Low-clutter film bulk acoustic resonator with multi-layer structure

Abstract

The invention discloses a low-clutter film bulk acoustic resonator with a multilayer structure, which comprises an upper electrode, a concave-convex structure is arranged on the inner side of the upper boundary of the upper electrode, the concave-convex structure comprises a plurality of layers of convex structures and a concave structure which are sequentially arranged along the axial direction, and the concave structure is positioned on the inner side of the boundary of the plurality of layers of convex structures. According to the invention, the multi-layer projection structure is formed by the plurality of projections with vertical height difference, and the Bragg reflection layer is formed by the multi-layer projection structure, so that leakage of transverse sound waves is inhibited, and the Q value is improved; and meanwhile, parasitic vibration generated by the film bulk acoustic wave resonator is inhibited through the concave structure, so that the effect of inhibiting clutters generated by the film bulk acoustic wave resonator is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of acoustic wave resonators, and in particular to a low-noise thin film bulk acoustic wave resonator with a multi-layer structure. Background Art

[0002] With the development of wireless communication systems, communications have long entered the 5G era, and the application of bulk acoustic wave devices has gradually become widespread. Among bulk acoustic wave devices, thin film bulk acoustic wave resonators have been more widely used in RF filters due to their excellent characteristics such as low insertion loss, high Q value, and high frequency, and have gradually become a research hotspot for RF filters. As the basic building block of the filter, the resonator needs to meet the characteristics of low noise and high Q value to ensure that the filter designed based on the resonator has excellent characteristics such as small in-band fluctuation, low insertion loss, low phase fluctuation, and high rectangularity.

[0003] As attached Figure 1 The figure shows a two-dimensional plane schematic diagram of an air gap type thin film bulk acoustic wave resonator in the prior art, and the structure of the resonator includes a substrate 1, a first air cavity 2, a support layer 3, a lower electrode 4, a piezoelectric layer 5, an upper electrode 6, and a frequency modulation layer 7. When an electrical signal is applied between the upper electrode 6 and the lower electrode 4, the piezoelectric material in the piezoelectric layer 5 generates a piezoelectric effect due to its piezoelectric characteristics, thereby forming an oscillation caused by an acoustic wave. Even if the first air cavity can suppress the longitudinal acoustic wave energy in the piezoelectric oscillation stack, there are still many transverse RL waves that leak out, thereby affecting the Q value of the resonator. At the same time, due to the existence of the TE-1 mode in the RL wave, the resonator will generate transverse parasitic vibrations in the resonance region, so that the designed thin film bulk acoustic wave resonator has clutter, which greatly reduces the performance of the filter composed of the resonator.

[0004] Therefore, in the field of micro-acoustic devices, in order to design high-performance film bulk acoustic wave filters, it is necessary to suppress the noise of the film bulk acoustic wave resonator and improve the Q value of the film bulk acoustic wave resonator. The Q value here specifically refers to the film bulk acoustic wave resonator at the parallel resonance point f p Q value Q p How to achieve this goal has become a technical problem that technical personnel in this field need to solve urgently. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is: how to provide a multi-layered low-noise FBAR that can suppress the noise of the FBAR and improve the Q value of the FBAR.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A multi-layer low-noise film bulk acoustic wave resonator includes an upper electrode, wherein a concave-convex structure is provided on the inner side of the upper boundary of the upper electrode, wherein the concave-convex structure includes a multi-layer convex structure and a concave structure sequentially arranged along the axial direction, and the concave structure is located on the inner side of the boundary of the multi-layer convex structure. Thus, the present scheme arranges a concave-convex structure on the inner side of the upper boundary of the upper electrode, wherein the multi-layer convex structure can constitute a Bragg reflection layer, and the Bragg reflection layer can enhance the reflection of transverse sound waves and suppress the leakage of transverse sound waves, so that the transverse sound waves can be confined within the resonance region, thereby improving the Q value of the resonator. The Q value here specifically refers to the Q value of the film bulk acoustic wave resonator at the parallel resonance point. f p Q value at Q p The concave structure can generate a "piston" mode to suppress the TE-1 mode in the transverse RL wave, thereby suppressing the parasitic vibration generated by the film bulk acoustic wave resonator, and thus achieving the effect of suppressing the generation of clutter by the film bulk acoustic wave resonator. Therefore, this solution can suppress the clutter of the film bulk acoustic wave resonator and improve the Q value of the film bulk acoustic wave resonator.

