Elastic wave filter, demultiplexer, and communication device

Abstract

A filter body having: a series arm including a plurality of series resonators connected in series with each other, and one or more parallel resonators, which are connected in a ladder configuration. The series arm has a folded-back portion. The series resonator closest to the first terminal side in the circuit among the plurality of series resonators and the parallel resonator closest to the first terminal side in the circuit among the plurality of parallel resonators do not coincide with the series resonator closest to the second terminal side in the circuit among the plurality of series resonators and the parallel resonator closest to the second terminal side in the circuit among the plurality of parallel resonators when observed in the propagation direction of the elastic wave.

Description

Technical Field

[0001] The present disclosure relates to an elastic wave filter for filtering an electrical signal, a demultiplexer including the elastic wave filter, and a communication device. The elastic wave is, for example, SAW (Surface Acoustic Wave). Background Art

[0002] There is known an elastic wave filter formed by connecting a plurality of elastic wave resonators in a ladder shape (for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses a ladder-shaped elastic wave filter in which a shield conductor is provided between an input terminal or an output terminal and a wiring, where the input terminal inputs a signal to the elastic wave filter, the output terminal outputs a signal from the elastic wave filter, and the wiring transmits a signal within the elastic wave filter.

[0004] Patent Document 2 discloses a duplexer having a transmission filter and a reception filter, where the transmission filter includes a ladder-shaped elastic wave filter and the reception filter includes a ladder-shaped elastic wave filter. The transmission filter and the reception filter are connected together to one input / output terminal and are configured as a whole in a substantially U shape. Patent Document 2 also discloses a method of providing a shield conductor between the transmission filter and the reception filter.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Laid-Open No. 07-154201

[0008] Patent Document 2: Japanese Patent Laid-Open No. 2010-239612 Summary of the Invention

[0009] One aspect of the present disclosure relates to an elastic wave filter including a piezoelectric substrate, a first terminal, a second terminal, and a filter body. The filter body is located on the piezoelectric substrate. In the filter body, series arms and a plurality of parallel resonators are connected in a ladder shape. The series arms include a plurality of series resonators connected in series between the first terminal and the second terminal. And the series arms include a first divided arm and a second divided arm. The first divided arm extends from one side to the other side in a specified direction with respect to the piezoelectric substrate and includes at least one of the series resonators. The second divided arm turns back from the other side of the first divided arm and extends toward the one side and includes at least one of the series resonators. And regions obtained by extending straight lines parallel to the propagation direction of elastic waves from the series resonator closest to the first terminal side in terms of circuitry among the plurality of series resonators and the parallel resonator closest to the first terminal side in terms of circuitry among the plurality of parallel resonators, and the series resonator closest to the second terminal side in terms of circuitry among the plurality of series resonators and the parallel resonator closest to the second terminal side in terms of circuitry among the plurality of parallel resonators do not overlap.

[0010] One aspect of the present disclosure relates to a demultiplexer having an antenna terminal, a transmit filter connected to the antenna terminal, and a receive filter connected to the antenna terminal; at least one of the transmit filter and the receive filter includes the above-described elastic wave filter.

[0011] The communication device according to the present disclosure includes the above-described elastic wave filter, an antenna connected to one end of the series arm, and an IC connected to the other end of the series arm. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a top view showing the structure of a SAW resonator.

[0013] Figure 2 schematically shows a SAW filter including Figure 1 the SAW resonator of.

[0014] Figure 3 schematically shows Figure 2 a modified example of the SAW filter of.

[0015] Figure 4 schematically shows Figure 2 a modified example of the SAW filter of.

[0016] Figure 5 shows Figure 4 a line graph of the frequency characteristics of the SAW filter shown in and the SAW filter of the comparative example.

[0017] Figure 6 is a diagram schematically showing a demultiplexer as an application example of a SAW filter Figure 2 .

[0018] Figure 7 is a block diagram showing the structure of the main part of a communication device as an application example of a demultiplexer Figure 6 . DETAILED DESCRIPTION

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In addition, the drawings used in the following description are schematic drawings, and the dimensional ratios and the like on the drawings do not necessarily match the actual situation.

[0020] (Structure of SAW resonator)

[0021] Figure 1 is a top view showing the structure of the SAW resonator 1 used in the SAW filter 51 ( Figure 2 ) of the embodiment.

[0022] The SAW resonator 1 (SAW filter 51) can have any direction as the upper or lower side. However, in the following description, for convenience, an orthogonal coordinate system composed of the D1 axis, D2 axis, and D3 axis is defined, and the positive side of the D3 axis ( Figure 1 the near side of the paper surface of

[0023] is set as the upper side, and terms such as the upper surface may be used. In addition, the D1 axis is defined to be parallel to the propagation direction of the SAW propagating along the upper surface of the piezoelectric substrate 5 described later (the near side of the paper surface. Usually, the widest surface (main surface)), the D2 axis is defined to be parallel to the upper surface of the piezoelectric substrate 5 and orthogonal to the D1 axis, and the D3 axis is defined to be orthogonal to the upper surface of the piezoelectric substrate 5.

[0024] The SAW resonator 1 constitutes a so-called single-port SAW resonator. For example, when an electrical signal of a predetermined frequency is input from one of the two terminals 3 schematically shown, resonance occurs, and a signal generated by this resonance is output from the other of the two terminals 3.

[0025] In addition, as described above, strictly speaking, the SAW resonator 1 includes the piezoelectric substrate 5. However, as described later, in the present embodiment, a combination of a plurality of IDT electrodes 7 and a pair of reflectors 9 is provided on one piezoelectric substrate 5 to constitute a plurality of SAW resonators 1 (1S1, 1P1, etc.) (see Figure 2) Therefore, in the following description, for convenience, the combination of the IDT electrode 7 and a reflector 9 (the electrode portion of the SAW resonator 1) is referred to as the SAW resonator 1.

