Bulk acoustic wave resonator capable of reducing stray modes and bulk acoustic wave filter

Abstract

The invention relates to the technical field of bulk acoustic wave resonators, and particularly provides a bulk acoustic wave resonator and a bulk acoustic wave filter capable of reducing stray modalities, and the resonator comprises a substrate, a bottom electrode, a piezoelectric layer and a top electrode which are sequentially connected from bottom to top; the top electrode is provided with a plane part and an irregular frame part which are located above the sound reflecting mirror, the irregular frame part protrudes out of or is sunken into the plane part, and the outer contour of the cross section of the irregular frame part is irregular; the outer boundary of the projection of the irregular frame portion in the plan view direction is located within the outer boundary of the projection of the planar portion in the plan view direction and the outer boundary of the projection of the acoustic mirror in the plan view direction, and the irregular frame portion is located within the planar portion in the plan view direction. The resonator can effectively solve the problems that a stray mode is formed near a series resonant frequency and the performance of a bulk acoustic wave filter is deteriorated due to improper size setting of the convex structure or the concave structure.

Description

Technical Field

[0001] The present application relates to the technical field of bulk acoustic wave resonators, and in particular to a bulk acoustic wave resonator and a bulk acoustic wave filter for reducing stray modes. Background Art

[0002] The related technology uses BAW filters as the core components of RF front-end modules, and widely applies BAW filters in fields such as communication filtering and navigation positioning. The related BAW filters are composed of multiple BAW resonators connected in series and parallel. The related art usually improves the quality factor of the BAW resonator by setting a protruding structure or a recessed structure on an electrode located above the acoustic reflector of the BAW resonator. If the size of the protruding structure or the recessed structure is improperly set (for example, the protruding structure is too wide, the recessed structure is too wide, the protruding structure is too high, or the recessed structure is too deep), the protruding structure or the recessed structure will form an independent resonator with other film layers of the BAW resonator. The characteristic frequency generated by the vibration of the independent resonator is different from the target characteristic frequency of the BAW resonator, thereby forming a spurious mode near the series resonance frequency (within the range of the series resonance frequency - 100 MHz to the series resonance frequency). The spurious mode formed near the series resonance frequency will attenuate the insertion loss in the passband of the BAW filter, thereby causing the performance of the BAW filter to deteriorate. That is, the related art has the problem of forming a spurious mode near the series resonance frequency and deteriorating the performance of the BAW filter due to improper size setting of the protruding structure or the recessed structure.

[0003] There is no effective technical solution to the above problems. It should be noted that the above information disclosed in this section is only used to understand the background of the present invention, and therefore may contain information that does not constitute prior art. Summary of the invention

[0004] The purpose of the present application is to provide a bulk acoustic wave resonator and a bulk acoustic wave filter that reduce stray modes, which can effectively solve the problem of stray modes formed near the series resonance frequency and performance deterioration of the bulk acoustic wave filter due to improper size setting of the protruding structure or the recessed structure.

[0005] In a first aspect, the present application provides a bulk acoustic wave resonator for reducing spurious modes, comprising: A substrate, a bottom electrode, a piezoelectric layer and a top electrode are connected in sequence from bottom to top, and an acoustic reflector is arranged on the substrate; The top electrode comprises a planar portion and an irregular frame portion located above the acoustic reflector, the irregular frame portion protrudes or is recessed in the planar portion, the outer contour of the cross section of the irregular frame portion is irregular, the outer boundary of the projection of the irregular frame portion in the top-view direction is located within the outer boundary of the projection of the planar portion in the top-view direction and the outer boundary of the projection of the acoustic reflector in the top-view direction, and the irregular frame portion is located within the planar portion in the top-view direction.

