Patent Document

BACKGROUND 
   The present disclosure relates to a piezoelectric device equipped with a drawing electrode electrically coupled to an exciting electrode on a piezoelectric element and with a substrate bonded to this drawing electrode with a metallic brazing material. 
     FIG. 7  is a schematic sectional diagram of an existing piezoelectric device  1  (see, e.g., Unexamined Patent Publication No. 2004-328442). 
   This piezoelectric device is composed of three stacked crystal substrates  2 ,  3 ,  4 . 
   The crystal substrate  2  is disposed between the crystal substrates  3  and  4 . Upper and lower planes of a central portion  2   a  of the crystal substrate  2  are recessed and shaped into so-called inverse mesas, thereby forming inner spaces Ss above and under the central portion  2   a . Exciting electrodes  5   a ,  5   b  are provided on the upper and lower planes of the central portion  2   a  of the crystal substrate  2  to actively vibrate the central portion. The exciting electrode  5   b  on the lower plane is electrically coupled to a mounting terminal portion  7  via a drawing electrode  6   b . The exciting electrode  5   a  on the upper plane is drawn via a drawing electrode  6   a  up to an inner plane of a through hole  9  and electrically coupled to the mounting terminal portion  7 . 
   The crystal substrate  3  has through holes  8 ,  8  at positions where the drawing electrodes  6   a ,  6   b  are provided. Filled in these through holes  8 ,  8  are conductive materials  10 , connected to the drawing electrodes  6   a ,  6   b . These conductive materials  10 ,  10  are slightly protruding from a lower plane of the crystal substrate  3 , and the protruding portions make the mounting terminal portions  7 ,  7 . 
   Further, the crystal substrates  3  and  4  are bonded and fixed using a metallic brazing material  11  such as gold/tin, interposing the crystal substrate  2  therebetween. Since it is necessary to seal the inner space S, the brazing material  11  is circumferentially provided and then heated and melted to bond the three crystal substrates  2 ,  3 ,  4  together. 
   Unexamined Patent Publication No. 2004-328442 
   Such a piezoelectric device  1  is structured so that the drawing electrodes  6   a ,  6   b  come in contact with the brazing material  11 . Thus, when the brazing material  11  is heated and melted in order to bond the crystal materials  2 ,  3 ,  4  together, the metallic brazing material  11  such as gold/tin spreads to the drawing electrodes  6   a ,  6   b . If the spreading extends to the exciting electrodes  5   a ,  5   b , the brazing material  11  attaches to the exciting electrodes  5   a ,  5   b  and increases the weight of the central portion  2   a . This results in fluctuation of the crystal impedance level (hereunder referred to as “IC level”) and the frequency, making it impossible to obtain desired characteristics of the piezoelectric device. 
   Also, when the brazing material  11  is heated and melted so as to bond the crystal substrates  2 ,  3 ,  4 , so-called solder eating occurs, in which the drawing electrodes  6   a ,  6   b  are absorbed in the metallic brazing material such as gold/tin. If such solder eating spreads to the exciting electrodes  5   a ,  5   b , portions of the exciting electrodes  5   a ,  5   b  are absorbed, reducing the weight of the central portion  2   a . This results in fluctuation of the CI level and the frequency, making it impossible to obtain the desired characteristics of the piezoelectric device. 
   As herein described, there is a problem that the CI level and the frequency fluctuate due to the spreading of brazing material  11  or the solder eating and that it becomes impossible to obtain the desired characteristics of the piezoelectric device. 
   SUMMARY 
   In order to solve the problem above, an objective of the disclosure is to provide a piezoelectric device with which it is possible to prevent the brazing material from attaching to a vibrating area, prevent the solder eating, and to thereby obtain excellent vibration characteristics. 
