Elastic wave resonator, elastic wave filter, splitter and communication device

Abstract

Provided are an elastic wave resonator, an elastic wave filter, a splitter, and a communication device. The SAW resonator comprises a piezoelectric substrate, an IDT electrode, and a pair of reflectors. The IDT electrode comprises a plurality of electrode fingers arranged on the piezoelectric substrate in the propagation direction of the SAW. The pair of reflectors are located on both sides of the propagation direction relative to the plurality of electrode fingers on the piezoelectric substrate. Furthermore, the IDT electrode comprises a plurality of regions, each of which is assigned a plurality of electrode fingers and has mutually different resonant frequencies. The plurality of regions includes at least three regions. The second highest resonant frequency among all regions is lower than the intermediate value between the lowest resonant frequency among all regions and the highest resonant frequency among all regions.

Description

[0001] This application is a divisional application of the invention patent application with the application date of January 27, 2017, application number 201780007791.2, and invention name “Elastic wave resonator, elastic wave filter, splitter and communication device”. Technical Field

[0002] The present disclosure relates to an elastic wave resonator, an elastic wave filter, a wave splitter, and a communication device that utilize elastic waves such as surface acoustic waves (SAW). Background Art

[0003] An elastic wave resonator comprising a piezoelectric substrate and an IDT (InterDigital Transducer) electrode disposed on the principal surface (the widest surface (front or back) of the plate-shaped member) of the piezoelectric substrate is known (e.g., Patent Documents 1-3). The IDT electrode comprises a pair of comb-shaped electrodes. Each comb-shaped electrode has a plurality of electrode fingers extending parallel to one another. The comb-shaped electrodes are arranged so that the electrode fingers alternate in the direction of propagation of the elastic wave. In other words, the comb-shaped electrodes are arranged so as to interlock with one another.

[0004] In the aforementioned elastic wave resonator, the spacing between the multiple electrode fingers (electrode finger pitch) is essentially fixed. When a voltage is applied to a pair of comb-shaped electrodes, an elastic wave is excited in the piezoelectric substrate, with the electrode finger spacing set to half the wavelength (λ / 2). The frequency of this elastic wave is called the resonant frequency (fr). Furthermore, the antiresonant frequency (fa) is determined by the resonant frequency and the capacitance ratio (γ) of the IDT electrode (fa = fr × √(1 + 1 / γ)). The capacitance ratio γ of the IDT electrode is represented by the ratio (C1 / C0) of C0, which represents the mechanical vibration when the IDT electrode is replaced with an equivalent circuit, to the electrostatic capacitance C1. For example, when an elastic wave filter is constructed using an elastic wave resonator, the difference between the resonant frequency and the antiresonant frequency (Δf = fa - fr) affects the steepness of the change in attenuation at the boundary between the passband and the outer frequency band.

[0005] In particular, although not cited in prior literature, if one wishes to reduce Δf, one can connect a capacitor element in parallel with the IDT electrode. This capacitor element apparently increases the capacitance ratio of the IDT electrode, thereby reducing the antiresonant frequency relative to the resonant frequency. This reduces Δf.

[0006] Furthermore, Patent Documents 1 to 3 do not aim to reduce Δf. These documents propose providing regions in the IDT electrode where the electrode finger pitches are different from each other, or providing narrow-pitch portions where the electrode finger pitches are smaller than other portions.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 11-88112

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2012-156741

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2015-73207 Summary of the Invention

[0012] One aspect of the present disclosure relates to an elastic wave resonator having a piezoelectric substrate, an IDT electrode, and a pair of reflectors. The IDT electrode has a plurality of electrode fingers arranged on the piezoelectric substrate in the propagation direction of the elastic wave. The pair of reflectors are located on both sides of the propagation direction relative to the plurality of electrode fingers on the piezoelectric substrate. The IDT electrode has a plurality of regions. The plurality of regions are each assigned a plurality of the plurality of electrode fingers, and have different resonant frequencies. Furthermore, the plurality of regions include at least: a region having the lowest resonant frequency among all regions; a region having the highest resonant frequency among all regions; and a region having a resonant frequency that is higher than the lowest resonant frequency and the second highest resonant frequency among all regions. The second highest resonant frequency is lower than the intermediate value between the lowest resonant frequency and the highest resonant frequency.

[0013] One aspect of the present disclosure relates to an elastic wave resonator having a piezoelectric substrate, an IDT electrode, and a pair of reflectors. The IDT electrode has a plurality of electrode fingers arranged on the piezoelectric substrate in the propagation direction of the elastic wave. The pair of reflectors are located on both sides of the propagation direction relative to the plurality of electrode fingers on the piezoelectric substrate. The IDT electrode has a plurality of regions. The plurality of electrode fingers are respectively allocated to the plurality of regions. The electrode finger spacing in each region is fixed. The electrode finger spacing between the plurality of regions is different from each other. Between any two adjacent regions among the plurality of regions, the electrode finger at the end of one region on the side of the other region and the electrode finger at the end of the other region on the side of the one region are two adjacent electrode fingers. The electrode finger spacing between these two electrode fingers is different from any electrode finger spacing between the two regions and is smaller than the intermediate value of the electrode finger spacing between the two regions.

[0014] An elastic wave filter according to one aspect of the present disclosure includes one or more series resonators and one or more parallel resonators connected in a ladder formation, wherein at least one of the one or more parallel resonators is formed of any of the elastic wave resonators described above.

[0015] A demultiplexer according to one aspect of the present disclosure includes: an antenna terminal; a transmission filter that filters a transmission signal and outputs it to the antenna terminal; and a reception filter that filters a reception signal from the antenna terminal. At least one of the transmission filter and the reception filter includes the elastic wave filter described above.

[0016] A communication device according to one aspect of the present disclosure includes: an antenna; the aforementioned branching filter whose antenna terminal is connected to the antenna; and an IC connected to the transmission filter and the reception filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a plan view showing a SAW resonator according to an embodiment of the present disclosure.

[0018] Figure 2 Yes Figure 1 Schematic diagram of the variation of the electrode finger pitch in a SAW resonator.

[0019] Figure 3 (a) and Figure 3 (b) in the sentence means Figure 1 A diagram of the absolute value and phase of the impedance of a SAW resonator.

[0020] Figure 4 It is used for Figure 1 A diagram illustrating an example of setting the size of the region in a SAW resonator.

[0021] Figure 5 It is used for investigation Figure 1 A diagram showing an overview of the conditions and results of a simulation of the effect of the spacing outside the region on the characteristics of a SAW resonator.

[0022] Figure 6 (a)~ Figure 6 (f) is for Figure 5 A portion of the simulation results shows a diagram of the phase of the impedance.

[0023] Figure 7 This is a diagram showing a list of conditions and results of other simulations for investigating the influence of the spacing outside the region on the characteristics.

[0024] Figure 8 (a)~ Figure 8 (f) is for Figure 7 A portion of the simulation results shows a diagram of the phase of the impedance.

[0025] Figure 9 It means as Figure 1 Schematic diagram of a ladder-type SAW filter using an example of SAW resonator.

[0026] Figure 10 (a) to Figure 10 (d) in represents Figure 9 a diagram showing an example of setting the spacing in the parallel resonator of the SAW filter.

[0027] Figure 11 (a) to Figure 11 (e) in represents Figure 9 a diagram showing the characteristics of the SAW filter.

[0028] Figure 12 represents as Figure 1 a schematic diagram of a demultiplexer as an example of utilization of the SAW resonator.

[0029] Figure 13 represents as Figure 1 a schematic diagram of a communication device as an example of utilization of the SAW resonator.

[0030] Figure 14 is a top view showing the SAW resonator related to the modification example.

[0031] Figure 15 (a) to Figure 15 (c) in represents Figure 14 a diagram showing the vibration intensity and impedance of the SAW resonator.

[0032] -Symbol Explanation-

[0033] 1…SAW resonator (elastic wave resonator), 3…piezoelectric substrate, 5…IDT electrode, 7…reflector, 13…electrode finger, 19…region. Detailed Implementation Manner

[0034] Hereinafter, regarding the embodiments of the present disclosure, an explanation will be given with reference to the accompanying drawings. Among them, the drawings used in the following explanation are schematic drawings, and the dimensional ratios on the drawings do not necessarily have to be the same as those of actual products.

[0035] Regarding the same or similar structures, sometimes, such as "first region 19A" and "second region 19B", different letters are given to the same name for distinction, and in this case, it is sometimes simply referred to as "region 19", and no distinction is made between them.

[0036] <SAW Resonator>

[0037] (Basic Structure)

[0038] Figure 1 is a top view showing the structure of the SAW resonator 1 related to the embodiment of the present disclosure.

[0039] Although the SAW resonator 1 can be oriented in any direction as the upper or lower direction, in the following description, for convenience, an orthogonal coordinate system including the D1 axis, the D2 axis, and the D3 axis is defined, and the positive side of the D3 axis ( Figure 1 The upper side is defined as the upper side, and terms such as the upper surface are used. In addition, the D1 axis is defined as being parallel to the propagation direction of the SAW propagating along the upper surface (the surface on the front side of the paper, usually the main surface) of the piezoelectric substrate 3 described later, the D2 axis is defined as being parallel to the upper surface of the piezoelectric substrate 3 and orthogonal to the D1 axis, and the D3 axis is defined as being orthogonal to the upper surface of the piezoelectric substrate 3.

[0040] The SAW resonator 1 constitutes a so-called one-port SAW resonator. For example, when an electrical signal of a given frequency is input to one of the schematically shown first terminal 51A and second terminal 51B, resonance occurs, and the resonant signal is output from the other of the first terminal 51A and second terminal 51B. A bus bar (described later) or wiring extending from the bus bar may also function as the terminal 51.

[0041] The SAW resonator 1 , which is such a one-port SAW resonator, includes, for example, a piezoelectric substrate 3 , an IDT electrode 5 provided on the piezoelectric substrate 3 , and a first reflector 7A and a second reflector 7B located on both sides of the IDT electrode 5 .

[0042] The piezoelectric substrate 3 includes, for example, a single crystal having piezoelectricity. The single crystal is, for example, a lithium niobate (LiNbO3) single crystal or a lithium tantalate (LiTaO3) single crystal. The cutting angle can be appropriately set according to the type of SAW used, etc. For example, the piezoelectric substrate 3 is a substrate that rotates Y and cuts X. That is, the X-axis is parallel to the upper surface (D1 axis) of the piezoelectric substrate 3, and the Y-axis is inclined at a given angle relative to the normal to the upper surface of the piezoelectric substrate 3. In addition, the piezoelectric substrate 3 can also be a structure that is formed relatively thin and has a supporting substrate composed of an inorganic material or an organic material attached to the back side (the surface on the negative side of the D3 axis).

