Filter and forming method thereof
By using a mass block made of the same material as the electrode layer and an integrally molded structure in the surface acoustic wave filter, the problems of poor alignment accuracy and interface mismatch caused by multi-layer metal structures are solved, and the filter is manufactured efficiently and its performance is improved.
Patent Information
- Application Number
- CN202511676153.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-06-13
- Filing Date
- 2025-11-14
- Publication Date
- 2026-02-24
AI Technical Summary
Traditional surface acoustic wave (SAW) filters suffer from poor alignment accuracy and complex manufacturing processes due to the combination of multi-layer metal electrode structures with mass blocks. Furthermore, repeated metal deposition and etching processes can easily lead to interface mismatch and stress concentration, affecting filter performance.
Using a metal of the same material as the first electrode layer as the mass block, the metal deposition steps are simplified through an integral molding structure, the sidewalls of the mass block and the electrode fingers are self-aligned, the interface mismatch is reduced, the high-temperature stability is enhanced, and the damage to the piezoelectric substrate is reduced through the design of electrode layers with different etching rates.
This improved the filter's clutter suppression capability, enhanced the alignment accuracy of the electrode fingers and mass block, simplified the process flow, increased the yield and electrode durability, and achieved miniaturization and high performance of the filter.
Smart Images
Figure CN121567098A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of filter technology, and more specifically, to a filter. Background Technology
[0002] With the application of SAW (Surface Acoustic Wave) filters, IDT (Interdigital Transducer) is a core component. The design of the interdigital structure in the interdigital transducer can achieve the function of filtering. In order to reduce clutter in the passband, PST (Plasma Block Structure) is usually designed at the top of the interdigital tip to suppress clutter.
[0003] Traditional surface acoustic wave (SAW) filters typically employ multi-layer metal structures to improve electrode performance. However, the combination of multi-layer metal electrodes with mass blocks requires multiple metal depositions and etching processes during manufacturing, which can easily lead to poor alignment accuracy and complex manufacturing processes. Summary of the Invention
[0004] To address the aforementioned problems, the present invention provides a filter comprising: a piezoelectric substrate; an interdigital transducer disposed on the piezoelectric substrate, the interdigital transducer comprising: an electrode finger and a mass block; the mass block being disposed at the end of the electrode finger; the electrode finger comprising a first electrode layer adjacent to the mass block, the first electrode layer being made of the same material as the mass block.
[0005] Using a metal of the same material as the first electrode layer as the mass block to suppress harmonics reduces the number of metal deposition steps in the process, while providing adjustment space for the electrode fingers and facilitating the adjustment of the first electrode layer thickness. Using the same material also solves the problem of interface mismatch between dissimilar materials, and the same material ensures consistent thermal expansion coefficients, enhancing high-temperature stability and avoiding stress concentration. Since the mass block and the first electrode layer are made of the same material, they can be deposited simultaneously, and their sides can be etched together, thus aligning the sidewalls of the mass block with the sidewalls of the first electrode layer. This alignment improves the alignment accuracy between the electrode fingers and the mass block, thereby enhancing the filter's ability to suppress clutter and ultimately improving the filter's performance.
[0006] Furthermore, the first electrode layer and the mass block are integrally formed.
[0007] The one-piece molding structure can eliminate the contact resistance at the interface between the first electrode layer and the mass block, thereby improving power tolerance; it also avoids lateral corrosion defects in the etching process, thus improving the yield.
[0008] Furthermore, in the lateral direction of the multilayer electrode layer, the mass block coincides with the projection of the multilayer electrode layer onto the piezoelectric substrate.
[0009] By aligning the mass block with the multilayer electrode layer, the mass block can completely cover the ends of the electrode layer, thus improving the clutter suppression effect.
[0010] Furthermore, the multilayer electrode layer also includes a second electrode layer disposed between the piezoelectric substrate and the first electrode layer, wherein under the same etching conditions, the first electrode layer has a greater etching rate than the second electrode layer.
[0011] By using different etching rates for the first and second electrode layers, damage to the piezoelectric substrate can be reduced during the etching process.
