CN113746449A - Elastic wave broadband filter - Google Patents
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- CN113746449A CN113746449A CN202111302758.7A CN202111302758A CN113746449A CN 113746449 A CN113746449 A CN 113746449A CN 202111302758 A CN202111302758 A CN 202111302758A CN 113746449 A CN113746449 A CN 113746449A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
- H03H9/6423—Means for obtaining a particular transfer characteristic
- H03H9/6433—Coupled resonator filters
- H03H9/644—Coupled resonator filters having two acoustic tracks
- H03H9/6456—Coupled resonator filters having two acoustic tracks being electrically coupled
- H03H9/6469—Coupled resonator filters having two acoustic tracks being electrically coupled via two connecting electrodes
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/125—Driving means, e.g. electrodes, coils
- H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
- H03H9/14502—Surface acoustic wave [SAW] transducers for a particular purpose
- H03H9/14514—Broad band transducers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
- H03H9/6406—Filters characterised by a particular frequency characteristic
- H03H9/6413—SAW comb filters
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Abstract
The invention discloses an elastic wave broadband filter, which belongs to the technical field of surface acoustic wave filters, wherein each interdigital transducer of a multi-order longitudinal coupling elastic wave filter structure in the elastic wave broadband filter is provided with a plurality of electrode finger space areas which are arranged according to a certain sequence, and 2 novel resonance peaks can be introduced in the mode, so that a pass band of the elastic wave filter is supported by 5 resonance peaks, the pass band is widened, and the broadband elastic wave filter with the relative bandwidth of more than 8% can be realized. Meanwhile, the phases of the multi-order longitudinal coupling elastic wave filter formed in the mode are continuous, and ripples and insertion loss in the pass band of the whole elastic wave filter can be optimized.
Description
Technical Field
The invention relates to the technical field of surface acoustic wave filters, in particular to an elastic wave broadband filter.
Background
A surface acoustic wave is an elastic wave that propagates along the surface of an object. The elastic wave filter has the characteristics of low cost, small volume, multiple functions and the like, is widely applied to the fields of radar, navigation, identification and the like, and has huge application requirements on the filter with ultra-large broadband and low loss in future communication systems along with the continuous development of mobile communication technology. Elastic wave filters mainly have a ladder structure and DMS (longitudinally coupled elastic wave) type filters, which are superior in low-end rejection and volume, and thus are widely used in elastic wave filter and duplexer designs. The bandwidth of the conventional DMS-type filter is narrow (about 4% of the relative bandwidth), and in order to satisfy the performance requirement of a larger relative bandwidth, an LC filter (passive filter) or a MEMS (Micro-Electro-Mechanical System) filter must be used, and the volume of the LC filter or the MEMS filter is much larger than that of the conventional low-loss elastic wave filter.
United states SNAPTRACK discloses in US10680580B2 two DMS filters with different center frequencies connected in parallel on a 36-48 ° YX-LiTaO3 (lithium tantalate) substrate, and aligning the low frequency formants of the pass band (high frequency) of the DMS2 filter with the high frequency formants of the pass band (low frequency) of the DMS1 filter to realize pass band synthesis and obtain a wider pass band of the filter.
The relative bandwidth of the elastic wave filter can reach 8%, however, because a certain phase difference exists between the low-frequency harmonic peak of the pass band of the DMS2 filter and the high-frequency harmonic peak of the pass band of the DMS1 filter at the frequency point aligned with each other, a notch exists at the pass band merging frequency point of the transmission curve S21 of the elastic wave filter, so that the loss and the echo in the pass band of the filter are deteriorated, and the actual use of the filter is affected.
Disclosure of Invention
Aiming at the defects in the prior art, the elastic wave broadband filter provided by the invention solves the problem that the elastic filter adopts two DMS filters with different central frequencies in parallel, so that the passband merging frequency point of a transmission curve S21 is sunken, the loss and the echo in the passband of the filter are deteriorated, and the practical use of the filter is influenced.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that: an elastic wave broadband filter comprising: the first series resonance arm, the second series resonance arm, the multi-order longitudinal coupling elastic wave filter, the first parallel resonance arm and the second parallel resonance arm;
the input end of the multistage longitudinal coupling elastic wave filter is connected with the output end of the first series resonance arm, and the output end of the multistage longitudinal coupling elastic wave filter is connected with the input end of the second series resonance arm; the input end of the first series resonance arm is connected with the input end of the first parallel resonance arm and serves as the input end of the elastic wave broadband filter; the output end of the first parallel resonance arm is grounded; the output end of the second series resonance arm is connected with the input end of the second parallel resonance arm and is used as the output end of the elastic wave broadband filter; and the output end of the second parallel resonance arm is grounded.
