WO2024128164A1 - Acoustic wave device, filter, and communication device - Google Patents

Abstract

The present invention improves the frequency characteristics of an acoustic wave device. An acoustic wave device according to the present invention includes a piezoelectric layer and an IDT electrode which is located on the piezoelectric layer and which has a plurality of electrode fingers. When the pitch of the electrode fingers is represented by p, the thickness of the piezoelectric layer is no more than 2p. The acoustic wave device also includes a dielectric layer located between the piezoelectric layer and the IDT electrode in a first region which includes the tips of the electrode fingers and which does not include the center of a region where the electrode fingers intersect. The acoustic wave device is configured so as to excite waves in A1 mode.

Description

Acoustic wave device, filter, and communication device

One aspect of the present disclosure relates to an elastic wave device.

The following Patent Document 1 discloses an example of the configuration of an elastic wave device.

International Publication No. 2020/045442

An elastic wave device according to one aspect of the present disclosure includes a piezoelectric layer and an IDT electrode located on the piezoelectric layer and having a plurality of electrode fingers, where the thickness of the piezoelectric layer is 2p or less when the pitch of the electrode fingers is represented as p, the elastic wave device further includes a dielectric layer located between the piezoelectric layer and the IDT electrode in a first region that includes the tips of the electrode fingers and does not include the center of the intersection region of the electrode fingers, and the elastic wave device is configured to excite a wave in the A1 mode.

1 shows a schematic top view of an elastic wave device according to a first embodiment. 1 illustrates a schematic diagram of a layered structure of an elastic wave device according to a first preferred embodiment of the present invention. The configurations of MODEL-REF to MODEL2 are shown diagrammatically. Examples of impedance characteristics of MODEL-REF to MODEL-2 are shown below. An example of the phase characteristics of MODEL-REF to MODEL-2 is shown. FIG. 6 is an enlarged view of a region GM1 in FIG. 5 . FIG. 6 is an enlarged view of a region GM2 in FIG. 5 . Another example of the phase characteristics of MODEL-REF to MODEL-2 is shown. Examples of BodeQ for MODEL-REF to MODEL2 are shown below. Examples of FOM1 to FOM3 and FOMt in MODEL-REF to MODEL2 are shown below. An example of the relationship between t, dov, and FOM2 when a dummy is used is shown below. An example of the relationship between t, dov, and FOM2 when no dummy is used is shown below. An example of frequency characteristics in the case of "piezoelectric layer: LT, dielectric layer: absent" is shown. An example of frequency characteristics in the case of "piezoelectric layer: LN, dielectric layer: none" is shown. The sound velocity of each dielectric layer material is shown. An example of the relationship between VL and FOM2 in the "piezoelectric layer: LT" is shown. An example of the relationship between VL and FOM2 in "piezoelectric layer: LN" is shown. An example of the phase characteristics of MODEL-REF and MODEL3 is shown. Examples of FOM1 to FOM3 and FOMt in MODEL-REF and MODEL3 are shown below. The configuration of MODEL4 is shown diagrammatically. An example of the phase characteristics of MODEL-REF and MODEL4 is shown. An example of the relationship between t and dfr in the "piezoelectric layer: LT" is shown below. An example of the relationship between t and dfr in "piezoelectric layer: LN" is shown. An example of the relationship between dfr and FOMt in the "piezoelectric layer: LT" is shown. An example of the relationship between εr and dfr in the “piezoelectric layer: LT” is shown. Numerical examples of the coefficients corresponding to the curves in FIG. 25 are shown below. An example of the relationship between dfr and FOMt in the case of "piezoelectric layer: LN" is shown. An example of the relationship between εr and dfr in the case where the piezoelectric layer is LN is shown. Numerical examples of the coefficients corresponding to the curves in FIG. 28 are shown below. An example of dfr calculated using actual physical property values of each dielectric layer material is shown below. An example of FOMt calculated using actual physical property values of each dielectric layer material is shown below. 5A and 5B are schematic diagrams illustrating a layered structure of an elastic wave device according to a second embodiment of the present invention. 13 shows an example of frequency characteristics in the case of "piezoelectric layer: LT, dielectric layer: absent" of the second embodiment. 13 shows an example of frequency characteristics in the second embodiment where the piezoelectric layer is LN and the dielectric layer is absent. 13 shows an example of the relationship between VL and FOM2 in the “piezoelectric layer: LT” of the second embodiment. 13 shows an example of the relationship between VL and FOM2 in the "piezoelectric layer: LN" of the second embodiment. 13 shows an example of the relationship between dfr and FOMt in the “piezoelectric layer: LT” of the second embodiment. 13 shows an example of the relationship between εr and dfr in the “piezoelectric layer: LT” of the second embodiment. Numerical examples of the coefficients corresponding to the curves in FIG. 38 are shown below. 13 shows an example of the relationship between dfr and FOMt in the "piezoelectric layer: LN" of the second embodiment. 13 shows an example of the relationship between εr and dfr in the “piezoelectric layer: LN” of the second embodiment. Numerical examples of the coefficients corresponding to the curves in FIG. 41 are shown below. In the second embodiment, an example of dfr calculated using actual physical property values of each dielectric layer material is shown. 13 shows an example of the relationship between dfr and FOMt in the third embodiment. 13 shows an example of a phase characteristic in the third embodiment. 13 shows an example of the relationship between dfr and FOMt in the fourth embodiment. 13 shows an example of a phase characteristic in the fourth embodiment. 13 illustrates a schematic configuration of a filter according to a fifth embodiment. 13 illustrates a schematic configuration of a communication device according to a sixth embodiment.

[Embodiment 1]
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 given the same reference numerals in the following embodiments, and the explanations will not be repeated. For the sake of brevity, the explanations of known technical matters will be omitted as appropriate. Each component, each material, and each numerical value described in this specification are merely exemplary unless otherwise inconsistent. Therefore, for example, unless otherwise inconsistent, the positional relationship and connection relationship of each component are not limited to the examples in each figure. In addition, each figure is not necessarily drawn to scale. In this specification, unless otherwise inconsistent, the notation "A to B" for two numbers A and B means "greater than or equal to A and less than or equal to B".

(One Configuration Example of Elastic Wave Device 1)
1 and 2 show an example configuration of an elastic wave device 1 according to embodiment 1. Fig. 1 shows a schematic top view of the elastic wave device 1, and Fig. 2 shows a schematic view of a layered structure of the elastic wave device 1. For convenience of explanation, the present specification introduces an orthogonal coordinate system (D1-D2-D3 coordinate system) shown in Figs. 1 and 2 .

In the example of embodiment 1, the D1 direction is the propagation direction of an elastic wave propagating within the piezoelectric layer 2 of the elastic wave device 1. As shown in FIG. 1, the multiple electrode fingers 32 of the elastic wave device 1 may be arranged in the D1 direction. The D2 direction is an example of a direction intersecting the D1 direction. The electrode fingers 32 may extend in the D2 direction. FIG. 2 is an example of a cross-sectional view obtained when the elastic wave device 1 of FIG. 1 is cut along a cut surface that overlaps with the dummy electrode finger 35 and is parallel to the D2 direction. The D3 direction is the thickness direction of each part of the elastic 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.

FIG. 1 shows a portion of the elastic wave device 1. Specifically, FIG. 1 shows half of the elastic wave device 1 in the D2 direction (e.g., the right half). Therefore, although not explicitly shown in FIG. 1, the elastic wave device 1 also has the remaining half in the D2 direction (e.g., the left half). This also applies to the other figures corresponding to FIG. 1.

2, the elastic wave device 1 may have a support substrate 6 that supports each part of the elastic wave device 1. As an example, the support substrate 6 may be a Si substrate. The elastic wave device 1 may have a piezoelectric layer 2 above the support substrate 6. The elastic wave device 1 may have an IDT (Inter-Digital Transducer) electrode 3 on the piezoelectric layer 2. The IDT electrode 3 is also called an excitation electrode. In FIGS. 1 and 2, even in the D1 direction, only a portion of the elastic wave device 1 is shown. For example, several hundred IDT electrodes 3 may be arranged in the D1 direction. In addition, a reflector consisting of another shorted IDT electrode may be arranged outside the IDT electrode 3.

The piezoelectric layer 2 may be made of a single crystal material having piezoelectricity. An example of the material (piezoelectric layer material) of the piezoelectric layer 2 is lithium tantalate (also referred to as LiTaO ₃ :LT). The piezoelectric layer according to one embodiment of the present disclosure is an LT layer, which is also referred to as "piezoelectric layer:LT". Thus, in this specification, the LT layer is also abbreviated as LT. The cut angle of the LT may be set appropriately. For example, the piezoelectric layer 2 may be a 115°±30° Y-cut X-propagation LT. In other words, the piezoelectric layer 2 may be an 85° to 145° Y-cut X-propagation LT.

The X-axis and Y-axis are the crystal orientation axes of the piezoelectric layer 2. For example, "85° Y-cut X-propagation LT" means "LT cut by a plane whose normal line is an axis rotated 85° from the Y-axis around the X-axis, 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 direction of the X-axis 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.

Another example of the piezoelectric layer material may be lithium niobate (also referred to as LiNbO ₃ :LN). In this specification, when the piezoelectric layer according to one embodiment of the present disclosure is an LN layer, it is also written as "piezoelectric layer: LN". Thus, in this specification, the LN layer is also abbreviated as LN. The cut angle of the LN may be set appropriately. For example, the piezoelectric layer 2 may be 120°±30° Y-cut X-propagation LN. In other words, the piezoelectric layer 2 may be 90°-150° Y-cut X-propagation LT.

The elastic wave device 1 may have a dielectric layer 4 between the piezoelectric layer 2 and the IDT electrode 3. As will be understood from the following descriptions, the dielectric layer 4 is an additional component that contributes to improving the frequency characteristics of the elastic wave device 1. For this reason, the dielectric layer 4 is also called an additional film. Examples of the material (dielectric layer material) of the dielectric layer 4 include SiO ₂ (silicon oxide), HfO ₂ (hafnium oxide), AlN (aluminum nitride), Al ₂ O ₃ (aluminum oxide), Ta ₂ O ₅ (tantalum nitride), SiN _x (silicon nitride), Si (silicon), ZrO ₂ (zirconium oxide), TiO ₂ (titanium oxide), and diamond. The dielectric layer material may be a combination of the above-mentioned materials. The dielectric layer 4 will be described in detail later. As will be described later, the dielectric layer 4 can contribute to improving the frequency characteristics of the elastic wave device 1.

