A film bulk acoustic resonator

Abstract

The application provides a film bulk acoustic resonator, comprising a substrate, an acoustic reflection structure arranged on one side of the substrate, a bottom electrode arranged on one side of the acoustic reflection structure, a piezoelectric film covering the bottom electrode, and a top electrode arranged on the side of the piezoelectric film away from the bottom electrode, wherein the side of the top electrode away from the piezoelectric film is provided with an interdigital protruding frame, the interdigital protruding frame comprises oppositely arranged first and second protruding frames, at least one pair of interdigital structures are formed by extending the first and second protruding frames towards each other and being spaced apart by a preset distance and being overlapped, and each interdigital structure comprises two interdigital structures spaced apart by a preset distance along the overlapping direction. The application can reflect two or more transverse Rayleigh-Lamb waves to achieve high reflection efficiency and improve the Q value corresponding to the anti-resonance frequency of the resonator. The peeling residue problem caused by the closed loop of the existing protruding frame can be improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of resonators, and more particularly, to a film bulk acoustic resonator. BACKGROUND

[0002] Film bulk acoustic resonator (FBAR) is a kind of resonator manufactured by using silicon substrate, MEMS technology and thin film technology. It can realize image elimination, parasitic filtering and channel selection in wireless transceiver, and has high Q value and easy miniaturization.

[0003] The conventional film bulk acoustic resonator is usually composed of a bottom electrode, a piezoelectric layer and a top electrode. When a radio frequency electrical signal is applied to the top electrode and the bottom electrode during operation, mechanical vibration is generated in the piezoelectric film in the longitudinal direction under the action of the inverse piezoelectric effect, and bulk acoustic waves are formed. Due to the full reflection boundary condition of the upper and lower motor surfaces, the propagating bulk acoustic waves will be constrained in the transducer, and the bulk acoustic waves of a specific frequency form a longitudinal propagating standing wave. Under the action of the piezoelectric effect, these bulk acoustic waves are converted into electrical signals, and the strength of the electrical signals converted by the bulk acoustic waves at the resonance frequency is the maximum, and the strength of the electrical signals converted by the bulk acoustic waves at the anti-resonance frequency is the minimum, thereby realizing the selection of electrical signals of different frequencies. However, due to factors such as the existence of tilt of the C-axis of the grown piezoelectric layer material and the boundary electrical condition, the acoustic wave mode excited by the conventional film bulk acoustic resonator not only has the expected longitudinal wave propagating in the thickness direction of the film, but also contains transverse parasitic acoustic waves (mainly Rayleigh-Lamb waves) propagating in the horizontal direction of the film. When these transverse parasitic acoustic waves escape from the edge of the resonant region to the outside of the resonant region, they will take away the energy of the resonant region, thereby reducing the quality factor (Q value) of the resonator. SUMMARY

[0004] In view of the defects of the related art, the purpose of the present application is to provide a film bulk acoustic resonator, which aims to solve the problem of low quality factor of the related resonator.

[0005] To achieve the above-mentioned purpose, the present application provides a film bulk acoustic resonator, which comprises a substrate, an acoustic reflection structure arranged on one side of the substrate, a bottom electrode arranged on one side of the acoustic reflection structure, a piezoelectric film covering the bottom electrode, and a top electrode arranged on the side of the piezoelectric film away from the bottom electrode. The side of the top electrode away from the piezoelectric film is provided with an interdigital protruding frame, the interdigital protruding frame comprises a first protruding frame and a second protruding frame arranged opposite to each other, and at least one pair of interdigital structures formed by extending from the first protruding frame and the second protruding frame respectively and overlapping with each other, each interdigital structure comprises two interdigital fingers spaced by a predetermined distance in the overlapping direction.

[0006] Preferably, the interdigital structure comprises a first extended protrusion and a second extended protrusion connected to the first protrusion frame at a side close to the second protrusion frame and arranged in a spaced manner, a third extended protrusion and a fourth extended protrusion connected to the second protrusion frame at a side close to the first protrusion frame and arranged in a spaced manner, wherein the first extended protrusion and the third extended protrusion are arranged in a spaced manner with a preset distance and overlap to form an interdigital structure; and the second extended protrusion and the fourth extended protrusion are arranged in a spaced manner.

[0007] Preferably, the second extended protrusion is arranged in a spaced manner with the fourth extended protrusion in a direction of extension of the second extended protrusion, or the second extended protrusion and the fourth extended protrusion are arranged in a spaced manner with a preset distance and overlap to form an interdigital structure.

