A surface acoustic wave filter and radio frequency front end module

Abstract

This invention relates to the field of filter technology and discloses a surface acoustic wave (SAW) filter and an RF front-end module, comprising: a first port, a second port, and a filtering path connecting the first port and the second port; the filtering path includes at least one series arm resonator and at least one parallel arm resonator; the series arm resonator includes a first piezoelectric layer and a first interdigital transducer electrode on the first piezoelectric layer; the parallel arm resonator includes a second piezoelectric layer and a second interdigital transducer electrode on the second piezoelectric layer; at least one series arm resonator is a target series arm resonator; the density of the first interdigital transducer electrode of the target series arm resonator is greater than the density of the second interdigital transducer electrode of any parallel arm resonator. This invention can improve the rectangularity of the right side of the filter passband while maintaining the overall passband width and in-band insertion loss, and can also reduce the overall size of the filter, which is beneficial for device miniaturization.

Description

Technical Field

[0001] This invention relates to the field of filter technology, specifically to a surface acoustic wave filter and a radio frequency front-end module. Background Technology

[0002] In the design of surface acoustic wave (SAW) filters, to simplify manufacturing processes, the interdigital transducer electrodes of series-arm and parallel-arm resonators typically use the same metal material and the same stacked structure. For example, the interdigital transducer electrodes of both series-arm and parallel-arm resonators use a titanium / aluminum-copper (Ti / AlCu) stacked structure. This design approach limits the flexibility of the filter's passband adjustment. However, some RF applications require a high degree of rectangularity on the right edge of the filter's passband; that is, the transition region from the passband to the high-frequency band needs to be as narrow as possible, and the transition slope as steep as possible. When using the same electrode material for both series and parallel arms, improving the rectangularity of the right band edge often simultaneously compresses the bandwidth of the parallel arm, resulting in a reduced overall passband width and higher in-band insertion loss. It is difficult to achieve a balance between improving rectangularity and maintaining passband performance. Furthermore, due to the low density of the Ti / AlCu stack structure, the corresponding sound velocity is high, which results in a larger surface acoustic wave wavelength corresponding to the interdigital transducer electrode at the same frequency. This leads to a larger geometric size and volume of the interdigital transducer electrode, which is not conducive to the miniaturization of the resonator and cannot improve the device integration.

[0003] Therefore, a solution is needed that can improve the rectangularity of the right side of the filter's passband and increase the device integration density while keeping the filter's passband width and in-band insertion loss constant. Summary of the Invention

[0004] This invention provides a surface acoustic wave (SAW) filter and an RF front-end module to solve the problem in related technologies that SAW filters are difficult to improve the right band rectangularity of the passband while keeping the passband width unchanged and the in-band insertion loss unchanged. This results in the inability to simultaneously improve the passband width, in-band insertion loss and right band rectangularity, as well as the limitation on device miniaturization.

[0005] In a first aspect, the present invention provides a surface acoustic wave filter, comprising: A first port, a second port, and a filter path connecting the first port and the second port; the filter path includes at least one series arm resonator and at least one parallel arm resonator. The series arm resonator includes a first piezoelectric layer and a first interdigital transducer electrode on the first piezoelectric layer; the parallel arm resonator includes a second piezoelectric layer and a second interdigital transducer electrode on the second piezoelectric layer. At least one series arm resonator is the target series arm resonator; the density of the first interdigital transducer electrode of the target series arm resonator is greater than the density of the second interdigital transducer electrode of any parallel arm resonator.

[0006] The surface acoustic wave (SAW) filter provided by this invention includes at least one series-arm resonator as the target series-arm resonator. The density of the first interdigital transducer electrode in the target series-arm resonator is greater than that of the second interdigital transducer electrode. This allows adjustment of the bandwidth of the target series-arm resonator, resulting in a narrower and steeper transition slope in the right-side transition region of the filter's passband from the passband to the stopband, effectively improving the rectangularity of the right-side passband. Simultaneously, the parallel-arm resonator maintains a lower electrode density, ensuring the filter's bandwidth remains unaffected and maintaining high impedance throughout the passband, guaranteeing sufficient overall passband width and preventing an increase in in-band insertion loss. Furthermore, the higher density of the first interdigital transducer electrode in the target series-arm resonator reduces the acoustic wave propagation speed, shortening the wavelength of the SAW at the same operating frequency. This allows for a smaller geometric dimension of the interdigital transducer electrode in the target series-arm resonator, thereby reducing the volume of the target series-arm resonator and the overall filter, facilitating miniaturization design. Therefore, the surface acoustic wave filter provided by the present invention can improve the rectangularity of the right side of the passband and enhance the device integration while ensuring that the passband width and in-band insertion loss of the filter remain unchanged.

[0007] In one alternative implementation, the first interdigital transducer electrode of each target series arm resonator includes a first metal layer; the second interdigital transducer electrode of each parallel arm resonator includes a second metal layer; the density of the first metal layer is greater than the density of the second metal layer. The density of the first interdigital transducer electrode of the target series arm resonator is greater than or equal to 10 g / cm³ and less than or equal to 30 g / cm³.

