A surface acoustic wave filter
By employing a platinum and aluminum interdigitated electrode structure in the surface acoustic wave (SAW) filter, combined with a titanium or chromium diffusion barrier layer, the problem of insufficient resonant performance of the SAW filter was solved, achieving structural miniaturization and improved electrical performance, extending device lifespan, and reducing cost and process complexity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- NINGBO SEMICON INT CORP
- Filing Date
- 2025-08-07
- Publication Date
- 2026-07-03
AI Technical Summary
Existing surface acoustic wave filters have the problem of needing to improve their resonant performance.
An interdigitated electrode structure is adopted, wherein the first metal layer uses platinum or an alloy with platinum as the main component, and the second metal layer uses aluminum or an alloy with aluminum as the main component. By optimizing the material combination through stacking, the mechanical strength and chemical stability of the interdigitated electrode are enhanced, and the risk of interlayer delamination is reduced. Furthermore, by setting a third and fourth metal layer, such as titanium or chromium, as a diffusion barrier layer, the structural stability and electrical performance are further improved.
This achievement enables the miniaturization of the interdigital electrode structure, improves electrical performance and long-term operational stability, extends the device's lifespan, reduces material costs and process complexity, and ensures the acoustic performance stability of the piezoelectric layer.
Smart Images
Figure CN224459764U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of semiconductor technology, and specifically to a surface acoustic wave filter. Background Technology
[0002] Surface acoustic wave (SAW) filters have input and output electrodes fabricated on the surface of a piezoelectric substrate. An alternating voltage is applied to the input terminal, and electrical energy is converted into acoustic energy using the piezoelectric effect. This type of device is less expensive than BAW filters and smaller in size than traditional cavity and ceramic filters, so it is widely used in mobile communication systems.
[0003] Research and design of different types of SAW resonators are still ongoing, while increasing integration and miniaturization requirements have gradually become mainstream in recent products. However, the resonant performance of existing surface acoustic wave filters needs to be improved. Utility Model Content
[0004] The problem solved by this invention is that the resonance performance of existing surface acoustic wave filters needs to be improved.
[0005] To address the above problems, this utility model provides a surface acoustic wave (SAW) filter, which includes:
[0006] piezoelectric layer;
[0007] Interdigitated electrodes are disposed on the piezoelectric layer and include at least a first metal layer and a second metal layer stacked on top of each other.
[0008] The first metal layer is made of platinum or an alloy with platinum as the main component, and the second metal layer is made of aluminum or an alloy with aluminum as the main component.
[0009] Optionally, the thickness of the first metal layer is greater than the thickness of the second metal layer.
[0010] Technical benefits: The thicker platinum layer enhances the mechanical strength of the entire interdigital electrode, providing more stable support for the second metal layer and ensuring the stability and support of the interdigital electrode. At the same time, the thinner aluminum layer achieves good step coverage and gap filling at a lower cost, optimizing material cost and process complexity while meeting performance requirements. In addition, the increased platinum layer thickness enhances its adhesion to the substrate, reducing the probability of the interdigital electrode peeling off due to thermal cycling or mechanical vibration, thereby extending the device's lifespan.
[0011] Optionally, in a direction perpendicular to the piezoelectric layer, the orthographic projection of the second metal layer falls within the orthographic projection of the first metal layer, or the orthographic projection of the second metal layer coincides with the orthographic projection of the first metal layer.
[0012] Technical benefits: It can avoid the aluminum layer edge from extending beyond the platinum layer to form a "suspended" structure, reducing the risk of stress concentration, breakage or detachment of the aluminum layer edge due to insufficient local support; at the same time, the chemical stability of platinum is far superior to that of aluminum, and its design of completely covering the area under the aluminum layer can isolate the direct contact between aluminum and the piezoelectric layer, preventing the piezoelectric layer from being damaged by diffusion, oxidation or corrosion of aluminum during long-term operation, thus ensuring the acoustic performance stability of the piezoelectric layer.
[0013] Optionally, the second metal layer and the first metal layer are in direct contact.
[0014] Technical benefits: Platinum and aluminum can form a stable metal-metal interface through direct contact, which can avoid the problem of increased contact resistance caused by the introduction of an intermediate layer, and also allow the second metal layer and the first metal layer to interact through metal bonds to form a certain interfacial adhesion, reducing the risk of interlayer peeling.