Referring again to FIG. 1, the IDT electrode 3 may have a busbar 30. In the acoustic wave device 1, a pair of busbars 30 may face each other in the D2 direction. One of the pair of busbars 30 is shown in FIG. 1. The busbar 30 shown in FIG. 1 is also referred to as the first busbar 30a. The other busbar not shown in FIG. 1 is also referred to as the second busbar 30b.

The IDT electrode 3 may have a plurality of electrode fingers 32. The electrode fingers 32 may extend from the busbar 30. In FIG. 1, a first electrode finger 32a and a second electrode finger 32b are shown as the electrode fingers 32. The first electrode finger 32a may extend from the first busbar 30a toward the second busbar 30b. The second electrode finger 32b may extend from the second busbar 30b toward the first busbar 30a. Thus, the acoustic wave device 1 may have an intersection region RK where the first electrode finger 32a and the second electrode finger 32b intersect with each other.

The multiple electrode fingers 32 may be alternately positioned on the piezoelectric layer 2 with a generally constant spacing in the D1 direction. In this specification, the pitch of the electrode fingers 32 is represented as p. p may be, for example, the pitch (repetition interval) in the D2 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 elastic wave excited by the IDT electrode 3. In this case, λ may be defined as twice the length of p. Thus, in embodiment 1, a case where λ=2p is illustrated as an example. In this specification, other dimensions may also be expressed with p as the reference.

Furthermore, 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 elastic 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 the duty of electrode finger 32. By changing the duty, the frequency characteristics of elastic wave device 1 can be controlled.

The IDT electrode 3 may have a plurality of dummy electrode fingers 35. The dummy electrode fingers 35 allow for more precise control of the frequency characteristics of the acoustic wave device 1. The dummy electrode fingers 35 may extend from the busbar 30. FIG. 1 shows dummy electrode fingers 35 extending from the first busbar 30a. The dummy electrode fingers 35 shown in FIG. 1 are also referred to as first dummy electrode fingers 35a. The dummy electrode fingers 35 not shown in FIG. 1 (dummy electrode fingers 35 extending from the second busbar 30b) are also referred to as second dummy electrode fingers 35b.

The pitch of the dummy electrode fingers 35 may be set to a value equal to the pitch of the electrode fingers 32. Therefore, the dummy electrode fingers 35 may face the electrode fingers 32. For example, as shown in FIG. 1, the first dummy electrode finger 35a may face the tips of each of the multiple second electrode fingers 32b across a gap. Also, although not shown in FIG. 1, the second dummy electrode finger 35b may face the tips of each of the multiple first electrode fingers 32a across a gap.

As shown in FIG. 1, the acoustic wave device 1 may have a first region R1 that includes the tips of the electrode fingers 32 but does not include the center of the intersection region RK. As shown in FIG. 2, the dielectric layer 4 may be located between the piezoelectric layer 2 and the IDT electrode 3 in the first region R1.

As shown in FIG. 1, the first region R1 may extend along the direction D1 (the arrangement direction of the electrode fingers 32). The first region R1 may be located at both ends of the intersection region RK.

As shown in FIG. 1, at least a portion of the first region R1 may be located between the tip of the electrode finger 32 and the bus bar 30. The dimension dov shown in FIG. 1 represents the length of overlap between the electrode finger 32 and the first region R1 in the direction D2. dov may also be referred to as the first overlap length.

Also, as shown in FIG. 1, the first region R1 may include the tip of the dummy electrode finger 35. The dimension ddm shown in FIG. 1 represents the length of overlap between the dummy electrode finger 35 and the first region R1 in the direction D2. ddm may also be referred to as the second overlap length. In the example of FIG. 1, ddm is equal to the length of the dummy electrode finger 35.

The dimension ta shown in FIG. 2 represents the thickness of the piezoelectric layer 2. The dimension t represents the thickness of the dielectric layer 4 in the example of FIG. 2. In the first embodiment, a case where ta is sufficiently small (where the piezoelectric layer 2 is sufficiently thin) is illustrated.

As an example, ta in embodiment 1 may be equal to or less than λ (i.e., equal to or less than 2p). In this case, the IDT electrode 3 may excite a plate wave (Lamb wave) as an elastic wave. For example, the IDT electrode 3 may excite an A1 mode wave as a plate wave. Thus, embodiment 1 illustrates a case in which a plate wave (e.g., an A1 mode Lamb wave) propagates within the piezoelectric layer 2. In this manner, the elastic wave device 1 may be configured to excite an A1 mode wave.

As shown in FIG. 2, the acoustic wave device 1 may further include a multilayer reflective film 5 in which (i) low acoustic impedance layers 5a having an acoustic impedance lower than that of the piezoelectric layer 2 and (ii) high acoustic impedance layers 5b having an acoustic impedance higher than that of the low acoustic impedance layers 5a are alternately stacked. The multilayer reflective film 5 may be located between the piezoelectric layer 2 and the support substrate 6.

As shown in Fig. 2, the multilayer reflective film 5 may be a laminate unit formed by laminating one low acoustic impedance layer 5a and one high acoustic impedance layer 5b. In the example of Fig. 2, the acoustic wave device 1 includes four laminate units. An example of the material of the low acoustic impedance layer 5a is _SiO2 . An example of the material of the high acoustic impedance layer 5b is a dielectric material such as _HfO2 and _Ta2O5 . Another example of the material of the high acoustic impedance layer _5b is a metal material such as Mo and W.

(Simulation model)
The present inventor (hereinafter, abbreviated as the inventor) constructed simulation models MODEL-REF, MODEL 1, and MODEL 2 in order to study the frequency characteristics of elastic wave device 1. Fig. 3 shows schematic configurations of MODEL-REF to MODEL 2.

As shown in FIG. 3, MODEL-REF does not have a dielectric layer 4. Therefore, in MODEL-REF, t=0. MODEL-REF is a simulation model (reference simulation model) that serves as a baseline for evaluating the performance of the elastic wave device 1. In this specification, for example, an elastic wave device that does not have a dielectric layer according to one aspect of the present disclosure is also expressed as "dielectric layer: no." MODEL-REF is an example of "dielectric layer: no."

As shown in FIG. 3, MODEL 1 corresponds to the elastic wave device 1 in the example of FIG. 1. Therefore, MODEL 1 has a dielectric layer 4 and has dummy electrode fingers 35. In this specification, for example, the fact that the elastic wave device has dummy electrode fingers according to one embodiment of the present disclosure is also expressed as "dummy present." Thus, in this specification, dummy electrode fingers are also abbreviated as dummy. MODEL 1 is an example of "dielectric layer: present, dummy present." Unlike MODEL 1, MODEL 2 does not have dummy electrode fingers 35. Therefore, in MODEL 2, ddm = 0. MODEL 2 is an example of "dielectric layer: present, dummy not present."

The inventor derived the frequency characteristics of MODEL-REF to MODEL-2 by simulation using FEM (Finite Element Method). The inventor set the simulation conditions as follows:
Piezoelectric layer: 125° Y-cut X-propagation LT (ta=0.41p)
Low acoustic impedance layer: _SiO2 (thickness: 0.15p)
High acoustic impedance layer: _HfO2 (thickness: 0.19p)
Number of layers in multilayer reflective film: 8
IDT electrode: Al (thickness: 0.13p)
p = 1 μm
The inventor then set the following:
Dielectric layer in MODEL 1: AlN (t=0.03p, dov=p)
Dielectric layer in MODEL 2: AlN (t=0.05p, dov=p)
The inventor also set ddm in MODEL1 to 4p.

Figure 4 shows examples of impedance characteristics of MODEL-REF to MODEL-2 derived by simulation. The horizontal axis of the graph in Figure 4 shows frequency (unit: MHz), and the vertical axis shows the absolute value (magnitude) of impedance (unit: Ohm).

Figure 5 shows an example of the phase characteristics of MODEL-REF to MODEL-2 derived by simulation. The horizontal axis of the graph in Figure 5 indicates frequency, and the vertical axis indicates the phase of impedance (unit: degree). In Figure 5, degree (angle) is abbreviated as deg. In the following explanation, the phase of impedance is simply abbreviated as phase.

The resonant frequency of an elastic wave device is the frequency at which the absolute value of the impedance of the elastic wave device is at a minimum. The resonant frequency is also the frequency at which the phase is 0° in a frequency band where the phase increases monotonically. The anti-resonant frequency of an elastic wave device is the frequency at which the absolute value of the impedance of the elastic wave device is at a maximum. The anti-resonant frequency is also the frequency at which the phase is 0° in a frequency band where the phase decreases monotonically.

The band of an elastic wave device is defined by the resonant frequency and anti-resonant frequency of the elastic wave device. As can be seen from FIG. 4, in the elastic wave devices according to each simulation model, the resonant frequency is approximately 5450 MHz and the anti-resonant frequency is approximately 5650 MHz. In this specification, the frequency band lower than the resonant frequency is also referred to as the first frequency band, the band is also referred to as the second frequency band, and the frequency band higher than the anti-resonant frequency is also referred to as the third frequency band.

FIG. 6 is an enlarged view of region GM1 in FIG. 5. In the graph of FIG. 6, the phase region near 90° in some frequency bands in the graph of FIG. 5 is enlarged. The frequency bands in the graph of FIG. 6 roughly coincide with the second frequency band. The maximum value of phase (hereinafter referred to as MaxPhase) is one of the indicators that show the performance of an elastic wave device. The ideal maximum value of MaxPhase is 90°. The higher MaxPhase is (i.e., the closer MaxPhase is to 90°), the smaller the energy loss (hereinafter abbreviated as loss) in the elastic wave device.

As shown in FIG. 6, MODEL 1 and MODEL 2 have reduced loss in the second frequency band compared to MODEL-REF. This confirms that the dielectric layer 4 can contribute to reducing loss in the second frequency band. Furthermore, MODEL 1 and MODEL 2 have reduced ripple in the second frequency band compared to MODEL-REF. This confirms that the dielectric layer 4 can also contribute to reducing ripple in the second frequency band. In this way, the dielectric layer 4 can reduce transverse mode spurious (transverse mode ripple) that occurs in the second frequency band. As described above, the dielectric layer 4 can contribute to reducing loss and ripple in the second frequency band.