[0008] The surface acoustic wave (SAW) filter provided by this invention has two advantages. First, the use of a high-density first metal layer on the first interdigital transducer electrode of the target series arm resonator effectively improves the rectangularity of the right side of the passband. Simultaneously, it reduces the sound velocity of the first metal layer, thereby reducing the size of the target series arm resonator and facilitating miniaturization. Furthermore, the use of a low-density second metal layer on the second interdigital transducer electrode of the parallel arm resonator ensures that the filter's bandwidth and in-band insertion loss remain unaffected, guaranteeing the stability of the overall passband characteristics. Second, the overall density of the first interdigital transducer electrode of the target series arm resonator is controlled within the range of 10 g / cm³ to 30 g / cm³. This ensures sufficient sound velocity reduction and bandwidth adjustment while avoiding manufacturing difficulties caused by excessive density.

[0009] In one alternative embodiment, the material of the first metal layer includes a heavy metal; the first metal layer includes one or more layers selected from molybdenum, platinum, and tungsten.

[0010] The surface acoustic wave (SAW) filter provided by this invention comprises a first metal layer made of heavy metals, including one or more layers selected from molybdenum, platinum, and tungsten. On one hand, by selecting heavy metals such as molybdenum, platinum, or tungsten as the first metal layer, the sufficiently high density of heavy metals effectively improves the rectangularity of the right-side passband and reduces the acoustic velocity of the interdigital transducer electrodes. Simultaneously, by adjusting the thickness and material of each heavy metal layer in the first metal layer, the bandwidth of the passband can be further adjusted. On the other hand, because molybdenum, platinum, and tungsten layers have melting points and electromigration resistance far exceeding those of aluminum-based alloys, they can withstand localized temperature rises and high current density surges under high-power operating conditions, significantly improving the power handling capacity and long-term reliability of the target series arm resonator. Furthermore, the high elastic modulus of these heavy metals causes the electrodes to exhibit smaller nonlinear deformation under high-power acoustic field excitation, further improving harmonic suppression characteristics. In addition, the combination of one or more heavy metals in the first metal layer increases the design flexibility of the first metal layer, allowing selection based on actual bandwidth adjustment and power requirements.

[0011] In one alternative implementation, the first interdigital transducer electrode of the target series arm resonator further includes a first conductive layer disposed on the surface of the first metal layer facing away from the first piezoelectric layer; the density of the first conductive layer is less than the density of the first metal layer.

[0012] The surface acoustic wave filter provided by this invention improves the overall conductivity of the electrodes by setting a first conductive layer on the surface of a first metal layer. The higher-density first metal layer and the lower-density first conductive layer form a stacked electrode structure with a combination of high and low densities. This allows for the adjustment of the filter bandwidth and sound velocity using the higher-density first metal layer, while effectively utilizing the first conductive layer to compensate for the parasitic resistance caused by the heavy metal material, thereby improving the overall conductivity of the electrodes and reducing transmission loss.

[0013] In one optional embodiment, the second interdigital transducer electrode of the parallel arm resonator further includes a second conductive layer, which is disposed on the surface of the second metal layer facing away from the second piezoelectric layer; the second metal layer is a titanium layer, and the second conductive layer is an aluminum-copper alloy layer.

[0014] The surface acoustic wave filter provided by this invention uses a low-density aluminum-copper alloy layer for the second interdigital transducer electrode of the parallel arm resonator, which can ensure that the bandwidth and in-band insertion loss of the filter are not affected. Thus, it can maintain a low in-band insertion loss while ensuring sufficient bandwidth, and ensure the stability of the overall passband characteristics of the filter.

[0015] In one optional implementation, the filtering path includes multiple series arm resonators and multiple parallel arm resonators. The multiple series arm resonators are connected in series between the first port and the second port, and the multiple parallel arm resonators are respectively connected between the node between adjacent series arm resonators and the reference ground port. Multiple series-arm resonators are all target series-arm resonators; the density of the first interdigital transducer electrode of the target series-arm resonator is greater than the density of the second interdigital transducer electrode of any parallel-arm resonator.

[0016] The surface acoustic wave (SAW) filter provided by this invention utilizes high-density first interdigital transducer electrodes in all series arm resonators within the trapezoidal filtering path, which further increases the bandwidth adjustment range of the passband and significantly improves the rectangularity of the right edge of the passband. Simultaneously, it reduces the sound velocity of each series arm resonator, thereby reducing the volume of each target series arm resonator, and consequently reducing the overall volume and integration density of the SAW filter.

[0017] In one alternative implementation, the first port includes an antenna port; the series arm resonator closest to the antenna port is the target series arm resonator. The second port includes a transmitting port, and the surface acoustic wave filter includes a transmitting filter; and / or: the second port includes a receiving port, and the surface acoustic wave filter includes a receiving filter.

[0018] The surface acoustic wave (SAW) filter provided by this invention improves the harmonic characteristics of the filter by using the series arm resonator closest to the antenna port as the target series arm resonator and ensuring that the density of the first interdigital transducer electrode of the series arm resonator closest to the antenna port is greater than the density of the second interdigital transducer electrode. Simultaneously, since the SAW filter serves as both a transmit and / or receive filter, it enhances the design flexibility of SAW filters.

[0019] In one optional embodiment, the material of the first piezoelectric layer is lithium tantalate or lithium niobate; the material of the second piezoelectric layer is lithium tantalate or lithium niobate. The first piezoelectric layer and the second piezoelectric layer are on the same piezoelectric substrate; or the first piezoelectric layer and the second piezoelectric layer are on different piezoelectric substrates.

