Piezoelectric resonator and electronic component comprising the piezoelectric resonator

Abstract: A piezoelectric resonator (10) capable of being mounted without a directional restriction is provided. The piezoelectric resonator (10) includes a laminated body (12). In the laminated body (12), two groups of internal electrodes (14,14 ) are alternately laminated with piezoelectric layers (13) interposed therebetween. Strips of first insulating film (16) are formed on two side faces perpendicular to each other in four side faces of the laminated body (12). Strips of second insulating film (18) are formed on the other two side faces perpendicular to each other. A first external electrode (20a,22a) is formed on one of the two side faces on which the first and second insulating films (16,18) are formed, and a second external electrode (20b,22b) is formed on the other of these two side faces. The first and second external electrodes (20a,20b) are connected to the second group of internal electrodes (14 ). On the other hand, another first external electrode (22a) is formed on one of the two side faces on which the second insulating film (18) is formed, and another second external electrode (22b) is formed on the other of these two side faces. These first and second external electrodes (22a,22b) are connected to the first group of internal electrodes (14).

Description: BACKGROUND OF THE INVENTION The present invention relates to a piezoelectric resonator and to an electronic component comprising the piezoelectric resonator. The piezoelectric resonator uses mechanical vibration of a piezoelectric member. The electronic component is served as, for example, a ladder type filter, an oscillator or a discriminator using the piezoelectric resonator. Fig. 19 is a perspective view of a laminated piezoelectric resonator 1 which the applicant of the present invention proposed in Japanese Patent Application No. 8-110475 which is still unlaid-open. Fig. 20 is a diagram showing the disposition of external electrodes on the piezoelectric resonator. The laminated piezoelectric resonator 1 includes a laminated body 2 which has the shape of a rectangular block and which is formed by integrally laminating a plurality of piezoelectric layers 3 and internal electrodes 4 interposed between the piezoelectric layers 3. Each piezoelectric layer 3 is formed of a piezoelectric ceramic. The internal electrodes 4 are positioned a predetermined distance apart from each other and have their major surfaces set perpendicular to the longitudinal direction of the laminated body 2. The piezoelectric layers 3 are polarized along the longitudinal direction of the laminated body 2 so that the adjacent pair of the piezoelectric layers 3 on the opposite sides of each internal electrode 4 are polarized in opposite directions, as indicated by the arrows in Fig. 19, thereby forming a vibrating section 5. Strips of insulating film 6 and strips of insulating film 7 are respectively formed on two opposite side faces of the laminated body 2. Edges of the internal electrodes 4 exposed in one of the opposite side faces of the laminated body 2 are alternately covered and left uncovered with insulating film 6. In edges of the internal electrodes 4 exposed in the other side face of the laminated body 2, those opposite from the exposed edges not covered with insulating film 6 in the former side face are covered with insulating film 7. Further, on the side faces of the laminated body 2 on which insulating films 6 and 7 are formed, external electrodes 8 and 9 provided as input/output electrodes are also formed. The external electrode 8 is connected to the internal electrodes 4 not covered with insulating film 6 while the external electrode 9 is connected to the internal electrodes 4 not covered with insulating film 7. That is, each adjacent pair of the internal electrodes 4 are respectively connected to the external electrodes 8 and 9. When an alternating current signal having a voltage the direction of which changes with time is input to the laminated piezoelectric resonator 1, the laminated body 2 vibrates in the longitudinal direction. That is, when an electric field is applied to each piezoelectric layer 3 in the same direction as the polarization, the piezoelectric layer 3 expands along the longitudinal direction of the laminated body 2 and the entire of the laminated body 2 also extends along the longitudinal direction. When an electric field is applied to each piezoelectric layer 3 in the direction opposite to the direction of the polarization, the piezoelectric layer 3 contracts along the longitudinal direction of the laminated body 2 and the entire of the laminated body 2 also contracts along the longitudinal direction. These movements are alternately repeated. In the piezoelectric resonator 1 constructed as described above, all the directions of expansion or contraction of the piezoelectric layers 3 caused when electric fields are applied thereto are the same. In the piezoelectric resonator 1, therefore, an input signal can be efficiently converted into mechanical vibration and the electromechanical coupling coefficient can be increased, so that ΔF which is the difference between the resonant frequency F and the antiresonant frequency Fa can be comparatively large. Therefore, the piezoelectric resonator 1 having such characteristics is suitable for use as, for example, a wide band filter. Fig. 21 shows an example of a ladder type filter constructed by combining a plurality of laminated piezoelectric resonators 1. The ladder type filter 100 shown in Fig. 21 includes a substrate 102 formed of alumina. Thick film electrodes 104 are formed on a surface of the substrate 102. The thick film electrodes 104 are formed of patterns on the substrate 102 such as to establish connections such as those indicated