Elastic wave device and module including elastic wave device

Abstract

To provide an elastic wave device that can improve a frequency temperature characteristic while preventing the increase in chip size.SOLUTION: An elastic wave device includes a piezoelectric substrate, and a plurality of parallel resonators and four or more serial resonators formed on the piezoelectric substrate and functioning as a bandpass filter. When a first serial resonator, a second serial resonator, a third serial resonator, and a fourth serial resonator are arranged in the order that the antiresonance frequency of the serial resonators is closer to a high range end of a passing band of the bandpass filter, the duty ratio of the first serial resonator is smaller than the duty ratio between the second serial resonator and the third serial resonator.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an elastic wave device and a module including the elastic wave device.

Background Art

[0002] Patent Document 1 discloses an elastic wave device. In the elastic wave device, an IDT electrode is covered with a silicon dioxide film. The frequency temperature characteristics of the elastic wave device can be improved by the silicon dioxide film.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the elastic wave device disclosed in Patent Document 1, various problems occur due to the structure in which the IDT electrode is covered with a silicon dioxide film. For example, the chip size of the elastic wave device increases.

[0005] The present disclosure has been made to solve the above problems. An object of the present disclosure is to provide an elastic wave device capable of improving frequency temperature characteristics while preventing an increase in chip size, and a module including the elastic wave device.

Means for Solving the Problems

[0006] The elastic wave device according to the present disclosure includes: a piezoelectric substrate; a plurality of parallel resonators and four or more series resonators formed on the piezoelectric substrate and functioning as a band-pass filter; and When the anti-resonance frequencies of the plurality of series resonators are the first series resonator, the second series resonator, the third series resonator, and the fourth series resonator in order from closest to the high-frequency end of the passband of the band-pass filter, The duty ratio of the first series resonator is smaller than the duty ratios of the second series resonator and the third series resonator.

[0007] In one aspect of the present disclosure, the duty ratio of the second series resonator is smaller than the duty ratio of the third series resonator.

[0008] In one aspect of the present disclosure, the duty ratio of the third series resonator is smaller than the duty ratio of the fourth series resonator.

[0009] In one aspect of the present disclosure, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the second series resonator and the duty ratio of the third series resonator.

[0010] In one aspect of the present disclosure, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the third series resonator and the duty ratio of the fourth series resonator.

[0011] In one aspect of the present disclosure, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the second series resonator and the duty ratio of the fourth series resonator.

[0012] In one aspect of the present disclosure, the plurality of parallel resonators and the plurality of series resonators function as a transmission filter.

[0013] In one aspect of the present disclosure, there is provided a module including the elastic wave device.

Advantages of the Invention

[0014] According to the present disclosure, it is possible to provide an elastic wave device capable of improving frequency-temperature characteristics while preventing an increase in chip size, and a module including the elastic wave device.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0016] Embodiments will be described with reference to the accompanying drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions of such parts are appropriately simplified or omitted.

[0017] Embodiment 1. FIG. 1 is a cross-sectional view of the elastic wave device in Embodiment 1.

[0018] As shown in FIG. 1, the elastic wave device 1 includes a wiring substrate 2, a chip substrate 3, a plurality of bumps 4, and a sealing portion 5.

[0019] For example, the wiring board 2 is a multilayer board containing resin. For example, the wiring board 2 is a Low Temperature Co-fired Ceramics (LTCC) multilayer board composed of a plurality of dielectric layers. For example, the wiring board 2 is a High Temperature Co-fired Ceramics (HTCC) multilayer board composed of a plurality of dielectric layers. For example, the wiring board 2 incorporates passive elements (not shown) such as capacitors or inductors.

[0020] In FIG. 1, the upper surface of the wiring board 2 is a component mounting surface. A plurality of conductive pads 2A are formed on the upper surface of the wiring board 2. For example, the plurality of conductive pads 2A are formed of copper. The lower surface of the wiring board 2 is an attachment surface to a mother board or the like. A plurality of conductive pads 2B are formed on the lower surface of the wiring board 2. For example, the plurality of conductive pads 2B are formed of copper. A plurality of internal conductors 2C are incorporated in the wiring board 2. For example, the plurality of internal conductors 2C are formed of copper. Each of the internal conductors 2C electrically connects the conductive pads 2A and the conductive pads 2B that correspond to each other.

