Patent Publication Number: US-2013241358-A1

Title: Quartz crystal device and method for fabricating the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Japan application serial no. 2012-057076, filed on Mar. 14, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     TECHNICAL FIELD 
     This disclosure relates to a quartz crystal device that includes a quartz-crystal vibrating piece and a base plate, and to a method for fabricating the quartz crystal device. The quartz-crystal vibrating piece and the base plate are formed by wet-etching a quartz substrate. 
     DESCRIPTION OF THE RELATED ART 
     It is preferred that a large amount of surface mount quartz crystal devices can be fabricated at a time. A quartz crystal device disclosed in Japanese Unexamined Patent Application Publication No. 2006-148758 (hereinafter referred to as Patent Literature 1) is fabricated such that a quartz-crystal wafer including a plurality of quartz-crystal vibrating pieces is sandwiched between a lid wafer and a base wafer with the same shape as the quartz-crystal wafer and made of a glass material. The method for fabricating the quartz crystal device disclosed in Patent Literature 1 forms through holes at the lid wafer and the base wafer, thus forming side portion wirings at four corners of the quartz crystal device (castellations). The side portion wiring electrically connects an excitation electrode and an external terminal of the quartz-crystal vibrating piece. The quartz crystal devices fabricated on a wafer scale are individually separated by dicing for completion. 
     However, since the quartz-crystal wafer differs in thermal expansion coefficient from the lid wafer or the base wafer, which are made of a glass material, the quartz crystal device is unusable in an environment where thermal fluctuation is large. On the other hand, in the case where the lid wafer or the base wafer is made of a quartz-crystal material, through holes formed on the lid wafer and the base wafer have varied wet-etching speeds depending on an axis direction due to anisotropy of the crystal, thus forming a different size of through hole in the axial direction. This does not allow forming castellations in positions with the same distance from the center of the quartz crystal device. The through holes are different in size depending on the axial direction. Accordingly, when the bonded wafer is diced into individual quartz crystal devices, side wiring formed on the castellation may be chipped off. 
     A need thus exists for a quartz crystal device and a method for fabricating the quartz crystal device which are not susceptible to the drawback mentioned above. 
     SUMMARY 
     A method for fabricating a quartz crystal device according to a first aspect uses an AT-cut base wafer. The AT-cut base wafer includes a plurality of base plates in rectangular shapes. The base plate has at least a pair of through holes in an X-axis direction. The quartz crystal device includes a quartz-crystal vibrating piece and the base plate. The method includes forming a corrosion-resistant film on a first surface of the base wafer and a second surface at an opposite side of the first surface, exposing a photoresist on the first surface and the second surface in a position corresponding to the through hole after forming the photoresist on the corrosion-resistant film, etching the corrosion-resistant film corresponding to the through hole of the first surface and the second surface, and performing wet-etching on the first surface and the second surface to form the pair of through holes after the etching corrosion-resistant film. The through hole formed by the wet-etching connects the first surface to the second surface. The through hole has a cross section at a +X-axis side and a cross section at a −X-axis side. The cross section at the +X-axis side includes a first inclined surface, a second inclined surface, and a first top. The first inclined surface is formed toward a center side of the cross section from the first surface. The second inclined surface is formed toward the center side of the cross section from the second surface. The first top is formed at an intersection of the first inclined surface and the second inclined surface. The cross section at the −X-axis side includes a third inclined surface, a fourth inclined surface, and a second top. The third inclined surface is formed toward the center side of the cross section from the first surface. The fourth inclined surface is formed toward the center side of the cross section from the second surface. The second top connects the third inclined surface to the fourth inclined surface. The exposing exposes the first surface and the second surface in a position corresponding to the through hole such that a distance from a center in the X-axis direction of the base plate to the first top becomes equal to a distance from the center in the X-axis direction of the base plate to the second top. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of a quartz crystal device  100 ; 
         FIG. 2  is a cross-sectional view taken along the line A-A of  FIG. 1 ; 
         FIG. 3A  is a plan view of a surface at the +Y′-axis side of the base plate  120 ; 
         FIG. 3B  is a plan view of a surface at the −Y′-axis side of the base plate  120 ; 
         FIG. 4A  is a plan view of the base plate  120  where an electrodes has not been formed; 
         FIG. 4B  is a cross-sectional view taken along the line B-B of  FIG. 4A ; 
         FIG. 5  is a flowchart illustrating a method for fabricating the quartz crystal device  100 ; 
         FIG. 6A  is a plan view of the surface at the +Y′-axis side of the base wafer W 120 ; 
         FIG. 6B  is a plan view of the surface at the −Y′-axis side of the base wafer W 120 ; 
         FIGS. 7A to 7D  illustrate a flowchart of a method for fabricating the base wafer W 120 ; 
         FIGS. 8A to 8D  illustrate a flowchart of the method for fabricating the base wafer W 120 ; 
         FIG. 9  is a plan view of a surface at the +Y′-axis side of a lid wafer W 110 ; 
         FIG. 10A  is a partial cross-sectional view of the base wafer W 120  where a quartz-crystal vibrating piece  130  has been placed; 
         FIG. 10B  is a partial cross-sectional view of the quartz-crystal vibrating piece  130 , the base wafer W 120 , and the lid wafer W 110 ; 
         FIG. 11A  is a cross-sectional view of a base plate  120   a;    
         FIG. 11B  is a cross-sectional view of a base plate  120   b;    
         FIG. 12  is an exploded perspective view of a quartz crystal device  200   a;    
         FIG. 13  is a cross-sectional view taken along the line E-E of  FIG. 12 ; 
         FIG. 14A  is a plan view of a surface at the +Y′-axis side of a quartz-crystal vibrating piece  230   a;    
         FIG. 14B  is a plan view of a surface at the −Y′-axis side of the quartz-crystal vibrating piece  230   a;    
         FIG. 14C  is a cross-sectional view of the quartz-crystal vibrating piece  230   a;    
         FIG. 15A  is a plan view of a surface at the +Y′-axis side of a base plate  220   a;    
         FIG. 15B  is a plan view of a surface at the −Y′-axis side of the base plate  220   a;    
         FIG. 15C  is a cross-sectional view of the base plate  220   a;    
         FIG. 16  is a plan view of a quartz-crystal wafer W 230 ; 
         FIG. 17A to 17D  illustrate a flowchart of a method for fabricating the quartz-crystal wafer W 230 ; 
         FIG. 18A to 18D  illustrate a flowchart of the method for fabricating the quartz-crystal wafer W 230 ; 
         FIG. 19A  is a plan view of a surface at the +Y′-axis side of a base wafer W 220 ; 
         FIG. 19B  is a plan view of a surface at the −Y′-axis side of the base wafer W 220 ; 
         FIG. 20A  is a partial cross-sectional view of the base wafer W 220  where the quartz-crystal wafer W 230  is placed; 
         FIG. 20B  is a partial cross-sectional view of the quartz-crystal wafer W 230 , the base wafer W 220 , and the lid wafer W 110 ; 
         FIG. 21  is an exploded perspective view of a quartz crystal device  300 ; 
         FIG. 22A  is a cross-sectional view taken along the line H-H of  FIG. 21 ; 
         FIG. 22B  is a plan view of a surface at the −Y′-axis side of the quartz crystal device  300 ; 
         FIG. 23A  is a plan view of a surface at the +Y′-axis side of a base plate  320 ; and 
         FIG. 23B  is a cross-sectional view of the base plate  320 . 
     
    
    
     DETAILED DESCRIPTION 
     The preferred embodiments of this disclosure will be described with reference to the attached drawings. It will be understood that the scope of the disclosure is not limited to the described embodiments, unless otherwise stated. 
     Configuration of a Quartz Crystal Device  100  of a First Embodiment 
       FIG. 1  is an exploded perspective view of a quartz crystal device  100 . The quartz crystal device  100  includes a lid plate  110 , a base plate  120 , and a quartz-crystal vibrating piece  130 . The quartz-crystal vibrating piece  130  and the base plate  120  employ, for example, an AT-cut crystal wafer. The AT-cut crystal wafer has a principal surface (in the Y-Z plane) that is tilted by 35° 15′ about the Y-axis of crystallographic axes (XYZ) in the direction from the Z-axis to the Y-axis around the X-axis. In the following description, the new axes tilted with reference to the axis directions of the AT-cut crystal wafer are denoted as the Y′-axis and the Z′-axis. This disclosure defines, in the quartz crystal device  100 , the long side direction of the quartz crystal device  100  as the X-axis direction, the height direction of the quartz crystal device  100  as the Y′-axis direction, and the direction perpendicular to the X and Y′-axis directions as the Z′-axis direction. 
