JP2020098970A - Elastic surface wave element, splitter, and communication device - Google Patents

Abstract

To provide a SAW element that can reduce a loss near an antiresonance frequency.SOLUTION: In a SAW resonator 1, an IDT electrode 7 has a plurality of electrode fingers 17 extending in a D2 direction in parallel with each other on a top face 3a of a piezoelectric material 3. Reflectors 9 are located on both ends in a D1 direction with respect to one IDT electrode 7. At least one of a plurality of insertion conductors 11 is located on each of both ends in the D1 direction of the IDT electrode 7. Each of the plurality of insertion conductors 11 has an even number of insertion electrode fingers 25 and a pair of connection parts 27. The even number of insertion electrode fingers 25 extend in parallel with the plurality of electrode fingers 17. The pair of connection parts 27 connect the even number of insertion electrode fingers 25 with each other on both sides in the D2 direction. In each of the plurality of insertion conductors 11, the insertion electrode fingers 25 on both sides in the D1 direction of the even number of insertion electrode fingers 25 are adjacent to any ones of the plurality of electrode fingers 17.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a surface acoustic wave (SAW) element, a duplexer, and a communication device.

A SAW resonator having a piezoelectric substrate, an IDT (Interdigital Transducer) electrode located on the piezoelectric substrate, and a pair of reflectors located on the piezoelectric substrate and sandwiching the IDT electrode is known (for example, a SAW resonator). Patent Document 1). Patent Document 1 discloses a technique of reducing the loss in the vicinity of the anti-resonance frequency by shifting the reflector to the IDT electrode side with respect to the general arrangement position of the reflector.

Patent Documents 2 and 3 do not relate to a SAW resonator in which one IDT electrode is sandwiched by a pair of reflectors, but relate to a SAW filter in which a plurality of IDT electrodes are arranged. Patent Documents 2 and 2 disclose a technique of inserting an electrode finger for reflection into the IDT electrode. Patent Documents 2 and 3 advocate flattening in the pass band of the filter, improvement of insertion loss, improvement of steepness, etc. as effects by inserting such electrode fingers for reflection.

International Publication No. 2016/017730 JP 2002-353777 A Japanese Patent No. 2008-98902

It is desired to provide a surface acoustic wave element, a duplexer, and a communication device that can reduce the loss near the anti-resonance frequency.

A surface acoustic wave device according to an aspect of the present disclosure includes a piezoelectric body having a first surface that extends in a first direction and a second direction that intersects the first direction, and a piezoelectric body that has the first surface and the first surface. One IDT electrode having a plurality of electrode fingers extending in parallel in the second direction, and one IDT electrode located on both sides in the first direction with respect to the IDT electrode and adjacent to the IDT electrode. A pair of reflectors, and a plurality of insertion conductors, at least one of which is located at each end of the IDT electrode on both sides in the first direction, each of the plurality of insertion conductors being An even number of insertion electrode fingers extending in parallel to the plurality of electrode fingers, and a pair of connecting portions connecting the even number of insertion electrode fingers to each other at both ends in the second direction, In each of the plurality of insertion conductors, the insertion electrode fingers on both sides in the first direction of the even-numbered insertion electrode fingers are adjacent to any one of the plurality of electrode fingers.

A duplexer according to an aspect of the present disclosure includes an antenna terminal, a transmission filter that filters a transmission signal and outputs the transmission signal to the antenna terminal, and a reception filter that filters a reception signal from the antenna terminal. The transmission filter or the reception filter has the surface acoustic wave element.

A communication device according to an aspect of the present disclosure includes an antenna, the demultiplexer having the antenna terminal connected to the antenna, and an RF-IC electrically connected to the demultiplexer. doing.

According to the above configuration, the loss near the anti-resonance frequency can be reduced.

It is a top view which shows the structure of the SAW resonator which concerns on embodiment. It is a top view which shows a part of modification of the SAW resonator of FIG. 3A is a diagram showing frequency characteristics of impedance phase in the SAW resonator of FIG. 1, FIG. 3B is an enlarged view of a region Rb of FIG. 3A, and FIG. FIG. 4 is an enlarged view of a region Rc of FIG. 4(a), 4(b) and 4(c) are diagrams showing the influence of the pitch size of the insertion electrode fingers on the frequency characteristics of the impedance phase in the SAW resonator. FIG. 5A and FIG. 5B are diagrams showing impedance phases of SAW resonators according to a plurality of examples. FIG. 6A and FIG. 6B are diagrams showing Q values of SAW resonators according to a plurality of examples. It is a circuit diagram explaining the duplexer concerning an embodiment. It is a schematic diagram explaining a communication apparatus concerning an embodiment. It is a top view which shows the structure of the SAW resonator which concerns on a reference example. FIG. 10A and FIG. 10B are diagrams showing frequency characteristics of impedance phase in the SAW resonator according to the reference example.

[SAW resonator]
Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like in the drawings do not always match the actual ones.

The SAW element according to the present disclosure may be either upward or downward, but for convenience sake, in the following, an orthogonal coordinate system including the D1 axis, the D2 axis, and the D3 axis is defined, and The term "upper surface" or "lower surface" may be used with the positive side of the D3 axis as the upper side. The D1 axis is defined to be parallel to the propagation direction of the SAW propagating along the upper surface of the piezoelectric body described later, and the D2 axis is defined to be parallel to the upper surface of the piezoelectric body and orthogonal to the D1 axis. , D3 axis is defined to be orthogonal to the upper surface of the piezoelectric body.

(Overall structure of SAW resonator)
FIG. 1 is a plan view showing a configuration of a main part of a SAW resonator 1 which is an example of a SAW element. In this figure, for ease of illustration, the surface of the conductor layer 5 described later is hatched (that is, the surface that is not a cross section).

The SAW resonator 1 constitutes a so-called 1-port SAW resonator. For example, when an electric signal of a predetermined frequency is input from one of the two schematically illustrated terminals 51, the SAW resonator 1 causes resonance, and the resonance occurs. The output signal is output from the other of the two terminals 51.

The SAW resonator 1 has, for example, a piezoelectric body 3 and a conductor layer 5 located on the upper surface 3 a of the piezoelectric body 3. The conductor layer 5 has an IDT electrode 7, a pair of reflectors 9 located on both sides of the IDT electrode 7, and a plurality of insertion conductors 11 inserted in the IDT electrode 7. In addition to this, the conductor layer 5 may have a wiring and a terminal 51 that connect the IDT electrode 7 and the terminal 51.

(Piezoelectric body)
The piezoelectric body 3 is made of a single crystal having piezoelectricity. The single crystal is, for example, a lithium niobate (LiNbO ₃ ) single crystal or a lithium tantalate (LiTaO ₃ ) single crystal. The cut angle may be appropriately set depending on the type of SAW used and the like. For example, the piezoelectric body 3 has a rotation Y-cut X-propagation. That is, the X axis is parallel to the upper surface (D1 axis) of the piezoelectric body 3, and the Y axis is inclined at a predetermined angle with respect to the normal line of the upper surface of the piezoelectric body 3.

The structure, shape, dimensions, and the like of the piezoelectric body 3 may be appropriate. For example, the piezoelectric body 3 is configured in a layer shape (including a plate shape) having a constant thickness. Such a layered piezoelectric body 3 may be composed of, for example, a piezoelectric substrate that is basically used alone. Further, for example, the layered piezoelectric body 3 may be configured by the piezoelectric substrate which is a composite substrate having a piezoelectric substrate and a support substrate bonded to the lower surface of the piezoelectric substrate. Further, for example, the layered piezoelectric body 3 may be configured by a piezoelectric body film included in a multilayer film configured by laminating a plurality of thin films made of different materials. The thickness of the piezoelectric body 3 (direction D3) may be, for example, 0.05λ or more, 0.3λ or more, 1λ or more, or 3λ or more with reference to a wavelength λ (=2×p1) described later.

