Acoustic wave filter

Abstract

The application provides an acoustic wave filter, at least two resonators have different interdigital duty cycles, the interdigital period and the interdigital duty cycle of the resonators on the series arm and the parallel arm are respectively arranged to regulate the vibration characteristics of the spurious mode from the perspective of the excitation of the acoustic wave mode, the excitation principle and the vibration characteristics of the spurious acoustic wave mode are explained, the vibration characteristic change trend of the spurious mode under different thickness wavelength ratios is utilized to realize the superposition and cancellation of the directional spurious stress and strain, thereby the spurious mode is suppressed, the influence of the spurious response on the filter passband is eliminated, the passband response of the acoustic wave filter is effectively purified and the flat passband is realized, the insertion loss is reduced, the transmission efficiency of the passband signal is improved, and the device structure and the preparation process are relatively simple, and the device is easy to realize and apply.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology and relates to an acoustic wave filter. Background Technology

[0002] Thanks to its advantages of small size, low cost and high performance, acoustic filter technology has become one of the mainstream filter technologies.

[0003] Due to the strong anisotropy of the physical parameters of piezoelectric single-crystal materials, various acoustic wave modes with different sound velocities can be excited in single-crystal piezoelectric substrates, which can meet the filtering requirements of different frequency bands. In addition to traditional acoustic wave filter technology based on single-crystal piezoelectric substrates, existing technologies have also proposed acoustic wave resonators and filters based on piezoelectric heterostructure substrates. These combine piezoelectric thin films with high-velocity acoustic support substrates to simultaneously utilize the anisotropy of piezoelectric materials and the high-velocity acoustic characteristics of the support substrate to effectively excite other acoustic wave modes with even higher sound velocities, thus expanding into high-frequency application areas.

[0004] However, regardless of whether it is a single-crystal piezoelectric substrate or a piezoelectric heterostructure substrate, the anisotropy of the piezoelectric single crystal leads to non-single acoustic wave excitation in a given propagation direction. Therefore, when one acoustic wave mode is defined as the target mode, the excitation of other acoustic waves will become unwanted stray modes. These stray modes will cause severe jitter in the filter passband or band edge, thus affecting signal transmission. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an acoustic filter to solve the stray response problem in or near the passband of the acoustic filter in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides an acoustic wave filter comprising a plurality of resonators, wherein at least two of the resonators have different interdigitated duty cycles, and the plurality of resonators are combined to form an electrical topology, the electrical topology comprising resonator series arms and resonator parallel arms.

[0007] Optionally, the cross-finger duty cycle ranges from 0.15 to 0.85.

[0008] Optionally, when the interdigitated period is used to define the wavelength of the sound wave, the interdigitated period of the resonator located on the parallel arm of the resonator is greater than the interdigitated period of the resonator located on the series arm of the resonator, and the interdigitated duty cycle of the resonator located on the parallel arm of the resonator is greater than the interdigitated duty cycle of the resonator located on the series arm of the resonator.

[0009] Optionally, the interdigital periods of the resonators located on the series arms of the resonators may be the same, different, or partially the same, and the duty cycles of the interdigital periods of the resonators located on the series arms of the resonators may be the same, different, or partially the same; the interdigital periods of the resonators located on the parallel arms of the resonators may be the same, different, or partially the same, and the duty cycles of the interdigital periods of the resonators located on the parallel arms of the resonators may be the same, different, or partially the same.

[0010] Optionally, the interdigital thickness of the resonator may be one or a combination of the same and different, and the interdigital arrangement direction of the resonator may be one or a combination of the same and different.

[0011] Optionally, the resonator includes a piezoelectric substrate and interdigitated electrodes stacked from bottom to top. The piezoelectric substrate is made of materials including lithium niobate, lithium tantalate, quartz, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, lead magnesium niobate titanate, gallium nitride, gallium oxide, or gallium arsenide.

