Elastic wave device

Abstract

An elastic wave device (1) comprises: a support member that includes a support substrate (34); a piezoelectric layer (31) that is disposed on the support member and has main surfaces (31a and 31b) facing each other; an IDT electrode (10) that is disposed on the main surface (31a); an IDT electrode (20) that is disposed on the main surface (31b); and a dielectric film (41) that covers at least a portion of the IDT electrode (10). The IDT electrode (20) is covered by the support member, and when the main surfaces (31a and 31b) are seen in plan view, a first electrode finger among a plurality of electrode fingers included in the IDT electrode (10) at least partially overlaps a second electrode finger among a plurality of electrode fingers included in the IDT electrode (20). The electrode finger duty of the second electrode finger is less than the electrode finger duty of the first electrode finger.

Description

Elastic Wave Device

[0001] The present invention relates to an acoustic wave device.

[0002] Patent Document 1 discloses an elastic wave device including a support member, a piezoelectric layer provided on the support member, a first IDT (InterDigital Transducer) electrode provided on a first main surface of the piezoelectric layer, and a second IDT electrode provided on a second main surface of the piezoelectric layer and embedded in the support member.

[0003] International Publication No. 2022 / 202917

[0004] In the acoustic wave device disclosed in Patent Document 1, by covering the first IDT electrode with a dielectric film, it is possible to suppress variations in resonance frequency during manufacturing by adjusting the film thickness of the dielectric film.

[0005] However, in a configuration in which IDT electrodes are arranged on both main surfaces of the piezoelectric layer (hereinafter sometimes referred to as a double-sided IDT structure), the frequency adjustment function of the dielectric film is reduced compared to a configuration in which IDT electrodes are arranged on only one main surface (hereinafter sometimes referred to as a single-sided IDT structure), making it difficult to stabilize the resonant frequency during manufacturing.

[0006] SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an acoustic wave device having a double-sided IDT structure with improved frequency adjustment function during manufacturing.

[0007] In order to achieve the above object, an elastic wave device according to one aspect of the present invention includes a support member including a support substrate, a piezoelectric layer arranged on the support member and having first and second principal surfaces facing each other, a first IDT electrode arranged on the first principal surface, a second IDT electrode arranged on the second principal surface, and a dielectric film covering at least a portion of the first IDT electrode, wherein the second IDT electrode is covered by the support member, and when the first and second principal surfaces are viewed in a plane, a first electrode finger of a plurality of electrode fingers included in the first IDT electrode at least partially overlaps with a second electrode finger of a plurality of electrode fingers included in the second IDT electrode, and the electrode finger duty of the second electrode finger is smaller than the electrode finger duty of the first electrode finger.

[0008] Furthermore, an elastic wave device according to one aspect of the present invention includes a support member including a support substrate, a piezoelectric layer disposed on the support member and having first and second principal surfaces facing each other, a first IDT electrode disposed on the first principal surface, a second IDT electrode disposed on the second principal surface, and a dielectric film covering at least a portion of the first IDT electrode, wherein the second IDT electrode is covered by the support member, and when the first and second principal surfaces are viewed in a plane, each of the plurality of electrode fingers included in the first IDT electrode at least partially overlaps with each of the plurality of electrode fingers included in the second IDT electrode in a one-to-one relationship, and in the above planar view, a first electrode finger of the plurality of electrode fingers included in the first IDT electrode at least partially overlaps with a second electrode finger of the plurality of electrode fingers included in the second IDT electrode, and the electrode finger width of the second electrode finger is narrower than the electrode finger width of the first electrode finger.

[0009] According to the present invention, it is possible to provide an acoustic wave device having a double-sided IDT structure with improved frequency adjustment function during manufacturing.

[0010] FIG. 1 illustrates a plan view and a cross-sectional view of an elastic wave device according to an embodiment. FIG. 2A is a graph showing the relationship between the thickness of a dielectric film and the amount of change in resonant frequency in an elastic wave device having a single-sided IDT structure and an elastic wave device having a double-sided IDT structure. FIG. 2B is a graph showing the relationship between the thickness of a dielectric film and the amount of change in anti-resonant frequency in an elastic wave device having a single-sided IDT structure and an elastic wave device having a double-sided IDT structure. FIG. 3 is a cross-sectional view illustrating the electrode finger duty, electrode finger pitch, and wavelength of an elastic wave device. FIG. 4A is a graph showing the relationship between the electrode finger duty of the lower (upper) IDT electrode and the rate of change in frequency when the electrode finger duty of the upper (lower) IDT electrode is fixed to 0.2 in the elastic wave device according to Example 1. FIG. 4B is a graph showing the relationship between the electrode finger duty of the lower (upper) IDT electrode and the rate of change in frequency when the electrode finger duty of the upper (lower) IDT electrode is fixed to 0.4 in the elastic wave device according to Example 1. 4C is a graph showing the relationship between the electrode finger duty of the lower (upper) IDT electrode and the rate of change of frequency when the electrode finger duty of the upper (lower) IDT electrode is fixed to 0.6 in the elastic wave device according to Example 1. 4D is a graph showing the relationship between the electrode finger duty of the lower (upper) IDT electrode and the rate of change of frequency when the electrode finger duty of the upper (lower) IDT electrode is fixed to 0.8 in the elastic wave device according to Example 1. 5 is a graph showing the relationship between the electrode finger duty of the lower (upper) IDT electrode and the capacitance of the elastic wave resonator when the electrode finger duty of the upper (lower) IDT electrode is fixed to 0.45 in the elastic wave device according to Example 1. 6A is a graph showing the relationship between the thickness of the dielectric film and the resonant frequency in the elastic wave device according to Example 1. 6B is a graph showing the relationship between the thickness of the dielectric film and the amount of change of the resonant frequency in the elastic wave device according to Example 1. 7 is a graph showing the relationship between the electrode finger duty of the lower (upper) IDT electrode and the frequency change rate when the electrode finger duty of the upper (lower) IDT electrode is fixed at 0.5 in the elastic wave device of Example 2. FIG. 8 is a graph showing the resonance band ratio when the electrode finger duty of the upper IDT electrode and the electrode finger duty of the lower IDT electrode are changed in the elastic wave device of Example 1.FIG. 9 is a graph showing the relationship between the electrode finger duty of the upper IDT electrode and the electrode finger duty of the lower IDT electrode for each resonance band ratio of the elastic wave device in accordance with Example 1. In FIG.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component arrangements, and connection configurations shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components that are not recited in independent claims will be described as optional components. Furthermore, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0012] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

[0013] In the circuit configurations of the present disclosure, "connected" includes not only direct connection by connection terminals and / or wiring conductors, but also electrical connection via matching elements such as inductors and capacitors, and switch circuits. "Connected between A and B" means connected to both A and B between A and B.

[0014] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not only represent strict meanings, but also include substantially equivalent ranges, for example, including an error of a few percent.

[0015] In the following embodiments, the passband of a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum value of insertion loss within the passband.

[0016] Furthermore, in the resonance characteristics of the elastic wave device of the present disclosure, the resonance frequency and anti-resonance frequency are derived, for example, by contacting an RF probe with two input / output electrodes of the elastic wave device when the elastic wave device is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) using a network analyzer or the like.

[0017] In this disclosure, the term "major component of a material" refers to a component that accounts for more than 50% by weight of the material. The major component may be present in any one of single crystal, polycrystalline, and amorphous states, or a mixture of these states.

[0018] In addition, in the present disclosure, two signals being in phase means that the phases are substantially the same, including a range in which the phases of the two signals differ by about 30%, for example.