(Conductor layer)
The conductor layer 5 is formed of, for example, the same material and a constant thickness over the IDT electrode 7, the reflector 9, and the insertion conductor 11. However, the conductor layer 5 may be different in thickness and/or material from other portions in a part of the IDT electrode 7, the reflector 9 and the insertion conductor 11. In the description of the present embodiment, the conductor layer 5 has the former mode (constant thickness and the same material) unless otherwise specified.

The material of the conductor layer 5 may be, for example, metal. The metal may be of any suitable type, for example, aluminum (Al) or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an aluminum-copper (Cu) alloy. The conductor layer 5 may be composed of a plurality of metal layers. For example, a relatively thin layer made of titanium (Ti) may be provided between the Al or Al alloy and the piezoelectric body 3 in order to enhance the bondability between them. The thickness of the conductor layer 5 may be appropriately set according to the specifications required for the SAW resonator 1. For example, the thickness of the conductor layer 5 may be 0.005λ or more and 0.1λ or less.

(IDT electrode)
The IDT electrode 7 includes a pair of comb-teeth electrodes 13. Each comb-shaped electrode 13 includes, for example, a bus bar 15, a plurality of electrode fingers 17 extending in parallel from the bus bar 15, and a dummy electrode 19 protruding from the bus bar 15 between the plurality of electrode fingers 17. The pair of comb-teeth electrodes 13 are arranged so that the plurality of electrode fingers 17 mesh with each other (intersect). In other words, the comb-teeth electrode 13 has a plurality of electrode fingers 17 positioned in parallel with each other.

The bus bar 15 is, for example, formed in a long shape that extends linearly in the SAW propagation direction (D1 direction) with a substantially constant width, except for a recess 15r described later. The pair of bus bars 15 are opposed to each other in the direction (D2 direction) orthogonal to the SAW propagation direction. In addition, the bus bar 15 may change in width (besides the concave portion 15r) or may be inclined with respect to the SAW propagation direction.

Each of the electrode fingers 17 is, for example, formed in an elongated shape having a substantially constant width and linearly extending in a direction (D2 direction) orthogonal to the SAW propagation direction. In each comb-teeth electrode 13, the plurality of electrode fingers 17 are arranged in the SAW propagation direction. The plurality of electrode fingers 17 of the one comb-teeth electrode 13 and the plurality of electrode fingers 17 of the other comb-teeth electrode 13 are basically arranged alternately. In other words, the other electrode finger 17 is inserted in the one electrode finger 17.

The pitch p1 of the plurality of electrode fingers 17 (for example, the center-to-center distance between two electrode fingers 17 adjacent to each other; the same applies to the pitches pr and p2 described later) is basically constant in the IDT electrode 7. It should be noted that a part of the IDT electrode 7 may be provided with a narrow pitch part in which the pitch p1 is narrower than the other part, or a wide pitch part in which the pitch p1 is wider than the other part.

In the following description, when simply referred to as the pitch p1 or the pitch of the electrode fingers 17, unless otherwise specified, a portion (a plurality of electrode fingers) excluding a peculiar portion such as the narrow pitch portion or the wide pitch portion as described above. (Most of 17). Also, in the case where the plurality of electrode fingers 17 except for the peculiar portion have different pitches, the average value of the pitches of the plurality of electrode fingers 17 is set as the value of the pitch p1. May be used.

The number of electrode fingers 17 may be appropriately set according to the electrical characteristics required for the SAW resonator 1. Since FIG. 1 is a schematic diagram, the number of electrode fingers 17 is small. In practice, more electrode fingers 17 (for example, 50 or more) than shown may be arranged. The same applies to the reflective electrode fingers 23 of the reflector 9 described later.

The lengths of the plurality of electrode fingers 17 are, for example, equal to each other. The IDT electrode 7 may be so-called apodized, in which the lengths of the plurality of electrode fingers 17 (intersection widths from another perspective) change according to the position in the propagation direction. The length and width of the electrode finger 17 may be appropriately set according to required electrical characteristics and the like.

The dummy electrode 19 is, for example, formed in a shape having a substantially constant width and protruding in a direction orthogonal to the SAW propagation direction. The width is, for example, equal to the width of the electrode finger 17. The plurality of dummy electrodes 19 are arranged at the same pitch as the plurality of electrode fingers 17, and the tip of the dummy electrode 19 of the one comb-tooth electrode 13 is the tip of the electrode finger 17 of the other comb-tooth electrode 13. And are facing through a gap. The IDT electrode 7 may not include the dummy electrode 19.

(Reflector)
The pair of reflectors 9 are located on both sides of the IDT electrode 7 in the SAW propagation direction. The reflector 9 is formed in, for example, a lattice shape. That is, the reflector 9 has a pair of reflective bus bars 21 facing each other and a plurality of reflective electrode fingers 23 extending between the pair of reflective bus bars 21.

The shape and dimensions of the reflective bus bar 21 and the reflective electrode finger 23 are basically the same as those of the IDT electrode 7 except that both ends of the reflective electrode finger 23 are connected to the pair of reflective bus bars 21. It may be similar to the finger 17.

For example, the reflective bus bar 21 is generally formed in a long shape that linearly extends in the SAW propagation direction (D1 direction) with a constant width. Each of the reflective electrode fingers 23 is formed in an elongated shape having a constant width and extending linearly in a direction (D2 direction) orthogonal to the SAW propagation direction. Further, the plurality of reflective electrode fingers 23 are arranged, for example, in the SAW propagation direction and have the same length. The width of the plurality of reflective electrode fingers 23 is equal to the width of the plurality of electrode fingers 17, for example. The pitch pr of the plurality of reflective electrode fingers 23 is, for example, equal to the pitch p1 of the plurality of electrode fingers 17. The equivalence here may be, for example, in the case of |p1-pr|<Cp×p1 and Cp is 0.1, 0.05, or 0.01.

The number of the plurality of reflective electrode fingers 23 is set, for example, so that the reflectance of the SAW in the mode intended to be used is approximately 100% or more. The theoretical minimum required number is, for example, several to 10 or so, and is usually 20 or more or 30 or more with a margin.

Each reflector 9 is adjacent to the IDT electrode 7 in the SAW propagation direction. That is, the electrode finger 17 located at the most end of the IDT electrode 7 and the reflective electrode finger 23 located at the most IDT electrode 7 side of the reflector 9 are adjacent to each other. The pitch between the electrode finger 17 and the reflective electrode finger 23 adjacent to each other is, for example, equal to the pitch p1 of the plurality of electrode fingers 17. For equality here, the pitch between the electrode finger 17 and the reflective electrode finger 23 may be replaced with the pitch pr, and the formula in the case where the pitch pr is equal to the pitch p1 may be used.

The reflector 9 is electrically disconnected from the IDT electrode 7, for example. The reflector 9 may be in an electrically floating state (a state in which no potential is applied from the outside), or a reference potential may be applied. However, the reflector 9 may be electrically connected to one of the pair of comb-teeth electrodes 13 of the IDT electrode 7.

(Insert conductor)
Each insertion conductor 11 connects, for example, even-numbered (two in the example of FIG. 1) insertion electrode fingers 25 extending in parallel to the plurality of electrode fingers 17 and end portions of the even-numbered insertion electrode fingers 25. And a pair of connecting portions 27. From another point of view, the shape of the insertion conductor 11 is, for example, a rectangular shape (with two insertion electrode fingers 25) or a lattice shape (see FIG. 2; with four or more insertion electrode fingers 25) as a whole. is there. The connection portion between the insertion electrode finger 25 and the connection portion 27 (corner portion of the insertion conductor 11) may be regarded as any part of the insertion electrode finger 25 and the connection portion 27, but in the description of the present embodiment, For convenience, it is assumed to be a part of the connecting portion 27.