[0012] Furthermore, the first electrode layer and the mass block are made of tungsten or molybdenum, and / or the second electrode layer is made of an aluminum-copper alloy or aluminum.
[0013] Tungsten or molybdenum materials offer advantages such as high density and high hardness. The high density of tungsten enhances acoustic wave confinement in the first electrode layer and mass block, while its high hardness reduces electrode wear and extends electrode lifespan. The second electrode layer, made of aluminum-copper alloy or aluminum, reduces resistance. Using a tungsten-aluminum stack for both the first and second electrode layers allows for smaller linewidths, facilitating chip miniaturization, while also providing a high electromechanical coupling coefficient and quality factor.
[0014] Furthermore, the electrode also includes a third electrode layer disposed between the second electrode layer and the piezoelectric substrate, wherein the density of the third electrode layer is greater than the density of the second electrode layer.
[0015] Using a higher density in the third electrode layer helps improve the filter's quality factor. At the same time, for a higher density electrode layer, using a smaller electrode spacing can ensure the frequency and achieve miniaturization.
[0016] Furthermore, the second electrode material layer is made of aluminum-copper alloy or aluminum, and / or the third electrode material layer is made of tungsten or molybdenum.
[0017] Furthermore, the multilayer electrode layer also includes a fourth electrode layer, which is disposed on the side away from the piezoelectric substrate and adjacent to the piezoelectric substrate. The material of the fourth electrode layer includes titanium, chromium, titanium nitride, aluminum nitride or titanium tungsten.
[0018] The fourth electrode layer, made of titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten, can enhance the adhesion of the electrode fingers to the piezoelectric substrate.
[0019] The present invention also provides a method for forming a filter, the method comprising: forming an electrode finger material layer and a mass block material layer on a piezoelectric substrate; processing the mass block material layer to form an initial mass block at the end of the electrode finger target region; and simultaneously processing the electrode finger material layer and the initial mass block to form the electrode finger and the mass block.
[0020] The target area for electrode fingers is the area where electrode fingers will ultimately be formed. The electrode finger material layer and the mass block material layer are deposited in one step, and the electrode fingers and mass blocks can be made through two processes, which can effectively improve production efficiency.
[0021] Furthermore, the formation of the electrode finger material layer and the mass block material layer on the piezoelectric substrate specifically includes: the electrode finger material layer comprising multiple electrode layers, wherein the multiple electrode material layers are sequentially deposited on the piezoelectric substrate, and the electrode material layer adjacent to the mass block material layer is deposited simultaneously with the mass block material layer.
[0022] Furthermore, the process of processing the mass block material layer to form an initial mass block at the end of the target region of the electrode specifically includes: covering the first target region of the mass block material layer with a first mask layer, and etching the region outside the first mask layer to form the initial mass block.
[0023] The first target region is the region where the mass block will eventually be formed, as well as the region with gaps between adjacent mass blocks. The extension direction of the first target region is orthogonal to the extension direction of the electrode fingers. After the mass block material layer is coated and protected by the first mask layer, only the initial mass block of the first target region is left after etching. The initial mass block can be completed by removing the part between adjacent mass blocks to form gaps when processing the electrode finger material layer. Therefore, multiple metal depositions are not required, resulting in higher efficiency.
[0024] Furthermore, the simultaneous processing of the electrode finger material layer and the initial mass block to form the electrode finger and the mass block specifically includes: covering the second target area of the electrode finger material layer with a second mask layer, and etching the area outside the second mask layer to form the electrode finger and the mass block.
[0025] The second target area is the area where the electrode fingers will eventually be formed, which also includes the area where the mass block will eventually be formed. After the electrode finger material layer and the initial mass block are coated and protected by the second mask layer, only the electrode fingers and the mass block in the second target area are left after etching. Therefore, there are fewer processes and higher efficiency.
[0026] Furthermore, the electrode finger material layer has a stacked structure, with the topmost electrode finger material layer serving as the first electrode material layer, and the electrode finger material layer located at the bottom of the first electrode material layer serving as the second electrode material layer. There is a removal selectivity ratio between the first electrode material layer and the second electrode material layer.
