High Q-value and electromechanical coupling coefficient surface acoustic wave element and its fabrication method
Patent Information
- Application Number
- CN202610977978.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-02
- Publication Date
- 2026-10-27
AI Technical Summary
[0004]针对现有技术下叉指换能器的两层金属薄膜结构实现的表面声波产品，两层金属膜之间键合效果较差，阻抗较大，导致叉指换能器的Q值和机电耦合系数较低，性能较差，插入损耗较大的问题，本发明提供了一种高Q值和机电耦合系数的声表面波元件，本发明中的声表面波元件可以谐振器或滤波器等产品
本发明在现有技术的基础上，使第一电极指膜与第二电极指膜的汇流条重叠区域与电极指直接相连，上汇流条与下汇流条重叠的区域完全覆盖电极指端部区与汇流条相连接的区域，以优化叉指换能器的叠层结构，增加了有效导电接触面积，同时减少了因键合不良产生的非导电杂质或微小空隙，提升两层金属膜之间的键合效果，改善叉指换能器表面物理与化学状态，从而减小了两层金属膜之间的阻抗问题。由于叉指换能器表面阻抗减小，良好的键合效果形成更连续、稳定的金属晶体结构，减少了电子散射，降低电阻率，因此产品的Q值和机电耦合系数得到了明显的提升，同时保留叉指换能器在末端的激励效应，阻断横向模式波纹的产生。该结构相比于现有技术，能完全应用于实际工艺生产，得到性能优良、可靠性更高的SAW表面声波产品。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of integrated circuit device manufacturing technology, specifically relating to a surface acoustic wave element with high Q value and electromechanical coupling coefficient and its preparation method. Background Technology
[0002] Surface acoustic wave (SAW) filters are widely used in the field of radio frequency communication due to their small size and suitability for mass production. Furthermore, as communication systems become increasingly complex, the industry is gradually adopting composite film substrates (bonded substrates / multilayer thin film substrates) to meet market demands for high Q, high isolation, low loss performance, and high temperature stability.
[0003] However, products manufactured using composite film substrate technology place high demands on the structure and film layers of interdigital transducers. The structure and metal film layer design of the interdigital transducer significantly impact lateral modes, Q-value, and electromechanical coupling coefficient. Many existing technologies result in severe lateral mode ripple, which generates stray responses, reduces the insertion loss of SAW resonators / filters, causes passband ripple, lowers the Q-value and electromechanical coupling coefficient, reduces device sensitivity, and significantly affects device performance. Therefore, optimizing the structure and film layers of interdigital transducers to suppress lateral modes while improving the Q-value and electromechanical coupling coefficient of filters is a critical challenge and an urgent problem to be solved in the industry. Summary of the Invention
[0004] To address the problems of poor bonding and high impedance between the two metal thin film structures of existing interdigital transducers in surface acoustic wave (SAW) products, resulting in low Q-value and electromechanical coupling coefficient, poor performance, and high insertion loss, this invention provides a SAW element with high Q-value and electromechanical coupling coefficient. The SAW element in this invention can be used as a resonator or filter, etc.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A surface acoustic wave (SAW) element with high Q-value and electromechanical coupling coefficient includes a piezoelectric substrate and an interdigital transducer formed on the piezoelectric substrate; the interdigital transducer is composed of a first electrode finger film and a second electrode finger film; wherein: The first electrode finger film is formed on the surface of the piezoelectric substrate, including a pair of lower busbars disposed opposite to each other and a plurality of pseudo fingers and electrode finger tip regions extending from the lower busbars and arranged in a cross-spaced manner, wherein the pseudo fingers and electrode finger tip regions connected to one of the lower busbars are respectively arranged opposite to the electrode finger tip regions and pseudo fingers connected to the other lower busbar. The second electrode finger film is formed on the surface of the piezoelectric substrate and covers a portion of the first electrode finger film. It includes a pair of upper busbars and a plurality of parallel, spaced electrode fingers extending from the upper busbars. The upper busbars are formed on top of the lower busbars, and the area of the upper busbars is not greater than the area of the lower busbars. The overlapping area of the upper and lower busbars forms the busbars of the interdigital transducer. Each electrode finger includes a main body segment located between the pair of upper busbars and an extension segment extending from the main body segment toward the upper busbars. The extension segment covers the tip area of the electrode finger and overlaps with the tip area of the electrode finger; the overlapping area constitutes the tip of the interdigital transducer. The extension segment is also connected to the upper busbars. A gap exists between the electrode finger and the pseudo-finger.
