Filter device and method for forming filter device

Abstract

A filter device and a method for forming the same. The filter comprises: a substrate comprising a plurality of first regions, a plurality of second regions, and one or more third regions; a plurality of first resonators located in the first region, each comprising a first interdigital transducer (IDT) comprising a first metal layer; a plurality of second resonators located in the second region, each comprising a second IDT comprising a second metal layer and a third metal layer located on the second metal layer; the first filter comprising a plurality of the first resonators and a plurality of the second resonators, wherein the plurality of the first resonators are series resonators in a ladder circuit of the filter, and the plurality of the second resonators are parallel resonators in the ladder circuit of the filter; a plurality of third IDTs located in the third region, each comprising a fourth metal layer; and the second filter comprising a plurality of the third IDTs. The performance of the filter is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a filter device and a method for forming the filter device. Background Art

[0002] The radio frequency (RF) front-end chips for wireless communication devices include power amplifiers, antenna switches, RF filters, multiplexers, and low-noise amplifiers. RF filters include piezoelectric surface acoustic wave (SAW) filters, piezoelectric bulk acoustic wave (BAW) filters, micro-electro-mechanical system (MEMS) filters, and integrated passive device (IPD) filters.

[0003] SAW resonators have a high quality factor (Q value). RF filters made from SAW resonators have low insertion loss and high out-band rejection. These filters are the mainstream RF filters used in wireless communication devices such as mobile phones and base stations.

[0004] To save area, the RF front-end often uses a duplexer or multiplexer that integrates multiple filters. A duplexer includes a transmit filter and a receive filter. The transmit filter is connected between the signal transmitter and the antenna, while the receive filter is connected between the antenna and the signal receiver.

[0005] However, the performance of existing duplexers needs to be improved. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a filter device and a method for forming the filter device to improve the performance of a duplexer.

[0007] In order to solve the above technical problems, the technical solution of the present invention provides a filtering device, including a first filter and a second filter, including: a substrate, the substrate including a plurality of first regions, a plurality of second regions and one or more third regions; a plurality of first resonators respectively located in the plurality of first regions, wherein the first resonator includes a first interdigital transducer located on the substrate, the first interdigital transducer including a first metal layer; a plurality of second resonators respectively located in the plurality of second regions, wherein the second resonator includes a second interdigital transducer located on the substrate, the second interdigital transducer including a second metal layer and a third metal layer located on the second metal layer, the density of the third metal layer material being less than that of the second metal layer. The density of the metal layer material is smaller than the density of the first metal layer material; the first filter includes a plurality of the first resonators and a plurality of the second resonators, wherein a plurality of the first resonators are series resonators in the filter ladder circuit, and a plurality of the second resonators are parallel resonators in the filter ladder circuit; a plurality of third interdigital transducers located in one or more of the third regions are located on the substrate, the third interdigital transducers include a fourth metal layer, the density of the fourth metal layer is smaller than the density of the second metal layer material, and the density of the fourth metal layer material is smaller than the density of the first metal layer material; the second filter includes a plurality of the third interdigital transducers.

[0008] Optionally, the first filter is a transmitting-end filter, and the second filter is a receiving-end filter.

[0009] Optionally, the first metal layer and the second metal layer are made of the same material.

[0010] Optionally, materials of the first metal layer and the second metal layer include: molybdenum, ruthenium, tungsten, platinum, iridium, copper, chromium, magnesium, scandium or tantalum.

[0011] Optionally, the third metal layer and the fourth metal layer are made of the same material; the third metal layer and the second metal layer are made of different materials.

[0012] Optionally, the materials of the third metal layer and the fourth metal layer include: aluminum or aluminum alloy.

[0013] Optionally, it also includes: a protective layer located on the substrate, covering the plurality of first interdigital transducers, the plurality of second interdigital transducers and the plurality of third interdigital transducers, the protective layer corresponding to the plurality of first interdigital transducers, the plurality of second interdigital transducers and the plurality of third interdigital transducers being concave and convex; the material of the protective layer includes a dielectric material, and the dielectric material includes: silicon dioxide, silicon nitride, aluminum nitride, silicon oxynitride or aluminum oxide.