[0019] 1A and 1B are a plan view and a cross-sectional view, respectively, of an elastic wave device 1 according to an embodiment of the present invention. 1A is a plan view (see-through) of a main surface 31a of a piezoelectric layer 31 from the positive side of the z-axis. 1B is a cross-sectional view taken along line Ib-Ib in 1A, viewed from the negative side of the y-axis.

[0020] 1 , acoustic wave device 1 includes substrate 3, IDT electrodes 10 and 20, reflective electrode 15, and dielectric film 41. Note that acoustic wave device 1 shown in FIG. 1 is intended to illustrate a typical structure of an acoustic wave resonator that constitutes acoustic wave device 1, and the number and lengths of electrode fingers that constitute IDT electrodes 10 and 20 and reflective electrode 15 are not limited to this.

[0021] The substrate 3 has piezoelectric properties and includes a piezoelectric layer 31, a low acoustic velocity layer 32, a high acoustic velocity layer 33, and a support substrate 34, as shown in FIG.

[0022] The piezoelectric layer 31 has opposing main surfaces 31a and 31b and is disposed above (in the positive direction of the z-axis) a laminate composed of the low acoustic velocity layer 32, the high acoustic velocity layer 33, and the support substrate 34. The piezoelectric layer 31 may be made of, for example, lithium tantalate or lithium niobate, or a material containing any of these materials as its main component. Alternatively, the piezoelectric layer 31 may be made of a material such as quartz or potassium nitride.

[0023] The low acoustic velocity layer 32 is an example of a first dielectric layer, and is disposed between the support substrate 34 and the piezoelectric layer 31. The shear wave velocity of the low acoustic velocity layer 32 is lower than the shear wave velocity of the piezoelectric layer 31 and the high acoustic velocity layer 33. The low acoustic velocity layer 32 contains, for example, at least one of silicon oxide and silicon oxynitride. The low acoustic velocity layer 32 may also be made of a dielectric such as silicon oxide, silicon oxynitride, glass, lithium oxide, tantalum pentoxide, or a compound in which fluorine, carbon, or boron is added to silicon oxide, or a material containing any of the above materials as a main component.

[0024] The high acoustic velocity layer 33 is an example of a second dielectric layer and is disposed between the support substrate 34 and the low acoustic velocity layer 32. The shear wave acoustic velocity of the high acoustic velocity layer 33 is higher than the shear wave acoustic velocity of the low acoustic velocity layer 32. The high acoustic velocity layer 33 includes, for example, at least one of silicon nitride and silicon oxynitride. The high acoustic velocity layer 33 may also be made of a piezoelectric material such as silicon nitride, silicon oxynitride, aluminum nitride, aluminum oxide, lithium niobate, or quartz; a ceramic material such as sapphire, magnesia, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite; a dielectric material such as DLC (diamond-like carbon), diamond, or glass; a semiconductor material such as silicon or gallium nitride; a resin; or a material containing any of the above materials as a main component.

[0025] The support substrate 34 is disposed below the high acoustic velocity layer 33 (in the negative direction of the z-axis), and supports the IDT electrodes 10 and 20, the reflective electrode 15, the piezoelectric layer 31, the low acoustic velocity layer 32, and the high acoustic velocity layer 33. The support substrate 34 can be made of, for example, a piezoelectric material such as silicon, aluminum nitride, aluminum oxide, lithium niobate, or quartz; a ceramic material such as sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite; a dielectric material such as diamond or glass; a semiconductor material such as gallium nitride; a resin; or a material containing any of the above materials as a main component.

[0026] The laminated body made up of the low acoustic velocity layer 32, the high acoustic velocity layer 33, and the support substrate 34 is an example of a support member.

[0027] The high acoustic velocity layer 33 may be omitted. In this case, the support member is a laminate of the low acoustic velocity layer 32 and the support substrate 34, and the shear wave acoustic velocity of the low acoustic velocity layer 32 is lower than the shear wave acoustic velocity of the piezoelectric layer 31 and the support substrate 34.

[0028] The low acoustic velocity layer 32 and the high acoustic velocity layer 33 may be omitted. In this case, the support member is a support substrate 34, and the acoustic velocity of the bulk wave in the support substrate 34 is faster than the acoustic velocity of the shear wave propagating through the piezoelectric layer 31. In this case, the support substrate 34 may be made of, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectric materials such as aluminum oxide, silicon oxynitride, DLC, and diamond; semiconductors such as silicon; or materials containing the above materials as their main components. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl ２ O ４ , FeAl ２ O ４ , ZnAl ２ O ４ , MnAl ２ O ４Examples include:

[0029] Furthermore, instead of the laminate of the support substrate 34, the high acoustic velocity layer 33, and the low acoustic velocity layer 32, the support member may be a laminate composed of the support substrate 34 and an energy trapping layer.

[0030] The energy trapping layer is disposed between the support substrate 34 and the piezoelectric layer 31 and consists of one or more layers, and the shear wave acoustic velocity propagating through at least one of the layers is greater than the shear wave acoustic velocity propagating near the piezoelectric layer 31. For example, the energy trapping layer may have a laminated structure of a low acoustic velocity layer and a high acoustic velocity layer. The low acoustic velocity layer is a film in which the shear wave acoustic velocity in the low acoustic velocity layer is slower than the shear wave acoustic velocity propagating through the piezoelectric layer. The high acoustic velocity layer is a film in which the shear wave acoustic velocity in the high acoustic velocity layer is faster than the shear wave acoustic velocity propagating through the piezoelectric layer. The support substrate may also be the high acoustic velocity layer.

[0031] The energy trapping layer may also be an acoustic impedance layer having a configuration in which low acoustic impedance layers with a relatively low acoustic impedance and high acoustic impedance layers with a relatively high acoustic impedance are alternately stacked.

[0032] The IDT electrode 10 is an example of a first IDT electrode and is arranged on the main surface 31a as shown in Fig. 1B. As shown in Fig. 1A, the IDT electrode 10 has a plurality of electrode fingers 11a and a plurality of electrode fingers 11b, and busbar electrodes 12a and 12b. The plurality of electrode fingers 11a are an example of a plurality of third electrode fingers and are arranged parallel to each other. The plurality of electrode fingers 11b are an example of a plurality of fourth electrode fingers and are arranged parallel to each other. The plurality of electrode fingers 11a and the plurality of electrode fingers 11b are arranged parallel to each other so as to be interdigitated with each other.

[0033] The busbar electrode 12a is an example of a first busbar electrode and is configured to connect one ends of the electrode fingers 11a to each other. The busbar electrode 12a extends in a direction (x-axis direction) intersecting the extension direction of the electrode fingers 11a (y-axis direction in FIG. 1 ).

[0034] The busbar electrode 12b is an example of a second busbar electrode and is configured to connect one ends of the electrode fingers 11b to each other. The busbar electrode 12b extends in a direction (x-axis direction) intersecting the extension direction of the electrode fingers 11b (y-axis direction in FIG. 1 ). The busbar electrodes 12a and 12b are arranged opposite each other with the electrode fingers 11a and the electrode fingers 11b sandwiched therebetween. The other ends of the electrode fingers 11a face the busbar electrode 12b, and the other ends of the electrode fingers 11b face the busbar electrode 12a.

[0035] The reflective electrodes 15 are arranged on both sides of the IDT electrode 10 so as to be adjacent to the IDT electrode 10 in a direction (x-axis direction) perpendicular to the extension direction of the electrode fingers 11 a and the electrode fingers 11 b. The reflective electrodes 15 are configured to confine a predetermined high-frequency signal that resonates in the IDT electrode 10 within the IDT electrode 10. Note that the reflective electrodes 15 may not be included in the acoustic wave device 1.

