Acoustic wave device

Abstract

To improve frequency characteristics of an acoustic wave device.SOLUTION: An acoustic wave device has: a piezoelectric material; an interdigital transduce (IDT) electrode which is located in the vicinity of the piezoelectric material; and an acoustic reflection film which is located below the piezoelectric material. The acoustic reflection film has a lamination structure consisting of low-acoustic impedance layers and high-acoustic impedance layers. The acoustic reflection film has: a first layer which is the low-acoustic impedance layer located closest to the piezoelectric material among all of the low-acoustic impedance layers and the high-acoustic impedance layers; a second layer which is the high-acoustic impedance layer making contact with a lower surface of the first layer; and a third layer which is the low-acoustic impedance layer making contact with a lower surface of the second layer. When a thickness of the first layer is denoted as T1, and a thickness of the third layer is denoted as T3, then T1<T3 holds true.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] [Patent Document 1] International Publication WO2023 / 033032 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to improve the frequency characteristics of acoustic wave devices. [Means for solving the problem]

[0005] An elastic wave device according to one aspect of the present disclosure includes a piezoelectric body, an IDT electrode located near the piezoelectric body, and an acoustic reflection film located below the piezoelectric body. The acoustic reflection film has a laminated structure of low acoustic impedance layers and high acoustic impedance layers. The acoustic reflection film includes: a first layer, which is the low acoustic impedance layer that is located closest to the piezoelectric body among all the low acoustic impedance layers and high acoustic impedance layers; a second layer, which is the high acoustic impedance layer that is in contact with a lower surface of the first layer; and a third layer, which is the low acoustic impedance layer that is in contact with a lower surface of the second layer. When a thickness of the first layer is denoted as T1 and a thickness of the third layer is denoted as T3, <T3である。

[0006] an IDT electrode positioned near the piezoelectric body; and an acoustic reflection film positioned below the piezoelectric body, the acoustic reflection film having a laminated structure of low acoustic impedance layers and high acoustic impedance layers, the acoustic reflection film including: a first layer which is the low acoustic impedance layer that is positioned closest to the piezoelectric body among all the low acoustic impedance layers and high acoustic impedance layers; a second layer which is the high acoustic impedance layer in contact with a lower surface of the first layer; a third layer which is the low acoustic impedance layer in contact with a lower surface of the second layer; a fourth layer which is the high acoustic impedance layer in contact with a lower surface of the third layer; a fifth layer which is the low acoustic impedance layer in contact with a lower surface of the fourth layer; and a sixth layer which is the high acoustic impedance layer in contact with a lower surface of the fifth layer; When the thickness of the fourth layer is denoted as T4 and the thickness of the sixth layer is denoted as T6, T6 <T2 and, T6 <T4 At least one of the following is satisfied.

[0007] An elastic wave device according to one aspect of the present disclosure includes a piezoelectric body, an IDT electrode located near the piezoelectric body, and an acoustic reflection film located below the piezoelectric body, the acoustic reflection film having a laminated structure of low acoustic impedance layers and high acoustic impedance layers, and the sum of the number of the low acoustic impedance layers and the number of the high acoustic impedance layers in the acoustic reflection film is 4 or more and 5 or less, and the acoustic reflection film includes: a first layer which is the low acoustic impedance layer located closest to the piezoelectric body among all the low acoustic impedance layers and high acoustic impedance layers; a second layer which is the high acoustic impedance layer in contact with a lower surface of the first layer; a third layer which is the low acoustic impedance layer in contact with a lower surface of the second layer; and a fourth layer which is the high acoustic impedance layer in contact with a lower surface of the third layer, wherein when a thickness of the first layer is denoted as T1, a thickness of the second layer is denoted as T2, and a thickness of the fourth layer is denoted as T4, 0.825×T1 <T2 and, 0.825×T1 <T4 At least one of the following is satisfied. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, the frequency characteristics of an acoustic wave device can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows an example of the configuration of an acoustic wave device according to a first embodiment. [Figure 2] An example of the relationship between pitch and frequency characteristics in an acoustic wave device obtained in the first study is shown below. [Figure 3] An example of the relationship between the duty and frequency characteristics in an acoustic wave device obtained in the first study is shown below. [Figure 4] An example of the relationship between the thickness of the piezoelectric body and the frequency characteristics in the acoustic wave device obtained in the first study is shown below. [Figure 5] An example of the relationship between the thickness of the IDT electrode and the frequency characteristics in an acoustic wave device obtained in the first study is shown below. [Figure 6] An example of the relationship between T1 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 7] An example of the relationship between T2 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 8] An example of the relationship between T3 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 9] An example of the relationship between T4 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 10] An example of the relationship between T5 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 11] An example of the relationship between T6 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 12] An example of the relationship between T7 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 13] An example of the relationship between T8 and frequency characteristics in an acoustic wave device obtained in the second study is shown below. [Figure 14] An example of frequency characteristics of an acoustic wave device obtained in the third study is shown below. [Figure 15] An example of the frequency characteristics of the acoustic wave device obtained in the fourth study is shown below. [Figure 16] The results obtained in the fifth study are shown in outline. [Figure 17] The results obtained in the sixth study are summarized below. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment 1] Embodiment 1 will be described below. For convenience of explanation, components having the same functions as those described in Embodiment 1 will be denoted by the same reference numerals in the following embodiments, and their description will not be repeated. For simplicity, descriptions of well-known technical matters will be omitted as appropriate. Each component, material, and numerical value described in this specification is merely exemplary unless there is a contradiction in the content. Therefore, for example, the positional relationship and connection relationship of each component are not limited to the examples in each figure unless there is a contradiction in the content. Furthermore, each figure is not necessarily drawn to scale.

[0011] (One Configuration Example of Elastic Wave Device 1) Fig. 1 shows an example of the configuration of an elastic wave device 1 according to Embodiment 1. Fig. 1 shows a schematic front view of the layered structure of the elastic wave device 1. For convenience of explanation, the present specification introduces a Cartesian coordinate system (D1-D2-D3 coordinate system) shown in Fig. 1 .

[0012] As shown in FIG. 1 , the multiple electrode fingers 32 in the acoustic wave device 1 may be arranged in the D1 direction. In the example of embodiment 1, the D1 direction is the main propagation direction of acoustic waves propagating within the piezoelectric body 4 of the acoustic wave device 1. The D2 direction is an example of a direction intersecting the D1 direction. The electrode fingers 32 may extend in the D2 direction. The D3 direction is the thickness direction of each component of the acoustic wave device 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. The D1 to D3 directions may be referred to as the first to third directions, respectively. The D1 direction may be referred to as the width direction of the acoustic wave device 1, and the D2 direction may be referred to as the longitudinal direction of the acoustic wave device 1.

