An integrated surface acoustic wave filter and its fabrication method

Abstract

This invention discloses an integrated surface acoustic wave (SAW) filter and its fabrication method. The method involves sequentially forming a piezoelectric layer and an interdigitated circuit layer on a substrate, then coating with photoresist, exposing and developing the photoresist to create vias connecting electrodes to the interdigitated circuit layer and trenches with encapsulated circuit patterns. Conductive material is then filled into the vias and trenches to form an encapsulated circuit layer connected to the interdigitated circuit layer. Repeating these steps produces a rapidly integrated SAW filter. This method achieves rapid integrated fabrication simultaneously, eliminating the need to separate wafer fabrication and packaging. It requires less equipment, simplifies the process, and reduces costs, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of filters, and in particular to an integrally molded surface acoustic wave filter and its manufacturing method. Background Technology

[0002] Surface acoustic wave (SAW) filters are transducer-type passive bandpass filters made using the piezoelectric effect of piezoelectric ceramics, lithium niobate, quartz and other piezoelectric quartz crystal oscillator materials and the physical characteristics of surface acoustic wave propagation. They are specialized filtering devices made using piezoelectric materials such as quartz crystals and piezoelectric ceramics, utilizing their piezoelectric effect and the physical characteristics of surface acoustic wave propagation.

[0003] Traditional methods for manufacturing surface acoustic wave (SAW) filters:

[0004] (1) Using piezoelectric material wafers (lithium tantalate, lithium niobate, etc.), semiconductor processes (coating / exposure / development / evaporation / etching, etc.) are used on the piezoelectric material to fabricate interdigitated circuit structures that meet the design requirements of different filtering functions, and finally complete the fabrication of the wafer segment.

[0005] (2) The circuit of the packaging substrate (ceramic or resin) needs to be specially designed for different filter requirements in order to meet the filter performance such as insertion loss and isolation required by the design, and to manufacture the packaging substrate of the filter.

[0006] (3) Single design units are obtained by cutting wafer segments and soldered onto the packaging substrate using upright or flip-chip technology. Finally, resin is injected for molding and cutting into individual chips. The test tapes are then sold.

[0007] Traditional surface acoustic wave (SAW) filter fabrication methods are complex and cumbersome, involving separate wafer fabrication and packaging substrate fabrication, ultimately assembling them into a single unit through ball bonding. This method results in high cost, long production time, and requires extensive equipment, hindering large-scale industrial production. Summary of the Invention

[0008] To address the problems of complex and cumbersome manufacturing processes, high costs, long time consumption, and unfavorable conditions for large-scale industrial production of traditional surface acoustic wave (SAW) filters, this application proposes an integrated surface acoustic wave filter and its manufacturing method to solve these problems.

[0009] According to a first aspect, embodiments of this application propose a method for fabricating an integrally molded surface acoustic wave filter, comprising the following steps:

[0010] S1, Photoresist is coated on a substrate on which a piezoelectric layer and an interdigitated circuit layer are sequentially formed;

[0011] S2, expose and develop the photoresist to create through holes and trenches;

[0012] S3, fill the through holes and the trenches with conductive material to form an encapsulated circuit layer connected to the interdigitated circuit layer;

[0013] S4. Repeat steps S1-S3 to produce the surface wave filter.

[0014] In an optional embodiment, the packaged circuit layer has 2-6 layers, and each packaged circuit layer is connected to the others through the vias.

[0015] In an optional embodiment, step S1 specifically includes:

[0016] S11, piezoelectric material is vapor-deposited on the substrate to form the piezoelectric layer;

[0017] S12, the interdigitated circuit layer is fabricated using conductive materials through screen printing or 3D printing technology;

[0018] S13 is coated with photoresist with a thickness of 0.5um to 5um.

[0019] In an optional embodiment, step S2 specifically includes:

[0020] S21, the first preset area of ​​the photoresist corresponding to the conductive material is exposed and developed for the first time to form the through hole;

[0021] S22, the second preset area of ​​the photoresist is exposed and developed for the second time to form the trench with the encapsulation circuit pattern on the surface of the photoresist. The depth of the trench is 0.5um to 5um.

