Acoustic wave device and module including the same

Abstract

To provide an acoustic wave device having improved steepness between a passband and a stopband.SOLUTION: An elastic wave device includes a bandpass filter including a plurality of series resonators and a plurality of parallel resonators, and configured to pass signals of a predetermined frequency band, and the plurality of series resonators include a first series resonator having a first anti-resonant frequency and a second anti-resonant frequency, and the first anti-resonant frequency is near a lowest frequency in the frequency band, and the second anti-resonant frequency is higher than the highest frequency in the frequency band.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Due to recent technological advancements, smartphones and the like, typified by mobile communication terminals, have been remarkably miniaturized and lightened. As such an elastic wave device used in such a mobile communication terminal, an elastic wave device capable of miniaturization is used. Further, as a mobile communication system, the number of communication systems for simultaneous transmission and reception has rapidly increased, and the demand for duplexers has rapidly increased.

[0003] With the changes in mobile communication systems, the required specifications for elastic wave devices have become more stringent. That is, characteristics superior to those of the prior art are required.

[0004] Between the passband and the stopband, characteristics with higher steepness are required.

[0005] Patent Document 1 discloses a technique for improving the steepness of pass characteristics on the high-frequency side of the passband.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the elastic wave device described in Patent Document 1, the steepness between the passband and the stopband is not sufficient.

[0008] The present disclosure has been made to solve the above-described problems. An object of the present disclosure is to provide an elastic wave device with improved steepness between a pass band and a stop band, and a module including the elastic wave device.

Means for Solving the Problems

[0009] The elastic wave device according to the present disclosure includes a plurality of series resonators and a plurality of parallel resonators, and includes a band-pass filter that passes a signal in a predetermined frequency band. The plurality of series resonators includes a first series resonator having a first anti-resonance frequency and a second anti-resonance frequency. The first anti-resonance frequency is near the lowest frequency in the frequency band. The second anti-resonance frequency is higher than the highest frequency in the frequency band, and the elastic wave device is thus configured.

[0010] In one aspect of the present invention, the first series resonator is a resonator to which an electrical signal is first applied among the plurality of series resonators.

[0011] In one aspect of the present disclosure, the band-pass filter is a ladder-type filter, and the first series resonator is one of the series resonators obtained by dividing in series the series resonators constituting one stage of the ladder of the ladder-type filter.

[0012] In one aspect of the present invention, the first series resonator is an elastic surface wave resonator including an IDT, a central region having a first pitch, both regions (non-central regions) adjacent to the central region having a second pitch, and both regions (outer regions) adjacent to the outside of the non-central region having a third pitch, and the first pitch is smaller than the second pitch, and the second pitch is larger than the third pitch.

[0013] The first series resonator includes a pair of reflectors adjacent to the IDT, and in a region closest to the IDT, the pitch of the reflectors is smaller than the second pitch, and in a region farthest from the IDT, the pitch of the reflectors is larger than the second pitch, which is one aspect of the present invention.

[0014] In one aspect of the present disclosure, the duty ratio of the central region is larger than the duty ratio of the non-central region.

[0015] In one aspect of the present disclosure, the frequency band of the bandpass filter is 100 MHz or less.

[0016] In one aspect of the present disclosure, a value obtained by dividing a difference between the highest frequency and the lowest frequency in the frequency band of the bandpass filter by the center frequency of the frequency band is 0.5% or more and 4.0% or less.

[0017] A module including the surface acoustic wave device is one aspect of the present disclosure.

Advantages of the Invention

[0018] According to the present disclosure, it is possible to improve the attenuation characteristics on the low-frequency side and the high-frequency side of the passband of the surface acoustic wave device.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] 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. The redundant description of such parts will be simplified or omitted as appropriate.

[0021] Embodiment 1. FIG. 1 is a longitudinal sectional view of the elastic wave device in Embodiment 1.

[0022] As shown in FIG. 1, the elastic wave device 20 includes a wiring substrate 23, external connection terminals 24, a device chip 25, electrode pads 26, bumps 27, and a sealing portion 28.

[0023] For example, the wiring substrate 23 is a multilayer substrate made of resin. For example, the wiring substrate 23 is a low temperature co-fired ceramics (LTCC) multilayer substrate composed of a plurality of dielectric layers.

[0024] A plurality of external connection terminals 24 are formed on the lower surface of the wiring substrate 23.

[0025] A plurality of electrode pads 26 are formed on the main surface of the wiring substrate 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 from 10 μm to 20 μm.

[0026] The bumps 27 are formed on the respective upper surfaces of the electrode pads 26. For example, the bumps 27 are gold bumps. For example, the height of the bumps 27 is from 10 μm to 50 μm.

[0027] A gap 29 is formed between the wiring substrate 23 and the device chip 25.

