Thin-film bulk acoustic resonator

Abstract

The present invention provides a thin-film bulk acoustic resonator. The resonator comprises a substrate, an acoustic reflection structure arranged on one side of the substrate, a bottom electrode stacked on the side of the acoustic reflection structure distant from the substrate, a piezoelectric film stacked on the side of the bottom electrode distant from the acoustic reflection structure, a top electrode stacked on the side of the piezoelectric film distant from the bottom electrode, and a protruding frame arranged on the side of the top electrode distant from the piezoelectric film; a spatial region formed by overlapping of the acoustic reflection structure, the bottom electrode, the piezoelectric film and the top electrode in the thickness direction of the thin-film bulk acoustic resonator is a resonance region; the protruding frame is located in the resonance region; and a plurality of holes are formed in the side of the protruding frame distant from the top electrode. According to the present invention, the area ratio of the protruding frame in the resonance region can be reduced, the intensity of a parasitic resonance peak caused by the protruding frame is reduced, the Q value of the resonator is not reduced, and steps of the manufacturing process are not increased.

Description

Thin Film Bulk Acoustic Resonator Technical Field

[0001] The present invention belongs to the field of resonators, and more particularly, relates to a thin film bulk acoustic resonator. Background Art

[0002] A film bulk acoustic wave resonator (FBAR) is a resonator manufactured using a silicon substrate using MEMS and thin film technologies. It can perform functions such as image cancellation, parasitic filtering, and channel selection in wireless transceivers. It has a high quality factor and is easily miniaturized.

[0003] The main structure of a thin film bulk acoustic wave resonator consists of a bottom electrode, a piezoelectric layer, and a top electrode. Its working principle is as follows: when a radio frequency electrical signal is applied to the top and bottom electrodes, the piezoelectric film generates mechanical vibrations in the longitudinal direction under the action of the inverse piezoelectric effect, and forms bulk acoustic waves. Under the action of the piezoelectric effect, these bulk acoustic waves are converted into electrical signals, thereby realizing the selection of electrical signals of different frequencies. In the related art, a RAF (raised frame) is provided in the thin film bulk acoustic wave resonator. The RAF has a higher acoustic impedance than the central area. The RAF increases the acoustic impedance mismatch between the central area and the outside of the resonance region, causing the transverse parasitic acoustic waves (mainly Rayleigh-Lamb waves) propagating outside the resonance region to be reflected back to the resonance region at the boundary of the region. Therefore, the energy leaked at the edge of the resonance region is reduced, and the Q value of the resonator is higher.

[0004] Since the relationship curve between the resonator's Qp and RAF width is periodic, as the RAF width increases, the resonator's Qp will increase, and the area ratio of RAF in the resonance region will continue to increase, resulting in the appearance of RAF parasitic resonance peaks in the frequency band where the resonator is far away from fs, and the intensity of the RAF parasitic resonance peak tends to increase with the area ratio of RAF in the resonance region. Technical issues

[0005] The object of the present invention is to provide a thin film bulk acoustic resonator, aiming to solve the problem of excessively high parasitic resonance peak intensity introduced by the raised frame. Technical Solutions

[0006] To achieve the above-mentioned objectives, the present invention provides a thin film bulk acoustic wave resonator, which includes a substrate, an acoustic reflection structure arranged on one side of the substrate, a bottom electrode stacked on a side of the acoustic reflection structure away from the substrate, a piezoelectric film stacked on a side of the bottom electrode away from the acoustic reflection structure, a top electrode stacked on a side of the piezoelectric film away from the bottom electrode, and a raised frame arranged on a side of the top electrode away from the piezoelectric film. The spatial region formed by the overlapping of the acoustic reflection structure, the bottom electrode, the piezoelectric film and the top electrode along the thickness direction of the thin film bulk acoustic wave resonator is a resonance region. The raised frame is located in the resonance region, and a plurality of openings are provided on a side of the raised frame away from the top electrode.

[0007] In some embodiments of the present invention, the openings are arranged in sequence along the horizontal extension direction of the raised frame, and a distance between two adjacent openings is greater than a diameter of the opening.