[0014] Optionally, the material of the substrate includes a piezoelectric material, and the piezoelectric material includes: lithium tantalate, lithium niobate, quartz, zinc oxide or aluminum nitride.

[0015] Optionally, the material of the second metal layer is the same as that of the third metal layer.

[0016] Correspondingly, the technical solution of the present invention also provides a method for forming a filtering device, including forming a first filter and a second filter, including: providing a substrate, the substrate including a plurality of first regions, a plurality of second regions and one or more third regions; forming a plurality of first resonators in the plurality of first regions respectively, wherein forming the first resonators includes forming a first interdigital transducer located on the substrate, and forming the first interdigital transducer includes forming a first metal layer; forming a plurality of second resonators in the plurality of second regions respectively, wherein forming the second resonators includes forming a second interdigital transducer located on the substrate, and forming the second interdigital transducer includes forming a second metal layer and a third metal layer located on the second metal layer, and the density of the material of the third metal layer is less than that of the first resonator. The density of the second metal layer material, the density of the third metal layer material is less than the density of the first metal layer material; forming a first filter includes forming a number of the first resonators and a number of the second resonators, wherein a number of the first resonators are series resonators in the filter ladder circuit, and a number of the second resonators are parallel resonators in the filter ladder circuit; forming a number of third interdigital transducers in one or more of the third regions, located on the substrate, wherein forming the third interdigital transducers includes forming a fourth metal layer, the density of the fourth metal layer is less than the density of the second metal layer material, and the density of the fourth metal layer material is less than the density of the first metal layer material; forming a second filter includes forming a number of the third interdigital transducers.

[0017] Optionally, it also includes: forming a first metal material layer located above the substrate; removing the first metal material layer located in the third area; forming a second metal material layer located above the first metal material layer in the first area and the second area and above the substrate in the third area; removing the second metal material layer located in the first area; forming a first interdigital transducer includes: patterning the first metal material layer in the first area to form the first metal layer; forming a second interdigital transducer includes: patterning the first metal material layer and the second metal material layer in the second area to form the second metal layer and the third metal layer, respectively; forming a third interdigital transducer includes: patterning the second metal material layer in the third area to form the fourth metal layer.

[0018] Optionally, when the material of the second metal layer is the same as the material of the third metal layer, the process of forming the second metal layer is different from the process of forming the third metal layer, or the process of forming the second metal layer and the process of forming the third metal layer are the same process with different process parameters.

[0019] Optionally, the method further includes: forming a protective layer on the substrate, wherein the protective layer covers the first IDTs, the second IDTs and the third IDTs.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0021] The technical solution of the present invention is to form several first interdigital transducers respectively in several first areas, wherein the first interdigital transducers include a first metal layer; and several second interdigital transducers respectively formed in several second areas, wherein the second interdigital transducers include a second metal layer and a third metal layer on the second metal layer, wherein the density of the third metal layer material is less than the density of the second metal layer material, and the density of the third metal layer material is less than the density of the first metal layer material; and several third interdigital transducers are formed in the third area, wherein the third interdigital transducers include a fourth metal layer, wherein the density of the fourth metal layer material is less than the density of the second metal layer material, and the density of the fourth metal layer material is less than the density of the first metal layer material. Therefore, when the first resonators corresponding to the first interdigital transducers are series resonators, due to the large density of the first metal layer, the first metal layer can generate sufficient mass load and obtain a sufficient electromechanical coupling coefficient. At the same time, the activation energy of the first metal layer is high and it is not easy to fail under high power. Therefore, the first resonators in series do not need to be split to withstand high-power signals, which reduces the loss of the first filter and reduces the layout of the first filter chip. In addition, the second interdigital transducer has the second metal layer and the third metal layer located on the second metal layer. Therefore, the cross-sectional area of ​​the second interdigital transducer is increased, so that the resistance of the second interdigital transducer is reduced, which can reduce the resistance of the second resonators corresponding to the second interdigital transducers in parallel, improve the Q value of the resonator, and thus improve the performance of the first filter. While meeting the different requirements of the series resonator and the parallel resonator in the first filter, the resistance of the second filter is reduced, the Q value of the resonator is improved, and thus the performance of the second filter is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 and Figure 2 is a circuit diagram of a surface acoustic wave filter in one embodiment;

