Lamb wave resonators and filters

Abstract

The application provides a Lamb wave resonator and filter, the Lamb wave resonator comprising a piezoelectric substrate, a first interdigital transducer and a second interdigital transducer, the first interdigital transducer and the second interdigital transducer are both in the shape of a long strip; an axis along the length direction of the first interdigital transducer and located in the middle of the first interdigital transducer and the second interdigital transducer is defined as a middle axis, the first interdigital transducer and the second interdigital transducer are arranged in mirror image symmetry about the middle axis; the duty cycle of the first interdigital transducer along the length direction and the duty cycle of the second interdigital transducer along the length direction both comprise a plurality of and change synchronously, each duty cycle of the first interdigital transducer is the same as the duty cycle of the second interdigital transducer adjacent to the first interdigital transducer and perpendicular to the length direction. The technical scheme of the application can improve the in-band insertion loss, reduce the ripple, has high in-band smoothness and good filtering performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit, in particular to a Lamb wave resonator and filter. BACKGROUND

[0002] At present, the development of wireless communication technology. Wireless communication technology from 1G frequency band to 5G frequency band, the frequency band is higher and higher, at the same time, the bandwidth is also larger and larger. For example, the bandwidth of N77 frequency band and N79 frequency band in 5G frequency band reaches 900MHz and 600MHz respectively. Bulk acoustic wave filter can meet the bandwidth requirement of 5G frequency band. The XBAR filter in the bulk acoustic wave filter can achieve an electromechanical coupling coefficient of 20% or more, thereby achieving a larger bandwidth. Among them, the Lamb wave resonator is an important component of the XBAR filter.

[0003] The Lamb wave resonator of the related art generally includes a high acoustic velocity material substrate and a piezoelectric layer located above the high acoustic velocity material substrate, and a first interdigital transducer and a second interdigital transducer are respectively arranged on the upper surface and the lower surface of the piezoelectric layer. The interdigital transducer (IDT for short). The interdigital electrodes of the first interdigital transducer and the second interdigital transducer are opposite to each other in the stacking direction through the piezoelectric layer, and have the same electrode width, electrode thickness, electrode spacing and excitation acoustic wave wavelength λ.

[0004] However, the Lamb wave resonator of the related art has the same electrode width, and this structure causes the existence of the main mode and other modes, that is, the special vibration form in the first interdigital transducer and the second interdigital transducer, which is easily affected by the transverse mode or other modes, and produces unnecessary ripple, etc., which is a limitation to actual use. To solve this problem, some other Lamb wave resonators use different duty cycles to solve the influence of the vibration form, the duty cycle of the grid-shaped electrode of the comb-shaped electrode in the center region of the overlapping region is different from the duty cycle of the grid-shaped electrode of the comb-shaped electrode in the edge region of the overlapping region, the grid-shaped electrode of each of the comb-shaped electrodes overlaps with the grid-shaped electrode of the other comb-shaped electrode in the overlapping region, and the width of the grid-shaped electrode of the first comb-shaped electrode in the center region is different from the width of the grid-shaped electrode of the second comb-shaped electrode in the center region. However, this structure has many unnecessary vibration modes in the passband. These modes will have adverse effects on the passband in the passband. How to improve the in-band insertion loss and reduce the ripple, improve the in-band smoothness, and further improve the filtering performance is a technical problem to be solved.

[0005] Therefore, it is necessary to provide a new Lamb wave resonator and related filter to solve the above problems. SUMMARY

[0006] In order to solve the above technical problems, the present application provides a Lamb wave resonator and filter with improved in-band insertion loss, reduced ripples, high in-band smoothness and good filtering performance.

[0007] In order to solve the above technical problems, the present application provides a Lamb wave resonator and filter with improved in-band insertion loss, reduced ripples, high in-band smoothness and good filtering performance.

