High-Q-value bulk acoustic wave resonator for suppressing clutters and preparation method of high-Q-value bulk acoustic wave resonator

Abstract

The invention discloses a clutter suppression high-Q-value bulk acoustic wave resonator and a preparation method thereof, the high-Q-value bulk acoustic wave resonator comprises a substrate, and the substrate is provided with a cavity; the piezoelectric stack structure is located on the substrate, the piezoelectric stack structure comprises a seed layer, a lower electrode, a piezoelectric layer, an upper electrode and a passivation layer from bottom to top, and an air bridge and a drooping arm part are arranged at the edge of the upper electrode. The bulk acoustic wave resonator has a proper Q value and can well suppress clutters.

Description

Technical Field

[0001] The invention belongs to the technical field of filters, and in particular relates to a high-Q-value bulk acoustic wave resonator for suppressing clutter and a preparation method thereof. Background Art

[0002] With the rapid advancement of wireless communication technology and the rapid increase in frequency bands, the demand for various devices in chip modules is increasing. This is especially true for resonators and filters with low insertion loss, small ripple, and high frequency bands. In the field of high-end filters, film bulk acoustic resonators (FBARs) have become a hot topic in recent years due to their high quality factor, small size, and high resonant frequency. They have also been rapidly commercialized due to their broad application prospects in high-frequency communications and huge market.

[0003] At present, there are three main types of widely used FBAR structures: 1. Back-etching type. That is, micromachining is used to reversely etch from the substrate surface, thereby removing most of the substrate material, forming an interface between air and piezoelectric resonance, and reflecting the sound waves back to the sandwich resonance structure; 2. Air gap type. That is, through surface micromachining technology, the upper surface of the substrate SI is now filled with a target sacrificial layer, and then the sacrificial layer is removed through the release hole, so that an air cavity is formed directly below the sandwich resonance structure. The cavity forms a high acoustic impedance area to reflect the sound waves back to the sandwich resonance structure. 3. Solid-state assembly type. That is, high and low acoustic impedance materials are alternately stacked to form a Bragg reflector, which is placed under the sandwich resonance structure, and the sound waves are confined to the sandwich resonance structure through the Bragg reflector. Among the three types, the back-etching type removes a large amount of substrate, resulting in a significant reduction in device strength and affecting device quality; the solid-state assembly type requires multiple layers of thin films to prepare Bragg reflectors, which greatly increases the process difficulty and cost; the air gap type does not require the removal of the substrate, nor does it require the preparation of multiple layers of Bragg reflectors, and high-performance resonators can also be obtained.

[0004] The BAW thin film resonator excites longitudinal acoustic waves through electrodes located on the upper and lower sides of the piezoelectric material. The longitudinal acoustic wave is the main mode of operation of the resonator, and the resonant frequency point and anti-resonant frequency point are obtained in this mode. In addition to the longitudinal acoustic waves required for the resonator, there are various types of clutter in the resonant structure, among which the Lamb wave propagating laterally has the most significant impact. The Lamb wave will cause various spurious modes through lateral transmission, which will not only greatly reduce the Q value of the resonator, but also generate many unnecessary peaks around the resonant frequency point, which will reduce the quality of the filter.

[0005] The invention patent application with publication number CN114938213A discloses a thin film bulk acoustic wave resonator and a preparation method thereof, which relates to the field of semiconductor technology, and includes a substrate and a lower electrode, a piezoelectric layer and an upper electrode located on the upper surface of the substrate; the lower electrode has a first arched portion to form a first cavity between the first arched portion and the substrate; a first reflection cavity is arranged between the lower electrode and the piezoelectric layer, and the first reflection cavity is located at the slope of the first arched portion. Since the lower electrode has a first arched portion, the first reflection cavity can be located at the slope on the slope of the first arched portion. In this way, the slope can be used to make the first reflection cavity reflect the transverse acoustic wave multiple times when reflecting the transverse acoustic wave, thereby consuming the energy of the transverse transverse wave, so as to further reduce the transverse parasitic mode, which is helpful to improve the quality factor of the thin film bulk acoustic wave resonator. However, the effect of suppressing the transverse stray mode by the air bridge structure in the reference document is limited, so it is urgent to design a bulk acoustic wave resonator with a suitable Q value while being able to better suppress the clutter. Summary of the invention

[0006] The invention provides a high-Q-value bulk acoustic wave resonator for suppressing clutter. The bulk acoustic wave resonator has a suitable Q value and can suppress clutter well.

