Method of manufacturing piezoelectric resonator

Abstract: The invention provides a method of manufacturing a resonance element, comprising the steps of: preparing a multilayered body comprising a plurality of piezoelectric layers and a plurality of inner electrodes laminated to each other; forming an insulating film on one surface of said multilayered body at exposed portions of said inner electrodes, said insulating film having a plurality of openings constituting parallel rows which is parallel to the laminating direction of said multilayered body; forming an outer electrode on substantially the entire surface on which said insulating film is formed; forming a plurality of grooves on the surface on which said outer electrode was formed and cutting said multilayered body parallel to said grooves; wherein a group of said openings in one of said rows are disposed on every alternate exposed portion of said internal electrodes, and the other group of said openings in the other row adjacent to said one of said rows are disposed on every different alternate exposed portion of said internal electrodes; said one of said rows and the other row adjacent to said one of said rows are separated from each other with a predetermined distance; and said groove is formed between said one of said rows and the other row adjacent to said one of said rows.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a piezoelectric resonator. More particularly, the present invention relates to a method of manufacturing a piezoelectric resonator which is used for electronic parts, such as an oscillator, a discriminator, and a filter, and which uses mechanical resonance of a piezoelectric body. 2. Description of the Related Art Fig. 26 is a perspective view showing an example of a conventional piezoelectric resonator. A piezoelectric resonator 1 includes a piezoelectric substrate 2, for example, in the shape of a rectangular plate in plan view. The piezoelectric substrate 2 is polarized along the thickness direction. Electrodes 3 are formed on both surfaces of the piezoelectric substrate 2. As a result of inputting a signal between these electrodes 3, an electric field is applied along the thickness direction of the piezoelectric substrate 2, causing the piezoelectric substrate 2 to vibrate along the length direction. The piezoelectric resonator shown in Fig. 26 is of unstiffened type, in which the vibration direction is different from the electric-field direction and the polarization direction. An electro-mechanical coupling coefficient of a piezoelectric resonator of this unstiffened type is lower than that of a stiffened piezoelectric resonator, in which the electric-field direction, the polarization direction, and the vibration direction coincide with each other. Therefore, in the unstiffened type piezoelectric resonator, the difference ΔF between the resonance frequency and the anti-resonance frequency is relatively small. This fact leads to the drawback that when a piezoelectric resonator is used for a filter, the bandwidth is small. Therefore, the degree of characteristic design freedom is small in a piezoelectric resonator and electronic parts using it. Furthermore, in the piezoelectric resonator shown in Fig. 26, a primary resonance of a length mode is used, and from a structural point of view, an odd-number multiple high-order mode, such as a third order or a fifth order, and a large spurious emission of a width mode are generated. From US 4 564 782 A a piezoelectric resonator having a multilayered structure is known. Accordingly, in Japanese Patent Application No. 8-110475 submitted by the applicant of the present invention, a piezoelectric resonator of a multilayered structure has been proposed such that a base having a longitudinal direction is formed as a result of a plurality of piezoelectric layers and a plurality of electrodes being alternately multilayered, the plurality of piezoelectric layers are polarized along the length direction of the base, and a fundamental vibration of a longitudinal vibration is excited. The piezoelectric resonator of such a multilayered structure is of a stiffened type, in which the polarization direction, the electric-field direction, and the vibration direction coincide with each other, and there are the advantages that spurious emissions are smaller than that of a unstifffened type, and the difference ΔF between the resonance frequency and the anti-resonance frequency is large. Next, an example of a piezoelectric resonator having such a multilayered structure will be described in detail. Fig. 1 is a perspective view showing an example of a conventional piezoelectric resonator having a multilayered structure, against the background of which the present invention has been achieved. Fig. 2 is a schematic view of the piezoelectric resonator of Fig. 1. Fig. 3 is a plan view of the essential portion of the piezoelectric resonator. A piezoelectric resonator 10 of this multilayered structure includes a base 12, for example, in the shape of a rectangular-parallelepiped body. The base 12 includes a plurality