Device for elastic shafts

Abstract

Elastic wave filter device (1) with a branch filter (11) comprising series arm and parallel arm resonators (S1-S4, P1-P4) formed from elastic wave resonators, wherein Each of the elastic wave resonators (S1-S4, P1-P4) comprises a piezoelectric body (15), a first busbar (17) and a second busbar (18) facing each other, several first electrode fingers (19), each having a base end connected to the first busbar (17) and a front end located on a side thereof closer to the second busbar (18), and several second electrode fingers (20), each having a base end connected to the second busbar (18) and a front end located on a side thereof closer to the first busbar (17), wherein the first busbar (17), the second busbar (18), the several first electrode fingers (19) and the several second electrode fingers (20) are provided on the piezoelectric body (15).wherein the multiple first electrode fingers (19) and the multiple second electrode fingers (20) are arranged between each other, wherein , the first electrode fingers (19) and the second electrode fingers (20) overlap in a direction of elastic wave propagation in a crossing region (A), the crossing region comprising a central region (A0) located centrally in a direction in which the first electrode fingers and the second electrode fingers extend, a first edge region (A1) located on a side of the central region (A0) that is closer to the first busbar (17), and a second edge region (A2) located on a side of the central region (A0) that is closer to the second busbar (18), thereby making a sound velocity in the first edge region (A1) and in the second edge region (A2) lower than a sound velocity in the central region (A0), in at least one series arm resonator (S1) of the series arm resonators (S1-S4) each of the first electrode fingers has a large-width section (19a) with a width greater than the width of any remaining section in the second boundary region, and each of the second electrode fingers has a large-width section (20a) with a width greater than the width of any remaining section in the first boundary region (A1), and in at least one of the remaining series arm resonator(s) (S2-S4) and the parallel arm resonators (P1-P4) each of the first electrode fingers (19A) has a large-width section (19a, 19b) with a width greater than the width of any remaining section in both the first boundary region (A1) and the second boundary region (A2), and each of the second electrode fingers (20A) has a large-width section (20a, 20b) with a width greater than the width of any remaining section in both the first boundary region (A1) and the second boundary region (A2).

Description

TECHNICAL FIELD

[0001] The invention relates to an elastic wave device using a surface acoustic wave or boundary acoustic wave, and more particularly relates to an elastic wave device using a piston mode. STATE OF THE ART

[0002] Various types of elastic wave filters utilizing a piston mode have been proposed recently. For example, JP 2014-131351 A describes an electrode finger crossing region in which an edge region, where the sound velocity is relatively low, is provided on either side of a central region. The width of each electrode finger in the edge region is made larger than that of the remaining portion. Such a large-width portion is provided to form a piston mode and thereby suppress ripple caused by transverse modes.

[0003] An elastic wave filter device according to US 2016 / 0 065 176 A1 comprises series and parallel arms and a plurality of elastic wave resonators with an IDT electrode, wherein, when a direction in which the electrode fingers extend is taken as a width direction of the IDT electrode, the IDT electrode includes a central region at the middle in the width direction and a low acoustic velocity region at a side portion outer to the center and a high acoustic velocity region at a side portion further outward, and a width of the low acoustic velocity region of at least one elastic wave resonator is different from a width of the low acoustic velocity region of the other elastic wave resonators. SUMMARY OF THE INVENTIONTechnical Problem

[0004] Meanwhile, elastic wave filter devices are required to achieve both increased steepness in the filter characteristics and reduced loss in the passband. For example, a method for adjusting the layer thickness of interdigital transducer (IOT) electrodes or a method for adjusting the bandwidth ratio of elastic wave resonators using a bypass capacitance are being investigated. However, these methods struggle to control the layer thickness of IDT electrodes or the bandwidth ratio of elastic wave resonators with high accuracy while simultaneously achieving both increased steepness and reduced loss in the passband.

[0005] An object of the invention is to provide an elastic wave filter device capable of suppressing transverse mode ripple and achieving both increased steepness in the filter characteristics and less loss in the passband with certainty. Solution to the task

[0006] An elastic wave filter device according to a first aspect of the invention of the present application comprises a ladder filter including series-arm and parallel-arm resonators formed of elastic wave resonators, each of the elastic wave resonators comprising a piezoelectric body, a first bus bar and a second bus bar facing each other, a plurality of first electrode fingers each having a base end connected to the first bus bar and a front end located on a side thereof closer to the second bus bar, and a plurality of second electrode fingers each having a base end connected to the second bus bar and a front end located on a side thereof closer to the first bus bar, wherein the first bus bar, the second bus bar,the plurality of first electrode fingers and the plurality of second electrode fingers are provided on the piezoelectric body, wherein the plurality of first electrode fingers and the plurality of second electrode fingers are arranged between each other. The first electrode fingers and the second electrode fingers overlap in a propagation direction of elastic waves in an intersection region, wherein the intersection region includes a central region arranged centrally in a direction in which the first electrode fingers and the second electrode fingers extend, a first edge region arranged on one side of the central region closer to the first busbar, and a second edge region arranged on one side of the central region closer to the second busbar.and wherein a speed of sound in the first edge region and in the second edge region is made lower than a speed of sound in the central region. In at least one series-arm resonator of the series-arm resonators, each of the first electrode fingers has a large-width portion with a width greater than a width of a remaining portion in the second edge region, and each of the second electrode fingers has a large-width portion with a width greater than a width of a remaining portion in the first edge region. In at least one of the remaining series-arm resonators and the parallel-arm resonators, each of the first electrode fingers has a large-width portion with a width greater than a width of a remaining portion in both the first edge region and the second edge region, and each of the second electrode fingers has a large-width portion with a width,which is greater than a width of a remaining portion in both the first edge region and the second edge region.

