A transverse exciter acoustic resonator and its fabrication method

Abstract

The present invention discloses a transversely excited bulk acoustic wave resonator and a preparation method thereof, wherein the transversely excited bulk acoustic wave resonator comprises: a substrate; a plurality of interdigital electrodes located on one side of the substrate; the plurality of interdigital electrodes are arranged along a first direction and all extend along a second direction; the first direction intersects with the second direction and are all parallel to the plane where the substrate is located; an acoustic impedance structure located on both sides of the interdigital electrodes along the first direction, the acoustic impedance structure contacts the interdigital electrodes, and the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigital electrodes. By adopting the above technical means, by arranging the acoustic impedance structure on both sides of the interdigital electrodes along the first direction, the electric field lines can be reshaped, thereby suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a transversely excited bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] Acoustic wave resonators are important components for a variety of applications, such as filters, oscillators, and sensors. The latest development in this field is the transversely excited bulk acoustic wave resonator, which is based on the principle of exciting shear acoustic waves in a rectangular resonant plate with laterally placed electrodes. Compared with traditional BAW resonators (i.e., traditional cavity BAW filters and film BAW resonators), transversely excited BAW resonators have better power handling capabilities and can achieve wider bandwidths while having excellent quality factors.

[0003] At present, in order to suppress the radiation of bulk acoustic waves from the resonant plate (i.e., piezoelectric film) to the supporting substrate, the following two methods are generally used: independent resonators or fixedly mounted resonators. The piezoelectric film suspended by the independent structure provides acoustic isolation from air or vacuum, and is also the best choice from the perspective of electromechanical coupling. However, the mechanical stress on the resonant plate is challenging to achieve mechanical stability and high thermal efficiency. On the other hand, the firmly mounted resonator uses acoustic Bragg reflection under the piezoelectric layer, providing mechanical stability and high thermal efficiency. The Bragg reflector grating consists of alternating high and low acoustic impedance layers, which effectively reflects the bulk acoustic waves radiated downward in the piezoelectric film. However, horizontal resonances very close to the antiresonance frequency of the laterally excited bulk acoustic wave resonator may be encountered. Although the resonant plate is designed to minimize stray resonances, great efforts are still required to reduce the impact of these unintended resonant modes. Summary of the invention

[0004] The embodiment of the present invention provides a transversely excited bulk acoustic wave resonator and a preparation method thereof, which can reshape the electric field lines, thereby suppressing the horizontal harmonics near the anti-resonance frequency of the main mode and improving the working performance of the resonator.

[0005] In a first aspect, an embodiment of the present invention provides a transversely excited bulk acoustic wave resonator, comprising:

[0006] substrate;

[0007] A plurality of interdigital electrodes are located on one side of the substrate; the plurality of interdigital electrodes are arranged along a first direction and extend along a second direction; the first direction intersects with the second direction and are parallel to the plane where the substrate is located;

[0008] The acoustic impedance structure is located at both sides of the interdigital electrode along the first direction, the acoustic impedance structure is in contact with the interdigital electrode, and the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigital electrode.

[0009] Optionally, the transversely excited bulk acoustic wave resonator further includes: a bus bar; the bus bar includes a first bus bar and a second bus bar arranged along the second direction;

[0010] The interdigital electrodes include a first interdigital electrode and a second interdigital electrode; the first interdigital electrode is electrically connected to the first bus bar, and the second interdigital electrode is electrically connected to the second bus bar;

[0011] The transversely excited bulk acoustic wave resonator further comprises an effective aperture region, the first interdigital electrode comprises a first electrode section located in the effective aperture region, the second interdigital electrode comprises a second electrode section located in the effective aperture region, and the first electrode section and the second electrode section are alternately arranged in sequence along the first direction;

[0012] The acoustic impedance structure is located in the effective aperture area.

[0013] Optionally, the transversely excited bulk acoustic wave resonator further includes a bus bar; the bus bar includes a first bus bar and a second bus bar arranged along the second direction;

[0014] The interdigital electrodes include a first interdigital electrode and a second interdigital electrode; the first interdigital electrode is electrically connected to the first bus bar, and the second interdigital electrode is electrically connected to the second bus bar;

[0015] The transversely excited bulk acoustic wave resonator further comprises an effective aperture region and a spacing region;

[0016] The first interdigitated electrode comprises a first electrode portion located in the effective aperture region, the second interdigitated electrode comprises a second electrode portion located in the effective aperture region, and the first electrode portion and the second electrode portion are alternately arranged in sequence along the first direction;

[0017] Along the second direction, the spacing area is located between the effective aperture area and the bus bar;

[0018] The acoustic impedance structure is located in the effective aperture area and the spacing area.

[0019] Optionally, along the second direction, the length of the acoustic impedance structure is equal to the length of the interdigital electrodes.

[0020] Optionally, along the first direction, widths of the acoustic impedance structures located on both sides of the same interdigital electrode are equal.

[0021] Optionally, along the thickness direction of the transversely excited bulk acoustic wave resonator, the thickness of the acoustic impedance structure is equal to the thickness of the interdigital electrodes.

