Acoustic filter with low temperature drift

Abstract

The present invention provides an acoustic filter with low temperature drift. At least one equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency is arranged on the series arm of the resonator in its electrical topology structure, and the absolute value of the TCF of the at least one equivalent series resonator is less than the absolute value of the TCF of all other equivalent series resonators. Without affecting the passband response, this acoustic filter can effectively enhance the frequency temperature stability of the passband frequency and the frequency at the right edge of the passband of the acoustic filter, reduce the requirement for the resonator bandwidth. Especially when the frequency band adjacent to the right side of the target frequency band of the acoustic filter is crowded, it improves the fault tolerance range on the right side of the target frequency band of the acoustic filter and reduces the design difficulty of the acoustic filter. In addition, when the support substrate of the acoustic wave resonator in the acoustic filter uses a material with high thermal conductivity, the heat dissipation performance of the device can also be improved, further assisting in reducing frequency drift.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronic technology, and particularly relates to an acoustic filter with low temperature drift. Background Art

[0002] With the development of communication technology and the expansion of application frequency bands, most of the 3 GHz and lower frequency bands have been allocated to serve a variety of rich application scenarios such as communication, data transmission, and the Internet of Things. On the one hand, the efficient utilization of frequency bands effectively expands the application fields of intelligent services, and at the same time improves communication speed and service quality, and different applications proceed in an orderly manner within their allocated frequency bands; on the other hand, there is also a problem that the frequency band below 3 GHz is becoming increasingly crowded. To ensure the precise transmission of signals within a specific frequency band, the stability requirements of filtering devices have also increased. However, the stability of the filter passband is closely related to both the operating temperature of the device and the temperature coefficient of the intrinsic frequency (Temperature Coefficient of Frequency, TCF) of the device structure.

[0003] As one of the current mainstream filter technologies, acoustic filter technology has the advantages of small size, low cost, and high performance. The frequency temperature coefficients of common piezoelectric materials such as lithium niobate, lithium tantalate, aluminum nitride, etc. are all negative, that is, as the operating temperature of the device increases, the frequency of the corresponding resonator admittance response decreases, and the overall passband of the corresponding filter moves to the low frequency. The shift of the operating frequency will not only cause distortion of the passband signal and an increase in the loss of the sideband signal, but may also affect the out-of-band rejection of this passband relative to other frequency bands. When the frequency of the acoustic filtering device changes significantly with temperature, the drifted frequency part also needs to be incorporated into the design when designing the filter to ensure that the target passband frequency will not be biased due to temperature changes. This obviously increases the requirements for the resonator bandwidth; and when the target frequency band is adjacent to a crowded frequency band, the reserved frequency band also needs to consider the out-of-band rejection level relative to the adjacent frequency band, and the tolerance range is small. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an acoustic filter with low temperature drift, which is used to solve the problems in the prior art that the frequency temperature stability of the target frequency band of the acoustic filter is poor, increasing the requirements for the resonator bandwidth, or when the target frequency band of the acoustic filter is adjacent to a crowded frequency band, reducing the tolerance range of the acoustic filter design, that is, increasing the design difficulty of the acoustic filter.

[0005] To achieve the above object and other related objects, the present invention provides an acoustic filter with low temperature drift, the acoustic filter includes: m equivalent series resonators and n equivalent parallel resonators, both m and n are natural numbers greater than or equal to 1, and m≥n;

[0006] The m equivalent series resonators are connected in series in turn between the input end and the output end to form a series arm of resonators;

[0007] One ends of the n equivalent parallel resonators are respectively connected to m - 1 nodes between adjacent ones of the equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 parallel arms of resonators; or one ends of the n equivalent parallel resonators are respectively connected to m - 1 nodes between adjacent ones of the equivalent series resonators and the head or the tail of the series arm of resonators, and the other ends of the n equivalent parallel resonators are grounded to form m parallel arms of resonators;

[0008] The resonance frequency of at least one of the equivalent series resonators in the series arm of resonators is higher than that of other equivalent series resonators in the series arm of resonators, the anti - resonance frequency of the at least one equivalent series resonator is lower than that of other equivalent series resonators in the series arm of resonators, and the absolute value of the TCF of the at least one equivalent series resonator is less than the absolute value of the TCF of other equivalent series resonators in the series arm of resonators.

[0009] Optionally, m is an odd number greater than 1;

[0010] All the equivalent series resonators are arranged in a symmetric distribution in physical structure in turn with respect to the ((m + 1) / 2)-th equivalent series resonator;

[0011] The resonance frequency of the ((m + 1) / 2)-th equivalent series resonator in the series arm of resonators is higher than that of other equivalent series resonators in the series arm of resonators, the anti - resonance frequency of the ((m + 1) / 2)-th equivalent series resonator is lower than that of other equivalent series resonators in the series arm of resonators, and the absolute value of the TCF of the ((m + 1) / 2)-th equivalent series resonator is less than the absolute value of the TCF of other equivalent series resonators in the series arm of resonators.

[0012] Further, n = m - 1, and one ends of the n equivalent parallel resonators are respectively connected to m - 1 nodes between adjacent ones of the equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 parallel arms of resonators.

[0013] Further, all the equivalent parallel resonators are arranged in a symmetric distribution in physical structure in turn with respect to the ((m + 1) / 2)-th equivalent series resonator.

[0014] Optionally, the resonance frequency of the equivalent parallel resonator on at least one of the resonator parallel arms among all the resonator parallel arms is higher than that of the equivalent parallel resonators on the other resonator parallel arms, the anti-resonance frequency of the equivalent parallel resonator on the at least one resonator parallel arm is lower than that of the equivalent parallel resonators on the other resonator parallel arms, and the absolute value of the TCF of the equivalent parallel resonator on the at least one resonator parallel arm is smaller than the absolute value of the TCF of the equivalent parallel resonators on the other resonator parallel arms.

[0015] Further, m is an odd number greater than 1, and n = m - 1;

[0016] One ends of the n equivalent parallel resonators are respectively connected to m - 1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 resonator parallel arms;

[0017] All the equivalent series resonators and all the equivalent parallel resonators are arranged in a symmetric distribution in physical structure successively with respect to the (m + 1) / 2-th equivalent series resonator;

[0018] The resonance frequency of the (m + 1) / 2-th equivalent series resonator in the resonator series arm is higher than that of the other equivalent series resonators in the resonator series arm, the anti-resonance frequency of the (m + 1) / 2-th equivalent series resonator is lower than that of the other equivalent series resonators in the resonator series arm, and the absolute value of the TCF of the (m + 1) / 2-th equivalent series resonator is smaller than the absolute value of the TCF of the other equivalent series resonators in the resonator series arm;

[0019] The resonance frequencies of the equivalent parallel resonators on at least two resonator parallel arms that are symmetrically distributed in physical structure with respect to the (m + 1) / 2-th equivalent series resonator among all the resonator parallel arms are higher than those of the equivalent parallel resonators on the other resonator parallel arms, the anti-resonance frequencies of the equivalent parallel resonators on the at least two resonator parallel arms that are symmetrically distributed in physical structure with respect to the (m + 1) / 2-th equivalent series resonator are lower than those of the equivalent parallel resonators on the other resonator parallel arms, and the absolute values of the TCFs of the equivalent parallel resonators on the at least two resonator parallel arms that are symmetrically distributed in physical structure with respect to the (m + 1) / 2-th equivalent series resonator are smaller than the absolute values of the TCFs of the equivalent parallel resonators on the other resonator parallel arms.

[0020] Optionally, the equivalent series resonator is equivalently formed by one acoustic wave resonator, or the equivalent series resonator is equivalently formed by multiple acoustic wave resonators in series and / or parallel; the equivalent parallel resonator is equivalently formed by one acoustic wave resonator, or the equivalent parallel resonator is equivalently formed by multiple acoustic wave resonators in series and / or parallel.

[0021] Optionally, the acoustic filter is formed based on a heterogeneous substrate structure; the heterogeneous substrate structure includes a high-speed support substrate with anisotropy and a piezoelectric thin film with in-plane anisotropy located on the high-speed support substrate, wherein the slow shear wave velocity of the high-speed support substrate is higher than the velocity of the target acoustic wave mode in the piezoelectric thin film.

[0022] Furthermore, the target mode of the acoustic filter is a horizontal shear wave or a longitudinal leaky wave or a longitudinal wave.

[0023] Optionally, the material of the piezoelectric thin film is one 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, gallium arsenide, and the thickness of the piezoelectric thin film does not exceed 0.45λ, where λ is the wavelength of the acoustic wave of the target mode of the acoustic filter; the material of the high-speed support substrate is one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like, gallium nitride, boron carbide, boron nitride, aluminum nitride, and the material of the high-speed support substrate is different from the material of the piezoelectric thin film.

[0024] The present invention also provides an acoustic filter with low temperature drift, which includes: m equivalent series resonators and n equivalent parallel resonators, where m and n are both natural numbers greater than or equal to 1, and m≥n;

[0025] The m equivalent series resonators are connected in series in turn between the input end and the output end to form a resonator series arm;

[0026] One end of each of the n equivalent parallel resonators is respectively connected to m - 1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 resonator parallel arms; or one end of each of the n equivalent parallel resonators is respectively connected to m - 1 nodes between adjacent equivalent series resonators and the head or tail of the resonator series arm, and the other ends of the n equivalent parallel resonators are grounded to form m resonator parallel arms;

[0027] The resonant frequency of the equivalent parallel resonator on at least one of the resonator parallel arms among all the resonator parallel arms is higher than that of the equivalent parallel resonators on the other resonator parallel arms, the anti-resonant frequency of the equivalent parallel resonator on the at least one resonator parallel arm is lower than that of the equivalent parallel resonators on the other resonator parallel arms, and the absolute value of the TCF of the equivalent parallel resonator on the at least one resonator parallel arm is less than the absolute value of the TCF of the equivalent parallel resonators on the other resonator parallel arms.