[0036] The IDT electrode 20 is an example of a second IDT electrode and is arranged on the principal surface 31b as shown in FIG. 1B . The IDT electrode 20 includes a plurality of electrode fingers 21a and a plurality of electrode fingers 21b, and busbar electrodes 22a and 22b (not shown). The plurality of electrode fingers 21a are arranged parallel to one another. The plurality of electrode fingers 21b are arranged parallel to one another. The plurality of electrode fingers 21a and the plurality of electrode fingers 21b are arranged parallel to one another so as to be interdigitated with one another. When the principal surfaces 31a and 31b are viewed in plan, the plurality of electrode fingers 21a overlap with the plurality of electrode fingers 11a in a one-to-one relationship, and the plurality of electrode fingers 21b overlap with the plurality of electrode fingers 11b in a one-to-one relationship. The plurality of electrode fingers 11a and the plurality of electrode fingers 21a are excited in phase, and the plurality of electrode fingers 11b and the plurality of electrode fingers 21b are excited in phase. This makes it possible to suppress spurious responses such as higher-order modes.

[0037] The IDT electrode 20 is covered with a low acoustic velocity layer 32 (supporting member), which allows unwanted waves to leak toward the low acoustic velocity layer 32 (supporting member).

[0038] The plurality of electrode fingers 21 a and the plurality of electrode fingers 11 a do not have to completely overlap one-to-one in the plan view, but it is sufficient that each of the plurality of electrode fingers 21 a at least partially overlaps one-to-one with one of the plurality of electrode fingers 11 a. Furthermore, the plurality of electrode fingers 21 b and the plurality of electrode fingers 11 b do not have to completely overlap one-to-one in the plan view, but it is sufficient that each of the plurality of electrode fingers 21 b at least partially overlaps one-to-one with one of the plurality of electrode fingers 11 b.

[0039] Furthermore, reflective electrodes may be arranged on both sides of the IDT electrode 20 so as to be adjacent to the IDT electrode 20 in a direction (x-axis direction) perpendicular to the extension direction of the plurality of electrode fingers 21a and the plurality of electrode fingers 21b on the main surface 31b.

[0040] Furthermore, a dielectric film or an insulating film may be disposed between the IDT electrode 10 and the main surface 31a and / or between the IDT electrode 20 and the main surface 31b.

[0041] The IDT electrode 10 has a layered structure of titanium (Ti), aluminum (Al), and titanium (Ti). However, the IDT electrode 10 is not limited to the above layered structure, and may be made of a material containing at least one of copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), and chromium (Cr), or an alloy or layered film containing some of these metals.

[0042] The IDT electrode 20 has a layered structure of titanium (Ti), aluminum (Al), platinum (Pt), and titanium (Ti). The IDT electrode 20 is not limited to the above layered structure, and may be made of a material containing at least one of copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), and chromium (Cr), or an alloy or layered film containing some of these metals. From the viewpoint of acoustic impedance, the IDT electrode 20 preferably contains a material with a higher density than the low acoustic velocity layer 32 disposed around the IDT electrode 20.

[0043] The dielectric film 41 is disposed on the main surface 31a so as to cover at least a portion of the IDT electrode 10. The dielectric film 41 includes, for example, at least one of silicon oxide, silicon nitride, and silicon oxynitride. The dielectric film 41 may also be made of a material such as tantalum pentoxide, amorphous silicon, polycrystalline silicon, aluminum oxide, aluminum nitride, or silicon carbide, or may be a laminate film of these materials.

[0044] According to the above-described configuration of elastic wave device 1, IDT electrodes 10 and 20 and piezoelectric layer 31 form a single elastic wave resonator having a resonant frequency at which the impedance is minimized and an antiresonant frequency at which the impedance is maximized.

[0045] In elastic wave device 1 according to this embodiment, IDT electrodes 10 and 20 may have a piston structure. Specifically, a difference in sound velocity between the center and tip portions of the electrode fingers may be created by thickening the tip portions of the electrode fingers (2D piston) or by arranging a load film at the tip portions of the electrode fingers (3D piston). This makes it possible to suppress transverse mode ripples generated in elastic wave device 1.

[0046] [2 Frequency Adjustment Function of Elastic Wave Devices According to Comparative Examples] The frequency adjustment function of elastic wave devices having IDT electrodes will now be described. FIG. 2A is a graph showing the relationship between the thickness of the dielectric film and the amount of change in resonant frequency for elastic wave devices according to Comparative Examples 1 and 2. FIG. 2B is a graph showing the relationship between the thickness of the dielectric film and the amount of change in anti-resonant frequency for elastic wave devices according to Comparative Examples 1 and 2. The vertical axis of FIG. 2A represents the difference frequency (amount of change in resonant frequency) between the resonant frequency when dielectric film 41 is not provided and the resonant frequency when dielectric film 41 is provided. The vertical axis of FIG. 2B represents the difference frequency (amount of change in anti-resonant frequency) between the anti-resonant frequency when dielectric film 41 is not provided and the anti-resonant frequency when dielectric film 41 is provided.

[0047] The elastic wave device of Comparative Example 1 has the same configuration as elastic wave device 1 of the embodiment, including substrate 3, IDT electrode 10, reflective electrode 15, and dielectric film 41, but does not include IDT electrode 20 (as indicated in FIGS. 2A and 2B as "IDT electrode arranged only on the top surface"). The electrode finger duty of IDT electrode 10 is 0.5.

[0048] The elastic wave device in accordance with Comparative Example 2 has the same configuration as elastic wave device 1 in accordance with the preferred embodiment, including substrate 3, IDT electrodes 10 and 20, reflective electrode 15, and dielectric film 41 (indicated in FIGS. 2A and 2B as "IDT electrodes arranged on both sides"), except that the electrode finger duties of IDT electrodes 10 and 20 are both 0.5.

[0049] As shown in FIG. 2A , the resonant frequency change increases linearly as the thickness of the dielectric film 41 increases. Furthermore, as shown in FIG. 2B , the antiresonant frequency change increases linearly as the thickness of the dielectric film 41 increases. This indicates that by adjusting the thickness of the dielectric film 41 disposed on the IDT electrode 10, variations in the resonant frequency and antiresonant frequency during manufacturing can be suppressed. Here, the elastic wave device of Comparative Example 2 (IDT electrodes arranged on both surfaces) exhibits a smaller slope of the frequency change with respect to variations in the thickness of the dielectric film 41 than the elastic wave device of Comparative Example 1 (IDT electrodes arranged only on the top surface). That is, although the elastic wave device of Comparative Example 2 (IDT electrodes arranged on both surfaces) has IDT electrodes formed on both main surfaces of the piezoelectric layer 31, which increases the factors that contribute to frequency variation, the frequency adjustment function of the dielectric film 41 is reduced compared to the elastic wave device of Comparative Example 1 (IDT electrodes arranged only on the top surface). Therefore, it is difficult to stabilize the resonant frequency and antiresonant frequency during manufacturing in the elastic wave device of Comparative Example 2 (IDT electrodes arranged on both surfaces).

[0050] [3 Electrode Finger Duty and Wavelength of IDT Electrodes] Next, the electrode finger duty of an acoustic wave device will be defined. FIG. 3 is a cross-sectional view illustrating the electrode finger duty, electrode finger pitch, and wavelength of acoustic wave device 1 according to an embodiment. The drawing shows a cross-sectional view of piezoelectric layer 31, low acoustic velocity layer 32, IDT electrodes 10 and 20, and dielectric film 41 that constitute acoustic wave device 1 according to an embodiment.

[0051] The wavelength λ1 of the IDT electrode 10 is a unit of length defined by the repetition period of the electrode fingers 11a (or 11b). The electrode finger pitch P1 of the IDT electrode 10 is ½ of the wavelength λ1.

