Surface acoustic wave filter and radio frequency front-end module

Abstract

The embodiment of the present application provides a surface acoustic wave filter and a radio frequency front end module, the surface acoustic wave filter comprising: at least two surface acoustic wave resonators forming an electrical cascade; the surface acoustic wave resonator comprising a reflector and an interdigital transducer; the reflector is distributed on both sides of the interdigital transducer; wherein the interdigital transducer comprises a plurality of spaced electrode fingers; the plurality of electrode fingers are divided into a central finger area and an edge finger area; the distance between the central finger area and the reflector is greater than the distance between the edge finger area and the reflector; in different surface acoustic wave resonators, at least one modulation characteristic parameter is different; wherein the modulation characteristic parameter comprises: the period of the reflector, the period of the edge finger area. Through the embodiment of the present application, the formation of the notch in the passband of the surface acoustic wave filter is suppressed, and the flatness in the passband of the surface acoustic wave filter is improved.

Description

Technical Field

[0001] The embodiments in this application relate to the field of semiconductor manufacturing technology, specifically to a surface acoustic wave filter and a radio frequency front-end module. Background Technology

[0002] Filters are crucial components in mobile communication systems, primarily used to receive radio frequency (RF) signals of specific frequencies and filter out signals of other frequencies. With the continuous advancement of RF front-end module technology, high performance, miniaturization, and increased complexity have become inevitable trends in filter technology development. Among the many types of filters, surface acoustic wave (SAW) filters occupy an important position in the mobile communication field due to their advantages of high performance, low cost, and small size.

[0003] With the continuous development of communication technology, the requirements for signal transmission are constantly increasing, necessitating surface acoustic wave (SAW) filters with greater power handling capacity and better frequency response flatness for filtering. In existing technologies, the overall power handling capacity of SAW filters is mainly improved by cascading multiple resonators.

[0004] However, cascading multiple resonators with existing structures can cause a dip in the passband of the surface acoustic wave (SAW) filter, reducing the passband flatness of the SAW filter and making it difficult to meet the increasingly high filtering performance requirements of SAW filters. Summary of the Invention

[0005] In view of this, several embodiments of this application provide a surface acoustic wave filter and an RF front-end module to improve the passband flatness of the surface acoustic wave filter.

[0006] In one aspect, an embodiment of this application provides a surface acoustic wave (SAW) filter, comprising: at least two SAW resonators forming an electrical cascade; each SAW resonator includes a reflective grating and an interdigital transducer; the reflective grating is distributed on both sides of the interdigital transducer; wherein the interdigital transducer includes a plurality of spaced electrode strips; the plurality of electrode strips are divided into a central strip region and an edge strip region; the distance between the central strip region and the reflective grating is greater than the distance between the edge strip region and the reflective grating; in different SAW resonators, at least one modulation characteristic parameter is different; wherein the modulation characteristic parameter includes: the period of the reflective grating and the period of the edge strip region.

[0007] Optionally, the period of the center finger region of different surface acoustic wave (SAW) resonators is the same; when the period of the reflector grating of different SAW resonators is different, the ratio of the period of the center finger region to the period of the reflector grating of different SAW resonators falls within the range of 1:0.94 to 1:1.06; when the period of the edge finger region of different SAW resonators is different, the ratio of the period of the center finger region to the period of the edge finger region of different SAW resonators falls within the range of 1:0.94 to 1:1.06.

[0008] Optionally, the period of the center finger region of different surface acoustic wave resonators is the same; when the period of the edge finger region of different surface acoustic wave resonators is different, the ratio of the period of the center finger region to the period of the edge finger region of different surface acoustic wave resonators all fall within the range of 1:0.94 to 1:1.06.

[0009] Optionally, the reflective grid includes a plurality of spaced-apart strip electrodes; the number of the strip electrodes falls within the range of 8 to 25.

[0010] Optionally, the number of electrode fingers included in the edge finger area falls within the range of 3 to 20.

[0011] Optionally, the surface acoustic wave filter further includes: a substrate; the substrate includes a piezoelectric layer; the electrode fingers of the interdigital transducer are formed on the surface of the piezoelectric layer; with the normal direction of the substrate as the thickness direction, at least one structural parameter is different in different surface acoustic wave resonators; wherein, the structural parameter includes: the thickness of the piezoelectric layer, the material of the piezoelectric layer, the thickness of the electrode fingers, and the material of the electrode fingers.

[0012] Optionally, when the thickness of the electrode fingers of different surface acoustic wave resonators is different, the ratio of the thickness of the electrode fingers of different surface acoustic wave resonators falls within the range of 1:0.97 to 1:1.03.

[0013] Optionally, when the thickness of the piezoelectric layer of different surface acoustic wave resonators is different, the ratio of the thickness of the piezoelectric layer of different surface acoustic wave resonators falls within the range of 1:0.8 to 1:1.2.

[0014] Optionally, the piezoelectric layer is made of one or more of aluminum nitride, zinc oxide, lithium niobate, lithium tantalate, polyvinylidene fluoride, and titanium lead oxide; the electrode fingers are made of one or more of platinum, gold, copper, silver, titanium, aluminum, nickel, and lead.