[0026] The piezoelectric substrate 5 includes, for example, a single crystal having piezoelectricity. The single crystal is, for example, a lithium niobate (LiNbO3) single crystal or a lithium tantalate (LiTaO3) single crystal. The cut angle can be appropriately set according to the type of SAW used, etc. For example, the piezoelectric substrate 5 is a substrate with a rotated Y-cut X-propagation. That is, the X-axis is parallel to the upper surface (D1 axis) of the piezoelectric substrate 5, and the Y-axis is inclined at a prescribed angle with respect to the normal of the upper surface of the piezoelectric substrate 5. In addition, the piezoelectric substrate 5 can be formed to be relatively thin, and a support substrate containing an inorganic material or an organic material is bonded to the back surface (the surface on the negative side of the D3 axis). Further, an intermediate layer can be interposed between the piezoelectric substrate 5 and the support substrate. The intermediate layer can be either a single layer or multiple layers stacked.

[0027] The IDT electrode 7 and the reflector 9 are constituted by a layered conductor provided on the piezoelectric substrate 5. The IDT electrode 7 and the reflector 9 are, for example, constituted by the same material and thickness. The layered conductor constituting them is, for example, a metal. The metal is, for example, Al or an alloy mainly composed of Al (Al alloy). The Al alloy is, for example, an Al-Cu alloy. The layered conductor can also be constituted by multiple metal layers. The thickness of the layered conductor is appropriately set according to the electrical characteristics required for the SAW resonator 1, etc. As an example, the thickness of the layered conductor is 50 nm or more and 600 nm or less.

[0028] The IDT electrode 7 has a pair of comb-shaped electrodes 11 (one of them is hatched for easy visibility improvement). Each comb-shaped electrode 11 has, for example: a bus bar 13, a plurality of electrode fingers 15 extending side by side from the bus bar 13, and a plurality of dummy electrodes 17 protruding from the bus bar 13 between the plurality of electrode fingers 15.

[0029] The pair of comb-shaped electrodes 11 are arranged such that the plurality of electrode fingers 15 mesh (cross) with each other. Sometimes the meshed portion is referred to as the cross region R1. The two bus bars 13 of the pair of comb-shaped electrodes 11 are arranged opposite to each other, and the electrode fingers 15 of one comb-shaped electrode 11 and the electrode fingers 15 of the other comb-shaped electrode 11 are arranged substantially alternately in their width directions. Further, the distal ends of the plurality of dummy electrodes 17 of one comb-shaped electrode 11 are opposite to the distal ends of the electrode fingers 15 of the other comb-shaped electrode 11.

[0030] The bus bar 13 is formed, for example, in a long strip shape that extends linearly in the propagation direction (D1-axis direction) of the SAW with a substantially constant width. Also, a pair of bus bars 13 are opposed to each other in the direction (D2-axis direction) orthogonal to the propagation direction of the SAW. The mutually opposing edge portions of the pair of bus bars 13 are, for example, parallel to each other. Additionally, the width of the bus bar 13 may vary or be inclined with respect to the propagation direction of the SAW.

[0031] Each electrode finger 15 is formed, for example, in a long strip shape that extends linearly in the direction (D2-axis direction) orthogonal to the propagation direction of the SAW with a substantially constant width. A plurality of electrode fingers 15 are arranged, for example, along the propagation direction of the SAW and have equal lengths. Additionally, the IDT electrode 7 may also be implemented with so-called apodization where the lengths (crossing widths in other viewpoints) of the plurality of electrode fingers 15 vary according to the position in the propagation direction.

[0032] The number of electrode fingers 15, the length, and the width w (in other viewpoints, the duty ratio which is the ratio of the width w to the pitch p) can be appropriately set according to the electrical characteristics required for the SAW resonator 1, etc. Additionally, since Figure 1 etc. are schematic diagrams, the number of electrode fingers 15 is shown as being less. In reality, more (for example, 100 or more) electrode fingers 15 can be arranged than shown in the figure. The same applies to the strip electrodes 21 of the reflector 9 described later.

[0033] The pitch p (electrode finger pitch) of the plurality of electrode fingers 15 is set, for example, to be substantially constant throughout the IDT electrode 7. Additionally, the pitch p is, for example, the center-to-center distance between two mutually adjacent electrode fingers 15 (or the strip electrodes 21 described later). The pitch p is basically set to be half of the wavelength λ of the SAW propagating on the piezoelectric substrate 5 that has the same frequency as the frequency at which resonance is to be achieved (p = λ / 2).

[0034] The plurality of dummy electrodes 17 are formed, for example, in a long strip shape that protrudes linearly in the direction (D2-axis direction) orthogonal to the propagation direction of the SAW with a substantially fixed width. The width, number, and pitch of the plurality of dummy electrodes 17 are equal to those of the plurality of electrode fingers 15. Additionally, the width of the dummy electrode 17 may also be different from that of the electrode finger 15. The IDT electrode 7 may not have the dummy electrode 17. In the following description, the description and illustration of the dummy electrode 17 may sometimes be omitted.

[0035] As described above, the distal ends of the plurality of electrode fingers 15 of one comb electrode 11 and the distal ends of the other comb electrode 11 (more specifically, the distal ends of the dummy electrodes 17 of the other comb electrode 11 in this embodiment) face each other with a gap Gp therebetween in the extending direction (D2-axis direction) of the plurality of electrode fingers 15. The size of the gap Gp in the D2-axis direction is, for example, equal between the plurality of electrode fingers 15.

[0036] The reflector 9 is formed in a lattice shape, for example. That is, the reflector 9 has a pair of bus bars 19 facing each other, and a plurality of strip-shaped electrodes 21 extending between the pair of bus bars 19.

[0037] The shapes of the bus bars 19 and the strip-shaped electrodes 21 can be the same as those of the bus bars 13 and the electrode fingers 15 of the IDT electrode 7, except that both ends of the strip-shaped electrodes 21 are connected to the pair of bus bars 19.