(Shape and dimensions of insertion electrode finger and connection part)
The shape and size of the insertion electrode finger 25 may be the same as that of the electrode finger 17, except for the length (D2 axis direction), for example. For example, the insertion electrode finger 25 is generally formed in a long shape having a constant width and linearly extending in the direction (D2 direction) orthogonal to the SAW propagation direction.

The length of the insertion electrode finger 25 may be set appropriately. For example, the insertion electrode finger 25 has a length equal to or larger than the cross width W of the plurality of electrode fingers 17. The crossing width is, for example, parallel to the electrode fingers 17 from the tip of one electrode finger 17 of the two electrode fingers 17 connected to different bus bars 15 and adjacent to each other to the tip of the other electrode finger 17. It is the distance in the right direction. In other words, the cross width is a length in which two electrode fingers 17 connected to different bus bars and adjacent to each other overlap each other when viewed in the SAW propagation direction. Then, for example, the insertion electrode finger 25 overlaps the entire region defined by the cross width when viewed in the SAW propagation direction and/or the extending direction of the bus bar 15 (in the present embodiment, the D1 direction). There is. The extending direction of the busbars 15 is, for example, a direction parallel to the mutually facing edge portions (excluding the concave portions 15r) of the pair of busbars 15.

Further, for example, the insertion electrode finger 25 has a length extending between the edges (excluding the recess 15r) of the pair of bus bars 15 that face each other. Then, for example, the insertion electrode finger 25 overlaps with both the electrode finger 17 and the dummy electrode 19 as a whole in the SAW propagation direction and/or in the extending direction of the bus bar 15. By doing so, the end portion of the insertion electrode finger 25 has the same structure as the dummy electrode, and it is possible to reduce the occurrence of loss due to the inhibition of the dummy electrode effect of confining the SAW in the resonator. ..

The width of the insertion electrode finger 25 is, for example, the same as the width of the electrode finger 17. The pitch p2 of the even number of insertion electrode fingers 25 in each insertion conductor 11 is equal to the pitch p1 of the plurality of electrode fingers 17, for example. The pitch between the insertion electrode fingers 25 and the electrode fingers 17 adjacent to each other is equal to the pitch of the plurality of electrode fingers 17. However, the width and pitch of the insertion electrode fingers 25 may be different from the width and pitch of the electrode fingers 17. For example, the pitch p2 of the insertion electrode fingers 25 may be made larger than the pitch p1 of the electrode fingers 17 and/or the pitch pr of the reflective electrode fingers 23. More specifically, for example, the pitch p2 may be 1.05 times or more and 1.15 times or less the pitch p1 and/or the pitch pr.

The shape of the connecting portion 27 may be set appropriately. In the illustrated example, the shape of the connection portion 27 is a rectangular shape that extends parallel to the SAW propagation direction and/or the extending direction of the bus bar 15 (in the present embodiment, the D1 direction). The length of the connecting portion 27 (the SAW propagation direction and/or the extending direction of the bus bar 15) is the length over the array of all the insertion electrode fingers 25 included in each insertion conductor 11. The width (D2 direction) of the connection portion 27 may be smaller than, equal to, or larger than the width (D1 direction) of the insertion electrode finger 25, for example.

(Number of insertion electrode fingers, etc.)
The plurality of insertion conductors 11 may have the same number of insertion electrode fingers 25 (the illustrated example) or different numbers. In each insertion conductor 11, the number of insertion electrode fingers 25 may be appropriately set as long as it is an even number. In the example of FIG. 1, the number of insertion electrode fingers 25 is two. In the example of FIG. 2, the number of insertion electrode fingers 25 is four. Although not particularly shown, the number of insertion electrode fingers 25 in each insertion conductor 11 may be an even number of 6 or more. The upper limit of the number of insertion electrode fingers 25 in each insertion conductor 11 may be, for example, a number smaller than the number of reflection electrode fingers 23 in one reflector 9, or 8 or 6.

The number of the insertion conductors 11 located at one end of the IDT electrode 7 in the D1 direction may be one or plural (three in the example of FIG. 1). Further, this number may be set in consideration of the number of insertion electrode fingers 25. For example, the number of insertion conductors 11 located at one end of the IDT electrode 7 may be set so that the total number of insertion electrode fingers 25 located at the one end is 16 or less. In this case, for example, when the insertion conductor 11 having the two insertion electrode fingers 25 is used, the number of the insertion conductors 11 located at one end may be 8 or less. Further, for example, when the insertion conductor 11 having the four insertion electrode fingers 25 is used, the number of the insertion conductors 11 located at one end may be 4 or less.

Each insertion conductor 11 is adjacent to the electrode finger 17 of the IDT electrode 7 on both sides in the SAW propagation direction. That is, among the even number of insertion electrode fingers 25 of each insertion conductor 11, the insertion electrode fingers 25 on both sides in the D1 direction are adjacent to the electrode fingers 17. In each of the insertion conductors 11, the plurality of insertion electrode fingers 25 do not have the electrode fingers 17 extending from the bus bar 15 therebetween, as is apparent from the fact that both ends in the D2 direction are connected by the connection portions 27. ..

From another point of view, it is the electrode fingers 17 and not the insertion electrode fingers 25 that are adjacent to the reflector 9. Further, in a mode in which two or more insertion conductors 11 are provided at one end of the IDT electrode 7, at least one electrode finger 17 is interposed between the insertion conductors 11, and the insertion conductors 11 are adjacent to each other. It doesn't fit.

The number of electrode fingers 17 located outside (on the reflector 9 side) of the insertion conductor 11 located at the end in the IDT electrode 7 may be set appropriately. For example, the number may be 5 or less, or 3 or less, and may be 1 or 2. The number of electrode fingers 17 located between the insertion conductors 11 may be set appropriately. For example, the number may be 5 or less, or 3 or less, and may be 1 or 2.

In the IDT electrode 7, the range in which all the insertion conductors 11 are arranged, in other words, the end of the IDT electrode 7 may be appropriately defined. For example, when the number of the electrode fingers 17 and the insertion electrode fingers 25 is counted from one end of the IDT electrode 7 (the electrode finger 17 adjacent to one of the reflectors 9), the first number is taken as one end. .. Further, when the number of the electrode fingers 17 and the insertion electrode fingers 25 is counted from the other end of the IDT electrode 7 (the electrode finger 17 adjacent to the other reflector 9), the second number up to the other number of the IDT electrode 7 is counted. And the end. At this time, each of the first number and the second number is, for example, 20 or less and 20% or less of the total number of the electrode fingers 17 and the insertion electrode fingers 25. In a mode where the total number exceeds 100, the end portion is defined by the condition of 20 or less, and in a mode where the total number is less than 100, the end portion is defined by the condition of 20% or less.

The insertion conductor 11 is electrically disconnected from the IDT electrode 7 and the reflector 9, for example. The insertion conductor 11 may be in an electrically floating state or may be given a reference potential. However, the insertion conductor 11 may be electrically connected to one of the pair of comb-teeth electrodes 13 of the IDT electrode 7, for example. In the following description, the insertion conductor 11 is not connected to either the IDT electrode 7 or the reflector 9 and is in an electrically floating state, unless otherwise specified.

