Piezoelectric resonator and electronic component using the same

Abstract: A piezoelectric resonator (10) has a base member (12). The base member (12) includes a plurality of piezoelectric layers laminated with internal electrodes (14) disposed therebetween. A first vibrating section (24a) is formed in the most part of the base member (12). In the first vibrating section (24a), adjacent piezoelectric layers sandwiching one internal electrode (14) therebetween are polarized in opposite directions in the longitudinal direction of the base member (12). At both sides of the first vibrating section (24a), second vibrating sections (24b) are formed. A piezoelectric layer of each of the second vibrating sections (24b) is polarized in the same direction as the adjacent piezoelectric layer in the first vibrating section (24a) with an internal electrode placed (14) therebetween. An electric field is applied in opposite directions to adjacent piezoelectric layers disposed on both sides of an internal electrode (14) in the base member.

Description: BACKGROUND OF THE INVENTION The present invention as it is defined in the appended claims relates to piezoelectric resonators and electronic components using the same, and more particularly, to a piezoelectric resonator comprising a base member having a longitudinal direction, polarized piezoelectric member constituting at least a part of said base member, and a pair of external electrodes provided with said base member. The piezoelectric resonator uses the mechanical resonance of a piezoelectric member. And electronic components using the piezoelectric resonator is a ladder filter, an oscillator, a discriminator, or a filter, for example. Fig. 18 is a perspective view of a piezoelectric resonator which the applicant has proposed at an application number of 8-110475 to the Japan Patent Office and not yet published and which in related to the European Application published as EP-A-0 800 269. Fig. 19 is a view showing the internal structure of the piezoelectric resonator shown in Fig. 18. A piezoelectric resonator 1 includes a base member 2 having, for example, a rectangular-parallelpiped shape. The base member 2 is formed by integrally laminating a plurality of piezoelectric layers with electrodes 3 disposed therebetween. The piezoelectric layers are made from piezoelectric ceramic. The electrodes 3 are disposed such that their surfaces are perpendicular to the longitudinal direction of the base member 2 and they have a certain interval therebetween. The piezoelectric layers are polarized in opposite directions at both sides of electrodes 3 in the longitudinal direction of the base member 2 as shown in Fig. 19, and thereby a vibrating section 4 is formed as shown by hatching in Fig. 19. Since electrodes are not formed at both ends of the base member 2 in the longitudinal direction in the piezoelectric resonator 1, the piezoelectric layers disposed at both ends of the base member 2 serve as piezoelectrically inactive dummy layers "d." On opposite side faces of the base member 2, a plurality of insulating films 5 and 6 is formed, respectively. On one side face of the base member 2, alternate exposed portions of the electrodes 3 are covered by the insulating film 5. On the other side face of the base member 2, alternate exposed portions of the electrodes 3 which are not covered by the insulating film 5 on the above-described side face are covered by the insulating film 6. On the side faces of the base member 2 on which the insulating films 5 and 6 are formed, that is, connection sections, external electrodes 7 and 8 are formed. Therefore, the external electrode 7 is connected to electrodes 3 which are not covered by the insulating film 5 and the external electrode 8 is connected to electrodes 3 which are not covered by the insulating film 6. In other words, adjacent electrodes among the electrodes 3 are connected to the external electrodes 7 and 8, respectively. The external electrodes 7 and 8 are used as input and output electrodes. Figs. 20A and 20B illustrate vibration conditions in the piezoelectric resonator shown in Figs. 18 and 19. The piezoelectric resonator 1 shown in Figs. 20A and 20B has the same structure as the piezoelectric resonator described above. Among three rows of arrows shown in the base member 2 of the piezoelectric resonator 1 in Figs. 20A and 20B, the upper row of arrows indicate the direction in which an electric field is applied, the middle row of white arrows indicate the direction of polarization, and the lower row of arrows indicate the direction in which each piezoelectric layer expands and contracts in the stiffened piezoelectric resonator. When an AC signal, which changes its direction of voltage as time elapses, is input to the piezoelectric resonator 1, the base member 2 alternately changes its condition between those shown in Fig. 20A and Fig. 20B to vibrate in the longitudinal direction. In other words, when an electric field is applied to each piezoelectric layer in the same direction as that of polarization as shown in Fig. 20A, each piezoelectric layer expands in the longitudinal direction of the base member 2 and the base member 2 expands in the longitudinal direction as a whole. On the other hand, when an electric field is applied to each piezoelectric layer in the direction opposite that of polarization