Further, the number of series resonators in the first series resonance arm and the second series resonance arm is greater than or equal to 1, and the number of parallel resonators in the first parallel resonance arm and the second parallel resonance arm is greater than or equal to 1.
Further, the series resonators in the first series resonator arm and the second series resonator arm, the parallel resonators in the first parallel resonator arm and the second parallel resonator arm, and the interdigital transducers in the multi-order longitudinally-coupled elastic wave filter each include: the device comprises a substrate, a first comb-tooth-shaped electrode and a second comb-tooth-shaped electrode, wherein the first comb-tooth-shaped electrode and the second comb-tooth-shaped electrode are positioned on the substrate;
the first comb-teeth-shaped electrode includes: a plurality of upper electrode fingers and a first bus bar electrode; the plurality of upper electrode fingers are all connected with the first bus bar electrode; the second comb-teeth-shaped electrode includes: a plurality of lower electrode fingers and a second bus bar electrode; the plurality of lower electrode fingers are all connected with the second bus bar electrode; the upper electrode fingers and the lower electrode fingers are arranged in a staggered mode.
Further, the first comb-tooth-shaped electrode and the second comb-tooth-shaped electrode each include: a main electrode layer and a sealing layer;
the seal layer is located between the main electrode layer and the substrate.
Further, the thickness of the main electrode layer is 150 nm; the thickness of the adhesion layer is 50 nm.
Further, an aluminum material doped with 2% of copper element is used for the main electrode layer, and titanium is used for the adhesion layer.
Furthermore, a protective layer is arranged on the surfaces of the substrate, the first comb-tooth-shaped electrode and the second comb-tooth-shaped electrode.
Further, the thickness of the protective layer is 15nm, and the substrate is a lithium tantalate piezoelectric material with the thickness of 200 um.
Further, the material of the protective layer includes: silicon dioxide.
Further, each interdigital transducer of the multi-order longitudinally-coupled elastic wave filter comprises, connected in sequence: the distance between the electrode fingers of the first interdigital group, the second interdigital group, the third interdigital group, the fourth interdigital group, the fifth interdigital group, the sixth interdigital group and the seventh interdigital group meets the following conditions: b1= B7, B2= B6, B3= B5 and B4> B2> B3> B1, where B1 is the electrode finger pitch of the first interdigital set, B2 is the electrode finger pitch of the second interdigital set, B3 is the electrode finger pitch of the third interdigital set, B4 is the electrode finger pitch of the fourth interdigital set, B5 is the electrode finger pitch of the fifth interdigital set, B6 is the electrode finger pitch of the sixth interdigital set, and B7 is the electrode finger pitch of the seventh interdigital set.
The beneficial effects of the above further scheme are: the phase in the filter passband can be inverted by satisfying the electrode finger spacing, so that two new resonance peaks are introduced. And the lowest frequency resonance peak moves towards the low frequency direction, and the highest frequency resonance peak moves towards the high frequency direction, so that the bandwidth of the longitudinal coupling elastic wave filter DMS is increased, and the elastic wave filter with wider bandwidth is obtained.
In conclusion, the beneficial effects of the invention are as follows: conventional longitudinally coupled elastic wave filters can realize up to 3 resonance peaks to support the passband, and therefore the achievable relative bandwidth is about 4% at the maximum. Each interdigital transducer of the multi-order longitudinal coupling elastic wave filter structure in the elastic wave broadband filter is provided with a plurality of electrode finger space areas which are arranged according to a certain sequence, 2 novel resonance peaks can be introduced in the mode, so that the passband of the elastic wave filter is supported by 5 resonance peaks, the passband is widened, and the broadband elastic wave filter with the relative bandwidth larger than 8% can be realized. Meanwhile, the phases of the multi-order longitudinal coupling elastic wave filter formed in the mode are continuous, and ripples and insertion loss in the pass band of the whole elastic wave filter can be optimized.