[0008] In some embodiments of the present invention, the opening is a through hole that passes through two opposite sides of the raised frame; and / or, the opening is a blind hole.

[0009] In some embodiments of the present invention, the raised frame is annularly arranged near the resonance region along a projected edge in the thickness direction of the FBAR, and each of the openings is opened in a partial area on a horizontally extending plane of the raised frame.

[0010] In some embodiments of the present invention, the cross section of the opening is a combination of one or more shapes including circular, elliptical or rectangular.

[0011] In some embodiments of the present invention, a recessed frame is formed on the surface of the top electrode and is close to the inner peripheral wall of the raised frame.

[0012] In some embodiments of the present invention, the FBAW resonator further includes a cantilever beam connected to an outer peripheral wall of the top electrode and extending in a direction away from the piezoelectric film, with an air gap between the cantilever beam and the piezoelectric film.

[0013] In some embodiments of the present invention, the raised frame is provided with at least one cutout, and the cutout passes through the inner peripheral wall and the outer peripheral wall of the raised frame.

[0014] In some embodiments of the present invention, the closest distance between the edge of the opening and the edge of the raised frame is an odd multiple of a quarter wavelength of the transverse parasitic acoustic wave.

[0015] In some embodiments of the present invention, the FBAR further includes a protection layer stacked between the top electrode and the raised frame.

[0016] In some embodiments of the present invention, the acoustic reflection structure is a cavity formed inside the substrate, or a cavity formed on the side of the substrate close to the bottom electrode, or a Bragg reflector formed on the surface of the substrate. When the acoustic reflection structure is a cavity, the projection of the bottom electrode along the thickness direction of the thin film bulk acoustic resonator is at least partially located outside the acoustic reflection structure. Beneficial effects

[0017] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0018] The present invention provides a thin film bulk acoustic wave resonator, which includes a substrate, an acoustic reflection structure disposed on one side of the substrate, a bottom electrode stacked on a side of the acoustic reflection structure away from the substrate, a piezoelectric film stacked on a side of the bottom electrode away from the acoustic reflection structure, a top electrode stacked on a side of the piezoelectric film away from the bottom electrode, and a raised frame disposed on a side of the top electrode away from the piezoelectric film. The acoustic reflection structure, the bottom electrode, the piezoelectric film, and the top electrode overlap along the thickness direction of the thin film bulk acoustic wave resonator to form a spatial region that serves as a resonance region. The raised frame is located within the resonance region, and a plurality of openings are formed on a side of the raised frame away from the top electrode. The present invention can reduce the area ratio of the raised frame in the resonance region and reduce the intensity of the parasitic resonance peak introduced by the raised frame without reducing the Q value of the resonator and without increasing the number of manufacturing process steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1a is a top view of a thin film bulk acoustic resonator according to an embodiment of the present invention;

[0020] FIG1b is a cross-sectional view of the thin film bulk acoustic resonator in FIG1a along the line A-A;

[0021] FIG1c is an impedance curve diagram showing a RAF parasitic resonance peak in a thin film bulk acoustic resonator according to an embodiment of the present invention;

[0022] FIG1d is a data graph showing the corresponding peak intensity of RAF parasitic resonance and different area ratios of RAF in the resonance region in thin film bulk acoustic resonators according to various embodiments of the present invention;

[0023] FIG2 is a top view of a film bulk acoustic resonator in another embodiment of the present invention, in which a local area of ​​a raised frame is provided with an opening;

[0024] FIG3 is a cross-sectional view of the thin film bulk acoustic resonator in FIG2 along the line AA;

[0025] FIG4 is a top view of a FBAR in another embodiment of the present invention, in which the cross section of the opening of the raised frame is an ellipse;

[0026] FIG5 is a cross-sectional view of the thin film bulk acoustic resonator in FIG4 along the line AA;

[0027] FIG6 is a top view of a FBAR in another embodiment of the present invention in which the opening of the raised frame is a blind hole;

[0028] FIG7 is a cross-sectional view of the thin film bulk acoustic resonator in FIG6 along the line AA;

[0029] FIG8 is a top view of a FBAR in another embodiment of the present invention, in which the openings of the convex frame are arranged as a combination of blind holes and through holes;