[0008] Preferably, when the second extended protrusion is arranged in a spaced manner with the fourth extended protrusion in a direction of extension of the second extended protrusion, the interdigital structure further comprises a connecting protrusion connecting the second extended protrusion and the fourth extended protrusion.

[0009] Preferably, a first additional protrusion is arranged in a spaced manner with the second protrusion frame with a preset distance and overlap to form an interdigital structure, and a second additional protrusion is arranged in a spaced manner with the first protrusion frame with a preset distance and overlap to form an interdigital structure.

[0010] Preferably, the first extended protrusion and the second extended protrusion are respectively connected to opposite ends of the first protrusion frame in a direction of extension of the first protrusion frame, and the third extended protrusion and the fourth extended protrusion are respectively connected to positions close to the ends of the second protrusion frame in a direction of extension of the second protrusion frame and located in a space enclosed by the first protrusion frame, the first extended protrusion and the second extended protrusion.

[0011] Preferably, the preset distance is an integer multiple of a quarter wavelength of a transverse parasitic acoustic wave.

[0012] Preferably, the acoustic reflection structure is a cavity formed in the substrate, or a cavity formed in a side of the substrate close to the bottom electrode, or a Bragg reflector formed on a surface of the substrate, and when the acoustic reflection structure is a cavity, a projection of the bottom electrode in a thickness direction of the film bulk acoustic resonator is at least partially located outside the acoustic reflection structure.

[0013] Preferably, the acoustic reflection structure, the bottom electrode, the piezoelectric thin film and the top electrode jointly overlap to form a space region in the thickness direction of the film bulk acoustic resonator, and the interdigital protruding frame is located in the resonant region and is arranged close to the edge of the resonant region.

[0014] Preferably, the interdigital protruding frame is a metal material or a dielectric material or a composite material of the metal material and the dielectric material.

[0015] Compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects in general:

[0016] The present application can realize reflection of transverse Rayleigh-Lamb waves according to the acoustic impedance difference of different regions by setting the interdigital protruding frame, thereby improving the resistance Rp and Qp corresponding to the anti-resonance frequency fp of the resonator. Compared with the existing ring protruding frame technology (mainly for one kind of transverse Rayleigh-Lamb acoustic wave), the interdigital protruding frame technology of the present application can reflect two or more kinds of transverse Rayleigh-Lamb acoustic waves to achieve high reflection efficiency, further reduce the energy leaked to the outside of the resonant region, and improve the resistance Rp and Qp corresponding to the anti-resonance frequency fp of the resonator. In addition, the interdigital protruding frame is a non-closed loop structure, which is conducive to the realization of the peeling process, and the peeling residue phenomenon is not easy to occur after using the peeling process, thereby ensuring the yield of the resonator, and without increasing the preparation process steps of the resonator. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a top view of a film bulk acoustic resonator provided by a first implementation manner of the present application;

[0018] Figure 2a is an A-A direction sectional view of a first film bulk acoustic resonator provided by the first implementation manner of the present application;

[0019] Figure 2b is an A-A direction sectional view of a second film bulk acoustic resonator provided by the first implementation manner of the present application;

[0020] Figure 2c is an A-A direction sectional view of a third film bulk acoustic resonator provided by the first implementation manner of the present application;

[0021] Figure 3 is a comparison diagram of impedance curves of a film bulk acoustic resonator provided by the first implementation manner of the present application and a film bulk acoustic resonator of the prior art;

[0022] Figure 4 is a top view of a film bulk acoustic resonator provided by a second implementation manner of the present application;

[0023] Figure 5is a top view of a film bulk acoustic resonator provided by a third implementation manner of the present application;

[0024] Figure 6 is a top view of a film bulk acoustic resonator provided by a fourth implementation manner of the present application;

[0025] Figure 7 is a top view of a film bulk acoustic resonator provided by a fifth implementation manner of the present application. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application 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 only used to explain the present application and not used to limit the present application. The specific embodiments described herein take a rectangle as an example for the film bulk acoustic resonator, but the film bulk acoustic resonator is not limited to a rectangle in practice, and can also be other polygons or ellipses in practice.