     The quartz-crystal vibrating piece  130  includes a vibrator  134 , an excitation electrode  131 , and an extraction electrode  132 . The vibrator  134  vibrates at a predetermined vibration frequency and has a rectangular shape. The excitation electrodes  131  are formed on surfaces at the +Y′-axis side and the −Y′-axis side of the vibrator  134 . The extraction electrode  132  is extracted from each excitation electrode  131  to the −X-axis side. The extraction electrode  132  is extracted from the excitation electrode  131  that is formed on the surface at the +Y′-axis side of the vibrator  134 . The extraction electrode  132  is extracted from the excitation electrode  131  to the −X-axis side, and is further extracted to the surface at the −Y′-axis side of the vibrator  134  via the side surface at the +Z′-axis side of the vibrator  134 . The extraction electrode  132  is extracted from the excitation electrode  131  that is formed on the surface at the −Y′-axis side of the vibrator  134 . The extraction electrode  132  is extracted from the excitation electrode  131  to the −X-axis side, and is formed up to the corner at the −X-axis side and the −Z′-axis side of the vibrator  134 . 
     The base plate  120  employs a base material of the AT-cut crystal wafer with the surface where an electrode is formed. A bonding surface  122  is formed at the peripheral area of the surface at the +Y′-axis side of the base plate  120 . The bonding surface  122  is to be bonded to the lid plate  110  via a sealing material  142  (see  FIG. 2 ). The base plate  120  includes a depressed portion  121  at the center of the surface at the +Y′-axis side. The depressed portion  121  is depressed from the bonding surface  122  in the −Y′-axis direction. The depressed portion  121  includes a pair of connecting electrodes  123 . Each connecting electrode  123  electrically connects to an extraction electrode  132  of the quartz-crystal vibrating piece  130  via a conductive adhesive  141  (see  FIG. 2 ). The base plate  120  includes a mounting terminal on the surface at the −Y′-axis side. The mounting terminal mounts the quartz crystal device  100  to a printed circuit board or similar member. In the base plate  120 , the mounting terminal includes a hot terminal  124   a  (see  FIG. 2  and  FIG. 3B ) and a grounding terminal  124   b  (see  FIG. 2  and  FIG. 3B ). The hot terminal  124   a  is a terminal that electrically connects to an external electrode and a similar member for applying a voltage to the quartz crystal device  100 . At the +Z′-axis side and the −Z′-axis side of a side surface at the +X-axis side of the base plate  120 , castellations  126   a  depressed toward the inside of the base plate  120  are formed. At the +Z′-axis side and the −Z′-axis side of a side surface at the −X-axis side of the base plate  120 , castellations  126   b  depressed toward the inside of the base plate  120  are formed. The castellations  126   a  and the castellations  126   b  have side surfaces where respective side surface electrodes  125  are formed. The hot terminal  124   a  electrically connects to the connecting electrode  123  via the side surface electrode  125 . 
     The lid plate  110  includes a depressed portion  111  on the surface at the −Y′-axis side. The depressed portion  111  is depressed in the +Y′-axis direction. A bonding surface  112  is formed to surround the depressed portion  111 . The bonding surface  112  is to be bonded to the bonding surface  122  of the base plate  120  via the sealing material  142  (see  FIG. 2 ). 
       FIG. 2  is a cross-sectional view taken along the line A-A of  FIG. 1 . A sealed cavity  101  is formed in the quartz crystal device  100  by bonding the bonding surface  122  of the base plate  120  and the bonding surface  112  of the lid plate  110  together via the sealing material  142 . The cavity  101  houses the quartz-crystal vibrating piece  130 . The extraction electrode  132  electrically connects to the connecting electrode  123  of the base plate  120  via the conductive adhesive  141 . The hot terminal  124   a  electrically connects to the connecting electrode  123  via the side surface electrodes  125 . Accordingly, the excitation electrode  131  electrically connects to the hot terminal  124   a.    
     The castellation  126   a  formed at the +X-axis side of the base plate  120  has a side surface formed of a first inclined surface  127   a  and a second inclined surface  127   b . The first inclined surface  127   a  connects to the surface at the +Y′-axis side of the base plate  120 . The second inclined surface  127   b  connects to the surface at the −Y′-axis side of the base plate  120 . The first inclined surface  127   a  and the second inclined surface  127   b  intersect with each other at a first top  128   a . The castellation  126   b  formed at the −X-axis side of the base plate  120  has a side surface formed of a third inclined surface  127   c  and a fourth inclined surface  127   d . The third inclined surface  127   c  connects to the surface at the +Y′-axis side of the base plate  120 . The fourth inclined surface  127   d  connects to the surface at −Y′-axis side of the base plate  120 . The third inclined surface  127   c  and the fourth inclined surface  127   d  intersect with each other at a second top  128   b . The first top  128   a  is formed at the +X-axis side of the base plate  120  compared with the first inclined surface  127   a  and the second inclined surface  127   b . The second top  128   b  is formed at the −X-axis side of the base plate  120  compared with the third inclined surface  127   c  and the fourth inclined surface  127   d . In the base plate  120  of the quartz crystal device  100 , as illustrated in  FIG. 2 , the sealing material  142  is also formed on the first inclined surface  127   a  and the third inclined surface  127   c . Accordingly, the base plate  120  is bonded to the bonding surface  112  of the lid plate  110  at the first inclined surface  127   a , the third inclined surface  127   c , and the bonding surface  122 . 
       FIG. 3A  is a plan view of the surface at the +Y′-axis side of the base plate  120 . The base plate  120  includes the depressed portion  121  at the center of the surface at the +Y′-axis side. The bonding surface  122  is formed to surround the depressed portion  121 . Castellations  126   a  are formed at the +Z′-axis side and the −Z′-axis side on the side surfaces at the +X-axis side of the base plate  120 . Castellations  126   b  are formed at the +Z′-axis side and the −Z′-axis side on the side surfaces at the −X-axis side. The depressed portion  121  includes the pair of connecting electrodes  123 . The castellation  126   a  and the castellation  126   b  each include the side surface electrodes  125 . The pair of connecting electrodes  123  electrically connect to the side surface electrodes  125  of the castellation  126   a  formed at the +X-axis side and the −Z′-axis side and the castellation  126   b  formed at the −X-axis side and the +Z′-axis side. 
       FIG. 3B  is a plan view of the surface at the −Y′-axis side of the base plate  120 . The surface at the −Y′-axis side of the base plate  120  includes, as the mounting terminals, the pair of hot terminals  124   a  and the pair of grounding terminals  124   b . One hot terminal  124   a  is formed at the +X-axis side and the −Z′-axis side while the other hot terminal  124   a  is formed at the −X-axis side and the +Z′-axis side on the surface at the −Y′-axis side of the base plate  120 . The hot terminals  124   a  electrically connect to the respective side surface electrodes  125 . One grounding terminal  124   b  is formed at the +X-axis side and the +Z′-axis side while the other grounding terminal  124   b  is formed at the −X-axis side and the −Z′-axis side of the base plate  120 . While in the base plate  120  illustrated in  FIG. 3B , the grounding terminals  124   b  does not electrically connect to the side surface electrodes  125 , the grounding terminals  124   b  may electrically connect to the side surface electrodes  125 . 
       FIG. 4A  is a plan view of the base plate  120  where an electrode has not been formed. The depressed portion  121  of the base plate  120  includes a sidewall and a bottom surface  121   c . In the base plate  120 , the depressed portion  121  has respective widths SA of the bonding surface  122  in the X-axis direction at the +X-axis side and the −X-axis side. Furthermore, the base plate  120  has a width KB of the castellation  126   a  in the X-axis direction on the surface at the +Y′-axis side while the base plate  120  has a width KA 1  of the castellation  126   a  in the X-axis direction on the first top  128   a . The base plate  120  has a width KC of the castellation  126   b  in the X-axis direction on the surface at the +Y′-axis side while the base plate  120  has a width KA 2  of the castellation  126   b  in the X-axis direction on the second top  128   b . A sidewall  121   a  at the +X-axis side of the depressed portion  121  and the first top  128   a  form a width KD 1  while a sidewall  121   b  at the −X-axis side of the depressed portion  121  and the second top  128   b  form a width KD 2 . The width KD 1  and the width KD 2  are respectively a width at the −X-axis side of the castellation  126   a  and a width at the +X-axis side of the castellation  126   b  in the bonded area over which the sealing material  142  is actually to be applied. In the base plate  120 , the width KA 1  is equal to the width KA 2  while the width KD 1  is equal to the width KD 2 . 
       FIG. 4B  is a cross-sectional view taken along the line B-B of  FIG. 4A . The castellation  126   a  and the castellation  126   b  each have a width KC in the X-axis direction on the surface at the −Y′-axis side. In the castellation  126   a  and the castellation  126   b , the first top  128   a  and the second top  128   b  each have the narrowest width in the X-axis direction. The base plate  120  has a distance KE 1  between the center  173  and the first top  128   a  in the X-axis direction while the base plate  120  has a distance KE 2  between the center  173  and the second top  128   b . The distance KE 1  is equal to the distance KE 2 . 
     Method for Fabricating the Quartz Crystal Device  100   
       FIG. 5  is a flowchart illustrating a method for fabricating the quartz crystal device  100 . Hereinafter, a description will be given of the method for fabricating the quartz crystal device  100  following the flowchart of  FIG. 5 . 
