JP2024061050A - Elastic wave device and module including the elastic wave device - Google Patents

Abstract

To provide an elastic wave device with improved power resistance.SOLUTION: An elastic wave device includes a piezoelectric substrate and a plurality of resonators constituting a bandpass filter formed on the piezoelectric substrate. At least one of the plurality of resonators is a multistep split resonator including a first split resonator to which an input electric signal is input first, a second split resonator to which the input electric signal is input the last, and a third split resonator disposed between the first split resonator and the second split resonator, which are split in series. The resonance frequency of the multistep split resonator is on the high frequency side among bandpass filter frequency bands. The resonance frequency of the first split resonator and the resonance frequency of the second split resonator are lower than the resonance frequency of the third split resonator.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to an acoustic wave device and a module including the acoustic wave device.

Due to recent technological advances, mobile communication terminals such as smartphones have become significantly smaller and lighter. Acoustic wave devices that can be miniaturized are used as acoustic wave devices for such mobile communication terminals. In addition, the number of mobile communication systems that can simultaneously transmit and receive is rapidly increasing, and the demand for duplexers is also growing rapidly.

As mobile communication systems change, the required specifications for acoustic wave devices are becoming stricter. In other words, there is a need for acoustic wave devices that are smaller than before. However, if acoustic wave devices are made smaller, the SAW resonators must also be made smaller, which reduces the power handling capability.

The electrodes of a SAW resonator are repeatedly subjected to internal stress in response to the applied voltage and frequency. This stress tends to cause the metal atoms that make up the electrodes to diffuse and move along grain boundaries, causing short circuits due to the formation of protrusions and breaks due to the formation of voids, resulting in a significant deterioration of characteristics. This phenomenon is generally known as stress migration. Therefore, as acoustic wave devices become more compact, it is necessary to improve the power resistance of the electrodes of SAW resonators.

Patent document 1 discloses a technique for dividing SAW resonators in series to improve power durability.

JP 2006-74202 A

However, in the acoustic wave device described in Patent Document 1, in a series split resonator divided into three or more parts, heat from the split resonator located on the inside is difficult to escape. As a result, stress migration is likely to occur in the split resonator located on the inside, and the acoustic wave device does not have sufficient power resistance.

The present disclosure has been made to solve the above-mentioned problems. The purpose of the present disclosure is to provide an acoustic wave device and a module including the acoustic wave device that further suppresses stress migration of the series split resonator adopted for the purpose of improving power durability and has improved power durability. It is also to provide an acoustic wave device that consumes less power and has excellent environmental performance, and a module including the acoustic wave device.

The acoustic wave device according to the present disclosure comprises:
A piezoelectric substrate;
a plurality of resonators constituting a bandpass filter formed on the piezoelectric substrate;
At least one of the plurality of resonators is a multi-stage split resonator including a first split resonator to which an input electrical signal is input first, a second split resonator to which an input electrical signal is input last, and a third split resonator disposed between the first split resonator and the second split resonator, the multi-stage split resonator being divided in series;
The resonant frequency of the multi-stage split resonator is on the high frequency side of the bandpass filter frequency band, and the resonant frequency of the first split resonator and the resonant frequency of the second split resonator are lower than the resonant frequency of the third split resonator.

In one aspect of the present invention, the resonant frequency of the multi-stage split resonator is on the high frequency side of the bandpass filter frequency band.

It is an aspect of the present disclosure that the capacitance of the third split resonator is greater than the capacitance of the first split resonator and the capacitance of the second split resonator.

The multi-stage split resonator includes a fourth split resonator arranged between the first split resonator and the third split resonator, and a fifth split resonator arranged between the second split resonator and the third split resonator, and the resonant frequencies of the third split resonator, the fourth split resonator, and the fifth split resonator are higher than the resonant frequencies of the first split resonator and the second split resonator, according to one aspect of the present invention.

It is an aspect of the present invention that the resonant frequency of the third split resonator is higher than the resonant frequencies of the fourth split resonator and the fifth split resonator.

