JP5949445B2 - Piezoelectric filter - Google Patents

Description

  The present invention relates to a piezoelectric filter using a thickness shear vibration of a piezoelectric plate.

  Piezoelectric filters are filters that are widely used in the field of communication equipment and the like. The piezoelectric filter has two divided electrodes opposed to each other at a predetermined interval on one surface of a piezoelectric plate made of a quartz plate or the like for input / output, and the pair of divided electrodes on the other surface. There is one in which one common electrode facing the electrode in common with the piezoelectric plate in between is formed.

  In such a piezoelectric filter, the resonance frequency fs of the symmetric mode generated in the piezoelectric plate and the resonance frequency fa of the asymmetric mode are superimposed on each other by utilizing the acoustic coupling between the vibrations by both divided electrodes, and the center frequency is approximately fa. A so-called multimode filter having a pass bandwidth of approximately 2 × (fa−fs) is realized (see, for example, Patent Document 1).

  Such a piezoelectric filter is mounted on an adhesive pad in a package, and a vibrating electrode such as a divided electrode or a common electrode is pulled out to the corner of the piezoelectric plate by an extraction electrode, and then bonded to the adhesive pad with a conductive adhesive. ing.

Japanese Patent No. 3507206

  In such a piezoelectric filter, when used for a low frequency band, the area of the vibrating electrode is enlarged. However, when the electrode area is enlarged, the conductive adhesive applied to the extraction electrode and the vibrating electrode are reduced. Get closer in distance.

  However, when the distance between the conductive adhesive and the vibrating electrode approaches in this way, even if the position and state of application of the conductive adhesive slightly change, the insertion loss is adversely affected. Therefore, when the area of the vibrating electrode is enlarged and the conductive adhesive and the vibrating electrode are close in distance, it is necessary to apply the conductive adhesive with high precision and accurately apply the conductive adhesive. Become.

  In addition, since the number of extraction electrodes in the piezoelectric plate is three for the two divided electrodes and one common electrode, there are three places where the conductive adhesive is applied with high precision. It was difficult to apply the conductive adhesive to all three corners of the plate with a dispenser, which is an automatic application machine, with high accuracy, and the defective rate of the piezoelectric filter after application was high and the yield was low.

  The present invention has been made in view of the above, and in the case of expanding the area of the vibrating electrode for a low frequency band, the yield rate when a conductive adhesive is applied to three corners of the piezoelectric plate It is an object to provide a piezoelectric filter with improved yield and high yield.

  In order to achieve the above-mentioned object, the present inventor has conducted extensive research, and among the three corners of the piezoelectric plate to be coated with the conductive adhesive, the portion where the conductive adhesive is required to be applied with high accuracy. As a structure that can be reduced to at most one place, a piezoelectric filter that can be manufactured at a high yield is completed.

That is, the piezoelectric filter according to the first aspect of the present invention includes a plurality of divided electrodes on one surface of a rectangular piezoelectric plate, and a common electrode opposed to the plurality of divided electrodes in common on the other surface, Lead electrodes are formed at three corners of the four corners on the outer peripheral edge of the piezoelectric plate, and conductive adhesive is applied to the three corners from which the lead electrodes are drawn. A piezoelectric filter that is applied, wherein a location where a center line that passes through the center of one side of the piezoelectric plate intersects with a center line that passes through the center of the other side is the center of the piezoelectric plate, and the piezoelectric plate The central portion of the common electrode is displaced along the one side direction and is displaced along the other side direction, whereby the conductive adhesive of the piezoelectric plate is applied. Not eccentric in the direction of the remaining one corner That, characterized in that.

  Here, the central part of the common electrode is an electrode having a rectangular shape in plan view or an “H” shape in plan view and having a symmetrical shape in the vertical and horizontal directions. The symmetric axis of the direction and the symmetric axis of the left and right direction intersect with each other, and this is the geometric center of gravity.

  The geometric centroid is the centroid in the planar shape of the common electrode.

  The number of piezoelectric plates accommodated in the package may be one or two or more.

  The number of the divided electrodes is not particularly limited as long as it is two or more.