[0027] Because of the height difference between the first electrode material layer and the initial mass block, during etching, the first electrode material layer region is etched to the second electrode material layer before the initial mass block. With a removal selectivity ratio between the first and second electrode material layers, the etching can be stopped synchronously at the surface of the second electrode material layer. This ensures that when etching the second electrode material layer, the piezoelectric substrate surface can be etched to almost simultaneously, thus avoiding damage to the piezoelectric substrate and affecting device performance if the piezoelectric substrate surface is not reached at the same time.
[0028] Furthermore, the removal selectivity ratio between the first electrode layer and the second electrode layer is greater than or equal to 10:1.
[0029] The selection of removal between the first electrode layer and the second electrode layer is relatively large, which avoids increasing the probability of the second electrode layer being removed during the etching of the first electrode material layer and the initial mass block, and also avoids the second electrode layer providing poor protection for the underlying piezoelectric substrate.
[0030] Furthermore, the electrode material layer further includes a third electrode material layer located between the piezoelectric substrate and the second electrode material layer, wherein the density of the third electrode material layer is greater than the density of the second electrode material layer.
[0031] The third electrode layer uses a higher density to improve the device's quality factor and allows for frequency control. Specifically, for a higher density electrode layer, a smaller electrode spacing can ensure the frequency while achieving miniaturization.
[0032] Furthermore, after etching the area outside the second mask layer, the formation method also includes thickening the area outside the second mask layer.
[0033] Because the etching amount and etching uniformity are difficult to control precisely during the etching process, the thickness of the remaining electrode fingers may differ from the preset value, and the surface of the electrode fingers may also be uneven. After etching, the thickness of the electrode fingers can be adjusted to further meet the device performance requirements.
[0034] Furthermore, after etching the area outside the second mask layer, the method further includes removing the second mask layer and, after removing the second mask layer, trimming the thickness of the electrode fingers.
[0035] Without removing the second mask layer, metal atoms are prone to sputtering at the sidewall of the second mask layer during the thickness trimming process. This results in burrs on the edges of the electrode fingers or mass blocks after removing the second mask layer, which cannot be removed in subsequent processes. Consequently, this affects the subsequent process of the device and its performance. Therefore, removing the second mask layer before performing thickness trimming can avoid affecting the subsequent process and allows for better frequency adjustment of the device, thus improving its performance.
[0036] In summary, the above-mentioned technical solutions of this application can have one or more of the following advantages or beneficial effects: i) Using metal of the same material as the electrode fingers as the mass block to suppress harmonics can reduce the metal deposition steps and simplify the process; ii) Using the same material also solves the problem of interface mismatch between heterogeneous materials, reduces the scattering loss of sound waves at the interface, and improves the Q value (quality factor); iii) Using the same material achieves the same coefficient of thermal expansion, enhances high-temperature stability, and avoids stress concentration; iv) The mass block and electrode fingers work together to optimize the sound wave energy confinement capability; v) The mass block and the first electrode layer are of the same material and can be etched together to achieve self-alignment between the sidewalls of the mass block and the sidewalls of the first electrode layer, thereby improving the filter's ability to suppress noise and thus improving the filter's performance; vi) Using tungsten-aluminum stacks can achieve smaller linewidths, which is beneficial for chip miniaturization, while having a higher effective electromechanical coupling coefficient and quality factor; In terms of harmonic suppression, compared with pure molybdenum electrodes and pure rhodium electrodes, the electrode capability of tungsten-aluminum electrodes is close to that of the former two, but tungsten-aluminum electrodes are cheaper and more cost-effective than other precious metals. Attached Figure Description
[0037] Figure 1 A schematic diagram of the structure of a filter provided by the present invention; Figure 2 A flowchart of a filter formation method provided by the present invention; Figure 3 This is the state diagram of the filter in step S1; Figure 4 This is one of the state diagrams of the filter in step S2; Figure 5 This is the second state diagram of the filter in step S2; Figure 6 This is one of the state diagrams of the filter in step S3; Figure 7 This is the second state diagram of the filter in step S3; Figure 8 This is the third state diagram of the filter in step S3; Figure 9 for Figure 5 Another perspective on the state diagram of the filter; Figure 10 for Figure 6 Another perspective on the state diagram of the filter; Figure 11 for Figure 8 A state diagram of the filter from another perspective.