[0043] The IDT electrode 5 and the reflector 7 are formed by a layered conductor provided on the piezoelectric substrate 3. The IDT electrode 5 and the reflector 7 are formed, for example, of the same material and thickness. The layered conductor constituting them is, for example, a metal. The metal is, for example, Al or an alloy having Al as a main component (Al alloy). The Al alloy is, for example, an Al-Cu alloy. The layered conductor may also be formed of a plurality of metal layers. The thickness of the layered conductor can be appropriately set according to the electrical characteristics required of the SAW resonator 1, etc. As an example, the thickness of the layered conductor is 50 nm to 600 nm.

[0044] The IDT electrode 5 has a first comb-tooth electrode 9A and a second comb-tooth electrode 9B. Each comb-tooth electrode 9 has a bus bar 11 and a plurality of electrode fingers 13 extending in parallel from the bus bar 11. A pair of comb-tooth electrodes 9 is configured so that the plurality of electrode fingers 13 interlock (intersect) with each other. That is, the two bus bars 11 of a pair of comb-tooth electrodes 9 are arranged opposite each other, and the electrode fingers 13 of the first comb-tooth electrode 9A and the electrode fingers 13 of the second comb-tooth electrode 9B are arranged basically alternately in the width direction thereof. In addition, in addition to the above, each comb-tooth electrode 9 may also have a so-called dummy electrode, for example, which protrudes from the bus bar 11 between the electrode fingers 13 toward the bus bar 11 side of the other comb-tooth electrode 9 and is opposite to the front end of the electrode finger 13 of the other comb-tooth electrode 9.

[0045] The busbar 11 is formed, for example, in the form of a long strip with a substantially constant width extending linearly in the SAW propagation direction (the D1 axis). Furthermore, a pair of busbars 11 are positioned opposite each other in a direction perpendicular to the SAW propagation direction (the D2 axis). The busbars 11 may also have varying widths or be inclined relative to the SAW propagation direction.

[0046] Each electrode finger 13 is formed, for example, as a strip extending linearly in a direction perpendicular to the SAW propagation direction (the D2 axis) with a substantially constant width. Multiple electrode fingers 13 are arranged, for example, in the SAW propagation direction and are of equal length. The IDT electrode 5 may also be apodized, where the length (or, in other terms, the cross width) of the multiple electrode fingers 13 varies depending on their position in the propagation direction.

[0047] The number of electrode fingers 13 can be appropriately set according to the electrical characteristics required of the SAW resonator 1. Figure 1 The figures are schematic diagrams, so the number of electrode fingers 13 is shown as small. In reality, more electrode fingers 13 (e.g., 100 or more) can be arranged. The same applies to the strip electrodes 17 of the reflector 7 described later.

[0048] The reflector 7 is formed in a lattice shape, for example. Specifically, the reflector 7 includes a pair of bus bars 15 facing each other and a plurality of strip electrodes 17 extending between the pair of bus bars 15 .

[0049] The shapes of the busbar 15 and the strip electrode 17 can be the same as the busbar 11 and the electrode fingers 13 of the IDT electrode 5, except that both ends of the strip electrode 17 are connected to a pair of busbars 15. For example, the busbar 15 is formed into a long strip with a substantially constant width extending linearly in the propagation direction of the SAW (the D1 axis direction). Each strip electrode 17 is formed into a long strip with a substantially constant width extending linearly in a direction perpendicular to the propagation direction of the SAW (the D2 axis direction). Furthermore, the multiple strip electrodes 17 are arranged, for example, in the propagation direction of the SAW and have the same length. A pair of reflectors 7 are located on both sides of the IDT electrode 5 in the propagation direction of the SAW, and the multiple strip electrodes 17 are arranged immediately following the arrangement of the multiple electrode fingers 13.

[0050] Although not specifically shown, the upper surface of the piezoelectric substrate 3 may be covered with a protective film made of SiO2 or the like, extending from the IDT electrode 5 and the reflector 7. The protective film may simply be used to suppress corrosion of the IDT electrode 5 or the like, or it may also be a film that facilitates temperature compensation. Furthermore, when a protective film is provided, an additional film made of an insulator or metal may be provided on the upper or lower surface of the IDT electrode 5 and the reflector 7 to improve the SAW reflection coefficient.

[0051] Furthermore, in a SAW device including the SAW resonator 1, for example, although not specifically shown, a space that allows vibration of the upper surface of the piezoelectric substrate 3 and facilitates the propagation of the SAW can be formed on the piezoelectric substrate 3. This space can be formed, for example, by forming a box-shaped housing that covers the upper surface of the piezoelectric substrate 3, or by interposing a bump between the main surface of the circuit substrate and the upper surface of the piezoelectric substrate 3 so that the two surfaces face each other.

[0052] (Electrode finger pitch setting)

[0053] The pitch Pt (electrode finger pitch) between the plurality of electrode fingers 13 is, for example, the distance between the centers of two adjacent electrode fingers 13. Similarly, the pitch Pt between the plurality of strip electrodes 17, or the pitch Pt between electrode fingers 13 and strip electrodes 17, is also, for example, the distance between their centers. While the pitch Pt is fundamentally a distance, for convenience in the following description, it is sometimes used roughly synonymously with the area between the electrode fingers 13. For example, expressions such as "the number of pitches Pt" may be used.

[0054] In a conventional SAW resonator, the pitch Pt between the plurality of electrode fingers 13 and the plurality of strip electrodes 17 is substantially constant throughout the entire SAW resonator. The operation of such a conventional SAW resonator is as follows.

[0055] When a voltage is applied to the piezoelectric substrate 3 through the electrode fingers 13 of the IDT electrode 5, a SAW of a given mode is excited near the upper surface of the piezoelectric substrate 3 and propagates along the upper surface in the D1 axis direction. The excited SAW is mechanically reflected by the electrode fingers 13. As a result, a standing wave is formed with the spacing of the electrode fingers 13 set to half a wavelength. The standing wave is converted into an electrical signal of the same frequency as the standing wave and is taken out through the electrode fingers 13. In this way, the SAW resonator functions as a resonator. Its resonant frequency is approximately the same as the frequency of the SAW propagating on the piezoelectric substrate 3 with the spacing of the electrode fingers set to half a wavelength.

[0056] In the description of this embodiment, the resonant frequency refers to the frequency of resonance (main resonance) generated by the SAW of the intended period and pattern described above, and does not refer to the frequency of so-called spurious or sub-resonance.

[0057] The SAW excited in the IDT electrode 5 is mechanically reflected by the strip electrode 17 of the reflector 7. Furthermore, because adjacent strip electrodes 17 are interconnected by the bus bar 15, the SAW from the IDT electrode 5 is also electrically reflected by the strip electrodes 17. This suppresses the divergence of the SAW, allowing a stronger standing wave to appear in the IDT electrode 5, thereby improving the resonator function of the SAW resonator 1.

[0058] In the SAW resonator 1 of this embodiment, as in the prior art, the resonant frequency is determined by the pitch Pt. One of the characteristics of the SAW resonator 1 of this embodiment is that it is configured to have multiple pitches Pt (or, from another perspective, multiple resonant frequencies) of varying sizes. This is described in detail below.

[0059] The IDT electrode 5 includes multiple (three in the illustrated example) regions 19 (first region 19A to third region 19C), each of which is assigned a plurality of electrode fingers 13 (pitch Pt), with pitches Pt varying in size. Within each region 19, the multiple pitches Pt are constant. Pitch Pt x 2 (wavelength λ) is, for example, 1.5 μm to 6 μm.

[0060] The number of regions 19 and the number of types of pitches Pt may be the same or different. In other words, all regions 19 may have pitches Pt of different sizes, or some regions 19 may have pitches Pt of the same size. The description of this embodiment primarily uses the former as an example. The size relationship of the pitches Pt between the multiple regions 19 and the relative positions of the multiple regions 19 (for example, whether the region 19 with the smallest pitch Pt is on the outside or inside) can be set appropriately.

[0061] Figure 1In the example, the order from the area with the smallest pitch Pt to the area with the largest pitch Pt is the second area 19B, the third area 19C, and the first area 19A. In another viewpoint, the second area 19B with the smallest pitch Pt is arranged between the other areas 19 (the first area 19A and the third area 19C).

[0062] The number of electrode fingers 13 (pitch Pt) may be the same or different among the plurality of regions 19. In the latter case, the number of pitches Pt may be different among all regions 19 or the same among some regions. Figure 1 In the example of , the number of pitches Pt is different among all regions 19. Specifically, the number of pitches Pt increases in the region 19 where the pitch Pt is smaller.

[0063] The width of the electrode finger 13 can be set according to the size of the pitch Pt and can be different between the multiple regions 19, or it can be set independently of the size of the pitch Pt and can be the same between the multiple regions 19. Figure 1 The former case is exemplified in FIG. For example, the ratio (duty ratio) of the width of the electrode finger 13 to the size of the pitch Pt is common across multiple regions 19, resulting in different sizes (absolute values) across multiple regions 19. For example, the width of the electrode finger 13 is not less than 0.4 and not more than 0.7 of the size of the pitch Pt.

[0064] Furthermore, the IDT electrode 5 has inter-region spacings 21 (first inter-region spacing 21A and second inter-region spacing 21B) between two adjacent regions 19 (between the first region 19A and the second region 19B, and between the second region 19B and the third region 19C). Unlike the regions 19 that have multiple pitches Pt, each inter-region spacing 21 includes only a single pitch Pt. This single pitch Pt is the distance between the electrode fingers 13 at the end of one region 19 on the side of the other region 19 and the electrode fingers 13 at the end of the other region 19 on the side of the first region 19. Furthermore, the size of the inter-region spacing 21 is different from any pitch Pt between the two regions 19 on the side.

[0065] The pitch Pt between the pair of reflectors 7 can be the same or different between the pair of reflectors 7. The description of this embodiment mainly uses the former as an example. Furthermore, the pitch Pt between the reflectors 7 can be the same as or different from the pitch Pt between the plurality of regions 19. The description of this embodiment mainly uses the latter as an example.

[0066] The width of the strip-shaped electrode 17 can be set appropriately. The duty ratio of the strip-shaped electrode 17 may be the same as or different from the duty ratio of the electrode fingers 13 .

