Acoustic wave device

Abstract

To provide an acoustic wave device that enables the suppression of transverse modes.SOLUTION: An acoustic wave device includes a piezoelectric layer and an IDT electrode formed on the piezoelectric layer. The IDT electrode includes a first busbar 11a and a second busbar 11b. These busbars have a plurality of step portions parallel to the propagation direction of surface acoustic waves on the sides where the first busbar and the second busbar face each other in a top view, and a step portion is provided between adjacent step portions. The step portions of the first busbar and the step portions of the second busbar are spaced the same distance apart in a top view.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device using surface acoustic waves. [Background technology]

[0002] A surface acoustic wave (SAW) resonator having an IDT (InterDigital Transducer) electrode provided on the main surface of a piezoelectric substrate is known as an acoustic wave device using surface acoustic waves. This SAW resonator is used, for example, in the transmission filter and reception filter of a duplexer. This acoustic wave device generates a transverse mode. Since the transverse mode has adverse effects such as spurious and loss in the passband, it is desirable to suppress it.

[0003] Patent Document 1 discloses an IDT electrode having curved sections arranged to impart curvature to the waveguide of an acoustic wave device in order to suppress transverse modes of the acoustic wave device. In the acoustic wave device (SAW resonator) described in Patent Document 2, in order to suppress the transverse mode of the acoustic wave device, the transverse mode reflected by one bus bar and the transverse mode reflected by the other bus bar cancel each other out, thereby suppressing the transverse mode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-92422 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-286663 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in an acoustic wave device using such an IDT electrode, further improvement is required by suppressing the transverse mode.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an acoustic wave device in which transverse modes are suppressed. [Means for solving the problem]

[0007] One aspect of the acoustic wave device of the present invention is a device comprising: a piezoelectric layer; an IDT electrode formed on the piezoelectric layer, the IDT electrode includes a first bus bar and a second bus bar facing each other; the first bus bar and the second bus bar are provided with a plurality of step portions that are parallel to a propagation direction of a surface acoustic wave on sides where the first bus bar and the second bus bar face each other in a top view; adjacent step portions of the plurality of step portions are provided at different positions in a direction from the first bus bar to the second bus bar in a top view, a step portion is provided between adjacent step portions, The step portions of the first bus bar and the step portions of the second bus bar are spaced the same distance apart from each other when viewed from above. In this way, adjacent step portions are provided at different positions in the direction from the first bus bar to the second bus bar, so that an acoustic wave device in which transverse modes are suppressed can be realized.

[0008] As a specific embodiment of the above-described aspect, the acoustic wave device of the present invention includes: The width of the step in the IDT electrode in a direction perpendicular to the propagation direction of the surface acoustic wave is less than 1.5λ, where λ is the wavelength of the surface acoustic wave.

[0009] In a specific aspect of the acoustic wave device of the present invention, the first bus bar and the second bus bar each include three step portions: the first step portion, a second step portion adjacent to the first step portion, and a third step portion adjacent to the second step portion; a step portion between the first step portion and the second step portion is a step portion that forms a step in a direction from the first bus bar to the second bus bar as going from the first step portion to the second step portion, The step portion between the second step portion and the third step portion forms a step in the direction from the second bus bar to the first bus bar as it goes from the second step portion to the third step portion.

[0010] One aspect of the acoustic wave device of the present invention is the first bus bar and the second bus bar each include three step portions: a first step portion, a second step portion adjacent to the first step portion, and a third step portion adjacent to the second step portion; The step portion between the first step portion and the second step portion and the step portion between the second step portion and the third step portion all form steps in the same direction as going toward the first step portion, the second step portion, and the third step portion, and form steps in the direction from the second bus bar to the first bus bar, or form steps in the direction from the first bus bar to the second bus bar.

[0011] In one aspect of the acoustic wave device of the present invention, the first bus bar and the second bus bar have, on opposing sides in a top view, a plurality of step portions parallel to a propagation direction of a surface acoustic wave, and step portions provided between adjacent step portions are formed in a direction perpendicular to the propagation direction of the surface acoustic wave, The first bus bar and the second bus bar each have three step portions: a first step portion, a second step portion adjacent to the first step portion, and a third step portion adjacent to the second step portion.

[0012] As a specific aspect of the above-described aspect, the acoustic wave device of the present invention is such that, in top view, the first bus bar and the second bus bar have, on opposing sides thereof, a plurality of step portions parallel to the propagation direction of the surface acoustic wave, and step portions provided between adjacent step portions have sloped shapes inclined with respect to the propagation direction of the surface acoustic wave. The first bus bar and the second bus bar each have three step portions: a first step portion, a second step portion adjacent to the first step portion, and a third step portion adjacent to the second step portion.

