A temperature-compensated surface acoustic wave resonator and its fabrication method

Abstract

This invention discloses a surface acoustic wave (SAW) resonator with temperature compensation and its fabrication method, placing it within the technical field of SAW resonators. Through a first insertion layer, different sound velocity propagation regions can be formed along a first direction, generating reflections of transverse mode stray sound waves at the interface of different media. This avoids exciting transverse mode resonance and does not affect the main acoustic propagation mode, effectively suppressing transverse stray modes. The weighted gradient design of the finger strip length causes various stray modes to reflect in different directions, making it less likely for resonance to form, avoiding additional energy dissipation, and more effectively improving the resonator's performance. Compared to resonators that require abrupt changes in sound velocity on the finger strip, this invention eliminates the need for such a feature, reducing the resonator's area. The second temperature compensation layer has a lower density than the first temperature compensation layer; this relatively loose second temperature compensation layer does not affect the temperature compensation effect and shortens the deposition time.

Description

Technical Field

[0001] This invention relates to the field of surface acoustic wave (SAW) resonators, and more particularly to a temperature-compensated SAW resonator and its fabrication method. Background Technology

[0002] For TC-SAW (Temperature Compensated-Surface Acoustic Wave) resonators, there are transverse resonant modes, that is, clutter appears in and near the passband. This clutter increases device losses, causes the quality factor Q to fluctuate significantly, and reduces the performance of the resonator and filter.

[0003] To suppress transverse stray modes in temperature-compensated surface acoustic wave (SAW) resonators, one approach is to add dummy fingers. This involves adding dummy fingers to the busbar opposite the electrode fingers to alter the sound velocity and suppress transverse modes. However, the suppression effect of dummy fingers is poor, and it also increases the area occupied by the acoustic device. Another approach is to add a sound velocity abrupt change section. This involves adding abrupt change structures at the ends of the electrode fingers or other locations to suppress transverse modes. However, due to limitations in photolithography, the formation of the sound velocity abrupt change section is often size-restricted, resulting in an excessively large device area and the potential for acoustic diffraction. A third approach is to modify the substrate structure. This involves etching grooves into the substrate and creating sound velocity-changing structures within them to suppress transverse modes. However, this complicates the process, increases the number of mask layers, and raises manufacturing costs. Furthermore, the suppression effect is also affected by material limitations.

[0004] Therefore, how to suppress transverse stray modes in a temperature-compensated surface acoustic wave resonator is the key problem that this technical solution aims to solve. Summary of the Invention

[0005] In order to solve at least one of the technical problems mentioned in the background art, the present invention aims to provide a temperature-compensated surface acoustic wave resonator and its manufacturing method, which can utilize a finger strip weighted gradient structure, combined with a first insertion layer with unchanged or gradient boundaries to form reflection to avoid exciting transverse mode resonance, avoid setting fake fingers, thereby reducing the area of ​​the resonator, reducing the process difficulty and accelerating the manufacturing speed.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, embodiments of the present invention provide a temperature-compensated surface acoustic wave resonator, including... piezoelectric substrate; An interdigitated structure layer is located on one side of the piezoelectric substrate along a third direction; the interdigitated structure layer includes a first bus bar and a second bus bar disposed opposite each other in a first direction, and fingers arranged crosswise on the first bus bar and the second bus bar; the fingers on the first bus bar are spaced apart in a second direction; the fingers on the second bus bar are spaced apart in a second direction; the first direction and the second direction are parallel to the surface of the piezoelectric substrate, and the first direction and the second direction are perpendicular to each other; A first temperature compensation layer is located on one side of the piezoelectric substrate along a third direction and completely covers the interdigitated structure layer in the third direction; the lengths of adjacent fingers on the first busbar / second busbar are different; and it also includes: The first insertion layer is located on the side of the first temperature compensation layer away from the interdigital structure layer, and its projection in the third direction covers all the fingers in the second direction; The projection of the first boundary of the first insertion layer in a third direction lies between the end of the shortest finger and the end of the longest finger on the second busbar, and the projection of the second boundary of the first insertion layer in a third direction lies between the end of the shortest finger and the end of the longest finger on the first busbar; or The contour of the projection of the first insertion layer in the third direction is the fitted curve of the end of the finger strip.

[0007] Furthermore, in any adjacent intersecting finger strips, the distance along the first direction between the finger strip end on the first busbar and the finger strip end on the second busbar is the aperture, and the difference between the maximum and minimum values ​​of the aperture is set within a first range, the first range being 1-5 times the wavelength of the sound wave in the main acoustic mode.

[0008] Furthermore, it also includes a second temperature compensation layer, which is located on one side of the first temperature compensation layer along the third direction and completely covers the first insertion layer in the third direction.

[0009] Furthermore, the material of the first insertion layer includes silicon nitride.

[0010] Furthermore, the material of the first temperature compensation layer and / or the second temperature compensation layer includes silicon dioxide.

[0011] Furthermore, the second temperature compensation layer has a lower density than the first temperature compensation layer.