[0008] Preferably, the duty cycle of the first interdigital transducer along the length direction and the duty cycle of the second interdigital transducer along the length direction both include two; the first interdigital transducer includes a first segment and a second segment extended from the first segment, and the second interdigital transducer includes a third segment and a fourth segment extended from the third segment; the duty cycle of the first segment is the same as that of the third segment, and the duty cycle of the second segment is the same as that of the fourth segment.

[0009] Preferably, the width of the first segment is greater than that of the second segment, and the width of the third segment is greater than that of the fourth segment.

[0010] Preferably, the duty cycle of the first segment and the duty cycle of the third segment are both 0.3, and the duty cycle of the second segment and the duty cycle of the fourth segment are both 0.2.

[0011] Preferably, the duty cycle ranges from 0.1 to 0.9.

[0012] Preferably, along the length direction, the duty cycle of the first interdigital transducer gradually decreases from one end to the other end, and the duty cycle of the second interdigital transducer gradually decreases or increases from one end to the other end.

[0013] Preferably, the piezoelectric substrate is made of AlN material, ZnO material or LiTaO3 material with fixed cut angle.

[0014] Preferably, the thickness of the piezoelectric substrate is 0.1λ to 4λ, and λ is the wavelength of the Lamb wave.

[0015] Preferably, the sum of the width of the first interdigital transducer or the width of the second interdigital transducer and the spacing distance of the first interdigital transducer and the second interdigital transducer is a period P, and the following formula is satisfied: λ=2P.

[0016] In a second aspect, embodiments of the present application provide a filter comprising the above-mentioned Lamb wave resonator provided by embodiments of the present application.

[0017] Compared with the related art, the Lamb wave resonator and the filter of the present application form two-dimensional electrodes on a two-dimensional plane by respectively spacing the first interdigital transducer and the second interdigital transducer on the same side of the piezoelectric substrate, and mirror-symmetrically arranging the first interdigital transducer and the second interdigital transducer about the central axis, and the duty cycles of the first interdigital transducer and the second interdigital transducer along the length direction both include multiple and synchronously change. This structure makes the Lamb wave resonator retain the main mode while suppressing other redundant modes, and the advantages of the synchronously changing duty cycles are that the Lamb wave resonator can improve the in-band insertion loss and reduce the ripple, and can further improve the smoothness in the passband, thereby improving the filtering performance of the Lamb wave resonator. Therefore, this circuit structure makes the Lamb wave resonator and the filter can improve the in-band insertion loss and reduce the ripple, have high in-band smoothness and good filtering performance. BRIEF DESCRIPTION OF DRAWINGS

[0018] The present application will be described in detail below with reference to the accompanying drawings. The above or other aspects of the present application will become more apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 FIG. 1 is a structural schematic diagram of a Lamb wave resonator according to an embodiment of the present application;

[0020] Figure 2 FIG. 2 is a structural schematic diagram of a first interdigital transducer and a second interdigital transducer of the Lamb wave resonator according to an embodiment of the present application;

[0021] Figure 3 FIG. 3 is an abs parameter frequency curve schematic diagram of the Lamb wave resonator according to an embodiment of the present application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0023] The specific embodiments described herein are shown in the drawings as specific embodiments of the application, and to explain the best mode contemplated, and are not meant to be limiting as to the scope of the application. Other embodiments will occur to those skilled in the art upon consideration of the specification and may be derived from the disclosure, including variations and modifications from the specific embodiments described herein, without departing from the scope of the application. Accordingly, the application is not limited as to either the specific embodiments disclosed herein or to the general description of applications thereof, including other embodiments that will occur to one of ordinary skill in the art. Changes in form and substitution of equivalents are contemplated as circumstances can suggest such alterations.

[0024] The embodiment of the application provides a Lamb wave resonator 100.

[0025] Please refer to Figures 1-2 as shown in the drawings, wherein, Figure 1 is a schematic structural diagram of the Lamb wave resonator.

[0026] The Lamb wave resonator 100 comprises a piezoelectric substrate 1, a first interdigital transducer 2 and a second interdigital transducer 3.

[0027] In the embodiment, the piezoelectric substrate 1 is made of AlN material or ZnO material or LiTaO3 material with fixed cutting angle.