[0007] The present invention provides a high-Q value bulk acoustic wave resonator for suppressing clutter, comprising: A substrate, wherein a cavity is provided on the substrate; A piezoelectric stack structure is located on a substrate and comprises, from bottom to top, a seed layer, a lower electrode, a piezoelectric layer, an upper electrode and a passivation layer, and an air bridge and a drooping arm are arranged at the edge of the upper electrode.

[0008] The present invention utilizes the synergistic effect of the air bridge and the drooping arm portion arranged at the edge of the upper electrode. Compared with a single air bridge, it can better suppress the outward leakage of lateral sound waves and better reflect the energy of the outward leakage of lateral sound waves, so that there are fewer unnecessary peaks around the resonance frequency point and the resonance curve is smoother. At the same time, the drooping arm portion is used to adjust the Q value so that the bulk acoustic wave resonator has a suitable Q value.

[0009] When the transverse parasitic noise propagates from the central effective area to the edge, a part of the wave is reflected back due to encountering the air gap, which leads to the improvement of the quality factor of the resonator, and the other part of the wave continues to diffuse laterally along the upper electrode, and this part of the wave produces stray peaks. The present invention adds a downward arm structure with an acoustic impedance mismatch on the outside of the air bridge, creating a boundary condition in which the transverse noise cannot continue to propagate. The transverse mode that continues to propagate along the upper electrode is reflected, and the height of the downward arm affects the propagation mode. When the height does not match, new high-order modes will be generated, and these modes will cause the quality factor to decrease.

[0010] Preferably, the upper electrode comprises, from bottom to top, a first upper electrode and a second upper electrode; An air bridge is provided between the edge of the second upper electrode and the edge of the first upper electrode and the piezoelectric layer; A drooping arm portion is provided at the edge of the second upper electrode, and the drooping arm portion is located on the air bridge.

[0011] Preferably, the air bridge comprises, from bottom to top, a first air gap and a second air gap; The first air gap is arranged between the edge of the second upper electrode and the piezoelectric layer, and the hanging arm portion is located on the first air gap; The second air gap is arranged between the side portion of the second upper electrode and the edge of the first upper electrode, and the second air gap prevents the wave from leaking downward through the drooping arm.

[0012] Preferably, the height of the first air gap is consistent with the height of the second air gap.

[0013] Preferably, a Pison protrusion structure is provided at an edge of the second upper electrode and at the same position laterally as the second air gap.

[0014] Preferably, a Bragg reflection layer is filled in the cavity.

[0015] On the other hand, the present invention also provides a method for preparing the high-Q bulk acoustic wave resonator for suppressing clutter, comprising: Obtaining a substrate, opening a cavity on the substrate, and growing a first sacrificial layer on the cavity; Forming a piezoelectric stack structure above the substrate, the piezoelectric stack structure is located on the substrate, and the piezoelectric stack structure includes, from bottom to top, a seed layer, a lower electrode, a piezoelectric layer, a first upper electrode, a second upper electrode, and a passivation layer; forming a seed layer above the cavity; forming a lower electrode above the seed layer; forming a piezoelectric layer over the lower electrode and the seed layer; forming a first upper electrode above the piezoelectric layer; growing a second sacrificial layer at an edge of the first upper electrode; forming a second upper electrode on the second sacrificial layer and the first upper electrode; forming a passivation layer on the second upper electrode; The first sacrificial layer and the second sacrificial layer are released to obtain a cavity, an air bridge and a hanging arm.