[0006] As a preferred technical solution, the shape of the upper busbar is the same as the shape of the lower busbar. That is, the upper busbar completely overlaps and covers the top of the lower busbar, and the area of the upper busbar is the same as the area of the lower busbar.
[0007] As a preferred technical solution, the length of the upper busbar is the same as the length of the lower busbar, and the width of the upper busbar is smaller than the width of the lower busbar. That is, the upper busbar partially covers the top of the lower busbar, and the area of the upper busbar is smaller than the area of the lower busbar.
[0008] As a preferred technical solution, the upper busbar is composed of multiple parallel and spaced strip-shaped units; the width of the strip-shaped unit is the same as the width of the lower busbar, and the strip-shaped unit is connected to the tip region of the electrode finger.
[0009] As a preferred technical solution, the piezoelectric substrate is a bonding substrate or a multilayer thin film substrate. The bonding substrate includes a substrate and a piezoelectric layer located on top of the substrate; the multilayer thin film substrate includes a substrate and, from bottom to top, a high-resistivity film, a functional layer, and a piezoelectric layer located on top of the substrate. The propagation direction ψ of the elastic wave in the piezoelectric layer in the bonding substrate is defined by the Euler angle (Φ, θ, ψ) of the piezoelectric single crystal, preferably LiTaO3 with a (35-60) degree YX cut, and the thickness is preferably 0.2λ~0.5λ (100nm~4000nm); the functional layer is preferably SiO2 with a thickness of 0.2λ~0.6λ (100nm~4500nm); the high-resistivity film is preferably polycrystalline silicon (Poly-Si) with a thickness of 100nm~1000nm; the substrate is preferably high-resistivity silicon (Si), preferably with a resistivity of 100Ωcm or more, preferably with a crystal phase of (001) / (100) / (010), preferably with a crystal plane of (100) / (110) / (111), and a thickness greater than 100um.
[0010] As a preferred technical solution, the thickness of the first electrode finger membrane is 0.01λ~0.05λ; the constituent material of the first electrode finger membrane is at least one of aluminum, copper, and titanium. The first electrode finger membrane mainly serves to reduce the sound velocity at the end of the electrode finger membrane, so the metal thickness is relatively low. As a preferred technical solution, the thickness of the second electrode finger film is 0.05λ~0.12λ; the constituent material of the second electrode finger film is at least one of aluminum, copper, and titanium. The second electrode finger film is the main functional layer of the interdigital transducer, and its thickness is the electrode thickness commonly used in semiconductor filter processes, and its thickness is greater than that of the first electrode finger film.
[0011] The present invention also provides a method for fabricating the surface acoustic wave element described above, comprising the following steps: The first electrode finger film is formed on the piezoelectric substrate by photolithography, evaporation, and resist / etching methods. The second electrode finger film is formed on the piezoelectric substrate on which the first electrode finger film is formed by photolithography, vapor deposition, and resist removal / etching.
[0012] The present invention has the following beneficial effects: This invention, based on existing technology, directly connects the overlapping area of the busbars of the first and second electrode finger films to the electrode fingers. The overlapping area of the upper and lower busbars completely covers the area where the electrode finger tip connects to the busbar, optimizing the stacked structure of the interdigital transducer, increasing the effective conductive contact area, and reducing non-conductive impurities or micro-voids caused by poor bonding. This improves the bonding effect between the two metal layers, enhances the physical and chemical state of the interdigital transducer surface, and thus reduces the impedance problem between the two metal layers. Because the surface impedance of the interdigital transducer is reduced, the good bonding effect forms a more continuous and stable metal crystal structure, reducing electron scattering and lowering resistivity. Therefore, the Q value and electromechanical coupling coefficient of the product are significantly improved, while retaining the excitation effect at the end of the interdigital transducer and blocking the generation of transverse mode ripples. Compared with existing technologies, this structure can be fully applied to actual process production, resulting in SAW surface acoustic wave products with superior performance and higher reliability. Attached Figure Description
[0013] Figure 1 This is a schematic diagram of the structure of the surface acoustic wave element provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the bonding substrate structure; Figure 3 This is a schematic diagram of the structure of a multilayer thin film substrate; Figure 4 This is a schematic diagram of the structure of the first electrode finger film formed on the top of the piezoelectric substrate; Figure 5This is a schematic diagram of the structure of a surface acoustic wave element in the prior art; Figure 6 This is a comparison chart of the performance test results of the products in Example 1 and the comparative example; Figure 7 Schematic diagram of the connection method of different electrode finger films; Figure 8 for Figure 7 Interlayer impedance results obtained from testing different electrode finger membrane connection methods; Figure 9 This is a schematic diagram of the surface acoustic wave element provided in Embodiment 2 of the present invention; Figure 10 This is a schematic diagram of the surface acoustic wave element provided in Embodiment 3 of the present invention; Figure 11 This is a summary of the performance test results of the products in Examples 1 to 3 and Comparative Example 1.