by the broken lines in Fig. 21. The laminated piezoelectric resonators 1 each having the above-described structure are mounted on the substrate 102 with an electroconductive paste 106 interposed therebetween. One external electrode 9 of one of the laminated piezoelectric resonators 1 is connected to one of the pattern electrodes 102 on the substrate 102 by electroconductive paste 106 while the other external electrode 8 is electrically connected to the external electrode 8 of another of the laminated piezoelectric resonators 1 or to one of the thick film electrodes 104 on the substrate 102. A metallic cap 112 for protecting the laminated piezoelectric resonators 1 is bonded to the substrate 102 by an adhesive 110. In the above-described laminated piezoelectric resonator 1, a pair of external electrodes 8 and 9 are formed on opposite side faces or on one side face and are used for connection to an external circuit or a different kind of electronic circuit. In the above-described laminated piezoelectric resonator 1, however, since the external electrode 8 is formed, for example, on only one of four side faces of the cuboid laminated body 2 as shown in Fig. 20, connection to the external electrode 8 is impossible on the other three side faces. The same can also be said with respect to the external electrode 9. Thus, the above-described laminated piezoelectric resonator 1 has a directionality when mounted on a substrate or the like and there is a need for a process step of arranging laminated piezoelectric resonators 1 so that each piezoelectric resonator 1 faces in a predetermined direction in the process of manufacturing an electronic component. Due to such a mounting directionality, considerable restrictions are imposed on the design and manufacture of a ladder type filter formed by combining a plurality of laminated piezoelectric resonators 1, so that it is difficult to reduce the size and manufacturing cost of the filter. For example, in the case of the ladder type filter 100 shown in Fig. 21, there is a directional restriction on mounting laminated piezoelectric resonators 1 such that the laminated piezoelectric resonators 1 must be arranged in a direction parallel to the surface of the substrate 102, so that the mounting area of the substrate 102 is disadvantageously large. Moreover, there is also a problem of complicated wiring using wires 104 for connecting external electrodes 8 or 9. SUMMARY OF THE INVENTION In view of these circumstances, a main object of the present invention is to provide a piezoelectric resonator which can be mounted without a directional restriction. To achieve this object, according to one aspect of the present invention, there is provided a piezoelectric resonator, comprising a laminated body, a group of internal electrodes and piezoelectric layers alternately laminated in at least a part of said laminated body, at least one first external electrode provided on a side face of said laminated body, a second external electrode provided on a side face of said laminated body different from the side face on which said first external electrode is provided, said first and second external electrodes being connected to each other through said internal electrodes. According to the piezoelectric resonator of the present invention, the first and second external electrodes formed on different side faces are connected in common to a group of internal electrodes, thereby removing a directional restriction on mounting the piezoelectric resonator on a substrate or the like. In the avove piezoelectric rezonator, two said first external electrodes may be provided, one of said first external electrode and said second external electrode may be electrically connected to each other through said internal electrode, and the other of said first external electrodes may be provided on a side face of said laminated body different from the side faces on which one of said first external electrodes and said second external electrode may be provided. In the avove piezoelectric rezonator, the other of said second external electrodes may be provided on a side face of said laminated body different from the side faces on which the other first and second external electrodes may be provided, and the other of said first external electrodes and the the other of said second external electrodes may be electrically connected to each other through said internal electrode. In the avove piezoelectric rezonator, one of said first external electrodes and one of said second external electrodes may be provided on the adjacent side faces of said laminated body respectively, and the other of said first external electrodes and the other of said second external electrodes may be provided on the other adjacent side faces of said laminated body respectively. In the above described piezoelectric resonator, the laminated body may have a longitudinal direction and vibrates in a longitudinal mode. In the above described piezoelectric resonator, the laminated body may include a vibrating section in which a plurality of said internal electrodes and said piezoelectric layers are alternately laminated, said internal electrodes may be arranged such that their major surface are perpendicular to the longitudinal direction of said laminated body, said piezoelectric layers may be polarized along the longitudinal direction of said laminated body, said at least one first external electrode may be connected to one of the opposing pair of said internal electrodes located on opposite sides on each of said piezoelectric layer, and said second external electrode may be connected to said first external electrode through said one of the opposing pair of said internal electrodes. Also in this piezoelectric resonator of the present invention, the first and second external electrodes formed on