Acoustic wave device and module including the same

Abstract

To provide an acoustic wave device that has improved steepness between a pass band and a stop band.SOLUTION: An acoustic wave device includes a bandpass filter that includes a plurality of series resonators and a plurality of parallel resonators, which are surface acoustic wave resonators having an IDT, and that passes signals in a predetermined frequency band. The bandpass filter is a ladder-type filter, and the first series resonator is a series resonator that forms one stage of the ladder of the ladder-type filter. 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 the 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 acoustic wave device and a module including the acoustic wave device. [Background technology]

[0002] Recent technological advances have led to remarkable miniaturization and weight reduction of mobile communication terminals, such as smartphones. The acoustic wave devices used in these mobile communication terminals are compact acoustic wave devices. Furthermore, the number of mobile communication systems capable of simultaneous transmission and reception has rapidly increased, resulting in a surge in demand for duplexers.

[0003] As mobile communication systems evolve, the specifications required for acoustic wave devices are becoming more stringent, meaning that better characteristics than ever before are being demanded.

[0004] Between the pass band and the stop band, a characteristic with a higher steepness is required.

[0005] Patent Document 1 discloses a technique for improving the steepness of the pass characteristics on the high frequency side of the pass band. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-160888 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the acoustic wave device described in Patent Document 1, the steepness between the pass band and the stop band is insufficient.

[0008] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide an acoustic wave device with improved steepness between a pass band and a stop band, and a module including the acoustic wave device. [Means for solving the problem]

[0009] The acoustic wave device according to the present disclosure includes: a bandpass filter including a plurality of series resonators and a plurality of parallel resonators, which are surface acoustic wave resonators each having an IDT, and which passes signals in a predetermined frequency band; the plurality of series resonators include a first series resonator having a first anti-resonant frequency and a second anti-resonant frequency; the bandpass filter is a ladder-type filter, and the first series resonator is a series resonator that forms one stage of a ladder of the ladder-type filter, the first anti-resonant frequency is near the lowest frequency in the frequency band, The second anti-resonant frequency of the acoustic wave device is higher than the highest frequency in the frequency band.

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

[0011] According to one aspect of the present invention, the first series resonator includes a central region having a first pitch, two regions (non-central regions) adjacent to the central region having a second pitch, and two 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.

[0012] According to one aspect of the present invention, 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 is larger than the second pitch in the region farthest from the IDT.

[0013] In one aspect of the present disclosure, the duty ratio of the central region is greater than the duty ratio of the non-central regions.

[0014] In one aspect of the present disclosure, the width of the frequency band of the bandpass filter is 100 MHz or less.

[0015] In one embodiment of the present disclosure, the difference between the highest frequency and the lowest frequency in the frequency band of the bandpass filter divided by the center frequency of the frequency band is 0.5% or more and 4.0% or less.

[0016] A module including the acoustic wave device is one aspect of the present disclosure. [Effects of the Invention]

[0017] 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 pass band of an acoustic wave device. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a longitudinal sectional view of an acoustic wave device according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of an acoustic wave element (resonator) of the acoustic wave device according to the first embodiment. [Figure 3] FIG. 3 illustrates an example of an acoustic wave device according to the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating the anti-resonance characteristics of the series resonator S1-1 of the receive filter 30 of the acoustic wave device 20 according to the first embodiment. [Figure 5]FIG. 5 is a diagram illustrating the pass characteristic of the receiving filter 30 of the acoustic wave device 20 according to the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating pitch modulation when the series resonator S1-1 of the receive filter 30 of the acoustic wave device 20 according to the first embodiment is a SAW resonator including an IDT electrode. [Figure 7] FIG. 7 is a vertical cross-sectional view of a module to which the acoustic wave device according to the first embodiment is applied. DETAILED DESCRIPTION OF THE INVENTION

[0019] The embodiments will be described with reference to the accompanying drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals. Duplicate descriptions of these parts will be appropriately simplified or omitted.

[0020] Embodiment 1 FIG. 1 is a longitudinal sectional view of an acoustic wave device according to a first embodiment.

[0021] As shown in FIG. 1, an acoustic 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 .

[0022] For example, the wiring board 23 is a multi-layer board made of resin, or a low temperature co-fired ceramics (LTCC) multi-layer board made of a plurality of dielectric layers.

