HK1206157B - Antenna sharing device - Google Patents

Description

Antenna sharing device

The present application is a divisional application of patent application No.201080020711.5 entitled "duplexer" having an application date of 10/5/2010.

Technical Field

The present invention relates to a duplexer having a transmission filter and a reception filter.

Background

In general, an duplexer has two filters, i.e., a transmission filter and a reception filter, for dividing a signal of a transmission band and a signal of a reception band adjacent to a high-frequency side of the transmission band. In particular, as the transmission filter, a ladder filter in which series resonators and parallel resonators are connected in a ladder shape is used.

Here, in Band2 of the W-CDMA standard specification, the interval (cross Band) between the transmission Band and the reception Band is 20MHz, and is very narrow. The duplexer corresponding to such a transmission/reception band having a narrow cross band requires steepness at the cross band between the transmission band and the reception band in order to ensure isolation (isolation) between the transmission signal and the reception signal. In other words, steepness of the attenuation characteristic on the high frequency side of the passband of the transmission filter and steepness of the attenuation characteristic on the low frequency side of the passband of the reception filter are required.

As a technique for improving the steepness of the attenuation characteristic at a higher frequency side than the passband of the transmission filter, a technique for weighting IDT electrodes of resonators in the transmission filter is known.

However, in the transmission filter of the conventional duplexer, if the steepness of the attenuation characteristic is increased on the high frequency side of the passband of the transmission filter, the loss of the transmission passband increases. In addition, in the reception filter of the conventional duplexer, if the steepness of the attenuation characteristic is improved on the lower frequency side than the passband, the loss of the reception passband is also increased.

Therefore, in the conventional duplexer, it is required to achieve both sharpness in the cross band and low loss in the pass band.

As prior art literature information related to the invention of the present application, for example, patent document 1 is known.

Prior art documents

Patent document

Patent document 1: japanese Kokai publication Hei-2001-500697

Disclosure of Invention

The antenna duplexer of the present invention includes: a first elastic wave filter for passing a signal of a first frequency band; and a second elastic wave filter for passing a signal of a second frequency band higher than the first frequency band. The first elastic wave filter has a ladder filter including a first series resonator and a second series resonator having an anti-resonance frequency higher than that of the first series resonator. The first series resonator has: a first IDT electrode having a plurality of electrode fingers; and a first dielectric film formed to cover the first IDT electrode and further having a first protrusion above the electrode finger. The second series resonator has: a second IDT electrode having a plurality of electrode fingers; and a second dielectric film formed to cover the second IDT electrode and further having a second protrusion above the electrode finger. The cross-sectional area of the first convex portion in the excitation direction of the elastic wave of the first series resonator is larger than the cross-sectional area of the second convex portion in the excitation direction of the elastic wave of the second series resonator.

According to this configuration, in the first elastic wave filter of the duplexer, the electromechanical coupling coefficient of the first series resonator can be made smaller than the electromechanical coupling coefficient of the second series resonator. Since the first series resonator having a lower antiresonant frequency than the second series resonator contributes to a larger degree of steepness of the attenuation characteristic on the high frequency side of the first elastic wave filter, the steepness of the cross band (high frequency side of the first elastic wave filter) can be improved by making the electromechanical coupling coefficient ratio of the first series resonator small. Further, since the second series resonator having an antiresonant frequency higher than that of the first series resonator contributes to a reduction in loss in the pass band of the first elastic wave filter to a large extent, the second series resonator can have a large electromechanical coupling coefficient ratio, thereby achieving a reduction in loss in the pass band.

Further, the duplexer of the present invention includes: a first elastic wave filter for passing a signal of a first frequency band; and a second elastic wave filter for passing a signal of a second frequency band higher than the first frequency band. The second elastic wave filter has a ladder filter including a first parallel resonator and a second parallel resonator having a resonance frequency lower than that of the first parallel resonator. The first parallel resonator has: a third IDT electrode having a plurality of electrode fingers; and a third dielectric film formed to cover the third IDT electrode and further having a third projection above the electrode finger. The second parallel resonator has: a fourth IDT electrode having a plurality of electrode fingers; and a fourth dielectric film formed to cover the fourth IDT electrode and further having a fourth convex portion above the electrode fingers. The cross-sectional area of the third convex portion in the excitation direction of the elastic wave of the first parallel resonator is larger than the cross-sectional area of the fourth convex portion in the excitation direction of the elastic wave of the second parallel resonator.