[0027] The present application provides a film bulk acoustic resonator, which combines Figure 1 、 2a -2c, the resonator comprises a substrate 1, an acoustic reflection structure 2 arranged on one side of the substrate 1, a bottom electrode 3 arranged on one side of the acoustic reflection structure 2, a piezoelectric film 4 covering the bottom electrode 3, and a top electrode 5 arranged on the side of the piezoelectric film 4 away from the bottom electrode 3, the side of the top electrode 5 away from the piezoelectric film 4 is provided with an interdigital protruding frame, the interdigital protruding frame comprises a first protruding frame 61 and a second protruding frame 62 arranged in opposite directions, and at least one pair of interdigital structures formed by the first protruding frame 61 and the second protruding frame 62 extending towards each other and spaced apart by a preset distance and overlapping each other.

[0028] The film bulk acoustic resonator provided by the present application can reflect the transverse Rayleigh-Lamb wave according to the difference in acoustic impedance Za of different regions, so as to improve the Q value of the resonator. Compared with the ring-shaped protruding frame technology in the prior art, the interdigital structure formed by the interdigital protruding frame 6 can reflect two or more transverse Rayleigh-Lamb acoustic waves to achieve higher reflection efficiency, further reduce the energy leaked to the outside of the resonant region, and improve the resistance Rp and Qp corresponding to the anti-resonance frequency fp of the resonator. Figure 3 is a comparison diagram of the impedance curve of the interdigital protruding frame FBAR (film bulk acoustic resonator) provided by the present application and the ordinary FBAR and the FBAR with the protruding frame in the prior art, wherein the width W1 and W2 of the interdigital protruding frame FBAR are designed as an integer multiple of 1 / 4 wavelength of two modes in four Rayleigh-Lamb acoustic wave (S0, A0, S1 and A1) modes. From Figure 3It can be seen from the results that the Rp of the interdigital protruding frame FBAR provided by the present application is obviously higher than the Rp of the protruding frame FBAR in the prior art, which indicates that the interdigital protruding frame has higher reflection efficiency on the transverse Rayleigh-Lamb acoustic wave, and also indicates that the FBAR using the interdigital protruding frame has higher Qp. At the same time, the interdigital protruding frame 6 in the present application is a non-closed loop structure, which is beneficial to improve the peeling residue problem caused by the closed loop of the existing protruding frame, and does not increase the preparation process steps of the resonator.

[0029] Further, the interdigital structure includes the first extension protrusion 611 and the second extension protrusion 612 connected to the first protruding frame 61 and arranged at a distance from each other on the side close to the second protruding frame 62, and the third extension protrusion 621 and the fourth extension protrusion 622 connected to the second protruding frame 62 and arranged at a distance from each other on the side close to the first protruding frame 61, wherein the first extension protrusion 611 and the third extension protrusion 621 are arranged at a distance and overlap to form an interdigital structure, and the second extension protrusion 612 and the fourth extension protrusion 622 are arranged at a distance.

[0030] Further, the second extension protrusion 612 is arranged opposite to the fourth extension protrusion 622 at a distance in the extension direction of the second extension protrusion 612, or the second extension protrusion 612 and the fourth extension protrusion 622 are arranged at a distance and overlap to form an interdigital structure.

[0031] Based on the above design idea, the present application provides five design examples of implementation modes:

[0032] In the first implementation mode of the present application, in combination with Figure 1 The first extension protrusion 611 is connected to the end of the first protruding frame 61, the second extension protrusion 612 is connected to the first protruding frame 61 and has a distance from the other end of the first protruding frame 61, the third extension protrusion 621 is connected to the second protruding frame 62 and has a distance from one end of the second protruding frame 62, and the fourth extension protrusion 622 is connected to the end of the other end of the second protruding frame 62. Therefore, in the present implementation mode, the interdigital protruding frame 6 is centrally symmetrically arranged, the first extension protrusion 611 and the third extension protrusion 621 are arranged at a distance and overlap to form an interdigital structure, and the second extension protrusion 612 and the fourth extension protrusion 622 are arranged at a distance and overlap to form an interdigital structure.

[0033] In the second implementation mode of the present application, in combination with Figure 4Different from the first implementation, the first extending protrusion 611 and the second extending protrusion 612 are respectively connected to opposite ends of the first protrusion frame 61 along the extending direction thereof, and the third extending protrusion 621 and the fourth extending protrusion 622 are respectively connected to positions close to the ends of the second protrusion frame 62 along the extending direction thereof and are located in the space surrounded by the first protrusion frame 61, the first extending protrusion 611 and the second extending protrusion 612. Specifically, the first extending protrusion 611 is connected to the end of the first protrusion frame 61, the second extending protrusion 612 is connected to the other end of the first protrusion frame 61, the third extending protrusion 621 is connected to the second protrusion frame 62 and has a spacing from one end of the second protrusion frame 62, and the fourth extending protrusion 622 is connected to the second protrusion frame 62 and has a spacing from the other end of the second protrusion frame 62. Therefore, taking the view angle of the drawings as an example, in the present implementation, the first extending protrusion 611 and the third extending protrusion 621 are spaced apart by a preset distance to form an interdigital structure, and the second extending protrusion 612 and the fourth extending protrusion 622 are spaced apart by a preset distance to form an interdigital structure.