of piezoelectric layers 12a, which are formed from, for example, a piezoelectric ceramic, and multilayered. In the plurality of piezoelectric layers 12a in the intermediate portion along the length direction of the base 12, a plurality of internal electrodes 14 are formed on each of both main surfaces intersecting at right angles to the length direction of the base 12. Therefore, a plurality of internal electrodes 14 are disposed with a spacing in a direction intersecting at right angles to the length direction of the base 12 and along the length direction of the base 12. Also, the plurality of piezoelectric layers 12a in the intermediate portion along the length direction of the base 12, as indicated by the arrows in Fig. 2, are polarized along the length direction of the base 12 so that they are opposite to each other on both sides of the respective internal electrodes 14. However, the piezoelectric layers 12a of both end portions along the length direction of the base 12 are not polarized. In this base 12, the internal electrodes 14 are exposed onto the four side surfaces parallel to the length direction of the base 12. A groove 15 which extends along the length direction of the base 12 is formed on one side surface of the base 12. The groove 15 is formed in the center in the width direction of the base 12, dividing one side surface of the base 12 into two portions. Furthermore, as shown in Fig. 2, a first insulation film 16 and a second insulation film 18 are formed on the side surfaces divided by the groove 15. On one side divided by the groove 15 on the side surface of the base 12, every alternate exposed portion of the internal electrodes 14 is covered by the first insulation film 16. Also, on the other side divided by the groove 15 on the side surface of the base 12, the exposed portions of the internal electrodes 14 that are not covered by the first insulation film 16 on one side of the groove 15 are covered by the second insulation film 18. Furthermore, at the portions where the first and second insulation films 16 and 18 of the base 12 are formed, that is, on both sides of the groove 15, two external electrodes 20 and 22 are formed. Therefore, the internal electrodes 14 that are not covered by the first insulation film 16 are connected to the external electrode 20, and the internal electrodes 14 that are not covered by the second insulation film 18 are connected to the external electrode 22. That is, adjacent internal electrodes 14 are connected to the external electrode 20 and the external electrode 22, respectively. In this piezoelectric resonator 10, the external electrodes 20 and 22 are used as input and output electrodes. At this time, in the intermediate portion along the length direction of the base 12, since the section between adjacent internal electrodes 14 is polarized and an electric field is applied between the adjacent internal electrodes 14, it becomes active from a piezoelectric point of view. In this case, since mutually opposite voltages are applied to the portions of the base 12 which are mutually oppositely polarized, the base 12 tries to expand or shrink in the same direction as a whole. Therefore, in the entire piezoelectric resonator 10, a fundamental vibration of a longitudinal vibration, in which the center portion along the length direction of the base 12 is a node, is excited. Both end portions along the length direction of the base 12, are not polarized, and an electric field is not applied thereto because no electrode is formed. Therefore, both end portions become piezoelectrically inactive. In this piezoelectric resonator 10, the polarization direction of the base 12, the electric-field direction by the input signal, and the vibration direction of the base 12 coincide with each other. That is, this piezoelectric resonator 10 is a piezoelectric resonator of a stiffened type. This piezoelectric resonator 10 has an electro-mechanical coupling coefficient greater than that of an unstiffened type, such that the polarization direction, the electric-field direction, and the vibration direction are different from each other. Therefore, in this piezoelectric resonator 10, it is possible to increase the selectable width of the difference ΔF between the resonance frequency and the anti-resonance frequency in comparison with a piezoelectric resonator of an unstiffened type. Therefore, in this piezoelectric resonator 10, it is possible to obtain a characteristic with a larger bandwidth than that of an unstiffened type. Furthermore, this piezoelectric resonator 10 has spurious emissions smaller than that of an unstiffened type. Furthermore, in this piezoelectric resonator 10, since the external electrodes 20 and 22 are formed on one side surface thereof, it can be surface-mounted onto, for example, an insulator substrate. A method of manufacturing this piezoelectric resonator 10 will be described below with reference to Figs. 4 to 13. In these figures, for convenience of description, the number of layers of green sheets which form the piezoelectric layers 12a does not coincide with the number