According to this configuration, in the second elastic wave filter of the duplexer, the electromechanical coupling coefficient of the first parallel resonator can be made smaller than the electromechanical coupling coefficient of the second parallel resonator. Since the first parallel resonator having a higher resonance frequency than the second parallel resonator contributes to a large degree of steepness of the attenuation characteristic of the second elastic wave filter on the low frequency side, the steepness in the cross band (on the low frequency side of the second elastic wave filter) can be improved by making the electromechanical coupling coefficient ratio of the first parallel resonator small. Further, since the second parallel resonator having a lower resonance frequency than the first parallel resonator contributes to a large reduction in loss in the pass band of the second elastic wave filter, the second parallel resonator can have a large electromechanical coupling coefficient, thereby achieving a reduction in loss in the pass band.

Drawings

Fig. 1 is a circuit diagram of a duplexer in embodiment 1.

Fig. 2 is a diagram showing the passing characteristics of the duplexer in embodiment 1.

Fig. 3 is a perspective view of the resonator in embodiment 1.

Fig. 4A is a cross-sectional view taken along line 4A-4A of fig. 3.

Fig. 4B is an enlarged view of a portion T in fig. 4A.

Fig. 5 is a diagram showing the electromechanical coupling coefficient of the duplexer in embodiment 1.

Fig. 6A is a sectional view of the resonator in embodiment 1.

Fig. 6B is a sectional view of the resonator in embodiment 1.

Fig. 6C is a sectional view of the resonator in embodiment 1.

Fig. 6D is a sectional view of the resonator in embodiment 1.

Fig. 7 is a diagram showing the passing characteristics of the duplexer in embodiment 1.

Fig. 8 is a circuit diagram of the duplexer in embodiment 2.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to these embodiments.

Embodiment mode 1

Fig. 1 is a circuit diagram of a duplexer in embodiment 1. More specifically, fig. 1 is a schematic circuit diagram of a duplexer for Band2 in the W-CDMA standard in embodiment 1.

In fig. 1, duplexer 100 includes a first elastic wave filter 103 as a transmission filter and a second elastic wave filter 104 as a reception filter, which are connected to antenna terminal 102, respectively.

For example, in duplexer 100 for Band2, first elastic wave filter 103 passes signals in a transmission frequency Band of 1.85GHz to 1.91GHz (hereinafter referred to as a first frequency Band), and second elastic wave filter 104 passes signals in a reception frequency Band of 1.93GHz to 1.99GHz higher than the first frequency Band (hereinafter referred to as a second frequency Band).

First elastic wave filter 103 and second elastic wave filter 104 will be described in detail below.

First elastic wave filter 103 is a ladder filter in which a plurality of resonators are arranged in a ladder shape. That is, first elastic wave filter 103 includes: a reception terminal 105; a series resonator 106, a series resonator 107, a series resonator 108, and a series resonator 109 connected in series in this order from the reception terminal 105 to the antenna terminal 102. Furthermore, first elastic wave filter 103 further includes: a parallel resonator 110 connected in parallel to ground between the series resonator 106 and the series resonator 107; a parallel resonator 111 connected in parallel to ground between the series resonator 107 and the series resonator 108; and a parallel resonator 112 connected in parallel to ground between the series resonator 108 and the series resonator 109.

The second elastic wave filter 104 includes: a series resonator 114 connected to the antenna terminal 102; a multimode elastic wave filter 115 and a multimode elastic wave filter 116 connected to the branches of the series resonator 114; and a multimode elastic wave filter 117 cascade-connected to these filters. Second elastic wave filter 104 further includes receiving terminals 118 and 119 connected to multimode elastic wave filter 117. Then, the reception signals are balanced and output from the reception terminals 118 and 119.

