WO2023176814A1

WO2023176814A1 - Ladder filter, module, and communication device

Info

Publication number: WO2023176814A1
Application number: PCT/JP2023/009794
Authority: WO
Inventors: 富夫金澤
Original assignee: 京セラ株式会社
Priority date: 2022-03-18
Filing date: 2023-03-14
Publication date: 2023-09-21

Abstract

In this ladder filter, a plurality of parallel resonators each connect an input terminal side or an output terminal side of one of a plurality of series resonators with a reference potential portion. Each of the plurality of parallel resonators includes an IDT electrode comprising a plurality of electrode fingers. The plurality of parallel resonators include a first parallel resonator and a second parallel resonator. A connecting position of the first parallel resonator with respect to the plurality of series resonators is closer to the output terminal side electrically than a connecting position of the second parallel resonator with respect to the plurality of series resonators. A value obtained by dividing the width of each of the plurality of electrode fingers by the pitch of the plurality of electrode fingers is referred to as the duty. The duty of the first parallel resonator is smaller than the duty of the second parallel resonator.

Description

Ladder filters, modules and communication devices

The present disclosure relates to a ladder filter that uses elastic waves, and also relates to a module and a communication device including the ladder filter.

A ladder type filter in which a plurality of resonators are connected in a ladder type is known (for example, Patent Document 1 below). The resonator is, for example, an elastic wave resonator that uses elastic waves. As an acoustic wave resonator, for example, one having a piezoelectric substrate having piezoelectricity on at least the upper surface and an IDT (Interdigital Transducer) electrode located on the upper surface of the piezoelectric substrate is known. The IDT electrode has a plurality of electrode fingers arranged in the propagation direction of elastic waves. In such an elastic wave resonator, an elastic wave whose length of one wavelength is approximately twice the pitch of the plurality of electrode fingers is used.

Japanese Patent Application Publication No. 2013-168996

A ladder filter according to one aspect of the present disclosure includes a plurality of series resonators and a plurality of parallel resonators. The plurality of series resonators are connected in series between an input terminal and an output terminal. Each of the plurality of parallel resonators connects the input terminal side or the output terminal side of one of the series resonators among the plurality of series resonators to a reference potential section. Further, each of the plurality of parallel resonators has an IDT electrode including a plurality of electrode fingers. The plurality of parallel resonators include a first parallel resonator and a second parallel resonator. A connection position of the first parallel resonator to the plurality of series resonators is located electrically closer to the output terminal than a connection position of the second parallel resonator to the plurality of series resonators. A value obtained by dividing each width of the plurality of electrode fingers by the pitch of the plurality of electrode fingers is called Duty. At this time, the duty of the first parallel resonator is smaller than the duty of the second parallel resonator.

A module according to an aspect of the present disclosure includes the ladder filter, an antenna connected to one of the input terminal and the output terminal, and an integrated circuit element connected to the other of the input terminal and the output terminal. It has .

A communication device according to an aspect of the present disclosure includes the ladder filter, an antenna connected to one of the input terminal and the output terminal, and an integrated circuit connected to the other of the input terminal and the output terminal. and a housing housing the ladder filter and the integrated circuit element.

FIG. 1 is a schematic diagram showing the configuration of a duplexer including a ladder filter according to an embodiment. FIG. 2 is a plan view showing the configuration of an elastic wave resonator included in the ladder filter of FIG. 1; A sectional view taken along the line III-III in FIG. 2. FIG. 3 is a diagram showing an example of frequency characteristics of the absolute value of impedance of an elastic wave resonator. FIG. 3 is a diagram showing an example of the frequency characteristics of the impedance phase of an elastic wave resonator. 3 is a diagram showing transmission characteristics of ladder filters according to Comparative Example 1 and Example 1. FIG. 3 is a diagram showing transmission characteristics of ladder filters according to Comparative Example 2 and Example 2. FIG. 6 is a diagram showing transmission characteristics of ladder filters according to Comparative Example 2 and Example 3. FIG. FIG. 1 is a block diagram schematically showing the configuration of a communication device according to an embodiment.

Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. Note that the drawings are schematic, and the shapes and/or dimensions on the drawings do not necessarily correspond to the actual ones. However, the actual shape and/or dimensions may be as shown in the drawings, or the features such as the shape and/or dimensions may be extracted from the drawings.

(Summary of embodiment)
FIG. 1 is a schematic diagram showing the configuration of main parts of a duplexer 101 including a ladder filter according to an embodiment.

The branching filter 101 is configured as a duplexer, for example. The duplexer includes, for example, a transmission filter 109 that filters the transmission signal from the transmission terminal 105 and outputs it to the antenna terminal 103, and a reception filter 111 that filters the reception signal from the antenna terminal 103 and outputs it to the reception terminal 107. are doing.

The transmission filter 109 is configured to include, for example, a ladder type filter. The ladder type filter is configured by connecting a plurality of resonators 15 (more specifically, 15S1 to 15S4 and 15P1 to 15P4 in the illustrated example) in a ladder type.

More specifically, the plurality of resonators 15 include, for example, a plurality of (four in the illustrated example) series resonators 15S (more specifically, 15S1 to 15S4) and a plurality (four in the illustrated example) of parallel resonators 15S. It has a resonator 15P (more specifically, 15P1 to 15P4). The plurality of series resonators 15S are connected in series between the transmission terminal 105 and the antenna terminal 103. Note that a signal path including the plurality of series resonators 15S may be referred to as a series arm 115. The plurality of parallel resonators 15P connect the plurality of positions of the series arm 115 and the reference potential section 113. Each signal path from the series arm 115 to the reference potential section 113 via the parallel resonator 15P is sometimes referred to as a parallel arm (symbol omitted).

FIG. 2 is a schematic plan view showing an example of the configuration of each resonator 15. FIG. 3 is a sectional view taken along line III--III in FIG. 2.

For convenience, an orthogonal coordinate system D1D2D3 is attached to these figures. As will be understood from the explanation below, the D3 direction is the normal direction of the upper surface of the composite substrate 3. The D1 direction is the propagation direction of elastic waves propagating along the upper surface of the composite substrate 3. The D2 direction is a direction orthogonal to the D1 direction and the D3 direction. The resonator 15 may be directed upward or downward. However, in the description of the embodiment, terms such as an upper surface or a lower surface may be used with the +D3 side as the upper side for convenience.

The resonator 15 includes, for example, a piezoelectric substrate (composite substrate 3 in this embodiment) having piezoelectricity on at least its upper surface, and an IDT electrode 19 located on the composite substrate 3. The composite substrate 3 has, for example, a piezoelectric layer 11 that constitutes the upper surface of the composite substrate 3. The IDT electrode 19 has a pair of comb-teeth electrodes 23 that engage with each other. Each comb-teeth electrode 23 has a plurality of electrode fingers 27 extending in a direction (D2 direction) orthogonal to the propagation direction of elastic waves. The plurality of electrode fingers 27 of one comb-teeth electrode 23 and the plurality of electrode fingers 27 of the other comb-teeth electrode 23 are basically arranged alternately in the propagation direction of the elastic wave (direction D1).

When a voltage is applied to the pair of comb-teeth electrodes 23, the voltage is applied to the piezoelectric layer 11 by the plurality of electrode fingers 27, and the piezoelectric layer 11 of the composite substrate 3 vibrates. That is, elastic waves are excited. Among the elastic waves of various wavelengths propagating in various directions, the elastic waves propagating in the arrangement direction of the plurality of electrode fingers 27 with the pitch p of the plurality of electrode fingers 27 approximately half a wavelength (λ/2) are Since the plurality of waves excited by the electrode fingers 27 overlap in the same phase, the amplitude tends to become large.

Furthermore, the elastic waves propagating through the piezoelectric layer 11 are converted into electrical signals by the plurality of electrode fingers 27. At this time, in the same way as when the elastic waves are excited, the pitch p of the plurality of electrode fingers 27 is approximately half a wavelength (λ/2), and the elastic waves propagating in the arrangement direction of the plurality of electrode fingers 27 are converted into electricity. The signal strength tends to be strong.

Due to the above-mentioned actions (and other actions whose explanation will be omitted here), the resonator 15 functions as a resonator whose resonant frequency is the frequency of an elastic wave with a pitch p of approximately half a wavelength (λ/2). do. Further, for example, in a ladder filter having a plurality of resonators 15 (transmission filter 109 in this embodiment), the resonant frequency of the series resonator 15S is approximately the center frequency of the passband, and the resonant frequency of the series resonator 15S is parallel to the resonant frequency of the series resonator 15S. It functions as a filter whose width is slightly narrower than the difference from the resonant frequency of the resonator 15P and is half the width of the passband.

Note that λ is usually a symbol indicating wavelength. The actual wavelength of an elastic wave may deviate from 2p. If the actual wavelength and 2p deviate from each other, λ in the description of the embodiments means 2p rather than the actual wavelength.

Among the elastic waves of various wavelengths propagating in various directions generated in the piezoelectric layer 11 as described above, the frequency of the elastic wave (the elastic wave intended to be used) having a pitch p of approximately half a wavelength is approximately The amplitude of an elastic wave having three times the frequency (sometimes referred to as a "third harmonic wave") may become large. and/or the intensity of the electrical signal into which the third harmonic is converted may increase. That is, spurious waves due to the third harmonic may occur. As a result, for example, in a ladder filter, the characteristics deteriorate in a frequency band approximately three times the passband.

The ratio (w/p) of the width w (FIG. 2) of the electrode fingers 27 to the pitch p is referred to as Duty. Further, among the plurality of parallel resonators 15P, the one whose connection position to the series arm 115 (in other words, the plurality of series resonators 15S) is electrically closest to the input terminal (transmission terminal 105 in the illustrated example) In the example, one of the parallel resonators (for example, the parallel resonator 15P4) other than the parallel resonator 15P1) will be referred to as a "first parallel resonator". In addition, a parallel resonator 15P whose connection position to the series arm 115 is electrically located closer to the input terminal (transmission terminal 105) than the connection position of the first parallel resonator to the series arm 115 is referred to as a "second parallel resonator". ”.

Note that the reason for saying "electrically" regarding the positional relationship of the connection positions is to avoid confusion with spatial positional relationship (positional relationship on coordinates). However, in the following, for convenience, "electrically" may not be specified. Furthermore, the term "connection position with respect to the series arm 115" may also be omitted, and the parallel resonator 15P may simply be expressed as being close to or far from the antenna terminal 103 or the transmission terminal 105.

