Interdigital transducer and elastic wave resonator

Abstract

The invention discloses an interdigital transducer and an elastic wave resonator, and belongs to the technical field of surface acoustic waves. The interdigital transducer comprises an interdigital transduction electrode structure, the interdigital transduction electrode structure comprises a first interdigital electrode and a second interdigital electrode which are oppositely arranged in the first direction and form an aperture area, the finger edge of the first interdigital electrode forms a first curve, and the finger edge of the second interdigital electrode forms a second curve; the mass loads are formed on the interdigital transduction electrode structure and located in the aperture area, and the mass loads are arranged to form at least one third curve and at least one fourth curve; wherein the first curve, the second curve, the third curve and the fourth curve all meet a specific apodization function. According to the interdigital transduction electrode, apodization is carried out on the edge of a finger strip in the interdigital transduction electrode structure, an apodization mass load is arranged in an aperture area, and a specific apodization curve is adopted, so that propagation of a transverse mode is blocked, the transverse mode is inhibited, and meanwhile, quality factors are not reduced.

Description

Technical Field

[0001] This application belongs to the field of surface acoustic wave technology, and particularly relates to an interdigital transducer and an elastic wave resonator. Background Technology

[0002] Filters composed of elastic wave resonators possess advantages such as low insertion loss, high suppression, and small size, making them widely used in radio frequency filtering. In elastic wave devices excited by interdigital transducers, reflections of transversely propagating acoustic waves at the boundaries cause transverse modes to appear in the resonator. Elastic wave devices excited by interdigital transducers (IDTs) include various acoustic wave devices utilizing surface wave (SAW), Lamb waves, and higher-order SH modes. The presence of transverse modes leads to ripple in the in-band and near-passband of piezoelectric filters. These ripples increase device losses and degrade the performance of the resonator and filter. Therefore, suppressing transverse modes in elastic wave devices is a problem that needs to be solved. Summary of the Invention

[0003] This application aims to at least solve one of the technical problems existing in the prior art. To this end, this application proposes an interdigital transducer and an elastic wave resonator, in which apodization is performed on the edge of the interdigital transducer electrode structure, and a mass load of apodization is provided in the aperture region, thereby blocking the propagation of transverse modes, suppressing transverse modes, and without reducing the quality factor.

[0004] In a first aspect, this application provides an interdigital transducer, comprising:

[0005] The interdigitated transducer electrode structure includes a first interdigitated electrode and a second interdigitated electrode arranged opposite to each other along a first direction. Multiple fingers in the first interdigitated electrode and the second interdigitated electrode are staggered along a second direction to form an aperture region. The edges of the fingers of the first interdigitated electrode form a first curve, and the edges of the fingers of the second interdigitated electrode form a second curve. The first curve and the second curve are located on both sides of the center line of the interdigitated transducer electrode structure. The first direction and the second direction intersect, and the center line is parallel to the second direction.

[0006] Multiple mass loads are formed on the interdigitated transducer electrode structure and located within the aperture region. Each mass load is arranged to form at least one third curve and at least one fourth curve, with the third curve and the fourth curve located on both sides of the center line.

[0007] Reflective gratings are arranged along the second direction on both sides of the interdigital transducer structure;

[0008] Among them, the first curve, the second curve, the third curve, and the fourth curve all satisfy the following apodization function:

[0009] y=(arccos(a / cos(x*arccos(a)*2)) / arccos(a)) / 2;

[0010] x is the normalized coordinate of the interdigital transducer structure in the second direction, with a value range of [-0.5, 0.5]; y is the normalized coordinate of the interdigital transducer structure in the first direction, with a value range of [0, 0.5]; a is the weighting factor, with a value range of [0.01, 0.99].

[0011] According to the interdigital transducer of this application, by apodizing the edges of the interdigital transducer electrode structure and providing apodization mass load in the aperture region, and employing a specific apodization curve, the propagation of the transverse mode is blocked, thereby suppressing the transverse mode without reducing the quality factor.

[0012] According to one embodiment of this application, the number of the first curve and the number of the second curve are both one, and they are connected on the center line; the number of the third curve and the number of the fourth curve are also both one, and they are connected on the center line.