[0023] Figures 3 to 81 is a structural diagram of the process of forming a filter device in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] As described in the background art, the performance of the duplexer needs to be improved.

[0025] Figure 1 and Figure 2 FIG. 4 is a circuit diagram of a surface acoustic wave filter in one embodiment.

[0026] Please refer to Figure 1 The SAW filter generally adopts a ladder topology circuit, which is composed of several series SAW resonators and several parallel SAW resonators. The several series SAW resonators include a first series resonator S1, a second series resonator S2, a third series resonator S3 and a fourth series resonator S4. The several parallel SAW resonators include a first parallel resonator T1, a second parallel resonator T2 and a third parallel resonator T3. One end of the first parallel resonator T1 is connected to the first series resonator S1 and the second series resonator S2, and the other end of the first parallel resonator T1 is grounded. One end of the second parallel resonator T2 is connected to the second series resonator S2 and the third series resonator S3, and the other end of the second parallel resonator T2 is grounded. One end of the third parallel resonator T3 is connected to the third series resonator S3 and the fourth series resonator S4, and the other end of the third parallel resonator T3 is grounded.

[0027] The interdigital transducer of the SAW resonator is composed of two layers of metal. The bottom metal is usually a metal with a higher density (such as molybdenum, tungsten, platinum, tantalum, etc.) to generate sufficient mass load and obtain a higher electromechanical coupling coefficient; the top metal is usually a metal with a lower density and lower resistivity (such as aluminum or aluminum alloy) to reduce the overall resistance of the interdigital transducer, thereby reducing the insertion loss of the filter.

[0028] A SAW resonator has two resonant points: the positive resonance point has the lowest resistance, while the antiresonance point has the highest resistance. When the resonator is at positive resonance, the current flowing through it is maximum, which puts the IDT at its highest stress and makes it susceptible to burnout. Conversely, at the antiresonance point, the resistance is maximum and the current is minimum, making the IDT less susceptible to burnout.

[0029] It should be noted that the activation energy of aluminum metal is relatively low, and it is prone to failure under high current and high stress. Therefore, under high current conditions, aluminum atoms in the IDT are prone to migrate in the grains, forming protrusions and voids, which cause the IDT to fail when it is turned on. High-density metals have higher activation energy. For example, the activation energy of molybdenum is more than three times that of aluminum, and it is not easy to migrate under high current.

[0030] When a high-power signal passes through the filter passband, the series resonator is at the positive resonance point, and the aluminum metal layer in its interdigital transducer is prone to failure, further causing the resonator to fail and affecting the performance of the filter.

[0031] In order to avoid the failure of the series resonator, one or more series resonators can be split into N resonators (N≥2) with an area N times larger than the original series resonator, and connected in series to disperse the power distribution and reduce the power that a single resonator needs to bear. Figure 2 , Figure 2 For the general Figure 1 The first series resonator S1 in the circuit is split into three resonators S1a, S1b and S1c. Figure 1 The second series resonator S2 in the circuit is split into two resonators S2a and S2b. Figure 1 The fourth series resonator S4 in is split into two resonators S4a and S4b.

[0032] However, this approach will bring two problems: first, N resonators are connected in series to replace the function of the original resonator, which increases the resistance in the series circuit and the insertion loss of the filter; second, splitting into multiple resonators increases the layout area of ​​the filter and the size of the filter chip, resulting in increased chip cost.