[0020] The surface acoustic wave filter provided by this invention has a first piezoelectric layer and a second piezoelectric layer located in the same common piezoelectric substrate, which can integrate all resonators in the same common piezoelectric substrate, which is beneficial to simplify the packaging process, reduce manufacturing costs and device size; while the first piezoelectric layer and the second piezoelectric layer are located in different piezoelectric substrates, which can be physically isolated and the parameters can be independently optimized according to the performance requirements of the target series arm resonator and parallel arm resonator, thus improving design flexibility.

[0021] In one optional embodiment, the interdigital transducer electrode of the target series arm resonator includes two busbars disposed opposite each other along a first direction, and a plurality of electrode fingers connected between the two busbars and spaced apart along a second direction; the plurality of electrode fingers connected to the two busbars are distributed in an interdigital pattern; the starting end of the electrode finger is connected to one busbar and the end is close to another busbar; the target series arm resonator also includes an additional metal structure located on the surface or bottom of the electrode fingers, and the additional metal structure is located at the starting segment and / or end of the electrode fingers.

[0022] The surface acoustic wave filter provided by this invention adjusts the local mass load of the first interdigital transducer electrode of the target series arm resonator by setting additional metal structures at the beginning and / or end of the electrode fingers of the target series arm resonator, thereby effectively suppressing the generation of parasitic transverse modes and further improving the transverse mode suppression characteristics and overall frequency response smoothness of the target series arm resonator.

[0023] In a second aspect, the present invention also provides a radio frequency front-end module, including a surface acoustic wave filter corresponding to the first aspect and any embodiment thereof. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structural topology of a surface acoustic wave filter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structural topology of another surface acoustic wave filter according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the target series arm resonator in a surface acoustic wave filter according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of a series arm resonator in a surface acoustic wave filter according to an embodiment of the present invention; Figure 5 This is a curve showing the relationship between the thickness of the first metal layer in the target series arm resonator according to an embodiment of the present invention, normalized to wavelength, and the pole-zero distance of the target series arm resonator. Figure 6 This is a curve showing the relationship between the thickness of the first metal layer in the target series arm resonator according to an embodiment of the present invention, normalized to wavelength, and the sound velocity of the target series arm resonator. Figure 7 These are the admittance curves of the target series arm resonators corresponding to Comparative Example 1, Example 1-1, Example 1-2 and Example 1-3 according to embodiments of the present invention; Figure 8 These are the admittance curves of the surface acoustic wave filters corresponding to Comparative Example 2 and Example 2 according to embodiments of the present invention; Figure 9 These are full-band curves of the surface acoustic wave filters corresponding to Comparative Example 2 and Example 2 according to embodiments of the present invention; Figure 10 This is a right-hand curve of the passband of the surface acoustic wave filter corresponding to Comparative Example 2 and Example 2 according to embodiments of the present invention; Figure 11 This is a schematic diagram of the structure of the first piezoelectric layer and the second piezoelectric layer located on the same common piezoelectric substrate according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the target series arm resonator in another surface acoustic wave filter according to an embodiment of the present invention.

[0026] Figure label: 10. First port; 11. Second port; 100. Antenna port; 101. Transmit port; 102. Receive port; 20. Series arm resonator; 30. Parallel arm resonator; 211. Target series arm resonator; 21. First piezoelectric layer; 22. First interdigital transducer electrode; 201. First metal layer; 202. First conductive layer; 31. Second piezoelectric layer; 32. Second interdigital transducer electrode; 301. Second metal layer; 302. Second conductive layer; 40. Busbar; 50. Electrode finger bar; 60. Reflector grid busbar; 70. Reflector grid finger bar; 80. Additional metal structure; 23. Reflector grid structure. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention and not all structures. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] In the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These drawings are not to scale, and some details are enlarged for clarity, and some details may be omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0029] Surface acoustic wave (SAW) filters are widely used in mobile communications, satellite navigation, and RF front-end modules due to their small size, low cost, and excellent performance. A typical SAW filter usually includes a first port, a second port, and a filtering path connecting the first and second ports. The filtering path contains series arm resonators and parallel arm resonators, each of which is composed of interdigital transducer (IDT) electrodes on a piezoelectric layer.

[0030] In the design of surface acoustic wave (SAW) filters in related technologies, to simplify the manufacturing process, the interdigital transducer electrodes of series-arm resonators and parallel-arm resonators typically use the same metal material and the same stacked structure. For example, both series-arm and parallel-arm resonators use a titanium / aluminum-copper (Ti / AlCu) stacked structure. With this design approach, when a high degree of rectangularity is required on the right edge of the filter's passband, it is difficult to simultaneously improve the right-band rectangularity without increasing the in-band insertion loss, and the space for further optimization to miniaturize the device is limited.

[0031] Therefore, a solution is needed that can improve the rectangularity of the right side of the filter's passband and increase the device integration density while keeping the filter's passband width and in-band insertion loss constant.

[0032] like Figure 1 and Figure 2As shown, this embodiment provides a surface acoustic wave filter, including: a first port 10, a second port 11, and a filtering path connected between the first port 10 and the second port 11; the filtering path includes at least one series arm resonator 20 and at least one parallel arm resonator 30; as shown Figure 3 and Figure 4 As shown, the series arm resonator 20 includes a first piezoelectric layer 21 and a first interdigital transducer electrode 22 on the first piezoelectric layer 21; the parallel arm resonator 30 includes a second piezoelectric layer 31 and a second interdigital transducer electrode 32 on the second piezoelectric layer 31; at least one series arm resonator 20 is a target series arm resonator 211; the density of the first interdigital transducer electrode 22 of the target series arm resonator 211 is greater than the density of the second interdigital transducer electrode 32 of any parallel arm resonator.