     In step S 101 , a plurality of quartz-crystal vibrating pieces  130  are prepared. Step S 101  is a process for preparing a quartz-crystal vibrating piece. In step S 101 , first, outlines of the plurality of quartz-crystal vibrating piece  130  are formed on a quartz-crystal wafer, which is made of a quartz-crystal material, by etching or similar method. Further, the excitation electrode  131  and the extraction electrode  132  are formed on each quartz-crystal vibrating piece  130  by a method such as sputtering or vacuum evaporation. The plurality of quartz-crystal vibrating pieces  130  are prepared by folding and removing the quartz-crystal vibrating piece  130  from the quartz-crystal wafer. 
     In step S 201 , the base wafer W 120  is prepared. Step S 201  is a process for preparing a base wafer. A plurality of base plates  120  are formed on the base wafer W 120 . The base wafer W 120  employs a base material of the AT-cut quartz-crystal material. On the base wafer W 120 , the depressed portion  121  and a through hole  172  (see  FIG. 6A  and  FIG. 6B ) are formed by etching. The through hole  172  becomes the castellation  126   a  or the castellation  126   b  after the base wafer W 120  is cut. On the base wafer W 120 , the connecting electrode  123 , the side surface electrodes  125 , the hot terminal  124   a , and the grounding terminal  124   b  are formed. 
       FIG. 6A  is a plan view of the surface at the +Y′-axis side of the base wafer W 120 . The base wafer W 120  includes a plurality of base plates  120 . Each base plate  120  is aligned in the X-axis direction and the Z′-axis direction. In  FIG. 6A , a scribe line  171  is illustrated at a boundary between the base plates  120  adjacent one another. The scribe line  171  is a line that indicates a position at which the wafer is cut in step S 403 , which will be described below. On the scribe line  171  extending in the X-axis direction, the through hole  172  is formed. The through hole  172  passes through the base wafer W 120  in the Y′-axis direction. After the wafer is cut in step S 403  described below, the through hole  172  becomes the castellation  126   a  and the castellation  126   b . On the surface at the +Y′-axis side of each base plate  120 , the depressed portion  121  and the connecting electrode  123  are formed. 
       FIG. 6B  is a plan view of the surface at the −Y′-axis side of the base wafer W 120 . The base wafer W 120  has the surface at the −Y′-axis side where the hot terminal  124   a  and the grounding terminal  124   b  are formed. The hot terminal  124   a  electrically connects to the connecting electrode  123  via the side surface electrodes  125  formed at the through hole  172 . In the base wafer W 120 , the side surface electrode  125  formed at one through hole  172  electrically connects to one hot terminal  124   a  only. 
       FIGS. 7A to 7D  and  FIGS. 8A to 8D  illustrate a flowchart of a method for fabricating the base wafer W 120 . Hereinafter, by referring to  FIGS. 7A to 7D  and  FIGS. 8A to 8D , a detailed description will be given of step S 201  in  FIG. 5 , which is a process for preparing the base wafer W 120 . 
     In step S 211  of  FIGS. 7A to 7D , a base wafer formed of an AT-cut quartz-crystal material is prepared.  FIG. 7A  is a partial cross-sectional view of the base wafer W 120  formed of an AT-cut quartz-crystal material.  FIG. 7A  and views in  FIGS. 7A to 7D  and  FIGS. 8A to 8D  described below are cross-sectional views of cross sections corresponding to the cross section taken along the line C-C of  FIG. 6A  and  FIG. 6B . Each cross-sectional view illustrates the scribe line  171 . An area surrounded by the scribe lines  171  forms one base plate  120 . The base wafer W 120  prepared in step S 211  is formed in a planar shape. 
     In step S 212 , a corrosion-resistant film is formed.  FIG. 7B  is a partial cross-sectional view of the base wafer W 120  where a corrosion-resistant film  151  has been formed. The corrosion-resistant film  151  is formed on the surfaces at the +Y′-axis side and the −Y′-axis side of the base wafer W 120 . The corrosion-resistant film  151  is formed, for example, by forming a chromium (Cr) layer (not shown) on the surfaces at the +Y′-axis side and the −Y′-axis side of the base wafer W 120  and forming a gold (Au) layer (not shown) on a surface of the chromium layer. Step S 212  is a process for forming the corrosion-resistant film. 
     In step S 213 , a photoresist is formed.  FIG. 7C  is a partial cross-sectional view of the base wafer W 120  where a photoresist  152  has been formed. The photoresist  152  is formed on the surface of the corrosion-resistant film  151 , which is formed in step S 212 . 
     In step S 214 , the photoresist is exposed and developed.  FIG. 7D  is a partial cross-sectional view of the base wafer W 120  where the photoresist has been exposed and developed. The base wafer W 120  is exposed through a mask  153 , and developed to remove the photoresist  152 . The photoresist  152  to be removed in step S 214  is on an area where the through hole  172  and the depressed portion  121  on the surface at the +Y′-axis side of the base wafer W 120  are formed, and on an area where the through hole  172  on the surface at the −Y′-axis side of the base wafer W 120  is formed. The photoresist  152  to be removed for forming the through hole  172  has the width KB from the scribe line  171  at the +X-axis side on the surface at +Y′-axis side of each base plate  120 . The photoresist  152  has the width KC from the scribe line  171  at the −X-axis side on the surface at the +Y′-axis side, and at the +X-axis side and the −X-axis side on the surface at the −Y′-axis side of each base plate  120 . The width KB is about 10 to 30% wider than the width KC. Step S 213  and Step S 214  are exposure processes. 
     In step S 215  of  FIGS. 8A to 8D , the corrosion-resistant film is etched.  FIG. 8A  is a partial cross-sectional view of the base wafer W 120  where the corrosion-resistant film  151  has been etched. In step S 215 , the corrosion-resistant film  151  with an exposed surface where the photoresist  152  has been removed in step S 214  is removed by etching. This exposes the quartz-crystal material in the area where the through hole  172  and the depressed portion  121  are to be formed on the base wafer W 120 . Step S 215  is a process for etching the corrosion-resistant film. 
     In step S 216 , the quartz-crystal material is processed by wet-etching.  FIG. 8B  is a partial cross-sectional view of the base wafer W 120  where the quartz-crystal material has been etched. In step S 216 , the quartz-crystal material is processed by wet-etching to form the through hole  172  and the depressed portion  121  in the base wafer W 120 . The base wafer W 120  employs the base material of the AT-cut quartz-crystal material. Thus, anisotropy of the crystal causes the through hole  172  with a side surface near the center portion that is narrow toward the inside of the through hole  172 . Step S 216  is a wet-etching process. 
     In step S 217 , the corrosion-resistant film and the photoresist are removed.  FIG. 8C  is a partial cross-sectional view of the base wafer W 120  where the corrosion-resistant film  151  and the photoresist  152  have been removed. At the through hole  172 , a width in the −X-axis direction and a width in the +X-axis direction from the scribe line  171  to the side surface of the base plate  120  are respectively the width KA 1  and the width KA 2 . The width KA 1  is equal to the width KA 2 . 
     In step S 218 , electrodes are formed on the base wafer W 120 .  FIG. 8D  is a partial cross-sectional view of the base wafer W 120  where the electrodes have been formed. In step S 218 , the chromium layer is formed on the base wafer W 120 . The gold layer is formed on the surface of the chromium layer to form the connecting electrode  123 , the hot terminal  124   a , the grounding terminal  124   b , and the side surface electrodes  125  on the base wafer W 120 . 
     Returning to  FIG. 5 , in step S 301 , the lid wafer W 110  is prepared. On the lid wafer W 110 , a plurality of lid plates  110  are formed. On the surface at the −Y′-axis side of each lid plate  110 , the depressed portion  111  is formed. 
       FIG. 9  is a plan view of the surface at the +Y′-axis side of a lid wafer W 110 . On the lid wafer W 110 , a plurality of lid plates  110  are formed. On the surface at the −Y′-axis side of each lid plate  110 , the depressed portion  111  and the bonding surface  112  are formed. In  FIG. 9 , a two-dot chain line is drawn between the lid plates  110  adjacent one another. This two-dot chain lines become the scribe lines  171 . 
     In step S 401 , the quartz-crystal vibrating piece  130  is placed on the base wafer W 120 . The quartz-crystal vibrating piece  130  is placed on each depressed portion  121  on the base wafer W 120  with the conductive adhesive  141 . 
       FIG. 10A  is a partial cross-sectional view of the base wafer W 120  where a quartz-crystal vibrating piece  130  has been placed.  FIG. 10A  illustrates a cross-sectional view including a cross section taken along the line C-C of  FIG. 6A  and  FIG. 6B . The extraction electrode  132  and the connecting electrode  123  of the quartz-crystal vibrating piece  130  are electrically connected together via the conductive adhesive  141 . Thus, the quartz-crystal vibrating piece  130  is placed on the depressed portion  121  of the base wafer W 120 . This electrically connects the excitation electrode  131  and the hot terminal  124   a , which is formed on the surface at the −Y′-axis side of the base wafer W 120 . 
     In step S 402 , the base wafer W 120  and the lid wafer W 110  are bonded together. The base wafer W 120  and the lid wafer W 110  are bonded such that the bonding surface  122 , the first inclined surface  127   a , and the third inclined surface  127   c  of the base wafer W 120  face the bonding surface  112  of the lid wafer W 110  via the sealing material  142 . 