[0033] In order to solve the above problems, the technical solution of the present invention provides a filtering device and a method for forming a filtering device, wherein a plurality of first interdigital transducers are formed in a plurality of first areas, wherein the first interdigital transducers include a first metal layer; a plurality of second interdigital transducers are formed in a plurality of second areas, wherein the second interdigital transducers include a second metal layer and a third metal layer on the second metal layer, wherein the density of the third metal layer material is less than the density of the second metal layer material, and the density of the third metal layer material is less than the density of the first metal layer material; a plurality of third interdigital transducers are formed in the third area, wherein the third interdigital transducers include a fourth metal layer, wherein the density of the fourth metal layer material is less than the density of the second metal layer material, and the density of the fourth metal layer material is less than the density of the first metal layer material. Therefore, when the first resonators corresponding to the first interdigital transducers are series resonators, due to the large density of the first metal layer, the first metal layer can generate sufficient mass load and obtain a sufficient electromechanical coupling coefficient. At the same time, the activation energy of the first metal layer is high and it is not easy to fail under high power. Therefore, the first resonators in series do not need to be split to withstand high-power signals, which reduces the loss of the first filter and reduces the layout of the first filter chip. In addition, the second interdigital transducer has the second metal layer and the third metal layer located on the second metal layer. Therefore, the cross-sectional area of ​​the second interdigital transducer is increased, so that the resistance of the second interdigital transducer is reduced, which can reduce the resistance of the second resonators corresponding to the second interdigital transducers in parallel, improve the Q value of the resonator, and thus improve the performance of the first filter. While meeting the different requirements of the series resonator and the parallel resonator in the first filter, the resistance of the second filter is reduced, the Q value of the resonator is improved, and thus the performance of the second filter is improved.

[0034] In order to make the above-mentioned objects, features and beneficial effects of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] Figures 3 to 8 1 is a structural diagram of the process of forming a filter device in an embodiment of the present invention.

[0036] Please refer to Figure 3 , providing a substrate 200, wherein the substrate 200 includes a plurality of first regions I, a plurality of second regions II and one or more third regions III.

[0037] The substrate 200 is made of piezoelectric materials, including lithium tantalate (LiTaO 3 , LT for short), lithium niobate (LiNbO 3 , LN for short), quartz, zinc oxide (ZnO), and the like.

[0038] Next, a first filter is formed in the first regions I and the second regions II, including: forming a plurality of first resonators in the first regions I, each of the first resonators comprising a first interdigital transducer located above the substrate; forming a plurality of second resonators in the second regions II, each of the second resonators comprising a second interdigital transducer located above the substrate; the first filter includes a plurality of first resonators and a plurality of second resonators, wherein the first resonators are series resonators in the first filter ladder circuit, and the second resonators are parallel resonators in the first filter ladder circuit. Furthermore, a second filter is formed in the third region III, wherein the second filter includes a plurality of third interdigital transducers located above the substrate.

[0039] In this embodiment, the first filter is a transmitting filter, and the second filter is a receiving filter. The transmitting filter is connected between the signal transmitting end and the antenna end, and the receiving filter is connected between the antenna end and the signal receiving end. The transmitting filter and the receiving filter constitute a duplexer.

[0040] In this embodiment, the first interdigital transducer includes a first metal layer; the second interdigital transducer includes a second metal layer and a third metal layer located on the second metal layer, the density of the third metal layer material is less than the density of the second metal layer material, and the density of the third metal layer material is less than the density of the first metal layer material; the third interdigital transducer includes a fourth metal layer, the density of the fourth metal layer is less than the density of the second metal layer material, and the density of the fourth metal layer material is less than the density of the first metal layer material.

[0041] In this embodiment, the first metal layer and the second metal layer are formed based on the same material layer; the third metal layer and the fourth metal layer are formed based on the same material layer.

[0042] The formation process of the first interdigital transducer, the second interdigital transducer and the third interdigital transducer can be referred to Figures 3 to 7 .