[0006] The present application provides a bulk acoustic wave resonator for reducing stray modes, which is equivalent to using an irregular frame portion to replace the existing protruding structure and recessed structure and making the outer contour of the cross-section of the irregular frame portion irregular so that the stray mode will not be formed near the series resonance frequency or the stray mode is eliminated. Even if the size of the irregular frame portion of the present application is improperly set and the stray mode cannot be eliminated, the present application can prevent the stray mode from being formed near the series resonance frequency, and the stray mode not formed near the series resonance frequency will not attenuate the insertion loss in the passband of the bulk acoustic wave filter. Therefore, the present application can effectively solve the problem of stray modes being formed near the series resonance frequency and the performance of the bulk acoustic wave filter being deteriorated due to improper size setting of the protruding structure or the recessed structure.

[0007] Optionally, the top electrode has two irregular frame portions distributed inside and outside, wherein one irregular frame portion protrudes from the plane portion, and the other irregular frame portion is recessed in the plane portion.

[0008] Since the top electrode of the technical solution has two irregular frame parts distributed inside and outside, and one of the irregular frame parts protrudes from the planar part, and the other irregular frame part is recessed in the planar part, the technical solution can suppress the parasitic mode at the series resonance frequency while suppressing the shear wave leakage of the bulk acoustic wave resonator, thereby effectively improving the quality factor of the bulk acoustic wave resonator.

[0009] Optionally, the irregular frame portion protruding from the plane portion is located outside the irregular frame portion recessed in the plane portion.

[0010] Optionally, the two irregular frame portions are concentric in shape when viewed from above.

[0011] Optionally, the maximum vertical distance between the irregular frame portion and the planar portion is 1 nm-1 μm, and the width of the irregular frame portion is 0.1-5 μm.

[0012] This technical solution avoids the situation where the irregular frame portion is too high or too deep by setting the maximum vertical spacing between the irregular frame portion and the plane portion to 1nm-1μm, and avoids the situation where the irregular frame portion is too wide by setting the width of the irregular frame portion to 0.1-5μm, that is, this technical solution is equivalent to setting the size of the irregular frame portion appropriately. Therefore, this technical solution can effectively reduce the stray modes generated by improper size setting of the irregular frame portion, thereby further improving the performance of the bulk acoustic wave resonator.

[0013] Optionally, the outer contour of the cross section of the irregular frame portion is formed by connecting a plurality of base lines, and the base lines are arc segments or straight line segments.

[0014] Optionally, outer contours of different cross sections of the irregular frame portion are the same.

[0015] Optionally, the outer contour of the cross section of the irregular frame portion changes continuously.

[0016] Optionally, a ratio of an average distance between an outer boundary of the irregular frame portion in the top view direction and an outer boundary of the planar portion in the top view direction to the length of the acoustic reflector is 1:35-1:25.

[0017] In a second aspect, the present application further provides a bulk acoustic wave filter, which includes a bulk acoustic wave resonator for reducing spurious modes provided in the first aspect.

[0018] The present application provides a bulk acoustic wave filter, which is equivalent to replacing the existing protruding structure and recessed structure with an irregular frame portion and preventing spurious modes from being formed near the series resonance frequency or eliminating the spurious modes by setting the outer contour of the cross section of the irregular frame portion to an irregular manner. Even if the size of the irregular frame portion of the present application is improperly set and the spurious modes cannot be eliminated, the present application can prevent the spurious modes from being formed near the series resonance frequency, and the spurious modes that are not formed near the series resonance frequency will not attenuate the insertion loss within the passband of the bulk acoustic wave filter. Therefore, the present application can effectively solve the problem of spurious modes being formed near the series resonance frequency and the performance of the bulk acoustic wave filter being deteriorated due to improper size setting of the protruding structure or the recessed structure.

[0019] From the above, it can be seen that the present application provides a BAW resonator and BAW filter for reducing stray modes, which is equivalent to using an irregular frame portion to replace the existing protruding structure and recessed structure and making the outer contour of the cross-section of the irregular frame portion irregular so that the stray mode will not be formed near the series resonant frequency or the stray mode will be eliminated. Even if the size of the irregular frame portion of the present application is improperly set and the stray mode cannot be eliminated, the present application can prevent the stray mode from being formed near the series resonant frequency, and the stray mode not formed near the series resonant frequency will not attenuate the insertion loss in the passband of the BAW filter. Therefore, the present application can effectively solve the problem of stray modes formed near the series resonant frequency and deterioration of the performance of the BAW filter due to improper size setting of the protruding structure or the recessed structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic cross-sectional structure diagram of a bulk acoustic wave resonator for reducing stray modes provided by the first technical solution of the present application.