       FIG. 10B  is a partial cross-sectional view of the quartz-crystal vibrating piece  130 , the base wafer W 120 , and the lid wafer W 110 .  FIG. 10B  illustrates a cross-sectional view including a cross section taken along the line C-C of  FIG. 6A  and  FIG. 6B  and a cross section taken along the line D-D of  FIG. 9 . The base wafer W 120  and the lid wafer W 110  are bonded such that the bonding surface  122 , the first inclined surface  127   a , and the third inclined surface  127   c  face the bonding surface  112  via the sealing material  142 . The lid wafer W 110  and the base wafer W 120  are bonded together via the sealing material  142 . Thus, the sealed cavity  101  is formed. In the cavity  101 , the quartz-crystal vibrating piece  130  is placed. 
     In step S 403 , the base wafer W 120  and the lid wafer W 110  are cut. The base wafer W 120  and the lid wafer W 110  are cut (diced) with a dicing blade (not shown) along the scribe line  171  to form individual quartz crystal devices  100 . Step S 403  is a dicing process. As illustrated in  FIG. 10B , the scribe line  171  at the through hole  172  has a distance of the width KA 2  from the side surface electrodes  125  at the +X-axis side of the scribe line  171 . Additionally, the scribe line  171  has a distance of the width KA 1  from the side surface electrodes  125  at the −X-axis side of the scribe line  171 . The quartz crystal device  100  is formed to have the width KA 1  equal to the width KA 2 . Accordingly, the scribe line  171  is the most distant from the side surface electrodes  125 . This prevents the side surface electrodes  125  from being chipped off by a dicing blade. 
     Since the AT-cut quartz-crystal material is anisotropic in wet-etching. The castellations formed on the base plate changes in shape and dimensions at the +X-axis side and the −X-axis side of the base plate. For example, in  FIG. 4B , the width KA 1  and the width KA 2  may be different. In such a case, the side surface electrodes formed on the side surface of the castellation may have been chipped off in the dicing process. In the case where the base plate has different bonded areas of the sealing material at the +X-axis side and at the −X-axis side, variation in bonding strength of the sealing material at the +X-axis side and at the −X-axis side of the base plate easily break the seal of the cavity at a weak bonding strength side. 
     The quartz crystal device  100  is formed to have the width KA 1  equal to the width KA 2 , thus preventing the side surface electrodes  125  from being chipped off in the dicing process. The width KD 1  is formed to be equal to the width KD 2 . Thus, the base plate  120  has the same widths at the +X-axis side and the −X-axis side in the bonded area. This provides the same bonding strengths of the sealing material  142  at the +X-axis side and the −X-axis side of the cavity  101 . This prevents breaking the seal of the cavity  101 . 
     Modification of the Base Plate  120   
       FIG. 11A  is a cross-sectional view of the base plate  120   a . The base plate  120   a  is a modification of the base plate  120 .  FIG. 11A  illustrates a cross-sectional view of the base plate  120   a  corresponding to the cross section of the base plate  120  in  FIG. 4B . The base plate  120   a  has a width KB 2  in the X-axis direction on the surface at the −Y′-axis side of the castellation  126   a  at the +X-axis side while the base plate  120   a  has the width KC in the X-axis direction on the surface at the +Y′-axis side. In the base plate  120   a , a size of the width KB 2  is adjusted to form the width KA 1  equal to the width KA 2 . In the base plate  120   a , similarly to the base plate  120 , the width KD 1  is equal to the width KD 2 . 
       FIG. 11B  is a cross-sectional view of a base plate  120   b . The base plate  120   b  is a modification of the base plate  120 .  FIG. 11B  illustrates a cross-sectional view of the base plate  120   b  corresponding to the cross section of the base plate  120  in  FIG. 4B . The base plate  120   b  has a width KB 3  in the X-axis direction on the surfaces at the +Y′-axis side and the −Y′-axis side of the castellation  126   a  at the +X-axis side. In the base plate  120   b , a size of the width KB 3  is adjusted to form the width KA 1  equal to the width KA 2 . In the base plate  120   b , similarly to the base plate  120 , the width KD 1  is equal to the width KD 2 . 
     Second Embodiment 
     The quartz-crystal vibrating piece may employ a quartz-crystal vibrating piece where a framing body surrounds the peripheral area of the vibrator. Hereinafter, a description will be given of a quartz crystal device  200   a  that employs the quartz-crystal vibrating piece with the framing body. The embodiment will now be described wherein like reference numerals designate corresponding or identical elements throughout the embodiments. 
     Configuration of the Quartz Crystal Device  200   a    
       FIG. 12  is an exploded perspective view of the quartz crystal device  200   a . The quartz crystal device  200   a  includes the lid plate  110 , a base plate  220   a , and a quartz-crystal vibrating piece  230   a . The quartz crystal device  200   a  employs, similarly to the first Embodiment, an AT-cut quartz-crystal vibrating piece as the quartz-crystal vibrating piece  230   a.    
     The quartz-crystal vibrating piece  230   a  vibrates at a predetermined vibration frequency and includes a vibrator  234 , a framing body  235 , and connecting portions  236 . The vibrator  234  is formed in a rectangular shape. The framing body  235  is formed to surround the peripheral area of the vibrator  234 . The connecting portions  236  connect the vibrator  234  and the framing body  235  together. Between the vibrator  234  and the framing body  235 , through grooves  237  are formed. The through grooves  237  pass through the quartz-crystal vibrating piece  230   a  in the Y′-axis direction. The vibrator  234  and the framing body  235  do not directly contact each other. At the +X-axis side and the −Z′-axis side of the framing body  235 , a castellation  238   a  is formed. At the −X-axis side and the +Z′-axis side of the framing body  235 , a castellation  238   b  is formed. The vibrator  234  and the framing body  235  are connected together at the +Z′-axis side and the −Z′-axis side at the −X-axis side of the vibrator  234  by the connecting portions  236 . On the surface at the +Y′-axis side and the surface at the −Y′-axis side of the vibrator  234 , excitation electrodes  231  are formed. From each of the excitation electrodes  231 , an extraction electrode  232  is extracted to the framing body  235 . The extraction electrode  232 , which is extracted from the excitation electrode  231  on the surface at the +Y′-axis side of the vibrator  234 , is extracted via the connecting portion  236  at the +Z′-axis side and the castellation  238   b  at the −X-axis side. The extraction electrode  232  is extracted to the −X-axis side and the +Z′-axis side of the surface at the −Y′-axis side of the framing body  235 . The extraction electrode  232 , which is extracted from the excitation electrode  231  on the surface at the −Y′-axis side of the vibrator  234 , is extracted via the connecting portion  236  at the −Z′-axis side. The extraction electrode  232  is extracted to the −X-axis side of the framing body  235 , and additionally extracted to the castellation  238   a  at the +X-axis side of the framing body  235  and the peripheral area of the castellation  238   a.    
     In the base plate  220   a , the bonding surface  122  is formed in the peripheral area of the surface at the +Y′-axis side of the base plate  220   a . The bonding surface  122  is to be bonded on the surface at the −Y′-axis side of the framing body  235  via the sealing material  142  (see  FIG. 13 ). In the center of the surface at the +Y′-axis side of the base plate  220   a , the depressed portion  121  depressed from the bonding surface  122  in the −Y′-axis direction is formed. At the −Z′-axis side of a side surface at the +X-axis side of the base plate  220   a , a castellation  226   a  depressed toward inside of the base plate  220   a  is formed. At the +Z′-axis side of the side surface at the −X-axis side of the base plate  220   a , a castellation  226   b  depressed toward inside of the base plate  220   a  is formed. The castellation  226   a  and the castellation  226   b  each have a side surface where a side surface electrode  225  is formed. The castellation  226   a  and the castellation  226   b  of the bonding surface  122  each have a peripheral area where a connecting electrode  223  is formed. The connecting electrodes  223  electrically connect to the extraction electrode  232  and the side surface electrodes  225  of the quartz-crystal vibrating piece  230   a . Furthermore, the base plate  220   a  has the surface at the −Y′-axis side where a pair of mounting terminals  224   a  (see  FIG. 13 ) is formed. Each of the mounting terminals  224   a  electrically connects to the corresponding side surface electrode  225  formed at the castellation  226   a  or the castellation  226   b.    
       FIG. 13  is a cross-sectional view taken along the line E-E of  FIG. 12 . In the quartz crystal device  200   a , the bonding surface  112  of the lid plate  110  is bonded to the surface at the +Y′-axis side of the framing body  235  via the sealing material  142  while the bonding surface  122  of the base plate  220   a  is bonded to the surface at the −Y′-axis side of the framing body  235  via the sealing material  142 . In the bonding of the quartz-crystal vibrating piece  230   a  and the base plate  220   a , the castellation  238   a  of the quartz-crystal vibrating piece  230   a  and the castellation  226   a  of the base plate  220   a  are stacked in the Y′-axis direction while the castellation  238   b  of the quartz-crystal vibrating piece  230   a  and the castellation  226   b  of the base plate  220   a  are stacked in the Y′-axis direction. When the quartz-crystal vibrating piece  230   a  and the base plate  220   a  are bonded together, the extraction electrode  232  and the connecting electrode  223  are electrically bonded together. This electrically connects the excitation electrode  231  to the mounting terminal  224   a.    
