Piezoelectric component

Abstract: A piezoelectric component (10) designed to improve the strength of connection between a substrate (12) and a piezoelectric resonator (18) and to have improved electrical reliability. The piezoelectric resonator includes an insulating substrate (12) having pattern electrodes (14,16). A piezoelectric resonator (18) capable of vibrating, for example in a longitudinal vibration mode is mounted on the substrate (12). A supporting member (24) prepared separately as a formed material is bonded to the piezoelectric resonator (18) at a nodal point of the same. A first flat surface of the supporting member (24) is bonded to a vibrating electrode on the piezoelectric resonator (18) by a first piece of supporting material (26) while a second flat surface of the supporting member (24) is bonded to one of the pattern electrodes (16) on the substrate (12) by a second piece of supporting material (28). The length of bonding between the piezoelectric resonator (18) and the first piece of supporting material (26) along the longitudinal direction of the piezoelectric resonator (18) is set to 25 % or less of the overall length of the piezoelectric resonator (18). A central portion of another vibrating electrode of the piezoelectric resonator (18) is connected to the other pattern electrode (14) on the substrate (12) by a conductor wire.

Description: BACKGROUND OF THE INVENTION The present invention relates to a piezoelectric component and, more particularly, to a piezoelectric resonator comprising a substrate, and at least one piezoelectric resonator disposed on a surface of said substrate. The piezoelectric component utilizes mechanical vibration of a piezoelectric member for example, and is used as an oscillator, particularly a voltage controlled oscillator, a discriminator, a filter and so on. Fig. 13 is a sectional view of an essential portion of a structure for supporting a piezoelectric resonator on a substrate in a conventional piezoelectric component 1 related to the present invention. The piezoelectric component 1 includes a piezoelectric resonator 2, which includes a piezoelectric substrate 3, which has, for example, the shape of a flat block having rectangular major surfaces (obverse and reverse surfaces). The piezoelectric substrate 3 is polarized along the direction of the thickness thereof, for example. Electrodes 4a and 4b are respectively formed on the obverse and reverse surfaces of the piezoelectric substrate 3. When a signal is input between the electrodes 4a and 4b, an electric field is applied to the piezoelectric substrate 3 along the direction of the thickness of the piezoelectric substrate 3, and the piezoelectric substrate 3 vibrates in the longitudinal direction. The piezoelectric resonator 2 is supported on an insulating substrate 5 having a predetermined pattern electrode 6 on its surface. The piezoelectric resonator 2 has its nodal portion supported on the insulating substrate 5 by a mounting member 7 formed of an electroconductive adhesive or the like. The mounting member 7 is formed by applying an electroconductive adhesive to the reverse surface of the piezoelectric resonator 2 from one end to the other end of same in the widthwise direction and at the center in the longitudinal direction. In this conventional piezoelectric component, the mounting member 7 is formed on the reverse surface of the piezoelectric substrate 3 by printing using a metal mask, for example. The piezoelectric resonator 2 and the insulating substrate 5 are bonded to each other through the mounting member 7. The electrode 4b on the reverse side of the piezoelectric resonator 2 and the pattern electrode 6 on the obverse surface of the insulating substrate 5 are thereby connected mechanically and electrically. However, in the structure for supporting the piezoelectric resonator 2 on the insulating substrate 5 as shown in Fig. 13, the mounting member 7 becomes rounded, for example, by mechanical stress such as surface tension, so that the area of contact between the piezoelectric resonator 2 and the insulating substrate 5 is small. That is, the strength of bonding between the electrode 4b on the reverse surface of the piezoelectric resonator 2 and the pattern electrode 6 on the insulating substrate 5 is reduced. Correspondingly, the electrical connection between the piezoelectric resonator 2 and the pattern electrode 6 is weak. In some case, therefore, undesirable reliability of the piezoelectric component 1 results. Further, in the conventional supporting structure shown in Fig. 13, the thickness of the mounting member 7 is small and the piezoelectric resonator 2 and the insulating substrate 5 are placed very close to each other when the piezoelectric resonator 2 is supported on the insulating substrate 5. Under such a condition, there is a risk of the insulating substrate 5 resonating with the vibration of the piezoelectric resonator 2 to cause an unnecessary response in electrical characteristics of the piezoelectric resonator 2. A piezoelectric component having the features of the preamble of claim 1 is described in EP-A-0 626 212. SUMMARY OF THE INVENTION In view of the above described problems, a main object of the present invention is to provide a piezoelectric component capable of connecting a substrate and a piezoelectric resonator with a high connection strength and having improved electrical reliability. This object is