[0028] Optionally, m is an odd number greater than 1, and n = m - 1;

[0029] One end of each of the n equivalent parallel resonators is respectively connected to m - 1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 resonator parallel arms;

[0030] All the equivalent parallel resonators are arranged in a symmetric distribution in sequence with respect to the (m + 1) / 2-th equivalent series resonator in terms of physical structure;

[0031] The resonant frequency of the equivalent parallel resonators on at least two resonator parallel arms that are symmetrically distributed with respect to the (m + 1) / 2-th equivalent series resonator in terms of physical structure among all the resonator parallel arms is higher than that of the equivalent parallel resonators on the other resonator parallel arms, the anti-resonant frequency of the equivalent parallel resonators on the at least two resonator parallel arms that are symmetrically distributed with respect to the (m + 1) / 2-th equivalent series resonator in terms of physical structure is lower than that of the equivalent parallel resonators on the other resonator parallel arms, and the absolute value of the TCF of the equivalent parallel resonators on the at least two resonator parallel arms that are symmetrically distributed with respect to the (m + 1) / 2-th equivalent series resonator in terms of physical structure is less than the absolute value of the TCF of the equivalent parallel resonators on the other resonator parallel arms.

[0032] Further, all the equivalent series resonators are arranged in a symmetric distribution in sequence with respect to the (m + 1) / 2-th equivalent series resonator in terms of physical structure.

[0033] Optionally, the equivalent series resonator is equivalently formed by one acoustic wave resonator, or the equivalent series resonator is equivalently formed by multiple acoustic wave resonators in a series and / or parallel manner; the equivalent parallel resonator is equivalently formed by one acoustic wave resonator, or the equivalent parallel resonator is equivalently formed by multiple acoustic wave resonators in a series and / or parallel manner.

[0034] Optionally, the acoustic filter is formed based on a heterogeneous substrate structure; the heterogeneous substrate structure includes a high sound velocity support substrate with anisotropy and a piezoelectric thin film with in-plane anisotropy located on the high sound velocity support substrate, wherein the slow shear wave sound velocity of the sound velocity support substrate is higher than the sound velocity of the target acoustic wave mode in the piezoelectric thin film.

[0035] Furthermore, the target mode of the acoustic filter is a horizontal shear wave or a longitudinal leaky wave or a longitudinal wave.

[0036] Optionally, the material of the piezoelectric thin film is one 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, gallium arsenide, and the thickness of the piezoelectric thin film does not exceed 0.45λ, where λ is the wavelength of the acoustic wave of the target mode of the acoustic filter; the material of the high sound velocity support substrate is one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like, gallium nitride, boron carbide, boron nitride, aluminum nitride, and the material of the high sound velocity support substrate is different from the material of the piezoelectric thin film.

[0037] As described above, for the low-temperature-drift acoustic filter of the present invention, at least one equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency is arranged on the series arm of the resonator in its electrical topology structure, and the absolute value of the TCF of the at least one equivalent series resonator is less than the absolute value of the TCF of all other equivalent series resonators. The first transmission zero on the right side of the passband of the acoustic filter thus formed corresponds to the anti-resonance frequency point of the at least one equivalent series resonator, and the frequency points of the 3dB sideband of the acoustic filter are located near the anti-resonance frequency point of the at least one equivalent series resonator and at the same time within the passband of other equivalent series resonators, so that the at least one equivalent series resonator has the greatest influence on the right-side band of the passband of the acoustic filter, and the at least one equivalent series resonator has the smallest absolute value of the TCF value. Thus, without affecting the passband response of the acoustic filter, the frequency temperature stability of the passband frequency and the right-edge frequency of the acoustic filter can be effectively enhanced, the loss of the passband and sideband signals of the acoustic filter due to frequency drift can be reduced, the requirement for the resonator bandwidth is lowered, especially when the adjacent frequency band on the right side of the target frequency band of the acoustic filter is relatively crowded, the fault tolerance range on the right side of the target frequency band of the acoustic filter is increased, and the design difficulty of the acoustic filter is reduced; in addition, when the support substrate of the acoustic wave resonator in the acoustic filter adopts a material with high thermal conductivity, the heat dissipation performance of the device can also be improved, further assisting in reducing frequency drift. Description of the Drawings

[0038] Figures 1 to 11 Schematic diagrams of multiple electrical topologies of the low-temperature-drift acoustic filter according to Embodiment 1 of the present invention are shown.

[0039] Figures 12 to 16 Schematic diagrams of multiple electrical topologies of the low-temperature-drift acoustic filter according to the second embodiment of the present invention.

[0040] Figure 17 Schematic cross-sectional structure diagram of the physical structure of the low-temperature-drift acoustic filter of the present invention.

[0041] Figure 18 Schematic diagram of the electrical topology of the acoustic filter of Comparative Example 1.

[0042] Figure 19 Frequency response curve of the acoustic resonator in the acoustic filter of Comparative Example 1 and passband response curve of the corresponding acoustic filter.

[0043] Figure 20 Schematic diagram of the electrical topology of the acoustic filter of Experimental Example 1.

[0044] Figure 21 Frequency response curve of the acoustic resonator in the acoustic filter of Experimental Example 1 and passband response curve of the corresponding acoustic filter.

[0045] Figure 22 Frequency temperature coefficient TCF and electromechanical coupling coefficient of the resonance point of the resonator based on X-tangent LiNbO3 piezoelectric thin film / SiC high-speed acoustic support substrate Variation trend curve diagram with respect to the in-plane propagation direction theta.

[0046] Figure 23 Frequency temperature coefficient TCF and electromechanical coupling coefficient of the anti-resonance point of the resonator based on X-tangent LiNbO3 piezoelectric thin film / SiC high-speed acoustic support substrate Variation trend curve diagram with respect to the in-plane propagation direction theta.

[0047] Figure 24 Schematic diagram of the change in the passband of the acoustic filter of Comparative Example 1 when the temperature changes.

[0048] Figure 25 Schematic diagram of the change in the passband of the acoustic filter of Experimental Example 1 when the temperature changes.

[0049] Figure 26 Frequency temperature coefficient TCF and electromechanical coupling coefficient of the resonance point of the resonator based on YX-cut lithium niobate (LiNbO3) piezoelectric thin film / SiC high-speed acoustic support substrate Variation trend curve diagram with respect to the in-plane propagation direction theta.

[0050] Figure 27Show the temperature coefficient of frequency drift TCF and the electromechanical coupling coefficient of the anti-resonant point of the resonator shown as a piezoelectric thin film of YX-cut lithium niobate (LiNbO3) / SiC high acoustic velocity support substrate. The curve graph of the variation trend with the in-plane propagation direction theta.

[0051] Figures 28 to 30 Show several equivalent circuit topology schematic diagrams of the equivalent series resonator and / or the equivalent parallel resonator in the low-temperature-drift acoustic filter of the present invention, which are connected by multiple acoustic wave resonators.

[0052] Element label description

[0053] 10 Electrical topology

[0054] 11 Resonator series arm

[0055] 110 Equivalent series resonator

[0056] 12 Resonator parallel arm

[0057] 120 Equivalent parallel resonator

[0058] 13 Input terminal

[0059] 14 Output terminal

[0060] 15 Acoustic wave resonator

[0061] 20 Heterogeneous substrate structure

[0062] 200 High acoustic velocity support substrate

[0063] 201 Piezoelectric thin film

[0064] 21 Interdigital electrode

[0065] 22 Physical structure Specific implementation manner

[0066] The following illustrates the implementation manner of the present invention through specific specific examples. 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 different specific implementation manners. 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.

[0067] When detailing the embodiments of the present invention, for the convenience of description, the cross-sectional view showing the device structure will be locally enlarged out of the general proportion, and the schematic diagram is only an example, which should not limit the protection scope of the present invention here. In addition, in actual production, three-dimensional spatial dimensions including length, width, and depth should be included.

[0068] For ease of description, spatial relationship terms such as "below", "beneath", "lower", "under", "above", "on" etc. may be used herein to describe the relationship of one element or feature shown in the drawings with other elements or features. It will be understood that these spatial relationship terms are intended to encompass other directions of the device in use or operation, in addition to the directions depicted in the drawings. Embodiments may include those in which the first and second features are formed in direct contact, and may also include 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. Additionally, when a layer is referred to as being "between" two layers, it may be between the two layers.

[0069] Please refer to Figures 1 to 27 Note that the diagrams provided in this embodiment only illustrate the basic concept of the present invention schematically. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation may be arbitrarily changed, and the component layout type may also be more complex.