[0013] The x-axis coordinate range of the apodization function is normalized by the total length of the aperture region in the second direction, and the x-axis coordinate range of the apodization function is normalized by the width of the aperture region from the center line to one side in the first direction.

[0014] According to one embodiment of this application, there are multiple first curves, second curves, third curves and fourth curves, all of which are arranged along a second direction. Adjacent curves in the second direction are connected, and the first curves and second curves that are opposite to each other in the first direction are connected on the center line. The third curves and fourth curves that are opposite to each other in the first direction are connected on the center line.

[0015] The x-axis coordinate range of the apodization function is normalized by the length L / M of the interdigital transducer structure in the second direction, and the y-axis coordinate range of the apodization function is normalized by the width of the interdigital transducer structure from the center line to one side in the first direction. Here, L is the total length of the interdigital transducer structure in the second direction, and M is the number of the first curve, the second curve, the third curve, or the fourth curve.

[0016] According to one embodiment of this application, the mass load is made of metal and has a dot-like shape; or,

[0017] The mass load is made of dielectric material and has the shape of a dot or strip.

[0018] According to one embodiment of this application, when the mass load is in the form of a point, the length of the mass load in the first direction is 0.3λ-2λ, where λ is the acoustic wavelength defined by the interdigital transducer structure; the width of the mass load in the second direction is 0.5-1.5 times the width of the finger strip.

[0019] According to one embodiment of this application, the first interdigital electrode includes a first true finger and a first virtual finger, and the second interdigital electrode includes a second true finger and a second virtual finger. The first true finger and the second virtual finger are arranged opposite to each other along a first direction, and the second true finger and the first virtual finger are arranged opposite to each other along the first direction. The edge of the finger strip of the first true finger forms a first curve, and the edge of the finger strip of the second true finger forms a second curve.

[0020] According to one embodiment of this application, at least a portion of the mass load is located at the fingertip of the first or second true finger.

[0021] According to one embodiment of this application, the first curve, the second curve, the third curve, and the fourth curve all further satisfy the following random function:

[0022] y'=y±b*W;

[0023] Where y' is the corrected y value, b is a random number with a value range of (0, 0.1], and W is the total width of the aperture region in the first direction.

[0024] According to one embodiment of this application, the weighting factor 'a' in the apodization function takes values ​​ranging from [0.4, 0.6].

[0025] Secondly, this application provides an elastic wave resonator, including a piezoelectric layer and an interdigital transducer formed on the piezoelectric layer according to the foregoing.

[0026] According to the elastic wave resonator of this application, by employing an interdigital transducer that effectively suppresses transverse modes, the in-band and passband ripple can be reduced, device losses can be avoided, and device performance can be improved.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 This is one of the structural schematic diagrams of the interdigital transducer provided in the embodiments of this application;

[0030] Figure 2 This is one of the structural schematic diagrams of interdigital transducers in related technologies;

[0031] Figure 3 This is a contour diagram of the fundamental modes of a two-dimensional resonant cavity for an interdigital transducer;

[0032] Figure 4 This is a graph of the change function provided in the embodiments of this application;

[0033] Figure 5 This is a second schematic diagram of the structure of the interdigital transducer provided in the embodiments of this application;

[0034] Figure 6 This is the second schematic diagram of the structure of the interdigital transducer in the related technology;

[0035] Figure 7 This is the third schematic diagram of the structure of the interdigital transducer in the related technology;

[0036] Figure 8 These are admittance performance curves for various interdigital transducers;

[0037] Figure 9 These are real part admittance performance curves for various interdigital transducers;

[0038] Figure 10 This is a Bode-Q curve graph of various interdigital transducers;

[0039] Figure 11 This is a schematic diagram of the structure of the elastic wave resonator provided in the embodiments of this application.

[0040] Figure label:

[0041] Interdigital transducer 10, interdigital transducer electrode structure 11, first interdigital electrode 111, second interdigital electrode 112, aperture region 113, first reflective grating 12, second reflective grating 13, mass load 14, piezoelectric layer 20. Detailed Implementation

[0042] The embodiments of this application are described in detail below, examples of which are illustrated in the accompanying drawings. In the drawings, for clarity, the dimensions of layers, regions, elements, and their relative dimensions may be exaggerated. The same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0043] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this disclosure, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And the discussion of a second element, component, area, layer, or portion does not imply that the first element, component, area, layer, or portion necessarily exists in this disclosure.