[0012] Secondly, embodiments of the present invention provide a method for fabricating a temperature-compensated surface acoustic wave resonator, including... Provide piezoelectric substrates; An interdigitated structure layer is formed on one side of a piezoelectric substrate. The interdigitated structure layer includes a first busbar and a second busbar disposed opposite each other in a first direction, and fingers arranged crosswise on the first busbar and the second busbar. The fingers on the first busbar are spaced apart in a second direction, and the fingers on the second busbar are spaced apart in a second direction. The first direction and the second direction are parallel to the surface of the piezoelectric substrate, and the first direction and the second direction are perpendicular to each other. A first temperature compensation layer is formed on one surface of the piezoelectric substrate along a third direction, the first temperature compensation layer completely covering the interdigitated structure layer in the third direction; the lengths of adjacent fingers on the first busbar / second busbar are different; and it also includes: A first insertion layer is formed on the side of the first temperature compensation layer away from the interdigitated structure layer, and the projection of the first insertion layer in the third direction covers all the fingers in the second direction; The first boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the second busbar, and the second boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the first busbar; or The contour of the projection of the first insertion layer in the third direction is the fitted curve of the end of the finger strip.

[0013] Furthermore, in any adjacent intersecting finger strips, the distance along the first direction between the finger strip end on the first busbar and the finger strip end on the second busbar is the aperture, and the difference between the maximum and minimum values ​​of the aperture is set to 1-5 times the acoustic wavelength of the main acoustic mode.

[0014] Furthermore, it also includes: A second temperature compensation layer is formed on one side of the first temperature compensation layer along the third direction, and the second temperature compensation layer completely covers the first insertion layer in the third direction.

[0015] Furthermore, the material of the first insertion layer includes silicon nitride.

[0016] Furthermore, the material of the first temperature compensation layer and / or the second temperature compensation layer includes silicon dioxide.

[0017] Furthermore, the second temperature compensation layer has a lower density than the first temperature compensation layer.

[0018] Compared with the prior art, the beneficial effects of the present invention are: by adding a first insertion layer on the side of the first temperature compensation layer away from the interdigitated structure layer, a sound propagation region with different sound speeds along the first direction can be formed, and reflection of transverse mode stray sound waves can be generated at the interface of different media, avoiding the excitation of transverse mode resonance and not affecting the main acoustic propagation mode, effectively suppressing transverse stray modes and improving the performance of the resonator. The weighted gradient design of the finger bar length causes various miscellaneous modes to reflect in different directions, making it less likely to form resonance, avoiding additional energy dissipation, and more effectively improving the performance of the resonator; Compared to resonators that require a sudden change in sound velocity on the finger bar, the technical solution of the present invention does not require a sudden change in sound velocity, which can reduce the area of ​​the resonator; The second temperature compensation layer has a lower density than the first temperature compensation layer. The relatively loose second temperature compensation layer will not affect the temperature compensation effect and can shorten the deposition time. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of a temperature-compensated surface acoustic wave resonator in a vertical cross section is provided for an embodiment of the present invention; Figure 2 This is a top view of a structure with a rectangular first insertion layer added to a temperature-compensated surface acoustic wave resonator according to an embodiment of the present invention; Figure 3 A schematic diagram of a cross-sectional line provided for an embodiment of the present invention; Figure 4 A schematic diagram of an interdigitated structure layer with unevenly varying finger length provided in an embodiment of the present invention; Figure 5 A top view of a structure with an elliptical first insertion layer added to a temperature-compensated surface acoustic wave resonator provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of a double-layer temperature-compensated surface acoustic wave resonator in a vertical cross section, provided by an embodiment of the present invention. Figure 7 This is a schematic diagram illustrating the change in sound speed perpendicular to the direction of sound wave propagation, provided as an embodiment of the present invention. Figure 8 This is a simulation result comparing the admittance-frequency curves of a temperature-compensated surface acoustic wave resonator and a conventional resonator provided in an embodiment of the present invention. Figure 9 This is a simulation result comparing the conductance-frequency curves of a temperature-compensated surface acoustic wave resonator and a traditional resonator according to an embodiment of the present invention. Figure 10 This is a schematic diagram of the structure of a SAW resonator in a vertical cross section, provided by an embodiment of the present invention. Figure 11 A schematic diagram of the structure of a TF-SAW resonator in a vertical cross section is provided for an embodiment of the present invention; Figure 12 A flowchart illustrating a method for fabricating a temperature-compensated surface acoustic wave resonator according to an embodiment of the present invention; Figure 13 A flowchart illustrating a method for fabricating a double-layer temperature-compensated surface acoustic wave resonator, as provided in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Surface acoustic wave (SAW) resonators and filters are widely used acoustic devices in the radio frequency (RF) field, combining low insertion loss and good suppression performance in a small size. They primarily utilize the piezoelectric effect to convert electrical energy into and out of mechanical energy. However, SAW also has limitations, one of which is its susceptibility to temperature changes: as temperature rises, the stiffness of the substrate material decreases, and the velocity of sound also decreases. Based on this, a new device design has gradually gained increasing application in RF filtering devices in recent years: temperature-compensated SAW filters (TC-SAW). TC-SAW improves temperature drift by coating the interdigitated electrode structure with a layer of material whose stiffness increases with temperature.

[0022] For TC-SAW resonators, laterally propagating acoustic waves cause the resonator to exhibit lateral resonant modes, i.e., clutter appearing in and near the passband. This clutter increases device losses, causes significant fluctuations in the Q value, and degrades the performance of the resonator and filter. Therefore, how to suppress lateral spurious modes in surface acoustic wave resonators with temperature compensation is the key problem that this technical solution aims to solve.

[0023] To address the aforementioned problems in the prior art, this invention provides a temperature-compensated surface acoustic wave resonator and its fabrication method, which will be described in detail below.

[0024] In a first aspect, embodiments of the present invention provide a surface acoustic wave resonator with temperature compensation function.

[0025] Example 1: like Figure 1 As shown, Figure 1 A schematic diagram of the structure of a temperature-compensated surface acoustic wave resonator in a vertical cross-section is provided for an embodiment of the present invention, including... Piezoelectric substrate 101; Interdigitated structure layer 102; First temperature compensation layer 103; First insertion layer 104.