[0067] The SAW resonator 1 has outer spacings 23 (first outer spacing 23A and second outer spacing 23B) between the IDT electrode 5 and the reflector 7 (between the first region 19A and the first reflector 7A, and between the third region 19C and the second reflector 7B). Each outer spacing 23 is a region between the IDT electrode 5 and the reflector 7. Therefore, it only includes the pitch Pt (one) between the strip electrode 17 at the end of the reflector 7 located on the IDT electrode 5 side and the electrode fingers 13 at the end of the region 19 adjacent to the reflector 7 located on the reflector 7 side. This pitch Pt can be the same as or different from the pitch Pt of the strip electrode 17 of the reflector 7 adjacent to the pitch Pt or the pitch Pt of the electrode fingers 13 of the region 19 adjacent to the pitch Pt. In the description of this embodiment, the latter is mainly used as an example.

[0068] Figure 2 1 is a diagram showing an example of the magnitude relationship among a plurality of pitches Pt of the SAW resonator 1 .

[0069] In this figure, the horizontal axis (n) represents the position in the SAW propagation direction (D1-axis direction), and the vertical axis represents the size of the pitch Pt. The units on the horizontal axis are the number of pitches Pt, counted from the edge of the SAW resonator 1. The units on the vertical axis can be viewed as absolute values ​​or as ratios relative to a reference pitch Pt. The plotted points represent the position and size of the pitch Pt, and the lines connecting the points are for easier viewing of the figure.

[0070] As reference Figure 1 As described above, the sizes of the pitches Pt are different between the multiple regions 19. Figure 2 middle, also harmonious Figure 1 Similarly, the pitch Pt in all three regions 19 is different from each other. The case where the second region 19B having the smallest pitch Pt is located at the center of the IDT electrode 5 is exemplified.

[0071] The size of the pitch Pt of the inter-region space 21 may be set to a value intermediate to the sizes of the pitch Pt of the two regions 19 on both sides thereof, a value larger than the intermediate value, or a value smaller than the intermediate value.

[0072] Here, the intermediate value refers to the value halfway between two values. For example, when the size of the pitch Pt of one region 19 is set to a and the size of the pitch Pt of the other region 19 is set to b, the intermediate value is (a+b) / 2. In other words, as long as the intermediate value between a and b does not deviate toward either a or b, it will not be the average value obtained by dividing the sum of the sizes of the pitches Pt of the two regions 19 by the total number of pitches Pt of the two regions. Of course, there may be bias due to manufacturing accuracy. The same applies to the other intermediate values ​​described later.

[0073] In the illustrated example, the pitch Pt of the inter-region spacing 21 is smaller than the median of the two pitches Pt on either side (indicated by dashed lines L1 and L2). Specifically, the pitch Pt of the first inter-region spacing 21A is smaller than the median of the pitch Pt of the first region 19A and the pitch Pt of the second region 19B (dashed line L1). The pitch Pt of the second inter-region spacing 21B is smaller than the median of the pitch Pt of the second region 19B and the pitch Pt of the third region 19C (dashed line L2). Thus, when the pitch Pt of the inter-region spacing 21 is smaller than the median of the two pitches Pt on either side, the degree of reduction can be appropriately set.

[0074] Although the size of the pitch Pt of the reflector 7 can be appropriately set as described above, for example, Figure 2 As shown, when the pitch Pt of the region 19 with the smallest pitch Pt (the second region 19B in the illustrated example) is set to the minimum pitch Pt_min and the pitch Pt of the region 19 with the second smallest pitch Pt (the third region 19C in the illustrated example) is set to the pitch Pt_2nd, the size of the pitch Pt of the reflector 7 is greater than Pt_min and less than Pt_2nd.

[0075] The pitch Pt of the outer spacers 23 may be an intermediate value between the pitch Pt of adjacent regions 19 and the pitch Pt of adjacent reflectors 7 , a value larger than the intermediate value, or a value smaller than the average value.

[0076] In the illustrated example, the pitch Pt of the outer spacer 23 is smaller than the average of the two pitches Pt on either side (indicated by dashed lines L3 and L4). Specifically, the pitch Pt of the first outer spacer 23A is smaller than the average of the pitch Pt of the first region 19A and the pitch Pt of the first reflector 7A (dashed line L3). The pitch Pt of the second outer spacer 23B is smaller than the average of the pitch Pt of the third region 19C and the pitch Pt of the second reflector 7B (dashed line L4). Thus, when the pitch Pt of the outer spacer 23 is smaller than the average of the pitches Pt on either side, the degree of reduction can be appropriately set.

[0077] (The role of multiple regions)

[0078] Figure 3 (a) and Figure 3 (b) is a diagram showing the impedance of the SAW resonator 1 for explaining the operation of the SAW resonator 1 .

[0079] Figure 3 In (a) of FIG. 1 , the horizontal axis (f (Hz)) represents the frequency, and the vertical axis (|Z| (Ω)) represents the absolute value of the impedance of the SAW resonator 1 . Figure 3In (b), the horizontal axis (f (Hz)) represents the frequency, and the vertical axis (θ (°)) represents the phase of the impedance of the SAW resonator 1. Figure 3 (a) and Figure 3 The scales of the horizontal axes of (b) are substantially the same.

[0080] Figure 3 In (a), the dashed line L11 represents the characteristics of a conventional SAW resonator in which the pitch Pt is constant across the entire IDT electrode 5. In conventional SAW resonators, the absolute value of the impedance reaches a minimum (a resonance point appears) at the SAW frequency (resonance frequency fr') where the pitch Pt is half the wavelength. Furthermore, the absolute value of the impedance reaches a maximum (an antiresonance point appears) at the antiresonance frequency fa', which is determined by the ratio of the resonant frequency fr' to the capacitance of the IDT electrode 5.

[0081] Figure 3 In (a), the solid line L13 represents the characteristics of the SAW resonator 1 according to the embodiment. The IDT electrode 5 of the SAW resonator 1 is divided into multiple regions 19 and connected in parallel. Meanwhile, the resonance point is the resonance point of a series resonant circuit. Therefore, in the SAW resonator 1, the pitch Pt of the multiple regions 19 varies, resulting in multiple resonance points.

[0082] For example, one resonance point appears at the SAW frequency (resonance frequency fr3) when the pitch Pt of the second region 19B, which has the smallest pitch Pt, is set to half the wavelength. Another resonance point appears at the SAW frequency (resonance frequency fr2) when the pitch Pt of the third region 19C, which has the next smallest pitch Pt, is set to half the wavelength. Furthermore, another resonance point appears at the SAW frequency (resonance frequency fr1) when the pitch Pt of the first region 19A, which has the largest pitch Pt, is set to half the wavelength.

[0083] On the other hand, the antiresonance point is the resonance point of a parallel resonant circuit. Therefore, in the SAW resonator 1 of the embodiment, there is essentially only one antiresonance point (antiresonance frequency fa). The antiresonance frequency fa is generally close to the value obtained by averaging the antiresonance frequencies of all regions 19 when the IDT electrode 5 is composed solely of each region 19.

[0084] Furthermore, the SAW resonator 1 can be used as a resonator in which Δf is defined by the highest resonant frequency fr3 and the anti-resonant frequency fa.

[0085] Therefore, for example, assuming that the minimum pitch Pt_min of the SAW resonator 1 of the embodiment is equal to the pitch Pt of the conventional SAW resonator, and that the capacitance of the IDT electrode 5 of the embodiment is the same as that of the conventional IDT electrode 5, the resonant frequencies (fr3, fr') of the SAW resonator 1 of the embodiment and the conventional SAW resonator are identical. Meanwhile, the antiresonant frequency fa of the SAW resonator 1 of the embodiment is lower than the antiresonant frequency fa' of the conventional SAW resonator due to the effect of region 19 having a pitch Pt greater than the minimum pitch Pt_min. As a result, Δf of the embodiment is smaller than Δf' of the conventional SAW resonator.

[0086] From another perspective, in conventional SAW resonators, when the pitch Pt decreases (or increases), both the resonant frequency fr' and the antiresonant frequency fa' decrease (or increase), resulting in a relatively small change in Δf. In contrast, in this embodiment, by inserting region 19 with a large pitch Pt, only the antiresonant frequency fa increases. Alternatively, by inserting region 19 with a small pitch Pt, the resonant frequency fr increases at a greater rate than the antiresonant frequency fa. As a result, Δf is preferably reduced.

[0087] Furthermore, by reducing Δf without using a new structure such as an additional capacitance element, it is possible to eliminate, for example, strain caused by the piezoelectric substrate or characteristic changes due to temperature changes that may be caused by the additional capacitance element.

[0088] (Differences between multiple resonant frequencies (differences between multiple types of pitches))

[0089] The differences between the multiple resonant frequencies (fr1 to fr3) can be appropriately set. For example, the differences between the multiple resonant frequencies (fr1 to fr3) can be large. In this case, for example, the effect of reducing Δf is enhanced. Specifically, for example, taking the intermediate value fr_mid between the highest resonant frequency (fr3) and the lowest resonant frequency (fr1) as a reference, fr_mid = (fr1 + fr3) / 2 (not shown), the ratio of the intermediate value fr_mid of fr1 (or fr3) to the difference from the intermediate value fr_mid (|fr1 - fr_mid| / fr_mid × 100) is 0.5% or greater, or 1% or greater.

[0090] On the lower frequency side of the highest resonant frequency (fr3), a prohibited region where no resonant frequencies exist can be provided, and multiple other resonant frequencies can be set to frequencies away from the highest resonant frequency. For example, all resonant frequencies (fr2, and other resonant frequencies may also exist) between the lowest resonant frequency (fr1) and the highest resonant frequency (fr3) can be located lower than the midpoint between the two, fr_mid. In other words, within multiple regions 19, the second-highest resonant frequency (fr2) can be lower than the midpoint fr_mid. In other words, the difference between the second-highest resonant frequency and the highest resonant frequency (fr3-fr2) is greater than 50% of the difference between the lowest and highest resonant frequencies (fr3-fr1). Alternatively, the former is greater than 60% of the latter.

[0091] By providing a prohibited region in this manner, it is possible to achieve, for example, a characteristic in which the impedance changes steeply near the highest resonant frequency (fr3) used for the regulation of Δf, while also achieving a characteristic in which the impedance decreases over a wide range at frequencies lower than this. Achieving this characteristic enables, for example, excellent filter characteristics when the SAW resonator 1 is used as a parallel resonator in a ladder-type SAW filter (described later).

[0092] If conditions affecting the resonant frequency (e.g., the thickness and duty cycle of the electrode fingers 13) other than the electrode finger pitch remain the same across multiple regions 19, changes in the pitch Pt are roughly proportional to changes in the resonant frequency. Therefore, the magnitudes illustrated above can be used as examples of differences in resonant frequency between multiple different pitches Pt.