[0034] In the third implementation of the present application, in combination with Figure 5 On the basis of the first implementation, the second extending protrusion 612 is bent and extended in the direction of the first extending protrusion 611 towards the end of the second protrusion frame 62 to have a first additional protrusion 613, and the third extending protrusion 621 is bent and extended in the direction of the fourth extending protrusion 622 towards the end of the first protrusion frame 61 to have a second additional protrusion 623; the first additional protrusion 613 is arranged in parallel with the second protrusion frame 62 and spaced apart by a preset distance to form an interdigital structure, and the second additional protrusion 623 is arranged in parallel with the first protrusion frame 61 and spaced apart by a preset distance to form an interdigital structure.

[0035] In the fourth implementation of the present application, in combination with Figure 6 Different from the first implementation, the first extending protrusion 611 is connected to the end of the first protrusion frame 61, the second extending protrusion 612 is connected to the end of the other end of the first protrusion frame 61, the third extending protrusion 621 is connected to the second protrusion frame 62 and has a spacing from one end of the second protrusion frame 62, and the fourth extending protrusion 622 is connected to the end of the other end of the second protrusion frame 62. Therefore, in the present implementation, the first extending protrusion 611 and the third extending protrusion 621 are spaced apart by a preset distance to form an interdigital structure, and the second extending protrusion 612 is arranged in opposition to the fourth extending protrusion 622 in the extending direction thereof.

[0036] In the fifth implementation of the present application, in combination with Figure 7When the second extending protrusion 612 is arranged opposite to the fourth extending protrusion 622 in the extending direction of the second extending protrusion 612, the interdigital structure further comprises a connecting protrusion 63 connecting the second extending protrusion 612 and the fourth extending protrusion 622, that is, in the fourth implementation, the second extending protrusion 612 and the fourth extending protrusion 622 are integrated and extend in the same direction.

[0037] Further, in the foregoing various implementations, the preset distance is an integer multiple of a quarter wavelength of the transverse parasitic acoustic wave.

[0038] Further, the acoustic reflection structure 2 can be a cavity formed inside the substrate 1 or a cavity formed on the side of the substrate 1 close to the bottom electrode 3 or a Bragg reflector formed on the surface of the substrate 1. When the acoustic reflection structure is a cavity, the projection of the bottom electrode 3 in the thickness direction of the film bulk acoustic resonator at least partially locates outside the acoustic reflection structure 2. Figure 2a In the acoustic reflection structure 2 is a cavity formed inside the substrate 1; Figure 2b In the acoustic reflection structure 2 is a cavity formed above the substrate 1, in this case, a support layer can be arranged between the substrate 1 and the bottom electrode 3 to form the cavity; Figure 2c In the acoustic reflection structure 2 is a Bragg reflector formed on the surface of the substrate 1, the Bragg reflector comprises low acoustic impedance layers 21 and high acoustic impedance layers 22 arranged alternately in the thickness direction of the film bulk acoustic resonator, wherein the material of the low acoustic impedance layer is silicon oxide (SiO2) or the like, and the material of the high acoustic impedance layer is tungsten (W), molybdenum (Mo), ruthenium (Ru), iridium (Ir) or the like.

[0039] Further, the space region formed by the acoustic reflection structure 2, the bottom electrode 3, the piezoelectric thin film 4 and the top electrode 5 in the thickness direction of the film bulk acoustic resonator is a resonance region, and the interdigital protrusion frame 6 is located in the resonance region and arranged close to the edge of the resonance region.

[0040] Further, the interdigital protrusion frame 6 is a metal material or a dielectric material or a composite material of a metal material and a dielectric material. Specifically, it can be one or more of Al, Pt, Au, W, Mo, Ru, Ir, AlN and Si3N4.