[0012] Optionally, the resonator includes a support substrate, a piezoelectric thin film, and interdigitated electrodes stacked from bottom to top, wherein the slow shear wave velocity of the support substrate is higher than the velocity of the piezoelectric thin film. The support substrate is made of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, or aluminum nitride. The piezoelectric thin film is made of lithium niobate, lithium tantalate, quartz, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, lead magnesium niobate titanate, gallium nitride, gallium oxide, or gallium arsenide.

[0013] Optionally, a dielectric layer is further disposed between the supporting substrate and the piezoelectric thin film. The dielectric layer includes a high-velocity dielectric layer with a sound velocity higher than that of the supporting substrate or a low-velocity dielectric layer with a sound velocity lower than that of the piezoelectric thin film. The high-velocity dielectric layer is made of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, aluminum nitride, or silicon nitride. The low-velocity dielectric layer is made of silicon oxide, fluorinated silicon oxide, silicon oxynitride, polycrystalline silicon, tantalum pentoxide, or tellurium dioxide.

[0014] Optionally, the dielectric layer may further include a layer disposed on the piezoelectric film or on the interdigitated electrode.

[0015] Optionally, the interdigital electrodes in the resonator are made of any one or an alloy of copper, silver, gold, aluminum, platinum, nickel, molybdenum, tungsten, chromium, and titanium; the interdigital electrodes include single-layer interdigital electrodes or composite multilayer interdigital electrodes.

[0016] As described above, the acoustic filter of the present invention has at least two resonators with different interdigital duty cycles. By setting the interdigital period and interdigital duty cycle of the resonators on the series arm and parallel arm respectively, the vibration characteristics of stray modes are controlled from the perspective of acoustic mode excitation. This explains the excitation principle and vibration characteristics of stray acoustic modes. By utilizing the variation trend of the vibration characteristics of stray modes under different thickness-wavelength ratios, the superposition and cancellation of directional clutter stress and strain are achieved, thereby suppressing stray modes, eliminating the influence of stray response on the filter passband, effectively purifying the passband response of the acoustic filter and achieving a flat passband, reducing insertion loss, improving the transmission efficiency of the passband signal, and the device structure and fabrication process are relatively simple, making it easy to implement and apply. Attached Figure Description

[0017] Figure 1 The diagram shown is a cross-sectional schematic of the acoustic resonator in Comparative Example 1 of the present invention.

[0018] Figure 2 The simulated admittance response curve and mode shape at typical frequency points of the acoustic resonator in Comparative Example 1 of this invention are shown.

[0019] Figure 3 The figure shown is a comparison of the simulated admittance response curves of the acoustic resonator in Comparative Example 1 of this invention under different interdigital periods.

[0020] Figure 4 The diagram shows the simulated admittance response curve and mode shape at typical frequency points of the acoustic resonator in Comparative Example 1 of this invention when only the e15 parameter of the piezoelectric thin film is effective.

[0021] Figure 5 The diagram shows the simulated admittance response curve and mode shape at typical frequency points of the acoustic resonator in Comparative Example 1 of this invention when only the c14 and c34 parameters of the piezoelectric thin film are valid.

[0022] Figure 6 The diagram shows the simulated admittance response curve and mode shape at typical frequency points of the acoustic resonator in Comparative Example 1 of this invention when only the c56, e31, and e33 parameters of the piezoelectric thin film are valid.

[0023] Figure 7 The diagram shows the electrical topology and interdigitated structure of the acoustic resonator in Comparative Example 2 of this invention.

[0024] Figure 8 The resonator and filter responses of Comparative Example 2 of this invention are shown when using a conventional interdigital duty cycle.

[0025] Figure 9 The diagram shows the electrical topology of the acoustic filter and the interdigitated resonator structure in Example 1 of this invention.

[0026] Figure 10 The resonator and filter responses are shown in Example 1 of this invention when using the interdigital duty cycle design proposed in this invention.

[0027] Figure 11 The diagram shown illustrates the electrical topology of an acoustic filter according to the present invention.

[0028] Explanation of reference numerals in the attached figures

[0029] 100 Supporting substrate

[0030] 200 dielectric layer

[0031] 300 piezoelectric film

[0032] 400 interdigital electrodes Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0035] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include orientations of the device in use or operation other than those depicted in the drawings, and may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact. Furthermore, when a layer is referred to as “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0036] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0037] This application provides an acoustic wave filter, which includes multiple resonators, wherein at least two of the resonators have different interdigital duty cycles (DF), and the multiple resonators are combined to form an electrical topology, which includes resonator series arms and resonator parallel arms.