[0026] and Figure 1 Correspondingly, such as Figure 2 As shown, Figure 2 This is a top view of a structure with a rectangular first insertion layer added to a temperature-compensated surface acoustic wave resonator provided in an embodiment of the present invention.

[0027] The interdigitated structure layer 202 is located on the surface of the piezoelectric substrate 201 along a third direction, including a first busbar 2021 and a second busbar 2022 disposed opposite to each other in a first direction, and interdigitated fingers 2023 arranged crosswise on the first busbar 2021 and the second busbar 2022; the fingers 2023 on the first busbar 2021 are spaced apart in a second direction, and the fingers 2023 on the second busbar 2022 are spaced apart in a second direction; the first direction and the second direction are parallel to the surface of the piezoelectric substrate 201, and the first direction and the second direction are perpendicular to each other; The lengths of adjacent finger strips 2023 on the first busbar 2021 and the second busbar 2022 are different; The first temperature compensation layer (which coincides with the piezoelectric substrate in the top view and is therefore not shown in the figure) is located on one side of the piezoelectric substrate 201 along the third direction and completely covers the interdigitated structure layer 202 in the third direction. It also includes: a first insertion layer 204 (shaded part in the figure), located on the side of the first temperature compensation layer away from the interdigitated structure layer 202, whose projection in the third direction covers all the fingers 2023 in the second direction; The projection of the first boundary of the first insertion layer in the third direction lies between the end of the shortest finger and the end of the longest finger on the second busbar, and the projection of the second boundary of the first insertion layer in the third direction lies between the end of the shortest finger and the end of the longest finger on the first busbar.

[0028] The aforementioned "first direction" refers to the direction parallel to the finger strip, the "second direction" refers to the direction parallel to the first bus bar / second bus bar, and the "third direction" refers to the direction perpendicular to the plane containing any surface of the piezoelectric substrate 201.

[0029] It should be noted that, Figure 1 The cross-sectional structure shown is a "schematic diagram" because it is necessary to simultaneously represent structural features such as busbars and electrode fingers in one drawing. Figure 1 It is equivalent to combining the feature parts of two vertical cross-sectional images.

[0030] like Figure 3As shown, Figure 3 This is a schematic diagram of a cross-sectional line provided for an embodiment of the present invention. Figure 3 It contains two section lines, AA' and BB'. The sectional views obtained along these two section lines are combined to form a... Figure 1 The diagram shows a vertical cross-section.

[0031] The piezoelectric substrate 201 can be made of materials such as quartz, aluminum nitride, LN (lithium niobate, LiNbO3), LT (lithium tantalate, LiTaO3), etc. This invention does not limit the materials used, but lithium niobate or lithium tantalate is preferred. These materials have advantages such as excellent piezoelectric effect and electromechanical coupling effect, and are widely used in surface acoustic wave devices.

[0032] The interdigitated structure layer 202, deposited on the piezoelectric substrate 201, is the most basic unit constituting the surface acoustic wave resonator. It includes a first busbar 2021 and a second busbar 2022 spaced apart in a first direction, and two sets of interdigitated fingers 2023 spaced alternately in a second direction. One set of interdigitated fingers 2023 extends from the first busbar 2021 toward the second busbar 2022, but does not touch the second busbar 2022. The other set of interdigitated fingers 2023 extends from the second busbar 2022 toward the first busbar 2021, but does not touch the first busbar 2021. The lengths of adjacent interdigitated fingers 2023 on the first busbar 2021 and the lengths of adjacent interdigitated fingers 2023 on the second busbar 2022 are different, and the variation can be uniform or non-uniform.

[0033] For example, Figure 2 The lengths of the finger strips 2023 on the first busbar 2021 and the second busbar 2022 both exhibit a uniform variation. For example... Figure 4 As shown, Figure 4 This is a schematic diagram of an interdigitated finger structure layer with unevenly varying finger strip length, provided in an embodiment of the present invention. Figure 4 The lengths of the finger strips 2023 on the first busbar 2021 and the second busbar 2022 both exhibit uneven variations.

[0034] In any adjacent intersecting finger strips, the distance along the first direction between the finger strip ends on the first busbar 2021 and the finger strip ends on the second busbar 2022 is the aperture. Due to variations in finger strip length, different finger strip aperture sizes are formed. Figure 2 For example, the aperture of 2024 is obviously larger than that of 2025. The different apertures of adjacent finger strips are conducive to the reflection of various miscellaneous modes in different directions, thus making it less likely to form resonance, avoiding additional energy dissipation, and more effectively improving the performance of the resonator.

[0035] The difference between the maximum and minimum aperture values ​​is set within a first range, preferably 1-5 times the wavelength of the acoustic wave in the main acoustic mode (i.e., 1λ-5λ). The range of 1λ-5λ is an experimentally optimal conclusion. If the value is too large, it will cause the aperture gradient to be too large, thereby affecting the propagation of the main acoustic mode and causing energy loss. Limiting it to the range of 1λ-5λ can suppress the transverse mode and avoid affecting the propagation of the main acoustic mode.

[0036] Since SAW devices are susceptible to temperature changes, temperature drift can be mitigated by coating them with a temperature compensation material that has a positive frequency temperature coefficient.

