Elastic wave device

Abstract

Provided is an elastic wave device capable of improving the response level in the attenuation region outside the passband. The elastic wave device (1) of the present invention includes a piezoelectric substrate (2), a first IDT electrode (3A) provided on the piezoelectric substrate (2), and a first reflector (4A) and a second reflector. The first IDT electrode (3A), the first reflector (4A), and the second reflector each have a plurality of electrode fingers. At least any one of the first IDT electrode (3A), the first reflector (4A), and the second reflector has a duty ratio uneven portion in which the duty ratios of three electrode fingers that are continuous in the elastic wave propagation direction are all different.

Description

Technical Field

[0001] This invention relates to elastic wave devices. Background Technology

[0002] Previously, elastic wave devices have been widely used in filters for portable telephones, etc. Patent Document 1 discloses an example of a longitudinally coupled resonator type elastic wave filter as an elastic wave device. In this elastic wave device, multiple comb-shaped electrode sections are provided on a piezoelectric substrate. Each comb-shaped electrode section has a pair of comb-tooth-shaped electrodes. In each comb-shaped electrode section, the duty cycle of one comb-tooth-shaped electrode is different from that of the other. This improves the insertion loss.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2004-112591 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, when using the elastic wave device described in Patent Document 1, the filter characteristics sometimes deteriorate due to unwanted resonance. In particular, in longitudinally coupled resonator type elastic wave filters that utilize longitudinal modes to form the attenuation region, the intensity of the longitudinal modes increases, and the response level of the attenuation region may deteriorate.

[0008] The purpose of this invention is to provide an elastic wave device capable of improving the response level in the attenuation region outside the passband.

[0009] means for solving problems

[0010] In a broad aspect of the elastic wave device of the present invention, it comprises: a piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; and a first reflector and a second reflector disposed on both sides of the IDT electrode on the piezoelectric substrate in the elastic wave propagation direction, wherein the IDT electrode, the first reflector and the second reflector each have a plurality of electrode fingers, and at least one of the IDT electrode, the first reflector and the second reflector has a duty cycle non-uniform portion, wherein the duty cycle non-uniform portion is a portion in which the duty cycles of three consecutive electrode fingers in the elastic wave propagation direction are all different.

[0011] In another broad aspect of the elastic wave device of the present invention, it comprises: a piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; and a first reflector and a second reflector disposed on both sides of the IDT electrode on the piezoelectric substrate in the elastic wave propagation direction. The IDT electrode, the first reflector, and the second reflector each have a plurality of electrode fingers. When the average width ratio of the arbitrary electrode finger is defined as the value obtained by dividing the width of any electrode finger by the average width of all the electrode fingers of the IDT electrode, the first reflector, and the second reflector, at least one of the IDT electrode, the first reflector, and the second reflector has a non-uniform portion of the average width ratio, which is the portion in which the average width ratios of three consecutive electrode fingers in the elastic wave propagation direction are all different.

[0012] Invention Effects

[0013] The elastic wave device according to the present invention can improve the response level in the attenuation region outside the passband. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of a filter device including the elastic wave device of the first embodiment of the present invention.

[0015] Figure 2 This is a schematic top view showing the first reflector and the vicinity of the first IDT electrode of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 3 This is a schematic front cross-sectional view near three consecutive electrode fingers in the elastic wave propagation direction of the first IDT electrode of the first embodiment of the present invention.

[0017] Figure 4 This is a diagram showing the duty cycle of each electrode finger of the plurality of IDT electrodes, the first reflector, and the second reflector in the first embodiment of the present invention.

[0018] Figure 5 This is a diagram showing the attenuation frequency characteristics of a filter device having an elastic wave device according to the first embodiment of the present invention and a first comparative example.

[0019] Figure 6 This is a graph showing the relationship between the standard deviation of the duty cycle of the filter device of the elastic wave device having the first embodiment of the present invention and the response level outside the passband.

[0020] Figure 7 This is a schematic top view showing the first reflector and the vicinity of the first IDT electrode of the elastic wave device, which is a first variation of the first embodiment of the present invention.

[0021] Figure 8 This is a schematic top view of the vicinity of the first reflector and the first IDT electrode of the elastic wave device, which is a second variation of the first embodiment of the present invention.