[0070] Embodiment 1

[0071] As Figures 1 to 11 shown, this embodiment provides an acoustic filter with low temperature drift. The acoustic filter includes: m equivalent series resonators 110 and n equivalent parallel resonators 120, where both m and n are natural numbers greater than or equal to 1, and m ≥ n;

[0072] The m equivalent series resonators 110 are connected in series in turn between the input end 13 and the output end 14 to form a resonator series arm 11;

[0073] One end of each of the n equivalent parallel resonators 120 is respectively connected to m - 1 nodes between adjacent equivalent series resonators 110, and the other end of the n equivalent parallel resonators 120 is grounded to form m - 1 resonator parallel arms 12 (as Figure 1 shown); or one end of each of the n equivalent parallel resonators 120 is respectively connected to m - 1 nodes between adjacent equivalent series resonators 110 and the head or tail of the resonator series arm 11, and the other end of the n equivalent parallel resonators 120 is grounded to form m resonator parallel arms 12 (as Figure 2 and Figure 3 shown);

[0074] The resonance frequency of at least one of the equivalent series resonators 110 in the resonator series arm 11 is higher than that of the other equivalent series resonators 110 in the resonator series arm 11. The anti-resonance frequency of the at least one equivalent series resonator 110 is lower than that of the other equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the frequency temperature coefficient (TCF) of the at least one equivalent series resonator 110 is smaller than the absolute value of the TCF of the other equivalent series resonators 110 in the resonator series arm 11. The resonator series arm 11 and all the resonator parallel arms 12 form the electrical topology 10 of the acoustic filter.

[0075] For the acoustic filter with low temperature drift in this embodiment, at least one equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency is arranged on the resonator series arm of its electrical topology, and the absolute value of the TCF of the at least one equivalent series resonator is smaller than the absolute value of the TCF of all other equivalent series resonators. The first transmission zero on the right side of the passband of the thus formed acoustic filter corresponds to the anti-resonance frequency point of the at least one equivalent series resonator, and the frequency points of the 3dB sideband of the acoustic filter are located near the anti-resonance frequency point of the at least one equivalent series resonator and at the same time within the passband of the other equivalent series resonators, so that the at least one equivalent series resonator has the greatest influence on the right sideband of the passband of the acoustic filter. And the at least one equivalent series resonator has the smallest absolute value of the TCF value, so that without affecting the passband response of the acoustic filter, the frequency temperature stability of the passband frequency and the right edge of the passband of the acoustic filter can be effectively enhanced, the loss of the passband and sideband signals of the acoustic filter caused by frequency drift can be reduced, the requirement for the resonator bandwidth is lowered. Especially when the adjacent frequency band on the right side of the target frequency band of the acoustic filter is relatively crowded, the fault tolerance range on the right side of the target frequency band of the acoustic filter is improved, and the design difficulty of the acoustic filter is reduced; in addition, when the support substrate of the acoustic wave resonator in the acoustic filter is made of a material with high thermal conductivity, the heat dissipation performance of the device can be improved, further assisting in reducing frequency drift.

[0076] It should be noted here that for the sake of easy understanding, in the drawings of this embodiment, the arrangement directions of the equivalent series resonators and / or equivalent parallel resonators with resonance frequencies and anti-resonance frequencies different from those of other equivalent series resonators and / or equivalent parallel resonators are drawn differently to clearly understand the setting positions of the special equivalent series resonators and / or equivalent parallel resonators.

[0077] Any of the equivalent series resonators 110 in this embodiment can be formed by one acoustic wave resonator; as Figures 28 to 30 shown, it can also be split into multiple acoustic wave resonators 15 according to the equivalent principle, and the multiple acoustic wave resonators are connected in series and / or parallel, such asFigure 28 The equivalent series resonator 110 described therein is equivalently formed by two serially connected acoustic wave resonators 15, as Figure 29 The equivalent series resonator 110 described therein is equivalently formed by two parallel-connected acoustic wave resonators 15, as Figure 30 The equivalent series resonator 110 described therein is equivalently formed by two serially connected acoustic wave resonators 15 in parallel with one acoustic wave resonator 15. Similarly, any of the equivalent parallel resonators 120 in this embodiment can be formed by one acoustic wave resonator; as Figures 28 to 30 shown, it can also be split into multiple acoustic wave resonators 15 according to the equivalent principle, and these multiple acoustic wave resonators are connected in series and / or in parallel, as Figure 28 The equivalent parallel resonator 120 described therein is equivalently formed by two serially connected acoustic wave resonators 15, as Figure 29 The equivalent parallel resonator 120 described therein is equivalently formed by two parallel-connected acoustic wave resonators 15, as Figure 30 The equivalent parallel resonator 120 described therein is equivalently formed by two serially connected acoustic wave resonators 15 in parallel with one acoustic wave resonator 15. In practice, the specific forms of the equivalent series resonator 110 and the equivalent parallel resonator 120 are set according to actual needs and are not overly restricted herein.

[0078] In this embodiment, m of the equivalent series resonators 110 are serially connected in turn between the input end 13 and the output end 14 to form a resonator series arm 11; in addition, the number and positions of the resonator parallel arms 12 vary slightly according to the connection positions of the equivalent parallel resonators 120. By way of example, as Figure 1 shown, one end of three equivalent parallel resonators 120 is respectively connected to three nodes between four adjacent equivalent series resonators 110 in turn, and the other ends of the three equivalent parallel resonators 120 are grounded, thus forming three resonator parallel arms 12; as Figure 2 shown, one end of three equivalent parallel resonators 120 is respectively connected to three nodes between four adjacent equivalent series resonators 110 in turn, and one end of another equivalent parallel resonator 120 is connected to the end of the resonator series arm 11, and the other ends of the four equivalent parallel resonators 120 are grounded, thus forming four resonator parallel arms 12; as Figure 3 shown, one end of three equivalent parallel resonators 120 is respectively connected to three nodes between four adjacent equivalent series resonators 110 in turn, and one end of another equivalent parallel resonator 120 is connected to the beginning of the resonator series arm 11, and the other ends of the four equivalent parallel resonators 120 are grounded, thus forming four resonator parallel arms 12.

[0079] As a specific example, m is an odd number greater than 1; all the equivalent series resonators 110 are arranged in a symmetric distribution in sequence with respect to the ((m + 1) / 2)-th equivalent series resonator 110 in terms of physical structure; the resonance frequency of the ((m + 1) / 2)-th equivalent series resonator 110 in the resonator series arm 11 is higher than that of the other equivalent series resonators 110 in the resonator series arm 11, the anti-resonance frequency of the ((m + 1) / 2)-th equivalent series resonator 110 is lower than that of the other equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the TCF of the ((m + 1) / 2)-th equivalent series resonator 110 is less than the absolute value of the TCF of the other equivalent series resonators 110 in the resonator series arm 11. It should be noted here that the physical structure of the equivalent series resonator 110 refers to the actual physical structure of the acoustic wave resonator included in the equivalent series resonator 110, generally including a support substrate, a piezoelectric thin film, and interdigital electrodes, and all the interdigital electrodes are electrically connected through a bulk electrode according to the required connection method to form the required electrical topology structure 10. In this specific example, m is defined as an odd number greater than 1, and the middle equivalent series resonator 110 on the resonator series arm 11 is set as a special equivalent series resonator, that is, its resonance frequency is the maximum among the other equivalent series resonators 110 on the resonator series arm 11, and the anti-resonance frequency is the minimum. The number and position of the resonator parallel arms 12 are not overly restricted. For example, as Figure 4 shown, 5 equivalent series resonators 110 are connected in series in sequence between the input end 13 and the output end 14 to form a resonator series arm 11. The middle 3rd equivalent series resonator 110 is set as a special equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency. In addition, one end of 4 equivalent parallel resonators 120 is respectively connected to 4 nodes between 5 adjacent equivalent series resonators 110 in sequence, and one end of another equivalent parallel resonator 120 is connected to the head end of the resonator series arm 11, and the other ends of the 5 equivalent parallel resonators 120 are grounded, thus forming 5 resonator parallel arms 12; as Figure 5 shown, 5 equivalent series resonators 110 are connected in series in sequence between the input end 13 and the output end 14 to form a resonator series arm 11. The middle 3rd equivalent series resonator 110 is set as a special equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency. In addition, one end of 4 equivalent parallel resonators 120 is respectively connected to 4 nodes between 5 adjacent equivalent series resonators 110 in sequence, and one end of another equivalent parallel resonator 120 is connected to the tail end of the resonator series arm 11, and the other ends of the 5 equivalent parallel resonators 120 are grounded, thus forming 5 resonator parallel arms 12; as Figure 6As shown, five equivalent series resonators 110 are connected in series in turn between the input terminal 13 and the output terminal 14 to form a series arm 11 of resonators. The third equivalent series resonator 110 in the middle is set as a special equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency. In addition, one end of each of the four equivalent parallel resonators 120 is connected to four nodes between five adjacent equivalent series resonators 110 in turn, and the other ends of the four equivalent parallel resonators 120 are grounded, thus forming four parallel arms 12 of resonators. Preferably, the equivalent parallel resonators 120 are arranged in a manner similar to Figure 6 That is, n = m - 1, and one end of each of the n equivalent parallel resonators 120 is connected to m - 1 nodes between adjacent equivalent series resonators 110, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 parallel arms 12 of resonators. More preferably, on the basis of selecting a manner similar to Figure 6 The equivalent parallel resonators 120 are also arranged in a symmetric distribution about the (m + 1) / 2-th equivalent series resonator 110 in terms of physical structure, so as to Figure 6 Take as an example, that is, from left to right, the physical structure of the first equivalent parallel resonator 120 is the same as that of the fourth equivalent parallel resonator 120, and the physical structure of the second equivalent parallel resonator 120 is the same as that of the third equivalent parallel resonator 120.