[0044] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] In related technologies, elastic wave resonators typically employ weighted curves, such as cosine function curves, at the finger tips of the interdigital transducer. Alternatively, a load can be applied to the finger tips of the interdigital transducer to suppress transverse modes. However, these methods have limited effectiveness in suppressing transverse modes, and in some applications, elastic wave resonators require higher transverse mode suppression capabilities.

[0046] Embodiments of this application provide an interdigital transducer and an elastic wave resonator. By apodizing the edges of the interdigital transducer electrode structure and providing a mass load of apodization in the aperture region, and employing a specific apodization curve, the propagation of transverse modes is blocked, thereby suppressing transverse modes without reducing the quality factor.

[0047] Reference Figure 1 , Figure 1The structure of a first type of interdigital transducer is shown. One embodiment of this application proposes an interdigital transducer 10. In this embodiment, the interdigital transducer 10 includes an interdigital transducer electrode structure 11, a first reflective grating 12, a second reflective grating 13, and a plurality of mass loads 14. The interdigital transducer electrode structure 11 includes a first interdigital electrode 111 and a second interdigital electrode 112 arranged opposite each other along a first direction X. A plurality of fingers in the first interdigital electrode 111 and the second interdigital electrode 112 are staggered along a second direction Y to form an aperture region 113. The first direction X and the second direction Y intersect. The first reflective grating 12 and the second reflective grating 13 are arranged along the second direction Y on both sides of the interdigital transducer electrode structure 11. The mass loads 14 are formed on the interdigital transducer electrode structure 11 and located within the aperture region 113.

[0048] In this structure, the edges of the fingers of the first interdigital electrode 111 form a first curve, and the edges of the fingers of the second interdigital electrode 112 form a second curve. The first and second curves are located on both sides of the center line cl of the interdigital transducer structure, and the center line cl is parallel to the second direction Y. Each mass load 14 is arranged to form at least one third curve and at least one fourth curve, which are located on both sides of the center line of the interdigital transducer structure. The first, second, third, and fourth curves all satisfy the following apodization function:

[0049] y=(arccos(a / cos(x*arccos(a)*2)) / arccos(a)) / 2;

[0050] x is the normalized coordinate of the interdigital transducer structure in the second direction, with a value range of [-0.5, 0.5]; y is the normalized coordinate of the interdigital transducer structure in the first direction, with a value range of [0, 0.5]; a is the weighting factor, with a value range of [0.01, 0.99].

[0051] Interdigital transducers can be used to form elastic wave resonators, and are formed above the piezoelectric layer. When an alternating electrical signal is applied to the interdigital transducer, a periodically distributed electric field is generated. Due to the inverse piezoelectric effect, corresponding elastic deformation is excited near the surface of the piezoelectric medium, causing vibration of solid particles and forming surface acoustic waves propagating along the substrate surface. The first reflective grating 12 and the second reflective grating 13 reflect the signal at the interdigital transducer electrode structure 11, forming a resonant cavity. This resonant cavity can limit the propagation range of the surface acoustic wave energy, concentrating it mainly in the region composed of the two reflective gratings.

[0052] In some embodiments, the first interdigital electrode 111 includes a first true finger and a first virtual finger, and the second interdigital electrode 112 includes a second true finger and a second virtual finger. The first true finger and the second virtual finger are arranged opposite to each other along a first direction X, and the second true finger and the first virtual finger are arranged opposite to each other along the first direction X. The edge of the first true finger forms a first curve, and the edge of the second true finger forms a second curve. The first curve and the second curve may be axially symmetrical about the center line cl.

[0053] There are gaps between the first true finger and the second imaginary finger, as well as between the second true finger and the first imaginary finger, and the lengths of each gap in the first direction X are approximately equal. Therefore, when the edge of the first true finger forms a first curve, the edge of the second imaginary finger also forms a first curve; when the edge of the second true finger forms a second curve, the edge of the first imaginary finger also forms a second curve.