FIG. 7 is an enlarged view of region GM2 in FIG. 5. In the graph of FIG. 7, the phase region around -90° in some frequency bands in the graph of FIG. 5 is enlarged. The frequency bands in the graph of FIG. 7 include the first frequency band to the third frequency band. As shown in FIG. 7, in the third frequency band, the phases of MODEL1 and MODEL2 are closer to -90° than the phase of MODEL-REF. This indicates that the loss in the third frequency band is reduced in MODEL1 and MODEL2 compared to MODEL-REF. In this way, the dielectric layer 4 can also contribute to reducing the loss in the third frequency band.

On the other hand, in the first frequency band, the phases of MODEL 1 and MODEL 2 are slightly larger than the phase of MODEL-REF. This suggests that depending on the design conditions of the dielectric layer 4, the dielectric layer 4 may lead to an increase in loss in the first frequency band. Based on this result, the inventor conducted a more detailed study of the frequency characteristics of MODEL-REF to MODEL 2. Specifically, the inventor conducted a quantitative study based on the FOM (Figure of Merit).

(FOM-based review)
FIG. 8 shows another example of the phase characteristics of MODEL-REF to MODEL-2. In the example of FIG. 8, the material of the dielectric layer 4 in MODEL-1 and MODEL-2 is different from that in the example of FIG. 5. The inventor derived the BodeQ of each of MODEL-REF to MODEL-2 based on the phase characteristics of FIG. 8. FIG. 9 shows an example of the BodeQ of MODEL-REF to MODEL-2. The vertical axis in the graph of FIG. 9 is BodeQ. BodeQ is one index that indicates the loss characteristics of an elastic wave device. It can be said that the larger the BodeQ, the better the loss characteristics of the elastic wave device.

The inventor then derived the average value of BodeQ in each of the regions DD1 to DD3 in FIG. 9 for each of MODEL-REF to MODEL2. Regions DD1 to DD3 in FIG. 9 correspond to the first to third frequency bands, respectively. In this specification, the average value of BodeQ in region DD1 is referred to as BodeQ1, the average value of BodeQ in region DD2 is referred to as BodeQ2, and the average value of BodeQ in region DD3 is referred to as BodeQ3.

Next, the inventor set BodeQ1 to BodeQ3 in MODEL-REF as reference values and derived the FOM for each of the regions DD1 to DD3. Generally, the larger the FOM, the better the loss and ripple characteristics. Specifically, the inventor standardized BodeQ1 in each simulation model by BodeQ1 in MODEL-REF to derive the FOM for region DD1 (hereinafter referred to as FOM1). Then, the inventor standardized BodeQ2 in each simulation model by BodeQ2 in MODEL-REF to derive the FOM for region DD2 (hereinafter referred to as FOM2). The inventor then derived the FOM in domain DD3 (hereafter referred to as FOM3) by normalizing BodeQ3 in each simulation model by BodeQ3 in MODEL-REF.

Furthermore, the inventors have derived a total FOM (hereinafter, referred to as FOMt) that comprehensively indicates the frequency characteristics of the first to third frequency bands by using FOM1 to FOM3.
FOMt = FOM1 x FOM2 x FOM3 ... (1)
The above-mentioned FOM1 to FOM3 can be considered as indices for local frequency bands. In contrast, the FOMt can be considered as an index for a global frequency band.

Figure 10 shows examples of FOM1 to FOM3 and FOMt for MODEL-REF to MODEL2 derived by the inventor. As shown in Figure 10, MODEL1 obtained an FOM1 that was slightly smaller than MODEL-REF. On the other hand, MODEL1 obtained FOM2 and FOM3 that were larger than MODEL-REF. As a result, MODEL1 obtained an FOMt that was larger than MODEL-REF.

With MODEL2, an FOM1 was obtained that was significantly smaller than with MODEL-REF. On the other hand, with MODEL2, an FOM3 was obtained that was slightly larger than with MODEL-REF. Also, with MODEL2, an FOM2 equivalent to that of MODEL-REF was obtained. As a result, with MODEL2, an FOMt was obtained that was slightly smaller than with MODEL-REF.

The results in Figure 10 show that MODEL 1 has better overall frequency characteristics than MODEL-REF. On the other hand, the results in Figure 10 show that MODEL 2 has worse overall frequency characteristics than MODEL-REF. Based on these results, the inventors conducted a more detailed study of each design condition of the elastic wave device.

(Consideration of the relationship between t and dov)
The inventors have studied the design conditions for an elastic wave device with a dielectric layer. The inventors varied t and dov for MODEL 1 (with dummy) and derived FOM2 for each case. FIG. 11 is a graph showing the relationship between t and dov and FOM2 when a dummy is present. The horizontal axis of the graph is t, and the vertical axis is FOM2. The inventors derived FOM2 for each of the cases of "dov=0.5p, p, 1.5p."

As shown in Figure 11, a high FOM2 was obtained for all dov values when t was between 0.03p and 0.05p. Therefore, for example, when a dummy is used, t may be between 0.03p and 0.06p.

Next, the inventors varied t and dov for MODEL2 (no dummy) and derived FOM2 for each case. Figure 12 is a graph showing the relationship between t and dov and FOM2 when no dummy is used. Figure 12 is a paired diagram with Figure 11.

As shown in Figure 12, a high FOM2 was obtained when t was between 0.04p and 0.07p for all dov. Therefore, for example, when there is no dummy, t may be between 0.04p and 0.07p.

As described above, a high FOM2 was obtained at dov ranging from 0.5p to 1.5p, regardless of whether a dummy was used. For this reason, for example, regardless of whether a dummy was used, the first region R1 may include a portion with a length of 0.1p to 2p from the tip of the electrode finger 32 toward the center of the intersection region RK, and may not include a portion with a length exceeding 2p from the tip toward the center.

(Consideration of piezoelectric layer materials)
The inventors have conducted a study on the design conditions of the elastic wave device for each of the "piezoelectric layer: LT" and the "piezoelectric layer: LN".
LT layer: 121° Y-cut X-propagating LT (ta=0.41p)
LN layer: 125° Y-cut X-propagating LN (ta=0.41p)
The LT layer and the LN layer were set as follows. The inventor set the width (crossing width) of the crossing region RK in MODEL 1 and MODEL 2 to 23p. The inventor varied t in MODEL 1 and MODEL 2 in various ways within the range of 0.01p to 0.1p and conducted an investigation. Furthermore, the inventor varied dov in MODEL 1 in various ways within the range of 0.5p to 2p and conducted an investigation.

First, the inventor derived the frequency characteristics for MODEL-REF (dielectric layer: no) in the cases of "piezoelectric layer: LT" and "piezoelectric layer: LN". Figure 13 shows an example of the frequency characteristics for "piezoelectric layer: LT, dielectric layer: no". In Figure 13, reference numeral 1300A indicates the impedance characteristics, and reference numeral 1300B indicates the phase characteristics. Figure 14 shows an example of the frequency characteristics for "piezoelectric layer: LN, dielectric layer: no". In Figure 14, reference numeral 1400A indicates the impedance characteristics, and reference numeral 1400B indicates the phase characteristics.

As shown in Figures 13 and 14, the piezoelectric layer material can affect the frequency characteristics of the elastic wave device. For example, it is believed that the acoustic characteristics of the piezoelectric layer 2 affect the frequency characteristics. Therefore, it is believed that the acoustic characteristics of the dielectric layer 4 also affect the frequency characteristics. Therefore, the inventors investigated the relationship between the dielectric layer material and the frequency characteristics for each of MODEL 1 (with dummy) and MODEL 2 (without dummy).

The inventors conducted a study using the materials shown in Fig. 15 as the dielectric layer materials. Fig. 15 shows the sound velocity VL (unit: m/s) of each dielectric layer material. The sound velocity VL of a certain material (e.g., dielectric layer material) is calculated by the following formula (2):
VL = (E / ρ) ^1/2 ... (2)
where E is the Young's modulus of the material (unit: Pa) and ρ is the density of the material (unit: kg/m ³ ).

Please note that VL in this specification does not represent the sound speed c of the A1 mode wave excited by the acoustic wave device. VL is a value determined only by the dielectric layer material, and is the sound speed of the sound wave propagating through the dielectric layer material. On the other hand, c is the speed at which sound waves propagate inside the acoustic wave device, and varies not only with the material that constitutes the acoustic wave device, but also with the structure and design of the acoustic wave device. Also, for example, if the width w of the electrode fingers 32 is wider in a certain part of the acoustic wave device, c in that part may decrease as the mass of the electrode fingers 32 in that part increases.

As will be appreciated by those skilled in the art, the VL of a dielectric layer material is also related to the acoustic impedance Z of the dielectric layer material, which is given by the following equation (3):
Z = (E × ρ) ^1/2 ... (3)
is given by:

The inventors,
E = 50 GPa, 150 GPa, 250 GPa, 350 GPa
ρ=2000 kg/ ^m3 , 3500 kg/ ^m3 , 5000 kg/ ^m3 , 6500 kg/ ^m3 , 8000 kg/ ^m3
εr=3, 8, 13, 23, 33, 43
Simulations were performed by setting the physical property values of the dielectric layer 4 as shown in Table 1. εr is the relative dielectric constant of the dielectric layer material. The physical property values set as above roughly cover the actual physical property values of the materials shown in FIG.

(FOM2 Consideration)
The inventor derived the relationship between VL and FOM2 in the case of "piezoelectric layer: LT" with and without a dummy. Fig. 16 is a graph showing an example of the relationship derived by the inventor. The horizontal axis of the graph is VL, and the vertical axis is FOM2. In Fig. 16,
・Reference number 1600A: "Piezoelectric layer: LT, t=0.03p, with dummy"
Reference number 1600B: "Piezoelectric layer: LT, t=0.05p, with dummy"
・Code 1600C: "Piezoelectric layer: LT, t=0.03p, no dummy"
・Code 1600D: "Piezoelectric layer: LT, t=0.05p, no dummy"
The graph shows the case.