[0021] The chip board 3 faces the wiring board 2. For example, the chip board 3 includes at least a piezoelectric substrate 3A. For example, the piezoelectric substrate 3A is formed of a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz. For example, the piezoelectric substrate 3A is formed of piezoelectric ceramics.

[0022] The chip board 3 may include a support substrate 3B. For example, the support substrate 3B is formed of sapphire, silicon, alumina, spinel, quartz, or glass. For example, the support substrate 3B is joined to the piezoelectric substrate 3A via an adhesive layer (not shown).

[0023] For example, a band-pass filter is formed on the main surface (the lower surface in FIG. 1) of the chip board 3. For example, a receiving filter and a transmitting filter are formed. The receiving filter and the transmitting filter constitute a duplexer.

[0024] The receiving filter is formed so that an electrical signal in a desired frequency band can pass therethrough. For example, the receiving filter includes a ladder filter composed of a plurality of series resonators and a plurality of parallel resonators.

[0025] The transmitting filter is formed so that an electrical signal in a desired frequency band can pass therethrough. For example, the transmitting filter includes a ladder filter composed of a plurality of series resonators and a plurality of parallel resonators.

[0026] For example, the chip substrate 3 includes a wiring pattern 6 and a plurality of surface acoustic wave elements 7. For example, the wiring pattern 6 is formed of a metal or alloy such as silver, aluminum, copper, titanium, palladium, etc. For example, the wiring pattern 6 is formed by laminating a plurality of metal layers. For example, the thickness of the wiring pattern 6 is from 150 nm to 400 nm. For example, the plurality of surface acoustic wave elements 7 receive a high-frequency electric field through the wiring pattern 6 to excite a surface acoustic wave, and obtain desired filter characteristics by converting the surface acoustic wave into a high-frequency electric field by piezoelectric action.

[0027] Each of the plurality of bumps 4 is gold, a conductive adhesive, solder, etc. For example, the height of the bump 4 is from 20 μm to 50 μm. Each of the plurality of bumps 4 electrically connects the conductive pad 2A and the wiring pattern 6 at corresponding positions.

[0028] The sealing portion 5 hermetically seals the chip substrate 3 together with the wiring substrate 2 while leaving a space 8 between the wiring substrate 2 and the chip substrate 3. For example, the sealing portion 5 is formed of an insulator such as a synthetic resin. The synthetic resin is an epoxy resin, a polyimide, etc.

[0029] Next, an example of the surface acoustic wave element 7 will be described with reference to FIG. 2. FIG. 2 is a diagram showing an example of the surface acoustic wave element of the surface acoustic wave device in Embodiment 1.

[0030] In FIG. 2, the elastic wave element 7 is a SAW (Surface Acoustic Wave) resonator. As shown in FIG. 2, a pair of IDT electrodes 7A and a pair of reflectors 7B are formed on the main surface of the chip substrate 3. The pair of IDT electrodes 7A and the pair of reflectors 7B are provided so as to be able to excite elastic surface waves.

[0031] For example, the pair of IDT electrodes 7A and the pair of reflectors 7B are formed of an alloy of aluminum and copper. For example, the pair of IDT electrodes 7A and the pair of reflectors 7B are formed of an appropriate metal such as titanium, palladium, silver or an alloy thereof. For example, the pair of IDT electrodes 7A and the pair of reflectors 7B are formed of a laminated metal film in which a plurality of metal layers are laminated.

[0032] The IDT electrode 7A includes a plurality of electrode fingers 7C and a bus bar 7D. The plurality of electrode fingers 7C are arranged with their longitudinal directions aligned. The bus bar 7D connects the plurality of electrode fingers 7C so as to face each other. One of the pair of reflectors 7B is adjacent to one side of the pair of IDT electrodes 7A. The other of the pair of reflectors 7B is adjacent to the other side of the pair of IDT electrodes 7A. For example, the pair of IDT electrodes 7A and the pair of reflectors 7B are formed and patterned by the same process as the wiring pattern 6 (not shown in FIG. 2).

[0033] Next, the connection relationship of the resonator will be described with reference to FIG. 3. FIG. 3 is a circuit diagram corresponding to the chip substrate of the elastic wave device in Embodiment 1.