[0016] The present invention utilizes the growth of a second sacrificial layer at the edge of the first upper electrode, and controls the size of the second sacrificial layer to achieve control of the size of the drooping arm and the air bridge of the second upper electrode, thereby being able to efficiently and flexibly obtain a BAW resonator with a desired Q value and better suppression of clutter.

[0017] Preferably, the material of the second sacrificial layer is silicon nitride or silicon oxide, and the second sacrificial layer is released by wet etching or HF fumigation. Silicon nitride and silicon oxide can be etched by HF and carried away by HF vapor, and an air gap is formed in the original place.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Compared with the prior art of using an air bridge or an air gap alone, the present invention provides a drooping arm at the edge of the upper electrode and at the outer edge of the air bridge, so that the lateral noise not suppressed by the air bridge is suppressed by the drooping arm, so that the resonator performance curve is updated and smooth, the effect of suppressing noise is more significant, and a suitable Q value can be obtained at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A cross-sectional view of a substrate 100 having a cavity 101 provided for a specific embodiment of the present invention; Figure 2 A cross-sectional view of a cavity 101 filled with a sacrificial layer material 115 provided in a specific embodiment of the present invention; Figure 3 A cross-sectional view of growing an aluminum nitride seed layer 102 on a silicon substrate and growing a lower electrode 103 on the aluminum nitride seed layer provided in a specific embodiment of the present invention; Figure 4 A cross-sectional view of forming a piezoelectric layer 104 on a lower electrode 103 and a seed layer 102 provided in a specific embodiment of the present invention; Figure 5 A cross-sectional view of forming a first upper electrode 106 on a piezoelectric layer 104 according to a specific embodiment of the present invention; Figure 6 A cross-sectional view of forming a second sacrificial layer 112 on a first upper electrode 106 formed on a piezoelectric layer 104 provided in a specific embodiment of the present invention; Figure 7 A cross-sectional view of forming a second upper electrode 111 on the first upper electrode 106 and the second sacrificial layer 112 provided in a specific embodiment of the present invention; Figure 8 A cross-sectional view of forming a passivation layer 108 on the second upper electrode 111 according to a specific embodiment of the present invention; Fig. 9 A cross-sectional view of a high-Q bulk acoustic wave resonator for suppressing clutter provided in a specific embodiment of the present invention; Fig.10 A Smith chart and a phase curve diagram of a high-Q BAW resonator for suppressing clutter provided by a specific embodiment of the present invention and a BAW resonator with a common air bridge structure; Fig.11A comparison diagram of the Q values ​​of a high-Q BAW resonator for suppressing clutter provided by a specific embodiment of the present invention and a BAW resonator with a common air bridge structure; Fig.12 A Q value curve diagram of a high-Q bulk acoustic wave resonator with different widths of drooping arms for suppressing clutter provided by a specific embodiment of the present invention; Fig.13 Structural diagram of a bulk acoustic wave resonator with a common air bridge structure. DETAILED DESCRIPTION

[0020] The following is a detailed description in conjunction with specific implementation examples. The following examples are only relevant parts of the present invention, which will help relevant personnel understand the principles of the present invention and do not limit the present invention in any way. It should be noted that corresponding structural adjustments and changes can be made based on the concept of the present invention, and such changes all belong to the protection scope of the present invention.

[0021] A specific embodiment of the present invention provides a high-Q bulk acoustic wave resonator that suppresses clutter, such as Fig. 9 As shown, it includes a substrate 100 and a piezoelectric stack structure, wherein a cavity 101 is opened on the substrate 100, and the piezoelectric stack structure includes a seed layer 102, a lower electrode 103, a piezoelectric layer 104, an upper electrode and a passivation layer 108 from bottom to top. The present invention introduces a drooping arm 114 and an air bridge between the edge of the upper electrode and the piezoelectric layer, thereby changing the boundary acoustic impedance, suppressing the stray mode caused by the lateral sound wave, making the resonance curve smoother, and thus improving the resonator performance.