(Shape corresponding to the insertion conductor of the bus bar)
The pair of bus bars 15 have recesses 15r that are opposed to the end portions of the insertion conductor 11 in the D2 direction in the edge portions that face each other in a plan view. The width of the recess 15r (D1 direction) is larger than the width of the insertion conductor 11 (the length of the connecting portion 27 in the D1 direction). As a result, the length of the insertion conductor 11 (of the insertion electrode finger 25) in the D2 direction can be increased while preventing the insertion conductor 11 and the bus bar 15 from being short-circuited.

The depth of the recess 15r (D2 direction) may be set, for example, so that a distance in the D2 direction between the insertion conductor 11 and the edge of the recess 15r facing the D2 direction can be appropriately secured. Similarly, the width of the recess 15r (D1 direction) may be set so as to appropriately secure the separation distance in the D1 direction between the insertion conductor 11 and the edge of the recess 15r facing the D1 direction. The separation distance may be approximately the same as the distance between the adjacent electrode fingers 17 and/or the distance between the tip of the electrode finger 17 and the tip of the dummy electrode 19, for example. The shape of the recess 15r may be an appropriate shape such as a rectangular shape.

In the illustrated example, the end portion of the insertion conductor 11 enters the recess 15r. However, the end of the insertion conductor 11 does not have to enter the recess 15r. Even in this case, the effect that the insertion conductor 11 can be lengthened in the D1 direction so as not to be short-circuited with the bus bar 15 is exhibited to some extent.

(Other configurations of SAW element)
Although not particularly shown, the upper surface 3a of the piezoelectric body 3 may be covered with a protective film made of SiO ₂ , Si ₃ N _4, or the like from above the conductor layer 5. The protective film may be a laminate of a plurality of layers made of these materials. The protective film may simply prevent corrosion of the conductor layer 5 or may contribute to temperature compensation. When a protective film is provided, an additional film made of an insulator or a metal may be provided on the upper surface or the lower surface of the IDT electrode 7 and the reflector 9 in order to improve the SAW reflection coefficient.

In the SAW resonator 1, the piezoelectric body 3 may be used alone as the substrate on which the conductor layer 5 is located, or a composite substrate including the thin piezoelectric body 3 and a supporting substrate directly or indirectly bonded thereto. May be.

The SAW resonator 1 may be packaged appropriately. The package may be, for example, one in which the piezoelectric body 3 is mounted on the substrate so that the upper surface 3a of the piezoelectric body 3 is opposed to the substrate (not shown) via a gap, and the resin is sealed from above. Alternatively, a wafer-level package type in which a box-shaped cover having a downward opening is placed on the upper surface 3a of the piezoelectric body 3 may be used. The lower portion of the cover may be located on the piezoelectric body 3 or, if there is another layer wider than the piezoelectric body 3 below the piezoelectric body 3, may be located on the other layer.

(Operation of SAW resonator)
When a voltage is applied to the pair of comb-teeth electrodes 13, a voltage is applied to the piezoelectric body 3 by the electrode fingers 17, and a predetermined mode of propagating in the D1 direction along the upper surface 3a near the upper surface 3a of the piezoelectric body 3 is generated. SAW is excited. The excited SAW is mechanically reflected by the electrode fingers 17. As a result, a standing wave having a pitch of the electrode fingers 17 of a half wavelength is formed. The standing wave is converted into an electric signal having the same frequency as the standing wave, and is taken out by the electrode finger 17. In this way, the SAW resonator 1 functions as a resonator. The resonance frequency is substantially the same as the frequency of the SAW propagating on the piezoelectric body 3 with the pitch p1 of the electrode fingers 17 as a half wavelength.

The SAW excited in the IDT electrode 7 is mechanically reflected by the reflective electrode finger 23 of the reflector 9. Further, since the reflective electrode fingers 23 adjacent to each other are connected to each other by the reflective bus bar 21, the SAW from the IDT electrode 7 is also electrically reflected by the reflective electrode fingers 23. Thereby, the divergence of SAW is suppressed, the standing wave in the IDT electrode 7 becomes strong, and the function of the SAW resonator 1 as a resonator is improved.

At the boundary between the IDT electrode 7 and the reflector 9, part of the SAW is converted into a bulk wave and leaks into the piezoelectric body 3. As a result, loss occurs near the anti-resonance frequency. The insertion conductor 11 contributes to the reduction of this loss.

(Example)
The characteristics of the SAW resonators according to the comparative example and the example were examined by simulation calculation using FEM (Finite Element Method). As a result, it has been confirmed that the loss is reduced in the vicinity of the antiresonance frequency by providing the insertion conductor 11. Specifically, it is as follows.

(Common simulation conditions)
The conditions common to the SAW resonators according to the comparative example and the example are shown below.
Piezoelectric body 3:
Material: LiTaO ₃
Thickness: infinity Cut angle: 42° rotation Y cut X propagation Conductor layer 5:
Material: Al
Thickness: 0.08λ
IDT electrode 7:
Total number of electrode fingers 17 and insertion electrode fingers 25: 100 pitch p1: 1 μm (λ=2 μm)
Duty: 0.5
Reflector 9:
Number of reflective electrode fingers 23: 30 for each reflector (60 in total)
Pitch pr: Same as pitch p1

As described above, the total number of the electrode fingers 17 and the insertion electrode fingers 25 is the same in the comparative example and the example. For example, in the comparative example having no insertion electrode finger 25, the number of electrode fingers 17 is 100. On the other hand, in the embodiment having 12 (=2×6 sets) insertion electrode fingers 25 as shown in FIG. 1, the number of electrode fingers 17 is 88 (=100-12). The duty is the ratio of the width of the electrode fingers 17 to the pitch p1 of the electrode fingers 17. In the case where a plurality of insertion conductors 11 are provided, unless otherwise specified, the configuration of the insertion conductor 11 (the number of insertion electrode fingers 25, the pitch, the duty, the number of electrode fingers 17 between the insertion conductors 11, etc.) is The same applies to a plurality of insertion conductors.

(Influence of presence or absence of insertion conductor)
FIG. 3A is a diagram showing a simulation result regarding the influence of the presence or absence of the insertion conductor on the characteristics of the SAW resonator. FIG. 3B is an enlarged view of the region Rb in FIG. FIG. 3C is an enlarged view of the region Rc in FIG.

In this figure, the horizontal axis represents frequency (MHz). The vertical axis represents the impedance phase θ (°). The line in the coordinate plane shows the characteristics of the SAW resonator according to the comparative example and the example. On the right side of FIG. 3A, the correspondence between the types of lines on the coordinate plane and the types of SAW resonators (Comparative Examples CE1 and CE2 and Example E1) is shown.

In the frequency band between the resonance frequency (around 1960 MHz in the illustrated example) and the anti-resonant frequency (around 2030 MHz in the illustrated example), the SAW resonator has less loss as the phase θ approaches 90°. In the SAW resonator, the loss is smaller as the phase θ approaches −90° outside the above frequency band.

The SAW resonators of Comparative Examples CE1 and CE2 do not have the insertion conductor 11. Further, in Comparative Example CE1, the pitch p1 of the electrode fingers 17, the pitch pr of the reflective electrode fingers 23, and the pitch between the IDT electrode 7 and the reflector 9 are all the same. On the other hand, in Comparative Example CE2, the pitch in the vicinity of the boundary between the IDT electrode 7 and the reflector 9 is narrower than the pitch in other portions (most portions) (pitch 0.92 μm). The other conditions are basically the same between Comparative Examples CE1 and CE2 and Example E1.