[0015] In another aspect, one embodiment of this application provides a radio frequency front-end module including a surface acoustic wave filter as described in the above embodiments.

[0016] Several embodiments of this application provide a surface acoustic wave (SAW) filter including at least two SAW resonators forming an electrical cascade. Each SAW resonator includes an interdigital transducer and a reflective grating, with the reflective grating distributed on both sides of the interdigital transducer. The interdigital transducer includes multiple spaced electrode strips, which are divided into a central strip region and an edge strip region. The distance between the central strip region and the reflective grating is greater than the distance between the edge strip region and the reflective grating. By setting different periods for the reflective gratings and / or edge strip regions of different SAW resonators, the formation of in-passband dips in the SAW filter is suppressed, and the in-passband flatness of the SAW filter is improved. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in describing the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A top view schematic diagram of a surface acoustic wave filter including two cascaded resonators, provided for related technologies.

[0019] Figure 2 for Figure 1 The diagram shows the admittance curves of the two surface acoustic wave resonators and the insertion loss curve of the surface acoustic wave filter.

[0020] Figure 3 This is a top view schematic diagram of the first surface acoustic wave filter provided in an embodiment of this application.

[0021] Figure 4 This is a top view schematic diagram of the second surface acoustic wave filter provided in an embodiment of this application.

[0022] Figure 5 For along Figure 3 A schematic diagram of a cross-section along the A-A' direction.

[0023] Figure 6 A cross-sectional schematic diagram showing the different thicknesses of the electrode fingers for different surface acoustic wave resonators.

[0024] Figure 7 Cross-sectional schematic diagrams showing different piezoelectric layer thicknesses for different surface acoustic wave resonators.

[0025] Figure 8A schematic diagram comparing the insertion loss curves of surface acoustic wave (SAW) filters provided for related technologies and SAW filters provided in the embodiments of this application.

[0026] Figure 9 The diagram shows the admittance curves of two surface acoustic wave (SAW) resonators and the insertion loss curves of a SAW filter when the ratio of the period of the reflection grating of different SAW resonators to the period of the center finger strip region of the interdigital transducer is set to 1.04:1 and 1.05:1, respectively.

[0027] Figure 10 The diagram shows the admittance curves of two surface acoustic wave (SAW) resonators and the insertion loss curves of a SAW filter when the ratio of the period of the reflection grating of different SAW resonators to the period of the central finger strip region of the interdigital transducer is set to 1.03:1 and 1.1:1, respectively.

[0028] Figure 11 This is a schematic diagram showing the admittance curves of the two surface acoustic wave (SAW) resonators and the insertion loss curve of the SAW filter when only the electrode finger thicknesses of the two SAW resonators are changed, and h1:h2 = 1:1.04.

[0029] Figure 12 This is a schematic diagram showing the admittance curves of the two surface acoustic wave (SAW) resonators and the insertion loss curve of the SAW filter when only the electrode finger thicknesses of the two SAW resonators are changed, and h1:h2 = 1:1.02.

[0030] Figure 13 A schematic diagram showing the admittance curves of the two surface acoustic wave (SAW) resonators and the insertion loss curve of the SAW filter when the period of the reflection grating, the period of the edge finger region, and the thickness of the electrode fingers of the two SAW resonators are changed simultaneously.

[0031] Figure 14 This is a schematic diagram of the circuit connection of the surface acoustic wave filter provided in the embodiments of this application.

[0032] Figure 15 This is a schematic diagram of an RF front-end module that includes the surface acoustic wave filter provided in the embodiments of this application.

[0033] Structural designation explanation

[0034] 100, First surface acoustic wave filter; 100a, Second surface acoustic wave filter; 110, First resonator; 111, First reflector grating; 112, First interdigital transducer; 1121, First busbar; 1122, First electrode bar; 120, Second resonator; 121, Second reflector grating; 122, Second interdigital transducer; 1221, Second busbar; 1222, Second electrode bar; 130, Third resonator; 131, Third reflector grating; 132, Third interdigital transducer; 1321. Third busbar; 1322, Third electrode finger; 140, Fourth resonator; 141, Fourth reflector grating; 142, Fourth interdigital transducer; 1421, Fourth busbar; 1422, Fourth electrode finger; 501, Substrate; 502, Isolation layer; 503, Piezoelectric layer; 504, Electrode finger; 700, RF front-end module; 701, Transmitter; 702, Transmission antenna; 703, Receiver; 704, Series resonator; 705, Parallel resonator; 706, Dual-mode coupled surface acoustic wave filter. Detailed Implementation

[0035] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0036] The accompanying drawings provided in this application are only schematic illustrations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component may be changed, and the layout of the components may also be more complex.

[0037] In the description of the embodiments of this application, it should be understood that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "center," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of the stated features.

