Filter device

Abstract

A filter device is provided with a plurality of resonators including an elastic wave resonator (1). An elastic wave resonator (1) is provided with: a piezoelectric layer (5) having a first main surface (5a) and a second main surface (5b) that face each other; an IDT electrode (8) provided on a first main surface (5a) of the piezoelectric layer (5) and having a plurality of electrode fingers; a first dielectric film (6) provided on a first main surface (5a) of the piezoelectric layer (5); and a second dielectric film (7) provided on a second main surface (5b) of the piezoelectric layer (5). The piezoelectric film has a relative bandwidth of 8.5% or more, and 0.322 lt, where Tp is a thickness in an intersection region of the piezoelectric layer (5), Tdf is a thickness of a portion of the first dielectric film (6) that overlaps the intersection region in plan view, and Tdb is a thickness of a portion of the second dielectric film (7) that overlaps the intersection region in plan view; (Tdf / Tp) + (Tdb / Tp) lt; 0.786, and (Tdf / Tp)-(Tdb / Tp) lt; and 0.196 of the total weight.

Description

Technical Field

[0001] This invention relates to a filter device having an elastic wave resonator. Background Technology

[0002] Previously, filter devices with elastic wave resonators were widely used in filters for portable telephones, etc. In recent years, elastic wave resonators utilizing thickness shear mode bulk waves, as described in Patent Document 1 below, have been proposed. In this elastic wave resonator, a piezoelectric layer is provided on a support. An IDT (Interdigital Transducer) is provided on the piezoelectric layer. Electrode fingers are alternately arranged in the IDT. By applying an alternating voltage between the electrode fingers, a thickness shear mode bulk wave is excited.

[0003] In Patent Document 1, the surface of the piezoelectric layer where the IDT is disposed is designated as the surface. The surface of the piezoelectric layer opposite to the surface is designated as the back surface. A frequency setting layer, serving as a dielectric layer, is disposed on both the surface and the back surface. Patent Document 1 describes that when the ratio of the thickness of the frequency setting layer disposed on the back surface to the total thickness of the frequency setting layer is at least 30%, the A2 mode generated on the high-frequency side of the passband is reduced by more than 20%. Furthermore, the term A2 mode refers to a second-order mode in the thickness direction.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: U.S. Patent Application Publication No. 2021 / 044272 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In filter devices with wide passbands used in 5G and other applications, a trapezoidal circuit structure can be considered, for example. For the series arm resonators and parallel arm resonators in this circuit structure, elastic wave resonators utilizing the thickness shear mode of body waves can be used.

[0009] In general RF (Radio Frequency) filters, high attenuation characteristics are required in the frequency band near integer multiples of the passband frequency. However, in elastic wave resonators utilizing thickness shear modes of bulk waves, not only second-order modes but also higher-order modes such as third, fourth, and fifth orders are generated. Furthermore, these higher-order modes are generated at higher frequency bands than the frequencies at which second-order modes are generated. Moreover, in the case of third-order modes being generated in parallel arm resonators in a trapezoidal circuit structure, this is because the response of the third-order mode is located at frequencies near twice the passband. Therefore, it is possible that the required attenuation characteristics are not met at frequencies near twice the passband.

[0010] The purpose of this invention is to provide a filter device that can broaden the passband and suppress second-order and third-order modes in an elastic wave resonator.

[0011] Technical solutions for solving the problem

[0012] The filter device of the present invention is a filter device with a passband, comprising a plurality of resonators including elastic wave resonators. The elastic wave resonator comprises: a piezoelectric layer having a first main surface and a second main surface opposite to each other; an IDT electrode disposed on the first main surface of the piezoelectric layer, having a plurality of electrode fingers; a first dielectric film disposed on the first main surface of the piezoelectric layer; and a second dielectric film disposed on the second main surface of the piezoelectric layer. A direction orthogonal to the extension direction of the plurality of electrode fingers is defined as the electrode finger orthogonal direction. When viewed from the electrode finger orthogonal direction, the area where adjacent electrode fingers overlap is a cross region. The first dielectric film and the second dielectric film, when viewed from above, overlap with the cross region. When the highest frequency in the passband is set to FH, the lowest frequency in the passband is set to FL, and the center frequency of the passband is set to FC, the relative bandwidth width expressed by ((FH-FL) / FC)×100[%] is greater than 8.5%. When the thickness in the cross region of the piezoelectric layer is set to Tp, the thickness of the portion of the first dielectric film that overlaps with the cross region in top view is set to Td_f, and the thickness of the portion of the second dielectric film that overlaps with the cross region in top view is set to Td_b, 0.322<(Td_f / Tp)+(Td_b / Tp)<0.786, and |(Td_f / Tp)-(Td_b / Tp)|<0.196.

[0013] Invention Effects

[0014] According to the filter device of the present invention, the passband can be widened and the second-order and third-order modes can be suppressed in the elastic wave resonator. Attached Figure Description

[0015] Figure 1 This is a circuit diagram of a filter device according to the first embodiment of the present invention.

[0016] Figure 2 This is a schematic front sectional view of the elastic wave resonator in the first embodiment of the present invention.

[0017] Figure 3 This is a schematic top view of the elastic wave resonator in the first embodiment of the present invention.

[0018] Figure 4 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of an elastic wave resonator according to the first embodiment of the present invention.

[0019] Figure 5 This is a graph showing the impedance-frequency characteristics of the elastic wave resonator in the comparative example.

[0020] Figure 6 This is a graph showing the impedance-frequency characteristics of the elastic wave resonator according to the first embodiment of the present invention.

[0021] Figure 7 This is a schematic diagram showing the distribution of displacement in the thickness direction based on the first-order mode at the center of the electrode fingers of the stacked portion in the first embodiment of the present invention.

[0022] Figure 8 This is a schematic diagram showing the distribution of displacement in the thickness direction based on the second-order mode at the center of the electrode fingers of the stacked portion in the first embodiment of the present invention.

[0023] Figure 9 This is a schematic diagram showing the distribution of displacement in the thickness direction based on the third-order mode at the center of the electrode fingers of the stacked portion in the first embodiment of the present invention.

[0024] Figure 10 This is a schematic diagram showing the distribution of stress in the thickness direction based on the first-order mode at the center of the electrode fingers of the laminate in the first embodiment of the present invention.

[0025] Figure 11 This is a schematic diagram showing the distribution of stress in the thickness direction based on the second-order mode at the center of the electrode fingers of the laminate in the first embodiment of the present invention.

[0026] Figure 12 This is a schematic diagram showing the distribution of stress in the thickness direction based on the third-order mode at the center of the electrode fingers of the laminate in the first embodiment of the present invention.

[0027] Figure 13 This is a schematic diagram showing the distribution of stress in the thickness direction based on the third-order mode at the center of the electrode fingers of the laminate under the condition of suppressing the third-order mode.

[0028] Figure 14 This is a schematic diagram showing the distribution of stress in the thickness direction based on the third-order mode at the center of the electrode fingers of the laminate when the third-order mode is suppressed in the reference example.

[0029] Figure 15 This shows the electromechanical coupling coefficient K between Td_f / Tp and the third-order mode when Td_f = Td_b. 2 eff A diagram showing the relationships between them.

[0030] Figure 16 This shows the electromechanical coupling coefficient K between Td_f / Tp and the second-order mode when (Td_f / Tp+Td_b / Tp) = 0.54. 2 eff A diagram showing the relationships between them.

[0031] Figure 17 This is a graph showing the relationship between the ratio Td_f / Tp and the ratio Fr3 / Fr1.

[0032] Figure 18 This is a schematic front sectional view showing a portion of a filter device according to a first variation of the first embodiment of the present invention.

[0033] Figure 19 This is a schematic front sectional view showing a portion of a filter device according to a second variation of the first embodiment of the present invention.

[0034] Figure 20 This is a schematic front sectional view showing a portion of a filter device according to a third variation of the first embodiment of the present invention.

[0035] Figure 21 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of an elastic wave resonator in a fourth variation of the first embodiment of the present invention.

[0036] Figure 22 This is a schematic front sectional view showing the vicinity of a pair of electrodes of an elastic wave resonator in the second embodiment of the present invention.

[0037] Figure 23 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of an elastic wave resonator in the third embodiment of the present invention.

[0038] Figure 24This is a schematic top view of the elastic wave resonator in the fourth embodiment of the present invention.

[0039] Figure 25 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of an elastic wave resonator according to the fifth embodiment of the present invention.

[0040] Figure 26 This is a graph showing the relationship between Tp / p and the relative bandwidth of the elastic wave resonator.

[0041] Figure 27 This is a graph showing the relationship between the relative bandwidth and the normalized spurious magnitude in an elastic wave resonator.

[0042] Figure 28 This is a graph showing the relationship between Tp / p, metallization rate (MR), and relative bandwidth.

[0043] Figure 29 This is a diagram showing the mapping of the relative bandwidth to the Euler angles (0°, θ, ψ) of LiNbO3 when Tp / p approaches 0 infinitely.

[0044] Figure 30 This is a schematic diagram of the coordinate system after the crystal axis of the piezoelectric crystal has been transformed using Euler angles.

[0045] Figure 31 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 0°) of the lithium niobate constituting the piezoelectric layer is greater than 0° and less than 60°.

[0046] Figure 32 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 90°) of the lithium niobate constituting the piezoelectric layer is greater than -15° but less than 0°.

[0047] Figure 33 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 0°) of the lithium niobate constituting the piezoelectric layer is greater than 180° and less than 240°.

[0048] Figure 34 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 90°) of the lithium niobate constituting the piezoelectric layer is greater than 165° and less than 180°.

[0049] Figure 35 This is a piezoelectric response microscopy image showing an example of polarization reversal occurring in a piezoelectric layer.

[0050] Figure 36This is a graph showing the admittance frequency characteristics of an elastic wave resonator with polarization reversal occurring in the piezoelectric layer and without polarization reversal occurring in the piezoelectric layer.

[0051] Figure 37 This is a diagram illustrating an example of the throughput characteristics of a filter device. Detailed Implementation

[0052] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0053] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.

[0054] Figure 1 This is a circuit diagram of a filter device according to the first embodiment of the present invention.

[0055] The filter device 10 is a bandpass filter with a passband. In this specification, the term "passband" refers to the passband guaranteed by the filter device. The specific method for determining the passband of the filter device will be described later. Figure 1 The filter device 10 shown is widely used in communication devices and the like. The passband of the filter device 10 is the passband of n79. The passband of n79 is 4400MHz to 5000MHz. However, the passband of the filter device 10 is not limited to the above-mentioned passband.

[0056] Specifically, the filter device 10 is a trapezoidal filter. The filter device 10 has multiple series-arm resonators and multiple parallel-arm resonators serving as multiple resonators. Furthermore, the circuit structure of the filter device 10 is not limited to... Figure 1 The circuit structure shown. The filter device 10 only needs to include a trapezoidal circuit section. The trapezoidal circuit section only needs to include at least one series arm resonator and at least one parallel arm resonator.

[0057] In this specification, the highest frequency in the passband is designated as the upper end, and the lowest frequency in the passband is designated as the lower end. In this specification, the upper and lower ends of the passband refer to the upper and lower ends of the passband guaranteed by the filter device. When the upper end of the passband is set to FH, the lower end to FL, and the center frequency of the passband is set to FC, FC = (FH + FL) / 2. In the filter device 10 of this embodiment, the relative bandwidth, expressed as ((FH - FL) / FC) × 100 [%], is 8.5% or more. Thus, the passband of the filter device 10 is relatively wide. On the other hand, the upper limit of the relative bandwidth is not particularly limited; for example, the relative bandwidth can be set to 40% or less. In this case, the filter device 10 can be easily manufactured.

[0058] The filter device 10 has multiple resonators, all of which are elastic wave resonators. However, it is not limited to this. The multiple resonators only need to include at least one elastic wave resonator. For example... Figure 1 As shown, the plurality of resonators includes an elastic wave resonator 1. In this embodiment, the elastic wave resonator 1 is a parallel arm resonator. The specific structure of the elastic wave resonator 1 will be described below.

[0059] Figure 2 This is a schematic front sectional view of the elastic wave resonator in the first embodiment.

[0060] The elastic wave resonator 1 includes a piezoelectric layer 5, a first dielectric film 6, a second dielectric film 7, and an IDT electrode 8. The piezoelectric layer 5 has a first main surface 5a and a second main surface 5b. The first main surface 5a and the second main surface 5b are opposite to each other. The first dielectric film 6 is disposed on the first main surface 5a. More specifically, the IDT electrode 8 is disposed on the first main surface 5a. The first dielectric film 6 is disposed on the first main surface 5a such that it covers the IDT electrode 8. On the other hand, the second dielectric film 7 is disposed on the second main surface 5b.

[0061] In this embodiment, the piezoelectric layer 5 comprises lithium niobate. More specifically, the piezoelectric layer 5 comprises LiNbO3. The first dielectric film 6 and the second dielectric film 7 comprise silicon oxide. More specifically, the first dielectric film 6 and the second dielectric film 7 comprise SiO2. In this specification, the term "a component comprises a certain material" includes cases where the component contains trace amounts of impurities to a degree that does not significantly degrade the electrical characteristics of the elastic wave resonator. Furthermore, the materials of the piezoelectric layer 5, the first dielectric film 6, and the second dielectric film 7 are not limited to the materials described above.