[0038] By setting the interdigital duty cycles of at least two of the resonators to be different, spurious responses can be eliminated or shifted to regions far from the passband, thereby suppressing spurious modes, eliminating the influence of spurious responses on the filter passband, effectively purifying the passband response of the acoustic filter and achieving a flat passband, reducing insertion loss, and improving the transmission efficiency of the passband signal.

[0039] As an example, the interdigital duty cycle can range from 0.15 to 0.85, such as DF being 0.15, 0.3, 0.5, 0.6, 0.85, etc. When the interdigital duty cycle of the resonator is adjusted, the stress and strain that excite stray modes can be controlled, thereby changing the vibration characteristics of the stray modes and achieving the suppression of stray modes.

[0040] As an example, when the wavelength of an acoustic wave is defined using the interdigitated period, the interdigitated period of the resonator located on the parallel arm of the resonator is greater than the interdigitated period of the resonator located on the series arm of the resonator, and the interdigitated duty cycle of the resonator located on the parallel arm of the resonator is greater than the interdigitated duty cycle of the resonator located on the series arm of the resonator.

[0041] As an example, the interdigital periods of the resonators located on the series arms of the resonators may be the same, different, or partially the same, and the interdigital duty cycles of the resonators located on the series arms of the resonators may be the same, different, or partially the same; the interdigital periods of the resonators located on the parallel arms of the resonators may be the same, different, or partially the same, and the interdigital duty cycles of the resonators located on the parallel arms of the resonators may be the same, different, or partially the same.

[0042] Specifically, the interdigital periods and duty cycles of the multiple resonators connected in series on the series arm of the resonator can be all the same, or they can be different from each other, or several of the resonators can have the same interdigital periods and duty cycles. The design of having the same interdigital period and the same interdigital duty cycle is independent; it can be that only the interdigital period is the same, only the interdigital duty cycle is the same, both the interdigital period and duty cycle are the same, or neither the interdigital period nor the duty cycle is different, depending on the requirements. Similarly, the interdigital periods and duty cycles of the multiple resonators connected in parallel on the parallel arm of the resonator can be deduced, but will not be elaborated here.

[0043] As an example, the interdigital thickness of the resonator may be one or a combination of the same and different, and the interdigital arrangement direction of the resonator may be one or a combination of the same and different.

[0044] Specifically, the interdigitated finger thickness of the resonator located on the series arm and the resonator located on the parallel arm can be the same, and the interdigitated finger arrangement direction can be the same; or the interdigitated finger thickness is the same, and the interdigitated finger arrangement direction is different; or the interdigitated finger thickness is different, and the interdigitated finger arrangement direction is the same; or the interdigitated finger thickness is different, and the interdigitated finger arrangement direction is different. The specific configuration can be set as needed.

[0045] As an example, the resonator may include a piezoelectric substrate and interdigitated electrodes stacked from bottom to top. The material of the piezoelectric substrate may include lithium niobate, lithium tantalate, quartz, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, lead magnesium niobate titanate, gallium nitride, gallium oxide, or gallium arsenide.

[0046] As an example, the resonator may include a support substrate, a piezoelectric thin film, and interdigitated electrodes stacked from bottom to top, and the sound velocity of the support substrate may be higher than that of the piezoelectric thin film. The material of the support substrate may include silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, or aluminum nitride. The material of the piezoelectric thin film may include lithium niobate, lithium tantalate, quartz, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, lead magnesium niobate titanate, gallium nitride, gallium oxide, or gallium arsenide.

[0047] As an example, a dielectric layer may also be disposed between the supporting substrate and the piezoelectric thin film. The dielectric layer may include a high-velocity dielectric layer with a sound velocity higher than that of the supporting substrate or a low-velocity dielectric layer with a sound velocity lower than that of the piezoelectric thin film. The high-velocity dielectric layer may be made of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, aluminum nitride, or silicon nitride. The low-velocity dielectric layer may be made of silicon oxide, fluorinated silicon oxide, silicon oxynitride, polycrystalline silicon, tantalum pentoxide, or tellurium dioxide.