The conditions relating to the insertion conductor 11 in Example E1 are as follows.
Number of insertion conductors 11 at each end: 3 Number of insertion electrode fingers 25 in each insertion conductor 11: 2 Pitch of insertion electrode fingers 25 p2: 1.0×p1
The number of electrode fingers 17 located outside the outermost insertion conductor 11 at each end: 1
Number of electrode fingers 17 located between two adjacent insertion conductors 11 at each end: 2

As indicated by the arrow y1 in FIG. 3B, the comparative example CE2 and the example E1 have a phase θ near the anti-resonance frequency and on the resonance frequency side (low frequency side) as compared with the comparative example CE1. Is close to 90°, and the loss is reduced. Further, as indicated by the arrow y2 in FIG. 3C, the comparative example CE2 and the example E1 are near the anti-resonance frequency and on the opposite side (high frequency) from the comparative example CE1. The phase θ on the side) is close to −90°, and the loss is reduced.

However, as indicated by the arrow y3 in FIG. 3B, the comparative example CE2 has a phase θ close to the resonance frequency and 90 degrees on the anti-resonance frequency side (high frequency side) as compared with the comparative example CE1. It is far from ° and the loss is large. On the other hand, in Example E1, almost no such loss occurs or the loss is reduced.

Further, as indicated by an arrow y4 in FIG. 3C, Comparative Example CE2 is closer to the resonance frequency and on the side opposite to the anti-resonance frequency side (lower frequency side) than Comparative Example CE1. The ripple (wave in which the phase θ sharply rises from the −90° side to the 90° side) is large. On the other hand, in Example E1, such ripples are smaller than in Comparative Example CE2.

Further, as indicated by an arrow y5 in FIG. 3B, in Comparative Example CE2, as compared with Comparative Example CE1, the rise of phase θ in the vicinity of the resonance frequency to 90° is on the anti-resonance frequency side ( There is a slight shift to the high frequency side. From another viewpoint, the frequency difference df between the resonance frequency and the anti-resonance frequency is slightly smaller. On the other hand, in Example E1, such shift is reduced as compared with Comparative Example CE2.

As described above, in the example E1, the loss in the vicinity of the anti-resonance frequency is reduced as compared with the comparative example CE1, and the characteristic deterioration in the vicinity of the resonant frequency is reduced as compared with the comparative example CE2.

(Influence of pitch size of insertion electrode fingers)
FIG. 4A, FIG. 4B and FIG. 4C are diagrams showing simulation results regarding the influence of the size of the pitch p2 of the insertion electrode fingers 25 on the characteristics of the SAW resonator. These drawings are similar to FIGS. 3(a), 3(b) and 3(c). On the right side of FIG. 4A, the correspondence between the types of lines on the coordinate plane and the types of SAW resonators (Comparative Example CE1 and Examples E2 to E5) is shown.

Comparative example CE1 is the same as comparative example CE1 shown in FIGS. 3(a) to 3(c). The examples E2 to E5 are basically different from the comparative example CE1 only in the configuration related to the insertion conductor 11. In addition, in Examples E2 to E5, the pitch p2 of the insertion electrode fingers 25 is different from each other. Specifically, the size of the pitch p2 in each example is E2:1×p1, E3:1.05×p1, E4:1.10×p1, when the pitch p1 of the electrode fingers 17 is used. E5: 1.15×p1. The conditions other than the pitch p2 are basically the same between Examples E2 to E5.

In Examples E2 to E5, the conditions regarding the insertion conductor 11 are as follows.
Number of insertion conductors 11 at each end: 3 Number of insertion electrode fingers 25 in each insertion conductor 11: 2 Number of electrode fingers 17 located outside the outermost insertion conductor 11 at each end: 1
Number of electrode fingers 17 located between two adjacent insertion conductors 11 at each end: 2

As indicated by the arrow y11 in FIG. 4A and the arrow y12 in FIG. 4C, increasing the pitch p2 of the insertion electrode fingers 25 can reduce the ripple near the resonance frequency. it can. In the illustrated example, when the pitch p2 is 1.1 times or more the pitch p1, the ripple can be reduced as compared with the comparative example CE1.

(Influence of the number of inserted conductors, etc.)
5(a), 5(b), 6(a) and 6(b) are diagrams showing simulation results regarding the influence of the number of insertion conductors 11 and the like on the characteristics of the SAW resonator. ..

In these figures, the horizontal axis represents a value df/fr×100 (%) obtained by dividing the frequency difference df (=fa-fr) between the resonance frequency fr and the anti-resonance frequency fa by the resonance frequency fr and normalizing the value. There is. There are various methods for reducing df, such as a method of connecting a capacitor in parallel to the IDT electrode 7. On the other hand, as described with reference to FIG. 3B, the SAW resonator 1 of the example is likely to have a smaller df than the comparative example. Therefore, in this embodiment, it is assumed that the larger the df, the better the characteristics. In the comparative example and the example, the resonance frequency fr is within the range of 1961 MHz or more and 1967 MHz or less.

The vertical axis of FIG. 5A indicates the minimum value θmin (°) of the phase θ on the side opposite to the resonance frequency (higher frequency side) than the anti-resonance frequency. The smaller the value (closer to −90°), the smaller the loss.

The vertical axis of FIG. 5B indicates the value of the phase θ near the anti-resonance frequency and on the resonance frequency side (low frequency side). Specifically, the value of the phase θ at a frequency lower than the antiresonance frequency by 5 MHz (about 2.5% of the resonance frequency fr) is shown. The larger the value (closer to 90°), the smaller the loss.

The vertical axis in each of FIGS. 6A and 6B represents a Q value (Quality factor; referred to as Qa in the figure) at the anti-resonance frequency. The Q value in FIG. 6A is obtained by a method of calculating from the slope of the phase of the impedance near the anti-resonance. The Q value in FIG. 6B is obtained by a method based on Bode's theory. In the SAW resonator, a high Q value indicates a small loss.

The upper part of each figure shows the correspondence between the plot type and the SAW resonator type (Comparative Example CE1 and Examples E11 to E17). This correspondence is common in FIG. 5(a), FIG. 5(b), FIG. 6(a) and FIG. 6(b).

The comparative example CE1 is the same as the comparative example CE1 shown in FIG. In Examples CE11 to 17, the number of insertion conductors 11 at each end of the IDT electrode 7 (denoted by Na) and the number of electrode fingers 17 located between the adjacent insertion conductors 11 at each end of the IDT electrode 7 are provided. (Nb), the number of electrode fingers 17 (Nc) located outside the outermost insertion conductor 11 at each end of the IDT electrode 7 is different from each other. Further, E11 to E16 have two insertion electrode fingers 25 (Nd) forming each insertion conductor 11, and E17 has four. What is shown as one type of embodiment in the drawing includes a plurality of embodiments in which the number Nb of the electrode fingers 17 between the insertion conductors 11 is different from each other. These different conditions are as follows.

Example E11:
Na: 2
Nb: 1, 2, 3, 4 or 5 (Example E11 includes 5 Examples)
Nc: 1
Nd: 2
Example E12:
Na: 3
Nb: 1, 2, 3 or 4 (Example E12 includes 4 Examples)
Nc: 1
Nd: 2
Example E13:
Na: 4
Nb: 1, 2 or 3 (Example E13 includes 3 Examples)
Nc: 1
Nd: 2
Example E14:
Na: 3
Nb: 1-2, 2-4 or 3-6 (Example E14 includes three examples)
Nc: 1
Nd: 2
Example E15:
Na: 3
Nb: 1, 2, 3 or 4 (Example E15 includes 4 Examples)
Nc: 2
Nd: 2
Example E16:
Na: 3
Nb: 1, 2, 3 or 4 (Example E16 includes 4 Examples)
Nc: 3
Nd: 2
Example E17:
Na: 2
Nb: 1, 2, 3 or 4 (Example E17 includes 4 Examples)
Nc: 1
Nd: 4

In Examples E11, E12, and E13, the number Na of insertion conductors 11 is 2, 3 or 4, respectively. Therefore, for example, the influence of the number Na of the insertion conductors 11 can be seen from these comparisons.