[0022] Figure 9 This is a schematic front cross-sectional view near three consecutive electrode fingers in the elastic wave propagation direction in the first IDT electrode of a third variation of the first embodiment of the present invention.

[0023] Figure 10 This is a schematic top view of the elastic wave device according to the second embodiment of the present invention.

[0024] Figure 11 This is a diagram showing the average width ratio of each electrode finger of the IDT electrode, the first reflector, and the second reflector in the second embodiment of the present invention.

[0025] Figure 12 This is a graph showing the attenuation frequency characteristics of a filter device having the elastic wave device of the second embodiment of the present invention and a second comparative example.

[0026] Figure 13 This is a graph showing the relationship between the standard deviation of the average width ratio of the electrode fingers of the filter device having the elastic wave device of the second embodiment of the present invention and the response level of the longitudinal mode ripple. Detailed Implementation

[0027] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0028] It should be noted that the embodiments described in this specification are illustrative, and it is indicated in advance that partial substitutions or combinations of structures can be made between different embodiments.

[0029] Figure 1 This is a circuit diagram of a filter device including the elastic wave device according to the first embodiment of the present invention. It should be noted that... Figure 1 The elastic wave device 1 is shown in simplified form in the figure.

[0030] The elastic wave device 1 in this embodiment is a longitudinally coupled resonator type elastic wave filter. The filter device 10 includes the aforementioned elastic wave device 1. It should be noted that the filter device 10 is a filter device according to one embodiment of the present invention. The filter device 10 is a receiving filter. However, the filter device 10 can also be a transmitting filter. The circuit structure of the filter device 10 is not particularly limited. The filter device 10 can include the elastic wave device 1 of the present invention.

[0031] Figure 2This is a schematic top view showing the vicinity of the first reflector and the first IDT electrode of the elastic wave device according to the first embodiment of the present invention. It should be noted that... Figure 2 The wiring connecting to the elastic wave device 1 is omitted in the text. Figure 2 The same applies to the top view outside of it.

[0032] The elastic wave device 1 is a 7IDT type longitudinally coupled resonator elastic wave filter. The elastic wave device 1 has a piezoelectric substrate 2. Multiple IDT electrodes are disposed on the piezoelectric substrate 2. Elastic waves are excited by applying an AC voltage to each IDT electrode. In this embodiment, surface acoustic waves are excited in the elastic wave device 1. The multiple IDT electrodes are arranged along the elastic wave propagation direction. A pair of reflectors are disposed on both sides of the multiple IDT electrodes on the piezoelectric substrate in the elastic wave propagation direction. More specifically, the pair of reflectors are... Figure 1 The first reflector 4A and the second reflector 4B are shown. Starting from the first reflector 4A, a first IDT electrode 3A, a second IDT electrode 3B, a third IDT electrode 3C, a fourth IDT electrode 3D, a fifth IDT electrode 3E, a sixth IDT electrode 3F, and a seventh IDT electrode 3G are arranged sequentially as multiple IDT electrodes. It should be noted that the number of IDT electrodes in the elastic wave device 1 is not limited to seven. The elastic wave device 1 can also be, for example, a 3-IDT type or a 5-IDT type, etc.

[0033] like Figure 2 As shown, the first IDT electrode 3A has a pair of busbars and multiple electrode fingers. The pair of busbars includes a first busbar 12 and a second busbar 13. The first busbar 12 and the second busbar 13 are opposite to each other. The multiple electrode fingers of the first IDT electrode 3A are multiple first electrode fingers 14 and multiple second electrode fingers 15. One end of each of the multiple first electrode fingers 14 is connected to the first busbar 12. One end of each of the multiple second electrode fingers 15 is connected to the second busbar 13. The multiple first electrode fingers 14 and multiple second electrode fingers 15 are inserted alternately. The other IDT electrodes also have a pair of busbars and multiple electrode fingers in the same way as the first IDT electrode 3A.

[0034] The first reflector 4A has multiple electrode fingers 16. Similarly, the second reflector 4B also has multiple electrode fingers. In this embodiment, the electrode finger spacing of each IDT electrode, the first reflector 4A, and the second reflector 4B is all the same. Electrode finger spacing refers to the distance between the centers of adjacent electrode fingers. However, the electrode finger spacing of each IDT electrode, the first reflector 4A, and the second reflector 4B may not be exactly the same.