Drawings
FIG. 1 is a schematic structural diagram of an elastic wave broadband filter;
FIG. 2 is a schematic diagram of a top view configuration of a series resonator, parallel resonator, or interdigital transducer;
FIG. 3 is a schematic cross-sectional view of a series resonator, parallel resonator, or interdigital transducer;
FIG. 4 is a schematic structural diagram of a 5 th order longitudinally coupled elastic wave filter;
FIG. 5 is a schematic structural view of a central interdigital transducer of embodiment 1;
fig. 6 is an elastic wave filter of comparative example 1;
fig. 7 is a schematic diagram showing electrode finger pitches of center interdigital transducers of longitudinally coupled elastic wave filters of example 1 and comparative example 1;
fig. 8 is an admittance Y-curve of the longitudinally coupled elastic wave filters of example 1 and comparative example 1;
fig. 9 is a transmission curve in a wide frequency range of the elastic wave broadband filters according to example 1 and comparative example 1;
fig. 10 is a transmission curve in the pass band range of the elastic wave broadband filter according to example 1 and comparative example 1;
fig. 11 is a transmission curve of the elastic wave broadband filter of example 2 and an admittance curve of the structure of the longitudinally coupled elastic wave filter (DMS4) of example 2;
wherein, 1, a first series resonance arm; 2. a second series resonant arm; 3. a multi-order longitudinally coupled elastic wave filter; 4. a first parallel resonant arm; 5. a second parallel resonant arm; 41. a first parallel resonator; 42. a second parallel resonator; 51. a third parallel resonator; 52. a fourth parallel resonator; 6. a central interdigital transducer; 61. a first set of interdigitations; 62. a second set of fingers; 63. a third set of three pronged fingers; 64. a fourth set of interdigitations; 65. a fifth set of interdigitations; 66. a sixth set of interdigitations; 67. a seventh set of interdigitations.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
Example 1: as shown in fig. 1, an elastic wave broadband filter includes: the device comprises a first series resonance arm 1, a second series resonance arm 2, a multi-order longitudinal coupling elastic wave filter 3, a first parallel resonance arm 4 and a second parallel resonance arm 5;
the input end of the multi-order longitudinal coupling elastic wave filter 3 is connected with the output end of the first series resonance arm 1, and the output end of the multi-order longitudinal coupling elastic wave filter is connected with the input end of the second series resonance arm 2; the input end of the first series resonant arm 1 is connected with the input end of the first parallel resonant arm 4 and serves as the input end of the elastic wave broadband filter; the output end of the first parallel resonant arm 4 is grounded; the output end of the second series resonance arm 2 is connected with the input end of the second parallel resonance arm 5 and serves as the output end of the elastic wave broadband filter; the output end of the second parallel resonant arm 5 is grounded.
The number of series resonators in the first series resonator arm 1 and the second series resonator arm 2 is greater than or equal to 1, and the number of parallel resonators in the first parallel resonator arm 4 and the second parallel resonator arm 5 is greater than or equal to 1.
In the present embodiment, the first parallel resonator arm 4 includes a first parallel resonator 41 and a second parallel resonator 42 connected in series; the second parallel resonator arm 5 comprises a third parallel resonator 51 and a fourth parallel resonator 52 connected in series. The first parallel resonator 41, the second parallel resonator 42, the third parallel resonator 51, and the fourth parallel resonator 52 are all elastic wave resonators.
In addition, circuit elements such as inductors and capacitors can be added at the connection nodes of the devices to match the impedance of the filter and obtain better performance.
As shown in fig. 2 to 3, the series resonators, the parallel resonators, and the interdigital transducers in the multi-stage longitudinally coupled elastic wave filter 3 each include: a substrate 214, and a first comb-tooth-shaped electrode 11 and a second comb-tooth-shaped electrode 12 located on the substrate 214;
the first comb-teeth electrode 11 includes: a plurality of upper electrode fingers 111 and first bus bar electrodes 112; the plurality of upper electrode fingers 111 are all connected to the first bus bar electrode 112; the second comb-teeth-shaped electrode 12 includes: a plurality of lower electrode fingers 121 and second bus bar electrodes 122; the plurality of lower electrode fingers 121 are all connected to the second bus bar electrode 122; the upper electrode fingers 111 and the lower electrode fingers 121 are arranged in a staggered manner.
The first comb-teeth electrode 11 and the second comb-teeth electrode 12 each include: a main electrode layer 212 and an adhesion layer 213; the adhesion layer 213 is located between the main electrode layer 212 and the substrate 214.
The adhesion layer 213 is used to improve adhesion between the substrate 214 and the main electrode layer 212, and the material of the adhesion layer 213 is titanium.