In one embodiment (one IDT electrode 7), when three or more insertion conductors 11 are provided at each end of the IDT electrode 7, there are also two or more gaps between the insertion conductors 11. The numbers Nb of the electrode fingers 17 located in the gaps of 2 or more are the same except for the embodiment E14. In the embodiment E14, the number of the electrode fingers 17 is different between the gaps such that Nb=1 in one of the two gaps and Nb=2 in the other while Na=3 as in the case of the embodiment E12. .. The numbers of these two types of Nb are shown as 1-2, 2-4, and 3-6 in the above. Therefore, for example, from the comparison of Examples E12 and E14, it is possible to see the influence when the number Nb is made different in one IDT electrode 7.

In the examples E15 and E16, the number Nc of the electrode fingers 17 outside the insertion conductor 11 is different from each other while Na=3 as in the case of the example E12. Thus, for example, the effect of the number Nc can be seen from a comparison of Examples E12, E15 and E16.

In Example E17, the number (Nd) of the insertion electrode fingers 25 forming each insertion conductor 11 was set to 4, and the effect of the number of insertion electrode fingers 25 can be seen by comparing with E13.

In Examples E11 to E17, the conditions other than the insertion conductor 11 were the same as those in Comparative Example CE1. The conditions regarding the insertion conductor 11 common to Examples E11 to E17 are as follows.
Pitch of insertion electrode finger 25 p2:1×p1

As shown in these drawings, in Examples E11 to E16, the loss in the vicinity of the antiresonance frequency was reduced as compared with Comparative Example CE1. Further, in Example E17, the loss on the high frequency side near the anti-resonance frequency (FIG. 5A) is reduced as compared to Comparative Example CE1, but the loss on the low frequency side near the anti-resonance frequency (FIG. 5(b)). )) is equivalent to Comparative Example CE1. That is, in all the illustrated examples, the loss in the vicinity of the antiresonance frequency is suppressed to be approximately equal to or less than the loss in the comparative example CE1.

Therefore, for example, from FIG. 5A to FIG. 6B, it was confirmed that the effect of loss reduction in the vicinity of the anti-resonance frequency is exhibited even under the following conditions. The number Na of the insertion conductors 11 is 2 or more and 4 or less. The number Nb of electrode fingers 17 between the insertion conductors 11 is 1 or more and 3 or less. The number Nc of the electrode fingers 17 outside the insertion conductor 11 is 1 or more and 3 or less.

In Examples E11 to E17, examples in which the number of the electrode fingers 17 and the insertion electrode fingers 25 from one end of the IDT electrode 7 to the insertion electrode finger 25 located at the innermost side (denoted by Ne) are large are as follows. be able to. Nb=4 (Ne=21) of Example E17, Nb=3 (Ne=18) of Example E13 or E17, and Nb=4 (Ne=17) of Example E16. Therefore, if all the insertion conductors 11 are located within the range from one end of the IDT electrode 7 to the position where the number of the electrode fingers 17 and the insertion electrode fingers 25 is 20, counting from the one end, the anti-resonance frequency is reached. It was confirmed that the effect of loss reduction in the vicinity was obtained. In the embodiment, the total number of the electrode fingers 17 and the insertion electrode fingers 25 (Nt) in one IDT electrode 7 is 100. Therefore, the electrode fingers are counted from one end of the IDT electrode 7 and counted from the one end. It was confirmed that the loss reduction effect near the anti-resonance frequency can be obtained if all the insertion conductors 11 are positioned within a range up to the position where the number of 17 and insertion electrode fingers 25 is 20% of the total number Nt. ..

Further, from the comparison of Examples E11 to E13, it can be seen that when the number of insertion conductors 11 is increased, the effect of reducing the loss in the vicinity of the anti-resonance frequency tends to be improved.

As described above, in the present embodiment, the SAW element (SAW resonator 1) has the piezoelectric body 3, the IDT electrode 7, the pair of reflectors 9, and the plurality of insertion conductors 11. The piezoelectric body 3 has a first surface (upper surface 3a) extending in a first direction (D1 direction) and a second direction (D2 direction) intersecting the D1 direction. The IDT electrode 7 has a plurality of electrode fingers 17 extending in the D2 direction in parallel with each other on the upper surface 3a of the piezoelectric body 3. The reflectors 9 are located on both sides of the one IDT electrode 7 in the D1 direction and are adjacent to the one IDT electrode 7. At least one of the plurality of insertion conductors 11 is located at each end of the IDT electrode 7 on both sides in the D1 direction. Each of the plurality of insertion conductors 11 has an even number of insertion electrode fingers 25 and a pair of connection portions 27. The even number of insertion electrode fingers 25 extend in parallel to the plurality of electrode fingers 17. The pair of connecting portions 27 connect the even number of insertion electrode fingers 25 to each other at both ends in the D2 direction. In each of the plurality of insertion conductors 11, the insertion electrode fingers 25 on both sides in the D1 direction of the even number of insertion electrode fingers 25 are adjacent to any of the plurality of electrode fingers 17.

Therefore, as shown in the embodiment, by providing the insertion conductor 11, the SAW leakage near the boundary between the IDT electrode 7 and the reflector 9 can be reduced, and the loss near the anti-resonance frequency can be reduced. Moreover, as compared with the mode in which the pitch of the electrode fingers 17 and/or the reflective electrode fingers 23 near the boundary between the IDT electrode 7 and the reflector 9 is reduced, the characteristic deterioration near the resonance frequency can be reduced. Specifically, in the vicinity of the resonance frequency, the loss is reduced, the ripple is reduced, and the degree of df is also suppressed.

A range from one end of the IDT electrode 7 to a position where the number of the electrode fingers 17 and the insertion electrode fingers 25 counted from the one end becomes the first number, and from the other end of the IDT electrode 7 to the electrode counted from the other end. It is assumed that all the insertion electrode fingers 25 are located within a range up to the position where the numbers of the fingers 17 and the insertion electrode fingers 25 become the second number. At this time, each of the first number and the second number may be 20 or less and 20% or less of the total number of the electrode fingers 17 and the insertion electrode fingers 25.

In this case, for example, as shown in FIG. 5A, the effect of reducing the loss in the vicinity of the anti-resonance frequency is achieved. Further, as compared with the mode in which the insertion electrode fingers 25 are arranged up to the center side of the IDT electrode 7, the reduction in the number of electrode fingers 17 due to the insertion of the insertion electrode fingers 25 can be suppressed, so that the number of electrode fingers 17 can be reduced. The characteristic deterioration due to the reduction is reduced.

Further, the SAW resonator 1 may have two or more insertion conductors 11 at both ends of the IDT electrode 7 on both sides in the D1 direction. In this case, for example, the effect of reducing the loss in the vicinity of the anti-resonance frequency is improved as compared with the case where there is one insertion conductor 11.

The SAW resonator 1 may have only four insertion conductors 11 at both ends of the IDT electrode 7 on both sides in the D1 direction. Further, each of the total eight insertion conductors 11 may have only two insertion electrode fingers 25.

In this case, the number of insertion conductors 11 is relatively large, and it is expected that the effect of loss reduction near the anti-resonance frequency is improved. On the other hand, since the number of insertion electrode fingers 25 is suppressed to eight per one end of the IDT electrode 7, the characteristic deterioration due to the reduction of the number of electrode fingers 17 is reduced.