[0013] The acoustic wave device 1 includes a piezoelectric body 4. An example of the material of the piezoelectric body 4 is a single crystal material having piezoelectric properties. As one example, the material of the piezoelectric body 4 may be lithium tantalate (also referred to as LiTaO3:LT). As another example, the material of the piezoelectric body 4 may be lithium niobate (also referred to as LiNbO3:LN).

[0014] The acoustic wave device 1 has an IDT (Interdigital Transduce) electrode 3 that excites an acoustic wave. The IDT electrode 3 is also referred to as an excitation electrode. Examples of materials for the IDT electrode 3 include Al, Cu, Au, Pt, W, Mo, and various alloys. In the first embodiment, the IDT electrode 3 is configured to excite a plate wave. An example of the plate wave in the first embodiment is an Al-Lamb wave.

[0015] 1, the IDT electrode 3 is located on the upper surface of the piezoelectric body 4. However, the position of the IDT electrode 3 is not necessarily limited to this example. The IDT electrode 3 may be located in the vicinity of the piezoelectric body 4.

[0016] For example, unlike the example of Fig. 1, the IDT electrode 3 may be configured as a so-called buried electrode. When the IDT electrode 3 is configured as a buried electrode, the piezoelectric body 4 has a plurality of grooves on the upper or lower surface of the piezoelectric body 4. At least some of the electrode fingers 32 are located inside the grooves.

[0017] The IDT electrode 3 may have a first bus bar and a second bus bar (not shown) that face each other in the direction D2. In this case, the IDT electrode 3 has (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.

[0018] 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. In this case, the second electrode fingers 32b are interdigitated with the first electrode fingers 32a in the direction D2.

[0019] As shown in FIG. 1 , the plurality of electrode fingers 32 may be alternately positioned at approximately constant intervals in the D1 direction. In this specification, the pitch of the electrode fingers 32 is represented as p. p may also be referred to as the electrode finger pitch of the IDT electrode 3. p may be, for example, the pitch (repetition interval) in the D1 direction between the centers of two adjacent electrode fingers 32. As an example, p may be set equal to half the wavelength λ (λ / 2) of the acoustic wave excited in the D1 direction by the IDT electrode 3. In this case, λ may be defined as twice the length of p. That is, λ may be defined as 2p.

[0020] 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 in accordance with p. The ratio of w to p (w / p) is also referred to as the duty of electrode finger 32. For example, the frequency characteristics of acoustic wave device 1 can be controlled by changing the duty.

[0021] As an example, the thickness of the piezoelectric body 4 in the first embodiment may be λ or less (that is, 2p or less). In this case, the IDT electrode 3 in the first embodiment can excite an A1 Lamb wave.

[0022] Acoustic wave device 1 may include a support substrate 6 that supports each component of acoustic wave device 1. Support substrate 6 is located below each component. For example, support substrate 6 may be made of Si.

[0023] 1 includes an acoustic reflection film 5 located below a piezoelectric body 4. As shown in FIG. 1, the acoustic reflection film 5 may be located between the piezoelectric body 4 and a support substrate 6.

[0024] The acoustic reflecting film 5 has a laminated structure of low acoustic impedance layers 5a and high acoustic impedance layers 5b. As an example, the acoustic reflecting film 5 may be a multilayer film in which the low acoustic impedance layers 5a and the high acoustic impedance layers 5b are alternately laminated.

[0025] For example, the low acoustic impedance layer 5a may have a lower acoustic impedance than the piezoelectric body 4. The main component of the low acoustic impedance layer 5a may be, for example, SiO2. On the other hand, the high acoustic impedance layer 5b may have a higher acoustic impedance than the low acoustic impedance layer 5a. The main component of the high acoustic impedance layer 5b may be, for example, at least one of HfO2, Ta2O5, ZrO2, SiN, AlN, Al2O3, W, Pt, Ta, and Hf.

[0026] In the first embodiment, the low acoustic impedance layer 5a is made of SiO2, and the high acoustic impedance layer 5b is made of HfO2. In this case, the thickness of the high acoustic impedance layer 5b (i.e., the HfO2 layer) may be set to be smaller than the thickness of the low acoustic impedance layer 5a (i.e., the SiO2 layer). When the HfO2 layer is thinner than the SiO2 layer, warpage of the acoustic wave device 1 can be reduced.

[0027] In the example of Fig. 1, a unit consisting of one low acoustic impedance layer 5a and one high acoustic impedance layer 5b is referred to as a laminate unit UN. Fig. 1 illustrates a case in which the acoustic reflecting film 5 has four laminate units UN. Therefore, the acoustic reflecting film 5 in Fig. 1 has four low acoustic impedance layers 5a and four high acoustic impedance layers 5b.

[0028] 1, of all the multilayer units UN, the multilayer unit UN that is located closest to the piezoelectric body 4 is referred to as the first multilayer unit UN-1. In other words, of all the multilayer units UN, the first multilayer unit UN-1 is the multilayer unit UN that is the shortest distance from the piezoelectric body 4.

[0029] Of all the multilayer units UN, the unit UN with the second shortest distance from the piezoelectric body 4 is referred to as the second multilayer unit UN-2. Of the four multilayer units UN, the unit UN with the third shortest distance from the piezoelectric body 4 is referred to as the third multilayer unit UN-3. Of the four multilayer units UN, the unit UN with the fourth shortest distance from the piezoelectric body 4 is referred to as the fourth multilayer unit UN-4.

[0030] In the example of FIG. 1, the first laminate unit UN-1 is in contact with the lower surface of the piezoelectric body 4. The second laminate unit UN-2 is in contact with the lower surface of the first laminate unit UN-1. The third laminate unit UN-3 is in contact with the lower surface of the second laminate unit UN-2. The fourth laminate unit UN-4 is in contact with the lower surface of the third laminate unit UN-3.

[0031] As described above, in the example of embodiment 1, the numbers indicating the multilayer units UN increase from the top to the bottom (i.e., as the distance between the multilayer units UN and the piezoelectric body 4 increases). Therefore, in embodiment 1, the numbers indicating the layers of the acoustic reflection film 5 described below also increase from the top to the bottom.

[0032] In the example of Fig. 1, the first laminate unit UN-1 has a first layer 5-1 and a second layer 5-2. The first layer 5-1 in the example of Fig. 1 is the low acoustic impedance layer 5a that is located closest to the piezoelectric body 4 among all the low acoustic impedance layers 5a and high acoustic impedance layers 5b. In the example of Fig. 1, the first layer 5-1 is in contact with the lower surface of the piezoelectric body 4. The first layer 5-1 may also be referred to as a first low acoustic impedance layer.

[0033] The second layer 5-2 in the first laminate unit UN-1 is a high acoustic impedance layer 5b that is in contact with the lower surface of the first layer 5-1. The second layer 5-2 may be referred to as a first high acoustic impedance layer. The first high acoustic impedance layer is the high acoustic impedance layer 5b that is the shortest distance from the piezoelectric body 4 among all the high acoustic impedance layers 5b.