[0022] A specific embodiment of the present invention provides that the upper electrode includes, from bottom to top, a first upper electrode 106 and a second upper electrode 107, the second upper electrode 107 includes an edge portion and a middle portion, the middle portion of the second upper electrode 107 is located on the first upper electrode 106, an air bridge is provided between the edge portion of the second upper electrode 107 and the edge of the first upper electrode 109 and the piezoelectric layer, a second air gap 110 is provided between the edge portion of the second upper electrode 107 and the edge of the first upper electrode 109, a first air gap 109 is provided between the edge portion of the second upper electrode 107 and the piezoelectric layer, and the first air gap 109 and the second air gap 110 are connected to form an air bridge.

[0023] The second upper electrode of the present invention has a drooping arm 114 and a Pison protrusion 111 at its edge. The drooping arm 114 is located on the air bridge. The Pison protrusion 111 and the second air gap 110 are located at the same lateral position, that is, the centers of the two are located in the same axial direction.

[0024] The specific embodiment of the present invention also provides a method for preparing the high-Q bulk acoustic wave resonator for suppressing clutter, comprising: (1) If Figure 1As shown, the substrate 100 is cleaned by ultrasonic washing with acetone and isopropanol. The crystal orientation of the silicon substrate is (111) or (100). The cavity 101 with a depth of 3um and a lateral width of 150um is etched on the silicon substrate by ICP etching using the BOSCH process.

[0025] (2) If Figure 2 As shown, a 3-5 um phosphosilicate material (PSG) is deposited on the silicon surface by a conventional low-pressure chemical vapor deposition process as a sacrificial layer material of the cavity, namely, the first sacrificial layer 115, and then patterned by chemical mechanical polishing (CMP).

[0026] (3) If Figure 3 As shown, a 100nm thick aluminum nitride seed layer 102 is deposited on the surface of the silicon substrate and the first sacrificial layer in the cavity by a low-pressure chemical deposition process or magnetron sputtering, and the seed layer has a good C-axis orientation. A 320nm thick metal molybdenum is deposited on the surface of the aluminum nitride seed layer 102 by thermal evaporation or magnetron sputtering as the lower electrode 103, and the metal molybdenum is patterned by wet etching or plasma method.

[0027] (4) If Figure 4 As shown, a layer of 800 nm ALN piezoelectric film 104 with good C orientation is sputtered on the surface of the seed layer and the surface of the lower electrode 103 .

[0028] (5) If Figure 5 As shown, 100 nm of metal molybdenum is deposited on the surface of the piezoelectric layer 103 by thermal evaporation or magnetron sputtering as the first upper electrode 106 .

[0029] (6) Figure 6 As shown, a second sacrificial layer 112 is deposited on the surface of the first upper electrode 106 and the piezoelectric layer 104 by low pressure chemical vapor deposition. The material may be silicon nitride (SiNx) or silicon oxide (SiO2), etc., and is patterned by chemical mechanical polishing.

[0030] (7) Figure 7 As shown, 350nm of metal molybdenum is deposited on the first upper electrode 106 and the second sacrificial layer 112 by thermal evaporation or magnetron sputtering as the second upper electrode 107, and a piston protrusion structure 111 is provided on the edge of the second upper electrode 107, and patterned by plasma or wet etching.

[0031] (8) Figure 8 As shown, a passivation layer 108 with a thickness of 80 nm is sputtered on the surface of the second upper electrode 107 , and the material is aluminum nitride (ALN).

[0032] (9) Fig. 9As shown, the first sacrificial layer and the second sacrificial layer are removed by wet etching or HF fumigation to form a cavity 101, a first air gap 109, a second air gap 110 and a drooping arm 114, and the drooping arm 114 is located on the first air gap 109.

[0033] The substrate material is one of silicon, glass, silicon carbide, ceramic, silicon oxide or any combination thereof, and there is no specific limitation. The cavity 101 can be formed by wet etching or plasma etching. The cross-sectional shape of the cavity 101 can be any one of trapezoid, triangle, rectangle or any combination thereof. The depth of the cavity is generally 2-8um, and the lateral width depends on the requirements of the device design and is not less than the lateral size of the lower electrode 102.