[0030] FIG9 is a cross-sectional view of the thin film bulk acoustic resonator in FIG8 along the line AA;

[0031] FIG10 is a top view of a film bulk acoustic resonator having a recessed frame in accordance with another embodiment of the present invention;

[0032] FIG11 is a cross-sectional view of the thin film bulk acoustic resonator in FIG10 along the line AA;

[0033] FIG12 is a top view of a cantilever beam provided in a thin film bulk acoustic resonator according to another embodiment of the present invention;

[0034] FIG13 is a cross-sectional view of the thin film bulk acoustic resonator in FIG12 along the line AA;

[0035] FIG14 is a top view of a FBAR having a raised frame with cutouts in accordance with another embodiment of the present invention;

[0036] FIG15 is a cross-sectional view of the thin film bulk acoustic resonator in FIG14 along the line AA;

[0037] FIG16 is a top view of a thin film bulk acoustic resonator provided with a protective layer in another embodiment of the present invention;

[0038] FIG17 is a cross-sectional view of the thin film bulk acoustic resonator taken along line AA in FIG16 . Modes for Carrying Out the Invention

[0039] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. In the specific embodiments described herein, the FBAR is exemplified by a rectangular shape. However, this is not intended to limit the FBAR to a rectangular shape; in practice, the FBAR may also be a polygonal or elliptical shape.

[0040] 1a and 1b , the present invention provides a thin film bulk acoustic wave resonator, which includes a substrate 50, an acoustic reflection structure 60 arranged on one side of the substrate 50, a bottom electrode 40 stacked on a side of the acoustic reflection structure 60 away from the substrate 50, a piezoelectric film 30 stacked on a side of the bottom electrode 40 away from the acoustic reflection structure 60, a top electrode 20 stacked on a side of the piezoelectric film 30 away from the bottom electrode 40, and a raised frame 10 arranged on a side of the top electrode 20 away from the piezoelectric film 30. The spatial region formed by the overlapping of the acoustic reflection structure 60, the bottom electrode 40, the piezoelectric film 30 and the top electrode 20 along the thickness direction of the thin film bulk acoustic wave resonator is a resonance region. The raised frame 10 is located in the resonance region, and a plurality of openings 101 are provided on a side of the raised frame 10 away from the top electrode 20.

[0041] Among them, electric energy is applied to the top electrode 20 and the bottom electrode 40 to induce an electric field in the piezoelectric film 30. The electric field will produce an inverse piezoelectric effect in the piezoelectric film 30, converting the electric energy into mechanical energy. The mechanical energy exists in the form of sound waves, and the sound waves have two vibration modes: transverse waves and longitudinal waves.

[0042] In this embodiment, the acoustic reflection structure 60 is a cavity formed inside the substrate 50, or a cavity formed on the side of the substrate 50 close to the bottom electrode 40, or a Bragg reflector formed on the surface of the substrate 50. When the acoustic reflection structure 60 is a cavity, the projection of the bottom electrode 40 along the thickness direction of the thin film bulk acoustic wave resonator is at least partially located outside the acoustic reflection structure 60. The acoustic reflection structure 60 of the thin film bulk acoustic wave resonator provided on the substrate 50 allows the sound waves to be confined to the cavity of the substrate 50, making it difficult for the sound wave energy to be lost, thereby effectively improving the performance of the thin film bulk acoustic wave resonator. The acoustic reflector can also be a layer structure formed on the surface of the substrate 50, the layer structure being composed of a high acoustic impedance layer and a low acoustic impedance layer overlapping each other, the low acoustic impedance layer being silicon oxide, and the high acoustic impedance layer being at least one of tungsten (W), molybdenum (Mo), ruthenium (Ru), iridium (Ir), and the like.

[0043] Under the action of the piezoelectric effect, these bulk acoustic waves are converted into electrical signals, thereby realizing the selection of electrical signals of different frequencies. In the related art, a raised frame 10 is provided in the thin film bulk acoustic wave resonator, and the raised frame 10 has a higher acoustic impedance than the central area. The raised frame 10 increases the acoustic impedance mismatch between the central area and the outside of the resonance area, so that the transverse parasitic acoustic waves (mainly Rayleigh-Lamb waves) propagating outside the resonance area are reflected back to the resonance area at the boundary of the area. Therefore, the energy leaked at the edge of the resonance area is reduced, and the Q value of the thin film bulk acoustic wave resonator is higher.