[0034] The second laminate unit UN-2 has a third layer 5-3 and a fourth layer 5-4. The third layer 5-3 is a low acoustic impedance layer 5a that is in contact with the lower surface of the second layer 5-2. The third layer 5-3 may be referred to as a second low acoustic impedance layer. The second low acoustic impedance layer is the low acoustic impedance layer 5a that is the second shortest distance from the piezoelectric body 4 among all the low acoustic impedance layers 5a.

[0035] The fourth layer 5-4 in the second laminate unit UN-2 is a high acoustic impedance layer 5b that is in contact with the lower surface of the third layer 5-3. The fourth layer 5-4 may be referred to as a second high acoustic impedance layer. The second high acoustic impedance layer is the high acoustic impedance layer 5b that is the second shortest distance from the piezoelectric body 4 among all the high acoustic impedance layers 5b.

[0036] The third laminate unit UN-3 has a fifth layer 5-5 and a sixth layer 5-6. The fifth layer 5-5 is a low acoustic impedance layer 5a that is in contact with the lower surface of the fourth layer 5-4. The fifth layer 5-5 may be referred to as the third low acoustic impedance layer. The third low acoustic impedance layer is the low acoustic impedance layer 5a that is the third shortest distance from the piezoelectric body 4 among all the low acoustic impedance layers 5a.

[0037] The sixth layer 5-6 in the third stack unit UN-3 is a high acoustic impedance layer 5b that is in contact with the lower surface of the fifth layer 5-5. The sixth layer 5-6 may be referred to as the third high acoustic impedance layer. The third high acoustic impedance layer is the high acoustic impedance layer 5b that is the third shortest distance from the piezoelectric body 4 among all the high acoustic impedance layers 5b.

[0038] The fourth laminate unit UN-4 has a seventh layer 5-7 and an eighth layer 5-8. The seventh layer 5-7 is a low acoustic impedance layer 5a that is in contact with the lower surface of the sixth layer 5-6. The seventh layer 5-7 may be referred to as the fourth low acoustic impedance layer. The fourth low acoustic impedance layer is the low acoustic impedance layer 5a that is the fourth shortest distance from the piezoelectric body 4 among all the low acoustic impedance layers 5a.

[0039] The eighth layer 5-8 in the fourth stack unit UN-4 is a high acoustic impedance layer 5b that contacts the lower surface of the seventh layer 5-7. The eighth layer 5-8 may be referred to as the fourth high acoustic impedance layer. The fourth high acoustic impedance layer is the high acoustic impedance layer 5b that is the fourth shortest distance from the piezoelectric body 4 among all the high acoustic impedance layers 5b.

[0040] In this specification, the total number of layers in the acoustic reflection film 5 is represented as N. In the first embodiment, for the sake of clarity, it is assumed that the acoustic reflection film 5 does not have any additional components other than the low acoustic impedance layers 5a and the high acoustic impedance layers 5b. Therefore, N in the first embodiment is represented as the sum of the number Na of the low acoustic impedance layers 5a and the number Nb of the high acoustic impedance layers 5b. In the example of FIG. 1, Na = Nb = 4, so N = Na + Nb = 8.

[0041] In this specification, the thickness of the j-th layer in the acoustic reflection film 5 is denoted as Tj. j is an index indicating the layer number in the acoustic reflection film 5. j may be any natural number satisfying 1≦j≦N. FIG. 1 illustrates thicknesses T1 of the first layer 5-1 to T8 of the eighth layer 5-8.

[0042] (First Study on Frequency Characteristics of Elastic Wave Device 1) The frequency characteristics of the elastic wave device 1 can vary depending on various design conditions of the elastic wave device 1. Therefore, by selecting appropriate design conditions, the frequency characteristics of the elastic wave device 1 can be improved. As an example, the inventor of the present application (hereinafter abbreviated as "the inventor") conducted a simulation study to determine design conditions for reducing spurious emissions in a frequency band around 4000 MHz.

[0043] First, the inventors constructed a basic simulation model for the acoustic wave device 1 shown in Fig. 1. In this specification, the simulation model is abbreviated to "model," and the basic model is referred to as "basic model." Furthermore, the frequency characteristics of the acoustic wave device 1 are abbreviated to simply "frequency characteristics."

[0044] The design conditions for the basic model set by the inventor are: Material of piezoelectric element 4: LN Euler angles of piezoelectric element 4 = (0°, 30°, 0°) Thickness of piezoelectric element 4: 0.47 μm IDT electrode 3 material: Al IDT electrode 3 thickness: 0.09 μm p=1.2μm Duty=0.55 Material of low acoustic impedance layer 5a: SiO2 Thickness of low acoustic impedance layer 5a: 0.2 μm Material of high acoustic impedance layer 5b: HfO2 Thickness of high acoustic impedance layer 5b: 0.165 μm As stated above.

[0045] Therefore, in the basic model, (i) T1=T3=T5=T7=0.2 μm, and (ii) T2=T4=T6=T8=0.165 μm.

[0046] As a first study, the inventors conducted a simulation study to examine the influence of design conditions other than the acoustic reflection film 5 on the frequency characteristics. For example, depending on the design conditions of the acoustic wave device 1, it is possible that at least one of the dimensions of the IDT electrode 3 and the dimensions of the piezoelectric element 4 affects the frequency characteristics.

[0047] Therefore, the inventor further constructed models by varying (i) p (pitch), (ii) duty, (iii) thickness of the piezoelectric body 4, and (iv) thickness of the IDT electrode 3 with respect to the basic model. Then, the inventor derived frequency characteristics for each of the constructed models through simulation.

[0048] 2 to 5 each show an example of the frequency characteristics (more specifically, the phase characteristics) obtained in the first study. In the graphs of FIGS. 2 to 5, the horizontal axis represents frequency, and the vertical axis represents the phase (unit: degrees) of the impedance of elastic wave device 1. In these graphs, angles are expressed as degrees. In the following description, the phase of the impedance will be abbreviated to simply "phase."

[0049] As will be described below, the graphs denoted by reference numerals 220, 320, 420, and 520 in Figures 2 to 5 correspond to the basic model, and therefore the graphs denoted by these reference numerals are all equivalent.

[0050] FIG. 2 shows an example of frequency characteristics when only p is changed. That is, FIG. 2 shows an example of the relationship between p and frequency characteristics. In FIG. 2, reference numeral 210 indicates frequency characteristics when p=1.1 μm, reference numeral 220 indicates frequency characteristics when p=1.2 μm, and reference numeral 230 indicates frequency characteristics when p=1.3 μm. The example of reference numeral 220 corresponds to the basic model. In the example of reference numeral 210, p is set smaller than that of the basic model. On the other hand, in the example of reference numeral 230, p is set larger than that of the basic model.

