Low temperature drift acoustic filter

Abstract

The invention provides an acoustic filter with low temperature drift, which is characterized in that at least one equivalent series resonator with the maximum resonant frequency and the minimum anti-resonant frequency is arranged on a resonator series arm of an electrical topological structure of the acoustic filter, and the absolute value of the TCF of the at least one equivalent series resonator is smaller than the absolute values of the TCFs of all other equivalent series resonators. The acoustic filter can effectively enhance the passband frequency of the acoustic filter and the frequency temperature stability of the right side edge of the passband under the condition that the passband response is not influenced, reduces the requirement on the bandwidth of the resonator, and particularly, when the right side close frequency band of the target frequency band of the acoustic filter is relatively crowded, the bandwidth of the resonator is reduced. The fault-tolerant range of the right side of the target frequency band of the acoustic filter is improved; the design difficulty of the acoustic filter is reduced; in addition, when the supporting 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, and frequency drift is further reduced in an auxiliary mode.

Description

Technical Field

[0001] The invention belongs to the field of microelectronic technology, and in particular 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 3GHz and lower frequency bands have been allocated to serve a variety of application scenarios such as communication, data transmission, and the Internet of Things. On the one hand, the efficient use of frequency bands has effectively expanded the application field of intelligent services, and at the same time improved communication speed and service quality. Different applications are carried out in an orderly manner within their allocated frequency bands; on the other hand, there is also the problem of increasing congestion in the frequency bands below 3GHz. In order to ensure the accurate transmission of signals within a specific frequency band, the stability requirements of filter devices are also increased. However, the stability of the filter passband is closely related to the device operating temperature and the intrinsic frequency temperature coefficient (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 commonly used 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 corresponding filter passband moves to a low frequency as a whole. The offset of the operating frequency will not only cause the passband signal distortion and increase the loss of the sideband signal, but may also affect the out-of-band suppression of this passband relative to other frequency bands. When the frequency of the acoustic filter device changes significantly with temperature, the drift frequency part should also be included in 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 crowded with adjacent frequency bands, the reserved frequency band also needs to consider the out-of-band suppression level relative to the adjacent frequency band, and the fault tolerance range is small. Summary of the invention

[0004] In view of the shortcomings of the prior art mentioned above, the object of the present invention is to provide an acoustic filter with low temperature drift, which is used to solve the problem that the frequency temperature stability of the target frequency band of the acoustic filter in the prior art is poor, the requirement for the resonator bandwidth is increased, or when the adjacent frequency bands of the target frequency band of the acoustic filter are relatively crowded, the fault tolerance range of the acoustic filter design is reduced, that is, the difficulty of acoustic filter design is increased.

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

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

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

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

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

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

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

[0012] Further, n=m-1, and one end of the n equivalent parallel resonators is respectively connected to m-1 nodes between adjacent equivalent series resonators, and the other end of the n equivalent parallel resonators is grounded, forming m-1 resonator parallel arms.

[0013] Furthermore, in terms of physical structure, all the equivalent parallel resonators are symmetrically distributed and arranged in sequence with respect to the (m+1) / 2th equivalent series resonator.

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

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

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

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

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

[0019] The resonant frequency of the equivalent parallel resonators on at least two of the resonator parallel arms that are symmetrically distributed about the (m+1) / 2th equivalent series resonator in physical structure among all the resonator parallel arms is higher than the resonant frequency of the equivalent parallel resonators on other resonator parallel arms, the anti-resonant frequency of the equivalent parallel resonators on at least two of the resonator parallel arms that are symmetrically distributed about the (m+1) / 2th equivalent series resonator in physical structure is lower than the anti-resonant frequency of the equivalent parallel resonators on other resonator parallel arms, and the absolute value of the TCF of the at least two of the equivalent parallel resonators on the resonator parallel arms that are symmetrically distributed about the (m+1) / 2th equivalent series resonator in physical structure is smaller than the absolute value of the TCF of the equivalent parallel resonators on 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 connected in series and / or in 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 connected in series and / or in parallel.

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

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

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

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

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

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

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

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

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

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

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

[0032] Furthermore, in terms of physical structure, all the equivalent series resonators are symmetrically distributed and arranged in sequence with respect to the (m+1) / 2th equivalent series resonator.

[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 connected in series and / or in 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 connected in series and / or in parallel.

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

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

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

[0037] As described above, the low temperature drift acoustic filter of the present invention has at least one equivalent series resonator with the maximum resonant frequency and the minimum anti-resonant frequency arranged on the resonator series arm of its electrical topology structure, and the absolute value of the TCF of the at least one equivalent series resonator is smaller than the absolute values ​​of the TCF of all other equivalent series resonators. The first transmission zero point on the right side of the acoustic filter passband thus formed corresponds to the anti-resonance frequency point of at least one equivalent series resonator, and the frequency point of the 3dB sideband of the acoustic filter is located near the anti-resonance frequency point of the at least one equivalent series resonator and is simultaneously located within the passband of other equivalent series resonators, so that the at least one equivalent series resonator has the greatest impact on the right sideband of the acoustic filter passband, and the at least one equivalent series resonator has a 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 of the acoustic filter and the right edge of the passband can be effectively enhanced, the loss of the acoustic filter passband and sideband signals due to frequency drift is reduced, and the requirements for the resonator bandwidth are reduced, especially when the adjacent frequency bands on the right side of the target frequency band of the acoustic filter are 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 supporting 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figures 1 to 11 Shown are schematic diagrams of multiple electrical topological structures of a low temperature drift acoustic filter according to a first embodiment of the present invention.

[0039] Figures 12 to 16 Shown are schematic diagrams of multiple electrical topological structures of a low temperature drift acoustic filter according to a second embodiment of the present invention.