   In a first embodiment, the mentioned objective is achieved by a piezoelectric device including: a piezoelectric element having, on a surface of a piezoelectric body, an exciting electrode and a drawing electrode that is electrically coupled to the exciting electrode and draws an electrode to an external section, and a substrate bonded to the drawing electrode with a metallic brazing material, in that: the piezoelectric element contains a connecting electrode connecting the exciting electrode with the drawing electrode; and the connecting electrode and/or the exciting electrode contains an underlying layer provided on the surface of the piezoelectric body and a surface layer section provided on a surface of this underlying layer, wherein: the underlying layer is provided using the metallic brazing material and a metallic material of adverse wettability; and a portion of the surface layer section is removed in a manner that the exciting electrode and the drawing electrode are separated. 
   According to the structure of the first embodiment, the piezoelectric device is equipped with the piezoelectric element having the exciting electrode and the drawing electrode electrically coupled to the exciting electrode and with the substrate bonded to the drawing electrode with the metallic brazing material. Also, the piezoelectric element includes the connecting electrode connecting the exciting electrode to the drawing electrode. Thus, there is a possibility that, when bonding the drawing electrode to the substrate, the heated and melted metallic brazing material flows along the connecting electrode to the exciting electrode. 
   However, according to the structure of the first embodiment, the underlying layer of the connecting electrode and/or the exciting electrode is provided using the metallic brazing material and the metallic material of adverse wettability, and the portion of the surface layer section is removed in a manner that the exciting electrode is separated from the drawing electrode. Accordingly, the surface layer section is divided so that the exciting electrode is separated from the drawing electrode at a position of the connecting electrode, for example, and this divided portion exposes the metallic brazing material and the metallic material of adverse wettability and stops the spread of the metallic brazing material. Therefore, it is possible to effectively prevent a situation in which the metallic brazing material flows toward the exciting electrode and to further prevent the solder eating by blocking the metallic brazing material from flowing. 
   As a result, it is possible to prevent the brazing material from attaching to the vibrating area, prevent the solder eating, and to thereby provide the piezoelectric device having excellent vibration characteristics. 
   In a second embodiment according to the structure of the first embodiment, the drawing electrode, the exciting electrode, and the connecting electrode are composed of a same layer structure and a same material except the portion of the surface layer section. 
   According to the structure of the second embodiment, the drawing electrode, the exciting electrode, and the connecting electrode are composed of the same layer structure and material and thus can be provided simultaneously. As a result, the structure may be formed relatively simply, except the portion of the surface layer section, and may respond to a downsized piezoelectric device. 
   In a third embodiment according to the structure of the first or the second embodiment, the piezoelectric body contains a frame surrounding the exciting electrode, a principal plane of the frame having the drawing electrode; and the substrate includes a lid substrate and a base substrate interposing the principal plane of the frame therebetween. 
   According to the structure of the third embodiment, the piezoelectric body contains the frame surrounding the exciting electrode, and the principal plane of the frame is provided with the drawing electrode. However, the principal plane of the frame is interposed between the lid substrate and the base substrate. Thus, when placed between the lid substrate and the base substrate, a pressure is applied, and the metallic brazing material starts flowing along the connecting electrode more toward the exciting electrode. However, because the third embodiment includes the structure of the first embodiment, the metallic brazing material may be effectively prevented from flowing to the exciting electrode. 
   In a fourth embodiment according to the structure of any of the first to third embodiments, the connecting electrode is sloped downward from a side adjacent to the drawing electrode to a side adjacent to the exciting electrode. 
   According to the structure of the fourth embodiment, because the connecting electrode is sloped downward from the side adjacent to the drawing electrode to the side adjacent to the exciting electrode, the metallic brazing material that has spread along the connecting electrode more readily flows toward the exciting electrode. However, because the fourth embodiment includes the structure of the first embodiment, the flow of the metallic brazing material to the exciting electrode may be effectively prevented. 
   In a fifth embodiment according to the structure of any of the first to fourth embodiment, the connecting electrode contains a recess whose inner bottom surface is the exposed metallic material of adverse wettability. 
   According to the structure of the fifth embodiment, the connecting electrode contains the recess whose inner bottom surface is the exposed metallic material of adverse wettability. As a result, even if the metallic brazing material flows to the exposed metallic material of adverse wettability, the metallic brazing material is accumulated inside the recess, and it is possible to prevent the metallic brazing material from flowing to the exciting electrode. 