     The side surface of the castellation  238   a  formed at the +X-axis side of the quartz-crystal vibrating piece  230   a  is formed of a first inclined surface  239   a  and a second inclined surface  239   b . The first inclined surface  239   a  connects to the surface at the +Y′-axis side of the framing body  235  in the quartz-crystal vibrating piece  230   a . The second inclined surface  239   b  connects to the surface at the −Y′-axis side of the framing body  235  in the quartz-crystal vibrating piece  230   a . The first inclined surface  239   a  and the second inclined surface  239   b  intersect with each other at a first top  240   a . The side surface of the castellation  238   b  formed at the −X-axis side of the quartz-crystal vibrating piece  230   a  is formed of a third inclined surface  239   c  and a fourth inclined surface  239   d . The third inclined surface  239   c  connects to the surface at the +Y′-axis side of the framing body  235  in the quartz-crystal vibrating piece  230   a . The fourth inclined surface  239   d  connects to the surface at the −Y′-axis side of the framing body  235  in the quartz-crystal vibrating piece  230   a . The third inclined surface  239   c  and the fourth inclined surface  239   d  intersect with each other at a second top  240   b . The first top  240   a  is formed at the +X-axis side of the quartz-crystal vibrating piece  230   a  compared with the first inclined surface  239   a  and the second inclined surface  239   b . The second top  240   b  is formed at the −X-axis side of the quartz-crystal vibrating piece  230   a  compared with the third inclined surface  239   c  and the fourth inclined surface  239   d.    
     The quartz-crystal vibrating piece  230   a  includes the +Y′-axis side of the framing body  235  where the sealing material  142  is formed in an area that includes the first inclined surface  239   a  and the third inclined surface  239   c . On the surface at the −Y′-axis side of the framing body  235 , the extraction electrode  232  connects to the connecting electrode  223 . Accordingly, the sealing material  142  is not formed on the extraction electrode  232  that directly connects to the connecting electrode  223 . 
     The side surface of the castellation  226   a  formed at the +X-axis side of the base plate  220   a  is formed of a first inclined surface  227   a  and a second inclined surface  227   b . The first inclined surface  227   a  connects to the bonding surface  112  of the base plate  220   a . The second inclined surface  227   b  connects to the surface at the −Y′-axis side of the base plate  220   a . The first inclined surface  227   a  and the second inclined surface  227   b  intersect with each other at a first top  228   a . The side surface of the castellation  226   b  formed at the −X-axis side of the base plate  220   a  is formed of a third inclined surface  227   c  and a fourth inclined surface  227   d . The third inclined surface  227   c  connects to the bonding surface  112  of the base plate  220   a . The fourth inclined surface  227   d  connects to the surface at the −Y′-axis side of the base plate  220   a . The third inclined surface  227   c  and the fourth inclined surface  227   d  intersect with each other at a second top  228   b . The first top  228   a  is formed at the +X-axis side of the base plate  220   a  compared with the first inclined surface  227   a  and the second inclined surface  227   b . The second top  228   b  is formed at the −X-axis side of the base plate  220   a  compared with the third inclined surface  227   c  and the fourth inclined surface  227   d.    
       FIG. 14A  is a plan view of the surface at the +Y′-axis side of the quartz-crystal vibrating piece  230   a . From the excitation electrode  231  formed on the surface at the +Y′-axis side of the vibrator  234 , the extraction electrode  232  passes through the connecting portion  236 , and is extracted to the castellation  238   b  formed at the −X-axis side of the framing body  235 . The castellation  238   b  formed at the −X-axis side of the framing body  235  has a width KC 2  in the X-axis direction on the surface at the +Y′-axis side. The castellation  238   b  has a width KA 4  in the X-axis direction of the second top  240   b . The framing body  235  at the −X-axis side of the vibrator  234  has a width SA in the X-axis direction. The bonded area at the +X-axis side of the castellation  238   b  has a width SA 1 . 
     The castellation  238   a  formed at the +X-axis side of the framing body  235  has a width KB 4  in the X-axis direction on the surface at the +Y′-axis side. The castellation  238   a  has a width KA 3  in the X-axis direction of the first top  240   a . The framing body  235  has the width SA in the X-axis direction. The castellation  238   a  has the width SA 1  of the bonded area at the −X-axis side. 
       FIG. 14B  is a plan view of the surface at the −Y′-axis side of the quartz-crystal vibrating piece  230   a . From the excitation electrode  231  formed at the −Y′-axis side of the vibrator  234 , the extraction electrode  232  passes through the connecting portion  236  at the −Z′-axis side, is extracted to the framing body  235 , and is further extracted to the peripheral area of the castellation  238   a  formed at the +X-axis side of the framing body  235 . 
     The castellation  238   a  formed at the +X-axis side of the framing body  235  has the width KC 2  in the X-axis direction on the surface at the −Y′-axis side. A portion excluding the extraction electrode  232  formed in the peripheral area of the castellation  238   a  has a width SA 2  in the X-axis direction of the framing body  235 . The castellation  238   b  formed at the −X-axis side of the framing body  235  has the width KC 2  in the X-axis direction on the surface at the −Y′-axis side. A portion excluding the extraction electrode  232  formed in the peripheral area of the castellation  238   b  has the width SA 2  in the X-axis direction of the framing body  235 . These areas with the width SA 2  are bonded areas where the framing body  235  is bonded to the base plate  220   a  via the sealing material  142 . 
       FIG. 14C  is a cross-sectional view of the quartz-crystal vibrating piece  230   a .  FIG. 14C  illustrates a cross-sectional view taken along the line E-E of  FIG. 14A  and  FIG. 14B . On the surface at the +Y′-axis side of the framing body  235  in the quartz-crystal vibrating piece  230   a , the sealing material  142  is formed in the area with the width SA 1 . On the surface at the −Y′-axis side of the framing body  235 , the sealing material  142  is formed in the area with the width SA 2 . The areas where the sealing material  142  is formed are uniformly formed at the +X-axis side and the −X-axis side of the quartz-crystal vibrating piece  230   a . In the quartz-crystal vibrating piece  230   a , the width KA 3  is equal to the width KA 4 . 
       FIG. 15A  is a plan view of the surface at the +Y′-axis side of a base plate  220   a . The base plate  220   a  has the width SA in the X-axis direction at each of the +X-axis side and the −X-axis side of the depressed portion  121  on the bonding surface  122 . Portions excluding the respective connecting electrodes  223  at the −X-axis side of the castellation  226   a  and the +X-axis side of the castellation  226   b  have the width SA 2  in the X-axis direction on the bonding surface  122 . These areas with the width SA 2  are bonded areas to be bonded to the surface at the −Y′-axis side of the framing body  235  in the quartz-crystal vibrating piece  230   a  via the sealing material  142 . The first top  228   a  of the castellation  226   a  has the width KA 1  in the X-axis direction while the second top  228   b  of the castellation  226   b  has the width KA 2  in the X-axis direction. In the base plate  220   a , the width KA 1  is equal to the width KA 2 . 
       FIG. 15B  is a plan view of the surface at the −Y′-axis side of the base plate  220   a . On the surface at the −Y′-axis side of the base plate  220   a , a pair of mounting terminals  224   a  are formed. Each mounting terminal  224   a  electrically connects to the corresponding side surface electrodes  225  where the castellation  226   a  or the castellation  226   b  is formed. The surface at the −Y′-axis side of the castellation  226   a  has the width KB 2  in the X-axis direction while the surface at the −Y′-axis side of the castellation  226   b  has the width KC in the X-axis direction. 
       FIG. 15C  is a cross-sectional view of the base plate  220   a . In the base plate  220   a , the surface at the −Y′-axis side of the castellation  226   a  has the width KB 2  that is about 10% to 30% larger than the width KC in the X-axis direction. This forms the width KA 1  equal to the width KA 2 . 
     Method for Fabricating the Quartz Crystal Device  200   a    
     The quartz crystal device  200   a  can be fabricated according to the flowchart illustrated in  FIG. 5 . Hereinafter, a description will be given of the method for fabricating the quartz crystal device  200   a  by referring to the flowchart of  FIG. 5 . 
     In step S 101 , a quartz-crystal wafer is prepared. In step S 101 , the quartz-crystal wafer W 230  is prepared. The quartz-crystal wafer W 230  includes a plurality of quartz-crystal vibrating pieces  230   a  and a plurality of quartz-crystal vibrating pieces  230   b.    