[0034] FIG. 3 is an example of a circuit that functions as a duplexer as a whole. In FIG. 3, the wiring pattern 6 includes a plurality of ground bump pads GND, a reception bump pad RX, a transmission bump pad TX, and an antenna bump pad ANT. These bump pads are portions that are electrically connected to the bump 4 (not shown in FIG. 3).

[0035] The plurality of elastic wave elements 7 includes four or more series resonators and a plurality of resonators. For example, the plurality of elastic wave elements 7 includes a plurality of series resonators TS1, TS2, TS3, TS4, etc., a plurality of parallel resonators TP1, TP2, TP3, TP4, etc., and a multi-mode resonator DMS. The plurality of series resonators TS1, TS2, TS3, TS4, etc., the plurality of parallel resonators TP1, TP2, TP3, TP4, etc., and the multi-mode resonator DMS are electrically connected via the wiring pattern 6.

[0036] The series resonators other than the plurality of series resonators TS1, TS2, TS3, TS4, the parallel resonators other than the plurality of parallel resonators TP1, TP2, TP3, TP4, and the multi-mode resonator DMS function as a receiving filter. Specifically, when a high-frequency electrical signal is input to the antenna bump pad ANT, the electrical signal passes through the series resonators other than the plurality of series resonators TS1, TS2, TS3, TS4, the parallel resonators other than the plurality of parallel resonators TP1, TP2, TP3, TP4, and the multi-mode resonator DMS. At this time, only the electrical signal in the desired frequency band reaches the receiving bump pad RX. As a result, only the electrical signal in the desired frequency band is output from the receiving bump pad RX.

[0037] The plurality of series resonators TS1, TS2, TS3, TS4 and the plurality of parallel resonators TP1, TP2, TP3, TP4 function as a transmitting filter. Specifically, when a high-frequency electrical signal is input to the transmitting bump pad TX, the electrical signal passes through the plurality of series resonators TS1, TS2, TS3, TS4 and the plurality of parallel resonators TP1, TP2, TP3, TP4. At this time, only the electrical signal in the desired frequency band reaches the antenna bump pad ANT. As a result, only the electrical signal in the desired frequency band is output from the antenna bump pad ANT.

[0038] In recent years, filters and duplexers have become smaller, and the required approved power has also increased. Therefore, improving the power resistance is very important.

[0039] In terms of withstand voltage, the most severe condition is when the frequency on the high-frequency side of the transmission band of the transmission filter (including the transmission section of the duplexer and the transmit-receive filter) is applied.

[0040] Here, Table 1 shows an example of the relationship between the Duty ratio (the ratio of the width of the electrode finger to the pitch of the electrode fingers) and the frequency-temperature characteristics.

[0041]

Table 1

[0042] In Table 1, "TxIL L-side" indicates the low-frequency side of the transmission band of the transmission filter for Band 28. "TxIL R-side" indicates the high-frequency side of the transmission band of the transmission filter for Band 28. "Duty65" indicates that the Duty ratio is 65%. "Duty60" indicates that the Duty ratio is 60%. "Duty55" indicates that the Duty ratio is 55%. "Duty50" indicates that the Duty ratio is 50%. Each numerical value indicates the value of the frequency-temperature characteristics at the position where the insertion loss is -5 dB.

[0043] For example, on the low-frequency side of the passband of the transmission filter for Band 28, at the position where the insertion loss of the transmission filter is -5 dB, the frequency-temperature characteristics of the resonator with a Duty ratio of 65% are -17.5 ppm / °C. The frequency-temperature characteristics of the resonator with a Duty ratio of 60% are -16.4 ppm / °C. The frequency-temperature characteristics of the resonator with a Duty ratio of 55% are -15.4 ppm / °C. The frequency-temperature characteristics of the resonator with a Duty ratio of 50% are -14.1 ppm / °C.

[0044] For example, at the high-frequency end of the passband of the transmission filter of band 28, at the position where the insertion loss of the transmission filter is -5 dB, the frequency-temperature characteristic of the resonator with a duty ratio of 65% is -36.1 ppm / °C. The frequency-temperature characteristic of the resonator with a duty ratio of 60% is -33.4 ppm / °C. The frequency-temperature characteristic of the resonator with a duty ratio of 55% is -32.2 ppm / °C. The frequency-temperature characteristic of the resonator with a duty ratio of 50% is -30.8 ppm / °C.