  When the number of piezoelectric plates is one and the number of divided electrodes formed on the piezoelectric plate is two, the piezoelectric filter is a two-pole type, and when the number of divided electrodes is three, the piezoelectric filter Becomes a 3-pole type. Further, when the number of piezoelectric plates is two, two divided electrodes are formed on each piezoelectric plate, and the piezoelectric plates are connected in cascade, the four-pole type is used. The present invention includes any of these types.

  The shape of the common electrode is not particularly limited, but is preferably a rectangular shape in plan view. The shape of the common electrode may be an “H” shape in plan view that matches the shape of the divided electrodes. In addition, an electrode shape in which an electrode is added to the “H” shape by partial adjustment to form a rectangular shape in plan view, or a partial adjustment electrode is not included, and a rectangular shape in plan view is included from the beginning.

  The conductive adhesive is not particularly limited as long as it is a conductive adhesive. The conductive adhesive is applied by an application machine such as a dispenser or the like. The conductive adhesive is preferably one that can be thermally cured when heated to a predetermined temperature or higher, and that can join the extraction electrode to the adhesive pad by this thermal curing.

  According to the first aspect of the present invention, the central portion of the common electrode is eccentric with respect to the central portion of the piezoelectric plate in the direction of the remaining corner portion where the conductive adhesive is not applied. In the two application locations located in the direction opposite to the eccentric direction as seen from the remaining corner, the distance from the divided electrode and the common electrode is increased, and as a result, the conductive adhesive is removed from the two application locations. The influence of vibration can be reduced even when the coating accuracy is low.

  As a result, unlike the conventional piezoelectric filter in which the conductive adhesive needs to be applied with high precision in all three places where the conductive adhesive is applied, in the present invention, at most one place. Therefore, a piezoelectric filter that can be manufactured with a high yield for low frequency can be provided.

  The piezoelectric filter according to the second aspect of the present invention has a rectangular common electrode opposed to a plurality of rectangular divided electrodes on one surface of a rectangular piezoelectric plate and the plurality of divided electrodes on the other surface. Electrode is provided, and lead electrodes are formed at three corners out of four corners on the outer periphery of the piezoelectric plate, and the three corners from which the lead electrodes are led out are electrically conductive. A piezoelectric filter coated with a conductive adhesive, wherein at least the corners on the outer peripheral edge of the divided electrode and the common electrode facing the three corners are chamfered or notched, and the electrodes are formed by the chamfering or notch. The divided electrode or the common electrode having a reduced area is elongated in one side direction or the other side direction of the piezoelectric plate in accordance with the reduced electrode area, so that it is horizontally longer than before the chamfering or notching or Portrait Characterized in that it is an electrode.

  According to the second aspect of the present invention, when the lead-out electrode led out to each of the three corners of the four corners of the piezoelectric plate is joined to the three corners by a conductive adhesive on an adhesive pad. Since the corners of the divided electrode and the extraction electrode facing each other are chamfered or cut away, the distance from the application location at the three corners of the piezoelectric plate to the divided electrode and the common electrode is increased. As a result, the accuracy of applying the conductive adhesive to the extraction electrodes at the three corners can be lower than before, so that a piezoelectric filter with a high yield can be provided by increasing the electrode area for the low frequency band.

  Further, in the divided electrode or common electrode in which the electrode area is reduced due to the chamfering or notch, the reduced electrode area is extended in one side direction or the other side direction of the piezoelectric plate to be more horizontally long. Alternatively, since the electrode is longer, the piezoelectric filter suitable for the low frequency band can be provided because the electrode area does not decrease.

The third piezoelectric filter of the present invention includes a plurality of rectangular divided electrodes on one surface of a rectangular piezoelectric plate, and a rectangular common electrode facing the other surface in common with the plurality of divided electrodes. And lead electrodes are formed at three corners of the four corners on the outer peripheral edge of the piezoelectric plate, and the three corners from which the lead electrodes are drawn are electrically conductive. A piezoelectric filter to which an adhesive is applied, wherein a center line passing through the center of one side of the piezoelectric plate intersects with a center line passing through the center of the other side is the center of the piezoelectric plate, When the central portion of the common electrode is displaced along the one side direction with respect to the central portion of the piezoelectric plate, and is displaced along the other side direction, the conductive adhesive of the piezoelectric plate becomes Eccentric in the direction of the remaining corner that has not been applied In addition, at least the corners on the outer peripheral edges of the divided electrode and the common electrode facing the three corners are chamfered or notched, and the divided electrode or the common electrode having a reduced electrode area due to the chamfering or notch, In accordance with the reduced electrode area, the piezoelectric plate is elongated in one side direction or the other side direction to form a horizontally or vertically longer electrode than before chamfering or notching. To do.