[0035] In this specification, the duty cycle is defined for each electrode finger. That is, in each IDT electrode, the width of any electrode finger divided by the electrode finger spacing is the duty cycle of that arbitrary electrode finger. More specifically, when the duty cycle is set as d, the width of the electrode finger as w, and the electrode finger spacing as p, d = w / p. It should be noted that the width of the electrode finger is its dimension along the direction of elastic wave propagation.

[0036] Furthermore, the portion where the duty cycles of three consecutive electrode fingers in the direction of elastic wave propagation are all different is defined as a duty cycle non-uniformity portion. In this specification, the electrode finger spacing when calculating the duty cycle is set as the average of the center-to-center distances between any given electrode finger and the electrode fingers flanking that given electrode finger. Figure 3 The diagram shows details of the electrode finger spacing and examples of duty cycle non-uniformity.

[0037] Figure 3 This is a schematic front cross-sectional view showing the vicinity of three consecutive electrode fingers in the elastic wave propagation direction of the first IDT electrode according to the first embodiment. Electrode finger 18A is an electrode finger at one end of the first IDT electrode 3A in the elastic wave propagation direction. Electrode fingers 18A, 18B, and 18C are three consecutive electrode fingers in the elastic wave propagation direction.

[0038] calculate Figure 3 The electrode finger spacing shown for the duty cycle of electrode finger 18B is the average of the center-to-center distance L1 between electrode fingers 18B and 18A, and the center-to-center distance L2 between electrode fingers 18B and 18C. More specifically, the electrode finger spacing for the duty cycle of electrode finger 18B is equal to the distance A from the center between the center of electrode finger 18B and the center of electrode finger 18A to the center between the center of electrode finger 18B and the center of electrode finger 18C.

[0039] On the other hand, the electrode finger spacing when calculating the duty cycle of one or the other electrode finger in the direction of elastic wave propagation is the center-to-center distance between that electrode finger and its adjacent electrode finger. For example, Figure 3 The electrode finger spacing shown when calculating the duty cycle of electrode finger 18A is the center-to-center distance L1 between electrode fingers 18A and 18B. The same applies to the first reflector 4A and the second reflector 4B.

[0040] exist Figure 3 In the portion shown, the spacing between the electrode fingers is fixed, but the widths of electrode fingers 18A, 18B, and 18C are all different. Therefore, this portion is a duty cycle non-uniform region.

[0041] This embodiment is characterized in that at least one of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B has a duty cycle non-uniformity. This improves the response level in the attenuation region outside the passband. The details of this effect will be explained below along with the details of this embodiment.

[0042] Figure 4 This is a diagram showing the duty cycles of the electrodes of the plurality of IDT electrodes, the first reflector, and the second reflector in the first embodiment. The duty cycles are as follows: [Diagram showing duty cycles from the first reflector 4A side towards the second reflector 4B side]. Figure 4 The larger the electrode number on the horizontal axis, the better.

[0043] In this embodiment, the duty cycles of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B are random. All portions of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B constitute a duty cycle non-uniformity region. The minimum duty cycle of the elastic wave device 1 is 0.39. The maximum duty cycle is 0.62. The average duty cycle is 0.5. It should be noted that in the elastic wave device 1, 95% of the duty cycles of all electrodes are between 0.45 and 0.55. In the elastic wave device 1, the standard deviation of the distribution of all duty cycles of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B is 0.024.

[0044] It should be noted that the circuit structure of the filter device 10 in this embodiment is as follows: Figure 1 As shown. More specifically, the filter device 10 has a first signal terminal 5 and a second signal terminal 6. The first signal terminal 5 is an antenna terminal. The first signal terminal 5 is connected to an antenna. The first signal terminal 5 and the second signal terminal 6 can be configured as electrode pads or as wiring. In addition, the filter device 10 has elastic wave resonators S1, S2, P1, and P2. Elastic wave resonators S1 and S2 are series-connected traps. Elastic wave resonator S1 is connected between the first signal terminal 5 and the elastic wave device 1. Elastic wave resonator S2 is connected between the elastic wave device 1 and the second signal terminal 6. Elastic wave resonators P1 and P2 are parallel-connected traps. Elastic wave resonator P1 is connected between the connection point between elastic wave resonator S1 and the elastic wave device 1 and the ground potential. Elastic wave resonator P2 is connected between the second signal terminal 6 and the ground potential.