[0015] Optionally, a third metal layer is disposed between the second metal layer and the first metal layer, the material of the third metal layer including titanium or chromium.
[0016] Technical benefits: By setting a third metal layer between the second metal layer and the first metal layer, the bonding force between the layers can be enhanced, reducing the risk of interlayer delamination of the interdigitated electrodes during long-term operation or thermal cycling. The third metal layer can also act as a diffusion barrier layer to effectively block the interdiffusion path between aluminum and platinum.
[0017] Optionally, the interdigitated electrode further includes a fourth metal layer disposed on the side of the second metal layer away from the first metal layer, and the material of the fourth metal layer includes chromium.
[0018] Technical benefits: Chromium is harder than aluminum. As the topmost metal, chromium provides a physical barrier for the aluminum layer below, effectively preventing scratches from external forces that may be encountered during device manufacturing, packaging, or use. It also prevents the aluminum layer from suffering localized degradation of conductivity or damage to its structural integrity due to surface damage.
[0019] Optionally, the thickness of the second metal layer is greater than the thickness of the fourth metal layer.
[0020] Technical benefits: The thicker second metal layer ensures that the electrode has sufficient current carrying capacity, thus providing a reliable guarantee for the stability of the electrical performance of the interdigital electrode. The thinner chromium layer can avoid the increase in the overall resistance of the electrode due to excessive thickness, and can also effectively resist external scratches to achieve a protective function.
[0021] Optionally, in a direction perpendicular to the piezoelectric layer, the orthographic projection of the fourth metal layer falls within the orthographic projection of the second metal layer, or the orthographic projection of the fourth metal layer coincides with the orthographic projection of the second metal layer.
[0022] Technical effect: The chromium layer completely covers the aluminum layer or is aligned with the boundary of the aluminum layer, so that the protective effect of the chromium layer is precisely applied to the key areas of the aluminum layer, avoiding the chromium layer from extending beyond the aluminum layer and forming unnecessary edge structures, thereby reducing unnecessary metal consumption caused by the extension of the chromium layer.
[0023] Optionally, the interdigitated electrode further includes a fifth metal layer disposed between the first metal layer and the piezoelectric layer, the fifth metal layer being made of titanium.
[0024] Technical benefits: This effectively solves the problem of insufficient interfacial bonding force that may exist when platinum is in direct contact with the piezoelectric layer, ensuring the structural stability between the interdigitated electrodes and the piezoelectric layer, and providing a fundamental support for the efficient transmission of surface acoustic wave filters. In addition, titanium, as a transition layer, can block direct contact between platinum and the piezoelectric layer, avoiding chemical reactions between the two during high-temperature processing, thereby protecting the crystal structure integrity of the piezoelectric layer.
[0025] Optionally, the thickness of the fourth metal layer is greater than the thickness of the fifth metal layer.
[0026] Technical benefits: A thicker chromium layer can form a sufficiently tough physical barrier to effectively resist external scratches, while a thinner titanium layer can achieve strong adhesion through interfacial chemical bonds. The combination of "thick protection + thin adhesion" optimizes material costs and process adaptability.
[0027] The surface acoustic wave (SAW) filter provided in this application includes a piezoelectric layer and interdigitated electrodes. The interdigitated electrodes comprise at least a first metal layer and a second metal layer stacked together. The first metal layer is made of platinum or an alloy with platinum as the main component, and the second metal layer is made of aluminum or an alloy with aluminum as the main component. Aluminum has good step coverage and gap-filling capabilities. Setting the material of the second metal layer to aluminum or an alloy with aluminum as the main component effectively improves the uniformity of metal coverage in the electrode structure, avoiding excessive local resistance or structural defects due to poor coverage. Simultaneously, platinum has good chemical stability and mechanical strength. Setting the material of the first metal layer to platinum or an alloy with platinum as the main component provides reliable support for the second metal layer, reducing the risk of deformation or corrosion of the aluminum layer in subsequent processes. Therefore, the interdigitated electrodes, through a complementary stacked structure of two materials, achieve both structural miniaturization and improved overall electrical performance and structural reliability, contributing to optimized energy conversion efficiency and long-term operational stability of the SAW device. Attached Figure Description
[0028] Figure 1 This is a schematic diagram of the structure of the surface acoustic wave filter provided in the embodiments of this application;
[0029] Figure 2 for Figure 1 The diagram shows another structural schematic of a surface acoustic wave filter.