different side faces are connected in common to a group of internal electrodes, thereby removing a directional restriction on mounting the piezoelectric resonator on a substrate or the like. According to another aspect of the present invention, there is provided an electronic component comprising the above described electric resonator which is characterized in that said first piezoelectric resonator and a second piezoelectric resonator having a pair of external electrodes on its different side faces are superposed one on another, said second external electrode of said first piezoelectric resonator and one of said external electrodes of said second piezoelectric resonator are connected to each other. - This electronic component of the present invention can be formed by superposing the above-described piezoelectric resonator and the same/other type piezoelectric resonator one on another on a substrate, so that the area of the substrate can be reduced and the packaging density can be increased. There is also provided an electronic component comprising the above described electric resonator which is characterized in that said plurality of piezoelectric resonators are superposed one on another and mounted on a substrate, the first external electrode of one of said piezoelectric resonators are connected to a pattern electrode provided on said substrate, and the second external electrode of said one of said piezoelectric resonators and one of the external electrodes of said piezoelectric resonators superposed are connected to each other. This electronic component of the present invention can be formed by superposing a plurality of the piezoelectric resonators of the invention one on another on a substrate, so that the area of the substrate can be reduced and the packaging density can be increased. In the piezoelectric resonator of the present invention, because the first and second external electrodes formed on different side faces of the laminated body are connected in common to a group of internal electrodes, external pattern electrodes or the like can be connected to the same internal electrodes through different side faces, so that directional restrictions at the time of mounting are reduced in comparison with the conventional arrangement. Thus, the degree of freedom in designing an electronic component can be increased by using the piezoelectric resonator of the present invention. Also, the packaging density in an electronic component can be improved if the piezoelectric resonator of the present invention is used. Therefore, an electronic component, e.g., an oscillator, a discriminator or a filter can be designed so as to be smaller in size according to the present invention. Further, such an electronic component can be manufactured at a lower cost because a process step of arranging piezoelectric resonators so that each piezoelectric resonator faces in a predetermined direction at the time of manufacturing can be removed, and because the connections between the elements can be simplified. The above-described and other objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments of the invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of an example of a piezoelectric resonator of the present invention; Fig. 2A is a cross-sectional view taken along the line IIA-IIA of Fig. 1; Fig. 2B is a cross-sectional view taken along the line IIB-IIB of Fig. 1; Fig. 3 is a diagram of connections between external electrodes in the laminated body of the piezoelectric resonator shown in Fig. 1; Fig. 4 is a front view of an electronic component using the piezoelectric resonator shown in Fig. 1; Fig. 5 is a side view of the piezoelectric resonator shown in Fig. 1, showing wiring in the resonator; Fig. 6 is a perspective view of another example of the piezoelectric resonator of the present invention; Fig. 7A is a cross-sectional view taken along the line VIIA-VIIA of Fig. 6; Fig. 7B is a cross-sectional view taken along the line VIIB-VIIB of Fig. 1; Fig. 8 is a diagram of connections between external electrodes in the laminated body of the piezoelectric resonator shown in Fig. 6; Fig. 9 is a perspective view of still another example of the piezoelectric resonator of the present invention; Fig. 10A is a cross-sectional view taken along the line XA-XA of Fig. 9; Fig. 10B is a cross-sectional view taken along the line XB-XB of Fig. 9; Fig. 11 is a diagram of connections between external electrodes in the laminated body of the piezoelectric resonator shown in Fig. 9; Fig. 12 is a perspective view of a further example of the piezoelectric resonator of the present invention; - Fig. 13A is a cross-sectional view taken along the line XIIIA-XIIIA of Fig. 12; Fig. 13B is a cross-sectional view taken along the line XIIIB-XIIIB of Fig. 12; Fig. 14 is a diagram of connections between external electrodes in the laminated body of the piezoelectric resonator shown in Fig. 12; Fig. 15 is a partially-cutaway longitudinal sectional view of an electronic component using the piezoelectric resonator shown in Fig. 12; Fig. 16 is a transverse sectional view of the electronic component shown in Fig. 15, showing electrical connections in the electronic component; Fig. 17 is a perspective view of a substrate used in the electronic component shown in Figs. 15 and 16; Fig. 18 is a circuit diagram of the electronic component shown in Figs. 15 and 16; Fig. 19 is a perspective view of a laminated piezoelectric resonator which the applicant of the present invention proposed in Japanese Patent Application No. 8-110475 which is still unlaid-open; Fig. 20 is a diagram of the disposition of external electrodes on the piezoelectric resonator shown in Fig. 19; and Fig. 21 is a diagram of a ladder type filter constructed by combining a plurality of the laminated piezoelectric resonators shown in Fig. 19. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a piezoelectric resonator 10 which represents an embodiment of the present invention. As shown in Fig. 1, the piezoelectric resonator 10 includes a laminated body 12 which has, for example, the shape of a rectangular block. The laminated body 12 has a vibrating section 24 which is formed by laminating a plurality of piezoelectric layers 13 and a plurality of internal electrodes 14, 14' interposed between the piezoelectric layers 13. Each piezoelectric layer 13 is formed of a piezoelectric ceramic. The internal electrodes 14, 14' are formed a predetermined distance apart from each other and have their major surfaces set perpendicular to the longitudinal direction of the laminated body 12. In this specification, for ease of explanation, one of each adjacent pair of internal electrodes between which one of the piezoelectric layers 13 forming the laminated body 12 is interposed is referred to as internal electrode 14 while the other of the adjacent pair of internal electrodes is referred to as internal electrode 14'. That is, the internal electrodes 14 and the internal electrodes 14' are alternately arranged along the longitudinal direction of the laminated body 12. The vibrating section 24 is provided for excitation of vibration of the laminated body 12 in the longitudinal basic mode. In the vibrating section 24, each adjacent pair of piezoelectric layers 13 between which one internal electrode 14 or 14' is interposed are polarized in opposite directions along the longitudinal direction of the laminated body 12, as are those polarized in the directions of the arrows shown in Fig. 19. Strips of insulating film 16 are formed on each of two side faces perpendicular to each other in the four side faces of the laminated body 12. These strips of insulating film 16 cover exposed edges of the internal electrodes 14. On each of the other two side faces perpendicular to each other, strips of insulating film 18 are formed. These strips of insulating film 18 cover exposed edges of the internal electrodes 14' not covered with insulating film 16 on the former two side faces. That is, insulating film 16 and insulating film 18 are formed on different side faces of the laminated body 12 and are placed alternately with each other along the longitudinal direction of the laminated body 12. On one of the two side faces on which insulating film 16 is formed, a first external electrode 20a is formed from one end to the other end of the laminated body 12 in the longitudinal direction. On the other of the two side faces on which insulating film 16 is formed, a second external electrode 20b is formed from one end to the other end of the laminated body 12 in the longitudinal direction. The first and second external electrodes 20a and 20b are connected to the internal electrodes 14' not covered with insulating film 16. - On the other hand, on one of the two side faces on which insulating film 18 is formed, another first external electrode 22a is formed from one end to the other end of the laminated body 12 in the longitudinal direction. On the other of the two side faces on which insulating film 18 is formed, another second external electrode 22b is formed from one end to the other end of the laminated body 12 in the longitudinal direction. These first and second external electrodes 22a and 22b are connected to the internal electrodes 14 not covered with insulating film 18. The connections of the first external electrodes 20a and 22a and the second external electrodes 20b and 22b thereby made in the laminated body 12 are as shown in Fig. 3. That is, the first and second external electrodes 20a and 20b are connected to each other through the internal electrodes 14' in the laminated body 12 while the other first and second external electrodes 22a and 22b are connected to each other through the other internal electrodes 14 in the laminated body 12. Therefore, an alternating current signal for applying an electric field to the piezoelectric layer 13 interposed between each opposing pair of internal electrodes 14 and 14' can be input through the first external electrodes 20a and 22a and/or the second external electrodes 20b and 22b used as input/output electrodes, thereby making the vibrating section 24 of the laminated body 12 piezoelectrically active. Vibration is thereby excited in the longitudinal vibration mode with a node corresponding to a central portion of the laminated body 12. Fig. 4 is a schematic front view of an example of an electronic component 50 which uses the piezoelectric resonator shown in Fig. 1, and Fig. 5 is a side view of the electronic component 50, showing wiring in the electronic component 50. The electronic component 50 shown in Figs. 4 and 5 is used as an discriminator. The discriminator 50 includes an insulating substrate 52. Pattern electrodes 54 and 55 are formed on the insulating substrate 52. The piezoelectric resonator 10 is bonded to the pattern electrode'54 by an electroconductive adhesive 56 provided as a conductor material. In this example, the electroconductive adhesive 56 is fixed on the first external electrode 22a of the piezoelectric resonator 10 at the center in the longitudinal direction. The electroconductive adhesive 56 electrically connects the first external electrode 22a and the pattern electrode 54 and functions as a supporting member for fixing the piezoelectric resonator 10. In this example, therefore, the electroconductive adhesive 56 is formed into the shape of a rectangular block. In this discriminator 50, the first external electrode 20a and the pattern electrode 55 are connected by a wire 58. The piezoelectric resonator 10, the wire 58 and other components on the substrate are covered with, for example, a metallic cap (not shown), thus completing the discriminator 50. Since