[0021] Figure 2 A schematic cross-sectional structure diagram of a bulk acoustic wave resonator for reducing stray modes provided by the second technical solution of the present application.

[0022] Figure 3 A schematic cross-sectional structure diagram of a bulk acoustic wave resonator for reducing stray modes provided by the third technical solution of the present application.

[0023] Figure 4 A schematic structural diagram of a bulk acoustic wave resonator for reducing stray modes provided by the technical solution of the present application.

[0024] Figure 5 A schematic diagram comparing the particle displacement of a BAW resonator for reducing stray modes provided by the technical solution of the present application with the particle displacement of an existing BAW resonator.

[0025] Figure 6 A cross-sectional schematic diagram of the bottom electrode, piezoelectric layer and irregular frame portion provided in the technical solution of the present application.

[0026] Figure numerals: 1. substrate; 2. bottom electrode; 3. piezoelectric layer; 4. plane portion; 5. acoustic reflector; 6. irregular frame portion. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0028] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0029] First, as Figure 1-Figure 6 As shown, the present application provides a bulk acoustic wave resonator for reducing stray modes, which includes: A substrate 1, a bottom electrode 2, a piezoelectric layer 3 and a top electrode are connected in sequence from bottom to top, and an acoustic reflector 5 is provided on the substrate 1; The top electrode has a planar portion 4 and an irregular frame portion 6 located above the acoustic reflector 5. The irregular frame portion 6 protrudes or is recessed from the planar portion 4. The outer contour of the cross section of the irregular frame portion 6 is irregular. The outer boundary of the projection of the irregular frame portion 6 in the top view direction is located within the outer boundary of the projection of the planar portion 4 in the top view direction and the outer boundary of the projection of the acoustic reflector 5 in the top view direction. The irregular frame portion 6 is located within the planar portion 4 in the top view direction.