[0022] Optionally, the material of the acoustic impedance structure includes silicon dioxide, the material of the interdigital electrodes includes aluminum, the substrate includes a piezoelectric layer, and the material of the piezoelectric layer includes lithium niobate; the acoustic impedance of the acoustic impedance structure is smaller than the acoustic impedance of the interdigital electrodes, and the acoustic impedance of the interdigital electrodes is smaller than the acoustic impedance of the piezoelectric layer;

[0023] Alternatively, the material of the acoustic impedance structure includes hafnium dioxide, the material of the interdigitated electrodes includes tungsten, the substrate includes a piezoelectric layer, and the material of the piezoelectric layer includes lithium niobate; the acoustic impedance of the acoustic impedance structure is greater than the acoustic impedance of the interdigitated electrodes, and the acoustic impedance of the interdigitated electrodes is greater than the acoustic impedance of the piezoelectric layer.

[0024] In a second aspect, an embodiment of the present invention further provides a method for preparing a transversely excited bulk acoustic wave resonator, comprising:

[0025] providing a substrate;

[0026] A plurality of interdigital electrodes and an acoustic impedance structure are prepared on one side of the substrate; the plurality of interdigital electrodes are arranged along a first direction and extend along a second direction; the first direction intersects with the second direction and are parallel to the plane where the substrate is located; along the first direction, the acoustic impedance structure is located on both sides of the interdigital electrodes, and the acoustic impedance structure is in contact with the interdigital electrodes; there is a difference between the acoustic impedance of the acoustic impedance structure and the acoustic impedance of the interdigital electrodes.

[0027] Optionally, a plurality of interdigital electrodes and an acoustic impedance structure are prepared on one side of the substrate, including:

[0028] preparing a plurality of interdigitated electrodes on one side of the substrate;

[0029] Acoustic impedance structures are prepared on both sides of the interdigital electrodes along the first direction.

[0030] Optionally, a plurality of interdigital electrodes and an acoustic impedance structure are prepared on one side of the substrate, including:

[0031] preparing an acoustic impedance structure on one side of the substrate;

[0032] The interdigital electrodes are prepared between two adjacent acoustic impedance structures along a first direction.

[0033] The technical solution of the embodiment of the present invention is to set an acoustic impedance structure on both sides of the interdigitated electrode along the first direction. The acoustic impedance structure is in contact with the interdigitated electrode, and the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigitated electrode. In this way, the mechanical stress generated by the external electric field and the mass of the interdigitated electrode can be changed through the acoustic impedance structure, thereby reshaping the electric field lines, suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a top view schematic diagram of a transversely excited bulk acoustic wave resonator in the prior art;

[0035] Figure 2 for Figure 1 A schematic cross-sectional view of a transversely excited bulk acoustic wave resonator along a section line AA' is provided;

[0036] Figure 3 A schematic top view of a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention;

[0037] Figure 4 for Figure 3 A schematic cross-sectional view of a transversely excited bulk acoustic wave resonator along a section line BB' is provided;

[0038] Figure 5 A schematic top view of another transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention;

[0039] Figure 6 A schematic top view of another transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention;

[0040] Figure 7 for Figure 6 A schematic diagram of a cross-sectional structure of a transversely excited bulk acoustic wave resonator along a cross-sectional line CC' is provided;

[0041] Figure 8 is a schematic diagram of a response curve of a transversely excited bulk acoustic wave resonator in the prior art;

[0042] Fig. 9 A corresponding curve schematic diagram of a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention;

[0043] Fig.10 A schematic flow chart of a method for preparing a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention;

[0044] Fig.11 A schematic flow chart of another method for preparing a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention;

[0045] Fig.12 A schematic flow chart of another method for preparing a transversely excited bulk acoustic wave resonator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0047] Before describing the technical solution of the embodiment of the present invention in detail, the working principle of the lateral excitation bulk acoustic wave resonator in the prior art is described first. Figure 1 is a schematic top view of a transversely excited bulk acoustic wave resonator in the prior art, Figure 2 for Figure 1 A cross-sectional schematic diagram of a transversely excited bulk acoustic wave resonator along the section line AA' is provided, as shown in FIG. Figure 1 and Figure 2 As shown, transversely excited BAW resonators are widely used, especially in the new radio bands of the cellular spectrum for mobile communication technology, where broadband bandpass filtering is an essential requirement. The relatively high quality factor of transversely excited BAW resonators is crucial for designing filters with fast roll-off, high selectivity and low insertion loss, helping to meet the stringent requirements of mobile communication networks.

[0048] Specifically, the two interdigitated electrodes 20' correspond to the lower displacement region 200' and the displacement region 300', respectively. Due to the provision of the interdigitated electrodes 20', the substrate 10' will undergo a small deformation. The interdigitated electrodes 20' are electrically connected to the busbars 40' on one side, respectively. When an AC signal of a certain frequency is applied to the busbars 40', an asymmetric shear acoustic mode 100', i.e., the main mode, also called a shear acoustic wave, can be excited on the substrate 10'. The generated electric field 400' is perpendicular to the excited shear acoustic mode 100'. The two interdigitated electrodes 20' generate force interaction through the electric field 400', thereby exciting an acoustic energy flow 500'. The acoustic energy flow 500' of this mode is orthogonal to the surface of the substrate 10', i.e., the acoustic energy flow 500' is perpendicular to the upper and lower surfaces of the substrate 10'. The shear acoustic mode 100' generated by this excitation vibrates in the region between the lower displacement region 200' and the displacement region 300' corresponding to the two interdigitated electrodes 20'. When the shear acoustic wave passes through the substrate 10 ′, it will cause mechanical displacement of the substrate 10 ′, thereby generating an electrical response, and then the electrical response can be obtained by detecting the interdigital electrodes 20 ′, thereby achieving the purpose of analyzing the wave.

