Interdigital transducer structure and application thereof in surface acoustic wave filter

Abstract

The invention relates to the technical field of filters, in particular to an interdigital transducer structure and application of the interdigital transducer structure in a surface acoustic wave filter, and the interdigital transducer structure comprises a first bus electrode and a second bus electrode which are oppositely arranged, and a plurality of first interdigital electrodes and a plurality of second interdigital electrodes which are periodically and alternately arranged at intervals; wherein the interdigital transducer at least comprises a platinum-aluminum alloy layer. According to the invention, the intervention of the platinum-aluminum alloy layer can shorten the period of the interdigital transducer during design, so that the size of the filter can be further reduced, and the Q value can be obviously improved; meanwhile, compared with a pure metal layer, the Pt-A alloy has moderate hardness and toughness compared with a Pt material, is more suitable for a micro-nano machining process, is easy to prepare a high-precision I DT material through processes such as photoetching and etching, and is more helpful for a high-frequency filter.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and particularly relates to an interdigital transducer structure and its application in a surface acoustic wave filter. Background Art

[0002] The miniaturization of surface acoustic wave filters (SAW) is a key trend in the development of wireless communication technologies, aiming to meet the growing demands of portable devices and high-performance radio frequency front-ends. With continuous technological progress, it is expected that the size of SAW filters will be further reduced in the future, providing more possibilities for high-density integration and multi-functional integration. At the same time, with the development of 5G, the requirements for the performance and size of filters have become more stringent.

[0003] However, the size of the filter is affected by various factors:

[0004] Substrate materials, different substrate materials have different sound velocities, piezoelectric constants, and loss characteristics.

[0005] The structural design of the interdigital transducer (IDT), parameters such as the width, spacing, length, and number of finger bars will all occupy the spatial layout.

[0006] Piezoelectric materials and film thickness, piezoelectric materials are the key materials for realizing acoustic-electric conversion, and their performance plays a decisive role in the performance of SAW filters.

[0007] Process production capacity, advanced process technologies often require expensive equipment and complex process flows, and have extremely high requirements for the accuracy of process control.

[0008] Packaging, traditional packaging methods often occupy a large amount of space, restricting the miniaturization of filters.

[0009] Filter design flexibility, it is difficult to achieve various functions and performance requirements within a limited space.

[0010] Layout, when performing layout, various factors such as electromagnetic interference, thermal management, and parasitic inductance need to be considered to ensure the performance and reliability of the filter.

[0011] Although certain progress has been made in the existing technologies for reducing the size of SAW filters, there are still some drawbacks, such as limited size reduction, high technical barriers, and material costs. For example, higher-performance substrate materials require expensive substrate materials, and there are high requirements for the orientation, cutting, grinding, and manufacturing of the substrates, which limit the flexibility and cost-effectiveness of size reduction. To reduce the size of SAW filters, currently, it mainly includes: a. developing piezoelectric materials with higher sound velocity and lower loss; b. using wafer-level packaging technology to reduce the size and thickness of SAW filters; c. adopting advanced manufacturing technologies; d. optimizing the design and circuit layout; e. optimizing the IDT thickness.

[0012] The above measures do not have advantages in terms of process cost and processing difficulty, and will also sacrifice the performance of the filter to a certain extent. Therefore, the present invention has developed an interdigital transducer structure and its application in a surface acoustic wave filter to solve the problems existing in the prior art. Summary of the Invention

[0013] The object of the present invention is to provide an interdigital transducer structure and its application in a surface acoustic wave filter to solve the problem of limited size reduction of filters in the prior art.

[0014] The technical solution of the present invention is: an interdigital transducer structure, including a first bus electrode and a second bus electrode arranged opposite to each other, and a plurality of first interdigital electrodes and a plurality of second interdigital electrodes arranged at periodic intervals and alternately.

[0015] Among them, the interdigital transducer at least includes a platinum-aluminum alloy layer.