[0048] Furthermore, the dielectric layer may also be disposed on the piezoelectric film or on the interdigitated electrode.

[0049] As an example, the interdigital electrodes in the resonator are made of any one or an alloy of copper, silver, gold, aluminum, platinum, nickel, molybdenum, tungsten, chromium, and titanium; the interdigital electrodes include single-layer interdigital electrodes or composite stacked interdigital electrodes.

[0050] The following section, with comparative examples and specific illustrations, further introduces the specific principles, usage, and effects of the acoustic filter described in this application.

[0051] like Figure 1 As shown, a sapphire substrate is used as the supporting substrate 100, silicon oxide (SiO2) is used as the dielectric thin film 200, a lithium niobate (LiNbO3) layer rotated YX 36° is used as the piezoelectric thin film 300, and metallic copper (Cu) is used as the interdigitated electrode 400. The target acoustic wave mode to be excited is the horizontal shear surface acoustic wave (SH-SAW) mode.

[0052] Comparative Example 1:

[0053] based on Figure 1 The structure shown provides an acoustic resonator with the following structural parameters: a Cu electrode thickness of 96 nm, an interdigital period of 1.6 μm, an interdigital electrode duty cycle of 0.5, a LiNbO3 thin film with a thickness of 360 nm cut by YX 36° rotation and Euler angles of (0, 54, 0), a SiO2 dielectric layer thickness of 200 nm, a Sapphire substrate, and SH-SAW excitation.

[0054] Figure 2 The simulated admittance response and mode shapes at typical frequencies of the acoustic resonator corresponding to Comparative Example 1 are shown. The simulated admittance response corresponds to... Figure 2 (a), and Figure 2 In (a), the four frequency points are (i) 2056MHz, (ii) 2095MHz, (iii) 2102MHz and (iv) 2358MHz, and the mode shapes correspond to... Figure 2 (b)- Figure 2 (d) By comparison, it can be seen that the stray responses (ii) and (iii) correspond to Rayleigh waves, and the resonance peak appears in the passband of the target mode.

[0055] Figure 3 The diagram shows a comparison of the simulated admittance response curves of the acoustic resonators based on the structure and thin film parameters described in Comparative Example 1, with only the interdigital period parameter changed from 1.2 μm to 2.4 μm. It can be seen that the stray response Rayleigh resonance peaks all appear within the passband of the target mode. If a filter is built using a resonator with such a stray response within the passband, it will cause severe jitter within the filter's passband, resulting in signal distortion.

[0056] Regarding Comparative Example 1 and the Rayleigh spurious mode, the following describes the principle of Rayleigh mode suppression achieved by this application using at least two resonators with different interdigital duty cycles. This analysis method can be extended to other resonators, filter structures, and other spurious modes.

[0057] Specifically, the reasons for the appearance of Rayleigh resonance peaks can be divided into the following two types: one is intrinsically excited Rayleigh resonance, and the other is strain excited by stress in other directions or torsional strain on other surfaces.

[0058] The piezoelectric constant matrix of a LiNbO3 piezoelectric thin film rotated YX 36° is shown below.

[0059]

[0060] When a specific parameter is not zero, it contributes to the excitation of the acoustic mode. Taking three parameters as examples, we can illustrate the contribution of the piezoelectric constant to the excitation of the Rayleigh mode. Parameter e15 corresponds to the strain in the xz plane excited by the electric field along the x-direction (first direction) of the acoustic wave propagation, which is the source of Rayleigh intrinsic excitation. Parameter e31 corresponds to the strain in the x-direction excited by the electric field along the z-direction (third direction) of the thickness, thus causing strain in the x-direction. Parameter e33 corresponds to the strain in the z-direction excited by the electric field along the third direction, thus causing strain in the z-direction. The strain in the x-direction and the strain in the z-direction together cause strain in the xz plane, leading to the excitation of Rayleigh.