  The third aspect of the present invention has both the first and second effects of the present invention.

  In the first to third aspects of the present invention, a preferred embodiment is a 4-pole type in which two piezoelectric plates used in the piezoelectric filter described above are connected in cascade.

  In this embodiment, the two divided electrodes facing each other on one of the piezoelectric plates are both horizontally elongated in the facing direction, and the two facing divided electrodes on the other piezoelectric plate are both A vertically long shape with respect to the facing direction.

  In the first aspect of the present invention, in a preferred embodiment, two piezoelectric filter forming regions are formed on the piezoelectric plate, and each piezoelectric filter forming region has a two-pole type piezoelectric filter including two divided electrodes and a common electrode. The four piezoelectric filter forming regions as a whole are of a four-pole type, and among the four corners of each piezoelectric filter forming region, the three corners to which the conductive adhesive is applied are A lead electrode is formed from each electrode, and the central portion of the common electrode in each piezoelectric filter forming region is one corner portion where the conductive adhesive is not applied to the central portion of each piezoelectric filter forming region. The position is eccentric in the direction of.

  In this embodiment, more preferably, in each of the piezoelectric filter forming regions, at least the corners of the divided electrode and the extraction electrode facing the three corners are chamfered or notched.

  In the first to third aspects of the present invention, in a preferred embodiment, the piezoelectric plate is a flat plate, a reverse mesa type, or a mesa type AT-cut quartz plate.

  In the present invention, when the area of the electrode formed on the piezoelectric plate is increased and used for low frequency, among the four corners of the piezoelectric plate, the three corners to which the conductive adhesive is applied are applied from each electrode. The lead electrode is formed, and the central portion which is the geometric center of gravity of the common electrode with respect to the central portion of the piezoelectric plate is decentered in the direction of the remaining corner portion where the conductive adhesive of the piezoelectric plate is not applied, The number of places where it is necessary to apply the conductive adhesive with high accuracy can be reduced from the conventional three to one, and the insertion loss is above the standard level compared to the piezoelectric filter that is not eccentric. As a result, it is possible to provide a piezoelectric filter for a low frequency band that is easy to design for a low frequency band and has a high yield.

1 is a schematic plan view of a piezoelectric filter according to an embodiment of the present invention. It is an enlarged plan view of two piezoelectric plates of the piezoelectric filter of FIG. It is a schematic plan view of the piezoelectric filter which concerns on other embodiment of this invention. It is a schematic plan view of the piezoelectric filter which concerns on further another embodiment of this invention. It is a schematic plan view of the piezoelectric filter which concerns on further another embodiment of this invention. It is a schematic plan view of the piezoelectric filter which concerns on further another embodiment of this invention. It is a schematic plan view of the piezoelectric filter which concerns on further another embodiment of this invention. It is a figure which shows the size of the common electrode of the piezoelectric filter used for a characteristic test. It is a figure which compares the yield of the conventional and the piezoelectric filter of this invention.

  Hereinafter, a piezoelectric filter according to an embodiment of the present invention will be described with reference to the accompanying drawings. The piezoelectric material of this piezoelectric filter is AT-cut quartz, but is not limited to this, and can be applied to other piezoelectric materials such as lithium tantalate and lithium niobate.

  With reference to FIG. 1, the piezoelectric filter of embodiment is demonstrated. 1A is a schematic plan view of the piezoelectric filter, and FIG. 1B is a cross-sectional view taken along line AA of FIG.

  The piezoelectric filter 1 is formed by cascading two-pole type piezoelectric plates 2 and 3, and the piezoelectric plates 2 and 3 are housed in a package 4. The opening of the package 4 is hermetically sealed by a lid (not shown).