[0051] FIG. 3 shows an example of frequency characteristics when only the duty cycle is changed. That is, FIG. 3 shows an example of the relationship between the duty cycle and the frequency characteristics. In FIG. 3, reference numeral 310 indicates the frequency characteristics when the duty cycle is 0.45, reference numeral 320 indicates the frequency characteristics when the duty cycle is 0.55, and reference numeral 330 indicates the frequency characteristics when the duty cycle is 0.65. The example of reference numeral 320 corresponds to the basic model. In the example of reference numeral 310, the duty cycle is set smaller than that of the basic model. On the other hand, in the example of reference numeral 330, the duty cycle is set larger than that of the basic model.

[0052] FIG. 4 shows an example of frequency characteristics when only the thickness of the piezoelectric body 4 is changed. That is, FIG. 4 shows an example of the relationship between the thickness of the piezoelectric body 4 and the frequency characteristics. In FIG. 4, reference numeral 410 indicates the frequency characteristics when the thickness of the piezoelectric body 4 is 0.46 μm, reference numeral 420 indicates the frequency characteristics when the thickness of the piezoelectric body 4 is 0.47 μm, and reference numeral 430 indicates the frequency characteristics when the thickness of the piezoelectric body 4 is 0.48 μm. The example indicated by reference numeral 420 corresponds to the basic model. In the example indicated by reference numeral 410, the thickness of the piezoelectric body 4 is set smaller than that of the basic model. On the other hand, in the example indicated by reference numeral 430, the thickness of the piezoelectric body 4 is set larger than that of the basic model.

[0053] FIG. 5 shows an example of frequency characteristics when only the thickness of the IDT electrode 3 is changed. That is, FIG. 5 shows an example of the relationship between the thickness of the IDT electrode 3 and the frequency characteristics. In FIG. 5, reference numeral 510 indicates the frequency characteristics when the thickness of the IDT electrode 3 is 0.07 μm, reference numeral 520 indicates the frequency characteristics when the thickness of the IDT electrode 3 is 0.09 μm, and reference numeral 530 indicates the frequency characteristics when the thickness of the IDT electrode 3 is 0.11 μm. The example indicated by reference numeral 520 corresponds to the basic model. In the example indicated by reference numeral 510, the thickness of the IDT electrode 3 is set smaller than that of the basic model. On the other hand, in the example indicated by reference numeral 530, the thickness of the IDT electrode 3 is set larger than that of the basic model.

[0054] 2 to 5, in the basic model, spurious emissions occur in a frequency band around 4000 MHz (see the positions of the vertical dotted lines in Figs. 2 to 5). The results shown in Figs. 2 to 5 indicate that even if p, duty, the thickness of the piezoelectric body 4, or the thickness of the IDT electrode 3 is changed, the frequency band of the spurious emissions does not change significantly, and the spurious emissions are not significantly reduced.

[0055] (Second Consideration) 2 to 5, it is thought that the above-mentioned spurious may be caused, for example, by the design conditions of the acoustic reflection film 5. Therefore, as a second study, the inventors conducted a simulation study on the influence of the design conditions of the acoustic reflection film 5 on the frequency characteristics.

[0056] For example, depending on the design conditions of the acoustic wave device 1, it is thought that at least one of the thicknesses T1 to T8 of the acoustic reflection film 5 may have a relatively high correlation with spurious emissions. Therefore, the inventors constructed additional models in which one of T1 to T8 was changed from the basic model. The inventors then derived frequency characteristics for each of the constructed models through simulation.

[0057] 6 to 13 show examples of frequency characteristics obtained in the second study. These figures are counterparts of the above-mentioned Figures 2 to 5. As will be described below, the graphs denoted by 620, 720, 820, 920, 1020, 1120, 1220, and 1320 in these figures correspond to the basic model. Therefore, the graphs denoted by these figures are all equivalent.

[0058] FIG. 6 shows an example of frequency characteristics when only T1 is changed. That is, FIG. 6 shows an example of the relationship between T1 and frequency characteristics. In FIG. 6, reference numeral 610 indicates frequency characteristics when T1=0.1 μm, reference numeral 620 indicates frequency characteristics when T1=0.2 μm, and reference numeral 630 indicates frequency characteristics when T1=0.3 μm. The example of reference numeral 620 corresponds to the basic model. In the example of reference numeral 610, T1 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 630, T1 is set larger than that of the basic model.

[0059] FIG. 7 shows an example of frequency characteristics when only T2 is changed. That is, FIG. 7 shows an example of the relationship between T2 and frequency characteristics. In FIG. 7, reference numeral 710 indicates frequency characteristics when T2=0.1 μm, reference numeral 720 indicates frequency characteristics when T2=0.165 μm, and reference numeral 730 indicates frequency characteristics when T2=0.23 μm. The example of reference numeral 720 corresponds to the basic model. In the example of reference numeral 710, T2 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 730, T2 is set larger than that of the basic model.

[0060] FIG. 8 shows an example of frequency characteristics when only T3 is changed. That is, FIG. 8 shows an example of the relationship between T3 and frequency characteristics. In FIG. 8, reference numeral 810 indicates frequency characteristics when T3=0.1 μm, reference numeral 820 indicates frequency characteristics when T3=0.2 μm, and reference numeral 830 indicates frequency characteristics when T3=0.3 μm. The example of reference numeral 820 corresponds to the basic model. In the example of reference numeral 810, T3 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 830, T3 is set larger than that of the basic model.

[0061] FIG. 9 shows an example of frequency characteristics when only T4 is changed. That is, FIG. 9 shows an example of the relationship between T4 and frequency characteristics. In FIG. 9, reference numeral 910 indicates the frequency characteristics when T4=0.1 μm, reference numeral 920 indicates the frequency characteristics when T4=0.165 μm, and reference numeral 930 indicates the frequency characteristics when T4=0.23 μm. The example of reference numeral 920 corresponds to the basic model. In the example of reference numeral 910, T4 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 930, T4 is set larger than that of the basic model.

[0062] FIG. 10 shows an example of frequency characteristics when only T5 is changed. That is, FIG. 10 shows an example of the relationship between T5 and frequency characteristics. In FIG. 10, reference numeral 1010 indicates frequency characteristics when T5=0.1 μm, reference numeral 1020 indicates frequency characteristics when T5=0.2 μm, and reference numeral 1030 indicates frequency characteristics when T5=0.3 μm. The example of reference numeral 1020 corresponds to the basic model. In the example of reference numeral 1010, T5 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 1030, T5 is set larger than that of the basic model.