   In a sixth embodiment according to the structure of any of the first to fifth embodiment, the underlying layer has a thickness dimension larger than a thickness of at least the surface layer section. 
   According to the structure of the sixth embodiment, the underlying layer has the thickness dimension larger than the thickness of at least the surface layer section. Thus, the conductivity of the underlying layer may improve by increasing the sectional area of the underlying layer made of the metallic material. As a result, it is possible to effectively solve a problem of decrease in the conductivity between the drawing electrode and the exciting electrode that occurs in a situation that the surface layer section is removed at the portion exposing the underlying layer. 
   In a seventh embodiment according to the structure of any of the first to sixth embodiment, the underlying layer is composed of at least three layers, a mid layer thereof being made by disposing a metal having an electric resistance value lower than that of the metallic material of adverse wettability. 
   According to the structure of the seventh embodiment, the underlying layer is composed of at least three layers, and the mid layer is made by disposing a metal having an electric resistance value lower than that of the metallic material of adverse wettability. Therefore, even if the portion of the metallic material of adverse wettability has high electric resistance and low conductivity, it is possible to obtain a piezoelectric device with excellent vibration characteristics by establishing good conductance between the drawing electrode and the exciting electrode at the mid layer metal portion having a low electric resistance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded, perspective, schematic view of a piezoelectric device according to a first embodiment of the disclosure; 
       FIG. 2(   a ) is a schematic sectional diagram taken on a line A-A of the piezoelectric device of  FIG. 1  as assembled.  FIG. 2(   b ) is an enlarged sectional diagram of a portion surrounded by a dash-dotted circular line of  FIG. 2(   a ); 
       FIG. 3  is an enlarged sectional diagram of a portion corresponding to the enlarged sectional portion shown in  FIG. 2(   b ), explaining the characteristic features of a piezoelectric device according to a second embodiment of the disclosure; 
       FIG. 4  is an enlarged sectional diagram of a portion corresponding to the enlarged sectional portion shown in  FIG. 2(   b ), explaining the characteristic features of a piezoelectric device according to a third embodiment of the disclosure; 
       FIG. 5  is an exploded, perspective, schematic view of a piezoelectric element used in a piezoelectric device according to a fourth embodiment of the disclosure; 
       FIG. 6  show schematic plan diagrams of modified examples of the piezoelectric element used in the piezoelectric device of the disclosure; and 
       FIG. 7  is a schematic sectional diagram of an existing piezoelectric device. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIGS. 1 and 2  show a piezoelectric device  30  according to the first embodiment of the disclosure.  FIG. 1  is an exploded, perspective, schematic view of the device  30 .  FIG. 2(   a ) is a schematic sectional diagram taken on a line A-A of the piezoelectric device of  FIG. 1  as assembled, and  FIG. 2(   b ) is an enlarged sectional diagram of a portion surrounded by a dash-dotted circular line of  FIG. 2(   a ). 
   In these drawings, the piezoelectric device  30  exemplifies a piezoelectric resonator and includes a piezoelectric element  20  and a substrate  32  that is bonded to this piezoelectric element  20 . In the present embodiment, the substrate  32  is composed of a lid substrate  40  and a base substrate  50  interposing the piezoelectric element  20  therebetween. 
   The piezoelectric element  20  will be described first. 
   The piezoelectric element  20  includes exciting electrodes  42 ,  43  and drawing electrodes  46 ,  47  on the surface of a piezoelectric body  41 . 
   The piezoelectric body  41  is made of quartz crystal, for example. Other than quartz crystal, piezoelectric materials such as lithium tantalite may be used. In this embodiment, the piezoelectric body  41  is so-called AT cut, in that a quartz crystal wafer is cut in predetermined directions. Also, the piezoelectric body  41  is equipped with a vibrating section  22  in the center, a frame  24  surrounding this vibrating section  22 , and supports  26 ,  27  connecting the vibrating section  22  with the frame  24 . 