[0037] A first temperature compensation layer is coated on the interdigitated structure layer 202 and can be made of silicon dioxide, but is not limited to this material. The thickness of the first temperature compensation layer is greater than the thickness of the interdigitated structure layer 202 (i.e., it must completely cover the interdigitated structure layer), and is generally set in the range of 0.2 to 0.5 times (i.e., 0.2λ to 0.5λ) of the wavelength of the main acoustic mode. It is used to compensate for the negative temperature effect of the resonator. In addition, sandwiched between the interdigitated structure layer 202 and the first insertion layer 204, it can also provide an insulating effect. For certain special piezoelectric substrates (e.g., 128°YXLiNbO3 substrates), the first temperature compensation layer can effectively suppress the transverse shear wave mode excited by the finger strips.

[0038] The first insertion layer 204 is deposited on the first temperature compensation layer and can be made of silicon nitride (Si3N4). Silicon nitride can improve the sound velocity. The sound wave of the main acoustic mode propagates along the length of the busbar in the interdigitated structure layer. The projection of the first insertion layer in the third direction covers all the fingers in the second direction. Figure 2 For example, Figure 2 The first insertion layer 204 is rectangular, with its longer side covering all the finger strips.

[0039] The projection of the first boundary of the first insertion layer 204 in the third direction lies between the end of the shortest finger and the end of the longest finger on the second busbar 2022, and the projection of the second boundary in the third direction lies between the end of the shortest finger and the end of the longest finger on the first busbar 2021. Figure 2 For example, Figure 2 The first boundary (i.e., the left boundary) of the first insertion layer 204 is projected in the third direction between the end of the longest finger and the end of the shortest finger on the second busbar 2022, and the second boundary (i.e., the right boundary) is projected in the third direction between the end of the longest finger and the end of the shortest finger on the first busbar 2021, further enhancing the effect of sound velocity variation.

[0040] Sound waves are a typical type of elastic wave. When elastic waves propagate through matter, they encounter the interface between different media (i.e., regions with different sound velocities), which reflects waves whose propagation direction is not parallel to the interface direction. This prevents the formation of stray modes and thus avoids energy dissipation. Therefore, by increasing the sound velocity in this region through the first insertion layer, sound waves in directions other than the propagation direction of the main acoustic mode are reflected at the sound velocity interface, thereby dissipating their energy. The arrangement of the first insertion layer (projection in the third direction covering all finger strips in the second direction) ensures that sound waves in the propagation direction of the main acoustic mode (i.e., along the direction of the busbar) are not affected, thus achieving the removal of transverse stray modes.

[0041] Example 2: The difference from Embodiment 1 is that the two side boundaries of the first insertion layer located between the first busbar and the second busbar are not straight lines parallel to the second direction, but curves, satisfying that the contour of the projection of the first insertion layer in the third direction is the fitting curve of the end of the finger bar.

[0042] like Figure 5 As shown, Figure 5 This is a top view of a structure with an elliptical first insertion layer added to a temperature-compensated surface acoustic wave resonator, as provided in an embodiment of the present invention.

[0043] Figure 5 In this process, any point on the end of each finger strip (preferably the midpoint of the finger strip end) is taken as a discrete point. The fitting curve obtained after fitting these discrete points is approximately an ellipse. The curve fitting method can be some common fitting methods such as least squares method, polynomial fitting, spline interpolation method, etc. This embodiment of the invention does not limit this. The fitting curve is used as the outline of the projection of the first insertion layer in the third direction. That is to say, the projection of the first insertion layer in the third direction does not need to perfectly coincide with the end of the finger strip. As long as it can roughly cover the end of the finger strip, the effect of sound speed change can be achieved, reducing the process difficulty and saving manufacturing time.

[0044] It should be noted that, Figure 5 This is just one example. By adjusting the length of the finger strips in the interdigital structure layer, the fitting curves at the ends of the finger strips can be varied. For example, if the length of the finger strips is designed to gradually shorten from the middle to the sides, the curve formed at the ends of the finger strips is approximately an ellipse; if the length of the finger strips is designed to gradually lengthen from the middle to the sides, the curve formed at the ends of the finger strips is approximately a hyperbola. Of course, it is not limited to these two cases. The curve formed at the ends of the finger strips can also be any other irregular shape, as long as the projection contour of the first insertion layer in the third direction roughly covers the ends of the finger strips.

[0045] The first insertion layer, through a gradient design, creates distinct regions of different sound velocities in the direction parallel to the finger strips, reflecting transverse miscellaneous modes and avoiding the excitation of transverse mode resonance.

[0046] Sound waves are a typical type of elastic wave. When elastic waves propagate through matter, they encounter the interface between different media (i.e., regions with different sound velocities), which reflects waves whose propagation direction is not parallel to the interface direction. This prevents the formation of stray modes and thus avoids energy dissipation. Therefore, by increasing the sound velocity in this region through the first insertion layer, sound waves in directions other than the propagation direction of the main acoustic mode are reflected at the sound velocity interface, thereby dissipating their energy. The arrangement of the first insertion layer (projection in the third direction covering all finger strips in the second direction) ensures that sound waves in the propagation direction of the main acoustic mode (i.e., along the direction of the busbar) are not affected, thus achieving the removal of transverse stray modes.

[0047] Example 3: Based on Embodiment 1 or Embodiment 2, a second temperature compensation layer is further included, located on one side of the first temperature compensation layer along the third direction, and completely covering the first insertion layer in the third direction.

[0048] like Figure 6 As shown, Figure 6 This is a schematic diagram of the structure of a double-layer temperature-compensated surface acoustic wave resonator in a vertical cross section, provided as an embodiment of the present invention.