  The piezoelectric plates 2 and 3 have, for example, a new Y′-axis that is 35.15 ° away from the Y-axis that is the mechanical axis and an X-axis as the electrical axis, and 35.15 from the Z′-axis that is the optical axis. It forms a rectangular parallelepiped shape formed along each crystal axis as a new Z ′ axis that is deviated by, for example, an AT-cut quartz plate having a substantially rectangular shape in plan view.

  The package 4 includes a recess 4c having a bottom portion 4a and a peripheral portion 4b erected around the bottom portion 4a. A plurality of adhesive pads 5 are formed at appropriate locations on the inner bottom surface of the bottom portion 4a. Each of the two piezoelectric plates 2 and 3 constituting the piezoelectric filter 1 is mounted with the conductive adhesive 6 being undercoated.

  By this undercoating, the divided electrodes 7a, 7b; 8a, 8b on the back side of the piezoelectric plates 2, 3 are joined to the bonding pads 5 respectively. The lead electrodes 9 c and 9 d of the common electrodes 9 a and 9 b on the surface side of the piezoelectric plates 2 and 3 are overcoated with the conductive adhesive 10 and bonded to the adhesive pad 5. The reason why the common electrodes 9a and 9b have the “H” shape in plan view corresponding to the shapes of the divided electrodes 7a and 7b; 8a and 8b is to satisfy the spurious standard.

  In the 4-pole type, the divided electrode 7a of the piezoelectric plate 2 is an input side divided electrode, and the divided electrode 7b is an output side divided electrode. Further, the output side divided electrode 7b of the piezoelectric plate 2 is connected to the input side divided electrode 8c of the piezoelectric plate 3 via wiring passing through the inside of the package 4. The divided electrode 8c of the piezoelectric plate 3 becomes an input side divided electrode, and the divided electrode 8d becomes an output side divided electrode.

  As a result, the piezoelectric filter 1 uses two sets of two-pole type piezoelectric plates 2 and 3 connected in cascade, and utilizes the mutual acoustic coupling of vibrations by the divided electrodes 7a and 7b; 8a and 8b of the piezoelectric plates 2 and 3, A four-pole type in which the resonance frequency fs of the symmetric mode generated in the piezoelectric plates 2 and 3 and the resonance frequency fa of the asymmetric mode are superposed so that the center frequency is about fa and the pass bandwidth is about 2 × (fa−fs). The piezoelectric filter is realized.

  The arrangement of the electrodes on the piezoelectric plates 2 and 3 will be described with reference to FIG. FIG. 2 omits the illustration of the package. The piezoelectric plates 2 and 3 shown in FIG. 2 have the same relationship as that of FIG.

  Since the piezoelectric plates 2 and 3 have a rectangular shape in plan view, a center line L1 passing through the center of the side (long side) in the X-axis direction and a center line L2 passing through the center of the side (short side) in the Z′-axis direction. Are the central portions O1 and O2 of the piezoelectric plates 2 and 3, respectively.

  The piezoelectric plate 2 having a rectangular shape in plan view has four corners A1 to D1 that are substantially perpendicular to the outer peripheral edge, and of these, the lead electrodes 7c, 7d; 9c are drawn and the conductive adhesives 6, 10 are formed. The corners to be applied are A1, B1, and C1, and the corners to which the conductive adhesives 6 and 10 are not applied are D1.

  Similarly, the piezoelectric plate 3 having a rectangular shape in plan view has four corners A2 to D2, and among them, the corners to which the lead electrodes 8c, 8d; 9d are drawn and the conductive adhesives 6, 10 are applied. Are A2, B2, and C2, and the corners where the conductive adhesives 6 and 10 are not applied are D2.

  In each of the piezoelectric plates 2 and 3, the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b are X1 and Z′-axis directions in the X-axis direction with respect to the central portions O1 and O2 of the piezoelectric plates 2 and 3, respectively. In addition, only Z′1 is eccentric in the direction of the corners D1 and D2 where the conductive adhesive is not applied. In this case, the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b are geometric centroids.