In this embodiment, the duty of the first parallel resonator is smaller than the duty of the second parallel resonator. Thereby, for example, compared to a mode in which the duty of the first parallel resonator is the same as the duty of the second parallel resonator, the spurious caused by the third harmonic generated in the first parallel resonator can be reduced. As a result, spurious noise occurring in the ladder filter can be reduced.

The spurious caused by the third harmonic generated in the second parallel resonator is transmitted from the second parallel resonator of the ladder filter (transmission filter 109) in the process of being transmitted toward the output terminal (antenna terminal 103). It is also likely to be attenuated by the part located on the output terminal side. Conversely, spurious noise generated in the first parallel resonator relatively located closer to the output terminal is less likely to be attenuated. Therefore, by reducing the duty in the first parallel resonator to reduce spurious, it is possible to efficiently reduce spurious.

From another point of view, since the duty of some parallel resonators (first parallel resonators) among the plurality of parallel resonators 15P is reduced, other parallel resonators 15P (second parallel resonators) Regarding, the duty can be set so as to improve characteristics other than spurious caused by the third harmonic. This makes it easier to ensure the characteristics in the passband, for example.

The above is an overview of the ladder type filter (transmission filter 109) according to the embodiment. Below, the embodiments will be briefly described in the following order.
1. Resonator 15 (Figures 2 and 3)
2. Ladder type filter (transmission filter 109, Figure 1)
3. Duplexer 101 (Figure 1)
4. Duty of parallel resonator
5. Examples and comparative examples (Figures 4 to 8)
6. Example of using ladder filter (Figure 9)
7. Summary of embodiments

(1. Resonator)
The resonator 15 shown in FIG. 2 is configured as a so-called one-port acoustic wave resonator. The resonator 15 generates resonance when an electrical signal of a predetermined frequency is input from one of the

terminals

17A and 17B shown conceptually and schematically, and can output the signal that caused the resonance from the

other terminal

17A and 17B. It is.

As described above, the resonator 15 includes a piezoelectric substrate (composite substrate 3 in this embodiment) having piezoelectricity on at least its upper surface, and an IDT electrode 19. From another perspective, the resonator 15 includes a composite substrate 3 and a conductor layer 5 that overlaps the upper surface of the composite substrate 3 and includes an IDT electrode 19.

In the resonator 15 as a one-port acoustic wave resonator, the conductor layer 5 includes, in addition to the IDT electrode 19, a pair of reflectors 21 located on both sides thereof. The pair of reflectors 21 reflect the elastic waves and contribute to confining the energy in the region where the IDT electrode 19 is arranged. Note that the region of the resonator 15 where the IDT electrode 19 is arranged (the configuration excluding the region where the reflector 21 is located) is also a resonator. This resonator may be referred to as a resonator 16.

As described above, the resonator 15 includes at least a portion of the upper surface side of the composite substrate 3. At least a portion of the piezoelectric layer 11 includes, for example, a piezoelectric layer 11 and a low sound velocity film 9 (described later). However, in the description of the embodiment, for convenience, it may be expressed as if only the IDT electrode 19 and the pair of reflectors 21 (the configuration excluding the composite substrate 3) are the resonator 15.

The elastic waves intended to be used in the resonator 15 may be any appropriate type. For example, the elastic wave may be a surface acoustic wave, a bulk wave, a plate wave (Lamb wave), or it may be indistinguishable as described above. . The elastic waves to be utilized are, for example, the material, cut angle and thickness of the piezoelectric layer 11, the configuration of the lower surface side of the piezoelectric layer 11 (configuration of the low sound velocity film 9, etc.), and the configuration of the upper surface side of the piezoelectric layer 11 (configuration of the low sound velocity film 9, etc.). The structure of the conductor layer 5, etc. differs depending on the configuration.

Below, the resonator 15 will be roughly explained in the following order.
1.1. Piezoelectric substrate (composite substrate 3)
1.2. Conductor layer 5
1.3. Other configurations of resonator 15

(1.1. Piezoelectric substrate (composite substrate))
The piezoelectric substrate constituting the resonator 15 shown in FIGS. 2 and 3 may have various configurations in which at least the upper surface has piezoelectricity. For example, the piezoelectric substrate may be a composite substrate including a piezoelectric layer and one or more layers overlapping the bottom surface of the piezoelectric layer (as shown in the figure), or the entire substrate is basically made of piezoelectric material. It may be assumed that the Note that in the description of the embodiments, the "layer" may include, for example, a film-like layer (for example, a relatively thin layer) and a substrate-like layer (for example, a relatively thick layer).

The composite substrate 3 in the illustrated example includes a support substrate 7 (FIG. 3), a low sound velocity film 9 (FIG. 3) located on the support substrate 7, and a piezoelectric layer 11 located on the low sound speed film 9 (FIG. 2). and FIG. 3). The sound speed in the low sound speed film 9 is lower than the sound speed in the piezoelectric layer 11. The low sound velocity film 9 contributes to, for example, reflecting the elastic waves propagating through the piezoelectric layer 11 and confining the energy of the elastic waves in the piezoelectric layer 11 . The support substrate 7 contributes to reinforcing the strength of the composite substrate 3, for example.

Although not particularly illustrated, the composite substrate may have a configuration different from the illustrated example. For example, the configuration of the composite substrate may be such that a high-sonic membrane is added to the configuration of the composite substrate 3 in the illustrated example. The high sound velocity film has a higher sound velocity than the sound velocity in the piezoelectric layer 11 . The high-sonic membrane may be located, for example, between the piezoelectric layer 11 and the low-sonic membrane 9 and/or between the low-sonic membrane 9 and the support substrate 7.

Note that, for example, when it is expressed that the low sound velocity film 9 is spread along the lower surface of the piezoelectric layer 11, a high sound velocity film may or may not be interposed therebetween. Further, for example, when it is expressed that the piezoelectric layer 11 and the low sound velocity membrane 9 overlap, unless otherwise specified, it refers to the fact that they directly overlap when viewed acoustically. The same applies to the other two layers that overlap each other.

When the piezoelectric layer 11 and the low sound velocity membrane 9 directly overlap from an acoustic point of view, there is a layer ( For example, there is no intervening membrane (high-sonic membrane). Conversely, when viewed more microscopically, there is another layer interposed between the two layers that has almost no acoustic effect on the elastic waves propagating through the piezoelectric layer 11. Good too. Examples of other layers include a bonding layer that contributes to bonding the two. Whether or not two layers directly overlap each other when viewed acoustically may be determined rationally in light of common technical knowledge and the like. The other layers (for example, the bonding layer) have a thickness that has almost no acoustic effect on the elastic waves propagating through the piezoelectric layer 11, for example. Such thickness varies depending on the materials of other layers, etc., but to give a specific example, it is 0.005λ or less or 0.001λ or less. In the description of the embodiments, the existence of the bonding layer is basically ignored. The same applies to the other two layers that overlap each other.

Also, for example, the composite substrate may have still another configuration. For example, the composite substrate may include a support substrate 7, a multilayer film overlapping the support substrate 7, and a piezoelectric layer 11 overlapping the multilayer film. The multilayer film may have, for example, a structure in which a plurality of layers (for example, 3 or more or 5 or more) having different acoustic impedances and/or sound velocities are alternately laminated. Further, the composite substrate may include a support substrate 7 and a piezoelectric layer 11 overlapping the support substrate 7. Further, the composite substrate may have a cavity that is in contact with the lower surface of the piezoelectric layer 11 and overlaps at least a portion of the resonator 15 when seen in plan view.

Below, each layer of the composite substrate 3 will be explained in the following order. Furthermore, a high-sonic membrane (not shown) will also be explained.
1.1.1. Piezoelectric layer 11
1.1.2. Low sound velocity membrane 9
1.1.3. Support board 7
1.1.4. High sound velocity membrane

(1.1.1. Piezoelectric layer)
The piezoelectric layer 11 is made of, for example, a piezoelectric single crystal. Examples of materials constituting such a single crystal include lithium tantalate (LiTaO ₃ , hereinafter sometimes abbreviated as LT), lithium niobate (LiNbO ₃ , hereinafter sometimes abbreviated as LN), and Quartz (SiO ₂ ) can be mentioned. The cut angle of these single crystals is arbitrary. Note that the piezoelectric layer 11 may be made of polycrystal.

The thickness of the piezoelectric layer 11 is arbitrary. For example, the thickness of the piezoelectric layer 11 may be 0.05λ or more or 0.1λ or more. With such a thickness, for example, elastic waves propagating through the piezoelectric layer 11 can be used. Further, for example, the thickness of the piezoelectric layer 11 may be 1.0λ or less. In this case, for example, it is possible to reduce insertion loss or to use elastic waves in a relatively fast mode.

(1.1.2. Low sound velocity membrane)
The material of the low sound velocity film 9 is arbitrary as long as the sound velocity in the low sound velocity film 9 is lower than the sound velocity in the piezoelectric layer 11. Physical property values (density, Young's modulus, acoustic impedance, etc.) that mutually influence the speed of sound may also be set arbitrarily.

The sound speed in the comparison between the sound speed in the low sound speed film 9 and the sound speed in the piezoelectric layer 11 may be, for example, the sound speed of a bulk wave propagating through each layer. Bulk waves generally include three types: longitudinal waves, slow shear waves, and fast shear waves. The slow transverse wave or the fast transverse wave is, for example, either an SV (shear vertical) wave or an SH (shear vertical) wave. The bulk wave used for comparison may be, for example, a bulk wave that propagates through the piezoelectric layer 11 and corresponds to a component mainly included in an elastic wave that is intended to be used, among the three types of bulk waves. This is because the low sound velocity film 9 is expected to have the effect of confining the elastic waves propagating through the piezoelectric layer 11, as described above. For example, in the case where the elastic waves in the piezoelectric layer 11 that are intended to be used mainly include SH waves, the sound speed of the SH waves in the piezoelectric layer 11 and the sound speed of the SH waves in the low-sonic film 9 may be compared. . Although SH waves have been taken as an example, the same applies to SV waves or longitudinal waves. Furthermore, if it is intended to use an elastic wave that is a combination of a longitudinal wave and a transverse wave, the sound speed of the transverse waves may be compared, for example.