this discriminator 50 has the first external electrode 20a and the second external electrode 20b connected in common to the internal electrodes 14' and also has the other first external electrode 22a and the other second external electrode 22b connected in common to the internal electrodes 14, the piezoelectric resonator 10 may be rotated by 90° about its longitudinal axis from the position shown in Fig. 5 to connect the second external electrode 20b to the pattern electrode 54 and to connect the other second external electrode 22b to the pattern electrode 55. The piezoelectric resonator 10 may be further rotated by 90° to connect the first external electrode 20a to the pattern electrode 54 and to connect the other first external electrode 22a to the pattern electrode 55. That is, this piezoelectric resonator 10 is free from a directional restriction at the time of mounting. Accordingly, the need for a step for predetermined directional positioning of the piezoelectric resonator 10 in the process of manufacturing the discriminator 50 can be eliminated, thereby simplifying manufacturing operations and reducing the manufacturing cost. A ceramic oscillator may also be made by using the same construction as that shown in Figs. 4 and 5. Fig. 6 is a perspective view of another piezoelectric resonator 10 according to the present invention. Fig. 7A is a cross-sectional view taken along the line VIIA-VIIA of Fig. 6, and Fig. 7B is a cross-sectional view taken along the line VIIB-VIIB of Fig. 6. Fig. 8 is a diagram showing connections between external electrodes in a laminated body 12 of the piezoelectric resonator 10 shown in Fig. 6. The piezoelectric resonator 10 shown in Fig. 6 differs from the piezoelectric resonator 10 shown in Fig. 1 in the arrangement of insulating films 16 and 18. That is, in the piezoelectric resonator 10 shown in Fig. 6, strips of insulating film 16 are formed on two side faces of the laminated body 12 opposite form each other in the direction of the thickness of the laminated body 12. These strips of insulating film 16 cover exposed edges of internal electrodes 14. On the other hand, strips of insulating film 18 are formed on the other two side faces of the laminated body 12 opposite form each other in the direction of the thickness of the laminated body 12. These strips of insulating film 18 cover exposed edges of internal electrodes 14' not covered with insulating film 16 on the former two side faces. On one of the two side faces on which insulating film 16 is formed, a first external electrode 20a is formed from one end to the other end of the laminated body 12 in the longitudinal direction. On the other of the two side faces, a second external electrode 20b is formed from one end to the other end of the laminated body 12 in the longitudinal direction. The first and second external electrodes 20a and 20b are connected to the internal electrodes 14' not covered with insulating film 16. On the other hand, on one of the two side faces on which insulating film 18 is formed, another first external electrode 22a is formed from one end to the other end of the laminated body 12 in the longitudinal direction. On the other of the two side faces, another second external electrode 22b is formed from one end to the other end of the laminated body 12 in the longitudinal direction. These first and second external electrodes 22a and 22b are connected to the internal electrodes 14 not covered with insulating film 18. The connections of the first external electrodes 20a and 22a and the second external electrodes 20b and 22b thereby made in the laminated body 12 are as shown in Fig. 8. That is, the first and second external electrodes 20a and 20b are connected to each other through the internal electrodes 14' in the laminated body 12 while the other first and second external electrodes 22a and 22b are connected to each other through the other internal electrodes 14 in the laminated body 12. The piezoelectric resonator 10 shown in Fig. 6 operates in the same manner and is as advantageous as that shown in Fig. 1. Fig. 9 is a perspective view of still another piezoelectric resonator 10 according to the present invention. Fig. 10A is a cross-sectional view taken along the line XA-XA of Fig. 9, and Fig. 10B is a cross-sectional view taken along the line XB-XB of Fig. 9. Fig. 11 is a diagram showing connections between external electrodes in a laminated body 12 of the piezoelectric resonator 10 shown in Fig. 9. The piezoelectric resonator 10 shown in Fig. 9 differs from the piezoelectric resonator 10 shown in Fig. 1 in that on the side face opposite from the side surface on which a second external electrode 20b is formed, another second external electrode 22b is not formed, and in that, on this side face, insulating film 18 is not formed. In other respects, this piezoelectric resonator is essentially the same as the piezoelectric resonator shown in Fig. 1. In this piezoelectric resonator 10, however, each of strips of insulating films 16 and 18 has a length substantially equal to the width of the laminated body 12. The piezoelectric resonator 10 shown in Fig. 9 operates in the same manner and is as advantageous as that shown in Fig. 1. Fig. 12 is a perspective view of a further piezoelectric resonator 10 according to the present invention. Fig. 13A is a cross-sectional view taken along the line XIIIA-XIIIA of Fig. 12, and Fig. 13B is a cross-sectional view taken along the line XIIIB-XIIIB of Fig. 12. Fig. 14 is a diagram showing connections between external electrodes in a laminated body 12 of the piezoelectric resonator 10 shown in Fig. 12. The piezoelectric resonator 10 shown in Fig. 12 differs from the piezoelectric resonator shown in Fig. 1 in the arrangement of insulating films 16 and 18 and in the formation of external electrodes. That is, in