Acoustic wave filter and communication device

Abstract

The present invention improves the performance of acoustic wave filters. An acoustic wave element of this acoustic wave filter includes a piezoelectric layer, an IDT electrode located on the piezoelectric layer, a low velocity film having a lower sound velocity than the piezoelectric layer, and a support substrate having a higher sound velocity than the piezoelectric layer. If λ represents the wavelength of an acoustic wave excited by the IDT electrode, the thickness of the piezoelectric layer is λ or less. The acoustic wave filter has a transmission filter including a first group of acoustic wave elements among a plurality of said acoustic wave elements, and a reception filter including a second group of acoustic wave elements different from the first group of acoustic wave elements among the plurality of acoustic wave elements. The passband of the transmission filter is located on the high frequency side of the passband of the reception filter, and the width of the passband of the transmission filter is wider than the width of the passband of the reception filter.

Description

[Technical Field]

[0001] One aspect of the present disclosure relates to an acoustic wave filter. [Background technology]

[0002] Patent Document 1 listed below discloses an example of the configuration of a multiplexer as an example of an acoustic wave filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-5742 Summary of the Invention

[0004] An acoustic wave filter according to one embodiment of the present disclosure is an acoustic wave filter having a plurality of acoustic wave elements, each of which includes a piezoelectric layer, an IDT electrode located on the piezoelectric layer, a low acoustic velocity film having a lower acoustic velocity than the piezoelectric layer, and a support substrate having a higher acoustic velocity than the piezoelectric layer. When the wavelength of an acoustic wave excited by the IDT electrode is represented as λ, the thickness of the piezoelectric layer is λ or less. The acoustic wave filter includes a transmit filter including a first acoustic wave element group among the plurality of acoustic wave elements, and a receive filter including a second acoustic wave element group among the plurality of acoustic wave elements that is different from the first acoustic wave element group. The pass band of the transmit filter is located at a higher frequency than the pass band of the receive filter, and the width of the pass band of the transmit filter is wider than the width of the pass band of the receive filter.

[0005] Furthermore, an acoustic wave filter according to one embodiment of the present disclosure is an acoustic wave filter having a plurality of acoustic wave elements, each of which includes a piezoelectric layer, an IDT electrode located on the piezoelectric layer, a low acoustic velocity film having a lower acoustic velocity than the piezoelectric layer, and a support substrate having a higher acoustic velocity than the piezoelectric layer, wherein the thickness of the piezoelectric layer is λ or less when the wavelength of an acoustic wave excited by the IDT electrode is represented as λ, and the acoustic wave filter includes a transmit filter including a first acoustic wave element group among the plurality of acoustic wave elements, and a receive filter including a second acoustic wave element group among the plurality of acoustic wave elements that is different from the first acoustic wave element group, wherein the pass band of the transmit filter is separated from the pass band of the receive filter by 50 MHz or more, and the width of the pass band of the transmit filter is wider than the width of the pass band of the receive filter. [Brief explanation of the drawings]

[0006] [Figure 1] 2 shows an example of the configuration of an acoustic wave element in an acoustic wave filter according to Embodiment 1. [Figure 2] 1 shows an example of the configuration of an acoustic wave filter according to a first embodiment. [Figure 3] 3A and 3B schematically illustrate examples of frequency characteristics of acoustic wave filters according to a comparative example and an example. [Figure 4] 10A and 10B schematically show examples of frequency characteristics of one acoustic wave element in a comparative example and an example. [Figure 5] 1 shows examples of frequency characteristics of acoustic wave filters according to first and second embodiments. [Figure 6] 10 shows an example of the power consumption characteristics of each series resonator in the first and second embodiments. [Figure 7] 10 illustrates a schematic configuration of a communication device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Embodiment 1] The acoustic wave filter 100 according to the first embodiment will be described below. For convenience of explanation, components having the same functions as those described in the first embodiment will be denoted by the same reference numerals in the following embodiments, and their descriptions will not be repeated. For simplicity, descriptions of well-known technical matters will be omitted as appropriate. The components, materials, and numerical values ​​described in this specification are merely examples, unless otherwise inconsistent. Therefore, unless otherwise inconsistent, for example, the positional and connection relationships of the components are not limited to those shown in the figures. Furthermore, the figures are not necessarily drawn to scale.

[0008] (Example of the configuration of an acoustic wave element) FIG. 1 shows an example of the configuration of an acoustic wave element 1 in an acoustic wave filter 100. The acoustic wave element 1 is also called an acoustic wave resonator. FIG. 1 schematically shows the layered structure of the acoustic wave element 1. FIG. 1 also shows a portion of one acoustic wave element 1. As shown in FIG. 2 (described later), the acoustic wave filter 100 may include multiple acoustic wave elements 1. Specifically, as described later, the acoustic wave filter 100 may include a series resonator 1S and a parallel resonator 1P as the acoustic wave elements 1.