[0045] As described above, in this embodiment, the response level in the attenuation region outside the passband can be improved. This effect is shown by comparing the filter device 10 with the first comparative example. It should be noted that the filter device of the first comparative example differs from that of this embodiment in that the duty cycles of the plurality of IDT electrodes, the first reflector, and the second reflector in the longitudinally coupled resonator type elastic wave filter are fixed.

[0046] Figure 5 This is a diagram showing the attenuation frequency characteristics of the filter device having the elastic wave device of the first embodiment and the first comparative example.

[0047] like Figure 5 As indicated by arrows B1, B2, and B3, in the first comparative example, the response level caused by unwanted waves is high outside the passband. In contrast, it can be seen that in the first embodiment, the response level caused by unwanted waves is lower. In particular, as indicated by arrow B1, the response level in the attenuation region outside the passband can be improved in the first embodiment.

[0048] In the first comparative example, the duty cycle is fixed, therefore, the reflected signals in adjacent electrode fingers are in phase. This sometimes leads to unwanted resonance. In contrast, in the first embodiment, a duty cycle non-uniformity is provided. In the duty cycle non-uniformity, the phase of the reflected signals in adjacent electrode fingers is difficult to match. Consequently, the Q value associated with the resonance of unwanted waves such as the longitudinal mode indicated by arrow B1 becomes lower. Therefore, unwanted resonance can be suppressed, and the response level caused by unwanted waves can be improved.

[0049] Here, in the filter device 10, the standard deviations of the distributions of all duty cycles of the multiple IDT electrodes, the first reflector 4A, and the second reflector 4B of the elastic wave device 1 are made different, and the out-of-band response level is measured. It should be noted that the frequency at which the response level is measured is... Figure 5 The frequency indicated by arrow B1 in the diagram.

[0050] Figure 6 This is a graph showing the relationship between the standard deviation of the duty cycle of the filter device of the elastic wave device having the first embodiment and the response level outside the passband.

[0051] like Figure 6 As shown, when the standard deviation of the duty cycle is 0.015 or higher, the response level caused by the longitudinal mode, which is a useless wave, is lower compared to when the standard deviation is less than 0.015. Therefore, the standard deviation of the distribution of all duty cycles of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B of the elastic wave device 1 is preferably 0.015 or higher. This further improves the response level in the attenuation region outside the passband.

[0052] It should be noted that the standard deviation of the distribution of all duty cycles of the multiple IDT electrodes, the first reflector 4A, and the second reflector 4B in the elastic wave device 1 is preferably below 0.55. This makes it difficult for filter characteristics such as insertion loss to deteriorate.

[0053] In the distribution of all duty cycles of the multiple IDT electrodes, the first reflector 4A, and the second reflector 4B in the elastic wave device 1, let the average value of the duty cycle be d. ave At that time, d is preferred over 95%. ave Duty cycle within ±0.05. Under this condition, filter characteristics such as insertion loss are unlikely to deteriorate.

[0054] As described above, in this embodiment, the duty cycle of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B is random. However, it is acceptable for at least any one of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B to have a duty cycle non-uniformity. In this case, the response level in the attenuation region outside the passband can also be improved.

[0055] However, in this embodiment, the electrode finger spacing of each IDT electrode, the first reflector 4A, and the second reflector 4B is all the same. On the other hand, the width of the electrode fingers of each IDT electrode, the first reflector 4A, and the second reflector 4B is random. Therefore, the duty cycle becomes random. Here, the average width ratio of that arbitrary electrode finger is defined as the value obtained by dividing the width of any arbitrary electrode finger by the average width of all the electrode fingers of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B. More specifically, the average width ratio is defined as wc, the width of the electrode finger as w, and the average width of the electrode fingers as wc. ave At that time, wc = W / W ave The portion where the average width ratios of three consecutive electrode fingers in the direction of elastic wave propagation are all different is defined as the portion with a non-uniform average width ratio. In the elastic wave device 1, all portions of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B are portions with a non-uniform average width ratio. However, it is sufficient that at least one of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B has a portion with a non-uniform average width ratio. In this case, the response level in the attenuation region outside the passband can also be improved. It should be noted that the electrode finger spacing of each IDT electrode, the first reflector 4A, and the second reflector 4B may not all be the same.