   The vibrating section  22  in the center is a vibrating area having a thickness corresponding to an oscillation frequency. In this embodiment, the vibrating section  22  is made by being cut into rectangles by chemical etching or blasting using a resist pattern that is formed by photolithography, and is further made to be thinner than the frame  24 . Consequently, as shown in  FIG. 2 , when the vibrating section  22  is disposed between the lid substrate  40  and the base substrate  50 , a sealed inner space S 1  is created around the vibrating section  22 . 
   Then, the exciting electrodes  42 ,  43  of opposite polarities are provided on upper and lower planes that are main planes of this thin area, by sputtering chromium (Cr), nickel (Ni), or titanium (Ti) on the base (underlying layer) and gold (Au) or silver (Ag) on the front surface (surface layer section). As a result, an electric field is efficiently generated between the exciting electrode on the upper plane and the exciting electrode on the lower plane, and the vibrating section  22  performs thickness slide oscillation. 
   The frame  24  is formed surrounding the vibrating section  22 . The principal plane of the frame  24  is interposed between the lid substrate  40  and the base substrate  50 , and this interposed region becomes a region for securing the piezoelectric element  20 . 
   In this embodiment, the outer dimension of the frame  24  is substantially equal to the outer dimensions of the lid substrate  40  and the base substrate  50 . Also, the frame  24  is made thicker than the vibration section  22 , and, as shown in  FIG. 1 , castellations  24   a ,  24   b ,  24   c ,  24   d  are provided by cutting near the corners of the frame  24  into four quarters of a circle in plan view. These castellations  24   a ,  24   b ,  24   c ,  24   d  become a guide for cutting out the piezoelectric element  20  from a wafer and conductive paths for electrically coupling the exciting electrodes  42 ,  43  with mounting terminal portions  44 ,  45  disposed on the bottom surface. 
   In other words, on the entire periphery of the upper and lower planes, that is the principal planes, of the frame  24 , the drawing electrodes  46 ,  47  that are electrically coupled to the exciting electrodes  42 ,  43  while drawing the electrodes outside are provided. These drawing electrodes  46 ,  47  are composed of the same layer structure and material as are the exciting electrodes  42 ,  43  and made by sputtering, e.g., chromium (Cr), nickel (Ni), or titanium (Ti) on the base and gold (Au) or silver (Ag) on the front surface. Then, the drawing electrode  46  on the upper plane is drawn via the castellations  24   a ,  24   b  on the front and right sides of  FIG. 1  and via castellations  50   a ,  50   b  of the base substrate  50  on the front and right sides of  FIG. 1  and is coupled to the mounting terminal portion  45 . Also, the drawing electrode  47  on the lower plane is drawn via a castellation  50   d  provided on the base substrate  50  on the left side of  FIG. 1  and via a castellation (not shown) on the rare side of  FIG. 1  and is coupled to the mounting terminal portion  44 . 
   Then, the vibrating section  22  in the center is connected to the frame  24  surrounding this vibrating section  22  with the supports  26 ,  27 . The supports  26 ,  27  support the vibrating section  22  by suspending the same and act as the paths for electrically coupling the exciting electrodes  42 ,  43  to the drawing electrodes  46 ,  47 . 
   Specifically, only two supports  26 ,  27  are provided at about the center of the opposing side surfaces of the vibrating section  22 . Thus, a space between the vibrating section  22  and the frame  24 , where the supports  26 ,  27  are not provided, becomes a through hole  28 . 
   Provided on the upper surface of one support  26 , out of the plurality of supports  26 ,  27 , is a connecting electrode  48  connecting the exciting electrode  42  of the vibrating section  22  with the drawing electrode  46  of the frame  24 . Provided also on the other, lower surface of the support  27 , as shown in  FIG. 2 , is a connecting electrode  49  connecting the exciting electrode  43  of the vibrating section  22  with the drawing electrode  47  of the frame  24 . The connecting electrodes  48  and  49  are arranged so as not to come in contact with each other. 