[0023] A plurality of external connection terminals 24 are formed on the lower surface of the wiring board 23 .

[0024] A plurality of electrode pads 26 are formed on the main surface of the wiring substrate 23. For example, the electrode pads 26 are made of copper or an alloy containing copper. For example, the thickness of the electrode pads 26 is 10 μm to 20 μm.

[0025] 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.

[0026] A gap 29 is formed between the wiring substrate 23 and the device chip 25 .

[0027] 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 plurality of electrode pads 26 via the plurality of bumps 27.

[0028] The device chip 25 is, for example, a surface acoustic wave device chip. The device chip 25 includes a piezoelectric substrate made of a piezoelectric material. The piezoelectric substrate is a substrate made of a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz.

[0029] The thickness of the piezoelectric substrate can be, for example, 100 to 300 μm. According to another example, the piezoelectric substrate is a substrate made of piezoelectric ceramics.

[0030] According to yet another example, the device chip 25 is a substrate in which a piezoelectric substrate and a support substrate are bonded together. The support substrate is made of, for example, 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.

[0031] The acoustic wave elements 52 are 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.

[0032] 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 .

[0033] The transmit filter is formed so as to allow passage of electrical signals in a desired frequency band, and is, for example, a ladder-type filter made up of a plurality of series resonators and a plurality of parallel resonators.

[0034] The receive filter is configured to allow electrical signals in a desired frequency band to pass through, and is, for example, a ladder filter.

[0035] The sealing portion 28 is formed so as to cover the device chip 25. For example, the sealing portion 28 is made of an insulating material such as a synthetic resin. For example, the sealing portion 28 is made of a metal.

[0036] When the sealing portion 28 is made of a synthetic resin, the synthetic resin is an epoxy resin, a polyimide, or the like. Preferably, the sealing portion 28 is made of an epoxy resin using a low-temperature curing process. A gap 29 is formed in the region where the wiring substrate 23 and the device chip 25 face each other.

[0037] Next, an example of acoustic wave element 52 formed on device chip 25 will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of an acoustic wave element (resonator) of the acoustic wave device according to the first embodiment.

[0038] 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 provided so as to be able to excite acoustic waves (mainly SH waves).

[0039] For example, the IDT electrode 52a and the pair of reflectors 52b are formed of an alloy of aluminum and copper, or an appropriate metal such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, or silver, or an alloy thereof.

[0040] 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 stacked, and the thickness of the IDT electrode 52a and the pair of reflectors 52b is, for example, 150 nm to 450 nm.

[0041] The IDT electrode 52a includes a pair of comb-shaped electrodes 52c that face each other and include a plurality of electrode fingers 52d and a bus bar 52e.

[0042] The electrode fingers 52d are arranged with their longitudinal directions aligned. The bus bar 52e connects the electrode fingers 52d.

[0043] One of the pair of reflectors 52b is adjacent to one side of the IDT electrode 52a, and the other of the pair of reflectors 52b is adjacent to the other side of the IDT electrode 52a.

[0044] 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 the acoustic wave device according to the first embodiment.

[0045] 3, a receiving filter 30, which is a band-pass 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.

[0046] The receive filter 30 includes series resonators S1-1, S1-2, S2, S3-1, S3-2, and S4. The receive filter 30 also includes parallel resonators P1-1, P1-2, P1-3, P2, P3-1, and P3-2. The receive filter 30 is a ladder filter.

[0047] The series resonator S1-1 is located closest to the input pad IN in terms of circuitry, and is the resonator to which an electrical signal is first applied. The series resonators S1-1 and S1-2 are formed by dividing the first-stage series resonator S1 of the ladder filter in series.

[0048] Similarly, the series resonators S3-1 and S3-2 are also obtained by dividing the series resonator S3 in series.

[0049] The parallel resonators P1-1, P1-2, and P1-3 are formed by dividing the first-stage parallel resonator P1 of the ladder filter in parallel. Similarly, the parallel resonators P3-1 and P3-2 are formed by dividing the parallel resonator P3 in parallel.

[0050] 4 is a diagram showing the anti-resonance characteristics of the series resonator S1-1 of the receive filter 30 of the acoustic wave device 20 according to Embodiment 1. The anti-resonance characteristics of the series resonator S1-1 are indicated by a solid line.

[0051] The anti-resonance characteristics of a conventional series resonator are shown by a broken line as a reference example. 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.