[0062] The elastic wave resonator 1 has a support member 2. The support member 2 includes a support substrate 3 and an insulating layer 4. The insulating layer 4 is disposed on the support substrate 3. A second dielectric film 7 is disposed on the insulating layer 4. Therefore, a piezoelectric layer 5 is indirectly disposed on the insulating layer 4 through the second dielectric film 7.

[0063] For example, semiconductors such as silicon and ceramics such as alumina can be used as the material for the support substrate 3. Suitable dielectrics such as silicon oxide or tantalum oxide can be used as the material for the insulating layer 4. Alternatively, the support member 2 may be composed solely of the support substrate 3. Or, the support member 2 may not necessarily be required.

[0064] Figure 3 This is a schematic top view of the elastic wave resonator in the first embodiment. The above-mentioned... Figure 2 It is along Figure 3 A schematic cross-sectional view of line II in the diagram. Additionally, in... Figure 3The wiring connecting the elastic wave resonator 1 and the first dielectric film 6 are omitted. Figure 3 The same applies to the schematic top view.

[0065] The IDT electrode 8 has a pair of busbars and a plurality of electrode fingers. Specifically, the pair of busbars is a first busbar 16 and a second busbar 17. The first busbar 16 and the second busbar 17 are opposite to each other. Specifically, the plurality of electrode fingers is a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each of the plurality of first electrode fingers 18 is connected to the first busbar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second busbar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interleaved and interlocked.

[0066] The IDT electrode 8 comprises a stacked metal film. Specifically, in the IDT electrode 8, a Ti layer and an Al layer are sequentially stacked from the piezoelectric layer 5 side. Furthermore, the material of the IDT electrode 8 is not limited to the aforementioned materials. Alternatively, the IDT electrode 8 may also comprise a single-layer metal film.

[0067] Hereinafter, the first electrode finger 18 and the second electrode finger 19 will sometimes be referred to simply as electrode fingers. The direction in which the multiple electrode fingers extend is defined as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is defined as the electrode finger orthogonal direction. When viewed from the electrode finger orthogonal direction, the area where adjacent first electrode fingers 18 and second electrode fingers 19 overlap is the intersection region A. The first dielectric film 6 and the second dielectric film 7 only need to overlap with the intersection region A when viewed from above.

[0068] In this specification, the term "top view" refers to a view from an angle equivalent to... Figure 2 The view is taken from the upper direction along the stacking direction of the support member 2 and the piezoelectric layer 5. Additionally, in... Figure 2 In this context, for example, the piezoelectric layer 5 side is considered the upper side, specifically the side of the support substrate 3 and the side of the piezoelectric layer 5. Furthermore, in this specification, a top view and a view from the main face orientation are considered synonymous. The main face orientation is the direction in which the first main face 5a and the second main face 5b of the piezoelectric layer 5 are opposite each other. More specifically, the main face orientation is, for example, the normal direction of the first main face 5a.

[0069] The elastic wave resonator 1 is configured to utilize a bulk wave in a thickness shear mode. Specifically, the elastic wave resonator 1 of this embodiment is configured to utilize a bulk wave in a first-order thickness shear mode as the dominant mode. More specifically, in the elastic wave resonator 1, when the thickness in the cross region A of the piezoelectric layer 5 is set to Tp and the center-to-center distance between adjacent first electrode fingers 18 and second electrode fingers 19 is set to p, Tp / p is 0.5 or less. Therefore, a bulk wave in a thickness shear mode can be appropriately excited.

[0070] The region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap in the orthogonal direction of the electrode fingers, and the region between the centers of adjacent first electrode fingers 18 and second electrode fingers 19, is the excitation region C. That is, the cross region A contains multiple excitation regions C. In addition, the cross region A and the excitation region C are regions of the piezoelectric layer 5 defined based on the structure of the IDT electrode 8. In each excitation region C, a bulk wave of thickness shear mode can be excited. However, the elastic wave resonator 1 can also be configured to utilize plate waves. In this case, the excitation region is the cross region A.

[0071] Furthermore, in this embodiment, the cutting angle of the piezoelectric layer 5 is ZY. ZY refers to the fact that the Z-axis of the crystal constituting the piezoelectric layer 5 is perpendicular to the first principal plane 5a of the piezoelectric layer 5, and the Y-axis of the crystal is parallel to the orthogonal direction of the electrode. In this embodiment, the crystal constituting the piezoelectric layer 5 is a LiNbO3 crystal. However, the material and cutting angle of the piezoelectric layer 5 are not limited to the above-described material and cutting angle.

[0072] Figure 4 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of the elastic wave resonator in the first embodiment.

[0073] Hereinafter, the thickness of the portion of the first dielectric film 6 that overlaps with the intersection region A when viewed from above is defined as Td_f. Specifically, the thickness Td_f is the thickness of the portion of the first dielectric film 6 located between the electrode fingers. The thickness of the portion of the second dielectric film 7 that overlaps with the intersection region A when viewed from above is defined as Td_b.

[0074] This embodiment is characterized by a relative bandwidth of 8.5% or more, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp) - (Td_b / Tp)| < 0.196. When a filter device is used in a communication device, when the passband of the filter device is wide, higher-order modes such as second-order and third-order modes often become the cause of communication quality degradation. In contrast, in this embodiment, the filter device 10 has the above-described structure, thereby widening the passband and suppressing second-order and third-order modes in the elastic wave resonator 1. By comparing this embodiment and a comparative example, the effect of suppressing second-order and third-order modes will be explained in detail. Then, it is shown that when the relative bandwidth is 8.5% or more, problems caused by higher-order modes are prone to occur.

[0075] The comparative example differs from the first embodiment in that 0.786 < (Td_f / Tp) + (Td_b / Tp). The impedance frequency characteristics of both the first embodiment and the comparative example were derived using FEM (Finite Element Method) simulation. The design parameters for the elastic wave resonator 1 with the structure of the first embodiment are as follows. Furthermore, the electrode finger spacing in the design parameters is the center-to-center distance between adjacent first electrode fingers 18 and second electrode fingers 19 in the orthogonal direction of the electrode fingers. The width of an electrode finger is the dimension of the electrode finger along the orthogonal direction of the electrode fingers.

[0076] Piezoelectric layer: Material…LiNbO3, cleavage angle…ZY, thickness Tp…356nm

[0077] First dielectric film: Material…SiO2, thickness Td_f…89nm

[0078] Second dielectric film: Material…SiO2, thickness Td_b…89nm

[0079] IDT electrode: Layer structure... Ti layer / Al layer from the piezoelectric layer side, thickness... 10nm / 100nm from the piezoelectric layer side.

[0080] Electrode finger spacing: 4μm

[0081] Electrode finger width: 0.8μm

[0082] Td_f / Tp: 0.25

[0083] Td_b / Tp: 0.25

[0084] (Td_f / Tp) + (Td_b / Tp): 0.5

[0085] |(Td_f / Tp)-(Td_b / Tp)|: 0

[0086] The design parameters of the elastic wave resonator in the comparative example are as follows.

[0087] Piezoelectric layer: Material…LiNbO3, cleavage angle…ZY, thickness Tp…294nm

[0088] First dielectric film: Material…SiO2, thickness Td_f…132nm

[0089] Second dielectric film: Material…SiO2, thickness Td_b…132nm

[0090] IDT electrode: Layer structure... Ti layer / Al layer from the piezoelectric layer side, thickness... 10nm / 100nm from the piezoelectric layer side.

[0091] Electrode finger spacing: 4μm

[0092] Electrode finger width: 0.8μm

[0093] Td_f / Tp: 0.45

[0094] Td_b / Tp: 0.45

[0095] (Td_f / Tp) + (Td_b / Tp): 0.9

[0096] |(Td_f / Tp)-(Td_b / Tp)|: 0

[0097] Furthermore, the resonant frequency of the elastic wave resonator 1 in the first embodiment involved in this comparison is 4200MHz. Therefore, the elastic wave resonator 1 can be appropriately used as a parallel arm resonator in a filter device 10 having a passband of n79. The resonant frequency of the elastic wave resonator in the comparative example is also 4200MHz. In addition, the passband of n79 is 4400MHz to 5000MHz.

[0098] Figure 5 This is a graph showing the impedance-frequency characteristics of the elastic wave resonator in the comparative example. Figure 6 This is a graph showing the impedance-frequency characteristics of the elastic wave resonator in the first embodiment. Figure 5 as well as Figure 6 The passband of n79 is shown in the diagram. Figure 5 as well as Figure 6 The diagram also shows a frequency band B, ranging from 8800MHz to 10000MHz, which is twice the frequency of the aforementioned passband. Figure 5 China and Figure 6 Arrow D2 indicates the frequency range where the second-order mode is generated. Arrow D3 indicates the frequency range where the third-order mode is generated.

[0099] like Figure 5 As shown, in the comparative example, the second-order mode generated near 7000MHz was suppressed. On the other hand, a large spurious signal caused by the third-order mode was generated near 9500MHz. This spurious signal occurred near the center frequency of band B, which is twice the frequency of the passband with a frequency of n79. Therefore, in the filter device with a passband of n79, when the elastic wave resonator in the comparative example is used as a parallel arm resonator, the attenuation characteristics deteriorate near band B. This becomes the cause of the degradation in communication quality in the filter device.

[0100] In contrast, such as Figure 6As shown, in the first embodiment, not only second-order modes but also third-order modes can be suppressed. Furthermore, in the filter device 10 with a passband of n79, the elastic wave resonator 1 of the first embodiment is used as a parallel arm resonator. This improves the attenuation characteristics near frequency band B. Therefore, when the filter device 10 is used in a communication device, the communication quality is less likely to deteriorate.

[0101] As described above, the elastic wave resonator 1 can suppress both second-order and third-order modes. The reasons for this are explained below. Figure 2 As shown, the elastic wave resonator 1 has a stacked portion 9. Specifically, the stacked portion 9 is a portion in which a piezoelectric layer 5, a first dielectric film 6, and a second dielectric film 7 are stacked. In the first embodiment, the stacked portion 9 is located in a portion that does not overlap with the IDT electrode 8 when viewed from above. The stacked portion 9 includes a plurality of electrode finger central portions 9a. Specifically, the so-called electrode finger central portion 9a is the portion of the stacked portion 9 located at the center between the electrode fingers. Figures 7-12 The image shows the displacement and stress distribution at a certain instant based on each mode at the central portion 9a between the electrode fingers of the laminated portion 9.

[0102] Figure 7 This is a schematic diagram showing the distribution of displacement in the thickness direction based on the first-order mode at the center of the electrode fingers of the stacked portion in the first embodiment. Figure 8 This is a schematic diagram showing the distribution of displacement in the thickness direction based on the second-order mode at the center of the electrode fingers of the stacked portion in the first embodiment. Figure 9 This is a schematic diagram showing the distribution of displacement in the thickness direction based on the third-order mode at the center of the electrode fingers of the stacked portion in the first embodiment.

[0103] exist Figures 7-9 In the diagram, the horizontal axis represents the magnitude of the displacement, and the vertical axis represents the position of the laminate 9 in the thickness direction. For convenience, the sign of the displacement in one of the two directions orthogonal to and opposite to the thickness direction of the laminate 9 is set to "+", and the sign of the displacement in the other direction is set to "-". Specifically, Figures 7-9 Set the right side of the symbol to "+" and the left side to "-". Figures 7-9 The upper end of the vertical axis represents the surface of the first dielectric film 6. Figures 7-9 The lower end of the vertical axis represents the surface of the second dielectric film 7. The upper and lower ends of the vertical axis will be discussed later. Figures 10-14 The same applies to China.

[0104] like Figure 7As shown, the first-order mode is a wave whose displacement direction is orthogonal to the thickness direction of the stacked portion 9. Furthermore, the so-called first-order mode in the first embodiment is a thickness shear first-order mode. Similarly, as... Figure 8 as well as Figure 9 As shown, the second-order and third-order modes are also waves whose displacement direction is orthogonal to the thickness direction of the stack 9. In other words, the first-order, second-order, and third-order modes in the first embodiment are modes in the thickness direction. Moreover, the higher the order of the mode, the shorter the wavelength. Specifically, in the first embodiment, half a wavelength of the first-order mode corresponds to the overall thickness of the stack 9. One wavelength of the second-order mode corresponds to the overall thickness of the stack 9. 1.5 wavelengths of the third-order mode corresponds to the overall thickness of the stack 9.