The main electrode layer 212 uses an aluminum material doped with 2% of copper element. The thickness of the main electrode layer 212 was 150 nm; the thickness of the adhesion layer 213 is 50 nm.
The surfaces of the substrate 214, the first comb-tooth-shaped electrode 11 and the second comb-tooth-shaped electrode 12 are provided with a protective layer 211.
The substrate 214 is a 200um thick 42 ° YX-LiTaO3 (lithium tantalate) piezoelectric material, but may be other corner cut piezoelectric materials such as LiTaO3 (lithium tantalate), lithium niobate (LiNbO 3), quartz, and the like. The substrate 214 may have a structure in which a high acoustic velocity support layer, a low acoustic velocity film, and a piezoelectric film are sequentially stacked.
The protective layer 211 is a layer for protecting the main electrode layer 212 from the external environment, adjusting the frequency temperature characteristics, improving the moisture resistance, and the like, and is a dielectric film containing silicon dioxide as a main component, for example. The thickness of the main electrode layer 212 is, for example, 15 nm.
The first comb-shaped electrodes 11 and the second comb-shaped electrodes 12 form IDT electrodes alternately, and the resonator wavelength is defined by a wavelength λ that is a repetition period of the plurality of upper electrode fingers 111 and the plurality of lower electrode fingers 121 that form the IDT electrode shown in fig. 3. The electrode finger pitch is 1/2 of the wavelength λ, and is defined as (W + S) when the line width of the electrode fingers constituting the first comb-tooth-shaped electrode 11 and the second comb-tooth-shaped electrode 12 is W and the space width between the adjacent electrode fingers is S. As shown in fig. 2, the intersection width L of the pair of comb-teeth-shaped electrodes is the length of the electrode fingers that overlap when viewed from the elastic wave propagation direction. The electrode duty of each resonator is a line width occupancy of the plurality of electrode fingers, is a ratio of the line width of the plurality of electrode fingers to the sum of the line width and the space width, and is defined by W/(W + S). The heights, i.e., the thicknesses of the first comb-teeth-shaped electrode 11 and the second comb-teeth-shaped electrode 12 are set to h. The parameters that determine the shape and size of the IDT electrode of the resonator, such as the wavelength λ, the cross width L, the electrode duty, and the thickness h of the IDT electrode, are referred to as electrode parameters.
As shown in fig. 4 to 5, each interdigital transducer in the multi-order longitudinally-coupled elastic wave filter 3 is designed, and each interdigital transducer comprises: a first set of fingers 61, a second set of fingers 62, a third set of fingers 63, a fourth set of fingers 64, a fifth set of fingers 65, a sixth set of fingers 66, and a seventh set of fingers 67, with electrode finger spacings satisfying: b1= B7, B2= B6, B3= B5 and B4> B2> B3> B1, where B1 is the electrode finger pitch of first interdigital set 61, B2 is the electrode finger pitch of second interdigital set 62, B3 is the electrode finger pitch of third interdigital set 63, B4 is the electrode finger pitch of fourth interdigital set 64, B5 is the electrode finger pitch of fifth interdigital set 65, B6 is the electrode finger pitch of sixth interdigital set 66, and B7 is the electrode finger pitch of seventh interdigital set 67.
Shown in fig. 4 is a preferred longitudinally coupled elastic wave filter of order 5, denoted by DMS 3.
In this way, 2 novel harmonic peaks can be introduced, and the elastic wave broadband filter of example 1 has a passband supported by the above 5 harmonic peaks, so that the passband of the elastic wave mode filter can be widened, and an elastic wave broadband filter with a relative bandwidth of about 8% can be realized. And the phase of the elastic wave broadband filter is continuous, so that the ripple and the insertion loss in a passband can be optimized.
Comparative example 1: as shown in fig. 6, the elastic wave broadband filter of comparative example 1 is obtained by replacing the multi-step longitudinally coupled elastic wave filter 3 in fig. 1 with a longitudinally coupled elastic wave filter composed of two 3-step DMS (low-frequency DMS1 and high-frequency DMS2) connected in parallel, and the structures and performances of the low-frequency DMS1 and the high-frequency DMS2 are described in detail below:
each interdigital transducer of the low-frequency DMS1 and the high-frequency DMS2 has 3 different electrode finger pitches, the electrode finger pitch of the center of each interdigital transducer is the largest, the electrode finger pitches of two side parts are smaller and equal, and 3 resonant peaks can be formed in a pass band. And aligning the frequency of the low-frequency harmonic peak of the passband (high frequency) of the high-frequency DMS2 with the frequency of the high-frequency harmonic peak of the passband (low frequency) of the low-frequency DMS1, realizing passband synthesis and obtaining a wider filter passband. However, a certain phase difference exists between the low-frequency harmonic peak of the passband of the high-frequency DMS2 and the high-frequency harmonic peak of the passband of the low-frequency DMS1 at the frequency point where the peaks are aligned, and a notch exists at the passband merging frequency point of the transmission curve S21 of the elastic filter, so that loss and echo in the passband of the filter deteriorate, and the actual use of the filter is affected.