[0052] The electrode finger duty D1 of the IDT electrode 10 is the line width (electrode finger width) occupancy rate of the electrode fingers 11a and 11b. This is the ratio of the line width L1 to the sum of the line width L1 and the space width S1, and is defined as L1 / (L1+S1). The cross section of the electrode fingers 11a and 11b is trapezoidal as shown in FIG. 3 due to the etching process using photolithography. Corresponding to this electrode finger shape, the line width L1 is defined as the line segment of the electrode finger that contacts the principal surface 31a (the length of the lower base of the trapezoid). Therefore, the electrode finger pitch P1 is defined as the length from the left end of the line segment that contacts the principal surface 31a of the electrode finger 11a to the left end of the line segment that contacts the principal surface 31a of the electrode finger 11b adjacent to the electrode finger 11a to the right (positive direction of the x-axis). Similarly, wavelength λ1 is defined as the length from the left end of the line segment tangent to the major surface 31a of the electrode finger 11a to the left end of the line segment tangent to the major surface 31a of the electrode finger 11a that is closest to the right of the electrode finger 11a (positive direction of the x-axis).

[0053] The wavelength λ2, electrode finger pitch P2, and electrode finger duty D2 of the IDT electrode 20 are defined in the same manner as the wavelength λ1, electrode finger pitch P1, and electrode finger duty D1 of the IDT electrode 10, respectively.

[0054] In the IDT electrode 10, when the interval between adjacent electrode fingers is not constant, the wavelength λ1 of the IDT electrode 10 is the average wavelength λ1 of the IDT electrode 10. ＡＶＥ The mean wavelength λ1 of the IDT electrode 10 is defined as follows: ＡＶＥis defined as 2×Di / (Ni-1), where Ni is the total number of electrode fingers 11a, 11b included in the IDT electrode 10, and Di is the center-to-center distance between the electrode finger located at one end of the IDT electrode 10 and the electrode finger located at the other end in the acoustic wave propagation direction.

[0055] In addition, when the IDT electrode 10 includes a so-called withdrawal electrode, the average wavelength λ1 ＡＶＥ In calculating the total number of electrode fingers Ni, the number of withdrawal electrodes is excluded from the total number of electrode fingers Ni, and the line width L1 of the withdrawal electrode and one of the two spaces (space width S1) adjacent to the withdrawal electrode are excluded from the center-to-center distance Di.

[0056] The withdrawal electrodes include floating withdrawal electrodes, polarity-reversed electrodes, and solid electrodes. A floating withdrawal electrode is an electrode finger that is not connected to either of the two opposing busbar electrodes and is arranged parallel to the electrode fingers connected to one of the two busbar electrodes. A polarity-reversed electrode is an electrode finger that is connected to the same busbar electrode as the busbar electrodes to which the adjacent electrode fingers are connected and is arranged parallel to the adjacent electrode fingers. A solid electrode is an electrode finger that has an electrode finger width that is at least twice the average electrode finger width of the electrode fingers excluding the solid electrodes and is arranged parallel to the electrode fingers excluding the solid electrodes.

[0057] Furthermore, when the spacing between adjacent electrode fingers in the IDT electrode 20 is not constant and when the IDT electrode 20 includes withdrawal electrodes, the wavelength λ2 of the IDT electrode 20 is ＡＶＥ is defined as the mean wavelength λ2 ＡＶＥ The calculation method is the average wavelength λ1 of the IDT electrode 10. ＡＶＥ The calculation method is the same as that of

[0058] Furthermore, when the IDT electrode 10 has a so-called 2D piston structure in which the electrode finger width at the tip is wider than at the center, the wavelength λ1 is defined as the wavelength at the center. Furthermore, when the IDT electrode 10 has a 2D piston structure but the electrode finger width at the tip is not wider than at the center, the wavelength λ1 is defined as the average wavelength in the range excluding both ends of the overlap width region of the electrode fingers. Furthermore, when the electrode finger width varies periodically in the overlap width direction of the electrode fingers, the wavelength λ1 is defined as the average wavelength in the overlap width region of the electrode fingers.

[0059] When the IDT electrode 20 has a 2D piston structure, the method for calculating the wavelength λ2 is the same as the method for calculating the wavelength λ1. When the electrode finger width of the IDT electrode 20 varies periodically in the cross width direction of the electrode fingers, the method for calculating the wavelength λ2 is the same as the method for calculating the wavelength λ1.

[0060] In addition, when the electrode finger duty D1 of the IDT electrode 10 is not constant, the electrode finger duty D1 of the IDT electrode 10 is equal to the average electrode finger duty D1 of the IDT electrode 10. ＡＶＥ The average electrode finger duty D1 of the IDT electrode 10 is defined as follows: ＡＶＥ The total number of electrode fingers 11a and 11b included in the IDT electrode 10 is Ni, and the total line width obtained by adding the line width L1 of (Ni-1) electrode fingers is L1. ＡＬＬ The total space width obtained by adding up the (Ni-1) space widths S1 included in the IDT electrode 10 is S1 ＡＬＬ In this case, L1 ＡＬＬ / (L1 ＡＬＬ +S1 ＡＬＬ ) is defined as

[0061] In addition, when the electrode finger duty D2 of the IDT electrode 20 is not constant, the electrode finger duty D2 of the IDT electrode 20 is equal to the average electrode finger duty D2 of the IDT electrode 20. ＡＶＥ The average electrode finger duty D2 of the IDT electrode 20 is defined as ＡＶＥ The calculation method is to calculate the average electrode finger duty D1 of the IDT electrode 10. ＡＶＥ The calculation method is the same as that of

[0062] When the IDT electrode 10 includes a so-called withdrawal electrode, the average electrode finger duty D1 ＡＶＥ When calculating the total line width L1 ＡＬＬ The line width L1 of the withdrawal electrode is excluded, and the total space width S1 ＡＬＬ One of the two spaces (space width S1) adjacent to the withdrawal electrode is excluded.

[0063] Furthermore, when the IDT electrode 20 includes withdrawal electrodes, the average electrode finger duty D2 ＡＶＥ The calculation method of the average electrode finger duty D1 when the IDT electrode 10 includes withdrawal electrodes is ＡＶＥ The calculation method is the same as that of

[0064] Furthermore, when the IDT electrode 10 has a 2D piston structure and the electrode finger width at the tip end is wider than that at the center, the electrode finger duty D1 of the IDT electrode 10 is defined as the electrode finger duty at the center. Furthermore, when the IDT electrode 10 has a 2D piston structure but the electrode finger width at the tip end is not wider than that at the center, the electrode finger duty D1 of the IDT electrode 10 is defined as the average electrode finger duty in the range excluding both ends of the overlap width region of the electrode fingers. Furthermore, when the electrode finger width varies periodically in the overlap width direction of the electrode fingers, the electrode finger duty D1 of the IDT electrode 10 is defined as the average electrode finger duty in the overlap width region of the electrode fingers.

[0065] When the IDT electrode 20 has a 2D piston structure, the method for calculating the electrode finger duty D2 of the IDT electrode 20 is the same as the method for calculating the electrode finger duty D1. When the electrode finger width of the IDT electrode 20 varies periodically in the cross width direction of the electrode fingers, the method for calculating the electrode finger duty D2 of the IDT electrode 20 is the same as the method for calculating the electrode finger duty D1.