[0028] The thickness h1 of the piezoelectric substrate 1 is 0.1 lambda to 4 lambda, and lambda is a Lamb wave wavelength. The piezoelectric substrate 1 with the thickness h1 of 0.1 lambda to 4 lambda can be matched with the first interdigital transducer 2 and the second interdigital transducer 3 of the application, and the structure can make the Lamb wave resonator 100 have different impedances caused by mechanical vibration near the resonance frequency of the first interdigital transducer 2 and the second interdigital transducer 3, and suppress the transverse mode, so that the Lamb wave resonator 100 retains the main mode while suppressing other redundant modes.

[0029] The first interdigital transducer 2 and the second interdigital transducer 3 are located on the same side of the piezoelectric substrate 1 and are arranged at intervals. The first interdigital transducer 2 and the second interdigital transducer 3 form two-dimensional electrodes on a two-dimensional plane. Specifically, the first interdigital transducer 2 is used to be connected to an external signal source. The second interdigital transducer 3 is used to be connected to the ground. The first interdigital transducer 2 generates resonance with the second interdigital transducer 3 after receiving the signal sent by the signal source, and has different impedances caused by mechanical vibration near the resonance frequency, so as to realize filtering of the signal.

[0030] In the embodiment, the material of the first interdigital transducer 2 and the second interdigital transducer 3 can be single element materials such as Al, Cu, Pt, Au and Ti, or alloys, or a stack of single element materials such as Al, Cu, Pt, Au and Ti.

[0031] The first interdigital transducer 2 and the second interdigital transducer 3 are both in the same long strip shape. That is, the first interdigital transducer 2 and the second interdigital transducer 3 are made of the same material and have the same shape, so that the first interdigital transducer 2 and the second interdigital transducer 3 are beneficial to the layout design and process manufacturing of the Lamb wave resonator 100, and are beneficial to the design and application of the Lamb wave resonator 100.

[0032] Specifically, an axis along the length direction of the first interdigital transducer 2 and located in the middle of the first interdigital transducer 2 and the second interdigital transducer 3 is defined as a middle axis X. The length direction is consistent with the direction of the middle axis X. The first interdigital transducer 2 and the second interdigital transducer 3 are mirror-symmetrically arranged about the middle axis X. That is, the first interdigital transducer 2 and the second interdigital transducer 3 have the same shape.

[0033] Please refer to Figure 1 As shown in the figure, the sum of the width W1 of the first interdigital transducer 2 or the width W2 of the second interdigital transducer 3 and the interval distance W3 of the first interdigital transducer 2 and the second interdigital transducer 3 is the period P. Specifically, the period of the first interdigital transducer 2 is P1, and the period of the second interdigital transducer 3 is P2. Since the width W1 and the width W2 are the same, that is, P1=P2=P. The Lamb wave wavelength λ satisfies the following formula: λ=2P.

[0034] The duty cycle is defined as the ratio of the width of the two-dimensional electrode to the period P. The duty cycle of the first interdigital transducer 2 is W1 / P1. The duty cycle of the second interdigital transducer 3 is W2 / P2. In this embodiment, the duty cycle ranges from 0.1 to 0.9. Of course, it is not limited to this, and the numerical range of the duty cycle can also be adjusted according to the design needs.

[0035] In order to improve the in-band insertion loss and reduce the ripple, and improve the in-band smoothness, thereby improving the filtering performance, the first interdigital transducer 2 and the second interdigital transducer 3 are not simple long strip structures, but have certain changes in the two-dimensional plane. The duty cycle of the first interdigital transducer 2 along the length direction and the duty cycle of the second interdigital transducer 3 along the length direction both include multiple and change synchronously. Each duty cycle of the first interdigital transducer 2 and the duty cycle of the second interdigital transducer 3 adjacent to the first interdigital transducer 2 and perpendicular to the length direction are the same. That is, the duty cycle of the first interdigital transducer 2 and the duty cycle of the second interdigital transducer 3 perpendicular to the length direction are the same.