[0063] FIG. 11 shows an example of frequency characteristics when only T6 is changed. That is, FIG. 11 shows an example of the relationship between T6 and frequency characteristics. In FIG. 11, reference numeral 1110 shows frequency characteristics when T6=0.1 μm, reference numeral 1120 shows frequency characteristics when T6=0.165 μm, and reference numeral 1130 shows frequency characteristics when T6=0.23 μm. The example of reference numeral 1120 corresponds to the basic model. In the example of reference numeral 1110, T6 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 1130, T6 is set larger than that of the basic model.

[0064] FIG. 12 shows an example of frequency characteristics when only T7 is changed. That is, FIG. 12 shows an example of the relationship between T7 and frequency characteristics. In FIG. 12, reference numeral 1210 shows frequency characteristics when T7=0.1 μm, reference numeral 1220 shows frequency characteristics when T7=0.2 μm, and reference numeral 1230 shows frequency characteristics when T7=0.3 μm. The example of reference numeral 1220 corresponds to the basic model. In the example of reference numeral 1210, T7 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 1230, T7 is set larger than that of the basic model.

[0065] FIG. 13 shows an example of frequency characteristics when only T8 is changed. That is, FIG. 13 shows an example of the relationship between T8 and frequency characteristics. In FIG. 13, reference numeral 1310 shows frequency characteristics when T8=0.1 μm, reference numeral 1320 shows frequency characteristics when T8=0.165 μm, and reference numeral 1330 shows frequency characteristics when T8=0.23 μm. The example of reference numeral 1320 corresponds to the basic model. In the example of reference numeral 1310, T8 is set smaller than that of the basic model. On the other hand, in the example of reference numeral 1330, T8 is set larger than that of the basic model.

[0066] Of the examples shown in Figures 6 to 13, in (i) the example of reference numeral 730 in Figure 7, (ii) the example of reference numeral 830 in Figure 8, and (iii) the example of reference numeral 930 in Figure 9, it was confirmed that the spurious around 4000 MHz that occurred in the basic model was effectively shifted to the low-frequency region and that the spurious was effectively reduced.

[0067] From this, it is considered that the three thicknesses T2, T3, and T4 have a relatively high correlation with spurious emissions in the example of Fig. 1. Therefore, it is expected that the frequency characteristics can be improved by setting at least one of T2, T3, and T4 to a value larger than a predetermined value.

[0068] (Third Consideration) T2 in the example indicated by reference numeral 730 in Fig. 7 and T4 in the example indicated by reference numeral 930 in Fig. 9 are both the thickness of high acoustic impedance layer 5b in Fig. 1. Based on the results of the second study, the inventors conducted further study on the thickness of high acoustic impedance layer 5b as a third study.

[0069] Specifically, the inventors performed a simulation of the basic model by varying either T2 or T4 over a wider range than in the second study, and, for comparison with T2 and T4, the inventors further performed a simulation of the basic model by varying T6 over a wider range than in the second study.

[0070] FIG. 14 shows an example of frequency characteristics obtained in the third study. The minimum values ​​of T2, T4, and T6 in the third study are 0.165 μm (value in the basic model). As shown in FIG. 14, the phase at the minimum value is approximately −82°. In the third study, the phase at the minimum value is used as the reference value for the phase.

[0071] Reference numeral 1410 in Fig. 14 indicates an example of frequency characteristics when only T2 is changed. In the example of reference numeral 1410, as T4 increases from its minimum value, the phase decreases. In the example of reference numeral 1410, the phase reaches its minimum value when T2 is approximately 0.325 µm. Thereafter, the phase increases as T2 increases. Then, at T2 = 0.456 µm, the phase reaches its reference value.

[0072] The smaller the phase value, the more the spurious is reduced. Therefore, it can be said that in the range of T2 where the phase is equal to or less than the reference value, the spurious does not increase compared to the basic model. From this, in order to improve the frequency characteristics by setting T2 to a value greater than the minimum value, for example, 0.165 μm <T2≦0.456μm …(1) T2 can be selected within this range.

[0073] Reference numeral 1420 in Fig. 14 indicates an example of frequency characteristics when only T4 is changed. In the example of reference numeral 1420, the phase also decreases as T4 increases from its minimum value. In the example of reference numeral 1410, the phase reaches its minimum value when T4 is approximately 0.225 µm. Thereafter, the phase increases as T4 increases. Then, the phase reaches its reference value when T4 is 0.245 µm.

[0074] Therefore, in order to improve the frequency characteristics by setting T4 to a value greater than the minimum value, for example, 0.165 μm <T4≦0.245μm …(2) In this range, T4 should be selected.

[0075] 14, reference numeral 1430 indicates an example of frequency characteristics when only T6 is changed. In the example of reference numeral 1430, unlike the examples of reference numerals 1410 and 1420, it was confirmed that the phase tends to increase as T6 increases from its minimum value.

[0076] For this reason, increasing T6 in the example of Figure 1 is not considered to contribute to improving the frequency characteristics. Therefore, in the following, we will mainly consider T2 and T4 with respect to high acoustic impedance layer 5b. In the following examples, unless otherwise specified, the thickness of high acoustic impedance layer 5b other than second layer 5-2 and fourth layer 5-4 is maintained at a constant value of 0.165 μm.

[0077] (Fourth Consideration) In the example of reference numeral 830 in Fig. 8, T3 is the thickness of the low acoustic impedance layer 5a in Fig. 1. Based on the results of the second study, the inventors conducted a fourth study on the thickness of the low acoustic impedance layer 5a. The fourth study is a counterpart to the third study.

[0078] Specifically, the inventors performed a simulation on the basic model by varying T3 over a wider range than in the second study, and then, for comparison with T3, the inventors performed a further simulation on the basic model by varying T5 over a wider range than in the second study.

[0079] Fig. 15 shows an example of frequency characteristics obtained in the fourth study. The minimum values ​​of T3 and T5 in the fourth study are 0.2 µm (values ​​in the basic model). In the example of Fig. 15, the phase at the minimum values ​​(approximately -82°) is also the same as in the example of Fig. 14. In the fourth study, the phase at the minimum values ​​is used as the reference value for the phase.

[0080] Reference numeral 1510 in FIG. 15 indicates an example of frequency characteristics when only T3 is changed. In the example of reference numeral 1510, as T3 increases from its minimum value, the phase decreases. In the example of reference numeral 1510, the phase reaches its minimum value when T3 is approximately 0.35 μm. Thereafter, as T2 increases, the phase repeatedly increases and decreases. Next, after T3 is approximately 0.55 μm, the phase increases as T3 increases. Finally, at T3=0.59 μm, the phase reaches its reference value.

[0081] Therefore, in order to improve the frequency characteristics by setting T3 to a value greater than the minimum value, for example, 0.2 μm <T3≦0.59μm …(3) In this range, T3 can be selected.

[0082] Reference numeral 1520 in Fig. 15 indicates an example of frequency characteristics when only T5 is changed. In the example of reference numeral 1520, unlike the example of reference numeral 1510, it was confirmed that the phase tends to increase as T5 increases from the minimum value.