[0038] With the widespread adoption of 5G technology, surface acoustic wave (SAW) filters used in radio frequency (RF) front-end modules require greater power handling capacity to support wider transmission spectrum ranges, higher data transmission rates, and more complex transmission network architectures. SAW resonators are the basic building blocks of SAW filters. In related technologies, multiple SAW resonators are typically cascaded to distribute the overall input power of the SAW filter, thereby improving its overall power handling capacity.

[0039] Please see Figure 1 and Figure 2 In related technologies, surface acoustic wave (SAW) filters typically consist of multiple identical SAW resonators cascaded together. During SAW propagation, each SAW resonator may exhibit stray modes such as transverse modes, longitudinal modes, or volume waves, leading to abnormal peaks in the admittance curves of the SAW resonators. Figure 2 It can be seen that at the frequency position where the abnormal peak appears in the admittance curve of the surface acoustic wave resonator, a dip appears in the passband of the insertion loss curve of the surface acoustic wave filter, which leads to a decrease in the passband flatness of the surface acoustic wave filter and a deterioration in the filtering performance.

[0040] Further investigation reveals that the passband dip in the surface acoustic wave (SAW) filter is caused by the identical structure of the cascaded SAW resonators. Each SAW resonator exhibits the same response mode at a specific frequency, meaning it displays the same stray modes. These stray modes interact and superimpose. Reflected on the resonator admittance curves, the anomalous peaks generated by the stray modes on each SAW resonator's own admittance curve appear at the same frequency. The superposition of multiple anomalous peaks at the same frequency increases the insertion loss at that frequency, resulting in a significant dip in the SAW filter's passband.

[0041] Therefore, it is necessary to provide a surface acoustic wave filter that includes at least two surface acoustic wave resonators forming an electrical cascade. By setting different modulation characteristic parameters in different surface acoustic wave resonators, including the period of the reflector grating and the period of the edge finger strip region, the superposition of abnormal peaks in the admittance curve of the surface acoustic wave resonator is suppressed, thereby suppressing the formation of the passband dip of the surface acoustic wave filter.

[0042] One embodiment of this application provides a surface acoustic wave (SAW) filter. The SAW filter may include at least two SAW resonators arranged in an electrical cascade. Among the different SAW resonators arranged in the electrical cascade, at least one modulation characteristic parameter is different.

[0043] In this embodiment, the modulation characteristic parameters can be design parameters that affect the insertion loss performance of the surface acoustic wave resonator. Specifically, the modulation characteristic parameters may include the period of the reflector grating and the period of the edge finger strip region.

[0044] In this embodiment, the surface acoustic wave (SAW) resonator can be used to generate resonance at a specific frequency. Specifically, the SAW resonator may include a reflective grating and an interdigital transducer (IDT). The reflective grating is used to reflect sound waves and form a resonant cavity, while the interdigital transducer is used to excite electroacoustic conversion. Along the direction of sound wave propagation, the reflective grating may be distributed on both sides of the interdigital transducer.

[0045] In this embodiment, the period of the reflective grating can affect the frequency selectivity and standing wave mode formation of the surface acoustic wave resonator. Specifically, the reflective grating may include multiple spaced-apart strip electrodes. Taking the distribution direction of the strip electrodes as the width direction of the strip electrodes, the period of the reflective grating can be the distance between the centers of two adjacent strip electrodes, that is, the sum of the width of a single strip electrode along the width direction and the spacing between two adjacent strip electrodes along the width direction.

[0046] To enhance the reflection effect and optimize the adjustment capability of the resonator's frequency response, in this embodiment, the number of strip electrodes can fall within the range of 8 to 25. For example, the number of strip electrodes can be 8, 14, 20, or 25.

[0047] In this embodiment, the interdigital transducer may include a busbar and multiple electrode fingers made of metal. Different electrode fingers may be spaced apart and arranged in an alternating pattern, and electrically connected through the busbar. When an AC voltage is applied to the electrode fingers, the electrode fingers can convert the electrical signal into mechanical vibration according to the inverse piezoelectric effect to generate sound waves. The electrode fingers may be cuboids or cuboid-like shapes; this embodiment does not specifically limit the shape of the electrode fingers.

[0048] In this embodiment, along the propagation direction of the surface acoustic wave (SAW), the multiple electrode strips of the interdigital transducer are divided into a central strip region and an edge strip region. The distance between the central strip region and the reflector grating is greater than the distance between the edge strip region and the reflector grating. Using the SAW propagation direction as the width direction of the electrode strips, the period of the edge strip region can be the distance between the centers of two adjacent electrode strips, that is, the sum of the width of a single electrode strip along the width direction and the spacing between two adjacent electrode strips along the width direction.

[0049] To reduce unnecessary reflections and lower the probability of stray modes, in this embodiment, the number of electrode fingers included in the edge finger region can fall within the range of 3 to 20. For example, the number of electrode fingers included in the edge finger region can be 3, 9, 15, or 20.

[0050] Taking the first surface acoustic wave filter 100, which includes a first resonator 110 and a second resonator 120, as an example, the first surface acoustic wave filter 100 will be described in detail.