[0013] As a specific aspect of the above-described aspect of the acoustic wave device of the present invention, the first bus bar and the second bus bar are configured such that, when viewed from above, the total step height of the two adjacent step portions in the direction from the first bus bar to the second bus bar is less than 2.0λ, where λ is the wavelength of the acoustic wave. [Effects of the Invention]

[0014] According to the present invention, adjacent step portions provided on the first bus bar and the second bus bar of the IDT electrode are provided at different positions in the direction from the first bus bar to the second bus bar, thereby realizing an acoustic wave device in which transverse modes are suppressed. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view illustrating an embodiment of an acoustic wave device according to the present invention. [Figure 2] 1 is a plan view of an IDT electrode of an acoustic wave device according to a first embodiment of the present invention. [Figure 3a]10 is a graph showing the real part of admittance versus frequency for the acoustic wave device of Example 1. [Figure 3b] 10 is a graph showing the real part of admittance versus frequency of the acoustic wave device of Example 2. [Figure 3c] 10 is a graph showing the real part of admittance versus frequency for an acoustic wave device according to a comparative example. [Figure 4] 1 is a graph showing the real part of admittance versus frequency for Example 1, Example 2, and the comparative example. [Figure 5] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device of a comparative example. [Figure 6] 10 is a graph showing the real part of admittance versus frequency for Example 3 and the comparative example. [Figure 7] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device according to a second embodiment of the present invention. [Figure 8a] 10 is a graph showing a change in the real part of admittance with respect to frequency in the acoustic wave device of Example 4. [Figure 8b] 10 is a graph showing a change in the real part of admittance with respect to frequency in the acoustic wave device of Example 5. [Figure 8c] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device of a comparative example. [Figure 9] 10 is a graph showing the real part of admittance versus frequency for Example 4, Example 5, and the comparative example. [Figure 10] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device according to a third embodiment of the present invention. [Figure 11] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device according to a fourth embodiment of the present invention. [Figure 12] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device according to a fifth embodiment of the present invention. [Figure 13] FIG. 10 is a partially enlarged view of an IDT electrode according to a fifth embodiment of the present invention. [Figure 14] FIG. 10 is a plan view of an IDT electrode of an acoustic wave device according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment 1 is a cross-sectional view showing a first embodiment of an acoustic wave device. The acoustic wave device 1 is a SAW resonator that includes a support substrate 2, a piezoelectric layer 3, an IDT electrode 4 formed on the piezoelectric layer 3, and an intermediate layer 6 provided between the support substrate 2 and the piezoelectric layer 3.

[0017] 2 is a plan view of the IDT electrode 4 and reflectors 5 provided on the main surface of the piezoelectric layer 3 in the acoustic wave device 1. In Fig. 2, the IDT electrode 4 includes a first bus bar 11a, a second bus bar 11b, a plurality of electrode fingers 12a extending from the first bus bar 11a toward the second bus bar 11b, a plurality of electrode fingers 12b extending from the second bus bar 11b toward the first bus bar 11a, and dummy electrodes 15a and 15b facing the electrode fingers 12a and 12b, respectively. Gaps 17b and 17a are formed between the tips 13a and 13b of the electrode fingers 12a and 12b and the dummy electrodes 15b and 15a, respectively.

[0018] The first bus bar 11a and the second bus bar 11b are connected to an input terminal (not shown) and an output terminal (not shown), respectively. When a high-frequency signal is input to the input terminal and the output terminal, an electric field is generated between the electrodes, and a surface acoustic wave is excited and propagates on the piezoelectric layer 3. The surface acoustic wave is reflected by the reflector 5, and an electrical resonance occurs. The resonant frequency f R is determined by P=λ / 2, where λ is the wavelength of the surface acoustic wave propagating through the piezoelectric layer 3 and P is the electrode period.

[0019] For example, silicon having a non-amorphous crystalline form or crystalline sapphire is used for the support substrate 2. However, the material used for the support substrate 2 is not limited to these, and other materials such as polycrystalline silicon, polycrystalline alumina, and spinel may be used as long as they can solve the problems of the present invention.

[0020] Lithium tantalate (LiTaO3) or lithium niobate (LiNbO3) is used for the piezoelectric layer 3. However, the piezoelectric layer 3 is not limited to these materials, and other materials can also be used.

[0021] The IDT electrodes 4 may be made of, for example, Al, Au, Cu, Ni, Pt, Ti, Cr, Ag, or alloys thereof, but other metals or alloys may also be used. The IDT electrodes 4 may also be formed by laminating these metals or alloys.