[0009] For ease of explanation, this specification introduces a Cartesian coordinate system (D1-D2-D3 coordinate system) shown in FIG. 1 . In the example of embodiment 1, the D1 direction is the propagation direction of an elastic wave propagating within piezoelectric layer 2 of elastic wave element 1. As shown in FIG. 1 , multiple electrode fingers 32 of elastic wave element 1 may be arranged in the D1 direction. The D2 direction is an example of a direction intersecting the D1 direction. Electrode fingers 32 may extend in the D2 direction. The D3 direction is the thickness direction of each part of elastic wave element 1. In this specification, the positive direction of the D3 direction is described as the upward direction. Therefore, the negative direction of the D3 direction is the downward direction.

[0010] The acoustic wave element 1 may include (i) a piezoelectric layer 2, (ii) an IDT (Interdigital Transduce) electrode 3 located on the piezoelectric layer 2, (iii) a low acoustic velocity film 5, and (iv) a support substrate 6. The support substrate 6, the low acoustic velocity film 5, and the piezoelectric layer 2 may be common to multiple acoustic wave elements 1. Alternatively, each of the multiple acoustic wave elements 1 may include an individual IDT electrode 3. The IDT electrode 3 is also referred to as an excitation electrode.

[0011] The support substrate 6 supports each component of the acoustic wave element 1. Therefore, the support substrate 6 may be located below the low acoustic velocity film 5. The support substrate 6 may have a higher acoustic velocity than the piezoelectric layer 2. Therefore, for example, the support substrate 6 may contain Si as a material.

[0012] The piezoelectric layer 2 may be made of a single crystal material having piezoelectric properties. The piezoelectric layer 2 may contain lithium tantalate (LiTaO3:LT) as a material. The cut angle of the LT may be set appropriately. As an example, the piezoelectric layer 2 may contain Y-cut, X-propagation LT with a cut angle of 40° or less as a material (see Example 1 below). As another example, the piezoelectric layer 2 may contain Y-cut, X-propagation LT with a cut angle of 25°±3° as a material (see Example 2 below).

[0013] The X-axis and Y-axis are the crystal orientation axes of the piezoelectric layer 2. For example, "Y-cut X-propagation LT with a cut angle of 40°" means "LT cut along a plane having the X-axis as the central axis and an axis rotated 40° from the Y-axis as the normal, when the X-axis direction is the propagation direction of the elastic wave." The X-axis and Y-axis may be related to the D1 to D3 directions. For example, the X-axis direction may coincide with the D1 direction. However, the X-axis and Y-axis do not have to be related to the D1 to D3 directions.

[0014] The IDT electrode 3 may have a first bus bar and a second bus bar (not shown) facing each other in the direction D2. The IDT electrode 3 may have (i) a plurality of first electrode fingers 32a connected to the first bus bar, and (ii) a plurality of second electrode fingers 32b connected to the second bus bar. In this specification, the first electrode fingers 32a and the second electrode fingers 32b are collectively referred to as electrode fingers 32.

[0015] The first electrode fingers 32a may extend from the first bus bar toward the second bus bar in the direction D2. The second electrode fingers 32b may extend from the second bus bar toward the first bus bar in the direction D2. Therefore, the second electrode fingers 32b may be interdigitated with each of the first electrode fingers 32a in the direction D2.

[0016] The plurality of electrode fingers 32 may be alternately and repeatedly positioned on the piezoelectric layer 2 at approximately constant intervals in the D1 direction. In this specification, the pitch of the electrode fingers 32 is represented as p. p is also referred to as the electrode finger pitch of the IDT electrode 3. p may be, for example, the pitch (repetition interval) between the centers of two adjacent electrode fingers 32 in the D1 direction.

[0017] In this specification, the wavelength of the acoustic wave excited by the IDT electrode 3 is represented as λ. As an example, p may be set equal to half the value of λ (λ / 2). In this case, λ may be defined as twice the length of p. Therefore, in the first embodiment, a case where λ=2p is illustrated.

[0018] In this specification, the length of electrode finger 32 in direction D1 is referred to as width w of electrode finger 32. w may be set appropriately depending on, for example, the electrical characteristics required of acoustic wave device 1. As an example, w may be set depending on p. In this specification, the ratio of w to p (w / p) is referred to as duty of electrode finger 32.

[0019] As one example, the frequency characteristics of acoustic wave element 1 can be controlled by changing the fill factor. As another example, the frequency characteristics of acoustic wave element 1 can be controlled by changing either w or p while maintaining a constant fill factor. In this way, by changing the design of IDT electrode 3 for each of multiple acoustic wave elements 1, the frequency characteristics of each of multiple acoustic wave elements 1 can be controlled. As described above, the frequency characteristics of acoustic wave filter 100 can be controlled by changing the design of IDT electrode 3.

[0020] In this specification, the thickness of the piezoelectric layer 2 is represented as T. In the first embodiment, the case where the piezoelectric layer 2 is sufficiently thin, that is, the case where T is sufficiently small, is exemplified. As an example, T may be equal to or less than λ. In this case, the IDT electrode 3 can excite plate waves (Lamb waves) as the acoustic waves. As an example, the IDT electrode 3 can excite A1 Lamb waves as the plate waves.

[0021] The low acoustic velocity film 5 is an example of an intervening layer located between the piezoelectric layer 2 and the support substrate 6. The low acoustic velocity film 5 may be located below the piezoelectric layer 2. The low acoustic velocity film 5 may have a lower acoustic velocity than the piezoelectric layer 2. Therefore, for example, the low acoustic velocity film 5 may contain SiO2 as a material.