achieved with a piezoelectric component having the features of claim 1. The subclaims are directed to preferable embodiments. According to the present invention, the supporting member is used, so that the area of bonding between the supporting member and the piezoelectric resonator by the first supporting means and the area of bonding between the supporting member and the substrate by the second supporting means can be suitably increased relative to the bonding area in the conventional structure. The strength of connection between the substrate and the piezoelectric resonator is thereby increased. Thus, the electrical connection therebetween is stabilized, thus making it possible to obtain a piezoelectric component having improved electrical reliability. The supporting member may have flat surfaces respectively facing the substrate and the piezoelectric resonator. Also, since the supporting member is used, the substrate and the piezoelectric resonator can be suitably spaced apart from each other when the piezoelectric resonator is supported at a predetermined position on the substrate. Thus, the substrate and the piezoelectric resonator is not so close to each other as in the conventional supporting structure. By this spacing, the substrate is prevented from resonating with vibration of the piezoelectric resonator, thus preventing an unnecessary response in electrical characteristics of the piezoelectric resonator. Further, according to the present invention, the bonding length, i.e., the length along the longitudinal direction of the piezoelectric resonator of the portions of the piezoelectric resonator and the first supporting means bonded to each other, is set to 25 % or less of the length of the piezoelectric resonator, thereby preventing the supporting means from acting as a substantial load on the piezoelectric resonator such as to reduce the quality factor. In the piezoelectric component of the present invention, first supporting means is used for bonding between the piezoelectric resonator and the supporting member while second supporting means is used for bonding between the supporting member and the substrate. If each of the first and second supporting means is formed by an elastic electroconductive adhesive, the first supporting means can support the piezoelectric resonator on the supporting member while electrically connecting the piezoelectric resonator and the supporting member, and the second supporting means can support the supporting member on the substrate while electrically connecting the supporting member and the substrate. Also in the piezoelectric component according to the present invention, the first supporting means for bonding between the piezoelectric resonator and the substrate can support the piezoelectric resonator on the substrate while electrically connecting the piezoelectric resonator and the substrate if it is an electroconductive adhesive. Moreover, if the electroconductive adhesive layer is elastic, it can absorb a vibration leak from the piezoelectric resonator. That is, the substrate is prevented from resonating with vibration of the piezoelectric resonator. Thus, unnecessary response in electrical characteristics of the piezoelectric resonator can be prevented more reliably. If the supporting member has a conductive portion formed thereon, it can establish electrical connection between the piezoelectric resonator and the substrate. A conductive portion may be formed on the supporting member to enable, for example, a predetermined pattern electrode on the substrate and a predetermined electrode of the piezoelectric resonator to be electrically connected to each other even if the supporting member is formed of a nonconductor. As such a conductive portion, a metal foil such as copper foil may be provided on a portion of the supporting member other than the flat surfaces facing the substrate and the piezoelectric resonator to establish electrical connection between the piezoelectric resonator and the substrate. The above-described and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a piezoelectric component which represents an embodiment of the present invention; Fig. 2 is an enlarged fragmentary sectional view of an essential portion of the piezoelectric component shown in Fig. 1; Figs. 3A and 3B are diagrams showing an example of the method of attaching a supporting member to a piezoelectric vibrator element, applied to the piezoelectric component shown in Figs. 1 and 2; Fig. 3A is a perspective view of a mother substrate for the piezoelectric vibrator element with a supporting member bonded to the mother substrate; Fig. 3B is an enlarged perspective view of the piezoelectric vibrator element with the supporting member obtained by cutting the mother substrate along the double-dot-dash lines shown in Fig. 3A and having conductors formed on its side surfaces; Fig. 4 is a graph showing the relationship between the sharpness of resonance and the ratio of the length of the bonded portions of the piezoelectric vibrator element and the supporting member to the overall length of the piezoelectric vibrator element; Fig. 5 is a graph showing the relationship between the spacing between the piezoelectric vibrator element and the insulating substrate and the degree of resonance between the piezoelectric vibrator element and the insulating substrate; Fig. 6 is an exploded perspective view of a piezoelectric component which