Elastic wave resonator, elastic wave filter, wave divider, communication device
By designing gradually varying electrode fingers and reflector duty cycles in the elastic wave resonator and adjusting the electrode finger spacing, the problems of non-uniform resonant frequency and stray frequency were solved, achieving frequency homogenization and performance improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- KYOCERA CORP
- Filing Date
- 2021-06-22
- Publication Date
- 2026-07-21
AI Technical Summary
In existing elastic wave filters, the difference in duty cycle and spacing of the electrode fingers leads to non-uniform resonant frequencies, which causes the generation of stray frequencies and affects the characteristics of the filter.
By designing the duty cycles of the electrode fingers and reflectors to gradually change, and adjusting the spacing within the electrode finger configuration area, frequency uniformity is achieved by eliminating resonant frequency differences.
The characteristics of the elastic wave resonator were improved, the spurious intensity was reduced, the frequency uniformity was increased, and the overall performance of the filter was enhanced.
Smart Images
Figure CN115885471B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to elastic wave devices. Background Technology
[0002] Existing document 1 describes an elastic wave filter, which includes multiple interdigital transducers located on a piezoelectric substrate and having a specific resonant frequency.
[0003] Existing technical documents
[0004] Patent documents
[0005] Patent Document 1: International Publication No. WO2005 / 050837 Summary of the Invention
[0006] An elastic wave resonator according to one aspect of this disclosure includes: a piezoelectric element; and a plurality of electrode fingers located on the piezoelectric element and arranged in the direction of propagation of the elastic wave. The plurality of electrode fingers includes: a first group of electrode fingers; and a second group of electrode fingers formed between the electrode fingers of the first group. The duty cycle of the electrode fingers of the first group gradually varies in either direction of the propagation direction based on a first variation. The duty cycle of the electrode fingers of the second group gradually varies in either direction of the propagation direction based on a second variation different from the first variation. In the region where the plurality of electrode fingers are located, the spacing between the electrode fingers varies to eliminate the effect of differences in the duty cycles of the electrode fingers on the resonant frequency. Attached Figure Description
[0007] Figure 1 This is a schematic top view of an elastic wave resonator according to Embodiment 1 of this disclosure.
[0008] Figure 2 This is a schematic cross-sectional view of an elastic wave resonator according to Embodiment 1 of this disclosure.
[0009] Figure 3 This is a graph showing the change in the duty cycle of the electrode fingers of the elastic wave resonator according to Embodiment 1 of this disclosure.
[0010] Figure 4 This is a diagram used for comparing the characteristics of elastic wave resonators according to Embodiment 1 and the comparison method of this disclosure.
[0011] Figure 5 This is a schematic top view showing an enlarged view of the vicinity of the reflector of the elastic wave resonator of Embodiment 2 of this disclosure.
[0012] Figure 6 This is a schematic diagram illustrating the communication device of various embodiments of the present disclosure.
[0013] Figure 7 This is a circuit diagram illustrating the various embodiments of the demultiplexer disclosed herein. Detailed Implementation
[0014] [Implementation Method 1]
[0015] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. Furthermore, the drawings used in the following description are schematic diagrams and do not strictly represent the dimensions of the components in the drawings to scale.
[0016] <Structure of a Resonator>
[0017] The elastic wave filter of this embodiment includes at least one elastic wave resonator. For example, the elastic wave filter is configured as a trapezoidal filter by connecting multiple elastic wave resonators in a trapezoidal shape. The elastic wave filter of this embodiment may also include multiple elastic wave resonators arranged side by side in a direction orthogonal to the propagation direction of the elastic wave in each elastic wave resonator.
[0018] The following is for reference Figure 1 as well as Figure 2 The elastic wave resonator 4 of this embodiment will be described in more detail. Figure 1 This is a schematic top view of the elastic wave resonator 4 in this embodiment. Figure 2 An enlarged top view of region A. Figure 2 This is a schematic cross-sectional view of the elastic wave resonator 4 in this embodiment, along... Figure 1 A cross-sectional view of the BB line in the diagram. Furthermore, in this specification, the propagation direction TD of the elastic wave in the elastic wave resonator 4 is defined in the diagram including... Figure 1 In the top view of the elastic wave resonator 4, it is positioned vertically towards the plane of the paper, including... Figure 2 In the cross-sectional view of the elastic wave resonator 4, it is positioned in the left-right direction facing the plane of the paper. Furthermore, in this specification, including... Figure 2 In the cross-sectional view of the elastic wave resonator 4, only the components in the cross section are shown for the sake of simplicity, and the components inside the cross section are omitted.
[0019] like Figure 1 as well as Figure 2 As shown, the elastic wave resonator 4 of this embodiment includes at least: a piezoelectric element 6; and an IDT electrode 8 on the piezoelectric element 6. Furthermore, this specification includes... Figure 2 In the cross-sectional view of the elastic wave resonator 4, the IDT electrode 8 is shown positioned on the upper side facing the paper relative to the piezoelectric body 6.
[0020] The piezoelectric body 6 is made of a piezoelectric material. For example, a single crystal of lithium tantalate (hereinafter also referred to as LT), lithium niobate, etc. can be used. In the elastic wave resonator 4, by applying a voltage to the conductive layer including the IDT electrode 8 described later, an elastic wave propagating in the piezoelectric body 6 in the propagation direction TD is excited. In the present embodiment, as Figure 2 shown, the piezoelectric body 6 may have a certain thickness D6. In addition, in this specification, "constant thickness" does not necessarily mean that the thickness is strictly constant, but some variations are allowed within a range that does not significantly affect the characteristics of the elastic wave propagating in the piezoelectric body 6.