[0038] Explanation of reference numerals in the attached figures: 100 - Filter; 110 - Piezoelectric substrate; 120 - Electrode finger; 120a - First electrode finger; 120b - Second electrode finger; 121 - First electrode layer; 122 - Second electrode layer; 123 - Third electrode layer; 124 - Fourth electrode layer; 125 - Electrode finger material layer; 130 - Mass block; 131 - Mass block material layer; 132 - Initial mass block; 140 - Busbar; 141 - First busbar; 142 - Second busbar; 151 - First mask layer; 152 - Second mask layer. Detailed Implementation
[0039] The purpose of this invention is to provide a filter that reduces the number of metal deposition steps while providing adjustment space for the electrode metal.
[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0041] See Figure 1 The present invention provides a filter 100, the filter 100 including: a piezoelectric substrate 110; an interdigital transducer disposed on the piezoelectric substrate 110, the interdigital transducer including: an electrode finger 120 and a mass block 130; the mass block 130 is disposed at the end of the electrode finger 120; the electrode finger 120 includes a first electrode layer 121 adjacent to the mass block 130, the first electrode layer 121 and the mass block 130 are made of the same material.
[0042] In this embodiment, a metal of the same material as the first electrode layer 121 is selected as the mass block 130 to suppress harmonics. This reduces the number of metal deposition steps and provides adjustment space for the metal of the electrode fingers 120, facilitating adjustment of the thickness of the first electrode layer 121. Using the same material also solves the problem of interface mismatch between dissimilar materials, ensuring consistent thermal expansion coefficients, enhancing high-temperature stability, and avoiding stress concentration. Since the mass block 130 and the first electrode layer 121 are of the same material, they can be deposited simultaneously, and their sides can be etched together. Therefore, the sidewalls of the mass block 130 and the first electrode layer 121 are aligned. This alignment improves the alignment accuracy of the electrode fingers 120 and the mass block 130, thereby enhancing the noise suppression effect of the filter 100 and improving its performance.
[0043] In one specific embodiment, the first electrode layer 121 and the mass block 130 are integrally formed.
[0044] It should be noted that integral molding means that the first electrode layer 121 and the mass block 130 are formed together in the same process by physical vapor deposition or chemical vapor deposition, etc. The thickness at the time of formation is at least the sum of the thicknesses of the first electrode layer 121 and the mass block 130. Then, the first electrode layer 121 and the mass block 130 above it are formed by etching.
[0045] This can improve deposition efficiency, eliminate contact resistance at the interface between the first electrode layer 121 and the mass block 130, enhance power tolerance, avoid lateral corrosion defects in the etching process, and improve yield.
[0046] In one specific embodiment, in the lateral direction of the multilayer electrode layer, the mass block 130 coincides with the projection of the multilayer electrode layer onto the piezoelectric substrate 110. Here, the lateral direction refers to the direction perpendicular to the extension direction of the electrode finger 120.
[0047] It should be noted that by overlapping the mass block 130 with the multilayer electrode layer, the mass block 130 can completely cover the end of the electrode layer, thereby improving the clutter suppression effect.
[0048] In one specific embodiment, the multilayer electrode layer further includes a second electrode layer 122 disposed between the piezoelectric substrate 110 and the first electrode layer 121. Under the same etching conditions, the first electrode layer 121 has a greater etching rate than the second electrode layer 122.
[0049] It should be noted that by using different etching rates for the first electrode layer 121 and the second electrode layer 122, damage to the piezoelectric substrate can be reduced during the etching process.
[0050] In one specific embodiment, the first electrode layer 121 and the mass block 130 are made of tungsten or molybdenum, and / or the second electrode layer 122 is made of aluminum-copper alloy or aluminum.