as shown in Fig. 20B, each piezoelectric layer contracts in the longitudinal direction of the base member 2 and the base member 2 contracts in the longitudinal direction as a whole. These operations are repeated, and the base member 2 vibrates in the longitudinal direction. The piezoelectric resonator 1 has a structure in which each piezoelectric layer expands and contracts in the same direction when an electric field is applied, as shown in Figs. 20A and 20B. In other words, each piezoelectric layer has a driving force in the same direction, generated due to the inverse piezoelectric effect. Therefore an input signal is efficiently converted to mechanical vibration in the piezoelectric resonator 1, and it can have a larger electromagnetic coupling coefficient and also have a relatively large ΔF, which is a difference between the resonant frequency Fr and the antiresonant frequency Fa. A resonator having a large ΔF is suited to, for example, a wide-frequency-band filter. A narrow-frequency-band filter and an oscillator may, however, require a small ΔF. To obtain a small ΔF in the piezoelectric resonator 1 described by referring to Figs. 18 to 20B, the area of each electrode, or the size or thickness of the piezoelectric layers need to be changed, and troublesome work is required. SUMMARY OF THE INVENTION Accordingly, it is the main object of the present invention to provide a piezoelectric resonator having a small ΔF and being suited to a narrow-frequency-band filter and an oscillator. The foregoing object is achieved in one aspect of the present invention through the provision of a piezoelectric resonator of the above mentioned kind, which is characterized in that a laminated member section constituting at least a part of said base member is provided by alternately laminating a plurality of piezoelectric layers and a plurality of internal electrodes, said piezoelectric layers is made of said piezoelectric member and polarized in the longitudinal direction of said base member, said internal electrodes are perpendicular to the longitudinal direction of said base member and are connected to said pair of external electrodes respectively, and said laminated member section includes a first vibrating section and a second vibrating section which respectively excite longitudinal basic vibrations in opposite phases each other. In the above piezoelectric resonator, when an electric field is applied to the piezoelectric layer of said first vibrating section in the same direction as the direction of polarization, an electric field may be applied to the piezoelectric layer of said second vibrating section in the direction opposite the direction of polarization, and when an electric field is applied to the piezoelectric layer of said first vibrating section in the direction opposite the direction of polarization, an electric field may be applied to the piezoelectric layer of said second vibrating section in the same direction as the direction of polarization. The forgoing object is achieved in a further aspect of the present invention through the provision of an electronic component for use with the above described piezoelectric resonator, which is characterized in that said base member is supported by a support member via a mounting member, and said mounting member is provided at a center section of said base member in the longitudinal direction. In the above electronic component, said support member may be an insulating substrate on which a pattern electrode is formed. In the above electronic component, a plurality of said piezoelectric resonators connected in a ladder shape in series and in parallel may be mounted on said insulating substrate. In the above electronic component, a cap may be disposed on the insulating substrate so as to cover the base members. In a piezoelectric resonator according to the present invention, longitudinal basic vibration is excited in the base member when an electric field is applied in the longitudinal direction of the base member. This vibration is generated in a stiffened piezoelectric resonator. Therefore, vibrations in modes such as the width and thickness modes, which are different from the basic vibration, are unlikely to occur and superior characteristics are obtained. Since the first and second vibrating sections of the base member in which longitudinal basic vibration is excited vibrate in opposite phases each other in a piezoelectric resonator according to the present invention, ΔF becomes small. When an electronic component such as a ladder filter, an oscillator, a discriminator, and a filter is made using this piezoelectric resonator, the piezoelectric resonator is mounted on an insulating substrate on which pattern electrodes are formed and may be covered by a cap to form a chip-type (surface mount) electronic components. By adjusting the ratio or positional relationship between the second vibrating section and the first vibrating section in a piezoelectric resonator according to the present invention, ΔF can be selected from a wide range without changing the dimensions of the piezoelectric resonator, implementing various values of ΔF. According to the present invention, a piezoelectric resonator having a small ΔF can be obtained. Therefore, a piezoelectric resonator suited to a narrow-frequency-band filter and an oscillator is