[0056] Similar to the duty cycle distribution described above, the standard deviation of the distribution of the average width ratio of all electrode fingers of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B of the elastic wave device 1 is preferably 0.015 or more. This further improves the response level in the attenuation region outside the passband. The standard deviation of the distribution of the average width ratio of all electrode fingers of the plurality of IDT electrodes, the first reflector 4A, and the second reflector 4B of the elastic wave device 1 is preferably 0.55 or less. This makes it difficult for filter characteristics such as insertion loss to deteriorate.

[0057] In the distribution of the average width ratio of all electrode fingers of the multiple IDT electrodes, the first reflector 4A, and the second reflector 4B in the elastic wave device 1, it is preferably more than 95% within the range of 1 ± 0.05. In this case, filter characteristics such as insertion loss are less likely to deteriorate.

[0058] Figure 7 This is a schematic top view showing the first reflector and the vicinity of the first IDT electrode of the elastic wave device of the first modified example of the first embodiment.

[0059] In this modified example, the first IDT electrode 23X has a portion with a fixed duty cycle and a duty cycle non-uniform portion C. More specifically, in the first IDT electrode 23X, the duty cycle is fixed in all portions except for the duty cycle non-uniform portion C. It should be noted that the first IDT electrode 23X may also have multiple duty cycle non-uniform portions C. In this case, the portion with a fixed duty cycle and the duty cycle non-uniform portion C are arranged alternately. The number of electrodes in the duty cycle non-uniform portion C need to be three or more. On the other hand, in this modified example, the duty cycles of the multiple IDT electrodes other than the first IDT electrode 23X, as well as the first reflector 24A and the second reflector, are fixed.

[0060] In this modified example, the duty cycle non-uniformity C is also the average width ratio non-uniformity. The first IDT electrode 23X has a portion with a fixed width of the electrode fingers and an average width ratio non-uniformity portion. It should be noted that the first IDT electrode 23X may also have multiple average width ratio non-uniformities. In this case, the portion with a fixed width of the electrode fingers and the average width ratio non-uniformity portion are arranged alternately. The number of electrode fingers in the average width ratio non-uniformity portion only needs to be three or more. On the other hand, in this modified example, the widths of the electrode fingers of the multiple IDT electrodes other than the first IDT electrode 23X, as well as the first reflector 24A and the second reflector, are fixed. In this modified example, the response level in the attenuation region outside the passband can also be improved.

[0061] Figure 8 This is a schematic top view showing the first reflector and the vicinity of the first IDT electrode of the elastic wave device in a second variation of the first embodiment.

[0062] In this modified example, the first IDT electrode 23Y has a first region D, a second region E, and a third region F. The first region D is located at one end in the direction of elastic wave propagation. The second region E is located at the other end in the direction of elastic wave propagation. The third region F is adjacent to both the first region D and the second region E. The first region D and the second region E each include a plurality of electrode fingers. The spacing between the electrode fingers in the first region D and the second region E is narrower than the spacing between the electrode fingers in other regions.

[0063] In this modified example, the duty cycle non-uniformity C and the average width ratio non-uniformity include the central electrode finger of the first IDT electrode 23Y. The duty cycle non-uniformity C and the average width ratio non-uniformity are not located at the boundary between the first region D and the third region F. Similarly, the duty cycle non-uniformity C and the average width ratio non-uniformity are also not located at the boundary between the second region E and the third region F. However, in this modified example, it is sufficient that the duty cycle non-uniformity C and the average width ratio non-uniformity are not located at the aforementioned boundaries. The duty cycle non-uniformity C and the average width ratio non-uniformity may also exclude the central electrode finger of the first IDT electrode 23Y. In this modified example, the response level in the attenuation region outside the passband can also be improved.

[0064] like Figure 3 As shown, in this embodiment, the piezoelectric substrate 2 is a piezoelectric substrate that includes only a piezoelectric layer. Materials used for the piezoelectric layer include, for example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate). However, the piezoelectric substrate 2 may also be a multilayer substrate including a piezoelectric layer.

[0065] Figure 9 This is a schematic front cross-sectional view near three consecutive electrode fingers in the elastic wave propagation direction in the first IDT electrode of a third variation of the first embodiment.

[0066] In this modified example, the piezoelectric substrate 22 includes a support substrate 25, a high-velocity film 26 as a high-velocity material layer, a low-velocity film 27, and a piezoelectric layer 28. More specifically, the high-velocity film 26 is disposed on the support substrate 25. The low-velocity film 27 is disposed on the high-velocity film 26. The piezoelectric layer 28 is disposed on the low-velocity film 27.