  Further, the distances of eccentricity in the X-axis direction and the Z′-axis direction can be variously set by experiments. The setting of the eccentric distance in the present invention and the demonstration of the yield based on this will be described later. The divided electrodes 7a and 7b; 8a and 8b are formed corresponding to the common electrodes 9a and 9b.

  Due to the eccentricity of the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b, the two application positions of the conductive adhesives 10 and 6 on the corner portions B1 and C1; B2 and C2 of the piezoelectric plates 2 and 3 are divided electrodes. 7b, 8b and the common electrodes 9a, 9b are separated from each other by distance, so that the conductive portions in the corner portions B1, C1; B2, C2 of the piezoelectric plates 2, 3 with respect to the divided electrodes 7b, 8b and the common electrodes 9a, 9b are separated. Of the adhesive adhesives 10 and 6 is reduced.

  On the other hand, the application positions of the conductive adhesive 6 at the corners A1 and A2 of the piezoelectric plates 2 and 3 are divided by the eccentricity of the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b. , 9b is not necessarily spaced apart from the distance, it is necessary to pay attention to the application of the conductive adhesive 6 at the corners A1, A2 of the piezoelectric plates 2, 3.

  Therefore, conventionally, the common electrodes 9a and 9b are piezoelectrically formed by vapor deposition or the like so that the central portions O1 and O2 of the piezoelectric plates 2 and 3 coincide with the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b. Since it was formed on the plates 2 and 3, it is necessary to apply the conductive adhesive with high precision in all three portions of the corner portions A1 to C1 and A2 to C2 of the piezoelectric plates 2 and 3. The filter yield was very low.

  On the other hand, in this embodiment, among the three portions of the corner portions A1 to C1; A2 to C2 of the piezoelectric plates 2 and 3, conductive bonding is performed at the two portions of the corner portions B1 and C1; B2 and C2. As a result, the influence of the application on the filter characteristics is reduced as a result of the increase in the distance from the application position of the agents 10 and 6 to the electrodes, and the number of defective piezoelectric filters is greatly reduced compared to the conventional case, and the yield of piezoelectric filters is increased Greatly improved.

  The degree of eccentricity of the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b with respect to the central portions O1 and O2 of the piezoelectric plates 2 and 3 can be appropriately set by experiment.

  The common electrodes 9a and 9b have a “H” shape in plan view in order to satisfy the spurious standard, but the shape in plan view of the common electrodes 9a and 9b is not particularly limited. In addition, the common electrodes 9a and 9b in FIG. 2 are not subjected to partial adjustment, and therefore, an electrode whose frequency is adjusted by depositing a thin film of the same material as the common electrodes 9a and 9b is not shown. However, the common electrodes 9a and 9b may include the central portions O1 ′ and O2 ′ including the electrodes for partial adjustment.

  A piezoelectric filter according to another embodiment of the present invention will be described with reference to FIG. 3, parts corresponding to those in FIG. 1 are denoted by the same reference numerals.

  The piezoelectric filter 11 includes piezoelectric plates 2 and 3. These piezoelectric plates 2 and 3 are housed in a package 4 and mounted on an adhesive pad 5 as in FIG.

  In this embodiment, the corners of the divided electrodes 7a and 7b; 8a and 8b and the common electrodes 9a and 9b facing the corners A1 to D1; A2 to D2 of the piezoelectric plates 2 and 3 are chamfered. It is characterized by that.

  The chamfered portions of the common electrodes 9a and 9b of these piezoelectric plates 2 and 3 are M1 to M4, and the chamfered portions of the divided electrodes 7a and 7b; 8a and 8b are N1 to N4.

  When the corners of the divided electrodes 7a and 7b; 8a and 8b and the common electrodes 9a and 9b are chamfered, the divided electrodes 7a and 7b; 8a and 8b and the common electrodes 9a and 9b are formed at the corners A1 and A1 of the piezoelectric plates 2 and 3, respectively. B1, C1; away from the application position of the conductive adhesives 6, 10 applied to A2, B2, C2. This greatly reduces the influence of the application of the conductive adhesives 6 and 10 on the filter characteristics of the piezoelectric filter 11 by chamfering the corners of the common electrodes 9a and 9b and the divided electrodes 7a and 7b; 8a and 8b. can do.