[0040] Fig.17 A schematic cross-sectional view showing the physical structure of the low temperature drift acoustic filter of the present invention.

[0041] Fig.18 Shown is a schematic diagram of the electrical topology of the acoustic filter of comparative example 1.

[0042] Fig.19 Shown is a frequency response curve of the acoustic wave resonator in the acoustic filter of comparative example 1 and a passband response curve of the corresponding acoustic filter.

[0043] Fig. 20 Shown is a schematic diagram of the electrical topology of the acoustic filter of Experimental Example 1.

[0044] Fig.21 Shown is the frequency response curve of the acoustic wave resonator in the acoustic filter of Experimental Example 1 and the passband response curve of the corresponding acoustic filter.

[0045] Fig. 22 Displayed as X-tangent LiNbO 3 Temperature drift coefficient TCF and electromechanical coupling coefficient of the resonator resonance point of piezoelectric film / SiC high acoustic velocity support substrate A graph showing the trend of theta as the propagation direction in the plane changes.

[0046] Fig.23 Displayed as X-tangent LiNbO 3 Frequency temperature drift coefficient TCF and electromechanical coupling coefficient of the anti-resonance point of the resonator based on piezoelectric film / SiC high acoustic velocity support substrate A graph showing the trend of theta as the propagation direction in the plane changes.

[0047] Fig.24 The diagram shows the change in the passband of the acoustic filter of comparative example 1 when the temperature changes.

[0048] Fig.25 The diagram shows the change in the passband of the acoustic filter of Experimental Example 1 when the temperature changes.

[0049] Fig.26 Displayed as YX-cut lithium niobate (LiNbO 3 )Temperature drift coefficient TCF and electromechanical coupling coefficient of the resonator resonance point of piezoelectric film / SiC high acoustic velocity support substrate A graph showing the trend of theta as the propagation direction in the plane changes.

[0050] Fig. 27 Displayed as YX-cut lithium niobate (LiNbO 3 )Temperature drift coefficient TCF and electromechanical coupling coefficient of the anti-resonance point of the resonator of piezoelectric film / SiC high acoustic velocity support substrate A graph showing the trend of theta as the propagation direction in the plane changes.

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

[0052] Component number description

[0053] 10 Electrical topology

[0054] 11 Resonator series arms

[0055] 110 Equivalent Series Resonator

[0056] 12 Resonator parallel arms

[0057] 120 Equivalent Parallel Resonator

[0058] 13 Input

[0059] 14 Output

[0060] 15. Acoustic Resonator

[0061] 20 Heterogeneous Substrate Structure

[0062] 200 High acoustic velocity support substrate

[0063] 201 Piezoelectric film

[0064] 21 Interdigitated electrodes

[0065] 22 Physical Structure DETAILED DESCRIPTION

[0066] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0067] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0068] For convenience of description, spatial relational terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatial relational terms are intended to include other orientations of the device in use or operation in addition to the orientation depicted in the drawings, and may include embodiments 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, so that the first and second features may not be in direct contact. In addition, when a layer is referred to as being "between" two layers, it may be between the two layers.

[0069] See also Figures 1 to 27 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0070] Embodiment 1

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

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

[0073] One end 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, forming m-1 resonator parallel arms 12 (such as Figure 1 or one end of the n equivalent parallel resonators 120 is respectively connected to the m-1 nodes between the adjacent equivalent series resonators 110 and the head end or the end 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 shown in FIG. Figure 2 and Figure 3 shown);

[0074] The resonant frequency of at least one equivalent series resonator 110 in the resonator series arm 11 is higher than the resonant frequency of the other equivalent series resonators 110 in the resonator series arm 11, the anti-resonant frequency of the at least one equivalent series resonator 110 is lower than the anti-resonant frequency of the other equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the temperature coefficient of frequency (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 constitute the electrical topology 10 of the acoustic filter.

[0075] The low temperature drift acoustic filter of this embodiment has at least one equivalent series resonator with the maximum resonant frequency and the minimum anti-resonant frequency arranged on the resonator series arm of its electrical topology structure, and the absolute value of the TCF of the at least one equivalent series resonator is smaller than the absolute values ​​of the TCF of all other equivalent series resonators. The first transmission zero point on the right side of the acoustic filter passband thus formed corresponds to the anti-resonance frequency point of at least one equivalent series resonator, and the frequency point of the 3dB sideband of the acoustic filter is located near the anti-resonance frequency point of the at least one equivalent series resonator and is simultaneously located within the passband of other equivalent series resonators, so that the at least one equivalent series resonator has the greatest impact on the right sideband of the acoustic filter passband, and the at least one equivalent series resonator has a 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 of the acoustic filter and the right edge of the passband can be effectively enhanced, the loss of the acoustic filter passband and sideband signals due to frequency drift is reduced, and the requirements for the resonator bandwidth are reduced, especially when the adjacent frequency bands on the right side of the target frequency band of the acoustic filter are 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 supporting 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.

[0076] It should be noted here that, for ease of understanding, in the drawings of this embodiment, the arrangement directions of the equivalent series resonators and / or equivalent parallel resonators whose resonant frequencies and anti-resonant frequencies are different from those of other equivalent series resonators and / or equivalent parallel resonators are drawn differently, so as to clearly understand the setting position of the special equivalent series resonator and / or equivalent parallel resonator.