[0054] Mass load 14 is disposed within aperture region 113, specifically on the first and second interdigital transducers. Mass load 14 forms a third curve and a fourth curve on either side of the center line c1, and these curves can be axially symmetrical about the center line c1. Mass load 14 can alter the resonant frequency of the interdigital transducer. By arranging mass load 14 according to the aforementioned function curves, transverse modes can be better suppressed. The shape of aperture region 113 can be rectangular or elliptical, etc., and this embodiment is not limited in this respect.

[0055] As an example, the busbars near the first interdigital electrode 112 are formed by a first curve and a third curve, which are adjacent to each other. That is, the edge of the first true finger's bar forms the first curve, and a portion of the mass load 14 is arranged near the end of the first true finger's bar. The busbars near the first interdigital electrode 111 are formed by a second curve and a fourth curve, which are adjacent to each other. That is, the edge of the second true finger's bar forms the second curve, and a portion of the mass load 14 is arranged near the end of the first true finger's bar.

[0056] Reference Figure 2 and Figure 3 , Figure 2 The structure of the interdigital transducer in the first related technology is shown. Figure 3 The contour lines of the fundamental modes of a two-dimensional resonant cavity are shown.

[0057] by Figure 2 Taking the interdigital transducer 10 shown as an example, the horizontal axis x represents the normalized coordinate relative to the length L of the interdigital transducer electrode structure 11 in the second direction Y, and the vertical axis y represents the normalized coordinate relative to the maximum overlap length W of the interdigital electrodes in the first direction X. Based on the two-dimensional resonant cavity, when both sides are reflection boundaries, the following calculations are obtained: Figure 2 The contour lines shown are schematic diagrams.

[0058] In this embodiment, by means of Figure 3 The contour map shown is transformed using coordinates to obtain a series of function curves. The mathematical expressions for these functions are:

[0059] y=(arccos(a / cos(x*arccos(a)*2)) / arccos(a)) / 2;

[0060] Where x is the normalized coordinate of the interdigital transducer electrode structure 11 in the second direction Y, and its value ranges from [-0.5, 0.5]; y is the normalized coordinate of the interdigital transducer electrode structure 11 in the first direction X, and its value ranges from [0, 0.5]; a is the weighting factor, and its value ranges from [0.01, 0.99].

[0061] Reference Figure 4 , Figure 4 The function curve corresponding to the above mathematical expression is shown. Figure 4 In the function curve shown, the x-axis coordinate ranges from [-0.5, 0.5], and the y-axis coordinate ranges from [0, 0.5]. The larger the value of the weighting factor a, the smoother the weighted function will be. The edges of the finger strips in the first interdigital electrode 111 and the edges of the finger strips in the second interdigital electrode 112 are arranged according to the function curve corresponding to the above mathematical expression with a determined weighting factor a.

[0062] In some embodiments, the weighting factor 'a' in the apodization function takes values ​​in the range of [0.4, 0.6].

[0063] It should be noted that the larger the value of the weighting factor 'a', the better the suppression effect on the transverse mode when the fingers in the interdigital transducer electrode structure 11 are arranged according to the corresponding function curve, but it may lead to a decrease in the quality factor Q. Therefore, to balance the two performance characteristics, a median weighting factor can be used. For example, the weighting factor 'a' can be equal to 0.4, 0.5, or 0.6, etc.

[0064] It should be noted that normalization refers to the coordinate transformation of the target length or target width of the interdigital transducer structure 11 in one direction. Since the third and fourth curves are formed within the aperture region 113, which is located within the area enclosed by the first and second curves, the corresponding lengths or widths of the third and fourth curves during normalization are less than or equal to the corresponding lengths or widths of the first and second curves.

[0065] by Figure 1Taking the interdigital transducer 10 shown as an example, the number of the first, second, third, and fourth curves is one each. The total length L of the interdigital transducer electrode structure 11 in the second direction Y is normalized as the target length. That is, the midpoint of the total length L is taken as the origin, and the two ends are taken as -0.5 and 0.5 respectively. After normalization, a set of points with a value range of [-0.5, 0.5] is formed, which serves as the x-axis of the first, second, third, and fourth curves. The midpoint of the total width W of the interdigital transducer electrode structure 11 in the first direction X is taken as the origin, and both ends are taken as 0.5. The target width is normalized with W / 2. From the midpoint of the total width W, normalization is performed to both sides to form two set of points with a value range of [0, 0.5], which serve as the y-axis of the first, second, third, and fourth curves respectively.