[0083] For this reason, it is believed that increasing T5 in the example of Figure 1 does not contribute to improving the frequency characteristics. Therefore, in the following, we will mainly consider T3 with respect to the low acoustic impedance layer 5a. In the following examples, unless otherwise specified, the thickness of the low acoustic impedance layer 5a other than the third layer 5-3 is maintained at a constant value of 0.2 μm.

[0084] (Fifth Consideration) Based on the results of the third and fourth studies, the inventors further studied the respective numerical ranges of T2, T4, and T3. In the fifth study, the inventors further studied the respective numerical ranges of T2, T4, and T3 when N≧6. In this specification, the case of N≧6 is also referred to as the "case of 6 layers or more."

[0085] 16 shows a schematic diagram of the results obtained in the fifth study. In the following explanation, any one of the multiple layers in the acoustic reflection film 5 will be referred to as the layer of interest. First, we will discuss the case where the layer of interest is the second layer, i.e., the case where we focus on T2.

[0086] When the layer of interest is the second layer, a more general formula can be obtained by normalizing the above formula (1) by a predetermined reference thickness Tn corresponding to T2. As an example, when the layer of interest is the second layer, the thickness of one of the multiple high acoustic impedance layers 5b can be used as Tn.

[0087] As described above, when N≧6, for example, the thickness T6 of the sixth layer 2-6 is maintained at a constant value. Therefore, in the fifth study, when the layer of interest is the second layer, Tn is defined as Tn=T6=0.165 μm.

[0088] First, by dividing each side of equation (1) by Tn, 0.165 / Tn <T2 / Tn≦0.456 / Tn …(1a) T2 / Tn may be referred to as the normalized thickness of T2.

[0089] When the layer of interest is the second layer, Tn=0.165 μm, and therefore, by calculating the specific values ​​of the leftmost and rightmost sides of equation (1a), 1 <T2 / Tn≦2.764 …(1b) is obtained.

[0090] Then, by multiplying each side of equation (1b) by T6, T6<(T2 / Tn)×T6≦2.764×T6 …(1c) is obtained.

[0091] When the layer of interest is the second layer, Tn=T6, so from equation (1c), T6 <T2≦2.764×T6 …(1d) is obtained.

[0092] Therefore, when N≧6, for example, by selecting T2 as a parameter for the constant value T6 so as to satisfy equation (1d), excellent frequency characteristics can be achieved.

[0093] Next, we will discuss the case where the layer of interest is the fourth layer, i.e., the case where we focus on T4. When the layer of interest is the fourth layer, a more general formula can be obtained by normalizing the above formula (2) by Tn corresponding to T4. Based on the same concept as when the layer of interest is the third layer, when the layer of interest is the fourth layer, Tn may also be determined as Tn = T6 = 0.165 μm.

[0094] First, by dividing each side of equation (2) by Tn, 0.165 / Tn <T4 / Tn≦0.245 / Tn …(2a) T4 / Tn may be referred to as the normalized thickness of T4.

[0095] When the layer of interest is the fourth layer, Tn=0.165 μm, and therefore, by calculating the specific values ​​of the leftmost and rightmost sides of equation (2a), 1 <T4 / Tn≦1.485 …(2b) is obtained.

[0096] Then, by multiplying each side of equation (2b) by T6, T6<(T4 / Tn)×T6≦1.485×T6 …(2c) is obtained.

[0097] When the layer of interest is the fourth layer, Tn=T6, so from equation (2c), T6 <T4≦1.485×T6 …(2d) Therefore, when N≧6, for example, excellent frequency characteristics can also be achieved by selecting T4 as a parameter for the constant value T6 so as to satisfy equation (2d).

[0098] Next, we will discuss the case where the layer of interest is the third layer, i.e., the case where we focus on T3. When the layer of interest is the third layer, a more general formula can be obtained by normalizing the above formula (3) by Tn, which corresponds to T3. As an example, when the layer of interest is the third layer, it is possible to use the thickness of one low acoustic impedance layer 5a among the multiple low acoustic impedance layers 5a as Tn.

[0099] As described above, when N≧6, for example, T1, which is the thickness of the first layer 2-1, is maintained at a constant value. Therefore, in the fifth study, when the layer of interest is the third layer, Tn is defined as Tn=T1=0.2 μm.

[0100] First, by dividing each side of equation (3) by Tn, 0.2 / Tn <T3 / Tn≦0.59 / Tn …(3a) T3 / Tn may be referred to as the normalized thickness of T3.

[0101] When the layer of interest is the third layer, Tn=0.2 μm, and by calculating the specific values ​​of the leftmost and rightmost sides of equation (3a), 1 <T3 / Tn≦2.950 …(3b) is obtained.

[0102] Then, by multiplying each side of equation (2b) by T1, T1<(T3 / Tn)×T1≦2.950×T1 …(2c) is obtained.

[0103] When the layer of interest is the third layer, Tn=T1, so from equation (3c), T1 <T3≦2.950×T1 …(3d) Therefore, when N≧6, for example, excellent frequency characteristics can also be achieved by selecting T3 as a parameter for the constant value T1 so as to satisfy equation (3d).

[0104] As can be understood from the above explanations, when N≧6, for example, when at least one of the above-mentioned formulas (1d), (2d), and (3d) is satisfied, excellent frequency characteristics are realized.

[0105] (Sixth Consideration) As mentioned above, the fifth study described the case where N≧6. However, depending on the design specifications of the acoustic wave device 1, N smaller than 6 may be adopted. Therefore, in the sixth study, the inventors investigated the respective numerical ranges of T2, T4, and T3 when 4≦N≦5. In this specification, the case where 4≦N≦5 is also referred to as the "case where there are four or more layers and five or less layers."

[0106] FIG. 17 shows a schematic diagram of the results obtained in the sixth study. When 4≦N≦5, unlike the case of N≧6 described above, there is not necessarily a high acoustic impedance layer 5b whose thickness is maintained at a constant value. Therefore, in the sixth study, Tn is set as Tn=T1=0.2 μm in all of the following cases: (i) when the layer of interest is the second layer, (ii) when the layer of interest is the fourth layer, and (iii) when the layer of interest is the third layer. This is because T1, the thickness of the first layer 2-1, is maintained at a constant value even when 4≦N≦5.

[0107] First, we will discuss the case where the layer of interest is the second layer. In the sixth study, Tn=0.2 μm, so by calculating the specific values ​​of the leftmost and rightmost sides of the above formula (1a), 0.825 <T2 / Tn≦2.28 …(1e) is obtained.

[0108] Then, by multiplying each side of equation (1e) by T1, 0·825×T1<(T2 / Tn)×T1≦2.28×T1 …(1f) is obtained.