[0022] Acoustic wave element 1 may further include an intervening layer different from low acoustic velocity film 5. For example, acoustic wave element 1 may include an acoustic reflection film between piezoelectric layer 2 and support substrate 6 as the intervening layer. The acoustic reflection film may be a multilayer reflection film in which (i) low acoustic impedance layers having an acoustic impedance lower than that of piezoelectric layer 2 and (ii) high acoustic impedance layers having an acoustic impedance higher than that of piezoelectric layer 2 are alternately stacked.

[0023] The multilayer reflective film may be a laminate unit formed by laminating one low acoustic impedance layer and one high acoustic impedance layer. The acoustic wave device 1 may have, for example, four laminate units. The low acoustic impedance layer may contain, for example, SiO2 as a material. The high acoustic impedance layer may contain, for example, HfO2 as a material.

[0024] (Example of an acoustic wave filter configuration) 2 shows an example of the configuration of the acoustic wave filter 100. In the first embodiment, the acoustic wave filter 100 is a multiplexer (branching filter). For clarity of explanation, the first embodiment illustrates the acoustic wave filter 100 as a duplexer.

[0025] The acoustic wave filter 100 may include a transmit filter 109T and a receive filter 111R. In FIG. 2, the transmit filter 109T and the receive filter 111R are illustrated as ladder filters. The transmit filter 109T and the receive filter 111R may be connected to an antenna 159 via an antenna terminal ANT (see also FIG. 7, which will be described later).

[0026] Transmit filter 109T and receive filter 111R may each have a plurality of acoustic wave elements 1. For ease of explanation, in this specification, of the plurality of acoustic wave elements 1, the acoustic wave elements belonging to transmit filter 109T are denoted by the symbol T, and the acoustic wave elements belonging to receive filter 111R are denoted by the symbol R.

[0027] In this specification, a group of acoustic wave elements 1 belonging to transmit filter 109T is referred to as a first acoustic wave element group. On the other hand, a group of acoustic wave elements 1 belonging to receive filter 111R is referred to as a second acoustic wave element group. The second acoustic wave element group is different from the first acoustic wave element group. By differentiating the second acoustic wave element group from the first acoustic wave element group, the transmit band and the receive band, which will be described later, can be made different. Furthermore, by not including a common acoustic wave element 1 between the first acoustic wave element group and the second acoustic wave element group, it becomes easier to separate the transmit band and the receive band.

[0028] The transmit filter 109T may have four series resonators 1S located in series arms of the transmit filter 109T. In the example of Fig. 2, the four series resonators 1S in the transmit filter 109T are referred to as series resonators 1S-1T to 1S-4T, respectively. The series resonators 1S-1T to 1S-4T may be collectively referred to as the series resonator 1S-T.

[0029] The series arm of the transmit filter 109T may be connected to the transmit terminal TX and the antenna terminal ANT. In the example of Fig. 2, the series resonator 1S-1T is the series resonator closest to the transmit terminal TX. On the other hand, the series resonator 1S-4T is the series resonator closest to the antenna terminal ANT.

[0030] The transmit filter 109T may have four parallel resonators 1P located in parallel arms of the transmit filter 109T. In the example of Fig. 2, the four parallel resonators 1P in the transmit filter 109T are referred to as parallel resonators 1P-1T to 1P-4T, respectively. The parallel resonators 1P-1T to 1P-4T may be collectively referred to as the parallel resonator 1P-T. The parallel resonators 1P-T may be grounded.

[0031] In the example of Fig. 2, the parallel resonator 1P-1T is the parallel resonator closest to the transmitting terminal TX. The parallel resonator 1P-1T may be located in a parallel arm extending between the series resonator 1S-1T and the transmitting terminal TX. On the other hand, the parallel resonator 1P-4T is the parallel resonator closest to the antenna terminal ANT. The parallel resonator 1P-4T may be located in a parallel arm extending between the series resonator 1S-4T and the series resonator 1S-3T.

[0032] The receive filter 111R may have four series resonators 1S located in series arms of the receive filter 111R. In the example of Fig. 2, the four series resonators 1S in the receive filter 111R are referred to as series resonators 1S-1R to 1S-4R, respectively. The series resonators 1S-1R to 1S-4R in the receive filter 111R may be collectively referred to as the series resonator 1S-R.

[0033] The series arm of the receiving filter 111R may be connected to the receiving terminal RX and the antenna terminal ANT. In the example of Fig. 2, the series resonator 1S-1R is the series resonator closest to the antenna terminal ANT. On the other hand, the series resonator 1S-4R is the series resonator closest to the receiving terminal RX.

[0034] The receiving filter 111R may have three parallel resonators 1P located in parallel arms of the receiving filter 111R. In the example of Fig. 2, the three parallel resonators 1P in the receiving filter 111R are referred to as parallel resonators 1P-1R to 1P-3R, respectively. The parallel resonators 1P-1R to 1P-3R may be collectively referred to as parallel resonator 1P-R. The parallel resonator 1P-R may be grounded.