[0007] Preferably, the thin film bulk acoustic wave resonator further includes a frequency tuning layer, and a second air cavity is formed between the multi-layer protrusion structure and the frequency tuning layer.

[0008] In this way, the second air cavity can confine the longitudinal sound waves within the piezoelectric oscillator stack, further enhancing the reflection capability of the longitudinal sound waves, and can also form a Bragg reflection layer in the lateral direction, thereby enabling the thin film bulk acoustic wave resonator to obtain a higher Q value.

[0009] Preferably, the multi-layer protrusion structure includes two or more protrusions with a vertical height difference, and the second air cavity is formed between the frequency modulation layer and the protrusion with a non-maximum vertical height.

[0010] In this way, the multiple protrusions are designed to have different vertical heights. On the one hand, the multiple protrusions can form a multi-layer structure with a height difference. On the other hand, an air gap can exist between the protrusion with the non-maximum vertical height and the frequency modulation layer, and the air gap forms a second air cavity.

[0011] Preferably, the axial widths of the protrusions are the same.

[0012] Preferably, the protrusion with the minimum vertical height is the same height as or higher than the upper electrode.

[0013] In this way, the protrusion with the minimum vertical height is equal to or higher than the upper electrode, which can avoid the formation of a second recessed structure. If the second recessed structure is formed, the lateral mode in the resonance region will leak.

[0014] Preferably, the vertical height of the second air cavity is greater than 0 and less than or equal to the maximum vertical height of the multi-layer protrusion structure.

[0015] Preferably, the multi-layer protrusion structure includes a first protrusion and a second protrusion, the second protrusion has a vertical height smaller than the first protrusion, the recessed structure is located inside the second protrusion, and the second air cavity is formed between the frequency modulation layer and the second protrusion.

[0016] Preferably, the vertical height of the second protrusion is half of the vertical height of the first protrusion.

[0017] Preferably, each protrusion of the multi-layer protrusion structure and the upper electrode are made of metal materials, and the metal materials used include molybdenum, platinum, aluminum, copper, gold, and tungsten.

[0018] Preferably, the support layer and the frequency modulation layer are both made of high Young's modulus materials, and the high Young's modulus materials used include silicon dioxide, silicon nitride, silicon carbide, aluminum oxide, aluminum nitride or new piezoelectric materials with high dielectric constant and high electromechanical coupling coefficient.

[0019] Compared with the prior art, the present invention improves the Q value by using a multi-layer protrusion structure composed of multiple protrusions with vertical height differences and a second air cavity, wherein the multi-layer protrusion structure is used to form a Bragg reflection layer to suppress the leakage of lateral sound waves and improve the Q value, and the second air cavity is used to enhance the reflection ability of longitudinal sound waves and form a Bragg reflection layer in the lateral direction to improve the Q value; at the same time, the concave structure is used to suppress the parasitic vibration generated by the thin film bulk acoustic wave resonator, thereby achieving the effect of suppressing the generation of clutter by the thin film bulk acoustic wave resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the two-dimensional plane structure of an air gap type thin film bulk acoustic resonator in the prior art; Figure 2 is the admittance curve of the air gap type thin film bulk acoustic resonator in the prior art; Figure 3 is a Q value curve of an air gap type thin film bulk acoustic resonator in the prior art; Figure 4 It is a schematic diagram of a two-dimensional planar structure of a low-noise thin film bulk acoustic resonator with a multi-layer structure in Embodiment 1 of the present invention; Figure 5 The admittance curve of the low-noise thin film bulk acoustic resonator with a multilayer structure in the first embodiment of the present invention; Figure 6 The Q value curve of the low-noise thin film bulk acoustic resonator with a multilayer structure in the first embodiment of the present invention; Figure 7It is a schematic diagram of the two-dimensional planar structure of a low-noise thin film bulk acoustic resonator with a multi-layer structure in the second embodiment of the present invention; Figure 8 It is a schematic diagram of the two-dimensional planar structure of a multi-layer low-noise thin film bulk acoustic resonator in the third embodiment of the present invention.

[0021] Explanation of the reference numerals: substrate 1, first air cavity 2, supporting layer 3, lower electrode 4, piezoelectric layer 5, upper electrode 6, frequency modulation layer 7, first protrusion 8, second protrusion 9, recessed structure 10, second air cavity 11, third protrusion 12. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meaning understood by people with general skills in the field to which the present invention belongs.