[0051] Please see Figure 3 The first resonator 110 may include a first reflective grating 111 and a first interdigital transducer 112. The first reflective grating 111 may include multiple strip electrodes, and the first interdigital transducer 112 may include a first busbar 1121 and multiple first electrode fingers 1122. The spacing between any two adjacent first electrode fingers 1122 is equal, and along the propagation direction of the surface acoustic wave, the multiple first electrode fingers 1122 are divided into a central finger region and an edge finger region.

[0052] The second resonator 120 may include a second reflector grating 121 and a second interdigital transducer 122. The second interdigital transducer 122 includes a second busbar 1221 and a plurality of second electrode fingers 1222. The spacing between any two adjacent second electrode fingers 1222 is equal. Along the propagation direction of the surface acoustic wave, the plurality of second electrode fingers 1222 are divided into a central finger region and an edge finger region. The first resonator 110 and the second resonator 120 are electrically cascaded through adjacent first busbars 1121 and second busbars 1221. The period of the central finger region of the first interdigital transducer 112 is equal to the period of the central finger region of the second interdigital transducer 122.

[0053] To reduce the risk of signal mismatch or interference between electrically cascaded surface acoustic wave resonators, in this embodiment, the period of the central finger strip region of the two interdigital transducers is used as a reference. The ratio of the period of the central finger strip region of the first interdigital transducer 112 to the period of the first reflector grating 111, and the ratio of the period of the central finger strip region of the second interdigital transducer 122 to the period of the second reflector grating 121, can both fall within the range of 1:0.94 to 1:1.06. Specifically, let the period of the first reflector grating 111 be n1, the period of the central finger strip region of the first interdigital transducer 112 be n3, the period of the second reflector grating 121 be n1', and the period of the central finger strip region of the second interdigital transducer 122 be n3'. Then the ratio of n3 to n1 and the ratio of n3' to n1' can both fall within the range of 1:0.94 to 1:1.06. To disperse the energy distribution of stray modes and reduce the superposition of abnormal peaks in the resonator admittance curve at specific frequencies, the periods of the first reflective grating 111 and the second reflective grating 121 are different. Therefore, the ratio of the period of the first reflective grating 111 to the period of the central finger strip region of the first interdigital transducer 112 is different from the ratio of the period of the second reflective grating 121 to the period of the central finger strip region of the second interdigital transducer 122. For example, n3:n1 = 1:0.94, and n3':n1' = 1:0.98, or n3:n1 = 1:1.02, and n3':n1' = 1:1.06.

[0054] Please see Figure 4 Taking the second surface acoustic wave filter 100a, which includes a third resonator 130 and a fourth resonator 140, as an example, the second surface acoustic wave filter 100a will be described in detail.

[0055] The third resonator 130 may include a third reflector grating 131 and a third interdigital transducer 132. The third interdigital transducer 132 may include a third bus bar 1321 and a plurality of third electrode bars 1322. Along the propagation direction of the surface acoustic wave, the plurality of third electrode bars 1322 are divided into a central bar region and an edge bar region. The spacing between any two adjacent third electrode bars 1322 in the central bar region is equal, and the spacing between any two adjacent third electrode bars 1322 in the edge bar region is equal.

[0056] The fourth resonator 140 may include a fourth reflector grating 141 and a fourth interdigital transducer 142. The fourth interdigital transducer 142 may include a fourth bus bar 1421 and multiple fourth electrode bars 1422. Along the propagation direction of the surface acoustic wave, the multiple fourth electrode bars 1422 are divided into a central bar region and an edge bar region. The spacing between any two adjacent fourth electrode bars 1422 in the central bar region is equal, and the spacing between any two adjacent fourth electrode bars 1422 in the edge bar region is equal. The third resonator 130 and the fourth resonator 140 are electrically cascaded through adjacent third bus bars 1321 and fourth bus bars 1421. The period of the central bar region of the third interdigital transducer 132 is equal to the period of the central bar region of the fourth interdigital transducer 142.