[0077] Any of the equivalent series resonators 110 of this embodiment may be formed by an acoustic wave resonator; Figures 28 to 30 As 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 in parallel, such as Fig.28 The equivalent series resonator 110 is formed by two acoustic wave resonators 15 connected in series. Fig.29 The equivalent series resonator 110 is formed by two acoustic wave resonators 15 connected in parallel. Fig.30 The equivalent series resonator 110 is formed by connecting two acoustic wave resonators 15 connected in series and one acoustic wave resonator 15 in parallel. Similarly, any equivalent parallel resonator 120 of this embodiment can be formed by one acoustic wave resonator; Figures 28 to 30 As 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 in parallel, such as Fig.28 The equivalent parallel resonator 120 is formed by two acoustic wave resonators 15 connected in series. Fig.29 The equivalent parallel resonator 120 is formed by two parallel-connected acoustic wave resonators 15, as shown in FIG. Fig.30 The equivalent parallel resonator 120 is formed by connecting two acoustic wave resonators 15 connected in series and one acoustic wave resonator 15 in parallel. 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 excessively limited here.

[0078] In this embodiment, m equivalent series resonators 110 are connected in series between the input terminal 13 and the output terminal 14 to form a resonator series arm 11; in addition, the number and position of the resonator parallel arm 12 are slightly different according to the connection position of the equivalent parallel resonator 120. For example, Figure 1 In the embodiment, one end of the three equivalent parallel resonators 120 is respectively connected to three nodes between four adjacent equivalent series resonators 110, and the other end of the three equivalent parallel resonators 120 is grounded, thereby forming three resonator parallel arms 12; Figure 2 In the embodiment, one end of three equivalent parallel resonators 120 is respectively connected to three nodes between four adjacent equivalent series resonators 110, 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, thereby forming four resonator parallel arms 12; Figure 3 In the figure, one end of three equivalent parallel resonators 120 is respectively connected to three nodes between four adjacent equivalent series resonators 110, 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 four equivalent parallel resonators 120 are grounded, thereby 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 sequence and symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in physical structure; the resonant frequency of the (m+1) / 2th equivalent series resonator 110 in the resonator series arm 11 is higher than the resonant frequency of other equivalent series resonators 110 in the resonator series arm 11, the anti-resonant frequency of the (m+1) / 2th equivalent series resonator 110 is lower than the anti-resonant frequency of other equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the TCF of the (m+1) / 2th equivalent series resonator 110 is smaller than the absolute value of the TCF of 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 contained in the equivalent series resonator 110, which generally includes a supporting substrate, a piezoelectric film and interdigital electrodes, and all interdigital electrodes are electrically connected through block electrodes according to the actual required connection method to form the required electrical topology 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 resonant frequency is the largest and the anti-resonant frequency is the smallest compared to the resonant frequencies of other equivalent series resonators 110 on the resonator series arm 11, and the number and position of the resonator parallel arm 12 are not excessively restricted. For example, Figure 4 As shown, five equivalent series resonators 110 are sequentially connected in series between the input terminal 13 and the output terminal 14 to form a resonator series arm 11, and the third equivalent series resonator 110 in the middle is set as a special equivalent series resonator with the largest resonant frequency and the smallest anti-resonant frequency. In addition, one end of four equivalent parallel resonators 120 is respectively connected to four nodes between five adjacent equivalent series resonators 110, 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 five equivalent parallel resonators 120 are grounded, thereby forming five resonator parallel arms 12; as shown in FIG. Figure 5 As shown, five equivalent series resonators 110 are sequentially connected in series between the input terminal 13 and the output terminal 14 to form a resonator series arm 11, and the third equivalent series resonator 110 in the middle is set as a special equivalent series resonator with the largest resonant frequency and the smallest anti-resonant frequency. In addition, one end of four equivalent parallel resonators 120 is respectively connected to four nodes between five adjacent equivalent series resonators 110, 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 five equivalent parallel resonators 120 are grounded, thereby forming five resonator parallel arms 12; as shown in FIG. Figure 6As shown, five equivalent series resonators 110 are sequentially connected in series between the input end 13 and the output end 14 to form a resonator series arm 11, and the third equivalent series resonator 110 in the middle is set as a special equivalent series resonator with the largest resonant frequency and the smallest anti-resonant frequency. In addition, one end of four equivalent parallel resonators 120 is respectively connected to four nodes between the five adjacent equivalent series resonators 110, and the other ends of the four equivalent parallel resonators 120 are grounded, thereby forming four resonator parallel arms 12. Preferably, the setting method of the equivalent parallel resonator 120 is selected similar to the following Figure 6 In this way, n=m-1, and one end of the n equivalent parallel resonators 120 is respectively connected to the m-1 nodes between the adjacent equivalent series resonators 110, and the other end of the n equivalent parallel resonators is grounded, forming m-1 resonator parallel arms 12. More preferably, the arrangement of the equivalent parallel resonator 120 is similar to the following: Figure 6 On the basis of the method, it is also set that all the equivalent parallel resonators 120 are symmetrically distributed and arranged in sequence with respect to the (m+1) / 2th equivalent series resonator 110 in physical structure, so that Figure 6 Taking this as an example, from left to right, the physical structure of the first equivalent parallel resonator 120 is the same as the physical structure of the fourth equivalent parallel resonator 120 , and the physical structure of the second equivalent parallel resonator 120 is the same as the physical structure of the third equivalent parallel resonator 120 .

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

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

[0082] One end 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, forming m-1 resonator parallel arms 12 (such as Fig. 9or one end of the n equivalent parallel resonators 120 is respectively connected to the m-1 nodes between the adjacent equivalent series resonators 110 and the head end or the end 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 shown in FIG. Figure 7 and Figure 8 shown);