[0007] Preferably, in the at least one series-arm resonator, when a length of the first peripheral region and the second peripheral region in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt1, and a length of the central region in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt2, Apt1 / Apt2 is 0.0638 or more and 0.094047 or less. In this case, the bandwidth ratio in the at least one series-arm resonator can be further reduced. Accordingly, steepness in the filter characteristics in a high-frequency range in the passband can be further increased.

[0008] An elastic wave filter device according to a second aspect of the invention of the present application comprises a ladder filter including series arm resonators and parallel arm resonators formed of elastic wave resonators, each of the elastic wave resonators comprising a piezoelectric body, a first bus bar and a second bus bar facing each other, a plurality of first electrode fingers each having a base end connected to the first bus bar and a front end located on a side thereof closer to the second bus bar, and a plurality of second electrode fingers each having a base end connected to the second bus bar and a front end located on a side thereof closer to the first bus bar, wherein the first bus bar, the second bus bar,the plurality of first electrode fingers and the plurality of second electrode fingers are provided on the piezoelectric body, and the plurality of first electrode fingers and the plurality of second electrode fingers are arranged between each other. The first electrode fingers and the second electrode fingers overlap in a propagation direction of elastic waves in an intersection region, wherein the intersection region includes a central region located centrally in a direction in which the first electrode fingers and the second electrode fingers extend, a first edge region located on one side of the central region closer to the first busbar, and a second edge region located on one side of the central region closer to the second busbar.wherein a sound velocity in the first edge region and in the second edge region is made lower than a sound velocity in the central region. In at least one series arm resonator of the series arm resonators, and in at least one of the series arm resonators other than the at least one series arm resonator and the parallel arm resonators, each of the first electrode fingers has a large-width portion with a width greater than a width of a remaining portion in both the first edge region and the second edge region, and each of the second electrode fingers has a large-width portion with a width greater than a width of a remaining portion in both the first edge region and the second edge region. In the at least one series arm resonator, when a length of the first edge region and the second edge region in the direction,In this case, the length of the central region in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt3, and the length of the central region in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt4, Apt3 / Apt4 being 0.083423 or more and 0.10881 or less. In this case, transverse modes can be effectively suppressed in the other series-arm resonator(s) and in the parallel-arm resonators, and the bandwidth ratio can be further reduced. Accordingly, the steepness of the filter characteristics can be further increased.

[0009] The first and second aspects are hereinafter referred to generally as this aspect.

[0010] In this aspect, the at least one series-arm resonator is preferably a series-arm resonator having the largest electrode finger pitch among the series-arm resonators. In this case, the filter characteristics in a high-frequency range in the passband can be more effectively enhanced.

[0011] In this aspect, the at least one series-arm resonator is preferably a series-arm resonator having the lowest anti-resonance frequency among the series-arm resonators. In this case, the filter characteristics can be more effectively enhanced by the steepness in a high-frequency range within the passband.

[0012] In this aspect, the series-arm resonators and the parallel-arm resonators are preferably formed on a single piezoelectric substrate. In this case, the elastic wave filter device according to this aspect can be provided as a single-chip component.

[0013] In this aspect, when the ladder filter is a first bandpass filter having a first passband, the elastic wave filter device preferably further comprises a second bandpass filter having a second passband in a higher frequency range than the first passband, the second bandpass filter and the first bandpass filter being commonly connected at one end thereof. In this case, an elastic wave filter device suitable for, for example, carrier aggregation (CA) can be provided.