[0038] A pair of reflectors 9 are adjacent to both sides of the IDT electrode 7 in the propagation direction of the SAW, for example. Therefore, the plurality of strip-shaped electrodes 21 are arranged following the arrangement of the plurality of electrode fingers 15. The distance between the strip-shaped electrodes 21 and the electrode fingers 15 adjacent to each other between the reflector 9 and the IDT electrode 7 is equal to the distance between the plurality of electrode fingers 15 (and the plurality of strip-shaped electrodes 21), for example.

[0039] In addition, the upper surface of the piezoelectric substrate 5 can also be covered with an unillustrated protective film containing SiO2 or the like from above the IDT electrode 7 and the reflector 9. This protective film can be thinner than the IDT electrode 7 or thicker than the IDT electrode 7. Further, in the case where a protective film is provided, etc., in order to increase the reflection coefficient of the SAW, an additional film made of an insulator or a metal can also be provided on the upper surface or the lower surface of the IDT electrode 7 and the reflector 9.

[0040] Moreover, the terminal 3 and the bus bar 13 are electrically connected through a wiring 23.

[0041] When a voltage is applied to the pair of comb-shaped electrodes 11, the voltage is applied to the piezoelectric substrate 5 through the electrode fingers 15, and a SAW of a specified mode that propagates in the D1 axis direction along the upper surface near the upper surface of the piezoelectric substrate 5 is excited. The excited SAW is mechanically reflected by the electrode fingers 15. As a result, a standing wave having a half wavelength equal to the distance between the electrode fingers 15 is formed. The standing wave is converted into an electrical signal having the same frequency as the standing wave and is extracted by the electrode fingers 15. In this way, the SAW resonator 1 functions as a resonator. Its resonance frequency is approximately the same as the frequency of the SAW that propagates on the piezoelectric substrate 5 with the electrode finger pitch as the half wavelength.

[0042] The SAW excited in the IDT electrode 7 is mechanically reflected by the strip-shaped electrodes 21 of the reflector 9. In addition, since the mutually adjacent strip-shaped electrodes 21 are connected to each other through the bus bar 19, the SAW from the IDT electrode 7 is also electrically reflected by the strip-shaped electrodes 21. As a result, the divergence of the SAW is suppressed, a strong standing wave is generated in the IDT electrode 7, and the function of the SAW resonator 1 as a resonator is improved.

[0043] In addition, regarding the connection of the SAW resonator 1, unless otherwise specified, as schematically shown by the two terminals 3, it refers to the connection in such a way that voltage is applied to a pair of comb electrodes 11.

[0044] For the improvement or fine-tuning of characteristics, the IDT electrode 7 sometimes sets a pitch p of a size different from that of most of the pitches p in a part thereof (for example, less than 50% of the total number of pitches p, or less than 5%). For example, the IDT electrode 7 sometimes provides narrow pitch portions on both sides in the propagation direction of the SAW where the pitch p is smaller than that of most of the others. In addition, for example, sometimes a prescribed number (for example, 1 to 3) of electrode fingers 15 of a pair of comb electrodes 11 arranged alternately are removed, or the width w or arrangement of the electrode fingers 15 is changed substantially equivalently, that is, so-called pitch extraction is performed. In the present disclosure, when referring to the pitch p, width w, or duty ratio (w / p), unless otherwise specified, such special different parts are not considered. In addition, when the pitch p or width w varies within a minute range throughout the IDT electrode 7, their average values can be used.

[0045] (Overview of SAW Filter)

[0046] Figure 2 is a top view schematically showing the structure of the SAW filter 51 including the SAW resonator 1. In this figure, from the reference numerals of the IDT electrode 7 and the reflector 9 shown in the upper left side of the drawing paper, it can be known that Figure 1 these conductors are shown more schematically.

[0047] The SAW filter 51 has the piezoelectric substrate 5 described above. And the SAW filter 51 has various terminals 3 (such as 31 and 32, etc.) for inputting and outputting signals, and a filter body 52 for filtering signals on the piezoelectric substrate 5.

[0048] The plurality of terminals 3 can include, for example: an input terminal 31 (first terminal) for inputting an electrical signal from the outside of the SAW filter 51, an output terminal 32 (second terminal) for outputting an electrical signal to the outside, first to third GND terminals 331 to 333 for applying a reference potential from the outside, and dummy terminals 34 for bonding. In addition, the SAW filter 51 can also use the input terminal 31 as the output terminal and the output terminal 32 as the input terminal.

[0049] In addition, for the first to third GND terminals 331 to 333, they are sometimes only referred to as "GND terminals 33" without distinguishing them. The input terminal 31, output terminal 32, and / or GND terminal 33 are equivalent to Figure 1 the terminals 3 shown. Sometimes these terminals are not distinguished and are only referred to as terminals 3.

[0050] The filter body 52 is configured to filter an electrical signal from the input terminal 31 and output it to the output terminal 32. In addition, the filter body 52 is configured to cause useless components (signals outside the passband) included in the electrical signal to escape to the GND terminal 33 during the above filtering.

[0051] The filter body 52 is constituted by connecting a plurality of SAW resonators 1 (in the illustrated example, 1S1 to 1S6 and 1P1 to 1P5) in a ladder shape between the input terminal 31, the output terminal 32, and one or more GND terminals 33 to form a circuit. The plurality of terminals 3 and the plurality of SAW resonators 1 are connected by a plurality of wirings 23.

[0052] In addition, the package and / or mounting structure of the SAW filter 51 can be set in various ways. For example, the SAW filter 51 is arranged such that the upper surface (+D3 side surface) of the piezoelectric substrate 5 faces a circuit substrate (not shown), and the various terminals 3 are joined to the pads of the circuit substrate by protrusions, thereby performing packaging or mounting. Or, for example, a box-shaped cover portion (not shown) is covered on the upper surface of the piezoelectric substrate 5, and columnar conductors (not shown) penetrating the cover portion are erected on the various terminals 3. And the SAW filter is arranged such that the upper surface of the cover portion faces a circuit substrate (not shown), and the columnar conductors exposed from the upper surface of the cover portion are joined to the pads of the circuit substrate by protrusions, thereby performing mounting.

