A bulk acoustic resonator and bulk acoustic filter for reducing stray modes

Abstract

This application relates to the field of bulk acoustic wave resonator technology, specifically providing a bulk acoustic wave resonator and bulk acoustic wave filter for reducing stray modes. The resonator includes: a substrate, a bottom electrode, a piezoelectric layer, and a top electrode connected sequentially from bottom to top; the top electrode has a planar portion and an irregular frame portion located above an acoustic reflector. The irregular frame portion protrudes or is recessed in the planar portion, and 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. The irregular frame portion is located within the planar portion in the top view direction. This resonator can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic wave filter due to improper dimensional settings of the protruding or recessed structure.

Description

Technical Field

[0001] This application relates to the field of bulk acoustic resonator technology, and more specifically, to a bulk acoustic resonator and bulk acoustic filter for reducing stray modes. Background Technology

[0002] Related technologies use bulk acoustic wave filters as the core device of radio frequency front-end modules and widely apply bulk acoustic wave filters in fields such as communication filtering and navigation positioning. The relevant bulk acoustic wave filters are composed of multiple series and parallel bulk acoustic wave resonators. Related technologies typically improve the quality factor of a bulk acoustic wave (BAS) resonator by setting protruding or recessed structures on the electrodes above the acoustic reflector of the BAS resonator. However, if the size of the protruding or recessed structure is improperly set (e.g., the protrusion is too wide, the recess is too wide, the protrusion is too high, or the recess is too deep), the protruding or recessed structure will form an independent resonator with the other diaphragms of the BAS resonator. The characteristic frequency generated by the vibration of this independent resonator is different from the target characteristic frequency of the BAS resonator, resulting in the formation of stray modes near the series resonant frequency (within the range of series resonant frequency -100MHz to series resonant frequency). These stray modes formed near the series resonant frequency will attenuate the insertion loss in the passband of the BAS filter, thereby degrading the performance of the BAS filter. In other words, related technologies have the problem of stray modes forming near the series resonant frequency and degrading the performance of the BAS filter due to improper size setting of the protruding or recessed structure.

[0003] Currently, there is no effective technical solution to the above-mentioned problems. It should be noted that the information disclosed in this section is only for understanding the background of the present invention and therefore may include information that does not constitute prior art. Summary of the Invention

[0004] The purpose of this application is to provide a bulk acoustic resonator and bulk acoustic filter that reduces stray modes, which can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic filter due to improper size setting of the protruding or recessed structure.

[0005] In a first aspect, this application provides a bulk acoustic resonator for reducing stray modes, comprising:

[0006] The substrate, bottom electrode, piezoelectric layer and top electrode are connected in sequence from bottom to top, and an acoustic reflector is provided on the substrate;

[0007] The top electrode has 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. The irregular frame portion is located within the planar portion in the top view direction.

[0008] This application provides a bulk acoustic resonator for reducing stray modes. It replaces existing protruding and recessed structures with an irregular frame portion and makes the outer contour of the cross-section of the irregular frame portion irregular, thus preventing stray modes from forming near the series resonant frequency or eliminating stray modes altogether. Even if the dimensions of the irregular frame portion in this application are improperly set and stray modes cannot be eliminated, this application can still prevent stray modes from forming near the series resonant frequency. Since stray modes not forming near the series resonant frequency do not attenuate the insertion loss within the passband of the bulk acoustic filter, this application can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic filter due to improper dimensional settings of the protruding or recessed structures.

[0009] Optionally, the top electrode has two irregularly shaped frame portions distributed inside and outside, one of which protrudes from the planar portion and the other is recessed into the planar portion.

[0010] Because the top electrode of this technical solution has two irregularly shaped frame portions distributed inside and outside, with one irregular frame portion protruding from the planar portion and the other irregular frame portion recessed in the planar portion, this technical solution can suppress the transverse wave leakage of the bulk acoustic resonator while suppressing the parasitic modes at the series resonant frequency, thereby effectively improving the quality factor of the bulk acoustic resonator.

[0011] Optionally, the irregular frame portion protruding from the planar portion is located outside the irregular frame portion recessed in the planar portion.

[0012] Optionally, the two irregular frame sections are concentric in shape in the top view direction.

[0013] 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.

[0014] This technical solution avoids the irregular frame portion being too high or too deep by setting the maximum vertical distance between the irregular frame portion and the planar portion to 1nm-1μm, and avoids the irregular frame portion being too wide by setting the width of the irregular frame portion to 0.1-5μm. In other words, this technical solution is equivalent to setting the size of the irregular frame portion appropriately. Therefore, this technical solution can effectively reduce stray modes caused by improper size setting of the irregular frame portion, thereby further improving the performance of the bulk acoustic resonator.

[0015] Optionally, the outer contour of the cross-section of the irregular frame portion is formed by connecting multiple base lines, where the base lines are arc segments or straight line segments.