[0022] The intermediate layer 6 is a layer provided for at least one of the purposes of increasing the bonding strength between the support substrate 2 and the piezoelectric layer 3 or increasing the propagation speed of the elastic wave. When the intermediate layer 6 is provided for the purpose of increasing the bonding strength between the support substrate 2 and the piezoelectric layer 3, silicon dioxide (SiO2) or the like is used for the intermediate layer 6. When the intermediate layer 6 is provided as a layer for increasing the speed of the elastic wave, for example, aluminum nitride (AlN) or boron aluminum nitride (B X Al 1-X In this embodiment, the intermediate layer 6 may be omitted.

[0023] When manufacturing such an acoustic wave device 1, the piezoelectric layer 3 is made of, for example, 36° or 42° Y-cut X-propagation lithium tantalate (LiTaO 3 ).

[0024] 2, the IDT electrode 4 has a first busbar and a second busbar that are provided with a plurality of step portions that are parallel to the propagation direction of the surface acoustic waves (direction X in FIG. 2) on the sides where the first busbar 11a and the second busbar 11b face each other in a top view (plan view). The first busbar 11a has a first step portion 21a, a second step portion 22a, and a third step portion 23a. The second busbar 11b has a first step portion 21b, a second step portion 22b, and a third step portion 23b. These step portions and step portions, which will be described later, form a stepped shape on the sides where the busbars 11a and 11b face each other.

[0025] The IDT electrode 4 has three regions in the X direction indicated by the arrow in Figure 2: a first flat region 51, a second flat region 52, and a third flat region 53. The first flat region 51, the second flat region 52, and the third flat region 53 are regions where the first step portion 21a, the second step portion 22a, and the third step portion 23a are located, respectively.

[0026] The first step portion 21a is provided at the level of the virtual line L1a (in this embodiment, level means the height in the direction parallel to the extension direction of the electrode fingers, i.e., the direction from the first bus bar to the second bus bar). The second step portion 22a is provided at the level of the virtual line L2a. The third step portion 23a is provided at the level of the virtual line L3a. The step portion 21b is provided at the level of the virtual line L1b. The step portion 22b is provided at the level of the virtual line L2b. The step portion 23b is provided at the level of the virtual line L3b. The distances between opposing step portions are equal. That is, the distance between the virtual line L1a and the virtual line L1b, the distance between the virtual line L2a and the virtual line L2b, and the distance between the virtual line L3a and the virtual line L3b are equal.

[0027] The IDT electrode 4 is provided with a step portion 31a, a step portion 31b, a step portion 32a, and a step portion 32b. The step portion 31a is provided between the first step portion 21a and the adjacent second step portion 22a. The step portion 31a is formed so as to form a step in the direction from the first busbar 11a to the second busbar 11b as it progresses from the first step portion 21a to the second step portion 22a. The step portion 31b is provided between the step portion 21b and the adjacent step portion 22b. The step portion 31b is formed so as to form a step in the direction from the first busbar 11a to the second busbar 11b as it progresses from the step portion 21b to the step portion 22b. The step portion 32a is provided between the second step portion 22a and the adjacent third step portion 23a. The step portion 32a is formed so as to form a step in the direction from the first busbar 11a to the second busbar 11b as it goes from the second step portion 22a to the third step portion 23a. The step portion 32b is provided between the step portion 22b and the adjacent step portion 23b. The step portion 32b is formed so as to form a step in the direction from the first busbar 11a to the second busbar 11b as it goes from the step portion 22b to the step portion 23b. These step portions 31a, 31b, 32a, and 32b are formed in the direction from the first busbar 11a to the second busbar 11b, i.e., in the same direction as the direction perpendicular to the propagation direction X of the surface acoustic wave. The step portions and step portions are arranged alternately to form a staircase pattern. In the description of the embodiments of the present invention, the step means the distance between adjacent step portions in the extending direction of the electrode fingers (the direction from the first bus bar to the second bus bar).

[0028] In the IDT electrode 4, the electrode fingers 12a on the first bus bar 11a side and the electrode fingers 12b on the second bus bar 11b side are the same in length. The dummy electrodes 15a and 15b are all the same in length. The distances from the nearest step portions to the gaps 17a and 17b are all the same. The opening length (the length of the intersection region in the electrode finger direction) of the IDT electrode 4 is the same in all of the first flat region 51, the second flat region 52, and the third flat region 53.