[0057] To improve the consistency of the frequency response of the cascaded surface acoustic wave resonators, in this embodiment, the ratio of the period of the central finger region of the two interdigital transducers to the period of the third interdigital transducer 132, the ratio of the period of the central finger region of the fourth interdigital transducer 142 to the period of the fourth reflection grating 141, the ratio of the period of the central finger region of the third interdigital transducer 132 to the period of the edge finger region of the third interdigital transducer 132, and the ratio of the period of the central finger region of the fourth interdigital transducer 142 to the period of the edge finger region of the fourth interdigital transducer 142 can all fall within the range of 1:0.94 to 1:1.06. Specifically, let the period of the third reflector grating 131 be n4, the period of the edge finger strip region of the third interdigital transducer 132 be n5, the period of the center finger strip region of the third interdigital transducer 132 be n6, the period of the fourth reflector grating 141 be n4', the period of the edge finger strip region of the fourth interdigital transducer 142 be n5', and the period of the center finger strip region of the fourth interdigital transducer 142 be n6'. Then the ratios of n6 to n4, n6' to n4', n6 to n5, and n6' to n5' can all fall within the range of 1:0.94 to 1:1.06. To suppress the generation of stray modes and further reduce the superposition of abnormal peaks in the resonator admittance curve at specific frequencies, the periods of the third reflector grating 131 and the fourth reflector grating 141 are different, and the periods of the edge finger regions in the third interdigital transducer 132 and the fourth interdigital transducer 142 are different. Therefore, the ratio of the period of the third reflector grating 131 to the period of the central finger region of the third interdigital transducer 132 is different from the ratio of the period of the fourth reflector grating 141 to the period of the central finger region of the fourth interdigital transducer 142, and the ratio of the period of the edge finger region of the third interdigital transducer 132 to the period of the central finger region of the third interdigital transducer 132 is different from the ratio of the period of the edge finger region of the fourth interdigital transducer 142 to the period of the central finger region of the fourth interdigital transducer 142. In the same surface acoustic wave resonator, the ratio of the period of the reflective grating to the period of the central finger region of the interdigital transducer and the ratio of the period of the edge finger region to the central finger region of the interdigital transducer are not specifically limited in this embodiment. They can be the same or different. For example, n6:n4 = 1:0.94, n6':n4' = 1:0.98, and n6:n5 = 1:0.95, n6':n5' = 1:0.97, or n6:n4 = 1:1.01, n6':n4' = 1:1.03, and n6:n5 = 1:1.02, n6':n5' = 1:1.04.

[0058] Please see Figure 5 The structure of the surface acoustic wave filter provided in the embodiments of this application will be specifically described from a cross-sectional perspective.

[0059] In this embodiment, the surface acoustic wave (SAW) filter may further include a substrate. Specifically, the substrate may include a substrate 501, an isolation layer 502, and a piezoelectric layer 503. The substrate 501 serves as the basis for forming the SAW filter. The substrate 501 may be made of high-resistivity silicon to reduce current leakage and interference caused by acoustic wave reflection. The isolation layer 502 is used to isolate the electrodes from the substrate 501 to reduce signal loss and interference. The isolation layer 502 may be made of oxide. The piezoelectric layer 503 is used to achieve the conversion between electrical signals and acoustic waves. The electrode fingers 504 of the interdigital transducer may be formed on the surface of the piezoelectric layer 503. The piezoelectric layer 503 may be made of one or more of aluminum nitride, zinc oxide, lithium niobate, lithium tantalate, polyvinylidene fluoride, and titanium lead oxide. The electrode fingers 504 of the interdigital transducer may be made of one or more of platinum, gold, copper, silver, titanium, aluminum, nickel, and lead.

[0060] During experiments, researchers discovered that altering the propagation speed of sound waves within cascaded resonators can change the resonant frequencies of these resonators, resulting in slight differences in their resonant frequencies. This weakens the superposition effect of stray modes within the cascaded resonators. Therefore, in some embodiments, at least one structural parameter differs among the cascaded surface acoustic wave (SAW) resonators. Specifically, the structural parameters can be design parameters that influence the resonant frequency of the SAW resonator. Taking the normal direction of the substrate as the thickness direction, the structural parameters can include: the thickness of the piezoelectric layer 503, the material of the piezoelectric layer 503, the thickness of the electrode fingers 504, and the material of the electrode fingers 504.

[0061] Please see Figure 6 Taking two surface acoustic wave (SAW) resonators with the same material but different thicknesses of electrode fingers 504 as an example, assuming the thicknesses of the two SAW resonators' electrode fingers 504 are h1 and h2 respectively, then the ratio of h1 to h2 can fall within the range of 1:0.97 to 1:1.03. For example, h1:h2 = 1:0.97, or h1:h2 = 1:0.99, or h1:h2 = 1:1.01, or h1:h2 = 1:1.03.

[0062] Please see Figure 7 Taking two surface acoustic wave (SAW) resonators with the same piezoelectric layer 503 material but different thicknesses as an example, assuming the thicknesses of the piezoelectric layer 503 in the two SAW resonators are h3 and h4 respectively, then the ratio of h3 to h4 can fall within the range of 1:0.8 to 1:1.2. For example, h3:h4 = 1:0.8, or h3:h4 = 1:0.9, or h3:h4 = 1:1.1, or h3:h4 = 1:1.2.