[0016] Preferably, the interdigital transducer includes a titanium metal layer and a platinum-aluminum alloy layer.

[0017] Preferably, the interdigital transducer includes a titanium metal layer and a platinum-aluminum alloy layer sequentially deposited on a substrate, forming a Ti / Pt-Al layer.

[0018] Preferably, the interdigital transducer includes a titanium metal layer, a platinum-aluminum alloy layer, and a titanium metal layer sequentially deposited on a substrate, forming a Ti / Pt-Al / Ti layer.

[0019] Preferably, the thickness of the titanium metal layer is less than the thickness of the platinum-aluminum alloy layer.

[0020] Preferably, the relative thickness of the interdigital transducer satisfies:

[0021] 9.3% ≤ H Pt-Al / λ ≤ 13.3%;

[0022] Among them, H Pt-Al / λ is the relative thickness of the interdigital transducer, and H Pt-Alt is the thickness of the interdigital transducer, and λ is the interdigital period.

[0023] Preferably, the first bus electrode and the second bus electrode are also connected with dummy fingers. The dummy fingers connected to the first bus electrode are arranged opposite to the second interdigital electrode, and the dummy fingers connected to the second bus electrode are arranged opposite to the first interdigital electrode.

[0024] This application also discloses the applications of the interdigital transducer structure, mainly including:

[0025] The application of the interdigital transducer structure in TC-SAW. TC-SAW includes a piezoelectric substrate arranged under the interdigital transducer and a SiO2 covering layer formed above the interdigital transducer.

[0026] The application of the interdigital transducer structure in TF-SAW. TF-SAW includes a POI substrate arranged under the interdigital transducer and a passivation layer formed above the interdigital transducer.

[0027] The application of the interdigital transducer structure in Normal SAW. Normal SAW includes a piezoelectric substrate arranged under the interdigital transducer and a passivation layer formed above the interdigital transducer.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) In this application, the interdigital transducer includes at least a platinum-aluminum alloy layer. Under the condition of meeting the filter performance, the intervention of the platinum-aluminum alloy layer can reduce the period of the interdigital transducer during design, thereby further reducing the size of the filter, and the Q value can also be significantly improved. At the same time, compared with the pure metal layer, the Pt-Al alloy has moderate hardness and toughness, is more suitable for micro-nano processing technology, and is easy to prepare high-precision IDT materials through processes such as photolithography and etching, which is more helpful for high-frequency filters.

[0030] (2) In the actual application scenario, the alloy ratio of Pt / Al can also be adjusted to balance resistivity, thermal stability, power tolerance, Q value, etc. It has stronger adaptability compared with the IDT structure with each layer being a pure metal.

[0031] (3) The application of the platinum-aluminum alloy layer also increases the relative thickness of the interdigital transducer, avoiding the double-peak phenomenon in the case where the first interdigital electrode / second interdigital electrode is too thick. The increase in the thickness of the finger bars can withstand a higher current density and is not prone to overheating or burning, etc. Moreover, it can change the electrical parameters such as capacitance and inductance of the interdigital transducer, enabling the interdigital transducer to obtain a flatter and more stable frequency response within a specific frequency range, reducing frequency fluctuations and distortion, and improving the accuracy and quality of signal processing. Description of the Drawings

[0032] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0033] Figure 1 It is a schematic structural diagram of the interdigital transducer of the present invention;

[0034] Figure 2 It is a cross-sectional view of the Normal SAW of the present invention;

[0035] Figure 3 It is a simulated admittance curve diagram of the Normal SAW described in Embodiment 1 of the present invention;

[0036] Figure 4 It is a comparative simulated admittance curve diagram of the Normal SAW described in Embodiments 1 and 2 of the present invention;

[0037] Figure 5 It is a simulated admittance curve diagram of the Normal SAW described in Embodiment 3 of the present invention;

[0038] Figure 6 It is a cross-sectional view of the TF-SAW of the present invention;