[0029] <About the effects> The suppression of transverse modes in an acoustic wave device configured as described above will now be described. To verify the effect of the acoustic wave device 1 of this embodiment, several acoustic wave devices (SAW resonators of comparative examples and examples) with different step portions were fabricated and measured. FIG. 3(a) is a graph showing the change in the real part of the admittance (conductance) Re(Y) versus frequency for an acoustic wave device having a step height of 1.0λ due to step portions 31a, 31b, 32a, and 32b as Example 1. FIG. 3(b) is a graph showing the change in the real part of the admittance Re(Y) versus frequency for an example of acoustic wave device 1 having a step height of 0.5λ as Example 2. FIG. 3(c) is a graph showing the change in the real part of the admittance Re(Y) versus frequency for an acoustic wave device without a step portion as a comparative example. FIG. 4 is a graph superimposing these three frequency characteristics. The horizontal axis of these graphs is frequency [MHz], and the vertical axis is the real part of the admittance Re(Y) [dB]. In order to enlarge and display the real part of the admittance Re(Y) of these graphs below -30 [dB], the part of the admittance real part Re(Y) exceeding -30 [dB] is omitted.

[0030] 5 is a plan view of an IDT electrode 4X and a reflector 5X of an acoustic wave device according to a comparative example. As shown in FIG. 5, the IDT electrode 4X does not have a step.

[0031] The conditions common to the comparative example, example 1 and example 2 are shown below.

[0032] Wavelength λ: 4.1μm Piezoelectric substrate 3: Material: 42° rotated Y-cut X-propagation lithium tantalate substrate Thickness: 0.27λ Middle tier 6: Material SiO2 Thickness 0.61λ Support substrate 2: Material: Spinel Thickness: 97.6λ IDT electrode finger: The IDT film consists of a lower Ti film (130 nm), a middle AlCu film (268 nm), and an upper Ti film (15 nm). Pitch: 0.5λ Duty: 46% Number of electrode finger pairs: 114 Aperture length: 17.5λ Dummy electrode length: 0.5λ Gap: 0.45μm Reflector logarithm: 10

[0033] As can be seen particularly from the circled portions in Figure 4, Example 2, in which the step indicated by the dashed line is 0.5λ, has a smaller peak in the real part of the admittance, and the transverse mode is more suppressed, than the comparative example without the dashed line step (denoted as "0λ" in Figure 4 for convenience). Furthermore, Example 1, in which the step indicated by the solid line is 1.0λ, has a smaller peak in the real part of the admittance, and the transverse mode is more suppressed, than Example 2, in which the step is 0.5λ. Therefore, it can be seen that the transverse mode of the acoustic wave device of the first embodiment is suppressed by providing the step portions 31a, 31b, 32a, and 32b.

[0034] In FIG. 6 , the solid line indicates the real part of the admittance versus frequency for the acoustic wave device in Example 3, where the step heights of the stepped portions 31a, 31b, 32a, and 32b are 1.5λ, while the dashed line indicates the real part of the admittance versus frequency for an acoustic wave device without any stepped portions. This graph reveals that the real part of the admittance increases, particularly in the region from about 942 MHz to about 980 MHz, which is the anti-resonance frequency Fa. This increase in frequency range is undesirable because it is believed that the device does not adequately block surface acoustic waves when used as a filter. Furthermore, the real part of the admittance in the region from about 942 MHz to about 980 MHz tends to increase as the step height of the stepped portions increases. Therefore, it is preferable that the step height be less than 1.5λ. Furthermore, a larger total step height in the IDT electrode 4 is undesirable because it increases energy loss. Specifically, the total length of the steps of step portion 31a and step portion 32a (the distance from virtual line L1a to virtual line L3a) is preferably less than 2.0λ. Similarly, the total length of the steps of step portion 31b and step portion 32b (the distance from virtual line L1b to virtual line L3b) is preferably less than 2.0λ.

[0035] Second Embodiment FIG. 7 is a plan view of an IDT electrode 4A of an acoustic wave device according to a second embodiment. In the following description, parts having the same names and functions as those in the previously described embodiments are designated by the same reference numerals and will not be described again. In the second embodiment, the IDT electrode 4A has a two-stage structure consisting of a first flat region 54 and a second flat region 55. A step 33a is formed in the first busbar 11a between a first step 24a and a second step 25a adjacent to the first step 24a. A step 33b is formed in the second busbar 11b between a first step 24b and a second step 25b adjacent to the first step 24b. The first step 24a is located on the imaginary line La1. The second step 25a is located on the imaginary line La2. The first step 24b is located on the imaginary line Lb1. The second step portion 25b is located at the position of the imaginary line Lb2.

[0036] The following describes how the transverse mode is suppressed in an acoustic wave device having two stages of IDT electrode 4A as described above. In order to confirm the effect of acoustic wave device 1 of this embodiment, a number of acoustic wave devices (SAW resonators of comparative examples and examples) with different step heights were fabricated and measured.

