Abstract:
A method of fabricating a piezoelectric vibrator comprises providing a piezoelectric oscillating plate having a piezoelectric vibrator piece and frame integrally connected to a base end portion of the piezoelectric vibrator piece and surrounding the piezoelectric vibrator piece. A pair of excitation electrodes is disposed on surfaces of two sides of the piezoelectric vibrator piece for vibrating the piezoelectric vibrator piece. Bond films are formed on upper and lower surfaces of the frame and are connected to the excitation electrodes. Shortcircuiting electrodes are disposed on the piezoelectric oscillating plate for causing a shortcircuit to electrically connect the bond films to each other. The piezoelectric vibrator piece is covered to seal the piezoelectric vibrator piece in an airtight manner via the bond films without hampering vibration of the piezoelectric vibrator piece.

Description:
This application is a division of application Ser. No. 09/771,066 filed Jan. 26, 2001, now U.S. Pat. No. 6,504,290. 
    
    
     BACKGROUND OF THE INVENTION 
     1.Field of the Invention 
     The present invention relates to an electrode structure of and a method of fabricating a piezoelectric vibrator for a portable telephone and a portable information terminal. 
     2.Description of Related Art 
     As a piezoelectric vibrator of a related art, there is provided a structure in which, for example, upper and lower face of a vibrator comprising a piezoelectric vibrator piece and an upper portion of frame integrally formed at a base end portion of the piezoelectric vibrator piece, are provided with a pair of a lid and a base having recess portions having spaces to a degree of not hampering vibration of the piezoelectric vibrator piece. 
     When a plurality of respective members of piezoelectric vibrators as describe above are formed on a wafer having a large area and mass-produced by a unit of the wafer, according to an electrode pattern such as an excitation electrode film formed on an individual vibration piece, in order to grasp electric properties by individually exciting the vibration piece, it is necessary to arrange independently each of electrode patterns. 
     According to such a structure, when there is adopted a method of bonding the respective members under high temperature and applying voltage by interposing a bond film as in anode bonding, by feeding electricity respectively to a plurality of the electrode patterns provided to a face of the wafer opposed to a side of a lid formed with a plurality of the vibrators, electricity is fed to the bond film of the wafer formed with the base and the vibrators and the bases are bonded earlier. Successively, extension electrodes to outer electrodes are formed at the wafer formed with the bases, electricity is fed to the respective extension electrodes, electricity is fed to the bond films on the side of the lids and the lids and vibrators are bonded. 
     However, according to the above-described method, when the lids and the bases are formed at a wafer having a material with thermal expansion different from that of the wafer formed with the vibrators, at a time point of bonding the wafer formed with the vibrators and the bases, by a difference in the thermal expansion coefficient of the wafer formed with the vibrators and the bases, warp is caused and therefore, a large area thereof enlarging a warp amount can not be bonded. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing drawbacks in the conventional art, it is an object of the invention to provide a method of fabricating a piezoelectric vibrator having an electrode structure which prevents the occurrence of warp in a bonding operation and which is capable of bonding a large area with high productivity. 
     According to an aspect of the invention resolving the above-described problem, when there is fabricated, in a unit of wafer, a piezoelectric vibrator having a structure including a pair of a lid and a base having recess portions having spaces to a degree of not hampering vibration of a piezoelectric vibrator piece on upper and lower faces of an vibrator comprising the piezoelectric vibrator piece and a frame-like portion integrally connected to a base end portion of the piezoelectric vibrator piece and surrounding the piezoelectric vibrator piece, there is provided an electrode structure of the piezoelectric vibrator characterized in that a plurality of the vibrators each comprising the piezoelectric vibrator piece and the frame-like portion are formed on the wafer, a plurality of electrode patterns each comprising a pair of excitation electrodes formed on the piezoelectric vibrator piece and bond films on the frame-like portion connected to the excitation electrodes and respectively formed independently from each other, are added with sputter films for shortcircuiting capable of being bonded to lids for shortcircuiting respectives thereof and the plurality of electrode patterns are connected to each other. By forming the sputter films for shortcircuiting and connecting all of the respective electrode patterns, electricity can be supplied simultaneously to the bond films on two faces of the substrate. Thereby, according to the invention, three sheets of wafers can be bonded simultaneously, occurrence of warp after bonding can be prevented and a large area can be bonded. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a disassembled perspective view of a piezoelectric vibrator according to an embodiment of the invention; 
     FIG. 2 is a top view of a vibrator  20  according to the embodiment of the invention; 
     FIG. 3 is a sectional view of the piezoelectric vibrator according to the embodiment of the invention; 
     FIG. 4 is a sectional view of the piezoelectric vibrator formed on a wafer according to the embodiment of the invention; 
     FIG. 5 is a outline view of a quartz wafer according to the embodiment of the invention; 
     FIG. 6 is an outline view of the quartz wafer according to the embodiment of the invention after forming a sputter film for shortcircuiting; and 
     FIG. 7 shows constitution and arrangement in bonding the wafer according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A detailed explanation will be given of the invention in reference to the drawings as follows. 