[0066] Furthermore, when the electrode fingers of IDT electrodes 10 and 20 have a curved shape, the magnitude relationship between electrode finger duty D1 of IDT electrode 10 and electrode finger duty D2 of IDT electrode 20 can be evaluated in terms of the magnitude relationship between the area occupied by electrode fingers 11a and 11b in the intersection region of electrode fingers 11a and 11b of IDT electrode 10 and the area occupied by electrode fingers 21a and 21b in the intersection region of electrode fingers 21a and 21b of IDT electrode 20. That is, when the main surfaces 31a and 31b are viewed in a plan view, each of the multiple electrode fingers 11a of the IDT electrode 10 at least partially overlaps with each of the multiple electrode fingers 21a of the IDT electrode 20 in a one-to-one relationship, and each of the multiple electrode fingers 11b of the IDT electrode 10 at least partially overlaps with each of the multiple electrode fingers 21b of the IDT electrode 20 in a one-to-one relationship, and if the area occupied by the electrode fingers 21a and 21b of the IDT electrode 20 in the intersection region is smaller than the area occupied by the electrode fingers 11a and 11b of the IDT electrode 10 in the intersection region, then the electrode finger duty D2 of the IDT electrode 20 is defined as being smaller than the electrode finger duty D1 of the IDT electrode 10.

[0067] The wavelength λ1, electrode finger pitch P1, and electrode finger duty D1 of the IDT electrode 10, as well as the wavelength λ2, electrode finger pitch P2, and electrode finger duty D2 of the IDT electrode 20, can be measured by using a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a transmission electron microscope (TEM) to view the main surfaces 31 a and 31 b of the piezoelectric layer 31 on which the IDT electrodes 10 and 20 are formed in a plan view and / or to view a cut surface perpendicular to the extension direction of the electrode fingers 11 a, 11 b, 21 a, and 21 b in a cross-sectional view, thereby measuring the line widths L1 and L2 and the space widths S1 and S2.

[0068] The area occupied by the electrode fingers in the crossing region of the IDT electrodes 10 and 20 can be obtained by subjecting an image of the IDT electrode surface taken with an optical microscope or SEM to binarization processing or the like.

[0069] [4 Frequency Adjustment Function of Elastic Wave Device] Next, it will be described how elastic wave device 1 according to the present embodiment can improve the frequency adjustment function compared to the elastic wave device according to the comparative example. Elastic wave device 1 according to the present embodiment can improve the frequency adjustment function compared to the elastic wave device according to the comparative example by making the electrode finger duty of IDT electrode 20 smaller than the electrode finger duty of IDT electrode 10. The frequency adjustment function of elastic wave device 1 according to the embodiment will be described using the elastic wave device according to Example 1 as an example. The elastic wave device according to Example 1 is an example of elastic wave device 1 according to the embodiment. Table 1 shows the structural parameters of the elastic wave device according to Example 1.

[0070]

[0071] 4A is a graph showing the relationship between the electrode finger duty of the IDT electrode 20(10) and the rate of change of frequency when the electrode finger duty of the IDT electrode 10(20) is fixed to 0.2 in the elastic wave device in accordance with Example 1. FIG. 4B is a graph showing the relationship between the electrode finger duty of the IDT electrode 20(10) and the rate of change of frequency when the electrode finger duty of the IDT electrode 10(20) is fixed to 0.4 in the elastic wave device having a double-sided IDT structure. FIG. 4C is a graph showing the relationship between the electrode finger duty of the IDT electrode 20(10) and the rate of change of frequency when the electrode finger duty of the IDT electrode 10(20) is fixed to 0.6 in the elastic wave device having a double-sided IDT structure. FIG. 4D is a graph showing the relationship between the electrode finger duty of the IDT electrode 20(10) and the rate of change of frequency when the electrode finger duty of the IDT electrode 10(20) is fixed to 0.8 in the elastic wave device having a double-sided IDT structure. The relationship between the electrode finger duty and the frequency change rate shown in FIGS. 4A to 4D was evaluated by a simulation using the finite element method.

[0072] In each of Figures 4A to 4D, the vertical axis shows the change in resonant frequency (frequency change rate (MHz / nm)) (per unit thickness of dielectric film 41) obtained by changing the thickness of dielectric film 41 from 10 to 100 nm.

[0073] 4A to 4D, the frequency change rate at the point where the electrode finger duty D1 of the IDT electrode 10 (hereinafter sometimes referred to as the upper surface duty) and the electrode finger duty D2 of the IDT electrode 20 (hereinafter sometimes referred to as the lower surface duty) are equal increases as both the upper surface duty and the lower surface duty decrease. Furthermore, the frequency change rate increases as the upper surface duty is fixed and the lower surface duty is made smaller than the upper surface duty. On the other hand, the frequency change rate decreases when the lower surface duty is fixed and the upper surface duty is made smaller than the lower surface duty.

[0074] 5 is a graph showing the relationship between the electrode finger duty of IDT electrode 20 (10) and the capacitance of the acoustic wave resonator including IDT electrodes 10 and 20 in the acoustic wave device according to Example 1 when the electrode finger duty of IDT electrode 10 (20) is fixed at 0.45. It can be seen from the graph that the capacitance of the acoustic wave resonator decreases as the electrode finger duty of IDT electrodes 10 and 20 decreases, and that the difference in capacitance change is small regardless of whether the top surface duty or the bottom surface duty is changed. Note that a decrease in the capacitance of the acoustic wave resonator has the disadvantage of requiring the acoustic wave device to be larger in size to ensure the corresponding capacitance.

[0075] 4A to 4D and 5, it can be seen that by making the bottom surface duty smaller than the top surface duty, it is possible to increase the frequency change rate while minimizing capacitance reduction in the acoustic wave resonator. In other words, by making electrode finger duty D2 of multiple electrode fingers 21 a and 21 b included in IDT electrode 20 smaller than electrode finger duty D1 of multiple electrode fingers 11 a and 11 b included in IDT electrode 10, it is possible to improve the frequency adjustment capability while suppressing capacitance reduction in the acoustic wave resonator including IDT electrodes 10 and 20.

[0076] 4A to 4D , the effect of improving the frequency adjustment capability while suppressing a decrease in capacitance of the acoustic wave resonator can be obtained when the electrode finger duty D1 of IDT electrode 10 is 0.2 or more and 0.8 or less. If the electrode finger duty D1 is less than 0.2, the electrode finger resistance of IDT electrodes 10 and 20 increases, resulting in greater signal transmission loss due to resistance loss. If the electrode finger duty D1 is greater than 0.8, the risk of electrostatic breakdown of IDT electrode 10 increases.

[0077] Note that the elastic wave device 1 according to this preferred embodiment is not limited to the case where the electrode finger duty D2 of all the electrode fingers included in the IDT electrode 20 is smaller than the electrode finger duty D1 of all the electrode fingers included in the IDT electrode 10. That is, it is sufficient that the electrode finger duty D2 of at least one second electrode finger among the plurality of electrode fingers 21 a and 21 b included in the IDT electrode 20 is smaller than the electrode finger duty D1 of at least one first electrode finger among the plurality of electrode fingers 11 a and 11 b included in the IDT electrode 10. Note that, when the principal surfaces 31 a and 31 b are viewed in plan, the first electrode finger and the second electrode finger at least partially overlap. Furthermore, the first electrode finger and the second electrode finger are excited in phase.

[0078] This provides the effect of improving the frequency adjustment capability of acoustic wave device 1 while suppressing a decrease in capacitance of the acoustic wave resonator including IDT electrodes 10 and 20 .

[0079] In addition, when the electrode fingers 11 a of the IDT electrode 10 and the electrode fingers 21 a of the IDT electrode 20 at least partially overlap one-to-one in the above-mentioned planar view, and when the electrode fingers 11 b of the IDT electrode 10 and the electrode fingers 21 b of the IDT electrode 20 at least partially overlap one-to-one in the above-mentioned planar view, the configuration in which the electrode finger duty D2 is smaller than the electrode finger duty D1 can be replaced with a configuration in which the electrode finger width of the electrode fingers included in the IDT electrode 20 is narrower than the electrode finger width of the electrode fingers included in the IDT electrode 10.