[0037] FIG. 8a is a graph showing the change in the real part of admittance Re(Y) versus frequency when the step difference due to the step portions 33a and 33b of the IDT electrode 4A of FIG. 7 is 1.0λ as Example 4. FIG. 8b is a graph showing the change in the real part of admittance Re(Y) versus frequency when the step difference due to the step portions 33a and 33b of the IDT electrode 4A of FIG. 7 is 0.5λ as Example 5. FIG. 8c is a graph showing the change in the real part of admittance Re(Y) versus frequency for the acoustic wave device having the above-mentioned IDT electrode without a step (see FIG. 5) as a comparative example. FIG. 9 is a graph superimposing these three frequency characteristics. The conditions for fabrication and measurement are the same as those for Examples 1, 2, and 3.

[0038] As can be seen from the dashed circled area in FIG. 9 , the peak of the real part of the admittance in Example 5, where the step height is 0.5λ, is smaller than that in the comparative example without a step height, indicating that the transverse mode is suppressed. Furthermore, the peak of the real part of the admittance in Example 4, where the step height is 1.0λ, is smaller than that in Example 5, where the step height is 0.5λ, indicating that the transverse mode is more suppressed. Therefore, it can be seen that the transverse mode of the acoustic wave device is suppressed by providing the IDT electrode 4A of the acoustic wave device according to the second embodiment with the steps 31a, 31b, 32a, and 32b. These results demonstrate that the transverse mode of the acoustic wave device is suppressed when the IDT electrode has steps.

[0039] <Third embodiment> The IDT electrode of the acoustic wave device according to the third embodiment is shown in Fig. 10. As shown in Fig. 10, the IDT electrode has a three-stage structure, with a step extending downward (toward the second bus bar 11b) from the first flat region 61 to the second flat region 62, and a step extending upward (toward the first bus bar 11a) from the second flat region 62 to the third flat region 63.

[0040] In this way, steps are provided by the stepped portions 31a, 31b, 35a, and 35b, so that transverse modes can be suppressed in the acoustic wave device.

[0041] <Fourth embodiment> A plan view of an IDT electrode 4C of an acoustic wave device according to the fourth embodiment is shown in Fig. 11. As shown in Fig. 11, the IDT electrode 4C includes a first flat region 81, a second flat region 82, a third flat region 83, and slope regions 91 and 92 as regions in which inclined steps are provided.

[0042] In the IDT electrode 4C, the first flat region 81 to the second flat region 82 descends downward (in the direction from the first bus bar 11a to the second bus bar 11b) in FIG. 11 due to the slope region 91, and the second flat region 82 to the third flat region 83 ascends upward (in the direction from the second bus bar 11b to the first bus bar 11a) due to the slope region 92.

[0043] The slope regions 91 and 92 are regions in which the bases 18a, 18b, and 18c of the electrode fingers or the bases 19a, 19b, and 19c of the dummy electrodes are arranged along the inclined imaginary lines S1a, S1b, S2a, and S2b. In the slope regions 91 and 92, the bases 18a, 18b, and 18c of the electrode fingers or the bases 19a, 19b, and 19c of the dummy electrodes are arranged adjacent to the inclined imaginary lines S1a, S1b, S2a, and S2b, thereby forming a sloped step (slope portion). The sloped shape is formed by the arrangement of these bases.

[0044] Bases 19a, 19b, and 19c of dummy electrode 15b are provided on imaginary line S1a of slope region 91. In the extension direction of the electrode fingers, base 19a is provided at the position of step portion 71a (imaginary line M1a), base 19b is provided at the position of step portion 72a (imaginary line M2a), and base 19c is provided so as to be located between imaginary lines M1a and M2a.

[0045] Bases 18a, 18b, and 18c of electrode finger 12b are provided on imaginary line S1b of slope region 91. In the extension direction of the electrode fingers, base 18a is provided at the position of step portion 71b (imaginary line M1b), base 18b is provided at the position of step portion 72b (imaginary line M2b), and base 19c is provided so as to be located between imaginary line M1b and imaginary line M2b.

[0046] In this way, in the slope region 91, at least one base 18c or 19c is provided between the steps 37a or 37b, so that adjacent bases are arranged diagonally, forming a slope shape, thereby forming a slope region. In this embodiment, one base is provided between the steps 37a or 37b per virtual line (virtual line S1a or virtual line S1b), but multiple bases may be provided.

[0047] Bases 18a, 18b, and 18c of the electrode finger 12a are provided on the imaginary line S2a of the slope region 92. In the extension direction of the electrode fingers, the base 18a is provided at the position of the step portion 72a (imaginary line M2a), the base 12b is provided at the position of the step portion 73a (imaginary line M1a), and the base 18c is provided so as to be located between the imaginary lines M1a and M2a.