As shown in FIG. 16, FOM2 depends on VL. And FOM2 also depends on t and εr. As shown in the graphs with reference numbers 1600A and 1600B, when t=0.03p, a high FOM2 (i.e., good frequency characteristics in the second frequency band) is obtained for a VL in the range of approximately 3000 to 12500 m/s. Also, as shown in the graphs with reference numbers 1600C and 1600D, when t=0.05p, a high FOM2 is obtained for a VL in the range of approximately 5000 to 12500 m/s. From these, for example, VL may be 3000 m/s to 13000 m/s. And VL may be 5000 m/s to 12000 m/s (see also the explanation of FIG. 17 below).

Furthermore, as shown in the graphs with reference numerals 1600A and 1600B, when t = 0.03p, a particularly high FOM2 is obtained when VL ≈ 9000 m/s. For this reason, for example, when the piezoelectric layer 2 is a 115° ± 30° Y-cut X-propagation LT, t may be within the range of 0.03p ± 25%. In other words, t may be 0.0225p to 0.0375p. And VL may be within the range of 9000 m/s ± 1000 m/s. In other words, VL may be 8000 m/s to 10000 m/s.

Furthermore, as shown in the graphs of symbols 1600C and 1600D, when t = 0.05p, a particularly high FOM2 is obtained when VL ≈ 10,000 m/s. For this reason, for example, when the piezoelectric layer 2 is a 115° ± 30° Y-cut X-propagation LT, t may be within the range of 0.05p ± 25%. In other words, t may be 0.0375p to 0.0625p. And VL may be within the range of 10,000 m/s ± 1,000 m/s. In other words, VL may be 9,000 m/s to 11,000 m/s.

Next, the inventor derived the relationship between VL and FOM2 in the case of "piezoelectric layer: LN" with and without a dummy. Fig. 17 is a graph showing an example of the relationship derived by the inventor. Fig. 17 is a diagram paired with Fig. 16. In Fig. 17,
・Reference number 1700A: "Piezoelectric layer: LN, t=0.03p, with dummy"
・Reference number 1700B: "Piezoelectric layer: LN, t=0.05p, with dummy"
・Code 1700C: "Piezoelectric layer: LN, t=0.03p, no dummy"
・Reference number 1700D: "Piezoelectric layer: LN, t=0.05p, no dummy"
The graph shows the case.

As shown in the graphs labeled 1700A and 1700B, when t = 0.03p, a high FOM2 is obtained for a VL in the range of approximately 3000 to 12000 m/s. Also, as shown in the graphs labeled 1700C and 1700D, when t = 0.05p, a high FOM2 is obtained for a VL in the range of approximately 5000 to 12000 m/s.

Furthermore, as shown in the graphs denoted by symbols 1700A and 1700B, when t = 0.03p, a particularly high FOM2 is obtained when VL ≈ 8000 m/s. For this reason, for example, when the piezoelectric layer 2 is 120° ± 30° Y-cut X-propagation LN, t may be within the range of 0.03p ± 25%. And VL may be within the range of 8000 m/s ± 1000 m/s. In other words, VL may be 7000 m/s to 9000 m/s.

Furthermore, as shown in the graphs labeled 1700C and 1700D, when t = 0.05p, a particularly high FOM2 is obtained when VL ≈ 9000 m/s. For this reason, for example, when the piezoelectric layer 2 is 120° ± 30° Y-cut X-propagation LN, t may be within the range of 0.05p ± 25%. And VL may be within the range of 9000 m/s ± 1000 m/s. In other words, VL may be 8000 m/s to 10000 m/s. The inventors have also confirmed that in these parameter ranges where the characteristics of the second frequency band (FOM2) improve, the characteristics of the third frequency band (FOM3) also improve.

(FOM1 Consideration)
As described above, the inventors have found design conditions for an elastic wave device to improve FOM2. However, when FOM1 is small, FOMt may deteriorate even if FOM2 is improved. To consider this, the inventors have constructed a new simulation model, MODEL3. MODEL3 is an example of "Dielectric layer: yes, dummy yes". MODEL3 is the same as MODEL1 except for the material of dielectric layer 4. The inventors set the physical properties of dielectric layer 4 in MODEL3 to E = 150 GPa, ρ = 3500 kg/ ^cm3 , and εr = 8.

Figure 18 shows examples of phase characteristics of MODEL-REF and MODEL3 derived by simulation. As shown in Figure 18, in MODEL3, the phase characteristics in the second and third frequency bands are improved compared to MODEL-REF1. On the other hand, in MODEL3, ripples occur in the first frequency band. As a result, in MODEL3, the phase characteristics in the first frequency band are worse than in MODEL-REF1.

Figure 19 shows examples of FOM1 to FOM3 and FOMt for MODEL-REF and MODEL-3 derived by the inventor. As shown in Figure 19, MODEL-3 obtained larger FOM2 and FOM3 than MODEL-REF. On the other hand, MODEL-3 obtained a significantly smaller FOM1 than MODEL-REF. The small FOM1 in MODEL-3 is caused by ripples in the first frequency band. As a result, MODEL-3 obtained a smaller FOMt than MODEL-REF.

The ripples in the first frequency band are believed to be caused by the dielectric layer 4. For example, when VL is small, the addition of the dielectric layer 4 may reduce the resonant frequency in the first region R1 of the elastic wave device. This reduction in resonant frequency is believed to cause ripples in the first frequency band. The inventors therefore quantitatively investigated the variation in the resonant frequency that accompanies the addition of the dielectric layer 4.

Specifically, the inventors have found that
dfr = (fr1 - fr0) / fr0 ... (4)
The study was performed using dfr given by the following equation. dfr may also be referred to as the resonant frequency change rate. fr0 is the acoustic velocity of a wave (e.g., an A1 mode wave) excited by the acoustic wave device at the center of the intersection region RK. fr1 is the acoustic velocity of the wave at the tip of the electrode finger 32 in the first region R1.

fr0 may be calculated, for example, as the resonant frequency of an elastic wave device with no dielectric layer (e.g., MODEL-REF). The inventors used MODEL-REF to calculate fr0 = 5236 MHz.

For example, fr1 may be calculated as the resonance frequency of a simulation model MODEL4 in which a dielectric layer 4 is added to the entire upper surface of the piezoelectric layer 2 in MODEL-REF. Fig. 20 shows a schematic configuration of MODEL4. The inventors set the physical properties of the dielectric layer 4 in MODEL4 to E = 50 GPa, ρ = 3500 kg/ ^m3 , and εr = 8. Using MODEL4, the inventors calculated a value of fr1 = 5200 MHz. Therefore, a value of dfr = -0.69% was obtained from equation (4).

The fact that dfr is non-zero means that the resonant frequency of the elastic wave device changes with the addition of the dielectric layer 4. Specifically, the fact that dfr is negative means that the resonant frequency decreases with the addition of the dielectric layer 4. On the other hand, the fact that dfr is positive means that the resonant frequency increases with the addition of the dielectric layer 4.

Figure 21 shows an example of the phase characteristics of MODEL-REF and MODEL-4 derived by simulation. As shown in Figure 21, the phase characteristics of MODEL-4 are generally shifted toward the lower frequency side compared to the phase characteristics of MODEL-REF. As is clear from this, a decrease in the resonant frequency occurs in MODEL-4 compared to MODEL-REF.

(Consideration of the relationship between t and dfr)
The inventors varied t and the dielectric layer material for MODEL 4 and derived dfr for each case. Figure 22 is a graph showing an example of the relationship between t and dfr in "piezoelectric layer: LT". The horizontal axis of the graph is t, and the vertical axis is dfr.

Reference numeral 2200A in FIG. 22 is a graph showing the relationship between t and dfr for each of the dielectric layer materials " _{diamond, AlN, Al2O3 , SiO2, SiNx, and Si". Reference numeral 2200B in FIG. 22 is a graph showing the relationship between t and dfr for each of the dielectric layer materials "HfO2, Ta2O5 , TiO2 , ZrO2 , LiTaO3 , and LiNbO3} ". As shown in FIG. 22, dfr depends on t. Specifically, dfr changes approximately linearly with the change in t. dfr also depends on the dielectric layer material.

FIG. 23 is a graph showing an example of the relationship between t and dfr in "piezoelectric layer: LN". FIG. 23 is a paired diagram with FIG. 22. The dielectric layer material in the graph labeled 2300A in FIG. 23 is the same as the example labeled 2200A described above. The dielectric layer material in the graph labeled 2300B in FIG. 23 is the same as the example labeled 2200B described above. As can be seen from FIG. 22 and FIG. 23, dfr also depends on the piezoelectric layer material.

22 to 23, it should be noted that when a specific material is selected as the dielectric layer material and a specific film thickness t is selected, the resonant frequency remains almost unchanged (dfr ≒ 0) or increases (dfr > 0). In general, when a dielectric layer is provided on the surface of an acoustic wave element (on the piezoelectric layer and on the IDT electrode), the resonant frequency tends to decrease (dfr < 0) due to the effect of adding mass. However, the inventors have discovered that in an acoustic wave device using the A1 mode, when a dielectric layer is provided between the IDT electrode and the piezoelectric layer, dfr ≒ 0 or even dfr > 0 may occur. In other words, the acoustic wave device according to one aspect of the present disclosure can prevent the decrease in the resonant frequency in the first region R1 described above. Therefore, for example, an acoustic wave device can be provided in which the deterioration of FOM1 is small and the improvements in FOM2 and FOM3 are large. In other words, an acoustic wave device with a large FOMt can be provided.

Further considerations regarding LT
The inventor derived the relationship between dfr and FOMt in the case of "piezoelectric layer: LT" with and without a dummy. Fig. 24 is a graph showing an example of the relationship derived by the inventor. The horizontal axis of the graph is dfr, and the vertical axis is FOMt. In Fig. 24,
・Code 2400A: "Piezoelectric layer: LT, t=0.03p, with dummy"
Reference number 2400B: "Piezoelectric layer: LT, t=0.05p, with dummy"
・Code 2400C: "Piezoelectric layer: LT, t=0.03p, no dummy"
・Code 2400D: "Piezoelectric layer: LT, t=0.05p, no dummy"
The graph shows the case.

