Abstract:
A piezoelectric vibrator has a piezoelectric vibration plate having a piezoelectric vibration piece. First and second oscillation electrode films are disposed on the piezoelectric vibration plate for undergoing oscillating movement to vibrate the piezoelectric vibration plate. Each of the first and second oscillation electrode films terminates in a bonding film portion. A pair of cover members form a hermetically sealed cavity containing the piezoelectric vibration piece of the piezoelectric vibration plate. The cover members are anodically bonded together through the bonding film portions of the first and second oscillation electrode films. Each lead electrode of a pair of lead electrodes has a portion connected to a respective one of the bonding film portions of the first and second oscillation electrode films.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a piezoelectric vibrator for use in devices such as portable telephones and portable information terminals. 
     As a conventional piezoelectric vibrator, there is known, for example, a structure shown in FIG. 8 having oscillation electrode films  63  for vibrating piezoelectric vibration pieces having one end connected to lead electrodes  62  provided on upper and lower surfaces of a piezoelectric vibration plate  61  integrally formed with a piezoelectric vibration piece and a frame portion, and a pair of lid members  66  bonded through bonding materials  64  on the oscillation electrode films  63  and each having a recess  65  defining such a degree of a space as not to prevent vibration of the piezoelectric vibration pieces. 
     In such a piezoelectric vibrator, generally the oscillation electrode films  63  are respectively extended from different longitudinal ends of the piezoelectric vibration plate  61  to a side surface and connected to lead electrodes  62 . This lead electrode  62  is extended to a surface of one lid member  66 . 
     However, in the above construction, a gap occurs between the piezoelectric vibration plate  61  and the lid member  66  at the vicinity of the lengthwise end of the piezoelectric vibration plate  61  on a surface opposite to a side from which the oscillation electrode film  63  extends. Due to this, a space A is formed at an inner side of the lead electrode  62 . There is a problem that in this portion the lead electrode  62  is low in strength and hence there is a high possibility of disconnection. 
     The present invention has been made in view of such a circumstance, and it is an object to provide a piezoelectric vibrator in which the possibility of disconnection of a lead electrode is lowered and its reliability is improved. 
     SUMMARY OF THE INVENTION 
     In first form of the invention for solving the object, a piezoelectric vibrator comprises a piezoelectric vibration plate having a piezoelectric vibration piece and a frame portion connected integrally with a base portion thereof and surrounding the piezoelectric vibration piece; a pair of oscillation electrodes provided on opposite surfaces of the piezoelectric vibration plate to vibrate the piezoelectric vibration plate; and a pair of lid members which are bonded through bonding films and which are connected to face each of the oscillation electrodes for hermetically sealing the piezoelectric vibration piece without interfering vibration thereof; the pair of oscillation electrodes has a first electrode formed on a first one of the opposite surfaces of the piezoelectric vibration plate and extending lengthwise to one end of the piezoelectric vibration plate on the first surface, and a second electrode formed on the other of the opposite surfaces of the piezoelectric vibration plate and extending lengthwise to another end of the piezoelectric vibration plate on the second surface; and wherein at least one of the electrodes extends from one of the surfaces to the opposite surface of the piezoelectric vibration plate through a side surface of the end. 
     In a second form of the invention, the one pair of oscillation electrodes of both electrodes are extended to a surface on an opposite side through an end side surface on an extension side. 
     In a third form of the invention, the one pair of oscillation electrodes at lengthwise both ends are connected with face to face each lead electrode extended to a surface of the lid member on a side that at least one electrode is extended to a surface on an opposite side of the piezoelectric vibration plate. 
     In the invention as described above, it is possible to prevent disconnection of the lead electrode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a quartz crystal resonator according to one embodiment of the present invention; 
     FIG. 2 is a sectional view of the quartz crystal resonator according to the one embodiment of the present invention; 
     FIG. 3 is a plan view showing a general arrangement of a quartz wafer according to the one embodiment of the present invention; 
     FIG. 4 is a plan view showing a general arrangement of a lid member forming substrate according to the one embodiment of the present invention; 
     FIG. 5 is a sectional view showing a manufacturing process for a piezoelectric vibrator according to the present invention; 
     FIG. 6 is a sectional view of a quartz crystal resonator according to another embodiment of the present invention; 
     FIG. 7 is a sectional view of a quartz crystal resonator according to another embodiment of the present invention; and 
     FIG. 8 is a sectional view showing an example of a piezoelectric vibrator according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder, the present invention will be explained in detail based on the drawings. 
     FIG. 1 is an exploded perspective view of a piezoelectric vibrator according to one embodiment of the present invention, and FIG. 2 is a sectional view thereof. 
     A piezoelectric vibrator of the present embodiment is, for example, a quartz crystal resonator  10  having a quartz crystal vibration piece  11  of a tuning-fork type formed of quartz (SiO 2 ) and provided as shown with a quartz crystal plate  12  having the quartz crystal vibration piece  11  and a pair of cover or lid members  14  bonded to respective surfaces of this quartz crystal plate  12  to hermetically seal the quartz crystal vibration piece  11  in a vibratable state. 