[0048] Bases 19a, 19b, and 19c of dummy electrode 15b are provided on imaginary line S2b of slope region 92. In the extension direction of the electrode fingers, base 19a is provided at the position of step portion 72b (imaginary line M2b), base 19b is provided at the position of step portion 73b (imaginary line M1b), and base 19c is provided so as to be located between imaginary lines M1a and M2a.

[0049] In this manner, in the slope region 92, at least one base 18c or 19c is provided between the steps 37a or 37b, thereby forming a slope shape in which adjacent bases are arranged diagonally, thereby forming a slope region. In this manner, in the present embodiment, one base is provided between the steps 37a or 37b per virtual line (virtual line S2a or virtual line S2b), but multiple bases may be provided.

[0050] The first busbar 11a has a first step portion 71a, a second step portion 72a, and a third step portion 73a provided as flat portions parallel to the X direction. The first step portion 71a and the third step portion 73a are located at the position of an imaginary line M1a, and the second step portion 72a is located at the position of an imaginary line M2a. The imaginary lines M1a and M2a are spaced apart by a step 37a (the vertical width on the drawing in FIG. 12).

[0051] The second busbar 11b is provided with a first step portion 71b, a second step portion 72b, and a third step portion 73b. The first step portion 71b and the third step portion 73b are located at the position of the imaginary line M1b, and the second step portion 72b is located at the position of the imaginary line M2b. The imaginary lines M1a and M2a are spaced apart by a step 37b (the vertical width on the drawing in FIG. 12).

[0052] In this way, the IDT electrode 4C has slope regions 91 and 92, which provide a step difference of only steps 37a and 37b between adjacent step portions in the direction from the first bus bar to the second bus bar (a direction perpendicular to the propagation direction X of the surface acoustic wave), thereby suppressing the transverse mode of the acoustic wave device. Furthermore, since the sloped steps in this embodiment, in which bases 18b and 19c are provided between steps 37a and 37b, can be formed, the Q value can be improved more than when non-sloped steps are provided as in the first to third embodiments. In this embodiment, the steps 37a and 37b of slope region 91 and slope region 92 are the same, but they may be different. As in the first embodiment, the width of the step in the extension direction of the electrode fingers is preferably less than 1.5λ, and the combined length of the steps of step portion 37a and step portion 38a (the distance from virtual line M1a to virtual line M3a) and the combined length of the steps of step portion 37b and step portion 38b (the distance from virtual line M1b to virtual line M3b) are preferably less than 2.0λ.

[0053] The width of the slope regions 91 and 92 in the X direction will be described. The width of the slope regions 91 and 92 in the X direction is shorter than that of the first step portion 71b, the second step portion 72b, and the third step portion 73b. By configuring the width of the slope regions 91 and 92 to be shorter than that of the flat regions, that is, the first step portion 71b, the second step portion 72b, and the third step portion 73b, it is possible to prevent a peak in the high-frequency region (a peak similar to the peak near 988 MHz in FIG. 9 is thought to occur in the real part of the admittance for the frequency of this embodiment) from shifting toward the resonant frequency (for example, near 910 MHz in FIG. 9 ) (lower frequency side) and thereby preventing an adverse effect on the frequency characteristics.

[0054] In the IDT electrode 4C, the electrode fingers 12a on the first bus bar 11a side and the electrode fingers 12b on the second bus bar 11b side are the same length. The dummy electrodes 15a and 15b are all the same length. The distances from the electrode finger bases 18 to the step or slope regions nearest to each of the gaps 17a and 17b are all substantially the same. The IDT electrode 4 is formed so that the opening lengths (the electrode finger direction lengths of the intersection regions) are substantially the same in all regions (first flat region 81, second flat region 82, third flat region 83, slope region 91, and slope region 92). Furthermore, in the slope regions 91 and 92, the gaps 17a and 17b are also arranged diagonally and continuously in a sloped shape.

[0055] Fifth Embodiment 12 shows a plan view of an IDT electrode 4D of an acoustic wave device according to the fifth embodiment. As shown in Fig. 12, the IDT electrode 4D includes a first flat region 81, a second flat region 82, a third flat region 84, and slope regions 91 and 93 as regions in which inclined steps are provided. The IDT electrode 4D is sloped downward (from the first bus bar 11a to the second bus bar 11b) between the first flat region 81 and the second flat region 82 in Fig. 12 due to the slope region 91, and is sloped downward between the second flat region 82 and the third flat region 84 due to the slope region 93. The slope regions 91, 93 are regions in which the bases 18a, 18b, and 18c of the electrode fingers 12a or 12b, or the bases 19a, 19b, and 19c of the dummy electrodes, are arranged along imaginary lines S1a, S1b, S3a, and S3b that are inclined with respect to the extension direction of the electrode fingers and the propagation direction of the surface acoustic wave.