[0023] The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "a", "an" or "the" and other similar words do not indicate a quantitative limitation, but indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before "include" or "comprise" cover the features, wholes, steps, operations, elements and / or components listed after "include" or "comprise", and do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0024] Embodiment 1: As attached Figure 4 As shown, a multi-layer low-noise film bulk acoustic wave resonator includes a substrate 1 and a piezoelectric oscillation stack located on the substrate 1, wherein the piezoelectric oscillation stack includes a supporting layer 3, a lower electrode 4, a piezoelectric layer 5, an upper electrode 6, and a frequency modulation layer 7. A first air cavity 2 recessed toward the substrate 1 is provided between the substrate 1 and the supporting layer 3. The first air cavity 2 confines the longitudinal sound wave within the piezoelectric oscillation stack, so that the film bulk acoustic wave resonator provided by the present invention obtains low noise.

[0025] A concave-convex structure is also provided inside the upper boundary of the upper electrode 6, and the concave-convex structure includes a multi-layer convex structure and a concave structure 10 arranged in sequence along the axial direction, and the concave structure 10 is located inside the boundary of the multi-layer convex structure. A second air cavity 11 is formed between the multi-layer convex structure and the frequency modulation layer 7. The multi-layer convex structure can constitute a Bragg reflection layer, which can enhance the reflection of the transverse sound wave and suppress the leakage of the transverse sound wave, so that the transverse sound wave can be confined within the resonance region, thereby improving the Q value of the resonator. The Q value here specifically refers to the film bulk acoustic wave resonator at the parallel resonance point f p Q value Q p The concave structure 10 can generate a "piston" mode to suppress the TE-1 mode in the transverse RL wave, thereby suppressing the parasitic vibration generated by the thin film bulk acoustic wave resonator, and further achieving the effect of suppressing the generation of clutter by the thin film bulk acoustic wave resonator. The second air cavity 11 can confine the longitudinal sound wave in the piezoelectric oscillator stack, further enhancing the reflection ability of the longitudinal sound wave, and at the same time can also form a Bragg reflection layer in the transverse direction, so that the thin film bulk acoustic wave resonator obtains a higher Q value.

[0026] The multi-layer protrusion structure includes two or more protrusions with a vertical height difference, and the axial width of each protrusion is the same. The second air cavity 11 is formed between the frequency modulation layer 7 and the protrusion with the non-maximum vertical height. The vertical height of the second air cavity 11 is greater than 0 and less than or equal to the maximum vertical height of the multi-layer protrusion structure, and the protrusion with the minimum vertical height is the same height as the upper electrode 6 or higher than the upper electrode 6. In this way, the formation of the second recessed structure 10 can be avoided. If the second recessed structure 10 is formed, the lateral mode in the resonance region will leak.

[0027] Each protrusion of the multilayer protrusion structure and the upper electrode 6 are made of metal materials, and the metal materials used include molybdenum, platinum, aluminum, copper, gold, and tungsten. The support layer 3 and the frequency modulation layer 7 are made of high Young's modulus materials, and the high Young's modulus materials used include silicon dioxide, silicon nitride, silicon carbide, aluminum oxide, aluminum nitride, or a new piezoelectric material with a high dielectric constant and a high electromechanical coupling coefficient. Specifically, Pb 1-x (Mg 1 / 3 Nb 2 / 3 ) 3-x PbTiO3 (PMN-PT) is used as a new piezoelectric material. The material used in the piezoelectric layer 5 is one of piezoelectric materials such as aluminum nitride, zinc oxide, PZT, single crystal lithium niobate, and a new piezoelectric material.

[0028] Specifically, the multilayer protrusion structure in this embodiment includes a first protrusion 8 and a second protrusion 9, the vertical height of the second protrusion 9 is less than the vertical height of the first protrusion 8, the vertical height of the second protrusion 9 can be any height between 0 and the vertical height of the first protrusion 8, the vertical height of the second protrusion 9 is greater than 0 so that the second protrusion 9 is not lower than the upper electrode 6, so as to avoid the formation of the second recessed structure 10 at the upper electrode, and the vertical height is less than the first protrusion 8 in order to form a second air cavity 11 between the second protrusion 9 and the frequency modulation layer 7. In this specific embodiment, the vertical height of the second protrusion 9 is half of the vertical height of the first protrusion 8, the two protrusions constitute a Bragg reflection layer, the recessed structure 10 is located on the side of the second protrusion 9, and the second air cavity 11 is formed between the second protrusion 9 and the frequency modulation layer 7.