[0053] (Terminals and wirings)

[0054] The terminal 3 and the wiring 23 include a conductor layer located on the upper surface of the piezoelectric substrate 5. This conductor layer is, for example, the same as the conductor layer constituting the IDT electrode 7 and the reflector 9 (same material and thickness). However, at the position of the terminal 3, a conductor layer including other materials may also be formed on the conductor layer common to the IDT electrode 7, the reflector 9, and the wiring 23. Of course, the terminal 3, the wiring 23, and other conductor layers may also be constituted by mutually different materials.

[0055] The shape, size, etc. of the terminal 3 can be set appropriately. In addition, the terminal 3 does not need to be distinguished from the wiring 23 according to its own structure (shape, material, etc.), and it may also be a part of the wiring 23. For example, the position or range of the terminal 3 can also be determined by an insulating layer that covers the wiring 23 but not the terminal 3, or by a component (such as a protrusion) that abuts against the terminal 3 when the piezoelectric substrate 5 is packaged.

[0056] All or part of the GND terminals 33 may be short-circuited to each other, or may not be short-circuited.

[0057] The specific path, width, etc. of the wiring 23 can be set appropriately. Figure 2In the figure, for convenience, the wiring 23 is shown as having a certain width and being relatively thin. However, the width of the wiring 23 may be varied, or may be as follows: Figure 1 Although the bus bar 13 is formed thicker as shown, it may also have a width equal to the length (D1 axis direction) of the bus bar 13 in a portion. Figure 2 In the example shown in the figure, the wiring 23 does not overlap each other, but there may be a part where the wiring 23 intersects each other in three dimensions through an insulator.

[0058] (Connection relationship of SAW resonators in the filter body)

[0059] The filter body 52 is formed by a so-called ladder-type SAW filter. That is, the filter body 52 has: a series arm 53 (arrow y is indicated along the series arm 53) connecting the input terminal 31 and the output terminal 32, and one or more (in the illustrated example, multiple (5)) parallel arms 55 connecting the series arm 53 and the GND terminal 33. The series arm 53 helps to transmit the passband signal. The parallel arm 55 helps to make the signal outside the passband flow to the GND terminal 33. In addition, in the description of this embodiment, the case where the number of parallel arms 55 is multiple is basically taken as an example.

[0060] The series arm 53 includes the first series resonator 1S1 to the sixth series resonator 1S6 (hereinafter, sometimes simply referred to as "series resonator 1S" without distinguishing them) connected in series between the input terminal 31 and the output terminal 32. Each parallel arm 55 includes any one of the first parallel resonator 1P1 to the fifth parallel resonator 1P5 (hereinafter, sometimes simply referred to as "parallel resonator 1P" without distinguishing them) that connects the input side (input terminal 31 side) or the output side (output terminal 32 side) of any series resonator 1S to the GND terminal 33. The plurality of parallel arms 55 (parallel resonators 1P) are connected at electrically different positions relative to the series arm 53 (positions with different relative relationships relative to the series resonator 1S).

[0061] In addition, in the description of the present embodiment, in the case where the series arm 53 (in other viewpoints, one or more series resonators 1S) and the parallel arm 55 (in other viewpoints, one or more parallel resonators 1P) are connected in a ladder type, as described above, it refers to a state in which the series arm 53 (in other viewpoints, one series resonator or multiple series resonators 1S connected in series) is connected between the input terminal 31 and the output terminal 32, and one or more parallel arms 55 (in other viewpoints, one or more parallel resonators 1P) are connected between the input side or output side of one or more series resonators 1S and the GND terminal 33.

[0062] The number of series resonators 1S and the number of parallel resonators 1P can be appropriately set, Figure 2 and the numbers shown in the figure are just examples. In the illustrated example, no parallel resonator 1P is connected to the input side of the first series resonator 1S1 closest to the input terminal 31 side, but a parallel resonator 1P can also be connected to the input side of the first series resonator 1S1. Similarly, no parallel resonator 1P is connected to the output side of the sixth series resonator 1S6 closest to the output terminal 32 side, but a parallel resonator 1P can also be connected to the output side of the sixth series resonator 1S6.

[0063] The multiple parallel resonators 1P can be individually (one-to-one) connected to multiple GND terminals 33 that are not short-circuited to each other, or all or part of them can be connected to the same GND terminal 33 or multiple GND terminals 33 that are short-circuited to each other. In the illustrated example, the first parallel resonator 1P1 is connected to the first GND terminal 331, the second parallel resonator 1P2 and the third parallel resonator 1P3 are both connected to the second GND terminal 332, and the fourth parallel resonator 1P4 and the fifth parallel resonator 1P5 are both connected to the third GND terminal 333.

[0064] The series resonator 1S and the parallel resonator 1P are respectively constituted by, for example, referring to the Figure 1 SAW resonator 1 described. However, specific values such as the number of electrode fingers 15, the length and / or pitch p of the electrode fingers 15 are set according to the characteristics required for each resonator.

[0065] The series resonator 1S and the parallel resonator 1P can be respectively constituted by one SAW resonator 1, or can be respectively constituted by multiple SAW resonators 1. In the illustrated example, the first series resonator 1S1 is constituted by two SAW resonators 1 (the first divided resonator 1S1-1 and the second divided resonator 1S1-2), and the other resonators are constituted by one SAW resonator 1. In addition, from another perspective, the first series resonator 1S1 can also be understood as being constituted by dividing one SAW resonator 1 into multiple (here two) SAW resonators 1.