[0080] When high requirements are imposed on the frequency-temperature stability of the frequency points on both the left and right sides of the passband of the acoustic filter, in addition to enhancing the frequency-temperature stability of the passband frequency and the right-edge frequency of the passband of the acoustic filter by the above method, it is also necessary to enhance the frequency-temperature stability of the passband frequency and the left-edge frequency of the passband of the acoustic filter. At this time, the electrical topology structure 10 of the acoustic filter is designed as, such as Figures 7 to 11 Shown: m equivalent series resonators 110 and n equivalent parallel resonators 120, where m and n are natural numbers greater than or equal to 1, and m ≥ n;

[0081] The m equivalent series resonators 110 are connected in series in turn between the input terminal 13 and the output terminal 14 to form a series arm 11 of resonators;

[0082] One end of each of the n equivalent parallel resonators 120 is connected to m - 1 nodes between adjacent equivalent series resonators 110, and the other ends of the n equivalent parallel resonators 120 are grounded to form m - 1 parallel arms 12 of resonators (such as Figure 9as shown); or one end of each of the n equivalent parallel resonators 120 is respectively connected to m - 1 nodes between adjacent ones of the equivalent series resonators 110 and the head or tail end of the resonator series arm 11, and the other ends of the n equivalent parallel resonators 120 are grounded to form m resonator parallel arms 12 (as Figure 7 and Figure 8 shown);

[0083] The resonance frequency of at least one of the equivalent series resonators 110 in the resonator series arm 11 is higher than that of the other equivalent series resonators 110 in the resonator series arm 11, the anti-resonance frequency of the at least one equivalent series resonator 110 is lower than that of the other equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the frequency temperature coefficient (TCF) of the at least one equivalent series resonator 110 is less than the absolute value of the TCF of the other equivalent series resonators 110 in the resonator series arm 11;

[0084] The resonance frequency of the equivalent parallel resonator 120 on at least one of the resonator parallel arms 12 is higher than that of the equivalent parallel resonators 120 on the other resonator parallel arms 12, the anti-resonance frequency of the equivalent parallel resonator 120 on the at least one resonator parallel arm 12 is lower than that of the equivalent parallel resonators 120 on the other resonator parallel arms 12, and the absolute value of the TCF of the equivalent parallel resonator 120 on the at least one resonator parallel arm 12 is less than the absolute value of the TCF of the equivalent parallel resonators 120 on the other resonator parallel arms 12.

[0085] By providing at least one equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency on the series arm of the resonator in the electrical topology, and making the absolute value of the TCF of the at least one equivalent series resonator less than the absolute values of the TCFs of all other equivalent series resonators, the frequency temperature stability of the passband frequency and the right edge of the passband of the acoustic filter can be effectively enhanced; in addition, by setting the resonance frequency of the equivalent parallel resonator on at least one resonator parallel arm in the electrical topology to be the maximum and the anti-resonance frequency to be the minimum, and making the absolute value of its TCF less than the absolute values of the TCFs of all other equivalent parallel resonators, at this time, the first transmission zero on the left side of the passband of the acoustic filter corresponds to the resonance frequency point of the equivalent parallel resonator on the at least one resonator parallel arm, and the frequency points of the 3dB sideband of the acoustic filter are located within the passbands of all equivalent parallel resonators, so that the equivalent parallel resonator on the at least one resonator parallel arm has the greatest influence on the left sideband of the passband of the acoustic filter, and the equivalent parallel resonator on the at least one resonator parallel arm has the TCF value with the smallest absolute value, so that the frequency temperature stability of the passband frequency and the left edge of the passband of the acoustic filter can be effectively enhanced, reducing the loss of the passband and sideband signals of the acoustic filter due to frequency drift, and finally realizing the improvement of the frequency temperature stability of the passband frequency and the left and right edges of the passband of the acoustic filter without affecting the passband response of the acoustic filter, reducing the requirement for the resonator bandwidth. Especially when the adjacent frequency bands on the left and right sides of the target frequency band of the acoustic filter are relatively crowded, the fault tolerance range on the left and right sides of the target frequency band of the acoustic filter is increased, and the design difficulty of the acoustic filter is reduced; in addition, when the support substrate of the acoustic wave resonator in the acoustic filter is made of a material with high thermal conductivity, the heat dissipation performance of the device can also be improved, further assisting in reducing frequency drift.

[0086] As a preferred example, such as Figure 10 and Figure 11 shown, m is an odd number greater than 1, and n = m - 1;

[0087] One end of each of the n equivalent parallel resonators 120 is respectively connected to m - 1 nodes between adjacent equivalent series resonators 110, and the other ends of the n equivalent parallel resonators 120 are grounded to form m - 1 resonator parallel arms 12;

[0088] All the equivalent series resonators 110 and all the equivalent parallel resonators 120 are arranged symmetrically in sequence with respect to the (m + 1) / 2-th equivalent series resonator 110 in terms of physical structure;

[0089] The resonance frequency of the ((m + 1) / 2)-th equivalent series resonator 110 in the resonator series arm 11 is higher than that of the other equivalent series resonators 110 in the resonator series arm 11. The anti-resonance frequency of the ((m + 1) / 2)-th equivalent series resonator 110 is lower than that of the other equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the TCF of the ((m + 1) / 2)-th equivalent series resonator 110 is smaller than the absolute value of the TCF of the other equivalent series resonators 110 in the resonator series arm 11;

[0090] The resonance frequencies of the equivalent parallel resonators 120 on at least two resonator parallel arms 12 that are symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator 110 among all the resonator parallel arms 12 are higher than those of the equivalent parallel resonators 120 on the other resonator parallel arms 12. The anti-resonance frequencies of the equivalent parallel resonators 120 on the at least two resonator parallel arms 12 that are symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator 110 are lower than those of the equivalent parallel resonators 120 on the other resonator parallel arms 12, and the absolute value of the TCF of the equivalent parallel resonators 120 on the at least two resonator parallel arms 12 that are symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator 110 is smaller than the absolute value of the TCF of the equivalent parallel resonators 120 on the other resonator parallel arms 12.

[0091] Such as Figure 10As shown, one end of each of the 4 equivalent parallel resonators 120 is respectively connected to 4 nodes between adjacent equivalent series resonators 110, and the other ends of the 4 equivalent parallel resonators 120 are grounded, forming 4 resonator parallel arms 12; the 5 equivalent series resonators 110 and the 4 equivalent parallel resonators 120 are arranged in a symmetric distribution in physical structure successively with respect to the 3rd equivalent series resonator 110; the resonance frequency of the 3rd equivalent series resonator 110 in the resonator series arm 11 is higher than that of the other 4 equivalent series resonators 110 in the resonator series arm 11, the anti-resonance frequency of the 3rd equivalent series resonator 110 is lower than that of the other 4 equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the TCF of the 3rd equivalent series resonator 110 is less than the absolute value of the TCF of the other 4 equivalent series resonators 110 in the resonator series arm 11; the resonance frequencies of the equivalent parallel resonators 120 on the 1st and 4th resonator parallel arms 12 among the 4 resonator parallel arms 12 that are symmetrically distributed with respect to the 3rd equivalent series resonator 110 are higher than those of the equivalent parallel resonators 120 on the other 2 resonator parallel arms 12, the anti-resonance frequencies of the 2 equivalent parallel resonators 120 on the at least two resonator parallel arms 12 that are symmetrically distributed with respect to the 3rd equivalent series resonator 110 are lower than those of the 2 equivalent parallel resonators 120 on the other 2 resonator parallel arms 12, and the absolute value of the TCF of the equivalent parallel resonators 120 on the at least two resonator parallel arms 12 that are symmetrically distributed with respect to the 3rd equivalent series resonator 110 is less than the absolute value of the TCF of the equivalent parallel resonators 120 on the other 2 resonator parallel arms 12.

[0092] Figure 11 The electrical topology of Figure 10 is basically the same, except that Figure 11 the equivalent parallel resonator 120 on the 2nd resonator parallel arm symmetrically distributed with respect to the 3rd equivalent series resonator 110 in Figure 10 has a different propagation direction from the equivalent parallel resonator 120 on the 3rd resonator parallel arm in

[0093] As an example, the acoustic target modes of the equivalent parallel resonator and the equivalent series resonator in the acoustic filter can be horizontal shear waves, longitudinal leakage waves, longitudinal waves, etc.

[0094] As a specific example, such as Figure 17As shown, the acoustic filter is formed based on the heterogeneous substrate structure 20, that is, the physical structures of all the equivalent parallel resonators and equivalent series resonators on the acoustic filter are all obtained based on the same heterogeneous substrate structure 20. The heterogeneous substrate structure 20 includes a high-speed support substrate 200 with anisotropy and a piezoelectric thin film 201 with in-plane anisotropy located on the high-speed support substrate 200. Among them, the slow shear wave velocity of the high-speed support substrate 200 is higher than the sound velocity of the target acoustic wave mode in the piezoelectric thin film 201. Selecting the piezoelectric thin film 201 with in-plane anisotropy can enable the setting of equivalent parallel resonators and equivalent series resonators in the required frequency band by adjusting the parameters of the interdigital electrodes 21 thereon. For example, by adjusting the different arrangement directions of the interdigital electrodes 21 on the piezoelectric thin film 201, the propagation directions of the acoustic wave resonators are different, so as to realize the adjustment of the frequency band of the acoustic wave resonators.