[0030] Explanation of reference numerals in the attached figures:
[0031] 1. Surface acoustic wave filter; 11. Piezoelectric layer; 12. Interdigitated electrode;
[0032] 121. First metal layer; 122. Second metal layer; 123. Third metal layer; 124. Fourth metal layer; 125. Fifth metal layer. Detailed Implementation
[0033] To make the above-mentioned objectives, features and superior structure of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below.
[0034] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a surface acoustic wave (SAW) filter provided in an embodiment of this application. The SAW filter 1 includes a piezoelectric layer 11 and interdigitated electrodes 12. The interdigitated electrodes 12 are disposed on the piezoelectric layer 11 and include at least a first metal layer 121 and a second metal layer 122 stacked on top of each other. The first metal layer 121 is made of platinum or an alloy with platinum as the main component, and the second metal layer 122 is made of aluminum or an alloy with aluminum as the main component. Aluminum has good step coverage and gap filling capabilities. Setting the material of the second metal layer 122 to aluminum or an alloy with aluminum as the main component can effectively improve the uniformity of metal coverage in the electrode structure, avoiding excessive local resistance or structural defects due to poor coverage. Simultaneously, platinum has good chemical stability and mechanical strength. Setting the material of the first metal layer 121 to platinum or an alloy with platinum as the main component can provide reliable support for the second metal layer 122, reducing the risk of deformation or corrosion of the aluminum layer in subsequent processes. Therefore, by using a layered structure of two complementary materials, the interdigital electrode 12 achieves both structural miniaturization and improves the overall electrical performance and structural reliability of the interdigital electrode 12, which helps to optimize the energy conversion efficiency and long-term operational stability of the surface acoustic wave filter 1.
[0035] It should be noted that platinum-based alloys refer to alloys in which platinum accounts for more than 50% of the mass or atomic composition, with the remainder being other metallic elements. The platinum percentage can be, for example, 70%, 80%, etc., and the specific proportion can be flexibly adjusted according to the requirements of the material properties such as mechanical strength, conductivity, and cost in the actual application scenario. This solution does not impose a specific limitation on this. Similarly, aluminum-based alloys refer to alloys in which aluminum accounts for more than 50% of the mass or atomic composition, with the remainder being other metallic elements. The specific proportion of aluminum can be flexibly adjusted according to the requirements of the material properties such as mechanical strength, conductivity, and cost in the actual application scenario.
[0036] In addition, this application will use platinum as the material of the first metal layer and aluminum as the material of the second metal layer as an example for illustrative purposes. It should be noted that this example is only selected for the purpose of understanding the technical solution and is not a limitation on the materials of the first metal layer and the second metal layer.
[0037] In some embodiments, the thickness of the first metal layer 121 is greater than the thickness of the second metal layer 122. Since aluminum has relatively low material cost and high film-forming efficiency, the "thick platinum + thin aluminum" stacked structure can both enhance the mechanical strength of the entire interdigital electrode 12 through the thicker platinum layer, providing more stable support for the second metal layer 122 and ensuring the stability and support of the interdigital electrode 12, and achieve good stepped coverage and gap filling at a lower cost through the thinner aluminum layer. This optimizes material cost and process complexity while meeting performance requirements. Furthermore, the increased platinum layer thickness enhances its adhesion to the substrate, reducing the probability of the electrode peeling off due to thermal cycling or mechanical vibration, thereby extending the device's lifespan.
[0038] In some embodiments, the thickness of the first metal layer 121 is 2500 nm to 3500 nm in a direction perpendicular to the plane where the surface acoustic wave resonator is located.
[0039] In some embodiments, the thickness of the second metal layer 122 is 2000 nm to 3500 nm in the direction perpendicular to the plane where the surface acoustic wave resonator is located.
[0040] It is understood that in some embodiments, when mechanical stability and film integrity are balanced, the thickness of the first metal layer 121 can also be equal to the thickness of the second metal layer 122. This avoids the situation where the overall structure is not supported enough due to the platinum layer being too thin, and also prevents the situation where the complex morphology area is not covered evenly due to the aluminum layer being too thin. In addition, the low contact resistance of platinum and the high conductivity of aluminum can form a more uniform current transmission path when the thickness is equal.