Note that the conditions for comparison do not necessarily need to be as strict as described above. From another point of view, when comparing the sound speed in the piezoelectric layer 11 and the sound speed in the low sound speed film 9, the sound speeds of both do not need to be strictly specified. For example, when comparing the transverse sound velocity of the low sound velocity film 9 and the transverse sound velocity of the piezoelectric layer 11, the difference between fast transverse waves and slow transverse waves in the low sound velocity film 9 is relatively small (transverse sound velocity of the low sound velocity film 9). and the transverse wave sound speed of the piezoelectric layer 11), even if fast transverse waves and slow transverse waves in the low sound speed film 9 are not particularly distinguished, the transverse sound speed of the low sound speed film 9 is relatively large. When it is clear that the transverse wave is lower than the sound speed, there is no need to distinguish between fast and slow transverse waves in the low-sonic membrane 9. From another point of view, the components mainly included in the elastic waves of the piezoelectric layer 11 that are intended to be used do not need to be strictly specified.

The sound velocity in the piezoelectric layer 11 varies depending on, for example, the direction in which the sound velocity is specified and the cut angle and thickness of the piezoelectric layer 11. to be influenced. The same can be said about the low sound velocity membrane 9. Therefore, when comparing the sound speeds in the two layers (here, the piezoelectric layer 11 and the low sound speed membrane 9), the relationship between the sound speeds of the two layers may vary depending on the conditions under which the comparison is made. Therefore, when the sound speeds in the two layers are compared, for example, the sound speeds in the D1 direction (the arrangement direction of the plurality of electrode fingers 27) in the actual product may be compared. In other words, specific sound velocities may be compared in consideration of the effects of a specific cut angle, thickness, and the like.

However, the effects of cut angle, thickness, etc. do not necessarily have to be taken into consideration. From another perspective, when comparing the sound speeds in two layers (here, the piezoelectric layer 11 and the low sound speed film 9), the speeds of sound between the two layers do not need to be strictly specified. For example, in a case where it is clear that the sound speed in the low sound speed film 9 is lower than the sound speed in the piezoelectric layer 11, regardless of the cut angle and/or thickness of the piezoelectric layer 11 and the thickness of the low sound speed film 9. , it is not necessary to specify the sound velocity in the D1 direction in the actual product. In such a case, the sound speed may be calculated from a simple theoretical formula based on density, Young's modulus, etc. and compared.

The speed of the elastic wave is also affected by the conductor layer 5 and the like located on the piezoelectric layer 11, and also differs from region to region within the resonator 15. In comparing the sound speeds in the two layers (here, the piezoelectric layer 11 and the low sound speed membrane 9), for example, the sound speed in the intersection region of the IDT electrodes 19 may be used. Although not particularly shown, the intersection region is sandwiched between an imaginary line connecting the tips of the plurality of electrode fingers 27 of one comb-teeth electrode 23 and an imaginary line connecting the tips of the plurality of electrode fingers 27 of the other comb-teeth electrode 23. It may be considered as an area where If the speed of sound differs even within the intersection region, the sound speed in the central region of the intersection region (if the speed of sound differs also within the central region, the average value) may be used. The central area here may be the same as the central area described in "4.5. Supplement regarding Duty" described later.

However, for example, if it is clear that the sound velocity in the low-sonic membrane 9 is lower than the sound velocity in the piezoelectric layer 11 regardless of the presence or absence of the influence of the conductor layer 5, etc., or if the sound velocity is low in the same area when viewed through a plane, In cases such as when it is clear that the sound velocity in the membrane 9 is lower than the sound velocity in the piezoelectric layer 11, the sound velocity in such an intersection region does not need to be determined strictly.

Specific materials for the low sound velocity film 9 include, for example, silicon dioxide (SiO ₂ ), tantalum oxide (Ta ₂ O ₃ ), silicon oxynitride (Si ₂ N ₂ O), and glass. Further, a compound in which fluorine, carbon, boron, or the like is added to SiO ₂ may be used. The various materials mentioned for the piezoelectric layer 11 (for example, LT and LN) and the materials mentioned here may be arbitrarily combined. Note that the conditions for comparing the sound speed in the piezoelectric layer 11 and the sound speed in the low sound speed film 9 have been described in detail so far. However, if the material of the low sound velocity membrane 9 is the material exemplified in this paragraph, some or all of the comparison conditions described above may be ignored.

The thickness of the low-sonic membrane 9 is arbitrary. For example, the thickness of the low sound velocity film 9 may be thinner than the thickness of the piezoelectric layer 11 (as shown in the illustrated example), or may be equal to or thicker. Further, for example, the thickness of the low sound velocity film 9 may be 0.01λ or more or 0.1λ or more, or may be 0.6λ or less or 0.5λ or less. The above lower limit and upper limit may be arbitrarily combined. When such a thickness is adopted, it is easy to reduce insertion loss, for example.

(1.1.3. Support substrate)
The material and dimensions of the support substrate 7 are arbitrary. Since the elastic waves propagating through the piezoelectric layer 11 are basically reflected by the low-sonic film 9, the direct influence of the material and dimensions of the support substrate 7 on the elastic waves propagating through the piezoelectric layer 11 is comparatively small. The target is small.

The material of the support substrate 7 may have a coefficient of thermal expansion lower than that of the piezoelectric layer 11 and the like. In this case, for example, it is possible to reduce the possibility that the frequency characteristics of the resonator 15 will change due to temperature changes. Examples of such materials include semiconductors such as silicon (Si), single crystals such as sapphire, and ceramics such as aluminum oxide sintered bodies. Note that the support substrate 7 may be configured by laminating a plurality of layers made of mutually different materials. The thickness of the support substrate 7 is thicker than the piezoelectric layer 11, for example.

(1.1.4. High-sonic membrane)
As mentioned above, unlike the example shown, the composite substrate may have a high sonic membrane. The material for the high-sonic membrane is arbitrary as long as the sound velocity in the high-sonic membrane is higher than that in the piezoelectric layer 11. Physical property values (density, Young's modulus, acoustic impedance, etc.) that mutually influence the speed of sound may also be set arbitrarily. Regarding the conditions for comparing the sound speeds, the explanation given regarding the low sound speed membrane 9 may be used. Specific materials for the high-speed sonic film include, for example, aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), and aluminum nitride (AlN). In addition, in the case where the material of the high sound speed membrane is the material exemplified in this paragraph, some or all of the conditions for comparison of sound speeds explained by taking the low sound speed membrane 9 as an example may be ignored.

The thickness of the high-sonic membrane is arbitrary. For example, the thickness of the high sonic velocity film may be thinner, equal to, or thicker than the thickness of the piezoelectric layer 11 and/or the low sonic velocity film 9. Further, for example, the thickness of the high-sonic film interposed between the piezoelectric layer 11 and the low-sonic film 9 may be 0.01λ or more and 0.2λ or less. When such a thickness is adopted, it is easy to reduce insertion loss, for example.

(1.2. Conductor layer)
The conductor layer 5 is made of metal, for example. The specific type of metal is arbitrary. For example, the metal may be aluminum (Al) or an alloy containing Al as a main component (Al alloy). The Al alloy may be, for example, an aluminum-copper (Cu) alloy. Note that 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 Al or Al alloy and the piezoelectric layer 11 to strengthen the bonding properties between them. The thickness of the conductor layer 5 may be set as appropriate depending on the characteristics required of the resonator 15. For example, the thickness of the conductor layer 5 may be 0.02λ or more and 0.10λ or less, and/or 50nm or more and 600nm or less.

As described above, the conductor layer 5 includes the IDT electrode 19 and a pair of reflectors 21. Below, the conductor layer 5 will be roughly explained in the following order.
1.2.1. IDT electrode 1.2.2. reflector

(1.2.1.IDT electrode)
The IDT electrode 19 includes a pair of comb-teeth electrodes 23, as described above. Note that in FIG. 2, one comb-teeth electrode 23 is hatched for better visibility. Each comb-teeth electrode 23 includes, for example, a busbar 25, a plurality of electrode fingers 27 extending in parallel from the busbar 25, and a dummy electrode 29 protruding from the busbar 25 between the plurality of electrode fingers 27. The pair of comb-teeth electrodes 23 are arranged so that the plurality of electrode fingers 27 interlock with each other (cross each other).

The bus bar 25 has, for example, a shape that generally has a constant width and extends linearly in the elastic wave propagation direction (D1 direction). A pair of bus bars 25 are opposed to each other in a direction (D2 direction) that intersects the propagation direction of elastic waves. Unlike the illustrated example, the bus bar 25 may have a varying width or may be inclined with respect to the propagation direction of the elastic wave. In the latter embodiment, the intersection area may also be sloped.

Each electrode finger 27 has, for example, a shape that generally has a constant width and extends linearly in the direction (D2 direction) orthogonal to the propagation direction of the elastic wave. However, the width w of the electrode finger 27 may change depending on the position in the length direction (D2 direction). An example of such an electrode finger 27 is one that uses a piston mode. Note that a method for calculating Duty (w/p) when the width w is not constant in the length direction will be described later (see "4.5. Supplement regarding Duty"). In each comb-teeth electrode 23, the plurality of electrode fingers 27 are arranged in the propagation direction of the elastic wave (direction D1). Moreover, the plurality of electrode fingers 27 of one comb-teeth electrode 23 and the plurality of electrode fingers 27 of the other comb-teeth electrode 23 are basically arranged alternately.

The pitch p of the plurality of electrode fingers 27 (for example, the distance between the centers of two adjacent electrode fingers 27) is basically constant within the IDT electrode 19. However, a part of the IDT electrode 19 may be provided with a narrow pitch part in which the pitch p is narrower than in most other parts, or a wide pitch part in which the pitch p is wider than in most other parts. Further, a thinned out portion where the electrode fingers 27 are substantially thinned out may exist in a part of the IDT electrode 19. Note that a method of calculating the pitch p and Duty (w/p) when the pitch p is not constant will be described later (see "4.5. Supplement regarding Duty").

As understood from the above description, the pitch p may be set according to the intended resonance frequency. For example, the pitch p may be 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, and may be 10 μm or less, 5 μm or less, or 2 μm or less. The above lower limit and upper limit may be arbitrarily combined.