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

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

[0085] By arranging at least one equivalent series resonator with the maximum resonant frequency and the minimum anti-resonant frequency on the resonator series arm of the electrical topology structure, and making the absolute value of the TCF of the at least one equivalent series resonator smaller than the absolute values ​​of the TCF 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 resonant frequency of the equivalent parallel resonator on at least one resonator parallel arm to the maximum and the anti-resonant frequency to the minimum in the electrical topology structure, and making the absolute value of its TCF smaller than the absolute values ​​of the TCF of all other equivalent parallel resonators, at this time, the first transmission zero point on the left side of the passband of the acoustic filter corresponds to the resonant frequency point of the equivalent parallel resonator on the at least one resonator parallel arm, and the frequency point of the 3dB sideband of the acoustic filter is located within the passband of all equivalent parallel resonators, so that the equivalent parallel resonator on the at least one resonator parallel arm The parallel resonator has the greatest impact on the left sideband of the acoustic filter passband, and the equivalent parallel resonator on the parallel arm of the at least one resonator has a TCF value with the smallest absolute value, which can effectively enhance the frequency-temperature stability of the acoustic filter passband frequency and the left edge of the passband, reduce the loss of the acoustic filter passband and sideband signals due to frequency drift, and ultimately achieve the improvement of the frequency-temperature stability of the acoustic filter passband frequency and the left and right edges of the passband without affecting the passband response of the acoustic filter, thereby reducing the requirements 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, thereby improving the fault tolerance range on the left and right sides of the target frequency band of the acoustic filter, and reducing the design difficulty of the acoustic filter; in addition, when the supporting 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, Fig.10 and Fig.11 As shown, m is an odd number greater than 1, n=m-1;

[0087] One end 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, forming m-1 resonator parallel arms 12;

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

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

[0090] The resonant frequency of the equivalent parallel resonator 120 on at least two of the resonator parallel arms 12 that are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in terms of physical structure is higher than the resonant frequency of the equivalent parallel resonator 120 on the other resonator parallel arms 12, and the at least two resonator parallel arms 12 that are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in terms of physical structure are The anti-resonance frequency of the equivalent parallel resonator 120 on the (m+1) / 2th equivalent series resonator 110 is lower than the anti-resonance frequency of the equivalent parallel resonator 120 on other resonator parallel arms 12, and the absolute value of the TCF of the equivalent parallel resonator 120 on at least two resonator parallel arms 12 that are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in physical structure is smaller than the absolute value of the TCF of the equivalent parallel resonator 120 on other resonator parallel arms 12.

[0091] like Fig.10As shown, one end of the four equivalent parallel resonators 120 is respectively connected to four nodes between adjacent equivalent series resonators 110, and the other end of the four equivalent parallel resonators 120 is grounded to form four resonator parallel arms 12; the five equivalent series resonators 110 and the four equivalent parallel resonators 120 are symmetrically distributed and arranged in sequence with respect to the third equivalent series resonator 110 in terms of physical structure; the third equivalent series resonator in the resonator series arm 110 is connected to the first resonator series arm 120, and the second equivalent series resonator 110 is connected to the first resonator series arm 120. The resonant frequency of the resonator 110 is higher than the resonant frequency of the other four equivalent series resonators 110 in the resonator series arm 11, the anti-resonant frequency of the third equivalent series resonator 110 is lower than the anti-resonant frequency of the other four equivalent series resonators 110 in the resonator series arm 11, and the absolute value of the TCF of the third equivalent series resonator 110 is less than the absolute value of the TCF of the other four equivalent series resonators 110 in the resonator series arm 11. The resonant frequency of the equivalent parallel resonator 120 on the first and fourth resonator parallel arms 12 that are symmetrically distributed with respect to the third equivalent series resonator 110 in physical structure is higher than the resonant frequency of the equivalent parallel resonator 120 on the other two resonator parallel arms 12, and the at least two resonator parallel arms 12 that are symmetrically distributed with respect to the third equivalent series resonator 110 in physical structure are The anti-resonance frequency of two of the equivalent parallel resonators 120 is lower than the anti-resonance frequency of the two equivalent parallel resonators 120 on the other two 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 third equivalent series resonator 110 in physical structure is smaller than the absolute value of the TCF of the equivalent parallel resonators 120 on the other two resonator parallel arms 12.

[0092] Fig.11 The electrical topology and Fig.10 Basically the same, the difference is that Fig.11 The equivalent parallel resonator 120 on the second resonator parallel arm and the equivalent parallel resonator 120 on the third resonator parallel arm are symmetrically distributed. Fig.10 The propagation direction is different.

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

[0094] As a specific example, Fig.17As shown, the acoustic filter is formed based on a heterogeneous substrate structure 20, that is, the physical structures of all equivalent parallel resonators and equivalent series resonators on the acoustic filter are obtained based on the same heterogeneous substrate structure 20, and the heterogeneous substrate structure 20 includes a high-acoustic-velocity support substrate 200 with anisotropy and a piezoelectric film 201 with in-plane anisotropy located on the high-acoustic-velocity support substrate 200, wherein the slow shear wave velocity of the acoustic-velocity support substrate 200 is higher than the velocity of the target acoustic wave mode in the piezoelectric film 201. Selecting the piezoelectric film 201 with in-plane anisotropy can achieve the setting of equivalent parallel resonators and equivalent series resonators of the required frequency band by adjusting the parameters of the interdigital electrodes 21 thereon, for example, by adjusting the different directions in which the interdigital electrodes 21 are arranged on the piezoelectric film 201 to make the propagation directions of the acoustic wave resonators different, so as to achieve the adjustment of the frequency band of the acoustic wave resonator.

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

[0096] like Fig.17 As shown, as an example, the material of the interdigitated electrode 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 thereof; the interdigitated electrode 102 includes a single-layer interdigitated electrode or a composite stacked interdigitated electrode.