[0066] In this example, the midpoint of the total width W of the interdigital transducer structure 11 in the first direction X is taken as the origin. Therefore, the first curve, the second curve, the third curve, and the fourth curve are connected on the center line cl. Of course, the target length and / or target width can also be selected according to requirements. For example, a certain distance can be reserved on both sides of the interdigital transducer structure 11 in the second direction Y to prevent apodization, and / or they can not intersect on the center line in the first direction X.

[0067] According to the interdigital transducer 10 of this application, by apodizing the edges of the interdigital transducer electrode structure 11 and providing apodization mass load 14 in the aperture region 113, a specific apodization curve is used to block the propagation of the transverse mode, thereby suppressing the transverse mode without reducing the quality factor.

[0068] Reference Figure 5 , Figure 5 The structure of a second type of interdigital transducer is shown. In some embodiments, there are multiple first, second, third, and fourth curves, all arranged along the second direction Y. Adjacent curves in the second direction Y are connected, and the first and second curves opposite each other along the first direction X are connected on the center line. The third and fourth curves opposite each other along the first direction X are connected on the center line.

[0069] In this embodiment, multiple first curves, second curves, third curves, and fourth curves can be set. Multiple target lengths are formed by dividing the total length L along the second direction Y of the interdigital transducer structure 11. Each target length is normalized to form a set of points with values ​​ranging from [-0.5, 0.5], which serves as the x-axis of each of the first, second, third, and fourth curves. The normalization of the y-axis of each of the first, second, third, and fourth curves can be referred to the foregoing. Therefore, the interdigital transducer structure 11 can be envelope-weighted using the aforementioned function curves, and the transverse mode can be suppressed as needed.

[0070] The x-axis coordinate range of the apodization function is normalized by the length L / M of the interdigital transducer electrode structure 11 in the second direction Y, and the y-axis coordinate range of the apodization function is normalized by the width of the interdigital transducer electrode structure 11 from the center line to one side in the first direction X, where L is the total length of the interdigital transducer electrode structure 11 in the second direction Y, and M is the number of the first, second, third, or fourth curves. Alternatively, a portion of the length within the aperture region 113 can be reserved without apodization.

[0071] In some embodiments, the mass load 14 is made of metal and is shaped like a dot; or the mass load 14 is made of dielectric material and is shaped like a dot or a strip.

[0072] The metal can be copper, silver, or gold, etc. A dielectric is an insulating material that can generate polarization under the influence of an external electric field, possessing good insulation and the ability to store charge. Dielectrics can be crystalline or amorphous. Crystalline dielectrics include quartz or sapphire; amorphous dielectrics include glass, resin, or ceramics, etc.

[0073] It should be noted that a point-like mass load 14 refers to a mass load 14 with a small length-to-width ratio in the two perpendicular directions, and its outer contour can be a regular or irregular circle, ellipse, or polygon. A strip-like mass load 14 refers to a mass load 14 with a large length-to-width ratio in the two perpendicular directions, usually elongated, and its length direction is usually the same as the extension direction of the strip. When the mass load 14 is point-like, the curve it forms can be the curve formed by connecting the centers of the mass load 14. When the mass load 14 is strip-like, the curve it forms can be the curve formed by connecting the midpoints between the two ends of the mass load 14 in the length direction.

[0074] In some embodiments, when the mass load 14 is dot-shaped, the length of the mass load 14 in the first direction is 0.3λ-2λ, where λ is the acoustic wavelength defined by the interdigital transducer electrode structure 11; the width of the mass load 14 in the second direction is 0.5-1.5 times the width of the finger strip. By adjusting the size of the mass load 14, the suppression effect of the mass load 14 on the transverse mode can be further optimized.

[0075] In some embodiments, the first curve, the second curve, the third curve, and the fourth curve also satisfy the following random function:

[0076] y'=y±b*W;

[0077] Where y' is the corrected y value, b is a random number with a value range of (0, 0.1], and W is the total width of the aperture region in the first direction.