[0066] The first divided resonator 1S1-1 and the second divided resonator 1S1-2 are connected in series with each other. The connection can be made through the wiring 23, or can be made by sharing the bus bars 13 of the two. The first divided resonator 1S1-1 and the second divided resonator 1S1-2, for example, have substantially the same structure. However, the two can also have different structures.

[0067] Thus, by dividing a series resonator 1S or a parallel resonator 1P, for example, the voltage applied to the SAW resonator 1 (here, the first divided resonator 1S1-1 or the second divided resonator 1S1-2) can be reduced, thereby improving the power resistance of the entire series resonator 1S or the entire parallel resonator 1P. When the SAW filter 51 is a transmission filter (described later) used for wireless communication, the intensity of the electrical signal on the input terminal 31 side is higher than the intensity of the electrical signal on the output terminal 32 side. In this case, as shown in the illustrated example, by dividing the SAW resonator 1 closest to the input terminal 31, the power resistance of the entire SAW filter 51 can be improved.

[0068] In addition, when a plurality of SAW resonators 1 connected in series are provided in the series arm 53, whether each SAW resonator 1 is a divided resonator or a form in which a single body constitutes a series resonator 1S can be determined, for example, based on the connection position with the parallel arm 55. For example, if there is no connection with the parallel arm 55 between two SAW resonators 1 connected in series with each other, these two SAW resonators 1 can be regarded as divided resonators that jointly constitute a series resonator 1S.

[0069] (Shape of the path of the series arm)

[0070] As can be understood from the arrows y (y1, y2, y3) marked along the series arm 53, the SAW filter 51 is configured such that the series arm 53 turns back midway on the piezoelectric substrate 5 (substantially U-shaped). The number of turnbacks can be one or more. In this example, the path turns back twice midway, and is substantially S-shaped as a whole. In other words, the series arm 53 has a first divided arm 59A, a second divided arm 59B, and a third divided arm 59C (hereinafter, sometimes simply referred to as "divided arm 59" without distinguishing them). The first divided arm 59A extends from one side (-D2 side) in the specified direction (D2-axis direction) on the piezoelectric substrate 5 to the other side (+D2 side) (along the arrow y1 direction), the second divided arm 59B turns back from the other side (+D2 side) of the first divided arm 59A and extends toward one side (-D2 side) (along the arrow y2 direction), and the third divided arm 59C turns back from one side (-D2 side) of the second divided arm 59B and extends toward the other side (+D2 side) (along the arrow y3 direction). These structures are specifically as described below, for example.

[0071] The piezoelectric substrate 5 is configured to be substantially rectangular in a top view and has four sides. The side on the -D2 side is the first side 61A, the side on the +D1 side is the second side 61B, the side on the +D2 side is the third side 61C, and the side on the -D1 side is the fourth side 61D.

[0072] In this example, the input terminal 31 is located closer to the first side 61A than the middle of the region where the electrode groups are arranged in the SAW filter 51, and the output terminal 32 is located closer to the third side 61C than the center of the region where the electrode groups are arranged in the SAW filter 51. Moreover, the input terminal 31 and the output terminal 32 are located on the diagonal line of the rectangular piezoelectric substrate 5. Accordingly, interference between the input and output terminals can be reduced.

[0073] The first divided arm 59A extends generally from the input terminal 31 toward the +D2 side (the third side 61C which is the opposite side of the first side 61A) and reaches the turning-back portion (the connecting portion of the first divided arm 59A and the second divided arm 59B) 63A. The turning-back portion 63A is formed, for example, by the wiring 23 connecting the two series resonators 1S3 and 1S4 to each other, and is located relatively closer to the third side 61C.

[0074] The second divided arm 59B extends generally from the turning-back portion 63A toward the -D2 side (the first side 61A side) and reaches the turning-back portion 63B. The turning-back portion 63B is formed, for example, by the wiring 23 connecting the two series resonators 1S4 and 1S5 to each other.

[0075] The third divided arm 59C extends generally from the turning-back portion 63B at the end on the -D2 side of the second divided arm 59B toward the +D2 side (the third side 61C side) and reaches the output terminal 32.

[0076] As Figure 2 As indicated by the reference symbols on the right side of the drawing paper, among the pair of comb-shaped electrodes 11 of the series resonator 1S, the comb-shaped electrode 11 on the input terminal 31 side (input side, one side) with respect to the flow of the electric signal is defined as the input-side comb-shaped electrode 11A, and the comb-shaped electrode 11 on the output terminal 32 side (output side, the other side) with respect to the flow of the electric signal is defined as the output-side comb-shaped electrode 11B. That is, among the pair of comb-shaped electrodes 11, the one connected to the input terminal 31 via or without passing through other series resonators 1S is the input-side comb-shaped electrode 11A, and among the pair of comb-shaped electrodes 11, the one connected to the output terminal 32 via or without passing through other series resonators 1S is the output-side comb-shaped electrode 11B. In addition, the direction in the D2 axis direction from the bus bar 13 of the input-side comb-shaped electrode 11A to the bus bar 13 of the output-side comb-shaped electrode 11B is sometimes referred to as the direction with respect to the piezoelectric substrate 5 from the input-side comb-shaped electrode 11A to the output-side comb-shaped electrode 11B, etc.

[0077] Sometimes, the turning-back portions 63A and 63B are not distinguished and are collectively referred to as the turning-back portion 63 (the reference numeral is Figure 3). Here, the "returning portion 63" means that the direction of the signal flow from the terminal 31 to the terminal 32 between each split arm 59 is reversed. "The direction of the signal flow is reversed" means that when the direction of the signal in each split arm is represented by a vector, the angle formed by the two vectors is greater than 90° and less than 270°. In other words, "the direction of the signal flow is reversed" refers to a resonator including a resonant having an opposite direction from the input side comb electrode 11A to the output side comb electrode 11B. Figure 2 In the example shown, there are two sets of such split arms 59 with opposite signal flows, namely, a combination of the first split arm 59A and the second split arm 59B, and a combination of the second split arm 59B and the third split arm 59C. In the case of a U-shape, there is one set.