obtained. Since a chip-type electronic component can be made using the piezoelectric resonator, it is easy to mount the component on a circuit board. The above-described object, other objects, other features, and other advantages of the present invention will be made clear in the following description noted by referring to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a piezoelectric resonator according to the present invention. Fig. 2 is a view showing the structure of the piezoelectric resonator shown in Fig. 1. Figs. 3A and 3B illustrate vibration conditions of the piezoelectric resonator shown in Figs. 1 and 2. Fig. 4 is a view showing changes in thickness of each piezoelectric layer during vibration in a piezoelectric resonator of the present invention. Fig. 5 is a view of a piezoelectric resonator according to the present invention used for checking the characteristics. Fig. 6 is a view of a piezoelectric resonator shown for comparison. Figs. 7A and 7B illustrate a structure and vibration conditions of another piezoelectric resonator according to the present invention. Figs. 8A and 8B illustrate a structure and vibration conditions of still another piezoelectric resonator according to the present invention. Fig. 9 is a circuit diagram of the piezoelectric resonator shown in Fig. 8. Fig. 10 is a perspective view of an electronic component using the piezoelectric resonator according to the present invention. Fig. 11 is a perspective view of an insulating substrate used in the electronic component shown in Fig. 10. Fig. 12 is an exploded perspective view of the electronic component shown in Fig. 10. Fig. 13 is a perspective view of a further piezoelectric resonator according to the present invention. Fig. 14 is a view showing a structure of the piezoelectric resonator shown in Fig. 13. Fig. 15 is a perspective view of a main section of an electronic component using the piezoelectric resonator shown in Figs. 13 and 14. Fig. 16 is an exploded perspective view of the main section of the electronic component shown in Fig. 15. Fig. 17 is a circuit diagram of the electronic component shown in Figs. 15 and 16. Fig. 18 is a perspective view of a piezoelectric resonator which the applicant has proposed and not yet published. Fig. 19 is a view showing the internal structure of the piezoelectric resonator shown in Fig. 18. Figs. 20A and 20B illustrate vibration conditions of the piezoelectric resonator shown in Figs. 18 and 19. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a perspective view of a piezoelectric resonator according to an embodiment of the present invention. Fig. 2 shows the internal structure of the piezoelectric resonator. The piezoelectric resonator 10 includes a base member 12 having, for example, a rectangular-parallelepiped shape. The base member 12 has a laminated member section formed by laminating a plurality of piezoelectric layers with internal electrodes 14 disposed therebetween. The laminated member section includes a first vibrating section 24a and second vibrating sections 24b. The piezoelectric layers are made from piezoelectric ceramic. A plurality of internal electrodes 14 is formed such that their faces are perpendicular to the longitudinal direction of the base member 12 and the electrodes have a certain interval therebetween. The first vibrating section 24a occupies the most part of the base member 12 in the piezoelectric resonator 10 and excites longitudinal basic vibration to the base member 12. In the first vibrating section 24a, adjacent piezoelectric layers having one internal electrode 14 therebetween are polarized in opposite directions in the longitudinal direction of the base member 12 as shown by black arrows in Fig. 2. Second vibrating sections 24b are formed at both sides of the first vibrating section 24a. The second vibrating sections 24b reduce ΔF of the piezoelectric resonator 10 while slightly preventing vibration efficiency in the first vibrating section 24a. The piezoelectric layer of each of the second vibrating sections 24b is polarized in the same direction as the adjacent piezoelectric layer of the first vibrating section 24a with the internal electrode 14 disposed therebetween, as shown by white arrows in Fig. 2. At both sides of the vibrating sections 24b, dummy layers "d" are formed. The dummy layers "d" need not to be formed if not required. On opposing side faces of the base member 12, a plurality of insulating films 16 and 18 is formed, respectively. On one side face of the base member 12, the insulating film 16 covers the exposed section of every other internal electrode 14. On the other side face of the base member 12, the insulating film 18 covers the exposed section of every other internal electrode 14 not covered by the insulating film 16 on the above-described side face. The two side faces of the base member 12 on which the insulating films 16 and 18 are formed serve as connection sections to external electrodes, which will be described later. In these connection sections, namely, the side faces of the base member 12 on which the insulating films 16 and 18 are formed, external electrodes 20 and 22 are formed. The external electrode 20 connects to internal electrodes 14 which are not covered by the insulating film 16, and the external electrode 22 connects to internal electrodes 14 which are not covered