[0049] However, the sound waves will be reflected on the two sides of the interdigital electrode 20', resulting in pseudo-resonance, and since there is a mechanical boundary at the intersection of the area covered by the interdigital electrode 20' and the area not covered by the interdigital electrode 20', the electric field 400' will be divided into multiple areas, which will lead to horizontal harmonic resonance, that is, spurious mode, which will affect the working performance of the resonator.

[0050] The embodiment of the present invention can reshape the electric field lines by providing acoustic impedance structures on both sides of the interdigital electrodes, thereby suppressing the horizontal harmonics near the anti-resonance frequency of the main mode and improving the working performance of the resonator. Next, the technical case of the embodiment of the present invention is described in detail.

[0051] Figure 3 A schematic top view of a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention, Figure 4 for Figure 3 A cross-sectional schematic diagram of a transversely excited bulk acoustic wave resonator along the section line BB' is provided, as shown in FIG. Figure 3 and Figure 4 As shown, the transversely excited bulk acoustic wave resonator comprises: a substrate 10; a plurality of interdigital electrodes 20 located on one side of the substrate 10; the plurality of interdigital electrodes 20 extending along a first direction (eg Figure 3 The X direction shown in FIG. 1 is arranged along the second direction (such as Figure 3 The first direction X and the second direction Y intersect and are both parallel to the plane where the substrate 10 is located; the acoustic impedance structure 30 is located on both sides of the interdigital electrode 20 along the first direction X, the acoustic impedance structure 30 is in contact with the interdigital electrode 20, and the acoustic impedance of the acoustic impedance structure 30 is different from the acoustic impedance of the interdigital electrode 20.

[0052] Specifically, the interdigitated electrodes 20 are electrically connected to the bus bar 40. When an AC signal of a certain frequency is applied to the bus bar 40, an asymmetric shear acoustic mode can be excited on the substrate 10. An acoustic impedance structure 30 is arranged on both sides of the interdigitated electrodes 20. The acoustic impedance structure 30 is in the same layer and in contact with the interdigitated electrodes 20. In this way, on the one hand, the acoustic impedance structure 30 can reduce the reflection of acoustic waves on both sides of the interdigitated electrodes 20. On the other hand, by arranging the acoustic impedance structure 30 on both sides of the interdigitated electrodes 20, the distribution of mechanical stress can be changed, that is, the rigidity of the coverage area of ​​the acoustic impedance structure 30 is between the rigidity of the coverage area of ​​the interdigitated electrodes 20 and the rigidity of the uncovered area. In this way, the electric field lines can be reshaped, thereby suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, which is beneficial to guiding the electric field lines in a manner that is beneficial to the main mode and improving the working performance of the resonator.

[0053] Specifically, acoustic impedance can be understood as the product of material density and the propagation speed of sound waves in the material, and there is a difference between the acoustic impedance of the acoustic impedance structure 30 and the acoustic impedance of the interdigital electrode 20. In other words, the material density of the acoustic impedance structure 30 is different from that of the interdigital electrode 20, and / or the propagation speed of sound waves in the acoustic impedance structure 30 is different from that in the interdigital electrode 20. Thus, by providing the acoustic impedance structure 30 on both sides of the interdigital electrode 20, it is beneficial to distribute mechanical stress, thereby reshaping the electric field lines, suppressing horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator.

[0054] Exemplarily, the substrate 10 includes a piezoelectric layer 101, and the piezoelectric layer 101 includes a top side and a bottom side, the top side can be understood as a surface in contact with the interdigital electrode 20, and the bottom side can be understood as a surface located on the side of the top side away from the interdigital electrode 20. The piezoelectric layer 101 can be, but is not limited to, lithium niobate, lithium tantalate, zinc oxide, aluminum nitride, gallium nitride or barium titanate. The single crystal piezoelectric layer can be a rotated Y cut or a rotated YX cut. The specific rotation angle maximizes the coupling between the electrical mode and the mechanical mode, thereby obtaining a high electromechanical coupling coefficient. The specific crystal orientation causes the sound wave to propagate in a direction perpendicular to the electrode interdigital.

[0055] Exemplarily, all areas of the bottom side of the piezoelectric layer 101 except for the diaphragm are attached to the dielectric layer 102, thereby forming a free space 103, which can extend all the way through the substrate 104, or form a cavity supporting the substrate 104. The material of the dielectric layer 102 can be silicon oxide, aluminum nitride or other materials with a higher dielectric constant. The substrate 104 provides mechanical support for the resonator. The substrate 104 can be silicon, sapphire or other materials and / or a combination of several materials. The width of the piezoelectric layer 101 is determined by the number of pairs of interdigital electrodes 20 and the center spacing between adjacent interdigital electrodes 20. In one embodiment, along the first direction X, the center spacing between two adjacent interdigital electrodes 20 ranges from 2μm to 10μm, so the width of the piezoelectric layer 101 ranges from (2*the number of interdigital electrode pairs*2)μm to (2*the number of interdigital electrode pairs*10)μm.

[0056] The laterally excited bulk acoustic wave resonator provided by an embodiment of the present invention is configured by arranging an acoustic impedance structure on both sides of the interdigitated electrodes along a first direction. The acoustic impedance structure is in contact with the interdigitated electrodes, and the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigitated electrodes. In this way, the external electric field and the mechanical stress generated by the mass of the interdigitated electrodes can be changed through the acoustic impedance structure, thereby reshaping the electric field lines, suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator.