[0035] In the example of Fig. 2, the parallel resonator 1P-1R is the parallel resonator closest to the antenna terminal ANT. The parallel resonator 1P-1R may be located in a parallel arm extending between the series resonators 1S-1R and 1S-2R. On the other hand, the parallel resonator 1P-3R is the parallel resonator closest to the receiving terminal RX. The parallel resonator 1P-3R may be located in a parallel arm extending between the series resonators 1S-3R and 1S-4R.

[0036] The transmit filter 109T may have a first acoustic wave element group including a series resonator 1S-T and a parallel resonator 1P-T, while the receive filter 111R may have a second acoustic wave element group including a series resonator 1S-R and a parallel resonator 1P-R.

[0037] (Schematic example of frequency characteristics of an elastic wave filter) 3 schematically illustrates example frequency characteristics (specifically, attenuation characteristics) of an acoustic wave filter according to a comparative example (e.g., a conventional acoustic wave filter) and an acoustic wave filter according to an embodiment (e.g., acoustic wave filter 100). In FIG. 3, reference numeral 300A indicates an example of the attenuation characteristics of the comparative example, and reference numeral 300B indicates an example of the attenuation characteristics of the embodiment.

[0038] In the graph of Figure 3, the horizontal axis represents frequency (unit: Hz), and the vertical axis (Transmission) represents attenuation (unit: dB). Attenuation can also be interpreted as insertion loss. In the following explanation, the passband of the transmit filter is referred to as the transmit band, and the passband of the receive filter is referred to as the receive band.

[0039] In Figure 3, the transmission bands and pass bands depicted by bracketed objects indicate the transmission bands and reception bands, respectively, specified by the standard. In this specification, the transmission band specified by the standard is referred to as the "specified transmission band." Also, the reception band specified by the standard is referred to as the "specified reception band."

[0040] The actual transmission band of a transmit filter may be defined as, for example, the frequency band from the low-frequency cutoff frequency to the high-frequency cutoff frequency of the transmit filter. As will be clear to those skilled in the art, the attenuation characteristics of a frequency filter have -3 dB attenuation points (points where the attenuation amount is -3 dB) on both the low-frequency side and the high-frequency side with respect to the peak frequency that indicates the frequency at which the attenuation amount is minimum.

[0041] The high-frequency cutoff frequency of the transmit filter (for convenience, referred to as fcut1_T) is the frequency at the -3 dB attenuation point on the high-frequency side of the peak frequency of the transmit filter. The low-frequency cutoff frequency of the transmit filter (for convenience, referred to as fcut2_T) is the frequency at the -3 dB attenuation point on the low-frequency side of the peak frequency of the transmit filter.

[0042] Therefore, the transmission band in this specification may be defined as a frequency band ranging from fcut2_T to fcut1_T. As described above, the transmission bandwidth (width of the transmission band) can be defined as the width from the -3 dB attenuation point on the low-frequency side to the -3 dB attenuation point on the high-frequency side in the attenuation characteristics of the transmission filter. In this case, fcut2_T is the frequency at the end of the low-frequency side of the transmission band, and fcut1_T is the frequency at the end of the high-frequency side of the transmission band.

[0043] The actual reception band of a receive filter may be defined as, for example, a frequency band from the lower cutoff frequency to the higher cutoff frequency of the receive filter. The higher cutoff frequency of the receive filter (for convenience, referred to as fcut1_R) is the frequency of the -3 dB attenuation point on the higher frequency side of the peak frequency of the receive filter. The lower cutoff frequency of the receive filter (for convenience, referred to as fcut2_R) is the frequency of the -3 dB attenuation point on the lower frequency side of the peak frequency of the receive filter.

[0044] Therefore, the reception band in this specification may be defined as the frequency band ranging from fcut2_R to fcut1_R. As described above, the reception bandwidth (width of the reception band) can be defined as the width from the -3 dB attenuation point on the low-frequency side to the -3 dB attenuation point on the high-frequency side in the attenuation characteristics of the reception filter. In this case, fcut2_R is the frequency at the low-frequency end of the reception band, and fcut1_R is the frequency at the high-frequency end of the reception band.

[0045] Unless otherwise stated, the transmit band in this specification may be understood to refer to the frequency band defined by the −3 dB attenuation point of the attenuation characteristics of a transmit filter, and the receive band in this specification may be understood to refer to the frequency band defined by the −3 dB attenuation point of the attenuation characteristics of a receive filter.

[0046] The transmit filters in the comparative example and the working example are both designed so that the transmit band includes the designated transmit band. The receive filters in the comparative example and the working example are both designed so that the receive band includes the designated receive band. As will be apparent to those skilled in the art, the transmit band and the receive band may differ depending on the standard to which the acoustic wave filter must comply.

[0047] 3, in a conventional acoustic wave filter, the transmission band may be located at a lower frequency than the reception band due to, for example, standard requirements (see, for example, Patent Document 1). Therefore, in the comparative example, the frequency characteristics of the transmission filter and the reception filter are set so that the transmission band is located at a lower frequency than the reception band.