As shown in Figure 24, FOMt depends on dfr. And FOMt also depends on εr. As can be understood from the above explanations regarding dfr, when dfr is negative, FOMt may deteriorate (e.g., FOMt may fall below 1). On the other hand, when dfr takes a large positive value, FOMt may also deteriorate. In this case, the deterioration of FOMt is caused by VL becoming too large.

The inventor derived the graph of Fig. 25 based on Fig. 24. Fig. 25 is a graph showing an example of the relationship between εr and dfr in the case of "piezoelectric layer: LT". The horizontal axis of the graph is εr, and the vertical axis is dfr. In Fig. 25,
・Code 2500A: "Piezoelectric layer: LT, t=0.03p, with dummy"
・Code 2500B: "Piezoelectric layer: LT, t=0.05p, with dummy"
・Code 2500C: "Piezoelectric layer: LT, t=0.03p, no dummy"
・Code 2500D: "Piezoelectric layer: LT, t=0.05p, no dummy"
In each graph of FIG. 25, a combination of εr and dfr for actual dielectric layer materials is also plotted.

The curve "FOMt>1 upper limit" in Figure 25 shows the upper limit value of dfr at which FOMt>1 is realized at a certain εr. The curve "FOMt>1 lower limit" shows the lower limit value of dfr at which FOMt>1 is realized at a certain εr. The curve "FOMt>1.5 upper limit" shows the upper limit value of dfr at which FOMt>1.5 is realized at a certain εr. The curve "FOMt>1.5 lower limit" shows the lower limit value of dfr at which FOMt>1.5 is realized at a certain εr.

Each curve in FIG. 25 is expressed by the following formula (5):
dfr=a1×ln(1/εr)+b1 ... (5)
In equation (5), ln represents the natural logarithm function, and a1 and b1 are coefficients determined by data fitting.

Fig. 26 shows an example of each coefficient corresponding to the curve in Fig. 25. As shown in Fig. 26, for example, the coefficients corresponding to each curve in the graph with reference numeral 2500A are as follows:
FOMt>1 Upper limit: a1 = 0.801, b1 = 3.137
FOMt>1 Lower limit: a1=0.065, b1=-0.493
FOMt>1.5 Upper limit: a1=0.964, b1=2.846
FOMt>1.5 Lower limit: a1=0.161, b1=-0.058
As stated above.

Further Considerations Regarding LN
Next, the inventor derived the relationship between dfr and FOMt in the case of "piezoelectric layer: LN" with and without a dummy. Fig. 27 is a graph showing an example of the relationship derived by the inventor. Fig. 27 is a diagram paired with Fig. 24. In Fig. 27,
・Reference number 2700A: "Piezoelectric layer: LN, t=0.03p, with dummy"
・Reference number 2700B: "Piezoelectric layer: LN, t=0.05p, with dummy"
・Code 2700C: "Piezoelectric layer: LN, t=0.03p, no dummy"
・Code 2700D: "Piezoelectric layer: LN, t=0.05p, no dummy"
The graph shows the case.

The inventor derived the graph of Fig. 28 based on Fig. 27. Fig. 28 is a graph showing an example of the relationship between εr and dfr in the case of "piezoelectric layer: LN". Fig. 28 is a diagram paired with Fig. 25. In Fig. 28,
・Code 2800A: "Piezoelectric layer: LN, t=0.03p, with dummy"
・Reference number 2800B: "Piezoelectric layer: LN, t=0.05p, with dummy"
・Code 2800C: "Piezoelectric layer: LN, t=0.03p, no dummy"
・Code 2800D: "Piezoelectric layer: LN, t=0.05p, no dummy"
28 shows a graph for the case where each curve in FIG. 28 is also expressed by the above-mentioned formula (5).

Fig. 29 shows an example of coefficients corresponding to the curves in Fig. 28. As shown in Fig. 29, for example, the coefficients corresponding to the curves in the graph with reference numeral 2800A are as follows:
FOMt>1 Upper limit: a1=1.515, b1=5.824
FOMt>1 Lower limit: a1=0.612, b1=1.012
FOMt>1.5 Upper limit: a1=1.751, b1=5.562
FOMt>1.5 Lower limit: a1=0.671, b1=1.389
As stated above.

(Considerations regarding dielectric layer materials)
If FOMt>1, the frequency characteristics of the elastic wave device are improved by adding the dielectric layer 4. Therefore, for example, the frequency characteristics can be improved by using a dielectric layer material that falls between the curves "FOMt>1 lower limit" and "FOMt>1 upper limit" in the graphs of Figures 25 and 28. Furthermore, the frequency characteristics can be further improved by using a dielectric layer material that falls between the curves "FOMt>1.5 lower limit" and "FOMt>1.5 upper limit."

As shown in Figures 25 and 28, a dfr in the range of -1% to 2% is generally located between the curves "FOMt>1 lower limit" and "FOMt>1 upper limit". For this reason, in an elastic wave device according to one aspect of the present disclosure, the dfr may be -1% to 2%. By designing an elastic wave device so that the dfr falls within this range, it is expected that the frequency characteristics of the elastic wave device can be improved.

Furthermore, as shown in the graphs of Figures 25 and 28, a tendency was found for dfr to decrease with an increase in εr. For this reason, εr may be less than 20, for example. And dfr may be -0.2% or more, for example. In this case, the decrease in the resonant frequency of the elastic wave device due to the addition of the dielectric layer 4 does not have a significant adverse effect on the frequency characteristics. As another example, dfr may be 0% or more. In this case, there is no decrease in the resonant frequency due to the addition of the dielectric layer 4. As yet another example, dfr may be greater than 0%. In this case, the resonant frequency increases with the addition of the dielectric layer 4.

Major candidates for the dielectric layer material include Al ₂ O ₃ , AlN, SiN _x , Si, and SiO _2. These materials are generally located between the curves "FOMt>1 lower limit" and "FOMt>1 upper limit" in the graphs of Figures 25 and 28. Therefore, the dielectric layer 4 may include at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a material. As another example, the dielectric layer 4 may include at least one of Al ₂ O ₃ , AlN, SiN _x , and Si as a material.

By the way, in the graphs of FIG. 25 and FIG. 28, Ta ₂ O ₅ , ZrO ₂ , and HfO ₂ are located below the curve "FOMt>1 lower limit". On the other hand, diamond is located above the curve "FOMt>1 upper limit". From this, the dielectric layer 4 does not have to contain any of Ta ₂ O ₅ , ZrO ₂ , HfO ₂ , and diamond as a main component. Instead, for example, the dielectric layer 4 may contain at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a main component. As another example, the dielectric layer 4 may contain at least one of Al ₂ O ₃ , AlN, SiN _x , and Si as a main component.

In this specification, "dielectric layer 4 contains material X as a main component" may be understood to mean, for example, that "the content of material X in dielectric layer 4 is 50% or more." However, it should be noted that the definition of the main component is not necessarily limited to the above example.

(Numerical examples of dfr for various dielectric layer materials)
The inventors calculated dfr under various design conditions using actual physical properties of various dielectric layer materials. Figure 30 shows examples of dfr calculated by the inventors. As can be seen from the four examples on the bottom side of Figure 30, the dielectric layer 4 may include a first dielectric layer and a second dielectric layer having different sound velocities.

In FIG. 30, for example, the notation "Al ₂ O ₃ /SiO ₂ " represents a two-layer structure in which the first dielectric layer is an Al ₂ O ₃ layer and the second dielectric layer is an SiO ₂ layer. t in FIG. 30 represents the total thickness of the dielectric layer 4 when the dielectric layer 4 is a one-layer structure. On the other hand, t in FIG. 30 represents the thickness of the first layer (first dielectric layer) when the dielectric layer 4 is a two-layer structure. The thickness of the second dielectric layer in the example of FIG. 30 is 0.005p. In this specification, the total thickness of the dielectric layer 4 of the two-layer structure (i.e., the sum of the thickness of the first dielectric layer and the thickness of the second dielectric layer) is also represented as tt. In the example of FIG. 30, tt = t + 0.005p. Therefore, tt is 0.035p or 0.055p. These matters in the example of FIG. 30 also apply to each of the following figures.

By appropriately selecting the material of the first dielectric layer and the material of the second dielectric layer, the dielectric layer 4 having a desired sound velocity can be realized. As an example, the material of the first dielectric layer may be a material having a relatively high sound velocity. For example, the first dielectric layer may contain at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a main component. As another example, the first dielectric layer may contain at least one of Al ₂ O ₃ , AlN, SiN _x , and Si as a main component.

On the other hand, the material of the second dielectric layer may be a material having a relatively low sound velocity. For example, the second dielectric layer may contain at least one of _Ta2O5 , _ZrO2 , and _HfO2 as a main component. Also, as shown in FIG. 30, the second dielectric layer may contain _SiO2 as a main component.

By appropriately setting the thickness of the first dielectric layer and the thickness of the second dielectric layer, it is also possible to realize a dielectric layer 4 having a desired sound speed. As an example, a two-layer structure may be designed in which the first dielectric layer is the primary layer and the second dielectric layer is the secondary layer. Thus, for example, t may be 50% or more of tt. Each example in Figure 30 satisfies this condition.

(Numerical examples of FOMt for various dielectric layer materials)
Next, the inventors calculated FOMt under various design conditions using actual physical property values of various dielectric layer materials. Fig. 31 shows examples of FOMt calculated by the inventors. In Fig. 31, by applying a design condition that satisfies "FOMt>1", the frequency characteristics of the elastic wave device are improved with the addition of dielectric layer 4. Furthermore, by applying a design condition that satisfies "FOMt>1.5", the frequency characteristics can be further improved.

As described above, dfr can be controlled by selecting the dielectric layer material in the one-layer or two-layer dielectric layer 4. In addition, dfr can also be controlled by controlling the thickness of the first dielectric layer, the thickness of the second dielectric layer, and the thickness of the IDT electrode 3. And, dfr can also be controlled by changing the duty at the tip of the electrode finger 32. Also, dfr can also be controlled by changing the thickness at the tip of the electrode finger 32.

[Embodiment 2]
Fig. 32 is a schematic diagram illustrating a layered structure of an elastic wave device 1M according to a second embodiment. Fig. 32 is a paired view with Fig. 2. The elastic wave device 1M in Fig. 32 is an example of a membrane-type elastic wave device. In the second embodiment, the results of studies by the inventors on membrane-type elastic wave devices will be described.