[0057] Optional, Figure 5 A schematic top view of another transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention is shown in FIG. Figure 5As shown, the laterally excited BAW resonator further includes: a bus bar 40; the bus bar 40 includes a first bus bar 401 and a second bus bar 402 arranged along the second direction Y; the interdigitated electrode 20 includes a first interdigitated electrode 201 and a second interdigitated electrode 202; the first interdigitated electrode 201 is electrically connected to the first bus bar 401, and the second interdigitated electrode 202 is electrically connected to the second bus bar 402; the laterally excited BAW resonator further includes an effective aperture region 50, the first interdigitated electrode 201 includes a first electrode portion 2011 located in the effective aperture region 50, the second interdigitated electrode 202 includes a second electrode portion 2021 located in the effective aperture region 50, and the first electrode portion 2011 and the second electrode portion 2021 are alternately arranged in sequence along the first direction X; the acoustic impedance structure 30 is located in the effective aperture region 50.

[0058] Specifically, the effective aperture area 50 can also be understood as an active area. Along the second direction Y, the interdigital electrodes 20 are electrically connected to the bus bar 40 on one side, and there is a gap between the interdigital electrodes 20 and the bus bar 40 on the other side, that is, along the second direction Y, there is a gap between the effective aperture area 50 and the bus bar 40, that is, the spacing area. Exemplarily, the first interdigital electrode 201 is electrically connected to the first bus bar 401, and along the second direction Y, there is a gap between the effective aperture area 50 and the second bus bar 402.

[0059] Furthermore, since the sound waves are mainly concentrated in the effective aperture area 50, the acoustic impedance structure 30 is located in the effective aperture area 50, that is, along the first direction X, the acoustic impedance structure 30 is located on both sides of the first interdigitated electrode division 2011, and the acoustic impedance structure 30 is also located on both sides of the second interdigitated electrode division 2021. This can reshape the electric field lines in the effective aperture area 50, which is beneficial to suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, thereby improving the performance of the resonator.

[0060] Understandably, Figure 5 Only the technical solution is shown in which the length of the acoustic impedance structure 30, the length of the first interdigitated electrode portion 2011 and the length of the second interdigitated electrode portion 2021 are all equal along the second direction Y. It should be noted that, along the second direction Y, the length of the acoustic impedance structure 30 can also be greater than the length of the interdigitated electrode 20 in the effective aperture area 50, which can further suppress the horizontal harmonics near the anti-resonance frequency of the main mode and improve the working performance of the resonator.

[0061] Optional, continue to refer to Figure 3 Along the second direction Y, the length of the acoustic impedance structure 30 is equal to the length of the interdigital electrode 20, that is, along the second direction Y, the acoustic impedance structure 30 is arranged on both sides of each interdigital electrode 20, that is, the acoustic impedance structure 30 wraps the two sides of the interdigital electrode 20, so that the horizontal harmonics near the anti-resonance frequency of the main mode can be further suppressed, thereby improving the working performance of the resonator.

[0062] Optional, Figure 6 A schematic top view of another transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention, Figure 7 for Figure 6 A schematic diagram of a cross-sectional structure of a transversely excited bulk acoustic wave resonator along a cross-sectional line CC' is provided, as shown in FIG. Figure 6 and Figure 7 As shown, the laterally excited BAW resonator further includes a bus bar 40; the bus bar 40 includes a first bus bar 401 and a second bus bar 402 arranged along the second direction Y; the interdigitated electrode 20 includes a first interdigitated electrode 201 and a second interdigitated electrode 202; the first interdigitated electrode 201 is electrically connected to the first bus bar 401, and the second interdigitated electrode 202 is electrically connected to the second bus bar 402; the laterally excited BAW resonator further includes an effective aperture region 50 and a spacing region 60; the first interdigitated electrode 201 includes a first electrode portion 2011 located in the effective aperture region 50, the second interdigitated electrode 202 includes a second electrode portion 2021 located in the effective aperture region 50, and the first electrode portion 2011 and the second electrode portion 2021 are alternately arranged in sequence along the first direction X; along the second direction Y, the spacing region 60 is located between the effective aperture region 50 and the bus bar 40; the acoustic impedance structure 30 is located in the effective aperture region 50 and the spacing region 60.

[0063] Specifically, along the second direction Y, an acoustic impedance structure 30 is provided between the effective aperture region 50 and the spacer region 60, so that when the acoustic wave is along the second direction Y, a sound velocity difference is generated, which can suppress the lateral mode and improve the Q value of the resonator. In addition, by providing the acoustic impedance structure 30 in the spacer region 60, it is helpful to balance the different mechanical interfaces caused by the applied electric field and the mass load of the interdigital electrode 20, and further suppress the horizontal harmonics near the anti-resonance frequency of the main mode, thereby improving the working performance of the resonator.

[0064] Understandably, continue to refer to Figure 7 The interdigital electrodes 20 and the bus bar 40 may be disposed in the same layer, and the acoustic impedance structure 30 located in the spacing area 60 may be disposed in the same layer and in contact with the interdigital electrodes 20 and the bus bar 40 .

[0065] Optional, continue to refer to Figure 3 and 4 , in the first direction X, the widths of the acoustic impedance structures 30 located on both sides of the same interdigital electrode 20 are equal.

[0066] Specifically, the widths of the acoustic impedance structures 30 located on both sides of the same interdigital electrode 20 are equal, that is, the acoustic impedance structures 30 located on both sides of the same interdigital electrode 20 are symmetrical about the center of the interdigital electrode 20, thereby ensuring that the electric field on both sides of the interdigital electrode 20 is uniform, thereby suppressing horizontal harmonics and improving the performance of the resonator.