   These connecting electrodes  48 ,  49  are composed of the same layer structure and material as are the exciting electrodes  42 ,  43  and the drawing electrodes  46 ,  47 , except a portion (portion where an underlying layer  48   a  is exposed) of a surface layer section  48   b  which will be described later. These connecting electrodes  48 ,  49  will be described in detail hereafter. 
   Further, the supports  26 ,  27  are formed in a manner that they become gradually thinner from the frame  24  toward the vibrating section  22 . Thus, the connecting electrode  48  is sloped downward from the drawing electrode  46  to the exciting electrode  42 . That is, the connecting electrode  48  has a sloped plane that is high at a side adjacent the frame  24  and low at a side adjacent the vibrating section  22 . 
   The substrate  32  will now be described. 
   The substrate  32  is a member to be bonded and fixed to the piezoelectric element  20  so as to seal the vibrating area. In the embodiment, the substrate  32  is bonded to the piezoelectric element  20  by thermo-compression with the frame interposed therebetween and includes the lid substrate  40  and the base substrate  50 . 
   Specifically, the substrate  32  is formed using an insulating material. In the embodiment, a member such as quartz crystal or glass having substantially the same thermal expansion coefficient as that of the piezoelectric element  20  is selected in order to avoid cracks that may be made by a stress generated when heating the piezoelectric element  20  interposed between the lid substrate  40  and the base substrate  50 . 
   The lid substrate  40  has substantially the same outer dimension as that of the piezoelectric element  20  and is formed in a rectangle shape. The entire circumferential edge of a lower plane of the lid substrate  40  is coated with a bonding metal film  52  through sputtering, e.g., chromium (Cr) and gold (Au). As shown in  FIG. 2(   a ), a metallic brazing material  54  such as gold/tin is applied between the bonding metal film  52  and the drawing electrode  46  on the surface of the frame  24 , thereby bonding the lid substrate  40  to the frame  24 . 
   The base substrate  50 , also, has substantially the same outer dimension as that of the piezoelectric element  20  and is formed in a rectangle shape. Further, as shown in  FIG. 1 , the base material  50  includes the mounting terminal portions  44 ,  45  on the lower plane thereof and the castellations  50   a ,  50   b ,  50   d  that become the conductive paths for electrically coupling these mounting terminal portions  44 ,  45  to the drawing electrodes  46 ,  47 . 
   Then, the entire circumferential edge of the base substrate  50  is bonded to the frame  24  of the piezoelectric element  20 . An upper plane of the base substrate  50  is coated with a bonding metal film  56  through sputtering, e.g., chromium (Cr) and gold (Au). As shown in  FIG. 2(   a ), a metallic brazing material  58  such as gold/tin is applied between the bonding metal film  56  and the drawing electrode  47  on a lower plane of the frame  24 , thereby bonding the base substrate  50  to the frame  24 . 
   The connecting electrodes  48 ,  49  that connect the exciting electrodes  42 ,  43  with the drawing electrodes  46 ,  47  have the following characteristics. Note that, because the connecting electrodes  48  and  49  have substantially the same structure, except that they are facing different directions, only the connecting electrode  48  will be described below. 
   Referring to  FIG. 2(   b ), the connecting electrode  48  includes the underlying layer  48   a  provided on the surface of the piezoelectric body  41  and the surface layer section  48   b  provided on the surface of this underlying layer  48   a.    
   The surface layer section  48   b  is a member that enables good conduction between the exciting electrodes  42 ,  43  and the drawing electrodes  46 ,  47  and is formed by sputtering, e.g., gold (Au) or silver (Ag). 
   The underlying layer  48   a  is a member that bonds the surface layer section  48   b  having good conductivity with the supports  26 ,  27  of the piezoelectric body  41  made of quartz crystal. The underlying layer  48   a  in the embodiment is formed using the metallic brazing material  54  and a metallic material of adverse wettability through sputtering, e.g., chromium (Cr), nickel (Ni), or titanium (Ti). 