[0067] The low-velocity membrane 27 is a membrane with relatively low sound speed. More specifically, the sound speed of bulk waves propagating in the low-velocity membrane 27 is lower than the sound speed of bulk waves propagating in the piezoelectric layer 28. As a material for the low-velocity membrane 27, materials mainly composed of glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum pentoxide, or compounds obtained by adding fluorine, carbon, or boron to silicon oxide can be used.

[0068] The hypersonic material layer is a layer with relatively high sound speed. More specifically, the sound speed of bulk waves propagating in the hypersonic material layer is higher than the sound speed of elastic waves propagating in the piezoelectric layer 28. Materials used as the hypersonic material layer include, for example, silicon, alumina, silicon carbide, silicon nitride, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) film, or diamond, etc., and media with the above materials as the main components.

[0069] The materials used as the support substrate 25 can include, for example, piezoelectric materials such as alumina, lithium tantalate, lithium niobate, and quartz, bauxite, sapphire, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, magnesium olivine, diamond, glass, semiconductors such as silicon and gallium nitride, or resins.

[0070] In this modified piezoelectric substrate 22, a high-velocity acoustic material layer, a low-velocity acoustic film 27, and a piezoelectric layer 28 are stacked. This allows the energy of the elastic wave to be effectively contained within the piezoelectric layer 28. Furthermore, similar to the first embodiment, the response level in the attenuation region outside the passband can be improved.

[0071] It should be noted that the hypersonic material layer can also be a hypersonic support substrate. In this case, the piezoelectric substrate can also be a stacked substrate of a hypersonic support substrate, a low-velocity film 27, and a piezoelectric layer 28. Here, in the third variation, the piezoelectric layer 28 is indirectly disposed on the hypersonic material layer through the low-velocity film 27. However, the piezoelectric layer 28 can also be directly disposed on the hypersonic material layer. The piezoelectric substrate can also be a stacked substrate without the low-velocity film 27. In this case, the piezoelectric substrate can also be a stacked substrate of a hypersonic support substrate and a piezoelectric layer 28. Alternatively, the piezoelectric substrate can also be a stacked substrate of a support substrate 25, a hypersonic film 26, and a piezoelectric layer 28. In these cases, the energy of the elastic wave can also be effectively confined to the piezoelectric layer 28 side. Furthermore, the response level in the attenuation region outside the passband can be improved.

[0072] It should be noted that a piezoelectric layer 28 and an acoustic reflective membrane can also be constructed as a laminate. The acoustic reflective membrane includes at least one low acoustic impedance layer and at least one high acoustic impedance layer. The low acoustic impedance layer is a layer with relatively low acoustic impedance. The high acoustic impedance layer is a layer with relatively high acoustic impedance. The low acoustic impedance layer and the high acoustic impedance layer are stacked alternately. In this case, the energy of the elastic wave can also be effectively confined to the piezoelectric layer 28 side. Furthermore, similar to the first embodiment, the response level in the attenuation region outside the passband can be improved.

[0073] In the first embodiment and its variations, an example of an elastic wave device of the present invention being a longitudinally coupled resonator type elastic wave filter is shown. It should be noted that the elastic wave device of the present invention can also be an elastic wave resonator. This example is shown in the following second embodiment.

[0074] Figure 10 This is a schematic top view of the elastic wave device according to the second embodiment.

[0075] The elastic wave device 31 is an elastic wave resonator. The elastic wave device 31 has an IDT electrode 33, a first reflector 4A, and a second reflector 4B. The duty cycle of the IDT electrode 33, the first reflector 4A, and the second reflector 4B is random. In this embodiment, all portions of the IDT electrode 33, the first reflector 4A, and the second reflector 4B are portions with non-uniform duty cycles. It should be noted that the width of the electrodes in the IDT electrode 33, the first reflector 4A, and the second reflector 4B is random. All portions of the IDT electrode 33, the first reflector 4A, and the second reflector 4B are portions with non-uniform average width ratios. However, it is acceptable for at least any one of the IDT electrode 33, the first reflector 4A, and the second reflector 4B to have either a portion with non-uniform duty cycles or a portion with non-uniform average width ratios.