[0048] In contrast, in the embodiment, the transmission band is located on the lower frequency side than the reception band, as shown by reference numeral 300B in Fig. 3. Therefore, in the embodiment, the frequency characteristics of the transmission filter and the reception filter are set so that the transmission band is located on the higher frequency side than the reception band.

[0049] (Schematic example of frequency characteristics of an acoustic wave element) 4 is a schematic diagram illustrating an example of the frequency characteristics of one acoustic wave element in the comparative example and the example. In FIG. 4, reference numeral 400A indicates an example of the impedance characteristics of the acoustic wave element, and reference numeral 400B indicates an example of the power consumption characteristics of the acoustic wave element.

[0050] In the example of Fig. 4, for clarity of illustration, the transmission band in the comparative example and the transmission band in the embodiment are shown at the same position. However, it should be noted that in reality, as shown in Fig. 3, the transmission band in the comparative example is located on the lower frequency side than the reception band, and the transmission band in the embodiment is located on the higher frequency side than the reception band.

[0051] The horizontal axis of each of reference numerals 400A and 400B in FIG. 4 represents frequency. The vertical axis of reference numeral 400A represents the magnitude (absolute value) of the impedance of the acoustic wave element. In the following description, unless otherwise inconsistent, the magnitude of the impedance will be abbreviated to simply "impedance." The vertical axis of reference numeral 400B represents the power consumption of the acoustic wave element.

[0052] In this specification, the resonance frequency of the elastic wave element (for convenience, referred to as fr) is defined as the frequency at which the impedance is minimized. On the other hand, the anti-resonance frequency of the elastic wave element (for convenience, referred to as fa) is defined as the frequency at which the impedance is maximized.

[0053] Generally, the power consumption increases as the impedance increases. As shown in FIG. 4, the power consumption is minimized near fr. Ideally, the power consumption is minimized at fr. On the other hand, the power consumption is maximized near fa. Ideally, the power consumption is maximized at fa.

[0054] In the example of FIG. 4, fr < fa. In the example of FIG. 4, it is assumed that fr in the comparative example and the example is equal. In the example of FIG. 4, fr belongs to the transmission band. Also, in the example of FIG. 4, it is assumed that the maximum value of the impedance in the comparative example and the example is equal. Therefore, in the example of FIG. 4, it is assumed that the maximum value of the power consumption in the comparative example and the example is also equal.

[0055] However, in the example of FIG. 4, fa in the comparative example and the example are different. Specifically, in the example of FIG. 4, fa in the example is higher than fa in the comparative example. The bandwidth of the elastic wave element may be defined as Δf = |fa - fr|. Therefore, in the example of FIG. 4, Δf in the example is larger than Δf in the comparative example.

[0056] Generally, the temperature of the elastic wave element rises as the power consumption of the elastic wave element increases. Also, the low-frequency side shoulder of the transmission band in the elastic wave filter may shift to the low-frequency side as the temperature of the elastic wave element rises. In order to compensate for the shift of the low-frequency side shoulder of the transmission band to the low-frequency side, for example, it is conceivable to design the elastic wave filter so that the high-frequency side shoulder of the transmission band shifts to the high-frequency side.

[0057] However, in a typical multiplexer, it is required to separate the transmission band and the reception band, and therefore, in the comparative example in which the transmission band is located on the lower frequency side than the reception band, it may be difficult to shift the high-frequency shoulder of the transmission band to the higher frequency side in order to separate the transmission band and the reception band.

[0058] In light of this, the comparative example in Fig. 3 illustrates a case where the transmission bandwidth is the same as the reception bandwidth. Therefore, in the comparative example, as shown in Fig. 4, the increase in power consumption with increasing frequency can be significant near the high-frequency end of the transmission band.

[0059] On the other hand, in the embodiment, since the transmission band is located on the higher frequency side than the reception band, even if the high frequency shoulder of the transmission band is shifted to the higher frequency side, the separation between the transmission band and the reception band can be maintained.

[0060] In view of this, the embodiment in Fig. 3 illustrates a case where the transmission bandwidth is wider than the reception bandwidth. As an example, in an acoustic wave filter according to one embodiment of the present disclosure, the transmission bandwidth may be wider than the reception bandwidth by 2 MHz or more. As another example, the transmission bandwidth may be wider than the reception bandwidth by 4 MHz or more.

[0061] For the above reasons, the embodiment provides a higher degree of freedom in frequency selection on the high-frequency side of the transmission band than the comparative example. Therefore, it is easier to set fa higher in the embodiment than in the comparative example. In other words, it is easier to set Δf larger in the embodiment than in the comparative example. As shown in FIG. 4, power consumption generally increases monotonically with increasing frequency in the range from the high-frequency end of the transmission band to fa. However, since Δf can be set larger in the embodiment than in the comparative example, the degree of increase in power consumption with increasing frequency can be made more gradual than in the comparative example.

[0062] As a result, the embodiment can reduce the variation in power consumption among the acoustic wave elements in the frequency filter compared to the comparative example. Therefore, the embodiment can realize a frequency filter having higher power durability than the comparative example. Therefore, the embodiment can realize a frequency filter that is excellent in mass productivity, for example.

[0063] As described above, the acoustic wave filter 100 can achieve, for example, a wider transmission band and improved power durability. In this way, the acoustic wave filter 100 can improve the performance of acoustic wave filters compared to conventional filters.