by the insulating film 18. In other words, adjacent internal electrodes 14 are connected to the external electrodes 20 and 22, respectively. The external electrodes 20 and 22 are used as input and output electrodes in this piezoelectric resonator 10. Since an electric field is applied between adjacent internal electrodes 14, the base member is piezoelectrically active. Figs. 3A and 3B illustrate vibration conditions in the piezoelectric resonator shown in Figs. 1 and 2. The piezoelectric resonator 10 shown in Figs. 3A and 3B has the same structure as the piezoelectric resonator shown in Figs. 1 and 2. Among three rows of arrows shown in the base member 12 of the piezoelectric resonator 10 in Figs. 3A and 3B, the upper row of arrows indicate the direction in which an electric field is applied, the middle row of white arrows indicate the direction of polarization, and the lower row of arrows indicate the direction in which each piezoelectric layer expands and contracts in the stiffened piezoelectric resonator. When an AC signal, which changes its direction of voltage as time elapses, is input to the external electrodes 20 and 22 of the piezoelectric resonator 10, an electric field is applied in opposite directions to adjacent piezoelectric layers at both sides of an internal electrode 14, constituting the base member 12, and longitudinal basic vibration is excited with the center of the base member 12 serving as a node. The base member 12 alternately changes its condition between those shown in Fig. 3A and Fig. 3B to vibrate in the longitudinal direction. When an electric field is applied to each piezoelectric layer in the first vibrating section 24a in the same direction as that of polarization as shown in Fig. 3A, each piezoelectric layer expands in the longitudinal direction of the base member 12 and the base member 12 expands in the longitudinal direction as a whole. Since an electric field is applied to each piezoelectric layer of the second vibrating sections 24b in the direction opposite that of polarization, however, the second vibrating sections 24b contract in the longitudinal direction of the base member 12. On the other hand, when an electric field is applied to each piezoelectric layer in the direction opposite that of polarization as shown in Fig. 3B, each piezoelectric layer contracts in the longitudinal direction of the base member 12 and the base member 12 contracts in the longitudinal direction as a whole. Since an electric field is applied to each piezoelectric layer of the second vibrating sections 24b in the same direction as that of polarization, however, the second vibrating sections 24b expand in the longitudinal direction of the base member 12. Fig. 4 is a view showing changes in thickness of each piezoelectric layer during vibration in the piezoelectric resonator 10 according to the present invention. In Fig. 4, the thickness of each piezoelectric layer before contraction of the base member 12 is indicated by t, and the thicknesses of the piezoelectric layers after contraction are indicated by t 1 , t 2 , and t 3 . These thicknesses have a relationship of t > t 3 > t 2 > t 1 . The piezoelectric layers contract more as they are disposed closer to the center of the base member 12. As described above, in the piezoelectric resonator 10 shown in Figs. 1 to 3B, the second vibrating sections 24b, which occupy a part of the base member 12 in which longitudinal basic vibration is excited, vibrate in the direction opposite the direction of vibration in the first vibrating section 24a, which occupies the most part of the base member 12. Therefore, the vibration efficiency in the first vibrating section 24a is slightly prevented and Δf of the piezoelectric resonator 10 is reduced. Hence, a piezoelectric resonator suited to a narrow-frequency-band filter and an oscillator is obtained. In addition, since the piezoelectric resonator 10 is of a stiffened type and longitudinal basic vibration is excited in it, vibrations in modes such as the width and thickness modes, which are different from the basic vibration, are unlikely to occur and superior characteristics are obtained. By adjusting the ratio or positional relationship between the second vibrating sections 24b and the first vibrating section 24a in the piezoelectric resonator 10, ΔF can be selected from a wide range due to its structure without changing the dimensions of the piezoelectric resonator 10, implementing various values of ΔF. In the embodiment shown in Figs. 1 and 2, for example, the second vibrating sections 24b are formed at both sides of the first vibrating section 24a. The structure is not limited to that in this embodiment. The second vibrating sections 24b may be disposed at the center of the base member 12. In the piezoelectric resonator 10, the second vibrations 24b are formed at both sides of the first vibrating section 24a, one layer at each side. The structure is not limited to this structure. Only one layer of a second vibrating section 24b may be formed inside the first vibrating section 24a. A plurality of layers of the second vibrating sections 24b may be formed. Fig. 5 is a view showing a piezoelectric resonator according to the present invention for checking the characteristics. Fig. 6 shows a piezoelectric resonator for comparison. A piezoelectric resonator 10 shown in Fig. 