[0045] As shown in Table 1, the frequency-temperature characteristic is a negative value. Therefore, when the temperature rises due to power application, the resonant frequency and the anti-resonant frequency shift in the lower direction. As a result, the insertion loss at the shoulder on the high-frequency side of the frequency of the transmission filter increases. This leads to a further temperature rise. Furthermore, it may even lead to the destruction of the transmission filter. Therefore, when the frequency-temperature characteristic on the high-frequency side of the transmission filter is improved, the power resistance is also improved.

[0046] As can be seen from Table 1, if the duty ratio is lowered, the frequency-temperature characteristic is improved. However, at a small duty ratio, the capacitance per unit area becomes small. For this reason, the area of the resonator becomes large. Therefore, it is not a good idea to lower the duty ratio of all the series resonators of the transmission filter.

[0047] On the other hand, it is considered as one means to lower the duty ratio of only the series resonator that has the most influence on the shoulder on the high-frequency side of the transmission band of the transmission filter. However, in reality, the series resonator with the second lowest anti-resonant frequency and the series resonator with the third lowest anti-resonant frequency also have an impact, although the degree of influence gradually becomes smaller.

[0048] Therefore, in the elastic wave device 1 of the present disclosure, the duty ratios of the series resonators are set so as to decrease in the order of decreasing anti-resonance frequency. Further, since the degree of influence decreases as the anti-resonance frequency increases, the difference in the duty ratios between the series resonator having the lowest anti-resonance frequency and the series resonator having the second lowest anti-resonance frequency is set to be larger than the difference in the duty ratios between any two of the series resonators from the series resonator having the second lowest anti-resonance frequency to the series resonator having the fourth lowest anti-resonance frequency.

[0049] Specifically, in the plurality of series resonators of the present disclosure, they are defined as the first series resonator, the second series resonator, the third series resonator, and the fourth series resonator in the order of decreasing anti-resonance frequency close to the high-frequency end of the passband of the band-pass filter. This definition is independent of the layout and connection relationship of the series resonators. The duty ratios are set for the first series resonator, the second series resonator, the third series resonator, and the fourth series resonator.

[0050] For example, the duty ratio of the first series resonator is set to be smaller than the duty ratios of the second series resonator and the third series resonator. For example, the duty ratio of the second series resonator is set to be smaller than the duty ratio of the third series resonator. For example, the duty ratio of the third series resonator is set to be smaller than the duty ratio of the fourth series resonator.

[0051] For example, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is set to be larger than the difference between the duty ratio of the second series resonator and the duty ratio of the third series resonator. For example, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is set to be larger than the difference between the duty ratio of the third series resonator and the duty ratio of the fourth series resonator. For example, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is set to be larger than the difference between the duty ratio of the second series resonator and the duty ratio of the fourth series resonator.

[0052] Next, the frequency characteristics of the elastic wave device 1 will be described with reference to FIG. 4. FIG. 4 is a diagram showing the high-frequency end vicinity of the passband of the frequency characteristics of the elastic wave device in Embodiment 1.

[0053] In FIG. 4, F shows the frequency characteristics when the elastic wave device 1 functions as a transmission filter corresponding to band 28. W is the passband of the transmission filter. A shows the frequency characteristics of the first series resonator alone. B shows the frequency characteristics of the second series resonator alone. C shows the frequency characteristics of the third series resonator alone. D shows the frequency characteristics of the fourth series resonator alone.

[0054] In this example, the duty ratio of the first series resonator is set to 45%. The duty ratio of the second series resonator is set to 50%. The duty ratio of the third series resonator is set to 52%. The duty ratio of the fourth series resonator is set to 54%.

[0055] As shown in FIG. 4, the anti-resonant frequency of the first series resonator is closer to the high-frequency end of the passband than the anti-resonant frequency of the second series resonator. The anti-resonant frequency of the second series resonator is closer to the high-frequency end of the passband than the anti-resonant frequency of the third series resonator. The anti-resonant frequency of the third series resonator is closer to the high-frequency end of the passband than the anti-resonant frequency of the fourth series resonator.