of layers of the piezoelectric layers 12a which form the piezoelectric resonator 10 shown in Figs. 2 and 3. However, the following manufacturing process is the same regardless of the number of piezoelectric layers. When manufacturing this piezoelectric resonator 10, as shown in Fig. 4, a green sheet 30 is prepared first. Conductive paste containing, for example, silver, palladium, an organic binder, and the like, is coated onto one surface of the green sheet 30, forming a conductive paste layer 32. The conductive paste layer 32 is formed on the entire surface excluding one end side of the green sheet 30. A plurality of these green sheets 30 are multilayered. At this time, the green sheets 30 are multilayered so that alternate end portions which are not formed with the conductive paste layer 32 are disposed in mutually opposite directions. Furthermore, since a conductive paste is coated onto the opposing side surfaces of the multilayered body and then sintered, a multilayered base 34 such as that shown in Fig. 5 is formed. Inside the multilayered base 34, as a result of the conductive paste layer 32 being sintered, a plurality of internal electrodes 36 are formed. These internal electrodes 36 are alternately exposed to the opposing portions of the multilayered base 34. Then, in the opposing portions of the multilayered base 34, electrodes 38 and 40 for polarization are formed, to which each alternate internal electrode 36 is connected. By applying a direct-current voltage to these polarization electrodes 38 and 40, a polarization process is performed on the multilayered base 34. At this time, inside the multilayered base 34, a direct-current high electric-field is applied between adjacent internal electrodes 36, and the directions are opposite to each other. Therefore, the multilayered base 34 is polarized in mutually opposite directions on both sides of the internal electrodes 36, as indicated by the arrows in Fig. 5. Next, as indicated by the dotted line in Fig. 6, the multilayered base 34 is cut by a dicer or the like in such a manner as to intersect at right angles to the plurality of internal electrodes 36 and the polarization electrodes 38 and 40. As a result, a multilayered body 42 such as that shown in Fig. 7 is formed. Then, as shown in Fig. 8, an insulation film 44 is formed in such a manner as to form a checkered pattern on one main surface of the multilayered body 42. In this case, in one row in the vertical direction with respect to the internal electrodes 36 of a checkered pattern, the insulation film 44 is formed on alternate internal electrodes 36 in the vertical direction with respect to the internal electrodes 36 of the multilayered body 42. Also, in a row vertical with respect to the adjacent internal electrodes 36 of the multilayered body 42, the insulation film 44 is formed on the internal electrodes 36 which are not formed with the insulation film 44 in the adjacent row. Thereafter, in this multilayered body 42, on the entire surface where the insulation film 44 is formed, as shown in Fig. 9, an external electrode 48 is formed by sputtering or the like. Next, in the multilayered body 42, the groove 15 is formed in such a manner as to intersect at right angles to the surface of the internal electrodes 36 by a dicing machine in the portion indicated by the one-dot-chain line in Fig. 10, specifically, in the portion between the one-dot-chain lines of Fig. 11, that is, on the main surface of the multilayered body 42 in the boundary portion of adjacent rows of the insulation film 44 formed in a checkered pattern, and further, by cutting the multilayered body 42 as shown in Fig. 12, the piezoelectric resonator 10 shown in Figs. 1 and 2 is formed in the portion indicated by the dotted line in Fig. 10, specifically, in the portion between the one-dot-chain lines of Fig. 11, that is, in the intermediate portion of these grooves 15. However, in the above-described method, when the position at which the groove 15 is formed in the multilayered body 42 is deviated by 1/2 or more of the edge thickness (corresponding to the width of the groove 15) of a dicing machine, for example, as shown in Fig. 13, it is deviated from the boundary of the adjacent rows of the insulation film 44. In this case, in the piezoelectric resonator 10 to be formed, as shown in Fig. 14, the internal electrodes 36 (14) to be insulated are not insulated completely by the insulation film 44 (16), and the section between external electrodes 48 (20) and 48 (22) is short-circuited. In this manner, in the above-described method, the groove 15 must be formed in such a manner as to include the edge of the insulation film 44, and the position at which the groove 15 is formed requires high accuracy, making it difficult to manufacture the piezoelectric resonator 10 with a high yield. SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide a method of manufacturing a piezoelectric resonator, such that a surface-mountable piezoelectric resonator of a multilayered structure can easily be manufactured with a high yield. The present invention provides