  Therefore, in the piezoelectric filter 11 of FIG. 3, the central part of the common electrodes 9 a and 9 b of the piezoelectric plates 2 and 3 has a corner D <b> 1 of the piezoelectric plates 2 and 3 with respect to the central part of the piezoelectric plates 2 and 3. , D2 and the common electrodes 9a, 9b and the divided electrodes 7a, 7b; 8a, 8b by chamfering, the corners A1, B1, C1; A2, B2, C2 of the electric plates 2, 3 In all three locations, the effect of coating on the filter characteristics due to the application of the conductive adhesives 10 and 6 is reduced, and the number of defective piezoelectric filters is greatly reduced as compared with the conventional one, and the yield of the piezoelectric filters is remarkably increased. To improve.

  A piezoelectric filter 12 according to still another embodiment of the present invention will be described with reference to FIG. Since the piezoelectric filter 11 of FIG. 3 has chamfered corners of the divided electrodes 7a and 7b; 8a and 8b and the common electrodes 9a and 9b, the electrode area is reduced. In the piezoelectric filter 12 of FIG. 4, the electrode is extended in the X-axis direction (vertical direction in the figure) in one piezoelectric plate 2 and the electrode in the other piezoelectric plate 3 so that the electrode area is not reduced by the chamfering. Is stretched in the Z′-axis direction (lateral direction in the figure). The electrode area before chamfering is the same as the electrode area after chamfering.

  In the piezoelectric filter 12 of FIG. 4 as well, the central portions of the common electrodes 9a and 9b of the piezoelectric plates 2 and 3 are at the corners D1 of the piezoelectric plates 2 and 3 with respect to the central portions of the piezoelectric plates 2 and 3, respectively. , Eccentric in the direction D2. Furthermore, in the piezoelectric filter 12 of FIG. 4, the divided electrodes 7a and 7b; 8a and 8b and the common electrodes 9a and 9b are all chamfered, and the electrode area before chamfering and after chamfering are obtained. In order to make the electrode area the same, the piezoelectric plate 2 is a combination in which the electrode shape is vertically long in the X-axis direction, and the piezoelectric plate 3 is a combination in which the electrode shape is horizontally long in the Z′-axis direction.

  A piezoelectric filter according to still another embodiment of the present invention will be described with reference to FIG. The piezoelectric filter 13 shown in FIG. 5 includes a single rectangular piezoelectric plate (piezoelectric wafer) 14, and the piezoelectric plate 14 has two piezoelectric filter forming regions R 1 and R 2 having an equal area. In the formation region R1, a two-pole type piezoelectric filter 13a including divided electrodes 7a and 7b and a common electrode 9a is formed, and in the other piezoelectric filter formation region R2, the divided electrodes 7c and 7d and the common electrode 9b are formed. The two-pole type piezoelectric filter 13b is formed, and the piezoelectric filter 13a and 13b in each of the piezoelectric filter forming regions R1 and R2 form a four-pole type piezoelectric filter 13 as a whole.

  Also in this piezoelectric filter 13, the piezoelectric filters 13a and 13b are in the respective piezoelectric filter forming regions R1 and R2, and the central portions O1 'and O2' of the common electrodes 9a and 9b are respectively in the piezoelectric filter forming regions R1 and R2. Center O1. The piezoelectric filter forming regions R1 and R2 are eccentric with respect to O2 in the corner direction where the conductive adhesive is not applied.

  A piezoelectric filter according to still another embodiment of the present invention will be described with reference to FIG. In FIG. 1, the piezoelectric filter 15 corresponds to the piezoelectric filter 1 composed of the piezoelectric plates 2 and 3 each having the common electrodes 9a and 9b having an "H" shape in plan view corresponding to the divided electrodes 7a and 7b; 8a and 8b. Thus, electrodes 15a and 15b for partial adjustment are formed. The electrodes 15a and 15b are hatched for convenience of illustration.