[0022] In an optional embodiment, step S3 specifically includes:

[0023] S31, the conductive material is deposited on the photoresist on which the through holes and the trenches are formed;

[0024] S32, Remove excess conductive material so that the surface of the conductive material in the via and the trench is flush with the surface of the photoresist.

[0025] In an optional embodiment, step S4 further includes the following steps:

[0026] S41, an external electrode is fabricated on the conductive material of the outermost encapsulation circuit layer;

[0027] S42, the wafer having the surface acoustic wave filter device is diced.

[0028] In an optional embodiment, the material of the piezoelectric layer includes lithium tantalate, lithium niobate, or ZnO.

[0029] In an optional embodiment, the conductive material includes copper or silver.

[0030] In an optional embodiment, the substrate material includes Si or Al2O3.

[0031] Secondly, embodiments of this application also propose an integrated surface acoustic wave filter fabricated using the above-described fabrication method, comprising a piezoelectric layer, an interdigitated circuit layer, and a multilayer encapsulation circuit layer sequentially stacked on a substrate. The encapsulation circuit layer includes photoresist and conductive material disposed in vias and trenches. Each encapsulation circuit layer is connected to the interdigitated circuit layer through vias. The trenches on the photoresist have encapsulation circuit patterns, and the surface of the encapsulation circuit layer is provided with external electrodes.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) Non-conductive photoresist is used to expose and develop vias connecting the interdigitated circuit layer and trenches with encapsulated circuit patterns. Conductive material is then filled into the vias and trenches, and the encapsulated circuit layer is formed through multi-layer stacking. This eliminates the need to fabricate the wafer segment and the encapsulation segment of the surface acoustic wave filter separately, requires less equipment, simplifies the process, reduces costs, and enables rapid integrated molding.

[0034] (2) The interdigitated circuit layer is fabricated on the piezoelectric layer by screen printing or 3D printing technology, and the interdigitated circuit structure can meet the design of different filtering functions, which is conducive to large-scale industrial production. Attached Figure Description

[0035] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. Other embodiments and many anticipated advantages of the embodiments will be readily recognized as they become better understood through reference to the following detailed description. Elements in the drawings are not necessarily to scale. The same reference numerals refer to corresponding similar parts.

[0036] Figure 1a-1j This is a schematic flowchart illustrating the fabrication method of an integrally molded surface wave filter according to an embodiment of this application. Detailed Implementation

[0037] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be 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, only the parts relevant to the invention are shown in the accompanying drawings.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] refer to Figure 1a and 1b A substrate 101 is provided, which can be Si or Al2O3. A piezoelectric layer 201 is formed by vapor deposition of a piezoelectric material on the substrate 101. In this embodiment, a substrate 101 made of a piezoelectric material is not required; the piezoelectric layer 201 can be formed on a substrate 101 of other materials. In this embodiment, inexpensive substrates such as Si and Al2O3 can be used, thus significantly reducing production costs. In optional embodiments, the material of the piezoelectric layer 201 includes lithium tantalate, lithium niobate, ZnO, etc. In a preferred embodiment, the thickness of the piezoelectric layer 201 is greater than 1 micrometer.

[0040] refer to Figure 1c An interdigitated circuit layer 301 is fabricated on the piezoelectric layer 201 using conductive materials via screen printing or 3D printing technology. The conductive materials can be copper paste, silver paste, copper powder, or silver powder, etc. Screen printing is characterized by simple equipment, convenient operation, low cost, easy plate making, and a wide range of substrates. 3D printing technology uses a layer-by-layer processing and stacking method to add material layer by layer. Compared to traditional surface acoustic wave filters, the embodiments of this application can fabricate interdigitated circuit layers 301 on the piezoelectric layer 201 using screen printing or 3D printing technology to meet different filtering function designs. Furthermore, after forming the interdigitated circuit layer 301, the encapsulation circuit layer can be directly fabricated on top, achieving rapid integrated molding.