[0109] In the sixth study, Tn=T1, so from equation (1f), 0.825×T1 <T2≦2.28×T1 …(1g) is obtained.

[0110] Therefore, when 4≦N≦5, for example, excellent frequency characteristics can be achieved by selecting T2 as a parameter for the constant value T1 so as to satisfy formula (1g). As described above, the range of T2 that is expected to be beneficial for improving frequency characteristics can differ depending on N.

[0111] Next, we will discuss the case where the layer of interest is the fourth layer. In the sixth study, Tn=0.2 μm, so by calculating the specific values ​​of the leftmost and rightmost sides of the above equation (2a), 0.825 <T4 / Tn≦1.225 …(2e) is obtained.

[0112] Then, by multiplying each side of equation (2e) by T1, 0.825×T1<(T4 / Tn)×T1≦1.225×T1 …(2f) is obtained.

[0113] In the sixth study, Tn=T1, so from equation (2f), 0.825×T1 <T4≦1.225×T1 …(2g) is obtained.

[0114] Therefore, when 4≦N≦5, for example, excellent frequency characteristics can be achieved by selecting T4 as a parameter for the constant value T1 so as to satisfy formula (2g). As described above, the range of T4 that is expected to be beneficial for improving frequency characteristics may also differ depending on N.

[0115] Next, we will discuss the case where the layer of interest is the third layer. When the layer of interest is the third layer, Tn = 0.2 μm in the sixth study, as in the fifth study. Therefore, in the sixth study, as in the fifth study, the above formula (3d) is obtained.

[0116] Therefore, even when 4≦N≦5, excellent frequency characteristics can be achieved by selecting T3 as a parameter for a constant value of T1 so as to satisfy, for example, equation (3d). From the above, unlike the examples of T2 and T4, the range of T3 that is expected to be beneficial for improving frequency characteristics is thought to be independent of N.

[0117] As can be understood from the above explanations, when 4≦N≦5, for example, when at least one of the above-mentioned formulas (1g), (2g), and (3d) is satisfied, excellent frequency characteristics are realized.

[0118] (effect) As described above, in the elastic wave device 1, the frequency characteristics can be improved by appropriately setting at least one of T2, T3, and T4. For example, spurious emissions in a specific frequency band (e.g., 4000 MHz frequency band) can be reduced.

[0119] For example, by appropriately setting T3, the frequency characteristics can be improved. As described in the fifth and sixth studies, the above formula (3d) is applicable to both (i) the case where N≧6 and (ii) the case where 4≦N≦5.

[0120] Therefore, for example, the condition on the left side of equation (3d), i.e., T1 <T3 …(3d-1) The frequency characteristics can be improved by designing the acoustic wave device 1 so that N satisfies the following equation (3d-1): As can be seen from equation (3d-1), in the acoustic wave device 1, it is sufficient that N≧3.

[0121] By designing acoustic wave device 1 so that the above formula (3d) is satisfied, the frequency characteristics can be further improved when N≧3.

[0122] When N≧6, it is possible to improve the frequency characteristics by appropriately setting at least one of T2 and T4. When N≧6, for example, the frequency characteristics can be improved by designing acoustic wave device 1 so that at least one of the conditions on the left side of Equation (1d) and the conditions on the left side of Equation (2d) is satisfied.

[0123] That is, when N≧6, T6 <T2 …(1d-1) and, T6 <T4 …(2d-1) By designing the acoustic wave device 1 so that at least one of the above is satisfied, the frequency characteristics can be improved.

[0124] Furthermore, by designing acoustic wave device 1 so that at least one of formula (1d) and formula (2d) is satisfied, the frequency characteristics can be further improved when N≧6.

[0125] Even when 4≦N≦5, the frequency characteristics can be improved by appropriately setting at least one of T2 and T4. When 4≦N≦5, the frequency characteristics can be improved by designing acoustic wave device 1 so that at least one of the conditions on the left side of equation (1g) and the left side of equation (2g) is satisfied.

[0126] That is, when 4≦N≦5, 0.825×T1 <T2 …(1g-1) and, 0.825×T1 <T4 …(2g-1) By designing the acoustic wave device 1 so that at least one of the above is satisfied, the frequency characteristics can be improved.

[0127] By designing acoustic wave device 1 so that at least one of formula (1g) and formula (2g) is satisfied, the frequency characteristics can be further improved when 4≦N≦5.

[0128] [Embodiment 2] In the first embodiment, the IDT electrode 3 is configured to excite a plate wave. However, the IDT electrode 3 may be configured to excite a wave other than a plate wave. For example, the IDT electrode 3 may be configured to excite a bulk wave.

[0129] 〔summary〕 An elastic wave device according to a first aspect of the present disclosure includes a piezoelectric body, an IDT electrode located near the piezoelectric body, and an acoustic reflection film located below the piezoelectric body. The acoustic reflection film has a laminated structure of low acoustic impedance layers and high acoustic impedance layers. The acoustic reflection film includes: a first layer that is the low acoustic impedance layer located closest to the piezoelectric body among all the low acoustic impedance layers and high acoustic impedance layers; a second layer that is the high acoustic impedance layer in contact with a lower surface of the first layer; and a third layer that is the low acoustic impedance layer in contact with a lower surface of the second layer. When the thickness of the first layer is denoted as T1 and the thickness of the third layer is denoted as T3, <T3である。

[0130] An elastic wave device according to a second aspect of the present disclosure is the same as in the first aspect, except that: T1 <T3≦2.950×T1 It may be.

[0131] An elastic wave device according to a third aspect of the present disclosure includes a piezoelectric body, an IDT electrode located near the piezoelectric body, and an acoustic reflection film located below the piezoelectric body. The acoustic reflection film has a laminated structure of low acoustic impedance layers and high acoustic impedance layers. The acoustic reflection film includes: a first layer which is the low acoustic impedance layer located closest to the piezoelectric body among all the low acoustic impedance layers and high acoustic impedance layers; a second layer which is the high acoustic impedance layer in contact with a lower surface of the first layer; a third layer which is the low acoustic impedance layer in contact with a lower surface of the second layer; a fourth layer which is the high acoustic impedance layer in contact with a lower surface of the third layer; a fifth layer which is the low acoustic impedance layer in contact with a lower surface of the fourth layer; and a sixth layer which is the high acoustic impedance layer in contact with a lower surface of the fifth layer. When the thickness of the second layer is denoted as T2, the thickness of the fourth layer is denoted as T4, and the thickness of the sixth layer is denoted as T6, T6 <T2 and, T6 <T4 At least one of the following is satisfied.

[0132] An elastic wave device according to a fourth aspect of the present disclosure is the same as in the third aspect, except that: T6 <T2≦2.764×T6 and, T6 <T4≦1.485×T4 At least one of the following may be satisfied.