[0078] The apodization curve formed by the edge of the interdigital transducer electrode structure 11 and the apodization curve formed by the mass load 14 can also be superimposed with a random function. For example, taking the apodization curve formed by the edge of the finger strip of the real finger as an example, under the superimposed random function, the length of the real finger can be randomly increased or decreased by a certain length (i.e., b*W), and the corresponding imaginary finger will be decreased or increased by a certain length (i.e., b*W). Furthermore, the position of the mass load 14 on the real finger can be adjusted by a certain length (i.e., b*W) along the extension of the finger strip, and this length does not exceed 10% of the total width W of the interdigital transducer electrode structure 11 in the first direction X.

[0079] As an example, in an apodization curve of an interdigital transducer electrode structure 11, one or more random numbers can be set. In this apodization curve, the random function can be superimposed only on a portion of the finger edges and / or the mass load 14, or it can be superimposed on all the finger edges and / or the mass load 14. When an interdigital transducer electrode structure 11 includes multiple first curves and multiple second curves, the random numbers among the first curves can be the same or different, and the random numbers among the second curves can be the same or different.

[0080] In some embodiments, the random number b in the random function takes values ​​in the range of [0.04, 0.06].

[0081] It should be noted that superimposing a portion of the random function onto the apodization function can suppress spurious modes near the resonant point. However, this will slightly reduce the resonator's quality factor. To achieve a more balanced device performance, the random number can typically be set to an intermediate value. For example, the random number b could be 0.04, 0.05, or 0.06.

[0082] Reference Figure 6 and Figure 7 , Figure 6 The structure of the interdigital transducer in the second related technology is shown. Figure 7 The structure of the interdigital transducer in the second related technology is shown. Figure 1 The structure shown is an example of Embodiment 1. Figure 6 The structure shown is used as a comparative example. Figure 2 The structure shown serves as a comparative example two and Figure 7 The structure shown is used as Comparative Example 3 for performance comparison. Figure 6 In the structure shown, only the edges of the interdigital transducer electrode structure 11 use the apodization function in the above embodiment, but no mass load is set.

[0083] Reference Figure 8 , Figure 9 and Figure 10 , Figure 8The admittance performance curves of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown. Figure 9 The admittance real part performance curves of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown. Figure 10 Bode-Q curves for quality factors are shown for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0084] As can be seen from the figures, the comparison between Example 1 and Comparative Example 2 illustrates that Example 1 can suppress transverse modes without reducing the quality factor. The comparison between Example 1 and Comparative Example 1 further illustrates that Example 1 can suppress transverse modes without affecting the quality factor. The comparison between Comparative Example 1 and Comparative Example 2 illustrates that Comparative Example 1, using the weighting function proposed herein, can suppress transverse modes to a large extent, but some transverse modes remain. Comparative Example 3, using mass loading, can suppress transverse modes compared to Comparative Example 2, but a significant portion remains. Example 1 further suppresses transverse modes compared to Comparative Example 3. Therefore, the interdigital transducer 10 provided by the embodiments of this application has a further improved transverse mode suppression effect without reducing the quality factor of the resonator.

[0085] Reference Figure 11 One embodiment of this application also provides an elastic wave resonator, including a piezoelectric layer 20 and an interdigital transducer 10 formed on the piezoelectric layer 20 according to the foregoing. The specific structure and principle of the interdigital transducer 10 can be referred to the foregoing embodiments, and will not be repeated here.

[0086] When the interdigital transducer 10 is excited by an alternating electrical signal, it generates a periodically distributed electric field. Due to the inverse piezoelectric effect, corresponding elastic deformation is excited near the surface of the piezoelectric layer 20, causing the piezoelectric layer 20 to vibrate and forming surface acoustic waves propagating along the surface. Elastic wave resonators can also be used to form filters, etc.

[0087] According to the elastic wave resonator of this application, by employing an interdigital transducer that effectively suppresses transverse modes, in-band and passband ripple can be reduced, device losses can be avoided, and device performance can be improved. The interdigital transducer 10 can also employ the technical solutions mentioned in the above embodiments, which also have the corresponding technical effects.