[0078] Thus, by providing the return portion 63 in the middle of the path, the area of the region where the electrode group constituting the SAW filter 51 is arranged can be reduced, which can contribute to the miniaturization of the SAW filter 51. In addition, by setting the path of the series arm 53 to an S-shape, the straight-line distance between the terminal 31 and the terminal 32 can be increased. In other words, the terminal 31 and the terminal 32 can be arranged on a diagonal line. Thus, interference between the two terminals can be prevented.

[0079] (Resonator Configuration)

[0080] As described above, when the series arm 53 includes the folded portion 63 , a plurality of resonators 1 may overlap in the D1 direction. In other words, another resonator 1 may be located on an extension line of a certain resonator 1 in the D1 direction.

[0081] In contrast, according to the SAW filter 51 of the present disclosure, the resonators (1S6 and 1P5) closest to the signal terminal 32 on the circuit do not overlap with any of the resonators (1S1 and 1P1) closest to the input terminal 31 on the circuit in the D1 direction.

[0082] Here, the resonators "overlap" in the D1 direction means that the intersection regions R1 where the electrode fingers 15 of the SAW resonators 1 cross overlap in the D1 direction. In other words, even if the busbars 13 and dummy electrodes 17 overlap between the resonators 1, as long as the intersection regions R1 do not overlap, it can be said that the two resonators 1 do not overlap. More specifically, when the intersection region R1 of one SAW resonator 1 is extended in the D1 direction, if the other SAW resonator 1 is not located in the extended region, it can be said that the two SAW resonators 1 "do not overlap" in the D1 direction.

[0083] In addition, "the closest to the input terminal side on the circuit" is distinguished from the positional relationship in the layout in the top-down view, and represents the positional relationship in the case shown in the circuit diagram showing the electrical connection state between the resonators. That is, "the resonator that is the most on the input terminal side on the circuit" refers to the resonator among the series resonators that is the closest to the input terminal side along the flow direction of the high-frequency signal, and the resonator among the parallel resonators that is the closest to the input terminal side. Similarly, "the closest to the output terminal side on the circuit" is distinguished from the positional relationship in the layout in the top-down view, and represents the positional relationship in the case shown in the circuit diagram showing the electrical connection state between the resonators. That is, "the resonator that is the closest to the output terminal side on the circuit" refers to the resonator that is the closest to the output terminal side along the flow direction of the high-frequency signal.

[0084] In Figure 2 In the example shown, the resonators 1S6 and 1P5 are arranged so as not to overlap with the resonators 1S1 and 1P1. By arranging them in this way, since interference between the resonators directly below the terminals can be prevented, a SAW filter 51 with excellent electrical characteristics can be provided.

[0085] In addition, in the above example, the case where the resonators 1P1, 1S1, 1P5, and 1S6 do not overlap with each other in the D1 direction is taken as an example for explanation. However, by making at least one of these resonators not overlap, compared with the case where all of them overlap, there is an effect of improving the electrical characteristics. Here, even if the SAW resonator 1S1 overlaps with the SAW resonator 1P1 in the D1 direction, the influence on the characteristics is small. However, in the case where the SAW resonator 1S1 overlaps with the SAW resonator 1S6 or the SAW resonator 1P5, and in the case where the SAW resonator 1P1 overlaps with the SAW resonator 1S6 or the SAW resonator 1P5, the electrical characteristics are affected.

[0086] In addition, when the piezoelectric substrate 5 is formed thin and the support substrate containing an inorganic material or an organic material is directly or indirectly bonded to its back surface (the surface on the negative side of the D3 axis), the elastic wave propagates farther compared to a thick piezoelectric substrate. Therefore, when the piezoelectric substrate 5 is thinner than 1λ, due to the increased influence of the interference of the elastic wave, the arrangement of the resonators becomes important.

[0087] (Modified Example)

[0088] In the above example, the case where the path of the series arm 53 is S-shaped is taken as an example for explanation, but it is not limited to this. For example, as Figure 3 shown, it can also be U-shaped. That is, it can also have one turning portion 63, and the first divided arm 59A facing the y1 direction and the second divided arm 59B facing the y2 direction opposite to the y1 direction are electrically connected through the turning portion 63, thereby becoming substantially U-shaped.

[0089] In addition, as Figure 4 shown, a piezoelectric substrate 5 may include two or more filters including an elastic wave filter 51A. In Figure 4 the example shown, a transmission filter Tx is included in the area on the right side of the drawing, and a SAW filter 51A acting as a reception filter Rx is included in the area on the left side of the drawing.

[0090] In Figure 4 , compared with Figure 2 and Figure 3 , the shape of the SAW resonator 1 is represented in a further simplified manner. Specifically, the outer edge portion of the IDT electrode 7 is represented by a rectangle, and the illustration of the reflector 9 is omitted.

[0091] The transmission filter Tx and the SAW filter 51A share a terminal 31 as a terminal for transmitting and receiving signals from the antenna. That is, Figure 4 an example of a demultiplexer having two filters is shown. In the Tx filter, a plurality of SAW resonators 1 are connected in a ladder shape. Moreover, the series arm 53 does not have a bent portion and extends in one direction to a terminal 3Tx for inputting a transmission signal from the terminal 31. In other words, in the series resonator 1S, the positional relationship between the input side comb teeth electrode 11A and the output side comb teeth electrode 11B in a plan view is not configured to face in opposite directions.