[0021] <Details of IDT electrode and reflector>
[0022] The IDT electrode 8 includes a pair of comb electrodes 10. In particular, in the present embodiment, as Figure 1 shown, the comb electrode 10 includes a first comb electrode 10A and a second comb electrode 10B as a pair of comb electrodes. In addition, in this specification, in the top view of the elastic wave resonator 4 including Figure 1 , for improving visibility, the first comb electrode 10A is marked with hatching lines. The comb electrode 10 includes, for example: a bus bar 12; a plurality of electrode fingers 14 extending side by side from the bus bar 12; and a plurality of dummy electrodes 16 located between the plurality of electrode fingers 14 and protruding from the bus bar 12. In a pair of comb electrodes 10, the plurality of electrode fingers 14 are arranged to mesh with each other.
[0023] The bus bar 12 has a substantially constant width and is formed substantially along the propagation direction TD. In addition, a pair of bus bars 12 are opposed to each other in a direction substantially orthogonal to the propagation direction TD. In particular, the bus bar 12 includes: a first bus bar 12A formed as the bus bar of the first comb electrode 10A; and a second bus bar 12B formed as the bus bar of the second comb electrode 10B and opposed to the first bus bar 12A. In addition, within a range that does not significantly affect the elastic wave propagating through the piezoelectric body 6, the width of the bus bar 12 can be changed, or it can be formed inclined with respect to the propagation direction TD.
[0024] Each electrode finger 14 is formed in a long strip shape substantially along the width direction of the bus bar 12. In each comb electrode 10, the plurality of electrode fingers 14 are arranged along the propagation direction TD of the elastic wave. In addition, the electrode fingers 14 extending from one bus bar 12 and the electrode fingers 14 extending from the other bus bar 12 are alternately arranged in the propagation direction TD.
[0025] The number of each electrode finger 14 is not limited to the number Figure 1 shown, and can be appropriately designed according to the characteristics required for the elastic wave resonator 4. In addition, the length of each electrode finger 14, as Figure 1As shown, the lengths can be roughly fixed, or they can vary depending on their position in the propagation direction TD, implemented as a so-called apodization. Furthermore, a portion of the electrode fingers 14 within a portion of the IDT electrode 8 can also be "removed." In other words, a portion of the IDT electrode 8 may include areas where a portion of the electrode fingers 14 is not formed.
[0026] Each dummy electrode 16 protrudes generally along the width direction of the busbar 12. Furthermore, the dummy electrode 16 protruding from one busbar 12 faces the tip of the electrode finger 14 extending from the other busbar 12 across a gap in a direction orthogonal to the propagation direction TD. Alternatively, the elastic wave resonator 4 of this embodiment may not include the dummy electrodes 16.
[0027] The elastic wave resonator 4 also includes a pair of reflectors 18, which are located at opposite ends of the propagation direction TD on the piezoelectric body 6, relative to the electrode fingers 14. Each reflector 18 includes a plurality of strip electrodes 22 extending from a pair of opposing busbars 20. The reflectors 18 can be electrically floating, or they can be given a reference potential. Furthermore, the IDT electrodes 8 and reflectors 18 can be in the same layer or contained within a conductive layer. The IDT electrodes 8 and reflectors 18 are formed of a metallic material, such as an alloy with Al as the main component. Additionally, the number, shape, etc., of the strip electrodes 22 of the reflectors 18 are not limited to... Figure 1 The structure shown can be designed appropriately according to the characteristics required by the elastic wave resonator 4, just like electrode finger 14.
[0028] Furthermore, in this specification, "electrode fingers" includes: a plurality of electrode fingers 14 of the IDT electrode 8; and a plurality of strip electrodes 22 of the reflector 18 (in the case where the elastic wave resonator 4 includes the reflector 18).
[0029] In the elastic wave resonator 4 of this embodiment, as Figure 1 as well as Figure 2 As shown, the plurality of electrode fingers 14 of the IDT electrode 8 are located within the electrode finger configuration region 24 when viewed from above. Furthermore, in this embodiment, the electrode finger configuration region 24 includes at least a first region 24A and a second region 24B.
[0030] Here, as Figure 1 As shown, one of the propagation directions TD is designated as the first direction T1. Furthermore, in Figure 1 In the middle, let the first direction T1 be: in the propagation direction TD, the direction towards Figure 1 The paper surface is arranged from top to bottom. Furthermore, as... Figure 1As shown, in this embodiment, the electrode finger configuration region 24 includes a second region 24B on the side further in the first direction T1 than the first region 24A. For example, as Figure 1 As shown, half of the electrode fingers 14 can be formed in the first region 24A, and the other half can be formed in the second region 24B.
[0031] <Duty cycle of the electrode>
[0032] In the elastic wave resonator 4 of this embodiment, as Figure 1 as well as Figure 2 As shown, the IDT electrode 8 has multiple electrode fingers 14, including a first electrode finger group 14A and a second electrode finger group 14B. The first electrode finger group 14A extends from the first busbar 12A, and the second electrode finger group 14B extends from the second busbar 12B. Therefore, as Figure 1 and Figure 2 As shown, the second electrode finger group 14B is formed between the electrode fingers of the first electrode finger group 14A.
[0033] The elastic wave resonator 4 of this embodiment is characterized in terms of the duty cycle of each electrode finger 14. The duty cycle of the electrode finger 14 is the value obtained by dividing the width W of a certain electrode finger 14 by the distance between that electrode finger 14 and the adjacent electrode finger 14.
[0034] In this embodiment, the duty cycle of at least a portion of the electrode fingers 14 gradually changes in any direction of the propagation direction TD. Specifically, in this embodiment, the duty cycle of at least a portion of the electrode fingers 14 in the first electrode finger group 14A gradually changes in any direction of the propagation direction TD based on a first change amount. Correspondingly, the duty cycle of at least a portion of the electrode fingers 14 in the second electrode finger group 14B gradually changes in any direction of the propagation direction TD based on a second change amount different from the first change amount.