Further, the SAW resonator 1 may have only two insertion conductors 11 at both ends of the IDT electrode 7 on both sides in the D1 direction. Each of the four insertion conductors 11 in total may have only four insertion electrode fingers 25.

In this case, since the number of insertion electrode fingers 25 included in one insertion conductor 11 is relatively large, it is expected that the effect of reducing the loss in the vicinity of the anti-resonance frequency is improved. On the other hand, since the number of insertion electrode fingers 25 is suppressed to eight per one end of the IDT electrode 7, the characteristic deterioration due to the reduction of the number of electrode fingers 17 is reduced.

Further, in the present embodiment, the reflector 9 has a plurality of reflective electrode fingers 23 extending in parallel with each other in the D2 direction. When the pitch of the plurality of electrode fingers 17 is p1, the pitch of the plurality of reflective electrode fingers 23 is pr, and the pitch of the plurality of insertion electrode fingers 25 is p2, |p1-pr|<0.1×p1, p2> It is possible that p1 and p2>pr.

In this case, for example, as described with reference to FIG. 4C, the ripple generated near the resonance frequency can be reduced. As a result, for example, the characteristics are improved both near the resonance frequency and near the anti-resonance frequency.

In addition, in the present embodiment, the plurality of insertion conductors 11 are not connected to the IDT electrode 7. In this case, for example, compared to the case where the insertion conductor 11 is connected to the IDT electrode 7, it is possible to suppress the degree of decrease in df.

Further, in the present embodiment, the IDT electrodes 7 are located on both sides in the D2 direction with respect to the plurality of electrode fingers 17, and a pair of bus bars to which a part or the rest of the plurality of electrode fingers 17 are respectively connected. Have 15. The pair of bus bars 15 has a plurality of recesses 15r facing the plurality of insertion conductors 11.

Therefore, the insertion conductor 11 can be lengthened in the D2 direction so as not to short-circuit the insertion conductor 11 and the bus bar 15. As a result, when viewed in the SAW propagation direction and/or the extension direction of the bus bar 15 (D1 direction in the embodiments), the overlap between the electrode finger 17 (and the dummy electrode 19) and the insertion electrode finger 25 is increased. The effect of providing the insertion conductor 11 can be improved.

In any of the configurations, it has been confirmed that when the number of the insertion electrode fingers 25 forming one insertion conductor 11 is an odd number, a large ripple is generated near the resonance frequency. Also, in any of the configurations, it has been confirmed that the waveform is significantly disturbed even when the connecting portion 27 is removed and the insertion electrode finger 25 is opened. From this, it is possible to obtain the effect of the above-described embodiment by setting the number of the insertion electrode fingers 25 constituting one insertion conductor 11 to be an even number and providing the connecting portion 27 to short-circuit the insertion electrode fingers 25. I understand.

[Example of use of SAW resonator: duplexer]
FIG. 7 is a circuit diagram schematically showing the configuration of the duplexer 101 as an example of using the SAW resonator 1. As can be seen from the reference numerals shown in the upper left of the drawing, the comb-teeth electrode 13 is schematically shown by a forked shape in this figure, and the reflector 9 is a single line bent at both ends. It is represented by. Here, the illustration of the insertion conductor 11 is omitted.

The demultiplexer 101 filters, for example, a transmission signal from the transmission terminal 105 and outputs the signal to the antenna terminal 103, and a reception signal from the antenna terminal 103 to output to the pair of reception terminals 107. It has a reception filter 111.

The transmission filter 109 is configured by, for example, a ladder type filter configured by connecting a plurality of SAW resonators 1 in a ladder type. That is, the transmission filter 109 includes a plurality of (one may be one) SAW resonators 1 (series SAW resonators 1S) connected in series between the transmission terminal 105 and the antenna terminal 103, and a series line (series). It has a plurality of SAW resonators 1 (parallel SAW resonators 1P; parallel arms from another perspective) that connect the arms to the reference potential. The plurality of SAW resonators 1 forming the transmission filter 109 are provided on the upper surface 3a of the same piezoelectric body 3, for example.

The plurality of series SAW resonators 1S basically have resonance frequencies fr that are equal to each other and anti-resonance frequencies fa that are equal to each other. Basically, the plurality of parallel SAW resonators 1P have resonance frequencies fr that are equal to each other and anti-resonance frequencies fa that are equal to each other. In the series SAW resonator 1S and the parallel SAW resonator 1P, the resonance frequency fr and the anti-resonance frequency fa are set so that the resonance frequency fr of the series SAW resonator 1S and the anti-resonance frequency fa of the parallel SAW resonator 1P substantially match. To be done. As a result, the transmission filter 109 functions as a filter having a pass band in a range slightly narrower than the frequency range (attenuation range) from the resonance frequency fr of the parallel SAW resonator 1P to the anti-resonance frequency fa of the series SAW resonator 1S. .. The width of the attenuation region is approximately the sum of the frequency difference df of the parallel SAW resonator 1P and the frequency difference df of the series SAW resonator 1S. The frequency arrangement, the number of IDTs, and the crossing width of each of these resonators are appropriately set so that the desired filter characteristics are exhibited.

The reception filter 111 includes, for example, the SAW resonator 1 and a multimode filter (including a double mode filter) 113. The multimode filter 113 has a plurality of (three in the illustrated example) IDT electrodes 7 arranged in the SAW propagation direction, and a pair of reflectors 9 arranged on both sides thereof. The SAW resonator 1 and the multimode filter 113 that form the reception filter 111 are provided on the upper surface 3 a of the same piezoelectric body 3, for example. The transmission filter 109 and the reception filter 111 may be provided on the upper surface 3a of the same piezoelectric body 3 or may be provided on the upper surfaces 3a of the piezoelectric bodies 3 different from each other.

FIG. 7 is merely an example of the configuration of the demultiplexer 101. Therefore, for example, the reception filter 111 may be configured by a ladder type filter like the transmission filter 109. Further, capacitors and/or inductors may be provided at appropriate positions. Further, as the duplexer 101, the duplexer including the transmission filter 109 and the reception filter 111 has been described, but the duplexer (multiplexer) may include three or more filters. Although it has been described that all of the plurality of SAW resonators are configured by the SAW resonator 1 of the embodiment, only some of the SAW resonators may be configured by the SAW resonator 1 of the embodiment.

[Example of use of SAW resonator: communication device]
FIG. 8 is a block diagram showing a main part of a communication device 151 as a usage example of the SAW resonator 1. The communication device 151 performs wireless communication using radio waves and includes the duplexer 101.

In the communication device 151, a transmission information signal TIS including information to be transmitted is modulated and frequency is increased (converted into a high frequency signal having a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153, and the transmission signal TS is transmitted. It is said that. The transmission signal TS has unnecessary components other than the transmission pass band removed by the band pass filter 155, is amplified by the amplifier 157, and is input to the demultiplexer 101 (transmission terminal 105). Then, the demultiplexer 101 (transmission filter 109) removes unnecessary components other than the transmission pass band from the input transmission signal TS, and outputs the removed transmission signal TS from the antenna terminal 103 to the antenna 159. .. The antenna 159 converts the input electric signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

Further, in the communication device 151, a radio signal (radio wave) received by the antenna 159 is converted into an electric signal (received signal RS) by the antenna 159 and input to the duplexer 101 (antenna terminal 103). The demultiplexer 101 (reception filter 111) removes unnecessary components other than the reception pass band from the input reception signal RS and outputs it from the reception terminal 107 to the amplifier 161. The output reception signal RS is amplified by the amplifier 161, and unnecessary components other than the reception pass band are removed by the band pass filter 163. Then, the reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 153 to be a reception information signal RIS.