The transmission characteristics of first elastic wave filter 103 will be described with reference to fig. 2. Fig. 2 is a diagram showing the passing characteristics of the duplexer in embodiment 1. Fig. 2 shows the passing characteristics (dB) near the high frequency side of the first frequency band (1.88GHz-1.98 GHz). In fig. 2, pass characteristic 120 represents pass characteristics of first elastic wave filter 103. In the ladder filter such as first elastic wave filter 103, the anti-resonance frequencies of the resonators arranged mainly in the series arm out of the resonators arranged in the series arm and the parallel arm form the attenuation characteristics of cross band 120B on the high frequency side of pass band 120A.

Fig. 2 is a diagram showing the passing characteristics of the duplexer in embodiment 1. 121, 122, 123, 124 in fig. 2 are the passing characteristics of the series resonators 106, 107, 108, 109, respectively, and have different antiresonant frequencies 121a, 122a, 123a, 124 a. In this way, the attenuation characteristics of pass characteristic 120 of first elastic wave filter 103 in cross band 120B are formed by combining the pass characteristics of series resonators 106, 107, 108, and 109.

In the pass characteristic 120, the gradient of the boundary portion between the pass band 120A and the cross band 120B of the first elastic wave filter 103 is referred to as steepness. The larger the steepness is, the larger the attenuation characteristic at the cross band is, and the isolation between transmission and reception in the duplexer 100 can be ensured. Hereinafter, as an index indicating the steepness, the difference between the frequency having a-3 dB pass characteristic and the frequency having a-50 dB pass characteristic is set to be a steepness.

In the pass characteristic 120 of the first elastic wave filter 103, the frequency of the pass characteristic of-3 dB is 1.910GHz, and the frequency of the pass characteristic of-50 dB is 1.928GHz, so the steepness is 18 MHz. The index indicating steepness is not limited to a steepness, and may be an index indicating a magnitude of a gradient between a pass band and a stop band (blocking band) of the filter.

As can be seen from fig. 2, the pass characteristic 121 of the series resonator 106 most contributes to the steepness of the high-frequency side of the pass characteristic 120 of the first elastic wave filter 103. That is, the series resonator having the lowest antiresonant frequency among the series resonators constituting first elastic wave filter 103 contributes most to the steepness of pass characteristic 120 of first elastic wave filter 103 on the high frequency side. On the other hand, the series resonator having the highest antiresonant frequency among the series resonators constituting first elastic wave filter 103 contributes most to reducing the loss in passband 120A of first elastic wave filter 103.

Here, as a method of adjusting the antiresonant frequency of a resonator using a piezoelectric body, a method of adjusting the electromechanical coupling coefficient of the resonator is effective. The electromechanical coupling coefficient is an index indicating the conversion efficiency between electrical energy and mechanical energy in a resonator using a piezoelectric body, and can be obtained from the resonance frequency and the antiresonance frequency of the resonator. When a ladder filter is configured by combining resonators using piezoelectric bodies, if the electromechanical coupling coefficient of each resonator is increased, the passband of the ladder filter becomes narrow and the attenuation characteristic becomes steep. On the other hand, when the electromechanical coupling coefficient of each resonator is reduced, the passband of the ladder filter becomes wider, and the attenuation characteristic becomes gentle. Therefore, by appropriately combining a plurality of resonators having different electromechanical coupling coefficients, both sharpness of the ladder filter and low loss in the pass band can be achieved.

A method of adjusting the electromechanical coupling coefficient of a resonator using a piezoelectric body will be described with reference to fig. 3 to 7.

Fig. 3 is a perspective view of the resonator in embodiment 1. The resonator 1 includes, for example: a piezoelectric substrate 2 using lithium tantalate or lithium niobate; an idt (inter digital transducer) electrode 3 formed on the piezoelectric substrate 2 and having a plurality of electrode fingers 3 a. Further, the resonator 1 further includes: a pair of reflectors 4 formed on both sides of the IDT electrode 3 in the excitation direction (excitation direction) of the elastic wave; one end of the signal line 5 is electrically connected to the IDT electrode 3, and the other end is electrically connected to another electrode such as an IDT electrode or a receiving terminal. In the resonator 1, the piezoelectric substrate 2, the IDT electrode 3, the reflector 4, and the signal wiring 5 are covered with a dielectric film 6 (not shown in fig. 3).