As shown in FIG. 32, the elastic wave device 1M does not have to have a multilayer reflective film 5. Furthermore, the elastic wave device 1M may have a support substrate 6M instead of the support substrate 6. The elastic wave device 1M may have a hollow portion MA surrounded by the piezoelectric layer 2 and the support substrate 6M. In other words, the elastic wave device 1M may have a membrane structure defined by the hollow portion MA.

In embodiment 2, the inventors constructed simulation models MODEL-REFM, MODEL1M, and MODEL2M to study the frequency characteristics of elastic wave device 1M. MODEL-REFM is an example of embodiment 2 with "dielectric layer: no". MODEL1M is an example of embodiment 2 with "dielectric layer: with, dummy with". MODEL2M is an example of embodiment 2 with "dielectric layer: with, dummy without".

The inventors set the simulation conditions in the second embodiment as follows:
LT layer: 121° Y-cut X-propagating LT (ta=0.41p)
LN layer: 125° Y-cut X-propagating LN (ta=0.41p)
IDT electrode: Al (thickness: 0.13p)
The inventor then set the following:
Duty in "piezoelectric layer: LT": 0.55
Duty in "Piezoelectric layer: LN": 0.60
It was set as follows.

(Study by simulation in the second embodiment)
The inventors conducted the same study on the second embodiment as on the first embodiment. First, as shown in Figs. 33 and 34, the inventors derived frequency characteristics in the cases of "piezoelectric layer: LT" and "piezoelectric layer: LN" using MODEL-REFM (dielectric layer: absent). Fig. 33 shows an example of frequency characteristics in the case of "piezoelectric layer: LT, dielectric layer: absent". In Fig. 33, reference numeral 3300A indicates impedance characteristics, and reference numeral 3300B indicates phase characteristics. Fig. 34 shows an example of frequency characteristics in the case of "piezoelectric layer: LN, dielectric layer: absent". In Fig. 34, reference numeral 3400A indicates impedance characteristics, and reference numeral 3400B indicates phase characteristics.

Next, the inventors conducted further studies using MODEL1M and MODEL2M. As shown in Fig. 35, the inventors derived the relationship between VL and FOM2 for the case of "piezoelectric layer: LT".
・Reference number 3500A: "Piezoelectric layer: LT, t=0.03p, with dummy"
・Reference number 3500B: "Piezoelectric layer: LT, t=0.05p, with dummy"
・Code 3500C: "Piezoelectric layer: LT, t=0.03p, no dummy"
・Reference number 3500D: "Piezoelectric layer: LT, t=0.05p, no dummy"
The graph shows the case.

As shown in Fig. 36, the inventor derived the relationship between VL and FOM2 in the case of "piezoelectric layer: LN".
・Reference number 3600A: "Piezoelectric layer: LN, t=0.03p, with dummy"
・Reference number 3600B: "Piezoelectric layer: LN, t=0.05p, with dummy"
・Reference number 3600C: "Piezoelectric layer: LN, t=0.03p, no dummy"
・Reference number 3600D: "Piezoelectric layer: LN, t=0.05p, no dummy"
The graph shows the case.

Next, as shown in FIG. 37, the inventor derived the relationship between dfr and FOMt in the case of "piezoelectric layer: LT". In FIG. 37,
Reference number 3700A: "Piezoelectric layer: LT, t=0.03p, with dummy"
Reference number 3700B: "Piezoelectric layer: LT, t=0.05p, with dummy"
・Reference number 3700C: "Piezoelectric layer: LT, t=0.03p, no dummy"
・Reference number 3700D: "Piezoelectric layer: LT, t=0.05p, no dummy"
The graph shows the case.

As shown in FIG. 38, the inventor derived the relationship between εr and dfr in the case of "piezoelectric layer: LT".
・Reference number 3800A: "Piezoelectric layer: LT, t=0.03p, with dummy"
・Reference number 3800B: "Piezoelectric layer: LT, t=0.05p, with dummy"
・Code 3800C: "Piezoelectric layer: LT, t=0.03p, no dummy"
・Code 3800D: "Piezoelectric layer: LT, t=0.05p, no dummy"
Each curve in FIG. 38 is also expressed by the above-mentioned formula (5).

Fig. 39 shows an example of each coefficient corresponding to each curve in Fig. 38. As shown in Fig. 39, for example, the coefficients corresponding to each curve in the graph with reference numeral 3800A are as follows:
FOMt>1 Upper limit: a1=0.979, b1=3.783
FOMt>1 Lower limit: a1 = 0.097, b1 = -0.689
FOMt>1.5 Upper limit: a1=0.954, b1=3.499
FOMt>1.5 Lower limit: a1=0.065, b1=-0.593
As stated above.

Next, as shown in Fig. 40, the inventor derived the relationship between dfr and FOMt in the case of "piezoelectric layer: LN".
・Code 4000A: "Piezoelectric layer: LN, t=0.03p, with dummy"
・Code 4000B: "Piezoelectric layer: LN, t=0.05p, with dummy"
・Code 4000C: "Piezoelectric layer: LN, t=0.03p, no dummy"
・Code 4000D: "Piezoelectric layer: LN, t=0.05p, no dummy"
The graph shows the case.

As shown in FIG. 41, the inventor derived the relationship between εr and dfr in the case of "piezoelectric layer: LN".
Reference number 4100A: "Piezoelectric layer: LN, t=0.03p, with dummy"
Reference number 4100B: "Piezoelectric layer: LN, t=0.05p, with dummy"
・Reference number 4100C: "Piezoelectric layer: LN, t=0.03p, no dummy"
Reference number 4100D: "Piezoelectric layer: LN, t=0.05p, no dummy"
41 shows a graph for the case where each curve in FIG. 41 is also expressed by the above-mentioned formula (5).

Fig. 42 shows an example of each coefficient corresponding to each curve in Fig. 41. As shown in Fig. 42, for example, the coefficients corresponding to each curve in the graph of reference numeral 4100A are as follows:
FOMt>1 Upper limit: a1=1.164, b1=4.181
FOMt>1 Lower limit: a1 = 0.239, b1 = -0.724
FOMt>1.5 Upper limit: a1=1.143, b1=4.039
FOMt>1.5 Lower limit: a1=0.239, b1=-0.624
As stated above.

In the second embodiment, the inventors calculated dfr under various design conditions using actual physical property values of various dielectric layer materials. Fig. 43 shows an example of dfr calculated by the inventors in the second embodiment. As can be understood from the above descriptions, the simulations of the second embodiment also showed roughly the same trends as those of the first embodiment. As is clear from this, an elastic wave device according to one aspect of the present disclosure may be a membrane-type elastic wave device (e.g., elastic wave device 1M).
[Embodiment 3]

The inventors have further investigated the design conditions of a non-membrane type elastic wave device (e.g., elastic wave device 1 of embodiment 1) through simulation. The results of the investigation are described in embodiments 3 and 4. In embodiment 3, the results of the investigation in the case of "piezoelectric layer: LT" are described.

The simulation conditions in the third embodiment are as follows.
Piezoelectric layer 2
Material: LT
Orientation: (Φ, θ, ψ) = (0°, 24°, 0°)
Thickness (ta): 0.4 μm
Support substrate 6
Material: Si
Orientation: (Φ, θ, ψ) = (-45°, -54.7°, 0°)
Multilayer reflective film 5
Material of low acoustic impedance layer 5a: _SiO2
Thickness of low acoustic impedance layer 5a: 0.19 μm
Material of high acoustic impedance layer 5b: _HfO2
Thickness of high acoustic impedance layer 5b: 0.166 μm
IDT electrode 3
Material: Aluminum
Thickness: 0.13 μm
Length of dummy electrode finger (ddm): 4 μm
Gap length: 0.4 μm
Intersection width: 23 μm
First overlap length (dov): 1 μm

Under the above simulation conditions, the inventors set the following acoustic wave devices (resonators) Types 1 to 4 in the third embodiment.
Elastic wave device type 1
Pitch (p): 1.0438 μm
Duty: 0.4
Elastic wave device type 2
Pitch: 1.1085 μm
Duty: 0.45
Elastic wave device type 3
Pitch: 1.1924 μm
Duty: 0.6
Elastic Wave Device Type 4
Pitch: 1.2231 μm
Duty: 0.6

The inventors varied the dielectric layer material and the thickness (t) of the dielectric layer 4, and derived the relationship between dfr and FOMt for each of the acoustic wave device types 1 to 4. Specifically, the inventors selected the dielectric layer material from among "AlN, SiO ₂ , HfO ₂ , Ta ₂ O ₅ , ZrO ₂ , diamond, Al ₂ O ₃ , SiN _x , and TiO ₂ " and selected t from among "0.01 μm, 0.03 μm, 0.05 μm, and 0.07 μm" to derive the above relationship.

FIG. 44 shows an example of the relationship between dfr and FOMt in embodiment 3. Reference characters 4400A to 4400D in FIG. 44 indicate graphs for elastic wave device types 1 to 4, respectively. As shown in the dotted circled areas in FIG. 44, it was confirmed that in all of elastic wave device types 1 to 4, FOMt becomes particularly large near dfr = 0. Therefore, by setting dfr ≒ 0, the frequency characteristics of the elastic wave device can be further improved.

44, it was confirmed that the FOMt was large when the dielectric layer materials were _SiO2 , AlN, _SiNx , _Al2O3 , and _TiO2 . In the third embodiment, it was confirmed that the FOMt was particularly large when the dielectric layer materials were _SiO2 and _SiNx . Therefore, in the third embodiment, the frequency characteristics of the elastic wave device can be further improved by using _SiO2 or _SiNx as _the dielectric layer material.

The inventors then derived the phase characteristics of elastic wave device types 1 to 4 for combinations of dielectric layer materials and t that belong to the dotted circled area in Figure 44. Figure 45 shows examples of phase characteristics in embodiment 3. References 4500A to 4500D in Figure 45 show graphs for elastic wave device types 1 to 4, respectively. For each of references 4500A to 4500D, a graph enlarging the area near a phase of 90° is also shown. The legend "Ref" in Figure 45 represents the above-mentioned MODEL-REF. Therefore, for "Ref" in Figure 45, t=0.