[0056] In this way, by setting the positions and duty ratios of the anti-resonant frequencies of the plurality of series resonators, while preventing the size of the chip substrate 3 including the plurality of series resonators from increasing, the frequency temperature characteristics are improved. As a result, the power resistance is also improved.

[0057] According to Embodiment 1 described above, the anti-resonant frequencies of the plurality of series resonators are the first series resonator, the second series resonator, the third series resonator, and the fourth series resonator in order from closest to the high-frequency end of the passband of the bandpass filter. The duty ratio of the first series resonator is smaller than the duty ratios of the second series resonator and the third series resonator. For this reason, in the elastic wave device 1, while preventing the chip size from increasing, the frequency temperature characteristics can be improved. As a result, the power resistance can also be improved.

[0058] At this time, the adjustment of the duty ratio can be easily performed during the patterning of the IDT electrode 7A. Therefore, the frequency-temperature characteristics can be improved by a simple manufacturing method.

[0059] Also, the duty ratio of the second series resonator is smaller than that of the third series resonator. Therefore, in the surface acoustic wave device 1, while preventing the chip size from increasing, the frequency-temperature characteristics can be more reliably improved.

[0060] Also, the duty ratio of the third series resonator is smaller than that of the fourth series resonator. Therefore, in the surface acoustic wave device 1, while preventing the chip size from increasing, the frequency-temperature characteristics can be more reliably improved.

[0061] Also, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the second series resonator and the duty ratio of the third series resonator. Therefore, in the surface acoustic wave device 1, while preventing the chip size from increasing, the frequency-temperature characteristics can be more reliably improved.

[0062] Also, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the third series resonator and the duty ratio of the fourth series resonator. Therefore, in the surface acoustic wave device 1, while preventing the chip size from increasing, the frequency-temperature characteristics can be more reliably improved.

[0063] Also, the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the second series resonator and the duty ratio of the fourth series resonator. Therefore, in the surface acoustic wave device 1, while preventing the chip size from increasing, the frequency-temperature characteristics can be more reliably improved.

[0064] In addition, the plurality of parallel resonators and the plurality of series resonators function as a transmission filter. Therefore, even for a transmission filter with a large amount of heat generation, it is possible to more reliably improve the frequency-temperature characteristics while preventing the chip size from increasing.

[0065] Next, a modified example of the chip substrate 3 will be described with reference to FIG. 5. FIG. 5 is a circuit diagram corresponding to a modified example of the chip substrate of the surface acoustic wave device in Embodiment 1.

[0066] FIG. 5 is an example of a circuit that functions as a transmission filter as a whole. As shown in FIG. 5, the wiring pattern 6 includes a plurality of ground bump pads GND, an input bump pad IN, and an output bump pad OUT.

[0067] The plurality of surface acoustic wave elements 7 include a plurality of series resonators TS1, TS2, TS3, TS4 and a plurality of parallel resonators TP1, TP2, TP3, TP4. The plurality of series resonators TS1, TS2, TS3, TS4 and the plurality of parallel resonators TP1, TP2, TP3, TP4 are electrically connected via the wiring pattern 6.

[0068] The plurality of series resonators TS1, TS2, TS3, TS4 and the plurality of parallel resonators TP1, TP2, TP3, TP4 function as a transmission filter. Specifically, when a high-frequency electrical signal is input to the input bump pad IN, the electrical signal passes through the plurality of series resonators TS1, TS2, TS3, TS4 and the plurality of parallel resonators TP1, TP2, TP3, TP4. At this time, only the electrical signal in the desired frequency band reaches the output bump pad OUT. As a result, only the electrical signal in the desired frequency band is output from the output bump pad OUT.

[0069] Also in this modified example, as in Embodiment 1, the positions of the anti-resonance frequencies and the duty ratios of the plurality of series resonators are set.

[0070] According to the modification described above, in the elastic wave device 1, similar to the first embodiment, it is possible to improve the frequency temperature characteristics while preventing the chip size from increasing.

[0071] Embodiment 2. FIG. 6 is a cross-sectional view of a module to which the elastic wave device in Embodiment 2 is applied. Note that the same reference numerals are given to the same or corresponding parts as those in the first embodiment, and the description of such parts is omitted.