Fig. 4A is a cross-sectional view taken along line 4A-4A of fig. 3. As shown in fig. 4A, the piezoelectric substrate 2, the IDT electrode, the reflector 4, and the signal wiring are covered with a dielectric film 6. By the dielectric film 6, foreign substances can be prevented from adhering to the piezoelectric substrate 2, the IDT electrode, and the like, and the reliability of the resonance characteristics of the resonator 1 can be ensured.

Further, as the dielectric film 6, silicon dioxide (SiO) is used₂) Thereby, the frequency-temperature characteristics of the resonator 1 can be improved. The piezoelectric material such as lithium tantalate or lithium niobate used for the piezoelectric substrate 2 has a negative frequency-temperature characteristic. This is because: as the dielectric film 6, if silicon dioxide or the like is laminated in an appropriate film thicknessA material having a positive frequency-temperature characteristic can make the frequency-temperature characteristic close to zero for the resonator as a whole.

Further, by forming the dielectric film 6 so as to have the convex portions 6a above the electrode fingers 3a, the occurrence of spurious (spurious) in the pass band 120A of the resonator 1 can be suppressed. This is because: by controlling the shape of the convex portion, the electromechanical coupling coefficient of a Rayleigh wave (Rayleigh wave) which causes the occurrence of spurious waves can be made close to zero.

The convex portion 6a of the dielectric film 6 can be formed by a method of forming a film by sputtering while applying a bias voltage to the substrate side, for example, when forming a silicon dioxide film as a dielectric film.

Fig. 4B is an enlarged view of a portion T in fig. 4A. The shape of the convex portion 6a formed above the electrode finger 3a will be described below using the height (H) of the convex portion, the width (W) of the convex portion, and the inclination angle (K) of the trapezoidal convex portion.

Fig. 5 is a diagram showing the electromechanical coupling coefficient of the duplexer in embodiment 1. More specifically, the relationship between the ratio of the electrode width of the electrode fingers 3a to the electrode finger pitch (hereinafter referred to as metallization ratio) and the electromechanical coupling coefficient is shown. In fig. 5, H1, H2, and H3 show the relationship between the metallization ratio and the electromechanical coupling coefficient when the upper surface of the dielectric film 6 is made flat. D1, D2, and D3 show the relationship between the metallization ratio and the electromechanical coupling coefficient when the dielectric film 6 is formed into a trapezoidal shape so as to have the convex portions 6a above the electrode fingers 3 a. Here, since the protruding portion 6a is formed to have substantially the same width as the electrode finger 3a, the width of the protruding portion 6a increases in proportion to the metallization ratio.

The difference indicated by H1, H2, and H3 in fig. 5 is due to the difference in the film thickness of the dielectric film 6 (the height (H) from the upper portion of the electrode to the projection 6 a). When λ is defined as the pass band of first elastic wave filter 103, that is, the wavelength of the center frequency (1.88GHz) of the first frequency band, H1 represents that the film thickness of dielectric film 6 is 20% (0.2 λ) of λ. Similarly, H2 and H3 represent the cases where the film thickness of the dielectric film 6 is 30% and 40% of λ.

D1, D2, and D3 in fig. 5 show the cases where the film thickness of the dielectric film 6 is 20%, 30%, and 40%, respectively, of λ.

As can be seen from fig. 5: in the case where the upper surface of the dielectric film 6 is made flat, the electromechanical coupling coefficient decreases in the order of H1, H2, and H3. That is, the electromechanical coupling coefficient becomes smaller as the film thickness of the dielectric film 6 is increased. By adjusting the film thickness of the dielectric film 6 using this relationship, the electromechanical coupling coefficient of the resonator 1 can be adjusted, and the anti-resonance frequency of the resonator 1 can be adjusted. In first elastic wave filter 103, for example, by making the film thickness of series resonator 106 larger than the film thickness of series resonator 107, the anti-resonance frequency of series resonator 106 can be made lower than the anti-resonance frequency of series resonator 107.