45, when the dielectric layer material was _SiO2 and t = 0.03 μm, good phase characteristics were obtained in all of acoustic wave device types 1 to 4. Also, when the dielectric layer material was AlN, _Al2O3 , or _SiNx , good phase characteristics were generally obtained.
[Embodiment 4]

In the fourth embodiment, the results of the study on the case where the piezoelectric layer is LN will be described. The simulation conditions in the fourth embodiment are as follows.
Piezoelectric layer 2
Material: LN
Orientation: (Φ, θ, ψ) = (0°, 15°, 0°)
Thickness (ta): 0.376 μm
Support substrate 6
Material: Si
Orientation: (Φ, θ, ψ) = (-45°, -54.7°, 0°)
Multilayer reflective film 5
Material of low acoustic impedance layer 5a: _SiO2
Thickness of low acoustic impedance layer 5a: 0.19 μm
Material of high acoustic impedance layer 5b: _HfO2
Thickness of high acoustic impedance layer 5b: 0.166 μm
IDT electrode 3
Material: Aluminum
Thickness: 0.11 μm
Length of dummy electrode finger (ddm): 4 μm
Gap length: 0.4 μm
Intersection width: 23 μm
First overlap length (dov) = 1 μm

In the fourth embodiment, the inventors set the following acoustic wave device types 1 to 4 under the above simulation conditions.
Elastic wave device type 1
Pitch (p): 0.9411 μm
Duty: 0.55
Elastic wave device type 2
Pitch: 0.9876 μm
Duty: 0.55
Elastic wave device type 3
Pitch: 1.3096 μm
Duty: 0.45
Elastic Wave Device Type 4
Pitch: 1.3449 μm
Duty: 0.45

The inventor derived the relationship between dfr and FOMt in elastic wave device types 1 to 4 of embodiment 4 for the same combination of dielectric layer material and t as in embodiment 3. FIG. 46 shows an example of the relationship between dfr and FOMt in embodiment 4. FIG. 46 is a diagram paired with FIG. 44 in embodiment 3. References 4600A to 4600D in FIG. 46 indicate graphs for elastic wave device types 1 to 4 of embodiment 4, respectively. As shown in the dotted circled areas in FIG. 46, it was confirmed that in all of elastic wave device types 1 to 4 of embodiment 4, FOMt becomes particularly large near dfr = 0. Therefore, in embodiment 4 as well, by setting dfr ≒ 0, the frequency characteristics of the elastic wave device can be further improved.

46 , it was also confirmed in the fourth embodiment that the FOMt was large when the dielectric layer material was SiO ₂ , AlN, SiN _x , Al ₂ O ₃ , and TiO _2. It was confirmed in the fourth embodiment that the FOMt was particularly large when the dielectric layer material was SiO _2. Therefore, in the fourth embodiment, by using SiO ₂ as the dielectric layer material, it is possible to further improve the frequency characteristics of the elastic wave device.

The inventors then derived the phase characteristics of elastic wave device types 1 to 4 of embodiment 4 for combinations of the dielectric layer materials and t that belong to the dotted circled area in Figure 46. Figure 47 shows an example of phase characteristics in embodiment 4. Figure 47 is a paired diagram with Figure 45 in embodiment 3. Reference numerals 4700A to 4700D in Figure 47 denote graphs for elastic wave device types 1 to 4 of embodiment 4, respectively.

47, in the fourth embodiment as well, when the dielectric layer material was _SiO2 and t = 0.03 μm, good phase characteristics were obtained in all of the acoustic wave device types 1 to 4. In the fourth embodiment as well, when the dielectric layer material was AlN, _Al2O3 , or _SiNx , generally good phase characteristics were obtained.

[Embodiment 5]
48 illustrates a schematic configuration of a filter 100 (frequency filter) according to the fifth embodiment. The filter 100 may include an acoustic wave device (e.g., the acoustic wave device 1) according to one aspect of the present disclosure. As illustrated in FIG. 48 , the filter 100 may be a ladder-type filter having a series arm SL and a parallel arm PL. The filter 100 may have a plurality of acoustic wave resonators Res. The acoustic wave resonators Res may have, for example, a common piezoelectric layer 2. Meanwhile, each of the acoustic wave resonators Res may have an individual IDT electrode 3.

The filter 100 may have, as the multiple elastic wave resonators Res, (i) at least one series elastic wave resonator Res1S located in the series arm SL, and (ii) at least one parallel elastic wave resonator Res1P located in the parallel arm PL. In the example of FIG. 48, the filter 100 has two series elastic wave resonators Res1S and one parallel elastic wave resonator Res1P.

The series arm PL may be connected to the input terminal Pin and the output terminal Pout. In the example of FIG. 48, the series elastic wave resonator Res1S-1 is the series elastic wave resonator Res1S connected to the input terminal Pin. The series elastic wave resonator Res1S-2 is the series elastic wave resonator Res1S connected to the output terminal Pout. The parallel arm PL may extend from between the series elastic wave resonators Res1S-1 and Res1S-2. The parallel arm PL may be connected to the ground terminal GND.

The filter 100 may have a first acoustic wave resonator located in the parallel arm PL as an acoustic wave device according to one aspect of the present disclosure. As an example, the first acoustic wave resonator may be a parallel acoustic wave resonator Res1P. Thus, for example, the filter 100 may have an acoustic wave device 1 as the parallel acoustic wave resonator Res1P.

The filter 100 may further include a second acoustic wave resonator located in the series arm SL. The second acoustic wave resonator may not include the dielectric layer 4. Thus, for example, the filter 100 may include a series acoustic wave resonator Res1S as the second acoustic wave resonator.

In general, it is considered that the effect of the series acoustic wave resonator Res1S on the frequency characteristics of the filter 100 is greater than the effect of the parallel acoustic wave resonator Res1P on the frequency characteristics. For this reason, when the first acoustic wave resonator is the parallel acoustic wave resonator Res1P, even if a decrease in FOM1 occurs in the first acoustic wave resonator due to the dielectric layer 4, the effect of the first acoustic wave resonator on the frequency characteristics of the filter 100 in the first frequency band can be reduced. Furthermore, since the second acoustic wave resonator does not have a dielectric layer 4, no decrease in FOM1 occurs in the second acoustic wave resonator. In this way, the filter 100 can achieve a filter with excellent frequency characteristics.

[Embodiment 6]
49 illustrates a schematic configuration of a communication device 151 according to the sixth embodiment. The communication device 151 is an application example of an acoustic wave filter according to an aspect of the present disclosure, and performs wireless communication using radio waves. The communication device 151 may include one duplexer 101 as a transmission filter 109 and another duplexer 101 as a reception filter 111. Each of the two duplexers 101 may include a filter (e.g., filter 100) according to an aspect of the present disclosure. In this manner, the communication device 151 may include a filter according to an aspect of the present disclosure.

In the communication device 151, a transmission information signal TIS containing information to be transmitted may be modulated and frequency-increased (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 153, and converted into a transmission signal TS. A bandpass filter 155 may remove unnecessary components from the TS outside the transmission passband. Next, the TS after the unnecessary components have been removed may be amplified by an amplifier 157 and input to the transmission filter 109.

The transmit filter 109 may remove unnecessary components outside the transmission passband from the input transmit signal TS. The transmit filter 109 may output the TS after removing the unnecessary components to the antenna 159 via an antenna terminal (e.g., the above-mentioned TCin). The antenna 159 may convert the TS, which is an electrical signal input to itself, into radio waves as a wireless signal, and transmit the radio waves to the outside of the communication device 151.

The antenna 159 may also convert the received external radio waves into a received signal RS, which is an electrical signal, and input the RS to the receiving filter 111 via the antenna terminal. The receiving filter 111 may remove unnecessary components from the input RS outside the receiving passband. The receiving filter 111 may output the received signal RS after the unnecessary components have been removed to the amplifier 161. The outputted RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unnecessary components from the amplified RS outside the receiving passband. The RS after the unnecessary components have been removed may be frequency-downgraded and demodulated by the RF-IC 153, and converted into a received information signal RIS.

The TIS and RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the TIS and RIS may be analog voice signals or digitized voice signals. The passband of the wireless signals may be set as appropriate and may conform to various known standards.

〔summary〕
An elastic wave device according to aspect 1 of the present disclosure comprises a piezoelectric layer and an IDT electrode located on the piezoelectric layer and having a plurality of electrode fingers, where the thickness of the piezoelectric layer is 2p or less when the pitch of the electrode fingers is represented as p, and the elastic wave device further comprises a dielectric layer located between the piezoelectric layer and the IDT electrode in a first region that includes the tips of the electrode fingers and does not include the center of the intersection region of the electrode fingers, and the elastic wave device is configured to excite a wave in A1 mode.

In the elastic wave device according to aspect 2 of the present disclosure, in aspect 1, the sound velocity of the wave at the center of the intersection region is represented as fr0, the sound velocity of the wave at the tip of the electrode finger in the first region is represented as fr1, and dfr given by the above formula (4) may be greater than or equal to -1% and less than or equal to 2%.

In the elastic wave device according to aspect 3 of the present disclosure, in aspect 2, the relative dielectric constant of the dielectric layer may be less than 20.

In the elastic wave device according to aspect 4 of the present disclosure, in aspect 3, dfr may be -0.2% or more.

In the elastic wave device according to a fifth aspect of the present disclosure, in any one of the first to fourth aspects, the dielectric layer may contain at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a material.

In the elastic wave device according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, the dielectric layer may contain at least one of Al ₂ O ₃ , AlN, SiN _x , and Si as a material.

In the elastic wave device according to a seventh aspect of the present disclosure, in any one of the first to sixth aspects, the dielectric layer does not necessarily contain any of Ta ₂ O ₅ , ZrO ₂ , HfO ₂ , and diamond as a main component.

In the elastic wave device according to an eighth aspect of the present disclosure, in any one of the first to seventh aspects, the dielectric layer may contain at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a main component.

In the elastic wave device according to aspect 9 of the present disclosure, in any one of aspects 1 to 4, the dielectric layer may include a first dielectric layer and a second dielectric layer having different sound velocities.

In an elastic wave device according to aspect 10 of the present disclosure, in accordance with aspect 9, the _first dielectric layer may contain at least one of _Al2O3 , AlN, _SiNx , Si, and _SiO2 as a main component, and the thickness of the first dielectric layer may be 50% or more of the sum of the thickness of the first dielectric layer and the thickness of the second dielectric layer.

