals  125  are formed on the mounting surface (lower or outer main surface of the quartz-crystal vibrating device) at each corner of the package base  12  by sputtering and etching (i.e., the same method as used in step S 102 ). Simultaneously, the base edge-surface electrodes  123   a ,  123   b  are formed in the base through-holes BH 1 , and the connecting electrodes  124   a ,  124   b  are formed on the second edge-surface M 2 . 
         [0057]    In step S 13 , the quartz-crystal vibrating piece  10  (manufactured in protocol S 10 ) is mounted onto the first peripheral surface M 1  of the package base  12  using electrically conductive adhesive. The quartz-crystal vibrating piece  10  is mounted onto the first peripheral surface M 1  of the package base  12  so as to align the extraction electrodes  103   a ,  103   b  formed on the quartz-crystal vibrating piece  10  with respective connecting electrodes  124   a ,  124   b  formed on the first peripheral surface M 1  of the package base  12 . Since the areas for connecting the respective electrodes are relatively large, the extraction electrodes  103   a ,  103   b  are electrically connected to their respective connecting electrodes  124   a ,  124   b  with high reliability (refer to  FIG. 2 ). 
         [0058]    In step S 14  probes PB 1 , PB 2  for measuring vibration frequency are contacted to respective connecting electrodes  124   a ,  124   b , and thus the vibration frequency of each quartz-crystal vibrating piece  10  is measured. Thus, the vibration frequency of each quartz-crystal vibrating piece  10  can be measured easily and precisely since the respective areas of the connecting electrodes  124   a ,  124   b  are relatively large. In step S 14 , the probes PB 1 , PB 2  for measuring vibration frequency are touched to respective connecting electrodes  124   a ,  124   b ; alternatively, the probes can be touched to the mounting terminals  125   a ,  125   b  for measuring vibration frequency. 
         [0059]    In step S 15  the thickness of the excitation electrode  102   a  on the quartz-crystal vibrating piece  10  is adjusted. The thickness can be adjusted by sputtering a metal onto the electrode to increase its mass (and to decrease its vibration frequency), or by evaporating some metal from the excitation electrode  102   a  to decrease its mass (and to increase its vibration frequency). This method for adjusting vibration frequency is discussed in Japan Unexamined Patent Document 2009-141825, in which the assignee is the same as the assignee of the present disclosure. If the measured vibration frequency is within its pre-specified proper range, then adjustment of vibration frequency is not required. 
         [0060]    Several hundreds to several thousands of quartz-crystal vibrating pieces  10  are formed simultaneously on a single base wafer  12 W. Measurement of the vibration frequency of each quartz-crystal vibrating piece  10  on the wafer (step S 14 ) is followed in step S 15  by adjustment (as required) of the vibration frequency of the particular quartz-crystal vibrating piece  10  (step S 15 ). This sequence is repeated for all of the quartz-crystal vibrating pieces  10  on the base wafer  12 W. Alternatively, step S 14  can be conducted on each quartz-crystal vibrating piece  10  on the base wafer  12 W, followed by performing step S 15  on each quartz-crystal vibrating piece  10  on the base wafer  12 W. 
         [0061]    In step S 16  the low-melting-point glass LG is heated as the lid wafer  11 W and base wafer  12 W are compressed against each other. Thus, the lid wafer  11 W and base wafer  12 W are bonded together by the low-melting-point glass LG. 
         [0062]    In step S 17  the bonded-together lid wafer  11 W and base wafer  12 W is cut up to separate individual quartz-crystal vibrating devices  100  from the wafer and from each other. This cutting is performed by cutting along scribe lines SL, denoted by dot-dash lines in  FIGS. 6 and 7 , using a dicing unit such as a laser beam or a dicing saw. Thus, several hundreds to several thousands of quartz-crystal piezoelectric vibrating devices  100  are produced. 
       Alternative to First Embodiment of Piezoelectric Vibrating Device 
       [0063]    This alternative configuration of the first embodiment of a piezoelectric vibrating device  100 ′ is described with references to  FIGS. 8A-8B  and  9 .  FIG. 8A  is a perspective view of the vibrating device  100 ′ after the quartz-crystal vibrating piece  10  has been mounted onto the package base  12 ′ but before bonding the package lid  11  to the package base  12 ′.  FIG. 8B  is a plan view of the lower main surface of the quartz-crystal vibrating device  100 ′, and  FIG. 9  is a plan view of the lower main surface of the base wafer  12 W′ used for producing multiple vibrating devices  100 ′ simultaneously. 