[0080] That is, in the above-mentioned planar view, each of the multiple electrode fingers included in the IDT electrode 10 overlaps at least partially with one of the multiple electrode fingers included in the IDT electrode 20 in a one-to-one relationship, and the electrode finger width of each of the multiple electrode fingers included in the IDT electrode 20 is narrower than the electrode finger width of each of the multiple electrode fingers included in the IDT electrode 10.

[0081] As a result, the electrode finger duty D2 of the multiple electrode fingers 21 a and 21 b included in the IDT electrode 20 becomes smaller than the electrode finger duty D1 of the multiple electrode fingers 11 a and 11 b included in the IDT electrode 10, making it possible to improve the frequency adjustment capability while suppressing a decrease in the capacitance of the acoustic wave resonator including the IDT electrodes 10 and 20.

[0082] Note that the elastic wave device 1 according to this preferred embodiment is not limited to the case where the electrode finger width of all the electrode fingers included in the IDT electrode 20 is narrower than the electrode finger width of all the electrode fingers included in the IDT electrode 10. That is, it is sufficient that the electrode finger width of a second electrode finger, which is at least one of the plurality of electrode fingers 21 a and 21 b included in the IDT electrode 20, is narrower than the electrode finger width of a first electrode finger, which is at least one of the plurality of electrode fingers 11 a and 11 b included in the IDT electrode 10. Note that, in the above plan view, each of the plurality of electrode fingers included in the IDT electrode 10 at least partially overlaps with one of the plurality of electrode fingers included in the IDT electrode 20 in a one-to-one relationship, and the first electrode finger and the second electrode finger at least partially overlap.

[0083] This provides the effect of improving the frequency adjustment capability of acoustic wave device 1 while suppressing a decrease in capacitance of the acoustic wave resonator including IDT electrodes 10 and 20 .

[0084] 6A is a graph showing the relationship between the thickness of the dielectric film 41 and the resonant frequency in the elastic wave device according to Example 1. As shown in the figure, the change in the resonant frequency relative to the change in the thickness of the dielectric film 41 is not linear. In this case, the process of adjusting the frequency of the elastic wave device becomes complicated. Furthermore, since a thicker dielectric film 41 increases mechanical loss, a thinner dielectric film 41 is desirable.

[0085] 6B is a graph showing the relationship between the thickness of the dielectric film 41 and the amount of change in the resonant frequency in the elastic wave device in accordance with Example 1. In the graph, the vertical axis represents the R-squared value of the amount of change in the resonant frequency shown in FIG. 6A. According to FIG. 6B, by setting the thickness of the dielectric film 41 to a range greater than 0 and equal to or less than 160 nm (=0.08λ), the R-squared value of the amount of change in the resonant frequency relative to the thickness of the dielectric film 41 can be reduced. ２ is 0.99 or more, improving the accuracy of frequency adjustment during manufacturing. Furthermore, by setting the thickness of dielectric film 41 to 160 nm or less, the mechanical loss of the elastic wave resonator can be reduced.

[0086] 7 is a graph showing the relationship between the electrode finger duty of IDT electrode 20 (10) and the frequency change rate when the electrode finger duty of IDT electrode 10 (20) is fixed to 0.5 in the acoustic wave device in accordance with Example 2. The relationship between the electrode finger duty and the frequency change rate shown in FIG. 7 was evaluated by simulation using the finite element method.

[0087] The acoustic wave device in accordance with the second embodiment differs from the acoustic wave device in accordance with the first embodiment only in the material configuration of the dielectric film 41. The dielectric film 41 in the acoustic wave device in accordance with the second embodiment is made of silicon nitride.

[0088] 7 shows that by making the bottom surface duty smaller than the top surface duty, the rate of frequency change of the acoustic wave resonator can be increased while suppressing a decrease in capacitance. In other words, by making the electrode finger duty D2 of IDT electrode 20 smaller than the electrode finger duty D1 of IDT electrode 10, it is possible to improve the frequency adjustment capability while suppressing a decrease in capacitance of the acoustic wave resonator formed by IDT electrodes 10 and 20.

[0089] FIG. 8 is a graph showing the resonance band ratio when the electrode finger duty D1 of the upper IDT electrode (IDT electrode 10) and the electrode finger duty D2 of the lower IDT electrode (IDT electrode 20) are changed in the acoustic wave device in accordance with the first embodiment.

[0090] As shown in FIG. 8, by setting the electrode finger duties D1 and D2 within a predetermined range, the resonance frequency band ratio (the value obtained by dividing the frequency difference between the antiresonance frequency and the resonance frequency by the center frequency of the antiresonance frequency and the resonance frequency) of an acoustic wave resonator including the IDT electrodes 10 and 20 can be made 5% or more.

[0091] 9 is a graph showing the relationship between the electrode finger duty D1 of the upper IDT electrode (IDT electrode 10) and the electrode finger duty D2 of the lower IDT electrode (IDT electrode 20) for the resonance bandwidth ratio of the elastic wave device in accordance with Example 1. The graph shows three functions, expressed by the following equation 0, that provide a resonance bandwidth of approximately 5%.

[0092] D2=-2.33×D1 ２ +2.33×D1+0.0739 D2=-1.852×D1+0.626 D1=-2.07×D2 ２ +1.58×D2+0.4337 (Formula 0)

[0093] From Equation 0, the combination of electrode finger duties D1 and D2 that results in a resonance band ratio of the acoustic wave resonator of 5% or more is expressed by Equation 1.

[0094] D2≦-2.33×D1 ２ +2.33×D1+0.0739, and D2≧−1.852×D1+0.626, and D1≦−2.07×D2 ２ +1.58×D2+0.4337 (Formula 1)

[0095] By setting the electrode finger duties D1 and D2 within the range of Equation 1, it is possible to improve the frequency adjustment function and provide an acoustic wave filter having a wide passband.

[0096] [5. Effects, etc.] As described above, elastic wave device 1 according to the embodiment includes a support member including support substrate 34, piezoelectric layer 31 arranged on the support member and having principal surfaces 31 a and 31 b facing each other, IDT electrode 10 arranged on principal surface 31 a, IDT electrode 20 arranged on principal surface 31 b, and dielectric film 41 covering at least a portion of IDT electrode 10, wherein IDT electrode 20 is covered by the support member, and when principal surfaces 31 a and 31 b are viewed in a plan view, a first electrode finger of the plurality of electrode fingers included in IDT electrode 10 at least partially overlaps with a second electrode finger of the plurality of electrode fingers included in IDT electrode 20, and the electrode finger duty of the second electrode finger is smaller than the electrode finger duty of the first electrode finger.

[0097] This makes it possible to increase the rate of change of the resonant frequency (anti-resonant frequency) with respect to changes in the film thickness of dielectric film 41 while suppressing a decrease in capacitance of the acoustic wave resonator including IDT electrodes 10 and 20 by making the electrode finger duty of the second electrode fingers smaller than that of the first electrode fingers. This makes it possible to provide acoustic wave device 1 having a double-sided IDT structure with improved frequency adjustment capability during manufacturing.

[0098] In the acoustic wave devices according to the first and second embodiments, the electrode finger duty D2 of the plurality of electrode fingers included in the IDT electrode 20 is smaller than the electrode finger duty D1 of the plurality of electrode fingers included in the IDT electrode 10.

[0099] This makes it possible to increase the rate of change in the resonant frequency (anti-resonant frequency) with respect to the change in film thickness of the dielectric film 41 while suppressing a decrease in capacitance of the acoustic wave resonator including the IDT electrodes 10 and 20. Therefore, it is possible to provide an acoustic wave device having a double-sided IDT structure with improved frequency adjustment capability during manufacturing.