the piezoelectric resonator 10 shown in Fig. 12, pieces of insulating film 16 for covering internal electrodes 14 are formed adjacent to one of the longer sides of one side face of the laminated body 12 while pieces of insulating film 18 for covering internal electrodes 14' are formed adjacent to the other longer side of this side face. Over the pieces of insulating film 16, a first external electrode 20a is formed from one end to the other end of the laminated body 12 in the longitudinal direction. Over the pieces of insulating film 18, another first external electrode 22 is formed from one end to the other end of the laminated body 12 in the longitudinal direction. On the side face opposite from this side face of the laminated body 12 in the direction of the thickness, pieces of insulating film 16 for covering the internal electrodes 14 are also formed. Over these pieces of insulating film 16, a second external electrode 20b is formed from one end to the other end of the laminated body 12 in the longitudinal direction. The first and second external electrodes 20a and 20b are connected to the internal electrodes 14' not covered with insulating film 16 while the other first external electrode 22 is connected to the internal electrode 14 not covered with insulating film 18. The piezoelectric resonator 10 shown in Fig. 12 operates in the same manner and is as advantageous as that shown in Fig. 1. This piezoelectric resonator 10 is easier to mount in a surface mount manner because the first external electrode 20a connected to the internal electrodes 14' and the first external electrode 22 connected to the internal electrodes 14 are formed on one side face. Moreover, to one piezoelectric resonator 10 of this type, another piezoelectric resonator 10 can be connected by being superposed thereon because the second external electrode 20b connected to the first external electrode 20a through the internal electrodes 14' is formed on the side face opposite in the direction of the thickness of the laminated body 12 from the side face on which the external electrode 20a is formed. In the above-described piezoelectric resonators 10 shown in Figs. 1 to 12, insulating film 16 or 18 is used for insulation of each of the external electrodes 20a, 20b, 22, 22a and 22b from the internal electrode 14 or 14'. However, other means for this insulation are possible according to the present invention. For example, each piezoelectric resonator 10 may be constructed in the same manner as described in Japanese Patent Application 8-110475 made by the applicant of the present invention, that is, each of the internal electrodes 14 and 14' may be insulated from the external electrode 20a, 20b, 22, 22a or 22b on one side face of the laminated body 12 in such a manner that the internal electrodes 14 and 14' alternately have exposed and unexposed edges by reducing the area of their major surfaces relative to the sectional area of the laminated body 12, each of the internal electrodes 14 and 14' being insulated from the external electrode 20a, 20b, 22, 22a or 22b at the unexposed edges. Fig. 15 is a partially-cutaway longitudinal sectional view of an electronic component 60 using the piezoelectric resonator shown in Fig. 12. Fig. 16 is a transverse sectional view showing electrical connections in the electronic component 60. Fig. 17 is a perspective view of a substrate 62 used in the electronic component 60 shown in Figs. 15 and 16. The electronic component 60 shown in Figs. 15 and 16 is constructed as a ladder type filter. The ladder type filter 60 includes piezoelectric resonators 10a and 10b of the same construction as the piezoelectric resonator 10 shown in Fig. 12, and laminated piezoelectric resonators 1a and 16 of the same construction as the laminated piezoelectric resonator 1 shown in Figs. 19 and 20. This ladder type filter 60 also includes the insulating substrate 62 which has, for example, the shape of a rectangular plate. Pattern electrodes on the insulating substrate 62 will next be described with reference to Fig. 17. The broken lines in Fig. 17 indicate the positions of the two piezoelectric resonators 10a and 10b disposed on the insulating substrate 62. A first pattern electrode 64 is formed on one major surface of the insulating substrate 62 (obverse surface as viewed in Fig. 17) at one end in the longitudinal direction of the insulating substrate 62 so as to extend from one end to the other end in the widthwise direction of the insulating substrate 62. The two ends of the first pattern electrode 64 are connected to input/output electrodes 66 on two side surfaces of the insulating substrate 62. Each input/output electrode 66 is formed into an angle shape such as to extend from the side surface to a position on the reverse surface of the insulating substrate 62. The first pattern electrode 64 has an extension which extends from a position in the vicinity of one of the longer sides of the obverse surface of the insulating substrate 62 to a position at the center of the insulating substrate 62 in the longitudinal direction of the insulating substrate 62. The first pattern electrode 64 is connected at the end of this extension to the first external electrode 20a of the piezoelectric resonator 10a. This connection is made by using an electroconductive adhesive 68 as a conductor material, as shown in Figs. 15 and 16. A second pattern electrode 70 is formed at the center of the insulating substrate 62 so as to extend in the widthwise direction of the insulating substrate 62. The second pattern electrode 70 connects, through its two end portions, the other first external electrode 22 of the piezoelectric resonator 10a and the first external electrode 20a of the piezoelectric resonator 10b. These connections are made by using electroconductive adhesives 72 and 74, as shown