[0044] Please refer to Figures 1c and 1d. As the RAF width increases, the resonator Qp will increase, and the area ratio of RAF in the resonance region will continue to increase, resulting in the appearance of RAF parasitic resonance peaks in the frequency band of the resonator away from fs, and the intensity of the RAF parasitic resonance peak increases with the area ratio of RAF in the resonance region. The use of a raised frame 10 with an opening 101 can effectively reduce the area ratio of the raised frame 10 in the resonance region and reduce the intensity of the RAF parasitic resonance peak introduced by the excessive width of the annular raised frame 10 (as shown in Figure 3), avoiding the impact of large-amplitude RAF parasitic resonance peaks on the performance of the filter in the frequency band, while not reducing the Q value of the resonator. In addition, the acoustic impedance of the opening 101 structure introduced by the raised frame 10 is different from that of the surrounding area. This acoustic impedance difference can enhance the reflection effect of transverse Rayleigh-Lamb waves.

[0045] Furthermore, the raised frame 10 with the opening 101 can be arranged on the side of the top electrode 20 away from the piezoelectric film 30, or on the side of the bottom electrode 40 away from the piezoelectric film 30, or on the side of the top electrode 20 or the bottom electrode 40 facing the piezoelectric film 30, or in the middle position of the piezoelectric film 30, all of which are in the resonance zone and the opening 101 effectively reduces the area occupied by the raised frame 10 in the resonance zone, thereby reducing the parasitic resonance peak intensity introduced by the raised frame 10.

[0046] In one embodiment of the present invention, the openings 101 are arranged in sequence along the horizontal extension direction of the raised frame 10, and the distance d1 between two adjacent openings 101 is greater than the diameter d of the opening 101, wherein the distance d1 between two adjacent openings 101 is the distance between the geometric centers of the two openings 101. Then, the distance d1 between the two openings 101 is greater than the hole diameter d, indicating that there is a spacing between the adjacent openings 101, and the portion of the raised frame 10 in the spacing space plays a role in reflecting the transverse Rayleigh-Lamb wave, thereby improving the Q value of the thin film bulk acoustic resonator.

[0047] Furthermore, an angle is formed between the wall of the opening 101 of the raised frame 10 and the top electrode 20, and the angle range is 30-90 degrees. For example, the angle can be 30 degrees, 60 degrees, 90 degrees, etc. The opening 101 thus configured has different shapes. The angle between the wall of the opening and the top electrode 20 indicates that the bottom of the opening 101 can be bent or flat, making the opening 101 expandable and diverse.

[0048] In order to enable the raised frame 10 to enhance the acoustic impedance and reflect transverse Rayleigh-Lamb waves, in this embodiment, the material of the raised frame 10 includes a metal material or a dielectric material, or a combination of one or more metal materials and dielectric materials. The metal material can be aluminum (Al), platinum (Pt), gold (Au), tungsten (W), tungsten (Mo), ruthenium (Ru), iridium (Ir), etc., and the dielectric material can be aluminum nitride (AlN) and silicon nitride (Si3N4), etc. The width of the raised frame 10 can range from 10nm to 10000nm, for example, 10nm, 100nm, 1000nm, 10000nm, etc.; the height can range from 10nm to 5000nm, for example, 10nm, 50nm, 500nm, 5000nm, etc.

[0049] Furthermore, the opening 101 of the raised frame 10 may be filled with a material different from that in the non-through hole 101a region, such as AlN, SiO2, SiN, etc.

[0050] In some embodiments, referring to Figures 6 to 9, the opening 101 is a through hole 101a extending through opposite sides of the raised frame 10; and / or, the opening 101 is a blind hole 101b. The blind hole 101b may be opened on the side of the raised frame 10 away from the top electrode 20, or on the side of the raised frame 10 facing the top electrode 20. In other embodiments, the raised frame 10 may be provided with multiple through holes 101a and multiple blind holes 101b. The through holes 101a and blind holes 101b are pre-set and can be combined to adjust the area ratio of the raised frame 10 in the resonance region according to actual needs.