[0030] Among them, the material of the substrate 1 of this embodiment is preferably silicon material, the materials of the bottom electrode 2 and the top electrode of this embodiment are preferably any one or more of metal materials with high electrical conductivity, large acoustic impedance and large Young's modulus (such as gold, silver, ruthenium, tungsten, molybdenum, aluminum, platinum, niobium or hafnium), the material of the bottom electrode 2 of this embodiment is preferably the same as the material of the top electrode, and the material of the bottom electrode 2 of this embodiment is preferably aluminum nitride or scandium (Sc)-doped aluminum nitride. Specifically, when the top electrode is externally connected to a signal source (equivalent to applying a voltage signal or an electrical signal to the top electrode), an electric field is formed at both ends of the piezoelectric layer 3 to excite bulk acoustic waves (equivalent to exciting the piezoelectric layer 3 to generate longitudinal waves), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic wave resonator. An acoustic reflector 5 is provided on the substrate 1 of this embodiment, and the acoustic reflector 5 is preferably arranged on the top of the substrate 1. The top electrode of this embodiment has a plane portion 4 and an irregular frame portion 6 located above the acoustic reflector 5. The outer boundary of the projection of the irregular frame portion 6 in the top view direction is located within the outer boundary of the projection of the plane portion 4 in the top view direction and the outer boundary of the projection of the acoustic reflector 5 in the top view direction. The irregular frame portion 6 is located within the plane portion 4 in the top view direction, that is, this embodiment is equivalent to making the irregular frame portion 6 surround the plane portion 4 and shrink inwardly in the plane portion 4. The irregular frame portion 6 protrudes or is recessed in the plane portion 4. Specifically, in the irregular When the frame portion 6 protrudes from the plane portion 4, the irregular frame portion 6 of this embodiment can suppress the transverse wave leakage of the bulk acoustic wave resonator to improve the quality factor of the bulk acoustic wave resonator. When the irregular frame portion 6 is recessed in the plane portion 4, the irregular frame portion 6 can suppress the parasitic mode at the series resonance frequency to improve the quality factor of the bulk acoustic wave resonator. That is, the present application is equivalent to replacing the existing protruding structure with the irregular frame portion 6 protruding from the plane portion 4 and replacing the existing recessed structure with the irregular frame portion 6 recessed in the plane portion 4. The outer contour of the cross section of the irregular frame portion 6 of this embodiment is irregular. Specifically, when the irregular frame portion 6 protrudes from the plane portion 4, the outer contour of the cross section of the irregular frame portion 6 is the cross-sectional contour of the top surface of the irregular frame portion 6. When the irregular frame portion 6 is recessed in the plane portion 4, the outer contour of the cross section of the irregular frame portion 6 is the cross-sectional contour of the bottom surface of the irregular frame portion 6. Refer to Figure 5 ( Figure 5 The left figure in FIG. 1 is a schematic diagram of particle displacement of a bulk acoustic wave resonator for reducing stray modes provided by the present application. Figure 5 The right figure in FIG. 1 is a schematic diagram of particle displacement of a conventional BAW resonator with a convex structure. It should be understood that in order to better illustrate the irregular shape of the outer contour of the cross section of the irregular frame portion 6, Figure 5 and Figure 6The outer contour of the cross section of the irregular frame portion 6 is enlarged) It can be seen that the particle displacement of the existing BAW resonator with a convex structure is twice the sum of the thickness of the planar portion 4, the thickness of the convex structure, the thickness of the piezoelectric layer 3 and the thickness of the bottom electrode 2. The present application makes the outer contour of the cross section of the irregular frame portion 6 irregular so that the particle displacement is greater than twice the sum of the thickness of the planar portion 4, the thickness of the irregular frame portion 6, the thickness of the piezoelectric layer 3 and the thickness of the bottom electrode 2. That is, compared with the prior art, the present application can effectively increase the particle displacement. Since the particle displacement is positively correlated with the wavelength, and the frequency The rate is negatively correlated with the wavelength, that is, the particle displacement is negatively correlated with the frequency. Therefore, this embodiment can reduce the frequency of the stray mode or reduce the stray mode by increasing the particle displacement. It should be understood that even if the BAW resonator for reducing the stray mode of the present application cannot eliminate the stray mode, the present application can also make the frequency of the stray mode less than the series resonance frequency of the BAW resonator -100MHz by making the outer contour of the cross-section of the irregular frame portion 6 irregular. That is, even if there is a stray mode caused by improper size setting of the irregular frame portion 6, the stray mode will not be formed near the series resonance frequency.

[0031] The present application provides a bulk acoustic wave resonator for reducing stray modes, which is equivalent to using an irregular frame portion 6 to replace the existing protruding structure and recessed structure and making the outer contour of the cross section of the irregular frame portion 6 irregular so that the stray mode will not be formed near the series resonance frequency or the stray mode is eliminated. Even if the size of the irregular frame portion 6 of the present application is improperly set and the stray mode cannot be eliminated, the present application can prevent the stray mode from being formed near the series resonance frequency, and the stray mode not formed near the series resonance frequency will not attenuate the insertion loss in the passband of the bulk acoustic wave filter. Therefore, the present application can effectively solve the problem of stray modes formed near the series resonance frequency and deterioration of the performance of the bulk acoustic wave filter due to improper size setting of the protruding structure or the recessed structure.

[0032] In some preferred embodiments, Figure 3 As shown, the top electrode has two irregular frame portions 6 distributed inside and outside, one of which protrudes from the plane portion 4, and the other irregular frame portion 6 is recessed in the plane portion 4. Since the top electrode of this embodiment has two irregular frame portions 6 distributed inside and outside, one of which protrudes from the plane portion 4, and the other irregular frame portion 6 is recessed in the plane portion 4, this embodiment can suppress the parasitic mode at the series resonance frequency while suppressing the shear wave leakage of the BAW resonator, thereby effectively improving the quality factor of the BAW resonator.