[0033] In specific implementation, the density of the first interdigital transducer electrode 22 of the target series arm resonator 211 refers to the average mass density of the first interdigital transducer electrode 22 per unit area. The density of the second interdigital transducer electrode 32 of the parallel arm resonator refers to the average mass density of the second interdigital transducer electrode 32 per unit area.

[0034] The surface acoustic wave (SAW) filter provided in this embodiment uses at least one series-arm resonator as the target series-arm resonator. The density of the first interdigital transducer electrode in the target series-arm resonator is greater than that of the second interdigital transducer electrode. This allows adjustment of the bandwidth of the target series-arm resonator, resulting in a narrower and steeper transition slope in the right-side transition region of the filter's passband from the passband to the stopband, effectively improving the rectangularity of the right-side passband. Simultaneously, the parallel-arm resonator maintains a lower electrode density, ensuring the filter's bandwidth remains unaffected and maintaining high impedance throughout the passband, guaranteeing sufficient overall passband width and preventing an increase in in-band insertion loss. Furthermore, the higher density of the first interdigital transducer electrode in the target series-arm resonator reduces the acoustic wave propagation speed, shortening the wavelength of the SAW at the same operating frequency. This allows for a smaller geometric dimension of the interdigital transducer electrode in the target series-arm resonator, thereby reducing the volume of the target series-arm resonator and the overall filter, which is beneficial for device miniaturization design. Therefore, the surface acoustic wave filter provided in this embodiment can improve the rectangularity of the right side of the passband and enhance the device integration while ensuring that the passband width and in-band insertion loss of the filter remain unchanged.

[0035] In some alternative implementations, the filtering path includes a plurality of series arm resonators 20 and a plurality of parallel arm resonators 30. The plurality of series arm resonators 20 are connected in series between the first port 10 and the second port 11, and the plurality of parallel arm resonators 30 are respectively connected between the nodes of adjacent series arm resonators 20 and the reference ground port.

[0036] In some alternative implementations, such as Figure 1 As shown, at least one series-arm resonator 20 is a target series-arm resonator 211, and the density of the first interdigital transducer electrode 22 of the target series-arm resonator 211 is greater than the density of the second interdigital transducer electrode 32 of any parallel-arm resonator 30. Optionally, the density of the first interdigital transducer electrode 22 of the series-arm resonators 20 other than the target series-arm resonator 211 is the same as the density of the second interdigital transducer electrode 32 of the parallel-arm resonators 30.

[0037] In some alternative implementations, all series arm resonators 20 are target series arm resonators 211; the density of the first interdigital transducer electrode 22 of each target series arm resonator 211 is greater than the density of the second interdigital transducer electrode 32 of any parallel arm resonator 30.

[0038] The surface acoustic wave (SAW) filter provided in this embodiment utilizes high-density first interdigital transducer electrodes in all series arm resonators within the trapezoidal filtering path, which further increases the bandwidth adjustment range of the passband and significantly improves the rectangularity of the right edge of the passband. Simultaneously, it reduces the sound velocity of each series arm resonator, thereby reducing the volume of each target series arm resonator, and consequently, the overall size and integration of the SAW filter.

[0039] In some alternative implementations, such as Figure 2 As shown, the first port 10 includes an antenna port 100; the series arm resonator 20 closest to the antenna port 100 is the target series arm resonator 211.

[0040] In some alternative implementations, such as Figure 2 As shown, the second port 11 includes a transmit port 101; the surface acoustic wave filter includes a transmit filter; and / or: the second port 11 includes a receive port 102; the surface acoustic wave filter includes a receive filter.

[0041] The surface acoustic wave (SAW) filter provided in this embodiment improves the harmonic characteristics of the filter by using the series arm resonator closest to the antenna port as the target series arm resonator and ensuring that the density of the first interdigital transducer electrode of the series arm resonator closest to the antenna port is greater than the density of the second interdigital transducer electrode. Furthermore, since the SAW filter serves as both a transmit and / or receive filter, it enhances the design flexibility of the SAW filter.

[0042] In some alternative implementations, such as Figure 2 As shown, the surface acoustic wave filter is a duplexer, which includes a transmitting filter and a receiving filter.

[0043] In some optional embodiments, the transmit filter includes a first port 10, a second port 11, and a filter path connecting the first port 10 and the second port 11; wherein the first port 10 is an antenna port 100, the second port 11 is a transmit port 101, and the filter path connecting the first port 10 and the second port 11 is a transmit filter path. That is, the transmit filter includes an antenna port 100, a transmit port 101, and a transmit filter path connecting the antenna port 100 and the transmit port 101. The transmit filter includes a plurality of series-arm resonators 20 and a plurality of parallel-arm resonators 30.

[0044] In some optional embodiments, the receiving filter includes a first port 10, a second port 11, and a filtering path connecting the first port 10 and the second port 11; wherein the first port 10 is an antenna port 100, the second port 11 is a receiving port 102, and the filtering path connecting the first port 10 and the second port 11 is a receiving filtering path. That is, the receiving filter includes an antenna port 100, a receiving port 102, and a receiving filtering path connecting the antenna port 100 and the receiving port 102. The receiving filter includes a plurality of series-arm resonators 20 and a plurality of parallel-arm resonators 30.