  Unlike the common electrodes 9a and 9b of the piezoelectric filter 1 shown in FIG. 1, the piezoelectric filter 15 has partial adjustment electrodes 15a and 15b. However, with respect to the central portions O1 and O2 of the piezoelectric plates 2 and 3, respectively. The eccentricity of the central portions O1 ′ and O2 ′ of the common electrodes 9a and 9b is the same as in the case of FIG.

  In the embodiment, the piezoelectric plates 2 and 3 are flat plates. However, as shown in the piezoelectric plate 16 in FIGS. 7A and 7B, the central portion is a thin portion (vibration region) 16a. It may be an inverted mesa type piezoelectric plate in which a thick part 16b that reinforces the vibration region is formed around the part 16a. In FIG. 7, parts corresponding to those in FIGS. 1 to 6 are denoted by the same reference numerals. In the piezoelectric plate 16 shown in FIG. 7, the divided electrodes 7 a and 7 b and the common electrode 9 a are chamfered at the corners facing the corners of the piezoelectric plate 16. The piezoelectric plates 2 and 3 are not shown, but may have a mesa structure.

  The piezoelectric plate 16 shown in FIG. 7 is not shown in a state of being housed in a package. However, in order to use the same package size and a large electrode area for low frequencies, Thus, the central portion of the entire common electrode 9a is decentered in the direction of the corner portion of the four corner portions of the piezoelectric plate 16 excluding the three corner portions to which the conductive adhesives 6 and 10 are applied. Then, the divided electrodes 7a and 7b and the common electrode 9a are extended in the one side direction or the other side direction of the piezoelectric plate 16 by the electrode area reduced by the chamfering to form a horizontally or more vertically long electrode.

  FIG. 8 shows the planar view shape and size of the common electrode used in the example. The piezoelectric filter of the embodiment has two piezoelectric plates juxtaposed in the Z′-axis direction in the package, and FIG. 8A shows the shape of the common electrode on one of the two piezoelectric plates. FIG. 8B shows the shape and dimensions of the common electrode on the other piezoelectric plate. The illustration of the piezoelectric plate itself is omitted. Although the conventional piezoelectric filter is not shown, the central portion of the piezoelectric plate coincides with the central portion of the common electrode, whereas the piezoelectric filter of the present invention has a central portion of the common electrode with respect to the central portions of the piezoelectric plates O1 and O2. O1 ′ and O2 ′ are offset by 0.1 mm in the X-axis direction and 0.1 mm in the Z′-axis direction. In addition, the shape and dimension of each common electrode of FIG. 8 are as showing in figure, The detailed description is abbreviate | omitted.

  In FIG. 9A, the horizontal axis represents the insertion loss [dB], and the vertical axis represents the ratio [%] of the number of samples having the insertion loss with respect to the number of samples 100% [%]. It is a figure showing distribution of insertion loss with a bar graph. As shown in this bar graph, in the conventional piezoelectric filter, when the insertion loss is larger than the standard line near 3.3 dB, the defective product and the one with low insertion loss are good products, the number of defective products is extremely large and the yield is very high. It ’s bad.

  FIG. 9B is a bar graph showing the distribution of insertion loss with respect to 200 to 300 samples of the product of the present invention. In the product of the present invention, there are no defective products exceeding the standard line, and all non-defective products are below the standard line. Met. Therefore, the yield of the product of the present invention is significantly improved compared to the conventional product.

  FIG. 9 (c) is a bar graph showing the distribution of insertion loss for another sample number of 200 to 300 according to the present invention. The product of the present invention also has no defective products exceeding the standard line, and all are below the standard line. It was a good product. Therefore, the yield of the product of the present invention is significantly improved over this sample as compared with the conventional product.

  As described above, in the present invention, when the electrode area is increased and the piezoelectric filter for the low frequency band is used, with respect to the insertion loss (loss), as is clear from FIG. Compared with a conventional product in which the central portion of the common electrode is not decentered in the direction of the corner where the conductive adhesive is not applied, the yield is greatly improved.