Therefore, although the method of adjusting the electromechanical coupling coefficient based on the adjustment of the film thickness of the dielectric film 6 is useful, as described above, the frequency-temperature characteristics of the resonator 1 change when the film thickness of the dielectric film 6 changes.

On the other hand, H1, H2, and H3, which flatten the upper surface of the dielectric film 6, show a substantially flat characteristic with a small change in electromechanical coupling coefficient with respect to metallization ratio. That is, it is difficult to adjust the electromechanical coupling coefficient based on the adjustment of the metallization ratio.

Even when the dielectric film 6 is formed in a trapezoidal shape so as to have the convex portions 6a above the electrode fingers 3a, the electromechanical coupling coefficient of the resonator 1 can be reduced by increasing the size of the dielectric film 6, such as D1, D2, and D3. Further, when the convex portion 6a is provided on the dielectric film 6, the thickness of the dielectric film 6 can be reduced by increasing the metallization ratio. Therefore, in this case, the electromechanical coupling coefficient of the resonator 1 may be adjusted by adjusting the film thickness of the dielectric film 6, or the electromechanical coupling coefficient of the resonator 1 may be adjusted by adjusting the metallization ratio (i.e., adjusting the width (W) direction of the convex portion 6 a). That is, the electromechanical coupling coefficient of the resonator 1 can be adjusted by adjusting the cross-sectional area of the dielectric film 6 (the grid portion in fig. 6) (hereinafter, referred to as the cross-sectional area of the convex portion) formed above the electrode fingers 3a in the cross-section of the resonator 1 in the excitation direction of the elastic wave.

Although the height of the protruding portion 6a is set to be equal to the height of the electrode finger 3a, in practice, the height of the protruding portion 6a varies by about 10% due to the process for forming the dielectric film 6. In the resonator used in the duplexer for Band2, the height of the electrode finger 3a is preferably about 8% of the wavelength λ, and is therefore, for example, about 160 nm. In this case, the height of the projection is about 160 nm. + -. 10%.

Fig. 6 is a sectional view of the resonator in embodiment 1. Fig. 6 shows a method for adjusting the cross-sectional area (mesh portion) of the convex portion of the dielectric film 6 above the electrode finger 3 a. Fig. 6A to 6D show portions of the dotted line portion T of fig. 4A.

In fig. 6A, the metallization ratio η 1 is w1/(w1+ w2), and the height of the convex portion is (h2+ h 3). At this time, the cross-sectional area S1 of the convex portion is expressed by the following (formula 1).

S1＝w1×h2+(w1+w3)×h3/2

Fig. 6B shows a case where the height of the convex portion is set to (h4+ h3) larger than (h2+ h 3). In this case, the cross-sectional area S2 of the projection is larger than S1, and the electromechanical coupling coefficient is smaller than that in fig. 6A.

Fig. 6C shows a case where the metallization ratio is increased and η 2 ═ w4/(w4+ w5) (> η 1). In this case, the cross-sectional area S3 of the projection is larger than S1, and the electromechanical coupling coefficient is smaller than that in fig. 6A.

Fig. 6D shows a case where the inclination angle (K) of the convex portion is reduced. In this case, the cross-sectional area S4 of the projection is smaller than S1, and the electromechanical coupling coefficient is larger than that in fig. 6A.

As described above, the electromechanical coupling coefficient of the resonator 1 can be adjusted according to the cross-sectional area of the convex portion of the dielectric film 6. In first elastic wave filter 103, for example, the cross-sectional area of the convex portion of the dielectric film of series resonator 106 is made larger than the cross-sectional area of the convex portion of the dielectric film of series resonator 107, whereby the anti-resonance frequency of series resonator 106 can be made lower than the anti-resonance frequency of series resonator 107.