[0039] Figure 7 It is a comparative simulated admittance curve diagram of the TF-SAW described in Embodiments 4 and 5 of the present invention;

[0040] Figure 8 It is a comparative simulated admittance curve diagram of the TF-SAW described in Embodiments 4 and 6 of the present invention;

[0041] Figure 9 It is a simulated admittance curve diagram of the TF-SAW described in Embodiment 7 of the present invention;

[0042] Figure 10 It is a cross-sectional view of the TC-SAW of the present invention;

[0043] Figure 11 It is a comparative simulated admittance curve diagram of the TC-SAW described in Embodiments 8 and 9 of the present invention;

[0044] Figure 12 It is a comparative simulated admittance curve diagram of the TC-SAW described in Embodiments 8 and 10 of the present invention;

[0045] Figure 13 It is a comparison diagram of the interdigital transducers corresponding to Embodiments 8 and 10 of the present invention.

[0046] Among them: 1. First bus electrode, 2. Second bus electrode, 3. Second interdigital electrode, 4. First interdigital electrode, 5. First dummy finger electrode, 6. Second dummy finger electrode, 7. Gap. Detailed Embodiments

[0047] The following further elaborates on the content of the present invention in conjunction with specific embodiments:

[0048] A surface acoustic wave filter mainly includes a substrate, interdigital transducers, and a passivation layer; for the interdigital transducer (IDT), as Figure 1 shown, mainly includes:

[0049] a. A first bus electrode 1 disposed on the substrate;

[0050] b. A second bus electrode 2 disposed on the substrate. The first bus electrode 1 and the second bus electrode 2 are opposite and parallel to each other. The first bus electrode 1 and the second bus electrode 2 are also referred to as bus bars;

[0051] c. A plurality of first interdigital electrodes 4 (also referred to as finger bars) arranged periodically. The first interdigital electrodes 4 extend from the first bus electrode 1 towards the second bus electrode 2, and the length of the first interdigital electrodes 4 is less than the distance between the first bus electrode 1 and the second bus electrode 2; in combination with Figure 1 shown, the distance between two adjacent first interdigital electrodes 4 is defined as an interdigital period λ, and an interdigital period λ is equal to the sum of the finger bar width and the adjacent interdigital gap;

[0052] d. A plurality of second interdigital electrodes 3 arranged periodically. The second interdigital electrodes 3 extend from the second bus electrode 2 towards the first bus electrode 1, and the first interdigital electrodes 4 and the second interdigital electrodes 3 are alternately arranged at intervals. The distance between two adjacent second interdigital electrodes 3 is defined as an interdigital period λ, and the distance between an adjacent first interdigital electrode 4 and a second interdigital electrode 3 is defined as an interdigital pitch p, p = λ / 2; furthermore, assuming the thickness of the first interdigital electrodes 4 and the second interdigital electrodes 3 is H, then the relative thickness of the first interdigital electrodes 4 and the second interdigital electrodes 3 is H / λ;

[0053] e. A first dummy finger electrode 5 connected to the first bus electrode 1 and opposite to the second interdigital electrodes 3; a second dummy finger electrode 6 connected to the second bus electrode 2 and opposite to the first interdigital electrodes 4; the first dummy finger electrode 5 and the second dummy finger electrode 6 can reduce external interference signals, help improve the signal-to-noise ratio of the overall system, and have significant effects in improving frequency response characteristics, suppressing parasitic effects, and enhancing mechanical stability. A gap 7 is formed between the first dummy finger electrode 5 and the second interdigital electrode 6, and a gap 7 is also formed between the second dummy finger electrode and the first interdigital electrode.

[0054] The above is the detailed structure of the interdigital transducer, which is mainly applied to Normal SAW, TF-SAW, and TC-SAW. Briefly, Normal SAW refers to the process of fabricating circuits directly on a single-layer piezoelectric substrate, TF-SAW refers to the multi-layer thin-film substrate process, and TC-SAW still uses a single-layer piezoelectric substrate, but a relatively thick SiO2 layer is covered on the chip surface. The interdigital transducer is formed on the surface of the substrate by a process. The following provides corresponding embodiments for Normal SAW, TF-SAW, and TC-SAW respectively.