     The vibration piece  11  has a base portion  11   a  and two vibratory tines  11   b ,  11   c  extending from the base portion  11   a . The quartz crystal plate  12  of the present embodiment has the tuning-fork type quartz crystal vibration piece  11 , opposed main surfaces  12   a ,  12   b , side surfaces  12   c ,  12   d  at respective opposite ends, and a frame portion  15  integrally connected with the base portion  11   a  of and surrounding the quartz crystal vibration piece  11 . 
     The pair of lid members  14  are formed, for example, of soda-lime glass or the like. Each lid member  14  has a recess  13 . When the lid members are connected, the recesses  13  define a space or cavity for housing the quartz crystal vibration piece  11  in such an extent as not to prevent vibration of the quartz crystal vibration piece  11 . 
     The quartz crystal plate  12  bonded with the lid members  14 , as shown in FIG. 2, has oscillation electrode films  16  formed on the opposite main surfaces and on the side surfaces to vibrate the quartz crystal vibration piece  11 , and bonding films  17 ,  18  formed of a same material as the oscillation electrode films  16  in an area of the main surfaces corresponding to the frame portion  15  and providing actual bonding portions to the lid members  14 . The bonding films  17 ,  18  and the lid members  14  are, although hereinafter described in detail, bonded through so-called anodic bonding, thereby providing a bonding between the quartz crystal plate  12  and the lid members  14 . 
     Each oscillation electrode film  16  formed on the main surfaces of the quartz crystal plate  12  is extended lengthwise to an end of each surface, and in the present embodiment is further extended to a region facing the lid member  14  on an opposite-side surface through respective end side surfaces in a lengthwise direction of the quartz crystal plate  12 . That is, in the present embodiment an electrode  16   a  as one pole of the oscillation electrode film  16  is extended to the end portion on a right end in the figure to become a terminal connection bonding film  17   a  on the same surface, and further provided continuous to a turning-back portion  17   c  on an opposite side surface through a connection portion  17   b  on an end side surface. Meanwhile, an electrode  16   b  as another pole is extended to an end on a left end in the figure to become a terminal connection bonding film  18   a , and provided continuous to a turning-back portion  18   c  on an opposite side surface through a connection portion  18   b  on an end side surface. By doing so, at the end portion of the quartz crystal plate  12  usually projecting from the lid members  14 , bonding films  17   a - 17   c ,  18 - 18   c  are provided between the lid member  14  without having gaps which are connected to each electrode  16   a ,  16   b . Accordingly, external connection becomes easy. In the present embodiment, a lead electrode  19  is provided contacting the bonding films  17   b ,  17   c  while a lead electrode  20  is provided contacting the bonding films  18   b ,  18   c . Contact portions  19   a ,  20   a  are provided in an upper part of the figure. 
     Incidentally, at least parts of terminal connection bonding films  17   a ,  18   a  formed on the respective surfaces of the quartz crystal plate  12  are formed respectively to surround the concave portions  13  on both main surfaces. After bonding, the concave portions  13  are hermetically sealed. 
     In this manner, in the present embodiment the bonding film  17  formed on each surface of the quartz crystal plate  12  was provided extending from the lengthwise end portion of the quartz crystal plate  12  through the side surface to the region on the opposite side surface facing the lid member  14 . Due to this, even if lead electrodes  19 ,  20  are provided, no spaces will be formed at an inside thereof. The lead electrodes  19 ,  20  are positively adhered to the bonding film  17   b ,  17   c  and  18   b ,  18   c  and to the lid member  14 . Therefore, it is possible to form a quartz crystal resonator in which the possibility of disconnection of the lead electrodes  19 ,  20  is significantly lowered, thereby improving reliability. 
     Hereunder, explanation is made on a manufacturing process for such a quartz crystal resonator. Incidentally, FIG. 3 is a plan view showing a quartz wafer according to the present embodiment. FIG. 4 is a plan view showing an outline of a lid member forming substrate according to the present embodiment. 
     First, as shown in FIG. 3, a quartz wafer  21  having a thickness of, for example, 0.1-0.2 mm is etched to thereby form a plurality of quartz crystal vibration pieces  11  on one quartz wafer  21 . That is, a plurality of quartz crystal plates  12  are formed integrally with the quartz wafer  21 . Also, at the same time, through-holes  21   a  are formed between the quartz crystal vibration pieces  11  in a lengthwise direction of the quartz crystal vibration pieces  11 . This through-hole  21   a  has an inner surface to be formed into part of a side surface of a quartz crystal plate  12  after cutting the quartz wafer  21 . 
     Also, as shown in FIG. 4, for example, a lid forming member  22  formed of soda-lime glass is etched to thereby form recesses  13  for the quartz crystal vibration pieces  11  of the quartz wafer  21 . That is, a plurality of lid members  14  are formed integrally with the lid forming member  22 . Also, at the same time, at corresponding areas of the quartz wafer  21  to the through-holes  21   a , through-holes  22   a  are formed greater than the through-holes  21   a . This through-hole  22   a  has an inner surface to be formed into part of a side surface of the lid member  14 . 