Fig. 7 is a schematic diagram showing electrode finger pitches of the center interdigital transducers 6 of the longitudinally coupled elastic wave filters of embodiment 1 and comparative example 1.
The electrode finger pitch of the high-frequency DMS2 of comparative example 1 is smaller than the electrode finger pitch of the low-frequency DMS1 because the passband frequencies of the high-frequency DMS2 are higher than the passband frequencies of the low-frequency DMS 1. The center electrode finger pitch B4 of the DMS3 of the present invention is the largest and satisfies the electrode finger pitch condition of B4> B2= B6> B3= B4> B1= B7. The electrode finger spacings of the other interdigital transducers next to the central interdigital transducer 6 of the DMS3 also satisfy the above-described conditions.
Fig. 8 is an admittance Y-curve of the longitudinally coupled elastic wave filters of example 1 and comparative example 1. The passband synthesis is achieved by the 5 formants formed by the 3 formants in the pass bands of the low frequency DMS1 and the high frequency DMS2 of comparative example 1 aligned in frequency with the low frequency formant in the pass band of the high frequency DMS2 and the high frequency formant in the pass band of the low frequency DMS1, and a wider filter pass band is obtained. DMS3 of example 1 introduces 2 novel formants, the elastic filter passband is also supported by 5 formants, and the bandwidth between the lowest frequency formant and the highest frequency formant is wider than that of comparative example 1, so that a broadband elastic wave filter having a larger relative bandwidth can be realized.
Fig. 9 shows that the out-of-band rejection is better on both sides of the pass band in embodiment 1, because the peak value of 5 resonance peaks of DMS3 is higher, the energy of the longitudinally coupled elastic wave filter (DMS) is more concentrated, the Q value of the quality factor is higher, and the filter can obtain better in-band loss and out-of-band rejection in the optimum design. The 3dB bandwidths of example 1 and comparative example 1 were 230MHz and 220MHz, respectively, and the relative bandwidths were 8.85% and 8.45%, respectively, and the manner of example 1 can obtain elastic wave filters having wider bandwidths.
Fig. 10 shows that the low-frequency resonance peak of the pass band (high frequency) of the high-frequency DMS2 of comparative example 1 is frequency-aligned with the high-frequency resonance peak of the pass band (low frequency) of the low-frequency DMS1, and a broadband elastic wave filter is obtained. However, a certain phase difference exists between the low-frequency harmonic peak of the passband of the high-frequency DMS2 and the high-frequency harmonic peak of the passband of the low-frequency DMS1 at the frequency point where the peaks are aligned, and a notch exists at the passband merging frequency point of the transmission curve S21 of the elastic filter, so that loss and echo in the passband of the filter deteriorate, and the actual use of the filter is affected.
Embodiment 1 has no notch point at the passband merging frequency point, and the transmission curve S21 in the passband is smoother and the in-band ripple is better. In addition, the pass band total loss of comparative example 1 is about 0.7dB lower than that of example 1. This is because the high-frequency DMS2 and the low-frequency DMS1 have a phase difference over the entire passband, and after the passband is synthesized, the energy dissipation of the longitudinally coupled elastic wave filter (DMS) increases, the Q value of the quality factor decreases, and the loss in the band increases, and particularly, the maximum difference between the loss of comparative example 1 and that of example 1 on the right side of the passband is as high as 1.2 dB.
Example 2: embodiment 2 is to change the multi-step longitudinally coupled elastic wave filter of embodiment 1 to a 7-step longitudinally coupled elastic wave filter DMS4, where the electrode finger pitch of each interdigital transducer of the 7-step longitudinally coupled elastic wave filter DMS4 is also 7, and the electrode finger pitch condition of B4> B2= B6> B3= B4> B1= B7 is satisfied, and the rest of the electrical connection structure is the same as that of embodiment 1.
Fig. 11 shows that the 3dB bandwidth of example 2 is 235MHz, and the relative bandwidth is 9.04%.