[0055] Regarding Normal SAW:

[0056] As Figure 2 shown, Normal SAW includes a substrate composed of a piezoelectric substrate, an interdigital transducer disposed on the piezoelectric substrate, and a passivation layer covering the interdigital transducer; wherein, the piezoelectric substrate can be made of lithium tantalate (LiTaO3), and of course, quartz or lithium niobate substrates can also be used.

[0057] Embodiment 1

[0058] In the interdigital transducer (IDT) of Normal SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0059] The IDT layer includes a titanium metal layer and an aluminum metal layer (Ti / Al);

[0060] The interdigital pitch p = 2 μm;

[0061] The relative thickness H of the interdigital transducer Al / λ = 9.5%.

[0062] In this embodiment, a titanium metal layer (Ti) and an aluminum metal layer (Al) are sequentially formed on the piezoelectric substrate. Titanium metal has good adhesion characteristics and can be tightly combined with various substrate materials (such as piezoelectric materials like quartz and lithium niobate), preventing the aluminum metal layer from peeling off the substrate during use and improving the stability and reliability of the IDT layer; at the same time, the chemical properties of the titanium metal layer are relatively stable, which can block the possible chemical reactions between the substrate and aluminum to a certain extent and avoid the deterioration of electrical properties caused by chemical reactions. The aluminum metal layer is a metal with excellent conductivity and low resistivity, which can effectively transmit electrical signals. Since the titanium metal layer plays a role in connecting stability, the titanium metal layer belongs to the functional layer. In the actual preparation process, the thickness of the titanium metal layer is less than that of the platinum-aluminum alloy layer.

[0063] Regarding the selection of the above IDT structure and materials, the corresponding admittance curve simulation results are as Figure 3 shown.

[0064] Example 2

[0065] In the interdigital transducer of Normal SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0066] The IDT layer includes a titanium metal layer and a platinum metal layer (Ti / Pt);

[0067] The interdigital pitch p = 1.4 μm;

[0068] The relative thickness H of the interdigital transducer Pt / λ = 9.5%;

[0069] For the selection of the above IDT structure and materials, the corresponding admittance curve simulation results are as Figure 4 shown. Comparing the IDT layer with the Ti / Al combination and the IDT layer with the Ti / Pt combination, it can be seen that the interdigital period of the IDT layer with the Ti / Pt combination is reduced, and the reduction ratio is 1.4 / 2 = 0.7. On this basis, the reduction limit of the resonator area is 1 - 0.7×0.7 = 0.51, that is, the IDT can be reduced by 51% in the limit state. Considering packaging and layout, the actual limit reduction of the die size can reach about 40%. Therefore, using the Ti / Pt combination material has a significant effect on reducing the resonator size. In addition, the bandwidth of the Ti / Pt combination resonator is slightly wider than that of the Ti / Al combination resonator, and the Q value is much larger.

[0070] Example 3

[0071] In the interdigital transducer of Normal SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0072] The IDT layer includes a titanium metal layer and a platinum metal layer (Ti / Pt);

[0073] The interdigital pitch p = 1.4 μm;

[0074] The relative thickness H of the interdigital transducer Pt / λ = 10.7%;

[0075] For the selection of the above IDT structure and materials, the corresponding admittance curve simulation results are as Figure 5 shown. At this time, a double-peak phenomenon appears between the resonance point and the anti-resonance point, and the signal transmission is prone to distortion, which will reduce the signal fidelity and accuracy, and will also cause an increase in interference and noise.

[0076] Through experiments and simulation analysis, when the IDT layer uses the Ti / Pt combination, the interdigital pitch p = 1.4 μm, and the relative thickness H PtWhen / λ≥10.7%, a double-peak phenomenon will occur between the resonance point and the anti-resonance point, thus affecting the performance of the filter. Therefore, the finger thickness cannot be too thick.