a method of manufacturing a plurality of resonance elements, comprising the steps of: preparing a multilayered body comprising a plurality of piezoelectric layers and a plurality of inner electrodes laminated to each other; forming an insulating film on one surface of said multilayered body at exposed portions of said inner electrodes, said insulating film having a plurality of openings constituting parallel rows extending in the laminating direction of said multilayered body; forming an outer electrode on substantially the entire surface of said multilayered body on which said insulating film is formed; forming a plurality of grooves on the surface on which said outer electrode was formed and cutting said multilayered body parallel to said grooves; wherein a group of said openings in one of said rows are disposed on every alternate exposed portion of said internal electrodes, and the other group of said openings in the other row adjacent to said one of said rows are disposed on every different alternate exposed portion of said internal electrodes; said one of said rows and the other row adjacent to said one of said rows are separated from each other with a predetermined distance; and said groove is formed between said one of said rows and the other row adjacent to said one of said rows. In the above described method, preferably 0<x<(W - a)/2 is satisfied where W is the width of said piezoelectric resonator, a is the width of said groove, and x is the dimension of said predetermined distance between said one of said rows and the other row adjacent to said one of said rows. According to the present invention, a surface-mountable piezoelectric resonator of a multilayered structure is manufactured. Also, in a method of manufacturing a piezoelectric resonator in accordance with the present invention, an insulation film is formed in such a way that one of said rows and the other row adjacent to said one of said rows are separated from each other with a predetermined distance. Therefore, even if the position at which a groove is formed in the multilayered body is slightly deviated from a predetermined position, no short-circuit occurs between electrodes, and it is easy to manufacture a piezoelectric resonator with a high yield. Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a perspective view showing an example of a piezoelectric resonator, as a background of the present invention. Fig. 2 is a schematic view of the piezoelectric resonator shown in Fig. 1. Fig. 3 is a plan view of the essential portion of the piezoelectric resonator shown in Fig. 1. Fig. 4 is a perspective view showing a state in which ceramic green sheets and the like are multilayered to manufacture a piezoelectric resonator. Fig. 5 is a schematic view showing a multilayered body base made from ceramic green sheets shown in Fig. 4. Fig. 6 is a schematic view showing a portion where the multilayered body base shown in Fig. 4 is cut. Fig. 7 is a schematic view showing a multilayered body such that the multilayered body base shown in Fig. 6 is cut. Fig. 8 is a schematic view showing a state in which an insulation film is formed in the multilayered body shown in Fig. 7. Fig. 9 is a schematic view showing a state in which an external electrode is formed in the multilayered body shown in Fig. 8. Fig. 10 is a schematic view showing a step for manufacturing a piezoelectric resonator by forming a groove in the multilayered body shown in Fig. 9 and cutting the multilayered body. Fig. 11 is a schematic view of the essential portion of the step shown in Fig. 10. Fig. 12 is a schematic view showing the piezoelectric resonator manufactured in the step shown in Fig. 11. Fig. 13 is a schematic view of the essential portion showing a step in a case in which the position at which a groove is formed in the multilayered body and the position at which the multilayered body is cut are deviated in the step shown in Fig. 11. Fig. 14 is a schematic view showing the piezoelectric resonator manufactured in the step shown in Fig. 13. Fig. 15 is a schematic view of the essential portion showing a step for manufacturing a piezoelectric resonator by forming a groove in the multilayered body and cutting the multilayered body in the method of manufacturing a piezoelectric resonator according to the present invention. Fig. 16 is a schematic view showing the piezoelectric resonator manufactured in the step shown in Fig. 15. Fig. 17 is a schematic view of the essential portion showing a step in a case in which the position of a groove and cutting position are deviated in the step shown in Fig. 15. Fig. 18 is a schematic view showing the piezoelectric resonator manufactured in the step shown in Fig. 17. Fig. 19 is a schematic view of the essential portion showing a step in a case in which the position of a groove and cutting position are deviated in the step shown in Fig. 15. Fig. 20 is a schematic view showing the piezoelectric resonator manufactured in the step shown in Fig. 19. Fig. 21 is an exploded perspective view showing an example of an electronic part using the piezoelectric