[0045] In some alternative implementations, in the transmit filter, at least one series arm resonator 20 is a target series arm resonator 211, and the density of the first interdigital transducer electrode 22 of the target series arm resonator 211 is greater than the density of the second interdigital transducer electrode 32; and / or: in the receive filter, at least one series arm resonator 20 is a target series arm resonator 211, and the density of the first interdigital transducer electrode 22 of the target series arm resonator 211 is greater than the density of the second interdigital transducer electrode 32.

[0046] In some alternative implementations, such as Figure 2 As shown, the surface acoustic wave filter is a duplexer, comprising an antenna port 100, a transmit port 101, a receive port 102, a transmit filter path connecting the antenna port 100 and the transmit port 101, and a receive filter path connecting the antenna port 100 and the receive port 102. In the transmit filter path, all series-arm resonators 20 are target series-arm resonators 211, and the density of the first interdigital transducer electrode 22 of each target series-arm resonator 211 is greater than the density of the second interdigital transducer electrode 32 of any parallel-arm resonator 30.

[0047] In some alternative implementations, the density of the first interdigital transducer electrode 22 of the target series arm resonator 211 is greater than the density of the second interdigital transducer electrode 32 of any parallel arm resonator 30. Specifically, the average mass density of the first interdigital transducer electrode 22 per unit area is greater than the average mass density of the second interdigital transducer electrode 32 per unit area.

[0048] In some alternative implementations, such as Figure 3 As shown, the first interdigital transducer electrode 22 of each target series arm resonator 211 includes a first metal layer 201. (As...) Figure 4 As shown, the second interdigital transducer electrode 32 of each parallel arm resonator 30 includes a second metal layer 301, and the density of the first metal layer 201 is greater than the density of the second metal layer 301.

[0049] The surface acoustic wave (SAW) filter provided in this embodiment uses a high-density first metal layer for the first interdigital transducer electrode of the target series arm resonator, which effectively improves the rectangularity of the right side of the passband. Simultaneously, it reduces the sound velocity of the first metal layer, thereby reducing the size of the target series arm resonator and facilitating miniaturization. Using a low-density second metal layer for the second interdigital transducer electrode of the parallel arm resonator ensures that the filter's bandwidth and in-band insertion loss are unaffected, guaranteeing the stability of the overall passband characteristics of the filter.

[0050] In some optional embodiments, a portion of the series arm resonators 20 in the surface acoustic wave filter are target series arm resonators 211. Correspondingly, the first interdigital transducer electrode 22 of the target series arm resonator 211 includes a first metal layer 201. The series arm resonators 20 other than the target series arm resonator 211 include a third metal layer. The density of the first metal layer 201 is greater than the density of the third metal layer. Optionally, the density of the third metal layer is equal to the density of the second metal layer 301.

[0051] In some alternative implementations, the density of the first interdigital transducer electrode 22 of the target series arm resonator 211 is greater than or equal to 10 g / cm³ and less than or equal to 30 g / cm³.

[0052] In specific implementation, the average mass density of the first interdigital transducer electrode 22 per unit area in the target series arm resonator 211 ranges from 10 g / cm³ to 30 g / cm³.

[0053] The surface acoustic wave filter provided in this embodiment controls the overall density of the first interdigital transducer electrode of the target series arm resonator within the range of 10 g / cm³ to 30 g / cm³. This ensures that the target series arm resonator produces sufficient sound velocity reduction and bandwidth adjustment range, while avoiding the manufacturing difficulties caused by excessive density.

[0054] In some alternative implementations, such as Figure 3 As shown, the material of the first metal layer 201 includes heavy metals; the first metal layer 201 includes one or more layers of molybdenum, platinum and tungsten.

[0055] The surface acoustic wave (SAW) filter provided in this embodiment uses a first metal layer made of heavy metals, including one or more layers of molybdenum, platinum, and tungsten. On one hand, by selecting heavy metals such as molybdenum, platinum, or tungsten as the first metal layer, the sufficiently high density of heavy metals effectively improves the rectangularity of the right-side passband and reduces the acoustic velocity of the interdigital transducer electrodes. Simultaneously, by adjusting the thickness and material of each heavy metal layer in the first metal layer, the bandwidth of the passband can be further adjusted. On the other hand, because molybdenum, platinum, and tungsten layers have melting points and electromigration resistance far exceeding those of aluminum-based alloys, they can withstand local temperature rises and high current density shocks under high-power operating conditions, significantly improving the power handling capacity and long-term reliability of the target series arm resonator. Furthermore, the high elastic modulus of these heavy metals causes the electrodes to exhibit smaller nonlinear deformation under high-power acoustic field excitation, further improving harmonic suppression characteristics. In addition, the combination of one or more heavy metals in the first metal layer increases the design flexibility of the first metal layer, allowing selection based on actual bandwidth adjustment and power requirements.

[0056] In some alternative implementations, the wavelength of the target series arm resonator 211 is λ; the thickness h of the first metal layer 201 satisfies 0.1% ≤ h ≤ 9%.