[0052] Furthermore, as shown in FIG. 4, in the reference example, there is only one anti-resonance characteristic corresponding to the second anti-resonance frequency Fa2, and there is no anti-resonance characteristic corresponding to the first anti-resonance frequency Fa1.

[0053] The series resonator S1-1 and the series resonator S1-2 form the first-stage series resonator S1 of the ladder filter. In other words, the series resonator S1-1 is one of the series-divided series resonators 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 Figure 3.

[0054] 5 is a diagram showing the pass characteristics of the receive filter 30 of the acoustic wave device 20 according to Embodiment 1. The solid line indicates the pass characteristics of the receive filter 30 according to Embodiment 1. The dashed line indicates the pass characteristics of a reference example.

[0055] The first anti-resonant frequency Fa1 of the series resonator S1-1 described in Figure 5 is 2150 MHz, which is set near the lower frequency side of the system frequency range of 2170 MHz to 2200 MHz in the passband of the receiving filter 30 (between the lowest system frequency and -25 MHz).

[0056] The receive filter 30 in the first embodiment has a passband of 2170 MHz to 2200 MHz in the satellite communication receive band. The passband width is 30 MHz. The fractional bandwidth is 1.37%.

[0057] Here, the fractional bandwidth refers to the value obtained by dividing the difference between the highest frequency and the lowest frequency in a frequency band by the center frequency of the frequency band.

[0058] It can be seen that the anti-resonant frequency of the series resonator S1-1 is 2250 MHz, which is higher than the highest frequency in the pass band of the receive filter 30.

[0059] By setting the first anti-resonant frequency Fa1 of the series resonator S1-1 to a frequency close to the low-frequency side of the pass characteristic of the receiving filter 30 (between the lowest system frequency and -25 MHz), the coupling coefficient of the series resonator S1-1 is low on the low-frequency side of the pass characteristic formed by the first anti-resonant frequency Fa1, thereby improving the steepness.

[0060] The first anti-resonant frequency Fa1 of the series resonator S1-1 is set to a frequency close to the low frequency side of the pass characteristic of the receive filter 30 (between the lowest system frequency and −25 MHz), thereby improving the temperature characteristic.

[0061] More specifically, the left shoulder (low frequency side) of the passband is usually configured with the resonance characteristics of a parallel resonator, but the absolute value of the frequency temperature coefficient of the resonance characteristics is larger than that of the anti-resonance characteristics, and the temperature characteristics are poor.

[0062] The first anti-resonant frequency Fa1 of the series resonator S1-1, whose absolute value of the frequency temperature coefficient is smaller than that of the resonant frequency, contributes to the formation of the left shoulder (low frequency side) of the pass band, thereby improving the temperature characteristics of the band pass filter on the low frequency side.

[0063] Furthermore, since the first anti-resonant frequency Fa1 contributes to forming the left shoulder (low frequency side) of the pass band, and the second anti-resonant frequency Fa2 contributes to attenuation on the high frequency side of the pass band, the width of the pass band is within the difference in frequency between the first anti-resonant frequency Fa1 and the second anti-resonant frequency Fa2 that can be formed. Specifically, the width of the pass band that can produce a significant effect is within 100 MHz.

[0064] FIG. 6 is a diagram illustrating pitch modulation when the series resonator S1-1 of the receive filter 30 of the acoustic wave device 20 according to the first embodiment is a SAW resonator including an IDT electrode.

[0065] The central region CR of the IDT electrode has a pitch of 1.753 μm and a duty ratio of 55%. The non-central regions NCR adjacent to the central region CR of the IDT electrode have a pitch of 1.813 μm and a duty ratio of 50%.

[0066] The pitch of the outer regions OR adjacent to the non-central region NCR of the IDT electrode is not constant, but the pitch of the outer regions OR is smaller than the pitch of the non-central region NCR.

[0067] The duty ratio of the outer region OR is 50%. The duty ratio is the ratio of the electrode finger width to one period. In this reference example, the pitch in the central region is equal to the pitch in the non-central region.

[0068] By making the pitch of the central region different from the pitch of the non-central region, two anti-resonant frequencies, 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.

[0069] Also, the reflector pitch modulation 52bP is smaller than the pitch of the non-central regions NCR in the region closest to the IDT electrode, but is larger than the pitch of the non-central regions NCR in the region farthest from the IDT electrode.