[0043] Please continue to refer to Figure 3 , forming a first metal material layer 201 on the first region I, the second region II and the third region III; and removing the first metal material layer 201 located on the third region III.

[0044] The method for removing the first metal material layer 201 on the third region III includes: forming a second mask layer (not shown) on the surface of the first metal material layer 201, the second mask layer exposing the surface of the first metal material layer 201 on the third region III; using the second mask layer as a mask, etching the first metal material layer 201 on the third region III until the surface of the substrate 200 is exposed, and retaining the first metal material layer 201 on the first region I and the second region II. Please refer to Figure 4 A second metal material layer 202 is formed on the first metal material layer 201 on the first region I and the second region II and on the third region III.

[0045] Please refer to Figure 5 , remove the second metal material layer 202 on the first region I, and retain the second metal material layer 202 located on the second region II and the third region III.

[0046] After the second metal material layer 202 on the first region I is removed, only the first metal material layer 201 is left on the first region I, and only the second metal material layer 202 is left on the third region III.

[0047] Please refer to Figure 6 and Figure 7 , Figure 7 for Figure 6 A top view of Figure 6 for Figure 7 Schematic diagram of the cross-sectional structure along the section lines BB1, CC1 and DD1, respectively, the first metal material layer 201 of the first zone I is patterned to form the first metal layer 204; the first metal material layer 201 and the second metal material layer 202 of the second zone II are patterned to form the second metal layer 205 and the third metal layer 206, respectively; the second metal material layer 202 of the third zone III is patterned to form the fourth metal layer 207.

[0048] In this embodiment, the method for forming the first metal layer 204, the second metal layer 205, the third metal layer 206 and the fourth metal layer 207 includes: forming a patterned mask layer (not shown) on the second metal material layer 202 and the first metal material layer 201; etching the second metal material layer 202 and the first metal material layer 201 using the patterned mask layer as a mask until the surface of the substrate 200 is exposed, forming the first metal layer 204 and the second metal layer 205 based on the first metal layer 201, and forming the third metal layer 206 and the fourth metal layer 207 based on the second metal material layer 202, thereby forming a number of the first interdigital transducers on the first area I, forming a number of the second interdigital transducers on the second area II, and forming a number of the third interdigital transducers on the third area III.

[0049] In other embodiments, the process of patterning the first metal material layer in the first region, patterning the first metal material layer and the second metal material layer in the second region, and patterning the second metal material layer in the third region includes a lift-off process.

[0050] The first interdigital transducer includes the first metal layer 204; the second interdigital transducer includes the second metal layer 205 and the third metal layer 206 located on the second metal layer 205, the density of the material of the third metal layer 206 is less than the density of the material of the second metal layer 205, and the density of the material of the third metal layer 206 is less than the density of the material of the first metal layer 204; the third interdigital transducer includes a fourth metal layer 207, the density of the fourth metal layer 207 is less than the density of the material of the second metal layer 205, and the density of the material of the fourth metal layer 207 is less than the density of the material of the first metal layer 204.

[0051] In this embodiment, the first metal layer 204 and the second metal layer 205 are formed based on the same material layer, and the first metal layer 204 and the second metal layer 205 are made of the same material.

[0052] The materials of the first metal layer 204 and the second metal layer 205 include: molybdenum, ruthenium, tungsten, platinum, iridium, copper, chromium, magnesium, scandium or tantalum.

[0053] The material density of the first metal layer 204 and the second metal layer 205 is relatively high, so that the first metal layer 204 and the second metal layer 205 can generate sufficient mass load and obtain a sufficient electromechanical coupling coefficient.

[0054] In other embodiments, the materials of the first metal layer and the second metal layer may be different.

[0055] In this embodiment, the materials of the third metal layer 206 and the second metal layer 205 are different. In other embodiments, the materials of the third metal layer and the second metal layer can be the same.