It is an aspect of the present disclosure that the capacitance of the third split resonator, the fourth split resonator, and the fifth split resonator is greater than the capacitance of the first split resonator and the second split resonator.

It is one aspect of the present disclosure that the capacitance of the third split resonator is greater than the capacitance of the fourth split resonator and the fifth split resonator.

In one aspect of the present disclosure, the piezoelectric substrate is a substrate made of a single crystal of lithium niobate or lithium tantalate.

In one embodiment of the present disclosure, the piezoelectric substrate is provided with a support substrate on a main surface opposite to the main surface on which the multiple resonators are formed, and the support substrate is a substrate made of sapphire, silicon, alumina, spinel, quartz, or glass.

In one embodiment of the present disclosure, the multiple resonators include multiple series resonators and multiple parallel resonators that form a ladder-type bandpass filter, and the multi-stage split resonator is a series resonator that receives an input electrical signal first or second among the multiple series resonators.

It is one aspect of the present disclosure that the multiple resonators function as a duplexer.

A module including the acoustic wave device is one aspect of the present disclosure.

This disclosure makes it possible to improve the power durability of acoustic wave devices.

FIG. 1 is a vertical cross-sectional view of an acoustic wave device according to a first embodiment. FIG. 2 is a diagram illustrating an example of an acoustic wave element (resonator) of the acoustic wave device according to the first embodiment. In FIG. FIG. 3 is a diagram illustrating an example of an acoustic wave device according to the first embodiment. FIG. 4 is a diagram showing the power handling capability of the second series resonator in the first embodiment and a resonator of a comparative example. Figure 5 shows the power handling capabilities of the resonators in a modified example in which the capacitances of the five series split resonators of the second series resonator in embodiment 1 are all set to the same value, the resonant frequency of the third series split resonator D3 is made the highest, followed by the fourth series split resonator D4 and the fifth series split resonator D5, and the resonant frequencies of the first series split resonator D1 and the second series split resonator D2 are made the lowest, as well as the second comparative example. FIG. 6 is a diagram showing power consumption of the second series resonator in the first embodiment and a resonator of the comparative example. FIG. 7 is a diagram showing the power consumption of the resonator of the modified example and the resonator of the second comparative example. FIG. 8 is a vertical cross-sectional view of a module to which the acoustic wave device according to the first embodiment is applied.

The embodiment will be described with reference to the attached drawings. In each drawing, the same or corresponding parts are given the same reference numerals. Duplicate explanations of the parts will be appropriately simplified or omitted.

Embodiment 1.
FIG. 1 is a vertical cross-sectional view of an acoustic wave device according to a first embodiment.

As shown in FIG. 1, the acoustic wave device 20 includes a wiring substrate 23, an external connection terminal 24, a device chip 25, electrode pads 26, bumps 27, and a sealing portion 28.

For example, the wiring board 23 is a multi-layer board made of resin. For example, the wiring board 23 is a low temperature co-fired ceramics (LTCC) multi-layer board made of multiple dielectric layers.

Multiple external connection terminals 24 are formed on the underside of the wiring board 23.

Multiple electrode pads 26 are formed on the main surface of the wiring board 23. For example, the electrode pads 26 are formed of copper or an alloy containing copper. For example, the thickness of the electrode pads 26 is 10 μm to 20 μm.

The bumps 27 are formed on the upper surface of each of the electrode pads 26. For example, the bumps 27 are gold bumps. For example, the height of the bumps 27 is 10 μm to 50 μm.

A gap 29 is formed between the wiring board 23 and the device chip 25.

The device chip 25 is mounted on the wiring substrate 23 by flip-chip bonding via the bumps 27. The device chip 25 is electrically connected to the multiple electrode pads 26 via the multiple bumps 27.

The device chip 25 is, for example, a surface acoustic wave device chip. The device chip 25 has a piezoelectric substrate formed from a piezoelectric material. The piezoelectric substrate is a substrate formed from a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz.