[0035] Here, typically, in the elastic wave propagating through the piezoelectric element 6, the resonant frequency of the elastic wave excited by the elastic wave resonator 4 varies depending on the duty cycle of the electrode finger 14; for example, it becomes higher as the duty cycle of the electrode finger 14 decreases. Therefore, in the elastic wave resonator 4, while the parameters contributing to the aforementioned resonant frequency, other than the duty cycle of the electrode finger 14, are approximately constant depending on the position of the elastic wave resonator 4, the resonant frequency will vary depending on the position of the elastic wave resonator 4.
[0036] Furthermore, in this specification, "resonant frequency" refers to the resonant frequency of the elastic wave excited by the main resonant mode in the elastic wave excited by the elastic wave resonator 4, and not the frequency of the elastic wave excited by the secondary resonant or stray mode.
[0037] <Example of duty cycle of electrode fingers>
[0038] Reference Figure 3 This section provides a more detailed example of the variation in the duty cycle of the respective electrode fingers 14 of the first electrode finger group 14A and the second electrode finger group 14B in this embodiment. Figure 3 This is a diagram showing the relationship between the position of the electrode finger 14 of the elastic wave resonator 4 in the propagation direction TD and the duty cycle of the electrode finger 14 in this embodiment. Figure 3 In the diagram, the horizontal axis represents the position of electrode finger 14 formed on the elastic wave resonator 4 in the propagation direction TD; the vertical axis represents the duty cycle of electrode finger 14 at that position. 24A and 24B, shown on the horizontal axis, correspond to the positions forming the first region 24A and the second region 24B, respectively.
[0039] In addition, Figure 3 In the diagram, the positive direction of the horizontal axis corresponds to the first direction T1. Furthermore, in... Figure 3 In the diagram, the solid line represents the duty cycle of the electrode finger 14 of the first electrode finger group 14A, and the dashed line represents the duty cycle of the electrode finger 14 of the second electrode finger group 14B.
[0040] Furthermore, since the duty cycle of an electrode finger is determined by each individual electrode finger, therefore, originally Figure 3 The diagram should show the duty cycle values discretely. However, in this specification, when the change in the duty cycle of the electrode finger 14 is represented graphically, for the sake of simplicity, the duty cycle of the electrode fingers 14 of the first electrode finger group 14A and the second electrode finger group 14B is considered to change continuously and is shown graphically.
[0041] In the elastic wave resonator 4 of this embodiment, the duty cycle of the electrode fingers 14 of the first electrode finger group 14A located in the first region 24A is, for example, as Figure 3 As shown in Figure 301, the duty cycle gradually increases from 0.3 to 0.6 towards the first direction T1. Correspondingly, in this elastic wave resonator 4, the duty cycle of the electrode finger 14 of the second electrode finger group 14B located in the first region 24A gradually increases from 0.4 to 0.5 towards the first direction T1.
[0042] On the other hand, in the elastic wave resonator 4 of this embodiment, the duty cycle of the electrode fingers 14 of the first electrode finger group 14A located in the second region 24B is, for example, as Figure 3 As shown, the duty cycle gradually decreases from 0.6 to 0.3 towards the first direction T1. Correspondingly, in this elastic wave resonator 4, the duty cycle of the electrode finger 14 of the second electrode finger group 14B located in the second region 24B gradually decreases from 0.5 to 0.4 towards the first direction T1.
[0043] Therefore, in the first region 24A of the aforementioned elastic wave resonator 4, the duty cycle of the electrode fingers 14 of the first electrode finger group 14A gradually increases towards the first direction T1 based on a change greater than that of the electrode fingers 14 of the second electrode finger group 14B. Conversely, in the second region 24B of the aforementioned elastic wave resonator 4, the duty cycle of the electrode fingers 14 of the first electrode finger group 14A gradually decreases towards the first direction T1 based on a change greater than that of the electrode fingers 14 of the second electrode finger group 14B.
[0044] Furthermore, the change in the duty cycle of each electrode finger 14 of the elastic wave resonator 4 in this embodiment is not limited to... Figure 3 The example shown in Figure 301. For example, in the elastic wave resonator 4 of this embodiment, the duty cycle of the electrode finger 14 of the second electrode finger group 14B located in the first region 24A can also be as follows: Figure 3 As shown in Figure 302, the duty cycle gradually decreases from 0.5 to 0.4 towards the first direction T1. In this case, the duty cycle of the electrode finger 14 of the second electrode finger group 14B located in the second region 24B can also be as follows: Figure 3 As shown in Figure 302, the value gradually decreases from 0.4 to 0.5 towards the first direction T1. Furthermore, in relation to... Figure 3 In the elastic wave resonator 4 corresponding to Figures 301 and 302, the duty cycle of the electrode fingers 14 of the first electrode finger group 14A can also change in the same way.
[0045] As described above, in the elastic wave resonator 4 of this embodiment, the change in the duty cycle of the electrode finger 14 relative to either direction of the propagation direction TD differs in the first electrode finger group 14A and the second electrode finger group 14B in each of the first region 24A and the second region 24B.
[0046] <Electrode finger spacing>
[0047] Multiple electrode fingers 14 are arranged with a certain distance P between them. Furthermore, the resonant frequency of the elastic wave excited by the elastic wave resonator 4 depends on the distance P between the electrode fingers 14. Generally, the resonant frequency of the elastic wave excited by the elastic wave resonator 4 increases as the distance P between the electrode fingers 14 narrows.
[0048] In this embodiment, the spacing P varies within the electrode finger arrangement region 24 to eliminate the effect of differences in the duty cycles of the electrode fingers 14 on the resonant frequency. In other words, compared to the case where the spacing P is approximately constant at any position, the difference in the resonant frequency of the elastic wave resonator 4 oscillating at various positions in the electrode finger arrangement region 24 is smaller in this embodiment.