[0014] Reference numerals: 1-Piezoelectric substrate, 11-Substrate, 12-High resistivity film, 13-Functional layer, 14-Piezoelectric layer, 2-First electrode finger film, 21-Lower busbar, 22-Dummy finger, 23-Electrode finger end region, 3-Second electrode finger film, 31-Upper busbar, 32-Electrode finger, 321-Main body segment, 322-Extension segment, 4-Interdigital transducer busbar, 5-Interdigital transducer end region; BB-Interdigital transducer busbar region in Example 1, CB-Non-intersecting region of the second electrode finger film, AB-Non-intersecting region of the first electrode finger film, DB-Interdigital transducer end region, EB-Interdigital transducer busbar region in the comparative example, ZB indicates the cross-sectional direction. Detailed Implementation
[0015] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. Furthermore, unless otherwise specified, the preparation processes in the following embodiments are conventional methods in the prior art, and therefore will not be described in detail. In this application, "false finger" is a term in the art, referring to an existing structure that is parallel to the electrode finger and electrically levitated.
[0016] According to the formula, the propagation speed of the medium That is, wave speed equals wavelength With vibration frequency As can be seen from the product, for sound waves propagating in a piezoelectric crystal with a specified tangential direction (same tangential direction, same propagation speed), the wavelength will be different at different device operating frequencies due to the different frequencies. Since filter devices are designed differently according to different operating frequency requirements, using different values of λ, the material parameters mentioned below are directly proportional to λ, i.e., inversely proportional to the operating frequency.
[0017] Example 1 refer to Figures 1 to 3 This embodiment provides a surface acoustic wave (SAW) element with high Q-value and electromechanical coupling coefficient, comprising: a piezoelectric substrate 1 and an interdigital transducer formed on the piezoelectric substrate; wherein: The piezoelectric substrate is a bonding substrate or a multilayer thin film substrate. Figure 2 This is a schematic diagram of the bonding substrate, including a substrate 11 and a piezoelectric layer 14 located on top of the substrate; Figure 3 This is a schematic diagram of a multilayer thin film substrate, including a substrate 11 and, from bottom to top, a high-resistivity film 12, a functional layer 13, and a piezoelectric layer 14 located on top of the substrate.
[0018] The interdigital transducer consists of a first electrode finger membrane 2 and a second electrode finger membrane 3; wherein: The first electrode finger film 2 is formed on the surface of the piezoelectric substrate 1, including a pair of lower busbars 21 disposed opposite to each other and a plurality of pseudo fingers 22 and electrode finger tip regions 23 extending from the lower busbars 21 and arranged in a cross-spaced manner. The pseudo fingers and electrode finger tip regions connected to one of the lower busbars are respectively arranged opposite to the electrode finger tip regions and pseudo fingers connected to the other lower busbar. The second electrode finger film 3 is formed on the surface of the piezoelectric substrate 1 and covers the top portion of the first electrode finger film 2. It includes a pair of upper busbars 31 and a plurality of parallel and spaced electrode fingers 32 extending from the upper busbars 31. The upper busbars 31 are formed on top of the lower busbars 21, and the area of the upper busbars is equal to the area of the lower busbars. The overlapping area of the upper and lower busbars forms the busbars 4 of the interdigital transducer, and this area is the busbar overlap area BB. The electrode fingers 32 include a main body segment 321 located between the pair of upper busbars and an extension segment 322 extending from the main body segment in the direction of the upper busbars. The main body segment 321 of the electrode fingers is the non-crossing area CB of the second electrode finger film 3. The extension segment 322 covers the electrode finger tip area and overlaps with the electrode finger tip area. The overlapping area constitutes the interdigital transducer tip 5, and this area is DB. The total thickness of the DB area is the sum of the total thicknesses of the first electrode finger film and the second electrode finger film. The extension segment is also connected to the upper busbars. The non-crossing area of the first electrode finger film 2 is AB.