[0105] Figure 10 This is a schematic diagram showing the distribution of stress in the thickness direction based on the first-order mode at the center of the electrode fingers of the laminate in the first embodiment. Figure 11 This is a schematic diagram showing the distribution of stress in the thickness direction based on the second-order mode at the center of the electrode fingers of the laminate in the first embodiment. Figure 12 This is a schematic diagram illustrating the distribution of stress in the thickness direction based on a third-order mode at the center of the electrode fingers of the laminated portion in the first embodiment. Figures 10-12 In the diagram, the horizontal axis represents the magnitude of the stress, and the vertical axis represents the position of the laminate 9 in the thickness direction. For convenience, the stress that produces one type of deformation within the laminate 9, which generates a thickness shear mode, is marked with a "+", and the stress that produces another type of deformation is marked with a "-". Specifically, the stress that produces a thickness shear mode within the laminate 9 is marked with a "-". Figures 10-12 In this context, the right side is set to "+", and the left side is set to "-". (This will be discussed later.) Figure 13 as well as Figure 14 The same applies to China.

[0106] like Figures 10-12 As shown, the distribution along the thickness direction based on each mode is represented as a waveform. The waveform of stress based on the first-order mode corresponds to the phase and... Figure 7 The waveform shown is a wave staggered as a first-order mode. That is, the wavelength of the waveform based on the stress of the first-order mode is the same as the wavelength of the wave as a first-order mode. The same applies to the second-order and third-order modes.

[0107] like Figure 11 As shown, the stress distribution based on the second-order mode is located in both the "+" and "-" directions. In the stress distribution based on the second-order mode, the integral value in the "+" direction is the same as the integral value in the "-" direction. Therefore, the integral value of the stress based on the second-order mode in the entire thickness direction of the laminate 9 is 0.

[0108] like Figure 12 As shown, the stress based on the third-order mode is also distributed in both the "+" and "-" directions. However, the integral value of the stress based on the third-order mode in the thickness direction of the entire laminate 9 is not zero.

[0109] The integral value of the stress distribution along the thickness direction, located in the piezoelectric layer, is proportional to the electromechanical coupling coefficient. This is shown in J. Kaitila, “Review of Wave Propagation in BAW Thin Film Devices Progress and Prospects”, Proc. IEEE Ultrasonics Symposium Proceedings, 2007, pp. 120-129.

[0110] The integral value of the portion of the piezoelectric layer 5 based on the stress of each mode varies depending on the relationship between the thickness Tp of the piezoelectric layer 5, the thickness Td_f of the first dielectric film 6, and the thickness Td_b of the second dielectric film 7. In the design parameters described above in the first embodiment, Td_f = Td_b. In this case, the integral value of the portion of the piezoelectric layer 5 based on the stress of the second-order mode is 0. Therefore, the electromechanical coupling coefficient of the second-order mode is small. Therefore, as Figure 6 As shown, in the first embodiment, second-order modes can be suppressed. That is, in the first embodiment, second-order modes are theoretically not stimulated.

[0111] In the design parameters described above in the first embodiment, Td_f = Td_b = 0.25Tp. Therefore, 2 / 3 of the overall thickness of the stacked portion 9 is the thickness Tp of the piezoelectric layer 5. Furthermore, in this case, (Td_f / Tp) + (Td_b / Tp) = 0.5. This suppresses the third-order mode, which will be explained below.

[0112] Figure 13 This is a schematic diagram illustrating the distribution of stress along the thickness direction based on the third-order mode at the center of the electrode fingers in the laminate, under the condition of suppressing the third-order mode. Figure 13 The solid lines extending left and right from the upper side in the diagram show the boundary between the piezoelectric layer 5 and the first dielectric film 6. (This will be discussed later.) Figure 14 The same applies to China. Figure 13 The solid lines extending to the left and right from the lower side show the boundary between the piezoelectric layer 5 and the second dielectric film 7.

[0113] The overall thickness of the laminate 9 is equivalent to 1.5 wavelengths of the waveform of stress based on a third-order mode. Figure 13The figure shows the case where 2 / 3 of the wavelength corresponds to the thickness of piezoelectric layer 5. In this case, the integral value of the portion of piezoelectric layer 5 based on the stress of the third-order mode is 0. Therefore, the electromechanical coupling coefficient of the third-order mode is small. Thus, as Figure 6 As shown, in the first embodiment, the third-order mode can be suppressed.

[0114] However, the suppression of the third-order mode is not limited to the case where (Td_f / Tp) + (Td_b / Tp) = 0.5. For example, when (Td_f / Tp) + (Td_b / Tp) is close to 0.5, the thickness of the piezoelectric layer 5 is approximately equivalent to one wavelength of the waveform of the stress based on the third-order mode. In this case, the absolute value of the integral of the stress based on the third-order mode located in the portion of the piezoelectric layer 5 is small. Therefore, the electromechanical coupling coefficient of the third-order mode can be reduced, and the third-order mode can be suppressed.

[0115] exist Figure 14 In this example, as a reference, the stress distribution based on the third-order mode is shown in a structure having only the first dielectric film 6 (one of the first dielectric film 6 and one of the second dielectric films 7). In this example, the laminate is a portion in which the first dielectric film 6 and the piezoelectric layer 5 are laminated. Furthermore, Td_f = 0.5Tp, Td_b = 0, and (Td_f / Tp) + (Td_b / Tp) = 0.5. In this example, two-thirds of the overall thickness of the laminate is also the thickness Tp of the piezoelectric layer 5. Therefore, the third-order mode can be suppressed. However, in this example, it is difficult to suppress the second-order mode.

[0116] Based on the above, when (Td_f / Tp) + (Td_b / Tp) is around 0.5, the third-order mode can be suppressed regardless of the relationship between the thickness Td_f of the first dielectric film 6 and the thickness Td_b of the second dielectric film 7.

[0117] Furthermore, the differences in physical properties such as density and elastic constants in the piezoelectric layer 5, the first dielectric film 6, and the second dielectric film 7 actually affect the integral value of the stress based on the third-order mode in the portion located in the piezoelectric layer 5. Therefore, even if it is not (Td_f / Tp) + (Td_b / Tp) = 0.5, the above integral value sometimes becomes 0.

[0118] Similar to the 3rd-order mode, other higher-order modes can be suppressed when the absolute value of the integral value of the portion of the piezoelectric layer 5 based on the stress of other higher-order modes is small. The following shows the conditions under which the aforementioned integral value becomes 0 in the 4th to 8th-order modes.

[0119] If Td_f = Td_b or (Td_f / Tp) + (Td_b / Tp) is 1, then the above integral value of stress based on the 4th-order mode becomes 0. If (Td_f / Tp) + (Td_b / Tp) is 0.25 or 1.5, then the above integral value of stress based on the 5th-order mode becomes 0. If Td_f = Td_b or (Td_f / Tp) + (Td_b / Tp) is 0.5 or 2, then the above integral value of stress based on the 6th-order mode becomes 0. If (Td_f / Tp) + (Td_b / Tp) is 0.167, 0.75, or 2.5, then the above integral value of stress based on the 7th-order mode becomes 0. If Td_f = Td_b or (Td_f / Tp) + (Td_b / Tp) is 0.333, 1, or 3, then the above integral value of stress based on the 8th-order mode becomes 0.

[0120] In the design parameters described above in the first embodiment, Td_f = Td_b. Therefore, in the first embodiment, not only the 2nd-order and 3rd-order modes can be suppressed, but also the 4th-order, 6th-order, and 8th-order modes can be suppressed.

[0121] In addition, such as Figure 10 As shown, the stress based on the first-order mode is distributed only in the "+" direction. Therefore, the larger the proportion of the piezoelectric layer 5 thickness Tp in the overall thickness of the stack 9, the larger the integral value of the stress based on the first-order mode located in the portion of the piezoelectric layer 5. As a result, the electromechanical coupling coefficient of the first-order mode can be increased.

[0122] like Figure 10 As shown, the absolute value of the stress based on the first-order mode is smaller closer to the surface side of the first dielectric film 6 in the stack 9. Similarly, the absolute value of the stress based on the first-order mode is smaller closer to the surface side of the second dielectric film 7 in the stack 9. Therefore, the closer the thickness Td_f of the first dielectric film 6 is to the thickness Td_b of the second dielectric film 7, the larger the integral value of the stress based on the first-order mode in the portion located in the piezoelectric layer 5. As a result, the electromechanical coupling coefficient of the first-order mode can be increased.

[0123] In the design parameters described above in the first embodiment, Td_f = Td_b. Therefore, in the first embodiment, it is possible to suppress the second-order and third-order modes and to strongly excite the first-order mode.

[0124] Furthermore, the relationships between the thickness Tp of the piezoelectric layer 5, the thickness Td_f of the first dielectric film 6, and the thickness Td_b of the second dielectric film 7, which suppress the second-order and third-order modes, are derived. More specifically, the admittance frequency characteristics of the elastic wave resonator 1 are derived using the formula shown in V. Plessky, et al. “A formula for the admittance of laterally excited bulk wave resonators (XBARs)”, Electronics Letters 57.20 (2021): 773-775. Using this formula, the admittance frequency characteristics of higher-order modes in the thickness direction, including the first-order, second-order, and third-order modes, can be derived.

[0125] Furthermore, in deriving the aforementioned admittance frequency characteristics, the resonant frequency of the first-order mode is made to be consistent with... Figure 6 The resonant frequencies shown in the impedance-frequency characteristics are consistent. Specifically, the thickness Tp of the piezoelectric layer 5, the thickness Td_f of the first dielectric film 6, and the thickness Td_b of the second dielectric film 7 were adjusted.

[0126] The resonant frequencies Fr and anti-resonant frequencies Fa of the first, second, and third-order modes in the aforementioned admittance frequency characteristics were determined. Then, using the resonant frequencies Fr and Fa of each mode, the electromechanical coupling coefficient K of each mode was calculated using the following formula. 2 eff .

[0127] [Mathematical Expression 1]

[0128]

[0129] The ratio of the thickness Td_f of the first dielectric film 6 to the thickness Tp of the piezoelectric layer 5, Td_f / Tp, and the ratio of the thickness Td_b of the second dielectric film 7 to the thickness Tp of the piezoelectric layer 5, Td_b / Tp, were derived, along with the electromechanical coupling coefficient K for each mode. 2 eff The relationship.

[0130] First, without stimulating the second-order mode, the electromechanical coupling coefficient K is derived compared to Td_f / Tp and the third-order mode. 2 eff The relationship is as follows. Specifically, under the condition that Td_f / Tp = Td_b / Tp, the electromechanical coupling coefficient K of the third-order mode is calculated whenever the ratios Td_f / Tp and Td_b / Tp are changed. 2 eff .

[0131] Figure 15 This shows the electromechanical coupling coefficient K between Td_f / Tp and the third-order mode when Td_f = Td_b. 2 eff The graph shows the relationship. Additionally, since Td_f = Td_b, therefore... Figure 15 The relationship shown is related to the ratio Td_b / Tp and the electromechanical coupling coefficient K of the third-order mode. 2 eff The relationship is the same.

[0132] like Figure 15 As shown, when the ratio Td_f / Tp is around 0.27, the electromechanical coupling coefficient K of the third-order mode is... 2 eff It becomes a local minimum. Because Td_f = Td_b, the electromechanical coupling coefficient K of the third-order mode becomes local minimum when Td_f / Tp and Td_b / Tp are around 0.27 and (Td_f / Tp) + (Td_b / Tp) are around 0.54. 2 eff It becomes a minimum value. Specifically, this electromechanical coupling coefficient K 2 eff It becomes almost zero. In this case, the 3rd-order mode is hardly stimulated. Additionally, since Td_f = Td_b, the 2nd-order mode is not stimulated.

[0133] However, even when (Td_f / Tp) + (Td_b / Tp) is not 0.54, the electromechanical coupling coefficient K of the third-order mode can still be reduced. 2 eff The following shows the electromechanical coupling coefficient K that can reduce the third-order mode. 2 eff It can also suppress the range of (Td_f / Tp) + (Td_b / Tp) in the 3rd order mode.

[0134] Under the condition that 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, the electromechanical coupling coefficient K of the third-order mode can be made... 2 eff Less than 2%. Under the condition that 0.354 < (Td_f / Tp) + (Td_b / Tp) < 0.746, the electromechanical coupling coefficient K of the third-order mode can be made... 2 eff Less than 1.5%. Under the condition that 0.39 < (Td_f / Tp) + (Td_b / Tp) < 0.704, the electromechanical coupling coefficient K of the third-order mode can be made... 2 effLess than 1%. When 0.432 < (Td_f / Tp) + (Td_b / Tp) < 0.65, the electromechanical coupling coefficient K of the third-order mode can be made 2 eff Less than 0.5%. When 0.488 < (Td_f / Tp) + (Td_b / Tp) < 0.586, the electromechanical coupling coefficient K of the third-order mode can be made 2 eff Less than 0.1%.

[0135] Under the condition of hardly exciting the third-order mode, the relationship between the ratio Td_f / Tp and the electromechanical coupling coefficient K of the second-order mode was derived 2 eff Specifically, in the state where (Td_f / Tp) + (Td_b / Tp) = 0.54, whenever the ratio Td_f / Tp and the ratio Td_b / Tp are changed, the electromechanical coupling coefficient K of the second-order mode was calculated 2 eff .

[0136] Figure 16 is a graph showing the relationship between the ratio Td_f / Tp and the electromechanical coupling coefficient K of the second-order mode in the case of (Td_f / Tp + Td_b / Tp) = 0.54 2 eff .