[0057] In practice, the appropriate thickness of the first metal layer 201 is selected based on the sound velocity and bandwidth requirements of the target series arm resonator 211.

[0058] Figure 5 The graphs show the relationship between the thickness of the first metal layer 201 made of different materials and the normalized wavelength, as well as the pole-zero distance (PZD) of the target series arm resonator 211. It can be seen that when the first metal layer 201 is a molybdenum layer, a platinum layer, or a tungsten layer, the resonator bandwidth first increases and then decreases with increasing thickness, and the variation patterns for the molybdenum, platinum, and tungsten layers are not entirely the same. In practical designs, one or more layers of different molybdenum, platinum, and tungsten layers can be selected as the first metal layer 201 according to requirements, and an appropriate thickness can be chosen to adjust the resonator bandwidth.

[0059] Figure 6The graphs show the relationship between the thickness of the first metal layer 201 made of different materials and the normalized wavelength, as well as the sound velocity of the target series arm resonator 211. It can be seen that when the first metal layer 201 is a molybdenum layer, a platinum layer, or a tungsten layer, the sound velocity of the resonator gradually decreases with increasing thickness, and the reduction rates are different for the molybdenum, platinum, and tungsten layers. In practical designs, one or more layers of different molybdenum, platinum, and tungsten layers can be selected as the first metal layer 201 according to requirements, and an appropriate thickness can be chosen to adjust the sound velocity of the resonator, thereby adjusting the size of the target series arm resonator 211.

[0060] In some alternative implementations, such as Figure 3 As shown, the first interdigital transducer electrode 22 of the target series arm resonator 211 also includes a first conductive layer 202, which is disposed on the surface of the first metal layer 201 facing away from the first piezoelectric layer 21; the density of the first conductive layer 202 is less than the density of the first metal layer 201.

[0061] The surface acoustic wave filter provided in this embodiment improves the overall conductivity of the electrodes by setting a first conductive layer on the surface of the first metal layer. The higher-density first metal layer and the lower-density first conductive layer form a stacked electrode structure with high and low densities. This allows the higher-density first metal layer to be used to adjust the filter bandwidth and sound velocity, while the first conductive layer effectively compensates for the parasitic resistance caused by the heavy metal material, thereby improving the overall conductivity of the electrodes and reducing transmission loss.

[0062] In some alternative implementations, such as Figure 3 As shown, the first conductive layer 202 is an aluminum layer.

[0063] In some alternative implementations, such as Figure 3 As shown, the first interdigital transducer electrode 22 of the target series arm resonator 211 is a stack of a first metal layer 201 and a first conductive layer 202. The first metal layer 201 is a molybdenum layer, a platinum layer, or a tungsten layer, and the first conductive layer 202 is an aluminum layer. The structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 is a stack of a molybdenum layer and an aluminum layer (i.e., a Mo / Al stack), a stack of a platinum layer and an aluminum layer (i.e., a Pt / Al stack), or a stack of a tungsten layer and an aluminum layer (i.e., a W / Al stack).

[0064] The surface acoustic wave filter provided in this embodiment has an aluminum layer as the first conductive layer. The aluminum layer's good conductivity and low density characteristics are combined with a high-density first metal layer to form a stacked electrode with balanced performance. Furthermore, the aluminum layer has a mature manufacturing process and low cost, which can reduce the overall manufacturing difficulty and cost of the device.

[0065] In some alternative embodiments, the first metal layer 201 includes one or more layers selected from molybdenum, platinum, and tungsten. In other examples, the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 can also be a stack of molybdenum, tungsten, and aluminum layers (i.e., a Mo / W / Al stack); or the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 can also be a stack of molybdenum, platinum, and aluminum layers (i.e., a Mo / Pt / Al stack); or the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 can also be a stack of tungsten, platinum, and aluminum layers (i.e., a W / Pt / Al stack); or the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 can also be a stack of molybdenum, tungsten, platinum, and aluminum layers (i.e., a Mo / W / Pt / Al stack). The positions and thicknesses of the molybdenum, platinum, and tungsten layers can be set as needed.

[0066] To verify the performance of the target series arm resonator 211 provided by the present invention, this application provides Comparative Example 1, Example 1-1, Example 1-2, and Example 1-3, respectively. Figure 7 The admittance curves are shown for the target series arm resonator 211 in Comparative Example 1, Example 1-1, Example 1-2, and Example 1-3. In Comparative Example 1, the first interdigital transducer electrode 22 of the target series arm resonator 211 is a Ti / Al stack (i.e.,...). Figure 7 (The red curve in the image); the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 in Example 1-1 is a Mo / Al stack (i.e., Figure 7 (The blue curve in the image); the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 in Example 1-2 is W / Al stack (i.e., Figure 7 (The pink curve in the image); the structure of the first interdigital transducer electrode 22 of the target series arm resonator 211 in Examples 1-3 is a Pt / Al stack (i.e., Figure 7 (The black curve in the image). According to Figure 7 It can be seen that the bandwidth of the target series arm resonator 211 gradually decreases from the Ti / Al stack, Mo / Al stack, W / Al stack to Pt / Al stack. Therefore, it can be seen that, compared to the Ti / Al stack, choosing the structure of the first interdigital transducer electrode 22 with Mo / Al, W / Al, and then Pt / Al stacks can reduce the resonant point on the high-frequency side, thereby improving the rectangularity of the resonator on the high-frequency side (i.e., the right edge of the passband). At the same time, a suitable stack structure can be selected according to the bandwidth requirements of the filter.