The thickness of the piezoelectric substrate can be, for example, 100 μm to 300 μm. According to another example, the piezoelectric substrate is a substrate formed of piezoelectric ceramics.

According to yet another example, the device chip 25 is a substrate in which a piezoelectric substrate and a support substrate are bonded. The support substrate is, for example, a substrate made of sapphire, silicon, alumina, spinel, quartz, or glass. In this case, the thickness of the piezoelectric substrate can be, for example, 0.3 μm to 5 μm.

An acoustic wave element 52 is formed on the piezoelectric substrate. For example, a transmission filter or a reception filter including a plurality of acoustic wave elements 52 is formed on the main surface of the device chip 25.

According to another example, a duplexer including a transmit filter and a receive filter is formed on the main surface of the device chip 25.

The transmit filter is formed so that electrical signals in the desired frequency band can pass through. For example, the transmit filter is a ladder-type filter consisting of multiple series resonators and multiple parallel resonators.

The receiving filter is formed so that electrical signals in the desired frequency band can pass through. For example, the receiving filter is a ladder filter.

The sealing portion 28 is formed to cover the device chip 25. For example, the sealing portion 28 is formed of an insulating material such as a synthetic resin. For example, the sealing portion 28 is formed of a metal.

When the sealing portion 28 is formed of a synthetic resin, the synthetic resin is an epoxy resin, a polyimide, or the like. Preferably, the sealing portion 28 is formed of an epoxy resin using a low-temperature curing process.

Next, an example of an acoustic wave element 52 formed on the device chip 25 will be described with reference to Figure 2. Figure 2 is a diagram showing an example of an acoustic wave element (resonator) of the acoustic wave device in embodiment 1.

As shown in FIG. 2, an IDT (Interdigital Transducer) electrode 52a and a pair of reflectors 52b are formed on the main surface of the device chip 25. The IDT electrode 52a and the pair of reflectors 52b are arranged so as to excite elastic waves (mainly SH waves).

For example, the IDT electrode 52a and the pair of reflectors 52b are formed of an alloy of aluminum and copper. For example, the IDT 52a and the pair of reflectors 52b are formed of a suitable metal such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, silver, or an alloy of these metals.

For example, the IDT electrode 52a and the pair of reflectors 52b are formed from a laminated metal film in which multiple metal layers are stacked. For example, the thickness of the IDT electrode 52a and the pair of reflectors 52b is 150 nm to 450 nm.

The IDT electrode 52a has a pair of comb electrodes 52c. The pair of comb electrodes 52c face each other. The comb electrodes 52c have a plurality of electrode fingers 52d and a bus bar 52e.

The multiple electrode fingers 52d are arranged with their longitudinal directions aligned. The bus bar 52e connects the multiple electrode fingers 52d.

One of the pair of reflectors 52b is adjacent to one side of the IDT electrode 52a. The other of the pair of reflectors 52b is adjacent to the other side of the IDT electrode 52a.

Next, an example of a transmission filter formed on the device chip 25 will be described with reference to FIG. 3. FIG. 3 is a diagram showing an example of an acoustic wave device according to the first embodiment.

As shown in FIG. 3, a transmit filter 30, which is a bandpass filter, is formed on the device chip 25. The transmit filter 30 includes, for example, a first series resonator S1 and a second series resonator S2, which are multiple series resonators. The transmit filter 30 is a ladder-type filter that includes, for example, a first parallel resonator P1 and a second parallel resonator P2, which are multiple parallel resonators, and also includes an input pad IN, an antenna pad ANT, and a ground pad GND.

The first series resonator S1 includes a plurality of series split resonators. The second series resonator S2 includes a plurality of series split resonators, namely, a first series split resonator D1, a second series split resonator D2, a third series split resonator D3, a fourth series split resonator D4, and a fifth series split resonator D5.

The first series split resonator D1, the second series split resonator D2, the third series split resonator D3, the fourth series split resonator D4 and the fifth series split resonator D5 may include an IDT electrode.