[0064] (Further Consideration of Frequency Characteristics of Acoustic Wave Filter According to the Embodiment) The inventors of the present application further investigated the examples through simulations. Specifically, the inventors conducted simulations for each of Examples 1 and 2 described below.

[0065] In the simulation of Example 1, the inventors set the design conditions of acoustic wave device 1 as follows: Piezoelectric layer: LT (thickness T=0.35λ) Low sound velocity film: SiO2 (thickness: 0.1λ) Support substrate: Si (thickness: 40λ) IDT electrode thickness: 0.09λ LT cutting angle: 40° It was set as follows.

[0066] Meanwhile, the inventors set the design conditions of elastic wave device 1 in Example 2 by changing the LT cut angle to 26° among the design conditions of elastic wave device 1 in Example 1. The design conditions of elastic wave device 1 except for the LT cut angle are common to Examples 1 and 2.

[0067] The inventors have derived frequency characteristics of the acoustic wave filters in each of the first and second embodiments through simulations. FIG. 5 shows examples of the frequency characteristics of the acoustic wave filters in the first and second embodiments derived by the inventors. FIG. 5 corresponds to the example indicated by reference numeral 300B in FIG. 3 described above. As shown in FIG. 5, the second embodiment can further widen the transmission bandwidth toward the high frequency side compared to the first embodiment. Therefore, the second embodiment can further reduce power consumption on the high frequency side compared to the first embodiment.

[0068] As can be seen from the above explanation, by setting the LT cut angle to 40° or less, the performance of the acoustic wave filter can be improved compared to conventional filters. In addition, by setting the LT cut angle to 25°±3°, the performance of the acoustic wave filter can be further improved.

[0069] (Further Consideration of Power Consumption Characteristics of Series Resonators According to the Examples) Next, the inventors performed simulations to derive the frequency characteristics of the power consumption of the acoustic wave elements in each of Examples 1 and 2. Specifically, the inventors derived the frequency characteristics of the power consumption of the series resonators 1S-1T to 1S-4 for each of Examples 1 and 2.

[0070] 6 shows examples of power consumption characteristics derived by the inventors for the series resonators in Examples 1 and 2. In Fig. 6, reference numeral 600A indicates an example of power consumption characteristics in Example 1, and reference numeral 600B indicates an example of power consumption characteristics in Example 2.

[0071] The transmission band shown in FIG. 6 is a designated transmission band. Therefore, the transmission band described with respect to the example of FIG. 6 refers to the designated transmission band. The horizontal axis of the graph in FIG. 6 indicates frequency on a normalized frequency scale. The normalized frequency is the quantity obtained by dividing the frequency by the center frequency of the transmission band. Therefore, in the example of FIG. 6, the frequency corresponding to the value "1" on the horizontal axis is equal to the center frequency of the transmission band.

[0072] In both Example 1 and Example 2, the series resonators 1S-1T to 1S-4 have power consumption peaks on both the low-frequency side and the high-frequency side of the transmission band. In the example of Fig. 6, attention is focused on the power consumption peaks on the high-frequency side of the transmission band. In this specification, the frequency at which the power consumption reaches its peak value is referred to as the power consumption peak frequency (power consumption peak frequency).

[0073] As shown in FIG. 6, in both Example 1 and Example 2, the power consumption peak frequency of at least one of the series resonators 1S-1T to 1S-4 is located in the range of 1.035 or more on the horizontal axis (see, for example, the graph for the series resonator 1S-2T in FIG. 6).

[0074] As described above, in an acoustic wave filter according to one aspect of the present disclosure, the peak power consumption frequency of the series resonator may be equal to or greater than 1.035 times the normalized frequency. In this case, the peak power consumption frequency of the series resonator can be sufficiently separated from the transmission band on the high-frequency side. This effectively reduces the power consumption of the series resonator during operation of the acoustic wave filter.

[0075] As can be understood from the above descriptions, the second embodiment can set a larger Δf than the first embodiment. As described above, in the acoustic wave filter according to one aspect of the present disclosure, a large Δf can be obtained by appropriately setting the cut angle of LT. Therefore, as shown in FIG. 6 , the second embodiment can increase the power consumption peak frequency of the series resonator compared to the first embodiment. As a result, the second embodiment can reduce power consumption more effectively than the first embodiment.

[0076] [Embodiment 2] In the first embodiment, the transmission band of the acoustic wave filter according to the embodiment of the present disclosure is located at a higher frequency than the reception band. However, the transmission band of the acoustic wave filter according to the embodiment of the present disclosure does not necessarily have to be located at a higher frequency than the reception band. For example, if the transmission band and the reception band are sufficiently separated from each other, the transmission bandwidth can be made wider than the reception bandwidth even if the transmission band is located at a lower frequency than the reception band.

[0077] For example, in an acoustic wave filter according to an embodiment of the present disclosure, the transmit band may be separated from the receive band by 50 MHz or more, or may be separated from the receive band by 300 MHz or more.