resonator shown in Fig. 1. Fig. 22 is a side view showing the mounting construction of the piezoelectric resonator in the electronic part shown in Fig. 21. Fig. 23 is a plan view of the essential portion showing an example of a ladder filter using the piezoelectric resonator shown in Fig. 1. Fig. 24 is an exploded perspective view of the essential portion of the ladder filter shown in Fig. 23. Fig. 25 is a circuit diagram of the ladder filter shown in Fig. 23. Fig. 26 is a perspective view showing an example of a conventional piezoelectric resonator, as a background of the present invention. PREFERRED EMBODIMENT OF THE PRESENT INVENTON A preferred embodiment of a method of manufacturing a piezoelectric resonator similar to the piezoelectric resonator 10 shown in Figs. 1 and 12 will now be described. Initially, a multilayered body 42 shown in Fig. 7 is made by the same step as that of a method of manufacturing the piezoelectric resonator 10 shown in Figs. 1 and 12. Then, as shown in Fig. 15, an insulation film 44 is formed in one surface of this multilayered body 42 in such a way that overlapping portions 46 which are continuous in a vertical direction with respect to the internal electrodes 36 occur in comparison with the checkered pattern shown in Fig. 8, and the like. That is, one of the rows of openings 48 and the other row adjacent to said one of the rows of openings 48, each of which being parallel to the laminating direction of the multilayered body, are separated from each other with a predetermined distance. Thereafter, in this multilayered body 42, as shown in Fig. 15, external electrodes 48 are formed by sputtering and the like on the entire surface of the surface where the insulation film 44, including the overlapping portion 46, is formed. Next, in the multilayered body 42, a groove 15 is formed by a dicing machine in such a manner as to intersect at right angles to the surface of the internal electrodes 36 in the portion indicated by the one-dot-chain line in Fig. 15, that is, in a nearly central portion in a direction parallel to the internal electrodes 36 of the overlapping portions 46 of the insulation film 44, and in the portion between the dotted lines in Fig. 15, that is, in the intermediate portion of these grooves 15, by cutting the multilayered body 42, a piezoelectric resonator 10' shown in Fig. 16 is formed. In comparison with the piezoelectric resonator 10 shown in Fig. 1, in the piezoelectric resonator 10' shown in Fig. 16, the overlapping portions 46 of the insulation film 44 are left on both sides of the groove 15. However, since the internal electrodes 36 (14) are not completely insulated in the overlapping portion 46, the internal electrodes 36 (14) do not cause a connection failure. As a result, the piezoelectric resonator 10' becomes substantially the same as the piezoelectric resonator 10 shown in Fig. 1, and has similar functions. In the above-described method which is a preferred embodiment of the present invention, when the width of the piezoelectric resonator is denoted as W, the width of the groove is denoted as a, and the width of the overlapping portion 46 of the insulation film 44 is denoted as x, 0<x<(W - a)/2 is set. Therefore, even if the position at which the groove 15 is formed in the multilayered body 42 is deviated by 1/2 or more of the edge thickness of the dicing machine, it is not deviated completely from the overlapping portion 46 of the insulation film 44, as shown, for example, in Fig. 17. In this case, in a piezoelectric resonator 10" to be formed, as shown in Fig. 18, the overlapping portions 46 of the insulation film 44 are left on one side of the groove 15. However, the internal electrodes 36 (14) are not completely insulated in the overlapping portion 46, the internal electrodes 36 (14) are exposed on the other side of the base 12, and the internal electrodes 36 (14) do not cause a connection failure. As a result, the piezoelectric resonator 10" becomes substantially the same as the piezoelectric resonator 10 shown in Fig. 1, and has similar functions. Therefore, in the above-described method which is an embodiment of the present invention, even if the position at which the groove 15 is formed slightly deviated from a predetermined position (the central portion in a direction parallel to the internal electrodes of the overlapping portions of the insulation film), a short-circuit does not occur between the electrodes, and it is easy to manufacture a surface-mountable piezoelectric resonator of a multilayered structure with a high yield. When, as shown in Fig. 19, the groove 15 is formed alongside the overlapping portion 46 of the insulation film 44, if the dimension x of the overlapping portion 46 is (W - a)/2 or more, the internal electrodes 36 (14) are completely insulated in the overlapping portions 46, as shown in Fig. 20. Even in such a case, if the dimension x of the overlapping portion 46 of the insulation film 44 is set such that 0<x<(W - a)/2, the internal electrodes 36 (14) are not insulated completely. Also in the present invention, if the thickness a