[0028] 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 a plurality of electrode pads 26 via a plurality of bumps 27.

[0029] The device chip 25 is, for example, a surface acoustic wave device chip. The device chip 25 includes a piezoelectric substrate formed of a piezoelectric material. The piezoelectric substrate is a substrate formed of a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz.

[0030] The thickness of the piezoelectric substrate can be, for example, from 100 μm to 300 μm. According to another example, the piezoelectric substrate is a substrate formed of piezoelectric ceramics.

[0031] According to yet another example, the device chip 25 is a substrate in which a piezoelectric substrate and a support substrate are joined. The support substrate is, for example, a substrate formed of sapphire, silicon, alumina, spinel, quartz, or glass. In this case, the thickness of the piezoelectric substrate can be, for example, from 0.3 μm to 5 μm.

[0032] An elastic wave element 52 is formed on the piezoelectric substrate. For example, on the main surface of the device chip 25, a transmission filter or a reception filter including a plurality of elastic wave elements 52 is formed.

[0033] According to another example, a duplexer including a transmission filter and a reception filter is formed on the main surface of the device chip 25.

[0034] The transmission filter is formed so that an electric signal in a desired frequency band can pass through. For example, the transmission filter is a ladder filter composed of a plurality of series resonators and a plurality of parallel resonators.

[0035] The reception filter is formed so that an electric signal in a desired frequency band can pass through. For example, the reception filter is a ladder filter.

[0036] The sealing portion 28 is formed so as to cover the device chip 25. For example, the sealing portion 28 is formed of an insulator such as a synthetic resin. For example, the sealing portion 28 is formed of metal.

[0037] 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. A void 29 is formed in the region where the wiring substrate 23 and the device chip 25 face each other.

[0038] Next, an example of the elastic wave element 52 formed on the device chip 25 will be described with reference to FIG. 2. FIG. 2 is a diagram showing an example of an elastic wave element (resonator) of the elastic wave device in the first embodiment.

[0039] As shown in FIG. 2, the IDT (Interdigital Transducer) electrode 52a and the 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 provided so as to be able to excite elastic waves (mainly SH waves).

[0040] 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 an appropriate metal such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, silver, or an alloy thereof.

[0041] For example, the IDT electrode 52a and the pair of reflectors 52b are formed of a laminated metal film in which a plurality of metal layers are laminated. For example, the thickness of the IDT electrode 52a and the pair of reflectors 52b is from 150 nm to 450 nm.

[0042] The IDT electrode 52a includes a pair of comb-shaped electrodes 52c. The pair of comb-shaped electrodes 52c face each other. The comb-shaped electrode 52c includes a plurality of electrode fingers 52d and a bus bar 52e.

[0043] The plurality of electrode fingers 52d are arranged with their longitudinal directions aligned. The bus bar 52e connects the plurality of electrode fingers 52d.

[0044] 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.

[0045] Next, an example of a bandpass 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 elastic wave device in the first embodiment.

[0046] As shown in FIG. 3, a receiving filter 30, which is a bandpass filter, is formed on the device chip 25. The receiving filter 30 includes an input pad IN, an output pad OUT, and a ground pad GND.

[0047] The receiving filter 30 also includes series resonators S1-1, S1-2, S2, S3-1, S3-2, and S4. The receiving filter 30 also includes parallel resonators P1-1, P1-2, P1-3, P2, P3-1, and P3-2. The receiving filter 30 is a ladder-type filter.

[0048] In addition, the series resonator S1-1 is arranged closest to the input pad IN circuitously and is the resonator to which an electrical signal is first applied. Also, the series resonator S1-1 and the series resonator S1-2 are the result of a series division of the series resonator S1 at the first stage of the ladder-type filter.

[0049] Similarly, the series resonator S3-1 and the series resonator S3-2 are also the result of a series division of the series resonator S3.

[0050] In addition, the parallel resonators P1-1, P1-2, and P1-3 are the result of a parallel division of the parallel resonator P1 at the first stage of the ladder-type filter. Similarly, the parallel resonators P3-1 and P3-2 are also the result of a parallel division of the parallel resonator P3.

[0051] FIG. 4 is a diagram showing the anti-resonance characteristics of the series resonator S1-1 of the receiving filter 30 of the surface acoustic wave device 20 in Embodiment 1. The anti-resonance characteristics of the series resonator S1-1 are shown by a solid line.

[0052] Also, as a reference example, the anti-resonance characteristics of a conventional series resonator are shown by a dashed line. The first anti-resonance frequency Fa1 of the series resonator S1-1 is 2150 MHz. The second anti-resonance frequency Fa2 of the series resonator S1-1 is 2245 MHz.