[0049] The difference from Embodiment 1 or Embodiment 2 is that a second temperature compensation layer 605 is added above the first insertion layer. This second temperature compensation layer 605 can be made of silicon dioxide or other temperature compensation materials with a positive frequency temperature coefficient. The present invention does not limit the material to this. The second temperature compensation layer covers the first insertion layer and has a thickness of 1 to 1.5 times that of the first insertion layer. It can be used to fine-tune the frequency of the resonator through a trimming process, protect the first insertion layer and the internal structure of the resonator, and further compensate for negative temperature effects. In a preferred embodiment, the width of the second temperature compensation layer is consistent with the width of the first temperature compensation layer. Both layers cover an interdigitated structure layer in the third direction, which can further improve the temperature drift phenomenon without increasing the additional process cost.

[0050] Example 4: Building upon Example 3, a faster deposition rate is used when forming the second temperature compensation layer, resulting in a more porous temperature compensation layer. Those skilled in the art can select an appropriate deposition rate based on their experience. Since the second temperature compensation layer is used to improve the temperature compensation effect and protect the insertion layer, it does not affect the temperature compensation effect, improves thickness uniformity, and shortens the time required for the vapor deposition process.

[0051] For refractory materials like SiO2, electron beam evaporation is a commonly used process. This involves vaporizing the material, allowing particles to condense and form a film on the substrate surface. Upon reaching the surface, particles undergo reflection, surface diffusion, and collisions, forming clusters. When the number of particles exceeds a certain critical value, these clusters become stable nuclei, attracting further particles and ultimately forming a thin film. Clearly, for dense structures, the higher diffusion and collision rates amplify the critical value, leading to a greater thickness variation and poorer uniformity compared to porous structures. Therefore, using a porous structure can improve thickness uniformity while reducing the evaporation process time.

[0052] like Figure 7 As shown, Figure 7 This is a schematic diagram illustrating the change in sound speed perpendicular to the direction of sound wave propagation, provided as an embodiment of the present invention. Figure 7 In the diagram, the sound velocity is highest in the gap between the finger strip and the busbar. The finger strip and busbar reduce the sound velocity, with the finger strip having a higher sound velocity than the busbar because the busbar area is near the edge and has already attenuated due to energy dissipation. The first insertion layer, being made of silicon nitride, can increase the sound velocity, so the sound velocity in the first insertion layer area is higher than that in the finger strip areas not covered by the first insertion layer. The dashed lines correspond to the weighted gradient part of the finger strip. Since the aperture changes, the sound velocity also changes accordingly, hence the dashed lines represent this.

[0053] By using the gradual change in the length of the finger strip to form apertures of different widths, and in conjunction with the first insertion layer structure with unchanged or gradually changing boundaries, the effect of sound velocity variation is further improved, forming different sound velocity propagation regions. This maximizes the sound velocity difference at the interface, generating as many reflections of transverse mode stray sound waves as possible at this interface, thereby suppressing clutter without affecting the main acoustic propagation mode.

[0054] like Figure 8 As shown, Figure 8 This is a simulation comparison of the admittance-frequency curves of a temperature-compensated surface acoustic wave resonator (SAW) provided in this embodiment of the invention and a conventional resonator. The solid line represents the conventional resonator, and the dashed line represents the temperature-compensated SAW resonator provided in this embodiment of the invention.

[0055] Due to the excitation of transverse modes, the resonant frequency and anti-resonant frequency of a traditional resonator without a first insertion layer exhibit irregular fluctuations. However, by adding a first insertion layer, the admittance-frequency curve becomes smooth, demonstrating that it can effectively suppress transverse spurious modes in the passband range and improve the performance of the resonator.

[0056] like Figure 9 As shown, Figure 9This is a simulation comparison of the conductance-frequency curves of a temperature-compensated surface acoustic wave resonator provided in this embodiment of the invention and a conventional resonator. The solid line represents the conventional resonator, and the dashed line represents the resonator provided in this embodiment of the invention that suppresses transverse spurious modes.

[0057] In the improved resonator's conductance-frequency curve, interference is greatly reduced. Taking a frequency of around 750MHz as an example, the excitation of transverse modes at this frequency is suppressed by more than 30dB.

[0058] Example 5: The aperture weighting and first insertion layer design described in Embodiment 1 or Embodiment 2 can also be used in ordinary SAW resonators. Figure 10 As shown, Figure 10 A schematic diagram of the structure of a SAW resonator in a vertical cross-section is provided for an embodiment of the present invention, including... Piezoelectric substrate 1001; An interdigitated structure layer 1002 is located on the surface of the piezoelectric substrate 1001 along a third direction, including a first busbar 10021 and a second busbar 10022 disposed opposite to each other in a first direction, and interdigitated fingers 10023 arranged crosswise on the first busbar 10021 and the second busbar 10022; the fingers 10023 on the first busbar 10021 are spaced apart in a second direction; the fingers 10023 on the second busbar 10022 are spaced apart in a second direction; the first direction and the second direction are parallel to the surface of the piezoelectric substrate 1001, and the first direction and the second direction are perpendicular to each other; The first dielectric layer 1003 is located on one side of the piezoelectric substrate 1001 along the third direction and completely covers the interdigitated structure layer 1002 in the third direction. The lengths of adjacent finger bars on the first bus bar 10021 and the second bus bar 10022 are different; The first insertion layer 1004 is located on the side of the first dielectric layer 1003 away from the interdigital structure layer 1002, and its projection in the third direction covers all the fingers 10023 in the second direction. The projection of the first boundary of the first insertion layer 1004 in a third-party direction lies between the end of the shortest finger and the end of the longest finger on the second busbar 10022, and the projection of the second boundary of the first insertion layer 1004 in a third-party direction lies between the end of the shortest finger and the end of the longest finger on the first busbar 10021; or The profile of the first insertion layer 1004 projected in the third direction is the fitted curve of the end of the finger strip.