[0076] In this embodiment, the electrode finger spacing of the IDT electrode 33, the first reflector 4A, and the second reflector 4B is all the same. It should be noted that the electrode finger spacing of each IDT electrode 33, the first reflector 4A, and the second reflector 4B may not all be the same.

[0077] Figure 11 This is a diagram showing the average width ratio of each electrode finger of the IDT electrode, the first reflector, and the second reflector in the second embodiment. The wider the distance from the first reflector 4A side towards the second reflector 4B side, the... Figure 11 The larger the electrode number on the horizontal axis, the better. Numbers 1 to 11 represent the electrode numbers of the first reflector 4A. Numbers 12 to 92 represent the electrode numbers of the IDT electrode 33. Numbers 93 to 103 represent the electrode numbers of the second reflector 4B.

[0078] like Figure 11As shown, the average width ratio in this embodiment is 0.95 or higher and 1.05 or lower. The standard deviation of the distribution of the average width ratio of all electrode fingers of the IDT electrode 33, the first reflector 4A, and the second reflector 4B of the elastic wave device 31 is 0.024. Furthermore, the design parameters of the elastic wave device 31 are as follows. Here, the area where adjacent electrode fingers of the IDT electrode overlap when viewed from the direction of elastic wave propagation is defined as the intersection region. The dimension of the intersection region along the direction in which the multiple electrode fingers extend is defined as the intersection width. The center-to-center distance between the electrode finger at the end of the IDT electrode in the direction of elastic wave propagation and the electrode finger of the reflector located closest to the IDT electrode is defined as the IR gap.

[0079] Number of electrode fingers pairs in IDT electrode 33: 40.5 pairs

[0080] Cross width of IDT electrode 33: 50μm

[0081] Number of electrode fingers for the first reflector 4A and the second reflector 4B: 11

[0082] The distance between the electrode fingers of IDT electrode 33, the first reflector 4A, and the second reflector 4B is 4 μm.

[0083] IR gap: 4μm

[0084] In this embodiment, the response level in the attenuation region outside the passband can also be improved in the same way as in the first embodiment. This is shown by comparing the filter device including the elastic wave device 31 of this embodiment with a second comparative example. It should be noted that the filter device of the second comparative example differs from that of this embodiment in that the duty cycle and the width of the electrode fingers in the IDT electrode, the first reflector, and the second reflector of the elastic wave resonator are all fixed.

[0085] Figure 12 This is a diagram showing the attenuation frequency characteristics of the filter device having the elastic wave device of the second embodiment and the second comparative example. Figure 12 Arrow G in the diagram represents longitudinal mode ripple.

[0086] like Figure 12 As shown, in the second embodiment, longitudinal mode ripple is suppressed compared to the second comparative example. Therefore, in the second embodiment, the response caused by longitudinal mode ripple can be suppressed. Therefore, when the elastic wave device 31 of the second embodiment is used in a filter device or multiplexer, the response level in the attenuation region outside the passband can be improved.

[0087] Here, by varying the standard deviations in the distribution of the average width ratios of all electrode fingers of the IDT electrode 33, the first reflector 4A, and the second reflector 4B of the elastic wave device 31, the out-of-band response level was measured. It should be noted that the frequency at which the response level was measured was... Figure 12 The frequency indicated by arrow G in the diagram.

[0088] Figure 13 This is a graph showing the relationship between the standard deviation of the average width ratio of the electrode fingers of the filter device of the elastic wave device having the second embodiment and the response level of the longitudinal mode ripple. Figure 13 The diagram shows that the higher the position on the vertical axis, the more the vertical modulus is suppressed.

[0089] like Figure 13 As shown, when the standard deviation of the average width ratio of the electrode fingers is greater than 0.015, longitudinal mode ripple is suppressed compared to when the standard deviation is less than 0.015. Therefore, in this case, the response level in the attenuation region outside the passband can be further improved.