[0041] The width of the interdigital protruding frame can range from 1 nm to 20,000 nm, such as 50 nm, 500 nm, 5,000 nm, 10,000 nm, 15,000 nm, etc.; the height can range from 1 nm to 10,000 nm, such as 10 nm, 100 nm, 1,000 nm, 3,000 nm, 5,000 nm, 7,000 nm, 8,000 nm, etc. The width of the two protruding frames constituting the interdigital structure can be different or the same. For example, the width of the protruding frame close to the inner side of the enclosed space is greater than the width of the protruding frame close to the outer side, and the ratio of the width of the protruding frame close to the inner side of the enclosed space to the width of the protruding frame close to the outer side can be between 1.1 and 2, such as 1.3, 1.5, 1.7, etc. Of course, the width of the protruding frame close to the inner side of the enclosed space can also be less than the width of the protruding frame close to the outer side, and the ratio of the width of the protruding frame close to the inner side of the enclosed space to the width of the protruding frame close to the outer side can be between 0.5 and 0.95, such as 0.6, 0.7, 0.8, etc.

[0042] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A film bulk acoustic resonator comprising a substrate, an acoustic reflecting structure provided on one side of the substrate, a bottom electrode provided on one side of the acoustic reflecting structure, a piezoelectric film covering the bottom electrode, and a top electrode provided on the side of the piezoelectric film distal from the bottom electrode, characterized in that, The side of the top electrode away from the piezoelectric thin film is provided with an interdigital protruding frame, the interdigital protruding frame comprises a first protruding frame and a second protruding frame arranged oppositely, and at least one pair of interdigital structures formed by extending from the first protruding frame and the second protruding frame oppositely and overlapping with each other, each of the interdigital structures comprises two interdigital structures spaced by a preset distance along the overlapping direction. The interdigital structure comprises a first extending protrusion and a second extending protrusion connected to the first protruding frame and arranged oppositely near the second protruding frame, and a third extending protrusion and a fourth extending protrusion connected to the second protruding frame and arranged oppositely near the first protruding frame, wherein the first extending protrusion and the third extending protrusion are spaced by a preset distance and overlap to form an interdigital structure, and the second extending protrusion and the fourth extending protrusion are arranged oppositely.

2. The film bulk acoustic resonator of claim 1, wherein, The second extending protrusion is arranged oppositely to the fourth extending protrusion along the extending direction of the second extending protrusion, or the second extending protrusion and the fourth extending protrusion are spaced by a preset distance and overlap to form an interdigital structure.

3. The film bulk acoustic resonator of claim 2, wherein, When the second extending protrusion is arranged oppositely to the fourth extending protrusion along the extending direction of the second extending protrusion, the interdigital structure further comprises a connecting protrusion connecting the second extending protrusion and the fourth extending protrusion.

4. The film bulk acoustic resonator of claim 2, wherein, The end of the second extending protrusion near the second protruding frame is bent and extended in the direction of the first extending protrusion to form a first additional protrusion, and the end of the third extending protrusion near the first protruding frame is bent and extended in the direction of the fourth extending protrusion to form a second additional protrusion; the first additional protrusion is arranged parallel to the second protruding frame and spaced by a preset distance to overlap and form an interdigital structure, and the second additional protrusion is arranged parallel to the first protruding frame and spaced by a preset distance to overlap and form an interdigital structure.

5. The film bulk acoustic resonator of claim 2, wherein, The first extending protrusion and the second extending protrusion are connected to the opposite ends of the first protruding frame along the extending direction of the first protruding frame, and the third extending protrusion and the fourth extending protrusion are connected to the positions near the ends of the second protruding frame along the extending direction of the second protruding frame and located in the space enclosed by the first protruding frame, the first extending protrusion and the second extending protrusion.

6. The film bulk acoustic resonator of any one of claims 1-5, wherein, The preset distance is an integer multiple of the quarter wavelength of the transverse parasitic acoustic wave.

7. The film bulk acoustic resonator of claim 1, wherein, The acoustic reflection structure is a cavity formed in the substrate, a cavity formed on the side of the substrate near 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 film bulk acoustic resonator is at least partially located outside the acoustic reflection structure.

8. The film bulk acoustic resonator of claim 1, wherein, The space region formed by the acoustic reflection structure, the bottom electrode, the piezoelectric thin film and the top electrode overlapping and coinciding along the thickness direction of the film bulk acoustic resonator is a resonance region, and the interdigital protruding frame is located in the resonance region and arranged near the edge of the resonance region.

9. The film bulk acoustic resonator of claim 1, wherein, The interdigital protruding frame is a metal material, a dielectric material or a composite material of metal material and dielectric material.

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