[0049] As a result, the frequency of the elastic wave excited at each location of the piezoelectric element 6 is homogenized, improving the characteristics of the elastic wave resonator 4. Furthermore, the spacing P between each electrode finger 14 can be easily determined through simulation based on the differences in the duty cycle of each electrode finger 14.
[0050] In this embodiment, the resonant frequencies oscillating in at least a portion of the electrode finger arrangement region 24 can be the same. Furthermore, the resonant frequencies oscillating in more than 80% of the electrode finger arrangement region 24 can be the same. As a result, the frequency of the elastic wave excited at each location of the piezoelectric element 6 is more uniform, improving the characteristics of the elastic wave resonator 4.
[0051] Furthermore, in this specification, "same frequency" does not necessarily mean that the frequencies are strictly the same. For example, within a range that does not significantly affect the characteristics of the elastic wave resonator 4, some differences are allowed in the resonant frequency of the main resonance of the elastic wave propagating through the piezoelectric element 6 in the electrode finger configuration region 24.
[0052] Specifically, in determining whether "the resonant frequencies in a certain region are the same", the value obtained by dividing the difference in resonant frequencies in the region by the desired resonant frequency and multiplying it by 100 (dfr) can be used. For example, if dfr is between -0.856 and 0.856, it can also be considered that "the resonant frequencies in the region are the same".
[0053] When the value of dfr meets the above range, the elastic wave resonator 4, in terms of frequency characteristics, can suppress the generation of spurious signals caused by differences in resonant frequencies at various locations. Furthermore, in this embodiment, when the above range is met, the absolute value of the difference in resonant frequencies in this region is 50 MHz or less.
[0054] Furthermore, when dfr is -1.028 or 1.028, spurious emissions are confirmed. In this case, in this embodiment, the absolute value of the difference in resonant frequencies in this region is equivalent to 60 MHz.
[0055] Here, the value of the spacing P can be, for example, around 0.70 nm to 0.75 nm. Furthermore, the thickness D6 of the piezoelectric element 6 can also be less than or equal to the spacing P between any of the electrode fingers 14. Therefore, by including the elastic wave resonator 4 with relatively wide spacing of the electrode fingers 14, the resonant frequency can be increased.
[0056] Furthermore, although the thickness D6 of the piezoelectric element 6 is not particularly limited, in this embodiment, it is, for example, about 0.4 to 1.2 times that of either the first spacing PA or the second spacing PB. For example, the thickness D6 of the piezoelectric element 6 is about 0.28 μm to 0.9 μm.
[0057] Furthermore, in this embodiment, the thickness D14 of each electrode finger 14 can be the same within the electrode finger arrangement area 24. The thickness D14 of the electrode finger 14 is, for example, approximately 0.16 times the spacing P between any two electrode fingers 14. Additionally, the thickness of the strip electrode 22 of the reflector 18 can also be the same as the thickness of the electrode fingers 14.
[0058] <Fixed base plate>
[0059] Returning to the description of each structure of the elastic wave resonator 4, as follows: Figure 2 As shown, the elastic wave resonator 4 also includes a support substrate 26, which is located further away from the IDT electrode 8 than the piezoelectric body 6. In this embodiment, the support substrate 26 has a sufficiently small impact on the characteristics of the elastic wave propagating through the piezoelectric body 6. Therefore, the material and dimensions of the support substrate 26 can be appropriately designed. For example, the support substrate 26 comprises an insulating material and may comprise resin or ceramic. The thickness of the support substrate 26 is, for example, greater than the thickness D6 of the piezoelectric body 6. To further reduce the influence of temperature changes on the elastic wave characteristics, the support substrate 26 may be formed of a material with a lower coefficient of linear expansion than that of the piezoelectric body 6.
[0060] Furthermore, the elastic wave resonator 4 includes a reflective multilayer film 30 between the piezoelectric body 6 and the supporting substrate 26. The elastic wave resonator 4 may also include a sealing layer 28 between the reflective multilayer film 30 and the supporting substrate 26. In addition, the laminate including the piezoelectric body 6, the supporting substrate 26, the sealing layer 28, and the reflective multilayer film 30 is sometimes referred to as the fixed substrate 36.
[0061] The sealing layer 28 is inserted to improve the adhesion between the support substrate 26 and the reflective multilayer film 30, and has a sufficiently small effect on the elastic wave characteristics propagated through the piezoelectric material 6.
[0062] The reflective multilayer film 30 includes an alternately stacked first layer 32 and a second layer 34. The material of the first layer 32 has a lower acoustic impedance compared to the material of the second layer 34. As a result, the reflectivity of the elastic wave is increased at the interface between the first layer 32 and the second layer 34, thus reducing the leakage of the elastic wave propagating through the piezoelectric element 6 to the outside of the elastic wave filter.
[0063] For example, the first layer 32 is formed of silicon dioxide (SiO2). Alternatively, for example, the second layer 34 is formed of hafnium oxide (HfO2). Furthermore, the second layer 34 can also be formed of any one of tantalum pentoxide (Ta2O5), zirconium dioxide (ZrO2), titanium oxide (TiO2), and magnesium oxide (MgO).
[0064] The reflective multilayer film 30 may include at least one first layer 32 and one second layer 34, and the number of layers is not particularly limited. Furthermore, the total number of the first layer 32 and the second layer 34 can be either odd or even. Here, although the layer in contact with the piezoelectric element 6 is the first layer 32, the layer in contact with the sealing layer 28 can be either the first layer 32 or the second layer 34.
[0065] For example, the reflective multilayer film 30 may include a first layer 32 and a second layer 34, which together comprise 3 to 12 layers. However, the reflective multilayer film 30 may consist of only a single first layer 32 and a single second layer 34. Furthermore, from the viewpoint of improving the adhesion between the layers of the reflective multilayer film 30 and preventing the diffusion of elastic waves in the reflective multilayer film 30, an adhesive layer 28 may be formed between each of the first layer 32 and the second layer 34.