[0014] In this aspect, the first bandpass filter is preferably a transmission filter and the second bandpass filter is a reception filter to form a duplexer. Advantageous effects of the invention

[0015] With the elastic wave filter device according to the invention, both increased steepness in the filter characteristics and less loss in the passband can be achieved with certainty, while transverse mode ripple can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit diagram of an elastic wave filter device according to a first embodiment of the present invention. Fig. 2 is a plan view for describing an electrode structure of an elastic wave resonator of a first type. Fig. 3 is a partially sectioned view showing a part of Fig. 2 in an enlarged manner. Fig. 4 is a partially sectional view for describing the shapes of electrode fingers of residual series arm resonators according to the first embodiment of the present invention. Fig.5 is a diagram showing the resonance characteristics of the first type elastic wave resonator, a second type elastic wave resonator, and, for reference purposes, an example elastic wave resonator subjected to apodization weighting. Fig. 6 is a diagram showing the S32 transmission characteristics of a transmission filter according to the first embodiment and a transmission filter according to a comparative example. Fig. 7 is a diagram showing a major part of Fig. 6 in an enlarged manner. Fig. Figure 8 is a diagram showing changes in resonance characteristics in a case where the electrostatic capacitance is fixed and the cut width is changed in the first-type elastic wave resonator. Fig.9 is a diagram showing changes in resonance characteristics in a case where the electrostatic capacitance is fixed and the cut width is changed in the second-type elastic wave resonator. Fig. 10 is a plan view showing the electrode structure of the first type elastic wave resonator according to a first modification. Fig. 11 is a plan view showing the electrode structure of the first type elastic wave resonator according to a second modification. Fig. 12 is a plan view showing the electrode structure of the first type elastic wave resonator according to a third modification. Fig. 13 is a plan view showing the electrode structure of the first type elastic wave resonator according to a fourth modification. Fig.14 is a plan view showing the electrode structure of the first type elastic wave resonator according to a fifth modification. Fig. 15 is a plan view showing the electrode structure of the first type elastic wave resonator according to a sixth modification. Fig. 16 is a plan view showing the electrode structure of the first type elastic wave resonator according to a seventh modification. Fig. 17 is a plan view showing the electrode structure of the first type elastic wave resonator according to an eighth modification. Fig. 18 is a plan view showing the electrode structure of the first type elastic wave resonator according to a ninth modification. Fig. 19 is a plan view showing the electrode structure of the first type elastic wave resonator according to a tenth modification. Fig. 20 is a circuit diagram of a bundle type elastic wave filter device in which a plurality of bandpass filters are bundled at one end thereof. DESCRIPTION OF EMBODIMENTS

[0016] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings to disclose the present invention.

[0017] It should be noted that embodiments described herein are exemplary and configurations may be partially interchanged or combined in different embodiments.

[0018] Fig.1 is a circuit diagram of an elastic wave filter device according to a first embodiment of the present invention. An elastic wave filter device 1 is a duplexer used in the RF stage of a mobile phone. The elastic wave filter device 1 includes an antenna terminal 2 connected to an antenna. The antenna terminal 2 is connected to a common node 3. An impedance adjusting inductor L1 is connected between the common node 3 and a reference potential. A transmission filter 11 is connected between the common node 3 and a transmission terminal 4. A reception filter 12 is connected between the common node 3 and a reception terminal 5.

[0019] The elastic wave filter device 1 is characterized by the transmission filter 11, which is a branch filter.

[0020] Note that the passband of the receive filter 12 is in a higher frequency range than the passband of the transmit filter 11.

[0021] The transmission filter 11 comprises a plurality of series arm resonators S1, S2, S3 and S4 and a plurality of parallel arm resonators P1, P2, P3 and P4.

[0022] The series arm resonator S1, the series arm resonator S2, the series arm resonator S3 and the series arm resonator S4 are arranged in this order from a side closer to the transmission terminal 4, as shown in Fig. 1. The parallel-arm resonator P1 is connected between the transmission terminal 4 and the reference potential. The parallel-arm resonator P2 is connected between a node between the series-arm resonator S1 and the series-arm resonator S2 and a common node 13. An inductor L2 is connected between the parallel-arm resonator P1 and the reference potential.

[0023] The parallel-arm resonator P3 is connected between a node between the series-arm resonator S2 and the series-arm resonator S3 and the common node 13. An inductor L3 is connected between the common node 13 and a ground potential.

[0024] The parallel-arm resonator P4 is connected between a node between the series-arm resonator S3 and the series-arm resonator S4 and the reference potential. An inductor L4 is connected between the parallel-arm resonator P4 and the reference potential.

[0025] The reception filter 12 is not particularly limited. In this embodiment, the reception filter 12 includes a longitudinally coupled resonator-type elastic wave filter 101, series-arm resonators S102, S103, and S104, and parallel-arm resonators P105 and P106.

[0026] In the transmission filter 11, the series-arm resonators S1 to S4 and the parallel-arm resonators P1 to P4 are each constituted by an elastic wave resonator. In the transmission filter 11, the first and second edge regions are provided in a crossover region to suppress transverse mode ripple. The structure described in Patent Document 1, in which an edge region is provided on either side of a central region in a crossover region to suppress transverse mode ripple, is known. For example, in a ladder filter including a plurality of series-arm resonators, similar edge regions are formed in each series-arm resonator.

[0027] In the transmission filter 11, the series-arm resonator S1, which is closest to the transmission terminal 4 among a plurality of series-arm resonators S1 to S4, has an electrode structure different from that of the remaining series-arm resonators S2, S3, and S4. Accordingly, both increased steepness in the filter characteristics and reduced insertion loss in the passband can be achieved. This will be described in more detail below.