Claims (10)
1. An elastic wave broadband filter, comprising: the device comprises a first series resonance arm (1), a second series resonance arm (2), a multi-order longitudinal coupling elastic wave filter (3), a first parallel resonance arm (4) and a second parallel resonance arm (5);
the input end of the multi-order longitudinal coupling elastic wave filter (3) is connected with the output end of the first series resonance arm (1), and the output end of the multi-order longitudinal coupling elastic wave filter is connected with the input end of the second series resonance arm (2); the input end of the first series resonance arm (1) is connected with the input end of the first parallel resonance arm (4) and is used as the input end of the elastic wave broadband filter; the output end of the first parallel resonance arm (4) is grounded; the output end of the second series resonance arm (2) is connected with the input end of the second parallel resonance arm (5) and is used as the output end of the elastic wave broadband filter; and the output end of the second parallel resonance arm (5) is grounded.
2. The elastic wave broadband filter according to claim 1, wherein the number of series resonators in the first series resonator arm (1) and the second series resonator arm (2) is 1 or more, and the number of parallel resonators in the first parallel resonator arm (4) and the second parallel resonator arm (5) is 1 or more.
3. The elastic wave broadband filter according to claim 1, wherein the series resonators in the first series resonator arm (1) and the second series resonator arm (2), the parallel resonators in the first parallel resonator arm (4) and the second parallel resonator arm (5), and the interdigital transducers in the multi-step longitudinally coupled elastic wave filter (3) each comprise: a substrate (214), and a first comb-tooth-shaped electrode (11) and a second comb-tooth-shaped electrode (12) which are located on the substrate (214);
the first comb-tooth-shaped electrode (11) includes: a plurality of upper electrode fingers (111) and first bus bar electrodes (112); the plurality of upper electrode fingers (111) are all connected with the first bus bar electrode (112); the second comb-tooth-shaped electrode (12) includes: a plurality of lower electrode fingers (121) and second bus bar electrodes (122); the plurality of lower electrode fingers (121) are all connected with the second bus bar electrode (122); the upper electrode fingers (111) and the lower electrode fingers (121) are arranged in a staggered mode.
4. The elastic wave broadband filter according to claim 3, wherein the first comb-tooth-shaped electrode (11) and the second comb-tooth-shaped electrode (12) each comprise: a main electrode layer (212) and an adhesion layer (213);
the adhesion layer (213) is located between the main electrode layer (212) and the substrate (214).
5. The elastic wave broadband filter according to claim 4, characterized in that the thickness of the main electrode layer (212) is 150 nm; the thickness of the adhesion layer (213) is 50 nm.
6. The elastic wave broadband filter according to claim 4, wherein the main electrode layer (212) is made of an aluminum material doped with 2% of copper element, and the material of the adhesion layer (213) is titanium.
7. The elastic wave broadband filter according to claim 3, characterized in that the surfaces of the substrate (214), the first comb-tooth-shaped electrode (11) and the second comb-tooth-shaped electrode (12) are provided with a protective layer (211).
8. The elastic wave broadband filter according to claim 7, characterized in that the thickness of the protective layer (211) is 15nm and the substrate (214) is 200um thick lithium tantalate piezoelectric material.
9. The elastic wave broadband filter according to claim 7, wherein the material of the protective layer (211) comprises: silicon dioxide.
10. The elastic wave broadband filter according to claim 1, characterized in that each interdigital transducer of the multi-order longitudinally coupled elastic wave filter (3) comprises, connected in series: a first interdigital set (61), a second interdigital set (62), a third interdigital set (63), a fourth interdigital set (64), a fifth interdigital set (65), a sixth interdigital set (66) and a seventh interdigital set (67), wherein the electrode finger spacing satisfies: b1= B7, B2= B6, B3= B5 and B4> B2> B3> B1, where B1 is the electrode finger pitch of the first interdigital set (61), B2 is the electrode finger pitch of the second interdigital set (62), B3 is the electrode finger pitch of the third interdigital set (63), B4 is the electrode finger pitch of the fourth interdigital set (64), B5 is the electrode finger pitch of the fifth interdigital set (65), B6 is the electrode finger pitch of the sixth interdigital set (66), and B7 is the electrode finger pitch of the seventh interdigital set (67).
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| CN117097298A (en) * | 2023-10-19 | 2023-11-21 | 苏州声芯电子科技有限公司 | Filter circuit for improving out-of-band rejection |
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