[0093] For example, the area 19 ( Figure 2 In the example of the second region 19B), the pitch Pt is set to the minimum pitch Pt_min, and the region 19 ( Figure 2 In the example of the first region 19A, the pitch Pt is set to the maximum pitch Pt_ma, and the intermediate value between the two is set to Pt_mid. In this case, the ratio of Pt_max (or Pt_min) to the difference between Pt_mid and Pt_mid (|Pt_max-Pt_mid| / Pt_mid×100) is 0.5% or more, or 1% or more.

[0094] Furthermore, for example, the second smallest Pt region 19 ( Figure 2 In the example of the third region 19C, the pitch Pt is set to Pt_2nd. In this case, the difference between the second smallest pitch and the minimum pitch (Pt_2nd-Pt_min) is, for example, greater than 50% or 60% of the difference between the maximum pitch and the minimum pitch (Pt_max-Pt_min).

[0095] Furthermore, the difference between the pitch Pt of the region 19 with the largest Pt value and the pitch Pt of the region 19 with the smallest Pt value may be set to be equal to or smaller than the difference between the resonant frequency and the antiresonant frequency of the SAW resonator 1 .

[0096] (Number of gaps in each area (size of each area))

[0097] A sufficient number of pitches Pt of the multiple regions 19 can be ensured for each size type (for each region 19 when the number of regions 19 and the number of types of pitches Pt are the same). In this case, the aforementioned effect of reducing Δf by using the highest resonant frequency (fr3) and the averaged antiresonant frequency (fa) can be more reliably achieved. For example, for all types of pitches Pt of the multiple regions 19, the number of pitches Pt of a single type is 20 or more, or 30 or more. Furthermore, for example, for all types of pitches Pt of the multiple regions 19, the number of pitches Pt of a single type is 5% or more, 10% or more, or 30% or more of the total number of pitches Pt in the IDT electrode 5.

[0098] The number of pitches Pt may be substantially the same or different between different types of pitch Pt sizes or between regions 19. Furthermore, from another perspective, the size (length) of the regions 19 in the propagation direction (D1-axis direction) may be the same or different between regions 19. Furthermore, when the sizes of the regions 19 in the propagation direction are the same, the number of pitches Pt increases relatively in regions 19 with smaller pitches Pt.

[0099] The size of a region 19 in the propagation direction is generally an integer multiple of the pitch Pt. On the other hand, to achieve desired characteristics, the sizes of multiple regions 19 in the propagation direction can be set to a common multiple of multiple pitches Pt. Therefore, in the description of this embodiment, even when the sizes of multiple regions 19 in the propagation direction are equal, this also includes cases where there is a difference smaller than the pitch Pt (relatively large pitch between multiple regions 19).

[0100] The size of region 19 in the propagation direction can be set by considering the SAW vibration intensity (amplitude). For example, assuming that multiple regions 19 have equal sizes in the propagation direction and a voltage with a frequency within or around Δf is applied to SAW resonator 1, if a region 19 with increased vibration intensity exists, that region 19 will be larger in the propagation direction than the other regions 19. In other words, the number of pitches Pt increases compared to a case where multiple regions 19 are equal in size. This situation can achieve the following effects, for example.

[0101] Figure 4This is a diagram for explaining an example of setting the size of the region 19 in the propagation direction (the number of electrode fingers 13 or the pitch Pt in another viewpoint).

[0102] In this figure, the horizontal axis (D) represents the position in the propagation direction of the SAW (D1 axis direction), and the vertical axis (Sv) represents the vibration intensity. Here, the vibration intensity represents the vibration intensity at frequencies near the passband. The units of the horizontal axis and Figure 2 The difference is the distance (e.g., μm). The difference between the multiple regions 19 of pitch Pt (difference between pitches Pt1 to Pt3) is, for example, 1% to 4%. In the region 19 with a wide range represented by the horizontal axis, the number of pitches Pt is generally large.

[0103] This figure illustrates a case where three pitches Pt (pitch Pt1 to Pt3) are provided. Specifically, three regions 19 are provided, each with a different pitch Pt. Furthermore, the outermost portion of the range of pitches Pt1 to Pt3 represents the arrangement range of reflectors 7. The inter-region spacing 21 and outer spacing 23 are omitted from this figure.

[0104] Line L21 shows the case where the three regions 19 have the same size in the propagation direction (the range of the horizontal axis (D) of the pitches Pt1 to Pt3 and Figure 4 The example shown is different from the case. This case is also included in the technology involved in the present disclosure. ) Example of vibration intensity under. In this example, the vibration intensity in region 19 at a spacing of Pt2 (the maximum value in region 19. The same applies to the case of comparison between regions 19 below) is relatively increased. In addition, in this example, in region 19 at a spacing of Pt1 and region 19 at a spacing of Pt3, although the vibration intensity in region 19 at a spacing of Pt1 is relatively slightly increased, the vibration intensities of the two regions 19 are roughly the same.

[0105] One of the reasons for the change in vibration intensity with respect to the position in the propagation direction is that a plurality of regions 19 having different pitches Pt are provided.

[0106] For example, by providing a plurality of regions 19 with different pitches Pt, SAW with various cycles is generated. When a signal near a resonant frequency corresponding to the various cycles is applied, the vibration intensity in a specific region 19 increases.

[0107] Furthermore, for example, when the SAW resonator 1 is used to form a parallel resonator of a ladder-type SAW filter, signals in a frequency band adjacent to the passband on the lower frequency side tend to flow into region 19 having the highest resonance frequency.

[0108] In the conventional SAW resonator, such a change in vibration intensity does not occur or is small, and the shape of the line representing the vibration intensity is substantially trapezoidal (a shape similar to line L25 ).

[0109] As the vibration intensity increases, the voltage generated on the upper surface of the piezoelectric substrate 3 by the vibration increases, which in turn reduces the electrical resistance of the electrode fingers 13. Therefore, for example, if the vibration intensity increases relatively strongly in any of the multiple regions 19, the electrical resistance of the IDT electrode 5 may be uneven. Furthermore, the electrical resistance of the entire IDT electrode 5 is determined by the relatively low-resistance region 19. Furthermore, the specifications required for the SAW resonator 1 may not be met.

[0110] For example, line L23 represents the permissible limit for vibration intensity. This permissible limit is set, for example, to meet the required electrical resistance of SAW resonator 1. In the illustrated example, the vibration intensity represented by line L21 in region 19 exceeds line L23. In other words, because the electrical resistance in region 19 is low, SAW resonator 1 cannot meet the required electrical resistance, regardless of whether the electrical resistance in other regions 19 is within the permissible range.

[0111] Here, as described above, the number of pitches Pt (the number of electrode fingers 13) in the region 19 where the vibration intensity increases, as indicated by line L21, can be increased compared to the case where the sizes of the plurality of regions 19 in the propagation direction are made equal. From another perspective, the size of the region 19 in the propagation direction where the vibration intensity is high can be increased compared to the case where the IDT electrode 5 is equally divided in the propagation direction by the plurality of regions 19. For example, Figure 4 In the example, the number of pitches Pt2 increases.

[0112] This reduces the peak in vibration intensity, as shown by line L25. From another perspective, the positional bias in vibration intensity relative to the propagation direction is mitigated. As a result, the electrical resistance of the SAW resonator 1 as a whole is improved, making it easier to meet required specifications. Increasing the number of pitches Pt in the region 19 with high vibration intensity reduces the vibration intensity. This is achieved, for example, by distributing the voltage that increases the vibration intensity across a larger number of electrode fingers 13.

[0113] Furthermore, compared to a case where multiple regions 19 have the same size in the propagation direction, the region 19 with high vibration intensity, indicated by line L21, is enlarged, making it relatively larger than the other regions 19. Furthermore, while the region 19 with high vibration intensity, indicated by line L21, is enlarged in the propagation direction, the other regions 19 can be simultaneously reduced in the propagation direction. This prevents, for example, the capacitance of the IDT electrode 5 from significantly deviating from its initial design value, making it easier to achieve desired characteristics. However, the region 19 with high vibration intensity, indicated by line L21, is larger in the propagation direction than the other regions 19.

[0114] When setting the size of region 19 in the propagation direction (the number of pitches Pt), the size relationship between the three or more regions 19 can be appropriately adjusted. The same applies when considering vibration intensity as described above. For example, region 19 with the greatest vibration intensity, as indicated by line L21, can be made the largest in the propagation direction, while the other two or more regions 19 can be of equal size. Furthermore, for example, all regions 19 can be arranged to increase in size in the propagation direction, in descending order of vibration intensity, as indicated by line L21.

[0115] The degree to which the number of pitches Pt is increased in a specific region 19 can also be appropriately set. For example, the number of pitches Pt in region 19, where the vibration intensity is greatest, represented by line L21, can be set to the minimum number required to keep the peak of the vibration intensity below a given tolerance, or to the number required to achieve a line representing the vibration intensity that forms a roughly trapezoidal shape, such as line L25 (or both). Furthermore, the distribution of the number of pitches Pt at which the maximum vibration intensity is minimized after adjusting the number of pitches Pt can also be observed.

[0116] The region 19 with increased vibration intensity indicated by line L21 can be observed through experiments or simulations. Furthermore, the setting of the size (number of pitches Pt) of the plurality of regions 19 in the propagation direction where the vibration intensity falls below a given allowable limit can also be appropriately observed through experiments or simulations.

[0117] Among them, as mentioned above, the reason why the peak of vibration intensity appears as represented by line L21 is that the voltage of the frequency adjacent to the passband has a greater influence, so if the number of spacings Pt is increased in the area 19 where the resonant frequency is the highest (the spacing Pt is the smallest), then in most cases the electrical resistance is improved.

[0118] Furthermore, according to the above results, in most cases, the area with the highest vibration intensity has a larger size (length) located most in the propagation direction.

[0119] The change in vibration intensity relative to position in the propagation direction (change in pitch Pt) varies depending on the frequency of the applied voltage. Considering the various configurations used in SAW resonator 1, it is possible to assume voltages at frequencies around Δf or its surroundings. Therefore, whether the number of pitches Pt is increased (increased in the propagation direction) in the region 19 where vibration intensity increases, as in this embodiment, represented by line L21, can be determined by, for example, assuming a voltage at the center frequency of Δf (the midpoint between the highest resonant frequency fr3 and the antiresonant frequency fra).