[0041] In the direction perpendicular to the piezoelectric layer 11, the orthographic projection of the second metal layer 122 falls within the orthographic projection of the first metal layer 121, or the orthographic projection of the second metal layer 122 coincides with the orthographic projection of the first metal layer 121. This means the entire area of the aluminum layer is within the support range of the platinum layer. This avoids the aluminum layer edges extending beyond the platinum layer to form a "suspended" structure, reducing the risk of stress concentration, breakage, or detachment at the aluminum layer edges due to insufficient local support. Simultaneously, platinum's chemical stability is far superior to aluminum, and its complete coverage of the area beneath the aluminum layer isolates direct contact between aluminum and the piezoelectric layer 11, preventing damage to the piezoelectric layer 11 from diffusion, oxidation, or corrosion during long-term operation, thus ensuring the acoustic performance stability of the piezoelectric layer 11.
[0042] In some embodiments, the second metal layer 122 and the first metal layer 121 are in direct contact. Direct contact between platinum and aluminum can form a stable metal-metal interface, thereby avoiding the problem of increased contact resistance caused by the introduction of an intermediate layer, and allowing the second metal layer 122 and the first metal layer 121 to form a certain interfacial adhesion through metallic bond interaction, reducing the risk of interlayer peeling.
[0043] Please continue reading. Figure 2 , Figure 2 for Figure 1 The diagram shows another structural schematic of the surface acoustic wave filter. In some embodiments, a third metal layer 123 is disposed between the second metal layer 122 and the first metal layer 121. The material of the third metal layer 123 includes titanium or chromium. By disposing of the third metal layer 123 between the second metal layer 122 and the first metal layer 121, the interlayer bonding force can be enhanced, reducing the risk of interlayer delamination of the interdigitated electrodes 12 during long-term operation or thermal cycling. In addition, in high-temperature processes, aluminum and platinum may interdiffusion. By disposing of titanium or chromium as a diffusion barrier layer between the second metal layer 122 and the first metal layer 121, its low atomic diffusion coefficient and ability to form a dense structure can effectively block the interdiffusion path of aluminum and platinum. At the same time, the dense oxide film formed after the oxidation of titanium or chromium, such as TiO2 or Cr2O3, can further isolate aluminum and platinum, preventing them from directly reacting chemically and ensuring the chemical stability of the electrode interface.
[0044] The interdigitated electrode 12 also includes a fourth metal layer 124, which is disposed on the side of the second metal layer 122 away from the first metal layer 121. The material of the fourth metal layer 124 includes chromium. Chromium is harder than aluminum. As the outermost metal, chromium provides a physical barrier for the aluminum layer below, effectively preventing scratches from external forces that may be encountered during device manufacturing, packaging, or use. It also prevents the aluminum layer from experiencing localized degradation of conductivity or destruction of structural integrity due to surface damage. In addition, chromium readily forms a dense oxide film Cr2O3 in air. This oxide film has high chemical stability and can prevent the underlying aluminum from being further oxidized.
[0045] The thickness of the second metal layer 122 is greater than that of the fourth metal layer 124. As the core conductive layer of the interdigital electrode 12, the greater thickness of the second metal layer 122 ensures that the electrode has sufficient current carrying capacity, thus providing a reliable guarantee for the stability of the electrical performance of the interdigital electrode 12. At the same time, since the core function of the fourth metal layer 124 is surface protection, the high hardness of chromium allows it to effectively resist external scratches even when the thickness is relatively thin, thus achieving the protective function. Considering that the resistivity of chromium is higher than that of aluminum, a thinner chromium layer can avoid the situation where the overall resistance of the electrode increases due to excessive thickness. In addition, since the thermal expansion coefficients of chromium and aluminum are significantly different, an excessively thick chromium layer is prone to interlayer cracking. Therefore, a thinner chromium layer can also reduce the stress mismatch between the chromium layer and the underlying aluminum layer, further ensuring the stability of the layer structure in the interdigital electrode 12.
[0046] In the direction perpendicular to the piezoelectric layer 11, the orthographic projection of the fourth metal layer 124 falls within the orthographic projection of the second metal layer 122, or the orthographic projection of the fourth metal layer 124 coincides with the orthographic projection of the second metal layer 122. This ensures that the chromium layer completely covers the aluminum layer or is aligned with the boundary of the aluminum layer, allowing the protective effect of the chromium layer to be precisely applied to the critical areas of the aluminum layer. This prevents the chromium layer from extending beyond the aluminum layer and forming unnecessary edge structures, thereby reducing unnecessary metal consumption due to chromium layer extension, lowering material costs and reducing etching difficulty. Furthermore, it prevents the edges of the chromium layer from being exposed outside the aluminum layer, forming sharp protrusions or burrs, reducing the risk of short circuits or mechanical interference caused by edge structures in subsequent processes.