[0066] In addition, such as Figure 2 As shown, the first layer 32 can have a certain thickness D32, and the second layer 34 can have a certain thickness D34. The thicknesses D32 and D34 can be, for example, about 0.25 to 2 times the spacing P between any of the electrode fingers 14.
[0067] <Characteristic changes caused by differences in spacing and duty cycle>
[0068] To evaluate the characteristics of the elastic wave resonator 4 of this embodiment, a comparison with the characteristics of the elastic wave resonator of the comparative embodiment is provided. In the elastic wave resonator of the comparative embodiment, the duty cycle of all electrode fingers 14 is constant, which is 0.55; and the spacing P between all electrode fingers 14 is constant. Apart from the above aspects, the elastic wave resonator of the comparative embodiment includes the same structure as the elastic wave resonator 4 of this embodiment.
[0069] Figure 4 This is a graph showing the characteristics of the elastic wave excited in the elastic wave resonator in both the comparison method and this embodiment, and it is a graph showing the impedance phase in the elastic wave resonator at each frequency. In other words, Figure 4 The graph represents the intensity of the elastic wave oscillating in the elastic wave resonator at each frequency. Figure 4 In the graph, the vertical axis represents phase (unit: degrees), and the horizontal axis represents frequency (unit: MHz).
[0070] Figure 4 Figure 401 shows the calculation results obtained through simulation in the elastic wave resonator of the comparison method. Additionally, Figure 4 Figure 402 shows: Figure 3 The change in duty cycle of electrode finger 14 shown in Figure 301 is calculated using simulations performed on the elastic wave resonator 4 of this embodiment. Furthermore, in Figure 4 Figure 402 shows the characteristics of the elastic wave resonator 4. The spacing P of the electrode fingers 14 is determined to be: with Figure 4 Figure 401 shows the characteristics of an elastic wave resonator with the same resonant frequency. Therefore, as Figure 4 As shown in the figures, the elastic wave resonators of the comparison method and this embodiment each have a main resonant frequency around 4700MHz.
[0071] Here, from Figure 4 As shown in Figure 401, in the elastic wave resonator of the comparison method, in addition to the main resonant frequency, excitation spurious signals are generated at frequencies around 6000MHz and around 6750MHz. On the other hand, from... Figure 4 As shown in Figure 402, the stray intensity is reduced in the elastic wave resonator of this embodiment compared to the elastic wave resonator of the comparison method.
[0072] Typically, in an elastic wave resonator, the frequency of the elastic wave excited in stray mode has a different dependence on the frequency of the elastic wave excited in the main resonance and anti-resonance modes, depending on the changes in the duty cycle and spacing of the electrode fingers. Therefore, in an elastic wave resonator, if the frequency of the main resonance is kept constant, changing the spacing and duty cycle of the electrode fingers will change the frequency of the elastic wave excited in stray mode.
[0073] Here, in the elastic wave resonator 4 of this embodiment, the duty cycle of the electrode fingers 14 changes within the electrode finger arrangement region 24. In other words, in the elastic wave resonator 4 of this embodiment, the resonant spurious frequency varies depending on the position within the electrode finger arrangement region 24. Therefore, compared to an elastic wave resonator including electrode fingers with a fixed duty cycle, the elastic wave resonator 4 of this embodiment can suppress the concentration of the resonant spurious frequency at a certain value, and can reduce the spurious intensity as a whole.
[0074] Furthermore, in the elastic wave resonator 4 of this embodiment, the duty cycle of the electrode fingers 14 changes within the electrode finger arrangement region 24, and the frequency difference of the main resonance decreases. Therefore, as Figure 4 As shown in Figure 402, while maintaining the frequency uniformity of the main resonance, it is possible to reduce the spurious intensity and improve the characteristics.
[0075] Furthermore, in the elastic wave resonator 4 of this embodiment, there is a difference in the amount of change in the duty cycle of the electrode fingers 14 relative to the first direction T1 between the first electrode finger group 14A and the second electrode finger group 14B. In other words, there is a difference in the pattern of duty cycle change for the electrode fingers 14 that are adjacent to each other in the propagation direction TD of the elastic wave resonator 4 of this embodiment.
[0076] Therefore, in the elastic wave resonator 4 of this embodiment, the difference in duty cycle can be made more efficient for the adjacent electrode fingers 14 in the propagation direction TD. In addition, in the elastic wave resonator 4 of this embodiment, by designing the spacing P between the electrode fingers 14, the change in resonant frequency caused by the change in the duty cycle of the electrode fingers 14 can be more easily homogenized.
[0077] In addition, in this embodiment, such as Figure 3 As shown, the maximum duty cycle value of the electrode fingers 14 in the first electrode finger group 14A may also be different from the maximum duty cycle value of the electrode fingers 14 in the second electrode finger group 14B. Specifically, in this embodiment, as... Figure 3 As shown, the maximum duty cycle of the electrode fingers 14 in the first electrode finger group 14A can be greater than the maximum duty cycle of the electrode fingers 14 in the second electrode finger group 14B.
[0078] Furthermore, in this embodiment, as Figure 3 As shown, the minimum duty cycle value of the electrode fingers 14 in the first electrode finger group 14A may also be different from the minimum duty cycle value of the electrode fingers 14 in the second electrode finger group 14B. Specifically, in this embodiment, as... Figure 3 As shown, the minimum duty cycle of the electrode fingers 14 in the first electrode finger group 14A can be less than the minimum duty cycle of the electrode fingers 14 in the second electrode finger group 14B.
[0079] Furthermore, in this embodiment, such as Figure 3 As shown, the difference between the maximum and minimum duty cycle values in the electrode fingers 14 of the first electrode finger group 14A can also be different from the difference between the maximum and minimum duty cycle values in the electrode fingers 14 of the second electrode finger group 14B.