In this way, when the dielectric film 6 is formed in a trapezoidal shape so as to have the convex portions above the electrode fingers 3a, it is possible to suppress rayleigh waves and reduce loss, and the electromechanical coupling coefficient of the resonator 1 can be adjusted by adjusting the cross-sectional area of the convex portions of the dielectric film 6. In particular, when the cross-sectional area of the convex portion of the dielectric film 6 is adjusted according to the metallization ratio or the inclination angle K of the convex portion of the dielectric film 6, the film thickness of the dielectric film 6 does not need to be changed, and therefore, the frequency-temperature characteristics of the resonator are not affected.

Fig. 7 is a diagram showing the passing characteristics of the duplexer in embodiment 1. Fig. 7 shows a pass characteristic 131 of a conventional elastic wave filter in which the pass characteristic 130 of the first elastic wave filter 103 according to the present embodiment is equal to the cross-sectional area of the convex portions of the series resonators 107 and 109. In the pass characteristic 131 of the conventional elastic wave filter, the frequency of the pass characteristic of-3 dB is 1.911GHz, the frequency of the pass characteristic of-50 dB is 1.931GHz, and the steepness is 20 MHz. On the other hand, the steepness of the first elastic wave filter 103 according to this embodiment is 18MHz as described above, and the steepness is improved. Again, the losses in the pass band are the same. Thus, by adopting the configuration of the present embodiment, it is possible to realize a duplexer in which sharpness in the cross band is improved without deteriorating loss in the pass band.

Embodiment mode 2

The differences from embodiment 1 will be mainly described with respect to the characteristic portions of embodiment 2.

Fig. 8 is a circuit diagram of the duplexer in embodiment 2. In fig. 8, diplexer 200 uses a ladder filter, that is, first elastic wave filter 103, as a transmission filter, and diplexer 200 uses a ladder filter, that is, second elastic wave filter 201, as a reception filter.

Second elastic wave filter 201 includes series resonator 202, series resonator 203, series resonator 204, and series resonator 205 connected in series in this order from antenna terminal 102 to reception terminal 209. Furthermore, second elastic wave filter 201 further includes: a parallel resonator 206 connected in parallel to ground between the series resonator 202 and the series resonator 203; a parallel resonator 207 connected in parallel to ground between the series resonator 203 and the series resonator 204; and a parallel resonator 208 connected in parallel to ground between the series resonator 204 and the series resonator 205.

Since the second frequency band, which is the passband of second elastic wave filter 201, is a higher frequency band than the first frequency band, which is the passband of first elastic wave filter 103, it is necessary to increase the sharpness of second elastic wave filter 201 on the low frequency side in order to ensure isolation between transmission and reception in duplexer 200.

By making the resonance frequency of any one of parallel resonators 206, 207, and 208 constituting second elastic wave filter 201 close to the passband, steepness of the passband of second elastic wave filter 201 on the low frequency side can be increased.

By increasing the cross-sectional area of the convex portion of the dielectric film 6 in any of the parallel resonator 206, the parallel resonator 207, and the parallel resonator 208 shown in fig. 5, the electromechanical coupling coefficient can be reduced, and as a result, the resonance frequency can be brought close to the passband.

As a method of increasing the cross-sectional area of the convex portion of the dielectric film 6 in the parallel resonator, a method of increasing the height of the convex portion, a method of increasing the width of the convex portion by increasing the metallization ratio, a method of increasing the inclination K of the convex portion, and the like shown in fig. 6A to 6D can be employed.

(availability in industry)

The duplexer according to the present invention has the effect of making it possible to achieve both sharpness in the cross band and low loss in the transmission passband, and is applicable to electronic devices such as mobile phones.

Description of the symbols: 1-resonator, 2-piezoelectric substrate, 3-IDT electrode, 3 a-electrode finger, 4-reflector, 5-signal wiring, 6-dielectric film, 6 a-bump, 100, 200-duplexer, 102-antenna terminal, 103-first elastic wave filter, 104, 201-second elastic wave filter, 105, 118, 119, 209-receiving terminal, 106, 107, 108, 109, 114-series resonator, 110, 111, 112-parallel resonator, 115, 116, 117-multimode elastic wave filter, 120, 121, 122, 123, 124, 130, 131-pass characteristic, 120A-passband, 120B-cross band, 121a, 122a, 123a, 124 a-antiresonance frequency, 202, 203, 204, 205-series resonator, 206. 207, 208-parallel resonator.