[0070] By configuring the series resonator S1-1 in this manner, in addition to the anti-resonance characteristics at the second anti-resonance frequency Fa2, which ensures the attenuation characteristics on the high-frequency side of the passband, which is the role of conventional series resonators, the first anti-resonance frequency Fa1 is set to a frequency close to the low-frequency side (between the lowest system frequency and -25 MHz), thereby improving the steepness on the low-frequency side.

[0071] According to the first embodiment described above, it is possible to provide an acoustic wave device with improved steepness between the pass band and the stop band.

[0072] Embodiment 2 7 is a longitudinal sectional view of a module to which the acoustic wave device according to Embodiment 1 is applied. Note that the same reference numerals are used to designate parts that are the same as or equivalent to parts in Embodiment 1, and a description of these parts will be omitted.

[0073] 7, 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.

[0074] A plurality of external connection terminals 131 are formed on the lower surface of wiring substrate 130. A plurality of external connection terminals 131 are mounted on a motherboard of a preset mobile communication terminal.

[0075] 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.

[0076] The acoustic wave device 20 is mounted on the main surface of the wiring substrate 130 .

[0077] 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).

[0078] The sealing portion 117 seals a plurality of electronic components including the acoustic wave device 20 .

[0079] According to the second embodiment described above, the module 100 includes the acoustic wave device 20. Therefore, it is possible to provide a module including an acoustic wave device with improved steepness between the pass band and the stop band.

[0080] Having described several aspects of at least one embodiment, 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 this disclosure, and are intended to be within the scope of this disclosure.

[0081] It is to be understood that the embodiments of the methods and apparatus described herein are not limited in their application to the details of construction and the arrangement of components set forth in the above description or illustrated in the accompanying drawings, and that the methods and apparatus may be implemented in other embodiments and practiced or carried out in various ways.

[0082] The specific implementation examples are provided here for illustrative purposes only and are not intended to be limiting.

[0083] The phraseology and terminology used in this disclosure are for the purpose 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 and additional items.

[0084] References to "or" may be construed as meaning that any term described using "or" refers to one, more than one, and all of the described terms.

[0085] All references to front, back, left, right, top, bottom, top, bottom, width, length, and front and back are intended for convenience of description. Such references do not limit the components of this disclosure to any one positional or spatial orientation. Accordingly, the foregoing description and drawings are by way of example only. [Explanation of symbols]

[0086] 20 acoustic wave device, 23 wiring board, 24 external connection terminal 25 device chip, 26 electrode pad, 27 bump, 28 sealing portion 30 Receive Filter 52 acoustic wave element, 52a IDT electrode, 52b reflector 52c Interdigital electrode, 52d Electrode finger, 52e Bus bar IN Input pad, OUT Output pad, GND Ground pad 100 module, 130 wiring board, 131 external connection terminal IC integrated circuit components, 111 inductors, 117 sealing parts

Claims

1. a bandpass filter including a plurality of series resonators and a plurality of parallel resonators, which are surface acoustic wave resonators each having an IDT, and which passes signals in a predetermined frequency band; the plurality of series resonators includes a first series resonator having a first anti-resonant frequency and a second anti-resonant frequency; the bandpass filter is a ladder filter, and the first series resonator is a series resonator that forms one stage of a ladder of the ladder filter, the first anti-resonance frequency is near the lowest frequency in the frequency band, The second anti-resonant frequency of the acoustic wave device is higher than the highest frequency in the frequency band.

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

3. 2. The acoustic wave device according to claim 1, wherein the first series resonator includes a central region having a first pitch, two regions (non-central regions) adjacent to the central region having a second pitch, and two 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.

4. 4. The acoustic wave device according to claim 3, wherein 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 a region closest to the IDT and is larger than the second pitch in a region farthest from the IDT.

5. The acoustic wave device according to claim 3 , wherein the duty ratio of the central region is greater than the duty ratio of the non-central regions.

6. The acoustic wave device according to claim 1 , wherein the width of the frequency band of the bandpass filter is 100 MHz or less.

7. 2. The acoustic wave device according to claim 1, wherein the difference between the highest frequency and the lowest frequency in the frequency band of the bandpass filter divided by the center frequency of the frequency band is 0.5% or more and 4.0% or less.

8. A module comprising the acoustic wave device according to claim 1 .

Images