of the edge for forming the groove 15 is formed to be larger than the width x of the overlapping portion 46 of the insulation film 44, in the case where the groove 15 is formed at a predetermined position, it is possible to obtain a piezoelectric resonator 10 having no overlapping portion 46 of the insulation film 44. In such a case, even if the groove 15 is formed at a position deviated slightly from a predetermined position, it is possible to obtain a piezoelectric resonator 10 having no overlapping portion 46 of the insulation film 44. By using the above-described piezoelectric resonator 10, an electronic part, such as an oscillator and a discriminator, is manufactured. Fig. 21 is a perspective view showing an example of an electronic part 60. The electronic part 60 includes an insulator substrate 62. Two recesses 64 are formed in each of the opposing end portions of the insulator substrate 62. Two pattern electrodes 66 and 68 are formed on one main surface of the insulator substrate 62. One of the pattern electrodes 66 is formed between the opposing recesses 64 in such a way that it extends in the shape of a letter L from one end of the recess toward the central portion of the insulator substrate 62. Also, the other pattern electrode 68 is formed between the other opposing recesses 64 in such a way that it extends in the shape of a letter L from the other end of the recess toward the central portion of the insulator substrate 62. Then, near the central portion of the insulator substrate 62, the two pattern electrodes 66 and 68 are formed so as to oppose each other with a spacing. These pattern electrodes 66 and 68 are formed in such a manner as to extend around from the end portion of the insulator substrate 62 toward the other surface. As shown in Fig. 22, a support member 24 formed from a conductive material, formed in each of the central portion of the external electrodes 20 and 22 of the piezoelectric resonator 10, is connected by, for example, a conductive bonding agent to the end portion of the pattern electrode 66 and the pattern electrode 68 in the central portion of the insulator substrate 62. As a result, the external electrodes 20 and 22 of the piezoelectric resonator 10 are fixed onto the insulator substrate 62 and also electrically connected to the pattern electrodes 66 and 68. Furthermore, a metal cap 74 is put on the insulator substrate 62. At this time, an insulating resin is coated onto the insulator substrate 62 and the pattern electrodes 66 and 68 so that the metal cap 74 does not conduct with the pattern electrodes 66 and 68. Then, as a result of the metal cap 74 being put, the electronic part 60 is manufactured. In this electronic part 60, the pattern electrodes 66 and 68 formed in such a manner as to extend around from the end portion of the insulator substrate 62 toward the rear surface are used as input and output terminals for connection with an external circuit. In this electronic part 60, since the piezoelectric resonator 10 is supported by the support member 24 formed in the central portion along the length direction of the base 12, the end portion of the piezoelectric resonator 10 is positioned in a state apart from the insulator substrate 62, thereby allowing vibration. Also, the central portion, which is a node of the piezoelectric resonator 10, is fixed by the support member 24, and the external electrodes 20 and 22 and the pattern electrodes 66 and 68 are electrically connected to each other. At this time, since the support member 24 is formed in the piezoelectric resonator 10 in advance, accurate positioning at the node of the piezoelectric resonator 10 can be performed. Therefore, in comparison with a case in which a projection-shaped support member is formed on the pattern electrodes 66 and 68 side and the piezoelectric resonator is put thereon, it is possible to support the node with accuracy. Therefore, leakage of vibration of the piezoelectric resonator 10 can be prevented, and satisfactory characteristics can be obtained. Also, there is no need to use a lead wire for connecting the external electrodes 20 and 22 of the piezoelectric resonator 10 to the pattern electrodes 66 and 68, and the electronic part 60 can be manufactured at a low cost. Furthermore, this electronic part 60, together with ICs and the like, is mounted in a circuit substrate, and is used as an oscillator and a discriminator. Since the electronic part 60 of such a construction is hermetically sealed and protected by the metal cap 74, this can be used as a chip part which can be mounted by reflow soldering or the like. In the case where this electronic part 60 is used as an oscillator, since the above-described piezoelectric resonator 10 is used, spurious emission can be minimized, and abnormal vibration due to spurious emission can be prevented. Also, since the capacitance value of the piezoelectric resonator 10 can be set freely, it is easy to obtain impedance matching with an external circuit. In particular, when it is used as an oscillation element for a voltage-controlled oscillator, since ΔF of the