[0100] Furthermore, for example, in the acoustic wave devices according to the first and second embodiments, when the electrode finger duty of the plurality of electrode fingers included in the IDT electrode 10 is D1 and the electrode finger duty of the plurality of electrode fingers included in the IDT electrode 20 is D2, D2≦−2.33×D1 ２ +2.33×D1+0.0739, and D2≧−1.852×D1+0.626, and D1≦−2.07×D2２ +1.58×D2+0.4337.

[0101] This makes it possible to provide an acoustic wave filter that has an improved frequency adjustment function and a wide passband with a resonance ratio band of 5% or more.

[0102] Furthermore, the elastic wave device 1 according to the embodiment includes a support member including a support substrate 34, a piezoelectric layer 31 arranged on the support member and having opposing principal surfaces 31 a and 31 b, an IDT electrode 10 arranged on principal surface 31 a, an IDT electrode 20 arranged on principal surface 31 b, and a dielectric film 41 covering at least a portion of the IDT electrode 10, wherein the IDT electrode 20 is covered by the support member, and when the principal surfaces 31 a and 31 b are viewed in a plane, each of the multiple electrode fingers included in the IDT electrode 10 and each of the multiple electrode fingers included in the IDT electrode 20 at least partially overlap in a one-to-one relationship, and in the above-mentioned plane view, a first electrode finger of the multiple electrode fingers included in the IDT electrode 10 and a second electrode finger of the multiple electrode fingers included in the IDT electrode 20 at least partially overlap, and the electrode finger width of the second electrode finger is narrower than the electrode finger width of the first electrode finger.

[0103] This makes the electrode finger duty of the second electrode fingers smaller than that of the first electrode fingers, thereby suppressing a decrease in capacitance of the acoustic wave resonator including IDT electrodes 10 and 20 and increasing the rate of change of the resonant frequency (antiresonant frequency) with respect to a change in the film thickness of dielectric film 41. This makes it possible to provide acoustic wave device 1 having a double-sided IDT structure with improved frequency adjustment capability during manufacturing.

[0104] Furthermore, for example, in the acoustic wave devices according to the first and second embodiments, the electrode finger width of each of the plurality of electrode fingers included in IDT electrode 20 is narrower than the electrode finger width of each of the plurality of electrode fingers included in IDT electrode 10 .

[0105] This makes it possible to increase the rate of change in the resonant frequency (anti-resonant frequency) with respect to the change in film thickness of the dielectric film 41 while suppressing a decrease in capacitance of the acoustic wave resonator including the IDT electrodes 10 and 20. Therefore, it is possible to provide an acoustic wave device having a double-sided IDT structure with improved frequency adjustment capability during manufacturing.

[0106] Furthermore, for example, in the acoustic wave device 1, the first electrode fingers and the second electrode fingers are excited in phase.

[0107] This makes it possible to suppress spurious signals such as higher modes.

[0108] Furthermore, for example, in the acoustic wave device 1, the electrode finger duty of the plurality of electrode fingers included in the IDT electrode 10 is not less than 0.2 and not more than 0.8.

[0109] According to this, by setting the electrode finger duty of the IDT electrode 10 to 0.2 or more, an increase in signal transmission loss due to an increase in the electrode finger resistance of the IDT electrodes 10 and 20 can be suppressed, and by setting the electrode finger duty of the IDT electrode 10 to 0.8 or less, the risk of electrostatic breakdown of the IDT electrode 10 can be reduced.

[0110] Furthermore, for example, in the elastic wave device 1, the IDT electrode 10 includes a plurality of electrode fingers 11 a and a plurality of electrode fingers 11 b arranged parallel to each other, a busbar electrode 12 a configured to connect one ends of the plurality of electrode fingers 11 a to each other, and a busbar electrode 12 b configured to connect one ends of the plurality of electrode fingers 11 b to each other and arranged opposite the busbar electrode 12 a across the plurality of electrode fingers 11 a and the plurality of electrode fingers 11 b, and when the repeating period of the plurality of electrode fingers 11 a is wavelength λ1, the film thickness of the dielectric film 41 is 0.08 × λ1 or less.

[0111] According to this, the change in the resonant frequency with respect to the thickness of the dielectric film 41, R ２ is 0.99 or more, improving the accuracy of frequency adjustment during manufacturing. Furthermore, by setting the thickness of dielectric film 41 to 0.08×λ1 or less, the mechanical loss of the elastic wave resonator can be reduced.

[0112] Furthermore, in the acoustic wave device 1, the dielectric film 41 includes at least one of silicon oxide, silicon nitride, and silicon oxynitride.

[0113] Furthermore, in the acoustic wave device 1, the piezoelectric layer 31 includes either lithium tantalate or lithium niobate.

[0114] For example, in the elastic wave device 1, the support member includes a support substrate 34 and a low acoustic velocity layer 32 arranged between the support substrate 34 and the piezoelectric layer 31, the low acoustic velocity layer 32 having a lower shear wave acoustic velocity than the shear wave acoustic velocity of the piezoelectric layer 31 and the support substrate 34.

[0115] According to this, the low acoustic velocity layer 32 is disposed so as to cover at least a part of the IDT electrode 20, so that unwanted waves of higher modes can be efficiently leaked to the low acoustic velocity layer 32 side.

[0116] In the acoustic wave device 1, the low acoustic velocity layer 32 includes at least one of silicon oxide and silicon oxynitride.

[0117] In addition, for example, in the acoustic wave device 1 , the support member further includes a high acoustic velocity layer 33 disposed between the support substrate 34 and the low acoustic velocity layer 32 and having a higher shear wave velocity than the shear wave velocity of the low acoustic velocity layer 32 .

[0118] This makes it possible to suppress unwanted waves in higher modes.

[0119] In the acoustic wave device 1, the high acoustic velocity layer 33 includes at least one of silicon nitride and silicon oxynitride.

[0120] While the elastic wave device according to the present invention has been described above with reference to embodiments and examples, the present invention is not limited to the above embodiments and examples. The present invention also includes other embodiments realized by combining any of the components in the above embodiments and examples, as well as modifications that are conceivable by those skilled in the art without departing from the spirit and scope of the present invention.

[0121] The features of the acoustic wave devices described based on the above embodiments and examples will be described below.

[0122] <1> An acoustic wave device comprising: a support member including a support substrate; a piezoelectric layer disposed on the support member and having first and second principal surfaces opposing each other; a first IDT electrode disposed on the first principal surface; a second IDT electrode disposed on the second principal surface; and a dielectric film covering at least a portion of the first IDT electrode, wherein the second IDT electrode is covered by the support member; when the first and second principal surfaces are viewed in a plane, a first electrode finger of a plurality of electrode fingers included in the first IDT electrode at least partially overlaps with a second electrode finger of a plurality of electrode fingers included in the second IDT electrode; and an electrode finger duty of the second electrode finger is smaller than an electrode finger duty of the first electrode finger.

[0123] <2> The acoustic wave device according to <1>, wherein an electrode finger duty of the plurality of electrode fingers included in the second IDT electrode is smaller than an electrode finger duty of the plurality of electrode fingers included in the first IDT electrode.

[0124] <3> When the electrode finger duty of the plurality of electrode fingers included in the first IDT electrode is D1 and the electrode finger duty of the plurality of electrode fingers included in the second IDT electrode is D2, D2≦−2.33×D1 ２ +2.33×D1+0.0739, and D2≧−1.852×D1+0.626, and D1≦−2.07×D2 ２ +1.58×D2+0.4337.