[0077] The parameter designs in Examples 1 - 3 are mainly as shown in Table 1 below:

[0078] Table 1. Parameter Table of Normal SAW in Examples 1 - 3

[0079] IDT layer Finger pitch Relative thickness Comparison result Example 1 Ti / Al 2μm 9.5 —— Example 2 Ti / Pt 1.4μm 9.5 The size is reduced by 51% Example 3 Ti / Pt 1.4μm 10.7 A bimodal phenomenon will occur

[0080] Regarding TF-SAW:

[0081] The main difference between the TF-SAW filter and the Normal SAW filter is the choice of the substrate. The TF-SAW substrate is mainly composed of a multi-layer thin film structure and is used to design filters with higher performance and higher frequencies. As Figure 6 shown, the top layer is a piezoelectric layer of several hundred nanometers. Below the piezoelectric layer is a temperature compensation layer, and below the temperature compensation layer is a buffer layer. The bottom layer is a high-resistivity silicon material. In the following embodiments, the substrate uses a POI substrate. POI is a substrate material for surface acoustic wave (SAW) filters, with a high-resistivity silicon as the substrate, an oxidized buried layer in the middle layer, and a thin and uniform single-crystal piezoelectric layer on the top.

[0082] Example 4

[0083] In the interdigital transducer of TF-SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0084] The IDT layer includes a titanium metal layer and an aluminum metal layer (Ti / Al);

[0085] The interdigital pitch p = 1 μm;

[0086] For the above selection of IDT structure and materials, the corresponding admittance curve simulation results are as Figure 7 shown.

[0087] Example 5

[0088] In the interdigital transducer of TF-SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0089] The IDT layer includes a titanium metal layer and a platinum-aluminum metal layer (Ti / Pt-Al);

[0090] The interdigital pitch p = 1 μm;

[0091] For the above selection of IDT structure and materials, the corresponding admittance curve simulation results are as Figure 7 shown.

[0092] Combined withFigure 7 As shown, in the TF-SAW filter, from the simulation comparison results of the Ti / Al combined resonator and the Ti / Pt-Al combined resonator, it can be seen that the finger periods of the two materials are the same. The optimized structure with the platinum-aluminum metal layer has a lower frequency, a larger Q value, and almost no change in bandwidth.

[0093] Example 6

[0094] In the interdigital transducer of TF-SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0095] The IDT layer includes a titanium metal layer and a platinum-aluminum metal layer (Ti / Pt-Al);

[0096] The interdigital pitch p = 0.9 μm.

[0097] As Figure 8 shown, in the TF-SAW filter, by comparing Example 4 and Example 6, when the IDT layer selects the Ti / Al combination, p = 1 μm; when the IDT layer selects the Ti / Pt-Al combination, p = 0.9 μm; the reduction ratio of the resonator area is 0.9 / 1 = 0.9, and the reduction limit of the resonator area is 1 - 0.9×0.9 = 0.19. That is to say, theoretically, when the IDT layer selects the Ti / Pt-Al combination, compared with the traditional finger structure of the Ti / Al combination, the finger period is reduced by 19%; but in the actual application scenario, considering packaging and layout, the limit reduction of the actual bare die size is about 12% or so. Using the Ti / Pt-Al combination material has a significant effect on reducing the resonator size. Since the price of the POI substrate is much higher than that of the lithium niobate and lithium tantalate substrates, small size is particularly important for TF-SAW.