[0092] In addition, the number of resonators of the SAW filter 51A is different from that of the SAW filter 51. Specifically, the SAW filter 51A includes series resonators 1S1 to 1S4 and parallel resonators 1P1 to 1P4. Since the series resonator 1S1 is located directly below the antenna, it becomes a split resonator, and in order to suppress lateral spurs, the direction in which the bus bar extends is inclined with respect to the direction (D2) perpendicular to the direction D1. The first turning portion 63A is located between the resonator 1S2 and the resonator 1S3, and the second turning portion 63B is located between the resonator 1S4 and the resonator 1P4. Moreover, the resonator 1S4 is closer to the first turning portion 63A (+D2) than the resonators 1S1 and 1P1, and the resonator 1P4 is located between the resonator 1S1 and the resonator 1P1.

[0093] The transmission filter Tx and the reception filter Rx are arranged in a direction orthogonal to the propagation direction of the SAW.

[0094] Here, the transmission filter Tx requires higher power than the reception filter Rx, and the number, size, etc. of the resonators constituting the transmission filter Tx may be larger than those of the resonators constituting the reception filter Rx. As a result, the area where the electrode group constituting the reception filter Rx is arranged (hereinafter referred to as the Rx area) is sometimes smaller than the area where the electrode group constituting the transmission filter is arranged (hereinafter referred to as the Tx area). For example, the Rx area is an area of 1 / 2 or less of the Tx area.

[0095] In this case, when using the surface acoustic wave filter 51 or 51A of the present disclosure as the reception filter, resonators can be arranged in a limited space without degrading the electrical characteristics. In addition, when the length of the reception filter in the D2 direction of the Rx area is shorter than the sum of the widths of the resonators constituting the reception filter in the D2 direction, the effect of providing a turning portion in the series arm 53 is particularly achieved.

[0096] (Verification of the effect)

[0097] As an example, in Figure 4 the shown demultiplexer, the filter characteristics of the SAW filter 51A are measured. Similarly, in addition, as a comparative example, a filter in which the arrangement of the resonators is not considered in the SAW filter 51A is manufactured, and the filter characteristics are measured. That is, in the reception filter related to the comparative example, the resonator close to the input terminal (31) and the resonator close to the output terminal (32) coincide in the D1 direction.

[0098] Figure 5 Indicates the filter characteristics. Figure 5 Indicates the transmission characteristics. The horizontal axis represents the frequency (unit: MHz). The vertical axis represents the transmission characteristics (unit: dB). The solid line represents the characteristics of the example. The dotted line represents the characteristics of the comparative example.

[0099] From Figure 5 it can be seen that in the reception filter using the SAW filter 51A of the present disclosure, it is confirmed that the attenuation characteristics on the low-frequency side of the passband are improved. Specifically, in the case of the comparative example, although multiple spurs are confirmed on the low-frequency side of the passband, the spurs are reduced in the example.

[0100] From the above, it can be confirmed that the SAW filter according to the present disclosure can provide a SAW filter with high attenuation characteristics and, as a result, excellent electrical characteristics.

[0101] (Application example of the surface acoustic wave filter: demultiplexer)

[0102] Figure 6It is a circuit diagram schematically showing the structure of a diplexer 101 (e.g., a duplexer) as an application example of a SAW filter 51 or 51A. As can be seen from the symbols shown in the upper left of the paper surface of this figure, in this figure, the comb-shaped electrode 11 is schematically represented by a bifurcated fork shape, and the reflector 9 is represented by a single wire with both ends bent. In addition, in this figure, the number of series resonators 1S and parallel resonators 1P is less than the number in Figure 2 and the specific configuration of the SAW resonator 1 on the piezoelectric substrate 5 (e.g., the S-shaped shape of the series arm) is omitted.

[0103] The diplexer 101 has, for example: a transmit filter 109 that filters the transmit signal from the transmit terminal 105 and outputs it to the antenna terminal 103; and a receive filter 111 that filters the receive signal from the antenna terminal 103 and outputs it to a pair of receive terminals 107.

[0104] In Figure 4 the example shown, an example of applying the SAW filter 51A in the receive filter is illustrated, but in this example, the transmit filter 109 is constituted by, for example, the SAW filter 51 (or 51A) of the embodiment. The transmit terminal 105 is the input terminal 31 or a terminal connected to the input terminal 31. The antenna terminal 103 is the output terminal 32 or a terminal connected to the output terminal 32.

[0105] The receive filter 111 is constituted by, for example, including the SAW resonator 1 and a multi-mode filter (assuming including a dual-mode filter.) 113. The multi-mode filter 113 has a plurality of (three in the illustrated example) IDT electrodes 7 arranged in the propagation direction of the elastic wave, and a pair of reflectors 9 arranged on both sides thereof. In addition, the SAW resonator 1 and the multi-mode filter 113 constituting the receive filter 111 are, for example, provided on the same piezoelectric substrate 5.

[0106] In addition, the transmit filter 109 and the receive filter 111 may be provided on the same piezoelectric substrate 5 or on different piezoelectric substrates 5. Figure 6 This is just an example of the structure of the diplexer 101. For example, the receive filter 111 may also be constituted by a ladder-type filter in the same way as the transmit filter 109. The diplexer 101 is not limited to a duplexer. For example, it may be a duplexer or a multiplexer including three or more filters.

[0107] (Application Example of Elastic Wave Device: Communication Device)

[0108] Figure 7This is a block diagram showing the main part of a communication device 151 as an application example of a SAW filter 51 (or a demultiplexer 101 from another perspective). The communication device 151 performs wireless communication using radio waves and includes a demultiplexer 101.

[0109] In the communication device 151, a transmission information signal TIS containing information to be transmitted is modulated and frequency - up - converted (converted to a high - frequency signal at the carrier frequency) by an RF - IC (Radio Frequency Integrated Circuit) 153 to form a transmission signal TS. The transmission signal TS removes unnecessary components outside the transmission passband through a band - pass filter 155, is amplified by an amplifier 157, and is input to the demultiplexer 101 (transmission terminal 105). Then, the demultiplexer 101 (transmission filter 109) removes unnecessary components outside the transmission passband from the input transmission signal TS, and outputs the processed transmission signal TS from the antenna terminal 103 to the antenna 159. The antenna 159 converts the input electrical signal (transmission signal TS) into a wireless signal (radio wave) for transmission.