[0056] Bases 19a, 19b, and 19c of dummy electrode 15a are arranged in a sloped manner along the inclined imaginary line S1a of slope region 91. In the extension direction of the electrode fingers, base 19a is provided at the position of step portion 71a (position of imaginary line M1a), base 19b is provided at the position of step portion 72a (position of imaginary line M2a), and base 19c is provided so as to be located between imaginary lines M1a and M2a.

[0057] Bases 18a, 18b, and 18c of the electrode fingers 12b are arranged in a sloped manner along the inclined imaginary line S1b of the slope region 91. In the extension direction of the electrode fingers, the base 18a is provided at the position of the step portion 71b (the position of the imaginary line M1b), the base 18b is provided at the position of the step portion 72b (the position of the imaginary line M2b), and the base 18c is provided so as to be located between the imaginary lines M1b and M2b.

[0058] Bases 18a, 18b, and 18c of the electrode fingers 12a are arranged in a sloped manner along the inclined imaginary line S3a of the slope region 93. In the extension direction of the electrode fingers, the base 18a is provided at the position of the step portion 72a (the position of the imaginary line M2a), the base 18b is provided at the position of the step portion 74a (the position of the imaginary line M3a), and the base 18c is provided so as to be located between the imaginary lines M2a and M3a.

[0059] Bases 19a, 19b, and 19c of dummy electrode 15b are arranged in a sloped manner along the inclined imaginary line S3b of slope region 93. In the extension direction of the electrode fingers, base 19a is provided at the position of step portion 72b (position of imaginary line M2b), base 19b is provided at the position of step portion 74b (position of imaginary line M3b), and base 19c is provided so as to be located between imaginary lines M1a and M2a.

[0060] The first busbar 11a is provided with a first step portion 71a, a second step portion 72a, and a third step portion 74a. The first step portion 71a is located at the position of the imaginary line M1a. The second step portion 72a is located at the position of the imaginary line M2a. The third step portion 74a is located at the position of the imaginary line M3a. The imaginary lines M1a and M2a are spaced apart by a step 37a (the vertical width on the drawing in FIG. 12). The imaginary lines M2a and M3a are spaced apart by a step 38a.

[0061] The second busbar 11b is provided with a first step portion 71b, a second step portion 72b, and a third step portion 74b. The first step portion 71b is located at the position of the imaginary line M1b. The second step portion 72b is located at the position of the imaginary line M2b. The third step portion 74b is located at the position of the imaginary line M3b. The imaginary lines M1a and M2a are spaced apart by a step 37b (the vertical width on the drawing in FIG. 12). The imaginary lines M2b and M3b are spaced apart by a step 38b.

[0062] In this way, the slope regions 91 and 93 of the IDT electrode 4D provide steps 37a, 37b, 38a, and 38b between adjacent step portions in the extension direction of the electrode fingers (a direction perpendicular to the propagation direction X of the surface acoustic wave), thereby making it possible to suppress the transverse mode of the acoustic wave device.

[0063] Fig. 13 is a partial enlarged view of the IDT electrode 4D. Regarding the position of the base 18c of the electrode finger, if there is a difference in the left and right positions of the base of the electrode finger (the portion where the intersection region side end 100 and the intersection region side end 101 of the bus bar 11b intersect with the outline of the electrode finger 12b) in the extension direction of the electrode finger (the direction perpendicular to the direction X), as shown in Fig. 13, the base 18c of the electrode finger is assumed to be located between them (near the portion surrounded by the dotted line in Fig. 13). This also applies when the left and right base positions of the bases of the other electrode fingers and the dummy electrodes are different.

[0064] Sixth Embodiment FIG. 14 shows a plan view of an IDT electrode 4E of an acoustic wave device according to a sixth embodiment. As shown in FIG. 14, the IDT electrode 4E does not include a dummy electrode in this embodiment. In the IDT electrode 4E, the intersection region-side ends 20 of the busbars 11a and 11b are arranged in a sloping pattern along the inclined imaginary lines S4b and S5a at positions corresponding to the bases of the dummy electrodes in the previous embodiments. Furthermore, the bases 18 of the electrode fingers are arranged in a sloping pattern along the inclined imaginary lines S4a and S5b. The IDT electrode 4E includes a first flat region 86, a second flat region 87, a third flat region 88, and slope regions 95 and 96, which are regions where inclined steps are provided. The IDT electrode 4E rises upward (from the second bus bar 11b toward the first bus bar 11a) in FIG. 14 between the first flat region 86 and the second flat region 87 due to the slope region 95, and falls downward between the second flat region 87 and the third flat region 88 due to the slope region 96.