Among the series split resonators of the second series resonator S2, the first series split resonator D1 is a series split resonator arranged at a position where the electrical signal applied to the input pad IN is first applied. The capacitance and resonant frequency of the first series split resonator D1 can be, for example, 2.54 pF and 2543.2 MHz in a Band 7 transmit filter.

Among the series split resonators of the second series resonator S2, the second series split resonator D2 is a series split resonator arranged at a position where the electrical signal applied to the input pad IN is finally applied. The capacitance and resonant frequency of the second series split resonator D2 can be, for example, 2.56 pF and 2546.2 MHz in a Band 7 transmit filter.

Among the series split resonators of the second series split resonator S2, the third series split resonator D3 is a series split resonator arranged between the first series split resonator D1 and the second series split resonator D2. The capacitance and resonant frequency of the third series split resonator D3 can be, for example, 2.61 pF and 2549.3 MHz in a Band 7 transmit filter.

Among the series split resonators of the second series split resonator S2, the fourth series split resonator D4 is a series split resonator arranged between the first series split resonator D1 and the third series split resonator D3. The capacitance and resonant frequency of the fourth series split resonator D4 can be, for example, 2.56 pF and 2546.2 MHz in a Band 7 transmit filter.

Among the series split resonators of the second series split resonator S2, the fifth series split resonator D5 is a series split resonator arranged between the second series split resonator D2 and the third series split resonator D3. The capacitance and resonant frequency of the fifth series split resonator D5 can be, for example, 2.54 pF and 2543.2 MHz in a Band 7 transmit filter.

Bumps 27 are arranged on the input pad IN, antenna pad ANT, and ground pad GND, and are electrically connected to bump pads 26 formed on the wiring board 23.

Here, the resonator including the series split resonator generates heat when an electrical signal is applied and excited. If heat dissipation is insufficient, the high temperature state continues for a long time, which can easily cause stress migration and destroy the resonator. The resonator dissipates heat mainly from the bumps through the wiring. Heat can also be dissipated through the piezoelectric substrate, but the piezoelectric substrate generally has poor thermal conductivity and is therefore difficult to dissipate heat.

Here, the first series split resonator D1 and the second series split resonator D2 are smaller in distance to the bump 27 formed on the input pad IN and the bump 27 formed on the ground pad GND than the third series split resonator D3. Therefore, the first series split resonator D1 and the second series split resonator D2 are easier to dissipate heat than the third series split resonator D3.

In other words, the third series split resonator D3 is less susceptible to heat dissipation than the first series split resonator D1 and the second series split resonator D2, and is required to have higher power resistance from the standpoint of heat dissipation.

Furthermore, the third series split resonator D3 is a series split resonator located in the center. When the third series split resonator D3 is excited and generates heat, the first series split resonator D1 and the second series split resonator D2 are also excited and generate heat. The third series split resonator D3 is sandwiched between the heat generating body, and the amount of heat that can be dissipated from the heat dissipation path is smaller than that of the first series split resonator D1 and the second series split resonator D2.

Therefore, of the series split resonators of the second series resonator S2, the third series split resonator D3 located in the center is required to have higher power resistance from the viewpoint of heat dissipation.

The fourth series split resonator D4 is a series split resonator arranged between the first series split resonator D1 and the third series split resonator D3. When the fourth series split resonator D4 is excited and generates heat, the first series split resonator D1 and the third series split resonator D3 are also excited and generate heat. The fourth series split resonator D4 is sandwiched between the heat generating body, and the amount of heat that can be dissipated from the heat dissipation path is less than that of the first series split resonator D1, but it is easier to dissipate heat than the third series split resonator D3.

Therefore, from the viewpoint of heat dissipation, the fourth series split resonator D4 of the series split resonators of the second series split resonator S2 is required to have higher power resistance than the first series split resonator D1, but is not required to have higher power resistance than the third series split resonator D3.