[0110] In addition, in the communication device 151, the wireless signal (radio wave) received by the antenna 159 is converted into an electrical signal (received signal RS) by the antenna 159 and is input to the demultiplexer 101 (antenna terminal 103). The demultiplexer 101 (reception filter 111) removes unnecessary components outside the reception passband from the input received signal RS, and outputs it from the reception terminal 107 to the amplifier 161. The output received signal RS is amplified by the amplifier 161, and unnecessary components outside the reception passband are removed by a band - pass filter 163. Then, the received signal RS is frequency - down - converted and demodulated by the RF - IC 153 to form a received information signal RIS.

[0111] In addition, the transmission information signal TIS and the received information signal RIS can be low - frequency signals (baseband signals) containing appropriate information, such as analog voice signals or digitized voice signals. The passband of the wireless signal can be set appropriately according to various well - known specifications. The modulation method can be phase modulation, amplitude modulation, frequency modulation, or any combination of two or more of these. Although the direct conversion method is illustrated, the circuit method can also be set to other appropriate methods, such as the double superheterodyne method. In addition, Figure 7 This is a diagram only schematically showing the main part. A low - pass filter, isolator, etc. can be added at appropriate positions. In addition, the positions of amplifiers, etc. can also be changed.

[0112] In addition, in the above - mentioned embodiments and variations, the SAW filter 51 is an example of an elastic - wave filter.

[0113] The technology related to the present disclosure is not limited to the above embodiments and variations, and can be implemented in various ways.

[0114] For example, the elastic wave is not limited to SAW. The elastic wave can be an appropriate wave that can generally propagate along the propagation direction of the piezoelectric substrate. For example, it can be BAW (Bulk Acoustic Wave), elastic boundary wave, or plate wave (however, these waves may not necessarily be distinguishable from SAW).

[0115] As mentioned in the description of the embodiment, in the receiving filter, in the region of the filter body in the piezoelectric substrate, the length in the direction (D2 direction) orthogonal to the propagation direction of the elastic wave can be less than the sum of the lengths in the D2 direction of all the series resonators of the receiving filter and the sum of the lengths in the D2 direction of all the parallel resonators of the receiving filter (or less than or equal to the sum of these lengths). This length relationship can also be applied to filters for uses other than the receiving filter (such as a transmitting filter).

[0116] Symbol Explanation

[0117] 1S, series resonator; 1P, parallel resonator; 5, piezoelectric substrate; 51, SAW filter (elastic wave filter); 52, filter body; 53, series arm; 59A, first divided arm; 59B, second divided arm.

Claims

1. An elastic wave filter, comprising: a piezoelectric substrate; a first terminal; a second terminal; and a filter body on the piezoelectric substrate, having a series arm including a plurality of series resonators connected in series between the first terminal and the second terminal, and a plurality of parallel resonators connected in a ladder shape; The series arm has: a first divided arm extending from one side in a specified direction to the other side with respect to the piezoelectric substrate and including at least one of the series resonators, a second divided arm extending from the other side to the one side and including at least one of the series resonators, a third divided arm extending from the one side to the other side, a first turning portion electrically connecting the end portion on the other side of the first divided arm and the end portion on the other side of the second divided arm, a second turning portion electrically connecting the end portion on the one side of the second divided arm and the end portion on the one side of the third divided arm; Regions linearly extended along a straight line parallel to the propagation direction of the elastic wave from the series resonator closest to the first terminal side in the circuit among the plurality of series resonators and the parallel resonator closest to the first terminal side in the circuit among the plurality of parallel resonators do not overlap with the series resonator closest to the second terminal side in the circuit among the plurality of series resonators and the parallel resonator closest to the second terminal side in the circuit among the plurality of parallel resonators.

2. An elastic wave filter, comprising: a piezoelectric substrate; a first terminal; a second terminal; and a filter body on the piezoelectric substrate, having a series arm including a plurality of series resonators connected in series between the first terminal and the second terminal, and a plurality of parallel resonators connected in a ladder shape; The series arm has: a first divided arm extending from one side in a specified direction to the other side with respect to the piezoelectric substrate and including at least one of the series resonators, a second divided arm extending from a portion on the other side of the first divided arm to the one side and including at least one of the series resonators; Regions linearly extended along a straight line parallel to the propagation direction of the elastic wave from the series resonator closest to the first terminal side in the circuit among the plurality of series resonators and the parallel resonator closest to the first terminal side in the circuit among the plurality of parallel resonators do not overlap with the series resonator closest to the second terminal side in the circuit among the plurality of series resonators and the parallel resonator closest to the second terminal side in the circuit among the plurality of parallel resonators; In a region of the piezoelectric substrate where the filter body is located, the length in a direction orthogonal to the propagation direction of the elastic wave is less than or equal to the sum of the lengths of the plurality of series resonators in the direction orthogonal to the propagation direction of the elastic wave and the sum of the lengths of the plurality of parallel resonators in the direction orthogonal to the propagation direction of the elastic wave.

3. A diplexer, comprising: an antenna terminal; a transmit filter connected to the antenna terminal; and a receive filter connected to the antenna terminal; At least one of the transmit filter and the receive filter includes the elastic wave filter according to claim 1 or 2.

4. The demultiplexer according to claim 3, wherein only the receiving filter is constituted by the surface acoustic wave filter according to claim 1 or 2; The transmitting filter and the receiving filter share the piezoelectric substrate, and the transmitting filter has an electrode group located on the piezoelectric substrate; On the piezoelectric substrate, the area of the region where the filter body is located is less than or equal to half of the area of the region where the electrode group is located.

5. A communication device, comprising: The demultiplexer according to claim 3 or 4; An antenna connected to one end of the series arm; and An IC connected to the other end of the series arm.

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