represents a second embodiment of the present invention; Fig. 7 is an enlarged fragmentary sectional view of an essential portion of the piezoelectric component shown in Fig. 6; Figs. 8A and 8B are diagrams showing an example of the method of mounting a conductor formed on a supporting member used in the piezoelectric component shown in Figs. 6 and 7; Fig. 8A is a perspective view of a supporting member mother substrate with metal foil formed on two major surfaces of the mother substrate; Fig. 8B is an enlarged perspective view of the supporting member obtained by cutting the mother substrate along the double-dot-dash lines shown in Fig. 8A and having conductors formed on its side surfaces; Fig. 9 is a plan view of an essential portion of a piezoelectric component which represents a third embodiment of the present invention; Fig. 10 is an exploded perspective view of the essential portion of the piezoelectric component shown in Fig. 9; Fig. 11 is an enlarged fragmentary sectional view of the portion of the piezoelectric component shown in Figs. 9 and 10; Fig. 12 is a circuit diagram of the piezoelectric component shown in Figs. 9, 10 and 11; and Fig. 13 is a sectional view of an essential portion of a structure for supporting a piezoelectric resonator on a substrate in a conventional piezoelectric component. DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric component which is used as an oscillator and which represents a first embodiment of the present invention will be described. Referring to Fig. 1, a piezoelectric component 10 includes an insulating substrate 12 made of alumina or the like and having the shape of a rectangular plate. Two pattern electrodes 14 and 16, for example, are formed on one of two major surfaces of the insulating substrate 12 (obverse surface as viewed in Fig. 1) by being suitably spaced apart from each other. The pattern electrode 14 is formed of a line electrode 14a which extends straight along one of the shorter sides of the obverse surface of the insulating substrate 12 from one end to the other end in the widthwise direction of the insulating substrate 12, and a line electrode 14b which extends straight in the longitudinal direction of the insulating substrate 12 from a position in the vicinity of one longitudinal direction end of the line electrode 14a. The pattern electrode 16 is formed of a line electrode 16a which extends straight along the other shorter side of the obverse surface of the insulating substrate 12 from one end to the other end in the widthwise direction of the insulating substrate 12, and a line electrode 16b which extends straight in the longitudinal direction of the insulating substrate 12 from a position in the vicinity of one longitudinal direction end of the line electrode 16a. The pattern electrodes 14 and 16 have extensions formed as to extend to positions on the reverse surface of the insulating substrate 12 in a roundabout fashion, although they are not illustrated. A piezoelectric vibrator element 18 used as a piezoelectric resonator is provided on the obverse side of the insulating substrate 12. The piezoelectric vibrator element 18 includes a piezoelectric substrate 20 which is, for example, a piezoelectric ceramic member having the shape of a flat block having rectangular major surfaces (obverse and reverse surfaces). A vibrating electrode 22a is formed, for example, on the entire obverse surface of the piezoelectric substrate 20 while a vibrating electrode 22b is formed on the entire reverse surface of the piezoelectric substrate 20. For example, this piezoelectric vibrator element 18 vibrates in a longitudinal vibration mode and is used a piezoelectric resonator. This piezoelectric vibrator element 18 is attached to the insulating substrate 12 at a predetermined position by a supporting member 24 and first and second elastic adhesive layers 26 and 28 interposed therebetween as first and second supporting means. For example, the supporting member 24 is formed into the shape of a small flat block having rectangular major surfaces, and which is made of an epoxy resin or the like. The supporting member 24 has a pair of flat opposite surfaces 24a and 24b (major surfaces). The supporting member 24 is placed between the piezoelectric vibrator element 18 and the insulating substrate 12 so that the flat surface 24a faces the reverse surface of the piezoelectric vibrator element 18 while the other flat surface 24b faces the obverse surface of the insulating substrate 12. Specifically, the supporting member 24 is positioned substantially at the center of the piezoelectric vibrator element 18 in the longitudinal direction, as shown in Fig. 1. To the flat surface 24a, i.e., the upper surface of the supporting member 24 as seen in Fig. 1, an electroconductive adhesive 26a prepared as first supporting means by mixing a filler of an electroconductive material such as silver in an elastic thermosetting resin such as a silicone or epoxy resin is adhered, thereby forming the first electroconductive adhesive layer 26. The flat surface 24a of the supporting member 24 is bonded by the first electroconductive adhesive layer 26 to a vibration node region of the piezoelectric vibrator element 18, i.e., a portion at the center in the longitudinal direction of the piezoelectric vibrator element 18. More specifically, the flat surface 24a of the supporting member 24 is bonded to a portion of the vibrating