[0033] In some preferred embodiments, the irregular frame portion 6 protruding from the plane portion 4 is located outside the irregular frame portion 6 recessed in the plane portion 4. This embodiment is equivalent to making the outer side of the irregular frame portion 6 recessed in the plane portion 4 retract into the irregular frame portion 6 protruding from the plane portion 4.

[0034] In some preferred embodiments, the two irregular frame portions 6 are concentric in shape when viewed from above.

[0035] In some preferred embodiments, the maximum vertical spacing between the irregular frame portion 6 and the plane portion 4 is 1nm-1μm, and the width of the irregular frame portion 6 is 0.1-5μm. This embodiment avoids the irregular frame portion 6 being too high or too deep by setting the maximum vertical spacing between the irregular frame portion 6 and the plane portion 4 (equivalent to the difference between the maximum height of the irregular frame portion 6 and the height of the plane portion 4) to 1nm-1μm, and avoids the irregular frame portion 6 being too wide by setting the width of the irregular frame portion 6 to 0.1-5μm, that is, this embodiment is equivalent to setting the size of the irregular frame portion 6 appropriately, so this embodiment can effectively reduce the stray modes generated by improper size setting of the irregular frame portion 6, thereby further improving the performance of the BAW resonator.

[0036] In some preferred embodiments, the outer contour of the cross section of the irregular frame portion 6 is formed by connecting a plurality of base lines, and the base lines are arc segments or straight line segments. Figure 5 As shown, the outer contour of the cross section of the irregular frame portion 6 of this embodiment may be composed of straight line segments of different inclination angles and / or lengths, such as Figure 6 As shown, the outer contour of the cross section of the irregular frame portion 6 of this embodiment can also be composed of arc segments and straight line segments with different inclination angles and / or lengths. The outer contour of the cross section of the irregular frame portion 6 of this embodiment can also be composed of arc segments with different radii and / or curvature directions.

[0037] In some preferred embodiments, the outer contours of different cross sections of the irregular frame portion 6 are the same. Since the outer contours of different cross sections of the irregular frame portion 6 of this embodiment are the same, this embodiment is equivalent to ensuring the consistency and symmetry of the irregular frame portion 6, thereby effectively improving the performance stability of the BAW resonator.

[0038] In some preferred embodiments, the outer contour of the cross section of the irregular frame portion 6 changes continuously. Since the irregular patterns corresponding to different cross sections of the irregular frame portion 6 of this embodiment are different, this embodiment can effectively interfere with the propagation path of the stray mode, thereby better reducing the frequency of the stray mode or eliminating the stray mode.

[0039] In some preferred embodiments, the ratio of the average distance between the outer boundary of the irregular frame portion 6 in the top view direction and the outer boundary of the plane portion 4 in the top view direction and the length of the acoustic reflector 5 is 1:35-1:25. This embodiment enables the BAW resonator to more effectively reduce stray modes by setting the ratio of the average distance between the outer boundary of the irregular frame portion 6 in the top view direction and the outer boundary of the plane portion 4 in the top view direction and the length of the acoustic reflector 5 to 1:35-1:25.

[0040] From the above, it can be seen that the present application provides a bulk acoustic wave resonator for reducing stray modes, which is equivalent to using an irregular frame portion 6 to replace the existing protruding structure and recessed structure and making the outer contour of the cross section of the irregular frame portion 6 irregular so that the stray mode will not be formed near the series resonance frequency or the stray mode is eliminated. Even if the size of the irregular frame portion 6 of the present application is improperly set and the stray mode cannot be eliminated, the present application can prevent the stray mode from being formed near the series resonance frequency, and the stray mode not formed near the series resonance frequency will not attenuate the insertion loss in the passband of the bulk acoustic wave filter. Therefore, the present application can effectively solve the problem of stray modes formed near the series resonance frequency and deterioration of the performance of the bulk acoustic wave filter due to improper size setting of the protruding structure or the recessed structure.