The number of electrode fingers 27 may be appropriately set depending on the electrical characteristics required of the resonator 15. Since FIG. 2 is a schematic diagram, the number of electrode fingers 27 is shown to be small. In reality, more electrode fingers 27 than shown may be arranged. The same applies to the strip electrode 33 of the reflector 21, which will be described later.

The lengths of the plurality of electrode fingers 27 are, for example, equal to each other. Unlike the illustrated example, the IDT electrode 19 has a so-called apodized structure in which the length of the plurality of electrode fingers 27 (from another point of view, the so-called crossing width) changes depending on the position in the propagation direction of the elastic wave (D1 direction). may be applied. The length and width of the electrode fingers 27 may be set as appropriate depending on required electrical characteristics and the like.

The dummy electrode 29 has, for example, a shape that approximately has a constant width and protrudes in a direction perpendicular to the propagation direction of the elastic wave. Its width is, for example, equivalent to the width of the electrode finger 27. The plurality of dummy electrodes 29 are arranged at the same pitch as the plurality of electrode fingers 27, and the tip of the dummy electrode 29 of one comb-teeth electrode 23 is in a gap with the tip of the electrode finger 27 of the other comb-teeth electrode 23. are facing each other through. Note that the IDT electrode 19 may not include the dummy electrode 29.

(1.2.2.Reflector)
The pair of reflectors 21 are located on both sides of the IDT electrode 19 in the propagation direction of the elastic wave. For example, each reflector 21 may be electrically floating or may be provided with a reference potential. Each reflector 21 is formed, for example, in a lattice shape. That is, the reflector 21 includes a pair of bus bars 31 facing each other and a plurality of strip electrodes 33 extending between the pair of bus bars 31. The pitch between the plurality of strip electrodes 33 and the pitch between the electrode fingers 27 and the strip electrodes 33 that are adjacent to each other are, for example, equivalent to the pitch between the plurality of electrode fingers 27.

(1.3. Other configurations of resonator)
Although not particularly illustrated, the upper surface of the piezoelectric layer 11 may be covered from above the conductor layer 5 with a protective film made of SiO ₂ and/or Si ₃ N ₄ or the like. The protective film may contribute, for example, to reducing corrosion of the conductor layer 5 and/or to temperature compensation regarding the properties of the resonator 15. In cases where a protective film is provided, an additional film made of an insulator or metal may be provided on the upper or lower surfaces of the IDT electrode 19 and reflector 21. The additional film contributes to improving the reflection coefficient of elastic waves, for example.

The resonator 15 may be packaged as appropriate. For example, the packaging may be such that the illustrated configuration is mounted on a substrate (not shown) so that the upper surfaces of the piezoelectric layers 11 face each other with a gap therebetween, and the piezoelectric layer 11 is sealed with resin from above. A wafer level package type in which a box-shaped cover is provided on the body layer 11 may be used. As will be understood from the description below, packaging may be performed, for example, for each filter (109 or 111), or for each part of the filter, or for packaging the duplexer 101 (in other words, It may be performed for each filter (all two or more filters).

(2. Ladder type filter (transmission filter))
Below, the ladder type filter (transmission filter 109) will be roughly explained in the following order.
2.1. Configuration of transmission filter 109 (Figure 1)
2.2. Frequency characteristics of resonator 15 and passband of filter (109)

(2.1. Configuration of transmission filter)
As described above, the transmission filter 109 shown in FIG. 1 includes a ladder type filter. Note that the transmission filter 109 may include filters other than the ladder type filter. However, for convenience, in the description of the embodiment, unless otherwise specified, it is assumed that the transmission filter 109 is configured only by a ladder type filter. Therefore, in the description of the embodiments, the two may not be distinguished.

Furthermore, the ladder filter may include components (for example, an inductor, a capacitor, and/or a resistor) other than the series resonator 15S and the parallel resonator 15P. However, in the description of the embodiment, for convenience, unless otherwise specified, the ladder filter (transmission filter 109) includes only the series resonator 15S and the parallel resonator 15P (and wiring connecting these).

The plurality of resonators 15 that constitute the transmission filter 109 (ladder type filter) are provided, for example, on the same piezoelectric substrate (composite substrate 3). However, the plurality of resonators 15 may be provided on different piezoelectric substrates. For example, a plurality of series resonators 15S may be provided on the first piezoelectric substrate, and a plurality of parallel resonators 15P may be provided on the second piezoelectric substrate. In the description of this embodiment, it is assumed that all the resonators 15 of the ladder filter are provided on the same piezoelectric substrate unless otherwise specified.

The number of series resonators 15S is arbitrary. For example, the number of series resonators 15S is generally plural (as shown in the figure), or may be one. In the illustrated example, the number of series resonators 15S is four. This is just one example. The number of series resonators 15S may be 2, 3, or 5 or more.

The number of parallel resonators 15P is also arbitrary. Note that in a normal ladder filter, the number of parallel resonators 15P may be one. However, in the ladder type filter of the embodiment, the number of parallel resonators 15P is plural. In the illustrated example, the number of parallel resonators 15P is four. This is just one example. The number of parallel resonators 15P may be 2, 3, or 5 or more.

Each parallel resonator 15P connects the antenna terminal 103 side or the transmission terminal 105 side of any series resonator 15S to the reference potential section 113. In other words, the plurality of parallel resonators 15P connect a plurality of electrically different positions on the series arm 115 and the reference potential section 113. In other words, the connection position of the parallel resonator 15P to the series arm 115 is a position between adjacent series resonators 15S, a position on the antenna terminal 103 side with respect to the entire plurality of series resonators 15S, and a position where the parallel resonator 15P is connected to the series arm 115. This is any position on the transmission terminal 105 side with respect to the entire child 15S.

In the illustrated example, a parallel resonator 15P1 is connected to a position on the transmission terminal 105 side with respect to the entire plurality of series resonators 15S, and a parallel resonator is connected to a position between adjacent series resonators 15S. 15P2 to 15P4 are provided. Although not particularly illustrated, a parallel resonator 15P connected to the antenna terminal 103 side with respect to the entire plurality of series resonators 15S may be provided. Moreover, conversely, the parallel resonator 15P1 may be omitted.

As understood from the above description, the number of parallel resonators 15P is typically the same (as in the illustrated example), one less, or one more than the number of series resonators 15S. However, this is not necessarily the case. For example, it is also possible to use a parallel resonant circuit configured to include an inductor and a capacitor in place of the resonator 15.

Note that in this embodiment, at least two parallel resonators 15P (a first parallel resonator and a second parallel resonator) are elastic wave resonators as described with reference to FIGS. 2 and 3. Furthermore, in the description of this embodiment, unless otherwise specified, all the resonators 15 are assumed to be elastic wave resonators as described with reference to FIGS. 2 and 3.

Although not particularly illustrated, each resonator 15 (for example, a series resonator 15S) is divided into two or more resonators (referred to as "split resonators" in this paragraph) connected in series (or in parallel). Good too. Each divided resonator has, for example, the configuration of an elastic wave resonator as described with reference to FIGS. 2 and 3. By dividing, for example, the voltage applied to the divided resonators can be divided to improve voltage resistance. Note that the parallel resonators 15P are usually not connected between divided resonators obtained by dividing one series resonator 15S into series.

In FIG. 1, the connection position of the parallel resonator 15P to the series arm 115 is indicated by a node (number omitted) located on the wiring (number omitted) connected to each series resonator 15S. The actual connection position may be substantially the same position as the above-mentioned node from an electrical point of view. For example, the wiring extending from the parallel resonator 15P may be directly connected to one bus bar 25 of the series resonator 15S, or one bus bar 25 of the parallel resonator 15P may be directly connected to the bus bar 25 of the series resonator 15S. You may.

In FIG. 1, the plurality of reference potential sections 113 to which the plurality of parallel resonators 15P are connected are drawn as mutually different reference potential sections 113. These reference potential sections 113 may be located at different locations in the actual product, or may be partially or entirely the same location. Furthermore, the plurality of reference potential sections 113 as mutually different parts may be insulated from each other within the transmission filter 109 or within the duplexer 101, or may be partially or entirely connected to each other.

(2.2. Resonator frequency characteristics and filter passband)
As described above, the resonator 15 functions as a resonator whose resonant frequency is the frequency of an elastic wave whose pitch p is approximately half a wavelength. At the resonance frequency, the impedance of the resonator 15 takes a minimum value (see region Rr in FIG. 4, which will be described later). Further, the impedance of the resonator 15 takes a maximum value (see region Ra in FIG. 4) at the anti-resonance frequency. The anti-resonance frequency is determined by the resonance frequency, the capacitance of the resonator 15, and the like. The anti-resonant frequency is, for example, higher than the resonant frequency.

The plurality of series resonators 15S are configured so that their resonant frequencies are equal to each other and their anti-resonant frequencies are equal to each other. For example, the plurality of series resonators 15S have substantially the same values of parameters (pitch p, duty, etc.) that affect the resonant frequency and the anti-resonant frequency. However, in order to improve the transmission characteristics, the resonant frequency and/or the anti-resonant frequency (from another point of view) are In some cases, the values of influencing parameters) may be different among the plurality of series resonators 15S.

The description in the previous paragraph may be applied to the parallel resonator 15P by replacing the words "series resonator 15S" and "parallel resonator 15P".

The resonant frequency and anti-resonant frequency of the series resonator 15S and the parallel resonator 15P are set so that the resonant frequency of the series resonator 15S and the anti-resonant frequency of the parallel resonator 15P approximately match. As a result, these resonators 15 as a whole (ladder type filter) function as a bandpass filter whose pass band is slightly narrower than the frequency range from the resonant frequency of the parallel resonator 15P to the anti-resonant frequency of the series resonator 15S. Function.

(3. Duplexer)
The duplexer 101 shown in FIG. 1 includes a transmission filter 109 and a reception filter 111, as described above.

The reception filter 111 is a bandpass filter that has a passband that is different from (does not overlap) the passband of the transmission filter 109. The configuration of the reception filter 111 is arbitrary. For example, like the transmission filter 109, the reception filter 111 may include an elastic wave filter that uses elastic waves, or may not include an elastic wave filter. The latter includes, for example, a filter that utilizes a parallel resonant circuit including an inductor and a capacitor. Note that in the description of this embodiment, unless otherwise specified, expressions may be made on the premise that the reception filter 111 is an elastic wave filter.