[0059] Similar to Embodiment 1 or Embodiment 2 described above, the SAW resonator with aperture weighting and a first insertion layer design, compared to the traditional SAW resonator, can avoid the formation of stray modes and thus avoid energy dissipation. The first insertion layer increases the sound velocity in this region and reflects sound waves from directions other than the propagation direction of the main acoustic mode at the sound velocity interface, thereby preventing transverse resonance. The arrangement of the first insertion layer (projecting in the third direction to cover all finger strips in the second direction) ensures that sound waves in the propagation direction of the main acoustic mode (i.e., along the busbar direction) are unaffected, thus achieving the removal of transverse stray modes. Furthermore, the aperture weighting gradient structure design causes various stray modes to reflect in different directions, making it less likely for them to form resonance, avoiding additional energy dissipation, and more effectively improving the resonator's performance.

[0060] Example 6: The aperture weighting and first insertion layer design described in Embodiment 1 or Embodiment 2 can also be used in TF-SAW resonators. For example... Figure 11 As shown, Figure 11 A schematic diagram of the structure of a TF-SAW resonator in a vertical cross-section is provided for an embodiment of the present invention, including... Piezoelectric substrate 1101; A piezoelectric thin film 1102 covers a piezoelectric substrate 1101; An interdigitated structure layer 1103 is located on the surface of the piezoelectric substrate 1101 along a third direction, including a first busbar 11031 and a second busbar 11032 disposed opposite to each other in a first direction, and interdigitated fingers 10033 arranged crosswise on the first busbar 11031 and the second busbar 11032; the fingers 11033 on the first busbar 11031 are spaced apart in a second direction; the fingers 11033 on the second busbar 11032 are spaced apart in a second direction; the first direction and the second direction are parallel to the surface of the piezoelectric substrate 1101, and the first direction and the second direction are perpendicular to each other; The first dielectric layer 1104 is located on one side of the piezoelectric substrate 1101 along the third direction and completely covers the interdigitated structure layer 1103 in the third direction. The adjacent finger strips on the first bus bar 11031 and the second bus bar 11032 have different lengths; The first insertion layer 1105 is located on the side of the first dielectric layer 1104 away from the interdigital structure layer 1103, and its projection in the third direction covers all the fingers 11033 in the second direction. The projection of the first boundary of the first insertion layer 1105 in a third-party direction lies between the end of the shortest finger and the end of the longest finger on the second busbar 11032, and the projection of the second boundary of the first insertion layer 1105 in a third-party direction lies between the end of the shortest finger and the end of the longest finger on the first busbar 11031; or The profile of the first insertion layer 1105 projected in the third direction is the fitted curve of the end of the finger strip.

[0061] Similar to Embodiment 1 or Embodiment 2 described above, the TF-SAW resonator with aperture weighting and a first insertion layer design, compared to the traditional TF-SAW resonator, can avoid the formation of stray modes and thus avoid energy dissipation. The first insertion layer increases the sound velocity in this region and reflects sound waves from directions other than the main acoustic mode propagation direction at the sound velocity interface, thereby preventing transverse resonance. The arrangement of the first insertion layer (projecting in the third direction to cover all finger strips in the second direction) ensures that sound waves in the main acoustic mode propagation direction (i.e., along the busbar direction) are unaffected, thus achieving the removal of transverse stray modes. Furthermore, the aperture weighting gradient structure design causes various stray modes to reflect in different directions, making them less prone to resonance and avoiding additional energy dissipation, thus more effectively improving the resonator's performance.

[0062] Secondly, corresponding to the above-described embodiments of the temperature-compensated surface acoustic wave resonator, the present invention also provides a method for manufacturing a temperature-compensated surface acoustic wave resonator.

[0063] Example 7: like Figure 12 As shown, Figure 12 A flowchart illustrating a method for fabricating a temperature-compensated surface acoustic wave resonator according to an embodiment of the present invention includes the following steps: Step 1201: Provide a piezoelectric substrate.

[0064] Specifically, piezoelectric substrates can be formed by physical vapor deposition sputtering or chemical vapor deposition. The materials used can be quartz, aluminum nitride, LN (lithium niobate, LiNbO3), LT (lithium tantalate, LiTaO3), etc. This invention does not limit the materials used, but lithium niobate or lithium tantalate is preferred. These materials have advantages such as excellent piezoelectric effect and electromechanical coupling effect, and are widely used in surface acoustic wave devices.

[0065] Step 1202: An interdigitated structure layer is formed on one side of the piezoelectric substrate. The interdigitated structure layer includes a first busbar and a second busbar disposed opposite to each other in a first direction, and fingers arranged crosswise on the first busbar and the second busbar. The fingers on the first busbar are spaced apart in a second direction, and the fingers on the second busbar are spaced apart in a second direction. The first direction and the second direction are parallel to the surface of the piezoelectric substrate, and the first direction and the second direction are perpendicular to each other. The lengths of adjacent finger bars on the first bus bar / second bus bar mentioned above are different.

[0066] A metal thin film is deposited on one side of the piezoelectric substrate, and then etched to form fingers and busbars, forming an interdigitated structure layer.

[0067] In any adjacent cross bar, the distance along the first direction between the end of the bar on the first bus bar and the end of the bar on the second bus bar is the aperture. Due to the variation in bar length, different sizes of bar apertures are formed. The different apertures of adjacent bar apertures are conducive to the reflection of various miscellaneous modes in different directions, thus making it less likely to form resonance, avoiding additional energy dissipation, and more effectively improving the performance of the resonator.