[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 consistent with that in the first embodiment. The difference is that this embodiment mainly has high requirements for the frequency temperature stability of the frequency points on the left side of the passband of the acoustic filter. In this case, the frequency temperature stability of the frequency points on the left side of the passband of the acoustic filter is mainly improved. Figures 12 to 16 As 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 equivalent series resonators 110 are connected in series between the input terminal 13 and the output terminal 14 to form a resonator series arm 11;

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

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

[0102] The low temperature drift acoustic filter of this embodiment sets the resonant frequency of the equivalent parallel resonator on at least one resonator parallel arm to the maximum and the anti-resonant frequency to the minimum in the electrical topology structure, and makes the absolute value of its TCF smaller than the absolute value of the TCF of all other equivalent parallel resonators. At this time, the first transmission zero point on the left side of the passband of the acoustic filter corresponds to the resonant frequency point of the equivalent parallel resonator on the at least one resonator parallel arm, and the frequency point of the 3dB sideband of the acoustic filter is within the passband 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 at least one resonator and The equivalent parallel resonator on the connecting arm has the smallest TCF value in 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 can be effectively enhanced, the loss of the passband and sideband signals of the acoustic filter due to frequency drift can be reduced, and the requirement for the bandwidth of the resonator can be reduced. 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 supporting 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.

[0103] As a specific example, Fig.15 and Fig.16 As shown, m is an odd number greater than 1, n=m-1; one end 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, forming m-1 resonator parallel arms 12;

[0104] All the equivalent parallel resonators 120 are arranged in sequence in a symmetrical distribution with respect to the (m+1) / 2th equivalent series resonator 110 in terms of physical structure;

[0105] The resonant frequency of the equivalent parallel resonator 120 on at least two of the resonator parallel arms 12 that are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in terms of physical structure is higher than the resonant frequency of the equivalent parallel resonator 120 on the other resonator parallel arms 12, and the at least two resonator parallel arms 12 that are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in terms of physical structure are The anti-resonance frequency of the equivalent parallel resonator 120 on the (m+1) / 2th equivalent series resonator 110 is lower than the anti-resonance frequency of the equivalent parallel resonator 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 two resonator parallel arms 12 that are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in physical structure is smaller than the absolute value of the TCF of the equivalent parallel resonator 120 on the other resonator parallel arms 12. Further, as Fig.15 and Fig.16 As shown, all the equivalent series resonators 110 are arranged in sequence and are symmetrically distributed about the (m+1) / 2th equivalent series resonator 110 in terms of physical structure.

[0106] like Fig.15 In the embodiment, one end of the four equivalent parallel resonators 120 is respectively connected to four nodes between adjacent equivalent series resonators 110, and the other end of the four equivalent parallel resonators 120 is grounded to form four resonator parallel arms 12; the four equivalent parallel resonators 120 are symmetrically distributed with respect to the third equivalent series resonator 110 in terms of physical structure and are arranged in sequence; the first and fourth of the four resonator parallel arms 12 are symmetrically distributed with respect to the third equivalent series resonator 110 in terms of physical structure, and the resonant frequency of the equivalent parallel resonator 120 on the resonator parallel arms 12 is higher than that on the other two (the second and the third) resonator parallel arms 12. The resonant frequency of the equivalent parallel resonator 120 of the equivalent parallel resonator 120, the anti-resonant frequency of the two equivalent parallel resonators 120 on the at least two resonator parallel arms 12 that are symmetrically distributed with respect to the third equivalent series resonator 110 in physical structure is lower than the anti-resonant frequency of the two equivalent parallel resonators 120 on the other two resonator parallel arms 12, and the absolute value of the TCF of the at least two equivalent parallel resonators 120 on the resonator parallel arms 12 that are symmetrically distributed with respect to the third equivalent series resonator 110 in physical structure is smaller than the absolute value of the TCF of the equivalent parallel resonators 120 on the other two resonator parallel arms 12.

[0107] Fig.16 The electrical topology and Fig.15 Basically the same, the difference is that Fig.16 The equivalent parallel resonator 120 on the second resonator parallel arm and the equivalent parallel resonator 120 on the third resonator parallel arm are symmetrically distributed. Fig.15 The propagation direction is different.

[0108] It should be noted here that, for ease of understanding, in the drawings of this embodiment, the arrangement directions of the equivalent series resonators and / or equivalent parallel resonators whose resonant frequencies and anti-resonant frequencies are different from those of other equivalent series resonators and / or equivalent parallel resonators are drawn differently, so as to clearly understand the setting position of the special equivalent series resonator and / or equivalent parallel resonator.

[0109] Any of the equivalent series resonators 110 of this embodiment may be formed by an acoustic wave resonator; Figures 28 to 30 As 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 in parallel, such as Fig.28 The equivalent series resonator 110 is formed by two acoustic wave resonators 15 connected in series. Fig.29 The equivalent series resonator 110 is formed by two acoustic wave resonators 15 connected in parallel. Fig.30 The equivalent series resonator 110 is formed by connecting two acoustic wave resonators 15 connected in series and one acoustic wave resonator 15 in parallel. Similarly, any equivalent parallel resonator 120 of this embodiment can be formed by one acoustic wave resonator; Figures 28 to 30 As 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 in parallel, such as Fig.28 The equivalent parallel resonator 120 is formed by two acoustic wave resonators 15 connected in series. Fig.29 The equivalent parallel resonator 120 is formed by two parallel-connected acoustic wave resonators 15, as shown in FIG. Fig.30 The equivalent parallel resonator 120 is formed by connecting two acoustic wave resonators 15 connected in series and one acoustic wave resonator 15 in parallel. 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 excessively limited here.

[0110] As an example, the acoustic wave target modes of the equivalent parallel resonator and the equivalent series resonator in the acoustic filter may be horizontal shear waves, longitudinal leakage waves, longitudinal waves, and the like.

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

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

[0113] like Fig.17 As shown, as an example, the material of the interdigitated electrode 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 thereof; the interdigitated electrode 102 includes a single-layer interdigitated electrode or a composite stacked interdigitated electrode.