       FIG. 16  is a plan view of the quartz-crystal wafer W 230 . The quartz-crystal wafer W 230  includes the plurality of quartz-crystal vibrating pieces  230   a  and the plurality of quartz-crystal vibrating pieces  230   b . The quartz-crystal vibrating piece  230   b  is formed to be mirror symmetric of the quartz-crystal vibrating piece  230   a . The quartz-crystal vibrating piece  230   b  has dimensions of, for example, the framing body  235  and the castellations  238   a  and  238   b , which are similar to the dimensions of the quartz-crystal vibrating piece  230   a . In the quartz-crystal wafer W 230 , the quartz-crystal vibrating piece  230   a  and the quartz-crystal vibrating piece  230   b  are alternately formed in the X-axis direction and the Z′-axis direction. In the fabrication of the quartz crystal device  200   a , the quartz crystal device  200   b  is also fabricated simultaneously with the quartz crystal device  200   a . The quartz crystal device  200   b  is formed of the lid plate  110 , the quartz-crystal vibrating piece  230   b , and the base plate  220   b  (see  FIG. 19A  and  FIG. 19B ). 
       FIGS. 17A to 17D  and  FIGS. 18A to 18D  illustrate a flowchart of a method for fabricating the quartz-crystal wafer W 230 . Hereinafter, by referring to  FIGS. 17A to 17D  and  FIGS. 18A to 18D , a detailed description will be given of step S 101  in  FIG. 5  that is a process for preparing a quartz-crystal wafer. 
     In step S 111  of  FIGS. 17A to 17D , an AT-cut quartz-crystal wafer is prepared.  FIG. 17A  is a partial cross-sectional view of the AT-cut quartz-crystal wafer W 230 .  FIG. 17A  and views in  FIGS. 17A to 17D  and  FIGS. 18A to 18D  described below are cross-sectional views of cross sections corresponding to the cross section taken along the line F-F of  FIG. 16 . Each cross-sectional view illustrates the scribe lines  171 . An area surrounded by the scribe lines  171  forms one quartz-crystal vibrating piece  230   a . The quartz-crystal wafer W 230  prepared in step S 111  is formed in a planar shape. 
     In step S 112 , a corrosion-resistant film is formed.  FIG. 17B  is partial cross-sectional view of the quartz-crystal wafer W 230  where the corrosion-resistant film  151  has been formed. The corrosion-resistant film  151  is formed on the surfaces at the +Y′-axis side and the −Y′-axis side of the quartz-crystal wafer W 230 . The corrosion-resistant film  151  is formed, for example, by forming a chromium (Cr) layer (not shown) on the surfaces at the +Y′-axis side and the −Y′-axis side of the quartz-crystal wafer W 230  and forming a gold (Au) layer (not shown) on a surface of the chromium layer. Step S 112  is a process for forming the corrosion-resistant film. 
     In step S 113 , a photoresist is formed.  FIG. 17C  is a partial cross-sectional view of the quartz-crystal wafer W 230  where the photoresist  152  has been formed. The photoresist  152  is formed on the surface of the corrosion-resistant film  151 , which is formed in step S 112 . 
     In step S 114 , the photoresist is exposed and developed.  FIG. 17D  is a partial cross-sectional view of the quartz-crystal wafer W 230  where the photoresist  152  has been exposed and developed. The quartz-crystal wafer W 230  is exposed through a mask  154 , and developed to remove the photoresist  152 . The photoresist  152  to be removed in step S 114  is on an area where the through hole  172  and the through groove  237  on the surface at the +Y′-axis side of the quartz-crystal wafer W 230  are formed, and on an area where the through hole  172  and the through groove  237  on the surface at the −Y′-axis side of the quartz-crystal wafer W 230  are formed. The photoresist  152  to be removed for forming the through hole  172  has the width KB 4  from the scribe line  171  at the +X-axis side on the surface at the +Y′-axis side of each quartz-crystal vibrating piece  230   a  and each quartz-crystal vibrating piece  230   b . The photoresist  152  has the width KC 2  from the scribe line  171  at the −X-axis side on the surface of the +Y′-axis side, and at the +X-axis side and the −X-axis side on the surface at the −Y′-axis side of each quartz-crystal vibrating piece  230   a  and each quartz-crystal vibrating piece  230   b . Step S 113  and step S 114  are exposure processes. 
     In step S 115  of  FIGS. 18A to 18D , the corrosion-resistant film  151  is etched.  FIG. 18A  is a partial cross-sectional view of the quartz-crystal wafer W 230  where the corrosion-resistant film  151  has been etched. In step S 115 , the corrosion-resistant film  151  with an exposed surface which is removed in step S 114  is removed by etching. This exposes the quartz-crystal material in the area where the through hole  172  and the through groove  237  are formed on the quartz-crystal wafer W 230 . Step S 115  is a process for etching the corrosion-resistant film. 
     In step S 116 , the quartz-crystal material is processed by wet-etching.  FIG. 18B  is a partial cross-sectional view of the quartz-crystal wafer W 230  where the quartz-crystal material has been processed by wet-etching. In step S 116 , the quartz-crystal material is processed by wet-etching to form the through hole  172  and the through groove  237  in the quartz-crystal wafer W 230 . The quartz-crystal wafer W 230  employs the AT-cut quartz-crystal material. Thus, anisotropy of the crystal causes the through hole  172  with a side surface near the center portion that is narrow toward the inside of the through hole  172 . Step S 116  is a wet-etching process. 
     In step S 117 , the corrosion-resistant film  151  and the photoresist  152  are removed.  FIG. 18C  is a partial cross-sectional view of the quartz-crystal wafer W 230  where the corrosion-resistant film  151  and the photoresist  152  have been removed. As illustrated in  FIG. 18C , at the through hole  172 , a width in the −X-axis direction and a width in the +X-axis direction from the scribe line  171  to the side surface of the base plate  220   a  are respectively the width KA 3  and the width KA 4 . The width KA 3  is equal to the width KA 4 . 
     In step S 118 , electrodes are formed on the quartz-crystal wafer W 230 .  FIG. 18D  is a partial cross-sectional view of the quartz-crystal wafer W 230  where the electrodes have been formed. In step S 118 , the chromium layer is formed on the quartz-crystal wafer W 230 , and the gold layer is formed on the surface of the chromium layer. This forms the excitation electrode  231  and the extraction electrode  232  on the quartz-crystal wafer W 230 . 
     Returning to  FIG. 5 , in step S 201 , the base wafer is prepared. In step S 201 , the base wafer W 220  that includes a plurality of base plates  220   a  and a plurality of base plates  220   b  are prepared. 
       FIG. 19A  is a plan view of the surface at the +Y′-axis side of the base wafer W 220 . On the base wafer W 220 , the plurality of base plates  220   a  and the plurality of base plates  220   b  are formed. The base plate  220   b  is formed to be mirror symmetric of the base plate  220   a . In the base wafer W 220 , the base plate  220   a  and the base plate  220   b  are alternately formed in the X-axis direction and the Z′-axis direction. The peripheral area of the through hole  172  of the bonding surface  122  has the connecting electrode  223 . 
       FIG. 19B  is a plan view of the surface at the −Y′-axis side of the base wafer W 220 . The base plate  220   a  has a pair of mounting terminals  224   a  while the base plate  220   b  has a pair of mounting terminals  224   b . In the base wafer W 220 , one through hole  172  electrically connects to the mounting terminal  224   a  and the mounting terminal  224   b.    
     Returning to  FIG. 5 , in step S 301 , the lid wafer W 110  is prepared. In step S 301 , the lid wafer W 110 , which includes the plurality of lid plates  110 , is prepared. In step S 401 , the quartz-crystal wafer W 230  is placed on the base wafer W 220 . In step S 401 , the quartz-crystal wafer W 230  is stacked on the base wafer W 220  to place the quartz-crystal wafer W 230  on the base wafer W 220 . 
       FIG. 20A  is a partial cross-sectional view of the base wafer W 220  where the quartz-crystal wafer W 230  has been placed.  FIG. 20A  illustrates a cross-sectional view including a cross section taken along the line F-F of  FIG. 16  and a cross section taken along the line G-G of  FIG. 19A  and  FIG. 19B . The extraction electrode  232  and the connecting electrode  223  of the quartz-crystal wafer W 230  are electrically connected together. The quartz-crystal wafer W 230  and the base wafer W 220  are bonded together by the sealing material  142 . This electrically connects the excitation electrode  231  to the mounting terminal  224   a  on the surface at the −Y′-axis side of the base wafer W 220 . 
     In step S 402 , the quartz-crystal wafer W 230  and the lid wafer W 110  are bonded together. The quartz-crystal wafer W 230  and the lid wafer W 110  are bonded such that the sealing material  142  is applied over the surface at +Y′-axis side of the framing body on the quartz-crystal wafer W 230  or the bonding surface  112  of the lid wafer W 110 , and then the framing body of the quartz-crystal wafer W 230  faces the bonding surface  112  of the lid wafer W 110  via the sealing material  142 . 
       FIG. 20B  is a partial cross-sectional view of the quartz-crystal wafer W 230 , the base wafer W 220 , and the lid wafer W 110 .  FIG. 20B  illustrates a cross-sectional view including a cross section taken along the line F-F of  FIG. 16  and a cross section taken along the line G-G of  FIG. 19A  and  FIG. 19B . The quartz-crystal wafer W 230  and the lid wafer W 110  are bonded together via the sealing material  142  on the surface at the +Y′-axis side of the framing body  235  and on the bonding surface  122 . The sealing material  142  in the quartz-crystal wafer W 230  is applied not only over the bonding surface  122  but also over the first inclined surface  239   a  and the third inclined surface  239   c . The lid wafer W 110  and the&#39;quartz-crystal wafer W 230  are bonded together via the sealing material  142  to form the sealed cavity  201 . The vibrator  234  is placed in the cavity  201 . 