resonator is large, it is possible to obtain a wider variable frequency range than was previously possible. When this electronic part 60 is used as a discriminator, the feature that ΔF of the resonator is large leads to the feature that peak separation is wide. Furthermore, since the capacitance design range of the resonator is wide, it is easy to obtain impedance matching with an external circuit. Furthermore, use of a plurality of piezoelectric resonators 10 makes it possible to manufacture a ladder filter. Fig. 23 is a plan view of the essential portion showing an example of an electronic part used as a ladder filter having a ladder-type circuit. Fig. 24 is an exploded perspective view of the essential portion thereof. In the electronic part 60 shown in Figs. 23 and 24, four pattern electrodes 90, 92, 94, and 96 are formed on the insulator substrate 62. Five lands disposed in one row with a spacing are formed on these pattern electrodes 90 to 96. In this case, a first land from one end of the insulator substrate 62 is formed in the pattern electrode 90, a second land and a fifth land are formed in the pattern electrode 92, a third land is formed in the pattern electrode 94, and a fourth is formed in the pattern electrode 96. The support member 24 formed in the external electrodes 20 and 22 of the respective piezoelectric resonators 10a, 10b, 10c, and 10d is mounted to these lands. In this case, in order that the ladder-type circuit shown in Fig. 25 is obtained, the piezoelectric resonators 10a to 10d are mounted. Then, a metal cap (not shown) is put onto the insulator substrate 62. This electronic part 60 is used as a ladder filter having a ladder-type circuit, such as that shown in Fig. 25. At this time, for example, two piezoelectric resonators 10a and 10d are used as series resonators, and the other two piezoelectric resonators 10b and 10c are used as parallel resonators. Such a ladder filter is designed so that the capacitance of the parallel resonators 10b and 10c exceeds the capacitance of the series resonators 10a and 10d. The attenuation of the ladder filter depends upon the capacitance ratio of the series resonator to the parallel resonator. In this electronic part 60, by varying the number of multilayers of the piezoelectric resonators 10a to 10d, the capacitance can be adjusted. Therefore, by adjusting the capacitance of the piezoelectric resonators 10a to 10d, it is possible to realize a ladder filter having a larger attenuation with a smaller number of resonators than in a case in which a conventional piezoelectric resonator utilizing a transverse piezoelectric effect is used. Also, since ΔF of the piezoelectric resonators 10a to 10d is larger than that of the conventional piezoelectric resonator, it is possible to realize a ladder filter having a wider passing bandwidth than that using a conventional piezoelectric resonator. While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled man in the art that the forgoing and other changes in form and details may be made therein without departing from the scope of the invention, which is defined in the claims.

Claims: A method of manufacturing a plurality of resonance elements (10"), comprising the steps of: 1) preparing a multilayered body comprising a plurality of piezoelectric layers (12a) and a plurality of inner electrodes (36) laminated to each other; 2) forming an insulating film (44) on one surface of said multilayered body at exposed portions of said inner electrodes, said insulating film having a plurality of openings (48) constituting parallel rows extending in the laminating direction of said multilayered body; 3) forming an outer electrode (48, 20, 22) on substantially the entire surface of said multilayered body on which said insulating film (44) is formed; 4) forming a plurality of grooves (15) on the surface on which said outer electrode was formed and cutting said multilayered body parallel to said grooves; wherein a group of said openings (48) in one of said rows are disposed on every alternate exposed portion of said internal electrodes (36), and the other group of said openings (48) in the other row adjacent to said one of said rows are disposed on every different alternate exposed portion of said internal electrodes (36), said one of said rows and the other row adjacent to said one of said rows are separated from each other with a predetermined distance (46), and said groove (15) is formed between said one of said rows and the other row adjacent to said one of said rows. The method according to claim 1, wherein 0<x<(W - a)/2 is satisfied where W is the width of said resonance element (10"), a is the width of said groove (15), and x is the dimension of said predetermined distance (46) between said one of said rows and the other row adjacent to said one of said rows.

Inventors: KAWAI YUTAKA, KUSABIRAKI SHIGEMASA, TAKESHIMA TETSUO, YAMAZAKI TAKESHI, KAWAI, YUTAKA, KUSABIRAKI, SHIGEMASA, TAKESHIMA, TETSUO, YAMAZAKI, TAKESHI
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1998
Main classification: H03H3
IPC codes: H03H9, H03H3, H01L41