[0090] Explanation of reference numerals in the attached figures

[0091] 1…elastic wave device;

[0092] 2…piezoelectric substrate;

[0093] 3A~3G…First IDT electrode~Seventh IDT electrode;

[0094] 4A, 4B... First reflector, second reflector;

[0095] 5, 6… First signal terminal, second signal terminal;

[0096] 10… filter device;

[0097] 12, 13… First busbar, Second busbar;

[0098] 14, 15… First electrode finger, second electrode finger;

[0099] 16, 18A~18C… electrode references;

[0100] 22…Piezoelectric substrate;

[0101] 23X, 23Y… First IDT electrode;

[0102] 24A…First reflector;

[0103] 25...support base plate;

[0104] 26…high-speed sound membrane;

[0105] 27…low-velocity membrane;

[0106] 28…piezoelectric layer;

[0107] 31…elastic wave device;

[0108] 33…IDT electrode;

[0109] C…duty cycle non-uniformity;

[0110] D~F…First region~Third region;

[0111] P1, P2, S1, S2… elastic wave resonators.

Claims

1. An elastic wave device, comprising: piezoelectric substrate; An IDT electrode, disposed on the piezoelectric substrate; and The first reflector and the second reflector are disposed on both sides of the elastic wave propagation direction of the IDT electrode on the piezoelectric substrate. The IDT electrode, the first reflector, and the second reflector each have multiple electrode fingers. At least one of the IDT electrode, the first reflector, and the second reflector has a duty cycle non-uniformity, wherein the duty cycle non-uniformity is the portion in which all three consecutive electrodes in the direction of elastic wave propagation have different duty cycles. The standard deviation of the distribution of all duty cycles of the IDT electrode, the first reflector, and the second reflector is greater than 0.

015.

2. The elastic wave device according to claim 1, wherein, In the section with uneven duty cycle, the distance between all electrode fingers is the same.

3. The elastic wave device according to claim 1 or 2, wherein, The IDT electrode has: The first region and the second region respectively include the electrode finger at one end and the other end of the elastic wave propagation direction of the IDT electrode; as well as The third region is adjacent to the first region and also adjacent to the second region. The non-uniform duty cycle portion is located outside the boundary between the first region and the third region, and outside the boundary between the second region and the third region.

4. The elastic wave device according to claim 1 or 2, wherein, The IDT electrode, the first reflector, and the second reflector each include a portion with a fixed duty cycle.

5. The elastic wave device according to claim 1 or 2, wherein, The elastic wave device is an elastic wave resonator equipped with one of the IDT electrodes.

6. The elastic wave device according to claim 1 or 2, wherein, The elastic wave device includes multiple IDT electrodes. The elastic wave device is a longitudinally coupled resonator type elastic wave filter in which the plurality of IDT electrodes are arranged along the direction of elastic wave propagation.

7. An elastic wave device, comprising: piezoelectric substrate; An IDT electrode, disposed on the piezoelectric substrate; and The first reflector and the second reflector are disposed on both sides of the elastic wave propagation direction of the IDT electrode on the piezoelectric substrate. The IDT electrode, the first reflector, and the second reflector each have multiple electrode fingers. When the average width ratio of any given electrode finger is defined as the value obtained by dividing the width of any given electrode finger by the average width of all the electrode fingers of the IDT electrode, the first reflector, and the second reflector, at least one of the IDT electrode, the first reflector, and the second reflector has a non-uniform portion of the average width ratio, wherein the non-uniform portion is the part where the average width ratios of all three consecutive electrode fingers in the direction of elastic wave propagation are different. The standard deviation of the distribution of the average width ratio of all the electrode fingers of the IDT electrode, the first reflector, and the second reflector is greater than 0.

015.

8. The elastic wave device according to claim 7, wherein, In the region where the average width ratio is uneven, the distance between the electrode fingers is all the same.

9. The elastic wave device according to claim 7 or 8, wherein, The IDT electrode has a first region and a second region, the first region and the second region respectively including the electrode finger at one end and the other end in the elastic wave propagation direction of the IDT electrode. The portion of the average width ratio non-uniformity is located outside the boundary between the first region and the region adjacent to the first region, and outside the boundary between the second region and the region adjacent to the second region.

10. The elastic wave device according to claim 7 or 8, wherein, The IDT electrode, the first reflector, and the second reflector each include a portion with a fixed duty cycle.

11. The elastic wave device according to claim 7 or 8, wherein, The elastic wave device is an elastic wave resonator equipped with one of the IDT electrodes.

12. The elastic wave device according to claim 7 or 8, wherein, The elastic wave device includes multiple IDT electrodes. The elastic wave device is a longitudinally coupled resonator type elastic wave filter in which the plurality of IDT electrodes are arranged along the direction of elastic wave propagation.

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