[0051] Specifically, the raised frame 10 is annularly arranged near the resonance region along the projected edge in the thickness direction of the FBAR, and each opening 101 is formed in a portion of the horizontally extending plane of the raised frame 10. The shape of the raised frame 10 can be rectangular, circular, elliptical, or other polygonal.

[0052] In some embodiments, referring to Figures 2 and 3, the openings 101 can be provided on the periphery of the raised frame 10. For example, when the raised frame 10 is rectangular, the openings 101 can be provided on each side of the raised frame 10. The number of openings 101 on each side can be equal or different. The openings 101 can also be provided in a portion of the periphery of the raised frame 10. For example, when the raised frame 10 is rectangular, the openings 101 can be provided on two adjacent sides of the rectangle. The openings 101 on the raised frame 10 are all provided on the propagation path of the transverse Rayleigh-Lamb wave propagating outside the resonance region. When the raised frame 10 reflects the transverse Rayleigh-Lamb wave, the area occupied by the raised frame 10 in the resonance region is reduced, thereby reducing the intensity of the parasitic resonance peak of the raised frame 10. The arrangement of the openings 101 can be provided along a ring pattern as described above, and the arrangement range can be part of or all of the raised frame 10.

[0053] Further, referring to Figures 4 and 5 , in some embodiments of the present invention, the cross-section of the opening 101 can be a combination of one or more of circular, elliptical, or rectangular shapes, or other shapes that can reduce the area of ​​the raised frame 10. On this basis, the opening 101 of one or a combination of multiple shapes can be a through hole 101a or a blind hole 101b, or a combination of through holes 101a and blind holes 101b.

[0054] Referring to Figures 10 and 11 , a recessed frame 201 is recessed on the surface of the top electrode 20, adjacent to the inner circumferential wall of the raised frame 10. The recessed frame 201 can alter the acoustic impedance within the resonance region, where the acoustic impedance within the recessed frame 201 differs from the acoustic impedance outside the recessed frame 201, and the acoustic impedance provided by the recessed frame 201 exhibits discontinuity. Therefore, the acoustic impedance mismatch provided by the recessed frame 201 advantageously improves the performance of the FBAR. Compared to conventional FBARs, incorporating the recessed frame 201 into the FBAR helps reduce the intensity of the parasitic resonance peak introduced by the raised frame 10 in the FBAR's resonance region, thereby improving the Q factor of the FBAR.

[0055] 12 and 13 , the FBAW resonator further includes a cantilever beam 202 connected to the outer wall of the top electrode 20 and extending away from the piezoelectric film 30, with an air gap between the cantilever beam 202 and the piezoelectric film 30. Due to the acoustic impedance mismatch, the cantilever beam 202 effectively reflects transverse acoustic waves, enhancing the Q factor of the resonator.

[0056] In one embodiment, referring to Figures 14 and 15, the raised frame 10 is provided with at least one cutout 102, which passes through the inner and outer peripheral walls of the raised frame 10. The inner side of the raised frame 10 is the central area of ​​the resonance zone, and the outer side is the outer area of ​​the resonance zone. The multiple cutouts 102 effectively connect the central and outer areas of the resonance zone. The cutouts 102 of the raised frame 10 can also be provided in a non-through manner on the inner or outer peripheral wall, with the depth of the cutout 102 being a fraction of the width of the raised frame 10. The above configurations can reduce the area of ​​the raised width, reduce the intensity of the parasitic resonance peak caused by the raised frame 10, and thus improve the Q value of the thin film bulk acoustic resonator.