   In other words, in the embodiment, the connecting electrode  48  is composed of the same layer structure and material as are the drawing electrode  46  and the exciting electrode  42 . 
   Then, a part of the surface layer section  48   b  is removed so as to separate the exciting electrode  42  from the drawing electrode  46 . In the embodiment, the surface layer section  48   b  in the middle of the connecting electrode  48  is removed so as to divide the surface layer section  48   b . As a result, the metallic material of adverse wettability of the underlying layer  48   a  is exposed, separating the exciting electrode  42  from the drawing electrode  46 . 
   More specifically, with reference to  FIG. 1 , the underlying layer  48   a  takes the whole width of the connecting electrode  48  and is exposed to the inner space S 1 . Referring to  FIG. 2(   b ), a recess  57  is provided, and the inner bottom of the recess  57  is a portion  48 - 1  of this exposed metallic material of adverse wettability. Accordingly, even if the metallic brazing material  54  flows toward the exciting electrode  42 , the metallic brazing material  54  is accumulated inside this recess  57 , thereby effectively preventing the metallic brazing material  54  from flowing to the exciting electrode  42 . 
   Then, as described above, the exposed portion  48 - 1  of the underlying layer  48   a  is exposed to the inner space  51  while taking the whole width of the connecting electrode  48 , and, thus, the exposed portion  48 - 1  is in such a situation that the surface layer section  48   b  enabling good conduction is removed. Thus, there is a possibility that the conductivity between the exciting electrode  42  and the drawing electrode  46  deteriorates. Therefore, with the understanding that the conductivity improves if the sectional area increases, the underlying layer  48   a  of the embodiment is made to have a thickness H 1  larger than the thickness of at least the surface layer section  48   b  so as to secure conductivity between the drawing electrode  46  and the exciting electrode  42 . The thickness H 1  can be determined depending on the kind of member composing the underlying layer  48   a.    
   The first embodiment of the disclosure has the structure as described above, in which the underlying layer  48   a  of the connecting electrode  48  is composed of the metallic brazing material  54  and the metallic material of adverse wettability, and in which the metallic material of adverse wettability is exposed while separating the exciting electrode  42  from the drawing electrode  46 . Therefore, when bonding the drawing electrode  46  to the substrate  32 , the heated and melted metallic brazing material  54  stops spreading because of its adverse wettability at the position of the exposed underlying layer  48   a  even if the material  54  runs to the connecting electrode  48 . Accordingly, it is possible to effectively prevent the metallic brazing material  54  from running along the connecting electrode  48  to flow toward the exciting electrode  42 . 
   Also, in the embodiment, because the drawing electrode  46  and the exciting electrode  42  are composed of the same layer structure and material as is the connecting electrode  48  as described above, the drawing electrode  42 , the exciting electrode  46 , and the connecting electrode  48  can be formed simultaneously. Therefore, it is relatively easy to expose the underlying layer  48   a  and to respond to the downsized piezoelectric device  30 . In other words, even though the structure of the embodiment is employed so that the outflow of the metallic brazing material  54  is prevented, it is still possible to provide the downsized piezoelectric device  30 . 
   Moreover, because the surface layer section  48   b  is split at the exposed portion of the underlying layer  48   a , it is possible to prevent the so-called solder eating, in which the surface layer section  48   b  is absorbed in the metallic brazing material  54 , at the exposed portion of the underlying layer  48   a.    
   As a result, it is possible to provide the piezoelectric device with which the spread of the brazing material or the solder eating caused by the brazing material is prevented and with which excellent vibration characteristics are obtained. 
     FIG. 3  is a diagram explaining the characteristic features of a piezoelectric device  60  according to the second embodiment of the disclosure and shows an enlarged section of a portion corresponding to the enlarged sectional portion shown in  FIG. 2(   b ). 
   In this drawing, the elements with identical reference numbers have the same structures as those used in  FIGS. 1 and 2 . Thus, the explanations thereof will not be repeated, and differences will mainly be explained. 