[0114] The following is a further explanation and verification of the beneficial effects of the low temperature drift acoustic filter in the present application in combination with comparative examples and experimental examples. Obviously, the experimental examples described are only part of the experimental examples of the present invention, not all of the experimental examples. Based on the experimental examples of the present invention, all other experimental examples obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0115] Comparative Example 1:

[0116] Set the target frequency band of the acoustic filter passband to B41 (2.496-2.696 GHz). Fig.17The heterogeneous substrate structure 20 of the acoustic filter is shown, wherein the material of the high acoustic velocity support substrate 200 is SiC, and the material of the piezoelectric film 201 is lithium niobate LiNbO with a X tangent. 3 , excite horizontal shear waves as the target acoustic wave mode; adopt Fig.18 The electrical topology 10 shown in the figure designs an acoustic filter: five acoustic wave resonators S1, S2, S3, S2, and S1 are sequentially connected in series on the resonator series arm 11, and the four acoustic wave resonators S1, S2, S2, and S1 are symmetrically distributed about 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 set on the four resonator parallel arms 12, for a total of four acoustic wave resonators P1, P2, P2, P1, and 4 The acoustic wave resonators P1, P2, P2, P1 are symmetrically distributed about 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 arm 12 is the schematic sound 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 the 5 acoustic wave resonators with different parameters are shown in Table 1 below.

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

[0118]

[0119] For the five acoustic wave resonators based on the same physical structure, the acoustic wave propagation direction is consistent, and the acoustic wave wavelength and the corresponding resonant frequency are close, so the electromechanical coupling coefficient between the corresponding acoustic wave resonators is As shown in Table 1, the resonance frequencies of the three acoustic wave resonators S1, S2, and S3 on the resonator series arm 11 are close, and the variation range is within ±50MHz. The resonance frequencies of the two acoustic wave resonators P1 and P2 on the resonator parallel arm 122 are close, and the variation range is within ±20MHz. Moreover, the propagation directions of all acoustic wave resonators are the same. The difference between them is about 20%, which means that they should not differ by more than 1%.

[0120] like Fig.19This is the admittance response curve of the acoustic wave resonator of this comparative example and the passband response curve of the composed acoustic filter. At this time, the first transmission zero point on the right side of the passband of the acoustic filter corresponds to the anti-resonance frequency point of the acoustic wave resonator S1 on the resonator series arm 11, and the frequency point of the 3dB sideband of the acoustic filter is located near the anti-resonance frequency point of the acoustic wave resonator S1, and is also located in the passband of the acoustic wave resonator series resonators S2 and S3 on other resonator series arms 11; the first transmission zero point on the left side of the passband of the acoustic wave filter corresponds to the resonant frequency point of the acoustic wave resonator P2 on the resonator parallel arm 12, and the frequency point of the 3dB sideband of the acoustic filter is located in the passband of the acoustic wave resonators P1 and P2. At this time, when the anti-resonance frequency of the acoustic wave resonator S1 and the resonant frequency of the acoustic wave resonator P2 change with temperature, the sideband of the acoustic filter drifts accordingly, and is most affected by the drift of the anti-resonance frequency and resonant frequency of the two acoustic wave resonators S1 and P2. Therefore, the frequency temperature drift and instability of the passband of the acoustic filter will occur, such as Fig.24 The figure shows the passband change of the acoustic filter of this comparative example at -25℃, 55℃ and 125℃. It can be seen from the figure that as the temperature increases, the passband drift of the acoustic filter to the low frequency band intensifies. This is because when SiC is used as the supporting substrate, the lithium niobate LiNbO 3 The piezoelectric film is used as the piezoelectric layer, and the horizontal shear wave is excited as the target acoustic wave mode. When the Euler angle is (theta, -90°, -90°), since the frequency temperature coefficients of lithium niobate and silicon carbide are both negative, the resonant frequency and the anti-resonant frequency both decrease with increasing temperature. When the device generates heat during operation or is placed in a variable temperature environment, the overall temperature rise of the device will cause the corresponding filter passband to move toward a low frequency as a whole. At this time, the passband of the acoustic filter may deviate from the target frequency band, which will cause the performance of the acoustic filter to deteriorate. The effective compensation method adopted at this time is generally to reserve frequency bands during design to compensate for the passband drift caused by temperature changes, otherwise the signal stability will be lost. However, this method simply increases the requirements for the bandwidth of the acoustic filter, and when the allocated frequency band is crowded, it is difficult to reserve frequency bands.

[0121] Experimental Example 1:

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

[0123] In terms of physical structure, it still adopts Fig.17 In the heterogeneous substrate structure 20 shown, the material of the support substrate 200 is SiC, the material of the piezoelectric film 201 is X-tangent lithium niobate LiNbO3, and horizontal shear waves are excited as the target acoustic wave mode.

[0124] Use Fig. 20 The electrical topology 10 shown is designed to design an acoustic filter: five acoustic wave resonators S1, S2, S3, S2, and S1 are sequentially connected in series on the resonator series arm 11, wherein the four acoustic wave resonators S1, S2, S2, and S1 are symmetrically distributed about 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 the four resonator parallel arms 12, for a total of four acoustic wave resonators P1, P2, P2, and P1. The four acoustic wave resonators P1, P2, P2, and P1 are symmetrically distributed about 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 arm 12 is the schematic sound 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 the 5 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 same as Comparative Example 1 is that the resonant frequencies of the acoustic resonators S1, S2, and S3 on the resonator series arm 11 of this experimental example are close, and the range of variation is within ±50MHz. The resonant frequencies of the acoustic resonators P1 and P2 on the resonator parallel arm 12 are also close, and the range of variation is within ±20MHz. The difference from Comparative Example 1 is that the propagation directions of the acoustic resonators are different, and the acoustic propagation directions of the acoustic resonators S1, S2, and P2 remain unchanged and consistent, so the electromechanical coupling coefficients of the corresponding acoustic resonators are It is still about 20%, while for the acoustic wave resonators S3 and P1, a counterclockwise rotation angle of 26° is generated in the plane compared with the comparative example 1, 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, corresponding to the electromechanical coupling coefficient of the two acoustic wave resonators S3 and P1. There were also some sacrifices, which were reduced to 11.98% and 12.00% respectively.