electrode 22b of the piezoelectric vibrator element 18 corresponding to the center in the longitudinal direction. The bonding length W, i.e., the length along the longitudinal direction of the piezoelectric vibrator 18 of the portion of the first electroconductive adhesive layer 26 as the first supporting means and the portion of the piezoelectric resonator 18 bonded to each other, is set to 25 % or less of the overall length L of the piezoelectric vibrator element 18. In this embodiment, the piezoelectric vibrator element 18 is formed so that, for example, its overall length L is approximately 4.0 mm, its width is approximately 0.6 mm and its thickness is approximately 0.4 mm. On the other hand, on the obverse surface of the insulating substrate 12, the second electroconductive adhesive layer 28 formed of an electroconductive adhesive 28a is formed as the second supporting means at the position corresponding to a substrate portion on which the piezoelectric vibrator element 18 is mounted. In this embodiment, the electroconductive adhesive 28a is adhered to a longitudinal direction end portion of the line electrode 16b of the pattern electrode 16 on the insulating substrate 12 surface. As electroconductive adhesive 28a, the same electroconductive adhesive as the electroconductive adhesive 26a forming the above-described first supporting means is used. The other flat surface 24b, i.e., the lower end surface, of the supporting member 24 bonded to the piezoelectric vibrator element 18 is adhered to the electroconductive adhesive 28a adhered to the insulating substrate 12 surface. The vibrating electrode 22a of the piezoelectric vibrator element 18 is connected to the pattern electrode 14 on the insulating substrate 12 by a conductor wire 30 or the like. The conductor wire 30 is connected between a longitudinal direction central portion of the vibrating electrode 22a and a longitudinal direction end portion of the line electrode 14b of the pattern electrode 14. Further, a metallic cap (not shown) or the like is placed on the insulating substrate 12. To prevent the metal cap from being short-circuited to the pattern electrodes 14 and 16, an insulating resin is applied to the insulating substrate 12 and the pattern electrodes 14 and 16 in advance. By capping with the metallic cap, the manufacture of the piezoelectric component 10 is completed. In this piezoelectric component 10, the portions (not shown) of the pattern electrodes 14 and 16 formed so as to extend from edges of the insulating substrate 12 to positions on the reverse surface of the insulating substrate 12 in a roundabout fashion are used as input/output terminals for connection to an external circuit. An example of the method of making the supporting member 24 of this embodiment will now be described with reference mainly to Figs. 1 and 3. First, a mother substrate 100 for forming the piezoelectric vibrator element 18 is prepared by being formed so as to have, for example, a length of 30 mm, a width of 4 mm and a thickness of 0.4 mm. A formed material 102 for the supporting member 24, having a predetermined size in length, width and thickness and made by being cut off from a mother substrate (not shown) for the supporting member 24 separately from the mother substrate 100, is bonded to a portion of one surface of the mother substrate 100 corresponding to the center in the widthwise direction of the mother substrate 100. For example, the formed material 102 is formed so as to have a length of 30 mm, a width of 0.8 mm and a thickness of 0.25 mm. The formed material 102 is bonded to the central portion of the mother substrate 100 by electroconductive adhesive 26a, as shown in Fig. 3A. In this embodiment, the width of the formed material 102 for the supporting member 24 is set to about 0.8 mm, approximately 20 % of the overall length of the piezoelectric vibrator element 18. Thereafter, the mother substrate 100 is cut along a plurality of planes with a pitch p of 0.6 mm corresponding to the width of the piezoelectric vibrator element 18, as indicated by the double-dot-dash lines in Fig. 3A. The mother substrate 100 is thereby cut into pieces each having the structure shown in Fig. 3B, thus making the piezoelectric vibrator element 18 with the supporting member 24. That is, to a portion of one major surface of the piezoelectric vibrator element 18 corresponding to the center in the longitudinal direction of the piezoelectric vibrator element 18 (at a nodal point), one of the opposite flat surfaces, i.e., flat surface 24a, of the supporting member 24 is bonded by the first electroconductive adhesive layer 26 formed of the electroconductive adhesive 26a (first supporting means). In the piezoelectric component 10 of this embodiment, the supporting member 24 is formed and bonded to the portion of the piezoelectric vibrator element 18 corresponding to the center in the longitudinal direction and to the line electrode 16b on the insulating substrate 12 by the electroconductive adhesives 26a and 28a. Certain spaces are thereby maintained between the ends of the piezoelectric vibrator element 18 and the insulating substrate 12, so that vibration of the piezoelectric vibrator element 18 is not considerably impeded by the insulating substrate 12. Also, the central portion of the piezoelectric vibrator element 18 corresponding to a node is fixed on the supporting member 24 and has a connection to the conductor