[0080] With the above structure, in the elastic wave resonator 4 of this embodiment, the electrode fingers 14 that are adjacent to each other in the propagation direction TD can more efficiently make the difference in duty cycle.
[0081] [Implementation Method Two]
[0082] <Duty cycle of the reflector's strip electrode>
[0083] Figure 5 This is a schematic top view showing an enlarged view of the periphery of the reflector 18 of the elastic wave resonator 4A in this embodiment. The elastic wave resonator 4A of this embodiment, for example, may include the same structure as the elastic wave resonator 4 of the above-described embodiment, except for the structure of the reflector 18. Furthermore, Figure 5 The reflector 18 shown is Figure 1Compared to the reflector 18 shown, the number of strip electrodes 22 is different. However, the elastic wave resonator 4 of the above embodiment may also include: having the same... Figure 5 The reflector 18 shown has the same number of strip electrodes 22 as the reflector 18.
[0084] In the elastic wave resonator 4A of this embodiment, as follows: Figure 5 As shown, the plurality of strip electrodes 22 are located within the electrode finger arrangement area 24 when viewed from above. Furthermore, in this embodiment, the electrode finger arrangement area 24 includes at least a first area 24C and a second area 24D.
[0085] Here, as Figure 5 As shown, one of the propagation directions TD is designated as the first direction T1. Furthermore, in Figure 5 In this context, let the first direction T1 be defined as: in the propagation direction TD, the direction towards Figure 5 The paper surface is arranged from top to bottom. Furthermore, as... Figure 5 As shown, in this embodiment, the electrode finger configuration region 24 includes a second region 24D on the side further in the first direction T1 than the first region 24C. For example, as... Figure 5 As shown, half of the strip electrode 22 can be formed in the first region 24C, and the other half can be formed in the second region 24D.
[0086] like Figure 5 As shown, the strip electrode 22 of the elastic wave resonator 4A in this embodiment includes: a first strip electrode group 22A and a second strip electrode group 22B. Furthermore, in Figure 5 In order to improve visibility, the strip electrodes 22 of the first strip electrode group 22A are marked with shaded lines.
[0087] Here, as Figure 5 As shown, the strip electrodes 22 of the first strip electrode group 22A and the strip electrodes 22 of the second strip electrode group 22B are alternately formed in the propagation direction TD. In other words, the strip electrodes 22 of the second strip electrode group 22B are formed between the strip electrodes 22 of the first strip electrode group 22A.
[0088] The elastic wave resonator 4A of this embodiment is characterized in terms of the duty cycle of each strip electrode 22. The duty cycle of the strip electrode 22 is the value obtained by dividing the width W of a certain strip electrode 22 by the distance between the strip electrode 22 and the adjacent strip electrode 22.
[0089] In this embodiment, the duty cycle of at least a portion of the strip electrodes 22 gradually changes in any direction of the propagation direction TD. Specifically, in this embodiment, the duty cycle of at least a portion of the strip electrodes 22 in the first strip electrode group 22A gradually changes in any direction of the propagation direction TD based on a first change amount. Correspondingly, the duty cycle of at least a portion of the strip electrodes 22 in the second strip electrode group 22B gradually changes in any direction of the propagation direction TD based on a second change amount different from the first change amount.
[0090] Here, typically, in the elastic wave propagating through the piezoelectric element 6, the resonant frequency of the elastic wave excited by the elastic wave resonator 4A also varies depending on the duty cycle of the strip electrode 22. Therefore, in the elastic wave resonator 4A, while the parameters contributing to the aforementioned resonant frequency, other than the duty cycle of the strip electrode 22, are approximately constant depending on the position of the elastic wave resonator 4A, the resonant frequency will differ depending on the position of the elastic wave resonator 4A.
[0091] In this embodiment, the change in the duty cycle of the strip electrode 22 can also be, for example, as follows: Figure 3 The change in duty cycle of electrode finger 14 shown in any of the figures is replaced with the change in duty cycle of strip electrode 22.
[0092] Multiple strip electrodes 22 are arranged with a certain spacing P between them. In addition, the resonant frequency of the elastic wave excited by the elastic wave resonator 4A depends on the spacing P of the strip electrodes 22.
[0093] In this embodiment, the spacing P varies within the electrode finger arrangement region 24 to eliminate the effect of differences in the duty cycle of the strip electrodes 22 on the resonant frequency. In other words, compared to the case where the spacing P is approximately constant at any position, the difference in the resonant frequency of the elastic wave resonator 4A oscillating at various positions in the electrode finger arrangement region 24 is smaller.
[0094] Therefore, the frequency of the elastic wave excited at each location of the piezoelectric element 6 is homogenized, improving the characteristics of the elastic wave resonator 4A. Furthermore, the spacing P between each strip electrode 22 can be easily determined through simulation based on the difference in the duty cycle of each strip electrode 22. Additionally, the width and thickness of each strip electrode 22 can be made similar to the width and thickness of the electrode fingers 14 of the IDT electrode 8.
[0095] Here, in the elastic wave resonator 4A of this embodiment, the duty cycle of the strip electrode 22 changes within the electrode finger arrangement region 24. In other words, in the elastic wave resonator 4A of this embodiment, the resonant stray frequency varies depending on the position within the electrode finger arrangement region 24. Therefore, compared to an elastic wave resonator that includes a reflector with a strip electrode having a fixed duty cycle, the elastic wave resonator 4A of this embodiment can suppress the concentration of the resonant stray frequency at a certain value, and can reduce the stray intensity as a whole.
[0096] Furthermore, in the elastic wave resonator 4A of this embodiment, the duty cycle of the strip electrode 22 changes within the electrode finger arrangement region 24, and the frequency difference of the main resonance decreases. Therefore, while maintaining the frequency uniformity of the main resonance, it is possible to reduce spurious intensity and improve characteristics.