The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, and are, for example, analog voice signals or digitized voice signals. The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. Although the direct conversion method is illustrated in FIG. 8 as the circuit method, any other suitable circuit method may be used, and for example, a double superheterodyne method may be used. Further, FIG. 8 schematically shows only a main part, and a low-pass filter, an isolator or the like may be added at an appropriate position, or the position of the amplifier or the like may be changed.

In the above embodiment, the D1 direction is an example of the first direction. The D2 direction is an example of the second direction. The upper surface 3a of the piezoelectric body 3 is an example of the first surface. The SAW resonator 1 is an example of a SAW element. Each of the transmission filter 109, the reception filter 111, and the demultiplexer 101 may be regarded as an example of a SAW element or a usage example of a SAW element.

The technology according to the present disclosure is not limited to the above embodiments and may be implemented in various modes.

In the description of the embodiment, the configuration in which the pitch in the vicinity of the boundary between the IDT electrode and the reflector is reduced has been described as a comparative example. However, such a configuration may be combined with the insertion conductor.

In addition, the example of the above-described embodiment describes a case where an insertion conductor that is not connected to the IDT electrode is positioned at the end of the IDT electrode in order to reduce the leakage of SAW at the boundary between the IDT electrode and the reflector. However, this is not the case.

For example, as shown in FIG. 9, the electrode finger 17 of the IDT electrode 7 may be omitted and weighted at the end of the IDT electrode 7. In other words, the electrode fingers 17 connected to the same potential may be “thinned” at the ends of the IDT electrodes 7 so as to be adjacent to each other. Specifically, in FIG. 9, a plurality (three in this example) of the electrode fingers 17 of the IDT electrode 7 that are adjacent to the reflector 9 are continuously connected to one of the electrode fingers 17, and Next to that, a plurality of electrode fingers (three in this example) connected to the other potential are continuously positioned. In the first three electrode fingers of this example, the electrode finger 17 adjacent to the reflector 9 is a part of the IDT electrode 7, and the two electrode fingers adjacent thereto constitute the insertion electrode finger 25. Can be considered equivalent to The dummy electrodes are not shown in FIG.

Even with such a configuration, it is possible to reduce the loss between the resonance frequency and the anti-resonance frequency as shown in FIG. 10 and also reduce the loss on the high frequency side of the anti-resonance frequency. Note that FIG. 10A is a diagram corresponding to FIG. 3B, and FIG. 10B is an enlarged diagram near the arrow y2 in FIG. 3C. Similar to FIG. 3, Model 1 is a model of a normal resonator that does not include an insertion conductor or a thinning portion, and Model 2 is a model in which thinning is evenly distributed in the entire area of the IDT electrode 7 instead of only in the end portion. The model 3 is a model in which the thinning portion is provided only near the end portion. In the figure, the phase characteristic of the model 1 is shown by a solid line, the phase characteristic of the model 2 is shown by a long broken line, and the phase characteristic of the model 3 is shown by a short broken line.

As is clear from FIG. 10, the model 3 can provide a SAW element with reduced loss as compared with the models 1 and 2. It should be noted that although the normal thinning-out reduces Δf, the effect of reducing Δf in Model 3 was small even if the thinning-out was performed. Further, in the model 3, ripples may occur on the lower frequency side than the resonance frequency. On the other hand, the pitch pr of the reflector 9 is 1.002 times to 1.03 times p1, or the electrode finger center distance between the IDT electrode and the reflector is 1.05 times to 1.4 times p1. The ripple can be reduced by doubling it.

Further, the insertion conductor and the thinning at the end may be combined. Specifically, the electrode fingers between the insertion conductor and the reflector may be used as the thinning portion.

From the above, the following concept different from the present invention can be extracted.
[Invention 1]
A piezoelectric body having a first surface extending in a first direction and a second direction intersecting the first direction;
One IDT electrode having a plurality of electrode fingers extending in the second direction in parallel with each other on the first surface;
A pair of reflectors located on both sides of the IDT electrode in the first direction and adjacent to the IDT electrode;
An omission weighting section, at least one of which is located in each of the regions continuous from both ends of the IDT electrode in the first direction;
Has
The omission weighting unit,
The plurality of electrode fingers includes a first electrode finger connected to a first potential and a second electrode finger connected to a second potential,
A surface acoustic wave device in which a portion where a plurality of the first electrode fingers are adjacent to each other and a portion where a plurality of the second electrode fingers are adjacent to each other are positioned adjacent to each other.

DESCRIPTION OF SYMBOLS 1... SAW resonator (SAW element), 3... Piezoelectric body, 3a... Top surface (first surface) of piezoelectric body, 7... IDT electrode, 9... Reflector, 11... Insert conductor, 17... Electrode finger, 25... Insert Electrode fingers, 27... Connection part.

Claims (10)

A piezoelectric body having a first surface extending in a first direction and a second direction intersecting the first direction;
One IDT electrode having a plurality of electrode fingers extending in the second direction in parallel with each other on the first surface;
A pair of reflectors located on both sides in the first direction with respect to the IDT electrode and adjacent to the IDT electrode;
A plurality of insertion conductors, at least one of which is located at each of both ends of the IDT electrode in the first direction,
Has
Each of the plurality of insertion conductors,
An even number of insertion electrode fingers extending in parallel with respect to the plurality of electrode fingers,
And a pair of connection parts that connect the even number of insertion electrode fingers to each other at both ends in the second direction,
In each of the plurality of insertion conductors, the insertion electrode fingers on both sides in the first direction of the even number of insertion electrode fingers are adjacent to any one of the plurality of electrode fingers. The range from one end of the IDT electrode to a position where the number of the electrode fingers and the insertion electrode fingers is the first number counted from the one end, and the other end of the IDT electrode is counted from the other end. All the insertion electrode fingers are located in a range up to a position where the number of the electrode fingers and the insertion electrode fingers is the second number,
The surface acoustic wave device according to claim 1, wherein each of the first number and the second number is 20 or less and 20% or less of a total number of the electrode fingers and the insertion electrode fingers. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device has two or more insertion conductors at both ends of the IDT electrode on both sides in the first direction. The IDT electrode has only four insertion conductors at each end on both sides in the first direction,
The surface acoustic wave device according to claim 3, wherein each of the eight insertion conductors in total has only two insertion electrode fingers. The IDT electrode has only two insertion conductors at each end on both sides in the first direction,
The surface acoustic wave device according to claim 3, wherein each of the four insertion conductors in total has only four insertion electrode fingers. The reflector has a plurality of reflective electrode fingers extending in parallel to each other in the second direction,
When the pitch of the plurality of electrode fingers is p1, the pitch of the plurality of reflective electrode fingers is pr, and the pitch of the plurality of insertion electrode fingers is p2, |p1-pr|<0.1×p1, p2> The surface acoustic wave device according to any one of claims 1 to 5, wherein p1 and p2>pr are satisfied. The surface acoustic wave device according to claim 1, wherein the plurality of insertion conductors are not connected to the IDT electrode. The IDT electrodes are located on both sides in the second direction with respect to the plurality of electrode fingers, and each has a pair of bus bars to which a part or the rest of the plurality of electrode fingers are connected. ,
The surface acoustic wave device according to claim 1, wherein the pair of bus bars has a plurality of recesses facing the plurality of insertion conductors. Antenna terminal,
A transmission filter that filters the transmission signal and outputs it to the antenna terminal,
A reception filter for filtering a reception signal from the antenna terminal,
The said transmission filter or said reception filter is a duplexer which has the surface acoustic wave element of any one of Claims 1-8. With an antenna,
The duplexer according to claim 9, wherein the antenna terminal is connected to the antenna.
An RF-IC electrically connected to the duplexer,
A communication device having.

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