[0057] Furthermore, the closest distance between the edge of the opening 101 and the edge of the raised frame 10 is an odd multiple of a quarter wavelength of the transverse parasitic acoustic wave. The acoustic impedance of the opening 101 structure introduced by the raised frame 10 is different from that of the surrounding area. This acoustic impedance difference can enhance the reflection of transverse Rayleigh-Lamb waves. In particular, when the distance d2 between the opening 101 and the edge of the raised frame 10 is 1 / 4 wavelength of the transverse Rayleigh-Lamb wave or an odd multiple of 1 / 4 wavelength, the raised frame 10 has the highest reflection efficiency for this transverse Rayleigh-Lamb wave, minimizes the energy leakage from the edge of the resonance region in this mode, and improves the Q value of the thin film bulk acoustic resonator.

[0058] 16 and 17 , the FBAR further includes a protective layer 203 stacked between the top electrode 20 and the raised frame 10. The protective layer 203 is an etching protection layer used to protect the top electrode 20 when etching the raised frame 10 having the opening 101. The protective layer 203 is made of a dielectric material.

[0059] The above description is only an embodiment of the present invention. It should be pointed out that those skilled in the art can make improvements without departing from the creative concept of the present invention, but these improvements all fall within the scope of protection of the present invention.

Claims

1. A thin film bulk acoustic wave resonator, the resonator comprising a substrate, an acoustic reflection structure disposed on one side of the substrate, a bottom electrode stacked on a side of the acoustic reflection structure away from the substrate, a piezoelectric thin film stacked on a side of the bottom electrode away from the acoustic reflection structure, a top electrode stacked on a side of the piezoelectric thin film away from the bottom electrode, and a convex frame disposed on a side of the top electrode away from the piezoelectric thin film, a spatial region formed by the acoustic reflection structure, the bottom electrode, the piezoelectric thin film, and the top electrode overlapping and coinciding with each other along the thickness direction of the thin film bulk acoustic wave resonator is a resonance region, and the convex frame is located in the resonance region, characterized in that, A plurality of through holes are formed on a side of the raised frame away from the top electrode.

2. The thin film bulk acoustic resonator according to any one of claims 1, characterized in that The through holes are arranged in sequence along the horizontal extension direction of the raised frame, and the distance between two adjacent through holes is greater than the diameter of the through holes.

3. The thin film bulk acoustic wave resonator according to claim 2, characterized in that, The through holes are through holes penetrating through opposite sides of the raised frame; and / or, the through holes are blind holes.

4. The thin film bulk acoustic wave resonator according to claim 3, characterized in that, The raised frame is annularly arranged along a projection edge in the thickness direction of the thin film bulk acoustic wave resonator near the resonance region, and each of the through holes is formed in a partial area on the horizontal extension plane of the raised frame.

5. The thin film bulk acoustic wave resonator according to claim 3, characterized in that, The cross section of the through hole is one or a combination of shapes of a circle, an ellipse or a rectangle.

6. The thin film bulk acoustic resonator according to claim 1, characterized in that, A recessed frame is concavely formed on the surface of the top electrode near the inner peripheral wall of the raised frame.

7. The thin film bulk acoustic resonator according to claim 6, characterized in that, The thin film bulk acoustic wave resonator further includes a cantilever beam connected to the outer peripheral wall of the top electrode and extending away from the piezoelectric thin film, and an air gap is formed between the cantilever beam and the piezoelectric thin film.

8. The thin film bulk acoustic wave resonator according to claim 1, characterized in that, At least one notch is formed in the raised frame, and the notch penetrates through the inner peripheral wall and the outer peripheral wall of the raised frame.

9. The thin film bulk acoustic resonator according to any one of claims 1-8, characterized in that, The closest distance from the edge of the through hole to the edge of the raised frame is an odd multiple of a quarter wavelength of the transverse parasitic acoustic wave.

10. The thin film bulk acoustic wave resonator according to claim 1, characterized in that, The thin film bulk acoustic wave resonator further includes a protective layer stacked between the top electrode and the raised frame.

11. The thin film bulk acoustic wave resonator according to claim 1, wherein The acoustic reflection structure is a cavity formed inside the substrate or a cavity formed on a side of the substrate close to the bottom electrode or a Bragg reflector formed on the surface of the substrate. When the acoustic reflection structure is a cavity, at least a part of the projection of the bottom electrode in the thickness direction of the thin film bulk acoustic wave resonator is located outside the acoustic reflection structure.

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