In an elastic wave device according to aspect 11 of the present disclosure, in any one of aspects 1 to 10, the Young's modulus of the dielectric layer may be expressed as E (unit: Pa), the density of the dielectric layer may be expressed as ρ (unit: kg/ ^m3 ), and the sound velocity VL (unit: m/s) of the dielectric layer given by the above formula (2) may be 3000 m/s or more and 13000 m/s or less.

In the elastic wave device according to aspect 12 of the present disclosure, in aspect 11, VL may be 5000 m/s or more and 12000 m/s or less.

In the elastic wave device according to aspect 13 of the present disclosure, in the above-mentioned aspect 11, the piezoelectric layer may be a 115°±30° Y-cut X-propagation LT layer, the thickness of the dielectric layer may be within the range of 0.03p±25%, and VL may be 8000 m/s or more and 10000 m/s or less.

In the elastic wave device according to aspect 14 of the present disclosure, in the above-mentioned aspect 11, the piezoelectric layer may be a 115°±30° Y-cut X-propagation LT layer, the thickness of the dielectric layer may be within the range of 0.05p±25%, and VL may be 9000 m/s or more and 11000 m/s or less.

In the elastic wave device according to aspect 15 of the present disclosure, in the above-mentioned aspect 11, the piezoelectric layer may be a 120°±30° Y-cut X-propagation LN layer, the thickness of the dielectric layer may be within the range of 0.03p±25%, and VL may be 7000 m/s or more and 9000 m/s or less.

In the elastic wave device according to aspect 16 of the present disclosure, in the above-mentioned aspect 11, the piezoelectric layer may be a 120°±30° Y-cut X-propagation LN layer, the thickness of the dielectric layer may be within the range of 0.05p±25%, and VL may be 8000 m/s or more and 10000 m/s or less.

In the elastic wave device according to aspect 17 of the present disclosure, in any one of aspects 1 to 16, the first region may be located at both ends of the intersection region and may extend along the arrangement direction of the electrode fingers.

In the elastic wave device according to aspect 18 of the present disclosure, in any one of aspects 1 to 17, the IDT electrode may further include a bus bar, and at least a portion of the first region may be located between the tips of the electrode fingers and the bus bar.

In an elastic wave device according to aspect 19 of the present disclosure, in any one of aspects 1 to 18, the IDT electrode may further include a plurality of dummy electrode fingers that respectively face the plurality of electrode fingers, and the first region may include the tips of the dummy electrode fingers.

In an elastic wave device according to aspect 20 of the present disclosure, in any one of aspects 1 to 19, the IDT electrode may further include a plurality of dummy electrode fingers that respectively face a plurality of the electrode fingers, the thickness of the dielectric layer may be 0.03p or more and 0.06p or less, and the first region may include a portion having a length of 0.1p or more and 2p or less from the tip of the electrode finger toward the center of the intersection region, and may not include a portion having a length of more than 2p from the tip of the electrode finger toward the center of the intersection region.

In an elastic wave device according to aspect 21 of the present disclosure, in any one of aspects 1 to 18, the IDT electrode may not have a dummy electrode finger that faces at least one of the plurality of electrode fingers, the thickness of the dielectric layer may be 0.04p or more and 0.07p or less, and the first region may include a portion having a length of 0.1p or more and 2p or less from the tip of the electrode finger toward the center of the intersection region, and may not include a portion exceeding 2p from the tip of the electrode finger toward the center of the intersection region.

The filter according to aspect 22 of the present disclosure may include an acoustic wave device according to any one of aspects 1 to 21.

The filter according to aspect 23 of the present disclosure may be a ladder-type filter having a series arm and a parallel arm in the above-mentioned aspect 22, and the filter may have a first acoustic wave resonator located in the parallel arm as the acoustic wave device.

The filter according to aspect 24 of the present disclosure may further include a second acoustic wave resonator located in the series arm in the aspect 23, and the second acoustic wave resonator may not include the dielectric layer.

The communication device according to aspect 25 of the present disclosure may include a filter according to any one of aspects 22 to 24.

[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-mentioned 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 the embodiments obtained by appropriately combining the technical means disclosed in the 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.

1 Elastic wave device 1M Elastic wave device (membrane type elastic wave device)
2 Piezoelectric layer 3 IDT electrode 4 Dielectric layer 30 Bus bar 32 Electrode finger 35 Dummy electrode finger 100 Filter (ladder type filter)
151 Communication device R1 First region RK Intersection region PL Parallel arm SL Series arm Res1P Parallel acoustic wave resonator (first acoustic wave resonator)
Res1S series elastic wave resonator (second elastic wave resonator)

Claims (25)

1. 1. An acoustic wave device, comprising:
   A piezoelectric layer;
   an IDT electrode located on the piezoelectric layer and having a plurality of electrode fingers;
   When the pitch of the electrode fingers is represented as p, the thickness of the piezoelectric layer is 2p or less,
   the elastic wave device further includes a dielectric layer located between the piezoelectric layer and the IDT electrode in a first region that includes tips of the electrode fingers but does not include a center of an intersection region of the electrode fingers,
   The acoustic wave device is configured to excite waves in an A1 mode.
2. The sound speed of the wave at the center of the intersection region is denoted as fr0,
   The acoustic velocity of the wave at the tip of the electrode finger in the first region is represented as fr1,
   The following formula,
   dfr=(fr1-fr0)/fr0
   2. The acoustic wave device of claim 1, wherein dfr given by: is greater than or equal to −1% and less than or equal to 2%.
3. The elastic wave device of claim 2, wherein the dielectric layer has a relative dielectric constant of less than 20.
4. The elastic wave device according to claim 3, wherein dfr is -0.2% or more.
5. The acoustic wave device according to claim 1 , wherein the dielectric layer contains at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a material.
6. The acoustic wave device according to claim 1 , wherein the dielectric layer contains at least one of Al ₂ O ₃ , AlN, SiN _x , and Si as a material.
7. The acoustic wave device according to claim 1 , wherein the dielectric layer does not contain any of Ta ₂ O ₅ , ZrO ₂ , HfO ₂ , and diamond as a main component.
8. The acoustic wave device according to claim 1 , wherein the dielectric layer contains at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a main component.
9. The elastic wave device according to any one of claims 1 to 4, wherein the dielectric layer includes a first dielectric layer and a second dielectric layer having different sound velocities.
10. The first dielectric layer contains at least one of Al ₂ O ₃ , AlN, SiN _x , Si, and SiO ₂ as a main component;
    The acoustic wave device according to claim 9 , wherein a thickness of the first dielectric layer is equal to or greater than 50% of a sum of a thickness of the first dielectric layer and a thickness of the second dielectric layer.
11. The Young's modulus of the dielectric layer is represented as E (unit: Pa),
    The density of the dielectric layer is represented as ρ (unit: kg/m ³ ),
    The following formula,
    VL = (E/ρ) ^1/2
    11. The elastic wave device according to claim 1, wherein a sound velocity VL (unit: m/s) of the dielectric layer given by: is 3000 m/s or more and 13000 m/s or less.
12. The elastic wave device according to claim 11, wherein VL is 5000 m/s or more and 12000 m/s or less.
13. The piezoelectric layer is a 115°±30° Y-cut X-propagation LT layer,
    The thickness of the dielectric layer is within the range of 0.03p±25%;
    The acoustic wave device according to claim 11, wherein VL is not less than 8000 m/s and not more than 10000 m/s.
14. The piezoelectric layer is a 115°±30° Y-cut X-propagation LT layer,
    The thickness of the dielectric layer is within the range of 0.05p±25%;
    The acoustic wave device according to claim 11 , wherein VL is not less than 9000 m/s and not more than 11000 m/s.
15. The piezoelectric layer is a 120°±30° Y-cut X-propagation LN layer,
    The thickness of the dielectric layer is within the range of 0.03p±25%;
    The acoustic wave device according to claim 11 , wherein VL is not less than 7000 m/s and not more than 9000 m/s.
16. The piezoelectric layer is a 120°±30° Y-cut X-propagation LN layer,
    The thickness of the dielectric layer is within the range of 0.05p±25%;
    The acoustic wave device according to claim 11, wherein VL is not less than 8000 m/s and not more than 10000 m/s.
17. The elastic wave device according to any one of claims 1 to 16, wherein the first region is located at both ends of the intersection region and extends along the arrangement direction of the electrode fingers.
18. The IDT electrode further includes a bus bar,
    The acoustic wave device according to claim 1 , wherein at least a portion of the first region is located between a tip of the electrode finger and the bus bar.
19. the IDT electrode further includes a plurality of dummy electrode fingers facing the plurality of electrode fingers,
    The acoustic wave device according to claim 1 , wherein the first region includes a tip of the dummy electrode finger.
20. the IDT electrode further includes a plurality of dummy electrode fingers facing the plurality of electrode fingers,
    The thickness of the dielectric layer is 0.03p or more and 0.06p or less,
    20. An elastic wave device according to claim 1, wherein the first region includes a portion having a length of 0.1p or more and 2p or less from the tip of the electrode finger toward the center of the intersection region, and does not include a portion having a length exceeding 2p from the tip of the electrode finger toward the center of the intersection region.
21. the IDT electrode does not have a dummy electrode finger opposed to at least one of the plurality of electrode fingers,
    The thickness of the dielectric layer is 0.04p or more and 0.07p or less,
    19. An elastic wave device according to claim 1, wherein the first region includes a portion having a length of 0.1p or more and 2p or less from the tip of the electrode finger toward the center of the intersection region, and does not include a portion having a length exceeding 2p from the tip of the electrode finger toward the center of the intersection region.
22. A filter comprising an acoustic wave device according to any one of claims 1 to 21.
23. the filter is a ladder-type filter having a series arm and a parallel arm,
    The filter according to claim 22 , wherein the filter includes a first acoustic wave resonator located in the parallel arm as the acoustic wave device.
24. the filter further includes a second acoustic wave resonator located in the series arm,
    The filter of claim 23 , wherein the second acoustic wave resonator does not have the dielectric layer.
25. A communication device comprising a filter according to any one of claims 22 to 24.

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