[0016] Optionally, the outer contours of different cross sections of the irregular frame section are the same.

[0017] Optionally, the outer contour of the cross-section of the irregular frame portion changes continuously.

[0018] Optionally, the ratio of the average distance between the outer boundary of the irregular frame portion in the top view and the outer boundary of the planar portion in the top view to the length of the acoustic reflector is 1:35-1:25.

[0019] Secondly, this application also provides a bulk acoustic wave filter, which includes a bulk acoustic wave resonator for reducing stray modes provided in the first aspect above.

[0020] This application provides a bulk acoustic wave filter that replaces existing protruding and recessed structures with an irregular frame portion. By setting the outer contour of the cross-section of the irregular frame portion to be irregular, stray modes are prevented from forming near the series resonant frequency or are eliminated. Even if the size of the irregular frame portion in this application is improperly set and stray modes cannot be eliminated, this application can still prevent stray modes from forming near the series resonant frequency. Since stray modes not forming near the series resonant frequency do not attenuate the insertion loss in the passband of the bulk acoustic wave filter, this application can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic wave filter due to improper size setting of the protruding or recessed structure.

[0021] As can be seen from the above, the bulk acoustic resonator and bulk acoustic filter provided in this application for reducing stray modes are equivalent to replacing the existing protruding and recessed structures with an irregular frame portion and making the outer contour of the cross-section of the irregular frame portion irregular, so that stray modes will not form near the series resonant frequency or will be eliminated. Since even if the size of the irregular frame portion of this application is improperly set and stray modes cannot be eliminated, this application can still prevent stray modes from forming near the series resonant frequency. The stray modes not formed near the series resonant frequency will not attenuate the insertion loss in the passband of the bulk acoustic filter. Therefore, this application can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic filter due to improper size setting of the protruding or recessed structure. Attached Figure Description

[0022] Figure 1 This is a cross-sectional structural schematic diagram of a bulk acoustic resonator for reducing stray modes, provided for the first technical solution of this application.

[0023] Figure 2 A cross-sectional structural schematic diagram of a bulk acoustic resonator for reducing stray modes, provided as the second technical solution of this application.

[0024] Figure 3 This is a cross-sectional structural schematic diagram of a bulk acoustic resonator for reducing stray modes, provided as the third technical solution of this application.

[0025] Figure 4 A schematic diagram of a bulk acoustic resonator for reducing stray modes provided in this application.

[0026] Figure 5 A schematic diagram showing the comparison between the particle displacement of the bulk acoustic resonator with reduced stray modes provided in this application and the particle displacement of existing bulk acoustic resonators.

[0027] Figure 6 A cross-sectional schematic diagram of the bottom electrode, piezoelectric layer, and irregular frame portion provided for the technical solution of this application.

[0028] Reference numerals: 1. Substrate; 2. Bottom electrode; 3. Piezoelectric layer; 4. Planar portion; 5. Acoustic reflector; 6. Irregular frame portion. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0030] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0031] Firstly, such as Figures 1-6 As shown, this application provides a bulk acoustic resonator for reducing stray modes, comprising:

[0032] From bottom to top, a substrate 1, a bottom electrode 2, a piezoelectric layer 3 and a top electrode are connected in sequence, and an acoustic reflector 5 is provided on the substrate 1;

[0033] The top electrode has a planar portion 4 located above the acoustic reflector 5 and an irregular frame portion 6. The irregular frame portion 6 protrudes or is recessed in 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.