     Next, as shown in FIG.  5 ( a ), a metal film  23  is film-formed by sputtering or the like over the entire surface of the quartz wafer  21  thus formed. This metal film  23  is a film to constitute bonding films  17 ,  18  becoming actual bonding portions to lid forming members  22  and oscillation electrode films  16  for vibrating the quartz crystal vibration pieces  11 . The material thereof is not especially limited but preferably uses, for example, chromium, aluminum or the like. In the present embodiment chromium was used. 
     Next, as shown in FIG.  5 ( b ), the metal film  23  is patterned to form oscillation electrode films  16  and bonding films  17  in a peripheral area corresponding to the frame  15 . 
     Next, as shown in FIG.  5 ( c ), a pair of lid forming members  22  are bonded onto respective surfaces of the quartz wafer  21  trough the bonding films by anodic bonding in an inert gas or in vacuum, hermetically sealing the quartz crystal vibration pieces  11  in the space formed by the recesses  13 . After the anodic bonding, particularly when using soda-lime glass, it is necessary to heat each member to, e.g. 100° C.-150° C., lower than a glass softening point, and apply respective d.c. voltages of 3-5 kV to the bonding films  17 ,  18  on the respective surfaces of the quartz wafer  21  and to the lid forming member  22  with an anode given on a lid forming member  22  side by a direct current power source. For example, in the present embodiment each member was heated to 120° C. and applied with a direct current voltage of about 3.5 kV, thus performing anodic bonding. 
     In this manner, by anodically bonding between the quartz crystal plate  12  and the lid members  14  through bonding films  17 ,  18  under such conditions as the one stated above, the bonding films  17 ,  18  and the lid members  14  can be well bonded. That is, the quartz oscillation plate  12  and the lid members  14  are well bonded through the bonding films  17 ,  18 , and there is no occurrence of cracking or the like. 
     Here, quartz as a material of the quartz oscillation plate  12  has a thermal expansion coefficient of 13.7 ppm/°C. Soda-lime glass used as a lid member  14  has a thermal expansion coefficient of 8.5 ppm/°C. That is, the difference between these thermal expansion coefficients is 5.2 ppm/°C. and comparatively large. It is therefore difficult to perform anodic bonding on them under the conventionally-known condition. However, as in the present embodiment, by setting the bonding temperature to a low temperature of about 100-150° C. and applying a comparatively high direct current voltage of about 3-5 kV to perform anodic bonding, the affection of thermal expansion coefficient can be reduced to extremely small. Preferred bonding is possible even for members that are comparatively large in thermal expansion coefficient. 
     After bonding the quartz wafer  21  and the lid forming members  22  by anodic bonding in this manner, next as shown in FIG.  5 ( d ) a metal film is film-formed over surfaces of the bonding films  17 ,  18  and one lid member  14  by sputtering or the like which is for example of chromium (Cr) and gold (Au) and the like. Furthermore, this metal film is patterned to form end electrodes  19 ,  20 . 
     Incidentally, in the case that the bonding films  17 ,  18  are formed of chromium as in the present embodiment, lead electrodes  19 ,  20  are easy to form over a surface thereof by sputtering. However, where the bonding films  17 ,  18  are formed of aluminum, aluminum will be oxidized during patterning the bonding films  17 ,  18 . Accordingly, the lead electrodes  19 ,  20  are difficult to film-form by sputtering. It is preferred to form, for example, by inverted sputtering or the like. 
     Thereafter, as shown in FIG.  5 ( e ), the quartz wafer  21  and lid forming member  22  are mechanically cut in predetermined positions using a technique of dicing or the like into individual quartz crystal resonators  10 . 
     Incidentally, in the present embodiment the individual bonding films  17 ,  18  connected with each oscillation electrode film  16  on both surface of the quartz crystal plate  12  were respectively extended to a surface on an opposite side of the quartz crystal plate  12 . However, the invention is not limited to this. For example, as shown in FIG. 6 only the bonding film  17  on one surface side of the quartz crystal plate  12  may be extended to a surface on an opposite side while the bonding film  18  on the other surface side be extended to the side surface of the quartz crystal plate  12 . In this case, if the lead electrodes  19 ,  20  are extended from the bonding films  17 ,  18  to a lid member  14  surface on a side the bonding film  17  is extended, a similar effect to the one stated above is obtainable. 
     Also, in the present embodiment, the quartz crystal plate  12  and the lid member  14  were bonded by anodic bonding. However, the invention is not limited to this. For example, as shown in FIG. 7 it is of course possible to bond the quartz crystal plate  12  and the lid member  14 , for example, through a bonding member  25  such as low melting point glass. Even with such structure, a similar effect to the above is obtainable by extending the bonding film on at least one surface of the quartz crystal plate  12  to an opposite side of the quartz crystal plate. 
     As explained above, in the present invention, the oscillation electrode films provided on both main surfaces of the piezoelectric vibration plate are respectively extended to a surface on an opposite side of the piezoelectric vibration plate through a side surface at a lengthwise one end of the piezoelectric vibration plate. Due to this, it is possible to form a lead electrode without defining a space at an inside thereof. Accordingly, the possibility of disconnection of the lead electrode is significantly lowered, thereby improving the reliability of the piezoelectric oscillator.