In the embodiment in which the reception filter 111 includes an elastic wave filter, its specific configuration is arbitrary. For example, the reception filter 111 may include a ladder filter and/or a multimode filter (including a dual mode filter). Although not particularly shown, the multimode filter includes two or more IDT electrodes 19 (resonators 16 from another perspective) arranged in the propagation direction of elastic waves and adjacent to each other, and a pair of IDT electrodes 19 located on both sides of the IDT electrodes 19 (resonators 16 from another perspective). It has a reflector 21.

In an embodiment in which the reception filter 111 includes a plurality of resonators 15 (or 16), the plurality of resonators 15 may be provided on the same piezoelectric substrate (composite substrate 3) similarly to the transmission filter 109. , may not be provided on the same piezoelectric substrate. Furthermore, the reception filter 111 (a part or all of it) and the transmission filter 109 (a part or all of it) may be provided on the same piezoelectric substrate (composite substrate 3), or may be provided on the same piezoelectric substrate It does not have to be provided. The former includes, for example, a mode in which the entire receiving filter 111 and the entire transmitting filter 109 are provided on the same piezoelectric substrate. The latter includes, for example, a mode in which the piezoelectric substrate provided with the reception filter 111 and the piezoelectric substrate provided with the transmission filter 109 are mounted on the same mounting substrate (not shown).

The duplexer 101 may include the above-mentioned antenna terminal 103, transmission terminal 105, and reception terminal 107 as constituent elements. The antenna terminal 103 is connected, for example, directly or indirectly to an antenna (not shown). The transmission terminal 105 is connected, for example, directly or indirectly to a high frequency circuit for transmission (not shown here). The reception terminal 107 is connected, for example, directly or indirectly to a high frequency circuit for reception (not shown here).

The illustrated antenna terminal 103, transmission terminal 105, and reception terminal 107 may be external terminals that contribute to the connection between the duplexer 101 and the outside of the duplexer 101, or may be connected to such external terminals. It may also be an internal terminal of the duplexer 101. Furthermore, in any case, the specific configurations of the various terminals are arbitrary. For example, various terminals may be constituted by a conductor layer 5 located on the upper surface of the composite substrate 3.

In the illustrated example, each terminal consists of only one and outputs an unbalanced signal. However, at least one type of terminal (for example, the transmission terminal 105 or the reception terminal 107) may be composed of two terminals capable of outputting a balanced signal. For example, two transmission terminals 105 may be provided by interposing a multimode elastic wave filter between the ladder type filter of the transmission filter 109 and the transmission terminal 105. Further, for example, two reception terminals 107 may be provided by the reception filter 111 being constituted by a multimode elastic wave filter.

The branching filter may be something other than a duplexer. For example, the duplexer may be a diplexer, or may include three or more filters (for example, a triplexer or a quadplexer).

The duplexer 101 is included in one chip-type electronic component, for example. However, the transmission filter 109 and the reception filter 111 may be included in different chip-type electronic components. In any aspect, the transmission filter 109, the reception filter 111, or the duplexer 101 may be regarded as one elastic wave device 1.

(4. Duty of parallel resonator)
As described above, in this embodiment, the connection position of the first parallel resonator to the series arm 115 is electrically closer to the output terminal (antenna terminal 103) than the connection position of the second parallel resonator to the series arm 115. It's on the side. Further, the duty of the first parallel resonator is smaller than the duty of the second parallel resonator. For convenience, the configuration described above may be referred to as "requirement A."

In the description of the embodiment, the term "first parallel resonator" refers to only one of the parallel resonators 15P when there are multiple parallel resonators 15P that can be regarded as the first parallel resonator. In some cases, it refers to two or more parallel resonators 15P. The same applies to the "second parallel resonator".

Below, the duty of the parallel resonator 15P will be roughly explained in the following order.
4.1. Parallel resonators serving as the first parallel resonator and the second parallel resonator 4.2. Number of duty values of parallel resonators 4.3. How to set the Duty value 4.4. Specific example of Duty value 4.5. Supplement regarding Duty

(4.1. Parallel resonators serving as the first parallel resonator and the second parallel resonator)
In an embodiment in which the ladder filter includes three or more parallel resonators 15P, the first parallel resonator and the second parallel resonator that satisfy requirement A may be any of the parallel resonators 15P. Further, the number of first parallel resonators may be one, or two or more. Similarly, the number of second parallel resonators may be one, or two or more. There may be a parallel resonator 15P that cannot be classified as either the first parallel resonator or the second parallel resonator. The number of first parallel resonators and the number of second parallel resonators may be equal to each other, or one may be greater than the other.

For example, in the illustrated example, the parallel resonator 15P4 may be the first parallel resonator, and any one, two, or three of the parallel resonators 15P1 to 15P3 may be the second parallel resonators. In other words, the parallel resonator 15P closest to the output terminal (antenna terminal 103) is the first parallel resonator, and some (one or more) or all of the other parallel resonators 15P are the second parallel resonators. may be considered.

In the illustrated example, the parallel resonator 15P closest to the output terminal (antenna terminal 103) is connected between the series resonator 15S closest to the output terminal and the series resonator 15S next closest to the output terminal. This is a parallel resonator 15P. As understood from the above description, the parallel resonator 15P closest to the output terminal may be connected between the entire plurality of series resonators 15S and the output terminal.

Furthermore, for example, in the illustrated example, the parallel resonators 15P4 and 15P3 may be the first parallel resonators, and any one or two of the parallel resonators 15P1 and 15P2 may be the second parallel resonators. In other words, two or more consecutive parallel resonators 15P including the parallel resonator 15P closest to the output terminal (antenna terminal 103) are the first parallel resonators, and some (one (or a plurality of parallel resonators) or all may be used as the second parallel resonator.

In other words, the above two examples state that the first parallel resonator may be one or more parallel resonators 15P including the parallel resonator 15P closest to the antenna terminal 103. In such an embodiment, or in an embodiment different from such an embodiment, the second parallel resonator is, for example, the parallel resonator 15P (parallel resonator 15P1 in the illustrated example) closest to the input terminal (transmission terminal 105). It may be one or more (one or more) parallel resonators 15P including.

In the illustrated example, the parallel resonator 15P closest to the input terminal (transmission terminal 105) is the parallel resonator 15P connected between the entire plurality of series resonators 15S and the input terminal. As understood from the above description, the parallel resonator 15P closest to the input terminal is connected between the series resonator 15S closest to the input terminal and the series resonator 15S next closest to the input terminal. It may be something.

(4.2. Number of duty values of parallel resonators)
In an embodiment in which the ladder filter has three or more parallel resonators 15P, the number (types) of different values of Duty may be two or three or more. The number of different values of Duty is two means, for example, that among the four parallel resonators 15P, the duties of three parallel resonators 15P are all the first value (for example, 0.60), and one parallel resonator 15P has two different values. This refers to a mode in which the duty of the resonator 15P is the second value (for example, 0.50). The number of mutually different values of Duty is three, for example, the Duty of two parallel resonators 15P among four parallel resonators 15P are both the first value (for example, 0.60), and one parallel This refers to an embodiment in which the duty of the resonator 15P is a second value (for example, 0.55), and the duty of the remaining one parallel resonator 15P is a third value (for example, 0.50).

The number (types) of different values of Duty may be less than or equal to the number of parallel resonators 15P. In an embodiment in which the number of different values of Duty is three or more, Duty may become smaller as it approaches the output terminal (antenna terminal 103), temporarily become larger in the middle, or the duty may become smaller as it approaches the output terminal (antenna terminal 103). It may also grow to the side.

The duty values of the parallel resonators 15P1 to 15P4 are expressed as Duty1 to Duty4, and an example of the magnitude relationship of Duty1 to Duty4 will be briefly shown below.
(a1) Duty1=Duty2=Duty3>Duty4
(a2) Duty1=Duty2>Duty3=Duty4
(a3) Duty1>Duty2=Duty3=Duty4
(a4) Duty1>Duty2>Duty3>Duty4
(a5) Duty1=Duty2>Duty3, Duty3<Duty4
(a6) Duty1<Duty2, Duty2=Duty3>Duty4

The above (a1) is the duty value of the parallel resonator 15P (first parallel resonator) closest to the output terminal (antenna terminal 103) and the duty value of all other parallel resonators 15P (second parallel resonators). In this example, only two types of values are set. The above (a2) is the duty value of two or more consecutive parallel resonators 15P (first parallel resonators) including the parallel resonator 15P4 closest to the output terminal, and the duty values of all other (one or more) parallel resonators. This is an example in which only two values are set, including the duty value of the child 15P (second parallel resonator).

The above (a1) and (a2) are examples in which the number of first parallel resonators is equal to or less than the number of second parallel resonators. In this case, for example, the influence of reducing the Duty on the passband is reduced. Of course, as shown in (a3) above, the number of first parallel resonators may be greater than the number of second parallel resonators.

The above (a4) is an example in which the number (types) of Duty values is three or more. When focusing on Duty1>Duty2, it can be said that the parallel resonator 15P2 is the first parallel resonator and the parallel resonator 15P1 is the second parallel resonator. Similarly, focusing on Duty2>Duty3, Duty3>Duty4, Duty1>Duty3, Duty1>Duty4, or Duty2>Duty4, the two parallel resonators 15P related to each magnitude relationship are used as the second parallel resonator and the first parallel resonator. can be captured. In this way, the above-mentioned requirement A may be satisfied in combination.

The above (a5) is an example showing that requirement A may not be satisfied (Duty3<Duty4) on the output terminal (antenna terminal 103) side of the position where requirement A is satisfied (Duty2>Duty3). be. Furthermore, (a6) above indicates that requirement A may not be satisfied (Duty1<Duty2) on the input terminal (transmission terminal 105) side of the position where requirement A is satisfied (Duty2=Duty3>Duty4). This is an example shown.

(4.3. How to set the Duty value)
Various methods may be used to set specific values of the duty of the first parallel resonator and the second parallel resonator on the input terminal side (transmission terminal 105 side) than the first parallel resonator. For example, by simulation calculations and/or experiments (prototypes), when various values are set as the duty values of the plurality of parallel resonators 15P, the characteristics of the passband and the frequency band of the third harmonic (and if necessary characteristics in other frequency bands) may be identified. Then, based on the results, a specific value of Duty that improves the characteristics may be searched for. The specific procedure for performing simulation calculations and/or experiments is also arbitrary.