[0067] It should be noted that if the widths of the acoustic impedance structures 30 on both sides of the same interdigital electrode 20 are not equal, pseudo resonance will occur, thereby affecting the performance of the resonator.

[0068] Optional, continue to refer to Figure 4 , along the thickness direction of the transversely excited BAW resonator (e.g. Figure 4 The thickness of the acoustic impedance structure 30 is equal to the thickness of the interdigital electrode 20 .

[0069] Specifically, along the thickness direction Z of the transversely excited BAW resonator, the thickness of the acoustic impedance structure 30 is equal to the thickness of the interdigital electrode 20, that is, the upper surface of the acoustic impedance structure 30 is flush with the upper surface of the interdigital electrode 20. This is beneficial to ensuring the uniformity of the resonator surface and simplifying the production process. On the other hand, it ensures that the thickness of the acoustic impedance structure 30 is equal to the thickness of the interdigital electrode 20. The optimization of the resonator performance by setting the acoustic impedance structure 30 can be analyzed only by analyzing the width of the acoustic impedance structure 30.

[0070] Optional, continue to refer to Figure 3 and Figure 4 , the material of the acoustic impedance structure 30 includes silicon dioxide, the material of the interdigitated electrode 20 includes aluminum, the substrate 10 includes a piezoelectric layer 101, and the material of the piezoelectric layer 101 includes lithium niobate; the acoustic impedance of the acoustic impedance structure 30 is smaller than the acoustic impedance of the interdigitated electrode 20, and the acoustic impedance of the interdigitated electrode 20 is smaller than the acoustic impedance of the piezoelectric layer 101; or, the material of the acoustic impedance structure 30 includes hafnium dioxide, the material of the interdigitated electrode 20 includes tungsten, the substrate 10 includes a piezoelectric layer 101, and the material of the piezoelectric layer 101 includes lithium niobate; the acoustic impedance of the acoustic impedance structure 30 is greater than the acoustic impedance of the interdigitated electrode 20, and the acoustic impedance of the interdigitated electrode 20 is greater than the acoustic impedance of the piezoelectric layer 101.

[0071] As a feasible implementation, when the material of the interdigital electrode 20 is a low acoustic impedance material, illustratively, the material of the interdigital electrode 20 may be aluminum, and in this case the material of the acoustic impedance structure 30 is also a low acoustic impedance material, namely silicon dioxide. The acoustic impedance of the acoustic impedance structure 30 is less than the acoustic impedance of the interdigital electrode 20, and the acoustic impedance of the interdigital electrode 20 is less than the acoustic impedance of the piezoelectric layer 101, so that along the first direction X, by arranging the acoustic impedance structure 30 on both sides of the interdigital electrode 20, the horizontal harmonics near the anti-resonance frequency of the main mode can be suppressed. In addition, the material of the acoustic impedance structure 30 is silicon dioxide, which can also perform temperature compensation on the resonator, thereby improving the performance of the resonator.

[0072] As another feasible implementation, when the material of the interdigital electrode 20 is a heavy acoustic impedance material, illustratively, the material of the interdigital electrode 20 may be tungsten, and in this case, the material of the acoustic impedance structure 30 is also a heavy acoustic impedance material, i.e., hafnium dioxide. The acoustic impedance of the acoustic impedance structure 30 is greater than the acoustic impedance of the interdigital electrode 20, and the acoustic impedance of the interdigital electrode 20 is greater than the acoustic impedance of the piezoelectric layer 101. Thus, along the first direction X, by arranging the acoustic impedance structure 30 on both sides of the interdigital electrode 20, horizontal harmonics near the anti-resonance frequency of the main mode can be suppressed, thereby improving the performance of the resonator.

[0073] In summary, in the laterally excited bulk acoustic wave resonator provided by the embodiment of the present invention, when the interdigital electrodes adopt low acoustic impedance material, the acoustic impedance structure located on both sides of the interdigital electrodes also adopts low acoustic impedance material, and the acoustic impedance of the acoustic impedance structure is smaller than the acoustic impedance of the interdigital electrodes; when the interdigital electrodes adopt heavy acoustic impedance material, the acoustic impedance structure located on both sides of the interdigital electrodes also adopts heavy acoustic impedance material, and the acoustic impedance of the acoustic impedance structure is greater than the acoustic impedance of the interdigital electrodes, thereby suppressing horizontal harmonics near the anti-resonance frequency of the main mode, thereby improving the performance of the resonator.

[0074] Figure 8 is a schematic diagram of a response curve of a transversely excited bulk acoustic wave resonator in the prior art, Fig. 9 This is a schematic diagram of a corresponding curve of a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention, such as Figure 8 and Fig. 9 As shown, curve a' represents the phase response, while curve b' represents the admittance amplitude response. Curve a represents the phase response, while curve b represents the admittance amplitude response. Figure 8 and Fig. 9 In the admittance amplitude response curve and phase response curve, the curves in the area c' and area c covered by the ellipse are slightly different, which shows that the transverse excitation BAW resonator provided by the embodiment of the present invention is not affected by the mechanism used compared with the transverse excitation BAW resonator in the prior art. Figure 8In the conventional BAW resonator, strong parasitic resonances are shown in regions d' and e', which are manifested as abnormal phase responses. It can be understood that regions d' and e' can correspond to the corresponding regions of horizontal harmonics. Fig. 9 In comparison, the lateral excitation bulk acoustic wave resonator provided in the embodiment of the present invention shows a cleaner response in regions d and e. It can be seen that the embodiment of the present invention can suppress spurious modes and improve the performance of the resonator by arranging an acoustic impedance structure on both sides of the interdigital electrode.