         [0064]    As shown in  FIG. 8A , the base edge-surface electrodes  123   a ′,  123   b ′ are not formed on the entire surfaces of the respective castellations  122   a ,  122   b  on the package base  12 ′. Rather, these electrodes as formed have substantially the same width as the connecting electrodes  124   a ,  124   b  in the Z′-axis direction. Therefore, the mounting terminals  125   a ′,  125   b ′ and  125 ′, shown in  FIG. 8B , are disposed to leave spaces  127  near the edges of the package base  12 ′ in the X-axis directions. Similarly, the mounting terminals  125   a ′,  125   b ′, and  125 ′ are disposed so as to form spaces  128  near the edges of the package base  12 ′ in the Z′-axis directions. 
         [0065]    According to this configuration, as indicated in  FIG. 9 , each mounting terminal attached to each package base  12 ′ disposed on the base wafer  12 W′ is formed apart from all other mounting terminals. This prevents adjacent mounting terminals formed on the package base  12 ′ from electrically contacting each other. Consequently, when the vibration frequencies of the quartz-crystal vibrating pieces  10  on the base wafer are measured using the probes PB 1 , PB 2  (refer to  FIG. 2 ), each quartz-crystal vibrating piece is not affected by other quartz-crystal vibrating pieces mounted on adjacent package bases  12 ′. This allows the respective vibration frequencies of the quartz-crystal vibrating pieces to be measured more precisely. 
       Second Embodiment of Quartz-Crystal Vibrating Device 
       [0066]    The overall configuration of the second embodiment of a quartz-crystal vibrating device  200  is explained with reference to  FIGS. 10 ,  11 , and  12 A- 12 B. The second embodiment of a quartz-crystal vibrating device  200  comprises a tuning-fork type quartz-crystal vibrating piece  20 . Consequently, its coordinates do not correspond to the coordinates for the AT-cut coordinates used in the first embodiment. Therefore, in  FIGS. 10 ,  11 ,  12 A- 12 B,  13 , and  14 , the same X-axis direction is used, but the extension direction of the vibrating arms  205  is referred as the Y-axis direction and the direction normal to both the X-axis direction and Y-axis direction is referred to as the Z-axis direction. 
         [0067]    Turning to  FIG. 10 , the second embodiment of a quartz-crystal vibrating device  200  comprises a package lid  21 , a lid recess  211  defined by a concavity of the inner main surface of the package lid  21 , a package base  22 , a base recess  221  defined by a concavity of the inner main surface of the package base  22 , and a tuning-fork type quartz-crystal vibrating piece  20 . The vibrating piece  20  comprises a pair of vibrating arms  205 , which are mounted on the package base  22 . 
         [0068]    The tuning-fork type quartz-crystal vibrating piece  20  comprises a base  204  formed on the −Y-axis side of the vibrating arms  205 . The base  204  has a nearly rectangular-shape as viewed from the Z-axis direction. The vibrating arms  205  extend from one side of the base  204  in the +Y-axis direction. The cross-section of a vibrating arm  205  is nearly rectangular in shape. On each vibrating arm, a respective excitation electrode  202   a ,  202   b  is formed on each upper surface, each lower surface, and on both side surfaces. A respective groove  207 , extending in the Y-axis direction, can be formed on each upper surface and each lower surface of each vibrating arm  205 . Whenever the excitation electrodes extend into the respective grooves  207 , the electrical field generated on the vibrating arms  205  is enhanced, which reduces the crystal impedance (CI). Each vibrating arm  205  also can include a weight  208  on the distal end of the vibrating arms  205  (in the +Y-axis direction). The weights  208  are formed so that the vibrating arms  205  on the tuning-fork type quartz-crystal vibrating piece  20  can vibrate easier. The weights  208  also facilitate adjustment of vibration frequency of the arms. The tuning-fork type quartz-crystal vibrating piece  20  is distinctly small, and exhibits a vibration frequency of, for example, 32.768 kHz. 