[0028] Hereinafter, the elastic wave resonator having the electrode structure of the series arm resonator S1 is referred to as the first type elastic wave resonator, and the elastic wave resonator having the electrode structure of the remaining series arm resonators S2 to S4 is referred to as the second type elastic wave resonator.

[0029] Fig.Figure 2 is a plan view for describing the electrode structure of the first-type elastic wave resonator. In the first-type elastic wave resonator, the electrode structure shown is formed on a piezoelectric substrate 15. Fig. 2 shows an IDT electrode 16 and a reflector 16A. Although not shown, a reflector is similarly provided on a side of the IDT electrode 16 opposite to the side thereof on which the reflector 16A is provided, thereby forming a 1-port type elastic wave resonator.

[0030] The IDT electrode 16 includes a first bus bar 17 and a second bus bar 18 facing each other. The base end of each first electrode finger 19 is connected to the first bus bar 17. The front end of each first electrode finger 19 is located on a side thereof closer to the second bus bar 18. Each second electrode finger 20 has a base end connected to the second bus bar 18 and a front end located on a side thereof closer to the first bus bar 17. The plurality of first electrode fingers 19 and the plurality of second electrode fingers 20 are arranged between each other.

[0031] The first electrode fingers 19 and the second electrode fingers 20 overlap in a propagation direction of elastic waves, as seen from an intersection region A. In the intersection region A, a voltage is applied between the first electrode fingers 19 and the second electrode fingers 20, and an elastic wave is excited.

[0032] In the crossing region A, a first edge region A1 is provided on one side of a central region A0, and a second edge region A2 is provided on the other side thereof to suppress transverse mode ripple. In the first edge region A1 and the second edge region A2, the sound velocity is made lower than that in the central region A0. In an outer side portion of the first edge region A1 and an outer side portion of the second edge region A2, a region in which the sound velocity is higher than that in the first edge region A1 and the second edge region A2 is provided. That is, a region between a first thin bus bar 21 and the front end of each second electrode finger 20 is the region in which the sound velocity is relatively high.Furthermore, in a region between a second thin bus bar 22 and the front end of each first electrode finger 19, the sound velocity is made higher than that in the second edge region A2. Accordingly, transverse mode ripple is suppressed.

[0033] In the first-type elastic wave resonator, the plurality of electrode fingers 19 each have a large-width portion 19a in the second edge region A2. The large-width portion 19a is a portion having a width larger than that of the remaining portion of the first electrode finger 19. Accordingly, the speed of sound in the second edge region A2 is reduced. Similarly, the second electrode fingers 20 each have a large-width portion 20a in the first edge region A1. Accordingly, the speed of sound in the first edge region A1 is reduced.

[0034] The width of the large-width portion 19a at the front end of the first electrode finger 19, which is located in an end portion in the elastic wave propagation direction, and that of the large-width portion 20a at the front end of the second electrode finger 20, which is located in an end portion in the elastic wave propagation direction, are smaller than the width of the large-width portions 19a of the remaining first electrode fingers 19 and those of the large-width portions 20a of the remaining second electrode fingers 20. Although the widths need not be specifically limited to these, the widths are set so as to make the outer peripheral portions of the first electrode finger 19 and that of the second electrode finger 20 at the respective ends of the IDT electrode straight in the elastic wave propagation direction.

[0035] Further, dummy electrodes 23 and 24 are provided in an outer side portion of the first thin busbar 21 and an outer side portion of the second thin busbar 22, respectively, to form a high acoustic velocity region and a medium acoustic velocity region. The first thin busbar 21, the second thin busbar 22, the dummy electrodes 23, and the dummy electrodes 24 may not necessarily be provided.

[0036] As in Fig. As shown in Figure 3, in every second electrode finger 20, the large-width portion 20a is provided at the front end thereof, and thus, the portion in which the large-width portion 20a is provided forms the first edge region A1. Accordingly, the speed of sound is reduced in the first edge region A1.

[0037] As described above, the series arm resonator S1 is formed by the first type elastic wave resonator thus configured.

[0038] Fig. 4 is a partially sectional view for describing the electrode structure of the second type elastic wave resonator.

[0039] In the second-type elastic wave resonator 31, a reflector 33 is provided on one side of an IDT electrode 32 in the elastic wave propagation direction. Although not shown, a reflector 33 is also provided on the other side thereof in the elastic wave propagation direction, thereby forming a 1-port elastic wave resonator. As shown in Fig.4, a plurality of first electrode fingers 19A and a plurality of second electrode fingers 20A are provided so as to be arranged between each other. The second type elastic wave resonator differs from the first type elastic wave resonator in that each first electrode finger 19A has a large width portion 19b in the first edge region. Although in Fig.4, each second electrode finger 20A has a large-width portion not only at the front end thereof but also in the second edge region. That is, in the second-type elastic wave resonator 31, each first electrode finger 19A has the large-width portion in both the first edge region and the second edge region, and each second electrode finger 20A has the large-width portion in both the first edge region and the second edge region. Accordingly, the sound velocity in the first edge region and the second edge region can be reduced more effectively.