[0041] In a second aspect, the present application further provides a bulk acoustic wave filter, which includes a bulk acoustic wave resonator for reducing spurious modes provided in the first aspect.

[0042] An embodiment of the present application provides a bulk acoustic wave filter, which includes a bulk acoustic wave resonator for reducing stray modes provided by the first aspect above. The principle of the bulk acoustic wave filter provided by the embodiment of the present application is the same as the principle of the bulk acoustic wave resonator for reducing stray modes provided by the first aspect above, and will not be discussed in detail here.

[0043] From the above, it can be seen that the present application provides a BAW resonator and BAW filter for reducing stray modes, which is equivalent to using an irregular frame portion 6 to replace the existing protruding structure and recessed structure and making the outer contour of the cross section of the irregular frame portion 6 irregular so that the stray mode will not be formed near the series resonance frequency or the stray mode is eliminated. Even if the size of the irregular frame portion 6 of the present application is improperly set and the stray mode cannot be eliminated, the present application can prevent the stray mode from being formed near the series resonance frequency, and the stray mode not formed near the series resonance frequency will not attenuate the insertion loss in the passband of the BAW filter. Therefore, the present application can effectively solve the problem of stray modes formed near the series resonance frequency and deterioration of the performance of the BAW filter due to improper size setting of the protruding structure or the recessed structure.

[0044] In the embodiments provided in the present application, it should be understood that, herein, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0045] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A bulk acoustic wave resonator for reducing spurious modes, characterized in that: The bulk acoustic wave resonator for reducing spurious modes comprises: A substrate, a bottom electrode, a piezoelectric layer and a top electrode are connected in sequence from bottom to top, and an acoustic reflector is arranged on the substrate; The top electrode comprises a planar portion and an irregular frame portion located above the acoustic reflector, the irregular frame portion protrudes or is recessed from the planar portion, the outer contour of the cross section of the irregular frame portion is irregular, the outer boundary of the projection of the irregular frame portion in the top-view direction is located within the outer boundary of the projection of the planar portion in the top-view direction and the outer boundary of the projection of the acoustic reflector in the top-view direction, and the irregular frame portion is located within the planar portion in the top-view direction.

2. The bulk acoustic wave resonator for reducing spurious modes according to claim 1, characterized in that: The top electrode has two irregular frame parts distributed inside and outside, wherein one of the irregular frame parts protrudes from the plane part, and the other irregular frame part is recessed in the plane part.

3. The bulk acoustic wave resonator for reducing spurious modes according to claim 2, characterized in that: The irregular frame portion protruding from the plane portion is located outside the irregular frame portion recessed from the plane portion.

4. The bulk acoustic wave resonator for reducing spurious modes according to claim 2, characterized in that: The two irregular frame parts are concentric in shape when viewed from above.

5. The bulk acoustic wave resonator for reducing spurious modes according to claim 1, characterized in that: The maximum distance between the irregular frame portion and the planar portion is 1 nm-1 μm, and the width of the irregular frame portion is 0.1-5 μm.

6. The bulk acoustic wave resonator for reducing spurious modes according to claim 1, characterized in that: The outer contour of the cross section of the irregular frame portion is formed by connecting a plurality of base lines, and the base lines are arc segments or straight line segments.

7. The bulk acoustic wave resonator for reducing spurious modes according to claim 1, characterized in that: The outer contours of different cross sections of the irregular frame portion are the same.

8. The bulk acoustic wave resonator for reducing spurious modes according to claim 1, characterized in that: The outer contour of the cross section of the irregular frame portion changes continuously.

9. The bulk acoustic wave resonator for reducing spurious modes according to claim 1, characterized in that: The ratio of an average distance between an outer boundary of the irregular frame portion in a top view direction and an outer boundary of the planar portion in a top view direction and a length of the acoustic reflector is 1:35-1:

25.

10. A bulk acoustic wave filter, characterized in that: The BAW filter comprises a BAW resonator for reducing spurious modes as claimed in any one of claims 1 to 9.

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