[0088] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. An interdigital transducer, characterized in that, include: The interdigitated transducer electrode structure includes a first interdigitated electrode and a second interdigitated electrode arranged opposite to each other along a first direction. Multiple fingers of the first interdigitated electrode and the second interdigitated electrode are staggered along a second direction to form an aperture region. The edges of the fingers of the first interdigitated electrode form a first curve, and the edges of the fingers of the second interdigitated electrode form a second curve. The first curve and the second curve are located on both sides of the center line of the interdigitated transducer electrode structure. The first direction and the second direction intersect, and the center line is parallel to the second direction. Multiple mass loads are formed on the interdigitated transducer structure and located within the aperture region. Each mass load is arranged to form at least one third curve and at least one fourth curve, which are located on both sides of the center line. Reflective gratings are arranged along the second direction on both sides of the interdigital transducer structure; The first curve, the second curve, the third curve, and the fourth curve all satisfy the following apodization function: y=(arccos(a / cos(x*arccos(a)*2)) / arccos(a)) / 2; x is the normalized coordinate of the interdigital transducer electrode structure in the second direction, with a value range of [-0.5, 0.5]; y is the normalized coordinate of the interdigital transducer electrode structure in the first direction, with a value range of [0, 0.5]; a is the weighting factor, with a value range of [0.01, 0.99].

2. The interdigital transducer according to claim 1, characterized in that, The number of the first curve and the number of the second curve are both one, and they are connected on the center line. The number of the third curve and the number of the fourth curve are also both one, and they are connected on the center line. The x-axis coordinate range of the apodization function is normalized by the total length of the aperture region in the second direction, and the x-axis coordinate range of the apodization function is normalized by the width of the aperture region from the center line to one side in the first direction.

3. The interdigital transducer according to claim 1, characterized in that, There are multiple first curves, second curves, third curves and fourth curves, and they are all arranged along the second direction. Adjacent curves in the second direction are connected, and the first curve and the second curve that are opposite to each other in the first direction are connected on the center line. The third curve and the fourth curve that are opposite to each other in the first direction are connected on the center line. Wherein, the x-axis coordinate range of the apodization function is normalized by the length L / M of the interdigital transducer structure in the second direction, and the y-axis coordinate range of the apodization function is normalized by the width of the interdigital transducer structure from the center line to one side in the first direction, where L is the total length of the interdigital transducer structure in the second direction, and M is the number of the first curve, the second curve, the third curve, or the fourth curve.

4. The interdigital transducer according to any one of claims 1-3, characterized in that, The mass load is made of metal and has a dot-like shape; or, The mass load is made of dielectric material and has a dot-like or strip-like shape.

5. The interdigital transducer according to claim 4, characterized in that, When the mass load is in the form of a point, the length of the mass load in the first direction is 0.3λ-2λ, where λ is the acoustic wavelength defined by the interdigital transducer structure; the width of the mass load in the second direction is 0.5-1.5 times the width of the finger strip.

6. The interdigital transducer according to any one of claims 1-3, characterized in that, The first interdigital electrode includes a first true finger and a first virtual finger, and the second interdigital electrode includes a second true finger and a second virtual finger. The first true finger and the second virtual finger are arranged opposite to each other along the first direction, and the second true finger and the first virtual finger are arranged opposite to each other along the first direction. The edge of the finger strip of the first true finger forms the first curve, and the edge of the finger strip of the second true finger forms the second curve.

7. The interdigital transducer according to claim 6, characterized in that, At least a portion of the mass load is located at the fingertip of the first or second true finger.

8. The interdigital transducer according to any one of claims 1-3, characterized in that, The first curve, the second curve, the third curve, and the fourth curve also satisfy the following random function: y'=y±b*w; Where y' is the corrected y value, b is a random number with a value range of (0, 0.1], and w is the total width of the aperture region in the first direction.

9. The interdigital transducer according to any one of claims 1-3, characterized in that, The weighting factor 'a' in the apodization function has a value range of [0.4, 0.6].

10. An elastic wave resonator, characterized in that, It includes a piezoelectric layer and an interdigital transducer formed on the piezoelectric layer according to any one of claims 1-9.

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