[0040] Fig.Figure 5 is a diagram showing the resonance characteristics of the first-type elastic wave resonator and the second-type elastic wave resonator, which are similarly configured except for the configuration of the large-width sections, and a sample elastic wave resonator for reference. The reference sample is subjected to apodization weighting, so that a section outlined by the shell is a rhombus region. The solid line represents the resonance characteristics of the sample elastic wave resonator for reference. The dashed line represents the resonance characteristics of the first-type elastic wave resonator, and the dot-dash line represents the resonance characteristics of the second-type elastic wave resonator.With the first-type elastic wave resonator and the second-type elastic wave resonator using the piston mode described above, the bandwidth ratio representing the frequency difference between the resonant frequency and the anti-resonant frequency is small. Furthermore, the bandwidth ratio of the first-type elastic wave resonator can be smaller than the bandwidth ratio of the second-type elastic wave resonator.

[0041] In the transmission filter 11 according to this embodiment, the series arm resonator S1 is formed by the first type elastic wave resonator.

[0042] Although the Q factor of the first-type elastic wave resonator is lower than that of the second-type elastic wave resonator, the bandwidth ratio of the first elastic wave resonator is smaller than that of the second-type elastic wave resonator, and thus, steepness in the filter characteristics can be increased. This is because the anti-resonance frequency of the series-arm resonators S1 to S4 forms an attenuation pole in a high-frequency region of the transmission filter 11. At least one of the series-arm resonators, that is, the series-arm resonator S1, is constituted by the first-type elastic wave resonator, and the remaining series-arm resonators S2 to S4 are each constituted by the second-type elastic wave resonator.The antiresonance frequency of the first-type elastic wave resonator is in a lower frequency range than that of the second-type elastic wave resonator, and therefore, transconductance in a high-frequency range of the transmission filter 11, which is a ladder filter, can be effectively increased.

[0043] Fig. 6 is a diagram showing the S32 transmission characteristics of the transmission filter according to the first embodiment and a transmission filter according to a comparative example. Fig. 7 is a diagram showing a part defined by the circle B in Fig. 6, in an enlarged manner. Note that the passband of the transmission filter 11 ranges from 1850 Hz to 1910 Hz.

[0044] In Fig. 6 and Fig.7, the solid line represents the S32 transmission characteristics of the transmission filter 11 according to the first embodiment, and the dashed line represents the S32 transmission characteristics of a transmission filter according to a comparative example configured similarly to the first embodiment except that each series arm resonator is formed by the second type elastic wave resonator.

[0045] The frequency position in a high frequency range in the passband of the transmission filter according to the first embodiment and that of the transmission filter according to the comparative example for each attenuation, namely 3 dB, 3.5 dB, 50 dB, and 55 dB, are as shown in Table 1 below. The slope, which is the difference between the attenuation for 3.5 dB and the attenuation for 50 dB, and the slope, which is the difference between the attenuation for 3.5 dB and the attenuation for 50 dB, are also shown in Table 1. Table 1 Insertion loss in the transmission band Isolation in the receive band steepness 3 dB 3.5 dB 50 dB 55 dB 3.5 - 50 dB 3.5 - 555 dB Comparison example 1913,652 1915,324 1926,246 1927,104 10,922 11,78 first embodiment 1913,686 1915,433 1925,891 1926,728 10,458 11,295 improvement 0,464 0,485

[0046] As can be seen from Table 1, according to the first embodiment, steepness in the filter characteristics in a high frequency range in the pass band can be effectively increased compared to the comparative example. Fig. 6 and Fig. As can be seen from Figure 7, it was found that not only the steepness of the filter characteristics can be increased, but also the insertion loss in the passband can be reduced.

[0047] Note that in the first embodiment, the series-arm resonator S1 is constituted by the first-type elastic wave resonator, and the remaining series-arm resonators S2 to S4 are each constituted by the second-type elastic wave resonator. However, in the present invention, the resonators are not limited to these, and at least one of the series-arm resonators must be the first-type elastic wave resonator, and at least one of the remaining series-arm resonators and the parallel-arm resonators must be the second-type elastic wave resonator. When the first-type elastic wave resonator is used in an elastic wave filter device, steepness in the filter characteristics can be increased and insertion loss can be reduced.

[0048] Fig.8 is a diagram showing the resonance characteristics in a case where the electrostatic capacitance is fixed and the cut width is changed to 30.0 λ, 20.0 λ, 17.5 λ, 15.0 λ, 12.5 λ or 7.5 λ in the first type elastic wave resonator.

[0049] Here, λ is a wavelength determined based on the electrode finger spacing of the IDT electrode.