[0036] Along the length direction, the duty cycle of the first interdigital transducer 2 gradually synchronously decreases from one end to the other end; the duty cycle of the second interdigital transducer 3 gradually synchronously decreases or increases from one end to the other end. The first interdigital transducer 2 and the second interdigital transducer 3 synchronously decrease or increase in the two-dimensional plane can make the Lamb wave resonator 100 suppress other modes while keeping the main mode, so as to improve the in-band insertion loss and reduce the ripple.

[0037] In the embodiment, the same two-dimensional electrode adopts two width long strips to form a synchronous change structure. The width refers to the length of the two-dimensional electrode perpendicular to the length direction. Specifically, the duty cycle of the first interdigital transducer 2 along the length direction and the duty cycle of the second interdigital transducer 3 along the length direction both include two. The first interdigital transducer 2 includes a first section 21 and a second section 22 extended from the first section 21. The width W11 of the first section 21 is greater than the width W12 of the second section 22.

[0038] The second interdigital transducer 3 includes a third section 31 and a fourth section 32 extended from the third section 31. The width W21 of the third section 31 is greater than the width W22 of the fourth section 32.

[0039] Therefore, the first interdigital transducer 2 and the second interdigital transducer 3 synchronously decrease along the direction of the central axis X.

[0040] The duty cycle of the first section 21 is W11 / P11; the duty cycle of the third section 31 is W31 / P21. The interval distance between the first section 21 and the third section 31 is W31, where W31 is the same as W11, so P21 is the same as P11. The duty cycle of the first section 21 is the same as the duty cycle of the third section 31. The duty cycle of the first section 21 and the duty cycle of the third section 31 are both 0.3. That is, the above-mentioned duty cycle of the first interdigital transducer 2 and the duty cycle of the second interdigital transducer 3 perpendicular to the length direction are the same.

[0041] The duty cycle of the second section 22 is W12 / P12; the duty cycle of the fourth section 32 is W32 / P22. The interval distance between the second section 22 and the fourth section 32 is W32, where W32 is the same as W12, so P22 is the same as P12. The duty cycle of the second section 22 is the same as the duty cycle of the fourth section 32. The duty cycle of the second section 22 and the duty cycle of the fourth section 32 are both 0.2.

[0042] The first interdigital transducer 2 is configured with a first segment 21 and a second segment 22, and the second interdigital transducer 3 is configured with a third segment 31 and a fourth segment 32. The same two-dimensional electrode uses two wide strips to form a synchronously changing structure. This structure is simple and easy to design and apply. The synchronous change of the first interdigital transducer 2 and the second interdigital transducer 3 allows for impedance differences caused by mechanical vibration near the resonant frequency, enabling signal filtering and further improving passband smoothness and suppressing transverse modes. To verify the technical effect of the synchronous change of the first interdigital transducer 2 and the second interdigital transducer 3, the parameters of the Lamb wave resonator 100 are evaluated through model simulation. The simulation verification is as follows:

[0043] Compared with related technologies, specifically, the advantage of the synchronously changing duty cycle of the first interdigital transducer 2 and the second interdigital transducer 3 is that it can further improve the smoothness within the passband, thereby improving the filtering performance of the Lamb wave resonator 100. Please refer to the appendix. Figure 3 As shown, Figure 3 This is a schematic diagram of the frequency curve of the ABS parameter of the Lamb wave resonator 100 of the present invention. The 5G band exhibits high smoothness and good filtering performance within its passband. The thickness h1 of the piezoelectric substrate 1 is 0.1λ to 4λ, and the duty cycle of the first interdigital transducer 2 and the second interdigital transducer 3 varies synchronously, as determined by the attached... Figure 3 Simulation results show that the Lamb wave resonator 100 of the present invention can improve in-band insertion loss and reduce ripple, further improve in-band smoothness, and further suppress transverse modes, resulting in good filtering performance.