[0125] <4> An elastic wave device comprising: a support member including a support substrate; a piezoelectric layer disposed on the support member and having first and second principal surfaces opposing each other; a first IDT electrode disposed on the first principal surface; a second IDT electrode disposed on the second principal surface; and a dielectric film covering at least a portion of the first IDT electrode, wherein the second IDT electrode is covered by the support member; when the first and second principal surfaces are viewed in a plane, each of a plurality of electrode fingers included in the first IDT electrode at least partially overlaps with each of a plurality of electrode fingers included in the second IDT electrode in a one-to-one relationship; when viewed in a plane, a first electrode finger of the plurality of electrode fingers included in the first IDT electrode at least partially overlaps with a second electrode finger of the plurality of electrode fingers included in the second IDT electrode; and the electrode finger width of the second electrode finger is narrower than the electrode finger width of the first electrode finger.

[0126] <5> The acoustic wave device according to <4>, wherein the electrode finger width of each of the plurality of electrode fingers included in the second IDT electrode is narrower than the electrode finger width of each of the plurality of electrode fingers included in the first IDT electrode.

[0127] <6> The acoustic wave device according to any one of <1> to <5>, wherein the first electrode fingers and the second electrode fingers are excited in phase.

[0128] <7> The acoustic wave device according to any one of <1> to <6>, wherein an electrode finger duty of the plurality of electrode fingers included in the first IDT electrode is not less than 0.2 and not more than 0.8.

[0129] <8> The elastic wave device according to any one of <1> to <7>, wherein the first IDT electrode includes: a plurality of third electrode fingers and a plurality of fourth electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the plurality of third electrode fingers to each other; and a second bus bar electrode configured to connect one ends of the plurality of fourth electrode fingers to each other and arranged to face the first bus bar electrode with the plurality of third electrode fingers and the plurality of fourth electrode fingers interposed therebetween; and wherein, when a repetition period of the plurality of third electrode fingers is a wavelength λ, a film thickness of the dielectric film is 0.08 × λ or less.

[0130] <9> The acoustic wave device according to any one of <1> to <8>, wherein the dielectric film includes at least one of silicon oxide, silicon nitride, and silicon oxynitride.

[0131] <10> The acoustic wave device according to any one of <1> to <9>, wherein the piezoelectric layer contains either lithium tantalate or lithium niobate.

[0132] <11> The elastic wave device according to any one of <1> to <10>, wherein the support member includes: a support substrate; and a first dielectric layer disposed between the support substrate and the piezoelectric layer, the first dielectric layer having a shear wave velocity lower than the shear wave velocity of the piezoelectric layer and the support substrate.

[0133] <12> The acoustic wave device according to <11>, wherein the first dielectric layer includes at least one of silicon oxide and silicon oxynitride.

[0134] <13> The elastic wave device according to <11> or <12>, wherein the support member further includes a second dielectric layer disposed between the support substrate and the first dielectric layer, the second dielectric layer having a shear wave velocity higher than a shear wave velocity of the first dielectric layer.

[0135] <14> The acoustic wave device according to <13>, wherein the second dielectric layer includes at least one of silicon nitride and silicon oxynitride.

[0136] INDUSTRIAL APPLICABILITY The present invention can be widely used as an acoustic wave device disposed in a front end portion of communication devices such as mobile phones.

[0137] REFERENCE SIGNS LIST 1 Acoustic wave device 3 Substrate 10, 20 IDT electrodes 11a, 11b, 21a, 21b Electrode fingers 12a, 12b, 22a, 22b Bus bar electrodes 15 Reflecting electrodes 31 Piezoelectric layers 31a, 31b Main surfaces 32 Low acoustic velocity layers 33 High acoustic velocity layers 34 Support substrate 41 Dielectric film

Claims

1. An acoustic wave device comprising: a support member including a support substrate; a piezoelectric layer disposed on the support member and having first and second principal surfaces facing each other; a first IDT electrode disposed on the first principal surface; a second IDT electrode disposed on the second principal surface; and a dielectric film covering at least a portion of the first IDT electrode, wherein the second IDT electrode is covered by the support member; when the first and second principal surfaces are viewed in a plane, a first electrode finger of a plurality of electrode fingers included in the first IDT electrode at least partially overlaps with a second electrode finger of a plurality of electrode fingers included in the second IDT electrode; and the electrode finger duty of the second electrode finger is smaller than the electrode finger duty of the first electrode finger.

2. The acoustic wave device according to claim 1, wherein the electrode finger duty of the plurality of electrode fingers included in the second IDT electrode is smaller than the electrode finger duty of the plurality of electrode fingers included in the first IDT electrode.

3. When the electrode finger duty of the plurality of electrode fingers included in the first IDT electrode is D1 and the electrode finger duty of the plurality of electrode fingers included in the second IDT electrode is D2, D2≦−2.33×D1 ２ +2.33×D1+0.0739, and D2≧−1.852×D1+0.626, and D1≦−2.07×D2 ２ +1.58×D2+0.4337.

4. An elastic wave device comprising: a support member including a support substrate; a piezoelectric layer disposed on the support member and having first and second principal surfaces opposing each other; a first IDT electrode disposed on the first principal surface; a second IDT electrode disposed on the second principal surface; and a dielectric film covering at least a portion of the first IDT electrode, wherein the second IDT electrode is covered by the support member; when the first and second principal surfaces are viewed in a plane, each of a plurality of electrode fingers included in the first IDT electrode and each of a plurality of electrode fingers included in the second IDT electrode at least partially overlap in a one-to-one relationship; when viewed in a plane, a first electrode finger of the plurality of electrode fingers included in the first IDT electrode and a second electrode finger of the plurality of electrode fingers included in the second IDT electrode at least partially overlap; and the electrode finger width of the second electrode finger is narrower than the electrode finger width of the first electrode finger.

5. The acoustic wave device according to claim 4, wherein the electrode finger width of each of the plurality of electrode fingers included in the second IDT electrode is narrower than the electrode finger width of each of the plurality of electrode fingers included in the first IDT electrode.

6. The acoustic wave device according to any one of claims 1 to 5, wherein the first electrode fingers and the second electrode fingers are excited in phase.

7. The acoustic wave device according to claim 1, wherein the electrode finger duty of the plurality of electrode fingers included in the first IDT electrode is not less than 0.2 and not more than 0.

8.

8. The elastic wave device according to any one of claims 1 to 7, wherein the first IDT electrode includes: a plurality of third electrode fingers and a plurality of fourth electrode fingers arranged parallel to each other; a first bus bar electrode configured to connect one ends of the plurality of third electrode fingers together; and a second bus bar electrode configured to connect one ends of the plurality of fourth electrode fingers together and arranged opposite the first bus bar electrode with the plurality of third electrode fingers and the plurality of fourth electrode fingers in between; and wherein, when the repeating period of the plurality of third electrode fingers is wavelength λ, the film thickness of the dielectric film is 0.08 × λ or less.

9. The acoustic wave device according to claim 1, wherein the dielectric film includes at least one of silicon oxide, silicon nitride, and silicon oxynitride.

10. The acoustic wave device according to any one of claims 1 to 9, wherein the piezoelectric layer contains either lithium tantalate or lithium niobate.

11. The elastic wave device according to any one of claims 1 to 10, wherein the support member includes: a support substrate; and a first dielectric layer disposed between the support substrate and the piezoelectric layer, the first dielectric layer having a shear wave velocity lower than the shear wave velocity of the piezoelectric layer and the support substrate.

12. The acoustic wave device according to claim 11, wherein the first dielectric layer includes at least one of silicon oxide and silicon oxynitride.

13. The elastic wave device according to claim 11 or 12, wherein the support member further includes a second dielectric layer disposed between the support substrate and the first dielectric layer, the second dielectric layer having a shear wave velocity higher than that of the first dielectric layer.

14. The acoustic wave device according to claim 13, wherein the second dielectric layer includes at least one of silicon nitride and silicon oxynitride.

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