[0050] Table 2 below shows relationships between the bandwidth ratio and a value of Apt1 / Apt2 in a case where the cutting width is changed as described above. Table 2 Cutting width 30.0 λ 20.0 λ 17.5 λ 15.0 λ 12.5 λ 7.5 λ Bandwidth ratio of the resonator for elastic waves of the first type 52,5 52,5 50,83 51,633 50 48,3 Apt1 / Apt2 0,04298 0,0549 0,0638 0,0759 0,094047 0,1792

[0051] In Table 2, Apt1 is the length of the first edge region A1 and the second edge region A2 in a direction in which the first and second electrode fingers extend, and Apt2 is the length of the central region A0 in the direction in which the first and second electrode fingers extend.

[0052] As can be seen from Table 2, in a case where the capacity is fixed and the cutting width is changed, the bandwidth ratio for the cutting width of 17.5 λ or less is smaller than the bandwidth ratio for the cutting width of 20 λ or more. Fig. As can be seen from Figure 8, a transverse mode ripple occurs between the resonant frequency and the antiresonant frequency when the cut width is 7.5 λ, and a slight transverse mode ripple occurs when the cut width is 12.5 λ. Therefore, it is preferable to set Apt1 / Apt2 to 0.0638 or more and 0.094047 or less. Accordingly, a transverse mode ripple can be suppressed, and the bandwidth ratio can be sufficiently reduced. More preferably, Apt1 / Apt2 is 0.0759 or less. In this case, a transverse mode ripple can be suppressed more effectively.

[0053] Fig.9 is a diagram showing changes in resonance characteristics in a case where the electrostatic capacitance is fixed and the intersection line width is changed to 30.0 λ, 20.0 λ, 17.5 λ, 15.0 λ, 12.5 λ, 10.0 λ, or 7.5 λ in the second-type elastic wave resonator.

[0054] Relationships between the magnitude of the bandwidth ratio and Apt3 / Apt4 in a case where the cutting width is changed as described above are given below in Table 3. Table 3 Cutting width 30.0 λ 20.0 λ 17.5 λ 15.0 λ 12.5 λ 10.0 λ 7.5 λ Bandwidth ratio of the resonator for elastic waves of the second type 52,5 52,5 52,5 52,5 50,883 50,000 49,166 Apt3 / Apt4 0,03167 0,04907 0,05687 0,06764 0,083423 0,10881 0,15644

[0055] In Table 3, Apt3 is the length of the first edge region A1 and the second edge region A2 in a direction in which the first and second electrode fingers extend, and Apt4 is the length of the central region A0 in the direction in which the first and second electrode fingers extend.

[0056] As can be seen from Table 3, in the second-type elastic wave resonator, it is found that transverse mode ripple can be effectively suppressed when the cut width is 10 λ or more. Therefore, it is desirable to set Apt3 / Apt4 to 0.10881 or less. When Apt3 / Apt4 is 0.083423 or more, the bandwidth ratio can be reduced. Therefore, it is preferable to set Apt3 / Apt4 to 0.083423 or more and 0.10881 or less.

[0057] The electrode structure in the elastic wave resonator of the first type is not limited to the Fig. 2 and may be subject to the first to tenth modifications described in the following Fig. 10 to Fig. 19. In the first, in Fig.In the modification shown in FIG. 10, the above-described first thin busbar 21, second thin busbar 22, and dummy electrodes 23 and 24 are not provided. Therefore, the first thin busbar 21 and second thin busbar 22 do not necessarily need to be provided.

[0058] In the second, in Fig. In the modification shown in Figure 11, the wide-width portion 20a of each second electrode finger 20 in the first edge region A1 in the second electrode finger 20 is off-center in the elastic wave propagation direction. Accordingly, the center of the wide-width portion of each second electrode finger may be shifted from the center of the remaining portion thereof in the elastic wave propagation direction.

[0059] In the third, in Fig.In the modification shown in FIG. 12, a large-width portion 19c is provided in each first electrode finger 19 in a portion overlapping the leading end of the second electrode fingers 20 in the elastic wave propagation direction, and a large-width portion 20c is provided in each second electrode finger 20 in a region overlapping the leading end of the first electrode fingers 19. That is, each first electrode finger 19 has the large-width portion 19c in the first edge region A1, and each second electrode finger 20 has the large-width portion 20c in the second edge region A2.

[0060] In the fourth, in Fig. In the modification shown in Fig. 13, each dummy electrode 23A is provided to face the front end of a corresponding one of the second electrode fingers 20, and each dummy electrode 24A is provided to face the front end of a corresponding one of the first electrode fingers 19.

[0061] In the fifth, in Fig. In the modification shown in Figure 14, a portion of each first electrode finger other than the large-width portion 19a includes two portions having different widths, and a portion of each second electrode finger other than the large-width portion 20a includes two portions having different widths. That is, portions 19d and 20d, which are narrower than the large-width portions 19a and 20a, and portions 19e and 20e, which are even narrower than the large-width portions 19a and 20a, are provided.

[0062] In the sixth, in Fig. In the modification shown in Fig. 15, the portions 19d and 20d which are narrower than the large width portions 19a and 20a, and portions 19f and 20f which are narrower than the large width portions 19a and 20a and wider than the narrow portions 19d and 20d are provided.