wire 30. Therefore, longitudinal vibration excited in the piezoelectric vibrator element 18 is not attenuated. Specifically, in the piezoelectric component 10 of this embodiment, the piezoelectric vibrator element 18 used as a piezoelectric resonator is supported at a predetermined position on the insulating substrate 12 by the supporting member 24 and by being bonded by electroconductive adhesives 26a and 28a adhered to the flat surfaces 24a and 24b of the supporting member 24. In this bonding, the flat surface 24a of the supporting member 24 is bonded to the piezoelectric vibrator element 18 by the electroconductive adhesives 26a while the flat surface 24b of the supporting member 24 is bonded to the insulating substrate 12 by the other electroconductive adhesives 28a. Therefore, the area of bonding between the supporting member 24 and the piezoelectric vibrator element 18 and between the supporting member 24 and the insulating substrate 12 can be increased relative to, for example, that in the conventional arrangement shown in Fig. 13. As a result, the strength of connection between the insulating substrate 12 and the piezoelectric vibrator element 18 is improved and the electrical connection between the insulating substrate 12 and the piezoelectric vibrator element 18 is stabilized, thus obtaining the piezoelectric component 10 having improved electrical reliability. Because a formed material separately made is used as the supporting member 24, the supporting member 24 can have a suitable thickness such that the insulating substrate 12 and the piezoelectric vibrator element 18 can be suitably spaced apart from each other when the piezoelectric vibrator element 18 is bonded to and supported on the insulating substrate 12 at the predetermined position by the electroconductive adhesives 26a and 28a. Thus, the distance between the insulating substrate 12 and the piezoelectric vibrator element 18 can be set to a more suitable value in the piezoelectric component 10 of the present invention than in the conventional piezoelectric component, thereby preventing resonance of the insulating substrate 12 with vibration of the piezoelectric vibrator element 18. Consequently, it is possible to prevent occurrence of an unnecessary response in electrical characteristics of the piezoelectric vibrator element 18. Moreover, since a formed material separately made is used as the supporting member 24, the supporting member 24 can be formed accurately into the shape of the desired size and can be made at a lower cost. Also, the electronic component can be made stable in electrical characteristics by selecting the kind, quality and size of the formed material 24 without causing resonance with the piezoelectric vibrator element and a reduction in quality factor. Further, in the piezoelectric component 10 of this embodiment, the bonded structure is formed so that the bonding length of the bonded portions of the piezoelectric vibrator element 18 and the first supporting means, i.e., the first adhesive layer 26, along the longitudinal direction of the piezoelectric vibrator element 18, is not larger than 25 % of the overall length of the piezoelectric vibrator element 18, and so that the area of contact therebetween is sufficiently large. Therefore, the first supporting means, i.e., the first electroconductive layer 26, and the supporting material 24 do not act as a load on the piezoelectric vibrator element 18 to reduce the quality factor. An experiment made by the inventors of the present invention revealed the following. If the length (overall length) of the piezoelectric vibrator element 18 in this piezoelectric component 10 is L and the length of the portion of the first supporting means along the longitudinal direction of the piezoelectric vibrator element 18, i.e., the first electroconductive adhesive layer 26 and the portion of the piezoelectric vibrator element 18 bonded to each other is W, then the relationship between the quality factor and the ratio W/L is as shown in Fig. 4. That is, the quality factor is reduced when the ratio W/L exceeds 25 %. When the ratio W/L is not higher than 25 %, the quality factor is not reduced. In general, in a piezoelectric component using a piezoelectric vibrator element, the substrate is liable to resonate with vibration of the piezoelectric vibrator element if the distance between the piezoelectric vibrator element and the substrate is small, that is, the piezoelectric vibrator element and the substrate are disposed excessively close to each other. The inventors of the present invention has experimentally found that, with respect to the piezoelectric component 10 of this embodiment, the degree of resonance between the piezoelectric vibrator element 18 and the insulating substrate 12 is increased so that resonance can occur easily therebetween if the distance G between the piezoelectric vibrator element 18 and the insulating substrate 12 is in the range below 0.2 mm, as shown in Fig. 5. In the piezoelectric component 10 of this embodiment, a vibration leak from the piezoelectric vibrator element 18 can be absorbed by the first and second elastic electroconductive adhesive layers 26 and 28 formed as the first and second supporting means. That is, resonance of the insulating substrate 12 with the vibration of the piezoelectric vibrator element 18 can be limited to reduce the undesirable effect of causing an unnecessary response in