[0098] Combined with Figure 7 、 Figure 8 shown, in the TF-SAW filter, when the IDT layer structure is the Ti / Pt-Al alloy, the Q value has a tendency to increase. At the same time, the Pt-Al alloy has moderate hardness and toughness compared with the Pt material, is more suitable for micro-nano processing technology, and is easy to prepare high-precision IDT materials through processes such as photolithography and etching, which is more helpful for high-frequency filters; by optimizing the alloy composition, the interfacial bonding force between the Pt-Al alloy and the piezoelectric substrate material (such as lithium niobate and lithium tantalate) can be enhanced. The resistivity of the Pt-Al alloy is lower than that of the Pt material because the resistivity of aluminum is relatively low. The resistivity of the Pt-Al alloy is usually between 10 -8 ~10 -7between Ω·m; for the receiving filter, the high-power tolerance is crucial for improving the device performance. The use of Pt-Al alloy in the IDT electrode can effectively improve the power tolerance, mainly due to its low resistivity, high melting point, resistance to electromigration, and thermal stability. By optimizing the alloy composition and process, its potential in high-power surface acoustic wave devices can be further exploited.

[0099] Example 7

[0100] In the interdigital transducer of TF-SAW, the structure and material characteristics of the IDT layer are mainly as follows:

[0101] The IDT layer includes a titanium metal layer and a platinum-aluminum alloy layer (Ti / Pt-Al);

[0102] The interdigital pitch p = 1.43 μm;

[0103] The relative thickness H of the first interdigital electrode and the second interdigital electrode Pt-Al / λ = 13.3%.

[0104] For the above selection of IDT structure and materials, the corresponding admittance curve simulation results are as Figure 9 shown.

[0105] Combined Figure 9 shown, in the TF-SAW filter, the Ti / Pt-Al combined resonator can avoid the appearance of a double-peak phenomenon when the finger bars are too thick (relative thickness reaching 13.3%). And the increase in the thickness of the finger bars can withstand a higher current density and is not prone to overheating or burning, etc. Moreover, it can change the electrical parameters such as the capacitance and inductance of the interdigital transducer, enabling the interdigital transducer to obtain a flatter and more stable frequency response within a specific frequency range, reducing frequency fluctuations and distortion, and improving the accuracy and quality of signal processing.

[0106] In the actual application process, the thickness of the finger bars cannot be too small either. If the thickness of the finger bars is too small, the electromechanical coupling between the finger bars and the piezoelectric substrate will become weak. When an electrical signal is applied to the interdigital transducer, due to the relatively thin finger bars, the generated mechanical vibration is weak, resulting in less energy converted into surface acoustic waves, thus reducing the electro-acoustic conversion efficiency. At the same time, problems such as low mechanical strength of the structure and weak signal transmission ability are also avoided. The minimum relative thickness of the first interdigital electrode and the second interdigital electrode can reach 9.3%.

[0107] The parameter designs in Examples 4 - 7 are mainly as shown in Table 2 below:

[0108] Table 2. Parameter table of TF-SAW in Examples 4 - 7

[0109] IDT layer Finger pitch Relative thickness Comparison result Example 4 Ti / Al 1μm —— —— Example 5 Ti / Pt-Al 1μm —— Lower frequency and larger Q value Example 6 Ti / Pt-Al 0.9μm —— The size is reduced by 19% Example 7 Ti / Pt-Al 1.43μm 13.3％ Even if it is too thick, the bimodal phenomenon will not appear

[0110] Regarding TC-SAW:

[0111] TC-SAW still uses a single-layer piezoelectric substrate, but a relatively thick SiO2 layer will be covered on the chip surface. Its structure includes a piezoelectric substrate, interdigital transducers arranged on the piezoelectric substrate, acoustic gratings, and a SiO2 covering layer. The SiO2 covering layer is used to achieve temperature compensation, which can greatly reduce the frequency-temperature coefficient of the filter, reduce the frequency drift caused by temperature changes, and meet the temperature stability.

[0112] Example 8

[0113] In the interdigital transducers of TC-SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0114] The IDT layer includes a titanium metal layer, a copper metal layer, and a titanium metal layer (Ti / Cu / Ti);

[0115] The interdigital pitch p = 2.2 μm.