[0120] (Tendency of the influence of the size of the inter-region spacing and the outer spacing)

[0121] The inventors of this application variously varied the pitch Pt between the inter-region spacing 21 and the outer spacing 23, and conducted simulations for various conditions. The results showed that when the pitch Pt between the inter-region spacing 21 and the outer spacing 23 was smaller than the midpoint between the two pitches Pt on either side, the characteristics of the SAW resonator 1 improved. Specifically, this improvement is described below.

[0122] The conditions common to various situations are as follows.

[0123] Piezoelectric substrate 3: 46° Y-plate X-propagation lithium tantalate (LiTaO3) single crystal

[0124] The conditions for the IDT electrode 5 and the reflector 7 to be shared are:

[0125] Film thickness: 2×8% of Pt (Pt is the average value of all pitches of the electrode fingers 13.)

[0126] Duty cycle: 0.5

[0127] IDT electrode 5:

[0128] Number of Region 19: Three

[0129] Pitch Pt:

[0130] Area 19 at one end: 1.025×2.55μm

[0131] Central area 19: 1.000×2.55μm

[0132] Area 19 at the other end: 1.027×2.55μm

[0133] Number of electrode fingers 13: 41 in any region 19 (the number of pitches Pt between regions 19 is 40)

[0134] Reflector 7:

[0135] Pitch Pt: 1.022×2.55μm for any reflector

[0136] Figure 5 Indicates conditions that differ from one another among a plurality of situations, and indicates simulation results.

[0137] The "Model" column shows numbers assigned to various situations. As shown in this column, simulations were performed for 19 situations, namely, Ca1 to Ca19.

[0138] The "Content" column summarizes the different conditions for various conditions. Conditions other than Ca1 are performed with the Ca1 condition as the reference, with the pitch Pt of the inter-region spacing 21 and / or the outer spacing 23 set to 0.9 times or 1.1 times. This is indicated as "Standard" for "Ca1" and "x0.9" or "x1.1" for other conditions.

[0139] Here, "Pt_R1" represents the pitch Pt of the outer spacing 23 between the region 19 at the one end and the reflector 7 outside it. "Pt_R2" represents the pitch Pt of the outer spacing 23 between the region 19 at the outer end and the reflector 7 outside it. "Pt_I1" represents the pitch Pt of the inter-region spacing 21 between the region 19 at the one end and the central region 19. "Pt_I2" represents the pitch Pt of the inter-region spacing 21 between the region 19 at the outer end and the central region 19.

[0140] For example, a condition written as "Pt_R1x0.9" means that Pt_R1 is 0.9 times Pt_R1 relative to Ca1. When two or more "R1," "R2," "11," or "12" are written with slashes, as in "R1 / R2," this means that all the intervals written are 0.9 times or 1.1 times.

[0141] Moreover, as indicated in the "Content", simulations were performed for the conditions where the pitch Pt of only one interval was made 0.9 times relative to the condition of Ca1 (Ca2, Ca4, Ca8, Ca10), the conditions where the pitch Pt of only one interval was made 1.1 times (Ca3, Ca5, Ca9, Ca11), the conditions where the pitch Pt of two homogeneous intervals was made 0.9 times (Ca6, Ca12), the conditions where the pitch Pt of two homogeneous intervals was made 1.1 times (Ca7, Ca13), and the conditions where 0.9 times and 1.1 times were appropriately combined for 4 intervals (Ca14 to Ca19).

[0142] Here, the size of the pitch Pt of each interval in the condition Ca1 is as follows.

[0143] Pt_R1=1.024×2.55μm

[0144] Pt_I1=1.013×2.55μm

[0145] Pt—I2=1.014×2.55—μμm

[0146] Pt_R2=1.025×2.55μm

[0147] As can be understood from the above-mentioned conditions of the pitch Pt between the three regions 19 and the two reflectors 7, the pitch Pt for any interval is the median of the pitches Pt on either side thereof, although slight differences may occur due to rounding.

[0148] The "Calculation Results" column shows the results of whether the resonant characteristics have improved compared to the situation in Ca1. "Resonance Side" shows the results of the determination on the resonant frequency side, and "Anti-Resonance Side" shows the results of the determination on the anti-resonance frequency side. "-" is displayed for situations where there is no further improvement.

[0149] As shown in the "Calculation Results" column, reducing the pitch Pt (Ca8, Ca10, Ca12, Ca16, and Ca19) of the inter-region spacing 21 improves the resonance characteristics on the resonant side. Furthermore, reducing the pitch Pt (Ca2, Ca4, Ca6, Ca16, and Ca18) of the outer spacing 23 improves the resonance characteristics on the antiresonant side.

[0150] Figure 6 (a)~ Figure 6 (f) in the formula is for Figure 5 A diagram showing characteristics of the SAW resonator 1 obtained by simulation of a part of the situation.

[0151] In these graphs, the horizontal axis represents frequency (MHz) and the vertical axis represents impedance phase (°). Figure 6 (a)~ Figure 6 (c) shows the results of the condition of Ca1 and the conditions (Ca12, Ca16, and Ca19) where the pitch Pt of the inter-region gap 21 is reduced. Figure 6 (d)~ Figure 6 (f) shows the results of the condition of Ca1 and the conditions (Ca6, Ca16, and Ca18) where the pitch Pt of the outer spacers 23 is reduced. Figure 6 (b) and Figure 6 (c) in the Figure 6 A magnified view of a portion of (a). Figure 6 (e) and Figure 6 (f) in Figure 6 A partial enlarged view of (d) in FIG. Based on these figures, it can be confirmed Figure 5Furthermore, it was confirmed that Δf could be reduced in any of the conditions compared to the case where the pitch of the entire IDT electrodes 5 was the same.

[0152] (Examples of the sizes of the intervals between areas and the outer intervals)

[0153] Next, based on the above-described simulation results, simulations were performed for various situations in order to investigate the influence of the degree of reduction when the pitch Pt between the inter-region spacing 21 and the outer spacing 23 is reduced.

[0154] Figure 7 This figure shows different conditions and simulation results between various situations. Figure 5 Again, the description of the format is omitted. Figure 5 The same simulation.

[0155] As shown in the "Details" column of this figure, simulations were conducted with the pitch Pt of each spacing varied within a range of 0.7 to 0.9 times the baseline Cb1 condition (same conditions as Ca1). Furthermore, simulations were conducted for conditions where the pitch Pt of both the inter-region spacing 21 and the outer spacing 23 was increased (Cb11 to Cb16).

[0156] As shown in the "Calculation Results" column of this figure, for the outer spacing 23, even when the pitch Pt is set to 0.7 times that of Cb1, the characteristics on the antiresonant side are improved (Cb2-Cb4 and Cb8-13). On the other hand, for the inter-region spacing 21, if the pitch Pt is too small, the effect of improving the characteristics on the resonant side is not achieved (Cb6, Cb7, Cb9, Cb10, Cb15, and Cb16). In other words, when the pitch Pt is 0.9 times or greater, the effect of improving the characteristics on the resonant side is achieved (Cb5, Cb8, and Cb14).

[0157] Figure 8 (a)~ Figure 8 (f) in the formula is for Figure 7 A diagram showing resonance characteristics of a portion of the situation obtained by simulation.

[0158] In these graphs, the horizontal axis represents frequency (MHz) and the vertical axis represents impedance phase (°). Figure 8 (a)~ Figure 8 (c) shows the results of the condition Cb1 and the conditions (Cb2 to Cb4) where the pitch Pt of the outer spacers 23 is set to 0.7 to 0.9 times the size. Figure 8 (d)~ Figure 8(f) shows the results of the case where the pitch Pt of all the gaps is set to 0.7 to 0.9 times (Cb8 to Cb10). Figure 8 (b) and Figure 8 (c) in the Figure 8 A magnified view of a portion of (a). Figure 8 (e) and Figure 8 (f) in Figure 8 A partial enlarged view of (d) in FIG. Based on these figures, it can be confirmed Figure 7 The validity of the judgment results shown.

[0159] <Ladder Type SAW Filter>

[0160] (Basic Structure)

[0161] Figure 9 1 is a schematic diagram showing a ladder-type SAW filter 109 as an example of utilization of the SAW resonator 1 .

[0162] The SAW filter 109 includes, for example, a plurality of series resonators 57 connected in series between an input terminal 105 for inputting a signal and an output terminal 103 for outputting a signal, and a plurality of parallel resonators 59 (a first parallel resonator 59A to a fourth parallel resonator 59D) connecting the series line to a reference potential portion.

[0163] Moreover, as can be understood from the symbols assigned to the IDT electrode 5, reflector 7, comb electrode 9 and electrode finger 13, among the series resonators 57 in the upper left portion of the paper, at least any one of the multiple series resonators 57 and the multiple parallel resonators 59 is composed of the SAW resonator 1 of the present embodiment described above, and the rest are composed of, for example, existing SAW resonators (SAW resonators with a substantially constant pitch Pt throughout the entire IDT electrode).

[0164] For example, in the ladder-type SAW filter 109 , all the series resonators 57 are formed of conventional SAW resonators, and at least one (or all) of the plurality of parallel resonators 59 are formed of the SAW resonator 1 of this embodiment.

[0165] As is well known, the characteristics of the series resonator 57 and the parallel resonator 59 are set so that the antiresonance frequency of the parallel resonator 59 substantially matches the resonant frequency of the series resonator 57. The passband is a range slightly narrower than the range obtained by adding Δf of the two resonators.

[0166] The multiple sets of IDT electrodes 5 and reflectors 7 that constitute the multiple series resonators 57 and the multiple parallel resonators 59 are, for example, disposed on the same piezoelectric substrate 3. The number of the multiple series resonators 57 and the multiple parallel resonators 59 can be appropriately set. Furthermore, the multiple series resonators 57 can be fine-tuned so that the resonant frequencies and antiresonant frequencies differ slightly from each other. Similarly, the multiple parallel resonators 59 can be fine-tuned so that the resonant frequencies and antiresonant frequencies differ slightly from each other. The SAW filter 109 can also include structures other than resonators, such as inductors, at appropriate locations.

[0167] (Example of Setting the Pitch in a Ladder-Type SAW Filter)

[0168] Figure 10 (a)~ Figure 10 (d) is a diagram showing an example of setting the pitch Pt in the first to fourth parallel resonators 59A to 59D formed by the SAW resonator 1 of the present embodiment.