[0063] In the seventh, in Fig.In the modification shown in Figure 16, dielectric layers 41 and 42 are provided. The dielectric layer 41 extends in the elastic wave propagation direction such that it extends over the large-width portions 20a in the first edge region A1. The dielectric layer 42 extends in the elastic wave propagation direction such that it extends over the large-width portions 19a in the second edge region A2. Various dielectrics, such as SiO2, can be used as dielectrics.

[0064] In the eighth, in Fig.In the modification shown in Figure 17, in each first electrode finger 19, a narrow portion 19g having a width relatively smaller than the width of the remaining electrode finger portion is provided in the first peripheral region A1, and in each second electrode finger 20, a narrow portion 20g having a width relatively smaller than the width of the remaining electrode finger portion is provided in the second peripheral region A2. In this case, the sound velocity in the second peripheral region A2 must also be made lower than in the central region having the large-width portions 19a and the narrow portions 20g, and the sound velocity in the first peripheral region A1 must be made lower than in the central region having the large-width portions 20a and the narrow portions 19g.

[0065] In the ninth, in Fig. 18 shown modification, in addition to the structure according to the Fig. In the modification shown in FIG. 17, the width of each first electrode finger 19 is increased in a high acoustic velocity region, which is an outer side portion of the first peripheral region A1, and the width of each second electrode finger 20 is increased in a high acoustic velocity region, which is an outer side portion of the second peripheral region A2. Therefore, the width of each first electrode finger 19 in the high acoustic velocity outer region and the width of each second electrode finger 20 in the high acoustic velocity outer region can be easily increased as long as the acoustic velocity in the high acoustic velocity outer regions is higher than the acoustic velocity in the first peripheral region A1 and the second peripheral region A2, which are low acoustic velocity regions.

[0066] In the tenth, in Fig.19, the width of each first electrode finger 19 in the central region A0 may be made larger than the width of the first electrode finger 19 in the first peripheral region A1 and that in the high acoustic velocity outer region, and the width of each second electrode finger 20 in the central region A0 may be made larger than the width of the second electrode fingers 20 in the second peripheral region A2 and that in the high acoustic velocity outer region.

[0067] As in Fig. 10 to Fig. As shown in Figure 19, in the first-type elastic wave resonator, the electrode shapes of the large-width sections and the electrode shapes of other sections with different widths can be modified as needed. The same applies to the second-type elastic wave resonator.

[0068] Furthermore, the invention is as in Fig.20, is applicable to an elastic wave filter device in which a plurality of band-pass filters 51 to 53 are bundled at one end thereof. Furthermore, in a duplexer and the above-described bundle-type elastic wave filter device, a ladder filter configured according to the invention is preferably used to configure a band-pass filter having a first passband that is a relatively low passband. In this case, steepness in the filter characteristics in a high-frequency region of the first passband of the first band-pass filter can be effectively increased. LIST OF REFERENCE SYMBOLS 1 filter device for elastic waves 2 antenna connections 3 common nodes 4 Transmission connection 5 Reception connection 11 Transmission filters 12 reception filters 13 common nodes 15 piezoelectric substrate 16 IDT electrode 16A reflector 17, 18 first busbar, second busbar 19, 20 first electrode finger, second electrode finger 19A, 20A first electrode finger, second electrode finger 19a, 19b, 19c, 20a, 20c Large width sections 19d, 20d, 19e, 20e, 19f, 20f sections 19g, 20g narrow sections 21, 22 first thin busbar, second thin busbar 23, 23A, 24, 24A dummy electrode 31 Resonator for elastic waves 32 IDT electrode 33 Reflector 41, 42 dielectric layer 51 to 53 bandpass filters 101 longitudinally coupled resonator-type elastic wave filter A0 central area A1, A2 first margin, second margin L1 impedance adjustment inductor L2, L3, L4 inductor S1, S2, S3, S4 series arm resonator P1, P2, P3, P4 Parallel arm resonator S102, S103, S104 Reihenarmresonator P105, P106 Parallelarmresonator