[0116] For the above selection of IDT structure and materials, the corresponding admittance curve simulation results are as Figure 11 shown.

[0117] Example 9

[0118] In the interdigital transducers of TC-SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0119] The IDT layer includes a titanium metal layer, a platinum-aluminum alloy layer, and a titanium metal layer (Ti / Pt-Al / Ti);

[0120] The interdigital pitch p = 2.2 μm.

[0121] As Figure 11 shown, in the TC-SAW filter, in Example 8 and Example 9, the finger periods of the IDTs of the two materials are the same. The filter corresponding to the IDT layer of the Ti / Pt-Al / Ti combination has a lower frequency, a larger Q value, and almost no change in bandwidth; at the same time, the thinner the SiO2 layer, the larger the Q value and the larger the bandwidth.

[0122] Example 10

[0123] In the interdigital transducers of TC-SAW, the structural and material characteristics of the IDT layer are mainly as follows:

[0124] The IDT layer includes a titanium metal layer, a platinum-aluminum alloy layer, and a titanium metal layer (Ti / Pt-Al / Ti);

[0125] The interdigital pitch p = 1.8 μm.

[0126] AsFigure 12 As shown, in a TC-SAW filter, comparing Example 8 with Example 10, when the simulation results of the two IDT layer structures have the same frequency, when the IDT layer selects the Ti / Cu / Ti combination, p = 2.2 μm; when the IDT layer selects the Ti / Pt-Al / Ti combination, p = 1.8 μm; the reduction ratio of the resonator area is 1.8 / 2.2 ≈ 0.82, and the reduction limit of the resonator area is 1 - 0.82×0.82 ≈ 0.33. Theoretically, the finger pitch is reduced by about 33% on the original basis, as Figure 13 shown, based on the selection of the interdigital spacing, it can be clearly observed that the size of the Ti / Pt-Al / Ti combination resonator can be significantly improved.

[0127] Combined with Figure 11 、 Figure 12 As shown, in a TC-SAW filter, the bandwidth is almost unchanged. When the IDT layer is a titanium metal layer, a platinum-aluminum alloy layer, and a titanium metal layer (Ti / Pt-Al / Ti), the Q value has an increasing trend. Selecting appropriate IDT combined thickness and alloy ratio can make the performance better. In practical applications, it is found that the Pt-Al alloy has moderate hardness and toughness compared with the pure metal Pt material, is suitable for micro-nano processing technology, and is easy to prepare high-precision IDT materials through processes such as photolithography and etching; by optimizing the alloy composition, the interfacial bonding force between the Pt-Al alloy and the piezoelectric substrate material (such as lithium niobate and lithium tantalate) and the temperature compensation layer (such as SiO2) can be enhanced, so that voids are not likely to appear between SiO2 and the IDT, thus affecting the filter performance. It should be noted that due to the use of the Pt-Al alloy, the regulation of the Pt / Al alloy ratio is realized, and thus the resistivity, thermal stability, power tolerance, Q value, etc. can be balanced; compared with the IDT structure with each layer being a pure metal, the adaptability is stronger.

[0128] The parameter designs in Examples 8 - 10 are mainly as shown in Table 3 below:

[0129] Table 3. Parameter table of TC-SAW in Examples 8 - 10

[0130] IDT layer Finger pitch Comparison result Example 8 Ti / Cu / Ti 2.2μm —— Example 9 Ti / Pt-Al / Ti 2.2μm Lower frequency and larger Q value Example 10 Ti / Pt-Al / Ti 1.8μm The size is reduced by 33%

[0131] To sum up, whether it is for Normal SAW, TF-SAW or TC-SAW, when a Pt-Al alloy is used in the interdigital transducer (IDT), compared with the traditional IDT structure, the size of the improved interdigital transducer is significantly reduced, and at the same time, the double-peak phenomenon can be avoided when the interdigital electrode is too thick.