     In step S 403 , the quartz-crystal wafer W 230 , the base wafer W 220 , and the lid wafer W 110  are cut. The quartz-crystal wafer W 230 , the base wafer W 220 , and the lid wafer W 110  are cut (diced) along the scribe lines  171  to form individual quartz crystal devices  200   a  and individual quartz crystal devices  200   b . Step S 403  is a dicing process. 
     The quartz crystal device  200   a  is formed to have a uniform width of the bonded areas in the X-axis direction at the +X-axis side and the −X-axis side of the cavity  201 . This prevents breaking the seal of the cavity  201 . The width KA 1  is formed to be equal to the width KA 2  while the width KA 3  is formed to be equal to the width KA 4 . This prevents the side surface electrodes  225  and the extraction electrode  232  from being chipped off in the dicing process. 
     Third Embodiment 
     The quartz-crystal vibrating piece may employ a quartz-crystal vibrating piece where a framing body surrounds the peripheral area of the vibrator and the framing body does not include the castellation. Hereinafter, a description will be given of a quartz crystal device  300  that employs the quartz-crystal vibrating piece including the framing body without the castellation. The embodiment will now be described wherein like reference numerals designate corresponding or identical elements throughout the first Embodiment. 
     Configuration of the Quartz Crystal Device  300   
       FIG. 21  is an exploded perspective view of the quartz crystal device  300 . The quartz crystal device  300  includes the lid plate  110 , a base plate  320 , and a quartz-crystal vibrating piece  330 . The quartz crystal device  300  employs, similarly to the first Embodiment, an AT-cut quartz-crystal vibrating piece as the quartz-crystal vibrating piece  330 . 
     The quartz-crystal vibrating piece  330  vibrates at a predetermined vibration frequency and includes a vibrator  334 , a framing body  335 , and connecting portions  336 . The vibrator  334  is formed in a rectangular shape. The framing body  335  surrounds the peripheral area of the vibrator  334 . The connecting portion  336  connects the vibrator  334  and the framing body  335  together. Between the vibrator  334  and the framing body  335 , through grooves  337  are formed. The through grooves  337  pass through the quartz-crystal vibrating piece  330  in the Y′-axis direction. The vibrator  334  and the framing body  335  do not directly contact each other. The vibrator  334  and the framing body  335  are connected together at the +Z′-axis side on the side surface at the −X-axis side of the vibrator  334  and at the −Z′-axis side on the side surface at the +X-axis side of the vibrator  334 . In the quartz-crystal vibrating piece  330 , thicknesses in the Y′-axis direction of the vibrator  334  and the connecting portion  336  are formed thinner than a thickness in the Y′-axis direction of the framing body  335 . The surfaces at the +Y′-axis side and the surface at the −Y′-axis side of the vibrator  334  each have an excitation electrode  331 . From each of the excitation electrodes  331 , an extraction electrode  332  is extracted to the framing body  335 . The extraction electrode  332 , which is extracted from the excitation electrode  331  on the surface at the +Y′-axis side of the vibrator  334 , is extracted via the connecting portion  336  at the +Z′-axis side. The extraction electrode  332  is extracted to the −X-axis side and the +Z′-axis side on the surface at the −Y′-axis side of the framing body  335 . The extraction electrode  332 , which is extracted from the excitation electrode  331  on the surface at the −Y′-axis side of the vibrator  334 , is extracted via the connecting portion  336  at the −Z′-axis side. The extraction electrode  332  is extracted to the +X-axis side and the −Z′-axis side of the framing body  335 . 
     In the base plate  320 , the surface at the +Y′-axis side does not have the depressed portion and is formed in a planar shape. In the quartz crystal device  300 , a thickness of the vibrator  334  in the quartz-crystal vibrating piece  330  is formed thinner than a thickness of the framing body  335  (see  FIG. 22A ). Although the base plate  320  does not have the depressed portion, the vibrator  334  does not contact the base plate  320 . In the base plate  320 , the peripheral area of the surface at the +Y′-axis side has a bonding surface  322  to be bonded to the surface at the −Y′-axis side of the framing body  335  via the sealing material  142  (see  FIG. 22A ). The surface at the −Y′-axis side of the base plate  320  includes mounting terminals for mounting the quartz crystal device  300  on a printed circuit board or similar. In the base plate  320 , the mounting terminals include hot terminals  324   a , which electrically connects to an external electrode and a similar member, and grounding terminals  324   b  (see  FIG. 22B ). At the +Z′-axis side and the −Z′-axis side on the side surface at the +X-axis side, castellations  326   a  are formed. At the +Z′-axis side and the −Z′-axis side on the side surface at the −X-axis side, castellations  326   b  are formed. The hot terminal  324   a  electrically connects to the extraction electrode  332  of the quartz-crystal vibrating piece  330  via the castellation  326   a  or the castellation  326   b.    
       FIG. 22A  is a cross-sectional view taken along the line H-H of  FIG. 21 . The castellation  326   a  of the base plate  320  is formed in the same shape as the shape of the castellation  226   a  illustrated in  FIG. 13 , and includes the first inclined surface  227   a , the second inclined surface  227   b , and the first top  228   a . The castellation  326   b  of the base plate  320  is formed in the same shape as the shape of the castellation  226   b  illustrated in  FIG. 13 , and includes the third inclined surface  227   c , the fourth inclined surface  227   d , and the second top  228   b . In the quartz crystal device  300 , the bonding surface  112  of the lid plate  110  and the surface at the +Y′-axis side of the framing body  335  are bonded together via the sealing material  142 . The bonding surface  322 , the first inclined surface  227   a , and the third inclined surface  227   c  of the base plate  320  are bonded to the surface at the −Y′-axis side of the framing body  335  via the sealing material  142 . The hot terminal  324   a  electrically connects to the extraction electrode  332  via the side surfaces of the castellation  326   a  or  326   b  and the sealing material  142 . This electrically connects the excitation electrode  331  to the hot terminal  324   a.    
       FIG. 22B  is a plan view of a surface at the −Y′-axis side of the quartz crystal device  300 . The surface at the −Y′-axis side of the base plate  320  that is the surface at the −Y′-axis side of the quartz crystal device  300  includes a pair of hot terminals  324   a  and a pair of grounding terminals  324   b . The hot terminals  324   a  and the grounding terminals  324   b  are extracted to the respective castellations  326   a  and  326   b . The surface at the −Y′-axis side of the castellation  326   a  has the width KB 2  in the X-axis direction similarly to the castellation  226   a  illustrated in  FIG. 15B  while the surface at the −Y′-axis side of the castellation  326   b  has the width KC in the X-axis direction similarly to the castellation  226   b  illustrated in  FIG. 15B . The castellation  326   a  has the width KA 1  in the X-axis direction of the first top  228   a  while the castellation  226   b  has the width KA 2  in the X-axis direction at the second top  228   b . The base plate  320  is formed to have the width KA 1  equal to the width KA 2 . In the base plate  320  is formed, similarly to the base plate  220   a , the surface at the −Y′-axis side of the castellation  326   a  has the width KB 2  in the X-axis direction that is about 10 to 30% wider than the width KC. This makes the width KA 1  equal to the width KA 2 . 
       FIG. 23A  is a plan view of the surface at the +Y′-axis side of the base plate  320 . As illustrated in  FIG. 22A , in the base plate  320 , the bonding surface  322 , the first inclined surface  227   a  of the castellation  326   a , the third inclined surface  227   c  of the castellation  326   b  form a bonded area by forming the sealing material  142 . This bonded area is to be bonded to the quartz-crystal vibrating piece  330 . The base plate  320  has the width SA in the X-axis direction at the +X-axis side and the −X-axis side of the bonding surface  322 . The width of the bonded area at the −X-axis side of the castellation  326   a  and the width of the bonded area at the −X-axis side of the castellation  326   b  are width SA 3 . The width SA 3  is a size of the width SA minus the width KA 1  or the width KA 2 . 
       FIG. 23B  is a cross-sectional view of the base plate  320 . The cross-sectional view of  FIG. 23B  illustrates a cross section taken along the line H-H of  FIG. 23A . The bonded area of the base plate  320  has the width SA at the +X-axis side and the −X-axis side of the base plate  320 , and additionally has the width SA 3  in the portion where the castellation  326   a  or  326   b  is formed. That is, the bonded area has a uniform width in the X-axis direction at the +X-axis side and the −X-axis side of the base plate  320 . This provides uniform bonding strength of the sealing material  142  at the +X-axis side and the −X-axis side of the bonded area. This prevents breaking the seal of the quartz crystal device  300 . 
     Method for Fabricating the Quartz Crystal Device  300   
     A method for fabricating the quartz crystal device  300  basically follows the flowchart illustrated in  FIG. 5 . Hereinafter, a description will be given especially of differences from the first Embodiment or the second Embodiment. 