[0068] The difference between the maximum and minimum aperture values ​​is set within a first range, preferably 1-5 times the wavelength of the acoustic wave in the main acoustic mode (i.e., 1λ-5λ). The range of 1λ-5λ is an experimentally optimal conclusion. If the value is too large, it will cause the aperture gradient to be too large, thereby affecting the propagation of the main acoustic mode and causing energy loss. Limiting it to the range of 1λ-5λ can suppress the transverse mode and avoid affecting the propagation of the main acoustic mode.

[0069] Step 1203: A first temperature compensation layer is formed on one side of the piezoelectric substrate along the third direction, and the first temperature compensation layer completely covers the interdigitated structure layer in the third direction.

[0070] To mitigate temperature drift, a first temperature compensation layer is deposited on the interdigitated structure layer. Silicon dioxide can be used, but is not limited to this material. The thickness of the first temperature compensation layer is greater than the thickness of the interdigitated structure layer (i.e., it must completely cover the interdigitated structure layer). It is typically set within 0.2 to 0.5 times the wavelength of the dominant acoustic mode (i.e., 0.2λ to 0.5λ) to compensate for the negative temperature effect of the resonator. Furthermore, sandwiched between the interdigitated structure layer and the first insertion layer, it also provides insulation. For certain piezoelectric substrates (e.g., 128°YXLiNbO3 substrates), the first temperature compensation layer can effectively suppress transverse shear wave modes excited by the finger strips.

[0071] Step 1204: A first insertion layer is formed on the side of the first temperature compensation layer away from the interdigitated structure layer, and the projection of the first insertion layer in the third direction covers all the fingers in the second direction. The first boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the second busbar, and the second boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the first busbar; or The profile of the first insertion layer projected onto the third direction is the fitted curve of the end of the finger strip.

[0072] A first insertion layer is deposited on the first temperature compensation layer. Silicon nitride (Si3N4) can be used, as it can increase the velocity of sound. Sound waves propagate along the length of the busbars in the interdigitated structure layer. The projection of the first insertion layer in the third direction onto the second direction (i.e., the direction of sound wave propagation in the primary acoustic mode) covers all the fingers. The projection of the first boundary of the first insertion layer in the third direction lies between the end of the shortest finger and the end of the longest finger on the second busbar, and the projection of the second boundary in the third direction lies between the end of the shortest finger and the end of the longest finger on the first busbar; or Take any point on the end of each finger strip (preferably the midpoint of the finger strip end) as a discrete point, and use the fitted curve obtained by fitting these discrete points as the contour of the projection of the first insertion layer in the third direction. The curve fitting method can be some common fitting methods such as least squares method, polynomial fitting, spline interpolation method, etc. The embodiments of the present invention do not limit this. That is to say, the projection of the first insertion layer in the third direction does not need to perfectly coincide with the end of the finger strip. As long as it can roughly cover the end of the finger strip, the effect of sound speed change can be achieved, reducing the process difficulty and saving manufacturing time.

[0073] By using a weighted gradient design, different sound propagation regions along the first direction can be formed, generating reflections of transverse mode stray sound waves at the interface of different media. This avoids exciting transverse mode resonances and does not affect the main acoustic propagation mode, effectively suppressing transverse stray modes and improving the performance of the resonator. Furthermore, the weighted gradient structure design causes various stray modes to reflect in different directions, making it less likely for resonance to occur, avoiding additional energy dissipation, and further improving the performance of the resonator.

[0074] Example 8: like Figure 13 As shown, Figure 13 A flowchart illustrating a method for fabricating a double-layer temperature-compensated surface acoustic wave resonator according to an embodiment of the present invention includes the following steps: Step 1301, provide a piezoelectric substrate; Step 1302: An interdigitated structure layer is formed on one side of the piezoelectric substrate. The interdigitated structure layer includes a first busbar and a second busbar disposed opposite to each other in a first direction, and fingers arranged crosswise on the first busbar and the second busbar. The fingers on the first busbar are spaced apart in a second direction, and the fingers on the second busbar are spaced apart in a second direction. The first direction and the second direction are parallel to the surface of the piezoelectric substrate and are perpendicular to each other. The lengths of adjacent finger strips on the first busbar / second busbar mentioned above are different; Step 1303: A first temperature compensation layer is formed on one side of the piezoelectric substrate along the third direction, and the first temperature compensation layer completely covers the interdigitated structure layer in the third direction. Step 1304: A first insertion layer is formed on the side of the first temperature compensation layer away from the interdigitated structure layer, and the projection of the first insertion layer in the third direction covers all the fingers in the second direction. The first boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the second busbar, and the second boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the first busbar; or The profile of the first insertion layer projected onto the third direction is the fitted curve of the end of the finger strip; Step 1305: A second temperature compensation layer is formed on one side of the first temperature compensation layer along the third direction, and the second temperature compensation layer completely covers the first insertion layer in the third direction.

[0075] The difference from Embodiment 7 lies only in step 1305, where a second temperature compensation layer is deposited on the first insertion layer. This second temperature compensation layer can be made of silicon dioxide or other temperature compensation materials with a positive frequency temperature coefficient; the present invention does not limit this. The second temperature compensation layer covers the first insertion layer and has a thickness of 1 to 1.5 times that of the first insertion layer. It can be used to fine-tune the frequency of the resonator through a trimming process, protect the first insertion layer and the internal structure of the resonator, and further compensate for negative temperature effects. In a preferred embodiment, the width of the second temperature compensation layer is consistent with the width of the first temperature compensation layer, and both cover an interdigitated structure layer in the vertical projection direction, which can further improve the temperature drift phenomenon without increasing additional process costs.