DESCRIPTION OF SYMBOLS 1 Piezoelectric filter 2,3 Piezoelectric plate 7a, 7b; 8a, 8b Divided electrode 9a, 9b Common electrode

Claims (8)

A rectangular piezoelectric plate having a plurality of divided electrodes on one surface and a common electrode facing the other divided surface in common on the other surface, four corners on the outer peripheral edge of the piezoelectric plate Piezoelectric filters in which lead electrodes for pulling out the respective electrodes are formed at three corners of the part, and a conductive adhesive is applied to the three corners from which the lead electrodes are drawn,
A location where a center line passing through the center of one side of the piezoelectric plate and a center line passing through the center of the other side of the piezoelectric plate intersect is defined as the center of the piezoelectric plate, and the common electrode with respect to the center of the piezoelectric plate The center portion of the piezoelectric plate is displaced along the one side direction and is displaced along the other side direction, so that the conductive plate of the piezoelectric plate is not applied with the conductive adhesive. A piezoelectric filter characterized by being eccentric. A plurality of rectangular divided electrodes are provided on one surface of the rectangular piezoelectric plate, and a rectangular common electrode facing the plurality of divided electrodes is provided on the other surface, and the outer peripheral edge of the piezoelectric plate. Piezoelectric filter in which lead electrodes for pulling out the respective electrodes are formed at three of the four corners on the top, and a conductive adhesive is applied to the three corners from which the lead electrodes are drawn Because
The corners on the outer periphery of the divided electrode and the common electrode facing at least the three corners are chamfered or notched, and the divided electrode or the common electrode whose electrode area is reduced by the chamfering or notch is reduced. The piezoelectric film is extended in one side direction or the other side direction of the piezoelectric plate according to an electrode area, and becomes a horizontally or vertically longer electrode than before the chamfering or notching. filter. A plurality of rectangular divided electrodes are provided on one surface of the rectangular piezoelectric plate, and a rectangular common electrode facing the plurality of divided electrodes is provided on the other surface, and the outer peripheral edge of the piezoelectric plate. Piezoelectric filter in which lead electrodes for pulling out the respective electrodes are formed at three of the four corners on the top, and a conductive adhesive is applied to the three corners from which the lead electrodes are drawn Because
A location where a center line passing through the center of one side of the piezoelectric plate and a center line passing through the center of the other side of the piezoelectric plate intersect is defined as the center of the piezoelectric plate, and the common electrode with respect to the center of the piezoelectric plate The center portion of the piezoelectric plate is displaced along the one side direction and is displaced along the other side direction, so that the conductive plate of the piezoelectric plate is not applied with the conductive adhesive. With eccentricity,
The corners on the outer periphery of the divided electrode and the common electrode facing at least the three corners are chamfered or notched, and the divided electrode or the common electrode whose electrode area is reduced by the chamfering or notch is reduced. The piezoelectric film is extended in one side direction or the other side direction of the piezoelectric plate according to an electrode area, and becomes a horizontally or vertically longer electrode than before the chamfering or notching. filter.   4. The piezoelectric filter according to claim 1, wherein two of the piezoelectric plates are cascaded to form a 4-pole type. 5.   The two divided electrodes facing each other on one of the piezoelectric plates have a horizontally long shape in the facing direction, and the two facing divided electrodes on the other piezoelectric plate are both vertically elongated in the facing direction. The piezoelectric filter according to claim 4, wherein the piezoelectric filter has a shape.   Two piezoelectric filter forming regions are formed on the piezoelectric plate, and a two-pole type piezoelectric filter including two divided electrodes and a common electrode is formed in each piezoelectric filter forming region, so that both piezoelectric filter forming regions In the four-pole type, out of the four corners of each piezoelectric filter forming region, the lead electrodes from the respective electrodes are formed at three corners to which the conductive adhesive is applied. The central portion of the common electrode in each piezoelectric filter forming region is eccentric with respect to the central portion of each piezoelectric filter forming region in the direction of one corner where the conductive adhesive is not applied. The piezoelectric filter according to claim 1.   7. The piezoelectric filter according to claim 6, wherein, in each of the piezoelectric filter formation regions, at least corners of the divided electrode and the extraction electrode facing the three corners are chamfered or notched. The piezoelectric plate is flat, inverted mesa, or Ru AT cut quartz crystal plate der mesa, the piezoelectric filter according to any one of claims 1 to 7, characterized in that.

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