electrical characteristics of the piezoelectric vibrator element 18. The piezoelectric component 10 of this embodiment is used as, for example, an oscillator or discriminator by being mounted on a circuit board together with an integrated circuit or the like. The piezoelectric component 10 constructed as described above is enclosed tightly and protected by the metallic cap (not shown) and can therefore be used as a chip component mountable by reflow soldering. Fig. 6 is an exploded perspective view of a piezoelectric component 10 which represents a second embodiment of the present invention, and Fig. 7 is an enlarged sectional view of an essential portion of the electronic component 10 shown in Fig. 6. The piezoelectric component 10 described below is used as, for example, a discriminator, a voltage controlled oscillator or a filter. This piezoelectric component 10 differs from the above-described piezoelectric component 10 in that conductors 40 and 42 for electrically connecting first supporting means formed on the upper surface of a supporting member 24 and second supporting means formed on the lower surface of the supporting member 24 are formed on side surfaces of the supporting member 24. In Figs. 6 and 7, portions or members indicated by the same reference characters or having the same names as those of the embodiment shown in Figs. 1 to 3 have the same or similar structures, and the construction of such common portions will not specially be described. The piezoelectric component 10 of the embodiment shown in Fig. 6 and 7 includes an insulating substrate 12. Predetermined pattern electrodes 14 and 16 are formed on the obverse surface of the insulating substrate 12. A piezoelectric vibrator element 32 having a laminated structure is bonded to and supported on the insulating substrate 12 at a predetermined position. The piezoelectric vibrator element 32 includes a base member 34 having a longitudinal shape, as shown in Fig. 6. The base member 34 is formed of a piezoelectric material. A plurality of electrodes (not shown) are formed in the base member by being arranged so that their major surfaces are perpendicular to the longitudinal direction of the base member. Thus, the base member 34 has a laminated structure in which a plurality of piezoelectric layers and internal electrodes are alternately laminated. The piezoelectric layers are polarized along the longitudinal direction of the base member 34 in such a manner that the pair of the piezoelectric layers on the opposite sides of each internal electrode are polarized in opposite directions. Strips of insulating films (not shown) are formed in two rows on one side face of the base member 34. One row of the strips of insulating films are formed so that the internal electrodes exposed in the side face of the base member 34 are alternately covered and left uncovered with the insulating film. The other row of the strips of insulating films are formed so as to cover the internal electrodes not covered with the insulating films. External electrodes 36 and 38 are formed over the thus-formed two rows of the strips of insulating films. The internal electrodes not covered with the one row of the insulating films is connected to the external electrode 36 while the internal electrodes not covered with the other row of the insulating film are connected to the external electrode 38. In the piezoelectric vibrator element 32, the piezoelectric layers in a central section of the base member 34 are polarized. When an electric field is applied between each pair of the internal electrodes in the central section, the piezoelectric layers are made piezoelectrically active. On the other hand, two end sections of the base member 34 at the opposite ends in the longitudinal direction are not polarized, and no electrodes are formed in the end sections. Therefore, the end sections are not made piezoelectrically active. Thus, the central section of the base member 34 is defined as an active section which is piezoelectrically active while the two end sections of the base member 34 are defined as inactive sections which are piezoelectrically inactive. When a signal is applied between the two external electrodes 36,38, an AC electric field in the longitudinal direction of the base member 34 is applied to each of the piezoelectric layer in the active section to generate an expansion and contraction drive force in the piezoelectric layer, thereby exciting vibration in the longitudinal basic mode in the entire base member 34. The piezoelectric layers and internal electrodes in the base member 34 may alternatively be formed in such a manner that the internal electrodes have lead-out portions formed alternately at one end and at the other end and extending to end surfaces of the piezoelectric layers facing in one direction. In one side face of the laminated body of the base member 34 formed by laminating the piezoelectric layers and internal electrodes formed in this manner, the two rows of electrode portions are exposed, as shown in Fig. 10. External electrodes 36 and 38 are formed over exposed portions of the internal electrodes. The internal electrode are thereby connected alternately to the external electrodes 36 and 38. In this piezoelectric component 10, conductors 40 and 42 made of a metal foil, e.g., copper foil are formed on the entire areas of a pair of opposite side surfaces other than the opposite flat surfaces 24a and 