[0061] In addition, the elastic constant matrix of the LiNbO3 piezoelectric thin film rotated YX 36° is shown below.

[0062]

[0063] When a specific parameter is not zero, the resulting stress or strain may also contribute to the excitation of the acoustic mode. Taking three parameters as examples, we can illustrate the contribution of the elastic constant to the excitation of the Rayleigh mode. Parameter c14 corresponds to the following: when there is stress in the first direction x, it will cause strain in the yz plane. When strain occurs in the yz plane, it will also lead to stress in the first direction x. Since the bottom of the piezoelectric film is connected to the SiO2 layer and the Sapphire substrate (i.e., the bottom is fixed), the strain in the yz plane will also transmit and cause strain in the xz plane, thus leading to Rayleigh mode excitation. Rayleigh mode excitation; parameter c34 corresponds to: when there is stress in the z-direction, it will cause strain in the yz plane; when strain occurs in the yz plane, it will drive the generation of stress in the z-direction. Similarly, since the bottom of the piezoelectric film is fixed, the strain in the yz plane will be transmitted to cause strain in the xz plane, thus leading to the excitation of Rayleigh mode; parameter c56 corresponds to: when there is stress in the xy direction, it will cause strain in the xz plane, and when strain occurs in the xz plane, it will also drive the generation of stress in the xy direction, thus also leading to the excitation of Rayleigh mode.

[0064] Since the stress or Rayleigh strain generated by these parameters is directional, when all of them are present (not zero), the forces in different directions are superimposed to form the final Rayleigh vibration mode. Therefore, when the stress or Rayleigh strain generated by the superposition of the effects of these parameters exactly cancels each other out, Rayleigh resonance no longer exists. That is, no stray response will appear in the resonance response of the target mode SH-SAW, and Rayleigh resonance can be successfully eliminated.

[0065] Based on the above analysis and the principles derived therefrom, and utilizing these principles, the excitation and suppression of stray modes can be controlled from the perspective of stress and strain superposition, thereby eliminating stray modes or migrating them to regions far from the target mode passband to eliminate interference.

[0066] Regarding the parameters mentioned above that contribute to Rayleigh excitation, when only the piezoelectric constant e15 is considered for the intrinsic excitation of Rayleigh, such as Figure 4As shown in (a), the Rayleigh mode becomes very weak and almost non-existent as the interdigital duty cycle changes from 0.2 to 0.8. This indicates that when a strong Rayleigh response exists, it is mainly due to the stress generated by other parameters or the strain on other surfaces that drives the excitation of Rayleigh. Therefore, it is mainly necessary to control the influence of parameters other than e15, such as c14, c34, c56, e31, and e33. In addition, the stress distribution of Rayleigh at DF = 0.5 and 0.6 was extracted. In the simulation model, the electric field direction is from right to left. Here, we define: when the stress is from right to left (in the same direction as the electric field), it is called normal stress; conversely, when the stress is from left to right (opposite to the electric field direction), it is called reactive force. Figure 4 (b) and Figure 4 As shown in (c), the intrinsically excited Rayleigh stress direction is from left to right, which is the reactive force. From the preceding analysis, it is known that the Rayleigh mode excitation caused by the two parameters c14 and c34 is caused by strain in the xz plane through strain transfer from the yz plane. Therefore, these two can be considered together, with c14 and c34 grouped into group 1, and c56, e31, and e33 grouped into group 2. Figure 5 As shown, when only c14 and c34 are not 0, and the other parameters c56, e31, and e33 are all 0, that is, only the two parameters of the first group are considered to excite Rayleigh, and the stress direction is also a reaction force from left to right, the same as the intrinsically excited stress. Since the parameters of the second group are 0 at this time, that is, there is no stress to counteract this reaction force, Rayleigh gradually strengthens as the interdigital duty cycle increases, indicating that the reaction force gradually becomes stronger as the interdigital duty cycle increases. In order to counteract Rayleigh resonance, it is necessary to increase the opposite normal stress to counteract Rayleigh resonance. The phenomenon that Rayleigh gradually strengthens as the interdigital duty cycle increases also shows that adjusting the interdigital duty cycle can effectively adjust the vibration characteristics of Rayleigh, including stress and strain. On the other hand, considering the influence of the second group of parameters, such as Figure 6As shown, when only c14 and c34 are 0, and the other parameters c56, e31, and e33 are not 0, that is, considering only the three parameters of the second group to excite Rayleigh, the stress direction is a normal stress from right to left, opposite to the stress direction of the first group, which can form a counteracting stress, consistent with the conclusion of the first group above. Since the parameters of the first group are 0 at this time, that is, there is no stress to counteract this normal stress, Rayleigh gradually strengthens as the interdigital duty cycle increases, indicating that the normal stress gradually becomes stronger as the interdigital duty cycle increases. In order to counteract Rayleigh resonance, it is necessary to increase the opposite reaction force to counteract Rayleigh resonance. In addition, it is also shown here that the stress directions caused by these two sets of parameters are opposite. In order to eliminate or suppress stray modes, their magnitudes need to be kept at a consistent level, that is, when the stress caused by the first set of parameters is large, the stress caused by the second set of parameters also needs to be relatively large.