[0034] The seed layer 102 provided in the specific embodiment of the present invention is aluminum nitride with a thickness of 30-100 nm and a good C-axis orientation, which serves to better grow the metal molybdenum lower electrode 103 so that it has a better crystal orientation.

[0035] The lower electrode 103 provided in the specific embodiment of the present invention can be any one or a combination of metals such as molybdenum, copper, tungsten, aluminum, silver, gold, etc., with a thickness of 50nm-1000nm, and the metal is patterned by wet etching, plasma etching and other schemes to obtain the desired pattern.

[0036] The piezoelectric layer 104 provided in the specific embodiment of the present invention can be made of piezoelectric materials such as aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lithium niobate, lead zirconate titanate, etc., and has good roughness.

[0037] The material of the first upper electrode 106 provided in the specific embodiment of the present invention can be any one or a combination of metals such as molybdenum, copper, tungsten, aluminum, silver, gold, etc., with a thickness of 50nm-200nm, which is determined according to the actual design requirements of the device, and the metal is patterned by wet etching, plasma etching and other schemes to obtain the desired pattern.

[0038] The sacrificial layer 112 provided in the specific embodiment of the present invention is made of silicon nitride, silicon oxide and their combination, which functions to facilitate the formation of an air bridge structure and a drooping arm structure; the second upper electrode 107 can be made of any one or a combination of metals such as molybdenum, copper, tungsten, aluminum, silver, gold, etc., which covers the first upper electrode 106 and the sacrificial layer 112, and has a uniform lateral height of 100nm-1000nm. The sacrificial layer 112 is removed by wet etching or HF fumigation, and an air gap 1 and an air gap 2 are formed between the edge of the second upper electrode and the first upper electrode and the piezoelectric layer to obtain an air bridge structure. At the same time, a drooping arm 114 is obtained at the edge of the second upper electrode, and its width is 113. Since the second upper electrode has a uniform lateral height, a piston protrusion structure is formed above the air gap 1.

[0039] The material of the passivation layer 108 provided in the specific embodiment of the present invention may be aluminum nitride, scandium aluminum nitride, lithium niobate, lead zirconate titanate, etc.

[0040] The film bulk acoustic wave resonator in the above example can be a cavity type FBAR, that is, the cavity 101 is formed by releasing the sacrificial layer to form a cavity; or the film bulk acoustic wave resonator can also be a FABR with a Bragg reflection layer structure, that is, a solid-state assembly type FABR, and the cavity 101 is filled with a Bragg reflection layer; no matter which of the above structures is adopted, the structural design based on the present invention can reduce unnecessary clutter generated by the device while maintaining a high Q value, and the required droop arm width 113 can be designed according to actual device parameters to obtain a better Q value.

[0041] Fig.10 a and b are phase curve comparison diagrams of the structure with and without a drooping arm under the air bridge structure, as well as Smith chart comparison diagrams. For a resonator without a drooping arm structure, when noise appears, the phase curve will have a depression or a peak, and a rough circle will appear on the Smith chart. Compared with the resonator without a drooping arm structure, the device with a drooping arm structure provided in the specific embodiment of the present invention has a smoother phase curve and Smith chart, which means that the structure has a good suppression effect on the lateral stray mode, which is of great significance to the improvement of the resonator performance and the filter performance.

[0042] Fig.11 This is a comparison chart of the Q values ​​of the structure with and without a drooping arm based on the bridge structure. Fig.11 The width of the drooping arm of the corresponding BAW resonator with a drooping arm structure is 1.2um-2um. It should be noted that the width of the drooping arm should match the resonator parameters and is not limited to this width. Fig.12 As shown, the width of the drooping arm shown in the specific embodiment of the present invention is 1.2um-2um, when the drooping arm width is 1.2-1.45um, the Q value of the resonator is lower than the resonator without a drooping arm structure, when the drooping arm width is 1.45-1.65um, the Q value of the resonator is higher than the resonator without a drooping arm structure, when the drooping arm width is 1.7-2um, the Q value of the resonator is lower than the resonator without a drooping arm structure, and the Q value of the resonator with a drooping arm structure will oscillate within a certain range as the drooping arm width changes.