     FIG. 1 is a disassembled perspective view of the invention, FIG. 2 is a top perspective view of the invention and FIG. 3 is a sectional view of a piezoelectric vibrator of the invention. 
     A piezoelectric vibrator of the embodiment is, for example, a quartz vibrator having a tuning fork type quartz vibrator piece  110  comprising quartz (SiO 2 ) and, as illustrated, provided with an vibrator  20  having the quartz vibrator piece  110  and a lid  10  and a base  30  constituting a pair of lids bonded to two faces of the vibrator  20  for sealing in air tight the quartz vibrator piece  110  in an oscillatable state. As shown by FIG. 1, FIG.  2  and FIG. 3, the vibrator  20  of the embodiment includes the tuning fork type quartz vibrator piece  110  and a frame-like portion  100  integrally connected to a base end portion of the quartz vibrator piece  110  for surrounding the quartz vibrator piece  110 . 
     The lid  10  and the base  30  constituting the pair of cover members or lids, are formed by, for example, soda lime glass and are provided with recess portion cavities  90  to partition spaces to a degree of not hampering vibration of the quartz vibrator piece  110  respectively at regions in correspondence with the quart vibrator piece  110 . 
     Further, the bond film  41  is extended to a surface of the vibrator  20  on an opposed side via a side face of an end portion of the frame-like portion  100  in the short side direction on the side of the base end portion of the quartz vibrator piece  110  of the vibrator  20 , that is, via an inner wall face of the through hole  121  of the quartz wafer  130 . Further, at least portions of the bond film  40  and the bond film  41  formed on the two faces of the vibrator  20  are formed to surround the recess portion cavities  90  of the lid  10  and the base  30  respectively at the two faces and, after bonding, inner portions of the cavities  90  of the recess portions are sealed in an air tight manner. 
     Further, by the bond films  40  and  41 , the lid  10  and the base  30  are bonded to upper and lower faces of the vibrator  20  by so-to-speak anode bonding although a detailed description thereof will be given later. 
     In steps of fabricating the quartz vibrator according to the embodiment, pluralities of the vibrators  20 , the lids  10  and the bases  30  are respectively formed on a wafer by etching by photolithography. As shown by FIG. 4, the vibrator  20  is formed with a plurality of the quarts vibrator pieces  110  on a single sheet of a quartz wafer  130  which is a first wafer. That is, a plurality of the vibrators  20  are integrally formed at the quartz wafer  130 . Further, simultaneously therewith, through holes  121  are formed among the respective quartz vibrator pieces  110  in the longitudinal direction of the quartz vibrator piece  110 , and inner faces of the through hole  121  constitute portions of side faces of the vibrators  20  after cutting the quartz wafer  130 . 
     The lids  10  and the bases  30  are formed at glass wafers  140  and  150  comprising, for example, soda lime glass. Pluralities of the recess portion cavities  90  are formed on the wafers in correspondence with the respective quartz vibrator pieces  110  of the quartz wafer  130  by etching by photolithography. That is, there are integrally formed the plurality of lids  10  at the glass wafer  140  constituting a second wafer and the plurality of bases  30  at the glass wafer  150  constituting a third wafer. Further, simultaneously therewith, at portions of the glass wafer  150  in correspondence with the through holes  121  of the quartz wafer  130 , there are formed through holes  120  larger than the through holes  121  of the quartz wafer  130  and inner faces of the through holes  120  formed at the glass wafer  150  constitute portions of side faces of the lids  10  and the bases  30  respectively after cutting the glass wafers  140  and  150 . 
     As shown by FIG. 5, the upper and lower faces and the side faces of the quartz vibrator pieces  110  of the plurality of vibrators  20  formed on the quartz wafer  130 , are formed with the excitation electrode films  80  and  81 , the bond films  40  and  41  at the upper and lower faces of the frame-like portion  100 , and extension electrodes  50  are formed at base end portions of the quartz vibrator pieces  110 , by the same sputter film formed over an entire surface of the quartz wafer  130 . Although as material of the sputter film, there is used Al, Cr or an alloy of these, in this embodiment, Al is used for forming thereof. By patterning the Al sputter film by photolithography, electrode patterns comprising electrodes of the excitation electrodes  80  and  81  and the extension electrodes  50  and the bond films  40  and  41  are formed on upper and lower faces of the respective vibrators  20 . 
     The excitation electrode film  80  constituting one electrode is extended and connected to the bond film  40  and the excitation electrode  81  constituting other electrode is extended and connected to the bond film  41 , respectively. 