         [0069]    The tuning-fork type quartz-crystal vibrating piece  20  comprises a respective supporting arm  206   a ,  206   b  associated with each vibrating arm  205   a ,  205   b . Each supporting arm extends from the base  204  outward in the X-axis direction and then in the Y-axis direction to about mid-length of the vibrating piece  20 . The distal tip of each supporting arm extends further in the X-axis directions. The supporting arms  206   a ,  206   b  prevent vibrations produced by the vibrating arms  205  from propagating outside the quartz-crystal vibrating device  200 . The supporting arms  206   a ,  206   b  also enhance the resistance of the vibrating piece to physical and thermal shocks while being mounted inside the cavity CT. The base  204 , vibrating arms  205 , and supporting arms  206   a ,  206   b  are formed at the same thickness and are formed simultaneously by wet-etching. 
         [0070]    On the tuning-fork type quartz-crystal vibrating piece  20 , respective extraction electrodes  203   a ,  203   b  are formed on each side and extending from the respective vibrating arms  205  to the distal ends of the respective supporting arms  206   a ,  206   b . The extraction electrodes  203   a ,  203   b  are connected to the respective excitation electrodes  202   a ,  202   b  on the vibrating arms  205 . 
         [0071]    An exemplary length L 7  of the tuning-fork type quartz-crystal vibrating piece  20  in the Y-axis direction is 2,000 μm; an exemplary width W 7  is 1,800 μm, and an exemplary height H 7  is 100 μm. The length L 7  refers to the distance between the distal end of the respective vibrating arm  205  (in the +Y-axis direction) and the distal end of the base  204  (in the −Y-axis direction). The width W 7  refers to the distance between the distal end of the respective supporting arm  206   a ,  206   b  (in the +X-axis direction) and the distal end of the respective supporting arm (in the −X-axis direction). 
         [0072]    The package base  22  comprises a first peripheral surface M 1  extending around the periphery of the upper main surface (main surface in the +Z-axis direction) of the base recess  221 . On the package base  22 , respective base castellations  222   a ,  222   b  are formed on each X-axis direction side. The castellations are formed simultaneously with forming the base through-holes BH 2  (refer to  FIG. 14 ) and extend in the Y-axis directions. On the base castellations  222   a ,  222   b  are respective base edge-surface electrodes  223   a ,  223   b  (refer to  FIG. 12A ). Also, on the first peripheral surface M 1  of the package base  22  in the +X-axis direction, a respective connecting electrode  224   a  is formed for providing electrical connection to the base edge-surface electrode  223   a . Similarly, on the first peripheral surface M 1  of the package base  22  in the −X-axis direction, respective connecting electrodes  224   a ,  224   b  are formed for providing electrical connection to the respective base edge-surface electrodes  223   a ,  223   b . Furthermore, on the mounting surface of the quartz-crystal vibrating device (i.e., lower main surface of the package base  22 ), a pair of mounting terminals  225   a ,  225   b  are provided for forming electrical connections to respective base edge-surface electrodes  223   a ,  223   b  (refer to  FIG. 12B ). 
         [0073]    Turning to  FIG. 11 , the outer dimension of the package base  22  is as same as of the package base  12  of the first embodiment. The length L 2  of the base castellations  222   a ,  222   b  in the Y-axis direction is approximately in the range of ⅓ to ½ the length L 1  of the package base  22 , which corresponds to 1,000 to 1,600 μm. The length L 3  of the connecting electrodes  224   a ,  224   b  in the Y-axis direction is approximately in the range of equal to the length L 2  to half the length L 2  of the base castellations  222   a ,  222   b , which corresponds to 800 to 1,600 μm. 
         [0074]    In  FIG. 12A , the width W 5  of the base recess  221  in the X-axis direction is approximately 1,500 μm, which is shorter than the width W 7  (approximately 1,800 μm) of the tuning-fork type quartz-crystal vibrating piece  20  in the X-axis directions. The depth of the base recess  121  is approximately 40 μm. The base edge-surface electrodes, connecting electrodes, and mounting terminals all have the same configurations as the excitation electrodes and extraction electrodes. 