5 measures 3.78 mm in length, 1.0 mm in height, and 1.0 mm in width. At the center of a base member 12 of the piezoelectric resonator 10, a first vibrating section 24a is formed by laminating four piezoelectric layers with internal electrodes 14 sandwiched therebetween. Second vibrating sections 24b in each of which one piezoelectric layer is sandwiched by internal electrodes 14 are integrally formed with the first vibrating section 24a at both sides of the first vibrating section 24a. At each end of the base member 12, an electrode 14 is formed. The piezoelectric layers constituting the base member 12 have the same thickness. The piezoelectric resonator 1 for comparison shown in Fig. 6 has the same dimensions as the piezoelectric resonator 10 shown in Fig. 5. A base member 2 of the piezoelectric resonator 1 is formed by integrally laminating six piezoelectric layers with electrodes 3 sandwiched therebetween. At each end of the base member 2, an electrode is formed. The piezoelectric layers constituting the base member 2 have the same thickness. In Figs. 5 and 6, white arrows indicate the directions of polarization in the piezoelectric layers. In the piezoelectric resonator 10 according to an embodiment of the present invention shown in Fig. 5, the piezoelectric layers constituting the second vibrating sections 24b are polarized in the same direction as the adjacent piezoelectric layer of the first vibrating section 24a with the electrode 14 placed therebetween. The first vibrating section 24a and the second vibrating sections 24b vibrate in opposite phases. On the other hand, in the piezoelectric resonator 1 shown in Fig. 6 for comparison, adjacent piezoelectric layers with an electrode 3 disposed therebetween are polarized in opposite directions in the longitudinal direction of the base member 2. The piezoelectric resonator 1 does not have a second vibrating section. To examine a difference in characteristics between these two piezoelectric resonators, the finite-element method is used to calculate the resonant frequencies Fr and the antiresonant frequencies Fa of the piezoelectric resonator 10 shown in Fig. 5 and the piezoelectric resonator 1 shown in Fig. 6, and their difference ΔF. Table 1 shows the results. Fr (kHz) Fa (kHz) ΔF (kHz) Piezoelectric resonator of this invention 470.3 503.7 33.4 piezoelectric resonator for comparison 470.3 531.2 60.9 As shown in Table 1, the piezoelectric resonator 10 shown in Fig. 5 has a smaller ΔF than the piezoelectric resonator 1 shown for comparison in Fig. 6. Figs. 7A and 7B illustrate a structure and vibration conditions of another piezoelectric resonator according to the present invention. Among three rows of arrows shown in the base member 12 of a piezoelectric resonator 10 in Figs. 7A and 7B, the upper row of arrows indicate the direction in which an electric field is applied, the middle row of white arrows indicate the direction of polarization, and the lower row of arrows indicate the direction in which each piezoelectric layer expands and contracts in the stiffened piezoelectric resonator. The piezoelectric resonator 10 shown in Figs. 7A and 7B differs from the piezoelectric resonator shown in Fig. 2 in direction of polarization in a piezoelectric layer of a second vibrating section 24b and in arrangement of insulating films 16 and 18. In the piezoelectric resonator 10 shown in Figs. 7A and 7B, a second vibrating section 24b is formed at the right-hand side of the base member 12. The second vibrating section 24b is made up of one piezoelectric layer sandwiched by an internal electrode 14 and a dummy electrode 14'. In the piezoelectric resonator 10, the piezoelectric layer constituting the second vibrating section 24b is polarized in the direction opposite that of the piezoelectric layer in a first vibrating section 24a disposed adjacent with the dummy electrode 14' placed therebetween. The dummy electrode 14' is insulated by the insulating films 16 and 18 at both side faces of the base member 12 and not connected to external electrodes 20 and 22. The internal electrode 14 disposed immediately left of the dummy electrode 14' in Figs. 7A and 7B is insulated by the insulating film 16, not connected to the external electrode 20, and is connected to the external electrode 22. The internal electrode 14 disposed immediately right of the dummy electrode 14' in Figs. 7A and 7B is insulated by the insulating film 18, not connected to the external electrode 22, and is connected to the external electrode 20. Therefore, as shown in Figs. 7A and 7B, an electric field is applied to the piezoelectric layers disposed at both sides of the dummy electrode 14' in the same direction in the longitudinal direction of the base member 12, that is, from one end to the other end, or vice versa. With this structure, when an electric field is applied to the piezoelectric layer of the first vibrating section 24a in the same direction as that of polarization, an electric field is applied to the piezoelectric layer of the second vibrating section 24b in the direction opposite that of polarization. On the other hand, when an electric field is applied to the piezoelectric layer of the first vibrating section 24a in the direction opposite that of polarization, an electric field is applied to the piezoelectric layer of the second vibrating section 24b in