[0056] However, the processes for forming the third metal layer and the second metal layer are different, or the processes for forming the second metal layer and the third metal layer are the same process with different process parameters, so that the densities of the third metal layer and the second metal layer are different.

[0057] The process of forming the second metal layer includes deposition, sputtering, evaporation or electroplating, and the process of forming the third metal layer includes deposition, sputtering, evaporation or electroplating.

[0058] When the second metal layer and the third metal layer are formed using the same process, the voltage, pressure, or power during the formation process can be adjusted. For example, the voltage, pressure, or power used to form the second metal layer can be increased to increase the density of the formed second metal layer. In this embodiment, the third metal layer 206 and the fourth metal layer 207 are formed based on the same material layer, and the third metal layer 206 and the fourth metal layer 207 are made of the same material.

[0059] The materials of the third metal layer 206 and the fourth metal layer 207 include aluminum or aluminum alloy.

[0060] The material density of the fourth metal layer 207 is relatively low. The second filter includes the third interdigital transducer, and the third interdigital transducer includes the fourth metal layer 207. The second filter is a receiving filter and has a low power requirement, thereby further reducing the loss resistance of the second filter.

[0061] In other embodiments, the third metal layer and the fourth metal layer may be made of different materials.

[0062] In this embodiment, a plurality of first resonators are connected in series via the connection layer 220 , and a plurality of second resonators are respectively connected to the plurality of first resonators connected in series via the connection layer 220 .

[0063] Forming a first filter includes forming a plurality of first resonators and a plurality of second resonators, wherein a plurality of first interdigital transducers are respectively formed in a plurality of first regions I, and the first interdigital transducers include a first metal layer 204; a plurality of second interdigital transducers are respectively formed in a plurality of second regions II, and the second interdigital transducers include a second metal layer 205 and a third metal layer 206 on the second metal layer 205, wherein the density of the third metal layer 206 material is less than the density of the second metal layer 205 material, and the density of the third metal layer 206 material is less than the density of the first metal layer 204 material; and a plurality of third interdigital transducers are formed in a third region III, and the third interdigital transducers include a fourth metal layer 207, wherein the density of the fourth metal layer 207 is less than the density of the second metal layer 205 material, and the density of the fourth metal layer 207 material is less than the density of the first metal layer 204 material. Therefore, when the first resonators corresponding to the first interdigital transducers are series resonators, due to the large density of the first metal layer 204, the first metal layer 204 can generate sufficient mass load and obtain a sufficient electromechanical coupling coefficient. At the same time, the activation energy of the first metal layer 204 is high and it is not easy to fail under high power. Therefore, the first resonators in series do not need to be split and can withstand high-power signals, which reduces the loss of the first filter and reduces the layout of the first filter chip. In addition, the second interdigital transducer has the second metal layer 205 and the third metal layer 206 located on the second metal layer 205. Therefore, the cross-sectional area of ​​the second interdigital transducer is increased, so that the resistance of the second interdigital transducer is reduced, which can reduce the resistance of the second resonators corresponding to the second interdigital transducers in parallel, improve the Q value of the resonator, and thus improve the performance of the first filter. While meeting the different requirements of the series resonator and the parallel resonator in the first filter, the resistance of the second filter is reduced, the Q value of the resonator is improved, and thus the performance of the second filter is improved.

[0064] Please refer to Figure 8 A protective layer 208 is formed on the substrate 200, and the protective layer 208 covers the plurality of first IDTs, the plurality of second IDTs, and the plurality of third IDTs. The protective layer 208 has a concave-convex shape corresponding to the plurality of first IDTs, the plurality of second IDTs, and the plurality of third IDTs.

[0065] The material of the protection layer 208 includes a dielectric material, and the dielectric material includes silicon dioxide, silicon nitride, aluminum nitride, silicon oxynitride, or aluminum oxide.