     In step S 201  of  FIG. 5 , the base wafer (not shown), which includes a plurality of base plates  320 , is prepared. On the base wafer in step S 201 , electrodes are not formed but only an outline of each base plate  320  is formed by etching. 
     Between step S 402  and step S 403 , that is, in step S 402 , the base wafer and the quartz-crystal wafer (not shown), which includes a plurality of quartz-crystal vibrating pieces  330 , are bonded together. Subsequently, electrodes are formed on the surface at the −Y′-axis side of the base wafer by a method such as sputtering or vacuum evaporation. This forms the hot terminals  324   a  and the grounding terminals  324   b  on the base wafer. Electrodes are also formed at the castellations  326   a  and  326   b . Accordingly, as illustrated in  FIG. 22A , the hot terminal  324   a  electrically connects to the extraction electrode  332  of the quartz-crystal vibrating piece  330 . 
     Representative embodiments are described in detail above; however, as will be evident to those skilled in the relevant art, this disclosure may be changed or modified in various ways within its technical scope. 
     The method for fabricating the quartz crystal device according to a second aspect, in the first aspect, is configured as follows. The exposing exposes the photoresist such that a distance from the center in the X-axis direction of the base plate to the through hole at the +X-axis side has a shorter size on the first surface than a size on the second surface. 
     The method for fabricating the quartz crystal device according to a third aspect, in the first aspect, is configured as follows. The exposing exposes the photoresist such that a distance from the center of the base plate to the through hole at the +X-axis side becomes equal to a distance from the center of the base plate to the through hole at the −X-axis side on the first surface, and a distance from the center of the base plate to the through hole at the +X-axis side becomes shorter than a distance from the center of the base plate to the through hole at the −X-axis side on the second surface. 
     The method for fabricating the quartz crystal device according to a fourth aspect, in the first aspect, is configured as follows. The exposing exposes the photoresist such that a distance from the center of the base plate to the through hole at the +X-axis side becomes shorter than a distance from the center of the base plate to the through hole at the −X-axis side on the first surface, and a distance from the center of the base plate to the through hole at the +X-axis side becomes shorter than a distance from the center of the base plate to the through hole at the −X-axis side on the second surface. 
     The method for fabricating the quartz crystal device according to a fifth aspect, in the first aspect to the fourth aspect, is configured as follows. The quartz-crystal vibrating piece is an AT-cut crystal wafer in a rectangular shape. The method includes bonding a quartz-crystal vibrating piece wafer and the base wafer. The quartz-crystal vibrating piece wafer has at least a pair of through holes in the X-axis direction of the AT-cut crystal wafer. The method for fabricating the quartz crystal device includes forming a corrosion-resistant film on a first surface of the quartz-crystal vibrating piece wafer and a second surface at an opposite side of the first surface, exposing a photoresist on the first surface and the second surface in a position corresponding to the through hole after forming the photoresist on the corrosion-resistant film, etching the corrosion-resistant film corresponding to the through hole on the first surface and the second surface, and performing wet-etching on the first surface and the second surface to form the pair of through holes after the etching corrosion-resistant film. The through hole formed by the wet-etching connects the first surface to the second surface. The through hole has a cross section at a +X-axis side and a cross section at a −X-axis side. The cross section at the +X-axis side includes a first inclined surface, a second inclined surface, and a first top. The first inclined surface is formed toward a center side of the cross section from the first surface. The second inclined surface is formed toward the center side of the cross section from the second surface. The first top is formed at an intersection of the first inclined surface and the second inclined surface. The cross section at the −X-axis side includes a third inclined surface, a fourth inclined surface, and a second top. The third inclined surface is formed toward the center side of the cross section from the first surface. The fourth inclined surface is formed toward the center side of the cross section from the second surface. The second top connects the third inclined surface to the fourth inclined surface. The method further includes the exposing the first surface and the second surface in a position corresponding to the through hole such that a distance from a center of the AT-cut crystal wafer to the first top becomes equal to a distance from the center of the AT-cut crystal wafer to the second top. 
     The method for fabricating the quartz crystal device according to a sixth aspect, in the fifth aspect, further includes dicing the quartz-crystal vibrating piece wafer and the base wafer bonded together along a middle of the first top and the second top. 
     A quartz crystal device according to a seventh aspect includes an AT-cut quartz-crystal vibrating piece and an AT-cut quartz-crystal base plate in a rectangular shape. The AT-cut quartz-crystal vibrating piece includes an excitation electrode and an extraction electrode. The extraction electrode is extracted from the excitation electrode. The quartz-crystal base plate supports the quartz-crystal vibrating piece. The base plate has a first surface and a second surface at an opposite side of the first surface. The base plate has a pair of short sides disposed in ±X-axis directions. The short sides each have a castellation depressed toward a center side. The castellation has a cross section at a +X-axis side and a cross section at a −X-axis side. The cross section at the +X-axis side includes a first inclined surface, a second inclined surface, and a first top. The first inclined surface is formed toward a center side of the cross section from the first surface. The second inclined surface is formed toward the center side of the cross section from the second surface. The first top is formed at an intersection of the first inclined surface and the second inclined surface. The cross section at the −X-axis side includes a third inclined surface, a fourth inclined surface, and a second top. The third inclined surface is formed toward the center side of the cross section from the first surface. The fourth inclined surface is formed toward the center side of the cross section from the second surface. The second top connects the third inclined surface to the fourth inclined surface. A distance from a center of the base plate to the first top is equal to a distance from the center in the X-axis direction of the base plate to the second top. 
     The quartz crystal device according to an eighth aspect, in the seventh aspect, is configured as follows. The first surface of the base plate has a bottom surface and a depressed portion. The bottom surface is depressed from the first surface. The depressed portion has sidewalls that extend from the bottom surface. A distance from the sidewall at the +X-axis side of the depressed portion to the first top is equal to a distance from the sidewall at the −X-axis side of the depressed portion to the second top. 
     The quartz crystal device according to a ninth aspect, in the seventh aspect and the eighth aspect, is configured as follows. The first surface of the base plate has a connecting electrode. The connecting electrode connects to the extraction electrode of the quartz-crystal vibrating piece. The second surface of the base plate has a mounting terminal. The mounting terminal mounts the quartz crystal device. The castellation of the base plate has a side surface electrode. The side surface electrode connects the connecting electrode to the mounting terminal. A sealing material is formed on the first inclined surface and the third inclined surface. 
     The quartz crystal device according to a tenth aspect, in the seventh aspect to the ninth aspect, is configured as follows. The AT-cut crystal wafer includes a framing body in a rectangular shape and a castellation. The framing body includes a first surface and a second surface at an opposite side of the first surface. The framing body has a pair of short sides disposed in ±X-axis directions. The castellation is depressed toward a center side at the short sides. The castellation of the AT-cut crystal wafer has a cross section at a +X-axis side and a cross section at a −X-axis side. The cross section at the +X-axis side includes a first inclined surface, a second inclined surface, and a first top. The first inclined surface is formed toward a center side of the cross section from the first surface. The second inclined surface is formed toward the center side of the cross section from the second surface. The first top is formed at an intersection of the first inclined surface and the second inclined surface. The cross section at the −X-axis side includes a third inclined surface, a fourth inclined surface, and a second top. The third inclined surface is formed toward the center side of the cross section from the first surface. The fourth inclined surface is formed toward the center side of the cross section from the second surface. The second top connects the third inclined surface to the fourth inclined surface. A distance from a center in the X-axis direction of the AT-cut crystal wafer to the first top is equal to a distance from the center in the X-axis direction of the base plate to the second top. 
     The quartz crystal device according to an eleventh aspect, in the seventh aspect to the ninth aspect, is configured as follows. The first surface of the base plate has a circular bonded area. The bonded area is bonded to a lid plate via a sealing material. The lid plate seals the quartz-crystal vibrating piece. The bonded area at the +X-axis side of the base plate without a contact with the castellation in the X-axis direction and the bonded area at the −X-axis side of the base plate have a same width in the X-axis direction. The bonded area at the +X-axis side of the base plate in contact with the castellation in the X-axis direction and the bonded area at the −X-axis side of the base plate have a same width in the X-axis direction. 
     The quartz crystal device according to a twelfth aspect, in the tenth aspect, is configured as follows. The first surface of the base plate has a circular bonded area. The bonded area is to be bonded to the framing body via a sealing material. The base plate has an area without a contact with the castellation in the X-axis direction. The bonded area at the +X-axis side of the base plate and the bonded area at the −X-axis side of the base plate have a same width in the X-axis direction in the area without a contact with the castellation. The base plate has an area in contact with the castellation in the X-axis direction. The bonded area at the +X-axis side of the base plate and the bonded area at the −X-axis side of the base plate have a same width in the X-axis direction in the area in contact with the castellation. 
     With the quartz crystal device and the method for fabricating the quartz crystal device according to the embodiment, the castellation can be formed at a uniform distance from the center of the base plate even in the case where the base wafer formed of the quartz-crystal material is used. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.