[0137] As Figure 16 shown, when 0.172 < Td_f / Tp < 0.368, the electromechanical coupling coefficient K of the second-order mode 2 eff becomes less than 2%. On the other hand, since the ratio Td_b / Tp of the thickness Td_b of the second dielectric film 7 to the thickness Tp of the piezoelectric layer 5 is in the range of (Td_f / Tp) + (Td_b / Tp) = 0.54, so 0.172 < Td_b / Tp < 0.368. In these ranges of the ratio Td_f / Tp and the ratio Td_b / Tp, |(Td_f / Tp) - (Td_b / Tp)| < 0.196. In this range, the electromechanical coupling coefficient K of the second-order mode can be made 2 eff Less than 2%, and the second-order mode can be suppressed.

[0138] Hereinafter, the range of |(Td_f / Tp) - (Td_b / Tp)| that can effectively reduce the electromechanical coupling coefficient K of the second-order mode 2 eff and can effectively suppress the second-order mode is shown.

[0139] When 0.186 < Td_f / Tp < 0.354, |(Td_f / Tp) - (Td_b / Tp)| < 0.168, the electromechanical coupling coefficient K of the second-order mode can be 2 eff 1.5%. When 0.203 < Td_f / Tp < 0.337, |(Td_f / Tp) - (Td_b / Tp)| < 0.134, the electromechanical coupling coefficient K of the second-order mode can be 2 eff less than 1%. When 0.223 < Td_f / Tp < 0.317, |(Td_f / Tp) - (Td_b / Tp)| < 0.094, the electromechanical coupling coefficient K of the second-order mode can be 2 eff less than 0.5%. When 0.249 < Td_f / Tp < 0.291, |(Td_f / Tp) - (Td_b / Tp)| < 0.042, the electromechanical coupling coefficient K of the second-order mode can be 2 eff less than 0.1%.

[0140] According to the results based on Figure 15 and Figure 16 shown, in the structure of the first embodiment above, the second-order mode and the third-order mode can be suppressed. That is, in the first embodiment, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp) - (Td_b / Tp)| < 0.196. Thus, the electromechanical coupling coefficients K of the second-order mode and the third-order mode can be 2 eff less than 2%, and the second-order mode and the third-order mode can be suppressed.

[0141] Preferably, 0.354 < (Td_f / Tp) + (Td_b / Tp) < 0.746, and |(Td_f / Tp) - (Td_b / Tp)| < 0.168. Thus, the electromechanical coupling coefficients K of the second-order mode and the third-order mode can be 2 eff less than 1.5%.

[0142] More preferably, 0.39 < (Td_f / Tp) + (Td_b / Tp) < 0.704, and |(Td_f / Tp) - (Td_b / Tp)| < 0.134. Thus, the electromechanical coupling coefficients K of the second-order mode and the third-order mode can be 2 eff less than 1%.

[0143] More preferably, 0.432 < (Td_f / Tp) + (Td_b / Tp) < 0.65, and |(Td_f / Tp) - (Td_b / Tp)| < 0.094. Therefore, the electromechanical coupling coefficient K of the second-order and third-order modes can be made... 2 eff Less than 0.5%.

[0144] More preferably, 0.488 < (Td_f / Tp) + (Td_b / Tp) < 0.586, and |(Td_f / Tp) - (Td_b / Tp)| < 0.042. Therefore, the electromechanical coupling coefficient K of the second-order and third-order modes can be made... 2 eff Less than 0.1%.

[0145] Furthermore, within the aforementioned preferred range, the electromechanical coupling coefficient K of the first-order mode... 2 eff The efficiency is as high as 23% or more. Therefore, the elastic wave device of the present invention can be appropriately used as an elastic wave resonator in a filter device with a wide passband, such as 5G.

[0146] In typical high-frequency filters used in communications, high attenuation characteristics are required in the frequency band near integer multiples of the frequency in the passband. For example, Figure 5 The frequency band B shown is a band with a frequency twice that of the passband. For example, if a third-order mode is generated in frequency band B, the attenuation characteristics deteriorate in frequency band B. This will cause a degradation in the communication quality in high-frequency filters. However, whether a third-order mode is easily generated in frequency band B varies depending on the relative bandwidth. In addition, the ratio of the resonant frequency of the third-order mode to the resonant frequency of the first-order mode depends on ratios such as Td_f / Tp. Furthermore, when the resonant frequency of the first-order mode is set to Fr1 and the resonant frequency of the third-order mode is set to Fr3, the aforementioned ratio is Fr3 / Fr1.

[0147] Figure 17 This is a graph showing the relationship between the ratio Td_f / Tp and the ratio Fr3 / Fr1.

[0148] First, the anti-resonant frequency of the first-order mode of the parallel arm resonator lies within the passband of the filter device. The resonant frequency Fr1 of the first-order mode of the parallel arm resonator is slightly lower than the lower end FL of the filter device's passband. Furthermore, as... Figure 17As shown, the resonant frequency Fr3 of the third-order mode is 2.2 to 2.9 times the resonant frequency Fr1 of the first-order mode. Therefore, the third-order mode is generated at a frequency more than twice the lower end FL of the filter's passband. In the case of a narrower passband, the third-order mode is generated at a frequency more than twice the upper end FH of the passband. That is, no third-order mode is generated in frequency band B. Therefore, when the filter is used in a communication device, it is less likely to cause degradation in communication quality.

[0149] On the other hand, with a relatively wide passband, third-order modes can occur at frequencies lower than twice the upper limit (FH) of the passband. For example, a wide passband is required in 5G high-frequency filter devices. Moreover, when the relative bandwidth is 8.5% or more, third-order modes are easily generated in band B. As mentioned above, the degradation of attenuation characteristics in band B becomes a cause of communication quality degradation. Therefore, when the relative bandwidth of the filter device is 8.5% or more, it is particularly necessary to suppress third-order modes. Details are shown below.

[0150] The lower end FL of the filter device's passband is set to 4400MHz, and the upper end FH of the passband is varied, thereby changing the passband bandwidth. Furthermore, when the passband bandwidth is set to R, R = FH - FL. Then, the difference between the lower end FL of the passband and the resonant frequency of the first-order mode of the parallel arm resonator is set to 0.33 times the bandwidth R. That is, it is set to |FL - Fr1| / R = 0.33.

[0151] Here, in Figure 5 In the comparative example shown, in the parallel-arm resonator, the resonant frequency Fr1 of the first-order mode is 4200 MHz, and the resonant frequency Fr3 of the third-order mode is 9500 MHz. In this case, the resonant frequency Fr3 of the third-order mode in the parallel-arm resonator is 2.26 times the resonant frequency Fr1 of the first-order mode. Similarly, in this study, Fr3 / Fr1 is set to 2.26. However, in this study, the resonant frequency Fr1 of the first-order mode is not limited to 4200 MHz.

[0152] With FL = 4400MHz, |FL-Fr1| / R = 0.33, and Fr3 / Fr1 = 2.26, the resonant frequency Fr3 of the third-order mode of the parallel arm resonator coincides with twice the frequency of the upper passband FH, which is 4817MHz. At this point, the relative bandwidth becomes 9%. Furthermore, with a wider relative bandwidth, the resonant frequency Fr3 of the third-order mode becomes lower than twice the frequency of the upper passband FH. Additionally, twice the frequency of the upper passband FH is the highest frequency in band B. Therefore, when the relative bandwidth is 9% or more, a third-order mode is generated in band B. However, in reality, deviations occur at various frequencies due to temperature variations and manufacturing deviations. Therefore, when the relative bandwidth is 8.5% or more, it is particularly necessary to suppress the third-order mode.

[0153] In the first embodiment, the filter device 10 has a relative bandwidth of 8.5% or more, and is able to suppress second-order and third-order modes in the elastic wave resonator 1. Therefore, the filter device 10 can be appropriately used as a filter device for 5G, etc., and the communication performance is not easily degraded.

[0154] The structure of the first embodiment will be described in more detail below.

[0155] like Figure 1 As shown, the filter device 10 includes a first signal terminal 13, a second signal terminal 14, multiple series-arm resonators, and multiple parallel-arm resonators. The first signal terminal 13 is connected to the input potential. The second signal terminal 14 is connected to the output potential. Alternatively, the first signal terminal 13 can also be connected to the output terminal, and the second signal terminal 14 can also be connected to the input potential. The first signal terminal 13 and the second signal terminal 14 can be configured as electrode pads, or they can be configured as wiring.

[0156] Specifically, the multiple series-arm resonators are series-arm resonators S1, S2, S3, S4, and S5. These multiple series-arm resonators are connected in series between the first signal terminal 13 and the second signal terminal 14. Furthermore, starting from the first signal terminal 13 side, series-arm resonators S1, S2, S3, S4, and S5 are arranged sequentially.

[0157] Specifically, the multiple parallel-arm resonators are elastic wave resonator 1, parallel-arm resonator P2, parallel-arm resonator P3, and parallel-arm resonator P4. Elastic wave resonator 1 is connected between the connection point of series-arm resonators S1 and S2 and the ground potential. Parallel-arm resonator P2 is connected between the connection point of series-arm resonators S2 and S3 and the ground potential. Parallel-arm resonator P3 is connected between the connection point of series-arm resonators S3 and S4 and the ground potential. Parallel-arm resonator P4 is connected between the connection point of series-arm resonators S4 and S5 and the ground potential.

[0158] In the design of trapezoidal filters, it is necessary to ensure that the resonant frequencies of the series arm resonators and the parallel arm resonators are different from each other. This yields the desired passband, etc. Furthermore, by making the resonant frequencies different among multiple series arm resonators or multiple parallel arm resonators, the filter characteristics can be improved.

[0159] exist Figure 2 In the filter device 10 shown, an IDT electrode 8, serving as a functional electrode, is disposed on the piezoelectric layer 5, thereby forming an elastic wave resonator. Such a filter device 10 is sometimes referred to as a chip. It is sufficient that, within a chip, at least the resonant frequencies of the series arm resonators and the parallel arm resonators are different from each other.

[0160] In the bulk wave resonator using a thickness shearing mode in this invention, the resonant frequency can be adjusted, for example, by adjusting the thickness of at least one of the piezoelectric layer 5, the first dielectric film 6, and the second dielectric film 7. Multiple elastic wave resonators with different thicknesses of the piezoelectric layer 5, the first dielectric film 6, or the second dielectric film 7 can also be constructed within a single chip. Thus, at least in series-arm resonators and parallel-arm resonators, the resonant frequencies can be made different.

[0161] Examples of multiple elastic wave resonators with different thicknesses of the piezoelectric layer 5, the first dielectric film 6, or the second dielectric film 7 are shown in the first to third modifications of the first embodiment. Furthermore, in this specification, if... Figure 2 Taking the first embodiment shown as an example, the thickness of the piezoelectric layer 5 in each elastic wave resonator is the thickness of the portion of the piezoelectric layer 5 located at the center portion 9a between the electrode fingers of the stacked portion 9. Similarly, the thickness of the first dielectric film 6 and the second dielectric film 7 in each elastic wave resonator is the thickness of the portion of the first dielectric film 6 and the second dielectric film 7 located at the center portion 9a between the electrode fingers of the stacked portion 9.

[0162] The circuit structures of the first to third modifications are the same as those of the first embodiment. In the first to third modifications, the relative bandwidth is 8.5% or more. Moreover, in all elastic wave resonators, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp) - (Td_b / Tp)| < 0.196. Therefore, in the first to third modifications, similar to the first embodiment, the passband can be widened, and the second-order and third-order modes can be suppressed in the elastic wave resonator.

[0163] Alternatively, in at least one elastic wave resonator, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp) - (Td_b / Tp)| < 0.196.

[0164] exist Figure 18 In the first modified example shown, the piezoelectric layer 5A has a thickness variation region 5X. The thickness variation region 5X is a region in the layer where the thickness varies. In this modified example, multiple elastic wave resonators share the same piezoelectric layer 5A. Figure 18 In the section shown, a thickness variation region 5X is provided between adjacent elastic wave resonators. Therefore, in Figure 18 In the section shown, elastic wave resonators with different thicknesses of piezoelectric layer 5A are adjacent to each other.

[0165] exist Figure 19 In the second modified example shown, the first dielectric film 6A has a thickness variation region 6X. Figure 19 In the portion shown, elastic wave resonators with different thicknesses of the first dielectric film 6A are adjacent to each other. On the other hand, in Figure 20 In the third modified example shown, the second dielectric film 7A has a thickness variation region 7X. Figure 20 In the section shown, elastic wave resonators with different thicknesses of the second dielectric film 7A are adjacent to each other.

[0166] In the first to third modifications, each thickness variation region is configured as a stepped portion. In the piezoelectric layer, the first dielectric film, or the second dielectric film, portions with different thicknesses are provided, with the thickness variation regions serving as boundaries. Alternatively, the thickness variation regions may be configured as inclined surfaces connecting the portions with different thicknesses.