[0051] It should be noted that tungsten or molybdenum materials have the advantages of high density and high hardness. The high density of tungsten enhances the acoustic wave confinement capability, while its high hardness reduces electrode wear and extends electrode lifespan. The second electrode layer 122, made of aluminum-copper alloy or aluminum, can reduce resistance. The use of a tungsten-aluminum stack for the first electrode layer 121 and the second electrode layer 122 enables smaller linewidths, facilitating chip miniaturization, while also providing a high electromechanical coupling coefficient and quality factor.
[0052] The first electrode layer 121 and the mass block 130 are made of tungsten or molybdenum, which have high density and high load, so the thickness of the mass block 130 can be thinner. In one specific embodiment, the electrode finger 120 further includes a third electrode layer 123 disposed between the second electrode layer 122 and the piezoelectric substrate 110, wherein the density of the third electrode layer 123 is greater than the density of the second electrode layer 122.
[0053] It should be noted that using a higher density in the third electrode layer 123 is beneficial to improving the quality factor of the filter. At the same time, for a higher density electrode layer, using a smaller electrode spacing can ensure the frequency and achieve miniaturization.
[0054] Among them, the second electrode layer 122 and the third electrode layer 123 are the main electrode layers in the electrode finger 120, that is, the two electrode layers with the largest thickness.
[0055] When tungsten / molybdenum is selected as the first electrode layer 121, its frequency response is close to and sufficiently large with that of the thickest third electrode layer 123. When adjusting and compensating for the thickness uniformity of the second electrode layer 122 and the third electrode layer 123, the thickness difference of the entire electrode layer will not be too large, thus affecting the etching of the electrode finger 120.
[0056] In one specific embodiment, the second electrode layer 122 is made of aluminum-copper alloy or aluminum, and / or the third electrode layer 123 is made of tungsten or molybdenum.
[0057] Table 1 shows the performance of the main electrode layer of the electrode finger 120 using different metal materials under the same frequency conditions. Where IDT_metal is the material of the main electrode layer; OX is the oxide layer thickness; Pitch is the electrode finger 120 spacing; a / p is the electrode finger 120 duty cycle; CD is the static capacitance per unit area of the electrode finger 120; IDT_X is the electrode layer thickness in the electrode finger 120 excluding aluminum; IDT_AL is the aluminum layer thickness in the electrode finger 120; fs is the series resonant frequency; fp is the parallel resonant frequency; keff 2 is the effective electromechanical coupling coefficient; h / 2p is the normalized electrode thickness.
[0058] In one specific embodiment, the multilayer electrode layer further includes a fourth electrode layer 124, which is disposed on the side away from and adjacent to the piezoelectric substrate 110. The material of the fourth electrode layer 124 includes titanium, chromium, titanium nitride, aluminum nitride, or titanium tungsten.
[0059] It should be noted that the fourth electrode layer 124 is made of titanium, chromium, titanium nitride, aluminum nitride or titanium tungsten, which can enhance the adhesion of the electrode fingers to the piezoelectric substrate 110.
[0060] In one specific embodiment, the filter 100 further includes: a bus bar 140 disposed on the substrate, the bus bar 140 including a first bus bar 141 and a second bus bar 142 disposed opposite to each other, and both the first bus bar 141 and the second bus bar 142 extending in a direction orthogonal to the electrode finger 120; the electrode finger 120 includes a first electrode finger 120a connected to the first bus bar 141 and a second electrode finger 120b connected to the second bus bar 142, the first electrode finger 120a and the second electrode finger 120b being arranged in a cross pattern.
[0061] It should be noted that the busbar 140 and electrode finger 120 can make full use of the formed space, resulting in a high pattern density and saving space area without interfering with each other.
[0062] Specifically, when the first busbar 141 and the first electrode finger 120a serve as input terminals, the second busbar 142 and the second electrode finger 120b serve as output terminals. The input terminals are used to convert electrical signals into acoustic signals, and the output terminals are used to convert acoustic signals into electrical signals, thereby achieving filtering. In other embodiments, the first busbar 141 and the first electrode finger 120a can also serve as output terminals, and the second busbar 142 and the second electrode finger 120b can serve as input terminals.