[0029] As attached Figure 2 The prior art is shown in Figure 1 The admittance curve of the film bulk acoustic wave resonator is shown in Figure 2. Figure 5 is the admittance curve of the thin film bulk acoustic wave resonator of the present invention, Figure 2 The parasitic vibration of the FBAW resonator in the prior art is mainly manifested at the series resonance point f of the FBAW resonator. s There were noises before, but the thin film bulk acoustic wave resonator with low noise and high Q value provided by the present invention can effectively suppress the noises caused by the TE-1 mode in the RL wave.

[0030] As attached Figure 3 The prior art is shown in Figure 1 The Q value curve of the film bulk acoustic wave resonator is shown in the figure. Figure 6 The Q value curve of the film bulk acoustic wave resonator of the present invention is as follows. Compared with the air gap film bulk acoustic wave resonator of the prior art, the low-noise high-Q value film bulk acoustic wave resonator provided by the present invention has a Q value Q at the parallel resonance point. p The improvement (from 23.5867 to 32.4623) is quite obvious, reaching 47.8%.

[0031] Embodiment 2: The difference from the first embodiment is that the multi-layer protrusion structure of this embodiment includes a first protrusion 8, a second protrusion 9 and a third protrusion 12, wherein the first protrusion 8 and the third protrusion 12 have the same vertical height, the second protrusion 9 has a vertical height less than the first protrusion 8 and the third protrusion 12, and the recessed structure 10 is located inside the third protrusion 12. In specific implementation, the number of protrusions is not limited.

[0032] Embodiment three: The difference from the first embodiment is that the protrusion structure of this embodiment includes a first protrusion 8 and a second protrusion 9, and the vertical height of the second protrusion 9 is 0.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A multi-layer low-noise film bulk acoustic resonator, comprising an upper electrode, characterized in that: A concavo-convex structure is provided inside the upper boundary of the upper electrode, wherein the concavo-convex structure comprises a multi-layer convex structure and a concave structure sequentially arranged along the axial direction, and the concave structure is located inside the boundary of the multi-layer convex structure.

2. The multi-layer low-noise thin film bulk acoustic resonator according to claim 1, characterized in that: The thin film bulk acoustic wave resonator further includes a frequency tuning layer, and a second air cavity is formed between the multi-layer protrusion structure and the frequency tuning layer.

3. The multi-layer low-noise thin film bulk acoustic resonator according to claim 2, characterized in that: The multi-layer protrusion structure includes two or more protrusions with a vertical height difference, and the second air cavity is formed between the frequency modulation layer and the protrusion with a non-maximum vertical height.

4. The multi-layer low-noise thin film bulk acoustic resonator according to claim 3, characterized in that: The axial widths of the protrusions are the same.

5. The multi-layer low-noise thin film bulk acoustic resonator according to claim 3, characterized in that: The protrusion with the minimum vertical height is equal to or higher than the upper electrode.

6. The multi-layer low-noise thin film bulk acoustic resonator according to claim 3, characterized in that: A vertical height of the second air cavity is greater than 0 and less than or equal to a maximum vertical height of the multi-layer protrusion structure.

7. The multi-layer low-noise thin film bulk acoustic resonator according to claim 3, characterized in that: The multi-layer protrusion structure includes a first protrusion and a second protrusion, the second protrusion has a vertical height smaller than that of the first protrusion, the recessed structure is located inside the second protrusion, and the second air cavity is formed between the frequency modulation layer and the second protrusion.

8. The multi-layer low-noise thin film bulk acoustic resonator according to claim 7, characterized in that: The vertical height of the second protrusion is half of the vertical height of the first protrusion.

9. The multi-layer low-noise thin film bulk acoustic resonator according to claim 3, characterized in that: Each protrusion of the multi-layer protrusion structure and the upper electrode are made of metal materials, and the metal materials used include molybdenum, platinum, aluminum, copper, gold, and tungsten.

10. The multi-layer low-noise thin film bulk acoustic resonator according to claim 1, characterized in that: The support layer and the frequency modulation layer are both made of high Young's modulus materials, and the high Young's modulus materials used include silicon dioxide, silicon nitride, silicon carbide, aluminum oxide, aluminum nitride or new piezoelectric materials with high dielectric constant and high electromechanical coupling coefficient.

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