For example, first, when the duties of the plurality of parallel resonators 15P are the same, the duty value that provides the best characteristics of the passband (and other frequency bands as necessary) is investigated by simulation calculation and/or experiment. It's okay to be. The Duty value obtained through this exploration may be used as the reference value. Next, simulation calculations and/or experiments were performed in which the above reference value was set as the Duty value of the second parallel resonator, and various values smaller than the reference value were set as the Duty value of the first parallel resonator. The duty value of the first parallel resonator that improves the characteristics in the pass band and third harmonic frequency band (and other frequency bands as necessary) may be searched for.

In the example of the above procedure, not only the Duty value of the first parallel resonator is set to various values smaller than the reference value, but also the Duty value of the second parallel resonator is set to a value different from the reference value (for example, the Duty value of the second parallel resonator is set to a value different from the reference value). value) may be set in various ways. In addition, without determining the reference value as described above, simulation calculations and/or experiments are performed assuming various values as the Duty values of the first parallel resonator and the second parallel resonator from the beginning. A Duty value that improves the characteristics of the frequency band and third harmonic frequency band (and other frequency bands as necessary) may be searched for.

As can be understood from the above example of how to set the duty value, the duty values of the first parallel resonator and the second parallel resonator are set according to the desired characteristics of the ladder filter (transmission filter 109) as a whole. may be set as appropriate to meet the specifications. However, unlike the above description, the duty values of the first parallel resonator and the second parallel resonator may be set so that the characteristics of each resonator 15 are desired. In any case, the specific values of the duty of the first parallel resonator and the second parallel resonator may be various values, and there is no need to satisfy a specific numerical range.

(4.4. Specific example of Duty value)
As described above, the specific value of the duty of the parallel resonator 15P may be set as appropriate and may take various values.

For example, in general, the value of Duty is often set to 0.50 or a value close to this. When the duty of the first parallel resonator is Duty_S and the duty of the second parallel resonator is Duty_L, these values may satisfy any of the following relationships with respect to 0.50. Note that in the following inequality, the inequality sign (<) on the left or right side of 0.50 may be replaced with an equal sign (=) as long as Duty_S<Duty_L is satisfied.
(b1) Duty_S<0.50<Duty_L
(b2) Duty_S<Duty_L<0.50
(b3) 0.50<Duty_S<Duty_L

Furthermore, the average value of the duties of all the parallel resonators 15P is set as Duty_Av1. At this time, the following relationship may be satisfied.
(b4) Duty_S<Duty_Av1<Duty_L
In the above relationship, Duty_Av1 may be smaller than, equal to, or larger than 0.50.

Further, the average value of the duties of all the parallel resonators 15P except the first parallel resonator is set as Duty_Av2. At this time, the following relationship may be satisfied.
(b5) Duty_S<Duty_Av2
In the above relationship, Duty_Av2 may be smaller than, equal to, or larger than 0.50 and/or Duty_L. Further, for example, when Duty_Av2 is a value exceeding 0.50, Duty_S may be set to 0.50 or less. In addition, in the case where there are two or more parallel resonators 15P that can be considered as the first parallel resonators, the first parallel resonator referred to in this paragraph may refer to only one of them, or may refer to some ( 2 or more) or all of them.

Although the upper and lower limits of the duty of the parallel resonator 15P are not particularly limited, examples are shown below. Duty_S may be set to 0.40 or more or 0.45 or more, and may be set to 0.60 or less or 0.50 or less. The above lower limit and upper limit may be arbitrarily combined so that no contradiction occurs. Duty_L may be set to 0.45 or more or 0.50 or more, and may be set to 0.65 or less or 0.60 or less, as long as it does not conflict with Duty_S<Duty_L. The above lower limit and upper limit may be arbitrarily combined so that no contradiction occurs. Within these value ranges, it is easy to ensure a certain level of characteristics as a ladder filter.

(4.5. Supplement regarding Duty)
The duties of the plurality of parallel resonators 15P may differ from each other due to manufacturing errors. The difference in duty due to manufacturing error is naturally not the difference in duty (intentional difference in duty) as used in this embodiment. When the Duties of the plurality of parallel resonators 15P are different from each other, whether or not the differences are due to manufacturing errors can be determined by taking into account various circumstances such as the equipment configuration and manufacturing conditions related to manufacturing the resonators 15. may be judged accordingly.

However, in cases where it is difficult to make a rational judgment as described above (or even in cases where it is possible to make a rational judgment), the judgment may be made as follows, for example. Round off the measured Duty value to the third decimal place. Then, when a difference of 0.02 or more exists, it may be determined that the two are different. For example, 0.475 and 0.484 are both 0.48 when rounded to the third decimal place, and may be determined to be the same value. Also, for example, 0.484 and 0.485 become 0.48 and 0.49 when rounded to the third decimal place, but the difference between them is 0.01 (less than 0.02), so they are the same. It may be determined that the value is .

As described above, unlike the example in FIG. 2, the width w of the electrode finger 27 may change depending on the position of the electrode finger 27 in the length direction (D2 direction). From another point of view, Duty (w/p) may vary in the length direction of the electrode fingers 27. In this case, when comparing the duties of the resonators 15 or determining whether the duties of the resonators 15 fall within a predetermined range, the value of the central area of the intersection area is used as the duty value. It's fine. This is because normally, elastic waves that propagate in the center region are intended to be used, and the duty is also set based on the value of the center region.

More specifically, for example, although not particularly illustrated, the electrode finger 27 of the IDT electrode 19 that uses the piston mode typically has a first portion located at the center in the D2 direction of the intersection region, and a first portion located at the center in the D2 direction of the intersection region. and a second portion adjacent to the inner side of the intersection area with respect to the edge of the direction. The first portion extends, for example, with a constant width, and occupies most (for example, 1/2 or more or 2/3 or more) of the width (D2 direction) of the intersection area. In this case, the duty of the first portion described above may be used as the duty of the central region (as the duty to be compared between the parallel resonators 15P). That is, the region where the first portion is located in the D2 direction may be the center region described in the previous paragraph.

An example of a mode other than the typical IDT electrode 19 that utilizes the piston mode as described above is a mode in which the width w of the electrode finger 27 gradually changes. Furthermore, although the first portion of the electrode fingers 27 located at the center of the intersection area extends with a constant width, its length (in the D2 direction) is relatively short and occupies most of the width of the intersection area. There are some cases where it cannot be said that the In these embodiments, for example, a region having the center of the intersection region in the D2 direction as the center and having a width of 2/3 of the width of the intersection region may be the center side region described in the second paragraph before. Then, the average value of Duty in the central region may be used as a Duty value for various determinations.

Furthermore, as described above, the IDT electrode 19 may have a narrow pitch portion, a wide pitch portion, and/or a thinned-out portion regarding the pitch p. In the description of the embodiment, the pitch p refers to the pitch of the remaining portion (most of the plurality of electrode fingers 27) excluding such a unique portion. In addition, if the pitch changes in most of the plurality of electrode fingers 27 (for example, 80% or more of all the electrode fingers 27 selected to exclude unique parts), the above-mentioned large The average value of the pitches of the plurality of electrode fingers 27 in the portion may be used as the value of the pitch p. The above naturally applies to the pitch p used to calculate Duty.

As for the width w, some of the plurality of electrode fingers 27 may have a unique part, or may vary among the plurality of electrode fingers 27. Therefore, the explanation regarding pitch p in the previous paragraph may be applied to width w by replacing the word pitch p with width w.

Although not particularly shown, a typical ladder filter may be modified by using two or more resonators connected in parallel (referred to as "divided resonators" in this paragraph) instead of one parallel resonator 15P. A ladder type filter may be constructed. In such a case, the duty of the parallel resonator 15P is to function in the same way as one parallel resonator 15P (for example, one electrical position on the input side or output side of the series resonator 15S and the reference potential section 113). The average duty of two or more resonators may be used.

(5. Examples and comparative examples)
The inventor of the present application has confirmed through simulation calculations that the ladder type filter (transmission filter 109) according to the embodiment can reduce spurious waves caused by third harmonics while ensuring passband characteristics. Some of them are illustrated below. Below, an outline will be explained in the following order.
5.1. First common condition for simulation 5.2. Example of characteristics of single resonator 15 5.3. Example of ladder filter characteristics

(5.1. First common condition of simulation)
Conditions common to various simulations to be described later (hereinafter sometimes referred to as "first common conditions") are as follows.
・Composite board 3
...Piezoelectric layer 11
...Material: LT
... Cut angle: 26° rotation Y cut X propagation ... Thickness: 1.84 μm
・Low sound velocity membrane 9
...Material: _SiO2
...Thickness: 0.58μm
...Support board 7
...Material: Si
...Direction: [111]
...Thickness: 130μm
・Conductor layer 5
・・Material: Al-Cu alloy・・Thickness: 5000Å
・Resonator 15
... Pitch of strip electrode 33 of reflector 21: Same as pitch p of electrode fingers 27 of IDT electrode 19 in each resonator 15 (different for each resonator 15)
...Number of strip electrodes 33 in one reflector 21: 20
・Duty of series resonator 15S: 0.50

(5.2. Example of characteristics of a single resonator)
4 and 5 are diagrams showing examples of characteristics of the resonator 15 alone. In these figures, the horizontal axis indicates frequency (MHz). The vertical axis in FIG. 4 indicates the absolute value of impedance |Z|(Ω). The vertical axis in FIG. 5 indicates the phase (°) of impedance. The lower diagram in FIG. 4 is an enlarged view of the region R1 in the upper diagram in FIG. The lower diagram in FIG. 5 is an enlarged view of region R2 in the upper diagram in FIG.

As shown in the legend in the figure, the lines in the figure indicate frequency characteristics related to the impedance of the resonators 15 with different Duty values. The Duty value varies by 0.05 in the range of 0.45 or more and 0.65 or less.

In the simulation calculation of the illustrated example, conditions other than the first common condition are as follows.
- Pitch p of electrode fingers 27: 2.8 μm
・Number of electrode fingers 27: 200
・Intersection width of electrode fingers 27: 112 μm

As shown in the left diagram of FIG. 4 and as already mentioned, the absolute value of the impedance of the resonator 15 takes a minimum value at the resonant frequency (see region Rr), and also at the antiresonance It takes a local maximum value at the frequency (see region Ra). In the illustrated example, the resonant frequency and anti-resonant frequency are set around approximately 700 MHz.