[0047] The interdigitated electrode 12 also includes a fifth metal layer 125, which is disposed between the first metal layer 121 and the piezoelectric layer 11. The material of the fifth metal layer 125 includes titanium. Titanium has a very strong surface affinity for the piezoelectric layer 11, forming stable chemical bonds with oxygen atoms on the surface of the piezoelectric layer 11, and simultaneously forming strong metallic bonds with the upper platinum layer. This effectively solves the problem of insufficient interfacial bonding force that may exist when platinum is in direct contact with the piezoelectric layer 11, ensuring the structural stability between the interdigitated electrode 12 and the piezoelectric layer 11, and providing a fundamental support for the efficient transmission of the surface acoustic wave filter 1. In addition, as a transition layer, titanium can block direct contact between platinum and the piezoelectric layer 11, avoiding chemical reactions between the two during high-temperature processing, thereby protecting the crystal structure integrity of the piezoelectric layer 11.
[0048] In some embodiments, the thickness of the fourth metal layer 124 is greater than the thickness of the fifth metal layer 125. The thicker chromium layer forms a sufficiently robust physical barrier to effectively resist external scratches, while the titanium layer only needs a thinner thickness to achieve strong adhesion through interfacial chemical bonds. Excessive thickness may lead to negative effects due to stress accumulation or material redundancy. Furthermore, increasing the thickness of the chromium layer has a limited impact on the overall resistance, while the thin titanium layer reduces the impedance increase caused by high resistivity, thus ensuring the electrical performance of the interdigital electrode 12. In addition, the combination of "thick protection + thin adhesion" optimizes material costs and process compatibility, reducing the consumption of high-cost titanium materials while ensuring protection and adhesion. The uniform film formation of the thin titanium layer provides a good substrate for subsequent processes, achieving both reliability and process economy for the interdigital electrode 12.
[0049] It should be noted that the thickness of the fourth metal layer 124 and the fifth metal layer 125 can also be the same. The specific thickness value can be set according to the actual application scenario, such as device protection requirements and interface bonding strength requirements, and no specific restrictions are made here.
[0050] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A surface acoustic wave filter, characterized by, The surface acoustic wave filter includes: piezoelectric layer; Interdigitated electrodes are disposed on the piezoelectric layer and include at least a first metal layer and a second metal layer stacked on top of each other. The first metal layer is made of platinum or an alloy with platinum as the main component, and the second metal layer is made of aluminum or an alloy with aluminum as the main component.
2. The surface acoustic wave filter according to claim 1, characterized by, The thickness of the first metal layer is greater than the thickness of the second metal layer.
3. The surface acoustic wave filter according to claim 1, characterized by, In the direction perpendicular to the piezoelectric layer, the orthographic projection of the second metal layer falls within the orthographic projection of the first metal layer, or the orthographic projection of the second metal layer coincides with the orthographic projection of the first metal layer.
4. The surface acoustic wave filter according to claim 1, characterized by, The second metal layer and the first metal layer are in direct contact.
5. The surface acoustic wave filter according to claim 1, wherein A third metal layer is disposed between the second metal layer and the first metal layer, and the material of the third metal layer includes titanium or chromium.
6. The surface acoustic wave filter according to any one of claims 1 to 5, characterized by, The interdigitated electrode further includes a fourth metal layer disposed on the side of the second metal layer away from the first metal layer, and the material of the fourth metal layer includes chromium.
7. The surface acoustic wave filter according to claim 6, characterized in that, The thickness of the second metal layer is greater than the thickness of the fourth metal layer.
8. The surface acoustic wave filter according to claim 6, wherein In the direction perpendicular to the piezoelectric layer, the orthographic projection of the fourth metal layer falls within the orthographic projection of the second metal layer or the orthographic projection of the fourth metal layer coincides with the orthographic projection of the second metal layer.
9. The surface acoustic wave filter according to claim 6, wherein The interdigitated electrode further includes a fifth metal layer disposed between the first metal layer and the piezoelectric layer, and the material of the fifth metal layer includes titanium.
10. The surface acoustic wave filter according to claim 9, wherein, The thickness of the fourth metal layer is greater than the thickness of the fifth metal layer.