   The differences between this piezoelectric device  60  and the piezoelectric device  30  of the first embodiment are the structures of the underlying layers of the connecting electrodes  48 ,  49  (see  FIG. 2 ). Since the connecting electrodes  48 ,  49  have substantially the same structure, only the connecting electrode  48  will be explained below. 
   With reference to  FIG. 3 , the underlying layer  48   a  of the connecting electrode  48  is composed of three layers  60   a ,  60   b ,  60   c . Similar to the first embodiment, an uppermost layer  60   c  is made by disposing the metallic brazing material  54  and the metallic material of adverse wettability (e.g., chromium, nickel, or titanium), with one portion  48 - 1  thereof exposed to the inner space S 1 . 
   A mid layer  60   b  of the three layers is made by disposing a metal that is a member that bonds strongly with the uppermost layer  60   c  and has an electric resistance value lower than that of the uppermost layer  60   c  made of the metallic material of adverse wettability. Specifically, the mid layer  60   b  is made of gold (Au) or silver (Ag). 
   A lowermost layer  60   a  is made from a member that bonds the mid layer  60   b  to the piezoelectric body  41 , such as chromium (Cr), nickel (Ni), or titanium (Ti). 
   Note that, with the piezoelectric device  60  of the second embodiment, also, the drawing electrode  46  and the exciting electrode  42  (see  FIG. 2 ) have the three-layer structure made from the same members as does the connecting electrode  48 . 
   Further, the disclosure is not limited to the above-mentioned structure. For example, the underlying layer  48   a  of the connecting electrode  48  may be composed of four or more layers. However, it is preferable that the underlying layer  48   a  of the connecting electrode  48  be composed of the three layers  60   a ,  60   b ,  60   c  as in the second embodiment, from a viewpoint that the thickness dimension of the entire the piezoelectric device  60  should be downsized. 
   The second embodiment is composed as described above and, accordingly, has the same operational effect as that of the first embodiment. Also, the underlying layer  48   a  is composed of the three layers  60   a ,  60   b ,  60   c , and the mid layer  60   b  is made by disposing the metal having an electric resistance value lower than that of the uppermost layer  60   c  made of the metallic material of adverse wettability. Therefore, even if one portion of the connecting electrode  48  lacks the surface layer section  48   b  that enables conductivity, it is possible to establish good conductance between the drawing electrode  46  and the exciting electrode  42  because of the portion of the mid layer  60   b  made of the metal with low electric resistance. As a result, it is possible to obtain the piezoelectric device  60  having excellent vibration characteristics. 
     FIG. 4  is a diagram explaining the characteristic features of a piezoelectric device  70  according to the third embodiment of the disclosure and shows an enlarged sectional diagram of a portion corresponding to the enlarged sectional portion shown in  FIG. 2(   b ). 
   In this drawing, the elements with identical reference numbers have the same structures as those used in  FIGS. 1 and 2 , and the explanations thereof will not be repeated. 
   The differences between this piezoelectric device  70  and the piezoelectric device  30  of the first embodiment are the structures of the connecting electrodes  48 ,  49  (see  FIG. 2 ). Since the connecting electrodes  48 ,  49  have substantially the same structure, only the connecting electrode  48  will be explained. 
   In this embodiment, the surface layer section  48   b  and the underlying layer  48   a  of the connecting electrode  48  are removed (split in this embodiment) at the same position, separating the exciting electrode  42  from the drawing electrode  46  (see  FIG. 2 ). Also, a metal film  48   c  is formed in this split section  76 . 
   This metal film  48   c  is made of the metallic brazing material  54  and the metallic material of adverse wettability, such as chromium (Cr), nickel (Ni), or titanium (Ti), through sputtering. The metal film  48   c  is coated not only on the split section  76  but also on the surface layer section  48   b  adjacent to the split section  76 . 
   In the third embodiment, also, the heated and melted metallic brazing material  54  stops spreading at the position of the metal film  48   c  due to its adverse wettability. Accordingly, it is possible to effectively prevent the metallic brazing material  54  from flowing toward the exciting electrode  42 . 