the same direction as that of polarization. Therefore as shown by the lower rows of arrows in Figs. 7A and 7B, the first vibrating section 24a and the second vibrating section 24b vibrate in opposite phases. Hence, the piezoelectric resonator 10 shown in Figs. 7A and 7B also has the same advantages as the piezoelectric resonator described by referring to Figs. 1 to 6. Figs. 8A and 8B illustrate a structure and vibration conditions of still another piezoelectric resonator according to the present invention. Fig. 9 is a circuit diagram of the piezoelectric resonator shown in Figs. 8A and 8B. The piezoelectric resonator shown in Figs. 8A and 8B has the same structure as the piezoelectric resonator described by referring to Figs. 1 to 6 except that a base member 12 is formed such that capacitor sections 26 are integrally formed at both sides of second vibrating sections 24b. The capacitor sections 26 are formed by piezoelectric layers not polarized such as PZT which are sandwiched by internal electrodes 14. One of the internal electrodes 14 sandwiching a capacitor section 26 is connected to an external electrode 20, and the other internal electrode 14 is connected to an external electrode 22. As shown in Fig. 9, the capacitor sections 26 are connected in parallel to the first vibrating section 24a and the second vibrating sections 24b. Therefore, ΔF in longitudinal basic vibration can be changed by adjusting the capacitor sections 26 in the piezoelectric resonator 10 shown in Figs. 8A and 8B. As the capacitance of the dielectric layers increases, for example, damping capacitance increases and ΔF decreases. In the piezoelectric resonator 10 shown in Figs. 8A and 8B, ΔF can be adjusted in a wide range and a high degree of freedom is provided in design. Therefore, the piezoelectric resonator 10 can have a small ΔF so as to be suited to a narrow-frequency-band filter and an oscillator. In the piezoelectric resonator 10 shown in Figs. 8A and 8B, by changing the ratio of the first vibrating section 24a and the second vibrating sections 24b to the capacitor sections 26, or by changing the positions of the capacitor sections 26 in relation to those of the first vibrating section 24a and the second vibrating sections 24b, ΔF can be selected from a wide range. In the piezoelectric resonator 10 shown in Figs. 8A and 8B, for example, the capacitor sections 26 are formed at both sides of the base member 12. The structure is not limited to that in this embodiment. The capacitor sections 26 may be disposed at the center of the base member 12. Then, ΔF becomes small. In the piezoelectric resonator 10 shown in Figs. 8A and 8B, the capacitance of the entire piezoelectric resonator 10 can be increased by adjusting the capacitance of the capacitor sections 26. The capacitance of the capacitor sections 26 is adjusted by changing the overlapping area of the opposing portions of internal electrodes 14 or the thickness of the dielectric layers. The capacitor sections 26 may be formed by laminating a plurality of dielectric layers with internal electrodes 14 disposed therebetween. Also in this case, the capacitor sections 26 are connected in parallel to the vibrating sections 24a and 24b. As the number of laminated layers increases, ΔF becomes smaller and the capacitance increases. Various materials having dielectric constants can be used as a material for the capacitor sections 26, in addition to PZT. A material having a larger dielectric constant than PZT, such as BaTO 3 , may be used. An electronic component such as an oscillator and a discriminator including a piezoelectric resonator having the above-described structure will be described below by referring to Figs. 10 to 12. The piezoelectric resonator 10 used in the electronic component may be identical to the piezoelectric resonator described by referring to Figs. 1 to 6, the piezoelectric resonator shown in Figs. 7A and 7B, or the piezoelectric resonator shown in Figs. 8A and 8B. Fig. 10 is a perspective view of the electronic component 60. The electronic component 60 includes an insulating substrate 62. At opposing end portions of the insulating substrate 62, two indentations 64 are formed, respectively. On one surface of the insulating substrate 62, two pattern electrodes 66 and 68 are formed as shown in Fig. 11. One pattern electrode 66 is formed between opposing indentations 64 and extends in an L-shaped manner from a point near one end toward the center of the insulating substrate 62. The other pattern electrode 68 is formed between the other opposing indentations 64 and extends straight from a point near the other end toward the center of the insulating substrate 62. The pattern electrodes 66 and 68 are formed such that they are routed in a roundabout fashion from the ends of the insulating substrate 62 to the opposite surface. At one end of the pattern electrode 66 disposed at the center of the insulating substrate 62, a mounting member 70 is formed with electrically conductive adhesive. As shown in Fig. 12, the above-described piezoelectric resonator 10 is mounted on the mounting member 70 such that the center of the base member 12 in the longitudinal direction is disposed on the mounting member 70. An external electrode 22 of the piezoelectric resonator 10 is, for example, united with the mounting member 70 to connect to the pattern