[0076] Example 9: Based on Example 8, a faster deposition rate is used when forming the second temperature compensation layer, resulting in a more porous temperature compensation layer. Those skilled in the art can select an appropriate deposition rate based on their experience. Since the second temperature compensation layer is used to improve the temperature compensation effect and protect the insertion layer, it does not affect the temperature compensation effect, improves thickness uniformity, and shortens the time required for the vapor deposition process.

[0077] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0078] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0079] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0080] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0081] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intermediate element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intermediate element present. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0082] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0083] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A temperature-compensated surface acoustic wave resonator, comprising: piezoelectric substrate; An interdigitated structure layer is located on one side of the piezoelectric substrate along a third direction; the interdigitated structure layer includes a first bus bar and a second bus bar disposed opposite each other in a first direction, and fingers arranged crosswise on the first bus bar and the second bus bar; the fingers on the first bus bar are spaced apart in a second direction; the fingers on the second bus bar are spaced apart in a second direction; the first direction and the second direction are parallel to the surface of the piezoelectric substrate, and the first direction and the second direction are perpendicular to each other; A first temperature compensation layer, located on one side of the piezoelectric substrate along a third direction and completely covering the interdigitated structure layer in the third direction; characterized in that adjacent fingers on the first busbar / second busbar have different lengths; further comprising: The first insertion layer is located on the side of the first temperature compensation layer away from the interdigital structure layer, and its projection in the third direction covers all the fingers in the second direction; The projection of the first boundary of the first insertion layer in a third direction lies between the end of the shortest finger and the end of the longest finger on the second busbar, and the projection of the second boundary of the first insertion layer in a third direction lies between the end of the shortest finger and the end of the longest finger on the first busbar; or The contour of the projection of the first insertion layer in the third direction is the fitted curve of the end of the finger strip.

2. The temperature-compensated surface acoustic wave resonator according to claim 1, characterized in that, In any adjacent intersecting finger strips, the distance along a first direction between the finger strip ends on the first busbar and the finger strip ends on the second busbar is the aperture. The difference between the maximum and minimum values ​​of the aperture is set within a first range, which is 1 to 5 times the wavelength of the acoustic wave in the main acoustic mode.

3. The temperature-compensated surface acoustic wave resonator according to claim 1, characterized in that, It also includes a second temperature compensation layer, which is located on one side of the first temperature compensation layer along the third direction and completely covers the first insertion layer in the third direction.

4. The temperature-compensated surface acoustic wave resonator according to claim 1, characterized in that, The material of the first insertion layer includes silicon nitride.

5. The temperature-compensated surface acoustic wave resonator according to claim 3, characterized in that, The material of the first temperature compensation layer and / or the second temperature compensation layer includes silicon dioxide.

6. The temperature-compensated surface acoustic wave resonator according to claim 3, characterized in that, The second temperature compensation layer has a lower density than the first temperature compensation layer.

7. A method for fabricating a temperature-compensated surface acoustic wave resonator, comprising: Provide piezoelectric substrates; An interdigitated structure layer is formed on one side of a piezoelectric substrate. The interdigitated structure layer includes a first busbar and a second busbar disposed opposite each other in a first direction, and fingers arranged crosswise on the first busbar and the second busbar. The fingers on the first busbar are spaced apart in a second direction, and the fingers on the second busbar are spaced apart in a second direction. The first direction and the second direction are parallel to the surface of the piezoelectric substrate, and the first direction and the second direction are perpendicular to each other. A first temperature compensation layer is formed on one surface of the piezoelectric substrate along a third-direction direction, the first temperature compensation layer completely covering the interdigitated structure layer in the third-direction direction; characterized in that... The adjacent finger strips on the first busbar / second busbar have different lengths; it also includes: A first insertion layer is formed on the side of the first temperature compensation layer away from the interdigitated structure layer, and the projection of the first insertion layer in the third direction covers all the fingers in the second direction; The first boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the second busbar, and the second boundary of the first insertion layer is located between the end of the shortest finger and the end of the longest finger on the first busbar; or The contour of the projection of the first insertion layer in the third direction is the fitted curve of the end of the finger strip.

8. The method for fabricating a temperature-compensated surface acoustic wave resonator according to claim 7, characterized in that, In any adjacent intersecting finger strips, the distance along the first direction between the finger strip ends on the first busbar and the finger strip ends on the second busbar is the aperture, and the difference between the maximum and minimum values ​​of the aperture is set to 1-5 times the wavelength of the sound wave in the main acoustic mode.

9. The method for fabricating a temperature-compensated surface acoustic wave resonator according to claim 7, characterized in that, Also includes: A second temperature compensation layer is formed on one side of the first temperature compensation layer along the third direction, and the second temperature compensation layer completely covers the first insertion layer in the third direction.

10. The method for fabricating a temperature-compensated surface acoustic wave resonator according to claim 7, characterized in that, The material of the first insertion layer includes silicon nitride.

11. The method for fabricating a temperature-compensated surface acoustic wave resonator according to claim 9, characterized in that, The material of the first temperature compensation layer and / or the second temperature compensation layer includes silicon dioxide.

12. The method for fabricating a temperature-compensated surface acoustic wave resonator according to claim 9, characterized in that, The second temperature compensation layer has a lower density than the first temperature compensation layer.

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