[0034] In this embodiment, the substrate 1 is preferably made of silicon. The bottom electrode 2 and the top electrode are preferably made of one or more metals with high conductivity, high acoustic impedance and high Young's modulus (e.g., gold, silver, ruthenium, tungsten, molybdenum, aluminum, platinum, niobium or hafnium). The bottom electrode 2 is preferably made of the same material as the top electrode. The bottom electrode 2 is preferably made of aluminum nitride or scandium (Sc)-doped aluminum nitride. Specifically, when an external signal source is connected to the top electrode (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 the bulk acoustic wave (equivalent to exciting the piezoelectric layer 3 to generate a longitudinal wave), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic resonator. The substrate 1 in this embodiment is provided with an acoustic reflector 5, which is preferably disposed on the top of the substrate 1. In this embodiment, the top electrode has a planar portion 4 located above the acoustic reflector 5 and an irregular frame portion 6. 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. That is, in this embodiment, the irregular frame portion 6 is equivalent to surrounding the planar portion 4 and being recessed within the planar portion 4. The irregular frame portion 6 protrudes or is recessed in the planar portion 4. Specifically, in the irregular... When the frame portion 6 protrudes from the planar portion 4, the irregular frame portion 6 in this embodiment can suppress the transverse wave leakage of the bulk acoustic wave resonator, thereby improving the quality factor of the bulk acoustic wave resonator. When the irregular frame portion 6 is recessed into the planar portion 4, the irregular frame portion 6 can suppress parasitic modes at the series resonant frequency, thereby improving the quality factor of the bulk acoustic wave resonator. That is, this application is equivalent to replacing the existing protruding structure with the irregular frame portion 6 protruding from the planar portion 4 and replacing the existing recessed structure with the irregular frame portion 6 recessed into the planar portion 4. The outer contour of the cross-section of the irregular frame portion 6 in this embodiment is irregular. Specifically, when the irregular frame portion 6 protrudes from the planar 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 into the planar 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 the image is a schematic diagram of the particle displacement of the bulk acoustic resonator for reducing stray modes provided in this application. Figure 5 The right figure in the diagram is a schematic diagram of the particle displacement of an existing bulk acoustic resonator with a protruding structure. It should be understood that the diagram is designed to better illustrate the irregular shape of the outer contour of the cross-section of the irregular frame section 6. Figure 5 and Figure 6(The outer contour of the cross-section of the irregular frame portion 6 has been magnified.) It can be seen that the particle displacement of existing bulk acoustic resonators with protruding structures is twice the sum of the thickness of the planar portion 4, the thickness of the protruding structure, the thickness of the piezoelectric layer 3, and the thickness of the bottom electrode 2. However, this application, by making the outer contour of the cross-section of the irregular frame portion 6 irregular, makes the particle displacement greater than twice the sum of the thicknesses of the planar portion 4, the irregular frame portion 6, the piezoelectric layer 3, and the bottom electrode 2. That is, compared to the prior art, this application can effectively increase the particle displacement. Since the particle displacement is positively correlated with wavelength, and frequency... Since the frequency is negatively correlated with the wavelength, that is, the particle displacement is negatively correlated with the frequency, this embodiment can reduce the frequency of stray modes or reduce stray modes by increasing the particle displacement. It should be understood that even if the bulk acoustic resonator for reducing stray modes in this application cannot eliminate stray modes, this application can make the frequency of stray modes less than the series resonant frequency of the bulk acoustic resonator -100MHz by making the outer contour of the cross-section of the irregular frame portion 6 irregular. That is, even if there are stray modes caused by improper size setting of the irregular frame portion 6, the stray modes will not form near the series resonant frequency.

[0035] This application provides a bulk acoustic resonator for reducing stray modes. This is equivalent to replacing existing protruding and recessed structures with an irregular frame portion 6, and preventing stray modes from forming near the series resonant frequency or eliminating stray modes by making the outer contour of the cross-section of the irregular frame portion 6 irregular. Even if the dimensions of the irregular frame portion 6 are improperly set and stray modes cannot be eliminated, this application can still prevent stray modes from forming near the series resonant frequency. Since stray modes not forming near the series resonant frequency do not attenuate the insertion loss in the passband of the bulk acoustic filter, this application can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic filter due to improper dimensional settings of the protruding or recessed structures.

[0036] In some preferred embodiments, such as Figure 3 As shown, the top electrode has two irregularly shaped frame portions 6 distributed internally and externally, one of which protrudes from the planar portion 4, and the other is recessed into the planar portion 4. Because the top electrode of this embodiment has two irregularly shaped frame portions 6 distributed internally and externally, with one protruding from the planar portion 4 and the other recessed, this embodiment can suppress parasitic modes at the series resonant frequency while suppressing the transverse wave leakage of the bulk acoustic resonator, thereby effectively improving the quality factor of the bulk acoustic resonator.

[0037] In some preferred embodiments, the irregular frame portion 6 protruding from the planar portion 4 is located outside the irregular frame portion 6 recessed in the planar portion 4. This embodiment is equivalent to the irregular frame portion 6 recessed in the planar portion 4 being recessed inward to the irregular frame portion 6 protruding from the planar portion 4.

[0038] In some preferred embodiments, the two irregular frame portions 6 are concentric in shape in the top view direction.

[0039] In some preferred embodiments, the maximum vertical distance between the irregular frame portion 6 and the planar portion 4 is 1 nm-1 μm, and the width of the irregular frame portion 6 is 0.1-5 μm. This embodiment avoids the irregular frame portion 6 being too high or too deep by setting the maximum vertical distance between the irregular frame portion 6 and the planar portion 4 (equivalent to the difference between the maximum height of the irregular frame portion 6 and the height of the planar portion 4) to 1 nm-1 μm, and avoids the irregular frame portion 6 being too wide by setting the width of the irregular frame portion 6 to 0.1-5 μm. That is, this embodiment is equivalent to setting the size of the irregular frame portion 6 appropriately. Therefore, this embodiment can effectively reduce stray modes caused by improper size setting of the irregular frame portion 6, thereby further improving the performance of the bulk acoustic resonator.