[0066] Accordingly, the embodiment of the present invention further provides a filtering device, including a first filter and a second filter, please continue to refer to Figure 8 ,include:

[0067] A substrate 200 comprising a plurality of first regions I, a plurality of second regions II, and one or more third regions III;

[0068] a plurality of first resonators respectively located in the plurality of first regions I, wherein the first resonators include first interdigital transducers located on the substrate, and the first interdigital transducers include a first metal layer 204;

[0069] a plurality of second resonators respectively located in a plurality of the second regions II, wherein the second resonators include a second interdigital transducer located on the substrate, the second interdigital transducer including a second metal layer 205 and a third metal layer 206 located on the second metal layer 205, the density of the material of the third metal layer 206 being less than the density of the material of the second metal layer 205, and the density of the material of the third metal layer 206 being less than the density of the material of the first metal layer 204;

[0070] The first filter includes a plurality of the first resonators and a plurality of the second resonators, wherein the plurality of the first resonators are series resonators in a filter ladder circuit, and the plurality of the second resonators are parallel resonators in the filter ladder circuit;

[0071] a plurality of third IDTs located in one or more third regions III, located on the substrate, the third IDTs comprising a fourth metal layer 207, wherein the density of the fourth metal layer 207 is less than the density of the second metal layer 205, and the density of the fourth metal layer 207 is less than the density of the first metal layer 204;

[0072] The second filter includes a plurality of the third interdigital transducers. In this embodiment, the first filter is a transmitting filter, and the second filter is a receiving filter.

[0073] In this embodiment, the first metal layer 204 and the second metal layer 205 are made of the same material.

[0074] In this embodiment, the materials of the first metal layer 204 and the second metal layer 205 include: molybdenum, ruthenium, tungsten, platinum, iridium, copper, chromium, magnesium, scandium or tantalum.

[0075] In this embodiment, the third metal layer 206 and the fourth metal layer 207 are made of the same material; the third metal layer 206 and the second metal layer 205 are made of different materials.

[0076] In this embodiment, the material of the third metal layer 206 and the fourth metal layer 207 includes aluminum or aluminum alloy.

[0077] In this embodiment, the present invention further includes: a protective layer 208 located on the substrate 200, covering the plurality of first IDTs, the plurality of second IDTs and the plurality of third IDTs, wherein the protective layer 208 has a concave-convex shape corresponding to the plurality of first IDTs, the plurality of second IDTs and the plurality of third IDTs; the material of the protective layer 208 includes a dielectric material, and the dielectric material includes: silicon dioxide, silicon nitride, aluminum nitride, silicon oxynitride or aluminum oxide.

[0078] In this embodiment, the substrate 200 is made of a piezoelectric material, and the piezoelectric material includes lithium tantalate, lithium niobate, quartz, zinc oxide, or aluminum nitride.

[0079] In this embodiment, the material of the second metal layer 205 is the same as that of the third metal layer 206 .

[0080] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A filtering device comprising a first filter and a second filter, characterized in that: include: a substrate comprising a plurality of first regions, a plurality of second regions, and one or more third regions; a plurality of first resonators respectively located in a plurality of the first regions, wherein the first resonators include first interdigital transducers located on the substrate, and the first interdigital transducers include a first metal layer; a plurality of second resonators respectively located in a plurality of the second regions, wherein the second resonators include a second interdigital transducer located on the substrate, the second interdigital transducer including a second metal layer and a third metal layer located on the second metal layer, the density of the third metal layer material is less than the density of the second metal layer material, and the density of the third metal layer material is less than the density of the first metal layer material; The first filter includes a plurality of the first resonators and a plurality of the second resonators, wherein the plurality of the first resonators are series resonators in a filter ladder circuit, and the plurality of the second resonators are parallel resonators in the filter ladder circuit; a plurality of third interdigital transducers located in one or more of the third regions, located on the substrate, the third interdigital transducers comprising a fourth metal layer, wherein the density of the fourth metal layer is less than the density of the second metal layer material, and the density of the fourth metal layer material is less than the density of the first metal layer material; The second filter includes a plurality of the third interdigital transducers.