[0097] Furthermore, in the elastic wave resonator 4A of this embodiment, there is a difference in the amount of change in the duty cycle of the strip electrodes 22 relative to the first direction T1 between the first strip electrode group 22A and the second strip electrode group 22B. In other words, the duty cycle changes differently for the strip electrodes 22 that are adjacent to each other in the propagation direction TD of the elastic wave resonator 4A of this embodiment.
[0098] Therefore, in the elastic wave resonator 4A of this embodiment, the difference in duty cycle of the adjacent strip electrodes 22 in the propagation direction TD can be made more efficient. Furthermore, in the elastic wave resonator 4A of this embodiment, by designing the spacing P between the strip electrodes 22, the change in resonant frequency caused by the change in the duty cycle of the strip electrodes 22 can be more easily homogenized.
[0099] <Other variations>
[0100] In each embodiment, examples of elastic wave resonators 4 and 4A including a reflective multilayer film 30 are described. However, this disclosure is not limited to this. The fixed substrate 36 of the elastic wave resonators 4 and 4A may also be formed directly on the Si support substrate 26, or may include an insulating layer made of SiO2 or the like instead of the reflective multilayer film 30.
[0101] Furthermore, in the elastic wave resonators 4 and 4A of each embodiment, a gap may exist between the inner side of the region in the piezoelectric body 6 where the IDT electrode 8 is formed and the support substrate 26. In this case, the elastic wave resonators 4 and 4A of each embodiment may also be, for example, a so-called film in which the piezoelectric body 6 is disposed on the support substrate 26 including the recess.
[0102] <Overview of Communication Devices and Demultiplexer Structure>
[0103] Figure 6This is a block diagram of the main parts of the communication device 40 according to an embodiment of the present disclosure. The communication device 40 uses radio waves for wireless communication. The demultiplexer 42 has the function of demultiplexing the signal at the transmission frequency and the signal at the reception frequency in the communication device 40.
[0104] In the communication device 40, the transmission information signal TIS, which includes the information to be transmitted, is modulated and frequency-boosted (converted into a high-frequency signal with a carrier frequency) by the RF-IC 44, thus becoming the transmission signal TS. The transmission signal TS is passed through a bandpass filter 46 to remove unnecessary components outside the transmission passband, and then amplified by an amplifier 48 before being input to a demultiplexer 42. The demultiplexer 42 removes unnecessary components outside the transmission passband from the input transmission signal TS and outputs it to the antenna 50. The antenna 50 converts the input electrical signal (transmission signal TS) into a wireless signal and transmits it.
[0105] In the communication device 40, the wireless signal received through the antenna 50 is converted into an electrical signal (received signal RS) and input to the demultiplexer 42. The demultiplexer 42 removes unnecessary components outside the passband from the input received signal RS and outputs it to the amplifier 52. The output received signal RS is amplified by the amplifier 52 and then passes through the bandpass filter 54 to remove unnecessary components outside the passband. Then, the received signal RS is converted into a received information signal RIS by the RF-IC 44 for frequency reduction and demodulation.
[0106] Furthermore, the Transmit Information Signal (TIS) and the Receive Information Signal (RIS) can be low-frequency signals (baseband signals) containing appropriate information, such as analog or digitized audio signals. The wireless signal passband can conform to various standards such as UMTS (Universal Mobile Telecommunications System). Modulation methods can be phase modulation, amplitude modulation, frequency modulation, or any combination of two or more of these.
[0107] Figure 7 This is a circuit diagram illustrating the structure of a demultiplexer 42 according to one embodiment of the present disclosure. The demultiplexer 42 is... Figure 6 The demultiplexer 42 used in the communication device 40.
[0108] like Figure 7As shown, the transmitting filter 56 includes series resonators S1 to S3 and parallel resonators P1 to P3. The demultiplexer 42 mainly consists of an antenna terminal 58, a transmitting terminal 60, a receiving terminal 62, a transmitting filter 56 disposed between the antenna terminal 58 and the transmitting terminal 60, and a receiving filter 64 disposed between the antenna terminal 58 and the receiving terminal 62. The transmitting signal TS from the amplifier 48 is input to the transmitting terminal 60. The transmitting signal TS input to the transmitting terminal 60 is filtered in the transmitting filter 56 to remove unnecessary components outside the passband used for transmission, and then output to the antenna terminal 58. Additionally, the receiving signal RS is input from the antenna 50 to the antenna terminal 58. The receiving filter 64 removes unnecessary components outside the passband used for reception, and then outputs to the receiving terminal 62.
[0109] The transmitting filter 56 is, for example, a trapezoidal elastic filter. Specifically, the transmitting filter 56 includes: three series resonators S1, S2, and S3 connected in series between its input and output sides; and three parallel resonators P1, P2, and P3 disposed between the series arm and the reference potential section G; the series arm is wiring for connecting the series resonators. That is, the transmitting filter 56 is a trapezoidal filter with a three-stage structure. However, in the transmitting filter 56, the number of stages of the trapezoidal filter is arbitrary.
[0110] An inductor L is provided between the parallel resonators P1 to P3 and the reference potential section G. By setting the inductance of the inductor L to a predetermined value, an attenuation pole is formed outside the passband of the transmitted signal, thereby increasing the attenuation outside the frequency band. The multiple series resonators S1 to S3 and the multiple parallel resonators P1 to P3 are each formed by elastic wave resonators.
[0111] The receiving filter 64 includes, for example, a multi-mode elastic wave filter 66 and an auxiliary resonator 68 connected in series with its input side. Furthermore, in this embodiment, multi-mode includes dual-mode. The multi-mode elastic wave filter 66 has a balanced-to-unbalanced conversion function, and the receiving filter 64 is connected to the two receiving terminals 62 that output a balanced signal. The receiving filter 64 is not limited to being composed of a multi-mode elastic wave filter 66; it can be composed of a trapezoidal filter, or it can be a filter without a balanced-to-unbalanced conversion function.