[0067] In some alternative implementations, such as Figure 4As shown, the second interdigital transducer electrode 32 of the parallel arm resonator 30 also includes a second conductive layer 302, which is disposed on the surface of the second metal layer 301 facing away from the second piezoelectric layer 31; the second metal layer 301 is a titanium layer, and the second conductive layer 302 is an aluminum-copper alloy layer.

[0068] In some alternative implementations, the second interdigital transducer electrode 32 of each parallel arm resonator 30 is a stacked structure of aluminum-copper alloy layer and titanium layer (i.e., Ti / AlCu stack).

[0069] The surface acoustic wave filter provided in this embodiment uses a low-density aluminum-copper alloy layer for the second interdigital transducer electrode of the parallel arm resonator. This ensures that the bandwidth and in-band insertion loss of the filter are not affected, thus maintaining a low in-band insertion loss while ensuring sufficient bandwidth and ensuring the stability of the overall passband characteristics of the filter.

[0070] In some alternative implementations, a portion of the series arm resonators 20 in the surface acoustic wave filter are target series arm resonators 211. The series arm resonators 20 other than the target series arm resonators 211 include a third metal layer and a third conductive layer.

[0071] Optionally, the density of the third metal layer is the same as the density of the second metal layer 301; and / or, the density of the third conductive layer is the same as the density of the second conductive layer 302.

[0072] Optionally, the material of the third metal layer is the same as the material of the second metal layer 301; and / or, the material of the third conductive layer is the same as the material of the second conductive layer 302.

[0073] In some alternative embodiments, the third metal layer is a titanium layer and the third conductive layer is an aluminum-copper alloy layer. That is, the structure of the first interdigital transducer of the series arm resonator 20 outside the target resonator is a stacked structure of aluminum-copper alloy layer and titanium layer (i.e., Ti / AlCu stack).

[0074] To verify the performance of the surface acoustic wave filter provided by this invention, this application provides Comparative Example 2 and Example 2, both with the following topologies. Figure 2 As shown, in the transmit filter path, all series arm resonators 20 are target series arm resonators 211. In Comparative Example 2, the interdigital transducer electrodes of all series arm resonators 20 and all parallel arm resonators 30 in both the transmit and receive filter paths have a Ti / AlCu stack structure. The difference between Example 2 and Comparative Example 2 is that in Example 2, the first interdigital transducer electrode 22 of the target series arm resonator 211 has a Pt / Al stack structure. The second interdigital transducer electrode 32 of the parallel arm resonator 30 still uses a Ti / AlCu stack structure.

[0075] Figure 8 The figures show the admittance curves of the surface acoustic wave filters corresponding to Comparative Example 2 and Example 2, where the solid black line represents Example 2 and the dashed black line represents Comparative Example 2. It can be seen that, compared to Comparative Example 2, the rectangularity of the right edge of the passband in Example 2 is significantly improved.

[0076] Figure 9 The graphs show the full-band rejection of the surface acoustic wave (SAW) filters corresponding to Comparative Example 2 and Example 2. The solid black line represents Example 2, and the dashed black line represents Comparative Example 2. It can be seen that Example 2 also shows a certain improvement in out-of-band rejection compared to Comparative Example 2.

[0077] Figure 10 The right-hand side of the passband curves for the surface acoustic wave filters corresponding to Comparative Example 2 and Example 2 is shown, where the solid black line represents Example 2 and the dashed black line represents Comparative Example 2. It can be seen that, compared to Comparative Example 2, Example 2 exhibits a significant improvement in near-band out-of-band suppression.

[0078] In some alternative embodiments, the first piezoelectric layer 21 is made of lithium tantalate or lithium niobate; the second piezoelectric layer 31 is made of lithium tantalate or lithium niobate.

[0079] In some alternative embodiments, the first piezoelectric layer 21 and the second piezoelectric layer 31 are located within the same common piezoelectric substrate, such as... Figure 11 As shown.

[0080] In some alternative embodiments, the first piezoelectric layer 21 and the second piezoelectric layer 31 are located on different piezoelectric substrates.

[0081] The surface acoustic wave filter provided in this embodiment has a first piezoelectric layer and a second piezoelectric layer located in the same common piezoelectric substrate. This allows all resonators to be integrated within the same common piezoelectric substrate, which simplifies the packaging process, reduces manufacturing costs and device size. Conversely, if the first piezoelectric layer and the second piezoelectric layer are located in different piezoelectric substrates, physical isolation and independent parameter optimization can be performed according to the respective performance requirements of the target series arm resonators and parallel arm resonators, improving design flexibility.

[0082] In some alternative implementations, such as Figure 12 As shown, the interdigital transducer electrode of the target series arm resonator 211 includes two busbars 40 arranged opposite each other along a first direction, and a plurality of electrode fingers 50 connected between the two busbars 40 and spaced apart along a second direction; the plurality of electrode fingers 50 connected to the two busbars 40 are distributed in an interdigital shape; the starting end of the electrode finger 50 is connected to one busbar 40 and the end is close to the other busbar 40.

[0083] In some alternative implementations, such as Figure 12As shown, the target series arm resonator 211 also includes an additional metal structure 80, which is located on the surface or bottom of the electrode finger strip 50, and the additional metal structure 80 is located at the beginning and / or end of the electrode finger strip 50.