[0132] Specifically, in the application of Normal SAW, when the IDT electrode material is Ti+Pt-Al alloy, the resonator size is significantly reduced, the bandwidth is increased, the Q value is significantly increased, and the process is easier to implement.

[0133] In the application of TF-SAW, when the IDT electrode structure material is Ti+Pt-Al alloy, compared with the traditional Ti+Al structure, the size is significantly smaller, the Q value shows an increasing trend, and the power is improved; compared with the Ti+Pt structure, the resistivity and thermal stability can be balanced by adjusting the Pt / Al alloy ratio; the interfacial bonding force between the Pt-Al alloy and the piezoelectric material can be improved, and the interfacial voids and interfacial losses can be reduced; compared with the Ti+Pt+Al structure, the number of structural layers is less, and the process cost is lower; at the same time, the Pt-Al alloy is easier to prepare high-precision IDT finger bars than Pt, which is suitable for the application in high-frequency filters.

[0134] In the application of TC-SAW, when the IDT electrode structure material is Ti+Pt-Al alloy+Ti, compared with the traditional Ti+Cu+Ti structure, the size is significantly smaller, the Q value shows an increasing trend, and the power is improved; compared with the Ti+Pt+Ti structure, the resistivity and thermal stability can also be balanced by adjusting the Pt / Al alloy ratio; the interfacial bonding force between the Pt-Al alloy and the piezoelectric material can be improved, and the interfacial voids and interfacial losses can be reduced; the Pt-Al alloy is easier to prepare high-precision IDT finger bars than Pt, etc.

[0135] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention. The purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. An interdigital transducer structure, characterized in that, It includes a first bus electrode and a second bus electrode which are oppositely arranged, and a plurality of first interdigital electrodes and a plurality of second interdigital electrodes which are arranged alternately at periodic intervals; Among them, the interdigital transducer at least includes a platinum-aluminum alloy layer.

2. The interdigital transducer structure according to claim 1, wherein: The interdigital transducer includes a titanium metal layer and a platinum-aluminum alloy layer.

3. The interdigital transducer structure according to claim 2, wherein: The interdigital transducer includes a titanium metal layer and a platinum-aluminum alloy layer which are sequentially deposited on a substrate, forming a Ti / Pt-Al layer.

4. The interdigital transducer structure according to claim 2, wherein: The interdigital transducer includes a titanium metal layer, a platinum-aluminum alloy layer, and a titanium metal layer which are sequentially deposited on a substrate, forming a Ti / Pt-Al / Ti layer.

5. The interdigital transducer structure according to claim 2, characterized in that: The thickness of the titanium metal layer is less than the thickness of the platinum-aluminum alloy layer.

6. The interdigital transducer structure according to claim 1, wherein: The relative thickness of the interdigital transducer satisfies: 9.3% ≤ H Pt-Al / λ ≤ 13.3%; Among them, H Pt-Al / λ is the relative thickness of the interdigital transducer, H Pt-Al is the thickness of the interdigital transducer, and λ is the interdigital period.

7. The interdigital transducer structure according to claim 1, characterized in that: The first bus electrode and the second bus electrode are also connected with dummy fingers. The dummy fingers connected to the first bus electrode are oppositely arranged with the second interdigital electrode, and the dummy fingers connected to the second bus electrode are oppositely arranged with the first interdigital electrode.

8. Application of the interdigital transducer structure according to any one of claims 1-7 in a TC-SAW. The TC-SAW includes a piezoelectric substrate arranged below the interdigital transducer and a SiO2 covering layer formed above the interdigital transducer.

9. Application of the interdigital transducer structure according to any one of claims 1-7 in a TF-SAW. The TF-SAW includes a POI substrate arranged below the interdigital transducer and a passivation layer formed above the interdigital transducer.

10. Application of the interdigital transducer structure according to any one of claims 1-7 in a NormalSAW. The NormalSAW includes a piezoelectric substrate arranged below the interdigital transducer and a passivation layer formed above the interdigital transducer.

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