[0053] Also, as shown in FIG. 4, in the reference example, only one anti-resonance characteristic corresponding to the second anti-resonance frequency Fa2 exists, and no anti-resonance characteristic corresponding to the first anti-resonance frequency Fa1 exists.

[0054] The series resonator S1-1, together with the series resonator S1-2, constitutes the series resonator S1 at the first stage of the ladder-type filter. In other words, the series resonator S1-1 is one of the series divisions of the series resonator S1 and is the resonator to which the electrical signal input from the input pad IN is first applied, as shown in FIG. 3.

[0055] FIG. 5 is a diagram showing the passing characteristics of the receiving filter 30 of the elastic wave device 20 in Embodiment 1. The solid line shows the passing characteristics of the receiving filter 30 in Embodiment 1. The broken line shows the passing characteristics of the reference example.

[0056] The first anti-resonance frequency Fa1 of the series resonator S1-1 described with reference to FIG. 5 is 2150 MHz, and is set in the vicinity of the frequency on the lower frequency side (between the lowest frequency of the system frequency and -25 MHz) among the system frequencies of 2170 MHz to 2200 MHz in the passing band of the receiving filter 30.

[0057] The receiving filter 30 in Embodiment 1 has a passing band of 2170 MHz to 2200 MHz in the satellite communication receiving band. The width of the passing band is 30 MHz. Also, the specific band is 1.37%.

[0058] Here, the specific band means a value obtained by dividing the difference between the highest frequency and the lowest frequency in the frequency band by the center frequency of the frequency band.

[0059] It can be seen that the anti-resonance frequency of the series resonator S1-1 is 2250 MHz, which is higher than the highest frequency in the passing band of the receiving filter 30.

[0060] Since the first anti-resonance frequency Fa1 of the series resonator S1-1 is set in the vicinity of the frequency on the lower frequency side of the passing characteristics of the receiving filter 30 (between the lowest frequency of the system frequency and -25 MHz), the steepness can be improved because the coupling coefficient of the series resonator S1-1 is low on the lower frequency side of the passing characteristics constituted by the first anti-resonance frequency Fa1.

[0061] Since the first anti-resonance frequency Fa1 of the series resonator S1-1 is set in the vicinity of the frequency on the lower frequency side of the passing characteristics of the receiving filter 30 (between the lowest frequency of the system frequency and -25 MHz), the temperature characteristics are improved.

[0062] More specifically, usually, the left shoulder (low-frequency side) of the passband is constituted by the resonance characteristics of the parallel resonator. However, the resonance characteristics have a larger absolute value of the frequency temperature coefficient than the anti-resonance characteristics, and the temperature characteristics are poor.

[0063] By contributing to the formation of the left shoulder (low-frequency side) of the passband with the first anti-resonance frequency Fa1 of the series resonator S1-1 having an absolute value of the frequency temperature coefficient smaller than that of the resonance frequency, the temperature characteristics on the low-frequency side of the bandpass filter are improved.

[0064] Also, since the first anti-resonance frequency Fa1 contributes to the formation of the left shoulder (low-frequency side) of the passband and the second anti-resonance frequency Fa2 contributes to the attenuation on the high-frequency side of the passband, the width of the passband is within the width of the difference in frequency between the first anti-resonance frequency Fa1 and the second anti-resonance frequency Fa2 that can be formed. Specifically, the width of the passband where a significant effect is obtained is within 100 MHz.

[0065] FIG. 6 is a diagram showing pitch modulation in the case where the series resonator S1-1 of the receiving filter 30 of the elastic wave device 20 in the first embodiment is a SAW resonator including an IDT electrode.

[0066] The central region CR of the IDT electrode has a pitch of 1.753 μm. Also, the duty ratio is 55%. The two adjacent regions (non-central regions) NCR adjacent to both sides of the central region CR of the IDT electrode have a pitch of 1.813 μm. Also, the duty ratio is 50%.

[0067] The two adjacent regions (outer regions) OR adjacent to the outside of the non-central region NCR of the IDT electrode do not have a constant pitch. However, the pitch of the outer region OR is smaller than the pitch of the non-central region NCR.

[0068] Also, the duty ratio of the outer region OR is 50%. Note that the duty ratio is the ratio of the electrode finger width in one cycle. In the reference example, the pitch in the central region and the pitch in the non-central region are made equal.

[0069] By making the pitch of the central region different from that of the non-central region, two anti-resonant frequencies, namely the second anti-resonant frequency Fa2 and the first anti-resonant frequency Fa1, are generated. Also, the resonant frequency exists between the second anti-resonant frequency Fa2 and the first anti-resonant frequency Fa1.

[0070] Also, the pitch modulation 52bP of the reflector is smaller than the pitch of the non-central region NCR in the region closest to the IDT electrode, but larger than the pitch of the non-central region NCR in the region farthest from the IDT electrode.