[0084] In some alternative implementations, such as Figure 12 As shown, the target series arm resonator 211 also includes a reflective grid structure 23 located on both sides of the interdigital transducer electrodes. The reflective grid structure 23 includes two reflective grid busbars 60 arranged opposite each other along a first direction, and a plurality of reflective grid fingers 70 connected between the two reflective grid busbars 60 and spaced apart along a second direction; the two ends of each reflective grid finger 70 are respectively connected to the two reflective grid busbars 60. The reflective grid structure 23 also includes an additional metal structure 80, which is located on the surface or bottom of the reflective grid fingers 70, and the additional metal structure 80 is close to the starting segment and / or end of the reflective grid fingers 70.

[0085] The surface acoustic wave filter provided in this embodiment adjusts the local mass load of the first interdigital transducer electrode of the target series arm resonator by setting additional metal structures at the beginning and / or end of the electrode fingers of the target series arm resonator, thereby effectively suppressing the generation of parasitic transverse modes and further improving the transverse mode suppression characteristics and overall frequency response smoothness of the target series arm resonator.

[0086] The present invention also provides an RF front-end module, including a surface acoustic wave filter corresponding to any of the above embodiments.

[0087] In the description of this specification, the references to terms such as "this embodiment," "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction. Furthermore, 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 as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0088] The above description does not provide detailed explanations of the technical aspects of each layer's patterning, etching, etc. However, those skilled in the art should understand that various technical means can be used to form layers and regions of the desired shape. Furthermore, to form the same structure, those skilled in the art can also design methods that are not entirely identical to those described above. Additionally, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.

[0089] The above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of protection of the present invention is determined by the scope of the appended claims.

Claims

1. A surface acoustic wave filter, characterized in that, include: A first port, a second port, and a filtering path connecting the first port and the second port; The filtering path includes at least one series arm resonator and at least one parallel arm resonator; The series arm resonator includes a first piezoelectric layer and a first interdigital transducer electrode on the first piezoelectric layer; The parallel arm resonator includes a second piezoelectric layer and a second interdigital transducer electrode on the second piezoelectric layer; At least one of the series arm resonators is the target series arm resonator; The density of the first interdigital transducer electrode of the target series arm resonator is greater than the density of the second interdigital transducer electrode of any of the parallel arm resonators.

2. The surface acoustic wave filter according to claim 1, characterized in that, The first interdigital transducer electrode of each of the target series arm resonators includes a first metal layer; The second interdigital transducer electrode of each of the parallel arm resonators includes a second metal layer; The density of the first metal layer is greater than the density of the second metal layer; The density of the first interdigital transducer electrode of the target series arm resonator is greater than or equal to 10 g / cm³ and less than or equal to 30 g / cm³.

3. The surface acoustic wave filter according to claim 2, characterized in that, The material of the first metal layer includes heavy metals; the first metal layer includes one or more layers selected from molybdenum, platinum and tungsten.

4. The surface acoustic wave filter according to claim 2, characterized in that, The first interdigital transducer electrode of the target series arm resonator further includes a first conductive layer, which is disposed on the surface of the first metal layer facing away from the first piezoelectric layer; the density of the first conductive layer is less than the density of the first metal layer.

5. The surface acoustic wave filter according to claim 3, characterized in that, The second interdigital transducer electrode of the parallel arm resonator further includes a second conductive layer, which is disposed on the surface of the second metal layer facing away from the second piezoelectric layer; the second metal layer is a titanium layer, and the second conductive layer is an aluminum-copper alloy layer.

6. The surface acoustic wave filter according to claim 1, characterized in that, The filtering path includes multiple series arm resonators and multiple parallel arm resonators. The multiple series arm resonators are connected in series between the first port and the second port, and the multiple parallel arm resonators are respectively connected between the node between adjacent series arm resonators and the reference ground port. All of the aforementioned series arm resonators are target series arm resonators; The density of the first interdigital transducer electrode of the target series arm resonator is greater than the density of the second interdigital transducer electrode of any of the parallel arm resonators.

7. The surface acoustic wave filter according to claim 1, characterized in that, The first port includes an antenna port; the series arm resonator closest to the antenna port is the target series arm resonator; The second port includes a transmitting port, and the surface acoustic wave filter includes a transmitting filter; and / or: the second port includes a receiving port, and the surface acoustic wave filter includes a receiving filter.

8. The surface acoustic wave filter according to claim 1, characterized in that, The first piezoelectric layer is made of lithium tantalate or lithium niobate; the second piezoelectric layer is made of lithium tantalate or lithium niobate. The first piezoelectric layer and the second piezoelectric layer are on the same piezoelectric substrate; or the first piezoelectric layer and the second piezoelectric layer are on different piezoelectric substrates.

9. The surface acoustic wave filter according to claim 1, characterized in that, The first interdigital transducer electrode of the target series arm resonator includes two busbars arranged opposite each other along a first direction, and a plurality of electrode fingers connected between the two busbars and spaced apart along a second direction; the plurality of electrode fingers connected to the two busbars are distributed in an interdigital shape; the starting end of each electrode finger is connected to one of the busbars and the end is close to the other busbar; The target series arm resonator also includes an additional metal structure located on the surface or bottom of the electrode fingers, specifically at the beginning and / or end of the electrode fingers.

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

Images