[0129] like Fig.21It is the admittance response curve of the acoustic wave resonator of this experimental example and the passband response curve of the composed acoustic filter. At this time, the first transmission zero point on the right side of the passband of the acoustic filter corresponds to the anti-resonance frequency point of the acoustic wave resonator S3 on the resonator series arm 11, and the frequency point of the 3dB sideband of the acoustic filter is located near the anti-resonance frequency point of the acoustic wave resonator S3, and is located in the passband of the acoustic wave resonator series resonators S1 and S2 on other resonator series arms 11; in addition, a transmission zero point is added to the right side of the band edge of the acoustic wave filter, making the band edge steeper; similarly, a transmission zero point is also added to the left side of the band edge of the acoustic wave filter, making the band edge steeper, and the first transmission zero point 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 resonator parallel arm 12, and the frequency point of the 3dB sideband of the acoustic filter is located near the resonant frequency point of the acoustic wave resonator P1. At this time, when the antiresonance frequency of the acoustic wave resonator S3 and the resonant frequency of the acoustic wave resonator P1 change with temperature, the sideband of the acoustic filter drifts accordingly and is most affected by the drift of the antiresonance frequency and the resonant frequency of the two acoustic wave resonators S3 and P1.

[0130] like Fig. 22 and Fig.23 Shown is the X-tangent LiNbO 3 The frequency temperature drift coefficient TCF and electromechanical coupling coefficient of the acoustic resonator resonant frequency point and anti-resonant frequency point when the piezoelectric film / SiC high acoustic velocity support substrate excites the horizontal shear wave as the target acoustic wave mode The trend curve of the change with the in-plane propagation direction theta, where the horizontal axis 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, Fig. 22 As shown, when theta is near 0 degrees, When theta is in the range of 0° to 40°, TCF gradually improves with the increase of theta, and in the range of 0° to 60°, TCF remains in a good range (less than the absolute value of 1). In particular, when theta is in the range of 0° to 40°, TCF gradually improves with the increase of theta. In the range of 0° to 60°, TCF remains in a good range (less than the absolute value of 1). When the maximum value is 60%, the TCF becomes 87% of the maximum value, which is a relative decrease of 13%. When it reaches 45% of the maximum value, TCF becomes 82% of the maximum value, a relative decrease of 18%, both showing an improvement in frequency stability; Fig.23 As shown, when theta is near 0 degrees, Take the maximum value, at this time TCF is 75% of the maximum value, that is, the two parameters can achieve a good state at the same time; in the range of theta from 0 to 40 degrees, as theta increases, TCF gradually improves; in particular, when When the maximum value is 60%, the TCF becomes 63% of the maximum value. Based on the anisotropic characteristics of the piezoelectric film and the high acoustic velocity support substrate, the electromechanical coupling coefficient can be adjusted by changing the frequency design of the acoustic wave resonator in the electrical topology of the acoustic filter and changing the relative rotation angle between the acoustic wave resonators. According to actual needs, the parameters of the acoustic wave resonator are comprehensively designed to make the correspondence between the zero point position, passband and characteristic frequency point of the acoustic filter more accurate, and the anisotropy of the piezoelectric film material is used to realize the electromechanical coupling coefficient. In this experimental example, the electromechanical coupling coefficient between the sideband of the acoustic filter and the two acoustic resonators S3 and P1 is adjusted. The absolute values ​​of TCF of the two acoustic wave resonators S3 and P1 are reduced from 50 and 50 in the comparative example 1 to 31.5 and 43.5, that is, under the condition of meeting the requirements of the acoustic filter on the electromechanical coupling coefficient, some electromechanical coupling coefficients are sacrificed in a predetermined manner to reduce the absolute value of TCF of the acoustic resonator corresponding to the sideband of the acoustic filter as much as possible, so as to ensure the passband of the acoustic filter and improve the frequency temperature stability of the acoustic filter, and reduce the loss of the passband and sideband signals due to frequency drift; on the other hand, the figure of merit is As a constant, when The reduction in θ and the improvement in the quality factor Q value can bring about a higher Q value and a steeper band edge, which is also beneficial to improving the frequency temperature stability.

[0131] like Fig.25 The figure shows the schematic diagram of the passband change of the acoustic filter of 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 passband to the low frequency band is effectively reduced, that is, the stability of the passband of the acoustic filter in a variable temperature environment is significantly improved.

[0132] like Fig.26 and Fig. 27 As shown, the YX bevel tangent LiNbO 3 The frequency temperature drift coefficient TCF and electromechanical coupling coefficient of the acoustic resonator resonant frequency point and anti-resonant frequency point when the piezoelectric film / SiC high acoustic velocity support substrate excites the horizontal shear wave as the target acoustic wave mode The trend curve of the change with the in-plane propagation direction theta, where the horizontal axis 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 Similarly, when the acoustic filter is implemented using the heterogeneous substrate structure, the anisotropic characteristics of specific sound waves in the heterogeneous substrate structure can also be used to define the propagation angle range in which TCF and the electromechanical coupling coefficient are effectively compromised. Within this angle range, by changing the frequency design of the acoustic wave resonator in the electrical topology of the acoustic filter and adjusting the electromechanical coupling coefficient, the correspondence between the zero point position, passband and characteristic frequency point of the acoustic filter is made more accurate, and the passband edge of the acoustic filter is made steeper. At the same time, the anisotropy of the piezoelectric film material is used to achieve the neutralization of the electromechanical coupling coefficient and TCF, thereby improving the frequency-temperature stability of the passband of the acoustic filter.