[0078] [Embodiment 3] 7 illustrates a schematic configuration of a communication device 151 according to the third embodiment. The communication device 151 performs wireless communication using radio waves. The communication device 151 may include an acoustic wave filter (e.g., the acoustic wave filter 100) according to an aspect of the present disclosure.

[0079] In communication device 151, a transmission information signal TIS containing information to be transmitted may be modulated and frequency-raised (converted into a high-frequency signal having a carrier frequency) by RF-IC (Radio Frequency-Integrated Circuit) 153, and converted into a transmission signal TS. Bandpass filter 155 may remove unwanted components from the TS outside the transmission passband. Next, the TS after removing the unwanted components may be amplified by amplifier 157 and then input to transmission filter 109T.

[0080] The transmission filter 109T may remove unnecessary components outside the transmission passband from the transmission signal TS input via a transmission terminal TX (not shown in FIG. 7). The transmission filter 109T may output the TS after removing the unnecessary components to the antenna 159 via an antenna terminal ANT (not shown in FIG. 7). The antenna 159 may convert the TS, which is an electrical signal input thereto, into radio waves as a wireless signal and transmit the radio waves to the outside of the communication device 151.

[0081] Furthermore, the antenna 159 may convert a received external radio wave into a received signal RS, which is an electrical signal. The antenna 159 may input the RS to the receiving filter 111R via the antenna terminal ANT. The receiving filter 111R may remove unwanted components outside the receiving passband from the input RS. The receiving filter 111R may output the received signal RS after the unwanted components have been removed to the amplifier 161 via the receiving terminal RX (not shown in FIG. 7). The output RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unwanted components outside the receiving passband from the amplified RS. The RS after the unwanted components have been removed may be frequency-downshifted and demodulated by the RF-IC 153, and converted into a received information signal RIS.

[0082] The TIS and RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the TIS and RIS may be analog audio signals or digitized audio signals. The passband of the wireless signals may be set appropriately and may comply with various known standards.

[0083] 〔summary〕 An acoustic wave filter according to a first aspect of the present disclosure is an acoustic wave filter having a plurality of acoustic wave elements, each of which includes a piezoelectric layer, an IDT electrode located on the piezoelectric layer, a low acoustic velocity film having a lower acoustic velocity than the piezoelectric layer, and a support substrate having a higher acoustic velocity than the piezoelectric layer. When the wavelength of an acoustic wave excited by the IDT electrode is represented as λ, the thickness of the piezoelectric layer is equal to or less than λ. The acoustic wave filter includes a transmit filter including a first acoustic wave element group among the plurality of acoustic wave elements, and a receive filter including a second acoustic wave element group among the plurality of acoustic wave elements that is different from the first acoustic wave element group. The pass band of the transmit filter is located at a higher frequency than the pass band of the receive filter, and the width of the pass band of the transmit filter is wider than the width of the pass band of the receive filter.

[0084] An acoustic wave filter according to a second aspect of the present disclosure is an acoustic wave filter having a plurality of acoustic wave elements, each of which includes a piezoelectric layer, an IDT electrode located on the piezoelectric layer, a low acoustic velocity film having a lower acoustic velocity than the piezoelectric layer, and a support substrate having a higher acoustic velocity than the piezoelectric layer. When the wavelength of an acoustic wave excited by the IDT electrode is represented as λ, the thickness of the piezoelectric layer is λ or less. The acoustic wave filter includes a transmit filter including a first acoustic wave element group among the plurality of acoustic wave elements, and a receive filter including a second acoustic wave element group among the plurality of acoustic wave elements that is different from the first acoustic wave element group. The pass band of the transmit filter is separated from the pass band of the receive filter by 50 MHz or more, and the width of the pass band of the transmit filter is wider than the width of the pass band of the receive filter.

[0085] In an acoustic wave filter according to a third aspect of the present disclosure, in the second aspect, the pass band of the transmission filter may be spaced apart from the pass band of the reception filter by 300 MHz or more.

[0086] In an acoustic wave filter according to aspect 4 of the present disclosure, in any one of aspects 1 to 3, when the width of the passband of the transmit filter is determined by the width from the −3 dB attenuation point on the low frequency side to the −3 dB attenuation point on the high frequency side in the attenuation characteristics of the transmit filter, and the width of the passband of the receive filter is determined by the width from the −3 dB attenuation point on the low frequency side to the −3 dB attenuation point on the high frequency side in the attenuation characteristics of the receive filter, the width of the passband of the transmit filter may be 2 MHz or more wider than the width of the passband of the receive filter.

[0087] In an acoustic wave filter according to aspect 5 of the present disclosure, in any one of aspects 1 to 4, when the width of the passband of the transmit filter is determined by the width from the −3 dB attenuation point on the low frequency side to the −3 dB attenuation point on the high frequency side in the attenuation characteristics of the transmit filter, and the width of the passband of the receive filter is determined by the width from the −3 dB attenuation point on the low frequency side to the −3 dB attenuation point on the high frequency side in the attenuation characteristics of the receive filter, the width of the passband of the transmit filter may be 4 MHz or more wider than the width of the passband of the receive filter.

[0088] In an acoustic wave filter according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, the piezoelectric layer may contain Y-cut X-propagation LT with a cut angle of 40° or less as a material, the low acoustic velocity film may contain SiO2 as a material, and the support substrate may contain Si as a material.