[0112] An impedance matching circuit composed of inductors or the like can be inserted between the connection point between the transmitting filter 56, the receiving filter 64, and the antenna terminal 58 and the ground potential section G.
[0113] The elastic wave filters in the above embodiments are, for example, made of... Figure 6The elastic wave element is composed of a ladder-shaped filter circuit of at least one of the transmitting filter 56 or the receiving filter 64 in the wave divider 42 shown. If either the transmitting filter 56 or the receiving filter 64 is an elastic wave filter of the above embodiments, then all or at least a portion of the elastic wave resonators included in the filter are elastic wave resonators 4, 4A to 4G of the above embodiments.
[0114] By employing a demultiplexer 42 that includes such a transmit filter 56 or a receive filter 64, the filter characteristics of the communication device 40 can be improved.
[0115] This invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims; embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of this invention.
[0116] Explanation of reference numerals in the attached figures
[0117] 2. Elastic wave filter; 4. 4A~4G elastic wave resonators; 6. Piezoelectric element; 8. IDT electrode; 14. Electrode finger; 14A. First electrode finger group; 14B. Second electrode finger group; 14C. Intermediate electrode finger group; 18. Reflector; 24. Electrode finger configuration area; 24A. First area; 24B. Second area; 24C. Intermediate area; 26. Support substrate; 30. Reflective multilayer film; 38. Protective film; 40. Communication device; 42. Demultiplexer; 44. RF-IC; 50. Antenna; 56. Transmitting filter; 58. Antenna terminal; 64. Receiving filter.
Claims
1. An elastic wave resonator, including: piezoelectric elements; and, Multiple electrodes located on the piezoelectric body and arranged in the direction of elastic wave propagation; The plurality of electrode fingers includes: a first electrode finger group; and a second electrode finger group formed between the electrode fingers of the first electrode finger group; The duty cycle of the electrode fingers in the first electrode finger group gradually changes in any direction of the propagation direction based on a first change amount; the duty cycle of the electrode fingers in the second electrode finger group gradually changes in any direction of the propagation direction based on a second change amount different from the first change amount. In the region where the plurality of electrode fingers are located, the spacing between each electrode finger varies to eliminate the effect of the difference in duty cycle of the electrode fingers on the resonant frequency difference; The thickness of the piezoelectric element is the thickness below any one of the distances between the electrode fingers.
2. The elastic wave resonator according to claim 1, wherein the resonant frequency of the main resonance of the elastic wave is the same in more than 80% of the regions where the plurality of electrodes are located.
3. The elastic wave resonator according to claim 1 or 2, wherein the region where the plurality of electrodes are located includes: In the first region, the duty cycle of the electrode fingers of the first electrode finger group gradually increases toward a first direction, where the first direction is one of the propagation directions. And, in the second region, the duty cycle of the electrode fingers of the first electrode finger group gradually decreases toward the first direction.
4. The elastic wave resonator according to claim 3, wherein in the first region, the duty cycle of the electrode fingers of the second electrode finger group gradually increases toward the first direction; and in the second region, the duty cycle of the electrode fingers of the second electrode finger group gradually decreases toward the first direction.
5. The elastic wave resonator according to claim 3, wherein in the first region, the duty cycle of the electrode fingers of the second electrode finger group gradually decreases toward the first direction; and in the second region, the duty cycle of the electrode fingers of the second electrode finger group gradually increases toward the first direction.
6. The elastic wave resonator according to claim 1, wherein the difference between the maximum and minimum duty cycle values of the electrode fingers in the first electrode finger group is different from the difference between the maximum and minimum duty cycle values of the electrode fingers in the second electrode finger group.
7. The elastic wave resonator according to claim 1, wherein the maximum value of the duty cycle in the electrode fingers of the first electrode finger group is different from the maximum value of the duty cycle in the electrode fingers of the second electrode finger group.
8. The elastic wave resonator according to claim 1, wherein the minimum duty cycle of the electrode fingers in the first electrode finger group is different from the minimum duty cycle of the electrode fingers in the second electrode finger group.
9. The elastic wave resonator according to claim 1, wherein the maximum value of the duty cycle in the electrode fingers of the first electrode finger group is greater than the maximum value of the duty cycle in the electrode fingers of the second electrode finger group; The minimum duty cycle of the electrode fingers in the first electrode finger group is less than the minimum duty cycle of the electrode fingers in the second electrode finger group.
10. The elastic wave resonator according to claim 1, wherein the piezoelectric body includes an IDT electrode, the IDT electrode including at least a portion of the plurality of electrode fingers.
11. The elastic wave resonator according to claim 1, wherein the piezoelectric element comprises: IDT electrode, wherein the IDT electrode includes a portion of the plurality of electrode fingers; And a pair of reflectors, the pair of reflectors being located at opposite ends of the propagation direction relative to the IDT electrodes, each comprising another portion of the plurality of electrodes.
12. The elastic wave resonator according to claim 10 or 11, wherein the IDT electrode comprises: First busbar; and, the second busbar opposite to the first busbar; At least a portion of the electrode fingers of the first electrode finger group extends from the first busbar, and at least a portion of the electrode fingers of the second electrode finger group extends from the second busbar.
13. An elastic wave filter, comprising at least one elastic wave resonator according to any one of claims 1 to 12.
14. A demultiplexer, including: Antenna terminals; A transmission filter is used to filter the transmitted signal and output it to the antenna terminal; and, A receiving filter is used to filter the received signal from the antenna terminal. At least one of the transmitting filter and the receiving filter includes the elastic wave filter of claim 13.
15. A communication device, comprising: antenna; The demultiplexer of claim 14, wherein the antenna terminal is connected to the antenna; and, the IC connected to the transmitting filter and the receiving filter.