[0063] Among them, the busbar 140 is also a stacked structure, and the stacked distribution of the busbar 140 is the same as that of the electrode finger 120. The busbar 140 and the electrode finger 120 are formed synchronously.
[0064] See Figures 2-11 The present invention also provides a method for forming a filter 100, the method comprising: Step S1: Form an electrode finger material layer 125 and a mass block material layer 131 on the piezoelectric substrate 110; Step S2: Process the mass block material layer 131 to form an initial mass block 132 at the end of the target area of the electrode finger 120; Step S3: Simultaneously process the electrode finger material layer 125 and the initial mass block 132 to form the electrode finger 120 and the mass block 130.
[0065] It should be noted that the target area of electrode finger 120 is the area where electrode finger 120 will eventually be formed; the electrode finger material layer 125 and the mass block material layer 131 are deposited in one step, and the electrode finger 120 and the mass block 130 can be made through two processes, which can effectively improve production efficiency.
[0066] In one specific embodiment, an electrode finger material layer 125 and a mass block material layer 131 are formed on a piezoelectric substrate 110. Specifically, the electrode finger material layer 125 includes multiple electrode layers, and multiple electrode layers are sequentially deposited on the piezoelectric substrate 110, wherein the electrode layer adjacent to the mass block material layer 131 is deposited simultaneously with the mass block material layer 131.
[0067] In one specific embodiment, processing the mass block material layer 131 to form an initial mass block 132 at the end of the target region of the electrode finger 120 specifically includes: coating a first mask layer 151 on the first target region of the mass block material layer 131, and performing photolithography on the region outside the first mask layer 151 to form the initial mass block 132.
[0068] It should be noted that the first target area is the area where the mass block 130 is ultimately formed, as well as the area with gaps between adjacent mass blocks 130. The extension direction of the first target area is orthogonal to the extension direction of the electrode finger 120. After the mass block material layer 131 is coated and protected by the first mask layer 151, only the initial mass block 132 of the first target area is left after etching. The initial mass block 132 can be completed by removing the part between adjacent mass blocks 130 to form gaps when processing the electrode finger material layer 125. Therefore, multiple metal depositions are not required, resulting in higher efficiency.
[0069] Preferably, the material of the first mask layer 151 includes photoresist. Photoresist has high resolution, allowing for precise control of the area to be removed; simultaneously, photoresist is easy to remove, thereby reducing process complexity and improving production efficiency. In other embodiments, the first mask layer 151 may also be made of other materials that can serve as an etching mask and are easy to remove.
[0070] Optionally, after the initial mass block 132 is formed, the first mask layer 151 is removed by a dry etching process.
[0071] It should be noted that the dry etching process has anisotropic etching characteristics, which is beneficial to improving the dimensional accuracy of the initial mass block 132 and the morphological quality of the electrode layer.
[0072] In this embodiment, the dry etching process includes one or both of reaction-coupled plasma etching and ion beam etching.
[0073] In one specific embodiment, after the initial mass block 132 is formed, the metal surface of the electrode finger 120 is exposed, and then the metal surface of the electrode finger 120 is trimmed to increase uniformity. Preferably, ion beam or physical grinding is used for trimming.
[0074] In one specific embodiment, the electrode finger material layer 125 and the initial mass block 132 are processed simultaneously to form the electrode finger 120 and the mass block 130. Specifically, this includes: coating the second target area of the electrode finger material layer 125 with a second mask layer 152, and etching the area outside the second mask layer 152 to form the electrode finger 120 and the mass block 130.
[0075] It should be noted that the second target area, which is the area where the electrode finger 120 will eventually be formed, also includes the area where the mass block 130 will eventually be formed. After the electrode finger material layer 125 and the initial mass block 132 are coated and protected by the second mask layer 152, only the electrode finger 120 and the mass block 130 in the second target area are left after etching. Therefore, there are fewer processes and higher efficiency.