     Further, the bond film  41  is extended to a surface of the vibrator  20  on an opposed side via a side face of an end portion of the frame-like portion  100  in the short side direction on the side of the base end portion of the quartz vibrator piece  110  of the vibrator  20 , that is, via an inner wall face of the through hole  121  of the quartz wafer  130 . Further, at lease portions of the bond film  40  and the bond film  41  formed on the two faces of the vibrator  20 , are formed to surround the recess portion cavities  90  of the lid  10  and the base  30  respectively at the two faces and after bonding, inner portions of the cavities  90  of the recess portions are sealed in air tight. 
     At this stage, electrode patterns  160  of the respective vibrators  20  are independent from each other as shown by FIG. 5, characteristics of the vibrators can be adjusted by using the extension electrodes  50  constituting poles different from those of seal portions and the frequencies of the quartz vibrator pieces  110  are adjusted at this stage. 
     Different from the related art, according to the invention, after forming respectives of the vibrators  20 , the lids  10  and the bases  30  in the wafers, the three wafers are simultaneously bonded by the anode bonding. The bonding is carried out in high vacuum. However, it is difficult to supply electricity to all of the vibrators  20  sandwiched by the lids  10  and the bases  30  since the electrodes of the respective vibrators are independent from each other as describe above. Hence, according to the invention, after adjusting frequencies of the respectives of the plurality of quartz vibrator pieces  110  formed at the quartz wafer  130 , by forming sputter films  70  for shortcircuiting of metal films, the bond films  40  and  41  in the individual electrode patterns  160  are connected to each other, thereby, electricity can be supplied to the bond films  40  and  41  of all the vibrators. Although according to the embodiment, as shown by FIG. 6, the sputter films  70  for shortcircuiting are formed to connect to each other corner portions of the respective electrode patterns  160 , that is, corner portions of the bond films  40  and  41  on the frame-like portions  100 , the invention is not limited thereto but the respective electrode patterns may be connected to each other. 
     Al is used for the sputter film  70  for shortcircuiting such that the sputter film  70  per se can be bonded and the film thickness is formed to be as thin as about 1000 A (Angstrom). A range of overlapping the bond films  40  and  41  at the corner portions of the electrode patterns  160  and the sputter films  70  for shortcircuiting, is set to a range of not hampering bonding the bond films  40  and  41  when the bond films  40  and  41  are used for the anode bonding and the films may be overlapped by each other by about 10 through 20 micrometers. 
     As shown by FIG. 7, in bonding the three wafers, the quartz wafer  130  formed with the vibrators  20 , are sandwiched by the glass wafer  140  formed with the lids  10  and the glass wafer  150  formed with the bases  30  in vacuum, and the assembly is connected to a direct current power source such that the electrode patterns  160  comprising Al films of upper and lower faces of the quartz wafer  130  constituting the excitation electrodes  80  and  81  and the bond films  40  and  41  connected to each other by the sputter films  70  for shortcircuiting, constitute a positive pole and the glass wafer  140  and glass wafer  150  constitute a negative pole and three sheet of the wafers are simultaneously bonded by the anode bonding. At this occasion, by forming the sputter films  70  for shortcircuiting on the vibrators  20  and connecting the electrode patterns  160  thereto, there are connected all of the electrode patterns  160  from the bond films  40  and the bond films  41  to the upper and lower faces of the quartz wafer  130  and electricity can be supplied to all of the upper and lower faces. Therefore, the glass wafer  140  formed with the lids  10  and the glass wafer  150  formed with the bases  30  can simultaneously be bonded to the upper and lower faces of the quartz wafer  130  by the anode bonding. Although warp is caused in bonding by a difference between the thermal expansion coefficients of quartz and glass, by simultaneously bonding the glass wafers  140  and  150  to the both upper and lower faces of the quartz wafer  130 , the problem of warping is resolved and a large area can be bonded with high productivity. 
     After finishing the bonding operation, there are formed extension electrodes  60  and  61  from side faces of end portions in the short side direction of the bases  30 , that is, from inner wall faces of the through holes  121  of the glass wafer  150  to surfaces of the bases  30  via inner wall faces of the through holes  120 , for example, by partially sputtering metal films comprising chromium (Cr) and gold (Au). The extension electrode  60  is provided be brought into contact with the bond film  40  and the extension electrode  61  is provided to be brought into contact with the bond film  41 . 
     Further, by using technology of a dicing saw, the bonded wafers bonded and integrated with three sheets of the wafers, are mechanically cut at predetermined positions to thereby finish the individual quartz vibrators. 
     As has been explained above, according to the invention, there is prevented the problem of warp posed when the materials having different thermal expansion are used for the lids by the method of bonding under high temperature and applying voltage such as the anode bonding and large area can be bonded with high productivity.