[0044] The present invention also provides a filter. The filter includes the Lamb resonator 100. Because the filter uses the Lamb resonator 100 of the present invention, the filter can improve in-band insertion loss and reduce ripple, and has high in-band smoothness and good filtering performance.

[0045] Compared with related technologies, the Lamb resonator and filter of the present invention form two-dimensional electrodes on a two-dimensional plane by spaced first and second interdigital transducers on the same side of a piezoelectric substrate, and the first and second interdigital transducers are mirror-symmetrically arranged about the central axis. The duty cycles of both the first and second interdigital transducers along the length direction include multiple components and change synchronously. This structure allows the Lamb resonator to retain the dominant mode while suppressing other redundant modes. The synchronously changing duty cycle not only simplifies manufacturing but also improves in-band insertion loss and reduces ripple, further enhancing passband smoothness and thus improving the filtering performance of the Lamb resonator. Therefore, this circuit structure enables the Lamb resonator and filter to improve in-band insertion loss, reduce ripple, achieve high in-band smoothness, and provide excellent filtering performance.

[0046] It is to be understood that the embodiments described above are merely illustrative of the present application and should not be considered limiting thereof as the present application can be modified or varied in many ways. Additionally, unless otherwise indicated, terms used herein are to be understood in an "inclusive" rather than an "exclusive" sense. That is, all uses of a term (for example, a numeral or the like) include both of the term's connotations, unless otherwise noted. Furthermore, unless otherwise indicated, all or a portion of any embodiment can be used in combination with all or a portion of any other embodiment.

Claims

1. A Lamb wave resonator, characterized in that, The Lamb wave resonator includes a piezoelectric substrate and a first interdigital transducer and a second interdigital transducer located on the same side of the piezoelectric substrate and spaced apart. Both the first and second interdigital transducers are elongated strips. The axis along the length of the first interdigital transducer and located between the first and second interdigital transducers is defined as the central axis. The first and second interdigital transducers are mirror-symmetrical about the central axis. The duty cycles of the first and second interdigital transducers along the length are both multiple and change synchronously. Each duty cycle of the first interdigital transducer is the same as the duty cycle of the second interdigital transducer adjacent to the first interdigital transducer and perpendicular to the length. The first interdigital transducer has two duty cycles along the length direction, and the second interdigital transducer has two duty cycles along the length direction; the first interdigital transducer includes a first segment and a second segment extending from the first segment, and the second interdigital transducer includes a third segment and a fourth segment extending from the third segment; The duty cycle of the first segment is the same as that of the third segment, and the duty cycle of the second segment is the same as that of the fourth segment.

2. The Lamb wave resonator according to claim 1, characterized in that, The width of the first segment is greater than the width of the second segment, and the width of the third segment is greater than the width of the fourth segment.

3. The Lamb wave resonator according to claim 2, characterized in that, The duty cycle of the first segment and the duty cycle of the third segment are both 0.3, and the duty cycle of the second segment and the duty cycle of the fourth segment are both 0.

2.

4. The Lamb wave resonator according to claim 1, characterized in that, The duty cycle ranges from 0.1 to 0.

9.

5. The Lamb wave resonator according to claim 1, characterized in that, Along the length direction, the duty cycle of the first interdigital transducer gradually decreases synchronously from one end to the other; the duty cycle of the second interdigital transducer gradually decreases or increases synchronously from one end to the other.

6. The Lamb wave resonator according to claim 1, characterized in that, The piezoelectric substrate is made of AlN material, ZnO material, or LiTaO3 material with a fixed chamfer.

7. The Lamb wave resonator according to claim 1, characterized in that, The thickness of the piezoelectric substrate is 0.1λ to 4λ, where λ is the Lamb wave wavelength.

8. The Lamb wave resonator according to claim 6, characterized in that, The sum of the width of the first interdigital transducer or the width of the second interdigital transducer and the interval distance between the first interdigital transducer and the second interdigital transducer is the period P, which satisfies the following formula: λ=2P.

9. A filter, characterized in that, The filter includes a Lamb wave resonator as described in any one of claims 1-8.

Images