[0019] The specific structural parameters of the surface acoustic wave element in Embodiment 1 above are as follows: The bonding substrate is a piezoelectric substrate, which is high-resistivity silicon (Si) with a crystal phase of (001) / (100) / (010) and a crystal plane of (100) / (110) / (111). The piezoelectric layer is a LiTaO3 film cut by YX with a cutting angle of 42°. The cross width of the electrode fingers of the interdigital transducer is 20λ, where λ is the wavelength determined by the distance between the electrode fingers, and λ = 2μm. The duty cycle in the interdigital transducer is 0.3~0.7λ. The thickness of the first electrode finger film is 0.02λ, the thickness of the second electrode finger film is 0.08λ, and the thickness of the LiTaO3 film is 0.25λ.
[0020] The preparation method is as follows: Step 1: The first electrode finger film (sound velocity conversion layer) is formed on the selected piezoelectric substrate using photolithography, evaporation, and resist / etching methods. Its top view and front cross-sectional view are shown below. Figure 4 As shown; Step 2: On the piezoelectric substrate where the first electrode finger film has been formed, a second electrode finger film is formed through photolithography, evaporation, and resist removal / etching, resulting in a top view and a front cross-sectional view as shown below. Figure 1 As shown.
[0021] Comparative Example Figure 5 The diagram below shows the structure of a surface acoustic wave (SAW) element in the prior art. Compared with Embodiment 1, the main difference is that the busbar region of the interdigital transducer only has the lower busbar of the first electrode finger film, and the second electrode finger film does not have the upper busbar 31. That is, the busbar region of the interdigital transducer in the prior art is a non-intersecting region. Figure 4 The region marked EB.
[0022] Figure 6 The performance test results of the products in Example 1 and the comparative example are compared. The calculated Q value and K2 (electromechanical coupling coefficient) of the products are shown in Table 1. Table 1
[0023] As can be seen from the above results, compared with the comparative example, the Q value and electromechanical coupling coefficient of the product in Embodiment 1 of the present invention have been significantly improved. The reason for the poor performance of the product in the comparative example is that the bonding effect between the two metal layers of the first electrode finger film and the second electrode finger film is poor, resulting in a large impedance, which leads to a lower Q value and electromechanical coupling coefficient of the interdigital transducer, poorer performance, and a larger insertion loss.
[0024] As can be seen from the comparison of the product structures in Example 1 and the comparative example, the solution provided by the present invention mainly involves designing the busbar area of the interdigital transducer as the intersection area of the first electrode finger film and the second electrode finger film, and connecting it to the electrode finger intersection area in the interdigital transducer, thereby greatly reducing the interlayer impedance between the busbar and the interdigital transducer, and thus improving the performance of the interdigital transducer.
[0025] To further verify the interlayer impedance between the first electrode finger film and the second electrode finger film, this invention focuses on this study, with examples including... Figure 7 As shown, the connection methods of different electrode membranes are in Figure 7 The values are as follows: Z1: The first electrode finger film and the second electrode finger film do not intersect; Z2: The first electrode finger film and the second electrode finger film intersect; Z3: The first electrode finger film; Z4: The second electrode finger film. The specific parameters for the interlayer impedance test are as follows: the thickness of the first and second electrode finger films are the same as in Example 1; the test area consists of two larger metal blocks on the left, each 120*120µm in size; the metal trace width is fixed at 20µm, with each segment spaced 75µm apart (the intersection area is the same); the test frequency range is 10MHz-6GHz; the test frequency point is 40MHz-41MHz; the actual interlayer impedance results obtained from the test are as follows: Figure 8 As shown.
[0026] from Figure 8 As can be seen, the interlayer impedance of structure Z1 is significantly larger. This structure is similar to that of existing technologies, verifying the interlayer impedance problem between two electrode finger films in existing technologies. Z4, because it only has a second electrode finger film, i.e., a single-layer metal, does not have the contact resistance problem caused by the bonding of two-layer metal, and the film thickness is relatively thick, so the interlayer impedance is the smallest. However, a single-layer metal does not have the ability to form a low-velocity cross region at the end region of the interdigital transducer. Therefore, in order to achieve transverse mode suppression, we need to use a two-layer metal finger film structure. The interlayer impedance of the two-layer electrode finger film structure of Z2 is close to that of Z4, and the interlayer impedance is smaller, which also verifies the effective implementation of the present invention.