[0076] Preferably, the material of the second mask layer 152 includes photoresist. Photoresist has high resolution, allowing for precise control of the area to be removed; simultaneously, photoresist is easy to remove, thereby reducing process complexity and improving production efficiency. In other embodiments, the second mask layer 152 may also be made of other materials that can serve as an etching mask and are easy to remove.
[0077] Optionally, after the initial mass block 132 is formed, the second mask layer 152 is removed by a dry etching process.
[0078] It should be noted that the dry etching process has anisotropic etching characteristics, which is beneficial to improving the dimensional accuracy of the mass block 130 and the morphological quality of the electrode fingers 120.
[0079] In this embodiment, the dry etching process includes one or both of reaction-coupled plasma etching and ion beam etching.
[0080] In one specific embodiment, the electrode finger material layer 125 is a stacked structure, with the topmost electrode finger material layer 125 serving as the first electrode material layer 121, and the electrode finger material layer 125 located at the bottom of the first electrode material layer 121 serving as the second electrode material layer 122. There is a removal selectivity ratio between the first electrode material layer 121 and the second electrode material layer 122.
[0081] It should be noted that, due to the height difference between the first electrode material layer 121 and the initial mass block 132, during etching, the first electrode material layer 121 region is etched to the second electrode material layer 122 before the initial mass block 132. When there is a removal selectivity between the first electrode material layer 121 and the second electrode material layer 122, the etching can be stopped synchronously on the surface of the second electrode material layer 122. This ensures that when etching the second electrode material layer 122, the surface of the piezoelectric substrate 110 can be etched to approximately the same extent. This avoids damage to the piezoelectric substrate 110 and affecting device performance if the piezoelectric substrate 110 is not reached at the same time.
[0082] In one specific embodiment, the removal selectivity ratio between the first electrode material layer 121 and the second electrode material layer 122 is greater than or equal to 10:1.
[0083] It should be noted that the removal selectivity between the first electrode material layer 121 and the second electrode material layer 122 is relatively large, which avoids increasing the probability of the second electrode material layer 122 being removed during the etching of the first electrode material layer 121 and the initial mass block 132, and also avoids the second electrode material layer 122 providing poor protection for the underlying piezoelectric substrate 110.
[0084] In one specific embodiment, the electrode material layer 125 further includes a third electrode material layer 123 located between the piezoelectric substrate 110 and the second electrode material layer 122, wherein the density of the third electrode material layer 123 is greater than the density of the second electrode material layer 122.
[0085] It should be noted that the third electrode material layer 123 uses a higher density to improve the device's quality factor and to control the frequency. Specifically, for a higher density electrode material layer, a smaller electrode spacing can ensure the frequency while achieving miniaturization.
[0086] In one specific embodiment, the electrode finger material layer 125 and the initial mass block 132 are processed simultaneously to form the busbar 140. Specifically, a second mask layer 152 is coated on the second target area of the electrode finger material layer 125 and the third target area of the busbar 140, and the area outside the second mask layer 152 is etched to form the electrode finger 120, the mass block 130, and the busbar 140.
[0087] The busbar 140 has the same stacked structure as the electrode finger 120.
[0088] In one specific embodiment, after etching the area outside the second mask layer 152, the method further includes thickness trimming of the area outside the second mask layer 152.
[0089] Since the etching amount and etching uniformity are difficult to control precisely during the etching process, the thickness of the remaining electrode finger 120 may differ from the preset value, and the surface of the electrode finger 120 may also be uneven. After etching, the thickness of the electrode finger 120 can be adjusted to further meet the device performance requirements.
[0090] In one specific embodiment, after etching the area outside the second mask layer 152, the method further includes removing the second mask layer 152 and, after removing the second mask layer 152, performing thickness trimming on the electrode fingers.
[0091] Without removing the second mask layer 152, during the thickness trimming process, metal atoms are prone to backsplashing at the sidewall of the second mask layer 152. This results in burrs on the edges of the electrode fingers 120 or mass blocks 130 after removing the second mask layer 152, which cannot be removed in subsequent processes. This affects the subsequent process of the device and its performance. Therefore, removing the second mask layer 152 before performing thickness trimming can avoid affecting the subsequent process and also allows for better frequency adjustment of the device, thus improving its performance.