[0067] When adjusting the ratio of the piezoelectric film thickness to the interdigital period (hereinafter referred to as the "thickness-to-wavelength ratio") of the resonator structure, if the interdigital period remains constant, as the thickness of the piezoelectric film increases, the thickness-to-wavelength ratio increases, the torsional stress on the yz plane relatively decreases, and the strain transmitted to the xz plane also relatively decreases. Therefore, the required stress in the opposite direction must also decrease to maintain a similar stress level to counteract Rayleigh vibrations and excitation. Similarly, as the thickness-to-wavelength ratio decreases, if the thickness of the piezoelectric film remains constant and the acoustic wavelength increases, the torsional stress on the yz plane relatively increases, and the strain transmitted to the xz plane also relatively increases. Therefore, the required stress in the opposite direction must also increase to counteract this increased stress and strain and to counteract Rayleigh vibrations and excitation.

[0068] Comparison Figure 5 and Figure 6 The response curves for different interdigital duty cycles show that as the duty cycle increases, the stress increases. Therefore, when the wavelength increases, a relatively larger interdigital duty cycle needs to be matched to achieve mutual cancellation of Rayleigh vibrations. Similarly, when the interdigital duty cycle decreases, the stress decreases. Therefore, when the wavelength decreases, a relatively smaller interdigital duty cycle needs to be matched to achieve mutual cancellation of Rayleigh vibrations. Therefore, when all interdigital duty cycles are 0.5, and Rayleigh clutter occurs, appropriately adjusting the interdigital periods and duty cycles of the resonators on the series and parallel arms, and setting the interdigital duty cycle and the thickness-to-wavelength ratio of the resonator structure to a suitable value, will allow Rayleigh to cancel out and disappear, thus no longer adversely affecting the filter's passband response. Generally, in acoustic filter structures, the interdigital period of the resonator on the parallel arm is greater than that of the resonator on the series arm. Therefore, to eliminate Rayleigh clutter, the interdigital duty cycle of the resonator on the parallel arm must also be correspondingly greater than that of the resonator on the series arm.

[0069] The usage and effects of the acoustic filter of this application are illustrated below through comparison with Example 2 and Example 1, wherein the structure of the acoustic resonator is based on Figure 1 The structure shown has a LiNbO3 thin film with a thickness of 360 nm cut by rotating YX 36°, with its Euler angle set to (0, 54, 0), a SiO2 layer with a thickness of 200 nm, a Sapphire supporting substrate, a Cu interdigitated electrode with a thickness of 96 nm, a target excitation mode of SH-SAW, and as previously mentioned, a Rayleigh wave stray response.