24b, i.e., flat surfaces 24c and 24d of the supporting member 24. An example of the method of making supporting members 24 having conductors 40 and 42 will be described with reference mainly to Figs. 6 and 8. First, a mother substrate 200 for forming supporting member 24, made of an epoxy resin material or the like and having a predetermined size, is prepared. Next, foils 202 and 204 of a metal, e.g., copper are formed on the entire areas of two major surfaces of the mother substrate 200. The mother substrate 200 with metal foils 202 and 204 is cut, for example, along a group of planes spaced a predetermined distance apart from each other in the widthwise direction and along another group of planes spaced a predetermined distance apart from each other in the longitudinal direction, as indicated by the double-dot-dash lines in Fig. 8A. Supporting members 24 each having a predetermined size and having conductors 40 and 42 formed of a metal foil on its side surfaces, as shown in Fig. 8B, for example, are thereby made. Electroconductive adhesives 44a and 48a are adhered to flat surfaces 24a of the supporting members 24. On the other hand, electroconductive adhesive layers 46a and 50a are adhered to the line electrode 16b of the pattern electrode 16 and to the line electrode 14b of the pattern electrode 14, respectively. The upper surfaces of the supporting members 24 are bonded to portions of the reverse surface of the piezoelectric vibrator element 32 corresponding to the center in the longitudinal direction of the piezoelectric vibrator element 32 (a nodal point) by electroconductive adhesives 44a and 48a. The electroconductive adhesive 44a adheres to the external electrode 36 of the piezoelectric vibrator element 38 while the electroconductive adhesive 50a adheres to the other external electrode 112. Also, the lower surfaces of the supporting members 24 are bonded to the insulating substrate 12 at predetermined positions by electroconductive adhesives 46a and 50a. The lower surfaces of the supporting members 24 opposite from electroconductive adhesives 44a and 48a are adhered to electroconductive adhesives 46a and 50a, respectively. That is, in this piezoelectric component 10, the external electrode 36 of the piezoelectric vibrator element 32 is mechanically and electrically connected to the pattern electrode 16 on the insulating substrate 12 by the first electroconductive adhesive layer 44 (first supporting means), the conductors 40 and 42 and the second electroconductive adhesive layer 46 (second supporting means). Also, the external electrode 38 of the piezoelectric vibrator element 32 is mechanically and electrically connected to the pattern electrode 14 on the insulating substrate 12 by the first electroconductive adhesive layer 48 (first supporting means), the conductors 40 and 42 and the second electroconductive adhesive layer 50 (second supporting means). In this embodiment, the bonded structure is formed so that the bonding length along the longitudinal direction of the piezoelectric resonator 32 is not larger than 25 % of the overall length of the piezoelectric resonator 100, and so that the bonding area is sufficiently large, as is that in the above-described embodiment. In the piezoelectric component 10 of this embodiment, conductors 40 and 42 are respectively formed on two side surfaces 24c and 24d of the supporting member 24. However, a conductor, used instead of conductors 40 and 42, may be formed on only one of the two side surfaces. This embodiment uses the same structure for supporting the piezoelectric vibrator element 32 on the insulating substrate 12 as that in the first embodiment and is, therefore, essentially equivalent to the above-described first embodiment in terms of operation and advantage. Fig. 9 is a plan view of an essential portion of a piezoelectric component 50 which represents a third embodiment of the present invention, Fig. 10 is an exploded perspective view of the portion shown in Fig. 9, and Fig. 11 is an enlarged fragmentary sectional view of the portion shown in Fig. 10. Fig. 12 is a circuit diagram of the piezoelectric component shown in Figs. 9, 10, and 11. The piezoelectric component 50 described below as the third embodiment is a ladder filter having a ladder type circuit such as that shown in Fig. 12. In the piezoelectric component 50, four pattern electrode 54, 56, 58, and 60 are formed on an insulating substrate 52. The pattern electrodes 54 to 60 have first to fifth lands arranged in a row in the direction from one end toward the other end of the supporting substrate 52 while being spaced apart from each other. The first land is formed as a portion of the pattern electrode 54, the second and fifth lands are formed as portions of the pattern electrode 56, the third land is formed as a portion of the pattern electrode 58, and the fourth land is formed as a portion of the pattern electrode 60. A supporting member 62 is attached to the first land. Two supporting members 64 and 66 are attached to the second land; two supporting members 68 and 70 to the third land; and two supporting members 72 and 74 to the fourth land. A supporting member 76 is attached to the fifth land. Each of the supporting members 62 to 76 is bonded to the land by an electroconductive adhesive or the like. The supporting members 62 to 76 are arranged in a row while being spaced apart from each other. External electrodes 82 and 84 of