[0092] 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 invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A filter, characterized in that, The filter includes: Piezoelectric substrate (110); An interdigital transducer is disposed on the piezoelectric substrate (110). The interdigital transducer includes: electrode fingers (120) and mass blocks (130); the mass blocks (130) are disposed at the ends of the electrode fingers (120). The electrode finger (120) includes a first electrode layer (121) adjacent to the mass block (130), and the first electrode layer (121) is made of the same material as the mass block (130).
2. The filter according to claim 1, characterized in that, The first electrode layer (121) and the mass block (130) are integrally formed.
3. The filter according to claim 1 or 2, characterized in that, In the transverse direction of the electrode finger (120), the mass block (130) and the projection of the multilayer electrode layer on the piezoelectric substrate (110) coincide.
4. The filter according to claim 1 or 2, characterized in that, The electrode finger (120) also includes a second electrode layer (122) disposed between the piezoelectric substrate (110) and the first electrode layer (121). Under the same etching conditions, the first electrode layer (121) has a greater etching rate than the second electrode layer (122).
5. The filter according to claim 4, characterized in that, The first electrode layer (121) and the mass block (130) are made of tungsten or molybdenum, and / or the second electrode layer (122) is made of aluminum-copper alloy or aluminum.
6. The filter according to claim 4, characterized in that, The electrode finger (120) further includes a third electrode layer (123) disposed between the second electrode layer (122) and the piezoelectric substrate (110), wherein the density of the third electrode layer (123) is greater than the density of the second electrode layer (122).
7. The filter according to claim 6, characterized in that, The second electrode material layer (122) is made of aluminum-copper alloy or aluminum, and / or the third electrode material layer (123) is made of tungsten or molybdenum.
8. The filter according to claim 6, characterized in that, The electrode finger (120) further includes a fourth electrode layer (124), which is disposed on the side away from the piezoelectric substrate (110) and adjacent to the piezoelectric substrate (110). The material of the fourth electrode layer (124) includes titanium, chromium, titanium nitride, aluminum nitride or titanium tungsten.
9. A method for forming a filter, characterized in that, The forming method includes: An electrode finger material layer and a mass block material layer are formed on a piezoelectric substrate; Process the mass block material layer to form an initial mass block at the end of the electrode pointing to the target region; The electrode finger material layer and the initial mass block are processed simultaneously to form the electrode finger and the mass block.
10. The forming method according to claim 9, characterized in that, The process of processing the mass block material layer, forming an initial mass block at the end of the electrode pointing to the target region, specifically includes: A first mask layer is covered over the first target area of the mass block material layer, and the area outside the first mask layer is etched to form the initial mass block.
11. The forming method according to claim 10, characterized in that, The simultaneous processing of the electrode finger material layer and the initial mass block to form the electrode finger and the mass block specifically includes: A second mask layer is covered over the second target area of the electrode finger material layer, and the area outside the second mask layer is etched to form the electrode finger and the mass block.
12. The forming method according to claim 11, characterized in that, The electrode finger material layer has a stacked structure, with the topmost electrode finger material layer serving as the first electrode material layer, and the electrode finger material layer located at the bottom of the first electrode material layer serving as the second electrode material layer. There is a removal selectivity ratio between the first electrode material layer and the second electrode material layer.
13. The forming method according to claim 12, characterized in that, The removal selectivity ratio between the first electrode material layer and the second electrode material layer is greater than or equal to 10:
1.
14. The forming method according to claim 12, characterized in that, The electrode material layer further includes a third electrode material layer located between the piezoelectric substrate and the second electrode material layer, wherein the density of the third electrode material layer is greater than the density of the second electrode material layer.
15. The forming method according to claim 11, characterized in that, After etching the area outside the second mask layer, the forming method further includes adjusting the thickness of the area outside the second mask layer.
16. The forming method according to claim 11, characterized in that, After etching the area outside the second mask layer, the forming method further includes removing the second mask layer and, after removing the second mask layer, trimming the thickness of the electrode fingers.