[0169] These pictures and Figure 4 Similarly. In these figures, the curves drawn with single-dot dashed lines represent the vibration intensity of an example in which the sizes of multiple (three in the illustrated example) regions 19 in the propagation direction are set to the same (an example in which the range on the horizontal axis (D) of the spacing Pt1 to Pt3 is different from the illustrated example. These examples are also included in the technology involved in the present disclosure.). The curves drawn with solid lines represent the vibration intensity of an example in which the number of spacings Pt (the size in the propagation direction of the region 19) is adjusted (an example in which the range on the horizontal axis (D) of the spacings Pt1 to Pt3 is illustrated). The curve representing the vibration intensity can be obtained by simulation calculation. As shown in these figures, a plurality of parallel resonators 59 can be set to a structure in which the value of the spacing Pt is set to a closer value and the spacings Pt are different from each other. The details are as follows.

[0170] Figure 10 (a) shows an example of setting the pitch Pt of the first parallel resonator 59A. Figure 4 Similarly, the pitch Pt2 is smallest in the central region 19. Furthermore, if the multiple regions 19 are of equal size in the propagation direction, the vibration intensity increases in the central region 19. Furthermore, by increasing the number of pitches Pt2 (relatively increasing the size of the central region 19 in the propagation direction), the vibration intensity can be reduced relative to the permissible limit indicated by the dotted line.

[0171] Figure 10 (b) shows an example of setting the pitch Pt of the second parallel resonator 59B. In this example, Figure 4Similarly, the spacing Pt2 in the central region 19 is the smallest. Moreover, Pt1>Pt3. Figure 10 Compared to the first parallel resonator 59A in (a), the difference between pitches Pt1 to Pt3 is relatively small. Therefore, when the three regions 19 are of equal size in the propagation direction, the vibration intensity is less uneven and remains below the permissible vibration intensity limit. Furthermore, the vibration intensity increases not only in the central region 19 but also in the region 19 with the higher intensity in the central region 19 and in the region 19 with pitch Pt3. Furthermore, by making the number of pitches Pt the same in all three regions 19 (the size of the regions 19 in the propagation direction varies among the three regions 19 due to the differences in the sizes of pitches Pt1 to Pt3), the high vibration intensity is further reduced.

[0172] Figure 10 (c) in FIG. 5 shows an example of setting the pitch Pt of the third parallel resonator 59C. In this example, Figure 4 Similarly, the spacing Pt2 in the central region 19 is the smallest. Furthermore, if the multiple regions 19 are made equal in size in the propagation direction, the vibration intensity increases in the central spacing Pt. Moreover, by increasing the number of spacings Pt2 (relatively increasing the central region 19 in the propagation direction), the vibration intensity can be reduced compared to the allowable limit indicated by the dotted line. Figure 10 In the example (c), as can be understood from comparison with other figures, the regions 19 are not provided with a pitch Pt different from the pitch Pt of the regions 19, and the regions 19 are directly adjacent to each other. The same applies to the regions 19 and the reflectors 7.

[0173] Figure 10 (d) in the figure shows an example of setting the pitch Pt of the fourth parallel resonator 59D. In this example, Pt3 < Pt1 < Pt2. Furthermore, if the multiple regions 19 are set to the same size in the propagation direction, the vibration intensity increases in the regions 19 with a pitch of Pt3. Furthermore, by increasing the number of regions 19 with a pitch of Pt3 (making the regions 19 with a pitch of Pt3 relatively larger in the propagation direction), the vibration intensity can be reduced relative to the allowable limit indicated by the dotted line.

[0174] In addition, for Figure 10 (a)~ Figure 10 For any of (d) in the above, the difference between the multiple resonant frequencies also becomes the form described in the description of the SAW resonator 1. That is, in each parallel resonator 59, the second highest resonant frequency is lower than the middle value between the lowest resonant frequency and the highest resonant frequency. Specifically, the highest resonant frequency and the second highest resonant frequency ( Figure 3 The difference between fr2) in (a) and the highest resonant frequency ( Figure 3(a) fr3) and the lowest resonant frequency ( Figure 3 The ratio of the difference between fr1) in (a) ((fr3-fr2) / (fr3-fr1)×100) is 62% ( Figure 10 (a) in), 67% ( Figure 10 (b) in), 93% ( Figure 10 (c) in), 69% ( Figure 10 (d) in the above figure.

[0175] Furthermore, Figure 10 (a)~ Figure 10 In (d), the highest resonant frequencies are relatively close to each other, while the second-highest resonant frequency or the lowest resonant frequency is relatively far apart. By setting the resonant frequencies of the plurality of parallel resonators 59 in this manner, the rising edge of the curve representing the passband characteristic on the low-frequency side of the passband can be made steep, and attenuation can be ensured over a wide frequency band further to the low-frequency side than the passband.

[0176] Specifically, in Figure 10 (a)~ Figure 10 In the example (d) of FIG, for the highest resonant frequency (fr3), Figure 10 (a)~ Figure 10 The ratio ((fr3_max - fr3_min) / fr3_mid × 100) of the difference between the highest frequency (fr3_max) and the lowest frequency (fr3_min) in (d) to the midpoint between the two (fr3_mid = (fr3_max + fr3_min) / 2) is 0.68%. In other words, it is less than 1%. On the other hand, for the second highest resonant frequency (fr2), the same ratio ((fr2_max - fr2_min) / fr2_mid × 100) is 2.74%, and for the lowest resonant frequency (fri), the same ratio ((fr1_max - fr1_min) / fr1_mid × 100) is 2.66%, which is 2% or more.

[0177] Therefore, the ratio of the difference between the minimum and maximum values ​​between the multiple parallel resonators 59 with respect to the resonance frequency of the region 19 having the lowest resonance frequency (fr1) to the intermediate value of these minimum and maximum values ​​(2.66%) is greater than the ratio of the difference between the minimum and maximum values ​​between the multiple parallel resonators 59 with respect to the resonance frequency of the region 19 having the highest resonance frequency (fr3) to the intermediate value of these minimum and maximum values ​​(0.68%).

[0178] (Characteristics of Ladder-Type SAW Filter)

[0179] Figure 11(a)~ Figure 11 (e) in FIG. 1 is a diagram showing simulation results for the above-described SAW filter 109 .

[0180] Figure 11 In (a) of FIG. 1 , the horizontal axis represents frequency (MHz) and the vertical axis represents passband characteristic (dB). Figure 11 (b) in the Figure 11 An enlarged view of the passband and its surroundings in (a). Figure 11 (c) in the Figure 11 (b) is an enlarged view of a region with high transmission characteristics. Figure 11 (d) in FIG. 1 is the standing wave ratio on the input terminal 105 side. Figure 11 (e) in FIG. 1 is the standing wave ratio on the output terminal 103 side.

[0181] In each figure, line L31 represents the characteristics of a conventional SAW filter, and line L33 represents the characteristics of the SAW filter 109 of this embodiment. In the SAW filter 109 whose characteristics are represented by line L33, all parallel resonators 59 are constituted by the SAW resonator 1 of the embodiment.

[0182] These figures confirm that even when a ladder-type SAW filter 109 is constructed using the SAW resonator 1 of this embodiment having multiple regions 19 (multiple resonance points), filter characteristics with improved passband characteristics within the passband can be achieved, similar to the conventional technology. Furthermore, the small Δf of the parallel resonator 59 confirms that the rising edge of the curve representing the passband characteristics becomes steeper on the low-frequency side of the passband compared to the conventional technology, thereby improving the passband characteristics. Furthermore, it can be confirmed that the standing wave ratio can also be reduced.

[0183] <Wavelength Splitter>

[0184] Figure 12 1 is a schematic diagram showing a demultiplexer 101 as an example of the use of the SAW resonator 1. Figure 9 The same or similar structures are shown, sometimes using different names but the same symbols.

[0185] The branching filter 101 includes, for example, a transmission filter 109 that filters a transmission signal from the transmission terminal 105 and outputs the signal to the antenna terminal 103 , and a reception filter 111 that filters a reception signal from the antenna terminal 103 and outputs the signal to the pair of reception terminals 107 .

[0186] For example, the transmission filter 109 is similar to Figure 9 The ladder-type SAW filter 109 described above is the same as or similar to the above-described one.

[0187] The reception filter 111 is formed, for example, by a SAW resonator 61 and a SAW filter 63 connected in series. The IDT electrode 5 and the reflector 7 forming these components are provided, for example, on the same piezoelectric substrate 3. The piezoelectric substrate 3 forming the reception filter 111 and the piezoelectric substrate 3 forming the transmission filter 109 may be the same or different.

[0188] The SAW filter 63 is, for example, a longitudinally coupled multimode (including dual-mode) resonator filter having a plurality of IDT electrodes 5 arranged in the SAW propagation direction and a pair of reflectors 7 disposed on both sides thereof.

[0189] <Communication device>

[0190] Figure 13 1 is a block diagram showing the main parts of a communication device 151 as an example of utilization of the SAW resonator 1 .

[0191] The communication device 151 performs wireless communication using radio waves. The communication device 151 includes the above-mentioned branching filter 101, thereby utilizing the SAW resonator 1. The details are as follows.

[0192] In communication device 151, a transmission information signal TIS, which includes information to be transmitted, is modulated and frequency-upgraded (converted to a high-frequency signal with a carrier frequency) by RF-IC (Radio Frequency Integrated Circuit) 153 to produce a transmission signal TS. Transmission signal TS passes through bandpass filter 155 to remove unnecessary components outside the transmission passband. Amplifier 157 amplifies the signal before inputting demultiplexer 101 (transmitting terminal 105). Demultiplexer 101 removes unnecessary components outside the transmission passband from the input transmission signal TS and outputs the removed transmission signal TS from antenna terminal 103 to antenna 159. Antenna 159 converts the input electrical signal (transmission signal TS) into a wireless signal (radio wave) and transmits it.

[0193] Furthermore, in communication device 151, a wireless signal (radio wave) received by antenna 159 is converted by antenna 159 into an electrical signal (received signal RS) and input to demultiplexer 101. Demultiplexer 101 removes unnecessary components outside the reception passband from the input received signal RS and outputs the signal to amplifier 161. The output received signal RS is amplified by amplifier 161, and unnecessary components outside the reception passband are removed by bandpass filter 163. RF-IC 153 then down-converts and demodulates received signal RS to produce received information signal RIS.

[0194] The transmitted information signal TIS and the received information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, such as analog audio signals or digitized audio signals. The passband of the wireless signal may be a frequency band in accordance with various standards such as UMTS (Universal Mobile Telecommunications System). The modulation method may also be phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more of these. Figure 13 Although the direct conversion method is shown as an example, it can be set to another appropriate method, for example, a double conversion superheterodyne method. Figure 13 Only the main parts are schematically shown, and a low-pass filter, an isolator, etc. may be added at appropriate positions, and the positions of the amplifiers, etc. may also be changed.