[0075] It should be noted that the data parameters of the transversely excited bulk acoustic wave resonator provided in the embodiment of the present invention are collected by analyzing using the finite element method (FEM) simulation technology. In this particular case, a periodic three-dimensional simulation is applied, in which continuous periodic conditions are applied in the length dimension to simulate the entire structure of the resonator in the transverse direction (along the interdigitated electrodes). Figure 8 The curve in FIG. 1 is a conventional lateral excitation bulk acoustic wave resonator having a pair of interdigital electrodes simulated by FEM, and the specific structure is as follows: the pitch is 12.6 μm, and the pitch can be understood as the distance from the center of the first interdigital electrode to the center of the second interdigital electrode along the first direction, and the distance can be half of the period of the interdigital electrodes, that is, it can be understood as the pitch of the interdigital electrodes; the width of the interdigital electrodes is 0.63 μm; the thickness of the interdigital electrodes is 100 nm, and the piezoelectric substrate is 128Y lithium niobate, and its thickness is 502 nm. Fig. 9 The curve in is the FEM simulation of a lateral excitation BAW resonator with a pair of interdigital electrodes. The specific structure is as follows: the pitch of the interdigital electrodes is 12.6μm; the width of the interdigital electrodes is 0.63μm; the thickness of the interdigital electrodes is 100nm; the material of the acoustic impedance structure is silicon dioxide, the thickness of which is 100nm, the width of the acoustic impedance structure is 0.767μm, and the piezoelectric substrate is 128YX lithium niobate, the thickness of which is 502nm. Figure 8 and Fig. 9 It can be found from the curve in that the embodiment of the present invention effectively reduces the occurrence of stray resonance of the laterally excited BAW resonator near the anti-resonance frequency by arranging the acoustic impedance structure on both sides of the forked electrode, which means that the laterally excited BAW resonator provided with the acoustic impedance structure has higher reliability in phase response, helps to improve the signal-to-noise ratio in the laterally excited BAW resonator, and is conducive to clearer and more accurate signal detection, thereby improving the sensitivity and accuracy of the resonator in various applications.

[0076] The transversely excited bulk acoustic wave resonator provided by the embodiment of the present invention has wide applicability in different fields such as wireless communication equipment, acoustic wave sensors and actuators, frequency control equipment, and radio frequency filters and duplexers.

[0077] Based on the same inventive concept, an embodiment of the present invention further provides a method for preparing a transversely excited bulk acoustic wave resonator. Fig.10 A schematic flow chart of a method for preparing a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention is shown in FIG. Fig.10 As shown, the preparation method of the transversely excited bulk acoustic wave resonator includes:

[0078] S101. Provide a substrate.

[0079] For details, please refer to Figure 3 The substrate 10 includes a piezoelectric layer 101 , a dielectric layer 102 , a substrate 104 , and a free space 103 between the substrate 104 and the piezoelectric layer 101 .

[0080] S102. Prepare a plurality of interdigitated electrodes and an acoustic impedance structure on one side of a substrate; the plurality of interdigitated electrodes are arranged along a first direction and extend along a second direction; the first direction intersects with the second direction and are parallel to the plane where the substrate is located; along the first direction, the acoustic impedance structure is located on both sides of the interdigitated electrodes, and the acoustic impedance structure is in contact with the interdigitated electrodes; there is a difference in the acoustic impedance of the acoustic impedance structure and the acoustic impedance of the interdigitated electrodes.

[0081] For details, please refer to Figure 3 and Figure 4 The interdigitated electrodes 20 are electrically connected to the bus bar 40. When an AC signal of a certain frequency is applied to the bus bar 40, an asymmetric shear acoustic mode can be excited on the substrate 10. Acoustic impedance structures 30 are arranged on both sides of the interdigitated electrodes 20. The acoustic impedance structure 30 is in the same layer as and in contact with the interdigitated electrodes 20. In this way, on the one hand, the acoustic impedance structure 30 can reduce the reflection of acoustic waves on both sides of the interdigitated electrodes 20. On the other hand, by arranging the acoustic impedance structure 30 on both sides of the interdigitated electrodes 20, the distribution of mechanical stress can be changed, that is, the rigidity of the coverage area of ​​the acoustic impedance structure 30 is between the rigidity of the coverage area of ​​the interdigitated electrodes 20 and the rigidity of the uncovered area. In this way, the electric field lines can be reshaped, thereby suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, which is beneficial to guiding the electric field lines in a manner that is beneficial to the main mode and improving the working performance of the resonator.

[0082] The method for preparing a laterally excited bulk acoustic wave resonator provided in an embodiment of the present invention is to prepare an acoustic impedance structure on both sides of an interdigitated electrode along a first direction, the acoustic impedance structure is in contact with the interdigitated electrode, and the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigitated electrode. In this way, the external electric field and the mechanical stress generated by the mass of the interdigitated electrode can be changed through the acoustic impedance structure, thereby reshaping the electric field lines, suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator.