[0095] As an example, the material of the piezoelectric thin film 201 can be selected from one 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, gallium arsenide. The thickness of the piezoelectric thin film 201 does not exceed 0.45λ, where λ is the wavelength of the acoustic wave of the target mode of the acoustic filter; the material of the high-speed support substrate 200 can be selected from one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like, gallium nitride, boron carbide, boron nitride, aluminum nitride, and the material of the high-speed support substrate 200 is different from the material of the piezoelectric thin film 201. However, it is not limited to this, and other suitable materials for the piezoelectric thin film 201 and the high-speed support substrate 200 are also available.

[0096] As Figure 17 shown, as an example, the material of the interdigital electrodes 21 on the heterogeneous substrate structure 20 can be selected from any one of copper, silver, gold, aluminum, platinum, nickel, molybdenum, tungsten, chromium, titanium or an alloy composed thereof; the interdigital electrodes 102 include single-layer interdigital electrodes or composite laminated interdigital electrodes.

[0097] Embodiment 2

[0098] This embodiment provides an acoustic filter with low temperature drift. The design principle of the acoustic filter in this embodiment is the same as that in Embodiment 1. The difference is that this embodiment mainly has higher requirements for the frequency temperature stability of the frequency points on the left side of the passband of the acoustic filter. At this time, it is only necessary to improve the frequency temperature stability of the frequency points on the left side of the passband of the acoustic filter. As Figures 12 to 16 shown, the acoustic filter includes: m equivalent series resonators 110 and n equivalent parallel resonators 120, where m and n are both natural numbers greater than or equal to 1, and m≥n;

[0099] m of the equivalent series resonators 110 are connected in series in turn between the input end 13 and the output end 14 to form a resonator series arm 11;

[0100] One end of n of the equivalent parallel resonators 120 is respectively connected to m - 1 nodes between adjacent ones of the equivalent series resonators 110, and the other ends of the n equivalent parallel resonators 120 are grounded to form m - 1 resonator parallel arms 12 (as Figures 14 to 16 shown); or one end of n of the equivalent parallel resonators 120 is respectively connected to m - 1 nodes between adjacent ones of the equivalent series resonators 110 and the first end (as Figure 13 shown) or the last end (as Figure 12 shown) of the resonator series arm 11, and the other ends of the n equivalent parallel resonators 120 are grounded to form m resonator parallel arms 12;

[0101] The resonance frequency of the equivalent parallel resonator 120 on at least one of all the resonator parallel arms 12 is higher than that of the equivalent parallel resonators 120 on other resonator parallel arms 12, the anti - resonance frequency of the equivalent parallel resonator 120 on the at least one resonator parallel arm 12 is lower than that of the equivalent parallel resonators 120 on other resonator parallel arms 12, and the absolute value of the TCF of the equivalent parallel resonator 120 on the at least one resonator parallel arm 12 is less than the absolute value of the TCF of the equivalent parallel resonators 120 on other resonator parallel arms 12.

[0102] The acoustic filter with low temperature drift in this embodiment sets the resonance frequency of the equivalent parallel resonator on at least one resonator parallel arm to be the maximum and the anti-resonance frequency to be the minimum in the electrical topology, and makes the absolute value of its TCF less than the absolute values of the TCFs of all other equivalent parallel resonators. At this time, the first transmission zero on the left side of the passband of the acoustic filter corresponds to the resonance frequency point of the equivalent parallel resonator on at least one resonator parallel arm, and the frequency points of the 3dB sideband of the acoustic filter are within the passbands of all equivalent parallel resonators, so that the equivalent parallel resonator on at least one resonator parallel arm has the greatest influence on the left sideband of the passband of the acoustic filter. And the equivalent parallel resonator on at least one resonator parallel arm has the TCF value with the smallest absolute value, so that without affecting the passband response of the acoustic filter, the frequency temperature stability of the passband frequency and the left edge of the passband of the acoustic filter can be effectively enhanced, the loss caused by frequency drift of the passband and sideband signals of the acoustic filter can be reduced, the requirement for the resonator bandwidth is lowered. Especially when the adjacent frequency bands on the left side of the target frequency band of the acoustic filter are relatively crowded, the fault tolerance range on the left side of the target frequency band of the acoustic filter is improved, and the design difficulty of the acoustic filter is reduced; in addition, when the support substrate of the acoustic wave resonator in the acoustic filter uses a material with high thermal conductivity, the heat dissipation performance of the device can be improved, further assisting in reducing frequency drift.

[0103] As a specific example, as Figure 15 and Figure 16 shown, m is an odd number greater than 1, and n = m - 1; one ends of the n equivalent parallel resonators 120 are respectively connected to m - 1 nodes between the adjacent equivalent series resonators 110, and the other ends of the n equivalent parallel resonators 120 are grounded to form m - 1 resonator parallel arms 12;

[0104] All the equivalent parallel resonators 120 are symmetrically distributed and arranged in sequence with respect to the (m + 1) / 2-th equivalent series resonator 110 in the physical structure;

[0105] The resonance frequencies of the equivalent parallel resonators 120 on at least two of the resonator parallel arms 12, where all the resonator parallel arms 12 are symmetrically distributed physically with respect to the (m + 1) / 2-th equivalent series resonator 110, are higher than those of the equivalent parallel resonators 120 on the other resonator parallel arms 12. The anti-resonance frequencies of the equivalent parallel resonators 120 on the at least two resonator parallel arms 12, which are symmetrically distributed physically with respect to the (m + 1) / 2-th equivalent series resonator 110, are lower than those of the equivalent parallel resonators 120 on the other resonator parallel arms 12. And the absolute value of the TCF of the equivalent parallel resonators 120 on the at least two resonator parallel arms 12, which are symmetrically distributed physically with respect to the (m + 1) / 2-th equivalent series resonator 110, is less than the absolute value of the TCF of the equivalent parallel resonators 120 on the other resonator parallel arms 12. Further, as Figure 15 and Figure 16 shown, all the equivalent series resonators 110 are arranged in sequence and symmetrically distributed physically with respect to the (m + 1) / 2-th equivalent series resonator 110.

[0106] As Figure 15 in, one ends of 4 equivalent parallel resonators 120 are respectively connected to 4 nodes between adjacent equivalent series resonators 110, and the other ends of the 4 equivalent parallel resonators 120 are grounded to form 4 resonator parallel arms 12; the 4 equivalent parallel resonators 120 are arranged in sequence and symmetrically distributed physically with respect to the 3rd equivalent series resonator 110; the resonance frequencies of the equivalent parallel resonators 120 on the 1st and 4th resonator parallel arms 12, which are symmetrically distributed physically with respect to the 3rd equivalent series resonator 110, among the 4 resonator parallel arms 12 are higher than those of the equivalent parallel resonators 120 on the other 2 (the 2nd and 3rd) resonator parallel arms 12. The anti-resonance frequencies of the 2 equivalent parallel resonators 120 on the at least two resonator parallel arms 12, which are symmetrically distributed physically with respect to the 3rd equivalent series resonator 110, are lower than those of the 2 equivalent parallel resonators 120 on the other 2 resonator parallel arms 12. And the absolute value of the TCF of the equivalent parallel resonators 120 on the at least two resonator parallel arms 12, which are symmetrically distributed physically with respect to the 3rd equivalent series resonator 110, is less than the absolute value of the TCF of the equivalent parallel resonators 120 on the other 2 resonator parallel arms 12.

[0107] Figure 16 The electrical topology of Figure 15 is basically the same, except that,Figure 16 The equivalent parallel resonator 120 on the second resonator parallel arm and the equivalent parallel resonator 120 on the third resonator parallel arm, which are symmetrically distributed with respect to the third equivalent series resonator 110 described above, have Figure 15 different propagation directions from those in

[0108] It should be noted here that, for the convenience of understanding, in the drawings of this embodiment, the arrangement directions of the equivalent series resonators and / or equivalent parallel resonators with resonance frequencies and anti-resonance frequencies different from those of other equivalent series resonators and / or equivalent parallel resonators are drawn differently to clearly understand the installation positions of these special equivalent series resonators and / or equivalent parallel resonators.

[0109] Any of the equivalent series resonators 110 in this embodiment can be formed by one acoustic wave resonator; as Figures 28 to 30 shown, it can also be split into multiple acoustic wave resonators 15 according to the equivalent principle, and these multiple acoustic wave resonators are connected in series and / or in parallel, as Figure 28 the equivalent series resonator 110 described in Figure 29 is equivalently formed by 2 serially connected acoustic wave resonators 15, as Figure 30 the equivalent series resonator 110 described in Figures 28 to 30 is equivalently formed by 2 parallel-connected acoustic wave resonators 15, as Figure 28 the equivalent series resonator 110 described in Figure 29 is equivalently formed by 2 serially connected acoustic wave resonators 15 in parallel with 1 acoustic wave resonator 15. Similarly, any of the equivalent parallel resonators 120 in this embodiment can be formed by one acoustic wave resonator; as Figure 30 shown, it can also be split into multiple acoustic wave resonators 15 according to the equivalent principle, and these multiple acoustic wave resonators are connected in series and / or in parallel, as

[0110] the equivalent parallel resonator and the equivalent series resonator in the acoustic filter can have acoustic target modes such as horizontal shear waves, longitudinal leaky waves, longitudinal waves, etc. as an example.