[0072] In FIG. 6, the module 100 includes a wiring board 101, an integrated circuit component 102, an elastic wave device 1, an inductor 103, and a sealing portion 104.

[0073] The wiring board 101 is equivalent to the wiring board 2 in the first embodiment. The integrated circuit component 102 is mounted inside the wiring board 101. The integrated circuit component 102 includes a switching circuit and a low-noise amplifier. The elastic wave device 1 is mounted on the main surface of the wiring board 101. The inductor 103 is mounted on the main surface of the wiring board 101. The inductor 103 is mounted for impedance matching. For example, the inductor 103 is an Integrated Passive Device (IPD). The sealing portion 104 seals a plurality of electronic components including the elastic wave device 1.

[0074] According to the second embodiment described above, the module 100 includes the elastic wave device 1. Therefore, it is possible to realize the module 100 including the elastic wave device 1 with improved frequency temperature characteristics without increasing the chip size.

[0075] Although some aspects of at least one embodiment have been described, it should be understood that various modifications, corrections, and improvements can be easily conceived by those skilled in the art. Such modifications, corrections, and improvements are intended to be part of the present disclosure and are intended to be within the scope of the present disclosure.

[0076] It should be understood that the embodiments of the methods and apparatuses described herein are not limited to the details of the structures and arrangements of the components described in the above description or illustrated in the accompanying drawings. The methods and apparatuses can be implemented in other embodiments and can be carried out or executed in various manners.

[0077] Specific implementation examples are provided herein for illustrative purposes only and are not intended to be limiting.

[0078] The expressions and terms used in this disclosure are for explanatory purposes and should not be regarded as limiting. The use of "including", "comprising", "having", "containing" and variations thereof herein means the inclusion of the items listed hereinafter and their equivalents as well as additional items.

[0079] References to "or (alternatively)" can be construed such that any term described using "or (alternatively)" indicates one, more than one, and all of the terms described in the said description.

[0080] References to front and back, left and right, top and bottom, vertical and horizontal, front and back are all for the purpose of convenience of description. Such references do not limit the components of the present disclosure to any one positional or spatial orientation. Therefore, the above description and drawings are merely illustrative.

Description of Reference Numerals

[0081] 1 Elastic Wave Device, 2 Wiring Substrate, 2A Conductive Pad, 2B Conductive Pad, 2C Internal Conductor, 3 Chip Substrate, 3A Piezoelectric Substrate, 3B Support Substrate, 4 Bump, 5 Sealing Portion, 6 Wiring Pattern, 7 Elastic Wave Element, 7A IDT Electrode, 7B Reflector, 7C Electrode Finger, 7D Bus Bar, 8 Space, 100 Module, 101 Wiring Substrate, 102 Integrated Circuit Component, 103 Inductor, 104 Sealing Portion

Claims

1. A piezoelectric substrate, A plurality of parallel resonators and four or more series resonators formed on the piezoelectric substrate and functioning as a band-pass filter, Comprising, When the anti-resonance frequencies of the plurality of series resonators are the first series resonator, the second series resonator, the third series resonator, and the fourth series resonator in order of being close to the high-frequency end of the passband of the band-pass filter, An elastic wave device in which the duty ratio of the first series resonator is smaller than the duty ratios of the second series resonator and the third series resonator.

2. The elastic wave device according to claim 1, wherein the duty ratio of the second series resonator is smaller than the duty ratio of the third series resonator.

3. The elastic wave device according to claim 2, wherein the duty ratio of the third series resonator is smaller than the duty ratio of the fourth series resonator.

4. The elastic wave device according to claim 3, wherein the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the second series resonator and the duty ratio of the third series resonator.

5. The elastic wave device according to claim 3, wherein the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the third series resonator and the duty ratio of the fourth series resonator.

6. The elastic wave device according to claim 3, wherein the difference between the duty ratio of the first series resonator and the duty ratio of the second series resonator is larger than the difference between the duty ratio of the second series resonator and the duty ratio of the fourth series resonator.

7. The elastic wave device according to claim 1, wherein the plurality of parallel resonators and the plurality of series resonators function as a transmission filter.

8. A module comprising the elastic wave device according to any one of claims 1 to 7.

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