[0083] Optional, Fig.11A schematic flow chart of another method for preparing a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention, Fig.11 Based on the above embodiments, the operation of preparing a plurality of interdigital electrodes and an acoustic impedance structure on one side of a substrate is described in detail. Fig.11 As shown, the preparation method of the transversely excited bulk acoustic wave resonator includes:

[0084] S201, providing a substrate.

[0085] S202, preparing a plurality of interdigital electrodes on one side of the substrate; the plurality of interdigital electrodes are arranged along a first direction and extend along a second direction; the first direction intersects with the second direction and are parallel to the plane where the substrate is located.

[0086] Specifically, on one side of the substrate, a whole first metal layer is first prepared, and then photoresist is coated on the first metal layer. Photolithography technology is used to form interdigital electrodes and bus bars on the photoresist, that is, an interdigital transducer structure is formed.

[0087] S203, preparing an acoustic impedance structure on both sides of the interdigital electrode along the first direction; the acoustic impedance structure is in contact with the interdigital electrode; and the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigital electrode.

[0088] Specifically, after preparing the interdigital transducer, a photoresist is coated, and after the photoresist is patterned, an acoustic impedance layer is deposited on the interdigital transducer structure. The thickness of the photoresist is 1.2-1.5 times the thickness of the first metal layer. The thickness of the acoustic impedance layer is about 1.5-2 times the thickness of the photoresist layer. Next, a chemical mechanical planarization process is used to remove the excess acoustic impedance layer, so that the surface acoustic impedance layer is planarized and the photoresist layer is exposed. Subsequently, a dry etching technique is used to selectively remove the acoustic impedance layer to form an acoustic impedance structure and expose the first metal layer. Once the interdigital transducer structure in the first metal layer is exposed, the photoresist layer is removed, and a second metal layer, usually aluminum, is deposited on the exposed interdigital transducer structure. The second metal layer can be used as a pad for a radio frequency detection device. Finally, a back film release or a front film release is prepared.

[0089] The method for preparing a laterally excited bulk acoustic wave resonator provided in an embodiment of the present invention first prepares interdigitated electrodes on one side of a substrate, and then prepares an acoustic impedance structure on both sides of the interdigitated electrodes. The preparation method is simple and compatible with existing preparation processes. In addition, the acoustic impedance structure can change the mechanical stress generated by the external electric field and the mass of the interdigitated electrodes, thereby reshaping the electric field lines, suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator.

[0090] Optional, Fig.12 A schematic flow chart of another method for preparing a transversely excited bulk acoustic wave resonator provided by an embodiment of the present invention, Fig.12Based on the above embodiments, the operation of preparing a plurality of interdigital electrodes and an acoustic impedance structure on one side of a substrate is described in detail. Fig.12 As shown, the preparation method of the transversely excited bulk acoustic wave resonator includes:

[0091] S301, providing a substrate.

[0092] S302, preparing an acoustic impedance structure on one side of the substrate.

[0093] Specifically, an acoustic impedance layer is sputtered on one side of the substrate. For example, the thickness of the acoustic impedance layer can be three times the thickness of the interdigital transducer layer. This process includes ion bombardment of the target material, so that atoms are ejected into the surrounding plasma. A chemical mechanical polishing process is used, that is, chemical and mechanical effects are used to flatten and smooth the surface of the acoustic impedance layer.

[0094] Specifically, photoresist is coated on the surface of the acoustic impedance layer to cover areas that do not need to be etched or need to be protected from the etching material. Dry etching is used to etch grooves in the acoustic impedance layer for subsequent deposition of interdigital electrodes. Once the etching is completed, the photoresist is removed.

[0095] S303, preparing interdigitated electrodes between two adjacent acoustic impedance structures along the first direction; a plurality of interdigitated electrodes are arranged along the first direction and all extend along the second direction; the first direction intersects with the second direction and both are parallel to the plane where the substrate is located; the acoustic impedance structure is in contact with the interdigitated electrodes; there is a difference between the acoustic impedance of the acoustic impedance structure and the acoustic impedance of the interdigitated electrodes.

[0096] Specifically, a first metal layer is deposited, and the first metal layer is patterned to form interdigital electrodes and bus bars, i.e., an interdigital transducer structure, wherein the interdigital electrodes are located between two adjacent acoustic impedance structures along a first direction. A second metal layer, usually aluminum, is deposited on the exposed interdigital transducer structure, and the second metal layer can serve as a pad layer for a radio frequency detection device. Finally, a back film release or a front film release is prepared.

[0097] The method for preparing a laterally excited bulk acoustic wave resonator provided by an embodiment of the present invention first prepares an acoustic impedance structure on one side of a substrate, and then prepares an interdigitated electrode between two adjacent acoustic impedance structures. The preparation method is simple and compatible with existing preparation processes. In addition, the acoustic impedance structure can change the external electric field and the mechanical stress generated by the mass of the interdigitated electrodes, thereby reshaping the electric field lines, suppressing the horizontal harmonics near the anti-resonance frequency of the main mode, and improving the working performance of the resonator.

[0098] It should be noted that various conventional process steps, such as surface preparation, cleaning, inspection, photolithography, baking, annealing, monitoring, testing, etc., can be performed before, between, after, or even during the steps shown in the provided preparation method flow. These additional steps help ensure the overall quality and functionality of the final device.

[0099] It should be noted that the specific order and content of these conventional process steps may vary depending on the specific manufacturing requirements, technology and equipment used. The provided manufacturing process flow highlights the main steps of the embodiments of the present invention, while the additional processes emphasize the comprehensive nature and complexity of semiconductor device manufacturing.