[0133] In summary, the low temperature drift acoustic filter of the present invention has at least one equivalent series resonator with the largest resonant frequency and the smallest anti-resonant frequency arranged on the resonator series arm of its electrical topology structure, and the absolute value of the TCF of the at least one equivalent series resonator is smaller than the absolute values ​​of the TCF of all other equivalent series resonators. The first transmission zero point on the right side of the acoustic filter passband thus formed corresponds to the anti-resonance frequency point of at least one equivalent series resonator, and the frequency point of the 3dB sideband of the acoustic filter is located near the anti-resonance frequency point of the at least one equivalent series resonator and is simultaneously located in 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 acoustic filter passband, and the at least one equivalent series resonator has the smallest absolute value of TCF value, so that without affecting the passband response of the acoustic filter, the frequency temperature stability of the passband frequency of the acoustic filter and the right edge of the passband can be effectively enhanced, the loss of the passband and sideband signals of the acoustic filter due to frequency drift is reduced, and the requirements for the bandwidth of the resonator are reduced, especially when the adjacent frequency bands on the right side of the target frequency band of the acoustic filter are 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 supporting 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, and the frequency drift can be further assisted to be reduced. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0134] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall 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 comprises: 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; 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 the n equivalent parallel resonators is respectively connected to the m-1 nodes between the adjacent equivalent series resonators, and the other end of the n equivalent parallel resonators is grounded to form m-1 resonator parallel arms; or one end of the n equivalent parallel resonators is respectively connected to the m-1 nodes between the adjacent equivalent series resonators and the head end or the end of the resonator series arm, and the other end of the n equivalent parallel resonators is 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 the resonant frequency of other equivalent series resonators in the resonator series arm, the anti-resonant frequency of the at least one equivalent series resonator is lower than the anti-resonant frequency of 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 smaller than the absolute value of the TCF of other equivalent series resonators in the resonator series arm.

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 in sequence in a symmetrical distribution with respect to the (m+1) / 2th equivalent series resonator in terms of physical structure; The resonant frequency of the (m+1) / 2th equivalent series resonator in the resonator series arm is higher than the resonant frequency of other equivalent series resonators in the resonator series arm, the anti-resonant frequency of the (m+1) / 2th equivalent series resonator is lower than the anti-resonant frequency of other equivalent series resonators in the resonator series arm, and the absolute value of the TCF of the (m+1) / 2th equivalent series resonator is smaller than the absolute value of the TCF of other equivalent series resonators in the resonator series arm.

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

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

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

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

7. The low temperature drift acoustic filter 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 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.

8. The low temperature drift acoustic filter according to claim 1, characterized in that: The acoustic filter is formed based on a heterogeneous substrate structure; the heterogeneous substrate structure includes an anisotropic high-acoustic-velocity supporting substrate and a piezoelectric film with in-plane anisotropy located on the high-acoustic-velocity supporting substrate, wherein the slow shear wave velocity of the acoustic-velocity supporting substrate is higher than the velocity of a target acoustic wave mode in the piezoelectric film.

9. The low temperature drift acoustic filter according to claim 8, characterized in that: The target modes of the acoustic filter are horizontal shear waves or longitudinal leakage waves or longitudinal waves.

10. The low temperature drift acoustic filter according to claim 8, characterized in that: The material of the piezoelectric 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, and gallium arsenide. The thickness of the piezoelectric film does not exceed 0.45λ, where λ is the wavelength of the target mode sound wave of the acoustic filter. The material of the high acoustic velocity support substrate is one of silicon carbide, silicon, sapphire, quartz, diamond, diamond-like carbon, gallium nitride, boron carbide, boron nitride, and aluminum nitride, and the material of the high acoustic velocity support substrate is different from the material of the piezoelectric film.

11. An acoustic filter with low temperature drift, characterized in that: The acoustic filter comprises: 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; 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 the n equivalent parallel resonators is respectively connected to the m-1 nodes between the adjacent equivalent series resonators, and the other end of the n equivalent parallel resonators is grounded to form m-1 resonator parallel arms; or one end of the n equivalent parallel resonators is respectively connected to the m-1 nodes between the adjacent equivalent series resonators and the head end or the end of the resonator series arm, and the other end of the n equivalent parallel resonators is grounded to form m resonator parallel arms; The resonant frequency of the equivalent parallel resonator on at least one of all the resonator parallel arms is higher than the resonant frequency of the equivalent parallel resonators on other resonator parallel arms, the anti-resonant frequency of the equivalent parallel resonator on at least one of the resonator parallel arms is lower than the anti-resonant frequency of the equivalent parallel resonators on other resonator parallel arms, and the absolute value of the TCF of the equivalent parallel resonator on at least one of the resonator parallel arms is smaller than the absolute value of the TCF of the equivalent parallel resonators on other resonator parallel arms.

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

13. The low temperature drift acoustic filter according to claim 12, characterized in that: In terms of physical structure, all the equivalent series resonators are symmetrically distributed and arranged in sequence with respect to the (m+1) / 2th equivalent series resonator.

14. The low temperature drift acoustic filter according to claim 11, 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 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.

15. The low temperature drift acoustic filter according to claim 11, characterized in that: The acoustic filter is formed based on a heterogeneous substrate structure; the heterogeneous substrate structure includes an anisotropic high-acoustic-velocity supporting substrate and a piezoelectric film with in-plane anisotropy located on the high-acoustic-velocity supporting substrate, wherein the slow shear wave velocity of the acoustic-velocity supporting substrate is higher than the velocity of a target acoustic wave mode in the piezoelectric film.

16. The low temperature drift acoustic filter according to claim 15, characterized in that: The target modes of the acoustic filter are horizontal shear waves or longitudinal leakage waves or longitudinal waves.

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

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