[0195] As described above, the SAW resonator 1 involved in this embodiment has a piezoelectric substrate 3, an IDT electrode 5 and a pair of reflectors 7. The IDT electrode 5 has a plurality of electrode fingers 13 arranged along the propagation direction of the SAW on the piezoelectric substrate 3. The pair of reflectors 7 are located on both sides of the propagation direction relative to the plurality of electrode fingers 13 on the piezoelectric substrate 3. Furthermore, the IDT electrode 5 has a plurality of regions 19 to which the plurality of electrode fingers 13 are allocated and the resonance frequencies are different from each other. The plurality of regions 19 include at least three regions 19. The second highest resonance frequency ( Figure 3 (a) is fr2) than the lowest resonant frequency in all regions 19 ( Figure 3 (a) in fr1) and the highest resonant frequency in all regions 19 ( Figure 3 The intermediate value of fr3) in (a) is still low.

[0196] Therefore, as already described, the SAW resonator 1 can be used as a resonator in which the difference between the highest resonant frequency and the averaged antiresonant frequency is set to Δf, thereby reducing Δf. Therefore, Δf can be reduced by eliminating the need for a capacitor connected in parallel with the IDT electrode 5 or by reducing the capacitance of the capacitor. This makes it easier to miniaturize the SAW resonator 1, for example. Furthermore, compared to the case of providing a capacitor, the temperature characteristics can be improved.

[0197] Furthermore, unlike the present embodiment, if, for example, Δf is reduced by gradually varying the electrode finger pitch across the entire IDT electrode 5 without providing multiple regions 19 with mutually different resonant frequencies, it becomes difficult to form a SAW with a constant wavelength across the multiple electrode finger pitches, thus deteriorating the resonant characteristics. However, in the present embodiment, each region 19 can have the same structure as a conventional IDT electrode, thereby achieving excellent resonant characteristics. Consequently, the entire SAW resonator 1 can also achieve excellent resonant characteristics.

[0198] Furthermore, as already described, by relatively increasing the difference between the highest resonant frequency and the second and subsequent resonant frequencies, the resonance point with the highest frequency, which defines Δf, is clearly identified. Simultaneously, multiple resonance points can be generated across a wide frequency band at frequencies lower than this resonance point. As a result, for example, when the SAW resonator 1 is used as the parallel resonator 59 of a ladder-type SAW filter 109, the rising edge of the curve representing the passband characteristic can be made steeper at frequencies lower than the passband, while maintaining attenuation across a wide frequency band lower than the passband.

[0199] In this embodiment, the electrode finger pitch (the pitch Pt of the electrode fingers 13) is constant in each of the plurality of regions 19. The region 19 having the lowest resonance frequency ( Figure 1 The first region 19A has the largest electrode finger pitch ( Figure 2 The region 19 with the highest resonant frequency ( Figure 1 The second region 19B has the smallest electrode finger pitch among all regions 19 ( Figure 2 The region 19 with the second highest resonance frequency ( Figure 1 The third region 19C has the second smallest electrode finger pitch ( Figure 2 The second smallest electrode finger pitch is greater than the middle value of the largest electrode finger pitch and the smallest electrode finger pitch ( Figure 2 The middle is Pt_mid) which is larger.

[0200] Therefore, by appropriately setting the electrode finger pitches of the multiple regions 19, it is possible to achieve the aforementioned multiple, mutually different resonant frequencies. While the resonant frequency can be adjusted based on other conditions, such as the thickness of the IDT electrode 5 and / or the duty cycle of the electrode fingers 13, adjusting the electrode finger pitch is fundamental to the theory of SAW resonators and facilitates achieving the desired multiple resonant frequencies.

[0201] Furthermore, in this embodiment, each of the pair of reflectors includes a plurality of strip electrodes 17 arranged in the propagation direction. The pitch of the plurality of strip electrodes 17 is greater than the minimum electrode finger pitch ( Figure 2 Pt_min) is larger than the second smallest electrode finger pitch ( Figure 2 The middle one is Pt_2nd) which is small.

[0202] Therefore, for example, the SAW associated with the highest resonance frequency of a predetermined Δf can be preferentially reflected, while SAWs of various wavelengths can be reflected, thereby achieving good resonance characteristics as a whole.

[0203] In addition, in this embodiment, among the multiple areas 19, other areas ( Figure 1 The first region 19A and the third region 19C are located in the region 19 ( Figure 1 The middle is the two sides of the second area 19B).

[0204] Therefore, for example, the region 19 having a resonant frequency of a predetermined Δf is arranged at the position where the standing wave is most likely to appear (the center side in the propagation direction of the IDT electrode 5). As a result, for example, a resonant point of a predetermined Δf can be clearly generated, and excellent characteristics can be achieved for the entire SAW resonator 1.

[0205] In the above embodiment, the SAW resonator 1 is an example of an elastic wave resonator, and the SAW filter 109 is an example of an elastic wave filter.

[0206] (Variation)

[0207] Figure 14 It is a plan view showing the structure of a SAW resonator 201 according to a modification.

[0208] The SAW resonator 201 differs from the SAW resonator 1 only in that it can perform so-called electrode finger thinning; otherwise, it is the same as the SAW resonator 1. The following description of the SAW resonator 201 uses the same reference numerals as those used in the SAW resonator 1, and basically only the differences from the SAW resonator 1 are described.

[0209] Figure 14 In the example shown, electrode fingers 13F, shown shaded, can be thinned out. In IDT electrode 5, electrode fingers 13 of first comb-shaped electrode 9A and electrode fingers 13 of second comb-shaped electrode 9B are basically arranged alternately. Thinning out eliminates electrode fingers 13 that should be arranged in accordance with the regularity of this alternating arrangement. Figure 14In the example, at the position where the electrode finger 13 of the first comb-tooth electrode 9A should be configured (the position of the electrode finger 13F), the electrode finger 13 of the first comb-tooth electrode 9A is set to be non-configured (the electrode finger 13 of the second comb-tooth electrode 9B is configured in violation of the regularity), thereby enabling interval elimination.

[0210] At the position where the spacing is removed, as in the example shown in the figure, the electrode fingers 13 of the comb-tooth electrode 9 (the second comb-tooth electrode 9B in the example shown in the figure) that engage with the comb-tooth electrode 9 (the first comb-tooth electrode 9A in the example shown in the figure) having the electrode fingers 13 to be arranged can be arranged. Furthermore, unlike the example shown in the figure, the position where the spacing is removed can also be set to a position where no electrode fingers 13 of the comb-tooth electrode 9 are arranged. In addition, the electrode fingers 13 with a wider width can also be located at the position where the spacing is removed. For example, at Figure 14 In the second comb-shaped electrode 9B, the electrode fingers 13 may have a width covering the position of the electrode finger 13F and the positions of the electrode fingers 13 adjacent to both sides thereof, which is a total of three electrode fingers.

[0211] In addition, the concept of spacing elimination is based on the premise that there is a certain degree of regularity in the configuration of the electrode fingers 13 in the majority of the region 19 (excluding the portion that has been spacing eliminated). Therefore, the determination of whether the various forms illustrated in the description of the SAW resonator 1 are valid can be made by excluding the spacing elimination portion (or assuming that the spacing elimination is not performed), and it is also possible to make the determination in this way. The characteristics of the SAW resonator are generally determined by the majority with regularity. For example, in each region 19, the determination of whether the electrode finger pitch Pt is fixed can be made by excluding the spacing elimination portion. Furthermore, when comparing the size of the electrode finger pitch between multiple regions (for example, when determining whether the region with the lowest resonant frequency has the largest electrode finger pitch among all regions), the comparison can also be made by excluding the spacing elimination portion.

[0212] Thinning can be performed in any of the multiple regions 19. For example, the region 19 that can be thinned out is the region 19 with the highest resonant frequency or the region 19 with the smallest electrode finger pitch (here, either of these is the second region 19B). Furthermore, assuming that the multiple regions 19 are of equal size in the D1-axis direction (the propagation direction of the SAW), and that a voltage having a frequency ((fr3 + fa) / 2) intermediate between the highest resonant frequency fr3 and the antiresonant frequency fa of the IDT electrode 5 is applied to the IDT electrode 5, the region 19 that can be thinned out is the region 19 with the highest vibration intensity among the multiple regions 19.

[0213] Figure 14In the example, only electrode finger 13F is thinned out. That is, only one electrode finger is thinned out. Alternatively, two or more electrode fingers 13F may be thinned out, for example, where two adjacent electrode fingers 13 of the first comb-tooth electrode 9A are also thinned out. Furthermore, rather than thinning out two adjacent electrode fingers 13, at least one electrode finger 13 may be thinned out at each of the multiple locations where the electrode fingers 13 of the first comb-tooth electrode 9A and the electrode fingers 13 of the second comb-tooth electrode 9B are alternately arranged.

[0214] Interval elimination can also be performed at any position in the region 19 in the propagation direction of the SAW (D1 axis direction). For example, interval elimination can be performed in the center of the region 19. The center referred to here is, for example, based on the distance in the D1 axis direction of the region 19. The spacing between the electrode fingers in the region 19 is basically fixed, so the center can also be based on the number of electrode fingers 13. In the case where two electrode fingers 13 are arranged to sandwich the center of the region 19 (for example, when the number of electrode fingers 13 in the region 19 is an even number), even if any one of the two electrode fingers 13 is interval eliminated, it can be regarded as interval elimination in the center.

[0215] Figure 15 (a)~ Figure 15 (c) in FIG. 1 is a diagram for explaining the effect of thinning. These diagrams are based on simulation calculations. In this calculation condition,

[0216] Figure 15 (a) in the equation is Figure 4 The same graph shows the relationship between the position D in the D1-axis direction (horizontal axis) and the vibration intensity Sv (vertical axis).

[0217] Line L41 corresponds to an example without thinning, and lines L42 to L44 correspond to an example with thinning. That is, line L41 corresponds to the SAW resonator 1 of the embodiment, and lines L42 to L44 correspond to the SAW resonator 201 of the modified example. Furthermore, line L42 corresponds to an example in which thinning is performed in one location, line L43 corresponds to an example in which thinning is performed in three locations, and line L44 corresponds to an example in which thinning is performed in seven locations. The three or seven locations (plurality) referred to here refer to the number of locations where the electrode fingers 13 of the first comb electrode 9A and the electrode fingers 13 of the second comb electrode 9B are separated by an alternating arrangement. Furthermore, thinning is performed on one electrode in each location. In any of lines L42 to L44, thinning is performed only in region 19 where the electrode finger pitch Pt is the smallest (region 19 where the pitch Pt is 2).