[0167] Figure 18 The portions of varying thickness in the piezoelectric layer 5A shown can be created, for example, by film deposition or by etching. Figure 19 as well as Figure 20The same applies to the first dielectric film 6A and the second dielectric film 7A shown. However, compared to piezoelectric materials such as lithium niobate, dielectrics such as silicon oxide are easier to form or etch. Therefore, it is preferable to provide portions of different thicknesses in the first dielectric film 6A and / or in the second dielectric film 7A.

[0168] The following will show several possible thicknesses of the piezoelectric layer, the first dielectric film, or the second dielectric film in the filter device, denoted as the order of the thickness of the piezoelectric layer, the first dielectric film, or the second dielectric film. The more orders of the piezoelectric layer thickness in the filter device, the more reliably the filter characteristics of the filter device can be improved. The same applies when the number of orders of the thickness of the first dielectric film or the second dielectric film is large.

[0169] On the other hand, when the thickness of the piezoelectric layer, the first dielectric film, or the second dielectric film has many levels, the manufacturing process of the filter device becomes complex, which may lead to increased costs. Therefore, it is preferable that the thickness of a filter device (i.e., each chip) has 6 or fewer levels.

[0170] like Figure 18 As shown, the piezoelectric layer 5A in the first modified example has a diaphragm portion 5Y. Specifically, the diaphragm portion 5Y is the part of the piezoelectric layer 5A that overlaps with the void portion 2a. For example, assuming that the thickness variation region 5X of the piezoelectric layer 5A is located in the diaphragm portion 5Y, the diaphragm portion 5Y may break. This is because, when the thickness variation region 5X overlaps with the void portion 2a in a top view, stress tends to concentrate in the thickness variation region 5X. More specifically, in the event of a temperature change, mechanical vibration, or impact, stress tends to concentrate in the thickness variation region 5X. Because such a stress concentration area is located in the diaphragm portion 5Y, the diaphragm portion 5Y may break.

[0171] As in the first modified example, the thickness variation region 5X is preferably located in the area where the laminate 9A, which includes the piezoelectric layer 5A, the first dielectric film 6, and the second dielectric film 7, contacts the insulating layer 4. This prevents the film portion 5Y from being easily damaged.

[0172] In addition, Figure 19 , Figure 20 In the second and third modifications shown, the piezoelectric layer 5 also has a film portion 5Y. Furthermore, in Figure 19 The thickness variation region 6X shown Figure 20Stress tends to concentrate in the thickness variation region 7X shown. Therefore, assuming that the thickness variation regions 6X and 7X are located in the portions of the first dielectric film 6A and the second dielectric film 7A that are stacked with the film portion 5Y of the piezoelectric layer 5, the film portion 5Y may break. As in the second and third modifications, it is preferable that the thickness variation regions 6X and 7X are located in the regions where the stacked portions 9B and 9C contact the insulating layer 4. As a result, the film portion 5Y is less likely to break.

[0173] Furthermore, the circuit structure of the filter device 10 is not limited to the circuit structure described above. As mentioned above, the filter device 10 only needs to include a trapezoidal circuit section. In the first embodiment, the elastic wave resonator 1 is the parallel arm resonator closest to the first signal terminal 13 among a plurality of parallel arm resonators. However, the configuration of the elastic wave resonator 1 is not limited to the configuration described above.

[0174] like Figure 2 As shown, a recess is provided in the insulating layer 4. A second dielectric film 7 and a piezoelectric layer 5 are provided on the insulating layer 4 to seal the recess. This forms a hollow portion. This hollow portion is a cavity 2a. In the first embodiment, the support member 2 and the piezoelectric layer 5 are arranged such that a part of the support member 2 and a part of the piezoelectric layer 5 sandwich the cavity 2a and face each other. However, the recess in the support member 2 may also be provided across the insulating layer 4 and the support substrate 3. Alternatively, only the recess provided in the support substrate 3 may be sealed by the insulating layer 4. The recess may also be provided in the piezoelectric layer 5, for example. In addition, the cavity 2a may also be a through hole provided in the support member 2.

[0175] The cavity 2a is the acoustic reflection part in this invention. It is sufficient that at least a portion of the IDT electrode 8 overlaps with the acoustic reflection part in plan view. Specifically, it is sufficient that at least a portion of the plurality of electrode fingers overlaps with the acoustic reflection part in plan view. The acoustic reflection part can confine the energy of the elastic wave to the piezoelectric layer 5 side. Alternatively, an acoustic reflection membrane, described later, can also be provided as the acoustic reflection part. However, when the acoustic reflection part is the cavity 2a, the energy of the elastic wave can be more effectively confined to the piezoelectric layer 5 side.

[0176] Preferably, multiple excitation regions C overlap with the acoustic reflection section when viewed from above. This allows the energy of the elastic wave to be more reliably contained within the piezoelectric layer 5.

[0177] In the first embodiment, the piezoelectric layer 5 comprises lithium niobate. Furthermore, the material of the piezoelectric layer 5 is not limited to the materials described above; for example, lithium tantalate such as LiTaO3, aluminum nitride such as AlN, scandium aluminum nitride such as ScAlN, or PZT (lead zirconate titanate) can also be used.

[0178] However, the preferred piezoelectric layer 5 comprises lithium niobate. Lithium niobate is a single crystal with low viscous loss, which can reduce the energy loss of the main mode. In addition, lithium niobate has high piezoelectricity, thus making it easy to widen the passband of the filter device 10.

[0179] As the material for the piezoelectric layer 5, lithium niobate is more preferably used in the form of Z-cut, Y-cut with 80° to 160° rotation and X-propagation, or Y-cut with 70° to 100° rotation and X-90° propagation. This increases the electromechanical coupling coefficient of the first-order mode. Furthermore, when the piezoelectric layer 5 includes Z-cut lithium niobate, the electromechanical coupling coefficient of the first-order mode can be increased regardless of the propagation direction. The propagation direction referred to here is a direction parallel to the first principal surface 5a of the piezoelectric layer 5 and parallel to the orthogonal direction of the electrode pointer. In this specification, when "~" is used in the range of the cutting angle, it indicates a value greater than or equal to the value before "~" and less than or equal to the value after "~".

[0180] In the first embodiment, the first dielectric film 6 and the second dielectric film 7 comprise silicon oxide. Furthermore, the materials of the first dielectric film 6 and the second dielectric film 7 are not limited to the materials described above; for example, silicon nitride, aluminum oxide, silicon oxynitride, or silicon carbide such as SiOC can be used. However, it is preferable that the first dielectric film 6 and the second dielectric film 7 comprise silicon oxide. In this case, the absolute value of the temperature coefficient of frequency (TCF) of the elastic wave resonator 1 can be reduced, and the temperature characteristics of the elastic wave resonator 1 can be improved. In addition, the processing of the elastic wave resonator 1 becomes easier.

[0181] The materials of the first dielectric film 6 and the second dielectric film 7 can also be different from each other. The first dielectric film 6 and the second dielectric film 7 are not limited to single-layer dielectric films. At least one of the first dielectric film 6 and the second dielectric film 7 can also be a laminated film. Furthermore, although the first dielectric film 6 and the second dielectric film 7 have the same thickness in the first embodiment, they do not necessarily have to be the same thickness and can be different from each other. The thickness of these films can be appropriately selected based on conditions such as filter characteristics, reliability, and ease of manufacturing.

[0182] Figure 2 The insulating layer 4 and the second dielectric film 7 shown can be integrally formed using the same material. In this case, the thickness Td_b of the second dielectric film 7 is also the thickness of the portion of the second dielectric film 7 that overlaps with the intersection region A when viewed from above. Alternatively, the insulating layer 4 and the second dielectric film 7 can also be separately formed using different materials.

[0183] In the first embodiment, the second main surface 5b of the first main surface 5a and the second main surface 5b of the piezoelectric layer 5 is the main surface on the side of the support member 2. However, it is also possible that the first main surface 5a of the first main surface 5a and the second main surface 5b is the main surface on the side of the support member 2. In this case, the first dielectric film 6 is provided on the insulating layer 4. The insulating layer 4 and the first dielectric film 6 can be integrally formed using the same material. In this case, the thickness Td_f of the first dielectric film 6 is also the thickness of the portion of the first dielectric film 6 that overlaps with the intersection region A when viewed from above. Alternatively, the insulating layer 4 and the first dielectric film 6 can also be separately provided using different materials.

[0184] like Figure 4 As shown, in the first embodiment, the thickness Td_f of the first dielectric film 6 is thinner than the thickness of each electrode finger of the IDT electrode 8. Therefore, the surface of the first dielectric film 6 has an uneven shape. Specifically, the distance between the surface of the portion of the first dielectric film 6 covering the electrode fingers and the first main surface 5a of the piezoelectric layer 5 is different from the distance between the surface of the portion of the first dielectric film 6 located between the electrode fingers and the first main surface 5a. However, this is not a limitation.

[0185] For example, in Figure 21 In the fourth variation of the first embodiment shown, the thickness of the first dielectric film 6B is thicker than the thickness of each electrode finger of the IDT electrode 8. Furthermore, the first dielectric film 6B covers the IDT electrode 8. Moreover, the surface of the first dielectric film 6B is flat. In this case, as long as the relative bandwidth is 8.5% or more, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp) - (Td_b / Tp)| < 0.196, it is sufficient. Therefore, similar to the first embodiment, the passband of the filter device can be widened, and second-order and third-order modes can be suppressed in the elastic wave resonator.

[0186] Examples of differences in the stacked structure or electrode structure in the elastic wave resonator compared to the first embodiment are shown through embodiments 2 to 5. In embodiments 2 to 5, similar to the first embodiment, the relative bandwidth is 8.5% or more, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp) - (Td_b / Tp)| < 0.196. Therefore, in embodiments 2 to 5, the passband can be widened, and second-order and third-order modes can be suppressed in the elastic wave resonator.

[0187] Figure 22 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of the elastic wave resonator in the second embodiment.

[0188] The difference between this embodiment and the first embodiment is that the first dielectric film 6 in the elastic wave resonator 21 is disposed between the first main surface 5a of the piezoelectric layer 5 and the IDT electrode 8. Apart from the aspects described above, the filter device of this embodiment is configured similarly to the filter device 10 of the first embodiment.

[0189] In structures other than the second embodiment of the present invention, the structure in the elastic wave resonator 21 in which a first dielectric film 6 is disposed between the piezoelectric layer 5 and the IDT electrode 8 can also be used.

[0190] Figure 23 This is a schematic front sectional view showing the vicinity of a pair of electrode fingers of the elastic wave resonator in the third embodiment.

[0191] The difference between this embodiment and the first embodiment is that the acoustic reflection part in the elastic wave resonator 31 is an acoustic reflection membrane 38. Another difference between this embodiment and the first embodiment is that the support member 32 only includes a support substrate. Apart from the aspects described above, the filter device of this embodiment is configured similarly to the filter device 10 of the first embodiment.

[0192] An acoustic reflective membrane 38 is provided on the surface of the support member 32. A second dielectric membrane 7 is provided on the acoustic reflective membrane 38. Therefore, a piezoelectric layer 5 is indirectly provided on the acoustic reflective membrane 38 through the second dielectric membrane 7. In addition, the support member 32 and the piezoelectric layer 5 can be arranged such that at least a portion of the support member 32 and at least a portion of the piezoelectric layer 5 sandwich the acoustic reflective membrane 38 and face each other.

[0193] The acoustic reflector 38 is a stack of multiple acoustic impedance layers. Specifically, the acoustic reflector 38 has multiple low acoustic impedance layers and multiple high acoustic impedance layers. The low acoustic impedance layers are layers with relatively low acoustic impedance. More specifically, the multiple low acoustic impedance layers of the acoustic reflector 38 are low acoustic impedance layer 33a, low acoustic impedance layer 33b, and low acoustic impedance layer 33c.

[0194] On the other hand, the high acoustic impedance layer is a layer with relatively high acoustic impedance. More specifically, the multiple high acoustic impedance layers of the acoustic reflective film 38 are high acoustic impedance layer 34a and high acoustic impedance layer 34b. Low acoustic impedance layers and high acoustic impedance layers are stacked alternately. In addition, the low acoustic impedance layer 33a is the layer located on the side closest to the piezoelectric layer 5 in the acoustic reflective film 38. The second dielectric film 7 is directly disposed on the low acoustic impedance layer 33a.

[0195] The acoustic reflector 38 has three low acoustic impedance layers and two high acoustic impedance layers. However, the acoustic reflector 38 may simply have at least one low acoustic impedance layer and one high acoustic impedance layer.

[0196] Materials used as low acoustic impedance layers include, for example, silicon oxide or aluminum. Materials used as high acoustic impedance layers include, for example, metals such as platinum or tungsten, aluminum nitride, silicon nitride, or dielectrics such as hafnium oxide.

[0197] For example, the second dielectric film 7 could function as a low acoustic impedance layer. In this case, it would suffice if 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786 and |(Td_f / Tp) - (Td_b / Tp)| < 0.196.