Claims (12)

1. An elastic wave filter comprising:

a first series resonator including a first interdigital transducer electrode having a plurality of electrode fingers;

a second series resonator comprising a second interdigital transducer electrode having a plurality of electrode fingers, the second series resonator having an anti-resonance frequency higher than that of the first series resonator, the first series resonator having an electromechanical coupling coefficient smaller than that of the second series resonator; and

and a first dielectric film covering the first series resonator and the second series resonator, the first dielectric film having a first convex portion above an electrode finger of the first interdigital transducer electrode and a second convex portion above an electrode finger of the second interdigital transducer electrode, a cross-sectional area of the first convex portion in an excitation direction of an elastic wave of the first series resonator being larger than a cross-sectional area of the second convex portion in an excitation direction of an elastic wave of the second series resonator.

2. The elastic wave filter according to claim 1, wherein a width of the first convex portion in an excitation direction of an elastic wave of the first series resonator is larger than a width of the second convex portion in an excitation direction of an elastic wave of the second series resonator.

3. The elastic wave filter according to claim 1, wherein a height of the first convex portion in an excitation direction of an elastic wave of the first series resonator is larger than a height of the second convex portion in an excitation direction of an elastic wave of the second series resonator.

4. The elastic wave filter according to claim 1, wherein an inclination angle of a trapezoid of the first convex portion in an excitation direction of the elastic wave of the first series resonator is larger than an inclination angle of a trapezoid of the second convex portion in an excitation direction of the elastic wave of the second series resonator.

5. The elastic wave filter according to claim 4, wherein a thickness of the first dielectric film above the first series resonator is the same as a thickness above the second series resonator.

6. An elastic wave filter comprising:

a first parallel resonator including a third interdigital transducer electrode having a plurality of electrode fingers;

a second parallel resonator comprising a fourth interdigital transducer electrode having a plurality of electrode fingers, the second parallel resonator having a resonance frequency lower than that of the first parallel resonator, the first parallel resonator having an electromechanical coupling coefficient smaller than that of the second parallel resonator; and

and a second dielectric film covering the first parallel resonator and the second parallel resonator, the second dielectric film including a third convex portion above an electrode finger of the third interdigital transducer electrode and a fourth convex portion above an electrode finger of the fourth interdigital transducer electrode, wherein a cross-sectional area of the third convex portion in an excitation direction of an elastic wave of the first parallel resonator is larger than a cross-sectional area of the fourth convex portion in an excitation direction of an elastic wave of the second parallel resonator.

7. The elastic wave filter according to claim 6, wherein a width of the third convex portion in a direction of excitation of the elastic wave of the first parallel resonator is larger than a width of the fourth convex portion in a direction of excitation of the elastic wave of the second parallel resonator.

8. The elastic wave filter according to claim 6, wherein a height of the third convex portion in a direction of excitation of the elastic wave of the first parallel resonator is larger than a height of the fourth convex portion in a direction of excitation of the elastic wave of the second parallel resonator.

9. The elastic wave filter according to claim 6, wherein an inclination angle of a trapezoid of the third convex portion in an excitation direction of the elastic wave of the first parallel resonator is larger than an inclination angle of a trapezoid of the fourth convex portion in an excitation direction of the elastic wave of the second parallel resonator.

10. The elastic wave filter according to claim 9, wherein a thickness of the second dielectric film above the first parallel resonator is the same as a thickness above the second parallel resonator.

11. A diplexer, comprising:

the elastic wave filter of any one of claims 1 to 5 for passing a signal of a first frequency band; and

a filter for passing signals of a second frequency band higher than the first frequency band.

12. A diplexer, comprising:

the elastic wave filter of any one of claims 6 to 10 for passing signals of a first frequency band; and

a filter for passing signals of a second frequency band higher than the first frequency band.