Furthermore, as shown in the diagram on the left side of FIG. 5, the phase of the impedance of the resonator 15 is 90° in the range between the resonant frequency and the anti-resonant frequency (referred to as the "first range" in this paragraph). and, outside the first range, approaches −90°. Generally, in the first range, the closer the impedance phase is to 90°, the better the characteristics are, and outside the first range, the closer the impedance phase is to −90°, the better the characteristics.

Region R1 in FIG. 4 and region R2 in FIG. 5 indicate a frequency band having a frequency that is approximately three times the resonant frequency and the anti-resonant frequency (near 700 MHz). That is, it shows a frequency band in which spurious waves due to third harmonics may appear. As shown in the lower diagram of FIG. 4, which is an enlarged view of region R1 and region R2, and the lower diagram of FIG. 5, the spurious is reduced by decreasing the Duty value. There is. More specifically, in the illustrated example, the smaller the Duty value, the more the spurious is reduced. Furthermore, when the Duty is 0.50 or less, spurious signals hardly appear.

(5.3. Example of characteristics of ladder type filter)
6 to 8 are diagrams each showing the characteristics of a ladder type filter. The horizontal axis of these drawings indicates frequency (MHz). The vertical axis indicates transmission characteristics (dB).

In the simulation calculations related to these figures, the number and connection relationship of the series resonators 15S and parallel resonators 15P are the same as in the transmission filter 109 of FIG. 1. Further, conditions common to the simulation calculations related to these figures (hereinafter referred to as "second common conditions") are as follows.
・Series resonator 15S1
...Pitch p of electrode fingers 27: 2.70981μm
・Number of electrode fingers 27: 126
... Crossing width of electrode fingers 27: 92.8 μm
・Series resonator 15S2
...Pitch p of electrode fingers 27: 2.71384μm
・Number of electrode fingers 27: 164
... Crossing width of electrode fingers 27: 79 μm
・Series resonator 15S3
...Pitch p of electrode fingers 27: 2.71401μm
・Number of electrode fingers 27: 140
... Crossing width of electrode fingers 27: 81 μm
・Series resonator 15S4
...Pitch p of electrode fingers 27: 2.70750μm
・Number of electrode fingers 27: 130
... Crossing width of electrode fingers 27: 82 μm
・Parallel resonator 15P1
...Pitch p of electrode fingers 27: 2.87142μm
・Number of electrode fingers 27: 106
... Crossing width of electrode fingers 27: 130 μm
・Parallel resonator 15P2
...Pitch p of electrode fingers 27: 2.85045μm
・Number of electrode fingers 27: 120
... Crossing width of electrode fingers 27: 128 μm
・Parallel resonator 15P3
... Pitch p of electrode fingers 27: 2.84357μm
・Number of electrode fingers 27: 170
... Crossing width of electrode fingers 27: 160 μm
・Parallel resonator 15P4
...Pitch p of electrode fingers 27: 2.87380μm
・Number of electrode fingers 27: 266
... Crossing width of electrode fingers 27: 130 μm

The resonant frequency and anti-resonant frequency of each resonator 15 are roughly the same as the characteristics of the resonator 15 whose characteristics are shown in FIGS. 4 and 5. Therefore, the passband of the ladder filter is approximately located around 700 MHz. Further, spurious waves caused by the third harmonic appear around approximately 2100 MHz.

In FIG. 6, line LC1 indicates the characteristics of the first comparative example. Line LE1 shows the characteristics of the first embodiment. In the first comparative example and the first example, simulation conditions other than the first common condition and the second common condition are as follows.
- First comparative example... Duty of parallel resonator 15P1: 0.60
... Duty of parallel resonator 15P2: 0.60
... Duty of parallel resonator 15P3: 0.60
... Duty of parallel resonator 15P4: 0.60
・First example... Duty of parallel resonator 15P1: 0.60
... Duty of parallel resonator 15P2: 0.60
... Duty of parallel resonator 15P3: 0.48
... Duty of parallel resonator 15P4: 0.48

As understood from the above conditions, in the first comparative example, the plurality of parallel resonators 15P have the same duty. On the other hand, in the first embodiment, the duty of at least one first parallel resonator (15P3 and 15P4) located closer to the output terminal (antenna terminal 103) than at least one second parallel resonator (15P1 and 15P2) is is smaller than the duty of the second parallel resonator (from another point of view, than the duty of the first comparative example). In other words, requirement A is satisfied.

As shown in FIG. 6, the transmission characteristics in the passband (around 700 MHz) are almost the same between the first comparative example and the first example. On the other hand, in a band having a frequency approximately three times the frequency of the passband (around 2100 MHz), the first example has lower transmission characteristics than the first comparative example (the characteristics as a filter have improved). ).

In FIG. 7, line LC2 shows the characteristics of the second comparative example. Line LE2 shows the characteristics of the second embodiment. The lower right diagram in FIG. 7 is an enlarged view of region R5 in the upper left diagram in FIG. Region R5 corresponds to a band (near 2100 MHz) having a frequency that is approximately three times the frequency of the passband (near 700 MHz).

In the second comparative example and the second example, simulation conditions other than the first common condition and the second common condition are as follows.
-Second comparative example...Duty of parallel resonator 15P1: 0.63
... Duty of parallel resonator 15P2: 0.63
... Duty of parallel resonator 15P3: 0.63
... Duty of parallel resonator 15P4: 0.63
- Second example... Duty of parallel resonator 15P1: 0.63
... Duty of parallel resonator 15P2: 0.63
... Duty of parallel resonator 15P3: 0.63
... Duty of parallel resonator 15P4: 0.50

As understood from the above conditions, in the second comparative example, the plurality of parallel resonators 15P have the same duty. On the other hand, in the second embodiment, the duty of at least one first parallel resonator (15P4) located closer to the output terminal (antenna terminal 103) than at least one second parallel resonator (15P1 to 15P3) is The duty of the second parallel resonator is smaller than the duty of the second parallel resonator (from another point of view, the duty of the second comparative example). In other words, requirement A is satisfied.

As shown in FIG. 7, the transmission characteristics in the passband (around 700 MHz) are almost the same between the second comparative example and the second example. On the other hand, in a band having a frequency approximately three times the frequency of the passband (around 2100 MHz), the second example has lower transmission characteristics than the second comparative example (the characteristics as a filter have improved). ).

In FIG. 8, line LC2 is similar to line LC2 in FIG. 7, and indicates the characteristics of the second comparative example. Line LE3 shows the characteristics of the third embodiment. The lower right diagram in FIG. 8 is an enlarged view of region R7 in the upper left diagram in FIG. Region R7 corresponds to a band (near 2100 MHz) having a frequency that is approximately three times the frequency of the passband (near 700 MHz).

In the third example, simulation conditions other than the first common condition and the second common condition are as follows.
-Third example...Duty of parallel resonator 15P1: 0.63
... Duty of parallel resonator 15P2: 0.63
... Duty of parallel resonator 15P3: 0.50
... Duty of parallel resonator 15P4: 0.50

As can be understood from a comparison between the conditions of the second example and the conditions of the third example, the number of first parallel resonators whose duty is reduced in the third example is smaller than that of the second example. There are many (specifically +1). From another point of view, in the second embodiment, the number of first parallel resonators was smaller than the number of second parallel resonators, but in the third embodiment, the number of both is the same. From a further point of view, in the second embodiment, the number of first parallel resonators is one, but in the third embodiment, the number of first parallel resonators is plural (specifically, two). It is said that

As shown in FIG. 8, the transmission characteristics in the passband (near 700 MHz) are almost the same between the second comparative example and the third example. On the other hand, in a band having a frequency approximately three times the frequency of the passband (around 2100 MHz), the third example has lower transmission characteristics than the second comparative example (the characteristics as a filter have improved). ). Further, when comparing FIG. 7 and FIG. 8, by increasing the number of first parallel resonators, the transmission characteristics are reduced in the vicinity of 2100 MHz (the characteristics as a filter are improved).

(6. Example of using ladder type filter)
The ladder filter (transmission filter 109) may be used, for example, in a communication module and/or a communication device. An example is shown below.

FIG. 9 is a block diagram showing the main parts of a communication device 151 as an example of how the duplexer 101 is used. The communication device 151 includes a module 171 and a housing 173 that accommodates the module 171. The module 171 performs wireless communication using radio waves, and includes a duplexer 101.

In the module 171, the transmission information signal TIS containing the information to be transmitted is modulated and frequency increased (conversion of carrier frequency to a high frequency signal) by an RF-IC (Radio Frequency Integrated Circuit) 153 (an example of an integrated circuit element). The transmitted signal is then used as a transmission signal TS. The transmission signal TS has unnecessary components outside the transmission passband removed by a bandpass filter 155, is amplified by an amplifier 157, and is input to the duplexer 101 (transmission terminal 105). Then, the duplexer 101 (transmission filter 109) removes unnecessary components other than the transmission passband 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 wireless signal (radio wave) and transmits the signal.

Furthermore, in the module 171, the wireless signal (radio wave) received by the antenna 159 is converted into an electric signal (received signal RS) by the antenna 159, and is input to the duplexer 101 (antenna terminal 103). The duplexer 101 (reception filter 111) removes unnecessary components outside the reception passband from the input reception signal RS, and outputs the result from the reception terminal 107 to the amplifier 161. The output reception signal RS is amplified by an amplifier 161, and a bandpass filter 163 removes unnecessary components outside the reception passband. The received signal RS is then lowered in frequency and demodulated by the RF-IC 153 to become a received information signal RIS.

Note that the transmission information signal TIS and the reception information signal RIS may be low frequency signals (baseband signals) containing appropriate information, such as analog audio signals or digitized audio signals. The passband of the wireless signal may be set as appropriate. The modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. Although a direct conversion system is shown as the circuit system, any other appropriate circuit system may be used, for example, a double superheterodyne system may be used. Further, FIG. 9 schematically shows only the main parts, and a low-pass filter, an isolator, etc. may be added at an appropriate position, or the position of an amplifier, etc. may be changed.

The module 171 has, for example, components from the RF-IC 153 to the antenna 159 on the same circuit board. That is, the ladder filter (transmission filter 109) is modularized by combining with other components. Note that the ladder filter may be included in the communication device 151 without being modularized. Further, the components illustrated as the components of the module 171 may be located outside the module or may not be housed in the housing 173. For example, the antenna 159 may be exposed outside the housing 173.