[0071] By setting the series resonator S1-1 in this way, in addition to the anti-resonant characteristics at the second anti-resonant frequency Fa2 that ensure the attenuation characteristics on the high-frequency side of the passband, which is the role of the conventional series resonator, the first anti-resonant frequency Fa1 is set in the vicinity of the low-frequency side (between the lowest frequency of the system frequency and -25 MHz), and the steepness on the low-frequency side can be improved.

[0072] According to the first embodiment described above, an elastic wave device with improved steepness between the passband and the stopband can be provided.

[0073] Embodiment 2. FIG. 7 is a longitudinal sectional view of a module to which the elastic wave device of the first embodiment is applied. Note that the same reference numerals are given to the same or corresponding parts as those of the first embodiment. The description of such parts is omitted.

[0074] In FIG. 7, the module 100 includes a wiring substrate 130, a plurality of external connection terminals 131, an integrated circuit component IC, an elastic wave device 20, an inductor 111, and a sealing portion 117.

[0075] The plurality of external connection terminals 131 are formed on the lower surface of the wiring substrate 130. The plurality of external connection terminals 131 are mounted on a motherboard of a preset mobile communication terminal.

[0076] 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.

[0077] The surface acoustic wave device 20 is mounted on the main surface of the wiring board 130.

[0078] 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).

[0079] The sealing portion 117 seals a plurality of electronic components including the surface acoustic wave device 20.

[0080] According to the second embodiment described above, the module 100 includes the surface acoustic wave device 20. Therefore, it is possible to provide a module including a surface acoustic wave device with improved steepness between the passband and the stopband.

[0081] 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.

[0082] 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 implemented or executed in various manners.

[0083] The specific implementation examples are provided herein for illustrative purposes only and are not intended to be limiting.

[0084] The expressions and terms used in this disclosure are for illustrative purposes and should not be construed 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.

[0085] References to "or (alternatively)" shall be construed such that any term described using "or (alternatively)" may indicate one, more than one, and all of the terms described therein.

[0086] References to front, back, left, right, top, bottom, vertical, horizontal, front, and back are for the convenience of description. Such references do not limit the components of the present disclosure to any one positional or spatial orientation. Accordingly, the above description and drawings are merely illustrative.

Description of Reference Numerals

[0087] 20 Elastic wave device, 23 Wiring substrate, 24 External connection terminal 25 Device chip, 26 Electrode pad, 27 Bump 28 Sealing portion 30 Receiving filter 52 Elastic wave element, 52a IDT electrode, 52b Reflector 52c Comb-shaped electrode, 52d Electrode finger, 52e Bus bar IN Input pad, OUT Output pad, GND Ground pad 100 Module, 130 Wiring substrate, 131 External connection terminal IC Integrated circuit component, 111 Inductor, 117 Sealing portion

Claims

1. A band-pass filter including a plurality of series resonators and a plurality of parallel resonators, for passing a signal in a predetermined frequency band, wherein the plurality of series resonators includes a first series resonator having a first anti-resonant frequency and a second anti-resonant frequency, wherein the first anti-resonant frequency is near the lowest frequency of the frequency band, and the second anti-resonant frequency is higher than the highest frequency of the frequency band, an elastic wave device.

2. The elastic wave device according to claim 1, wherein the first series resonator is a resonator to which an electrical signal is first applied among the plurality of series resonators.

3. The band-pass filter is a ladder-type filter, and the first series resonator is one of the series resonators that form one stage of the ladder of the ladder-type filter and are divided in series, the elastic wave device according to claim 1.

4. The first series resonator is a surface acoustic wave resonator including an IDT, and includes a central region having a first pitch, both regions (non-central regions) adjacent to the central region having a second pitch, and both regions (outer regions) adjacent to the outside of the non-central region having a third pitch, wherein the first pitch is smaller than the second pitch, and the second pitch is larger than the third pitch, the elastic wave device according to claim 1.

5. The first series resonator includes a pair of reflectors adjacent to the IDT, and the pitch of the reflectors is smaller than the second pitch in the region closest to the IDT and larger than the second pitch in the region farthest from the IDT, the elastic wave device according to claim 4.

6. The elastic wave device according to claim 4, wherein the duty ratio of the central region is larger than the duty ratio of the non-central region.

7. The elastic wave device according to claim 1, wherein the frequency band of the band-pass filter is 100 MHz or less.

8. The elastic wave device according to claim 1, wherein a value obtained by dividing a difference between the highest frequency and the lowest frequency of the frequency band of the band-pass filter by the center frequency of the frequency band is 0.5% or more and 4.0% or less.

9. A module including the elastic wave device according to any one of claims 1 to 8.

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