[0111] As a specific example, as Figure 17As shown, the acoustic filter is formed based on the heterogeneous substrate structure 20, that is, the physical structures of all the equivalent parallel resonators and equivalent series resonators on the acoustic filter are all obtained based on the same heterogeneous substrate structure 20. The heterogeneous substrate structure 20 includes a high-speed support substrate 200 with anisotropy and a piezoelectric thin film 201 with in-plane anisotropy located on the high-speed support substrate 200. Among them, the slow shear wave velocity of the high-speed support substrate 200 is higher than the sound velocity of the target acoustic wave mode in the piezoelectric thin film 201. Selecting a piezoelectric thin film 201 with in-plane anisotropy can enable the setting of equivalent parallel resonators and equivalent series resonators in the required frequency band by adjusting the parameters of the interdigital electrodes 21 thereon. For example, by adjusting the different arrangement directions of the interdigital electrodes 21 on the piezoelectric thin film 201, the propagation directions of the acoustic wave resonators are different, so as to realize the adjustment of the frequency band of the acoustic wave resonators.

[0112] As an example, the material of the piezoelectric thin film 201 can be selected from one 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, gallium arsenide. The thickness of the piezoelectric thin film 201 does not exceed 0.45λ, where λ is the wavelength of the acoustic wave of the target mode of the acoustic filter; the material of the high-speed support substrate 200 can be selected from one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like, gallium nitride, boron carbide, boron nitride, aluminum nitride, and the material of the high-speed support substrate 200 is different from the material of the piezoelectric thin film 201. However, it is not limited to this, and other suitable materials for the piezoelectric thin film 201 and the high-speed support substrate 200 are also possible.

[0113] As Figure 17 shown, as an example, the material of the interdigital electrodes 21 on the heterogeneous substrate structure 20 can be selected from any one of copper, silver, gold, aluminum, platinum, nickel, molybdenum, tungsten, chromium, titanium or an alloy composed thereof; the interdigital electrode 102 includes a single-layer interdigital electrode or a composite laminated interdigital electrode.

[0114] The beneficial effects of the low-temperature-drift acoustic filter in the present application will be further described and verified below with reference to comparative examples and experimental examples. Obviously, the described experimental examples are only a part of the experimental examples of the present invention, rather than all the experimental examples. Based on the experimental examples of the present invention, all other experimental examples obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0115] Comparative Example 1:

[0116] Set the target frequency band of the passband of the acoustic filter to B41 (2.496 - 2.696 GHz). As Figure 17Shown is the heterogeneous substrate structure 20 of an acoustic filter, where the material of the high sound velocity support substrate 200 is selected as SiC, the material of the piezoelectric thin film 201 is selected as lithium niobate LiNbO3 with X tangent, and the excited level shear wave is used as the target acoustic wave mode; as Figure 18 Shown is the electrical topology structure 10 for designing an acoustic filter: on the resonator series arm 11, 5 acoustic wave resonators S1, S2, S3, S2, S1 are connected in series in sequence. The 4 acoustic wave resonators S1, S2, S2, S1 are symmetrically distributed with respect to the middle acoustic wave resonator S3, that is, the first acoustic wave resonator S1 is the same as the fourth acoustic wave resonator S1, and the second acoustic wave resonator S2 is the same as the third acoustic wave resonator S2; on each of the 4 resonator parallel arms 12, an acoustic wave resonator is provided, a total of 4 acoustic wave resonators P1, P2, P2, P1. The 4 acoustic wave resonators P1, P2, P2, P1 are symmetrically distributed with respect to the acoustic wave resonator S3 in the middle of the resonator series arm 11, that is, the first acoustic wave resonator P1 is the same as the fourth acoustic wave resonator P1, and the second acoustic wave resonator P2 is the same as the third acoustic wave resonator P2; the placement direction of the acoustic wave resonators on the resonator series arm 11 and the resonator parallel arms 12 is the indicated acoustic wave propagation direction. At this time, there are 5 acoustic wave resonators with different parameters, namely S1, S2, S3, P1, and P2. The specific designs of these 5 acoustic wave resonators are shown in Table 1 below.

[0117] Table 1: Specific design parameters of 5 acoustic wave resonators with different parameters

[0118]

[0119] For these 5 acoustic wave resonators with the same physical structure, the acoustic wave propagation directions are the same. When their acoustic wave wavelengths and corresponding resonance frequencies are close, the electromechanical coupling coefficients between the corresponding acoustic wave resonators are relatively small. As can be seen from Table 1, the resonance frequencies of the 3 acoustic wave resonators S1, S2, S3 on the resonator series arm 11 are close, and the variation range is within ±50 MHz. The resonance frequencies of the 2 acoustic wave resonators P1, P2 on the resonator parallel arm 122 are close, and the variation range is within ±20 MHz; and the propagation directions of all acoustic wave resonators are the same, all about 20%, that is, it is required that the difference between them does not exceed 1%.

[0120] As Figure 19The admittance response curve of the acoustic resonator of this comparative example and the passband response curve of the composed acoustic filter. At this time, the first transmission zero on the right side of the passband of the acoustic filter corresponds to the anti-resonant frequency point of the acoustic resonator S1 on the series arm 11 of the resonator, and the frequency points of the 3dB sideband of the acoustic filter are near the anti-resonant frequency point of the acoustic resonator S1, and at the same time are within the passbands of the acoustic resonators S2 and S3 on the other series arms 11 of the resonator; the first transmission zero on the left side of the passband of the acoustic filter corresponds to the resonant frequency point of the acoustic resonator P2 on the parallel arm 12 of the resonator, and the frequency points of the 3dB sideband of the acoustic filter are within the passbands of the acoustic resonators P1 and P2. At this time, when the anti-resonant frequency of the acoustic resonator S1 and the resonant frequency of the acoustic resonator P2 change with temperature, the sidebands of the acoustic filter drift accordingly, and are most affected by the drift of the anti-resonant frequency and resonant frequency of these two acoustic resonators S1 and P2. Therefore, frequency-temperature drift and instability of the passband of the acoustic filter will occur, as Figure 24 Shown is a schematic diagram of the passband change of the acoustic filter of this comparative example at -25°C, 55°C, and 125°C. It can be seen from the figure that as the temperature of the acoustic filter increases, the passband drifts more severely towards the low-frequency band. This is because when using SiC as the supporting substrate, lithium niobate LiNbO3 piezoelectric thin film with X cut as the piezoelectric layer, and exciting the horizontal shear wave as the target acoustic wave mode, and the Euler angle is (theta, -90°, -90°), since the frequency-temperature coefficients of both lithium niobate and silicon carbide are negative, the resonant frequency and anti-resonant frequency both decrease as the temperature increases. When the device generates heat during operation or operates in a variable-temperature environment, the overall temperature rise of the device will cause the overall passband of the corresponding filter to shift towards the low frequency. At this time, the passband of the acoustic filter may deviate from the target frequency band, which will lead to a decline in the performance of the acoustic filter. At this time, the effective compensation method generally adopted is to reserve a frequency band during design to compensate for the passband drift caused by temperature changes. Otherwise, signal stability will be lost. However, this method only increases the requirement for the bandwidth of the acoustic filter, and it is difficult to achieve reserving a frequency band when the allocated frequency band is relatively crowded.

[0121] Experimental Example 1:

[0122] Based on the problems existing in the acoustic filter of Comparative Example 1, in this experimental example, the design principle of the acoustic filter proposed by the present invention is adopted to optimize the design of the acoustic filter in the target frequency band B41 (2.496 - 2.696 GHz) of Comparative Example 1.

[0123] In terms of physical structure, it still adopts the heterogeneous substrate structure 20 as shown in Figure 17 where the material of the supporting substrate 200 is selected as SiC, the material of the piezoelectric thin film 201 is selected as lithium niobate LiNbO3 with X cut, and the horizontal shear wave is excited as the target acoustic wave mode.

[0124] An acoustic filter is designed using the electrical topology structure 10 as shown in Figure 20 : Five acoustic wave resonators S1, S2, S3, S2, S1 are sequentially connected in series on the resonator series arm 11. Among them, four acoustic wave resonators S1, S2, S2, S1 are symmetrically distributed with respect to the middle acoustic wave resonator S3, that is, the first acoustic wave resonator S1 is the same as the fourth acoustic wave resonator S1, and the second acoustic wave resonator S2 is the same as the third acoustic wave resonator S2; One acoustic wave resonator is respectively arranged on each of the four resonator parallel arms 12, a total of four acoustic wave resonators P1, P2, P2, P1. The four acoustic wave resonators P1, P2, P2, P1 are symmetrically distributed with respect to the middle acoustic wave resonator S3 of the resonator series arm 11, that is, the first acoustic wave resonator P1 is the same as the fourth acoustic wave resonator P1, and the second acoustic wave resonator P2 is the same as the third acoustic wave resonator P2; The placement directions of the acoustic wave resonators on the resonator series arm 11 and the resonator parallel arms 12 are the indicated acoustic wave propagation directions. At this time, there are a total of five acoustic wave resonators with different parameters, namely S1, S2, S3, P1, and P2. The specific designs of these five acoustic wave resonators with different parameters are shown in Table 2 below.