[0063] To verify the effect of the above modulation characteristic parameter setting method on improving the passband flatness of the filter, researchers first used the controlled variable method and simulation software to simulate the working state of the surface acoustic wave (SAW) filter provided in this application embodiment and the SAW filter provided in related technologies. A two-dimensional coordinate system was established with frequency as the abscissa and insertion loss as the ordinate. Based on this two-dimensional coordinate system, the insertion loss curves of the SAW filter provided in this application embodiment and the SAW filter provided in related technologies were compared and displayed. Specifically, the controlled variable is the period of the edge finger strip region of the interdigital transducer forming the cascaded SAW resonators. That is, in the SAW filter provided in this application embodiment, the periods of the edge finger strip regions of the interdigital transducers of different resonators are different, and the ratios of the period of the edge finger strip region to the period of the center finger strip region are 1.004:1 and 0.988:1, respectively. In contrast, in the SAW filters provided in related technologies, the periods of the edge finger strip regions of the interdigital transducers of different resonators are the same. Other simulation conditions include: in the substrate of the surface acoustic wave (SAW) filter, the substrate material is high-resistivity silicon with a thickness of 1000 nm, the isolation layer material is silicon dioxide with a thickness of 650 nm, and the piezoelectric layer material is lithium tantalate with a thickness of 950 nm. The SAW filter consists of two SAW resonators forming an electrical cascade. In the two SAW resonators, the material and thickness of the electrode fingers are the same, i.e., both electrode fingers are made of aluminum with a thickness of 353 nm; the period of the reflector grid is the same, i.e., the ratio of the period of the reflector grid to the period of the central finger region of the interdigital transducer is 1.03:1; the duty cycle of the reflector grid is the same, i.e., both are 0.5; the number of strip electrodes included in the reflector grid is the same, i.e., both are 15; the duty cycle of the edge finger region of the interdigital transducer is the same, i.e., both are 0.5; the number of electrode fingers included in the edge finger region is the same, i.e., both are 8.

[0064] Please see Figure 8 The solid line represents the insertion loss curve of the surface acoustic wave (SAW) filter provided by related technologies, while the dashed line represents the insertion loss curve of the SAW filter provided in this embodiment. Simulation results show that the SAW filter provided by related technologies exhibits significant dips in the passband, while the SAW filter provided in this embodiment is smoother in the passband. In other words, the passband flatness of the SAW filter provided in this embodiment is higher than that of the SAW filter provided by related technologies. This demonstrates that by setting different periods for the edge finger strip regions of the interdigital transducers of cascaded resonators, and ensuring that the ratio of the period of the edge finger strip region to the period of the center finger strip region falls within a certain range, the passband flatness of the SAW filter can be improved.

[0065] Please refer to the following: Figure 9 and Figure 10To determine the appropriate numerical range for the period of the edge finger region of the reflector grating and / or interdigital transducer to achieve better passband flatness improvement, the researchers employed a controlled variable method. They set the ratio of the reflector grating period to the period of the center finger region of the interdigital transducer within theoretically derived ranges. A two-dimensional coordinate system was established with frequency on the x-axis and insertion loss and admittance on the y-axis. Based on this coordinate system, the admittance curves of the two surface acoustic wave (SAW) resonators and the insertion loss curve of the SAW filter were compared and displayed under the aforementioned reflector grating period settings. Specifically, the controlled variable is the period of the reflector grating forming the cascaded SAW resonators, i.e., in... Figure 9 In the simulation results shown, the ratio of the period of the reflective grating of different resonators to the period of the central finger strip region of the interdigital transducer is set to 1.04:1 and 1.05:1, respectively. Figure 10 In the simulation results shown, the ratio of the period of the reflector grating to the period of the central finger strip region of the interdigital transducer was set to 1.03:1 and 1.1:1, respectively. Other simulation conditions included: in the substrate of the surface acoustic wave (SAW) filter, the substrate material was high-resistivity silicon with a thickness of 1000 nm, the insulating layer material was silicon dioxide with a thickness of 650 nm, and the piezoelectric layer material was lithium tantalate with a thickness of 950 nm. The SAW filter consisted of two electrically cascaded SAW resonators. In both SAW resonators, the material and thickness of the electrode fingers were the same, i.e., both were aluminum with a thickness of 353 nm; the duty cycle of the reflector grating was the same, i.e., 0.5; the number of strip electrodes included in the reflector grating was the same, i.e., 15 in each; the duty cycle of the edge finger strip region of the interdigital transducer was the same, 0.5 in each; and the number of electrode fingers included in the edge finger strip region was the same, 8 in each.

[0066] exist Figure 9 and Figure 10 In the diagram, the solid and dashed lines with similar trends represent the admittance curves of two surface acoustic wave (SAW) resonators, respectively, while the other solid line represents the insertion loss curve of the SAW filter. (Comparison) Figure 9 and Figure 10It can be seen that when the periods of the reflector gratings of different resonators are different, and the ratio of the period of the reflector grating of different resonators to the period of the central finger strip region of the interdigital transducer all fall within the range of 0.94:1 to 1.06:1, the passband of the surface acoustic wave filter is relatively flat. However, when the ratio of the period of the reflector grating of the resonator to the period of the central finger strip region of the interdigital transducer exceeds the range of 0.94:1 to 1.06:1, some "glitch" exists in the passband of the surface acoustic wave filter. This proves that when the periods of the reflector gratings of different resonators are different, and the ratio of the period of the reflector grating of different resonators to the period of the central finger strip region of the interdigital transducer all fall within the range of 0.94:1 to 1.06:1, the effect on improving the passband flatness of the surface acoustic wave filter is better.