[0100] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A transversely excited bulk acoustic wave resonator, characterized in that: include: substrate; a plurality of interdigitated electrodes located on one side of the substrate; The plurality of interdigital electrodes are arranged along the first direction and extend along the second direction; The first direction intersects with the second direction and both are parallel to the plane where the base is located; an acoustic impedance structure located at both sides of the interdigital electrode along the first direction, the acoustic impedance structure is in contact with the interdigital electrode, and an acoustic impedance of the acoustic impedance structure is different from that of the interdigital electrode; Wherein, when the material of the interdigital electrodes is a low acoustic impedance material, the material of the acoustic impedance structure is a low acoustic impedance material; when the material of the interdigital electrodes is a heavy acoustic impedance material, the material of the acoustic impedance structure is a heavy acoustic impedance material; Wherein, along the first direction, there is a gap between two adjacent acoustic impedance structures, and the widths of the acoustic impedance structures located on both sides of the same interdigital electrode are equal.

2. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The transversely excited bulk acoustic wave resonator further includes: a bus bar; the bus bar includes a first bus bar and a second bus bar arranged along the second direction; The interdigital electrodes include a first interdigital electrode and a second interdigital electrode; the first interdigital electrode is electrically connected to the first bus bar, and the second interdigital electrode is electrically connected to the second bus bar; The transversely excited bulk acoustic wave resonator further comprises an effective aperture region, the first interdigital electrode comprises a first electrode section located in the effective aperture region, the second interdigital electrode comprises a second electrode section located in the effective aperture region, and the first electrode section and the second electrode section are alternately arranged in sequence along the first direction; The acoustic impedance structure is located in the effective aperture area.

3. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The transversely excited bulk acoustic wave resonator further includes a bus bar; the bus bar includes a first bus bar and a second bus bar arranged along the second direction; The interdigital electrodes include a first interdigital electrode and a second interdigital electrode; the first interdigital electrode is electrically connected to the first bus bar, and the second interdigital electrode is electrically connected to the second bus bar; The transversely excited bulk acoustic wave resonator further comprises an effective aperture region and a spacing region; The first interdigitated electrode comprises a first electrode portion located in the effective aperture region, the second interdigitated electrode comprises a second electrode portion located in the effective aperture region, and the first electrode portion and the second electrode portion are alternately arranged in sequence along the first direction; Along the second direction, the spacing area is located between the effective aperture area and the bus bar; The acoustic impedance structure is located in the effective aperture area and the spacing area.

4. The transversely excited bulk acoustic wave resonator according to claim 3, characterized in that: Along the second direction, the length of the acoustic impedance structure is equal to the length of the interdigital electrodes.

5. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: Along the thickness direction of the transversely excited bulk acoustic wave resonator, the thickness of the acoustic impedance structure is equal to the thickness of the interdigital electrodes.

6. The transversely excited bulk acoustic wave resonator according to claim 1, characterized in that: The material of the acoustic impedance structure includes silicon dioxide, the material of the interdigital electrodes includes aluminum, the substrate includes a piezoelectric layer, and the material of the piezoelectric layer includes lithium niobate; the acoustic impedance of the acoustic impedance structure is smaller than the acoustic impedance of the interdigital electrodes, and the acoustic impedance of the interdigital electrodes is smaller than the acoustic impedance of the piezoelectric layer; Alternatively, the material of the acoustic impedance structure includes hafnium dioxide, the material of the interdigitated electrodes includes tungsten, the substrate includes a piezoelectric layer, and the material of the piezoelectric layer includes lithium niobate; the acoustic impedance of the acoustic impedance structure is greater than the acoustic impedance of the interdigitated electrodes, and the acoustic impedance of the interdigitated electrodes is greater than the acoustic impedance of the piezoelectric layer.

7. A method for preparing a transversely excited bulk acoustic wave resonator, characterized in that: include: providing a substrate; preparing a plurality of interdigitated electrodes and an acoustic impedance structure on one side of the substrate; The plurality of interdigital electrodes are arranged along a first direction and extend along a second direction; the first direction intersects with the second direction and is parallel to the plane where the substrate is located; along the first direction, the acoustic impedance structure is located on both sides of the interdigital electrodes, and the acoustic impedance structure is in contact with the interdigital electrodes; the acoustic impedance of the acoustic impedance structure is different from the acoustic impedance of the interdigital electrodes; Wherein, when the material of the interdigital electrodes is a low acoustic impedance material, the material of the acoustic impedance structure is a low acoustic impedance material; when the material of the interdigital electrodes is a heavy acoustic impedance material, the material of the acoustic impedance structure is a heavy acoustic impedance material; Wherein, along the first direction, there is a gap between two adjacent acoustic impedance structures, and the widths of the acoustic impedance structures located on both sides of the same interdigital electrode are equal.

8. The method for preparing a transversely excited bulk acoustic wave resonator according to claim 7, characterized in that: A plurality of interdigital electrodes and an acoustic impedance structure are prepared on one side of the substrate, comprising: preparing a plurality of interdigitated electrodes on one side of the substrate; Acoustic impedance structures are prepared on both sides of the interdigital electrodes along the first direction.

9. The method for preparing a lateral excitation bulk acoustic wave resonator according to claim 7, wherein a plurality of interdigital electrodes and an acoustic impedance structure are prepared on one side of the substrate, comprising: preparing an acoustic impedance structure on one side of the substrate; The interdigital electrodes are prepared between two adjacent acoustic impedance structures along a first direction.

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