The fifth series split resonator D5 is a series split resonator arranged between the second series split resonator D2 and the third series split resonator D3. When the fifth series split resonator D5 is excited and generates heat, the second series split resonator D2 and the third series split resonator D3 are also excited and generate heat. The fifth series split resonator D5 is sandwiched between the heat generating body, and the amount of heat that can be dissipated from the heat dissipation path is less than that of the second series split resonator D2, but it is easier to dissipate heat than the third series split resonator D3.

Therefore, from the viewpoint of heat dissipation, the fifth series split resonator D5 of the series split resonators of the second series split resonator S2 is required to have higher power resistance than the second series split resonator D2, but is not required to have higher power resistance than the third series split resonator D3.

In general, the larger the capacitance of a resonator, the smaller the displacement of the IDT electrode and the greater the power handling capability. Therefore, the third series-split resonator D3 has a larger capacitance than the first series-split resonator D1 and the second series-split resonator D2. This improves the power handling capability of the second series-split resonator S2.

In addition, the fourth series split resonator D4 and the fifth series split resonator D5 have a larger capacitance than the first series split resonator D1 and the second series split resonator D2. This further improves the power handling capability of the second series split resonator S2.

In this way, the capacitance is increased and the displacement is reduced for series split resonators located in the center where heat tends to accumulate. In contrast, the capacitance of series split resonators located on the outside is forced to be smaller, resulting in a larger displacement and reduced power handling capability, but within the limited size of the resonator, the power handling capability of the resonator as a whole is higher.

The passband of the transmit filter 30 can be, for example, 2500 MHz to 2570 MHz in Band 7. The resonant frequency of the second series resonator S2 in the first embodiment is 2543.2 to 2549.3 Hz, which is on the high-frequency side of the frequency band of the transmit filter 30, which is a band-pass filter.

Here, the series resonator of the ladder filter is more likely to generate heat the closer its resonant frequency is to 2570 MHz (system frequency), which is the highest frequency in the passband, on the higher frequency side.

Therefore, among the series split resonators of the second series resonator S2, the third series split resonator D3, which requires the highest power handling capability, has a resonant frequency of 2549.3 MHz, and among the series split resonators of the second series resonator S2, the first series split resonator D1, which has the best heat dissipation capability, has a resonant frequency of 2543.2 MHz. This further improves the power handling capability of the second series resonator S2.

Figure 4 shows the power resistance of the second series resonator in embodiment 1 and the resonator in the comparative example. The solid line shows the power resistance of the second series resonator in embodiment 1. The dashed line shows the power resistance of the resonator in the comparative example.

The resonator in the comparative example has five series-split resonators, each with the same capacitance.

Here, power durability is compared using the SDV value, which is the product of power consumption and electrode finger displacement divided by the area of the resonator. The SDV value is the SAW durability value, which indicates the load the resonator is subjected to per unit area, and a lower value indicates a higher power durability.

As shown in Figure 4, it can be seen that the second series resonator in embodiment 1 has better power handling capability than the resonator in the comparative example.

Figure 5 shows the power handling capability of the resonators in a modified example in which the capacitances of the five series-split resonators of the second series resonator in embodiment 1 are all set to the same value, the resonant frequency of the third series-split resonator D3 is set to the highest, the resonant frequencies of the fourth series-split resonator D4 and the fifth series-split resonator D5 are set to the next highest, and the resonant frequencies of the first series-split resonator D1 and the second series-split resonator D2 are set to the lowest, as well as the second comparative example. The solid line shows the power handling capability of the modified example in embodiment 1. The dashed line shows the power handling capability of the resonators in the second comparative example.

The resonator in the second comparative example has five series-split resonators, all of which have the same capacitance and resonant frequency.

As shown in Figure 5, the resonator of the modified example has better power resistance than the resonator of the second comparative example.

Figure 6 shows the power consumption of the second series resonator in the first embodiment and the resonator in the comparative example. The solid line shows the power consumption of the second series resonator in the first embodiment. The dashed line shows the power consumption of the resonator in the comparative example.