electrode 66. The other external electrode 20 is connected to the pattern electrode 68 with electrically conductive wire 72. The electrically conductive wire 72 is connected to the center of the external electrode 20 of the piezoelectric resonator 10 in the longitudinal direction. A metal cap 74 is placed on the insulating substrate 62 to complete the electronic component 60. To prevent the metal cap 74 from being short-circuited to the pattern electrodes 66 and 68, insulating resin is applied to the insulating substrate 62 and the pattern electrodes 66 and 68 in advance. The electronic component 60 uses the pattern electrodes 66 and 68, which are formed such that they are routed to the rear surface from ends of the insulating substrate 62, as input and output terminals for connecting to external circuits. Since the center of the piezoelectric resonator 10 in the longitudinal direction is secured to the mounting member 70 in the electronic component 60, the ends of the piezoelectric resonator 10 are disposed separately from the insulating substrate 62 so vibration is not prevented. Excited longitudinal vibration is not weakened because the center of the piezoelectric resonator 10, which serves as a node, is secured to the mounting member 70 and is connected to the electrically conductive wire 72. The electronic component 60 is mounted on a circuit board together with IC chips and other components to form an oscillator or a discriminator. Since the electronic component 60 is sealed and protected by the metal cap 74, it can be used as a chip-type (surface mount) component which can be mounted by reflow soldering. When the electronic component 60 is used in an oscillator, spurious vibrations are suppressed to a low level and unusual vibration caused by the spurious vibrations are prevented due to the features of the piezoelectric resonator 10 used in the electronic component 60. It is also easy to achieve impedance matching with an external circuit since the capacitance of the piezoelectric resonator 10 can be set to any desired value. When the electronic component 60 is used for a discriminator, a narrow peak-separation range is provided due to a small Δf of the resonator. In addition, since the resonator provides a wide range in capacitance design, it is easy to achieve impedance matching with an external circuit. Fig. 13 is a perspective view of a further piezoelectric resonator according to the present invention. Fig. 14 is a view illustrating a structure of the piezoelectric resonator shown in Fig. 13. The piezoelectric resonator shown in Figs. 13 and 14 has the same structure as the piezoelectric resonator described with Figs. 1 to 6 except that two external electrodes 20 and 22 are formed on one side face of the base member 12. Two rows of insulating films 16 and 18 are formed on one side face of the base member 12 and two rows of connection sections are formed. The insulating film 16 is formed at one end in the width direction of the base member 12 and the insulating film 18 is formed at the other end in the width direction of the base member 12. These two rows of insulating films 16 and 18 are formed on respective alternate internal electrodes 14. Namely, the two rows of insulating films 16 and 18 are formed on different internal electrodes 14. On these two rows of insulating films 16 and 18, two rows of external electrodes 20 and 22 are formed, respectively. The piezoelectric resonators 10 also has the same advantages as the piezoelectric resonator described above. Since the two external electrodes 20 and 22 are formed on one side face of the base member 12 in the piezoelectric resonator 10, the piezoelectric resonator 10 can be face-bonded on a circuit board to form an electronic component such as a ladder filter, an oscillator, or a discriminator. In other words, since the piezoelectric resonator 10 having the structure shown in Fig. 13 and 14 can be secured to the insulating substrate by face bonding without use of wire, an electronic component is manufactured more easily. Fig. 15 is a plan of a main section of an electronic component using the piezoelectric resonator shown in Figs. 13 and 14. Fig. 16 is an exploded perspective view of the main section. In the electronic component 60 shown in Figs. 15 and 16, four piezoelectric resonators 10a, 10b, 10c, and 10d all of which have the structure shown in Figs. 13 and 14 are used. In the electronic component 60, four pattern electrodes 90, 92, 94, and 96 are formed on an insulating substrate 62 serving as a support member, as shown in Fig. 16. Five lands disposed in line at a certain interval are formed on the pattern electrodes 90, 92, 94, and 96. The first land R1, which is closest to an end of the insulating substrate 62, is formed on the pattern electrode 90, the second land R2 and the fifth land R5 are formed on the pattern electrode 92, the third land R3 is formed on the pattern electrode 94, and the fourth land R4 is formed on the pattern electrode 96. To connect the piezoelectric resonators 10a to 10d to the first land R1 to the fifth land R5, rectangular-block-shaped mounting members 98, 100, 102, 104, 106, 108, 110, and 112 in which at least their surfaces are made from an electrically conductive member are prepared. These mounting members are mounted to the electrodes 20 and 22 disposed at the node sections