Claims

[1] An elastic wave filter device (1) comprising a ladder filter (11) comprising series arm and parallel arm resonators (S1-S4, P1-P4) formed of elastic wave resonators, wherein each of the elastic wave resonators (S1-S4, P1-P4) comprises a piezoelectric body (15), a first bus bar (17) and a second bus bar (18) facing each other, a plurality of first electrode fingers (19), each of which has a base end connected to the first bus bar (17) and a front end located on a side thereof closer to the second bus bar (18), and a plurality of second electrode fingers (20), each of which has a base end connected to the second bus bar (18) and a front end located on a side thereof closer to the first bus bar (17), wherein the first bus bar (17), the second bus bar (18), the plurality of first electrode fingers (19), and the plurality of second electrode fingers (20) are provided on the piezoelectric body (15),wherein the plurality of first electrode fingers (19) and the plurality of second electrode fingers (20) are arranged between each other, wherein, the first electrode fingers (19) and the second electrode fingers (20) overlap in a propagation direction of elastic waves in a crossing region (A), the crossing region comprising a central region (A0) arranged centrally in a direction in which the first electrode fingers and the second electrode fingers extend, a first edge region (A1) arranged on a side of the central region (A0) that is closer to the first busbar (17), and a second edge region (A2) arranged on a side of the central region (A0) that is closer to the second busbar (18), whereby a sound speed in the first edge region (A1) and in the second edge region (A2) is made lower than a sound speed in the central region (A0), in at least one series arm resonator (S1) of the series arm resonators (S1-S4), each of the first electrode fingers has a large width portion (19a) with a width that is greater than a width of a remaining portion in the second edge region, and each of the second electrode fingers has a large width portion (20a) with a width that is greater than a width of a remaining portion in the first edge region (A1), and in at least one of the remaining series arm resonator(s) (S2-S4) and the parallel arm resonators (P1-P4), each of the first electrode fingers (19A) has a large width portion (19a, 19b) with a width that is greater than a width of a remaining portion in both the first edge region (A1) and the second edge region (A2), and each of the second electrode fingers (20A) has a large width portion (20a, 20b) with a width that is greater than a width of a remaining portion in both the first edge region (A1) and the second edge region (A2). [2] The elastic wave filter device (1) according to claim 1, wherein in the at least one series arm resonator (S1), when a length of the first edge region (A1) and the second edge region (A2) in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt1, and a length of the central region (A0) in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt2, Apt1 / Apt2 is 0.0638 or more and 0.094047 or less. [3] An elastic wave filter device (1) comprising a ladder filter (11) comprising series arm resonators (S1-S4) and parallel arm resonators (P1-P4) formed of elastic wave resonators, wherein each of the elastic wave resonators (S1-S4, P1-P4) comprises a piezoelectric body (15), a first bus bar (17) and a second bus bar (18) facing each other, a plurality of first electrode fingers (19), each of which has a base end connected to the first bus bar (17) and a front end located on a side thereof closer to the second bus bar (18), and a plurality of second electrode fingers (20), each of which has a base end connected to the second bus bar (18) and a front end located on a side thereof closer to the first bus bar (17), wherein the first bus bar (17), the second bus bar (18), the plurality of first electrode fingers (19), and the plurality of second electrode fingers (20) are provided on the piezoelectric body (15),the plurality of first electrode fingers (19) and the plurality of second electrode fingers (20) are arranged between each other, wherein, the first electrode fingers (19) and the second electrode fingers (20) overlap in a propagation direction of elastic waves in a crossing region (A), the crossing region (A) comprising a central region (A0) arranged centrally in a direction in which the first electrode fingers and the second electrode fingers extend, a first edge region (A1) arranged on a side of the central region (A0) that is closer to the first busbar (17), and a second edge region (A2) arranged on a side of the central region (A0) that is closer to the second busbar (18), whereby a sound speed in the first edge region (A1) and in the second edge region (A2) is made lower than a sound speed in the central region (A0), in at least one series arm resonator (S2-S4) of the series arm resonators and in at least one of the series arm resonator(s) other than the at least one series arm resonator and the parallel arm resonators (P1-P4), each of the first electrode fingers (19A) has a large width portion (19a, 20a) with a width that is greater than a width of a remaining portion in both the first edge region (A1) and the second edge region (A2), and each of the second electrode fingers (20A) has a large width portion (20a, 20b) with a width that is greater than a width of a remaining portion in both the first edge region (A1) and the second edge region (A2), and in the at least one series arm resonator (S2-S4), when a length of the first edge region (A1) and the second edge region (A2) in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt3, and a length of the central region (A0) in the direction in which the first electrode fingers and the second electrode fingers extend is represented by Apt4, Apt3 / Apt4 is 0.083423 or more and 0.10881 or less. [4] The elastic wave filter device (1) according to any one of claims 1 to 3, wherein the at least one series arm resonator is a series arm resonator having the largest electrode finger pitch of the series arm resonators (S1-S4). [5] The elastic wave filter device (1) according to any one of claims 1 to 4, wherein the at least one series arm resonator is a series arm resonator having the lowest anti-resonance frequency among the series arm resonators (S1-S4). [6] The elastic wave filter device (1) according to any one of claims 1 to 5, wherein the series arm resonators (S1-S4) and the parallel arm resonators (P1-P4) are formed on a single piezoelectric substrate (15). [7] The elastic wave filter device (1) according to any one of claims 1 to 6, wherein, when the ladder filter (11) is a first band-pass filter having a first pass band, the elastic wave filter device further comprises a second band-pass filter (12) having a second pass band in a higher frequency range than the first pass band, the second band-pass filter (12) and the first band-pass filter (11) being commonly connected at one end thereof. [8] The elastic wave filter device (1) according to claim 7, wherein the first bandpass filter (11) is a transmission filter and the second bandpass filter (12) is a reception filter to form a duplexer.

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