As shown in Figure 6, the second series resonator in embodiment 1 consumes less power and has better environmental performance than the resonator in the comparative example.

Figure 7 shows the power consumption of the resonator of the modified example and the resonator of the second comparative example. The solid line shows the power consumption of the resonator of the modified example. The dashed line shows the power consumption of the resonator in the second comparative example.

As shown in Figure 7, the resonator of the modified example consumes less power and has better environmental performance than the resonator of the second comparative example.

According to the first embodiment described above, in a series-split resonator that requires high power resistance, the power resistance can be improved without increasing the size. Therefore, an acoustic wave device with improved power resistance can be provided. In addition, an acoustic wave device with low power consumption and excellent environmental performance can be provided.

Embodiment 2.
8 is a vertical cross-sectional view of a module to which the acoustic wave device according to the first embodiment is applied. Note that the same reference numerals are used to designate the same or corresponding parts as those in the first embodiment, and the description of these parts is omitted.

In FIG. 8, the module 100 includes a wiring board 130, a plurality of external connection terminals 131, an integrated circuit component IC, an acoustic wave device 20, an inductor 111, and a sealing portion 117.

The multiple external connection terminals 131 are formed on the lower surface of the wiring board 130. The multiple external connection terminals 131 are mounted on the motherboard of a preset mobile communication terminal.

For example, the integrated circuit component IC is mounted inside the wiring board 130. The integrated circuit component IC includes a switching circuit and a low-noise amplifier.

The acoustic wave device 20 is mounted on the main surface of the wiring board 130.

The inductor 111 is mounted on the main surface of the wiring board 130. The inductor 111 is mounted for impedance matching. For example, the inductor 111 is an integrated passive device (IPD).

The sealing portion 117 seals multiple electronic components including the acoustic wave device 20.

According to the second embodiment described above, the module 100 includes an acoustic wave device 20. This makes it possible to provide a module including an acoustic wave device with improved power resistance.

While several aspects of at least one embodiment have been described, it should be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of, and are intended to be within the scope of, this disclosure.

It should be understood that the embodiments of the methods and apparatus described herein are not limited in their application to the details of construction and arrangement of components set forth in the above description or illustrated in the accompanying drawings. The methods and apparatus may be implemented in other embodiments and practiced or carried out in various ways.

The specific implementation examples are provided here for illustrative purposes only and are not intended to be limiting.

The phraseology and terminology used in this disclosure are for purposes of description and should not be regarded as limiting. The use herein of "including," "comprising," "having," "including" and variations thereof means the inclusion of the items listed thereafter and equivalents thereof as well as additional items.

References to "or" may be construed as meaning that any term described using "or" refers to one, more than one, and all of those described terms.

All references to front, back, left, right, top, bottom, top, bottom, width, length, front and back are intended for convenience of description. Such references are not intended to limit the components of this disclosure to any one positional or spatial orientation. Accordingly, the above description and drawings are by way of example only.

20 Acoustic wave device, 23 Wiring board, 24 External connection terminal 25 Device chip, 26 Electrode pad, 27 Bump 28 Sealing portion 52 Acoustic wave element, 52a IDT electrode, 52b Reflector
52c Interdigital electrode, 52d Electrode finger, 52e Bus bar 30 Transmission filter, S1 First series resonator, S2 Second series resonator
P1: first parallel resonator, P2: second parallel resonator
IN: input pad, ANT: antenna pad, GND: ground pad D1: first series split resonator, D2: second series split resonator, D3: third series split resonator, D4: fourth series split resonator, D5: fifth series split resonator 100: module, 130: wiring board, 131: external connection terminal IC: integrated circuit component, 111: inductor, 117: sealing portion