[0070] Comparative Example 2:

[0071] like Figure 7 (a) illustrates the electrical topology of an acoustic filter, wherein the series arm of the resonators includes five resonators, namely S1, S2, S3, S4 and S5, wherein S1 and S5 have the same structure, and S1 and S2 differ only in the number of interdigitated electrode pairs; the parallel arm of the resonators includes four resonators, namely P1, P2, P3 and P4, wherein P1 and P4 have the same structure, P2 and P3 have the same structure, and P1 and P2 differ only in the number of interdigitated electrode pairs. Figure 7 (b) and Figure 7 (c) The structural diagrams of the interdigital electrodes of the resonators are shown respectively. The interdigital period of resonators S1-S5 is 1.6μm and the interdigital duty cycle DF is 0.5. The interdigital period of resonators P1-P4 is 1.94μm and the DF is also 0.5.

[0072] Figure 8 The resonator response when using a standard interdigital duty cycle, i.e., DF = 0.5, is presented, along with the filter response designed using this standard interdigital duty cycle. For example, Figure 8 (a) shows the simulated admittance response diagrams of the resonators on the series and parallel arms. Figure 8 (b) shows the corresponding enlarged passband diagram, in which Rayleigh spurious modes appear. Substituting these two into... Figure 7 The passband response of the acoustic filter constructed from the electrical topology of (a) is as follows: Figure 8 (c)- Figure 8 As shown in (d), where S11 is the reflection parameter and S21 is the transmission parameter, it is obvious that from Figure 8 As shown in the magnified passband diagram of (d), since the Rayleigh spurious responses at both locations fall between the resonant and anti-resonant frequencies, they will cause significant jitter within the filter's passband, resulting in substantial insertion loss and signal distortion. Example 1:

[0073] like Figure 9Figure (a) illustrates the structure of the acoustic filter proposed in this application, wherein resonators S1, S2, S3, S4, and S5 constitute a series arm of the resonators, and resonators P1, P2, P3, and P4 constitute a parallel arm of the resonators, maintaining the same connection with... Figure 7 (a) The electrical topology of the acoustic filter remains unchanged. For the same frequency band, such as Figure 9 (b)- Figure 9 As shown in (c), the DF of resonators S1-S5 on the series arm is designed to be 0.3 and the interdigital period is designed to be 1.77μm; the DF of resonators P1-P4 on the parallel arm is designed to be 0.64 and the interdigital period is designed to be 1.91μm.

[0074] like Figure 10 (a)- Figure 10 (b) Shows the simulated admittance response and passband magnification of the series and parallel resonators after optimization, and... Figure 8 The comparison shows that Figure 10 The stray response Rayleigh resonance peaks in the data have all been eliminated, and as... Figure 10 (c)- Figure 10 As shown in (d), the filter built with this optimized clutter-free resonator has a very flat passband and no longer exhibits significant jitter caused by the Rayleigh response, achieving the expected effect.

[0075] Therefore, the acoustic filter provided by this invention can achieve a clutter-free passband response, and has a simple and flexible structure, simple manufacturing process, low cost, and is suitable for large-scale applications.

[0076] Furthermore, such as Figure 11 As shown, in the electrical topology of the acoustic filter of this application, the resonators electrically connected on the series arm can be different, that is, the resonators on the series arm can have different interdigital periods and / or different interdigital duty cycles. Similarly, the resonators electrically connected on the parallel arm can be different, that is, the resonators on the parallel arm can have different interdigital periods and / or different interdigital duty cycles.

[0077] Furthermore, according to the acoustic filter provided by the present invention, a multi-zero acoustic filter can also be designed, such as designing the interdigital period and duty cycle of each resonator separately.

[0078] For other acoustic resonator structures, the same analysis can be performed on the target acoustic wave and stray acoustic waves using the method described above to determine the directionality of the stress or strain generated by different parameters. By analyzing the clutter vibration mode formed by the superposition of forces with different parameters and directions, the interdigital period and interdigital duty cycle can be designed so that the clutter stress or strain excited after superposition can be exactly canceled out, thereby eliminating stray modes.