[0198] When an elastic wave is excited in the elastic wave resonator 31, heat is generated in multiple excitation regions C. However, in this embodiment, the portions of the multiple excitation regions C in the piezoelectric layer 5 are supported by the acoustic reflection film 38. This improves heat dissipation in the elastic wave resonator 31. Consequently, the elastic wave resonator 31 is less prone to damage when large power is applied. Therefore, the power handling capability of the elastic wave resonator 31 and the filter device can be improved. Furthermore, because the piezoelectric layer 5 is supported by the acoustic reflection film 38, the piezoelectric layer 5 is less susceptible to damage from thermal stress or mechanical impact.

[0199] In structures other than the third embodiment of the present invention, the structure in the elastic wave resonator 31 in which the acoustic reflection part is the acoustic reflection membrane 38 can also be adopted.

[0200] Figure 24 This is a schematic top view of the elastic wave resonator in the fourth embodiment.

[0201] The difference between this embodiment and the first embodiment is that the elastic wave resonator 41 has a pair of reflectors 46 and 47. Another difference is that the elastic wave resonator 41 is configured to utilize plate waves such as Lamb waves. Apart from the aspects described above, the filter device of this embodiment has the same structure as the filter device 10 of the first embodiment.

[0202] Reflectors 46 and 47 are disposed on the first main surface 5a of the piezoelectric layer 5. Specifically, reflectors 46 and 47 are positioned opposite each other, sandwiching the IDT electrode 8 in the orthogonal direction of the electrodes. Furthermore, if the IDT electrode 8 is disposed on the first dielectric film 6, each reflector can also be disposed on the first dielectric film 6.

[0203] Reflector 46 has a pair of reflector busbars and a plurality of reflector electrode fingers 45. Specifically, the pair of reflector busbars are a first reflector busbar 43 and a second reflector busbar 44. The first reflector busbar 43 and the second reflector busbar 44 are opposite to each other. One end of each of the plurality of reflector electrode fingers 45 is connected to the first reflector busbar 43. The other end of each of the plurality of reflector electrode fingers 45 is connected to the second reflector busbar 44. Reflector 47 is configured in the same manner as reflector 46.

[0204] When the elastic wave resonator 41 is configured to utilize plate waves, it is preferable to have a pair of reflectors. This improves the resonance characteristics of the elastic wave resonator 41.

[0205] Figure 25 This is a schematic top view showing the vicinity of a pair of electrodes of the elastic wave resonator in the fifth embodiment.

[0206] The difference between this embodiment and the first embodiment is that, in the elastic wave resonator 51, IDT electrodes are provided on both the first main surface 5a and the second main surface 5b of the piezoelectric layer 5. Apart from the aspects described above, the filter device of this embodiment has the same structure as the filter device 10 of the first embodiment.

[0207] Similar to the first embodiment, an IDT electrode 8 is provided on the first main surface 5a of the piezoelectric layer 5. On the other hand, an IDT electrode 58 is provided on the second main surface 5b. The IDT electrode 58 is configured similarly to the IDT electrode 8. That is, the IDT electrode 58 has a pair of busbars and a plurality of electrode fingers. In this embodiment, the intersection region defined based on the IDT electrode 8 and the intersection region defined based on the IDT electrode 58 overlap in top view.

[0208] In this embodiment, the thickness Td_b of the second dielectric film 7 is the thickness of the portion of the second dielectric film 7 located between the electrode fingers.

[0209] The elastic wave resonator 51 utilizes the thickness shear mode as the dominant mode. However, the elastic wave resonator 51 can also be configured to utilize plate waves. In this case, it is preferable to provide a pair of reflectors on both the first main surface 5a and the second main surface 5b of the piezoelectric layer 5. Specifically, it is preferable to provide a pair of reflectors on the first main surface 5a, such that the IDT electrodes 8 are positioned opposite each other in the orthogonal direction of the electrodes. It is preferable to provide a pair of reflectors on the second main surface 5b, such that the IDT electrodes 58 are positioned opposite each other in the orthogonal direction of the electrodes.

[0210] The preferred structure of the present invention will be described below.

[0211] When using the thickness shear mode as the dominant mode, it is preferable that Tp / p ≤ 0.5, and more preferably Tp / p ≤ 0.24. This allows for appropriate excitation of the thickness shear mode of the volume wave and sufficiently increases the relative bandwidth of the elastic wave resonator. Furthermore, the relative bandwidth referred to here is not the relative bandwidth of the filter device, but rather the relative bandwidth of an elastic wave resonator. This relative bandwidth can be expressed as (|Fa-Fr| / Fr) × 100 [%].

[0212] Figure 26 This is a graph showing the relationship between Tp / p and the relative bandwidth of the elastic wave resonator.

[0213] according to Figure 26 It is clear that when Tp / p > 0.5, the relative bandwidth is less than 5%. In contrast, when Tp / p ≤ 0.5, the relative bandwidth can be greater than 5%. Therefore, the electromechanical coupling coefficient of the bulk wave in the thickness shear mode can be increased. When Tp / p ≤ 0.24 or less, the relative bandwidth can be greater than 7%. Therefore, the electromechanical coupling coefficient of the bulk wave in the thickness shear mode can be effectively increased. However, while the electromechanical coupling coefficient of the first-order thickness shear mode can be increased, the second-order and third-order modes can be suppressed in this invention.

[0214] When the metallization rate of the electrode fingers relative to the excitation region C is set as MR, it is preferable to satisfy MR ≤ 1.75(Tp / p) + 0.075. In this case, the relative bandwidth of the elastic wave resonator will not become too large, and spurious emissions between the resonant frequency and the anti-resonant frequency can be suppressed. Details are shown below.

[0215] Furthermore, in this specification, the metallization rate MR of the electrode fingers relative to the excitation region C is the proportion of the portion of the piezoelectric layer 5 that forms the metal coating of the electrode fingers in the excitation region C when viewed from above. Specifically, the metallization rate MR is the ratio of the area of ​​the first electrode finger 18 and the second electrode finger 19 in the excitation region C to the area of ​​the excitation region C when viewed from above. In addition, when the width of the electrode fingers located in the excitation region C is fixed, the metallization rate MR can also be calculated by dividing the total width of the electrode fingers located in the excitation region C by the dimension of the excitation region C along the orthogonal direction of the electrode fingers.

[0216] Figure 27 This is a graph showing the relationship between the relative bandwidth and the normalized spurious magnitude in an elastic wave resonator. Figure 27 The diagram shows the results of measuring the stray phase rotation as the relative bandwidth changes by varying the thickness of the piezoelectric layer and the size of the electrode fingers. Specifically, Figure 27The normalized spurious magnitude is a value normalized using a 180° phase rotation of the spurious impedance. Although Figure 27 The results shown are for the case where a piezoelectric layer containing Z-cut LiNbO3 was used, but the same tendency is observed even when piezoelectric layers with other cut angles are used.

[0217] exist Figure 27 Within the region enclosed by the ellipse E, the normalized spurious magnitude between the resonant frequency and the anti-resonant frequency is 1.0. If the relative bandwidth of the elastic wave resonator exceeds 17%, the normalized spurious magnitude may become 1.0 or higher. Therefore, the relative bandwidth is preferably 17% or less. This allows spurious frequencies between the resonant and anti-resonant frequencies to be suppressed.

[0218] Figure 28 This is a graph showing the relationship between Tp / p, metallization rate (MR), and relative bandwidth. Figure 28 The diagram shows the results of calculating the relative bandwidth whenever Tp / p and the metallization rate MR are different.

[0219] exist Figure 28 In the diagram, the area shown by the shading is the region with a relative bandwidth of 17% or less. The boundary between the shading and unshading regions can be roughly represented by a dashed line G. The dashed line G can be represented by MR = 1.75(Tp / p) + 0.075. Moreover, it is preferable that MR ≤ 1.75(Tp / p) + 0.075. In this case, it is easy to achieve a relative bandwidth of 17% or less.

[0220] On the other hand, through Figure 28 The dashed line G1 in the diagram shows that the slope of the change in metallization rate MR relative to the change in Tp / p is the same as that of the dashed line G, and the relative bandwidth becomes the boundary of 17% or less across the entire range. The dashed line G1 can be represented by MR = 1.75(Tp / p) + 0.05. Moreover, it is more preferable that MR ≤ 1.75(Tp / p) + 0.05. In this case, the relative bandwidth can be made to be 17% or less more reliably.

[0221] Figure 29 This is a diagram showing the mapping of the relative bandwidth to the Euler angles (0°, θ, ψ) of LiNbO3 when Tp / p approaches 0 infinitely. Figure 29 The area shown by the shading is the region where a relative bandwidth of at least 5% can be obtained. If the range of this region is approximated, it becomes the range represented by the following equations (1), (2) and (3).

[0222] (0°±10°, 0°~20°, any ψ) … Equation (1)

[0223] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ~180°) …Equation (2)

[0224] (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, any ψ)…Equation (3)

[0225] Preferably, the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer are within the range of Equations (1), (2), or (3) above. This allows for a sufficiently widened relative bandwidth of the elastic wave resonator. The same applies when the piezoelectric layer contains lithium tantalate.

[0226] The Euler angle of the piezoelectric crystal that constitutes the piezoelectric layer affects the material constants of the piezoelectric crystal, such as its piezoelectric constant, elastic constant, and dielectric constant. Therefore, by keeping the Euler angle within the aforementioned range, the relative bandwidth of the elastic wave resonator is broadened.

[0227] Furthermore, in this specification, when “~” is used to indicate the range of any angle in Euler angles, it means that the range of that angle is above the value before “~” and below the value after “~”.

[0228] Euler angles are one of the indicators of the in-plane orientation of a piezoelectric crystal used in elastic wave devices such as elastic wave resonators. The angles φ, θ, and ψ in Euler angles are rotation angles relative to the crystal axis of the piezoelectric crystal. Specifically, for example, the rotation angles when transforming the crystal axis of the piezoelectric crystal to the coordinate system used in the elastic wave device are Euler angles.

[0229] The Euler angles will now be explained in more detail. In this explanation, a right-handed coordinate system with four axes will be used. A right-handed coordinate system is a coordinate system with three mutually orthogonal axes, assigned in the order of the thumb, index finger, and middle finger of the right hand. For example, in the case of (α, β, γ), the α axis is assigned to the thumb, the β axis to the index finger, and the γ axis to the middle finger.

[0230] With Euler angles (φ, θ, ψ), the coordinate system is transformed using the following rotation operations 1) to 3). 1) Rotate (α, β, γ) around the γ-axis by "φ", resulting in (α1, β1, γ1). Next, 2) Rotate (α1, β1, γ1) around the α1-axis by "θ", resulting in (α2, β2, γ2). Next, 3) Rotate (α2, β2, γ2) around the γ2-axis by "ψ", resulting in (α3, β3, γ3). Furthermore, the right-hand rotation direction is set as the positive rotation direction.

[0231] Through the rotation operations 1) to 3) above, (α, β, γ) becomes (α3, β3, γ3). The coordinate systems of (α, β, γ) and (α3, β3, γ3) share the same origin. In addition, the method of Euler angles and coordinate transformation is described in the "Technical Handbook of Elastic Wave Elements", page 549.

[0232] Unless otherwise stated, the following examples are... Figure 1 The structure of the elastic wave resonator 1 in the filter device 10 shown makes... Figure 3 Examples of different materials and Euler angles are shown for piezoelectric layer 5.

[0233] In manufacturing elastic wave devices such as elastic wave resonators 1, for example, a wafer containing a piezoelectric crystal is sliced. This results in multiple piezoelectric layers 5. For example, in a structure where an IDT electrode 8 is provided on the main surface of the wafer and the piezoelectric layer 5, a coordinate system is provided containing an axis extending in the normal direction of the main surface and an axis extending in the orthogonal direction of the electrode. The index representing the relationship between the crystal axis of the wafer and the piezoelectric layer 5 and the aforementioned coordinate system is the Euler angle.

[0234] Specifically, when the crystal axis of the wafer and piezoelectric layer 5 is set to (X, Y, Z) and the coordinate system of the wafer and piezoelectric layer 5 is set to (x1, x2, x3), (X, Y, Z) is transformed into (x1, x2, x3) by Euler angles (φ, θ, ψ).

[0235] Figure 30 This is a schematic diagram of the coordinate system after the crystal axis of the piezoelectric crystal has been transformed using Euler angles.

[0236] exist Figure 30 The image schematically shows a wafer 105 and an IDT electrode 8 disposed on the wafer 105. The x1 axis in the coordinate system of the wafer 105 extends parallel to the orthogonal direction of the electrode. The x3 axis extends in the direction of the normal to the principal surface of the wafer 105. The x2 axis is perpendicular to both the x1 and x3 axes. After the wafer 105 is diced... Figure 3The same applies to the piezoelectric layer 5 shown. Specifically, the x3 axis extends in the normal direction of the first principal surface 5a of the piezoelectric layer 5, and the x1 axis extends parallel to the direction orthogonal to the electrode finger.

[0237] Furthermore, the piezoelectric layer 5 has a negative face and a positive face in the polarization direction. In this specification, the main face, which is positive in the polarization direction by approximately 95% or more, is designated as the positive face. The main face, which is negative in the polarization direction by approximately 95% or more, is designated as the negative face. Moreover, in this specification, the direction from "-" to "+" in the polarization state is defined as the +Z direction. The +Z direction is the polarization direction of the piezoelectric crystal constituting the piezoelectric layer 5.