(7. Summary of embodiments)
As described above, the ladder filter (transmission filter 109) includes a plurality of series resonators 15S and a plurality of parallel resonators 15P. The plurality of series resonators 15S are connected in series between an input terminal (transmission terminal 105) and an output terminal (antenna terminal 103). Each of the plurality of parallel resonators 15P connects the transmission terminal 105 side or the antenna terminal 103 side of one of the plurality of series resonators 15S to the reference potential section 113. . Each of the plurality of parallel resonators 15P has an IDT electrode 19 including a plurality of electrode fingers 27. The plurality of parallel resonators 15P include a first parallel resonator (eg, parallel resonator 15P4) and a second parallel resonator (eg, parallel resonator 15P1). The connection position of the first parallel resonator to the plurality of series resonators 15S is located electrically closer to the antenna terminal 103 than the connection position of the second parallel resonator to the plurality of series resonators 15S. When the value obtained by dividing each width w of the plurality of electrode fingers 27 by the pitch p of the plurality of electrode fingers 27 is called Duty, the Duty of the first parallel resonator is smaller than the Duty of the second parallel resonator.

Therefore, for example, as described in the explanation of the overview of the embodiment, spurious caused by the third harmonic can be efficiently reduced, and characteristics in the passband can be easily ensured.

The connection position of the first parallel resonator (15P4) to the plurality of series resonators 15S is the electrically closest output terminal (antenna terminal 103) among the connection positions of the plurality of parallel resonators 15P to the plurality of series resonators 15S. It's good to be close to.

In this case, for example, the effects described above are improved. Specifically, for example, it is as follows. The spurious generated in the parallel resonator 15P (for example, the second parallel resonator) that is relatively far from the output terminal (antenna terminal 103) is transmitted from the parallel resonator 15P that is far away from the ladder filter in the process of being transmitted to the output terminal. The signal is also attenuated by the portion located on the antenna terminal 103 side. Conversely, the spurious of the parallel resonator 15P4 located closest to the antenna terminal 103 is difficult to attenuate. By using such a parallel resonator 15P4 as a first parallel resonator whose duty is reduced to reduce spurious, it is possible to efficiently reduce spurious as a whole of the ladder filter.

The connection position of the second parallel resonator (15P1) to the plurality of series resonators 15S is the electrically closest output terminal (antenna terminal 103) among the connection positions of the plurality of parallel resonators 15P to the plurality of series resonators 15S. It's good to be far away.

In this case, for example, the effects described above are improved. Specifically, for example, it is as follows. The spurious generated in the parallel resonator 15P (for example, the second parallel resonator) that is relatively far from the output terminal (antenna terminal 103) is transmitted to the output terminal from the parallel resonator 15P that is far away from the ladder filter. The signal is also attenuated by the portion located on the antenna terminal 103 side. For this reason, in the parallel resonator 15P1 where the spurious is attenuated the most, there is relatively little need to reduce the Duty from the viewpoint of reducing the third harmonic spurious. Therefore, in the parallel resonator 15P1, the duty can be adjusted from another viewpoint. This improves, for example, the effect of making it easier to ensure the characteristics of the passband.

The duty of the first parallel resonator (for example, 15P4) may be the smallest among the duties of the plurality of parallel resonators 15P.

As shown in FIGS. 4 and 5, the smaller the Duty, the easier the spurious caused by the third harmonic is reduced. Therefore, the effects described above are improved by minimizing the duty of the first parallel resonator. Note that when it is said that the Duty of one first parallel resonator is "the smallest", it means that the other parallel resonators 15P (other first parallel resonators) have the same Duty as that of the first parallel resonator. It does not matter if there is something that can be captured or something that cannot be captured as such from the point of view of the connection position.

The average duty (Duty_Av2) of the plurality of parallel resonators 15P excluding the first parallel resonator (for example, 15P4) may exceed 0.50. The duty of the first parallel resonator may be 0.5 or less.

In this case, for example, spurious caused by the third harmonic in the first parallel resonator can be more reliably reduced. In addition, in the case where there are two or more parallel resonators 15P that can be considered as the first parallel resonators as in the first or third embodiment, the first parallel resonators in the previous paragraph are the two or more parallel resonators described above. It may refer to one of the resonators 15P, some (two or more), or all of the resonators 15P.

The first parallel resonator (for example, 15P4) may include a piezoelectric layer 11, a low sound velocity film 9, and a support substrate 7. An IDT electrode 19 may be located on the top surface of the piezoelectric layer 11. The low sound velocity film 9 may extend along the lower surface of the piezoelectric layer 11 and may have a sound velocity lower than the sound velocity in the piezoelectric layer 11 . The support substrate 7 may extend along the lower surface of the low-sonic membrane 9 .

In this case, for example, the energy of the elastic wave can be confined in the piezoelectric layer 11 to reduce the insertion loss of the first parallel resonator. On the other hand, the energy of the third harmonic wave is also likely to be trapped, and as a result, spurious waves due to the third harmonic wave are likely to appear. Therefore, the effect of spurious reduction by making the duty of the first parallel resonator smaller than the duty of the second parallel resonator is effectively achieved. In particular, when λ is twice the pitch p of the plurality of electrode fingers 27, if the thickness of the piezoelectric layer 11 is 1λ or less, and/or the thickness of the low sound velocity film 9 is 0.5λ or less, , spurious waves due to third harmonic waves are likely to appear, and the above effects are effectively achieved.

The piezoelectric layer 11 may be made of lithium tantalate single crystal. The low sound velocity membrane 9 may be composed of silicon dioxide. The support substrate 7 may be made of silicon.

In this case, the materials of each layer are the same as the conditions of the simulation calculation described above. Therefore, it has been confirmed that by making the duty of the first parallel resonator smaller than the duty of the second parallel resonator, the effect of reducing the spurious caused by the third harmonic can be achieved. Note that the reason why the spurious caused by the third harmonic is reduced is that the duty is relatively small or 0.5 or less, so that the amplitude of the elastic wave is integrated over the width w of the electrode finger 27. This is thought to be due to the value of time approaching 0. Therefore, the materials to which the configuration of this embodiment is applied are not limited to the above.

The output terminal may constitute the antenna terminal 103 connected to the antenna 159.

In other words, the ladder filter may be the transmission filter 109. In this case, for example, the spurious caused by the third harmonic is reduced in the transmitting filter 109, which has a higher signal strength than the receiving filter 111. As a result, the characteristics of the entire circuit and device including the transmission filter 109 are improved.

Note that in the above embodiments, the transmission filter 109 is an example of a ladder type filter. Transmission terminal 105 is an example of an input terminal. Antenna terminal 103 is an example of an output terminal. The parallel resonator 15P4 is an example of a first parallel resonator. The parallel resonator 15P1 is an example of a second parallel resonator.

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

The transmission filter 109 is illustrated as an example of a ladder type filter. However, the ladder type filter may constitute the reception filter 111. In this case, the antenna terminal 103 is an example of an input terminal, and the receiving terminal 107 is an example of an output terminal. Moreover, the ladder type filter may be a filter that does not fit the concepts of a transmission filter and a reception filter.

15S... Series resonator, 15P... Parallel resonator, 15P1... Second parallel resonator, 15P4... First, 19... IDT electrode, 27... Electrode finger, 103... Antenna terminal (input terminal), 105... Transmission terminal (input terminal), 113...Reference potential section.

Claims

a plurality of series resonators connected in series between an input terminal and an output terminal;
a plurality of parallel resonators each connecting the input terminal side or the output terminal side of any one of the plurality of series resonators to a reference potential section;
It has
Each of the plurality of parallel resonators has an IDT electrode including a plurality of electrode fingers,
The plurality of parallel resonators include a first parallel resonator and a second parallel resonator,
A connection position of the first parallel resonator to the plurality of series resonators is located electrically closer to the output terminal than a connection position of the second parallel resonator to the plurality of series resonators,
When the value obtained by dividing each width of the plurality of electrode fingers by the pitch of the plurality of electrode fingers is called Duty, the Duty of the first parallel resonator is smaller than the Duty of the second parallel resonator.
The connection position of the first parallel resonator to the plurality of series resonators is electrically closest to the output terminal among the connection positions of the plurality of parallel resonators to the plurality of series resonators. Ladder type filter as described.
The connection position of the second parallel resonator to the plurality of series resonators is electrically farthest from the output terminal among the connection positions of the plurality of parallel resonators to the plurality of series resonators. The ladder type filter described in 2.
The ladder filter according to claim 1, wherein the first parallel resonator has the smallest duty among the plurality of parallel resonators.
The average duty of the plurality of parallel resonators excluding the first parallel resonator exceeds 0.50,
The ladder type filter according to any one of claims 1 to 4, wherein the first parallel resonator has a duty of 0.50 or less.
The first parallel resonator is
a piezoelectric layer on which the IDT electrode is located;
a low sound velocity film that extends along the lower surface of the piezoelectric layer and has a sound velocity lower than the sound velocity in the piezoelectric layer;
The ladder-type filter according to any one of claims 1 to 5, further comprising a support substrate extending along the lower surface of the low-sonic membrane.
The ladder filter according to claim 6, wherein the piezoelectric layer has a thickness of 1λ or less, where λ is twice the pitch of the plurality of electrode fingers.
The ladder type filter according to claim 6 or 7, wherein the thickness of the low sound velocity film is 0.5λ or less, where λ is twice the pitch of the plurality of electrode fingers.
The piezoelectric layer is made of lithium tantalate single crystal,
The low sound velocity membrane is made of silicon dioxide,
The ladder type filter according to any one of claims 6 to 8, wherein the support substrate is made of silicon.
The ladder type filter according to any one of claims 1 to 9, wherein the output terminal constitutes an antenna terminal connected to an antenna.
The ladder type filter according to any one of claims 1 to 10,
an antenna connected to one of the input terminal and the output terminal;
an integrated circuit element connected to the other of the input terminal and the output terminal;
A module that has.
The ladder type filter according to any one of claims 1 to 10,
an antenna connected to one of the input terminal and the output terminal;
an integrated circuit element connected to the other of the input terminal and the output terminal;
a casing housing the ladder filter and the integrated circuit element;
A communication device that has