[0027] Example 2 The structural diagram of the product in Example 2 is as follows: Figure 9 As shown, compared with Embodiment 1, the difference in this embodiment is that the area of the upper busbar is smaller than the area of the lower busbar, that is, the upper busbar does not completely cover the lower busbar, and the upper busbar only overlaps with a part of the lower busbar. In this embodiment, the length of the upper busbar is the same as the length of the lower busbar, but the width of the upper busbar is smaller than the width of the lower busbar. All other structures are the same as in Embodiment 1.
[0028] Example 3 The structural diagram of the product in Example 3 is as follows: Figure 10As shown, compared with Embodiment 1, the difference in this embodiment is that: the upper busbar is composed of multiple parallel and spaced strip-shaped units; the width of the strip-shaped units is the same as the width of the lower busbar, and the strip-shaped units are connected to the electrode fingertip area. All other structures are the same as in Embodiment 1 and are superior to the comparative example.
[0029] Figure 11 This is a summary of the performance test results of the products from Examples 1 to 3 and Comparative Example 1, from... Figure 11 It can be seen that the performance parameters obtained by the product structure in Examples 2 and 3 are basically the same as those in Example 1. The Q value and electromechanical coupling coefficient of the obtained products are significantly improved, both of which are better than the comparative example.
[0030] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.
Claims
1. A surface acoustic wave (SAW) element with high Q-value and electromechanical coupling coefficient, comprising a piezoelectric substrate and an interdigital transducer formed on the piezoelectric substrate; wherein the interdigital transducer comprises a first electrode finger film and a second electrode finger film; wherein: The first electrode finger film is formed on the surface of the piezoelectric substrate and includes a pair of lower busbars disposed opposite each other and a plurality of pseudo fingers and electrode finger tip regions arranged in a cross-spaced manner extending from the lower busbars; The second electrode finger film is formed on the surface of the piezoelectric substrate and covers a portion of the first electrode finger film. It includes a pair of upper busbars and a plurality of parallel and spaced electrode fingers extending from the upper busbars. The upper busbars are formed on top of the lower busbars, and the area of the upper busbars is not greater than the area of the lower busbars. The overlapping area of the upper and lower busbars forms the busbars of the interdigital transducer. The electrode finger includes a main body segment located between the pair of upper busbars and an extension segment extending from the main body segment toward the upper busbars. The extension segment covers the tip area of the electrode finger and overlaps with the tip area of the electrode finger. The overlapping area constitutes the tip of the interdigital transducer. The extension segment is also connected to the upper busbars.
2. The surface acoustic wave element according to claim 1, characterized in that, The shape of the upper busbar is the same as the shape of the lower busbar.
3. The surface acoustic wave element according to claim 1, characterized in that, The upper busbar has the same length as the lower busbar, and the width of the upper busbar is smaller than the width of the lower busbar.
4. The surface acoustic wave element according to claim 1, characterized in that, The upper busbar is composed of multiple parallel and spaced strip-shaped units; the width of the strip-shaped unit is the same as the width of the lower busbar, and the strip-shaped unit is connected to the tip area of the electrode finger.
5. The surface acoustic wave element according to any one of claims 1 to 4, characterized in that, The piezoelectric substrate is a bonding substrate or a multilayer thin film substrate.
6. The surface acoustic wave element according to any one of claims 1 to 4, characterized in that, The thickness of the first electrode film is 0.01λ~0.05λ.
7. The surface acoustic wave element according to claim 6, characterized in that, The first electrode membrane is composed of at least one of aluminum, copper, and titanium.
8. The surface acoustic wave element according to any one of claims 1 to 4, characterized in that, The thickness of the second electrode film is 0.05λ~0.12λ.
9. The surface acoustic wave element according to claim 8, characterized in that, The second electrode membrane is composed of at least one of aluminum, copper, and titanium.
10. The method for fabricating a surface acoustic wave element according to any one of claims 1 to 9, characterized in that, Includes the following steps: The first electrode finger film is formed on the piezoelectric substrate by photolithography, evaporation, and resist / etching methods. The second electrode finger film is formed on the piezoelectric substrate on which the first electrode finger film is formed by photolithography, vapor deposition, and resist removal / etching.