in Fig. 16. A third pattern electrode 65 is formed at the other end of the insulating substrate 62 in the longitudinal direction so as to extend from one end to the other end in the widthwise direction of the insulating substrate 62, as shown in Fig. 17. The two ends of the third pattern electrode 65 are connected to input/output electrodes 67 on the two side surfaces of the insulating substrate 62. Each input/output electrode 67 is formed into an angle shape such as to extend from the side surface to a position on the reverse surface of the insulating substrate 62. The third pattern electrode 65 has an extension which extends from a position in the vicinity of the other longer side of the obverse surface of the insulating substrate 62 to a position at the center of the insulating substrate 62 in the longitudinal direction of the insulating substrate 62. The second pattern electrode 65 is connected at the end of this extension to the other external electrode 22 of the piezoelectric resonator 10b. This connection is made by using an electroconductive adhesive 76 as a conductor material, as shown in Fig. 16. Insulators 78 are formed on a peripheral end portion of the insulating substrate 62. The insulators 78 are provided for insulation between a metallic cap 88 described below and each of the first and second pattern electrodes 64 and 65. The insulators 78 are spaced apart from each other at two positions on the opposite sides of the center of the insulating substrate 62 in the widthwise direction. In the spacing areas between the insulators 78, ground electrodes 80 to be connected to the metallic cap 88 are formed. Each ground electrode 80 extends to a position on the reverse surface of the insulating substrate 62 via the side surface of the insulating substrate 62. The above-described electroconductive adhesives 68, 72, 74 and 76 electrically connect the electrodes and also serve as members for supporting the piezoelectric resonators 10a and 10b at the center in the longitudinal direction. Accordingly, each of the electroconductive adhesives 68, 72, 74 and 76 is formed into the shape of a rectangular block, for example. The laminated piezoelectric resonators 1a and 1b provided on the insulating substrate 62 and the placement and connection of the metallic cap 88 will next be described. The laminated piezoelectric resonator 1a is superposed on the piezoelectric resonator 10a. The external electrode 8 of the laminated piezoelectric resonator 1a and the second external electrode 20b of the piezoelectric resonator 10a are connected to each other by an electroconductive adhesive 82 provided as a conductor material. The laminated piezoelectric resonator 1b is superposed on the piezoelectric resonator 10b. The external electrode 8 of the laminated piezoelectric resonator 1b and the second external electrode 20b of the piezoelectric resonator 10b are connected to each other by an electroconductive adhesive 84 provided as a conductor material. These electroconductive adhesives 82 and 84 electrically connect the electrodes and also serve as members for supporting the laminated piezoelectric resonators 1a and 1b at the center in the longitudinal direction. Accordingly, each of the electroconductive adhesives 82 and 84 is formed into the shape of a rectangular block, for example. A spring terminal 86 formed of a plate-spring-like member is provided on the laminated piezoelectric resonators 1a and 1b for the purpose of urging central portions of the laminated bodies of the laminated piezoelectric resonators 1a and 1b toward the insulating substrate 62 and electrically connecting the external electrodes 9-and the metallic cap 88. The metallic cap 88 having an electroconductive property is attached as an overall cover above-the spring terminal 86. The spring terminal 86 is supported by the internal ceiling surface of the metallic cap 88. An edge portion of the metallic cap 88 is bonded to the insulators 78 on the insulating substrate 62 by an electroconductive adhesive 90. The metallic cap 88 is thereby insulated from the first and second pattern electrodes 64 and 65. On the other hand, where the insulators 78 are spaced apart from each other on the insulating substrate 62, the metallic cap 88 is directly bonded and electrically connected to the ground electrodes 80 by electroconductive adhesive 90. Electrical connections are thus made in the ladder type filter 60 to form a circuit such as that shown in Fig. 18. In this ladder type filter 60, the piezoelectric resonators 10a and 10b are constructed as described above to enable a plurality of laminated type piezoelectric resonators 1a and 1b to be superposed on the piezoelectric resonators 10a and 10b. Therefore, the area of the insulating substrate 62 can be reduced and the packaging density can be increased. As a result, the entire electrical component can be reduced in size. In this ladder type filter 60, since the piezoelectric resonators 10a and 10b are constructed as described above, there is no need for wire bonding, so that the connections between the elements can be simplified and the total manufacturing cost can be reduced. In the above-described ladder type filter 60, the laminated type piezoelectric resonator 1 is superposed on the piezoelectric resonator 10 of the present invention. However, any of the piezoelectric resonators 10 shown in Fig. 1 to 12 may alternatively be superposed instead of the laminated type piezoelectric resonator 1 to constitute an electronic component. The discriminator and the ladder type filter, which are examples of the electronic components using the piezoelectric resonator of the present invention, have been described as embodiments of the present invention. However, the present invention may also be used to form electronic components other than those described above.