[0067] To verify the effect of the above structural parameter settings on improving the passband flatness of the filter, the researchers then used the controlled variable method to try changing only the structural parameters of the two cascaded surface acoustic wave (SAW) resonators. Specifically, the controlled variable was the ratio of the thickness of the electrode fingers of the interdigital transducers of the two SAW resonators, that is, setting the ratio of the thickness of the electrode fingers of the interdigital transducers of the two resonators to 1:1.04 and 1:1.02, respectively. When the ratio of the thickness of the electrode fingers of the interdigital transducers of the two resonators was 1:1.04, the thicknesses of the electrode fingers were 353 nm and 367 nm, respectively; when the ratio of the thickness of the electrode fingers of the interdigital transducers of the two resonators was 1:1.02, the thicknesses of the electrode fingers were 353 nm and 361 nm, respectively. Other simulation conditions included: in the substrate of the SAW filter, the substrate material was high-resistivity silicon with a thickness of 1000 nm, the isolation layer material was silicon dioxide with a thickness of 650 nm, and the piezoelectric layer material was lithium tantalate with a thickness of 950 nm. The surface acoustic wave (SAW) filter consists of two electrically cascaded SAW resonators. In both SAW resonators, the electrode fingers are made of the same material and have the same thickness (353 nm). The reflector grids have the same period (the ratio of the period of the reflector grid to the period of the central finger region of the interdigital transducer is 1.03:1). The reflector grids also have the same duty cycle (0.5). The reflector grids contain the same number of strip electrodes (15). The edge finger regions of the interdigital transducers have the same period (the ratio of the period of the edge finger region to the period of the central finger region is 1:1). The edge finger regions of the interdigital transducers also have the same duty cycle (0.5) and contain the same number of electrode fingers (8).

[0068] Please see Figure 2 , Figure 11 and Figure 12 ,exist Figure 11 and Figure 12In the diagram, the solid and dashed lines with similar trends represent the admittance curves of two surface acoustic wave (SAW) resonators, respectively, while the other solid line represents the insertion loss curve of the SAW filter. Figure 2 In the comparison, the admittance curves of the two surface acoustic wave resonators coincide. Figure 2 , Figure 11 and Figure 12 It is known that simply changing the electrode finger thickness of the interdigital transducers in two cascaded surface acoustic wave (SAW) resonators has a limited effect on improving the passband flatness of the SAW filter. Based on this, the researchers considered combining changes to the modulation characteristic parameters with changes to the structural parameters.

[0069] Therefore, in the surface acoustic wave (SAW) filters provided in this application embodiment, in addition to having at least one different modulation characteristic parameter, at least one different structural parameter can also exist among the different SAW resonators forming an electrical cascade. Taking a SAW filter comprising two SAW resonators forming an electrical cascade as an example, the SAW filter can be formed by cascading two SAW resonators with different reflector grating periods and different piezoelectric layer thicknesses, or by cascading two SAW resonators with different reflector grating periods and different electrode finger thicknesses. This application does not impose specific limitations on the existence of different modulation characteristic parameters and different structural parameters in different resonators.

[0070] Researchers modified the modulation characteristic parameters and structural parameters of the two cascaded surface acoustic wave (SAW) resonators. Specifically, in the SAW filter provided in this embodiment, the ratio of the thickness of the electrode fingers of the interdigital transducers of the two resonators was set to 1:1.04; the ratio of the period of the reflector grating in the two resonators to the period of the central finger region of the interdigital transducer was set to 1.04:1 and 1.05:1, respectively; and the ratio of the period of the edge finger region to the period of the central finger region of the interdigital transducer was set to 1.002:1 and 0.997:1, respectively. Other simulation conditions included: in the substrate of the SAW filter, the substrate material was high-resistivity silicon with a thickness of 1000 nm, the isolation layer material was silicon dioxide with a thickness of 650 nm, and the piezoelectric layer material was lithium tantalate with a thickness of 950 nm. The two resonators have the same duty cycle for their reflective grids, i.e., 0.5; the reflective grids include the same number of strip electrodes, i.e., 15 each; the interdigital transducers have the same period for their edge finger strip regions, i.e., the ratio of the period of the edge finger strip region to the period of the center finger strip region is 1:1; the interdigital transducers have the same duty cycle for their edge finger strip regions, i.e., 0.5 each; and the edge finger strip regions contain the same number of electrode fingers, 8 each.

[0071] Please see Figure 13 .Depend on Figure 13It can be seen that when the period of the reflection grating of the two cascaded surface acoustic wave resonators, the period of the edge finger region of the interdigital transducer, and the thickness of the electrode finger of the interdigital transducer are all changed, the insertion loss curve of the surface acoustic wave filter is relatively smooth and the passband flatness is relatively high.

[0072] Please see Figure 14 and Figure 15 Another embodiment of this application provides a radio frequency (RF) front-end module 700. The RF front-end module 700 may include a transmitter (TX) 701, an antenna (ANT) 702, a receiver (RX) 703, a series resonator (SR) 704, a parallel resonator (PR) 705, and a dual-mode coupled surface acoustic wave (DMS) filter 706. The dual-mode coupled surface acoustic wave filter 706 may be implemented using a surface acoustic wave filter as described in the above embodiments.