[0040] In some preferred embodiments, the outer contour of the cross-section of the irregular frame portion 6 is formed by connecting multiple base lines, where the base lines are arc segments or straight line segments. For example... Figure 5 As shown, the outer contour of the cross-section of the irregular frame portion 6 in this embodiment can be formed by connecting straight line segments with 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 in this embodiment can also be formed by connecting arc segments and straight segments with different inclination angles and / or lengths. The outer contour of the cross-section of the irregular frame portion 6 in this embodiment can also be formed by connecting arc segments with different radii and / or curvature orientations.

[0041] 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 in 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 bulk acoustic resonator.

[0042] 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 in this embodiment are different, this embodiment can effectively interfere with the propagation path of stray modes, thereby better reducing the frequency of stray modes or eliminating stray modes.

[0043] In some preferred embodiments, the ratio of the average distance between the outer boundary of the irregular frame portion 6 and the outer boundary of the planar portion 4 in the top view direction to the length of the acoustic reflector 5 is 1:35-1:25. This embodiment enables the bulk acoustic 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 and the outer boundary of the planar portion 4 in the top view direction to the length of the acoustic reflector 5 to 1:35-1:25.

[0044] As can be seen from the above, the bulk acoustic resonator for reducing stray modes provided in this application is equivalent to replacing the existing protruding and recessed structures with an irregular frame portion 6, and making the outer contour of the cross-section of the irregular frame portion 6 irregular, so that stray modes will not form near the series resonant frequency or will be eliminated. Since even if the size of the irregular frame portion 6 in this application is improperly set and stray modes cannot be eliminated, this application can still prevent stray modes from forming near the series resonant frequency. The stray modes not formed near the series resonant frequency will not attenuate the insertion loss in the passband of the bulk acoustic filter. Therefore, this application can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic filter due to improper size setting of the protruding or recessed structure.

[0045] Secondly, this application also provides a bulk acoustic wave filter, which includes a bulk acoustic wave resonator for reducing stray modes provided in the first aspect above.

[0046] This application provides a bulk acoustic wave filter, which includes a bulk acoustic wave resonator for reducing stray modes provided in the first aspect above. The principle of the bulk acoustic wave filter provided in this application is the same as that of the bulk acoustic wave resonator for reducing stray modes provided in the first aspect above, and will not be discussed in detail here.

[0047] As can be seen from the above, the bulk acoustic resonator and bulk acoustic filter provided in this application for reducing stray modes are equivalent to replacing the existing protruding and recessed structures with an irregular frame portion 6, and making the outer contour of the cross-section of the irregular frame portion 6 irregular, so that stray modes will not form near the series resonant frequency or will be eliminated. Since even if the size of the irregular frame portion 6 in this application is improperly set and stray modes cannot be eliminated, this application can still prevent stray modes from forming near the series resonant frequency. The stray modes not formed near the series resonant frequency will not attenuate the insertion loss in the passband of the bulk acoustic filter. Therefore, this application can effectively solve the problem of stray modes forming near the series resonant frequency and the performance degradation of the bulk acoustic filter due to improper size setting of the protruding or recessed structure.

[0048] In the embodiments provided in this application, it should be understood that relational terms such as first and second are used only 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.

[0049] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A bulk acoustic resonator for reducing stray modes, characterized in that, The bulk acoustic resonator for reducing stray modes includes: The substrate, bottom electrode, piezoelectric layer and top electrode are connected in sequence from bottom to top, and an acoustic reflector is provided on the substrate; The top electrode has 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. The irregular frame portion is located within the planar portion in the top view direction. The top electrode has two irregularly shaped frame portions distributed inside and outside, one of which protrudes from the planar portion and the other is recessed into the planar portion; The outer contour of the cross-section of the irregular frame portion is formed by connecting multiple base lines, and the base lines are arc segments or straight line segments. The ratio of the average distance between the outer boundary of the irregular frame portion in the top view and the outer boundary of the planar portion in the top view to the length of the acoustic reflector is 1:35-1:

25.

2. The bulk acoustic resonator for reducing stray modes according to claim 1, characterized in that, The irregular frame portion protruding from the planar portion is located outside the irregular frame portion recessed in the planar portion.

3. The bulk acoustic resonator for reducing stray modes according to claim 1, characterized in that, The two irregular frame sections are concentric in shape in the top view direction.

4. The bulk acoustic resonator for reducing stray 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.

5. The bulk acoustic resonator for reducing stray modes according to claim 1, characterized in that, The outer contours of different cross sections of the irregular frame are the same.

6. The bulk acoustic resonator for reducing stray modes according to claim 1, characterized in that, The outer contour of the cross-section of the irregular frame portion changes continuously.

7. A bulk acoustic wave filter, characterized in that, The bulk acoustic filter includes a bulk acoustic resonator for reducing stray modes as described in any one of claims 1-6.

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