Claims: A piezoelectric resonator (10), comprising a laminated body (12), a group of internal electrodes (14,14') and piezoelectric layers (13) alternately laminated in at least a part of said laminated body (12), at least one first external electrode (20a,22a) provided on a side face of said laminated body, a second external electrode (20b,22b) provided on a side face of said laminated body (12) different from the side face on which said first external electrode (20a,22a) is provided, said first and second external electrodes (20a,22a)(20b,22b) being connected to each other through said internal electrodes (14,14'). A piezoelectric resonator (10) according to Claim 1, characterized in that two said first external electrodes (20a,22a) are provided, one of said first external electrode (20a) and said second external electrode (20b) are electrically connected to each other through said internal electrode (14'), and the other of said first external electrodes (22a) is provided on a side face of said laminated body (12) different from the side faces on which one of said first external electrodes (20a) and said second external electrode (20b) are provided. A piezoelectric resonator (10) according to Claim 1, characterized in that the other of said second external electrodes (22b) are provided on a side face of said laminated body (12) different from the side faces on which the other first and second external electrodes (20a,22a)(20b) are provided, and the other of said first external electrodes (22a) and the the other of said second external electrodes (22b) are electrically connected to each other through said internal electrode (14). A piezoelectric resonator (10) according to Claim 3, characterized in that one of said first external electrodes (20a) and one of said second external electrodes (20b) are provided on the adjacent side faces of said laminated body (12) respectively, and the other of said first external electrodes (22a) and the other of said second external electrodes (22b) are provided on the other adjacent side faces of said laminated body (12) respectively. A piezoelectric resonator (10) according to one of Claims 1to 4, characterized in that said laminated body (12) has a longitudinal direction and vibrates in a longitudinal mode. A piezoelectric resonator (10) according to Claim 5, characterized in that said laminated body (12) includes a vibrating section (24) in which a plurality of said internal electrodes (14,14') and said piezoelectric layers (13) are alternately laminated, said internal electrodes (14,14') are arranged such that their major surface are perpendicular to the longitudinal direction of said laminated body (12), said piezoelectric layers (13) are polarized along the longitudinal direction of said laminated body (12), said at least one first external electrode (20a,22a) is connected to one of the opposing pair of said internal electrodes (14',14) located on opposite sides on each of said piezoelectric layer (13), and said second external electrode (20b,22b) is connected to said first external electrode (20a,22a) through said one of the opposing pair of said internal electrodes (14',14). An electronic component(60) comprising at least one electric resonator (10a,10b) according to one of Claims 1 to 6, characterized in that said at least one piezoelectric resonator is one of a plurality of piezoelectric resonators (1a,1b)(10a,10b) having a pair of external electrodes (8,9)(20a,22,20b) included in said electronic component (60), said plurality of piezoelectric resonators are superposed one on another, said second external electrode (20b) of said at least one piezoelectric resonator (10a,10b) and one of said at least one piezoelectric resonator (10a,10b) and one of said external electrodes (8) of the other one of said plurality of piezoelectric resonators (1a,1b) are connected to each other.

Inventors: YAMAMOTO TAKASHI, YAMAMOTO, TAKASHI
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1997
Main classification: H03H9
IPC codes: H03H9