         [0075]    Thus, as shown in  FIG. 12A , in this second embodiment of a quartz-crystal vibrating device  200 , the width W 7  (1,800 μm) of the vibrating piece  20  is greater than the width W 5  of the base recess  221 . Therefore, whenever the tuning-fork type quartz-crystal vibrating piece  20  is mounted onto the package base  22  using electrically conductive adhesive  13 , the edges of the supporting arms  206   a ,  206   b  on the vibrating piece  20  are mounted onto the first peripheral surface M 1  of the package base  22 . The extraction electrodes  203   a ,  203   b  are electrically connected to respective connecting electrodes  224   a ,  224   b . Thus, the mounting terminals  225   a ,  225   b  are electrically connected to respective excitation electrodes  202   a ,  202   b  via respective base edge-surface electrodes  223   a ,  223   b , connecting electrodes  224   a ,  224   b , electrically conductive adhesive  13 , and respective extraction electrodes  203   a ,  203   b . Whenever an alternating voltage is applied across the mounting terminals  225   a ,  225   b , the vibrating arms  205  of the tuning-fork type quartz-crystal vibrating piece  20  vibrate. 
         [0076]    Since the connecting electrodes  224   a ,  224   b  on the package base  22  are formed wider (L 3 ; 800 μm), the extraction electrodes  203   a ,  203   b  can be connected reliably to the respective connecting electrodes  224   a ,  224   b  whenever the vibrating piece  20  is bonded to the package base  22 . This ensures that the extraction electrodes  203   a ,  203   b  are electrically connected to the respective connecting electrodes  224   a ,  224   b  with high reliability. 
         [0077]    In  FIG. 11  the vibration frequency of the tuning-fork type quartz-crystal vibrating piece  20  can be measured by contacting respective vibration-measurement probes PB 1 , PB 2  to respective connecting electrodes  224   a ,  224   b . Since the area of the connecting electrodes  224   a ,  224   b  is relatively large, the vibration frequency of the vibrating piece  20  can be measured easily and precisely. 
         [0078]    In  FIG. 12B  four mounting terminals  225  are formed on the mounting surface of the package base  22 . Among these four terminals, two mounting terminals  225   a ,  225   b  are electrically connected to respective base edge-surface electrodes  223   a ,  223   b . The remaining two mounting terminals are used as electrical-ground terminals. 
         [0079]    As shown in  FIGS. 10-12 , each quartz-crystal vibrating device  200  of this second embodiment comprises a package lid  21  defining a cavity CT. The cavity CT is filled with nitrogen gas or sealed in an airtight manner. 
         [0080]    The package lid  21  also defines a second peripheral surface M 2  extending around the periphery of the lid recess  211  in the −Z-axis direction. The second peripheral surface M 2  of the package lid  21  is bonded to the first peripheral surface M 1  of the package base  22  using non-electrically conductive adhesive; e.g., a low-melting-point glass LG. 
         [0081]    The outer dimension of the package lid  21  is as same as of the package lid  11  of the first embodiment. The width W 4  of the lid recess  211  in the X-axis direction is approximately 2,000 μm, which is longer length than the width W 7  (approximately 1,800 μm) of the vibrating piece  20  in the X-axis direction. The depth of the lid recess  211  is approximately 250 μm. Consequently, the width W 4  (2,000 μm) of the lid recess  211  is greater than the width W 7  (1,800 μm) of the vibrating piece  20  and the width W 5  (1,500 μm) of the base recess  221 . As shown in  FIGS. 10 ,  11  and  12 A- 12 B, the low-melting-point glass LG bonds the package lid  21  and the package base  22  around the outer periphery (first peripheral surface M 1  of the package base  22  (wherein the first peripheral surface has a width of approximately 250 μm). 
         [0082]    In the second embodiment, the base edge-surface electrodes are not formed on the entire surface of the respective castellations. Rather, these electrodes can be formed with substantially the same width as of the connecting electrodes (in the Y-axis directions), which is similar to the alternative to the first embodiment. 
       Method for Manufacturing the Second Embodiment of Quartz-Crystal Vibrating Device 
       [0083]    This method embodiment can be described with reference to  FIG. 4 . Also,  FIG. 13  is a plan view of the quartz-crystal wafer  20 W used in the method, and  FIG. 14  is a plan view of the base wafer  22 W. 