[0218] As described in the description of the SAW resonator 1, in the region 19 where the electrode finger pitch Pt is small, the vibration intensity tends to be higher than in the other regions 19. Figure 15 In (a), in any of the lines L41 to L44 , the vibration intensity increases in the region 19 of the electrode finger pitch Pt2 .

[0219] Comparing the uncut line L41 with the cut lines L42 to L44, the vibration intensity of lines L42 to L44 decreases in the cut areas compared to line L41. Consequently, the peak vibration intensity of lines L42 to L44 decreases in the cut area 19 compared to line L41. The cut area 19 has the highest vibration intensity among the multiple areas 19, so the peak vibration intensity of the IDT electrode 5 as a whole also decreases. As a result, for example, the electrical resistance of the IDT electrode 5 is improved.

[0220] On line L41, the peak of vibration intensity occurs at the center of region 19 within the electrode finger pitch Pt2. On the other hand, thinning is also performed at the center of region 19 within the electrode finger pitch Pt2 on any of lines L42 through L44. Therefore, the reduction in vibration intensity due to thinning occurs at the location where the peak of vibration intensity would occur if thinning were not performed. As a result, the peak of vibration intensity is effectively reduced.

[0221] When the vibration intensity is compared between the thinned-out lines L42 to L44 , the greater the number of thinned-out lines, the more locations where the vibration intensity decreases, thereby reducing the peak value of the vibration intensity.

[0222] Thinning out causes the vibration intensity in non-thinned areas 19 to increase inversely compared to thinned-out areas 19. Furthermore, the greater the number of thinned-out areas, the greater the increase. This indicates that the energy in thinned-out areas 19 is being distributed to non-thinned-out areas 19.

[0223] In the example shown, even if the vibration intensity of the unthinned region 19 increases due to thinning, it is still lower than the vibration intensity of the thinned region 19. Therefore, for example, the increase in the vibration intensity of the unthinned region 19 has little effect on the electrical resistance of the IDT electrode 5 as a whole.

[0224] Figure 15 (b) in the equation is Figure 3 The same graph as in (a) shows the relationship between the frequency (horizontal axis) and the absolute value of the impedance (vertical axis). Figure 15 (c) in the equation is Figure 3The same graph (b) shows the relationship between frequency (horizontal axis) and impedance phase (vertical axis). The relationship between line type and thinning in these graphs is the same as Figure 15 The same applies to (a) in .

[0225] like Figure 15 As shown in (b) of FIG. , thinning out reduces Δf. Furthermore, the greater the number of thinning out, the smaller Δf becomes. Therefore, for example, by applying the SAW resonator 201 of the modified example to the parallel resonator 59, the steepness of the low-frequency side of the passband can be improved.

[0226] In addition, Figure 15 In (b), it can be seen that if thinning is performed or the number of thinning is increased, the difference between the impedance at the resonant frequency and the impedance at the anti-resonant frequency will be reduced, although it is small. Figure 15 In (c), it can be seen that if thinning is performed or the number of thinned elements is increased, the impedance phase deviates from 90° on the high-frequency side within the passband. Therefore, the presence or number of thinned elements should be appropriately set by considering electrical resistance (vibration resistance), Δf, and other factors.

[0227] The technology according to the present disclosure is not limited to the above-described embodiments and modifications, and can be implemented in various forms.

[0228] Elastic waves are not limited to SAW. For example, elastic waves may be bulk waves that propagate within a piezoelectric substrate or boundary elastic waves that propagate at the boundary between the piezoelectric substrate and an insulating layer covering the piezoelectric substrate (which is a type of SAW in a broad sense).

[0229] The difference in resonant frequency between regions is not limited to the structure achieved by the difference in electrode finger spacing between regions. For example, the difference in resonant frequency between regions can also be achieved by the difference in electrode film thickness or duty cycle between regions. Specifically, if the electrode film thickness is increased (from another perspective, the mass of the electrode is increased), the resonant frequency and anti-resonant frequency can be reduced. In addition, if the width (duty cycle) of the electrode finger is increased, the resonant frequency and anti-resonant frequency can be reduced. Furthermore, for example, any two or more combinations of electrode finger spacing, electrode film thickness and duty cycle can be made different between regions, thereby achieving the difference in resonant frequency between regions.

[0230] In each region, the conditions that influence the resonant frequency (electrode finger pitch, electrode film thickness, duty cycle, etc.) are essentially constant throughout the entire region. However, critical portions may be provided in some regions for purposes such as fine-tuning the resonant characteristics. For example, as described in the modified example, so-called culling may be performed. Furthermore, the pitch of the electrode fingers may vary within a relatively small number of electrodes.

[0231] Furthermore, as mentioned in the description of the modified example, whether the electrode finger pitch within each region is constant can be determined by excluding the critical portion described above. This is because the concept of a critical portion presupposes the regularity of the remaining majority, and the characteristics of the elastic wave resonator are generally determined by the remaining majority. For example, if the electrode finger pitch is constant for most of a region, and the electrode finger pitch varies across multiple regions, the effect of reducing Δf can be achieved. Similarly, when comparing the electrode finger pitches across multiple regions, the critical portion can be excluded for comparison.

[0232] Furthermore, the IDT electrode may include portions having an electrode finger pitch (electrode finger) other than the regions, the inter-region spacing, and the outer spacing. For example, a narrow pitch portion where the electrode finger pitch narrows toward the outer sides may be provided outside the regions.

[0233] like Figure 10 As shown in the example in (c), there is no need to provide spacing between regions. That is, in two adjacent regions, electrode fingers located at the end of one region on the other side and electrode fingers located at the end of the other region on the one side can be shared. In this case, the width of the shared electrode fingers can be equal to the width of the electrode fingers in either region, or can be averaged with respect to the widths of the electrode fingers in both regions.

[0234] The number of resonant frequencies (e.g., the number of different electrode finger pitches) and the number of regions can be the same. In this case, for example, regions that are prone to generating standing waves of a fixed wavelength are grouped together, improving the resonant characteristics. Furthermore, two or more regions with the same resonant frequency can exist.

[0235] Alternatively, the parallel resonator 59 constituting the SAW filter 109 may be divided in series. In this case, by adopting the above-described design of the IDT electrode 5 for each of the divided parts, an elastic wave resonator having a higher power handling performance can be provided.

Claims

1. A 1-port SAW resonator having: Piezoelectric substrate; an IDT electrode having a plurality of electrode fingers arranged on the piezoelectric substrate in a propagation direction of the elastic wave; and a pair of reflectors located on the piezoelectric substrate on both sides of the propagation direction relative to the plurality of electrode fingers; The IDT electrode has a plurality of regions to which a plurality of electrode fingers are respectively allocated and the electrode finger pitches are different from each other. The plurality of regions include at least: a region having the largest electrode finger pitch among all regions; a region having the smallest electrode finger pitch among all regions; and a region having an electrode finger pitch that is smaller than the largest electrode finger pitch and the second smallest among all regions. The second smallest electrode finger pitch is larger than an intermediate value between the largest electrode finger pitch and the smallest electrode finger pitch.

2. The 1-port SAW resonator according to claim 1, wherein: In each of the plurality of regions, the electrode finger pitch is fixed.

3. The one-port SAW resonator according to claim 1 or 2, wherein: Assuming that the sizes of the multiple regions in the propagation direction are equal to each other, and when a voltage with a frequency intermediate between the resonant frequency of the region with the smallest electrode finger spacing and the anti-resonant frequency of the IDT electrode is applied to the IDT electrode, the region with the largest vibration intensity among the multiple regions has the largest size in the propagation direction among the multiple regions.

4. The one-port SAW resonator according to claim 1 or 2, wherein: The region having the smallest electrode finger pitch has the largest size in the propagation direction among the plurality of regions.

5. The one-port SAW resonator according to claim 1 or 2, wherein: The region having the smallest electrode finger pitch has portions where the plurality of electrode fingers are thinned out.

6. The 1-port SAW resonator according to claim 5, wherein: The thinned-out portion is located at the center of the region having the smallest electrode finger pitch.

7. The 1-port SAW resonator according to claim 1, wherein: Between any two adjacent regions among the multiple regions, the electrode finger at the end of one region on the side of the other region and the electrode finger at the end of the other region on the side of the one region are two adjacent electrode fingers, and the size of the electrode finger spacing between these two electrode fingers is different from the electrode finger spacing of any of the two regions and is smaller than the median value of the electrode finger spacing between the two regions.

8. The 1-port SAW resonator according to claim 1, wherein One reflector of the pair of reflectors has a plurality of strip electrodes arranged in the propagation direction, The size of the spacing between the strip electrode at the end of the one reflector located on the IDT electrode side and the electrode fingers at the end of the region adjacent to the one reflector among the multiple regions, is different from the spacing between the multiple strip electrodes and any spacing between the electrode fingers in the adjacent regions, and is smaller than the intermediate value of the spacing between the multiple strip electrodes and the spacing between the electrode fingers in the adjacent regions.

9. The 1-port SAW resonator according to claim 1, wherein: The pair of reflectors respectively have a plurality of strip electrodes arranged in the propagation direction, A pitch between the plurality of strip-shaped electrodes is larger than an electrode finger pitch in a region having the smallest electrode finger pitch and smaller than an electrode finger pitch in a region having the second smallest electrode finger pitch.

10. The 1-port SAW resonator according to claim 1, wherein Among the plurality of regions, other regions are located on both sides of the region having the smallest electrode finger pitch.

11. An elastic wave filter comprising: One or more series resonators and one or more parallel resonators connected in a ladder type, At least one of the one or more parallel resonators is formed of the one-port SAW resonator according to any one of claims 1 to 10.

12. The elastic wave filter according to claim 11, wherein The elastic wave filter includes a plurality of parallel resonators each consisting of the one-port SAW resonator according to any one of claims 1 to 10. The ratio of the difference between the minimum and maximum values ​​between the plurality of parallel resonators with respect to the resonant frequency of the region having the maximum electrode finger spacing to the intermediate value of these minimum and maximum values ​​is greater than the ratio of the difference between the minimum and maximum values ​​between the plurality of parallel resonators with respect to the resonant frequency of the region having the minimum electrode finger spacing to the intermediate value of these minimum and maximum values.

13. A wave splitter, comprising: Antenna terminal; a transmission filter for filtering a transmission signal and outputting the signal to the antenna terminal; and a reception filter for filtering a reception signal from the antenna terminal, At least one of the transmission filter and the reception filter includes the elastic wave filter according to claim 11 or 12.

14. A communication device comprising: The antenna, the IC, and the splitter according to claim 13, The antenna terminal is connected to the antenna, The IC is connected to the transmission filter and the reception filter.

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