[0041] refer to Figure 1d and 1eA photoresist 401 with a thickness of 0.5µm to 5µm is coated on the piezoelectric layer 201 and the interdigitated circuit layer 301. The thickness of the photoresist 401 is greater than that of the interdigitated circuit layer 301, thus covering the interdigitated circuit layer 301. After exposure and development, vias 402 connecting the electrodes of the interdigitated circuit layer 301 and trenches 403 forming the pattern required for the packaging circuit are created. Next, conductive material is deposited into the vias 402 and trenches 403 to form a packaging circuit layer connected to the interdigitated circuit layer 301 on the photoresist 401. The conductive material can be copper or silver, etc. Specifically, vias 402 are first formed by exposure and development on a first predetermined area of ​​the photoresist 401 corresponding to the conductive material. By filling the vias 402 with conductive material, the electrodes of the interdigitated circuit layer 301 can be brought out. Next, exposure and development are performed in the second predetermined area of ​​the photoresist 401 to form trenches 403 with encapsulation circuit patterns. The depth of the trenches 403 ranges from 0.5µm to 5µm. In a specific embodiment, the depth of the trenches 403 is less than or equal to the thickness of each layer of photoresist 401. The second predetermined area is located in other areas outside the first predetermined area, and the first and second predetermined areas partially overlap. The trenches 403 formed on the photoresist 401 are filled with conductive material to create the encapsulation circuit layer. Therefore, by using non-conductive photoresist 401 and filling the vias 402 and trenches 403 of the multilayer photoresist 401 with conductive material, the encapsulation of the surface acoustic wave filter can be completed. This method is low-cost and does not affect the performance of the surface acoustic wave filter.

[0042] refer to Figure 1f and 1g A conductive material 501 is deposited onto the photoresist 401 with vias and trenches to create a packaging circuit layer. The conductive material 501 is deposited onto the vias 402 and trenches 403, and then partially removed to make the surface of the conductive material 501 within the vias 402 and trenches 403 flush with the surface of the photoresist 401. Specifically, planarization can be used to remove excess conductive material 501. Planarization methods include chemical mechanical polishing (CMP) to grind the conductive material layer until some of the photoresist 401 on the surface is exposed. In other feasible embodiments, other processing methods can be used to remove excess conductive material 501. The conductive material 501 can be copper, silver, or conductive paste. This facilitates subsequent repeatable steps, ultimately resulting in the desired packaging circuit. Figure 1h The structure shown is illustrated. In the embodiments of this application, the encapsulation circuit layer is directly formed on the interdigitated circuit layer 301 using photoresist 401 and conductive material 501 through vapor deposition. This differs from the traditional technology of separately fabricating the filter encapsulation substrate, resulting in fewer steps and lower cost.

[0043] refer to Figure 1iAn external electrode 601 is fabricated on the outermost packaged circuit layer, and the electrodes of the interdigitated circuit layer 301 or the packaged circuit layer are connected to the outside through the external electrode 601.

[0044] refer to Figure 1j The wafer containing the surface acoustic wave filter device is cut into individual chips.

[0045] Furthermore, embodiments of this application also provide an integrally molded surface acoustic wave filter manufactured using the above-described method.

[0046] like Figure 1i As shown, the surface acoustic wave filter includes a piezoelectric layer 201, an interdigitated circuit layer 301, and a multilayer encapsulation circuit layer sequentially formed on a substrate 101. The encapsulation circuit layer includes a photoresist 401 and conductive material 501 disposed in vias and trenches of the photoresist 401. The vias in the photoresist 401 can connect the electrodes of the interdigitated circuit layer 301 and the multilayer encapsulation circuit layer. The trenches have encapsulation circuit patterns, and external electrodes 601 are provided on the surface of the interdigitated circuit layer 301.