[0238] Figure 31 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 0°) of the lithium niobate constituting the piezoelectric layer is greater than 0° and less than 60°.

[0239] The angle of inclination of the x3 axis, extending in the normal direction of the principal surface of piezoelectric layer 5, relative to the Z-axis of piezoelectric layer 5 is the angle θ in the Euler angles (φ, θ, ψ). Figure 31 In the example shown, the Euler angles (φ, θ, ψ) are 0°. Therefore, the x1 axis, which extends parallel to the orthogonal direction of the electrode fingers, coincides with the X-axis. The +Z direction, which is the polarization direction of the piezoelectric layer 5, is tilted by an angle θ relative to the x3 axis towards the x2 axis.

[0240] In this example, the first main surface 5a of the piezoelectric layer 5 is the front side. On the other hand, the second main surface 5b of the piezoelectric layer 5 is the back side. An IDT electrode 8 is disposed on the front side of the piezoelectric layer 5.

[0241] U.S. Patent No. 10,790,802 describes a key point: when the angle β in the Euler angle (0°, β, 0°) of the piezoelectric substrate is between 0° and 60°, bulk waves of the thickness shear mode can be appropriately excited, and unwanted waves can be suppressed. In U.S. Patent No. 10,790,802, the piezoelectric substrate comprises lithium niobate. Therefore, when the angle θ in the Euler angle (0°, θ, 0°) of the lithium niobate constituting the piezoelectric layer 5 is 0° or more and 60° or less, bulk waves of the thickness shear mode can be appropriately excited.

[0242] Furthermore, through the following Figure 32 This illustrates other examples of body waves that can be appropriately excited to exhibit thickness shear modes.

[0243] Figure 32 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 90°) of the lithium niobate constituting the piezoelectric layer is greater than -15° but less than 0°.

[0244] exist Figure 32 In the example shown, the Euler angles (φ, θ, ψ) have an angle φ of 0° and an angle ψ of 90°. Therefore, the angle of the x1 axis, which extends parallel to the orthogonal direction of the electrode fingers, relative to the X-axis becomes 90°. On the other hand, the direction of the x2 axis and the direction of the X-axis become parallel. However, the direction of the x2 axis and the direction of the X-axis are opposite to each other. The +Z direction, which is the polarization direction of the piezoelectric layer 5, is tilted relative to the x3 axis on the opposite side from the x1 axis by the absolute value of angle θ. This is because angle θ is a negative value. Alternatively, it can be said that the +Z direction is tilted by θ + 360° relative to the x3 axis on the x1 axis.

[0245] In this example, the first main surface 5a of the piezoelectric layer 5 is the front side. On the other hand, the second main surface 5b of the piezoelectric layer 5 is the back side. An IDT electrode 8 is disposed on the front side of the piezoelectric layer 5.

[0246] U.S. Patent No. 10,797,675 describes a key point: when the angle β in the Euler angles (0°, β, 90°) of the piezoelectric substrate is -15° or more but less than 0°, the electromechanical coupling coefficient of the bulk wave in the thickness shear mode increases. In U.S. Patent No. 10,797,675, the piezoelectric substrate comprises lithium niobate. Therefore, when the angle θ in the Euler angles (0°, θ, 90°) of the lithium niobate constituting the piezoelectric layer 5 is -15° or more but less than 0°, the bulk wave in the thickness shear mode can be appropriately excited.

[0247] Furthermore, in the *Journal of the Acoustical Society of Japan*, Vol. 36, No. 3 (1980), pp. 141-142, the characteristics of surface acoustic waves in LiTaO3, a trigonal (3m) crystal, were explained. The key point stated therein was that, due to the crystal's symmetry, it was sufficient to study the range of 0° ≤ θ ≤ 180° regarding the Euler angles (φ, θ, ψ). That is, when the angles θ differ by 180° between two trigonal (3m) crystals, the electrical characteristics are equal regardless of which crystal is used in elastic wave devices such as elastic wave resonators.

[0248] This is because, in a crystal, a 180° difference in the Euler angles (φ, θ, ψ) is equivalent to a 180° difference in the polarization direction. When the crystal's angles θ differ by 180°, the only change in electrical properties is generally the phase of the excited elastic wave. Therefore, even with a 180° difference in the crystal's angles θ, the electrical properties remain essentially unchanged in elastic wave devices such as elastic wave resonators.

[0249] Furthermore, like LiTaO3, LiNbO3 is also a trigonal (3m) piezoelectric crystal (i.e., trigonal point group 3m). Therefore, it can be said that the same applies to lithium niobate.

[0250] The following shows the range of angle θ in the Euler angles of the lithium niobate constituting the piezoelectric layer 5. Figure 31 as well as Figure 32 The examples shown are of the ranges that differ by 180°.

[0251] Figure 33 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 0°) of the lithium niobate constituting the piezoelectric layer is greater than 180° and less than 240°. Figure 34 This is a schematic diagram showing the coordinate system of the piezoelectric layer when the angle θ in the Euler angles (0°, θ, 90°) of the lithium niobate constituting the piezoelectric layer is greater than 165° and less than 180°.

[0252] exist Figure 33 In the example shown, with Figure 31 Similarly, in the example shown, the x1 axis, extending parallel to the orthogonal direction of the electrode, coincides with the X-axis. The +Z direction, which is the polarization direction of the piezoelectric layer 5, is tilted by an angle θ relative to the x3 axis towards the x2 axis. In this example, the first principal surface 5a of the piezoelectric layer 5 is the negative side. On the other hand, the second principal surface 5b of the piezoelectric layer 5 is the positive side. An IDT electrode 8 is disposed in the negative side of the piezoelectric layer 5.

[0253] exist Figure 34 In the example shown, with Figure 32 Similarly, in the example shown, the directions extending along the x2 axis and the x-axis are opposite to each other. The +Z direction, which is the polarization direction of the piezoelectric layer 5, is tilted by an angle θ relative to the x3 axis towards the x1 axis. In this example, the first principal surface 5a of the piezoelectric layer 5 is negative. On the other hand, the second principal surface 5b of the piezoelectric layer 5 is positive. An IDT electrode 8 is disposed in the negative surface of the piezoelectric layer 5.

[0254] Figure 33 as well as Figure 34 The range of the Euler angle θ in the lithium niobate constituting the piezoelectric layer 5 shown in the example is related to... Figure 31 as well as Figure 32 The examples shown differ by 180° in this range. Therefore, in Figure 33 as well as Figure 34 In the example shown, it is also related to Figure 31 as well as Figure 32 Similarly, the example shown can be used to appropriately excite bulk waves with thickness shear modes.

[0255] exist Figure 31 as well as Figure 32 In the example shown, the IDT electrode 8 is disposed on the front side of the piezoelectric layer 5. On the other hand, in Figure 33 as well as Figure 34 In the example shown, the IDT electrode 8 is disposed on the negative side of the piezoelectric layer 5. The inventors of this invention have discovered that when the IDT electrode is disposed on the negative side, polarization reversal is less likely to occur in the piezoelectric layer compared to when the IDT electrode is disposed on the positive side. Furthermore, when polarization reversal occurs in the piezoelectric layer used in an elastic wave resonator, the electrical characteristics of the elastic wave resonator deteriorate. This will be illustrated using a reference example.

[0256] The basic structure of the reference example is the same as that described in U.S. Patent No. 10,790,802. Specifically, a piezoelectric substrate is provided on a support member having a through hole. An IDT electrode is provided on the piezoelectric substrate.

[0257] Figure 35 This is a piezoelectric response microscopy image showing an example of polarization reversal occurring in a piezoelectric layer. Figure 36 This is a graph showing the admittance-frequency characteristics of an elastic wave resonator with and without polarization reversal in the piezoelectric layer. Additionally, Figure 35 This image is based on a piezoelectric response microscope image taken by an atomic force microscope (manufactured by Bruker Japan KK Corporation, product name Dimension-FastScan (Icon)).

[0258] like Figure 35 As shown, an IDT electrode 118 is provided on the front side of the piezoelectric layer 115. Figure 35 The portion marked with crosshairs represents the area where polarization reversal occurred on the front side. For example... Figure 36 As shown, when polarization reversal occurs in the piezoelectric layer 115, compared with the case where polarization reversal does not occur in the piezoelectric layer 115, the characteristics deteriorate near both the resonant frequency and the anti-resonant frequency.

[0259] In view of this, in the context of Figure 31 as well as Figure 32 The examples shown and Figure 33 as well as Figure 34 The examples shown are compared in the case of... Figure 33 as well as Figure 34 In the example shown, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. In addition, thickness shear modes can be appropriately excited.

[0260] Furthermore, when the volume wave of the thickness shear mode can be appropriately excited at Euler angles (0°, θ, 0°), the same applies when the angle φ in the Euler angles is within the range of 0° ± 10°. Similarly, when the angle ψ in the Euler angles is within the range of 0° ± 10°, the same applies to the volume wave of the thickness shear mode.

[0261] Based on the above, the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer 5 are preferably (0°±10°, 180°~240°, 0°±10°). Therefore, a bulk wave in a thickness shear mode can be appropriately excited in the elastic wave resonator 1. Furthermore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. Therefore, the filter characteristics of the filter device 10 including the elastic wave resonator 1 are less likely to deteriorate.

[0262] The Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer 5 are more preferably (0°, 180°~240°, 0°±3°), and even more preferably (0°, 180°~240°, 0°). Therefore, in the elastic wave resonator 1, bulk waves of the thickness shear mode can be excited more reliably and appropriately. Furthermore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. Therefore, the filter characteristics of the filter device 10 including the elastic wave resonator 1 are less likely to deteriorate.

[0263] Furthermore, when the volume wave of the thickness shear mode can be appropriately excited at Euler angles (0°, θ, 90°), the same applies when the angle φ in the Euler angles is within the range of 0° ± 10°. Similarly, when the angle ψ in the Euler angles is within the range of 90° ± 10°, the same applies when the volume wave of the thickness shear mode can be appropriately excited.

[0264] The Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer 5 are preferably (0°±10°, 165°~180°, 90°±10°). Therefore, a bulk wave in a thickness shear mode can be appropriately excited in the elastic wave resonator 1. Furthermore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. Therefore, the filter characteristics of the filter device 10 including the elastic wave resonator 1 are less likely to deteriorate.

[0265] The Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer 5 are more preferably (0°, 165°~180°, 90°±3°), and even more preferably (0°, 165°~180°, 90°). Therefore, in the elastic wave resonator 1, bulk waves of the thickness shear mode can be excited more reliably and appropriately. Furthermore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. Therefore, the filter characteristics of the filter device 10 including the elastic wave resonator 1 are less likely to deteriorate.

[0266] Furthermore, the elastic wave resonator 1 does not necessarily have to be configured to excite a bulk wave with a thickness shear mode. For example, the elastic wave resonator 1 can also be configured to excite a plate wave. Even when the elastic wave resonator 1 uses an elastic wave other than a bulk wave with a thickness shear mode, it is preferable to provide an IDT electrode 8 on the negative side of the piezoelectric layer 5. As a result, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate.

[0267] Specifically, the Euler angles (φ, θ, ψ) of the piezoelectric crystal with a trigonal point group of 3m constituting the piezoelectric layer 5 are preferably (0°±10°, θ, 0°±10°) and 90°<θ<270°. In this case, an IDT electrode 8 is provided on the negative side of the piezoelectric layer 5. Therefore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. In addition, the piezoelectric crystal with a trigonal point group of 3m is, for example, lithium niobate or lithium tantalate.

[0268] The Euler angles (φ, θ, ψ) of the piezoelectric crystal with trigonal point group 3m constituting the piezoelectric layer 5 are more preferably (0°, θ, 0°±3°) and 90°<θ<270°. The Euler angles (φ, θ, ψ) of the piezoelectric crystal with trigonal point group 3m constituting the piezoelectric layer 5 are further preferably (0°, θ, 0°) and 90°<θ<270°. Therefore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate.

[0269] On the other hand, the Euler angles (φ, θ, ψ) of the piezoelectric crystal with trigonal point group 3m constituting the piezoelectric layer 5 are preferably (0°±10°, θ, 90°±10°) and 90°<θ<270°. In this case, an IDT electrode 8 is also provided on the negative side of the piezoelectric layer 5. Therefore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate.

[0270] The Euler angles (φ, θ, ψ) of the piezoelectric crystal with trigonal point group 3m constituting the piezoelectric layer 5 are more preferably (0°, θ, 90°±3°) and 90°<θ<270°. The Euler angles (φ, θ, ψ) of the piezoelectric crystal with trigonal point group 3m constituting the piezoelectric layer 5 are further preferably (0°, θ, 90°) and 90°<θ<270°. Therefore, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate.

[0271] As described above, when the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer 5 are within the range of Equations (1), (2), or (3), the relative bandwidth of the elastic wave resonator can be sufficiently widened. In addition, the same effect can be obtained when the ranges of angles θ in Equations (1), (2), and (3) differ by 180°.