[0133] An elastic wave device according to a fifth aspect of the present disclosure includes a piezoelectric body, an IDT electrode located near the piezoelectric body, and an acoustic reflection film located below the piezoelectric body. The acoustic reflection film has a laminated structure of low acoustic impedance layers and high acoustic impedance layers. The sum of the number of the low acoustic impedance layers and the number of the high acoustic impedance layers in the acoustic reflection film is 4 or more and 5 or less. The acoustic reflection film includes: a first layer, which is the low acoustic impedance layer that is located closest to the piezoelectric body among all the low acoustic impedance layers and high acoustic impedance layers; a second layer, which is the high acoustic impedance layer, in contact with a lower surface of the first layer; a third layer, which is the low acoustic impedance layer, in contact with a lower surface of the second layer; and a fourth layer, which is the high acoustic impedance layer, in contact with a lower surface of the third layer. When the thickness of the first layer is denoted as T1, the thickness of the second layer is denoted as T2, and the thickness of the fourth layer is denoted as T4, 0.825×T1 <T2 and, 0.825×T1 <T4 At least one of the following is satisfied.

[0134] An elastic wave device according to a sixth aspect of the present disclosure is the same as in the fifth aspect, except that: 0.825×T1 <T2≦2.28×T1 and, 0.825×T1 <T4≦1.225×T1 At least one of the following may be satisfied.

[0135] In an elastic wave device according to aspect 7 of the present disclosure, in any one of aspects 1 to 6, the main component of the low acoustic impedance layer may be SiO2, and the main component of the high acoustic impedance layer may be at least one of HfO2, Ta2O5, ZrO2, SiN, AlN, Al2O3, W, Pt, Ta, and Hf.

[0136] An elastic wave device according to an eighth aspect of the present disclosure is any one of the first to seventh aspects, wherein the low acoustic impedance layer may be primarily composed of SiO2, and the high acoustic impedance layer may be primarily composed of HfO2.

[0137] In an acoustic wave device according to a ninth aspect of the present disclosure, in any one of the first to eighth aspects, the IDT electrode may be configured to excite a plate wave.

[0138] In an elastic wave device according to a tenth aspect of the present disclosure, in the ninth aspect, the plate wave may be an A1 Lamb wave.

[0139] In an acoustic wave device according to an eleventh aspect of the present disclosure, in any one of the first to eighth aspects, the IDT electrode may be configured to excite bulk waves.

[0140] In an acoustic wave device according to a twelfth aspect of the present disclosure, in any one of the first to eleventh aspects, the material of the piezoelectric body may be LT or LN.

[0141] [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]

[0142] 1. Elastic wave device 3 IDT electrode 4 Piezoelectric 5 Acoustic reflective film 5a Low acoustic impedance layer 5b High acoustic impedance layer 5-1 1st layer 5-2 Second layer 5-3 3rd layer 5-4 4th layer 5-5 5th layer 5-6 6th layer

Claims

1. A piezoelectric body; an IDT electrode located near the piezoelectric body; an acoustic reflection film located below the piezoelectric body, the acoustic reflection film has a laminated structure of a low acoustic impedance layer and a high acoustic impedance layer, The acoustic reflection film is a first layer, which is the low acoustic impedance layer located closest to the piezoelectric body among all the low acoustic impedance layers and the high acoustic impedance layers; a second layer, which is the high acoustic impedance layer, in contact with the lower surface of the first layer; a third layer that is the low acoustic impedance layer and is in contact with the lower surface of the second layer, The thickness of the first layer is denoted as T1, When the thickness of the third layer is denoted as T3, T1<T3 This is an elastic wave device.

2. T1<T3≦2.950×T1 The acoustic wave device according to claim 1 , wherein

3. A piezoelectric body; an IDT electrode located near the piezoelectric body; an acoustic reflection film located below the piezoelectric body, the acoustic reflection film has a laminated structure of a low acoustic impedance layer and a high acoustic impedance layer, The acoustic reflection film is a first layer, which is the low acoustic impedance layer located closest to the piezoelectric body among all the low acoustic impedance layers and the high acoustic impedance layers; a second layer, which is the high acoustic impedance layer, in contact with the lower surface of the first layer; a third layer, which is the low acoustic impedance layer, in contact with the lower surface of the second layer; a fourth layer, which is the high acoustic impedance layer, in contact with the lower surface of the third layer; a fifth layer, which is the low acoustic impedance layer, in contact with the lower surface of the fourth layer; a sixth layer that is the high acoustic impedance layer and is in contact with a lower surface of the fifth layer, The thickness of the second layer is denoted as T2, The thickness of the fourth layer is denoted as T4, When the thickness of the sixth layer is denoted as T6, T6<T2 and, T6<T4 At least one of the above is satisfied.

4. T6<T2≦2.764×T6 and, T6<T4≦1.485×T4 The acoustic wave device according to claim 3 , wherein at least one of the following is satisfied:

5. A piezoelectric body; an IDT electrode located near the piezoelectric body; an acoustic reflection film located below the piezoelectric body, the acoustic reflection film has a laminated structure of a low acoustic impedance layer and a high acoustic impedance layer, the sum of the number of the low acoustic impedance layers and the number of the high acoustic impedance layers in the acoustic reflection film is 4 or more and 5 or less, The acoustic reflection film is a first layer, which is the low acoustic impedance layer located closest to the piezoelectric body among all the low acoustic impedance layers and the high acoustic impedance layers; a second layer, which is the high acoustic impedance layer, in contact with the lower surface of the first layer; a third layer, which is the low acoustic impedance layer, in contact with the lower surface of the second layer; a fourth layer that is the high acoustic impedance layer and is in contact with the lower surface of the third layer, The thickness of the first layer is denoted as T1, The thickness of the second layer is denoted as T2, When the thickness of the fourth layer is denoted as T4, 0.825×T1<T2 and, 0.825×T1<T4 At least one of the above is satisfied.

6. 0.825 × T1 < T2 ≦ 2.28 × T1 and, 0.825×T1<T4≦1.225×T1 The acoustic wave device according to claim 5 , wherein at least one of the following is satisfied:

7. The main component of the low acoustic impedance layer is SiO ２ and The main component of the high acoustic impedance layer is HfO ２ , Ta ２ O ５ , ZrO ２ , SiN, AlN, Al ２ O ３ , W, Pt, Ta, and Hf.

8. The main component of the low acoustic impedance layer is SiO ２ and The main component of the high acoustic impedance layer is HfO ２ The acoustic wave device according to claim 1 , wherein

9. The acoustic wave device according to claim 1 , wherein the IDT electrode is configured to excite a plate wave.

10. The acoustic wave device according to claim 9 , wherein the plate wave is an A1 Lamb wave.

11. The acoustic wave device according to claim 1 , wherein the IDT electrode is configured to excite a bulk wave.

12. The acoustic wave device according to claim 1 , wherein the piezoelectric material is LT or LN.

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