         [0084]    In protocol S 10 , the tuning-fork type quartz-crystal vibrating piece  20  is manufactured. As shown in  FIG. 13 , the profile outlines of a plurality of quartz-crystal vibrating pieces  20  are formed on a planar quartz-crystal wafer  10 W by etching. Each vibrating piece  20  is connected to the quartz-crystal wafer  20 W by a respective joining portion  209 . As described previously with respect to step S 102  in  FIG. 4 , excitation electrodes  202   a ,  202   b , and extraction electrodes  203   a ,  203   b  are formed. Using a dicing unit such as a laser beam or dicing saw, the bonded quartz-crystal vibrating pieces  20  are cut along cut lines CL (denoted by dot-dash lines in  FIG. 13 ) to separate individual devices from each other. 
         [0085]    In protocol S 11 , the package lid  21  is manufactured. The package lid  21  in the second embodiment has the same shape as the package lid  11  in the first embodiment, but has different dimensions. Nevertheless, the package lid can be manufactured by following the same manufacturing method as used in the first embodiment. 
         [0086]    In protocol S 12 , the package base  22  is manufactured. As shown in  FIG. 14 , several hundreds to several thousands of base recesses  221  are formed on the base wafer  22 W, the latter being a circular, uniformly planar plate of quartz-crystal material. Respective rounded-rectangular through-holes BH 2  are formed on each side of the package base  22  in the X-axis directions, so as to extend depthwise through the base wafer  22 W. When each base through-hole BH 2  is cut in half, it forms a respective base castellation  222   a ,  222   b  (refer to  FIG. 10 ). Then, as explained in step S 102  in  FIG. 4 , the base edge-surface electrodes  223   a ,  223   b  are formed on the surfaces of the base through-holes BH 2 . The connecting electrodes  224   a ,  224   b  are formed on the second peripheral surface M 2 . 
         [0087]    In step S 13 , the tuning-fork type quartz-crystal vibrating piece  20  (manufactured in step S 10 ) is mounted onto the first peripheral surface M 1  of the package base  22  using electrically conductive adhesive  13 . 
         [0088]    In step S 14 , respective frequency-measurement probes PB 1 , PB 2  are contacted to the connecting electrodes  224   a ,  224   b  to measure the vibration frequency produced by the quartz-crystal vibrating piece  20 . 
         [0089]    In step S 15 , the vibration frequency is adjusted either by irradiating a laser beam on the weights  208  on the vibrating arms  205  to remove mass from the weights. The vibration frequency of each vibrating piece  20  can be adjusted after measuring the vibration frequencies produced by all the vibrating pieces  20  on the base wafer  22 W. Alternatively, the vibration frequencies can be measured and adjusted one by one. 
         [0090]    In step S 16  low-melting-point glass LG is heated while compressing the lid wafer ( FIG. 6 ) and base wafer  22 W together. Thus, the lid wafer and base wafer  22 W are bonded together by the low-melting-point glass LG. 
         [0091]    In step S 17 , the bonded-together lid wafer ( FIG. 6 ) and base wafer  22 W are cut to separate the several hundreds to several thousands of quartz-crystal piezoelectric vibrating devices  200  from each other. 
       INDUSTRIAL APPLICABILITY 
       [0092]    Representative embodiments are described in detail above; however, as will be evident to those skilled in the relevant art, the present invention may be changed or modified in various ways within its technical scope. 
         [0093]    In the first and second embodiments, although the package lid and package base are bonded together using low-melting-point glass LG, which is a non-electrically conductive adhesive, the low-melting-point glass can be replaced by a polyimide resin. Whenever polyimide resin is used, the manufacturing process can be replaced with screen-printing, or an exposure step can be performed after applying photolithographic polyimide resin on the entire surface. 
         [0094]    Although mounting terminals are formed on the four corners of the lower main bottom surface of the package base, they can be replaced with a pair of mounting terminals formed on both sides of the package in the X-axis directions. When forming mounting terminals in this manner, the grounding terminal(s) is not formed. 
         [0095]    Although a quartz-crystal vibrating piece was used in the embodiments described above, other embodiments can be made with equal facility that comprise piezoelectric materials such as lithium tantalite and/or lithium niobate. Further, the present disclosure may be directed to piezoelectric oscillators in which an IC accommodating an oscillating circuit is mounted inside the package on the package base. 
         [0096]    Furthermore, even though a plurality of quartz-crystal vibrating pieces are described as being formed on wafers simultaneously, the polishing, etching, and forming of electrodes can be done on individual quartz-crystal pieces.