[0089] In the acoustic wave filter according to the seventh aspect of the present disclosure, in any one of the first to sixth aspects, the piezoelectric layer may contain Y-cut X-propagation LT with a cut angle of 25°±3° as a material, the low acoustic velocity film may contain SiO2 as a material, and the support substrate may contain Si as a material.

[0090] In an elastic wave filter according to aspect 8 of the present disclosure, in any one of aspects 1 to 7, the transmit filter may have a series resonator as the elastic wave element, and the peak frequency of power consumption in the series resonator on the high-frequency side of the pass band of the transmit filter may be 1.035 times or more the center frequency of the pass band of the transmit filter.

[0091] A communication device according to a ninth aspect of the present disclosure may include the acoustic wave filter according to any one of the first to eighth aspects.

[0092] [Additional Notes] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0093] 1. Acoustic wave element 1S series resonator 1S-1T to 1S-4T Series resonators in transmit filters (series resonators belonging to the first acoustic wave element group) 1S-1R to 1S-4R Series resonators in receive filters (series resonators belonging to the second acoustic wave element group) 2 Piezoelectric layer 3 IDT electrode 5 Low sound velocity membrane 6 Support substrate 100 Acoustic Wave Filter 109T Transmit Filter 111R receiving filter 151 Communication equipment

Claims

1. An acoustic wave filter having a plurality of acoustic wave elements, The acoustic wave element is a piezoelectric layer; an IDT electrode located on the piezoelectric layer; a low acoustic velocity film having an acoustic velocity lower than that of the piezoelectric layer; a support substrate having a higher acoustic velocity than the piezoelectric layer, When the wavelength of an elastic wave excited by the IDT electrode is represented as λ, the thickness of the piezoelectric layer is λ or less, The acoustic wave filter includes: a transmit filter including a first acoustic wave element group among the plurality of acoustic wave elements; a receive filter including a second acoustic wave element group different from the first acoustic wave element group among the plurality of acoustic wave elements, the passband of the transmission filter is located on a higher frequency side than the passband of the reception filter, An acoustic wave filter, wherein the width of the passband of the transmission filter is wider than the width of the passband of the reception filter.

2. An acoustic wave filter having a plurality of acoustic wave elements, The acoustic wave element is a piezoelectric layer; an IDT electrode located on the piezoelectric layer; a low acoustic velocity film having an acoustic velocity lower than that of the piezoelectric layer; a support substrate having a higher acoustic velocity than the piezoelectric layer, When the wavelength of an elastic wave excited by the IDT electrode is represented as λ, the thickness of the piezoelectric layer is λ or less, The acoustic wave filter includes: a transmit filter including a first acoustic wave element group among the plurality of acoustic wave elements; a receive filter including a second acoustic wave element group different from the first acoustic wave element group among the plurality of acoustic wave elements, the passband of the transmit filter is separated from the passband of the receive filter by 50 MHz or more; An acoustic wave filter, wherein the width of the passband of the transmission filter is wider than the width of the passband of the reception filter.

3. The acoustic wave filter according to claim 2 , wherein the pass band of the transmission filter is separated from the pass band of the reception filter by 300 MHz or more.

4. a width of a passband of the transmission filter is determined by a width from a −3 dB attenuation point on a low frequency side to a −3 dB attenuation point on a high frequency side in the attenuation characteristics of the transmission filter; When the width of the passband of the receiving filter is determined by the width from the −3 dB attenuation point on the low frequency side to the −3 dB attenuation point on the high frequency side in the attenuation characteristics of the receiving filter, The acoustic wave filter according to claim 1 , wherein the width of the passband of the transmission filter is at least 2 MHz wider than the width of the passband of the reception filter.

5. a width of a passband of the transmission filter is determined by a width from a −3 dB attenuation point on a low frequency side to a −3 dB attenuation point on a high frequency side in the attenuation characteristics of the transmission filter; When the width of the passband of the receiving filter is determined by the width from the −3 dB attenuation point on the low frequency side to the −3 dB attenuation point on the high frequency side in the attenuation characteristics of the receiving filter, The acoustic wave filter according to claim 1 , wherein the width of the passband of the transmission filter is at least 4 MHz wider than the width of the passband of the reception filter.

6. The piezoelectric layer contains Y-cut X-propagating LT with a cut angle of 40° or less as a material, The low acoustic velocity film is made of SiO ２ It contains as an ingredient The acoustic wave filter according to claim 1 , wherein the support substrate contains Si as a material.

7. The piezoelectric layer contains Y-cut X-propagating LT with a cut angle of 25°±3° as a material, The low acoustic velocity film is made of SiO ２ It contains as an ingredient The acoustic wave filter according to claim 1 , wherein the support substrate contains Si as a material.

8. the transmit filter has a series resonator as the acoustic wave element, 4. The acoustic wave filter according to claim 1, wherein a peak frequency of power consumption in the series resonator on the high frequency side of a pass band of the transmission filter is equal to or greater than 1.035 times a center frequency of the pass band of the transmission filter.

9. A communication device comprising the acoustic wave filter according to claim 1 .

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