of the piezoelectric resonators 10a to 10d in advance with electrically conductive adhesive as shown in Fig. 13. The piezoelectric resonators 10a to 10d are turned upside down as shown in Fig. 16 and mounted with electrically conductive adhesive: one mounting member 98 on the first land R1; two mounting members 100 and 102 on the second land R2; two mounting members 104 and 106 on the third land R3; two mounting members 108 and 110 on the fourth land R4, and one mounting member 112 on the fifth land R5. In this case, the mounting members are disposed in line at a certain interval as shown in Fig. 15. As described above, the four piezoelectric resonator 10a to 10d are supported on the insulating substrate 62 by the mounting members 98, 100, 102, 104, 106, 108, 110, and 112, and the electrodes 20 and 22 of the piezoelectric resonators are connected to the pattern electrodes 90, 92, 94, and 96 on the insulating substrate 62. The pattern electrodes are formed such that the ladder-shaped circuit shown in Fig. 17 is obtained. A metal cap (not shown) is placed on the insulating substrate 62. The electronic component 60 is used as a ladder filter having the ladder-shaped circuit shown in Fig. 17. Two piezoelectric resonators 10a and 10c serve as series resonators and the other two piezoelectric resonator 10b and 10d serve as parallel resonators. In such a ladder filter, the parallel piezoelectric resonators 10b and 10d are designed to have substantially larger capacitances than the series piezoelectric resonators 10a and 10c. Attenuation in the ladder filter is determined by the capacitance ratio between the series resonators and the parallel resonators. In this electronic component 60, a ladder filter having a larger attenuation with fewer resonators is implemented by changing the capacitances of the piezoelectric resonators 10a to 10d. Since the piezoelectric resonators 10a to 10d have a smaller ΔF, a ladder filter having a narrow transmission frequency band is implemented. A ladder filter having a wide transmission band can be implemented by increasing differences in ΔF between those of the piezoelectric resonators 10a and 10c connected in series and those of the piezoelectric resonators 10b and 10d connected in parallel by reducing ΔF of each of the former resonators 10a and 10c and by increasing ΔF of each of the latter resonators 10b and 10d. In the electronic component shown in Figs. 15 and 16, since one electrode of each of adjacent piezoelectric resonators is mounted on the same land through a mounting member, the two electrodes of the adjacent piezoelectric resonators do not need to be insulated and thus the adjacent resonators can be disposed closely, enabling a compact component.

Claims: A piezoelectric resonator (10), comprising a base member (12) having a longitudinal direction, polarized piezoelectric member constituting at least a part of said base member (12), and a pair of external electrodes (20,22) provided with said base member, characterized in that a laminated member section constituting at least a part of said base member (12) is provided by alternately laminating a plurality of piezoelectric layers and a plurality of internal electrodes (14), said piezoelectric layers is made of said piezoelectric member and polarized in the longitudinal direction of said base member (12), said internal electrodes (14) are perpendicular to the longitudinal direction of said base member (12) and are connected to said pair of external electrodes (20,22) respectively, and said laminated member section includes a first vibrating section (24a) and a second vibrating section (24b) which respectively excite longitudinal basic vibrations in opposite phases each other. A piezoelectric resonator (10) according to claim 1, characterized in that when an electric field is applied to the piezoelectric layer of said first vibrating section (24a) in the same direction as the direction of polarization, an electric field is applied to the piezoelectric layer of said second vibrating section (24b) in the direction opposite the direction of polarization, and when an electric field is applied to the piezoelectric layer of said first vibrating section (24a) in the direction opposite the direction of polarization, an electric field is applied to the piezoelectric layer of said second vibrating section (24b) in the same direction as the direction of polarization. An electronic component (60) for use with the piezoelectric resonator (10) according to Claim 1 and 2, characterized in that said base member (12) is supported by a support member (62) via a mounting member (70), and said mounting member (70) is provided at a center section of said base member (12) in the longitudinal direction. An electronic component (60) according to Claim 3, characterized in that said support member (62) is an insulating substrate (62) on which a pattern electrode (66,68) is formed. An electronic component (60) according to Claim 4, characterized in that a plurality of said piezoelectric resonators (10a,10b,10c,10d) connected in a ladder shape in series and in parallel are mounted on said insulating substrate (62).

Inventors: UNAMI TOSHIHIKO, UNAMI, TOSHIHIKO, Unami, Toshihiko c/o Murata Mfg. Co. Ltd.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1997
Main classification: H03H9
IPC codes: H03H9, H01L41