[0125] Table 2: Specific design parameters of five acoustic wave resonators with different parameters

[0126]

[0127]

[0128] As can be seen from Table 2, the similarities with Comparative Example 1 are as follows: The resonance frequencies of the acoustic wave resonators S1, S2, and S3 on the resonator series arm 11 of this experimental example are close, and the variation range is within ±50 MHz. The resonance frequencies of the acoustic wave resonators P1 and P2 on the resonator parallel arm 12 are also close, and the variation range is within ±20 MHz. The differences from Comparative Example 1 are as follows: The propagation directions of the acoustic wave resonators are different. Among them, the acoustic wave propagation directions of the acoustic wave resonators S1, S2, and P2 remain unchanged and are consistent. Therefore, the electromechanical coupling coefficients of the corresponding acoustic wave resonators are still approximately 20%. For the acoustic wave resonators S3 and P1, in the plane, compared with Comparative Example 1, a counterclockwise rotation angle of 26° is respectively generated. That is, a counterclockwise rotation angle of 26° is generated between the two acoustic wave resonators S3, and a counterclockwise rotation angle of 26° is generated between the two acoustic wave resonators P1. The electromechanical coupling coefficients of the corresponding two acoustic wave resonators S3 and P1 are also sacrificed and are reduced to 11.98% and 12.00% in sequence.

[0129] As shown in Figure 21This is the admittance response curve of the acoustic wave resonator in this experimental example and the passband response curve of the composed acoustic filter. At this time, the first transmission zero on the right side of the passband of the acoustic filter corresponds to the anti-resonant frequency point of the acoustic wave resonator S3 on the series arm 11 of the resonator, and the frequency points of the 3dB sideband of the acoustic filter are near the anti-resonant frequency point of the acoustic wave resonator S3, and at the same time are within the passbands of the series resonant acoustic wave resonators S1 and S2 on the other series arms 11 of the resonator; in addition, a new transmission zero is added to the right sideband of the acoustic wave filter, making the sideband steeper; similarly, a new transmission zero is also added to the left sideband of the acoustic wave filter, making the sideband steeper, and the first transmission zero on the left side of the passband of the acoustic wave filter corresponds to the resonant frequency point of the acoustic wave resonator P1 on the parallel arm 12 of the resonator, and the frequency points of the 3dB sideband of the acoustic filter are near the resonant frequency point of the acoustic wave resonator P1. At this time, when the anti-resonant frequency of the acoustic wave resonator S3 and the resonant frequency of the acoustic wave resonator P1 change with temperature, the sidebands of the acoustic filter drift accordingly, and are most affected by the drift of the anti-resonant frequency and resonant frequency of these two acoustic wave resonators S3 and P1.

[0130] As Figure 22 and Figure 23 shown are the frequency temperature coefficient TCF and the electromechanical coupling coefficient of the resonant frequency point and anti-resonant frequency point of the acoustic wave resonator when exciting the horizontally polarized shear wave as the target acoustic wave mode based on the X-tangent LiNbO3 piezoelectric thin film / SiC high acoustic velocity supporting substrate The trend curve graph of the change with the in-plane propagation direction theta, where the abscissa is the in-plane rotation angle theta, and the left and right vertical axes are the normalized frequency temperature coefficient TCF and the normalized electromechanical coupling coefficient respectively First, as Figure 22 shown, when theta is near 0 degrees, takes the maximum value, but at this time the TCF is the worst, reaching the most negative state. At this time, the frequency response is very sensitive to temperature changes, which is not conducive to the stability of the passband of the acoustic wave filter; in the range of theta from 0° to 40°, as theta increases, the TCF gradually improves. In the range of theta from 0° to 60°, the TCF remains within a good range (less than the absolute value of 1); especially, when reaches 60% of the maximum value, the TCF becomes 87% of the maximum value, which has relatively decreased by 13%. When reaches 45% of the maximum value, the TCF becomes 82% of the maximum value, relatively decreasing by 18%, both showing an improvement in frequency stability; as Figure 23 shown, when theta is near 0 degrees, Take the maximum value. At this time, the TCF is 75% of the maximum value, that is, the two parameters can both achieve good states. When theta is in the range of 0 - 40 degrees, as theta increases, the TCF gradually improves. In particular, when reaches 60% of the maximum value, the TCF becomes 63% of the maximum value. Based on the anisotropic change characteristics of the piezoelectric thin film and the high - speed sound - supporting substrate, the frequency design of the acoustic wave resonator in the electrical topology structure of the acoustic filter can be changed, and the relative rotation angle between the acoustic wave resonators can be changed to adjust the electromechanical coupling coefficient According to actual needs, the parameters of the acoustic wave resonator are comprehensively designed to make the correspondence relationship between the zero - point position, pass - band of the acoustic filter and the characteristic frequency points of the acoustic wave resonator more accurate. At the same time, the anisotropy of the piezoelectric thin - film material is used to achieve the neutralization of the electromechanical coupling coefficient and TCF. In this experimental example, it is to adjust the electromechanical coupling coefficients of the side - band of the acoustic filter and the two acoustic wave resonators S3 and P1 to decrease, that is, from 20.12% and 19.51% in Comparative Example 1 to 11.98% and 12.00%. However, the absolute values of the TCF of the two acoustic wave resonators S3 and P1 decrease from 50 and 50 in Comparative Example 1 to 31.5 and 43.5. That is, under the condition of meeting the requirements of the electromechanical coupling coefficient of the acoustic filter, by sacrificially reducing some electromechanical coupling coefficients predictably, the absolute value of the TCF of the acoustic resonator corresponding to the side - band of the acoustic filter is reduced as much as possible to ensure the pass - band of the acoustic filter and improve the frequency - temperature stability of the acoustic filter, and reduce the loss caused by frequency drift of the pass - band and side - band signals. On the other hand, from the figure of merit being a constant, when decreases, the quality factor Q value increases, which can bring a higher Q value and a steeper band - edge, and is also beneficial to improving the frequency - temperature stability.

[0131] As Figure 25 shown is a schematic diagram of the pass - band change of the acoustic filter in this experimental example at - 25 °C, 55 °C and 125 °C. It can be seen from the figure that as the temperature of the acoustic filter increases, the drift of the pass - band to the low - frequency band is effectively reduced, that is, the stability of the pass - band of the acoustic filter in the variable - temperature environment is significantly improved.

[0132] As Figure 26 and Figure 27 shown, it shows the frequency - temperature drift coefficient TCF and electromechanical coupling coefficient of the resonance frequency point and anti - resonance frequency point of the acoustic wave resonator when exciting the horizontal shear wave as the target acoustic wave mode based on the YX - cut and tangent LiNbO3 piezoelectric thin film / SiC high - speed sound - supporting substrate Curve graph showing the variation trend with the in-plane propagation direction θ. Here, the abscissa is the in-plane rotation angle θ, and the left and right vertical axes are the normalized temperature coefficient of frequency TCF and the normalized electromechanical coupling coefficient respectively Similarly, when the acoustic filter is implemented using this heterogeneous substrate structure, the anisotropic characteristics of specific acoustic waves in this heterogeneous substrate structure can also be utilized to define the propagation angle range where the TCF and the electromechanical coupling coefficient are effectively balanced. Within this angle range, by changing the frequency design of the acoustic wave resonators in the electrical topology of the acoustic filter, the electromechanical coupling coefficient is adjusted, comprehensively making the corresponding relationship between the zero point position, the passband, and the characteristic frequency points of the acoustic wave resonators of the acoustic filter more accurate, the passband edge of the acoustic filter steeper, and at the same time, the anisotropy of the piezoelectric thin film material is used to balance the electromechanical coupling coefficient and the TCF, improving the frequency temperature stability of the passband of the acoustic filter.

[0133] In summary, for the acoustic filter with low temperature drift of the present invention, at least one equivalent series resonator with the maximum resonance frequency and the minimum anti-resonance frequency is provided on the series arm of the resonator in its electrical topology, and the absolute value of the TCF of the at least one equivalent series resonator is less than the absolute values of the TCFs of all other equivalent series resonators. The first transmission zero on the right side of the passband of the thus formed acoustic filter corresponds to the anti-resonance frequency point of the at least one equivalent series resonator, and the frequency points of the 3dB sideband of the acoustic filter are located near the anti-resonance frequency point of the at least one equivalent series resonator and at the same time within the passband of other equivalent series resonators, so that the at least one equivalent series resonator has the greatest influence on the right sideband of the passband of the acoustic filter, and the at least one equivalent series resonator has the smallest absolute value of the TCF value. Thus, without affecting the passband response of the acoustic filter, the frequency temperature stability of the passband frequency and the right edge of the passband of the acoustic filter can be effectively enhanced, the loss of the passband and sideband signals of the acoustic filter due to frequency drift can be reduced, the requirement for the resonator bandwidth is lowered, especially when the adjacent frequency band on the right side of the target frequency band of the acoustic filter is crowded, the fault tolerance range on the right side of the target frequency band of the acoustic filter is increased, and the design difficulty of the acoustic filter is reduced; in addition, when the support substrate of the acoustic wave resonator in the acoustic filter uses a material with high thermal conductivity, the heat dissipation performance of the device can also be improved, further assisting in reducing frequency drift. Therefore, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0134] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An acoustic filter with low temperature drift, characterized in that, The acoustic filter includes: m equivalent series resonators and n equivalent parallel resonators, where m and n are natural numbers greater than or equal to 1, and m≥n; The m equivalent series resonators are connected in series in turn between the input end and the output end to form a resonator series arm; One end of each of the n equivalent parallel resonators is respectively connected to m-1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m-1 resonator parallel arms; or one end of each of the n equivalent parallel resonators is respectively connected to m-1 nodes between adjacent equivalent series resonators and the head or tail of the resonator series arm, and the other ends of the n equivalent parallel resonators are grounded to form m resonator parallel arms; The resonant frequency of at least one of the equivalent series resonators in the resonator series arm is higher than that of the other equivalent series resonators in the resonator series arm, the anti-resonant frequency of the at least one equivalent series resonator is lower than that of the other equivalent series resonators in the resonator series arm, and the absolute value of the TCF of the at least one equivalent series resonator is less than the absolute value of the TCF of the other equivalent series resonators in the resonator series arm; The acoustic filter is formed based on a heterogeneous substrate structure; the heterogeneous substrate structure includes a high-speed sound-supporting substrate with anisotropy and a piezoelectric thin film with in-plane anisotropy located on the high-speed sound-supporting substrate, wherein the slow shear wave sound speed of the high-speed sound-supporting substrate is higher than the sound speed of the target acoustic wave mode in the piezoelectric thin film.