piezoelectric vibrator elements 80a, 80b, 80c, and 80d used as piezoelectric resonators are attached to the supporting members 62 to 76. In this embodiment a ladder type circuit such as that shown in Fig. 12 is thereby formed. A metallic cap (not shown) is placed on the supporting substrate 52. In the piezoelectric component 50 of this embodiment, the supporting members 62 to 76 have the same structure as that of the supporting member 24 described with respect to the embodiment shown in Figs. 6 and 7, and the piezoelectric vibrator elements 80a to 80d have the same structure as the piezoelectric vibrator element 32. The structure for supporting the piezoelectric vibrator elements 80a to 80d on the insulating substrate 52 by using the supporting members 62 to 76 is also the same as that in the embodiment shown in Figs. 6 and 7. The supporting structure will be described with respect to supporting members 66 and 68 by way of example. As shown in Fig. 11, a pair of conductors 86a and 86b made of a metal foil such as copper foil are respectively formed on two side surfaces of each of the supporting members 66 and 68. The upper surfaces of the supporting members 66 and 68 are respectively connected to the external electrodes 82 and 84 of the piezoelectric vibrator element 100b by elastic electroconductive adhesive layers 88 provided as first supporting means. The lower surfaces of the supporting members 66 and 68 are respectively connected to the pattern electrodes 56 and 58 of the insulating substrate 52 by elastic electroconductive adhesive layers 90 provided as second supporting means. Therefore, the piezoelectric component 50 of this embodiment, shown in Figs. 9, 10, and 11, operates in the same manner and is as advantageous as the piezoelectric component 10 of the embodiment shown in Fig. 6 and 7. In the piezoelectric component 50 shown in Figs. 9, 10, and 11, since adjacent two of the electrodes of each adjacent pair of the piezoelectric vibrator elements are attached to the two supporting members formed on one land, there is no need for insulation between the two electrodes, and the adjacent pair of the piezoelectric vibrator elements can be disposed close to each other. The piezoelectric vibrator elements cannot be so close to each other if they are mounted by the mounting structure of the piezoelectric component 10 shown in Figs. 6 and 7. Thus, the piezoelectric component 50 shown in Figs. 9, 10, and 11 can be smaller in overall size.

Claims: A piezoelectric component (10) comprising a substrate (12), and at least one piezoelectric resonator (18, 32) disposed on a surface of said substrate (12) via supporting means (26, 28, 44, 46, 48, 50) for bonding said piezoelectric resonator (18, 32) and said substrate (12) to each other, said supporting means comprising an electroconductive material, characterized by said electroconductive material comprising electroconductive adhesive and at least one supporting member (24) disposed within said electroconductive adhesive (26, 28, 44, 46, 48, 50) or between two layers of said electroconductive adhesive. A piezoelectric component (10) according to claim 1, characterized in that a centre portion in the longitudinal direction of said supporting member (24) is situated at a nodal point of said piezoelectric resonator (18, 32). A piezoelectric component (10) according to one of the claims 1 or 2, characterized in that a bonding length of said supporting means (26, 28, 44, 46, 48, 50) along the longitudinal direction of said piezoelectric resonator (18, 32) is 25% or less of a length of said piezoelectric resonator (18, 32) in the longitudinal direction. A piezoelectric component (10) according to claim 3, characterized in that a centre portion of said supporting means (26, 28, 44, 46, 48, 50) in the longitudinal direction of said piezoelectric resonator (18, 32) is situated at a nodal point of said piezoelectric resonator (18, 32). A piezoelectric component (10) according to one of the claims 1 to 4, characterized in that said electroconductive adhesive is elastic. A piezoelectric component (10) according to one of the claims 1 to 5, characterized in that said supporting member (24) has a conductive portion (40, 42) for electrically conducting between said piezoelectric resonator (32) and said substrate (12). A piezoelectric component (10) according to claim 6, characterized in that said conductive portion (40, 42) is a metal foil on said supporting member (24). A piezoelectric component according to one of the claims 1 to 7, characterized in that said piezoelectric resonator (18, 32) includes a base member (20, 34) having a longitudinal shape, and said base member (20, 34) includes a structure in which a plurality of piezoelectric layers and a plurality of electrodes each positioned perpendicularly to the longitudinal direction of said base member (20, 34) are alternately laminated. A piezoelectric component according to claim 8, characterized in that said base member excites a longitudinal mode vibration when an electric field is supplied to said plurality of piezoelectric layers via said plurality of electrodes.

Inventors: KUSABIRAKI SHIGEMASA, TAKESHIMA TETSUO, UNAMI TOSHIHIKO, YAMAMOTO TAKASHI, YOSHINO HIROHIDE, KUSABIRAKI, SHIGEMASA, TAKESHIMA, TETSUO, UNAMI, TOSHIHIKO, YAMAMOTO, TAKASHI, YOSHINO, HIROHIDE
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1997
Main classification: H03H9
IPC codes: H03H9