The acoustic wave device according to the present disclosure comprises:
A piezoelectric substrate;
a plurality of resonators constituting a bandpass filter formed on the piezoelectric substrate ;
An input pad formed on the piezoelectric substrate;
an output pad formed on the piezoelectric substrate;
a ground pad formed on the piezoelectric substrate;
Equipped with
At least one of the plurality of resonators is a multi-stage split resonator including a first split resonator to which the electrical signal input from the input pad is first input, a second split resonator to which the electrical signal input from the input pad is last input, and a third split resonator disposed between the first split resonator and the second split resonator, the multi-stage split resonator being divided in series;
a resonant frequency of the first split resonator and a resonant frequency of the second split resonator are lower than a resonant frequency of the third split resonator;
The capacitance of the third split resonator is larger than the capacitance of the first split resonator and the capacitance of the second split resonator .

In one aspect of the present invention, a resonant frequency of the multi-stage divided resonator is on the higher frequency side of a center frequency of the bandpass filter frequency band .

Among the series split resonators of the second series resonator S2, the second series split resonator D2 is a series split resonator arranged at a position where the electrical signal applied to the input pad IN is finally applied. The capacitance and resonant frequency of the second series split resonator D2 may be, for example, 2.54 pF and 2543.2 MHz in a Band 7 transmission filter.

Among the series split resonators of the second series split resonator S2, the fifth series split resonator D5 is a series split resonator disposed between the second series split resonator D2 and the third series split resonator D3. The capacitance and resonant frequency of the fifth series split resonator D5 may be, for example, 2.56 pF and 2546.2 MHz in a Band 7 transmission filter.

Claims (12)

A piezoelectric substrate;
a plurality of resonators constituting a bandpass filter formed on the piezoelectric substrate;
At least one of the plurality of resonators is a multi-stage split resonator including a first split resonator to which an input electrical signal is input first, a second split resonator to which an input electrical signal is input last, and a third split resonator disposed between the first split resonator and the second split resonator, the multi-stage split resonator being divided in series;
An acoustic wave device in which a resonant frequency of the first split resonator and a resonant frequency of the second split resonator are lower than a resonant frequency of the third split resonator. The acoustic wave device according to claim 1, wherein the resonant frequency of the multi-stage split resonator is on the high frequency side of the bandpass filter frequency band. The acoustic wave device of claim 1, wherein the capacitance of the third split resonator is greater than the capacitance of the first split resonator and the capacitance of the second split resonator. The elastic wave device of claim 1, wherein the multi-stage split resonator includes a fourth split resonator arranged between the first split resonator and the third split resonator, and a fifth split resonator arranged between the second split resonator and the third split resonator, and the resonant frequencies of the third split resonator, the fourth split resonator, and the fifth split resonator are higher than the resonant frequencies of the first split resonator and the second split resonator. The acoustic wave device of claim 4, wherein the resonant frequency of the third split resonator is higher than the resonant frequencies of the fourth split resonator and the fifth split resonator. The acoustic wave device of claim 4, wherein the capacitance of the third split resonator, the fourth split resonator, and the fifth split resonator is greater than the capacitance of the first split resonator and the second split resonator. The acoustic wave device of claim 4, wherein the capacitance of the third split resonator is greater than the capacitance of the fourth split resonator and the fifth split resonator. The acoustic wave device according to any one of claims 1 to 7, wherein the piezoelectric substrate is a substrate made of a single crystal of lithium niobate or lithium tantalate. The acoustic wave device according to any one of claims 1 to 7, further comprising a support substrate on a main surface of the piezoelectric substrate opposite to the main surface on which the plurality of resonators are formed, the support substrate being a substrate made of sapphire, silicon, alumina, spinel, quartz, or glass. The acoustic wave device according to any one of claims 1 to 7, wherein the plurality of resonators includes a plurality of series resonators and a plurality of parallel resonators that form a ladder-type bandpass filter, and the multi-stage split resonator is a series resonator to which an input electrical signal is input first or second among the plurality of series resonators. The acoustic wave device according to any one of claims 1 to 7, wherein the plurality of resonators function as a duplexer. A module comprising the acoustic wave device according to claim 1 .