   Moreover, because the surface layer section  48   b  is split while separating the exciting electrode  42  from the drawing electrode  46  as shown in  FIG. 2 , it is possible to prevent the so-called solder eating in which the surface layer section  48   b  is absorbed in the metallic brazing material  54  at the portion of the surface layer film  48   c.    
   As a result, it is possible to provide the piezoelectric device with which the spread of the brazing material or the solder eating caused by the brazing material is prevented, and with which excellent vibration characteristics are obtained. 
     FIG. 5  is an exploded, perspective, schematic view of the piezoelectric element  20  used in a piezoelectric device  80  according to the fourth embodiment of the disclosure. 
   In this drawing, the elements with identical reference numbers have the same structures as those used in  FIGS. 1 and 2 . Thus, the explanations thereof will not be repeated, and differences will mainly be explained. 
   The differences between this piezoelectric device  80  and the piezoelectric device  30  of the first embodiment are the structures of the connecting electrodes  48 ,  49  and the exciting electrode  42 ,  43 . Since the connecting electrodes  48 ,  49  have substantially the same structure, and the exciting electrodes  42 ,  43  have substantially the same structure, only the connecting electrode  48  and the exciting electrode  42  will be explained below. 
   With the piezoelectric device  80  of this embodiment, a portion exposing the underlying layer is not the portion of the connecting electrode  48  but a portion of the exciting electrode  42 . Specifically, a surface layer section, made of gold (Au) or silver (Ag), of the exciting electrode  42  adjacent to the connecting electrode  48  is removed, separating the drawing electrode  46  from the exciting electrode  42  and thereby exposing chromium (Cr), nickel (Ni), or titanium (Ti) that is the underlying layer  42   a.    
   In the fourth embodiment, also, the heated and melted metallic brazing material  54  stops spreading at the position of the metal film  48   c  due to its adverse wettability. Accordingly, it is possible to effectively prevent the metallic brazing material  54  from flowing toward the exciting electrode  42 . 
   Moreover, because the portion of the surface layer section of the exciting electrode  42  is removed while separating the drawing electrode  46  from the exciting electrode  42 , it is possible to prevent the so-called solder eating in which the surface layer section is absorbed in the metallic brazing material at the exposed portion of the underlying layer  42   a.    
   As a result, it is possible to provide the piezoelectric device with which the spread of the brazing material or the solder eating caused by the brazing material is prevented, and with which excellent vibration characteristics are obtained. 
   The disclosure is not limited to the above-described embodiments. Any structure of any of the embodiments may suitably be omitted, combined with other structures of other embodiments, or combined with structures not shown in the drawings. 
   For example, a plurality of exposed portions of the underlying layer may be provided at a plurality of places, or may be provided at both the portion of the connecting electrode and the portion of the exciting electrode. 
   Moreover, another embodiment is possible within the scope of the disclosure, in that the surface layer section of the drawing electrode and the surface layer section of the exciting electrode are not completely divided, as described in the following. 
     FIG. 6  shows schematic plan diagrams of modified examples of the piezoelectric element  20  used in the piezoelectric device of the disclosure. As shown in  FIG. 6(   a ) that is one of the modified examples, only a portion of the surface layer section of the connecting electrode  48  may be removed in a width direction, exposing the portion of the underlying layer  48   a  in the width direction. 
   Also, as shown in  FIG. 6(   b ) that is another one of the modified examples, the surface layer section and the underlying layer of the connecting electrode  48  may be removed in the width direction at the same one portion. The removed portion may include the metallic brazing material and the metal film  48   c  of adverse wettability. 
   Further, as shown in  FIG. 6(   c ) that is yet another one of the modified examples, a portion of the surface layer section of the exciting electrode  42  may be removed so that the drawing electrode  46  and the exciting electrode  42  are electrically connected at the surface layer section on the periphery of the exposed underlying layer  42   a.

Technology Category: 5