[0065] In this way, the IDT electrode 4E has slope regions 95, 96, which provide steps 39a, 39b between adjacent step portions in the extension direction of the electrode fingers (a direction perpendicular to the propagation direction X of the surface acoustic wave), making it possible to suppress the transverse mode of the acoustic wave device.

[0066] In the above-described embodiment, the positional relationship between the first bus bar 11a and the second bus bar 11b may be reversed. The present invention is also applicable to an acoustic wave device that does not have the dummy electrodes 15a and 15b of the IDT electrodes. The present invention is also applicable to an acoustic wave device that does not have the reflector 5.

[0067] It should be noted that the drawings used in the above explanation are schematic, and the dimensions and ratios on the drawings do not necessarily correspond to those of the actual product.

[0068] The present invention has been described above, but when specifically implementing the present invention as an acoustic wave device, it is not limited to the above-described embodiments, and various modifications and additions are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0069] 1. Acoustic wave devices 2 Support substrate 3 Piezoelectric layer 4 IDT electrode 5 reflector 6. Middle class 11a First busbar 11b Second busbar 12a Electrode finger 12b Electrode finger 21a, 21b, 22a, 22b, 23a, 23b Step section 31a, 31b, 32a, 32b Stepped parts 91, 92, 93, 95, 96 Slope area

Claims

1. a piezoelectric layer; an IDT electrode formed on the piezoelectric layer, the IDT electrode includes a first bus bar and a second bus bar facing each other; the first bus bar and the second bus bar are provided with a plurality of step portions that are parallel to a propagation direction of a surface acoustic wave on sides where the first bus bar and the second bus bar face each other in a top view; adjacent step portions of the plurality of step portions are provided at different positions in a direction from the first bus bar to the second bus bar in a top view, a step portion is provided between adjacent step portions, The step portions of the first bus bar and the step portions of the second bus bar are spaced the same distance apart from each other when viewed from above. Acoustic wave devices.

2. The width of the step in the IDT electrode in a direction perpendicular to the propagation direction of the surface acoustic wave is less than 1.5λ, where λ is the wavelength of the surface acoustic wave. The acoustic wave device according to claim 1 .

3. the first bus bar and the second bus bar each include three step portions: the first step portion, a second step portion provided adjacent to the first step portion, and a third step portion provided adjacent to the second step portion; a step portion between the first step portion and the second step portion is a step portion that forms a step in a direction from the first bus bar to the second bus bar as going from the first step portion to the second step portion, The step portion between the second step portion and the third step portion forms a step in a direction from the second bus bar to the first bus bar as going from the second step portion to the third step portion. The acoustic wave device according to claim 1 .

4. the first bus bar and the second bus bar each include three step portions: a first step portion, a second step portion adjacent to the first step portion, and a third step portion adjacent to the second step portion; The step portion between the first step portion and the second step portion and the step portion between the second step portion and the third step portion all form steps in the same direction as going to the first step portion, the second step portion, and the third step portion, and form steps in a direction from the second bus bar to the first bus bar, or form steps in a direction from the first bus bar to the second bus bar. The acoustic wave device according to claim 1 .

5. the first bus bar and the second bus bar have, on opposing sides in a top view, a plurality of step portions parallel to a propagation direction of a surface acoustic wave, and step portions provided between adjacent step portions are formed in a direction perpendicular to the propagation direction of the surface acoustic wave; The first bus bar and the second bus bar each have three step portions: a first step portion, a second step portion provided adjacent to the first step portion, and a third step portion provided adjacent to the second step portion. The acoustic wave device according to claim 1 .

6. the first bus bar and the second bus bar have, on opposing sides in a top view, a plurality of step portions parallel to a propagation direction of a surface acoustic wave, and step portions provided between adjacent step portions have slope shapes inclined with respect to the propagation direction of the surface acoustic wave; The first bus bar and the second bus bar each have three step portions: a first step portion, a second step portion provided adjacent to the first step portion, and a third step portion provided adjacent to the second step portion. The acoustic wave device according to claim 1 .

7. When viewed from above, the first bus bar and the second bus bar have two adjacent step portions, and the total step height in a direction from the first bus bar to the second bus bar is less than 2.0λ, where λ is the wavelength of an elastic wave. The acoustic wave device according to claim 5 or 6.

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