[0073] For the remaining technical effects of the RF front-end module described in the above embodiments, please refer to other embodiments of this application for comparison and explanation, and they will not be repeated here.

[0074] This application provides a surface acoustic wave (SAW) filter comprising at least two SAW resonators forming an electrical cascade. Each SAW resonator includes an interdigital transducer and a reflective grating, with the reflective grating distributed on both sides of the interdigital transducer. The interdigital transducer includes multiple spaced electrode strips, which are divided into a central strip region and an edge strip region. The distance between the central strip region and the reflective grating is greater than the distance between the edge strip region and the reflective grating. By setting different periods for the reflective gratings and / or edge strip regions of different SAW resonators, the superposition effect of stray modes of multiple cascaded SAW resonators is weakened, reducing the negative impact of superimposed stray modes on the insertion loss of the SAW filter. This suppresses the formation of in-passband dips in the SAW filter and improves the in-passband flatness of the SAW filter.

[0075] It is understood that the specific examples in this application are only intended to help those skilled in the art better understand the embodiments of this application, and are not intended to limit the scope of this application.

[0076] It is understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not limit the implementation process of the embodiments of this application in any way.

[0077] It is understood that the various embodiments described in this application can be implemented individually or in combination, and the embodiments of this application are not limited in this respect.

[0078] Unless otherwise stated, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items. The singular forms "a," "the," and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0079] As will be understood from the embodiments provided in this application, the disclosed surface acoustic wave filter and RF front-end module can be implemented in other ways. For example, the embodiments of the surface acoustic wave filter and RF front-end module described above are merely illustrative.

[0080] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A surface acoustic wave filter, characterized in that, include: At least two surface acoustic wave (SAW) resonators are electrically cascaded; each SAW resonator includes a reflector grating and an interdigital transducer; the reflector grating is distributed on both sides of the interdigital transducer; wherein the interdigital transducer includes a plurality of spaced electrode strips; the plurality of electrode strips are divided into a central strip region and an edge strip region; the distance between the central strip region and the reflector grating is greater than the distance between the edge strip region and the reflector grating; in different SAW resonators, at least one modulation characteristic parameter is different; wherein the modulation characteristic parameter includes: the period of the reflector grating and the period of the edge strip region.

2. The surface acoustic wave filter according to claim 1, characterized in that, The period of the central finger strip region of different surface acoustic wave resonators is the same; when the period of the reflector grating of different surface acoustic wave resonators is different, the ratio of the period of the central finger strip region to the period of the reflector grating of different surface acoustic wave resonators all fall within the range of 1:0.94 to 1:1.

06.

3. The surface acoustic wave filter according to claim 1, characterized in that, The period of the center finger region of different surface acoustic wave resonators is the same; when the period of the edge finger region of different surface acoustic wave resonators is different, the ratio of the period of the center finger region to the period of the edge finger region of different surface acoustic wave resonators all fall within the range of 1:0.94 to 1:1.

06.

4. The surface acoustic wave filter according to claim 1, characterized in that, The reflective grid includes a plurality of spaced-apart strip electrodes; the number of the strip electrodes falls within the range of 8 to 25.

5. The surface acoustic wave filter according to claim 1, characterized in that, The number of electrode fingers included in the edge finger area falls within the range of 3 to 20.

6. The surface acoustic wave filter according to claim 1, characterized in that, The surface acoustic wave filter further includes: A substrate; the substrate includes a piezoelectric layer; the electrode fingers of the interdigital transducer are formed on the surface of the piezoelectric layer; With the normal direction of the substrate as the thickness direction, at least one structural parameter differs in different surface acoustic wave resonators; wherein, the structural parameter includes: the thickness of the piezoelectric layer, the material of the piezoelectric layer, the thickness of the electrode fingers, and the material of the electrode fingers.

7. The surface acoustic wave filter according to claim 6, characterized in that, When the thickness of the electrode fingers of different surface acoustic wave resonators is different, the ratio of the thickness of the electrode fingers of different surface acoustic wave resonators falls within the range of 1:0.97 to 1:1.

03.

8. The surface acoustic wave filter according to claim 6, characterized in that, When the thickness of the piezoelectric layer of different surface acoustic wave resonators is different, the ratio of the thickness of the piezoelectric layer of different surface acoustic wave resonators falls within the range of 1:0.8 to 1:1.

2.

9. The surface acoustic wave filter according to claim 6, characterized in that, The piezoelectric layer is made of one or more of the following materials: aluminum nitride, zinc oxide, lithium niobate, lithium tantalate, polyvinylidene fluoride, and titanium lead oxide; the electrode fingers are made of one or more of the following materials: platinum, gold, copper, silver, titanium, aluminum, nickel, and lead.

10. A radio frequency front-end module, characterized in that, Includes the surface acoustic wave filter as described in any one of claims 1 to 9.

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