[0079] In summary, the acoustic filter of this invention has at least two resonators with different interdigital duty cycles. By setting the interdigital period and interdigital duty cycle of the resonators on the series arm and parallel arm respectively, the vibration characteristics (stress, strain, etc.) of stray modes are controlled from the perspective of acoustic mode excitation. This explains the excitation principle and vibration characteristics of stray acoustic modes. Furthermore, by utilizing the variation trend of the vibration characteristics of stray modes under different thickness-to-wavelength ratios, the superposition and cancellation of directional stray stress and strain are achieved, thereby suppressing stray modes, eliminating the influence of stray response on the filter passband, effectively purifying the passband response of the acoustic filter and achieving a flat passband, reducing insertion loss, and improving the transmission efficiency of the passband signal. Moreover, the device structure and fabrication process are relatively simple, making it easy to implement and apply.

[0080] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An acoustic wave filter, characterized in that, The acoustic filter includes multiple resonators, wherein at least two of the resonators have different interdigitated duty cycles, and the multiple resonators are combined to form an electrical topology. The electrical topology includes series arms and parallel arms of resonators. The interdigitated periods of the resonators located on the series arms may be the same, different, or partially the same, and the interdigitated duty cycles of the resonators located on the series arms may be the same, different, or partially the same. The interdigitated periods and interdigitated duty cycles of the resonators located on the parallel arms may be the same, different, or partially the same, and the interdigitated duty cycles of the resonators located on the parallel arms may be the same, different, or partially the same. By setting the interdigitated periods and interdigitated duty cycles of the resonators on the series arms and parallel arms respectively, the superposition and cancellation of directional clutter stress and strain can be controlled, and the vibration characteristics of stray modes can be controlled from the perspective of acoustic mode excitation, thereby achieving the suppression of stray modes.

2. The acoustic filter according to claim 1, characterized in that: The cross-finger duty cycle ranges from 0.15 to 0.

85.

3. The acoustic filter according to claim 1, characterized in that: When the interdigitated period is used to define the wavelength of an acoustic wave, the interdigitated period of the resonator located on the parallel arm of the resonator is greater than that of the resonator located on the series arm of the resonator, and the interdigitated duty cycle of the resonator located on the parallel arm of the resonator is greater than that of the resonator located on the series arm of the resonator.

4. The acoustic filter according to claim 1, characterized in that: The thickness of the interdigitated fingers corresponding to the resonator includes one or a combination of the same and different thicknesses, and the arrangement direction of the interdigitated fingers corresponding to the resonator includes one or a combination of the same and different orientations.

5. The acoustic filter according to claim 1, characterized in that: The resonator includes a piezoelectric substrate and interdigitated electrodes stacked from bottom to top. The piezoelectric substrate is made of materials including lithium niobate, lithium tantalate, quartz, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, lead magnesium niobate titanate, gallium nitride, gallium oxide, or gallium arsenide.

6. The acoustic filter according to claim 1, characterized in that: The resonator includes a support substrate, a piezoelectric thin film, and interdigitated electrodes stacked from bottom to top, wherein the slow shear wave velocity of the support substrate is higher than that of the piezoelectric thin film. The support substrate is made of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, or aluminum nitride. The piezoelectric thin film is made of lithium niobate, lithium tantalate, quartz, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, lead magnesium niobate titanate, gallium nitride, gallium oxide, or gallium arsenide.

7. The acoustic filter according to claim 6, characterized in that: A dielectric layer is further disposed between the supporting substrate and the piezoelectric thin film. The dielectric layer includes a high-velocity dielectric layer with a sound velocity higher than that of the supporting substrate or a low-velocity dielectric layer with a sound velocity lower than that of the piezoelectric thin film. The high-velocity dielectric layer is made of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, aluminum nitride, or silicon nitride. The low-velocity dielectric layer is made of silicon oxide, fluorinated silicon oxide, silicon oxynitride, polycrystalline silicon, tantalum pentoxide, or tellurium dioxide.

8. The acoustic filter according to claim 7, characterized in that: The dielectric layer also includes a layer disposed on the piezoelectric film or on the interdigitated electrode.

9. The acoustic filter according to claim 1, characterized in that: The interdigitated electrodes in the resonator are made of any one of copper, silver, gold, aluminum, platinum, nickel, molybdenum, tungsten, chromium, and titanium; the interdigitated electrodes include single-layer interdigitated electrodes or composite stacked interdigitated electrodes.

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