[0272] Specifically, for example, the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer 5 are preferably within the range of Equation (4), Equation (5), or Equation (6) below. As a result, the relative bandwidth of the elastic wave resonator 1 can be sufficiently widened.

[0273] (0°±10°, 180°~200°, any ψ) … Equation (4)

[0274] (0°±10°, 200°~260°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 200°~260°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ~180°) …Equation (5)

[0275] (0°±10°, [360°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~360°, any ψ)…Equation (6)

[0276] In addition, when the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer 5 are within the range of Equation (4), Equation (5), or Equation (6), an IDT electrode 8 is provided on the negative side of the piezoelectric layer 5. As a result, polarization reversal is less likely to occur in the piezoelectric layer 5, and the electrical characteristics of the elastic wave resonator 1 are less likely to deteriorate. As a result, the filter characteristics of the filter device 10 including the elastic wave resonator 1 are less likely to deteriorate.

[0277] The following describes a specific method for determining the passband of a filter device. First, if a data sheet exists for the filter device, it can be referred to directly. The passband recorded on the data sheet is the passband of the filter device. Examples of passbands are shown in Tables 1 to 5 below. Tables 1 and 2 show the passband for 4G. Tables 3 to 5 show the passband for 5G.

[0278] [Table 1]

[0279]

[0280] [Table 2]

[0281]

[0282] [Table 3]

[0283]

[0284] [Table 4]

[0285]

[0286] [Table 5]

[0287]

[0288] In the absence of a product datasheet for the filter device, the passband of the filter device can be determined simply by measuring its throughput characteristics. Specifically, for example, the throughput characteristics can be measured using a network analyzer. An example of a network analyzer could be "Keysight Technologies, model P5027B".

[0289] When measuring the pass characteristics of a filter device, a fixture for connecting the filter device and a network analyzer can also be used. This fixture may, for example, have a pair of connectors and a base plate. One connector is connected to a terminal in the filter device connected to the input potential. The other connector is connected to a terminal in the filter device connected to the output potential. The base plate grounds a terminal in the filter device connected to ground potential.

[0290] For example, first, a filter device is mounted on the substrate of the aforementioned fixture. Then, the terminal of the filter device connected to the ground potential is brought into contact with the substrate of the fixture. This grounds the terminal of the filter device connected to the ground potential.

[0291] The terminals in the filter device connected to the input potential and the terminals connected to the output potential are respectively connected to a pair of connectors of the aforementioned fixture. Furthermore, the characteristic impedance of the path from each connector of the fixture to each terminal of the filter device is typically designed to be 50Ω. For example, the connectors are connected to the input / output ports of a network analyzer via cables. Thus, the terminals in the filter device connected to the input potential and the terminals connected to the output potential are electrically connected to the input / output ports of the network analyzer.

[0292] The conditions for measuring the pass characteristics of a filter device are as follows.

[0293] Temperature: Room temperature

[0294] Input power: 0dBm

[0295] Measured pass characteristics: S21

[0296] Figure 37 This is a diagram illustrating an example of the throughput characteristics of a filter device.

[0297] While varying the frequency, the throughput characteristics are measured. This can be achieved by using a control group as an example. Figure 37 The passband of the filter device can be determined by the frequency band where the insertion loss decreases, indicated by the arrows, and the passbands shown in Tables 1 to 5. Furthermore, the passbands shown in Tables 1 to 5 are examples, and the passbands compared with the measured results are not limited to those in Tables 1 to 5.

[0298] Hereinafter, examples of the manner in which the filter device of the present invention is described are summarized.

[0299] <1> A filter device has a passband, wherein the filter device includes a plurality of resonators comprising elastic wave resonators, the elastic wave resonators comprising: a piezoelectric layer having a first main surface and a second main surface opposite to each other; an IDT electrode disposed on the first main surface of the piezoelectric layer having a plurality of electrode fingers; a first dielectric film disposed on the first main surface of the piezoelectric layer; and a second dielectric film disposed on the second main surface of the piezoelectric layer, wherein a direction orthogonal to the extension direction of the plurality of electrode fingers is defined as the electrode finger orthogonal direction, and the region where adjacent electrode fingers overlap when viewed from the electrode finger orthogonal direction is an intersection region, the first dielectric film and the second dielectric film overlapping the intersection region when viewed from above. When the highest frequency in the passband is set to FH, the lowest frequency in the passband is set to FL, and the center frequency of the passband is set to FC, the relative bandwidth width expressed by ((FH-FL) / FC)×100[%] is 8.5% or more. When the thickness in the cross region of the piezoelectric layer is set to Tp, the thickness of the portion of the first dielectric film that overlaps with the cross region in top view is set to Td_f, and the thickness of the portion of the second dielectric film that overlaps with the cross region in top view is set to Td_b, 0.322<(Td_f / Tp)+(Td_b / Tp)<0.786, and |(Td_f / Tp)-(Td_b / Tp)|<0.196.

[0300] <2> according to <1> The filter device, wherein,

[0301] The elastic wave resonator is configured to utilize a body wave with a thickness shear mode.

[0302] <3> according to <1> The filter device, wherein,

[0303] It also includes: a support member, which is stacked on the piezoelectric layer, and an acoustic reflector is formed in the support member at a position where it overlaps with the plurality of electrode fingers when viewed from above, and Tp / p is 0.5 or less when the center-to-center distance between adjacent electrode fingers is set as p.

[0304] <4> according to <3> The filter device, wherein,

[0305] Tp / p is below 0.24.

[0306] <5> according to <3> or <4> The filter device, wherein,

[0307] When the metallization rate of the electrode fingers relative to the excitation region is set as MR, MR ≤ 1.75(Tp / p) + 0.075 is satisfied.

[0308] The excitation region is the area where adjacent electrode fingers overlap each other in the orthogonal direction of the electrode fingers, and is the region between the centers of adjacent electrode fingers.

[0309] <6> according to <3> ~ <5> The filter device described in any of the above, wherein,

[0310] The acoustic reflection portion is a cavity, and the support member and the piezoelectric layer are configured such that a part of the support member and a part of the piezoelectric layer sandwich the cavity and are opposite to each other.

[0311] <7> according to <3> ~ <5> The filter device described in any of the above, wherein,

[0312] The acoustic reflector is an acoustic reflector membrane comprising a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance. The support member and the piezoelectric layer are configured such that at least a portion of the support member and at least a portion of the piezoelectric layer sandwich the acoustic reflector membrane and are opposite to each other.

[0313] <8> according to <1> The filter device, wherein,

[0314] It is configured to utilize plate waves.

[0315] <9> according to <1> ~ <8> The filter device described in any of the above, wherein,

[0316] The piezoelectric layer comprises lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formulas (1), (2) or (3).

[0317] (0°±10°, 0°~20°, any ψ) … Equation (1)

[0318] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ~180°) …Equation (2)

[0319] (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, any ψ)…Equation (3)

[0320] <10> The filter device according to any one of claims 1 to 8, wherein,

[0321] The piezoelectric layer comprises lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following equations (4), (5) or (6).

[0322] (0°±10°, 180°~200°, any ψ) … Equation (4)

[0323] (0°±10°, 200°~260°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 200°~260°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ~180°) …Equation (5)

[0324] (0°±10°, [360°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~360°, any ψ)…Equation (6)

[0325] <11> according to <1> ~ <10> The filter device described in any of the above, wherein,

[0326] The piezoelectric layer contains lithium niobate.

[0327] <12> according to <1> ~ <11> The filter device described in any of the above, wherein,

[0328] The first dielectric film and the second dielectric film comprise silicon oxide.

[0329] Explanation of reference numerals in the attached figures

[0330] 1: Elastic wave resonator;

[0331] 2: Supporting components;

[0332] 2a: Cavity;

[0333] 3: Support base plate;

[0334] 4: Insulation layer;

[0335] 5, 5A: Piezoelectric layer;

[0336] 5X: Thickness variation area;

[0337] 5Y: Membrane section;

[0338] 5a, 5b: First principal face, second principal face;

[0339] 6, 6A, 6B: First dielectric film;

[0340] 6X: Thickness variation area;

[0341] 7, 7A: Second dielectric film;

[0342] 7X: Thickness variation area;

[0343] 8: IDT electrode;

[0344] 9, 9A~9C: Stacked sections;

[0345] 9a: Central part between electrode fingers;

[0346] 10: Filter device;

[0347] 13, 14: Signal terminal 1 and signal terminal 2;

[0348] 16, 17: Busbar 1 and Busbar 2;

[0349] 18, 19: First electrode finger, second electrode finger;

[0350] 21: Elastic wave resonator;

[0351] 31: Elastic wave resonator;

[0352] 32: Supporting components;

[0353] 33a~33c: Low acoustic impedance layer;

[0354] 34a, 34b: High acoustic impedance layers;

[0355] 38: Acoustic reflector membrane;

[0356] 41: Elastic wave resonator;

[0357] 43, 44: Busbar for the first reflector and busbar for the second reflector;

[0358] 45: Reflector electrode index;

[0359] 46, 47: Reflectors;

[0360] 51: Elastic wave resonator;

[0361] 58: IDT electrode;

[0362] 105: Chip;

[0363] 115: Piezoelectric layer;

[0364] 118: IDT electrode;

[0365] A: Intersection area;

[0366] C: Incentive region;

[0367] P2~P4: Parallel arm resonators;

[0368] S1~S5: Series arm resonators.

Claims

1. A filter device having a passband, wherein, The filter device includes multiple resonators, including elastic wave resonators. The elastic wave resonator has: The piezoelectric layer has a first principal surface and a second principal surface that are opposite to each other; An IDT electrode is disposed on the first main surface of the piezoelectric layer and has multiple electrode fingers; A first dielectric film is disposed on the first main surface of the piezoelectric layer; as well as A second dielectric film is disposed on the second main surface of the piezoelectric layer. The direction orthogonal to the extending direction of the plurality of electrode fingers is defined as the electrode finger orthogonal direction. When viewed from the electrode finger orthogonal direction, the area where adjacent electrode fingers overlap is the intersection region. The first dielectric film and the second dielectric film overlap with the intersection region when viewed from above. When the highest frequency in the passband is set to FH, the lowest frequency in the passband is set to FL, and the center frequency of the passband is set to FC, the relative bandwidth, expressed as ((FH-FL) / FC)×100%, is greater than 8.5%. When the thickness of the cross region of the piezoelectric layer is set as Tp, the thickness of the portion of the first dielectric film that overlaps with the cross region in top view is set as Td_f, and the thickness of the portion of the second dielectric film that overlaps with the cross region in top view is set as Td_b, 0.322 < (Td_f / Tp) + (Td_b / Tp) < 0.786, and |(Td_f / Tp)-(Td_b / Tp)|<0.

196.

2. The filter device according to claim 1, wherein, The elastic wave resonator is configured to utilize a body wave with a thickness shear mode.

3. The filter device according to claim 1, wherein, It also includes: a support member, stacked on the piezoelectric layer, An acoustic reflector is formed in the support member at a position where it overlaps with the plurality of electrodes when viewed from above. When the center-to-center distance between adjacent electrodes is set as p, Tp / p is 0.5 or less.

4. The filter device according to claim 3, wherein, Tp / p is below 0.

24.

5. The filter device according to claim 3 or 4, wherein, When the metallization rate of the electrode fingers relative to the excitation region is set as MR, MR ≤ 1.75(Tp / p) + 0.075 is satisfied. The excitation region is the area where adjacent electrode fingers overlap each other in the orthogonal direction of the electrode fingers, and is the region between the centers of adjacent electrode fingers.

6. The filter device according to any one of claims 3 to 5, wherein, The sound-reflecting part is a hollow part. The support member and the piezoelectric layer are configured such that a portion of the support member and a portion of the piezoelectric layer sandwich the cavity and are opposite to each other.

7. The filter device according to any one of claims 3 to 5, wherein, The acoustic reflector is an acoustic reflector film comprising a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance. The support member and the piezoelectric layer are configured such that at least a portion of the support member and at least a portion of the piezoelectric layer sandwich the acoustic reflective membrane and are opposite to each other.

8. The filter device according to claim 1, wherein, It is configured to utilize plate waves.

9. The filter device according to any one of claims 1 to 8, wherein, The piezoelectric layer comprises lithium niobate or lithium tantalate. The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following equations (1), (2), or (3). (0°±10°, 0°~20°, any ψ) … Equation (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ~180°) …Equation (2) (0°±10°, [180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, any ψ)…Equation (3).

10. The filter device according to any one of claims 1 to 8, wherein, The piezoelectric layer comprises lithium niobate or lithium tantalate. The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following equations (4), (5), or (6). (0°±10°, 180°~200°, any ψ) … Equation (4) (0°±10°, 200°~260°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 200°~260°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 ~180°) …Equation (5) (0°±10°, [360°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~360°, any ψ)…Equation (6).

11. The filter device according to any one of claims 1 to 10, wherein, The piezoelectric layer contains lithium niobate.

12. The filter device according to any one of claims 1 to 11, wherein, The first dielectric film and the second dielectric film comprise silicon oxide.

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