2. The low-temperature-drift acoustic filter according to claim 1, characterized in that: m is an odd number greater than 1; All the equivalent series resonators are arranged symmetrically about the (m+1) / 2-th equivalent series resonator in terms of physical structure; The resonant frequency of the (m+1) / 2-th equivalent series resonator in the resonator series arm is higher than that of the other equivalent series resonators in the resonator series arm, the anti-resonant frequency of the (m+1) / 2-th equivalent series resonator is lower than that of the other equivalent series resonators in the resonator series arm, and the absolute value of the TCF of the (m+1) / 2-th equivalent series resonator is less than the absolute value of the TCF of the other equivalent series resonators in the resonator series arm.

3. The acoustic filter with low temperature drift according to claim 2, characterized in that: n=m-1, and one end of each of the n equivalent parallel resonators is respectively connected to m-1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m-1 resonator parallel arms.

4. The acoustic filter with low temperature drift according to claim 3, characterized in that: All the equivalent parallel resonators are arranged symmetrically about the (m+1) / 2-th equivalent series resonator in terms of physical structure.

5. The acoustic filter with low temperature drift according to claim 1, characterized in that: The resonance frequency of the equivalent parallel resonator on at least one of the resonator parallel arms among all the resonator parallel arms is higher than that of the equivalent parallel resonators on other resonator parallel arms, the anti-resonance frequency of the equivalent parallel resonator on the at least one resonator parallel arm is lower than that of the equivalent parallel resonators on other resonator parallel arms, and the absolute value of the TCF of the equivalent parallel resonator on the at least one resonator parallel arm is less than the absolute value of the TCF of the equivalent parallel resonators on other resonator parallel arms.

6. The acoustic filter with low temperature drift according to claim 5, characterized in that: m is an odd number greater than 1, and n = m - 1; one ends of the n equivalent parallel resonators are respectively connected to m - 1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 resonator parallel arms; All the equivalent series resonators and all the equivalent parallel resonators are arranged in a symmetric distribution in physical structure with respect to the (m + 1) / 2-th equivalent series resonator in sequence; The resonance frequency of the (m + 1) / 2-th equivalent series resonator in the resonator series arm is higher than that of other equivalent series resonators in the resonator series arm, the anti-resonance frequency of the (m + 1) / 2-th equivalent series resonator is lower than that of other equivalent series resonators in the resonator series arm, and the absolute value of the TCF of the (m + 1) / 2-th equivalent series resonator is less than the absolute value of the TCF of other equivalent series resonators in the resonator series arm; The resonance frequencies of the equivalent parallel resonators on at least two resonator parallel arms that are symmetrically distributed in physical structure with respect to the (m + 1) / 2-th equivalent series resonator among all the resonator parallel arms are higher than those of the equivalent parallel resonators on other resonator parallel arms, the anti-resonance frequencies of the equivalent parallel resonators on the at least two resonator parallel arms that are symmetrically distributed in physical structure with respect to the (m + 1) / 2-th equivalent series resonator are lower than those of the equivalent parallel resonators on other resonator parallel arms, and the absolute values of the TCFs of the equivalent parallel resonators on the at least two resonator parallel arms that are symmetrically distributed in physical structure with respect to the (m + 1) / 2-th equivalent series resonator are less than the absolute values of the TCFs of the equivalent parallel resonators on other resonator parallel arms.

7. The acoustic filter with low temperature drift according to claim 1, characterized in that: The equivalent series resonator is equivalently formed by one acoustic wave resonator, or the equivalent series resonator is equivalently formed by multiple acoustic wave resonators in a series and / or parallel manner; the equivalent parallel resonator is equivalently formed by one acoustic wave resonator, or the equivalent parallel resonator is equivalently formed by multiple acoustic wave resonators in a series and / or parallel manner.

8. The acoustic filter with low temperature drift according to claim 1, wherein: The target mode of the acoustic filter is a horizontal shear wave or a longitudinal leaky wave or a longitudinal wave.

9. The acoustic filter with low temperature drift according to claim 1, characterized in that: The material of the piezoelectric thin film is one 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, gallium arsenide. The thickness of the piezoelectric thin film does not exceed 0.45λ, where λ is the wavelength of the acoustic wave of the target mode of the acoustic filter; the material of the high-speed sound support substrate is one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like, gallium nitride, boron carbide, boron nitride, aluminum nitride, and the material of the high-speed sound support substrate is different from the material of the piezoelectric thin film.

10. An acoustic filter with low temperature drift, characterized in that, The acoustic filter includes: m equivalent series resonators and n equivalent parallel resonators, where m and n are natural numbers greater than or equal to 1, and m≥n; The m equivalent series resonators are sequentially connected in series between the input end and the output end to form a resonator series arm; One end of each of the n equivalent parallel resonators is respectively connected to m - 1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 resonator parallel arms; or one end of each of the n equivalent parallel resonators is respectively connected to m - 1 nodes between adjacent equivalent series resonators and the first or last end of the resonator series arm, and the other ends of the n equivalent parallel resonators are grounded to form m resonator parallel arms; The resonance frequency of the equivalent parallel resonators on at least one of the resonator parallel arms among all the resonator parallel arms is higher than that of the equivalent parallel resonators on other resonator parallel arms, the anti-resonance frequency of the equivalent parallel resonators on the at least one resonator parallel arm is lower than that of the equivalent parallel resonators on other resonator parallel arms, and the absolute value of the TCF of the equivalent parallel resonators on the at least one resonator parallel arm is less than the absolute value of the TCF of the equivalent parallel resonators on other resonator parallel arms; The acoustic filter is formed based on a hetero-substrate structure; the hetero-substrate structure includes a high-speed sound support substrate with anisotropy and a piezoelectric thin film with in-plane anisotropy located on the high-speed sound support substrate, where the slow shear wave sound speed of the high-speed sound support substrate is higher than the sound speed of the target acoustic wave mode in the piezoelectric thin film.

11. The acoustic filter with low temperature drift according to claim 10, characterized in that: m is an odd number greater than 1, n = m - 1; One end of each of the n equivalent parallel resonators is respectively connected to m - 1 nodes between adjacent equivalent series resonators, and the other ends of the n equivalent parallel resonators are grounded to form m - 1 resonator parallel arms; All the equivalent parallel resonators are symmetrically distributed and arranged in sequence with respect to the (m + 1) / 2-th equivalent series resonator in terms of physical structure; The resonance frequencies of the equivalent parallel resonators on at least two of all the parallel arms of the resonators, which are symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator, are higher than those of the equivalent parallel resonators on the other parallel arms of the resonators. The anti-resonance frequencies of the equivalent parallel resonators on the at least two parallel arms of the resonators, which are symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator, are lower than those of the equivalent parallel resonators on the other parallel arms of the resonators. And the absolute value of the TCF of the equivalent parallel resonators on the at least two parallel arms of the resonators, which are symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator, is smaller than the absolute value of the TCF of the equivalent parallel resonators on the other parallel arms of the resonators.

12. The acoustic filter with low temperature drift according to claim 11, characterized in that: All the equivalent series resonators are arranged in sequence symmetrically distributed physically with respect to the ((m + 1) / 2)-th equivalent series resonator.

13. The acoustic filter with low temperature drift according to claim 10, characterized in that: The equivalent series resonator is equivalently formed by one acoustic resonator, or the equivalent series resonator is equivalently formed by multiple acoustic resonators in series and / or parallel manners; the equivalent parallel resonator is equivalently formed by one acoustic resonator, or the equivalent parallel resonator is equivalently formed by multiple acoustic resonators in series and / or parallel manners.

14. The acoustic filter with low temperature drift according to claim 10, characterized in that: The target mode of the acoustic filter is a horizontal shear wave or a longitudinal leaky wave or a longitudinal wave.

15. The acoustic filter with low temperature drift according to claim 10, characterized in that: The material of the piezoelectric thin film is one 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, gallium arsenide, and the thickness of the piezoelectric thin film does not exceed 0.45λ, where λ is the wavelength of the acoustic wave of the target mode of the acoustic filter; the material of the high sound velocity support substrate is one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, aluminum nitride, and the material of the high sound velocity support substrate is different from the material of the piezoelectric thin film.

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