2. The filtering device according to claim 1, wherein The first filter is a transmitting-end filter, and the second filter is a receiving-end filter.

3. The filtering device according to claim 1, wherein The first metal layer and the second metal layer are made of the same material.

4. The filtering device according to claim 3, wherein Materials of the first metal layer and the second metal layer include: molybdenum, ruthenium, tungsten, platinum, iridium, copper, chromium, magnesium, scandium or tantalum.

5. The filtering device according to claim 1, wherein The third metal layer and the fourth metal layer are made of the same material; the third metal layer and the second metal layer are made of different materials.

6. The filtering device according to claim 5, wherein The materials of the third metal layer and the fourth metal layer include aluminum or aluminum alloy.

7. The filtering device according to claim 1, wherein Also includes: A protective layer located on the substrate covers the first interdigital transducers, the second interdigital transducers and the third interdigital transducers, and the protective layer corresponding to the first interdigital transducers, the second interdigital transducers and the third interdigital transducers is concave and convex; the material of the protective layer includes a dielectric material, and the dielectric material includes: silicon dioxide, silicon nitride, aluminum nitride, silicon oxynitride or aluminum oxide.

8. The filtering device according to claim 1, wherein The substrate is made of piezoelectric material, which includes lithium tantalate, lithium niobate, quartz, zinc oxide or aluminum nitride.

9. The filtering device according to claim 1, wherein The material of the second metal layer is the same as that of the third metal layer.

10. A method for forming a filter device, comprising forming a first filter and a second filter, characterized in that: include: Providing a substrate, the substrate comprising a plurality of first regions, a plurality of second regions, and one or more third regions; forming a plurality of first resonators in the plurality of first regions respectively, wherein forming the first resonators includes forming a first interdigital transducer located on the substrate, and forming the first interdigital transducer includes forming a first metal layer; forming a plurality of second resonators in the plurality of second regions, respectively, wherein forming the second resonators includes forming a second interdigital transducer located on the substrate, and forming the second interdigital transducer includes forming a second metal layer and a third metal layer located on the second metal layer, wherein the density of the material of the third metal layer is less than the density of the material of the second metal layer, and the density of the material of the third metal layer is less than the density of the material of the first metal layer; Forming the first filter includes forming a plurality of the first resonators and a plurality of the second resonators, wherein the plurality of the first resonators are series resonators in a filter ladder circuit, and the plurality of the second resonators are parallel resonators in the filter ladder circuit; forming a plurality of third interdigital transducers in one or more of the third regions, the interdigital transducers being located on the substrate, wherein forming the third interdigital transducers comprises forming a fourth metal layer, wherein the density of the fourth metal layer is less than the density of the second metal layer material, and the density of the fourth metal layer material is less than the density of the first metal layer material; Forming the second filter includes forming a plurality of the third interdigital transducers.

11. The method for forming a filter device according to claim 10, wherein: Also includes: forming a first metal material layer located above the substrate; and removing the first metal material layer located in the third region; forming a second metal material layer located above the first metal material layer in the first and second regions and above the substrate in the third region; removing the second metal material layer located in the first area; Forming a first interdigital transducer includes: patterning the first metal material layer in the first area to form the first metal layer; forming a second interdigital transducer includes: patterning the first metal material layer and the second metal material layer in the second area to form the second metal layer and the third metal layer, respectively; forming a third interdigital transducer includes: patterning the second metal material layer in the third area to form the fourth metal layer.

12. The method for forming a filter device according to claim 10, wherein: When the material of the second metal layer is the same as that of the third metal layer, the process of forming the second metal layer is different from the process of forming the third metal layer, or the process of forming the second metal layer and the process of forming the third metal layer are the same process with different process parameters.

13. The method for forming a filter device according to claim 10, wherein: Also includes: A protection layer is formed on the substrate, wherein the protection layer covers the first IDTs, the second IDTs and the third IDTs.

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