[0043] Fig.12 The Q value of the resonator with a drooping arm structure oscillates with the width of the drooping arm and by adjusting the width of the drooping arm, its Q value can be kept the same or even better than that of the resonator with a single air bridge structure in the range of 1.45-1.65um. At the same time, the change in width does not affect its suppression of clutter. The Q value of the resonator with a single air bridge structure is 1316.

[0044] The bulk acoustic wave resonator without a drooping arm structure provided by a specific embodiment of the present invention is as follows: Fig.13 shown.

[0045] The above is only an example of the present invention, and does not impose any specific limitation on the present invention. All relevant contents belong to the protection scope of the present invention. Any technician familiar with the art can make some changes or modifications to the above disclosed technical contents as equivalent test examples without departing from the technical scope of the present invention. However, any simple modification or equivalent change made to the above embodiments according to the technology of the present invention without departing from the technical solution of the present invention belongs to the technical solution of the present invention.

Claims

1. A high-Q bulk acoustic wave resonator for suppressing clutter, characterized in that: include: A substrate, wherein a cavity is provided on the substrate; A piezoelectric stacking structure is located on a substrate, and comprises from bottom to top a seed layer, a lower electrode, a piezoelectric layer, an upper electrode and a passivation layer, wherein an air bridge and a drooping arm are arranged at the edge of the upper electrode.

2. The high-Q BAW resonator for suppressing clutter according to claim 1, characterized in that: The upper electrode includes a first upper electrode and a second upper electrode from bottom to top; An air bridge is provided between the edge of the second upper electrode and the edge of the first upper electrode and the piezoelectric layer; A drooping arm portion is provided at the edge of the second upper electrode, and the drooping arm portion is located on the air bridge.

3. The high-Q BAW resonator for suppressing clutter according to claim 2, characterized in that: The air bridge comprises, from bottom to top, a first air gap and a second air gap; The first air gap is arranged between the edge of the second upper electrode and the piezoelectric layer, and the hanging arm portion is located on the first air gap; The second air gap is disposed between a side portion of the second upper electrode and an edge of the first upper electrode.

4. The high-Q BAW resonator for suppressing clutter according to claim 3, characterized in that: The height of the first air gap is consistent with the height of the second air gap.

5. The high-Q BAW resonator for suppressing clutter according to claim 3, characterized in that: A Pison protrusion structure is provided at the edge of the second upper electrode and at the same position as the second air gap in the lateral direction.

6. The high-Q BAW resonator for suppressing clutter according to claim 1, characterized in that: The cavity is filled with a Bragg reflection layer.

7. A method for preparing a high-Q bulk acoustic wave resonator for suppressing clutter according to any one of claims 1 to 6, characterized in that: include: Obtaining a substrate, opening a cavity on the substrate, and growing a first sacrificial layer on the cavity; Forming a piezoelectric stack structure above the substrate, the piezoelectric stack structure is located on the substrate, and the piezoelectric stack structure includes, from bottom to top, a seed layer, a lower electrode, a piezoelectric layer, a first upper electrode, a second upper electrode, and a passivation layer; forming a seed layer above the cavity; forming a lower electrode above the seed layer; forming a piezoelectric layer over the lower electrode and the seed layer; forming a first upper electrode above the piezoelectric layer; growing a second sacrificial layer at the edge of the first upper electrode; forming a second upper electrode on the second sacrificial layer and the first upper electrode; forming a passivation layer on the second upper electrode; The first sacrificial layer and the second sacrificial layer are released to obtain a cavity, an air bridge and a hanging arm.

8. The method for preparing a high-Q bulk acoustic wave resonator for suppressing clutter according to claim 7, characterized in that: The material of the second sacrificial layer is silicon nitride or silicon oxide, and the second sacrificial layer is released by wet etching or HF fumigation.

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