[0047] In specific embodiments, the substrate 101 can be Si or Al2O3, and it is not necessary to use a substrate 101 made of piezoelectric material. A thin piezoelectric layer 201 can be deposited on a substrate 101 of other materials. Furthermore, the embodiments of this application can use inexpensive substrates such as Si and Al2O3, thus significantly reducing production costs. In optional embodiments, the material of the piezoelectric layer 201 includes lithium tantalate, lithium niobate, ZnO, etc. In preferred embodiments, the thickness of the piezoelectric layer 201 is greater than 1 micrometer.

[0048] The surface acoustic wave filter fabrication method of this application can realize the integrated fabrication of wafer segment fabrication and packaging fabrication at the same time, without the need to separate wafer segment fabrication and packaging fabrication. It requires less equipment, simplifies the process, and reduces costs, which is conducive to large-scale industrial production.

[0049] The specific embodiments of this application have been described above, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0050] In the description of this application, it should be understood that the terms "upper," "lower," "inner," "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and for simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The simple fact that certain measures are recited in mutually different dependent claims does not indicate that combinations of these measures cannot be used for improvement. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A method for manufacturing an integrally molded surface acoustic wave filter, characterized in that, Includes the following steps: S1, Photoresist is coated on a substrate on which a piezoelectric layer and an interdigitated circuit layer are sequentially formed; S2, expose and develop the photoresist to create partially connected vias and trenches; S3, filling the vias and trenches with conductive material to form a packaged circuit layer connected to the interdigitated circuit layer specifically includes: S31, the conductive material is deposited on the photoresist on which the through holes and the trenches are formed; S32, Remove excess conductive material to make the surface of the conductive material in the via and the trench flush with the surface of the photoresist; S4. Repeat steps S1-S3 to produce the surface wave filter.

2. The method for manufacturing the integrated surface acoustic wave filter according to claim 1, characterized in that, The packaged circuit has 2-6 layers, and each packaged circuit layer is connected to the others through the vias.

3. The method for manufacturing the integrated surface acoustic wave filter according to claim 1, characterized in that, Step S1 specifically includes: S11, piezoelectric material is vapor-deposited on the substrate to form the piezoelectric layer; S12, the interdigitated circuit layer is fabricated using conductive materials through screen printing or 3D printing technology; S13 is coated with photoresist with a thickness of 0.5um to 5um.

4. The method for manufacturing the integrated surface acoustic wave filter according to claim 3, characterized in that, Step S2 specifically includes: S21, the first preset area of ​​the photoresist corresponding to the conductive material is exposed and developed for the first time to form the through hole; S22, the second preset area of ​​the photoresist is exposed and developed for the second time to form the trench with the encapsulation circuit pattern on the surface of the photoresist. The depth of the trench is 0.5um to 5um.

5. The method for manufacturing the integrated surface acoustic wave filter according to claim 1, characterized in that, Step S4 further includes the following steps: S41, an external electrode is fabricated on the conductive material of the outermost encapsulation circuit layer; S42, the wafer having the surface acoustic wave filter device is diced.

6. The method for manufacturing the integrated surface acoustic wave filter according to claim 1, characterized in that, The piezoelectric layer is made of lithium tantalate, lithium niobate, or ZnO.

7. The method for manufacturing the integrated surface acoustic wave filter according to claim 1 or 3, characterized in that, The conductive material includes copper or silver.

8. The method for manufacturing an integrated surface acoustic wave filter according to claim 1, characterized in that, The substrate material includes Si or Al2O3.

9. A one-piece molded surface acoustic wave filter manufactured using the method described in any one of claims 1-8, characterized in that, The package includes a piezoelectric layer, an interdigitated circuit layer, and a multilayer packaging circuit layer stacked sequentially on a substrate. The packaging circuit layer includes photoresist and conductive material disposed in vias and trenches. Each packaging circuit layer is connected to the interdigitated circuit layer through vias. The trenches on the photoresist have packaging circuit patterns. External electrodes are provided on the surface of the packaging circuit layer.

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